Ellipsometry measurement of the complex refractive index and thickness of polysilicon thin films

A scheme to measure precisely the complex refractive index, N - iK, and the thickness of polycrystalline silicon (poly-Si) film is proposed and demonstrated. The measurement is made by scanning the ellipsometer light beam along a beveled surface of the poly-Si film and by adopting a zero-layer model to derive the N_se - T plot, where N_se is the equivalent real refractive index and T is the thickness of the measured poly-Si film. The complex refractive index, N - iK, is obtained from the N_se - T plot, and the thickness is computed from the ellipsometry equation. Error analyses have been done on both the conventional ellipsometry method and the proposed method, and results show that the proposed method has more than an order-of-magnitude improvement in accuracy compared with the conventional method. Experimental results of applying this method to measure the complex refractive index of poly-Si films prepared at different processing conditions are also shown.