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Thermal analyses of bulk amorphous oxides and silicates of zirconium and hafnium

Published online by Cambridge University Press:  11 February 2011

S. V. Ushakov ,
C. E. Brown ,
A. Navrotsky ,
A. Demkov ,
C. Wang  and
B.-Y. Nguyen
S. V. Ushakov
Affiliation:
Thermochemistry Facility and NEAT ORU, University of California at Davis, One Shields Avenue, Davis, CA 95616anavrotsky@ucdavis.edu
C. E. Brown
Affiliation:
Thermochemistry Facility and NEAT ORU, University of California at Davis, One Shields Avenue, Davis, CA 95616anavrotsky@ucdavis.edu
A. Navrotsky
Affiliation:
Thermochemistry Facility and NEAT ORU, University of California at Davis, One Shields Avenue, Davis, CA 95616anavrotsky@ucdavis.edu
A. Demkov
Affiliation:
Physical Sciences Research Labs, AZ83/ML26 Motorola, Inc. 7700 S. River Parkway, Tempe, AZ 85284
C. Wang
Affiliation:
Digital DNA Laboratories, Semiconductor Products Sector, Motorola, Inc., 3501 Ed Bluestein Blvd., Austin, TX 78721
B.-Y. Nguyen
Affiliation:
Digital DNA Laboratories, Semiconductor Products Sector, Motorola, Inc., 3501 Ed Bluestein Blvd., Austin, TX 78721
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Abstract

Amorphous pure and Y-doped ZrO2 and HfO2 were prepared by precipitation with ammonia or hydrazine. Amorphous zirconium and hafnium silicates with SiO2 content from 10 to 90 mol % were prepared by sol-gel. Crystallization was studied by differential scanning calorimetry (DSC) at 20 °C/min and crystallite size after crystallization was determined from XRD data. ZrO2 crystallized into the tetragonal phase with ΔH -21 ±2 kJ/mol and HfO2 into the monoclinic phase with ΔH -31 ±2 kJ/mol. Doping with 20 at.% Y decreased crystallite size after crystallization. Crystallization temperatures for pure and Y-doped ZrO2 samples were in the range 420–440 °C. Crystallization temperatures for pure and Y-doped HfO2 samples varied from 470 to 570°C and correlate with surface area. Crystallization onset temperature in silicates increased with silica content from about 650 to 950 °C for ZrO2·SiO2 and from 740 to 1030 °C for HfO2·SiO2. Tetragonal zirconia and hafnia were the only crystalline phases formed below 1100 °C in all zirconium silicates and in hafnium silicates with more than 10 mol% SiO2. Crystallite size after crystallization decreased with increase in silica content. In hafnium silicate, a decrease in HfO2 crystallite size from 5 to 2.5 ±1 nm corresponds to a crystallization enthalpy change from -22 to -15 ±2 kJ/mol. The tetragonal HfO2/amorphous SiO2 interface energy can be calculated from calorimetric data as ∼0.25 J/m2. The critical particle size for the tetragonal to monoclinic transformation of HfO2 in HfO2-SiO2 system is about 6 nm. We predict that tetragonal HfO2 will be stabilized in films thinner than 2 nm.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 745: Symposium N – Novel Materials and Processes for Advanced CMOS , 2002 , N1.4
Copyright
Copyright © Materials Research Society 2003

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References

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