Method for single-side polishing of SOI wafer

Abstract

To provide a method for single-side polishing of an SOI wafer capable of bringing the film thickness distribution of an SOI layer within a target film thickness range.SOLUTION: The method for single-side polishing of an SOI wafer according to the present invention includes: a first step of measuring the film thickness distribution of an SOI layer to obtain in-plane shape data; a second step of starting single-side polishing; a third step of measuring, during polishing, a film thickness measurement value corresponding to a predetermined radial position of the SOI layer; a fourth step of updating the in-plane shape data by replacing the film thickness value of the in-plane shape data with the film thickness measurement value measured in the third step; and a fifth step of ending polishing of the SOI layer when the film thickness values at all positions in the in-plane shape data are equal to or less than a first film thickness.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for polishing a single side of an SOI wafer.

[0002] In recent years, SOI wafers having an SOI (Silicon on Insulator) structure have been attracting attention for various semiconductor device applications such as highly integrated CMOS elements, high-voltage elements, and image sensors.

[0003] SOI wafers generally have a structure in which an insulating layer such as silicon oxide (SiO2) and a semiconductor layer such as a single-crystal silicon layer used as the device active layer are sequentially formed on a support substrate wafer made of a single-crystal silicon wafer. This semiconductor layer is also called the SOI layer or active layer, and will be referred to as the "SOI layer" hereinafter. While bulk single-crystal silicon wafers have a relatively large parasitic capacitance that can occur between the device and the substrate, the SOI layer, which is formed on an insulating layer, can significantly reduce the parasitic capacitance. Therefore, SOI wafers are advantageous in terms of increasing device speed, increasing voltage resistance, and reducing power consumption, and are used for a variety of purposes.

[0004] The trend toward higher integration of semiconductor devices is accelerating, and this has led to demands for improvements in the surface quality of semiconductor wafers, such as flatness. To meet this demand, improvements have been made to semiconductor wafer polishing equipment and polishing methods.

[0005] For example, in the semiconductor wafer polishing apparatus described in Patent Document 1, a polishing head having a plurality of pressure chambers is used to prevent deformation of the semiconductor wafer due to the polishing pressure.

[0006] Furthermore, in Patent Document 2, in order to make the film thickness distribution of the SOI layer uniform, the radial film thickness distribution of the SOI layer is measured before polishing, focusing on the radial film thickness distribution of the SOI layer rather than the thickness distribution of the entire SOI wafer. Then, in Patent Document 2, the pressure distribution of the pressure control chamber in the polishing head is appropriately controlled based on the measurement results.

[0007] In Patent Document 2, a polishing apparatus having an optical film thickness measurement unit is used to evaluate the film thickness during polishing. This optical film thickness measurement unit has a light source capable of emitting measurement light and a light-receiving sensor capable of receiving reflected light of the measurement light. The incident measurement light from the light source is then collected by a lens via an optical fiber, and the measurement light is made to impinge on the exposed surface of the SOI layer (active layer) of the SOI wafer through a window in the surface plate. The incident light is reflected by the insulating layer, and the light-receiving sensor receives the reflected light of the measurement light via the lens and optical fiber. In this way, the single-sided polishing apparatus of Patent Document 2 measures the film thickness of the SOI layer (active layer) during polishing. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-131920 [Patent Document 2] Patent Publication No. 2021-106193 Summary of the Invention [Problem to be solved by the invention]

[0009] Referring to Figure 1, consider the radial thickness distribution of the SOI layer after polishing to the target thickness. The allowable thickness values ​​for the thickest and thinnest sides of the SOI layer thickness distribution are denoted as a. In recent years, there has been a demand for SOI wafers with SOI layer thickness distributions that fall within a specified thickness range. In other words, the SOI layer thickness distribution after polishing must fall within the range of [target thickness] ± a. With conventional technology, even if the overall thickness distribution after polishing could be made uniform, there were cases where the thickness of some regions within the SOI layer fell outside the thickness range due to insufficient or excessive polishing, leaving room for improvement.

[0010] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for polishing a single side of an SOI wafer, which is capable of keeping the film thickness distribution of the SOI layer within a target film thickness range. [Means for solving the problem]

[0011] The present inventors conducted extensive research to solve the above problems. They concluded that, in the post-polishing SOI layer film thickness distribution, it is better to keep the entire film thickness distribution within a film thickness range, rather than trying to make the average film thickness as close as possible to the target film thickness. Therefore, the present inventors came up with the idea of ​​measuring the SOI layer film thickness distribution before starting polishing to obtain shape data corresponding to the film thickness distribution, and then measuring the SOI layer film thickness during polishing while updating the shape data as needed, and ending polishing when the shape data meets specific conditions. The present inventors discovered that under these polishing conditions, it is possible to keep the SOI layer film thickness distribution within the target film thickness range. The gist of the present invention, which was completed based on the above findings, is as follows:

[0012] (1) A method for polishing a single side of an SOI wafer, comprising: a first step of measuring a film thickness distribution of an SOI layer of the SOI wafer to obtain in-plane shape data; a second step of starting single-sided polishing of the SOI layer; a third step of measuring a thickness of the SOI layer while polishing one side of the SOI layer to obtain a thickness measurement value corresponding to a predetermined radial position; a fourth step of replacing the film thickness value corresponding to the predetermined radial position in the in-plane shape data with the film thickness measurement value measured in the third step to update the in-plane shape data; a fifth step of terminating polishing of the SOI layer when the film thickness values ​​at all positions in the in-plane shape data are equal to or less than the first film thickness; A method for polishing a single side of an SOI wafer, comprising:

[0013] (2) further comprising a sixth step of terminating polishing of the SOI layer when any film thickness value in the in-plane shape data is less than the second film thickness; The method for polishing a single side of an SOI wafer according to (1) above, wherein the second film thickness is thinner than the first film thickness.

[0014] (3) The method for polishing a single side of an SOI wafer according to (1) or (2) above, wherein in the third step, the SOI layer is polished by applying uniform pressure.

[0015] (4) The method for polishing one side of an SOI wafer according to any one of (1) to (3) above, further comprising a pre-polishing step of polishing the SOI layer in advance of the first step.

[0016] (5) The method for polishing a single side of an SOI wafer according to (4) above, wherein in the pre-polishing step, the SOI layer is polished under polishing conditions different from the polishing conditions used in the second step.

[0017] (6) The method for polishing a single side of an SOI wafer according to claim (5), wherein in the pre-polishing step, polishing is performed by applying non-uniform pressure within the surface of the SOI layer. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a method for polishing a single side of an SOI wafer, which is capable of keeping the film thickness distribution of the SOI layer within a target film thickness range. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 10 is a schematic diagram for explaining a film thickness range. [Figure 2] 1 is a flowchart illustrating an embodiment of the present invention. [Figure 3A] FIG. 2 is a schematic diagram illustrating a first step in one embodiment of the present invention. [Figure 3B] FIG. 4 is a schematic diagram illustrating a fourth step in one embodiment of the present invention. [Figure 3C] FIG. 4 is a schematic diagram illustrating a fourth step in one embodiment of the present invention. [Figure 4A] FIG. 10 is a schematic diagram illustrating an example of a fifth step in one embodiment of the present invention. [Figure 4B] FIG. 10 is a schematic diagram illustrating another example of the fifth step in one embodiment of the present invention. [Figure 5A]FIG. 10 is a schematic diagram illustrating an example of a sixth step in one embodiment of the present invention. [Figure 5B] FIG. 10 is a schematic diagram illustrating another example of the sixth step in one embodiment of the present invention. [Figure 6] 1 is a diagram showing a portion of a single-side polishing apparatus for an SOI wafer according to an embodiment of the present invention. [Figure 7] 4 is a graph showing the radial film thickness distribution before and after polishing in Example 1. [Figure 8] 10 is a graph showing the radial film thickness distribution before and after polishing in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0020] A single-sided polishing method for SOI wafers according to one embodiment of the present invention will be described below with reference to the flowchart in FIG. 2. This method for polishing SOI wafers includes at least a first step (step S10), a second step (step S20), a third step (step S30), a fourth step (step S40), and a fifth step (step S50). The method for polishing SOI wafers according to this embodiment preferably further includes a sixth step (step S60), which is also illustrated in FIG. 2. In this embodiment, as shown in the flowchart in FIG. 2, after the fifth step S50, the method proceeds to the sixth step under certain conditions. Details of each step will be described below. As is commonly done in this technical field, in this embodiment, measurement data for the outermost periphery may be excluded from the measurement range of the film thickness distribution to avoid anomalous data.

[0021] <1st process> In the first step S10, the film thickness distribution of the SOI layer of the SOI wafer is measured to obtain in-plane shape data. Hereinafter, for convenience of explanation, the in-plane shape data obtained in this step will be referred to as "initial in-plane shape data." Because the first step S10 does not require measuring the SOI layer's film thickness during polishing, the method for measuring the film thickness distribution is not particularly limited. The film thickness distribution of the entire SOI layer can be measured using any film thickness measurement device, such as a Fourier transform infrared spectroscopy device, separate from the polishing apparatus, to obtain the initial in-plane shape data from the film thickness distribution. Alternatively, the radial film thickness distribution in any one direction can be measured and the measurement results can be used as the initial in-plane shape data. Alternatively, the film thickness distribution can be measured using an optical film thickness measurement mechanism built into the polishing apparatus, as described in Patent Document 2, and the results can be used as the initial in-plane shape data. For example, a data array can be prepared that associates the distance from the wafer center with the film thickness measurement value corresponding to that distance from the measured film thickness distribution. An example of the initial in-plane shape data is shown in Figure 3A. Figure 3A is a schematic graph showing the initial in-plane shape data before polishing of a wafer with a diameter of 200 mm, with film thickness displayed at every 10 mm radial distance from the wafer center. Note that Figure 3A excludes the film thickness at the outermost periphery, and shows the initial in-plane shape data within a range of ±90 mm from the wafer center. Also, although Figure 3A shows the initial in-plane shape data at 19 points, there is no limit to the number of data points. However, film thickness measurements during processing in later processes are taken while polishing is ongoing, and unlike this process, it is difficult to measure without limit. It is preferable to prepare the "initial in-plane shape" from a position that can be measured during polishing.

[0022] <Second process> In the second step S20, polishing of the SOI layer of the SOI wafer is started using a single-sided polishing machine equipped with a measurement mechanism, as exemplified in Patent Document 2, for example.

[0023] <3rd process> In the third step S30 following the second step S20, the thickness of the SOI layer is measured while polishing one side of the SOI layer, obtaining a film thickness measurement value at a predetermined radial position. For example, using the measurement mechanism exemplified in Patent Document 2, such film thickness measurement during polishing can be performed. Specifically, in a polishing apparatus with a measurement window on the surface plate, if an optical fiber of the measurement mechanism is fixed below the surface plate, the SOI layer film thickness measurement is performed when the optical fiber and the measurement window are aligned, and the film thickness value at the measurement window position can be obtained. Note that the distance from the center of the SOI wafer corresponding to the measurement position on the SOI wafer changes with the oscillation of the polishing head. Therefore, the SOI layer film thickness measurement is performed periodically based on the combination of the rotation speed of the surface plate, the oscillation speed of the polishing head, and the oscillation width, and therefore the measurement position of the film thickness value also exhibits periodicity.

[0024] <4th process> In the subsequent fourth step S40, the film thickness value at the radial position corresponding to the predetermined position (i.e., the position measured in the third step S30) in the in-plane shape data is replaced with the film thickness value measured in the third step S30, thereby updating the in-plane shape data. Hereinafter, the in-plane shape data updated in this step S40 will be referred to as the "updated in-plane shape data." Initially, the initial in-plane shape data is updated, and when this step is repeated, the updated in-plane shape data is sequentially updated. Data updating in this step will be specifically explained with reference to the previously referenced Figures 3A, 3B, and 3C. The in-plane shape data in Figure 3B is identical to the initial in-plane shape data, but shows candidates for deletion data to be updated. In the example of Figure 3B, if a film thickness measurement value is obtained at a measurement position 88 mm away from the wafer center, two points corresponding to positions 90 mm from the wafer center are candidates for deletion data to be updated. In Figure 3C, the film thickness value with the oldest measurement time is deleted, and new data is registered instead as the updated film thickness value.

[0025] That is, in the fourth step S40, first, (i) during the polishing process, each time a new film thickness measurement value is acquired, the film thickness value at the position closest to the film thickness measurement value is extracted from the in-plane shape data. (ii) The film thickness value to be deleted corresponding to the extracted film thickness value is determined and deleted. If there are multiple film thickness values ​​at the closest position, the oldest data acquisition time is extracted as the data to be updated, and one piece of data is deleted from the extracted film thickness value. If there are multiple film thickness values ​​at the closest position and the measurement times match, the data with the closest measurement position and closest film thickness value is selected and deleted. Immediately after the start of polishing, situations where film thickness measurement times match are likely to occur. (iii) A new film thickness value is registered at the deleted position in the in-plane shape data. The film thickness value is then associated with the wafer measurement position and measurement time and saved as data. This fourth step S40 is repeated until polishing is completed.

[0026] After being sequentially updated in this manner in the fourth step S40, the updated in-plane shape data approximates the radial film thickness distribution during polishing.

[0027] <5th process> In the fifth step S50, if the film thickness values ​​at all positions in the updated in-plane shape data are equal to or less than the first film thickness, polishing of the SOI layer is terminated (step S50-YES). Hereinafter, for convenience, the first film thickness is referred to as the upper limit of the allowable film thickness. If the film thickness distribution of the SOI wafer is concave, the decision to continue polishing tends to be based on the film thickness value at the periphery (FIG. 4A). If the film thickness distribution is convex, the decision tends to be based on the film thickness value at the center (FIG. 4B). If the film thickness values ​​at all points in the updated in-plane shape data are equal to or less than the upper limit of the allowable film thickness, the SOI layer film thickness distribution is highly likely to be within the film thickness range at this point. Therefore, by terminating polishing at this stage, the SOI layer film thickness distribution can be within the target film thickness range. On the other hand, if any of the film thickness values ​​at all positions in the updated in-plane shape data exceeds the upper limit of the allowable film thickness, the process proceeds to step S60 to determine whether to continue polishing the SOI layer (step S50-NO). For convenience, the first film thickness is referred to as the upper limit of the allowable film thickness, but this is merely an example, and the polishing accuracy may be further improved by finely adjusting the first film thickness above or below the upper limit of the allowable film thickness in consideration of the actual processing accuracy.

[0028] <6th process> In the sixth step S60, if any of the film thickness values ​​in the updated in-plane shape data is less than the second film thickness, polishing of the SOI layer is terminated (step S60-YES). Here, the second film thickness is assumed to be thinner than the first film thickness (the upper limit of the allowable film thickness). Hereinafter, for convenience, the second film thickness is referred to as the lower limit of the allowable film thickness. If any of the film thickness values ​​in the updated in-plane shape data is less than the second film thickness, it means that some film thicknesses within the SOI wafer are outside the target film thickness range. For example, if the SOI layer film thickness distribution is concave, the film thickness at the periphery exceeds the upper limit of the allowable film thickness, but reaches the lower limit of the allowable film thickness at the center, so polishing should be terminated (FIG. 5A). On the other hand, if the SOI layer film thickness distribution is convex, the film thickness at the center exceeds the upper limit of the allowable film thickness, but reaches the lower limit of the allowable film thickness at the periphery, so polishing should be terminated (FIG. 5B). If any of the film thickness values ​​in the in-plane shape data falls below the lower limit of the allowable film thickness, the film thickness at that position will decrease with continued polishing, making it difficult to achieve the target film thickness range. Therefore, in this case, it is preferable to immediately terminate polishing. If any film thickness in the updated in-plane shape data falls below the lower limit of the allowable film thickness, the SOI wafer after polishing may be diverted to a product with a different target film thickness range. Since the minimum removal allowance can be ensured by appropriately determining the second film thickness, other polishing conditions may be applied, such as intensively polishing only the portions exceeding the upper limit of the allowable thickness. If the film thickness at all positions in the updated in-plane shape data is equal to or greater than the lower limit of the allowable film thickness, the process returns to step S30, and polishing and updating of the in-plane shape data continue (step S60-NO).

[0029] According to the single-sided polishing method for SOI wafers of the present embodiment described above, it is possible to detect when the film thickness distribution has fallen within the allowable film thickness range and terminate polishing, thereby keeping the film thickness distribution of the SOI layer within the target film thickness range. As described above, since the updated in-plane shape data corresponds to a film thickness distribution that approximates the radial film thickness distribution during polishing, this embodiment does not completely keep the film thickness distribution of the SOI layer within the target film thickness range. However, compared to the prior art, this embodiment can more reliably keep the film thickness distribution of the SOI layer within the target film thickness range. Furthermore, by appropriately adjusting and setting the first film thickness and the second film thickness based on the target film thickness and its tolerance, it becomes easier to keep the film thickness distribution of the SOI layer within the target film thickness range.

[0030] 2, both the fifth step S50 and the sixth step S60 were performed. However, in the present invention, the sixth step S60 is not essential and may be omitted. In this case, if, in the fifth step S50, any one of the film thickness values ​​at all positions in the updated in-plane shape data exceeds the upper limit of the allowable film thickness, the process returns to step S30, where polishing is continued and the in-plane shape data is updated (step S50-NO). Even in this case, the film thickness distribution of the SOI layer can be more reliably kept within the target film thickness range than in the prior art.

[0031] Furthermore, in the above-described embodiment, an example in which the film thickness distribution before processing is concave or convex is referred to. However, even in the case of an SOI wafer in which the film thickness distribution before processing has a shape that is difficult to correct by polishing, such as an M-shape, the SOI film thickness after polishing can be kept within the upper and lower limits of the allowable film thickness.

[0032] In single-sided polishing of the SOI layer of an SOI wafer, polishing may be performed in multiple stages by changing the polishing conditions. For example, by adjusting the polishing conditions, such as by adjusting the pressure distribution of the polishing head, shape adjustment polishing of the SOI wafer may be performed in the first stage, and then, as the second stage of polishing, film thickness adjustment polishing may be performed to bring the film thickness within the target film thickness range. The single-sided polishing method of an SOI wafer according to the present embodiment described above is preferably applied to the latter stage of polishing. In this case, it is preferable to polish the SOI layer by applying uniform pressure in the second step S20. Uniform pressure makes it easier to uniformize the polishing removal amount, and it is expected that the film thickness distribution of the SOI layer will more reliably be brought within the target film thickness range.

[0033] Therefore, it is preferable to apply the present invention when polishing is performed in multiple stages by changing the polishing conditions. That is, a single-side polishing method for SOI wafers according to another embodiment of the present invention preferably further includes a pre-polishing step (not shown in the flowchart of FIG. 2) in which the SOI layer is polished in advance prior to the first step S10. In this case, it is preferable to measure the film thickness distribution in the first step S10 after completing the pre-polishing step. In this pre-polishing step, it is preferable to polish the SOI layer under polishing conditions different from the polishing conditions used in the second step S20. In particular, to adjust the shape of the SOI wafer, it is preferable to polish the SOI layer by applying non-uniform pressure to the SOI layer in the pre-polishing step. It is particularly preferable to process the SOI wafer in the pre-polishing step non-uniformly by adjusting the pressure conditions of the polishing head, and then to set the polishing conditions used in the second step S20 to uniform processing. This allows the shape of the SOI wafer to be adjusted, and then the film thickness to be adjusted to fall within the target film thickness range.

[0034] Specific embodiments applicable to the present invention will be described below, but the present invention is not limited to these.

[0035] <SOIウェーハ> To explain the SOI wafer to be polished once again, the SOI wafer has a support substrate wafer, an insulating layer provided on one surface of the support substrate wafer, and an SOI layer provided on the surface of the insulating layer. Here, the film thickness distribution of the SOI layer of the SOI wafer before polishing is not particularly limited, but generally, the SOI wafer has a larger variation in the radial direction than in the circumferential direction and increases or decreases uniformly in the radial direction. In addition, the overall thickness of the SOI wafer before polishing is approximately 400 to 1200 μm.

[0036] <<Support substrate wafer>> A single crystal silicon wafer made of single crystal silicon can be used as the support substrate wafer. The single crystal silicon wafer can be a slice of a single crystal silicon ingot grown by the Czochralski method (CZ method) or the floating zone melting method (FZ method) using a wire saw or the like. In addition, carbon and / or nitrogen may be added to the single crystal silicon wafer. Furthermore, arbitrary impurities may be added to make it n-type or p-type.

[0037] <<Insulating layer>> An insulating layer is usually made of a silicon oxide film. However, a film made of other materials may be used as long as it is an insulating material.

[0038] <<SOI layer>> The SOI layer is a single crystal silicon wafer made of single crystal silicon that has been thinned by grinding or the like after being bonded to the support substrate wafer through the insulating layer. The support substrate wafer and the conductivity type (p-type and n-type) may be the same or different.

[0039] (Single-sided polishing apparatus) An example of a single-sided polishing apparatus applicable to the above-described SOI wafer polishing method according to the present invention will now be described with reference to Fig. 6. The object to be polished by the single-sided polishing apparatus for SOI wafers in Fig. 6 is the surface of an SOI layer 13 of an SOI wafer 10, which includes a support substrate wafer 11, an insulating layer 12 provided on one surface of the support substrate wafer 11, and an SOI layer 13 provided on the surface of the insulating layer 12. This single-sided polishing apparatus for SOI wafers (hereinafter referred to as "single-sided polishing apparatus") includes a surface plate 20, a window 21, a polishing pad 30, a polishing head 40, and an optical film thickness measurement unit 60. The optical film thickness measurement unit 60 further includes a light source 61 and a sensor 62, and measures the film thickness distribution of the SOI layer 13 at least in the radial direction. Based on this measurement, the surface of the SOI layer 13 is polished by controlling the pressure distribution applied to the SOI wafer 10 by the polishing head 40. The film thickness distribution can be measured by collecting incident light of measurement light 60L from a light source 61 by a lens 65 via an optical fiber 63, and directing the measurement light 60L to the exposed surface of the SOI layer 13 of the SOI wafer 10 through the window 21 of the surface plate 20.

[0040] Here, the surface plate 20 is equipped with a rotation mechanism that rotates the rotation shaft 25, while the polishing head 40 can also be equipped with a rotation mechanism and a swing mechanism. In such an apparatus, the film thickness is measured when the surface plate rotates and the position of the light source 61 overlaps with the position of the window 21, so the film thickness is measured once per rotation of the surface plate. The polishing head 40 swings within the measurement range of the optical film thickness measurement unit 60, and during one swing cycle, the measurement position of the SOI wafer passes through the center and moves back and forth by the length of its diameter. The SOI layer thickness measured by the optical film thickness measurement unit 60 is recorded and linked to measurement position information obtained by a position sensor built into the polishing head or an external camera 70 shown in FIG. 6.

[0041] The single-side polishing apparatus also includes a polishing head 40, which can hold the SOI wafer 10. The polishing head 40 includes a head main body 41 and a backing plate 43, which is provided at the center of the lower surface of the head main body 41 and can adsorb the other side of the support substrate wafer 11 (i.e., the side opposite the insulating layer 12). The polishing head 40 may also be provided with a retainer ring 47 to prevent the SOI wafer 10 from popping out during polishing. The head main body 41 includes pressure control chambers 45 (45A, 45B, 45C, etc.) that can set a pressure distribution in multiple regions in the radial direction via the backing plate 43. The regions corresponding to 45A to 45C are sometimes referred to as zones 1 to 3, respectively. Note that FIG. 6 illustrates a case in which the pressure control chamber 45 is made up of pressure control chambers 45A, 45B, and 45C arranged symmetrically in the radial direction, but this is merely an example. It is possible to set a pressure distribution if there are two or more pressure control chambers. The pressure control chambers 45A, 45B, and 45C can be separated by partition membranes or the like, and the film thickness distribution of the SOI layer can be made uniform by controlling the pressure in each pressure control chamber with a fluid such as pressurized air.

[0042] It is also possible to apply the method for polishing a single side of an SOI wafer according to the present invention by providing a plurality of windows 21 and lenses 65 and measuring the film thickness of the SOI layer 13 at a plurality of locations.

[0043] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples in any way. [Example]

[0044] Example 1 A single-sided polishing of a 200 mm diameter SOI wafer was performed. The target center thickness of the SOI layer after finish polishing was 1.20 μm, with a tolerance of ±0.20 μm (i.e., upper limit: 1.40 μm, lower limit: 1.00 μm). The single-sided polishing machine used for this polishing corresponds to the machine described with reference to Figure 6. The polishing machine has a light window on the polishing platen and polishing cloth, allowing the thickness of the SOI layer on the SOI wafer to be measured during polishing. The film thickness is measured using a light source fixed below the polishing platen. The white light is measured when the window reaches the light source as the polishing platen rotates. The measurement position of the SOI wafer is also tracked using a position sensor connected to the polishing machine and a sensor built into the head. The SOI layer thickness measured by the polishing machine is recorded along with the SOI wafer position information and measurement time. The initial polishing prior to finish polishing created an uneven radial pressure distribution. Thereafter, prior to the execution of the finish polishing, the film thickness distribution over the entire surface of the SOI layer was measured, and in-plane shape data was set.

[0045] During the finish polishing, the in-plane pressure was set to be uniform, and the radial pressure distribution was set to be uniform. Then, while polishing one side of the SOI layer, the film thickness at the window position in the SOI layer and the radial distance from the center of the SOI wafer were measured using the single-sided polishing machine. Each time a film thickness measurement was obtained, the in-plane shape data obtained immediately before the start of finish polishing was replaced with the film thickness value at the radial position corresponding to the window position, and the in-plane shape data was continuously updated. Polishing was terminated when the maximum film thickness in this in-plane shape data reached the maximum allowable film thickness of 1.40 μm. After polishing was completed, the radial film thickness distribution was measured again. Figure 7 shows the radial film thickness distribution before and after finish polishing. Table 1 also lists the average film thickness, maximum film thickness, minimum film thickness, and film thickness range before and after finish polishing.

[0046] (Comparative Example 1) In Comparative Example 1, the radial film thickness distribution after polishing was calculated by simulation using the results of Example 1. Specifically, an SOI wafer was assumed to have the same radial film thickness distribution as Example 1 after initial polishing, and it was assumed that the polishing stock removal rate by finish polishing would be equivalent to that of Example 1 under the same polishing conditions as Example 1. Then, for this SOI wafer, polishing was continued until the average value of the film thickness at all points in the radial film thickness distribution reached the target center film thickness of 1.20 μm, and the radial film thickness distribution after polishing was calculated. The radial film thickness distribution before and after finish polishing is shown in FIG. 8. The average film thickness, maximum film thickness, minimum film thickness, and film thickness range before and after finish polishing are also shown in Table 1.

[0047] [Table 1]

[0048] The post-processing film thickness distribution of Example 1 had a maximum value of 1.40 μm and a minimum value of 1.01 μm, satisfying the target upper and lower allowable film thickness ranges. On the other hand, the post-processing film thickness distribution of Comparative Example 1 had a maximum value of 1.45 μm and a minimum value of 1.04 μm, and the film thickness in the radius range of 60 mm to 70 mm exceeded the upper limit of the allowable film thickness. The average film thickness value was 1.16 μm for the Example and 1.20 μm for the Comparative Example, and Example 1 had an average film thickness that deviated from the target center film thickness. [Industrial Applicability]

[0049] The present invention provides a method for polishing a single side of an SOI wafer, which can keep the film thickness distribution of the SOI layer within a target film thickness range. This improves yield, promotes efforts to reduce and reuse defective products, and reduces waste. [Explanation of symbols]

[0050] 10 SOI wafers 11 Support substrate wafer 12 Insulating layer 13 SOI layer 20 Surface Plate 21 Window 25 Rotation axis 30 polishing pads 40 Polishing Head 41 Head body 43 Backing Plate 45 Pressurization Control Room 60 Optical film thickness measurement unit 65 Lens 70 External Camera

Claims

1. A method for polishing a single side of an SOI wafer, comprising: a first step of measuring a film thickness distribution of an SOI layer of the SOI wafer to obtain in-plane shape data; a second step of starting single-sided polishing of the SOI layer; a third step of measuring a thickness of the SOI layer while polishing one side of the SOI layer to obtain a thickness measurement value corresponding to a predetermined radial position; a fourth step of replacing the film thickness value corresponding to the predetermined radial position in the in-plane shape data with the film thickness measurement value measured in the third step, thereby updating the in-plane shape data; a fifth step of terminating polishing of the SOI layer when the film thickness values ​​at all positions in the in-plane shape data are equal to or less than the first film thickness; A method for polishing a single side of an SOI wafer, comprising:

2. a sixth step of terminating polishing of the SOI layer when any film thickness value in the in-plane shape data is less than a second film thickness; 2. The method for polishing a single side of an SOI wafer according to claim 1, wherein the second film thickness is thinner than the first film thickness.

3. 2. The method for polishing a single side of an SOI wafer according to claim 1, wherein in the third step, the SOI layer is polished by applying uniform pressure to the SOI layer.

4. 4. The method for polishing a single side of an SOI wafer according to claim 1, further comprising a pre-polishing step of polishing the SOI layer in advance prior to the first step.

5. 5. The method for polishing a single side of an SOI wafer according to claim 4, wherein in the pre-polishing step, the SOI layer is polished under polishing conditions different from polishing conditions used in the second step.

6. 6. The method for polishing a single side of an SOI wafer according to claim 5, wherein the pre-polishing step polishes the SOI layer by applying non-uniform pressure to the surface of the SOI layer.

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