Profile control in forming epitaxy regions for transistors

A method includes etching a silicon layer in a wafer to form a first trench in a first device region and a second trench in a second device region, performing a pre-clean process on the silicon layer, performing a baking process on the wafer, and performing an epitaxy process to form a first silicon germanium region and a second silicon germanium region in the first trench and the second trench, respectively. The first silicon germanium region and the second silicon germanium region have a loading in a range between about 5 nm and about 30 nm.