Plasma in semiconductor manufacturing

(1) Film Deposition (Plasma Enhanced Chemical Vapor Deposition, PECVD)

One of the most critical processes in semiconductor manufacturing is "film deposition," where a thin film is formed on a wafer. A specialized, high-quality deposition technique is called "epitaxial growth," where a new single-crystal layer is grown on top of a single-crystal substrate, inheriting its crystal structure. This process is essential for manufacturing high-performance semiconductor devices.

Chemical Vapor Deposition (CVD) is a representative method used for such film deposition, including epitaxial growth. Among CVD techniques, Plasma Enhanced Chemical Vapor Deposition (PECVD) utilizes plasma to facilitate the reaction.

In a PECVD system, the source gas supplied over the substrate is turned into plasma using direct current (DC), radio frequency (RF), or microwaves. This activates neutral excited particles, causing a chemical reaction on the substrate to deposit the generated material and form a thin film. This technique is widely used for depositing films like silicon nitride (SiN) and silicon oxide (SiO₂).

The main advantage of PECVD over conventional thermal CVD methods (often used in an epitaxial growth system) is its ability to form films at lower temperatures. This low-temperature process allows for deposition on substrates with complex topographies or those that cannot withstand high heat.

(2) Plasma dry etching

Etching is the process of creating grooves and patterns on a substrate surface. While wet etching uses chemical solutions, dry etching utilizing gas or ions has become the mainstream method in modern manufacturing.

Plasma dry etching, also known as chemical-physical etching, removes material from the substrate surface using plasma. Similar to PECVD, a process gas is ionized into plasma. The ions accelerate and collide with the substrate while reacting chemically with the surface material. This allows for precise, anisotropic removal of material at the atomic scale. Common techniques include Reactive Ion Etching (RIE) using vacuum discharge plasmas such as Inductively Coupled Plasma (ICP) and Capacitively Coupled Plasma (CCP).

Unlike wet etching, this process does not generate liquid waste, making it a cleaner and more precise manufacturing method.

Deeper etching can also be used to separate semiconductor chips, known as plasma dicing. For dicing, please refer to "Back-End Semiconductor Manufacturing Process".

(3) Plasma cleaning

Plasma cleaning removes organic contaminants, such as oils, from substrate surfaces by decomposing and vaporizing them with plasma. This dry process eliminates the need for water or solvents, leaving no residue and ensuring a high level of cleanliness.

Additionally, plasma treatment can modify surface properties, such as increasing hydrophilicity by breaking molecular bonds and introducing hydroxyl groups. In semiconductor manufacturing, this technique is often used to improve adhesion on patterned surfaces like PDMS (polydimethylsiloxane).