JP7409815B2 - Semiconductor wafer polishing method - Google Patents

Description

The present invention relates to a method for polishing semiconductor wafers.

Conventionally, when polishing semiconductor wafers such as SiC wafers, GaN wafers, Si wafers, and Si oxide film wafers, polishing is performed on a polishing disk using a polishing slurry containing free abrasive grains or a polishing pad with fixed abrasive grains. was. For example, there is a CMP (Chemical Mechanical Polishing) method described in Patent Document 1. In polishing using such abrasive grains, normally the polishing slurry is circulated through a foreign matter removal filter to remove foreign matter in the polishing slurry, and after the foreign matter has been removed, the polishing slurry is supplied to the polishing disk again. It has become so.

Special issue number 2013-214784

In the conventional polishing method described above, if a filter with a very fine mesh is used to remove abrasive grains from the polishing slurry, it becomes clogged and cannot be used. Instead, a filter with a slightly larger mesh is used. When used, the removal ability of the filter is insufficient, and the abrasive particles remaining in the polishing slurry may cause scratches on the polished surface of the semiconductor wafer. In addition, the abrasive grains in the polishing slurry have a higher specific gravity than the dispersion liquid and tend to precipitate and coagulate in storage tanks and conveyance pipes. The abrasive grains tend to be dispersed non-uniformly, and non-uniform polishing may occur on the polished surface of the wafer.

The present invention has been made against the background of the above circumstances, and its purpose is to provide a polishing method that suppresses the occurrence of scratches and non-uniform polishing on the polished surface of a wafer during polishing. It is about providing.

As a result of continuing intensive research in order to suppress the occurrence of scratches and non-uniform polishing on the polishing surface of wafers, the present inventor prepared a polishing liquid that did not contain abrasive grains but contained permanganate ions, and The surprising fact is that if a polishing pad is made of a thermoplastic resin containing a polymer with oxygen interposed in its chain, for example, a polymer containing an ether group in its repeating unit, polishing can be performed without using abrasive grains. I found it. The reason for this is that polishing pads made of thermoplastic resins containing polymers with oxygen interposed in the carbon chain, such as polymers containing ether groups in their repeating units, can themselves have a reduction-inhibiting effect. By suppressing the reduction of permanganate ions in the polishing liquid, permanganate is precipitated on the polishing pad, so the permanganate functions as an abrasive grain and can perform polishing. Estimated. In this way, when the polishing liquid does not contain abrasive grains, the occurrence of scratches and non-uniform polishing on the polishing surface of the wafer is suitably suppressed.

That is, the gist of the present invention is a semiconductor wafer polishing method for polishing a semiconductor wafer using a polishing liquid and a polishing pad, the polishing liquid being obtained by dissolving permanganate in water. The polishing pad is an aqueous solution containing permanganate ions, and the polishing pad is made of a resin having a polymer with oxygen interposed in a carbon chain, which has the effect of suppressing the reduction of the permanganate ions in the polishing liquid. When the polishing liquid is brought into contact with the polishing pad, the permanganate produced by suppressing the reduction of the permanganate ions is deposited on the polishing pad. The purpose of the polishing pad is to polish the semiconductor wafer using the permanganate precipitated particles as polishing particles.

According to the polishing method of the present invention, the polishing liquid is an aqueous solution containing permanganate ions obtained by dissolving permanganate in water , and the polishing pad is configured to handle the permanganate in the polishing liquid. It is composed of a resin having a polymer with oxygen interposed in the carbon chain , which has the effect of suppressing the reduction of acid ions, and when the polishing liquid is brought into contact with the polishing pad, The permanganate produced by suppressing the reduction of the permanganate ion is precipitated on the polishing pad, and the polishing pad uses precipitated particles of the permanganate as polishing particles to polish the semiconductor. Since the wafer is polished, polishing can be performed even if the polishing liquid does not contain abrasive grains. Thereby, the occurrence of scratches and non-uniform polishing on the polishing surface of the wafer is suitably suppressed.

Here, preferably, the polishing pad is made of a thermoplastic resin having a polymer containing an ether group in each repeating unit, and the polishing pad is preferably made of a thermoplastic resin having a polymer containing an ether group in each repeating unit, and the polishing pad is made of a thermoplastic resin that includes permanganate ions in the polishing liquid. By suppressing the reduction of permanganate, permanganate is precipitated on the polishing pad, and the semiconductor wafer is polished using the permanganate precipitated particles as polishing particles. As a result, polishing can be performed even when no abrasive grains are included in the polishing liquid, so that scratches and non-uniform polishing can be suitably suppressed from occurring on the polishing surface of the wafer.

Preferably, the resin having a polymer containing an ether group in each repeating unit is a PEG (polyethylene glycol) resin, a PES (polyethersulfone) resin, a PEK (polyetherketone) resin, or a PEEK (polyetherketone) resin. The resin is any one of ether ether ketone) resin and PEs (polyester) resin. As a result, the polishing liquid containing metal ions comes into contact with the polishing pad, thereby generating metal oxide particles on the polishing pad.

Further, preferably, the polishing pad is made of a thermosetting resin having a network structure having a plurality of branch points, and is made of a resin having a polymer with oxygen interposed in the carbon chain between the branch points. The polishing pad is configured such that permanganate is precipitated on the polishing pad by suppressing the reduction of permanganate ions in the polishing liquid, and the permanganate precipitated particles are used as polishing particles. Polishing semiconductor wafers. As a result, polishing can be performed even when no abrasive grains are included in the polishing liquid, so that scratches and non-uniform polishing can be suitably suppressed from occurring on the polishing surface of the wafer.

Preferably, the resin having a polymer in which oxygen is interposed between carbon chains between branch points is an epoxy resin. As a result, the polishing liquid containing permanganate ions comes into contact with the polishing pad, and permanganate precipitate particles are generated on the polishing pad.

Also preferably, the permanganate is potassium permanganate. As a result, the polishing pad suppresses the reduction of permanganate ions, and the precipitated potassium permanganate functions as abrasive grains on the polishing pad, thereby properly polishing the wafer.

Preferably, the polishing pad includes a disc-shaped base resin formed from a resin having a polymer with oxygen interposed in the carbon chain, and a disc-shaped base resin formed on the base resin, and a polishing pad formed on the base resin. It is equipped with a communicating hole that encloses grains. As a result, the wafer is polished not only by the metal oxide particles but also by the polishing abrasive grains contained in the disk-shaped base material resin, so that the polishing efficiency is further improved.

FIG. 1 is a perspective view showing a sheet-shaped polishing pad that is an embodiment of the present invention and is used for polishing by CMP. 2 is a diagram showing a chemical structural formula of a PEG-based resin constituting the polishing pad of FIG. 1. FIG. 2 is a diagram showing a chemical structural formula of an epoxy resin constituting the polishing pad of FIG. 1. FIG. 2 is a diagram showing a chemical structural formula of a PES resin constituting the polishing pad of FIG. 1. FIG. 2 is a diagram showing a chemical structural formula of PEK resin that constitutes the polishing pad of FIG. 1. FIG. 2 is a diagram showing a chemical structural formula of PEEK resin that constitutes the polishing pad of FIG. 1. FIG. 2 is a diagram showing a chemical structural formula of PET resin that constitutes the polishing pad of FIG. 1. FIG. FIG. 2 is a schematic diagram showing a network structure of epoxy resin. FIG. 2 is a schematic diagram showing a part of a cross section perpendicular to the thickness direction of the polishing pad shown in FIG. 1, enlarged by X-ray CT. FIG. 2 is a schematic diagram illustrating a part of a longitudinal section in the thickness direction of the polishing pad shown in FIG. 1, enlarged by X-ray CT. 2 is an enlarged view schematically showing the configuration of the polishing pad shown in FIG. 1. FIG. FIG. 2 is a plan view, viewed from the axial direction of a polishing surface plate, showing the main part configuration of a CMP polishing apparatus in which the polishing pad shown in FIG. 1 is used. 13 is a front view of the polishing apparatus shown in FIG. 12. FIG. 13 is a diagram illustrating a polishing process using the polishing apparatus shown in FIG. 12. FIG. It is a bar graph showing polishing rates among the results of polishing tests on SiC wafers using a plurality of types of polishing pads. It is a bar graph showing surface roughness among the results of polishing tests on SiC wafers using a plurality of types of polishing pads. FIG. 17 is a diagram showing a chemical structural formula of a PPS resin constituting a polishing pad with a low polishing rate in the polishing tests of FIGS. 15 and 16. FIG. FIG. 17 is a diagram showing a chemical structural formula of a polyamide resin constituting a polishing pad with a low polishing rate in the polishing tests of FIGS. 15 and 16. FIG. FIG. 17 is a diagram showing a chemical structural formula of a hard polyurethane resin constituting a polishing pad with a low polishing rate in the polishing tests of FIGS. 15 and 16. FIG. FIG. 2 is a diagram showing a SEM photograph taken using a scanning electron microscope of a paste-like substance adhering to the polishing surface of a polishing pad. FIG. 21 is a diagram showing a comparison between the X-ray diffraction pattern obtained by performing X-ray diffraction of the particulate material shown in the SEM photograph of FIG. 20 and the X-ray diffraction pattern of potassium permanganate. It is a bar graph showing polishing rates among the results of polishing tests on GaN wafers using a plurality of types of polishing pads. It is a bar graph showing surface roughness among the results of polishing tests on GaN wafers using a plurality of types of polishing pads.

An embodiment of the present invention will be described below with reference to the drawings. Note that in the following examples, the figures are simplified or modified as appropriate, and the dimensional ratios, shapes, etc. of each part are not necessarily drawn accurately.

FIG. 1 is a perspective view showing a polishing pad 10 according to an embodiment of the present invention. The polishing pad 10 of this embodiment has a base resin 12 formed into a disk shape, and has dimensions of, for example, an outer diameter of 1000 (mmφ) and a thickness of about 2 (mm). As shown in FIG. 13, which will be described later, this polishing pad 10 is attached to a polishing surface plate 20 of a polishing device 19 and is used exclusively for polishing a semiconductor wafer 26 by CMP.

The base material resin 12 is composed of a resin that has the effect of suppressing the reduction of permanganate ions in the polishing liquid, specifically, a resin that has a polymer in which oxygen is interposed in the middle of the carbon chain. Ru. This resin is a thermoplastic resin having a polymer containing an ether group E (structural formula R-OR-R') in each repeating unit, such as PEG (polyethylene glycol) resin, PES (polyethylene glycol) resin, etc. The resin is one of the following: ethersulfone) resin, PEK (polyetherketone) resin, PEEK (polyetheretherketone) resin, PEs (polyester) resin, or a resin containing at least one of them. Furthermore, thermosetting resins include epoxy resins having polymers in which oxygen is interposed in the middle of carbon chains between branch points of polymers that intersect in a network. These thermoplastic resins and thermosetting resins have in common that they are resins with polymers in which oxygen is interposed in the middle of the carbon chain, and they have the effect of suppressing the reduction of permanganate ions in the polishing liquid. have

Figure 2 shows the chemical structural formula of PEG resin, Figure 3 shows epoxy resin, Figure 4 shows PES resin, Figure 5 shows PEK resin, Figure 6 shows PEEK resin, and Figure 7 shows the chemical structural formula of PET (polyethylene terephthalate) resin, which is PEs resin. are shown respectively. Both resins consist of polymers containing at least one ether group E per repeating unit. Note that FIG. 3 shows the chemical structural formula of a prepolymer before curing in which the epoxy resin is crosslinked into a network (network structure), and this prepolymer contains at least one ether group E for each repeating unit. It is a polymer. As shown in FIG. 8, the epoxy resin is composed of polymers that intersect in a network after curing, and oxygen is interposed in the carbon chains between the branch points BP of the network. Further, the polishing pad 10 may be made of a base resin 12 that does not include pores or abrasive grains. As shown in FIGS. 9, 10, and 11, the polishing pad 10 also includes a porous base resin 12 having communicating holes 16, and a large number of polishing stones enclosed in the communicating holes 16 of the base resin 12. The particles 14 may be included in the base resin 12. The polishing pad 10 in this case is also referred to as an LHA pad.

The abrasive grains 14 are preferably silica, but other abrasive grains such as at least one of ceria, alumina, zirconia, titania, manganese oxide, barium carbonate, chromium oxide, and iron oxide are used. may be used. As the silica, for example, fumed silica is preferably used. Fumed silica is silica fine particles obtained by burning silicon tetrachloride, chlorosilane, etc. at high temperature in the presence of hydrogen and oxygen. The average particle diameter of the polishing abrasive grains 14 is preferably 0.005 (μm) or more and 3.0 (μm) or less, more preferably 0.005 (μm) or more and 1.0 (μm) or less, and more preferably 0.005 (μm) or more and 1.0 (μm) or less. 02 (μm) or more and 0.6 (μm) or less, more preferably 0.08 (μm) or more and 0.5 (μm) or less, and even more preferably 0.08 (μm) or more and 0.3 (μm) or less . For example, if the average particle size of the polishing abrasive grains 14 exceeds 3.0 (μm), polishing scratches are likely to occur on the semiconductor wafer 26 due to the polishing grains 14 liberated from the base resin 12 during the polishing process described later. . Further, if the average particle diameter of the polishing abrasive grains 14 is less than 0.005 (μm), the polishing abrasive grains 14 tend to aggregate, and polishing scratches are likely to occur on the semiconductor wafer 26 in the polishing process described later. The particle size of the abrasive grains 14 is measured by a laser diffraction/scattering method, for example, using a particle size/particle size distribution measuring device Microtrac MT3300 manufactured by Nikkiso Co., Ltd., and the average particle size refers to the particle size. It is the arithmetic mean of the diameter. The particle size below the measurement limit of the laser diffraction/scattering method described above is measured by a dynamic light scattering method using, for example, a particle size/particle size distribution measuring device Nanotrack UPA-EX250 manufactured by Nikkiso Co., Ltd.

FIG. 9 is a part of a cross section parallel to the polishing surface 10a of the polishing pad 10 of this embodiment, and the region W1 surrounded by the dashed line in FIG. 1 is enlarged by X-ray CT (SMX-160LT manufactured by Shimadzu Corporation). FIG. FIG. 10 is a diagram showing a part of the cross section of the polishing pad 10 in the thickness direction enlarged by X-ray CT. As shown in FIGS. 9 and 10, longitudinal pores 18 are formed in a distributed manner on the surface and inside of the polishing pad 10. As shown in FIG. The vertically elongated pores 18 are formed so that the length in the thickness direction is longer than the length in the surface direction. Specifically, the length of the longitudinal pores 18 in the thickness direction of the polishing pad 10, that is, the depth of the longitudinal pores 18, is equal to the length of the pores in the surface direction of the polishing pad 10, that is, the maximum diameter (opening) of the longitudinal pores 18. Aperture) is formed to be larger than D. The longitudinally elongated pores 18 have variations in length in the thickness direction and length in the surface direction. For example, the elongated pores 18 may be those that penetrate the polishing pad 10 such as those that are open on both the polishing surface 10a and the surface opposite to the polishing surface 10a, or those that penetrate the polishing pad 10 that are open on both the polishing surface 10a or the surface opposite to the polishing surface 10a. One or both surfaces are non-penetrating with no openings. When polishing a semiconductor wafer 26 that has a large polishing area, the formation of the vertically long pores 18 prevents the polishing pad 10 from adsorbing to the semiconductor wafer 26, for example, and prevents the polishing pad 10 from adsorbing the semiconductor wafer 26. Processing resistance (sliding resistance) during polishing due to the negative pressure generated between the two is reduced.

The openings formed on the polishing surface side 10a of the vertical pores 18 are formed by surface finishing, for example, buffing, on the polishing surface 10a of the polishing pad 10, so that a portion of the base resin 12 is expanded to cover the openings. A lid-like structure (not shown) may be formed. The lid-like structure is formed to cover all or part of the openings of the longitudinal pores 18 on the polished surface 10a, and is formed to cover the openings of the longitudinal pores 18 to about 300 (μm) in the thickness direction, for example. and may fall off during use. Here, the lid-like structure is not porous but is formed to be dense, and during the polishing process described later, the lid-like structure does not adsorb to the semiconductor wafer 26 and therefore does not cause sliding resistance. Therefore, in this embodiment, a state in which the opening of the longitudinal pore 18 is completely or partially covered by the lid-like structure is considered to be open. The opening diameter D of the vertically elongated pore 18 covered by the lid-like structure is defined as the circular equivalent diameter of the opening of the vertically long pore 18 that is exposed when the lid-like structure is removed.

FIG. 11 is a diagram schematically showing the configuration of the polishing pad 10 of this example. As shown in FIG. 11, the base resin 12 has a fibrous shape with an average cross-sectional diameter of about 0.05 (μm), and the gaps between the fibrous base resin 12 have an average particle diameter of, for example, about 0.05 (μm). Polishing abrasive grains 14 having a diameter of 0.3 (μm) exist in a state where a portion thereof is fixed to the outer periphery of the base resin 12, or in a state where it is separated from the base resin 12 in the gap. Here, if we consider the communicating holes 16 that communicate the gaps between the fibrous base material resins 12, it can be said that the abrasive grains 14 are provided within the communicating holes 16. The communicating holes 16 are formed to communicate with the vertically elongated pores 18 and with each other. In other words, the abrasive grains 14 are partially attached to the inner wall of the communicating hole 16 or are separated from the base resin 12 within the communicating hole 16, and each communicating hole 16 is It is formed in the base resin 12 and includes at least one abrasive grain 14 therein.

In the polishing pad 10 of this embodiment, the polishing abrasive grains 14 are easily separated from the base resin 12 during the polishing process described later, and the base resin 12 and the polishing abrasive grains 14 have a necessary and sufficient bonding strength. Since the polishing pad 10 is fixed to each other by the polishing pad 10 and the semiconductor wafer 26, the polishing pad 10 can preferably self-supply free abrasive grains, that is, free polishing abrasive grains 14 between the polishing pad 10 and the semiconductor wafer 26. Therefore, in polishing using the conventional CMP method, it is essential to supply a slurry containing, for example, colloidal silica, but the polishing pad 10 of this embodiment does not require a slurry containing such abrasive grains. By supplying a polishing liquid PF that does not contain free abrasive grains but contains permanganate ions, it is possible to carry out polishing by CMP.

12 and 13 are schematic diagrams showing the configuration of essential parts of a CMP polishing apparatus 19 in which the polishing pad 10 of this embodiment is used. FIG. 12 is a plan view of the polishing surface plate 20 viewed from the axis C1 direction, and FIG. 13 is a front view. As shown in these figures, the polishing device 19 is provided with a polishing surface plate 20 rotatably supported around its axis C1, and the polishing surface plate 20 is driven by a surface plate drive (not shown). The motor rotates it in the direction of rotation shown by the arrow in FIG. The polishing pad 10 of this embodiment is attached to the upper surface of this polishing surface plate 20, that is, the surface against which the semiconductor wafer 26 is pressed. On the other hand, in the vicinity of the polishing surface plate 20, a workpiece holding member 22 for holding a semiconductor wafer 26 (workpiece) is supported so as to be rotatable around its axis C2 and movable in the direction of its axis C2. The workpiece holding member 22 is rotatably driven in the direction of rotation shown by an arrow in FIG. 12 by a workpiece drive motor (not shown). A semiconductor wafer 26 is adsorbed and held on the lower surface of the work holding member 22, that is, the surface facing the polishing pad 10, with an adsorption layer 24 interposed therebetween. Further, a polishing liquid supply nozzle 28 is disposed near the workpiece holding member 22, and during the polishing process, a polishing liquid PF, which is an aqueous solution containing metal ions, is sent out from a tank (not shown) through an appropriate filter for supplying the polishing liquid. It is supplied from the nozzle 28.

The semiconductor wafer 26 is, for example, a SiC wafer, a GaN wafer, a Si wafer, or a Si oxide film wafer. Further, the metal ion contained in the polishing liquid PF is a permanganate ion (MnO ₄ ⁻ ) obtained by dissolving a permanganate, for example, potassium permanganate in water.

As shown in FIGS. 12 and 13, the polishing device 19 is rotatable around an axis C3 parallel to the axis C1 of the polishing surface plate 20, and is rotatable in the direction of the axis C3 and the diameter of the polishing surface plate 20. An adjustment tool holding member 30 disposed so as to be movable in the direction, and a polishing pad adjustment tool 32 attached to the lower surface of the adjustment tool holding member 30, that is, the surface facing the polishing pad 10, are provided. The holding member 30 and the polishing pad adjustment tool 32 attached thereto are pressed against the polishing pad 10 while being rotationally driven in the direction of rotation shown by the arrow in FIG. By reciprocating the polishing surface plate 20 in the radial direction, the polishing pad 10 is adjusted and the surface condition of the polishing pad 10 is maintained in a state suitable for polishing.

Figure 14 illustrates the polishing process. For example, when polishing a semiconductor wafer 26 made of SiC, in the polishing preparation step P1, the polishing pad 10 is attached to the upper surface of the polishing surface plate 20 in the polishing device 19, and the semiconductor wafer 26 is attracted to the lower surface of the workpiece holding member 22. The semiconductor wafer 26 that is suctioned and held by the workpiece holding member 22 is sucked through the layer 24 and is supplied onto the surface of the polishing pad 10 from the polishing liquid supply nozzle 28 while the semiconductor wafer 26 is sucked and held by the polishing pad 10. It is pressed with a predetermined polishing pressure.

Next, in the polishing step P2, the polishing surface plate 20 and the polishing pad 10 attached thereto, and the workpiece holding member 22 and the semiconductor wafer 26 suctioned and held thereon are moved by the surface plate drive motor and the workpiece drive motor, respectively. While the polishing liquid PF is being supplied from the polishing liquid supply nozzle 28 onto the surface of the polishing pad 10 while being rotated around the axes C1 and C2, the semiconductor held by suction on the workpiece holding member 22 A wafer 26 is brought into sliding contact with the polishing pad 10. By doing so, precipitated particles CP of permanganate produced by suppressing the reduction of permanganate ions, which are metal ions contained in the polishing liquid PF, are generated on the surface of the polishing pad 10. The manganate precipitated particles CP function as polishing particles, and in cooperation with the mechanical polishing action of the polishing abrasive grains 14 self-supplied by the polishing pad 10, one surface of the semiconductor wafer 26 is polished flat. Ru.

The present inventors conducted the following polishing test. This polishing test consisted of an LHA pad with continuous pores and abrasive grains, an abrasive-free LHA pad with continuous pores but no abrasive grains, a PES resin pad made of PES resin without pores and no abrasive grains, and a PES resin pad with no pores and abrasive grains. and a PPS resin pad made of PPS resin without abrasive grains, a PEEK resin pad made of PEEK resin without pores and abrasive grains, and a PEG resin pad made of PEG resin with continuous pores but not containing abrasive grains. , a PEG-based resin pad made of a PEG-based resin that has continuous pores and contains abrasive grains, an epoxy resin pad that has continuous pores but is made of an epoxy resin that does not contain abrasive grains, and an epoxy resin pad that has continuous pores and contains abrasive grains. Epoxy resin pad made of resin, polyester resin pad made of polyester resin without pores and abrasive grains, polyamide resin pad made of polyamide resin without pores and abrasive grains, hard material with continuous pores but does not contain abrasive grains Twelve types of test pads were prepared: rigid polyurethane pads made of polyurethane resin. Next, for these test pads, a polishing test was performed on two types of semiconductor wafers, SiC wafers and GaN wafers, using a continuous generation type polishing device similar to the polishing device 19. Below, the polishing test conditions and polishing test results for SiC wafers will be explained using Tables 1 and 2, and the polishing test conditions and polishing test results for GaN wafers will be explained using Tables 3 and 4. A laser displacement meter SI-F80R manufactured by Keyence Corporation was used to measure the polishing rate under the polishing test conditions shown in Tables 1 and 3. Furthermore, a white interference microscope (BW-D500) manufactured by Nikon Corporation was used to measure the surface roughness Ra (nm) of the polished surfaces in Tables 2 and 4.

(Table 1)
(SiC wafer polishing test conditions)
Item Content
Semiconductor wafer 3 inch diameter φSiC Si surface (tilt angle 4°)
Work rotation speed 60rpm
Pad diameter 300mmφ
Pad rotation speed 60rpm
Polishing pressure 50KPa
Polishing liquid KMnO ₄ ( 0.25 mol/l) aqueous solution with pH=7.2
Polishing liquid flow rate 10ml/min

(Table 2)
(SiC wafer polishing test results)
Polishing rate (nm/h) Surface roughness Ra (nm)
LHA pad 1372 0.1
(With continuous ventilation holes and abrasive grains)
LHA pad 665 0.084
(With communicating holes)
PES resin pad 732 0.108
PPS resin pad 193 0.106
PEEK resin pad 854 0.1
PEG resin pad 870 0.183
(With communicating holes)
PEG resin pad 1532 0.103
(With continuous ventilation holes and abrasive grains)
Epoxy resin pad 560 0.112
(With communicating holes)
Epoxy resin pad 780 0.121
(With continuous ventilation holes and abrasive grains)
Polyester resin pad 801 0.11
Polyamide resin pad 193 0.114
rigid polyurethane
Resin pad 240 0.143
(With communicating holes)

FIG. 15 is a bar graph showing the polishing rate (nm/h) for each pad in the polishing test for the SiC wafer. FIG. 16 is a bar graph showing the roughness Ra (nm) of the polished surface for each pad in the polishing test for the SiC wafer described above.

In the polishing test results for the SiC wafers described above, no significant difference was found between test pads in terms of surface roughness Ra of the polished surface. However, there were significant differences in polishing rate among the test pads. The above polishing test results for SiC wafers show that when polishing using a PPS resin pad, polyamide resin pad, and hard polyurethane resin pad, other resin pads, namely LHA pad (with continuous holes and abrasive grains), LHA pad (continuous (with pores, no abrasive grains), PES resin pad, PEEK resin pad, PEG resin pad (with continuous ventilation holes), PEG resin pad (with continuous ventilation holes, with abrasive grains), epoxy resin pad (with continuous ventilation holes), epoxy Compared to the resin pad (with continuous holes and abrasive grains) and the polyester resin pad, a polishing rate as low as about 1/8 to 1/2.3 was obtained.

As shown in FIGS. 17, 18, and 19, the three types of resins constituting each of the test pads with a low polishing rate described above are resins made of polymers that do not contain ether groups in each repeating unit. Common. Furthermore, as shown in FIGS. 2 to 4 and 6, the six types of resins constituting each of the test pad groups with high polishing rates are resins made of polymers containing ether groups in each repeating unit. So, it's common. Note that since the PEEK resin shown in FIG. 5 has the same chemical structural formula as PEEK resin, it is estimated that it has the same polishing rate as PEEK resin.

In the SiC wafer polishing test described above, the present inventors discovered that a brown paste-like substance adhered to the polishing surface of the resin pad made of a polymer containing an ether group in each repeating unit, which constituted the test pad with a high polishing rate. The material was imaged using a scanning electron microscope (SEM). FIG. 20 is a SEM photograph obtained thereby. In this SEM photograph, fine precipitated particles CP with a diameter of 1 μm or less are observed. These fine particles are formed by suppressing the reduction of permanganate ion MnO ₄ ^- , which is a metal ion in polishing liquid PF, to manganese dioxide MnO ₂ by a resin made of a polymer containing an ether group in each repeating unit. It is estimated that these are crystalline precipitated particles CP precipitated as permanganate.

FIG. 21 is a diagram showing a comparison between a diffraction pattern obtained by powder X-ray diffraction of the precipitated particles CP and a known diffraction pattern of potassium permanganate. The diffraction pattern in FIG. 21 is shown in two-dimensional coordinates with the horizontal axis indicating the diffraction angle 2θ and the vertical axis indicating the diffraction intensity (CPS). The particle diffraction pattern of precipitated particles CP shown in the upper row of FIG. 21 matches well with the known diffraction pattern of potassium permanganate shown in the lower row, and the precipitated particles CP are potassium permanganate. It is identified as Therefore, it is presumed that one surface of the semiconductor wafer 26 was polished flat by the precipitated particles CP of potassium permanganate particles functioning as polishing particles.

(Table 3)
(GaN wafer polishing test conditions)
Item Content
Semiconductor wafer 2 inches in diameter φGaN Ga surface Work rotation speed 60 rpm
Pad diameter 300mmφ
Pad rotation speed 60rpm
Polishing pressure 50KPa
Polishing liquid KMnO ₄ ( 0.25 mol/l) aqueous solution with pH=1.0 + silica (12.5 wt%)
Polishing liquid flow rate 10ml/min

(Table 4)
(GaN wafer polishing test results)
Polishing rate (nm/h) Surface roughness Ra (nm)
LHA pad 432 0.12
(With continuous ventilation holes and abrasive grains)
LHA pad 34 0.097
(With communicating holes)
PES resin pad 64 0.11
PEG resin pad 32 0.099
(With communicating holes)
PEG resin pad 453 0.103
(With continuous ventilation holes and abrasive grains)
Epoxy resin pad 205 0.121
(With continuous ventilation holes and abrasive grains)
Hard polyurethane resin pad 8 0.143
(With communicating holes)
Hard polyurethane resin pad 85 0.132
(With continuous ventilation holes + free slurry)

FIG. 22 is a bar graph showing the polishing rate (nm/h) for each pad among the results in Table 4 obtained by a polishing test on GaN wafers using the test conditions in Table 3 above. FIG. 23 is a bar graph showing the roughness Ra (nm) of the polished surface for each pad in the polishing test for the GaN wafer described above.

In the polishing test results for the GaN wafers described above, no significant difference was found between test pads in terms of surface roughness Ra of the polished surface. However, there were significant differences in polishing rate among the test pads. The above polishing test results for GaN wafers show an LHA pad that does not contain abrasive grains, a PES resin pad, a PEG resin pad with continuous pores, a hard polyurethane resin pad with continuous pores, and a hard polyurethane resin pad with continuous pores (+ For polishing using a slurry containing free abrasive grains, other resin pads are used, namely LHA pad (with abrasive grains and continuous holes), PEG resin pad (with abrasive grains and continuous holes), and epoxy resin pad (with abrasive grains and continuous holes). The polishing rate was only about 1/90th to 1/2.4th compared to that of the case (with pores). In polishing using the LHA pad and PEG-based resin pad with high polishing rates, the two types of resin that make up each resin pad are both thermoplastic resins made of polymers containing ether groups in each repeating unit. They are similar in that they are polishing that includes abrasive grains. Further, the epoxy resin pad with a high polishing rate is a thermosetting resin, and polishes with abrasive grains included therein.

As described above, according to the polishing method of this embodiment, the semiconductor wafer 26 is polished using the polishing liquid PF and the polishing pad 10. The polishing pad 10 is made of a resin having a polymer containing manganate ions with oxygen interposed in the middle of the carbon chain, and the polishing pad 10 suppresses the reduction of the permanganate ions in the polishing liquid PF. The semiconductor wafer 26 is polished by precipitating potassium permanganate, which is a permanganate, on the polishing pad 10 and making the precipitated particles CP of potassium permanganate function as polishing particles. Polishing is possible even without abrasive grains. Thereby, the occurrence of scratches and non-uniform polishing on the polished surface of the semiconductor wafer 26 is suitably suppressed.

Further, according to the polishing method of this example, the resin having a polymer containing an ether group in each repeating unit is PEG (polyethylene glycol) resin, epoxy resin, PES (polyethersulfone) resin, PEK (polyether sulfone) resin, etc. etherketone) resin and PEEK (polyetheretherketone) resin. As a result, the polishing liquid containing permanganate ions comes into contact with the polishing pad 10, so that permanganate with suppressed reduction of permanganate ions is precipitated on the polishing pad 10.

Further, according to the polishing method of this embodiment, the polishing pad 10 is made of a thermosetting resin having a network structure having a plurality of branch points, and oxygen is interposed in the carbon chain between the branch points. It is made of epoxy resin with polymer. As a result, the polishing liquid containing permanganate ions comes into contact with the polishing pad, and permanganate precipitate particles are generated on the polishing pad.

Further, according to the polishing method of this embodiment, the polishing pad 10 includes a disk-shaped base resin 12 formed from a resin made of a polymer containing an ether group in each repeating unit, and a base resin 12 formed on the base resin 12. This is an LHA pad equipped with a communicating hole 16 containing abrasive grains 14. As a result, the wafer is polished not only by the permanganate precipitated particles CP but also by the polishing abrasive grains 14 contained in the LHA pad, so that the polishing efficiency is improved.

Although preferred embodiments of the present invention have been described above in detail based on the drawings, the present invention is not limited thereto and may be implemented in other embodiments.

For example, in the embodiment described above, the polishing pad 10 is called an LHA pad, and the base resin 12 is fibrous, but this is only a preferred form of the present invention. First, the base resin 12 in the polishing pad 10 of the present invention is composed of a dense resin without pores and abrasive grains, as long as it has a polymer containing an ether group in each repeating unit. Good too.

Furthermore, in the above-mentioned embodiment, the polishing pad 10, especially the LHA pad effective for polishing GaN wafers, was equipped with the mesh-like continuous air holes 16, but the polishing pad 10 was equipped with the mesh-like continuous air holes 16. Alternatively, it may be made of dense resin without communicating holes 16.

Furthermore, in the above embodiment, the polishing liquid PF may contain permanganate ions obtained by dissolving sodium permanganate in water. In this case, when the polishing liquid PF comes into contact with the polishing pad 10, sodium permanganate is precipitated on the polishing pad 10 as permanganate.

The above-mentioned embodiment is merely one embodiment, and although no other examples are given, the present invention can be implemented with various modifications and improvements based on the knowledge of those skilled in the art without departing from the spirit thereof. I can do it.

10: Polishing pad 12: Base material resin 14: Polishing abrasive grains 16: Communication pores 18: Vertical pores 26: Semiconductor wafer PF: Polishing liquid CP: Precipitated particles of permanganate (abrasive particles)

Claims (7)

A semiconductor wafer polishing method for polishing a semiconductor wafer using a polishing liquid and a polishing pad, the method comprising:
The polishing liquid is an aqueous solution containing permanganate ions obtained by dissolving permanganate in water ,
The polishing pad is made of a resin having a polymer with oxygen interposed in a carbon chain, which has the effect of suppressing the reduction of the permanganate ions in the polishing liquid ,
When the polishing liquid is brought into contact with the polishing pad, the permanganate produced by suppressing the reduction of the permanganate ions is deposited on the polishing pad,
A method for polishing a semiconductor wafer , wherein the polishing pad polishes the semiconductor wafer using precipitated particles of permanganate as polishing particles. 2. The method of polishing a semiconductor wafer according to claim 1, wherein the polishing pad is made of a thermoplastic resin having a polymer containing an ether group in each repeating unit. 3. The resin having a polymer containing an ether group in each repeating unit is any one of a PEG resin, a PES resin, a PEK resin, a PEEK resin, and a PEs resin. A method for polishing semiconductor wafers. The polishing pad is a thermosetting resin having a network structure having a plurality of branch points, and is made of a resin having a polymer with oxygen interposed in the carbon chain between the branch points. A method for polishing a semiconductor wafer according to claim 1. 5. The method of polishing a semiconductor wafer according to claim 4, wherein the resin having a polymer with oxygen interposed in the carbon chain between the branch points is an epoxy resin. 6. The method of polishing a semiconductor wafer according to claim 1, wherein the permanganate is potassium permanganate. The polishing pad includes a disc-shaped base resin made of a resin having a polymer with oxygen interposed in the carbon chain, and continuous vents formed in the base resin and containing abrasive grains. The method for polishing a semiconductor wafer according to any one of claims 1 to 6, comprising the following.

Images