AVS 47th International Symposium
    Plasma Science and Technology Tuesday Sessions
       Session PS-TuP

Paper PS-TuP20
Silicon Surface Roughness Induced by Reactive Ion Etching in SF@sub 6@ and SF@sub 6@/O@sub 2@ Plasmas

Tuesday, October 3, 2000, 5:30 pm, Room Exhibit Hall C & D

Session: Poster Session
Presenter: S.A. Moshkalyov, UNICAMP-University of Campinas, Brazil
Authors: S.A. Moshkalyov, UNICAMP-University of Campinas, Brazil
P. Verdonck, University of São Paulo - USP, Brazil
R.D. Mansano, University of São Paulo - USP, Brazil
M. Cotta, UNICAMP, Brazil
Correspondent: Click to Email
With the trend of continuous minimization of device structures in micro-fabrication, surface roughness induced by plasma processing becomes an important issue. The problem is of particular importance in the case of deep trench etching of silicon for MEMS applications. Mechanisms of roughness formation and development during plasma processing are not well understood. Surface roughness is closely related to the energies and flux densities of ions and reactive radicals coming from the plasma to the processed surface. A study of the evolution of surface morphology can provide better understanding of etching mechanisms. New opportunities for this kind of study arose with the recent introduction of high-resolution local probes like AFM, which allow to obtain real spatial surface images. Experiments were performed in a RF-driven RIE plasma etcher with SF@sub 6@ and SF@sub 6@/O@sub 2@ gas mixtures at medium gas pressures (50-150 mTorr). Small (100) silicon samples with an Al mask were etched with etch time varying from 2 to 30 min. After the process, etch rates were measured and surface morphology was analyzed by AFM in frames ranging from 2x2 mkm to 40x40 mkm. The results show a significant difference in roughness evolution for SF@sub 6@ and SF@sub 6@/O@sub 2@. For both cases, the roughness parameter rises almost linearly with time, but its rise is faster for oxygen contaning mixtures. For short etching times (2 min.) and small/medium oxygen content (10-30%) the rms roughness parameter was even slightly smaller for gas mixture (21-24 nm) than for pure SF@sub 6@ (26 nm). Furthemore, in the former case the surface morhology is distinctly more regular. The mechanisms reponsible for the formation of surface roughness in both cases are discussed.