TaN Etch in CF4/CHF3 gas for MEMS/Sensor application
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TaN was widely used as Cu diffusion barrier in CMOS Cu-BEOL technology, in which it was removed by CMP process. Some work was done on TaN etch by Br/Cl-based gas for metal gate application. But seldom work was done for TaN etch in CF-based gas. In this work TaN etching in CF4/CHF3 gas was investigated on CVD alpha-Si substrate for CMOS compatible MEMS/Sensor application. To avoid resist poisoning problem of metal nitrides, a thin layer of SiON and oxide was deposited on TaN. The patterning sequence included 248 nm lithography, etching thin SiON and oxide, followed by TaN etching. It was found serious residue problem on the unpatterned area. After EDX check, Ta was found in the residue. Assumption was made for the mechanism of residue formation. Based on this model, the process was optimized and a 4-step etching process was developed. The main feature of this process is TaN etching in CF4/CHF3 gas with low power and pressure including a post-etching de-fencing process to solve the residue problem. The optimized process can well control the TaN etching profile and Si loss during TaN over-etch, and was successfully used in the MEMS/Sensor patterning process.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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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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Resist heating is one of the major contributors to errors in high-throughput maskmaking using electron-beam lithography. Temperature affects the physical and chemical properties of resists. Response of resist sensitivity to the temperature was measured for a number of electron-beam resists. The following resists were characterized: PMMA, PBS, SPR-700, EBR-900, ZEP-7000, and chemically amplified resist UVII-HS. Two methods were used for such measurements: (a) using a heated stage, the temperature of which was controlled externally, (b) using a test pattern exposed at regular exposure conditions. Nonlinearity of sensitivity response was found for a number of resists. A resist heating quality parameter was introduced which allowed a practical comparison of resists in terms of heating. Resists were compared using this parameter.
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Dry etching
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Plasma Etching
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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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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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Although EUV lithography has been prepared for next generation litho-technique for several years, there are still lots of obstacles on its way. Especially, phase defect from the mask, and immaturity in the resist should be solved as soon as possible because they are directly related to realizing patterns on the wafer. ASET has been focusing on these two problems, that is, the mask-related defect control and the resist screening for EUV application. In this study, we concentrate on the resist evaluation for the EUV lithography application, mainly commercial CAR (Chemically- Amplified Resist) type resist, for example, ArF resist based on polymethacrylate and KrF resist based on poly(4- hydroxystyrene) (PHS). We screened tens of resists in viewpoint of resolution, photo-speed, and LWR (Line Width Roughness). We used two METs (Micro-Exposure Tools). The one is HiNA in ASET and the other is MET in Lawrence Berkeley National Lab. (LBNL) to evaluate resist. And we used EUV masks fabricated by DNP and ASET. Some resist showed modulation on the wafer for 28nm-hp line and space pattern and some resist showed very high photo-speed about 5mJ/cm2. Photo-speed could be improved about 25% by controlling the amount of additives, PAG and quencher. However, improvement in photo-speed caused degradation in resolution. This means there are trade-off relation between resolution and photo-speed. And we also evaluated polymer-bound PAG resist, which showed new possibility for EUV resist. And we encountered unexpected problem, pattern lifting, which was solved by using bufferlayer to increase attachment force between resist and wafer surface. We conclude that polymer bound PAG resist is a good approach to lower LWR of resist for EUVL application and bufferlayer tuning and matching with resist is also needed for low LWR. The EUVL masks were fabricated by Dai Nippon Printing Co., Ltd. The HiNA set-3 projection optics were developed and provided by Nikon Corporation. This work was supported by NEDO.
Extreme Ultraviolet Lithography
Extreme ultraviolet
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