Three Fundamental Aspects of Sapphire Substrates

Sapphire is a single crystal Al2O3 with a hexagonal (rhombohedral) crystal structure. Sapphire shows a unique combination of physical, chemical, and optical properties. It is a highly valuable material with much commercial importance. It is by far the strongest, toughest, thermal shock, and chemically resistant material available. Sapphire is an ideal material for a wide range of electronic substrates.

Here are a few important fundamental characteristics, applications, and properties of Sapphire Substrate.

Plane Orientations

Sapphire substrates are available in C, R, A, and M plane orientations. Presently, the C-plane sapphire wafer is the most widely used sapphire substrate. It is used for growing lll-V and ll-Vl compounds, such as gallium nitride or GaN, and for laser diodes, bright blue and green LED. It is also used in infrared detectors, mercury cadmium telluride, and general optics. Sapphire substrates are a suitable substitution for glass substrates when the optical transmission is required in the ultraviolet or infrared range. R-plane sapphire substrates are preferred for hetero-epitaxial deposition of silicon. It is used in the manufacturing of semiconductor, microwave, and microelectronic IC applications. R plane is the non-polar plane of sapphire. Hence, the changes in the positions of the R-plane in sapphire devices give it different mechanical, thermal, electrical, and optical properties. R-plane SoS (Silicon-on-Sapphire) chips are used extensively in integrated circuits and photovoltaics. A-Plane sapphire substrates find use in hybrid microelectronic, and optoelectronic applications. Researchers use Chemical Vapor Deposition (CVD) to grow AlGaN epi-layers on a-plane sapphire. Hence, sapphire substrates find wide applications in different industries based on their plane orientation and configurations.

Properties And Applications

Sapphire has exceptional electrical insulation, transparency, good thermal conductivity, and high rigidity properties. Hence it is an ideal material for substrates and is used in LED and microelectronic circuits, ultra-high-speed integrated circuits. It is used for growing III-V or II-VI compound semiconductors.  R-plane or M-plane is used for growing non-polar/semi-polar plane epitaxial layers, which helps in improving luminescence efficiency. Hybrid microelectronics, microelectronic IC applications use sapphire substrates. The stable dielectric constant and low dielectric loss makes it useful in hybrid microelectronics products.

Manufacturing Process

The plane orientation is the primary requirement for manufacturing and fabricating sapphire wafers. Check the degree of structural matching between the substrate and the epitaxial film. You need to precisely locate the sapphire crystal rod position on the slicing machine, and the rod cuts it into thin wafers. Once it cuts through it, you remove the chip cutting damage layer and improve the substrate’s flatness. Trim its edge into a circular arc for improving its mechanism strength at the edge. Once you are done with the trimming, polish the surface to remove any roughness and achieve accuracy in the epitaxial layer. Use appropriate cleaning measures to remove dust particles, metals, or any organic contaminants from its surface. Employ robust testing methods to inspect the quality of the sapphire substrate with a high precision instrument so that it adequately meets the client’s requests.

To Conclude:

Sapphire is among the most important substrate materials. The properties mentioned above define the characteristics and applications of sapphire substrates.