Silicon-on-Insulator

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The English term silicon-on-insulator (SOI, German » silicon on an insulator«) denotes a special insulating layer field effect transistor in which a thin silicon layer (SOI) is replaced by an insulating layer (mostly buried oxide , BOX, dt. »Buried oxide «, Called) is separated from the silicon substrate. This structure enables shorter switching times and lower power consumption , especially with regard to leakage currents . In addition, there is a reduced sensitivity to ionizing radiation .

variants

With regard to their mode of operation, SOI transistors can be divided into two types: fully-depleted (FD, dt. »Completely depleted «) and partially-depleted (PD, dt. »Partially impoverished«). The structure of both types essentially differs in the thickness of the SOI layer. PD-SOI transistors generally have a thicker SOI layer that is not depleted in the lower area. In FD-SOI transistors, on the other hand, the SOI layer is sufficiently thin to be completely depleted via the gate voltage. This offers further advantages, such as a lower threshold voltage , lower leakage currents and a reduced hysteresis effect ( floating body effect ).

history

The SOI technology was developed in 1963 by North American Aviation (now Boeing ). The first applications with general availability were e.g. B. the CDP-1802 -CPU from RCA and CPU of the HP-41 series from Hewlett Packard. IBM used 1998 in the production of PowerPC chips, AMD from 2003 for the AMD-K8 architecture. These were PD-SOI transistors, the first FD-SOI transistors were first sold commercially in 2002 by Oki Electric Industry (now Lapis Semiconductor) as part of Casio's G-Shock watches . Okis architecture, however, did not require a very thin SOI layer with layer thicknesses in the range of a quarter to a third of the gate length, as is used for today's FD SOI circuits for high performance. In 2012 the NovaThor processor from ST-Ericsson was announced as the first FD-SOI product. This used STMicroelectronics 28 nm FD SOI technology, which ST made available to other customers in the same year with its own production. In 2015, Globalfoundries were the first major semiconductor manufacturers to announce the development of a 22 nm FD SOI technology node (22FDX) and Samsung announced the development of a 28 nm FD SOI technology node (28FDS) based on the 28 nm FD SOI Technology from STMicroelectronics. The announcement of the 12 nm FD SOI technology node from Globalfoundries (12FDX) followed in 2016.

Important manufacturers of processors with SOI technology are Globalfoundries , Freescale and IBM. The industry leaders Intel and TSMC have so far not presented any products in SOI technology.

Construction and manufacture

Schematic structure of a CMOS chip in the 2000s (excerpt). In the production section FEOL is u. a. to see the representation of the SOI technology.

In contrast to normal transistors , which are manufactured directly on the silicon wafer , the transistors on an insulator layer have a lower electrical capacity , so that the charges required until switching are reduced. The shorter switching times enable higher clock rates. At the same time, the power consumption is reduced, which also results in a lower power loss, which makes it possible, for example, to operate with a weaker and thus quieter cooling. However, there were considerable delays in the development of the first large-scale series in SOI technology by AMD, which were initially suspected to be too high capacities and thus too low clock rates. Another advantage of SOI technology is its lower sensitivity to ionizing radiation .

A large number of manufacturing processes for SOI wafers are described in the literature. These include various processes that make it possible to produce a thin silicon layer on a wafer made of insulating material, for example sapphire (see Silicon-on-Sapphire ). For the later transistors, layers of monocrystalline silicon are usually required / preferred; The main reasons are the significantly better electrical properties. However, since most coating processes do not deposit a single-crystalline silicon layer (the corresponding epitaxial processes are an exception ), SOI manufacturing techniques also include recrystallization steps.

Other ways of producing SOI wafers are processes based on ion implantation (e.g. SIMOX) or special layer transfer techniques such as “ Smart Cut ”. With SIMOX technology ( separation by implanted oxygen ), oxygen ions are introduced into a silicon wafer. With ion implantation, it is possible to control the depth (a few 100 nm) and the width (approx. 50 nm) of the area in which the oxygen ions are introduced. In order to create a “buried” silicon dioxide layer, the crystal is “healed” in a high-temperature step. The oxygen introduced reacts with the silicon (after implantation mainly in interstitial spaces) and forms an insulating layer of silicon dioxide. Similar techniques are also available with nitrogen ( separation by implanted nitrogen , SIMNI) or carbon ( silicon carbide on insulator , SiCOI). The so-called “Smart-Cut” process is also based on ion implantation and also uses wafer bonding . In this process, hydrogen ions are first introduced into a previously oxidized silicon wafer. In the next step, this wafer is then connected to another non-oxidized wafer (“bonding”). The first wafer is then split in the implantation area of ​​the hydrogen ions (at temperatures greater than 500 ° C, mechanical tension is generated in the wafer in connection with the implanted hydrogen ions, which can cause this split) and then thinned down to a few micrometers .

Application in optics

In addition to the application mentioned in the introduction as a substrate for energy-saving integrated circuits in some current top products, SOI is also used in other areas. In optics, SOI is a widespread technique for integrating optical components. Silicon is transparent at wavelengths greater than 1,100 nm. As a result, it can be used as a light waveguide at common wavelengths in optical communication . In the near infrared, silicon has a refractive index of around 3.5, whereas the refractive index of silicon dioxide is only around 1.5. It is therefore possible to guide light in a structured silicon layer of an SOI structure by means of total reflection . Today, among other things, waveguides, couplers, wavelength multiplexers and photodiodes are manufactured on SOI wafers.

literature

  • Jean-Pierre Colinge: Silicon-on-Insulator Technology: Materials to VLSI. Springer, 1991, ISBN 978-0-7923-9150-0 .
  • Takayasu Sakurai, Akira Matsuzawa, Takakuni Douseki: Fully-Depleted SOI CMOS Circuits and Technology for Ultralow-Power Applications . Springer, New York / London 2006, ISBN 0-387-29217-9 .

Web links

Individual evidence

  1. George Imthurn: The History of Silicon-on-Sapphire. (PDF 300 kB) Accessed October 7, 2014 (English).
  2. ^ William O'Leary: IBM Advances Chip Technology With Breakthrough For Making Faster, More Efficient Semiconductors. August 3, 1998, accessed October 7, 2014 .
  3. Intel and Motorola / AMD's 130 nm processes to be revealed. Chip Architect, November 7, 2000, accessed October 7, 2014 .
  4. Takayasu Sakurai, Akira Matsuzawa, Takakuni Douseki: Fully-Depleted SOI CMOS Circuits and Technology for Ultralow-Power Applications . Springer, New York / London 2006, ISBN 0-387-29217-9 , pp. 14 .
  5. GLOBALFOUNDRIES presents the world's first 22 nm FD-SOI technology platform in Dresden. (PDF) Globalfoundries, July 13, 2015, accessed October 24, 2017 .
  6. Peter Clarke: Samsung Running 28nm FDSOI Chip Process. In: EETimes. Retrieved October 24, 2017 .
  7. GLOBALFOUNDRIES Extends FDX TM Roadmap with 12nm FD-SOI Technology. Globalfoundries, September 8, 2016, accessed October 24, 2017 .
  8. Christof Windeck: Globalfoundries developed T-RAM with. In: Heise-Online. May 20, 2009, accessed January 7, 2014 .
  9. Jean-Pierre Colinge: Silicon-on-Insulator Technology: Materials to VLSI. Springer Verlag, 1991, ISBN 978-0-7923-9150-0 , p. 10ff.
  10. Patent US7574090 : Semiconductor device using buried oxide layer as optical wave guides. Published on November 15, 2007 , inventor: Yoshiaki Shimooka.
  11. Patent EP2469596 : Light module for a lighting device of a motor vehicle with semiconductor light sources arranged on a silicon substrate. Published on June 27, 2012 , Inventors: Martin Gottheil, Michael Hiegler.
  12. Paul Müllner: Fundamental Characteristics of the SOI Slot Waveguide Structure. (PDF 59 MB) December 20, 2010, accessed October 7, 2014 .