Cathode Sputtering — A Commercial Application* 



By HAL F. FRUTH 



The theory of cathode sputtering with the advantages and limitations in 

 the application of this process is discussed, followed by a description of the 

 commercial equipment and methods for applying gold electrode surfaces 

 to diaphragms of certain types of microphones. 



By proper design of the vacuum chamber and the inside parts, a fairly 

 uniform discharge current density and a uniform deposit is obtained. A 

 constant sputtering rate is produced by the use of a bleeder valve which 

 maintains a proper residual pressure. Adherence and continuity are ob- 

 tained by the use of a special cleaning process. 



An extensive bibliography on cathode sputtering is included. 



Introduction 



ALTHOUGH the process of electrostatic deposition of metals by 

 high voltages in a partial vacuum, commonly known as cathode 

 sputtering, has been known for more than a half century, it has hereto- 

 fore found but little commercial application. Rather extensive use of 

 it has, however, been made in physics research laboratories for such 

 purposes as the production of highly reflecting surfaces on mirrors and 

 prisms, for spectrometers, interferometers, etc., and the making of 

 extremely thin metal films for fundamental studies in atomic structure 

 and electron theory. Sputtering has also been used in the manufac- 

 ture of very fine conducting quartz fibres for suspensions in sensitive 

 instruments such as quadrant and string electrometers, galvanometers, 

 and electrocardiographs, and, to some extent, for etching certain 

 metals. 



In the following paragraphs it is intended to give a brief explanation 

 of the process and a description of a commercial application in the 

 production of diaphragms for certain microphones. 



« 

 Theory 



Some fifty years ago, various investigators working on high voltage 

 discharges in vacuo discovered that disintegration of the cathode oc- 

 curs for nearly all metals and that the removed metal is deposited in a 

 very fine state of subdivision on nearby objects. Various theories have 

 been formulated as to the mechanism of this phenomenon. Some 

 investigators have attempted to explain it by stating that it is a type of 

 electrical evaporation where the electrical potential is analogous to the 

 temperature potential in ordinary thermal evaporation. More plaus- 

 ible theories, recently advanced, are that the metal atoms or particles 



* Physics, April, 1932. 



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