POLISHING PAD AND WAFER POLISHING METHOD

TECHNICAL FIELD

[0001]The present invention relates to a polishing pad and a wafer polishing method.

BACKGROUND ART

[0002]Japanese Patent Laid-Open No. 2019-46838, Japanese Patent Laid-Open No. 2019-118981, Japanese Patent Laid-Open No. 2020-49639 and Japanese Patent No. 5511266 disclose conventional polishing pads. The polishing pad disclosed in Japanese Patent Laid-Open No. 2019-46838, Japanese Patent Laid-Open No. 2019-118981 or Japanese Patent Laid-Open No. 2020-49639 is obtained by impregnating a nonwoven fabric with a paste and removing a solvent from the paste. The paste disclosed in Japanese Patent Laid-Open No. 2019-46838 is composed of urethane, a solvent such as dimethylformamide, polishing particles such as silica (SiO₂), and alkali fine particles such as sodium carbonate. The paste disclosed in Japanese Patent Laid-Open No. 2019-118981 is composed of ether-based urethane and a solvent such as N, N-dimethylformamide. The paste disclosed in Japanese Patent Laid-Open No. 2020-49639 is composed of urethane, a solvent, and a water repellent. When the solvent is removed by drying or the like, the urethane solidifies in a state of bonding to the nonwoven fabric. The polishing pad disclosed in Japanese Patent No. 5511266 is manufactured using a paste in which a binder resin, polishing particles and a solvent are mixed together.

[0003]The polishing pad disclosed in Japanese Patent Laid-Open No. 2019-46838 is used to polish an outer circumferential edge part of a disc-shaped wafer made of silicon or the like, which is used to manufacture semiconductor elements. That is, the wafer is retained on a rotary table that is rotatable around a rotation center. At this time, a central axis of the wafer is positioned at the rotation center of the rotary table. The polishing pad is provided at an upper end of a spindle such that an outer circumferential end surface of the polishing pad abuts on the outer circumferential edge part of the wafer. Then, a predetermined load is applied to between the outer circumferential edge part of the wafer and the outer circumferential end surface of the polishing pad while a polishing liquid is supplied thereto, thereby causing the rotary table and the spindle to rotate. This makes it possible to polish the outer circumferential edge part of the wafer. Consequently, it becomes possible to reduce the number of defects in semiconductor apparatuses attributed to the outer circumferential edge part of the wafer.

[0004]However, according to the inventors' test results, when any of the conventional polishing pads polishes the outer circumferential edge part of a disc-shaped wafer, the polishing pad exhibits insufficient polishing efficiency, has low flexibility, is unlikely to be deformed elastically, and exhibits poor followability to the wafer when pressing the wafer. Thus, the polishing process takes a long time, and an unpolished part is likely to occur. In addition, because the polishing pad does not contain polishing particles, when a polishing liquid containing polishing particles is used as loose abrasive polishing, it is necessary to remove remaining polishing particles adhering to the polished wafer, and therefore it is necessary to clean the wafer many times.

[0005]Particularly, to polish a wafer made of silicon carbide (SiC), which is usable to manufacture power semiconductors, the polishing pad needs a higher polishing capability.

SUMMARY OF THE INVENTION

[0006]Accordingly, one non-limiting object of the present teaching is to provide a polishing pad with high polishing efficiency for polishing the outer circumferential edge part of a disc-shaped wafer such that an unpolished part is less likely to occur, and the polished wafer is cleanable easily. Further developments of the present teaching are described in the dependent claims. In addition, another non-limiting object of the present teaching is to provide a wafer polishing method such that the outer circumferential edge part of a disc-shaped wafer is polishable with higher polishing efficiency, an unpolished part is less likely to occur, and the polished wafer is cleanable easily. These objects are achieved by the teachings according to the independent claims. Further developments of the present teaching are described in the dependent claims.

[0023]The polishing pad of the present teaching exhibits excellent polishing efficiency because the polishing particles are diamond particles.

[0024]In addition, according to the inventors' test results, when the outer circumferential edge part of a disc-shaped wafer is polished with the polishing pad (including diamond particles as the polishing particles) of the present teaching, the polishing pad exhibits excellent followability to the wafer, and therefore an unpolished part is unlikely to occur. Furthermore, in the polishing pad of the present teaching, because the polishing body constituting the polishing surface contains a numerous number of the polishing particles, a polishing liquid containing none of the polishing particles is usable. Thus, the number of the particles (polishing particles) remaining on the polished wafer is small, and therefore the polished wafer is cleanable easily.

[0025]Other aspects and advantages in the present invention should be clear from the working examples explained in the following description and shown in the attached drawings, from the illustrations in these drawings, and from the concept or gist of the present invention disclosed overall in the specification and these drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a cross-sectional view of a polishing pad (samples 1 to 20).

[0027]FIG. 2 is a schematic cross-sectional view showing a wafer polishing method according to working examples 1 to 20 and comparative examples 1 to 4.

[0028]FIG. 3 is a 300× SEM image of the polishing pad (sample 3).

[0029]FIG. 4 is a 3000× SEM image of the polishing pad (sample 3).

[0030]FIG. 5 is a 300× SEM image of the polishing pad (sample 7).

[0031]FIG. 6 is a 3000× SEM image of the polishing pad (sample 7).

[0032]FIG. 7 is a 300× SEM image of the polishing pad (sample 11).

[0033]FIG. 8 is a 3000× SEM image of the polishing pad (sample 11).

[0034]FIG. 9 is a 300× SEM image of the polishing pad (sample 15).

[0035]FIG. 10 is a 3000× SEM image of the polishing pad (sample 15).

DETAILED DESCRIPTION OF EMBODIMENTS

[0036]In a polishing pad of the present teaching, a polishing surface is formed of a polishing body, and the polishing body includes a base material and polishing particles. The base material is composed of a binder resin and fibers and has a plurality of pores formed therein. The polishing particles are retained in the base material or in the pores.

[0037]As the binder resin, a thermoplastic polyurethane (TPU) resin, a polyvinylidene fluoride (PVDF) resin, a polyethersulfone (PES) resin, a polyvinyl fluoride resin, a vinyl fluoride/hexafluoropropylene copolymer, a vinylidene fluoride/hexafluoropropylene copolymer, a polyethylene resin, a polymethylmethacrylate resin or the like is adoptable. These binder resins may be used singly or may be used in a mixture of two or more kinds thereof.

[0038]The polishing particles are diamond particles. The polishing body preferably includes a filler retained in the base material or in the pores. As the filler, an inorganic powder, inorganic fibers, a resin powder, resin fibers, a metal powder or metal fibers, which are softer than diamond, can be adopted. The filler is assumed to prevent aggregation of the polishing particles, to retain the polishing particles elastically, and to reduce the reaction force exerted on the polishing particles during a polishing process. In addition, the wear resistance of the polishing pad improves depending on the material of the filler.

[0039]As the inorganic powder used as the filler, for example, silica, alumina, talc, silicon carbide (SiC), calcium carbonate, or clay is adoptable. As the inorganic fibers used as the filler, for example, glass fibers or carbon fibers can be adopted. As the resin powder or the resin fibers, which are used as the filler, a cured thermosetting resin, a thermoplastic resin powder or thermoplastic resin fibers can be adopted. As the metal powder used as the filler, for example, iron, copper, aluminum, or nickel is adoptable. As the metal fibers used as the filler, for example, iron fibers, copper fibers, or aluminum fibers can be adopted. These may be used singly or may be used in a mixture of two or more kinds thereof.

[0040]As the fibers, polyethylene terephthalate (PET) fibers, polypropylene (PP) fibers, aramid fibers, glass fibers, cellulose fibers, nylon fibers, vinylon fibers, polyester fibers, polyethylene fibers, polyolefin fibers, rayon fibers, a low-density polyethylene resin, an ethylene vinyl acetate resin, synthetic rubber, a co-polymerized polyamide resin, a co-polymerized polyester resin or the like can be adopted. These may be used singly or may be used in a mixture of two or more kinds thereof. In addition, the shape of the fibers such as the fiber length or thickness is also selectable.

[0041]The fibers of the polishing pad may be fibers of a preformed fibrous web or may be discrete fibers. The fibrous web is formed of layers of fibers by arraying the fibers vertically, crossing the sequence of the fibers, or arraying the fibers randomly. A nonwoven fabric is made of fibrous webs in which fibers are bonded to each other.

[0045]A polishing body of the polishing pad to be obtained by the manufacturing method includes: a fibrous web as the fibers; and the binder resin and the polishing particles that are contained in the fibrous web. In this case, the preformed fibrous web is used as the fibers, and therefore the productivity of the polishing pad is high.

[0046]The paste contains the binder resin, a numerous number of the polishing particles, and a solvent. As the solvent, N-methyl-2-pyrolidon (NMP), dimethylformamide, dimethylsulfoxide, acetone, ethyl acetate, methyl ethyl ketone or the like is adoptable. These solvents may be used singly or may be used in a mixture of two or more kinds thereof. The solvents are selected according to the binder resin.

[0047]The paste may also contain alkali fine particles of sodium carbonate, piperazine, potassium hydroxide, sodium hydroxide, calcium oxide, potassium carbonate, magnesium oxide or the like. In addition, the paste may contain a water repellent such as a fluorine-based water repellent, a silicon-based water repellent, a hydrocarbon-based water repellent or a metal compound-based water repellent. Furthermore, the paste may contain a pigment such as an inorganic pigment, including titanium dioxide, calcium carbonate or carbon black, or an organic pigment, including an azo pigment or a polycyclic pigment. These may be used singly or may be used in a mixture of two or more kinds thereof.

[0048]When a polishing liquid is used, the polishing liquid may be pure water, may be oily, or may contain an acidic or alkaline chemical.

[0049]According to the inventors' test results, it is preferable that the binder resin be a thermoplastic polyurethane resin or a polyvinylidene fluoride resin and the fibers be polypropylene fibers. In this case, when the polishing pad presses a wafer, the polishing pad exhibits excellent followability to the wafer.

[0050]In addition, according to the inventors' test results, it is preferable that the binder resin be in a range from 9.5 to 34.6 vol %, the polishing particles be in a range from 2.2 to 14.3 vol %, the fibers be in a range from 5.1 to 10.2 vol %, the filler be in a range from 0 to 17.6 vol %, and the pores be in a range from 34.6 to 68.5 vol %. In this case, the polishing pad exhibits excellent wear resistance and excellent polishing efficiency.

(Test)

[0051]As shown in table 1, the combination of a fibrous web, a binder resin, and a particle diameter of polishing particles was changed, and polishing pads 1 (samples 1 to 20) were manufactured by a manufacturing method described below.

[0052]First of all, as a preparation step, a binder resin, a solvent, polishing particles, and a fibrous web were prepared as described below. The fibrous web is formed in a disc shape and is centered on a first rotation axis center P, in the same manner as the polishing pad 1 to be manufactured, which is shown in FIG. 1.

[0063]Then, as shown in table 1, the combination of the fibrous web, the binder resin, the particle diameter of the polishing particles and the paste was changed, and the binder resin, the polishing particles, the filler and the solvent were mixed in parts by mass shown in table 1 to make pastes.

[0064]At this time, regarding the polishing particles, the number of the polishing particles in each polishing pad 1 (each sample) was adjusted to be the same between the polishing pads 1 (the samples) even if the particle diameter of the polishing particles was different between the polishing pads 1 (the samples). In addition, when the binder resin was a powdered PVDF resin, the polishing particles and the binder resin were dry-mixed, and the mixture was mixed with a slurry, in which the solvent and the filler were mixed, to make a paste. Thereby, the polishing particles were caused to disperse in the paste. When the binder resin was a TPU resin in a bead form, the binder resin, the solvent, and the filler were mixed in advance to make a slurry, and the polishing particles were added to the slurry to make a paste. Then, the polishing particles were dispersed in the paste with a planetary centrifugal mixer.

[0065]Then, as an impregnation step, the paste was brought into contact with the fibrous web while a load was applied to front and rear surfaces of the fibrous web to impregnate the fibrous web with the paste, thereby producing an impregnated body. Then, as a solidification step, the obtained impregnated body was dried, thereby removing the solvent from the impregnated body and causing the binder resin to solidify. Consequently, a polishing body is obtained. An outer circumferential part and an inner circumferential part of the polishing body were removed while being centered on the first rotation axis center P to obtain the polishing pad 1 (each of samples 1 to 20).

[0066]As shown in FIG. 1, the polishing pad 1 (each sample) is formed in a disc shape and is centered on the first rotation axis center P. FIG. 3 shows a 300× SEM image of the polishing pad (sample 3), and FIG. 4 shows a 3000× SEM image of the polishing pad (sample 3). FIG. 5 shows a 300× SEM image of the polishing pad (sample 7), and FIG. 6 shows a 3000× SEM image of the polishing pad (sample 7). FIG. 7 shows a 300× SEM image of the polishing pad (sample 11), and FIG. 8 shows a 3000× SEM image of the polishing pad (sample 11). FIG. 9 shows a 300× SEM image of the polishing pad (sample 15), and FIG. 10 shows a 3000× SEM image of the polishing pad (sample 15).

[0067]As shown in FIG. 3 to FIG. 10, the polishing pad 1 (each sample) is formed of the polishing body that constitutes front and rear polishing surfaces. The polishing body includes a base material and the polishing particles. The base material is composed of the binder resin and the fibers and has a plurality of pores formed therein. The polishing particles are retained in the base material or in the pores. The polishing body includes: the fibrous web as the fibers; and the binder resin and the polishing particles that are contained in the fibrous web. The preformed fibrous web is used as the fibers, and therefore the productivity of the polishing pad 1 is high.

[0068]Table 2 shows volume percents (vol %) of the binder resin, the polishing particles, the fibers, the filler and the pores in the polishing pad 1 (each of samples 1 to 20). Particularly, the base material has a filler in samples 1 to 16, and the base material has no filler in samples 17 to 20.

[0069]In addition, table 3 shows a density (g/cm), a durometer hardness (D) and an elastic modulus (N/mm) of the polishing body of the obtained polishing pad 1 (each of samples 1 to 20).

[0070]A polishing apparatus, which is shown in FIG. 2, and a wafer 3 (diameter: 6 inches), which is made of silicon carbide (Sic), to be polished were prepared. The polishing apparatus is a “FINE SURFACE E-200” manufactured by BBS KINMEI CO., LTD. and includes: a drum (not shown) capable of rotating the wafer 3 around a central axis Q; and a chuck 5.

[0071]The wafer 3 has: the central axis Q; a front surface 3a that extends in a direction substantially orthogonal to the central axis Q; a rear surface 3b that is positioned opposite to the front surface 3a and extends in the direction substantially orthogonal to the central axis Q; an outer circumferential surface 3c that connects an outer circumferential edge of the front surface 3a and an outer circumferential edge of the rear surface 3b; a front surface-side outer circumferential edge part 3d that is formed by the front surface 3a and the outer circumferential surface 3c; and a rear surface-side outer circumferential edge part 3e that is formed by the rear surface 3b and the outer circumferential surface 3c.

[0072]The chuck 5 of the polishing apparatus is capable of retaining and rotating the polishing pad 1 (samples 1 to 20) at a predetermined rotation speed, and is configured to be capable of pressing the front polishing surface of the polishing pad 1 against the outer circumferential surface 3c, the front surface-side outer circumferential edge part 3d and the rear surface-side outer circumferential edge part 3e at a variable angle θ and a predetermined load.

[0073]The following shows: conditions for polishing a TOP part, which is a portion of the outer circumferential surface 3c, at the angle θ of 90°; conditions for polishing an ACF part, which is a portion of the front surface-side outer circumferential edge part 3d, at the angle θ of 21°; and conditions for polishing a BCF part, which is a portion of the rear surface-side outer circumferential edge part 3e, at the angle θ of 111°.

(TOP Part)

[0074]Rotation speed of the drum: 200 rpm (The drum presses the wafer against the polishing pad by centrifugal force.) Vertical movement speed of the wafer 3: 1.5 mm/second Rotation speed of the chuck 5: 10 rpm

(ACF Part and BCF Part)

[0078]As shown in table 4, in each of working examples 1 to 20, the wafer was polished in a first process or in the first process to a third process using any of samples 1 to 20. At this time, pure water was used as a polishing liquid. The process time for A/BCF shows a time taken to polish each of the ACF part and the BCF part.

[0079]In contrast, in comparative example 1, the wafer was polished in the first process using a nonwoven fabric pad (polyester fibers 100%, fiber diameter: 14 μm, thickness: 3.0 mm) as the polishing pad 1. At this time, a commercially available colloidal silica slurry (containing a 10000 ppm or less of SiO₂ particles having an average particle diameter of 50 nm) was used as the polishing liquid. The process time is 180 minutes.

[0080]In comparative example 2, the wafer was polished in the first process using an LHA pad (manufactured by NORITAKE CO., LIMITED using a paste obtained by mixing 11% by mass of the binder resin (PVDF resin), 34% by mass of the polishing particles and 56% by mass of the solvent by the manufacturing method disclosed in Japanese Patent No. 5511266) as the polishing pad 1. At this time, a commercially available lubricant (KMnO₄: 0.25 mol) was used as the polishing liquid. The process time is 115 minutes.

[0081]In comparative example 3, the wafer was polished in the first process using a silica-containing polishing pad (a fibrous web, which is made of PP fibers and has a basis weight of 200 g/m², impregnated with 12% by volume of SiO2 particles having an average particle diameter of 0.2 μm) as the polishing pad 1. At this time, a commercially available lubricant (KMnO₄: 0.25 mol) was used as the polishing liquid. The process time is 180 minutes.

[0082]In comparative example 4, the wafer was polished in the first process using a silica-containing polishing pad (a fibrous web, which is made of PP fibers and has a basis weight of 400 g/m², impregnated with 11% by volume of SiO2 particles having an average particle diameter of 0.2 μm) as the polishing pad 1. At this time, a commercially available lubricant (KMnO₄: 0.25 mol) was used as the polishing liquid. The process time is 180 minutes.

[0083]The polishing time and the presence or absence of an unpolished part, the surface roughness of the polished wafer 3, the particles, and the polishing liquid were evaluated. At this time, the surface roughness of the polished wafer 3 was evaluated by checking the outer circumferential surface 3c (TOP part), the front surface-side outer circumferential edge part 3d (ACF part) and the rear surface-side outer circumferential edge part 3e (BCF part).

[0084]The polishing time and the presence or absence of an unpolished part were evaluated as follows: a rating of E (Excellent) was given if the polishing time was 50 minutes or less, and no unpolished part was present; a rating of G (Good) was given if the polishing time was more than 50 minutes and 100 minutes or less, and no unpolished part was present; a rating of F (Fair) was given if the polishing time was more than 100 minutes and 150 minutes or less, and no unpolished part was present; and a rating of P (Poor) was given if the polishing time was more than 150 minutes and an unpolished part was present.

[0085]The surface roughness of the polished wafer was evaluated as follows: a rating of E (Excellent) was given if Sa was less than 10 nm; a rating of G (Good) was given if Sa was 10 nm or more and less than 20 nm; a rating of F (Fair) was given if Sa was 20 nm or more and less than 50 nm; and a rating of P (Poor) was given if Sa was 50 nm or more.

[0086]The particles (polishing particles) were evaluated by observing the number of the particles in a 5 μm×5 μm surface with an electronic microscope as follows: a) rating of E (Excellent) was given if the number of the particles was 0; a rating of G (Good) was given if the number of the particles was more than 0 and less than 5; a rating of F (Fair) was given if the number of the particles was 5 or more and less than 10; and a rating of P (Poor) was given if the number of the particles was 10 or more.

[0087]The polishing liquid was evaluated as follows: a rating of E (Excellent) was given if the concentration of the contained polishing particles was 0 ppm and polishing was possible; a rating of G (Good) was given if the concentration of the polishing particles was 1 ppm or more and lower than 1000 ppm, and polishing was possible; a rating of F (Fair) was given if the concentration of the polishing particles was 1000 ppm or more and less than 5000 ppm, and polishing was possible; and a rating of P (Poor) was given if the concentration of the polishing particles was 5000 ppm or more and 10000 ppm or less, and polishing was possible.

[0088]In the overall evaluation, a rating of G (Good) was given if a rating of F (Fair) or higher was given to all of the polishing time and the presence or absence of an unpolished part, the surface roughness of the polished wafer, the particles, and the polishing liquid, and a rating of E (Excellent) was given if a rating of G (Good) or higher was given to all of the above evaluation items. The results are shown in table 5 and table 6.

[0089]According to table 5 and table 6, because the polishing pad 1 (each of samples 1 to 20) includes diamond particles as the polishing particles, it is found that, the polishing pad 1 exhibits excellent polishing efficiency. In addition, because the polishing pad 1 (each of samples 1 to 20) has a density in a range from 0.58 to 0.81 g/cm³, a durometer hardness in a range from 16 to 27, and an elastic modulus in a range from 21.5 to 37.5 N/mm², the polishing pad 1 (including diamond particles as the polishing particles) exhibits excellent followability to the wafer 3 when polishing the wafer 3, and thus an unpolished part is unlikely to occur. Furthermore, in the polishing pad 1 (each of samples 1 to 20), because the polishing body constituting the polishing surface includes a numerous number of the polishing particles, mere water containing none of the polishing particles is usable. Thus, the number of the particles (polishing particles) remaining on the polished wafer 3 is small, and therefore the wafer is cleanable easily.

[0090]Therefore, according to the wafer polishing method in working examples 1 to 20 using the polishing pad 1 (each of samples 1 to 20), when the polishing pad 1 polishes the outer circumferential edge part of the disc-shaped wafer 3, the polishing pad 1 exhibits higher polishing efficiency, an unpolished part is less likely to occur, and the polished wafer is cleanable easily.

[0091]In contrast, for the wafer polishing method in each of comparative examples 1 to 4 using the conventional polishing pad 1, many unpolished parts occur, and the polishing pad 1 exhibits inferior polishing efficiency. Particularly, for the wafer polishing method in comparative example 1, it is difficult to clean the polished wafer easily.

[0092]The description above explained the present teaching based on working examples 1 to 20, but the present teaching is not limited to the above-mentioned working examples and is applicable by modification where appropriate within a range that does not deviate from the gist thereof.

[0093]In working examples 1 to 20, the wafer 3 made of SiC was polished, but the polishing pad and the wafer polishing method of the present teaching are also applicable to, for example, polishing wafers made of silicon (Si).

[0094]The present teaching is usable in manufacturing apparatuses of semiconductor apparatuses.

EXPLANATION OF THE REFERENCE NUMBERS

[0095]3 Wafer

[0096]1 Polishing pad

[0097]Q Central axis

[0098]3a Front surface

[0099]3b Rear surface