Patent Publication Number: US-2009239454-A1

Title: Cmp conditioner and process for producing the same

Description:
TECHNICAL FIELD 
     The present invention relates to a CMP conditioner used to condition the polishing pad in a CMP (chemical mechanical polishing) apparatus that polishes a semiconductor wafer or the like, and a process for producing the same. 
     BACKGROUND ART 
     A CMP conditioner of this type has been proposed, for example, in Patent Document 1, in which a plurality of columnar protruding portions are formed and spaced apart on the upper surface of a disk-shaped base (substrate), and a plurality of abrasive grains, such as diamond, are fixed on the surface of these protruding portions by a metal-plated bonding phase. 
     Also in Patent Document 2 brazed diamond abrasive grains have been proposed; and further in Patent Document 3 it has been proposed to cover the surface of a metallic bonding phase on which such abrasive grains are fixed with a coating film of ceramics, such as SiC, by vapor-phase coating techniques, such as CVD and ion plating. 
     In CMP apparatuses whose polishing pad is conditioned by such a CMP conditioner have a problem in that since an acidic or alkaline corrosive slurry is used to polish semiconductor wafers or the like, the metallic bonding phase to hold abrasive grains is corroded (dissolved) by the slurry and the abrasive grains drop out, and the semiconductor wafer is damaged by the dropped abrasive grains causing scratches. In particular, when the abrasive grains are diamond grains, and the bonding phase is a metal-plated phase, such as a nickel-plated phase, since the wetting properties of metal plating to the abrasive grains are poor, a gap, even though extremely small, is produced in the boundary portion (cavity) between them, and the slurry invades through the gap to corrode the metal-plated phase, the dropping of the abrasive grains is further accelerated. 
     In this aspect, in the CMP conditioner wherein the surface of the metallic bonding phase is coated with a ceramic film as described in Patent Document 3, the metallic bonding phase is protected by the ceramic film and the corrosion thereof is prevented; and therefore the dropping of the abrasive grains can be controlled. On the other hand, however, when the ceramic film is coated using a vapor-phase coating technique as described in Patent Document 3, the surfaces of abrasive grains such as diamond grains protruding from the metal coating phase are also coated with the coating film, which causes the problem that the sharpness of the abrasive grains becomes impaired and the polishing rate of the pad is significantly lowered. 
     Further, as methods to form a thick ceramic film on various base materials, aerosol deposition methods as disclosed in Patent-Documents 4 to 7 are known. 
     Patent Document 1: Japanese Patent Application Laid-Open No. 2001-71269 
     Patent Document 2: Japanese Patent Application Laid-Open No. 2002-273657 
     Patent Document 3: Japanese Patent Application Laid-Open No. 2001-210613 
     Patent Document 4: Japanese Patent No. 3348154 
     Patent Document 5: Japanese Patent Application Laid-Open No. 2002-309389 
     Patent Document 6: Japanese Patent Application Laid-Open No. 2003-034003 
     Patent Document 7: Japanese Patent Application Laid-Open No. 2004-091614 
     Patent Document 8: Japanese Patent Application Laid-Open No. 2003-183848 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     The present invention has been made under such a background, and it is an object thereof to provide a CMP conditioner that can reliably prevent the falling-out of abrasive grains even with the highly corrosive slurry used in a CMP apparatuses to suppress the occurrence of scratches. 
     Means for Solving the Problems 
     To solve the above-described problems, the CMP conditioner according to the present invention has a configuration wherein an abrasive grain layer is formed on a surface of a grindstone base, the abrasive grain layer having abrasive grains fixed in a metallic bonding phase, an oxide film is formed as a first protective layer at least on the surface of said metallic bonding phase of said abrasive grain layer by a sol-gel method, and a thick oxide film is formed as a second protective layer, the thick oxide film being polycrystalline and having substantially no grain boundary layer composed of a glass layer in the interface between crystals. 
     Here, the thick film is a film having a film thickness of 1 μm or more. 
     The first protective layer is preferably formed to cover the metallic bonding phase at least in the vicinity of the junction between the abrasive grains and the metallic bonding phase. 
     Such a structure is achieved by forming an oxide film, which is the first protective layer, by the sol-gel method. Since the sol-gel method is a method for forming an oxide film using a solution, the solution is attracted around the abrasive grains by surface tension, and as a result, it is considered that the film thickness becomes large in the peripheral portions of the abrasive grains compared with other portions. The formed oxide film covers the metallic bonding phase, and has excellent corrosion resistance, especially in the peripheral portions of the abrasive grains. 
     The film thickness of the first protective layer is thin in portions other than the peripheral portions of the abrasive grains, and stable corrosion resistance cannot be obtained. Therefore, by forming a thick oxide film which is polycrystalline and has substantially no grain boundary layer composed of a glass layer in the interface between the crystals, as a second protective layer, stable corrosion resistance can be obtained. 
     It is preferable that the second protective layer is not formed on the surfaces of the abrasive grains but formed only on the surface of the first protective layer. When the second protective layer is not formed on the surfaces of the abrasive grains, problems, such as change in the polishing performance of the CMP conditioner is not caused. 
     The second protective layer is preferably composed of an oxide that excels in corrosion resistance, such as alumina. 
     As a method for producing the second protective layer, a method for forming a thick oxide film by jetting and striking an aerosol obtained by dispersing fine particles of a brittle material in a gas onto the first protective layer is considered. 
     The above-described method is a method known as an aerosol deposition method as described in Patent Documents 4 to 7. 
     The aerosol deposition method is a method for forming a thick ceramic film on various base materials, and is characterized in that a film structure composed of fine particle components is directly formed on a base material by: jetting an aerosol obtained by dispersing fine ceramic particles in a gas from a nozzle toward the base material; striking the fine particles onto the base material, such as a metal, glass, ceramics and plastics; and causing the deformation or fracture of the fine particles by the impact of the collision to bond the particles together. In this method, particularly, the structure can be formed at a normal temperature without heating means, and the structure having mechanical strength equivalent to the mechanical strength of sintered materials can be obtained. The apparatus used in the method basically comprises an aerosol generator that generates aerosol, and a nozzle for jetting the aerosol toward the base material. When a structure having a larger area than the opening of the nozzle is fabricated, the apparatus has a position controlling means for relatively moving and swinging the base material and nozzle; when the structure is fabricated under a reduced pressure, the apparatus generally has a chamber and a vacuum pump for forming the structure, and a gas generating source for generating the aerosol. 
     The process temperature in the aerosol deposition method is normal temperature, and is characterized in that the structure is formed at a temperature sufficiently lower than the melting point of the fine-particle material, or specifically, several hundred degrees below the melting point. 
     Fine particles to be used are mainly composed of brittle materials such as ceramics, and fine particles composed of the same material can be used alone or in mixture, or different kinds of fine particles can be used in mixture or composite. A metallic material or an organic material can be partially mixed in ceramic fine particles, or can be coated on the surface of these materials. In these cases, the main material for forming the structure is ceramics. 
     When crystalline fine particles are used as the material for a film structure formed by this process, the film structure is characterized in that the film structure is a polycrystal having smaller crystallite size than the crystallite size of the material fine particles, and the crystal often has substantially no crystal orientation. It is considered that substantially no grain boundary layer composed of a glass layer is present in the interface between ceramic crystals, and further a part of the film structure often forms an anchor layer biting into the surface of the base material. 
     The film structure formed by this method has sufficient strength and is apparently different from so-called green compact that is formed by the fine particles packed with one another by pressure and held by physical adhesion. 
     In the formation of the film structure, the fracture and deformation of fine particles can be determined by measuring the size of crystallites in the fine particles used as the material and the formed film structure by X-ray diffraction method. 
     Terms related to the aerosol deposition method will be described below. 
     (Poly-Crystal) 
     In this application, “poly-crystal” means a structure composed by joining and integrating crystallites. Actually, one crystallite can constitute a crystal, and the diameter thereof is normally 5 nm or larger. However, although the case where a fine particle is not crushed and is incorporated in the structure rarely occurs, it is actually polycrystalline. 
     (Fine Particle) 
     When a primary particle is a dense particle, “fine particle” means a particle wherein the average particle diameter identified by grain-size distribution measurement or a scanning electron microscope is 10 μm or smaller. When a primary particle is a porous particle that is easily crushed by impact, “fine particle” means a particle wherein the average particle diameter is 50 μm or smaller. 
     (Aerosol) 
     “Aerosol” means that the above-described fine particles are dispersed in a gas, such as helium, nitrogen, argon, oxygen, dry air, and a mixture of these gases. Although the state wherein primary particles are dispersed is preferable, normally, agglomerated particles wherein these primary particles are agglomerated are included. Although any value can be allowed to the gas pressure and the temperature of the aerosol, it is preferable for the formation of the structure that the concentration of fine particles in the gas is within the range between 0.0003 mL/L and 5 mL/L as jetted from the nozzle when the gas pressure is 1 atm. and the temperature is 20° C. 
     (Interface) 
     The “interface” in the present application means the region that constitutes the boundaries of crystallites with one another. 
     (Grain Boundary Layer) 
     The “grain boundary layer” is a layer having a thickness located in the interface or the grain boundary in a sintered body (normally several nm to several microns), normally has an amorphous structure different from the crystalline structure in crystal grains, and accompanies the segregation of impurities in some case. 
     ADVANTAGES OF THE INVENTION 
     In the CMP conditioner according to the present invention, by forming both a first protective layer having excellent anticorrosive properties in the peripheral portions of abrasive grains and a second protective layer having a large film thickness and stable anticorrosive properties, the drop-out of the abrasive grains due to the corrosion of the metallic bonding phase can be prevented, and the occurrence of scratches can be suppressed in the intended polishing of high-grade semiconductor wafers and the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an enlarged sectional view of a CMP conditioner showing an embodiment of the CMP conditioner according to the present invention; and 
         FIG. 2  is a diagram showing an aerosol deposition apparatus related to an embodiment of the process for producing the CMP conditioner according to the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
       FIG. 1  is a schematic sectional view of a CMP conditioner  10  according to the present invention. In the CMP conditioner, substrate  101 , a metallic bonding phase  102  contacting substrate  101 , and an abrasive grain layer  11  on which a large number of abrasive grains  105 , such as diamond abrasive grains, are fixed by the metallic bonding phase  102  are formed; at least on the surface of the metallic bonding phase  102  of the abrasive grain layer  11 , an oxide film, such as a silica film and/or a titania film, made by a sol-gel method is formed as a first protective layer  103 ; and on the surface of the first protective layer  103  an alumina film having a thickness of 1 μm or more made by an aerosol deposition method is formed as a second protective layer  104 . 
     The sol-gel method, which is a method for forming the first protective layer will be described below. 
     After immersing a conditioner in a SiO 2  sol-gel solution prepared by mixing Si(OC 2 H 5 ) 4  and ethanol, or a TiO 2  sol-gel solution prepared by mixing Ti(OC 2 H 5 ) 4  and ethanol for one minute, the conditioner is dried at 200° C. for 2 hours, and thereafter, the conditioner is heat-treated at 500° C. for 8 hours to form an oxide film. As the sol-gel solution, a sol-gel solution such as TiO 2 , Al 2 O 3 , SnO 2 , ZnO, VO 2 , V 2 O 5 , MO 3 , WO 3 , TaO 5  and ZnO 2  sol-gel solutions can also be used. In place of ethanol, 2-propanol can also be used. 
     Next, the aerosol deposition method, which is a method for forming the second protective layer  104  will be described below. 
     The aerosol deposition method is characterized in that an aerosol prepared by dispersing the fine particles of a brittle material or the like in a gas is jetted from a nozzle toward the base material, striking the fine particles onto the base material such as metals, glass, ceramics and plastics, and joining the fine particles of a brittle material by causing deformation or fracture by the impact of the collision to directly form a structure composed of the components of the fine particles on the base material. Thereby, the structure can be formed at a normal temperature without requiring heating means, and the structure having a mechanical strength equivalent to the mechanical strength of the sintered body can be obtained. The apparatus used in this method basically includes an aerosol generator for generating an aerosol and a nozzle for jetting the aerosol toward the base material. When the structure having an area larger than the opening of the nozzle is fabricated, the apparatus also has location controlling means for relatively moving and swinging the base material and the nozzle; when fabrication is carried out under a reduced pressure, the apparatus has a chamber wherein the structure is formed and a vacuum pump; and the apparatus generally has a gas generating source for generating the aerosol. 
     The process temperature of the aerosol deposition method is a normal temperature, and it is a feature that the structure is formed at a temperature sufficiently lower than the melting point of the fine-particle material, specifically, at several hundred degrees or lower. Therefore, the base materials that can be selected are quite variable, and low melting point metals or plastic materials can be used without problems. 
     Fine particles to be used are mainly composed of brittle materials such as ceramics and semiconductor materials, and fine particles composed of the same material can be used alone or in mixture, or different kinds of fine particles of brittle materials can be used in mixture or composite. A metallic material or an organic material can be partially mixed in fine particles of brittle material, or can be coated on the surface of these materials. In these cases, the main material for forming the structure is also brittle materials. 
     When crystalline fine particles of brittle materials are used as the material for a structure formed by this process, the brittle material portion of the structure is a polycrystal, and characterized in that the crystallite size is smaller than the crystallite size of the material fine particles, and the crystal often has substantially no crystal orientation. Substantially no grain boundary layer composed of a glass layer is present in the interface between crystals of the brittle material, and further, a part of the structure often forms an anchor layer biting into the surface of the base material. 
     The film structure formed by this method has sufficient strength and is apparently different from so-called green compact that is formed by the fine particles packed with one another by pressure and held by physical adhesion. 
     In the formation of the structure, the fracture and deformation of fine particles of the brittle material can be determined by measuring the size of crystallites in the fine particles of the brittle material used as the material and the formed brittle material structure by X-ray diffraction method. Specifically, the size of crystallites in the structure formed by the aerosol deposition method shows a smaller value than the size of crystallites in the material fine particles. On the shear surface or the fracture surface formed by the fracture or deformation of fine particles, an emergent surface is formed wherein atoms originally present in the interior and bonded to other atoms are naked. It is considered that the structure is formed by joining the active emergent surface having a high surface energy to the surface of the adjacent brittle material, the emergent surface of the adjacent brittle material, or the surface of the substrate. When hydroxyl groups are moderately present on the surfaces of the fine particles, it is also considered that the local shear stress produced as the fine particles struck between the fine particles themselves or between the fine particles and the structure causes a mechanochemical acid-alkali dehydration reaction and joins them to one another. It is considered that the application of continuous mechanical impact from the exterior sequentially causes these phenomena, the development of joining and densification occur by repetitive deformation or fracture of fine particles to grow the brittle material structure. 
       FIG. 2  shows an aerosol deposition apparatus  20  for forming a second protective film among the CMP diamond conditioner of the present invention. On the top of a nitrogen gas cylinder  201 , an aerosol generator  203  is disposed via a gas carrier pipe  202 , and is connected to a nozzle  206  disposed in a ceramic film forming chamber  205  having, for example, an introducing opening of a diameter of 2 mm and a deriving opening of 10 mm×0.4 mm in the downstream side thereof, via an aerosol carrier pipe  204 . The aerosol generator  203  is filled with, for example, fine particle powder of aluminum oxide. On the tip of the opening of the nozzle  206 , an article to be coated  208  held on, for example, XYZθ stage  207 , is disposed. The ceramic film forming chamber  205  is connected to a vacuum pump  209 . 
     The operation of the aerosol deposition apparatus  20  for forming a ceramic film will be described below. The nitrogen gas cylinder  201  is opened to feed the gas to the aerosol generator  203  through the gas carrier pipe  202 , and at the same time, the aerosol generator  203  is operated to generate an aerosol wherein aluminum oxide fine particles and nitrogen gas are mixed in an appropriate ratio. The vacuum pump  209  is operated to produce a differential pressure between the aerosol generator  203  and the structure forming chamber  205 . The aerosol is introduced into the aerosol carrier pipe  204  in the downstream side by the differential pressure and accelerated, and jetted from the nozzle  206  toward the base material  208 . The base material  208  is freely swung by the XYZθ stage  207 , and while changing aerosol colliding locations, a membrane-like alumina film on a desired location of the article to be coated  208  is formed by the collision of the fine particles. 
     Although the ceramic film forming in chamber  205  is conducted under a reduced pressure environment using the vacuum pump  209  here, it is not indispensable to be under a reduced pressure environment, but the film can also be formed under atmospheric pressure. In addition, the gas is not limited to nitrogen, but helium or compressed air can be freely used. 
     EXAMPLE 
     In order to check the performance of the CMP conditioner according to the present invention, the CMP conditioner was immersed in a mixed solution of a CMP slurry (W2000, manufactured by Cabot Corporation) and a 3% hydrogen peroxide solution at 50° C. for 48 hours, and a corrosion resistance test was performed by observing the surface state before and after the immersion. 
     As the CMP conditioner according to the present invention used in the corrosion resistance test, a silica film as a first protective film is formed on the surface wherein diamond abrasive grains are fixed in Ni as a metallic bonding phase by immersing the conditioner in a sol-gel solution prepared by mixing a thin Si film forming material (manufactured by Mitsubishi Materials Corporation) and ethanol in 1:1 for 1 minute, drying at 200° C. for 2 hours, and heat-treating at 500° C. for 8 hours; then, an alumina film having a thickness of 3 to 5 μm was formed as a second protective film in the apparatus conforming to  FIG. 2 , by using fine particles of alumina having an average particle diameter of 0.6 μm, generating an aerosol at a flow rate of nitrogen gas of 7 L/min, and jetting the aerosol from the nozzle to the surface of the film. As a result of the corrosion resistance test, no discoloration due to corrosion was observed, and a sufficient corrosion resistance was known. The results are shown in Table 1. In Table 1, the results of Comparative Example 1 and Comparative Example 2 are also shown. 
     Comparative Example 1 
     In order to compare corrosion resistance, a CMP conditioner wherein only the second protective film in Example 1 was formed was fabricated, and the corrosion resistance test equivalent to the Example 1 was carried out. As a result of the corrosion resistance test, discoloration due to corrosion was observed in the vicinity of diamond abrasive grains, and the elution of Ni was also found. 
     Comparative Example 2 
     In order to compare corrosion resistance, a CMP conditioner without forming the first protective film and the second protective film in Example 1 was fabricated, and the corrosion resistance test equivalent to the Example 1 was carried out. As a result of the corrosion resistance test, discoloration was observed on the entire area of the surface where diamond abrasive grains were present, and the elution of Ni was also found. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Comparative 
                 Comparative 
               
               
                   
                 Example 1 
                 Example 1 
                 Example 2 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 First 
                 Present 
                 Absent 
                 Absent 
               
               
                 protective film 
               
               
                 Second 
                 Present 
                 Present 
                 Absent 
               
               
                 protective film 
               
               
                 General 
                 ∘ 
                 Δ 
                 x 
               
               
                 appearances 
                 No discoloration 
                 Discoloration due 
                 Discoloration 
               
               
                 after corrosion 
                 due to corrosion 
                 to corrosion in the 
                 due to 
               
               
                 resistance test 
                   
                 vicinity of diamond 
                 corrosion in 
               
               
                   
                   
                 abrasive grains 
                 entire area