Abstract:
A process for making a diamond film with low surface roughness. A substrate is provided. A diamond layer is deposited on the substrate. A binder layer is coated over the diamond layer. A carrier plate is provided to join with the binder layer, thereby forming a laminate structure. The substrate is then removed, thereby obtaining a diamond film with a low surface roughness with respect to the surface roughness of the removed substrate.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method for fabricating a diamond film having low surface roughness. More particularly, the present invention relates to a method for fabricating a diamond film having low surface roughness and products made thereof that are suited for surface acoustic wave (SAW) filters, transfer printing heads, and/or nano-scale transfer printing applications.  
         [0003]     2. Description of the Related Art  
         [0004]     Synthesized diamond films have been widely used in various industry fields such as traditional cutting tools and light communication devices because of the superior physical and chemical characteristics thereof. Typically, diamond films are deposited on a substrate using hot filament chemical vapor deposition (HF CVD) or plasma-assisted CVD. However, the average surface roughness of the diamond films either made by using the HF CVD or plasma-assisted CVD does not meet the restrict requirement of sophisticated electric components. In general, the average surface roughness of the diamond films either made by using the HF CVD or plasma-assisted CVD is about several microns.  
         [0005]     Reference is made to  FIG. 1 , which is a schematic cross-sectional view illustrating a diamond film fabricated according to the prior art. The diamond film  20   a  is deposited on a support substrate  10   a . After deposition of the diamond film  20   a , a polishing process is typically carried out to obtain a planar diamond surface with low surface roughness. For example, the polishing process may be mechanical polishing, ion beam processing, chemical assisted polishing, or thermal chemical mechanical processing, and the like.  
         [0006]     However, the above-described prior art diamond surface polishing processes still has several drawbacks. After treatment with a conventional mechanical energy or ion beam polishing processes, the surface roughness of the diamond surface can only be improved by several microns. Further, the prior art diamond surface polishing processes is time consuming. Typically, it takes several days to finish a batch of diamond film products. Moreover, the equipment required for the conventional diamond surface polishing processes is costly.  
       SUMMARY OF THE INVENTION  
       [0007]     Accordingly, the primary object of the present invention is to provide a process for making a diamond film with low surface roughness.  
         [0008]     Another object of the present invention is to provide a simplified process for making diamond films, which is cost effective and time saving.  
         [0009]     Still another object of the present invention is to provide a process for making diamond film with low surface roughness and microstructure. To achieve these and other advantages and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a process for making a diamond film with low surface roughness, comprising providing a substrate, depositing a diamond layer on the substrate, coating a binder layer over the diamond layer, providing a carrier plate joining with the binder layer, thereby forming a laminate structure, and removing the substrate. A diamond film with a low surface roughness with respect to the surface roughness of the removed substrate is thereby obtained.  
         [0010]     The present invention also discloses a process for fabricating a diamond film structure with low surface roughness, comprising providing a substrate, depositing a diamond layer on the substrate, coating a conductive layer over the diamond layer, forming a metal layer on the conductive layer and removing the substrate. A diamond film with a low surface roughness with respect to the surface roughness of the removed substrate is thereby obtained.  
         [0011]     The present invention, the present invention further discloses a process for making a diamond film with low surface roughness, comprising providing a support substrate and a carrier plate, each of which has a corresponding deposition face. The support substrate and the carrier plate are arranged so that there is a constant spacing between the depositing face of the support substrate and the depositing face of the carrier plate. Chemical vapor deposition is performed in the spacing to form a diamond layer between the depositing face of the support substrate and the depositing face of the carrier plate. The support substrate is then moved, thereby obtaining a diamond film with a low surface roughness with respect to the surface roughness of the removed substrate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Other objects, advantages and novel features of the invention will become more clearly and readily apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:  
         [0013]      FIG. 1  is a schematic cross-sectional view illustrating a diamond film fabricated according to the prior art;  
         [0014]      FIG. 2A  to  FIG. 2D  are schematic cross-sectional diagrams showing the first preferred embodiment of the present invention;  
         [0015]      FIG. 3  illustrates a joining face of the carrier plate according to the present invention;  
         [0016]      FIG. 4A  to  FIG. 4D  are schematic cross-sectional diagrams showing the second preferred embodiment of the present invention; and  
         [0017]      FIG. 5A  to  FIG. 5D  are schematic cross-sectional diagrams showing the third preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]     The present invention pertains to a method for fabricating a diamond film with a relatively low average surface roughness compared to the diamond film made by the prior art method. The present invention method substitutes joining techniques and etching techniques for the prior art mechanical energy or energy ion beam polishing methods. According to the present invention method, a large area, low surface roughness diamond film surface can be obtained with low cost. The manufacturing processes thereof are simplified. No complex and costly equipment is required. A great deal of processing time is also saved.  
         [0019]     Referring initially to  FIG. 2A  to  FIG. 2D , a support substrate  10  having a main surface with low surface roughness is provided. The support substrate  10  is made of silicon, Mo alloys, graphite, WC or similar materials. An intermediate layer  15  is sputtered onto the main surface of the support substrate  10 . The thickness of the intermediate layer  15  is about several nanometers. Preferably, the intermediate layer  15  is made of aluminum nitride or silicon carbide. Subsequently, a chemical vapor deposition (CVD) process is carried out to deposit a diamond film  20  on the intermediate layer  15 . A binder layer  30  is coated on the diamond film  20 . The binder layer  30  comprises binders such as polymer composite materials, sol-gel, epoxy, UV resins, glass binders, or metal composites. After coating the binder layer  30 , a carrier plate  40  and the binder layer  30  are joined together. It is noted that if the binder layer  30  is made of UV resins, the carrier plate  40  should be a transparent plate such as a quartz plate such that UV light can penetrate through the transparent carrier plate  40  to the subjacent binder layer  30 . Thereafter, the support substrate  10  and the intermediate layer  15  are removed by a wet chemical such as KOH or HNA, which process is known in the art. Dry etching methods for removing the support substrate  10  and the intermediate layer  15  are also practicable. As indicated in  FIG. 2D , after reversing the composite film stack shown in  FIG. 2C , a diamond film with low surface roughness is obtained. In this method, the intermediate layer  15  serves as a buffer layer between the support substrate  10  and the diamond film  20  to avoid peeling due to difference in thermal expansion coefficient. It is noted that before joining the carrier plate  40  to the binder layer  30 , several concentric circles of micro trenches  41  are etched into the joining face of the carrier plate  40 , as shown in  FIG. 3 . These concentric circles of micro trenches  41  can alleviate micro distortion due to heat extension of the diamond film  20 , the binder layer  30  and the carrier plate  40 , and thus preventing peeling of the diamond film  20  from the carrier plate  40 . In some cases, the intermediate layer  15  may be omitted.  
         [0020]     Referring to  FIG. 4A  to  FIG. 4D , a support substrate  10  having a main surface with low surface roughness is provided. An intermediate layer  15  is sputtered onto the main surface of the support substrate  10 . Subsequently, a chemical vapor deposition (CVD) process is carried out to deposit a diamond film  20  on the intermediate layer  15 . A conductive layer  50  is sputtered on the diamond layer  20 . The conductive layer  50  may be made of Ni, NiCo, TiNi, or Al, but is not limited thereto. Thereafter, a metal layer  60  such as Ni is electrically plated on the conductive layer  50  to form a laminate structure (substrate  10 /intermediate layer  15 /diamond film  20 /conductive layer  50 /metal layer  60 ). Finally, the substrate  10  and the intermediate layer  15  are removed to form a diamond film with a low surface roughness. Likewise, the intermediate layer may be omitted.  
         [0021]     Referring to  FIG. 5A  to  FIG. 5D , a support substrate  10  with a recess structure is provided. A carrier plate  40  having a protruding structure corresponding to the recess structure of the support substrate  10  is arranged under the support substrate  10 . An intermediate layer  15  is sputtered on the main surface of the support substrate  10  in advance. The spacing  70  between the support substrate  10  and the carrier plate  40  is substantially equal to the thickness of the diamond layer to be formed. After fixing the positions of the support substrate  10  and the carrier plate  40 , a chemical vapor deposition process is carried out to deposit a diamond layer in the spacing between the intermediate layer  15  and the deposition surface of the carrier plate  40 , as shown in  FIG. 5C . Finally, the support substrate  10  and the intermediate layer  15  are removed, thereby forming a diamond film  20  with low surface roughness.  
         [0022]     The intermediate layer  15  serves as a buffer layer between the support substrate  10  and the diamond film  20  to avoid peeling due to thermal expansion. It is noted that several concentric circles of micro trenches  41  are etched into the carrier plate  40 . These concentric circles of micro trenches  41  can alleviate micro distortion due to heat extension of the diamond film  20  and the carrier plate  40 , and thus preventing peeling of the diamond film  20  from the carrier plate  40 . In some cases, the intermediate layer  15  may be omitted.  
         [0023]     It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.