Overview

This chapter is concerned only with the tests and measurements that are performed while the wafer is still whole. After these tests, the MMICs are diced or sawn into individual chips or packaged, then jig-tested, a process that is outside the scope of this design book.

The whole wafers are tested at dc because these tests are used for the process control monitoring (PCM) function to ensure that the process was performed correctly and that the components are within their allowed specification ranges. The RF-on-wafer (RFOW) tests also confirm that the RF performance of the components is within the allowed ranges and can be used to check the performance of the MMIC designs. RFOW measurement of the MMIC _S, before dicing and assembly, allows quicker testing of prototype circuits and enables out-of-spec wafers to be rejected before costly dicing operations are performed. It also allows only known-good dies to be selected for production assembly, which reduces costly rework at later stages.

8.1 Process Control and Monitoring (PCM)

As mentioned in the layout chapter, process control monitors [1] are placed either in each array or in the drop-in arrays, and they contain at least one of each type of component from resistors to transistors, including chains of metal-layer interconnects and through-substrate vias. The PCMs have a standard pad layout and are generally autoprobed using a probe card with numerous probe needles and a wafer probe station (Figure 8.1). The probe card is positioned over the first PCM and is...