Structural characterization of free-standing gallium arsenide coiled membranes produced by micromachining

High-resolution X-ray diffraction techniques have been employed successfull y to evaluate crystalline quality and long-term stability of coiled membran es. The process of fabrication involves photolithography, implantation by 2 MeV N2+ ions in n-type GaAs substrates, followed by selective etching. A f ive-crystal X-ray diffractometer was employed in (+, -, +) setting with an Mo K alpha(1) exploring beam for high-resolution X-ray diffractometry and t opography experiments. The exploring-beam width was reduced to illuminate d ifferent segments of the coiled membrane. Diffraction curves recorded from the bulk crystal surrounding the sensor had a half width of 26 arcseconds, whereas the half widths from sensor segments were in the range similar to 5 8 to similar to 166 arcseconds. Different segments (particularly vertical o nes) were identified from the observed angular separations between differen t diffraction peaks as well as from the shape of the diffraction peaks. It was found that different segments of the sensor were tilted with respect to one another and the tilt angles were in the range 15-212 arcseconds. High- resolution X-ray diffraction topographs recorded from (5 (1) over bar 1) an d (400) diffracting planes revealed that the sides of the trough below the membrane created by etching are not vertical, but tapered. Also, there is a thin strip of crystal freely hanging over the tapered regions as a result of underetching. The surface of the cavity is uneven. The structural perfec tion of different membrane segments could also be ascertained from the cont rast in topographs.