But the industry has hit the wall in the quarter-micron generation. There are serious, serious, serious problems with yields at a quarter-micron. ... The power, signal-integrity, and metal-migration challenges are exceeding the capability of the tools. Instead of 80 percent yields, crosstalk is cutting yields for quarter-micron designs down to 30 or 40 percent at some companies.
• simulation, which verifies the design's functionality;
• logic synthesis, which translates the design to lower levels of abstraction, such as circuit schematics; and
• layout, which takes circuit schematics and creates masks for the fabrication process.
• test generation and fault simulation (TGFS),
• design rule checking (DRC), and
• design for test.
Reuse. The industry is moving toward design flows that reuse preexisting designs called cores or IP (intellectual property). The integration of these parts poses a significant problem for automation tools. If the cores came with an equivalent gate-level design that was modifiable, most tools could easily deal with these reusable parts when incorporated in a larger design. However, these cores come with restrictions that make them difficult or impossible to modify. For example, they can be rigid (the layout is already determined), or vendors may not reveal the core's gate-level model.
From a test perspective, the story revolves around the reuse of test patterns that come with a core and testing logic outside the core, without having the core's gate-level model. To solve these problems, the IEEE P1500 standards group is developing standards for core test. 3,4
Lower voltages. In nanometer technologies, the supply voltage and threshold voltages are also decreasing. As a result, the quiescent current—current measured when all the switching activity of the IC has settled—in the new technology generations is increasing. I DDQ is a test technique that relies on monitoring this current for variations that can indicate defects.
I DDQ testing works well when the leakage current of a defect-free IC is very small. As leakage current increases, the small increase in leakage current caused by a defect becomes more difficult to distinguish. 5 Despite such a limitation, I DDQ testing has significant value, and current research seeks to extend this technique's effectiveness for nanometer technologies.
New materials. Along with decreasing device size, the underlying technologies are also changing. For example, the use of copper interconnects and the introduction of silicon on insulator (SOI) will impact test. New technology has the potential to create new defects that need to be tested.