Electrical characterization of amorphous Al2O3 dielectric films on n-type 4H-SiC

R Y Khosa,M Winters,R Karhu,J Hassan,E Ö Sveinbjörnsson,E B Thorsteinsson,N Rorsman

doi:10.1063/1.5021411

R Y Khosa, M Winters + Show 5 more

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https://doi.org/10.1063/1.5021411

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Abstract

We report on the electrical properties of Al2O3 films grown on 4H-SiC by successive thermal oxidation of thin Al layers at low temperatures (200°C - 300°C). MOS capacitors made using these films contain lower density of interface traps, are more immune to electron injection and exhibit higher breakdown field (5MV/cm) than Al2O3 films grown by atomic layer deposition (ALD) or rapid thermal processing (RTP). Furthermore, the interface state density is significantly lower than in MOS capacitors with nitrided thermal silicon dioxide, grown in N2O, serving as the gate dielectric. Deposition of an additional SiO2 film on the top of the Al2O3 layer increases the breakdown voltage of the MOS capacitors while maintaining low density of interface traps. We examine the origin of negative charges frequently encountered in Al2O3 films grown on SiC and find that these charges consist of trapped electrons which can be released from the Al2O3 layer by depletion bias stress and ultraviolet light exposure. This electron trapping needs to be reduced if Al2O3 is to be used as a gate dielectric in SiC MOS technology.

Highlights

4H-SiC metal-oxide semiconductor field-effect transistors (MOSFETs) are promising devices for power electronics
A key problem is the high density of so called near-interface traps (NITs) detected at the SiO2/4H-SiC interface with energy levels near the SiC conduction band edge that limit the electron channel mobility.[3,4,5,6]
Those Al2O3 films are grown by atomic layer deposition (ALD) at 300◦C or thermal evaporation of metallic Al followed by low temperature oxidation to form Al2O3.16,17 As grown Al2O3 deposited on 4H-SiC by ALD typically contains a large number of negative charges which are reduced after annealing in Ar at 1000◦C but the Al2O3/SiC interface contains a high density of interface traps after such treatment.[9,10]

Summary

Introduction

4H-SiC metal-oxide semiconductor field-effect transistors (MOSFETs) are promising devices for power electronics. Such transistors are commercially available for blocking voltages above 900 V.1,2. FETs. SiC MOSFETs cannot compete with Si technology for lower blocking voltages because of poor electron channel mobility which limits the device on-resistance. Other large bandgap dielectrics such as AlN, Al2O3 and HfO2 have been investigated.[8,9,10,11,12,13,14] One of the alternatives is aluminum oxide (Al2O3) with bandgap of ∼ 7.0 eV.[8,11,15] Recently, an amorphous Al2O3 has been used as a gate dielectric in graphene field effect transistors with some success.[16,17] Those Al2O3 films are grown by atomic layer deposition (ALD) at 300◦C or thermal evaporation of metallic Al followed by low temperature oxidation to form Al2O3.16,17 As grown Al2O3 deposited on 4H-SiC by ALD typically contains a large number of negative charges which are reduced after annealing in Ar at 1000◦C but the Al2O3/SiC interface contains a high density of interface traps after such treatment.[9,10] More recently, studies on pre-deposition surface cleaning and post deposition annealing at different temperature in N2O ambient are been performed on ALD

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