Gallium nitride surface protection during RTA annealing with a GaO_xN_ycap-layer

Abstract

Gallium nitride (GaN) is generally considered a good candidate for power electronic devices such as Schottky barrier diodes (SBDs). Nevertheless, GaN has a strong sensitivity to high temperature treatments and a cap-layer is mandatory to protect the material surface during annealing at high temperature such as post-implantation treatments. In this work, an oxidized gallium nitride layer (GaO x N y ) was generated with Oxford PECVD equipment using a N 2 O plasma treatment to protect the GaN surface during a rapid thermal annealing (RTA), in the range of 1000 °C-1150 °C for a few minutes. Before annealing, c-TLM patterns were processed on the GaO x N y /GaN sample to characterize its sheet resistance. After the N 2 O plasma treatment, the sample exhibited lower sheet resistance, indicating a better n-type conduction of the GaO x N y layer due to an excess of free carriers, compared to the as-grown GaN layer. The GaO x N y /GaN surface was then annealed at 1150 °C for 3 min and observed through AFM imaging. The surface exhibited a good quality with a low roughness, nevertheless, a low density of small hexagonal pits appeared after annealing. Finally, studies to determine an efficient etching process of the GaO x N y cap-layer were conducted using both chemical and physical approaches. We observed that efficient etching of the layer was achieved using a heated hydrofluoridric acid (HF 25%) solution. To conclude, GaO x N y has proved to be an efficient cap-layer for GaN protection at high temperature.

Capping stability of Mg-implanted GaN layers grown on silicon

“…In this study, we will compare the two solutions corresponding to thick stacks of AlN(10 nm)/SiO 2 (100 nm) and of AlN(10 nm)/Si 3 N 4 (100 nm) layers deposited ex situ . Both caps show good resilience and surface morphology with a high thermal budget of up to 7 h at 1100 °C in N 2 (i.e., comparable to or even higher than published results ). Only an anneal of 1 h at 1200 °C in N 2 allowed us to highlight a difference.…”

“…Such cracking happens during the AlN layer deposition due to the difference in thermal expansion coefficients and lattice mismatch with GaN (SEM observations not shown here). Such behavior has been already observed in the literature for AlN deposited on GaN, reducing the resilience of the cap . Secondly, another kind of defect, consisting of local agglomerations of small outgrowths is seen.…”

“…Concerning the protective layer, AlN proved to be one of the most promising materials for GaN protection during annealing and efforts has also been made in developing a protection using various nitrides and oxides stacks . Regarding the thermal budget optimization, a two‐step annealing process combining a long annealing at moderate temperature ( T > 900 °C for duration >30 min to achieve crystal defect recovery) with rapid thermal annealing (RTA) or multicycle RTA (with T > 1200 °C to activate the dopant) is a promising strategy.…”

Dependence of reverse leakage on the edge termination process in vertical GaN power device

“…Besides crystal damage accompanied by unsaturated atomic bonds forming defect states, other atomistic mechanisms could promote the increase in leakage current. On the one hand, the creation of nitrogen vacancies introduced by the plasma bombardment [27], or the oxygen incorporation on nitrogensites-both defects acting as donors in GaN [28,29], could lead to the reduction of effective p-type doping concentration near the termination edge surface, thereby facilitating the charge transport between the highly doped n + layer on the top and the lower doped n − drift layer. On the other hand, Ga x N x O 1−x−y can also be formed on the GaN edge termination surface by O 2 -plasma treatment leading to enhanced conductivity in the altered surface structure [29].…”

Impact of Protective Layer Structures on High‐Temperature Annealing of GaN

“…Tensile stress between AlN and GaN, thermal expansion during annealing, and GaN decomposition in the growth of high crystal quality AlN films need to be solved. [ 12 ] Some other protective layers are also reported, including gallium oxynitride grown by PECVD, [ 13 ] PVD‐deposited NbN, [ 14 ] and PECVD‐grown SiO 2 combined with AlN by sputtering. [ 15 ] However, very few articles present GaN surface characterizations after annealing.…”