JP7650179B2 - Polishing pad and wafer polishing method - Google Patents

Description

The present invention relates to a polishing pad and a wafer polishing method.

Conventional polishing pads are disclosed in Patent Documents 1 to 4. The polishing pads in Patent Documents 1 to 3 are made by impregnating a nonwoven fabric with a paste and removing the solvent in the paste. The paste in Patent Document 1 is made of urethane, a solvent such as dimethylformamide, abrasive particles such as SiO ₂ , and alkaline fine particles such as sodium carbonate. The paste in Patent Document 2 is made of an ether-based urethane and a solvent such as N,N-dimethylformamide. The paste in Patent Document 3 is made of urethane, a solvent, and a water repellent. By removing the solvent by drying or the like, the urethane is solidified in a state bonded to the nonwoven fabric. The polishing pad in Patent Document 4 is manufactured using a paste in which a binder resin, abrasive particles, and a solvent are mixed.

The polishing pad of Patent Document 1 is used to polish the outer periphery of a disk-shaped wafer. That is, the wafer is held on a rotating table that can rotate around the center of rotation. At this time, the center of the wafer is positioned at the center of rotation of the rotating table. Meanwhile, a polishing pad is provided on the upper end of a spindle so that the outer peripheral end face of the polishing pad abuts against the outer periphery of the wafer. Then, a polishing liquid is supplied between the outer periphery of the wafer and the outer peripheral end face of the polishing pad, and a predetermined load is applied while the rotating table and spindle are rotated. This allows the outer periphery of the wafer to be polished. This makes it possible to suppress the occurrence of defects in semiconductor devices due to the outer periphery of the wafer.

JP 2019-46838 A JP 2019-118981 A JP 2020-49639 A Patent No. 5511266

However, according to the inventors' tests, conventional polishing pads do not have sufficient strength during polishing. As a result, cracks and breakages may occur in the polishing pad during polishing. For example, when a nitride such as a bare GaN wafer is used as the object to be polished, polishing cannot be performed with high polishing efficiency and high surface quality, and there is a risk of polishing defects. Furthermore, when the polishing liquid is strongly acidic or strongly alkaline, the polishing pad is easily deteriorated, and there is also a risk of polishing defects occurring.

In addition, since the polishing pad does not contain abrasive grains, if a polishing liquid containing abrasive grains is used for free abrasive polishing, there is a problem with cleaning due to the particles, which are abrasive particles remaining on the workpiece after polishing.

The present invention has been made in consideration of the above-mentioned conventional situation, and aims to provide a polishing pad that can polish the object to be polished with high efficiency, is unlikely to cause polishing defects on the object to be polished, and has excellent cleaning properties due to particles attached to the object to be polished after polishing. Also, the present invention aims to provide a wafer polishing method that can polish the object to be polished with high efficiency, is unlikely to cause polishing defects on the object to be polished, and has excellent cleaning properties due to particles attached to the object to be polished after polishing.

The polishing pad of the present invention constitutes a polishing surface for polishing an object to be polished in the presence of a polishing liquid that does not contain abrasive particles, and has a polishing layer that contains a binder resin, a countless number of abrasive particles, and fibers,
the binder resin is polyvinylidene fluoride or polyethersulfone,
The fibers are characterized by being made of at least one of polypropylene and polyethylene terephthalate.

The polishing pad of the present invention exhibits high strength during polishing because the polishing layer contains fibers. In particular, according to tests by the inventors, since the binder resin is made of polyvinylidene fluoride or polyethersulfone and the fibers are made of at least one of polypropylene and polyethylene terephthalate, polishing can be performed with high polishing efficiency and high surface quality even if the object to be polished is a nitride. Furthermore, even if the polishing liquid is strongly acidic or strongly alkaline, the polishing pad is resistant to deterioration.

In addition, the polishing pad of the present invention has an abrasive layer that constitutes the polishing surface and contains countless abrasive particles, so a polishing liquid that does not contain abrasive grains can be used, and the pad has excellent cleaning properties due to the particles that adhere to the workpiece after polishing.

The wafer polishing method of the present invention includes a first step of preparing a workpiece to be polished, a polishing pad, and a polishing liquid;
a second step of polishing the object to be polished by the polishing surface of the polishing pad while supplying the polishing liquid between the object to be polished and the polishing pad;
the polishing pad has an abrasive layer that constitutes the polishing surface and contains a binder resin and countless abrasive particles and fibers;
the binder resin is polyvinylidene fluoride or polyethersulfone,
The fibers are made of at least one of polypropylene and polyethylene terephthalate,
The second step is characterized in that the polishing surface is pressed against the object to be polished with a predetermined pressing force, and at least one of the object to be polished and the polishing pad is rotated relatively.

The object to be polished may be silicon-based, such as Si or SiC, but the inventors confirmed the effects of the present invention when the object to be polished is a nitride. In addition, the polishing liquid may have a pH greater than 1 and less than 14, but the inventors confirmed the effects of the present invention when the polishing liquid is strongly acidic with a pH of 1 or strongly alkaline with a pH of 14.

The polishing pad of the present invention can polish an object to be polished with high efficiency, is less likely to cause polishing defects on the object to be polished, and has excellent cleaning properties against particles adhering to the object to be polished after polishing. Also, the wafer polishing method of the present invention can polish an object to be polished with high efficiency, is less likely to cause polishing defects on the object to be polished, and has excellent cleaning properties against particles adhering to the object to be polished after polishing.

FIG. 1 is a schematic cross-sectional view showing a method for manufacturing the polishing pads of Examples 1 to 10. 2A to 2C are schematic cross-sectional views showing a method for manufacturing the polishing pads of Examples 1 to 10. 3A to 3C are schematic cross-sectional views showing a method for manufacturing the polishing pads of Examples 1 to 10. FIG. 4 is a schematic cross-sectional view showing a method for manufacturing the polishing pads of Examples 1 to 10. FIG. 5 is a schematic cross-sectional view of the polishing pads of Examples 1 to 10. FIG. 6 is a side view showing the test piece of Test 1. FIG. 7 is a graph showing the results of Test 1. FIG. 8 is a graph showing the results of Test 2. 9A and 9B show the polishing pad of Example 2, in which FIG. 9A is a SEM photograph of its surface at 30 times magnification, and FIG. 9B is a SEM photograph of its cross section at 30 times magnification. FIG. 10 relates to the polishing pad of Example 2, where FIG. 10A is an SEM photograph of its surface at 2000 times magnification, and FIG. 10B is an SEM photograph of its cross section at 2000 times magnification. FIG. 11 relates to the polishing pad of Example 2, where FIG. 11A is an SEM photograph of its surface at 5000 times magnification, and FIG. 11B is an SEM photograph of its cross section at 5000 times magnification.

The polishing pad of the present invention has an abrasive layer that contains a binder resin and countless abrasive particles and fibers. This abrasive layer constitutes the polishing surface.

Polyvinylidene fluoride (PVDF) or polyethersulfone (PES) is used as the binder resin. At least one of polypropylene (PP) and polyethylene terephthalate (PET) is used as the fiber. The shape of the fiber, such as the fiber length and thickness, can be selected. The fibers may be based on a preformed fiber web, or may not be preformed. A fiber web is a layer of fibers arranged vertically, crossed, or randomly. A nonwoven fabric is made by bonding the fibers of a fiber web together.

Abrasive particles may include silica, ceria, alumina, diamond, zirconia, titania, manganese oxide, barium carbonate, chromium oxide, boron carbide, iron oxide, etc. These may be used alone or in a mixture of two or more types.

The polishing pad of the present invention can be manufactured by the following manufacturing method. This manufacturing method includes a preparation step of preparing a paste containing a binder resin, a solvent for dissolving the binder resin, and a countless number of abrasive particles, and a fiber web;
an impregnation step of impregnating the fiber web with the paste to form an impregnated body;
and a solidification step of removing the solvent from the impregnated body to solidify the binder resin.

The polishing layer of the polishing pad obtained by this manufacturing method includes a fiber web that constitutes the fibers, and a binder resin and abrasive particles contained within the fiber web. In this case, since the fibers are preformed as a fiber web, the productivity of the polishing pad is high.

The paste contains a binder resin, numerous abrasive particles, and a solvent. Examples of the solvent that can be used include dimethylformamide, dimethyl sulfoxide, acetone, ethyl acetate, and methyl ethyl ketone. These may be used alone or in combination of two or more.

The paste may also contain alkaline fine particles such as sodium carbonate, piperazine, potassium hydroxide, sodium hydroxide, calcium oxide, potassium carbonate, and magnesium oxide. The paste may also contain water repellents such as fluorine-based water repellents, silicon-based water repellents, hydrocarbon-based water repellents, and metal compound-based water repellents. The paste may also contain pigments such as inorganic pigments such as titanium dioxide, calcium carbonate, and carbon black, and organic pigments such as azo pigments and polycyclic pigments. These may be used alone or in combination of two or more.

When using a polishing liquid, the polishing liquid may be pure water, may be oil-based, or may contain acidic or alkaline chemicals.

(Examples and Comparative Examples)
Examples 1 to 10 embodying the present invention and Comparative Examples 1 and 2 will be described below.

As shown in Table 1, the combinations of the fibers and basis weight (g/m ² ) of the fiber web, the binder resin and the abrasive particles were changed, and polishing pads of Examples 1 to 10 were produced by the following production method.

The fiber webs of Examples 1, 2, 6, and 7 have fiber diameters of 40 μm and 30 μm, and are 3.0 mm thick. The fiber webs of Examples 3 and 8 have fiber diameters of 27 μm and are 3.0 mm thick. The fiber webs of Examples 4 and 9 have fiber diameters of 26 μm and are 1.5 mm thick. The fiber webs of Examples 5 and 10 have fiber diameters of 25 μm and are 3.0 mm thick.

As a preparation step, the following binder resin, solvent, and abrasive particles were prepared.
(Binder resin)
PVDF (Polyvinylidene Fluoride)
PES (Polyethersulfone)
(solvent)
N-methyl-2-pyrrolidone (abrasive particles)
Silica ( _SiO2 ) (average particle size: 0.2 μm)

11% by weight of binder resin, 34% by weight of abrasive particles, and 56% by weight of solvent were mixed to make a paste.

In the impregnation process, as shown in FIG. 1, the paste is formed into a sheet on a base 1 to form a first sheet-like formed body 3. Then, a fiber web 5 is placed on the first sheet-like formed body 3. As a result, as shown in FIG. 2, the paste of the first sheet-like formed body 3 impregnates the lower part of the fiber web 5. This results in the formation of a first layer 71 consisting of only the paste, a second layer 72 consisting of the paste and the fiber web 5, and a third layer 73 consisting of only the fiber web 5.

The paste is then formed into a sheet on the fiber web 5 to form the second sheet-like formed body 3. As a result, as shown in FIG. 3, the paste of the second sheet-like formed body 3 is impregnated into the upper part of the fiber web 5. This forms a laminate 9 consisting of a first layer 71 consisting of only the paste, a second layer 72 consisting of the paste and the fiber web 5, a third layer 73 consisting of only the fiber web 5, a fourth layer 74 consisting of the paste and the fiber web 5, and a fifth layer 75 consisting of only the paste.

The laminate 9 is then vacuum-pressurized in the stacking direction. As a result, the first layer 71 and the fifth layer 75 are incorporated into the fiber web 5, forming the pressurized laminate 11 as an impregnated body. In other words, the pressurized molded body 11 is composed of a second layer 72 made of paste and fiber web 5, and a fourth layer 74 made of paste and fiber web 5, as shown in FIG. 4.

Next, in the solidification process, the pressurized laminate 11 is dried to remove the solvent from the pressurized laminate 11. Thus, the binder resin is solidified. Thus, the polishing pad 13 shown in FIG. 5 is obtained. This polishing pad 13 is composed of a lower polishing layer 92 in which the paste is solidified at the bottom of the fiber web 5, and an upper polishing layer 94 in which the paste is solidified at the top of the fiber web 5. In other words, the lower polishing layer 92 and the upper polishing layer 94 contain the fiber web 5 that constitutes the fibers, and the binder resin and abrasive particles contained within the fiber web 5. In this case, since the fibers are formed in advance as the fiber web 5, the productivity of the polishing pad 13 is high. The surface of the lower polishing layer 92 or the upper polishing layer 94 is ground to form an abrasive surface.

The durometer hardness, density (g/cm ³ ), elastic modulus (kgf/mm ² ) and folding endurance of the polishing surface of the polishing pads of Examples 1 to 10 thus obtained are shown in Table 2.

The modulus of elasticity was measured using a universal testing machine (Instron 5569). The folding resistance was evaluated by wrapping each polishing pad around an aluminum rod-shaped pipe with a diameter of 6 mm, and gradually bending the pipe to 90 degrees, and seeing whether the polishing pad cracked or broke. If no cracks or breaks occurred, it was marked as ◯, and if cracks or breaks occurred, it was marked as ×.

The polishing pad of Comparative Example 1 was manufactured by the manufacturing method described in Japanese Patent No. 5511266 using a paste containing 11% by weight of binder resin (PVDF), 34% by weight of abrasive particles, and 56% by weight of solvent.

The polishing pad of Comparative Example 2 was manufactured by the manufacturing method described in Japanese Patent No. 5511266 using a paste containing 11% by weight of binder resin (PES), 34% by weight of abrasive particles, and 56% by weight of solvent.

The durometer hardness, density, elastic modulus, and folding resistance of the polishing surfaces of the polishing pads of Comparative Examples 1 and 2 are also shown in Table 2.

(Test 1)
6 were cut out from the polishing pads of Examples 1 to 10 and Comparative Examples 1 and 2. The illustrated dimensions a to d of each test piece 15 are as follows:
a = 15 (mm)
b = 20 (mm)
c = 60 (mm)
d = 10 (mm)
Thickness = 2.5 (mm)

The tensile strength (maximum yield load÷cross-sectional area) (MPa) of each test piece was measured under the following conditions.
Testing machine: Universal testing machine (Instron 5569)
Test conditions: tensile speed = 5 mm/min

The tensile strength measured for each test piece 15 without any treatment was defined as the first tensile strength. A strong acid polishing solution was prepared by adding hydrogen peroxide to an aqueous potassium permanganate solution (0.25 mol/L, pH 7) until the pH reached 1, and the tensile strength measured for each test piece 15 after immersion in the strong acid polishing solution for 60 hours was defined as the second tensile strength. A strong alkaline polishing solution was prepared by adding potassium hydroxide to an aqueous potassium permanganate solution (0.25 mol/L, pH 7) until the pH reached 14, and the tensile strength measured for each test piece 15 after immersion in the strong alkaline polishing solution for 60 hours was defined as the third tensile strength.

The second tensile strength x 100/first tensile strength and the third tensile strength x 100/first tensile strength were also calculated. These results are shown in Table 3. The first tensile strength and the second tensile strength of the test pieces of Example 2 and Comparative Examples 1 and 2 are shown in Figure 7.

From Table 3 and Figure 7, it can be seen that the test pieces 15 of Comparative Examples 1 and 2 are prone to deterioration when the polishing liquid is strongly acidic or strongly alkaline. For this reason, there is a risk of polishing defects occurring with the polishing pads of Comparative Examples 1 and 2.

In contrast, it can be seen that the test pieces of Examples 1 to 10 are less likely to deteriorate, even if the polishing liquid is strongly acidic or strongly alkaline. For this reason, the polishing pads of Examples 1 to 10 are less likely to cause polishing defects. This is because the polishing pads of Examples 1 to 10 have a polishing layer that contains fibers, which provides high strength during polishing. In particular, the polishing pads of Examples 1 to 10 have a binder resin made of polyvinylidene fluoride or polyethersulfone, and fibers made of at least one of polypropylene and polyethylene terephthalate.

(Test 2)
A wafer polishing machine (Engis EJW-380), polishing pads (diameter 30 cm) of Example 2 and Comparative Examples 1 and 3, and a GaN bare wafer (2 inch) were prepared. The polishing pad of Comparative Example 1 was the same as that used in Test 1. The polishing pad of Comparative Example 3 was a commercially available nonwoven fabric pad (SUBA600 manufactured by Nitta Haas).

The GaN bare wafer was polished under the following conditions.
Flow rate of polishing liquid: 10 mL/min Load: 85 kPa
Rotation speed of the plate: 60 rpm
Carrier rotation speed: 60 rpm
Processing time: 60 minutes Polishing liquid: A potassium permanganate aqueous solution was used in Example 2 and Comparative Example 1. In Comparative Example 3, a colloidal silica slurry was used.

The GaN bare wafer was polished by the polishing surface of each polishing pad by rotating the platen and the carrier while supplying polishing liquid between the GaN bare wafer and each polishing pad. The results are shown in Figure 8.

As is clear from Figure 8, the polishing pad of Example 2 is capable of polishing with high polishing efficiency and high surface quality compared to the polishing pads of Comparative Examples 1 and 3, even when the object to be polished is a bare GaN wafer. As shown in Figures 9 to 11, the polishing pad of Example 2 exhibits high strength during polishing because it contains polypropylene fibers in the polyvinylidene fluoride matrix. As shown in Test 1, this effect is exhibited even when the polishing liquid is strongly acidic or strongly alkaline, because the polishing pad of Example 2 has high chemical resistance.

In addition, the polishing pad of Example 2 has an abrasive layer that constitutes the polishing surface and contains countless abrasive particles, so a polishing liquid that does not contain abrasive grains can be used, and it has excellent cleaning properties for particles that adhere to the GaN bare wafer after polishing.

Therefore, the polishing pad of Example 2 can polish the GaN bare wafer with high efficiency, is less likely to cause polishing defects on the GaN bare wafer, and has excellent cleaning properties against particles adhering to the GaN bare wafer after polishing. Also, the wafer polishing method of Example 2 can polish the GaN bare wafer with high efficiency, is less likely to cause polishing defects on the GaN bare wafer, and has excellent cleaning properties against particles adhering to the GaN bare wafer after polishing.

Although the present invention has been described above with reference to Examples 1 to 10, it goes without saying that the present invention is not limited to the above Examples 1 to 10, and can be modified as appropriate without departing from the spirit of the present invention.

For example, although a GaN bare wafer was polished in Example 2, the polishing pad and wafer polishing method of the present invention can also be applied to polishing wafers made of Si or SiC, or other nitrides such as Si ₃ N ₄ .

In addition, the polishing pad and wafer polishing method of the present invention can also be applied to polishing uneven parts of the workpiece, such as the outer edge of a wafer, due to the high tensile strength of the polishing pad of the present invention.

The present invention can be used in semiconductor device manufacturing equipment.

5... Fiber web 92, 94... Abrasive layer (92... Lower abrasive layer, 94... Upper abrasive layer)
13...Polishing pad

Claims (5)

A polishing pad having a polishing surface for polishing an object to be polished in the presence of a polishing liquid not containing abrasive particles, the polishing pad having a polishing layer containing a binder resin, a countless number of abrasive particles and fibers,
the binder resin is polyvinylidene fluoride or polyethersulfone,
1. A polishing pad, wherein the fibers are made of at least one of polypropylene and polyethylene terephthalate. 2. The polishing pad according to claim 1 , wherein the polishing layer includes a fiber web that constitutes the fibers, and the binder resin and the abrasive particles that are contained within the fiber web. A first step of preparing an object to be polished, a polishing pad, and a polishing liquid;
a second step of polishing the object to be polished by the polishing surface of the polishing pad while supplying the polishing liquid between the object to be polished and the polishing pad;
the polishing pad has an abrasive layer that constitutes the polishing surface and contains a binder resin and countless abrasive particles and fibers;
the binder resin is polyvinylidene fluoride or polyethersulfone,
The fibers are made of at least one of polypropylene and polyethylene terephthalate,
A wafer polishing method, characterized in that in the second step, the polishing surface is pressed against the object to be polished with a predetermined pressing force, and at least one of the object to be polished and the polishing pad is rotated relatively. 4. The method for polishing a wafer according to claim 3, wherein the object to be polished is a nitride. 5. The method of claim 3, wherein the polishing liquid is a strong acid having a pH of 1 or a strong alkaline having a pH of 14.

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