Monolithic vertical junction field effect transistor and Schottky barrier diode fabricated from silicon carbide and method for fabricating the same
View Patent ↗A switching element combining a self-aligned, vertical junction field effect transistor with etched-implanted gate and an integrated antiparallel Schottky barrier diode is described. The anode of the diode is connected to the source of the transistor at the device level in order to reduce losses due to stray inductances. The SiC surface in the SBD anode region is conditioned through dry etching to achieve a low Schottky barrier height so as to reduce power losses associated with the turn on voltage of the SBD.
1. A SiC semiconductor device comprising a vertical junction field effect transistor (JFET) comprising a source, a gate and a drain and a Schottky barrier diode (SBD) comprising an anode and a cathode, the device comprising:
a SiC semiconductor substrate layer of a first conductivity type;
a SiC drift layer of the first conductivity type on the substrate layer;
a plurality of SiC source regions of the first conductivity type on the drift layer;
a plurality of SiC gate regions of a second conductivity type different than the first conductivity type formed in the drift layer;
a Schottky junction including a Schottky metal layer adjacent the drift layer; and
a drain ohmic contact adjacent the substrate layer opposite the drift layer, a source ohmic contact adjacent the source region and a gate ohmic contact adjacent the gate region;
wherein the Schottky metal layer is in electrical contact with the source ohmic contact, wherein the drain ohmic contact is a contact for the drain of the JFET and the cathode of the SBD and wherein the source ohmic contact is a contact for the source of the JFET and is electrically connected to the anode of the SBD.
2. The device of claim 1 , wherein the material of the first conductivity type is an n-type semiconductor material and the material of the second conductivity type is a p-type semiconductor material.
3. The device of claim 1 , wherein the gate regions are formed by ion implantation of a dopant of the second conductivity type in the drift layer.
4. The device of claim 1 , further comprising final metal layers disposed on the Schottky metal layer and on the drain and gate ohmic contacts.
5. The device of claim 1 , wherein the drift layer comprises a drift region of the first conductivity type disposed on the substrate and a channel region also of the first conductivity type disposed on the drift region wherein the source regions are disposed on the channel region.
6. The device of claim 4 , wherein the channel region has a higher doping level than the underlying drift region.
7. The device of claim 1 , wherein the drift layer has a dopant concentration of 5×10 16 atoms·cm −3 or less.
8. The device of claim 1 , wherein the substrate layer has a dopant concentration of 10 18 atoms·cm −3 or greater.
9. The device of claim 1 , wherein the source regions have a dopant concentration of 10 18 atoms·cm −3 or greater.
10. The device of claim 1 , wherein the gate regions have a dopant concentration of 10 18 atoms·cm −3 or greater.
11. The device of claim 1 , wherein the gate regions have a dopant concentration of between 5×10 16 atoms·cm −3 and 10 18 atoms·cm −3 .
12. The device of claim 1 , wherein:
the drift layer has a dopant concentration of 5×10 16 atoms·cm −3 or less;
the substrate layer has a dopant concentration of 10 18 atoms·cm −3 or greater;
the source regions have a dopant concentration of 10 18 atoms·cm −3 or greater; and
the gate regions have a dopant concentration of at least 5×10 6 atoms·cm −3 .
13. The device of claim 1 , wherein the Schottky metal layer extends over the source ohmic contact such that the Schottky metal is in electrical contact with the source ohmic contact.
14. The device of claim 1 , further comprising a metal layer in contact with the Schottky metal layer and which extends over the source ohmic contact and which forms an electrical connection between the Schottky metal layer and the source ohmic contact.