Precision Fabrication of Thin Copper Substrate by Double-sided Lapping and Chemical Mechanical Polishing

Thin copper substrates with high flatness and surface integrity are highly required in precision physical experiments. Normally, fly cutting is used to fabricate the substrates. However, the flatness is difficult to be guaranteed after disassembly due to the clamping and machining stresses which are induced on the substrates. Besides, the surface integrity is hard to be improved because of the severe subsurface deformation and high residual stress. To solve the problem, a new process chain composed by double-sided lapping and chemical mechanical polishing (CMP) is proposed to acquire both high flatness and surface integrity on thin copper substrates. In the new process chain, double-sided lapping is employed to achieve high flatness and uniform distribution of surface residual stress, while double-sided CMP is adopted to obtain the ultra-smooth surface without damage and maintain the flatness. The results show that flatness superior to 4 mu m peak-to-valley (PV), and surface roughness less than 3 nm Ra are obtained. Moreover, both surfaces are damage-free with low surface residual stresses.