Polymer film formation in low-pressure RF discharge

Abstract

Summary form only given, as follows. As is known, when a discharge is burning in technology-relevant gases (CF/sub 4/, CCl/sub 4/, SF/sub 6/) a polymer film is deposited on electrodes, substrates and walls of the discharge vessel, that exerts a negative influence on plasma etching processing of semiconductor materials. A polymer film appearing on a substrate under processing can decrease strongly the etching rate of semiconductor material or even terminate the technological process. This report clarifies the conditions under which the polymer films are formed as well as their physical and chemical properties. We also study the influence of the growing polymer film on RF discharge characteristics. The experiments have been performed in the above mentioned gases with gas pressures in the interval p=0.01-10 Torr, RF voltages U<1000 V, RF frequency f=13.56 MHz and the gap between plane parallel stainless steel electrodes of 100 mm in diameter L=7-55 mm. We have observed that polymer films are deposited at pressures below or order of the pressure, corresponding to the minimum of the RF breakdown curve. These polymer films are dielectric coatings resistant to acids, soluble in alkali. On increasing the thickness of the polymer film the RF conductance current increases and achieves a plateau in 20-30 minutes after the switching on the discharge. The plasma density achieves a plateau already in 5-6 minutes of the discharge burning. We have observed that the growth rate of the polymer films is proportional to the discharge burning time and to value of the RF voltage applied.