Radio frequency transistor amplifiers having self-aligned double implanted source/drain regions for improved on-resistance performance and related methods

A method of forming a high electron mobility transistor, the method comprising:

• forming a semiconductor layer structure that comprises a Group III nitride-based channel layer and a Group III nitride-based barrier layer that has a higher bandgap than the Group III nitride-based channel layer on an upper surface of the Group III nitride-based channel layer;
• forming a first source/drain region in the semiconductor layer structure, the first source/drain region including a first implanted region and a first auxiliary implanted region that merges with the first implanted region;
• forming a second source/drain region in the semiconductor layer structure;
• forming a gate finger on the semiconductor layer structure, the gate finger having a first longitudinal axis that extends parallel to an upper surface of the semiconductor layer structure;
• forming a first source/drain contact on and above the first implanted region, the first source/drain contact having an inner sidewall that faces the gate finger and an outer sidewall opposite the inner sidewall;
• forming a second source/drain contact on and above the second source/drain region, the second source/drain contact having an inner sidewall that faces the gate finger and an outer sidewall opposite the inner sidewall;
• wherein a depth of the first implanted region is at least twice a depth of the first auxiliary implanted a region,
• wherein the first source/drain region extends inwardly a first distance from a lower edge of the inner sidewall of the first source/drain contact towards the second source/drain region along a transverse axis that extends parallel to a plane defined by the upper surface of the semiconductor layer structure and perpendicular to the longitudinal axis, and extends outwardly a second distance along the transverse axis from a lower edge of the outer sidewall of the first source/drain contact away from the second source/drain region, where the first distance exceeds the second distance, and
• wherein the first source/drain contact, the second source/drain contact and the gate finger are contacts of a first unit cell transistor.

A method of forming a high electron mobility transistor, the method comprising:

• forming a semiconductor layer structure that comprises a Group III nitride-based channel layer and a Group III nitride-based barrier layer that has a higher bandgap than the Group III nitride-based channel layer on an upper surface of the Group III nitride-based channel layer;
• forming a carbon-containing mask on an upper surface of the semiconductor layer structure;
• forming a first opening in the carbon-containing mask;
• performing a first ion implantation process to implant ions into the semiconductor layer structure through the first opening;
• changing a size the first opening in the carbon-containing mask to create a modified first opening;
• and
• performing a second ion implantation process to implant additional ions into the semiconductor layer structure through the modified first opening using the carbon-containing mask as an ion implantation mask,
• wherein the first and second ion implantation processes together form a first implanted region and a first auxiliary implanted region in the semiconductor layer structure, and
• wherein the first implanted region and the first auxiliary implanted region together form a first source/drain region in the semiconductor layer structure and the first implanted region extends further into the semiconductor layer structure than does the first auxiliary implanted region.