Silicon Processing Chemical Diagnostics and Control Using Diode Lasers

Infra-red diode laser absorption spectroscopy has long been a powerful tool for molecular spectroscopists and analytic chemists. Through recent improvements in lead salt laser fabrication lasers with modest power (up to several milliwatts), good beam quality and broad tunability (as much as 30% of center frequency) are now available. In addition, very low absorbence species detection, free of window induced interference fringes is now possible by utilizing a combination of frequency and wavelength modulation via the diode laser injection current.1 This modulation approach also lends itself to a simple feedback method that may be used to lock the laser frequency to a particular molecular absorption line and thus enable real time measurements of that species' absorbence in the presence of high levels of electrical background noise often found in industrial settings.2