As a result of continuous improvement of the resist process, the experimental ion projector in the Fraunhofer Institute in Berlin (manufactured by Ion Microfabrication Systems, IMS, Vienna) has been able to print 75 nm lines and spaces into 180 nm thick standard DUV resist UV II HS without pattern collapse. A new wafer flow process for more reliable open stencil mask making was developed by IMS –Chips, Stuttgart (Germany), based on SOT wafers. Resistless direct surface modification by He and Xe ions has been tested on metallic and magnetic films in the Berlin projector. This method opens up a new possibility for the production of patterned media for future magnetic storage disks.

The development of micro- and nanofabrication, their applications, and their dependent industries has progressed to a point where a bifurcation of technology development will likely occur. On the one hand, the semiconductor industry (at least in the USA) has decided to develop EUV and SCALPEL to meet its future needs. Even if the semiconductor industry is successful in this (which is by no means certain) such tools will not be useful in most other segments of industry and research that will employ nanolithography. As examples, MEMS, integrated optics, biological research, magnetic information storage, quantum-effect research, and multiple applications not yet envisioned will not employ the lithography tools of the semiconductor industry, either because they are too expensive, insufficiently flexible, or lacking in accuracy and spatial-phase coherence. Of course, direct-write electron-beam lithography can meet many of these non-semiconductor-industry needs, but in other cases a technique of higher throughput or broader process-latitude is necessary. Our experience at MIT in applying low-cost proximity x-ray nanolithography to a wide variety of applications leads us to conclude that this technology can provide an alternative path of a bifurcation. A new projection lithography technique, zone-plate-array lithography (ZPAL), does not require a mask, can operate from UV to EUV to x-rays, and has the potential to reach the limits of the lithographic process.

Advances in microlithographic resist materials have been a key enabler of the unabated productivity gains in the electronics industry and are continuing to help push the ultimate limits of optical lithography. The challenges posed by the introduction of new optical lithography technologies that use smaller wavelengths have been successfully met by the materials community through the design of chemically amplified resist technologies and 193 nm resist materials based on aliphatic polymers and dissolution inhibitors. With continued advances in resist materials, exposure systems and resolution enhancement and mask technologies, optical lithography will be capable of patterning ≤ 0.1 μm design rule devices in future fabs.

Direct-write electron beam lithography is a patterning technique that has rapidly evolved over the last 40 years. For many years it has been possible to use electrons to pattern lines with widths as narrow as 10 rum. Recent advances in resist materials, electron sources, and system integration have further enhanced the capabilities. High-sensitivity resists provide substantial increases in the throughput without sacrificing resolution. Thermal field-emission sources improve the stability and reduce the minimum attainable spot size. Modem lithography systems integrate the electron beam column with advanced control electronics, making a system capable of nanometer-scale placement accuracy. In addition to these improvements, the technology is more accessible now than ever before, thanks to the proliferation of lithography systems consisting of modified scanning electron microscopes.

As we rapidly approach the point at which solid-state electronic devices cease to be made any smaller, molecular scale electronics offers, perhaps, the best chance for a continued miniaturization of computational devices. We must, however, completely re-think our approach to lithography. Presented in this paper are our solution-phase and solid-support based syntheses of molecular wires of precise length and dimensions, and our methods of addressing these wires via molecular “alligator clips” to gold and platinum electrodes of macroscale dimensions.

We describe three different aspects of the self-organization of steps and domain boundaries of a 7×7 reconstruction on SI(111) surfaces. The first is the formation of a triangular-tiled pattern of “1×1’ and 7×7 domains during the phase transition. ‘1÷1’ and 7×7 domains have different surface stresses. The triangular-tiled pattern is stabilized through stress relaxation. The second is the step arrangement inside a hole, which was fabricated by a standard lithographic technique. The step arrangement in the hole depends on the temperature. Below the ‘1×1’-to-7×7 phase transition, the hole has a three-fold symmetry consisting of step-bunched and non-bunched regions. This is because the step arrangement on the vicinal Si(111) surfaces depends on the direction of the steps. The third aspect is the formation of a pattern of steps and domain boundaries induced by Si growth. During the step-flow growth on Si(111), steps preferentially protrude along the domain boundaries on the lower terrace. The resulting changes in step shape induce a unique rearrangement of the domain boundaries, the number of which decreases during growth. However, when a periodic pattern is formed in the initial stages, it remains stable during growth.

Structural evolution during initial epitaxial growth of Mo (111) and (110) on Al2O3 substrates has been studied using real-time reflection high energy electron diffraction and in-situ scanning tunneling microscopy. The Mo (111) growth on sapphire (0001) is initiated by the formation of small mound-like 3-dimensional (3D) islands that are correlated with unique length scales. The observed surface length scales depend on growth temperature and rate, and they coarsen as the thickness increases. The initial growth of Mo (110) on sapphire (1120) begins with layer-by-layer growth for the first monolayer, and subsequently the growth is 3D with mound-like features that are larger than those corresponding (111) counterparts. In both orientations lattice relaxation occurs within the first 2 – 3 monolayers.

We investigate step bunching during SiGe growth on vicinal Si(111) surfaces. Step bunching occurs irrespective of the misorientation angle and direction of the vicinal surface, the growth temperature, and the Ge concentration. At 550°C, the average number of the steps in the bunch increases with the Ge concentration. After growth of 10-nm-thick SiGe layers, twodimensional islands are formed on the terraces, which indicates that the terrace width has already been saturated. Therefore, the terrace width is mainly determined by the diffusion length of the adatom. The average number of steps in the bunch increases with the Ge concentration because the diffusion length increases with the Ge concentration. The diffusion length also increases with the temperature. So the higher the temperature is, the larger the step bunch becomes.

The work focuses on lithographic processes and materials for sub-50 nm lithography. Lithographic results of polymethyl methacrylates of molecular weights of 50,000, 100,000, 496,000, and 950, 000 are compared. It was found that the molecular weight and developer concentration do not affect smallest linewidth, within experimental error. However, the molecular weight does affect the line-to-line resolution in dense gratings of 40–60 nm in contrast and developer induced swelling. 40 nm period gratings are shown. The work next examines the use of chemically amplified resists for nanofabrication, with a focus on SAL-601. Sub-50 nm lines are defined with latitude of an order of magnitude in dose and a factor of two in post exposure bake time. The results are modeled with a diffusion reaction kinetic model and an approach to optimize resolution and reproducibility is presented. Challenges to attaining the ultimate resolution and line-to-line resolution in polymeric resists include contrast, mechanical stability, swelling, and adhesion. Metal binding self assembled monolayers (SAMs) are presented a class of resists, that circumvent the latter three complications. Work at the Naval Research Laboratory on SAM resists is outlined.

Electron projection lithography is considered to be one of the best candidates for sub-100 nm production circuits. One of the major problems that hinders its development is not related to machine fabrication issues but to electron proximity effects which stem from fundamental electron-polymer interactions. During the past two decades, efforts to reduce the electron proximity effects have essentially focused on the optimization of the resist exposure by means of dose modulation correction programs. We propose a novel approach where the structure of the resist can be tailored so that controlled anisotropy is introduced to laterally constrain the electron scattering. This novel approach does not require the use of high-voltage electron beams nor the processing of a large amount of data, which is a significant economic advantage. Some concepts for the synthesis of these anisotropic resists are discussed and the preliminary example of iron oxide nanorods aligned in poly(methylmethacrylate) (PMMA) is studied.

A nanocomposite resist system that incorporates sub-nm fullerene molecules ( C60 and/or C70) into a conventional resist material is proposed for nanolithograpy. Fullerene has physically and chemically resistant characteristics, and its incorporation reinforces the original resist film, leading to substantial improvements in resist performance: etching resistance, pattern contrast, mechanical strength and thermal resistance. We have prepared a system composed of a positive-type electron beam resist, ZEP520, and C60 or a C60/C70 mixture and through the fabrication of high electron mobility transistors (HEMTs), X-ray masks, and groove-grating mirrors for lasers with nanometer dimensions confirmed improved resist performance, particularly resolution improvements due to enhanced etching resistance. By making use of a characteristic unique to the nanocomposite, which is that sensitivity readily changes with the fullerene content due to a dissolution inhibiting effect of fullerene, we have constructed a fullerene-incorporated bilayer resist system for a lift-off process and have successfully fabricated a highly-ordered array of self-organized boxlike nanostructures and a mold for nanoprinting. Further, solubility enhancement by fullerene derivatives has been examined for a higher degree of fullerene incorporation and better sensitivity characteristics in future nanocomposite resist systems.

We report systematic studies of the response of C60 derivatives to electron beam irradiation. Films of fourteen different mono, tris and tetra adduct methanofullerene C60 derivatives were produced by spin coating on hydrogen terminated silicon substrates. Exposure of the films to a 20 keV electron beam substantially altered the dissolution rate of the derivative films in organic solvents such as monochlorobenzene. All of the derivatives exhibited negative tone resist behaviour with sensitivities between ∼ 8.5 × 10-4 and ∼ 4 × 10-3 C/cm2 107, much higher than that of C60. 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 (SAL601).

Polyhedral oligosilsesquioxane methacrylate (POSSMA)/methyl methacrylate(MMA)/tert-butyl methacrylate(TBMA)/tert-butyl acrylate(TBA) copolymers were synthesized by solution polymerization. Their preliminary lithography-related properties were studied. It is shown that the mass ratio of MMA/POSSMA=85.8/14.2 leads to an X-ray resist with a high contrast of 23.5 without sacrificing the sensitivity(1350 mJ/cm2) which remains comparable to that of standard PMMA. By careful manipulation of components and compositions, this generic type of polymer could potentially be utilized as a DUV or e-beam resist as well.

We report the development of a new family of electron beam resists based on liquid crystalline polysubstituted derivatives of triphenylene. These new resists show excellent performance in terms of both high resolution and high durability to plasma etching. Films of the derivatives have been produced in a controlled manner via room temperature spin coating on hydrogen terminated silicon substrates. The dissolution behaviour of the derivatives in various organic solvents was altered by exposure to a 20 keV electron beam. The solubility of the derivative hexapentyloxytriphenylene, in polar solvents, was substantially increased by electron doses greater than ∼ 3 × 10-4 C/cm2 (positive tone behaviour). Doses greater than ∼ 2.5 × 10-3 C/cm2 led to negative tone behaviour in both polar and non-polar solvents. Other derivatives also demonstrated a reduction in their dissolution rate for doses between ∼ 1 × 10-3 and ∼ 7 × 10-3 C/cm2. The derivative sensitivity was found to be roughly proportional to the molecular mass. Negative tone patterns were found to have an etch durability ∼ 70 % greater than that of a conventional novolac based negative tone resist (SAL601). The performance of these new resists has been demonstrated by the definition of line and space patterns with a resolution of ∼ 14 nm, whilst structures with an aspect ratio of.∼ 50 to 1 were etched into the silicon substrate.

Our research focuses on the line-edge roughness of resist patterns and how to reduce it in order to establish nanolithography as a practical tool. Commercially available e-beam resists exhibit a line-edge roughness of 3 nm (σ) or more. It is caused mainly by polymer aggregates in the resist. During development, they are extracted through dissolution of the surrounding polymer matrix. That is, the aggregates themselves dissolve more slowly than the surrounding matrix; and those that remain embedded in the resist produce line-edge roughness. To reduce the roughness, the effect of the aggregates must be suppressed. One way of doing this is to use a resist containing small aggregates. A good candidate is hydrogen silsesquioxane, which has a three-dimensional framework. Another way is to use a resist in which the aggregates are linked together, which makes them difficult to extract during development. A good example is an acrylate-type resist with a cross-linker mixed in.

Three major lithographic applications have emerged for electron beam exposure tools: optical mask fabrication, direct writing for device fabrication, and more recently projection e-beam printing. The traditional mask making process uses poly(butenesulfone) resist. A wet etch process was adopted to generate patterns on chrome. Recently, shrinking dimensions, optical proximity correction features, and the complexity of phase shift masks have forced the industry to a chrome dry etch process. ZEP, a poly(methyl α-chloroacrylate-co-α-methylstyrene) based resist, has been well accepted for most of the >180 nm device mask making. The acceptance of ZEP comes in spite of its low contrast, marginal etch resistance, organic solvent development, and concerns of resist heating associated with its high dose requirements. These issues have spawned interest in using chemically amplified resist (CAR) systems for direct write and mask making applications. We have developed a high contrast resist based on ketal protecting groups, KRS-XE, which is robust against airborne contamination and can be used for all forms of e-beam exposure in both chrome mask and silicon processing. This high contrast resist is processed with aqueous base developer and has a wide bake latitude. The development of KRS-XE has provided the capability of fabricating chrome masks for future generation (< 180 nm) devices and has potential for use with projection beam exposure systems.

Distribution and diffusion of two fluorinated ionic photoacid generators (PAGs) in thin polymer films have been investigated by depth profiling of the intrinsic label elements of both the PAGs and a silicon containing carrier polymer with Rutherford Backscattering Spectrometry (RBS) and dynamic Secondary Ion Mass Spectroscopy (SIMS). Distribution and diffusion of the PAGs in a bilayer film stack, which consists of a thin silicon containing polymer film on top of a thick thermally cross-linked Novolak film on a silicon substrate, have been studied as a function of the Novolak cross-linking temperature. Deposition of the PAG containing polymer films on top of the cross-linked Novolak films by spin coating results in an interphase with enriched PAG. Subsequent annealing of the film stack causes expansion of the interphase and diffusion of the PAG into the underlying Novolak film when Novolak is cross-linked at lower temperatures. On the other hand, there is a uniform PAG distribution and no detectable diffusion of the PAG into Novolak when it is cross-linked at high temperatures. The variations in the PAG distribution and diffusion are attributed to the changes in the chemical and physical properties of Novolak during cross-linking.

An organic film of a few nm in thickness was applied as a resist for photolithography and scanning probe lithography. This resist film was prepared on an oxide-covered Si substrate through chemisorption and spontaneous organization of organosilane molecules, e.g., n-octadecyltrimethoxysilane. The film belongs to a class of materials referred to as self-assembled monolayer (SAM). A SAM/Si sample was irradiated through a photomask with vacuum ultraviolet (VUV) light at a wavelength of 172 nm. The photomask image was transferred to the SAM through the decomposition of the SAM. Furthermore, we demonstrate nano-scale patterning of the SAM using an atomic force microscope (AFM) with an electrically conductive probe. The SAM was electrochemically degraded in the region where the AFM probe had been scanned. Both the photo-printed and AFM-genereated patterns were successfully transferred into the Si substrates based on wet chemical etching or on dry plasma etching. At present, using these VUV and AFM-based lithographies, we have succeeded in fabricating minute features of 2 μm and 20 nm in width, respectively.

Periodic polymer/metal (Pt or Ag) and polymer/semiconductor (PbS) nanocomposites are prepared using block copolymers dilated with carbon dioxide (CO2) as templates. Specifically, organometallic compounds (metal precursors) are dissolved into supercritical CO2 and infused into polystyrene-block-poly(acrylic acid) or polystyrene-block-poly(vinylpyridine) copolymers. Upon infusion, the acid or pyridine block selectively binds the metal precursor. The excess is removed from the polystyrene phase by subsequent CO2 extraction. Reduction of the bound organometallic with hydrogen or hydrogen sulfide yields the desired metal or semiconductor clusters, which are confined to the precursor-binding domain and remain positioned on the copolymer lattice. The composites are characterized by transmission electron microscopy, x-ray scattering and electron diffraction.

Spectroscopic ellipsometry has long been recognized as the technique of choice to characterize thin films and multilayers. It is now intensively used in microelectronics and especially for the microlithographic applications. Instrumentation for the next generation of UV lithography at 157nm requires special optical setup since oxygen and water are extremely absorbing below 190nm. The ellipsometer discussed in this paper works into a purged glove box to reduce the oxygen and water contamination in the part per million ranges. The optical setup has been especially studied for microlithographic applications. It includes for example a premonochromator in the polariser arm to avoid resist photobleaching. Technical details of the system and some first measurement results on substrates and thin films are reported hereafter.