Metal Organic Chemical Vapor Deposition (MOCVD): Principle and Device Structure

Metal Organic Chemical Vapor Deposition (MOCVD) is a crucial technique often utilized in the fabrication of semiconductor devices. The MOCVD process allows for the deposition of very thin layers of atoms onto the surface of a substrate with a high level of precision, thereby enabling the creation of complex multilayer structures necessary for advanced electronic and optoelectronic devices.

Principle of MOCVD

The primary principle behind MOCVD involves depositing a metalorganic compound onto a heated substrate. Specifically, this process occurs in a reactor chamber. There, the metalorganic compound is transported by a carrier gas. Subsequently, once inside the chamber, the metalorganic compound decomposes on the heated substrate. It leaves behind a layer of the desired material while the organic component of the compound volatilizes and is removed from the chamber as a gas.

Moreover, the MOCVD process is characterized by its uniform and conformal deposition. This results from the gas-phase reactions during the process. Likewise, the thickness and composition of the layers deposited through MOCVD can be precisely controlled. Namely, it is adjusted by regulating the temperature, pressure, and precursor gas flow rates. Consequently, this makes MOCVD a highly versatile technique for fabricating semiconductor devices.

Device Structure

An MOCVD system is comprised of several key components, each playing a critical role in the operation of the system.

Reactor Chamber

The reactor chamber is the heart of the MOCVD system. It is here that the deposition process occurs. The chamber is typically made of quartz or stainless steel and is designed to withstand high temperatures and pressures.

Gas Delivery System

The gas delivery system is responsible for delivering the metalorganic precursors to the reactor chamber. This system includes a series of mass flow controllers that regulate the flow rate of the precursor gases.

Substrate Holder

The substrate holder, or susceptor, is where the substrate is placed during the deposition process. The susceptor is heated to a specific temperature to facilitate the decomposition of the metalorganic precursors.

Temperature Control System

The temperature control system is crucial for maintaining the desired temperature within the reactor chamber. This system typically includes a heater and a cooling system.

Exhaust System

The exhaust system removes the byproducts of the deposition process from the reactor chamber. This system typically includes a vacuum pump and a scrubber to remove hazardous gases.

Advanced Ceramics in MOCVD

Boron nitride, notably in its hexagonal form, fundamentally interfaces with Metal-Organic Chemical Vapor Deposition (MOCVD) equipment. Namely, it serves as a substrate during the MOCVD growth process. Correspondingly, boron nitride ceramics possess exceptional thermal stability and a low coefficient of thermal expansion. Consequently, this allows them to withstand high temperatures without reacting or degrading. Subsequently, this provides a reliable foundation for the deposition of thin films or layers.
Moreover, certain MOCVD processes necessarily require a buffer layer between the substrate and active layer. Consequently, this buffer layer improves crystal quality and lattice matching. Likewise, due to their unique lattice structure and compatibility with various semiconductor materials, boron nitride plates function as effective buffer layers. Similarly, boron nitride is a machinable material that can be processed into different shapes as needed. In contrast, unlike hard ceramics like alumina, boron nitride manufacturing is not often constrained. Hence, this versatility allows for a wider adaptability of boron nitride ceramics in MOCVD equipment.
The use of boron nitride in MOCVD equipment offers several benefits. Primarily, it provides a stable, inert substrate that withstands harsh reactions and high temperatures. Concurrently, its compatibility as a buffer layer also improves deposited film quality by reducing lattice mismatch and enhancing crystal growth. Likewise, the machinability of boron nitride adds to its versatility, permitting customized shapes and configurations to meet specific MOCVD requirements. Furthermore, manufacturers of boron nitride ceramics, including QSAM, developed a lot of composite boron nitride materials to fit different applications. These composite materials including ALNBN(similar to BIN77), ZCBN and SICBN, giving the customers more flexibility in product design.

Conclusion

MOCVD is a versatile and powerful tool in the fabrication of semiconductor devices. Its ability to deposit thin, uniform layers of material with high precision makes it indispensable in the production of modern electronic and optoelectronic devices.

References

Stringfellow, Gerald B. "Metalorganic vapor phase epitaxy (MOVPE): History, status and prospects." Journal of Crystal Growth 414 (2015): 43-49.

Ohring, Milton. "Materials science of thin films." (2002).

Willmott, P. R. "An introduction to synchrotron radiation: techniques and applications." (2011).

Choy, K. L. "Chemical vapour deposition of coatings." Progress in materials science 48.2 (2003): 57-170.