There is a bit of a battle in the analytical arena when it comes to the best method for measuring trace contaminants on the surface of a silicon wafer. We described the analysis of trace metals on silicon wafers by Vapor Phase Decomposition – Inductively Coupled Plasma Mass Spectroscopy (VPD-ICPMS) in a previous blog post. TXRF or Total Reflection X-Ray Fluorescence is another technique that is often used in semiconductor manufacturing to monitor contamination.
| VPD-ICPMS | TXRF |
|---|---|
| Contaminants from the entire wafer surface are collected and analyzed. | Only the area excited by the X-Ray beam is analyzed. |
| Results are cumulative for the wafer surface, no spatial information is available. | TXRF can produce maps showing the impurity distribution on the wafer surface. |
| 10-100X greater sensitivity. | Lower sensitivity for many trace metals. |
| Detects light elements like Li, Na, and Mg where TXRF cannot. | Detects non-metals like Cl, and Ar where VPD-ICPMS cannot. |
| Considered destructive analysis. | Non-destructive analysis. |
| Wafer can only be analyzed once. | Wafer can be reanalyzed as needed. |
| Analyzes about 20 Angstroms or thickness of oxide film. | X-Ray beam penetrates about 500 Angstroms. |
| Can only analyze bare Si or Si with SiO2 films. | Will analyze oxide and any amorphous or crystalline film beneath it. |
VPD-ICPMS and TXRF use very different methods to analyze for contamination on wafer surfaces. Many semiconductor fabrication facilities use an integrated VPD-TXRF system to monitor contamination.