[B._Beckhoff,_et_al.]_Handbook_of_Practical_X-Ray_(b-ok.org).pdf

Fig 750 wafer surface preparation system modules wsps

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Fig. 7.50. Wafer surface preparation system modules (WSPS): a novel system for vapor phase decomposition preparation for wafer diameters 100 up to 300 mm cooperation with GeMeTec [177], Germany. Since then, this reliable mod- ulated system has dominated the market of automated VPD preparation systems. The operator loads the wafers in a carrier on the load/unload module (for follow up on the procedure please refer to Fig. 7.50) beginning at module no. 4, counting the modules from the left. A robot arm takes the wafers one by one into the HF vapor phase treatment module no. 2, then onto the droplet collection scanner module no. 1. Both the scanning pattern and the scanned area can be adjusted to individual requirements. The splitting of the droplet into two parts and placing the aliquot into a vial is optional and affords economical, simultaneous processing of expensive samples and evaluation by complementary methods. Then the robot transfers the wafer with the dried scanning droplet residue and a blank droplet to the drying station module no. 3. After controlled drying, the wafer arrives at the carrier unload module no. 4. The droplet residue remains concentrated in an area of 200 µ m without losing analyte, as shown in Fig. 7.51 [178]. By means of the automated VPD equipment both the LOD, at present in the upper range of areal density of 10 7 atoms/cm 2 , the procedural reproducibility (standard deviation < 30%) and the operational reliability ( > 90 %) of the VPD-TXRF procedure are improved [105]. The accuracy of VPD-TXRF is a sensitive function of the reliability of the standard reference material and of the reproducibility of the droplet drying Tachikawa-shi, 190 Japan; Purex Preparation Method for Wafer Analysis of Purex Engineering Co., Ltd., Tokyo, 103 Japan.
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Methodological Developments and Applications 519 (a) (b) Fig. 7.51. Dried scanning droplets, worst case ( a ): exploded droplet under enforced drying using an infrared lamp, droplet size of a few mm; optimized case ( b ): scanning droplet dried under controlled conditions using vacuum and carrier gas in the drying module of WSPS procedure [179]. Mass absorption sets the upper limit of reliable analyses at 10 14 atoms/cm 2 [123]. Concerning the recovery of less soluble fluorides such as CaF 2 , silicides, e.g., NiSi 2 and electroplating noble metals, solubility in aqueous HF solutions is the only matrix limitation of VPD-TXRF in any VPD preparation and hyphenated VPD-methods. Though the VPD preparation has been optimized for maximum recovery > 90% even for the electropositive Cu [105, 176], noble metals can only be dissolved when the oxidation potential of the scanning solution is higher than the reduction potential of the bare Si surface. Consequently, we suggest a vigilant approach in the diagnostic use of VPD, applying correlation with other, independent, and complementary methods. For this purpose, optional droplet-splitting facilitates simultaneous complementary analyses [180]. Current research focuses on issues of sample holders [181] and light element capabilities [130].
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