Martin J. J. Jak

Short period holographic structures for backlight display applications.

The use of holographic structures is promising for the realization of efficient systems in backlight applications for displays. By applying surface relief gratings on top of a side-lit lightguide we realize a backlight that avoids the use of color filters. The grating is used as a light outcoupling and color-separating element. The demands for this grating are stringent and calculations have been performed to meet them. A prototype backlight, including the grating structure, has been assembled and characterized. Results of experiments are discussed.

Grid spectral purity filters for suppression of infrared radiation in laser-produced plasma EUV sources

We have developed a grid-type spectral purity filter (SPF) for suppression of infrared radiation in laser-produced plasma (LPP) EUV sources for high-volume EUV lithography. The SPF is a silicon grid with sub-wavelength periodicity that is metalized to make it reflective for infrared radiation. EUV radiation is transmitted geometrically through the open area of the grid. The first prototype samples show an in-band EUV transmittance of 74% at normal incidence. Infrared spectrometry exhibits a clear cut-off behavior as expected, with a transmittance of <0.1% at a wavelength of 10.6 µm. In a first power-load test, a grid was exposed to a CO2 laser at 100 W/cm2 in vacuum for 8 hours. Another grid was kept at 800 °C in a vacuum oven for 24 hours. Both grids remained structurally intact and maintained an infrared transmittance of <0.1%.

Extreme ultraviolet multilayer mirror with near-zero IR reflectance

We have developed a multilayer mirror for extreme ultraviolet (EUV) radiation that has low reflectance for IR radiation at 10.6 mum wavelength. The mirror is based on a multilayer coating comprising alternating layers of diamondlike carbon and silicon, for which we demonstrate an EUV reflectance of up to 49.7%. We have made a functional prototype in which the multilayer coating is included as part of an antireflection coating for IR radiation, resulting in reflectance values of 42.5% and 4.4% for EUV and IR, respectively. The mirror can replace a standard Mo/Si mirror in an EUV lithography tool to form an efficient solution for the suppression of unwanted CO(2) laser radiation.

Hybrid spatial‐temporal color synthesis and its applications

— A novel approach of synthesizing display color by hybrid color processing in both the spatial and temporal domains is introduced. The rational basis for this approach is found in vision science, and more particularly in the spatial and temporal characteristics of the human visual system. Various examples of the new approach, aiming at different display-performance objectives, are described. Hybrid spatial-temporal color synthesis can be used to generate a three-primary RGB display, the analysis of which reveals a higher spatial resolution and a lower fixed-pattern noise. The concept has also been used to build, based on a conventional LCD panel in combination with an adapted backlight system, a six-primary LCD TV with a 22% wider color gamut. Finally, the approach is demonstrated in a four-primary mobile LCD and results in lower cost combined with a higher display luminance and a wider color gamut.

25.3: Spectrum Sequential Liquid Crystal Display

Conventional displays cannot show all real-world colours. We have made a 30-inch Spectrum Sequential LCD that uses two different types of fluorescent lamps that alternately illuminate the panel. In this way, a 6 primary display is obtained with a 22% larger colour gamut, without modifying the panel itself.

Color‐separating backlight for improved LCD efficiency

— A large part of the light generated in a backlight is usually absorbed in the color filters of the liquid-crystal display. A new backlight system that uses a grating to split the white light into different colors and a lens array to focus this light onto the pixels is presented. The absorbing filters can be eliminated and efficiency is improved. The system is characterized, as well as its different components.

Diffractive grating structures for colour-separating backlights

A colour-separating backlight can be made by using a surface-relief grating as an outcoupling structure on top of a lightguide. By combining such a structure with a birefringent layer, a polarised colour-separating backlight can be realised. We discuss experiments and simulations on a prototype of such backlight structures, as well as directions how to optimise them. First optimised samples of gratings made by laser-interference lithography show promising results.

Atomic-hydrogen cleaning of Sn from Mo/Si and DLC/Si extreme ultraviolet multilayer mirrors

We have investigated the use of atomic-hydrogen-based cleaning to remove Sn contamination from extreme ultraviolet (EUV) multilayer mirrors. Mo and Si surfaces were cleaned at a relatively slow rate due to catalyzed dissociation of tin hydride on these surfaces. Mo/Si mirrors with B4C and Si3N4 cap layers and DLC-terminated DLC/Si mirrors showed complete removal of 10 nm Sn in 20 sec with full restoration of EUV reflectance. In addition, a prolonged cleaning treatment of 300 sec of a DLC/Si mirror resulted in only a minor EUV peak reflection loss of 1.2% absolute and no significant changes in infrared reflectance.

DLC/Si multilayer mirrors for EUV radiation

In this paper, a new type of spectral filter mirrors for extreme ultraviolet radiation based on DLC/Si multilayer coatings is presented (DLC - diamond-like carbon). The coating is nearly transparent for infrared radiation (IR) of λ = 10.6 nm but highly reflective at λ = 13.5 nm (EUV). We deposited DLC/Si multilayers by ion beam sputter deposition with 40 and 60 periods exhibiting maximum EUV reflectances of about Rmax = 43 % and Rmax = 50 %, respectively. Combining IR antireflective and EUV reflective coatings, first prototype mirrors have been fabricated with an EUV reflectance of about 42.5 % and an IR reflectance of about 4.4 % at the same time. Investigations on the thermal behavior of the multilayer stack and the cleaning properties for tin contaminated mirror surfaces have been carried out. Excellent stabilities of EUV peak position and reflectance values have been found using annealing temperatures of up to 700 °C. Furthermore, several cycles of Sn etching under H2 reactive conditions have been applied to the mirrors without significant changes of the filter performance.