Gallium nitride based high electron mobility transistors are widely known for their operational instabilities regarding interface defects to the dielectric. In this paper, we discuss a III-N surface treatment that results in an electrically more defined interface and hence a narrower distribution of electrically present interface states compared to the original, untreated interface. This surface modification is caused by a remote plasma fluorination of the III-N surface. We show that it is a very distinctive surface processing which cannot be reproduced by other plasma techniques or ion implantation. Applying physical and chemical analyses, the fluorination is found to have a remarkable stability towards temperatures up to 700 °C and is also stable in air for up to 180 h. However, an aqueous clean allows the surface to return to its original state. Even though the exact physical origin of the responsible surface donor cannot be inferred, we suggest that fluorine itself might not directly represent the new surface donor but that it rather activates the III-N surface prior to the dielectric deposition or even substitutes and hence reduces the concentration of surface hydroxides.
Phone: þ43 (0)5 1777 3867Investigations of chemical species at the dielectric/III-N interface remain an important question in order to understand the chemical origin of the surface states, which are present at the heterostructure surface. In this work, we demonstrate a sample preparation technique to analyze the existing interface species by X-ray photoelectron spectroscopy (XPS) through thin uniform silicon nitride (Si 3 N 4 ) layers 1.4 AE 0.2 nm. We show that it is crucial that the layers are as thin as possible but as thick as necessary to avoid oxygen diffusion through the passivation. Due to the sufficient information depth provided by such layers, the photoelectrons are detected. This is an advantage over sputtering as no intermixing of atoms or cleavage of bonds occurs. We show that the deposited Si 3 N 4 hinders oxygen diffusion through the layer to the AlGaN surface. Selective SiO 2 over Si 3 N 4 etching and XPS depth profiles indicate that $1 nm of the thin Si 3 N 4 layer has formed a surface oxide. Angle-resolved XPS measurements confirm the accumulation of oxygen at the top and bottom Si 3 N 4 interfaces. No indication is found that interfacial oxygen is bound to any other than the group-13 metal.In agreement with the HSAB concept, the interfacial oxygen is bound to Al rather than Ga.Scheme of the nondestructive XPS interface analysis of the dielectric/AlGaN interface.
The customized substrates for manufacturing 300mm power semiconductors had to be prepared by deposition processes and epitaxial growth on standard substrates since they were not yet available from suppliers in both sufficient quality and quantity. Polysilicon films were deposited on wafer backsides and optimized regarding impurity gettering. Severe modifications of existing epitaxy reactors, the facilitation, and the infrastructure were prerequisite to develop extremely high doped, thick silicon layers with both supreme uniformity of layer thickness and dopant distribution to take full advantage of the productivity advantage of large diameter wafer processing. Simulation supporting these activities was also key to enable furnace processes with extremely tight temperature ranges. For the development of very thick, high resistivity silicon layers a 5-wafer 200mm batch tool was used to exploit the tool and process learning for the design and manufacturing of a similar 300mm batch tool. For pattern transfer the same advanced plasma etch equipment was mandatory to achieve similarly uniformities regarding etch rate, profile shape, and CD as in CD-driven advanced DRAMs and MPUs.
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