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

Paper PS-TuP18
Comparative Study of W, WN@sub x@ and Si RIE in SF@sub 6@/Ar using Actinometry Technique

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

Session: Poster Session
Presenter: J.W. Swart, UNICAMP, Brazil
Authors: S.A. Moshkalyov, UNICAMP, Brazil
C. Reyes-Betanzo, UNICAMP, Brazil
A.C. Ramos, UNICAMP-IFGW, Brazil
A. Diniz, UNICAMP, Brazil
J.W. Swart, UNICAMP, Brazil
Correspondent: Click to Email
The use of tungsten thin films in micro-fabrication attracts much attention. For etching of W and WN@sub x@ films, SF@sub 6@ is commonly used which provides high etch rates. However, for RIE reactors considerable undercutting of W/WN@sub x@ in SF@sub 6@ was usually reported. The objective of this study was to find conditions of anisotropic etching of tungsten films using conventional RIE medium-pressure reactor. To characterize the density of fluorine radicals in the plasma, an optical emission spectroscopy (actinometry) was employed. To provide considerable variation of radical/ion fluxes to the processed surfaces, the SF@sub 6@/Ar ratio was varied widely. Two sets of experiments were performed keeping either RF power or DC bias constant while changing the SF@sub 6@/Ar ratio. The results show that the silicon etch rate is nearly proportional to the fluorine radical density with only the minor effect of the DC bias (ion energy). Thus in the Si-F system the chemical (spontaneous) etching is the dominant mechanism. In contrast, in tungsten etching, the role of ion-induced effects is much more pronounced. Furthemore, the tungsten etch rate dependence on a fluorine density has a threshold behavior with the threshold depending on the ion energy. This indicates that at a relatively small (not saturated) surface coverage by fluorine, the ion bombardment provides strong enhancement of surface processes leading to efficient formation and desorption of volatile WF@sub 6@ etch products (most likely, an ion-induced associative desorption). Under these conditions, highly anisotropic etching of tungsten and tungsten nitride have been achieved using a conventional RIE reactor at relatively high etch rates (>100 nm/min).