Probe Study Of Space Characteristics Of Plasma In Radio Frequency Glow Discharge

Plasmas are widely used in the preparation of semiconductor film materials and microelectronic industry. The understanding and diagnosis of plasmas in different conditions is the prerequisite of heifer control of plasma film deposition and plasma etching. Langmuir Probe is one of the earliest and the most important methods of diagnosing the plasma characteristics. This diagnostic technique, after improved in many aspects such as tuned filtration, mitigation of radio frequency interference and contamination of the probe, etc, from the time it appeared till now, has become a quite a effective way of studying the plasmas. However, there are few cases in which the space characteristics of plasma are studied using Langmuir electro-static probe directly, and, no papers reported about it yet in the PECVD system up to now. In this paper, using the tuned, position-mobile probe to measure the I-V characteristic curves of the probe in radio frequency (RF) glow discharge in different axial positions between two electrodes, and obtain the important plasma characteristics parameters, such as the plasma potential, the electron energy distribution function, the electron mean energy and the electron density, etc, which are important for the study of the discharge mechanism of plasma and the deposition mechanism of thin-films. In digital process method of the I-V characteristic curves of the probe, we carry out the smooth treatment of the curves and obtain the second derivatives of the curves, using the ready-made software ORIGIN5.O. This is a simple and effective method. The results obtained by this method have less dependence on the parameters chosen, compared with the newly reported methods such as the Hayden method and the Fourier transform method, etc. We study the axial distribution of the plasma characteristics versus the input power. As for plasma potential distribution, we find it much similar to that of the direct current (DC) glow discharge. We account it for the self-bias effect of the powered electrode of the RF glow discharge. We find that, with increasing the input power, the space distribution of the electron density in plasma changes from the symmetrical distribution, i.e. high in intermediate region and low on both sides of the plasma, to the directional ones, i.e. decreasing with position from the powered electrode to the grounded electrode. Analyzed on the internal ionization and energy gain mechanism of plasma, we suggest that, with increasing the input power, the ion bombardment to the electrode and the y -electron emission effect of the electrode strengthen , which leads to the transition of electron heating modes. This is the responsibility for the above changes of electron density. The electron temperature increases with increasing in the distance from the powered electrode. The space gradient of the electron temperature decreases with the increase of the input power. At the same position, the electron temperature decreases with increasing the input power. The variation of the electron temperature is closely related to that of the plasma potential and the electron density.