F. R. Ladan

Stress and microstructure relationships in gold thin films

Abstract This work compares the mechanical properties of 0.4–2 μm gold polycrystalline thin films deposited on silicon wafers by electroplating, evaporation or sputtering. As-deposited films were observed to be under tensile stress of the order of 20–70 MPa for the electroplated films, 100–280 MPa for the evaporated ones and 120–240 MPa for the sputtered ones. The stress behaviour after annealing up to a temperature of 250°C was investigated. The intrinsic stress is discussed in relation to the microstructure of the deposits. Lower stress values can be obtained with electrodeposits but their stress stability vs temperature is also lower.

Diffraction properties of a 0.24-μm period multilayer laminar amplitude grating in the soft x-ray region

We report on the fabrication of a laminar multilayer amplitude grating, characterization in the soft x-ray region, and modeling of its properties. Holographic lithography was used to produce a 0.24-μm spatial period grating on a triode sputtered Mo/C multilayer mirror. The pattern was transferred into the multilayer mirror by reactive ion etching in an SF 6 plasma after an intermediate lift-off step. The position and relative efficiency of the different orders of a grating etched down to the silicon substrate were measured at the Cu L αβ line (1.33 nm). The results were interpreted in the framework of a scalar kinematic diffraction theory.

Semitransparent soft x-ray multilayer mirrors

We report on the conception, fabrication, and characterization of a multilayer beamsplitter for use at oblique incidence in the soft x-ray range. Thin film deposition, conventional patterning, and anisotropic etch techniques are used to produce the self-supporting silicon carbide carrier film. Large-area Mo/C multilayer beamsplitters (1 cm2) were fabricated. Experimental results on the reflection and transmission at 1.33 nm are presented and compared with theoretical calculations. The role of the supporting film and the flatness of the structure are addressed. Our process is compared with existing approaches from the literature.

Theoretical and experimental study of soft X-ray diffraction by a lamellar multilayer amplitude grating

The authors give a theoretical and experimental study of soft X-ray diffraction by a lamellar multilayer amplitude grating. Absolute efficiency measurements are obtained at 277 eV with a 1000 lines/mm grating etched in a Mo/C multilayer structure and comments based on numerical simulations performed in the framework of a dynamical theory of diffraction are presented. Effects which are not accounted for by a kinematical approach are made both experimentally and theoretically obvious.

Reactive ion etching of multilayer mirrors for X-ray projection lithography masks

Abstract Reflection masks for use in X-ray projection lithography can be obtained by etching synthetic multilayer interference mirrors. Reactive ion etching of such mirrors was investigated with respect to the etch rate and etch profile. Patterned Mo/C, W/C, Mo/Si, and W/Si multilayer mirrors were reactive ion etched in a fluorinated (SF 6 /CHF 3 ) gas mixture. Ni/C and Cr/C multilayer mirrors could be etched in a chlorinated gas (Cl 2 /Ar). The etching speed varied from 0.02 nm/s to 3 nm/s depending on the material and the process parameters. The groove depth could be controlled within one layer by following the reflectivity of the multilayer mirror with an helium-neon laser during the transfer process. Multilayer mirror features in the 0.1 μm range could be produced.

Fabrication of high-resolution multilayer reflection zone plate microlense for the soft x-ray range

The fabrication of linear, circular, and elliptical reflective zone plate lenses by a multistep process using microfabrication technologies is reported. The diffractive elements were generated by electron-beam lithography on a Mo/C multilayer mirror obtained by means of the triode sputtering technique. The patterns were transferred anisotropically into the multilayer mirror by reactive ion etching in a fluorinated plasma. An intermediate metallic mask made by the lift-off process was used for the transfer process. The groove depth could be monitored by following the reflectivity ofthe structure with a helium-neon laser during etching. Linear, circular (with 0.4-μm outer zones), and elliptical Fresnel zone plates (with 0.8-μ.m outer zones) were produced. Test patterns with a 50-nm top and 90-nm bottom resolution were produced. The groove profile and dimensional control were also investigated.

Performance of Etched Laminar Multilayer Gratings in the Soft X-ray Region

Mo/C laminar multilayer amplitude gratings for use in the 1 keV or 250 eV region were fabricated by holography or electron beam lithography followed by reactive ion etching. The gratings were tested with monochromatized synchrotron radiation and their performance was compared to theoretical values.

Application of e‐beam lithography and reactive ion etching to the fabrication of masks for projection x‐ray lithography

Mo/Si multilayer mirrors deposited on silicon wafers by triode sputtering were patterned by electron‐beam lithography and etched by reactive ion etching in a fluorinated plasma with an intermediate metallic mask made by the lift‐off process. The etch rate and etch profile were investigated as a function of the gas mixture, pressure, and plasma rf power. The groove depth was monitored by following the reflectivity of the structure with a helium‐neon laser during etching and comparing it with an optical model. Large structures consisting of gratings and Fresnel zone plates with potential applications to high‐resolution alignment for projection x‐ray lithography were fabricated in Mo/Si. The fabrication feasibility of finer structures such as gratings with 0.3–0.5 μm pitch and linewidths smaller than 100 nm as well as linear and circular Fresnel zone plates with a 0.4‐μm‐wide outer zones were investigated in the similar Mo/C multilayer system.

Fabrication and performance of linear multilayer gratings in the 44-130 angstrom wavelength range

Two types of linear multilayer gratings have been investigated with special attention on the influence of the fabrication method on performance. Rh/C and Mo/Si systems have been realized for use above the carbon K-edge at 43.6 A and the silicon L3 edge at 125 A, respectively. We analyzed in detail the performance of the multilayer coatings in relation with their structural behavior. Mo/Si amplitude gratings were manufactured by suppressing the soft X-ray reflectivity of the multilayer mirror in selective areas with gold coating and lift off process. This method provides a well-defined 3 micron period Au grating. The soft X-ray reflectivity of the multilayer alone reached a maximum of 45 percent at normal incidence, whereas it was measured around 12.5 percent after Au grating deposition. Up to 13 grating orders were detected in the grating scan and detector scan showing the very good quality of these structures. A more unusual method was applied to manufacture Rh/C multilayer gratings. A carbon grating was first patterned on a silicon substrate and the multilayer was deposited at the end of the process. Measured reflectivity around 60 A in conventional 0 - 20 scan shows a reduction of the performances by a factor three. This is probably due to the surface roughness of the carbon grating prior to the multilayer deposition.

Microfabrication Technologies Applied To The Production Of Large Area Stress Relieved Multilayer Beamsplitters

Large area multilayer beamsplitters (1 cm2 ) were produced for use at oblique incidence in the soft X-ray range. Mo/C multilayer reflectors were deposited on top of a self supporting silicon carbide carrier film. The role of the supporting film and the stress induced by the multilayer are addressed. Progress towards optimization of the flatness and transmission enhancement of the beamsplitters (thinning of the carrier layer and adjusting its stress through etching ) is presented. Experimental reflectivity and transmission results at 13.3 Å are compared with theory.