Comparative and integrative study of Langmuir probe and optical emission spectroscopy in a variable magnetic field electron cyclotron resonance chemical vapor deposition process used for depositing hydrogenated amorphous silicon thin films

摘要

An electron cyclotron resonance chemical vapor deposition (ECR-CVD) system applied in a hydrogenated amorphous silicon (a-Si:H) thin-film deposition process was diagnosed in-situ by using optical emission spectroscopy (OES) and a Langmuir probe. The optical actinometry technique was used to obtain the ratio of species concentration to the concentration of a trace gas (Ar). The electron temperature (T_e~(oes)) was estimated according to the spectrum intensity ratio of H_β to Ha or that of Si~* to SiH~*. and the two estimation approaches were evaluated by comparing the results (T_e~(LP)) of Langmuir probe measurement. The probe surface contaminants (a-Si:H) produced during in-situ measurement created errors in the measurement of parameters such as the electron temperature and density (N_e). The results indicated that, when a-Si:H was coated on the probe at thicknesses less than 150 nm, the errors were negligible. OES and Langmuir probe measurement were integrated and used to determine the dependence of the processing pressure and resonance magnetic field configuration on the properties of an a-Si:H film grown using ECR-CVD. When the process pressure was increased, the N_e, T_e~(oes) and T_e~(LP) decreased; moreover, the Fourier-transform infrared spectroscopy results indicated that structure factor (R~*) increased, and both the photosensitivity and hydrogen content (C_H) decreased. An analysis conducted using OES and Langmuir probe measurement revealed, that the decreased concentration of the H radical reduced the passivation effect, and surface diffusion decreased. Furthermore, the gas partial pressure exerted a substantial influence on OES measurement. The volatility of the Ar spectrum intensity equaled the product of the volatility of N_e and T_e~(LP) when the partial pressure effect is eliminated. Regarding the resonance magnetic field, the effects of plasma resonance position on film characteristics were substantial. The N_e decreased greatly when the distance between quartz and the resonance zone was increased.