Walter Steinberg

Performance data of a new 248-nm CD metrology tool proved on COG reticles and PSMs

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.

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.

Measurement results on after-etch resist coated features on the new Leica Microsystems' LWM270 DUV critical dimension metrology system

Process control in photomask manufacturing is crucial for improving and maintaining optimal yields. The LWM270DUV critical dimension (CD) measurement system is the first tool ever designed for photomask manufacturers that combines both UV (365 nm wavelength light) and DUV (248 nm wavelength light) for CD measurements. UV light illumination was integrated into the LWM270DUV to allow photomask makers to perform after etch inspection (AEI) on DUV resists minimizing exposure effects. The increased resolution of UV illumination allows for measurement of features as small as 300 nm. Improved measurement algorithms as well as improvements in the illumination system have reduced the uncertainty of measurements resulting in improved performance. This paper details recent measurement results of various feature types on different substrate types using UV transmitted light.

Development and characterization of new CD mask standards: a status report

We report on the current status of a project on development and characterization of CD photomasks with 6025 format to be used as reference standards for different type of CD metrology instruments. The project consortium consists of mask suppliers, manufacturers of CD metrology instruments, users of such instruments and calibration laboratories. Different type of CD metrology instrumentation, namely optical CD microscopes, CD-SEM, and AFM will be applied for investigation and measurement of microstructures, additionally supported by AIMS tool. We will describe the basic design criteria of the mask standard and first measurement results gained with different metrology tools on the prototype mask standards.