Alex P. G. Robinson

A Fullerene derivative as an electron beam resist for nanolithography

We have explored the application of chemical derivatives of C60 as high-resolution electron beam resists. Facile spin coating was used to produce ∼100-nm-thick films of a C60 tris adduct (three functional groups) on Si surfaces. We find that these films function as high-resolution negative resists for electron beam lithography using monochlorobenzene as a developer. The film has a sensitivity of ∼1 mC/cm2 for 20 keV electrons, an order of magnitude higher than that of C60 itself, and the dry-etch durability is much better than that of conventional novolac based electron beam resists. Features with widths of 20 nm were produced.

10 nm scale electron beam lithography using a triphenylene derivative as a negative/positive tone resist

We show that the liquid crystal triphenylene derivative 2,3,6,7,10,11-hexapentyl-oxytriphenylene acts as a high-resolution electron beam resist. Using pentanol as a developer, positive behaviour was observed for electron doses greater than ~300µC cm-2 at 20 keV. At higher doses (>2.5 mC cm-2), the resist rapidly assumes negative tone behaviour. With the developer monochlorobenzene, only negative behaviour was observed, with a sensitivity of ~2.5 mC cm-2 at 20 keV. The resist allows relatively facile definition of 14 nm patterns (negative tone) with a 30 keV electron beam and without the need for any complex pre-irradiation preparation or post-irradiation processing of the resist.

Electron beam induced fragmentation of fullerene derivatives

Abstract Spin coating has been used to produce films of various chemical derivatives of C 60 on the hydrogen terminated silicon (100) surface. Irradiation of these films using a 20 keV electron beam has been found to reduce substantially their dissolution rate in organic solvents such as monochlorobenzene and chloroform. Raman and FTIR spectroscopy have shown that the reduced solubility of the derivative films is due to fragmentation of the molecules. The electron dose threshold of the derivative films for fragmentation is between 10 −3 and 10 −2 C/cm 2 , suggesting that these derivatives could be used as electron beam resists.

EXPOSURE MECHANISM OF FULLERENE DERIVATIVE ELECTRON BEAM RESISTS

Abstract We report systematic studies of the response of C60 derivatives to electron beam irradiation. Films of nine different methanofullerene C60 monoadducts, produced by spin coating on Si surfaces, were irradiated with a 20 keV electron beam. All exhibited negative tone resist behaviour with a sensitivity much higher than that of C60. In the case of derivatives with two polyether chains, the sensitivity was found to be linearly dependent upon the derivative mass, consistent with an increasing electron cross-section for larger derivatives. Features with widths of 20 nm were produced using these compounds, and the etch ratios of the compounds were found to be more than twice those of a standard novolac-based resist.

A triphenylene derivative as a novel negative/positive tone resist of 10 nanometer resolution

We show that a triphenylene derivative, 2,3,6,7,10,11-hexapentyl-oxytriphenylene, acts as an electron beam resist of 10-nm resolution with high dry-etch durability. The triphenylene derivative exhibited positive and negative behaviors depending on the dose and developers. When pentanol was used as a developer, positive behavior was observed for electron doses between ~ 3 x 10^-^4 and ~ 1 x 10^-^3 C/cm^2 at 20 keV, and at higher doses, the resist exhibited negative behavior. When monochlorobenzene was used as a developer, only the negative behavior was observed with a sensitivity of 2x 10^-^3 C/cm^2 at 20 keV. Performance of the resists were demonstrated defining 10-nm dots and lines (negative tone), and fabricating a high aspect-ratio Si nanostructure with a single layer process.

Polysubstituted derivatives of triphenylene as high resolution electron beam resists for nanolithography

We have explored the application of polysubstituted derivatives of triphenylene as high resolution, high etch durability electron beam resists. Room temperature spin coating was used to produce films of the derivatives on silicon substrates. Exposure to a 20 keV electron beam was found to alter the dissolution rate of these derivatives in various organic solvents. Doses of between ∼3×10−4 and ∼2.5×10−3 C/cm2 substantially increased the solubility of the derivative hexapentyloxytriphenylene in polar solvents (positive tone behavior). Doses greater than ∼2.5×10−3 C/cm2 led to a decrease in solubility in both polar and nonpolar solvents (negative tone behavior). Other derivatives also demonstrated a reduction in their dissolution rate for doses between ∼1.5×10−3 and ∼6.5×10−3 C/cm2. The etch durabilities of the positive and negative tone patterns were found to be, respectively, ∼25% less and ∼70% greater than that of a conventional novolac based negative tone resist. Line and space patterns were defined in o...

Plasma etching of high-resolution features in a fullerene molecular resist

As resist films become thinner, so as to reduce problems of aspect ratio related pattern collapse at high-resolution, it is becoming increasingly difficult to transfer patterns with useful aspect ratio by directly etching the resist. It has become common to use the photoresist to pattern an intermediate hardmask, which then protects the silicon substrate during etching, allowing useful aspect ratios but adding process complexity. We have previously described a fullerene based electron beam lithography resist capable of 20 nm halfpitch and 12 nm sparse features, at a sensitivity of less than 10 μC/cm2 at 20 keV. The fullerene resist has high etch durability - comparable to that of commercial novolac resists - and has previously demonstrated an etch selectivity of 3:1 to silicon using electron cyclotron resonance microwave plasma etching with SF6. Here a study of the capabilities of this resist when using Inductively Coupled Plasma etching is presented. Line-space patterns with half-pitches in the range 25 nm to 100 nm, together with sparse features (~20 nm linewidth on a 200 nm pitch) were produced in ~30 nm thick resist films using electron beam lithography, and transferred to silicon using an inductively coupled plasma etcher. Several combinations of SF6, CF4, CHF3 and C4F8process gases were explored. Etch selectivity and anisotropy were studied as a range of etching parameters, such as ICP and RF power, gas flow rate, pressure and temperature were varied. Etch selectivities in excess of 9:1 were demonstrated. Techniques for minimizing aspect ratio dependent etching effects in dense features, including the use of ashing or high etching pressures were also examined.

Dynamic absorption coefficients of chemically amplified resists and nonchemically amplified resists at extreme ultraviolet

Abstract. The dynamic absorption coefficients of several chemically amplified resists (CAR) and non-CAR extreme ultraviolet (EUV) photoresists are measured experimentally using a specifically developed setup in transmission mode at the x-ray interference lithography beamline of the Swiss Light Source. The absorption coefficient α and the Dill parameters ABC were measured with unprecedented accuracy. In general, the α of resists match very closely with the theoretical value calculated from elemental densities and absorption coefficients, whereas exceptions are observed. In addition, through the direct measurements of the absorption coefficients and dose-to-clear values, we introduce a new figure of merit called chemical sensitivity to account for all the postabsorption chemical reaction ongoing in the resist, which also predicts a quantitative clearing volume and clearing radius, due to the photon absorption in the resist. These parameters may help provide deeper insight into the underlying mechanisms of the EUV concepts of clearing volume and clearing radius, which are then defined and quantitatively calculated.

How Nanoscience Translates into Technology: The Case of Self-Assembled Monolayers, Electron-Beam Writing, and Carbon Nanomembranes

One of the great quests in nanotechnology is to translate nanoprecision materials science into practical manufacturing processes. The paper by Angelova et al. in this issue of ACS Nano, which discusses the production of functional carbon-based membranes with a thickness of 0.5 to 3 nm, provides instructive insight into how researchers are pulling together complementary strands from a quarter century of nanoscience research to develop novel, hybrid processing schemes. In this Perspective, we reflect on the progress that is taking place in the two principal component technologies combined in this scheme, namely, (i) control of self-assembled monolayers, including their detailed atomic structures, and (ii) electron-induced manipulation and processing of molecular layers, as well as considering (iii) remaining challenges for thin membrane production in the future.

Chemically amplified phenolic fullerene electron beam resist

Molecular resist materials for electron beam lithography have received significant interest as a route to reducing line width roughness and improving resolution. However, they have often required the use of hazardous solvents in their processing. A new family of fullerene based negative tone chemically amplified e-beam resists, using industry compatible solvents, has been developed. A sensitivity of ∼40 μC cm−2 was achieved at 20 keV. Isolated features with a line width of 13.6 nm as well as ∼20 nm lines on a 36 nm pitch have been patterned, whilst one variant has demonstrated resolution to 15 nm half-pitch at slightly higher dose.