F. Rousseaux

Hardness and Young's modulus of amorphous a -SiC thin films determined by nanoindentation and bulge tests

Due to its interesting mechanical properties, silicon carbide is an excellent material for many applications. In this paper, we report on the mechanical properties of amorphous hydrogenated or hydrogen-free silicon carbide thin films deposited by using different deposition techniques, namely plasma enhanced chemical vapor deposition (PECVD), laser ablation deposition (LAD), and triode sputtering deposition (TSD). a -Si x C 1− x : H PECVD, a -SiC LAD, and a -SiC TSD thin films and corresponding free-standing membranes were mechanically investigated by using nanoindentation and bulge techniques, respectively. Hardness ( H ), Youngs modulus ( E ), and Poissons ratio ( v ) of the studied silicon carbide thin films were determined. It is shown that for hydrogenated a -Si x C 1− x : H PECVD films, both hardness and Youngs modulus are dependent on the film composition. The nearly stoichiometric a -SiC: H films present higher H and E values than the Si-rich a -Si x C 1−x : H films. For hydrogen-free a -SiC films, the hardness and Youngs modulus were as high as about 30 GPa and 240 GPa, respectively. Hydrogen-free a -SiC films present both hardness and Youngs modulus values higher by about 50% than those of hydrogenated a -SiC: H PECVD films. By using the FTIR absorption spectroscopy, we estimated the Si-C bond densities ( N SiC ) from the Si-C stretching absorption band (centered around 780 cm −1 ), and were thus able to correlate the observed mechanical behavior of a -SiC films to their microstructure. We indeed point out a constant-plus-linear variation of the hardness and Youngs modulus upon the Si-C bond density, over the N SiC investigated range [(4–18) × 10 22 bond · cm −3 ], regardless of the film composition or the deposition technique.

A study of the effect of composition on the microstructural evolution of a–Si x C 1 − x : H PECVD films: IR absorption and XPS characterizations

Amorphous silicon carbide films (a–Si x C 1 − x :H) deposited by the argon- or helium-diluted PECVD technique were studied as a function of their composition. Microstructural investigations were mainly achieved by means of FTIR and XPS techniques. Nuclear techniques were used to obtain precise information on the film hydrogen content. The Si–H IR-absorption band was deconvoluted in different monohydride and dihydride silicon environments. The existence of SiH 2 bonds in the Si-rich composition was evidenced. From the analysis of the C–H and Si–H absorption bands it is shown that hydrogen atoms are preferentially bonded to carbon atoms. The deconvolution of the Si 2 p core level peak suggests that above a composition of x ∊ 0.5, the noncarburized (Si, Si, H) local environment contribution increases to the detriment of the hydrocarburized (Si, C, H) environments. From the evolution of the C 1 s peak, it can be deduced that there is a change in the carbon atom bonding states when the film composition is varied. These results are correlated and discussed in terms of the local bonding environments and their evolution with film composition.

50‐nm x‐ray lithography using synchrotron radiation

A technology of proximity x‐ray lithography has been developed to replicate patterns of sub‐100‐nm feature size using synchrotron radiation. Process modeling has been done in advance in order to optimize the mask absorber thickness. It is shown that with tungsten absorber, a 0.3 μm thickness is the most desirable for 50 nm linewidth processing. Masks compatible with a Karl Suss stepper have been fabricated using 50 keV electron‐beam lithography and reactive ion etching techniques. As a result, well‐defined 50‐nm‐wide isolated W lines and small gratings of period down to 100 nm have been fabricated. Then they have been replicated under proximity condition using Super ACO synchrotron radiation. We present details of a replication procedure with gap settings down to 5 μm and show how sub‐100 nm structures can be 1:1 printed into both poly (methylmethacrylate) (PMMA) and (8.5%) MAA/PMMA resists. Finally, the results are analyzed in terms of a scaling rule to evaluate the resolution limit as a function of prox...

Sub-20 nm x-ray nanolithography using conventional mask technologies on monochromatized synchrotron radiation

The optimal wavelength range for x-ray lithography is usually estimated between 0.8 and 1.4 nm. In this work, the use of a monochromator working at 1.1 nm on synchrotron radiation is reported. Replication results in this monochromatic mode are compared with results obtained for a polychromatic synchrotron radiation centered at 0.8 nm in terms of resolution and image contrast. Two conventional mask technologies are used for this study. The influence of the mask contrast is also studied. A nondestructive soft contact system was chosen to lower the gap below 1 μm. An ultimate resolution of 20 nm is shown in PMMA resist as well as 35 nm in PMMA/MAA (8.5%) resist for the monochromatic mode. The effect of photoelectrons created in the substrate is also investigated by replications on Si substrates coated with a Cr/Au bilayer. In addition, the daughtering of high resolution masks at 1.1 nm is successfully performed in the 20 nm range by Au electroplating.

X-ray mask development based on SiC membrane and W absorber

We report a detailed description of x‐ray mask technology based on SiC membrane and tungsten absorber. Amorphous SiC films were prepared using either a 100 kHz plasma‐enhanced chemical vapor deposition (PECVD) system (allowing a high throughput) or a laser ablation deposition (LAD) technique. The PECVD a‐SixC1−x:H films have a maximum Si–C bond density at x=0.5, a hydrogen content of 27 at. % and a high‐compressive stress (1 GPa). The LAD films are stoichiometric, hydrogen‐free, and under high‐compressive stress (1.4 GPa). In order to achieve the tensile stress range (20–40 MPa) required for membrane fabrication, we developed a well‐controlled rapid thermal annealing (RTA) process. At 633 nm, the resulting PECVD and LAD membranes have an optical transparency of 75% and 40%, respectively, and their corresponding biaxial Young’s moduli are 250±30 and 360±60 GPa. A novel approach using RTA for ‘‘fine tuning’’ of the tungsten stress is also proposed. Low stress (≤10 MPa) is obtained for W layers initially und...

Properties of electromagnetic fields in x‐ray lithographic masks: Guided modes and beam propagation calculus

The modal fields within x‐ray lithographic masks are analyzed using standard optical waveguide theory and a ‘‘beam propagation method (BPM).’’ From the properties of the guided modes, it is shown that for small feature sizes the field no longer resembles the geometrical shape of the absorber structure, but strongly the shape of the modes. TE and TM modes behave almost identically and, thus, scalar diffraction calculations are generally valid in the domain of soft x rays. Mode cut‐off of the fundamental mode never occurs. Using such guiding properties it is possible to generate spatially concentrated (16 nm) x‐ray fields with much larger absorber openings (40 nm). A BPM with fast Fourier transforms is employed to efficiently calculate the accurate wave front propagation inside the mask, to determine the physical boundary condition downstream of the absorber structure and to calculate the diffracted image in the wafer plane. The BPM in free space is equivalent with the Rayleigh–Sommerfeld diffraction formul...

Edge diffraction enhanced printability in x-ray nanolithography

We study the edge diffraction enhanced printability in x-ray nanolithography under both proximity and soft-contact printing conditions. Theoretical modeling shows that the gap dependence of the edge diffraction is closely related to that of the minimum linewidth described by the common Fresnel formula and that the edge diffraction can significantly enhance the image contrast of nanometer scale features. Experimental results are also presented to show high resolution and high aspect ratio printability. Furthermore, a method for fabricating ultrahigh resolution and dense structure is discussed based on edge diffraction enhanced printability with very thin absorber masks.

Evaluation of a diamond‐based x‐ray mask for high resolution x‐ray proximity lithography

A high resolution x‐ray mask compatible with a commercial stepper has been realized with a diamond membrane and electroplated gold structures. The membrane was optimized to satisfy all the requirements needed for x‐ray proximity lithography using soft x rays at the super‐ACO synchrotron facility. Patterning was optimized using a conventional 50 keV vector scan generator. High density high resolution gold gratings were obtained with linewidth down to 60 nm with periods as small as 120 nm. It was found that the resolution for our current studies was mainly limited by the resist thickness and not by the diamond surface morphology or the electrodeposition process. Alignment performance has been evaluated. Preliminary results show that diamond material with a 20 nm root‐mean‐square surface roughness is acceptable for good alignment performance.

Fabrication of sub‐30 nm masks for x‐ray nanolithography

For the study of the ultimate resolution limits of x‐ray nanolithography, i.e., the contact printing of features smaller than 30 n m, the biggest task is the production of x‐ray nanomasks. The fabrication of such conventional masks with features as small as 12 nm for isolated dots and 25 nm for isolated lines is reported. High‐energy electron beam lithography, using a transmission electron microscope operating at a voltage of 200 kV was carried out in a 400‐nm‐thick single resist layer with an electron probe of 1 nm in diameter. The ability of gold plating to enter very narrow structures is demonstrated here: 12 nm width absorber features with a thickness of 360 nm are obtained. We demonstrate that sub‐30 nm features can be routinely produced with aspect ratios as high as 15 with a good process latitude.

Biaxial Young's modulus of silicon carbide thin films

We have investigated the biaxial Young’s modulus of amorphous SiC thin films which have been produced by using laser ablation, triode sputtering, and plasma enhanced chemical vapor deposition techniques. It is observed that the biaxial Young’s modulus increases with the Si—C bond density in the films.