Saburo Nonogaki

Microlithography Fundamentals in Semiconductor Devices and Fabrication Technology

Exposure systems in photolithography optical pattern transfer chemistry of photoresist materials practical processes in microlithography X-ray lithography electron-beam lithography variations in microlithographic process.

PGMA as a High Resolution, High Sensitivity Negative Electron Beam Resist

High resolution and high electron beam sensitivity are found in poly (glycidyl methacrylate) (PGMA). PGMA resists with sensitivities in the 1×10-7 to 5×10-6 C/cm2 range and γ-values in the 1.8 to 2.7 range are easily obtained using solution polymerization and fractional precipitation. The γ-value increases with decreasing polydispersity (Mw/Mn), and γ>1.8 is obtained when Mw/Mn<1.4. A resist pattern of lines 0.2 µm wide with 0.24 µm spacings is obtained on a silicon wafers. This resist is useful for pattern fabrication of chromium, silicon dioxide, and polycrystalline silicon layers.

A new contrast enhancement technique for electron‐beam lithography

A new electron‐beam process technique is proposed to improve resolution and aspect ratio in negative resist patterns. With this technique a modified surface layer, which acts as a dissolution barrier to the developer solution, is introduced on top of the negative resist film. The relationship between development rate and time is varied, and therefore, it becomes a nonlinear relationship. By exploiting this nonlinear development characteristic, resist film thickness loss during development in the electron exposed area can be suppressed significantly. This concept of contrast enhancement is confirmed using an electron‐beam resist profile simulator prior to experiment. Since negative resist microresist for shorter wavelengths (MRS) show strong absorption at deep UV, deep‐UV flood exposure on MRS provides ideally modified surface layers. The new process, combined deep‐UV and electron‐beam exposure, realizes 0.3–0.4‐μm line and space patterns delineated with very little film thickness loss. This technique is a...

A Rigorous Solution of Two-Dimensional Diffraction Based on the Huygens-Fresnel Principle

The problem of two-dimensional diffraction of light by a slit is solved rigorously on the basis of Huyagens-Fresnel principle assuming the amplitude of a secondary wavelet emitted from an infinite strip of infinitesimal width on the slip aperture to be proportional to cos (θ/2)/√r, where θ is the angle of diffraction and r the distance from the strip. The solution of the problem where a plane-wave of light is normally incident on a slit in a perfectly black screen is expressed in terms of the Fresnel integral. With slight modification, the method is also applicable to the diffraction in a light-absorbing medium.

High-Resolution Proximity Exposure through a Phase Shifter Mask

A simple method to fabricate fine lines of photoresist has been developed. The method utilizes a mask containing an equal-width line-and-space pattern of the half-wavelength phase shifter. A film of photoresist formed on a substrate is placed in close proximity to the mask and exposed through the mask by flooding with a beam of light. The beam, diffracted by the mask, produces an interference pattern, which extends long enough to expose the film patternwise. The film is then developed to form a resist pattern. An array of 0.2-µm-spaced, 0.1-µm-wide lines of a positive photoresist has been obtained by this method using the i-line with a peak intensity at the wavelength of 0.365 µm. Calculation based on a rigorous solution of the two-dimensional diffraction problem indicates that a high-contrast 0.1 µm line-and-space exposure using the i-line is feasible if the light is polarized.

A Novel, Diazonium-Phenolic Resin Two-Layer Resist System Utilizing Photoinduced Interfacial Insolubilization

This paper deals with a negative two-layer photoresist system utilizing a photoinduced insolubilization process at the interface. The bottom layer is a phenolic resin either with or without aromatic azide and the top layer is a photosensitive layer comprised of an aromatic diazonium compound and a water soluble polymer. Upon exposure to light, the diazo compound decomposes to cause insolubilization at the interface between the two layers. The system exhibits high contrast due to the combination of interfacial insolubilization and contrast enhancement by photobleaching of the diazonium compound. Patterns of 0.5 um lines and spaces are obtained using an i-line stepper and a resist system containing 4-diazo-N,N-dimethylaniline chloride zinc chloride in the top layer and 3-(4-azidostyry1)- 5,5-dimethyl- 2-cyclohexen-1-one in the bottom layer. Resists with varying spectral responses from mid-UV to g-line can be designed by selecting the kind of diazo compound used in the top layer.

A Series Of Azide-Phenolic Resin Resists For The Range Of Deep UV To Visible Light

A series of new type of negative photoresists composed of a phenolic resin and azide sensitizers has been developed. RD-2000N is sensitive in the deep UV region, RU-1000N in the mid UV region and RG-3000N in the mid UV to visible region. These resists are non-swelling aqueous developable, and give higher resolution compared to conventional cyclic rubber based negative resists. Resolution in less than 1 μm can be obtained by 1 : 1 projection or 10 : 1 reduction projection aligning method. Adequate exposure doses to define submicron patterns are 50 mJ/cm4(at 254nm),70 mJ/cm° (at 365 nm) and 180 mJ/cm2(at 436nm) for RD-2000N, RU-1000N and RG-3000N, respectively. The resistance to dry etch gases is also superior to conventional negative resists, and comparable with novolak resin based positive resists. Intense absorption of irradiating light by these resists makes them insensitive to reflected light from the substrate, resulting in a high resolution on stepped substrates without any antireflective layers which are necessary in positive resist applications.

Characteristics of Photoconductive Response Velocity of Cadmium Sulfide

銅ならびに塩素で活性化した硫化カドミウム微結晶の光電流の応答特性につき検討した。光導電性硫化カドミウム微結晶を合成樹脂中に充填し,1対の電極間に配置したものについて測定を行なった。光電流の立ち上り応答速度は,投射光の照度が低い場合は,空のトラップの濃度に比例しておそくなる。高照度の場合には,光電流が定常値の1-1/eの値にまで到達するに要する時間は自由電子の寿命時間Tにほとんど等しい。光電流の減衰の応答曲線を,照射光の強度により,再結合反応支配の部と,トラップから自由電子を補給する反応の支配する部の2部に分解して解析することができる。高照度の場合の初期の急速な減衰過程は主として再結合反応に基く段階の過程で,その減衰速度から,自由電子の寿命時間T の大体の値が推定され, その値は活性剤としての銅イオンの濃度にほぼ反比例して変化する。