Methods for reducing loading effects during film formation

A method for fabricating a semiconductor device comprising:

• providing a substrate comprising a first and second device structures;
• forming a first and a second exposed portions of the substrate adjacent to the first and second device structures respectively, wherein the first and second exposed portions are of different size;
• and
• selectively forming a first layer over the first and second exposed portions of the substrate by using a gas mixture comprising:
• first and second source gases that function as growth components for forming the first layer;
• and
• a reactant gas that functions as an etching component for controlling selectivity of the first layer growth, the reactant gas being different from the first and second source gases,
• wherein one of first and second source gases forms the first layer at a faster rate over the first exposed portion compared to the second exposed portion and the other source gas exhibits an opposite behavior.