Augustin Jeyakumar

A new nanocomposite resist for low and high voltage electron beam lithography

A novel nanocomposite photoresist was synthesized and characterized for use in both low and high voltage electron beam lithography. This resist system is shown to display the ideal combination of both enhanced etch resistance and enhanced sensitivity required to satisfy both low and high voltage patterning applications. Resist sensitivity was enhanced by the direct incorporation of a photoacid generating monomer into the resist polymer backbone while the etch resistance of the material was improved by copolymerization with a POSS containing monomer.

Low cost RF MEMS switches using photodefinable mixed oxide dielectrics

This paper presents the design, fabrication and testing of capacitive RF MEMS switches with a new, low processing cost dielectric layer on high-resistivity silicon substrate. The dielectric can be spun on the wafer and its parameters (dielectric constant and loss) can be controlled during fabrication to achieve the desired values. Both bridge- and cantilever-type switches were fabricated on high-/spl rho/ silicon substrate using a simple low cost four-mask process. Measured results are presented.

Electron beam lithography process using radiation sensitive carboxylate metalorganic precursors

A bilayer process has been developed for electron beam lithography using radiation sensitive metalorganic precursors as imaging layers in conjunction with organic planarizing layers. Upon electron beam irradiation, the precursor is converted to a metal oxide which serves as an etch mask for subsequent pattern transfer through the planarizing layer. In this article, a titanium(n-butoxide)2(2-ethylhexanoate)2 precursor was investigated that exhibits sensitivity and contrast of 495 μC/cm2 and 2.75, respectively, 10 keV accelerating potential. The sensitivity was further enhanced to 72 μC/cm2 using a pre-exposure thermal bake to partially convert the precursor to metal oxide prior to electron beam imaging. Additionally, it was found that combining the titanium(n-butoxide)2(2-ethylhexanoate)2 precursor with a similar precursor containing a higher atomic number metal center, barium(2-ethylhexanoate)2 in this work, also enhanced the sensitivity to 157 μC/cm2 for a 1:1 molar mixture of the precursors. After imagi...

Direct photopatterning of metal oxide materials using photosensitive organometallic precursor films

A novel class of photosensitive organometallic precursor materials is used to pattern thin film mixed-metal oxide structures. In this work a photosensitive organometallic precursor is coated onto a silicon substrate and exposed to ultraviolet light through a mask to form patterned oxide structures. This is a negative-tone process in which the unexposed areas can be washed away using a developer solvent. In this work, lithographic contrast curves were measured to characterize the sensitivity and contrast of thin films composed of a mixture of the organometallic precursors for the oxides barium, strontium and titanium. Experiments directed at finding methods to increase the photo-speed of these materials were also conducted. It was found that partial pre-exposure conversion of these films using thermal baking could be used to enhance the sensitivity of these materials. A pre-exposure bake performed at 150 degrees C for 15 seconds was found to decrease the required exposure dose by a factor of two. Dielectric properties were measured for photochemically converted oxide films via electrical measurements on parallel plate capacitor devices. X-ray photoelectron spectroscopy (XPS) was used to quantify the relative amounts of carbon present in the finished films, and it was determined that thermally processes films had higher levels of carbon contamination.

Material design and evaluation of nanocomposite resist for next generation lithography

A chemically amplified resist, Poly(4-hydroxystyrene-co-tertiarybutylmethacrylate-co-MethacrylphenylPOSS) with different Polyhedral oligosilsesquioxane (POSS) loading has been synthesized by free radical polymerization. The incorporation of POSS units into the resist matrix has been found to affect their RIE resistance in O2 plasma. The thickness of the films were monitored using ellipsometry at various etch intervals to determine the etch rate and selectivity. It was observed that etch rate of these nanocomposite resists were comparable to the standard PHOST and Novolac based resists. HRTEM and HAADF studies showed that the POSS units exhibit a morphology of rectangular crystallites that are responsible for the plasma etch behavior. We have obtained 120 nm (1:1) (Line/Space) feature using 248 nm lithography. The protecting group, tertiary butyl protecting group exhibits acceptable outgassing. Using e-beam lithography, 70nm pattern feature was obtained.

A comparative study between organic and inorganic resists in electron beam lithography using Monte Carlo simulations

A Monte Carlo study has been performed in order to understand the differences in exposure behavior between organic and inorganic electron beam resists. Typically inorganic resists constitute high atomic number species (Z>10) and are of higher density as compared to traditional organic resists such as acrylates. In this work, the consequences of tethering a high atomic number species such as a silicon or titanium atom onto a PMMA molecule on the electron beam energy deposition in the material have been investigated. The addition of these atoms increases the density of the hypothetical film and therefore the number of elastic and inelastic collisions suffered by an incident electron. The larger electron shell density associated with these high atomic number species more effectively shields the nucleus resulting in a larger average elastic scattering angle but the average inelastic scattering angle remains unaffected. The average radial and depth distance traveled by an incident electron decreases with increasing atomic number of the species tethered to the PMMA molecule. The radial and energy distribution of incident electrons in PMMA, HSQ, and a Titanium based metal-organic precursor film have also been compared. At low accelerating potentials, the broadening of the point source electron beam becomes larger with the increasing atomic number of the atoms in the resist material. However, at high accelerating potentials where the average depth distance traveled into the film increases, the point source electron beam broadening is essentially the same for both organic and inorganic films for thin films. Eventually, at large film thicknesses, the radial spread of incident electrons becomes broader in the inorganic films as a consequence of higher density and larger scattering atoms. Also, as a consequence of a larger number of collisions, the absorbed energy density in inorganic films increases, indicating that these materials will more efficiently capture electron beam energy as compared to traditional organic materials.

Enhancing the electron beam sensitivity of hydrogen silsesquioxane (HSQ)

The electron beam sensitivity of hydrogen silsesquioxane (HSQ) has been enhanced by including sensitizers that decompose to generate nucleophiles which catalyze the conversion of the silicon hydride (Si-H) moieties in HSQ into the insoluble siloxane (Si-O-Si) network. In this study, the consequences of including triphenylsulfonium hydroxide (TPS-OH) and 2-nitrobenzyl N-cyclohexylcarbamate (NBC) as a photodecomposable base (PDB) and photobase generator (PBG) were investigated, respectively. It was found that using 5 wt% loadings of TPS-OH or NBC in HSQ in conjunction with a post-exposure bake process enhanced the sensitivity of large features exposed at 25 keV accelerating voltage by approximately 50 and 40 %, respectively. Similarly, the electron beam doses required to print single pixel wide lines exposed at an accelerating voltage of 25 keV were enhanced by 70 and 50%, for 5 wt% loaded TPS-OH or NBC films, respectively. It was also found that the basicity and nucleophilic strength of the sensitizer affects the rate of the undesired hydrolysis reaction of HSQ which occurs in solution. For the sensitizers used in this study, the sterically hindered TPS-OH is a poor nucleophile which stabilized the solution against condensation and formation of a siloxane network, while the moderately nucleophillic NBC slightly decreased the stability of the solution. Also, it was found that thermal baking alone could be utilized to enhance the sensitivity of HSQ, but a drastic loss in contrast was observed. The combination of either TPS-OH or NBC and a post-exposure bake produced superior results, as compared to thermal baking alone, in terms of increasing the sensitivity of HSQ while maintaining good contrast.

Direct Photopatterning of Metal Oxide Structures Using Photosensitive Metallorganics

© 2004 The Electrochemical Society, Inc. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproduced, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS).

Hybrid bilayer imaging approach using single-component metal-organic precursors for high-resolution electron beam lithography

A hybrid bilayer imaging approach has been developed which uses a thin radiation sensitive, single component, metal-organic precursor film in conjunction with a thicker organic planarizing etch barrier. Upon electron beam irradiation, the metal-organic precursors are converted to a metal-oxide etch mask and the pattern can be transferred through the organic etch barrier layer using an oxygen reactive ion etch. These novel precursors can also be converted to the metal-oxide using deep ultraviolet optical irradiation or thermal baking. Therefore, a combination of blanket conversion steps followed by the patterning process can be utilized in order to reduce imaging doses. In this work, results of characterizing a titanium(n-butoxide)2(2-ethylhexanoate)2 precursor are presented due to its combined properties of hydrolytic stability and moderate sensitivity. It was found that using a blanket thermal bake step of 1, 2, and 3 minutes at 150°C prior to electron beam exposure increased the sensitivity of the materials to 200, 90, and 72 µC/cm2 respectively. However, the contrast of the material decreased from 4.40 to 2.17 as a consequence of pre-exposure thermal baking. The etching characteristics of the metal-organic precursor were also studied in ashing and silicon dioxide etching plasmas. It was found that the etch rate in the different plasmas depends strongly on the extent of conversion of the metal-organic film. Films with higher extents of conversion to the metal-oxide provide higher etch resistance in general. The patterning capability with these metal-organic precursors is demonstrated on top of both silicon substrates and hard baked novolac films.

Photodefinable Metal Oxide Dielectrics II: Direct Fabrication of Patterned High-k Dielectrics for Low Cost RF Capacitive MEMS Switches

In this paper, recent advancements related to a novel approach for fabricating low cost capacitive radio frequency microelectromechanical (RF MEMS) switches using directly photodefinable high dielectric constant metal oxides are discussed. In this approach, a radiation sensitive metal-organic precursor is deposited via spin coating and converted patternwise to a metal oxide using exposure to ultraviolet light. The feasibility of this approach has previously been demonstrated by fabricating bridge-type and cantilever-type RF MEMS switches. These early experiments showed that the photopatterned oxides displayed dielectric breakdown strengths that were insufficient for reliable operation of MEMS switches which required actuation voltages on the order of 20 V to 30 V. Recent work has focused on developing advanced processes based on the photodefinable metal-organic approach that can produce oxides with higher dielectric breakdown strengths and higher dielectric constants. A variety of post-patterning processes, including thermal baking and oxygen plasma annealing, were investigated and the impact of such processing on the resulting dielectric properties are discussed in this paper. It is shown that a combination of thermal annealing and oxygen plasma treatment can substantially improve the dielectric breakdown strength of the metal oxides produced using the photosensitive metal-organic process.