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An Introduction to Silicon on Sapphire Technology

An Introduction to Silicon on Sapphire Technology

Ⅰ. Introduction to the silicon on sapphire technology


Silicon on Sapphire (SOS) technology is a heteroepitaxial process used in the manufacture of metal oxide semiconductor (MOS) integrated circuits (ICs). It consists of a thin layer of silicon (usually less than 0.6 µm) grown on sapphire (Al2O3) Make up the wafer. SOS is part of the silicon-on-insulator (SOI) series of CMOS (complementary MOS) technology. Generally, high-purity artificially grown sapphire crystals are used.


Silicon is usually deposited on a heated sapphire substrate by the decomposition of silane gas (SiH4). The advantage of sapphire is that it is an excellent electrical insulator that prevents stray current caused by radiation from spreading to nearby circuit components. Due to the difficulty of manufacturing very small transistors used in modern high-density applications, SOS faces early challenges in commercial manufacturing.


This is because the silicon on sapphire technology will cause dislocations, twins and stacking faults due to the lattice difference between sapphire and silicon. In addition, some aluminum contaminates the substrate in the silicon closest to the interface.


Ⅱ. Why is silicon on sapphire technology so important to integrated circuits


Because sapphire has a high dielectric constant, it can eliminate the interaction between integrated circuit components, not only can reduce leakage current and parasitic capacitance, enhance radiation resistance, reduce power consumption, but also improve integration and two-layer wiring. Therefore, sapphire is an ideal material for large-scale and very large-scale integrated circuits.


The silicon on sapphire technology provides ideal isolation and reduces the parasitic capacitance at the bottom of the PN junction, so it is suitable for high-speed large-scale integrated circuits to achieve high speed and low power consumption. This process is generally used to make CMOS circuits.


In addition, in the design and production of SOS microelectronic circuits, various semiconductor devices usually need to be fabricated on a silicon film with a complete structure. Since the thermal expansion coefficient of silicon is similar to that of sapphire, single crystal silicon films can be fabricated. It grows on the surface orientation of the sapphire substrate by heteroepitaxial growth.


At present, sapphire crystal has become a substrate widely used for the growth of semiconductor materials.

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