CROSS-SECTION TEM FOR EXAMINATIONS OF SELECTIVE TUNGSTEN CVD FOR VIA HOLE FILLING

The reaction between tungsten layers [deposited by chemical vapor depo sition (CVD) as well as by physical vapor deposition (PVD)] and an alu minium alloy (AlSi) has been investigated. For CVD tungsten layers dep osited on AlSi by silane reduction of WF6 the formation of an aluminiu m fluoride interlayer has been established by cross-section transmissi on electron microscopy (XTEM). At the interface between PVD-W and AlSi , an intermetallic compound may be formed depending on the thermal tre atment. A crystalline intermediate layer has been found after annealin g at 400-degrees-C (twice for 30 min), whereas an interface between as deposited double layers showed no interlayer. For all samples investi gated, diffusion of aluminium into the tungsten layer was observed. Th e diffusion depth depends on the heat treatment and the tungsten morph ology. Intermediate layers - if they exist - limit the diffusion but d o not act as a diffusion barrier.