Methods for forming semiconductor devices using sacrificial capping and insulation layers

A method of fabricating a semiconductor device, the method comprising the steps of:

• providing a semiconductor substrate that includes a base substrate and a plurality of epitaxial layers over the base substrate, wherein the plurality of epitaxial layers include a channel layer, a barrier layer over the channel layer, and a permanent cap over the barrier layer, wherein the channel layer includes one or more layers of aluminum gallium nitride (AlXGa1-XN), wherein X takes on values between 0 and 1, wherein the barrier layer includes one or more layers of AlXGa1-XN, wherein the permanent cap is formed from one or more layers of gallium nitride (GaN), and wherein the permanent cap defines an upper surface of the semiconductor substrate;
• forming a sacrificial cap over the permanent cap in an active region of the device, wherein the sacrificial cap is selected from a structure consisting of an aluminum nitride (AlN) layer and a superlattice comprising AlGaN and AlN layers;
• forming a sacrificial insulating layer over the sacrificial cap in the active region of the device;
• forming a source region and a drain region in the semiconductor substrate in the active region of the device by performing an ion implantation process to implant ions through the sacrificial insulating layer and the sacrificial cap, and into the barrier layer;
• completely removing the sacrificial insulating layer and the sacrificial cap in the active region of the device, while refraining from removing the permanent cap;
• forming a source contact over the source region;
• and
• forming a drain contact over the drain region.

A partially-completed semiconductor device comprising:

• a semiconductor substrate that includes a base substrate and a plurality of epitaxial layers over the base substrate, wherein the plurality of epitaxial layers include a channel layer, a barrier layer over the channel layer, and a permanent cap over the barrier layer, wherein the channel layer includes one or more layers of aluminum gallium nitride (AlXGa1-XN), wherein X takes on values between 0 and 1, wherein the barrier layer includes one or more layers of AlXGa1-XN, wherein the permanent cap is formed from one or more layers of gallium nitride (GaN), and wherein the permanent cap defines an upper surface of the semiconductor substrate;
• a sacrificial cap over the permanent cap in an active region of the device, wherein the sacrificial cap is selected from a semiconductor material that includes aluminum (Al), a structure consisting of an aluminum nitride (AlN) layer, and a superlattice comprising AlGaN and AlN layers;
• a source region in the semiconductor substrate in the active region of the device, wherein the source region is formed from ions implanted through the sacrificial cap, and into the barrier layer;
• and
• a drain region in the semiconductor substrate in the active region of the device, wherein the drain region is formed from the ions implanted through the sacrificial cap, and into the barrier layer.