Steep profile resist patterns through 1:1 deep UV projection printing

Steep profile resist patterns of 1 µm lines and 1 µm spaces are delineated by 1:1 projection printing using a novel, deep uv, negative resist. Strong absorption of deep uv light and the absence of swelling caused by the developer contribute to the high resolution of the resist. The sensitivity is adequate and the optimum scanning exposure time for a 4 inch wafer is about one minute. The processing procedure is the same as that for conventional photolithography.     

Deep UV 1:1 projection lithography utilizing negative resist MRS

A negative deep UV resist Micro Resist for Shorter wavelengths (MRS) is successfully applied to 1:1 projection printing. The MRS is characterized by strong absorption of deep UV light and absence of swelling in the developer. It resolves steep profile images of 1-µm linewidth in 1-µm-thick films. The resist has extremely high sensitivity to deep UV light. Scanning exposure time necessary for a 4-in wafer is about 25 s. The MRS exhibits dry etching resistance superior to that of an AZ-type positive resist. Furthermore, MRS is not adversely affected by reflected light from stepped aluminum surfaces. Application of MRS should open the way to realization of a practical deep UV 1:1 projection lithography featuring high resolution and throughput.     

Structural Transformation of Acrylic Resin upon Controlled Electron‐Beam Exposure Yields Positive and Negative Resists

Zwitter polymers are defined as polymers that undergo transformation from a linear to a crosslinked structure under electron‐beam irradiation. A resist polymer may be either linear or crosslinked, depending on electron‐beam dosage. The structural transformation of acrylic resin make it suitable for applications in positive and negative resists in the semiconductor field. The contrast ratio and threshold dose both increase with increasing resist thickness for both the positive and negative resists, while the positive resist exhibits better contrast than the negative. The intensity of the characteristic Fourier‐transform infrared absorption band at 1612 cm^–1 (vinyl group) is used to explain the phenomena behind these resist transformations. We evaluate the effects of two important processing conditions: the soft baking and post‐exposure baking temperatures. Pattern resolution decreases upon increasing the baking temperature, except for soft baking of the negative resist. The effect of electron dose on the pattern resolution is also discussed in detail for both resists. High electron‐beam exposure does not improve the etching resistance of the resist because of the porous nature of the resist that develops after high‐dosage irradiation.     

22-nm Half-pitch extreme ultraviolet node development at the SEMATECH Berkeley microfield exposure tool

Microfield exposure tools continue to play a dominant role in the development of extreme ultraviolet (EUV) resists. Here we present an update on the SEMATECH Berkeley 0.3-NA microfield exposure tool and summarize the latest test results from high-resolution line-space printing. Printing down to 20-nm is presented with large process latitude at 22-nm half-pitch lines. Also presented are line-edge roughness results along with a discussion of the importance of mask contributors to line-edge roughness measured in resist. Finally we briefly describe an upgrade to the tool that will enable EUV resist development at the 16-nm half-pitch node and beyond. (This paper was presented in MNE 2008 conference, <http://www.mne08.org>, <http://www.mne-conf.org>).     

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.     

Optical lithography: The implications of the electromagnetic field theory

Optical projection lithography and the contact printing of a half plane are treated, based on the electromagnetic diffraction theory. Integral representations are given for the time-average electric-energy density distribution of the projected edges which are illuminated by a linearly polarized monochromatic wave or by a quasi-monochromatic incoherent beam. The image space is either homogeneous or a perfectly conducting screen is inserted normal to the optical axis. Contact printing is treated in terms of rigorous electromagnetic-field theory, by which the electromagnetic-field distribution is derived in a stratified substrate, each layer of which may have an arbitrary refraction index. Numerical results for boil contact printing and projection are given for edges which are illuminated by coherent beams with the polarization either normal or along the edge. In addition, the distribution due to the projection of an incoherent edge is given. The distributions obtained through contact printing are presented in the resist layer, Which is applied directly on the aluminum substrate or on an amorphous silicon antireflection coating as the intermediate stratum. The ultimate positive and negative resist patterns are systematically compared.     

Advances in the design of organic resist materials

The resist materials used today in the fabrication of semiconductor devices were not expressly designed for this application. They were originally developed for use in the printing industry and were simply adopted by the electronics industry with relatively minor modifications. The performance of these resists was more than adequate for initial applications and, as a result, it was not necessary completely understand the chemistry responsible for lithographic behavior. However, the current resolution requirements and severe processing conditions in device manufacturing make it necessary to understand resist chemistry not only to maximize the performance of available materials but also to allow for the rational design of new materials.The paper discusses three topics which demonstrate that one can specifically design a resist system for optimal performance. The first deals with the generation of a negative tone image from a positive photoresist. The second topic addresses techniques for significantly reducing the time required to expose a resist. And finally, the materials requirements for the next generation of multilayer resist (MLR) systems will be discussed.     

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.     

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.     

Characterization of a photoresist with wavelength selected tone

The line edge profile simulation of a tone-switching resist system, obtained from the dissolution model of dual-sensitized, novolak-based resist in aqueous developer, is described. The model incorporates the actinic response of both a positive and a negative sensitizer in a two-pattern lithographic process that simultaneously exposes the same resist film. These response data are combined with dissolution rate measurements to establish a model for the resist and carry out SAMPLE simulation of resist line edge profiles for contact and projection printing. The model predictions are compared with SEM micrographs of exposed resist features     

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).     

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.     

A General Approach to Semimetallic,Ultra‐High‐Resolution,Electron‐Beam Resists

Commercial electron‐beam resists are modified into semimetallic resists by doping with 1–3 nm metal nanoparticles, which improve the resolution, contrast, strength, dry‐etching resistance, and other properties of the resist. With the modified resists, fine resist nanopatterns from electron‐beam lithography are readily converted into 5–50 nm, high‐quality multilayers for metallic nanosensors or nanopatterns via ion‐beam etching. This method solves the problem of the fabrication of fine (<50 nm) metallic nanodevices via pattern transferring.     

Optimization of the composition of a new MRS-type negative resist

Sensitizer concentration is optimized for a new negative photoresist, MRL (Micro Resist for Longer wavelengths) with the assistance of computer simulation. The resist, which has photosensitivity in the ordinary UV region, resembles a deep UV resist MRS in terms of light absorption characteristic. It is found that a photosensitizer concentration of 20 wt% (based on the resin) is suitable for a reduction projection exposure system that utilizes UV light at 365 nm. A steep profile resist image of 0.7-µm lines and 0.7-µm spaces in a 1.0-µm thick resist layer is obtained using the MRL of optimized composition and the exposure system.     

Low energy electron proximity printing using a self-assembled monolayer resist

A simple method for high resolution (<100nm) lithography is reported. We use electrons with energies ranging from 100–300eV emitted by tungsten field emission tips for proximity printing of stencil masks. A comparison with other parallel fine line techniques, like proximity printing and projection lithography with x-rays, high energy electrons or ions, reveals the specific advantages and restrictions of our method.

The masks are made of ≈ 100nm thick silicon membranes structured by e-beam lithography and reactive ion etching (RIE). Free standing gratings with periods down to 100nm serve as test patterns for proximity printing with gaps of ≈15μm. due to the short penetration depth of the low energy electrons, ultrathin resist systems are needed. We have chosen self-assembled monolayers (SAMs) of hexadecane thiol on gold. The monolayer resist is degraded by the exposure, the structures can be transferred by wet chemical etching. Periodic gold structures below 100nm lines and spaces have been generated this way. It was found, that the SAM resist of hexadecane thiol can be used as a positive or negative tone resist depending on the exposure dose.     

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.     

Resists for fine-line lithography

Resists are radiation-sensitive materials used in the fabrication of integrated circuits (VLSI) for imaging the desired pattern onto the silicon wafer. Most resists in use today consist of polymeric solutions that are spin-coated onto the silicon wafer, exposed in a lithographic tool, developed, and completely removed after the pattern has been transferred to the substrate. This paper presents a historical development of resist materials, present uses of resists, and future requirements, dictated primarily by developments in lithographic tools.     

3D Printed Microstructures Erasable by Darkness

To advance the applications of direct laser writing (DLW), adaptability of the printed structure is critical, prompting a shift toward printing structures that are comprised of different materials, and/or can be partially or fully erased on demand. However, most structures that contain these features are often printed by complex processes or require harsh developing techniques. Herein, a unique photoresist for DLW is introduced that is capable of printing 3D microstructures that can be erased by exposure to darkness. Specifically, microstructures based on light-stabilized dynamic materials are fabricated that remain stable when continously irradiated with green light, but degrade once the light source is switched off. The degradation and light stabilization properties of the printed materials are analyzed in-depth by time-lapse scanning electron microscopy. It is demonstrated that these resists can be used to impart responsive behavior onto the printed structure, and –critically– as a temporary locking mechanism to control the release of moving structural features.     

Processing and characterization of a-Si:H photoresists for a vacuum-compatible photolithography process

The vision of achieving a completely in-vacuum process for fabricating HgCdTe detector arrays is contingent on the availability of a vacuumcompatible photolithography technology. One such technology for vacuum photolithography involves the use of amorphous-hydrogenated Si (a-Si:H) as a photoresist. In this work, we deposit a-Si:H resists via plasma-enhanced chemical-vapor deposition (PECVD) using an Ar-diluted silane precursor. The resists are then patterned via excimer laser exposure and development etched in a hydrogen plasma where etch selectivities between unexposed and exposed regions exceed 600:1. To determine the best conditions for the technique, we investigate the effects of different exposure environments and carry out an analysis of the a-Si:H surfaces before and after development etching. Analysis via transmission electron microscopy (TEM) reveals that the excimer-exposed surfaces are polycrystalline in nature, indicating that the mechanism for pattern generation in this study is based on melting and crystallization. To demonstrate pattern transfer, underlying CdTe films were etched (after development of the resist) in an electron cyclotron resonance (ECR) plasma, where etch selectivities of approximately 8:1 have been achieved. The significance of this work is the demonstration of laser-induced poly-Si as an etching mask for vacuum-compatible photolithography.