Method of controlling stress in a film

A method for controlling an amount of stress imparted to a substrate comprising the steps of:

• (a) depositing a first layer of intrinsic polycrystalline silicon on walls of a trench;
• (b) after step (a) depositing a first layer of doped polycrystalline silicon on the walls of the trench;
• (c) depositing amorphous silicon on the polycrystalline silicon to fill the trench;
• and
• (d) heating the substrate to (i) at least partially crystallize the amorphous silicon, (ii) to reduce compressive stress in the deposited layers filling the trench upon crystallization of the amorphous silicon, (iii) to diffuse dopant from the doped polycrystalline silicon into the amorphous silicon, and (iv) to impart a compressive stress from the deposited layers to the substrate upon crystallization of the amorphous silicon.