The Department of Defense (DoD) has initiated a major new program directed towards providing major improvements in high speed, high throughput signal and data processing capability in support of requirements for military systems in the mid-eighties and beyond. In this paper, the overall plan for that program, which has been entitled Very High Speed Integrated Circuits (VHSIC) is presented.

This paper discusses the use of vernier measuring techniques to determine various errors associated with step-and-repeat mechanisms. The design of GCA Burlington's Universal Vernier Test Target is described and the application of this target to measure reduction error, optical distortion, die rotation, system precision, system registration, and stage orthogonality of Mann Type 4800DSW TM Wafer Stepper TM systems is explained. Test results for recent instruments are given and compared to the manufacturer's specifications.

The use of a 10X reduction step and repeat system to produce 1 to gum geometries over a 14.5mm diameter image for high density semiconductor wafer fabrication is presented. The impact of standing wave patterns on the development properties of photoresists are examined for substrates of various reflectivity, and efforts to minimize these effects described. Data on alignment accuracies and critical dimension tolerances is also included.

A computer program for the Simulation And Modeling of Profiles for Lithography and Etching (SAMPLE) is used to explore the effects of partially coherent mask illumination on the image intensity distribution and on the developed resist profiles. Features of the image are discussed with respect to the degree of illumination coherence and to focus error. The impact of the image features on line-edge profiles in resist is explored via a resist development simulation. The minimum (toe) intensity of the image of narrow lines is defined and found to be an important factor in the control of resist linewidth. Simulated resist profiles of a typical mask pattern indicate a reasonable value of .7 for the partial coherence parameter o.

VLSI circuit fabrication will require new optical projection systems with micron resolution. If conventional incoherent illumination is used, large numerical aperture optics will be required, giving rise to smaller fields and reduced depth of focus. An attractive alternate approach is the use of nearly spatially coherent illumination which, for the same numerical aperture, gives higher resolution and better size control without sacrificing field size and depth of focus. Partially coherent illumination is defined and different designs for arc and laser sources are given. The effects on photoresist profile formation are analysed by using a resist behaviour model. It is shown that with partially coherent illumination, linewidths are less sensitive to variations of the energy absorbed in the resist and, consequently, are better controlled across oxide steps. A set of curves is given to determine the useful resolution and the linewidth variation amplitudes versus the coherence degree and the numerical aperture of the lenses. SEM micrographs confirm these results.

We demonstrate experimentally the ability of a wafer stepper to produce micron and submicron features with an aspect ratio of 2 or more. Vertical profiles developed in the resist layer cannot be explained by the usual assumption of vertical incidence, especially if high numerical apertures are used. Under spatially coherent illumination, we explain image formation and vertical profiles by interferences of 3 wavefronts (or more) issued from the discrete spectrum of the object in the Fourier plane of the lens : the surfaces of equal intensity resulting from these interferences are vertical planes in a domain ± Az over and under the best focus plane. A focus shift Az, like an aberration, disturbs phase relationships between wavefronts : if zero-order and first-order diffraction wavefronts present a phase shift equal to half-wavelength, lines and spaces are interchanged. This phenomenon is known as "contrast inversion". We assume the depth of focus as being proportional to this depth of inversion. We present a focus wedge technique giving an experimental evaluation of the ratio between depth of focus and depth of inversion, for 4 degrees of pupil coverage : 0,15 ; 0,29 ; 0,58 ; 0,87. The effect of wafer reflectivity is considered.

The carrying out of special evaluations in the design stage of projection lenses is essential in order to make lenses exhibit target performance during practical use. For example, the resolution of a designed lens cannot be fully estimated by the calculation of MTF alone since MTF is calculated without concern for illumination conditions actually employed. In this paper, estimation methods of resolution and depth of focus of a designed lens by calculation of image contrast from image intensity distribution under actual illumi nation conditions are introduced. Next, consideration is given to the relation between chromatic aberration and image properties, namely to the connection between residual Chromatic aberration and image contrast, and to the connection between polychromatic exposure and image properties of resist. Finally, estimation of lens-to-lens distortion, another important performance factor of projection lenses, is attempted.

A fully automatic through-the-lens alignment method is described for use in step-and-repeat projection aligners. The method utilizes dark field illumination of the wafer, which is aligned to the reticle. It is shown that 2.5 pm wide alignment marks that are 2 mils in length provide an ample signal-to-noise ratio for 0.1 pm alignment accuracies. Various contributions to alignment error are examined such as the visibility of the alignment features, surface scatter on the wafer, and shot noise in the detected signal. Applications of these results to x, y, and theta alignment in step-and-repeat printing are offered.

Alignment keys in the form of diffraction gratings are described which can be used for automatic alignment in photolithography for the fabrication of integrated circuits. This technique is suitable for proximity printirg and for projection printing, 1:1 projection as well as reduction projection with step-and-repeat on the wafer. The system uses a small He-Ne laser, a chopper, a beam collimator and a number of silicon photodiodes. The signals from these photodiodes give a quantitative measure of the degree and direction of misalignment between mask and wafer. With suitable electronics these signals can be used for the control of servo motors in order to obtain automatic alignment. Our experiments with a 10:1 reduction projection set-up show that an alignment accuracy of 0.1 µm and alignment times of less than 1 sec are feasible. The alignment range is as large as ± 450 /µm.

The increased density of today's VLSI circuits requires a tighter control at all semi-conductor processing parameters. Included is the need for improved lithography. This paper describes a new 1:1 projection mask aligner that uses ring-field reflective optics. Described are the improvements made in the optical design and fabrication, temperature control, vibration and alignment systems all of which are required to achieve a 2-micrometer production performance. The results of the improvements are presented in terms of lithography on resist-coated silicon wafers.

With VLSI technology advancement, comes a requirement for increased density, improved resolution, higher device yield, and lower mask cost; the necessary vehicle, of course, appears to be projection or non-contact printing of mask to wafer. Several systems are presently available, including: direct step on wafer, projection alignment, and proximity (shadow projection) alignment. This paper deals with the evaluation and production use of a new proximity printing system, the Sass MjB 55 Shadow projection aligner. Image quality and resolution will be discussed, with slides demonstrating resolution. approaching the one micron limit in positive photoresist and a two micron limit in negative photoresist. Aligner environmental requirements, along with performance in production mode, and operator Hcceptability is included. Wafer requirements, specifically flatness, are shown to be much less stringent than with projection systems, the Suss having very. acceptable critical dimension stability over a range of 20 microns. Throughput figures, both for alignment and non-alignment processing, far exceeds that of all other systems previously evaluated or under consideration for upgrading and improving photolithographic processing. Comparisons of mask degradation and device yield improvement versus con ventional contact printing and projection printing shows the Suss to be equivalent to other available systems. A. unique system of calibrating mask to wafer separation (2.5 micron steps, +1 micron repeatibility), improved viewing optics, and realistic illumination intensity of 2 to 20 milliwatts at better than +2% uniformity, coupled with a new deep-UV source, certainly leads one to believe that we may indeed have found "A Better Mousetrap."

At this point in time, some thirteen companle-73 have manufacturing electron beam exposure systems. In view of that fact, I feel it is time that the current practical realities of e-beam be presented to the rest of the industry. It is the purpose of this talk to present those realities and make some projections for the future. Capabilities for defect density, critical dimension uniformity, overlay registration and other mask related parameters will be discussed and quantified. Manufacturing considerations from design to the finished mask will be examined.

An automated electron beam lithographic system, Vector-Scan-1, was designed to write patterns directly on device wafers as well as generate chrome masks for conventional optical processing. Due to its high current density, conventional AZ-1350 resist can be used directly in the mask making process. Its vector scan capability not only saves exposure time but also provides extremely compact pattern data. Using its laser interferometer servo control, extremely large capacity chips in both 1X masters and 10X reticles can be exposed with relative ease. The accuracy and speed of generating high resolution 1X chrome masks and 10X reticles generated by the VS-1 lithographic system for magnetic bubble fabrication are discussed in detail.

A novel surface acoustic wave (SAW) structure was developed which accurately measures the abutment between adjacent electron beam field patterns. The construction of large devices (ICs or SAWs) requires a mosaic consisting of many smaller 60 mil fields to cover a six inch photomask. ()System software acquires field edge alignment marks with tolerance increments of +125 A. The SAW device examined converts a spatial error of 1 microinch (0.025 micron) into a frequency difference of 65 kHz. This variation is easily measured with great precision in the frequency domain using an electronic counter. The SAW geometry is a simple test pattern which is easily reproduced on most electron beam pattern generators and consists of a single level of metallization on a piezoelectric substrate. A second SAW 5 us pulse compression filter was constructed in 16 consecutive fields and analyzed with regard to abutment errors. Misalignment could be detected from the filter's time domain impulse response.

Orwell's world of 1984 utilizes a highly sophisticated computer and telecommunications network. At this time photoresists are still considered a necessary and vital component in the high volume microminiturization needed to produce these sophisticated electronics. Philip A. Hunt Chemical Corporation is deeply dedicated to the advancement of current photoresist technology, and presently has active research programs in electron beam, x-ray, and deep-uv lithography. The major aim of this paper will be to show how successfully the goals of our programs have been met. The primary emphasis will be to describe the results of our program to develop a marketable x-ray resist, and secondly, to discuss the current status of our programs on e-beam and deep-uv resists. Data will be given to show the performance of the various resists under active investigation.

Deep-UV conformable printing offers the capability of delineating submicrometer features with high aspect ratios. The profile of the resist image can easily be manipulated from overcut to vertical and undercut. However, making intimate contact between the mask and the wafer potentially induces defects. On the other hand, near-UV optical projection printing can be defect-free but cannot achieve a high aspect ratio in the photoresist image. In this paper a double layer resist system is used to combine the advantages of the two printing methods while eliminating the shortcomings. A thin AZ layer is spun on a thick PMMA layer. The AZ1350J layer is conventionally deliniated with a near-UV mask aligner. Because AZ1350J is opaque to deep-UV radiation, it acts as a built in conformable mask which can be carried with the wafer to a deep-UV blanket-exposure station to delineate the PMMA layer.

This paper describes three optical measuring machines which have been recently developed for state-of-the-art microlithography, as follows: (1) X-Y measuring machine for checking photomask registration. Utilizing a photoelectric microscope and a laser interferometer, this machine has a repeatability of less than O.lμm, covering a measuring range of 6 inches. (2) Measuring machine for critical line width (1 - 100µm) of photomask. This machine likewise utilizes the latest photoelectric detection technology; it has a repeatability of approximately 0.05µm. (3) Measuring machine for wafer and photomask micropatterns. A newly developed system which makes use of laser beam technology is incorporated in this machine; measurement repeatability is approximately 0.05µm.

The trend toward smaller device geometries to afford more die per wafer and the advances in photolithographic technology have resulted in the evergrowing use of projection printing systems which can routinely produce two micron lines. Image distortion has become critical and because it is difficult to compensate for a lack of flatness by either mechanical or optical means, wafer flatness has been afforded increasing importance as a silicon material parameter. This paper will offer an overview of the most typical wafer flatness test methods. It will demonstrate the importance of contamination considerations, show how flatness measurements are affected by vacuum chuck geometries, inches of mercury of clamping vacuum and review currently available equipment. Also, principles of operation are described and the scanning, and laser interferometric testing systems.

Ion beam milling combined with improved lithography will permit the etching of fine line circuits with controlled wall shapes in a wide variety of materials. This dry process has been used in the laboratory for several years and is now finding acceptance in the production of bubble memory devices and MOS circuitry. This paper will review the important characteristics of ion beam etching and comment on the state of the art in mass production equipment. The main difference between ion beam etching and conventional sputter etching is the use of a directed ion beam and a work chamber at a relatively low pressure. These differences produce four chief advantages. First, the low pressure results in less contamination and poisoning and, second, the directed beam permits control of the etching profile. Third, one can independently select the ion current, voltage, and pressure for reproducible results over a wide range of values. Fourth, the net charge of the positive ions can be balanced by low energy electrons, allowing the etching of any insulator or conductor. An organic or metal mask is utilized to pattern the material being etched. Typical removal rates in large batch processes range from 300 to 400 Å/min. Submicron soaced lines can be etched with either straight or sloped walls.

Strangely enough, many users of optical projection photolithography sometimes assume that their final process yield is more influenced by non-flat wafers than it is by crooked photoplates. This misconception is even more widespread when one is considering the larger wafers and photoplates in use. If you do not agree with this observation (or accusation), try to list the companies that offer wafer flatness analyzers for 5 inch wafers, for example. Virtually all manufacturers of wafer flatness testers sport 5 inch wafer test capability. Now try to name those companies that offer a 6 x 6 inch photomask flatness analyzer. Surely, if testing 5 inch wafers is important to you, then testing the corresponding 6 inch photomasks should also be important to you. I think you will find that although great interest and activity has been shown in the field of 5 inch wafer flatness and its effect on yield when used in conjunction with 1 : 1 projection or proximity printing, the lonely 6 inch photoplate has been forgotten. This fact is made more irrational when you consider the increased difficulties associated with manufacturing or obtaining "flat" 6 x 6 inch mask substrates. To fill this gap, Tropel recently introduced interferometers which are designed specifically to test the surface figures of large photoplates. This paper will describe the design, configuration and characteristics of this new flatness analyzer. A simple statistical evaluation of the machine's repeatability as well as the reproducability between two machines will be given.

The use of positive photoresists as ion implantation masks is considered in terms of processing advantage and specific applications. the relevant physical and functional properties are discussed with particular emphasis on thermal flow. Following the postbake study, ion implantation parameters are given, focusing on energy and dose ranges that facilitate complete and trouble-free resist removal. The use of new varian-extrion waycool stage for water cooling figure heavily here. Finally, the use of new positive photoresists for ion implantation mask in the future is reviewed.

Uniformity of etch in plasma is becoming increasingly important as wafer size increases and linewidth decreases. A great deal has been written about the effects on etch rate and uniformity of the fundamental variables of system configuration, gas mixtures, gas flows, wafer loading, etc. , but little has been said about the influence of photoresist processing on etch performance. Trace residues, especially develop residues associated with a negative process, can exert a major influence on plasma etch rate and uniformity. Chemical cleaning can be used effectively to compensate for deficiencies in plasma cleaning but the use of positive resist can achieve the same uniformity and repeatability without the need for additional processing. Recognition of the extreme sensitivity of plasma etching to certain trace residues and the possible ineffectiveness of plasma cleaning opens one more door for the optimization of plasma etch uniformity and repeatability.

This paper describes a low cost camera system which may be constructed by the user to develop prototype circuit masks in a minimum of time and at the lowest possible cost. The camera elements are standard Hasselblad units, the materials are commercially available and all processing chemicals are from Kodak. Its construction was primarily for new circuit evaluation but has proven adaptable to short production runs.

Nanometrics has designed two computerized optical measurement systems for use in micro-electronics photomask and wafer process control. The NanoSpec/AFT Automatic Film. Thickness Measurement System car measure with good precision the thickness of silicon dioxide, silicon nitride, polysilicon, photoresist and other films from. several hundred angstroms to several microns. A nine micron diameter measuring spot is employed which allows gates and pads as small as 10 microns to be measured. Recently its use has been extended to thickness measurement of photo and electron beam resists on chromium photomasks as well as wafers. The Nano-line Critical Dimension Computer is a line-width measuring instrument comprised of a micro-densitometer adapted to a high-magnification microscope and interfaced to a digital micro-processor computer. It can measure lines from less than one micron to 100 microns on masks and wafers with good precision. Both systems employ similar computer methods, are non-destructive, and very reliable in the manufacturing environment. They also provide results which minimize operator error. Their computers incorporate large memory capacity to store statistical data which allows the manufacturing engineer to determine and correct process variations and drift on a prompt basis.