N-channel field-effect mobility inversely proportional to the interface state density at the conduction band edges of SiO2/4H-SiC interfaces

Abstract

We investigated the effects of the interface state density (DIT) at the interfaces between SiO2 and the Si-, C-, and a-faces of 4H-SiC in n-channel metal-oxide-semiconductor field-effect transistors that were subjected to dry/nitridation and pyrogenic/hydrotreatment processes. The interface state density over a very shallow range from the conduction band edge (0.00 eV < EC − ET) was evaluated on the basis of the subthreshold slope deterioration at low temperatures (11 K < T). The interface state density continued to increase toward EC, and DIT at EC was significantly higher than the value at the conventionally evaluated energies (EC − ET = 0.1–0.3 eV). The peak field-effect mobility at 300 K was clearly inversely proportional to DIT at 0.00 eV, regardless of the crystal faces and the oxidation/annealing processes.

Interface carbon defects at 4H-SiC(0001)/SiO2 interfaces studied by electron-spin-resonance spectroscopy

“…6 They could be fully eliminated by optimum POAs by NO or POCl 3 . Based on the similarities between our ESR data and previous electrical characterization, 2,3,9,12 we suggest that the interface carbon defects are the major electron traps at the dry-oxidized 4H-SiC(0001)/SiO 2 interfaces, and hence both the POAs drastically improve l FE of Si-face 4H-SiC MOSFETs. In addition, we found that the POCl 3 POAs at 1000 C formed a high density (>1 Â 10 12 cm À2 ) of the P donors in the channel region, which is possibly related to further enhancement on l FE.…”

“…The POA process can make the field-effect mobility (l FE ) of 4H-SiC MOSFETs ten times larger than that before the POA. 1,2 The mechanism for this drastic l FE -improvement has recently been clarified by combining Hall and split capacitance-voltage measurements. 3 According to the recent findings, the NO POA process effectively increases the amount of free electrons by removing electron traps, while it does not increase the electron mobility itself much.…”

“…It is notable that the oxidation and POA processes we studied here were electrically characterized by previous works on MOS or MOSFET structures. 2,3,9,12 In the first step, we repeatedly tried dry oxidation. For ESR specimens after the dry oxidation, their Si face was protected by an acid-proof coat, and then C-face oxide was chemically removed by hydrofluoric-acid etching.…”

Electron-spin-resonance and electrically detected-magnetic-resonance characterization on PbC center in various 4H-SiC(0001)/SiO2 interfaces

“…1 The standard method for fabricating good 4H-SiC/SiO 2 interfaces is thermal oxidation by dry O 2 gas (dry oxidation) followed by interfacial nitridation such as NO post-oxidation anneal (POA). 2 This process can reduce shallow interface states near the conduction band edge (E C ) 2,3 and deeper electron traps, 4 resulting in a drastic improvement on the field-effect mobility (μ FE ) of SiC-MOSFETs. As a result, the improved μ FE reaches 30-40 cm 2 V −1 s −1 for 4H-SiC(0001) (so-called "Si face") MOS interfaces, realizing ultra-low-energy-loss performances of power SiC-MOSFETs as compared to those of conventional power Si-MOSFETs.…”

Reduction of interface states by hydrogen treatment at the aluminum oxide/4H-SiC Si-face interface

“…Low channel performance at SiO 2 /4H-SiC interfaces due to a high interface state density (D IT ) 1 and low channel mobility has been a problem of both scientific and practical interest. 2 Although SiC is advantageous in that SiO 2 can be formed by oxidation, improvement of the SiO 2 /4H-SiC channel performance has plateaued, despite intensive research and development efforts.…”