What are the basic characteristics of ammonia gas?

Ammonia gas is a colorless gas with a pungent odor, with the chemical formula NH₃. In the special environment of chip manufacturing, highly purified and strictly controlled ammonia gas is used to ensure that no impurities that may affect the performance of the chips are introduced. Its unique molecular structure makes it an ideal nitrogen source and reactant in semiconductor processes.

The key precursors for thin film deposition

In the process of chip manufacturing, one of the most important roles of ammonia is as a key precursor for the deposition of silicon nitride films. When ammonia and silane gas meet in a chemical vapor deposition equipment, a precise chemical reaction occurs: 3SiH₄ + 4NH₃ → Si₃N₄ + 12H₂. This reaction generates a uniform and dense silicon nitride film on the silicon wafer surface.

Silicon nitride films play multiple important roles in chips. Firstly, they serve as excellent barrier layers, effectively preventing water vapor and impurity ions from invading the sensitive circuit areas. Secondly, due to their high hardness and chemical stability, silicon nitride is often used as a stop layer in chemical mechanical polishing processes to ensure precise control of the polishing process. Moreover, at the final stage of chip manufacturing, silicon nitride films act as passivation layers, providing reliable protection for fragile circuits.

Effective tools for surface modification

Ammonia also plays a significant role in surface modification of chips. Through plasma technology, ammonia molecules are dissociated into active groups such as nitrogen and hydrogen, which can precisely modify the surface of the chips.

During the surface modification process, ammonia plasma can introduce nitrogen elements into the material's surface layer, improving the chemical properties of the material's surface and enhancing the adhesion of the subsequently deposited films. At the same time, the hydrogen groups in the plasma can effectively remove contaminants such as metal oxides, transforming the material's surface from a chemically inert state to an active state, creating ideal conditions for subsequent process steps.

An important participant in precision cleaning

In the highly demanding environment of chip manufacturing, the quality of the cleaning process directly affects the yield and performance of the products. Ammonia gas and its aqueous solution play a significant role in the chip cleaning process.

In the traditional RCA standard cleaning process, a mixture of ammonia water and hydrogen peroxide is used to remove organic residues and some metal contaminants from the surface of silicon wafers. This process is achieved through a complex chemical mechanism: hydrogen peroxide provides strong oxidizing ability to decompose organic substances, while ammonia water achieves the decontamination effect by forming soluble complexes with metal ions.

With the advancement of technology, the vapor-phase cleaning technology has gradually matured. In this advanced cleaning method, gaseous ammonia and hydrogen fluoride gases react directly under gaseous conditions, enabling the removal of trace contaminants on the surface without the need for liquid contact, achieving a more precise and damage-free cleaning effect.

The reason why ammonia gas can be widely used in chip manufacturing lies in its unique chemical properties. As a safe and reliable nitrogen source, ammonia gas exhibits excellent reactivity under controlled conditions. Moreover, its reaction by-products are usually hydrogen gas or water vapor, which are easily manageable. These characteristics make it highly favored in the precise manufacturing process.