Chemistry within the thermally activated boundary layer during APCVD of silicon dioxide from TEOS and ozone using in-situ infrared spectroscopy: Effects of phosphorus and boron on the gas phase chemistry

The deposition of phosphorus and boron doped silicon dioxide films at 450°C was studied in quasi real-time by probing the thermally activated boundary layer region near the growing surface during atmospheric pressure chemical vapor deposition. Quantitative methods are developed for FT-IR (Fourier transform infrared) spectroscopy during ozonation of TEOS (tetraethylorthosilicate), TMPi (trimethylphosphite), TEPi (triethylphosphite), and TMB (trimethylborate). The novel measurement of gaseous alcohols of boron and silicon alkoxides by FT-IR demonstrates the application of a new in-situ methodology which probes the high temperature region within the CVD environment. Upon addition of phosphite dopant sources a two fold reduction is noted in both the isolated ethoxysilanol (3737 cm−1) and isolated methoxyboranol (3705 cm−1) concentrations and leads to an understanding of the radical chain kinetics involving oxidation of phosphites, borates and silicates. Chemical boundary layer difference spectra (CBL-DS) formed by taking the 1:1 difference between FT-IR spectra before and after phosphite dopant addition provides vibrational spectra of ethoxysilanols ((EtO)_xSiOH) (3737, 960, 810 cm −1), siloxane (Si-O-Si) (1000–1250 cm−1), and phosphorus oxide (P-O) (1293 cm−1) film growth intermediates. Calculation of the standard deviation spectra from a series of CBL-DS shows that ethoxysilanol groups formed during ozonation are nearly independent of the amount of added phosphorus for gas phase phosphorus concentrations up to 10 mol %. Peroxy radical and phosphite radical reactions that produce phosphoranyl radical intermediates (R′OOP·(OR) ₃) during phosphite ozonation largely affect silanol and boranol product formation routes without significantly affecting the organic by-product concentrations. Partial least squares (PLS) Beer's law absorption models are used in the determination of TEOS, ozone and ethoxysilanol levels and yield the reaction stoichiometry between TEOS and ozone at 2:1, as well as the fractional reaction order in TEOS at 1.65(+/−.02). Similarly, the relative change in ethoxysilanol formed versus the amount of residual ozone during reaction was measured at ca. 1:3. A radical chain oxidative process involving direct reaction of ozone and TEOS is implicated in the mechanism of formation of active silanol groups and acetic acid. Subsequent dehydration reactions of silanol functionalities then lead to hydroxylated silica both in the gas phase and on the growing surface.