Asymmetric Cyclic Desposition Etch Epitaxy

A method to form an epitaxial layer within a recess, comprising:

• providing a substrate within a processing chamber, the substrate comprising a recess;
• exposing the substrate to a continuous etchant flow of one or more vapor etchants configured to selectively remove amorphous portions of an epitaxial material from the recess;
• exposing the substrate to a first periodic pulse of one or more source vapors configured to deposit a first layer comprising crystalline portions and amorphous portions of the epitaxial material on a surface within the recess, wherein the first periodic pulse comprises a first frequency and a first duration to achieve a first thickness;
• and
• exposing the substrate to a second periodic pulse of the one or more source vapors configured to deposit a second layer comprising crystalline portions and amorphous portions of the epitaxial material on a surface of the first layer, wherein the second periodic pulse comprises a second frequency and a second duration to achieve a second thickness.

A field-effect transistor (FET) formed on a substrate, comprising:

• a source region comprising an epitaxial material;
• a drain region comprising the epitaxial material;
• a gate disposed above a channel region which resides between the source region and the drain region;
• wherein the source region or drain region comprise a first plurality of first layers sequentially and epitaxially disposed above one another and the substrate to form a first layer comprising a first thickness;
• and
• wherein the source region or drain region further comprise a second plurality of second layers sequentially and epitaxially disposed above one another and a first layer to form a second layer comprising a second thickness.