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Satellite spots defects of size less than 1um are being experienced with UV series positive deep-UV photo resists at Chartered and it is believed to be formed as a result of the insoluble resist residue remaining on the BARC after the developing process. Though these defects reported are by far cosmetic defects that are not transferred after etch, we expect the results presented here to be significant and applicable to smaller geometries and to 12-inch wafer fabs. Figure 1 shows a typical satellite spots defect found in the open area where there are no resist patterns after the developing process. The spinning cycle of the developing process is thought to make the aqueous resist-developer dissolution adhere to the surface of the BARC in a satellite-like formation. In a small geometry on a patterned wafer under microgravity environment, the Marangoni convection occurs in the thin resist-developer dissolution during developing causing the micro dry spots in the dissolution under the spreading developer. The high surface tension of the deep-UV resists is believed to make it more difficult to remove after the hard bake process. The probabilistic model for the mechanism of resist-developer dissolution provides a theoretical backing to the resolution of satellite spots defect and it adequately accounts for the dissolution behavior of poly (hydroxystyrene) (PHS). Different developing recipes ranging from DI-water pre-wet, developer pre-wet, to high spin speed during DIW rinse were being investigated to find out the effectiveness in removing satellite spots. The combination of extended DIW rinse time, without resorting to high spin speed or high acceleration, and double developer puddling programs produce the lowest counts with the TMAH developer. Considerable defect density improvement after the developing process can be realized using the above control methodology. Although no significant yield improvement can be achieved at the present 0.25micrometers technology in Chartered, we believe that the results presented here will become significant as the Company moves towards smaller geometries.
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