Phosphoric acid’s role in the production of semiconductors

Phosphoric acid (H₃PO₄) is an essential chemical in semiconductor manufacturing, playing a critical role in etching, surface treatment, and doping processes. As the semiconductor industry continues to advance, the demand for high-purity phosphoric acid has increased due to its importance in producing high-performance electronic devices. This article explores the key applications of phosphoric acid in semiconductor fabrication.

1. Wet Etching of Silicon Nitride

One of the primary uses of phosphoric acid in semiconductor manufacturing is in the wet etching of silicon nitride (Si₃N₄). Silicon nitride is widely used as an insulating layer and passivation material in semiconductor devices. Phosphoric acid is used in a hot, aqueous solution to selectively etch silicon nitride while leaving underlying silicon dioxide (SiO₂) and silicon (Si) layers unaffected.

Etching Process: A heated phosphoric acid solution (typically around 150–180°C) is used to remove unwanted silicon nitride layers.

High Selectivity: Phosphoric acid offers excellent selectivity between silicon nitride and silicon dioxide, making it ideal for precise etching in microchip production.

Controlled Etching Rate: The etching rate can be controlled by adjusting temperature and acid concentration, allowing for precise material removal.

This application is crucial in the fabrication of transistors, capacitors, and other semiconductor components.

2. Surface Cleaning and Passivation

Phosphoric acid is used in cleaning processes to remove residues, oxides, and contaminants from semiconductor wafers. Its role in surface preparation helps ensure high-quality device performance by improving adhesion and reducing defects.

Removal of Metal Contaminants: Phosphoric acid is used to eliminate metallic impurities from wafer surfaces, preventing defects in semiconductor circuits.

Passivation Layer Formation: It can help form passivation layers that protect semiconductors from oxidation and environmental degradation.

3. Doping and Phosphorus-Containing Compounds

Phosphoric acid is also a source of phosphorus in semiconductor doping, a process that modifies the electrical properties of silicon wafers.

Phosphorus Diffusion: Phosphoric acid can be used to introduce phosphorus atoms into silicon substrates, creating n-type semiconductor materials.

Production of Phosphorus Oxychloride (POCl₃): Phosphoric acid is used in the synthesis of phosphorus oxychloride, a common dopant source for diffusion processes in semiconductor manufacturing.

Doping with phosphorus is essential in the production of transistors, diodes, and integrated circuits.

4. High-Purity Phosphoric Acid in Semiconductor-Grade Chemicals

Semiconductor manufacturing requires ultra-high-purity chemicals to prevent contamination and defects in microchips. Electronic-grade phosphoric acid (with purity levels above 99.999%) is used to meet the stringent cleanliness standards of the industry.

Ultra-High Purity (UHP) Standards: Semiconductor-grade phosphoric acid has extremely low levels of metal and particle contamination.

Strict Quality Control: Advanced purification techniques are used to ensure that phosphoric acid meets the purity requirements of semiconductor fabrication plants.

Conclusion

Phosphoric acid is a vital chemical in semiconductor manufacturing, particularly in silicon nitride etching, surface cleaning, doping, and the production of high-purity phosphorus compounds. As the demand for smaller and more powerful semiconductor devices grows, the role of high-purity phosphoric acid will remain crucial in ensuring precision, efficiency, and quality in chip fabrication.