In this paper we look into the litho and patterning challenges at the 22nm node. These challenges are different for
memory and logic applications driven by the difference in device layout. In the case of memory, very small pitches and
CDs have to be printed, close to the optical diffraction limit (k1) and resist resolution capability. For random logic
applications e.g. the printing of SRAM, real pitch splitting techniques have to be applied for the first time at the 22nm
node due to the aggressive dimensions of extreme small and compact area and pitch of SRAM bitcell. Common
challenges are found for periphery of memory and random logic SRAM cells: here the Best Focus difference per feature
type, limits the Usable Depth of Focus.
We describe progress in implementation of blur-based resolution metrics for EUV photoresists. Three sets of blur
metrics were evaluated as exposure-tool independent comparison methods using the Sematech-LBNL EUV microexposure
tool (MET) and ASML α-Demo Tool (ADT) full-field EUV scanner. For the two EUV resists studied here,
deprotection blurs of 15 nm are consistently measured using blur estimation methods based on corner rounding, contact
hole exposure latitude, and process window fitting using chemical amplification lumped parameter models. Agreement
between methods and exposure tools appears excellent. For both resists, SRAM-type lithographic diagnostic patterns at
80 nm pitch are only modestly sensitive to OPC blur compensation and display robust printability (RELS ~ ILS near 50
μm<sup>-1</sup> for multiple trench geometries) on the ASML ADT. These findings confirm the continuing utility of blur-based
metrics in a) guiding resist selection for use in EUV process development and integration at the 22 nm logic node and
below, and b) providing an exposure-tool independent set of metrics for assessing progress in EUV resist development.
We have used ASML's full field step-and-scan exposure tool for extreme ultraviolet lithography (EUVL), known as an
Alpha Demo Tool, to investigate one of the critical issues identified for EUVL, defectivity associated with EUV masks.
The main objective for this work was to investigate the infrastructure currently in place to examine defects on a EUV
reticle and identify their consequence in exposed resist. Unlike many previous investigations this work looks at
naturally occurring defects in a EUV exposed metal layer from a 45 nm node device. The EUV exposure was also
integrated into a standard process flow where the other layers were patterned using more conventional 193-nm
This presentation correlates reticle level defectivity to resulting wafer exposures. Defect inspection data from both the
28xx family of KLA-Tencor wafer inspection tool and Terascan reticle inspection tools are presented. Defect
populations were characterized with a KLA 5200 Review SEM. Observed defectivity modes were analyzed using both
conventional defect inspection methodology as well as advanced techniques in order to gain further insight. We find
good correlations between reticle level defects and the resulting wafer exposure defects.
The rapid expansion in the number of semiconductor manufactures using immersion imaging
systems confirms the acceptance of immersion lithography for critical layer imaging. One of the
early concerns in the development of immersion lithography was defect levels. These defects levels
have been dramatically reduced with each new system, and are now approaching defect levels
similar to dry systems. Continued reduction of defects will be required as smaller critical
dimensions are pursued on immersion systems with NAs well over one. In this work have studied
new ways to further reduce the number of defects. For this investigation an ASML 1150i &agr;-immersion scanner was used for both ultra pure water soaking and for image exposure. Previous
pre-exposure and post-exposure rinse/soak tests have been conducted on coater/developer tracks;
however using the track causes a significant time delay from soak to exposure, and vice-versa. For
this experimentation a dynamic soak of coated wafers immediately before exposure and
immediately after exposure was performed on the immersion scanner with controlled soak times.
The wafers were then processed as normal on a TEL-Lithius coater/developer track. Defect type and
size were analyzed to determine the interactions which reduced defects. The findings showed that
an immediate pre-exposure soak of 14 seconds reduced image expansion defects by 38%, compared
to no pre-exposure soak. Test results also indicated that the most frequent defect, bridging, was not
produced by water droplets.
To evaluate the effect of water exposure to a resist stack a set of experiments was designed that introduce a pre- and post-exposure wetting time to a coated wafer. The ASML 1150i α-immersion scanner, integrated with a TEL-Lithius coater track, was used to investigate the formation of defects related to the extended wetting. In the first approach, wetting was achieved using a dynamic DI-water rinse in the developer module of the track. For the second approach the immersion hood was positioned over the wafer at a fixed position and time, subjecting the wafer area below the immersion hood to the flowing water. We investigated various resists and topcoats. Defect inspections were performed on these film stacks after imaging.
Designing and operating exposure tools with a stable imaging performance becomes increasingly challenging as the exposure wavelength is decreased to improve resolution capabilities. At a wavelength of 157 nm, light is highly absorbed by most materials. In addition, the high photon energies readily induce photochemical degradation of the majority of organic materials. As a result many of the materials in the optical path of 157 nm exposure tools have been replaced and more stringent controls on the purge gas quality have been introduced. As the recipient of the first full field 157 nm scanners to be installed in the field, IMEC has implemented a tool-monitoring program to assess the performance of the exposure tool. The assessment includes characterization of the baseline operating conditions of the scanner and the evaluation of any potential trends in performance related to environmental interactions. This paper describes the techniques used to monitor the tool and reports on the results obtained during the initial months of tool operation.