Journal of Applied Science Studies - Ozean Publications

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Ozean Journal of Applied Sciences 1(1), 2008 a) 200mJ/cm 2 , -1.0 µ m b) 252mJ/cm2, -0.8 µ m c) 305mJ/cm 2 , -0.8 µ m d) 357mJ/cm 2 , -0.8 µ m e) 252mJ/cm 2 , -1.0 µm f) 305mJ/cm 2 , -1.0 µ m g) 357mJ/cm 2 , -1.0 µ m h) 410mJ/cm 2 , -0.2 µ m Figure 6. Contact holes size (nominally 0.8 micron) variation at different exposure energy and focus. 52
Ozean Journal of Applied Sciences 1(1), 2008 (a) (b) Figure 7. Cross-section of contact holes after dry etching process: (a) magnification 10kX, (b) magnification 20 kX. The value of exposure energy and focus range affected the size and shape of patterns and therefore their quality. Increasing the energy enlarged the hole size and reduced the sidewall slope. However, reducing the energy caused under-exposure, and reduced the hole size. The photoresist also tended to remain at the bottom of the holes. Since the lens system of the stepper is based on convex lenses. As such, a positive focus range will cause the lenses to move closer to the wafer, therefore, causing larger feature size of the patterns. Surface topology can also cause problem for the contact holes photolithography process. Since this step is the last one of the front end process, there are many layers and patterns underneath resulting in very uneven surface. These surfaces will cause undesirable reflection during photolithography process, and, as a result, feature size cannot be well controlled. The process of planarization is introduced to reduce such a problem, although, it cannot be totally eliminated. CONCLUSION This research was performed to develop the most suitable process parameters for the photolithography of contact hole patterning process. These conditions were found to be 305 mJ/cm 2 of exposure energy and -1.0 micron of focus range. They were incorporated in TMEC’s 0.8 micron CMOS fabrication process technology to be used for IC and sensor fabrications. REFERENCES Hong, X. (2001). CVD and Dielectric Thin Film. In S.Helba, Introduction to semiconductor manufacturing Technology (pp. 390-413). New Jersey: Prentice Hall. James, R., Sheets, Bruce, & W., Smith (1998). Multilayer Resist Technology. In Bruce W. Smith, Microlithography Science and Technology (pp. 575-577). New York: Marcel Dekker. Nasby, R.D., Sniegowski, J. J., Smith, J. H., Montague, S., Barron, C. C., Eaton, W. P., McWhorter, P. J. Hetherington, D. L., Apblett C. A. & Fleming, J. G. (1996). Application of chemicalmechanical polishing to planarization Of surface-micromachined devices. Technical Digest of the Solid State Sensor and Actuator Workshop, 48-53. Zheng, Y., Dutta, M., Kotecki, C., & Zincke, C. (2002). Planarization for the Integration of CMOS and micro mirror arrays. Proc. of SPIE: Metrology,Inspection and process control for microlithography XVI, 4689, 1070-1076. 53
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Wolf, S. (1995). The Submicron MOSF
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