Depth-profiling of vertical sidewall nanolayers on structured wafers by grazing incidence X-ray flourescence

The Physikalisch-Technische Bundesanstalt (PTB), Germany's national metrology institute, developed an alignment strategy to specify elemental depth profiling in vertical sidewall layers on structured wafers. For this purpose, PTB's irradiation chamber for 200 mm and 300 mm silicon wafers was used to combine total-reflection X-ray fluorescence (TXRF) and grazing incidence XRF (GIXRF) techniques by employing monochromatized undulator radiation of the BESSY II electron storage ring. 3-D test structures were fabricated to develop an optimal alignment strategy allowing for depth profiling in such nanolayers. The test structures consisted of silicon bars with widths/spacings either in the μm or in the nm range. In order to be able to differentiate the sidewalls more easily from the remainder of the structures, they were provided with an additional silicon nitride layer. Four structure types of different bar width and density parameters on two 200 mm silicon wafers were investigated. The alignment procedure developed in the present work consists of three main steps and allows for distinct excitation of multiple sidewalls of one kind. Information about depth-dependent sidewall contamination, layer thickness and composition can be obtained by this approach. First results obtained on these test structures demonstrate the application potential of this new technique. In principle, depth-dependent chemical speciation should also be possible using GIXRF in combination with near edge absorption X-ray fine structure (NEXAFS)