Abstract:
A method for removing a diamond-like carbon film on a substrate is provided. The diamond-like carbon film includes an amorphous carbon layer and an amorphous hydrogenated carbon layer formed on the amorphous hydrogen-free carbon layer. The method includes a step of electrolyzing the diamond-like carbon film in an acid solution. Compared with grinding, the electrolyzing process has advantages of low cost being cheaper, more convenient and results in a smoother surface.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a method for removing a diamond-like carbon film from a substrate. 
       DISCUSSION OF RELATED ART 
       [0002]    Amorphous carbon (a-C) and hydrogenated amorphous carbon (a-C:H) films have desirable properties such as hardness, low friction, electrical insulation, chemical inertness, optical transparency, biological compatibility, selective photon absorption, smoothness, etc. For a number of years, these economically and technologically attractive properties have drawn almost unparalleled interest towards these coatings. Carbon films which are very hard, and which have high resistivity, and good dielectric optical properties, are now described as diamond-like carbon (DLC). 
         [0003]    In order to improve adhesion between a DLC film and a substrate, an intermediate film is usually formed between the DLC film and the substrate. The intermediate film can be selected from the group consisting of chromium film, chromium nitride, chromium carbide and any combination thereof. Compared with amorphous hydrogenated carbon, amorphous carbon has better adhesion with the intermediate film, but amorphous hydrogenated carbon has better wear resistance and a lower friction coefficient, thus a DLC film usually includes an amorphous carbon layer formed on the intermediate film and an amorphous hydrogenated carbon layer formed on the amorphous carbon layer. 
         [0004]    Although the DLC film has good wear resistance, but after a long time period the DLC film may be worn away. In another case the DLC film may have a quality problem such as uneven film thickness. In these cases, the flawed DLC film must be removed and a new DLC film can be formed. Grinding is a useful process for removing the flawed DLC film. However, grinding has poor precision. Plasma bombardment can also be used for removing a DLC film formed on a substrate, but is very expensive. 
         [0005]    Therefore, there is a desire to proving a method for removing a DLC film from a substrate, which is cheap, and can be conducted with a high level of precision. 
       SUMMARY 
       [0006]    In one embodiment, a method for removing a diamond-like carbon film from a substrate is provided. The diamond-like carbon film includes an amorphous hydrogen-free diamond-like carbon layer and an amorphous hydrogenated diamond-like carbon layer formed on the amorphous hydrogen-free carbon layer. The method includes a step of electrolyzing the amorphous hydrogen-free diamond-like carbon layer in an acid solution thereby removing the diamond-like carbon film from the substrate. 
         [0007]    This and other features and advantages of the present invention as well as the preferred embodiments thereof in accordance with the invention will become apparent from the following detailed description and drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Many aspects of the present method for removing a DLC film on a substrate can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present invention. 
           [0009]      FIG. 1  is a schematic view of a substrate having a diamond-like carbon film to be removed; 
           [0010]      FIG. 2  is a flow chart in accordance with an embodiment of a method for removing the diamond-like carbon film of  FIG. 1 ; and 
           [0011]      FIG. 3  is schematic view of a vacuum chamber for removing a diamond-like carbon film. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0012]    Referring to  FIG. 1 , a DLC film  12  formed on a substrate  10  is shown. An intermediate film  14  is formed between the DLC film  12  and the substrate  10 . The DLC film includes an amorphous carbon layer  122  formed on the intermediate film  14  and an amorphous hydrogenated carbon layer  124  formed on the amorphous carbon layer  122 . The intermediate film  14  improves an adhesion between the DLC film  12  and the substrate  10 . The intermediate film  14  can be selected from the group consisting of chromium film, chromium nitride, chromium carbide and any combination thereof. In the preferred embodiment, the intermediate film  14  includes a chromium film  142  formed on the substrate  10 , a chromium nitride film  144  formed on the chromium and a chromium carbide film  146  formed on the chromium nitride film  144 . 
         [0013]    A method for removing the DLC film  12  on the substrate  10  in accordance with a first embodiment includes the step of electrolyzing the DLC film  12  in an acid solution until the DLC film  12  peels from the intermediate film  14 . Because amorphous carbon has a number of free electrons, the amorphous carbon layer  122  is conductive. The amorphous carbon layer  122  can act as an anode in the process of the electrolyzing and is oxidized into carbon oxide. 
         [0014]    The acid solution can be prepared from sulfur acid, hydrochloric acid and mixture thereof. Preferably, the pH value of the acid solution is in the approximate range from 1 to 3. Electrolyzing voltage should be higher than 2 volts. Preferably, the operation volt is in the approximate range from 2 volts to 100 volts. An operation current of the electrolyzing is higher than 0.1 amperes. Preferably, the operation current is in the approximate range from 0.1 amperes to 10 amperes. Preferably, the electrolyzing step is performed for a time period in the approximate range from 1 minute to 10 minutes. 
         [0015]    In the preferred embodiment, the DLC film is removed by using electrolysis. Compared with grinding, electrolysis is cheap, convenient and results in a higher level of smoothness. 
         [0016]    Referring to  FIG. 2 , a method for removing the DLC film  12  on the substrate  10  includes the steps of: 
       Step  1 , bombarding the DLC film  12  with oxygen plasma to form a number of holes on the amorphous hydrogenated carbon layer  124  thereby exposing the amorphous carbon layer  122 ; and 
     Step  2 , electrolyzing the DLC film  12  in an acid solution until the DLC film  12  peels off from the intermediate film  14 . 
       [0017]    In step  1 , preferably, the DLC film  12  is processed with oxygen plasma in a vacuum environment, for example, in a vacuum chamber. Referring to  FIG. 3 , a vacuum reactor  20  defines a vacuum chamber  24  therein. The vacuum reactor  20  also defines an inlet  221  configured (i.e., structured and arranged) for supplying oxygen and an outlet  222 . A first discharge electrode  211  and a second discharge electrode  212  are disposed in the vacuum chamber  24  and are spaced a distance from each other. The substrate  10  is disposed in the vacuum chamber  24  away from the first discharge electrode  211  and the second discharge electrode  212 . A bias electrode  23  is disposed adjacent to the first discharge electrode  211  and the second discharge electrode. The bias electrode  23  is electrically connected with the substrate  10 . A bias voltage is applied between the substrate  10  and the bias electrode  23 . A vacuum pump  25  is connected with the outlet  222  and is configured for depresurizing the vacuum chamber  24 . 
         [0018]    A voltage is applied between the first discharge electrode  211  and the second discharge electrode  212 . When discharge occurs between the first discharge electrode  211  and the second discharge electrode  212 , a number of free electrons are released. These free electrons bombard the oxygen atoms and ionize them thereby producing an oxygen plasma. The oxygen plasma includes oxygen atoms, free electrons, oxygen ions, oxygen cations, etc. The oxygen cations are accelerated by the oxygen cations and bombard the DLC film  12  on the substrate  10 . 
         [0019]    The accelerated oxygen cations have high reactivity and high energy. After being bombarded by the oxygen cations, chemical bonds between carbon atoms and hydrogen atoms are cut thus weakening or destroying the DLC film  12 . In other words, the DLC film  12  reacts with the oxygen cations and is oxidated to form carbon oxide and water, a number of holes are formed on the amorphous hydrogenated carbon layer  124  thus exposing the amorphous carbon layer  122 . 
         [0020]    In step  2 , the DLC film  12  is electrolyzed in an acid solution. Because the amorphous carbon layer  122  is exposed to the acid solution, the electrolyzing process is accelerated. 
         [0021]    The acid solution can be selected from the group consisting of sulfur acid, hydrochloric acid and a mixture of the two. Preferably, the pH value of the acid solution is in the approximate range from about 1 to about 3. An electrolysis voltage should be higher than 2 volts. Preferably, the operation volt is in the approximate range from 2 volts to 100 volts. An operation current of the electrolyzing is higher than 0.1 amperes. Preferably, the operational current is in the approximate range from 0.1 amperes to 10 amperes. Preferably, the electrolyzing step is performed for a time period in the approximate range from 1 minute to 10 minutes. 
         [0022]    Finally, it is to be understood that the above-described embodiments are intended to illustrate rather than limit the invention. Variations may be made to the embodiments without departing from the spirit of the invention as claimed. The above-described embodiments illustrate the scope of the invention but do not restrict the scope of the invention.