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 Leica's mask metrology tool set and the improvements on the individ-ual systems leading to the respective performance.
We report on the results of a recent round robin comparison on new linewidth or CD photomask standards in which several partners from different companies and institutes in Germany were involved. The round robin activity is at the end of a joint project targeting at the development of a new CD mask standard and it was intended to show the performance of the CD mask standard and to test its application in cross-calibration processes. Different type of CD metrology instrumentation was used, namely optical transmission microscopy including water immersion CD microscopes with NA of 1.2 and scanning electron microscopy, supported by additional scanning probe microscopy (SPM/AFM) characterizations. A set of differently processed CD mask standards with smallest line and space structures down to 0.1 μm and based on different mask blanks was produced with identical layout. At the PTB this set of CD standards was calibrated by UV transmission microscopy and by CD-SEM as well. For the round robin an unknown CD mask of the same design as the standards was used and the participants were asked to provide measurement data with their CD metrology tools, referred to their respective PTB calibration standards. It will be shown, that the agreement of measurement data between different CD metrology tools can be significantly improved if proper definitions of the measurand and a metrologically sound approach to signal modelling and interpretation of CD measurement values is applied. The outcome of this comparison provides a valuable source of information for cross calibration issues which are discussed in mask industry today and, moreover, it proves the performance of the newly developed CD mask standard, which now is available to other interested parties, too.
For next generation photomask lithography, improved resolution and precision are required to monitor lithography tools and photomask processes. The newly developed LWM9000 SEM Critical Dimension Scanning Electron Microscope (CD-SEM) for photomask applications will be presented. Its proprietary electron optics technology combined with an improved detection system leads to sub-nanometer CD measurement repeatability by almost completely eliminating the effect of charging and contamination. In an effort to minimize integration into production environments and to facilitate the ease of use the new CD-SEM utilizes a graphical user interface and data evaluation software based on Leica Microsystems’ LMS IPRO / LMS IPRO2. Presented in this paper is data showing leading edge CD measurement repeatability performance on chrome on glass substrates (COG), different types of phase shift masks (PSM), and resist plates. The virtual lack of charging in conjunction with a laser controlled stage, dramatically reduces the need for local feature alignment prior to CD measurement in most cases. The lack of need for local pattern alignment leads to increased throughput and high reliability during the measurement process. The standard system can be configured for manual loading or SMIF handling.
To keep pace with continuously shrinking design rules for masks and reticles Leica Microsystems has developed the new mask metrology tool LMS IPRO2. It is designed to measure pattern placement and CDs in transmitted light at i-line (365nm) illumination. Details on improvements over the previous system and performance data from the beta-site system are presented. The step to a shorter illumination wavelength leads to a better optical resolution power resulting in an improved edge detection. Transmitted light illumination enables to use the tool for CD measurement on quartz and phase shift masks.
For next generation photo mask lithography the tolerance range for pattern placement and critical dimensions (CD) is further shrinking. Improved optical resolution and precision of a metrology system are required to qualify the lithography tool and monitor the photo mask process. Edge detection methods in transmitted light mode for pattern placement and CD measurements are advantageous if the tightened resolution and precision requirements can be met. The new LMS IPRO2 using an illumination wavelength range of 360 to 410 nm has a significantly enhanced resolution for registration and CD measurements in both, transmitted and reflected light. A new laser interferometer with an enhanced resolution of 0.3 nm contributes to the overall improved system performance. The stage is designed to measure on quartz substrates and next generation lithography (NGL) reticles up to 230 mm square in transmitted light as well as in reflected light on 200 mm and 300 mm wafers for stepper qualification.
A new CD metrology system with 248 nanometer illumination is the subject of this paper. The system configuration and major component improvements is described. Test measurements on chrome-on-glass and attenuated phase shift masks were performed demonstrating improved CD linearity down to approximately 300 nm and long term repeatability performance in the 2 nm realm.
Continually shrinking features sizes coupled with tighter tolerances for critical dimensions and feature placement necessitate development of new metrology tools that can meet the demand for more precision and accuracy during the measurement process. With this in mind Leica Microsystems has developed a next general metrology system that is capable of fulfilling both the feature placement and critical dimension metrology requirements. This paper contains a brief description of the new system hardware and design changes incorporated into the Leica LMS IPRO2 as well as recent measurement data indicative of initial tool performance.
To keep pace with continuously shrinking design rules for masks and reticles Leica Microsystems has developed two new mask metrology tools. The LWM 250 DUV is designed to measure Critical Dimensions (CD) on mask in transmitted light at 248nm illumination. The LMS IPR02 is designed to measure pattern placement and CDs in transmitted light at I- line (365nm) illumination. System overview and first performance data are presented for both tools. The step to a shorter illumination wavelength leads to a better optical resolution power resulting in an improved edge detection and CD linearity compared to systems using white light or I-line illumination for imaging.
To keep pace with continuous shrinking design rules for masks and reticles a new 248 nm CD measurement system has been developed. The step to a shorter illumination wavelength leads to a better optical resolution power resulting in an improved CD linearity compared to systems using white light or I-line illumination for imaging. An overview of the system configuration is presented and first results of the improved optical performance as well as CD linearity and CD repeatability data are shown.
With continuously shrinking design rules enhanced techniques are required in mask manufacture which requires more sophisticated procedures for their characterization. As Phase Shift Masks (PSM) are of growing importance a new CD algorithm had to be developed to achieve the same or even higher level of CD accuracy and repeatability as on chrome masks. Major improvements in measurement performance on attenuated PSM have been achieved resulting from improving the PSM CD algorithm based on the experiences reported earlier. With shrinking feature sizes and masks layouts with denser patterns the quantification of corner rounding effects on contacts and line ends is of growing importance. Based on the algorithm developed for the effect of corner rounding on line end shortening a measurement procedure has been developed for contact holes. Measurement results have been shown. To further improving CD measurement automation and to enable easy measurement job modifications a highly flexible device has been developed to import measurement parameters into a macro template.
With continuously shrinking device structure sizes the photomask suppliers are facing increasing linewidth metrology control requirements. Therefore it is becoming more and more important for equipment suppliers to provide mask metrology tools capable of measuring 0.5 micrometer and smaller critical dimension (CD) features with high accuracy and repeatability, while offering high throughput for systems to be used in the production environment. CD measurement results obtained on the Leica LWM 250UV will be presented showing not only the considerably improved resolution power and measurement accuracy but also an extension of the linearity range to smaller feature sizes using UV light of 365 nm (I-line) instead of white light for illumination in transmitted mode. Results obtained after a system calibration against SEM measurement data show a further extension of the linearity regime. The higher lateral resolution of I-line compared to white light measurements also leads to a CD range value reduction for long term repeatability.