Empty Spaces in Silicon (ESS): An Alternative to SOI

Peter Singer, Editor-in-Chief -- Semiconductor International, 12/1/1999

In the future, the ability to form empty spaces in silicon could prove very useful, since air gaps are excellent insulators. Silicon voids could possibly replace some applications of dielectric materials, such as those used in silicon-on-insulator (SOI). SOI requires buried islands of an insulator, typically oxide, which could be replaced by an air gap.

The challenge in forming air gaps has so far been that it's difficult to do with the kind of precision needed for mass-produced, high-density devices. This could soon change, however, thanks to some recent research at Toshiba Corp. in Yokohama, Japan. Scientists there have developed a new technique based on silicon migration that is able to precisely form empty spaces in silicon of various shapes, including pipes, spheres and plates. The work is scheduled to be presented this month at the International Electron Devices Meeting (IEDM) in Washington, D.C.

The proposed technique for the formation of empty spaces in silicon (ESS) makes use of the self-organizing migration properties on the silicon surface. The Toshiba researchers explain that when deeply etched silicon substrates are annealed in a deoxidizing ambient, such as a hydrogen ambient, the silicon atoms on the surface migrate so as to minimize the surface energy. The sequence for the empty space formation is schematically illustrated in Fig. 1, where three typical shapes are shown: (a) sphere, (b) pipe and (c) plate.

Fig. 1 The self-organizing sequence for the empty space formation in silicon. Spherical empty space is formed at the bottom of the trench (a). Pipe-shaped empty space can be formed by combining the spherical empty spaces at the bottom of each trench (b). Plate-shaped empty space also can be formed when trenches are arranged in a lattice (c). Empty spheres with uniform size and shape, spaces at regular intervals, were formed beginning with a deep (6.5mm) trench, followed by an anneal in a hydrogen ambient at 1100°C.

An isolated deep trench is transformed to a spherical empty space or several spaces (Fig. 1a). Formation of spherical empty space begins at the bottom of the deep trench, because the radius of curvature is the smallest at the bottom. The diameter of the empty sphere is larger than that of the initial trench. Thus, trenches arranged in a row are transformed to an empty space shaped like a pipe, due to the combination of the grown empty spheres at the bottom of each trench (Fig. 1b). An empty space shaped like a plate can be fabricated by developing this technique. By arranging the trenches in a lattice, spherical empty spaces at the bottom of all trenches are combined, and they are transformed to a large, thin empty space (Fig. 1c). Work at Toshiba included the example shown in Fig. 2, where six spherical empty spaces were formed.   

  Survey Says...   

Results are in from a recent research project on copper, sponsored by Philips Analytical and SEMI. The study showed equipment suppliers' enthusiasm about the readiness of the copper tool set often is inconsistent with IC manufacturers' views. For example, semiconductor makers viewed tool sets for dielectric deposition, etch/polish steps, dielectric etch and barrier deposition as 'developing,' while equipment suppliers saw them as 'ready.' An even greater dichotomy was seen in the seed deposition tool set, which chip makers viewed as 'uncertain' and equipment makers as 'ready.' Both groups agreed the readiness of electroplating tools was 'uncertain.   

Talkback

We would love your feedback!

Post a comment

» VIEW ALL TALKBACK THREADS

Related Content

• Topics
• Author

Related Content

 

By This Author

• Through-Silicon Vias: Ready for Volume Manufacturing?
• Green Chips: IC Makers Looking to Cash In
• 2008: A Year of Cautious Optimism
• 1 THz InP Transistor Claims Speed Record
• Analysts Cautiously Optimistic for 2008
• » MORE

SPONSORED LINKS