Laser Phototypesetting Grating Light Valve Design And Production

Laser typesetter uses computer to edit the typesetting, making the information of the book become the lattice information. The MEMS (Micro electro-mechanical system) device GLV (Grating Light Valve) is introduced to act as the optical modulator of the laser typesetter. A GLV is made up of numbers of units, so it is easy to fabricate lots of pixels using the technique of micro-fabrication. In addition, the switching speed of the GLV is very fast, making it possible to scan fast and increase the speed. Moreover, the substrate of GLV is Silicon, which could bear the big intensity of the laser used in the laser typesetter. This dissertation shows the optical and electromechanical principle of GLV and based on the optical principle, introduces the simplified model of GLV.The process of micro-fabrication is very important to GLV. In order to solve the problems encountered in the fabrication of GLV, this dissertation introduces the principle of thin film and the processes of photolithography, photoresist and etching and discusses the problems and methods for solving them. Due to the small line-width of GLV, it is important to keep the pattern and good adhesion of photoresist. By experiments and analytical analysis, this dissertation puts forward the methods for solving these problems. The main reason of the photoresist deformation after the photoresist stops flow is the shrinkage of photoresist and shrinkage difference between the edge and non-edge of the photoresist in hard bake, which is caused by the high exothermicity of the resin curing process and the low thermal conductivity of the photoresist. The temperature of non-edge of the photoresist is higher than that of the edge and also higher than the baking temperature. The temperature distribution is measured with the infrared thermography and simulated by a two-dimensional simulation, both of which show that the surface deformation is highly related to the photoresist thickness and baking temperature. Experiments results demonstrate that the surface deformation can be overcome by proper baking process. The sources of the internal stress of the photoresist could be the shrinkage of photoresist during the curing process and the shrinkage difference between the photoresist and the substrate. Due to the high exothermicity of the resin curing process, the temperature of the photoresist is not uniform, which causes the shrinkage difference in the photoresist. The method that delay after soft bake and anneal after hard bake could promote the adhesion. The line-width control becomes better through these processes.The GLV analysis handles the interaction between structural and electric fields and ANSYS is used to simulate it. The fabrication of GLV involves the bulk micromachining and the line width must be kept. The line width of the grating is 5μm, which should be fabricated precisely.