As you might imagine, very few manual operations are performed on the production line. The main role of the operators is to transport the wafers from one stage to another and to oversee proper completion of the operations. To avoid damaging the surface of the wafers, they’re handled by the opposite surface using magnetic spatulas.
Working conditions are strict. All handling is done in a class 100 clean room, which guarantees no more than 100 particles larger than 0.5 microns per cubic meter of air, and operators must wear protective overalls. Still, the atmosphere is a long way from what you may have seen in the famous Intel ads, with figures wandering around in blue, pink and green hermetic suits.
If the yellowish tinge of these pictures has you wondering whether something’s wrong with our camera, don’t worry. The light in the clean room is actually yellow. The reason for this is the same as it is for darkrooms: photolithography requires the surface of the wafer to be sensitive to light, and especially UV light. Using normal white light would ruin the entire surface, so lighting must be highly controlled and limited to precise frequencies that don’t affect the wafers’ light-sensitive coating.
The head fabrication process is so complex that at certain stages it requires removal of part of certain layers that have already been deposited in earlier stages. This is done using selective masking and ion milling. In this process, deposits are cut away by a focused ion beam; once again, all operations are automated. These stages are very time-consuming, since they take place in a high vacuum that takes time to establish (up to two hours) despite the use of large pumps.
The wafers are tested at various stages of the fabrication process. The tests can be optical, via microscope, or electrical, using fine-pointed sensors. As you can see on the screen shown above, the success rate of each stage is not always very high, but Seagate claims yield rates of over 90% of total production. Those figures take into account only the number of valid wafers compared to the total number of wafers used. In fact, it’s possible to resurface a wafer that has failed during fabrication to bring it back to its original state, then send it back to the start of the production line.
Here’s what a finished wafer looks like. You can easily make out the rows of individual identical heads with the naked eye. The surface of the wafer is perfectly smooth and flat: a real mirror. The heads will later be cut up into strips, which will be cut into individual heads to be mounted onto drive arms.
Our tour also gave us the opportunity to talk to Alan Johnston, director of R&D at the Springtown fab, on the changes in hard disk technology we should expect in the coming years. We also touched on how Seagate plans to manufacture 10 TB or 20 TB hard disks, but that’s another topic. It’s worth spending some time on, of course, so we’ll be devoting a special article to it soon. Stay tuned.
In the meantime, you can get more details of our tour by looking at our photo album.
