JP6702485B1 - Wafer peripheral strain evaluation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for highly accurately evaluating the peripheral strain of a wafer having a polycrystalline film formed on its surface. A method for evaluating the outer peripheral strain of a wafer having a polycrystalline film formed on the surface thereof, wherein a pretreatment for removing the surface of the polycrystalline film is performed, and then an infrared laser is applied from the rear surface of the outer periphery of the wafer. Is evaluated and the peripheral strain of the wafer is evaluated from the polarization degree of the infrared laser after passing through the wafer. [Selection diagram] Figure 2

Description

The present invention relates to a method for evaluating wafer peripheral strain.

Generally, when an epitaxial layer is grown on a wafer after polishing by using a single-wafer type epitaxial wafer manufacturing apparatus, distortion occurs in the outer peripheral portion of the wafer due to thermal stress applied to the contact portion between the wafer and the susceptor. As a method of evaluating this distortion, a method of injecting an infrared laser from the back surface of the wafer and detecting the distortion from the polarization degree after passing through the wafer is used (Patent Document 1). In this evaluation, if the wafer is distorted, the degree of polarization of the incident light becomes large, so that the degree of distortion can be detected from the degree of polarization. Until now, when performing the main measurement on the epitaxial wafer, the wafer on which the epitaxial layer was grown was directly measured.

JP 2012-192216 A

On the other hand, since a single-wafer type epitaxial wafer manufacturing apparatus is also used to grow a wafer on which a polycrystalline film (Poly film) is grown, distortion is generated in the outer peripheral portion of the wafer according to the same principle as the epitaxial wafer during the growth process. .. The same evaluation method as the epitaxial wafer was used also in the strain evaluation of the wafer on which this polycrystalline film was grown, but the wafer on which the polycrystalline film was formed has an irregular crystal orientation of the polycrystalline film, In particular, it is difficult to apply the conventional measurement method because it is easily affected by noise in the outer peripheral portion. Therefore, it is necessary to establish a method for evaluating the strain of the wafer on which the polycrystalline film is formed.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a highly accurate evaluation method of the peripheral strain of a wafer having a polycrystalline film formed on its surface.

The present invention has been made to achieve the above object, is a method of evaluating the peripheral strain of a wafer having a polycrystalline film formed on the surface, pretreatment for removing the surface of the polycrystalline film. , And then, an infrared laser is incident from the back surface of the outer circumference of the wafer, and a method for evaluating the outer circumference distortion of the wafer is provided, which evaluates the outer circumference distortion of the wafer from the polarization degree of the infrared laser after passing through the wafer. ..

According to such an evaluation method, it is possible to reduce the influence of noise on the outer peripheral portion during measurement, and it is possible to accurately evaluate the outer peripheral distortion of the wafer on which the polycrystalline film is formed.

At this time, the pretreatment can be performed by polishing and/or etching.

Thereby, the surface of the polycrystalline film can be smoothed and/or the surface film thickness of the polycrystalline film can be reduced, the influence of noise in the outer peripheral portion at the time of measurement can be reduced, and the polycrystalline film is formed. Wafer peripheral strain evaluation can be performed effectively and with high accuracy.

At this time, the pretreatment may be performed by polishing to remove the surface by polishing to a thickness of 0.2 μm or more.

By setting the polishing amount within the above range, it is possible to more effectively reduce the influence of noise on the outer peripheral portion during measurement, and it is possible to perform the outer peripheral strain evaluation of the wafer on which the polycrystalline film is formed with higher accuracy.

Further, the pretreatment can be performed by etching to remove the surface by a thickness of 0.5 μm or more.

By setting the etching removal amount within the above range, it is possible to more effectively reduce the influence of noise on the outer peripheral portion during measurement, and it is possible to perform the outer peripheral strain evaluation of the wafer on which the polycrystalline film is formed with higher accuracy.

The pretreatment can be performed by vapor phase etching and/or liquid phase etching.

As a result, the influence of noise on the outer peripheral portion during measurement can be reduced, and the outer peripheral strain of the wafer on which the polycrystalline film is formed can be easily evaluated.

As described above, according to the method for evaluating the outer peripheral strain of the wafer having the polycrystalline film formed on the surface of the present invention, by performing the pretreatment, it is possible to reduce the influence of the noise on the outer peripheral portion during the measurement, Peripheral strain evaluation of a wafer having a crystal film formed thereon can be performed with high accuracy.

1 shows an outline of a single wafer type epitaxial wafer manufacturing apparatus. The structure of a strain measuring device is shown. It is a top view of a wafer and shows a measurement exclusion field and a measurement field.

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

As described above, in the evaluation method of the outer peripheral strain of the wafer on which the polycrystalline film is formed, the influence of the noise of the outer peripheral portion at the time of measurement is reduced, and the outer peripheral strain of the wafer on which the polycrystalline film is formed is accurately measured. There was a need for a way to evaluate.

The present inventors have made extensive studies on the above problems, a method of evaluating the peripheral strain of a wafer having a polycrystalline film formed on the surface, pretreatment for removing the surface of the polycrystalline film, Then, the infrared laser is incident from the back surface of the outer periphery of the wafer, and the outer peripheral portion of the wafer is evaluated from the peripheral distortion of the wafer from the polarization degree of the infrared laser after passing through the wafer. The present invention has been completed by finding that it is possible to reduce the influence of the noise of (1) and accurately evaluate the peripheral strain of the wafer on which the polycrystalline film is formed.

Hereinafter, description will be given with reference to the drawings.

The wafer on which the polycrystalline film is formed, which is the object of the wafer peripheral strain evaluation method according to the present invention, may be manufactured by any method. For example, it can be manufactured using the epitaxial wafer manufacturing apparatus described below.

First, the configuration of a single wafer processing epitaxial wafer manufacturing apparatus will be described with reference to FIG. In the epitaxial wafer manufacturing apparatus 1 of FIG. 1, wafers W such as silicon single crystal substrates are loaded one by one, and a silicon single crystal film, a polycrystalline silicon film, or the like is formed on the main surface of one wafer W that is input. This is a device for vapor phase growth of a film. Specifically, the epitaxial wafer manufacturing apparatus 1 includes a reaction furnace 2 into which a wafer W to be processed is charged, a susceptor 3 arranged in the reaction furnace 2 to horizontally support the charged wafer W, and a reaction furnace 2 And a heating unit 6 that is disposed so as to surround the chamber and heats the inside of the reaction furnace 2.

The susceptor 3 is made of, for example, graphite coated with silicon carbide (SiC) and has a disk shape. On the upper surface of the susceptor 3, a concave (circular in plan view) pocket portion 3a for mounting the wafer W horizontally, which is larger than the diameter of the wafer W by several millimeters, is formed. The depth of the pocket portion 3a is approximately the same as the thickness of the wafer W. In the example of FIG. 1, the pocket 3a has a stepped bottom surface so that the outer peripheral portion of the wafer W is in contact but the other portions are not in contact, but the entire back surface of the wafer W is in the pocket 3a. May be formed so as to contact the bottom surface of the. The susceptor 3 is provided rotatably around its central axis.

A gas supply port 4 for supplying various gases onto the main surface of the wafer W in the reaction furnace 2 is formed at one end of the reaction furnace 2. Further, on the side of the reaction furnace 2 opposite to the gas supply port 4, there is formed a gas discharge port 5 for discharging the gas that has passed over the main surface of the wafer W. The heating unit 6 can be, for example, a halogen lamp provided above and below the reaction furnace 2.

Next, with reference to FIG. 2, the configuration of an apparatus for measuring the outer peripheral strain of the wafer will be described. The measuring device 10 of FIG. 2 is configured as a device based on SIRD (Scanning Infrared Depolarization). Specifically, the measuring apparatus 10 includes a laser generator 11 that causes an infrared laser 31 to be incident on a strain measurement site of a wafer W to be measured, and polarization of light 32 that is transmitted from the wafer W on which the infrared laser 31 is incident. A detector 12 that detects a component (P-polarized component, S-polarized component), and a change in polarization degree (polarization displacement amount) is calculated based on the polarization component detected by the detector 12, and based on the change in polarization degree. And a processing unit 13 that performs processing such as calculation of a distortion position and a distortion amount.

Next, the distortion evaluation procedure of this embodiment will be described. First, a wafer whose strain is to be evaluated is prepared. As a wafer to be prepared, a wafer having a polycrystalline silicon film formed on its surface is prepared. The polycrystalline silicon film may be formed using, for example, the single-wafer processing epitaxial wafer manufacturing apparatus 1 illustrated in FIG. In this case, while the wafer W configured as, for example, a silicon single crystal substrate is placed in the pocket portion 3a of the susceptor 3, the heating portion 6 heats the wafer W to a predetermined temperature while the polycrystalline silicon is supplied from the gas supply port 4. A gas (for example, trichlorosilane) as a raw material for the film and a carrier gas (for example, hydrogen gas) are supplied into the reaction furnace 2 to grow a polycrystalline silicon film having a predetermined thickness on the surface of the wafer W. As a result, a wafer W having a polycrystalline silicon film on its surface is obtained.

Next, a pretreatment for removing the surface of the polycrystalline silicon film of the wafer W is performed. The removal method is not limited. By removing the surface of the polycrystalline silicon film of the wafer W, it is possible to reduce the influence of noise on the outer peripheral portion during measurement, and it is possible to accurately evaluate the outer peripheral strain of the wafer.

For example, the surface of the polycrystalline silicon film of the wafer W is removed by polishing and/or etching, and strain measurement is performed. By polishing the polycrystalline silicon film before the strain measurement, the surface of the polycrystalline silicon film can be smoothed, the influence of noise on the outer peripheral portion during measurement can be reduced, and the outer peripheral strain of the wafer can be accurately evaluated. In addition, by performing etching before strain measurement, the surface film thickness of the polycrystalline silicon film can be thinned, the influence of noise on the outer peripheral portion at the time of measurement can be reduced, and the outer peripheral strain of the wafer can be accurately evaluated. it can.

When the surface of the polycrystalline film is removed by polishing, the thickness removed by polishing is 0.2 μm or more, and when removed by etching, the thickness removed by etching is 0.5 μm or more, which is more effective. The influence of noise can be reduced and the evaluation can be performed more accurately. The upper limit of the removal amount of the polycrystalline film surface is not particularly limited, but it is preferably about 10 μm from the viewpoint of throughput (productivity).

Here, as the polishing method, a known substrate polishing method can be adopted. The etching may be vapor phase etching or liquid phase etching, but any method may be used as long as the surface can be removed. For example, in the case of vapor phase etching, hydrogen chloride can be used as an etching gas, and in the case of liquid phase etching, hydrofluoric acid or nitric acid can be used as an etching solution.

In the strain measurement, strain is likely to occur in the outer peripheral portion of the back surface which is in contact with the susceptor 3, so the infrared laser 31 is made incident on the outer peripheral portion of the rear surface of the wafer W.

Further, the strain measurement region 22 (see FIG. 3) in the wafer W is a region including the outer peripheral portion of the wafer W, and specifically, a predetermined width (for example, a predetermined width in the radial direction from the boundary line on the inner peripheral side of the measurement exclusion region 21). (Width of 4 mm). The strain measurement area 22 may be a circumferentially entire area (that is, a ring-shaped area) inside the outermost circumference 20 of the wafer W, or may be a partial area in the circumferential direction. Then, the incident position of the infrared laser 31 is scanned in the strain measurement region 22 to evaluate the strain position and strain amount in the strain measurement region 22.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto.

(Example 1)
First, in the method of measuring the strain of the outer peripheral portion of the wafer by polishing the surface, the amount of the outer peripheral strain of each of the epitaxial wafer and the wafer on which the polycrystalline film formed by polishing the polycrystalline film that has been removed by polishing was measured was measured. , And the coincidence rate of strain amount was investigated.

The diameter of the wafer was 300 mm, and the epitaxial wafer was prepared by reacting with a single wafer type epitaxial wafer manufacturing apparatus. Wafers are introduced one by one into a susceptor in a reaction furnace of an epitaxial wafer manufacturing apparatus, and while heating the wafers to a predetermined temperature (1100° C.) by a heating unit, a gas (trichlorosilane) or carrier gas as a raw material is supplied from a gas supply port By supplying (hydrogen), a silicon single crystal film having a film thickness of 5 μm was vapor-phase grown on the surface of the introduced wafer. On the other hand, a wafer on which a polycrystalline film is formed also reacts using an apparatus similar to an epitaxial wafer, but is characterized in that the heating temperature is in two stages. The reaction of the first layer was performed at a low temperature (900° C.), and the reaction of the second layer was performed at a high temperature (1100° C.) to grow a polycrystalline film having a thickness of 5 μm. Then, a pretreatment for polishing and removing the surface of the polycrystalline film was performed with the removal amount shown in Table 1 below.

In this example, the coincidence rate of strain between the epitaxial wafer and the wafer on which the polycrystalline film was formed was compared.However, since the location of the strain in the outer peripheral portion of the wafer is caused by the member such as the susceptor, the reaction conditions may vary. It is known that the difference does not change the place of occurrence. Therefore, it was evaluated how closely the locations where the strain was generated in the epitaxial wafer were the locations where the polycrystalline film was formed in the wafer. Table 1 shows the relationship between the polishing removal amount on the surface of the polycrystalline film and the matching rate of the strain amount.

Regarding the measurement area in the measurement of the strain in the outer peripheral portion, the strain measurement width was set to 4 mm with the outermost periphery 0.5 mm as the measurement exclusion area. The measurement interval is 2 mm in the circumferential direction and 1 mm in the radial direction.

(Comparative Example 1)
The evaluation was performed under the same conditions as in Example 1 except that the surface of the polycrystalline film was not removed by polishing (removal amount 0 μm). As a result, the agreement rate was 42%, which was not sufficient.

As shown in Table 1, a wafer having a removal amount of the polycrystalline film by polishing of 0.1 μm, 0.2 μm, 0.4 μm, 0.8 μm, 1.6 μm, and 4.0 μm was prepared, and The agreement rates were compared. As a result, when the polishing removal amount on the surface of the polycrystalline film was 0.1 μm, the matching rate was 78%, and when it was 0.2 μm or more, the matching rate was further improved to 90% or more. Since the polishing removal amount of the polycrystalline film surface is 0.2 μm or more and the coincidence rate is 90% or more, the noise in the outer peripheral portion can be removed and the strain amount can be evaluated with high accuracy.

As described above, according to the example of the present invention, the outer peripheral strain of the wafer on which the polycrystalline film is formed can be evaluated with high accuracy.

(Example 2)
The surface of the polycrystalline film was removed by vapor phase etching, and the distortion of the outer peripheral portion of the wafer was evaluated. The amount of peripheral strain of each of the wafer having a polycrystalline film formed by polishing the surface of the polycrystalline film of Example 1 by 0.8 μm and the wafer having the polycrystalline film formed by removing the polycrystalline film by etching is measured, The coincidence rate of the amount of distortion was investigated.

The method for producing a wafer on which a polycrystalline film is formed is the same as in Example 1, and the vapor phase etching is performed by etching gas (hydrogen chloride) in the reaction furnace after the polycrystalline film is grown in the reaction furnace of the epitaxial wafer manufacturing apparatus. ) Was supplied. Table 2 shows the relationship between the amount of vapor phase etching removal on the surface of the polycrystalline film and the matching rate of the amount of strain.

The measurement area for measuring the strain in the outer peripheral portion is the same as that in the first embodiment.

(Example 3)
The surface of the polycrystalline film was removed by liquid phase etching, and the strain on the outer peripheral portion of the wafer was evaluated. The amount of peripheral strain of each of the wafer having a polycrystalline film formed by polishing the surface of the polycrystalline film of Example 1 by 0.8 μm and the wafer having the polycrystalline film formed by removing the polycrystalline film by etching is measured, The coincidence rate of the amount of distortion was investigated.

The method for producing the wafer on which the polycrystalline film was formed was the same as in Example 1, and the liquid phase etching was performed using an etching solution (hydrofluoric acid) after taking out the wafer from the reaction furnace. Table 3 shows the relationship between the amount of liquid phase etching removal on the surface of the polycrystalline film and the coincidence rate of the strain amount.

The measurement area for measuring the strain in the outer peripheral portion is the same as that in the first embodiment.

(Comparative example 2)
When the conditions were the same as in Example 1 except that the surface of the polycrystalline film was not removed (removal amount 0 μm), the matching rate was 45%, which was not sufficient.

As shown in Table 2, wafers having vapor-phase-etched polycrystalline film removal amounts of 0.2 μm, 0.4 μm, 0.5 μm, 1.0 μm, 1.5 μm, and 3.0 μm were manufactured, and the strain generation amount was measured. The agreement rates of As a result, when the etching removal amount on the surface of the polycrystalline film was 0.2 μm or more, the matching rate was 60% or more, and when it was 0.5 μm or more, the matching rate was further improved to 90% or more. Since the etching removal amount on the surface of the polycrystalline film is 0.5 μm or more and the coincidence rate is 90% or more, noise on the outer peripheral portion can be removed and the strain amount can be evaluated with high accuracy.

As shown in Table 3, the amount of distortion generated by producing a wafer in which the removal amount of the polycrystalline film by liquid phase etching was 0.2 μm, 0.4 μm, 0.5 μm, 1.0 μm, 1.5 μm, 3.0 μm The agreement rates of As a result, when the etching removal amount on the surface of the polycrystalline film was 0.2 μm or more, the matching rate was 60% or more, and when it was 0.5 μm or more, the matching rate was further improved to 90% or more. Since the etching removal amount on the surface of the polycrystalline film is 0.5 μm or more and the coincidence rate is 90% or more, noise on the outer peripheral portion can be removed and the strain amount can be evaluated with high accuracy.

The present invention is not limited to the above embodiment. The above-described embodiment is merely an example, and the invention having substantially the same configuration as the technical idea described in the scope of claims of the present invention and exhibiting the same action and effect is the present invention It is included in the technical scope of.

W... Wafer, 1... Single wafer type epitaxial wafer manufacturing apparatus, 2... Reactor,
3... Susceptor, 3a... Pocket part, 4... Gas supply port, 5... Gas discharge port, 6... Heating part,
10... Measuring device, 11... Laser generating part, 12... Detecting part, 13... Processing part,
20... Outermost periphery of wafer, 21... Measurement exclusion area (evaluation exclusion area), 22... Strain measurement area,
31... Infrared laser, 32... Transmitted light.

Claims (5)

A method for evaluating the peripheral strain of a wafer having a polycrystalline film formed on its surface,
As the wafer having a polycrystalline film formed on the surface, a wafer having a polycrystalline film formed on the surface of a silicon single crystal substrate is used.
Pretreatment for removing the surface of the polycrystalline film,
Then, the infrared laser is incident from the back surface of the outer periphery of the wafer,
A method for evaluating peripheral distortion of a wafer, which comprises evaluating the peripheral distortion of the wafer from the degree of polarization of the infrared laser after passing through the wafer. The method for evaluating a peripheral strain of a wafer according to claim 1, wherein the pretreatment is performed by polishing and/or etching. The method for evaluating a peripheral strain of a wafer according to claim 2, wherein the pretreatment is performed by polishing to remove the surface by polishing to a thickness of 0.2 μm or more. The method for evaluating a peripheral strain of a wafer according to claim 2, wherein the pretreatment is performed by etching to remove the surface by etching to a thickness of 0.5 μm or more. The method for evaluating the outer peripheral strain of a wafer according to claim 2 or 4, wherein the pretreatment is performed by vapor phase etching and/or liquid phase etching.

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