Examining the Molecular Composition of Sub-10-nm Domains With Nano-Projectile Secondary Ion Mass Spectrometry

The use of extreme ultraviolet (EUV) light allows for sub-10-nm domains to be patterned. However, a limitation to continued progress on decreasing the size of device features is the performance of existing chemically amplified resists (CARs). These materials need to be examined at or below the desired feature sizes; thus, there is a pressing need to perform molecular analysis at scales at or below 10 nm.

Nano-projectile secondary ion mass spectrometry (NP-SIMS) is a surface analysis technique wherein an analyte surface is bombarded with a sequence of individual gold nano-projectiles separated in time and space. Three novel primary ions were tested as prospective projectiles for performing molecular analysis on sub-10-nm domains and compared to the reference projectile [Au₄₀₀]⁴⁺ (n/q = 100). Each projectile was tested on carbon foils, silicon wafers, and a model EUV CAR.

Based on examination of transmission electron microscopy micrographs of impact craters in carbon foil, all three novel projectiles produced craters less than 10 nm in diameter. Secondary ion yields on test samples scaled linearly with projectile momentum. The basis of NP-SIMS analysis is the equivalency of each projectile impact. We examined the equivalency of projectile impacts by calculating the correlation coefficient (Q) of ions from a uniform surface and found that Q did not deviate from unity (no observed correlation) for the reference projectile and the novel projectile n/q = 50.

The novel n/q 50 projectile is capable of sampling domains smaller than 10 nm. Each impact is equivalent and thus can be applied to examine the molecular homogeneity of a nonideal surface and examine surface domains that deviate by 2-3 standard deviations from the mean. This makes it an attractive probe for examining novel EUV resists that attempt to produce patterned features below the current 20-nm critical dimension.