Defect Density Control on 'Satellite Spots' or Chemical Stains for Deep-UV Resist Process

摘要

Satellite spots defects of size less than lum are being experienced with 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, the overwhelming number of "satellite spots" can be a nuisance to any Yield engineer from the Defect Density group as they often 'mask' away the genuine "killer" defects. Nonetheless, we expect the results presented here to be significant and recommendations made 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 effect of the developer/surfactant concentration is believed to have caused the polymer to form micelles during development termed affectionately as "satellite spots" defect by the Yield Engineers. In a small geometry on a patterned wafer under microgravity environment, the thin resist-developer dissolution during the developing cycle, causes the micro "dry" spots in the dissolution under the spreading developer probably due to Marangoni effect, 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 understanding and leads to the resolution of "satellite spots" defect. It adequately accounts for the dissolution behaviour of the HS/TBA copolymers (ESCAP-type) resist. 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 modifying the developing program can be realized using the above control methodology.