Evaluation method for surface roughness of silicon substrate and manufacturing process management method of silicon wafer

Abstract

To provide an easy and high-throughput evaluation method for surface roughness of an anisotropically etched silicon substrate.SOLUTION: The evaluation method for surface roughness of an anisotropically etched silicon substrate includes the steps of: preparing an anisotropically etched silicon substrate; emitting oblique light to the silicon substrate to obtain a reflection rate of oblique incident reflection light from the silicon substrate in a circumferential direction; and evaluating surface roughness of the silicon substrate from circumferential direction dependency of the obtained reflection rate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for evaluating the surface roughness of a silicon substrate and a method for controlling the manufacturing process of a silicon wafer. [Background technology]

[0002] In recent years, the feasibility of semiconductor integrated circuit elements using so-called {110} silicon wafers, in which the main surface of a silicon single crystal is the {110} plane or close to it, has increased. It is known that the use of silicon wafers with a {110} plane as the main surface has higher carrier mobility than wafers with a {100} plane as the main surface, and therefore transistor performance can be made faster than before. In particular, epitaxial wafers are used as materials for high-performance devices because the epitaxial layer has very few defects. For this reason, epitaxial wafers with a {110} plane as the main surface are expected to be applied especially to logic devices.

[0003] Given this background, epitaxial wafers with a {100} orientation as the main surface are currently used for logic devices, but it is fully expected that they will be replaced by epitaxial wafers with a {110} orientation as the main surface in the future.However, there has been little need for the manufacturing process of {110} epitaxial wafers, so the reality is that there is less experience and knowledge about them than for {100} epitaxial wafers.

[0004] Generally, the manufacturing process of semiconductor silicon wafers (hereinafter also referred to as polished wafers) consists of the steps of cutting (block cutting) from a pulled silicon single crystal ingot, grinding the outer diameter, slicing the wafers, chamfering, mechanically polishing (lapping or grinding), etching, double-sided polishing, single-sided polishing and cleaning, and producing polished wafers with high precision flatness. Epitaxial wafers are manufactured by forming an epitaxial layer on these polished wafers through epitaxial growth. That is, {110} epitaxial wafers are produced by epitaxially growing on {110} polished wafers.

[0005] In the manufacturing process of these polished wafers, various steps are performed, with some steps being replaced or repeated multiple times, or other steps such as heat treatment being added or replaced, depending on the purpose. Silicon wafers that have undergone mechanical processing processes such as block cutting, outer diameter grinding, slicing, lapping, or grinding have a damaged layer, i.e., a process-affected layer, on the surface. This process-affected layer induces crystal defects such as slip dislocations in the device manufacturing process, reduces the mechanical strength of the wafer, and adversely affects the electrical characteristics. In addition, if a double-side polishing process is performed with the process-affected layer still formed on the surface, it will cause cracks in the wafer, so it must be completely removed.

[0006] Etching is performed to remove this processing-affected layer. Etching is broadly divided into wet etching, which uses chemicals, and dry etching, which uses plasma-formed gas. Wet etching can be further divided into acid etching, which uses an acidic etching solution such as a mixture of hydrofluoric acid and nitric acid, and alkaline etching, which uses an alkaline etching solution such as NaOH, KOH, or TMAH. These etching methods are used according to the purpose. For example, dry etching is often used to form fine device structures. On the other hand, wet etching is often used in the manufacturing process of polished wafers. Generally, acid etching proceeds by oxidizing silicon with nitric acid and removing the silicon oxide film with hydrofluoric acid. This etching behavior is highly dependent on the concentration gradient of reactive species and reaction products on the wafer surface in the etching solution, making it difficult to control the etching rate and its uniformity on the surface. In contrast, alkaline etching proceeds by reacting and dissolving silicon with hydroxide ions in the solution, and is less affected by reaction products than acid etching, making it more controllable, and is therefore often used.

[0007] In addition, since alkaline etching proceeds by a chemical reaction between hydroxide ions and silicon as described above, the etching rate is strongly dependent on the crystal orientation. Therefore, as described in Patent Document 1, when a silicon wafer having a main surface with a plane orientation of {100} is subjected to alkaline etching, pits with local depths of several to several tens of μm are generated. It is known that this is due to the fact that the etching rate of the {111} plane is extremely lower than that of the {100} plane. Such geometric patterns along the crystal planes are called facets, and the occurrence of these facets cannot be avoided as long as alkaline etching is performed. It is also known that the shape of these facets changes depending on the plane orientation.

[0008] Patent Document 1 describes that the quality of silicon wafers after etching is improved by using an alkaline aqueous solution containing lithium ions. It also discloses that if the state of the etched surface changes, pits remain after mirror processing. In other words, it can be said that there is a correlation between the state of the etched surface and the quality after polishing. On the other hand, although Patent Document 1 does not mention it, it is an example of a silicon wafer with a surface orientation of {100} based on an optical microscope image. In other words, there is no known document that mentions the quality of a silicon wafer with a {110} main surface after alkaline etching and the subsequent manufacturing process of polished wafers, especially the quality after the double-side polishing process.

[0009] As a method for evaluating an etched surface, Patent Document 1 discloses a method for evaluating changes in patterns and facets from optical microscope images. This method allows the changes to be visually captured, but does not provide a quantitative evaluation using numerical values. In addition, microscope observation is time-consuming and has low throughput, making it unsuitable for use in managing the manufacturing process.

[0010] Patent Document 2 discloses that glossiness is used as an index. Glossiness is specified in the JIS standard (Z 8741-1997). A light beam with a specified divergence angle is incident on the sample surface at a specified angle of incidence, and the light beam with a specified divergence angle reflected in the direction of specular reflection is measured by a light receiver. Next, the specular reflected light beam from the measured sample surface for the specified angle of incidence θ, the specular reflected light beam from the standard surface, and the specular glossiness according to the specified angle of incidence are calculated, with the maximum being 100%. The glossiness measuring device (glossiness meter) is very simple and has good throughput.

[0011] Patent Document 3 discloses a method for inspecting the surface roughness of an etched surface from the brightness of an image acquired by an optical scanner.

[0012] By the way, the inventors of the present invention have produced {110} polished wafers in order to produce epitaxial wafers with {110} as the main surface, and have found that the quality may be significantly deteriorated in the double-sided polishing (DSP) process after alkaline etching. Specifically, the following is the case. Figure 10 shows confocal microscope images of a silicon wafer after lapping with a {110} surface orientation, after etching with an aqueous solution of sodium hydroxide (NaOH). The concentration is 3 levels, 30, 40, and 50 wt%, the temperature is 85°C, and the removal amount on both sides is about 25 μm. It can be seen that the surface morphology changes dramatically depending on the concentration. After processing these etched wafers with a double-sided polishing machine, the particles (inspection sensitivity: 200 nm Up) (hereinafter, the particles may be referred to as LLS) and the flatness GBIR (Global Backside Ideal Range) were investigated. As a result, it can be seen that the number of particles and the flatness are significantly deteriorated at 50 wt%. Although it is only a guess, it is presumed that the convex shape formed by etching is particularly sharp at 50 wt%, and damage to the abrasive cloth accumulates during processing. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] JP 2003-257927 A [Patent Document 2] JP 2011-103354 A [Patent Document 3] JP 2007-220996 A Summary of the Invention [Problem to be solved by the invention]

[0014] As described above, it was found that in the production of polished wafers with a {110} principal surface, depending on the conditions of anisotropic etching such as alkaline etching, the quality (number of particles and flatness) after double-sided polishing may deteriorate.

[0015] The present invention has been made in consideration of the above-mentioned problems in the conventional technology, and has an object to provide a method for evaluating the surface roughness of an anisotropically etched silicon substrate (hereinafter also referred to as a silicon wafer or simply a wafer) in a simple manner with good throughput. Furthermore, the present invention aims to provide a manufacturing process control method that is simple and has good throughput by using this evaluation method to evaluate the surface roughness of silicon substrates whose main surface is {110} and determine whether the substrate is suitable for use in a double-sided polishing process. [Means for solving the problem]

[0016] In order to solve the above problems, the method of evaluating the surface roughness of an anisotropically etched silicon substrate of the present invention comprises the steps of: preparing an anisotropically etched silicon substrate; directing light obliquely onto the silicon substrate to obtain the reflectance of the obliquely incident reflected light from the silicon substrate in a circumferential direction; and evaluating the surface roughness of the silicon substrate from the circumferential direction dependence of the obtained reflectance.

[0017] According to this evaluation method, the surface roughness of a silicon substrate can be evaluated simply and with good throughput from the circumferential direction dependency of the reflectance of the anisotropically etched silicon substrate.

[0018] The silicon substrate preferably has a convex etched surface.

[0019] The presence of such convex portions is more preferable because the circumferential direction dependency of the reflected light becomes significant due to reflection at the convex portions, and as a result, the circumferential direction dependency of the reflectance increases.

[0020] Moreover, it is preferable that the silicon substrate has a main surface with a {110} orientation.

[0021] Such a silicon substrate having a {110} principal surface is more suitable because convex portions can be easily formed by anisotropic etching, and the reflection from the convex portions results in a significant circumferential dependency of the reflected light, thereby increasing the circumferential dependency of the reflectance.

[0022] The anisotropic etching is preferably wet etching using an alkaline chemical solution.

[0023] Such an alkaline etching treatment is more preferable because it results in a significant anisotropy in the formation of convex portions on the silicon substrate surface and also results in a significant circumferential dependency of reflectance.

[0024] In addition, in the step of acquiring the reflectance in the circumferential direction, at least <110> Direction and <100> It is preferable to obtain directional reflectance.

[0025] Like this <110> Direction and <100> This is more preferable since the change in reflectance between directions is significant.

[0026] In addition, in the step of evaluating the surface roughness, <110> Direction and <100> It is preferable to evaluate the surface roughness of the silicon substrate based on a reflectance ratio in a direction.

[0027] By using such a reflectance ratio, the influence of fluctuation factors that contribute to the fluctuation of the reflectance and that do not have circumferential dependency (for example, dirt that adheres during the etching process) can be offset in the numerator and denominator in the calculation and eliminated, so that it can be used as an index that highlights the influence of surface roughness that has circumferential dependency, which is more preferable.

[0028] In the step of obtaining the reflectance in the circumferential direction, it is preferable to use a glossiness obtained using a glossiness meter as the reflectance.

[0029] Such a gloss meter is simple and has a high throughput, and since gloss is determined based on the reflectance at oblique incidence, it is suitable for determining the circumferential direction dependency of reflectance.

[0030] The present invention also provides a method for controlling the manufacturing process of silicon wafers having a {110} main surface, comprising the steps of: preparing a silicon wafer having a {110} main surface that has been anisotropically etched; evaluating the prepared silicon wafer having a {110} main surface by the method for evaluating the surface roughness of a silicon substrate; and <110> Direction and <100> and determining whether or not the surface roughness of the prepared silicon wafer having a {110} main surface is suitable for being input into a double-side polishing process, based on the reflectance ratio in the directions.

[0031] Such a process control method makes it possible to simply and with good throughput evaluate the surface roughness of single crystal silicon wafers having a {110} main surface and determine whether or not they are suitable for input into a double-side polishing process.

[0032] In the step of determining whether the substrate is good or bad, it is preferable to determine whether the substrate is good or bad based on a preset target reflectance ratio.

[0033] If such a target reflectance ratio is preset, the quality of the product can be promptly and easily determined.

[0034] It is also preferable that the reflectance ratio is a gloss ratio.

[0035] Since such glossiness is determined from the reflectance of oblique incidence in the first place, it is easy to convert the reflectance ratio into the glossiness ratio, and glossiness measurement is very simple and has a high throughput, making it suitable for process management.

[0036] In addition, when it is determined in the pass / fail judging step that the wafer is unsuitable for the double-side polishing step, it is preferable to carry out at least one of a manufacturing history investigation of the etching step and an improvement to the etching step.

[0037] By conducting a manufacturing history investigation of this type of etching process, it is possible to determine the reason why the product was judged to be unsuitable for use in the double-sided polishing process, and by improving the etching process, it is possible to improve it so that it is judged to be good (suitable) for use in the double-sided polishing process.

[0038] Furthermore, if it is determined in the pass / fail judging step that the substrate is unsuitable for the double-side polishing step, it is preferable to improve the etching step based on at least one of the concentration and temperature of the etching solution.

[0039] The concentration and temperature of such etching solution have a large effect on the surface roughness and are easy to adjust, so that the etching process can be effectively and easily improved. Effect of the Invention

[0040] As described above, the method for evaluating the surface roughness of an anisotropically etched silicon substrate of the present invention makes it possible to evaluate the surface roughness of a silicon substrate simply and with good throughput, based on the circumferential direction dependence of the reflectance of the anisotropically etched silicon substrate. Furthermore, the manufacturing process control method for silicon wafers having a {110} main surface of the present invention makes it possible to simply and with good throughput evaluate the surface roughness of single crystal silicon wafers having a {110} main surface and determine whether or not they are suitable for input into a double-side polishing process. [Brief description of the drawings]

[0041] [Figure 1] 1 is a flowchart showing an example of a method for evaluating a silicon substrate according to the present invention. [Diagram 2] In the {110} and {100} orientations <100> , <110> FIG. [Diagram 3] In a silicon wafer with a {110} surface orientation, <100> FIG. 13 is a schematic diagram showing how the gloss level in a direction is evaluated. [Figure 4]FIG. 1 shows confocal microscope images of the surface of a {110} silicon wafer etched with varying NaOH concentrations, and the distribution of glossiness in the circumferential direction. [Diagram 5] FIG. 1 shows confocal microscope images of the surface of a {100} silicon wafer etched with varying NaOH concentrations, and the distribution of glossiness in the circumferential direction. [Figure 6] This figure shows the results of evaluating the surface roughness after etching with 50 wt% NaOH for the plane orientations {100} and {110} using a contact roughness meter. [Figure 7] 1 is a flowchart showing an example of a method for managing a manufacturing process of a silicon wafer according to the present invention. [Figure 8] FIG. 2 is a diagram showing the measurement results of reflectance in Example 1. [Figure 9] FIG. 2 shows the results of confocal microscope observation in Example 1. [Figure 10] FIG. 13 shows a confocal microscope image of a silicon wafer after lapping, after etching with an aqueous sodium hydroxide solution, and the calculated Sa, particles after double-side polishing, and flatness. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] In order to solve the above problems, the inventors of the present invention have noticed that the pattern (morphology) of the alkali-etched surface of a silicon substrate having a {110} principal surface changes dramatically depending on the concentration, and that the change in the pattern is formed in a specific direction based on the crystal orientation. That is, they have conducted extensive research into the relationship between the reflection behavior of light obtained from incident light and reflected light, such as glossiness, and the pattern. As a result, they have newly discovered that the reflectance of obliquely incident reflected light from a silicon substrate has a circumferential direction dependency, and have completed the present invention.

[0043] That is, the present invention is a method for evaluating the surface roughness of an anisotropically etched silicon substrate, comprising the steps of: preparing an anisotropically etched silicon substrate; irradiating light obliquely onto the silicon substrate to obtain the reflectance of the obliquely incident reflected light from the silicon substrate in a circumferential direction; and evaluating the surface roughness of the silicon substrate from the circumferential direction dependence of the obtained reflectance.

[0044] The present invention also provides a method for controlling a manufacturing process of single crystal silicon wafers having a {110} main surface, the method comprising the steps of: preparing a silicon wafer having a {110} main surface that has been anisotropically etched; evaluating the prepared silicon wafer having a {110} main surface by the method for evaluating the surface roughness of a silicon substrate according to the evaluation results; <110> Direction and <100> and determining whether or not the surface roughness of the prepared silicon wafer having a {110} primary surface is suitable for input to a double-side polishing process, based on the reflectance ratio in the directions.

[0045] Hereinafter, an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

[0046] As described above, in the manufacturing process of silicon wafers whose main surfaces are {110}, the surface roughness formed by anisotropic alkaline etching affects the double-sided polishing process, so there has been a demand for a method for determining whether the surface roughness after alkaline etching is suitable for input into the double-sided polishing process.

[0047] Reference is now made to Figure 10, which shows a confocal microscope image of a silicon wafer after lapping, after etching with an aqueous solution of sodium hydroxide (NaOH), as well as the arithmetic mean height Sa of the surface roughness, the number of particles (LLS) after double-sided polishing (DSP), and the flatness (GBIR).

[0048] As shown in FIG. 10, when alkaline etching using NaOH was performed, the quality after DSP was good when the NaOH concentration was 30 or 40 wt% (both LLS and GBIR were small), and the quality after DSP was deteriorated when the NaOH concentration was 50 wt% (both LLS and GBIR increased). Therefore, when the alkaline etching process was performed, it is necessary to evaluate whether the surface roughness formed by etching is equivalent to a NaOH concentration of 30 or 40 wt%. On the other hand, as an index of general surface roughness, the relationship of the three-dimensional arithmetic mean height Sa is (large) 30 wt%>50 wt%>40 wt% (small) as shown in FIG. 10, so it is difficult to evaluate whether the surface roughness is suitable for input to the double-sided polishing process using Sa as an index. In addition, obtaining such a microscope image is very time-consuming, so it is not suitable as a method of managing the manufacturing process. In addition, obtaining an image and judging the quality from appearance may lead to different judgments depending on the operator, so it is more preferable to manage it numerically.

[0049] In light of this background, the present invention focuses on reflectance. Generally, when light is incident on a sample surface, phenomena such as reflection, absorption, and transmission occur. Here, the ratio of the reflected light beam ψ2 to the light beam ψ1 incident on the sample is called the reflectance, or ψ2 / ψ1. In addition, light reflected at the same angle as the incident angle is called specular reflected light, and the ratio of the specularly reflected light beams is called the specular reflectance. It is known that reflectance depends on the incident angle and the light source wavelength.

[0050] Generally, reflectance is often used when evaluating spectral characteristics and film thickness. In the present invention, as described later, in order to evaluate the circumferential direction dependency, it is necessary to irradiate the light source with oblique incidence. For example, the incident angle can be 20 to 85 degrees. There is no particular limit to the light receiving angle as long as the reflected light can be received, but it can also be the same as the incident angle. There is also no limit to the light source wavelength, but for example, a wavelength in the range of 250 to 2000 nm can be used. There is no particular limit to the reflectance measurement, and it may be measured by a known method.

[0051] Moreover, the degree of gloss of an object expressed one-dimensionally, focusing on the proportion of specular reflected light, is called glossiness. Glossiness can be measured by a method defined in the JIS standard. Specifically, glossiness is standardized by JIS (Z 8741-1997) and is called specular glossiness. For example, the incident angle and light receiving angle can be 20 degrees, 60 degrees, or 85 degrees. In these reflectance and glossiness measurements, the incident and receiving angles and the light source wavelength can be appropriately selected in consideration of the degree of reflection from the sample surface. As described above, since glossiness detects specular reflected light with the same incident angle and light receiving angle, it can be said that glossiness evaluates specular reflectance. That is, in the present invention, the glossiness obtained by a glossmeter can be used as an index for a method of evaluating reflectance.

[0052] Based on these, a specific evaluation method will be described. Figure 1 is a flow chart showing an example of the method of evaluating the surface roughness of a silicon substrate according to the present invention. S1 to S3 represent steps.

[0053] In step S1, an anisotropically etched silicon substrate is prepared. At this time, there is no limitation on the size, shape, or conductivity type of the substrate. There is also no limitation on the anisotropic etching method, and for example, dry etching such as reactive ion etching (RIE) or alkaline wet etching using an alkaline chemical solution may be used. There is also no limitation on the gases and chemical solutions used.

[0054] Next, in step S2, the reflectance of the obliquely incident reflected light from the silicon substrate is obtained in the circumferential direction. A reflectance measuring device or a gloss meter may be used. At this time, measurements are taken multiple times to measure the reflectance in the circumferential direction. Here, a silicon wafer with a diameter of 300 mm and a {110} main surface that has been alkali etched is shown as an example. Figure 2 shows the reflectance of a silicon wafer with {110} and {100} main surfaces. <110> and <100> As shown in Fig. 3, the main surface of single crystal silicon is {110}, and the crystal orientation is {110}. <100> The schematic diagram shows how the glossiness in the direction is measured. <100> or <110> It is possible to obtain the reflectance or glossiness in a specific direction such as the direction of the reflectance or glossiness in the circumferential direction at intervals of 10 degrees in order to obtain a more detailed evaluation.

[0055] Next, in step S3, the surface roughness of the silicon substrate is evaluated from the results of step S2. As an example, Figure 4 shows the results of glossiness obtained at 10 degree intervals for an alkali-etched wafer with a {110} main surface as shown in Figure 10. The actual glossiness value column in Figure 4 graphs the results as they are, and the glossiness standard value 0 degree reference column graphs each result as a ratio to the result at 0 degrees. The incident angle and receiving angle were 60 degrees, and the light source wavelength was 890 nm.

[0056] As a result, it can be seen that at concentrations of 30wt% and 40wt%, the glossiness changes depending on the measurement angle. In this way, the glossiness of a sample surface that has anisotropy in a specific direction changes in the circumferential direction depending on the pattern on the evaluation surface. Therefore, the surface roughness can be evaluated using this circumferential direction dependency of glossiness. Furthermore, the circumferential dependency can be confirmed more clearly by calculating the ratio with 0 degrees as the reference value.

[0057] Glossiness detects the specular reflected light component. This specular reflected light is affected by surface roughness as well as surface dirt. Therefore, by calculating the ratio, the effects of variable factors that do not depend on the circumferential direction (for example, dirt that adheres during etching) can be offset and eliminated in the numerator and denominator in the calculation, making it possible to highlight and evaluate the effects of surface roughness that does depend on the circumferential direction. As an example, <110> Glossiness in the direction and <100> When the ratio of gloss in the circumferential direction was calculated, differences were observed between 30wt%, 40wt% and 50wt%. That is, the ratio is far from 1 at 30wt% and 40wt%, and a clear dependency on the circumferential direction is observed, but at 50wt%, the ratio is almost 1, and no dependency on the circumferential direction is observed. Therefore, <110> Glossiness in the direction and <100> It is more preferable to obtain the glossiness in the direction of the surface. <110> Glossiness in the direction and <100> It is also possible to obtain only the directional glossiness.

[0058] The above evaluation method makes it possible to evaluate the surface roughness and determine whether the surface is suitable for use in the double-side polishing process without the need for microscopic observation.

[0059] For comparison with these results, Figure 5 shows the circumferential dependence of glossiness on lapped silicon wafers with a {100} surface orientation treated with NaOH concentrations of 30, 40, and 50 wt%. It can be seen that the circumferential dependence of glossiness is small for all three levels of surface orientation {100}. This is believed to be because the change in surface roughness is smaller compared to the main surface {110}. Comparing the surface irregularities of the main surface {110} and {100}, the main surface {110} has a convex shape, while the main surface {100} has a concave shape. The definitions of convex and concave portions in the present invention are as follows. Figure 6 shows the results of evaluating the surface roughness after etching with 50 wt% NaOH for plane orientations {100} and {110} using a contact roughness meter. It can be seen that {100} has many concave portions relative to the reference surface, while {110} has many convex portions relative to the reference surface. Therefore, in the present invention, a state in which there are relatively many concave portions relative to the reference surface is defined as a concave shape, and a state in which there are relatively many convex portions is defined as a convex shape. As an example of a convex shape, it is known that a pyramidal convex texture is formed on a silicon substrate in order to increase the conversion efficiency of solar cells.

[0060] Therefore, it is clear that the above-mentioned method for evaluating surface roughness is more suitable for evaluating the surface roughness of a convex shape.

[0061] As described above, by evaluating the circumferential direction dependency of the reflectance of obliquely incident reflected light, the surface roughness of an anisotropically etched silicon substrate can be evaluated quickly and with good throughput.

[0062] Next, a method for controlling the manufacturing process of silicon wafers using the above-mentioned method for evaluating surface roughness will be described. An example of the flowchart is shown in Fig. 7. S11 to S16 indicate steps.

[0063] In step S11, an alkaline etched wafer having a {110} main surface is prepared. For example, the silicon wafer may be one in which a processing strain layer is present on a main surface that has been lapped or ground, and the silicon wafer is etched with an alkaline chemical solution. Generally, in the manufacturing process of silicon wafers, wafers are manufactured as a wafer lot including a plurality of wafers. Therefore, in step S11, one or more wafers can be extracted from the wafer lot after the alkaline etching process. Then, the entire wafer lot can be evaluated based on the evaluation results of the extracted wafers.

[0064] In step S12 <110> Direction and <100> The reflectance or glossiness in a direction is obtained. Glossiness measurement can be evaluated based on the JIS standard.

[0065] In step S13 <100> and <110> The reflectance ratio or gloss ratio is calculated. <100> / <110> As a comparison, <110> / <100> A ratio may also be used.

[0066] In step S14, it is determined whether the reflectance ratio or gloss ratio calculated in step S13 falls within a preset range.

[0067] This setting range will be explained with reference to the example of FIG. 4. As described above, the inventors of the present invention have evaluated that in the double-sided polishing process, the surface roughness is good when etching is performed with NaOH concentrations of 30 and 40 wt %. <100> / <110> The gloss ratio was 1.22 at a NaOH concentration of 30 wt%, 0.87 at a NaOH concentration of 40 wt%, and 0.99 at a NaOH concentration of 50 wt%. <100> / <110> The gloss ratio can be set in a range of, for example, 1.1 or more and 0.9 or less as good, and a range of more than 0.9 and less than 1.1 as bad. With such a range, NaOH concentrations of 30 and 40 wt% can be judged as good, and NaOH concentration of 50 wt% can be judged as bad. As mentioned above, reflectance and gloss depend on the light source wavelength and incident angle, so it is more preferable that the device for investigating the setting range and the device for process control are the same.

[0068] For the set range thus set, it is judged whether the glossiness of the prepared wafer falls within the good range (1.1 or more or 0.9 or less) of the set range. For example, <100> / <110> If the gloss ratio is 0.86, it is within that range and can be judged as good. <100> / <110> If the gloss ratio is 0.98, it can be judged as "no." This judgment result can then be applied to the wafer lot that constitutes the prepared wafers.

[0069] Step S15 is performed when the wafer is determined to be good in step S14, and a double-side polishing process can be performed on the wafer lot including the prepared wafer.

[0070] Step S16 is performed when step S14 is judged as "no." In this case, it is judged that it is not appropriate to send the wafer lot including the prepared wafer to the double-sided polishing process. In this case, the cause can be investigated by providing feedback to the alkaline etching process and performing at least one of investigating the manufacturing history of the etching process and improving the etching process. For example, the cause can be identified by observing the wafer under a microscope to evaluate the surface pattern and roughness in detail, or investigating the history of the chemical concentration and temperature during etching.

[0071] According to the inventors' investigation, when the main surface is {110}, the temperature and concentration of the chemical solution are the main factors that determine the surface roughness, so it is preferable to investigate these factors. For example, if the investigation shows that the chemical solution concentration is not as desired, the result can be improved by readjusting the chemical solution concentration or remaking the chemical solution.

[0072] The above-described manufacturing process control method makes it possible to simply and efficiently evaluate the surface roughness of single crystal silicon wafers having a {110} primary surface and determine whether they are suitable for input to a double-side polishing process. In addition, the etching process can also be improved. EXAMPLES

[0073] The present invention will be further described below with reference to examples. However, these examples are presented for illustrative purposes and should not be construed as limiting.

[0074] [Method for evaluating the surface roughness of silicon substrates] Example 1 180 lapped silicon wafers with {110} orientation, 300 mm diameter, P conductivity type, and 10 Ωcm resistivity were prepared. These wafers were divided into 30 pieces each and subjected to 6 levels of alkaline etching. The removal amount was about 25 μm on both sides, and the chemical concentration and temperature were as shown in Table 1. [Table 1]

[0075] Table 1 shows the etching conditions (NaOH concentration, temperature) and gloss ( <100> , <110> ), gloss ratio ( <100> / <110> , <110> / <100> ) and after double-sided polishing (DSP).

[0076] Next, one wafer was taken from each standard, leaving a total of six wafers for evaluation, and the glossiness of each wafer was evaluated. The glossiness meter used was a Horiba IG-410. The light source wavelength was 890 nm, and the incidence angle and reception angle were 60 degrees. The glossiness was <100> Direction and <110> The gloss was then measured in the direction of the light. <100> / <110> Gloss ratio and <110> / <100> The gloss ratio was calculated.

[0077] where <100> / <110> Focusing on the gloss ratio, levels 1 to 3 were 0.99 to 1.00, while levels 4 to 6 were 1.14 to 1.17, which was a large difference. Therefore, it was determined that the surface roughness changed significantly between levels 1 to 3 and levels 4 to 6. <100> / <110> By setting the gloss ratio of 1.1 or more as the range of acceptable surface roughness, it is possible to judge surface roughness of levels 1 to 3 as poor and surface roughness of levels 4 to 6 as good. <110> / <100> By setting the gloss ratio at 0.9 or less as the acceptable range for surface roughness, it is possible to judge surface roughness as levels 1 to 3 as bad and surface roughness as levels 4 to 6 as good. The measurement time per sheet was 10 seconds.

[0078] Furthermore, when comparing levels 4 to 6, level 4 had a lower gloss than levels 5 and 6, but the gloss ratio was the same. Visual inspection of the surface of level 4 revealed a large amount of dirt adhering to it. Therefore, although it seemed that there was a difference in surface roughness between level 4 and levels 5 and 6 in terms of gloss, it was assessed that the surface roughness was the same based on the gloss ratio.

[0079] Next, 20 pieces of each level were polished on both sides, and the particles and flatness were evaluated. Levels 1 to 3 were poor, while levels 4 to 6 were good. This is because <100> / <110> Gloss ratio and <110> / <100> This corresponds perfectly to the results of the gloss ratio (surface roughness levels 1 to 3 were judged as bad, and surface roughness levels 4 to 6 were judged as good). This shows that the double-sided polishing quality depends on the surface roughness of the etched surface. Therefore, this example shows that it is possible to evaluate the surface roughness that affects the double-sided polishing process.

[0080] Furthermore, the reflectance of the central portion of the wafers of levels 1 and 5 was measured. The equipment used was a JA Woollam spectroscopic ellipsometer M-2000V. The measurement conditions were set to reflectance measurement mode, and evaluation was performed using a white light source with an incident angle of 85 degrees and a receiving angle of 85 degrees. The measurement direction was <100> Direction and <110> The reflectance measurement results are shown in Figure 8. Comparing the reflectance in the wavelength range of 250 to 1000 nm, the change in level 1 was small, while the change in level 5 was large across the entire wavelength range. <100> The direction is <110> At a wavelength of 890 nm, <100> / <110> The reflectance ratio was calculated to be 0.98 for level 1 and 1.15 for level 5. From these results, it can be determined that level 1 and level 5 have different surface roughness. It was confirmed that this result is almost consistent with the gloss ratio results in Table 1. The measurement time per sheet was 20 seconds.

[0081] Furthermore, wafers of each level were prepared, and the surfaces of the central parts of the wafers were observed using a confocal microscope. The results are shown in Figure 9. From Figure 9, it can be seen that the surface patterns are different between levels 1 to 3 and levels 4 to 6. Therefore, it can be determined that the surface roughness changes between levels 1 to 3 and levels 4 to 6. This result coincides with the gloss ratio results in Table 1. The measurement time per wafer was 3 minutes.

[0082] As described above, Example 1 was described. The results of the gloss ratio, reflectance ratio, and confocal microscope image were consistent, and all of them could evaluate the surface roughness. Here, the measurement time per sheet was 10 seconds, 20 seconds, and 3 minutes, respectively, so the surface roughness of the silicon substrate can be evaluated more simply and with a higher throughput by using the gloss ratio or reflectance ratio. In particular, the surface roughness of the silicon substrate can be evaluated most simply and with a higher throughput by using the gloss ratio.

[0083] Example 2 210 lapped silicon wafers with {110} orientation, 300 mm diameter, P conductivity type, and 10 Ωcm resistivity were prepared. These wafers were divided into 30 pieces each and subjected to 7 levels of alkaline etching. The removal amount was about 25 μm on both sides, and the chemical concentration and temperature were as shown in Table 2. [Table 2]

[0084] Table 2 shows the etching conditions (NaOH concentration, temperature) and gloss ( <100> , <110> ), gloss ratio ( <100> / <110> , <110> / <100> ) and after double-sided polishing (DSP).

[0085] Next, one wafer was selected from each standard range, leaving a total of seven wafers prepared as evaluation wafers. The glossiness of each wafer was evaluated in the same manner as in Example 1. <100> / <110> The gloss ratio was 0.99 for level 1, 1.18 to 1.22 for levels 2 to 6, and 0.82 for level 7. Therefore, it was determined that the surface roughness was different between level 1, levels 2 to 6, and level 7. <100> / <110> By setting the gloss ratio at 1.1 or more and 0.9 or less as the range of acceptable surface roughness, it is possible to judge a surface roughness of level 1 as poor and a surface roughness of levels 2 to 7 as good. <110> / <100> By setting the range of acceptable surface roughness as 1.1 or more and 0.9 or less using the gloss ratio, it is possible to judge a surface roughness of level 1 as bad and a surface roughness of levels 2 to 7 as good.

[0086] Where: <100> In terms of gloss, levels 1 and 7 are equivalent, which shows that surface roughness cannot be evaluated by the gloss in a single specific direction. Therefore, it is necessary to obtain the gloss in the circumferential direction and evaluate it based on the circumferential direction dependency.

[0087] [Silicon wafer manufacturing process management method] Example 3 First, based on the results of Examples 1 and 2, it is considered that the material is suitable for use in the double-sided polishing process. <100> / <110> The gloss ratio range was set to 0.9 or less and 1.1 or more.

[0088] To produce polished wafers with {110} orientation, a {110} silicon ingot was prepared. The diameter was approximately 300 mm, the conductivity type was p-type, and the resistivity was approximately 10 Ωcm.

[0089] Next, the prepared silicon ingot was cut into disk-shaped silicon wafers using a wire saw (slicing process). The surfaces of the cut silicon wafers had undulations and layers of processing distortion caused by the cutting process.

[0090] Next, the outer periphery of the silicon wafer, which had been roughened by cutting, was chamfered with a 3000-grit grinding wheel electroplated with diamond, forming a chamfered shape while at the same time preventing chipping and cracking during the wafer manufacturing process (chamfering process).

[0091] Next, in order to remove the surface distortion layer formed during the slicing process and to flatten the surface, a lapping liquid was poured between the lapping plate and the silicon wafer held by the carrier, and the silicon wafer surface was mechanically polished by rotating and rubbing under pressure (lapping process).

[0092] Next, these 420 wafers after lapping were etched with an NaOH concentration of 40 wt % at a chemical temperature of 70° C. so that the removal amount on both sides was approximately 25 μm.

[0093] Next, one of these was taken out and its glossiness was evaluated in the same manner as in Example 1. <100> Direction is 62.5, <110> The direction is 54.3, <100> / <110> The ratio was 1.15. Since this 1.15 exceeds the initially determined 1.1, it was determined that the etched surface was suitable for input to the double-side polishing process (good judgment).

[0094] Based on these results, the remaining 419 wafers were also judged to be good and were subjected to double-sided polishing. After double-sided polishing, the particle count was 1pcs / wf and the GBIR was 0.1μm, both of which were good results.

[0095] Next, the chamfered edge of the {110} silicon wafer after double-side polishing was mirror-finished using an abrasive cloth and polishing slurry, resulting in a mirror-finished edge without any damage caused by processing.

[0096] Next, the front surface of the silicon wafer was subjected to a single-side polishing process using an abrasive cloth and an abrasive slurry, which created a good polished surface on the front surface.

[0097] Next, a batch-type cleaning machine was used to perform SC1 and SC2 cleaning, followed by the final cleaning process, which removed particles and metal impurities adhering to the silicon wafers.

[0098] Through the above steps, {110} polished wafers were produced.

[0099] The present invention includes the following aspects. [1]: A method for evaluating the surface roughness of an anisotropically etched silicon substrate, comprising the steps of: preparing an anisotropically etched silicon substrate; irradiating light obliquely onto the silicon substrate to obtain a reflectance of the obliquely incident reflected light from the silicon substrate in a circumferential direction; and evaluating the surface roughness of the silicon substrate from the circumferential direction dependence of the obtained reflectance. [2]: The method for evaluating the surface roughness of an anisotropically etched silicon substrate according to [1] above, wherein the silicon substrate has a convex etched surface. [3]: The method for evaluating the surface roughness of an anisotropically etched silicon substrate according to [1] or [2] above, wherein the silicon substrate has a main surface of {110}. [4]: The method for evaluating the surface roughness of an anisotropically etched silicon substrate according to any one of [1] to [3] above, characterized in that the anisotropic etching is wet etching using an alkaline chemical solution. [5]: In the step of acquiring the reflectance in a circumferential direction, at least <110> Direction and <100> A method for evaluating the surface roughness of an anisotropically etched silicon substrate according to any one of [1] to [4] above, characterized by obtaining the reflectance in a direction. [6]: In the step of evaluating the surface roughness, <110> Direction and <100> The method for evaluating the surface roughness of an anisotropically etched silicon substrate according to any one of [1] to [5] above, characterized in that the surface roughness of the silicon substrate is evaluated based on a reflectance ratio in a direction. [7]: The method for evaluating the surface roughness of an anisotropically etched silicon substrate according to any one of [1] to [6] above, characterized in that in the step of acquiring the reflectance in the circumferential direction, the glossiness acquired using a glossiness meter is used as the reflectance. [8]: A manufacturing process control method for single crystal silicon wafers having a {110} main surface, comprising the steps of: preparing a silicon wafer having an anisotropically etched main surface of {110}; evaluating the prepared silicon wafer having a {110} main surface by the method for evaluating the surface roughness of a silicon substrate according to any one of the above [1] to [7]; and <110> Direction and <100> and determining whether or not the surface roughness of the prepared silicon wafer having a {110} primary surface is suitable for a double-side polishing process based on the reflectance ratio in the directions. [9]: The manufacturing process control method for silicon wafers having a {110} primary surface according to [8] above, wherein in the step of determining pass / fail, the pass / fail determination is made based on a preset target reflectance ratio.

[10] : The manufacturing process control method for silicon wafers having a {110} primary surface according to [8] or [9] above, wherein the reflectance ratio is a gloss ratio.

[11] : The manufacturing process control method for silicon wafers having a {110} primary surface according to any one of [8] to

[10] above, characterized in that, when it is determined in the pass / fail judging step that the wafer is unsuitable for being put into a double-sided polishing step, at least one of investigating a manufacturing history of an etching step and improving the etching step is performed.

[12] : The manufacturing process control method for silicon wafers having a {110} primary surface according to any one of [8] to

[10] above, characterized in that, when it is determined in the pass / fail judging step that the wafer is unsuitable for being put into a double-side polishing step, the etching step is improved based on at least one of a concentration and a temperature of an etching solution.

[0100] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and any configuration that is substantially the same as the technical idea described in the claims of the present invention and that provides similar effects is included in the technical scope of the present invention. [Explanation of symbols]

[0101] S1, S2, S3, S11, S12, S13, S14, S15, S16... steps.

Claims

1. A method for evaluating the surface roughness of an anisotropically etched silicon substrate, comprising the steps of: preparing an anisotropically etched silicon substrate; irradiating light obliquely onto the silicon substrate to obtain a reflectance of the obliquely incident reflected light from the silicon substrate in a circumferential direction; and evaluating the surface roughness of the silicon substrate from the circumferential direction dependence of the obtained reflectance.

2. 2. The method for evaluating the surface roughness of an anisotropically etched silicon substrate according to claim 1, wherein the silicon substrate has a convex etched surface.

3. 2. The method for evaluating the surface roughness of an anisotropically etched silicon substrate according to claim 1, wherein the silicon substrate has a main surface with a {110} orientation.

4. 2. The method for evaluating the surface roughness of a silicon substrate after anisotropic etching according to claim 1, wherein the anisotropic etching is wet etching using an alkaline chemical solution.

5. 2. The method for evaluating the surface roughness of an anisotropically etched silicon substrate according to claim 1, wherein in the step of acquiring the reflectance in the circumferential direction, the reflectance is acquired in at least the <110> direction and the <100> direction.

6. 2. The method for evaluating the surface roughness of an anisotropically etched silicon substrate according to claim 1, wherein in the step of evaluating the surface roughness, the surface roughness of the silicon substrate is evaluated based on a reflectance ratio between the <110> direction and the <100> direction.

7. 2. The method for evaluating the surface roughness of an anisotropically etched silicon substrate according to claim 1, wherein in the step of acquiring the reflectance in the circumferential direction, a glossiness acquired using a glossiness measuring device is used as the reflectance.

8. 8. A manufacturing process control method for a silicon wafer having a {110} main surface, comprising the steps of: preparing a silicon wafer having an anisotropically etched main surface of {110}; evaluating the prepared silicon wafer having a {110} main surface by the method for evaluating surface roughness of a silicon substrate according to any one of claims 1 to 7; and judging whether the surface roughness of the prepared silicon wafer having a {110} main surface is suitable for input to a double-side polishing process, based on a reflectance ratio between the <110> direction and the <100> direction of the evaluation result.

9. 9. The method for managing a manufacturing process of silicon wafers having a {110} principal surface according to claim 8, wherein in the step of determining whether the wafer is good or bad, the determination is made based on a preset target reflectance ratio.

10. 9. The method for controlling a manufacturing process of a silicon wafer having a {110} primary surface according to claim 8, wherein the reflectance ratio is a gloss ratio.

11. 9. The method for managing a manufacturing process of silicon wafers having a {110} primary surface according to claim 8, wherein, when it is determined in the pass / fail judging step that the wafer is unsuitable for being put into a double-side polishing step, at least one of investigating a manufacturing history of an etching step and improving the etching step is performed.

12. 9. The method for managing a manufacturing process of silicon wafers having a {110} primary surface according to claim 8, wherein, when it is determined in the pass / fail judging step that the wafer is unsuitable for being put into the double-side polishing step, the etching step is improved based on at least one of a concentration and a temperature of an etching solution.

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