Comparison of boranol and silanol reactivities in boron-doped SiO2 chemical vapor deposition from trimethyl borate and tetraethyl orthosilicate

Abstract

For the first time, the relative rates of consumption of surface boranols and silanols reacting with tetraethyl orthosilicate [TEOS, Si(OCH2CH3)4] have been measured. This comparison has direct bearing on understanding the growth of doped SiO2 films from TEOS and trimethyl borate [TMB, B(OCH3)3] sources since surface boranols and silanols are expected to be present during the thermal chemical vapor deposition process. The measurements were accomplished by first derivatizing a porous silica substrate with boranols and silanols via hydrolysis of the products from an initial trimethyl borate (TMB) chemisorption step. TEOS exposures in the mTorr pressure regime were then carried out in a cold-wall reactor. Reaction products on the surface were identified with Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy in analysis chambers adjoining the reactor. Although TEOS does not react with SiOH at 300 K, it does react with BOH at this temperature. Using the deuterated species (SiOD and BOD) to measure the relative rates of hydroxyl consumption without interference from concurrent hydroxyl formation, the reaction rate constant for boranols with TEOS at 1000 K was determined to be twice that of silanols. At 1000 K, subsequent decomposition of the TEOS chemisorption products regenerates both BOH and SiOH.