PART III - Large Scale Integration Technology

A brief review of today's processing of integvated circuits is given. The major trends in the development of advanced integvated electronics are identified as 1) the broadening of the integvated circuit concept to a large class of circuit function, 2) the processing of more complex circuits within relatively small chips of silicon, and 3) the processing of very large electronic functions on complete slices of silicon. This latter trend, called array technology, is then developed in detail. Emphasis is given to defining the key tech-nological problems. Current progress being made is illustrated. THIS paper will endeavor to identify the major trends in advanced integrated electronics technology. One of these, array technology, will be developed in some detail. The array technology discussion will identify the key problem areas. Since it is the scope of the entire meeting' to present specific progress in the science and technology of integrated electronics, we shall indicate general directions being explored rather than discuss comprehensively solutions to the problems. In order to set the stage for the discussion of future trends in integrated-electronics technology, let us briefly compare the processes by which circuits are fabricated through discrete-device technology with that of integrated circuits technology. The reader is referred to the December 1964 issue of Proceedings of IEEE2 for a comprehensive review of integrated electronics. The article3 by Jay Lathrop is an excellent discussion of integrated-circuits technology. A discussion of the history of semiconductor technology is contained in Ref. 4. A) Current Status of Integrated Electronics. Fig. 1 (top) shows the process by which circuits are constructed from discrete devices. Key points are: 1) Slices containing large numbers of transistors or diodes are processed separately. 2) The slices are scribed into small chips (on the order of 15 mils on a side is about as small as can be conveniently handled) each chip containing one transistor. 3) Each device is specified separately—circuit -function specs are derived largely from device specs. 4) Circuits are formed by connecting together the discrete devices. 5) The number of circuit connections required is approximately equal to the number of devices. 6) There are potentially many more discrete devices per inch2 of semiconductor—only our lack of ability to handle them in discrete form prevents us from going to several orders of magnitude higher density iin Fig. 1, 400,000 transistors are discussed at 1.5 mils on a side). The bottom part of Fig. 1 illustrates the integrated circuit process. Key points are: 1) On the same slice of silicon, transistors, diodes, and resistors are processed grouped to do a complete circuit function. 2) While still in slice form, the components are interconnected into circuit functions by an evaporation process, eliminating the need for separate interconnection steps later. Dramatic improvements in cost and reliability are realized. With a simple flash of metalization thousands of interconnections are reliably made. 3) The slices are scribed into chips which contain complete circuit functions. 4) The circuit functions are specified-not each component in the circuit. This important point was missed by some of the early opponents to integrated circuitry. They argued that, with device yields at x pct, integrated circuit yields would be pct, where n is the required number of devices to make a circuit. This argument leads to extremely low yields for integrated circuits. The fallacy of the argument is that in integrated circuits each device is not specified separately. Furthermore, since a device is forever integrated into a specific circuit function, it need meet only the requirements for that particular function. Discrete devices, on the other hand, are tightly specified so that they can be applied to a variety of circuit functions. 5) Extremely high packing densities are achievable because one need only make the basic devices as large as the circuit demands. Their size is not dictated by handling requirements. A current example