反応性イオンエッチングによる赤外ホログラム素子の加工

抄録

This paper concerns a fabrication of the hologram optical element for a carbon dioxide laser which is used on the scanner installed in the vision sensor of a mobile robot operating under harsh conditions.
Reactive ion etching (RIE) is employed to obtain a deep grating. The inclination angle of the wall of the grating can be adjusted by varying the oxygen gas flow rate, which varies the volume of undercut. The inclination angle is almost constant for the reactive gas flow condition and is not affected by the mask spacing. The calculated desirable profile of grating can be fabricated under suitable process conditions.
The irregularity of the fabricated grating profile on the hologram surface affects the local diffraction efficiency variation. As to the depth of the grating, the dimensional accuracy is increased by surrounding the material with a circular wall which evenly distributes the gas flow over the surface. However, the undercut or the inclination of the wall also slightly changes according to the location, and additional mechanical movement of the material or precise control of the gas flow is necessary to increase the accuracy.
The mean value for the diffraction efficiency of the fabricated hologram is 51.7%. An adequate image for recognition is obtained using a two-dimensional scanner with the hologram element and the galvano-mirror and image reproduction with reflected light from the target.