Method for improving inversion layer mobility in a silicon carbide MOSFET
View Patent ↗A method of manufacturing a semiconductor device based on a SiC substrate involves forming an oxide layer on a Si-terminated face of the SiC substrate at an oxidation rate sufficiently high to achieve a near interface trap density below 5×10 11 cm −2 ; and annealing the oxidized SiC substrate in a hydrogen-containing environment, to passivate deep traps formed in the oxide-forming step, thereby enabling manufacturing of a SiC-based MOSFET having improved inversion layer mobility and reduced threshold voltage. It has been found that the density of DTs increases while the density of NITs decreases when the Si-face of the SiC substrate is subject to rapid oxidation. The deep traps formed during the rapid oxidation can be passivated by hydrogen annealing, thus leading to a significantly decreased threshold voltage for a semiconductor device formed on the oxide.
1. A method of manufacturing a semiconductor device based on a SiC substrate, comprising:
forming an oxide layer on a Si-terminated face of said SiC substrate at an oxidation rate sufficiently high to achieve a near interface trap density below 5×10 11 cm −2 ; and
annealing said oxidized SiC substrate in a hydrogen-containing environment, in order to passivate deep traps formed in said oxide-forming step, thereby enabling manufacturing of a SiC-based MOSFET having improved inversion layer mobility and reduced threshold voltage.
2. The method of manufacturing a semiconductor device based on a SiC substrate according to claim 1 , wherein said oxidation rate has a maximum which is at least 700 Angstrom per hour at a temperature of 1150 degrees C.
3. The method of manufacturing a semiconductor device based on a SiC substrate according to claim 1 , wherein said sufficiently high oxidation rate is achieved by means of an oxidation rate enhancing agent.
4. The method of manufacturing a semiconductor device based on a SiC substrate according to claim 3 , wherein said oxidation rate enhancing agent is introduced in an oxidation chamber during oxidation of said Si-terminated face of said SiC substrate.
5. The method of manufacturing a semiconductor device based on a SiC substrate according to claim 3 , wherein said oxidation rate enhancing agent is an alkali metal.
6. The method of manufacturing a semiconductor device based on a SiC substrate according to claim 5 , wherein said oxidation rate enhancing agent is sodium.
7. The method of manufacturing a semiconductor device based on a SiC substrate according to claim 1 , wherein said oxide-forming step comprises:
providing said SiC substrate in an oxidation chamber; and
introducing sodium into said oxidation chamber during oxidation of a Si-terminated face of said SiC-substrate, thereby achieving a sufficiently high oxidation rate to reduce the density of near interface traps to below 5×10 11 cm −2 .
8. The method of manufacturing a semiconductor device based on a SiC substrate according to claim 7 , wherein said annealing step comprises:
subjecting said oxidized SiC substrate to a first post-oxidation anneal in an inert gas, to reduce an amount of mobile sodium in said oxidized SiC substrate; and
subjecting said sodium reduced oxidized SiC substrate to a second post-oxidation anneal in a hydrogen-containing environment, in order to passivate said deep traps.
9. A semiconductor device comprising:
a SiC substrate having a Si-terminated face; and
an oxide layer formed on said Si-terminated face of said SiC substrate, wherein:
a concentration of near interface traps at an interface between said SiC substrate and said oxide is lower than 5×10 11 cm −2 ; and
a concentration of passivated deep traps at said interface is in excess of 10 12 cm −2 .