Inserting a titanium layer between cobalt and silicon can control the phase formation sequence for cobalt silicide. In this study we show that sputtered Ti combines with surface oxide to form a stable permeable membrane <20Å thick. Below 500°C, the restricted diffusion of Co and Si through this interlayer allows Co2Si and CoSi2 to form above and below the interlayer, respectively. Because the interlayer is very thin, the type of substrate doping dominates the reaction sequence at higher temperatures. Given sufficient cobalt supply, at 500-600°C the initial phases transform to CoSi for an n-type Si substrate. For a p-type substrate the Co2Si phase converts to CoSi while the bottom CoSi2 phase remains stable. Above 650°C, the deposited cobalt fully converts to the final CoSi2 phase.
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