Vertical gallium nitride Schottky diode
A vertical conduction nitride-based Schottky diode is formed using an insulating substrate which was lifted off after the diode device is encapsulated on the front side with a wafer level molding compound. The wafer level molding compound provides structural support on the front side of the diode device to allow the insulating substrate to be lifted off so that a conductive layer can be formed on the backside of the diode device as the cathode electrode. A vertical conduction nitride-based Schottky diode is thus realized. In another embodiment, a protection circuit for a vertical GaN Schottky diode employs a silicon-based vertical PN junction diode connected in parallel to the GaN Schottky diode to divert reverse bias avalanche current.
1. A method for forming a vertical conduction nitride-based Schottky diode, comprising:
providing an insulating substrate;
forming a nitride-based semiconductor body of a first conductivity type on the insulating substrate;
forming a first metal layer on a front side of the nitride-based semiconductor body to form a Schottky junction, the first metal layer forming an anode electrode of the Schottky diode;
forming a second metal layer on the first metal layer;
forming a solder ball on the second metal layer;
forming a wafer level molding layer on the front side of the nitride-based semiconductor body, the wafer level molding layer encapsulating the second metal layer and at least part of the solder ball;
separating the insulating substrate from the semiconductor body to expose a backside of the nitride-based semiconductor body; and
forming a third metal layer on an exposed backside of the nitride-based semiconductor body, the third metal layer forming an ohmic contact with the semiconductor body and forming a cathode electrode of the Schottky diode,
wherein the Schottky diode has a vertical current path from the solder ball, through the anode electrode and the Schottky junction to the cathode electrode.
2. The method of claim 1 , further comprising:
planarizing the solder ball to a top surface of the wafer level molding layer.
3. The method of claim 1 , wherein forming a nitride-based semiconductor body of a first conductivity type on the insulating substrate comprises:
forming a heavily doped gallium nitride (GaN) layer of the first conductivity type on the insulating substrate; and
forming a lightly doped gallium nitride (GaN) layer of the first conductivity type on the heavily doped GaN layer,
wherein the first metal layer is formed on a top surface of the lightly doped GaN layer and the third metal layer is formed on a back surface of the heavily doped GaN layer after the insulating substrate has been removed.
4. The method of claim 1 , wherein separating the insulating substrate from the semiconductor body comprises:
separating the insulating substrate from the semiconductor body using a laser lift-off process.
5. The method of claim 1 , further comprising:
forming a termination structure at an edge of the first metal layer, the termination structure being configured to reduce electric field crowding at the edge of the anode electrode.
6. The method of claim 5 , wherein forming a termination structure comprises:
forming a guard ring comprising a nitride-based epitaxial layer of a second conductivity type, opposite the first conductivity type, on the front side of the nitride-based semiconductor body at the edge of the first metal layer, the nitride-based epitaxial layer having a step recess where the part of the epitaxial layer having a thinner thickness is disposed towards the Schottky junction of the Schottky diode; and
forming a dielectric field plate on a top surface of the nitride-based epitaxial layer, the dielectric field plate extending up to the step recess of the nitride-based epitaxial layer.
7. The method of claim 6 , wherein the nitride-based epitaxial layer comprises a gallium nitride layer of the second conductivity type and the dielectric field plate comprises a silicon nitride layer.
8. The method of claim 6 , wherein the first conductivity type comprises N-type conductivity and the second conductivity type comprises P-type conductivity.
9. The method of claim 1 , further comprising:
forming a passivation layer on the second metal layer to cover at least edges of the second metal layer.