AVS 50th International Symposium
    Plasma Science and Technology Tuesday Sessions
       Session PS-TuA

Paper PS-TuA10
Selective Silicon Nitride Etching by ECR Plasmas Using SF6 and NF3 Based Gas Mixtures

Tuesday, November 4, 2003, 5:00 pm, Room 315

Session: Dielectric Etch
Presenter: J.W. Swart, UNICAMP, Brazil
Authors: C. Reyes-Betanzo, INAOE- Instituto Nacional de Astrofisica, Mexico
S.A. Moshkalyov, UNICAMP, Brazil
A.C.S. Ramos, UNICAMP, Brazil
J.W. Swart, UNICAMP, Brazil
Correspondent: Click to Email
Removal of silicon nitride films is critical step in CMOS and other semiconductor technologies as possible overetch during the nitride layer processing may result in damages of a thin oxide or a silicon substrate. Hence high nitride etching selectivity over oxide and Si is required. In recent chemical dry etching experiments, mixtures rich in oxygen and nitrogen with small additions of fluorine containing gases were shown to etch the nitride selectively. The role of NO molecules in the surface chemistry was shown to be important for improvement of the etching selectivity. This is attributed to an exothermic reaction of NO molecules with surface nitrogen atoms which promotes the enhanced removal of nitrogen (in a molecular form) from the nitride surface and thus accelerates the overall reaction rate. Here, the results of a study of silicon nitride, oxide and Si etching in SF6 and NF3 based mixtures using a high-density ECR plasma are presented. For the two fluorine containing gases used, the main mechanisms responsible for selective nitride etching are distinctly different. In the SF6 case, best results are achieved in O2/N2 rich plasmas where the nitride etching by fluorine can be enhanced by NO molecules produced in gas phase reactions. Formation of NO molecules was observed in spectra emitted from the plasma. In NF3 based mixtures, the nitride etching is more likely to be dominated by NFx reaction intermediates rather than by NO radicals. Higher selectivities over oxide (up to 100) were obtained with NF3 , while higher selectivities over Si (up to 10) were obtained with SF6 based mixtures.