KEYWORDS: Transmittance, Global system for mobile communications, Glasses, Photoresist materials, Diffractive optical elements, Photomasks, Printing, Etching, Modulation, Spatial resolution
In the last years the application of gray-scale masks (GSM) for diffractive optics manufacturing attracts attention because of cost-effective possibility to produce a lot of diffractive elements on hard and heat-resistant thermally stable substrates. Direct laser writing of GSMs and fabrication of diffractive optical elements are effectively realized with application of LDW-glass (material for Laser Direct Write from CANYON MATERIALS, Inc). An important advantage of this material is the real-time change of transmittance in a single-step process without liquid development. It is shown that optimal transmittance range in which track width is not more than 1 micrometers is from 5-10% (transmittance of unexposed area) to 60-65% for LDW-glass type I having thinner colored layer. Power modulation and surroundings dependent peculiarities of direct laser writing on LDW-glass are discussed. Results of fabrication of diffractive optical elements using LDW-glass masks are presented. Among several types of LDW glasses studied the advantages of new GS-11 glass are elaborated. Application of GS-11 glass for GSMs allowed to fabricate blazed diffractive structures with backward slope width of 0.8 micrometers .
Analogue contact lithography is a suitable technology for the fabrication of continuous surface profiles. In this field HEBS-glass gray scale masks have a great potential, for instance for producing microoptical elements. This paper summarizes detailed investigations on the electron beam exposure of HEBS-glass masks. At first we give an idea of the effects we obtained by exposing HEBS-glass masks with different kinds of e-beam writers (Gaussian beam and variable shape e-beam writer). We found thermal effects and a bottleneck effect which have different consequences for the gray level of the exposed mask. To understand its physical causes the bottleneck effect was investigated in detail. Based on this knowledge we introduce two different strategies to overcome the problems caused by the different concepts of the e-beam writer. Selected examples of fabricated profiles demonstrate the facilities of HEBS-glass using these strategies.
KEYWORDS: Transmittance, Glasses, Photoresist materials, Quartz, Manufacturing, Global system for mobile communications, Silver, Fresnel lenses, Laser systems engineering, Modulation transfer functions
The perspective opportunity to fabricate gray-scale masks was given LDW-glasses (LDW--Laser Direct Writing) from Canyon Materials, Inc. LDW-glass blanks contain a large number density of coloring specks of silver in a surface glass layer. A focused laser beam is used to heat erase these coloring specks. Experiments on the influence of laser radiation on LDW-glasses was carried out using a circular laser writing system. The transmittance value from the blank of 0.1 - 5% up to 70 - 80% depending on laser beam power is obtained with the current write scheme. Results of research of LDW-glasses behavior in a wide range of laser beam scanning speeds are described. Laser pattern generation in LDW-glass including the spatial resolution is discussed. The technology of fabrication of continuous-phase diffractive elements was tested by making exemplary Fresnel lenses. Total 80% efficiency for quartz Fresnel lenses with minimal zone width of 8 micrometers was readily achieved in the preliminary experiments.
Micro-optics such as diffractive optics and computer generated holograms are essential components for modern optical design. To reduce their unit fabrication cost we describe a method of reproducing micro-optics in quantities. A true gray-level mask was fabricated in High Energy Beam Sensitive (HEBS)-Glass by means of a single e-beam direct write step. This gray-level mask was used in a optical contact aligner to print a multilevel Diffractive Optical Element (DOE) in a single optical exposure. A chemically assisted ion beam etching process has been used to transfer the DOE structure from the resist into the substrate.
Conference Committee Involvement (1)
Lithographic and Micromachining Techniques for Optical Component Fabrication II
3 August 2003 | San Diego, California, United States
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