Efficient stripping of photoresist on metallized wafers by a pause flow of supercritical fluid

Utilization of supercritical fluids (SCFs) is studied here on the premises of a saving of hazardous organic solvents and of the specification for stripping the photoresist (PR) on metallization layers, which is one of the integrated circuit processing modules. By using factorial experimental designs with five factors and four level ranges, this research focuses on determining an optimized recipe with high stripping efficiency and to determine the stripping mechanism. In the case of PR on an aluminum layer, the initial use of the pulse flow mode could increase the extraction ratio remarkably when compared to the conventional continuous flow mode. Based on the limitation of a total volume of 30 mL purging SCF-CO2 for economical considerations, the optimum conditions can be summarized as follows: 120 °C, oven temperature; 350 atm, CO2 pressure; 0.2 mL of ethylacetate spiking to SCF-CO2; 2.0 min, static equilibrium time; and five cycles of dynamic flow pausing. A recovery of 94.6% (n = 3, RSD = 6.5%) was obtained, while the diffusion of stripped PR from substrate matrix prevailed over the dissolution of binding PR into the SCF medium. In the case of copper, the optimum parameters in a pause flow mode were 140 °C, oven temperature; 500 atm, CO2 pressure; 0.75 mL, ethylacetate spiking volume; 5.0 min, static time; and six cycles of flow pausing. These extreme parameters still did not produce an SCF environment suitable for diffusion or dissolution mass transfer, and thus a recovery of 76.2% (n = 3, RSD = 7.5%) was only obtained. Removing PR coated on a Cu layer was harder than that on an Al layer.