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    Plasma Science Thursday Sessions
       Session PS-ThA

Paper PS-ThA3
Investigation of Fluorocarbon PECVD from c-C4F8 for use as Passivation during Deep Silicon Etching

Thursday, November 1, 2001, 2:40 pm, Room 104

Session: Feature Profile Evolution
Presenter: C.B. Labelle, Agere Systems
Authors: C.B. Labelle, Agere Systems
V.M. Donnelly, Agere Systems
G.R. Bogart, Agere Systems
R.L. Opila, Agere Systems
A.M. DeSantolo, Agere Systems
A. Kornblit, Agere Systems
Correspondent: Click to Email
Deep silicon plasma etching is of great importance in fields such as MEMS and photonics. The most commonly used etching technique is the so-called Bosch process, where etch (SF@sub 6@/O@sub 2@) and passivation (c-C@sub 4@F@sub 8@) steps are continuously alternated to achieve vertical profiles. To investigate the passivation step, fluorocarbon films were deposited from c-C@sub 4@F@sub 8@ in a Surface Technology Systems High Rate Advanced Silicon Etch tool, which uses an inductively coupled plasma source. Film deposition rate decreases from 1000 to 740 Å/min as pressure increases from 10 to 25 mTorr, while it increases from 350 to 1500 Å/min as power increases from 300 to 1000 W. Film refractive indices (n) increase roughly linearly from 1.373 to 1.381 for the same pressure range. Carbon 1s XPS shows that, for the ranges explored, pressure and power don't significantly affect the film composition, with films generally consisting of ~ 9% CF@sub 3@, 38% CF@sub 2@, 32% CF, and 21% C-CF. The high CF@sub 2@ and CF fractions correlate with the low refractive indices observed; the slight change in n with pressure is due to replacement of CF@sub 2@ by C-CF as pressure increases. OES data indicate that the C@sub 4@F@sub 8@ is largely broken down into C@sub 2@, F, CF@sub 2@, and CF. Therefore, the films may be formed by C@sub 2@ deposition with subsequent fluorination, CF@sub x@ deposition, or a combination of both. Quadrapole mass spectrometry of the chamber effluents indicates that CF@sub 4@ (50% of effluent), C@sub 2@F@sub 4@ (25%), and C@sub 2@F@sub 6@ (14%) are created. Therefore, recombination, most likely on the walls, can generate larger C@sub x@F@sub y@ species, which also contribute to the film. The effect of residual gases from the etching step on film composition and deposition mechanisms will also be discussed.