Shin Muramoto oral presentation (FN1-Mon4-2-2)
Redeposition and Changes in Crater Depth Caused by Low Angular Distribution of Sputtered Molecules during Gas Cluster Ion Beam Depth Profiling
NIST, 100 Bureau Dr, MD 20895 Gaithersburg, United States
Experimental data on the molecules sputtered by argon gas cluster sources indicate that they are ejected at very low angles with respect to the surface, as low as 10° for inorganic elements and 20° for organic molecules, respectively. During molecular depth profiling of very thick films (>40 µm) such as automotive paint, the low angular distribution of the sputtered flux forces some of the sputtered molecules to re-deposit along the crater wall and consequently onto the forward side of the crater bottom, resulting in the re-sputtering of previously sputtered material. The implication for this effect is three-fold: a tilting of the crater bottom, decreasing depth resolution along the tilted areas of the crater bottom, and a change in sputter yield due to the tilt that is not proportional with the average depth of the crater. This tilting effect will affect the calculation of the sputtered volume if using a one point measurement such as an AFM or profilometer to estimate the crater volume, and may lead to erroneous determinations of sputter yield. We observe that the threshold for this effect in organic films begins around a thickness of 2 µm, where enough sputtered material accumulated to create a tilt that is 300 nm high and extended roughly 25 µm from the edge to the center of the crater. At a depth of roughly 5.5 µm, this tilt extended to the center of the crater, which had significantly affected depth resolution. Using a PMMA/PAA multilayer (each layer was 230 nm), it was found that the depth resolution had degraded at an exponential rate at the center of the crater (100 µm analysis area, 500 µm sputter area), from roughly (57, 77, 96, to 172) nm at depths of (1450, 3350, 5175, and 6920) nm, respectively.