Silicon Single Crystal Wafers

Silicon is a semiconductor, meaning its electrical conductivity lies somewhere between a conductor (like metal) and an insulator (like glass). Silicon wafers like these are used to make integrated circuits for electronics and photovoltaics for solar cells. The wafers themselves are the substrates – like a blank sheet of paper – onto which the electronic components are built.

It’s important that silicon wafers like these are extremely pure; any unwanted impurities can negatively affect their performance, for example reducing the efficiency of solar cells and electronics. This includes disturbances in the crystal structure, which can disrupt electron flow, and this is why all silicon wafers destined for electronic applications must be single crystals. In single crystals, the atoms which make up the material are arranged in a perfectly repeating 3D structure without interruption. This is very difficult to achieve; most objects made from crystal-forming atoms contain billions of crystals bonded together, produced by mistakes in the structure caused by the conditions in which they form.

Single crystal silicon wafers like these can be formed by so-called Czochralski growth, invented by Polish chemist Jan Czochralski in 1915. In this process, a tiny single crystal called the “seed” is dipped into a molten bath of silicon whose temperature is precisely controlled. The silicon atoms in the liquid bath nearest to the seed crystal attach to it, falling in line with the seed’s perfect crystalline structure. The seed crystal is slowly pulled upwards from the melt, creating a large single crystal of silicon, called a boule. This is then carefully sliced into wafers with a wire saw, a bit like an industrial cheese wire. Czochralski discovered the process by accident after mistakenly dipping his pen not into his inkpot, but into molten tin. Withdrawing the pen produced a thin filament of tin, which he later found to be a single crystal.