Reaction of nitrous oxide and ammonia molecules at 4H-SiC/SiO2 interface: An ab initio study

doi:10.1016/j.susc.2022.122102

Surface Science

Volume 723, September 2022, 122102

https://doi.org/10.1016/j.susc.2022.122102 Get rights and content

Highlights

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The reaction N₂O and NH₃ molecules at 4H-SiC /SiO₂ interface are theoretically investigated.
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The desorption of carbon oxide in addition to Si–N bond formation occurs in the N₂O reaction.
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Various atomic configurations are formed depending on the plane orientation in the NH₃ reaction.
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The energy barriers for the N₂O and NH₃ reactions are higher than that of the NO reaction.

Abstract

The reactions of N $_{2}$ O and NH $_{3}$ molecules at the interface between 4H-SiC and SiO $_{2}$ during post oxidation annealing (POA) are theoretically investigated using ab initio calculations. We find that the reactions of N $_{2}$ O molecule at (0001) and (0001^¯) interfaces result in the desorption of carbon oxide molecules in addition to Si–N bond formation. For the reaction of NH $_{3}$ molecule, various atomic configurations are formed depending on the plane orientation. Furthermore, the energy barriers for the N $_{2}$ O and NH $_{3}$ reactions are found to be higher than that of the NO reaction owing to different atomic configurations at the transition state structure. The calculated results shed some insights for understanding POA process at 4H-SiC/SiO $_{2}$ interfaces.

Graphical abstract

Introduction

SiC has superior physical properties such as high thermal conductivity and high breakdown field, which is promising for applying in power electronics devices [1], [2]. Moreover, the ability to form SiO $_{2}$ by thermal oxidation is advantageous for fabricating metal-oxide-semiconductor field-effect transistors (MOSFETs) compared with other wide-gap semiconductors. However, it has been known that the degradation of MOSFET performance in SiC is caused by high interface trap density ( $D_{it}$ ) at SiC/SiO $_{2}$ interface, and suggested that carbon-related defects are the most likely physical origin of $D_{it}$ [3], [4]. To reduce $D_{it}$ and increase channel mobility, post oxidation annealing (POA) has been widely applied [5], [6], [7]. In general, nitric oxide (NO) is used as annealing gas because it leads to increased MOSFET performance and reliability. NO post-oxidation annealing (NO-POA) process has been widely recognized as a very effective approach [5], [6], [7]. Furthermore, it has been reported that POA using other nitrogen-containing molecules such as nitrous oxide (N $_{2}$ O) and NH $_{3}$ leads to even higher mobility and $D_{it}$ reduction. [8], [9], [10], [11], [12], [13], [14], [15], [16], [17] Chung et al. have demonstrated a significant passivation of the interface state density near the conduction band edge in SiC can be achieved with high temperature anneals using NH $_{3}$ molecules [9]. Swanson et al. have revealed that N $_{2}$ O POA leads to both a reduction of the fixed oxide charge and the interface state density and a disordered, carbon-rich transition layer is hardly formed at the SiC/SiO $_{2}$ interface [12]. In spite of these experimental findings, the knowledge for the behavior of annealing gas molecules near the interface with carbon-related defects as well as the atomic structures after POA is still lacking.

In our previous study, we have investigated the reaction of the NO molecule at the interface between 4H-SiC and SiO $_{2}$ (4H-SiC/SiO $_{2}$ ) on the basis of theoretical approach using ab initio calculations [18]. The reaction energies and energy barriers for the NO reaction have been calculated to discuss the physical origins of $D_{it}$ reduction. In the present study, we extend our theoretical study to clarify the effect of annealing gas species on the interfacial reaction during POA. For the N $_{2}$ O and NH $_{3}$ molecules, the reaction processes as well as the structural stability depending on the interface atomic configuration and surface orientation are clarified. By comparing the results of NO molecule[18] with those of N $_{2}$ O and NH $_{3}$ molecules obtained in the present study, the effects of reaction species on the structural stability and the reaction process are discussed. Furthermore, the analysis of electronic structures of atomic configurations after the reaction is carried out to discuss the physical origins of $D_{it}$ reduction in N $_{2}$ O-POA and NH $_{3}$ -POA.

Section snippets

Computational details

For the 4H-SiC/SiO $_{2}$ interfaces on the (0001) and (0001^¯) orientations, the c(2 $\sqrt{3} \times$ 3) slab models consisting of four 4H-SiC bilayers, two SiO $_{2}$ monolayers and an approximately 10 Å vacuum region are employed. Fig. 1 shows the side views of interface models on the (0001) and (0001) orientations, after the O $_{2}$ reactions obtained by in previous ab initio calculations [19]. The interfaces including C $-$ C bond on the (0001) interface shown in Fig. 1(a) and C=C bond on the (0001^¯) inteface shown in Fig. 1

Results and discussion

Prior to clarifying the reaction process of the N $_{2}$ O molecule at the interface, we explore stable and metastable structures of the interface as final states after annealing. The N $_{2}$ O molecule is stably located at the open space of the SiO $_{2}$ region at the interfaces including the C $-$ C and C double bond C defects on the (0001) and (0001) interfaces shown in Fig. 1(a) and (b), respectively. It is thus reasonable to consider these structures as the initial state of the POA process. Since the N $_{2}$ O molecule easily

Conclusion

We have studied the reactions of N $_{2}$ O and NH $_{3}$ molecules at 4H-SiC/SiO $_{2}$ interface by performing ab initio calculations. We have found that similar structural changes occur in the NO and N $_{2}$ O reactions with the desorption of carbon oxide such as CO and CO $_{2}$ molecules in addition to the formation of Si $_{4}$ –N and Si $_{3}$ –N in SiC region near the interface. In contrast, for the NH $_{3}$ reaction the C–C and C=C bonds at the interface change into various atomic configurations depending on the plane orientation. For

CRediT authorship contribution statement

Toru Akiyama: Conceptualization, Methodology, Investigation, Resources, Writing – original draft, Writing – review & editing, Funding acquisition. Tsunashi Shimizu: Conceptualization, Methodology, Investigation. Tomonori Ito: Resources, Writing – review & editing, Funding acquisition. Hiroyuki Kageshima: Conceptualization, Writing – review & editing. Kenji Shiraishi: Conceptualization, Writing – review & editing.

Declaration of Competing Interest

All authors have participated in (a) conception and design, or analysis and interpretation of the data; (b) drafting the article or revising it critically for important intellectual content; and (c) approval of the final version.

This manuscript has not been submitted to, nor is under review at, another journal or other publishing venue.

The authors have no affiliation with any organization with a direct or indirect financial interest in the subject matter discussed in the manuscript

Acknowledgments

This work was supported in part by JSPS Scientific Research Grant JP19K05268 and JP20K05324, CREST-JST Grant Number JPMJCR16N2, and the Collaborative Research Program of Research Institute for Applied Mechanics at Kyushu University. The computations were performed using the facilities in Research Center for Computational Science at National Institutes of Natural Sciences (Project: 22-IMS-C052) and Research Institute for Information Technology at Kyushu University.

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Reaction of nitrous oxide and ammonia molecules at 4H-SiC/SiO2 interface: An ab initio study

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Computational details

Results and discussion

Conclusion

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgments

Jpn. J. Appl. Phys.

Large‐band‐gap SiC, III‐V nitride, and II‐VI ZnSe‐based semiconductor device technologies

J. Appl. Phys.

Invited Review Paper Material science and device physics in SiC technology for high-voltage power devices

Jpn. J. Appl. Phys.

Interface trap profile near the band edges at the 4H-SiC/SiO24H-SiC/SiO2 interface

Appl. Phys. Lett.

Intrinsic SiC/SiO2 Interface States

Phys. Status Solidi A

Effect of nitric oxide annealing on the interface trap densities near the band edges in the 4H polytype of silicon carbide

Appl. Phys. Lett.

Characterization and modeling of the nitrogen passivation of interface traps in SiO2/4H–SiC

J. Appl. Phys.

Generation of very fast states by nitridation of the SiO2/SiC interface

J. Appl. Phys.

Improved interface properties of p-type 6H-SiC/SiO2 system by NH3 pretreatment

Appl. Phys. Lett.

Effects of anneals in ammonia on the interface trap density near the band edges in 4H–silicon carbide metal-oxide-semiconductor capacitors

Appl. Phys. Lett.

Significant Improvement in Reliability of Thermal Oxide on 4H-SiC (0001) Face using Ammonia Post-Oxidation Annealing

Mater. Sci. Forum

Effect of NH3 post-oxidation annealing on flatness of SiO2/SiC interface

Mater. Sci. Forum,

Effects of a post-oxidation annealing in nitrous oxide on the morphological and electrical properties of SiO2/4H-SiC interfaces

Mater. Sci. Forum

Threshold Voltage Instability of SiC-MOSFETs on Various Crystal Faces

Mater. Sci. Forum

Reaction of nitrous oxide and ammonia molecules at 4H-SiC/SiO $_{2}$ interface: An ab initio study

Interface trap profile near the band edges at the 4H-SiC/SiO₂4H-SiC/SiO₂ interface

Intrinsic SiC/SiO₂ Interface States

Characterization and modeling of the nitrogen passivation of interface traps in SiO₂/4H–SiC

Generation of very fast states by nitridation of the SiO₂/SiC interface

Improved interface properties of p-type 6H-SiC/SiO₂ system by NH₃ pretreatment

Effect of NH₃ post-oxidation annealing on flatness of SiO₂/SiC interface

Effects of a post-oxidation annealing in nitrous oxide on the morphological and electrical properties of SiO₂/4H-SiC interfaces