WO2007037579A1 - Surface polishing agent comprising nano sized tungsten carbide powders and polishing methods using the same - Google Patents

Surface polishing agent comprising nano sized tungsten carbide powders and polishing methods using the same Download PDF

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Publication number
WO2007037579A1
WO2007037579A1 PCT/KR2006/000270 KR2006000270W WO2007037579A1 WO 2007037579 A1 WO2007037579 A1 WO 2007037579A1 KR 2006000270 W KR2006000270 W KR 2006000270W WO 2007037579 A1 WO2007037579 A1 WO 2007037579A1
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WO
WIPO (PCT)
Prior art keywords
polishing
polishing agent
tungsten carbide
subject
carbide powder
Prior art date
Application number
PCT/KR2006/000270
Other languages
French (fr)
Inventor
Won Gun Lee
Young Je Bae
Yong Hwa Jung
Bum Rae Cho
Original Assignee
Tps Inc.
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Publication date
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Publication of WO2007037579A1 publication Critical patent/WO2007037579A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82B—NANOSTRUCTURES FORMED BY MANIPULATION OF INDIVIDUAL ATOMS, MOLECULES, OR LIMITED COLLECTIONS OF ATOMS OR MOLECULES AS DISCRETE UNITS; MANUFACTURE OR TREATMENT THEREOF
    • B82B3/00—Manufacture or treatment of nanostructures by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/02—Silicon
    • C01B33/021—Preparation
    • C01B33/023—Preparation by reduction of silica or free silica-containing material
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G41/00—Compounds of tungsten
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C19/00—Surface treatment of glass, not in the form of fibres or filaments, by mechanical means
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09G—POLISHING COMPOSITIONS; SKI WAXES
    • C09G1/00—Polishing compositions
    • C09G1/02—Polishing compositions containing abrasives or grinding agents
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K3/00—Materials not provided for elsewhere
    • C09K3/14—Anti-slip materials; Abrasives
    • C09K3/1454—Abrasive powders, suspensions and pastes for polishing
    • C09K3/1463—Aqueous liquid suspensions
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/302—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
    • H01L21/304—Mechanical treatment, e.g. grinding, polishing, cutting
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/302—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
    • H01L21/306—Chemical or electrical treatment, e.g. electrolytic etching
    • H01L21/30625—With simultaneous mechanical treatment, e.g. mechanico-chemical polishing
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
    • H01L21/3205—Deposition of non-insulating-, e.g. conductive- or resistive-, layers on insulating layers; After-treatment of these layers
    • H01L21/321—After treatment
    • H01L21/32115—Planarisation
    • H01L21/3212—Planarisation by chemical mechanical polishing [CMP]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures

Definitions

  • the present invention relates to a method of polishing the surface of a substrate, such as a single- crystal wafer or a glass plate, and a polishing agent used therefor, and more particularly, to a method of polishing a substrate, such as a wafer or plate, to thus assure a high polishing rate, high flatness, and good surface roughness, and to a polishing agent used therefor.
  • LEDs using gallium nitride have been applied to high-luminance white LEDs, LCD backlights, and signal lamps, and also to backlight sources of TFT-LCDs, backlight sources for mobile phones, and key pads.
  • illuminating LEDs have power consumption decreased by about 10-15% and a semi-permanent lifetime of 100,000 hours or longer, and are environmentally friendly, therefore energy consumption efficiency thereof is greatly improved. Accordingly, such LEDs are receiving attention as a next- generation technology capable of substituting for general illumination fixtures.
  • an essential material is a sapphire wafer having a semiconductor epitaxial layer formed of a gallium nitride- based compound, such as GaN or GaAlN.
  • the polished sapphire wafer has residual stress thereon, undesirably causing surface faults thereof.
  • lapping scratches, or microcracks, and dislocations may be distributed on the surface of the polished wafer to thus adversely affect the growth of a thin film.
  • a sapphire wafer having high hardness is subjected to polishing using diamond slurry, plate, or paste. That is, a conventional sapphire wafer is manufactured through first polishing using diamond slurry and second polishing using colloidal silica.
  • the surface roughness of the sapphire wafer thus polished is not sufficiently decreased. This is known to be because diamond, used for polishing, is harder than the sapphire wafer, and due to a problem with the shape of the diamond particles.
  • small diamonds should be used, however, it is difficult to process diamond at the nanoparticle level.
  • limitations are imposed on the ability to decrease the surface roughness.
  • a glass wafer and a synthetic quartz wafer are employed these days as a primary material for a microdisplay of a projection television set.
  • the level of quality required for the glass and synthetic quartz wafers is so high that a 0.25-0.35 ⁇ m process is mainly used.
  • the glass wafer and synthetic quartz wafer are in close contact with a lower silicon wafer with a predetermined space therebetween. As such, the space amounts to about 1 ⁇ m as the number of pixels is increased.
  • the glass wafer and synthetic quartz wafer should be very flat, and furthermore, the insertion of impurities smaller than the spaces between the pixels should be prevented.
  • the wafer For application to a large area of 50 inches or more, the wafer must have a flat smooth surface having minimum roughness because each pixel is magnified hundreds of times.
  • Conventional glass and synthetic quartz wafers have been manufactured through first polishing using cerium oxide material and then final polishing using colloidal silica or sub-micro cerium oxide particle slurry.
  • Such conventional polishing methods suffer because the period of time required for performing a final polishing process is increased in order to improve surface roughness, undesirably deteriorating flatness. Thereby, it is impossible to obtain a polished wafer having high flatness and good roughness.
  • an object of the present invention is to provide a method of polishing a substrate, such as a wafer or plate, comprising sapphire, silicon carbide, glass, synthetic quartz, silicon, or lithium tantalate, to thus exhibit minimum surface roughness, high flatness, and a high polishing rate upon polishing, and also a polishing agent used therefor.
  • Another object of the present invention is to provide a method of polishing a wafer formed of sapphire, glass and synthetic quartz, silicon carbide, single silicon crystals, or single lithium tantalate crystals using a dispersion or a mixture of spherical tungsten carbide particles having a size of tens to hundreds of run and hardness of 9.5 or more in an appropriate solution, to thus exhibit a high polishing rate, good surface roughness, and high flatness.
  • the present invention provides a method of polishing a subject, comprising providing a polishing agent including tungsten carbide powder and a lubricant onto a metal platen and polishing the subject with the polishing agent including tungsten carbide powder while rotating the metal platen.
  • the subject may comprise any one material selected from the group consisting of silicon carbide, silicon nitride, gallium nitride, indium gallium nitride, sapphire, silicon carbide, quartz, lithium tantalate, lithium borate, and silicon.
  • the tungsten carbide powder preferably has an average particle size of 3 ⁇ m or less.
  • the tungsten carbide powder has an average particle size of 10-300 nm.
  • the polishing agent may further comprise either colloidal silica or ceria.
  • the present invention provides a method of polishing a subject, comprising providing a first polishing agent, including nano sized tungsten carbide powder having an average particle size of 50 nm or more, on a first metal platen, rotating the first metal platen to thus polish the subject with the second polishing agent, providing a second polishing agent, including nano sized tungsten powder having an average particle size of 50 nm or less, on a second metal platen, and rotating the second metal platen to thus polish the subject with the second polishing agent.
  • this method may further comprise polishing the subject using a third polishing agent including an aqueous solution of tungsten carbide powder having an average particle size of 50 nm or less and either colloidal silica or ceria.
  • the present invention provides a method of manufacturing a subject having surface roughness of 5 ⁇ m or less and flatness of 3 ⁇ m or less, comprising polishing the subject with a polishing agent including spherical tungsten particles having an average particle size of 3 ⁇ m or less.
  • a polishing agent including spherical tungsten particles having an average particle size of 3 ⁇ m or less.
  • the present invention provides a polishing agent for polishing a subject, comprising an aqueous solution including spherical tungsten carbide powder having an average particle size of 3 ⁇ m or less dispersed therein.
  • the tungsten carbide powder preferably has an average particle size of 10 to 300 nm.
  • the aqueous solution may further comprise a lubricant, and, as well, may further comprise at least one of colloidal silica and ceria.
  • the tungsten carbide may be prepared by reducing and carbonizing tungsten oxide using carbon monoxide (CO) at 600 ⁇ 700°C. In this case, the reducing and carbonizing may be performed in the presence of a zeolite catalyst or a silica catalyst.
  • FIG. 1 is a photograph showing nano sized tungsten carbide powder having an average particle size of 20 run, observed using a transmission electron microscope (TEM) ;
  • FIG. 2 is a photograph showing the surface of a sapphire wafer polished using a polishing agent comprising colloidal silica, observed using an atomic force microscope (AFM) ;
  • AFM atomic force microscope
  • FIG. 3 is a photograph showing the surface of a sapphire wafer polished using a polishing agent comprising a mixture of nano sized tungsten carbide powder and colloidal silica, observed using an AFM;
  • FIG. 6 is a photograph showing the surface of a synthetic quartz wafer polished using a polishing agent comprising colloidal silica, observed using an AFM
  • FIG. 7 is a photograph showing the surface of a synthetic quartz wafer polished using a polishing agent comprising a mixture of nano sized tungsten carbide powder and colloidal silica, observed using an AFM;
  • FIG. 8 is a photograph showing the surface of a D263 optical glass substrate polished using a polishing agent comprising cerium oxide, observed using an AFM;
  • FIG. 9 is a photograph showing the surface of a D263 optical glass substrate polished using a polishing agent comprising nano sized tungsten carbide powder, observed using an AFM;
  • FIG. 10 is an interference pattern photograph showing the flatness of the surface of a D263 optical glass substrate polished using a polishing agent comprising cerium oxide, observed using a laser interferometer (F-60 Interferometer, available from Fujinon) ; and
  • FIG. 11 is an interference pattern photograph showing the flatness of the surface of a D263 optical glass substrate polished using a polishing agent comprising nano sized tungsten carbide powder, observed using a laser interferometer (F-60 Interferometer, available from Fujinon) .
  • F-60 Interferometer available from Fujinon
  • the polishing method of the present invention is applied when polishing a very solid material having the same polishing properties as diamond particles, for example, a sapphire wafer having high hardness (mohs hardness of 9.0 or more), using nano sized tungsten carbide powder, and also when polishing a material having relatively low hardness of about 5, such as glass or synthetic quartz.
  • nano sized tungsten carbide powder having an average particle size of 3 ⁇ m or less. Since the goal of the present invention is not to provide a method of preparing nano sized tungsten carbide powder, a particular description thereof is omitted. In place thereof, techniques for fining tungsten carbide powder are briefly introduced, including methods of preparing ultrafine tungsten carbide particles using a particle growth retardation agent and of conducting a chemical vapor reaction for preparing tungsten carbide by vaporizing WCl ⁇ or W(CO) 6 precursor to thus carbonize it at a high temperature in a non-acidification atmosphere. However, such methods are disadvantageous in that the particle size of tungsten carbide is not sufficiently controlled.
  • a reduction and carbonization process may be applied.
  • tungsten carbide is prepared by subjecting tungsten oxide to reduction and carbonization using carbon monoxide (CO) at 600 ⁇ 700°C.
  • a catalyst such as zeolite (Nax) or silica (WHITE) , is supplied in order to improve preparation efficiency.
  • nano sized tungsten carbide powder having various particle sizes of 20 run, 50 ran, or 100 run may be prepared.
  • FIG. 1 is a photograph illustrating the shape of the nano sized tungsten carbide powder having an average particle size of 20 nm prepared through the above-mentioned reduction and carbonization process, observed with a TEM (H-7600, available from Hitachi) .
  • the shape of the nano sized tungsten carbide powder can be seen to be spherical.
  • spherical particles are advantageous in that the formation of hidden scratches is prevented upon a polishing process. Therefore, in the case of using nano sized tungsten carbide powder as a polishing agent, scratches, which have frequently occurred in the polishing of sapphire, may be prevented.
  • the polishing agent and the polishing method using the same are characterized in that glass and synthetic quartz wafers or plates are polished using a tungsten carbide solution alone, or a mixture of tungsten carbide and cerium oxide or colloidal silica solution, instead of conventionally using only cerium oxide (ceria) , so that the mechanical polishing function of tungsten carbide is added to the chemical polishing function of cerium oxide, resulting in very fast and superfine polishing.
  • the polishing agent and the polishing method of the present invention may be applied to a final polishing process after a silicon single-crystal wafer, lithium tantalate (LiTaO 3 ) , lithium niobate (LiMbO 3 ) , or lithium borate (Li 2 B 4 O 7 ) is subjected to lapping with silicon carbide (GC type) or alumina (FO type) , or may be applied to a first polishing process using tungsten carbide alone or a mixture of tungsten carbide and another polishing slurry, that is, either colloidal silica or cerium oxide, at an appropriate mixing ratio, after a lapping process.
  • GC type silicon carbide
  • FO type alumina
  • Example 1 Both surfaces of a 2-inch sapphire wafer were lapped with silicon carbide (SiC, GC#320) under suitable pressure (0.85-2.89 g/cm 2 ) to thus manufacture a wafer 480 ⁇ m thick.
  • the wafer thus manufactured was attached to a ceramic block using wax, to thus first polish it by about 30 ⁇ m on a copper platen using nano sized tungsten carbide powder having a size of 50-300 run.
  • the first polished sapphire wafer was second polished by about 10 ⁇ m on a tin platen using tungsten carbide powder having a size of 20-50 nm. Thereafter, the second polished sapphire wafer was finally polished using a polishing agent comprising colloidal silica (Compol-80, available from Fujimi) and lubricant
  • the roughness of the sapphire wafer that is, the surface roughness thereof, was measured via atomic force microscopy. The results are shown in FIGS. 2 and 3.
  • Both surfaces of a 8-inch synthetic quartz wafer 1,000 ⁇ m thick were lapped with alumina material FO#1200 (Al 2 O 3 , available from Fujimi) , to thus manufacture a wafer
  • the wafer thus manufactured was first polished using nano sized tungsten carbide powder having a size of 50 nm with the use of a steel/epoxy carrier and a cerium pad.
  • the first polished 8-inch synthetic quartz wafer was subjected to final polishing using a polishing agent comprising colloidal silica (Compol-80, available from Fujimi) and lubricant (available from Engis) containing 1% tungsten carbide powder having an average particle size of 20 run, mixed at 1:1.
  • a polishing agent comprising colloidal silica (Compol-80, available from Fujimi) and lubricant (available from Engis) containing 1% tungsten carbide powder having an average particle size of 20 run, mixed at 1:1.
  • Table 2 The results are shown in Table 2 below, compared to those of conventional polishing using cerium oxide (E-10, available from Mitsui Mining & Smelting) as a first polishing agent and only colloidal silica as a final polishing agent.
  • Example 3 A 5-inch x 5-inch D263 optical glass substrate, available from Schott, Germany, was polished using nano sized tungsten carbide powder having a size of 20 ⁇ m with the use of a steel/epoxy carrier and a cerium pad. The results are shown in Table 3 below, compared to when using cerium oxide (E-10, available from Mitsui Mining & Smelting) .
  • FIG. 8 shows the surface roughness resulting from the conventional process using cerium oxide
  • FIG. 9 shows the surface roughness resulting from the process using nano sized tungsten carbide powder.
  • a formed bulk silicon carbide (SiC) sample having a size of 40 x 40 was attached to a ceramic block using wax, first polished using diamond particles having a size of 5 ⁇ m on a copper platen, and then finally polished using nano sized tungsten carbide powder having a size of 50 nm on a tin platen (Example A) .
  • the sample was first polished using nano sized tungsten carbide powder having a size of 300 nm on a copper platen and then finally polished using a polytex pad or a Suba pad (Example B) .
  • the polishing results are shown in Table 4 below.
  • a 4-inch lithium tantalate (LT) wafer was lapped with F0#l, 200 (available from Fujimi) , etched using ultrasonic waves and a mixture of fluoric acid and nitric acid, and washed.
  • the washed LT was attached to a ceramic block and then polished using nano sized tungsten carbide powder having a size of 50 nm.
  • the lapped LT wafer was finally polished using a polishing agent comprising colloidal silica (Compol-80, available from Fujimi) and lubricant (available from Engis) containing 1% nano sized tungsten carbide powder having a size of 50 nm, mixed at 1:1.
  • the results are shown in Table 5 below, compared to when using only colloidal silica.
  • a 6-inch silicon wafer was lapped with FO#1, 200 (available from Fujimi) , and was then polished in the same manner as in Example 5. The results are given in Table 6 below.
  • the present invention provides a surface polishing agent comprising nano sized tungsten carbide powder and a polishing method using the same.
  • a sapphire wafer having good surface roughness and high flatness may be manufactured. Further, microscratches, resulting from conventional polishing using diamond slurry, may be decreased.
  • problems that have not been overcome using colloidal silica and diamond can be solved.
  • the surface faults of a sapphire wafer are minimized and the flatness thereof is increased, therefore a sapphire wafer having high quality is fabricated.
  • Either or both surfaces of a wafer or plate formed of glass and synthetic quartz are polished to thus exhibit high flatness and good roughness, consequently resulting in superior effects on the fabrication of MEMS, BIO chips, or display devices.
  • the polishing agent including nano sized tungsten carbide powder of the present invention has technical properties, such as the shape of the particles and polishing rates, and price properties, including polishing costs, superior to those of conventional diamond, leading to decreased prices of products .

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Abstract

Disclosed are a method of polishing a body or a substrate such as a wafer for use in optical and electrical parts, and a polishing agent used therefor. This invention provides a method of polishing a subject, including providing a polishing agent containing tungsten carbide powder and a lubricant onto a metal platen and polishing the subject with the polishing agent containing tungsten carbide powder while rotating the metal platen. According to this invention, a subject that is good with respect to both flatness and roughness can be provided while assuring a fast polishing time period. Particularly, a sapphire wafer having minimum faults and glass and synthetic quartz plates having high flatness can be provided. Further, the method of this invention can be applied to polishing s ingle- crystal wafers such as silicon wafers or lithium tantalate wafers.

Description

[DESCRIPTION]
[invention Title]
SURFACE POLISHING AGENT COMPRISING NANO SIZED TUNGSTEN CARBIDE POWDERS AND POLISHING METHODS USING THE SAME
[Technical Field]
The present invention relates to a method of polishing the surface of a substrate, such as a single- crystal wafer or a glass plate, and a polishing agent used therefor, and more particularly, to a method of polishing a substrate, such as a wafer or plate, to thus assure a high polishing rate, high flatness, and good surface roughness, and to a polishing agent used therefor.
[Background Art] Recently, LEDs using gallium nitride have been applied to high-luminance white LEDs, LCD backlights, and signal lamps, and also to backlight sources of TFT-LCDs, backlight sources for mobile phones, and key pads. In addition, compared to conventional illumination fixtures represented by fluorescent lamps and incandescent lamps, illuminating LEDs have power consumption decreased by about 10-15% and a semi-permanent lifetime of 100,000 hours or longer, and are environmentally friendly, therefore energy consumption efficiency thereof is greatly improved. Accordingly, such LEDs are receiving attention as a next- generation technology capable of substituting for general illumination fixtures. In the fabrication of such LEDs, an essential material is a sapphire wafer having a semiconductor epitaxial layer formed of a gallium nitride- based compound, such as GaN or GaAlN. When the sapphire wafer is subjected to a general mechanical polishing process, the polished sapphire wafer has residual stress thereon, undesirably causing surface faults thereof. Hence, lapping scratches, or microcracks, and dislocations may be distributed on the surface of the polished wafer to thus adversely affect the growth of a thin film.
In this way, in the case where a lot of residual stress is present on the surface of the wafer in the mechanical polishing process, surface faults occur and lapping scratches, or microcracks, and dislocation are distributed. Therefore, when growing a nitride semiconductor thin film on the wafer, a distorted crystal structure and a high dislocation density are caused by such mechanical stress, resulting in negative effects on luminance, luminous efficiency, and the lifetime of the LED to be fabricated.
Typically, a sapphire wafer having high hardness is subjected to polishing using diamond slurry, plate, or paste. That is, a conventional sapphire wafer is manufactured through first polishing using diamond slurry and second polishing using colloidal silica. However, the surface roughness of the sapphire wafer thus polished is not sufficiently decreased. This is known to be because diamond, used for polishing, is harder than the sapphire wafer, and due to a problem with the shape of the diamond particles. In order to solve these problems, small diamonds should be used, however, it is difficult to process diamond at the nanoparticle level. Ultimately, limitations are imposed on the ability to decrease the surface roughness.
In addition, as a primary material for a microdisplay of a projection television set, a glass wafer and a synthetic quartz wafer are employed these days . In the microdisplay for a projection television set, the level of quality required for the glass and synthetic quartz wafers is so high that a 0.25-0.35 μm process is mainly used. The glass wafer and synthetic quartz wafer are in close contact with a lower silicon wafer with a predetermined space therebetween. As such, the space amounts to about 1 μm as the number of pixels is increased. Thus, the glass wafer and synthetic quartz wafer should be very flat, and furthermore, the insertion of impurities smaller than the spaces between the pixels should be prevented. Further, for application to a large area of 50 inches or more, the wafer must have a flat smooth surface having minimum roughness because each pixel is magnified hundreds of times. Conventional glass and synthetic quartz wafers have been manufactured through first polishing using cerium oxide material and then final polishing using colloidal silica or sub-micro cerium oxide particle slurry. However, such conventional polishing methods suffer because the period of time required for performing a final polishing process is increased in order to improve surface roughness, undesirably deteriorating flatness. Thereby, it is impossible to obtain a polished wafer having high flatness and good roughness.
[Disclosure]
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a method of polishing a substrate, such as a wafer or plate, comprising sapphire, silicon carbide, glass, synthetic quartz, silicon, or lithium tantalate, to thus exhibit minimum surface roughness, high flatness, and a high polishing rate upon polishing, and also a polishing agent used therefor.
Another object of the present invention is to provide a method of polishing a wafer formed of sapphire, glass and synthetic quartz, silicon carbide, single silicon crystals, or single lithium tantalate crystals using a dispersion or a mixture of spherical tungsten carbide particles having a size of tens to hundreds of run and hardness of 9.5 or more in an appropriate solution, to thus exhibit a high polishing rate, good surface roughness, and high flatness.
In order to accomplish the above objects, the present invention provides a method of polishing a subject, comprising providing a polishing agent including tungsten carbide powder and a lubricant onto a metal platen and polishing the subject with the polishing agent including tungsten carbide powder while rotating the metal platen. As such, the subject may comprise any one material selected from the group consisting of silicon carbide, silicon nitride, gallium nitride, indium gallium nitride, sapphire, silicon carbide, quartz, lithium tantalate, lithium borate, and silicon. Further, in the method of the present invention, the tungsten carbide powder preferably has an average particle size of 3 μm or less. More preferably, the tungsten carbide powder has an average particle size of 10-300 nm. Also, the polishing agent may further comprise either colloidal silica or ceria. In addition, the present invention provides a method of polishing a subject, comprising providing a first polishing agent, including nano sized tungsten carbide powder having an average particle size of 50 nm or more, on a first metal platen, rotating the first metal platen to thus polish the subject with the second polishing agent, providing a second polishing agent, including nano sized tungsten powder having an average particle size of 50 nm or less, on a second metal platen, and rotating the second metal platen to thus polish the subject with the second polishing agent. As such, this method may further comprise polishing the subject using a third polishing agent including an aqueous solution of tungsten carbide powder having an average particle size of 50 nm or less and either colloidal silica or ceria.
In addition, the present invention provides a method of manufacturing a subject having surface roughness of 5 μm or less and flatness of 3 μm or less, comprising polishing the subject with a polishing agent including spherical tungsten particles having an average particle size of 3 μm or less. In this way, in the method of the present invention, a subject that is good with respect to both roughness and flatness can be manufactured.
In addition, the present invention provides a polishing agent for polishing a subject, comprising an aqueous solution including spherical tungsten carbide powder having an average particle size of 3 μm or less dispersed therein. As such, the tungsten carbide powder preferably has an average particle size of 10 to 300 nm. Also, in the polishing agent of the present invention, the aqueous solution may further comprise a lubricant, and, as well, may further comprise at least one of colloidal silica and ceria. In the present invention, the tungsten carbide may be prepared by reducing and carbonizing tungsten oxide using carbon monoxide (CO) at 600~700°C. In this case, the reducing and carbonizing may be performed in the presence of a zeolite catalyst or a silica catalyst.
[Description of Drawings]
FIG. 1 is a photograph showing nano sized tungsten carbide powder having an average particle size of 20 run, observed using a transmission electron microscope (TEM) ; FIG. 2 is a photograph showing the surface of a sapphire wafer polished using a polishing agent comprising colloidal silica, observed using an atomic force microscope (AFM) ;
FIG. 3 is a photograph showing the surface of a sapphire wafer polished using a polishing agent comprising a mixture of nano sized tungsten carbide powder and colloidal silica, observed using an AFM;
FIG. 4 is a photograph showing the flatness of the surface of a synthetic quartz wafer polished using a polishing agent comprising colloidal silica, measured using an interferometer (Zygo PMR, S/N: 00-29-140, λ=0.6328 μm) ;
FIG. 5 is a photograph showing the flatness of the surface of a synthetic quartz wafer polished using a polishing agent comprising a mixture of nano sized tungsten carbide powder and colloidal silica, measured using an interferometer (Zygo PMR, S/N: 00-29-140, λ=0.6328 μm) ;
FIG. 6 is a photograph showing the surface of a synthetic quartz wafer polished using a polishing agent comprising colloidal silica, observed using an AFM; FIG. 7 is a photograph showing the surface of a synthetic quartz wafer polished using a polishing agent comprising a mixture of nano sized tungsten carbide powder and colloidal silica, observed using an AFM;
FIG. 8 is a photograph showing the surface of a D263 optical glass substrate polished using a polishing agent comprising cerium oxide, observed using an AFM;
FIG. 9 is a photograph showing the surface of a D263 optical glass substrate polished using a polishing agent comprising nano sized tungsten carbide powder, observed using an AFM;
FIG. 10 is an interference pattern photograph showing the flatness of the surface of a D263 optical glass substrate polished using a polishing agent comprising cerium oxide, observed using a laser interferometer (F-60 Interferometer, available from Fujinon) ; and
FIG. 11 is an interference pattern photograph showing the flatness of the surface of a D263 optical glass substrate polished using a polishing agent comprising nano sized tungsten carbide powder, observed using a laser interferometer (F-60 Interferometer, available from Fujinon) . [Mode for Invention]
Hereinafter, a detailed description will be given of the preferred embodiment of the present invention with reference to the appended drawings. The polishing method of the present invention is applied when polishing a very solid material having the same polishing properties as diamond particles, for example, a sapphire wafer having high hardness (mohs hardness of 9.0 or more), using nano sized tungsten carbide powder, and also when polishing a material having relatively low hardness of about 5, such as glass or synthetic quartz.
In the present invention, as a polishing agent, useful is nano sized tungsten carbide powder having an average particle size of 3 μm or less. Since the goal of the present invention is not to provide a method of preparing nano sized tungsten carbide powder, a particular description thereof is omitted. In place thereof, techniques for fining tungsten carbide powder are briefly introduced, including methods of preparing ultrafine tungsten carbide particles using a particle growth retardation agent and of conducting a chemical vapor reaction for preparing tungsten carbide by vaporizing WClβ or W(CO)6 precursor to thus carbonize it at a high temperature in a non-acidification atmosphere. However, such methods are disadvantageous in that the particle size of tungsten carbide is not sufficiently controlled. As a substitute, a reduction and carbonization process may be applied. According to this process, tungsten carbide is prepared by subjecting tungsten oxide to reduction and carbonization using carbon monoxide (CO) at 600~700°C. In the reduction and carbonization process, a catalyst, such as zeolite (Nax) or silica (WHITE) , is supplied in order to improve preparation efficiency. Further, depending on the reaction temperatures, nano sized tungsten carbide powder having various particle sizes of 20 run, 50 ran, or 100 run may be prepared.
FIG. 1 is a photograph illustrating the shape of the nano sized tungsten carbide powder having an average particle size of 20 nm prepared through the above-mentioned reduction and carbonization process, observed with a TEM (H-7600, available from Hitachi) . From FIG. 1, the shape of the nano sized tungsten carbide powder can be seen to be spherical. Compared to conventional angular diamond particles, spherical particles are advantageous in that the formation of hidden scratches is prevented upon a polishing process. Therefore, in the case of using nano sized tungsten carbide powder as a polishing agent, scratches, which have frequently occurred in the polishing of sapphire, may be prevented.
According to the present invention, the polishing agent and the polishing method using the same are characterized in that glass and synthetic quartz wafers or plates are polished using a tungsten carbide solution alone, or a mixture of tungsten carbide and cerium oxide or colloidal silica solution, instead of conventionally using only cerium oxide (ceria) , so that the mechanical polishing function of tungsten carbide is added to the chemical polishing function of cerium oxide, resulting in very fast and superfine polishing. Further, the polishing agent and the polishing method of the present invention may be applied to a final polishing process after a silicon single-crystal wafer, lithium tantalate (LiTaO3) , lithium niobate (LiMbO3) , or lithium borate (Li2B4O7) is subjected to lapping with silicon carbide (GC type) or alumina (FO type) , or may be applied to a first polishing process using tungsten carbide alone or a mixture of tungsten carbide and another polishing slurry, that is, either colloidal silica or cerium oxide, at an appropriate mixing ratio, after a lapping process.
A better understanding of the present invention may be obtained through the following examples which are set forth to illustrate, but are not to be construed as the limit of the present invention.
Example 1 Both surfaces of a 2-inch sapphire wafer were lapped with silicon carbide (SiC, GC#320) under suitable pressure (0.85-2.89 g/cm2) to thus manufacture a wafer 480 μm thick. The wafer thus manufactured was attached to a ceramic block using wax, to thus first polish it by about 30 μm on a copper platen using nano sized tungsten carbide powder having a size of 50-300 run. The first polished sapphire wafer was second polished by about 10 μm on a tin platen using tungsten carbide powder having a size of 20-50 nm. Thereafter, the second polished sapphire wafer was finally polished using a polishing agent comprising colloidal silica (Compol-80, available from Fujimi) and lubricant
(available from Engis) containing 1% tungsten carbide, mixed at 1:1. The results are shown in Table 1 below, compared to those of conventional polishing using diamond particles (2-3 μm) and using only colloidal silica as a final polishing agent.
The roughness of the sapphire wafer, that is, the surface roughness thereof, was measured via atomic force microscopy. The results are shown in FIGS. 2 and 3.
As is apparent from Table 1, although the use of nano-sized tungsten carbide powder led to slower first and second polishing rates than when using diamond, the period of time required for the final polishing process was considerably shortened, consequently generating greater economic benefits than when using diamond. In the quality of the wafer, the flatness and bow (P-I, available from Tencor) of the wafer were improved more than when using the diamond slurry. In addition, as in FIG. 2, surface roughness was determined to be 3.1 A in a conventional polishing process, however it was determined to be 0.9 A in the process using nano-sized tungsten carbide powder as in FIG. 3.
TABLE 1
Figure imgf000014_0001
Example 2
Both surfaces of a 8-inch synthetic quartz wafer 1,000 μm thick were lapped with alumina material FO#1200 (Al2O3, available from Fujimi) , to thus manufacture a wafer
880 μm thick. Subsequently, the wafer thus manufactured was first polished using nano sized tungsten carbide powder having a size of 50 nm with the use of a steel/epoxy carrier and a cerium pad. The first polished 8-inch synthetic quartz wafer was subjected to final polishing using a polishing agent comprising colloidal silica (Compol-80, available from Fujimi) and lubricant (available from Engis) containing 1% tungsten carbide powder having an average particle size of 20 run, mixed at 1:1. The results are shown in Table 2 below, compared to those of conventional polishing using cerium oxide (E-10, available from Mitsui Mining & Smelting) as a first polishing agent and only colloidal silica as a final polishing agent.
As is apparent from Table 2, the process using nano sized tungsten carbide powder could be seen to improve the polishing rate, flatness, and surface roughness more than a conventional colloidal silica process . The flatness of the wafer thus polished was measured using an interferometer (Zygo PMR, S/N: 00-29-140, λ=0.6328 μm) . The results are shown in FIGS. 4 and 5. Although the flatness was measured to be 5.8 μm in FIG. 4, it was confirmed to be improved by 3.2 μm in FIG. 5. In addition, the surface roughness was measured through atomic force microscopy. The surface roughness, which was determined to be 4.5 A in a conventional polishing process, is shown in FIG. 6, whereas the surface roughness, which was determined to be 1.7 A in the process using nano-sized tungsten carbide powder, is shown in FIG. 7.
The problems of micropits frequently occurring upon polishing were alleviated through the process of the present invention. The results are also shown in Table 2 below. TABLE 2
Figure imgf000016_0001
Example 3 A 5-inch x 5-inch D263 optical glass substrate, available from Schott, Germany, was polished using nano sized tungsten carbide powder having a size of 20 πm with the use of a steel/epoxy carrier and a cerium pad. The results are shown in Table 3 below, compared to when using cerium oxide (E-10, available from Mitsui Mining & Smelting) .
As is apparent from Table 3, the polishing time period was shortened by 1/2, and the surface roughness was decreased from 5.4 A to 2.2 A. After final washing, fewer cerium oxide particles remained. FIG. 8 shows the surface roughness resulting from the conventional process using cerium oxide, and FIG. 9 shows the surface roughness resulting from the process using nano sized tungsten carbide powder. As the results of measurement of the flatness of the polished wafer using a laser interferometer (F-60 Interferometer, available from Fujinon) , the flatness was observed to have improved from 5 μm to 3 μm. Further, the results of measurement of surface roughness are shown in FIGS. 10 and 11.
TABLE 3
Figure imgf000017_0001
Example 4
A formed bulk silicon carbide (SiC) sample having a size of 40 x 40 was attached to a ceramic block using wax, first polished using diamond particles having a size of 5 μm on a copper platen, and then finally polished using nano sized tungsten carbide powder having a size of 50 nm on a tin platen (Example A) . Separately, the sample was first polished using nano sized tungsten carbide powder having a size of 300 nm on a copper platen and then finally polished using a polytex pad or a Suba pad (Example B) . The polishing results are shown in Table 4 below.
As is apparent from Table 3, the polishing time and the surface roughness of Examples A and B were the same as in the polishing process using diamond. Moreover, the material having high hardness could be confirmed to be polished using nano sized tungsten carbide powder, although it was difficult to polish using the pad through the conventional process.
TABLE 4
Figure imgf000018_0001
Example 5
A 4-inch lithium tantalate (LT) wafer was lapped with F0#l, 200 (available from Fujimi) , etched using ultrasonic waves and a mixture of fluoric acid and nitric acid, and washed. The washed LT was attached to a ceramic block and then polished using nano sized tungsten carbide powder having a size of 50 nm. The lapped LT wafer was finally polished using a polishing agent comprising colloidal silica (Compol-80, available from Fujimi) and lubricant (available from Engis) containing 1% nano sized tungsten carbide powder having a size of 50 nm, mixed at 1:1. The results are shown in Table 5 below, compared to when using only colloidal silica.
As is apparent from Table 5, flatness and PLTV (Partial Local Thickness Variation) were measured using a wafer flatness instrument (FT-17, available from Nidek) , and were thus confirmed to be improved from 5 μm to 2 μm and from 80% to 100%, respectively. Further, as the result of measurement of the surface roughness using AFM (available from PSIA) , the surface roughness was determined to be 3.0 A through the above-mentioned process, and also to be 2.0 A and 1.3 A, respectively, in the process using nano sized tungsten carbide powder and in the process using the mixture of nano sized tungsten carbide powder and colloidal silica.
TABLE 5
Figure imgf000019_0001
Example 6
A 6-inch silicon wafer was lapped with FO#1, 200 (available from Fujimi) , and was then polished in the same manner as in Example 5. The results are given in Table 6 below.
TABLE 6
Figure imgf000019_0002
[industrial Applicability]
As described above, the present invention provides a surface polishing agent comprising nano sized tungsten carbide powder and a polishing method using the same. According to the present invention, in the case where the surface of a sapphire wafer is polished through the process of the present invention, a sapphire wafer having good surface roughness and high flatness may be manufactured. Further, microscratches, resulting from conventional polishing using diamond slurry, may be decreased. Furthermore, when polishing the very hard surface of a substrate comprising silicon carbide (SiC) or aluminum nitride (AlN) , problems that have not been overcome using colloidal silica and diamond can be solved.
In the case where the surface of the sapphire wafer is polished using the process of the present invention, a very flat surface may result and the number of polishing steps may be decreased compared to when using diamond, thus good price competitiveness may be obtained. Upon the growth of a thin film, since it is possible to manufacture a thin film having high quality, a blue light-emitting device having excellent properties can be fabricated.
Further, through the polishing process of the present invention, the surface faults of a sapphire wafer are minimized and the flatness thereof is increased, therefore a sapphire wafer having high quality is fabricated. Either or both surfaces of a wafer or plate formed of glass and synthetic quartz are polished to thus exhibit high flatness and good roughness, consequently resulting in superior effects on the fabrication of MEMS, BIO chips, or display devices. In addition, for polishing silicon carbide (SiC), aluminum nitride (AlN) or a sapphire wafer' having a high hardness of 9 or more, the polishing agent including nano sized tungsten carbide powder of the present invention has technical properties, such as the shape of the particles and polishing rates, and price properties, including polishing costs, superior to those of conventional diamond, leading to decreased prices of products .
Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims .

Claims

[CLAIMS]
[Claim l]
A method of polishing a subject, comprising: providing a polishing agent including tungsten carbide powder and a lubricant onto a metal platen; and polishing the subject with the polishing agent including tungsten carbide powder while rotating the metal platen.
[Claim 2]
The method according to claim 1, wherein the subject comprises any one material selected from the group consisting of silicon carbide, silicon nitride, gallium nitride, indium gallium nitride, sapphire, silicon carbide, quartz, lithium tantalate, lithium borate, and silicon.
[Claim 3]
The method according to claim 1, wherein the tungsten carbide powder has an average particle size of 3 μm or less.
[Claim 4]
The method according to claim 3, wherein the tungsten carbide powder has an average particle size of 10-300 nm.
[Claim 5] The method according to claim 1, wherein the polishing agent further comprises colloidal silica.
[Claim 6] The method according to claim 1, wherein the polishing agent further comprises ceria.
[Claim 7]
A method of polishing a subject, comprising: providing a first polishing agent, including nano sized tungsten carbide powder having an average particle size of 50 run to 300 ran, on a first metal platen; rotating the first metal platen to thus polish the subject with the second polishing agent; providing a second polishing agent, including nano sized tungsten powder having an average particle size of 50 ran or less, on a second metal platen; and rotating the second metal platen to thus polish the subject with the second polishing agent.
[Claim 8]
The method according to claim 7, further comprising polishing the subject using a third polishing agent including an aqueous solution of tungsten carbide powder having an average particle size of 50 nm or less and either colloidal silica or ceria.
[Claim 9]
A method of manufacturing a subject having surface roughness of 5 μm or less and flatness of 3 μm or less, comprising polishing the subject with a polishing agent including spherical tungsten particles having an average particle size of 3 μm or less.
[Claim 10] A polishing agent for polishing a subject, comprising an aqueous solution including spherical tungsten carbide powder having an average particle size of 3 μm or less dispersed therein.
[Claim 11]
The polishing agent according to claim 10, wherein the tungsten carbide powder has an average particle size of 10 to 300 nm.
[Claim 12]
The polishing agent according to claim 10, wherein the aqueous solution further comprises a lubricant.
[Claim 13] The polishing agent according to claim 10, wherein the aqueous solution further comprises colloidal silica.
[Claim 14]
The polishing agent according to claim 10, wherein the aqueous solution further comprises ceria.
[Claim 15]
The polishing agent according to claim 10, wherein the tungsten carbide is prepared by reducing and carbonizing tungsten oxide using carbon monoxide (CO) at 600~700°C.
[Claim 16]
The polishing agent according to claim 10, wherein the reducing and carbonizing are performed in the presence of a zeolite catalyst or a silica catalyst.
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Cited By (2)

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CN104987839A (en) * 2015-06-30 2015-10-21 安徽德诺化工有限公司 Sapphire substrate grinding fluid used for LED
CN105038605A (en) * 2015-06-16 2015-11-11 东莞市中微纳米科技有限公司 Sapphire coarse grinding fluid

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CN105038605A (en) * 2015-06-16 2015-11-11 东莞市中微纳米科技有限公司 Sapphire coarse grinding fluid
CN104987839A (en) * 2015-06-30 2015-10-21 安徽德诺化工有限公司 Sapphire substrate grinding fluid used for LED

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