Andrew C. Hourd

Reliable Sub-Nanometer Repeatability for CD Metrology in a Reticle Production Environment

The new MueTec , an advanced CD metrology and review station operating at DUV (248nm) wavelength, has been extensively characterised in a reticle production environment. Performance data including resolution, measurement repeatability and throughput will be discussed. The system has demonstrated the ability to image 100nm Cr lines and sub-nanometer (3-sigma) long-term repeatability on lines and spaces down to 200nm in size. Metrology capability on contact hole and serif structures will also be discussed. The paper will also introduce the application of a long working distance DUV objective compatible with pelliclised masks. With a 9% EAPSM reticle for 193nm wavelength a very appropriate image contrast was obtained with both objective types, allowing reliable automated linearity measurements on this type of reticle also. In addition to the metrology performance of the tool, its integration into a manufacturing environment will also be described. This will show how the availability of networked co-ordinate data (either in the form of ASCII files or CATS data) and the high-accuracy stage of the tool enable efficient, automated measurement of large numbers of dense features under production conditions.

Implementation of 248-nm based CD metrology for advanced reticle production

The MueTec advanced CD metrology and review station, operating at the DUV (248nm) wavelength, has been extensively characterised for a number of feature types relevant to advanced (9Onm technology node) reticles. Performance for resolution capability and measurement repeatability is presented here for chrome-on-glass feature types concentrating upon lines and spaces, contact holes and dots. The system has already demonstrated the ability to image 100nm Cr lines and sub-nanometre (3- sigma) long-term repeatability on lines and spaces down to 200nm in size. We will now show that this performance level can be achieved and sustained at production levels of throughput and under typical cleanroom environmental conditions. Performance of new software tools to support the advanced metrology of 90-nm node reticles will also be introduced and their performance evaluated. Comparison will be made between CD-SEM measurements and the advanced optical metrology offered by the tool. Finally, reliability data for the tool —both in terms of mechanical and sustained repeatability performance — will be given, following prolonged trials in a production environment.

Fully automated CD - Metrology and Mask Inspection in a Mask Production Environment using the MueTec DUV Tool

Besides the metrology performance of a CD measurement tool, its close integration into a manufacturing environment becomes more and more important. This is extremely driven by the ever increasing complexity of masks and their tightening specifications. Hence, this calls for the capability of fully automated CD measurements on a large number of dense and isolated lines and 2-dimensional features under production conditions. In this paper we report on such a highly automated measurement system for CD measurements from MueTec. Either an ASCII software interface or a specially developed software interface to connect the MueTec with the CATSTM mask data fracturing software handles the large amount of co-ordinates and other information like design images from the measurement sites and their surrounding, which are necessary for fully automated CD measurements. Because the latter is the standard in mask-making and data-formats, this level of automation guarantees a good industrial integration of the MueTec system. Fully automated and reliable CD measurements are based on very stable tool hardware and especially on a positioning stage with best possible positioning accuracy (range better 0.5 ?m), significantly improved possibilities of software controlled positioning and an automated job set up and execution. The time gain in relation to existing measurement programs in the extent of supply has turned out to be dramatically large. The User Interfaces and their applications will be described.

Through-pellicle-capable DUV-based CD metrology on reticles for wafer fab and R&D environment

A comparison has been made in terms of mask CD linearity measurements between the 2 tool versions of a 248nm based optical CD metrology tool for photomasks, i.e., the high-NA M5k-SWD and the through-pellicle M5k-LWD, as well as to a reticle SEM, i.e., the KLA-T 8250-XR. The measured pattern consists of lines and dots (dark features), and spaces arid contact holes (clear features), both in equal-lines-and-spaces and as isolated feature. Two masks have been measured with the same test pattern, i.e., a binary and a 9%-attPSM for 193nm lithography. The latter was especially challenging because typically such embedded phase shift masks are much more transparent at higher wavelengths than those for which they are optimized. All measurements on the M5k were made intentionally before calibration (apart fmm pitch calibration). The resolution performance of the M5k-LWD and the measurement offsets found between M5k and SEM, as well as between the two M5k-versions is discussed. In addition, two-dimensional metrology based on feature contour extraction from optical or from SEM images has been compared. Although its resolution is inherently lower than that of the high-NA M5k-SWD and a reticle SEM, the M5k-LWD offers a possibility to extend such assessment to pelliclized reticles, which is not possible on the alternative tools.

Advanced optical imaging platform for CD metrology and defect review on 130-nm to 100-nm node reticles: an overview of preliminary results

Critical Dimension fidelity continues to be one of the key driving parameters defining photomask quality and printing performance. The present advanced optical CD metrology systems, operating at i-line, will very soon be challenged as viable tools owing to their restricted resolution and measurement linearity impact on the ability to produce repeatable measurements. Alternative measurement technologies such as CD-SEM and -AFM have started to appear, but are also not without tier concerns in the field of reticle CD metrology. This paper introduces a new optical metrology system (MueTec /) operating at DUV wavelength (248nm), which has been specifically designed to meet the resolution and measurement repeatability requirements of reticle manufacture at the 130nm and 100nm nodes. The system is based upon a specially designed mechanical-optical platform for maximum stability and very advanced optical, illumination, alignment and software systems. The at wavelength operation of this system also makes it an ideal platform for defect printability analysis and review. The system is currently part of a European Commission funded assessment project (IST-2000-28086: McDOR) to develop a testing strategy to verify the system performance, agree on equipment specifications and demonstrate its capability on advanced production reticles - including long-term reliability. It is the preliminary results from this evaluation that are presented here.

New approach to optical proximity correction

A hierarchical rule based optical proximity effect correction approach is presented. The approach has been driven by maskmaking and production requirements to make OPC a practical problem solution. The model based rule generation is presented, as well as benchmark tests on different state-of- the-art test chips.

Impact of pattern proximity correction on die-to-database mask inspection

While the semiconductor industry is following a very aggressive roadmap without a corresponding reduction in exposure wavelength, the role of resolution enhancement techniques like PSM and OPC is becoming more and more important. Mask making for these advanced techniques is one of the most crucial parts in making these techniques work. Mask inspection is one of the major challenges in the mask making process, as it is one of the most performance critical steps in the entire mask making process. Especially contact or OPC patterns show difficulties in die-to-database inspection as the CAD data asks for square corners. LPC is a mask enhancement technique improving image quality and CD linearity for laser pattern generators. The paper present the impact of Laser Proximity Correction on contact and line patterns of 0.18 micrometers generation. The LBM is used to characterize Cd uniformity improvement of the entire plate.

Improvements to mask inspectability by use of pattern proximity correction

Inspection is one of the major challenges in mask making, as it is one of its most performance crucial steps in the entire mask making process. Especially contact patterns show difficulties in die-to-database inspection as the CAD data asks for square corners. The paper presents the impact of Laser Proximity Correction (LPC) on the inspectability of contact and line patterns. LPC is a mask enhancement technique improving image quality and CD linearity for laser pattern generators. The use of the linewidth bias monitor tool in order to characterize CD uniformity over the entire plate is demonstrated.

Application of a new approach to optical proximity correction

Optical proximity correction is one of the major hurdles chip manufacturing has to overcome. The paper presents evaluation results of CAPROX OPC, a rule based OPC software. Mask making influences as well as production requirements are discussed. Rule generation, one of the most critical parts in a rule based correction scheme is discussed. Two different applications are presented.

Hierarchical e-beam proximity correction in mask making

Both e-beam and optical proximity effects are still a major barrier in the transfer of an ULSI design from the CAD station to the printed result on wafer. Optical proximity effect correction (OPC) is shown to be a strong tool to improve the printing latitudes for i-line lithography of 0.35 micrometers feature sizes and below, but leads to fractal geometries around 0.1 micrometers (corresponding to 0.5 micrometers on a 5x reticle). This quantum leap in required minimum linewidth on the mask may urge mask makers to apply e-beam proximity effect correction (PEC), even more than a decrease in the reticle magnification from 5x to 4x (and further) would. For raster scan e-beams, which are typically used in mask making, correction by dose variation is not practical. Hence, PEC for these systems must be tackled by modifying the geometry of the design, in a way similar to OPC techniques. Both corrections must compromise between the accuracy achieved, which is dominated by the selected (correction and exposure) grid size, and the resulting throughput loss, caused by the use of a smaller grid size. Sigma-C now introduces a new algorithm, which enables the proximity effect correction by shape variation. It is included into CAPROX and supports hierarchy in the same manner as the other postprocessing operations. The exposure of the shape corrected pattern on a raster scan machine requires only one beam pass, whereas dose variation would require one pass for each dose. Exposures were made at IMEC and at Compugraphics. The first results on Leica EBMF10.5 and MEBES III are promising. The pure shape correction increases the line width uniformity and opens the process window for critical dimensions below 1 micrometers . Performance measurements show that the 64 Mb DRAM is a job of a few hours.