RECRYSTALLIZATION AND GRAIN-GROWTH PHENOMENA IN POLYCRYSTALLINE SI/COSI2 THIN-FILM COUPLES

This paper presents high-temperature effects on CoSi2/ polycrystalline silicon (poly-Si) bilayers, intended for metal-oxide- semiconductor gate applications. Both rapid thermal annealing and conventional furnace annealing were utilized for the investigation. At temperatures above 700°C the structure breaks down due to silicon recrystallization within the silicide and simultaneous silicide growth into the polycrystalline silicon film. Recrystallized silicon adopts the silicide texture and this process terminates when the entire polysilicon layer is consumed. After completion the layer configuration is inverted, i.e., the silicide is adjacent to the gate oxide and covered with elemental silicon at the surface. This surface layer consists of large grains with few crystal defects, very different from the columnar structure of the as-deposited silicon. With further annealing, grain growth in both phases continues, and each grain will ultimately extend from the oxide interface to the free surface. Lateral grain dimensions are typically a few times the total film thickness at this stage. Silicon recrystallization in the silicide layer can be suppressed if the polysilicon is doped with phosphorus prior to metal deposition, or the phenomenon can be alleviated by an arsenic or boron implantation into the silicide.