An official website of the United States government
Variable-pressure electron-beam lithography (VP-EBL) employs an ambient gas at subatmospheric pressures to reduce charging during electron-beam lithography. VP-EBL has been previously shown to eliminate pattern distortion and provide improved resolution when patterning poly(methyl methacrylate) (PMMA) on insulating substrates. However, it remains unknown how water vapor affects the contrast and clearing dose nor has the effect of water vapor on the negative-tone behavior of PMMA been studied. In addition, water vapor has recently been shown to alter the radiation chemistry of the VP-EBL process for Teflon AF. Such changes in radiation chemistry have not been explored for PMMA. In this work, VP-EBL was conducted on conductive substrates to study the effect of water vapor on PMMA patterning separately from the effects of charge dissipation. In addition, both positive and negative-tone processes were studied to determine the effect of water vapor on both chain scission and cross-linking. The contrast of PMMA was found to improve significantly with increasing water vapor pressure for both positive and negative-tone patterning. The clearing dose for positive-tone patterning increases moderately with vapor pressure as would be expected for electron scattering in a gas. However, the onset set dose for negative-tone patterning increased dramatically with pressure revealing a more significant change in the exposure mechanism. X-ray photoelectron spectra and infrared transmission spectra indicate that water vapor only slightly alters the composition of exposed PMMA. Also, electron scattering in water vapor yielded a much larger clear region around negative-tone patterns. This effect could be useful for increasing the range of the developed region around cross-linked PMMA beyond the backscattered electron range. Thus, VP-EBL for PMMA introduces a new means of tuning clearing/onset dose and contrast, while allowing additional control over the size of the cleared region around negative-tone patterns.
more »
« less
Effect of water vapor pressure on positive and negative tone electron-beam patterning of PMMA
Variable Pressure - Electron Beam Lithography was conducted to study the effect of water vapor pressure on patterning PMMA. Water vapor does not appear to alter the radiation chemistry of positive-tone exposure. However, water vapor does alter the negative tone behavior in a manner consistent with simultaneous cross-linking and etching.
more »
« less
- Award ID(s):
- 2135666
- PAR ID:
- 10481218
- Publisher / Repository:
- https://eipbn.org/abstracts
- Date Published:
- Journal Name:
- The 65th International Conference on Electron, Ion and Photon Beam Technology and Nanofabrication
- Format(s):
- Medium: X
- Location:
- New Orleans, LA
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Radiolysis is a complex phenomenon in which molecules subjected to ionizing radiation form new chemical species. Electron-beam irradiation has proven to be a versatile approach for significantly altering materials’ properties and forms the basis for electron-beam lithography using both organic and inorganic resists. Electron-beam exposure is normally carried out under high vacuum conditions to reduce contamination and allow for unhindered interaction between the electrons and the resist material. Exposure under an ambient gas at sub-atmospheric pressures has been found to provide a distinct mechanism which can be exploited to circumvent some of the challenges associated with material processing and significantly alter or enhance material’s properties. This dissertation discusses the modifications in standard electron beam resist characteristics during gas assisted electron beam pattering. We studied the effect of water vapor pressure on positive and negative tone electron-beam patterning of poly methyl methacrylate (PMMA). For both positive and negative-tone patterning, it was found that increasing the water vapor pressure considerably improved the contrast of PMMA. As expected from electron scattering in a gas, the clearing dosage for positive tone patterning gradually increased with vapor pressure. Also, electron scattering in water vapor yielded a substantially larger clear region around the negative-tone patterns. This effect could be useful for increasing the range of the developed region around cross-linked PMMA far beyond the backscattered electron range. As a result, VP-EBL for PMMA offers a new means of tuning clearing/onset dose and contrast while enabling more control over the size of the cleared region around negative-tone patterns. We provide a novel way to simultaneously tune the emission wavelength and enhance the fluorescence intensity of fluorophores formed by irradiating polystyrene with a focused electron beam under various gaseous environments. We studied the effect of electron dose and gas pressure on the emission spectra and photon yield of irradiated polystyrene film on a variety of substrates. Up to 10x enhancement in fluorescence yield was achieved using water vapor and the peak emission wavelength tuned over a wide wavelength range. Thus, localized electron-beam synthesis of fluorophores in polystyrene can be controlled by both dose and by ambient water-vapor pressure. This technique could enable innovative approaches to photonics where fluorophores with tunable emission properties can be locally introduced by electron-beam patterning. We also studied the effect of ambient gases on contrast and resolution of PMMA on conducting and insulating substrates. E-beam exposures were conducted under vacuum conditions and 1 mbar of water vapor, helium, nitrogen and argon to study their effect on contrast and resolution of PMMA on silicon, fused silica and soda lime glass substrates. On silicon, exposure under water vapor yielded contrast values significantly higher than vacuum exposure, consistent with our previous work. However, exposure under helium yielded slightly improved contrast compared to vacuum exposure. On insulating substrates exposure under helium environment yielded contrast values significantly higher compared to vacuum exposure. The clearing dose was found to increase with the gases’ molecular weight and proton number, consistent with the increase in scattering cross-section. The improved contrast and sensitivity (dose to clear) of PMMA under helium motivated us to study the resolution under various gases. Resolution testing indicated that despite the lower clearing dose, helium still exhibited the best resolution with 25-nm half-pitch dense lines and spaces clearly resolved on soda lime glass. Thus, VP-EBL of PMMA under helium yields higher sensitivity and contrast on insulating substrates without sacrificing resolution.more » « less
-
Thermal evaporation is an important technique for fabricating methylammonium lead iodide (MAPbI3), but the process is complicated by the need to co-evaporate methylammonium iodide (MAI) and PbI2. In this work, the effect of water vapor during the thermal deposition of MAPbI3 was investigated under high vacuum. The evaporation process was monitored with a residual gas analyzer (RGA), and the film quality was examined with X-ray photoelectron spectroscopy (XPS). The investigations showed that during evaporation, MAI decomposed while PbI2 evaporated as a whole compound. It was found that the residual water vapor reacted with one of the MAI-dissociated products. The higher iodine ratio suggests that the real MAI flux was higher than the reading from the QCM. The XPS analysis demonstrated that the residual water vapor may alter the elemental ratios of C, N, and I in thermally deposited MAPbI3. Morphologic properties were investigated with atomic force microscopy (AFM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). It was observed that a sample grown with high water vapor pressure had a roughened surface and poor film quality. Therefore, an evaporation environment with water vapor pressure below 10−8 Torr is needed to fabricate high quality perovskite films.more » « less
-
Abstract We investigate how climate, clouds, and convection change as the amount of water vapor in the atmosphere is varied by altering the saturation vapor pressure (SVP) by a constant in a one-dimensional climate model. We identify four effects of altering SVP on clouds in an Earthlike climate with distinct layers of low and high clouds. First, the anvils of high clouds get higher as SVP is increased (and vice versa) because they are bound by radiative constraints to occur at a lower temperature. The vapor pressure path above the cold anvils does not change in Earthlike climates. Second, low clouds get lower as SVP increases (and vice versa) because they are coupled to a convective boundary layer (CBL) that shallows primarily from an increase in the tropospheric static stability. The third and fourth effects follow from the first two, namely, that single-layer cloud states exist both in vapor-poor states with a merged cloud deck and vapor-rich states with an elevated cloud deck. We identify two cloud instability parameters that determine the transitions between single- and double-layer cloud regimes. Qualitatively, sufficiently vapor-poor states have a deep, diffusive layer that overlaps with a weaker convective layer (topping out at the tropopause) that cannot maintain low relative humidity in the midtroposphere through the drying of descending air, thus causing the cloud layers to merge. Sufficiently vapor-rich states lose their low clouds as the shallowing CBL drops below the lifting condensation level.more » « less
-
Abstract This study describes an apparatus for high-precision variable temperature measurement of liquid vapor pressure. The apparatus can be used to measure the vapor pressure using only 0.5 ml of the liquid sample. To evaluate the accuracy of the device measurement, water and 2-propanol are utilized as standard liquids, and their vapor pressure is measured with a maximum uncertainty of ∼1%. This apparatus can be replicated using inexpensive and commonly used laboratory fittings and fixtures, making it an indispensable tool for synthetic chemists and chemical engineers involved in the iterative synthesis of compounds, targeting different vapor–liquid equilibrium regimes.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- The DOI is not currently available.
