Application of polyimide Langmuir-Blodgett films to deep UV resists

The preparation of Langmuir-Blodgett (LB) films based on a photosensitive polyimide precursor 2 and their application to deep UV resists have been studied. LB films fabricated from a mixed monolayer of polyimide precursor 2-octadecyl alcohol-benzoin ethylether (molar ratio, 3:3:1) were found to act as negative working resists with a resolution of 0.5 μm space and 1.0 μm line, a sensitivity of 100 mJ cm^-2 and good plasma etching resistance. They are promising for application as KrF and ArF excimer laser resists corresponding to 16 and 64 Mbit dynamic random access memories.     

Organic–Inorganic Nanocomposites: Unique Resists for Nanolithography

Ultra large‐scale integration (ULSI) should lead to 100 nm production circuits by 2006 as predicted by the Semiconductor Industry Association (SIA). For sub‐100 nm lithography it is desirable to synthesize higher performance and higher contrast resists. An optimum combination of high contrast necessary for sub‐100 nm resolution, high sensitivity for high throughput can be achieved by carefully engineering organic–inorganic nanocomposites, acting as optimum resists for a given lithographic process. This review outlines emerging approaches towards the achievement of these goals. A section also highlights selected state‐of‐the‐art organic resists. Nanocomposite resists for sub‐100 nm features have included the incorporation of fullerene C₆₀ in a commercial resist ZEP520 (see Figure). Alternatively, nanoscale silica particles were incorporated in the polymer backbone as covalently bonded pendant clusters. The dispersion of 8–10 nm silica particles in a chemically amplified resist has also been reported. In all these approaches, a higher softening temperature (T_g) and increased rigidity, due to increased density of the film resulted. Higher etch resistance as well as increased mechanical properties and also enhanced resist performance for nanometer pattern fabrication have been obtained in these nanocomposites. Alternative approaches to conventional lithography, based on self‐assembled nanostructures, incorporating inorganic features as well as nanoimprinting via silicon polymer precursors, are also discussed.     

Derivation of Density — Thickness Curves for Soft X-Ray Radiographs from X-Ray Spectra

The response of evaporated layers of doped AgBr to irradiation with electrons is studied. The sensitivity, gamma value and maximum density are determined at various accelerating voltages. Resolution of 0.15 pm wide lines is achieved at extremely high sensitivity - 10^-9 C/cm², which is 2 to 4 orders of magnitude higher than that of commercial resists used in E-beam lithography.

It is established that the distribution of latent image centres in the bulk of AgBr microcrystals is similar to that of exposure to visible light and X-ray. On this basis the mechanism of the photographic process is discussed.     

A high resolution water soluble fullerene molecular resist for electron beam lithography

Traditionally, many lithography resists have used hazardous, environmentally damaging or flammable chemicals as casting solvent and developer. There is now a strong drive towards processes that are safer and more environmentally friendly. We report nanometre-scale patterning of a fullerene molecular resist film with electron beam lithography, using water as casting solvent and developer. Negative tone behaviour is demonstrated after exposure and development. The sensitivity of this resist to 20?keV electrons is 1.5 × 10(-2)?C?cm(-2). Arrays of lines with a width of 30-35?nm and pitches of 200 and 400?nm, and arrays of dots with a diameter of 40?nm and a pitch of 200?nm have been patterned at 30?keV. The etch durability of this resist was found to be ～2 times that of a standard novolac based resist. Initial results of the chemical amplification of this material for enhanced sensitivity are also presented.     

Evaporated AgBr Layers: Response to Soft X-Ray Irradiation

The response of evaporated layers of pure and doped AgBr to irradiation with soft A1 Kα X-rays (λ = 8.34 Å) is studied. The gamma values and maximum density are determined at various accelerating voltages. The layers’ sensitivity is by 3 to 5 orders of magnitude higher than that of commercial resists used in X-ray lithography. The distribution of latent image centres in the bulk of AgBr microcrystals is similar to that in the case of exposure to visible light. A qualitative estimation of the possibilities for reproduction of microstructures by X-rays is given.     

Recent improvements in monomolecular resists

This paper describes recent results obtained with ω-tricosenoic acid in the field of monomolecular electron resists, after a thorough purification in the course of the synthesis. The sensitivity is improved by a factor of 100 and reaches 0.5 μC cm^?2; contrast is increased from 0.7 to 2.4. These results seem to be due to an increase in the length of the polymer. The better contrast improves the resolution which is reduced to 600 Å on a film 900 Å thick.     

Verification of point-spread-function-based modeling of an extreme-ultraviolet photoresist

A crucial component of lithographic modeling is the resist. Resists typically used at extreme-ultraviolet (EUV) wavelengths are derivatives of deep-ultraviolet chemically amplified resists. Models that describe these resists are often very complicated and are dependent on a large number of free parameters. Point-spread-function-based resist modeling serves as a simple alternative. I show this type of modeling to be a viable technique at EUV wavelengths by directly comparing modeling results with a variety of printing metrics, including process windows and isodense bias.     

A small scale Z-pinch device as an intense soft X-ray source

A small scale (400 J) device to study the application of radiation emitted by a plasma Z-pinch to microscopy and microlithography has been built. As a pulsed emitter of soft X-rays the Z-pinch is an inexpensive source for high resolution flash microscopy of thin films, and live and unstained biological specimens. In the repetitive mode, radiation from the device was used to expose resists for microlithography. Windows of different plastics shielded the resists from debris and allowed exposure of resists in air. The use of different pinching gases allowed tunability of radiation.     

基于奇异值分解和混沌映射的脆弱认证水印

提出一种基于奇异值分解和混沌映射的图像脆弱认证水印算法,将混沌映射的初值敏感性应用到图像的篡改检测中.对图像子块进行奇异值分解,同时利用Logistic混沌映射产生认证水印;然后利用Logistic混沌映射设计了一个子块与子块之间的映射函数,将认证水印序列嵌入在相应映射块的LSB上.实验结果表明,算法不仅对篡改非常敏感,而且能够有效地抵抗拼贴攻击和区分篡改图像内容与篡改水印.     

厚胶光刻中曝光光强对光化学反应速率的影响

针对用于厚层光刻的重氮萘醌类正性光刻胶,利用动力学模型,分析了光化学反应速率的影响因素;给出了光化学反应速率明显受光强变化的影响以致互易律失效的原因。对厚度24μm的光刻胶AZP4620在相同曝光量而光强分别为3.2mW/cm2和0.63mW/cm2的条件下进行了数值模拟和实验。当曝光光强为3.2mW/cm2时仅需300s,即可显影完全,而当曝光光强为0.63mW/cm2时需要的时间长达2400s,才显影完全,且面形轮廓差异较大。因此,在厚胶光刻中,当曝光光强较大时应适当减小曝光量,反之,应适当增加曝光量。     

Asymmetric encryption algorithm for colour images based on fractional Hartley transform

This paper presents a new scheme for encryption of single-channel colour images. The scheme uses amplitude- and phase-truncation approach to introduce non-linearity for enhanced security. Further, the colour image encryption is performed in the fractional Hartley domain, which is relatively less investigated. The encryption starts with an affine transform of each channel of the input colour image. Thereafter, one of the channels is considered as the input amplitude image while the other two are used as phase masks, one in the spatial and the other in the frequency domain. A detailed analysis of the scheme’s sensitivity to various encryption parameters has been carried out. In addition, security analysis of the scheme against attacks establishes the scheme’s robustness. The combined use of the affine transform and phase-truncation approach for colour image encryption in the fractional Hartley domain is attempted for the first time in this study. It is shown that the proposed scheme resists the special attack.     

Sensitivity study of two high-throughput resolution metrics for photoresists

The resolution of chemically amplified resists is becoming an increasing concern, especially for lithography in the extreme ultraviolet (EUV) regime. Large-scale screening is currently under way to identify resist platforms that can support the demanding specifications required for EUV lithography. Current screening processes would benefit from the development of metrics that can objectively quantify resist resolution in a high-throughput fashion. Here we examine two high-throughput metrics for resist resolution determination. After summarizing their details and justifying their utility, we characterize the sensitivity of both metrics to known uncertainties in exposure tool aberrations and focus control. For an implementation at EUV wavelengths, we report aberration and focus-limited error bars in extracted resolution of approximately 1.25 nm rms for both metrics, making them attractive candidates for future screening and downselection efforts.     

Design and synthesis of an optimum performance crosslinking resist based on poly (2,4-dimethylstyrene)

We have successfully synthesized and optimized a range of copolymers of 2,4-dimethylstyrene and 3/4-chloromethylstyrene (vinyl benzyl chloride, VBC) as high-performance single-stage-crosslinking electron-beam resists. The formulations were synthesized by a reproducible free-radical-initiated solution polymerization technique which has the merit of simplicity. While the product polymers are not monodisperse, and hence cannot achieve optimal lithographic contrast, they benefit from a structural feature which prevents chain scission during irradiation and hence increases the intrinsic sensitivity of the resist. Resists with sensitivities very close to target values of 5 and 12 C cm^-2 have been demonstrated, with negligible chain scission and lithographic contrast of 2.3. ©1999 Kluwer Academic Publishers     

Design and performance of EUV resist containing photoacid generator for sub-100 nm lithography

To fulfill the SIA roadmap requirements for EUV resists, the development of entirely new polymer platforms is necessary. In order to address issues like Line Edge Roughness (LER) and photospeed, we have developed a novel chemically amplified photoresist containing a photoacid generator (PAG) in the main chain of the polymer. The incorporation of a cationic PAG unit, phenyl methacrylate dimethylsulfonium nonaflate (PAG), in the resist backbone showed increased sensitivity, when compared with analogous blend PAG resist samples. In addition, the overall lithographic performance improved by using the counter anion (nonaflate) in the PAG units. The newly synthesized polymer bound PAG resist, poly (4-hydroxystyrene-co-2-ethyl-2-adamantyl methacrylate-co-PAG) showed sub-50 nm features using EUV Lithography.     

The Action of Ferricyanide on Sulphur-Sensitized Emulsions

It is shown that sulphur-sensitized emulsions may be fogged or desensitized by ferricyanide, according to the concentration, provided that a sufficient supply of silver ions is made available. The distinction previously drawn betwsen this form of sensitization and silver-sensitization on the basis of response to ferricyanide is thus weakened.⁽⁷⁾ It is suggested that silver ions are adsorbed to sensitizing substance and promote adsorption of ferricyanide. Some results on the absorption of ferricyanide to unsensitized emulsion grains at various pAg levels are given. Slight effects can also be produced in unsensitized emulsions, pointing to the presence of foreign centres created during physical ripening. A small part of the sensitivity created by digestion, which resists the action of ferricyanide, is attributed to etching by the sensitizer. The amount of ferricyanide required to desensitize an emulsion at low pAg is slightly greater than that needed for latent image destruction. The response of digested emulsion to small amounts of ferricyanide (production of fog) would probably enable a very sensitive test for the latter to be worked out. In gensral, a parallel between the action of light and ferricyanide is noted.     

抗蚀剂的研究进展

综述了紫外光曝光的抗蚀剂、电子射线抗蚀剂、Ｘ射线抗蚀剂、电沉积抗蚀剂的组成、成像原理和分辨率,并对几种高性能抗蚀剂的原理及用于抗蚀剂的新材料做了介绍。     

Removing hardened organic materials during fabrication of integrated circuits

Several solvents were evaluated as etchants for highly adherent, hardened organic resists. A mixture comprised of 80–95% by volume anhydrous hydrazine and 20-5% of dimethyl sulfoxide was found to be the best for quick removal of the resist. The above mixture, if used below 40° C, leaves a stripped surface without deleteriously affecting any of the normal materials included in the integrated device structure. The solvent has been tested for stripping hard-baked resists, plasma-hardened resist and for lift-off of aluminum and co-sputtered materials.     

Ion-implanted resist removal using atomic hydrogen

We removed B-, P-, and As-ion-implanted positive-tone novolak resists with an implantation dose of 5 × 10¹² to 5 × 10¹⁵ atoms/cm² at 70 keV, using atomic hydrogen. Though the removal rate decreased with increase in the implantation dose, all of the ion-implanted resists were removed. The rates of thickness of the surface-hardened layer/all resist layer of B, P, and As implanted resists were 0.38, 0.26, and 0.16, respectively, by SEM observation. The removal rate decreased with increasing the rate of the surface-hardened layer. The energy supplied from the ions to the resist concentrated on the surface side in the increasing order of B-P-As.     

Nanopatterning on nonplanar and fragile substrates with ice resists

Electron beam (e-beam) lithography using polymer resists is an important technology that provides the spatial resolution needed for nanodevice fabrication. But it is often desirable to pattern nonplanar structures on which polymeric resists cannot be reliably applied. Furthermore, fragile substrates, such as free-standing nanotubes or thin films, cannot tolerate the vigorous mechanical scrubbing procedures required to remove all residual traces of the polymer resist. Here we demonstrate several examples where e-beam lithography using an amorphous ice resist eliminates both of these difficulties and enables the fabrication of unique nanoscale device structures in a process we call ice lithography. (1, 2) We demonstrate the fabrication of micro- and nanostructures on the tip of atomic force microscope probes, microcantilevers, transmission electron microscopy grids, and suspended single-walled carbon nanotubes. Our results show that by using amorphous water ice as an e-beam resist, a new generation of nanodevice structures can be fabricated on nonplanar or fragile substrates.