AVS 46th International Symposium
    Applied Surface Science Division Friday Sessions
       Session AS-FrM

Paper AS-FrM6
A Study of TOF-SIMS for the Analysis of Metal Contamination on Silicon Wafers

Friday, October 29, 1999, 10:00 am, Room 6A

Session: New or Improved Surface Related Analytical Techniques
Presenter: I.A. Mowat, Charles Evans & Associates
Authors: I.A. Mowat, Charles Evans & Associates
T.J. Schuerlein, Charles Evans & Associates
J. Metz, Charles Evans & Associates
R. Brigham, Charles Evans & Associates
D. Huffaker, Charles Evans & Associates
Correspondent: Click to Email
The current methods of choice for the analysis of metal contaminants on silicon wafers are Total Reflection X-Ray Fluorescence (TXRF) and SurfaceSIMS. TXRF is a survey technique, with good detection limits for transition metals (e.g. down to 10@super 9@atoms/cm@super 2@ for some elements). SurfaceSIMS is not usually used as a survey technique, but it has high sensitivity for species such aluminum and alkali metals (species not detected well by TXRF). Time-of-flight SIMS (TOF-SIMS) is a technique which offers a surface survey of all metal contaminants, with good detection limits. This paper details the investigation of TOF-SIMS as a possible tool for such analyses. Under the high beam current conditions used, elemental information is obtained with high sensitivity (under certain conditions, the detection limit for iron can be below 10@super 9@atoms/cm@super 2@, and is much lower for the alkali metals). Experiments were carried out to investigate the accuracy and precision of TOF-SIMS analyses of Si wafers. The areas of interest were: (1) short term variability of data from a standard spin coated wafer; (2) long term variability (over approximately six months) of data from the same wafer; (3) investigation of factors affecting the detection limits achievable by TOF-SIMS; (4) cross correlation of TOF-SIMS with established techniques such as TXRF and SurfaceSIMS. Short term variability was determined to be in the range 10-12%, and long term variability was ~20%. Work is underway to investigate the sources of this variability. Detection limits were studied by assessing wafers from different sources in the semiconductor industry, and were found to vary by up to a factor of five. Cross correlation with both TXRF and SurfaceSIMS have proven to be a good source of information to increase the accuracy of TOF-SIMS measurements. The information obtained will help assess the suitability of TOF-SIMS as an additional method for metal contamination measurement on silicon wafers.