H. Launois

Electron beam lithography: resolution limits and applications

Abstract We report on the resolution limits of Electron Beam Lithography (EBL) in the conventional polymethylmethacrylate (PMMA) organic resist. We show that resolution can be pushed below 10 nm for isolated features and how dense arrays of periodic structures can be fabricated at a pitch of 30 nm, leading to a density close to 700 Gbit/in2. We show that intrinsic resolution of the writing in the resist is as small as 3 to 5 nm at high incident electron energy, and that practical resolution is limited by the development of the resist after exposure and by pattern transfer. We present the results of our optimized process for reproducible fabrication of sub-10 nm lines by lift-off and 30-nm pitch pillar arrays by lift-off and reactive ion etching (RIE). We also present some applications of these nanostructures for the fabrication of very high density molds for nano-imprint lithography (NIL) and for the fabrication of Multiple Tunnel Junction devices that can be used for single electron device applications or for the connection of small molecules.

Design and fabrication of blazed binary diffractive elements with sampling periods smaller than the structural cutoff

We report here on the theoretical performance of blazed binary diffractive elements composed of pillars carefully arranged on a two-dimensional grid whose period is smaller than the structural cutoff. These diffractive elements operate under unpolarized light. For a given grating geometry, the structural cutoff is a period value above which the grating no longer behaves like a homogeneous thin film. Because the grid period is smaller than this value, effective-medium theories can be fully exploited for the design, and straightforward procedures are obtained. The theoretical performance of the blazed binary elements is investigated through electromagnetic theories. It is found that these elements substantially outperform standard blazed echelette diffractive elements in the resonance domain. The increase in efficiency is explained by a decrease of the shadowing effect and by an unexpected sampling effect. The theoretical analysis is confirmed by experimental evidence obtained for a 3λ-period prismlike grating operating at 633 nm and for a 20°-off-axis diffractive lens operating at 860 nm.

Blazed binary subwavelength gratings with efficiencies larger than those of conventional échelette gratings

We introduce a new structural cutoff beyond which subwavelength gratings cease to behave as homogeneous media and discuss its effects on the proper selection of the sampling periods of subwavelength diffractive elements. According to this analysis, a 3lambda-period blazed binary grating composed of square pillars is designed for He-Ne operation and is fabricated by etching of a TiO>(2) layer deposited upon a glass substrate. Its first-order measured diffraction efficiency is 12% larger than the theoretical efficiency of an ideal blazed échelette grating in glass with the same period.

HIGH-EFFICIENCY SUBWAVELENGTH DIFFRACTIVE ELEMENT PATTERNED IN A HIGH-REFRACTIVE-INDEX MATERIAL FOR 633 NM

We propose the use of high-index materials for the fabrication of subwavelength diffractive components operating in the visible domain. This approach yields a reduction of fabrication constraints and an improvement of theoretical performance. A blazed grating with subwavelength binary features and with a period of 5.75 wavelengths is designed and fabricated in a TiO(2) layer coated upon a glass substrate. The first-order diffraction efficiency measured with a He-Ne laser beam is 83%, which is slightly larger than that achieved theoretically by the best standard (continuous profile) blazed grating fabricated in glass with the same period.

A transmission polarizing beam splitter grating

We present the design, fabrication, and test of a polarizing beam splitter grating for operation at 633 nm under a angle of incidence. This component is compact and its fabrication is reproducible enough to be integrated in optical reconfigurable interconnect systems. For TE polarization, the incident beam is undeflected whereas TM beams exhibit a deviation. We used electromagnetic theory to optimize the performance of the polarizing beam splitter grating. We employed direct electron beam writing and reactive ion etching to fabricate a polarizing beam splitter etched in a layer deposited on a glass substrate. Experimental results show that diffraction efficiencies more than 80% and extinction ratios above 100 are manufacturable with present technology.

Nanoimprint lithography for a large area pattern replication

We report on replication of high resolution patterns over a 4 in. wafer area by imprint lithography with a commercial hydraulic press and a pair of hot plates. The experiments confirm that the imprint lithography can be used for large area patterning. As a result, sub-100 nm features were obtained by the imprint lithography and lift-off with a good uniformity and an accurate pattern placement over the 4 in. wafer area.

Irradiation induced effects on magnetic properties of Pt/Co/Pt ultrathin films

Abstract He+ ion irradiation-induced interface mixing modifies the magnetic properties of Pt/Co/Pt sandwiches. A strong decrease in magnetic anisotrophy (hence of the coercivity and Curie temperature) can be controlled without significant changes in sample roughness or optical properties. This opens exciting possibilities to develop a planar technology to pattern the magnetic properties of multilayers by irradiation through a lithographically defined mask.

Evidence of stress dependence in SiO2/Si3N4 encapsulation-based layer disordering of GaAs/AlGaAs quantum well heterostructures

Spatial selectivity of layer disordering induced in GaAs/AlGaAs quantum well heterostructures using SiO2 and Si3N4 capping and annealing was investigated using low temperature photoluminescence in conjunction with cross-sectional transmission electron microscopy. Comparative study reveals opposite behaviors for patterned Si3N4 covered with SiO2 and patterned SiO2 covered with Si3N4. In the former, layer disordering occurs in the regions located under the SiO2 strips and in the latter, layer disordering surprisingly occurs under the Si3N4 strips while it is inhibited in the SiO2-capped areas. These results are in agreement with a proposed interdiffusion model based on the effect on Ga vacancy diffusion of the stress distribution generated in the heterostructure during annealing by the capping layers. This work clearly demonstrates that the diffusion of point defects, such as the Ga vacancies, which are responsible for the layer disordering, can be piloted by the stress field imposed to the semiconductor an...

Modifications of magnetic properties of Pt/Co/Pt thin layers by focused gallium ion beam irradiation

We show how the magnetic properties of the Pt/Co ultrathin film structure can be modified and even controlled under uniform irradiation by Ga+ ions at low fluence in the 20–100 keV range. A systematic magneto-optical study is presented for the Pt/Co(1.4 nm)/Pt(111) ultrathin-film structure. At ion fluences below D=1014 Ga+/cm2, the coercive field is steadily reduced when increasing the fluence. At large fluences, in the range D=(5–10)×1014 Ga+ ions/cm2, the magnetization of the Co layer drops rapidly and the film finally becomes paramagnetic at room temperature for D>2×1015 Ga+ ions/cm2. We demonstrate that these magnetic changes are related to the effect of ion-induced collisional intermixing of the Co/Pt interfaces, leading to the formation of stable Co–Pt alloys with varying composition across the interfaces. A simple model is derived to relate the ion beam-induced mixing to the changes in magnetic properties. The present work allows us to gain a quantitative understanding of previous experiments using...

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...