Dependence of etch rates of silicon substrates on the use of C4F8 and C4F6 plasmas in the deposition step of the Bosch process

Abstract

The Bosch process was carried out using SF6∕C4F8 or SF6∕C4F6 plasmas during the etching/deposition steps to examine the etch profiles and etch rates of silicon. The fluorocarbon film deposited in a C4F6 plasma was thicker and more strongly bonded than the film deposited in a C4F8 plasma, which led to a shorter deposition time for the C4F6 plasma. The deposition rate of the fluorocarbon films on the different locations of the silicon substrate in both C4F8 and C4F6 plasmas decreased in the following order: top>bottom>sidewall. However, the normalized deposition rate of the bottom surface with respect to the top surface was higher for the C4F8 plasma (0.92) than for the C4F6 plasma (0.65), indicating that a thicker fluorocarbon film was deposited at the bottom of the pattern in C4F8 plasma under the same process conditions. This resulted in a higher etch rate of the silicon substrate using C4F6 plasma during the deposition step of the Bosch process, even though a fluorocarbon film with a similar thickness had been deposited on the top surface for both C4F8 and C4F6 plasmas.