Thermal atomic layer etching of germanium-rich SiGe using an oxidation and "conversion-etch" mechanism

The thermal atomic layer etching (ALE) of germanium-rich SiGe was demonstrated using an oxidation and "conversion-etch" mechanism with oxygen (O-2) or ozone (O-3), hydrofluoric acid (HF), and trimethylaluminum [TMA, Al(CH3)(3)] as the reactants. The crystalline germanium-rich SiGe film was prepared using physical vapor deposition and had a composition of Si0.15Ge0.85. In situ spectroscopic ellipsometry was employed to monitor the thickness of both the SiGe film and the surface oxide layer on the SiGe film during thermal ALE. Using a reactant sequence of O-2-HF-TMA, the etch rate of the SiGe film increased progressively with temperatures from 225 to 290 degrees C. At 290 degrees C, the SiGe film thickness decreased linearly at a rate of 0.57 angstrom /cycle with a surface oxide thickness of 18-19 angstrom. This etch rate was obtained using reactant pressures of 25, 0.2, and 0.4Torr and doses of 1.5, 1.0, and 1.0s for O-2, HF, and TMA, respectively. The TMA and HF reactions were self-limiting and the O-2 reaction was reasonably self-limiting at 290 degrees C. Using an O-3-HF-TMA reaction sequence, the SiGe ALE etch rate was 0.42 angstrom /cycle at 290 degrees C. This etch rate was obtained using reactant pressures of 15, 0.2, and 0.4Torr and dose times of 0.5, 1.0, and 1.0s for O-3, HF, and TMA, respectively. The O-3, TMA, and HF reactions were all self-limiting at 290 degrees C. Atomic force microscopy images revealed that thermal ALE with the O-2-HF-TMA or O-3-HF-TMA reaction sequences did not roughen the surface of the SiGe film. The SiGe film was etched selectively compared with Si or Si3N4 at 290 degrees C using an O-2-HF-TMA reaction sequence. The etch rate for the SiGe film was >10 times faster than Si(100) or Si3N4 that was prepared using low-pressure chemical vapor deposition. This selectivity for the SiGe film will be useful to fabricate Si nanowires and nanosheets using SiGe as the sacrificial layer.Peer reviewe

Improved high-temperature expansion and critical equation of state of three-dimensional Ising-like systems

High-temperature series are computed for a generalized $3d$ Ising model with arbitrary potential. Two specific ``improved'' potentials (suppressing leading scaling corrections) are selected by Monte Carlo computation. Critical exponents are extracted from high-temperature series specialized to improved potentials, achieving high accuracy; our best estimates are: $\gamma=1.2371(4)$, $\nu=0.63002(23)$, $\alpha=0.1099(7)$, $\eta=0.0364(4)$, $\beta=0.32648(18)$. By the same technique, the coefficients of the small-field expansion for the effective potential (Helmholtz free energy) are computed. These results are applied to the construction of parametric representations of the critical equation of state. A systematic approximation scheme, based on a global stationarity condition, is introduced (the lowest-order approximation reproduces the linear parametric model). This scheme is used for an accurate determination of universal ratios of amplitudes. A comparison with other theoretical and experimental determinations of universal quantities is presented.Comment: 65 pages, 1 figure, revtex. New Monte Carlo data by Hasenbusch enabled us to improve the determination of the critical exponents and of the equation of state. The discussion of several topics was improved and the bibliography was update