Manufacturing a Silicon Wafer

Growing a silicon ingot could take anywhere from one week to one month, relying on several considerations, including size, quality and the specification. Greater than 75% of all single crystal silicon wafers are grown by the Czochralski (CZ) process. CZ ingot development needs pieces of virgin polycrystalline silicon. These chunks are placed in a quartz crucible in addition to small quantities of certain Group III and Group V elements called dopants. The included dopants give the wanted electric properties for the grown up ingot. One of the most common dopants are boron, phosphorus, antimony and aresenic. Relying on which dopant is taken, the ingot comes to be a P or N type ingot (Boron: P type; Phosphorus, Antimony, Arsenic: N type).

The materials are after that warmed to a temperature above the boiling point of silicon, 1420 degrees Celsius. When the polycrystalline and also dopant combination has been dissolved, a single silicon crystal, the seed, is positioned in addition to the melt, barely touching the surface. The seed has the same crystal alignment needed in the finished ingot. To accomplish doping uniformity, the seed crystal and the crucible of molten silicon are turned in opposite directions. Once problems for the crystal growth have been met, the seed crystal is gradually raised out of the melt. Development starts with a rapid pulling of the seed crystal in order to reduce the variety of crystal problems within the seed at the start of the growing procedure. The pull rate is then minimized to allow the size of the crystal to raise. When the desired diameter is obtained the development problems are stabilized to maintain the size. As the seed is slowly increased over the melt, the surface tension between the seed as well as the melt causes a thin film of the silicon to adhere to the seed and after that to cool down. While cooling down, the atoms in the dissolved silicon orient themselves to the crystal structure of the seed.

As soon as the ingot is fully-grown, it is ground to a rough size diameter a little larger than the wanted diameter of the completed silicon wafer. The ingot is then given a notch or flat to show its alignment. Once it has passed a variety of inspections, the ingot is cut right into wafers. Because of the silicon's solidity, a diamond edge saw is used to precisely cut the silicon wafers so they are thicker than the desired requirements. The diamond saw additionally helps to reduce damages to the wafers, thickness variation as well as bow as well as warp defects.

After the wafers have been cut, the lapping process starts. Lapping the wafer removes saw marks and also surface problems from the front as well as behind of the wafer. It additionally helps and thins the wafer to eliminate stress built up in the wafer from the slicing procedure. When the silicon wafers are lapped, they undergo an etching as well as cleansing process using sodium hydroxide or acetic as well as nitric acids to minimize microscopic cracks and surface damage created by lapping. A critical edge grinding treatment happens to round the edges, considerably reducing the chance of breakage in the remaining steps of manufacturing and later when device makers utilize the wafers. After the edges are rounded, relying on the end user's spec, oftentimes the edges will certainly be polished, enhancing total cleanliness and also further lowering damage as much as 400%.

The last and most important action in the manufacturing process is polishing the wafer. This process takes place in a cleanroom. Clean spaces are rated and selection from Class 1 to Class 10,000. The rating corresponds to the variety of particles per cubic foot. For recommendation, these fragments are not visible to the naked eye and in an unchecked atmosphere, such as a living-room or workplace, the fragment matter would likely be 5 million each cubic foot. To assist keep this level of cleanliness, the employees need to use clean space matches that cover their body from visit toe as well as are made to not gather or bring any kind of fragments. They also will stand in a vacuum that blows away any little particles that could have accumulated before getting in the space.

The majority of prime grade silicon wafers undergo 2-3 stages of polishing utilizing gradually finer slurries or polishing compounds. Most of the time, wafers are polished on the front side just, excluding 300 mm wafers which are dual side polished. Sprucing up produces a mirror surface. The polished side is used for gadget manufacture. This surface has to be free of topography, micro-cracks, scratches, and recurring work damage. The polishing process happens in 2 actions. First, stock removal followed by last chemical mechanical polish (CMP). Both procedures use polishing pads and polishing slurry. The stock elimination procedure eliminates a very thin layer of silicon and is had to create a wafer surface that is damage totally free. The last polish doesn't get rid of any kind of material. Its single function is to remove a haze from the polished surface that is generated during the stock removal procedure.

After polish, the silicon wafers are refined with a last clean that takes a lengthy series of clean baths. This process removes surface fragments, trace metals as well as deposits. Often times a backside scrub is done to eliminate even the tiniest particles.

Once the wafers complete the last cleaning action, they are sorted to requirements and examined under high intensity lights or laser-scanning systems in order to find other problems or unwanted fragments. All wafers that satisfy spec are packaged in cassettes as well as secured with tape. Placed in a vacuum-sealed plastic bag, as well as an air tight foil outer bag to make sure that no particles or moisture go into the cassette upon leaving the clean space.

Since of the silicon's hardness, a diamond edge saw is used to properly slice the silicon wafers so they are thicker compared to the preferred requirements. Lapping the wafer removes saw marks and also surface flaws from the front and behind of the wafer. It additionally assists as well as thins the wafer to eliminate stress accumulated in the wafer from the cutting process. The majority of the time, wafers are polished on the front side just, leaving out 300 mm wafers which are dual side polished. After polish, the silicon wafers are processed using a final clean that uses a long series of clean baths.