Silicon is found in numerous compounds in the nature. Silicon is the key material for semiconductor devices. The advanced semiconductor technologies of today require mono crystalline Silicon with uniform chemical characteristics such as controlled dopant and oxygen content to produce quality devices.
The procedure to convert raw silicon into a usable crystal substrate for semiconductor processes begins with mining for pure Silicon Dioxide. Mainly, silicon now is made by the diminution of SiO2 with carbon in an electric kiln at a temperature ranges from 1500 to 2000oC. By carefully selecting the pure sand, the result is marketable brown metallurgical grade silicon of 97% purity, which is eventually used for semiconductors.
MG-Si is reacted with HCl to form tri-chlorosilane in a reactor at 300ºC. TCS (trichlorosilane) is a middle compound for poly-silicon manufacturing. In converting MG-Si to TCS, impurities, such as Fe, Al and B are removed. This pure TCS is subsequently diluted with H2. It ultimately flows into a deposition reactor, where it is transformed into silicon. After achieving the highest level of purity, the atomic structure of the silicon undergoes a process known as crystal growing to convert the poly-crystalline silicon into samples with a single crystal orientation, commonly known as ingots.
The Polysilicon is broken into 1 to 3 inch chunks that undergo stringent surface etching and cleaning. These pieces are then packed into quartz crucibles to meltdown in a furnace. A mono-crystalline Silicon is installed into a shaft in the upper chamber of the furnace. The seed is lowered so that it dips about 2mm into the melted Silicon. Then, the seed is slowly retracted from the surface, allowing the melted silicon to solidify.
Both the crucible and seeds are rotated in reverse directions to allow formation of round crystals. The kiln must be stable and isolated from vibrations. Once the growth process is complete, the crystal is cooled down in the furnace for up to 7 hours.
Silicon Wafer fabrication involves a series of defined chemical and mechanical process steps that are essential to turn the ingot segment into a wafer. During these steps, the wafer surfaces and dimensions must be accurate. Each step is designed to bring the wafer into proper shape.
The quality of a polished wafer is very important because the defects generated during crystal growth of the wafer needs to be removed completely. These defects on the surface of wafers can decline the performance of the devices. The finest solution to this problem is to deposit a supplementary layer of pure Silicon on the top of a polished Si wafer. After a last Polish and Clean, wafers are ready for a final inspection before delivery. Different Methods of Silicon wafer Fabrication:
Process of Oxide layer deposition in Silicon Wafers
CVD process has multiple application is semiconductor industry. This process is utilized in the design and fabrication of semiconductor devices.Silicon Wafers Cost Considerations
Silicon finds great application in electronic equipments. Electrical circuitry including computer chips; microprocessors, transistors all have silicon Wafers as a foundation.Benefits and Uses of Silicon
Silicon is a tetravalent, gray colored, brittle chemical element. It is the most abundant element in nature, all the mainstream micro chips and semiconductors are built on Silicon.