High-resolution actinic defect inspection for extreme ultraviolet lithography multilayer mask blanks by photoemission electron microscopy

Abstract

We report on the development and first experimental results of a “at wavelength” full-field imaging technique for defect inspection of multilayer mask blanks for extreme ultraviolet (EUV) lithography. According to the International Semiconductor Roadmap by Sematech, less than 5×10−3 defects per cm2 should be present on such multilayer mask blank to enable mass production of microelectronics using EUV lithography, thus fast high-resolution methods for mask defect inspection and localization are needed. Our approach uses a photoemission electron microscope in a normal incidence illumination mode at 13 nm to image the photoelectron emission induced by the EUV wave field on the multilayer mask blank surface. We show that by these means, buried defects in the multilayer stack can be probed down to a lateral size of 50 nm.

Photoemission Electron Microscopy of TiO2 Anatase Films Embedded with Rutile Nanocrystals

“…The PEEM technique has been widely applied in studies of catalytic reactions [1,2] and molecular diffusion on metal surfaces, [3] in characterization of organic electronic devices, [4] organic thin film growth, [5] formation of self assembled Ag nanowires, [6] photolithographic mask inspection, [7] and phase transformation in shape memory alloys. [8,9] When implemented using the two-photon photoemission technique, electronic dynamics can be resolved on femtosecond timescales.…”

Actinic extreme ultraviolet lithography mask blank defect inspection by photoemission electron microscopy

“…The spatial resolution of this instrument has been measured to be 29 nm ͑edge slope width, following a 16%-84% criterion͒ using a 248 nm wavelength Hg discharge lamp source in the normal incidence illumination configuration. 8 During our initial experiments with this near normal incidence illumination EUV-PEEM, a flat multilayer mirror was used as a microreflector to couple EUV light to illuminate the mask blank sample, and several minutes of acquisition time were required to obtain a clear EUV-PEEM image with a field of view of about 100 m. 9 This unsatisfactory long acquisition time is required due to the EUV focal size of diameter of about 1 mm on the mask blank sample, which is much larger than the field of view of the PEEM ͑a typical value of about 100 m͒ at high magnification mode. In order to increase the photon flux density on the sample, improvement was made to replace the flat multilayer mirror by a toroidal multilayer mirror ͑see photo in Fig.…”

A new approach for actinic defect inspection of EUVL multilayer mask blanks: Standing wave photoemission electron microscopy

“…The microscope provided by Focus GmbH employs an up to 15 kV extractor lens voltage and allows fields-of-view ranging 2.3 lm and 1 mm and swapping between different fields-of-view within seconds by changing the electrostatic lens voltages. A spatial resolution of 29 nm edge slope width (following a 16-84% criterion) has been measured at 250 nm wavelength (Hg discharge source) with this instrument in normal incidence illumination [12].…”

“…The left column image shows an overview, the right column images are detail views of the sample-extractor region from the left and right side, illustrating the beam deflection by 94°for near normal incidence illumination. A schematic overview of the hardware can be found in [12]. structures were fabricated in titanium by means of electron beam lithography and a lift-off technique.…”