Vertical field effect transistor device and method of fabrication
A method and vertical FET device fabricated in GaN or other suitable material. The device has a selective area implant region comprising an activated impurity configured from a bottom portion of a recessed regions, and substantially free from ion implant damage by using an annealing process. A p-type gate region is configured from the selective area implant region, and each of the recessed regions is characterized by a depth configured to physically separate an n+ type source region and the p-type gate region such that a low reverse leakage gate-source p-n junction is achieved. An extended drain region is configured from a portion of an n− type GaN region underlying the recessed regions. An n+ GaN region is formed by epitaxial growth directly overlying the backside region of the GaN substrate and a backside drain contact region configured from the n+ type GaN region overlying the backside region.
1. A method for fabricating a high voltage switching device, the method comprising:
providing a gallium and nitrogen containing substrate member, the gallium and nitrogen containing substrate member having a surface region and a backside region;
forming a first n+ type GaN layer overlying the surface region;
forming a n− type GaN layer overlying the first n+ type GaN layer;
forming a second n+ type GaN layer overlying the n-type GaN layer;
forming a hard mask material overlying the second n+ type GaN layer, the hard mask material having a hard mask surface region;
patterning the hard mask material to expose a plurality of trench regions;
subjecting the plurality of trench regions to a reactive ion etching process, including a chlorine gas, boron tri chloride, and argon gas, to cause formation of the plurality of trench regions, each of which has a selected depth extending vertically from the hard mask surface region, and causing formation of a plurality of finger regions, each of which is disposed between a pair of trench regions;
subjecting an exposed region of each of the finger regions and a bottom portion of the trench region to a wet chemical etch to cause exposure of a plurality of principle crystalline planes, including an m-plane and a c-plane or an a-plane or a c-plane;
forming a thickness of a conformal layer overlying exposed surfaces of each of the fingers, the trench regions, and a peripheral region;
performing an implantation process using a beryllium bearing species to form a plurality of implanted regions, each of which is spatially disposed between each pair of fingers, to form an outer implanted region on each exterior finger region, and to form a peripheral implant region;
activating, using an annealing process, the beryllium bearing species in the plurality of implanted regions, the outer implanted region, and the peripheral implanted region such that the activating forms a plurality of p-type regions;
forming a plurality of p-type metal contact regions, each of the p-type metal contact regions formed overlying one of the p-type regions;
forming a thickness of planarizing material overlying a surface region including each of the finger regions, the trench regions, and the peripheral region;
forming a plurality of openings, each of the openings exposing a portion of the second n+ type layer included in the finger region;
forming a plurality of n-type contact metal regions, each of which is connected to the portion of the n− type layer included in the finger region;
whereupon the high voltage switching device is configured from a drain region configured from the backside region of the gallium and nitrogen containing substrate member, a gate region configured from connection to each of the p-type metal contact regions, a channel region configured between a pair of p-type regions, and a source region configured from connection to each of the n-type contact metals.
2. The method of claim 1 wherein the wet chemical etch comprises a tetramethylammonium hydroxide (TMAH) etchant material.
3. The method of claim 1 where the wet chemical etch comprises tetramethylammonium hydroxide (TMAH) diluted in a water at an elevated temperature ranging from about 50 Degrees Celsius to about 150 Degrees Celsius.
4. The method of claim 1 wherein each of the finger regions has a portion of n− type layer, a portion of the second n+ type layer, and a portion of the hard mask material.
5. The method of claim 1 wherein the annealing process comprising a first isothermal anneal process, a laser anneal process to activate the beryllium bearing species, and a second isothermal anneal process.
6. The method of claim 5 wherein first isothermal anneal process comprises an annealing process at 1000° C. in hydrogen and ammonia gas near atmospheric pressure; wherein the laser anneal process comprises using an XeCl excimer laser at a 308 nm wavelength; and wherein the second isothermal anneal process comprises an annealing process at in nitrogen gas at 800° C.
7. The method of claim 1 wherein forming the first n+ type GaN layer, the n− type GaN layer, and the second n+ type GaN layer comprises an epitaxial growth process using a MOCVD reactor with a tri-ethyl gallium and an ammonia gas.
8. The method of claim 1 wherein the selected depth of the plurality of trench regions has an aspect ratio ranging from four-to-one to ten-to-one.
9. The method of claim 1 wherein forming the plurality of p-type metal contact regions comprises forming a plurality of contact openings within the conformal layer and forming the plurality of p-type metal contact regions within the plurality of contact openings.
10. The method of claim 1 further comprising forming a pad contact layer overlying the plurality of n-type metal contact regions.