Transistor with multi-level self-aligned gate and source/drain terminals and methods

A structure comprising:

• a stack of layers comprising:
• a channel layer;
• a barrier layer on the channel layer;
• and a dielectric layer on the barrier layer;
• source/drain terminals;
• a gate terminal positioned laterally between the source/drain terminals,
• wherein each source/drain terminal comprises:
• a first source/drain section within a source/drain opening;
• and a second source/drain section above the first source/drain section,
• wherein the source/drain opening extends through the dielectric layer and the barrier layer to the channel layer and includes:
• a lower portion within the barrier layer;
• and
• an upper portion within the dielectric layer and wider than the lower portion,
• wherein sidewalls of the upper portion are offset from sidewalls of the lower portion,
• wherein the gate terminal comprises:
• a first gate section within a gate opening that extends through the dielectric layer and has a bottom above the barrier layer;
• and a second gate section above the first gate section and the dielectric layer, and
• wherein the first source/drain section and the second source/drain section comprise a source/drain conductor material and the first gate section and the second gate section comprise a gate conductor material that is different from the source/drain conductor material;
• and
• sidewall spacers within the source/drain opening above the barrier layer and positioned laterally adjacent to essentially vertical surfaces of the dielectric layer, wherein the first source/drain section has an essentially uniform width within the lower portion and the upper portion of the source/drain opening.

A structure comprising:

• a stack of layers comprising:
• a channel layer;
• a barrier layer on the channel layer;
• a gate dielectric layer on the barrier layer;
• and a dielectric layer on the gate dielectric layer;
• source/drain terminals;
• and
• a gate terminal positioned laterally between the source/drain terminals,
• wherein each source/drain terminal comprises:
• a first source/drain section within a source/drain opening;
• and a second source/drain section above the first source/drain section,
• wherein the source/drain opening extends through the dielectric layer, the gate dielectric layer, and the barrier layer to the channel layer and includes:
• a lower portion within the barrier layer;
• a center portion within the gate dielectric layer;
• and
• an upper portion within the dielectric layer and wider than the lower portion and the center portion,
• wherein sidewalls of the upper portion are offset from vertically aligned sidewalls of the lower portion and the center portion,
• wherein the gate terminal comprises:
• a first gate section within a gate opening that extends through the dielectric layer and has a bottom above the barrier layer;
• and a second gate section above the first gate section and the dielectric layer, and
• wherein the first source/drain section and the second source/drain section comprise a source/drain conductor material and the first gate section and the second gate section comprise a gate conductor material that is different from the source/drain conductor material.