Method and apparatus for making diamond-like carbon films

Abstract

Ion-assisted plasma enhanced deposition of diamond-like carbon (DLC) films on the surface of photovoltaic solar cells is accomplished with a method and apparatus for controlling ion energy. The quality of DLC layers is fine-tuned by a properly biased system of special electrodes and by exact control of the feed gas mixture compositions. Uniform (with degree of non-uniformity of optical parameters less than 5%) large area (more than 110 cm 2 ) DLC films with optical parameters varied within the given range and with stability against harmful effects of the environment are achieved.

1 . A method for deposition of diamond-like carbon (DLC) films comprising: (i) using plasma ions C + , H + , N + , Ar + ; and (ii) varying ion kinetic energy, plasma discharge current, and spatial distribution of plasma density by controlling an electric field with a system of annular electrodes comprising a diaphragm, a neutralizer, and an accelerating electrode. 
     
     
         2 . The method according to  claim 1 , wherein the control of uniformity plasma density is performed by measurement of ion current density at the surface of said film. 
     
     
         3 . The method according to  claim 1 , wherein manufacturing DLC films with refractive index in the range of 1.48-2.60 is performed by variation of average kinetic energy of ions in the range of 20-140 eV, plasma current density in the range of 0.2-0.8 mA·cm −2 , and hydrocarbon content in the feed gas mixture in the range of 2-40%. 
     
     
         4 . The method according to  claim 1 , wherein manufacturing multilayer DLC films with discrete values of refractive index or the DLC films with continuous variation of refractive index along the direction normal to the surface is performed by either discrete or continuous variation of ion energy, plasma current, and feed gas mixture composition. 
     
     
         5 . The method according to  claim 1 , including mounting a substrate on a support device and rotating the support device about the axis in a vacuum chamber. 
     
     
         6 . A deposition apparatus, comprising:
 a vacuum chamber;   an anode and a cathode in the vacuum chamber positioned with space between the anode and the cathode to produce an electric field between the anode and the cathode;   a magnet positioned to provide a magnetic field perpendicular to the electric field;   means for providing feed gases to the electric field between the anode and the cathode to produce a plasma of dissociated ions of constituents of the feed gas in the vacuum chamber;   a support device positioned in the vacuum chamber for mounting a substrate in the vacuum chamber in a flow of ions produced in the plasma;   an annular, grounded diaphragm positioned in the vacuum chamber between the cathode and the support device;   an annular neutralizer electrode with an AC voltage positioned between the diaphragm and the support device; and   an accelerating electrode biased with a negative voltage positioned between the neutralizer electrode and the support device.   
     
     
         7 . The deposition apparatus of  claim 14 , wherein the neutralizer electrode is biased in a range of 30V to 50V. 
     
     
         8 . The deposition apparatus of  claim 14 , wherein the accelerating electrode is biased in a range of −50V to −400V. 
     
     
         9 . The deposition apparatus of  claim 14 , wherein the diaphragm, neutralizer electrode, and accelerating electrode are sized to produce an ion flow with an area of at least 100 cm 2 . 
     
     
         10 . The apparatus of  claim 14 , wherein the neutralizer electrode and the accelerating electrode are biased to produce the ion flow with energy of ions that does not vary more than 10% across the area of the ion flow. 
     
     
         11 . The apparatus of claim  16 , wherein the support device is rotatable about an axis that is parallel to the ion flow axis at a rate of 10-30 rpm. 
     
     
         12 . The apparatus of claim  16 , including a plurality of support devices mounted to rotate about an axis that is transverse to the flow of ions to move the support devices sequentially into and out of the flow of ions. 
     
     
         13 . The apparatus of claim  20 , including one plurality of the support devices mounted together in a first gang on a first wheel and at least a second plurality of support devices mounted together in a second gang on a second wheel, wherein said wheels are mounted on respective first and second struts that extend radically outward from a shaft that defines said transverse axis, said struts being rotatable about the transverse axis to move the gangs sequentially into and out of the flow of ions. 
     
     
         14 . The apparatus of claim  21 , wherein each of the said struts has a longitudinal axis perpendicular to said transverse axis and said wheels are rotatable about the respective longitudinal axes of the respective struts on which said wheels are mounted. 
     
     
         15 . The apparatus of claim  22 , wherein each of the support devices in each of said gangs is mounted on one of said wheels in a manner that rotates each of the support devices on that wheel about an axis parallel to the longitudinal axis of the strut on which that wheel is mounted.