Gerd Scheuring

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.

CD metrology on OPC features using light optical and electron optical tools

TO enable lithography at low k1 factors, OPC on photo masks is a method of strong and growing importance. But CD metrology of OPC features is suffering form several drawbacks: (1) OPC structures often do not have two parallel edges, which are required for usual CD metrology methods; (2) There are no commonly agreed standard definitions how and where to measure some types of OPC structures; (3) The CDs are very small; (4) There is no automated software for the measurement of OPC structures on operator level. A metrology method and a fully automated software for metrology of OPC structures based on LWM optical CD metrology tools is shown in this paper. It automatically distinguishes between hammerheads and serifs in various orientations. The method works analog to pitch measurements and requires only pitch calibration and no additional CD calibration. The results of light optical metrology tools with i-line and DUV wavelength is compared to CD SEM results.

Optical mask metrology for next generation lithography

This article addresses the state-of-the-art in optical mask CD metrology based on the most recent deep ultraviolet (DUV) microscope optics operating at 248 nm. It further points out the future potential and limitations of optical CD metrology in general and shows that DUV mask metrology has all of the capabilities to meet the ITRS needs, while avoiding the difficulties associated with scanning electron microscopy based metrology tools, including substrate charging and contamination.

New results from DUV water immersion microscopy using the CD metrology system LWM500 WI with a high NA condenser

New results using the worlds first optical DUV mask CD (critical dimension) metrology system based on water immersion (WI) technology (Vistec LWM500 WI) are presented. In order to improve repeatability and linearity, especially for feature sizes smaller than 300 nm, a new condenser with an increased numerical aperture (NA) was integrated and qualified. Comparative investigations between the previously used 0.55 NA condenser and the new 0.8 NA condenser are shown and the resulting improvements by the high NA condenser are discussed. This report focuses on results obtained on ArF half tone phase shift masks which are more critical than KrF half tone or binary masks due to the mismatch between measurement and exposure wavelengths.

Actual measurement data obtained on new 65nm generation mask metrology tool set

For 65nm photo mask lithography, metrology becomes significantly more important. Especially the requirements of the photo mask users versus critical dimension (CD) control, CD homogeneity and CD mean to target, give strong head-aches to lithography and process control engineers. Despite the fact that optical CD metrology has limitations versus resolution it still provides valuable information since measurement takes place in transmission similar to the application of the mask during printing to the wafer. The optical resolution should at least support to measure minimum features of 250nm on the masks in the linear regime. In order to qualify structure fidelity and width of assist structures and small contact holes as well as certain OPC pattern which are usually smaller than the limits of optical measurement capability, actually CD SEM systems are recognized as the tool of choice to qualify the reticles. No matter which kind of CD metrology tool is used, long-term repeatability over several days must be below 1nm (3 sigma). This paper will show measurement performance data on two types of reticle CD measurement systems targeting the 65nm node reticles. Another issue of high importance is pattern placement or registration metrology on reticles. Roadmaps of leading edge mask users request a maximum placement error of less than 13nm for the 65nm technology node. This strong require-ment challenges the control of the mask lithography tool and the long-term repeatability of the registration metrology system must not exceed 2.5nm. This paper summarizes the actual performance of Leicas mask metrology tool set and the improvements on the individ-ual systems leading to the respective performance.

DUV water immersion technology extends linearity: first results from the new 65nm node CD metrology system LWM500 WI

The increased requirements on reticles for the 65nm technology node with respect to CD homogeneity and CD mean to target requirements call for a metrology system with adequate measurement performance. We report on the new water immersion technique and the system concept of the worlds first optical CD metrology system based on this technology. The core of it is a new DUV immersion objective with a NA of 1.2, using illumination at a wavelength of 248nm. The largest challenge of the water immersion technology was the fluid handling. The key compo-nents, a water injection and removal unit, developed by MueTec, solve this issue. To avoid contaminations the purified DI water is micro-filtered. An environmental chamber guarantees extremely stable measurement conditions. The advantages of optical CD measurements in transmitted light compared to CD-SEM is shown. With this system, already installed, excellent results for short- and longterm repeatability for both linewidth and contact measurements were achieved on COG, KrF HT and ArF HT masks. The linearity range of the system is extended down to 220nm. A comparison of CD measurements between the different tool generations such as the Leica LWM250/270 DUV at 248nm with a NA of 0.9 is shown. An outlook on the future potentials of optical mask CD metrology finalises this report.

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.

A new approach for defect inspection on large area masks

Besides the mask market for IC manufacturing, which mainly uses 6 inch sized masks, the market for the so called large area masks is growing very rapidly. Typical applications of these masks are mainly wafer bumping for current packaging processes, color filters on TFTs, and Flip Chip manufacturing. To expose e.g. bumps and similar features on 200 mm wafers under proximity exposure conditions 9 inch masks are used, while in 300 mm wafer bumping processes (Fig. 1) 14 inch masks are handled. Flip Chip manufacturing needs masks up to 28 by 32 inch. This current maximum mask dimension is expected to hold for the next 5 years in industrial production. On the other hand shrinking feature sizes, just as in case of the IC masks, demand enhanced sensitivity of the inspection tools. A defect inspection tool for those masks is valuable for both the mask maker, who has to deliver a defect free mask to his customer, and for the mask user to supervise the mask behavior conditions during its lifetime. This is necessary because large area masks are mainly used for proximity exposures. During this process itself the mask is vulnerable by contacting the resist on top of the wafers. Therefore a regular inspection of the mask after 25, 50, or 100 exposures has to be done during its whole lifetime. Thus critical resist contamination and other defects, which lead to yield losses, can be recognized early. In the future shrinking feature dimensions will require even more sensitive and reliable defect inspection methods than they do presently. Besides the sole inspection capability the tools should also provide highly precise measurement capabilities and extended review options.