Characterization of an ultra high aspect ratio electron beam resist for nano-lithography (original) (raw)

High-energy Electron Beam Lithography for Nanoscale Fabrication

Lithography, 2010

Lithography 242 substrates. The electron scattering process depends greatly on incident electron energy and resist/substrate properties and is a very complex issue; thus the resultant energy-intensity distribution in the resist has to be calculated using Monte Carlo simulation. The calculated distribution is of Gaussian shape, and the contribution of secondary-electron exposure is exponentially suppressed with increased incident beam energy. Due to the long penetration depth in the resist, high-energy EBL allows for the exposure of very thick resists, which are useful for forming nanostructures with large height-to-width ratios. In multi-layer resists of different exposure sensitivities, the linewidth of each layer can be controlled separately by adjusting the development time and by using different developers after a single e-beam exposure. It will be shown that even after many development steps; the linewidth in the top layer remains unchanged. Precise control of the lower layers' linewidths makes the fabrication of sophisticated three-dimensional (3D) structures possible. In this chapter, we will first give an introduction to the state-of-the-art high-energy EBL technique. This will be followed by discussions on electron-optics, Monte-Carlo calculations of energy-intensity distribution, resist profile engineering, and mix-and-match techniques. Finally, we will give some examples to illustrate fabrications of nanoscale electronics and 3D structures, and discuss issues that have to be taken into account when using a 100keV EBL system.

Computer simulation of resist profiles at electron beam nanolithography

Microelectronic Engineering, 2010

In this paper, resist behavior peculiarities in nanolithography is studied. Experimental data for the development rate dependence on the exposure dose is presented and used for numerical simulation of the developed profiles at electron beam nanolithography (EBL). These data concerns the most important nanolithography organic resist – polymethyl methacrylate (PMMA), chemically amplified resist CAMP6 and for the inorganic resist hydrogen silsesquioxane (HSQ). For a study of the nonlinear resist behavior during the development process, simulated resist profiles in the case of delay effect for penetration of the developer in the fresh resist material are discussed. The results are obtained using a universal approach for computer simulation of predicted profiles. It is concluded that such an effect will decrease the average rate of development and could be observed only in the side wall shape of the developed profile.

A General Approach to Semimetallic, Ultra-High-Resolution, Electron-Beam Resists

Commercial electron-beam resists are modified into semi-metallic resists by doping with 1–3nm metal nanoparticles, which improve the resolution,contrast, strength, dry-etching resistance, and other properties of the resist. With the modified resists, fine resist nanopatterns from electron-beam lithography are readily converted into 5–50 nm, high-quality multilayers for metallic nanosensors or nanopatterns via ion-beam etching. This method solves the problem of the fabrication of fine (<50 nm) metallic nanodevices via pattern transferring.

Tuning the Performance of Negative Tone Electron Beam Resists for the Next Generation Lithography

Advanced Functional Materials

A new class of electron bean negative tone resist materials has been developed based on heterometallic rings. The initial resist performance demonstrates a resolution of 15 nm half-pitch but at the expense of a low sensitivity. To improve sensitivity a 3D Monte Carlo simulation is used that utilizes a secondary and Auger electron generation model. The simulation suggests that the sensitivity can be dramatically improved while maintaining high resolution by incorporating appropriate chemical functionality around the metal-organic core. The new resists designs based on the simulation have the increased sensitivity expected and illustrate the value of the simulation approach.

High resolution electron beam lithography using ZEP-520 and KRS resists at low voltage

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1996

ZEP-520 and KRS resist systems have been evaluated as candidates for use in low voltage electron beam lithography. ZEP-520 is a conventional chain scission resist which has a positive tone for over two orders of magnitude in exposure dose. KRS is a chemically amplified resist which can be easily tone reversed with a sensitivity ϳ8 C/cm 2 at 1 keV. Both resist systems are shown to have sensitivities ϳ1 C/cm 2 for positive tone area exposures to 1 keV electrons. A decrease in contrast in 50 nm thick resist layers is seen when exposure voltage is lowered from 2 to 1 keV, indicating nonuniform energy deposition over the resist thickness. High resolution single pass lines have been transferred into both Si and SiO 2 substrates at both low and high voltages in each resist system without using multilayer resist masks. The ZEP-520 and KRS resists are shown to have resolutions of 50 and 60 nm, respectively, at 1 kV, within a factor of 2 of their high voltage resolutions under identical development conditions. A cusp shaped etch profile in Si allows high aspect ratio 20 nm wide trenches to be fabricated using these resists on bulk Si. Low voltage exposures have been used to pattern gratings with periods as small as 75 and 100 nm in ZEP-520 and KRS, respectively. Low voltage exposures on SiO 2 show no indications of pattern distortion due to charging or proximity effects.

Electron beam lithography—Resolution limits

Microelectronic Engineering, 1996

Electron beam lithography is generally accepted to have the highest practical resolution capability. In this paper the state of the art in terms of resolution is reviewed. This covers conventional resists such as PMMA, contamination resist, inorganic resists and damage processes. Some insights into the resolution limiting factors are given although the precise limitations still remain unclear. Consideration is also given as to the best measure of resolution and it is suggested that the minimum line spacing is a more appropriate and less subjective measure than minimum achievable feature size.