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Improved Process for Fabricating Boron-Doped Silicon Membranes

IP.com Disclosure Number: IPCOM000102504D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 75K

Publishing Venue

IBM

Related People

Bassous, E: AUTHOR [+4]

Abstract

Disclosed is an improved process for fabricating boron-doped silicon structures, such as membranes, diaphragms, and foils. The process utilizes a silicon etchant system based on potassium hydroxide (KOH) in conjunction with silicon nitride films for masking purposes. The disclosed KOH/nitride process is much safer, less costly, and simpler to use than conventional processes that employ silicon etchants based on ethylenediamine (E), pyrocatechol (P), water (W) mixtures. EPW etchants are highly toxic and corrosive and require special handling procedures during their use and disposal.

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Improved Process for Fabricating Boron-Doped Silicon Membranes

       Disclosed is an improved process for fabricating
boron-doped silicon structures, such as membranes, diaphragms, and
foils.  The process utilizes a silicon etchant system based on
potassium hydroxide (KOH) in conjunction with silicon nitride films
for masking purposes. The disclosed KOH/nitride process is much
safer, less costly, and simpler to use than conventional processes
that employ silicon etchants based on ethylenediamine (E),
pyrocatechol (P), water (W) mixtures.  EPW etchants are highly toxic
and corrosive and require special handling procedures during their
use and disposal.

      A preferred process sequence for fabricating large-area
boron-doped silicon membranes for X-ray mask applications is
summarized below:
      1.  Wafer cleaning
      2.  Boron doping B > 1x1020/cm3
      3.  Etching BSG in dilute HF
      4.  Deposition of LPCVD Si3N4
      5.  Lithography
      6.  RIE Si3N4
      7.  Etching P++ Si
      8.  Etching bulk Si (KOH+H2O)
      9.  Selective etching Si (KOH+H2O+IPA)

      The above KOH/nitride process yields a novel laminated membrane
structure consisting of a boron-doped silicon layer coated with a
silicon nitride film.  The following are key features of the
fabrication process.
 1.  Boron doping, e.g., by diffusion, is performed on both surfaces
of a silicon wafer without the use of masking films, i.e., total
surface diffusion. The boron dopant concentration should be at least
1x1020/cm3 .  The borosilicate glass (BSG) film formed on the surface
should be etched off completely in dilute 5% hydrofluoric acid
solution.
 2.  Low Pressure Chemical Vapor Deposition (LPCVD) of silicon
nitride Si3N4 is applied on both surfaces of the doped wafer.  The
pref...