Plasma-assisted polishing method and device thereof

Abstract

To provide a plasma-assisted polishing method and a device thereof for easily performing attachment / detachment work of a polish pad and a work-piece while suppressing unsymmetrical wear of the polish pad in processing of a material hard to be processed using a plasma-assisted polishing method.SOLUTION: In a motion of relatively moving a work-piece W and a polish pad P, the work-piece is polished by the motion combining rotations of the work-piece and the polish pad having shafts in a first direction and an oscillation in a second direction that is orthogonal to the first direction and increases / decreases a distance between both the shafts. The work-piece and the polish pad are retained attachably / detachably on installation parts 10, 13 assembled with rotation shafts 9, 12 facing the first direction so as to be opposed to each other. When attaching / detaching the work-piece and / or the polish pad, in a state of stopping the rotations of the work-piece and the polish pad, the work-piece and / or the polish pad are moved to the second direction beyond the range of oscillation in usual polish processing and are attached / detached to / from the installation parts in a state of being exposed from the opposite member.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a plasma-assisted polishing method and an apparatus therefor that are suitable for precision finishing of difficult-to-process materials such as SiC, GaN, AlN, Ga2O3, and diamond. [Background technology]

[0002] In recent years, there has been active development of devices using wide band gap semiconductors, which are capable of reliable operation even in high temperature environments and have low loss, as power semiconductor device materials. Wide band gap semiconductors are exemplified by SiC, GaN, Ga2O3, and diamond, in order of decreasing band gap. These wide band gap semiconductors have physical properties such as band gap, dielectric breakdown field value, thermal conductivity, and electron mobility several to several tens of times larger than those of Si, so when power devices are manufactured using these materials, there are advantages such as high voltage resistance, reduced power consumption, and high speed operation. However, due to their high hardness and chemical inertness, they are difficult to process materials, and it is difficult to efficiently obtain the desired flatness and surface roughness by normal polishing.

[0003] Currently, wide band gap 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 defects of the material are eroded by the alkaline components, resulting in "etch pits", which deteriorate the surface roughness, and the abrasive grains aggregate and coarsen, which results in the material properties not being fully utilized. In addition, the polishing efficiency is low, and the yield is low, resulting in high costs.

[0004] Conventionally, plasma-assisted polishing (PAP) has been proposed as a method for processing difficult-to-machine materials such as SiC, GaN, or cemented carbide (Patent Document 1). In this PAP method, radicals generated in plasma are applied to the surface of a workpiece to form a surface-modified layer that is softer than the workpiece material, while the surface-modified layer is removed by dry mechanical polishing using an abrasive material to proceed with the machining. The PAP method is an excellent machining method that can perform precision machining without introducing scratches or a processing-affected layer on the workpiece based on the machining principle, if an abrasive material having an intermediate Mohs hardness between the workpiece material and the surface-modified layer is used. Patent Document 1 shows that, as a radical that oxidizes the surface of the workpiece and forms a surface-modified layer (oxide layer), OH radicals have a superior oxidizing effect on SiC and are more efficient than O radicals. For this purpose, high-frequency power is applied to an atmosphere containing a carrier gas and one or both of H2O and H2O2 to generate plasma, and OH radicals are generated.

[0005] Patent Document 2 discloses a machining method using radical adsorption and transport, in which the surface of a movable tool having a surface with corrosion resistance and adsorption ability against chemically reactive radicals is passed through a plasma generation region generated by using a reactive gas containing at least a gas containing an element or a substituent that generates the radicals and a rare gas, the radicals generated in the plasma generation region are adsorbed on the tool surface to give reactive species, the reactive species on the tool surface are transported to a workpiece surface arranged at a position different from the plasma generation region by moving the tool, and a reaction product generated by a chemical reaction between the atoms on the workpiece surface in contact with the tool and the reactive species is removed, thereby selectively machining only the part of the workpiece surface that is in contact with the tool surface using the tool surface as a machining reference surface. Here, it is also disclosed that the element that generates the radicals is a halogen element such as F or Cl, and the radicals are F radicals or Cl radicals, or that the substituent that generates the radicals 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 a tool acting as an abrasive move in contact with each other while moving relative to each other, so it can also be called a type of PAP.

[0006] Cited Document 3 discloses a processing method in which, in PAP, a polishing tool made of a vitrified bond grinding wheel in which abrasive grains are bonded with an inorganic glass-based bond material, or a resin bond 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 form a surface modification layer by fluorination or oxidation, 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. As a result, an automatic dressing action occurs in which the bond material of the polishing tool is etched to expose the abrasive grains, preventing a decrease in polishing speed due to "glazing" or "clogging," enabling precision processing that maintains a high polishing rate without dressing, and making it possible to process difficult-to-process materials such as SiC, GaN, and AlN.

[0007] Furthermore, Non-Patent Document 1 reports that a PAP suitable for processing diamond is a polishing pad made of quartz glass that is irradiated 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 is 0.3 nm under low polishing pressure conditions, such as 62.5 and 81.3 kPa. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 5614677 [Patent Document 2] Patent No. 6692010 [Patent Document 3] JP 2022-133198 A [Non-patent literature]

[0009] [Non-Patent Document 1] 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. Summary of the Invention [Problem to be solved by the invention]

[0010] It is common to offset the rotation axis of the polishing pad and the rotation axis of the workpiece when polishing, but even so, the polishing pad still wears unevenly, so the polishing pad needs to be regenerated frequently, and if it cannot be regenerated, it needs to be replaced. In particular, it is difficult to regenerate the quartz glass used when processing diamonds, and the high price of quartz glass makes it costly. In addition, when regenerating and replacing the polishing pad, it is important to easily attach and detach the polishing pad and the workpiece, which are major issues for mass production.

[0011] In view of the above-mentioned situation, the present invention aims to provide a plasma-assisted polishing method and apparatus that suppresses uneven wear of the polishing pad when processing difficult-to-process materials using plasma-assisted polishing and that makes it easy to attach and detach the polishing pad from the workpiece. [Means for solving the problem]

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

[0013] [Configuration 1] 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 a workpiece surface to form a surface modification layer on the workpiece surface that is softer than the workpiece; a polishing process in which the workpiece and a polishing pad are moved relative to each other while being brought into contact with each other at a predetermined contact pressure, thereby removing the surface modification layer of the workpiece; having A plasma-assisted polishing method, comprising: repeating the surface modification process and the polishing process alternately; or simultaneously carrying out both processes to polish the surface; In the operation of moving the workpiece and the polishing pad relatively, the workpiece is polished by a combination of a rotation of the workpiece and a rotation of the polishing pad, each of which has an axis in a first direction, and a swing in a second direction perpendicular to the first direction and increasing or decreasing the distance between the two axes. Plasma assisted polishing method.

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

[0015] [Configuration 3] The workpiece and the polishing pad are held in a freely detachable manner on a mounting part having a rotation axis facing a first direction, and are opposed to each other. When attaching or detaching the workpiece and / or the polishing pad, the workpiece and the 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 the polishing pad are attached or detached from the mounting part in a state where they are exposed from the opposing member. 2. The plasma-assisted polishing method according to claim 1.

[0016] [Configuration 4] The polishing pad is a plate having at least a surface 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 nonwoven fabric made of glass wool. The plasma-assisted polishing method according to claim 1, 2 or 3.

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

[0018] [Configuration 6] The workpiece is a substrate having at least a surface layer made of any one of single crystal diamond (SCD), polycrystalline diamond (PCD), or diamond-like carbon (DLC); The polishing pad has a vitrified bond grinding wheel on at least the surface thereof, and the abrasive grains are diamonds having a diameter of #1000 (average grain diameter 16 μm) to #20000 (average grain diameter 0.8 μm); The reactive gas contains water vapor (H2O) or hydrogen peroxide (H2O2) that generates OH radicals; Includes: 5. The plasma-assisted polishing method according to claim 4.

[0019] [Configuration 7] 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. 5. The plasma-assisted polishing method according to claim 4.

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

[0021] [Configuration 9] the workpiece and the polishing pad are held and opposed to each other by either a first mounting part of a first rotating unit or a second mounting part 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 counter electrode plate maintain an opposed state; 9. The plasma-assisted polishing apparatus according to claim 8.

[0022] [Configuration 10] 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. 10. The plasma-assisted polishing apparatus according to configuration 9.

[0023] [Configuration 11] The workpiece and the polishing pad are held and opposed to each other by either a first mounting part of a first rotating unit or a second mounting part of a second rotating unit, and in an attachment / detachment mode for attaching / detaching the workpiece and / or the polishing pad, the linear drive means is driven to a position where the workpiece and / or the polishing pad are exposed from the opposing member of the opposing first rotating unit and / or the opposing second rotating unit. 9. The plasma-assisted polishing apparatus according to claim 8.

[0024] [Configuration 12] The polishing pad is a plate having at least a surface 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 nonwoven fabric made of glass wool. 12. The plasma-assisted polishing apparatus according to any one of claims 8 to 11.

[0025] [Configuration 13] At the contact portion between the workpiece and the polishing pad, a flow path is formed that communicates with a space in which plasma is generated by a groove or an uneven structure provided on at least one surface of the workpiece and the polishing pad, and neutral radicals are supplied to the workpiece surface through the flow path. 9. The plasma-assisted polishing apparatus according to claim 8.

[0026] [Configuration 14] The workpiece is a substrate having at least a surface layer made of any one of single crystal diamond (SCD), polycrystalline diamond (PCD), or diamond-like carbon (DLC); The polishing pad has a vitrified bond grinding wheel on at least the surface thereof, and the abrasive grains are diamonds having a diameter of #1000 (average grain diameter 16 μm) to #20000 (average grain diameter 0.8 μm); The reactive gas contains water vapor (H2O) or hydrogen peroxide (H2O2) that generates OH radicals; Includes: 9. The plasma-assisted polishing apparatus according to claim 8.

[0027] [Configuration 15] An ultraviolet light source is disposed behind the polishing pad, and at least a part of the polishing pad and its mounting portion is provided with a structure for transmitting ultraviolet light from the ultraviolet light source and irradiating the polishing surface of the workpiece. 9. The plasma-assisted polishing apparatus according to claim 8. Effect of the Invention

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

[0029] In the operation of moving the workpiece and the polishing pad relatively, the workpiece is polished by a combination of the rotation of the workpiece and the rotation of the polishing pad, each of which has an axis in a first direction, and the oscillation in a second direction perpendicular to the first direction, which increases and decreases the distance between the two axes. This makes it possible to suppress uneven wear of the polishing pad, and reduces the frequency of regeneration and replacement of the polishing pad, which contributes to cost reduction and is expected to improve the uniformity of polishing and the polishing rate. In particular, when a polishing pad made of a quartz glass plate, which is expensive and difficult to regenerate, is used, the time until replacement can be extended. In addition, when a polishing pad made of a vitrified bond grinding wheel is used, shape control is obtained, and the roughness of the polished surface of the workpiece can be controlled by changing the type and grain size of the abrasive grains. In addition, when a polishing pad made of woven or non-woven glass wool is used, it is suitable for finish polishing. These polishing pads can be used to precisely finish difficult-to-machine materials such as SiC, GaN, AlN, Ga2O3, and 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 attaching or detaching the workpiece and / or polishing pad, the rotation of the workpiece and polishing pad are stopped and the workpiece and polishing pad are 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. This makes it easier to attach and detach the workpiece and polishing pad, increases the operating rate of the polishing equipment, and contributes to reducing polishing costs. [Brief description of the drawings]

[0031] [Figure 1] 1 is a vertical sectional view showing the concept of a plasma assisted polishing apparatus according to the present invention; [Diagram 2] FIG. [Diagram 3] FIG. [Figure 4] 1 shows an example of a polishing pad in which a lattice groove is formed on the surface of a quartz glass plate, where (a) is a plan view and (b) is a cross-sectional view taken along line XX of (a). [Diagram 5]1A and 1B show an example of a polishing pad in which multiple vitrified bond grinding wheels are attached to a base plate, where (a) is a plan view, (b) is a cross-sectional view taken along line Y1-Y1 in (a), and (c) is a cross-sectional view taken along line Y2-Y2 in (a). [Figure 6] 1A and 1B show another example of a polishing pad having multiple vitrified bonded grinding wheels attached to a base plate, where (a) is a plan view, (b) is a cross-sectional view taken along line Z1-Z1 of (a), and (c) is a cross-sectional view taken along line Z2-Z2 of (a). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Next, the present invention will be described in more detail with reference to the embodiment shown in the attached drawings. Figures 1 and 2 show a plasma-assisted polishing apparatus of the present invention, in which reference numerals 1 indicate a chamber, 2 a gas supply means, 3 a gas exhaust means, 4 a mechanical section, 5 a high-frequency power source, 6 a first rotation unit, 7 a second rotation unit, and 8 a linear drive means.

[0033] The plasma-assisted polishing apparatus of the present invention comprises a chamber 1 containing a process gas including 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 a mounting section 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 relatively while bringing them into contact with each other at a predetermined contact pressure F, and a high-frequency power source 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 rotating unit 6 having a rotating table 11 that also serves as an electrode plate and a rotating shaft 9 in a first direction and a first mounting section 10 that detachably holds the polishing pad P, a first rotating shaft 12 in the first direction, a second mounting section 13 that is smaller in area than the rotating table 11 and detachably holds the workpiece W, a second rotating unit 7 that is displaced in the first direction and has a pressing means 14 that applies a contact pressure F between the workpiece W and the polishing pad P and has a counter electrode plate 15 facing the rotating table 11, and a linear driving means 8 that linearly displaces the first rotating unit 6 in a second direction perpendicular to the first direction. The plasma-assisted polishing apparatus of this embodiment is suitable for polishing a workpiece W such as a semiconductor wafer to be flat.

[0035] In another embodiment, when a workpiece W is held on the first mounting portion 10 of the first rotating unit 6 and a polishing pad P is held on the second mounting portion 13 of the second rotating 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 rotating table 11 and the linear drive amount of the linear drive means 8.

[0036] In still another embodiment, the second rotating unit 7 can be linearly displaced in the second direction by the linear driving means 8. Here, a rotary swinging means having an arm instead of the linear driving means 8 is also considered, but since the first rotating unit 6 has the rotating table 11 and its drive system, and the second rotating 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, both of which are heavy in weight, the rotary swinging means is not preferable.

[0037] The present invention includes a surface modification process in which, using the above-mentioned plasma-assisted polishing apparatus, 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 the workpiece W to form a surface modification layer on the surface of the workpiece W that is softer than the workpiece, and a polishing process in which the workpiece W and a polishing pad P are moved relatively while being brought into contact with each other at a predetermined contact pressure F to remove the surface modification layer of the workpiece W. When the surface modification process and the polishing process are repeated alternately, or both processes are carried out simultaneously to polish the workpiece W and the polishing pad P, the operation of moving the workpiece W and the polishing pad P relative to each other comprises a combination of 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, to polish the workpiece.

[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 close to atmospheric pressure. The process gas pressure is preferably close to atmospheric pressure because of the need to sufficiently increase the neutral radical concentration that contributes to the oxidation rate of the surface modification process, and a reduced pressure state is preferable in consideration of the stability of the plasma. 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 is rare and expensive. Therefore, it is desirable to use relatively inexpensive Ar, but since He has inferior plasma stability to He, a stabilizing gas with a smaller ionization potential than the metastable level of Ar is added to ionize the gas by the Penning effect to generate electrons necessary for generating and maintaining plasma. Examples of the stabilizing gas include alcohol, hydrocarbon gas, and ammonia. Examples of the reactive gas include oxygen gas (O2), hydrogen gas (H2), water vapor (H2O), hydrogen peroxide (H2O2), fluorine gas (CF4, C2F6, C3F8, SF6, NF3), 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 part 16, a flange part 17 and a rotating table 11 at the upper end of the rotating shaft 9, the rotating shaft 9 penetrates inside a protective cylinder 18 fixed to the upper surface of the base part 16, and is rotatably supported inside via a thrust bearing 19 and a radial bearing 20, and the upper surface of the rotating table 11 is the first mounting part 10. In addition, a rotating motor 21 is arranged on the upper surface of the base part 16 in parallel with the protective cylinder 18, and its drive shaft 22 is linked to the rotating shaft 9 through a gear mechanism 23 inside the base part 16. The rotating table 11 is made of a conductive material and also serves as an electrode plate, and a polishing pad P can be detachably held on the first mounting part 10 provided on the upper surface.

[0041] The linear drive means 8 has two parallel linear guides 24, 24 provided on the bottom surface of the chamber 1, a plurality of moving bodies 25, ... sliding on the linear guides 24, and a linear actuator 26 arranged on the ridges 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 part 16 of the first rotating unit 6 is placed and fixed on the moving bodies 25, ..., and a movable part 29 of the ball screw feed mechanism 28 is fixed to the base part 16, so that the first rotating unit 6 is linearly driven in the second direction (horizontal direction) by the rotation of the drive motor 27. The rotating table 11 is electrically connected to the chamber 1 via the members of the first rotating unit 6, the linear guide 24, and the moving 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 with respect to the chamber 1, and the second mounting part 13 faces downward through an opening 30 provided in a part of the counter electrode plate 15, so that the workpiece W held by the second mounting part 13 comes into contact with the polishing pad P held by the first mounting part 10 of the rotating table 11. The second mounting part 13 is rotated by a rotating shaft 12 in a first direction (vertical direction). Here, the rotating shaft 12 is insulated from the counter electrode plate 15 to which high-frequency power is applied, although a rotation drive system for the rotating shaft 12 is omitted. In this embodiment, a structure is shown in which a support cylinder 31 made of an insulator is fixed to the upper surface around the opening 30 of the counter electrode plate 15, the rotating shaft 12 is supported by a shaft cylinder 33 rotatably supported by a bearing 32 relative to the supporting cylinder 31, the rotating shaft 12 is supported so as to be vertically slidable, and a pressing means 14 is provided to press the rotating shaft 12 downward with a predetermined load, but 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 rotating motor of the rotating shaft 12 must be securely insulated, and therefore it is preferable to have a structure in which it is installed outside the chamber 1. In addition, the mechanism 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. When the reactive gas is H2O or H2O2, which is a liquid at room temperature and pressure, a mechanism is required to vaporize it in 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] In a state where a process gas exists at a predetermined pressure in the chamber 1, a high frequency voltage is applied from a high frequency power supply 5 to the counter electrode plate 15, and plasma is generated in the space between the polishing pad P on the rotating table 10 and the counter electrode plate 15. Then, in a state where the polishing pad P and the workpiece W are in contact with each other at a predetermined contact pressure, the rotating table 11 (polishing pad P) is rotated at a predetermined rotation speed, and the second mounting part 13 (workpiece W) is rotated at a predetermined rotation speed. Furthermore, as shown in FIG. 2, the linear driving means 8 is driven to swing the first rotating unit 6 in the second direction (horizontal direction) with a predetermined amplitude, and the workpiece W is polished. This polishing is called a swing mode. Here, it is important that the overlapping area of ​​the rotating table 11 and the counter electrode plate 15 does not change even when the linear driving means 8 swings, that is, the capacitance of the capacitively coupled plasma does not change, and the plasma generation conditions are not changed. For this reason, the dimension of the counter electrode plate 15 in the second direction is set to be larger than the diameter of the rotating table 11 by at least the swing amplitude.

[0045] When the workpiece W before polishing is held in the second mounting part 13, or when the workpiece W after polishing is removed from the second mounting part 13, the workpiece W needs to be attached and detached. In addition, when the polishing time is long, 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 drive means 8 is driven to a position where the workpiece W and / or the polishing pad P are exposed from the opposing members of the opposing first rotating unit 6 and / or second rotating unit 7.

[0046] The polishing pad P is a plate having at least one of a quartz glass plate, a vitrified bond grindstone in which abrasive grains are bonded with an inorganic glass-based bond material, and a woven or nonwoven fabric made of glass wool on its surface. For example, SiO2, Al2O3, etc. can be used as the inorganic glass-based bond material of the vitrified bond grindstone, and the type and grain size (grain size) of the abrasive grains can be selected according to the material to be polished and the required surface roughness. The types of abrasive grains include CeO2, diamond, SiO2, Al2O3 (WA fine powder), CBN, SiC (GC fine powder), BaSO4, TiO2, ZnO, etc., and the grain size can be selected from a wide range of grain sizes from #46 (average grain size 355 μm) to #120,000 (average grain 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 grindstone made of diamond with abrasive grains of #1000 (average grain size 16 μm) to #20000 (average grain size 0.8 μm) is used as the polishing pad P. If the abrasive grains are coarser than #1000, the polishing rate is high, but large cracks and scratches are generated on the surface of the workpiece W, and the subsequent finish polishing takes time, which is not preferable. On the other hand, if the abrasive grains are finer than #20000, the polishing rate is low and the polishing time is long, but the improvement of the surface roughness does not progress, which is not preferable from the viewpoint of industrial polishing efficiency.

[0047] At the contact portion between the workpiece W and the polishing pad P, a flow path communicating with the space where plasma is generated is formed by a groove or uneven structure provided on at least one surface of the workpiece W and the polishing pad P, and neutral radicals can be supplied to the surface of the workpiece W through the flow path, so that the surface modification rate of the workpiece W is increased, which is preferable in terms of polishing efficiency. In addition, by having a groove or uneven structure at the contact portion between the workpiece W and the polishing pad P, polishing waste is collected in the recessed portion, so that the polishing efficiency is improved and the sticking of the contact portion can be suppressed. In this embodiment, a groove or uneven structure is provided on the surface of the polishing pad P, but a workpiece W having a groove on its surface can also be used. For example, when the workpiece W is a semiconductor wafer, it is possible to polish the workpiece W in a state where a groove is provided in advance along the scribe line for dividing the workpiece W into chip units by dicing. In this way, it has been confirmed that the polishing rate is improved by providing a groove or uneven structure on at least one surface of the contact portion between the workpiece W and the polishing pad P.

[0048] The polishing pad P1 shown in FIG. 4 has a structure in which a lattice-shaped groove 37 is formed on the surface of a quartz glass plate 36. The polishing pad P2 shown in FIG. 5 has a structure in which a plurality of small flat disk-shaped vitrified bond grinding wheels 39 are attached in a close-packed hexagonal lattice structure on the entire surface of a disk-shaped base plate 38. Here, a recess 40 having three apexes is formed between the three vitrified bond grinding wheels 39, .... The polishing pad P3 shown in FIG. 6 is a modified example of the above-mentioned polishing pad P2, and has a structure in which a plurality of small flat disk-shaped vitrified bond grinding wheels 39 are attached in a close-packed hexagonal lattice structure on each semicircular portion of the base plate 38, and are arranged in mirror symmetry on both sides of the diameter. In addition to the recess 40, this polishing pad P3 has a recess 41 having four apexes formed between four vitrified bond grinding wheels 39, ... on the diameter portion. The grooves or uneven structure formed in the polishing pad P are not limited to the above-mentioned shapes and structures. If the vitrified bond grindstones 39 are square, lattice-shaped recesses (lattice-shaped grooves) are formed between the grindstones by aligning them with gaps.

[0049] Wide band gap materials such as SiC, GaN, and diamond, which are the materials to be polished, are chemically very stable, so that even if 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, in order to further increase the MMR, it is desirable to irradiate the polishing surface of the material to be polished (workpiece) with ultraviolet light during the surface modification process to activate the polishing surface. For the ultraviolet light source, an ultraviolet lamp, an ultraviolet LED, an excimer laser, or the like is used. It is required that the wavelength of the ultraviolet light is equal to or less than the wavelength corresponding to the band gap energy of the material to be polished. For example, the band gap of 4H-SiC is 3.26 eV, so the wavelength of the ultraviolet light to be irradiated is 380 nm or less, the band gap of GaN is 3.42 eV, so the wavelength of the ultraviolet light to be irradiated is 362 nm or less, and the band gap of diamond is 5.47 eV, so the wavelength of the ultraviolet light to be 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, that is, if it is made of 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 penetrates from the front to the back, and the polishing surface of the workpiece W is irradiated with ultraviolet light 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 and the recesses 40, 41. The transmission hole may be blocked by providing a window formed of a material that transmits ultraviolet light. EXAMPLES

[0051] The workpiece (material to be polished) was a polycrystalline diamond plate (manufactured by Tomei Diamond Co., Ltd.) measuring 20 mm x 20 mm x t1 mm. The polishing pads used were #6000 (average grain size 2.7 μm) and #10000 (average grain size 1.6 μm) diamond vitrified bond grinding wheels (manufactured by Alpha Diamond Industrial Co., Ltd.) and a quartz glass plate. 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 the pit depth after PAP. The polishing conditions and polishing results are shown in Table 1.

[0052] [Table 1]

[0053] Comparing test numbers 1 and 2, which used #6000 diamond vitrified bond grinding wheels, the effect of surface modification by plasma is clear, and it was confirmed that by generating plasma, polycrystalline diamond plates can be polished at a high polishing rate of about 1 μm / hr. This polishing rate is comparable to or even exceeds that of test numbers 4 and 5, which used quartz glass plates. It was found that polycrystalline diamond plates can be polished industrially even if diamond vitrified bond grinding wheels are used instead of expensive quartz glass plates. In addition, comparing the polishing results of test numbers 1 and 3, which used #6000 and #10000 diamond vitrified bond grinding wheels, the polishing rate of #10000 is slightly lower, but the surface roughness improves due to the smaller grain size of the abrasive grains. For example, when polished for 60 minutes using a #6000 diamond vitrified bond grinding wheel, the surface roughness Sa at the center of a polycrystalline diamond plate was 7.452 nm, but when polished for 60 minutes using a #10000 diamond vitrified bond grinding wheel, the surface roughness Sa was 6.554 nm. [Explanation of symbols]

[0054] W work, P, P1, P2, P3 polishing pads, 1 chamber, 2 gas supply means; 3 Gas exhaust means, 4 Mechanical section, 5 High frequency power supply, 6 1st rotating unit, 7 Second rotating unit, 8 linear drive means, 9 rotation axis, 10 first mounting part, 11 Rotating table, 12 Rotation axis, 13 second mounting part, 14 Pressing means, 15 counter electrode plate, 16 Base part, 17 Flange portion, 18 Protective tube, 19 Thrust bearing, 20 radial bearings, 21 Rotational motor, 22 Drive shaft, 23 Gear mechanism, 24 Linear guide, 25 Mobile objects, 26 Linear Actuators, 27 Drive motor, 28 Ball screw feed mechanism, 29 Moving parts, 30 aperture, 31 Support tube, 32 bearings, 33 shaft cylinder, 34 Carrier gas cylinders, 35 Reactive gas cylinders, 36 Quartz glass plate, 37 lattice groove, 38 Base plate, 39 Vitrified bond grinding wheel, 40 recessed portion, 41 Recess.

Claims

1. 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 a workpiece surface to form a surface modification layer on the workpiece surface that is softer than the workpiece; a polishing process in which the workpiece and a polishing pad are moved relative to each other while being brought into contact with each other at a predetermined contact pressure, thereby removing the surface modification layer of the workpiece; having A plasma-assisted polishing method, comprising: repeating the surface modification process and the polishing process alternately; or simultaneously carrying out both processes to polish the surface; In the operation of relatively moving the workpiece and the polishing pad, the workpiece is polished by a combination of a rotation of the workpiece and a rotation of the polishing pad, each of which has an axis in a first direction, and a swing in a second direction perpendicular to the first direction and increasing or decreasing the distance between the two axes. Plasma assisted polishing method.

2. The plasma in the surface modification process is a capacitively coupled plasma, and the capacitance does not change during the swinging operation. The plasma assisted polishing method of claim 1.

3. The workpiece and the polishing pad are held in a freely detachable manner on a mounting part having a rotation axis facing a first direction, and are opposed to each other. When the workpiece and / or the polishing pad are attached or detached, the workpiece and the 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 the polishing pad are attached or detached from the mounting part in a state where they are exposed from the opposing member. The plasma assisted polishing method of claim 1.

4. The polishing pad is a plate having at least a surface 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 nonwoven fabric made of glass wool.

4. The plasma-assisted polishing method according to claim 1, 2 or 3.

5. At the contact portion between the workpiece and the polishing pad, a flow path is formed that communicates with a space in which plasma is generated by a groove or an uneven structure provided on at least one surface of the workpiece and the polishing pad, and neutral radicals are supplied to the workpiece surface through the flow path. The plasma assisted polishing method of claim 4.

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 wheel on at least the surface thereof, and the abrasive grains are diamonds having a diameter of #1000 (average grain diameter 16 μm) to #20000 (average grain diameter 0.8 μm); The reactive gas is water vapor (H ２ O) or hydrogen peroxide (H ２ O ２ ) Includes: The plasma assisted polishing method of claim 4.

7. 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. The plasma assisted polishing method of claim 4.

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

9. the workpiece and the polishing pad are held and opposed to each other by either a first mounting part of a first rotating unit or a second mounting part 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 counter electrode plate maintain an opposed state; 9. The plasma assisted polishing apparatus of claim 8.

10. The opposing electrode plate has a dimension in the second direction set to be larger than a diameter of the rotary table by at least an oscillation amplitude, so that the capacitance of the capacitively coupled plasma does not change in the oscillation mode.

10. The plasma assisted polishing apparatus of claim 9.

11. the workpiece and the 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 an attachment / detachment mode for attaching / detaching the workpiece and / or the polishing pad, the linear drive means is driven to a position where the workpiece and / or the polishing pad are exposed from the opposing member of the opposing first rotating unit and / or the opposing second rotating unit.

9. The plasma assisted polishing apparatus of claim 8.

12. The polishing pad is a plate having at least a surface 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 nonwoven fabric made of glass wool. The plasma-assisted polishing apparatus according to any one of claims 8 to 11.

13. At the contact portion between the workpiece and the polishing pad, a flow path is formed that communicates with a space in which plasma is generated by a groove or an uneven structure provided on at least one surface of the workpiece and the polishing pad, and neutral radicals are supplied to the workpiece surface through the flow path.

9. The plasma assisted polishing apparatus of claim 8.

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 wheel on at least the surface thereof, and the abrasive grains are diamonds having a diameter of #1000 (average grain diameter 16 μm) to #20000 (average grain diameter 0.8 μm); The reactive gas is water vapor (H ２ O) or hydrogen peroxide (H ２ O ２ ) Includes:

9. The plasma assisted polishing apparatus of claim 8.

15. An ultraviolet light source is disposed behind the polishing pad, and at least a part of the polishing pad and its mounting portion is provided with a structure for transmitting ultraviolet light from the ultraviolet light source and irradiating the polishing surface of the workpiece.

9. The plasma assisted polishing apparatus of claim 8.

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