Abstract:
The presently claimed invention provides a metal-free and low stress thick film of diamond-like carbon (DLC). The diamond-like carbon layer of the present invention has a wide range of applications such as automotive coating, hydrophobic-hydrophilic tuning, solar photovoltaic, decorative coating, protective coating and bio-compatible coating. The presently claimed invention further provides a method and an apparatus to grow a metal-free and low stress thick film of diamond-like carbon by performing deposition and plasma etching to stack more than one diamond-like carbon layers together in the same chamber.

Description:
COPYRIGHT NOTICE 
       [0001]    A portion of the disclosure of this patent document contains material, which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 
       CROSS REFERENCE TO RELATED APPLICATION 
       [0002]    Pursuant to 35 U.S.C. §119(e), this is a non-provisional patent application which claims benefit from U.S. provisional patent application Ser. No. 61/961,445 filed Oct. 15, 2013, and the disclosure of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0003]    The present invention relates to a carbon material, and particularly relates to diamond-like carbons (DLC) and diamond-like carbon films. More particularly, the present invention relates to metal-free and low stress thick film of diamond-like carbons. The present invention also relates to a method and apparatus for forming the metal-free and low stress thick film of diamond-like carbons. 
       BACKGROUND 
       [0004]    Diamond-like carbon films have a wide range of applications owing to their high hardness, wear resistance and low friction. However, presently available diamond-like carbon films present a number of technical challenges which constrain their applications, for example: 
         [0005]    (1) High stress limits the maximum thickness a diamond-like carbon film can be grown; 
         [0006]    (2) Fluorinated diamond-like carbon (F-DLC) has the hardness behavior which is comparable to that of diamond-like carbon but high stress; 
         [0007]    (3) Growth rate of diamond-like carbon is relatively slow; and 
         [0008]    (4) Metal-containing diamond-like carbon reduces the performance of low friction of diamond-like carbon. 
         [0009]    To tackle some of the above challenges, various attempts have been made but no significant progress has ever been attained and such attempts include, for example, incorporating fluorine into diamond-like carbon films. In case of doping different metal ions into the carbon complex, the resulting diamond-like carbon films will have high friction which is undesirable. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention reduces stress and enhances hardness in diamond-like carbon films which can be used for applications, for example, automotive coating, hydrophobic-hydrophilic tuning, solar photovoltaic, decorative coating, protective coating and bio-compatible coating. 
         [0011]    An object of the present invention is to produce a diamond-like carbon film stack with a sufficiently high thickness efficiently. A further object of the present invention is to overcome the constraint of saturating growth rate of depositing a diamond-like carbon layer. 
         [0012]    One embodiment of the present invention is a metal-free fluorinated diamond-like carbon film stack. The said metal-free fluorinated diamond-like carbon film stack can be formed by repeated deposition with etching of surface prior to the repeated deposition. The said metal-free fluorinated diamond-like carbon has a reduced stress, an enhanced hardness and a thickness as desired. 
         [0013]    Another embodiment of the present invention is a method of producing a metal-free fluorinated diamond-like carbon film stack. The said method comprises deposition and etching of diamond-like carbon layers. The words “layer” and “film” are used interchangeably hereinafter. The said method provides a high growth rate and can be implemented efficiently with the apparatus disclosed in the present invention. To prepare the surface for deposition of a new diamond-like carbon layer, etching is done on the existing diamond-like carbon layer prior to deposition in the same chamber without breaking the vacuum condition. 
         [0014]    One aspect of the present invention is to reduce the stress in a diamond-like carbon coating by providing a diamond-like carbon film stack. 
         [0015]    Another aspect of the present invention is to grow a thick diamond-like carbon film stack. 
         [0016]    The other aspect of the present invention is to provide an apparatus and a method to produce a metal-free fluorinated diamond-like carbon film stack with a high growth rate. The diamond-like carbon growth mechanism has a lot to do with the behavior of the incoming hydrogen H and H-passivated diamond-like carbon surface. Modified surface of H-passivated diamond-like carbon will modulate the growth rate of diamond-like carbon film and hence the stress behavior of the resulting film. 
         [0017]    The present invention relates to a mechanism of growing a diamond-like carbon film on substrates. 
         [0018]    The major uniqueness of the present invention lies in several aspects: 
         [0019]    (1) the novel idea of deposition and etching in separate but sequential steps instead of putting all the gases in the same deposition step or in two different chambers; 
         [0020]    (2) the new apparatus is capable of accommodating both plasma-enhanced chemical vapor deposition (PECVD) and etching in the same chamber with flexibilities; 
         [0021]    (3) fluorine-attenuated layer to reduce the stress while maintaining the basic property of hydrogenated diamond-like carbon. 
         [0022]    Silicon materials such as Si, SiO 2  and Si 3 N 4  are etched in fluorine chemistries such as SiF 2  and SiF 4  volatile species or fluorocarbon gases C x H y  or aldehydes C x H y O z . A plasma etching system is in the process of setting up to etch Si and SiO 2  with fluorine chemistry and if we put diamond-like carbon substrate in the etcher, the F* neutrals will attack both H— and C— in the diamond-like carbon in which case we can modify the diamond-like carbon surface through F neutral interaction. 
         [0023]    The present invention provides a diamond-like carbon film stack, comprising a plurality of layers of metal-free diamond-like carbon stacking together; and a fluorine-attenuate surface on at least a first layer of metal-free diamond-like carbon to which a second layer of metal-free diamond-like carbon is deposited. The fluorine-attenuate surface of such a diamond-like carbon film stack is formed by etching said first layer of metal-free diamond-like carbon before deposition of said second layer of metal-free diamond-like carbon. 
         [0024]    The present invention further provides a method of forming a diamond-like carbon film stack, comprising: depositing a first diamond-like carbon layer; etching the first diamond-like carbon layer to form a fluorine-attenuate surface on the first diamond-like carbon layer; and depositing a further diamond-like carbon layer on the fluorine-attenuate surface of the first diamond-like carbon layer to form a stack of diamond-like carbon layers. In an embodiment, the depositing uses one or more hydrocarbon gases. The etching and the depositing are performed in one single chamber without breaking vacuum condition. 
         [0025]    Such a method of forming a diamond-like carbon film stack, further comprising: determining the thickness of the stack of diamond-like carbon layers. 
         [0026]    Such a method of forming a diamond-like carbon film stack, further comprising: repeating for one or more times of etching of the top of the stack of diamond-like carbon layers and of depositing a new diamond-like carbon layer on the top of the stack of diamond-like carbon layers which has been etched until the thickness of the stack of diamond-like carbon layers reaches a desired value. The present invention further provides a diamond-like carbon film stack manufactured by the aforesaid method. 
         [0027]    The method of forming a diamond-like carbon film stack, further comprising: etching a substrate on which the first diamond-like carbon layer is deposited. In an embodiment, the etching uses one or more fluorocarbon gases. 
         [0028]    In an embodiment, different process parameters such as pressure and temperature are used for etching or depositing when repeating etching and depositing so that etching will be performed with a first set of process parameters and depositing will be performed with a second set of process parameters wherein the first set of process parameters are different from the second set of process parameters. 
         [0029]    The present invention further provides an apparatus for forming a diamond-like carbon film stack, comprising: a power supply for plasma generation capable of providing an output selected from the group consisting of a radiofrequency output, a pulsed output and an output combining a radiofrequency output with DC; a chamber with supply of one or more gases for etching and depositing; and an end-point detection device for detecting a fluorine-terminated surface. In an embodiment, each of said one or more gases has a gas flow controlled by variable waveforms. 
         [0030]    Such an apparatus further comprises: a plurality of ports for supplying said one or more gases from a plurality of locations of said chamber. 
         [0031]    Such an apparatus of claim  11 , further comprising: a substrate holder with a heated chuck for holding one or more substrates on which diamond-like carbon film stacks to be formed. 
         [0032]    In another embodiment, the chamber in such an apparatus generates a pulsed DC excited plasma and a radio-frequency excited plasma. And the radio-frequency excited plasma operates at a frequency ranging from 13.56 MHz to 60 GHz. 
         [0033]    In another embodiment, the chamber of such an apparatus has a plasma density control. 
         [0034]    In another embodiment, the chamber of such an apparatus has a plasma source selected from the group consisting of inductively coupled plasma and electron cyclotron resonance. 
         [0035]    In another embodiment, the chamber of such an apparatus supplies a tunable bias voltage to a substrate. 
         [0036]    In another embodiment, the end-point detection device of such an apparatus uses ellipsometry for monitoring the thickness of the diamond-like carbon film stack. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]    Embodiments of the present invention will now be described solely by way of example in more detail hereinafter with reference to the accompanying drawings, in which: 
           [0038]      FIG. 1A  is a graph showing change of growth rate of a diamond-like carbon film over time in a process of growing a diamond-like carbon film by continuous deposition without being intervened by any etching during deposition. 
           [0039]      FIG. 1B  is a graph showing change of thickness of a diamond-like carbon film over time in a process of growing a diamond-like carbon film by continuous deposition without being intervened by any etching during deposition. 
           [0040]      FIG. 1C  is a graph showing change of growth rate of a diamond-like carbon film over time in a process of growing a diamond-like carbon film by repeated depositions with etching as an intermediate step between every two deposition steps according to an embodiment of the present invention. 
           [0041]      FIG. 1D  is a graph showing change of thickness of a diamond-like carbon film over time in a process of growing a diamond-like carbon film by repeated depositions with etching as an intermediate step between every two deposition steps according to an embodiment of the present invention. 
           [0042]      FIGS. 2A-2F  are schematic diagrams depicting a series of steps of how etching and deposition is implemented in one embodiment of the present invention. 
           [0043]      FIG. 3  is a flow chart illustrating the steps of a method of growing diamond-like carbon using etching and deposition according to one embodiment of the present invention. 
           [0044]      FIG. 4  is a schematic diagram depicting an apparatus for deposition and etching according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0045]    In the following description, a method of etching and deposition to grow a diamond-like carbon film, and an apparatus for etching and deposition to grow a diamond-like carbon film are set forth as preferred examples. It will be apparent to those skilled in the art that modifications, including additions and/or substitutions, may be made without departing from the scope and spirit of the invention. Specific details may be omitted so as not to obscure the invention; however, the disclosure is written to enable one skilled in the art to practice the teachings herein without undue experimentation. 
         [0046]    For growing a diamond-like carbon film, deposition of diamond-like carbon on a substrate is completed in one continuous step.  FIG. 1A  is a graph showing change of growth rate of a diamond-like carbon film over time in a process of growing a diamond-like carbon film by one single continuous deposition without any etching of the surface on which a layer of diamond-like carbon is deposited. As shown by the graph in  FIG. 1A , the growth rate of a diamond-like carbon film during deposition will drop over time, having a peak level at the beginning of deposition and subsequently remaining at a low level throughout the rest of the deposition. 
         [0047]    As shown by the graph in  FIG. 1B , the thickness of a diamond-like carbon film will increase at a faster rate at the beginning of deposition. Subsequently, the rate of increase in the thickness of the diamond-like carbon film will drop over time and the thickness of the diamond-like carbon film will become saturated with less and less increase after depositing the diamond-like carbon on the substrate for a certain period of time continuously. 
         [0048]    Instead of depositing diamond-like carbon on a substrate in one single continuous step only, the present invention deposits diamond-like carbon on a substrate for a number of times repeatedly to form a stack of diamond-like carbon films. Therefore, deposition of diamond-like carbon film is carried out in an on and off manner. 
         [0049]      FIG. 1C  is a graph showing change of growth rate of a diamond-like carbon film over time in a process of growing a diamond-like carbon film by repeated depositions with etching of the surface of the diamond-like carbon before every deposition according to an embodiment of the present invention. As shown in  FIG. 1C , the first deposition step  101  starts with a high growth rate of diamond-like carbon film. Deposition will continue until the growth rate of diamond-like carbon film starts to decline. Therefore, when the growth rate of diamond-like carbon film drops to certain level or before it drops, the first deposition step  101  will be stopped and etching of the surface of the diamond-like carbon film will start. The growth rate for depositing diamond-like carbon film will drop after deposition for several seconds to hundreds of seconds depending on chamber geometry and it will drop to a level depending on the diffusion barrier length during deposition. The etching step  102  will last for a certain period of time until the surface of the diamond-like carbon film has been sufficiently modified for next deposition. The etching step  102  lasts for a period of time ranging from several seconds to hundreds of seconds depending chamber geometry and etching gas mixtures. 
         [0050]    Subsequent to the etching step  102 , deposition of diamond-like carbon film on a substrate will start again with a high growth rate of a diamond-like carbon film in the second deposition step  103 . This repeated deposition of diamond-like carbon film will stop when the growth rate of the diamond starts to decline or after a certain period of time. Subsequently, the diamond-like carbon film will be processed by etching again for a certain period of time. 
         [0051]    In every deposition step for forming a diamond-like carbon film stack, it takes around the same length of time for depositing a layer of diamond-like carbon to reach a desired thickness for each layer. However, the built-up stress with thick layer will eventually affect the length of time for each deposition. 
         [0052]    Similarly, in case of etching, the length of time for each etching step will remain almost the same. The built-up stress with thick layer will eventually affect length of time for etching in the same way the length of time for deposition is affected. 
         [0053]    The process of deposition followed by etching will be repeated for a number of times until the thickness of the diamond-like carbon film reaches a certain desirable level. The number of times for repeated deposition with prior etching depends on the desirable thickness of the diamond-like carbon film stack to be deposited and the chamber volume and the pumping speed of the pumps connected to the chamber where the deposition and the etching are performed. 
         [0054]    In the process of repeated deposition and etching, the thickness of the diamond-like carbon film will increase in a way as shown in  FIG. 1D . The thickness will increase when the first deposition step  101  takes place. The rate of increase in the thickness is higher at the beginning of the first deposition step and gradually drops over time, hence the increase in thickness of the diamond-like carbon film will get slower and slower. After depositing diamond-like carbon film on a substrate for a certain period of time in the first deposition step  101 , the thickness of the diamond-like carbon film will stop increasing and remain more or less the same at a later stage of deposition. 
         [0055]    Subsequent to the first deposition step  101 , etching of diamond-like carbon film will start and the thickness of the diamond-like carbon will remain roughly the same throughout the etching step  102 . 
         [0056]    After etching for a certain period of time, the etching step  102  will end and the second deposition step  103  will start. At the beginning of the second deposition step  103 , the thickness of the diamond-like carbon film increases faster and then the rate of increase in the thickness of the diamond-like carbon film will gradually drop. Towards the end of the second deposition step  103 , the thickness of the diamond-like carbon film will stop increasing and remain roughly the same. 
         [0057]    In a process of repeated deposition followed by etching, the thickness of the diamond-like carbon film can increase to the desired level by accumulating the thickness allowed by each step of deposition. 
         [0058]      FIGS. 2A-2F  are schematic diagrams depicting a series of steps of how etching and deposition is implemented in one embodiment of the present invention. 
         [0059]      FIG. 2A  shows a substrate  201  on which a diamond-like carbon film is to be grow on. As an example, the substrate  201  is illustrated as a flat rectangular sheet. Nevertheless, the present invention allows a diamond-like carbon film to be grown on a substrate  201  of any shape, for example, cone shape or with any surface including rugged or flat or any other profile. In a preferred embodiment, a flat surface is used for growing a diamond-like carbon layer thereon for uniformity control. 
         [0060]    Substrate  201  is made from materials such as, but not limited to, Si, SiO 2 , other silicon materials, or stainless steel coupon. Both organic and inorganic substrates are suitable for diamond-like carbon layer to grow on. The substrate  201  is placed inside a chamber where a diamond-like carbon film is grown on the substrate  201 . The said chamber provides an airtight environment for processing the substrate  201  to grow a diamond-like carbon film. 
         [0061]    In an embodiment, one or more additional adhesion layers are coated on the substrate  201  in order to facilitate the growth of diamond-like carbon layer on different substrate materials. The adhesion layer of the substrate  201  is made from materials such as Cr, Ti and W or other metals. 
         [0062]    In a preferred embodiment, the chamber in use allows both plasma etching and PECVD deposition to take place inside it so that both plasma etching and PECVD deposition will be performed in the same chamber. The chamber is a dual frequency chamber of radiofrequency (RF) biased (13.56 MHz up to 2.4 GHz). The chamber has a plasma density control for the source and the possible source for the chamber includes inductively coupled plasma (ICP) or electron cyclotron resonance (ECR). Various waveforms are used to control the gas flow into chamber, such as on and off (square wave), or gradually on and off (sinusoidal wave). Power supply for plasma etching and plasma-enhanced chemical vapour deposition (PECVD) can provide RF, alternate current (AC) and direct current (DC), or pulse output to bias the sample and enhance the plasma density. 
         [0063]    In a preferred embodiment, RF with a range of up to 1500 W is used as the power supply. 
         [0064]    In another preferred embodiment, DC with a range up to 10000 W is used as the power supply. 
         [0065]    In a further preferred embodiment, pulse current with a frequency range up to 500 kHz, power ratio up to 10 kW and a duty cycle up to 50% reverse time with reverse time of 0.5 to 10 μsec is used. 
         [0066]      FIG. 2B  shows a plasma etching step for cleaning the substrate  201 . In one preferred embodiment, the substrate  201  is cleaned with etching gases  211  containing fluorine-containing etch chemistries before growing any diamond-like carbon film on the substrate  201 . Fluorine-containing etch chemistries such as C x F y O z , C x F y  and SiF x  (e.g. SiF 2  and SiF 4 ) volatile species are used for etching. During the cleaning of the substrate  201 , the said chamber is supplied with one or more etching gases  211  such as fluorocarbon gases (e.g. CHF 3 , CF 4 , C 3 F 8 ) or fluorocarbon containing gases such as a mixture of C x F y  with other facilitating gases  222  such as Ar, N 2  and others. One or more kinds of S x F y    213  are released during plasma etching of the substrate  201 . Sputtering of Ar on the adhesion layer of the substrate  201  such as Cr, Ti and W or other metals is performed for substrate cleaning. 
         [0067]    In a preferred embodiment, plasma etching of the substrate  201  is performed at a temperature range of −40° C. to 400° C. and a pressure range of 100 Torr to 10 −5  Torr with 5%-100% of fluorine-containing gas. 
         [0068]      FIG. 2C  shows a step of deposition of diamond-like carbon material on top of the substrate  201 . Subsequent to substrate cleaning by plasma etching, first deposition of diamond-like carbon will be performed on the substrate  201 . In this first deposition step, a layer of diamond-like carbon  231  is deposited by plasma-enhanced chemical vapor deposition (PECVD) on the substrate  201  which has been cleaned with etching gases  211  such as fluorine-containing etch chemistries. A diamond-like carbon layer  231  is deposited on the substrate  201  using deposition gases  221  such as C x H y  or C x H y O z  together with one or more various facilitating gases  222  such as H 2 , Ar and N 2 . The combination and the concentration of each facilitating gases  222  vary with the numbers of carbon atoms x and number of hydrogen atoms y in each of the deposition gas molecules  221 . The incoming H will form a H-passivated diamond-like carbon surface  241  on the diamond-like carbon layer  231 . The H 2  is controlled according to the numbers of hydrogen atoms in the C x H y  or C x H y O z  group. 
         [0069]    In a preferred embodiment, the deposition gas  221  is CH 2 O. 
         [0070]    In a preferred embodiment, the substrate  201  is kept at a temperature ranging from 0° C. to 300° C. during the first deposition. 
         [0071]    In a preferred embodiment, deposition of diamond-like carbon film is performed at a temperature range of −40° C. to 400° C. and a pressure range of 100 Torr to 10 −5  Torr with 5%-100% of carbon-containing gas or vapour. 
         [0072]    During deposition of diamond-like carbon layer, the gas species for deposition are hydrogen-rich so that hydrogen can easily penetrate into 5% to 100% of the diamond-like carbon layer thickness. The removal of hydrogen depends on the critical thickness of hydrogen-containing diamond-like carbon layer and the penetration depth by fluorine, which is controlled by deposition and etching time. 
         [0073]    After deposition for a certain period of time, a H-passivated diamond-like carbon surface  241  will be formed on top of the newly deposited diamond-like carbon layer  231 . The H-passivated diamond-like carbon surface  241  is thin with a thickness of around several nm up to less than 100 nm. 
         [0074]      FIG. 2D  shows a step of etching of diamond-like carbon film with etching gases  211 . After first deposition of a diamond-like carbon layer  231 , the diamond-like carbon layer is etched with etching gases  211  such as fluorine-containing etch chemistries or a mixture of gases containing etching gases  211  and other facilitating gases  222 . The etching step is performed between any two deposition steps and acts as an intermediate step between a first deposition and a second deposition. During etching, the chamber is supplied with various etching gases  211  including fluorocarbon gases such as CHF 3 , CF 4 , C 3 F 8  and other facilitating gases  222  such Ar and N 2 . The etching of diamond-like carbon layer  231  uses C x F y  or C x F y  containing gases such as a mixture of C x F y  with Ar, N 2  and H 2 . The fluorine neutrals  212  from the etching gases  211  such as fluorine-containing etch chemistries attack both hydrogen and carbon in the diamond-like carbon layer  231  so that the etching modifies the surface of the diamond-like carbon layer  231 . During etching, a fluorine-attenuate layer  232  is formed on the surface of the diamond-like carbon layer  231  after fluorine neutrals attacks the hydrogen in the diamond-like carbon layer  231  to release HF  214 . 
         [0075]    Fluorine penetrates into the diamond-like carbon layer  231  and selectively removes the hydrogen in the diamond-like carbon layer  231 . In the meantime, the penetrating fluorine radicals also incorporate into the diamond-like carbon layer  231 . 
         [0076]    In a preferred embodiment, etching of diamond-like carbon film is performed at a temperature range of −40° C. to 400° C. and a pressure range of 100 Torr to 10 −5  Torr with 5%-100% of fluorine-containing gas. 
         [0077]    In another embodiment, etching of diamond-like carbon film may adopt typical semiconductor etching process parameters. 
         [0078]      FIG. 2E  shows a step of deposition of diamond-like carbon material on top of the substrate  201 . Subsequent to etching, second deposition of diamond-like carbon will be performed on the substrate  201 . In this second deposition step, a layer of diamond-like carbon  233  is deposited by plasma-enhanced chemical vapor deposition (PECVD) on the fluorine-attenuate surface  232  of the diamond-like carbon layer  231 . A diamond-like carbon layer  231  is deposited on the top of the surface of the diamond-like carbon layer  231  using deposition gases  221  such as C x H y O z  and C x H y , or using deposition gases  221  together with one or more various facilitating gases  222  such as Ar, N 2  and H 2 . 
         [0079]    In a preferred embodiment, the deposition gases  221  in use is CH 2 O. Depending on the number of hydrogen atoms x and the number of hydrogen atoms y in deposition gas  221  molecules of C x H y  and C x H y O z , the concentration, ratio, pressure of the various facilitating gases  222  are determined and used accordingly in one embodiment. 
         [0080]      FIG. 2F  shows the film stack having the desired thickness. The process of deposition followed by etching will be repeated to deposit a plurality of diamond-like carbon layers  231  on top of one another and form a final film stack with a desired thickness  250  as shown in  FIG. 2F . Every time after the deposition of a diamond-like carbon layer  231  is completed, etching will be performed on the newly deposited diamond-like carbon layer  231  before depositing another new layer of diamond-like carbon. The cycle of first deposition and then etching and then second deposition so on and so forth will continue until the thickness of the final film stack reaches the desired level  250 . For example, the desired thickness  250  is around several hundreds of microns. Particularly in an embodiment, the desired thickness of a diamond-like carbon film stack  250  is around 400 pm. 
         [0081]    In a preferred embodiment, the diamond-like carbon layers  231  being deposited to form a diamond-like carbon film stack is a metal-free diamond-like carbon. 
         [0082]    In another preferred embodiment, the diamond-like carbon layers  231  being deposited to form a diamond-like carbon film stack is a metal-free hydrogenated diamond-like carbon. 
         [0083]      FIG. 3  is a flow chart illustrating the steps of a method of growing diamond-like carbon film using etching and deposition according to one embodiment of the present invention. 
         [0084]    Firstly, there will be a substrate cleaning step  301  by etching a substrate using C x F y  or C x F y  containing gases in a plasma environment. The C x F y  containing gases is a mixture of C x F y , Ar, N 2  and other gases. 
         [0085]    Subsequent to cleaning the substrate  301 , a layer of diamond-like carbon is deposited on the substrate in a depositing step  302 . In a preferred embodiment, the depositing step  302  is a plasma-enhanced chemical vapour deposition (PECVD). A diamond-like carbon layer is deposited on a substrate using C x H y  or C x H y  containing gases. The C x H y  containing gases is a mixture of C x H y , H 2  and Ar. 
         [0086]    After depositing a diamond-like carbon layer in a depositing step  302 , the surface of the diamond-like carbon layer is then etched by C x F y O z , C x F y  or C x F y  containing gases in an etching step  304  to modify the surface of the diamond-like carbon layer and form a fluorine-attenuate surface on the diamond-like carbon layer. 
         [0087]    Being attacked by neutral fluorine atoms from fluorine-containing etch chemistries such as C x F y  containing gases, the hydrogen-containing diamond-like carbon layer is modified and releases HF during the etching step  304 . 
         [0088]    Subsequent to etching  304 , a further diamond-like carbon layer is deposited on the etched surface of the diamond-like carbon layer by repeating the depositing step  302 . The depositing step  302  is repeated for one or more times to form a stack of diamond-like carbon layers. Every time before a new diamond-like carbon layer is deposited 302 on the top of the stack of diamond-like carbon layers, the top of the stack of more than one diamond-like carbon layers is cleaned in an etching step  304 . In a preferred embodiment, the etching step  304  is a plasma etching. 
         [0089]    Before etching  304 , the thickness of the stack of diamond-like carbon layers may be determined in a thickness determining step  303 . If the thickness of the stack of diamond-like carbon layers reaches a desired value, no further etching or depositing of diamond-like carbon layer is necessary and the stack of diamond-like carbon layers with the desired thickness will be the DLC film stack  305 . 
         [0090]    If the thickness of the stack of diamond-like carbon layers has not reached a desired value, the etching  304  will be repeated with a set of parameters such as etching duration independent of any earlier depositing processing. This set of parameters for etching  304  may remain the same as or become different from the parameters being used before. After etching  304 , depositing 302 will be repeated with a set of parameters such as deposition duration independently determined to suit the deposition need of each time. 
         [0091]    For PECVD and plasma etching, the depositing step  302  and the etching step  304  are performed in a chamber where plasma is generated. The apparatus which provides such a chamber is described in  FIG. 4 . 
         [0092]      FIG. 4  is a schematic diagram depicting an apparatus  400  for depositing and etching diamond-like carbon layers according to one embodiment of the present invention. 
         [0093]    The apparatus  400  has a chamber  401 . The body of the chamber  401  is earthed. A first electrode  433  is connected to a first AC power supply  431  through a first matchbox  441 . A second electrode  435  is connected to a second AC power supply  432  through a second matchbox  442 . The first AC power supply  431  and the second AC power supply  432  operate with their respective matchbox to excite the particles in the chamber  401  and generate radio-frequency excited plasma in the chamber  401 . 
         [0094]    In a preferred embodiment, the radio-frequency excited plasma operates at a dual frequency ranging from 13.56 MHz up to 2.4 GHz. 
         [0095]    The first electrode  433  is connected to a DC power supply  434 . The DC power supply  434  generates the pulsed DC excited plasma. 
         [0096]    These first AC power supply  431  and second AC power supply  432  together with the DC power supply  434  act as a power supply for plasma generation and give various inputs such as a radiofrequency output, a pulsed output and an output combining a radiofrequency output with DC. 
         [0097]    The chamber  401  has a plasma density control (not shown) for the plasma source and the plasma source for the chamber  401  includes inductively coupled plasma (ICP) or electron cyclotron resonance (ECR). 
         [0098]    The chamber  401  provides a single chamber for both etching and deposition to take place therein. Different plasma conditions are applied to each etching cycle and deposition cycle respectively. Therefore, the chamber  401  provides a tunable bias for deposition and etching. 
         [0099]    One or more pipes or channels  418  connect one or more gas supplies  410  to the chamber  401 . Gas supplies  410  containing fluorocarbon gases C x F y    411 , aldehyde gases C x H y O z    412 , and other facilitating gases  413 . Other facilitating gases  413  include, for example, argon Ar, hydrogen H 2  and nitrogen N 2 . 
         [0100]    The channels  418  are connected to various ports (not shown) of the chamber  401 . Various ports are located at the top of the chamber  401 , at the bottom of the chamber  401  or on the sides of the chamber  401 . Through these ports, various gases are supplied to the chamber  401  by various gas introduction and pumping combinations. 
         [0101]    To control processing parameters such as pressure or gas concentration or gas flow rate in the chamber  401 , one or more mechanical pumps  422  or turbo molecular pumps  421  are used by the chamber  401  to pump gases in and out of the chamber  401 . 
         [0102]    Furthermore, gas supplies  410  are controlled by a gas flow control (not shown). The gas flow control controls the gas flow in accordance with different waveforms, for example, following a square function to turn on and off, or following a sinusoidal function to gradually turn on and off. 
         [0103]    The substrate  201  is placed on a substrate holder  402 . The substrate holder  402  is equipped with a chuck. The chuck is either lamp-heated or resistively heated. The substrate  201  will be heated on the substrate holder  402  by the chuck. In a preferred embodiment, the substrate  201  is maintained at a temperature range from 0° C. to 300° C. by the chuck during processing. 
         [0104]    The chamber  401  has an end-point detection device (not shown) which performs thickness measurement and determines when to stop etching. In addition, the thickness of the stack of diamond-like carbon layers is determined the end-point detection device and the end-point detection device determines when to stop deposition of any additional diamond-like carbon layer by measuring the thickness of the stack of diamond-like carbon layers. The end-point detection device makes use of various in-situ monitoring metrology such as ellipsometry and other optical non-destruction detection mechanisms and one example for such a device is an interferometer. 
         [0105]    The foregoing description of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to the practitioner skilled in the art. 
         [0106]    The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalence.