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Pnp transistor1/13/2024 ![]() ![]() The other components necessary to complete the circuit must be made during the same operations that form the NPN transistors.Ī cross-sectional view of an NPN transistor made by the six-mask planar-epitaxial process is shown in Figure 10.1.(It is cautioned that in this and following figures, relative dimensions have been grossly distorted in order to present clearly essential features. The six-mask process is tailored for making NPN transistors, and transistors with characteristics similar to those of virtually all discrete types can be formed by the process. The net result is that a large number of functioning circuits are obtained from each successfully processed silicon wafer at a low average cost per circuit. The circuits can be tested individually so localized defects can be eliminated. While the operation described above seems complex, particularly when we consider that it is repeated six times, a large number of complete circuits can be fabricated simultaneously. Following diffusion, the oxide is reformed and the masking process repeated to define new areas. The oxide layer itself thus forms a mask which permits \(N\)- or \(P\)-type dopants to be diffused into the silicon wafer. ![]() This layer is then etched away in the unprotected regions. This layer is photosensitized, and regions are defined by photographically exposing the wafer using a specific pattern, developing the resultant image, and removing unhardened photosensitive material to expose the oxide layer. A silicon-dioxide layer is first formed by exposing the silicon integrated-circuit material to steam or oxygen at elevated temperatures. Each masking operation itself involves a number of steps, the more important of which are as follows. This technology evolved from that used to make planar transistors. The most common process used to manufacture both linear and digital integrated circuits is the six-mask planar-epitaxial process. Some manufacturers do use processes that are more involved than the one described here and thus increase the variety and quality of the components they can form, but unfortunately the circuits made by these more complex processes can usually be easily recognized by their higher costs. Since the probabilities of success of each step of the fabrication process multiply to yield the probability of successfully completing a circuit, manufacturers are understandably reluctant to introduce additional operations that must reduce yields and thereby increase the cost of the final circuit. ![]() The process used to make monolithic integrated circuits dictates the type and performance of components that can be realized. ![]()
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