Plasma-Etch and Wet-Etch/Clean

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The underlying principle for the etch process is to form the volatile compounds between the material to be etched and the reactive radicals generated from the gas/plasma.  These volatiles are then pumped out of the reactor into the scrubber.

The following links summarize the material/gas combinations used in many etch processes.  This presentation is suitable to avoid any issues with copyrights and proprietary information.

Plasma Etching:  This presentation is from the  Microelectronics Research Center of the Georgia Institute of Technology, my alma mater.  The slides outline different etch processes.

Clarycon: a web site on Plasma Technology for Advanced Devices.  It has a wealth of information on many aspects of etching and plasma chemistry.

Etch Rates for MEMS are summarized in this link to the Nanofab of the University of British Columbia, Canada.  The interested reader will find the original source publications by doing a search on the internet using the authors' names.

March Plasma Systems web site has a nice collection of application notes.

An issue with halocarbons is their environmental impact.  ITRS published a paper (actually a table) listing certain restrictions on materials.

I am particularly interested in the topic of plasma and surface reactions.  Herbert Sawin and his group has contributed to the knowledge in this area.  You can browse through the Sawin's group publications and theses he supervised. 

Etch tools utilize dual-frequency discharges.  Frequency affects the energy distribution of the ions bombarding the surfaces: at high frequencies the distribution of energies peak at around the plasma potential and the bias, and at low frequencies, the ion energy distribution becomes broader, and may even change the shape of the distribution.  Here is a link to M.A. Lieberman's presentation outlining the reasons for dual-frequency etching.  Lieberman is the co-author of the text:  M. A. Lieberman and A. J. Lichtenberg, "Principles of Plasma Discharges and Materials Processing". Second Ed., Wiley, New York, 2005.

Another good book, beside Lieberman's book, is Francis F. Chen and Jane P. Chang's book "Lecture Notes on Principles of Plasma Processing".  The book comes with its CD.  Also, F. Chen has a well respected book in the field and now is in its second edition:  "Introduction to Plasma Physics and Controlled Fusion".  F. Chen was the "James Clerk Maxwell Prize in Plasma Physics" recipient for 1995.  Also recommended are the volumes by Daniel L. Flamm, and "Plasma Etching: An Introduction" edited by Dennis M. Manos and Daniel L. Flamm.

I decided to include a section on the wet-etch/clean processes under etch because they conceptually fit in this framework.  A wet-clean process usually follows the photoresist strip process.  Another process that straddles both etch and wet etch/clean is the post-implant strip and clean, as high-dose implant strip (HDIS), and low-dose implant strip (LDIS).  Post-implant clean (whether by plasma, plasma+wet clean, or solely by wet-clean) is a challenging task, and some interesting technologies are utilized to improve over the traditional Plasma+Wet processes as using supercritical fluids, and bombarding the surface with particles of solid carbon-dioxide (check EcoSnow).  A similar challenging process is cleaning the surface post plasma doping.  The interested reader will find an explanation for the integration difficulties with post-implant clean in the following and similar links:  Clean/Strip Challenges at 45 nm, Trends in Shallow Junction Engineering, and, of course, the ITRS web site.  (A group of researchers did Auger analysis on the residues remaining after ashing of arsenic implanted resist.  The results proved without doubt that the remaining residues were predominantly arsenic.  (Ref.:  Clifton Draper, et al., J. Mater. Res.,   Vol. 12(10), pp. 2799-2808, 1997.))

Advances in the technology for post-implant cleaning stresses the intertwining roles of the process engineer and the plasma source designer (or physicist).  The process engineer need to know the chemical nature of the crust portion of the photoresist (the crust results from the implantation) and plasma chemistry to effect etching of the crust.  A patent search following an OEM's press release revealed that a new plasma-source using remote plasma and RF-bias is capable of such task (United States Patent 6,955,177, and United States Patent Application 20080248656).

The information in this section is more of a cheat-sheet on chemical compositions, their names, and the materials these chemicals remove.  Again, this is with the general scheme of the purpose of this web site, namely, as a handy reference.

The Electrochemical Society (ECS) has good papers on wet etch/clean processes.  You need to be a member to download papers.  Also, on the "Research Resources" page  the journals mentioned have articles in the main.

Dr. Jerzy Ruzyllo of Penn State has a nice article on "Semiconductor cleaning technology for next generation material systems".

Resources related to clean and contamination control:

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This site was last updated 07/11/10

© 2009 Stephen Hyatt