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Sunday, April 6, 2014

#283 Silicon and oxygen

Among all elements silicon is interacting with in the course of device manufacturing, its strong affinity to oxygen is particularly distinct. First and foremost it manifests itself in the ease with which silicon reacts chemically with oxygen forming its native oxide SiO2 which happens to be an excellent insulator. No other semiconductor forms on its surface such a high quality native oxide by merely being exposed to elevated temperature in the presence of oxygen. What is equally important from the device manufacturing point of view is that silicon dioxide can be very easily etched off using HF based chemistry whether in liquid or in vapor form.


This ease of silicon oxidation combined with highly favorable etch characteristics and advantageous electronic properties of silicon dioxide, made technology driving silicon MOSFETs, and hence, CMOS, and hence, entire cutting-edge micro and nanoelectronics possible. The easy of silicon oxidation has also its drawbacks as the ultra-thin, typically not thicker than 1 nm, oxide spontaneously grown on Si surface in ambient air or during wet cleaning/rinsing operations, may adversely interfere with some follow up processes, most notably contact metallization and epitaxial deposition. Thus, it is imperative that such native/chemical needs to be controlled and/or removed.


While surface reactions of silicon and oxygen are well known, what is less obvious is that oxygen, similarly to carbon, finds its way into bulk Si during single-crystal fabrication process. Presence of oxygen in the bulk of Si wafers has its bad and a good side. Bad because oxygen in silicon may precipitate at high temperatures forming carrier recombination defects. Good, because oxygen present in silicon in moderate amounts actually strengthens silicon making wafer breakage less likely. All in all, there is no doubt that if not for the distinct, very favorable nature of silicon interactions with oxygen, electronic revolution of the last 50 years would not proceed the way it did.

Posted by Jerzy Ruzyllo at 06:26 PM | Semiconductors | Link is the personal blog of Jerzy Ruzyllo. With over 35 years of experience in academic research and teaching in the area of semiconductor engineering (currently holding position of a Distinguished Professor of Electrical Engineering and Professor of Materials Science and Engineering at Penn State University), he has a unique perspective on the developments in this progress driving technical domain and enjoys blogging about it.

With over 2000 terms defined and explained, Semiconductor Glossary is the most complete reference in the field of semiconductors on the market today.

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