Arrive extremely clean
Our wafer begins inside a fabrication plant, or fab, in a cleanroom around 10,000 times cleaner than outside air. A speck of dust that’s completely invisible to us can be enormous beside the features being built, so people wear full protective suits mainly to protect the wafer from themselves.
Dust is no longer a minor housekeeping issue. It’s an industrial saboteur.
Put on several coats
The wafer receives an extremely thin layer of conducting, insulating or semiconducting material. It’s then coated with photoresist, a substance that reacts to light, before being spun and baked.
This begins a repeated routine: add material, coat it, expose it, remove some of it, inspect it, then do the whole thing again. Modern chips can contain around 100 precisely aligned layers. Imagine building a 100-storey tower where every wall must line up within a few nanometres.
One nanometre is one millionth of a millimetre. At this point, normal human measurements have been asked to leave.
Get shot at with magic space light
Lithography prints tiny circuit patterns onto the photoresist. For the smallest and most critical features, manufacturers use extreme ultraviolet, or EUV, light with a wavelength of just 13.5 nanometres.
Producing that light is entirely normal, provided your definition of normal includes firing two high-powered lasers at individual droplets of molten tin travelling at over 240 km/h. This happens 50,000 times every second, creating plasma that emits EUV light.
Most materials absorb EUV, so ordinary lenses won’t work. The light is guided using mirrors with more than 100 engineered layers, polished smoother than the thickness of a single atom.
Obviously.
Remove most of the morning’s work
The exposed photoresist is developed, then reactive gases etch away selected material to leave the circuit pattern behind. Ions may then be fired into the wafer to alter how particular areas conduct electricity.
So far, it has been coated, baked, blasted with light, etched and bombarded with charged atoms. It hasn’t even had lunch.
Expose it
Remove some
Inspect it
Repeat
Inspection. Again.
At every major stage, the wafer is measured and inspected for contamination, missing material, incorrect dimensions and misaligned layers. At this scale, “slightly wrong” can mean an entire chip doesn’t work.
Different materials and defects respond differently to light, which is why wavelength, intensity and illumination angle matter so much in semiconductor inspection.
Quality control can’t wait until the end. There may be hundreds of tightly controlled steps, and one tiny defect can undo months of work.
Change the light, change what the system can see
Several months later: Clock off
Once complete, the wafer is tested, cut into individual dies, packaged and tested again.
LED illumination may continue to support machine vision and inspection as systems check wafer surfaces, individual dies, connections and final packaging.
This has been a slightly tongue-in-cheek look at semiconductor manufacturing and inspection. Our experience in creating LED illumination for it, however, is entirely serious.
From wavelength and optical power to illumination geometry, triggering and system integration, we work with equipment manufacturers to create illumination for some of the most demanding inspection and metrology applications around.
