Maciej W. Rudzinski

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.

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.

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.

Phase-enhanced DUV inspection of alternating phase-shift reticles

Alternating phase shift reticles are one proposed solution for printing features required at the 90 nm and 65 nm nodes using 193 nm lithography. A key enabler to the adoption of this technology is defect inspection so as to guarantee defect free reticles are delivered to wafer fab production. A test reticle with programmed sub-180 degree phase bump and divot defects has been developed that is representative of the sub-90 nm node. This reticle is characterized by SEM methods. This test reticle in turn is used to determine the defect detection performance of a DUV reticle inspection tool, which uses a phase contrast enhanced optical system to improve the detection of phase defects. This presentation discusses several of the challenges in the design and manufacture of the programmed defect test reticle, the reticle characterization results, and the inspection station results. Defect review methods are described which differentiate between chrome, phase bump, and phase divot defects. Additionally, a best known methodology (BKM) is discussed for the manufacture of alternating phase shift masks based upon detecting killer defects before significant additional value is added.

Extending TeraStar reticle inspection capability to the 90nm node through layer-specific algorithms

Sub-wavelength lithography used for 9Onm node devices requires new approaches to both lithography processes and reticle design. Reticle complexity has increased as OPC and Phase Shift techniques are used to improve lithography process windows at smaller design rules. This paper will discuss the results of algorithms developed for specific layers to extend the TeraStar reticle inspection tool to 9Onm reticle research and development applications. Lithographically challenging layers have been the focus of the algorithm development programs, specifically gate layers and contact/via layers. Alternating phase shift masks are gaining importance as a reticle enhancement technique to meet the ITRS Litho Roadmap 9Onm node line widths. A new class of TeraPhase algorithms has been developed for alternating phase shift mask inspection with a focus on gate layers. Die-to-die and die-to-database inspection results will be presented for alternating phase shift programmed defect test plates and production gate layers. Contact and via layer reticles are some of the most difficult layers for CD and lithography process window control. A new family of TeraFlux algorithms has been developed based on flux energy differences between contacts to significantly improve sensitivity to lithographically significant CD errors. Die-to-die and die-to-database inspection results will be presented for contact programmed defect test plates and production contact and via layers. Comparisons of the newly developed algorithms will be made to previous generation inspection capability.

Inspection of alternating phase-shift masks through the use of phase contrast techniques

Alternating Phase Shift Masks (altPSMs) are an option for the production of critical layers at the 100 nm technology node and below. Successful implementation of altPSMs into a wafer manufacturing process depends upon the ability to successfully inspect, disposition and repair defects that occur during the mask manufacturing process. One technique previously described to improve phase defect contrast was the use of simultaneous transmitted and reflected light [1][2]. The previous technique provided for improved phase defect detection in altPSMs produced for the 130 nm node at a 248 nm lithographic wavelength. This work describes the results from a die-to-die inspection method that improves phase defect contrast in transmitted light for altPSMs produced for the 100 nm node at a 193 nm wavelength. The improved phase defect detection technique addresses the challenges of decreasing linewidth/pitch and reduced defect phase resulting from the decrease in lithographic wavelength relative to the inspection wavelength of light. The improved phase defect detection method also provides a method to determine whether a defect is a binary, phase bump or phase divot type of defect. Results are compared against the previous inspection methods. A test vehicle for gathering sensitivity performance data is described along with the results obtained from the inspection system.

Alternating Phase Shift Mask Inspection Through the Use of Phase Contrast Enhancement Techniques

Alternating Phase Shift Masks (altPSM’s) are an option for the production of critical layers at the 100 nm technology node and below produced at ArF lithographic wavelength. Successful implementation of altPSM’s depends upon the ability to successfully inspect, disposition and repair defects that occur during the manufacturing process. One technique previously described to improve phase defect contrast was the use of simultaneous transmitted and reflected light. The previously described technique provided for improved phase defect detection in altPSM’s produced for the 130 nm node at a 248 nm lithographic wavelength. This work describes the results from a die-to-die inspection method that improves phase defect contrast in transmitted light for altPSM’s produced for the 100 nm node at a 193 nm wavelength. The improved phase defect detection technique addresses the challenges of decreasing linewidth/pitch and reduced defect phase resulting from the decrease in lithographic wavelength relative to the inspection wavelength of light. The improved phase defect detection method also provides a method to determine whether a defect is a binary, phase bump or phase divot type of defect. Results are compared against the previous inspection methods. A test vehicle for gathering sensitivity performance data is described along with the results obtained from the inspection system.

Reticle OPC defect printability and detectability for 180-nm technology

An investigation was performed to determine the printability and defect detectability of reticle OPC defects for the 180 nm technology node. Two different OPC approaches were investigated, one based upon assist bar/serif features and the other based upon serif/jog features. Several critical defects were studied, including chrome extension defects on assist bars and pindots between assist bars and primary features. Wafers were printed using a 0.6 NA, DUV stepper and resulting wafer resist images measured by CD SEM. Edge defects as small as 200 nm cause greater than 10% change in local linewidth, 400 nm defects cause catastrophic wafer defects, and chrome spot with 260 nm diameter can shorten gap between two line ends by 10%. CD defects less than 75 nm on the reticle were found to have a significant impact on the process window. The programmed defect test reticles used to print the wafers were inspected on KLA-Tencor reticle inspection systems and the defect sensitivity capture curves plotted. Defect capture rates indicated that smaller than 200 nm edge defects and 125 nm CD defects are detected. Defect printability simulations were performed using database and aerial images gathered from an automated defect inspection system and compared to the experimental wafer results. The purpose of this test is to determine the feasibility of performing printability predictions in a mask production environment. A correlation between the simulations and the wafer results are shown.