JP2010251542A - Method and device for discriminating working surface and method for manufacturing silicon wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To discriminate the surface and rear of a silicon wafer forming an EG layer by back-side damage treatment or the like. <P>SOLUTION: A method for discriminating a working surface includes a first process (steps S2 and S3) irradiating the first surface 2a and second surface 2b of the silicon wafer 2 with visible rays A and measuring the scattered rays B respectively; and a second process (the steps S4) discriminating the first surface 2a and the second surface 2b on the basis of the scattered rays B from the first surface 2a and the second surface 2b obtained by the first process. Since both the first surface 2a and second surface 2b of the silicon wafer 2 are irradiated with visible rays A and the surface and the rear are decided on the basis of the scattered rays B, the decision of the surface and the rear is extremely more accurate than the method deciding the surface and the rear from the absolute value of the scattered rays obtained from one surface. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a machined surface discriminating method and a machined surface discriminating apparatus, and more particularly, to a method and apparatus for discriminating a machined surface of a processing object having first and second surfaces whose surface states are different from each other by machining. The present invention also relates to a method for manufacturing a silicon wafer, and more particularly, to a method for manufacturing a silicon wafer including a step of performing processing that changes the surface state of one of the main surface and the back surface.

  It is known that the yield of semiconductor devices such as ICs decreases when contaminating impurities such as heavy metals are mixed. Therefore, the manufacturing process of the semiconductor device requires a very clean environment so that no contaminating impurities are mixed into the silicon wafer. However, it is difficult to completely prevent contamination impurities. For this reason, the silicon wafer is provided with a getter sink that captures and fixes the contaminated impurities, thereby isolating the contaminated impurities from the element formation region.

  As a gettering method, an intrinsic gettering (IG) method in which a getter sink is provided inside a silicon wafer and an extrinsic gettering (EG) method in which a getter sink is provided on the back surface of the silicon wafer are known. Among these, as one of the extrinsic gettering methods, a method is known in which defects are formed by performing backside damage processing on the back surface of a silicon wafer, and distortion (EG layer) generated thereby is used as a getter sink. .

  Since the defects formed by the backside damage process are very small, it is difficult to visually distinguish which side the backside damage process has been performed, that is, the front and back of the silicon wafer. . Such a problem becomes prominent in a wafer having a low glossiness (that is, having a large surface roughness) such as an etched wafer, a wrapped wafer, or a double-sided ground wafer. That is, when backside damage processing is performed on a wafer having a high glossiness, the glossiness of the processing surface is greatly reduced, so that the front / back discrimination is relatively easy. On the other hand, since the change in the glossiness of the wafer having a low glossiness is slight even when the backside damage process is performed, it is very difficult to discriminate between the front and the back by visual inspection.

  For this reason, when the silicon wafer subjected to the backside damage treatment is accommodated in a case for transportation or storage, the silicon wafer may be accommodated with the front and back reversed. When such a mistake occurs, in the subsequent processes, the surface (back surface) subjected to the backside damage process is erroneously handled as the device formation surface (main surface), and thus the wafer becomes a defective product. Therefore, there is a need for a method for correctly determining the front and back of a silicon wafer that has been subjected to backside damage processing.

  As a method of determining the front and back of the silicon wafer, a method of counting the defect density by performing detection etching such as Secco etching and dash etching after making OSF defects manifest by heat treatment can be considered. However, since this method involves heat treatment and etching treatment, it is a so-called destructive inspection. Therefore, it is impossible to carry out with respect to the total number of silicon wafers.

  On the other hand, as a method for discriminating the front and back of the silicon wafer, there are a method for measuring the roughness of the silicon wafer, a method for measuring the lifetime, and a method of imprinting a laser mark on the back surface of the silicon wafer. . As an example, Patent Document 1 describes measuring the surface roughness of a wafer after etching.

JP-A-8-330271

  However, since the unevenness formed by the backside damage process is very small, it is not easy to reliably distinguish the front and back in a short time by the method of measuring roughness. In addition, the method for measuring the lifetime is difficult to apply to mass-produced products because it is necessary to perform a passivation treatment before the measurement. Furthermore, in the method of marking with a laser mark or the like, the marking remains on the finished silicon wafer, which may not satisfy the specifications desired by the customer.

  On the other hand, a method of irradiating visible light that generates strong white light on one surface of the silicon wafer and discriminating the front and back of the silicon wafer from the absolute value of the obtained scattered light is also conceivable. According to this method, the front and back of the silicon wafer can be discriminated with non-destructive, low cost, and high throughput. However, this method is effective for wafers with sufficiently high glossiness, but as described above, the glossiness of wafers with low glossiness changes little even when backside damage treatment is performed. Therefore, this method is not always effective.

  Therefore, there is a need for a method capable of reliably discriminating the front and back surfaces of a silicon wafer having a low glossiness after non-destructive, low cost and high throughput after the backside damage treatment.

  Note that the above problem is not limited to the front / back determination of the silicon wafer after the backside damage process, but also occurs in the front / back determination after performing other processing that changes the surface state on one surface of the silicon wafer. It is a problem. For example, even when laser beam irradiation, ion implantation, lapping, grinding, etc. are performed on one surface of a silicon wafer, it may be difficult to visually determine the front and back. Even in such a case, it is necessary to reliably determine the front and back as in the case of performing the backside damage process.

  Furthermore, the above-mentioned problem is not limited to the front / back determination of a silicon wafer, but may occur also in the front / back determination of other processing objects. For example, after performing the shot peening process on one surface of the steel plate, it may be difficult to determine which surface is the processed surface. In addition, when texture processing is performed on one surface of a hard disk substrate, it may be difficult to determine which surface is the processed surface.

  Furthermore, the above problem is a problem that applies to all cases in which a surface subjected to processing whose surface state is changed among a plurality of surfaces (for example, each surface of a cube) of a three-dimensional object having an arbitrary shape is specified. is there. That is, the above problem is not limited to the determination of the front and back of the plate-like body.

  Therefore, an object of the present invention is to provide a machined surface discriminating method and a machined surface discriminating apparatus for discriminating a surface that has been subjected to machining whose surface state changes among a plurality of surfaces of a processing object.

  Another object of the present invention is to provide a method of manufacturing a silicon wafer that does not cause a mistake in the front and back in the manufacturing process.

  A processing surface discriminating method according to the present invention is a method for discriminating a processing surface of a processing object that has been subjected to processing that changes the surface state with respect to either one of the first and second surfaces. And the first step of irradiating the second surface with visible light and measuring the scattered light, respectively, and the scattered light from the first and second surfaces obtained in the first step. And a second step of discriminating which of the first and second surfaces is a processed surface.

  A machined surface discriminating apparatus according to the present invention is a machined surface discriminating apparatus for discriminating between the first and second surfaces of a processing object having first and second surfaces having different surface states. Based on a light source that irradiates visible light on the first and second surfaces, a photodetector that detects scattered light from the first and second surfaces, and a detection result of the scattered light by the photodetector, And a control unit for determining which of the first and second surfaces is a processed surface.

  According to the present invention, since both the processed surface and the non-processed surface are irradiated with visible light and the processed surface is determined based on the scattered light, the absolute value of the scattered light obtained from one surface Compared with the method of determining the machining surface from the above, extremely accurate determination is possible. That is, the absolute value of the scattered light obtained from one surface is used as a reference (reference), and the difference from the absolute value of the scattered light obtained from the other surface is obtained from these first and second surfaces. Reliable discrimination is possible even if the difference in scattered light is small. In addition, since it can be distinguished with non-destructive, low cost, and high throughput, it is considered to be extremely practical.

  In this invention, it is preferable that the said 1st and 2nd surface before performing the said process has the mutually same surface state. According to this, since the difference between the front and back surface states caused by the processing appears as the difference of the scattered light as it is, even if the obtained difference is very small, the determination can be made reliably.

  In the present invention, relatively large irregularities are formed on the first and second surfaces before the processing, and the processing is performed with respect to any one of the first and second surfaces. The treatment is preferably a process in which relatively small irregularities are formed. According to this, since the glossiness of the first and second surfaces before processing is lowered due to relatively large unevenness, even if relatively small unevenness is formed by processing, it is difficult to discriminate visually. . Even in such a case, according to the present invention, it is possible to reliably determine.

  In this case, it is preferable that the second step performs determination based on a blue wavelength component included in scattered light from the first and second surfaces. Due to Rayleigh scattering, among the visible light irradiated on the first and second surfaces, a large number of green wavelength components having a shorter wavelength and a blue wavelength component having a shorter wavelength than the red wavelength component are scattered, and as a result, the first light is scattered. And the ratio of the blue wavelength component in the scattered light from the second surface increases. Here, when visible light is irradiated on a surface with minute irregularities, the minute irregularities cause irregular reflection of visible light, resulting in irregular reflection compared to the case where visible light is irradiated on a surface without minute irregularities. Strength increases. For this reason, the irregular reflection intensity of the blue wavelength component in the scattered light is stronger on the surface on which the minute irregularities are formed than on the surface on which the minute irregularities are not formed. Therefore, if the determination is made based on the blue wavelength component, the processed surface can be reliably determined.

  In the present invention, it is preferable that the first step sequentially detects the scattered light from the first and second surfaces using the same light source and photodetector. According to this, since the first and second surfaces can be observed under exactly the same conditions, more accurate discrimination is possible. Here, when the processing object is a silicon wafer, the processing surface discrimination device switches the surface facing the light source and the photodetector among the first and second surfaces by inverting the silicon wafer. What is necessary is just to provide the possible inversion mechanism.

  In the present invention, the first step uses scattered light from the first and second surfaces using a light source and a photodetector provided on the first surface side and the second surface side, respectively. It is also preferable to detect them simultaneously. According to this, it becomes possible to perform a faster discrimination.

  In this invention, it is preferable that the said process target object is a plate-shaped object, and the said 1st and 2nd surface is the surface and back surface of the said plate-shaped body, respectively. According to this, it becomes possible to distinguish the front and back of a silicon wafer or a hard disk substrate.

  In this case, it is preferable that the processing object is a silicon wafer, the first surface is a main surface on which a device is formed, and the second surface is a back surface on which no device is formed. According to this, it is possible to easily discriminate even if it is difficult to visually distinguish the front and back after performing the backside damage processing on the back surface of the silicon wafer. As a case where front / back discrimination after backside damage processing is difficult, when the gloss before processing is low, for example, the silicon wafer before processing is an etched wafer, a wrapped wafer or a double-sided ground wafer A case is mentioned.

  In the silicon wafer manufacturing method according to the present invention, the first surface of the silicon wafer on which the device is formed and the back surface of the silicon wafer on which the device is not formed are processed to change the surface state. After performing the step and the first step, the main surface and the back surface are irradiated with visible light, the scattered light is measured respectively, and the obtained in the second step. And a third step of discriminating the main surface and the back surface based on scattered light from the main surface and the back surface.

  According to the present invention, both the main surface and the back surface of the silicon wafer are irradiated with visible light, and the processing surface is determined based on the scattered light, so that the front and back surfaces of the silicon wafer can be reliably determined. Can do. For this reason, it becomes possible to manufacture a silicon wafer without mistaken front and back.

  In the present invention, it is preferable that the first step is a backside damage process for forming minute defects on the back surface of the silicon wafer. This is because the unevenness formed by the backside damage process is extremely small, and it may be difficult to visually determine the front and back after the backside damage process.

  As described above, according to the machined surface discriminating method and machined surface discriminating apparatus of the present invention, it is possible to reliably discriminate the machined surface and the non-machined surface with non-destructive, low cost, and high throughput.

  Moreover, according to the silicon wafer manufacturing method of the present invention, it becomes possible to manufacture a silicon wafer without mistakes in the front and back.

3 is a flowchart illustrating a method for manufacturing a silicon wafer according to a preferred embodiment of the present invention. It is a figure which shows typically the structure of the processing surface discrimination | determination apparatus by preferable embodiment of this invention. It is a figure which shows the state which adhere | attached the carrier plate on the back surface side of the silicon wafer. It is a figure which shows typically the structure of the processing surface discrimination | determination apparatus by other preferable embodiment of this invention. 3 is a graph showing measurement results of Example 1. 6 is a graph showing measurement results of Example 2. It is a graph which shows the measurement result (absolute value) of Example 3. It is a graph which shows the measurement result (difference) of Example 3.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a flowchart illustrating a method for manufacturing a silicon wafer according to a preferred embodiment of the present invention. In the flowchart of FIG. 1, steps that are not directly related to the present invention, such as pulling up the silicon ingot, are omitted.

  As shown in FIG. 1, in this embodiment, first, a silicon wafer having a main surface and a back surface having the same surface state is prepared, and backside damage processing is performed on the back surface (step S1). Here, the “main surface of the silicon wafer” is the surface on which the device is formed, and the “back surface of the silicon wafer” is the surface opposite to the main surface. No device is formed on the back side of the silicon wafer. Examples of the silicon wafer having the same surface state on the main surface and the back surface include an etched wafer, a lapped wafer, and a double-side ground wafer.

  The backside damage process is a process of forming minute defects on the back surface of the silicon wafer, and a strain (or damage) layer (EG layer) generated thereby becomes a getter sink. That is, it is a kind of extrinsic gettering (EG) method. Although the specific method of the backside damage treatment is not particularly limited, it can be performed by spraying a slurry in which fine silica powder is dispersed in water onto the back surface of the silicon wafer. Thereby, on the back surface of the silicon wafer, a damage layer having a thickness of 1 μm or less, particularly about 0.2 to 0.3 μm is generated in the thickness direction of the wafer at the collision portion of the silica powder, and this becomes an EG layer. If the thickness of the EG layer is less than 0.2 μm, a sufficient EG effect cannot be obtained. On the other hand, when the thickness of the EG layer exceeds 1 μm, the productivity is lowered. Moreover, the injection time to the back surface of the wafer can be appropriately set between 10 seconds and 60 seconds in consideration of the thickness of the EG layer.

  When backside damage processing is performed, the surface state of the back surface of the silicon wafer changes compared to before processing. That is, the surface state is different from the main surface. However, since the defects formed by the backside damage process are very small, in a wafer having a low glossiness (that is, having a large surface roughness) such as an etched wafer, a wrapped wafer, or a double-side ground wafer. The change in the surface state before and after the backside damage treatment is slight. In other words, relatively large irregularities are already formed on the low-gloss wafer, and even if relatively small irregularities are further formed by backside damage processing, the appearance is dominated by the relatively large irregularities. Because it becomes.

  The silicon wafer that has undergone the backside damage processing is accommodated in the case in a predetermined direction. That is, the front and back surfaces of the plurality of silicon wafers accommodated in the case should all coincide with the determined orientation. However, there are rare mistakes in which the product is mistakenly stored in the reverse direction or the silicon wafer that has been correctly stored is once taken out and then stored in the reverse direction. In the following steps, it is detected whether or not there is such a reverse silicon wafer by determining the processed surface.

  FIG. 2 is a diagram schematically showing a configuration of a machined surface discriminating apparatus according to a preferred embodiment of the present invention.

  The processing surface discriminating apparatus 10 shown in FIG. 2 reverses the silicon wafer 2 by irradiating the silicon wafer 2 with a light source 11 that irradiates the silicon wafer 2 with visible light A, a photodetector 12 that detects scattered light B from the silicon wafer 2. A reversing mechanism 13 that switches a surface facing the light source 11 and the photodetector 12 and a control unit 14 that controls the light source 11, the photodetector 12, and the reversing mechanism 13 are provided.

  Although it does not specifically limit as the light source 11, It is preferable to use the light source which generate | occur | produces intense white light, for example, a halogen condensing lamp. Moreover, it is preferable that the light source 11 is configured so that the visible light A is irradiated on the entire one surface of the silicon wafer 2. Therefore, a light source having a single wavelength and a small beam diameter such as a laser light source is inappropriate.

The photodetector 12 is not particularly limited, but it is preferable to use a photo detector capable of detecting the light reception intensity by performing photoelectric conversion, for example, a CCD element using a photodiode. The position of the photodetector 12 needs to be set to a position where the specular reflection component A ′ of the visible light A is not directly incident. Preferably, when the incident angle of the visible light A incident on the silicon wafer 2 from the light source 11 is θ _A , the photodetector 12 is not disposed at a position corresponding to the reflection angle θ _B0 (= θ _A ). When the emission angle emitted from the silicon wafer 2 to the photodetector 12 is θ _B1 ,
θ _A ≠ θ _B1
Preferably set to
θ _A > θ _B1
It is particularly preferable to set to. Specifically, if the incident angle θ _A is set to about 20 to 80 ° and the emission angle θ _B1 is set to around 0 °, the light incident on the photodetector 12 is almost only scattered light. In FIG. 2, since the emission angle θ _B1 is set to 0 °, the line perpendicular to the silicon wafer 2 is expressed as “output angle θ _B1 ”.

  The reversing mechanism 13 is a mechanism for reversing the silicon wafer 2 to switch the surface facing the light source 11 and the photodetector 12 from the first surface 2a to the second surface 2b (or vice versa). That is, the light source 11 and the photodetector 12 are common to the first surface 2 a and the second surface 2 b of the silicon wafer 2. The reversing mechanism 13 shown in FIG. 2 reverses the silicon wafer 2, but the light source 11 and the light detector are fixed by fixing the silicon wafer 2 and reversing the positions of the light source 11 and the light detector 12. The surface facing 12 may be switchable.

  The control unit 14 is an element that controls the light source 11, the light detector 12, and the reversing mechanism 13, and determines the main surface and the back surface of the silicon wafer 2 based on at least the detection result of the scattered light B by the light detector 12. To play a role. The determination result is transmitted to the notification unit 15, whereby the operator can know which surface of the silicon wafer 2 is the main surface (or the back surface). A specific determination method by the control unit 14 is as follows.

  First, visible light A is irradiated to the first surface 2a of the silicon wafer 2 (at this time, whether it is the main surface or the back surface) using the light source 11, and the first surface 2a. The light detector 12 detects the intensity of the scattered light B scattered by. The detection result is transmitted to the control unit 14 (step S2).

  Next, the front and back of the silicon wafer 2 are reversed using the reversing mechanism 13, and the second surface 2b located on the back side of the first surface 2a (at this time, it is unknown whether it is the main surface or the back surface). Is directed to the light source 11 and the photodetector 12. In this state, similarly to the above, the visible light A is irradiated using the light source 11, and the intensity of the scattered light B scattered on the second surface 2 b is detected by the photodetector 12. The detection result is transmitted to the control unit 14 (step S3).

  And the control part 14 compares the intensity | strength of the scattered light B obtained from the 1st surface 2a, and the intensity | strength of the scattered light B obtained from the 2nd surface 2b, and the surface from which the stronger scattered light was obtained Is determined as the back surface of the silicon wafer 2 (step S4). The result of the determination is transmitted to the operator via the notification unit 15. As a transmission method to the operator, a method of displaying using a display, a method of transmitting by sound, and the like can be cited.

  The reason why the intensity of the scattered light B is stronger on the back surface than on the main surface of the silicon wafer 2 is that the minute irregularities formed by the backside damage treatment diffusely reflect the visible light A. Since the scattered light B is generated by Rayleigh scattering of the visible light A applied to the main surface or the back surface, the blue wavelength component is the main component. Accordingly, the photodetector 12 is preferably capable of detecting a wavelength region including a blue wavelength component, and more preferably capable of selectively detecting a blue wavelength component.

  If the intensity of the scattered light B to be obtained from the main surface of the silicon wafer 2 and the intensity of the scattered light B to be obtained from the back surface of the silicon wafer 2 are known, the threshold value is set to a substantially intermediate intensity. By setting, in principle, if the intensity of the scattered light B is detected only on one surface, the front / back determination is possible. That is, if the intensity of the scattered light B is weaker than the set threshold value, it can be determined as the main surface, and conversely, if the intensity of the scattered light B is higher than the set threshold value, it is the back surface. Judgment can be made.

  However, such single-sided evaluation is possible only for wafers with sufficiently high gloss. This is because a wafer with high glossiness has a large intensity change of the scattered light B before and after the backside damage treatment. On the other hand, the intensity change of the scattered light B before and after the backside damage processing is slight for a wafer having a low glossiness (that is, having a large surface roughness) such as an etched wafer, a wrapped wafer, or a double-side ground wafer. For this reason, in the single-sided evaluation, an erroneous determination result is obtained due to a slight measurement error. In order to avoid such a problem, in this embodiment, both sides of the silicon wafer 2 are evaluated, and the front / back determination is performed based on the difference. For this reason, even if it is a wafer with low glossiness, it becomes possible to perform front-back determination correctly.

  In addition, in the present embodiment, since the main surface and the back surface are evaluated using the same light source 11 and photodetector 12, the measurement error itself is very small. For this reason, more accurate front / back determination can be performed.

  When the front / back determination is completed in this way, the carrier plate 4 is bonded to the back surface 2d side of the silicon wafer 2 as shown in FIG. 3 (step S5), and the main surface 2c of the silicon wafer 2 is mirror-polished in this state. (Step S6). As a result, a polished wafer having the EG layer formed on the back surface 2d is completed. As described above, since the polishing is performed after the reliable front / back determination is performed, mistakes such as erroneous polishing of the back surface 2d on which the EG layer is formed are prevented.

  As described above, according to the present embodiment, it is possible to correctly perform the front / back determination even for a wafer having a low glossiness. In addition, since the optical evaluation is performed, the front / back determination can be performed with non-destructive, low cost, and high throughput.

  In addition, the processing surface discriminating apparatus 10 according to the present embodiment is transported if it is incorporated into a transport system that transports the backside damage processing device used in Step S1 and the bonding device used in Step S5 by a single wafer. It is possible to automatically perform the front / back determination during this. Alternatively, if the processing surface discriminating device 10 is incorporated in the backside damage processing device or the bonding device itself, the existing conveyance system can be used as it is.

  FIG. 4 is a diagram schematically showing the configuration of a machined surface discriminating apparatus according to another preferred embodiment of the present invention.

  The processing surface discrimination device 20 shown in FIG. 4 has the processing surface discrimination shown in FIG. 2 in that a light source 21 and a light detector 22 are added on the second surface 2b side and the reversing mechanism 13 is omitted. This is different from the apparatus 10. Since the other points are the same as those of the machined surface discriminating apparatus 10 shown in FIG. 2, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  In the present embodiment, the first surface 2a of the silicon wafer 2 (it is unknown whether it is the main surface or the back surface at this point) is evaluated using the light source 11 and the photodetector 12, and the silicon wafer 2 The second surface 2b (at this time, whether it is the main surface or the back surface is unknown) is evaluated using the light source 21 and the photodetector 22. Therefore, in this embodiment, step S2 and step S3 shown in FIG. 1 can be performed at the same time, and higher-speed discrimination becomes possible. However, the light source 21 and the photodetector 22 need to have substantially the same characteristics as the light source 11 and the photodetector 12, respectively.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say, it is included in the range.

  For example, in the above-described embodiment, the case where the front / back determination of the silicon wafer subjected to the backside damage processing is performed has been described as an example, but the present invention is not limited to this, and the surface of one surface of the silicon wafer is not limited to this. The present invention can also be applied to front / back determination after performing other processing in which the state changes.

  As an example, the present invention is applicable even when the EG layer is formed by performing laser beam irradiation, ion implantation, lapping, grinding, etc. on the back surface of the silicon wafer. . That is, even if the EG layer is formed by these treatments, it may be difficult to make a front / back determination visually. Even in such a case, as described in the above embodiment, if the scattered light is measured on both sides of the silicon wafer and the front / back determination is performed based on the difference, the front / back determination can be performed correctly. Become. Note that grinding and lapping are performed, for example, by bringing a polishing tape called a lapping film into contact with one side of the wafer. Examples of the wrapping film include a film in which various abrasive grains are coated with an adhesive on a polyester film as a base material.

  Further, in the above embodiment, the case where the front / back determination of the silicon wafer is performed has been described as an example, but the present invention is not limited to this, and can be applied to the front / back determination of other processing objects. .

  As an example, the present invention can also be applied to a case where it is determined whether the front or back surface is a processed surface after performing shot peening on one surface of a steel plate. The shot peening treatment is a treatment that hardens the metal surface by applying fine particles such as alumina or SiC to the metal surface at a high speed, thereby imparting wear resistance and the like. When such a process is performed only on one surface of a steel plate having the same roughness on the front and back surfaces, it may be difficult to determine which of the front and back surfaces is the processed surface. However, when shot peening is performed using fine particles, minute concave portions are formed on a rough metal surface, and therefore it is possible to reliably perform front / back determination by applying the present invention.

  As another example, the present invention can also be applied to front / back determination when texture processing is performed on one surface of a hard disk substrate (for example, an aluminum substrate). The texture processing is processing for forming a uniform minute groove on the surface of the hard disk substrate mainly for the purpose of increasing the storage capacity and preventing the adsorption of the head to the substrate surface. In general, hard disk substrates have the same surface state on the front and back surfaces, and the grooves formed by texturing are extremely small. Therefore, when such processing is performed only on one side, either the front or back side is the processed surface. It may be difficult to determine whether it is present. However, even in such a case, it is possible to reliably perform the front / back determination by applying the present invention.

  Furthermore, the present invention is not limited to the front / back determination of a processing object that is a plate-like body, but for all cases that specify a surface that has undergone a process that changes the surface state among a plurality of surfaces that cannot be identified by shape or the like. Applicable. For example, when it is necessary to determine which surface is a processed surface after performing processing that forms minute irregularities on a specific surface of a cube that has the same surface state on all six surfaces. The invention is applicable.

[Example 1]
First, a silicon wafer sample A1 having a diameter of 200 mm was prepared. The silicon wafer sample A1 is a double-sided ground wafer having the same surface state on the main surface and the back surface, and the glossiness is 120. Backside damage processing was performed on the back surface of such a silicon wafer sample A1, and an EG layer having a thickness of 0.3 μm was formed. Backside damage processing was not performed on the main surface. In the backside damage treatment, a slurry in which No. 3000 silica powder was dispersed in water was used, and this was sprayed onto the back surface of the silicon wafer sample A. The injection time is 30 seconds.

  Next, using the apparatus having the same structure as the machined surface discriminating apparatus shown in FIG. 2, the intensity of scattered light on the main surface and the back surface of the silicon wafer sample A was measured for each wavelength using a spectrophotometer. A halogen condenser lamp was used as the light source 11 and a CCD element was used as the photodetector 12. The measurement results are shown in FIG. The vertical axis in FIG. 5 indicates the intensity ratio at each wavelength, that is, the irregular reflection intensity ratio when the highest scattered light intensity (diffuse reflection intensity) is 1. As shown in FIG. 5, the intensity ratio of scattered light was stronger on the back surface than on the main surface, particularly in the blue wavelength region (about 380 nm to about 550 nm).

[Example 2]
Silicon wafer samples B1 to B3 having a diameter of 200 mm having different gloss levels were prepared. Any of the silicon wafer samples B1 to B3 is an etched wafer having the same main surface and back surface. The gloss levels are 160, 120, and 80, respectively. That is, the silicon wafer sample B1 has a relatively high gloss, the silicon wafer sample B2 has a relatively medium gloss, and the silicon wafer sample B3 has a relatively low gloss. Backside damage processing was performed on the back surfaces of such silicon wafer samples B1 to B3 under the same conditions as in Example 1. Backside damage processing was not performed on the main surface.

  Next, in the same manner as in Example 1, the intensity ratio of the scattered light on the main surface and the back surface of the silicon wafer samples B1 to B3 was measured. The measurement results are shown in FIG. The vertical axis in FIG. 6 is the same display as the vertical axis in FIG. As shown in FIG. 6, in the silicon wafer samples B1 to B3, the intensity ratio of scattered light was higher on the back surface than on the main surface in the blue wavelength region (about 380 nm to about 550 nm). However, the difference becomes smaller as the glossiness becomes lower, and the difference is slight in the silicon wafer sample B3 having the lowest glossiness. For this reason, it is considered that it is practically difficult to determine the front and back by single-sided evaluation for a silicon wafer with low glossiness.

[Comparative Example 1]
The roughness of the main surface and the back surface of the silicon wafer samples B1 to B3 prepared in Example 2 was measured with a stylus roughness meter described in Patent Document 1. The measurement results are shown in Table 1.

  As shown in Table 1, in the silicon wafer sample B1 having a relatively high gloss and the silicon wafer sample B2 having a relatively medium gloss, the ratio of (roughness of the back surface / roughness of the main surface) is 1. It was found that the front / back judgment can be made by the method of measuring the roughness. On the other hand, in the silicon wafer sample B3 having a relatively low gloss, the ratio of (roughness of the back surface / roughness of the main surface) is 1, and depending on the method of measuring the roughness, it may be impossible to determine the front and back. all right.

[Example 3]
A number of 200 mm diameter silicon wafer samples C1 to Cn having various glossinesses were prepared. The silicon wafer samples C1 to Cn are either etched wafers, lapped wafers, or double-sided ground wafers, and any silicon wafer samples C1 to Cn have the same surface state on the main surface and the back surface. Backside damage processing was performed on the back surfaces of such silicon wafer samples C1 to Cn under the same conditions as in Example 1. Backside damage processing was not performed on the main surface.

  Next, by using an apparatus having the same structure as the machined surface discriminating apparatus shown in FIG. The ratio was measured. FIG. 7 shows the result of determining the relationship between the brightness ratio and the blue component ratio. The vertical axis in FIG. 7 represents the ratio of the measured value of the blue component when the highest measured value of the blue component is 100, that is, the blue component ratio. The horizontal axis indicates the ratio of the measured value of brightness when the highest measured value of brightness is 100, that is, the brightness ratio. As a result of forming back-and-forth damage on the back surface, minute unevenness is formed on the back surface. As a result, the intensity of the scattered light when the back surface is irradiated with visible light is the scattered light when the main surface is irradiated with visible light. As a result, as shown in FIG. 7, the blue component ratio is larger on the back surface than on the main surface. Further, as the glossiness decreases on both the main surface and the back surface, that is, as the surface roughness increases, the intensity of the scattered light increases, and as a result, the brightness ratio of the scattered light detected by the CCD element increases. As shown in FIG. 7, in the high gloss region, a significant difference was observed between the main surface and the back surface, but the difference was smaller in the low gloss region. For this reason, it is considered that front / back determination by single-sided evaluation using a threshold value is difficult.

  On the other hand, FIG. 8 shows the difference ΔL (first brightness ratio of scattered light on the main surface and the back surface before the backside damage processing and after the backside damage processing for the same silicon wafer samples C1 to Cn. The brightness ratio of the second surface—the brightness ratio of the second surface) and the difference Δb (the blue component ratio of the first surface—the blue component ratio of the second surface) of the blue component ratio. . As shown in FIG. 8, before performing the backside damage process, ΔL is in the range of −2 to +6, Δb is in the range of −1 to +1, and the first and second surfaces are substantially the same surface state. It can be said that it has. On the other hand, after backside damage processing is performed on one surface of the silicon wafer samples C1 to Cn, ΔL is in the range of −10 to −2 and Δb is in the range of +1 to +6, and the backside damage processing is performed. It was confirmed that there was a clear difference compared to before. Here, as shown in FIG. 7, since the lightness ratio is smaller and the blue component ratio is larger on the back surface than on the main surface of the silicon wafer, the first surface is obtained when ΔL is negative and Δb is positive. Corresponds to the back surface. Conversely, when ΔL is positive and Δb is negative, the second surface corresponds to the back surface. In addition, when the first surface and the second surface were reversed after backside damage, ΔL was positive and Δb was negative, and the reverse relationship with that after backside damage was obtained. Further, in Example 3, all of the wafers after the backside damage processing have a negative value of ΔL and a positive value of Δb (when reversed, all of them have a positive value of ΔL and a negative value of Δb. It can be seen that there is no wafer in which the main surface and the back surface are reversed after the backside damage process, that is, all the wafers are accommodated in the case after the backside damage process. This is because, if there is a wafer with the main surface and the back surface reversed after the backside damage processing, both positive and negative values are calculated for both ΔL and Δb. As described above, according to the present invention, it is possible to make a front / back determination by evaluating both surfaces of a wafer even for a low-gloss wafer.

2 Silicon wafer 2a Silicon wafer first surface 2b Silicon wafer second surface 2c Silicon wafer main surface 2d Silicon wafer back surface 4 Carrier plate 10, 20 Processing surface discriminator 11, 21 Light source 12, 22 Photodetector 13 Inversion mechanism 14 Control unit 15 Notification unit A Visible light B Scattered light

Claims (14)

A method for discriminating a processing surface of an object to be processed in which processing for changing the surface state is performed on either one of the first and second surfaces,
A first step of irradiating the first and second surfaces with visible light and measuring the scattered light, respectively;
A second step of determining which one of the first and second surfaces is a processing surface based on the scattered light from the first and second surfaces obtained in the first step; A machined surface discrimination method comprising:   The processing surface discrimination method according to claim 1, wherein the first and second surfaces before the processing have the same surface state. A relatively large unevenness is formed on the first and second surfaces before the processing,
The processing surface discrimination method according to claim 2, wherein the processing is processing in which relatively small unevenness is formed on one of the first and second surfaces.   The processing surface discrimination method according to claim 3, wherein the second step performs discrimination based on a blue wavelength component included in scattered light from the first and second surfaces.   5. The first step according to claim 1, wherein scattered light from the first and second surfaces is sequentially detected using the same light source and photodetector. 6. Machining surface discrimination method.   In the first step, scattered light from the first and second surfaces is simultaneously detected using a light source and a photodetector provided on the first surface side and the second surface side, respectively. The processing surface discriminating method according to any one of claims 1 to 4 characterized by things.   The processing object according to claim 1, wherein the object to be processed is a plate-like body, and the first and second surfaces are a front surface and a back surface of the plate-like body, respectively. Surface discrimination method.   The said process target is a silicon wafer, The said 1st surface is a main surface in which a device is formed, The said 2nd surface is a back surface in which a device is not formed, The Claim 7 characterized by the above-mentioned. Machining surface discrimination method.   The processing surface discrimination method according to claim 8, wherein the processing is backside damage processing in which a minute defect is formed on the back surface of the silicon wafer.   10. The processing surface discrimination method according to claim 8, wherein the silicon wafer before the processing is an etched wafer, a lapped wafer, or a double-sided ground wafer. A machined surface discriminating apparatus for discriminating between the first and second surfaces of a processing object having first and second surfaces having different surface states,
A light source that irradiates visible light to the first and second surfaces;
A photodetector for detecting scattered light from the first and second surfaces;
A processing surface discriminating apparatus comprising: a control unit that discriminates which of the first and second surfaces is a processing surface based on a detection result of the scattered light by the photodetector. The object to be processed is a silicon wafer,
The light source and the photodetector are common to the first and second surfaces;
The processing according to claim 11, further comprising a reversing mechanism capable of switching a surface facing the light source and the photodetector among the first and second surfaces by reversing the silicon wafer. Surface discriminator. A first step of performing a process in which a surface state is changed on one of a main surface of a silicon wafer on which devices are formed and a back surface of the silicon wafer on which devices are not formed;
After performing the first step, a second step of irradiating the main surface and the back surface with visible light and measuring the scattered light, respectively,
And a third step of discriminating the main surface and the back surface based on the scattered light from the main surface and the back surface obtained in the second step.   The method of manufacturing a silicon wafer according to claim 13, wherein the first step is a backside damage process for forming a minute defect on a back surface of the silicon wafer.

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