JP2022050070A - Manufacturing method of silicon wafer - Google Patents

Abstract

To form a gettering site several μm directly below the surface layer while ensuring a sufficient defect-free layer on the surface layer.SOLUTION: A manufacturing method of a silicon wafer includes a first heat treatment step of inwardly diffusing oxygen on a surface layer of a silicon wafer obtained by slicing from a single crystal silicon ingot grown by a Czochralski method and freezing an atomic pore in a bulk portion of the silicon wafer, and a second heat treatment step of setting an experience time from the furnace temperature to 700°C less than two hours, performing holding at 800°C or higher and 1000°C or lower for one hour or more and ten hours or less, and then raising the temperature to 1100°C or higher and 1200°C or lower and maintaining the temperature for ten minutes or longer and four hours or shorter.SELECTED DRAWING: Figure 3

Description

The present invention relates to a method for manufacturing a silicon wafer.

Silicon wafers (hereinafter, may be simply abbreviated as wafers) used as substrates for semiconductor devices are not only defect-free on the surface layer, but also in recent years, the mechanical strength of wafers and metals for the purpose of improving device quality. So-called gettering performance that captures impurities is required. Gettering is a technology that reduces the adverse effect on the performance of final products by actively utilizing the phenomenon that impurities in the wafer gather in a specific area. It can be roughly divided.

In intrinsic gettering (hereinafter referred to simply as gettering), oxygen precipitates called BMD (Bulk Micro Defects) are designedly created inside the wafer to reduce the adverse effect on the performance of the final product. The BMD inside the wafer can serve to combine with and immobilize metal impurities. Then, in order to improve the gettering performance, it is important to properly control the region where the BMD is deposited. For example, in Patent Document 1, by subjecting a wafer to a rapid elevating heat treatment (hereinafter referred to as RTP) at 1300 ° C. or higher, a large amount of pores, which are point defects, remain in the bulk (inside, not the surface layer) of the wafer. Therefore, a method of forming BMD at a high density during the subsequent BMD precipitation heat treatment has been proposed.

Japanese Patent Application Laid-Open No. 2015-204326

By the way, in recent years, various heat treatments in the semiconductor device forming process tend to be performed at a low temperature and in a short time. This shortens the diffusion distance of metal impurities that unexpectedly enter the silicon wafer. Then, the metal impurities cannot be diffused to the depth of the gettering site where the BMD is formed, and a sufficient gettering effect cannot be obtained. Therefore, in recent years, there has been a demand for so-called proximity gettering wafers in which a gettering site is formed several μm directly below the surface layer while ensuring a sufficient defect-free layer on the surface layer of the silicon wafer.

In view of the above-mentioned problems, an object of the present invention is to provide a method for manufacturing a silicon wafer that contributes to forming a gettering site several μm directly below the surface layer while ensuring a sufficient defect-free layer on the surface layer. ..

In order to solve the above problems, in the method for manufacturing a silicon wafer of the present invention, the silicon wafer obtained by slicing from a single crystal silicon ingot grown by the Czochralski method is subjected to the silicon under an oxidizing atmosphere. The first heat treatment step of freezing atomic pores in the bulk portion of the silicon wafer while inwardly diffusing oxygen on the surface layer of the wafer, and the experience time from the furnace filling temperature to 700 ° C. are set to less than 2 hours, 800. It is provided with a second heat treatment step of holding at ° C. or higher and 1000 ° C. or lower for 1 hour or longer and 10 hours or less, and then raising the temperature to 1100 ° C. or higher and 1200 ° C. or lower and holding the temperature for 10 minutes or longer and 4 hours or shorter.

As described above, in the method for manufacturing a silicon wafer of the present invention, a BMD precipitation region is formed in a few μm directly below the device active layer by a combination of the first heat treatment step and the second heat treatment step. In the first heat treatment step, oxygen is diffused inward in the surface layer to increase the oxygen concentration in the surface layer region, and at the same time, atomic vacancies (hereinafter referred to as vacancies) are frozen in the wafer bulk portion. Then, in the second heat treatment step, oxygen precipitates are made apparent in the region of several μm of the surface layer.

In the second heat treatment step, the reason why the experience time from the furnace filling temperature to 700 ° C. is less than 2 hours is to prevent the formation of oxygen precipitates in the region of 1 μm directly below the surface. Further, the reason for keeping the temperature at 800 ° C. or higher and 1000 ° C. or lower is that the main nuclear generation temperature of oxygen precipitates generated due to vacancies. After that, the reason for holding at 1100 ° C. or higher and 1200 ° C. or lower for 10 minutes or more and 2 hours or less is to grow the nuclei of the generated oxygen precipitates, increase the surface area of the precipitates, and enhance the gettering power of metal impurities.

Further, in the first heat treatment step, it is preferable to keep the temperature at 1300 ° C. or higher and 1350 ° C. or lower for 1 second or longer and 60 seconds or lower, and to rapidly cool to 1000 ° C. or lower at a cooling rate faster than 50 ° C. / s and at 120 ° C. / s or lower. The reason why the cooling rate is made faster than 50 ° C. per second is that the oxygen concentration in the surface layer region is increased by holding it at 1300 ° C. or higher and 1350 ° C. or lower for 1 second or longer and 60 seconds or lower. This is to prevent a decrease in concentration due to outward diffusion. Further, the reason why the cooling rate is set to 120 ° C. per second or less is to prevent the occurrence of slip due to thermal stress.

Further, after the first heat treatment, it is preferable to continue the second heat treatment without removing the surface layer of the silicon wafer. This is to create a defect-free layer several μm from the surface of the silicon wafer and a region for forming oxygen precipitates directly under the defect-free layer.

Further, after the first heat treatment, the oxide film formed on the silicon wafer is peeled off, and then the second heat treatment is preferably performed in a non-oxidizing atmosphere. This is to promote the outward diffusion of oxygen and secure a defect-free region of about 2 μm.

Further, in the Czochralski method, it is preferable to use a defect-free silicon ingot obtained by controlling the crystal pulling speed and the temperature gradient in the crystal axial direction at the solid-liquid interface. In the first heat treatment method, void defects (defects introduced during crystal growth) remain in the region 1 μm from the surface. This problem can be avoided by using defect-free silicon that does not have void defects.

According to the present invention, it is possible to provide a method for manufacturing a silicon wafer that contributes to forming a gettering site several μm directly below the surface layer while ensuring a sufficient defect-free layer on the surface layer.

FIG. 1 is a cross-sectional view showing an outline of an example of an RTP apparatus used in the method for manufacturing a silicon wafer according to an embodiment of the present invention. FIG. 2 is a flowchart showing a procedure of a silicon wafer manufacturing method according to an embodiment of the present invention. FIG. 3 is a diagram showing a sequence of heat treatment in the method for manufacturing a silicon wafer according to the present invention. FIG. 4 is a diagram showing an oxygen concentration profile in the depth direction. FIG. 5 is a diagram showing changes in the thickness of the defect-free layer.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments described below. Further, in each drawing, the same or corresponding elements are appropriately designated by the same reference numerals. Furthermore, it should be noted that the drawings are schematic and the dimensional relationships of each element, the ratio of each element, etc. may differ from the actual ones. Even between the drawings, there may be parts where the relationship and ratio of the dimensions are different from each other.

FIG. 1 is a cross-sectional view showing an outline of an example of an RTP apparatus used in the method for manufacturing a silicon wafer according to an embodiment of the present invention.

As shown in FIG. 1, the RTP device 10 includes a chamber (reaction tube) 20 provided with an atmospheric gas introduction port 20a and an atmospheric gas discharge port 20b, and a plurality of lamps 30 arranged apart from each other in the upper part of the chamber 20. The reaction space 25 in the chamber 20 is provided with a wafer support portion 40 that supports the wafer W.

The wafer support portion 40 includes an annular susceptor 40a that supports the outer peripheral portion of the wafer W, and a stage 40b that supports the susceptor 40a. Further, the wafer support portion 40 includes a rotating means for rotating the wafer W around its central axis at a predetermined speed.

The chamber 20 is made of, for example, quartz. The lamp 30 is composed of, for example, a halogen lamp. The susceptor 40a is made of, for example, silicon. The stage 40b is made of, for example, quartz.

When performing RTP on the wafer W using the RTP device 10 shown in FIG. 1, the wafer W is introduced into the reaction space 25 and the wafer W is supported on the susceptor 40a of the wafer support portion 40. Then, the atmosphere gas described later is introduced from the atmosphere gas introduction port 20a, and the surface of the wafer W is irradiated with the lamp by the lamp 30 while rotating the wafer W.

In the temperature control in the reaction space 25 in the RTP device 10, a plurality of radiation thermometers 50 embedded in the stage 40b of the wafer support portion 40 determine the average temperature of multiple points in the wafer surface in the wafer radial direction at the bottom of the wafer W. The measurement is performed, and control of a plurality of halogen lamps 30 (individual ON-OFF control of each lamp, control of emission intensity of emitted light, etc.) is performed based on the measured temperature.

FIG. 2 is a flowchart showing a procedure of a silicon wafer manufacturing method according to an embodiment of the present invention. As shown in FIG. 2, the method for manufacturing a silicon wafer according to the embodiment of the present invention mainly includes a silicon wafer preparation step S1, a first heat treatment step S2, and a second heat treatment step S3.

In the silicon wafer preparation step S1, a silicon wafer sliced from a silicon single crystal ingot grown by the Czochralski method is prepared. The silicon single crystal ingot can be grown by the Czochralski method by a well-known method. Polycrystalline silicon filled in a quartz rut is heated to form a silicon melt, and the seed crystal is brought into contact with the seed crystal from above the liquid surface of this silicon melt, and the seed crystal and the quartz rut are pulled up while rotating to expand the diameter to the desired diameter. Then, a silicon single crystal ingot is manufactured by growing a straight body.

Here, in the Czochralski method, it is preferable to use a defect-free silicon ingot obtained by controlling the pulling speed of the crystal and the temperature gradient in the crystal axis direction at the solid-liquid interface. In the first heat treatment method in the subsequent stage, void defects (defects introduced during crystal growth) remain in the region 1 μm from the surface. This problem can be avoided by using defect-free silicon that does not have void defects.

The silicon single crystal ingot thus obtained is processed into a silicon wafer by a well-known method. After slicing a silicon single crystal ingot into a wafer shape with an inner peripheral blade or a wire saw, a silicon wafer before heat treatment is prepared through processing steps such as chamfering, wrapping, etching, and polishing of the outer peripheral portion.

In the first heat treatment step S2, oxygen is diffused inwardly on the surface layer of the silicon wafer in an oxidizing atmosphere, and atomic pores are frozen in the bulk portion of the silicon wafer. Then, in the second heat treatment step S3, oxygen precipitates are made apparent in the region of several μm of the surface layer. The optimum conditions in the first heat treatment step S2 and the second heat treatment step S3 will be described in detail later.

On the other hand, after the first heat treatment S2, it is preferable to continue the second heat treatment S3 without removing the surface layer of the silicon wafer. This is to create a defect-free layer several μm from the surface of the silicon wafer and a region for forming oxygen precipitates directly under the defect-free layer. Further, it is preferable that after the first heat treatment S2, the oxide film formed on the silicon wafer is peeled off, and then the second heat treatment S3 is performed in a non-oxidizing atmosphere. This is to promote the outward diffusion of oxygen and to secure a sufficient defect-free layer.

FIG. 3 is a diagram showing a sequence of heat treatment in the method for manufacturing a silicon wafer according to the present invention. In FIG. 3, the vertical axis T indicates the temperature and the horizontal axis t indicates the time. As shown in FIG. 3, the method for manufacturing a silicon wafer according to the present invention includes a first heat treatment step TH ₁ and a second heat treatment step TH ₂ .

As shown in FIG. 3, in the first heat treatment step TH ₁ , the temperature is raised to the temperature T ₁ , the temperature is maintained for D ₁ at the temperature, and the temperature is rapidly cooled at the cooling rate R ₁ . The first heat treatment step TH ₁ is performed in an oxidizing atmosphere using, for example, the RTP device 10 as shown in FIG.

The temperature T ₁ in the first heat treatment step TH ₁ is preferably 1300 ° C. or higher and 1350 ° C. or lower, and the time D ₁ is preferably 1 second or longer and 60 seconds or lower. This is to sufficiently increase the oxygen concentration in the surface layer region of the silicon wafer. Further, the cooling rate _R1 in the first heat treatment step TH ₁ is preferably faster than 50 ° C. / s and 120 ° C. / s or less. This is to prevent the concentration of oxygen increased in the silicon wafer by heating in an oxidizing atmosphere and the concentration decrease due to the outward diffusion of pores.

As shown in FIG. 3, the second heat treatment step TH ₂ raises the temperature to the temperature T ₂ and holds the temperature D ₂ at the temperature, then raises the temperature to the temperature T ₃ and holds the temperature D ₃ at the temperature. .. However, the temperature rise rate when raising the temperature to the temperature T ₂ is such that the experience time from the furnace filling temperature to the temperature T ₄ is less than the time D ₄ .

The temperature T ₂ in the second heat treatment step TH ₂ is preferably 800 ° C. or higher and 1000 ° C. or lower, and the time D ₂ is preferably 1 hour or longer and 10 hours or lower. This is because this temperature condition is the main nucleation temperature of the oxygen precipitates generated due to the vacancies, and is preferable for generating the oxygen precipitates. The temperature T ₃ is preferably 1100 ° C. or higher and 1200 ° C. or lower, and the time D ₃ is preferably 10 minutes or longer and 4 hours or lower. This is because the nuclei of the generated oxygen precipitates are grown to increase the surface area of the precipitates and enhance the gettering power of metal impurities.

Further, it is preferable that the temperature T ₄ at the time of raising the temperature in the second heat treatment step TH ₂ is 700 ° C., and the experience time D ₄ up to the temperature is less than 2 hours. This is to prevent the formation of oxygen precipitates in the region 1 μm directly below the surface and to secure a sufficiently wide defect-free layer.

〔Example〕
Next, an example in which the effect of the silicon wafer manufacturing method according to the present invention described above has been verified will be described.

(Verification experiment 1)
In the verification experiment 1, the relationship between the silicon wafers having different oxygen concentrations and the region where oxygen precipitates were generated was investigated. The silicon wafers of the examples used in the verification experiment 1 are as follows.

The silicon wafers of Examples A to C are subjected to the first heat treatment step and the second heat treatment step. In the first heat treatment step, the mixture was kept at a temperature of 1350 ° C. for 30 seconds under a 100% _O2 atmosphere, and then rapidly cooled at a cooling rate of 120 ° C. per second. Then, after the oxide film was peeled off, under the conditions of the second heat treatment step, the experience time from the furnace putting temperature of 600 ° C. to 700 ° C. was set to 60 minutes, and the temperature was maintained at 850 ° C. for 3 hours. Subsequently, it was held at a temperature of 1150 ° C. for 30 minutes.

For the silicon wafers of Examples A to C subjected to the first heat treatment step and the second heat treatment step, an oxygen concentration profile in the depth direction was used using a secondary ion mass spectrometer (SIMS). Was analyzed. FIG. 4 is a diagram showing an oxygen concentration profile in the depth direction. Note that FIG. 4 shows an example (comparative example) in which only the first heat treatment step is applied to Example B for comparison, and an example (calculation example) in which only the diffusion of oxygen is taken into consideration.

As shown in FIG. 4, in the example (comparative example) in which only the first heat treatment step was performed, the concentration increased in the surface layer due to the inward diffusion of oxygen. On the other hand, in the examples in which the first heat treatment step and the second heat treatment step were performed (Examples A to C), peaks due to oxygen precipitates were detected from a depth of 1 to 6 μm. The height of the peak of the oxygen precipitates in Examples A to C depends on the oxygen concentration in the silicon wafer before the first heat treatment step.

Further, in comparison with the example (calculation example) calculated by considering only the diffusion of oxygen, the oxygen concentration decreases toward the surface. On the other hand, in the examples in which the first heat treatment step and the second heat treatment step were performed (Examples A to C), peaks due to oxygen precipitates were detected from a depth of 1 to 6 μm, so that the principle of producing such a profile is obtained. Cannot be explained by oxygen diffusion alone.

Further, in the examples in which the first heat treatment step and the second heat treatment step are performed (Examples A to C), a defect-free layer (DZ) is formed up to about 1 μm from the surface. Moreover, the thickness of this defect-free layer does not depend on the oxygen concentration in the silicon wafer before the first heat treatment step.

As described above, from this verification experiment 1, in the second heat treatment step, the profile of the oxygen concentration inwardly diffused on the surface layer of the silicon wafer by the first heat treatment step is formed into a defect-free layer having a depth of about 1 μm, and the depth is 1 to 1. It was shown to be effective in forming gettering sites (GS) over 6 μm.

(Verification experiment 2)
Next, an experiment was conducted to verify the influence of the experience time from the furnace filling temperature to the temperature of 700 ° C. in the second heat treatment step. The silicon wafer used in this verification experiment 2 was a silicon wafer having an oxygen concentration of 1.2 × 10 ¹⁸ / cm ³ and a diameter of 300 mm, which was the same as in Example C.

In the first heat treatment step, as in the verification experiment 1, the mixture was held at a temperature of 1350 ° C. for 30 seconds under a 100% _O2 atmosphere, and then rapidly cooled at a cooling rate of 120 ° C. per second. Then, after the first heat treatment step, the oxide film was peeled off, and the second heat treatment step was continued without removing the surface layer of the silicon wafer.

In the first heat treatment step, the experience time was changed from the furnace filling temperature of 600 ° C. to 700 ° C. under a 100% Ar atmosphere, and the effect of this experience time on the peak of oxygen precipitates was tested. The peak of the oxygen precipitate is a peak in the oxygen concentration profile in the depth direction as shown in FIG. 4 described above. This oxygen concentration profile can be measured using a secondary ion mass spectrometer (SIMS) as in Verification Experiment 1.

In the verification experiment 2, the experience time from 600 ° C. to 700 ° C. to be changed was set to 30 minutes, 60 minutes, 120 minutes, 180 minutes, and 240 minutes. It was measured whether or not the peak of was formed. From the viewpoint of ensuring a sufficiently wide defect-free layer, a non-defective product is defined as a non-defective product (〇) when no oxygen precipitate peak is formed in the region 1 μm directly below the surface, and a defective product is defined as a defective product when an oxygen precipitate peak is formed in the 1 μm region directly below the surface. Let it be (x).

As shown in the above table, the experience time D ₄ up to 700 ° C. at the time of temperature rise in the second heat treatment step TH ₂ is preferably less than 2 hours. This is because it is possible to prevent the formation of oxygen precipitates in the region 1 μm directly below the surface of the silicon wafer and secure a sufficiently wide defect-free layer.

(Verification experiment 3)
Next, the conditions for creating a sufficiently wide defect-free layer were investigated. The silicon wafer used in this verification experiment 3 was a silicon wafer having an oxygen concentration of 1.2 × 10 ¹⁸ / cm ³ and a diameter of 300 mm, which was the same as in Example C.

In the first heat treatment step, as in the verification experiment 1, the mixture was held at a temperature of 1350 ° C. for 30 seconds under a 100% _O2 atmosphere, and then rapidly cooled at a cooling rate of 120 ° C. per second. After peeling off the oxide film, under the conditions of the second heat treatment step, the experience time from the furnace putting temperature of 600 ° C. to 700 ° C. was set to 60 minutes, and the temperature was maintained at 850 ° C. for 3 hours, but continued. The time of holding at a temperature of 1150 ° C. was varied from 1 minute to 5 hours. The change in the thickness of the defect-free layer was investigated for the silicon wafer obtained as a result. FIG. 5 is a diagram showing changes in the thickness of the defect-free layer.

As shown in FIG. 5, the thickness (DZ width) of the defect-free layer increases depending on the holding time at a temperature of 1150 ° C. This is because the longer the holding time at the temperature of 1150 ° C., the more the outward diffusion of oxygen in the surface layer progresses. However, if the holding time at a temperature of 1150 ° C. is shorter than 10 minutes, the thickness of the defect-free layer is insufficient, which is not preferable. On the other hand, even if the holding time at a temperature of 1150 ° C. is longer than 4 hours, the thickness of the defect-free layer does not change significantly, which is not preferable from the viewpoint of efficiency. Therefore, the holding time at a temperature of 1150 ° C. is preferably 10 minutes or more and 4 hours or less.

As described above, according to the method for manufacturing a silicon wafer of the present invention, a so-called proximity gettering wafer having a defect-free layer thickness of 1 to 2 μm and a gettering site depth of 1 to 6 μm is manufactured. Was shown to be possible.

Although the present invention has been described above based on the embodiments with reference to the drawings, the present invention is not limited to the above embodiments. In particular, it should be construed that the numerical range described in the present specification can be modified or changed without departing from the technical idea of the present invention.

10 RTP device 20 Chamber 20a Atmospheric gas inlet 20b Atmospheric gas outlet 25 Reaction space 30 Lamp 40 Wafer support

Claims (5)

For silicon wafers obtained by slicing from single crystal silicon ingots grown by the Czochralski method,
A first heat treatment step of inwardly diffusing oxygen on the surface layer of the silicon wafer and freezing atomic pores in the bulk portion of the silicon wafer in an oxidizing atmosphere.
The experience time from the furnace temperature to 700 ° C is set to less than 2 hours, the temperature is maintained at 800 ° C or higher and 1000 ° C or lower for 1 hour or longer and 10 hours or lower, and then the temperature is raised to 1100 ° C or higher and 1200 ° C or lower for 10 minutes or longer and 4 hours. The second heat treatment process to be held below and
A method for manufacturing a silicon wafer, which comprises. The first heat treatment step is characterized in that it is held at 1300 ° C. or higher and 1350 ° C. or lower for 1 second or longer and 60 seconds or lower, and is rapidly cooled to 1000 ° C. or lower at a cooling rate faster than 50 ° C. / s and at 120 ° C. / s or lower. The method for manufacturing a silicon wafer according to 1. The method for manufacturing a silicon wafer according to claim 1 or 2, wherein after the first heat treatment, the second heat treatment is continuously performed without removing the surface layer of the silicon wafer. One of claims 1 to 3, wherein after the first heat treatment, the oxide film formed on the silicon wafer is peeled off, and then the second heat treatment is performed in a non-oxidizing atmosphere. The method for manufacturing a silicon wafer according to the description. Claims 1 to 4, wherein in the Czochralski method, a defect-free silicon wafer obtained by controlling the pulling speed of the crystal and the temperature gradient in the crystal axial direction at the solid-liquid interface is used. The method for manufacturing a silicon wafer according to any one of them.

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