Vapor Phase Decomposition VPD and Droplet Collection

Vapor-phase decomposition and collection (Figs 4.16 to 4.18) is a standardized method of silicon wafer surface analysis [4.11]. The native oxide on wafer surfaces readily reacts with isothermally distilled HF vapor and forms small droplets on the hydrophobic wafer surface at room temperature [4.66]. These small droplets can be collected with a scanning droplet. The scanned, accumulated droplets finally contain all dissolved contamination in the scanning droplet. It must be dried on a concentrated spot (diameter approximately 150 pm) and measured against the blank droplet residue of the scanning solution [4.67-4.69]. VPD-TXRF has been carefully evaluated against standardized surface analytical methods. The user is advised to use reliable reference materials [4.70-4.72]. 

The accuracy of VPD-TXRF depends largely on the reliability of the reference material (cf Sect. 4.1.1.3) and on the reproducibility of the droplet drying procedure (Fig. 4.17) [4.75, 4.76]. Mass absorption sets the upper limit of reliable analyses to lO atoms cm [4.77]. 

VPD-TXRF is also a facile technique for interface analysis [4.78, 4.79]. Automated VPD equipment (Fig. 4.16) improves both the detection limit (upper range 10 atoms cm ) and the reliability (by 50%) of the VPD-TXRF measurement [4.14]. Current research focuses on sample holders [4.80, 4.81] and light-element detection capability [4.82-4.84]. 

Cu-filter. The three curves to the left were determined by the detection of K-peaks the three curves to the right, by that of L-peaks [4.21], after Refs [4.73] and [4.74]. 

Surface and Thin Film Analysis Principles, Instrumentation, Applications 

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