Probe Diagnosis Of Electron Space Characteristics In SiCl₄/H₂ Plasma During Polycrystalline Silicon Film Deposition

Plasma enhanced chemical vapor deposition (PECVD) technique transfers energy from electrons to neutral radicals. Compared to conventional chemical vapor deposition, the advantage of PECVD is its lower deposition temperature, higher deposition rate and higher quality of films. PECVD technique has been widely used for crystalline silicon films and many kinds of alloys (such as a-Si:H, Si₃N₄). It is being investigated as a potential technique for the deposition of thin films for microelectronics. However, the spatial nonuniformity of plasma results in the nonuniformity in the thickness of thin films. This has been hampered PECVD technique further developments and applications. In order to deposit high quality and uniform thin films, it is necessary that we study the plasma characteristics in PECVD system, especially the spatial distribution of electron characteristics.With the development of discharge technique, there are many improvements on Langmuir probe, such as tuned filtration, mitigation of radio frequency interference and contamination of the probe, etc. So Langmuir probe measurements have become a powerful and important means for determining key internal discharge parameters. Up to now, the spatial distributions of plasma characteristics have rarely been studied experimentally by Langmuir probe.In this paper, we propose and establish a movable probe. It is noted that the probe can be moved along the axial direction from the bottom (powered) electrode to the upper (grounded) electrode. Making use of it, we measured the axial distribution of the electron density and the mean electron density. The radial distribution of electron characteristics was obtained by changing the probe length in the direction parallel to the electrodes.For the stability of chemistry property and the simplicity of atom structure, we diagnose argon plasma by means of Langmuir probe at first. The effects of RF power and gas pressure on electron characteristics, especially the spatial distributions of electron characteristics have been studied. It is noted that we propose a model to simulate the radial distribution of the electron density according to ambipolar diffusion theory. The experimental result agrees well with the measured one. This is useful for us to settle the problem of film uniformity.Using the movable Langmuir probe, we have measured the electron characteristics and the radial distribution of them in SiCl₄/H₂ plasma during the polycrystalline silicon films deposition.