Comparison of the annealing behavior of thin Ta films deposited onto Si and SiO2 substrates.
Structural changes at annealing temperatures (T(an)) of 500-1,100 degrees C were investigated for thin Ta films which were sputter-deposited onto pure Si substrates and onto thermally oxidized Si. In the as-deposited state, the Ta layers predominantly consist of metastable tetragonal beta-Ta, whereby the [001] texture is independent of the substrate material. At lower annealing temperatures, the microstructural evolution is essentially the same for both Ta films. Incorporation of O atoms causes an increase of the intrinsic compressive stress, and diffusion of C atoms into the Ta layer leads to the formation of Ta(2)C. Additionally, a partial transformation of the original beta-Ta phase into a second phase with tetragonal unit cell (denoted as beta'-Ta) occurs. For the Ta/Si system, the formation of a Ta-Si intermixing layer is initiated at T(an)=550 degrees C, and nucleation of crystalline TaSi(2) occurs at T(an)=620 degrees C. The formation of a second Ta silicide was not detected up to T(an)=900 degrees C. In the case of the Ta film deposited onto the SiO(2) substrate, the metastable beta-Ta and the beta'-Ta transform completely into the thermodynamically stable cubic alpha-Ta at T(an)=750 degrees C. A marked reaction with the substrate indicated by the formation of Ta(2)O(5) and Ta(5)Si(3) occurs at T(an)=1,000 degrees C.
Hübner
R
R
Leibniz Institute for Solid State and Materials Research Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany. r.huebner@ifw-dresden.de
Hecker
M
M
Mattern
N
N
Hoffmann
V
V
Wetzig
K
K
Engelmann
H-J
HJ
Zschech
E
E
D000497:Alloys / Q000737:chemistry*; D003460:Crystallization; D008422:Materials Testing; D046529:Microscopy, Electron, Transmission / Q000379:methods; D012825:Silicon / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D013053:Spectrophotometry / Q000379:methods; D013499:Surface Properties; D013635:Tantalum / Q000737:chemistry*; D013696:Temperature; D014961:X-Ray Diffraction
D000497:Alloys; D013635:Tantalum; D012822:Silicon Dioxide; D012825:Silicon