Single layer of aluminum film was sputter deposited on to (100) oriented 4 inch silicon wafer to study effect of film thickness, D.C. power and sputtering gas pressure on the film stress. The as-deposited stress appeared to be increasing as film thickness increases and argon pressure decreases. Thermal stress originated from difference in CTE and temperature variation during and after sputtering seems to be a main factor in room temperature sputter deposited aluminum films. From observation of temperature-stress behavior, it was found that the pure aluminum film has an elastic modulus of 56GPA and compressive yield strength of -100MPA. The yield strength was improved to about -175MPA by alloying with 3wt.%Ti. Titanium alloying also proved to be useful in extending linear elastic region before plastic deformation occurs. However, it was hard to determine the stress level with buckling phenomena of ring/beam microstructures because of imperfections such as stress gradient and thermal deformation. In stead, those diagnostic microstructures could be applied to give an information on whether a plastic deformation was introduced or not in a structure of specific dimension.
Test equipment for the development and mass production of micromirror array have been devised. Test equipment for the static and dynamic response of a single micromirror consists of HeNe laser, lenses, XY stage, CCD camera, position- sensitive photodiode and PC. It can be used to measure reflectance, tilt angle--input voltage relation, response time and resonant frequency, in the developing stage. It can also check the lifetime and uniformity of mirror quality over the wafer. Test equipment for the evaluation of micromirror array consists of CCD camera, lenses, XY stage, video signal processor and PC. It can classify the error- state of micromirror, generate statistical data and map of the position of abnormal micromirrors. The test results are shown on the monitor as a map that shows the error state, position and statistical data. It takes about 90 seconds to evaluate 50 X 50 micromirror array.
A 100 X 100 micrometers 2 aluminum micromirror is designed and fabricated using a thick photoresist as a sacrificial layer and as a mold for nickel electroplating. The micromirror is composed of aluminum mirror plate, two nickel support posts, two aluminum hinges, and two address electrodes. The aluminum mirror plate, which is suppoorted by two nickel support posts, is overhung about 10 micrometers from the silicon substrate. We use thick photoresist to obtain 10 micrometers thick sacrificial layer and electroplate nickel to obtian 10 micrometers height support post. The aluminum mirror plate is actuated like a seesaw by electrostatic force generated by electrostatic potential difference applied between the mirror plate and the address electrode. We use reactive ion etching to release the micromirror plate from the silicon substrate. The edge of the mirror plate landed on the substrate (maximum deflection) when the potential difference between the mirror plate and the address electrode was 35 volts, and the mirror was released from the substrate when the potential difference reduced to 22 volts.
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