Commonly used industrial gases for semiconductors

1. Nitrogen

Nitrogen is a core gas used in various steps of the semiconductor manufacturing process due to its availability, but its main use is in the purge stage. In this stage, nitrogen is used to flush each channel and pipe network to remove any oxygen, impurities, etc. in the machines and tools, thereby protecting them from other gases and impurities that may contaminate the process.

2. Oxygen

Oxygen is an oxidant, so it is essential for producing deposition reactions. It is used to grow silicon oxide layers for various elements in the process, such as diffusion masks. When using oxygen for semiconductor manufacturing, the gas must be ultra-high purity to prevent any impurities from affecting the production and performance of the device. During the etching process, oxygen is also used to remove any extra material waste generated. It can also be used to make any etching patterns permanent. Finally, oxygen also helps to neutralize reactive gases through oxidation reactions that may change the quality of the product. Therefore, similar to nitrogen, oxygen also helps to ensure that no contamination occurs.

3. Argon

Argon is mainly used in the deposition and etching processes within ultraviolet lithography lasers to make the smallest patterns on semiconductor chips. During the manufacture of the required silicon wafers, argon is used to protect the silicon crystals formed on the wafer from any potential reactions with oxygen and nitrogen during the high-temperature growth process. Because argon is also a very inert gas, it is used to provide a non-reactive environment for metal sputtering deposition. Sometimes nitrogen is too reactive and can lead to the formation of metal nitrides. In addition, liquid argon is used with tools to clean the smallest and most fragile chips.

4. Hydrogen

Hydrogen, the use of hydrogen in semiconductor manufacturing is likely to increase due to the higher demand for gases due to industry development. In particular, hydrogen is used to react with chemical tin in the photolithography stage to produce tin hydride. Tin hydride is needed to prevent it from accumulating on expensive optical components. It is used in the deposition process for epitaxial deposition of silicon and silicon germanium, and is also used to prepare surfaces through annealing processes. Hydrogen is used to create new oxide layers to modify already existing films. This process occurs in a high-pressure and high-temperature environment, which means that control of flow rate, temperature, and pressure is very important. In addition, hydrogen is also used in the doping stage to help control decomposition, because the gas used for this process is highly toxic. So much so that they need to be stored in equipment that prevents leakage. Diborane is also a chemical used in the doping process, but due to thermal instability, it will slowly decompose, so hydrogen is needed to help stabilize it.

Common special gases and uses of semiconductors

1. Silane (SiH4): Toxic. Silane is mainly used in the semiconductor industry to make high-purity polysilicon, silicon dioxide film, silicon nitride film, polysilicon isolation layer, polysilicon ohmic contact layer and heterogeneous or homogeneous silicon epitaxial growth raw materials through vapor deposition, as well as ion implantation sources and laser media. It can also be used to make solar cells, optical fibers and photoelectric sensors.

2. Germane (GeH4): Highly toxic. Metallic germanium is a good semiconductor material. Germane is mainly used for chemical vapor deposition in the electronics industry to form various silicon-germanium alloys for the manufacture of electronic components.

3. Phosphine (PH3): Highly toxic. Mainly used as a dopant for silane epitaxy and an impurity source for phosphorus diffusion. It is also used in polysilicon chemical vapor deposition, epitaxial GaP materials, ion implantation, compound semiconductor MOCVD, phosphosilicate glass (PSG) passivation film preparation and other processes.

4. Arsine (AsH3): highly toxic. Mainly used as n-type dopant in epitaxy and ion implantation processes.

5. Antimony hydride (SbH3): highly toxic. Used as a gas phase dopant in the manufacture of n-type silicon semiconductors.

6. Diborane (B2H6): a highly toxic gas with a suffocating odor. Borane is a gaseous impurity source, a dopant for ion implantation and boron doping oxidation diffusion. It has also been used as a high-energy fuel for rockets and missiles.

7. Boron trifluoride (BF3): toxic and extremely irritating. Mainly used as a P-type dopant, ion implantation source and plasma etching gas.

8. Nitrogen trifluoride (NF3): highly toxic. Mainly used for cleaning chemical vapor deposition (CVD) equipment. Nitrogen trifluoride can be used alone or in combination with other gases as an etching gas for plasma processes. For example, NF3. NF3/Ar, and NF3/He are used for etching of silicon compounds MoSi2; NF3/CCl4 and NF3/HCl are used for etching of both MoSi2 and NbSi2.

9. Phosphorus trifluoride (PF3): extremely toxic. Used as a gaseous phosphorus ion implantation source.

10. Silicon tetrafluoride (SiF4): generates highly corrosive fluorosilicic acid when in contact with water. Mainly used for plasma etching of silicon nitride (Si3N4) and tantalum silicide (TaSi2), P-type doping of light-emitting diodes, ion implantation processes, silicon sources for epitaxial deposition diffusion, and raw materials for high-purity quartz glass for optical fibers.

11. Phosphorus pentafluoride (PF5): produces toxic hydrogen fluoride fumes in humid air. Used as a gaseous phosphorus ion implantation source.

12. Carbon tetrafluoride (CF4): As a commonly used working gas in plasma etching process, it is a plasma etchant for silicon dioxide and silicon nitride.

13. Hexafluoroethane (C2H6): As a dry etching gas for silicon dioxide and phosphosilicate glass in plasma process.

14. Perfluoropropane (C3F8): As an etching gas for silicon dioxide film and phosphosilicate glass film in plasma etching process.