Refractory metals are of interest for use in diffusion barriers and adhesion layers in ultra-large-scale integrated circuit metallization. An interesting feature of many of these materials is the reemission of some of the deposited flux during sputtering. This can be useful in depositing conformal layers in high aspect ratio contacts and vias. Overhanging structures have been used to study reemission in TiW, Ti, Nb, W, Ta, and Pt sputtering. While Ti and Nb show negligible reemission under typical sputtering conditions, Ta, W, and Pt show noticeable film deposition in regions obstructed from direct flux. TiW alloy sputtering shows evidence of the largest amount of reemitted flux. Sputtering conditions from 5 to 15 mT with power densities from 10 to 35 W/cm2 were studied, without significant change in the reemission flux. Variation of substrate temperature and moderate substrate bias was also not found to cause a measurable change in the reemission characteristics.

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Journal Journal of Vacuum Science and Technology A
Tait, R. (1998). Reemission of sputtered refractory metals during deposition. Journal of Vacuum Science and Technology A, 16(3), 1222–1226.