Silicon wafers are the corner stone of the semiconductor industry. On it's own, a wafer is a thinly sliced piece of material used for the creation of integrated circuits. The silicon wafer acts as a substrate for microelectronic devices. Many steps of microfabrication require a wafer, including etching, deposition, lithography, ion implantation, deposition, and many more. Though there are many different elements which wafers can be fabricated from, silicon is the standard wafer material.
Being so important, silicon wafers are made to very stringent mechanical specifications. While varying from plant to plant, there are general guidelines for how wafers should be developed. First is that wafer can effectively develop crystals as well as support the doping process. Second is the diameter of the wafer. Silicon wafers range from less than 50 mm to 450 mm, and have a thickness that goes up by 100 micrometers with each inch of diameter. Another aspect that must be taken into account in wafer fabrication is the total thickness variation, which examines how thick the wafer is throughout. Other important regulations for silicon wafers are the bow, warp, flatness, edge contour, and laser markings.
Silicon wafers are made in a complex process. A crucible is filled with polysilicon chips established from a reduction and purification of sand. After being distilled, it is deposited on either a tantalum or titanium tube. Once this has finished, crystal pulling begins. The newly formed granules of polysilicon are loaded into a crucible of quartz as well as a dopant. This mixture is melted at a high temperature with an argon gas ambient. A seed of the crystallized silicon is lowered into the melt, rotating it once the temperature has been altered in order to pull it from the silicon. An ingot of silicon is created in this manner, as some of the silicon will follow the seed out of the concoction. The machines and furnaces must be highly stable in order for this to work, as the high heats and vibrations can completely ruin the wafer.
Even though the silicon wafer has now been formed, it still requires a series of processes before it can be separated from the bulk ingot and smoothed over so that it is usable. These steps include slicing, in which the ingots are made into wafers using a diamond saw, lapping, in which the ingots have their saw marks removed and are flattened further, and polishing, which cleans up the wafers. After these steps, the wafer must then have one final cleaning in a chemical bath and then undergo sorting and inspection. If the wafer has few defects and passes the inspection, it is ready to go to work on things such as epitaxy or dicing.
Silicon wafers are an essential product for the semiconductor industry. The process through which they are created is a complex but easily definable one. It takes lots of time to make sure it is done correctly and efficiently. All flaws must be removed from the wafers to make sure they can carry out their jobs. Once the line of processes has been complete, however, they become integral for semiconductors.