Liquid Clean Formulations for Stripping High-Dose Ion-Implanted Photoresist from Microelectronic Devices

Liquid clean formulations comprised of an organosilane, Et3N, and toluene have been found to selectively strip thin films of high-dose arsenic-implanted polyhydroxystyrene photoresist and hardened carbonized crust without silicon/oxide loss. During the cleaning process, self-assembled monolayers (SAMs) of organosilanes were attached to the surface silanol groups in the Si/SiO2 regions of patterned wafers. It was determined that a higher surface density of organosilane SAMs improves the cleaning efficiency, and halide leaving groups further assist with photoresist and crust removal possibly due to chemical interactions with the arsenic ions. Wafers treated with the formulation containing Cl3SiMe resulted in the best cleaning efficiency (assessed by optical and scanning electron microscopy), yielding greater than 90% overall photoresist/crust removal in static cleaning mode and 100% removal in a dynamic cleaning mode, under optimal reaction conditions (70 deg C, 30 min). The SAMs were then stripped from the wafers. A solution of Et3N/HF in DMSO was found to depassivate the wafer after 2 min (static mode) while maintaining the structural integrity of the underlying silicon-containing layers. The surfaces were characterized by contact angle to determine wettability, atomic force microscopy, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy.