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Hydrogen Profiles in Water-Oxidized Silicon
Hydrogen Profiles in Water-Oxidized Silicon D. J. Breed Philips Research Laboratories, Eindhoven, Netherlands
and R. H. Doremus* Rensselaer Polytechnic Institute, Materials Engineering Depavtment, Troy, New York 1278 7 (Received April 5, 7976) Publication costs assisted by Philips Research Laboratories
The profile of hydrogen in the silica layer on silicon oxidized by water is derived from a model of molecular diffusion of water and hydrogen in the silica. A minimum in the total hydrogen concentration in the layer, and a sharp increase in hydrogen concentration a t the silicon-oxide interface are predicted by the model, and have been found experimentally, supporting the model of molecular diffusion in the silica.
Introduction The rate of oxidation of silicon by water is controlled by molecular diffusion of water through the oxide layer, according to D0remus.l At the oxide-silicon interface the water reacts with the silicon, forming oxide and hydrogen 2H20
+ Si = Si02 + 2Hz
(1)
The molecular hydrogen produced in this reaction diffuses out of the silica in the direction opposite to that of the incoming water flux. Both water2 and h y d r ~ g e ncan ~ , ~react with the silica to form hydroxyl groups 0.5H20
+ 0.5Si-0-Si
+
HZ Si-0-Si
=
= SiOH
(2)
+ HSi
(3)
SiOH
The profile of hydroxyl groups plus SiH groups (total reacted hydrogen) in silica on silicon oxidized by water was measured by Burkhardtj and by Beckmann and Harrick.6 The latter authors presented spectroscopic evidence for the presence of SiH groups. In this paper these profiles are shown to agree with a model of molecular diffusion of water in and hydrogen out of the silica layer and their reaction with the silica by eq 2 and 3.
Calculation of the Profile of Reacted Hydrogen The concentration C of molecularly dissolved water as a function of the distance x from the outer surface of the silica layer is C/Ci = 1 - XIX
(4)
as shown in the appendix of ref 1when C,
