Extrusion-spin coating: an efficient photoresist coating process for wafers

Coating photoresist onto semiconductor wafers is a critical step in the microlithography process. As the critical dimension of semiconductor devices becomes smaller, the process of coating wafers with photoresist must improve as well; the coating must be thinner, more uniform, and have fewer defects to yield satisfactory results. Spin coating is the typical method used to apply a thin coat of photoresist to semiconductor wafers. Although spin coating has basically met the coating uniformity, thickness, cycle time, and defect level requirements of the current industry standard, it has done so at the cost of wasting most of the photoresist applied to the wafers. Extrusion-spin coating, a newly developed coating method, has the potential to reduce the amount of photoresist used in the process while maintaining the other desirable attributes of spin coating. Our experimental results indicate that by using the extrusion-spin coating method, the coating efficiency can be improved to over 33% or better as compared to the efficiency of 12% achievable by the spin coating method.