Effects of wheel spindle vibration on surface formation in wafer self-rotational grinding process

Abstract

As a universal machining method, wafer self-rotational grinding is applied to obtain a planar surface with high processing accuracy. However, the wheel spindle vibration significantly deteriorates the wafer flatness but is rarely studied. This paper primarily focuses on the impacts caused by wheel spindle vibration on the surface topography of ground wafer. Firstly, a mathematical model is proposed to analyze the dynamic behaviors of wheel spindle, involving radial, axial and tilting movements. The dynamic response and frequency characteristics of vibration-induced errors are presented. Then, a surface formation model is developed, taking grinding kinematics, grain size randomness, vibration-induced error and overlapping effect into account. Two kinds of patterns, i.e., waviness along circumferential direction and waviness along mark direction, are observed from the simulated wafer surface. Moreover, their wavelengths are calculated to explore the effect of grinding parameters and vibration frequency on waviness features. Finally, grinding tests are performed under different machining conditions, as well as the spindle vibration signal and wafer topography are measured. The obtained waviness characteristics are consistent well with those in simulation. In addition, the variation of surface roughness under different vibration parameters is further revealed. This work is expected to provide new insight into the machined error prediction and wafer flatness improvement considering the dynamic performance of wheel spindle.