Tonglin Huo

Optical and structural performance of the Al(1%wtSi)/Zr reflection multilayers in the 17–19nm region

Two kinds of Al/Zr (Al(1%wtSi)/Zr and Al(Pure)/Zr) multilayers for extreme ultraviolet (EUV) optics were deposited on fluorine doped tin oxide coated glass by using direct-current magnetron sputtering technology. The comparison of the two systems shows that the Al(1%wtSi)/Zr multilayers have the lowest interfacial roughness and highest reflectivity. Based on the X-ray diffraction, the performance of the two systems is determined by the crystallization of Al layer. To fully understand the Al(1%wtSi)/Zr multilayer, we built up a two-layer model to fit situation of the AFM images, and simulate the grazing incident x-ray reflection-measurements of multilayers with various periods (N = 10, 40, 60, 80). Below 40 periods, the roughness components are lowered. After 40 periods, both surface and interfacial roughness increase with the period number, and decrease the reflectance. According to transmission electron microscope images, the model can represent the variable structure of the system.

High-efficiency multilayer-coated ion-beam-etched blazed grating in the extreme-ultraviolet wavelength region

We describe a simple method to fabricate blazed gratings used in the extreme ultraviolet wavelength region. The method uses an argon and oxygen mixed-gas ion beam to directly etch the grating substrate through a rectangular profile photoresist grating mask. With this method the etched grating groove profile can be well controlled. An Mo/Si multilayer-coated specimen with a blaze angle of 1.9 degrees was fabricated and measured. At an incident angle of 10 degrees and a wavelength of 13.62 nm, the diffraction efficiency of the negative second order reaches 36.2%.

High reflectivity multilayer for He-II radiation at 30.4 nm

SiC/Mg and B(4)C/Mo/Si multilayers were designed for He-II radiation at 30.4 nm. These multilayers were prepared by use of a direct current magnetron sputtering system and measured at the National Synchrotron Radiation Laboratory, China. The measured reflectivities were 38.0% for the SiC/Mg multilayer at an incident angle of 12 deg and 32.5% for the B(4)C/Mo/Si multilayer at 5 deg, respectively. A dual-function multilayer mirror was also designed by use of the aperiodic SiC/Mg multilayer. Annealing experiments were performed to investigate the thermal stability of the SiC/Mg multilayer. The interface of the SiC/Mg multilayer before and after annealing was studied by electron-induced x-ray emission spectra, which evidences the absence of thermal reaction products at the interfaces after annealing.

Thermal stability of Mg/Co multilayer with B 4 C, Mo or Zr diffusion barrier layers

The efficiency of B(4)C, Mo and Zr barrier layers to improve thermal stability of Mg/Co multilayer up to 400 °C is investigated. Multilayers were deposited by direct current magnetron sputtering and characterized using X-ray and extreme ultraviolet reflection. The results suggest that B(4)C barrier layer is not effective due to drastic diffusion at Mg-B(4)C interface. Although introducing Mo barriers improves the thermal stability from 200 to 300 °C, it increases the interface roughness and thus degrades the optical performances. On the contrary, Zr barriers can significantly increase the thermal stability of Mg/Co up to 400 °C without optical performance degradation. Thus, Mg/Zr/Co/Zr is suitable for EUV applications requiring both optimal optical performances and heat resistance.

Vacuum-ultraviolet blazed silicon grating anisotropically etched by native-oxide mask

We describe a simple and convenient method of controlling the profile of a blazed grating that consists of using a patterned native-oxide layer of off-cut silicon (111) wafers as the mask of anisotropic etching to maximize the smooth blaze facets of the desired blaze angle and to minimize the deficiencies of the groove apexes. With the blazed-grating profile well controlled by this technique, a 1200 g/mm blazed grating was fabricated that had a blaze angle of 5.0 degrees and smooth blaze facets of about 0.2 nm rms. It was measured to have blaze efficiency in the vacuum-ultraviolet wavelength region.

Broadband multilayer-coated normal incidence blazed grating with 10% diffraction efficiency through the 13-16 nm wavelength region

Diffraction gratings used in extreme UV are typically coated with periodic multilayer thin films. These coatings have a small bandwidth, thus leading to a narrow usable spectral region of multilayer gratings. Well-designed aperiodic multilayer coatings could provide high reflectivity over a much broader wavelength region, so they could broaden the usable spectral region of multilayer gratings. We designed and deposited an aperiodic Mo/Si multilayer coating onto a blazed grating substrate. At an incidence angle of 10°, the -2nd-order diffraction efficiency of the multilayer grating is ~10% through the wavelength range of 13-16 nm.

Al/Zr multilayer mirror and its thermal stability for EUV application

Two kinds of Al/Zr (Al(1%wtSi)/Zr and Al(Pure)/Zr) multilayers in the region of 17-19nm were deposited on fluorine doped tin oxide coated glass by using direct-current magnetron sputtering technology. Based on the fitting data of grazing incident X-ray reflection and near-normal incident (EUV) reflectance, the interfacial roughness in the Al(1%wtSi)/Zr is lower than that in Al(Pure)/Zr because of the presence of silicon in Al. For the further characterization of Al(1%wtSi)/Zr multilayers, six samples deposited on Si substrates were annealed from 100 °C to 500 °C temperature in a vacuum furnace for 1 h. Based on the results of EUV and X-ray diffraction, the Al(1%wtSi)/Zr multilayer has a stable structure up to 200 °C, and keeps almost the similar EUV reflectivity as the non-annealed sample. After 300 °C, the amorphous of Al-Zr alloy is transformed to polycrystalline in the interface, which could be the reason for the decrease of EUV reflectivity. The polycrystalline Al-Zr compound does not destroy the multilayer completely even up to 500 °C.

Fabrication of self-supporting transmission gratings for plasma diagnostics

With holographic-ion beam etching technique, a number of self-supporting transmission gratings have been fabricated for inertial confinement fusion diagnosis. In addition to the general process, a practical method for monitoring the evolution of the grating structures exposed in photoresist during development of the resist. The real-time monitor technique developed here is relatively simple in comparison with a He-Ne laser and detector, which needs delicate control.

SiC/W/Ir multilayer-coated grating for enhanced efficiency in 50-100 nm wavelength range in Seya-Namioka mount.

A broadband [SiC/W/Ir](2) multilayer coating was deposited onto a diffraction grating to enhance the grating efficiency in the 50-100 nm wavelength range in a Seya-Namioka mount. The holographic ion-beam etched grating had a laminar profile with 1200 lines/mm. The coating was designed by using the subquarterwave multilayer theory. The measurement results show that the efficiency in the -1st diffraction order is greater than 9.3% throughout the wavelength range of 50-100 nm, which is obviously higher than that of single-layer gratings with SiC, Ir, or Au coatings.

Mo/Si aperiodic multilayer broadband reflective mirror for 12.5-28.5-nm wavelength range

Aperiodic molybdenum/silicon (Mo/Si) multilayer designed as a broadband reflective mirror with mean reflectivity of 10% over a wide wavelength range of 12.5-28.5 nm at incidence angle of 5? is developed using a numerical optimized method. The multilayer is prepared using direct current magnetron sputtering technology. The reflectivity is measured using synchrotron radiation. The measured mean reflectivity is 7.0% in the design wavelength range of 12.5-28.5 nm. This multilayer broadband reflective mirror can be used in extreme ultraviolet measurements and will greatly simplify the experimental arrangements.