Atomic spectroscopy can monitor and control physical vapor deposition process

Researchers at Stanford University (Stanford, CA) and Focused Research (Santa Clara, CA) have developed an atomic-spectroscopy-based monitoring system for physical-vapor-deposition process control of yttrium. Based on frequency-modulation (FM) atomic-absorption spectroscopy, the scheme uses an external-cavity, 670-nm diode laser (New Focus, Santa Clara, CA). The laser beam was passed through an electro-optic phase modulator driven by a radio-frequency source, and its frequency was monitored wit

Nov 1st, 1995

Atomic spectroscopy can monitor and control physical vapor deposition process

Researchers at Stanford University (Stanford, CA) and Focused Research (Santa Clara, CA) have developed an atomic-spectroscopy-based monitoring system for physical-vapor-deposition process control of yttrium. Based on frequency-modulation (FM) atomic-absorption spectroscopy, the scheme uses an external-cavity, 670-nm diode laser (New Focus, Santa Clara, CA). The laser beam was passed through an electro-optic phase modulator driven by a radio-frequency source, and its frequency was monitored with a hollow-cathode lamp as reference. Single-mode optical fiber delivered the beam to the vacuum deposition chamber where it was focused onto a wideband photodetector.

Mixing the detector output with the RF signal driving the electro-optic phase modulator resulted in a signal proportional to the first derivative of the absorption profile. The second derivative was used for deposition-rate monitoring and control of the process because it is proportional to the peak absorption. Absorption as low as 10-6 could be measured, and deposition-rate control with an accuracy better than 1% at a rate of 3.5 Å/s was demonstrated, which corresponds to a deposition-rate resolution of 0.03 Å/s. The technique also has applications for understanding thin-film growth and the dynamics of vapor condensation on substrates.

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