Low-temperature selective epitaxy contact approach

A method of forming a semiconductor device, comprising:

• epitaxially growing a doped crystalline silicon-containing layer over a source/drain feature and growing a doped amorphous silicon-containing layer over a field region of a semiconductor layer, wherein a trench is formed in the semiconductor layer and the trench exposes the source/drain feature, the epitaxially growing comprising:
• flowing a higher order silane precursor gas and an n-type dopant precursor gas into a processing region of a process chamber, the higher order silane precursor gas having a chemical formula SixH(2x+2) where x is 2 or more;
• epitaxially growing an undoped crystalline silicon-containing capping layer over the doped crystalline silicon-containing layer and growing an undoped amorphous silicon-containing layer over the doped amorphous silicon-containing layer, comprising:
• flowing the higher order silane precursor gas into the processing region;
• and
• selectively removing the doped amorphous silicon-containing layer and the undoped amorphous silicon-containing layer relative to the undoped crystalline silicon-containing capping layer, comprising:
• flowing an etching gas comprising Cl2, GeCl2, GeCl4, GeH4, or a combination thereof.

A method of forming a semiconductor device, comprising:

• providing a device structure having a trench formed in a semiconductor layer, wherein the trench exposes a source/drain feature from a backside of the device structure and the semiconductor layer is formed over a device substrate;
• performing a first epitaxial deposition process to grow a doped crystalline silicon layer over the source/drain feature and grow a doped amorphous silicon layer over a field region of the semiconductor layer;
• performing a second epitaxial deposition process to grow an undoped crystalline silicon capping layer over the doped crystalline silicon layer and grow an undoped amorphous silicon layer over the doped amorphous silicon layer;
• and
• performing a selective etching process to remove the undoped amorphous silicon layer and the doped amorphous silicon layer relative to the undoped crystalline silicon capping layer.