Ulrich Wegmann

Toward a comprehensive control of full-field image quality in optical photolithography

This paper shows, that as resolution is pushed into regions below 0.6 (lambda) /NA, understanding the effects of wavefront aberrations is crucial to producing stepper systems that can meet end-user requirements. We show how aberrations can affect the choice of optimum NA and partial coherence for a given reticle object when considering critical dimension uniformity and depth of focus. The ability to measure the complete wavefront and extract meaningful full-field aberration data is shown using an advanced through-the-lens interferometer that operates at the wavelength and bandwidth of the lithographic radiation. The impact of aberrations an image quality criteria is shown through a sensitivity analysis using an imaging approximation model that represents various image criteria as a weighted sum of aberration coefficients. The validity and use of such a model is shown by correlation to full- field experimental measurements.

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.

Real-time wavefront measurement with lambda/10 fringe spacing for the optical shop

We will report on a new interferometer developed at Carl Zeiss, which has real-time measuring capability with instant visualization of results, is nearly insensitive to vibrations, has a variable fringe spacing from one lambda to lambda/1O (lambda represents the wavelength of the light used in the interferometric test), and can give lambda/100 accuracy through a simple calibration procedure. It can be handled with the same ease and in just the same way as conventional interferometers.