Chip that come into the museum are all scanned on a Canon 5600F flatbed scanner. It has a good (there is some better though) depth of field, and its fast. Typically chips are scanned at 300dpi, or for small ones (or ones that have a die visible) 600dpi. This keep the file sizes reasonable, yet still allows them to be studied in good detail on CPUShack.com as well our records.
There are on occasion chips that are VERY hard to scan, either the markings are very small, or very shallow. This is becoming common on more modern chips, for one the chips themselves are smaller, and second, they are most often laser marked, and there isn’t enough thickness in the package (or die on some) for the Grand Canyon engraving of the 80’s.
This is a Intel QG80331M500 IO Processor made by Intel in 2007. It is the replacement for the 80960 based I/O processors, using instead a 500 MHz XScale ARM Processor core. This scan was done at 1200 dpi, the part number is visible, barely, but the S-spec and FPO (lot code) are not. The markings are laser etched directly onto the surface of the silicon die. This is fairly common on this type of chip (as well as most all of Intel chipsets). How do we improve upon this? Bumping the resolution to 2400dpi just makes a bigger blurry picture (with more noise). What we need is better resolution, at where the scanner works best (less noise at 1200 dpi scan).
Thankfully we can use a ‘technology’ that is very much similar to how modern processors themselves are now made. Dumping water on the scanner, also known as immersion scanning.
In making IC’s the most common light source is 193nm light. Generally this would limit the feature size that could be resolved (in this case light through the mask onto the wafer) to 1/2 to 1/3 of that, depending on the quality of the lens. That means features of around 65nm. However, modern chip making replaces the air between the lens and the wafer with a liquid. The effective resolution is then increased by the refraction index of the liquid. Water, with 193nm light, has a refraction index of 1.44 (or 1.33 for mid-visible light), while some more exotic fluids created just for this, have indices of nearly 2.0
This exact concept also works on a scanner. A small amount of water is placed on the scanner bed (and contained as to not get IN the scanner, as that does NOT help the process). The chip is then placed in the water, thus the air between the glass and the chip is replaced. Air had a refraction index of approx. 1.0 while water is 1.3. You can clearly see the results. The S-spec is now clearly visible. The scan is still at a 1200 dpi resolution but there is much sharper features.
This same technique has been used for some time for film scanning, there are also much more sophisticated immersion fluids that work better than water, which with the continual shrinkage of chip markings, we may have to try. Just be sure to keep it on the scanner, and not in.