Optimizing Photoresist Strip to reduce fluorine outgassing causing bubble defect

BF2 may be implanted in a silicon wafer to create doped regions. When a sufficiently energetic BF2 molecule collides with a Si crystal, the B-F bond will be broken and both atoms will enter the Si crystal. Since F is an interstitial element in the Si lattice, the higher the dose/energy used for BF2 implantation, the higher the number of F atoms implanted. During photoresist strip, plasma generates Hradicals that penetrate the surface SiO2 and substrate, react with F-implants to form gaseous HF. During annealing, HF gas evolves, causing delamination in the surface oxide film. Subsequent SiN film deposition will enhance the delamination, which will be detected as a bubble defect (Fig. 1). This article evaluates a new photoresist strip recipe with shorter time and pins-up, as well as a different gas, to reduce fluorine outgassing, to eliminate subsequent process bubble defect issues.