Recently we have developed new class of non-ionic oxime sulfonate PAG. The compounds generate various kinds of sulfonic acids, such as n-propane, n-octane, camphor and p-toluene sulfonic acid under Deep-UV exposure and trifluoromethanesulfonic acid under ArF exposure and are applicable for the corresponding chemically amplified (CA) photoresists. The application-relevant properties of the compounds such as solubility in propylene glycol monomethyl ether acetate (PGMEA), ethyl lactate, ethyl 3-ethoxypropionate, and 2-heptanone, UV absorption, thermal stability with or without poly(4-hydroxystyrene) (PHS), volatility, perfomance in model resist formulations were evaluated. In addition, the microlithography simulation based on the results of DRM results of the trifluoromethanesulfonate was also studied.

View full abstract

Resist poisoning in via-first dual damascene was observed after trench lithography. The resist poisoning was more likely to occur when a low-k material was used. To examine the relationship between resist poisoning and the amount of basic contaminants, we analyzed basic molecules by capillary electrophoresis (CE), ion chromatography, and thermal desorption-atmospheric pressure ionization-mass spectrometry (TD-API-MS). It was found that three amines were adsorbed on a low-k wafer. The total amount of amines was related to the resist poisoning. We also conducted TD-API-MS experiments on wafers with a variety of via densities. These experiments well explained why isolated vias are more likely to suffer from resist poisoning. As a process approach toward the elimination of resist poisoning, we confirmed that quick heat treatment at a high temperature was effective in removing the amines from the low-k wafer. As a material approach, we tried to make resists with high resistance to resist poisoning. The addition of a quencher (organic base) in the resists effectively reduced the resist poisoning. The mechanism was verified by nonaqueous titrations of a model resist system. It was found from the model experiments that a buffer system composed of the photoacid and its conjugate base was working to keep the pH changes from external basic contaminants small.

View full abstract

We investigate the effect of surfactant and solvent in rinse liquid using ArF photoresist. The collapse behavior is quantified in terms of the first collapsed critical dimension (FCCD) in 90 nm L/S ArF resist patterns. The addition of small amount of isopropanol in rinse liquid is not helpful to suppress surface tension (ST). In-house rinse liquids (HR series) showed relatively lower ST (26 mN/m2) compared to commercial one (45 mN/m2) at 23°C. They greatly reduce pattern collapse behavior (PCB) of photoresist from FCCD 103 nm to 85 nm L/S using these solutions. However, some rinse showes defect by bubble and the others show bad compatibility with photoresist. Some of HR series satisfy all requirements.

View full abstract

We have studied the lithographic performance of resist pattern prepared by supercritical resist drying method. Patterns were exposed by proximity X-ray lithography and the supercritical resist drying was performed with CO₂ by 10 MPa and 60°C. We found that 70-nm-L/S patternswere prepared with the exposure gap of 15 μm, though it had not been ever obtained withoutsupercritical drying. The CD control and line-edge-roughness for those patterns are also measured.

View full abstract

We consider the consequences of treating a photoresist film as an element of an imaging optical system, by means of classical Fourier optics. The spatial resolution of the photoresist is described by a line spread function, or equivalently by its Fourier transform, the modulation transfer function (MTF). We then show that given a quantitative model for the development process, the MTF can be deduced from measurements of linewidth vs. dose for sinusoidal illumination patterns generated by interferometric lithography. Experimental results supporting the validity of this approach have been obtained for commercial deep-UV photoresist. This work provides a simple methodology to quantitatively describe the spatial resolution of a photoresist, which does not require highly optimized imaging optics.

View full abstract

Condensation properties of polymer aggregate are characterized by the typical AFM techniques, collapse, separation, indentation and manipulation. The association of polymer aggregate of approximately 50 nm size is clearly observed in the resist surface. By the separation technique, the cohesive property of associated polymer aggregate is analyzed. It is clearly indicated that two associated polymer aggregates are separated into 13 pieces of aggregates. The interaction force among polymer aggregates can be analyzed based on Derjaguin approximation. By the tip indentation, the condensation of polymer aggregate accompanying a certain vacancy can be analyzed. The polymer aggregate of 20 nm size can be manipulated and rearranged in linear position. One can safely state that polymer aggregate is regarded as a granular solid material which has a certain cohesive strength. The condensation model of polymer aggregate accompanying with vacancy resist is introduced.

View full abstract

General property of line-edge roughness (LER) in resist pattern and its transferability to under-lying layer were investigated. Longer-period components were found to have larger amplitudes in a resist pattern and to remain after dry etching. In addition, long-period LER strongly affects a transistor performance. Long-period LER in resist patterns, therefore, is as important as short-period LER. Metrology of LER was reconsidered to evaluate the both LER properly, and a guideline for choosing measurement parameters was proposed from a viewpoint of device performance estimation.

View full abstract

During extreme ultraviolet lithography, the surfaces of the imaging optics and mask become contaminated with organic compounds. As more and more contaminants are deposited on a Mo/Si multilayer, the reflectivity and exposure intensity become lower, and the resolution of the imaging optics is degraded. A novel in-situ method of removing contaminants without heating has been developed. In an O₂ atmosphere at a pressure of 5.0 × 10^-2 Pa and at an electron beam current of the synchrotron storage ring of 150 mA, it removes a 0.1-μm-thick layer of contamination in 7 hours. The removal of the contamination restores the reflectivity of a Mo/Si multilayer without causing any surface damage.

View full abstract

The current status of EUV resists is reviewed based on performance studies of line edge roughness (LER), sensitivity, resolution and pattern transfer. A large variation in polymer molecular weight (2.9-33.5 K g/mol) is found to have little effect on LER. Dissolution properties such as unexposed film thickness loss (UFTL) are shown to have a large effect on LER. Increasing resist contrast and image contrast are shown to improve resist LER. Variation in base level within resists based on EUV-2D shows a clear trade-off between sensitivity and LER. Acid difusion can play an important role in determining LER. Resist resolution and image transfer capabilities are also discussed.

View full abstract

Different concepts for the manufacture of masks for deep X-ray LIGA are presented. The variation in the accuracy of the final mask as a function of the mask manufacture concept (low, medium or high resolution) influences the sidewall roughness of the irradiated PMMA structures considerably. The mask membrane also influences structure quality. Graphite masks, which yield PMMA resist structures with straight sidewalls, have increased surface roughnesses (>2 μm Rz) comopared to beryllium.
A design of experiments approach to the optimisation of PMMA for LIGA applications with deep X-ray lithography has been undertaken. For the optimisation, 18 different resist mixtures were produced on the basis of the significant parameters, holding the parameters within values that were experimentally shown to be conducive for PMMA resist production. High ratios of crosslinker in the resist mixture was shown to lead to significant amounts of resist residue between the microstructures; resist development was significantly hindered. Other resists with higher ratios of adhesion promotor in the resist also had significant problems with development. PMMA resist mixtures containing between 2% and 5% adhesion promotor led to microstructures with sufficient adhesion to the substrate surface without any substantial problems with the development step.
A variant of the LIGA-process, which involves deep silicon etching for mastering, has successfully been applied for the fabrication of disposable plastic chips for 2-dimensional electrophoresis. The high precision and structure accuracy of the replicated plastic devices as well as the possibility to pattern complex multilevel structures demonstrate the huge potential of LIGA based on silicon micromachining for the realization of microfluidic and biomedical devices

View full abstract

We describe a technique for the formation of oriented single nanofibers, using an arrow shaped and scanned tip. The tip was dipped in a polymeric solution to gather a droplet as a deposition source. A sufficiently high potential, applied between the droplet and a counter electrode, initiated electrospray deposition of nanofibers on the counter electrode. By using our technique, we demonstrated the control of nanofiber fabrication and the nanofiber cross junction for the application of nanofiber based nanodevice.

View full abstract

Fabrication and characteristics of two-dimensional (2D) and three-dimensional (3D) periodic structures, recorded inside the bulk of negative SU8 photoresist film by multiple-beam interference are reported. The recording was performed by ultrashort laser pulses of 150 fs duration with central wavelength of 800 nm, multiple beams were generated using a diffractive beam splitter. Intensity-dependent photomodification of the photoresist was initiated by multi-photon absorption. The development process removed the exposed regions of resist film, leaving free-standing 2D and 3D periodic dielectric structures. Detailed examination of the samples is presented, which reveals close resemblance between the features of the fabricated structures, and those of the light intensity distributions in the multiple-beam interference fields. The microfabrication method used is demonstrated to be suitable for obtaining of photonic crystal templates. Phase control of the constituent beams allowed to monitor and control the light interference pattern to be recorded. Possibility to record the diamond lattice using this method is examined and discussed.

View full abstract

Patterning resists by molding with a stamp opens ways for the mass-fabrication of nanostructures. The versatility of nano-imprint lithography can be greatly enhanced when copies of valuable stamp originals can be made. For the stamp copying itself we are using nano-imprint, making it possible to generate structures with inverse profiles and different depths. By considering the nanorheological behavior we were able to successfully fabricate various stamp copies for different designs.

View full abstract

An array of iron oxide nanodots with 6 nm diameter was used as a nanometer size patterning mask for inductively coupled plasma (ICP) etching process. The array of nanodots was fabricated by biological pathway named bio-nano-process. A cage protein, ferritin, was employed to accommodate an iron oxide core with 6 nm diameter and a two dimensional array of ferritin was made using their self-assembling ability. The array of ferritin was transferred onto a silicon wafer and the protein moiety was selectively eliminated by ozone treatment. The array of nanodots was used as a patterning dry-etching mask. The ICP etching using CHF₃ gas at low temperature produced a combination of cone-shape peaks and plateaux. This result demonstrates the possibility that iron oxide nanodots array produced by bio-nano-process can be used as a dry-etching mask and that an array of nano-columns with high density could be produced. Taking a variety of bio-molecules which can accommodate inorganic materials into consideration, this bio-nano-process is expected to lead to a new approach for making nano-scale masks.

View full abstract

Electron beam (EB) lithography, together with ArF, F₂ and EUV (Extreme Ultra-Violet), is one of the most promising candidates for the next generation 65 nm node and below from the viewpoint of resolution and DOF (depth of focus). However, since EB lithography has a disadvantage in throughput compared with optical lithography, it is generally used for mask and ASIC (Application Specific Integrated Circuits) device manufacturing. The application for it in mass production has been a difficulty. Recently, EPL (Electron Beam Projection Lithography) and LEEPL (Low Energy Electron Proximity Lithography) are being developed to improve the throughput problem of EB. In this paper, we investigated the subject of high sensitivity for imaging resist, which is one of the current topics of EPL. We resulted in an imaging resist which has high sensitivity and small line edge roughness by applying a specific additive and specific resin. Furthermore, we also developed an imaging resist which has high sensitivity and excellent resolution by applying the acid generator which controlled the strength of acid, and diffusion.

View full abstract

In order to solve pattern collapse problems caused by high aspect ratio, new acetal-based chemically-amplified positive tone resists for electron beam lithography were investigated. Electron beam lithography is in the initial stages of utilization for device manufacturing and high-end mask making. The resist screening results using 70 kV direct writing electron beam tool showed high resolution, good pattern profiles and reduced substrate influence. Dry etching resistance was also studied.

View full abstract

In this study, we investigated the effect of surfactant-added rinse and soft bake on pattern collapse in ArF lithography. It was possible to obtain 21% narrower pattern with the aid of surfactant solution. Surfactant with low dynamic surface tension was more effective, so it seems to be required to consider dynamic properties of surfactant when we use spin dry. During the study, we found that pattern collapse occurred much earlier at the edge of wafer and we could decrease the positional difference by increasing bake time or temperature after resist coating. It is supposed that this result come from the relaxation of internal stress induced during spin coating

View full abstract

We found that the line edge roughness (LER) of resist pattern could be improved by improving the uniformity of the polymer itself, the main component of the photoresist, at stage of the polymerization. Also, we found that, by using the atomic force microscope (AFM), the aspect of the polymer aggregates had difference when we quantitatively comparison-measured photoresist surface, which was in process of dissolution. We believe that this difference is due to the individual aggregate dissolution property toward the developer. In this paper, we are focusing on the dissolution property of polymers toward developer, and discussing on the uniformity of the polymer and the correlation to the LER.

View full abstract