Dendrimer-Based Self-Assembled Monolayers as Resists for Scanning Probe Lithography

Abstract

The feature sizes of microelectronic circuitry components fabricated by current photolithographic processes are ultimately limited by the wavelength of the exposing radiation used for photochemical transformations. In the pursuit to develop faster and smaller semiconductor devices, both new materials and lithographic processes for nanofabrication are currently under exploration by industry and academia alike. The highest possible resolution is of the order of the size of the individual pixels that compose the image. Therefore, to obtain patterns with nanometer scale resolution, a lithographic process should manipulate materials made from molecules with dimensions no larger than the desired pixel size.We are currently exploring the use of dendrimer-based monolayers as resists for scanning probe lithography (SPL). The well-characterized globular and monodisperse properties of dendrimers make them ideally suited for selfassembly on a surface. [1±4] Due to their compact size, the ultra-thin films formed from dendrimers have a thickness much less than can be obtained by spin-coating ordinary linear polymers. In addition, we have observed that the dendritic monolayers are more stable than the analogous monolayers consisting of low molecular weight alkylsilanes. This may be due, in part, to the polymeric and dense nature of dendrimers, resulting in better protection of the anchoring group.The scanning probe microscope (SPM) has recently been shown to be a versatile tool for nanolithography. The SPM may be used for the anodization of passivated metal surfaces, [5±12] or it can act as a low energy electron source for patterning organic polymer thin films. [13±16] The scanning probe has also been used to pattern both organosilane [17] and alkanethiolate [18] monolayers on silicon and gold, respectively. We have been investigating the possibility of using ultra-thin polymeric films, such as dendrimer monolayers, as resists for SPL. Such resists might be attractive for SPL since a post-exposure wet development step would not be required prior to etching.We have investigated the properties of monolayers and ultra-thin films formed from poly(benzylether) dendrimers, [19,20] terminated with both benzyl and tert-butyldiphenylsilyl ether groups (Fig. 1), because of their relative ease of preparation and derivatization. We report here our studies on dendritic monolayer formation via covalent attachment to a silicon substrate and the lithographic patterning of these monolayers using SPL. Fig. 1. Structures of two poly(benzylether) dendrimers, terminated with both benzyl and tert-butyldiphenylsilyl ether groups.Both the benzyl ether terminated dendrons [20] (1a) and the silyl ether terminated dendrons [21] (1b) were prepared according to previously reported procedures. For the covalent attachment to the silicon wafer surface, the benzylic alcohol functionality of the dendrons was first acylated with 10-undecenoyl chloride to give esters 2a,b (Scheme 1). Platinum-catalyzed hydrosilylation of the terminal olefin with either mono-or...

Dendrimers and supramolecular chemistry

“…Because of their unique properties, dendrimer monolayers are finding a number of applications from surface-confined chemical sensor arrays (54,55) or affinity biosensors (62,63) to resists for nanolithography (60,61). Kim and coworkers' (62, 63) electrochemical biosensing device uses cyclic voltammetry to detect the avidin-biotin interaction by monitoring the redox properties of free glucose oxidase in a glucosecontaining electrolyte solution.…”

“…Dendrimer self-assembled monolayers, attached either covalently or ionically onto a silicon surface, have been used successfully as resist materials for nanolithography (60,61) (Fig. 8).…”

Novel Organic Resists for Nanoscale Imaging. From Chemically Amplified Cycloaliphatic Resists to Dendrimer Monolayer.

“…Higher applied voltages at constant scan speeds produced wider, taller lines, while increasing the scan speed at a given voltage usually produces narrower lines. Despite limitations imposed by our un-optimized tip (much larger that the dendrimer molecules themselves) and lithographic conditions, sub-100 nm features were demonstrated in our preliminary work (15). The dendrimer monolayer may be used as an etch resistant layer under aqueous hydrofluoric acid etching conditions (60 seconds in 1 M aqueous HF) in order to selectively remove the patterned oxide relief features.…”

“…As shown schematically in Figure 6, removal of the raised oxide relief features affords a positive tone image. We have demonstrated [15] …”

Biomolecular Materials. Report of the January 13-15, 2002 Workshop

“…For example, random copolymers obtained from a generic vinyl monomer and a dendritic macromonomer might provide a unique template along the polymer backbone capable of spatial assembly and organization of functional structures that have been linked to them. The preparation of a random styrenic copolymer with dendritic pendant groups has been demonstrated (Hawker 1992) as has the preparation of similar copolymers with pendant dendrons functionalized with easily removable protecting groups (Tully et al, 1999) for further synthesis.…”