Role of temperature gradients in blanket tungsten for microelectronic contacts

Abstract

A tungsten plug process is commonly employed in microelectronic interconnect technology. This paper provides a review of the relative advantages of the two variants-blanket and selective tungsten-and subsequently focuses on the former. Specifically, we address the role of thermal gradient that may naturally occur or be intentionally applied during blanket tungsten deposition, whereas most published literature examines the isothermal process. We present a one-dimensional mass transport and deposition model for a cylindrical contact hole/via. In the numerical calculations, a temperature gradient is imposed on a via hole such that its bottom is slightly hotter than the mouth from which the deposition gases enter. We find that the tendency to form a keyhole void diminishes when a temperature gradient is present, as compared to the isothermal process at a temperature corresponding to that either at the mouth or pore bottom. Furthermore, the extent of gain due to a thermal gradient depends on the temperature level; the advantage is greater at higher levels. However, in practical applications, the thermal conductivity of the dielectric layer in which the contact hole is formed should be low in order to achieve the required gradient. This aspect should also be kept in mind when searching for new materials with low dielectric constant.