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Reactive Ion Etching Process to Selectively Etch PSG Over SiO2

IP.com Disclosure Number: IPCOM000121913D
Original Publication Date: 1991-Oct-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 1 page(s) / 52K

Publishing Venue

IBM

Related People

Oehrlein, G: AUTHOR [+3]

Abstract

Disclosed is a reactive ion etching process which allows selective etching of PECVD phosphosilicate films (PSG) over thermal Si2 . The process relies on the large difference observed in the etch characteristics of the two films in mixtures of CF4 and H2 .

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Reactive Ion Etching Process to Selectively Etch PSG Over SiO2

      Disclosed is a reactive ion etching process which allows
selective etching of PECVD phosphosilicate films (PSG) over thermal
Si2 . The process relies on the large difference observed in the etch
characteristics of the two films in mixtures of CF4 and H2 .

      The samples are etched in a diode reactor with a
TEFLON*-covered cathode using 200 W of RF power, a pressure of 25
mTorr and a total gas flow of 40 sccm.  A mixture of CF4 and H2
is used and the proportion of hydrogen is varied between 50 and 100%
of the total gas flow.  The plasma chemistry is significantly
affected as the proportion of hydrogen in the mixture is varied,
leading to a transition from etching of oxide to deposition of a
fluorocarbon film on the oxide surface. For thermal SiO2, this
transition occurs near 50% H2 under the given experimental
conditions. In contrast to thermal oxide, PSG films with 7%
phosphorus continue to etch in mixtures with 80 to 90% H2 under the
same conditions, and the etch rate is insensitive to the proportion
of hydrogen below the deposition threshold.  This effect is due to
the presence of phosphorus in the doped oxide film since PECVD
borosilicate films show behavior similar to thermal oxide.
Furthermore, the point where the transition from etching to
deposition occurs is sensitive to the phosphorus concentration in the
doped film.

      Of crucial importance to the process is a reactor
preco...