TW202516628A - Adsorption control method and film forming device - Google Patents

Abstract

[Topic] Controlling the adsorption of the raw material of the second layer onto the first layer. [Solution] A method for controlling the adsorption of the raw material of the second layer onto the first layer is provided, which comprises: preparing a substrate having the first layer on a platform in a chamber; supplying the raw material of the second layer into the chamber so that the raw material is exposed to the surface of the first layer; and controlling the adsorption of the raw material onto the surface of the first layer by controlling the charge imparted to the defects on the surface of the first layer.

Description

Adsorption control method and film forming device

The present disclosure relates to an adsorption control method and a film forming device.

For example, Patent Document 1 describes the following method: in the process of forming a two-dimensional insulating material layer and a two-dimensional semiconductor material layer, after forming the two-dimensional insulating material layer, the surface is activated by ion doping, and a two-dimensional semiconductor material layer composed of transition metal chalcogenide, black phosphorous, silicene, germanium or graphene is formed by CVD or ALD. [Prior Art Document] [Patent Document]

[Patent Document 1] Specification of China Patent Application Publication No. 109962106

[Problems to be solved by the present invention]

This disclosure provides a technology that can "control the adsorption of the second layer's raw materials to the first layer." [Means for solving the problem]

According to one aspect of the present disclosure, a method for controlling adsorption of a second layer of raw materials onto a first layer is provided, which comprises: preparing a substrate having the first layer on a platform in a chamber; supplying the second layer of raw materials into the chamber so that the raw materials are exposed to the surface of the first layer; and controlling the adsorption of the raw materials onto the surface of the first layer by controlling the charge imparted to defects on the surface of the first layer. [Effect of the invention]

According to one aspect, the adsorption of the raw material of the second layer to the first layer can be controlled.

Hereinafter, referring to the drawings, the embodiments for implementing the present disclosure are described. In each of the drawings, the same components are sometimes given the same symbols and repeated descriptions are omitted.

[An example of hexagonal boron nitride] The deposition of transition metal dichalcogenides (hereinafter also referred to as "TMDC") to hexagonal boron nitride (hereinafter also referred to as "h-BN") is extremely important for the application of two-dimensional materials in industry. h-BN and TMDC are examples of two-dimensional material layers. h-BN is an example of a two-dimensional insulating material layer. TMDC is an example of a two-dimensional semiconductor material layer, and MoS ₂ , WS ₂ , MoSe ₂ , WSe ₂ , etc. can be cited.

FIG1 shows an example of pure, i.e., defect-free bilayer hexagonal boron nitride (bilayer h-BN). FIG1(a) shows the surface (XY plane) of h-BN. h-BN is a layered material, and FIG1(b) shows the layered structure of bilayer h-BN in the Z direction. The number of layers of h-BN is not limited to two layers, and it has a layered structure of a two-dimensional structure formed by stacking a plurality of six-membered rings bonded together, and the six-membered rings are formed by alternating covalent bonding of boron (B) and nitrogen (N).

Like h-BN, TMDC is a layered material with a two-dimensional (2D) structure. Since TMDC has a band gap of 1 to 2 eV and a high carrier (electron) mobility, it is used, for example, as a channel material for transistors. In order to maintain the carrier mobility and subcritical swing of TMDC at an ideal level, an inactive two-dimensional h-BN is required as a protective layer for TMDC. In addition, since h-BN has a large band gap of 4 to 5 eV, electrons will not flow unless energy greater than that of TMDC is applied, so it functions as an insulating film to prevent leakage.

However, it is difficult to deposit TMDCs directly on h-BN or other two-dimensional materials in order to make two-dimensional heterostructures. For example, WS ₂ is a promising candidate for future FET channels, which has a relatively wide bandgap and low subcritical swing among all TMDCs. _{WF 6} and H ₂ S precursors have been proposed as precursors for the ALD process to form WS ₂ by ALD (Atomic Layer Deposition) method.

However, since common precursors such as _WF6 and _H2S do not interact strongly with the pure h-BN surface, it is difficult to use these raw materials for the formation of _WS2 films on h-BN. Moreover, the reactivity of the h-BN surface cannot be controlled in the ALD process. Therefore, in the previous ALD process, the size of the _WS2 crystal domain cannot be controlled, resulting in _WS2 with small crystal domains of poor film quality. "Crystal domain" is similar to the meaning of crystal grain size. When the crystal grain size is larger, the ratio of the grain boundaries of the _WS2 film, which originally has poor properties, is reduced, and the film quality is improved.

In this regard, the inventors discovered using first-principles quantum simulation that although the adsorption of _WF6 onto pure h-BN is weak, the adsorption of _WF6 can be significantly enhanced by forming defects (vacancies) in h-BN.

The following is an explanation of an adsorption control method for "controlling the adsorption state of a precursor used for forming a TMDC film by adjusting the Fermi level of h-BN when forming a TMDC film on the surface of h-BN." In the description of the adsorption control method of this embodiment, WS ₂ is cited as an example of TMDC deposited on the surface of h-BN, and WF ₆ and H ₂ S are cited as precursors for forming a WS ₂ film.

Figures 1(c) and (d) show an example of a vacancy (vacancy) formed in h-BN. Figures 1(c) and (d) show the state of the surface (first layer) of h-BN. In Figure 1(c), the lattice point A1 where N originally existed in the first layer becomes a nitrogen vacancy (hereinafter also referred to as "V _N "). The boron (B) existing at the lattice point A1 refers to the B of the h-BN in the second layer existing at the position of the vacancy A1.

In FIG1(d), the lattice site A2 of the first layer where B originally existed becomes a boron vacancy (hereinafter also referred to as "V _B "). The nitrogen (N) existing at the lattice site A2 refers to the N of the h-BN of the second layer existing at the position of the vacancy A2.

[Simulation 1] In simulation 1, the changes in the adsorption energy of WF ₆ and H ₂ S on the h-BN surface were simulated for the case of pure h-BN and the case of h-BN with defects. The results are shown in Figure 2.

"Ideal" in Figure 2 is pure h-BN with no defects. "V _N " is a defect in which N is missing at the lattice point of h-BN (N defect). " _VB " is a defect in which B is missing at the lattice point (B defect). "Si _N -H", "C _N -H", and "C _N " are N atoms of h-BN replaced by SiH, CH, and C, respectively. "Si _B -H", "C _B -H", and "C _B " are B defects in which nearby nitrogen is replaced by SiH, CH, and C, respectively. "V _N -H " is H present near V _N , "B _N " is N atom replaced by B. " _NB " is B atom replaced by N. " _ON " is N atom replaced by O (oxygen). " _ON -H" means that the N atom is replaced by O (oxygen), and H (hydrogen) bonds with O.

In simulation 1, WF ₆ and H ₂ S are adsorbed on the surface of h-BN respectively for the case of pure h-BN and the case of h-BN with various defects as described above. In addition, the charge state in various h-BN defects is set to 0, that is, electrically neutral.

The vertical axis of Fig. 2 represents the adsorption energy E_ad of WF ₆ and H ₂ S on the surface of various h-BN. E_ad is represented by the following formula (1). E_final in formula (1) represents the adsorption energy of each molecule of WF ₆ and H ₂ S adsorbed on the surface of h-BN to optimize the structure and stabilize the state. E_h-BN represents the adsorption energy when each molecule of WF ₆ or H ₂ S is not adsorbed on the surface of h-BN. _{E_molecule} represents the adsorption energy of each molecule _of WF ₆ or H ₂ S. Therefore, the adsorption energy E_ad represents the difference between the adsorption energy of each molecule of WF 6 or H 2 S adsorbed on h-BN and the state before adsorption. The larger the absolute value of the adsorption energy E_ad, the stronger the adsorption.

In the case of pure h-BN indicated by "Ideal", the adsorption of each molecule of WF ₆ and H ₂ S to h-BN refers to weak adsorption caused by van der Waals force. On the other hand, in the case of "V _N ", the adsorption of WF ₆ to h-BN is enhanced. In the case of " _CB ", the adsorption of WF ₆ to h-BN is enhanced. In the case of "O _N ", the adsorption of WF ₆ and H ₂ S to h-BN is enhanced. The other above-mentioned adsorption of h-BN refers to weak adsorption caused by van der Waals force.

This shows that when the charge state of the defect is set to 0, in h-BN having defects such as "V _N ", "C _B ", and "O _N ", strong chemical adsorption occurs between the defects and WF ₆ .

Furthermore, it can be seen that when the charge state of the defect is set to 0, in h-BN having an " _ON " defect, strong chemical adsorption occurs between the defect and _H2S .

[Simulation 2] In simulation 2, the behavior of _WF6 adsorbed on the h-BN surface of "V _N " was calculated when the charge of the N defect was set to 0, -1, and +1. Figure 3 shows the results of simulation 2. Figure 3(a) shows the adsorption of _WF6 on "V _N " (hereinafter also marked as "V _N ⁰ ") when the charge of the N defect in the vacancy is set to 0. The number of electrons in the outermost shell of N is five. When the charge to the N defect is 0, it is electrically neutral, that is, electrons do not enter or exit the N defect, and the number of electrons in the outermost shell remains five. Therefore, since the number of electrons in the outermost shell is an odd number, electron spin is generated. Under this condition, strong chemical adsorption occurs between the N defect of h-BN and _WF6 .

Figure 3(b) shows the adsorption of _WF6 at " _VN " (hereinafter also referred to as " _VN ^-1 ") when the charge of the N defect in the vacancy is set to -1. When the charge of the N defect is -1, one electron enters the N defect. At this time, since the number of electrons in the outermost shell is even and h-BN is not a magnetic material, no electron spin is generated. Under this condition, strong chemical adsorption occurs between the N defect of h-BN and _WF6 .

Figure 3(c) shows the adsorption of _WF6 at " _VN " (hereinafter also referred to as " _VN ⁺¹ ") when the charge of the N defect in the vacancy is set to +1. When the charge of the N defect is +1, one electron is released from the defect. At this time, since the number of electrons in the outermost shell is an even number, no electron spin is generated. Under this condition, weak adsorption caused by the van der Waals force occurs between the N defect of h-BN and _WF6 .

FIG4 is a graph showing the change of adsorption energy due to ^the charge state of _VN . The horizontal axis of FIG4 shows the charge state of _{VN VN} ^-1 , _VN0 , _VN ⁺¹ , and the vertical axis shows the adsorption energy E_ad at each charge state. When the charge state of _VN is _VN ^{-1 or} _VN0 , W of _WF6 dissociates from F and adsorbs, the adsorption energy is low, and F is easily and stably adsorbed on the base layer. When the charge state of _VN is _VN ⁺¹ , the adsorption energy is high and unstable, and F is difficult to adsorb on the base layer.

[Simulation 3] In simulation 3, the state density of electrons on the surface of h-BN with N defects having charge states ^of " _VN0 ", " _VN ^-1 ", and " _VN ⁺¹ " was calculated. From the results of simulation 3, the mechanism of the difference in the adsorption state of _WF6 caused by the charge states of N defects shown in Figure 3 was estimated.

Figure 5 shows the results of simulation 3. The horizontal axis of Figure 5 represents energy levels, and the vertical axis represents the density of states (DOS) of electrons on the surface of h-BN at "V _N ⁰ ", "V _N ^-1 ", and "V _N ⁺¹ ". In simulation 3, the temperature is set to absolute zero (0 kelvin). As mentioned above, in the case of "V _N ^-1 " and "V _N ⁺¹ ", the number of electrons in the N defect is even, and no electron spin is generated. In the case of "V _N ⁰ ", the number of electrons in the N defect is odd, and spin is generated in the electron, which is polarized into positive (up spin) and negative (down spin).

Figure 5(a) shows the DOS of the h-BN surface in the case of "V _N ⁰ " and polarized electron spins to positive and negative. The energy level of about -3 to 2 (eV) is the energy band gap (of h-BN). According to the Fermi-Dirac distribution, there are fewer carriers outside the vicinity of the Fermi level. In addition, the energy level less than -3 (eV) is the valence band (valence band), and the energy level greater than 2 (eV) is the conduction band (acceptor band). The Fermi level in the energy band gap can be defined anywhere in the energy band gap. In Figures 5(a) to (c), the Fermi level is defined as 0 eV.

The upper part of Figure 5(a) shows the DOS of the h-BN surface in the case of up-spin electrons, and the lower part shows the DOS of the h-BN surface in the case of down-spin electrons. In the result of Figure 5(a), in the case of up-spin electrons, the DOS increases locally at the Fermi energy level (0eV). In the case of down-spin electrons, the DOS is 0 at the Fermi energy level (0eV). This means that in h-BN with electron spin "V _N ⁰ ", only electrons polarized to positive exist in isolated N defects.

In Figure 5(b), the energy level of about -3 to +1 (eV) is the band gap in h-BN with no electron spin at "V _N ^-1 ". In the result of Figure 5(b), DOS increases locally at the Fermi level (0 eV). This indicates that electrons exist in the N defect of h-BN at "V _N ^-1 ".

In Figure 5(c), in h-BN without electron spin at "V _N ⁺¹ ", the energy level above 0 eV is the energy band gap. In the result of Figure 5(c), DOS is 0 at the Fermi level (0 eV). This means that the physical properties of h-BN at "V _N ⁺¹ " are similar to those of pure h-BN.

In "V _N ⁰ " of FIG. 5 (a), h-BN with electron spin, and "V _N ^-1 " of FIG. 5 (b), h-BN without electron spin, the charge density of electrons in the space near the N defect becomes an electron distribution extending in the height direction from the XY plane of the h-BN surface.

When the wave function is set to Ψ, the probability of an electron being found in the space near the defect at a certain time t is equal to |Ψ(t)| ^2. Therefore, the charge density of the electron is proportional to the square root of the wave function of the electron, and the charge density of the electron can be indirectly expressed from the wave function of the electron.

In the case of h-BN of " _VN0 ^" and " _VN ^-1 ", from the wave function of the electrons filled in the space near the defect closest to the Fermi level, the electron orbit becomes _Pz (or π orbit), which becomes longer in the Z direction (vertical direction) from the XY plane of the h-BN surface. Therefore, the charge density of the electrons in the space near the defect becomes a distribution extending in the height direction from the plane of h-BN. In this case, since the reactivity in the N defect becomes higher, it is estimated that the adsorption force of _WF6 becomes stronger.

In the case of h-BN at "V _N ⁺¹ ", from the wave function of the electrons filled in the space near the defect closest to the Fermi level, the electron orbit takes the P _xy (or σ orbit), and the charge density of the electrons in the space near the defect becomes an electron distribution that is periodically scattered on the XY plane of the h-BN surface. In this case, the h-BN surface becomes a state similar to the physical properties of the original pure h-BN, and the adsorption of WF ₆ to h-BN is a weak adsorption caused by the van der Waals force.

[Correlation between Fermi Level and Formation Energy of Surface Defects] The results of "Correlation between Fermi Level and Formation Energy of Surface Defects (N Vacancy) in h-BN with "V _N " by simulation" are shown in FIG6. FIG6 is an example of a graph showing the correlation between Fermi Level and Formation Energy of Defects in an implementation form. The horizontal axis of FIG6 represents Fermi Level E _f (Fermi Level), and the vertical axis represents Formation Energy of Defects (Formation Energy). The lower the formation energy of a defect, the more stable the defect is.

As shown in the results of FIG6 , when the Fermi energy level E _f is shifted, the most stable charge state in the N defect (N Vacancy) changes. For example, when the Fermi energy level E _f is between 0 and greater than 2.5 eV, the N defect is set to a charge state of +1, thereby making the defect the most stable state. When the Fermi energy level E _f is greater than 2.5 eV to about 4 eV, the N defect is set to a charge state of 0, thereby making the defect the most stable state. When the Fermi energy level E _f is above about 4 eV, the N defect is set to a charge state of -1, thereby making the defect the most stable state.

The charge state with the lowest defect formation energy is the stable state of the defect. Therefore, by adjusting the Fermi level _Ef , h-BN is directly adjusted so that the N defect of h-BN with "V _N " becomes a stable charge state.

As a method of adjusting the Fermi level, the Fermi level can be adjusted by applying a direct current voltage from the outside and/or doping h-BN with impurities to impart charges to h-BN of "V _N ".

When a direct current voltage is applied from the outside to impart charge to h-BN, the potential of h-BN is set to positive or negative. Thus, the Fermi energy level can be adjusted to shift to the high energy side or the low energy side by the electric field applied to h-BN. The Fermi energy level is the lowest energy "V _N ⁺¹ " shown by the dot link line of +1 in Figure 6 when it is around 0ev (no potential) to 3eV, and the lowest energy is "V _N ⁰ " shown by the solid line of Neutral (0) when it is around 3eV to 5eV on the right. The lowest energy is "V _N ^-1 " shown by the dotted line of -1 when it is above 5eV on the right. In order to shift the Fermi energy level to the right, the h-BN surface is set to a negative potential. In order to shift the Fermi energy to the left, the h-BN surface is set to a positive potential.

When doping h-BN with impurities to impart charges to h-BN, p-type doping and n-type doping can be performed, and for p-type doping, for example, Mg and Be can also be used. However, in order to impart charges to h-BN, applying a direct current voltage from the outside has a higher degree of controllability and is better than doping h-BN.

As described above, in the adsorption control method of this embodiment, the electric field (voltage) applied to h-BN is controlled to shift the Fermi energy level. This adjusts the charge state of the defects in h-BN, thereby changing the reactivity of WF ₆ and controlling the adsorption of WF ₆ to h-BN.

FIG7 shows an example of the adjustment of the charge state of the N defect of h-BN in an embodiment and its effect. For example, as shown in FIG7(a), when the Fermi level is adjusted so that the charge to the N defect becomes +1 by applying a voltage to h-BN, a state similar to pure h-BN is obtained, and the adsorption force of _WF6 to h-BN becomes weak. As shown in FIG7(b), when the Fermi level is adjusted so that the charge to the N defect becomes -1 or 0 by applying a voltage to h-BN, the adsorption of _WF6 near the N defect of h-BN becomes strong. In addition, materials such as sapphire, _SiO2 , Si, and High-k can be used instead of h-BN.

[Adsorption control method] Next, an adsorption control method of an implementation form will be described while referring to FIG. 8 and FIG. 9. FIG. 8 is a flow chart showing an example of an adsorption control method of an implementation form. FIG. 9 is a diagram for illustrating an adsorption control method of an implementation form. The adsorption control method shown in FIG. 8 takes "film formation of WS ₂ to h-BN by ALD method" as an example. The adsorption control method is controlled, for example, by the control unit 3 of FIG. 10 described later, and implemented by the film forming device 1 of FIG. 10.

When the adsorption control method is started, in step S1, a substrate having h-BN containing N defects is prepared on a stage in a chamber. In addition, as a method of controlling N defects formed in h-BN, it is possible to control the number of N defects by performing film formation under a nitrogen deficiency state during h-BN film formation. However, since h-BN naturally generates N defects during film formation, it is not necessarily necessary to control N defects during h-BN film formation.

Next, in step S2, a negative DC voltage is applied to the electrode of FIG. 10 (electrode 40 of FIG. 10(a) and ^the like), thereby adjusting the Fermi level to " _VN0 " (charge to N defect is 0) or " _VN ^-1 " (charge to N defect is -1), while supplying a small amount _{of WF6} into the chamber. At this time, as shown in FIG. 9(a), the adsorption of _WF6 near the defects of h-BN becomes stronger, and _WF6 is adsorbed near the defects.

In step S2, WF ₆ is supplied for the first cycle. At this time, although the charge state of the N defect is adjusted to 0, the reactivity near the defect is increased and the adsorption of WF ₆ is enhanced, the supply amount of WF ₆ is controlled to be less than that after the second cycle. As a result, as shown in FIG. 9(a), WF ₆ molecules are adsorbed on a part of the N defect, and most of the N defect becomes a vacancy. In addition, in step S2 and the later-described step S5, WF ₆ and Ar can also be supplied. In this case, the first cycle of step S2 can also be diluted with Ar to set WF ₆ to a small amount compared to after the second cycle of step S5.

Next, in step S3 of the first cycle, H ₂ S is supplied into the chamber in the same state as step S2 (state of "V _N ⁰ " or "V _N ^-1 "). At this time, as shown in FIG. 9 (b), although the state of charge is 0 or not shown, H ₂ S is weakly adsorbed near the vacant N defect in the state of charge -1. On the other hand, H ₂ S reacts with the WF ₆ molecule adsorbed on the N defect to form a crystal nucleus of W(SH) _x . In step S3, H ₂ S is supplied in a sufficient amount to form a crystal nucleus. The crystal nucleus used here means a crystal nucleus that becomes the center of film growth. A bias voltage is applied as needed. For example, when forming a crystal nucleus, a predetermined bias voltage is applied. Since it is not necessary during film formation after the nucleus formation, the application of the bias voltage can be appropriately stopped.

Next, in step S4, it is determined whether to repeat the set number of cycles. When it is determined that the set number of cycles is not repeated, in step S5, a positive DC voltage is applied to the electrode, thereby adjusting the Fermi level to "V _N ⁺¹ (charge to N defects is +1)" while supplying WF ₆ into the chamber. As a result, the adsorption of WF ₆ is weakened, and adsorption of WF ₆ does not occur except in the portion where the crystal nucleus of W(SH) _x has been formed. As a result, a large crystal domain can be formed by two-dimensional growth in the lateral direction from a small number of controlled crystal nuclei. As a result, as shown in FIG. 9( c ), the particle size of the crystal nucleus of W(SH) _x can be increased. Next, in step S3 of the second cycle, H ₂ S is supplied into the chamber in the same state as step S5 (the "V _N ⁺¹ " state) to make W(SH) The crystal nucleus of _x grows further.

When the set number of cycles is three or more, step S5 and step S3 are further regarded as one cycle and are repeated until the set number of cycles is reached. However, since the charge to the N defect in step S5 after the third cycle has been adjusted to +1 in the second cycle, it is not necessary to apply a voltage to further adjust the Fermi level and supply WF ₆ . When it is determined in step S4 that the set number of cycles has been repeated, this process is terminated.

According to the adsorption control method of the present embodiment, WF ₆ is supplied into the chamber while adjusting the Fermi level, thereby adjusting the adsorption of WF ₆ to the h-BN surface. In addition, by controlling the supply amount of WF ₆ , the formation density of the crystal nuclei can be controlled. The more the number of crystal nuclei, the smaller the crystal domain and the lower the film quality of WS _2. Therefore, by reducing the number of crystal nuclei, the crystal domain is increased and the crystal domain boundary is reduced. In this way, by controlling the size of the crystal domain of WS ₂ , a good quality WS ₂ film can be formed. In addition, by controlling the number of crystal nuclei in the first cycle, there is no need to strictly control the number of defects in h-BN.

In addition, in step S2, the Fermi level can be adjusted by setting the charge state of the defect to -1 instead of setting it to 0. However, when the charge state of the defect is set to -1, a larger voltage is required than when the charge state of the defect is set to 0 to adjust the Fermi level. Therefore, setting the charge state of the defect to 0 makes the control easier and is also cost-effective.

In order to switch between WF ₆ and H ₂ S, it is preferable to perform a flushing process between the process of supplying WF ₆ in steps S2 and S5 and the process of supplying H ₂ S in step S3. In the flushing process, an inert gas such as Ar gas may be supplied.

The adsorption control method of this embodiment is preferably ALD. However, after the nucleus is formed, the film formation method of WS ₂ can also be CVD (Chemical Vapor Deposition) or MOCVD (Metal Organic Chemical Vapor Deposition).

In this embodiment, although the focus is on the improvement of WS ₂ film formation on h-BN caused by WF ₆ and H ₂ S, the adsorption control method of this embodiment can also be applied to other precursors (raw materials of transition metal dichalcogenide films) and other two-dimensional material layers.

For example, a method for controlling the adsorption of a raw material of a transition metal dichalcogenide film onto a two-dimensional material layer, the adsorption control method, comprises: preparing a substrate having a two-dimensional material layer on a platform in a chamber; supplying the raw material of the transition metal dichalcogenide film into the chamber so that the raw material is exposed to the surface of the two-dimensional material layer; and controlling the adsorption of the raw material onto the surface of the two-dimensional material layer by controlling the charge imparted to defects on the surface of the two-dimensional material layer.

The W precursor that is the raw material of WS ₂ is not limited to WF ₆ , and may be a gas containing tungsten and a halogen. Other examples of the W precursor include WCl ₅ , WCl ₆ , W(CO) ₆ , and W ₂ (NME ₂ ) ₆ .

The sulfur precursor that is the raw material of WS ₂ is not limited to H ₂ S, and may be a gas containing sulfur S. The gas containing sulfur S also contains sulfur in a gaseous state.

In the case of applying the ALD method, in the adsorption control method, the raw material of the transition metal dichalcogenide film may also include a first raw material (gas containing tungsten and halogen) and a second raw material (gas containing sulfur). The adsorption control method may also include: (A) supplying the first raw material into the chamber so that the first raw material is exposed to the surface of the two-dimensional material layer; (B) supplying the second raw material into the chamber so that the second raw material is exposed to the surface of the two-dimensional material layer; (C) repeatedly setting the number of cycles in the order of (A) and (B); and (D) when executing (A), by controlling the charge given to the defects on the surface of the two-dimensional material layer, the adsorption of the first raw material to the two-dimensional material layer is controlled.

The above adsorption control method can also be applied to the situation where "there are defects on the surface of the membrane (first layer, lower layer) on which the film formation other than the two-dimensional material is to be carried out, and the charge is controlled by the defects, so that the adsorption and reactivity of the raw materials of the second layer (upper layer) to the first layer change."

[Film-forming device] With reference to FIG. 10 , a film-forming device for implementing the adsorption control method described above will be described. FIG. 10 (a) to (c) are diagrams showing an example of a film-forming device 1 in an implementation form. The film-forming device 1 is a device that can generate plasma.

The film forming apparatus 1 shown in FIG. 10( a) to (c) includes a chamber 2, a control unit 3, a platform 11, and a gas supply unit 12. The gas supply unit 12 is configured to introduce at least one processing gas into the chamber 2. The gas supply unit 12 supplies, for example, WF ₆ and H ₂ S. The gas supply unit 12 includes a nozzle 13. The nozzle 13 is configured to introduce at least one processing gas from the gas supply unit 12 into a processing space. The nozzle 13 has a gas supply port 13a, a gas diffusion chamber 13b, and a plurality of gas introduction ports 13c. The processing gas supplied to the gas supply port 13a is introduced into the processing space from the plurality of gas introduction ports 13c through the gas diffusion chamber 13b.

The gas supply unit 12 may also include a gas source and a flow controller not shown. In one embodiment, the gas supply unit 12 is configured to supply at least one processing gas from a respectively corresponding gas source to the nozzle 13 via a respectively corresponding flow controller.

The platform 11 is arranged in the chamber 2, and carries a substrate W such as a wafer. The nozzle 13 is arranged above the platform 11. In one embodiment, the nozzle 13 constitutes at least a part of the top of the chamber 2. The chamber 2 has: at least one gas supply port for supplying at least one processing gas into the chamber 2; and at least one gas exhaust port for exhausting the gas from the chamber 2. The chamber 2 is grounded. The nozzle 13 and the platform 11 are electrically insulated from the shell of the chamber 2. The gas exhaust port is connected to an exhaust device not shown. The exhaust device may also include a pressure regulating valve and a vacuum pump. The pressure of the processing space in the chamber 2 is adjusted by the pressure regulating valve. The vacuum pump may also include a turbomolecular pump, a dry pump, or a combination thereof.

The RF (Radio Frequency) power source 31 is connected to the nozzle 13 via an impedance matching circuit (not shown) to supply RF power to the nozzle 13. The nozzle 13 also functions as an upper electrode. Thereby, plasma is formed from at least one processing gas supplied to the processing space. Therefore, the RF power source 31 can function as at least a part of a plasma generating unit, which is configured to generate plasma from one or more processing gases in the chamber 2.

The bias power source 32 is connected to the platform 11 via an impedance matching circuit (not shown) to supply bias power to the platform 11. The platform 11 also functions as a lower electrode. By supplying bias power to the lower electrode, a bias potential is generated on the substrate W, and ion components in the formed plasma can be attracted to the substrate W.

A DC (Direct Current) power source 33 is connected to the electrode to apply a direct current voltage to the electrode. In FIG10( a), the DC power source 33 is connected to the electrode 40. h-BN has a contact surface with the electrode 40. By pushing the electrode 40 to the contact surface and applying a direct current voltage, a potential difference is generated between the h-BN and the platform 11, and an electric field in a predetermined direction is generated on the surface of the h-BN. In this way, the Fermi energy level can be adjusted based on the relevant information of the Fermi energy level and the formation energy of the defect shown in FIG6, and the charge state of the defect of the h-BN can be directly adjusted. In addition, the electrode 40 can also be in a frame shape, a probe shape, or other shapes.

In FIG. 10( b ), a DC power source 33 is connected to an electrode 41. The electrode 41 is disposed between the platform 11 (lower electrode) and the nozzle 13 (upper electrode) and near the surface of the substrate W. The DC power source 33 applies a direct current voltage to the electrode 41, thereby generating a potential difference between the electrode 41 and the h-BN, and generating an electric field in a predetermined direction on the surface of the h-BN. In this way, the Fermi energy level can be adjusted based on the information related to the formation energy of the defect shown in FIG. 6 , and the charge state of the defect of the h-BN can be directly adjusted. In addition, the electrode 41 can also be in a grid shape, for example.

In FIG. 10( c ), a DC power source 33 is connected to the nozzle 13 (upper electrode). The DC power source 33 applies a DC voltage using the spraying surface (lower side) of the nozzle 13 as an electrode, thereby generating a potential difference between the spraying surface and the h-BN, and generating an electric field in a predetermined direction on the surface of the h-BN. In this way, the Fermi energy level can be adjusted based on the information related to the formation energy of the defect shown in FIG. 6 , and the charge state of the defect of the h-BN can be directly adjusted.

The control unit 3 processes computer executable commands that cause the film forming apparatus 1 to execute the various processes described in the present disclosure. The control unit 3 can be configured to control the various elements of the film forming apparatus 1 in a manner that executes the various processes described herein. In one embodiment, a part or all of the control unit 3 can also be included in the film forming apparatus 1. The control unit 3 can also include a processing unit, a memory unit, and a communication interface. The control unit 3 is implemented, for example, by a computer. The processing unit can be configured to perform various control actions by reading a program from the memory unit and executing the read program. The program can also be stored in the memory unit in advance, and can also be obtained through a medium when necessary. The acquired program is stored in the memory unit, and is read out from the memory unit by the processing unit and executed. The medium may be various memory media readable by a computer, or a communication line connected to a communication interface. The processing unit may be a CPU (Central Processing Unit). The memory unit may include RAM (Random Access Memory), ROM (Read Only Memory), HDD (Hard Disk Drive), SSD (Solid State Drive), or a combination thereof. The communication interface may communicate with the film forming device via a communication line such as a LAN (Local Area Network). The information related to the Fermi energy level and the defect formation energy in FIG. 6 may be stored in advance in the memory of the control unit 3, or may be obtained from a communication line connected to the communication interface.

Using the film forming apparatus 1 of FIG. 10 (a) to (c), the desired DC voltage is applied to the electrodes 40, 41 and the upper electrode, respectively, and WS ₂ is formed on h-BN by the ALD method using WF ₆ and H ₂ S. Thus, by adjusting the Fermi level, the charge state of the defects of h-BN and the adsorption state of the raw materials of WS ₂ can be adjusted, while the crystal domain size of WS ₂ can be controlled, so that a high-quality WS ₂ film can be formed.

[Others] For example, charges can be supplied to the h-BN surface by generating static electricity or charging it with UV light, etc., to adjust the charge state of the h-BN defects. That is, the substrate with h-BN charged in this way can be transported to the film forming apparatus 1, and WS ₂ can be formed on the h-BN by the ALD method using WF ₆ and H ₂ S.

Plasma may be generated in the film forming apparatus 1, and charged particles in the plasma may be supplied to the h-BN surface to adjust the charge state of the h-BN defects. That is, the substrate with the charge state of the h-BN defects adjusted in this way may be transported to the film forming apparatus 1, and WS ₂ may be formed on the h-BN by the ALD method using WF ₆ and H ₂ S.

After adjusting the charge state of the defects of h-BN, h-BN can be annealed at a high temperature, and _WF6 and _H2S can be supplied to the surface of the annealed h-BN to form a _WS2 film. After adjusting the charge state of the defects of h-BN, the defects can be moved or diffused by annealing h-BN before forming a _WS2 film. By annealing h-BN, atoms can be moved and the type and concentration of defects can be controlled.

The formation of h-BN and the formation of TMDC such as WS ₂ can also be performed by different film forming devices. The aforementioned annealing treatment can be performed by either the h-BN film forming device or the TMDC film forming device. In addition, the formation of h-BN can also be performed by using an ICP (Inductively Coupled Plasma) device without applying a bias voltage.

It is also possible to perform a treatment such as increasing defects on the surface of the h-BN film. That is, after the h-BN film is formed, defects may be increased on the surface of the h-BN film using an inert gas or the like. However, since defects already exist on the h-BN surface when the h-BN film is generally formed, there is no problem even if a treatment such as increasing the defects is not performed.

[Effect] The inventors found that although the adsorption of _WF6 to pure h-BN is weak, the adsorption _{of WF6} to h-BN can be significantly enhanced by introducing defects such as N vacancies (" _VN ", N defects) into h-BN. Furthermore, the reactivity of _WF6 with N defects depends on the charge of the N defects. This means that the reactivity of _WF6 with the h-BN defect surface can be controlled by electric fields, gates or excess doping and/or by adjusting the Fermi level of h-BN. Such controllable surface reactivity can be applied to various 2D and/or 3D deposition (film formation) states.

TMDC is a layered material with a 2D structure like h-BN. Since TMDC has a band gap of 1 to 2 eV and a high carrier mobility, it can be used as a channel material for transistors, for example. By forming a TMDC film using the adsorption control method of this embodiment, the carrier mobility and subcritical swing can be improved.

In addition, h-BN functions as a protective layer for TMDC, preventing the mobility of TMDC from deteriorating due to contamination caused by diffusion from the underlying layer, etc. In addition, since h-BN has a large band gap of 4 to 5 eV, electrons will not flow unless energy greater than that of TMDC is applied, so it can function as an insulating film to prevent leakage.

Furthermore, the crystal domain size of WS ₂ formed by the ALD method can be enlarged using the adsorption control method shown in FIG. 8 .

The surface reactivity of two-dimensional materials that can be electronically controlled can also be applied to the following fields (1) to (3), but is not limited thereto.

(1) Controllable TMDC deposition area size (2) Controllable TMDC deposition rate (3) Controllable area selectivity of deposition on different surfaces (e.g. h-BN or other 2D and/or 3D substrates)

It should be understood that the adsorption control method and film forming device of the embodiments disclosed herein are illustrative and non-restrictive in all aspects. The embodiments may be modified and improved in various forms without departing from the scope and subject matter of the attached patent application. The matters described in the above multiple embodiments may also adopt other structures within the scope of non-contradiction, and may be combined within the scope of non-contradiction.

According to the present adsorption control method, as shown in FIG. 2 , not only the adsorption of WF ₆ but also the adsorption of H ₂ S can be controlled.

The film forming apparatus disclosed in this specification can be applied to any of a single-wafer apparatus that processes substrates one by one, a batch apparatus that processes a plurality of substrates at a time, and a semi-batch apparatus.

The film forming apparatus disclosed in this specification is not limited to an apparatus that uses plasma to process a substrate, and may also be an apparatus that does not use plasma to process a substrate.

1: Film forming device 2: Chamber 3: Control unit 11: Platform 33: DC power supply 40,41: Electrode

[Figure 1] A diagram showing an example of hexagonal boron nitride. [Figure 2] A diagram showing the result of simulation 1 of adsorption energy of an embodiment. [Figure 3] A diagram showing the result of simulation 2 of the adsorption state of WF ₆ of an embodiment. [Figure 4] A diagram showing the change of adsorption energy caused by the charge state of V _N. [Figure 5] A diagram showing the result of simulation 3 of the surface state of h-BN of an embodiment. [Figure 6] A curve diagram showing the correlation between the Fermi step of an embodiment and the formation energy of surface defects. [Figure 7] A diagram showing an example of adjustment of the charge state of an embodiment and its effect. [Figure 8] A flow chart showing an example of an adsorption control method of an embodiment. [Figure 9] A diagram for explaining an adsorption control method of an embodiment. [Figure 10] A diagram showing an example of a film forming device of an embodiment.

Claims (20)

An adsorption control method is a method for controlling the adsorption of a second layer of raw materials onto a first layer. The adsorption control method is characterized by comprising: Preparing a substrate having the first layer on a platform in a chamber; Supplying the second layer of raw materials into the chamber so that the raw materials are exposed to the surface of the first layer; and Controlling the adsorption of the raw materials onto the surface of the first layer by controlling the charge imparted to defects on the surface of the first layer. As in claim 1, the adsorption control method, wherein, the aforementioned first layer is a two-dimensional material layer, and the aforementioned second layer is a transition metal dichalcogenide film. As in claim 2, the adsorption control method, wherein the transition metal dichalcogenide film is formed by ALD. The adsorption control method of claim 3, wherein the raw material of the transition metal dichalcogenide film comprises a first raw material and a second raw material, and comprises: (A) supplying the first raw material into the chamber so that the first raw material is exposed to the surface of the two-dimensional material layer; (B) supplying the second raw material into the chamber so that the second raw material is exposed to the surface of the two-dimensional material layer; (C) repeatedly setting the number of cycles in the order of (A) and (B); and (D) when executing (A), controlling the charge imparted to the defects on the surface of the two-dimensional material layer, thereby controlling the adsorption of the first raw material to the two-dimensional material layer. The adsorption control method of any one of claims 2 to 4, wherein, controlling the charge imparted to the defects on the surface of the two-dimensional material layer comprises: applying a direct current voltage to an electrode in contact with the contact surface of the two-dimensional material layer, an upper electrode facing the platform, or an electrode disposed between the platform and the upper electrode. The adsorption control method of claim 5, wherein the method comprises: Storing the relevant information of the Fermi energy level of the aforementioned two-dimensional material layer and the formation energy of the defects on the surface of the aforementioned two-dimensional material layer in a memory unit, Controlling the charge imparted to the defects on the surface of the aforementioned two-dimensional material layer by "referring to the aforementioned memory unit, and controlling the aforementioned DC voltage applied to the aforementioned electrode based on the aforementioned relevant information". The adsorption control method of any one of claims 2 to 4, wherein, controlling the charge imparted to the defects on the surface of the two-dimensional material layer comprises: preparing the substrate on the platform to impart the charge to the surface of the two-dimensional material layer in advance, or imparting the charge to the surface of the two-dimensional material layer of the substrate prepared on the platform from the plasma generated in the chamber. The adsorption control method of any one of claim 2 to claim 4, wherein, the adsorption of the raw material to the surface of the two-dimensional material layer is controlled by "after controlling the charge of defects imparted to the surface of the two-dimensional material layer, annealing the two-dimensional material layer, and supplying the raw material to the annealed surface of the two-dimensional material layer". The adsorption control method of any one of claim 2 to claim 4, wherein the raw material is a gas containing tungsten and halogen and/or a gas containing sulfur. The adsorption control method of claim 9, wherein the gas containing tungsten and halogen is any one of WF ₆ , WCl ₅ , WCl ₆ , W(CO) ₆ or W ₂ (NME ₂ ) ₆ , and the gas containing sulfur is H ₂ S. As in claim 4, the adsorption control method, wherein, the adsorption of the first raw material and the second raw material to the two-dimensional material layer is controlled so that the charge of the defects on the surface of the two-dimensional material layer in the first cycle of the set number of cycles becomes 0 or -1, and the charge of the defects on the surface of the two-dimensional material layer in the second cycle of the set number of cycles becomes +1. As in any one of claim 2 to 4, the adsorption control method, wherein, the aforementioned two-dimensional material layer is hexagonal boron nitride. As in claim 12, the adsorption control method, wherein, when the raw material is _WF6 , the surface defect of the hexagonal boron nitride is any one of a state of nitrogen deficiency, a state where the boron deficiency position is replaced by carbon, or a state where the nitrogen deficiency position is replaced by oxygen. The adsorption control method of claim 12, wherein, when the raw material is H ₂ S, the surface defect of the hexagonal boron nitride is a state where a nitrogen-deficient position is replaced by oxygen. The adsorption control method of claim 4, wherein the flow rate of the first raw material supplied to the chamber in the first cycle of the set number of cycles is less than the flow rate of the first raw material supplied to the chamber in the second cycle of the set number of cycles and thereafter. As in claim 15, the adsorption control method, wherein, based on the flow rate of the aforementioned first raw material supplied to the aforementioned chamber in the aforementioned first cycle, the formation density of crystal nuclei on the surface of hexagonal boron nitride is controlled. The adsorption control method of claim 4, wherein the first raw material is WF ₆ and the second raw material is H ₂ S. The adsorption control method according to any one of claims 2 to 4, wherein the transition metal dichalcogenide film is a WS ₂ film or a WSe ₂ film. A film forming device comprises a chamber, a platform disposed in the chamber and carrying a substrate, and a control unit, and forms a transition metal dichalcogenide film on a first layer of the substrate. The film forming device is characterized in that the control unit performs: preparing the substrate on the platform in the chamber; supplying a raw material of the transition metal dichalcogenide film into the chamber so that the raw material is exposed to the surface of the first layer; and controlling the adsorption of the raw material to the surface of the first layer by controlling the charge of defects on the surface of the first layer, thereby controlling the adsorption of the raw material to the first layer. As in claim 19, the film-forming device, wherein, the aforementioned first layer is a two-dimensional material layer.

Images