JP2009212537A - Method for producing silicon wafer and silicon wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain superior surface roughness, by reducing the thermal processing temperature or shortening the time required for the thermal processing and by suppressing the occurrence of a slip, in a method of manufacturing a silicon wafer and a silicon wafer. <P>SOLUTION: A thermal processing step of forming new vacancies in a silicon wafer W by thermally processing it in an atmospheric gas G is provided, and the atmospheric gas in the thermal processing step contains a nitrided gas, having a decomposition temperature which is lower than the temperature at which N<SB>2</SB>can be decomposed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a silicon wafer in which a silicon wafer is heat-treated in an atmospheric gas to form vacancies therein, and further heat-treated to form a DZ (Denuded Zone) layer on the surface layer, and silicon manufactured by this method Related to wafers.

  A silicon wafer produced by processing a silicon single crystal pulled and grown by the CZ (Czochralski) method contains a large amount of oxygen impurities. These oxygen impurities cause oxygen precipitates (dislocations, defects, etc.) BMD: Bulk Micro Defect). When this oxygen precipitate is present on the surface where the device is formed, it causes a leakage current increase, an oxide film breakdown voltage decrease, and the like, which greatly affects the characteristics of the semiconductor device.

  For this reason, conventionally, rapid thermal annealing (RTA: Rapid Thermal Annealing) at a high temperature of 1250 ° C or higher is performed on the silicon wafer surface in a predetermined atmosphere gas, and high-concentration thermal equilibrium atoms are internally contained. Vacancy (hereinafter referred to simply as “vacancy”) is formed, frozen by rapid cooling, and the DZ layer (defect-free layer) is uniformly formed by outward diffusion of the pores on the surface by subsequent heat treatment. (For example, the technique described in Patent Document 1). Then, after the formation of the DZ layer, a process of forming a BMD layer having a gettering effect by forming and stabilizing an oxygen precipitation nucleus as an internal defect layer by performing heat treatment at a temperature lower than the above temperature is employed.

In addition, as another conventional technique (for example, the technique described in Patent Document 2), first, heat treatment is performed in an oxygen atmosphere, and then heat treatment is performed in a non-oxidizing atmosphere, so that the DZ in the surface layer and the inside BMD formation is performed. Conventionally, N ₂ (nitrogen) is mainly used as an atmospheric gas in heat treatment for forming holes. That is, N ₂ is decomposed at a high temperature, and Si _x N _y (nitride film) is formed on the surface of the silicon wafer, thereby injecting holes.

International Publication No. 98/38675 Pamphlet International Publication No. 98/45507 Pamphlet Japanese Patent Laid-Open No. 1-1393

  However, the following problems remain in the silicon wafer heat treatment technology. Conventionally, for example, when heat treatment for forming holes is performed, the surface is covered with an oxide film, and heat treatment is performed in an atmospheric gas mainly containing N 2. In this case, in order to obtain a sufficient heat treatment effect, 1250 is obtained. A heat treatment of at least 10 ° C. and at least 10 seconds was necessary. For this reason, the silicon wafer has a disadvantage that a high temperature heat treatment causes a slip from a portion that comes into contact with the susceptor or the support pins, which causes cracks and the like. In addition, the surface of the silicon wafer before the heat treatment is oxidized to some extent to form a natural oxide film. However, since the heat treatment is performed, the surface of the natural oxide film is sublimated at a high temperature and the surface becomes rough. was there.

  The present invention has been made in view of the above-described problems, and can reduce the occurrence of slip by reducing the temperature or shortening the heat treatment, and can provide a silicon wafer manufacturing method and silicon capable of obtaining good surface roughness. An object is to provide a wafer.

The present invention employs the following configuration in order to solve the above problems.
That is, in the method for producing a silicon wafer according to the present invention, the silicon wafer is placed in a reaction chamber where heat treatment is performed, and an atmospheric gas containing a nitriding gas having a decomposition temperature lower than the temperature at which N ₂ can be decomposed is supplied into the reaction chamber. While, heat treatment of the silicon wafer, by forming a nitride film on the surface or by the surface nitriding action, has a hole injection heat treatment step of forming new holes in the interior,
The vacancy injection heat treatment step uses an atmosphere gas containing NH ₃ as the nitriding gas, the concentration of NH ₃ in the nitriding gas is 0.5% or more, or the flow rate of NH ₃ is 10 sccm or more, and the heat treatment temperature Is performed at a temperature from 1100 ° C. to 1150 ° C., the heat treatment time is 60 sec or less, and the cooling rate is 33.3 ° C./sec to 50 ° C./sec. It is characterized by doing.
According to the present invention, in the method for manufacturing a silicon wafer, the nitriding gas can be made into a plasma.
In the method for manufacturing a silicon wafer according to any one of the above, the present invention may include an oxide film removing step for removing or thinning an oxide film on the surface of the silicon wafer before the hole injection heat treatment step.
The present invention provides the silicon wafer manufacturing method according to any one of the above, wherein the oxide film removing step removes at least the oxide film until the film thickness becomes less than 2 nm when the atmosphere gas contains NH _3. be able to.
The present invention provides the method for producing a silicon wafer according to any one of the above, wherein the oxide film removing step performs a purging process for removing oxygen contained in an atmospheric gas in the reaction chamber and then the nitriding gas. It can be fed into the reaction chamber.
The present invention provides the method for producing a silicon wafer according to any one of the above, wherein after the hole injection heat treatment step, the silicon wafer is heat-treated at a temperature lower than the hole injection heat treatment step to form a defect-free layer on a surface layer. It can have a precipitation treatment step of forming and precipitating oxygen in the internal vacancies.
In the method for manufacturing a silicon wafer according to any one of the above, the present invention can use a mixed gas of Ar and NH ₃ as the atmospheric gas containing the nitriding gas.
The present invention provides the method for producing a silicon wafer according to any one of the above, wherein the heat treatment is performed by the following procedures (i) to (v).
(I) Before raising the temperature to 800 ° C., only Ar is supplied as an atmospheric gas, and a purge process is performed to replace the atmospheric gas in the heat treatment furnace and remove oxygen.
(Ii) With the oxygen completely removed from the furnace, the temperature is raised to 800 ° C. while supplying only Ar as the atmospheric gas.
(Iii) Next, while heating NH ₃ into the heat treatment furnace and supplying a mixed gas of Ar and NH ₃ as an atmospheric gas, rapid heating is performed from 800 ° C. to the heat treatment temperature, and the heat treatment temperature is constant and predetermined. Heat treatment for hours.
(Iv) Then, rapidly cool to 800 ° C.
(V) Thereafter, Ar is supplied as an atmospheric gas at a constant flow rate of 800 ° C. until NH ₃ is completely discharged, and the temperature is lowered again in the atmospheric gas containing only Ar after the discharge is completed.
According to the present invention, in the silicon wafer manufacturing method according to any one of the above, the cooling rate may be 33.3 ° C./second or 50 ° C./second.
According to the present invention, in the silicon wafer manufacturing method according to any one of the above, the flow rate in the atmosphere gas may be the NH ₃ / Ar: 2SLM / 2SLM.
The present invention provides a method for producing a silicon wafer according to any one of the above, wherein a region where interstitial silicon type point defects exist predominantly in a silicon single crystal ingot is defined as [I] in the silicon wafer. When the region where the hole type point defects exist predominantly is [V], and the perfect region where the aggregates of interstitial silicon type point defects and void type point defects do not exist is [P], It is possible to use a silicon wafer in which no agglomerates of point defects cut out from the ingot composed of the region [P] exist.
The silicon wafer of the present invention is produced by the method for producing a silicon wafer described above.

  The present invention can employ the following configurations in order to solve the above problems. That is, the silicon wafer manufacturing method of the present invention has a heat treatment step in which a silicon wafer is heat-treated in an atmospheric gas to newly form vacancies therein, and the atmospheric gas in the heat treatment step can decompose N2. It contains a nitriding gas having a decomposition temperature lower than the normal temperature.

In this silicon wafer manufacturing method, the atmospheric gas in the heat treatment step is a nitriding gas having a decomposition temperature lower than the temperature at which N ₂ can be decomposed, such as NH ₃ , NO, N ₂ O, N ₂ O ₂ , hydrazine or dimethylhydrazine. Etc., the nitriding gas is decomposed even at a lower heat treatment temperature or shorter heat treatment time than in the case of N ₂ , so that the silicon wafer surface can be nitrided (form a nitride film), and vacancies can be injected into the inside. The occurrence of slip at the time can be suppressed.

In the method for producing a silicon wafer of the present invention, it is preferable that the nitriding gas contains NH ₃ (ammonia). That is, in this silicon wafer manufacturing method, by using a nitriding gas containing NH ₃ , H (hydrogen) generated by decomposition of NH ₃ has a cleaning effect of removing a natural oxide film or the like on the surface of the silicon wafer. Therefore, nitriding of the surface and injection of vacancies are further promoted. Further, NH ₃ has an effect of nitriding the oxide film, and the injection of vacancies is promoted. The cleaning effect by NH _{3 is} due to the reducibility of hydrogen, and is different from mere evaporation (sublimation) at a high temperature of the natural oxide film.

In addition, the silicon wafer manufacturing method of the present invention employs a technique in which the NH ₃ concentration in the nitriding gas is 0.5% or more, or the flow rate of NH 3 is 10 sccm or more. That is, in this silicon wafer manufacturing method, the concentration of NH3 in the nitriding gas is 0.5% or more or the flow rate of NH3 is 10 sccm or more. Under these gas conditions, the nitriding reaction is reaction-controlled. If this is included, the nitride film thickness formed on the wafer surface is the same, and uniform vacancy injection within the wafer surface becomes possible.

  In the silicon wafer manufacturing method of the present invention, the nitriding gas is preferably made into a plasma. That is, in this silicon wafer manufacturing method, since the nitriding gas is made into a plasma, it becomes an activated nitriding gas, which further promotes nitriding of the surface and injection of vacancies.

  In the method for producing a silicon wafer of the present invention, it is preferable that the temperature of the heat treatment is a temperature from 900 ° C. to 1200 ° C., and the time of the heat treatment is a time of 60 sec (seconds) or less. That is, in this silicon wafer manufacturing method, the heat treatment temperature and heat treatment time within the above ranges can suppress slip generation and sufficiently inject vacancies, thereby obtaining an appropriate amount of BMD layer. Further, as will be described later, since the heat treatment is performed at a temperature of 1200 ° C. or less, the interstitial Si formed in the crystal is small, and the vacancies injected by the nitride film on the surface do not annihilate with the interstitial Si and are implanted. Efficiency can be increased.

  Moreover, it is preferable that the manufacturing method of the silicon wafer of this invention has the oxide film removal process of removing or thinning the oxide film of the said silicon wafer surface before the said heat treatment process. That is, this silicon wafer manufacturing method has an oxide film removing step for removing or thinning the oxide film on the silicon wafer surface before the heat treatment step, so that the oxide film such as a natural oxide film on the wafer surface is completely removed or removed. The RTA process is performed in a state of being almost removed, so that nitridation of the wafer surface and vacancy injection by the nitriding gas can be prevented from being hindered by the oxide film, and effective vacancy injection becomes possible.

Furthermore, in the method for producing a silicon wafer according to the present invention, it is preferable that in the oxide film removing step, at least the oxide film is removed until the film thickness becomes less than 2 nm when NH ₃ is contained in the atmospheric gas. As will be described later, when the oxide film is formed on the surface of 2 nm or more, the present inventors have said heat treatment conditions (the temperature of the heat treatment is a temperature from 900 ° C. to 1200 ° C., and the heat treatment time is 60 sec. It was found that the oxide film could not be completely removed or converted to an oxynitride film within a time of (second) or less), and the hole injection effect by the nitriding gas could not be sufficiently obtained. That is, in this silicon wafer manufacturing method, when the atmosphere gas contains NH ₃ in the oxide film removing step, at least the oxide film is removed until the film thickness becomes less than 2 nm. Can be sufficiently formed into an oxynitride film, and a sufficient effect of injecting holes can be obtained.

  In the silicon wafer manufacturing method of the present invention, in the heat treatment step, the silicon wafer is disposed in a reaction chamber in which the heat treatment is performed, and a purge process is performed to remove oxygen contained in the atmospheric gas in the reaction chamber. The atmospheric gas containing the nitriding gas is preferably supplied into the reaction chamber. That is, in this method for producing a silicon wafer, an atmosphere gas containing a nitriding gas is supplied into the reaction chamber after performing a purge process for removing oxygen contained in the atmosphere gas in the reaction chamber. It is possible to prevent the vacancy injection effect from being suppressed by surface oxidation.

  In the method for producing a silicon wafer of the present invention, after the heat treatment step, the silicon wafer is heat-treated at a temperature lower than the heat treatment step to form a defect-free layer on the surface layer and to precipitate oxygen in the internal vacancies. It has the process. That is, in this silicon wafer manufacturing method, after the heat treatment step, the silicon wafer is heat-treated at a temperature lower than that of the heat treatment step to form a defect-free layer on the surface layer and to precipitate oxygen in the internal vacancies. Therefore, a high-functional silicon wafer having a DZ layer suitable for device formation in the surface layer and a high BMD density region having a proximity gettering effect inside can be manufactured.

  The silicon wafer of the present invention is a silicon wafer in which holes are newly formed by heat treatment, and is produced by the above-described method for producing a silicon wafer of the present invention. That is, since this silicon wafer is produced by the above-described method for producing a silicon wafer according to the present invention, the occurrence of slip is suppressed, and a DZ layer sufficient for the surface layer and a moderately high BMD are formed by the subsequent heat treatment. A high-quality wafer having a high density can be obtained.

The silicon wafer according to the present invention is a silicon wafer in which holes are newly formed by heat treatment, and has a silicon oxynitride film whose surface is nitrided during the heat treatment on the surface. That is, this silicon wafer has a silicon oxynitride film whose surface is nitrided during heat treatment, that is, a silicon oxide film such as a natural oxide film on the surface during heat treatment, or a silicon oxynitride film formed by nitriding without evaporating oxygen. Therefore, it has a good surface roughness in which vacancies are sufficiently injected into the inside by surface nitriding and surface roughness is suppressed. Therefore, if this silicon wafer is further subjected to heat treatment for oxygen precipitation, a wafer having a BMD layer having a high BMD density inside and a DZ layer having a good surface roughness on the surface layer can be obtained.

  The silicon wafer of the present invention employs a technique in which a defect-free layer is formed at least on the surface layer and oxygen is precipitated in the internal vacancies. That is, in this silicon wafer, since a defect-free layer is formed at least on the surface layer and oxygen is deposited in the internal vacancies, the silicon wafer has a suitable DZ layer as a device formation region and has a sufficient BMD density inside. It is possible to obtain a proximity gettering effect.

The present invention has the following effects.
According to the silicon wafer manufacturing method and silicon wafer of the present invention, since the atmospheric gas in the heat treatment step includes a nitriding gas having a decomposition temperature lower than the temperature at which N ₂ can be decomposed, the heat treatment temperature is lower than in the case of N _2. Alternatively, even in a short heat treatment time, the nitriding gas is decomposed to nitride the silicon wafer surface, and vacancies can be injected into the inside, so that slip generation during heat treatment can be suppressed, and sufficient DZ layer can be obtained by the subsequent heat treatment. And a high-quality wafer having a moderately high BMD density inside. This is particularly effective for a 300 mm wafer having a diameter larger than 200 mm.

  In addition, since the silicon wafer of the present invention has a silicon oxynitride film whose surface is nitrided during heat treatment, it has a satisfactory surface roughness in which vacancies are sufficiently injected and surface roughness is suppressed. is doing. Therefore, if the silicon wafer is further subjected to heat treatment for oxygen precipitation, a wafer having a BMD layer having a high BMD density inside and a DZ layer having a good surface roughness on the surface can be obtained.

It is a rough whole sectional view showing the heat treatment furnace in one embodiment of a manufacturing method of a silicon wafer concerning the present invention, and a silicon wafer. It is a graph which shows the time chart of the heat processing temperature and gas flow rate (slm) in one Embodiment of the manufacturing method of the silicon wafer which concerns on this invention, and a silicon wafer. It is an expanded sectional view showing a wafer after heat treatment for RTA processing and subsequent oxygen precipitation in one embodiment of a manufacturing method of a silicon wafer concerning the present invention, and a silicon wafer. 1 is an enlarged cross-sectional view showing a wafer before and after an RTA treatment when a silicon oxynitride film is formed on the surface and after a heat treatment for oxygen precipitation in one embodiment of a silicon wafer manufacturing method and a silicon wafer according to the present invention; It is. Based on the Boronkov theory, when the V / G ratio is higher than the critical point, a void-rich ingot is formed, and when the V / G ratio is lower than the critical point, an interstitial silicon-rich ingot is formed, and the perfect region has the first critical ratio (( It is a figure which shows that it is below 2nd critical ratio ((V / G) ₂ ) above V / G) ₁ ). It is a graph which shows the relationship between the heat processing temperature and BMD density in the manufacturing method of the silicon wafer which concerns on this invention, and the Example of a silicon wafer. It is a graph which shows the relationship between the heat processing temperature and DZ width in the manufacturing method of the silicon wafer which concerns on this invention, and the Example of a silicon wafer. It is a graph which shows the relationship between the heat processing temperature and BMD density in case the heat processing temperature in the manufacturing method of the silicon wafer which concerns on this invention, and the Example of a silicon wafer is 1100 degreeC and 1150 degreeC. It is a graph which shows the slip length in the Example at the time of changing the manufacturing method of the silicon wafer concerning this invention, the prior art example of a silicon wafer, and heat processing temperature. It is a graph which shows the analysis result by the element distribution measurement of the depth direction from the surface in the Example when the manufacturing method of the silicon wafer which concerns on this invention, the prior art example of a silicon wafer, and the silicon oxynitride film were formed.

  Hereinafter, an embodiment of a method for producing a silicon wafer and a silicon wafer according to the present invention will be described with reference to FIGS.

  In FIG. 1, reference numeral 1 denotes a susceptor, and 2 denotes a reaction chamber. FIG. 1 shows a single wafer heat treatment furnace for carrying out the silicon wafer manufacturing method of the present invention. As shown in FIG. 1, the heat treatment furnace includes an annular susceptor 1 on which a silicon wafer W can be placed, and a reaction chamber 2 in which the susceptor 1 is housed. A lamp (not shown) for heating the silicon wafer W is disposed outside the reaction chamber 2.

  The susceptor 1 is formed of silicon carbide or the like, and a step portion 1a is provided on the inner side, and a peripheral portion of the silicon wafer W is placed on the step portion 1a. The reaction chamber 2 is provided with a supply port 2a for supplying the atmospheric gas G to the surface of the silicon wafer W and a discharge port 2b for discharging the supplied atmospheric gas G. The supply port 2a is connected to a supply source (not shown) of the atmospheric gas G.

The atmospheric gas G is a nitriding gas having a decomposition temperature lower than the temperature at which N2 can be decomposed, such as NH ₃ , NO, N ₂ O, N ₂ O ₂ , hydrazine, dimethylhydrazine, etc., a mixed gas thereof, or a nitriding gas thereof And Ar (argon), N ₂ (nitrogen), O ₂ (oxygen), H ₂ (hydrogen) and the like. In the present embodiment, an atmospheric gas G mainly composed of NH ₃ is used.

  Using this heat treatment furnace, the silicon wafer W is subjected to RTA treatment (heat treatment) in an atmospheric gas to newly form vacancies inside, and further, a DZ layer is formed on the surface layer of the wafer W and a BMD layer is formed inside. A method for performing the heat treatment to be formed will be described below. First, before performing the RTA process for injecting vacancies, it is preferable that the natural oxide film formed on the surface of the silicon wafer W or the oxide film by other processes is removed or thinned in advance. That is, the silicon wafer W before the heat treatment is washed with hydrofluoric acid or the like, and the oxide film on the surface is removed in advance. In this case, at least the oxide film is removed until the film thickness becomes less than 2 nm. When the natural oxide film has a thickness of less than 2 nm, the oxide film removal process does not need to be performed as will be described later.

  In order to perform heat treatment, particularly RTA treatment (rapid heating and rapid cooling heat treatment) on the silicon wafer W by this heat treatment furnace, after placing the silicon wafer W on the susceptor 1, the atmosphere gas G is supplied from the supply port 2a to the silicon wafer. Heat treatment with rapid heating / rapid cooling (for example, temperature increase / decrease of 50 ° C./second) in a short time with a heat treatment temperature in the range of 900 ° C. to 1200 ° C. and a heat treatment time of 60 sec or less while being supplied to the surface of W I do. This heat treatment includes spike annealing in which the heat treatment time at the heat treatment temperature is short (less than 1 sec).

  If it is the range of this heat processing temperature and heat processing time, while generating generation | occurrence | production of a slip reliably, sufficient DZ layer and BMD density can be obtained by the subsequent two-step heat processing mentioned later. In the present embodiment, the RTA treatment is performed under conditions more suitable for suppressing the occurrence of slip, a heat treatment temperature from 900 ° C. to 1180 ° C., and a heat treatment time of 30 sec or less.

  In the above heat treatment, for example, as shown in FIGS. 2A and 2B, first, only Ar is supplied as an atmospheric gas at a high flow rate before the temperature is raised to 800 ° C. A purge process for removing oxygen by replacing the atmospheric gas is performed. With the oxygen completely removed from the furnace, the temperature is then raised to 800 ° C. while supplying only Ar as an atmospheric gas at a predetermined flow rate.

Next, rapid heating is performed from 800 ° C. to a predetermined heat treatment temperature (eg, 1180 ° C.) while introducing NH ₃ into the heat treatment furnace at a predetermined flow rate and supplying a mixed gas of Ar and NH ₃ as an atmospheric gas. The heat treatment is performed for a predetermined time at a constant heat treatment temperature, and then rapidly cooled to 800 ° C. Thereafter, only Ar is supplied as an atmospheric gas at a constant temperature of 800 ° C. until NH ₃ is completely discharged, and the temperature is lowered again in the atmospheric gas containing only Ar after the discharge is completed. As described above, the low decomposition temperature nitriding gas is supplied as the atmospheric gas from the middle of the temperature rise to the middle of the rapid cooling / fall. The reason why the heat treatment temperature at the time of introducing NH ₃ is set to the same temperature (800 ° C.) as that at the time of purging after the heat treatment is to reduce the burden on the apparatus.

  After the heat treatment, the wafer W is rapidly cooled by taking it out of the heat treatment furnace. At this time, the internal oxygen donor can be erased by the heat treatment (800 ° C.) during the purge and the rapid cooling effect during the extraction. As a result of the above heat treatment, the surface of the silicon wafer W is sufficiently decomposed by the nitriding gas even at a heat treatment temperature lower than that of the prior art to nitride the surface, that is, form a nitride film, as shown in FIG. , Vacancy V can be sufficiently injected inside.

Further, after the heat treatment (RTA treatment), heat treatment (for example, heat treatment at 800 ° C. for 4 hours, N ₂ / O ₂ atmosphere) is performed in a heat treatment furnace or the like in order to perform oxygen precipitation in the vacancies V at a temperature lower than the heat treatment. As shown in FIG. 3 (b), the surface layer has a DZ layer formed on the surface layer by pair annihilation due to vacancy and interstitial Si injection due to the outward diffusion of vacancies and interstitial Si injection accompanying oxide film formation. DZ is formed, oxygen precipitation nuclei are stabilized, and further heat treatment (for example, heat treatment performed at 1000 ° C. for 16 hours) is performed to grow precipitates, and a BMD layer BMD having a high BMD density inside. Form. Note that the heat treatment for the DZ layer formation or oxygen precipitation is not particularly performed, and the heat treatment performed in the subsequent device manufacturing process may be performed.

Thus, in this embodiment, since the atmospheric gas G is a nitriding gas such as NH _{3 having a} decomposition temperature lower than the temperature at which N ₂ can be decomposed, the heat treatment temperature in the RTA process can be lowered. Slip generation during heat treatment can be suppressed. Further, by using the atmospheric gas G mainly composed of NH ₃ , H generated by decomposition of NH ₃ has a cleaning effect of removing a natural oxide film or the like on the surface of the silicon wafer W. Nitriding and injection of vacancies V are facilitated. Further, NH ₃ has an effect of nitriding the oxide film, and the injection of the holes V is promoted.

  Furthermore, in this embodiment, heat treatment is performed within a temperature range from 900 ° C. to 1200 ° C., and this heat treatment time is 60 seconds or less, so that generation of slips can be suppressed and holes V can be sufficiently injected, An appropriate amount of BMD layer can be obtained. Further, in the conventional high-temperature heat treatment exceeding 1200 ° C., vacancies called Frenkel pairs and interstitial Si are simultaneously generated in the crystal, and the vacancies injected in the RTA treatment are interstitial Si and interstitial Si. The pair disappears, and the density of vacancies that actually contribute to the precipitation decreases. On the other hand, in the present embodiment, since heat treatment is performed at a low temperature with little generation of Frenkel pairs, that is, 1200 ° C. or less, there are few interstitial Si formed in the crystal, and vacancies V are injected by the nitride film on the surface. Does not annihilate with interstitial Si, so that the injection efficiency can be increased and the injection can be deeper than before.

Further, since the oxide film on the surface of the silicon wafer W is removed or thinned before the RTA process, the RTA process is performed in a state in which an oxide film such as a natural oxide film on the surface of the wafer W is completely removed or almost removed. Thus, nitridation of the surface of the wafer W by the nitriding gas and hole injection can be prevented from being hindered by the oxide film, and effective hole injection becomes possible. Since at least the oxide film is removed until the film thickness is less than 2 nm, the remaining oxide film can be removed or formed into an oxynitride film by the cleaning effect or nitriding effect of NH ₃ , and vacancies V are sufficiently injected. Effect can be obtained.

  Further, after the RTA heat treatment, the silicon wafer W is heat-treated at a temperature lower than the heat treatment to form the DZ layer DZ on the surface layer, and oxygen is precipitated in the internal vacancies V to form the BMD layer BMD. A high-functional silicon wafer having a suitable DZ layer DZ as a surface layer and a BMD layer BMD having a high BMD density having a proximity gettering effect inside can be manufactured.

  The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

For example, in the above-described embodiment, the heat treatment temperature has been lowered compared to the conventional case. However, even if the heat treatment temperature is the same as that of N ₂ which has been conventionally used, the heat treatment time can be shorter than N _2. Even in this case, as in the case where the heat treatment temperature is lowered, the slip can be greatly reduced. Further, the nitriding gas converted into plasma may be used as the atmospheric gas. In this case, since the nitriding gas is activated by being turned into plasma, nitriding of the surface and injection of vacancies are further promoted.

When the atmosphere gas is a mixed gas of three or more types, one or more of them may be a nitriding gas such as NH ₃ . In addition, when the atmosphere gas is a mixed gas of two or more kinds, it is preferable that the contained nitriding gas is 0.5% or more or 10 sccm or more and is the smaller amount. In other words, the nitridation reaction in this range is reaction-controlled, and if the nitriding gas exceeding this minimum is included, the nitride film thickness formed on the wafer surface is the same. The vacancy concentration is the same and the amount of precipitation is the same. If the nitride film thickness is the same temperature and time within the range of 0.05% or more and less than 0.5% or less and 10 sccm or less, the amount of nitridation varies depending on the partial pressure of nitrogen. . Therefore, this region is diffusion-limited, and the amount of precipitation can be controlled by the amount of nitrogen.

Further, the pressure of the atmospheric gas may be any of reduced pressure, normal pressure, and increased pressure. Further, the nitride film and oxynitride film (silicon oxynitride film) formed on the wafer surface according to the above embodiment is Si _x N _y typified by Si ₃ N ₄ . Furthermore, when nitriding the oxide _{film, Si} 2 _N x _O 4-1.5x typified by _Si 2 _{N 2} O are formed. That is, a silicon oxynitride film is formed. This silicon oxynitride film is obtained by nitriding a natural oxide film, a chemical oxide film, or a thermal oxide film.

  These nitride films may further contain hydrogen in the film. In the above embodiment, a natural oxide film may be formed on the surface of the silicon wafer before the heat treatment. However, as described above, if the oxide film is about the natural oxide film, the cleaning effect such as NH3 or the oxide film A sufficient hole injection effect can be obtained by nitriding.

However, the natural oxide thick oxide film than film to a heat treatment in an atmosphere gas and the like containing oxygen before the heat treatment by the nitriding gas such as NH ₃ is formed on the silicon wafer surface, surface nitriding effects, such as NH ₃ It is not possible to sufficiently obtain the hole injection effect due to. This is because the oxide film on the surface is thick, and therefore a nitride film (including an oxynitride film) capable of good vacancy injection effect cannot be formed on the Si surface even when heat-treated with an atmospheric gas such as NH ₃ .

Therefore, before the heat treatment with the nitriding gas such as NH ₃ in the present embodiment, an oxide film thicker than the natural oxide film is positively formed on the silicon wafer, or the heat treatment is performed in an atmosphere gas containing oxygen before the heat treatment. It is not preferable to perform a simple process. In the present embodiment, it is preferable to perform a purge process for removing oxygen contained in the atmospheric gas before supplying the nitriding gas such as NH ₃ to the reaction chamber.

The case where the silicon oxynitride film is formed by the RTA process will be described below with reference to FIG. As shown in FIG. 4A, a natural oxide film (silicon oxide film) SO is formed on the surface of the silicon wafer W before the heat treatment, and no oxide film removal treatment is performed. In this state, when the above-described RTA treatment is performed and the natural oxide film SO and silicon on the surface are nitrided by NH ₃ , as shown in FIG. Then, a silicon oxynitride film SNO is formed.

  This silicon wafer has an oxynitride film whose surface is nitrided during the heat treatment, that is, a silicon oxynitride film SNO formed by nitriding the natural oxide film SO on the surface during the heat treatment. V has been implanted and has good surface roughness with suppressed surface roughness. Therefore, if the silicon wafer is further subjected to a heat treatment for oxygen precipitation, as shown in FIG. 4C, a DZ layer DZ having a BMD layer BMD with a high BMD density and a good surface roughness inside. Can be obtained on the surface layer.

  In the above embodiment, a silicon wafer sliced from an ingot pulled and grown by a normal CZ method is used. However, a silicon wafer from an ingot pulled and grown by another CZ method may be used. Absent. For example, in the silicon wafer, a region where interstitial silicon type point defects exist predominantly in a silicon single crystal ingot is [I], and a region where void type point defects exist predominantly is [V]. , When a perfect region where no agglomerates of interstitial silicon type point defects and agglomerates of vacancy type point defects exist is [P], agglomerates of point defects cut out from an ingot comprising the perfect region [P] A silicon wafer that does not exist may be used. A vacancy-type point defect is a defect due to a vacancy in which one silicon atom is separated from a normal one in a silicon crystal lattice, and an interstitial silicon point defect is a defect other than a lattice point of a silicon crystal. This refers to a defect when located at an interstitial site.

  That is, the silicon wafer consisting of this perfect region [P], for example, as proposed in Patent Document 3, pulls the ingot from the silicon melt in the hot zone by the CZ method based on the Boronkov theory. It is pulled up with a profile and is made by slicing this ingot. This ingot is thermally oxidized when the pulling speed is V (mm / min) and the temperature gradient in the vertical direction of the ingot near the interface between the silicon melt and the ingot in the crucible is G (° C./mm). The value of V / G (mm 2 / min · ° C.) is determined so that an OSF (Oxidation Induced Stacking Fault) generated in a ring shape disappears at the center of the wafer.

In the above-mentioned Boronkov theory, as shown in FIG. 5, the relationship between V / G and point defect concentration is shown with V / G on the horizontal axis and vacancy-type point defect concentration and interstitial silicon type defect concentration on the same vertical axis. Is described schematically, and it is explained that the boundary between the void region and the interstitial silicon region is determined by V / G. More specifically, when the V / G ratio is higher than the critical point, an ingot having a dominant vacancy-type point defect concentration is formed. On the other hand, when the V / G ratio is higher than the critical point, an ingot having a higher interstitial silicon type point defect concentration is formed. It is formed. In FIG. 5, [I] indicates a region where the interstitial silicon type point defect is dominant and an interstitial silicon point defect exists ((V / G) ₁ or less), and [V] indicates an ingot in the ingot. A region where vacancy-type point defects are dominant and agglomerates of vacancy-type point defects are present ((V / G) ₂ or less), and [P] is an agglomeration and lattice of vacancy-type point defects. The perfect area | region ((V / G) _1- (V / G) ₂ ) where the aggregate of an interstitial silicon type point defect does not exist is shown. A region [OSF] ((V / G) ₂ to (V / G) ₃ ) that forms an OSF nucleus exists in the region [V] adjacent to the region [P].

Therefore, the pulling speed profile of the ingot supplied to the silicon wafer is such that when the ingot is pulled from the silicon melt in the hot zone, the ratio of pulling speed to the temperature gradient (V / G) is an interstitial silicon type point defect. The first critical ratio ((V / G) ₁ ) or more for preventing the generation of aggregates of vacancy-type point defects is dominantly present in the center of the ingot. It is determined so as to be maintained below the second critical ratio ((V / G) ₂ ) limiting within the region.

  The profile of the pulling speed is determined based on the above-described Boronkov theory by experimentally slicing the reference ingot in the axial direction or by simulation.

  Thus, the silicon wafer produced in the perfect region [P] is a defect-free wafer having no OSF, COP, etc. However, since the IG effect is low, the heat treatment according to the above embodiment is performed. A sufficiently high density BMD layer can be formed inside, and a proximity gettering effect can be provided.

In addition, agglomerates of point defects such as COP may show different values for detection sensitivity and detection lower limit depending on the detection method. Therefore, in this specification, the meaning of “there is no agglomeration of point defects” means that the product of the observation area and the etching allowance is measured by an optical microscope after the mirror-finished silicon single crystal is subjected to non-stirring secco etching. Is observed as an inspection volume, each aggregate of flow pattern (vacancy type defects) and dislocation clusters (interstitial silicon type point defects) has one defect with respect to the inspection volume of 1 × 10 ⁻³ cm ^3. When the detected case is defined as a detection lower limit (1 × 10 ³ pieces / cm ³ ), it means that the number of point defect aggregates is equal to or lower than the detection lower limit.

  Next, a silicon wafer manufacturing method and a silicon wafer according to the present invention will be described in detail with reference to examples.

FIG. 6 shows the relationship between the heat treatment temperature (annealing temperature) and the BMD density when NH3 / Ar: 2SLM / 2SLM and NH3 / N2: 2SLM / 2SLM are actually flowed as the atmospheric gases based on the above embodiment. Show. Similarly, FIG. 7 shows the relationship between the heat treatment temperature and the DZ width when NH ₃ / Ar: 2SLM / 2SLM and NH ₃ / N 2: 2SLM / 2SLM are actually flowed as the atmospheric gases. For comparison, the case where N ₂ : 4SLM is flowed as the atmospheric gas as in the conventional case is also illustrated. As can be seen from FIGS. 6 and 7, in the heat treatment of the present invention containing NH ₃ as the atmospheric gas, a BMD density higher than the conventional one can be obtained even at a low heat treatment temperature, and a practically sufficient DZ width can be obtained. It has been.

FIG. 8 shows the relationship between the heat treatment time (annealing time) and the BMD density when the heat treatment temperature is 1100 ° C. and 1150 ° C. under the conditions of NH ₃ / N ₂ : 2SLM / 2SLM as the atmosphere gas. As can be seen from FIG. 8, at the same heat treatment time, a higher BMD density is obtained at 1150 ° C. than at 1100 ° C., which is a high temperature. Moreover, the difference in the effect becomes more remarkable as the heat treatment time is shorter.

  As a result of experiments conducted under various other conditions, according to the present invention, a sufficient BMD density can be obtained even at a lower temperature than in the prior art, and even if the flow rate ratio of the nitriding gas in the present invention is changed, the BMD It was found that the density did not change much. Furthermore, it has also been found that precipitation is increased when the cooling rate is increased in the present invention.

It was also found that the slip length was shorter for the heat treatment at low temperature and shorter for the higher cooling rate. Furthermore, it was found that when the atmosphere gas contains ammonia, the slip length is shorter when the amount of ammonia is relatively small. This is considered to be because H (hydrogen) having a relatively high thermal conductivity is reduced when ammonia is decomposed. Therefore, if heat treatment is performed using an atmosphere gas containing ammonia at a relatively low temperature and a small flow ratio, and cooling is performed at a higher cooling rate, slip can be further suppressed and a sufficient BMD density can be obtained. FIG. 9 shows a case where the wafer is held with quartz pins in order to clearly show the effect of slip by lowering the heat treatment temperature in the conventional method (N ₂ / Ar, 1220 ° C.) and the present invention (NH ₃ / Ar). It shows the length of the slip from the pin mark. The slip length is a measurement of the maximum distance between dislocation bits after 13 μm off by Seco etch. The slip which was extended by 3 mm in the conventional method became 0.4 mm or less in the present invention. It became zero at 1130 ° C. or less, and it was found that slip could be greatly reduced.

In addition, the composition of the surface reaction film is actually changed between the case where the conventional RTA treatment using N ₂ / Ar as the atmospheric gas is performed and the case where the silicon oxynitride film is formed on the surface based on the above embodiment. The results of analysis by an analysis method combining XPS and sputtering are shown in FIGS. As can be seen from the analysis results, in the case of the conventional example, as shown in FIG. 10A, almost no oxygen is detected on the surface, and only silicon and nitrogen are detected. In the example based on this embodiment, as shown in FIG. 10B, oxygen is detected on the surface at the same level as nitrogen, and a silicon oxynitride film is formed.

1 susceptor 2 reaction chamber BMD BMD layer DZ DZ layer (defect-free layer)
G Atmospheric gas SO Natural oxide film (silicon oxide film)
SNO Silicon oxynitride film V Vacancy
W Silicon wafer

Claims (12)

The silicon wafer is placed in a reaction chamber where heat treatment is performed, and the silicon wafer is heat-treated while supplying an atmospheric gas containing a nitriding gas having a decomposition temperature lower than the temperature at which N ₂ can be decomposed to surface nitridation. Or forming a nitride film on the surface thereof, and having a hole injection heat treatment step for forming new holes in the inside,
The vacancy injection heat treatment step uses an atmosphere gas containing NH ₃ as the nitriding gas, the concentration of NH ₃ in the nitriding gas is 0.5% or more, or the flow rate of NH ₃ is 10 sccm or more, and the heat treatment temperature Is performed at a temperature from 1100 ° C. to 1150 ° C., the heat treatment time is 60 sec or less, and the cooling rate is 33.3 ° C./sec to 50 ° C./sec. A method for producing a silicon wafer, comprising: 2. The method for manufacturing a silicon wafer according to claim 1, wherein the nitriding gas is made into a plasma. 3. The silicon wafer manufacturing method according to claim 1, further comprising an oxide film removing step for removing or thinning an oxide film on the surface of the silicon wafer before the hole injection heat treatment step. Manufacturing method. The method of manufacturing a silicon wafer according to claim 3, wherein the oxide film removing step, film thickness of at least the oxide film when containing NH ₃ to the atmospheric gas, and removing to below 2nm Silicon wafer manufacturing method. 5. The method for producing a silicon wafer according to claim 1, wherein the oxide film removing step performs a purging process for removing oxygen contained in an atmospheric gas in the reaction chamber, and then the nitriding gas is added to the nitriding gas. A method for producing a silicon wafer, characterized in that the silicon wafer is supplied into a reaction chamber. 6. The method of manufacturing a silicon wafer according to claim 1, wherein after the vacancy injection heat treatment step, the silicon wafer is heat-treated at a temperature lower than the vacancy injection heat treatment step to form a defect-free layer on a surface layer. A method for producing a silicon wafer, characterized by comprising a precipitation treatment step of forming and precipitating oxygen in internal vacancies. The method for manufacturing a silicon wafer according to claim 1, wherein a mixed gas of Ar and NH ₃ is used as the atmospheric gas containing the nitriding gas. 8. The method for manufacturing a silicon wafer according to claim 7, wherein the heat treatment is performed by the following procedures (i) to (v).
(I) Before raising the temperature to 800 ° C., only Ar is supplied as an atmospheric gas, and a purge process is performed to replace the atmospheric gas in the heat treatment furnace and remove oxygen.
(Ii) With the oxygen completely removed from the furnace, the temperature is raised to 800 ° C. while supplying only Ar as the atmospheric gas.
(Iii) Next, while heating NH ₃ into the heat treatment furnace and supplying a mixed gas of Ar and NH ₃ as an atmospheric gas, rapid heating is performed from 800 ° C. to the heat treatment temperature, and the heat treatment temperature is constant and predetermined. Heat treatment for hours.
(Iv) Then, rapidly cool to 800 ° C.
(V) Thereafter, Ar is supplied as an atmosphere gas at a constant flow rate of 800 ° C. until NH ₃ is completely discharged, and the temperature is lowered again in the atmosphere gas containing only Ar after the discharge is completed. 9. The method for producing a silicon wafer according to claim 1, wherein the cooling rate is 33.3 ° C./second or 50 ° C./second. 10. The method of manufacturing a silicon wafer according to claim 7, wherein a flow rate of the atmosphere gas is the NH ₃ / Ar: 2SLM / 2SLM. 11. 11. The method of manufacturing a silicon wafer according to claim 1, wherein a region where interstitial silicon type point defects exist predominantly in the silicon single crystal ingot is defined as [I] in the silicon wafer. When the region where the hole type point defects exist predominantly is [V], and the perfect region where the aggregates of the interstitial silicon type point defects and the hole type point defects do not exist is [P], A method for producing a silicon wafer, comprising using a silicon wafer free from agglomerates of point defects cut out from an ingot composed of region [P]. A silicon wafer produced by the method for producing a silicon wafer according to claim 1.

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