Research On Distribution Of Residual Stress On Silicon Wafer Machined By Rotational Grinding

Mono-crystalline silicon is an essential material in the integrated circuit (IC) industry. Along with the rapid development of digital and information technology and updating of electronic devices and intelligent products, the demand for wafer and chip thinning is rising higher. Rotational grinding is widely accepted among the contemporary thinning methods because of its advantage of high precision and efficiency. However, damage along with residual stress will be induced due to the mechanical effect of grits on the grinding wheel, which will bring about harmful effects to the wafers in process and the chips in products. The former researches usually focus on solving Stoney equation to get the average stress on the whole wafer. But the intrinsic characteristics of rotational grinding and the material properties of mono-crystalline silicon will lead to the variation of residual stress at different locations on wafer. This paper proposed a new method of inversion of residual stress based on load identification method in order to reveal the regulations and factors affecting the residual stress distribution. The method is verified at all aspects and applied to research on the regulation of residual stress distribution in wafers ground by different grit size and spark-out time, trying to discuss the factors affecting residual stress from various ways. The contents of research in this paper are listed as follows:(1) A new method of inversion based on load identification method is proposed, and the modeling and solving approach in the commercial FEA software ANSYS is realized. It is verified that the modeling and solving approach agrees well with the Stoney equation, while the accuracy of the optimization process in this approach is guaranteed. As a result, it is suitable for calculating the stress in the surface layer of silicon wafer.(2) The research on the distribution of residual stress on wafer ground by#3000 diamond wheel shows that the ratio of two principal stresses on parts of the wafer reaches 3:2, and their direction consists well with the grinding mark. There are no differences between the magnitude of principal stresses at different locations. However, the variation of deformation on different crystal orientations is observed due to the difference of elastic modulus.(3) The spark-out time during the rotational grinding and its influence on the average stress and stress distribution is analyzed. A conclusion is drawn that the spark-out time has no profound influence on average stress or stress distribution of wafer ground by fine diamond wheel; However, for wafers ground by#600 diamond wheel, no spark-out time will lead to the increase of stress from the center to the edge of wafer. Further research on TEM microscopy shows that the difference between different directions on a certain chip is mainly caused by the difficulty of sliding of different<110> planes. The difficulty of sliding of a certain plane depends on the grinding direction, which will eventually generate the two principal stress with different magnitudes, and parallel to and perpendicular to grinding marks, respectively.