以甲烷/氨氣和乙炔/氨氣混合物研製n型非晶質 射頻電漿輔助化學汽相沉積碳薄膜

Abstract

This study investigates the effect of ammonia/methane (NH3/CH4) and ammonia/acetylene (NH3/C2H2) mixtures on characteristics of nitrogen-doped amorphous hydrogenated carbon (a-C:H(N)) films prepared by plasma enhanced chemical vapor deposition. As the NH3/CH4 ratio increases from 0 to 0.2, the nitrogen/carbon ratio increases from 0 to 5.4%. The nitrogen-carbon bonds, nitrogen-hydrogen bonds, and sp2 carbon fraction of carbon films enlarge with increasing the NH3/CH4 ratio, while the deposition rate, ordered degree, optical band gap, reduced Young’s modulus, hardness, and residual stress of carbon films decrease. The a-C:H(N)/p-Si device has an optimum electrical property at the NH3/CH4 ratio of 0.15 (or at the N/C ratio of 4.7%). On the other hand, as the NH3/C2H2 ratio increases from 0 to 1.4, the nitrogen/carbon ratio increases from 0 to 6.9%. The nitrogen-carbon bonds and sp2 carbon fraction of carbon films enlarge with increasing the NH3/C2H2 ratio, while the ordered degree, Young’s modulus, and hardness of carbon films decrease. Furthermore, the a-C:H(N)/p-Si device has an optimal electrical property at the NH3/C2H2 ratio of 1 (or at the N/C ratio of 5.8%), which has an ideality factor of 1.59. Additionally, this study also investigates the residual stresses in thin films/substrate systems using viscoelastic theory. First, a simplified closed-form solution for viscoelastic deformation of multilayers due to residual stresses is derived. If the ratio of the total axial rigidity of thin films to that of the substrate is smaller than 0.02, the formulas of this study are valid to evaluate the relaxation of residual stresses in multi-layered thin films/substrate systems. The magnitude of stresses in the substrate and fims increases with increasing the difference of the thin film and substrate thermal expansion coefficients, the temperature change, and Young’s modulus and viscous coefficient of thin films, but it decreases with increasing the time. Second, the exact solution of viscoelastic stresses in the bilayer system is derived if both layers are Maxwell materials. As the thickness of one layer is much smaller than that of the other layer, the viscoelastic stress in the bilayer system can be reduced to that of the thin film/substrate system. The relative film thickness and the position in the thin film/ substrate system are included in this solution. The analytic result shows that the average film stress decreases with increasing the normalized time and finally equals zero in a long time. This exact solution can be used to evaluate the accurary of other approximate solutions.