Anal. Chem. 1999, 71, 5328-5334
Depth Profiling of Thin Films with Pulsed Glow Discharge Atomic Emission Spectrometry Chenglong Yang, Kristofor Ingeneri, Matt Mohill, and W. W. Harrison*
Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200
The application of microsecond pulsed Grimm glow discharge atomic emission spectrometry for depth profiling of thin films is examined. The effects of pulsed conditions including pulse voltage, pulse frequency, pulse width, and Ar pressure on depth profiling performance were characterized for Zn and Cu coatings on steel. Using optimized conditions, linear calibration curves of coating thickness for Zn (6.1-26.9 µm) and Cu (50-500 nm) on steel were achieved. A precision of 2-5% relative standard deviation was determined. An ultrathin coating of Cu (10 nm) on steel was also measured by this technique. Glow discharge (GD) spectroscopy, employing the Grimm lamp1 as an excitation source, is a rapid profiling method for the elemental analysis of surfaces, interfaces, and bulk materials.2,3 In 1973, Greene and Whelan introduced the use of the glow discharge lamp as a method for depth profiling.4 In the same year, Belle and Johnson showed an application of glow discharge atomic emission spectrometry (GD-AES) to the depth profiling of metal alloys.5 Quantitative methods of depth profiling by GD-AES were developed by Bengtson6 and Weiss,7 respectively. Further evaluation and development of depth resolution have also been reported.8-10 On the basis of these studies, GD spectroscopy evolved into a valuable technique for depth profiling. Instrumentation for the technique has become commercially available and has found broad usage. Major applications of depth profiling by GDAES have been found in the metallurgical, automotive, and nuclear industry.2 Most instruments are based on the Grimm lamp and are powered by either direct current (dc) or radio frequency (rf) sources.11,12 The effective depth range of thin-layer analysis has been approximately 10 nm to 100 µm.3 Pulsed operation of conventional glow discharges and hollow cathodes has been shown to enhance sputtering rate and signal (1) Grimm, W. Spectrochim. Acta Part B 1968, 23B, 443-454. (2) Glow Discharge Spectroscopies; Marcus, R. K., Ed.; Plenum Press: New York, 1993. (3) Glow Discharge Optical Emission Spectrometry: Payling, R., Jones, D., Bengston, A., Eds.; John Wiley & Sons: New York, 1997. (4) Greene, J. E.; Whelan, J. M. J. Appl. Phys. 1973, 44, 2509-2513. (5) Belle, C. J.; Johnson, J. D. Appl. Spectrosc. 1973, 27, 118-124. (6) Bengtson, A. Spectrochim. Acta Part B 1994, 49B, 411-429. (7) Weiss, Z. J. Anal. At. Spectrom. 1995, 10, 891-895. (8) Weiss, Z. Spectrochim. Acta Part B 1992, 47B, 859-876. (9) Bengtson, A.; Eklund, A.; Lundholm, M.; Saric, A. J. Anal. At. Spectrom. 1990, 5, 563-567. (10) Hamada, T.; Wagatsuma, K.; Hirokawa, K. Surf. Interface Anal. 1995, 23, 213-218.
5328 Analytical Chemistry, Vol. 71, No. 23, December 1, 1999
intensities by 1-4 orders of magnitude in emission, fluorescence, and mass spectrometry.13-18 The evolution of microsecond pulsed discharges to the Grimm GD lamp was reported by our group.19 Benefits include high sputtering rate and emission signals, low detection limits, and good precision (
