EB Exposure Research Articles

Lithography Simulator for Electon Beam/Deep UV Intra-Level Mix & Match

We have developed an electron beam/deep UV (EB/DUV) intra-level mix & match (IL M&M) lithography simulator. In the simulator, for EB and DUV exposure pattern to be exposed in the same resist layer in IL M&M lithography process, (1) energy distributions deposited by the EB and the DUV exposures are calculated in respective simulators separately. (2) The two energy distributions are blurred respectively by the Gaussian convolution whose standard deviation is called a lithography process parameter, ΔL. (3) The two blurred energy distributions are superposed on each other. (4) Development calculation is performed. The propriety of these calculations was confirmed by contrast with a corresponding experiment. By demonstrating two examples of the application of the simulator, the simulator is shown to be a helpful tool for precognition of results obtained by applying the EB/DUV IL M&M lithography process. The simulator is essential for optimizing the various conditions in the EB/DUV IL M&M lithography.

Cell cycle specificity of cytogenetic damage induced by 3,4-epoxy-1-butene

3,4-Epoxy-1-butene (EB), a primary metabolite of butadiene, is a direct-acting “S-dependent” genotoxicant that can induce sister chromatid exchanges (SCEs) and chromosome aberrations (CAs) in cycling cells in vitro. However, EB is almost inactive when splenic or peripheral blood lymphocytes are exposed at the G 0 stage of the cell cycle. To investigate whether repair of DNA lesions is responsible for the lack of cytogenetic responses seen after G 0 treatments, we used cytosine arabinoside (ara-C) to inhibit DNA polymerization during DNA repair. If enough repairable lesions are present, double-strand breaks should accumulate and form chromosome-type (“S-independent”) deletions and exchanges. This is exactly what occurred. EB induced chromosome deletions and dicentrics at the first division following treatment, when the EB exposure was followed by ara-C. Without ara-C treatment, there was no induction of CAs. These experiments indicate that the relatively low levels of damage induced by EB in G 0 lymphocytes are removed by DNA repair prior to DNA synthesis and thus, before the production of SCEs or chromatid-type aberrations.

Inhibition and Promotion Efficiency of Bis-phenol Type Dissolution Inhibitors During Development.

This paper focuses on the inhibition and the promotion efficiency of inhibitors in a novolac resin respecting dissolution rate into a developer. Several t-Boc derivatives of bis-phenols, which have different substituent groups on their methyl carbon, were synthesized as model compounds. Their properties were evaluated in the case of adding to a novolac resin. It was observed that the bulky substituent groups provided the inhibitors with a high inhibition efficiency, though polarity group such as esters, impaired inhibition efficiency. On the contrary, the decomposed form of inhibitor which containing ester group, promoted dissolution rate of resist efficiently. The authors have reported the high performance of the t-Boc derivative, named CP-Tboc which contained a lactone ring as a bulky substituent group. The decomposed form of CP-Tboc in the exposed area exhibits high promotion efficiency. To compare the promotion efficiency of CP-Tboc with an inhibitor having ethyl ester group, it was confirmed that the hy rolysis of lacton ring during the development increases the dissolution rate. This high promotion ability is advantages in that it avoids the influence of cross-linking of matrix polymer caused by EB exposure.

Relationship of glass transition temperature with thermal and mechanical properties of electron beam cured films

Urethane diacrylates (aliphatic and aromatic based) were diluted with a series of acrylated functional reactive diluent monomers in the proportions of oligomer/monomer = 50 25 and 50 50 w/w. Films were cured under EB exposure at a dose suitable to each individual formulation using a 300 keV accelerating voltage at 15 mA current in a nitrogen atmosphere. Tensile properties and shape memory temperatures were determined and related to the glass transition temperature, T g of the reactive diluent monomers. A good relationship has been established.

Poly[4-[bis(trimethylsilyl)methyl]styrene] for an electron-beam resist with a high resolution

Organosilicon-containing polymers, based on the poly(4-methylstyrene) [poly(MST)] skeleton, were synthesized. The T g of the monotrimethylsilylated MST polymer [poly(SMS)] was lower than that of poly(MST), while introduction of two trimethylsilyl groups at the methyl group in MST gave a significant increase in the T g (T g ≥ 150°C) of the polymer [poly(BSMS)]. All of these polymers and copolymers with glycidyl methacrylate thus obtained showed nega-working properties toward EB exposure. Sensitivity of the resists increased in proportion to their T g rather than to the Si content in the polymer

Synthesis of poly {4-[bis(trimethylstannyl)methyl]styrene} and its properties for electron-beam resist

To create high performance resist materials, synthesis of novel organostannun-containing polymer was investigated. 4-[Bis(trimethylstannyl)methyl]styrene (BSnMS) was synthesized by a reaction between trimethylstannyl chloride and 4-vinylbenzyllithium that was prepared through a metalation reaction of 4-methylstyrene by lithium diisopropylamide. Radical polymerization of BSnMS proceeded smoothly to give a polymer. Glass transition temperature of poly(BSnMS) (Tg=140°C) was fairly high among polystyrene homologues. Poly(BSnMS) thus obtained showed naga-working properties toward EB exposure. Sensitivity of the poly(BSnMS) was 9.0∼9.6 mC cm-2, keeping high γ-value (3.2∼4.9).

Molecular Design of Acid Generators for EB and ArF Excimer Laser Exposure Using Molecular Orbital Calculations.

Abstract: Quantum chemical calculation is applied to investigate the reaction mechanism of sulfonyl acid generator and the transparency of the resist material. We have found that electron absorbed dimethylsulfone can be easily decomposed by relatively low energy (2.95Kcal/mol), reaching to the decomposed status of methyl radical and CH3SO2 (methyl sulfonyl anion). This was thought to bean initial step in the electron acid generation reaction of the sulfonyl compounds. The total molecular energy of dimethyl sulfone anion was found to be higher than that of the neutral dimethylsulfone. On the other hand, sulfone derivatives with electron-withdrawing groups, such as methyl sulfonyl acetonitrile, usually have higher energy (about 41kcal/mol) than those for their anion. This suggests that the electron withdrawing groups enhance the electron affinity of the sulfone compounds, which are also considered to increase the efficiency of acid generation. Additionally, another quantum chemical study was carried out in order to improve transparency of the aromatic species in resist for ArF excimer laser. Using configuration interaction (CI) methods of molecular orbital theory, the substituent effects of UV absorption in the aromatic compounds were investigated. As a result significant red sifts in λmax were observed in the conjugated romatic rings, which increases the transparency at 193nm wavelength region.

Decomposition products of EBR-9 by X-ray and EB exposure.

Decomposition products of EBR-9 by X-ray and EB exposure.

Triangular Shaped Beam Technique in EB Exposure System EX-7 for ULSI Pattern Formation

The generation of a triangular and rectangular shaped beam is very useful in increasing throughput for writing ULSI patterns which often include many oblique lines. To make use of these shaped beams in ULSI pattern formation, a new rectangular and triangular shaped beam calibration method has been developed on the EB exposure system EX-7. The shaped beam calibration method is established by analyzing the beam current of shaped beams and the backscattered electron signal from a fine gold particle on the target. Resultant accuracies were 0.013 µm for a beam size of 1.6 µm and 0.025 %micro;m for the relative beam position on the target. Using this method, 0.2 µm ULSI patterns including oblique lines have been accurately formed.

Performance Control of Positive-Working Electron Beam Resists by Copolymerization and Blending

EB exposure characteristics, such as sensitivity and contrast, and durability against oxygen plasma were measured with linear copolymers and polymer blends of various composition, which were prepared from α-methylstyrene [MSt] and methyl methacrylate [MMA]. Moreover, new developers were examined for these polymers, since sensitivity and contrast of the positive-working resist system depend largely on dissolution kinetics concerning each combination of the resist polymer and the developer. Methyl isobutyl ketone and isoamyl acetate were used as the developer, though they were developers of excessive dissolving power for PMMA and /or PMSt homopolymers. The copolymers containing 30—50 mol% of MSt were as durable as PMSt homopolymer against oxygen plasma and had higher contrast than PMMA. The blend had dryetching durability as large as the copolymer of the same composition, and showed considerably high contrast, while the copolymer had higher sensitivity than the blend. The blends containing 21 mol% or less of MSt monomer units were much more durable than PMMA and of contrast as high as PMMA, but less sensitive than PMMA.

Advanced pattern data processing technique for a raster scan electron beam exposure system

With the increasing complexity and integration in recent LSI designs, the amount of data to be processed in EB exposure systems tends to increase steadily. This increase in data may lead to degradation in the systems’ throughputs. An overall technique associated with both software and hardware presents a realistic solution to this problem. Parallel processors combined with a simplified data format have provided efficient data manipulation. A compaction method working on smaller stripe areas is easily realized in hardware, yet can achieve significant data reduction. The data edit function, operating asynchronously with the data preparation procedure, eliminates repeated processing of identical chip patterns or chip element patterns. The feasibility of the technique thus featured has been proven on EB-105, a raster scan electron beam exposure system.