JPH0377330A - Processing of silicon single-crystal wafer - Google Patents

Abstract

PURPOSE:To make a gettering capacity among individual wafers nearly equal and to enhance the gettering capacity by a method wherein a silicon single- crystal wafer on which an oxide film has been formed is heat-treated in an atmosphere of nitrogen gas and within a specific temperature range, it is cooled at a specific cooling speed and, after that, a heat treatment for oxygen precipitation is executed. CONSTITUTION:A silicon single-crystal wafer which has been formed by slicing a silicon single-crystal ingot by a Czochralski method is used; an oxide film is formed on the surface of the silicon single-crystal wafer; after that, the silicon single-crystal wafer on which the oxide film has been formed is heat-treated in an atmosphere of nitrogen gas and within a temperature range of 1170 deg.C or higher and 1300 deg.C or lower. Thereby, nitrogen impurities are diffused and introduced into a crystal, and oxygen in an element formation region can be diffused to the outside. At the same time, very small defects formed during a crystal growth operation when the silicon single-crystal ingot is formed are decomposed. Then, the heat-treated silicon single-crystal wafer is cooled at a cooling speed of 100 deg.C/min or higher; after that, a heat treatment for oxygen precipitation of the cooled silicon single-crystal wafer is executed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for processing silicon single crystal wafers,
In particular, the present invention relates to a method for processing silicon single crystal wafers that have a strong dislocation fixing effect and a strong gettering ability.

A silicon single crystal wafer formed by slicing a silicon single crystal ingot formed by the Czochralski method (also called a pulling method) contains a large amount of oxygen impurities. This oxygen impurity has a fixing effect that fixes and suppresses dislocations that occur in silicon single crystal wafers, and
This oxygen impurity can be used for intrinsic gettering, and has the effect of absorbing heavy metals such as Fe-, Cu%Ns, etc. that enter the silicon single crystal wafer during the process, and the current amount is often used. There is.

[Conventional technology]

FIGS. 2(a) to 2(e) are diagrams illustrating a conventional method of processing a silicon single crystal wafer. The illustrated silicon single crystal wafer is a case where the silicon single crystal wafer is used for intrinsic gettering.

In this figure, 30 is a silicon single crystal ingot formed by the Czochralski method, 31 is a silicon single crystal wafer formed by slicing the silicon single crystal ingot 30, 32 is an oxygen atom, 34 is an oxygen precipitation nucleus, 3
5 is an oxygen precipitate, and 36 is an element formation region of the silicon single crystal wafer 31, which is also called a DZ (denoput zone).

Next, the processing method will be explained.

First, as shown in FIGS. 2(a) and (b), an appropriate oxygen concentration (30 p
A silicon single crystal ingot 30 containing an oxygen element 32 (about pm) is sliced to form a silicon single crystal wafer 3.
form 1. The silicon single crystal wafer 31 here is an as-grown crystal that has not been subjected to process heat treatment, and oxygen atoms 32 are uniformly contained in the crystal.

Next, as shown in FIG. 2(C), the silicon single crystal wafer 31 is subjected to high temperature heat treatment at 1100''C to 1150'C. is diffused externally and escapes, and the inside of the crystal 37
Oxygen atoms 32, also called interstitial oxygen, are formed only in the oxidation layer.

Next, as shown in FIG. 2(d), the silicon single crystal wafer 31 that has been subjected to high-temperature heat treatment is slowly cooled at a cooling rate of 20° C./min or less until it reaches a low temperature of 600 to 800° C. The silicon single crystal wafer 31 is subjected to low-temperature heat treatment by being maintained at a low temperature of 600 to 800°C. At this time, oxygen precipitation nuclei 34 larger than the oxygen atoms 32 shown in FIG. 2(C) are formed inside the crystal 37.

Then, as shown in FIG. 2Ce), the silicon single crystal wafer 31 that has been subjected to the low-temperature heat treatment is further subjected to a high-temperature heat treatment of about 1000'C. At this time, oxygen precipitates 35 larger than the oxygen precipitate nuclei 34 are formed inside the crystal 37 .

In this way, a defect-free layer having no oxygen precipitates 35 is formed in the element forming region 36 of the silicon single crystal wafer 31, and a defect-free layer having no oxygen precipitates 35 is formed in the crystal interior 37 of the silicon single crystal wafer 31.
A defective layer was formed.

[Problems to be Solved by the Invention] However, in such a conventional silicon single crystal wafer processing method, as-gr.

Even if the oxygen concentration of the silicon single crystal wafer 31 (before heat treatment), which is a wn crystal, is the same for each wafer, the oxygen concentration for each wafer may vary due to the thermal history received during crystal growth when forming the silicon single crystal ingot 30. Since the amount of precipitation varies, there is a problem in that the gettering ability varies from wafer to wafer.

For example, as shown in FIG. 2(a), the thermal history experienced during crystal growth is different between the crystal head portion x1 where the crystal is formed first and the crystal foot portion X2 where the crystal is formed last. , the amount of oxygen precipitated is different between the crystal head portion Xi and the crystal foot portion X2, and the gettering ability is also different. Since the crystal head portion X1 is subjected to more heat treatment than the crystal foot portion X2, the crystal head portion X1 has a larger amount of precipitated oxygen and a greater gettering ability. This ultimately has a significant impact on device yield. Specifically, gettering ability varies from wafer to wafer, and when a wafer with a weak gettering ability is formed, heavy metals such as Fe, Cu, and Ni that have invaded the element formation region during the process are removed from oxygen precipitates inside the crystal. (defect), it becomes impossible to absorb completely,
Heavy metals will remain in the device formation region, which will have an adverse effect on device performance. Therefore, a
Silicon single crystal wafer 3 which is s-growri crystal
1 (before heat treatment), if the oxygen concentration is the same, each wafer will show the same amount of precipitated oxygen when going through the same process,
It is also desirable that the gettering ability of each wafer be the same. Moreover, it is desirable that the gettering ability is high, and in order to improve this gettering ability, the inside of the crystal must be free from defects due to high density oxygen precipitates, and the element forming region must be defect-free without oxygen precipitates. is required.

Therefore, the present invention makes it possible to make the gettering ability approximately equal between each wafer, to improve the gettering ability, to form a good element formation area, and to have a high crystal strength. The purpose is to provide a method for processing silicon single crystal wafers.

[Means to solve the problem]

In order to achieve the above-mentioned object, the method for processing a silicon single crystal wafer according to the present invention uses a silicon single crystal wafer formed by slicing a silicon single crystal ingot formed by the Czochralski method. The step of forming an oxide film and the silicon single crystal wafer on which the oxide film is formed are subjected to 11 steps in a nitrogen gas atmosphere.
A step of heat treating at a temperature range of 70°C to 421,300"C, and heating the heat-treated silicon single crystal wafer for 10 minutes.
The method includes a step of cooling at a cooling rate of 0''C/min or more, and a step of performing an oxygen precipitation heat treatment on the cooled silicon single crystal wafer.

In the present invention, the silicon single crystal wafer is formed from a silicon single crystal ingot formed by the Czochralski method because multilegged oxygen atoms can be easily incorporated into the crystal. .

In the present invention, a preferable embodiment of the oxide film formed on the surface of a silicon single crystal wafer is a film having a thickness that allows nitrogen impurities to be easily introduced into the crystal and does not cause outward diffusion of nitrogen impurities. is preferable, and preferably 100 Å or more.

In the present invention, the temperature in a nitrogen gas atmosphere is set to 1170°C.
The lower limit was set at 1170'C because if the temperature was lower than 1170'C, the amount of nitrogen impurities entering the crystal would be very small, which would have almost no effect and be undesirable for practical use.The upper limit was also set at 1300'C. This is because if the temperature is higher than 1300° C., the silicon single crystal becomes soft and easily deformed, and dislocations will occur, which is not desirable in practice. In addition,
A preferable temperature L in a nitrogen gas atmosphere that allows a large amount of nitrogen impurities to be introduced and that makes it difficult for the silicon single crystal to deform! The temperature is 1200°C or more and 1270°C or less.

In the present invention, the cooling rate is set at 100"C/min or more because if the cooling rate is lower than 100"C/min and the cooling is slow, a large amount of nitrogen impurities introduced into the crystal will diffuse outward. This is because it is rarely effective and is not practical.

In the present invention, the step of performing oxygen precipitation heat treatment on a silicon single crystal wafer is a step of forming oxygen precipitation nuclei by low-temperature heat treatment at about 600 to 800° C. for several hours, for example.
This process includes two steps: a step of forming oxygen precipitates'@IJ (defects) by high-temperature heat treatment at, for example, about 1000° C. for several hours, which is performed after this step.

[Operation] In the present invention, a silicon single crystal wafer formed by slicing a silicon single crystal ingot formed by the Czochralski method is used, and after forming an oxide film on the surface of this silicon single crystal wafer, the oxide film is removed. This formed silicon single crystal wafer was heated for 1170' in a nitrogen gas atmosphere.
By performing heat treatment in a temperature range of C or more and 1,300"C or less, nitrogen impurities (nitrogen molecules) can be diffused and introduced into the crystal, and oxygen in the element formation region can be diffused outward. At the same time, it is possible to diffuse and introduce nitrogen impurities (nitrogen molecules) into the crystal. It is possible to decompose micro defects formed during crystal growth when forming a crystal ingot.At this time, nitrogen impurities are hardly affected by the oxide film formed on the silicon single crystal surface and are absorbed into the crystal. It can be introduced by diffusion. Conventionally, there was a problem that the gettering ability differed between each wafer because the amount of micro defects was different between each wafer, but by heat treatment at 117Q'C or more and 1300°C or less, ,
Since minute defects can be resolved, variations among wafers can be eliminated and gettering abilities can be made almost equal among wafers.

Next, the heat-treated silicon single crystal wafer was
After cooling at a cooling rate of C/min or more, the cooled silicon single crystal wafer is subjected to oxygen precipitation heat treatment. When the crystal is cooled here, if the cooling rate is as high as 100° C./min or more, the oxide film functions as a protective film and can suppress outward diffusion of nitrogen impurities. Here, the reason why the cooling rate is made higher than the conventional one (20° C./min or less) is to prevent nitrogen impurities from escaping from the crystal surface. Therefore, since a large amount of nitrogen impurities can be effectively frozen within the crystal, the amount of oxygen precipitated can be increased, the gettering ability can be improved, and a good device formation region can be formed. can. Also,
Like oxygen, this nitrogen impurity has the effect of fixing crystal dislocations, so it is possible to suppress the propagation and multiplication of dislocations more than in the case of conventional oxygen alone, and it is possible to increase the crystal strength.

〔Example〕

Figure 1 shows a silicon single crystal wafer on which an oxide film of 600 mm thick was formed at 115 °C at 1250 °C in a nitrogen gas atmosphere.
A silicon single crystal wafer (the present invention) was heat-treated for 1 minute and then rapidly cooled at a cooling rate of 1000°C/min by being pulled out of the heat treatment furnace at a rate of 4cm/sec. A silicon single crystal wafer that had been slowly cooled at a cooling rate of
A silicon single crystal wafer (Comparative Example 2) which was heat-treated at 50"C for 15 minutes and then rapidly cooled at a cooling rate of 1000°C/min by being pulled out of the heat treatment furnace at 4cm/sec, and a silicon single crystal wafer (Comparative Example 2) in which only the cooling rate was different from Comparative Example 2. A silicon single crystal wafer (Comparative Example 3) that was slowly cooled at a cooling rate of 7°C/min,
A silicon single crystal wafer with an oxide film formed with a thickness of 600 Å was heat treated at 1250°C for 115 minutes in a dry oxygen gas atmosphere, and then the silicon was rapidly cooled at a cooling rate of 1000°C/min by pulling it out of the heat treatment furnace at a rate of 4 cm/sec. A single crystal wafer (Comparative Example 4), and a silicon single crystal wafer that was slowly cooled at a cooling rate of 7°C/min (Comparative Example 5) with only the cooling rate changed from Comparative Example 4.
The figure shows the amount of oxygen precipitated when these were subjected to oxygen precipitation heat treatment at 700°C/20 hours + 1000°C/20 hours, respectively. The silicon single crystal wafer here was formed by slicing a silicon single crystal ingot using the Czochralski method, and had a diameter of 4 inches, an oxygen concentration of 30 ppm, a specific resistance of 10 ohm, and c.
m, boron doped.

As is clear from Fig. 1, an oxide film is formed on the surface and 1
Heat treated in a nitrogen gas atmosphere at 250°C and heated to 1000°C/
It was found that the silicon single crystal wafers of the present invention, which were quenched for 5 minutes and then heat-treated for oxygen precipitation, had a larger amount of oxygen precipitated and improved gettering ability than the silicon single crystal wafers of Comparative Examples 1 to 5. Here, the reason why the amount of oxygen precipitated in Comparative Example 1 is lower than that of the present invention is that nitrogen impurities diffuse outward during cooling because the cooling is performed slowly at a cooling rate of 7°C/min. This is presumed to be due to the fact that the effect of increasing the amount of oxygen precipitated due to the introduction of nitrogen impurities into the crystal is reduced.

Note that Comparative Example 3.5 was also subjected to slow cooling, so it was the same as described above. On the other hand, Comparative Example 2.4 is similar to the one of the present invention.
Rapid cooling was carried out at a cooling rate of 000'C/min, but first of all, in Comparative Example 2, no oxide film was formed, so nitrogen diffused outward and escaped, and nitrogen inert substances entered the crystal. This is presumed to be due to the fact that the effect of increasing the amount of oxygen precipitated becomes smaller. On the other hand, in Comparative Example 4, no nitrogen impurity was introduced. In addition, since the product of the present invention incorporates high-temperature heat treatment (1170°C or higher and 1300°C or lower), it is possible to decompose minute defects formed during crystal growth when forming a silicon single crystal ingot. , it is possible to avoid the influence of minute defects, and it is possible to make the gettering ability of each wafer almost equal. Moreover, since a large amount of nitrogen impurities can be effectively frozen within the crystal, oxygen precipitation can be increased, the gettering effect can be increased, and a good device formation region can be formed.

Furthermore, like oxygen, this nitrogen impurity has the effect of fixing crystal dislocations, so that the propagation and multiplication of dislocations can be inhibited, and the crystal strength can be increased.

[Effects of the Invention] According to the present invention, the gettering ability can be made almost equal between each wafer, and the gettering ability can be improved, the crystal strength can be increased, and a good element formation area can be created. It has the effect of being able to form.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a diagram illustrating the effects of an embodiment of the silicon single crystal wafer processing method according to the present invention, and FIG. 2 is a diagram illustrating a conventional processing method. . 30...Silicon single crystal ingot, 31...
...Silicon single crystal wafer 32...Oxygen atoms, 34...Oxygen precipitate nuclei, 35...Oxygen precipitates. (1)) (C) Figure 2 explaining the conventional processing method

Claims (1)

[Claims] A step of forming an oxide film on the surface of the silicon single crystal wafer using a silicon single crystal wafer formed by slicing a silicon single crystal ingot formed by the Czochralski method; a step of heat-treating the silicon single crystal wafer on which has been formed at a temperature range of 1170°C or more and 1300°C or less in a nitrogen gas atmosphere; and cooling the heat-treated silicon single crystal wafer at a cooling rate of 100°C/min or more. A method for processing a silicon single crystal wafer, comprising the steps of: performing an oxygen precipitation heat treatment on the cooled silicon single crystal wafer.