A two-step replacement for the four-step process used to clean silicon
wafers at critical steps during semiconductor microcontroller manufac
ture was studied and characterized in a spray tool and was shown to be
an improved cleaning process. The standard four-step process, commonl
y referred to as the RCA clean, consists of a treatment with an alkali
ne solution containing ammonium hydroxide followed by a water rinse an
d an acid solution containing hydrochloric acid followed by a water ri
nse; whereas the new clean consists of an alkaline solution containing
tetraalkylammonium hydroxide followed by a water rinse. To obtain a m
easure of the latitude afforded by this new clean, the variables studi
ed were chemical flow or spray rate, temperature, spray time, and conc
entration. The manufacturing process step used for the study was the c
lean prior to the growth of the tunnel oxide, and the key electrical p
arameter monitored was the tunnel oxide current and electrical stress
breakdown for very thin oxides. The results show that the main effect
of temperature had the greatest direct impact on the cleaning efficien
cy (measured by time to tunnel oxide break down), with the interaction
effects of temperature/time and temperature/flow being most significa
nt. The interaction of temperature and time had the largest impact on
the tunnel oxide uniformity across the wafer.