The Application And Process Improvement Of Photosensitive Polyimide In Wafer Fabrication

This thesis mainly discussed the application of photosensitive polyimide (PSPI), a new type of engineering polymer materials in the semiconductor wafer fabrication process. And then we investigated the mechanism of the application in wafer fabrication, also discussed and studied after film forming PSPI revealed the high rate of dots defects, the defect formation mechanism and process improvement. Specifically, the following are the main aspects:1) Photosensitive polyimide (PSPI) is a polymer that has both imide ring and photosensitive group in backbone chain, as compared with other polymer materials; it has excellent thermal stability, good mechanical and insulation, chemical resistance, photo and radiation protection. Using these properties, this new polymer material has been widely used in the microelectronics field. It shows the great potential and market competitiveness. Compared the wafer with and without polyimide films, explained the life difference between wafer covered with and without polyimide film.2) Polyimide does not dissolve in the general solvent, therefore, in the application forthe photoresist, not like other photoresist as it dissolved in a solvent first, then coated film. Generally, the method used was first coated "polyimide precursors (Precursor)", in today's semiconductor wafer fabrication, generally used polyimide precursors was a kind of polyester. Polyimide precursors cross-linked after UV exposure, and then after baking formed the final polyimide. This is the mechanism of photosensitive polyimide's application in wafer fabrication.2) Photosensitive Polyimide is light sensitive material; if it is exposed to general light, chemical reaction will occur, thus make it not ready for work. Lithography imaging process should be limited to special circumstances, because photoresist is most insensitive to the yellow light, and are generally carried out under the yellow light, lithography area is often called yellow room. As IC circuit complexity, the line width is under micron meter, it must be manufactured in the clean room, and the clean room temperature and humidity must be strictly controlled. The polyimide film process can be roughly divided into six major steps, soft bake, coating, alignment and exposure, developing, thermal curing. With the six steps, the graphic on the photomask finally transferred to polyimide film on the wafer. For each of the steps of the machine, process conditions and parameters has done a specific explanation.4) Photosensitive Polyimide process completed, the wafer must be carried out on the inspection process to ensure that the level of lithography mask meet the specifications of the request, which includes under strong light, naked eye examination and microscopic inspection. This paper studied the defect occurred during Photosensitive Polyimide application, in particular, to reduce one of the most common defects dots defect rate and a failure mode analysis (SEM, FIB and EDX), electricity (WAT and CP) and reliability testing (TC and HTS), discovered the flaw mechanism, and in order to eliminate this deficiency, through a series of experiments conducted in process improvement.