Characterization of CD-SEM metrology for iArF photoresist materials

Abstract

For many years, lithographic resolution has been the main obstacle for keeping the pace of transistor densification to meet Moore's Law. For the 45 nm node and beyond, new lithography techniques are being considered, including immersion ArF lithography (iArF) and extreme ultraviolet (EUV) lithography. As in the past, these techniques will use new types of photoresists with the capability to print 45 nm node (and beyond) feature widths and pitches.In a previous paper ("SEM Metrology for Advanced Lithographies," Proc SPIE, v6518, 65182B, 2007), we compared the effects of several types of resists, ranging from deep ultraviolet (DUV) (248 nm) through ArF (193 nm) and iArF to extreme UV (EUV, 13.5 nm). iArF resists were examined, and the results from the available resist sample showed a tendency to shrink in the same manner as the ArF resist but at a lower magnitude.This paper focuses on variations of iArF resists (different chemical formulations and different lithographic sensitivities) and examine new developments in iArF resists during the last year. We characterize the resist electron beam induced shrinkage behavior under scanning electron microscopy (SEM) and evaluate the shrinkage magnitude on mature resists as well as R&D resists. We conclude with findings on the readiness of SEM metrology for these challenges.

Electron-beam induced photoresist shrinkage influence on 2D profiles

“…It also allows us to predict the change in resist profile with electron dose and the influence of initial resist profile on shrinkage characteristics. In this work, the results from the previous paper will be shown to be consistent with numerically simulated results, thus lending credibility to these papers' postulations [1,4]. Also, results from this 2-D profile model can also give clues as to how we might, in the future, model the shrinkage of contour edges of 3-D shapes.…”

“…Important implications of these findings were discussed in the conclusions. The references should be reviewed for full details, but here we will highlight only the main points [1]. Figure 2 shows a set of shrinkage curves of a single immersion ArF material with features of varying width, all shrunk under identical conditions and at V acc = 800 V. The curves for the larger features are described as behaving by a "classical shrinkage" model similar to the results of work by Habermas et al [3].…”

The characterization of photoresist shrinkage difference in X-Y directions with CDSEM metrology

“…With dynamic CD measurements from 1 st to 11 th , ADI hole CD in diameter X and diameter Y both become larger, which is known to be the PR shrinkage effect induced by e-beams bombardment, which removes the carbonyl groups [1][2]. However, we found one interesting phenomenon that CD values of Y diameter were larger than those of X diameter and the CD difference of Y-X decreased to 0 nm from 4~8 nm with dynamic measurements.…”

Quantitative nanomechanical measurement of electron beam surface modification

“…This is consistent with hardening of the material and loss of hydrophilic groups through outgassing, as consistent with the assumptions of the model, and as postulated in other previous works. [1] Measuring across several features of varying sizes, the magnitude of the adhesion and modulus shifts appears to vary fairly reliably with feature size and pitch.…”

“…The problem has been extensively studied and modeled previously and the dimensional effects are now well understood [1,2]. However, a continuing outstanding issue is discerning and measuring material changes caused by the shrinkage.…”