Browse Prior Art Database

Removal of Si3N4 in the Presence of BSG

IP.com Disclosure Number: IPCOM000120459D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 1 page(s) / 32K

Publishing Venue

IBM

Related People

Beyer, KD: AUTHOR [+3]

Abstract

After the planarization of a BSG filled trench by chem.-mech. polishing, the Si3N4 polishing stop layer has to be removed selectively. The selective removal of Si3N4 over a pad oxide area can be accomplished by immersing the silicon device into hot phosphoric acid. However, during this immersion a large portion of the BSG trench fill would be removed, since BSG with a B2O3 concentration of 17.9% would etch eight times faster than Si3N4 in hot phosphoric acid. In order to retard the etching rate of BSG in hot phosphoric acid, wafers with "open" BSG trenches are subjected to boiling water for 20 minutes to remove boron from the outer surface area of the BSG filled trench. Subsequently, the outer surface layer depleted of boron is densified at 900~C for 30 minutes in N2 .

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Removal of Si3N4 in the Presence of BSG

      After the planarization of a BSG filled trench by chem.-mech.
polishing, the Si3N4 polishing stop layer has to be removed
selectively.  The selective removal of Si3N4 over a pad oxide area
can be accomplished by immersing the silicon device into hot
phosphoric acid.  However, during this immersion a large portion of
the BSG trench fill would be removed, since BSG with a B2O3
concentration of 17.9% would etch eight times faster than Si3N4 in
hot phosphoric acid.  In order to retard the etching rate of BSG in
hot phosphoric acid, wafers with "open" BSG trenches are subjected to
boiling water for 20 minutes to remove boron from the outer surface
area of the BSG filled trench. Subsequently, the outer surface layer
depleted of boron is densified at 900~C for 30 minutes in N2 .  Using
this process sequence, only 250 Angstroms of "treated" BSG were
removed in hot phosphoric acid, while 750 Angstroms of Si3N4 etched
in boiling water with a subsequent anneal enables the removal of
Si3N4 polishing stop layer without introducing a severe recess of the
BSG filled trench.

      Disclosed anonymously.