Overview

Many MMIC design rules and layout constraints are the result of the way the chips are manufactured, in other words, the wafer-processing technology. A basic understanding of the different processes, such as epitaxial growth, photolithography, and metal deposition, enables the MMIC designer to know which rules can be bent during the design phase and which rules cannot be broken under any circumstances. Indeed, it is usually the designers, pushing to improve the performance of their circuit designs, who know which design rules constrain the potential performance of the process and can help direct the process engineers in developing the next generation process. This sort of interaction between the MMIC designers and the foundry process engineers facilitates innovation not just in the development of the next generation process but also in the optimum use of the current process technology.

This chapter gives a brief overview of the typical wafer-processing steps involved in the fabrication of MMICs, from the original semiconductor material all the way through to the final chip. The reader needs to realize that this is just a generic overview, and individual foundries have their own specific process flows and associated design rules, which will be different from those described here. Much of this material is also based on a III V semiconductor process, which, while generally similar to a silicon fabrication process, will have different associated material systems and processing issues. A summary of these steps is given below:

• Substrate material growth: grow material from a single-crystal boule...