Effects of methyl silsesquioxane electron-beam curing on device characteristics of logic and four-transistor static random-access memory

The as-spun methyl silsesquioxane (MSQ) film cured by an electron beam (e-b eam) did not show water absorption after a five-day exposure to ambient ail : MSQ was applied to the triple-level metal (TLM) Logic and double-level me tal (DLM) foul-transistor (4-T) static random-access memory (SRAM) as inter metal dielectric by means of the non-etchback process. When MSQ treatment c onditions were properly controlled, the top layer of the as-spun films was cured by e-beam exposure while the bottom layer of the film was thermally c ured for a short period of time. The as-cured MSQ offered good surface plan arity. In addition, neither via poisoning, bowing nor cracking was observed . The results showed that, by the application of the e-beam cured MSQ in th e fabrication of intel connect structures, the cache time of DLM 4-T SRAM c ould be improved to 10 ns compared with 11.5 ns for the SRAM fabricated usi ng the conventional furnace cure spin-on-glass (SOG) process (400 degrees C annealing for one hour). E-beam exposure has little effect on n-channel me tal-oxide-semiconductor (NMOS) device characteristics, such as saturation c urrent threshold voltage and channel length. In contrast, e-beam exposure h as a significant effect on p-channel MOS (PMOS) device characteristics, res ulting in a shift of the threshold voltage as well as an increase in the ch annel length. It is notable that the e-beam exposure almost did not affect NMOS device characteristics in the 4-T SRAM, since the polysilicon load res istor could serve as a shield against electron bombardment. In such a case, the resistance of the polysilicon load resistor was significantly decrease d.