10 October 2011

IQE launches customizable SOI with improved thickness and doping control

Epiwafer foundry and substrate maker IQE plc of Cardiff, Wales, UK has announced the availability of ultra-smooth, customizable silicon-on-insulator (SOI) with improved thickness and doping control.

IQE says that, since its introduction into mainstream manufacturing, SOI has been integrated into a steadily growing number of applications, including advanced microprocessors, high-voltage devices and complex MEMS (micro-electro-mechanical systems) and sensors.

The electrostatic benefits of replacing bulk silicon wafers with SOI include the reduction of parasitic device capacitance and resistance to latch-up, says IQE. SOI also has desirable mechanical properties, e.g. the provision of an excellent etch-stop at the interface between the silicon device layer and the buried oxide, facilitating substrate removal for applications such as MEMS and sensors.

SOI is manufactured using a variety of methods including:

• Hydrogen implanted layer transfer (HILT), where a layer of implanted hydrogen atoms produces a cleave plane below the surface of a donor wafer. This thin layer is then exfoliated from the donor wafer to an oxidized handle wafer and annealed. This method produces thin-body SOI with excellent cross-wafer thickness uniformity, says IQE. However, it is limited by the depth at which an implanter can form a cleave plane in the donor wafer. SOI wafers produced by this method have an upper thickness limit of between 1–2 microns. The range of available doping options is also typically limited.

• Bond and etch-back involves directly bonding an oxidized silicon wafer with a second substrate. Most of the second substrate is subsequently removed, by a combination of physical grinding and chemical etching to leave a thinner device layer. The major limitation of this method is the poor control of cross-wafer uniformity, which becomes more challenging as more of the device layer is removed.

• Other methods include ELTRAN and SIMOX, but these are not commonly used in high-volume SOI manufacturing.

IQE Silicon Compounds Ltd is now able to offer a new range of SOI products and what is claimed to be one of the few commercial opportunities that allows customers to tune the SOI parameters to their own specifications in terms of doping type and device layer thickness. It can also provide customized SOI in volumes from as little as 50 wafers for smaller, niche-driven applications.

Another differentiator is that SOI device layers are typically epitaxial silicon films, which exhibit excellent crystal quality, improved gate oxide integrity and are COP (crystal originating particle)-free, says IQE. “Because we are able to determine the structure of the device layer epitaxially, it is possible to have very tight control of the important film parameters whilst at the same time having the flexibility to produce structures which are not available using current SOI production methods,” the firm adds. “This includes SOI with multiple silicon layers with different doping, or multiple layers of Si, Ge and SiGe alloys.”

To address the issues highlighted by its customers, IQE Silicon Compounds has launched its own SOI product range, offering high uniformity on both thin and thick device layers. It is also able to address SOI availability in small order quantities of between 50 and 500 wafers. The primary demand for SOI wafers is in 100mm, 150mm and 200mm wafer sizes, and IQE says that it can provide the complete range of products at these diameters.

Tags: IQE SOI

Visit: www.iqep.com