C. Perret

Mold deformation in nanoimprint lithography

In nanoimprint lithography (NIL), one of the key points to be addressed is the printing uniformity on large area. During the process, the silicon mold undergoes significant mechanical stress of different kinds (tension, compression, flexion, and torsion). These stresses are function of the mold design and appear under the concurrent influence of both the applied pressure on the backside of the mold and an opposite force due to the polymer viscoelastic behavior. This translates into non-negligible deformations within patterned or unpatterned zones. This is a major issue because it causes nonuniformity of the printing, mold pattern break and degradation of the polymer surface. In this article, we demonstrate that during the imprint process mold deformations really occur at the local scale of the patterns but also at a larger scale.

Influence of pattern density in nanoimprint lithography

Polymer selection and critical dimension control 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. In this work, three different polymers have been evaluated. The influence of the temperature and pressing time is analyzed to clarify the correlation between polymer behavior and printing uniformity as a function of the pattern density. Measurements of the polymer residual thickness show that the printing uniformity is strongly correlated with the thermal properties of the polymer.

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.

Measurement of residual thickness using scatterometry

Nanoimprint lithography (NIL) processes have the characteristic that a residual resist layer is always present between the nanoimprinted features. This residual resist layer must be removed to obtain usable resist masks for pattern transfer. As this resist layer is removed using oxygen-based plasma processes, the residual thickness nonuniformity translates into feature width dispersion. Thus, the uniformity of this residual thickness after imprint remains an important issue for nanoimprint lithography and a reliable metrology procedure is required for. At present, the standard measurement method is based on scanning electron microscopy (SEM) cross section, which is destructive, time consuming, and may sometimes provide only moderate accuracy. The work presented here will assess and show the interest of scatterometry, which is a nondestructive optical method of metrology that can be easily applied to NIL. This measurement procedure exhibits very good accuracy on the two-dimensional-feature geometry determi...

Nanoimprint lithography processes on 200mm Si wafer for optical application: Residual thickness etching anisotropy

It is well known that one limitation of thermal nanoimprint lithography is the difficulty to imprint simultaneously nano- and microstructures because of the resulting different residual layer thicknesses, which induce a very poor control of the pattern sizes during the etching steps. Line gratings with densities varying from 1 to 15 have been imprinted on 8in. wafers. The residual thickness varies from 38to158nm. Different plasma chemistries have been studied for the etching of the residual layer. The patterns have been characterized after the imprint and the etching steps by scatterometry. The results show that some chemistries are very promising for the control of the patterns during the etching step. A O2/C12/Ar process has been particularly studied, and it has been demonstrated that it presents a very high anisotropy, which allows the use of long etching times in order to remove the residual layer in gratings with various densities with no variation of the critical dimension.

Influence of residual solvent in polymers patterned by nanoimprint lithography

In nanoimprint lithography, one of the key points to be addressed is the printing uniformity. The limitation of the printing temperature is also of great importance to develop this technology for industrial applications. The thermal behavior of a commercial resist is characterized and related to the printing performance of the polymer. It is shown that the plasticizing effect of the solvent contained in the commercial resist decreases the glass transition temperature of the polymer (Tg) and favors a deeper penetration of the mold into the polymer at a specified printing temperature. We also demonstrate that the control of the residual solvent in the polymer can favor a better pattern uniformity and a decrease of the printing temperature.

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.

Influence of thermal properties of polymers on NanoImprint Lithography performance

Nanoimprint lithography (NIL) is a promising technique to obtain nanometer scale features on large size wafers. The patterns defined in a silicon mold are replicated by pressing a polymer film at high temperature. Previous studies have been mostly devoted to PMMA imprinting. Due to the low etch resistance of this polymer, a lift off step is needed to be able to transfer the patterns by plasma etching,. In this paper, we present results obtained with different polymers presenting a good etching resistance. They will be compared in terms of printed resolution and thermal properties.

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 ...

Nano-imprint of sub-100-nm dots and complex shape features on 8-inch wafer: influence of layout design

Sub 100 nm resolution on 200 mm silicon stamp have been hot embossed into commercial Sumitomo NEB 22 resist. A single dot pattern, exposed with electron beam lithography, has been considered to define the stamp and make thus possible to point out the impact of stamp design onto the printing. Moreover, more complex shapes (triangular, elliptic, random...) with sub 200 nm resolution with and without uniform surrounding frame have been also designed. A large scale of initial resist thickness, from 56 nm to 506 nm, has been printed to assess the effect of polymer flow properties onto the stamp cavities filling and the printed defects. The impact of the pattern symmetry breakdown onto defect generation is clearly shown in this paper in the printed areas as well as in the unprinted areas.