JP2014087900A - Polishing method - Google Patents

Abstract

A polishing method capable of obtaining a sufficient polishing rate is provided.
A polishing abrasive in which magnetic particles are coated with a continuous polishing layer between a first surface of an object to be polished having a first surface and a second surface and a polishing pad. Abrasive material 6 containing grains is supplied, and a magnetic field is applied to the object to be polished 8 from the second surface side by a permanent magnet 12 so that the magnetic flux density on the first surface is 40 mT or more and less than 200 mT, A polishing method in which the first surface is polished by the polishing pad 4.
[Selection] Figure 3

Description

  The present invention relates to a polishing method, and more specifically to a polishing method suitable for polishing an object to be polished such as a semiconductor wafer or a glass substrate.

  In the CMP (Chemical Mechanical Polishing) method using magnetic slurry as an abrasive, the polishing rate is uniformly improved in the wafer surface by changing the magnetic force distribution by a plurality of electromagnets arranged on the turntable and / or wafer chuck head. It is important to make it.

  Here, for example, in Patent Document 1 (Japanese Patent Application Laid-Open No. 08-155831), FIG. 1 shows the purpose of polishing a semiconductor wafer to a uniform thickness by maintaining the wafer chuck table and the turntable in parallel. A method using a polishing apparatus having a structure as shown has been proposed.

  In other words, in the polishing apparatus 100 of Patent Document 1, the first magnetic generator 108 is repelled inside the wafer chuck table 104 and the first magnetic generator 108 is repelled inside the turntable 107. The second magnetic generator 109 for generating the magnetism to be generated is provided, and the wafer chuck table 104 is provided by the repulsive force generated by the magnetism generated by the first magnetic generator 108 and the magnetism generated by the second magnetic generator 109. The semiconductor wafer is polished to a uniform film thickness while maintaining the parallelism between the lower surface of the substrate and the upper surface of the turntable 107 (Patent Document 1, Abstract, FIG. 1, etc.).

  Further, in Patent Document 2 (Japanese Patent Laid-Open No. 2001-252862), by optimizing the distribution in the wafer surface of the particle density contained in the slurry, it is easy to cope with variations in the uneven shape and material of the polished surface of the wafer. A polishing method and apparatus that can set an optimum particle distribution and intend to improve the uniformity of the polishing rate within a wafer surface are disclosed.

  That is, in the polishing apparatus 200 of Patent Document 2, the wafer 210 attached to the rotating plate 208 is pressed against the rotating polishing pad 204 and the surface of the wafer 210 is polished while supplying the slurry 205 containing magnetic particles. In the slurry that is distributed in the wafer surface by changing the magnetic polarity and the magnetic strength of the plurality of electromagnets 202 and 209 built in the rotary plate 208 and the rotary table 201 to cause magnetism to act on the slurry. It is supposed that the magnetic particle density distribution is uniform (Patent Document 2, Abstract, FIG. 2, etc.).

Japanese Patent Laid-Open No. 08-155831 JP 2001-252862 A

  However, the conventional techniques described in Patent Documents 1 and 2 still have room for improvement from the viewpoint of obtaining a sufficient polishing rate. Accordingly, an object of the present invention is to provide a polishing method capable of obtaining a sufficient polishing rate.

  In order to achieve the above-mentioned object, the present inventor has conducted intensive research on a polishing apparatus and a polishing material used in a polishing method. As a result, in order to reliably obtain a sufficient polishing rate, a polishing layer in which magnetic particles are continuously used as the polishing material. The present inventors have found that it is extremely effective to apply a magnetic field having a predetermined magnetic flux density from the surface opposite to the polishing surface to the object to be polished using the polishing abrasive grains coated with 1.

That is, the present invention
A polishing material comprising abrasive grains in which magnetic particles are coated with a continuous polishing layer between the first surface of the workpiece having the first surface and the second surface and the polishing pad. Supply
Applying a magnetic field from the second surface side to the object to be polished, the magnetic flux density on the first surface is 40 mT or more and less than 200 mT,
Polishing the first surface with the polishing pad;
A polishing method is provided.

  The shape of the abrasive grains used in the above-described polishing method of the present invention, in which magnetic particles are coated with a continuous polishing layer, is not particularly limited. For example, spherical, elliptical, needle-like, columnar, beaded, rod-like, plate Shape, lump shape, fiber shape, spindle shape, etc., and may have irregularities on the surface. Moreover, the shape which has an unevenness | corrugation on the surface is also included.

  As the polishing layer covering the magnetic particles, various conventionally known hard materials can be used as long as the effects of the present invention are not impaired, but it is preferable that the polishing layer is composed of silica (silicon dioxide).

  In the above polishing method of the present invention, a magnetic field is applied to the object to be polished from the second surface (back surface) side, and the magnetic flux density on the first surface (surface, polished surface) is 40 mT or more and less than 200 mT. And The magnetic flux density on the first surface can be measured by a gauss meter (for example, Tesla Meter TM-701 manufactured by Kanetec Corporation).

  According to the polishing method having such a configuration, the magnetic abrasive grains can be securely fixed to the first surface (surface, polished surface) of the object to be polished, and consumption of the magnetic abrasive grains can be suppressed. . Moreover, a high polishing rate can be obtained by sliding the polishing pad on the first surface. Accordingly, the polishing time can be shortened, the load on the objects to be polished can be reduced, and the number of objects to be polished that can be batch processed can be increased. In addition, highly efficient polishing can be achieved by coating the magnetic particles with a continuous polishing layer.

  According to the present invention, a polishing method capable of obtaining a sufficient polishing rate can be provided.

It is a schematic side view of the polish device in patent documents 1. It is a schematic side view of the polish device in patent documents 2. It is a schematic side view which shows the basic composition of one Embodiment of the grinding | polishing apparatus used in order to implement the grinding | polishing method of this invention. It is a schematic sectional drawing of the abrasive grain which coat | covered the magnetic particle used for this invention with the continuous grinding | polishing layer. 2 is a SEM photograph of iron oxide particles used in Example 1. 2 is a SEM photograph of silica-coated magnetic particles used in Example 1.

  Hereinafter, preferred embodiments of the polishing method of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to these. In the following description, the same or corresponding parts are denoted by the same reference numerals, and redundant description may be omitted. Further, since the drawings are for conceptually explaining the present invention, the dimensions and ratios of the components shown may be different from the actual ones.

  FIG. 3 is a schematic side view showing a basic configuration of an embodiment of a polishing apparatus used for carrying out the polishing method of the present invention. As shown in FIG. 3, in this polishing apparatus 1, a polishing pad 4 is disposed on a rotary table (polishing surface plate) 2, and a magnetic slurry 6 is supplied onto the polishing pad 4.

  Above the turntable 2, a wafer (or soda glass substrate) 8, which is a flat object having a first surface and a second surface, is fixed and rotated from the second surface (back surface) side. A head (mounting plate) 10 is provided, and a load is applied to the wafer 8 from the second surface to press the first surface (surface, surface to be polished) of the wafer 8 against the polishing pad 4.

  Further, above the head 10, a magnetic field is applied to the wafer 8, which is an object to be polished, so that the magnetic flux density on the first surface (surface, surface to be polished) of the wafer 8 is controlled within a predetermined range. A plurality of magnets 12 are arranged. Thereby, the distribution of the magnetic abrasive grains fixed to the first surface of the wafer 8 can be controlled substantially uniformly within the first surface.

  That is, in the polishing method of the present embodiment, the magnetic field shown in FIG. 4 is interposed between the first surface of the wafer 8 that is an object to be polished having the first surface and the second surface, and the polishing pad 4. Magnetic slurry 6 which is an abrasive including abrasive grains 20 coated with a continuous abrasive layer is supplied, and a magnetic field is applied to the wafer 8 from the second surface side, so that the magnetic flux density on the first surface Is 40 mT or more and less than 200 mT, and the first surface is polished by the polishing pad 4.

  Abrasive abrasive 20 in which magnetic particles are coated with a continuous polishing layer has magnetic particles 30 and a polishing layer 32, and the surface of magnetic particles 30 is continuously covered with polishing layer 32. The magnetic particles 30 are not exposed on the surface, and can prevent the polishing layer 32 from peeling off during polishing. As a method for coating the magnetic layer 30 with the polishing layer 32, for example, a sol-gel method, a CVD method, or the like can be used.

  As the magnetic particles 30, magnetic particles of various known materials can be used as long as the effects of the present invention are not impaired. For example, metals having ferromagnetism such as iron, nickel, cobalt, magnetite, sendust, and the like. An alloy, an oxide, etc. can be mentioned, These can be used individually or in arbitrary combinations, respectively.

  As the coating layer 32, various conventionally known hard materials can be used as long as the effects of the present invention are not impaired. For example, diamond, cerium oxide, silicon oxide, aluminum oxide, manganese dioxide, iron oxide, oxidation Zinc, silicon carbide and the like can be mentioned, and these can be used alone or in any combination, but silica is preferably used. Silica can be suitably used for precision glass polishing, and has a wide range of applications other than glass polishing applications. Cerium oxide can also be used for glass precision polishing, but is difficult to apply for other uses. In addition, cerium oxide contains rare earths and has a problem of high cost compared to silica.

  The shape of the abrasive grains 20 coated with a continuous abrasive layer of magnetic particles is not particularly limited. For example, a spherical shape, an elliptical shape, a needle shape, a columnar shape, a bead shape, a rod shape, a plate shape, a lump shape, a fiber shape, a spindle It may have various shapes such as a shape, and may have irregularities on the surface. Moreover, the shape which has an unevenness | corrugation on the surface is also included.

  In addition, the grain size of the abrasive grains 20 covered with a continuous abrasive layer of magnetic particles can take a conventional range as long as the effects of the present invention are not impaired. For example, 0.3 to 200 μm (median diameter) Is preferred. Specifically, the median diameter is measured by a laser diffraction method. Specifically, particles are measured by wet measurement using a laser diffraction particle size distribution analyzer (Microtrac MT3300EX II manufactured by Nikkiso Co., Ltd.) mainly using water as a dispersion solvent or other dispersion solvent suitable for particle dispersion. It is calculated by appropriately setting the refractive index, the dispersion solvent refractive index, selection of spherical or non-spherical, and selection of whether or not the particles are permeable.

  Further, the abrasive used in the polishing method of the present embodiment has the form of the magnetic slurry 6 including the abrasive grains 20 in which the magnetic particles are coated with the continuous polishing layer as described above. The abrasive comprising the magnetic slurry 6 is a fluid containing abrasive grains in which magnetic particles are covered with a continuous polishing layer, and a dispersion medium such as water. In some cases, a chemical solution such as alkali or acid is also added.

  In the polishing apparatus 1 shown in FIG. 3, both the rotary table 2 and the head 10 can rotate, and the head 10 may be rotated with the surface plate by Free rotation, and is forcibly driven to adjust the rotation speed. May be.

  In the polishing method of the present embodiment, a magnetic field is applied to the wafer 8 from the second surface (back surface) side so that the magnetic flux density on the first surface (front surface, polishing surface) is 40 mT or more and less than 200 mT. If the magnetic flux density is less than 40 mT, there is a demerit that the force to attract the magnetic abrasive grains is weak and the effect of the magnetic field cannot be sufficiently obtained. Therefore, there is a demerit that the mechanism for sliding the abrasive grains on the surface of the object to be polished by the function of the pad does not work sufficiently.

  As the polishing pad 4, a polishing pad composed of various conventionally known materials can be used as long as the effects of the present invention are not impaired, and the first surface (surface, object to be polished) of the wafer 8 that is an object to be polished. And the first surface can be polished by sliding while interposing magnetic abrasive grains between the wafer 8 and the polishing pad 4.

  Examples of the polishing pad 4 include woven and non-woven polishing pads. Further suitable polishing pads can include any suitable polymer having various densities, hardness, thickness, compressibility, ability to rebound upon compression, and compression modulus. Suitable polymers include, for example, polyvinyl chloride, polyvinyl fluoride, nylon, fluorocarbon, polycarbonate, polyester, polyacrylate, polyether, polyethylene, polyamide, polyurethane, polystyrene, polypropylene, and the like. Can be used in combination.

  Among these, as the polishing pad 4, it is preferable to use a polishing pad made of a nonwoven fabric from the viewpoint of effectively scraping and sliding the magnetic abrasive grains fixed on the surface of the object to be polished by a magnetic field. In addition, as a material constituting the nonwoven fabric, it has necessary performance such as suppression of scratch generation, retention of abrasive grains, penetration of polishing liquid, discharge of shavings, etc. due to appropriate hardness, voids, and hydrophilicity. From the viewpoint of abundantness and availability, it is preferable to impregnate a polyester fiber non-woven fabric with a urethane resin.

  As the permanent magnet 12, for example, a neodymium magnet, a samakoba magnet, a ferrite magnet, an alnico magnet and the like can be cited. From the viewpoint of obtaining a strong magnetic field with a high magnetic flux density, it is preferable to use a neodymium magnet.

  Regarding the number and shape of the permanent magnets 12, the magnetic flux density on the first surface (surface, surface to be polished) of the wafer 8 as the object to be polished is within the above range, and the magnetic abrasive grains are fixed substantially uniformly. It may be selected as appropriate.

  Next, the polishing method in the present embodiment will be described more specifically. The rotary table 2 is rotated at a constant speed by the rotary shaft 2a. A magnetic slurry 6 containing abrasive grains coated with a continuous polishing layer of magnetic particles is appropriately applied to the upper surface of the polishing pad 4 placed on the rotary table 2, and the magnetic slurry 6 spreads substantially uniformly on the polishing pad 4. Make it.

  On the other hand, the wafer 8 is turned over in advance (that is, the surface to be polished is down) and fixed to the head 10. While the head 10 is rotated at a constant speed by a rotating shaft (not shown), a load is applied from above the head 10 so that the first surface of the wafer 8 faces and contacts the polishing pad 4. Then, the first surface of the wafer 8 is pressed against the polishing pad 4 by the head 10 and polished.

  During this polishing, the magnetic field is distributed in the vicinity of the first surface (surface, surface to be polished) of the wafer 8 by the permanent magnets 12 installed on the rotary table 2 and the head 10, thereby magnetic polishing in the magnetic slurry 6. A substantially uniform density distribution of grains is formed. In FIG. 3, although two permanent magnets 12 are installed, the distribution of the polishing rate is determined by the material of the wafer 8 and the unevenness of the first surface, so that it matches the type (material, shape, etc.) of the wafer 8. The number of permanent magnets 12 and the magnetic flux density are selected in advance.

As mentioned above, although typical embodiment of this invention was described, this invention is not limited only to these, Various design changes are possible, and such a design change is also contained in this invention. For example, in the above embodiment, the case where a permanent magnet is used has been described, but an electromagnet may be used. In the above embodiment, the case where the surface of the magnetic particle 30 is continuously covered with the polishing layer 32 (that is, the case where the magnetic particle 30 is completely covered) has been described. The present invention also includes a case where a part of is covered with a polishing layer. That is, the present invention also includes a case where the polishing layer discontinuously covers the magnetic particles.
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

Example 1
Silica coating magnetic particles were prepared by applying silica coating having a film thickness of about 40 nm to iron oxide particles having a particle size of about 200 nm. SEM photographs of the iron oxide particles and silica-coated magnetic particles are shown in FIGS. 5 and 6, respectively. A scanning electron microscope (S-4800) manufactured by HITACHI was used for the SEM observation. A sol-gel method was used for silica coating, and the amounts of tetraethyl orthosilicate (TEOS), ammonia water 25%, and iron oxide particles were determined from the relationship between the surface area of the iron oxide particles and the target silica film thickness. Specifically, TEOS was 0.7 mol / EtOH, ammonia water was 2 mol / EtOH, and ion-exchanged water was 9 mol / EtOH.

  Next, the silica coating procedure will be described. The iron oxide was dispersed in ethanol by sonication, and 25% ammonia water (2 mol / EtOH) was added to the solution. Next, TEOS (0.7 mol / EtOH) was added to the solution and subjected to ultrasonic treatment for 2 hours while stirring at 350 rpm. Thereafter, MeOH was added to stop the reaction, and decantation and washing were repeated until the pH reached around 7 with ion-exchanged water and MeOH. Finally, the solution was dried at 120 ° C. for 20 hours to obtain silica-coated magnetic particles.

  Next, the silica-coated magnetic particles and water as a dispersion medium were mixed to prepare 200 g of a magnetic slurry composed of an aqueous dispersion containing 9% by mass of silica-coated magnetic particles. Table 1 shows the specific surface area and the total surface area of the silica-coated magnetic particles contained in the magnetic slurry. The specific surface area was measured using a fully automatic specific surface area measuring machine (Macsorb HM model-1201) manufactured by MOUNTECH, and the total surface area was obtained from the measured values.

Next, in the polishing apparatus (PM-5 manufactured by Logitech) having the structure shown in FIG. 3, a non-woven pad SUBA600 manufactured by Nitta Haas Co., Ltd. is used as a polishing pad, and a neodymium magnet (30 mm × 30 mm × 5 mm, surface magnetic flux density 330 mT) per glass substrate, 1st surface (surface to be polished) of soda lime glass substrate (diameter: 6.25 cm, specific gravity: 2.4) to be polished And a distance of 3 mm from the second surface on the opposite side. The magnetic flux density on the first surface (surface to be polished) of the soda lime glass substrate was 174 mT. The polishing conditions were such that the number of rotations of the rotary table was 30 rpm, the head was freely rotated, the polishing pressure was 280 gf / cm ² , and 15 minutes. The supply rate of the magnetic slurry was 10 cc / min.

[Evaluation]
With respect to the soda glass substrate polished as described above, the polishing rate was determined by measuring the weight reduction of the object to be polished and converting it from the density of the substrate and the substrate area. The results are shown in Table 2.

≪Comparative example 1≫
Colloidal silica having an average particle size of 80 nm and water as a dispersion medium were mixed to prepare 200 g of a slurry composed of an aqueous dispersion containing 5% by mass of silica particles. Table 1 shows the specific surface area and the total surface area of the colloidal silica contained in the slurry. The specific surface area was measured using a fully automatic specific surface area measuring machine (Macsorb HM model-1201) manufactured by MOUNTECH, and the total surface area was obtained from the measured values.

  A soda glass substrate was polished and the polishing rate and surface roughness were determined in the same manner as in Example 1 except that the above slurry was used instead of the magnetic slurry and no magnetic field was applied during polishing. The results are shown in Table 2. When colloidal silica is used, it has been confirmed in preliminary experiments that the presence or absence of magnetic field application does not affect the polishing rate and the surface roughness.

≪Comparative example 2≫
Colloidal silica having an average particle size of 80 nm and water as a dispersion medium were mixed to prepare 200 g of a slurry composed of an aqueous dispersion containing 40% by mass of silica particles. Table 1 shows the specific surface area and the total surface area of the colloidal silica contained in the slurry. The specific surface area was measured using a fully automatic specific surface area measuring machine (Macsorb HM model-1201) manufactured by MOUNTECH, and the total surface area was obtained from the measured values.

  A soda glass substrate was polished and the polishing rate and surface roughness were determined in the same manner as in Example 1 except that the above slurry was used instead of the magnetic slurry and no magnetic field was applied during polishing. The results are shown in Table 2. When colloidal silica is used, it has been confirmed in preliminary experiments that the presence or absence of magnetic field application does not affect the polishing rate and the surface roughness.

  From the results shown in Table 1, the silica-coated magnetic particles contained in the magnetic slurry of Example 1 and the colloidal silica contained in the slurry of Comparative Example 1 have the same total surface area, and the slurry of Comparative Example 2 The colloidal silica contained in has a total surface area 8 times that of the silica-coated magnetic particles contained in the magnetic slurry of Example 1.

  From the results shown in Table 2, it can be seen that according to the polishing method of the present invention (Example 1), a polishing rate superior to that obtained when colloidal silica is used (Comparative Example 1 and Comparative Example 2) can be obtained. The polishing rate in Example 1 shows a larger value than that in Comparative Example 2 using a slurry having an abrasive grain total surface area of 8 times.

Claims (2)

A polishing material comprising abrasive grains in which magnetic particles are coated with a continuous polishing layer between the first surface of the workpiece having the first surface and the second surface and the polishing pad. Supply
Applying a magnetic field from the second surface side to the object to be polished, the magnetic flux density on the first surface is 40 mT or more and less than 200 mT,
Polishing the first surface with the polishing pad;
A polishing method characterized by the above.   The polishing method according to claim 1, wherein the polishing layer is made of silica.