Methods of selectively depositing an epitaxial layer

A method of fabricating a semiconductor device, comprising:

• forming a gate stack having a non-monocrystalline surface on a substrate;
• etching the substrate on opposite sides of the gate stack to define etched regions where a source and a drain region is to be formed, wherein the etched regions formed in the substrate have monocrystalline surfaces;
• exposing the substrate and gate stack to a deposition gas to deposit a layer on the non-monocrystalline and monocrystalline surfaces, the layer having a first portion deposited on the monocrystalline surfaces and a second portion deposited on the non-monocrystalline surfaces;
• and
• exposing the substrate and gate stack to an etching gas separately from the deposition gas, the etching gas comprising a first gas comprising hydrogen and a halogen and a second gas comprising a Group V element to selectively etch the first portion of the layer at a slower rate than the second portion of the layer to form source/drain regions within the etched regions of the substrate.