Selectively doped semi-conductors and methods of making the same
The present invention is generally directed to methods of selectively doping a substrate and the resulting selectively doped substrates. The methods include doping an epilayer of a substrate with the selected doping material to adjust the conductivity of either the epilayers grown over a substrate or the substrate itself. The methods utilize lithography to control the location of the doped regions on the substrate. The process steps can be repeated to form a cyclic method of selectively doping different areas of the substrate with the same or different doping materials to further adjust the properties of the resulting substrate.
1. A method of forming a substrate having an epilayer that is selectively doped with a plurality of doping materials that affect the conductivity of the epilayer, the method comprising:
depositing a first doping material directly on the epilayer defined on the substrate, wherein the epilayer comprises a group III nitride epilayer, and wherein the first doping material comprises silicon oxide, silicon nitride, or silicon oxynitride;
depositing a photo-resist layer directly on the first doping material;
removing a first portion of the photo-resist layer to expose the underlying first doping material only directly under the first portion of the photo-resist layer removed, leaving a second portion of the photo-resist layer remaining on the first doping material;
applying an etchant to remove the second portion of the photo-resist layer remaining on the substrate and to remove the first doping material exposed by the first portion of the photo-resist layer removed such that the first doping material remaining on the substrate corresponds to where the second portion of the photo-resist layer is removed with the etchant;
annealing the substrate to dope about 10% to about 50% of the first doping material remaining on the substrate into the group III nitride epilayer to form first doped regions in the group III nitride epilayer while leaving an undoped portion of the first doping material remaining on the group III nitride epilayer;
removing the undoped portion of the first doping material remaining on the group III nitride epilayer;
after the removing the undoped portion, depositing a second doping material directly on the group III nitride epilayer, the second doping material comprising silicon oxide, silicon nitride, or silicon oxynitride;
after the depositing of the second doping material, depositing a second photo-resist layer directly on the second doping material;
removing a first portion of the second photo-resist layer to expose the underlying second doping material only directly under the first portion of the second photo-resist layer;
etching to remove the second photo-resist layer remaining on the substrate and to remove the second doping material exposed by the first portion of the second photo-resist layer removed, wherein the etching results in the second doping material remaining on the substrate corresponding to a location of the second photo-resist layer remaining on the substrate prior to the etching of the second photo-resist layer; and
annealing the substrate to dope about 10% to about 50% of the second doping material remaining on the substrate into the group III nitride epilayer to form second doped regions in the group III nitride epilayer.
2. The method as in claim 1 , wherein the first doping material is deposited using a digital oxide deposition technique, a digital nitride deposition technique, or a combination thereof.
3. The method as in claim 1 , wherein the first doping material is deposited to a thickness of 50 Å to about 250 Å.
4. The method as in claim 1 , wherein the second doping material is deposited to a thickness of 50 Å to about 250 Å.
5. The method as in claim 1 , wherein the second doping material is different than the first doping material.