Plasma-assisted polishing method and device therefor

Abstract

[Problem] To provide a plasma-assisted polishing method and a device therefor, capable of suppressing one-sided wear of a polishing pad and facilitating attachment / detachment work of a polishing pad and a workpiece in processing of a hard-to-work material using a plasma-assisted polishing method. [Solution] In an operation for relatively moving a workpiece W and a polishing pad P, the workpiece is polished by a combination of the rotation of the workpiece and the polishing pad each having an axis in a first direction, and the swing in a second direction orthogonal to the first direction and increasing or decreasing the distance between the two axes. The workpiece and the polishing pad face each other by being detachably held by mounting parts 10, 13 provided with rotary shafts 9, 12 each directed in the first direction. When the workpiece and / or the polishing pad is attached / detached, the workpiece and the polishing pad are moved in the second direction beyond a range of oscillation in a normal polishing process in a state of stopping the rotation of the workpiece and / or the polishing pad, and the workpiece and / or the polishing pad is attached / detached to / from the mounting part in a state where the workpiece and / or the polishing pad is exposed from the facing member.

Description

Plasma-assisted polishing method and apparatus

[0001] The present invention is based on SiC, GaN, AlN, Ga ２ O ３ The present invention relates to a plasma-assisted polishing method and apparatus suitable for precision finishing of difficult-to-process materials such as diamond.

[0002] In recent years, there has been active development of devices using wide bandgap semiconductors as power semiconductor device materials, which are capable of highly reliable operation even in high temperature environments and have low loss. Wide bandgap semiconductors are classified into the following groups in order of decreasing bandgap: SiC, GaN, and Ga. ２ O ３ , and diamond. These wide bandgap semiconductors have physical properties such as band gap, breakdown field value, thermal conductivity, and electron mobility several to several tens of times larger than those of Si, and therefore when power devices are fabricated using these materials, they offer advantages such as high breakdown voltage, reduced power consumption, and high-speed operation. However, because they are highly hard and chemically inert, they are difficult to process and it is difficult to efficiently achieve the desired flatness and surface roughness by ordinary polishing.

[0003] Currently, wide bandgap semiconductor wafers are finished by chemical mechanical polishing (CMP). However, because polishing is performed using a slurry containing alkaline chemicals and abrasive grains, the surface roughness deteriorates due to "etch pits" formed when surface defects in the material are eroded by the alkaline components, and "scratches" are formed due to the aggregation and coarsening of the abrasive grains, meaning that the material properties are not fully utilized. In addition, the polishing efficiency is low, resulting in low yields and high costs.

[0004] Plasma-assisted polishing (PAP) has been proposed as a method for machining difficult-to-machine materials such as SiC, GaN, or cemented carbide (see Patent Document 1). This PAP method involves applying radicals generated in plasma to the surface of a workpiece to form a surface-modified layer softer than the workpiece material. This layer is then removed by dry mechanical polishing using an abrasive material, and machining proceeds. The PAP method is an excellent machining method that, based on its processing principle, enables precision machining without introducing scratches or a process-affected layer into the workpiece by using an abrasive material whose Mohs hardness is intermediate between that of the workpiece material and the surface-modified layer. Patent Document 1 also shows that, for SiC, OH radicals are more efficient at oxidizing the surface of the workpiece and forming a surface-modified layer (oxide layer) than O radicals. To achieve this, high-frequency power is applied to an atmosphere containing a carrier gas and one or both of HO and HO to generate plasma, generating OH radicals.

[0005] Patent Literature 2 discloses a machining method utilizing radical adsorption and transport, in which the surface of a movable tool, having corrosion resistance and adsorption capacity for chemically reactive radicals, is passed through a plasma generation region generated using a reactive gas containing at least a gas containing an element or substituent that generates the radicals and a rare gas, the radicals generated in the plasma generation region are adsorbed onto the tool surface to provide reactive species, the reactive species on the tool surface are transported to a workpiece surface positioned at a location different from the plasma generation region by moving the tool, and reaction products generated by chemical reactions between atoms on the workpiece surface that contact the tool and the reactive species are removed, thereby selectively machining only the portion of the workpiece surface that contacts the tool surface, using the tool surface as a machining reference plane. It also discloses that the radical-generating element is a halogen element such as F or Cl, and the radicals are F radicals or Cl radicals, or that the radical-generating substituent is an OH group and the radicals are OH radicals. This processing method also involves the action of radicals on the surface of the workpiece, and the workpiece and the tool acting as an abrasive move in contact with each other, so it can be called a type of PAP.

[0006] Cited Document 3 discloses a processing method for PAP, in which a polishing tool consisting of a vitrified-bonded grinding wheel in which abrasive grains are bonded with an inorganic glass-based bond material, or a resin-bonded grinding wheel in which abrasive grains are bonded with a thermosetting resin bond material, is used to apply fluorine radicals or oxygen radicals to the surface of a workpiece to fluorinate or oxidize it, thereby forming a surface-modified layer, and fluorine radicals or oxygen radicals are also applied to the polishing tool, etching the bond material of the polishing tool to expose the abrasive grains, while processing the surface of the workpiece. This causes an automatic dressing action that etches the bond material of the polishing tool to expose the abrasive grains, preventing a decrease in polishing rate due to "glazing" or "clogging," enabling precision machining with a high polishing rate maintained without dressing, and enabling the machining of difficult-to-machine materials such as SiC, GaN, and AlN.

[0007] Furthermore, Non-Patent Document 1 reports that a PAP suitable for processing diamond is obtained by irradiating a polishing pad made of quartz glass with plasma containing an element that bonds with the carbon atoms that make up diamond, such as oxygen, and that the root mean square height Sq becomes 0.3 nm under low polishing pressure conditions such as 62.5 or 81.3 kPa.

[0008] Japanese Patent No. 5614677 Japanese Patent No. 6692010 Japanese Patent Application Publication No. 2022-133198

[0009] Nian Liu, et al. Effects of polishing pressure and sliding speed on the material removal mechanism of single crystal diamond in plasma-assisted polishing. Diamond and Related Materials,Volume 124, April 2022, 108899.

[0010] Although polishing is typically performed by offsetting the rotation axis of the polishing pad and the rotation axis of the workpiece, the polishing pad still wears unevenly, necessitating frequent regeneration of the polishing pad, and if regeneration is not possible, replacement is required. In particular, the quartz glass used in diamond processing is difficult to regenerate, and its high price leads to high costs. Furthermore, the ease of attaching and detaching the polishing pad and the workpiece during the regeneration and replacement process is a major challenge for mass production.

[0011] In view of the above-mentioned situation, the present invention aims to solve the problem of providing a plasma-assisted polishing method and apparatus that can suppress uneven wear of the polishing pad when processing difficult-to-process materials using plasma-assisted polishing and that can easily attach and detach the polishing pad to the workpiece.

[0012] In order to solve the above-mentioned problems, the present invention provides a plasma-assisted polishing method and apparatus configured as follows.

[0013] [Configuration 1] A plasma-assisted polishing method comprising: a surface modification process in which neutral radicals based on the reactive gas are generated by applying high-frequency power to a process gas containing a carrier gas and a reactive gas to generate plasma, and the neutral radicals are caused to act on the surface of a workpiece to form a surface-modified layer on the surface of the workpiece that is softer than the workpiece; and a polishing process in which the workpiece and a polishing pad are moved relatively while being brought into contact with each other at a predetermined contact pressure, thereby removing the surface-modified layer of the workpiece, wherein the surface modification process and the polishing process are alternately repeated, or both processes are carried out simultaneously to polish the workpiece, wherein the operation of moving the workpiece and the polishing pad relatively polishes the workpiece by a combination of rotation of the workpiece and rotation of the polishing pad, each of which has an axis in a first direction, and oscillation in a second direction that is perpendicular to the first direction and increases or decreases the distance between the two axes.

[0014] [Configuration 2] The plasma-assisted polishing method according to Configuration 1, wherein the plasma in the surface modification process is a capacitively coupled plasma, and the capacitance does not change during the oscillation operation.

[0015] [Configuration 3] The plasma-assisted polishing method according to Configuration 1, wherein the workpiece and polishing pad are each removably held and opposed to each other on a mounting part having a rotation axis facing a first direction, and when the workpiece and / or polishing pad are attached or detached, the workpiece and polishing pad are moved in a second direction beyond the range of oscillation in a normal polishing process while their rotation is stopped, and the workpiece and / or polishing pad are attached or detached to or from the mounting part in a state where they are exposed from the opposing member.

[0016] [Configuration 4] The plasma-assisted polishing method according to Configuration 1, 2, or 3, wherein the polishing pad is a plate having, on at least its surface, one of a quartz glass plate, a vitrified bond grinding wheel in which abrasive grains are bonded with an inorganic glass-based bond material, and a woven or nonwoven glass wool fabric.

[0017] [Configuration 5] The plasma-assisted polishing method according to Configuration 4, wherein a flow path communicating with a space where plasma is generated is formed by a groove or an uneven structure provided on at least one surface of the workpiece or polishing pad at the contact portion between the workpiece and the polishing pad, and neutral radicals are supplied to the workpiece surface through the flow path.

[0018] [Configuration 6] The workpiece is a substrate having at least a surface layer made of either single crystal diamond (SCD), polycrystalline diamond (PCD), or diamond-like carbon (DLC); the polishing pad has a vitrified bond grinding stone at least on its surface, and the abrasive grains are diamonds with a diameter of #1000 (average grain size 16 μm) to #20000 (average grain size 0.8 μm); the reactive gas is water vapor (H ２ O) or hydrogen peroxide (H ２ O ２ 5. The plasma-assisted polishing method of claim 4, comprising:

[0019] [Configuration 7] The plasma-assisted polishing method according to Configuration 4, wherein the surface modification process includes a step of irradiating the polishing surface of the workpiece with ultraviolet light that has been transmitted through at least a portion of the polishing pad.

[0020] [Configuration 8] A plasma-assisted polishing apparatus comprising: a chamber containing a process gas containing a carrier gas and a reactive gas and accommodating a mechanical section; a gas supply means for supplying the process gas into the chamber; a gas exhaust means for exhausting the process gas from the chamber; a mechanical section comprising an attachment part for detachably holding a workpiece to be polished and a polishing pad opposite each other, and for relatively moving the workpiece and the polishing pad while bringing them into contact with each other at a predetermined contact pressure; and a high-frequency power source for generating neutral radicals based on the reactive gas by applying high-frequency power between opposing electrode plates while maintaining the process gas at a predetermined pressure, wherein the mechanical section comprises: a first rotation unit having a rotation axis in a first direction and a first attachment part for detachably holding the polishing pad or the workpiece, and having a rotary table which also serves as an electrode plate; a second mounting portion having an area smaller than that of the rotary table and configured to detachably hold the workpiece or polishing pad; a second rotating unit having a counter electrode plate facing the rotary table and configured to be displaced in the first direction and to apply contact pressure between the workpiece and the polishing pad; and a linear driving means for linearly displacing the first rotating unit or the second rotating unit in a second direction perpendicular to the first direction.

[0021] [Configuration 9] The plasma-assisted polishing apparatus according to Configuration 8, wherein the workpiece and polishing pad are held and opposed to each other by either a first mounting portion of a first rotating unit or a second mounting portion of a second rotating unit, and in a swing mode in a normal polishing process, the linear drive means is driven so as to reciprocate within a range in which the rotary table and the counter electrode plate maintain an opposed state.

[0022] [Configuration 10] The plasma-assisted polishing apparatus according to Configuration 9, wherein the opposing electrode plate has a dimension in the second direction set to be larger than the diameter of the rotary table by at least the oscillation amplitude, so that the capacitance of the capacitively coupled plasma does not change in the oscillation mode.

[0023] [Configuration 11] The plasma-assisted polishing apparatus according to Configuration 8, wherein the workpiece and polishing pad are held and opposed by either a first mounting portion of a first rotating unit or a second mounting portion of a second rotating unit, and in an attachment / detachment mode for attaching / detaching the workpiece and / or polishing pad, the linear drive means is driven to a position where the workpiece and / or polishing pad are exposed from the opposing member of the first rotating unit and / or the second rotating unit.

[0024] [Configuration 12] The plasma-assisted polishing apparatus according to any one of Configurations 8 to 11, wherein the polishing pad is a plate having, on at least its surface, one of a quartz glass plate, a vitrified bond grinding wheel in which abrasive grains are bonded with an inorganic glass-based bond material, and a woven or nonwoven glass wool fabric.

[0025] [Configuration 13] The plasma-assisted polishing apparatus according to Configuration 8, wherein a flow path communicating with a space where plasma is generated is formed by a groove or an uneven structure provided on at least one surface of the workpiece and the polishing pad at the contact portion between the workpiece and the polishing pad, and neutral radicals are supplied to the workpiece surface via the flow path.

[0026] [Configuration 14] The workpiece is a substrate having at least a surface layer made of either single crystal diamond (SCD), polycrystalline diamond (PCD), or diamond-like carbon (DLC); the polishing pad has a vitrified bond grinding stone at least on its surface, and the abrasive grains are diamonds with a diameter of #1000 (average grain size 16 μm) to #20000 (average grain size 0.8 μm); the reactive gas is water vapor (H ２ O) or hydrogen peroxide (H ２ O ２ 9. The plasma-assisted polishing apparatus of claim 8, comprising:

[0027] [Configuration 15] The plasma-assisted polishing apparatus according to Configuration 8, further comprising an ultraviolet light source disposed behind the polishing pad, and a structure for transmitting ultraviolet light from the ultraviolet light source through at least a portion of the polishing pad and its mounting portion and irradiating the polishing surface of the workpiece.

[0028] The plasma-assisted polishing method and apparatus of the present invention described above have the following advantages.

[0029] The workpiece and polishing pad are moved relative to each other by a combination of rotation of the workpiece and rotation of the polishing pad, each of which has an axis in a first direction, and oscillation in a second direction perpendicular to the first direction, which increases or decreases the distance between the two axes. This prevents uneven wear on the polishing pad and reduces the frequency of polishing pad regeneration or replacement, contributing to cost reduction and further improving polishing uniformity and polishing rate. In particular, when using a polishing pad made of quartz glass plate, which is expensive and difficult to regenerate, the time until replacement can be extended. Furthermore, when a polishing pad with a vitrified bonded grinding wheel is used, shape control is achieved, and the roughness of the polished surface of the workpiece can be controlled by changing the type and size of the abrasive grains. Furthermore, when a polishing pad made of woven or nonwoven glass wool is used, it is suitable for finish polishing. These polishing pads can be used to polish SiC, GaN, AlN, Ga, etc. ２ O ３ It is possible to precisely finish difficult-to-process materials such as diamond.

[0030] The workpiece and polishing pad are each held facing each other in a removably attachable manner on a mounting part having a rotation axis facing a first direction, and when the workpiece and / or polishing pad are attached or detached, the workpiece and polishing pad are stopped from rotating and moved in a second direction beyond the range of oscillation in a normal polishing process, and the workpiece and / or polishing pad are attached or detached from the mounting part in a state where they are exposed from the opposing member, which makes it easier to attach and detach the workpiece and polishing pad, increases the operating rate of the polishing apparatus, and contributes to reducing polishing costs.

[0031] 1 is a longitudinal sectional view showing the concept of a plasma-assisted polishing apparatus according to the present invention; FIG. 2 is an abbreviated plan view showing the oscillation mode of the same; FIG. 3 is an abbreviated plan view showing the attachment / detachment mode of the same; FIG. 4 shows an example of a polishing pad having lattice grooves formed on the surface of a quartz glass plate, where (a) is a plan view, and (b) is a cross-sectional view along line X-X of (a); FIG. 5 shows an example of a polishing pad having multiple vitrified bond grinding wheels attached to a base plate, where (a) is a plan view, (b) is a cross-sectional view along line Y1-Y1 of (a), and (c) is a cross-sectional view along line Y2-Y2 of (a); FIG. 6 shows another example of a polishing pad having multiple vitrified bond grinding wheels attached to a base plate, where (a) is a plan view, (b) is a cross-sectional view along line Z1-Z1 of (a), and (c) is a cross-sectional view along line Z2-Z2 of (a);

[0032] The present invention will now be described in more detail with reference to the embodiments shown in the accompanying drawings. Figures 1 and 2 show a plasma-assisted polishing apparatus of the present invention, in which reference numerals 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 110, 111, 112, 113, 114, 115, 116, 117, 118, 120, 121, 122, 123, 124

[0033] The plasma-assisted polishing apparatus of the present invention comprises a chamber 1 containing a process gas containing a carrier gas and a reactive gas and accommodating a mechanical unit, a gas supply means 2 for supplying the process gas into the chamber 1, a gas exhaust means 3 for exhausting the process gas from the chamber 1, a mechanical unit 4 having an attachment part for detachably holding a workpiece W to be polished and a polishing pad P facing each other and moving the workpiece W and the polishing pad P relative to each other while bringing them into contact with each other at a predetermined contact pressure F, and a high-frequency power supply 5 for generating neutral radicals based on the reactive gas by applying high-frequency power between opposing electrode plates while maintaining the process gas at a predetermined pressure.

[0034] More specifically, the mechanical section 4 includes a first rotation unit 6 having a first rotation shaft 9, a first mounting section 10 for detachably holding the polishing pad P, and a rotary table 11 that also serves as an electrode plate, a first rotation shaft 12, a second mounting section 13 having an area smaller than that of the rotary table 11 and for detachably holding the workpiece W, a second rotation unit 7 having a pressing means 14 for applying contact pressure F between the workpiece W and the polishing pad P, and a counter electrode plate 15 facing the rotary table 11, and a linear drive means 8 for linearly displacing the first rotation unit 6 in a second direction perpendicular to the first direction. The plasma-assisted polishing apparatus of this embodiment is suitable for planarizing a workpiece W such as a semiconductor wafer.

[0035] In another embodiment, when a workpiece W is held on the first mounting portion 10 of the first rotary unit 6 and a polishing pad P is held on the second mounting portion 13 of the second rotary unit 7, it is possible to locally polish the surface of a large-area workpiece W with a small-area polishing pad P. In this case, the position of the polishing pad P relative to the workpiece W is controlled by numerically controlling the rotation angle of the rotary table 11 and the linear drive amount of the linear drive means 8.

[0036] In still another embodiment, the second rotation unit 7 can be linearly displaced in the second direction by the linear drive means 8. Here, a rotary swing means having an arm instead of the linear drive means 8 can be considered, but the first rotation unit 6 has the rotary table 11 and its drive system, and the second rotation unit 7 has the second mounting portion 13 and its drive system, the pressing means 14, and the counter electrode plate 15 with a large area, so that both would be heavy in weight, and therefore a rotary swing means is not preferable.

[0037] The present invention includes a surface modification process in which the above-mentioned plasma-assisted polishing apparatus is used to generate plasma by applying high-frequency power to a process gas containing a carrier gas and a reactive gas, thereby generating neutral radicals based on the reactive gas, and the neutral radicals are caused to act on the surface of the workpiece W to form a surface-modified layer on the surface of the workpiece W that is softer than the workpiece itself; and a polishing process in which the workpiece W and a polishing pad P are moved relative to each other while being brought into contact with each other at a predetermined contact pressure F, thereby removing the surface-modified layer of the workpiece W. When the surface modification process and the polishing process are repeated alternately, or when both processes are carried out simultaneously to polish the workpiece W and the polishing pad P, the workpiece is polished by a combination of the operation of moving the workpiece W and the polishing pad P relative to each other, which combines rotation of the workpiece W and rotation of the polishing pad P, each of which has an axis in a first direction, and oscillation in a second direction that is perpendicular to the first direction and increases or decreases the distance between the two axes.

[0038] This embodiment will be described in more detail. The chamber 1 does not need to be a large-scale vacuum vessel because the process gas pressure is near atmospheric pressure. The process gas pressure is preferably near atmospheric pressure to sufficiently increase the neutral radical concentration that contributes to the oxidation rate of the surface modification process, and a reduced pressure is preferable in consideration of plasma stability. Therefore, in this embodiment, the process gas pressure is set to 100 Pa (0.75 Torr) to 101.325 kPa (760 Torr).

[0039] The process gas is a mixture of a carrier gas for stably maintaining plasma and a reactive gas selected according to the material to be polished. As the carrier gas, an inert gas, particularly a rare gas such as helium (He) or argon (Ar), is used. Here, He has the advantage of being able to easily generate plasma under atmospheric pressure, but it is rare and expensive. Therefore, it is desirable to use relatively inexpensive Ar, but since He has inferior plasma stability compared to He, a stabilizing gas with a smaller ionization potential than the metastable level of Ar is added to ionize it by the Penning effect, generating electrons necessary for generating and maintaining plasma. Examples of the stabilizing gas include alcohol, hydrocarbon gas, and ammonia. As the reactive gas, oxygen gas (O ２), hydrogen gas (H ２ ), water vapor (H ２ O), hydrogen peroxide (H ２ O ２ ), fluorine-based gas (CF ４ , C ２ F ６ , C ３ F ８ , SF ６ , N.F. ３ ) etc.

[0040] The plasma-assisted polishing apparatus of this embodiment will be described in more detail. The first rotating unit 6 has a rotating shaft 9 facing a first direction (vertical direction) on the upper surface of a flat, box-shaped base 16. The upper end of the rotating shaft 9 has a flange 17 and a rotating table 11. The rotating shaft 9 passes through a protective tube 18 fixed to the upper surface of the base 16 and is rotatably supported therein via a thrust bearing 19 and a radial bearing 20. The upper surface of the rotating table 11 serves as the first mounting portion 10. A rotary motor 21 is disposed on the upper surface of the base 16 parallel to the protective tube 18, and its drive shaft 22 is linked to the rotating shaft 9 via a gear mechanism 23 inside the base 16. The rotating table 11 is made of a conductive material and also serves as an electrode plate. A polishing pad P can be detachably held on the first mounting portion 10 provided on the upper surface.

[0041] The linear drive means 8 includes two parallel linear guides 24, 24 provided on the bottom surface of the chamber 1, a plurality of movable bodies 25, ... that slide on the linear guides 24, and a linear actuator 26 disposed on the arbores of both linear guides 24, 24. The linear actuator 26 is composed of a drive motor 27 and a ball screw feed mechanism 28. The base 16 of the first rotation unit 6 is placed and fixed on the movable bodies 25, ..., and a movable part 29 of the ball screw feed mechanism 28 is fixed to the base 16, so that the first rotation unit 6 is linearly driven in the second direction (horizontal direction) by rotation of the drive motor 27. The rotary table 11 is electrically connected to the chamber 1 via the members of the first rotation unit 6, the linear guides 24, and the movable bodies 25, and the chamber 1 is grounded.

[0042] In the second rotating unit 7, the counter electrode plate 15 is fixed in an electrically insulated state relative to the chamber 1, and the second mounting portion 13 faces downward through an opening 30 provided in a portion of the counter electrode plate 15. The workpiece W held by the second mounting portion 13 comes into contact with the polishing pad P held by the first mounting portion 10 of the rotary table 11. The second mounting portion 13 is rotated by a rotating shaft 12 in a first direction (vertical direction). Here, the rotation drive system of the rotating shaft 12 is omitted, but it is insulated from the counter electrode plate 15 to which high-frequency power is applied. In this embodiment, a support cylinder 31 made of an insulating material is fixed to the upper surface around the opening 30 of the counter electrode plate 15, and the rotating shaft 12 is supported by a shaft cylinder 33 rotatably supported by bearings 32 relative to the support cylinder 31, so that the rotating shaft 12 can slide up and down. A pressing means 14 is provided to press the rotating shaft 12 downward with a predetermined load. However, the present invention is not limited to this structure. In particular, since a high frequency voltage is applied from the high frequency power supply 5 to the counter electrode plate 15 of the second rotating unit 7, the rotary motor of the rotary shaft 12 must be reliably insulated, and therefore it is preferable to install it outside the chamber 1. In addition, the mechanical part 4 has a structure that prevents corrosion against the process gas, plasma, and neutral radicals.

[0043] The gas supply means 2 supplies a carrier gas and a reactive gas from a carrier gas cylinder 34 and a reactive gas cylinder 35, respectively, into the chamber 1. Note that the reactive gas is H, which is a liquid at room temperature and pressure. ２ O and H ２ O ２ In this case, a mechanism is required to vaporize the gas using a liquid vaporizer and mix it with the carrier gas. The flow rates of various gases are accurately controlled via mass flow controllers (MFCs). The flow rate of liquids is accurately controlled via liquid mass flow controllers (LMFCs). The gas exhaust means 3 is composed of a vacuum pump. The pressure of the process gas in the chamber 1 is adjusted by the gas supply means 2 and the gas exhaust means 3.

[0044] With process gas present at a predetermined pressure in the chamber 1, a high-frequency voltage is applied from the high-frequency power supply 5 to the counter electrode plate 15, generating plasma in the space between the polishing pad P on the rotary table 10 and the counter electrode plate 15. Then, with the polishing pad P and the workpiece W in contact with each other at a predetermined contact pressure, the rotary table 11 (polishing pad P) is rotated at a predetermined rotational speed, and the second mounting unit 13 (workpiece W) is also rotated at a predetermined rotational speed. Furthermore, as shown in FIG. 2 , the linear drive means 8 is driven to oscillate the first rotation unit 6 in the second direction (horizontal direction) with a predetermined amplitude, thereby polishing the workpiece W. This polishing is referred to as an oscillation mode. It is important to keep the overlapping area between the rotary table 11 and the counter electrode plate 15 unchanged, i.e., to prevent the capacitance of the capacitively coupled plasma from changing, thereby preventing changes in the plasma generation conditions. To achieve this, the dimension of the counter electrode plate 15 in the second direction is set to be larger than the diameter of the rotary table 11 by at least the oscillation amplitude.

[0045] When holding the workpiece W before polishing in the second mounting part 13 or when removing the workpiece W from the second mounting part 13 after polishing, the workpiece W needs to be attached and detached. Furthermore, as the polishing time increases, the polishing pad P needs to be regenerated or replaced. For this purpose, a detachment mode is provided in this embodiment. In the detachment mode, as shown in FIG. 3 , the linear driving means 8 is driven to a position where the workpiece W and / or polishing pad P are exposed from the opposing members of the opposing first rotation unit 6 and / or second rotation unit 7.

[0046] The polishing pad P is a plate having, at least on its surface, one of a quartz glass plate, a vitrified bond grinding wheel in which abrasive grains are bonded with an inorganic glass-based bond material, and a woven or nonwoven fabric made of glass wool. ２ , Al ２ O ３ The type and grain size (grain size) of abrasive grains can be selected depending on the material to be polished and the required surface roughness. ２ , diamond, SiO２ , Al ２ O ３ (WA fine powder), CBN, SiC (GC fine powder), BaSO ４ , TiO ２ , ZnO, etc., and the particle size can be selected from a wide range, from #46 (average particle size 355 μm) to #120,000 (average particle size 0.05 μm). For example, when the workpiece W is a substrate having at least a surface layer of either single crystal diamond (SCD), polycrystalline diamond (PCD), or diamond-like carbon (DLC), a vitrified bond grinding wheel with abrasive grains of #1000 (average particle size 16 μm) to #20,000 (average particle size 0.8 μm) diamond is used as the polishing pad P. Abrasive grains coarser than #1000 increase the polishing rate, but large cracks and scratches occur on the surface of the workpiece W, which makes subsequent finish polishing time undesirable. On the other hand, abrasive grains finer than #20,000 decrease the polishing rate and increase the polishing time, but do not improve the surface roughness, which is undesirable from the standpoint of industrial polishing efficiency.

[0047] Furthermore, at the contact area between the workpiece W and the polishing pad P, grooves or uneven structures on at least one surface of the workpiece W and the polishing pad P form a flow path communicating with the space where plasma is generated, and neutral radicals can be supplied to the surface of the workpiece W through this flow path, thereby increasing the surface modification rate of the workpiece W and improving polishing efficiency. Furthermore, the presence of grooves or uneven structures at the contact area between the workpiece W and the polishing pad P allows polishing debris to be collected in the recesses, improving polishing efficiency and preventing adhesion at the contact area. In this embodiment, grooves or uneven structures are provided on the surface of the polishing pad P, but grooves can also be provided on the surface of the workpiece W. For example, if the workpiece W is a semiconductor wafer, it can be polished with grooves already provided along the scribe lines for dicing into chips. It has been confirmed that providing grooves or uneven structures on at least one surface of the contact area between the workpiece W and the polishing pad P improves the polishing rate.

[0048] The polishing pad P1 shown in Figure 4 has a structure in which lattice-shaped grooves 37 are formed on the surface of a quartz glass plate 36. The polishing pad P2 shown in Figure 5 has a structure in which multiple small, flat, disc-shaped vitrified bond grinding stones 39 are attached in a close-packed hexagonal lattice pattern to the entire surface of a disc-shaped base plate 38. A recess 40 with three cusps is formed between three vitrified bond grinding stones 39. The polishing pad P3 shown in Figure 6 is a modification of the polishing pad P2 described above. Multiple small, flat, disc-shaped vitrified bond grinding stones 39 are attached to each semicircular portion of the base plate 38 in a close-packed hexagonal lattice pattern, with mirror-symmetrical arrangements on both sides of the diameter. In addition to the recess 40, this polishing pad P3 also has a recess 41 with four cusps formed between four vitrified bond grinding stones 39 in the diameter portion. The grooves or uneven structure formed in the polishing pad P are not limited to the above-described shapes and structures. If the vitrified bond grinding wheels 39 are square, lattice-shaped recesses (lattice-shaped grooves) are formed between the grinding wheels by aligning them with gaps.

[0049] Wide bandgap materials such as SiC, GaN, and diamond, which are used for polishing, are chemically very stable. Therefore, even when OH radicals or O radicals are used, the surface modification (oxidation) rate is low, and therefore the material removal rate (MMR) is also low. Therefore, to further enhance the MMR, it is desirable to irradiate the polishing surface of the workpiece with ultraviolet light during the surface modification process to activate the surface. UV light sources include ultraviolet lamps, ultraviolet LEDs, and excimer lasers. The wavelength of the ultraviolet light must be equal to or less than the bandgap energy of the material being polished. For example, the bandgap of 4H-SiC is 3.26 eV, so the wavelength of the ultraviolet light irradiated is 380 nm or less; the bandgap of GaN is 3.42 eV, so the wavelength of the ultraviolet light irradiated is 362 nm or less; and the bandgap of diamond is 5.47 eV, so the wavelength of the ultraviolet light irradiated is 227 nm or less.

[0050] The polishing surface of the workpiece W is irradiated with ultraviolet light from an ultraviolet light source disposed behind the polishing pad P. If the polishing pad P is made of a material that transmits ultraviolet light, i.e., quartz glass, the ultraviolet light passes through the polishing pad P and irradiates the polishing surface of the workpiece W. On the other hand, if the polishing pad P is made of a material that does not transmit ultraviolet light, a transmission hole is provided in the polishing pad P that runs through from the front to the back, and the ultraviolet light is irradiated onto the polishing surface of the workpiece W through the transmission hole. Here, when a transmission hole is provided in the polishing pad P, it is sufficient to provide the transmission hole at the position of the groove 37 or the recesses 40, 41. The transmission hole may be blocked by providing a window made of a material that transmits ultraviolet light.

[0051] The workpiece (material to be polished) was a 20 mm x 20 mm x 1 mm polycrystalline diamond plate (manufactured by Tomei Diamond Co., Ltd.). The polishing pads used were #6000 (average particle size 2.7 μm) and #10000 (average particle size 1.6 μm) diamond vitrified bond grinding wheels (manufactured by Alpha Diamond Industrial Co., Ltd.) and quartz glass plates. A 1 mm square pit was formed in the center of the polycrystalline diamond plate, and the machining rate (MMR) was calculated from the change in pit depth after PAP. The polishing conditions and polishing results are shown in Table 1.

[0052]

[0053] Comparing Tests 1 and 2, which used a #6000 diamond vitrified bond grinding wheel, the effect of plasma surface modification was clear, confirming that plasma generation enabled polishing of polycrystalline diamond plates at a high polishing rate of approximately 1 μm / hr. This polishing rate was comparable to or even surpassed that achieved using quartz glass plates in Tests 4 and 5. It was found that industrial polishing of polycrystalline diamond plates is possible even when using a diamond vitrified bond grinding wheel instead of an expensive quartz glass plate. Furthermore, comparing the polishing results of Tests 1 and 3, which used #6000 and #10000 diamond vitrified bond grinding wheels, the polishing rate for #10000 was slightly lower, but the surface roughness improved due to the smaller abrasive grain size. For example, when polishing for 60 minutes using a #6000 diamond vitrified bond grinding wheel, the surface roughness Sa at the center of the polycrystalline diamond plate was 7.452 nm, but when polishing for 60 minutes using a #10000 diamond vitrified bond grinding wheel, Sa was 6.554 nm.

[0054] DESCRIPTION OF SYMBOLS W: Workpiece, P, P1, P2, P3: Polishing pad, 1: Chamber, 2: Gas supply means, 3: Gas exhaust means, 4: Mechanical section, 5: High frequency power supply, 6: First rotation unit, 7: Second rotation unit, 8: Linear drive means, 9: Rotation shaft, 10: First mounting section, 11: Rotary table, 12: Rotation shaft, 13: Second mounting section, 14: Pressing means, 15: Counter electrode plate, 16: Base section, 17: Flange section, 18: Protective tube, 19: Thrust bearing, 20: Radial bearing, 21: Rotation motor, 22: Drive shaft, 23: Gear mechanism, 24: Linear guide, 25: Moving body, 26: Linear actuator, 27: Drive motor, 28: Ball screw feed mechanism, 29: Movable section, 30: Opening, 31: Support tube, 32: Bearing, 33 barrel, 34 carrier gas cylinder, 35 reactive gas cylinder, 36 quartz glass plate, 37 grid-like groove, 38 base plate, 39 vitrified bond grinding wheel, 40 recess, 41 recess.

Claims

1. A plasma-assisted polishing method comprising: a surface modification process in which neutral radicals based on the reactive gas are generated by applying high-frequency power to a process gas containing a carrier gas and a reactive gas, and the neutral radicals are caused to act on the surface of a workpiece to form a surface modified layer on the surface of the workpiece that is softer than the workpiece; and a polishing process in which the workpiece and a polishing pad are moved relatively while being brought into contact with each other at a predetermined contact pressure, thereby removing the surface modified layer of the workpiece, wherein the surface modification process and the polishing process are alternately repeated, or both processes are carried out simultaneously to polish the workpiece, wherein in the operation of moving the workpiece and the polishing pad relatively, the workpiece is polished by a combination of an operation of rotating the workpiece and the polishing pad, each of which has an axis in a first direction, and an oscillation in a second direction that is perpendicular to the first direction and increases or decreases the distance between the two axes.

2. The plasma-assisted polishing method according to claim 1, wherein the plasma in the surface modification process is a capacitively coupled plasma, and the capacitance does not change during the oscillating action.

3. A plasma-assisted polishing method as described in claim 1, wherein the workpiece and polishing pad are each held in a removably manner and opposed to each other on a mounting part having a rotation axis facing a first direction, and when the workpiece and / or polishing pad are attached or detached, the workpiece and polishing pad are moved in a second direction beyond the range of oscillation in a normal polishing process while stopping their rotation, and the workpiece and / or polishing pad are attached or detached from the mounting part in a state where they are exposed from the opposing member.

4. The plasma-assisted polishing method according to claim 1, 2 or 3, wherein the polishing pad is a plate having at least a surface thereof made of a quartz glass plate, a vitrified bond grinding wheel in which abrasive grains are bonded with an inorganic glass-based bond material, or a woven or non-woven glass wool fabric.

5. A plasma-assisted polishing method as described in claim 4, wherein a flow path communicating with a space in which plasma is generated is formed by a groove or uneven structure provided on at least one surface of the workpiece and polishing pad at the contact area between the workpiece and the polishing pad, and neutral radicals are supplied to the workpiece surface via the flow path.

6. The workpiece is a substrate having at least a surface layer of either single crystal diamond (SCD), polycrystalline diamond (PCD), or diamond-like carbon (DLC); the polishing pad has a vitrified bond grinding wheel at least on its surface, and the abrasive grains are diamonds with a diameter of #1000 (average grain size 16 μm) to #20000 (average grain size 0.8 μm); the reactive gas is water vapor (H ２ O) or hydrogen peroxide (H ２ O ２ 5. The method of claim 4, comprising:

7. The plasma-assisted polishing method according to claim 4, wherein the surface modification process includes a step of irradiating the polishing surface of the workpiece with ultraviolet light that has been transmitted through at least a portion of the polishing pad.

8. A plasma-assisted polishing apparatus comprising: a chamber containing a process gas including a carrier gas and a reactive gas and accommodating a mechanical section; a gas supply means for supplying the process gas into the chamber; a gas exhaust means for exhausting the process gas from within the chamber; a mechanical section having an attachment section for detachably holding a workpiece to be polished and a polishing pad facing each other and for relatively moving the workpiece and the polishing pad while bringing them into contact with each other at a predetermined contact pressure; and a high-frequency power source for generating neutral radicals based on a reactive gas by applying high-frequency power between opposing electrode plates while maintaining the process gas at a predetermined pressure, wherein the mechanical section comprises: a first rotating unit having a rotating shaft in a first direction, and a first attachment section for detachably holding the polishing pad or the workpiece, and having a rotating table that also serves as an electrode plate; a second mounting portion having an area smaller than that of the rotating table and configured to detachably hold the workpiece or the polishing pad; a second rotating unit having a counter electrode plate opposed to the rotating table and displaceable in the first direction and a pressing means for applying contact pressure between the workpiece and the polishing pad; and a linear driving means for linearly displacing the first rotating unit or the second rotating unit in a second direction perpendicular to the first direction.

9. A plasma-assisted polishing apparatus as described in claim 8, wherein the workpiece and polishing pad are held and opposed to each other by either a first mounting portion of a first rotating unit or a second mounting portion of a second rotating unit, and in a swing mode in a normal polishing process, the linear drive means is driven so as to reciprocate within a range in which the rotating table and the opposing electrode plate maintain an opposed state.

10. The plasma assisted polishing apparatus according to claim 9, wherein the dimension of said counter electrode plate in the second direction is set to be larger than the diameter of said rotary table by at least the oscillation amplitude, so that the capacitance of the capacitively coupled plasma does not change in the oscillation mode.

11. A plasma-assisted polishing apparatus as described in claim 8, wherein the workpiece and polishing pad are held and opposed by either a first mounting portion of a first rotating unit or a second mounting portion of a second rotating unit, and in an attachment / detachment mode for attaching and detaching the workpiece and / or polishing pad, the linear drive means is driven to a position where the workpiece and / or polishing pad are exposed from the opposing member of the opposing first rotating unit and / or second rotating unit.

12. A plasma-assisted polishing apparatus according to any one of claims 8 to 11, wherein the polishing pad is a plate having, on at least its surface, a quartz glass plate, a vitrified bond grinding wheel in which abrasive grains are bonded with an inorganic glass-based bond material, or a woven or nonwoven glass wool fabric.

13. A plasma-assisted polishing apparatus as described in claim 8, wherein at the contact area between the workpiece and the polishing pad, a flow path communicating with a space in which plasma is generated is formed by a groove or uneven structure provided on at least one of the surfaces of the workpiece and the polishing pad, and neutral radicals are supplied to the workpiece surface via the flow path.

14. The workpiece is a substrate having at least a surface layer of either single crystal diamond (SCD), polycrystalline diamond (PCD), or diamond-like carbon (DLC); the polishing pad has a vitrified bond grinding wheel at least on its surface, and the abrasive grains are diamonds with a diameter of #1000 (average grain size 16 μm) to #20000 (average grain size 0.8 μm); the reactive gas is water vapor (H ２ O) or hydrogen peroxide (H ２ O ２ 9. The plasma assisted polishing apparatus of claim 8, comprising:

15. The plasma-assisted polishing apparatus according to claim 8, further comprising an ultraviolet light source disposed behind said polishing pad, and a structure for transmitting ultraviolet light from said ultraviolet light source through at least a portion of said polishing pad and its mounting portion and irradiating the polishing surface of said workpiece with the ultraviolet light.

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