A cantilever resonant microbeam, laser diodes, and a photodiode have been fabricated on the surface of a gallium arsenide substrate. The microbeam is excited photothermally by light from a laser diode. The vibration is detected with a photodiode as the variation in light output caused by the difference in optical length between the microbeam and another laser diode. A high carrier-to-noise ratio (45 decibels) is achieved with a short (3 micrometers) external cavity length. Such a small distance allows a lensless system, which increases the ease of fabrication. This work could lead to applications in which photomicrodynamic systems are monolithically integrated on a gallium arsenide substrate with surface micromachining technology.
Anisotropic etching of (110) silicon is used to fabricate high-aspect-ratio microstructures and electrostatic microactuators suitable for optical applications. The atomically smooth (111) sidewalls resulting from anisotropic etching of (110) silicon provide large-area, optical-quality surfaces. The reflectance of such (111) surfaces, which can be used as mirrors, was measured using a He-Ne laser and was found to be nearly the same as those for the mirror-polished surface of a typical (100) silicon wafer. Thin silicon plates with widths less than 2 mu m were found to be partially transparent (even at the value of He-Ne laser wavelength of 632.8 nm) and could be used as beam splitters. A novel electrostatically actuated micromirror was fabricated by (110) silicon etching and subsequent bonding to a glass substrate. The micromirror provides an optical beam deflection of 0.7 degrees for a 25 V excitation.
GaAs dry etching using reactive–fast-atom beam etching to obtain an etched mirrorlike surface is investigated. An etch rate of 0.1–0.6 μm/min is obtained when Cl2 gas is used, which is 50–100 times faster than when Ar gas is used. The etch rate ratio between GaAs and photoresist AZ-1350J is more than 30. As a result, a trench with a depth of more than 10 μm and a width of less than 2 μm is easily fabricated under the etch conditions of a Cl2 gas pressure of 5–6.5×10−2 Pa, an accelerate voltage of 1.5–1.8 kV, and a substrate temperature of about 100 °C. The radiation damage caused by this etching is very small, and it is similar to that caused by wet chemical etching, in spite of the relatively higher accelerator voltage. The thickness of an induced damage layer is only 150 Å. It is found that the radiation damage induced by reactive–fast-atom beam etching decreased with an increase of the etch rate. It is confirmed that vertical, smooth, damage-free etching can be easily attained with reactive–fast-atom beam etching.
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