US 3661758 A
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y 1972 w. H. JACKSON ETAL 3,661,758
RI" SIUTTERINU SYSTEM WITH THE ANODE ENCLOSING THE TARGET Filed June 26, 1970 I J o o 0 0 o o o u J i 44 l A l l I A Q T 22 7 1 l k u H a JW\A Figure 1 INVENTORS WELDON H. JACKSON BILLIE J. ROBISON g Fiure 2 (Sect. A-A) United States Patent O US. Cl. 204298 1 Claim ABSTRACT OF THE DISCLOSURE The plasma in an RF sputtering system is confined to the region between the anode and target by enclosing the target with the anode. The anode is in two parts which are connected electrically through sliding contacts that allow removal of one of the parts for access to the interior region of the anode.
BACKGROUND AND SUMMARY OF THE INVENTION In RF sputtering systems constructed according to the prior art the anode was usually a metal plate parallel to and larger than the target or cathode, and it sometimes included the parts of the vacuum chamber that were made of metal. The anode was connected to the RF power source through a flexible metal cable or through the metal parts of the vacuum system. This type of current path was usually highly resistive and inductive with respect to the RF source impedance, thus reducing system efficiency. In addition, plasmas would often form in areas of the vacuum system substantially removed from the anode and cathode, eroding parts of the system and causing impurities to be introduced into the system. Since an RF sputtering system is usually used to deposit thin layers of high purity materials on objects such as thin film circuit substrates, any impurities in the system will degrade or destroy the quality of the articles being processed.
Accordingly, it is an object of this invention to provide a sputtering system which minimizes the amount of impurities deposited on an article to be coated by confining the gas discharge plasma to the space between the anode and target.
It is a further object of this invention to provide a fixed and high conductivity return path for the RF currents originating at the target.
It is a still further object of this invention to provide an anode structure which will allow quick and easy access to the interior region of the anode where the articles to be coated are located.
DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view of the preferred embodiment.
FIG. 2 is a plan view of the preferred embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1 and 2 show a vacuum chamber comprised of a cylindrical wall 12, a top cover 14 and a base 16. A vacuum port 18 is attached to base 16 and a vacuum pump (not shown) is attached to vacuum port 18 for evacuating the air from chamber 10. A gas inlet 20 is attached to base 16 to supply small amounts of inert gas, usually argon, to chamber 10 to maintain a given gas pressure. An anode 22 is fastened to base 16 and a target 24 is mounted in and insulated from top cover 14 by an insulator 26. Target 24 is connected to an 'RF power source 28 through an impedance matching network 30 and the center conductor 32 of a coaxial cable 34. The outer or return conductor 36 of coaxial cable 34 is connected to top cover 14. A perforated enclosure 38 is fastened to top cover 14. Spring contacts 40, fastened to anode 22, make contact with enclosure 38 to electrically connect it to anode 22. Since top cover 14, enclosure 38, spring contacts 40, and anode 22 are all metal and are all in contact as previously described, they form an anode structure 46 which completely encloses cathode 24. Spring contacts 40 are used to connect enclosure 38 to anode 22 because top cover 14 is lifted off base 16 to remove or insert articles 44. Spring contacts 40 slide on the inner surface of enclosure 38 to permit vertical movement of enclosure 38 while maintaining electrical contact with it.
The principles of cathodic sputtering are well known (see, for example, Thin Film Technology, Berry, Hall, & Harris, D. Van Nostrand Co., Princeton, N.J., 1968) and will therefore not be described in detail here. When RF power from RF source 28 is applied across target 24 and anode 22 the gas in the space 42 between them ionizes and forms a plasma. The positive ions in the plasma knock bits of the target 24 material off and they are deposited on articles 44 beneath the target (thin film substrates, for example) forming a thin film coating. Anode structure 46 keeps the plasma confined to the immediate vicinity of the space 42 between anode 22 and target 24. If a plasma is allowed to form in other areas of vacuum chamber 10, the plasma will often erode parts of the chamber and thus introduce impurities which will be drawn into the space 42 and deposited on article 44. Since RF energy is being dissipated to ionize the gas, an RF curent is Howing between the target 24 and anode 22, and it is therefore necessary to provide a good RF current path between anode 22 and RF power source 28. Anode structure 46 provides the RF current path through spring contacts 40, enclosure 38 and top cover 14 to outer conductor 36 of coaxial cable 34 which connects to the RF power source 28. Such a current path has a very low and fixed resistance and inductance compared with the impedance of the plasma. The system is entirely suitable for DC sputtering as well as RF sputtering.
1. An RF sputtering system comprising:
an anode having first and second parts enclosing the target, the first and second parts being separable for access to the tar-get and the first part being perforated;
flexible electrical contact means attached to one of the first and second anode parts for making electrical contact between the first and second anode parts;
a gastight enclosure having first and second parts enclosing the anode and target, the first and second parts of the anode being attached respectively to the first and second parts of the gastight enclosure and 4 thefirst and second parts of the gastight enclosure References Cited bemggeparablet; hin twork conn cted to the anode UNITED STATES PATENTS gfz f gf zg? c g 6 3,391,071 7/1968 Theuerer 204-298 3,471,396 10/1969 Davidse 204298 a g gg f g g g gfggg cmnected the 5 3,516,919 6/1970 Gaydou et a1. 204298 a vacuum pumping system connected to the gastight enclosure for evacuating air therefrom; and JOHN MACK Primary Exammer a source of gas connected to the gastight enclosure for KANTER, Assistant EXaIIlillel maintaining a given gas pressure therein. 10