Positive Electron Beam Resists Research Articles

Scanning Probe Lithography with Negative and Positive Electron Beam Resists

In this research, we focus on scanning probe lithography (SPL) to create nanostructures of negative and positive electron beam (EB) resists on a silicon (Si) substrate by common scanning probe microscopy (SPM). Microposit SAL 601 and ZEP 520A are used as the negative and positive EB resists, respectively. The EB resist films of 40–50 nm thickness are used for writing nanopatterns with low-energy electrons emitted from the probe tip in SPM. The effect of the baking conditions on nanopatterning for each resist film is experimentally investigated, and suitable baking conditions for both EB resist films are determined. The nanostructures of both resists baked under each set of suitable conditions are created under several writing conditions in order to confirm the possibility of nanopatterning and the controllability of the line width of the nanostructures. In addition, we discuss the prediction method for the line width on the basis of analysis of the static electric field inside the resist films.

半導体用化学増幅ポジ型電子線レジストの開発

半導体用化学増幅ポジ型電子線レジストの開発

Fabrication of SIS junctions for space borne submillimeter wave mixers using negative resist e-beam lithography

We report on the development of a new process for the fabrication of Nb/Al-AlO/sub x//Nb tunnel junctions for channel 1 (480-640 GHz) Superconductor-Insulator-Superconductor (SIS) mixers of HIFI, the Heterodyne Instrument for FIRST (Far InfraRed & Submillimeter Telescope). The process is derived from a standard self-aligned lift-off process but uses negative resist electron beam lithography (EBL) for junction definition. The junction area is tightly controlled down to below 1 /spl mu/m/sup 2/ without the complexity of processes using positive electron beam resists. We describe process parameters and experimental results: DC-tests and Fourier Transform Spectrometer (FTS) measurements.

化学増幅ポジ型３成分系電子線レジストの設計と開発

化学増幅ポジ型３成分系電子線レジストの設計と開発

Structural Design of Resin Matrix and Acid-labile Dissolution Inhibitor of Chemical Amplification Positive Electron-beam Resist for Gigabit Lithography.

The effect of m/p-cresol novolak molecular-weight-distribution (MWD) and dissolution inhibitor structure on resist performance were investigated. A novolak resin richer in p-cresol ratio gave a large dissolution inhibition capability of polymeric dissolution inhibitor, tetrahydropyranyl (THP) protected-polymeric dissolution inhibitor. In particular, a high molecular-weight novolak resin richer in p-cresol ratio was regarded as an effective matrix of a chemical amplification (CA) positive resist. THP protected phenolic compounds with extended backbone structures showed a large dissolution inhibition. The resist with MWD controlled resin and a THP-protected phenolic compound can achieve high resolution patterns (100-nm contact holes ) with high sensitivity (6.0μC/cm2).

2-Phenylallyl-ended Poly(.ALPHA.-Methylstyrene): A New Positive Electron-Beam Resist.

2-Phenylallyl-ended Poly(.ALPHA.-Methylstyrene): A New Positive Electron-Beam Resist.

High Performance Chemically Amplified Positive Electron-Beam Resist: Optimization of Base Additives for Environmental Stabilization.

The effects of base additives in chemically amplified positive electron-beam (EB) resist are discussed. The amine additives can improve the resolution of the resist by preventing diffusion of acids outside the exposed area. As a result, 0.1-μm L/S patterns can be obtained, successfully. Additionally, the amine additives can also improve the environmental stability. However, it was demonstrated that the influence on environmental stability differs depending on the chemical structure of amine. The phenomenon is attributable to the process of a proton-base reaction which is investigated by semi-empirical molecular orbital calculation.

New Positive EB Resist with Strong Resistance to Plasma Damage

Copolymers of methyl methacrylate (MMA) and 3‐triethoxysilylpropyl methacrylate (ESPMA) were synthesized and employed as an electron beam (EB) resist. The copolymer with a content of 10 mol% ESPMA worked as a positive EB resist and had 4–10 times as strong a resistance as poly(methylmethacrylate) (PMMA) to plasma etching. The resolution and sensitivity were almost the same as those of PMMA. From experimental results concerning the insolubility of the plasma‐irradiated copolymer and measurement of IR spectra, the enhanced resistance to plasma etching appears to be caused by formation of a cross‐linking structure based on the Si‐O‐Si linkage.

Relationship between electron sensitivity and chemical structures of polymers as electron beam (EB) resists. V: Polyamides containing sulfur groups as positive eb resists

AbstractPolyamidethioethers were synthesized and evaluated as positive electron beam (EB) resists, The polyamidethioethers decomposed easily with EB exposure. At high doses (indicating low sensitivity), crosslinking reactions occurred for polyamidethioethers having C‐S bonds produced by Michael addition, but the other polyamidethioethers did not crosslink. The C‐S bonds produced by Michael addition may influence crosslinking rather than decomposition. The sensitivity of oxidized polyamidethioether was higher than that of the nonoxidized polymer with no change in resolution. The oxidized polyamidethioether had a high sensitivity and a high resolution, and is adaptable as a positive EB resist.

Relationship between electron sensitivity and chemical structures of polymers as EB resists: Poly(lactam thioether) as new positive EB resists

AbstractPoly(lactam thioether) was synthesized from tetrahydro‐1,4‐thiazepine‐5(4H)‐one by a ring opening reaction under various conditions and was evaluated as positive electron beam(EB) resist. It was found that poly(lactam thioether) was easily decomposed by EB irradiation. The decomposition by EB exposure may be attributed to cleavage of CS bonds in the polymer chains. The sensitivity of poly(lactam thioether) was influenced by prebake temperature, molecular weight, and developer, a high sensitivity of 5.3 × 10−6 coulomb/cm2 was observed with a good resolution of less than 1 μm. Poly(lactam thioether) showed a high sensitivity and a high resolution, and is suitable as a positive EB resist.

Copolymers of itaconic acid and methyl methacrylate as positive electron beam resists

The copolymers of itaconic acid with methyl methacrylate P(MMA–ItA), are expected to perform as highly sensitive electron beam resists based on their high e-beam chain scission efficiencies (Gs). The Gs for P(MMA–20% ItA) was 2.5 times that of PMMA, and the Gs for P(MMA–35% ItA) was nearly 5 times that of PMMA. The copolymers have exhibited improved thermal stability over PMMA, as indicated by a decomposition temperature for P(MMA–20% ItA) that is 30 °C higher than that of PMMA. Infrared analyses of the copolymers showed that anhydride formed during the prebake step of the lithographic evaluation. The anhydride was predominantly a five-membered intramolecular anhydride ring which formed within single monomeric itaconic acid units. Some intermolecular anhydride was suspected because of the reduced solubility of the baked copolymers. The copolymer resists were synthesized to contain 20 and 35 mole% itaconic acid. Copolymers of each composition were evaluated with varying prebake conditions to provide varying amounts of anhydride formation. These resists were then evaluated on the basis of sensitivity, contrast, and resolution. Appropriate solvent systems for developing the lithographic patterns were chosen using a three-dimensional solubility mapping technique based on polar, nonpolar, and hydrogen bonding solubility parameters. P(MMA–20% ItA), with a 160 °C prebake, exposed at 7.5×10−6 C/cm2 with an accelerating voltage of 20 kV, was developed using a mixture of ethyl acetate and MIBK without thinning of the unexposed resist. P(MMA–35% ItA) baked at 120 °C produced 1 μm wide images at 5 to 8 μC/cm2 with a contrast (γ) of 2.5 to 3.5. 10% thinning was observed when developing areas exposed at 8 μC/cm2. Vertical walls were obtained at about 10 μC/cm2, and undercutting was observed with higher doses.

A Dry Development Model for a Positive Electron Beam Resist

A dry development model for a positive electron beam resist is described. The proposed development model is simply described as a combination of additional scissions of polymer chains and the heat‐assisted vaporization of volatile products in the development process. Using this modeling, dependences of normalized thickness remaining in the unexposed regions, a scission fraction caused by a writing E‐beam, and a contrast due to an additional scission fraction required for complete development are shown. Above all, it is interesting to point out that the shape of initial molecular weight distribution has no important meaning for the dry development. It is shown that the low contrast of the dry development originates from the additive nature of scission fraction by E‐beam irradiation and by developing reaction.

Poly(Styrene Sulfone)—A Sensitive lon‐Millable Positive Electron Beam Resist

Poly (styrene sulfone) is a 2:1 copolymer of styrene to sulfur dioxide which degrades under high energy irradiation. It has a sensitivity of when exposed to 5 kV electrons. The resist is thermally stable to 250°C and is an excellent ion milling mask with a milling rate of 0.5 nm sec−1. It also serves as an etching mask for buffered . Polystyrene sulfone does not vapor develop.