During the anisotropic Si etching, the angle between the etched area and un-etched area has significant impact on characteristic for nanodevice fabrication using KOH wet etching process.
What are the practical methods to control or optimize this angle (V- shaped area)?
Yes, there are several, but few will change the angle dramatically. The first and most obvious is to change the crystal orientation of your wafer. A wafer will etch differently from a wafer. Secondly, if you don't need to use KOH, you can explore other etchants, which will have different selectivities for the {100} plane over the {111} plane. Tetramethyl ammonium hydroxide (TAMH) and ethylenediamone/pyrocathetcol (EDP) have selectivities of 37X and 17X of {100}/{111}, respectively. Also, EDP etching is sensitive to dopant concentration, whereas KOH is not. Or you can dry etch it, if you have the capability.
Read more on the wikipedia page:
http://en.wikipedia.org/wiki/Etching_(microfabrication)
and here:
http://www.microchemicals.eu/technical_information/silicon_etching.pdf
Dear all,
an extensive study of the structures you obtain after KOH etching (with different concentrations and temperature) was done in the past years by Irena Zubel and collaborators. According to the initial geometry of the window produced in a mask and the orientation of the silicon wafer used, differently oriented planes could emerge. If interested, you can read some of their paper (e.g.The effect of isopropyl alcohol on etching rate and roughness of (1 0 0) Si surface etched in KOH and TMAH solutions, I Zubel, M Kramkowska - Sensors and Actuators A: Physical, 2001 - Elsevier; just as an example).
Dear all Thank u very much for ur reply.
Dear Dr. Eric Lagally, Thank u very much. I used both TMAH and KOH for SOI wafer. Checked different concentration for KOh or even IPA as initiator with different concentration I followed Zubel experiments and other groups. The detail of our experiment can be found here.
http://www.nanoscalereslett.com/content/7/1/381/abstract
If u can think of anything else I will be so appreciated to know ur opinion again.
The points is that none of the methods were actually effective in controlling the pyramid shape. the results are not certain. Since I am working on device and after fabrication of NWT i need to characterize the device with full control of thickness (smaller than 90nm) and width (less than 100nm) is necessary.
Thank u dear Dr Gianluca Grenci. Since u r close to us, may be once u get time to visit KL, and it will be my pleasure to meet u and know ur valuable opinion.
Dear Dr. Guillaume Le Saux, thank u so much for ur expert opinion. The least angle we have reached in our experiment was 46.3 degree for V shaped arrange. I checked different temperature started from 50 to 70 degree, even the stirring or changing the brand of chemicals. It is not really stabilized. The point is, the etching process also get affected by the quality of the mask ( AFM -LAO nanolithography) for the same condition in parameters some times we have over etching. Can it come from the direction of the channel [110] for our device (JLT) on the SOI (100) wafer.
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