Argon Sputter Etching Research Articles

Fabrication of short channel MOSFETs with refractory metal gates using RF sputter etching

Fabrication of sub-μm p-channel MOSFETs with refractory metal gates using novel refinements of conventional photolithographic procedures is described. The method avoids the need for direct electron beam writing on the wafer and for ion implantation instead of diffusion. Autoregistration Mo gate structures down to 2 μm corresponding to an estimated channel length of 0 · 7 μm were made using RF sputter etching for the drain-source windows while masking with a positive photoresist. This was contact patterned using a chromium-on-glass mask made by electron beam writing and RF sputter etching. Sputter-deposited boron-doped SiO 2 was used as the diffusion source for the source-drain areas. The transistors were made on (100) phosphorus doped n-type silicon with an impurity concentration of 2 . 10 16 cm −3. Fabricated devices with channel lengths ≥ 1 · 7 μm had an apparent threshold voltage of 2·5 V (10 μA criterion) and for 1·7 μm channel length an apparent punch-through voltage of 18 V. A sputtered Mo layer ⋍ 1 μm thick was used as gate material. A distinct advantage of using sputter etching with a single system capable of both deposition and etching is that it is possible to go directly to the next steps without exposure to air. These steps are mask removal in a partial H 2 and O 2 plasma, followed by further Argon sputter-etching and sputter deposition of a doped oxide diffusion source on the sputter-etched cleaned surface. This promises a better reproducibility of surface doping as there should be less oxide and less contamination than in conventional processes. The characteristics of the fabricated transistors did not indicate any un-annealable drift or gate oxide damage due to the presence of the plasma provided the Mo layer was sufficiently thick. Thus sputter etching which offers good resolution can be used in MOS fabrication. Due to its lower resistivity, Mo, which can be used an an additional interconnection layer (isolated from the A1 layer) offers better speed potential than Si, in certain types of circuits, e.g. high speed memories with long address lines. With a proper background doping of the wafer and diffusion time and temperature it was possible to obtain ⋍ 0 · 6 μm lateral diffusion below the gate from both source and drain regions. It was thus possible to obtain sub-μm p-channel MOSFETs even while working close to the limits of normal optical contact production of micropatterns, which is 1–2 μm.

Ga1−x Alx As superlattices profiled by Auger electron spectroscopy

Superlattice structures made by molecular beam epitaxy are profiled by a combined technique of argon sputter etching and Auger electron spectroscopy. The superlattice, consisting of periodic layers of 50-Å GaAs and Ga1−xAlxAs, probably represents the structure with the shortest period ever made and analyzed in monocrystalline semiconductors. Also established is the dependence of the intensity ratio of aluminum to arsenic signals of Auger transitions on the aluminum composition in Ga1−xAlxAs.