C. Gourgon

Uniformity across 200 mm silicon wafers printed by nanoimprint lithography

Uniformity of the printing process is one of the key parameters of nanoimprint lithography. This technique has to be extended to large size wafers to be useful for several industrial applications, and the uniformity of micro and nanostructures has to be guaranteed on large surfaces. This paper presents results of printing on 200 mm diameter wafers. The residual thickness uniformity after printing is demonstrated at the wafer scale in large patterns (100 µm), in smaller lines of 250 nm and in sub-100 nm features. We show that a mould deformation occurs during the printing process, and that this deformation is needed to guarantee printing uniformity. However, the mould deformation is also responsible for the potential degradation of the patterns.

Electron beam photoresists for nanoimprint lithography

Abstract Polymer selection and critical dimension (CD) pattern uniformity across the wafer are key parameters for the nanoimprint lithography technique. This nanotechnology requires polymers having a low glass transition temperature (Tg) combined with a good etch resistance. The printing of a commercial E-beam photoresist is studied as a function of the pressing conditions and the pattern density on the wafer. The influence of the printing temperature is analyzed in order to understand the polymer behaviour during the printing process. The residual thickness uniformity across the wafer after pressing has been carefully studied and correlated to the thermal properties of the polymer. Our results show that high resolution resists are well adapted to obtain dense nanostructures with a good CD control.

Optical properties of CdTe/CdZnTe wires and dots fabricated by a final anodic oxidation etching

A two step etching process has been used to fabricate wire and dot nanostructures from CdTe/CdZnTe quantum wells with high optical qualities. Wires and dots are first etched by the usual process of electron beam lithography and ion beam etching then, anodic oxidation is used to etch nanostructures to their final lateral sizes. We have observed remarkable improvements in the optical properties of these nanostructures as compared to the single step etching process. Their photoluminescence spectra are similar to that of the reference quantum well, with an exciton linewidth of about 3 meV, even for the smallest wires (100 nm) and dots (250 nm) which were studied.

Comparison of monomer and polymer resists in thermal nanoimprint lithography

In this article, the authors compare a polymer resist to a thermally curable monomer resist in a full 8in. wafer thermal nanoimprint lithography process. Using exactly the same imprinting conditions, the authors compare the printing quality and investigate the resist distribution through large area gratings (6×6mm2) with various densities. It is shown that a liquid monomer solution greatly enhance the printing uniformity because of a much wider resist redistribution and flow during the process. Redistribution of the monomer resist is observed over an entire grating, while it is observed only over a few periods of a grating for the polymer in the same conditions. Furthermore, a low molecular weight resist allows reducing the imprinting force as well as the total cycle time.

Photoluminescence of CdTe / ZnTe semiconductor wires and dots

Arrays of wires and dots have been fabricated by electron beam lithography and Ar+ ion beam etching from CdTe / ZnTe quantum wells. The intrinsic exciton photoluminescence recombination (X line) is observed for wires (dots) as small as 100 nm (130 nm). In addition, photoluminescence intensity from excitons bound to localized centres (Y line) can be detected for the smallest wires (40 nm) and for the dots down to 100 nm. The emission intensity variation together with the polarization rate are also investigated as a function of the grating period.

Flat-top and patterned-topped cone gratings for visible and mid-infrared antireflective properties

Achieving a broadband antireflection property from material surfaces is one of the highest priorities for those who want to improve the efficiency of solar cells or the sensitivity of photo-detectors. To lower the reflectance of a surface, we are concerned with the study of the optical response of flat-top and patterned-topped cone shaped silicon gratings, based on previous work exploring pyramid gratings. Through rigorous numerical methods such as Finite Different Time Domain, we first designed several flat-top structures that theoretically demonstrate an antireflective character within the middle infrared region. From the opto-geometrical parameters such as period, depth and shape of the pattern determined by numerical analysis, these structures have been fabricated using controlled slope plasma etching processes. In order to extend the antireflective properties up to the visible wavelengths, patterned-topped cones have been fabricated as well. Afterwards, optical characterizations of several samples were carried out. Thus, the performances of the flat-top and patterned-topped cones have been compared in the visible and mid infrared range.

Benchmarking of 50 nm features in thermal nanoimprint

The objective of this benchmarking is to establish a comparison of several tools and processes used in thermal NIL with Si stamps at the nanoscale among the authors’ laboratories. The Si stamps have large arrays of 50nm dense lines and were imprinted in all these laboratories in a ∼100nm thick mr-18010E film. Other materials, such as mr-17010E, were also tested. Good patterns were obtained and some limitations were identified. Reducing the pressure to 15bars enables the printing of 50nm structures without pulling them off. At higher pressures, some bending effects resulting in pattern deformation were observed. It was proven that a pressure of 1.5bars is sufficient to imprint perfect 50nm lines. The influence of the antiadhesive layer and mold design has been characterized by the demonstration of pulled off lines in some cases. Moreover, it has been shown that the scatterometry method is particularly useful for the characterization of 50nm lines and that the residual layer thickness corresponds to the the...

Photopolymerization kinetic study of UV nanoimprint lithography dedicated resists

This article reports on the properties of ultraviolet nanoimprint lithography dedicated imprinting materials. Studied solutions are composed of a diacrylate-based monomer and a variable amount (1%, 2%, and 4% in weight) of three different photoinitiators from Ciba Specialty Chemicals (Irgacure 819, Irgacure OXE02, and Irgacure 379). Photopolymerization kinetic studies were conducted on these solutions. Quantity and type of photoinitiator could be optimized in order to obtain a polymerization rate higher than 95% with an exposure dose as low as 20mJ∕cm2. The etch resistance of this home-developed imprinting resist was characterized under standard plasma etching conditions. We observed that the polymerization rate has a large influence on the plasma etch resistance, and we show that the etch rates of our best material is comparable to the one measured for 193nm photolithography resists and makes it a very good candidate as a masking layer for direct pattern transfer.

CdTe quantum wires achieved by strain-induced lateral confinement

Abstract Nanometer-scale CdTe quantum wires have been fabricated using a two step epitaxial growth process. Modulation of the in-plane lattice constant of a [110] CdTe CdZnTe quantum well grown over a [001] CdTe CdZnTe strained superlattice laterally confines the carriers to one dimension. The photoluminescence of these quantum wires presents a large energy shift relative to the unmodulated [110] quantum well (QW) which is strongly dependent on the excitation density. The results compare very well with a theoretical model assuming no relaxation in the structure. With this calculation, the dependence on excitation density of the wire exciton transition energy can be explained by taking into account the lateral piezoelectric field present in these strained modulated [110] structures.

Influence of mold depth on capillary bridges in nanoimprint lithography

Nanoimprint lithography (NIL) processes are often plagued by different kinds of defects. The so-called capillary bridge is related to capillary forces between the stamp surface and the polymer during the pressing process. These defects affect both the printed and unprinted areas of the polymer film. Implementation of NIL as an industrial process requires that these defects be understood and minimized. As such, establishing a relationship between capillary bridge growing and pressing conditions, specifically the mold to polymer distance, is a key step. Two NIL stamps with various feature depths (12–224nm) were studied in this work to establish a link between bridge formation and mold filling. Printing processes were performed using small forces to guarantee contact between the mold and resist without totally filling stamp cavities. The resulting capillary bridges were characterized as a function of cavity depth and printing temperature. Results indicate that the number of defects is strongly influenced by ...