An Overview of Oxygen in Silicon
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AN OVERVIEW OF OXYGEN IN SILICON J. C. MIKKELSEN, JR. Xerox Research, 3333 Coyote Hill Road, Palo Alto, CA 94304 Oxygen in silicon has been an important scientific and technological subject for over 30 years. It derives its technological importance from the fact that silicon crystals pulled from silica crucibles have been the standard substrates for fabrication of integrated circuits. The scientific interest originates both from support of this technology and the wide variety of phenomena that occur when cooled Czochralski Furthermore, the (CZ) Si crystals become supersaturated with oxygen. semiconducting nature of Si permits the use of very sensitive electrical and optical probes to complement the structural and chemical characterization of these varied solid state phenomena. 2000
CZ
FZ
1600
Li + SiO2
G
Si:O Liquid Solution (Li)
1800 -
precipitation. (dislocations)
"(gettering)
1400 I
Si:O Solid Solution oxygen) (interstitial -_
the
thermal
/
-
donors,
complexes
wi
Polyhedra Platelets
New Donors
1000
Coesite Ribbon
IOld Donors
800 600 -
O-Vsi Complexes
400 Si:o ÷ Si02 two phase
200
Si0 1I 1l 1 l1
0 10
12
14
16
2
1
(silica crucible) -1
18
*
20
22
LOGio OXYGEN CONCENTRATION (cm-3)
The phenomena involving oxygen in Si are schematically superimposed on the Si-O phase diagram in Figure 1. Three broad categories of oxygen behavior can (1) identified: be intrinsic behavior of dissolved oxygen within the equilibrium Si:O solid solution, such as diffusivity and solubility, (2) non-equilibrium oxygen(metastable) structures containing involving
the
super-
saturated Si:O solutions, such as thermal donors and O-Vsi complexes, and (3) thermodynamioxide cally stable whose precipitates, shape and structure depend on their surface related energy and defect production. Dislocations and gettering are closely associated with precipitation: dislocations are nucleated by precipitates but can be pinned by interstitial
Figure 1. Schematic representation of oxygen-related phenomena superimposed on the Si-O phase diagram.
Mat- Res. Soc. Symp. Proc. Vo4.59- ý 1986 Materials Research Society
4
oxygen; strain and defects surrounding precipitates can attract metallic impurities. This overview serves only as an introductory guide to these phenomena; complete references are to be found in the individual contributions to the Proceedings. The behavior of interstitial oxygen, which exists in stable and supercooled Si :0 solid solution, is considered first in the oxygen section of the proceedings because an understanding of intrinsic oxygen diffusivity and solubility is critical to the modeling of more complex behavior. X-ray diffraction measurements determined that dissolved oxygen dilated the lattice, i.e., was interstitial. Polarized infrared absorption bands at 515 and 1106 cm- 1 from interstitial oxygen have been used to determine both the temperature-dependent oxygen solubility and, through the relaxation of stress-induced dichroism, the atomic hop frequency near 600K. Unfortunately the solubili
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