Formation of modern integrated circuits, micro- and nanostructures requires lithography resolution of less than 10 nm. The resolution of e-beam lithography is high enough but its throughput is extremely low. Mechanism of dry e-beam etching of resist has lots in common with chemical amplification of resist. It could be one of possible approaches to improve throughput of e-beam lithography. Dry e-beam etching of resist can provide sensitivity increase by a factor of hundreds. As a result, throughput of the e-beam lithography could be increased dramatically. Some structures obtained by the hybrid e-beam lithography (and exposure doses) are presented. For the simulation of electron tracks in PMMA/Si system “direct” Monte Carlo method is applied. In this method, all the dominant processes (elastic scattering, excitation, ionization and secondary electron generation for E < 20 keV) are simulated separately. The results of the simulation are presented.
This paper presents some new results concerning the mechanism, characteristics and feasibility for the suggested by the authors direct method of image formation in some positive resists directly during exposure by the electron beam in a vacuum (dry method of electron-beam etching resist - method DEBER). For PMMA resist as an example it has been shown in particular that the method DEBER very convenient for obtaining a relief micro and nanostructures with a rounded profile cross-section (including spherical, aspheric, sinusoidal etc.) in the PMMA resist. The examples presented of process conditions influence on the form of obtained relief structures. The examples are given to obtain spatial 3Dstructures with good accuracy by Z-axis and with good surface roughness. In general, according to the authors, the data presented indicate significant opportunities for applying the method DEBER, in particular for the manufacture of the optoelectronics elements (diffraction gratings, microlenses, focusers, optical waveguides, anti-reflective coatings, and others.).
KEYWORDS: Scanning electron microscopy, Silicon, Photomasks, Electron microscopes, Integrated circuits, Nanostructures, Electron beams, Etching, Sensors, Atomic force microscopy
We studied the effect of focusing of the electron probe of a scanning electron microscope (SEM), operating in the mode
of collection of slow secondary electrons, on the form of a signal obtained when scanning elements of nanorelief of two
kinds of objects with electron probe: (a) resist masks, and (b) protrusions and trenches on silicon. The shift of the
positions of the points of reference, the distance between which is usually used to determine the size of the relief
elements, was observed. The linear dependence of such distance on the size of the electron probe was found. We
propose a method to measure the width of the nanorelief element, based on the extrapolation of this linear dependence to
the zeroth size of the electron probe. With the help of this method, we measured the widths of nanorelief elements of
resist masks, as well as of protrusions and trenches on silicon.
Dry resistless process was studied of mask image formation by electron beam deposition from hydrocarbon
precursor undecane (C11H24) on substrates of SiO2 (layer 80 nm) on silicon and cupper (layer 430 nm) on silicon. A
mask in form of grating of 5-150 nm height strips was created in a cell introduced into the scanning electron microscope
CamScan. Strips thickness δ was considerably more than the beam size and depended on substrate material: for SiO2
δ=0.6 μm, for Cuδ=2 μm. Strong dependence of growth rate V (at Cu) on the line scan time τ was found out. At beam
current 1.0 nA varying τ from 20 ms to 13 s led to 7.4 times decreasing V. This effect most likely is caused by
significant diffusion delays at τ=13 s in precursor transport into reaction zone during the pixel time. The ion beam
etching of substrates through the deposited mask was carried out. SiO2 substrate was etched by SF6 ions, Cu substrate
was etched by Ar ions. In both cases etching rate of mask material were close to etching rate of substrate. In mask
deposited on SiO2 thin (about 1 nm) intermediate surface layer was found having significantly more (8-10 times)
etching resistance than the basic mask material.
Electron beam polymerization of monomers from vapour phase is advanced method of thin polymer layers (TPL) deposition on solid substrates. The structure features and properties of TPL formed from tetrafluoroethylene and methylmethacrylate vapour at different E-beam current densities were found to be different strongly. In 1-10 μA/cm2 field the low molecular mass PTFE films with tape and disk supramolecular structures formed. These films are low thermostable (to 250-300°C) because of sublimation under heating. Macromolecules in these films are regulated (mesomorphic state). The polymer chain axes are oriented perpendicularly toward substrate surface. In 102-103 μA/cm2 field the films with high thermostability (400-450°C) form. These films are probably crosslinked. In 104-106 μA/cm2 field the amorphous, strongly crosslinked, high thermostable, high uniform films form. Polymethylmethacrylate (PMIMA) films formed at 1-10 μA/cm2 rapidly dissolve in organic solvents. The PMMA films deposited at 102-103 μA/cm2 only swell in organic solvents. The observed differences of structure and properties of films deposited by E-VDP method are caused probably by different balance of chain polymerization and polyrecombination mechanisms in the film deposition processes. In highest current density range the polyrecombination mechanism predominates. In low current density the main mechanism of deposition is the radical-chain polymerization. The results obtained show great possibilities of controlled change of properties of E-VDP films deposited from the same precursor.
Iron based nanocomposites are of great interest in particular because of their magnetic properties. Preliminary results on image deposition from iron dodecacarbonyl by focused electron beam are presented. The specific electric resistance of fabricated lines was measured in the range from 4•10-2to 103 Ω cm dependently on deposition conditions. It was observed, that if the beam current increases, specific resistance sharply decreases. Positive temperature coefficient of conductivity for such material was determined. Effective activation energy of conductivity changed from 3-5kJ/mol for high conductivity lines to 15-25kJ/mol for low conductivity lines. Obtained data are considered on the base of representations of produced lines material as nanoclusters of iron spread in amorphous carbon matrix. The resistance change of deposited lines in media of different vapours and gases was estimated.
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