By Hank Hogan

Contamination detection today is a technology not only of sight and sound but also of the ion. The latest advances incorporate laser, soundwave, and helium ion-based detection technologies-all now in use in semiconductor manufacturing, as device suppliers seek to spot and eliminate contaminants.

The two images above help to illustrate behavioral differences of a) a helium ion beam and b) an electron beam when hitting a sample. The helium ion beam’s heavier particles interact with a narrower surface region with very little scattering. Thus, the images do not suffer from sub-surface blurring effects that are common in SEM images. The result is that the helium ion microscope can produce images with higher resolution and more surface-specific information. Images courtesy of Carl Zeiss SMT.Click here to enlarge image

An example of the first of the three can be found in the offerings of Tiger Optics (Warrington, PA). The company’s latest analyzers measure airborne contaminants that impact the process. “For cleanroom air applications, we’re doing ammonia, hydrogen chloride, and methane,” says Lisa Bergson, Tiger Optics’ CEO.

The company’s Tiger-i ambient cleanroom air products are being tested now at semiconductor sites, with plans to release the analyzers later this year. The company’s products use cavity ring-down spectroscopy, in which a laser pulse bounces between mirrors and decays away. If an absorbing molecule is present, the ring-down time will be altered; by using varying wavelength pulses, different molecules can be detected.

Such instruments offer a wide dynamic range. According to Bergson, the detectors can spot contaminant concentrations as low as 200 ppt and as high as 20 ppm.

At Sonoscan (Elk Grove Village, IL), imaging is done with sound, making use of technology similar to ultrasound medical imaging. Using frequencies ranging from 10 to 400 MHz, the sound waves are fired into the subject part and the reflections captured.

Steve Martell, Sonoscan’s manager of technical support, says the technique offers the ability to peer inside a packaged part and see how all the different layers are adhering to one another, which can be vital information. “You want to check out the parts once in a while to make sure you don’t have any contamination that has shown up that is now causing a disbond or improper bonding to materials.”

The company has recently added the technology to look at bond-line thickness. This inspection can be done in conjunction with contamination checks.

Another technology comes from the ALIS business unit (Peabody, MA) of Carl Zeiss SMT, which has developed a first-of-its-kind helium ion-beam microscope.

The helium ions penetrate the surface of a material, giving rise to secondary electrons and backscattered helium. The backscattered ions act as a nanoscopic probe of the material and so provide more than a simple image. Says Clarke Fenner, vice president of business development for ALIS, “When you look at contamination or do a defect review, this gives you the ability to differentiate between these different materials and potentially determine what the contaminants are on the nanoscopic level.”

Fenner reports that one of the first two systems shipped went to a chipmaker to use for failure analysis.