Larry S. Zurbrick

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.

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.

Detection of 60° phase defects on alternating PSMs

In this paper we present results of an algorithm that has been developed which is sensitive to phase defects of 60 degrees on i-line alternating PSMs. This algorithm consists of microcode and software, which can be loaded into existing inspection hardware. The algorithm works in die-to-die inspection mode and uses both transmitted and reflected light images to maximize sensitivity. Isolated phase defects as well as phase defects close to chrome edges were inspected. In addition, the algorithm is able to detect missing and mis-aligned shifter edges. A programmed phase defect test plate was developed to characterize defect detection sensitivity. Detection of 60 degrees defects smaller than 0.75 micrometers has been demonstrated with this algorithm. Defect sensitivity characterization and actual production plate effect results are shown. Finally, recent results showing the application of the algorithm to the inspection of Deep-UV multiphase reticles using a shorter inspection wavelength are presented.

High-resolution ultraviolet defect inspection of DAP (darkfield alternate phase) reticles

The manufacturing implementation of alternating aperture PSMs (AltPSM) has been gated by the impacts these techniques have on reticle manufacturing, specifically reticle defect inspection and repair. Die-to-die inspection techniques have been achieved for some clearfield multiphase alternate phase reticles, but the required die-to-database solutions are not currently available with defect inspection systems. In response to these mask manufacturing issues and IC design layout issues, resolution enhancing techniques based on Darkfield Alternate Phase (DAP) reticle designs are now of growing importance. A DAP Programmed Evaluation Reticle, DAPPER, was fabricated and inspected on a new high numerical aperture ultraviolet reticle inspection system. The results show reasonable defect sensitivity performance in the presence of both reticle geometry and quartz etch topography characteristic of 130-nm node advanced logic circuit DAP reticles.

Alternating phase-shift mask inspection using multiple simultaneous illumunation techniques

This paper discusses the challenges to alternating phase shift mask defect inspection and new approaches for phase defect detection using multiple illumination methods in conjunction with defect detection algorithm modifications. Die-to-die inspection algorithms were developed for the KLA-Tencor 365UV-HR (APS algorithm) and TeraStar SLF27 (TeraPhase algorithm) inspection systems based upon the use of simultaneous transmitted and reflected light signals. The development of an AltPSM programmed test vehicle is described and defect sensitivity characterization results from programmed phase defect reticles are presented. A comparison of the two approaches used for the different inspection systems is discussed. A comparison of TeraPhase to transmitted light only results from a programmed phase defect test mask shows improved phase defect detection results.

AltPSM Inspection Capability and Printability of Quartz Defects

Alternating phase shift masks (altPSMs) are a promising resolution enhancement technique to realize smaller design rules at the same lithography wavelength. Quartz defect inspection of altPSMs is challenging, as the optical contrast for defects within the quartz substrate is very small. AltPSM inspection capability was studied with different types of programmed test masks. The programmed quartz defects were characterized with a scanning electron microscope, an atomic force microscope and an aerial imaging microscope system. Finally a defect printability study was done. With the programmed test masks the performance of two altPSM inspection techniques was evaluated. Quartz defect detection was studied with respect to different pattern types and sizes. Quartz defect sensitivity was measured with respect to defect size as well as defect printability. It was found that quartz defect sensitivity with respect to defect size is constant for different pattern types, but decreases for decreasing line widths on 1:1 pitch line and space patterns. Whereas defect detection for the altPSM algorithms studied is governed by the defect’s extension perpendicular to the pattern line, defect printability is determined by the defect’s lateral area.

Phase defect inspection of 130-nm node phase-shift masks using a simultaneous transmitted and reflected light pattern inspection algorithm

Phase shifting mask technology will be necessary to product integrated circuits at the 130 nm node using KrF wavelength steppers. In order to successfully accomplish this goal, it is necessary to detect and repair phase shifting defects that may occur in the manufacture of these reticles. An inspection algorithm has been developed to improve the phase shift defect detection rate of an UV reticle inspection system and is based upon the simultaneous use of the transmitted and reflected light signals. This paper describes the phase defect sensitivity improvement over transmitted light only pattern inspection results and simultaneous transmitted and reflected light based contamination inspection results.

Reticle defect size calibration using low-voltage SEM and pattern recognition techniques for sub-200-nm defects

Programmed defect test reticles are required to characterize automatic defect inspection equipment. In order to perform meaningful, quantitative comparisons between inspection systems, a precise and accurate defect sizing methodology is required. Historically, commercially available programmed defect test reticles have not had traceable or well-documented defect sizing methods nor was information regarding the precision of these measurements provided. This paper describes the methods used and results obtained from the work performed to address these issues. Using a low voltage scanning electron microscope as an image acquisition system, defect sizing is accomplished using automated pattern recognition software. The software reports defect size metrics such as maximum inscribed circle diameter and area. Measurement precision better than 30 nm has been demonstrated for the maximum inscribed circle method. The correlation of SEM based measurements to historical optical metrology measurements is also discussed.

Effects of transparent and transmission reduction reticle defects

Transparent and transmission defects were studied by performing wafer printability studies. An Orion test reticle was fabricated with programmed thin resist artifacts on a conventional binary reticle to simulate transparent defects. The transparent defects on the Orion reticle printed larger than equivalent design size programmed chrome defects. Programmed transmission defects were created on contact geometry by selectively depositing thin layers of chromium over contacts on the reticle. The effect on wafer focus/exposure curves of contact transmission defects was studied.