Silicon (Si)

A gray, tetravalent, nonmetallic chemical element occurring abundantly in nature making up 27.8% of earth's crust. Silicon has the ability to take on dopants (Boron, Phosphorous, Arsenic, Antimony, etc) in order to conduct electricity in a controlled manner. Thus making Silicon the ideal material used in the production of most advanced semiconductor devices.

Manufacturing of Silicon Wafer

Manufacturing silicon wafers begin by growing a silicon ingot which can take one week to one month. More than 75% of all single crystal silicon wafers are grown by the Czochralski (CZ) method. Ingots are grown by placing chunks of polycrystalline silicon into a quartz crucible along with small quantities of dopants. The polycrystalline silicon are made from sand by means of a complex reduction and purification process using Trichlorosilane and Hydrogen. The dopants give the desired electrical properties for the grown ingot and determine the type of the ingot (P or N).

Crystal Pulling

Polysilicon chunks are loaded into quartz crucible of the furnace along with small amounts of dopants. The polysilicon is melted at a process temperature of 1400 deg. C in a high purity Argon gas ambient. Once the melt is achieved, a "seed" of a single crystal silicon is lowered into the melt and slowly pulled out. The surface tension of the seed and the molten silicon causes a small amount to rise with the seed, forming a perfect monocrystalline ingot with the same crystal orientation with the seed.

Shaping

Finished monocrystalline ingot is ground to a rough size diameter and is either "notched" or "flatted" along its length to indicate the orientation of the ingot.

Slicing

Ingots are sliced into wafers using a diamond ID saw.

Edge grinding

An important step in the manufacturing of silicon wafer to reduce wafer breakage in the remaining manufacturing processes or future device manufacturing processes. On Prime wafers, edges are also highly polished which can improve cleaning results and reduce breakage up to 400%.

Lapping

Wafers after slicing are rough with saw marks and defects on both sides of wafers. Lapping removes saw marks and defects from the surface of the wafers, while also thins and relieves stress accumulated in the wafer from the slicing process. In process checks are also conducted during this process and more fall-out will occur.

Etching and cleaning

Using sodium hydroxide or acetic and nitric acids, the microscopic cracks and surface damage caused by lapping are removed, then followed by deionized water rinses.

Polishing

Polishing requires a number of steps using progressively finer slurry (polishing compound). Polishing can be done on frontside or both side of the wafer. Prior to polishing wafers may receive "backside damag" such as a coating of polysilicon, bead blast or brush damage. All these treatments are for the purpose of "Gettering Defects". Gettering draws defects in the silicon towards the backside of the wafer and away from the frontside of the wafer where devices are being built.

Final Cleaning

This step is to remove trace metals, residues, and particles on the wafers. The cleaning method is developed by RCA in 1970's. The first part is called SC1 and consist of Ammonium Hydroxide followed by a diluted Hydrofluoric acid clean followed by a DI water rinse. Next the SC2 clean consists of Hydrochloric acid and Hydrogen peroxide followed by DI water rinse. After this cleaning and rinsing the finished wafers go through a frontside and backside scrub to remove the smallest particles.

Final sort and inspection

Wafers are inspected to meet customer's specifications. Most final sorting of wafers occurs on an automated system. These systems measure different parameters such as Thickness, Bow-Warp, TTV, Site & Global Flatness, Type and Resistivity. Particles, scratches and haze are measured on a separate automated system.