PECVD Process

Plasma Enhanced Chemical Vapor Deposition (PECVD) is a widely used technology in chip manufacturing. It utilizes the kinetic energy of electrons within plasma to activate chemical reactions in the gas phase, thereby achieving thin-film deposition. Plasma is a collection of ions, electrons, neutral atoms, and molecules, which is electrically neutral on a macroscopic scale. Plasma can store a large amount of internal energy and, based on its temperature characteristics, is categorized into thermal plasma and cold plasma. In PECVD systems, cold plasma is used, which is formed through low-pressure gas discharge to create a non-equilibrium gaseous plasma.

What are the Properties of Cold Plasma?

Random Thermal Motion: The random thermal motion of electrons and ions in plasma exceeds their directional motion.

Ionization Process: Primarily caused by collisions between fast electrons and gas molecules.

Energy Disparity: The average thermal motion energy of electrons is 1 to 2 orders of magnitude higher than that of heavy particles (such as molecules, atoms, ions, and radicals).

Energy Compensation Mechanism: The energy loss from collisions between electrons and heavy particles can be compensated by the electric field.

Due to the complexity of low-temperature non-equilibrium plasma, it is challenging to describe its characteristics with a few parameters. In PECVD technology, the primary role of plasma is to generate chemically active ions and radicals. These active species can react with other ions, atoms, or molecules, or initiate lattice damage and chemical reactions on the substrate surface. The yield of active species depends on electron density, reactant concentration, and yield coefficients, which are related to the electric field strength, gas pressure, and the mean free path of particle collisions.

How Does PECVD Differ from Traditional CVD?

The main difference between PECVD and traditional Chemical Vapor Deposition (CVD) lies in the thermodynamic principles of the chemical reactions. In PECVD, the dissociation of gas molecules within the plasma is non-selective, leading to the deposition of film layers that may have a unique composition in a non-equilibrium state, not constrained by equilibrium kinetics. A typical example is the formation of amorphous or non-crystalline films.

Characteristics of PECVD

Low Deposition Temperature: This helps to reduce internal stress caused by mismatched coefficients of linear thermal expansion between the film and the substrate material.

High Deposition Rate: Particularly under low-temperature conditions, this characteristic is advantageous for obtaining amorphous and microcrystalline films.

Reduced Thermal Damage: The low-temperature process minimizes thermal damage, reduces interdiffusion and reactions between the film and substrate material, and lessens the impact of high temperatures on the electrical properties of devices.