The Diagnosis Of Linearly Coaxially Coupled Microwave Plasma And The Preparation Of Silicon Thin Films

A plasma source has been a research hot-spot for large area, stability and controllability and widely used in solar cells industry and for semiconductor film materials fabrication, therefore a large area plasma source was designed-linearly coaxially coupled microwave plasma source. Electron density and electron temperature of plasma are the two key physical parameters of plasma diagnose, and they have a great influence on quality of the thin films. In this paper, electron density and electron temperature of the linearly coaxially coupled microwave plasma were diagnosed by the Langmuir single probe. Then, according to the plasma diagnosis, silicon thin films were deposited. The conclusions were as follows.(1) The electron density values are relatively high in the area near quartz tube of the horizontal plane that the distance is15cm from the quartz tube distance, while the electron density values are much lower in the middle area of chamber. On the whole, the electron density distributions are roughly axisymmetric distributed along the center line of the two quartz tube and the electronic temperature distribution are uniform. As the microwave power increased from400W to1200W, the electron density values increased from2.5E+8cm’3to1E+8cm"3and the uniformity of electron density distributions in the middle area are improving slowly and then gradually become worse; The electronic temperature values reduce from25eV to4eV. When the total flow of hydrogen and argon is60sccm, as reducing hydrogen flow and increasing argon flow, the electron density values showed a trend of decreasing at first and then increasing. The change of electronic temperature is not big and the range is3eV～8eV.(2) As the microwave power decreased from1200W to400W and Ds increased from9cm to15cm, the electron density values reduced from1.8E+10cm-3to2E+8cm-3and electron temperature values increased from2.5eV to45eV in Z direction and along the X axis direction.(3) According to uniform area of the electron density distributions, the silicon thin films were deposited in the site of (0,0),(3,0),(9,0) and (0,4) when hydrogen flow is60sccm and argon gas flow is20sccm. The deposition rates of silicon thin films are about8nm/min. Raman spectra results shows that the crystallinity of films is above97.07%. XRD shows that silicon thin film samples have three diffraction peaks of (111),(220) and (311).The grain size is about20nm. (4) The silicon thin films were deposited by orthogonal experiment method the experiment analysis was by using poor method of orthogonal experiment.Raman results show the crystallinitys of films are above95%. XRD shows that silicon thin film samples are polycrystalline silicon thin films. The analysis results of poor method shows that substrate temperature of three factors has the greatest influence on the grain size, while the influence of flow ratio of hydrogen and argon is minimal on the thin film.