Abstract:
A coating method on diamond abrasive grains is used to form a conductive film on diamond abrasive grains. The conductive film has chemical composition gradient giving the diamond abrasive grain an outwardly increasing electrical conductibility as a function of film thickness. The subsequent electroplating layer can therefore more effectively embed the modified diamond abrasive grains, whilst the adhesion/bonding strength between substrate (work piece for electroplating) and the diamond abrasive grains is improved.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to diamond abrasive grains. In particular, the present invention relates to diamond abrasive grains having electrical conductivity and electroplated tool having the same. 
         [0003]    2. Description of Related Art 
         [0004]    Diamond tools (i.e., abrasive tools) are widely used in semiconductor manufacturing industries, machining industries, aerospace industries and the polishing industries. The applications including cutting, drilling, sawing, grinding, lapping and polishing. The diamond tools are usually manufactured by electroplating methods. 
         [0005]    One specific process that uses the diamond tools is chemical mechanical polishing (CMP) and this process has become standard in the semiconductor and integrated circuit industries for polishing the wafers. As well known, a CMP pad is used in a planarization of wafers and a CMP pad conditioner is a type of grinding tools for improving performance and life of the CMP pad. The CMP pad conditioner can be produced by bonding the diamond abrasive particles, e.g., by brazing or electroplating, onto a metal substrate. For improving the bonding strength of the diamond abrasive particles and the substrate in the electroplating method, the surface of the diamond abrasive particles may be modified to be conductive. Thus, the electroplating layer may cover the diamond abrasive particles so as to avoid the diamond pop-out during application process. 
         [0006]    Sapphire substrates are well-known materials in LED industry. One method of marking sapphire substrates is utilizing a metal wire with diamond slurry to cut the ingot. However, the diamond slurry has a high price and thus the manufacturing cost is high. On the other hand, the cutting rate is slow. Now, a precision diamond wire saw (PWS) has been developed for manufacturing the sapphire substrates. The PWS can be produced by bonding diamond abrasive particles, e.g., by electroplating, onto a metal wire. By using the PWS instead of traditional slurry cutting, the sapphire ingot cutting time can be reduced from days to hours. 
         [0007]    In a traditional method of the electroplating, the un-modified diamond abrasive particles are mechanically bonded into the electroplating matrix. However, the diamond abrasive particles often cannot be firmly fixed in the electroplating layer due to insufficient metal matrix coverage and week mechanical supporting strength surrounding the diamond particles. During application process, the diamond abrasive particles may easily pop-out from the metal matrix (i.e., the metal substrate or the metal wire). The popped-out diamond abrasive particles may damage the processing materials, i.e., wafer or glass. For increasing the bonding strength, the thicker electroplating layer is required to firmly fix the diamond abrasive particles. However, when the diamond abrasive particles are covered by the thicker electroplating layer, it will result-in less free-cutting ability. 
         [0008]    Although the commercial coating for diamond particle, such as Ti coating-or Cr coating layers are widely used in the market, the metal coating layer has high electrical conductivity so that the coated diamond abrasive particles are easily stacked one another to form diamond clusters or nodules when processed in electroplating bath. 
       SUMMARY OF THE INVENTION 
       [0009]    One object of the instant disclosure is providing diamond abrasive grains which have an electrical conductive layer with micro-conductivity on the respective surface. As the character of conductive layer, a full coverage and chemical boned metal layer can be plated on the surface of the diamond abrasive grains in electroplating process. Thus, the bonding strength between the diamond abrasive grains and the substrate will be improved. 
         [0010]    Another object of the instant disclosure is providing diamond abrasive grains which have a conductive layer thereon. The conductive layer has an increasing electrical conductibility because the gradient of chemical composition. 
         [0011]    The instant disclosure provides diamond abrasive grains which have a conductive layer thereon. The conductive layer has micro-conductivity and the electrical conductibility of the conductive layer increases outwardly from the surface of the diamond abrasive grain. 
         [0012]    The instant disclosure provides an electroplated abrasive tool including a substrate (e.g., an abrasive surface of the abrasive tool) and a plurality of diamond abrasive grains. The diamond abrasive grains are firmly disposed on the abrasive surface of the substrate by an electroplated metal matrix. Each of the diamond abrasive grains includes a conductive layer on a surface of the diamond abrasive grain. The conductive layer has an increasing electrical conductibility as a function of the conductive layer thickness and the compositional gradient. 
         [0013]    Accordingly, the instant disclosure provides diamond abrasive grains which have an increasing electrical conductibility. The electrical conductibility of the diamond abrasive grains is increasing from the surface of the diamond abrasive grain outwardly. Thus, the electroplated metal may cover the surface of each diamond abrasive grain entirely or partially by controlling the gradient of conductive layer composition and the bonding strength between the diamond abrasive grains and the substrate can be improved. Due to the increased bonding strength, the diamond abrasive grains may not pop-out easily from the-substrate of the electroplated tool in sawing or polishing processes. Therefore, the surface accuracy of the electroplated tool can be controlled in the sawing or grinding/polishing processes. 
         [0014]    For further understanding of the present invention, drawing reference is made as the following detail description illustrating the embodiments and examples of the present invention. The description is for illustrative purpose only and is not intended to limit the scope of the claims 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  shows the diamond abrasive grains of the instant disclosure. 
           [0016]      FIG. 2  shows the electroplated tool of the instant disclosure, wherein each diamond abrasive grain is partially covered by the electroplated metal matrix. 
           [0017]      FIG. 3  shows the electroplated tool of the instant disclosure, wherein each diamond abrasive grain is entirely covered by the electroplated metal matrix. 
           [0018]      FIG. 4  shows a relationship between the flow rate of C 2 H 2  and the conductivity of the conductive layer of the instant disclosure. 
           [0019]      FIG. 5  shows a PECVD method to deposit the conductive layer on the diamond abrasive grain of the instant disclosure. 
           [0020]      FIG. 6  shows an AIP method to deposit the conductive layer on the diamond abrasive grain of the instant disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    The instant disclosure provides a diamond abrasive grain having modified surface. By modifying the surface of the diamond abrasive grain, the diamond abrasive grain has micro-conductivity so that the diamond abrasive grain can be firmly fixed on a surface of a substrate and an electroplated layer can be controlled for diamond particle coverage percentage. Thus, the bonding strength of the diamond abrasive grain on the substrate can be improved and the electroplated tool can have longer tool life and better grinding surface accuracy. 
         [0022]    The instant disclosure provides a modifying method of the surface of the diamond abrasive grains, and the method includes the following steps: 
         [0023]    Please refer to  FIG. 1 ; step 1 is providing the diamond abrasive grains  11 . In the exemplary embodiment, the diamond abrasive grains  11  can be natural or synthetic (i.e., artificial) micro-sized/nano-sized diamond powders, but not restricted thereby. Preferably, the average size of the exemplary diamond abrasive grains  11  is ranged from 1 um to- 600 um. 
         [0024]    Step 2 is providing a coating method to coat and form a conductive layer  12  on the surface of the diamond abrasive grains  11 . The coated conductive layer  12  has a metal content, a metal-carbide content or a metal-nitride content therein and the metal content, the metal-carbide content or the metal-nitride content have a gradient of chemical composition so that the diamond abrasive grains  11  have a property of micro-conductivity. In detail, the electrical conductibility of the conductive layer  12  is configured as a function of the conductive layer thickness and the compositional gradient; preferably, the composition of the metal content, the metal-carbide content or the metal-nitride content is a gradient from the surface of the diamond abrasive grain  11  outwardly. In an exemplary embodiment, a PECVD (plasma enhanced chemical vapor deposition) process is applied in step 2 and the exemplary PECVD process is set forth in  FIG. 5 . As can be seen in  FIG. 5 , the diamond abrasive grains  11  are placed in a rotatable vacuum deposition chamber  31 . A pumping device  32  incorporating with a vacuum gauge  33  evacuates the vacuum deposition chamber  31  and maintains the gas flow and pressure of the supplied gases, such as acetylene (C 2 H 2 ), inert gases. Furthermore, suitable saturated metal compounds are employed and introduced into the vacuum deposition chamber  31 . By using a generator  34  for initializing plasma of the introduced gas mixture, the conductive layer  12  is coated on the surface of the diamond abrasive grains  11  and the conductive layer  12  has a metal content therein. Preferably, the metal content may include boron (B), tungsten (W) or transition metals, and the transition metals, for example, comprise titanium (Ti), chromium (Cr), vanadium (V), zirconium (Zr) and so on. Due to the energy gap profile across the thickness of conductive layer  12 , the conductive layer  12  performs as a conductive shell on each diamond abrasive grain  11 . On the other hand, by varying the content composition of the metal content, an increasing electrical conductibility as a function of the thickness of the conductive layer  12  is achieved. For one example, the saturated or unsaturated TiCl 4  is introduced into the PECVD process to form a titanium-containing conductive layer  12  and the Ti-carbide content or the Ti-nitride has an increasing compositional gradient from the surface of each diamond abrasive grain  11  outwardly. Thus, the electric resistance of the conductive layer  12  is gradientally decreased in the direction away from the surface of the diamond abrasive grain  11 ; in other words, the electrical conductibility is increased. According to the experimental results, the electric resistance of the conductive layer  12  is decreased and ranged from 80 mΩ-cm to 20 mΩ-cm. Therefore, the metal content of the present invention is not restricted thereby and it is required that the electric resistance of the conductive layer  12  is decreased and ranged from 80 mΩ-cm to 20 mΩ-cm so that the issue of the diamond cluster stacked by the diamond abrasive grain  11  may be avoided in the electroplating process. 
         [0025]    In another exemplary embodiment, an AIP (Arc ion plating) process is applied in step 2 as illustrated in  FIG. 6 . A pumping device  43  evacuates the chamber and maintains the gas flow and pressure of the supplied gases, such as acetylene (C 2 H 2 ), inert gases (such as Ar). A metal target  44 , such as Cr target is provided to generated arc discharging plasma by applying current from power supply  41  and the metal target  44  is ionized and vaporized. On the other hand, a bias power supply  42  is able to apply a negative pulse bias voltage to the diamond abrasive grains  11 . According to the negative voltage is applied, the bombardment treatment of the ionized metal can be performed and results in the deposition on the surface of the diamond abrasive grains  1 . By executing the deposition reaction by changing the flow rate of the acetylene (C 2 H 2 ) decreased from 200 sccm to 40 sccm, the electric resistance of the conductive layer  12  is decreased and ranged from 80 mΩ-cm to 20 mΩ-cm as shown in  FIG. 4 . Preferably, suitable gas flow rate may be applied in the deposition process so as to obtain a low conductivity area  12 A (i.e., the inner portion proximate the surface of the diamond abrasive grain  11 ) of the conductive layer  12  having an electric resistance ranged from 70 mΩ-cm to 100 mΩ-cm and a high conductivity area  12 B (i.e., the outer portion away from the surface of the diamond abrasive grain  11 ) of the conductive layer  12  having an electric resistance ranged from 5 mΩ-cm to 20 mΩ-cm. 
         [0026]    While initializing the deposition process by introducing the higher acetylene (C 2 H 2 ) flow rate, the metal content is a metal-carbide content, such as C—Cr compound having a chemical formula of Cr x C y , for example, Cr 23 C 6 , Cr 7 C 3 , Cr 3 C 2  and so on. By decreasing the flow rate of the acetylene (C 2 H 2 ), the composition of the metal content, such as Cr content in the conductive layer  12  may increase so that the electric resistance is decreased (i.e., the electric conductivity is increased). Similarly, the tungsten (W) content in the conductive layer  12  may be formed as W—C content in a suitable processing condition and the vanadium (V) content in the conductive layer  12  may be formed as V—C content in a suitable processing condition. In other words, the metal content in the conductive layer  12  may be formed as metal-carbide content, such as C—Cr compound, C—W compound, C—V compound, C—B compound and so on. The metal-carbide content of the conductive layer  12  has a gradient of chemical composition increased from the surface of the diamond abrasive grain  11  outwardly so that the conductive layer  12  has an increasing electric conductivity to improve the performance of the electroplating. In an alternative embodiment, the metal content of the conductive layer  12  may be formed as metal-nitride content in a suitable processing condition. 
         [0027]    The present coated diamond abrasive grains  11  can be mounted on a surface of a substrate  21  by an electrodeposition/electroplating method, such as a nickel (Ni) electroplating method. The substrate  21  may be a wire, CMP pad conditioner or a grinding/polishing tool made of steel, stainless steel, aluminum alloy, titanium alloy or alloy steel. As shown in  FIG. 2 , the electroplated metal matrix (e.g., an electroplated layer)  22  extends from the surface of the substrate  21  onto the diamond abrasive grains  11  along the conductive layer  12  due to the micro-conductivity of the conductive layer  12  of the diamond abrasive grains  11 . In the embodiment, the electroplated metal matrix  22  is partially plated on the diamond abrasive grains  11 . Because that the diamond abrasive grains  11  are grabbed by the electroplated metal matrix  22  resulted from the electroplating process on the conductive layer  12 , the diamond abrasive grains  11  are firmly and stably bonded on the surface of the substrate  21  so as to form an electroplated tool. In this embodiment, the partial surface of the diamond abrasive grains  11  is exposed from the electroplated metal matrix  22  so that the electroplated tool provides better sawing or polishing performance. 
         [0028]    Alternatively, for further bonding the diamond abrasive grains  11  on the substrate  21 , the diamond abrasive grains  11  are entirely covered by the electroplated metal matrix  22  by controlling the gradient of conductive layer composition, as shown in  FIG. 3 . 
         [0029]    The advantages of the instant disclosure are following: 
         [0030]    1. Comparing with the traditional and un-coated diamond abrasive grains, the present modified/coated diamond abrasive grains may be firmly mounted on the substrate by thinner electroplated metal matrix. The present modified diamond abrasive grains can be exposed from the full coverage and thinner electroplated metal matrix in large area so that the sawing rate/ability and polishing rate/free-cutting ability are improved. 
         [0031]    2. The thinner electroplated metal matrix can be applied for bonding the diamond abrasive grains on the substrate; therefore, the electroplating process can benefit with less process time and cost. Moreover, the manufacturing efficiency of the electroplated tools, such as electroplated polishing tools, electroplated sawing tools may be improved. 
         [0032]    3. Due to the micro-conductivity of the diamond abrasive grains, the diamond clusters/nodules may not happen on the substrate surface. In other words, the diamond abrasive grains are separately and individually distributed on the surface of the substrate so that the surface accuracy of the electroplated tools is maintained. 
         [0033]    4. Due to the micro-conductivity of the diamond abrasive grains, the quality of the electroplating layer on the diamond abrasive grains may be improved. 
         [0034]    The description above only illustrates specific embodiments and examples of the present invention. The present invention should therefore cover various modifications and variations made to the herein-described structure and operations of the present invention, provided they fall within the scope of the present invention as defined in the following appended claims.