Kanishka,

Please ckeck out the following reference. I think it will help you.

Lydia

*******************

  Title: Low-cost PDMS seal ring for single-side wet etching of MEMS
  structures
  Author(s): Brugger, J.; Beljakovic, G.; Despont, M.; Biebuyck, H.; De
  Rooij, N.F.; Vettiger, P.
  Author affiliation: Zurich Res. Lab., IBM Res. Div., Ruschlikon,
  Switzerland
  Journal title: Sensors and Actuators A (Physical)
  Publication: Sens. Actuators A, Phys. (Switzerland)
  Conference Title: 9th International Solid State Sensors and Actuators
  Conference (Transducers '97)
  Volume and Issue number: vol.A70, no.1-2
  Volume: A70
  Issue: 1-2
  Inclusive page numbers: 191-4
  Start Page: 191
  Publication date: 1 Oct. 1998
  Publication year: 1998
  CODEN: SAAPEB
  ISSN: 0924-4247
  SICI: 0924-4247(19981001)A70:1/2L.191:CPSR;1-1
  Country of publication: Switzerland
  U.S. Copyright clearance center code: 0924-4247/98/$19.00
  Material identity number: N866-98011
  Document number: S0924-4247(98)00132-0
  Publisher: Elsevier
  Sponsor: IEEE Electron Devices Soc
  Conference date: 16-19 June 1997
  Location: Chicago, IL, USA
  Number of references: 8
  Language: English
  Treatment: Practical; Experimental
  Abstract: We describe a new O-ring setup for wet-etching processes of
  microelectromechanical systems (MEMS). Our new low-cost approach
  using siloxane-based seal rings entails the single-side etching of silicon
  and silicon dioxide using potassium hydroxide and buffered
  hydrofluoric acid, respectively. With this approach, the wafer is not
  immersed into the etching solution, but only the side to be etched is in
  contact with the solution, hence the previously fabricated device
  elements on the other side of the wafer are not damaged. In one process
  for etching silicon the etch solution is heated by an infrared lamp. We
  describe the fabrication of various cantilever-based sensors, such as
  arrays of 0.8- mu m-thick levers for a chemical/electronic nose, and 5-
  mu m-thick silicon cantilevers having piezoresistive sensors. Our
  technique has good uniformity and process control and, in addition,
  eliminates mechanical stress on the fragile wafers incurred by wafer
  chucks, which are required for the conventional immersion approach. It
  has improved process yield and reduces the waste of chemicals
  Controlled indexing: etching; microsensors; polymers; seals (stoppers)
  Uncontrolled indexing: PDMS seal ring; wet etching; MEMS; O-ring;
  microelectromechanical system; siloxane; sensor; lever array; chemical
  nose; silicon cantilever; piezoresistive sensor; electronic nose; infrared
  lamp heating; Si; SiO/sub 2/; HCl; KOH



Quoting KANISHKA BISWAS :

> Hi Everybody,
>               Can any one suggest a protective coating (polymer etc)for
> protecting the top surface of silicon wafer with aluminium lines while
> etching the back side of the wafer using KOH solution???? We have already
> tried out wax, black wax coatings but it did not work.
> Any help and references in this regard will be highly appreciated....
> Thanks
> Kanishka
>
>
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