Probing Process-Induced Defects in Si Using Infrared Photoelastic Stress Measurement Technique
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Probing Process-Induced Defects in Si Using Infrared Photoelastic Stress Measurement Technique X.H. Liu1,3, S.P. Wong1,3#, H.J. Peng1, N. Ke1,3, Shounan Zhao2 1
Department of Electronic Engineering, The Chinese University of Hong Kong, Hong Kong, China 2 Department of Applied Physics, South China University of Technology, Guangzhou, China 3 Materials Science and Technology Research Centre, The Chinese University of Hong Kong, Hong Kong, China Abstract The stress depth distribution in the silicon substrate under thin thermal oxide layers has been measured using the photoelastic technique. With the high sensitivity and improved spatial resolution of a newly developed low level birefringence detection system, it is confirmed that the stress distribution deviates significantly from the linear distribution predicted by classical bi-metallic strip theory. The deviation can be attributed to arising from Si self-interstitial injection during the thermal oxidation process. Long term changes in the stress distribution with time have also been observed and the changes can be understood in terms of point defect movements under the stress field in the substrate. Our preliminary results have demonstrated how we can probe microscopic point defect processes in thin film SiO2/Si substrate systems using a macroscopic photoelastic stress measurement technique. INTRODUCTION It is well known that many common semiconductor fabrication processes such as oxidation, implantation and diffusion will introduce stresses and produce extra defects in the semiconductor. In most cases the process-induced defects are inhomogeneously distributed resulting in an additional non-linear stress filed in the semiconductor. Obviously it is highly desirable to understand the relationship between these process-induced defects and stresses as they are highly related to the device performance and reliability. However, there has been only very limited progress made in this aspect due to the difficulty to measure these processinduced stress field inside the structure. In the past decade, the infrared (IR) photoelasticity (PE) method has been used increasingly to study the stress problem in semiconductors [1-7]. The PE technique is attractive because it is nondestructive, rapid, low cost and capable of wafer-scale visualization of stress field. Recently, we have developed a high sensitivity stress measurement technique based on the infrared photoelastic method using a low level birefringence detection (LLBD) system [8] and applied it to study the stress distribution in the Si substrate under thin oxide layers [9]. In this work, we shall further show how useful information about oxidation-induced defects can be obtained by measuring the stress distribution in the Si substrate using the PE method. EXPERIMENTAL DETAILS The details about the basic principle of the PE method, the LLBD system, and the experimental arrangements for applying the LLBD system to measure the stress distribution in the Si substrate have been given in references [1], [8], and [9], re
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