Planar field effect transistor structure having an angled crystallographic etch-defined source/drain recess and a method of forming the transistor structure
View Patent ↗Disclosed is a transistor that incorporates epitaxially deposited source/drain semiconductor films and a method for forming the transistor. A crystallographic etch is used to form recesses between a channel region and trench isolation regions in a silicon substrate. Each recess has a first side, having a first profile, adjacent to the channel region and a second side, having a second profile, adjacent to a trench isolation region. The crystallographic etch ensures that the second profile is angled so that all of the exposed recess surfaces comprise silicon. Thus, the recesses can be filled by epitaxial deposition without divot formation. Additional process steps can be used to ensure that the first side of the recess is formed with a different profile that enhances the desired stress in the channel region.
1. A field effect transistor comprising:
a substrate having a top surface;
a channel region in said substrate at said top surface;
a trench isolation region comprising:
a trench extending into said substrate from said top surface, said trench comprising a sidewall essentially normal to said top surface; and
an isolation material filling said trench; and
a source/drain region positioned laterally between said channel region and said sidewall of said trench isolation region, said source/drain region comprising:
a recess extending into said substrate from said top surface, said recess comprising:
an upper edge at said top surface of said substrate;
a bottom surface essentially parallel to said top surface of said substrate;
a first side surface adjacent to said channel region and extending from said upper edge to said bottom surface, said first side surface having a first profile normal to said top surface of said substrate; and
a second side surface opposite said first side surface and extending from said upper edge to said bottom surface, said second side surface having a second profile that is different from said first profile such that said first side surface and said second side surface are not symmetrical, said second profile comprising an angled profile relative to said top surface of said substrate and said sidewall of said trench isolation region such that only said upper edge of said recess at said top surface contacts said trench isolation region and said second side surface comprises only said substrate and not said isolation material; and
a semiconductor film filling said recess.
2. The field effect transistor of claim 1 , said semiconductor film comprising an epitaxial silicon germanium (eSiGe).
3. The field effect transistor of claim 1 , said second side surface extending from said upper edge of said recess at said top surface of said substrate immediately adjacent to said trench isolation region downward and away from said sidewall of said trench isolation region such that a triangular portion of said substrate separates said semiconductor film in said recess from said isolation material in trench isolation region.
4. The field effect transistor of claim 1 , said semiconductor film comprising a different semiconductor material than said substrate selected to apply a given strain on said channel region.
5. The field effect transistor of claim 1 , said second side surface tapering at an angle of approximately 55° away from said upper edge towards said bottom surface.
6. A p-type field effect transistor comprising:
a silicon substrate having a top surface;
a gate on said top surface;
a channel region in said substrate at said top surface aligned below said gate;
a trench isolation region comprising:
a trench extending into said substrate from said top surface and comprising a sidewall essentially normal to said top surface; and
an isolation material filling said trench; and,
a source/drain region positioned laterally between said channel region and said sidewall of said trench isolation region, said source/drain region comprising:
a recess extending into said substrate from said top surface, said recess comprising:
an upper edge at said top surface of said substrate;
a bottom surface;
a first side surface adjacent said channel region and extending from said upper edge to said bottom surface, said first side surface having a first profile normal to said top surface of said substrate; and
a second side surface opposite said first side surface, said second side surface having a second profile that is different from said first profile such that said first side surface and said second side surface are not symmetrical, said second profile comprising an angled profile relative to said top surface of said substrate and said sidewall of said trench isolation region such that only said upper edge of said recess at said top surface contacts said trench isolation region and said second side surface comprises only said substrate and not said isolation material; and
an epitaxial silicon germanium film completely filling said recess and imparting a compressive strain on said channel region to enhance hole mobility within said channel region.
7. The field effect transistor of claim 6 , said second side surface extending from said upper edge of said recess at said top surface of said substrate immediately adjacent to said trench isolation region downward and away from said sidewall of said trench isolation region such that a triangular portion of said substrate separates said epitaxial silicon germanium film in said recess from said isolation material in said trench isolation region.
8. The field effect transistor of claim 6 , said second side surface tapering at an angle of approximately 55° away from said upper edge towards said bottom surface.