A narrowly defined range of
zinc silicate glass compositions is found to produce
High Energy Beam Sensitive-glass (HEBS-glass) that possesses the essential properties of a true
gray level mask which is necessary for the fabrication of general three dimensional microstructures with one optical
exposure in a conventional photolithographic process. The essential properties are (1) A
mask pattern or image is grainiless even when observed under
optical microscope at 1000× or at higher magnifications. (2) The HEBS-glass is insensitive and / or
inert to photons in the spectral ranges employed in photolithographic processes, and is also insensitive and / or
inert to
visible spectral range of light so that a HEBS-glass
mask blank and a HEBS-glass mask are permanently stable under room lighting conditions. (3) The HEBS-glass is sufficiently sensitive to
electron beam
exposure, so that the cost of making a mask using an e-beam writer is affordable for at least certain applications. (4) The e-beam induced
optical density is a unique function of, and is a very reproducible function of
electron dosages for one or more combinations of the parameters of an e-beam writer. The parameters of e-beam writers include beam
acceleration voltage, beam current, beam spot size, addressing
grid size and number of retraces. A method of fabricating three-dimensional microstructures using HEBS-glass gray scale
photomask for three dimensional profiling of
photoresist and reproducing the
photoresist replica in the substrate with the existing
microfabrication methods normally used for the production of
microelectronics is described.