JP2025121584A - Silicon epitaxial substrate and method for heat treatment of silicon substrate - Google Patents

Abstract

【assignment】
An object of the present invention is to provide a Si{110} substrate in which the generation of depression-like defects is suppressed, and a method for heat treating a Si{110} substrate.
[Solution]
A silicon substrate having a principal surface with a {110} plane orientation, characterized in that the silicon substrate does not contain depression-like defects having a longitudinal length of 50 nm or more and 2000 nm or less on the surface.
[Selected Figure] Figure 1

Description

The present invention relates to a silicon substrate and a method for heat treating a silicon substrate.

In place of the Fin structure currently used in logic ICs, next-generation semiconductors are being proposed with GAA (Gate-All-Around) structures and even CFETs (Complementary Field Effect Transistors) stacking NMOS and CMOS, and these structures are being actively researched and developed. In this regard, one method of improving hole mobility is to use the (110) plane orientation of silicon (hereinafter also referred to as "Si"), one of several available plane orientations (Non-Patent Document 1).

JP 2008-091887 A Japanese Patent Application Laid-Open No. 2006-100596 Japanese Patent Application Laid-Open No. 2008-088045 JP 2014-239184 A Japanese Patent Application Laid-Open No. 2008-091891 Japanese Patent Application Laid-Open No. 2001-253797

The 1st Workshop of the Industry-Academia Collaboration Committee on Crystal Growth, Processing, and Evaluation of Semiconductors, Japan Society of Applied Physics, "Crystal Technology Supporting the Revival of Semiconductors" Yamada et al., "Fabrication of Si(110)-16x2 Single Domain Surface," Surface Science, 29(7), 401 (2008) Miyaji et al., "Observation of Si(110) reconstructed surface using ultra-high vacuum non-contact atomic force microscope," Journal of the Japan Institute of Metals, 72(4), 290 (2008)

However, problems with Si(110) substrates have been pointed out, such as high surface roughness and haze (Non-Patent Document 1). Haze, also known as the degree of cloudiness of the surface, represents surface roughness as a measure of the degree of light scattering, with higher haze indicating a rougher surface. Furthermore, the most stable structure of the Si(110) outermost surface was only identified relatively recently (Non-Patent Documents 2 and 3).

Furthermore, as described in Non-Patent Documents 2 and 3, the most stable structure of the Si(110) surface, the 16x2 domain (a region with a single structural unity), undergoes a phase transformation depending on the temperature, as shown in Figure 2, and the structure changes in the range of 600 to 800°C.

This structural change also leads to the phenomenon of step bunching. Step bunching is a phenomenon in which atomic-level irregularities called steps exist on the wafer surface in semiconductor materials such as silicon, and when surface atoms move due to heat treatment or other processes, the steps gather together, forming larger irregularities. Furthermore, for example, materials such as SiGe, which are stacked in GAA and CFETs, often require processing in this exact temperature range, making it easy to imagine that this makes understanding the surface structure even more difficult. The phenomenon associated with this phase change creates a large bias, hindering understanding of other phenomena (such as defects and contamination behavior).

This unique outermost surface structure of the Si(110) surface also affects the surface structure after etching. The step edges of the 16x2 domain surface structure are not single-atom structures like Si(100), but have a two-atom step. When the energy of the reaction system is low (equilibrium reaction), the reaction proceeds at the outermost surface atoms, resulting in a linear surface shape surrounded by the first-nearest neighbor Si(111) atoms after etching. On the other hand, when the energy of the reaction system is high, the outermost surface and atoms below it become involved in the reaction, resulting in a square shape surrounded by the second-nearest neighbor Si(111) atoms.

For Si(110) with this type of surface state, Patent Document 1 discloses a method for reducing surface roughness by tilting the orientation during epitaxial growth. Patent Document 2 discloses the same epitaxial growth method, but with the specification of the cooling rate and surface protection. Furthermore, Patent Document 3 discloses a method for similarly reducing surface roughness by specifying the surface orientation during crystal growth rather than during epitaxial growth. Patent Document 4 discloses polishing the epitaxial surface. Patent Document 5 discloses a technology that differs from Patent Document 1 in LPD detection size. Furthermore, Patent Document 6 discloses a method for reducing surface roughness that forms in a circular ring shape around the periphery, even when the epitaxial film thickness is very thick at 30 μm or more, by setting the off-angle during slicing to 0.5 to 7 degrees.

However, the inventors have clarified that in addition to defects caused by such surface roughness and crystal defects, Si(110) substrates, unlike Si(100) substrates, have a special 16x2 most stable structure, and therefore have unstable regions (referred to as "disordered regions" in Non-Patent Document 2) adjacent to the most stable 16x2 structure, and that minute protrusion-like defects are generated from these regions by heat treatments such as hydrogen baking before epitaxial growth and epitaxial growth, forming an in-plane distribution on the Si(110) substrate, and have proposed countermeasures for this.

As such, the surface of a Si (110) substrate has a very complex shape, and various methods have been published to reduce surface roughness. However, as mentioned above, unlike a Si (100) substrate, the most stable structure of a Si (110) substrate is a special 16x2 structure. Therefore, there are unstable regions adjacent to the most stable 16x2 structure. The inventors have discovered that these regions are the starting point for the generation of relatively large depression-shaped defects when subjected to heat treatments such as hydrogen baking before epitaxial growth or epitaxial growth.

The present invention was made to solve the above problems, and aims to provide a Si{110} substrate and a heat treatment method for a Si{110} substrate in which the generation of pit-like defects is suppressed.

The present invention has been made to achieve the above-mentioned objective, and provides a silicon substrate characterized by a principal surface having a {110} plane orientation and containing no depression-like defects on the surface with a longitudinal length of 50 nm or more and 2000 nm or less.

Such silicon substrates are of high quality, free of pit-like defects and with improved surface roughness, resulting in improved device characteristics.

In this case, the silicon substrate may have an off-angle of 0.23° or more in the plane orientation of the {110} principal surface.

This will further improve surface roughness and further enhance device characteristics.

The present invention has also been made to achieve the above-mentioned object, and provides a heat treatment method for a silicon substrate having a {110} principal surface orientation, the heat treatment method comprising a heating step of heating the silicon substrate to a heat treatment temperature higher than 570°C, a heat treatment step of performing heat treatment at that heat treatment temperature, and a cooling step of cooling the silicon substrate to a temperature lower than 570°C, wherein the sum of the product of the temperature and time of the silicon substrate during the period from when the temperature of the silicon substrate reaches 570°C in the heating step to when the temperature of the silicon substrate reaches 570°C in the cooling step is 60,000 (°C·sec) or less.

This type of heat treatment method for silicon substrates makes it possible to suppress the formation of pit-like defects.

In this case, the off-angle of the main surface of the silicon substrate can be set to 0.23° or more.

This further reduces the occurrence of dent-like defects.

As described above, the silicon substrate of the present invention is of high quality, free of pit-like defects and with improved surface roughness, leading to improved device characteristics. Furthermore, the heat treatment method for silicon substrates of the present invention makes it possible to suppress the formation of pit-like defects.

1 shows the results of AFM measurement of the surface of a Si(110) substrate of an example. 1 shows the results of AFM measurement of the surface of the Si(110) substrate of Comparative Example 1. 1 shows the results of AFM measurement of the surface of the Si(110) substrate of Comparative Example 2. 1 shows a cross-sectional structure diagram of an example of a Si(110) (Si{110}) substrate.

The present invention is described in detail below, but is not limited to these.

As described above, there is a need for a Si{110} substrate and a heat treatment method for a Si{110} substrate that suppresses the formation of pit-like defects.

After extensive research into the above-mentioned problems, the inventors discovered that a silicon substrate having a principal surface with a {110} orientation and free of depression-like defects measuring 50 nm to 2000 nm in length in the longitudinal direction on the surface can be made into a high-quality substrate with no depression-like defects and improved surface roughness, thereby improving device characteristics, and thus completed the present invention.

After extensive research into the above-mentioned problems, the inventors discovered that a heat treatment method for a silicon substrate having a {110} principal surface orientation, comprising a heating step of heating the silicon substrate to a heat treatment temperature higher than 570°C, a heat treatment step of performing heat treatment at that heat treatment temperature, and a cooling step of cooling the silicon substrate to a temperature lower than 570°C, wherein the sum of the product of the temperature and time of the silicon substrate from the time the temperature of the silicon substrate reaches 570°C in the heating step to the time the temperature of the silicon substrate reaches 570°C in the cooling step is 60,000 (°C·sec) or less, can suppress the generation of dent-like defects, and thus completed the present invention.

[Silicon substrate]
In the present invention, a plane orientation of {110} includes a plane whose orientation is equivalent to (110), and also includes a plane having an off angle of 0.23 to 0.5 degrees from the {110} plane.

Figure 4 shows a cross-sectional structure diagram of an example of a Si(110) substrate. As shown in Figure 4, Si(110) substrate 2 has surface 3 (the outermost surface of the surface stable structure). It is on surface 3 that pit-like defects with longitudinal lengths of 50 nm to 2000 nm (hereinafter simply referred to as "pit-like defects"), which are the subject of the present invention, exist.

When hydrogen annealing is performed on a Si(110) substrate before epitaxial growth, or when epitaxial growth (silicon, SiGe, etc.) or heat treatment is performed, depression-like defects such as those shown in Figure 2 may occur.

As described in Patent Document 2 and Non-Patent Documents 2 and 3, this defect is generated due to differences in the stable structure of Si(110). The researchers' research and studies have revealed that such long defects can exist in particular when stable structures such as 16x2 domains are connected.

For such long defects to form, atomic interactions must occur over a long distance. In other words, when considering a pit-like defect, an interaction of (surface energy) x (thermal energy) is required.

As shown in Figure 4, the silicon {110} substrate 2 of the present invention does not contain such depression-like defects on the surface 3 of the surface stable structure.

In addition, pit-like defects are affected not only by heat treatment conditions but also by the off-angle of the substrate's main surface. In other words, when considering pit-like defects, understanding that they are an interaction of (surface energy) x (thermal energy) can help prevent defects.

Here, the surface energy corresponds to the step-terrace width formed by the off-angle of the silicon (110) substrate, and as the off-angle becomes smaller and the terrace width becomes smaller, the surface energy becomes relatively larger.

In the present invention, the off-angle of the principal surface of the silicon {110} substrate 2 can be 0.23° or greater. There is no particular upper limit to the off-angle, but it may be set to 0.5°.

Such silicon substrates result in improved surface roughness and improved device characteristics. This is because the large off-angle generates the ES effect (Ahrlich-Schwebel effect: wider terraces allow for greater atomic diffusion, thereby suppressing step movement), which suppresses the generation of defects.

[Silicon substrate heat treatment method]
The heat treatment method for a silicon {110} substrate according to the present invention includes a heating step of heating the silicon substrate to a heat treatment temperature higher than 570°C, a heat treatment step of performing heat treatment at the heat treatment temperature, and a cooling step of cooling the silicon substrate to a temperature lower than 570°C.

Here, heat treatment refers to heat treatment in which the silicon substrate is treated at a temperature of 570°C or higher, and includes layer formation processes such as annealing and epitaxial growth. Heat treatment does not have to be performed at a constant temperature.

To reduce the above-mentioned pit-like defects, it is necessary to keep the sum of the product of the silicon substrate temperature and time, from the time when the silicon substrate temperature reaches 570°C in the heating process until the time when the silicon substrate temperature reaches 570°C in the cooling process, to 60,000 (°C·sec) or less.

In other words, when a Si (110) substrate with an off-angle of 0.26° on the principal surface was subjected to hydrogen annealing at a temperature of 1080°C for 60 seconds in the heat treatment process, depression-shaped defects with a longitudinal length of 1 μm, as shown in Figure 2, were generated. In this case, the sum of the product of the silicon substrate temperature and time from the time when the silicon substrate temperature reached 570°C in the heating process to the time when the silicon substrate temperature reached 570°C in the cooling process, was 65,000 (°C·sec).

Next, when a Si (110) substrate with the same principal surface off-angle of 0.26° as above was subjected to hydrogen annealing at a temperature of 900°C for 60 seconds in the heat treatment process, no pit-like defects were generated, as shown in Figure 1. In this case, the sum of the product of the silicon substrate temperature and time from the time when the silicon substrate temperature reached 570°C in the heating process to the time when the silicon substrate temperature reached 570°C in the cooling process was 57,000 (°C·sec).

In this way, by taking into consideration the heat treatment temperature and time, and performing heat treatment with the sum of the product of the silicon substrate temperature and time during the period from when the silicon substrate temperature reaches 570°C in the heating process to when the silicon substrate temperature reaches 570°C in the cooling process set to 60,000 (°C·sec) or less, it is possible to suppress the generation of pit-like defects.

The lower limit of the sum of the products of the above temperatures and times is not particularly limited, but may be set to 5400 (°C·sec).

In the heat treatment method for a Si {110} substrate according to the present invention, the off-angle of the principal surface of the silicon substrate can be set to 0.23° or more. This further suppresses the formation of pit-like defects. The upper limit of the off-angle is not particularly limited, but may be set to 0.5°.

The present invention will be explained in more detail below using examples, but these examples are not intended to limit the scope of the present invention.

(Example)
A silicon single crystal substrate with a diameter of 300 mm, a (110) orientation, boron doping, a resistivity of 10 Ω·cm, and an off-angle of 0.26° from the (110) principal surface was prepared and subjected to hydrogen annealing at a temperature of 900°C for 60 seconds at atmospheric pressure. During this time, the sum of the product of the temperature and time of the silicon substrate from the time when the temperature of the silicon substrate reached 570°C in the heating step to the time when the temperature of the silicon substrate reached 570°C in the cooling step was 57,000 (°C·sec).

Then, the angle of view was adjusted so that one side of the captured image was 1 μm, and AFM measurement was performed. The measurement results are shown in Figure 1. As shown in Figure 1, no dent-like defects were observed on the surface of the silicon substrate.

(Comparative Example 1)
The same silicon single crystal substrate as in the example was prepared and subjected to hydrogen annealing at atmospheric pressure for 60 seconds at a temperature of 1080°C. During this time, the sum of the product of the temperature of the silicon substrate and the time from the time when the temperature of the silicon substrate reached 570°C in the heating step to the time when the temperature of the silicon substrate reached 570°C in the cooling step was 65000 (°C·sec).

Then, the angle of view was adjusted so that one side of the captured image was 1 μm, and AFM measurement was performed. The measurement results are shown in Figure 2. A depression-shaped defect with a longitudinal length of 1 μm, as shown in Figure 2, was observed on the surface of the silicon substrate.

(Comparative Example 2)
A silicon single crystal substrate identical to that of the example was prepared, except that the off-angle of the main surface was 0.24°, and this was subjected to hydrogen annealing at a temperature of 1030°C for 60 seconds at atmospheric pressure. During this time, the sum of the product of the temperature of the silicon substrate and the time from the time when the temperature of the silicon substrate reached 570°C in the heating step to the time when the temperature of the silicon substrate reached 570°C in the cooling step was 65,000 (°C·sec).

Then, the angle of view was adjusted so that one side of the captured image was 1 μm, and AFM measurement was performed. The measurement results are shown in Figure 3. A 0.8 μm depression-like defect, as shown in Figure 3, was observed on the surface of the silicon substrate.

As described above, according to the examples of the present invention, heat treatment of a Si(110) substrate can be performed without generating pit-like defects on the surface, and a Si(110) substrate can be obtained that does not have pit-like defects of 50 nm to 2000 nm on the surface.

The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical concept described in the claims of the present invention and exhibits similar effects is within the technical scope of the present invention.

1... pit-like defect, 2... Si(110) (Si{110}) substrate,
3...Surface (surface stable structure).

Claims (4)

A silicon substrate having a principal surface with a {110} orientation and containing no depression-like defects with a longitudinal length of 50 nm or more and 2000 nm or less on the surface. The silicon substrate of claim 1, characterized in that the principal surface has a {110} plane orientation and the off-angle of the principal surface is 0.23° or greater. A method for heat treating a silicon substrate having a principal surface with a {110} plane orientation, comprising the steps of:
The heat treatment method includes a heating step of heating the silicon substrate to a heat treatment temperature higher than 570°C, a heat treatment step of performing heat treatment at the heat treatment temperature, and a cooling step of cooling the silicon substrate to a temperature lower than 570°C,
A heat treatment method for a silicon substrate, characterized in that the sum of the product of the temperature and time of the silicon substrate during the period from the time when the temperature of the silicon substrate reaches 570°C in the heating step to the time when the temperature of the silicon substrate reaches 570°C in the cooling step is 60,000 (°C·sec) or less. The heat treatment method for a silicon substrate according to claim 3, characterized in that the off-angle of the main surface of the silicon substrate is 0.23° or more.