JPH09199381A - Si substrate for epitaxial wafer and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an epitaxial wafer having a superior crystallinity without involving any dislocation in surface Si single crystal and no defect in view of the fine structure. SOLUTION: A Si substrate is heavily doped with Sb to provide a specified Sb concn. (Sbo ). Its surface Sb concn. (Sbs ) at its outermost face to grow an epitaxial film is 1×10<17> atoms/cm<3> or less and the Sb concn. increases at a gradient up to an Sb concn. (Sbx ) over (Sbo )×0.5 in the depth of at least 2 microns from the outermost face. The substrate can be produced by heat-treating its surface to grow the epitaxial film in a H -or/and Ar-containing gas atmosphere with (Sbs ) of at least 1×10<17> atoms/cm<3> or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon substrate for an epitaxial wafer and a method for manufacturing the same, and
An antimony-doped silicon substrate capable of epitaxially growing a silicon single crystal on the surface without warping or crystal lattice distortion with good crystallinity. Finally, a silicon substrate for an epitaxial wafer capable of manufacturing a high-performance semiconductor device such as a VLSI and its manufacturing method. Regarding

[0002]

2. Description of the Related Art In recent years, the degree of integration of semiconductor devices has been remarkably high, and a silicon wafer, which is a substrate thereof, is required to have high performance and to have better crystallinity. Therefore, an epitaxial silicon wafer has been conventionally used as a wafer for a DRAM or MPU substrate. Epitaxial silicon wafers generally contain a carrier source such as antimony (Sb) of 1 × 10 ¹⁸ ato.
A silicon single crystal film having a thickness of several μm is epitaxially grown on a surface of a heavily doped silicon substrate of ms / cm ³ or more. The epitaxial silicon single crystal film formed on the surface of this epitaxial silicon wafer usually has an antimony concentration of 1.5 × 10 5.
It is in a lightly doped state of ¹⁶ atoms / cm ³ or less.
At present, high performance is ensured by forming devices on a highly crystalline silicon film epitaxially grown on such an epitaxial silicon wafer.

[0003]

However, in ultra-high integration semiconductor memories represented by VLSIs of recent years, it is usual to form sub-micron-order elements on the surface of an epitaxial wafer, and only silicon on the surface is formed. Even if the crystal has good crystallinity, if there are strains in the microstructure of the entire wafer and differences in trace amounts, these microstructural strains have a great impact on the final semiconductor device. It will be. On the other hand, a silicon epitaxial film on which a device is formed is epitaxially grown on a silicon substrate having a predetermined antimony concentration with a different antimony concentration as described above, and although the interface with the substrate has an autodoping phenomenon due to diffusion, The concentration suddenly changes stepwise in a step function. The inventors are convinced that the abrupt change in the compositional composition in the epitaxial wafer as described above affects the entire epitaxial wafer and causes some inconvenience to the epitaxial film. We proceeded with a microstructural study of the epitaxial film on the surface. As a result, the change in the antimony concentration at the interface between the silicon substrate and the epitaxial silicon film causes lattice structural distortion and structural warp in the epitaxial wafer, and the relaxation is also corresponding to the discontinuous change in the silicon lattice constant. The present inventors have found that there is a risk of dislocation in an epitaxial crystal due to stress, and have arrived at the present invention to provide a more complete and highly crystalline epitaxial wafer as a substrate of a semiconductor device for which higher integration is required.

[0004]

According to the present invention, a silicon substrate having a predetermined heavy-doped antimony concentration [Sb ₀ ] is provided, and the surface antimony concentration at the outermost surface on which the epitaxial film of the substrate is grown. [Sb
_S ] is 1 × 10 ¹⁷ atoms / cm ³ or less, and the antimony concentration [Sb ₀ ] × 0.5 or more [Sb
_X ]], a silicon substrate for an epitaxial wafer, characterized in that the antimony concentration gradually increases with a gradient from the outermost surface to a depth of at least 2 μm. In the silicon substrate for an epitaxial wafer of the present invention,
The antimony concentration [Sb ₀ ] is 1 × 10 ¹⁸ atoms
/ Cm ³ or more is preferable.

Further, according to the present invention, the surface of a silicon substrate having a predetermined heavy-doped antimony concentration [Sb ₀ ] on which an epitaxial film is to be grown is heat-treated in a hydrogen gas and / or argon atmosphere to obtain at least a maximum. The surface antimony concentration [Sb _S ] is 1 × 10 ¹⁷ atoms /
Provided is a method for producing a silicon substrate for an epitaxial wafer, which is characterized in that the thickness is ³ cm ³ or less.

The heat treatment in the method for producing a silicon substrate for an epitaxial wafer according to the present invention is substantially 1000 to 1200 in a hydrogen gas and / or argon gas atmosphere.
The treatment time is preferably 120 to 1840 minutes at a temperature of ° C. For example, the treatment time is expressed by the following formula: D _T Δt _{T
^{= ∫ I F D (T)}} dt ( ^{_{where, ∫ I F D (T)}} dt is antimony from the start of the heat treatment in the heat treatment step to completion of the heat treatment (including substantially cooling process from Atsushi Nobori at 1000 ° C. or higher) , D _T is the diffusion coefficient (cm ² / sec) of antimony at T ° C., Δt _T is the heat treatment time corresponding to T ° C., that is, it is required when all the heat treatment steps are performed at T ° C. Heat treatment time)
It is preferably t _T.

The silicon substrate for an epitaxial wafer of the present invention is configured as described above, and the antimony concentration of the carrier source on the surface of the silicon substrate on which the epitaxial film is formed is set to a predetermined value of 1 × 10 ¹⁷ atoms / cm ³ or less. Since the antimony concentration gap at the interface with the lightly doped epitaxial film of 1 × 10 ¹⁵ to 1 × 10 ¹⁶ atoms / cm ³ is significantly reduced, the crystal lattice strain can be reduced and the crystal dislocation of the epitaxial film can be suppressed. And a more complete silicon crystal can be obtained. Further, since the antimony concentration is gradually decreased from the inside of the silicon substrate of a predetermined depth to the surface to have the above-mentioned predetermined concentration on the surface, discontinuity of the lattice constant can be eliminated, the lattice strain can be reduced, and the epitaxial strain can be reduced. It is possible to prevent deterioration of the film characteristics, and it is possible to provide a highly reliable device having good element characteristics with high yield. Further, the above-described silicon substrate for an epitaxial wafer can be easily manufactured by subjecting the silicon wafer to a heat treatment in a hydrogen gas and / or argon gas atmosphere under predetermined conditions, and thus has extremely high industrial practicality.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. As the silicon substrate of the present invention, a conventionally well-known one that is heavily doped with antimony for n-type semiconductor at a concentration of 1 × 10 ¹⁸ atoms / cm ³ or more can be used, and its surface has a predetermined crystal like a normal wafer. The one sliced into a surface and polished into a mirror surface is used. Next, it will be described that when a silicon film is epitaxially formed on the above-described silicon wafer heavily doped with antimony, inconvenience occurs in a fine structure such as crystal lattice distortion. The lattice constant of silicon doped with antimony is, for example, "Soviet Physics (Solid State)" Vol. 10, 224.
According to p. 7 (1969), the lattice constant of silicon is 5.
Antimony concentration [Sb] = 1 × 10 against 43070Å
It has been reported to increase to 5.43085Å at ¹⁹ atoms / cm ³ . Therefore, Vegal's law (Vegar
d's law) suggests that the lattice constant of antimony heavy-doped silicon increases in proportion to the antimony concentration. Considering the values of these lattice constants, the lattice constant a _{1 of} silicon doped with a certain antimony concentration [Sb] is a ₁ = 5.43070 (1 + 2.76 × 10
^-24 [Sb]), [Sb] <1 × 10 ¹⁸ at
In the case of oms / cm ³ , (5.43071-5.43)
070) = 1 × 10 ⁻⁵ Å or less, and it is known that the change is slight. Therefore, it is presumed that if the usual antimony light doping of 1.5 × 10 ¹⁶ atoms / cm ³ or less in the epitaxial wafer is performed, the change in the silicon crystal lattice constant is small and the distortion of the crystal lattice does not have to be a problem. It

In the present invention, the surface antimony concentration [Sb _S ] of the silicon substrate on which the epitaxial film is formed is
Antimony concentration of the above heavy-doped silicon substrate [S
b ₀ ]> 1 × 10 ¹⁸ atoms / cm ³ to 1 × 10 ¹⁷
It is reduced to atoms / cm ³ or less. In the above report,
When the antimony concentration is lower than 1 × 10 ¹⁸ atoms / cm ³ , the change in the crystal lattice constant of silicon is small and the lattice strain is small. However, the antimony concentration of the epitaxial film formed on the silicon substrate of the epitaxial wafer is 1 × 10 ¹⁵ to 1 × 10 ¹⁶ atoms / cm ³ , and as described above, the sudden change of the antimony concentration at the interface with the silicon substrate is There is a risk of causing crystal dislocation in the epitaxial film, and the same antimony concentration [Sb _S ] 1
It is preferable that the surface is not more than × 10 ¹⁷ atoms / cm ³ . Surface antimony concentration [Sb _S ] is 1 × 10 ¹⁷ a
When it exceeds toms / cm ³ , the lattice strain at the interface with the silicon substrate becomes large, which is not preferable.

The silicon substrate for an epitaxial wafer of the present invention has the above-mentioned surface antimony concentration, and the antimony concentration gradually increases toward the inside of the silicon substrate at a depth of at least about 2 μm with a concentration gradient. Heavy-doped antimony concentration [Sb ₀ ]> 1 × 10 ¹⁸
Antimony concentration of 50% or more of atoms / cm ³ , that is, [Sb ₀ ] × 0.5 or more of antimony concentration [Sb _X ]
Finally, the innermost part is composed of the original heavy-doped antimony silicon substrate. The reason why the antimony concentration has a gradient at a depth of at least about 2 μm in the inner direction is to reduce the lattice strain at the interface between the silicon substrate and the epitaxial film. If the antimony concentration has a gradient and the depth of increase is less than 2 μm, the profile of the antimony concentration at the interface rises rapidly,
The situation is close to a step function, and the lattice strain at the interface cannot be ignored, which is not preferable. Further, the reason why the antimony concentration [Sb _X ] at a depth of 2 μm is 50% or more of the heavy-doped antimony concentration [Sb ₀ ] is that the profile of the antimony concentration in the depth direction is asymptotic to the antimony concentration in the bulk portion. To get closer to.

As described above, the silicon substrate for an epitaxial wafer according to the present invention has a predetermined antimony concentration on the surface and a predetermined ratio of the antimony concentration on the silicon substrate at a predetermined depth inward. Since the original silicon substrate is retained internally by increasing the concentration to the concentration of, the crystallinity of the lattice constant of the antimonylite-doped epitaxial film formed on the surface is small and good crystallinity is not impaired. Therefore, it is possible to finally secure a good device formation region, suppress the occurrence of crystal dislocation during the device manufacturing process, and improve the characteristics and reliability of the manufactured device.

The method for producing a silicon substrate for an epitaxial wafer according to the present invention is not particularly limited as long as it can meet the above-mentioned requirements. For example, it can be manufactured by the following method. That is, first, a silicon wafer having an antimony concentration of 1 × 10 ¹⁸ atoms / cm ³ or more is manufactured by pulling it up by an ordinary Czochralski method or the like and performing mirror polishing through various steps such as slicing and polishing by a known method. . Next, the manufactured silicon wafer can be heat-treated in a hydrogen gas and / or argon gas atmosphere so as to meet the predetermined requirements. The heat treatment in the hydrogen gas and / or argon gas atmosphere of the present invention is performed by using a predetermined antimony-doped silicon wafer in a single gas atmosphere of either hydrogen gas or argon gas, or in a mixed gas atmosphere of an arbitrary mixture ratio of the two. At a temperature of 1000 to 1200 ° C. and 120 to 1
The treatment is performed for 840 minutes, and the antimony on the surface of the antimony heavy-doped silicon substrate is diffused outward, and the antimony concentration of at least the outermost surface for epitaxial growth is set to 1 × 10 ¹⁷ atoms / cm ³ or less.

In the heat treatment of the present invention, "substantially" means any of the following. That is, when the rate of temperature rise and rate of temperature drop in the furnace are extremely fast and a step function heat treatment schedule can be applied, for example,
A predetermined silicon wafer is set in a boat and placed in a heat treatment furnace, and the atmosphere in the furnace is set to a hydrogen gas and / or argon gas atmosphere at a temperature at which antimony can diffuse outwardly at about 1100 ° C. for about 800 minutes or more, about 1150 32 degrees Celsius
It is to hold for 0 minutes or more, and to hold at about 1200 ° C. for about 120 minutes or more for processing. In addition, the profile of the antimony concentration in the depth direction when the heat treatment is performed for t seconds in the heat treatment in this case is expressed by the following formula (1): [Sb (x, t)] = [Sb
_S ] + ([Sb ₀ ]-[Sb _S ]) erf (x / 2√D _T t) (However, [Sb
(x, t)] is the antimony concentration at a depth of x μm from the outermost surface of the silicon substrate when heat-treated at T ° C. for t seconds,
D _T is the diffusion coefficient of antimony at T ° C. (cm ² /
Seconds). ).

Alternatively, when it takes time to raise and lower the temperature in the furnace, a heat treatment schedule is applied in consideration of outward diffusion of antimony in the temperature raising and cooling steps. For example, a predetermined silicon wafer is set in a boat and placed in a heat treatment furnace, the atmosphere in the furnace is heated only with an inert gas, and when the temperature in the furnace reaches 1000 ° C., the hydrogen gas or And / or argon gas atmosphere, and after continuing the temperature rise, at about 1150 ° C. for about 80 minutes or 1200
The temperature is kept at about 30 minutes for about 30 minutes, and then the inside of the furnace is kept under hydrogen gas and / or argon gas atmosphere for 10 minutes.
This means that the temperature is lowered to 00 ° C., and when the temperature becomes 1000 ° C. or less, the atmosphere in the furnace is replaced with an inert gas again and the temperature is cooled to room temperature.
When the temperature is 000 ° C. or higher, the atmosphere is maintained in hydrogen gas and / or argon gas atmosphere. In the heat treatment in this case, the profile of the antimony concentration in the depth direction when the heat treatment is performed for t seconds is as follows: [Sb (x,
t)] = [Sb _S ] + ([Sb ₀ ]-[Sb _S ]) erf (x / 2√∫ _I ^F D (T) dt)
Is represented by The ∫ _I ^F D (T) dt In this formula, the following equation (3): to read as _{D T △ t T = ∫ I} F D (T) heat treatment temperature T ° C. heat treatment time corresponding by dt △ t _T You can (However, substantially heat treatment in [Sb (x, t)] antimony concentration in the silicon substrate from the outside surface of xμm depths when heat-treated t seconds at ^{_{T ℃, ∫ I F D (}} T) dt is the heat treatment step During the heating, for example, the antimony diffusion from the temperature rise at 1000 ° C. or higher to the cooling in the heat treatment step in the furnace is shown, and D _T is the antimony diffusion coefficient (cm ² / sec) at T ° C. _T is the heat treatment time corresponding to T ° C., that is, the heat treatment time required when it is assumed that the entire heat treatment process is performed at T ° C.)

The silicon substrate for an epitaxial wafer of the present invention can be manufactured by heat-treating a silicon substrate formed from a predetermined silicon ingot as described above. The obtained silicon substrate for an epitaxial wafer is an original antimony heavy-doped silicon substrate inside, and the surface antimony concentration corresponds to light doping. A silicon single crystal can be epitaxially grown on this surface in a conventional manner to form an epitaxial film having a predetermined thickness. The obtained epitaxial film has no crystal lattice constants at the interface with the silicon substrate and no drastic change in antimony concentration. It becomes a silicon single crystal layer with high properties and few defects. In this case, the heat treatment and the epitaxial treatment of the silicon substrate may be performed in the same furnace, and the epitaxial treatment may be performed immediately after the heat treatment. Further, the heat treatment and the epitaxial treatment of the silicon substrate may be performed using different furnaces. It is possible to select which method is to be adopted according to various conditions such as a processing environment and a processing device.

[0016]

EXAMPLES The present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples. The starting silicon substrate used in the following examples of the present invention is obtained by slicing a silicon single crystal ingot pulled up by the Czochralski method by a conventionally known method and polishing and mirror-polishing it.
These starting silicon substrates have a doped antimony concentration of 3 ×
N type of 10 ¹⁸ atoms / cm ³ , plane orientation (10
It was 0).

Example 1 Using the above starting silicon substrate, 1 in a hydrogen gas atmosphere
Heat treatment was performed at 200 ° C. for 2 hours. First, the starting silicon substrate was placed in a furnace in an Ar gas atmosphere at 800 ° C.
The temperature was raised from 00 ° C. to 1000 ° C. at a heating rate of about 10 ° C./min.
Replaced with 0% hydrogen gas, and 1000 ℃ to 1100 ℃
Were heated at a temperature rising rate of about 3 ° C./min, the temperature was increased from 1100 ° C. to 1200 ° C. at a temperature rising rate of 2 ° C./min and held at 1200 ° C. for 2 hours. Then 1100 ° C
After cooling at a temperature decrease rate of about 3 ° C./min to 800 ° C. at a temperature decrease rate of about 4 ° C./min, the atmosphere in the furnace was replaced with an inert gas, and the mixture was cooled to room temperature at 100 ° C./min and heat treated. A silicon substrate was obtained. The relationship between the concentration of antimony and the depth from the surface of the obtained heat-treated silicon substrate was analyzed by SIMS.
(Secondary ion mass spectrometry) was used. The result is shown as A in FIG.

Example 2 Similar to Example 1, the starting silicon substrate was heat-treated in the same manner as in Example 1 except that the atmosphere in the furnace was Ar gas. The relationship between the antimony concentration and the depth from the surface of the obtained heat-treated silicon substrate was similarly measured by SIMS.
The result is shown as A'in FIG. In addition, in FIG. 1, the result of having measured the starting silicon substrate similarly by SIMS is shown as B. As is clear from these results, the surface antimony concentration of the silicon substrate heat-treated in the atmosphere of either hydrogen gas or argon gas was 1 × 10 ¹⁷ at.
It can be seen that the antimony concentration is gradually reduced to the initial antimony concentration after decreasing to less than oms / cm ³ and gradually increasing to a depth of approximately 2 μm.

Example 3 On the heat-treated silicon substrate obtained in Example 1, SiH ₂ Cl ₂ was used as a source gas and treated at 1080 ° C. for 5 minutes to epitaxially grow a silicon single crystal film to a thickness of about 5 μm. Then, epitaxial wafers were obtained.
As a result of measuring the antimony concentration in the depth direction from the surface of the obtained epitaxial wafer by SIMS, the antimony concentration increases inward in a gentle gradient with a width of about 2 μm from the interface between the epitaxial film and the silicon substrate. It was observed. From this result, it is estimated that the antimony concentration of the epitaxial silicon film formed on the conventional heavy antimony-doped silicon substrate changes at the interface with the silicon substrate, whereas it is about 2 μm on the heat-treated silicon substrate of the present invention. It can be seen that the antimony concentration increases with a gradual gradient in the range of.

[0020]

EFFECTS OF THE INVENTION The silicon substrate for an epitaxial wafer of the present invention is such that the antimony concentration of the outermost surface on which epitaxial growth is carried out substantially corresponds to the light antimony doping concentration of the epitaxial silicon single crystal film while maintaining the heavy antimony doping inside. The epitaxial wafer obtained by epitaxially growing a silicon single crystal has no internal distortion of the crystal lattice constant and has fine structural defects. It has a good epitaxial silicon single crystal surface. Therefore, a good device formation region can be secured, and ultimately, a VLSI having excellent device characteristics without causing defects in the device formed thereon can be manufactured with high yield and reliability can be improved. it can.

[Brief description of drawings]

FIG. 1 is a SIMS analysis result of a hydrogen gas heat-treated silicon substrate (A), an argon gas atmosphere heat-treated silicon substrate (A ′) and a starting silicon substrate (B) before heat treatment obtained in an example of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenro Hayashi, 30 Soya, Hadano City, Kanagawa Prefecture, Toshiba Ceramics Co., Ltd.Development Research Laboratory (72) Inventor, Jun 30, Soya, Hadano City, Kanagawa In-house

Claims (5)

[Claims] 1. A silicon substrate having a predetermined heavy-doped antimony concentration [Sb ₀ ] having a surface antimony concentration [Sb _S ] of 1 × 10 ¹⁷ atoms at the outermost surface on which an epitaxial film is grown. / Cm
³ or less and at least 2 μm from the outermost surface until the antimony concentration [Sb _x ] of [Sb ₀ ] × 0.5 or more
A silicon substrate for an epitaxial wafer, wherein the antimony concentration has a gradient and gradually increases over the depth of. 2. The antimony concentration [Sb ₀ ] is 1 × 1.
The silicon substrate for an epitaxial wafer according to claim 1, which has a resistivity of 0 ¹⁸ atoms / cm ³ or more. 3. A surface of a silicon substrate having a predetermined heavy-doped antimony concentration [Sb ₀ ] on which an epitaxial film is grown is heat-treated in a hydrogen gas and / or argon gas atmosphere to obtain at least the outermost surface antimony concentration [ Sb _S ] is set to 1 × 10 ¹⁷ atoms / cm ³ or less, a method for manufacturing a silicon substrate for an epitaxial wafer. 4. The heat treatment is performed in an atmosphere of hydrogen gas and / or argon gas in a range of 1000 to 1200.
The method for producing a silicon substrate for an epitaxial wafer according to claim 3, which is performed at a temperature of ° C for a processing time of 120 to 1840 minutes. 5. The processing time is calculated by the following formula: D _T Δt _T = ∫
_I ^F D (T) dt (however, ∫ _I ^F D (T) dt is from the start of heat treatment to the end of heat treatment (substantially 1
(Including a cooling step from a temperature increase from 000 ° C. or higher), _DT is the diffusion coefficient (cm ² / sec) of antimony at T ° C., Δt _T is a heat treatment time corresponding to T ° C., that is, The heat treatment time required assuming that all the heat treatment steps are performed at T ° C. ) Δt _T
5. The method for manufacturing an epitaxial wafer substrate according to claim 4.