JP2003007710A - Silicon wafer and its evaluation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an evaluation method of a silicon wafer for simply evaluat ing the internal gettering (IG) capability of a silicon wafer where heat treatment is made non-destructively, to provide the silicon wafer where desired IG capabil ity is added by carrying out heat treatment under heat treatment conditions for adding the IG capability obtained by the evaluation method, and to provide a silicon epitaxial wafer. SOLUTION: In the evaluation method for evaluating a silicon wafer that has been subjected to heat treatment, the X-ray diffraction intensity of the silicon wafer is measured by an X-ray diffraction method, thus evaluating the IG capability of the silicon wafer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating a heat-treated silicon wafer (hereinafter sometimes referred to as a wafer), and a heat-treated silicon wafer and a silicon epitaxial wafer (hereinafter referred to as a silicon wafer) having a high gettering ability. , Abbreviated as an epitaxial wafer).

[0002]

[Related Art] Silicon wafers grown by the Czochralski (CZ) method have about 10 ¹⁸ atoms.
/ Cm ³ interstitial oxygen is included as an impurity. This interstitial oxygen is deposited because it becomes a supersaturated state in the thermal history from solidification during the pulling process until it is cooled to room temperature and in the heat treatment process in the manufacturing process of the semiconductor element, and a precipitate of silicon oxide ( Hereinafter, it may be referred to as an oxygen precipitate.) Is formed.

One of the qualities of silicon wafers and epitaxial wafers is the ability to capture heavy metal impurities during the device process and remove them from the device active layer (gettering ability). As one of the gettering methods for a silicon wafer, an intrinsic gettering (Internal) method using oxygen precipitates generated by heat treatment is used.
Gettering: IG).

In the case of ordinary silicon wafers and epitaxial wafers, the oxygen precipitates present are extremely small in the stage before the device process, and the IG capability cannot be exhibited. However, through the device process, the oxygen precipitate grows and exhibits the IG capability.

Generally, the IG capability is evaluated by the density of oxygen precipitates after heat treatment. In this case, in the actual device process, it is premised that the oxygen precipitates grow sufficiently to a size capable of exhibiting the IG capability.

However, in recent years, the device process has been lowered in temperature and shortened in time, and the growth of oxygen precipitates cannot be expected, and there is a concern that the IG capability will be insufficient. In such cases,
In the conventional measurement of oxygen precipitate density after heat treatment, I
It becomes impossible to evaluate G ability.

In order to have an IG capability in a device process that is performed at a low temperature and in a short time, it is necessary to form a large amount of oxygen precipitates at a high density before the device process. As a method thereof, it is conceivable to apply some heat treatment during the production of the silicon wafer. However, there is a problem that there is no simple method for evaluating the IG capability in such a case, and the optimum heat treatment condition for adding the IG capability is not clear.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and is an evaluation of a silicon wafer which can easily and non-destructively evaluate the IG capability of a heat-treated silicon wafer. An object of the present invention is to provide a silicon wafer and a silicon epitaxial wafer to which a desired IG capability is imparted by performing heat treatment under the heat treatment conditions for imparting the IG capability obtained using the method and the evaluation method thereof.

[0009]

In order to achieve the above object, the first aspect of the method for evaluating a silicon wafer of the present invention is a method for evaluating a heat-treated silicon wafer, which comprises an X-ray diffraction method. The IG capability of the silicon wafer is evaluated by measuring the X-ray diffraction intensity of the silicon wafer measured by.

A second aspect of the method for evaluating a silicon wafer according to the present invention is that X of each of the first silicon wafer before the heat treatment and the second silicon wafer after the heat treatment is X.
The X-ray diffraction intensity is measured by the X-ray diffraction method, and the ratio of the X-ray diffraction intensity of the first silicon wafer and the X-ray diffraction intensity of the second silicon wafer is determined to obtain the IG of the second silicon wafer after the heat treatment. Characterized by evaluating ability.

Since the X-ray diffraction method is a non-destructive evaluation method, the same first silicon wafer and second silicon wafer can be used, but when non-identical wafers are used, It is necessary that the silicon wafers have the same thickness.

The method for determining the conditions for heat treatment of a silicon wafer according to the present invention is such that the X-ray diffraction intensity of each of the first silicon wafer before the heat treatment and the second silicon wafer after the heat treatment is measured by the X-ray diffraction method. The heat treatment conditions to be applied to the second silicon wafer are determined so that the ratio B / A of the X-ray diffraction intensity A of the silicon wafer and the X-ray diffraction intensity B of the second silicon wafer is 1.1 or more. And

The silicon wafer of the present invention is a heat-treated silicon wafer which has been subjected to the heat treatment under the heat treatment conditions determined by the heat treatment condition determination method.

A first aspect of the silicon epitaxial wafer of the present invention is manufactured by performing an epitaxial process using a silicon wafer heat-treated under the heat treatment conditions determined by the heat treatment condition determination method as a substrate.

A second aspect of the silicon epitaxial wafer of the present invention is that the silicon wafer is used as a substrate to perform an epitaxial process, and then heat treatment is performed under the heat treatment conditions determined by the heat treatment condition determination method.

It is generally known that the X-ray diffraction method is highly sensitive to strain. Furthermore, it is a non-destructive evaluation method and has an advantage that it is hardly dependent on the resistivity of the wafer.

The inventors of the present invention have found that in a heat-treated wafer, the X-ray diffraction intensity ratio before and after the heat treatment, that is, the X-ray diffraction intensity B after the heat treatment / the X-ray diffraction intensity A before the heat treatment, and the IG capability after the heat treatment. It was found that there is a good relationship with
The technical idea of the present invention that the G capability can be evaluated has been reached.

Further, the present inventor performs heat treatment during the manufacturing process of silicon wafers and epitaxial wafers so that the X-ray diffraction intensity ratio B / A before and after the heat treatment becomes a specific value or more, so that the device process before the device process is performed. It has been found that a silicon wafer and an epitaxial wafer having IG capability can be provided at a stage.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. The illustrated examples are shown as examples, and various modifications can be made without departing from the technical idea of the present invention. Needless to say.

According to the method of the present invention, the X-ray diffraction intensity is measured by the X-ray diffraction method for the heat-treated (after heat treatment) silicon wafer to be evaluated, and the IG of the silicon wafer is determined based on the measured X-ray diffraction intensity. It is an evaluation of ability.

FIG. 1 is a flow chart showing an example of the order of steps of the silicon wafer evaluation method of the present invention. In the figure, first, a first silicon wafer that has not been heat-treated (before heat treatment) is prepared (step 100), and a heat-treated (after heat treatment) second silicon wafer to be evaluated is prepared (step 100). 101). Then the first
The X-ray diffraction intensity A is measured for the silicon wafer (1) (step 102), and the X-ray diffraction intensity B is measured for the second silicon wafer (step 103).
Further, the ratio B / A of these X-ray diffraction intensities A and B is obtained (step 104). The IG capability of the second silicon wafer is evaluated based on this X-ray diffraction intensity ratio B / A (step 106). The IG capability can be evaluated directly from the diffraction intensities A and B by omitting step 104 for obtaining the ratio B / A of the X-ray diffraction intensities.

FIG. 2 is a flowchart in which an IG capability and a heat treatment condition evaluation procedure are added to the flowchart of FIG. In the figure, steps 100 to 104 are the same as those in FIG. After the step (step 104) of obtaining the ratio B / A of the X-ray diffraction intensities, a step (step 108) of determining whether or not the ratio B / A of the X-ray diffraction intensities is 1.1 or more is provided. ing. If the ratio B / A of the X-ray diffraction intensities is 1.1 or more, it is determined that the IG capability of the second silicon wafer is good and the heat treatment conditions of the heat treatment applied to the second silicon wafer are also good. (Step 110). On the other hand, this X-ray diffraction intensity ratio B /
IG of the second silicon wafer when A is less than 1.1
It is judged that the capability is bad and the heat treatment condition of the heat treatment applied to the second silicon wafer is also bad (step 112).

FIG. 3 is a flow chart showing another example of the order of steps of the method for evaluating a silicon wafer of the present invention (when the first wafer and the second wafer are the same wafer). In the figure, not heat treated (before heat treatment)
A silicon wafer is prepared (step 200). The X-ray diffraction intensity A of this silicon wafer is measured (step 202). Next, the silicon wafer whose X-ray diffraction intensity A has been measured is heat-treated (step 204),
A heat-treated (post-heated) silicon wafer is obtained (step 206). The X-ray diffraction intensity B of the wafer after the heat treatment is measured (step 208). Further, the ratio B / A of these X-ray diffraction intensities A and B is obtained (step 210). The IG capability of the silicon wafer after the heat treatment is evaluated by the X-ray diffraction intensity ratio B / A (step 212).

FIG. 4 is a schematic explanatory view showing an example of the arrangement of each device for measuring the X-ray diffraction intensity of a silicon wafer by the X-ray diffraction method. In the figure, 10 is an X-ray source, and a first slit plate 12 is provided opposite to the X-ray source 10. A first slit 12a is opened at the center of the first slit plate 12. X-rays from the X-ray source 10 enter the sample W such as a silicon wafer through the first slit 12a. Reference numeral 14 denotes a second slit plate having a second slit 14a opened at the center thereof, which is opposed to the sample W,
The diffracted X-ray from the sample W is incident through the second slit 14a, and the X-ray diffraction intensity is measured by a counter 16 such as a scintillation counter.

The method of the present invention was made in view of the fact that the IG capability in the actual device process cannot be evaluated by the measurement of the oxygen precipitate density after the heat treatment, which has been generally performed as a conventional method for evaluating the IG capability. It is a thing. That is,
The method of the present invention uses
The ability is evaluated by the X-ray diffraction intensity measured by the X-ray diffraction method.

Since the X-ray diffraction intensity increases depending on the amount of strain associated with defects, it increases depending on both the density and size of oxygen precipitates formed by heat treatment. From that,
I is more accurate than the conventional method of measuring only the density of oxygen precipitates.
G ability can be evaluated. When measuring the X-ray diffraction intensity, a Laue case of the Lang method (an arrangement in which X-rays are incident from one surface of the wafer and diffracted X-rays are extracted from the opposite surface) is used to scintillate the intensity of 440 diffraction, for example. Measure at the counter.

Since the X-ray diffraction intensity also depends on the thickness of the wafer, it is preferable to obtain the diffraction intensity ratio before and after the heat treatment in order to accurately measure the change in the diffraction intensity due to the defects generated by the heat treatment. However, since the X-ray diffraction intensity before the heat treatment hardly changes due to factors other than the thickness of the wafer, the wafers before and after the heat treatment need not have the same thickness but have substantially the same thickness (about ± 5%).

Further, by performing a heat treatment such that the X-ray diffraction intensity ratio before and after the heat treatment is 1.1 or more during the manufacturing process of the silicon wafer and the epitaxial wafer, the silicon having the IG capability before the device process is performed. Wafers and epitaxial wafers can be provided.

The heat treatment step is, for example, in the middle of the step of producing a mirror-finished wafer from the grown silicon crystal. In the case of an epitaxial wafer, it may be before or after the epitaxial growth step. The interstitial oxygen concentration in the wafer is 15 to 25 ppma (JEIDA
(Standard), the heat treatment condition is, for example, about 1000 ° C. for 1 to 4 hours. JEIDA is an abbreviation for Japan Electronics Industry Promotion Association (currently renamed to JEITA: Japan Electronics and Information Technology Industries Association).

[0030]

The present invention will be described in more detail with reference to the following examples, but it goes without saying that these examples are shown by way of illustration and should not be construed as limiting.

(Example 1) Diameter 8 inches, plane orientation <10
0> and a resistivity of about 10 Ω · cm, a plurality of boron-added silicon wafers grown by the CZ method were prepared. The thickness of these silicon wafers is in the range of 725 ± 15 μm, and the oxygen concentration is 16.2, 17.5, 18.4, 19.
It is 4 ppma (JEIDA standard). The wafers were heat-treated at 1000 ° C. for 1 to 4 hours.

The arrangement shown in FIG. 4 was used for the measurement of the diffraction intensity by the X-ray diffraction method. The measuring method will be described below. First, X-rays generated from the molybdenum target of the X-ray source 10 were made to pass through the first slit 12a having a diameter of 1 mm and then made incident from the front surface side of the wafer W. Then, among the X-rays from the target, Kα1 rays (wavelength =
The angle of the wafer W was adjusted so that 0.709Å) satisfied the condition of 440 diffraction, and the intensity of the diffracted X-ray emitted from the back surface side of the wafer was measured by the scintillation counter 16. By such a method, the X-ray diffraction intensity before and after the heat treatment was measured, and the X-ray diffraction intensity ratio (after the heat treatment / before the heat treatment) was obtained. The X-ray diffraction intensity before the heat treatment was measured on a wafer having the same thickness (within the range of 725 ± 15 μm) as the wafer after the heat treatment.

The density of oxygen precipitates formed by the heat treatment was measured by the infrared scattering tomography method.

Further, in order to evaluate the IG capability of the heat-treated wafer, the following experiment was conducted. First, the surface of the wafer was contaminated with Ni having a surface concentration of about 1 × 10 ¹¹ / cm ² . Then, Ni was diffused inside the wafer by heat treatment at 800 ° C. for 15 minutes. After the heat treatment, a chemically selective etching method is used to remove N on the wafer surface.
i The presence or absence of surface defects due to contamination was examined.

FIG. 5 shows the relationship between the heat treatment time at 1000 ° C. and the X-ray diffraction intensity ratio before and after the heat treatment. It can be seen that the diffraction intensity ratio increases as the heat treatment time increases.
Further, in the same heat treatment time, the higher the oxygen concentration, the larger the diffraction intensity ratio.

FIG. 6 shows the relationship between the heat treatment time at 1000 ° C. and the density of oxygen precipitates. The higher the oxygen concentration, the higher the oxygen precipitate density. When the oxygen concentration was the same, the oxygen precipitate density was almost constant regardless of the heat treatment time. From this result, it can be judged that the increase in the X-ray diffraction intensity with the increase in the heat treatment time shown in FIG. 5 is caused by the increase in the size of the oxygen precipitates.

FIG. 7 shows the results for the presence or absence of surface defects due to Ni contamination. The generation of surface defects does not depend on the oxygen precipitate density. On the other hand, the X-ray diffraction intensity ratio is 1.1.
In the above cases, it can be seen that no surface defect has occurred. Since the surface defects are generated when Ni is not gettered by the oxygen precipitates, it can be judged that the gettering ability is surely obtained when the X-ray diffraction intensity ratio is 1.1 or more.

Comparative Example 1 A wafer similar to that of Example 1 was prepared. However, heat treatment was not performed. In these wafers, generation of surface defects due to Ni contamination was examined as in the case of Example 1. As a result, surface defects were observed on all the wafers, and I
It was confirmed that there was no G capability.

[0039]

As described above, according to the method of the present invention, the IG capability of a heat-treated silicon wafer is
Non-destructive and easy to evaluate, and by applying heat treatment under the conditions determined using the evaluation method,
It is possible to provide a silicon wafer and an epitaxial wafer having the IG capability at the stage before the device process.

[Brief description of drawings]

FIG. 1 is a flowchart showing an example of a process sequence of a method for evaluating a silicon wafer according to the present invention.

FIG. 2 is a flowchart in which an IG capability and a heat treatment condition evaluation procedure are added to the flowchart of FIG.

FIG. 3 is a flowchart showing another example of the order of steps of the method for evaluating a silicon wafer according to the present invention.

FIG. 4 is a schematic explanatory view showing an example of the arrangement of each device when measuring the X-ray diffraction intensity by the X-ray diffraction method.

5 is a graph showing the relationship between the heat treatment time and the X-ray diffraction intensity ratio before and after heat treatment in Example 1. FIG.

FIG. 6 is a graph showing the relationship between heat treatment time and oxygen precipitate density in Example 1.

FIG. 7 is a graph showing the relationship between the density of oxygen precipitates, the X-ray diffraction intensity ratio, and the presence / absence of surface defects in Example 1.

[Explanation of symbols]

10: X-ray source, 12: first slit plate, 12a: first slit, 14: second slit plate, 14a: second slit, 16: counter, W: sample.

Claims (7)

[Claims] 1. A method for evaluating a silicon wafer after heat treatment, characterized in that the IG capability of the silicon wafer is evaluated by measuring the X-ray diffraction intensity of the silicon wafer by an X-ray diffraction method. Evaluation method. 2. The X-ray diffraction intensity of each of the first silicon wafer before the heat treatment and the second silicon wafer after the heat treatment is measured by the X-ray diffraction method, and the X-ray diffraction intensity and the first silicon wafer of the first silicon wafer are measured. A method for evaluating a silicon wafer, characterized in that the IG capability of the second silicon wafer after the heat treatment is evaluated by obtaining a ratio of X-ray diffraction intensities of the second silicon wafer. 3. The method for evaluating a silicon wafer according to claim 2, wherein the first silicon wafer and the second silicon wafer are not the same but have the same thickness. 4. The X-ray diffraction intensity of each of the first silicon wafer before the heat treatment and the second silicon wafer after the heat treatment is measured by the X-ray diffraction method, and the X-ray diffraction intensity A and the X-ray diffraction intensity of the first silicon wafer are measured. A method for determining a heat treatment condition for a silicon wafer, wherein the heat treatment condition for the second silicon wafer is determined so that the ratio B / A of the X-ray diffraction intensity B of the second silicon wafer becomes 1.1 or more. 5. A heat-treated silicon wafer, wherein the heat treatment is performed under the heat treatment conditions determined by the method of claim 4. 6. A silicon epitaxial wafer manufactured by performing an epitaxial process using the heat-treated silicon wafer according to claim 5 as a substrate. 7. A silicon epitaxial wafer, which has been subjected to an epitaxial process using a silicon wafer as a substrate and then subjected to a heat treatment under the heat treatment conditions determined by the method of claim 4.