Polishing method and polishing apparatus

Abstract

The objective is to provide a polishing method that can control the flatness of a wafer without being affected by the lifespan of the polishing pad or the polishing characteristics of each polishing head axis. [Solution] A polishing method comprising: holding multiple workpieces with a holding plate; attaching the holding plate holding the workpieces to a polishing head; and using the polishing head to press the workpieces held on the holding plate against a polishing cloth attached to a polishing table with a predetermined pressure, thereby polishing the surface of the workpieces, the method comprising: a polishing step of polishing multiple workpieces; a step after the polishing step in which, while the workpieces are held on the holding plate within the polishing apparatus, the thickness of the workpieces is measured using a non-contact measuring means; and a step of determining the uneven shape of the multiple workpieces across the entire surface of the holding plate based on the measured thickness of the workpieces, and adjusting the pressure distribution of the holding plate by the polishing head according to the determined uneven shape to perform the polishing step of the next workpiece.

Description

Technical Field

[0001] The present invention relates to a polishing method and a polishing apparatus.

Background Art

[0002] For semiconductor wafers such as silicon wafers and compound semiconductor wafers, as the miniaturization of integrated circuits progresses, the flatness specifications have become tighter, and the required level has further increased, and a flatter shape is required. As a means for polishing a semiconductor wafer flat, there is a method in which a semiconductor wafer is attached and held on a holding plate (polishing plate) by adhesion or a template method and then polished.

[0003] Patent Document 1 discloses a polishing method using a polishing apparatus in which a holding plate to which a semiconductor wafer is attached is attached to the lower surface of a polishing head, and a pressure fluid is supplied to a sealed space (air bag) between the holding plate and a flexible thin film (or elastic film) attached to the lower surface of the polishing head, and the pressure is adjusted to uniformly press down the entire surface of the holding plate. The polishing head of this polishing apparatus has a structure in which the entire polishing pressure is applied to the outer peripheral portion of the polishing head when no pressure is applied to the sealed space.

[0004] The polishing method of Patent Document 1 will be described more specifically with reference to FIGS. 10 to 12. As shown in FIG. 10, in order to polish the surface of the wafer W, first, one or more wafers W are attached to a disk-shaped holding plate 108. Next, as shown in FIG. 11, the holding plate 108 to which the wafer W is attached is mounted on the polishing head 102. The polishing head 102 constitutes a polishing shaft 104 together with a polishing shaft 103 that rotates the polishing head 102 around an axis. The wafer W fixed to the holding plate 108 is brought into contact with a polishing cloth 106 attached to the polishing table 105 and polished.

[0005] At that time, by the polishing head 102 placed on the holding plate 108, while pressing the holding plate 108, the contact surfaces of each wafer W with the polishing cloth 106 are polished by the rotational movement of the polishing table 105 and the rotation of the polishing head 102.

[0006] When using a device that supplies pressurized fluid into a sealed space between a polishing head 102, as shown in Figure 11, and a flexible thin film 107 (or elastic film) attached to the lower surface of the polishing head 102, and adjusts the pressure to evenly pressurize the entire surface of the retaining plate 108 (also known as an airbag pressurized type), the polishing head 102 is structured so that when there is no pressure in the sealed space, the entire polishing pressure is applied to the outer circumference of the polishing head 102.

[0007] During actual polishing, the sealed space is set to an appropriate pressure to polish each wafer W uniformly. It is known that fluctuations in the pressure of this sealed space change the pressure distribution on the holding plate 108, thereby changing the polished shape of each wafer W fixed to the holding plate 108. Specifically, as shown in Figure 12, when the pressure in the sealed space is low, the pressure distribution shifts relatively towards the outer periphery of the holding plate 108, and when the pressure in the sealed space is high, the pressure distribution shifts towards the center of the holding plate 108. The wafer shape after polishing changes according to this pressure distribution.

[0008] Patent Document 2 discloses a method in which, before holding the workpiece to be polished with the holding plate, the shape of the holding surface of the holding plate is measured, and the pressure distribution of the polishing head on the holding plate is adjusted according to the shape of the holding surface before polishing the workpiece. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Special Publication No. 7-41534 [Patent Document 2] Japanese Patent Publication No. 2019-000917 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] However, even when polishing with a polishing head whose pressure distribution was appropriately adjusted by a sealed space (airbag) made of a flexible thin film, there was a problem in that the flatness (GBIR) varied from wafer to wafer.

[0011] The causes of the variations were diverse, including the usage time (lifespan) of the polishing pads used for polishing, the characteristics of the polishing head axis, and changes in the equipment environment. It was necessary to periodically monitor the wafer flatness after polishing and adjust the equipment polishing conditions accordingly.

[0012] Furthermore, in order to accurately determine the flatness, the workpiece must be removed from the holding plate and measured using an inspection device. This requires cleaning the wafer after polishing, and once removed from the holding plate, the positional relationship between the wafer's position during polishing and its position within the holding plate becomes unclear. Additionally, time is required to obtain the measurement results. As a result, the equipment had to be stopped or the workpiece had to be processed with a deteriorated flatness (GBIR) while waiting for the results.

[0013] The present invention has been made to solve the above problems and aims to provide a polishing method and polishing apparatus that can control the flatness of a wafer without being affected by the lifespan of the polishing pad and the polishing characteristics of each polishing head axis. [Means for solving the problem]

[0014] The present invention has been made to achieve the above objective, and is a polishing method for polishing the surface of a plurality of workpieces to be polished by holding a plurality of workpieces with a holding plate, attaching the holding plate holding the plurality of workpieces to be polished to a polishing head disposed in a polishing device, and pressing the plurality of workpieces held by the holding plate against a polishing cloth attached to a polishing table with a predetermined pressure using the polishing head, thereby causing relative movement of the workpieces to be polished, comprising: a polishing step of polishing the plurality of workpieces; after the polishing step, in the polishing device, with the plurality of workpieces to be polished still held by the holding plate, measuring the thickness of the workpieces at multiple radial locations on the upper surface of the holding plate using a non-contact measuring means; and based on the measured thickness of the workpieces, measuring the thickness of the workpieces corresponding to the measurement locations on the inner side of the upper surface of the holding plate and the outer circumference of the upper surface of the holding plate The present invention provides a polishing method comprising the steps of: calculating the difference in thickness of the workpiece to be polished corresponding to a measurement position; and determining the uneven shape of the plurality of workpieces to be polished across the entire surface of the holding plate based on the difference in thickness; wherein, in the step of determining the uneven shape, if the uneven shape is determined to be concave, the pressure applied by the polishing head to the outer circumference of the holding plate is made relatively smaller than the pressure applied to the inner surface of the holding plate to perform the next polishing step on the workpiece; if the uneven shape is determined to be convex, the pressure applied by the polishing head to the outer circumference of the holding plate is made relatively larger than the pressure applied to the inner surface of the holding plate to perform the next polishing step on the workpiece; and if the uneven shape is not determined to be concave or convex, the polishing step on the next workpiece is performed without changing the pressure distribution of the pressure applied by the polishing head to the holding plate.

[0015] This polishing method allows for the adjustment of the pressure distribution on the holding plate to match the actual shape of the workpiece measured within the polishing apparatus. This enables control of the flatness of the workpiece in response to changes in its actual shape due to polishing, without being affected by the lifespan of the polishing pad or the polishing characteristics of each polishing head axis. In particular, it improves the flatness of the workpiece and reduces variations in flatness between individual workpieces. Furthermore, the pressure distribution can be appropriately adjusted so that the product output quality (GBIR = flatness) reaches the desired value.

[0016] In this case, the polishing head used has a flexible thin film stretched across the surface that presses against the holding plate, and the pressure distribution on the holding plate can be adjusted by controlling the fluid pressure on the flexible thin film.

[0017] This allows for easy adjustment of the pressure distribution on the holding plate by controlling the internal fluid pressure in the flexible thin film.

[0018] In this case, a non-contact laser interferometer can be used as the non-contact measurement means.

[0019] This allows for more accurate measurement of the thickness of the workpiece W.

[0020] In this process, in measuring the thickness of the workpiece using a non-contact measuring means, measurements are taken at multiple points along the circumference with respect to the center of the holding plate, and only the required thickness data for the workpiece can be extracted from all the measured data.

[0021] This allows for a more accurate calculation of the thickness of the workpiece W.

[0022] At this time, median processing and averaging processing can be applied to the thickness data to obtain representative values ​​for the thickness of the workpiece on the inner and outer sides of the holding plate.

[0023] As a result, thickness data with even higher accuracy can be obtained.

[0024] At this time, a plurality of the workpieces to be polished can be held on the holding plate so as to be point-symmetric with respect to the center of the holding plate.

[0025] As a result, the workpieces to be polished can be arranged on the holding plate in a more balanced manner, and the flatness of the workpieces to be polished can be further improved.

[0026] At this time, 3 to 7 of the workpieces to be polished can be held on the holding plate.

[0027] As a result, the workpieces to be polished can be arranged on the holding plate in an even more balanced manner.

[0028] At this time, before the polishing process of polishing the plurality of workpieces to be polished, there is a step of obtaining the correlation between the usage time of the polishing cloth and the uneven shape after polishing for each polishing axis (usage time - uneven shape correlation) and the correlation between the pressing distribution of the polishing head on the holding plate and the amount of change in the thickness of the workpiece to be polished by polishing (pressing distribution - thickness change amount correlation). Based on the usage time - uneven shape correlation and the pressing distribution - thickness change amount correlation, the pressing distribution of the polishing head on the holding plate can be automatically adjusted for polishing.

[0029] As a result, the flatness of the workpiece to be polished can be controlled with even higher precision.

[0030] The present invention has also been made to achieve the above objective, and provides a polishing apparatus comprising a polishing head equipped with a holding plate for holding a plurality of objects to be polished, and a polishing table to which a polishing cloth for polishing the objects to be polished is attached, wherein the polishing head polishes the surfaces of the objects to be polished by pressing the plurality of objects to be polished held on the holding plate against the polishing cloth with a predetermined pressure and causing relative movement, and further comprising a non-contact measuring device capable of measuring the thickness of the plurality of objects to be polished while the plurality of objects to be polished are held on the holding plate, and a pressure distribution control unit that adjusts the pressure distribution of the polishing head against the holding plate according to the uneven shape of the plurality of objects to be polished over the entire surface of the holding plate.

[0031] With this type of polishing apparatus, by adjusting the pressure distribution on the holding plate according to the actual shape of the workpiece measured within the polishing apparatus, the flatness of the workpiece can be controlled in response to changes in the actual shape of the workpiece due to polishing, without being affected by the lifespan of the polishing pad or the polishing characteristics of each polishing head axis. This makes it possible to improve the flatness of the workpiece in particular and reduce the variation in flatness from one workpiece to another. Furthermore, it is possible to appropriately adjust the pressure distribution so that the output quality of the product (GBIR = flatness) reaches the desired value.

[0032] In this configuration, the polishing head may have a flexible thin film stretched across the surface that presses against the holding plate, and the pressure distribution control unit may be able to adjust the pressure distribution on the holding plate by controlling the fluid pressure on the flexible thin film.

[0033] This allows for easy adjustment of the pressure distribution on the holding plate by controlling the internal fluid pressure in the flexible thin film.

[0034] In this case, the non-contact measuring device may be equipped with a non-contact laser interference displacement meter.

[0035] This allows for more accurate measurement of the thickness of the workpiece W. [Effects of the Invention]

[0036] As described above, according to the polishing method of the present invention, by adjusting the pressure distribution on the holding plate to match the actual shape of the workpiece measured in the polishing apparatus and performing polishing, it is possible to control the flatness of the workpiece in response to changes in the actual shape of the workpiece due to polishing, without being affected by the lifespan of the polishing pad or the polishing characteristics of each polishing head axis. In particular, this makes it possible to improve the flatness of the workpiece and reduce the variation in flatness from one workpiece to another. Furthermore, it is possible to appropriately adjust the pressure distribution so that the output quality of the product (GBIR = flatness) reaches a desired value.

[0037] Furthermore, according to the polishing apparatus of the present invention, by adjusting the pressure distribution on the holding plate according to the actual shape of the workpiece measured within the polishing apparatus and performing polishing, the flatness of the workpiece can be controlled in response to changes in the actual shape of the workpiece due to polishing, without being affected by the lifespan of the polishing pad or the polishing characteristics of each polishing head axis. As a result, the flatness of the workpiece can be improved in particular, and the variation in flatness from one workpiece to another can be reduced. In addition, the pressure distribution can be appropriately adjusted so that the output quality of the product (GBIR = flatness) reaches a desired value. [Brief explanation of the drawing]

[0038] [Figure 1] This is a schematic diagram showing an example of the polishing apparatus of the present invention. [Figure 2] This is an example of a flowchart showing a first embodiment of the polishing method of the present invention. [Figure 3] This is an example of a flowchart illustrating a second embodiment of the polishing method of the present invention. [Figure 4] This is an explanatory diagram of the polishing system according to the present invention ((a) schematic side view of the laser interferometer, (b) plan view of the entire polishing system). [Figure 5] This document describes a method for calculating a representative value of the thickness of a polished workpiece. [Figure 6] This shows the relationship between the TV2 value and GBIR of the polished material. [Figure 7] This shows the airbag adjustment values ​​according to the pad life and polishing axis, so that the TV2 value falls within 0.5 μm. [Figure 8] This shows the variation in TV2 values ​​of the wafers in the comparative example and Example 1. [Figure 9] This graph shows the GBIR frequencies and cumulative frequencies of the wafers measured in Examples 1 and 2 and the Comparative Example. [Figure 10] This is a schematic diagram showing an example of a typical retaining plate. [Figure 11] This is a schematic diagram showing an example of a typical polishing apparatus. [Figure 12] This figure shows the pressure distribution of the retaining plate in accordance with the airbag pressure. [Figure 13] This is a schematic diagram showing the measurement points on the workpiece. [Modes for carrying out the invention]

[0039] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0040] As described above, there was a need for a polishing method and apparatus that could control the flatness of a wafer without being affected by the lifespan of the polishing pad (hereinafter simply referred to as "Pad life") or the polishing characteristics of each polishing head axis.

[0041] Based on Patent Document 2, the present inventors performed wafer polishing by measuring and selecting the shape of the holding plate and adjusting the pressure distribution on the holding plate by the polishing head, but there was a problem in that variations occurred in the flatness of the wafer.

[0042] Investigations revealed that this was due to variations in polishing characteristics caused by the pad life and the polishing head shaft used (resulting in different pressure distribution values ​​on the holding plate from the polishing head).

[0043] Therefore, we conceived the idea of ​​controlling the wafer flatness by measuring the shape of the polished workpiece while it is held in the holding plate within the polishing apparatus, adjusting the pressure distribution of the polishing head against the holding plate based on that shape, and then polishing the next workpiece.

[0044] As a result of diligent study on the above problem, the present inventors have found a polishing method comprising: holding a plurality of workpieces with a holding plate; attaching the holding plate holding the plurality of workpieces to a polishing head installed in a polishing device; and using the polishing head to press the plurality of workpieces held on the holding plate against a polishing cloth attached to a polishing table with a predetermined pressure and move relative to it, thereby polishing the surface of the workpieces, comprising a polishing step of polishing the plurality of workpieces, and after the polishing step, in the polishing device, the plurality of workpieces being held on the holding plate. The process includes the steps of: measuring the thickness of the workpiece to be polished at multiple locations in the radial direction on the upper surface of the retaining plate using a non-contact measuring means; calculating the difference between the thickness of the workpiece corresponding to the measurement location on the inner side of the upper surface of the retaining plate and the thickness of the workpiece corresponding to the measurement location on the outer circumference of the upper surface of the retaining plate, based on the measured thickness of the workpiece to be polished, and determining the uneven shape of the multiple workpieces over the entire surface of the retaining plate based on the difference in thickness, wherein in the step of determining the uneven shape, if the uneven shape is determined to be a concave shape, If the polishing head presses the outer circumference of the holding plate relatively less than the press on the inner surface of the holding plate to perform the next polishing step on the workpiece, and in the step of determining the uneven shape, if the uneven shape is determined to be convex, the polishing head presses the outer circumference of the holding plate relatively more than the press on the inner surface of the holding plate to perform the next polishing step on the workpiece, and in the step of determining the uneven shape, if the uneven shape is not determined to be concave or convex, the polishing head presses the holding plate without changing the pressure distribution to perform the next polishing step This polishing method, which performs the polishing process on the workpiece, adjusts the pressure distribution on the holding plate according to the actual shape of the workpiece measured within the polishing apparatus. This allows for control of the flatness of the workpiece in response to changes in its actual shape due to polishing, without being affected by the lifespan of the polishing pad or the polishing characteristics of each polishing head axis. As a result, it is possible to improve the flatness of the workpiece, reduce variations in flatness between workpieces, and ensure that the output quality of the product (GBIR = flatness) reaches the desired value.We discovered that it is also possible to appropriately adjust the pressure distribution, thus completing the present invention.

[0045] The present inventors have also conducted extensive research on the above problem and have come up with a polishing apparatus comprising a polishing head equipped with a holding plate for holding a plurality of workpieces to be polished, and a polishing table to which an abrasive cloth for polishing the workpieces is attached, wherein the polishing head polishes the surface of the workpieces by pressing the plurality of workpieces held on the holding plate against the abrasive cloth with a predetermined pressure and causing relative movement, wherein the apparatus comprises a non-contact measuring device capable of measuring the thickness of the plurality of workpieces while they are held on the holding plate, and a pressing device that adjusts the pressure distribution of the polishing head against the holding plate according to the uneven shape of the plurality of workpieces over the entire surface of the holding plate. By using a polishing apparatus equipped with a distribution control unit, the pressure distribution on the holding plate is adjusted according to the actual shape of the workpiece measured within the polishing apparatus. This allows for control of the flatness of the workpiece in response to changes in its actual shape due to polishing, without being affected by the lifespan of the polishing pad or the polishing characteristics of each polishing head axis. As a result, it is possible to improve the flatness of the workpiece, reduce variations in flatness between workpieces, and appropriately adjust the pressure distribution so that the output quality of the product (GBIR = flatness) reaches a desired value. This discovery led to the completion of the present invention.

[0046] [Polishing equipment] First, the polishing apparatus of the present invention will be described with reference to Figure 1. The polishing apparatus 1 of the present invention comprises a polishing head 2 equipped with a holding plate 8 that holds a plurality of workpieces (wafers) W, and a polishing table 5 to which a polishing cloth 6 for polishing the wafers W is attached. The polishing head 2, together with a polishing shaft 3 that rotates the polishing head 2 around its axis, constitutes a polishing axis 4. In this polishing apparatus 1 of the present invention, the polishing head 2 presses the plurality of wafers W held on the holding plate 8 against the polishing cloth 6 attached to the polishing table 5 with a predetermined pressure and causes relative movement, thereby polishing the surface of the wafers W.

[0047] Furthermore, the polishing apparatus 1 of the present invention includes a non-contact measuring device 10 that can measure the thickness of multiple workpieces W after polishing while they are held on the holding plate 8, and a pressure distribution control unit 9 that adjusts the pressure distribution of the polishing head 2 on the holding plate 8 according to the uneven shape of the multiple workpieces W across the entire surface of the holding plate 8 (the uneven shape based on the thickness distribution across the multiple workpieces W).

[0048] With such a polishing apparatus 1, the pressure distribution on the holding plate 8 can be adjusted according to the shape of the workpiece W on the holding plate 8, allowing for control of the flatness of the wafer W without being affected by shape variations caused by pad life, etc. This makes it possible to improve the flatness of each wafer W and reduce variations in flatness between wafers W. Furthermore, the pressure distribution can be appropriately adjusted so that the output quality of the product (GBIR = flatness) reaches the desired value according to the purpose.

[0049] Furthermore, by automatically controlling the appropriate pressure distribution according to the shape of the workpiece W using the pressure distribution control unit 9, the need for the operator to manually set the pressure distribution is eliminated, thereby further increasing productivity.

[0050] Furthermore, it is preferable that the polishing head 2 is of the airbag pressurized type and has a flexible thin film 7 stretched across the surface that presses against the holding plate 8, and that the pressure distribution control unit 9 can adjust the pressure distribution on the holding plate 8 by controlling the fluid pressure (airbag pressure) on the flexible thin film 7. By applying fluid pressure to the flexible thin film 7, the flexible thin film 7 expands towards the holding plate 8, so the pressure distribution on the holding plate 8 can be adjusted by adjusting the fluid pressure inside the airbag. With this design, the pressure distribution on the retaining plate 8 can be easily adjusted.

[0051] The non-contact measuring device 10 may be equipped with a non-contact laser interference displacement meter. Figure 4 is an explanatory diagram of the polishing system according to the present invention. Figure 4(a) is a schematic side view of the laser interference displacement meter, and Figure 4(b) is a plan view of the entire polishing system according to the present invention.

[0052] The sensor 50 of the measuring device (laser interferometer) 10 can be, for example, a Chrocodile DW2-1000 manufactured by PRECITEC. As shown in Figure 4(a), the thickness is measured by utilizing the reflection from the front and back surfaces of the workpiece W. Measurement can be performed regardless of the distance between the sensor 50 and the workpiece W.

[0053] As shown in Figure 4(b), the polishing system 51 may include an adhesive machine 52, an adhesive area press section 53, a plate cooling device 54, a five-barrel polishing machine 55, a peeling machine 56, a peeling area 57, a plate stocker 58, and a plate washing machine 59. The thickness of the wafer W can be measured, for example, on the holding plate using an in-line laser interferometer 10 in the five-barrel polishing machine 55. This allows for more accurate measurement of the thickness of the workpiece W.

[0054] Furthermore, the pressure distribution control unit 9 can have the function of automatically measuring the thickness of the workpiece W while it is still held in the holding plate 8 after polishing using a non-contact measuring device 10 within the polishing apparatus 1, and automatically calculating the difference (TV2) between the thickness of the workpiece W on the inside of the holding plate 8 and the thickness of the workpiece W on the outer circumference of the holding plate 8 from the thickness data.

[0055] The pressure distribution control unit 9 can also have the function of automatically controlling the pressure distribution by the polishing head 2 onto the holding plate 8 based on the pressure at which TV2 is within a set value, which is determined in advance for each polishing axis 4 and according to the pad life, and further based on the correlation between the pressure distribution for each shape of the workpiece held on the holding plate 8 and the flatness of the workpiece (wafer W) after polishing. In other words, the system can determine the correlation between usage time and surface shape for each polishing axis, and the correlation between the pressure distribution on the holding plate by the polishing head and the change in thickness of the workpiece due to polishing. Based on the correlation between usage time and surface shape and the correlation between pressure distribution and thickness change, the system can automatically adjust the pressure distribution on the holding plate by the polishing head.

[0056] If the pressure distribution control unit 9 has the automatic control function described above, the operator does not need to manually set the pressure distribution, allowing for more precise control of the flatness of the workpiece W and increasing productivity.

[0057] In this invention, the "inside of the retaining plate 8" refers to the region within R / 2 (half the radius) on the retaining plate 8, and the "outer circumference of the retaining plate 8" refers to the region outside R / 2 on the retaining plate 8.

[0058] [Polishing method] Next, a first embodiment of the polishing method of the present invention will be described with reference to the figures, using the polishing apparatus 1 described above as an example. Figure 2 is an example of a flowchart showing the first embodiment of the polishing method of the present invention.

[0059] The polishing method of the present invention involves holding multiple wafers W in a holding plate 8, attaching the holding plate 8 holding the multiple wafers W to a polishing head 2 installed in a polishing apparatus 1, and using the polishing head 2 to press the multiple wafers W held in the holding plate 8 against a polishing cloth 6 attached to a polishing table 5 with a predetermined pressure and move them relative to each other, thereby polishing the surface of the wafers W. After the polishing of the wafers W is completed, the holding plate 8 can be removed from the polishing head 2, and another holding plate 8 with the next wafer W to be polished attached can be attached to the polishing head 2 to perform the next polishing.

[0060] Furthermore, as shown in Figure 2, the polishing method of the present invention includes a polishing step S1 in which a plurality of workpieces W are polished; a step S2 in which, after the polishing step, with the plurality of workpieces W held on the holding plate 8 inside the polishing apparatus 1, the thickness of the workpieces W at multiple radial locations on the upper surface of the holding plate 8 is measured using a non-contact measuring means 10; and a step S3 in which, based on the measured thickness of the workpieces W, the difference between the thickness of the workpieces W corresponding to the measurement locations on the inner side of the upper surface of the holding plate 8 and the thickness of the workpieces W corresponding to the measurement locations on the outer periphery of the upper surface of the holding plate 8 is calculated, and the uneven shape of the plurality of workpieces W across the entire surface on the holding plate 8 is determined based on the difference in thickness.

[0061] It is preferable to hold multiple wafers W on the holding plate 8 so that they are positioned point-symmetrically with respect to the center of the holding plate 8 (three or more are preferable, and seven are more preferable). This allows the workpiece W to be polished to be evenly positioned on the holding plate 8, thereby improving the flatness of the workpiece W.

[0062] (polishing process) In the present invention, a single-sided polishing device is preferably used as the polishing device 1.

[0063] The workpiece W to be polished is held and fixed in place by the holding plate 8. The method of fixing the workpiece W to the holding plate 8 is not particularly limited, but examples include adhesive methods and template methods.

[0064] A holding plate 8, which holds multiple wafers W, is mounted on a polishing head 2 installed in a polishing apparatus 1. The polishing head 2 then presses the multiple wafers W held on the holding plate 8 against a polishing cloth 6 attached to a polishing table 5 with a predetermined pressure and causes relative movement, thereby polishing the surface of the wafers W.

[0065] It is preferable to use a polishing head 2 that has a flexible thin film 7 stretched across the surface that presses against the holding plate 8, and to adjust the pressure distribution on the holding plate 8 by controlling the fluid pressure on the flexible thin film 7. This allows for easy adjustment of the pressure distribution on the holding plate 8 by controlling the internal fluid pressure on the flexible thin film 7.

[0066] (A process of measuring the thickness of the workpiece using a non-contact measuring device.) After the polishing process, within the polishing apparatus 1, with multiple workpieces W held on the holding plate 8, the thickness of the workpieces W at multiple radial points on the upper surface of the holding plate 8 is measured using a non-contact measuring means 10. The accuracy increases with the number of radial measurement points, but from the viewpoint of data processing speed, the uneven shape can be determined with at least two measurements.

[0067] In this case, the measurement points for the thickness of the workpiece W are preferably those attached at equal intervals along a circle centered on the center of the holding plate 8, and the points corresponding to the inner and outer sides of the holding plate 8 are measured individually, excluding the workpiece W attached to the center of the holding plate 8.

[0068] A non-contact laser interferometer can be used as the non-contact measurement means 10. This allows for more accurate measurement of the thickness of the workpiece W.

[0069] (Step to determine the uneven shape of the workpiece to be polished) Based on the measured thickness of the workpiece W, the difference between the thickness of the workpiece W corresponding to the measurement position on the inner side of the upper surface of the holding plate 8 and the thickness of the workpiece W corresponding to the measurement position on the outer side of the upper surface of the holding plate 8 is calculated. Based on this difference in thickness, a TV2 value is calculated as the unevenness value on the holding plate, and based on this TV2 value, the unevenness shape of the multiple workpieces W across the entire surface of the holding plate 8 is determined.

[0070] While there are no particular limitations on the criteria for determination, a TV2 value greater than +0.5 μm can be determined to be convex, and a TV2 value less than -0.5 μm can be determined to be concave. If the TV2 value is between +0.5 μm and -0.5 μm, it can be determined to be neither concave nor convex.

[0071] As shown in S4 of Figure 2, in the step of determining the uneven shape, if the uneven shape is determined to be concave, the pressure applied by the polishing head 2 to the outer circumference of the holding plate 8 is made relatively smaller compared to the pressure applied to the inside of the holding plate 8, and the polishing step (S5) of the next workpiece W is performed. In the step of determining the uneven shape, if the uneven shape is determined to be convex, the pressure applied by the polishing head 2 to the outer circumference of the holding plate 8 is made relatively larger compared to the pressure applied to the inside of the holding plate 8, and the polishing step of the next workpiece W is performed. In the step of determining the uneven shape, if the uneven shape is not determined to be concave or convex, the polishing step of the next workpiece W is performed without changing the pressure distribution of the pressure applied by the polishing head 2 to the holding plate 8.

[0072] Since the obtained thickness data contains a lot of noise (unnecessary data), in the process of measuring the thickness of the workpiece using a non-contact measuring means, it is preferable to measure multiple points in the radial direction on the circumference with the center of the holding plate 8 as the reference point, and to extract only the thickness data required for the workpiece W from all the measured data. This allows for a more accurate calculation of the thickness of the workpiece W.

[0073] At this time, it is preferable to select data for the workpiece W to be polished and calculate a representative value for its thickness. Specifically, the obtained thickness data can be subjected to median processing and averaging processing to obtain a representative value for the thickness of the workpiece on the inner and outer sides of the holding plate 8.

[0074] The measurement position at this time can be, for example, when using seven wafers W, within a 5 mm width range on the circumference of the six wafers excluding the wafer W attached to the center of the holding plate 8, as shown in Figure 13, indicated by the dotted line.

[0075] Specifically, for example, the processing shown in Figure 5 can be applied. As shown in Figure 5(a), in the post-polishing stage, the wafer needs to be kept moist to prevent drying after polishing, and many noises are present, such as sensor protective covers and water films. First, only the data that is thought to correspond to the wafer thickness is extracted (Figure 5(b)).

[0076] Next, data from portion A of the wafer is extracted (Figure 5(c)). In the example in Figure 5, approximately 2000 data points were extracted. Subsequently, median values ​​of 125 data points are extracted from the raw data (moving extraction), and median processing and averaging are performed to calculate the average value of the 125 median values ​​(moving average), and the central thickness of the measurement area is taken as the measured value (Figure 5(d)). In other words, one representative thickness data point is obtained from 2000 data points. This allows us to obtain even more accurate thickness data.

[0077] In this way, using representative thickness data from the inner and outer edges of the holding plate 8 for the surrounding wafers W, excluding the wafer W attached in the center, the TV2 value (inner representative thickness data - outer representative thickness data) of the wafer W (workpiece) is determined, and further, the uneven shape across the entire surface of the holding plate 8 is determined from the thickness data of multiple workpieces W.

[0078] According to the polishing method described above, by adjusting the pressure distribution on the holding plate 8 to match the actual shape of the workpiece W measured within the polishing apparatus 1, the flatness of the workpiece W can be controlled in response to changes in its actual shape due to polishing, without being affected by the pad life or the polishing characteristics of each polishing head axis 4. This makes it possible to improve the flatness of the workpiece W, and to reduce the variation in flatness between individual workpieces W. Furthermore, the pressure distribution can be appropriately adjusted so that the output quality of the product (GBIR = flatness) reaches the desired value.

[0079] Furthermore, by automatically controlling the appropriate pressure distribution according to the shape of the workpiece W, the need for operators to manually set the pressure distribution is eliminated, thereby further increasing productivity.

[0080] Furthermore, for example, in the processing of silicon single-crystal wafers, primary, secondary, and finish polishing are typically performed. While the present invention is particularly effective in primary polishing, it may also be applied to secondary and finish polishing.

[0081] Furthermore, the workpiece W can be a wafer made entirely of silicon single crystal, or a wafer in which at least the surface to be polished is silicon single crystal (for example, an SOI wafer). In addition, the present invention can be applied to wafers other than silicon single crystals, as long as they can be fixed to a holding plate and polished.

[0082] In the polishing method of the present invention, conditions such as the composition of the polishing slurry, temperature, polishing allowance, and polishing speed are not particularly limited.

[0083] Next, a second embodiment of the polishing method of the present invention will be described with reference to Figure 3, using the polishing apparatus 1 described above as an example. Figure 3 is an example of a flowchart showing the second embodiment of the polishing method of the present invention.

[0084] In a second embodiment of the polishing method of the present invention, before the polishing step of polishing multiple workpieces W, there is a step S10 to determine the correlation between the Pad life and the uneven shape of the workpiece W after polishing, and the correlation between the pressure distribution on the holding plate 8 by the polishing head 2 and the amount of change in thickness of the workpiece W due to polishing. Based on the correlation between the usage time and the uneven shape and the correlation between the pressure distribution and the amount of change in thickness, the pressure distribution on the holding plate 8 by the polishing head 2 can be automatically adjusted for polishing.

[0085] To explain this in more detail, before the polishing process in which the workpiece W is polished, the correlation between the pad life and the uneven shape of the workpiece W after polishing is determined experimentally for each polishing shaft 4 used. Based on this correlation, the correlation between the pad life and the pressure distribution on the holding plate 8 by the polishing head 2 is determined so that a TV2 value of less than or equal to the set TV2 value is obtained.

[0086] Furthermore, the correlation between the pressure distribution on the holding plate 8 by the polishing head 2 and the change in the thickness of the workpiece W due to polishing is determined, and a "pressure distribution adjustment value table" is created based on these obtained correlations (S20).

[0087] After the polishing process and the process of determining the uneven shape of the workpiece W are completed, the Pad life of the polishing cloth 6 is checked (S30), and the pressure distribution adjustment value corresponding to the polishing shaft 2 and Pad life is calculated (S40). Then, in the process of determining the uneven shape (S3), if the uneven shape is determined to be concave (S4), the pressure applied by the polishing head 2 to the outer circumference of the holding plate 8 is made relatively smaller than the pressure applied to the inside of the holding plate 8, and the polishing process of the next workpiece W is performed (S5). In the process of determining the uneven shape, if the uneven shape is determined to be convex, the pressure applied by the polishing head 2 to the outer circumference of the holding plate 8 is made relatively larger than the pressure applied to the inside of the holding plate 8, and the polishing process of the next workpiece W is performed. In the process of determining the uneven shape, if the uneven shape is not determined to be concave or convex, the polishing process of the next workpiece W is performed without changing the pressure distribution of the pressure applied by the polishing head 2 to the holding plate 8. This allows for more precise control over the flatness of the workpiece being polished. [Examples]

[0088] The present invention will be described in detail below with reference to examples, but this is not intended to limit the present invention.

[0089] (Example 1) The silicon wafers were polished as follows. Here, the polishing was carried out under conditions that minimized GBIR.

[0090] <Basic polishing conditions, flatness measurement conditions> Seven polishing wafers, each 200 mm in diameter, were attached to a single holding plate using an adhesive method. Equipment: Single side polishing equipment Polishing head: Airbag pressurized type Amount of protrusion of the retaining plate: average value Primary polishing cloth: non-woven fabric Polishing slurry: Alkaline colloidal silica Polishing allowance: approximately 5-10 μm Polishing method: Primary + Secondary + Tertiary (Of these, only the primary polishing was performed using the polishing method of the present invention) In-machine polished object measuring device: PRECITEC Chrocodile DW2-1000 Flatness measuring device: KLA-Tencor ADE9800

[0091] <Prior confirmation> In adjusting the airbag pressure of the polishing head, we investigated how the GBIR value of the silicon wafer held in the holding plate changes for every 0.5 kPa change in airbag pressure. The results are shown in Figure 6. As can be seen from the graph in Figure 6, with the polishing head used here, it was found that increasing the airbag pressure resulted in the pressure at the center of the holding plate becoming relatively larger compared to the vicinity of the outer edge.

[0092] Furthermore, the pad life and standard airbag pressure for each polishing head axis that yield a TV2 value of 0.5 μm or less were determined. The results are shown in Figure 7. It was found that the airbag pressure value needs to be set differently for each polishing head axis and changes according to the pad life. In the embodiment of the present invention, TV2 = ±0.5 μm is used as the reference value for determining unevenness, and the airbag pressure is adjusted so that the TV2 value falls within ±0.5 μm.

[0093] <Main polishing> By applying the airbag values ​​determined through prior verification, and automatically determining the wafer's TV2 value within the polishing device every hour of polishing (approximately every 12 polishing processes), the device automatically applied the Pad Life and the airbag values ​​determined for each polishing head axis according to the unevenness, thereby adjusting the pressure distribution on the inner and outer edges of the polishing plate by the polishing head, and performing the polishing. After polishing N=78,000 sheets, the GBIR average value was 0.550 μm.

[0094] (Example 2) In Example 2, the TV2 of the wafer was automatically determined for each polishing process and automatically applied to the airbag pressure, similar to Example 1.

[0095] <Main polishing> The airbag values ​​obtained through the pre-verification in Example 1 were applied, and, similar to Example 1, the TV2 of the wafer was determined in the polishing apparatus for each polishing step. Polishing was then performed by applying the Pad Life and the airbag values ​​obtained for each polishing head axis each time. After polishing N=26,920 wafers, the GBIR average value was 0.514 μm.

[0096] (Comparative example) In the comparative example, the TV2 of the wafer was measured every 8 hours of processing (approximately every 96 polishing cycles) on the holding plate, and the airbag pressure was adjusted accordingly. However, the pad life and adjustments for each polishing head axis were not performed. Furthermore, since the measurement was performed using a contact-type measuring instrument with the workpiece still attached to the holding plate to determine TV2, the practical limit for measurement frequency was every 8 hours of processing.

[0097] <Main polishing> Polishing was performed using the airbag values ​​obtained through the preliminary check in Example 1. After polishing N=117,512 sheets, the GBIR average value was 0.635 μm.

[0098] Table 1 summarizes the results of the implementation in Examples 1 and 2 and the comparative example.

[0099] [Table 1]

[0100] In Examples 1 and 2, a non-contact measuring device was used, allowing for automatic measurement of the thickness of the workpiece. The pressure distribution from the polishing head to the holding plate was adjusted according to the shape of the workpiece, enabling the selection of an optimal pressure distribution and improving flatness. In contrast, in the comparative example, a contact-type measuring device was used to manually measure the thickness of the workpiece, resulting in a reduced measurement frequency compared to Examples 1 and 2. The GBIR average value increased by approximately 0.12 μm compared to Examples 1 and 2, resulting in inferior flatness. This demonstrates that increasing the frequency of airbag adjustment improves wafer flatness according to the polishing method of the present invention.

[0101] Furthermore, Figure 8 shows the results of calculating the degree of variation in TV2 values ​​for each wafer after polishing in the comparative example and Example 1. The standard deviation σ of TV2 for the comparative example was 0.40 μm, and the standard deviation σ of TV2 for Example 1 was 0.34 μm. It can be seen that, compared to the comparative example, the polishing method of Example 1 made it possible to automatically adjust the airbag value, resulting in an improved adjustment frequency and a smaller variation in flatness.

[0102] The polishing methods of Examples 1 and 2 and the Comparative Example were repeated, and the GBIR of each wafer after polishing was measured. The GBIR frequency and cumulative frequency were calculated. The results are shown in Figure 9. Figure 9 also shows that the polishing method of the Examples improves the flatness of the wafer after polishing compared to the Comparative Example.

[0103] As described above, according to the embodiments of the present invention, the flatness of each workpiece can be improved, and the variation in flatness among workpieces can be reduced. Furthermore, the pressure distribution can be adjusted so that the GBIR is a desired value (the minimum GBIR value in the embodiments). In addition, by automatically controlling the appropriate pressure distribution according to the shape of the workpiece, the need for operators to manually set the pressure distribution is eliminated, thereby increasing productivity.

[0104] This specification includes the following embodiments: [1]: A polishing method comprising: holding a plurality of workpieces with a holding plate; attaching the holding plate holding the plurality of workpieces to a polishing head disposed in a polishing device; and using the polishing head to press the plurality of workpieces held by the holding plate against a polishing cloth attached to a polishing table with a predetermined pressure and move relative to the workpieces, the polishing method comprising: a polishing step of polishing the plurality of workpieces; after the polishing step, within the polishing device, with the plurality of workpieces held by the holding plate, measuring the thickness of the workpieces at multiple radial locations on the upper surface of the holding plate using a non-contact measuring means; and based on the measured thickness of the workpieces, measuring the thickness of the workpieces corresponding to the measurement locations on the inner side of the upper surface of the holding plate and the thickness of the workpieces corresponding to the measurement locations on the outer circumference of the upper surface of the holding plate A polishing method comprising the steps of calculating the difference in thickness of the workpieces to be polished and determining the uneven shape of the plurality of workpieces over the entire surface of the holding plate based on the difference in thickness, wherein in the step of determining the uneven shape, if the uneven shape is determined to be concave, the pressure applied by the polishing head to the outer periphery of the holding plate is made relatively smaller than the pressure applied to the inner side of the holding plate to perform the next polishing step of the workpiece, if the uneven shape is determined to be convex in the step of determining the uneven shape, the pressure applied by the polishing head to the outer periphery of the holding plate is made relatively larger than the pressure applied to the inner side of the holding plate to perform the next polishing step of the workpiece, and if the uneven shape is not determined to be concave or convex in the step of determining the uneven shape, the polishing step of the workpiece is performed without changing the pressure distribution of the pressure applied by the polishing head to the holding plate. [2]: The polishing method of [1], wherein the polishing head has a flexible thin film stretched over the surface that presses against the holding plate, and the polishing method of [1] is further comprising adjusting the pressure distribution on the holding plate by controlling the fluid pressure on the flexible thin film. [3]: The polishing method according to [1] or [2] above, comprising using a non-contact laser interferometer as the non-contact measuring means. [4]: The polishing method according to [1], [2], or [3] above, which includes a step of measuring the thickness of the workpiece using a non-contact measuring means, wherein multiple measurements are taken at multiple points on the circumference with respect to the center of the holding plate, and only the thickness data required for the workpiece is extracted from all the measured data. [5]: The polishing method of [4] above, which includes applying median treatment and averaging treatment to the thickness data to obtain representative values ​​of the thickness of the workpiece on the inner and outer sides of the retaining plate. [6]: The polishing method according to [1], [2], [3], [4], or [5], further comprising holding a plurality of the objects to be polished on the holding plate so as to be point-symmetric with respect to the center of the holding plate. [7]: The polishing method according to [1], [2], [3], [4], [5], or [6] above, further comprising holding 3 to 7 of the objects to be polished on the holding plate. [8]: The polishing method according to [1], [2], [3], [4], [5], [6], or [7] above, which includes a step of determining the correlation between the usage time of the polishing cloth and the uneven shape after polishing for each polishing axis, and the correlation between the pressure distribution by the polishing head onto the holding plate and the amount of change in the thickness of the workpiece due to polishing, before the polishing step of polishing the plurality of workpieces. Based on the correlation between the usage time and the uneven shape and the correlation between the pressure distribution and the amount of change in thickness, the polishing method includes automatically adjusting the pressure distribution by the polishing head onto the holding plate to perform the polishing. [9]: A polishing apparatus comprising a polishing head fitted with a holding plate for holding a plurality of objects to be polished, and a polishing table to which a polishing cloth for polishing the objects to be polished is attached, wherein the polishing head polishes the surfaces of the objects to be polished by pressing the plurality of objects held on the holding plate against the polishing cloth with a predetermined pressure and causing relative movement, the apparatus comprising a non-contact measuring device capable of measuring the thickness of the plurality of objects to be polished while the plurality of objects to be polished are held on the holding plate, and a pressure distribution control unit that adjusts the pressure distribution of the polishing head against the holding plate according to the uneven shape of the plurality of objects to be polished over the entire surface of the holding plate.

[10] : The polishing apparatus according to [9], wherein the polishing head has a flexible thin film stretched over the surface that presses against the holding plate, and the pressure distribution control unit can adjust the pressure distribution to the holding plate by controlling the fluid pressure on the flexible thin film.

[11] : The polishing apparatus according to [9] or

[10] above, wherein the non-contact measuring device is equipped with a non-contact laser interferometer.

[0105] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention. [Explanation of Symbols]

[0106] 1... Polishing device, 2, 102... Polishing head, 3, 103... Polishing shaft, 4, 104… Polishing shaft, 5, 105… Polishing table, 6, 106… Polishing cloth, 7, 107... Flexible thin film, 8, 108... Holding plate, 9... Pressure distribution control unit, 50...Sensor, 51...Polishing system, 52...Bonding machine, 53...Adhesive area pressing section, 54...Plate cooling device, 55...5-stage polishing machine, 56...Peeling machine, 57...Peeling area, 58...Plate stocker, 59…Plate washing machine, W... The object being polished (wafer).

Claims

1. A polishing method comprising: holding multiple workpieces with a holding plate; attaching the holding plate holding the multiple workpieces to a polishing device to a polishing head installed in a polishing device; and using the polishing head to press the multiple workpieces held by the holding plate against a polishing cloth attached to a polishing table with a predetermined pressure and move relative to it, thereby polishing the surface of the workpieces, A polishing step for polishing the aforementioned multiple workpieces, After the polishing step, while the plurality of workpieces to be polished are held on the holding plate within the polishing apparatus, the thickness of the workpieces at multiple radial locations on the upper surface of the holding plate is measured using a non-contact measuring means. The process includes the steps of calculating the difference between the thickness of the workpiece corresponding to the measurement position on the inner side of the upper surface of the holding plate and the thickness of the workpiece corresponding to the measurement position on the outer circumference of the upper surface of the holding plate, based on the measured thickness of the workpiece, and determining the uneven shape of the plurality of workpieces over the entire surface of the holding plate based on the difference in thickness, based on the measurement difference of the measurement position on the upper surface of the holding plate, In the step of determining the uneven shape, if the uneven shape is determined to be concave, the pressure applied by the polishing head to the outer circumference of the holding plate is made relatively smaller than the pressure applied to the inner side of the holding plate, and the next polishing step of the workpiece is performed. In the step of determining the uneven shape, if the uneven shape is determined to be a convex shape, the pressing of the polishing head against the outer circumference of the holding plate is made relatively larger than the pressing on the inner side of the holding plate, and the next polishing step of the workpiece is performed. In the step of determining the uneven shape, if the uneven shape is not determined to be either concave or convex, the polishing method is characterized in that the next polishing step of the workpiece is performed without changing the pressure distribution of the polishing head pressing against the holding plate.

2. The polishing method according to claim 1, characterized in that the polishing head has a flexible thin film stretched over the surface that presses against the holding plate, and the pressure distribution on the holding plate is adjusted by controlling the fluid pressure on the flexible thin film.

3. The polishing method according to claim 1, characterized in that a non-contact laser interferometer is used as the non-contact measurement means.

4. The polishing method according to claim 1, characterized in that, in the step of measuring the thickness of the workpiece to be polished using a non-contact measuring means, measurements are taken at multiple points on the circumference with respect to the center of the holding plate, and only the required thickness data of the workpiece to be polished is extracted from all the measured data.

5. The polishing method according to claim 4, characterized in that median processing and averaging processing are applied to the thickness data to obtain representative values ​​for the thickness of the workpiece on the inner and outer sides of the holding plate.

6. The polishing method according to claim 1, characterized in that a plurality of the objects to be polished are held on the holding plate so as to be point-symmetric with respect to the center of the holding plate.

7. The polishing method according to claim 6, characterized in that three to seven of the objects to be polished are held on the holding plate.

8. The polishing method according to any one of claims 1 to 7, characterized in that, before the polishing step of polishing the plurality of works to be polished, the step is to determine the correlation between the usage time of the polishing cloth and the uneven shape after polishing for each polishing axis, and the correlation between the pressure distribution by the polishing head onto the holding plate and the amount of change in the thickness of the works to be polished due to polishing, and the polishing method is characterized in that the pressure distribution by the polishing head onto the holding plate is automatically adjusted and polished based on the correlation between the usage time and the uneven shape and the correlation between the pressure distribution and the amount of change in thickness.

9. A polishing apparatus comprising a polishing head fitted with a holding plate for holding multiple workpieces to be polished, and a polishing table to which an abrasive cloth for polishing the workpieces is attached, wherein the polishing head polishes the surfaces of the workpieces by pressing the multiple workpieces held on the holding plate against the abrasive cloth with a predetermined pressure and causing relative movement, A non-contact measuring device capable of measuring the thickness of the multiple workpieces while the multiple workpieces are held on the holding plate, A polishing apparatus characterized by having a pressure distribution control unit that adjusts the pressure distribution of the polishing head against the holding plate according to the uneven shape of the plurality of objects to be polished that cover the entire surface of the holding plate.

10. The polishing apparatus according to claim 9, characterized in that the polishing head has a flexible thin film stretched over the surface that presses against the holding plate, and the pressure distribution control unit can adjust the pressure distribution to the holding plate by controlling the fluid pressure on the flexible thin film.

11. The polishing apparatus according to claim 9 or 10, characterized in that the non-contact measuring device is equipped with a non-contact laser interferometer.

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