JPH1070131A - Heat treatment method for silicon wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the density of oxygen deposition in the vicinity of wafer surface by a method wherein a silicon wafer, which is cooled under specific condition when crystal is grown by a Czochralski method, is heat-treated in an oxidizing atmosphere under specific conditions. SOLUTION: Silicon wafers, whose temperature of 450 to 550 deg.C is cooled down for two or more hours, and they are heat-treated at 1000 deg.C or higher for thirty seconds in an oxidizing atmosphere before conduction of a device process, or heat treatment is conducted at 1100 deg.C for ten, seconds in an oxidizing atmosphere. As a result, the oxygen deposition nuclei, generated in the cooling process of 450 to 550 deg.C, are contracted or vanished and the oxygen deposition deposit density in the vicinity of silicon wafer is lowered. The time of residence of crystal in the temperature range of 450 to 550 deg.C when crystal is grown becomes longer, and the oxygen deposition density in the vicinity of the surface after heat treatment is increased by the presence of oxygen deposit in high density. Therefore, the microscopic oxygen deposition nuclei are contracted or quenched.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment method for reducing the density of oxygen precipitates in the vicinity of the surface of a wafer cut from a silicon single crystal pulled by the Czochralski method. A silicon wafer that can reduce the oxygen precipitation nuclei by performing a short-time high-temperature heat treatment before the device process in advance, and improve the device yield without generating oxygen precipitation nuclei near the wafer surface by the heat treatment in the device process. Heat treatment method.

[0002]

2. Description of the Related Art It has been practiced to use a high-temperature process in a device process to outwardly diffuse oxygen in the vicinity of the surface of a silicon wafer to suppress the deposition of oxygen near the surface. However, in such a process, depending on the thermal history of the wafer, an oxygen precipitate may be generated in the vicinity of the surface of the wafer, which may cause a failure in withstand voltage of an oxide film of the device or a failure in junction leakage.

[0003]

The inventors have found that such oxygen precipitation near the surface occurs by the following mechanism. In other words, during the crystal growth by the Czochralski method, if the residence time of the crystal at a temperature of around 500 ° C. becomes longer due to factors such as the pulling speed, the structure of the pulling furnace, and the length of the crystal, the fine oxygen precipitation nuclei become denser. And the concentration of interstitial silicon atoms increases.

When the wafer is processed in this state and subjected to a heat treatment at, for example, 900 ° C. in a device process, an oxygen precipitation nucleus grows, and when the concentration of released interstitial silicon atoms becomes higher than the thermal equilibrium concentration of 900 ° C., Outward diffusion of interstitial silicon atoms occurs near the surface, and since the interstitial silicon concentration is lower near the surface than inside the wafer, the oxygen precipitate density is higher near the surface than inside the wafer. After that, even after passing through a high-temperature process, the oxygen precipitate grown near the surface does not disappear easily but remains.

According to the present invention, when a silicon single crystal is grown by the Czochralski method, if the staying time of the crystal at a temperature near 500 ° C. becomes longer, the silicon wafer is subjected to a heat treatment of about 900 ° C. in a device process. In view of the problem that oxygen precipitates are generated near the surface and lower the device yield, oxygen precipitate nuclei generated at a temperature between 450 ° C. to 550 ° C. are shrunk or eliminated before device processing. It is another object of the present invention to provide a heat treatment method for reducing the density of oxygen precipitates near the wafer surface.

[0006]

DISCLOSURE OF THE INVENTION The inventors of the present invention aimed at investigating the influence of the heat history received when a silicon single crystal is grown by the Czochralski method on the oxygen precipitation behavior near the surface of a silicon wafer. The following experiment was performed.

[0007] A silicon single crystal having a diameter of 6 inches
When the crystal was pulled up by 900 mm at a constant speed of min, the pulling of the crystal was stopped, and after 5 hours, the silicon single crystal was separated from the silicon melt and rapidly cooled. The silicon single crystal grown in this manner is maintained for 5 hours at a temperature corresponding to the distance from the silicon melt at the time of stopping the pulling, that is, the distance from the end of the crystal.

A wafer was cut out from a portion of the silicon single crystal held at each temperature for 5 hours to obtain a sample.
FIG. 1 shows that at the temperature of 450 ° C. to 600 ° C. during crystal growth, 5
FIG. 6 is a distribution diagram of oxygen precipitates in a wafer cross-sectional direction when a wafer held for a time is subjected to a two-step heat treatment at 600 ° C. and 900 ° C. From this result, it can be seen that when the temperature is maintained in the temperature range of 450 ° C. to 550 ° C., the density of oxygen precipitates increases near the surface.

Next, the relationship between the difference in holding time in this temperature range and the density of oxygen precipitates near the surface was examined. In this experiment, a wafer cut out of a silicon single crystal that did not receive a special heat history such as stopping the pulling halfway was used as a sample. At 500 ° C
FIG. 2 shows the results of two-step heat treatment at 600 ° C. and 900 ° C. after the heat treatment for 4 hours, and the distribution of oxygen precipitates in the wafer cross-sectional direction. It can be seen that when the temperature is maintained at 500 ° C. for 2 hours or more, the density of oxygen precipitates increases near the surface.

From the results of FIGS. 1 and 2, 450 ° C. to 550 ° C.
It was clarified that the density of oxygen precipitates increased near the surface when the temperature was maintained for 2 hours or more in the above temperature range. Therefore, in order to suppress the oxygen precipitation near the surface, the temperature is set to 450 ° C. to 5 ° C.
What is necessary is to shrink and eliminate the minute oxygen precipitation nuclei generated in the temperature range between 50 ° C.

FIG. 3 shows that a wafer kept at 500 ° C. for 5 hours during crystal growth is subjected to a heat treatment at 800 ° C. to 1100 ° C. for 3 minutes in a lamp annealing furnace, and then to 600 ° C. and 900 ° C.
3 shows the results of examining the distribution of oxygen precipitates in the cross-sectional direction of the wafer by performing the two-step heat treatment. FIG. 3 shows that a temperature of 1000 ° C. or higher is effective for suppressing oxygen precipitation near the surface.

That is, the present inventors have found that 55
Even if the silicon wafer is cooled in a temperature range of 0 ° C. to 450 ° C. for 2 hours or more, if heat treatment is performed in advance at a temperature of 1000 ° C. or more, the density of oxygen precipitates near the surface after the subsequent heat treatment Was found not to be high.

According to the present invention, a silicon wafer which has been cooled in a temperature range of 550 ° C. to 450 ° C. for 2 hours or more at the time of crystal growth by the Czochralski method is heated to 1000 ° C. or more in an oxidizing atmosphere before device processing. 3 at temperature
This is a heat treatment method in which oxygen precipitate nuclei generated during a cooling process at 550 ° C. to 450 ° C. are shrunk or eliminated by performing a heat treatment for 0 second or more to reduce the density of oxygen precipitates near the wafer surface.

Further, the present invention provides a method in which a silicon wafer cooled to a temperature range of 550 ° C. to 450 ° C. for 2 hours or more at the time of crystal growth by the Czochralski method is subjected to 1100 ° C. in an oxidizing atmosphere before device processing. This is a heat treatment method in which a heat treatment is performed at the above temperature for 10 seconds or more to reduce or eliminate oxygen precipitate nuclei generated in a cooling process at 550 ° C. to 450 ° C., thereby reducing the density of oxygen precipitates near the wafer surface.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 550 ° C. to 450 ° C. during crystal growth
Since the residence time of the crystal in the temperature range of the above becomes longer and the high density of oxygen precipitate nuclei increases the density of oxygen precipitates near the surface after the subsequent heat treatment, the fine oxygen precipitate nuclei shrink. Or it may be extinguished. If the size of the oxygen precipitation nucleus is larger than the critical nucleus size at the heat treatment temperature, it grows, and if it is smaller, it shrinks and disappears. In the present invention, the wafer is heat-treated at 1000 ° C. or more in an oxidizing atmosphere before the device process, so that
By shrinking and eliminating oxygen precipitate nuclei generated in the cooling process at 450 ° C., it is possible to prevent the density of oxygen precipitates near the surface after the subsequent heat treatment from increasing.

The silicon wafer to be used in the present invention is a silicon wafer which has been cooled in a temperature range of 550 ° C. to 450 ° C. for 2 hours or more during crystal growth by the Czochralski method, regardless of the diameter of the silicon wafer.

The heat treatment conditions applied to the wafer before the device process are not particularly limited as long as there is no problem such as deformation of the wafer as the temperature range.
It is preferable to perform the treatment in an oxidizing atmosphere for at least 30 seconds or more (there is no particular upper limit). Further, if rapid cooling is performed from 1200 ° C. or more, abnormal precipitation may occur.
It is preferable to perform the treatment at a temperature of up to 1200 ° C. for 30 seconds or more.

[0018]

【Example】

Example 1 When a silicon single crystal having a diameter of 6 inches was pulled 900 mm at a constant speed of 1 mm / min, the pulling of the crystal was stopped, and after 5 hours, the silicon single crystal was cut off from the silicon melt and rapidly cooled. The wafer was cut out from the part held at 500 ° C. for 5 hours by stopping the lifting to make a sample.

The sample was placed in a lamp annealing furnace for 100
FIG. 4 shows the results of a pre-heat treatment at 0 ° C. for 0 to 60 seconds, followed by a two-stage heat treatment at 600 ° C. and 900 ° C. assuming a low-temperature device process, and the distribution of oxygen precipitates in the wafer cross-sectional direction. Show. By performing the pre-heat treatment at 1000 ° C. for 30 seconds or more, it was possible to prevent the density of oxygen precipitates near the surface from increasing.

Example 2 When a silicon single crystal having a diameter of 6 inches was pulled 900 mm at a constant speed of 1 mm / min, the pulling of the crystal was stopped. Five hours later, the silicon single crystal was separated from the silicon melt and rapidly cooled. The wafer was cut out from the part held at 500 ° C. for 5 hours by stopping the lifting to make a sample.

The sample was placed in a lamp annealing furnace for 110 hours.
FIG. 5 shows the results of a pre-heat treatment at 0 ° C. for 5 to 30 seconds, followed by a two-stage heat treatment at 600 ° C. and 900 ° C. assuming a low-temperature device process, and an examination of the distribution of oxygen precipitates in the wafer cross-sectional direction. Show. The pre-heat treatment temperature was set at 100
By setting the temperature to 1100 ° C., which is higher by 1 ° C., it was possible to prevent the density of oxygen precipitates near the surface from increasing in a shorter time than in Example 1, ie, 10 seconds.

Example 3 A wafer cut out from a position of 100 mm to 200 mm from a shoulder of a silicon single crystal having a diameter of 6 inches grown at a pulling rate of 0.4 mm / min was used as a sample. It takes about 8 hours for the portion of the crystal 100 mm to 200 mm from the shoulder to cool from 550 ° C. to 450 ° C. during growth.

This sample was subjected to a two-step heat treatment at 600 ° C. and 900 ° C. assuming a low-temperature device process, and the depth distribution of the oxygen precipitate density was examined. FIG. 6 shows the result. It can be seen that oxygen precipitates are concentrated near the surface.

On the other hand, FIG. 7 shows the distribution of the oxygen precipitate density in the depth direction when the pre-heat treatment is performed at 1100 ° C. for 3 minutes by the lamp annealing furnace before the two-step heat treatment at 600 ° C. and 900 ° C. . The pre-heat treatment for only 3 minutes reduced the oxygen precipitate density near the surface.

[0025]

According to the present invention, among silicon wafers cut from single crystal silicon grown by the Czochralski method, a silicon single crystal cooled in a temperature range of 550.degree. If the cut wafer is used as it is for device fabrication, high-density oxygen precipitates are generated near the surface of the wafer, resulting in low device yield. However, as is clear from the examples, according to the heat treatment of the present invention, 550 ° C.
By shrinking and eliminating oxygen precipitate nuclei generated in a temperature range of up to 450 ° C., high-density oxygen precipitation near the wafer surface can be prevented, and the device yield can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the temperature maintained for 5 hours by stopping pulling and the distribution of oxygen precipitates in the cross-sectional direction.

FIG. 2 is a diagram showing a relationship between a holding time at 500 ° C. and a distribution of oxygen precipitates in a sectional direction.

FIG. 3 is a diagram showing a relationship between a pre-heat treatment temperature and a cross-sectional distribution of oxygen precipitates.

FIG. 4 is a diagram showing a relationship between a pre-heat treatment time of 1000 ° C. and a distribution of oxygen precipitates in a cross-sectional direction.

FIG. 5 is a diagram showing a relationship between a pre-heat treatment time of 1100 ° C. and a distribution of oxygen precipitates in a cross-sectional direction.

FIG. 6 is a cross-sectional view of oxygen precipitates when a wafer cut from single crystal silicon grown at a pulling rate of 0.4 mm / min is subjected to a two-stage heat treatment at 600 ° C. for 3 hours or 8 hours and at 900 ° C. for 48 hours. It is a figure which shows a direction distribution.

FIG. 7 shows a wafer cut out of single crystal silicon grown at a pulling rate of 0.4 mm / min, subjected to a heat treatment for 3 minutes in a lamp annealing furnace according to the present invention, and then at 600 ° C.
FIG. 6 is a diagram showing the depth distribution of oxygen precipitates when two-stage heat treatment is performed at 8 hours and at 900 ° C. for 48 hours.

Claims (2)

[Claims] 1. A wafer cut from a silicon single crystal cooled in a temperature range of 550 ° C. to 450 ° C. for 2 hours or more during crystal growth by the Czochralski method, in an oxidizing atmosphere before device processing. Heat treatment at a temperature of 1000 ° C. or more for 30 seconds or more;
A heat treatment method for a silicon wafer in which the density of oxygen precipitates near the wafer surface is reduced by shrinking or eliminating oxygen precipitate nuclei generated in a cooling process at 0 ° C. 2. A wafer cut from a silicon single crystal cooled in a temperature range of 550 ° C. to 450 ° C. for 2 hours or more during crystal growth by the Czochralski method, in an oxidizing atmosphere before device processing. Heat treatment at a temperature of 1100 ° C. or more for 10 seconds or more;
A heat treatment method for a silicon wafer in which the density of oxygen precipitates near the wafer surface is reduced by shrinking or eliminating oxygen precipitate nuclei generated in a cooling process at 0 ° C.