Evaluation of the Selective Tungsten Deposition Process for VLSI Circuit Applications

Abstract

Tungsten films have been selectively deposited on oxide‐patterned silicon wafers using two successive deposition steps, i.e., the Si reduction of followed by the reduction of . The deposition process was performed in a horizontal hot wall LPCVD reactor. In this reactor, the surface of vertical wafers was parallel to the axis of the quartz tube. The thickness of W films obtained for a given deposition time was found to be dependent on the “history” (or the cleanliness) of the CVD reactor. The thickness uniformity across a wafer and from wafer to wafer was determined as a function of the wafer position in the CVD reactor. The selectivity of the process was evaluated by measuring the W nuclei density on the oxide (PSG) mask as a function of the thickness of W films. During the validity period of the CVD reactor, tungsten films of 220 nm in thickness were produced on 12 wafers per run with undetectable W nuclei on the mask (perfect selectivity). The CVD reactor appears to be suitable for selective deposition of W films used as diffusion barriers in Al/W/Si contact structures.