DUV Laser Critical for Next Generation Inspection
As integrated circuit (IC) manufactures continue to pursue Moore’s Law, smaller and smaller features are printed on chips. That’s an easy statement to make, but in practice it is very difficult and complicated to do, especially when there are tiny defects that are practically invisible.
A defect can be a small particle, a scratch or a bump on the surface of a wafer, a void in the material or a bridge between two lines. Some are big — although big in our world means just a few millionths of a meter — and some are very small.
Even with today’s advanced technology, defects below 50nm (the typical size of a virus) can prevent a chip from working properly. How can we detect, image and analyze such a tiny thing?
One key technology that serves process diagnostics tool manufactures, like Applied Materials, is the deep ultraviolet (DUV) laser. The DUV laser combines two important capabilities that help detect smaller and smaller defects.
First, it’s the Laser’s nature. The emitted laser light is notable for its high degree of spatial and temporal coherence, unattainable using other technologies. Spatial coherence is typically expressed through the output —a narrow beam. Laser beams can be focused on very tiny spots, achieving a very high irradiance. Temporal coherence implies a polarized wave at a single frequency whose phase is correlated over a relatively large distance along the beam.
Without getting too deeply into a physics discussion, the usage of lasers simply enables the production of more light with better control over the characteristics of that light.
The second important attribute of the light is its wavelength. Using shorter wavelengths enables higher resolution, but more importantly when we are trying to detect small particles, shorter wavelengths result in more light scattered from the particle’s surface, which makes the particle stand out more clearly becoming easier to find and resolve.
In today’s world, the most advanced detection systems are using Deep-UV as the wavelength for detecting small defects. DUV is not a scientific definition, but in general means wavelengths shorter than 300nm.
This week Applied Materials launched a new inspection system, the Applied DFinder, the first darkfield inspection system to use DUV laser scanning for unmatched particle sensitivity. The DFinder system’s exclusive DUV laser illumination technology uniquely enables the detection of all particles of interest at the 22nm technology node – down to 40nm in size.
With the launch of the DFinder system, Applied now has the industry’s only comprehensive portfolio of inspection solutions based on using exclusively DUV laser technology.
Since Moore’s Law is not expected to end any time soon, one can only ask “what next?”
Using stronger lasers with shorter wavelengths is one direction, but not necessarily the right one. Either because these lasers are too complicated and cost too much to use for production environments or because the resolution they can give is just not enough for the long term future.
What will be the technology of choice to replace lasers as the inspectors of the future? The answer is probably worth another post. So, stay tuned…