Dependence of etch rates of silicon substrates on the use of C 4 F 8 and C 4 F 6 plasmas in the deposition step of the Bosch process

The Bosch process was carried out using S F 6 ∕ C 4 F 8 or S F 6 ∕ C 4 F 6 plasmas during the etching/deposition steps to examine the etch profiles and etch rates of silicon. The fluorocarbon film deposited in a C 4 F 6 plasma was thicker and more strongly bonded than the film deposited in a C 4 F 8 plasma, which led to a shorter deposition time for the C 4 F 6 plasma. The deposition rate of the fluorocarbon films on the different locations of the silicon substrate in both C 4 F 8 and C 4 F 6 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 C 4 F 8 plasma (0.92) than for the C 4 F 6 plasma (0.65), indicating that a thicker fluorocarbon film was deposited at the bottom of the pattern in C 4 F 8 plasma under the same process conditions. This resulted in a higher etch rate of the silicon substrate using C 4 F 6 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 C 4 F 8 and C 4 F 6 plasmas.