Chip Manufacturing Technology: An Introduction
Computer chips are fundamental to the modern technology revolution. They are made mainly of transistors, which act as electrical switches in digital circuits, and metal wires. The most important type of transistor, from an economic perspective, is the complementary metal oxide semiconductor (CMOS) transistor. This is a three-terminal device consisting of a gate, a source, and a drain. The gate is an electrical switch that controls the flow of electrons from the source to the drain. Applying a voltage turns "on" the gate, which directs an electric field across a thin silicon dioxide film, causing the semiconductor material to become conductive and thereby allowing electrons to flow. If the gate voltage is turned "off," the electrons go away. Transistors being "on" or "off" correspond to the binary "1" and "0."
The devices and wires on a chip are fabricated at the same time, alongside hundreds of other chips, using a process known as batch fabrication. It does not cost any more to fabricate 1,000 transistors than 100 transistors—or many million of transistors for that matter. This is known as batch fabrication and it results in substantial economies of scale that make chips inexpensive despite their complexity.
It all starts with silicon —the primary constituent of sand, and therefore abundant and inexpensive. The silicon is purified, and large cylindrical crystals one to two meters (three to six feet) long and up to one-third meter in diameter are grown. These crystals are sliced into wafers 500–750 micrometers thick that form the substrate for the chips. The chip designer provides the chip manufacturer with a set of photomasks that contain a physical representation of the transistors and associated wires to be reproduced on the wafer. Photomasks are made of glass and chrome and define regions where light can penetrate (glass), and others where the light cannot penetrate (chrome), similar to a stencil..................
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