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IBM Journal of Research and Development

Issue 1.2 • Date Jan. 1997

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Displaying Results 1 - 18 of 18
  • Optical lithography: Introduction

    Page(s): 3 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (446 KB)  

    The dramatic increase in performance and cost reduction in the electronics industry are attributable to innovations processes. The speed and performance of the chips, their associated packages, and, hence, the computer systems are dictated by the lithographic minimum printable size. Lithography, which replicates a pattern rapidly from chip to chip, wafer to wafer, or substrate to substrate, also determines the throughput and the cost of electronic systems. A lithographic system includes exposure tool, mask, resist, and all of the processing steps to accomplish pattern transfer from a mask to a resist and then to devices. For further reading, we suggest several excellent reviews of the optical lithography of integrated circuit fabrication. View full abstract»

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  • Manufacturing with DUV lithography

    Page(s): 7 - 19
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1592 KB)  

    Deep-UV (DUV) lithography has been developed to scale minimum feature sizes of devices on semiconductor chips to sub-half-micron dimensions. This paper reviews early manufacturing experiences at the IBM Microelectronics Division with deep ultraviolet (DUV) lithography at a 248-nm wavelength. Critical steps in the processing of 1Mb DRAM, 16Mb DRAM, and logic gate conductors in devices are discussed. The evolution of DUV lithography tools is also briefly reviewed. View full abstract»

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  • Advanced DUV photolithography in a pilot line environment

    Page(s): 21 - 37
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1873 KB)  

    As the critical path to increasing circuit density, deep-ultraviolet (DUV) lithography has played a key role in the development of new semiconductor products. At present, DUV refers to imagery at the 248-nm wavelength, with the introduction of 193-nm photolithographic systems anticipated in the next few years. This paper presents an overview of DUV lithography applications in the IBM Advanced Semiconductor Technology Center (ASTC). Since 1990, we have used DUV lithography for critical levels of advanced generations of DRAM (64Mb, 256Mb, and 1Gb) and associated families of logic products. We describe the means by which DUV capability and productivity have increased in a decreasing process window environment. Tooling, processes, and process control systems have undergone continuous improvement to accommodate increasing wafer starts and the rapid introduction of new products. View full abstract»

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  • High-numerical-aperture optical designs

    Page(s): 39 - 48
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (806 KB)  

    This paper is an overview of the designs of high-numerical-aperture lenses for optical projection lithography at the IBM Thomas J. Watson Research Center. View full abstract»

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  • Lithography at a wavelength of 193 nm

    Page(s): 49 - 55
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (639 KB)  

    The trend in microelectronics toward printing features 0.25 µm and below has motivated the development of lithography at the 193-nm wavelength of argon fluoride excimer lasers. This technology is in its early stages, but a picture is emerging of its strengths and limitations. The change in wavelength from 248 to 193 nm requires parallel progress in projection systems, optical materials, and photoresist chemistries and processes. This paper reviews the current status of these various topics, as they have been engineered under a multiyear program at MIT Lincoln Laboratory. View full abstract»

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  • Impact of lens aberrations on optical lithography

    Page(s): 57 - 67
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1158 KB)  

    All optical projection systems for microlithography depart from perfection because of various lens aberrations, especially when large image field size is combined with high numerical aperture (NA). Such aberrations have a variety of effects on lithographic imaging: shifts in the image position, image asymmetry, reduction of the process window, and the appearance of undesirable imaging artifacts. These undesirable effects are sometimes exacerbated through use of resolution enhancement techniques such as phase-shift masks or nonstandard illumination. This paper examines the impact of different types of aberrations on lithographic imagery through simulation. New techniques for measuring aberrations by examining lithographically printed resist patterns are considered. View full abstract»

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  • Negative photoresists for optical lithography

    Page(s): 81 - 94
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1609 KB)  

    Negative photoresists are materials that become insoluble in developing solutions when exposed to optical radiation. They were the first systems used to pattern semiconductor devices, and still comprise the largest segment of the photoresist industry because they are widely used to define the circuitry in printed wiring boards. However, the current use of negative resists in the semiconductor industry has been limited by past difficulties in achieving high-resolution patterns. Recent advances in the chemistry of negative-resist systems, however, have provided materials with wide processing latitude and high resolution that are used to manufacture IBM's advanced CMOS devices and to achieve high-aspect-ratio patterns for micromachining applications. This paper provides an overview of the history and chemistry of negative-resist systems and their development in IBM. View full abstract»

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  • Photoresists for 193-nm lithography

    Page(s): 95 - 104
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1094 KB)  

    Photolithography using 193-nm light appears to be a viable route for the extension of optical lithography to the dimensions required for the manufacture of 1Gb DRAM and advanced CMOS microprocessors with 180-140-nm minimum feature sizes. In this paper, we discuss the origin of resist technology for 193-nm lithography and the current status of 193-nm photoresists, focusing on single-layer resist materials. We emphasize the photoresist design approaches under investigation, compare these with deep-UV (DUV) (248-nm) resist design and materials, and consider possible future lithography processes employing 193-nm lithography. Research and development on 193-nm photoresists by the lithography group at the IBM Almaden Research Center is highlighted. View full abstract»

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  • Thin-film imaging: Past, present, prognosis

    Page(s): 105 - 118
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1469 KB)  

    As the limitations of conventional optical lithography approach, potential extensions of a current technology are examined more closely. One of these extensions is to limit the photoresist thickness that is needed for recording the imaging information. Because the low etch resistance of resist typically precludes the use solely of resists utilizing very thin film, a variety of alternatives have been explored. These range from elaborate trilayer schemes to relatively simple processes such as top-surface imaging (TSI) and a number of combinations thereof. In all of these systems, the aim is to limit the imaging resist thickness to a thin layer by confining the radiation near the surface of the resist. This improves process latitude (e.g., depth of focus, exposure latitude) and also reduces reflective notching and thin-film interference effects. The imaged pattern in the thin-film resist processed by TSI is then transferred by plasma etching into a thicker underlayer. This “stack” then serves as the resis t mask for subsequent wafer processing. In this paper, we refer to all of these types of approaches as thin-film imaging (TFI) systems. We review TFI approaches from a historical perspective, examine a number of the schemes that have been proposed, and describe the various technical issues associated with the implementation of such systems. From this perspective, we suggest that TFI systems may find a role in manufacturing for lithographic applications at wavelengths at, or less than, 193 nm. View full abstract»

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  • Development and application of a new tool for lithographic mask evaluation, the stepper equivalent Aerial Image Measurement System, AIMS

    Page(s): 119 - 129
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1229 KB)  

    This paper describes the development of a new tool for evaluating lithographic masks, its software, and its application to the development of advanced mask designs, including phase-shifted features. This mask-imaging system, known as the stepper equivalent Aerial Image Measurement System (AIMS*), provides a means for rapid evaluation of masks. The key feature of AIMS is that the mask is imaged under conditions that emulate the image produced by a given lithographic exposure tool onto a resist layer. In the AIMS microscope, the image obtained is enlarged so as to permit quantitative measurement with a low-noise CCD camera. A quantitative record of selected features of the mask is useful in predicting the printability window for given mask and stepper combinations. Details of the optical system and extensive software capability are given, and examples are presented of feature printability of phase-shifted features, optical proximity, and other effects. Applications include the prediction of key critical mask dimensions as a function of exposure and depth of focus and the rapid checking of the effectiveness of repair actions prior to validation by resist runs. The AIMS microscope system is available as the Carl Zeiss MSM100 Microlithography Simulation Microscope and is now in use in a number of companies as a new tool for mask fabrication and development. View full abstract»

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  • Chemical amplification resists: History and development within IBM

    Page(s): 119 - 130
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (4681 KB)  

    The chemical amplification concept was invented at IBM Research and quickly brought into use in the production of dynamic random access memory devices in the company. It has remained as an important foundation for the design of advanced resist systems for use in short-wavelength (<300-nm) lithographic technologies. View full abstract»

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  • Large-field scanning laser ablation system

    Page(s): 131 - 142
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1046 KB)  

    A large-field scanning imaging system has been developed to perform imaging ablation using 308-nm excimer laser light. A 1× Dyson-like lens images a portion of the mask onto a portion of the substrate to be ablated. The lens has a field of 12 mm and a numerical aperture of 0.05, providing a resolution of about 6 µm. A mirror system comprising a roof and a plane mirror, with all three surfaces mutually orthogonal, ensures that the mask and the substrate have identical orientations. A common stage is used to hold the mask and the substrate. The stage is scanned in a serpentine manner to transfer the entire image. The illuminated region is diamond-shaped, and adjacent scans overlap by half its width to ensure uniformity. Illumination uniformity is provided by a light tunnel in the illumination system. Alignment is performed by optically combining images of mask marks and substrate marks formed by a pair of microscope objectives, one viewing the mask and the other viewing the substrate. The substrate is leveled, focused, and registered relative to the image of the mask by a stage with six degrees of freedom. View full abstract»

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  • Masks for laser ablation technology: New requirements and challenges

    Page(s): 143 - 148
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    Laser ablation is used as a dry patterning process in which an intense beam of light from an excimer laser is used to pattern a material directly. This process has found extensive application in the microelectronics industry for patterning of polymer materials. A typical laser ablation tool is very similar to a conventional optical lithography projection tool; the primary difference is the wavelength and the intensity of the light used in the ablation process. Conventional chromium-coated quartz masks are incompatible with 1× laser ablation tools because the chromium layer is rapidly damaged. This paper discusses a mask technology which has been developed specifically for excimer laser ablation. The mask consists of a quartz substrate with a stack of dielectric films which have been selected for the laser ablation wavelength. Mask fabrication is accomplished with standard microelectronic processes and equipment. Such masks have been used in IBM manufacturing since 1987 and have met all process specifications such as resolution, defect density, and damage resistance. View full abstract»

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  • Laser release process to obtain freestanding multilayer metal-polyimide circuits

    Page(s): 151 - 157
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    Some applications in microelectronics call for freestanding polyimide films with fine metallic wiring patterns that are thinner than commercially available copper-clad polyimide sheets, which are typically greater than 25 µm in thickness. This work describes a laser-assisted technique to fabricate freestanding multilayer thin-film wiring with polyimide dielectric insulating layers that are less than 10 µm thick. A release layer consisting of a thin polymeric film is first deposited on an optically transparent carrier and the multilayer thin-film structure is then fabricated on this substrate, with the polymeric release layer sandwiched between the transparent carrier and the multilayer structure. Excimer laser light passes through the transparent carrier and ablates the polymeric layer at the transparent carrier/polymer interface, resulting in separation of the sacrificial carrier from the multilayer structure. The optimal release process is carried out using a 308-nm XeCl excimer laser operati ng at a fluence of about 100 mJ/cm2 View full abstract»

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  • Lithography beyond light: Microcontact printing with monolayer resists

    Page(s): 159 - 170
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1270 KB)  

    We describe high-resolution lithography based on transfer of a pattern from an elastomeric “stamp” to a solid substrate by conformal contact: a nanoscale interaction between substrate and stamp on macroscopic scales that allows transport of material from stamp to substrate. The stamp is first formed by curing poly(dimethyl siloxane) (PDMS) on a master with the negative of the desired surface, resulting in an elastomeric solid with a pattern of reliefs, typically a few microns deep, on its surface. The stamp provides an “ink” that forms a self-assembled monolayer (SAM) on a solid surface by a covalent, chemical reaction. Because SAMs act as highly localized and efficient barriers to some wet etches, microcontact printing forms part of a convenient lithographic system not subject to diffraction or depth of focus limitations while still providing simultaneous transfer of patterned features. Our study helps to define the strengths and limitations of microcontact printing with SAMs, a process that is necessary to assess its worth to technology. We used lithography based on scanning tunneling microscopy (STM) to demonstrate that disruption of SAMs on gold allowed the formation of etched features as small as 20 nm using a CN/O2 etch. This result implied that etching occurred where damage of a few molecules in the ordered SAM allowed passage of cyanide, whereas adjacent molecules in the SAM remained unperturbed at this scale. Features as small as 30 nm etched in gold over areas greater than 1 cm2 resulted from microcontact printing with replicas of electron-beam-formed masters, with the transfer of these printed SAMs requiring only ≈1 s. STM studies of these transferred SAMs revealed an achievable order indistinguishable from that found for SAMs prepared from solution. Facile alignment of printing steps at submicron scales may result from new designs of stamps that exploit their limited deform- - ability and lock-and-key-type approaches to mate stamp and substrate. View full abstract»

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  • Fast and effective algorithms for graph partitioning and sparse-matrix ordering

    Page(s): 171 - 183
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1177 KB)  

    Graph partitioning is a fundamental problem in several scientific and engineering applications. In this paper, we describe heuristics that improve the state-of-the-art practical algorithms used in graph-partitioning software in terms of both partitioning speed and quality. An important use of graph partitioning is in ordering sparse matrices for obtaining direct solutions to sparse systems of linear equations arising in engineering and optimization applications. The experiments reported in this paper show that the use of these heuristics results in a considerable improvement in the quality of sparse-matrix orderings over conventional ordering methods, especially for sparse matrices arising in linear programming problems. In addition, our graph-partitioning-based ordering algorithm is more parallelizable than minimum-degree-based ordering algorithms, and it renders the ordered matrix more amenable to parallel factorization. View full abstract»

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  • Recent publications by IBM authors

    Page(s): 185 - 193
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    The information listed here is supplied by the Institute for Scientific Information and other outside sources. Reprints of the papers may be obtained by writing directly to the first author cited. Journals are listed alphabetically by title; papers are listed sequentially for each journal. View full abstract»

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  • Recent IBM patents

    Page(s): 195 - 200
    Save to Project icon | PDF file iconPDF (451 KB)  
    Freely Available from IEEE

Aims & Scope

The IBM Journal of Research and Development is a peer-reviewed technical journal, published bimonthly, which features the work of authors in the science, technology and engineering of information systems.

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Editor-in-Chief
Clifford A. Pickover
IBM T. J. Watson Research Center