Showing papers on "Resist published in 1975"

Optical lithography

Abstract: 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.

Deep uv lithography

Abstract: Using deep‐uv light ranging from 2000 to 2600 A, submicrometer patterns in photoresist with height‐to‐width aspect ratios as high as 15 can be achieved. The well known electron‐beam positive resist, polymethyl methacrylate (PMMA), is used as the deep‐uv photoresist. Its optical absorption coefficient, dissolution rate, and sensitivity are given in the deep‐uv wavelength region. Its absorption coefficient, being a factor of two lower than that of AZ 1350J, makes it suitable for deep penetration of submicrometer‐wide beams. The negligible sensitivity at wavelengths longer than 2600 A eliminates the need for an expensive filter. Both Xe–Hg arc lamps and deuterium spectral lamps have been used to expose the resist. Chrome or aluminum masks on quartz or sapphire substrates were found satisfactory. Chevron patterns of 1.6 μm width and 0.4 μm spacing and Y–I bars of 1.6 μm width and 0.2 μm gaps were printed in 3 μm of PMMA 2041, as well as Y–I bars of 0.5 μm width and 0.25 μm gaps in 1.78 μm of PMMA 2041. The ex...

EBES: A practical electron lithographic system

Abstract: An electron beam exposure system (EBES) has proven to be practical and economic for generating high-quality fine-featured integrated circuit masks. It is also capable of exposing patterns directly on resist-coated silicon wafers and, when so used, is an effective tool with which to develop new semiconductor devices. EBES combines continuous translation of the mask or wafer substrate with periodic deflection of the electron beam in a raster-scan mode of exposure. Substrate position is monitored by means of laser interferometers. The strategy permits both the electronic and mechanical subsystems to work well within their limits of capability and contributes to system reliability. It also permits the system to be stepped up to higher resolution and faster exposure as brighter electron sources, more sensitive resist, and faster data processing techniques are developed.

Methods for forming thick self-supporting masks

Abstract: A method of constructing a relatively thick, self-supporting mask suitable for electron beam projection processes. Thickness is achieved by multiple steps of coating with resist, exposure, development and plating. First an intermediate or lift off layer is deposited on a substrate. A plating or a cathode layer may then be deposited. Resist is then applied. A first mask layer comprises metal plated in accordance with the first pattern. For the second exposure a geometrically similar pattern is employed to generate larger apertures. Thus, if the first mask layer has 0.20 mil apertures, the second layer might have corresponding 0.21 mil to 0.22 mil apertures. For initial mask patterns of about 2 mil the second layer might be 2.02 mils. If desired, a third exposure can be employed with a third pattern, similar to the first two, but having larger apertures (by 0.02 to 0.03 mils) than the second pattern.

Method for forming patterned films utilizing a transparent lift-off mask

Abstract: A lift-off method for use in depositing thin films in the fabrication of integrated circuits which avoids edge tearing of the films. The method involves depositing an organic polymeric first masking material on a substrate, and forming on said material a layer of a polydimethylsiloxane resin material. The material, in turn, is covered by a second masking layer, preferably an organic polymeric resist material into which openings are placed in a selected pattern utilizing lithographic techniques. Then, conforming openings are placed in the underlying polydimethylsiloxane resin material and the openings are extended through the underlying resist material by successive reactive sputter etching steps to expose the substrate surface in the aforesaid selected pattern. The thin film to be deposited is then applied over the resulting structure; it is, thereby, deposited on the substrate in said openings. The final reactive sputter etching step affords edges in the openings through the resin material layer which overhang the edges in the openings through the first masking layer affording easy lift-off of the unwanted areas of the deposited film when the first masking layer is totally removed by application of solvent.

Method for making transistors

Abstract: Submicron plasma trimming of a patterened resist material is combined with ion implantation techniques to achieve submicron control of lateral doping profiles. This makes possible the high-yield fabrication of, for example, bipolar microwave transitors of the self-aligned-emitter type. The basic technique can also be supplied to the fabrication of high performance insulted-gate field-effect transistors, junction-gate field-effect transistors and Schottky-barrier field-effect transistors.

High speed replication of submicron features on large areas by X-ray lithography

Abstract: To achieve the high throughput necessary for a practical X-ray lithographic system, we have devised a new overall approach to X-ray lithography based on the use of X-rays with wavelengths of 4-6 A rather than the 8.34-A wavelength used in previous work. The principal advantage of the shorter wavelengths is that they allow a system to have X-ray windows so that large area patterns can be replicated under ambient conditions. In addition, the shorter wavelengths simplify the selection of mask substrate materials; thus we have developed a new X-ray mask structure using an optically transparent Mylar substrate. This permits realignment to be done by optical means. We also report results obtained with a new negative resist with high sensitivity to the shorter wavelength X-rays. We have achieved the replication of submicron size features using a 4.6-A rhodium X-ray source, a Mylar mask with 7000-A thick gold patterns, and the new resist, and have demonstrated the practicality of this system by the fabrication of propagating magnetic bubble structures with small features.

Linewidth variations in photoresist patterns on profiled surfaces

Abstract: Photoresist thickness nonuniformities in the vicinity of profile steps on substrate surfaces lead to linewidth variations of AZ 1350 photoresist geometries. The effect increases with increasing reflectivity of the substrate, decreasing photoresist layer thickness, and decreasing contrast transfer of the exposure system. It is shown that the photoresist linewidth is maximum when the resist thickness is a multiple of half the exposure wavelength in the resist.

Fabrication of high aspect ratio masks

Abstract: A method of constructing masks characterized by a high aspect ratio. The method includes at least a single exposure of a mask by radiation which is transmitted by the substrate before impinging on the resist. In a specific embodiment the mask is partially completed and the already deposited mask modulates the radiation transmitted by the substrate before it exposes the resist.

Molecular parameters and lithographic performance of poly(glycidyl methacrylate‐co‐ethyl acrylate): A negative electron resist

Abstract: To facilitate the production of a polymeric electron resist of consistent quality we must know how molecular parameters are related to lithographic performance. Previous work has indicated that for negative resists in general, sensitivity and contrast increase with increasing molecular weight and decreasing polydispersivity, respectively. We describe experiments on eight batches of a particular resist, poly(glycidyl methacrylate‐co‐ethyl acrylate) [P(GMA‐co‐EA)], which compare lithographic performance, in terms of sensitivity, contrast, and edge sharpness, with molecular weight (Mw), molecular content (%GMA), and polydispersivity (Mw/Mn). The earlier conclusions are borne out. To achieve a sensitivity of 4×10−7 C cm−2 at 10 kV and a contrast of about 1.0 (the latter being needed for lithography for chromium photomask production), the required values for this resist of Mw, %GMA, and Mw/Mn are, respectively, ?1.6×105, 70±2, and ?3.0.

Electron‐beam lithography using vector‐scan techniques

Abstract: A computer‐controlled electron‐beam microfabrication system has been developed for evaluation of micron and submicron lithographic technologies. Direct large‐field‐device exposures of complex patterns have been processed for FET and bubble memory fabrication. Experimental exposures have also been made to allow mask fabrication for alternative exposure apparatus. The system exposes the electron‐sensitive resist by sequentially filling in pattern elements (cells), whose geometry and size are determined by an off‐line pattern data processor. Abutting line scans, using a round electron probe, are used to expose each cell. The system normally exposes fields up to 4 mm square. Deflection resolution is 14 bits per axis. Exposure rate, pattern registration, pattern field adjustments (size, position offset, rotation, and orthogonality), and workstage position are among the functions which have been automated.

Planar insulation of conductive patterns by chemical vapor deposition and sputtering

Abstract: A method using a chemically vapor deposited (CVD) insulator to form a substantially planar layer of insulative material atop a conductive pattern on the surface of a substrate. The invention also features the use of a photoresist both as a mask for forming apertures in an underlying insulating layer as well as a lift-off material for a subsequently deposited conductive layer. In the method, a first insulating layer is deposited atop the substrate. Photoresist is then deposited; the resist pattern is exposed and developed; and the insulator is etched to expose selected areas of the substrate. A conductive film, preferably metal, is then deposited in blanket fashion in such quantity as to achieve the same height as the first insulator within the exposed apertures. The resist is lifted off, thereby leaving metal in the exposed apertures only. The pattern at this point consists of a single level of a conductive pattern and the insulator pattern with gaps between the conductors and the insulator. The gaps are the result of the unavoidable removal of a portion of the insulator below the photoresist during the etching process. Another insulating film is chemically vapor deposited (pyrolytically deposited) in blanket fashion. Notwithstanding the gaps between the conductors and first insulator, the second film is substantially planar if the thickness of this second insulating film equals or exceeds one-half the width of the largest of said gaps. The method is applicable to any level of conductive patterns (metallization) atop the substrate.

Recent developments in electron-resist evaluation techniques

Abstract: A simple procedure for evaluating the performance of any positive electron resist is presented. SEM examination of the developed resist edge profile after electron‐beam exposure and development gives simultaneous information on resist sensitivity and resolution for a given resist thickness. This method gives a unique exposure charge‐density point for optimum resolution for a given resist system independent of developer strength.

Poly(butene‐1 sulfone) —A highly sensitive positive resist

Abstract: The positive electron resist poly(butene‐1 sulfone) (PBS) has been reported previously. As with other electron resists, sensitivity has been shown to be dependent on a number of processing parameters such as accelerating voltage, developer, developer solvent, and polymer characteristics (namely, molecular weight, molecular weight distribution, etc.). Previous reports have involved resist samples and conditions resulting in sensitivities within the range of 4–6×10−6 C/cm2 at 10 kV. For certain uses, for example, on the Bell Laboratories electron beam exposure system (EBES), a sensitivity of better than 1×10−6 C/cm2 at 10 kV is desired for efficient operation. Recent studies involving samples of varying molecular parameters verify feasibility of sensitivities of 7–8×10−7 C/cm2 at 10 kV for carefully controlled molecular weight and molecular weight distribution. As expected, processing of PBS at this sensitivity requires careful attention to polymer dissolution mechanisms. An ideal developing system should d...

Resist reflow method for making submicron patterned resist masks

Abstract: The method for making patterned resist masks having minimum opening dimensions. The mask is prepared initially using standard photo or electron beam lithography techniques to yield the smallest aperture dimensions consistent with the state-of-the-art. Then, the resulting mask is placed within a chamber containing an atmosphere of resist solvent vapor. The vapor is absorbed by the patterned resist mask causing controlled resist reflow which uniformly reduces the dimensions of the resist openings by an amount determined by time, temperature, resist thickness, resist type and solvent used.

High-resolution sputter etching

Abstract: High-resolution sputter etching of a relatively thick layer (of, for example, gold) by directly utilizing a relatively thin layer of resist as a sputter-etching mask is often not feasible. In such a case, it is known to use a sputter-etching mask made of an etch-resistant material such as titanium interposed between the resist and the relatively thick layer. In accordance with the invention, patterning of the titanium is achieved by a technique of sputter etching in a halocarbon atmosphere.

High sensitivity resist system for lift-off metallization

Abstract: High sensitivity resist films for lift-off metallization are formed by coating a substrate with at least two layers of polymeric materials, each layer of which is developed by different developers that are mutual exclusive of one another. The resist can operate for lift-off at electron beam exposure equal to or greater than 5×10- 6 coulombs/cm2.

Method for making device for high resolution electron beam fabrication

Abstract: The disclosed method is one which provides an extremely thin substrate upon which there can be laid down a high resolution pattern of material such as metal by an electron beam fabrication technique. The latter technique is one wherein a resist is placed on the surface of the substrate. Thereafter, an electron beam is utilized to expose the resist in the desired pattern. The exposed resist is then removed and the metal or other material is laid down on the locations where the resist has been removed. With the use of the very thin substrate, the amount and effect of electron backscattering is substantially minimized whereby the consequent decrease of resolution due to exposure of the resist with the backscattered electrons is effectively eliminated. Accordingly, the resist exposure can be confined to much narrower widths than heretofore possible with known electron beam fabrication techniques.

Method of developing and stripping positive photoresist

Abstract: Baked novolak resin based positive photoresists are either developed after exposure or stripped, following the use of the pattern resist layer as an etch mask, in aqueous solutions of a combination of permanganate and phosphoric acid.

Positive resists containing dimethylglutarimide units

Abstract: A process for forming an image with a positive resist using a polymer containing dimethylglutarimide units. The polymer is sensitive to both electron beam and light radiation, has a high glass transition temperature, a high temperature resistance, and is capable of very fine spatial resolution, very suitable for micro circuitry processings.

X-ray lithography: Part I—Design criteria for optimizing resist energy absorption; part II—Pattern replication with polymer masks

Abstract: An X-ray lithography system is analyzed in terms of maximizing the absorbed energy density in the resist. The individual factors, such as X-ray quantum efficiency, electron-beam energy, wavelength, power dissipated in the anode, and the possible use of an X-ray window are discussed. It is shown that K-line radiation from an Al or Si source is the most efficient for mask membranes of either Si or a thin polymer film without an X-ray window and for a thin Be window. For thick Be windows, L-line radiation sources become more efficient. Fabrication procedures have been developed in our Laboratories for polymer film X-ray masks using both photo and electron-beam lithography. The advantages and disadvantages of such masks are discussed. Etched SiO 2 patterns made using polymer film masks show excellent replication of the mask patterns.

Method for making multilayer devices using only a single critical masking step

Abstract: A method for making multilayer devices, such as magnetic bubble domain devices, which are comprised of a plurality of layers that are deposited using only a single critical masking step. A first metallic layer is deposited on a substrate including a magnetic bubble domain film, which may or may not have a nonmagnetic material thereon. A first resist layer is then applied, selectively exposed, and developed to expose at least two areas of the first metallic film. A thicker metallic layer is then deposited in the exposed areas, or is electroplated. After this, another resist layer is applied without deforming the pattern in the first layer, selectively exposed, and developed to protect certain areas of the thick metallic layer from subsequent formation of another metallic layer. During this subsequent formation, a second metallic film is formed using the first resist layer as a mask. After this, the resists are removed and the now uncovered portions of the original thin metallic layer are etched away. In a particular embodiment, a magnetic bubble domain chip is provided in which the second resist layer is used to protect the sensor region of the chip. The second resist layer need not be critically aligned as it only functions as a protect mask. Exposure and development of the second resist layer does not adversely affect the underlying metal layers.

Modified processing of positive photoresists

Abstract: Positive photoresist layers including a base soluble resin and a diazo ketone sensitizer are treated with hydrogen ion following initial exposure to achieve changes in the developed resist profile and/or development in a negative mode.

Preparation of resist image with methacrylate polymers

Abstract: A positive resist image is produced by exposure of a layer of non-crosslinked polymeric material to high energy radiation in a predetermined pattern, the polymeric material containing alkyl methacrylate units and polymerized units of certain other ethylenically unsaturated monomers, followed by removal of the electron degraded material from the exposed areas.

Electron‐beam fabrication of chromium master masks

Abstract: Conventional photolithographic methods of mask manufacture in the semiconductor industry have limitations which can be overcome using electron lithography. This paper describes application of the electron‐beam exposure system (EBES) to the fabrication of chromium master masks using the negative electron resist poly(glycidyl methacrylate‐co‐ethyl acrylate). Lithographic characterization methods developed specifically for this application include the variation of feature size and develped resist thickness with exposure and have led to the choice of correct operating conditions for EBES. Writing time for a typical 2.5‐in. (6.35‐cm) mask is 30–60 min, and processing time is about 70 min (excluding inspection and handling). Linewidth control is better than ±0.5 μm and chip yields typically exceed 90% per mask level for LSI circuits. Masks with chip sizes up to 20×16 mm have been processed. One‐micrometer feature sizes are obtained routinely.

Processes for manufacturing semiconductor devices

Abstract: A process for manufacturing MES-FET transistors with self-aligned Schottky barrier gate electrode, in which a layer of metal is deposited on a semiconductor slice, a resist geometry corresponding to the spacing of the drain and source ohmic contacts is defined, the excess metal is etched away with controlled underetching under said resist, a metal is then evaporated for forming the ohmic contacts, the metal remaining after said etching constituting the self-aligned gate electrode.

Optimized source for x‐ray lithography of small area devices

Abstract: The design and performance of an optimized soft‐x‐ray source using an air‐cooled Al target are described in this paper. The technical considerations leading to the choice of mask material, source wavelength, vacuum enclosure, and electron optics are also described. Although the authors have previously shown the need for large, powerful x‐ray sources, the source described here is intended for exposure of small‐area surface‐acoustic‐wave (SAW) devices with submicrometer dimensions. Since distortion over large areas need not be controlled, the x‐ray source is limited to 1 mm in diameter and the electron beam power to 250 W. A 25‐μm‐thick Be vacuum window was developed which made it possible to use the Al Kα x‐ray wavelength with a thin Si mask and yet maintain the exposure area in He at atmospheric pressure. The custom‐designed electron gun, exposure monitor, and thermal control system are also described. Results are reported on the replication of a SAW device pattern in PMMA resist with 0.5‐μm linewidths.

Quantitative Evaluation of Photoresist Patterns in the 1 - microm Range.

Abstract: During exposure of photoresist layers the light distribution inside the resist is essentially determined by three factors: the incident light pattern generated by the exposure system at the resist surface; the absorption of light by the photoresist; and the reflected waves at the interfaces between layers. Due to standing wave effects, regions of different light intensity are created inside the resist, leading to steplike edge contours of the photoresist after development. The shape of photoresist patterns can be calculated.

Circuit pattern formation method and its device

Abstract: PURPOSE: In order to automatically form the circuit pattern by means of vaporizing the resist with laser ray. COPYRIGHT: (C)1977,JPO&Japio