Semiconductor applications of nanoliter droplet methodology with total reflection x-ray fluorescence analysis

• Published in: Spectrochimica acta. Part B: Atomic spectroscopy Vol. 59; no. 8; pp. 1117 - 1124
• Main Authors: Miller, Thomasin C., Sparks, Christopher M., Havrilla, George J., Beebe, Meredith R.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 31.08.2004
• Subjects: Micro X-ray fluorescence; Nanoliter dried spot deposition; Silicon wafer analysis; Total reflection X-ray fluorescence; Vapor phase decomposition; Micro X-ray fluorescence; Vapor phase decomposition; Silicon wafer analysis; Total reflection X-ray fluorescence; Nanoliter dried spot deposition
• ISSN: 0584-8547; 1873-3565
• DOI: 10.1016/j.sab.2003.11.010

In this study, the nanoliter dried spot method was applied to semiconductor contamination analysis to enhance vapor phase decomposition processes with total reflection X-ray fluorescence detection. Nanoliter-sized droplets (10 and 50 nl) were deposited onto native silicon oxide wafer surfaces in a clean room environment from both single and multielemental standards containing various concentrations of iron in different matrices. Direct comparisons were made to droplets formed by conventional VPD with similar iron standards. Nanoliter dried spots could be reproducibly deposited and dried in air with typical drying times ranging from 20 s to 2 min depending on the nanoliter volume deposited, compared to VPD spots which have drying times ranging from tens of minutes to several hours. Both types of residues showed a linear relationship between Fe intensity and mass deposited. Variable angle experiments showed that both nanoliter and VPD deposits of single element standards were film-like in character, while residues formed from much more complex matrices and higher mass loadings were particulate in character. For the experimental conditions used in this study (30 kV, 100 mA), typical TXRF spectral Fe limits of detection were calculated to be on the order of picograms or ∼1×10 10 atoms/cm 2 for a 0.8 cm 2 X-ray excitation beam area for both nanoliter dried spots and VPD spots prepared from single elemental standards. Calculated Fe detection limits for 200 mm diameter silicon wafers used in this study were in the ∼1×10 8 atoms/cm 2 range. By using nanoliter sized droplets, the required sample volume is greatly reduced resulting in higher sample throughput than with conventional VPD methods.