X-RAY FABRICATION OF NONORTHOGONAL STRUCTURES USING SURFACE MASKS

Standard x-ray lithographic techniques allow great flexibility of geom etry in two dimensions. Typically, the third dimension is limited to d epth, which is purely orthogonal to the surface. We have been developi ng a relatively simple technique using x-ray lithography and have fabr icated a whole family of precisely controlled nonorthogonal structures such as tapers, bridges and various ''leaning'' or blazed structures. Traditional soft x-ray masks, create the modulation required to print into x-ray resists by having the absorbing elements of the x-ray mask patterned on a thin membrane. This technique involves the creation of the gold absorbing elements of the x-ray mask directly on the surface of the photoresist, i.e., a ''surface'' mask. These surface masks can create nonorthogonal exposures creating blazed structures as well as ''bridges'' by tilting the sample with respect to the x-ray beam durin g exposure. The exposures can also be done while having the tilted sam ple rotated, creating tapered exposure profiles. In addition to the no vel geometries, a potentially useful feature of the rotated exposures is that the sidewalls have nanometer scale smoothness, due to the aver aging of intensities during rotation. (C) 1997 American Vacuum Society .