3D free forms in c-Si via grayscale lithography and RIE

Abstract

A grayscale technology process for structuring of true 3D shapes into crystalline silicon (c-Si) has been developed. The process combines maskless grayscale lithography and an optimized RIE process. To achieve a 1:1 transfer of the 3D photoresist patterns into c-Si, the RIE process was optimized for a selectivity of S=1 and an anisotropy Af close to one. Suitable process conditions of the RIE process are defined by SF6 flowrate of 3sccm, CHF3 flowrate of 35sccm, a RF power of 100W, a temperature of 10°C and a pressure of 10mTorr. The 3D pattern transfer is demonstrated at special test structures as well as at real 3D structures such as pyramids. The developed process allows a direct transfer from 3D CAD data via maskless grayscale lithography using Heidelberg Instrument DWL66FS to c-Si 3D structures. The pattern transfer accuracy is about 5% in respect to the 3D CAD data.