Thin Film Deposition Techniques and their Application in Silicon Carbide Devices
Silicon Carbide (SiC) has long been considered an excellent material for power devices due to its high breakdown voltage, high temperature operation capability and low on-state resistance. However, the utilization of SiC in high power devices has been limited due to difficulties in producing high quality epitaxial layers. In recent times, thin film deposition techniques have been developed, to overcome the limited availability of high quality SiC materials.
Thin film deposition is a process in which a thin layer of material is deposited on a substrate in order to produce a desired electrical, optical or mechanical property to the device. The most common forms of thin film deposition techniques are: physical vapor deposition (PVD), chemical vapor deposition (CVD) and thermal oxidation. Each of these techniques has its own unique advantages, and can be used alone or in combination to produce SiC devices with enhanced performance.
Physical vapor deposition (PVD) is mainly used for optical applications, where it can be used to produce fine layers of transparent metals or oxides of metals such as aluminum or titanium. PVD techniques can also be used for producing SiC devices with a desired breakdown voltage or resistance. PVD techniques are usually employed when the design requires multiple layers or when the layer must be very thin.
Chemical vapor deposition (CVD) is a process in which a gas containing a precursor chemical is heated and released in a chamber, where it decomposes and deposits on the substrate. Two of the most commonly used CVD processes for SiC devices are : Low Pressure Chemical Vapor Deposition (LPCVD) and High Pressure Chemical Vapor Deposition (HPCVD). LPCVD is more suitable for simpler device structures, while HPCVD is more suitable for complex device structures. The advantage of CVD over PVD is that it can be used to create thicker layers and finer etch mask, which is useful for device fabrication.
Thermal oxidation is a process in which a high temperature is used to convert the oxide of a metal on the substrate into its oxide form. This results in an oxide layer with a high breakdown voltage and improved resistance, which is suitable for SiC devices. The most common type of thermal oxidation process is oxidation annealing, where the temperature is maintained at a constant level for a period of time. This process allows for the development of high quality SiC structures, with strong adhesion properties and improved dielectric properties.
Thin film deposition techniques are versatile processes that can be used to create a variety of devices, such as structured or optically active substrates, capacitors, solar cells and transistors. In the case of SiC devices, the techniques can be used to increase the breakdown voltage and reduce the on-state resistance of the device, while maintaining a high temperature operating capability. As the technology improves, more applications of these methods can be explored, leading to even more efficient SiC devices.
