MOCVD (Metal-Organic Chemical Vapour Deposition) is a technology used to deposit ultra-thin, single crystal layers onto a semiconductor wafer. MOCVD is the most important manufacturing process for III-V compound semiconductors, especially those based on gallium nitride (GaN).
In the MOCVD process, a gas stream is passed over a heated wafer (typically at temperatures between 400°C - 1300°C depending on the material to be deposited). The gas flow contains so-called ‘precursors’, i.e. molecules such as trimethylgallium and ammonia (TMGa, NH3) which decompose when exposed to heat. For example, one gallium (Ga) and one nitrogen atom (N) per precursor molecule are released for the growth of GaN and incorporated into the crystal. In this way, the crystal layer continues upwards atomic layer by atomic layer. The crystal composition can be adjusted by the concentration of the precursor molecules in the gas stream. For example, trimethylindium (TMIn) can be added to the gas phase to produce layers of InGaN. The proportions of In and Ga in the semiconductor layer thus result from the relative concentrations of the precursor molecules in the gas phase.
The MOCVD process also enables the growth of different layers of material on top of each other through the rapid exchange of gases in the reactor. For example, thin layer sequences of GaN and InGaN form the heart of a blue or white LED.
A high yield with regard to the use of the precursors, but also uniformity of the semi-rotary wafers produced, is a basic prerequisite for cost-effective production. Special attention is paid to the design of the gas flow in the reactor, but also to the homogeneity of the temperature distribution.