Design of Digital Filters for Si Wafer Surface Profile Measurement – Noise Reduction by Lifting Scheme Wavelet Transform
Recently in semiconductor industry, production of ever flatter, thinner and larger silicon wafers are required to fulfill the demands of high-density packaging and cost reduction. In geometric evaluation of Si wafers, according to SEMI (Semiconductor Equipment and Materials International) standards, the required wafer flatness approaches to the 22 nanometers by year 2016 . For such application, uncertainty of measured data is encountered as a severe problem because the requirement has met the limit of available instrument in terms of resolution and reliability. In order to precisely evaluate the wafer profile, it is essential to remove the noise from the measured data. Described in this paper is design and development of digital filters for denoising. In previous paper, digital filters for denoising with Haar wavelet transform are described. In this paper, the new filters by use of 2nd generation wavelet transform (lifting scheme) are proposed and show better performance of decomposition in the spatial frequency domain and amplitude domain.
Yunn-Shiuan Liao, Chao-Chang A. Chen, Choung-Lii Chao and Pei-Lum Tso
K. Nonomura et al., "Design of Digital Filters for Si Wafer Surface Profile Measurement – Noise Reduction by Lifting Scheme Wavelet Transform", Advanced Materials Research, Vols. 126-128, pp. 732-737, 2010