AVS 50th International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS2-ThM

Paper PS2-ThM11
Study of CO addition to C@sub 4@F@sub 8@ or C@sub 4@F@sub 8@/Ar Plasmas for Selective Etching of Organosilicate Glass (OSG) over SiC

Thursday, November 6, 2003, 11:40 am, Room 315

Session: Low k Dielectric Etch
Presenter: L. Ling, University of Maryland, College Park
Authors: L. Ling, University of Maryland, College Park
G.S. Oehrlein, University of Maryland, College Park
X. Hua, University of Maryland, College Park
X. Li, University of Maryland, College Park
F.G. Celii, Texas Instruments
K.H.R. Kirmse, Texas Instruments
P. Jiang, Texas Instruments
Correspondent: Click to Email
We have examined the effect of CO addition to C@sub 4@F@sub 8@ or C@sub 4@F@sub 8@/Ar plasmas for selective etching of organosilicate glass over SiC etch stop layers. The variation of important gas phase species, thin film etching rates and surface chemistry with feedgas composition was determined. CO addition exhibits dramatically different consequences on OSG/SiC etching selectivity when added to either C4F8 or C@sub 4@F@sub 8@/Ar plasmas containing a high proportion of Ar (greater 80%). An improvement of the OSG/SiC etching selectivity results from CO addition to C@sub 4@F@sub 8@. Our data indicate little CO dissociation in this case, which is plausible considering the lower dissociation energy threshold of C@sub 4@F@sub 8@ relative to CO. X-ray photoelectron spectroscopy (XPS) analysis of OSG and SiC surfaces shows that the etching selectivity improvement for C@sub 4@F@sub 8@/CO may be explained by some incorporation of CO into deposited fluorocarbon films, an increase of the thickness and a reduction of the F/C ratio of the steady-state fluorocarbon surface layer on the SiC surface during etching. Adding CO to C@sub 4@F@sub 8@/90%Ar discharges leads to a reduction of the OSG/SiC etching selectivity. Significant dissociation of CO in Ar-rich C@sub 4@F@sub 8@/Ar/CO discharges is observed, consistent with the fact that the dissociation energy threshold of CO is lower than the Ar ionization and metastable energies. Oxygen incorporation in deposited fluorocarbon films and a reduction of the steady-state fluorocarbon surface layer thickness on SiC are observed by XPS in this case, explaining the loss of OSG/SiC etching selectivity for C@sub 4@F@sub 8@/Ar/CO discharges.