Thinking small to solve big problems
For the last 20 years, BAE Systems' Materials Capability Group in Manassas, Virginia, has used focused ion beam microscopy to mill complex components atom-by-atom to solve some of the company's toughest challenges.
Only a handful of U.S. Defense Department contractors have focused ion beam microscopy instruments – advanced, scanning electron microscopes with an additional ion beam used for localized milling. BAE Systems' Electronic Systems sector has two of these machines and has been performing "nanosurgery" on some of the company's most-delicate components for the last two decades.
Focused ion beams, or FIB, contain chemicals and liquid metal ion sources – platinum and gallium – to deposit conductive patterns, or etch and view various shapes in integrated circuit chips or thin coatings. The FIB ensures our products meet precise specifications.
"When problems arise with semiconductor device yield or performance, the foundries depend on failure analysis to determine root cause," said Linda Heath, Lexington foundry manager, noting that only an FIB can identify the structure or process causing the deviation in most cases. "This powerful tool allows us to quickly solve the problem and continue production. The FIB is also used routinely to monitor product quality, enabling us to consistently produce reliable, high-performance, low-cost products."
BAE Systems' first success with the technology came when the company investigated a new memory device with a defect that caused the integrated circuit chip to be permanently disabled and untestable. The FIB milled layers to repair the defective circuitry and proved that only one design change was required to qualify a new product. As it turns out, the lab is currently working on a similar project.
In 2009, a decade following the first success with the equipment, BAE Systems installed a new-generation dual beam focused ion beam. DBFIB allows engineers to mill, inspect, and measure thin film layers or defects at very high magnification. The ability to look for defects, misalignments, foreign object debris, electrostatic discharge damage, blistered or cracked layers, and determine root causes for a variety of failure modes is applicable for programs throughout the company. Identifying defects early, and determining root causes, allows us to deliver better, more-affordable products to our customers.
While the DBFIB towers over a desktop computer, it’s capable of magnifying the tiniest of particles.
"The DBFIB is ideally suited for creating cross-sectioned images of layers that include both hard and soft materials, such as ceramic substrates and conductor layers," said analyst Jim Bowman. "Unlike traditional cross-sectioning into a critical structure, where an analyst may only produce one or two cross sections per day, the DBFIB can provide hundreds of cross section images throughout the structure." Similar to examining organic tissue, the more cross sections you have to study, the less likely you are to miss something that could cause problems later.
The equipment is so precise, it literally mills objects atom-by-atom. One application for this is isolating specific sensor pixels having internal shorts. Little by little, a solder bump is milled away until it is completely gone, and then the FIB deposits a protective glass layer over the area where the solder bump once was. The device then passes customer imaging tests and is deliverable.
As a practice exercise, our Women in Technology program participants draw an object, which is then scanned into the instrument. They use the FIB to mill their image on the point of a needle to demonstrate how small some of the features of our most-advanced products can be.
"The FIB was fascinating, because it showed the level of detail that engineers have to go through in order to fix problems and ensure the reliability of products," said Jacqui Zimmerman, a WiT participant. "The fact that something as small as a piece of dust could be an issue is mind-boggling. Being able to interact with objects in such a minuscule scale was captivating."
With the past successes using the technology, BAE Systems is now investigating new xenon plasma FIBs, which have the capability of milling much larger features 50 times faster than our current equipment.
A plasma FIB would allow quick evaluation of anything from printed wiring board subsurfaces to larger solder joints. Any program within Electronic Systems can take advantage of this technology by contacting the Materials Capability Group.
By John Davis, Engineering, Manassas, Virginia