MICRO: Hot Button

Resist removal, selectivity, substrate damage top list of surface preparation challenges In the May Hot Button, the experts weighed in on what they saw as the critical topics facing the industry in back-end-of-line (BEOL) surface preparation. This issue's discussion focuses on the related yet distinct problems in the front end of the line, where the cleaning, stripping, and conditioning challenges at the 65-, 45-, and 32-nm tech nodes are at least as daunting as those seen in the interconnect process sequences. How can postgate cleans be nondamaging, provide excellent uniformity results, and hit their cleanliness specs? What combination of wet and dry photoresist strips will work best to maintain dose levels and leave ever-thinner feature structures intact? How difficult will high-k dielectric materials be to clean and prepare? Can megasonics be improved and extended, and will supercritical-carbon-dioxide cleaning ever become a mainstream process? These questions and more are addressed by this month's panel of experts from the chipmaker, research, OEM, and materials communities. GLENN GALE (vice president, FEOL cleaning project, SEZ) and HARALD OKORN-SCHMIDT (vice president of global R&D, SEZ): If asked to come up with a single word to characterize the current issues in front-end-of-line (FEOL) cleaning, stripping, etching, and surface-preparation processes, we would still say . On the one hand, the already-stringent defect-density requirements will extend into the 45-nm node and beyond. But in addition, the introduction of novel, sensitive substrates and materials such as strained silicon, high-k dielectrics, new silicides, and maybe even metal gates—partly being implemented or close to being introduced into manufacturing—underscore the need for fresh solutions with well-controlled selectivity among materials and structures. In the area of photoresist stripping, plasma-based processes have been used for many generations to break through the carbonized crust of heavily ion-implanted resist with adequate success. For future device generations, however,