Martin Schriever

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.

New paradigm in lens metrology for lithographic scanner: evaluation and exploration

A new paradigm of lens metrology, which is an on-board in-situ interferometer on a scanner, is evaluated. We called this system as Inline PMI and is based on a shearing type interferometer. Wavefront gradient data is measured and used to reconstruct a full high resolution wavefront. The system was evaluated based on short term and long term stabilities, sensitivity towards system parameters, correlation studies with PMI, a resist-based lens metrology tool and lithographic tests to establish accuracy, and model compliance test against lens model prediction. The lens was detuned with Z7-tilt and Z9 offset to extend the dynamic range of the tests. The metrology demonstrated good repeatability, accuracy and stability as well insensitivity toward environmental parameters and good compliance with lens model predictions. In addition, because of the high resolution nature of the inline PMI system high spatial frequency wavefront content can be recovered. With a derived transfer function we can recover approximately up a spatial frequency of 30 to 40 cycles/pupil diameter. This fills the gap in the power spectrum obtained by low order Zernike terms and traditional high frequency flare measurement from techniques such as disappearing pads. Inline PMI may thus enables a more complete analysis of flare in lithography, which is critical to evaluating double exposure techniques as well as bright field masks with widely varying pattern density. Overall, this on-board interferometry shows good technical performance and fast turnaround time, both of which are essential requirement in low k1-imaging in a manufacturing environment.