A single step selective implantation technology for multiply doped layers using proximity annealing

A selective doping technology has been developed for GaAs that allows layers with multiple doping profiles to be prepared in a single implantation step. In this procedure, qualified GaAs Cr-doped substrates were masked With Si
2
N
4
and photoresist levels. The extent of doping in the underlying layer was controlled with the nitride thickness, as Si
3
N
4
has a stopping power nearly that of GaAs. Photoresist was used to define the undoped regions for isolation; completely exposed substrate regions received the total schedule. Implanting the patterned slice at multiple energies allowed the source-drain and gate regions to be appropriately doped in a single step. Proximity annealing was then carried out for implant activation. Small signal 10 GHz GaAs FET's were successfully fabricated without gate recessing on layers prepared by this technique.