Analysis of trace impurities in semiconductor gas via cavity-enhanced direct frequency comb spectroscopy
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- Cossel, K.C., Adler, F., Bertness, K.A. et al. Appl. Phys. B (2010) 100: 917. doi:10.1007/s00340-010-4132-5
Cavity-enhanced direct frequency comb spectroscopy (CE-DFCS) has demonstrated powerful potential for trace-gas detection based on its unique combination of high bandwidth, rapid data acquisition, high sensitivity, and high resolution, which is unavailable with conventional systems. However, previous demonstrations have been limited to proof-of-principle experiments or studies of fundamental laboratory science. Here, we present the development of CE-DFCS towards an industrial application—measuring impurities in arsine, an important process gas used in III–V semiconductor compound manufacturing. A strongly absorbing background gas with an extremely complex, congested, and broadband spectrum renders trace detection exceptionally difficult, but the capabilities of CE-DFCS overcome this challenge and make it possible to identify and quantify multiple spectral lines associated with water impurities. Further, frequency combs allow easy access to new spectral regions via efficient nonlinear optical processes. Here, we demonstrate detection of multiple potential impurities across 1.75–1.95 μm (5710–5130 cm−1), with a single-channel detection sensitivity (simultaneously over 2000 channels) of ∼4×10−8 cm−1 Hz−1/2 in nitrogen and, specifically, an absorption sensitivity of ∼4×10−7 cm−1 Hz−1/2 for trace water doped in arsine.