Audio-frequency glow discharge for plasma chemical vapor deposition from organic compounds of the carbon family

An audio-frequency (af) (10–100 kHz) glow discharge has been used for plasma chemical vapor deposition of thin films from organic compounds of the carbon family. It has been realized employing a recently designed reactor, equipped with three electrodes—a small electrode on which films are deposited, and two main electrodes sustaining a glow discharge. The small electrode and one main electrode are connected by a variable capacitance $C.$ It has been found that small changes of $C$ can cause a drastic change in the electronic properties of deposited films. This effect, attributed to a transition between the amorphous insulator $(a-I)$ and amorphous semiconductor $(a-S),$ is discussed for hydrogenated carbon–silicon, carbon–germanium, carbon–tin, and carbon–lead films produced from adequate organometallic compounds. To better understand the deposition process in the reactor, the electrical characteristics of model argon plasma have been investigated by means of a Langmuir single probe movable in the space between the reactor electrodes. Both af potentials of the plasma and typical current–voltage characteristics have been measured. It has been found that energetic conditions of the plasma, and consequently, the plasma chemistry, are independent of $C.$ Changes of $C$ have, however, influence on the ion bombardment process taking place in the vicinity of the small electrode. The ion impact energy $Emax$ has been roughly estimated and a relation $Emax∝ln C$ is found. The calculated values of $Emax,$ which change from almost zero to several tens of electron volts, are in a good agreement with results of an experiment performed in the reactor with argon sputter etching of a gold film.