JP2012124531A - Manufacturing method of epitaxial silicon wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method in which a silicon wafer for epitaxial growth is subjected to RTA heat treatment at a lower temperature to suppress the silicon wafer from slipping and excellent oxygen precipitation is caused in the wafer to manufacture an epitaxial silicon wafer of high quality which has a sufficiently high BMD density and is free from slip.SOLUTION: A manufacturing method of an epitaxial silicon wafer includes: a step of preparing the silicon wafer: a step of performing the RTA heat treatment for the prepared silicon wafer in an atmospheric gas; and a step of growing an epitaxial layer on a surface of the silicon wafer for which the RTA heat treatment has been performed. The step of preparing the silicon wafer provides the silicon wafer in which an initial oxygen concentration is 16 to 20 ppma and a carbon concentration is greater than 1 ppma. The step of performing the RTA heat treatment performs the heat treatment at a temperature of less than 1200°C.

Description

  The present invention relates to a method for manufacturing an epitaxial silicon wafer in which an epitaxial layer is grown after performing an RTA heat treatment.

  As a substrate for forming a semiconductor element, a silicon wafer made of a single crystal grown by a CZ (Czochralski) method or an MCZ (Magnetic field CZ) method, or an epitaxial silicon having an epitaxial layer formed on the surface of the silicon wafer Conventionally, annealed wafers obtained by heat-treating wafers and silicon wafers have been used.

  In particular, since an epitaxial silicon wafer can form an electrically active layer having a resistivity different from that of a substrate from the viewpoint of manufacturing a semiconductor element, the degree of freedom in designing a semiconductor element is great. Since there are many advantages such as the ability to form a high-purity single crystal thin film to an arbitrary thickness, a high-voltage semiconductor element, an integrated circuit element, a solid-state imaging device (CCD <Charge-Coupled Device>, CIS <CMOS Image Sensor>), etc. It has been put to practical use in products.

  However, the epitaxial silicon wafer has a problem that its IG capability is low compared to a normal silicon wafer. That is, an epitaxial silicon wafer has an epitaxial layer growth process at a high temperature of about 1050 ° C. to 1150 ° C. and a high temperature rising rate at that time. Since oxygen precipitation nuclei such as holes are reduced or disappeared, or interstitial Si is injected, oxygen precipitates (BMD: Bulk Micro Defect) are hardly formed in the underlying silicon wafer even by subsequent heat treatment. Compared with the mirror surface wafer of IG, the IG capability was reduced.

  For this reason, conventionally, epitaxial silicon is grown by performing RTA heat treatment (RTA: Rapid Thermal Annealing) on a silicon wafer for epitaxial growth before injecting vacancies inside the wafer before the epitaxial layer growth step. There is a wafer manufacturing method. However, even in this case, it is difficult to form a high-density BMD.

  On the other hand, for example, Patent Document 1 describes a method for obtaining a desired BMD density by performing an RTA heat treatment at a temperature of 1200 ° C. or higher and then growing an epitaxial layer at a temperature of 1170 ° C. or lower.

  However, the manufacturing method as described above has a problem that a silicon wafer slips due to a relatively high temperature RTA heat treatment.

Patent No. 3791446

  Therefore, the present invention has been made in view of such problems, and it is possible to reduce the temperature of the RTA heat treatment applied to the silicon wafer for epitaxial growth, to suppress the occurrence of slip of the silicon wafer, and to improve the inside of the wafer. An object of the present invention is to provide a method capable of producing a high-quality epitaxial silicon wafer having a sufficiently high BMD density and having no slip by causing oxygen precipitation.

  In order to achieve the above object, the present invention provides at least a step of preparing a silicon wafer, a step of subjecting the prepared silicon wafer to RTA heat treatment in an atmospheric gas, and a surface of the silicon wafer subjected to the RTA heat treatment. A method of producing an epitaxial silicon wafer, comprising: preparing a silicon wafer having an initial oxygen concentration of 16 to 20 ppma and a carbon concentration of greater than 1 ppma in the step of preparing the silicon wafer. In the RTA heat treatment step, an epitaxial silicon wafer manufacturing method is provided, wherein heat treatment is performed at a temperature of less than 1200 ° C.

In this way, if the carbon concentration is a silicon wafer as described above, carbon can capture the interstitial silicon injected into the wafer during the epitaxial layer growth and effectively prevent the reduction of vacancies. In addition, if the initial oxygen concentration is a silicon wafer as described above, oxygen precipitation occurs efficiently during epitaxial growth or subsequent heat treatment.
Even when the RTA heat treatment for vacancy injection is performed at a temperature of less than 1200 ° C. while preventing slipping, the inside of the epitaxial silicon wafer can be prevented by preventing the reduction of the amount of vacancies and the effect of efficient oxygen precipitation. BMD having a sufficient density can be formed. For this reason, according to the manufacturing method of the present invention, a high-quality epitaxial silicon wafer having a sufficiently high BMD density and no slip can be manufactured.

At this time, in the RTA heat treatment step, as the atmospheric gas, use is made of nitrogen gas mixed with oxygen having a concentration of less than 100 ppm, or nitrogen gas mixed with moisture having a concentration of 10 ppm or more and 150 ppm or less. Is preferred.
By performing RTA heat treatment in such an atmospheric gas, vacancies can be efficiently injected even at a relatively low temperature, and a special apparatus is used because there is no need to use a toxic gas such as NH _3. There is no need, and an epitaxial silicon wafer having a higher density BMD layer can be manufactured at low cost.

At this time, the epitaxial layer can be grown at a temperature of 1080 ° C. or lower in the epitaxial layer growth step.
In this way, by reducing the epitaxial growth at a relatively low temperature, it is possible to more effectively prevent the vacancies from decreasing.

  According to the present invention, a high-quality epitaxial silicon wafer having a high-density BMD inside and having no slip can be produced.

It is a graph which shows the depth distribution from the surface of an average BMD density at the time of performing RTA heat processing and epitaxial growth by changing the conditions of initial oxygen concentration and carbon concentration. It is the schematic which shows an example of the heat processing furnace which can be used for the RTA heat processing of this invention.

Conventionally, vacancies have been injected by performing RTA heat treatment on a silicon wafer for epitaxial growth, but there are problems such as insufficient oxygen precipitation and occurrence of slip.
In contrast, the present inventors inject holes into the wafer by low-temperature heat treatment, and the BMD density is sufficiently high, for example, when the BMD density is 1 × 10 ⁶ (/ cm ² ) or more, We have earnestly studied about the method of manufacturing no epitaxial silicon wafer.

As a result of the examination, not only the high temperature during epitaxial growth but also the number of vacancies decreased due to the interstitial silicon implanted during the growth as the cause of the decrease in vacancies in the epitaxial layer growth process. It has been found that carbon can be doped into a silicon wafer for epitaxial growth as a method for preventing the vacancy reduction due to. Furthermore, it has been found that by adjusting the initial oxygen concentration, oxygen precipitation occurs satisfactorily, and therefore, a sufficiently high BMD density can be obtained even after the epitaxial step.
Even when RTA heat treatment is performed at a relatively low temperature of less than 1200 ° C. at which slip does not easily occur and vacancies are injected, an epitaxial silicon wafer having a sufficient BMD density is formed after the epitaxial layer growth step or heat treatment step in the subsequent step. The carbon doping concentration and the initial oxygen concentration that can be further examined.

Two steps for epitaxial layer growth and oxygen precipitation by RTA heat treatment at temperatures below 1200 ° C for carbon concentrations greater than 1 ppma and less than 1 ppma under four conditions of initial oxygen concentration of 14, 16, 18, 20 ppma The result of measuring the BMD density after the heat treatment is shown in FIG. If the initial oxygen concentration is higher than 20 ppma, precipitation may be excessive and problems such as warpage may occur. Therefore, the upper limit of the initial oxygen concentration is set to 20 ppma or less.
As shown in FIG. 1, when the initial oxygen concentration is 14 ppma, the BMD density is insufficient even when the carbon concentration is high. When the initial oxygen concentration is 16 to 20 ppma and the carbon concentration is higher than 1 ppma, the BMD density is 1 ×. It was found to be 10 ⁶ (/ cm ² ) or more.
In addition, generation | occurrence | production of the slip was not seen in these wafers.

  From the above, even when the RTA heat treatment is performed at a temperature of less than 1200 ° C., the initial oxygen concentration of the silicon wafer for epitaxial growth is set to 16 to 20 ppma and the carbon concentration is set to be higher than 1 ppma, thereby having a sufficiently high BMD density. It was found that no epitaxial silicon wafer could be produced and the present invention was completed.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. However, the present invention is not limited to these embodiments.

  First, a silicon wafer for epitaxial growth is prepared. In the manufacturing method of the present invention, a silicon wafer having an initial oxygen concentration of 16 to 20 ppma and a carbon concentration of more than 1 ppma is prepared.

Here, the method for producing a silicon wafer prepared by the production method of the present invention is not particularly limited. For example, a silicon single crystal rod doped with carbon by CZ (Czochralski) method is grown and grown. There is a method in which a single crystal rod is sliced with a cutting device such as an inner peripheral slicer or a wire saw, and then a silicon wafer is manufactured through processes such as chamfering, lapping, etching, and polishing.
In order to dope carbon into such a single crystal rod, a general method may be used. For example, when a seed crystal is brought into contact with a melt of a polycrystalline silicon raw material contained in a quartz crucible, and the silicon single crystal rod having a desired diameter is grown by slowly rotating the seed crystal, carbon is added to the atmosphere gas. The inclusions can be used, or high-purity carbon powder can be added to the raw material melt as a dopant, and carbon lump (granular carbon) can be put in a quartz crucible in advance. . Furthermore, carbon fibers and / or silicon carbide fibers can be used as the dopant.

At this time, a silicon wafer having a carbon concentration of more than 1 ppma can be produced by controlling the carbon doping amount in the single crystal rod by adjusting the carbon gas concentration, the introduction time, and the amount of added carbon powder.
In addition, regarding the initial oxygen concentration of the silicon wafer to be prepared, for example, when producing a single crystal rod by the Czochralski method, the initial oxygen concentration of 16 to 20 ppma is controlled by controlling appropriate conditions such as crucible rotation and temperature distribution. can do.

Next, in the manufacturing method of the present invention, the prepared silicon wafer is subjected to RTA heat treatment at a temperature of less than 1200 ° C.
If the temperature is less than 1200 ° C., the temperature is relatively low, so that it is possible to inject holes while preventing slippage in the silicon wafer.

FIG. 2 shows an example of a heat treatment furnace for RTA that can be used in the present invention. In the present invention, since the desired BMD density can be obtained by adjusting the conditions of the silicon wafer for epitaxial growth, there is no need to use a special apparatus or the like, and the heat treatment furnace is substantially the same as the conventional one. Can be used.
The heat treatment furnace 10 is provided with a lid 15 for closing the carry-in port of the silicon wafer W, a gas supply port 12 for supplying atmospheric gas, a gas discharge port 14 for discharging atmospheric gas, and a silicon wafer W. The susceptor 13 and the lamp 11 for heating the silicon wafer W are provided.
The silicon wafer W is placed in such a heat treatment furnace 10 and the RTA heat treatment is performed while flowing the atmospheric gas from the gas supply port 12.

  Conditions other than the temperature of the RTA heat treatment of the present invention are not particularly limited. For example, the temperature is raised at 20 to 50 ° C./sec, and after the heat treatment for 1 to 60 seconds, the temperature is 20 to 50 ° C. The temperature can be lowered at / sec.

Also, the atmosphere gas at the time of RTA heat treatment is not particularly limited. For example, nitrogen gas mixed with oxygen having a concentration of less than 100 ppm, or nitrogen gas mixed with moisture having a concentration of 10 ppm or more and 150 ppm or less. It is preferable to use the same.
By performing the RTA heat treatment in such an atmospheric gas, vacancies can be efficiently injected even at a relatively low temperature, and a special apparatus needs to be used because no toxic gas such as NH ₃ is used. In addition, an epitaxial silicon wafer having a higher density BMD layer can be manufactured at low cost.
In addition, as adjustment of the moisture concentration mixed in nitrogen gas, it can adjust comparatively easily by controlling the dew point of nitrogen gas. In the case of the moisture concentration range as described above, the dew point of nitrogen gas is controlled to −60 ° C. to −38 ° C.

Next, an epitaxial layer is grown on the surface of the silicon wafer subjected to the RTA heat treatment.
For example, it can be formed by introducing a source gas such as SiHCl ₃ into the chamber using H ₂ as a carrier gas and epitaxially growing it on the wafer placed on the susceptor by the CVD method. However, it is not particularly limited, and for example, the epitaxial layer can be grown at a temperature of 1080 ° C. or lower.
In this way, by reducing the epitaxial growth at a relatively low temperature, it is possible to more effectively prevent the vacancies from decreasing.

In the manufacturing method of the present invention as described above, since a silicon wafer having a carbon concentration higher than 1 ppma is used, carbon captures interstitial silicon injected into the wafer during epitaxial layer growth, which effectively reduces vacancies. Further, since a silicon wafer having a relatively high initial oxygen concentration of 16 to 20 ppma is used, oxygen precipitation is efficiently generated during epitaxial growth and subsequent heat treatment. Further, since the initial oxygen concentration is 20 ppma or less, it is possible to prevent the occurrence of warpage and defects on the surface without excessive precipitation.
Therefore, even when the RTA heat treatment for vacancy injection is performed while preventing slip at a temperature of less than 1200 ° C., the inside of the epitaxial silicon wafer is prevented by the effect of reducing the amount of vacancies and efficient oxygen precipitation. BMD having a sufficient density can be formed. For this reason, according to the manufacturing method of the present invention, a high-quality epitaxial silicon wafer having a sufficiently high BMD density and no slip can be manufactured.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.

(Examples and comparative examples)
As silicon wafers for epitaxial growth, silicon wafers having an initial oxygen concentration of 14, 16, 18, and 20 ppma (JEIDA) are obtained with carbon concentrations of 1.3 ppma, 1.1 ppma, 1.0 ppma, and 0.05 ppma. A total of 16 pieces of the following were prepared.
Next, an RTA heat treatment is performed on the silicon wafer by using a nitrogen gas having a moisture concentration of 100 ppm as an atmosphere gas, with an RTA heat treatment temperature of 1190 ° C., a heat treatment time of 30 seconds, a temperature increase rate of 50 ° C./sec, and a temperature decrease rate of 33 ° C./sec. Was given.

Next, an epitaxial layer was grown on the surface of the silicon wafer subjected to the RTA heat treatment at a temperature of 1130 ° C. to manufacture an epitaxial silicon wafer.
Thereafter, two-stage heat treatment (800 ° C./4 hours, 1000 ° C./16 hours) was performed for oxygen precipitation. The epitaxial silicon wafer after the two-stage heat treatment was cleaved and etched to measure the BMD density.
FIG. 1 shows the measurement results of the BMD density.

As can be seen from FIG. 1, when the initial oxygen concentration is 14 ppma, the BMD density is low, and when the initial oxygen concentration is 16 to 20 ppma, the BMD density is 1 × 10 ⁶ if the carbon concentration is higher than 1 ppma. It can be seen that it is sufficiently high as (/ cm ² ) or more. Further, when the carbon concentration is 1 ppm or less, a desired BMD density cannot be obtained under any initial oxygen concentration condition, and even when the initial oxygen concentration is 20 ppma, the BMD density is high in the vicinity of the surface layer. However, it is understood that oxygen precipitation is insufficient inside.

Further, if the carbon concentration is 1.1 ppma, the desired BMD density can be obtained if the initial oxygen concentration is 16 ppma or more, and sufficient oxygen precipitation occurred, but the carbon concentration was 1.0 ppma. In some cases, the desired BMD density could not be obtained when the oxygen concentration was low. Note that no slip occurred on the silicon wafer under any of the conditions.
From the above, it was found that even when the RTA heat treatment at less than 1200 ° C. was performed, sufficient oxygen precipitation occurred at an initial oxygen concentration of 16 ppma or more if the carbon concentration of the silicon wafer for epitaxial growth was higher than 1 ppma.

  The present invention is not limited to the above embodiment. The above embodiment is merely an example, and the present invention has the same configuration as that of the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

10 ... Heat treatment furnace, 11 ... Lamp, 12 ... Gas supply port,
13 ... susceptor, 14 ... gas outlet, 15 ... lid,
W: Silicon wafer.

Claims (2)

Epitaxial silicon having at least a step of preparing a silicon wafer, a step of subjecting the prepared silicon wafer to RTA heat treatment in an atmospheric gas, and a step of growing an epitaxial layer on the surface of the silicon wafer subjected to the RTA heat treatment A wafer manufacturing method comprising:
In the step of preparing the silicon wafer, a silicon wafer having an initial oxygen concentration of 16 to 20 ppma and a carbon concentration of greater than 1 ppma is prepared, and in the RTA heat treatment step, 10 ppm or more and 150 ppm or less of nitrogen gas is used as the atmosphere gas. A method for producing an epitaxial silicon wafer, wherein a heat treatment is performed at a temperature of less than 1200 ° C. using a mixture of moisture at a concentration.   The epitaxial silicon wafer manufacturing method according to claim 1, wherein the epitaxial layer is grown at a temperature of 1080 ° C. or less in the epitaxial layer growth step.

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