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1982 - David Baron examines a small photographic plate, known as a mask, which is the end product of the automated process

MASKS AUTOMATICALLY

CD 1967051 E&MP68.001

Integrated Circuits

March 23, no year

A group of researchers of International Business Machines Corporation has overcome a major difficulty in making complex arrangements of integrated circuits.

They have largely automated the design and fabrication of the circuit masks, cutting the time of these operations by more than a factor of ten.

In the photograph IBM technician David Baron examines a small photographic plate, which is the end product of the automated process.

The plate contains on of the mask patterns (10X), which was drawn by a light beam in an automated "light table."

With traditional preparation methods, the pattern for each mask is cut by hand from opaque material at 200 or 500 times final size.

An example is shown in the background. Manual preparation is a tedious, time-consuming process subject to many errors.

additional text found

March 24, 1967

IBM MAKES MASKS FOR INTEGRATED CIRCUITS AUTOMATICALLY

Researchers of International Business Machine Corporation have overcome a major difficulty in making complex arrangements of integrated circuits.

They have largely automated the design and fabrication of the circuit masks, cutting the time of these operations by more than a factor of ten.

Details of the newly developed technique were described today by Dr. Dale L. Critchlow at the Institute of Electrical and Electronic Engineers International Convention, which is being held at the N.Y. Coliseum this week.

In the process, most of the manual steps in design and fabrication of the circuit masks have been eliminated.

The system has been used to generate sets of masks for complex integrated circuit chips containing over 100 NOR circuits.

The time required to generate circuit masks of this complexity has been reduced to a matter of hours as compared to hundreds of hours if traditional techniques are used.

The NOR circuitry was implemented with insulated-gate-field-effect transistors, but the mask generating technique has been applied to bipolar integrated circuits as well.

Traditionally, circuit masks are made by the laborious and time consuming manual process.

First and exact scale drawing (200 or 500 times final size) is made from a rough sketch of the circuit layout.

Then the drawing is separated into a set of overlays -- one for each processing step, such as metalization, diffusion and contact holes.

Each overlay pattern is cut on an opaque material with transparent backing.

After stripping the opaque layer from the pattern areas, the overlays are reduced photographically to 10 times final size, ready for the step-and-repeat camera.

In the new process, the design and fabrication of masks consists of five basic steps.

First the designer draws a rough pencil sketch of the circuit layout.

Then he translates this into digital form by describing the circuitry in a symbolic notation -- a specially developed high-level language for the mask designer.

In step three, this symbolic language is fed to a computer and processed.

In processing, the circuit structures are automatically assigned to their appropriate masks.

The computer then generates a set of commands which can be used to drive a "light table" to draw the patterns for each layer of the mask set.

In the forth step, the actual patterns are drawn on high-resolution photographic plates by the light table at 10 to 20 times final size.

The plates are mounted on an x-y platform, which is driven by stepping motors.

As the table is moved, under commands prepared by the computer, a light beam from a xenon flash lamp draws the mask pattern on the plate.

The flashing of the lamp also is controlled by commands from the computer.

Four patterns of an insulated-gate-field-effect transistor chip of 122 circuits were written in about 1 hour; over 100 hours would be required to cut artwork by commercial techniques.

In the final step, the exposed and developed plates are placed in a step-and-repeat camera to form a complete array of chip patterns at final size on photographic plates which, in turn, are used to expose the array of chip patterns on the semiconductor wafer.

Th[is] photograph shows an integrated circuit chip of 55 NOR circuits, which was fabricated from masks generated in the experimental automated process.
1967 - a circuit chip containing 207 field-effect devices, is compared in size to crystals of common table saltA circuit chip containing 207 field-effect devices, is compared in size to crystals of common table salt.

Technical Details
Computer-Assisted Layout

A key development in the new process is an experimental language which was designed to describe, easily, the circuit patterns from a rough sketch.

With this language it is possible to define, by a simple code, anything that may appear in the circuitry, ranging from small diffusion area to a complex arrangement of devices making up a logic gate.

Having made these definitions and stored them in a tape library, the designer can specify the circuit layout in a skeleton form, forgetting about the details of geometry, such as line spacing and diffusion widths.

The language contains a hierarchy, so that a transistor can be defined by a simple instruction built up from a set of instructions which specify its detailed structure.

In turn, a higher-level circuit configuration of many transistors can be defined with a single instruction.

Such a facility permits a gradual accumulation of a library of parts which can be used over and over in different mask structures.

The language also contains a replication feature, so that a circuit or structure can be defined, and, with a simple command code, it can be replicated at any desired interval over the mask.

Light Table

The mask pattern on the plates is written at 10 or 20 times the final circuit size.

The plate is mounted on the platform of the light table which can be moved in steps of 1/2 mil over a field of 2.2 x 2.2 inches at a rate of 200 steps per second.

The absolute accuracy of the table within this range is 75 microinches, and repeatability is better than 50 microinches.

When used with a high quality step-and-repeat camera and lens system, masks with 0.1 mil lines over 200 mil fields can be made with positional repeatability of 15 microinches.
 



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Original Caption by Science Service
International Business Machines (IBM)



National Museum of American History

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