Sculpturing of single crystal silicon microstructures by elliptical vibration cutting

Abstract

Single crystal silicon is necessarily subjected to mechanical precision machining to fulfill its applications in semiconductor and optoelectronics industries. However, brittle defects are inevitably formed on machined surface of intrinsically single crystal silicon. Thus, achieving ductile material removal is critical to obtain ultra-smooth machined surface of single crystal silicon. In the present work, we investigate the feasibility of ductile ultra-precision machining of single crystal silicon by applying the elliptical vibration diamond cutting technology. Grooving experiments demonstrate that silicon micro groove can be successfully formed in ductile mode by employing the elliptical vibration cutting, in contrast to the ordinary cutting that causes serious deterioration of finished surface due to formation of brittle defects. Furthermore, the nominal critical depth of cut for the brittle to ductile transition in the elliptical vibration cutting of single crystal silicon is more than 12 times higher than that in the ordinary cutting. It is found that the extremely small instantaneous uncut chip thickness and small cutting forces in the elliptical vibration cutting are advantageous to suppress crack propagations. Moreover, it is found that the vibration amplitude in the depth of cut direction has a prominent influence on both the nominal critical depth of cut and the machined surface quality. Finally, based on the gained fundamental understanding of brittle to ductile transition mechanisms, two types of high precision silicon microstructures, as sinusoidal grid surface and independent dimple patterns, respectively, are successfully sculptured on single crystal silicon by applying the amplitude-controlled ductile mode sculpturing method with arbitrarily changed depth of cut.