Microstructural Changes in W-Polycide Gates Capped with A Thin Polysilicon Layer

We find that sheet resistance of tungsten polycide can be reduced up to 40% by depositing thin polysilicon layers on the top of the films. Transmission electron microscopy shows no significant differences in the crystal structure, grain size, or dislocation density inside the films by adding a polysilicon cap, but it clearly shows roughening of the top interface. Auger depth profiling shows substantial reduction of the Si/W ratio in the capped films. Both results imply that the excess Si segregates to both polysilicon interfaces, effectively lowering the Si/W ratio and resulting in a low sheet resistance.