H. Solak

Exposure of 38 nm period grating patterns with extreme ultraviolet interferometric lithography

Extreme ultraviolet (EUV, λ=13u200anm) lithography is considered to be the most likely technology to follow ultraviolet (optical) lithography. One of the challenging aspects is the development of suitable resist materials and processes. This development requires the ability to produce high-resolution patterns. Until now, this ability has been severely limited by the lack of sources and imaging systems. We report printing of 38 nm period grating patterns by interferometric lithography technique with EUV light. A Lloyd’s Mirror interferometer was used, reflecting part of an incident beam with a mirror at grazing incidence and letting it interfere with the direct beam at the wafer plane. High-density fringes (38 nm pitch) were easily produced. Monochromatized light of 13 nm wavelength from an undulator in an electron storage ring provided the necessary temporal and spatial coherence along with sufficient intensity flux. This simple technique can be extended to sub-10 nm resolution.

Measurement of strain in Al–Cu interconnect lines with x-ray microdiffraction

We report measurement of strain in patterned Al–Cu interconnect lines with x-ray microdiffraction technique with a ∼1 μm spatial resolution. Monochromatized x rays from an undulator were focused on the sample using a phase fresnel zone plate and diffracted light was collected by an area detector in a symmetric, angle dispersive x-ray diffraction geometry. Measurements were made before and after the line sample was stressed for electromigration. Results show an increase in inter- and intra-grain strain variation after the testing. Differences in strain behavior of grains with (111) and (200) crystallographic planes parallel to the substrate surface were observed. A position dependent variation of strain after the testing was measured whereas no such dependence was found before the testing.

An x-ray spectromicroscopic study of electromigration in patterned Al(Cu) lines

We studied the surface properties of patterned Al(Cu) lines related to the electromigration phenomena using photoemission spectromicroscopy techniques. We stressed the lines for electromigration in situ in the ultrahigh vacuum microscope chamber and observed the changes on the line surface. Our results show surface precipitation of Cu beneath the Al2O3 layer on the line surface as well as on side walls. Enrichment of grain boundaries in Cu due to electromigration flux was observed in areas downstream of voids with respect to the electron flow.

Image formation in EUV lithography: Multilayer and resist properties

We report the results of a modeling study of the image formation process in EUVL. Using a rigorous diffraction scheme, we compute the propagation of the mask image in the multilayer stack. The same approach is used to compute the aberrations induced by the multilayer stack on converging beams. We show that in the first case the multilayer stack introduces a change in the mask image that affects the final image projected on the water and that in the second case the multilayers introduce a non-negligible amount of spherical aberration in the propagating beam.

X-ray microdiffraction study of Cu interconnects

We have used x-ray microdiffraction to study the local structure and strain variation of copper interconnects. Different types of local microstructures have been found in different samples. Our data show that the Ti adhesion layer has a very dramatic effect on Cu microstructure. Strain measurement was conducted before and after electromigration test, Cu fluorescence was used to find the mass variations around voids and hillocks, and x-ray microdiffraction was used to measure the strain change around that interested region.

Multilayer roughness and image formation in the Schwarzschild objective

We present a study of the effect of multilayer‐surface‐roughness‐induced scattering in the image formation of the Schwarzschild objective (SO) used in the spectromicroscope MAXIMUM. The two mirrors comprising the SO are coated with Ru/B4C multilayers that have a peak reflectivity at 130 eV. We had long observed that a diffuse x‐ray background surrounds the focused x‐ray spot. The spatial resolution remains at 0.1 μm in spite of this. However, since a significant fraction of the flux is lost to the background, since too large an area of the sample is illuminated, and since the S/N ratio is degraded, the origins of this effect merit investigation. This diffuse background resulting from x‐ray scattering at the surface of the mirrors was mapped out using bidirectional knife edge scans. Complementary surface roughness simulations were carried out with the ray‐tracing program SHADOW. AFM experiments were also done to directly measure the surface roughness and power spectrum of representative multilayers. Follow...

AN X-RAY SPECTROMICROSCOPIC STUDY OF THE LOCAL STRUCTURE OF PATTERNED TITANIUM SILICIDE

Results from a spectromicroscopic study of the formation of TiSi2 in patterned structures are reported. An x-ray spectromicroscope was used to acquire spectra and images with photoabsorption signals using synchrotron radiation. A patterned TiSi2 sample with feature sizes ranging from 100 μm to 0.1 μm was studied. The silicidation reactions were carried out in ultrahigh vacuum using rapid thermal processing. Lateral variations in the local chemistry of the titanium silicide could be directly imaged and are attributed to the formation of the C54 phase in large areas and the C49 phase at feature edges and in narrow features.

A new beamline for EUV lithography research

We have recently completed construction of a new branch-line and exposure station for EUV lithography research at the Synchrotron Radiation Center. We use uniform area and interferometrically patterned exposures for the investigation of technologically relevant material properties under EUV exposure. Two multilayer mirrors are installed into an existing undulator beamline to extract the beam both before and after a spherical grating monochromator. Both beams are directed into a single experimental chamber by means of additional multilayer mirrors. In this way both the high flux raw undulator beam and the monochromatic beam are available for experiments.

EUV interferometric lithography for resist characterization

We report printing of sub-20nm line/space patterns by Interferometric Lithography technique with EUV light for the first time. EUV lithography is pursued as one of the candidate next generation lithography technologies. New photoresist materials need to be developed and characterized for this spectral region mainly because of high absorption coefficients of materials. EUV interferometric lithography is a useful tool for testing of materials with high resolution features especially because EUV lithographic systems are still under early development phases. It provides a cost effective and simple way of achieving this without the need for complicated imaging system. We employed a Lloyds Mirror Interferometry scheme with monochromatized undulator light from an electron storage ring. The technique is described and results showing the printed patterns are presented. Potential uses of the method for lithography research are discussed.

EUV nanolithography: sub-50-nm L/S

Extreme Ultra Violet Lithography (EUVL, (lambda) equals 13.4 nm) is one of the next generation lithography technologies developed for patterns smaller than 70 nm feature size. In our system, EUV light is obtained from an undulator in an electron storage ring. This provides a temporally and spatially coherent light source for Extreme Ultra Violet Interferometric lithography (EUV-IL). The patterning system uses a Lloyd mirror interferometer. Using EUV-IL to print high-resolution pattern allows us to study resist characteristic in the EUV. Previously we demonstrated 19 nmL/S fringe pattern by using IL technique with EUV light. In this paper, we will report our progress on development of sub-50 nm dense line/space patterns using EUV-IL, and the transferring patterns into 0.12 micrometer Poly-Si.