Method of forming an epitaxial layer

A method of forming a Si-comprising epitaxial layer selectively on a substrate, the method comprising:

• providing the substrate to a process chamber, the substrate comprising an exposed surface, the exposed surface comprising a first exposed surface and a second exposed surface, and
• performing a deposition process, thereby forming the Si-comprising epitaxial layer selectively on the first exposed surface, relative to the second exposed surface, the deposition process comprising providing, to the process chamber, a Si-containing precursor and a Ge-containing precursor,
• wherein the Si-containing precursor is a halopolysilane precursor and wherein the first exposed surface is a single crystalline surface and wherein the second exposed surface is a single crystalline surface having a different crystal orientation than the first exposed surface, and
• wherein the deposition process is a cyclic deposition process comprising one or more deposition cycles, wherein each deposition cycle further comprises providing an etching gas to the process chamber, thereby removing the Si-comprising epitaxial layer from the second exposed surface, and the cyclic deposition process is carried out until a desired thickness of the Si-comprising epitaxial layer is formed on the first exposed surface and where the second exposed surface is free of the Si-comprising epitaxial layer.