Research On Measurement And Characterization Method Of Nano-scale Semiconductor Line Edge Roughness

With the rapid development of semiconductor integrated circuit (IC) manufacturing, the line width of chip has been shrinked into sub-100nm as the critical dimension of process technologies. The more and more stringent control request on the nano-scale dimension of line structure makes the measurement and control of line edge roughness (LER) to be one of the serious issues in the field of lithography processes and IC industry. Atomic force microscopy (AFM) has become an important technique for its good 3D imaging capability, its insensitivity to sample materials, and its capability for working at ambient conditions. Aimed on some problems existing in LER measurement using AFM, this paper studied nano-scale LER measurement and charactrization method.Because there is no unambiguous definition of LER acceptable for the research field at present, the measurement results can not be compared effectively, which is not be propitious to monitoring and optimization of lithographical process technologies, establishing and testing the device performance simulation model as well as controlling and improving the precision of line width measurement. For the purpose of resolving this problem, in this paper based on the demand analysis of three aspects such as the semiconductor manufacturing technologies and LER formation, the impact on the linewidth measurement and electric performance of device, a new LER definition is proposed from the perspective of measure. Additionally combined with the intrinsical characteristics and application request of LER, the specific characterization parameters, including the amplitude parameters root mean square roughness value (RMS), spectral analysis parameter power spectral density (PSD) and spatial evaluation parameter autocorrelation function R(τ), are also provided.According to the proposed LER definition and considering the feature of AFM scanning image, a reasonable measurement model of LER is established. The main task of the model contains the determination of line edge location and evaluation benchmark in order to extract the LER feature. Firstly the edge detection method based on image processing technique is studied. In this method the sidewall topography and its location information are considered synthetically, and the line edge within the local height range is determined by the edge detection operator and height threshold value. Considering there exist the artificial chosen parameters in this method, which have an influence on LER measurement results. So the edge detection method based on essential points is presented. In this method 6 essential points are determined at each scan line profile using the change rate of adjacent data points, and thus the line edge points of different height region composed of essential points of all scan lines can be obtained. Each single line edge is fitted by a least squares line as the evaluation benchmark to extract the LER feature, and the characterization parameters are calculated, including the RMS value of left and right single line edge and line width roughnessσL,σR andσLWR, and the correlation length LcL and LcR. The AFM measurement data of the same sample is processed by these two methods, and analysis and comparison of measurement result are made.Aimed at the existing LER characterization parameters can not completely satisfy the measure requests, the multi-scale characterization method of LER based on redundant second generation wavelet transform (RSGWT) is proposed. The LER feature is decomposed into the separate spatial frequency range which contains different spatial frequency components, then the resconstructed signals at the different scale are analyzed furthermore, accordingly determining the roughness exponent R, the spectral property and RMS value of reconstructed signal at each scale, moreover the influence of high frequency noise is evaluated by means of the detail signal at the smallest scale.The LER multi-scale characterization method is testified using the random profile simulation data. The results show that for the line edge with approximately amplitude, the roughness exponent R can reflect the irregularity of line edge effectively, and provide the intuitionistic information of LER spatial frequency distribution. The results of experimental data of single crystal silicon show that LER multi-scale characterization method can effectively analyze high frequency LER which have greater effect on the IC device performance, and quantatively characterize the LER amplitude in the spectific spatial frequency range, accordingly provide the more perfect measurement base for the monitoring and optimizing the semiconductor manufacturing technologies.Based on the feature of AFM scanning mode and imaging, the influence factors of LER measurement by AFM are studied. The theortical and experimental analysis of the influence of various factors on LER measurement, including the size and shape of probe tips, the signal noises of AFM scanning images, the driving precision of piezo crystal, scan and sampling interval and so on. The error sources of nano-scale LER measurement and their effect degree are analyzed, and the methods for restraining and amending the errors are resepectively proposed to reducing the measurement error and improving the reliability of measure result.