Characteristics of Pure Ge₃N₄ Dielectric Layers Formed by High-Density Plasma Nitridation

Abstract

We have demonstrated the direct nitridation of Ge substrates to obtain pure germanium nitrides (Ge3N4). Physical characterization revealed that 3.5-nm-thick amorphous Ge3N4 layers with smooth surfaces and abrupt nitride/Ge interfaces were formed by the high-density plasma nitridation of Ge(100) substrates. We have investigated the thermal stability of the Ge3N4 layers, and found that the nitride was stable up to 550 °C and started to decompose around 580 °C under an N2 ambient, while maintaining smooth nitride surfaces during thermal decomposition. We also found that vacuum annealing did not affect the decomposition temperature and that nitrogen was the only desorption species during Ge3N4 decomposition, which led to the regrowth of smooth and crystalline Ge surfaces after the nitrides had been completely removed at 700 °C. These results demonstrate both the superior thermal stability of pure Ge3N4 as a gate insulator and feasibility of using nitride as a surface passivation layer in the fabrication of Ge-based devices.

Electrical Characteristics of Ge-Based Metal-Insulator-Semiconductor Devices with Ge<SUB>3</SUB>N<SUB>4</SUB> Dielectrics Formed by Plasma Nitridation

“…Moreover, in order to evaluate the interface state density (D it , SiO 2 with a thickness of 10 nm was deposited using a sputtering method on as-fabricated Ge nitride layers to suppress the gate leakage current, followed by PDA in N 2 ambient from 400 C to 650 C. C-V and conductance-voltage (G-V ) characteristics were measured at low temperature for D it evaluation of Ge 3 N 4 /Ge interfaces. In our previous study, 10 we confirmed formation of oxygen-free pure Ge 3 N 4 layers using plasma nitridation of Ge substrates by angle-resolved X-ray photoelectron spectroscopy (XPS). It was also found, through atomic force microscopy (AFM) observations, that the pure Ge 3 N 4 layers were uniform and had a smooth surface (RMS: 0.17 nm).…”

“…9 We have also succeeded in fabricating pure Ge 3 N 4 layers using high-density nitrogen plasma and obtained amorphous and oxygen-free Ge 3 N 4 layers with a smooth Ge 3 N 4 /Ge interface. 10 We also confirmed a higher thermal stability of Ge nitride than GeO 2 under vacuum and in a nitrogen ambient, but details of the electrical properties of the pure Ge 3 N 4 dielectric have not been clarified yet. In order to use the Ge nitride as a gate insulator or an interfacial layer under high-k gate dielectrics for Ge metal-insulatorsemiconductor (Ge-MIS) devices, electrical characteristics of the nitride layer and its thermal robustness need to be understood.…”

“…Our plasma nitridation system, which can be operated under atmospheric pressure conditions, has a porous electrode for generating large-scale and high-density plasma. [10][11][12] The chamber pressure during plasma nitridation was kept to the order of 10 3 Pa, and the other treatment conditions were as follows: nitridation time of 30 min, RF power of 50 W, distance between the electrode and Ge substrate of 1 cm, and substrate temperature of 450 C. After post nitridation annealing (PNA) in N 2 ambient at 450 C for 10 min, Au gate electrode was deposited by vacuum evaporation through a shadow mask. Sample transfer between the processing apparatuses was carried out immediately after each process steps.…”

Temperature Stress Response of Germanium MOS Vapacitors with HfO2/HfSiON Gate Dielectric

“…However, this interfacial GeN x layer may also limit the attainable downscaling of equivalent oxide thickness because of a lower dielectric constant than the high-dielectrics. As an alternative approach unique to this study, the interfacial GeN x layer was removed by using a 1 min PDA treatment in Ar at 800 °C, which was sufficient to dissociate Ge-N bonds in the interfacial layer [5]. Following the PDA and sacrificial layer removal, the high-films were assumed to be in direct contact with the Ge substrate.…”

(Invited) MOS Interface Control of High Mobility Channel Materials for Realizing Ultrathin EOT Gate Stacks

“…A variety of interfacial layers such as SiO 2 /Si [10][11][12][13][14], GeO 2 [7,8,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30], GeON [19,[31][32][33] and Ge 3 N 4 [16,[34][35][36][37] and their MOS interface properties have already been reported. Among them, GeO 2 /Ge interfaces have recently been regarded as one of the most superior Ge MOS interfaces [7,8,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30].…”