Manfred Maul

Experimental result and simulation analysis for the use of pixelated illumination from source mask optimization for 22nm logic lithography process

We demonstrate experimentally for the first time the feasibility of applying SMO technology using pixelated illumination. Wafer images of SRAM contact holes were obtained to confirm the feasibility of using SMO for 22nm node lithography. There are still challenges in other areas of SMO integration such as mask build, mask inspection and repair, process modeling, full chip design issues and pixelated illumination, which is the emphasis in this paper. In this first attempt we successfully designed a manufacturable pixelated source and had it fabricated and installed in an exposure tool. The printing result is satisfactory, although there are still some deviations of the wafer image from simulation prediction. Further experiment and modeling of the impact of errors in source design and manufacturing will proceed in more detail. We believe that by tightening all kind of specification and optimizing all procedures will make pixelated illumination a viable technology for 22nm or beyond. Publishers Note: The author listing for this paper has been updated to include Carsten Russ. The PDF has been updated to reflect this change.

Generation of arbitrary freeform source shapes using advanced illumination systems in high-NA immersion scanners

The application of customized and freeform illumination source shapes is a key enabler for continued shrink using 193 nm water based immersion lithography at the maximum possible NA of 1.35. In this paper we present the capabilities of the DOE based Aerial XP illuminator and the new programmable FlexRay illuminator. Both of these advanced illumination systems support the generation of such arbitrarily shaped illumination sources. We explain how the different parts of the optical column interact in forming the source shape with which the reticle is illuminated. Practical constraints of the systems do not limit the capabilities to utilize the benefit of freeform source shapes vs. classic pupil shapes. Despite a different pupil forming mechanism in the two illuminator types, the resulting pupils are compatible regarding lithographic imaging performance so that processes can be transferred between the two illuminator types. Measured freeform sources can be characterized by applying a parametric fit model, to extract information for optimum pupil setup, and by importing the measured source bitmap into an imaging simulator to directly evaluate its impact on CD and overlay. We compare measured freeform sources from both illuminator types and demonstrate the good matching between measured FlexRay and DOE based freeform source shapes.

Optimizing and Enhancing Optical Systems to Meet the Low k 1 Challenge

Current roadmaps show that the semiconductor industry continues to drive the usable Rayleigh resolution towards the fundamental limit (for 50% duty cycle lines) at k1=0.25. This is being accomplished through use of various resolution enhancement technologies (RETs), extremely low aberration optics with stable platforms, and resists processes that have ever-increasing dissolution contrast and smaller diffusion lengths. This talk will give an overview of the latest optical mechanisms that can be used to improve the imaging system for low k1 resolutions. We show 3 non-photoresist techniques to measure the optical parameters of a scanner: 1) a new fast phase measurement interferometer to measure aberrations is presented with an accuracy and repeatability of <3mλ, 2) we introduce a method to measure the illumination profile of the exposing source, and 3) a measurement system to monitor scattered light is presented with correlation to other techniques using a salted pellicle experiment to create controlled scattered light. The optimization of illumination and exposure dose is presented. We show the mechanism for customizing illumination based on specific mask layers. We show how this is done and compare process windows to other more conventional modes such as annular illumination or QUASAR. The optimum design is then implemented into hardware that can give extremely high optical efficiency. We also show how system level control mechanisms can be used to field-to-field and across-field exposure to compensate for lithography errors. Examples of these errors can include reticle CD deviations, wavefront aberrations, and across-field illumination uniformity errors. CD maps, facilitated by SEM and ELM, can give the prescribed changes necessary. We present a system that interfaces to new hardware to compensate these effects by active scanner corrections.

Speckle in optical lithography and its influence on linewidth roughness

In recent years speckle in optical projection microlithography received increasing interest because of its potential contribution to linewidth roughness (LWR). Speckle is a light interference effect that causes the dose delivered to the reticle to be nonuniform, causing a linewidth variation of the patterns imaged in the resist. The contrast of the speckle pattern is shown to be caused by a combination of temporal and spatial coherence effects of the light. The temporal part, determined by the bandwidth of the laser light and the duration of the laser pulse, is found to be the dominant contributor to speckle in todays ArF optical lithography. The spatial distribution of the speckle pattern depends on the intensity distribution of the light in the pupil. Consequently, the spatial frequencies of the LWR induced by speckle depend on the illumination condition, which is confirmed experimentally by exposing wafers with different amounts of speckle contrast. The experiments demonstrate that the amplitude of the LWR induced by speckle is consistent with theory and simulations. Its amplitude is small compared to other sources of LWR, but it is clearly present and should not be ignored when extending ArF optical lithography into future technology nodes.

Speckle in optical lithography and the influence on line width roughness

In recent years the topic of speckle in optical projection microlithography received increasing interest because of its potential contribution to line width roughness (LWR). Speckle is a light interference effect that causes the dose delivered to the reticle to be not uniform. This will cause a line width variation of the patterns imaged in the resist. The contrast of the speckle pattern is shown to be caused by a combination of temporal and spatial coherence effects of the light. The temporal part, determined by the bandwidth of the laser light and the duration of the laser pulse, is found to be the dominant contributor to speckle in todays ArF optical lithography. The spatial distribution of the speckle pattern depends on the intensity distribution of the light in the pupil. Consequently the spatial frequencies of the LWR induced by speckle will depend on the illumination condition, which is confirmed experimentally by exposing wafers with different amounts of speckle contrast. The experiments demonstrate that the amplitude of the LWR induced by speckle is consistent with theory and simulations. Its amplitude is small compared to other sources of LWR, but it is clearly present and should not be ignored when extending ArF optical lithography into future technology nodes.