- Shallow trench isolation
Shallow trench isolation (STI), also known as 'Box Isolation Technique', is an
integrated circuitfeature which prevents electrical currentleakage between adjacent semiconductor devicecomponents. STI is generally used on CMOSprocess technology nodes of 250 nanometers and smaller. Older CMOS technologies and non-MOS technologies commonly use isolation based on LOCOS. [Quirk, Michael & Julian Serda (2001). [http://smtbook.com/instructor_guide.pdf "Semiconductor Manufacturing Technology: Instructor's Manual"] , p. 25.]
STI is created early during the
semiconductor device fabricationprocess, before transistors are formed. The key steps of the STI process involve etching a pattern of trenches in the silicon, depositing one or more dielectricmaterials (such as silicon dioxide) to fill the trenches, and removing the excess dielectric using a technique such as chemical-mechanical planarization. [http://smtbook.com/features.htm]
Certain semiconductor fabrication technologies also include deep trench isolation, a related feature often found in analog integrated circuits.
The effect of the trench edge has given rise to what has recently been termed the "reverse narrow channel effect" [J-W. Jung et al., Jpn. J. Appl. Phys., 39, 2136-2140 (2000).] or "inverse narrow width effect". [A. Chatterjee et al., IEDM 1996.] Basically, due to the electric field enhancement at the edge, it is easier to form a conducting channel (by inversion) at a lower voltage. The threshold voltage is effectively reduced for a narrower transistor width. [J. Pretet et al., Solid-State Electronics, 46, 1699-1707 (2002).] [Y-H. Lee et al., Microelectronics Reliability, 41, 689-696 (2001).] The main concern for electronic devices is the resulting subthreshold leakage current, which is substantially larger after the threshold voltage reduction.
*Stack deposition (oxide + protective nitride)
*Trench fill with oxide
Chemical-mechanical polishingof the oxide
*Removal of the protective nitride
*Adjusting the oxide height to Si
* [http://www.clarycon.com/shallowtrenchisa.html Clarycon: Shallow trench isolation]
* [http://sst.pennnet.com/display_article/167270/5/ARTCL/none/none/1/Using-broadband-reflectometry-for-fast-trench-depth-measurement/ N and K Technologies: Shallow trench isolation]
* [http://www.dowcorning.com/content/etronics/etronicsspin/etronics_spin_stiov.asp Dow Corning: Spin on Dielectrics - Spin-on Shallow Trench Isolation]
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