Performance characteristics of diazo-type photoresists under e-beam and optical exposure

The performance characteristics of three different diazotype positive photoresists such as Shipley AZ2400, Kodak 809, and Polychrome PC129, are compared after optical exposure and electron-beam exposure. The development rates for both e-beam and optically exposed resists are measured by an in-situ automated technique using the IBM Film Thickness Analyzer. The optical exposure parameters are obtained at three wavelengths (4358, 4047, and 3650) by computer-controlled transmission measurements. The optical exposure and development parameters permit direct quantitative comparisons for these photoresists. The development rates of e-beam and optically exposed resists are compared. Also a comparison of e-beam sensitivity between the three resist systems is made by studying the resist profile shape after development in the scanning-electron microscope (SEM).     

光学光刻工艺中邻近效应的定量分析

随着超大规模集成电路 (VLSI)图形密度的增大 ,邻近效应已成为光学光刻的关键问题之一。通常在平整硅片上对 0 5 μm图形采用 0 5 4NA和传统的单层i线抗蚀工艺时 ,密集图形和孤立图形间的线宽差异大约为 0 0 8μm。然而 ,这一线宽差异已严重地影响了实际生产的工艺稳定性。阐述了邻近效应对图形尺寸、线条与间隙占空比、衬底膜种类、曝光过程的散焦效应、与抗蚀剂厚度变化有关的抗蚀工艺条件和显影时间的依赖性。同时 ,采用 2种不同抗蚀剂实验监测了不同潜像对比度引起的关键尺寸 (CD)偏差。为减小实际图形因抗蚀剂厚度变化引起的CD差异 ,获得最佳抗蚀剂厚度 ,进行了一种模拟研究。     

Properties of a high resolution negative photoresist

The recent advantages in designing large and very large integrated circuits have imposed stringent requirements on the processes used in the production of semiconductor devices. The requirements on photoresists have been increased not only with regard to improved exposure tools but also in view of other process steps such as plasma etching, ion implantation, etc. A new developed negative photoresist, Selectilux N, combines the well-known advantages of a cyclized polyisoprene-based resist with the capability to resolve features in the 1 to 2 micron range and a high thermal stability. The main properties are: high photospeed to reduce the influence of oxygen and to prevent thickness loss, high contrast to achieve good resolution in projection exposure, low flow distortion up to 240 C to ensure good image stability, low swelling during the development to prevent reduction of the resolution. Photospeed and contrast can be derived from the characteristic curve of Selectilux N which is obtained by the determination of the remaining thickness of the resist vs exposure energy.     

A high resolution negative electron resist by image reversal

The use of AZ 1350 family photoresists as negative electron resists is described. Conventional photolithographic technology is used to coat and process the resist, with the exception of an e-beam exposure for patterning. A flood UV exposure is used for image reversal. Using 1.5 µm initial thickness, the exposure threshold for 6 s development in 1 : 1 AZ : H2O developer is 7 µC/cm². The resist contrast under these conditions is 1.3; and the sensitivity is about 25 µC/cm²(70% thickness remaining). Useful resolution on SiO2/Si and Al/SiO2/Si substrates is demonstrated to be at least 0.5 µm, and the resist is shown to mask the plasma etching of Al.     

Profile simulation of negative resist MRS using the SAMPLE photolithography simulator

The profile simulation of a negative deep UV resist, MRS (micro-resist for shorter wavelengths), is realized by application of the SAMPLE photolithography process simulator developed on the basis of the modeling of AZ-type positive photoresists. The absence of swelling permits MRS to use the same simulation algorithm as AZ-type resists. Two exposure parameters (A and B) successfully represent the intense light absorption of MRS, and the simulation traces the development process to show the unique undercut profile of MRS.     

Azide-phenolic resin photoresists for deep UV lithography

A photosensitive composition, consisting of an aromatic azide compound (3,3'-diazidodiphenyl sulfone) and a phenolic resin (poly(p-vinylphenol)), called MRS-1, has been prepared and evaluated as a negative deep UV resist for high resolution lithography. Solubility of MRS-1 in an aqueous alkaline developer decreases upon exposure to deep UV radiation. The alkaline developer removes the unexposed areas of MRS-1 by an etching-type development process. No swelling-induced pattern deformation occurs, and images of submicrometer resolution are obtained. The resist is approximately two orders of magnitude more sensitive than PMMA(polymethyl methacrylate). The exposure time of 5 s is sufficient for deep UV contact printing using a 500-W Xe-Hg lamp. The resistance to dry etching of MRS-1 is comparable to that of conventional positive photoresists based on phenolic resin.     

微制造光刻工艺中光刻胶性能的比较

在MEMS微加工和实验过程过程中,出于制造成本、光刻胶性能的考虑,需要选用合适的光刻胶.本文介绍了常用的正性胶和负性胶以及其曝光、显影的过程,正性胶和负性胶曝光过程漫射的图形缺陷.比较了正性胶和负性胶的各种性能以及各种光刻方式下选用的正负性胶及它们的光刻灵敏度,为微加工过程和实验操作提供指导.     

Photosolubility of diazoquinone resists

The photochemical properties of a diazoquinone/novolak resist system were studied over a wide range of material and processing parameters in order to determine the optimum values for a given application. These resists are representative of the commercial positive-working photoresists being used for high-resolution lithography. The solubility of the resist in an alkaline developer depends on exposure E asDelta g^{-1} = [g_{0}(E/E_{e})^{m}]^{-1} + [Delta g_{infin}]^{-1}where the net development rate (Delta g) is the difference between solubility rates of the exposed (g) and unexposed (g0) sample. Three of these parameters characterize the lithographic response of the resist. They depend mainly on the resist composition but not on the processing conditions. Eeis a measure of the sensitivity and ranges from 10 to 20 mJ/cm²of 405-nm light for useful resist formulations. The contrast parameter (m) increases slowly with sensitizer concentration while the saturated solubility ratio (g_{infin}/g_{0}) inereases very rapidly. The fourth parameter (g0) depends strongly on processing parameters. It can readily be set to provide the desired development time, e.g., by adjusting the developer strength. On a more fundamental level, it is found that the dependence of the solubility on exposure can be expressed in a unified manner for all the resist formulations studied asg approx g_{0} exp (2 times 10^{-20} n_{e})where neis the number of exposed sensitizer molecules per cubic centimeter.     

Consequences of non-standard bleaching on microlithographic performance

Photobleaching of photoresists has been at the core of high resolution relative to a particular exposure wavelength, but the accelerated advancements dictated by the sharp economic considerations of the roadmap, as well as the complexity of exposure-material-technology triad, made photobleaching a secondary subject of interest. However, the still-strong innovation in optical photolithography as well as the emergence of biomedical microdevices as a major market for microfabrication, suggest that the reconsideration of the photobleaching as a main modulator of lithographic performance is fully warranted. This study reports on the photolithography simulations which implemented a non-standard bleaching behaviour, both documented previously and hypothetical. We show that minute changes in the photobleaching behaviour can result in important changes in the performance of the lithographic process latitude, speed and resist profile.     

Exact solution for the kinetics of the image reversal process

The model equations describing the image reversal process with positive photoresists have been solved by extending the recently derived analytical solution of Dill's equations for the exposure bleaching of positive photoresists. The solution is presented in a closed form that requires only simple numerical integrations to determine the time-dependent two-dimensional concentration profiles of the photoactive compound (PAC).     

Reciprocity behavior of photoresists in excimer laser lithography

The effect of high excimer-laser peak powers on the lithographic exposure process is quantitatively examined to investigate the reciprocity behavior of several photoresists. Using the bleaching of an absorption peak as the measure of resist response, it is found that there is no dependence of the resist sensitivity on the peak power of the radiation. Thus the higher UV intensity of excimer lasers can be fully exploited in faster exposures of the resists.     

3D Direct Laser Writing of Highly Absorptive Photoresist for Miniature Optical Apertures

The importance of 3D direct laser writing as an enabling technology increased rapidly in recent years. Complex micro-optics and optical devices with various functionalities are now feasible. Different possibilities to increase the optical performance are demonstrated, for example, multi-lens objectives, a combination of different photoresists, or diffractive optical elements. It is still challenging to create fitting apertures for these micro optics. In this work, a novel and simple way to create 3D-printed opaque structures with a highly absorptive photoresist is introduced, which can be used to fabricate microscopic apertures increasing the contrast of 3D-printed micro optics and enabling new optical designs. Both hybrid printing by combining clear and opaque resists, as well as printing transparent optical elements and their surrounding opaque apertures solely from a single black resist by using different printing thicknesses are demonstrated.     

Image reversal of positive photoresist: Characterization and modeling

We report on an investigation of a so-called image-reversal process where a negative tone image can be obtained with a positive resist. The reversal process is achieved by addition of a base to the exposed photoresist and a subsequent flood exposure. First, we characterize the image reversal by means of the characteristic curves, thus optimizing the process. A simple analytical model and a two-dimensional numerical simulation program have been developed in order to evaluate the dependence of the edge slope of the image-reversed resist line on resist and exposure parameters. Experimental investigation confirmed the simulation result that both positive and negative line edge slopes can be achieved with the image-reversal process by properly adjusting the exposure parameters. Finally, the image-reversal process has been compared experimentally to the standard positive process, considering linewidth control on profiled surfaces.     

Enhancement of resist plasma erosion rates by electron-beam hardening

A nonthermal method of hardening positive photoresists by means of a scanned high-energy electron beam in preference to direct resist heating is described. It has been established that moderate electron doses produce significant resist cross-linking without flow. Plasma etch resistance can be enhanced in the resists with no degradation of the as-developed line profile.     

Shorter-wavelength lithography utilizing MRS-type negative resists

New negative photoresists, called MRS-type resists, are successfully applied to deep-UV 1:1 projection printing and 365 nm 10:1 reduction projection printing. The MRS-type resists are characterized by intense absorption of exposure light and absence of swelling in aqueous developer solutions. They resolve steep profile submicron images in a 1.0 μ thick film. They are not adversely affected by reflected light from water surfaces. In order to use MRS-type resists with broader development latitude, optimizing the extent of light absorption is important because the resist profiles strongly depend on development conditions due to increasing solubility towards the resist bottom.     

用于注入层用途的湿法显影有机抗反射涂层

底部抗反射涂层(BARCs)和光刻胶已被广泛地用于半导体制造中的光刻加工工艺中。BARCs在光刻中的主要好处就是聚焦?曝光宽容度的改善,提高了关键尺寸的控制,消除了反射凹口,防止远紫外抗蚀剂由基底毒化。过去,BARCs主要被用于关键图层,例如栅和接触孔图层。但是随着集成电路特征尺寸的不断缩小,BARCs在注入层中的应用中由于基片表面形态引起的反射缺口和关键尺寸变化容差也变得更小,从而使BARCs的使用变得更为迫切。我们已成功开发了专门为注入层用途的湿法显影抗反射涂层。传统的干法刻蚀不适合用于注入层,因为它的工艺复杂而且在刻蚀过程中可能导致基片损坏。评述了产生注入光刻图层的工艺并讨论了湿法显影式抗反射涂层的设计标准和要求,同时还将讨论用于注入层光刻的湿法显影抗反射图层及其工艺的挑战。     

Exposure bleaching of nonlinear resist materials: Exact solution

Dill's model equations for the exposure bleaching of positive photoresists have been solved exactly in a closed form when the bleaching characteristics are nonlinear. As an application, the simultaneous bleaching of a positive photoresist and that of a polysilane contrast-enhancing film (CEF) is solved to determine the photoactive compound (PAC) concentration.     

Optical lithography

This is the first in a series of papers describing a theoretical process model for positive photoresist. This model, based upon a set of measurable parameters, can be used to calculate the response of photoresist to exposure and development in terms of image surface profiles. The model and its parameters are useful in many ways, from measuring quantitative differences between different resist materials to establishment of process sensitivities and optimization of the resist process within a manufacturing system. In this paper, the concepts of photoresist modeling are introduced by following the exposure and development of a photoresist film on silicon exposed by a uniform monochromatic light flux. This very simple example provides insight into the complex nature of the photoresist process for reflective substrates. The accompanying paper, "Characterization of Positive Photoresists," gives detail about measurement of the new photoresist parameters. It is supported by "In-Situ Measurement of Dielectric Thickness During Etching or Developing Processes" which discusses automated experimental techniques needed to establish photoresist development rates. These resist parameters provide a complete quantitative specification of the exposure and development properties of the resist. They also allow quantitative comparisons: lot to lot, material to material, and processing condition to processing condition. The fourth paper, "Modeling Projection Printing of Positive Photoresists," applies the process model to one technique of photoresist exposure. This paper contains the detailed mathematics of the model. The model is then used to calculate line-edge profiles For developed resist images.     

Investigation of photoresist-specific optical proximity effect

Optical proximity effects arising from individual resist characteristics are investigated. The parameters studied are those used in photoresist exposure and development simulation using the SOLID and Prolith/2 programs. The optical proximity effect is found to be independent of the exposure parameters but greatly affected by the development process and is shown to be a function of the Mack parameter, n, which is related to the resist contrast, γ. Finally, in order to put this effect into perspective with other resist selection criteria, the development parameter, n, is also shown to be related to wall angle and depth-of-focus (DOF).

The results of this investigation will therefore enable the user to select the most appropriate photoresist for a specific application.     

Dual-polarity, single-resist mixed (e-beam/photo) lithography

A lithographic process is described which involves electron-beam exposure of the small geometries of an integrated circuit pattern and optical exposure of the large geometries onto the same resist layer. A single development step produces both electron and optical images. With the use of a diazo-type resist, either positive or negative e-beam images can be obtained, so that suitable selection of the photomask tone allows complete flexibility in the choice of polarity of the composite pattern. Using AZ-2415, e-beam defined features as small as 0.4 µm joining large optically defined pads have been produced in doped polysilicon by plasma etching.