JP2020031105A - Manufacturing method of silicon wafer and silicon wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a silicon wafer capable of suppressing the amount of thermal donor generated even when subjected to low temperature heat treatment in a device process. SOLUTION: In the method for manufacturing a silicon wafer of the present invention, the silicon wafer is heat-treated while forming a thermal oxide film on the surface of the silicon wafer by heat treatment in an oxidizing atmosphere using a rapid thermal oxidation apparatus. It is formed through one step, a second step of cooling the silicon wafer on which the thermal oxide film is formed in the oxidizing atmosphere, and the first step and the second step, following the first step. A third step of removing the thermal oxide film is included. [Selection diagram] Fig. 1

Description

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

  Silicon wafers are widely used as semiconductor substrates when manufacturing various semiconductor devices such as RF (high frequency) devices, MOS devices, DRAMs, and NAND flash memories. In a so-called device process for manufacturing a semiconductor device using a silicon wafer, various heat treatments such as an oxidation treatment and a nitridation treatment, a plasma etching, and an impurity diffusion treatment are performed.

  Although oxygen present in a silicon crystal is usually electrically neutral, when a silicon wafer is subjected to a relatively low-temperature heat treatment of less than about 600 ° C. (hereinafter, low-temperature heat treatment), several to several tens of oxygen atoms are generated. Are known to form oxygen clusters in the silicon crystal. The oxygen cluster is a donor that emits electrons, and is called a thermal donor (TD: Thermal Donner). When a thermal donor receives a high-temperature heat treatment of about 650 ° C. or more, it returns to neutral electrically, and such a high-temperature heat treatment is called a donor killer heat treatment (donor killer annealing).

  With the low-temperature heat treatment in the device process, even if the silicon wafer has been subjected to the donor killer heat treatment, a thermal donor is generated again during the device process, so that the carrier concentration of the silicon wafer changes. As a result, the resistivity of the silicon wafer may change before and after the low-temperature heat treatment in the device process, or the conductivity type may be reversed in some cases. For example, if the silicon wafer is a very high resistance p-type wafer, it can be converted to an n-type wafer depending on the amount of thermal donor generated.

  Therefore, conventionally, silicon wafers capable of suppressing generation of thermal donors even when subjected to a device process have been studied. If the oxygen concentration of the substrate of the silicon wafer is low, a thermal donor is less likely to be generated than in the case of a high oxygen concentration. Have been.

In addition, the present applicant has proposed a technique capable of suppressing generation of thermal donors even in a silicon wafer having a relatively high oxygen concentration in Patent Document 1. Patent Literature 1 discloses that a silicon wafer having a carbon concentration of 5 × 10 ¹⁵ to 1 × 10 ¹⁷ atoms / cm ³ is subjected to a high-temperature heat treatment to form a DZ (Denuded Zone) layer on a wafer surface layer, A method for manufacturing a silicon wafer in which the concentration of residual oxygen in the wafer is 10 × 10 ¹⁷ atoms / cm ³ or more is disclosed.

  In Patent Literature 1, a silicon wafer is manufactured by performing heat treatment at 1100 ° C. or higher for a relatively long time so that a DZ layer can be formed on a silicon wafer that is a high-resistance substrate and is carbon-doped. When the silicon wafer thus manufactured is subjected to a low-temperature heat treatment in a device process, generation of a thermal donor can be suppressed.

International Publication No. 2004/008521

  As described above, by using the technique disclosed in Patent Document 1, it is possible to suppress generation of thermal donors due to low-temperature heat treatment in a device process. However, the heat treatment for forming the DZ layer requires a heat treatment at a high temperature and for a long time (disclosed in Patent Document 1 as about 1 to 5 hours), so that the production cost is high. Further, in Patent Document 1, since carbon doping is essential, characteristics (substrate characteristics) of a silicon wafer are limited.

  Therefore, the present invention is applicable to various substrate characteristics and can be manufactured at an excellent production cost, with a silicon wafer capable of suppressing the amount of generated thermal donors even when subjected to a low-temperature heat treatment in a device process. It is intended to provide a method capable of doing so. Still another object of the present invention is to provide a silicon wafer capable of suppressing the amount of generated thermal donors even when subjected to the low-temperature heat treatment.

  In order to solve the above-mentioned problems, the inventors of the present invention have made intensive studies and found that a silicon wafer is subjected to rapid thermal oxidation (RTO) and the growth conditions and cooling conditions of a thermal oxide film at that time are controlled. Inspired. It is presumed that the superheated interstitial silicon is generated in the silicon crystal of the silicon wafer due to the rapid heating and rapid cooling accompanying the RTO. The inventor has found that the formation of thermal donors can be suppressed by combining the supersaturated interstitial silicon with interstitial oxygen in the silicon crystal. The present invention is based on the above findings, and the gist configuration thereof is as follows.

(1) a first step of heat-treating the silicon wafer while forming a thermal oxide film on the surface of the silicon wafer by rapid thermal oxidation treatment in an oxidizing atmosphere;
Subsequent to the first step, a second step of cooling the silicon wafer on which the thermal oxide film is formed under the oxidizing atmosphere;
A third step of removing the thermal oxide film formed through the first step and the second step.

(2) The relationship between the growth rate X (nm / s) of the thermal oxide film in the first step and the cooling rate Y (° C./s) in the second step is represented by the following formula [1]:
Y> 7.5 × X ^−1.38 ... [1]
The method of manufacturing a silicon wafer according to (1), wherein the first step and the second step are performed so as to satisfy the following.

(3) the holding temperature after the temperature rise in the heat treatment in the first step is 1150 ° C. or more and the silicon melting point or less;
The method for manufacturing a silicon wafer according to (2), wherein the cooling rate Y in the second step is set to 20 ° C./s or more.

(4) The above (1) to (1), wherein the oxygen concentration of the silicon wafer before the first step is 1.0 × 10 ^{17 to} 15.0 × 10 ¹⁷ atoms / cm ³ (ASTM F-121, 1979). The method for manufacturing a silicon wafer according to any one of 3).

(5) the silicon wafer has an oxygen concentration of 1.0 × 10 ^{17 to} 15.0 × 10 ¹⁷ atoms / cm ³ (ASTM F-121, 1979);
The thermal donor generation amount after performing the heat treatment of the silicon wafer at 350 ° C. for 32 hours under a nitrogen atmosphere is 8.0 × 10 ¹² cm ⁻³ or more and 1.5 × 10 ¹³ cm ⁻³ or less. Characteristic silicon wafer.

  According to the present invention, a silicon wafer capable of suppressing the amount of thermal donor generation even when subjected to a low-temperature heat treatment in a device process can be applied to various substrate characteristics and has excellent production cost. Can be provided. Further, according to the present invention, it is possible to provide a silicon wafer capable of suppressing the amount of generated thermal donors even when subjected to the low-temperature heat treatment.

It is a schematic cross section explaining a manufacturing process of a manufacturing method according to one embodiment of the present invention, and a silicon wafer obtained thereby. It is a graph which shows the thermal donor generation amount of each sample in an Example. 4 is a graph showing a relationship between a growth rate X and a cooling rate Y of a thermal oxide film in an example. 5 is a graph showing the relationship between the interstitial silicon concentration of each sample and the amount of generated thermal donors in Examples.

(Method of manufacturing silicon wafer)
The method for manufacturing a silicon wafer according to one embodiment of the present invention includes a first step of performing a donor killer heat treatment on the silicon wafer while forming a thermal oxide film on the surface of the silicon wafer by a rapid thermal oxidation treatment in an oxidizing atmosphere. A second step of cooling the silicon wafer on which the thermal oxide film has been formed in the oxidizing atmosphere following the first step, and the heat formed through the first step and the second step. A third step of removing the oxide film. In the manufacturing method of the present invention, the silicon wafer after the third step is subjected to a heat treatment in order to control a growth rate of the thermal oxide film formed in the first step and a cooling rate of the cooling in the second step, respectively. , The amount of thermal donors generated when the heat treatment is performed can be suppressed. Hereinafter, details of each of the first to third steps will be sequentially described with reference to steps A to D in FIG. The silicon wafer 10A~10D in FIG. 1, the illustration of the thermal oxide film 20 and the thermal donor TD and interstitial silicon Si _I is schematic for the purpose of convenience of explanation. Therefore, these illustrations do not mean the actual size ratio and density.

<First step>
The first step will be described with reference to step A and step B in FIG. In the first step, a thermal oxide film 20 is formed on the surface of the silicon wafer 10A by a rapid thermal oxidation process (hereinafter, “RTO”) in an oxidizing atmosphere. The thermal oxide film 20 is formed on the silicon wafer 10A in Step A, and becomes the silicon wafer 10B in Step B. As will be described later, the thermal donor TD present in the silicon crystal of the silicon wafer 10A is subjected to donor killer heat treatment by the RTO in this step.

<< RTO >>
RTO can be performed by rapid heating treatment (RTA: Rapid Thermal Annealing) in an oxidizing atmosphere. RTO can be performed by using a general rapid heat treatment apparatus, and for example, Helios III manufactured by Mattoson, RTA-12000 manufactured by Advance Riko, and the like are known. The oxidizing atmosphere for performing the RTO is not particularly limited as long as a desired thermal oxide film can be obtained. For example, an oxidizing atmosphere consisting of only oxygen can be used. , Etc.). The rate of temperature rise and fall when performing RTO and the holding time after temperature rise can be controlled by a rapid heat treatment apparatus for performing RTO.

<< Silicon wafer 10A before performing RTO >>
As the silicon wafer 10A, a single crystal silicon ingot sliced with a wire saw or the like can be used. The conductivity type and the resistivity of the silicon wafer applicable to the present invention and the oxygen concentration are not limited at all. It can be applied to both p-type and n-type, and the resistivity is arbitrary from several mΩ · cm to several thousand Ω · cm. Here, the resistivity is a resistivity after the donor killer treatment, and the resistivity is measured according to JIS H 0602: 1995 described later. Also, the oxygen concentration can be set to 1.0 × 10 ^{17 to} 15.0 × 10 ¹⁷ atoms / cm ³ (ASTM F-121, 1979; hereinafter, the same standard is referred to for the oxygen concentration). Since the thermal donor is more likely to be generated as the oxygen concentration is higher, it is preferable to apply the present invention to a silicon wafer having an oxygen concentration of 8.0 × 10 ¹⁷ atoms / cm ³ or more. It is preferable to apply the present invention to a silicon wafer of ¹⁷ atoms / cm ³ or more.

The method of the present invention is applied to a silicon wafer obtained from a single crystal silicon ingot grown by the Czochralski method (CZ method) or the magnetic field type MCZ method (Magnetic field applied Czochralski). Since almost no oxygen is present in the crystal of the single crystal silicon ingot grown by the FZ method (oxygen concentration is less than 1.0 × 10 ¹⁷ atoms / cm ³ ), a thermal donor does not pose a problem.

  In a crystal of a single crystal silicon ingot obtained by the CZ method or the MCZ method, a thermal donor TD exists because oxygen atoms originating from a quartz crucible dissolve in the crystal. On the other hand, RTO involves a high-temperature heat treatment at 650 ° C. or higher, which is necessary for donor killer heat treatment. Therefore, the heat treatment accompanying the formation of the thermal oxide film 20 in this step also serves as a donor killer heat treatment for the thermal donor TD in the silicon crystal. Therefore, in the silicon wafer 10B that has been heated and maintained at a high temperature, the thermal donor TD existing in the silicon crystal of the silicon wafer 10A changes to a form that does not emit electrons such as oxygen monomers.

<< thermal oxide film >>
In the first step, the silicon oxide on the surface of the silicon wafer 10A is oxidized to form silicon oxide, whereby the thermal oxide film 20 is formed. The thickness of the thermal oxide film 20 to be formed depends on the temperature rising speed, the holding temperature after the temperature rise and the holding time, but is usually about several nm to several tens nm. The holding temperature and the holding time after the temperature rise are dominant to the growth rate and the film thickness of the thermal oxide film 20.

<Second step>
The second step will be described with reference to step B and step C in FIG. In the second step, subsequent to the first step, the silicon wafer 10B on which the thermal oxide film 20 has been formed is cooled in an oxidizing atmosphere to obtain a silicon wafer 10C. The cooling rate at the time of performing cooling in the second step can be controlled by a rapid heat treatment apparatus for performing RTO, and is also called rapid cooling.

  Since the rapid cooling is performed in the oxidizing atmosphere following the first step, the thickness of the thermal oxide film 20 may slightly increase. However, as described above, the growth of the thermal oxide film at the holding temperature and holding time after the temperature rise in the first step is dominant in the thickness of the thermal oxide film 20, and the thermal oxide film 20 grown alone in the second step is The film thickness is considered to be slight.

<Third step>
The third step will be described with reference to step C and step D in FIG. In the third step, the silicon wafer 10D is obtained by removing the thermal oxide film 20 on the surface of the silicon wafer 10C formed through the first step and the second step. If the silicon wafer 10C is taken out from the rapid thermal processing apparatus and the thermal oxide film 20 is removed by a general etching process using hydrofluoric acid (HF), a silicon wafer 10D is obtained.

  Here, in the manufacturing method of the present invention, the thermal oxide film is formed in the first step in order to suppress the amount of thermal donors generated when the silicon wafer 10D after the third step is subjected to the heat treatment. And controlling the cooling in the second step.

  Although not wishing to be bound by theory, the technical significance of the first step and the second step (steps A to C in FIG. 1) will be described together with the operational effects of the present invention. The present inventors consider the reason why the effects of the present invention can be obtained through experiments in which a silicon wafer is subjected to rapid thermal oxidation treatment (RTO) under various conditions.

First, the thermal oxide film 20 starts to be formed on the surface of the silicon wafer 10A with rapid heating in an oxidizing atmosphere. At this time, as the growth rate of thermal oxide film 20 increases, interstitial silicon Si _I is injected from thermal oxide film 20 into the silicon crystal in silicon wafer 10B. Although implanted interstitial silicon Si _I is outwardly diffused from the surface and the rear surface of the silicon wafer 10C with the cooling during the temperature decrease to the thermal oxide film 20, the diffusion of the more the cooling rate is larger interstitial silicon Si _I is small. Therefore, upon rapid cooling, the implanted interstitial silicon Si _I remains in the crystal. Thus in silicon crystal of the silicon wafer 10D silicon Si _I between residual lattice it becomes supersaturated. In the silicon wafer 10D, even when a low-temperature heat treatment in which a thermal donor is formed by interstitial silicon Si _I is performed, a thermal donor is less likely to be generated due to the interaction with interstitial oxygen.

  As described above, even if the silicon wafer 10D obtained according to the manufacturing method of the present invention is subjected to the low-temperature heat treatment in the device process, the generation amount of the thermal donor can be suppressed.

  Further, in the manufacturing method of the present invention, the amount of generated thermal donors can be suppressed without or almost without restrictions on the substrate characteristics such as the oxygen concentration and the carbon concentration of the silicon wafer 10A. Therefore, it is not necessary to reduce the oxygen concentration of the silicon wafer in order to control the resistivity, and even if the oxygen is reduced, the degree can be remarkably reduced as compared with the conventional technology. Further, since the degree of oxygen reduction can be reduced as described above, it is also advantageous in that a reduction in the wafer strength of the silicon wafer can be prevented. In addition, in the present invention, since the oxygen concentration of the silicon wafer can be made high, it is possible to generate oxygen precipitates (BMD) in the silicon crystal. That is, the production method of the present invention is advantageous in that a gettering ability by BMD generation can be imparted to a silicon wafer in which the amount of generated thermal donors is suppressed.

  Further, since the production method of the present invention employs rapid heating and rapid cooling by RTO, heat treatment can be performed in an extremely short time as compared with the DZ treatment according to the technique of Patent Document 1 described above, which is advantageous in terms of production cost. is there.

Here, the relationship between the growth rate X (nm / s) of the thermal oxide film 20 in the first step and the cooling rate Y (° C./s) in the second step is represented by the following equation [1]:
Y> 7.5 × X ^−1.38 ... [1]
It is preferable to perform the first step and the second step so as to satisfy the following. The present inventors experimentally confirmed that the operation and effect of the present invention can be more reliably obtained by doing so. When the growth rate X and the cooling rate Y satisfy the above formula [1], the interstitial silicon Si _I is injected during the growth of the thermal oxide film (first step) and the interstitial silicon during the rapid cooling (second step). It is presumed that because the outward diffusion of Si _I can be properly controlled.

In order to obtain the growth rate X, it is preferable that the holding temperature after the temperature rise in the heat treatment in the first step is 1150 ° C. or more and the silicon melting point or less. In this case, the cooling rate Y in the second step is preferably set to 20 ° C./s or more in order to appropriately control the outward diffusion of the interstitial silicon Si _I. Although the silicon melting point depends on the dopant concentration and the like, the melting point of the silicon element is about 1410 ° C. at normal temperature and normal pressure.

  The representative embodiments of the manufacturing method according to the present invention have been described above, but the present invention is not limited to these embodiments. Next, a silicon wafer according to an embodiment of the present invention will be described. The description of the same contents as those in the embodiment of the manufacturing method will be omitted.

(Silicon wafer)
Referring to step D of FIG. In the silicon wafer 10D according to one embodiment of the present invention, the oxygen concentration of the silicon wafer is 1.0 × 10 ^{17 to} 15.0 × 10 ¹⁷ atoms / cm ³ (ASTM F-121, 1979). The amount of generated thermal donors after heat treatment at 350 ° C. for 32 hours in a nitrogen atmosphere is not less than 8.0 × 10 ¹² cm ^{−3 and not} more than 1.5 × 10 ¹³ cm ⁻³ . The silicon wafer having the thermal donor generation amount at the above-mentioned level can be realized for the first time by the above-described method for manufacturing a silicon wafer of the present invention.

-Thermal donor generation-
The amount of thermal donor generation in the present specification is quantified according to the following procedures (i) to (iv).

(I) First, the resistivity of the silicon wafer after the heat treatment of the donor killer is measured in accordance with “Method of measuring resistivity of silicon single crystal and silicon wafer by four probe method” specified in JIS H 0602: 1995. . If a thermal oxide film has been formed, the thermal oxide film is removed by etching or the like before the measurement. In addition, as in the first step in the manufacturing method of the present invention, when the donor killer treatment has already been performed and the heat treatment under the condition that the thermal donor is generated is not performed thereafter, it is necessary to perform the donor killer heat treatment again. Absent.

(Ii) Next, the silicon wafer whose resistivity has been measured is subjected to a heat treatment in a nitrogen atmosphere at 350 ° C. for 32 hours to generate a thermal donor (hereinafter, thermal donor generation heat treatment). The thermal donor generation heat treatment corresponds to a heat treatment simulating a relatively long-time low-temperature heat treatment in a device process.

(Iii) The resistivity of the silicon wafer after the thermal donor generation heat treatment is measured according to JIS H 0602: 1995 as in (i) above.

(Iv) Based on the resistivity measured by the above (i) and (iii), the carrier concentration before and after the thermal donor generation heat treatment is obtained from the Irvin curve, respectively, and the difference in the carrier concentration is determined by the amount of carrier generated due to the thermal donor (hereinafter, referred to as the carrier generation amount) , Thermal donor generation).

  Hereinafter, although not intended to limit the method of manufacturing the silicon wafer of the present invention and the silicon wafer of the present invention, further specific embodiments of the silicon wafer applicable to the present invention will be described.

  The plane orientation of the silicon wafer is arbitrary, and a (100) wafer or a (110) wafer may be used.

  The silicon wafer may be doped with a dopant such as boron (B), phosphorus (P), arsenic (As), antimony (Sb), or carbon (C) or nitrogen (N ) May be doped.

  The diameter of the silicon wafer is not limited at all. The present invention can be applied to a general silicon wafer having a diameter of 300 mm or 200 mm. Of course, the present invention can be applied to a silicon wafer having a diameter larger than 300 mm and a silicon wafer having a smaller diameter.

  Note that the “silicon wafer” in this specification refers to a so-called “bulk” silicon wafer in which another layer such as an epitaxial layer or an insulating film made of silicon oxide or the like is not formed on the surface. However, a natural oxide film having a thickness of about several Å may be formed. Also, for the silicon wafer obtained by the present invention, another layer such as an epitaxial layer may be separately formed to produce an epitaxial silicon wafer, or used as a support substrate for a bonded wafer or a substrate for an active layer. For example, an SOI (Silicon on Insulator) wafer may be manufactured. The “bulk” silicon wafer serving as a base substrate of such a wafer is the silicon wafer in the present specification.

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

  Prior to the description of the sample preparation conditions, the measurement method in this example will be described.

-Thermal oxide film thickness-
The thickness of the thermal oxide film on the silicon wafer surface after the RTO was measured using a spectroscopic ellipsometer.

-Thermal oxide film growth rate-
During the holding after the temperature is raised to the maximum temperature during the RTO, the growth of the thermal oxide film is dominant. Therefore, the thermal oxidation is performed based on the thickness of the thermal oxide film and the holding time after the heating during the RTO. The growth rate of the film was determined. The time during the heating up to the holding temperature after the heating in the rapid heating and the cooling time during the rapid cooling are not used in calculating the growth rate of the thermal oxide film. The heating rate during RTO, the holding time after reaching the maximum temperature and the cooling rate were controlled by a rapid heating / cooling device.

-Thermal donor generation-
According to the above procedures (i) to (iv), the amount of generated thermal donors after heat treatment at 350 ° C. for 32 hours in a nitrogen atmosphere was determined.

<Sample 1>
A PZ type silicon single crystal ingot (resistivity after donor killer treatment: 10 Ω · cm) having a diameter of 300 mm, a plane orientation (100), and an oxygen concentration of 11 × 10 ¹⁷ atoms / cm ³ (ASTM F-121, 1979) is subjected to the CZ method. Developed by The silicon wafer before RTO was manufactured by slicing the silicon single crystal ingot.

  The obtained silicon wafer before RTO is subjected to RTO by rapid heating and rapid cooling combined with donor killer heat treatment in an oxidizing atmosphere composed of oxygen using the rapid heating / rapid cooling device to form a thermal oxide film. Formed. The holding temperature after the temperature rise in the rapid heating treatment is 800 ° C., and the holding time is 240 seconds. The cooling rate Y was 50 ° C./sec.

  The silicon wafer after RTO was taken out of the rapid heating / cooling device, and the thickness of the formed thermal oxide film was measured. In addition, the growth rate X (nm / s) of the thermal oxide film was determined.

  Next, the surface of the silicon wafer was etched using hydrofluoric acid (HF) to remove the thermal oxide film.

  The silicon wafer after removing the oxide film was subjected to a heat treatment at 350 ° C. for 32 hours in a nitrogen atmosphere, and the amount of thermal donor generated by the heat treatment was determined.

  Table 1 shows the holding temperature, holding time, growth rate X and cooling rate Y of the thermal oxide film by RTO. The graph in FIG. 2 shows the amount of thermal donor generated in Sample 1.

<Samples 2 to 19>
Samples 2 to 19 were produced in the same manner as Sample 1 except that the holding temperature and the holding time after the heating by RTO and the cooling rate Y were as shown in Table 1. Further, the growth rate X of the thermal oxide film and the amount of generated thermal donor were determined in the same manner as in Sample 1. The graph of FIG. 2 shows the amount of generated thermal donors of Samples 2 to 19.

<Sample 20>
Using the same silicon wafer before RTO as Sample 1, this was introduced into a vertical furnace in an oxidizing atmosphere and subjected to a donor killer heat treatment at 650 ° C. for 30 minutes. After the formed oxide film was removed in the same manner as in Sample 1, heat treatment was performed at 350 ° C. for 32 hours in a nitrogen atmosphere, and the amount of thermal donor generated by the heat treatment was determined. The graph in FIG. 2 shows the amount of thermal donor generated in Sample 20.

(Evaluation results and discussion)
It is confirmed from the graph of FIG. 2 that the amount of generated thermal donors of the samples 1 to 19 after the RTO is divided into a higher level and a lower level as compared with the generation rate of the sample 20 corresponding to the conventional example by the heat treatment in the vertical furnace. You. Among them, the level of the amount of generated thermal donors is about half that of the level with a large amount of thermal donors compared to the level of high thermal donors.

FIG. 3 shows a graph in which the growth rate X and the cooling rate Y of the thermal oxide film at the time of RTO are arranged in accordance with the following criterion in consideration of the thermal donor generation amount corresponding to the fact that the thermal donor generation amount is smaller than that of the sample 20.
：: Thermal donor generation amount is 1.5 × 10 ¹³ cm ⁻³ or less ×: Thermal donor generation amount exceeds 1.5 × 10 ¹³ cm ^-3

It can be seen from the graph of FIG. 3 that when the growth rate X of the thermal oxide film is high and the cooling rate Y is high, the amount of generated thermal donor is 1.5 × 10 ¹³ cm ⁻³ or less. The curve equation Y = 7.5 × X ^{−1.38 in} FIG. 3 is a boundary line that ^{separates the} symbol ○ from the symbol X in FIG. That is, by performing RTO so that the growth rate X and the cooling rate Y satisfy Y> 7.5 × X ^−1.38 , it is possible to reliably suppress the amount of thermal donors generated after the subsequent heat treatment. Was confirmed. It was also confirmed that by controlling the growth rate X and the cooling rate Y of the thermal oxide film at the time of RTO, the amount of thermal donors generated after heat treatment after RTO can be suppressed.

(Calculation and consideration of interstitial silicon concentration)
Since it is difficult to directly measure the interstitial silicon concentration, the interstitial silicon concentration remaining in the sample was determined by calculation as follows. More specifically, for each of the samples 1 to 6, 8, 13, 16, and 17, the diffusion equation is solved in the thickness direction of the silicon wafer from the start of the temperature increase in the RTO to the cooling process, thereby obtaining the silicon wafer. The interstitial silicon concentration at the center was determined. As the boundary condition of the interstitial silicon concentration on the front and back surfaces of the wafer, a steady value (Scott T. Dunham, J. Appl. Phys., 71 (1992) 685) at an arbitrary temperature and an oxide film growth rate was used. FIG. 4 shows the interstitial silicon concentrations of Samples 1 to 6, 8, 13, 16, and 17 and the amount of thermal donor generated after heat-treating these samples at 350 ° C. for 32 hours in a nitrogen atmosphere. Shows the relationship.

According to the graph of FIG. 4, the formation amount of the thermal donor increases depending on the interstitial silicon concentration up to 10 ¹¹ cm ⁻³ . On the other hand, when the interstitial silicon concentration exceeds 10 ¹² cm ^-3 , it is confirmed that the amount of generated thermal donors sharply decreases. Therefore, according to the above calculation results, the heat treatment after RTO is performed by supersaturating the interstitial silicon concentration at the central portion in the thickness direction of the silicon wafer to 1 × 10 ¹² cm ⁻³ or more, and further to 1 × 10 ¹³ cm ⁻³ or more. It can be concluded that the amount of generated thermal donors can be suppressed when receiving the gas.

  According to the present invention, a silicon wafer capable of suppressing the amount of thermal donor generation even when subjected to a low-temperature heat treatment in a device process can be applied to various substrate characteristics and has excellent production cost. Can be provided. Further, according to the present invention, it is possible to provide a silicon wafer capable of suppressing the amount of generated thermal donors even when subjected to the low-temperature heat treatment.

10A silicon wafer 10B silicon wafer 10C silicon wafer 10D silicon wafer 20 thermal oxide film TD thermal donor Si _I interstitial silicon

Claims (5)

A first step of heat-treating the silicon wafer while forming a thermal oxide film on the surface of the silicon wafer by rapid thermal oxidation treatment in an oxidizing atmosphere;
Subsequent to the first step, a second step of cooling the silicon wafer on which the thermal oxide film is formed under the oxidizing atmosphere;
A third step of removing the thermal oxide film formed through the first step and the second step. The relationship between the growth rate X (nm / s) of the thermal oxide film in the first step and the cooling rate Y (° C./s) in the second step is represented by the following formula [1]:
Y> 7.5 × X ^−1.38 ... [1]
The method for manufacturing a silicon wafer according to claim 1, wherein the first step and the second step are performed so as to satisfy the following. Holding temperature after the temperature rise in the heat treatment in the first step is 1150 ° C. or more and silicon melting point or less;
The method for manufacturing a silicon wafer according to claim 2, wherein the cooling rate Y in the second step is set to 20 ° C / s or more. Oxygen concentration in the silicon wafer before the first step is ^{1.0 × 10 17 ~15.0 × 10 17} atoms / cm 3 (ASTM F-121,1979), one of the claims 1 to 3 1 Item 14. The method for producing a silicon wafer according to Item 1. The oxygen concentration of the silicon wafer is 1.0 × 10 ^{17 to} 15.0 × 10 ¹⁷ atoms / cm ³ (ASTM F-121, 1979);
The thermal donor generation amount after performing the heat treatment of the silicon wafer at 350 ° C. for 32 hours under a nitrogen atmosphere is 8.0 × 10 ¹² cm ⁻³ or more and 1.5 × 10 ¹³ cm ⁻³ or less. Characteristic silicon wafer.

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