Negative PMMA as a high-resolution resist - the limits and possibilities

Hoole, A. C. F.; Welland, Mark E.; Broers, A. N.

doi:10.1088/0268-1242/12/9/017

Cited by 74 publications

(58 citation statements)

References 6 publications

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“…At low exposure doses, the scission process dominates, allowing PMMA to be used as a positive tone e-beam resist. At high [26]. Reprinted with permission from [26].…”

Section: Organic Resistsmentioning

confidence: 99%

“…In general, this negative tone is not often used due to the high exposure dose that is required to initiate it. Hoole et al [26] wrote lines approximately 15 nm wide at a 30 nm pitch in a 40 nm thick PMMA negative tone resist using an acceleration voltage of 300 keV and a 10 pA beam current. The line exposure doses (185 nC cm −1 ) were almost 100 times higher than the ones usually used for positive tone PMMA.…”

Section: Organic Resistsmentioning

confidence: 99%

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Resists for sub-20-nm electron beam lithography with a focus on HSQ: state of the art

2009

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In the past decade, the feature size in ultra large-scale integration (ULSI) has been continuously decreasing, leading to nanostructure fabrication. Nowadays, various lithographic techniques ranging from conventional methods (e.g. photolithography, x-rays) to unconventional ones (e.g. nanoimprint lithography, self-assembled monolayers) are used to create small features. Among all these, resist-based electron beam lithography (EBL) seems to be the most suitable technique when nanostructures are desired. The achievement of sub-20-nm structures using EBL is a very sensitive process determined by various factors, starting with the choice of resist material and ending with the development process. After a short introduction to nanolithography, a framework for the nanofabrication process is presented. To obtain finer patterns, improvements of the material properties of the resist are very important. The present review gives an overview of the best resolution obtained with several types of both organic and inorganic resists. For each resist, the advantages and disadvantages are presented. Although very small features (2-5 nm) have been obtained with PMMA and inorganic metal halides, for the former resist the low etch resistance and instability of the pattern, and for the latter the delicate handling of the samples and the difficulties encountered in the spinning session, prevent the wider use of these e-beam resists in nanostructure fabrication. A relatively new e-beam resist, hydrogen silsesquioxane (HSQ), is very suitable when aiming for sub-20-nm resolution. The changes that this resist undergoes before, during and after electron beam exposure are discussed and the influence of various parameters (e.g. pre-baking, exposure dose, writing strategy, development process) on the resolution is presented. In general, high resolution can be obtained using ultrathin resist layers and when the exposure is performed at high acceleration voltages. Usually, one of the properties of the resist material is improved to the detriment of another. It has been demonstrated that aging, baking at low temperature, immediate exposure after spin coating, the use of a weak developer and development at a low temperature increase the sensitivity but decrease the contrast. The surface roughness is more pronounced at low exposure doses (high sensitivity) and high baking temperatures. A delay between exposure and development seems to increase both contrast and the sensitivity of samples which are stored in a vacuum after exposure, compared to those stored in air. Due to its relative novelty, the capabilities of HSQ have not been completely explored, hence there is still room for improvement.Applications of this electron beam resist in lithographic techniques other than EBL are also discussed. Finally, conclusions and an outlook are presented.

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“…At low exposure doses, the scission process dominates, allowing PMMA to be used as a positive tone e-beam resist. At high [26]. Reprinted with permission from [26].…”

Section: Organic Resistsmentioning

confidence: 99%

Section: Organic Resistsmentioning

confidence: 99%

Resists for sub-20-nm electron beam lithography with a focus on HSQ: state of the art

2009

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“…11,19,20 The resulting nanowires are n-type, similar to ZnO in bulk or thin films. [15][16][17] Our technique (Figure 1) relies on the use of poly(methyl methacrylate) (PMMA) 22 as a negative resist 12,13 and electrically insulating layer. PMMA is commonly used as a positive resist for high-resolution electron-beam (e-beam) lithography.…”

mentioning

confidence: 99%

Broadband ZnO Single-Nanowire Light-Emitting Diode

Bao¹,

Zimmler²,

Capasso³

et al. 2006

Nano Lett.

534

285

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We present a novel technique for reliable electrical injection into single semiconductor nanowires for light-emitting diodes and lasers. The method makes use of a high-resolution negative electron-beam resist and direct electron-beam patterning for the precise fabrication of a metallic top contact along the length of the nanowire, while a planar substrate is used as a bottom contact. It can be applied to any nanowire structure with an arbitrary cross section. We demonstrate this technique by constructing the first zinc oxide single-nanowire light-emitting diode. The device exhibits broad sub-bandgap emission at room temperature.Semiconductor devices are found in a myriad of technological applications. These devices were made possible with the development of planar fabrication techniques, which allowed for the accurate control of their physical dimensions and, more importantly, their reproducibility. Semiconductor nanowire structures are now emerging as promising candidates for even further miniaturization, opening the door to interesting new functionalities. 1,2 A powerful hybrid approach for engineering their optical properties by means of lithographic techniques has been reported recently. 3 However, electrical injection into nanowires still remains a technical challenge. 4 In this Letter, we address this issue by demonstrating a new method for achieving reliable electrical injection into a semiconductor nanowire. We show the potential of this technique by constructing the first zinc oxide (ZnO) singlenanowire light-emitting diode (LED). Previous studies on ZnO nanowire LEDs were carried out on large numbers of nanowires simultaneously by defining a metallic contact on a thin film of nanowires. 5,6 ZnO is a large band-gap (E g ) 3.35 eV at 300 K) 7 semiconductor, with several desirable properties for nanowire laser diodes and LEDs, among many other applications. 5,6,[8][9][10] In particular, the high exciton binding energy (60 meV), which is the result of a strong Coulomb interaction between electrons and holes, causes an enhancement of the radiative transition rate in the ultraviolet (UV) part of the spectrum. 9,10 Furthermore, the electronic and optical properties of ZnO nanowires can be tailored by altering the growth conditions, as well as by appropriate post-growth treatment. 11 For example, as-made ZnO nanowires grown on sapphire substrates exhibit a prominent near band-edge UV peak, whereas nanowires grown on graphite flakes exhibit broad subbandgap luminescence. 11 In addition, a single ZnO nanowire can form a resonant cavity with two naturally faceted hexagonal end faces acting as reflecting mirrors. 9 The ZnO nanowires used in this study were grown by vaporizing and condensing a mixture of ZnO and graphite powder on carbon cloth. 11,19,20 The resulting nanowires are n-type, similar to ZnO in bulk or thin films. [15][16][17] Our technique (Figure 1) relies on the use of poly(methyl methacrylate) (PMMA) 22 as a negative resist 12,13 and electrically insulating layer. PMMA is commonly used as a ...

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“…Consequently, the highest spatial frequency that can be recorded in the recording medium sets a limit to the NA. To avoid this limitation the holograms were recorded in a high resolution photoresist, PMMA, that has the spatial resolution of ~ 10nm for e-beam exposure (Hoole et al, 1997, Yamazaki et al, 2004. The spatial resolution of the hologram is also limited by spatial and temporal coherence of illumination source and by digitization process.…”

Section: Coherence Limitation To the Spatial Resolution In Euv Hologrmentioning

confidence: 99%

Two and Three Dimensional Extreme Ultraviolet Holographic Imaging with a Nanometer Spatial Resolution

Wachulak¹,

Marconi²

2011

Advanced Holography - Metrology and Imaging

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Negative PMMA as a high-resolution resist - the limits and possibilities

Cited by 74 publications

References 6 publications

Resists for sub-20-nm electron beam lithography with a focus on HSQ: state of the art

Resists for sub-20-nm electron beam lithography with a focus on HSQ: state of the art

Broadband ZnO Single-Nanowire Light-Emitting Diode

Two and Three Dimensional Extreme Ultraviolet Holographic Imaging with a Nanometer Spatial Resolution

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