Detection of Trace Water Vapor in High-Purity Phosphine Using Cavity Ring-Down Spectroscopy

Abstract

The presence of trace water vapor in process gases such as phosphine, used for compound semiconductor epitaxial growth, can negatively affect the optical and electrical properties of the final device. Therefore, sensitive H2O measurement techniques are required to monitor precursor purity and detect unacceptable contamination levels. A commercial cavity ring-down spectrometer that monitors an H2O absorption line at a wavelength of 1392.53 nm was investigated for service in high purity PH3. Spectral parameters such as the line shape of water vapor in the presence of PH3 as well as background features due to PH3 were measured at different pressures and incorporated into the data analysis software for accurate moisture readings. Test concentrations generated with a diffusion vialbased H2O source and dilution manifold were used to verify instrument accuracy, sensitivity, linearity, and response time. H2O readings at 13.2 kPa corresponded well to added concentrations (slope=0.990+/-0.01) and were linear in the tested range (0-52.7 nmol mol-1). The analyzer was sensitive to changes in H2O concentration of 1.3 nmol mol-1 based on 3sigma of the calibration curve intercept for a weighted linear fit. Local PH3 absorption features that could not be distinguished from the H2O line were present in the purified PH3 spectra and resulted in an additional systematic uncertainty of 9.0 nmol mol-1. Equilibration to changing H2O levels at a flow rate of 80 std cm3 min-1 PH3 occurred in 10-30 minutes. The results indicate that cavity ring-down spectroscopy (CRDS) at 1392.53 nm may be useful for applications such as on-line monitoring (and dry-down) of phosphine gas delivery lines or the quality control of cylinder sources.

Pressure Broadening of H2O Absorption Lines in the 1.3 μm Region Measured by Continuous Wave-Cavity Ring-Down Spectroscopy: Application in the Trace Detection of Water Vapor in N2, SiH4, CF4, and PH3

“…A survey spectrum of PH 3 absorption in the 1.393 lm region using the current cw-CRD spectrometer revealed no PH 3 absorption bands. Recent measurements by Funke et al, 34 however, show very weak PH 3 absorption bands in this wavelength region (r peak ; 10 À27 cm 2 molecule À1 ) and these data are used in the calculation of the minimum detection limit of H 2 O in PH 3 (see below). Following procedures similar to those for SiH 4 and CF 4 bath gases, the measured broadening coefficient (HWHM) for line 1 perturbed by PH 3 was determined to be 0.1820 6 0.0083 cm À1 atm À1 .…”

Factors influencing the purity of electronic grade phosphine delivered to MOCVD tools

“…Cylinder 2 was analyzed multiple times using the CRDS method in [9] to investigate the behavior of H 2 O in the PH 3 delivered through the cylinder valve (Fig. 1A).…”

“…PH 3 gas is the most commonly used phosphorus source for InP and associated alloys and is manufactured to a 99.9999% purity level. However, even though the gas purity is confirmed with state-of-the-art instrumentation [9][10][11], there are many factors that may still influence device performance. Ultimately, device growth and performance tests such as low temperature photoluminescence (PL) and Hall mobility are used to provide complementary information that relate the atomic composition to critical parameters such as gas purity.…”

Quantitative Moisture Measurement with a Cavity Ring-down Spectrometer using Telecom Diode Lasers

“…Tunable diode laser absorption spectroscopy (TDLAS) is relatively simple and robust, therefore has been widely applied [8][9][10]. Cavity ringdown spectroscopy (CRDS) using cw diode lasers provides great enhancement in sensitivity and receives increasing interests in recent years [11][12][13][14][15]. The reported detection limit of water vapor varies from a few ppbv to several hundred pptv (part per trillion by volume).…”