Photoresist processing has been shown to contribute significantly to device yields in integrated circuit manufacturing. Primary factors in photo-resist processing are dimensional reproduction of photomask geometries, sensitivity to environmental and process conditions, and etch protection afforded by the photoresist. These factors are discussed relative to device yield. A series of scanning electron micrographs are presented which attempt to show the importance of adequate photoresist protection in integrated circuit processing. The unique capabilities of a positive photoresist are related to the factors which have the greatest impact on yield: dimensional reproducibility or fidelity, etch protection and tolerance to processing and environmental factors. The role of photoresist processing and its impact upon device yield has been clearly established in integrated circuit manufacturing. The imaging characteristics of a photoresist material plays a vital role in maintaining and improving device yields. Selection of a photo-resist material should, therefore be based upon imaging properties that fulfill the needs for improved device quality and yield. These properties are defined below:

The continued pressure for increased function complexity and more functions per package has led the semiconductor industry into a new generation of processing technology. The success of these complex functions in the marketplace (calculators, watches, home enter-tainment, etc.) has accelerated the need for very high volume imple-mentation of these process developments. Therefore, the semiconductor manufacturer has entered a new era of extremely precise process control coupled with a need for programming each process to the optimum yield performance. In addition to these quality measures, modern semi-conductor economics require practi-cal cost effective automation. This paper will cover the problems as-sociated with process optimization and automation of the photoresist facility. It will disclose the results of a survey of what industry needs in equipment to best attain the conditions. After the results are covered, you will be presented with Cobilt's answers to those needs.

Increasing demands for minimizing defect density in wafer processing have resulted in a significant emphasis on non-contact printing of the photoresist using either a proximity or projection mode of align-ment. Correspondingly, the need for shrinking geometry sizes to increase packing density and improve device performance is very important in coping with the complexity of LSI devices.

Standardization of terminology in the IC photomask industry needs to be accomplished in the near future. Some of the difficulties usually encountered when attempting standardization, as well as suggestions on how to approach standardization are discussed. Over 125 repre-sentative IC photomask terms have been selected, categorized, and defined.

Before commercial cameras were available, a twelve barrel step and repeat camera was constructed using one light source. Magnification adjustment, plate flatness, azimuthal control, pulsed exposure, grid register, random interconnection and also maintenance methods devised are summarised. A matched reduction camera completed the system.

A single barrel step and repeat camera using a 122x152 CM (4x5 ft.) condensing system provides advantageous control and labor economy.

Two plates are placed in an exposure frame using a vacuum applied around the periphery while atmospheric pressure is maintained on the outside surfaces to force the plates into contact without trapped gas between. Integrated watt-second exposure is used with a controlled coherence source, allowing micron images.

By stepping opaque rectangles which are closely adjacent, the gap between edges defines a single slit which by coherent illumination produces a diffraction pattern on film. This diffractogram recording is improved by an attenuator of decreasing density away from the axis. The method applies to step and repeat error measurement, as well as mask and copy line size evaluation.

The step and repeat camera specifically designed for the production of semiconductor integrated circuits today transcends all technological boundaries in its capabilities for meeting demands which are difficult to comprehend, even to those of us who design and use them on a daily basis. We speak in terms of "quarter micron" repeatability like a lathe hand speaks of "plus or minus a mil". Yet the magnitude of a quarter micron is so small that an objective lens with a numerical aperture of 0.57 is required to theoretically resolve it. Such a lens would have an equivalent f stop of f:0.9. While the analogy may not be accurate, the impact of the technogical requirements of the semiconductor industry may be reflected in such exhaustive and even exaggerated demands.

The use of hard surface film masks in integrated circuit photo-fabrication has increased dramatically in the past few years. The proven manufacturing economies and inherent resolution capability of hard surface masks are the major forces behind this increase.

Step-and-repeat cameras are relatively simple machines from a mechanical viewpoint but since the integrated circuit industry's tolerances are so small the burden of performance placed upon these machines is great. Mechanical performance tests are sometimes done as part of a series of general acceptance tests upon delivery of a new camera but are most often called upon to help locate trouble in an existing machine.

The need for high quality masks, extended mask life, and, to a greater extent, lesser defects in masking wafers, has led the MOS Department at Signetics to evolve from the use of emulsion-soda-lime masks, used in contact printing, to iron-oxide-alumina-soda-lime masks, used in proximity printing. In the beginning, emulsion photo plates held the most widespread recognition within the IC industry, and are considered by many as somewhat of a standard. Noteworthy reasons for their widespread acceptance are that emulsion masks are readily available, easily processed, inexpensive, and produce good quality images. However, their greatest drawback is quality as a working plate and its subsequent degradation, beginning with its first contact with the wafer. Also the quality of emulsion masks is less than desirable in critical dimension control, glass quality, and mask layer registration; and when these plates are used in contact printing, their life hovers around six to eight exposures per mask.

Many advantages in using projection mask alignment for the fabrication of integrated circuits include (1) the elimination of mask wear which allows a single plate to be used indefinitely and therefore justifies the added expense of obtaining defect-free masks, (2) greatly reduced defect densities in the photoresist patterns on the silicon wafers when compared with contact alignment methods, (3) better alignment accuracy in a projection aligner than with contact or proximity methods because the mask and wafer patterns are simultaneously in the focal plane of the alignment optics and there is no movement of the mask or wafer between alignment and exposure, and (4) higher resolution patterns on wafers by employing reducing optics.

Projection printing techniques have been developed and applied to the fabrication of fine pattern microwave integrated circuits. This paper deals with details of the applied projection printing tech-nologies through utilization of a commercially available projection printing system with magnification of 1/2. Results are reported for minimum pattern widths of the order of 1 to 2 microns produced in both positive and negative photoresist films on Si0₂ and metallic substrates. Of particular concern are processing problems peculiar to the reduction projection method as it relates to the fabrication of integrated circuit structures.

The results of a nationwide review of automated IC photomask inspection methods are presented. Major photomask inspection problems of detection of visual defects and registration errors, and the determination of critical dimensions and photoplate quality are discussed. This review indicates that for high-volume, large-scale integrated circuits, the greatest concern is for the detection of visual defects. Next in order of importance are the detection of registration errors, and then the accurate determination of critical dimensions. Automated inspection systems and technologies currently available for this are discussed including: microdensitometer-digital computer systems, laser beam scanning systems, spatial filtering systems and microscope-television-digital computer systems. Suggested criteria for an ideal photomask inspection system are the simultaneous inspection for 2-μm visual defects, the determination of registration tolerances to within ±0.5 μm and the determination of the accuracy of the critical dimensions to tolerances of ±0.5 μm on a single photomask in ten minutes.

An accurate electro-optical method was developed to measure slitwidths in the 0.5 to 400 micron range. A prototype instrument was built that gave experimental evidence of accuracy, resolution and reproducibility of measured data. The present setup covers a width range between 40 and 260 microns. Throughout this range a better than 1 percent resolution was demonstrated. The Atlantic Research technique uses a laterally moving optical fringe pattern, that is generated by two laser beams, converging at a small angle. The two laser beams are identical in intensity, derived from the same laser by using a Bragg cell as a beamsplitter. One of the two laser beams is shifted in frequency by an amount determined by the ultrasonic frequency of the Bragg cell, which causes the fringes to move in a direction perpendicular to their plane. Since the fringe spacing in the interference zone is constant (determined by the laser wavelength and the converging angle of the two laser beams), it can be used as a "yardstick" to compare its length to dimensions such as width of a slit. When the fringe spacing equals the slitwidth, the RF component of the transmitted radiation becomes zero. Accurate positioning of the slit (to be measured) in the fringe field is not necessary; however, a good angular alignment with the fringes is desired to obtain good signal-to-noise ratios.

While I was with Signetics, we successfully developed a process to effectively expose and align the wafers in proximity. This involved all layers of the masks. The MOS process was a P-channel, silicon gate. This resulted in a production line capacity of about 12,000 3" wafer outs per month. It wasn't until after the development stage that we went into full production with proximity and 3" wafers; because of this capability we were able to reduce mask costs and significantly increase dice yield. Now a lot of these things are nebulous because it depends on the particular process and the particular situation that you have, but we're judging this from a production environment. This all was an outgrowth of evaluating several types of masks including emulsion masks, iron oxide masks, chrome masks, and silicon masks. For our particular application the iron-oxide masks with a particular substrate was the best.

The use of plasmas -- low temperature gas discharges -- for semiconductor materials fabrication or processing is gaining widespread acceptance in the industry. This review will focus on the high application areas in micro-electronics for plasmas. These include photoresist removal, various substrate "cleaning" applications, etching of passivation layers, and thin film deposition.

This paper discusses the additive thin-film technology developed and employed at Aerojet. The rationale for the selection of an additive thin-film process, the fixturing, tooling and alignment techniques employed in this technology, the fabrication of the deposition masks, and some examples of the resulting thin-film imagery are described.

Recently, the Electronics industry has been in a period of rapid growth caused by several coincident factors. It is partially due to the over-contraction that the industry made during the early seventies as well as to a renewed market in some product areas with rapid development in new product areas. Probably the greatest single part of the industry enduring the greatest growth is that part involved with micro-electronics.

The rapid progress and growth which has been made in the semiconductor industry over the past decade has been due to the improvements in processes and equipment to manufacture integrated circuits. The most significant factor in the evolution of I.C.'s has been the increasing miniaturization of semiconductor devices. The reason for making circuits smaller is quite simple: If critical dimensions are cut in two, a fourfold increase in the number of devices per square area is achieved. As Figure 1 indicates, as the dimensions of a device are reduced, the power required per function decreases; the interelectrode capacitance decreases; and the frequency response improves. The cost of I.C.'s per function has steadily decreased over the past decade, and this is due to the increased packing density by the further miniaturization of the integrated circuit components. However, this rapid growth in microelectronics is being threatened by the photolithographic limit imposed by the wavelength of light.