Polishing apparatus and method

Abstract

To provide a polishing device capable of accurately polishing a workpiece.SOLUTION: A CMP device 1 is a polishing device that pushes a workpiece W held on a polishing head 10 against a polishing pad 5 on a platen 2, and polishes the workpiece W. The CMP device includes a chuck 19 capable of holding the workpiece W, a thickness sensor 7 for measuring in-plane thickness variation in the workpiece W, second air bags 16A to 16D which are aligned in the circumferential direction of the chuck 19, are expanded by air, and can press a part of the workpiece W toward the polishing pad 5, and a controller 6 which previously stores a polishing rate when the workpiece W corresponding to thickness variation in the circumferential direction of the workpiece W is polished in an unbalanced load state, and can control the pressure of the air supplied to the second air bags 16A to 16D, wherein the controller 6 calls the polishing rate corresponding to the in-plane thickness variation of the workpiece W acquired by the thickness sensor 7, controls the air supplied to each of the second air bags 16A to 16D so as to achieve the polishing rate, and polishes the workpiece W in the unbalanced load state.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a polishing apparatus and a polishing method for polishing a workpiece. [Background technology]

[0002] 2. Description of the Related Art In the field of semiconductor manufacturing, CMP devices are known that polish and flatten silicon wafers and the like (hereinafter referred to as "workpieces").

[0003] The polishing apparatus described in Patent Document 1 is a polishing apparatus that applies chemical mechanical polishing (CMP) technology. This CMP apparatus polishes a workpiece by pressing the workpiece, which is attached to a polishing head, against a polishing pad. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-159385 Summary of the Invention [Problem to be solved by the invention]

[0005] In back-side reference polishing, in which the back side of the workpiece is held in the chuck of the polishing head and the front side of the workpiece is pressed against the polishing pad to polish it, the pressure distribution acting on the workpiece is set to be approximately uniform in the circumferential direction of the workpiece. This can result in tilting of the workpiece shape after polishing due to the crystal orientation of the workpiece, or in workpieces with initial film thicknesses that are not uniform in the circumferential direction being unable to be polished to a uniform thickness.

[0006] Furthermore, the initial film thickness of the workpiece before polishing differs for each workpiece, and there was a problem that it was complicated to set the optimum polishing rate, etc. for each workpiece in accordance with the initial film thickness in order to polish each workpiece flat.

[0007] Therefore, a technical problem arises that must be solved in order to polish a workpiece with high precision, and an object of the present invention is to solve this problem. [Means for solving the problem]

[0008] In order to achieve the above object, a polishing apparatus according to the present invention is a polishing apparatus that polishes a workpiece held by a polishing head by pressing it against a polishing pad on a platen, and includes a chuck that can hold the workpiece, a thickness sensor that measures thickness variations within the surface of the workpiece, a plurality of partial pressing units that are arranged in parallel along the circumferential direction of the chuck and expand with air to press a portion of the workpiece against the polishing pad, and a controller that pre-stores a polishing rate corresponding to the thickness variations within the surface of the workpiece when polishing the workpiece under an unbalanced load condition and is capable of adjusting the pressure of air supplied to each partial pressing unit, wherein the controller retrieves the polishing rate corresponding to the circumferential thickness variation of the workpiece obtained by the thickness sensor, and adjusts the air supplied to each partial pressing unit to achieve the polishing rate, thereby polishing the workpiece under an unbalanced load condition.

[0009] According to this configuration, by expanding and contracting each of the multiple partial pressure applying sections, the pressure distribution acting on the workpiece can be freely adjusted in the circumferential direction of the workpiece. Therefore, the pressure distribution in the circumferential direction of the workpiece can be adjusted taking into account the crystal orientation and uneven initial film thickness of the workpiece, and different polishing pressures can be applied to the workpiece within the polishing surface, thereby enabling the workpiece to be polished flat with high precision.

[0010] Furthermore, the controller calls up a polishing rate that reduces the thickness variation within the workpiece surface measured by the thickness sensor, and the multiple partial pressing parts polish the workpiece under an uneven load at that polishing rate, so that the workpiece can be polished flat with high precision regardless of the workpiece's initial film thickness.

[0011] Furthermore, in order to achieve the above-mentioned object, a polishing method according to the present invention is a polishing method using a polishing apparatus that polishes a workpiece held by a polishing head by pressing it against a polishing pad on a platen, the polishing apparatus comprising: a chuck capable of holding the workpiece; a thickness sensor that measures thickness variations within the surface of the workpiece; a plurality of partial pressing units that are arranged in parallel along the circumferential direction of the chuck and expand with air to press parts of the workpiece against the polishing pad; and a controller that stores in advance a polishing rate when polishing the workpiece under an unbalanced load condition corresponding to the circumferential thickness variation of the workpiece and is capable of adjusting the pressure of air supplied to each partial pressing unit, the polishing method including the steps of: using the thickness sensor to measure thickness variations within the surface of the workpiece; and using the controller to retrieve the polishing rate corresponding to the circumferential thickness variation of the workpiece obtained by the thickness sensor, and adjusting the air supplied to each partial pressing unit so as to achieve the polishing rate, thereby polishing the workpiece under an unbalanced load condition.

[0012] According to this configuration, by expanding and contracting each of the multiple partial pressure applying sections, the pressure distribution acting on the workpiece can be freely adjusted in the circumferential direction of the workpiece. Therefore, the pressure distribution in the circumferential direction of the workpiece can be adjusted taking into account the crystal orientation and uneven initial film thickness of the workpiece, and different polishing pressures can be applied to the workpiece within the polishing surface, thereby enabling the workpiece to be polished flat with high precision.

[0013] Furthermore, the controller calls up a polishing rate that reduces the circumferential thickness variation of the workpiece measured by the thickness sensor, and the multiple partial pressing parts polish the workpiece under an unbalanced load at that polishing rate, so that the workpiece can be polished flat with high precision regardless of the workpiece's initial film thickness. [Effects of the Invention]

[0014] The present invention can polish a workpiece to a flat surface with high precision. [Brief explanation of the drawings]

[0015] [Figure 1]1 is a perspective view schematically showing a CMP apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a vertical cross-sectional view schematically showing a main part of the polishing head. [Figure 3] FIG. 3 is a plan view showing the positional relationship between a first airbag and a second airbag. [Figure 4] FIG. 4 is a plan view showing the positional relationship between the workpiece and the second airbag. [Figure 5] FIG. 2(a) is a schematic diagram showing pressure distribution caused by a first airbag, and FIG. 2(b) is a schematic diagram showing pressure distribution caused by the first airbag and the second airbag. [Figure 6] This is an image of the pressure acting on the workpiece W when the four secondary airbags are inflated and deflated. [Figure 7] FIG. 4 is a schematic diagram showing a process for calculating the pressure of air to be supplied to the second airbag when a desired pressure is applied to an arbitrary peak position. [Figure 8] 1(a) is a graph showing the amount of removal by polishing on the X axis in Examples 1 and 2 and Comparative Example 1, and FIG. 1(b) is a graph showing the amount of removal by polishing on the Y axis in Examples 1 and 2 and Comparative Example 1. FIG. [Figure 9] 10(a) is a graph showing the amount of removal by polishing on the X axis in Examples 3 and 4 and Comparative Example 2, and FIG. 10(b) is a graph showing the amount of removal by polishing on the Y axis in Examples 3 and 4 and Comparative Example 2. FIG. [Figure 10] 10(a) is a graph showing the thickness of the workpiece on the X axis in Example 5, and FIG. 10(b) is a graph showing the thickness of the workpiece on the Y axis in Example 5. FIG. [Figure 11] 10(a) is a graph showing the amount of removal by polishing on the X axis in Example 5, and FIG. 10(b) is a graph showing the amount of removal by polishing on the Y axis in Example 5. FIG. [Figure 12] 10 is a graph showing the thickness variation range of the workpiece in each process of Example 5. [Figure 13] 10(a) is a plan view schematically showing the workpiece polished in Example 6, and FIG. 10(b) is a graph showing the thickness of the workpiece on the X-axis and Y-axis. [Figure 14]13(b) is a graph showing the thickness variation in the circumferential direction at a position 80 mm away from the center of the workpiece shown in FIG. [Figure 15] 15 is a graph showing how the thickness of the workpiece shown in FIG. 14 changes when the workpiece is polished under a uniform load. [Figure 16] Graph (a) is a graph showing a schematic representation of the polishing rate (20±5 nm / sec) set on the X-axis, and graph (b) is a graph showing how the thickness of the workpiece shown in FIG. 14 changes when the workpiece is polished at the polishing rate shown in FIG. 16(a). [Figure 17] Graph (a) is a graph showing a schematic representation of the polishing rate (20±10 nm / sec) set on the X-axis, and graph (b) is a graph showing how the thickness of the workpiece shown in FIG. 14 changes when the workpiece is polished at the polishing rate shown in FIG. 17(a). [Figure 18] 10 is a graph showing how the thickness of a workpiece changes when polishing is performed under a uniform load after polishing under an unbalanced load in Example 6. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of the present invention will be described with reference to the drawings. Note that, hereinafter, when referring to the number, numerical value, amount, range, etc. of components, unless otherwise specified or when it is clearly limited to a specific number in principle, the number is not limited to the specific number, and may be more or less than the specific number.

[0017] Furthermore, when referring to the shape or positional relationship of components, etc., it includes things that are substantially similar or approximate to those shapes, etc., unless otherwise specified or when it is clearly considered otherwise in principle.

[0018] In addition, the drawings may exaggerate characteristic parts to make the features easier to understand, and the dimensional proportions of the components may not be the same as in reality. In addition, in cross-sectional views, hatching of some components may be omitted to make the cross-sectional structure of the components easier to understand.

[0019] 1 is a perspective view schematically showing a CMP apparatus 1 according to one embodiment of the present invention. The CMP apparatus 1 polishes one surface of a workpiece W to a flat surface. The CMP apparatus 1 includes a platen 2 and a polishing head 10. The workpiece W is, for example, a silicon wafer, but is not limited to this.

[0020] The platen 2 is formed in a disk shape and is connected to a rotary shaft 3 disposed below the platen 2. The rotary shaft 3 is rotated by the drive of a motor 4, causing the platen 2 to rotate in the direction of arrow D1 in Fig. 1. A polishing pad 5 is attached to the upper surface of the platen 2, and CMP slurry, which is a mixture of abrasives and chemicals, is supplied onto the polishing pad 5 from a nozzle (not shown).

[0021] The polishing head 10 has a smaller diameter than the platen 2 and is connected to a rotary shaft 10a disposed above the polishing head 10. The rotary shaft 10a is rotated by a motor (not shown), causing the polishing head 10 to rotate in the direction of arrow D2 in FIG. 1. The polishing head 10 is configured to be movable vertically and horizontally by a head movement mechanism (not shown). When polishing the workpiece W, the polishing head 10 descends to press the workpiece W against the polishing pad 5.

[0022] The operation of the CMP apparatus 1 is controlled by a controller 6. The controller 6 controls each of the components that make up the CMP apparatus 1. The controller 6 is, for example, a computer, and is composed of a CPU, memory, etc. The functions of the controller 6 may be realized by control using software, or may be realized by something that operates using hardware.

[0023] Next, a description will be given of the structure of the polishing head 10. FIG.

[0024] The polishing head 10 includes a head body 11 connected to a rotary shaft 10a. The head body 11 is connected to a base member 13 via a rotation transmission unit 12, and the head body 11, rotation transmission unit 12, and base member 13 rotate together with the rotary shaft 10a.

[0025] A plate holder 14 made of PPS is fastened via a bolt B1 to the upper part of the base member 13. This allows the rotational driving force input to the polishing head 10 to be transmitted to the plate holder 14 via the base member 13.

[0026] A first air bag 15 and a second air bag 16 are interposed between the plate holder 14 and the head body 11.

[0027] The first air bag 15 is formed in a substantially annular shape. The first air bag 15 can be inflated and deflated by air supplied from a compressed air source (not shown) via a compressed air line 15a. The pressure of the air supplied from the compressed air source is adjusted by a regulator (not shown) controlled by the controller 6. The first air bag 15 pressurizes the entire plate holder 14 in accordance with the pressure of the supplied air, thereby adjusting the polishing pressure at which the entire workpiece W is pressed against the polishing pad 5.

[0028] Four second air bags 16 are provided. The second air bags 16 are housed within the first air bag 15. As shown in Fig. 3, the four second air bags 16 are each formed in a substantially circular shape and are arranged on substantially concentric circles around the rotation center of the polishing head 10 in a plan view.

[0029] As shown in FIG. 4, the four second airbags 16 are arranged one in each of the positive and negative regions on the X-axis and Y-axis, which are orthogonal to each other and pass through the center of the workpiece W. Hereinafter, when distinguishing between the four second airbags 16, the second airbag 16 arranged in the negative region on the Y-axis close to the orientation flat OF will have the suffix "a" added to the reference numeral, and the second airbags 16 will have the suffixes "B," "C," and "D" added to the reference numerals in clockwise order as viewed from above, with second airbag 16A as the reference. Note that the number of second airbags 16 installed is not limited to four, and may be three or less, or five or more.

[0030] The second air bag 16 is inflated and deflated by air supplied from a compressed air source (not shown) via a compressed air line 16a. The pressure of the air supplied from the compressed air source is adjusted by a regulator (not shown) controlled by the controller 6. The second air bag 16 pressurizes a portion of the plate holder 14 located directly below the second air bag 16 in accordance with the pressure of the supplied air, thereby locally changing the polishing pressure with which the workpiece W is pressed against the polishing pad 5 in the circumferential direction of the workpiece W. Furthermore, because the second air bag 16 is fixed to the lower surface of the highly rigid head body 11 and configured to be inflatable downward, the inflation and deflation of the second air bag 16 can be more easily controlled than, for example, when the second air bag 16 is stacked on the lower surface of the inflatable first air bag 15.

[0031] 2, a porous chuck 17 is provided below the base member 13. The porous chuck 17 includes a chuck table 18 made of alumina and a chuck 19 made of porous alumina.

[0032] The chuck table 18 is fastened to the base member 13 via bolts B2. As a result, the rotational driving force input to the polishing head 10 is transmitted to the porous chuck 17 via the base member 13.

[0033] The chuck 19 is embedded in the underside of the chuck table 18. The chuck 19 is connected to a vacuum source and a cooling water source (not shown) via a line 18a. By activating the vacuum source, the workpiece W is adsorbed and held on the holding surface 17a of the porous chuck 17. The cooling water supplied from the cooling water source is adjusted to a temperature approximately equal to room temperature, and the chuck 19 is cooled by passing the water through it after polishing.

[0034] In this way, in the polishing head 10, the front surface of the workpiece W is pressed against the polishing pad 5 while the back surface of the workpiece W is held by suction on the chuck 19, and a load is transmitted to the workpiece W as the first air bag 15 and the second air bag 16 inflate, so that the workpiece W is polished so that the shape of the holding surface 17a as a polishing surface is transferred (back surface reference polishing). The holding surface 17a is set to a flatness of approximately 1 μm or less by lapping.

[0035] A thickness sensor 7 is provided below the platen 2. The thickness sensor 7 measures the thickness of the workpiece W in a non-contact manner. The thickness sensor 7 is, for example, a spectral interference type film thickness measuring device that receives light reflected by the workpiece W and measures the thickness of the workpiece W in real time.

[0036] Specifically, the thickness sensor 7 is positioned so that its optical axis passes through a transparent observation window 8 provided in the platen 2 and polishing pad 5 and reaches the workpiece W. The thickness sensor 7 irradiates white monitor light, for example, with a wavelength of 400 to 800 nm, toward the workpiece W. The thickness sensor 7 also receives the light reflected by the workpiece W. Note that the thickness sensor 7 is not limited to one that irradiates light perpendicularly to the observation window 8, and the optical path may be refracted by a reflective member or the like. The observation window 8 may be made of any material that is translucent, such as acrylic.

[0037] The light reflected from the front and back surfaces of the workpiece W interfere with each other, and the manner of interference changes depending on the thickness (optical path length) of the workpiece W. The thickness sensor 7 breaks down the light reflected from the workpiece W according to wavelength, generates a spectral waveform that indicates the relationship between the wavelength and the intensity of the reflected light, and calculates the thickness of the workpiece W being polished based on this spectral waveform. Note that possible methods for calculating the thickness of the workpiece W based on the spectral waveform include, for example, fast Fourier transform (FFT) analysis and comparing the spectral waveform with a theoretical waveform corresponding to the thickness of the workpiece W that is stored in advance.

[0038] In this way, every time the platen 2 makes one rotation, the monitor light passes through the observation window 8 and the thickness sensor 7 measures the thickness of the workpiece W. In addition, the head movement mechanism moves the polishing head 10 horizontally relative to the observation window 8, and by adjusting the relative positions of the observation window 8 and the polishing head 10, the monitor position within the workpiece W where the thickness sensor 7 measures the thickness can be changed.

[0039] Furthermore, the head movement mechanism of the polishing head 10 and the rotation shaft 3 of the platen 2 are each provided with a dog sensor capable of detecting the rotation angle, and the amount of movement of the monitor position in the circumferential direction within the workpiece W (the amount of movement of the monitor angle) can be changed as desired according to the phase difference between the rotation speed of the polishing head 10 and the rotation speed of the platen 2. The thickness sensor 7 is not limited to the configuration described above, and any sensor may be used as long as it is capable of measuring thickness variations within the surface of the workpiece W.

[0040] Next, a procedure for adjusting the load applied to the workpiece W by the first airbag 15 or the second airbag 16 will be described.

[0041] 5(a), a flat pressure distribution corresponding to the chuck flatness is obtained with the load from the first air bag 15 (hereinafter referred to as the "normal load"). Such a pressure distribution with the normal load is formed substantially uniformly in the circumferential direction of the workpiece W, and therefore is not suitable for polishing a workpiece W having a tilt after polishing due to crystal orientation or an uneven initial film thickness to a substantially uniform thickness.

[0042] The pressure distribution acting on the workpiece W can be changed by adjusting the pressure of the air supplied to each of the second airbags 16A-16D. Figures 6(a)-(i) are images of the pressure acting on the workpiece W measured using the Nitta Corporation's surface pressure distribution measurement system "I-SCAN" when the second airbags 16A-16D are inflated and deflated while the first airbag 15 is deflated; brighter areas indicate stronger pressure. Note that the images shown in Figures 6(a)-(i) show the pressure distribution acting on the workpiece W as viewed from the bottom, with the positive and negative directions of the X-axis reversed from those in Figure 4.

[0043] FIG. 6(a) shows the pressure acting on the workpiece W when air at a pressure of 8.5 psi is supplied to each of the second airbags 16C and 16D, FIG. 6(b) shows the pressure acting on the workpiece W when air at a pressure of 12 psi is supplied to the second airbag 16C, FIG. 6(c) shows the pressure acting on the workpiece W when air at a pressure of 8.5 psi is supplied to each of the second airbags 16B and 16C, FIG. 6(d) shows the pressure acting on the workpiece W when air at a pressure of 12 psi is supplied to the second airbag 16D, and FIG. 6(e) shows the pressure acting on the workpiece W when air at a pressure of 12 psi is supplied to any of the second airbags 16A to 16D. Figure 6(f) shows the pressure acting on the workpiece W when no air is supplied, Figure 6(f) shows the pressure acting on the workpiece W when air at a pressure of 12 psi is supplied to the second airbag 16B, Figure 6(g) shows the pressure acting on the workpiece W when air at a pressure of 8.5 psi is supplied to the second airbags 16A and 16D, Figure 6(h) shows the pressure acting on the workpiece W when air at a pressure of 12 psi is supplied to the second airbag 16A, and Figure 6(i) shows the pressure acting on the workpiece W when air at a pressure of 8.5 psi is supplied to the second airbags 16A and 16B.

[0044] As shown in Figures 6(b), (d), (f), and (h), when any one of the second airbags 16A to 16D is pressurized, the pressure acting directly below the pressurized second airbag 16A to 16D and its surroundings increases.

[0045] Furthermore, as shown in Figures 6(a), (c), (g), and (i), when two adjacent second airbags 16A to 16D are pressurized, the pressure acting directly below and around the two pressurized second airbags 16A to 16D and between them increases.

[0046] In this way, when the pressure distribution is moved in the circumferential direction of the workpiece W, as shown in Figure 7, the pressure F to be applied to the peak position P where the pressure distribution in the circumferential direction of the workpiece W is at its maximum is vector-decomposed according to the coordinates of the peak position P, and the air pressure to be supplied to each of the two second airbags 16A to 16D adjacent to each other on either side of the peak position P is calculated.

[0047] 7, when a peak position P is set between the second airbags 16C and 16D, if the angle formed by the line segment connecting the peak position P and the origin O and the X-axis is Θ, the pressure applied to the second airbag 16C is set to FsinΘ, and the pressure applied to the second airbag 16D is set to FcosΘ. For example, when the angle Θ is set to 60 degrees and the pressure applied to the peak position P is set to 12 psi, the pressure of the air supplied to the second airbag 16C is set to 10.4 psi, and the pressure of the air supplied to the second airbag 16D is set to 6 psi.

[0048] In this way, as shown in Fig. 5(b), the load from the second air bag 16 (hereinafter referred to as "partial load") results in a pressure distribution with a different shape from that obtained with the normal load. In other words, the pressure distribution under the partial load is formed unevenly in the circumferential direction of the workpiece W. As a result, by combining the normal load and the partial load, an appropriate pressure distribution can be set according to the crystal orientation and initial film thickness of the workpiece W, and a workpiece W with a substantially uniform film thickness after polishing can be obtained.

[0049] Since the second airbag 16 is housed within the first airbag 15, when the second airbag 16 is inflated while the first airbag 15 is inflated, the pressure of the air supplied to the second airbag 16 is set to be greater than the pressure of the air supplied to the first airbag 15.

[0050] Specifically, if the pressure of the air supplied to the first air bag 15 is Pall, the area of ​​the workpiece W is Sw, the area of ​​the first air bag 15 is Sa, and the pressure with which the porous chuck 17 pressurizes the workpiece W is WP, the pressure Pz of the air supplied to each second air bag 16 is set to satisfy the relational expression Pz>Pall=(Sw / Sa)*WP.

[0051] In this way, the second airbags 16A to 16D are arranged so as to overlap the first airbag 15 when viewed from above, so that the pressure distribution acting on the workpiece W can be easily adjusted by combining the uniform pressure distribution in the circumferential direction of the workpiece W by the first airbag 15 and the non-uniform pressure distribution in the circumferential direction of the workpiece W by the second airbags 16A to 16D.

[0052] Furthermore, the normal load and partial load can be applied simultaneously or sequentially. For example, the area around the orientation flat OF of the workpiece W can become a singular point, causing a phenomenon known as sagging, in which the amount of material removed during grinding and polishing increases locally. Therefore, after normal polishing, in which only the first air bag 15 is inflated to polish the workpiece W, the first air bag 15 is deflated, and then the second air bags 16B-16D are inflated sequentially to polish the workpiece W except for the area around the orientation flat OF. By polishing the entire surface of the workpiece W except for the area around the orientation flat OF, the sagging around the orientation flat OF can be eliminated. [Example]

[0053] Next, we will explain the case where a workpiece W made of LiTaO3 (lithium tantalate) is subjected to CMP polishing with a normal load (Comparative Example 1), and the case where CMP polishing is performed with a combination of a normal load and a partial load (Examples 1 and 2).

[0054] The polishing conditions for Comparative Example 1 and Examples 1 and 2 are shown in Table 1. The distribution of the amount of removal by polishing on the X axis (Y coordinate: 0) for Comparative Example 1 and Examples 1 and 2 is shown in Figure 8(a), and the distribution of the amount of removal by polishing on the Y axis (X coordinate: 0) is shown in Figure 8(b). Note that "Zone 3" and "Zone 4" in Table 1 correspond to the second airbags 16C and 16D, respectively. [Table 1]

[0055] 8(a) and (b), in Comparative Example 1, the amount of removal by polishing in the negative X coordinate region (particularly, -25 mm or less) is relatively larger than the amount of removal by polishing in the positive X coordinate region, and the amount of removal by polishing in the negative Y coordinate region (particularly, -25 mm or less) is relatively larger than the amount of removal by polishing in the positive Y coordinate region, which shows that there is a bias in the amount of removal by polishing within the surface of the workpiece W.

[0056] On the other hand, in Example 1, by applying partial loads from the second airbags 16C and 16D in addition to the normal load from the first airbag 15, it can be seen that the amount of polishing removal in the area where the X coordinate is positive and the amount of polishing removal in the area where the Y coordinate is positive increase, thereby alleviating the unevenness of the amount of polishing removal within the surface of the workpiece W.

[0057] In addition, in Example 2, by further increasing the pressure of the air supplied to the second air bags 16C and 16D, the amount of polishing removal in the positive X coordinate region and the amount of polishing removal in the positive Y coordinate region are further increased, and the amount of polishing removal in the positive X coordinate region is relatively larger than the amount of polishing removal in the negative X coordinate region, and the amount of polishing removal in the positive Y coordinate region is relatively larger than the amount of polishing removal in the negative Y coordinate region. Therefore, it can be seen that the unevenness of the amount of polishing removal within the surface of the workpiece W is in contrast to Comparative Example 1.

[0058] Next, a case where a workpiece W made of SiC (silicon carbide) was subjected to CMP polishing with a normal load (Comparative Example 2) and a case where a workpiece W was subjected to CMP polishing with a combination of a normal load and a partial load (Examples 3 and 4) will be described.

[0059] The polishing conditions for Comparative Example 2 and Examples 3 and 4 are shown in Table 2. The distribution of the polishing removal amount on the X axis (Y coordinate: 0) for Comparative Example 2 and Examples 3 and 4 is shown in Figure 9(a), and the distribution of the polishing removal amount on the Y axis (X coordinate: 0) is shown in Figure 9(b). Note that "Zone 4" in Table 1 corresponds to the second airbag 16D. [Table 2]

[0060] 9(a) and (b), in Comparative Example 2, the amount of polishing removal in the negative X coordinate region tends to be relatively larger than the amount of polishing removal in the positive X coordinate region, and it can be seen that there is a bias in the amount of polishing removal within the surface of the workpiece W.

[0061] On the other hand, in Example 3, by applying a partial load from the second airbag 16D in addition to the normal load from the first airbag 15, it can be seen that the amount of polishing removal in the positive X coordinate area increases and the imbalance in the amount of polishing removal within the surface of the workpiece W is alleviated.

[0062] In addition, in Example 4, by further increasing the pressure of the air supplied to the second air bag 16D, the amount of polishing removal in the positive X coordinate region further increases, and the amount of polishing removal in the positive X coordinate region tends to be relatively larger than the amount of polishing removal in the negative X coordinate region, and it can be seen that the bias in the amount of polishing removal within the surface of the workpiece W is in contrast to Comparative Example 2.

[0063] Next, we will explain Example 5, in which a workpiece W made of LiTaO3 is subjected to partial pressure in stages to improve sagging around the orientation flat OF. The polishing conditions for Example 5 are shown in Table 3. In Table 3, "Zone 1" corresponds to second airbag 16A, "Zone 2" corresponds to second airbag 16B, "Zone 3" corresponds to second airbag 16C, and "Zone 4" corresponds to second airbag 16D. [Table 3]

[0064] FIG. 10(a) shows the thickness of the workpiece W on the X-axis (Y-coordinate: 0) in each process, and FIG. 10(b) shows the thickness of the workpiece W on the Y-axis (X-coordinate: 0) in each process. FIG. 11(a) shows the distribution of the amount of polishing removal on the X-axis (Y-coordinate: 0) in each process, and FIG. 11(b) shows the distribution of the amount of polishing removal on the Y-axis (X-coordinate: 0) in each process. FIG. 12 is a graph showing the variation in thickness within the surface of the workpiece W in each process.

[0065] "Before polishing" in Figures 10(a), (b), and 12 indicates the workpiece W before CMP polishing under normal load. As shown in Figure 10(b), it can be seen that sagging has occurred around the orientation flat OF (Y coordinate: -50 mm or less), resulting in a significant reduction in the thickness of the workpiece W. Furthermore, as shown in Figure 12, it can be seen that thickness variation of approximately 0.34 μm has occurred within the surface of the workpiece W.

[0066] For such a workpiece W, first, only the first airbag 15 is inflated to polish the workpiece W (normal polishing). After normal polishing, as shown in Figs. 10(a) and (b), the workpiece W is polished into a concave shape where the vicinity of the center is the thinnest and gradually becomes thicker toward the outer periphery. This is obtained by processing the shape of the holding surface 17a into a convex shape. Also, as shown in Figs. 11(a) and (b), the polishing removal amount during normal polishing is the largest near the center and gradually decreases toward the outer periphery. However, as shown in Fig. 12, there is no significant change in the thickness variation within the surface of the workpiece W before and after normal polishing.

[0067] Next, after contracting the first airbag 15, the second airbags 16B to 16D are inflated in order to perform partial polishing (partial polishing 1) on the entire surface of the workpiece W excluding the periphery of the orifice OF. In partial polishing 1, as shown in Figs. 11(a) and (b), on the Y-axis, the periphery of the orifice OF is hardly polished, and it can be seen that the polishing removal amount in the region extending from the middle to the periphery of the workpiece W (X < -about 25 mm and about 25 mm < X, about 25 mm < Y) is significantly larger compared to the vicinity of the center of the workpiece W. As a result, after partial polishing 1, as shown in Figs. 10(a) and (b), the entire surface of the workpiece W excluding the periphery of the orifice OF is polished, and the concave shape of the workpiece W is relaxed. Also, as shown in Fig. 12, it can be seen that the thickness variation within the surface of the workpiece W is improved to 0.25 μm.

[0068] In this embodiment, after partial pressurization 1, a second-stage partial pressurization (partial polishing 2) is performed in which the second airbags 16A to 16D are inflated in order to further polish the workpiece W. Partial polishing 2 is for improving the concave shape generated during normal polishing to form the workpiece W into a substantially flat shape, and it may be omitted when the polishing removal amount during normal polishing is small and the concave of the workpiece W after normal polishing is shallow.

[0069] In partial polishing 2, as shown in FIGS. 11(a) and 11(b), it can be seen that the polishing removal amount in the region extending from the middle to the periphery of the workpiece W (X < -about 25 mm and about 25 mm < X, Y < -about 25 mm and about 25 mm < Y) is significantly larger than that near the center of the workpiece W. As a result, as shown in FIGS. 10(a) and 10(b), the concave shape in the middle of the workpiece W after partial polishing 2 is further alleviated. Also, as shown in FIG. 12, the thickness variation within the plane of the workpiece W is further improved to 0.2 μm.

[0070] Next, a case (Example 6) of automatically polishing the workpiece W while considering the variation in the initial film thickness for each workpiece W will be described. In Example 6, the thickness sensor 7 measures the thickness along the circumferential direction at an arbitrary distance from the center within the plane of the workpiece W, and after the thickness variation in the circumferential direction of the workpiece W is sufficiently reduced in a partial load state (partial load polishing mode) combining the normal load by the first airbag 15 and the partial load by the second airbag 16, the workpiece W is uniformly polished in a uniform load state (uniform polishing mode).

[0071] <Thickness measurement> The workpiece W before polishing illustrated in FIG. 13(a) is a silicon wafer with a diameter of 200 mm, and its initial film thickness is as shown in FIG. 13(b). As shown in FIG. 13(b), the workpiece W is formed to be substantially flat with a thickness of 700 μm on the Y-axis (X coordinate: 0) passing through the center O and the notch N. In contrast, on the X-axis (Y coordinate: 0), the thickness in the region where the X coordinate is negative is thinner than the thickness in the region where the X coordinate is positive, the workpiece W is formed thicker in proportion to the X coordinate, and a thickness variation of 3 μm occurs at both ends of the X-axis.

[0072] If the workpiece W is not evenly flat, the circumferential thickness of the workpiece W can be approximated by a sinusoidal wave. Therefore, as shown in FIG. 13(a), if r is the distance [μm] from the center O of the workpiece W to the monitor position MP where the thickness sensor 7 measures the thickness, Θ is the angle (monitor angle) [degrees] between the monitor position MP and the positive region of the X-axis, and T(r,Θ) is the thickness at the monitor position MP located at coordinates (r,Θ) within the workpiece W, the approximate equation T(r,Θ) = 700 + (rcosΘ / 100) * 1.5 can be obtained. FIG. 14 shows the initial circumferential thickness of the workpiece W when r = 80 mm. According to FIG. 14, the initial thickness of the workpiece W is maximum at the monitor position MP (80 mm, 0 degrees), where the maximum thickness is 701.2 μm, and minimum at the monitor position MP (80 mm, 180 degrees), where the minimum thickness is 698.8 μm.

[0073] <Uneven load polishing mode> When a workpiece W having a thickness variation of 3 μm on the X axis is to be polished approximately uniformly to a predetermined target thickness (approximately 694 μm), when the thickness sensor 7 starts the first thickness measurement at t=0 seconds from the monitor position MP at coordinates (80 mm, 0 degrees), if the rotation speed of the platen 2 is Vp [rpm], the rotation speed of the polishing head 10 is Vh [rpm], and the number of rotations of the platen 2 is n, the monitor angle Θ at the monitor position MP is Θ=(Vp-Vh)*360*n / Vp [degrees].

[0074] 15 is a graph showing the change in thickness T (80 mm, Θ) at monitor position MP when the rotation speed Vp of the platen 2 is 120 rpm, the rotation speed Vh of the polishing head 10 is 117 rpm, and the workpiece W is polished at a substantially uniform polishing rate of 20 nm / sec. In the waveform in FIG. 15, the peaks correspond to Θ = 0 degrees and the valleys correspond to Θ = 180 degrees. FIG. 15 shows that when the workpiece W is polished substantially uniformly, the 3 μm thickness variation of the workpiece W is not improved, and the entire workpiece W is polished thinly.

[0075] On the other hand, when a deviation of ±5 nm / sec is set in the polishing rate in the X direction within the workpiece W as shown in FIG. 16(a) by inflating the first air bag 15 and the second air bag 16D, that is, when the polishing rate in the negative X coordinate region is relatively smaller than the polishing rate in the positive X coordinate region and a deviation of ±5 nm / sec is set in the polishing rate at both ends of the X axis within the workpiece W and the workpiece W is polished to a predetermined target thickness (approximately 694 μm) under an unbalanced load, as shown in FIG. 16(b), when the polishing time reaches approximately 300 seconds, the thickness variation within the workpiece W is reduced and improved, and the workpiece W is polished to a substantially flat surface.

[0076] Furthermore, when a deviation of ±10 nm / sec is set in the polishing rate in the X direction within the workpiece W as shown in FIG. 17(a), that is, when the polishing rate in the negative X coordinate region is relatively smaller than the polishing rate in the positive X coordinate region, and a deviation of ±10 nm / sec is set in the polishing rate at both ends of the X axis within the workpiece W, and the workpiece W is polished to a predetermined target thickness (approximately 694 μm) under an unbalanced load, as shown in FIG. 17(b), when the polishing time reaches approximately 150 seconds, the thickness variation of the workpiece W decreases and improves to become approximately flat, and then it can be seen that thickness variation reoccurs within the workpiece W.

[0077] Therefore, the controller 6 retrieves suitable polishing conditions based on the circumferential thickness variation of the workpiece W measured by the thickness sensor 7, and the workpiece W is polished under the unbalanced load condition based on the polishing conditions. The controller 6 starts polishing the workpiece W under the unbalanced load condition that causes a deviation of ±10 nm / sec in the polishing rate in the X direction of the workpiece W shown in FIG. 17(a).

[0078] The controller 6 pre-stores polishing conditions suitable for improving the circumferential thickness variation of the workpiece W, corresponding to the circumferential thickness variation of the workpiece W. The polishing conditions for the unbalanced load polishing mode include polishing rates in the X-axis and Y-axis directions for improving the circumferential thickness variation of the workpiece W, which have been previously obtained through experiments or the like. If the polishing rate is too high, the circumferential thickness variation of the workpiece W will converge rapidly, and the number of peaks and valleys of the waveform required to derive the approximation formula described below will not be obtained, making it impossible to accurately predict the polishing endpoint of the unbalanced load polishing. If the polishing rate is too low, the polishing time will be unnecessarily long. Therefore, it is preferable to set an optimal polishing rate by considering the balance between the degree of improvement in thickness variation and the polishing time, for example.

[0079] The controller 6 calculates the polishing time (predicted end time of unbalanced load polishing) required for polishing under an unbalanced load condition until the maximum thickness and the minimum thickness in the workpiece W become approximately equal, and polishes under an unbalanced load condition until this predicted end time of unbalanced load polishing.

[0080] Specifically, after a sufficient amount of time has passed to produce multiple peaks and valleys in the waveform of the graph showing the thickness of the workpiece W, the controller 6 uses the least squares method to calculate a linear approximation line L1 (L1:T = -0.0279t + 701.19) connecting the thickness transitions at the monitor position MP (80 mm, 0 degrees) corresponding to the maximum thickness and a linear approximation line L2 (L2:T = -0.0119t + 698.8) connecting the thickness transitions at the monitor position MP (80 mm, 180 degrees) corresponding to the minimum thickness, as shown in Fig. 18. Then, the controller 6 calculates the predicted endpoint time (approximately 149 seconds) of the off-set load polishing from the intersection of the approximation equations L1 and L2, and continues polishing under the off-set load until this predicted endpoint time is reached.

[0081] <Uniform polishing mode> Next, the controller 6 resets the bias in the polishing rate of the workpiece W in the X direction, and then calls up pre-stored polishing conditions, and polishes the workpiece W, whose thickness variation has been improved, in a substantially uniform concentric pattern. Fig. 18 illustrates an example in which the necessary first air bag 15 and second air bag 16 are inflated, the rotation speed Vp of the platen 2 is set to 120 rpm, the rotation speed Vh of the polishing head 10 is set to 117 rpm, and the workpiece W is substantially uniformly polished at a polishing rate of 20 nm / sec. Then, when the thickness of the workpiece W measured in real time by the thickness sensor 7 reaches the target thickness (694 µm), the controller 6 ends polishing.

[0082] In this way, the CMP apparatus 1 according to this embodiment is a polishing apparatus that polishes a workpiece W held by a polishing head 10 by pressing it against a polishing pad 5 on a platen 2, and is equipped with a chuck 19 capable of holding the workpiece W, a thickness sensor 7 that measures thickness variations within the surface of the workpiece W, second air bags 16A to 16D that are arranged in parallel along the circumferential direction of the chuck 19 and that can be inflated with air to press a portion of the workpiece W against the polishing pad 5, and a controller 6 that pre-stores a polishing rate corresponding to the circumferential thickness variations of the workpiece W when polishing the workpiece W under an unbalanced load condition and that can adjust the pressure of the air supplied to each of the second air bags 16A to 16D. The controller 6 retrieves the polishing rate corresponding to the thickness variations within the surface of the workpiece W acquired by the thickness sensor 7, and adjusts the air supplied to each of the second air bags 16A to 16D to achieve the polishing rate, thereby polishing the workpiece W under an unbalanced load condition.

[0083] According to this configuration, by inflating and deflating the second air bags 16A to 16D, the pressure distribution acting on the workpiece W can be freely adjusted in the circumferential direction of the workpiece W. Therefore, the pressure distribution in the circumferential direction of the workpiece W can be adjusted taking into account the crystal orientation and uneven initial film thickness of the workpiece W. By applying different polishing pressures to the workpiece W within the polishing surface, the workpiece W can be polished flat with high precision.

[0084] Furthermore, the controller 6 calls up a polishing rate that reduces the circumferential thickness variation of the workpiece W measured by the thickness sensor 7, and the second airbags 16A to 16D polish the workpiece W at that polishing rate under an unbalanced load condition, so that the workpiece W can be polished flat with high precision regardless of the initial film thickness of the workpiece W.

[0085] Furthermore, the CMP apparatus 1 according to this embodiment is configured such that the controller 6 calculates the predicted end time of the unbalanced load polishing at which the maximum thickness and the minimum thickness in the workpiece W are approximately equal when polishing is performed under an unbalanced load condition, and polishing is performed under the unbalanced load condition until the predicted end time of the unbalanced load polishing is reached.

[0086] According to this configuration, polishing is performed under an unbalanced load condition until the thickness variation within the workpiece W is improved, so that the workpiece W can be polished flat with high precision without over-polishing, which would reverse the thickness variation.

[0087] Furthermore, in the CMP apparatus 1 according to this embodiment, the controller 6 calculates the predicted end time of the unbalanced load polishing based on the intersection of approximate equations L1 and L2 derived from the change in thickness at monitor position MP (80 mm, 0 degrees) corresponding to the maximum thickness that decreases as polishing progresses and the change in thickness at monitor position MP (80 mm, 180 degrees) corresponding to the minimum thickness, on a graph in which the vertical axis represents the circumferential thickness of the workpiece W acquired by the thickness sensor 7 and the horizontal axis represents the polishing time.

[0088] According to this configuration, the predicted endpoint time of unbalanced load polishing can be calculated with high accuracy based on the tendency for the thickness variation between the maximum thickness and the minimum thickness in the initial stage of unbalanced load polishing to decrease and improve.

[0089] Furthermore, the CMP apparatus 1 according to this embodiment is configured such that the controller 6 polishes the workpiece W under a substantially uniform load after the predicted end time of uneven load polishing has elapsed.

[0090] According to this configuration, after the thickness variation is improved by polishing under an unbalanced load state, the workpiece W can be polished approximately uniformly to the target thickness.

[0091] In addition, the polishing method using the CMP apparatus 1 according to this embodiment includes a process in which the thickness sensor 7 measures the circumferential thickness variation of the workpiece W, and a process in which the controller 6 retrieves a polishing rate corresponding to the thickness variation within the surface of the workpiece W acquired by the thickness sensor 7, and adjusts the air supplied to the second air bags 16A to 16D to achieve the polishing rate, thereby polishing the workpiece W under an unbalanced load condition.

[0092] According to this configuration, by inflating and deflating the second air bags 16A to 16D, the pressure distribution acting on the workpiece W can be freely adjusted in the circumferential direction of the workpiece W. Therefore, the pressure distribution in the circumferential direction of the workpiece W can be adjusted taking into account the crystal orientation and uneven initial film thickness of the workpiece W. By applying different polishing pressures to the workpiece W within the polishing surface, the workpiece W can be polished flat with high precision.

[0093] Furthermore, the controller 6 calls up a polishing rate that reduces the circumferential thickness variation of the workpiece W measured by the thickness sensor 7, and the second airbags 16A to 16D polish the workpiece W at that polishing rate under an unbalanced load condition, so that the workpiece W can be polished flat with high precision regardless of the initial film thickness of the workpiece W.

[0094] Furthermore, the present invention can be modified in various ways other than those described above without departing from the spirit of the present invention, and it goes without saying that the present invention also covers such modifications.

[0095] The approximation formula used to derive the predicted end time of unbalanced load polishing is not limited to the above-mentioned first-order approximation formula, but may be a second-order or higher approximation formula or other approximation formula. Furthermore, the predicted end time of unbalanced load polishing is not limited to the above-mentioned approximation formula, but may be derived using other methods.

[0096] Furthermore, in the above-described embodiment, an example was given of a CMP apparatus 1 equipped with a first air bag 15 that pressurizes the workpiece W with a substantially uniform pressure distribution in the circumferential direction, and second air bags 16A to 16D that pressurize the workpiece W with a non-uniform pressure distribution in the circumferential direction. However, for example, instead of the second air bags 16A to 16D, the first air bag 15 may be divided into multiple air chambers, and when the workpiece W is pressurized with a substantially uniform pressure distribution in the circumferential direction, all of the air chambers may be inflated, and when the workpiece W is pressurized with a non-uniform pressure distribution in the circumferential direction, at least one air chamber may be inflated. [Explanation of symbols]

[0097] 1:CMP equipment 2: Platen 3: (Platen) rotation axis 4: Motor 5: Polishing pad 6: Controller 7: Thickness sensor 8: Observation window 10: Polishing head 10a: Rotating shaft (of polishing head) 11: Head body 12: Rotation transmission part 13: Base material 14: Plate holder 15: First airbag (full pressure part) 16, 16A to 16D: Second airbag (partially pressing portion) 17:Porous chuck 17a: Holding surface 18: Chuck table 19: Zipper W: Work

Claims

1. A polishing apparatus that polishes a workpiece held by a polishing head by pressing the workpiece against a polishing pad on a platen, a chuck capable of holding the workpiece; a thickness sensor for measuring thickness variations within the work surface; a plurality of partial pressing portions arranged in parallel along the circumferential direction of the chuck, which are expanded by air to press a portion of the workpiece toward the polishing pad; a controller that stores in advance a polishing rate when polishing the workpiece under an unbalanced load condition corresponding to thickness variations in the circumferential direction of the workpiece, and that can adjust the pressure of air supplied to each partial pressing portion; Equipped with The controller calculates an estimated end time of the off-set load polishing, which is the polishing time when the maximum thickness and the minimum thickness within the workpiece are approximately equal while polishing under the off-set load condition, retrieves the polishing rate corresponding to the thickness variation within the workpiece surface acquired by the thickness sensor, and adjusts the air supplied to each partial pressing unit so as to realize the polishing rate, thereby polishing the workpiece under the off-set load condition until the estimated end time of the off-set load polishing.

2. The polishing apparatus according to claim 1, characterized in that the controller calculates as the predicted end time of the unbalanced load polishing the polishing time at which a plurality of approximate equations derived from the changes in thickness at the maximum thickness position and the minimum thickness position in the workpiece, which decrease as polishing progresses, intersect in a graph in which the circumferential thickness of the workpiece acquired by the thickness sensor is set on the vertical axis and the polishing time is set on the horizontal axis.

3. 3. The polishing apparatus according to claim 1, wherein the controller polishes the workpiece under a substantially uniform load after the predicted end time of the uneven load polishing has elapsed.

4. A polishing method using a polishing apparatus in which a workpiece held by a polishing head is pressed against a polishing pad on a platen to be polished, comprising: The polishing apparatus is a chuck capable of holding the workpiece; a thickness sensor for measuring thickness variations within the work surface; a plurality of partial pressing portions arranged in parallel along the circumferential direction of the chuck, which are expanded by air to press a portion of the workpiece toward the polishing pad; a controller that stores in advance a polishing rate when polishing the workpiece under an unbalanced load condition corresponding to thickness variations in the circumferential direction of the workpiece, and that can adjust the pressure of air supplied to each partial pressing portion; Equipped with a step in which the thickness sensor measures a thickness variation in the circumferential direction of the workpiece; the controller calculates an expected end time of unbalanced load polishing, which is a polishing time at which the maximum thickness and the minimum thickness in the workpiece are approximately equal when polishing is performed under the unbalanced load condition; the controller retrieves the polishing rate corresponding to the thickness variation in the work surface acquired by the thickness sensor, adjusts the air supplied to each partial pressing unit so as to realize the polishing rate, and polishes the workpiece under the unbalanced load condition until the unbalanced load polishing end point predicted time; A polishing method comprising:

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