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The Computer on a Chip

The invention of the light bulb in 1879 symbolized the beginning of electronics. Electronics then evolved into the use of vacuum tubes, then transistors, and now integrated circuits. Today's microminiaturization of electronic circuitry is continuing to have a profound effect on the way we live and work.
Current technology permits the placement of hundreds of thousands of transistors and electronic switches on a single chip. Chips already fit into wristwatches and credit cards, but electrical and computer engineers want them even smaller. In electronics, smaller is better. The ENIAC, the first full-scale digital electronic computer, weighed 50 tons and occupied an entire room. Today, a computer far more powerful than the ENIAC can be fabricated within a single piece of silicon the size of a child's fingernail.
Chip designers think in terms of nanoseconds (one billionth of a
second) and microns (one millionth of a meter). They want to pack as many circuit elements as they can into the structure of a chip. High-density packing reduces the time required for an electrical signal to travel from one circuit element to the next—resulting in faster computers. Circuit lines on the initial Intel processors (early 1980s) were 6.5 microns wide. Today's are less than .5 microns. The latter holds 35 million transistors and is 550 times as powerful as the initial one. By the turn of the century, researchers expect to break the .2 micro barrier.
Chips are designed and manufactured to perform a particular function. One chip might be a microprocessor for a personal computer. Another might be for primary storage or the logic for a talking vending machine. Cellular telephones use semiconductor memory chips.
The development of integrated circuits starts with a project review
team made up of representatives from design, manufacturing, and marketing. This group works together to design a product the customer needs. Next, team members go through prototype wafer manufacturing to resolve potential manufacturing problems. Once a working prototype is produced, chips are manufactured in quantity and sent to computer, peripheral, telecommunications, and other customers.
The manufacturing of integrated circuits involves a multistep process using various photochemical etching and metallurgical techniques. This complex and interesting process is illustrated here with photos, from silicon to the finished product. The process is presented in five steps: design, fabrication, packaging, testing, and installation.

1. Using CAD for Chip Design Chip designers use computer-aided design (CAD) systems to create the logic for individual circuits.
Although a chip can contain up to 30 layers, typically there are 10 to 20 patterned layers of varying material, with each layer
performing a different purpose. In this multilayer circuit design, each layer is color-coded so the designer can distinguish
between the various layers.

The product designer's computerized drawing of each circuit layer is transformed into a mask, or reticle, a glass or quartz plate with an opaque material (such as chrome) formed to create the pattern. The number of layers dependson the complexity of the chip's logic. The Pentium™ processor, for example, contains 20 layers. When all these unique layers are combined, they create the millions of transistors and circuits that make up the architecture of the processor. Photo courtesy of Micron Semiconductor, I

3. Creating Silicon Ingots Molten silicon is spun into cylindrical ingots. Because silicon, the second most abundant substance, is used in the fabrication of integrated circuits, chips are sometimes referred to as "intelligent grains of sand." © M/A-COM, Inc.

5. Wearing Bunny Suits

To help keep a clean environment, workers wear semi-custom-fitted Gortex® suits. They follow a hundred-step procedure when putting the suits on. Courtesy of Intel Corporation

4. Cutting the Silicon Wafers

The ingot is shaped and prepared prior to being cut into silicon wafers. Once the wafers are cut, they are polished to a perfect finish. © M/A-COM, Inc.

6. Keeping a Cfean House

Clean air confi'nuousCy flows from every pore of the ceiling and through the holes in the floor into a filtering system at the manufacturing plant. A normal room contains some 15 million dust particles per cubic foot, but a clean room contains less than 1 dust particle per cubic foot. All of the air in a "clean room" is replaced seven times every minute.
Portions of the micro chip manufacturing process are performed in yellow light because the wafers are coated with a light-sensitive material called "photoresist" before the next chip pattern is imprinted onto the surface of the silicon wafer.

7. Coating the Wafers

Silicon wafers that eventually will contain several hundred chips are placed in an oxygen furnace at 1200 degrees Celsius. In the furnace each wafer is coated with other minerals to create the physical properties needed to produce transistors and electronic switches on the surface of the wafer

8. Etching the Wafer

A photoresist is deposited onto the wafer surface creating a film-like substance to accept the patterned image. The mask is placed over the wafer and both are exposed to ultraviolet light. In this way the circuit pattern is transferred onto the wafer. The photoresist is developed, washing away the unwanted resist and leaving the exact image of the transferred pattern. Plasma (superhot gases) technology is used to etch the circuit pattern permanently into the wafer. This is one of several techniques used in the etching process. The wafer is returned to the furnace and given another coating on which to etch another circuit layer. The procedure is repeated for each circuit layer until the wafer is complete.

9. Tracking the Wafers

Fabrication production control tracks wafers through the fabricating process and measures layers at certain manufacturing stages to determine layer depth and chemical structure. These measurements assess process accuracy and facilitate real-time modifications.

10. Drilling the Wafers

It takes only a second for this instrument to drill 1440 tiny holes in a wafer. The holes enable the interconnection of the layers of circuits. Each layer must be perfectly aligned (within a millionth of a meter) with the others.