Silicon on Insulator

The English term silicon on insulator (SOI German " silicon on insulator " ) refers to a manufacturing technology for circuits based on silicon substrates. These are located on an insulating material, resulting in shorter response times and lower power consumption, particularly with respect to the leakage currents shown.

The technology was announced by IBM for the first time in 1998 for a commercial product and was first implemented by AMD for the AMD K8 in mass production. Major manufacturers of processors with SOI technology are Globalfoundries, Freescale and IBM. The industry leaders Intel and TSMC have been discussed so far are no products in SOI technology.

Design and production

In contrast to conventional transistors that are manufactured directly on the silicon wafer, the transistors on an insulating layer having a lower electric capacity so that the required to switch loads are reduced. By so reduced switching times higher clock rates are possible. At the same time as the power consumption is reduced, resulting in a lower power dissipation, which makes, for example, an operation with weaker and thus quieter cooling possible. However, there were significant delays in the development of the first large series in SOI technology by AMD, which were suspected to low clock rates in initially high -capacity and hence. Another advantage of the SOI technology is a lower sensitivity to ionizing radiation.

In the literature, a variety of manufacturing methods for the SOI wafer will be described. This includes different methods that allow a thin layer of silicon on a wafer manufactured from insulating material, for example sapphire (see Silicon On Sapphire). For subsequent layers of monocrystalline silicon transistors needed / usually preferred; The main reasons are the much better electrical properties. Since the majority of the coating process, however, no single-crystal silicon layer is deposited ( the exception is appropriate epitaxy ), the SOI manufacturing techniques include Rekristallisationsschritte.

Make more possibilities SOI wafers, methods based on ion implantation (e.g., SIMOX ) or special Schichttransfertechiken as "Smart Cut". In the SIMOX technique ( Separation by Implanted Oxygen Sheet ) are introduced into a silicon wafer, oxygen ions. By ion implantation depth, it is possible (a few 100 nm) and the width ( 50 nm) to control the range in which the oxygen ions are introduced. To generate a " buried " layer of silicon dioxide is " cured " by a high temperature step of the crystal, while the introduced oxygen reacts ( after implantation mainly interstitial ) with the silicon and forms an insulating layer of silicon dioxide. Similar techniques are also available with nitrogen ( engl. separation by implanted nitrogen, SIMNI ) or carbon ( engl. silicon carbide on insulator, SiCOI ). The so-called "Smart -cut " process is also based on the ion implantation and, in addition uses the wafer bonding. In this method, hydrogen ions are introduced into a pre- oxidized silicon wafer. In the next step of this wafer is then a further still unoxidized wafer connected ( " bonding "). Subsequently, the first wafer in the implantation area of ​​the hydrogen ions is cleaved ( at temperatures greater than 500 ° C is linked to the implanted hydrogen ions produces a mechanical stress in the wafer which can cause this cleavage ), and then thinned to a few micrometers.

Application in the optical

In addition to those already mentioned in the introduction application as a substrate for energy-efficient integrated circuits for some current top products SOI is also used in other areas. In optics SOI is a common technique to integrate optical components. Silicon is transparent at wavelengths greater than 1100 nm. Thus, it can be used for common wavelengths in the optical communication as optical waveguides. Silicon has a refractive index in the near infrared from about 3.5, whereas the refractive index of silicon dioxide is only about 1.5. Therefore, it is possible to perform in a structured silicon layer of an SOI structure by total internal reflection of light. Today, among other waveguides, couplers, wavelength division multiplexers and photodiodes fabricated on SOI wafers.