Sterling G. Watson

Wafer printability simulation accuracy based on UV optical inspection images of reticle defects

As semiconductor processes have moved towards lower k1 and mask inspection equipment has moved into the UV range, more subtle reticle defects have been found to cause manufacturing problems. Lower k1 and new lithography processes and reticle technologies, such as OPC and PSM, have made it difficult to determine the significant and these defects. This paper reports on the development of a simulation tool that will improve the yield and productivity of photomask manufacturers and wafer manufacturers by improving reticle defect assessment. This study demonstrates the accuracy of simulation software that predicts resist patterns based on sophisticated modeling software that uses optical images obtained from a state-of-the-art UV optical inspection system. A DUV 4X reduction stepper was used to print a reticle with programmed defects across an exposure/focus matrix, with the minimum feature size being 200 nm. Quantitative comparisons between predicted and measured wafer CDs were made. In summary, it was found that the simulation software based solely on aerial images predicted absolute CDs with limited accuracy, but differential CDs with limited accuracy, but differential CDs, obtained by utilizing both the reference and defect images, were predicted accurately. Comparison of simulations using both reticle SEM images and optical reticle inspection images showed good agreement, demonstrating the accuracy and high resolution of the optical reticle inspection images. Application of differential aerial images to a simple test case showed that it was possible to identify and therefore eliminate a significant number of defects that did not print, thereby improving defect assessment.

New die-to-database inspection algorithm for inspection of 90-nm node reticles

The implementation of low k1 193nm lithography for 90nm node IC production brings new challenges to reticle inspection systems. The inspection tools have to deal with new attenuating films, smaller and more complex features, and more aggressive OPC. In addition, low k1 lithography causes the mask error factor (MEEF) to increase, magnifying CD errors. This, in turn, makes reticle defect detection specifications more aggressive. Achieving high sensitivity, low false defect count, for a full plate inspection is a big challenge. Those three (high sensitivity, low false defect count, full plate inspection) are the three “legs” that must support real die-to-database inspection. In order to demonstrate inspection success, all three must be achieved. Without any of them, there is no die-to-database inspection solution. The capabilities described in this paper (the XPE die-to-database algorithm working with the KLA-Tencor TeraStar SLF87 system) were developed precisely because no tool in the industry was capable of meeting all of these requirements. The industry was in urgent need of a die-to-database system that is capable of inspecting reticles for the 90nm node at high sensitivity, with a low false defect count for a full plate inspection. XPE, the new die-to-database inspection algorithm for the TeraStar SLF87 (XPE-87), has been developed for the inspection of 193nm lithography reticles to be used for the 90nm node and beyond. XPE-87 uses new and improved methods for database rendering, defect detection and image contrast adjustment. The algorithm can accommodate the reticle characteritics, inspecting plates with complex features and addvanced Sub-Resolution Assist Features (SRAFs) at high sensitivity and low false defect count. Thanks to enhancements to system hardware and light calibration routines, the algorithm is very effective at inspecting 90 nm node ArF half-tone reticles. XPE-87 has been characterized with 193 nm and 248 nm EPSM versions of Spica, a new programmed defect test reticle. In the presence of complex OPC, results show a substantial improvement in sensitivity compared to previous die-to-database inspection algorithms. The new algorithm has also been used to inspect a variety of 193nmEPSM, 248 EPSM and chrome on glass production reticles. The results show significant improvement for the inspection of 90 nm node half-tone reticles including plates with SRAFs. Simulations were performed to verify the XPE-87 potential for defect detection. Evaluating changes in signal profile due to the presence of defects, a comparison was performed between the aerial profile of the XPE-87 at UV inspection aerial image and the wafer print aerial image at 193 nm. The results, show a larger signal for defects in small lines.

Results from a new die-to-database reticle inspection platform

A new DUV die-to-database high-resolution reticle defect inspection platform has been developed. This platform is designed to meet the 90nm through 65nm node 248/193nm lithography reticle qualification requirements of the IC industry. These design nodes typically include: COG layers, EPSM layers, and AltPSM layers, plus aggressive OPC which includes jogs, serifs, and SRAF (sub-resolution assist features). The architecture and technology of the new inspection platform is described. Die-to-database inspection results are shown on standard programmed defect test reticles, as well as, advanced 90nm through 65nm node reticles from industry sources. Results show high sensitivity and low false detections being achieved.

Results from a new reticle defect inspection platform

A new DUV high-resolution reticle defect inspection platform has been developed to meet the sub-90nm node 248/193nm lithography reticle qualification requirements of the IC industry. This advanced lithography process typically includes COG layers, EPSM layers, and AltPSM layers; aggressive OPC is typically used which includes jogs, serifs, and SRAF (sub-resolution assist features). The architecture and performance of the new reticle defect inspection platform is described. Die-to-die inspection results on standard programmed defect test reticles are presented showing typically 50nm edge placement defect sensitivity, 80nm point defect sensitivity, 5.5% flux defect sensitivity, and 100nm quartz phase defect sensitivity. Low false detection results are also shown on 90nm node and below product reticles. Direct comparisons with UV wavelength inspections show measurable sensitivity improvement and a reduction in false detections. New lithography oriented defect detectors are discussed and data shown.

Assessing EUV mask defectivity

This paper assesses the readiness of EUV masks for pilot line production. The printability of well characterized reticle defects, with particular emphasis on those reticle defects that cause electrical errors on wafer test chips, is investigated. The reticles are equipped with test marks that are inspected in a die-to-die mode (using DUV inspection tool) and reviewed (using a SEM tool), and which also comprise electrically testable patterns. The reticles have three modules comprising features with 32 nm ground rules in 104 nm pitch, 22 nm ground rules with 80 nm pitch, and 16 nm ground rules with 56 nm pitch (on the wafer scale). In order to determine whether specific defects originate from the substrate, the multilayer film, the absorber stack, or from the patterning process, the reticles were inspected after each fabrication step. Following fabrication, the reticles were used to print wafers on a 0.25 NA full-field ASML EUV exposure tool. The printed wafers were inspected with state of the art bright-field and Deep UV inspection tools. It is observed that the printability of EUV mask defects down to a pitch of 56 nm shows a trend of increased printability as the pitch of the printed pattern gets smaller - a well established trend at larger pitches of 80 nm and 104 nm, respectively. The sensitivity of state-of-the-art reticle inspection tools is greatly improved over that of the previous generation of tools. There appears to be no apparent decline in the sensitivity of these state-of-the-art reticle inspection tools for higher density (smaller) patterns on the mask, even down to 56nm pitch (1x). Preliminary results indicate that a blank defect density of the order of 0.25 defects/cm2 can support very early learning on EUV pilot line production at the 16nm node.

Multibeam high-resolution die-to-database reticle inspection

A new die-to-database reticle inspection system has been developed to meet the production requirements for 130nm node 4x reticles, as well as, the early inspection requirements for 100nm node 4x reticles. This new system is based on the TeraStarT platform1 developed recently by KLA-Tencor Corporation for high performance die-to-die and STARlightT inspection of 130nm node reticles. The TeraStar platform uses high-NA triple-beam scanning laser optics for high throughput. The platform also includes a new generation of defect detection algorithms and image processing hardware to inspect, with high sensitivity and low false detections, the small linewidths, aggressive OPC, and advanced EPSM 4x reticles characteristic of the 130nm node. The platform further includes the TeraProTM concurrent STARlight and die-to-die inspection mode for exceptional productivity. The necessary database elements have now been developed and added to the TeraStar platform, to give it die-to-database inspection capability. A new data format along with new data preparation, data rendering, and data modeling algorithms have been developed to allow high precision database matching with the optical image for exceptional die-to-database performance. The TeraPro high productivity features of the TeraStar platform have been extended to the die-to-database mode providing the opportunity to use STARlight and die-to-database modes concurrently.

1X HP EUV reticle inspection with a 193nm inspection system

The current industry plan is for EUV Lithography (EUVL) to enter High Volume Manufacturing (HVM) in the 2019/20 timeframe for the 1X nm half-pitch (HP) node (logic and memory). Reticle quality and reticle defects continue to be a top industry risk. The primary reticle defect quality requirement continues to be “no reticle defects causing 10% or larger CD errors on wafer (CDE)”. In 2013, KLA-Tencor reported on inspection of EUV reticles using a 193nm wavelength inspection system1. The report included both die-to-database (db) and die-to-die (dd) inspection modes. Results showed the capability to detect a wide variety of programmed and native reticle defects judged to be critical. We have developed extensions to the 193nm wavelength (193) inspection system for the typical 2019/20 HVM EUV reticle defect requirements. These improvements include innovations in: defect enhancement methods, database modeling, defect detection, and throughput. In this paper, we report on the latest data and results of this work, focusing on EUV reticle dieto- database inspection. Inspection results are shown using typical next generation EUV programmed defect test reticles and typical full field product-like EUV reticles, all from industry sources. Results show significant defect detection improvements versus the prior generation inspection system. We also report the test results of a high throughput die-todatabase inspection mode that could be used for the typical mask shop outgoing inspection of EUV reticles where particles are the primary defect to be detected and there is no pellicle (or the pellicle transmits 193nm wavelength2).

Multibeam resolution die-to-database reticle inspection

A new die-to-database reticle inspection system has been developed to meet the production requirements for 130nm node 4x reticles, as well as, the early inspection requirements for 100nm node 4x reticles. This new system is based on the TeraStar platform1 developed recently by KLA-Tencor Corporation for high performance die-to-die and STARlight inspection of 130nm node reticles. The TeraStar platform uses high-NA triple-beam scanning laser optics for high throughput. The platform also includes a new generation of defect detection algorithms and image processing hardware to inspect, with high sensitivity and low false detections, the small linewidths, aggressive OPC, and advanced EPSM 4x reticles characteristic of the 130nm node. The platform further includes the TeraPro concurrent STARlight and die- to-die inspection mode for exceptional productivity. The necessary database elements have now been developed and added to the TeraStar platform, to give it die-to-database inspection capability. A new data format along with new data preparation, data rendering, and data modeling algorithms have been developed to allow high precision database matching with the optical image for exceptional die-to- database performance. The TeraPro high productivity features of the TeraStar platform have been extended to the die-to- database mode providing the opportunity to use STARlight and die-to-database modes concurrently. The system design and in-house test results are discussed.

High-resolution UV wavelength reticle contamination inspection

A new reticle inspection system with laser UV imaging for contamination inspection has been developed to detect contamination defects on advanced reticles for DUV steppers and low k1 lithography. The extension to UV wavelength improves the resolution of the imaging optics while maintaining compatibility with current STARlight inspection algorithms, thus improving both sensitivity and minimum linewidth capability. This enables inspection of reticles for 4X lithography design rules at 0.18 micrometers , 0.15 micrometers and 0.13 micrometers . The system also is capable of inspecting Tri-Tone PSM and reticles with OPC assist bars.