Chemical Vapor Deposition

Chemical vapor deposition (CVD) is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (substrate) is exposed to one or more volatile precursors, which react and/ordecompose on the substrate surface to produce the desired deposit. Frequently, volatile by-products are also produced, which are removed by gas flow through the reaction chamber.

CVD is practiced in a variety of formats. These processes generally differ in the means by which chemical reactions are initiated.

• Classified by operating pressure:
  • Atmospheric pressure CVD (APCVD) – CVD at atmospheric pressure.
  • Low-pressure CVD (LPCVD) – CVD at sub-atmospheric pressures.^[1] Reduced pressures tend to reduce unwanted gas-phase reactions and improve film uniformity across the wafer.
  • Ultrahigh vacuum CVD (UHVCVD) – CVD at very low pressure, typically below 10⁻⁶ Pa (~10⁻⁸ torr). Note that in other fields, a lower division between high and ultra-high vacuum is common, often 10⁻⁷ Pa.

Most modern CVD is either LPCVD or UHVCVD.

• Classified by physical characteristics of vapor:
  • Aerosol assisted CVD (AACVD) – CVD in which the precursors are transported to the substrate by means of a liquid/gas aerosol, which can be generated ultrasonically. This technique is suitable for use with non-volatile precursors.
  • Direct liquid injection CVD (DLICVD) – CVD in which the precursors are in liquid form (liquid or solid dissolved in a convenient solvent). Liquid solutions are injected in a vaporization chamber towards injectors (typically car injectors). The precursor vapors are then transported to the substrate as in classical CVD. This technique is suitable for use on liquid or solid precursors. High growth rates can be reached using this technique.
• Plasma methods (see also Plasma processing):
  • Microwave plasma-assisted CVD (MPCVD)
  • Plasma-Enhanced CVD (PECVD) – CVD that utilizes plasma to enhance chemical reaction rates of the precursors.^[2] PECVD processing allows deposition at lower temperatures, which is often critical in the manufacture of semiconductors. The lower temperatures also allow for the deposition of organic coatings, such as plasma polymers, that have been used for nanoparticle surface functionalization.^[3]
  • Remote plasma-enhanced CVD (RPECVD) – Similar to PECVD except that the wafer substrate is not directly in the plasma discharge region. Removing the wafer from the plasma region allows processing temperatures down to room temperature.