Smooth Vertical Sidewalls Research Articles

Controlled beam dry etching of InP by using Br2-N2 Gas

When Indium phosphide dry etching is carried out using a reactive beam extracted from Br2-N2 mixture gas discharge plasma, two distinct types of etching mechanisms come into play as the Br2 gas pressure is changed. Smooth vertical side walls can be obtained at low Br2 gas pressure, where the etching rate has no temperature dependence, while undercutting with a temperature dependent etching rate is seen at high Br2 gas pressure. An analysis of the plasma discharge currents reveals that neutralized Br species generated by the discharge of Br2 gas itself form the undercut. A waveguide corner mirror with less than 1 dB loss can be made by using an etching beam with no neutralized Br species.

Imprint Lithography with 25-Nanometer Resolution

A high-throughput lithographic method with 25-nanometer resolution and smooth vertical sidewalls is proposed and demonstrated. The technique uses compression molding to create a thickness contrast pattern in a thin resist film carried on a substrate, followed by anisotropic etching to transfer the pattern through the entire resist thickness. Metal patterns with a feature size of 25 nanometers and a period of 70 nanometers were fabricated with the use of resist templates created by imprint lithography in combination with a lift-off process. With further development, imprint lithography should allow fabrication of sub-10-nanometer structures and may become a commercially viable technique for manufacturing integrated circuits and other nanodevices.

Contrast of ion beam proximity printing with nonideal masks

In ion beam proximity printing, a broad, collimated beam of light ions is directed through a stencil mask. For this process, aerial image contrast is limited primarily by scattering near the edges of the mask openings. Previous work by Karapiperis et al. [J. Vac. Sci. Technol. 19, 1259 (1981)] considered the energy deposited in resist (and resist profiles) for ideal incident ion beams. Randall, Stern, and Donnelly [J. Vac. Sci. Technol. B 4, 201 (1986)] have calculated mask contrast as a function of pattern density and mask thickness for grid support masks with smooth vertical sidewalls, showing that contrast is a function of mask aspect ratio. We present simulations from a modified version of TRIM85 including the effects of mask wall angle, roughness and thickness, ion incident angle, resist scattering, and pattern spatial frequency for infinite line and space patterns. Contrast of the deposited energy density and estimated process sensitivity are shown, as well as a simulated resist profile derived using a string development model. A histogram of the angular dependence of ion scattering shows that the effect is a diffuse exposure at reasonable mask-to-wafer gaps. It is also shown that for reentrant mask profiles the contrast increases with mask thickness. Our simulations show that 0.25 μm line and space patterns in 2 μm thick masks with reasonable parameters can have a contrast of 12, a contrast of 8 is attainable for 0.125 μm line and space patterns, and the stringent linewidth control required by surface acoustic wave devices can be achieved with ±5% dose control.

Use of CF3,Br/Al, discharges for reactive ion etching of III-V semiconductors

The reactive ion etching of GaAs, InP, InGaAs, and InAlAs in CF3Br/Ar discharges was investigated as a function of both plasma power density (0.56-1.3 W - cm−2) and total pressure (10-40 mTorr) The etch rate of GaAs in 19CF3Br:1Ar discharges at 10 m Torr increases linearly with power density, from 600 A min−1 at 0.56 W · cm−2, to 1550 A · min at 1.3 W · cm−2. The in-based materials show linear increases in etch rates only for power densities above − 1.0 W · cm−2. These etch rates are comparable to those obtained with CCI2F2:O2 mixtures under the same conditions. Smooth surface morphologies and vertical sidewalls are obtained over a wide range of plasma parameters. Reductions in the near-surface carrier concentration in n-type GaAs are evident for etching with power densities of >0.8 W cm−2, due to the introduction of deep level trapping centers. At 1.3 W· cm−2, the Schottky barrier height of TiPtAu contacts on GaAs is reduced from 0.74 to 0.53 eV as a result of this damage, and the photoluminescent intensity from the material is degraded. Alter RIE, we detect the presence of both F and Br on the surface of all of the semiconductors. This contamination is worse than with CCl2F2-based mixtures. High-power etching with CF3Br/Ar together with Al-containing electrodes can lead to the presence of a substantial layer of aluminum oxide on the samples if the moisture content in the reactor is appreciable.

MBE Regrowth of AlGaAs on Ion Etched GaAs/AlGaAs Microstructures

ABSTRACTThe combination of an ion beam assisted etching (IBAE) system and a Molecular Beam Epitaxy (MBE) growth chamber integrally connected in the same set of ultrahigh vacuum (UHV) chambers has allowed us to etch patterns defined by a strontium fluoride mask down into the underlying semiconductor wafer, and regrow monocrystalline material around these patterned structures entirely in situ. Scanning electron microscopy (SEM) analysis of the regrown structures reveals very directional deposition of the overgrown material. Cross-sectional transmission electron microscopy (TEM) reveals a smooth interface and vertical sidewalls at the boundary between the etched surfaces and the overgrowth. Material deposited on the sidewalls is shown to be monocrystalline, while that deposited over the mask is polycrystalline. The SrF2 mask material, previously shown to be an excellent IBAE mask for extremely fine nanostructures, is also shown to be compatible with the high temperatures need for overgrowth, and regrowth around structures as small as ˜200 nm in size has been demonstrated.