You heard the numbers. You read the reports. All the indicators are up. The semiconductor book-to-bill ratio in July, the ratio of new orders to shipments, was the highest ever recorded by the Semiconductor Industry Association. Semiconductor demand is outpacing supply. And the fabs are doing their best to satisfy the need for more devices.
So what’s driving this thirst for semiconductors, particularly ICs? Well, it should come as no surprise to anyone. The PC industry, for one, is enjoying a great year. Coupled with the release of Windows 95 by Microsoft this past summer, fourth-quarter sales of PCs should skyrocket. Other industries, such as automotive and communications, are gobbling up ICs at a dizzying pace.
This soaring demand for ICs has sent engineering professionals scrambling for information. They need to know how to test these devices, what test equipment is required and how to observe and identify defects. They need this information to perform their jobs efficiently. This is where EE can help.
The next three articles focus on IC test. We start off with QTAG: The Evolution of a Standard Monitor by David Leslie from IMS, followed by FE SEM/FIB System Tracks Down Killer Defects by three authors at AMD and finally Speedy, Wide-Bit and Deep DRAMs Challenge ATE by our Technical Editor, Gerry Jacob.
The QTAG article addresses the issue of measuring IDDQ in an IC. QTAG is the Quality Test Action Group that was formed at the International Test Conference in 1993 to promote IDDQ testing. As you know, IDDQ is a measurement of the current flowing through the VDD pin of a device while the device is in a quiescent state. A high IDDQ indicates a defective IC.
The trick is to accurately identify failed devices and to perform the IDDQ test in the least amount of time. Several implementations have been explored with limited success. This article discusses in detail a new standard monitor which would be mounted on the test fixture and work with any ATE system.
Our next article in the series focuses on characterizing defects in processed wafers at semiconductor fabs. Once defects have been characterized, they can be identified and eliminated as quickly as possible before yield is adversely affected. The laboratory that supports the AMD fab uses a focused ion beam (FIB) system combined with a field emission scanning electron microscope (FE SEM) to characterize defects.
The FIB, with its micromachining and microdeposition capabilities, exposes and cross- sections the defects while the high-resolution FE SEM locates and identifies the processing defects, which may be voids, shorts or equipment contamination. To illustrate the effectiveness of the combined system, two examples of killer wafer defects are presented: a poly-silicon and a metal 2 line defect.
Computer memory is one topic that gets a lot of attention these days. Whenever you upgrade to a new operating system or add a new application program, the first question you must answer is: Do I have enough memory in my PC? Many times you don’t, and this is the basis for the third article in our series on IC test.
Advancements in IC memory technology have been phenomenal. We have progressed from 64-kb to 16-Mb devices in only a few short years. But microprocessor speeds of well over 100 MHz are now putting a strain on conventional DRAM architectures. We are seeing new devices, such as extended data out DRAMs, synchronous DRAMs and cache DRAMs.
These new memory architectures are explained in this article, along with the impact they have on current and new memory test systems. We look at the large million-dollar memory ATE and the much smaller SIMM testers. And to help you choose the right tester for your application, we have included a comparison chart of recently introduced memory test systems.
We hope this focus on IC test provides you with the information you need to remain up-to-date in the rapidly changing world of IC technology.
Copyright 1995 Nelson Publishing Inc.
October 1995