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Philips Analytical characterizes 'ultra-thin SOI' (<1000 Å)

Philips Analytical has become one of the first companies to fully characterize thin and ultra-thin (1000 Ångström and below) SOI structures on wafers. Laser ellipsometry/reflectometry work at the company has demonstrated simultaneous characterization of all layers of the SOI (Silicon On Insulator) structure. Thickness measurement repeatability of < 0.03 Ångström for the gate oxide and 1 Ångström or less for the Si top layer and the SiO2 buried oxide (BOX) layer are achievable.

These figures make metrology inaccuracies negligible compared with SOI process control parameters. The work therefore promises to help both wafer and device manufacturers with the difficult and potentially painful process of integrating this new material now appearing in advanced semiconductors.

Future Application Specific Tools

Philips' work is part of its internal FAST (Future Application Specific Tools) program, which is driven by ITRS (International Technology Roadmap for Semiconductors) requirements. By focusing development work on specific applications, Philips aims to optimize tool performance and eliminate metrology-related bottlenecks in the semiconductor production process.

The thin SOI work will transfer directly to production environments, and will allow manufacturers to characterize the complete stack of layers found on thin SOI wafers now entering production at major wafer and device manufacturers worldwide. The techniques can even deal with the ultra-thin SOI layers now coming out of R&D, and will help keep Philips' customers well ahead of today's ITRS requirements. Philips' aim is to help their customers incorporate new materials and technologies by offering low cost-of-ownership metrology techniques into fabs while at the same time solving integration problems.

SOI - an alternative to silicon substrates

Much recent R&D effort has gone into developing SOI wafers as a serious alternative substrate material to bulk silicon. The material promises to either boost speed performance by 30%, or reduce power consumption by 30%. As most of the process related thickness uniformity issues for thin SOI (2000 Å) have been resolved, it has now become available as a substrate material. R&D is further progressing on ultra-thin SOI (300 - 1000 Å). This move to ultra-thin SOI is particularly driven by the need to move from partially-depleted to fully-depleted CMOS devices. Recent enhancements in laser based optical metrology performance have enabled Philips Analytical to offer next-generation-solutions today.

As reflectometry has conventionally been used as the core technology for controlling SOI processes on a wafer by wafer basis, with ever shrinking thicknesses, this technology has reached the end of its measurement capabilities. SOI wafer manufacturers are now looking for alternate metrology technologies like laser ellipsometry. The real challenge for these manufacturers is to make radical quality control improvements to deal with thin- and ultra-thin SOI films. By offering laser ellipsometry fully integrated with UV-based reflectometry, Philips will allow them to do just this with the minimum of effort and disruption to existing processes.

Quelle: Philips Analytical