Self-focusing SIMS: A metrology solution to area selective deposition

Micro- and nano-electronics is increasingly relying on heterogeneous, confined and three-dimensional structures, to continue the downscaling required for the next technology generations. Area-selective atomic layer deposition (ALD) is one suited methodology to create nm-scale features through (1) the area-selective self-assembly of a blocking layer (i.e. a thiol deposited on copper) and (2) the ALD growth on the areas not covered with the blocking layer (i.e. a dielectric deposited on low-k). Assessing the efficiency and defectivity of selective deposition on such samples would require a lateral resolution much smaller than the feature size of interest. Hence the need for characterization techniques appropriate to the device's dimensions. Recently, thanks to the Self-Focusing Secondary Ions Mass Spectrometry (SF-SIMS) concept, the SIMS applicability to analyze the composition of narrow (<20 nm) trenches has been enabled through the selection of characteristic cluster ions exclusively confined to the areas of interest. In this paper, we show that the SF-SIMS concept can be extended to area-selective ALD processes. More specifically, the assessment of the blocking layer deposition on copper is studied using the characteristic copper-sulphur cluster ions while the potential reaction with the low-k material is checked by looking at silicon-sulphur cluster ions. In the same way, the ALD growth of aluminum oxide on the low-k material is assessed using silicon-aluminum clusters while the detection of copper-aluminum clusters is exploited to assess the efficiency of the blocking layer.