3826
Appl. Phys. Lett., Vol. 79, No. 23, 3 December 2001
J. P. Chang and Y. Lin
TABLE II. Chemical reduction of ZrSiO4 and ZrO2 involving SiO2 forma-
tion and their ⌬G in kcal/mol, in descending ⌬G values. The equilibrium
pressures of SiO(g) and ZrO(g) are set at 0.01 Torr at all temperatures, and
that ⌬Goi ϭ⌬Gof ϩRT ln Pi is used for the gaseous species.
Reactions/temperatures ͑K͒
298
218
17
12
800
151
14
10
1000 1200 1400
ZrSiO4ϩSi→ZrOϩSiOϩSiO2
2ZrSiO4ϩ3Si→ZrO2ϩ3SiO2ϩZrSi2
ZrSiO4ϩ3Si→ZrSi2ϩ2SiO2
126 100
74
11
8
13
9
12
9
ZrSiO4ϩ2SiOϩ2Si→ZrSi2ϩ3SiO2
Ϫ118 Ϫ55 Ϫ31
Ϫ6
18
ZrO2ϩ2SiO→Zrϩ2SiO2
Ϫ86 Ϫ23
Ϫ384 Ϫ190 Ϫ115 Ϫ40
2
26
51
34
ZrO2ϩ6SiO→ZrSi2ϩ4SiO2
Therefore, we proposed that ZrO2 /ZrSixOy reacted with sili-
con to form ZrSi2, and SiO(g) and ZrO(g) desorbed in
vacuum at an elevated temperature. These assumptions stem
from the fact that ZrSi2 has the most negative free energy of
formation at a per zirconium basis, ZrO(g) has a comparable
free energy of formation comparing to SiO(g) , and Zr 4p and
O 2p photoemission intensities were significantly decreased
after the annealing. In considering the decomposition of
ZrSixOy , it is also possible that ZrSixOy first phase separated
into ZrO2 and SiO2 during the high temperature annealing,
which subsequently reacted with Si to form ZrO(g) and
SiO(g) . Several chemical reactions are thus proposed and
summarized in Table III, assuming an equal partial pressure
of ZrO(g) and SiO(g) at 0.01 Torr at all temperatures. It is
obvious that all the reactions become progressively favored
as the temperature increases, consistent with the reduced free
energy of formation for ZrO(g) and SiO(g) . The effect of the
reduced partial pressure is illustrated in Fig. 3 at 880 °C. It is
obvious from the slope of these lines that reactions leading to
SiO(g) formation are most favored as the pressure is reduced
into the 10Ϫ4 Torr range, and ZrO(g) formation emerges as
the pressure reduced further to Ͻ10Ϫ5 Torr. Note again that
the annealing experiment was carried at 880 °C and a pres-
sure of 10Ϫ9 Torr, which is likely to make the reactions en-
ergetically favored. Though other alternative reactions such
as in-diffusion or evaporation of zirconium silicide could
also account for the reduction in Zr 4p intensity, the desorp-
tion of ZrO(g) seems the most plausible given the thermody-
FIG. 3. Free energy of formation for equations in Table III, at 880 °C, with
varying partial pressure of SiO(g) and ZrO(g)
.
11 Torr, 820 °C for 1 min to form an ultrathin layer ͑ϳ0.5
nm͒ of SiNx , and it was carried out in the same reaction
chamber where ZrO2 /ZrSixOy was deposited. The thickness
of the SiNx layer was confirmed by medium energy ion scat-
tering to be ϳ0.7 nm, and the SiNx passivation makes the
ZrO2 /ZrSixOy /SiNx /Si stack thermally stable up to 950 °C.
The authors would like to acknowledge the financial
support from NSF Career Award ͑CTS-9985511͒, Mattson
and University of California Semiconductor Manufacturing
Alliance of Research and Training ͑SMART͒ under Award
No. SM98-14, and the UCLA Faculty Career Development
Award. The authors are grateful for the technical assistance
from Piero Pianetta and Yun Sun at the Stanford Synchrotron
Radiation Laboratory, and fruitful discussion with Jon-Paul
Maria at NCSU.
1 J. P. Chang and Y.-S. Lin, J. Appl. Phys. 90, 2964 ͑2001͒.
2 J. P. Chang, Y.-S. Lin, and K. Chu, J. Vac. Sci. Technol. B 19, 1782
͑2001͒.
3 G. D. Wilk and R. M. Wallace, Appl. Phys. Lett. 74, 2854 ͑1999͒.
4 W.-J. Qi, R. Nieh, E. Dharmarajan, B. H. Lee, Y. Jeon, L. Kang, K.
Onishi, and J. C. Lee, Appl. Phys. Lett. 77, 1704 ͑2000͒.
5 M. Copel, M. Gribelyuk, and E. Gusev, Appl. Phys. Lett. 76, 436 ͑2000͒.
6 J. P. Chang and Y.-S. Lin, Appl. Phys. Lett. 79, 3666 ͑2001͒.
7 D. R. Lide, CRC Handbook of Chemistry and Physics, 78th ed. ͑CRC,
New York, 1997͒.
8 R. J. Lewis, Sr., Hawley’s Condensed Chemical Dictionary, 12th ed. ͑Van
Nostrand Reinhold, New York, 1993͒.
namic consideration analogous to that of SiO(g)
.
To improve the thermal stability of the deposited
ZrO2 /ZrSixOy , the silicon substrate was nitrided with NH3 at
9 G. D. Wilk R. M. Wallace, and J. M. Anthony, J. Appl. Phys. 87, 484
͑2000͒.
10 Z. Song, X. Bao, U. Wild, M. Muhler, and G. Ertl, Appl. Surf. Sci. 134, 31
͑1998͒.
TABLE III. Chemical reduction of ZrSiO4 and ZrO2 involving SiO(g) and
ZrO(g) formation. The equilibrium pressures of SiO(g) and ZrO(g) are set at
0.01 Torr at all temperatures, and that ⌬Goi ϭ⌬Gof ϩRT ln Pi is used for the
gaseous species.
11 L. J. Whitman, S. A. Joyce, J. A. Yarmoff, F. R. McFeely, and L. J.
Tereminello, Surf. Sci. 232, 297 ͑1990͒.
12 C. C. Cheng, K. V. Guinn, V. M. Donnelly, and I. P. Herman, J. Vac. Sci.
Technol. A 12, 2630 ͑1994͒.
13 T. S. Jeon, J. M. White, and D. L. Kwong, Appl. Phys. Lett. 78, 368
͑2001͒.
Reactions/temperatures ͑K͒
298 800 1000 1200 1400
14 J. P. Maria ͑personal communication͒.
ZrSiO4ϩ5Si→4SiOϩZrSi2
272 141
620 358
90
256
39
155
Ϫ10
54
15 R. Tromp, G. W. Rubloff, P. Balk, F. K. LeGoues, and E. J. van Loenen,
Phys. Rev. Lett. 55, 2332 ͑1985͒.
2ZrSiO4ϩ7Si→ZrOϩ7SiOϩZrSi2
16 G. H. Lander, J. Appl. Phys. 33, 2089 ͑1962͒.
17 I. Brian and O. Knacke, Thermochemical Properties of Inorganic Sub-
stances ͑Springer, New York, 1993͒.
ZrSiO4→SiO2ϩZrO2
5
4
3
3
2
SiO2ϩSi→2SiO
130
349 219
65
40
168
15
118
Ϫ9
69
18 I. Brian, O. Knacke, and O. Kubaschewski, Thermochemical Properties of
Inorganic Substances ͑Springer, New York, 1997͒.
2ZrO2ϩ5Si→ZrOϩ3SiOϩZrSi2
141.214.17.222 On: Mon, 01 Dec 2014 03:59:29