The Experimental Study On The Uniformity Of Low Gas Pressure Capacitively Coupled Plasma

Capacitive coupled plasma(CCP) generated at low gas pressure has been widely used in the semiconductor, biomedical, environmental treatment industries and so on. In semiconductor processing, improving plasma uniformity can increase the quality of the plasma processing and improve the yield. Therefore, much attention has been paid on improving the plasma uniformity.Currently, the study of electrode type and configuration on plasma uniformity are mainly focused on the theoretical research and numerical simulation. In this paper, the effect of electrode type and configuration on the plasma uniformity was studied by using Langmuir double probe. The main contents are as follows:Firstly, using Langmuir double probe, the effect of perforated electrode lighting-up issue on plasma distribution was studied. The results indicate: if the light up issue occurs, it significantly increase the electron temperature, electron density and electron energy density around the light up hole. As a result, plasma uniformity decreases. At the same time, the influence of the light up issue on photoresist etching rate and its uniformity were verified by using oxygen plasma to etch photoresist.Secondly, the effect of electrode type and configuration on the argon capacitively coupled plasma uniformity was studied. Electrode type and configuration includes electrode with blind holes, electrodes with phase difference(△φ=00 and △φ=1800) and fence type electrodes with different size. The results indicate: all of electrode with blind holes, electrodes with phase difference and fence type electrodes can avoid the light up issue and improve the plasma uniformity. Using electrode with blind holes, the uniformity of electron density improve from 85.6% to 93.7% at power 50 W and from 63.6% to 84.6% at power 300 W, respectively. The uniformity of electron density for the electrodes with phase difference can reach to over 90% at power 50 W and 80% at power 300 W, respectively. The uniformity of fence type electrodes and electrode density are relevant with the light-avoiding fence width b and the light-transmitting fence width a. The best electron density uniformity will be 92.6% for a*b=1.0*0.5inch fence electrode at the power 50 W.Finally, the effect of electrode type and configuration on the plasma uniformity was studied by the experiment of oxygen etching photoresist. The results indicate: the photoresist etching uniformity was improved by using electrode with blind holes, electrodes with phase difference and a*b=1.0*0.5inch fence type electrodes. For electrode with blind holes, the etching uniformity of photoresist improves from 64% to 87% for that the samples are placed on the electrode surface, improves from 72 % to 91% for that the samples are placed in the middle of electrodes, respectively. For electrodes with opposite phase difference, the etching rate and uniformity of photoresist were 103nm/min and 86% for that the samples are placed on the electrode surface, and the etching rate and uniformity of photoresist were 92nm/min and 88% for that the samples are placed in the middle of electrodes, respectively. For a*b=1.0*0.5inch fence type electrodes, the etching rate and uniformity of photoresist were 104nm/min and 89% for that the samples are placed on the electrode surface, and the etching rate and uniformity of photoresist were 98nm/min and 93 % for that the samples are placed in the middle of electrodes, respectively.