Electron beam induced carbon deposition used as a negative resist for selective porous silicon formation
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Keywords:
Porous Silicon
Deposition
Carbon fibers
Poly(p-t-butyloxycarbonyloxystyrene) resist shows great potential for electron-beam nanolithography, particularly as a negative resist. The resist has been used to fabricate structures with linewidths as narrow as 18 nm. The resist can be processed in both positive and negative modes depending upon the developing solvent, and linewidths <40 nm have been obtained in both cases. The exposure mechanism is based upon a new resist design principle incorporating an acid catalyst. The sensitivity of the resist can be at least six times higher than that of polymethylmethacrylate (PMMA) exposed under the same conditions (i.e., 50 kV, thin membrane substrates). The exposure distribution for the resist in the negative mode has been determined, confirming its resolution potential. These data indicate that the increase in sensitivity realized through incorporation of a gain mechanism in the resist chemistry is not achieved at a large loss in resolution. In its negative mode, the resist exhibits adequate ion etch resistance for device fabrication. The resist compares favorably with other negative resists for nanolithography with regards to both resolution, and its ability to be cleanly removed by rf plasma oxidation after serving as an ion etch mask.
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Resist profile shapes become important for 22nm node and beyond as the process window shrinks. Degraded profile shapes for example may induce etching failures. Rigorous resist simulators can simulate a 3D resist profile accurately but they are not fast enough for correction or verification on a full chip. Compact resist models are fast but have traditionally modeled the resist in two dimensions. They provide no information on the resist loss and sidewall angle. However, they can be extended to predict resist profiles by proper setting of optical parameters and by accounting for vertical effects. Large resist shrinkages in NTD resists can also be included in the compact model. This article shows how a compact resist model in Calibre can be used to predict resist profiles and resist contours at arbitrary heights.
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A new two‐level resist patterning process is proposed. This process is based on the fact that, under deep‐UV exposure, polymethacrylate resist (such as FPM) can be etched by way of volatilization, and the etching rate is faster than that of novolak‐type resist (such as AZ). The two‐level structure consists of FPM as a bottom resist and AZ as a top resist. After delineating the top resist, the bottom resist is patterned using the AZ resist as a mask. This procedure provides a very simple technique for controlling the resist profile for use in lift‐off process.
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We have developed a DUV-defined-negative resist/EB-defined-positive resist two-layer resist system to fabricate T-shaped gates of GaAs MESFET devices. In this resist system, the head of the T-shaped gate is fabricated in the top layer negative resist using a deep-UV exposure and the foot of the T-shaped gate is fabricated in the bottom layer positive resist using an e-beam exposure. Resist profiles are easily controlled because exposures and developments of the top and bottom layers are completely separated. A sub quarter-micron T-shaped gate with the head of the width of more than one micron was successfully fabricated by using this two-layer resist system. This two-layer resist system has wide applicablity for the fabrication of GaAs MESFET devices.
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We have surveyed the commercial resist market with the dual purpose of identifying diazoquinone/novolac based resist that have potential for use as e-beam mask making resists and baselining these resist for comparison against future mask making resist candidates. For completeness, such a survey would require that each resists be compared with an optimized developer and develop process. To accomplish this task in an acceptable time period we have chosen to perform e-beam lithography modeling to quickly identify the resist developer combinations that will lead to superior resists performance. We describe the development and verification of a method to quickly screen commercial i-line resists under e-beam exposure with different developers. This was accomplished by determining modeling parameters for i-line resist from e-beam exposures, modeling the resist performance, and comparing predicted performance versus actual performance. We evaluated whether the technique of combining e-beam resist modeling with lithography can be used to quickly and efficiently screen i-line resists for use in e-beam mask making. This was accomplished by comparing experimentally determined resists sensitivities and profiles with those predicted from ProBeam/3D lithography modeling software.
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Two types of chemically amplified (CA) negative resists were compared lithographically. An acid catalyzed resist and a photopolymerizable type resist. The optimum lithographic performance of the acid catalyzed resist on Cu is in the thickness range below 15μm, with vertical profiles. This resist exhibits inverted profiles on Cu above 15μm of thickness. The Photopolymer type resist performs best above 25μm thickness, and can be used for 120μm thick applications with single coat. Top line rounding is more observed with this resist as its applied thickness is reduced below 20μm. This effect is believed to be related to oxygen uptake in the resist surface. Thus it has a more pronounced effect at relatively thinner films. Both resists are compatible with the electroplating process.
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In the manufacturing process of semiconductor device, MEMS, and so on, lithography which uses photo-resist is a key process to fabricate micro or nano-scale structures, and unnecessary resist should be removed after the process. Typically SPM is used for the resist removal. In this study, we apply the method of steam-water mixed spray that can remove resist without chemicals. In order to clarify the detail mechanism of resist removal, we performed resist removal experiment. In the experiment, spray is traversed over a resist-coated wafer and the removal area is evaluated. The resist-coated conditions such as bake temperature, rotating speed are changed to evaluate the effects of mechanical properties of resist. In addition, removal force is measured to estimate the mechanical properties of resist by using SAICAS. As a result, it is shown that thicker or harder resist tends to be difficult to remove and the results suggest that this method mainly utilizes the physical force of high-speed droplets impact.
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Nanoimprint lithography
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Thi s paper describes a positive resist formulation [PSi] containing silylated polystyrene polymer, made photosensitive at 436 nm wavelength, by means of an onium salt sensitizer and a dye photosensitizer. This resist system is highly resistant to etching in an oxygen plasma and could be integrated into a bilayer resist process as a thin imaging layer coated on a thick hard baked novolac resist layer. Its behaviour as a photosensitive resist at ’A = 436 nm and as a positive deep uv resist at ’A = 257 nm have been evaluated. The schematic function of the resist and its lithographic properties are given in this publication. These preliminary results favour their application as bi layer resist systems.
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The thickness dependence of resist performance has been investigated. It has been reported that principal properties such as resist sensitivity show strong dependence on resist film thickness. In current standard resist called chemically amplified resist, acids play the most important role in resist pattern formation. However, the dependence of acid concentration on resist thickness has not been reported. Better understanding of acid related issues is important for the development of high performance resists and the precise simulation of resist pattern profiles. In this work, the acid density in poly(4-hydroxystyrene), which is a widely-used backbone polymer for chemically amplified resists, was measured quantitatively by spectroscopic experiments. The average acid concentration nonlinearly increased by 14% with the increase of resist thickness from 65 to 4000 nm.
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