Alexander Menck

Aerial image measurement technique for today's and future 193-nm lithography mask requirements

The Aerial Image Measurement System (AIMS) for 193 nm lithography emulation has been brought into operation worldwide successfully. Adjusting optical equivalent settings to steppers/scanners the AIMS system for 193 nm allows to emulate any type of reticles for 193 nm lithography. The overall system performance is demonstrated by AIMS measurements at 193 nm wavelength on binary chrome masks and phase shift masks. Especially for evaluation of 65 nm node lithography performance process window results will be discussed. An ArF excimer laser is in use for illumination. Therefore a beam homogenizer is needed to reduce the speckles in the laser beam and ensure a similar illumination uniformity as the longer wavelength systems, 248 nm and longer, using an arc source. A new beam homogenizing technique will be presented and illumination results compared to the current solution. The latest results on enhanced illumination uniformity exceed the current performance. A newly developed hybrid objective for high resolution imaging is tested for use of high resolution imaging in order to review defects and investigate repairs which do not print under stepper equivalent optical settings. An outlook will be given for extension of 193 nm aerial imaging down to the 45 nm node. Polarization effects will be discussed.

Immersion mask inspection with hybrid-microscopic systems at 193 nm

The capability of a high NA, large working distance, microscope objective was demonstrated by investigating different mask features. The microscope objective is based on a hybrid concept combining diffractive and refractive optical elements. Resolution down to 125 nm lines and spaces (L/S) is demonstrated by investigating periodic chrome on glass structures. A significant additional improvement of the resolution is achieved by inducing a solid immersion lens (SIL).

Controlled diffraction using smart materials

By introducing sinusoidal deformations on piezoelectric crystals using surface acoustic waves with spatial frequencies > 30 mm-1 and amplitudes > 1 nm new optical diffractive elements can be generated. For high diffraction efficiencies it is necessary to produce amplitudes of the SAW as high as possible or to use light wavelength as short as possible. Conventional diffraction gratings are fixed in amplitude and spatial frequency whereas both can be varied for this new type of gratings. The gratings can operate in several environments such as N2, He gas or vacuum and be remote controlled. Therefore they are a very flexible tool. First results on these gratings with frequencies up to 200 MHz and amplitudes in the order of 5 nm are shown.