Study On Lithography Technique Of Thick Photoresist

Rapid development and extensive applications of Micro-Machine System (MEMS) drive the increasing improvement of micro-machining technique. Thick resist lithography technique inherits many merits of Integrated Circuits (IC) process technique, such as simple process, cheap cost, and some forced elements can be fabricated directly with the technique. Therefore it attracts more and more attention at present.Thick resist lithography is a kind of technique fabricating deep relief structures. Resist thickness used in the process usually is beyond 2 u m, even to hundred micrometers. So its experiment process is different from that of traditional lithography technique and there are many complicated factors affecting the imaging quality in thick resist lithography. With the development of MEMS, novel MEMS structures with high aspect ratio and complex figures need be designed and fabricated. Simulation of thick resists lithography process is indispensable to reduce the cost of MEMS research and improve the research speed. But their simulated results by existed lithography models are not compatible with experiment results because these models consider few special characters of thick resist. So developing an appropriate thick resist exposure model is important to study the transferring mechanism of figures in the resist and develop the whole thick resist lithography technique.Diffraction or scattering in the resist is critical to affect the lithography quality of thick resist. In the paper, an effective way, which can describe the optical field in thick resist in contact\proximity lithography, was established based on the Kirchhoff scalar diffraction theory and angular spectrum theory. The effect of mask linewidth, distance between mask and resist surface and resist thickness on the optical field wasdiscussed; Formation of latent figure in the exposure process is critical to the figure quality in thick resist lithography. So it is important to get the PAC concentration in the resist after exposure and establish suitable physical model to analyze the latent figure of thick resist. Based on the photochemistry reaction dynamics theory, the effect of some nonlinear factors (including process and its stability) on imaging of thick resist lithography was studied. Based on the character of varying resist index during exposure process and varying exposure parameters with resist thickness, an enhanced DILL model suitable for thick resist, which considered the diffraction or scattering in the resist and extend the definition range of exposure parameters in DILL model, was proposed; Experiment of extracting exposure parameters was developed and varying rules of exposure parameters with resist thickness and process condition were analyzed by surface response theory; At last, simulation tool for thick resist based on new exposure model of thick resist was worked out. And latent figures of lithography after exposure and some characters of thick resist relief after development were analyzed with the tool. These results would offer some directions to experiment.