Semiconductors are everywhere in modern technology, essential to all kinds of electronic devices and components. Most commonly silicon, semiconductors have a lengthy, involved process behind their fabrication. However, the key steps in silicon wafer manufacturing are similar across the industry, whether for standard components or custom specifications.
Growing Pure Crystal
Silicon manufacturing starts with creating an single crystal “ingot” of silicon through the Czochralski process. A crucible melts down highly pure silicon in a specialized “clean room”, then a seed crystal is introduced to the melt. Molten silicon begins to adhere to the seed and solidify as a crystal. The seed and growing ingot are steadily pulled out of the crucible, with pull speed and rotation influencing how the crystal grows. This can take anywhere from a week to a month.
The fully formed ingot is ground down along the diameter, then a diamond saw cuts the ingot into individual wafers. The diameter and thickness of the wafers is slightly higher than the target at this point. This is to account for expected loss of bulk material that follows, as further grinding and wearing down of the surface using abrasive slurry removes surface defects created during growth or sawing.
Truly pure silicon does not have the electronic properties needed for various applications. The solution is to add trace impurities to introduce free electrons or electron “holes” and facilitate a current, in a process called doping. Boron or gallium will reduce the available electrons, while phosphorus or arsenic add free electrons. This can occur as part of the melt, by treating the crystal ingot or by treating individual wafers.
Cleaning and Polishing
Following slicing, the wafers must be cleaned and polished. This is performed in multiple stages in the clean room, where airborne particles are minimized through use of environmental suits and air filtration. Each stage involves different cleaning agents to remove different contaminants: organic residue, then the oxide layer that forms and finally trace ionic compounds. Polishing also entails stages of increasingly fine abrasives. After this, the wafers can be shipped to the next stage of production.