We present a novel lithographic process for patterning controlled-width tracks onto anisotropically micromachined silicon. The technique is based on the use of computer-generated holographic masks with a custom alignment and exposure tool. Experimental and simulation results are presented. 3D holographic photolithography significantly reduces the problem normally present with photolithography on non-planar surfaces-namely diffractive line broadening. A negative-acting electrodepositable photoresist (InterVia 3D-N) is used in the study. Its deposition onto the 3D substrate is optimized by modification of coating temperature and thickness and of pre-exposure bake conditions. We show the successful patterning of a constant-width 8 μm line down the sloping sidewall of a 500 μm thick silicon wafer. This is beyond the conventional resolution limit and indicates the potential of the technique for realizing high-density vertical routing in electronic packages and MEMS.

GaN Schottky ultraviolet photodetectors using the metal-semiconductor-metal structure grown by metalorganic vapour phase epitaxy (MOVPE) are reported. The metal contacts used in this work are Ti/Au or Au. The devices characterised present a low dark current below 1 pA and typical photocurrent I-V characteristics at 360 nm. The photodetectors exhibit internal gain and visible blindness. The responsivity is 0.001 A N in the visible region, which is approximately three orders of magnitude less than the above gap responsivity.

No abstract

No abstract

We describe a technique whereby photolithography has been extended to the patterning of near micron-scale features onto grossly non-planar substrates. Examples will be given of track widths down to ten microns patterned over surfaces with vertical dimensions in excess of one centimetre -far outside the normal bounds of photolithography. The technique enables many novel microsystem packaging schemes and provides an alternative to the direct-write methods that are traditionally employed for patterning non-planar surfaces. The technique is based on the computation of the phase/amplitude distribution on the mask that, when illuminated with light of sufficient spatial coherence, will recreate the desired non-planar light distribution. This has some similarities to existing RET and inverse lithography techniques, but is extended to grossly non-planar surfaces. Exposure of an electrophoretic photoresist-coated substrate to the light field created by the mask enables the non-planar pattern to be transferred to the substrate. The holographic mask contains localized Fresnel patterns. We discuss the analytical methods used for their computation, the approximations necessary to enable mask manufacture and the effects of these approximations on image quality. We also discuss more general numerical methods of mask computation.