Zhaoning Yu

Study of spin-coated resist coverage on nanoscale topography using spectroscopic ellipsometry

Using spectroscopic ellipsometry and rigorous coupled wave analysis, we studied the spin-coated resist coverage on 72.6 nm pitch line-and-space patterns of various depths (from ∼20 to ∼130 nm). Within the margin of measurement error, we find the tested nano-patterns have no apparent effect on the spin-coated resist thickness. The result suggests that, during the spinning, the resist ceased to flow at a critical thickness much larger than the pattern depth, and the resist thinning afterwards was dominated by solvent evaporation. The methods and results demonstrated in this work can improve the characterization and process control in a number of applications where spin coating on high-density nano-scale topographies is required.

Cleaning induced imprint template erosion

Abstract. We studied the erosion and feature stability of fused silica patterns under different template cleaning conditions. The conventional sulfuric acid and hydrogen peroxide mixture (SPM) cleaning is compared with an advanced nonacid process. Spectroscopic ellipsometry optical critical dimension measurements were used to characterize the changes in pattern profile with good sensitivity. This study confirmed the erosion of the silica patterns in the traditional acid-based SPM cleaning mixture (H2SO4+H2O2) at a rate of ∼0.1  nm per cleaning cycle. However, the advanced nonacid cleaning process only showed critical dimension shift of ∼0.01  nm per cleaning. Contamination removal and pattern integrity of sensitive 20-nm features under MegaSonic assisted cleaning was also demonstrated.

Study of silica nano-pattern erosion in H2SO4-H2O2 mixture using spectroscopic ellipsometry

To overcome the difficulty in measuring the extremely slow erosion of transparent silica, we apply spectroscopic ellipsometry (SE) optical critical dimension measurements on a subwavelength surface relief grating instead of a blank silica substrate. By analyzing the nano-grating SE spectra, we find that the H2SO4-H2O2 Piranha cleaning widely used for organic contaminants removal also etches silica slowly—up to a molecular monolayer is partially removed from the silica surface by each cleaning cycle. Based on these findings, we conclude that silica dissolution is an important factor to be considered in applications such as template cleaning in nanoimprint lithography.

Spectroscopic ellipsometry optical critical dimension measurements of templates and imprinted resist for patterned magnetic media applications

The authors have applied spectroscopic ellipsometry optical critical dimension (SE-OCD) measurement to grating templates and imprinted resist patterns with a pitch of 72.6 nm, corresponding to a track density of 350 ktpi (kilotracks per inch) for discreet track recording media. Their experiments indicate that SE-OCD is sensitive in detecting topography features in template profiles. The measurement of imprinted resist pattern is complicated by parameter correlation. Comparison of SE-OCD reported template and imprinted resist profiles can be used to study imprint pattern fidelity.

Controlling template erosion with advanced cleaning methods

We studied the erosion and feature stability of fused silica patterns under different template cleaning conditions. The conventional SPM cleaning is compared with an advanced non-acid process. Spectroscopic ellipsometry optical critical dimension (SE-OCD) measurements were used to characterize the changes in pattern profile with good sensitivity. This study confirmed the erosion of the silica patterns in the traditional acid-based SPM cleaning mixture (H2SO4+H2O2) at a rate of ~0.1nm per cleaning cycle. The advanced non-acid clean process however only showed CD shift of ~0.01nm per clean. Contamination removal & pattern integrity of sensitive 20nm features under MegaSonic assisted cleaning is also demonstrated.

Optical critical dimension measurements for patterned media with 10's nm feature size

Patterned media is expected to be implemented in future generations of hard disk drives to provide data storage at densities exceeding 1012 bits/in2 and beyond. The implementation of patterned media, which would involve developing processing methods to offer high resolution (small bits), regular patterns, and high density, has posed a number of metrology challenges. Optical Critical Dimension (OCD) is the leading candidate to overcome the metrology challenges for patterned media. This paper presents the successful OCD measurements on the critical dimensions, sidewall-angles, and detailed sidewall shape of gratings of quartz template and imprint disk with pitch as small as 57nm.