AVS 47th International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS2-WeA

Paper PS2-WeA5
A Model for Si Etching in an Inductively Coupled SF@sub 6@/C@sub 4@F@sub 8@ Discharge

Wednesday, October 4, 2000, 3:20 pm, Room 311

Session: Feature Evolution
Presenter: S. Rauf, Motorola Inc.
Authors: S. Rauf, Motorola Inc.
W. Dauksher, Motorola Inc.
V. Arunachalam, Motorola Inc.
P. Ventzek, Motorola Inc.
L. Lea, Surface Technology Systems, UK
S. Hall, Surface Technology Systems, UK
Correspondent: Click to Email
Fluorine rich plasmas such as SF@sub 6@ are known to rapidly etch Si. However, due to inadequate polymerization in SF@sub 6@, it becomes difficult to anisotropically etch high aspect ratio features with straight sidewalls. Polymerizing gases such as C@sub 4@F@sub 8@ are therefore added, either directly in the SF@sub 6@ discharge or in a separate polymerization step, to obtain the desired etch profiles. To understand the dynamics of Si etching in SF@sub 6@/C@sub 4@F@sub 8@, an integrated equipment and feature scale model has been developed for these plasmas. The model is based on the Hybrid Plasma Equipment Model (HPEM) and Monte Carlo Feature Profile Model (MCFPM) from the University of Illinois. The gas phase chemical mechanisms for SF@sub 6@ and C@sub 4@F@sub 8@ are primarily based on electron impact cross-sections available in the literature. Judicious adjustments have however been made to match model predictions with experiments. The surface mechanism for SF@sub 6@ assumes reactive ion etching due to the combined effect of F and energetic ions. The C@sub 4@F@sub 8@ discharge can etch (due to the synergistic effect of ions, CF@sub x@ radicals and F) and deposit polymer (due to CF@sub x@ radicals). The equipment model has been validated using gas phase measurements while the feature scale model has been calibrated using etch/deposition rate measurements and comparing model predictions to etch profiles. Results show that the SF@sub 6@ plasma is quite electronegative with SF@sub 6@@super -@ and F@super -@ being the dominant negative ions. CF@sub 2@ is the primary CF@sub x@ radical in the C@sub 4@F@sub 8@ discharge, and it is the main precursor to polymer formation. The paper investigates Si etching in both a multi-step process (with separate etching and passivation steps) and a combined SF@sub 6@/C@sub 4@F@sub 8@ discharge.