1.1.2 Process Integration

The unit process steps described in the previous section have to be combined in a way to produce an IC. This task is commonly referred to as process integration. Process integration can be generally divided into three basic components: device fabrication, isolation technology, and interconnect technology. The device fabrication step determines the technology, e.g., NMOS, CMOS, bipolar or BiCMOS, in which the IC is realized. The technology choice strongly depends on the type and application of the IC. In any technology the individual devices have to be isolated from each other first and then connected through specific electrical paths to implement the desired functionality. These two steps are referred to as isolation and interconnection.

The process components are realized by so called process modules. The process modules are the fundamental building blocks of the entire manufacturing process. Usually one module comprises a lithography step followed by pattern transfer and one or more layer formation and/or modification steps. The combination of the process modules constitutes the process sequence and is described and documented in a flowchart. Most of the modules can be used in different technologies or at least for different circuit types realized in one technology. However, they cannot be processed independently from each other as a more or less strong interrelation exists. An obvious example is the thermal budget of a process module that influences all previous steps in an equal way.

The complexity of process integration tasks can vary from low level, like the modification of just one module, to high level, like the development of a new technology from scratch. One popular approach between these two extremes is the enhancement of the complete process sequence by shrinking the minimum feature size used in an already available technology. While such ``technology-shrinks'' are generally less complex than the tasks involved in the development of an entirely new complete process sequence, they usually entail more than just the implementation of higher resolution lithography. Many of the other process steps must also be modified, and entirely new ones may have to be developed.