In this study, we have performed a thorough characterization of the GaN surface after etching up to 100 nm in Cl2 plasma under various bias voltages and according to the carrier wafer used (Si, SiO2, Si3N4, and photoresist). The objective of this article is to evaluate the etch damage and contamination of the GaN surface when materials with other chemical nature are present during etching. The effects of etching conditions on surface morphology and chemical compositions of etched GaN films are studied in detail using XPS and AFM measurements. To this aim, a universal methodology is proposed to estimate accurately by XPS the stoichiometry of the GaN surface exposed to reactive plasmas when only an Al Kα x-ray source is available. The results indicate that the GaN etching mechanisms are very sensitive to the chlorine radical density present in the plasma, the latter being strongly influenced by the carrier wafer. Substrates that are more chemically reactive with Cl2 plasma such as silicon or photoresist compared to SiO2 or Si3N4 will lead to a greater loading of atomic chlorine, which in turn will lead to lower GaN etch rates. Moreover, the GaN surface contamination will depend on the etch by-products ejected by the carrier wafer. The GaN surface exposed to Cl2 plasma shows a Ga-depleted surface because of the more important reactivity of Cl with Ga rather than N, except in the SiO2 carrier wafer case. In this latter case, the formation of Ga–O bond limits the Ga removal. Regarding the surface roughness, it seems that the contaminants play a little role in the roughness formation except for the oxygen released by the SiO2 carrier wafer. On the other hand, the surface roughness evolution is clearly driven by the chlorine radical flux reaching the GaN surface. At low bias voltage, a preferential crystalline orientation etching driven by the Cl radicals leads to the formation of hexagonal shaped defects that are associated to screw-type threading dislocations already present in the pristine GaN material. At higher bias, the enlargement of the defects is limited, leading to a very low surface roughness value but to amorphized surfaces.

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Excited species, reactive neutral species and positive ions, produced during the etching of Ge, Se and GeSe 2 targets in Inductively Coupled Plasmas, were identified by means of Mass Spectrometry (MS) and Optical Emission Spectroscopy (OES). The surface of etched Ge 39 Se 61 thin films were analysed thanks to in situ X-ray photoelectron spectroscopy (XPS) and compared with those of Ge and Se etched samples. In 100% SF 6 , the successive adsorption of fluorine atoms forms SeF x (x = 2, 4, 6) and GeF x (x = 2, 4) stable and volatile products, generating a surface with few residues as interpreted with in situ XPS. The identification of SSeF + x (x = 2, 3, 7) ions confirms that sulfur atoms play a role during the etching of Se-containing materials. A 0D kinetic model predicted the evolution of reactive neutral fluxes, ion fluxes and plasma parameters (T e and n e) in SF 6 /Ar plasmas. It was found that the SeF 6 and GeF 4 concentrations, through SeF + 5 and GeF + 3 MS signals, were related to the fluorine atom flux. In SF 6 /O 2 , the simultaneous effect of fluorine and oxygen adsorption induces (Se) x-Ge-R 4−x environments (R = F, O) at the surface of the Ge 39 Se 61 thin films.

Controlling the plasma etching step involved in metal-oxide-semiconductor high-electron-mobility-transistor (MOSHEMT) GaN fabrication is essential for device performance and reliability. In particular, understanding the impact of GaN etching conditions on dielectric/GaN interface chemical properties is critically important. In this work, we investigate the impact of the carrier wafers (Si, photoresist, SiO2, and Si3N4) used during the etching of GaN in chlorine plasma on the electrical behavior of Al2O3/n-GaN metal–oxide–semiconductor (MOS) capacitors. X-ray Photoelectron spectroscopy (XPS) analyses show that the Al2O3/GaN interface layer contains contaminants from the etching process after the Al2O3 deposition. Their chemical nature depends on the plasma chemistry used as well as the chemical nature of the carrier wafer. Typically, Cl and C are trapped at the interface for all substrates. In the particular case of Si carrier wafer, a significant amount of SiOx is present at the Al2O3/GaN interface. The capacitance–voltage (C–V) characteristics of the MOS capacitors indicate that the presence of Si residues at the interface shifts the flat band voltage to negative values, while the presence of Cl or C at the interface increases the hysteresis. We demonstrate that introducing an in situ plasma cleaning treatment based on N2/H2 gas, before the atomic layer deposition, allows the removal of most of the residues except silicon and suppresses the hysteresis.