JP2004221480A - Embedded substrate crystal manufacturing method and embedded substrate crystal - Google Patents

Abstract

An object of the present invention is to manufacture a single crystal substrate suitable for manufacturing a device as a single crystal having a polarity A at least on a surface of a crystal in which different polarities A and B having a structure opposite to each other with respect to a crystal orientation are mixed. Is the purpose.
SOLUTION: In a crystal in which portions having different polarities A and B having structures opposite to each other with respect to the crystal orientation are mixed, one of the polarities B is etched to remove all or part thereof, and the crystal is re-applied thereon. Is grown to cover the surface with a crystal of polarity A or make the whole a single crystal of polarity A. Alternatively, a part of the polarity B is removed, or the polarity B is covered with a different substance without being removed, and the same crystal is grown to cover the surface with the crystal of the polarity A.
[Selection diagram] Fig. 4

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a manufacturing method for growing a crystal on a substrate having two polarities, and a crystal obtained by the manufacturing method. Here, polarity is not an electric dipole or magnetic north-south pole. A special term used only in this specification. It is used to mean the direction of different crystal structures antiparallel to a plane. A crystal in which a portion having a crystal orientation parallel to a surface and an antiparallel portion coexist is called a crystal in which polarity coexists. So, of course, in the case of a single crystal, there is no such thing in a crystal having inversion symmetry with respect to its surface. Such a state can only exist for a crystal without Inversion symmetry with respect to its surface. Since this term and its meaning are new and difficult to understand, a crystal in which polarity and polarity coexist will be described first.
[0002]
Crystals include single crystals and polycrystals. A crystal having mixed polarity is not a single crystal.
However, it is problematic to call it polycrystalline. It can be said that it is an intermediate crystal that is neither. Such a concept has never existed. Because no such entity has ever existed.
[0003]
A single crystal is a crystal having the same crystal orientation throughout and having translational symmetry and rotational symmetry as a whole. When a single crystal seed crystal is grown by the Czochralski method or the Bridgman method, a single crystal having the same orientation as the seed crystal grows. When a single crystal seed is used in other methods, a single crystal having an orientation following the seed is formed. In the case of crystal growth using a single crystal seed, a crystal in which polarity coexists cannot be formed.
[0004]
A polycrystal is a crystal having no regularity such that the crystal orientation is random and has neither translational symmetry nor rotational symmetry. However, at short distances, since they have the same crystal orientation, they can be said to be a collection of single crystal particles.
[0005]
In the case of polycrystal, since the orientation is random, it is not possible to obtain a crystal in which the polarity coexists regardless of the orientation. A crystal in which both polarities coexist cannot be obtained by such a conventional crystal manufacturing method. It is a new crystal form that appears only when special crystals are produced.
[0006]
Moreover, polar coexisting crystals are not worth their own. Instead, we want to make a single crystal, but there is a circumstance that a polar coexisting crystal is inevitably formed.
[0007]
The present invention proposes a method for producing a single crystal from a polar coexisting crystal. There is no problem if a single crystal can be formed from the beginning. According to a certain kind of crystal manufacturing method, a polar coexistence type crystal is formed. It is the intention of the present invention to make it a single crystal of uniform polarity.
[0008]
[Prior art]
Then, how can a crystal with polarity coexist? It states that. Gallium nitride (GaN) is useful as a blue light emitting element because of its wide band gap. Since a large GaN single crystal cannot be manufactured, an InGaN-based LED is currently manufactured using a sapphire single crystal as a substrate. The sapphire substrate is trigonal and has a regular hexagonal lattice structure. There is no triple symmetry or triple inversion symmetry around the c-axis. Sapphire and gallium nitride also have greatly different lattice constants and are lattice mismatched, and GaN and InGaN epitaxially grown on a sapphire substrate contain a large amount of defects.
[0009]
However, nevertheless, nitrides such as GaN, InGaN, and BeGaN on the sapphire substrate are stable and can emit light by forming a pn junction and flowing a current in the forward direction. Therefore, a GaN-based thin film is formed exclusively on a sapphire substrate. At present, only devices made on a sapphire substrate have a proven track record as InGaN light emitting devices.
[0010]
However, the sapphire substrate has no cleavage. The only way to separate elements is to mechanically dice. It is a tedious and low yielding method. In the case of using a laser, a naturally cleaved surface cannot be used as a resonator surface. Therefore, it is desired to finish a parallel smooth surface by polishing, but sapphire cannot. Furthermore, since sapphire is an insulator, it is not possible to take an n-electrode from the bottom. Both the n electrode and the p electrode need to be taken from the top. That is, an extra chip area is required because the effective area is reduced.
[0011]
Despite such difficulties, sapphire substrate InGaN-based light-emitting devices are still being mass-produced and used as blue light-emitting devices. This is because the sapphire substrate is easy to manufacture, and the GaN-based thin film formed thereon is stable and has excellent performance as a light emitting element.
[0012]
Although sapphire has a track record of such achievements, there is a strong desire to use gallium nitride single crystal as a substrate even in the worst case. It is still not possible to produce high quality gallium nitride single crystals with large areas, but if gallium nitride single crystal substrates can be used, all the disadvantages of sapphire substrates can be overcome.
[0013]
That is, there is a natural cleavage, so that it is convenient to separate the wafer into elements, and a resonator in the case of a laser can be easily formed by cleavage. Furthermore, since gallium nitride can be made to have a low resistivity by doping, there is an advantage that an n-electrode can be provided on the bottom surface to allow a current to flow vertically and the area can be reduced. For this reason, an attempt to manufacture a large GaN single crystal has been continued apart from the flow of the blue light emitting device of the InGaN / sapphire substrate, which has been proven.
[0014]
Since GaN does not melt only by heating, a melt cannot be produced. Therefore, a single crystal cannot be produced using the usual Czochralski method, Bridgman method, or the like, in which a solid is produced from a liquid raw material to produce a single crystal.
[0015]
For manufacturing a thin film of GaN, InGaN, BeGaN, or the like on a sapphire substrate, an organic metal CVD (MOCVD) method is exclusively used. It mixes gallium organic raw material such as trimethylgallium, indium raw material such as trimethylindium, and nitrogen raw material ammonia with a carrier gas such as hydrogen and feeds it to a cold wall reactor to heat it on a heated sapphire substrate. This is for growing a thin film such as GaN or InGaN. Although the growth rate is slow, it can be slow because a very thin thin film is produced.
[0016]
Another technique used to produce a GaN thin film is the HVPE (Hydride Vapor Phase Epitaxy) method. A Ga boat is placed above a hot-wall type reactor using gallium metal without using an organic raw material, and heated to form a Ga melt and spray HCl to obtain GaCl. Since the GaCl gas falls downward, when the ammonia gas is given, GaCl and ammonia react to form GaN, which is deposited on the sapphire substrate.
[0017]
A third method of forming a GaN thin film is called a MOC method (Metalorganic Chloride Method). Although trimethylgallium is used as a raw material, GaCl is reacted once with HCl gas, and is reacted with ammonia to form GaN. When an organic metal is used as a material and directly reacts with ammonia, carbon is likely to be mixed, and this deteriorates the electrical characteristics of GaN, so that GaCl is once formed to make it difficult for carbon to enter.
[0018]
In such a manner, a GaN thin film is formed on a sapphire substrate by a gas phase reaction to manufacture an InGaN-based light emitting device. Actually, since sapphire and GaN have too different lattice constants and increase stress, special measures are required to form a GaN thin film.
[0019]
In order to form a thick GaN film by a vapor growth method, it is necessary to reduce internal stress. The solution to that problem is the epitaxial lateral overgrowth method (ELO). It converts sapphire substrate to thin SiO ₂ A small window having a diameter of 1 μm to 2 μm is regularly opened so as to have a six-fold symmetry so that the substrate is exposed from the window, and a GaN thin film is grown thereon by MOCVD, MOC, HVPE or the like. . FIG. 8 is a plan view showing a state where the underlying substrate is covered with an ELO mask. FIG. 9 is a longitudinal sectional view thereof. 10 to 12 are for explaining ELO growth.
[0020]
An ELO mask 3 covers the base substrate 2 (for example, sapphire). It is SiO ₂ , SiN and the like. The base substrate 2 is exposed in the window 4. When gallium nitride is vapor-phase grown thereon, GaN nuclei are formed on the underlying substrate 2 but SiO 2 ₂ Since a GaN nucleus cannot be formed on the mask (ELO mask), a GaN crystal nucleus is initially generated inside the window 4 and grows (FIG. 10). When the thickness of the GaN crystal 5 exceeds the thickness of the mask, the GaN crystal 5 starts growing laterally on the ELO mask 3 (FIG. 11). Lateral, it is lateral. The inclined surface extending in the lateral direction is a facet 6 having a low surface index. The upper surface of the trapezoidal crystal is the C plane 8. When the crystal face (facet) 6 extending in the horizontal direction from the adjacent window 4 contacts on the bisector, the GaN crystal 5 grows in the vertical direction thereafter. As the growth in the vertical direction continues, the surface (C surface 8) becomes flat, and the growth continues while maintaining the flat C surface 8 (FIG. 12).
[0021]
The GaN crystal contains many dislocations 7. The dislocations 7 extend in the growth direction as they grow. Initially, dislocations 7 extend vertically. When ELO is used, the growth direction changes twice when the edge of the mask 3 is exceeded and when the crystal 5 that has advanced from the adjacent windows 4 and 4 comes into contact. At the same time, the direction in which the dislocation 7 extends changes, and the dislocation becomes discontinuous and decreases. Therefore, the dislocation density is 10 ⁹ cm ^-2 -10 ⁸ cm ^-2 Reduced to a degree. Many papers have been written on ELO, and various improvements have been proposed. For example
[0022]
(1) Akira Usui, “Growth of thick GaN crystal by hydride VPE,” IEICE Transactions C-II, vol. J81, no. 1, p58-64 (January 1998)
[0023]
(2) Akira Sakai, Akira Usui "Reduction of dislocation density by selective lateral growth of GaN" Applied Physics Vol. 68, No. 7, p774-779, 1999
And so on.
[0024]
ELO can also be used to grow a low dislocation thin film of GaN or InGaN on a sapphire substrate. In the case of a robust and robust sapphire substrate, the sapphire substrate cannot be peeled or removed by polishing, so that a single GaN crystal cannot be produced even if GaN is grown thick. The sapphire substrate remains attached.
[0025]
A method of growing a GaN thin film on a GaAs substrate by the ELO method has been performed by the present applicant. The GaAs substrate can be removed. If a thick GaN crystal can be grown on a GaAs substrate, there is a possibility that the GaAs substrate can be removed to produce a freestanding GaN film. Become the applicant
[0026]
(3) Japanese Patent Application No. 9-298300,
[0027]
(4) Japanese Patent Application No. Hei 10-9008
[0028]
Is a GaAs (111) single crystal substrate with a six-fold symmetry honeycomb-shaped window on it. ₂ Proposed a method of growing a GaN crystal from a window with a SiN mask, reducing initial dislocations, forming a thick GaN crystal, and removing a GaAs substrate to produce a freestanding GaN crystal.
[0029]
ELO is a method developed for the growth of GaN-based thin films. ELO is a contrivance only for the initial stage of growth, and is useful for reducing dislocations in a thin film.
[0030]
However, ELO alone does not result in a sufficiently low dislocation, and a GaN crystal obtained by growing GaN thickly has too many dislocations and a large strain to be unusable. Therefore, the present applicant has devised not a growth method for maintaining a flat C-plane but a clever method for intentionally producing a large number of facets and growing the crystal while maintaining them so as not to disappear. GaN is a hexagonal crystal and can be heteroepitaxially grown in the c-axis direction on the C-plane of another kind of single crystal substrate having a similar crystal system. Since the symmetry does not match, GaN cannot be grown on other planes (non-C plane).
[0031]
Sapphire single crystals are most frequently used. Sapphire is not hexagonal because Al: O = 2: 3 and the position of Al is biased. Although it is trigonal and has no three-fold symmetry or three-fold inversion symmetry, GaN can be grown on the C-plane on the C-plane.
[0032]
Conventionally, the growth was performed while maintaining the mirror surface (C surface). However, the present inventor has stopped the growth and grown the GaN while maintaining the facet. Here, the facet indicates a low-index crystal plane other than the C plane in this case. A low index surface such as {11-22} or {10-11} is a facet surface. GaN has threefold symmetry, and six facets gather to form a hexagonal pyramid hole, or 12 facets gather to form a 12-pyramidal hole. Sapphire has no three-fold symmetry about the c-axis, but GaN does.
[0033]
GaN has no inversion symmetry with respect to the c-axis direction. The lack of inversion symmetry is important for polarity generation. The concept of polarity was created here by the inventor for explanation. It is not a concept generally used in condensed matter physics such as polarization of a dielectric or polarity of a magnetic substance. Don't be confused. A crystal having inversion symmetry has no concept of polarity and is always nonpolar. Polarity is a problem because the crystal has no inversion symmetry.
[0034]
The present inventor has been able to reduce dislocations over the entire period of crystal growth by using a new technique called facet growth. that is
[0035]
(5) Japanese Patent Application No. 11-273882 (facet growth method)
Has been described in detail.
[0036]
This is illustrated in FIGS. FIG. 13 is a perspective view of a part surrounding a facet on the surface of a GaN crystal. The pits (holes) of the hexagonal pyramid or the 12-pyramid are randomly generated on the crystal surface. The pits 22 are pits 22 of the aggregate of the facet 9 and the facet 9 grows in the direction of the normal of the facet. The dislocations existing on the nine faces are pushed to the boundary ridge line 23 of the facet (arrow 25). Here, an arrow is drawn downward, but the pit moves upward as it grows, so it actually moves sideways.
[0037]
Since the dislocations gathered on the ridge line 23 follow the ridge line 23 and move downward (arrow 26), they are gathered on the pit bottom 24 of the hexagonal pyramid or the dodecagonal pyramid hole. The dislocations extending linearly move to the ridge line 23, and from the ridge line 23 to the pit bottom 24, and gather at the bottom. That is, since dislocations are collected at the center of the bottom 24 of the facet pyramid 22, dislocations at other portions are greatly reduced. Even though the total number of dislocations does not change, since the dislocations are localized at the bottom 24 of the pyramidal hole, dislocations in other portions are reduced. Looking at only the other parts, it means that the dislocation could be reduced.
[0038]
Maintaining facet growth is an important idea of the invention, but for that, it depends on conditions different from C-plane growth, such as slightly lowering the growth temperature or increasing the gas concentration.
[0039]
By the facet growth method, dislocations can be gathered at the bottom of the facet pit in the order of 1000 or 10000, and the dislocation density in other portions is 10 or less. ⁷ cm ^-2 -10 ⁶ cm ^-2 Can be reduced to a degree. This is an invention based on an excellent idea. However, the present invention has the disadvantage that the appearance of facet pits is random and stochastic and the position is not determined. The purpose is to form a thick GaN crystal, remove the underlying substrate, and use it as a GaN-based light emitting device substrate as a GaN free-standing film.
[0040]
In that case, it is necessary to prevent dislocation concentration points from being applied to important parts such as the active layer of the light emitting element. If the dislocation concentration points (pyramidal bottoms 24) are randomly distributed, the dislocation concentration points will be applied to the active layer of the chip no matter how the chips are arranged on the wafer. It can severely reduce yield.
[0041]
It would be advantageous if the location of the facet pit could be predetermined. For this purpose, the present applicant has proposed, in addition to the ELO mask, a mask (SiO ₂ , SiN) on an undersubstrate, and vapor-grown GaN thereon.
[0042]
(6) Japanese Patent Application No. 2001-284323 (dot-shaped closed defect accumulating region H)
This is a large two-dimensional period of SiO2 on the underlying substrate. ₂ , A mask covering portion of SiN is formed in a dot shape (in addition to the ELO mask), and GaN is facet-grown thereon. This will be described with reference to FIGS. The ELO mask is a negative type mask having a wider covering portion and a small window. The facet mask 30 is a positive type mask having a narrow covering portion and a wide exposed portion.
[0043]
The period is several tens to several hundred times the period of ELO. A facet mask having a coating portion 30 having a diameter of several tens μm to several hundreds μm on the base substrate 2 is formed. Although a wide opening 32 is drawn, a fine ELO mask is actually provided there. That is, it has a double mask structure. The ELO mask will not be described here because it becomes complicated. Since GaN hardly grows on the covering portion 30, the portion grows in a pyramid shape. The depression becomes a facet pit 22. That is, the entire surface of the mask covering portion 30 continues to grow as the facet 9.
[0044]
The dislocations converge on the bottom 24 of the pyramid pit 22, that is, on the center vertical line of the covering portion 30 (defect accumulating region H). Aggregated dislocations are surrounded by grain boundaries K (FIG. 17). The dislocations gathered at the bottom are not melted again because they are included by the grain boundaries K. Facet pits 22 are formed in the covering portion 30 of the facet mask, and dislocation aggregation portions (defect accumulating regions H) are formed there, and the other portions have low dislocations. The low dislocation portion is also divided into two types, and a single crystal low dislocation accompanying region Z formed immediately below the facet around the defect accumulating region H and a single crystal low dislocation extra region Y formed between the adjacent facets are distinguished. When such a facet crystal is grown thickly, the underlying substrate is removed, and a thin wafer is cut out parallel to the surface, resulting in a flat wafer (FIG. 18).
[0045]
Since a large amount of dislocations can be densely pushed into a narrow region, there is a possibility that a more usable GaN substrate can be manufactured. In the present invention, a crystal is grown by attaching a facet mask 30 having a dot-shaped covering portion. The dislocation concentrating portions H are two-dimensionally distributed in a dot shape with the covering portion 30 formed in advance as a center. In the case of manufacturing a laser device, the yield should be increased if important parts such as the active layer do not overlap the dislocation concentrating portion H. The present applicant has named the dislocation gathering portion a closed defect accumulating region H. It is so named because a large number of dislocations converge and are closed by grain boundaries and do not spread again. This has an advantage that the position of the defect accumulating region H can be designated in advance. This means that the light emitting element chip can be designed avoiding this.
[0046]
(7) Japanese Patent Application No. 2001-311018 (Striped defect accumulating region H)
In this method, a mask covering portion is isolated, and a linear covering portion provided in parallel at a predetermined interval, instead of a regularly distributed dot shape, is formed on a base substrate. Linear defect accumulating regions H are generated in parallel. When a laser chip is formed on a GaN substrate, it is convenient to make the chip end face in a certain direction (cleavage) so that the chip can be cut out by natural cleavage to form a resonator. Therefore, a facet growth method using a mask having a coating portion provided in parallel lines is proposed. It is convenient when cutting out laser chips and LED chips. The defect accumulating region H can be applied to an unimportant portion of the device or correspond to a cut portion.
[0047]
In the conventional examples (5), (6) and (7), the dislocations at other portions are reduced by localizing the dislocations to the bottom of the facet pit at a high density by the facet growth method. What is the localized defect accumulating region H? The applicant has sought variously on that matter. Certain defect accumulating regions H appear to be polycrystalline. Further, a certain defect accumulating region H is a single crystal, but the orientation may be slightly shifted from the surrounding single crystal. Alternatively, the orientation of the single crystal may be reversed with respect to the surrounding single crystal. As described above, there are various types of the identity of the defect accumulating region H, and it cannot be definitely determined.
[0048]
The GaN free-standing film excluding the base substrate is transparent, has uniform optical characteristics, and is indistinguishable from the defect accumulating region H with the naked eye. It has been found that the cathodoluminescence (CL) can distinguish the defect accumulating region H from the surrounding single crystal portion. According to CL observation, the surrounding single crystal portion was not uniform, and a portion having a large electric resistance and a portion having a small electric resistance could be clearly distinguished. It is also understood that the portion that grows immediately below the slope of the inverted pyramid-shaped pit becomes a low resistance portion, and the portion that grows on the C plane between adjacent pits outside the pit becomes a high resistance portion. Was. The portion grown following the facet pit is referred to as a single crystal low dislocation accompanying region Z. The portion of the C-plane grown between the pits is referred to as an extra low dislocation single crystal region Y. Both can be clearly distinguished by CL.
[0049]
At the center of a circular (specifically, hexagonal or dodecagonal) pit, there is a defect accumulating region H, concentrically with a single crystal low dislocation accompanying region Z, and a star shape between adjacent single crystal low dislocation accompanying regions Z. The single crystal low dislocation extra region Y is formed.
[0050]
Both the single crystal low dislocation accompanying region Z and the single crystal extra low dislocation region Y are single crystals, and the orientation is continuous. That portion may be used as a region including the active layer of the light emitting element.
[0051]
However, it has been found that the identity of H at the center of Z is finally a single crystal with inverted crystal orientation. That is, Z and Y are C-plane crystals having an upward c-axis, and H is a -C plane crystal having a downward c-axis.
[0052]
The base substrate is removed from the GaN thus grown to form a wafer as a self-standing film of GaN, and GaN is vapor-grown again using the base substrate as a base substrate. While a plane crystal grows, a -C plane crystal having a c-axis downward grows on H. In other words, when GaN is grown using the substrate as a seed, uniform C-plane crystals cannot be obtained, and -C-plane crystals are partially formed. In other words, when a thin film crystal is grown using a substrate including regions having different polarities, crystals having the same orientation as the seed are generated, so that only those having regions having different polarities in the same ratio can be obtained.
[0053]
The C-plane crystal containing Z and Y is a useful part with a large area and a main part. The -C plane crystal containing H has a small area and is unnecessary for manufacturing a light-emitting element, and may be an obstacle. Thus, it was found that two types of distinguishable regions coexist.
[0054]
There is a long way to get there. The outline is described here. Therefore, the polarity mentioned earlier is simply the c-axis direction in the case of GaN. GaN has threefold symmetry, and the M plane {-1100} and the A plane {2-1-10} are important planes orthogonal to the C plane. However, there is no distinction between the polarity A and the polarity B in GaN having the M-plane as the surface because of the inversion symmetry twice in these normal directions. Similarly, there is no distinction between polarity A and polarity B for GaN having the A-plane as the surface.
[0055]
Polarity depends not only on the symmetry of the crystal system, but also on what the surface is. In the case of GaN, the distinction between the polarity A and the polarity B occurs only when the C plane is the surface. This is because there is no inversion symmetry, no inversion symmetry, no inversion symmetry three times, no inversion symmetry three times, and no inversion symmetry in the C plane.
[0056]
In other words, only when the facet mask is attached to the base substrate and GaN is facet-grown, two distinguishable portions having opposite polarities are formed. So it is not a single crystal or a polycrystal. It cannot be said to be twin (Twin). There is no other state of solid physical properties.
[0057]
When a self-supported GaN single crystal substrate is manufactured, a number of InGaN-based LEDs and LDs are manufactured thereon. However, the fact that a large number of defect accumulating regions H are present as compared with a uniform single crystal substrate means that Inconvenient. Even if the LED and LD are produced while avoiding the defect accumulating region H, if the defect accumulating region H partially covers an important portion of the LD or LED chip, the LD or LED becomes defective.
[0058]
Therefore, a uniform gallium nitride single crystal having no defect accumulating region H is desired. As has been repeatedly described in the above description, GaN grown on the underlying substrate has large strain and many dislocations are peeled off. Therefore, a thick film with low dislocations cannot be formed unless ELO or facet growth is used. Then, the existence of the defect accumulating region H is unavoidable.
[0059]
[Problems to be solved by the invention]
It is urgently desired that a single crystal wafer has a uniform polarity without including portions having different polarities. The present invention has pursued such an object. To that end, Applicant has already
[0060]
(8) Japanese Patent Application No. 2002-219059 (skeleton substrate)
Has been proposed. This is based on a novel finding that when dry etching is performed using hydrogen chloride gas, only the defect accumulating region H is selectively removed. When a GaN free-standing film in which Z, Y, and H coexist was formed, it was found that Z + Y and H had different crystal orientations. At that time, it was not clearly understood that the defect accumulating region H was a portion where the crystal orientation was inverted. However, it was found that the behavior of dry etching with hydrogen chloride is still important. Therefore, the defect accumulating region H is removed by hydrogen chloride etching. It becomes a crystal substrate of only Y and Z which are single crystals having the same orientation. Since there are many vertical holes, it is called a skeleton board. When GaN is grown again on the skeleton substrate by vapor phase epitaxy, since it does not include the defect accumulating region H from the beginning, a single crystal film having the same orientation grows. Thereby, a GaN single crystal having a uniform structure is obtained.
[0061]
The present invention is an extension of such an invention. It is only necessary that the defect accumulating region H can be selectively removed. An object of the present invention is to manufacture a substrate having a uniform orientation and characteristics from a substrate having a defect accumulating region H. In order to distinguish the polarities, one crystal orientation (Y, Z) is referred to as polarity A, and the other inverted crystal orientation (H) is referred to as polarity B. FIG. 1 shows a part of a crystal in which the polarity A and the polarity B coexist. Such a thing cannot be performed by a normal single crystal growth method. It can only be done with a complicated method using the mask described so far. It can be said that it is an object of the present invention to produce a single crystal including only the portion of polarity A without the portion of polarity B in the crystal of FIG.
[0062]
[Means for Solving the Problems]
In the present invention, in a crystal in which portions having two different polarities A and B are mixed, the chemical characteristics of the portions having different polarities are different, so that one of the polar B portions is etched to remove all or a part thereof. A crystal is grown thereon and the surface is covered with a crystal of polarity A or the whole is a single crystal of polarity A.
[0063]
Alternatively, a part of the polarity B is removed or not removed, and the surface is coated with a different substance, and the same crystal is grown. Then, the surface is covered with a crystal of polarity A.
[0064]
Polarity A and polarity B have different chemical properties with respect to certain types of etching. It has been found that only one of the polarities can be selectively etched by dry etching using a certain substance or wet etching using a certain etchant. . Based on such a finding, the present invention removes part or all of only one polar region of a substrate having mixed polarities to create a cavity, crystal-grows again and fills the cavity, or at least the entire surface Single crystals with the same polarity.
[0065]
Another method is to mask the polarity B, grow a crystal on the mask, fill the polarity B portion, and use only the polarity A.
[0066]
Since all of them are single crystals or at least the surface is single crystals, they can be used as wafers for forming devices thereon. Since regions with different polarities do not coexist on the surface, there is no need to consider the position distribution of the active layers and stripes when fabricating semiconductor lasers and light emitting diodes thereon.
[0067]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a schematic view of a starting substrate for carrying out the present invention. This is, for example, a crystal obtained by facet growth using a dot type mask in which coating portions are regularly arranged. The portion indicated by A is the portion of polarity A. The portion denoted by B is a portion of polarity B. It is not essential that the starting substrate of the present invention has such regularly arranged portions of polarity B. They may be arranged at random. It is not necessary to be dot-shaped, and portions of polarity A and polarity B may be mixed linearly. It can be of any shape.
[0068]
However, the ratio is not so good if it is evenly divided. It is desirable that the region of either polarity greatly exceeds 50%. In the present invention, since the region of the unnecessary polarity is removed to form the cavity V and the crystal of the necessary polarity is grown again to fill the cavity V, the smaller the ratio of the cavity portion is, the better.
[0069]
Therefore, it is desirable that the unnecessary polarity is 30% or less. It is even better if it is 20% or less. In particular, it is more convenient if it is 10% or less. However, when the substrate is reversed, the polarity A and the polarity B are exchanged, so it is unnecessary. Even if the polarity is necessary, it is relative, and the region of either polarity is 30% or less or 20% or less, Preferably, it is 10% or less.
[0070]
[1. Departure board]
The starting substrate in which the polarity A and the polarity B are mixed is formed by adopting a special growth method as described above, and does not exist in nature. Such a substrate cannot be formed by the Czochralski method or the Bridgman method in which a single crystal is grown from a melt. The phenomenon of mixed polarity appears for the first time in the case of vapor phase growth while suppressing dislocations by various means.
[0071]
Therefore, the phenomenon of mixed polarity first appeared in the case of gallium nitride (GaN) crystals. Therefore, it is most important in the case of gallium nitride.
[0072]
However, the present invention can be applied if the polarity is mixed. Therefore, the present invention can be applied to any crystal having polarity. A crystal having inversion symmetry has no polarity, so there is no possibility of mixed polarity. For example, silicon (Si) and diamond (C) are cubic and have fourfold inversion symmetry, threefold symmetry, and mirror symmetry. Since it is composed of a single element, there is no concept of polarity because it has inversion symmetry even if it is cut at any plane.
[0073]
Groups 3 to 5 such as GaAs, GaP, and InP have the same crystal structure as silicon and have fourfold inversion symmetry, threefold symmetry, and mirror symmetry (denoted by -43m). -4 means four-fold inversion symmetry. There is no polarity in the axial direction four times because of the fourfold inversion symmetry. Therefore, the (100) plane substrate has no polarity.
[0074]
However, since two different elements are included and there is no inversion symmetry about the three-fold axis, a distinction in polarity occurs for the three-fold <111>. That is, the <111> direction is different from the <-1-1-1> direction. The (111) plane and the (-1-1-1) plane are not equivalent. Here, the plane orientation orthogonal to the <klm> direction is expressed as (klm). That is, the same plane index is used for the crystal plane and the crystal orientation orthogonal thereto. In the case of GaAs, a distinction is made between a (111) Ga plane and a (111) As plane. The former means that Ga atoms are exposed on the surface, and the latter means that As atoms are exposed. Single crystal GaAs having a (111) Ga surface on the front surface always has a (111) As surface on the back surface.
[0075]
Such a situation is common to Group III-V GaAs, InP and GaP having a zinc blende (ZnS; zincblend) structure. In the case of InP, a crystal cut by a plane orthogonal to the three-fold symmetry axis has a distinction between a (111) In plane and a (111) P plane. The same applies to GaP. In these cases, the surface where P and As are exposed is easily etched. Therefore, the polarity B is the (111) P, As plane, and the polarity A is the (111) Ga, In plane.
[0076]
Zinc blende type 3-5 group such as GaAs, InP and GaP can be melted at high pressure and high temperature. The liquid-encapsulated Czochralski (LEC) method and the Bridgman method (horizontal Bridgman HB, vertical Bridgman VB) can be used to grow a liquid crystal from a melt using a seed crystal. Can be manufactured. Crystals in which both polarities are mixed as described above do not usually occur. However, it means that the present invention can be applied if such a mixed polarity can be obtained.
[0077]
In the case of GaN which has been described so far, it belongs to Group 3-5, but the situation is different because it is not a zinc blende type. GaN and certain AlN have a wurtzite (Wurtzite) crystal structure. It is hexagonal and has threefold symmetry but no inversion symmetry with respect to the threefold axis (c-axis). Therefore, the (0001) plane (C plane) and the (000-1) plane (−C plane) are different. Also in this case, there is a surface on which only Ga emerges and a surface on which only N emerges. The former is distinguished by writing the (0001) Ga plane, and the latter is written as the (0001) N plane. The latter is the (000-1) plane, but is written with the N instead, such as the (0001) N plane. Also in this case, the surface from which nitrogen is exposed is the easy-to-etch surface, which corresponds to the polarity B described above. The surface from which Ga is exposed has polarity A.
[0078]
[2. Etching means]
As a dry etching method having selectivity with respect to polarity A and polarity B, the present inventor has proposed hydrogen chloride (HCl) or chlorine (Cl). ₂ ) Was found dry etching. The etching rate is significantly different depending on the polarity of GaN or GaAs. Therefore, only one of the polar regions can be selectively etched. There may be other dry-etching materials with polarity selectivity, but this is the only one known to the present inventors.
[0079]
An etchant having polarity selectivity for the polarity A and the polarity B was also found by the wet etching method. It is phosphoric acid + sulfuric acid (H ₃ PO ₄ + H ₂ SO ₄ ) Or potassium hydroxide (KOH). Care must be taken in the case of wet etching since the polarity is inverted on the front and back surfaces of the starting substrate. If only a part of the surface is to be removed, it is necessary to provide an etchant only on the surface and perform etching.
[0080]
[3. Skeleton board]
FIG. 2 is a sectional view of a part of the starting substrate. Only the narrow part containing one polarity B is shown. The portion of polarity B exists uniformly in the direction perpendicular to the surface because the film is grown by vapor phase using a mask. When it is etched, a substrate as shown in FIG. 3 is obtained. That is, only the polarity A remains and the polarity B is completely removed to form a cavity V. Since there is no polarity B, it is named "skeleton substrate" to distinguish it from the starting substrate.
[0081]
[4. Skeletal substrate]
A substrate that does not completely remove the polarity B but partially remains, that is, a substrate that includes the polarity A and a portion of the polarity B is referred to as a “skeleton substrate”. 19 and 22 show a skeleton substrate.
[0082]
[5. Degree of etching]
It is useful to remove all the polarity B to the bottom as shown in FIG. 3 (skeleton substrate). When vapor phase growth is performed thereon, only polarity A grows following the crystal orientation of the skeleton substrate, and a single crystal of polarity A is formed.
[0083]
However, only the upper part may be removed (skeleton substrate). This is because when the cavity V is narrow, the polarity A grows laterally from the cavity wall. In that case, the entire surface has polarity A. Looking at the surface alone, it is a single crystal of polarity A.
[0084]
For lateral growth, it is necessary that the diameter D of the cavity be 50 μm or less (D ≦ 50 μm) and the aspect ratio (height / diameter = H / D) be 2 or more.
[0085]
[6. Embedded substrate]
The same material is regrown (at least on the surface) on a skeletal, skeletal, or starting substrate to produce a void-free single crystal. The crystal, which is the object of the present invention, will be called an embedded substrate.
[0086]
When a mask is used, the polarity B may be removed by etching to such an extent that it is slightly depressed. In the case where a mask is used, it may not be necessary to perform etching at all. The following 7 to 10 list possible growth procedures.
[0087]
[7. Regrowth on the skeleton substrate (Figs. 3, 4, 5)]
As shown in FIG. 3, the same substance is grown on the skeleton substrate from which all the polarity B has been removed. As shown in FIG. 4, the inner wall of the cavity V becomes a seed, and a crystal of polarity A grows laterally from the seed. From the surface, a crystal A ′ of polarity A grows upward. Eventually, the cavity is filled with polarity A as shown in FIG. Crystal A ′ of polarity A is further deposited on the surface. As shown in FIG. 5, all of them have the crystal orientation of polarity A. Thereafter, the layers may be piled up by continuing the growth until the desired thickness is obtained.
[0088]
[8. Regrowth on skeletal substrate (FIGS. 19, 20, 21)]
If only part, but not all, of the polarity B is removed by selective etching, the time, chemicals, and cost required for etching can be reduced. This is advantageous because the cost can be reduced. In this case, if the diameter of the hole formed after removing the polarity B is 50 μm or less and the aspect ratio (height H / diameter D) of the hole is larger than 2, the polarity A of the wall is taken over from the side surface of the wall and the crystal is laterally crystallized. grow up. Therefore, the polarity A grows as shown in FIGS.
[0089]
[9. Regrowth with mask on skeletal substrate (Figs. 22, 23)]
When a crystal is grown on a skeletal substrate in which only a part of the polarity B is selectively etched, but not all, the above-described restriction on the diameter and height of the hole may be an obstacle. In such a case, SiN, SiO ₂ Attach a mask M such as The polarity B is closed by a mask. Then, since the side wall and the surface of the hole have the polarity A, the crystal of the polarity A grows. Polarity A covers the mask, and eventually the polarity A crystal entirely covers the mask.
[0090]
[10. Regrowth with mask on starting substrate (Figs. 6 and 7)]
It is possible to use a method of covering the polarity B by attaching the mask M to the starting substrate from the beginning without removing the polarity B at all. Will polarity A or polarity B grow on the mask? There is a problem. It is just such a mask that created the defect accumulating region H by facet growth, so it seems that the polarity B may grow when a similar mask is attached and regrown.
[0091]
However, the base substrate of the facet growth uses a different kind of material and has a weak power as a seed crystal like the same kind of material. However, in the case of the present invention, the desired polarity A also grows on the mask since the regrowth is performed on the starting substrate made of the same material. Although a portion of polarity B remains partially inside, a single crystal of polarity A can be formed on the surface. The one with the mask is called a coated substrate. FIG. 6 shows a coated substrate.
[0092]
【Example】
[Example 1 (GaN; KOH)]
A GaN crystal substrate having regions having different polarities was prepared. This is obtained by forming an ELO mask and a facet growth mask on a GaAs (111) base substrate as described above, growing a GaN crystal thick in the c-axis direction by HVPE, and removing the GaAs base substrate. GaN is a single independent standing film and is a crystal having a (0001) plane. Instead of a single crystal, polarity B is interspersed within polarity A as shown in FIG.
[0093]
The GaN starting substrate was heated to 700 ° C., left in an HCl gas atmosphere for 4 hours, and only one polar region was etched. As shown in FIG. 3, a skeleton substrate from which polarity B is completely removed is obtained.
[0094]
Thereafter, the GaN crystal was regrown on the GaN skeleton substrate using the HVPE method. A buried substrate in which the cavities were buried was obtained.
[0095]
The obtained substrate was etched in a KOH 0.02 M solution for 1 hour. Potassium hydroxide has different etching rates depending on polarity B and polarity A. Therefore, if the portions of both polarities coexist, the portion of the polarity B becomes hollow, so it can be seen whether or not they coexist. No local depression could be observed in this experiment. That is, it was found that the substrate surface was a substrate having a uniform polarity.
[0096]
[Example 2 (GaN; phosphoric acid: sulfuric acid = 1: 1)]
A GaN crystal substrate having both polarities A and B was prepared. Instead of etching with HCl gas in Example 1, etching was performed at 250 ° C. for 5 hours using a 1: 1 mixed solution of phosphoric acid and sulfuric acid. A skeleton substrate from which all the polarity B was removed was obtained. A GaN crystal was grown on the skeleton substrate by the HVPE method as in Example 1. The obtained buried GaN substrate was a substrate having only one polarity as in Example 1.
[0097]
Example 3 (GaN; potassium hydroxide (KOH))
The etching was performed for 10 hours using a potassium hydroxide solution instead of the etching with HCl gas in Example 1. As described in Example 1, KOH has selectivity for polarity A and polarity B. This time it is used to make a skeleton board.
Then, as in Example 1, GaN crystal growth was performed by HVPE. The obtained substrate was a substrate having only one polarity as in the example.
[0098]
[Example 4 (SiO ₂ mask)]
A GaN crystal substrate in which regions having different polarities were mixed was prepared. This time, no etching is performed. This is a method using a mask coating as shown in FIGS. SiO only on the part of polarity B ₂ A film was formed. The portion of polarity A remains uncoated. The whole is SiO ₂ And the mask over polarity A was removed by photolithography. Only the polarity A was exposed to the outside (FIG. 6).
[0099]
Thereafter, GaN crystal growth was performed using the HVPE method. The obtained substrate (FIG. 7) was a substrate having only one polarity, as in Example 1.
[0100]
[Example 5]
The dislocation density of the GaN substrates obtained in Examples 1 to 4 was evaluated using cathodoluminescence. According to CL, the dislocations appear as thin black lines, so that the number of dislocations appearing on the surface can be counted. As a result, the dislocation density is 10 ⁶ cm ^-2 It was below. It is about the same as the dislocation density at polarity A of the starting substrate.
[0101]
[Example 6]
Zinc selenium (ZnSe) was used instead of the GaN substrate used in Examples 1 to 4. ZnSe is not in group 3-5 but in group 2-6. Since the band gap is wide, it can be used as a substrate for a blue light emitting element. It is a cubic system and is sphalerite (ZnS; Zinc Blende type; -43 m). It has fourfold inversion symmetry, and there is no polarity A or polarity B around the fourfold axis. Since there is no reversal symmetry with respect to the threefold axis, a distinction is made between polarity A and polarity B. Since ZnSe does not become a melt even when heated to a high temperature, a single crystal cannot be produced by the Czochralski method or the Bridgman method. Single crystals can be obtained by iodine transport or sublimation, but not so large.
[0102]
Here, a ZnSe substrate having a diameter of 2 inches was used. The iodine transport method and the sublimation method use a seed crystal to transport ZnSe material in the gas phase and attach it to the seed. Therefore, if the seed has both polarity A and B, then ZnSe can be used. A substrate (starting substrate) can be made. Such a seed crystal can be manufactured by using a GaAs (111) substrate as a base substrate and performing facet growth by molecular beam epitaxial growth (MBE) or metal organic chemical vapor deposition (MOCVD) with a mask.
[0103]
By selectively etching with a hydrogen chloride gas using a ZnSe substrate having both polarities A and B as a starting material, only polarity B could be removed as in the previous example. When the skeleton substrate thus formed was regrown by the iodine transport method again, a ZnSe single crystal having only polarity A was obtained.
[0104]
[Example 7]
GaAs was used instead of the GaN substrate used in Examples 1 to 4. GaAs is cubic and is of the sphalerite type. Therefore, the (111) Ga plane and the (111) As plane have different chemical properties, and also have different etching rates by hydrogen chloride dry etching. GaAs can be easily manufactured into a large single crystal ingot by the LEC method, the VB method, and the HB method, and can be sliced into a single crystal wafer. Therefore, a crystal in which the polarity A and the polarity B coexist cannot usually be obtained. However, such can be produced.
[0105]
By selectively etching with a hydrogen chloride gas using a GaAs substrate having both polarities A and B as a starting material, only the polarity B could be removed as in the previous example. When the skeleton substrate thus formed was regrown by molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD), a ZnSe single crystal having only polarity A was obtained.
[0106]
Example 8
In place of the GaN substrate used in Examples 1 to 4, AlN was used. AlN is also of the wurtzite type and cannot be made of an AlN melt, and therefore cannot be of a large size. It can only be about 15 mmφ and about 1 mm thick. It is not usually the case that different polarities coexist, but it can be made by devising. Then, a skeleton substrate consisting of only the polarity A can be formed by selective etching with hydrogen chloride gas. When AlN was regrown thereon by vapor phase growth, a crystal having only polarity A was obtained.
[0107]
【The invention's effect】
When a crystal is grown by a special method to reduce dislocations, two regions having different polarities may coexist when the crystal orientation has no inversion symmetry with respect to the surface. In the case where two regions having different polarities coexist, the present invention removes all of one polarity by selective etching to a skeleton substrate as a cavity, or removes a part of one polarity to a skeleton substrate as a hole, or Is covered with a mask to form a coated substrate. When the skeleton substrate, the skeleton substrate, and the coated substrate are crystal-grown again as seed crystals, a single crystal having only one polarity is obtained at least on the surface. It can be used as a substrate wafer for making devices. Since it is not necessary to worry about the relationship between the device chip and the polarity, device design becomes easier.
[Brief description of the drawings]
FIG. 1 is a perspective view of a part of a crystal (starting substrate) in which a polarity A and a polarity B whose crystal structures face in opposite directions coexist.
FIG. 2 is a longitudinal sectional view of only a part including one polarity B of a starting substrate in which a polarity A and a polarity B coexist.
FIG. 3 shows that a starting substrate is selectively etched to remove a portion having a polarity B to form a cavity V in a portion having a polarity B, and the rest is only a portion including one cavity of a skeleton substrate having a polarity A. FIG.
FIG. 4 is a vertical sectional view showing only a part including one cavity of a growing substrate showing a process of vapor-phase growing the same material on the skeleton substrate and embedding a cavity V with a polarity A;
FIG. 5 is a longitudinal sectional view including only one buried portion of a buried substrate in which a crystal of the same polarity A is grown on a skeleton substrate by vapor phase growth to fill a cavity to form a uniform crystal of a uniform polarity A.
FIG. 6 is a vertical cross-sectional view of only a portion including one polarity B in a case where a mask M covering the polarity B of a starting substrate where the polarity A and the polarity B coexist is formed.
FIG. 7 is a longitudinal cross-sectional view of a crystal whose polarity B is covered with a mask M, where crystal growth is performed again, and at least the surface has only polarity A.
FIG. 8 is a plan view of a part of an under substrate provided with an ELO mask having windows that are isolated so as to have six-fold symmetry.
FIG. 9 is a partial longitudinal sectional view of a case where an ELO mask having an isolated window having six-fold symmetry is provided on a base substrate.
FIG. 10 shows a state in which GaN is vapor-phase grown on an underlying substrate provided with an ELO mask having a window having six-fold symmetry, and a GaN crystal is isolated and grown in a pyramid shape on the window. Sectional drawing of a part.
FIG. 11 shows a GaN vapor-phase grown on an undersubstrate provided with an ELO mask having a window having six-fold symmetry, and a GaN crystal grown on the window in an isolated pyramid shape, and then on the mask. FIG. 3 is a partial vertical cross-sectional view showing a state of growing horizontally.
FIG. 12 shows a GaN vapor-phase grown on an undersubstrate provided with an ELO mask having a window having a six-fold symmetry, and a GaN crystal grown on the window in an isolated pyramid shape. FIG. 3 is a partial vertical cross-sectional view showing a state in which the crystal grows in the horizontal direction and grows in the vertical direction when contacted.
FIG. 13 shows a method of forming pyramid-shaped facet pits composed of facets on the surface in the growth of GaN having the C-plane as a surface, and maintaining facet growth to collect dislocations at the bottom of the pits to reduce other portions to low dislocations. FIG. 2 is a perspective view of a portion near the surface of a GaN crystal for illustrating the state of FIG.
FIG. 14 shows a method of forming pyramid-shaped facet pits composed of facets on the surface in the growth of GaN having the C-plane as a surface, maintaining facet growth, and collecting dislocations at the bottom of the pits to reduce other portions to low dislocations. FIG. 4 is a plan view of pits near the surface of a GaN crystal for showing the pits.
FIG. 15 shows another example of a method of growing GaN having a C-plane as a surface by forming pyramid-shaped facet pits made of facets on the surface and maintaining facet growth to collect dislocations at the bottoms of the pits and create defect accumulating regions H at the bottoms. FIG. 4 is a perspective view of a part near the surface of a GaN crystal for illustrating a method of reducing dislocations in a portion of FIG.
FIG. 16 is a vertical cross-sectional view of an initial substrate in a facet growth method in which a mask that periodically includes isolated coating portions is formed on a base substrate.
FIG. 17 shows that facet pits are formed on a mask when GaN is vapor-phase grown on a masked base substrate, and the pits grow while retaining facet surfaces, so that a defect accumulating region H is formed at the bottom of the pits. FIG. 9 is a longitudinal sectional view showing that single crystal low dislocation accompanying regions Z are formed below the side surfaces of pits, and single crystal extra dislocation extra regions Y are formed between adjacent pits, and grow in the vertical direction.
FIG. 18 is a longitudinal sectional view of a GaN wafer cut by a plane perpendicular to the growth direction by removing a base substrate.
FIG. 19 is a diagram showing a case where a starting substrate having polarities A and B coexist is selectively etched to remove a portion above the polarities B and leave a lower half of the polarities B to form a cavity, which includes one cavity serving as a skeletal substrate. FIG. The diameter of the cavity is D and the depth is H.
FIG. 20 shows that when GaN is vapor-phase grown on a skeleton substrate provided with a cavity having a large aspect ratio (H / D), crystal growth occurs from the side wall rather than the bottom of the cavity, and the portion A ′ inherits the direction of polarity A. FIG. 5 is a longitudinal sectional view showing how the burglar grows.
FIG. 21 is a longitudinal section showing that when GaN is vapor-phase grown on a skeleton substrate having a cavity having a large aspect ratio, crystal growth inheriting the crystal orientation of the side wall occurs and a crystal having only polarity A grows on the surface. Area view.
FIG. 22 shows a starting substrate having both polarities A and B co-existed by selective etching to remove a portion above the polarities B and leave a lower half of the polarities B to form a cavity to serve as a skeletal substrate and provide a mask at the bottom of the cavity. FIG. 2 is a longitudinal sectional view of only a part including one cavity.
FIG. 23 is a longitudinal sectional view showing that GaN is vapor-phase grown on the skeletal substrate of FIG. 22 to grow a crystal A ′ having only polarity A.
[Explanation of symbols]
2 Base substrate
3 ELO mask
4 windows
5 GaN crystal
6 facets
7 Dislocation
8 C surface
9 facets
22 facet pit
23 ridgeline
24 Pit bottom
25 Direction of dislocation progression in facet
26 Direction of dislocation progression at ridge
28 Defect collection area following the bottom of the pit
30 Facet growth mask
32 opening
H defect accumulating area
Z single crystal low dislocation associated region
Y single crystal low dislocation extra region
A Polarity A
B Polarity B
K grain boundary
V cavity
M mask

Claims (11)

A single crystal region of polarity A having a front and back surface, having a crystal system having no inversion symmetry with respect to the front and back surfaces, having a parallel crystal orientation and penetrating the front and back surfaces, and having a crystal orientation antiparallel to the polarity A; The starting substrate having a single crystal region of polarity B penetrating on the front and back surfaces is dry-etched with hydrogen chloride gas or chlorine gas, or wet-etched with a mixture of phosphoric acid and sulfuric acid or a potassium hydroxide solution as an etchant. Is removed to form a skeleton substrate having a cavity penetrating the substrate, and the skeleton substrate is used as a seed crystal for vapor-phase growth or liquid-phase growth using the same material. A method for producing a buried substrate crystal, characterized by producing a buried substrate crystal having a polarity A as a whole by growing the crystal. A single crystal region of polarity A having a front and back surface, a crystal system having no inversion symmetry with respect to the front and back surfaces, having a parallel crystal orientation and penetrating the front and back surfaces, and a polarity having a crystal orientation antiparallel to the polarity A The starting substrate which is B and has a single crystal region having a diameter of 50 μm or less penetrating the front and back surfaces is dry-etched with a hydrogen chloride gas or a chlorine gas, or wetted with a mixture of phosphoric acid and sulfuric acid or a potassium hydroxide solution as an etchant. Etching is performed to obtain a skeletal substrate in which holes are formed by removing only the depth H where the aspect ratio H / D obtained by dividing the depth H from the surface by the diameter D is 2 or more, where D is the diameter of the region of polarity B and D is the diameter. The same material is used as a seed crystal for the skeletal substrate, and vapor-phase or liquid-phase growth is performed. The holes are filled with polar A crystals, and polar A crystals are grown on the surface. Ah Embedded substrate crystal manufacturing method is characterized in that the production of embedded substrate crystal. A single crystal region of polarity A having a front and back surface, a crystal system having no inversion symmetry with respect to the front and back surfaces, having a parallel crystal orientation and penetrating the front and back surfaces, and a polarity having a crystal orientation antiparallel to the polarity A The starting substrate, which is B and has a single crystal region penetrating on the front and back surfaces, is a coated substrate in which only the portion of polarity B is covered with a mask of a different material by photolithography. A buried substrate crystal, characterized in that a buried substrate crystal is produced by growing a phase or a liquid phase, covering both the mask and the portion of the polarity A without the mask with a crystal of the polarity A and having a surface portion of a single crystal of the polarity A. Production method. A single crystal region of polarity A having a front and back surface, having a crystal system having no inversion symmetry with respect to the front and back surfaces, having a parallel crystal orientation and penetrating the front and back surfaces, and having a crystal orientation antiparallel to the polarity A; The starting substrate having a single crystal region of polarity B penetrating on the front and back surfaces is dry-etched with hydrogen chloride gas or chlorine gas, or wet-etched with a mixture of phosphoric acid and sulfuric acid or a potassium hydroxide solution as an etchant. Is removed to form a skeleton substrate having a cavity penetrating the substrate, and the skeleton substrate is used as a seed crystal for vapor-phase growth or liquid-phase growth using the same material. A buried substrate crystal, characterized in that the whole obtained by growing the crystal is a single crystal of polarity A. A single crystal region of polarity A having a front and back surface, a crystal system having no inversion symmetry with respect to the front and back surfaces, having a parallel crystal orientation and penetrating the front and back surfaces, and a polarity having a crystal orientation antiparallel to the polarity A The starting substrate which is B and has a single crystal region having a diameter of 50 μm or less penetrating the front and back surfaces is dry-etched with a hydrogen chloride gas or a chlorine gas, or wetted with a mixture of phosphoric acid and sulfuric acid or a potassium hydroxide solution as an etchant. Etching is performed to obtain a skeletal substrate in which holes are formed by removing only the depth H where the aspect ratio H / D obtained by dividing the depth H from the surface by the diameter D is 2 or more, where D is the diameter of the region of polarity B and D is the diameter. By using the same material as a skeletal substrate as a seed crystal for vapor phase growth or liquid phase growth, filling the holes with polar A crystals, and growing a polar A crystal on the surface, the surface portion of polar A is obtained. single Embedded substrate crystal characterized in that it is a crystal. A single crystal region of polarity A having a front and back surface, a crystal system having no inversion symmetry with respect to the front and back surfaces, having a parallel crystal orientation and penetrating the front and back surfaces, and a polarity having a crystal orientation antiparallel to the polarity A The starting substrate, which is B and has a single crystal region penetrating on the front and back surfaces, is a coated substrate in which only the portion of polarity B is covered with a mask of a different material by photolithography. A buried substrate crystal characterized in that a surface portion obtained by phase growth or liquid phase growth, and a portion of the polarity A on and without a mask covered by a crystal of the polarity A is a single crystal of the polarity A. 7. The buried substrate crystal according to claim 4, wherein a dislocation density of a newly grown portion of the obtained buried crystal is 10 ⁶ cm ⁻² or less. The embedded substrate crystal according to claim 4, wherein the crystal is gallium nitride. The buried substrate crystal according to claim 4, wherein the buried substrate crystal is ZnSe. The buried substrate crystal according to claim 4, wherein the buried substrate crystal is GaAs. The embedded substrate crystal according to claim 4, wherein the crystal is AlN.

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