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Heteroepitaxial growth of silicon on (100) Yttria-Stabilized Zirconia (YSZ) and thermal oxidation of the Si-YSZ interface
Volume 2, number 6A&B
September 1984
MATERIALS LETTERS
HETEROEPITAXIAL GROWTH OF SILICON ON (100) YTTRIA-STABILIZED ZIRCONIA (YSZ) AND THERMAL OXIDATION OF THE Si-YSZ INTERFACE D. PRIBAT, L.M. MERCANDALLI, M. CROSET, D. DIEUMEGARD Thomson-CSFILCR, Domaine de Corbeville, B.P. 10, 91401 Orsay, France
and J. SIEJKA Groupe de Physique des Solides de I’Ecole Normale Supkrieure, Tour 23, 2 Place Jussieu, 75221 Paris Cedex 05, France Received 18 July 1984
(100) heteroepitaxial silicon films with thicknesses in the 0.4-l nm range have been deposited onto single-crystal substrates of yttria-stabilized zirconia (YSZ) by pyrolysis of SiH4 at = 980°C. Using the well-known oxygen transport properties of YSZ, we have subsequently been able to grow a buried thermal SiOa layer at the Si-YSZ interface, resulting in a Si(iOO)/amorphous SiOa/YSZ(lOO) structure, in which the most defective part of the initial epitaxial film has been eliminated. The interface SiOa layers have been characterized by Rutherford backscattering spectroscopy and scanning electron microscopy. The oxygen transport mechanism through the YSZ substrate is also briefly discussed.
1. Introduction
Yttria-stabilized zirconia single crystals have recently been used as substrates for epitaxial growth of silicon, with the aim of studying a potential replacement for silicon on sapphire (SOS) technology in integrated circuits requiring radiation-hard and high-speed performances [l-3]. Single crystals of YSZ can be obtained by the skull melting technique, and the incorporation of Y,O, into the melt is known to stabilize upon cooling the high-temperature cubic Zr02 phase. The substitution of Y,O, for ZrO, molecules leads to the creation of oxygen vacancies in the anion sublattice of the YSZ fluorite-type structure. Therefore 02- ions are able to move easily by a vacancy-type mechanism, making YSZ an excellent ionic conductor at high temperature. Our first transmission electron microscope (TEM) analysis of epitaxial Si deposits on YSZ have shown that similarly to SOS films (i) the interface between YSZ and the Si epi-layer is very defective and (ii) the defect density decreases as the thickness of the Si films increases * I. 524
We have used the oxygen-ion transport properties of YSZ in order to eliminate the most defective part of the epi-Si deposits (Si/YSZ interface) by oxidizing the Si layers through the YSZ substrates. In this paper, we report our preliminary results concerning such a thermal oxidation process which is primarily due to the oxygen semi-permeability of YSZ single crystals at high temperature.
2. Experimental
YSZ ingots purchased from Ceres Corporation, with 9.5 or 21.0 mol percent (m/o) Y20, content, were first oriented parallel to the I100 I direction. Slices, (100) oriented, were then cut and lapped to a final thickness in the 0.5-1.0 mm range. One side of the slices was given a first series of polishes with Sic and a final chemomechanical polish *r The TEM observations have been performed by M. Dupuy (LETI, Grenoble) and will be detailed elsewhere [ 41. The defects consist essentially of microtwins of the ~3 type. 0 167-557x/84/$ (North-Holland
03.00 0 Elsevier Physics
Publishing
Science Division)
Publishers
B.V.
Volume 2, number 6A&B
with colloidal silica at pH 8-9. Rutherford backscattering measurements (1.8 MeV 4He+) were carried out in channeling geometry on the as polished chemically cleaned substrates. The axial surface channeling yield (X minimum) in the I100 I direction for the Y + Zr sublattice was found to be as low as 3.5%, the surface peak integral amounting ~3 X 1015 at cme2 after subtraction of the theoretical surface contribution (5 X 1015 at cm-*). The silicon deposits were performed in a “Pan-cake” industrial CVD reactor by pyrolysis of silane in H2 carrier gas at typically 980°C. As already pointed out in refs. [ 1,3], an in situ annealing stage at high temperature (typically 1150°C during 90 min) prior to Si deposition was found to be necessary in order to obtain silicon single-crystal growth, The epi-Si layers have been characterized by RBS/channeling. A typical value of the I 100 I axial channeling yield for 0.5 pm thick epi-Si deposits was ~10% which is already comparable to commercially available SOS films [4].
3. Electrical transport
;
a typical value of Oi for YSZ single crystals doped with 9.5 m/o Y2O3 is 2 X lo-* (a cm)-l at 800°C [51* At room temperature, YSZ is an excellent electronic insulator; nevertheless, depending on the surrounding oxygen partial pressure, at elevated temperature, this material can also exhibit a hole (h), or an electron (e) conductivity [6] respectively expressed as: ch = $c~(~) and
ue =
p#4 u:(T) exp(-E,/U)
,
where up”(0 = h, e) is the pre-exponential factor, Ep the activation energy, k the Boltzmann constant and T the absolute temperature. The total conductivity UT of YSZ is of course UT = Ui' (Jet Uh, and we can define three transport numbers as fi = ui/uT, r, = U,/UT and th = ah/UT. The different domains of conductivity as a function of surrounding oxygen pressure and temperature are reported in fig. 1 for a 9.5 m/o YSZ ceramic material, according to the numerical values of Kleitz et al. [6]. Note that these different domains correspond to a ceramic material and that the actual domains for singlecrystal YSZ may substantially differ, since the gram boundaries can induce important electronic short circuits. However fig. 1 can be considered as a basis for the description of the oxidation mechanism (see below).
through YSZ
As already mentioned, YSZ is mainly an ionic conductor of oxygen ions, O*-. For a given Y203 concentration, the ionic conductivity, Ui, is independent of the external oxygen partial pressure, as long as the material is not severely reduced (say ~0~ > 10e30 atm). This means that in every case the intrinsic concentration of doubly positively charged oxygen vacancies within the crystal (which is directly related to Y2O3 concentration) remains practically constant. This ionic conductivity can be expressed as Ui= O:(7) eXp(-Ei/kT)
September 1984
MATERIALS LETTERS
exp(-+?&T)
h IONIC CONDUCTION ELECTROLYTICDOHAY FOR YSZ l9wolccA Y,O,I
_
ff \f
-20 -2b -29 ELECTRONIC -32 -
CONDUCTION
-36 -40 f
:: 6 4
1 30
I
6.0
I
5.0
I
6.0
I
I
7.0
IO
I
9.0
I
10.0
1
11.0
12.0
I
13.0
10'1T IK)
Fig. 1. Electrolytic domain boundaries for YSZ ceramic material in the log poz, 104/Tplane.
525
Volume 2, number 6A&B
MATERIALS LETTERS
4. Themal oxidation of the Si-YSZ interface Thermal oxidation of silicon through the YSZ substrates originates from the electrochemical semi-permeability of the oxygen concentration cell, which can be represented as follows:
External atmosphere
Growinbd Si O2 layers
On the external side (interface 1) the oxygen activity, al (aI 0:PO,), is fmed by the experimentator, whereas on the internal side (interface 2) the oxygen activity, a2, adjusts itself in order to equilibrate the oxygen flux released at interface 2 and the oxygen flux diffusing into the growing SiO, layer (a2 < al). The overall oxidation mechanism of the silicon film through YSZ material may be decomposed in several steps which can be viewed as follows: (i) oxygen reduction and 02- incorporation into the YSZ crystal at interface 1, (ii) 02- transport into the YSZ substrate, which has to be accompanied by a counter electron migration (or by a concomitant hole migration) in order to preserve electroneutrality, (iii) 02oxidation at interface 2 and oxygen release (probably in atomic form), (iv) oxygen transport into the SiO, growing layer and, finally, (v) oxidation of the silicon at the Si02-Si interface. Some details on impedance calculations of interface 1 (step (i)) are given in ref. [7]. Moreover in our case the YSZ substrates are predominantly hole conducting in the range of oxygen pressures we have been using (see below and fig. 1). Taking into account all these transfer and transport considerations, directly bounded to data from fig. 1, we have been working at 12OO’Cunder reduced oxygen pressure in the 1O-2-5 X 10-l atm range, in order to obtain a good compromise between silicon consumption at the top of the Si deposit and hole conductivity of the YSZ substrates (the normal oxidation rate of silicon is proportional to pg2 and the hole creation rate into YSZ is proportiona 1 to ~8:). Note that the 526
September 1984
use of reduced oxygen pressures has allowed us to avoid an add-on encapsulation step (pyrolytic Si02 or Si3N4) of the top of the Si film, since for such poz values the interface and surface oxidation rates are roughly the same, although not controlled by the same steps. The semi-permeability phenomenon (steps (i), (ii), (iii)), is due to the abovementioned hole conductivity of the YSZ material and can be understood as follows: a difference in oxygen activity on both sides of the YSZ solid electrolyte material induces a corresponding difference in hole concentrations (Nemst voltage). Therefore, in our case, a hole gradient is created from interface 1 to interface 2, acting as a driving force for hole diffusion. As the cell works under zero external current conditions, the hole diffusion phenomenon must be electrically balanced by a concomitant 02displacement leading to oxygen transport from interface 1 to interface 2. At interface 2, the holes recombine with the electrons released by 02- oxidation, so that there is no charge accumulation. Fig. 2 is a scanning electron micrograph of a cross section obtained on an =l pm thick epi-Si film deposited on an YSZ substrate doped with 21 m/o Y20,. The oxidation has been performed at 1200°C in a mixture of nitrogen and dry oxygen (poz = 0.3 atm) during 20 h. The cross section has been stained in an NH,F-HF solution prior to SEM observation, in order to evidence both the top and interface Si02 layers. The top Si02 layer (e = 4500 A) corresponds to the anticipated thickness accordin to the normal oxidation law of silicon (e a p$2 t1 $2). The interface Si02 layer (e = 1500 A), clearly evidenced on the tiicrograph, is ~3 times thinner than the one of the top. We can deduce from the above experimental results that the interface silicon oxidation rate is probably controlled by interface transfer (step (i) or (iii)) or by hole transport through the substrate (step (ii)), because the interface oxidation rate is found to be smaller than the oxidation rate of the top of the silicon film, which is controlled by 0, diffusion through the growing SiO, layer. The thickness of the interface Si02 layer has been found to vary by a factor of four from batch to batch for a given set of oxygen pressure and oxidation time. As we have not found any correlation between the yttria content and the interface oxidation rate, the observed variations of the latter would be related to the
0
8
s
8
x
+B <
**
3
x
8
I:
BACKSCATTERING YIELD ICOUNTS) Y E 6 ci? 8 :
d
6 f
Volume 2, number 6A&B
MATERIALS LETTERS
(uncontrolled) presence within the substrates of impurities that favor hole conductivity. Fig. 3 shows a RBS spectrum (2.2 MeV 4He+) obtained in random geometry on a (100) YSZ substrate (9.5 m/o Y203). The oxidation has been performed in a N,-0, mixture with an oxygen partial pressure of lo- 2 atm. The Si02 layers are clearly evidenced by the shoulders at both the surface and the interface. In both cases the height of the plateaux is typical of thermal SiO,. The interface SiO, thickness deduced from the integrated number of Si atoms into the interface shoulder is ~1500 A, which is in agreement with SEM observations performed on the same sample. Finally, we would like to point out that the adhesion of the Si films after oxidation was excellent and that no cracking or blistering have been observed.
5. Conclusions
We have shown that a buried SiO, layer could be grown at the interface between epi-Si layers and YSZ substrates, resulting in a SiO,-Si-SiO,/YSZ structure in which the most defective region of the epiSi layer has been replaced by a SiO, film. It seems that the high-temperature electronic properties of the YSZ substrates control the kinetics of interface silicon oxidation. It is worth pointing out that the uncontrolled doping of these substrates is likely to play a signiiicant role in electron-hole conductivity; this may explain
528
September 1984
the scatter of our experimental results for the SGYSZ interface oxidation rate.
Acknowledgement
The authors would like to thank N. Nouailles for the SEM work, S. Ries for the crystal orientations, C. Bussac and A. Penot for the polishing work and A. Sollier for assistance in the epi-deposits. One of the authors (DP) would also like to thank J. Fouletier for helpful discussions. A DRET grant in aid is gratefully acknowledged.
References [I] I. Golecki, H.M. Manasevit, L.A. Moudy, J.J. Yang and J.E. Mee, Appl. Phys. Letters 42 (1983) 501. [2] V.A. Loebs, T.W. Haas and J.S. Solomon, J. Vacuum Sci. Technol. Al (1983) 596. [3] H.M. Manasevit, I. Golecki, L.A. Moudy, J.J. Yang and J.E. Mee, J. Electrochem. Sot. 130 (1983) 1752. (41 L.M. Mercandali, D. Pribat, M. Croset, D. Dieumegard, M. Dupuy and J. Siejka, M.R.S. Conference, Boston, 1984, submitted for publication. [S] R.C. Buchanam and S. Pope, .I. Electrochem. Sot. 130 (1983) 962. [6] M. Kleitz, E. Fernandez, J. Fouletier and P. Fabry, in: Advances in ceramics, Vol. 3. Science and technology of zirconia (American Ceramic Society, Columbus, 198 1) p. 337. [7] M. Croset, L.M. Mercandalli, J.Ph. Schnell, S. Khanfir and J. Siejka, Rev. Tech. ThomsonCSF 16 (1984) 235.
September 1984
MATERIALS LETTERS
HETEROEPITAXIAL GROWTH OF SILICON ON (100) YTTRIA-STABILIZED ZIRCONIA (YSZ) AND THERMAL OXIDATION OF THE Si-YSZ INTERFACE D. PRIBAT, L.M. MERCANDALLI, M. CROSET, D. DIEUMEGARD Thomson-CSFILCR, Domaine de Corbeville, B.P. 10, 91401 Orsay, France
and J. SIEJKA Groupe de Physique des Solides de I’Ecole Normale Supkrieure, Tour 23, 2 Place Jussieu, 75221 Paris Cedex 05, France Received 18 July 1984
(100) heteroepitaxial silicon films with thicknesses in the 0.4-l nm range have been deposited onto single-crystal substrates of yttria-stabilized zirconia (YSZ) by pyrolysis of SiH4 at = 980°C. Using the well-known oxygen transport properties of YSZ, we have subsequently been able to grow a buried thermal SiOa layer at the Si-YSZ interface, resulting in a Si(iOO)/amorphous SiOa/YSZ(lOO) structure, in which the most defective part of the initial epitaxial film has been eliminated. The interface SiOa layers have been characterized by Rutherford backscattering spectroscopy and scanning electron microscopy. The oxygen transport mechanism through the YSZ substrate is also briefly discussed.
1. Introduction
Yttria-stabilized zirconia single crystals have recently been used as substrates for epitaxial growth of silicon, with the aim of studying a potential replacement for silicon on sapphire (SOS) technology in integrated circuits requiring radiation-hard and high-speed performances [l-3]. Single crystals of YSZ can be obtained by the skull melting technique, and the incorporation of Y,O, into the melt is known to stabilize upon cooling the high-temperature cubic Zr02 phase. The substitution of Y,O, for ZrO, molecules leads to the creation of oxygen vacancies in the anion sublattice of the YSZ fluorite-type structure. Therefore 02- ions are able to move easily by a vacancy-type mechanism, making YSZ an excellent ionic conductor at high temperature. Our first transmission electron microscope (TEM) analysis of epitaxial Si deposits on YSZ have shown that similarly to SOS films (i) the interface between YSZ and the Si epi-layer is very defective and (ii) the defect density decreases as the thickness of the Si films increases * I. 524
We have used the oxygen-ion transport properties of YSZ in order to eliminate the most defective part of the epi-Si deposits (Si/YSZ interface) by oxidizing the Si layers through the YSZ substrates. In this paper, we report our preliminary results concerning such a thermal oxidation process which is primarily due to the oxygen semi-permeability of YSZ single crystals at high temperature.
2. Experimental
YSZ ingots purchased from Ceres Corporation, with 9.5 or 21.0 mol percent (m/o) Y20, content, were first oriented parallel to the I100 I direction. Slices, (100) oriented, were then cut and lapped to a final thickness in the 0.5-1.0 mm range. One side of the slices was given a first series of polishes with Sic and a final chemomechanical polish *r The TEM observations have been performed by M. Dupuy (LETI, Grenoble) and will be detailed elsewhere [ 41. The defects consist essentially of microtwins of the ~3 type. 0 167-557x/84/$ (North-Holland
03.00 0 Elsevier Physics
Publishing
Science Division)
Publishers
B.V.
Volume 2, number 6A&B
with colloidal silica at pH 8-9. Rutherford backscattering measurements (1.8 MeV 4He+) were carried out in channeling geometry on the as polished chemically cleaned substrates. The axial surface channeling yield (X minimum) in the I100 I direction for the Y + Zr sublattice was found to be as low as 3.5%, the surface peak integral amounting ~3 X 1015 at cme2 after subtraction of the theoretical surface contribution (5 X 1015 at cm-*). The silicon deposits were performed in a “Pan-cake” industrial CVD reactor by pyrolysis of silane in H2 carrier gas at typically 980°C. As already pointed out in refs. [ 1,3], an in situ annealing stage at high temperature (typically 1150°C during 90 min) prior to Si deposition was found to be necessary in order to obtain silicon single-crystal growth, The epi-Si layers have been characterized by RBS/channeling. A typical value of the I 100 I axial channeling yield for 0.5 pm thick epi-Si deposits was ~10% which is already comparable to commercially available SOS films [4].
3. Electrical transport
;
a typical value of Oi for YSZ single crystals doped with 9.5 m/o Y2O3 is 2 X lo-* (a cm)-l at 800°C [51* At room temperature, YSZ is an excellent electronic insulator; nevertheless, depending on the surrounding oxygen partial pressure, at elevated temperature, this material can also exhibit a hole (h), or an electron (e) conductivity [6] respectively expressed as: ch = $c~(~) and
ue =
p#4 u:(T) exp(-E,/U)
,
where up”(0 = h, e) is the pre-exponential factor, Ep the activation energy, k the Boltzmann constant and T the absolute temperature. The total conductivity UT of YSZ is of course UT = Ui' (Jet Uh, and we can define three transport numbers as fi = ui/uT, r, = U,/UT and th = ah/UT. The different domains of conductivity as a function of surrounding oxygen pressure and temperature are reported in fig. 1 for a 9.5 m/o YSZ ceramic material, according to the numerical values of Kleitz et al. [6]. Note that these different domains correspond to a ceramic material and that the actual domains for singlecrystal YSZ may substantially differ, since the gram boundaries can induce important electronic short circuits. However fig. 1 can be considered as a basis for the description of the oxidation mechanism (see below).
through YSZ
As already mentioned, YSZ is mainly an ionic conductor of oxygen ions, O*-. For a given Y203 concentration, the ionic conductivity, Ui, is independent of the external oxygen partial pressure, as long as the material is not severely reduced (say ~0~ > 10e30 atm). This means that in every case the intrinsic concentration of doubly positively charged oxygen vacancies within the crystal (which is directly related to Y2O3 concentration) remains practically constant. This ionic conductivity can be expressed as Ui= O:(7) eXp(-Ei/kT)
September 1984
MATERIALS LETTERS
exp(-+?&T)
h IONIC CONDUCTION ELECTROLYTICDOHAY FOR YSZ l9wolccA Y,O,I
_
ff \f
-20 -2b -29 ELECTRONIC -32 -
CONDUCTION
-36 -40 f
:: 6 4
1 30
I
6.0
I
5.0
I
6.0
I
I
7.0
IO
I
9.0
I
10.0
1
11.0
12.0
I
13.0
10'1T IK)
Fig. 1. Electrolytic domain boundaries for YSZ ceramic material in the log poz, 104/Tplane.
525
Volume 2, number 6A&B
MATERIALS LETTERS
4. Themal oxidation of the Si-YSZ interface Thermal oxidation of silicon through the YSZ substrates originates from the electrochemical semi-permeability of the oxygen concentration cell, which can be represented as follows:
External atmosphere
Growinbd Si O2 layers
On the external side (interface 1) the oxygen activity, al (aI 0:PO,), is fmed by the experimentator, whereas on the internal side (interface 2) the oxygen activity, a2, adjusts itself in order to equilibrate the oxygen flux released at interface 2 and the oxygen flux diffusing into the growing SiO, layer (a2 < al). The overall oxidation mechanism of the silicon film through YSZ material may be decomposed in several steps which can be viewed as follows: (i) oxygen reduction and 02- incorporation into the YSZ crystal at interface 1, (ii) 02- transport into the YSZ substrate, which has to be accompanied by a counter electron migration (or by a concomitant hole migration) in order to preserve electroneutrality, (iii) 02oxidation at interface 2 and oxygen release (probably in atomic form), (iv) oxygen transport into the SiO, growing layer and, finally, (v) oxidation of the silicon at the Si02-Si interface. Some details on impedance calculations of interface 1 (step (i)) are given in ref. [7]. Moreover in our case the YSZ substrates are predominantly hole conducting in the range of oxygen pressures we have been using (see below and fig. 1). Taking into account all these transfer and transport considerations, directly bounded to data from fig. 1, we have been working at 12OO’Cunder reduced oxygen pressure in the 1O-2-5 X 10-l atm range, in order to obtain a good compromise between silicon consumption at the top of the Si deposit and hole conductivity of the YSZ substrates (the normal oxidation rate of silicon is proportional to pg2 and the hole creation rate into YSZ is proportiona 1 to ~8:). Note that the 526
September 1984
use of reduced oxygen pressures has allowed us to avoid an add-on encapsulation step (pyrolytic Si02 or Si3N4) of the top of the Si film, since for such poz values the interface and surface oxidation rates are roughly the same, although not controlled by the same steps. The semi-permeability phenomenon (steps (i), (ii), (iii)), is due to the abovementioned hole conductivity of the YSZ material and can be understood as follows: a difference in oxygen activity on both sides of the YSZ solid electrolyte material induces a corresponding difference in hole concentrations (Nemst voltage). Therefore, in our case, a hole gradient is created from interface 1 to interface 2, acting as a driving force for hole diffusion. As the cell works under zero external current conditions, the hole diffusion phenomenon must be electrically balanced by a concomitant 02displacement leading to oxygen transport from interface 1 to interface 2. At interface 2, the holes recombine with the electrons released by 02- oxidation, so that there is no charge accumulation. Fig. 2 is a scanning electron micrograph of a cross section obtained on an =l pm thick epi-Si film deposited on an YSZ substrate doped with 21 m/o Y20,. The oxidation has been performed at 1200°C in a mixture of nitrogen and dry oxygen (poz = 0.3 atm) during 20 h. The cross section has been stained in an NH,F-HF solution prior to SEM observation, in order to evidence both the top and interface Si02 layers. The top Si02 layer (e = 4500 A) corresponds to the anticipated thickness accordin to the normal oxidation law of silicon (e a p$2 t1 $2). The interface Si02 layer (e = 1500 A), clearly evidenced on the tiicrograph, is ~3 times thinner than the one of the top. We can deduce from the above experimental results that the interface silicon oxidation rate is probably controlled by interface transfer (step (i) or (iii)) or by hole transport through the substrate (step (ii)), because the interface oxidation rate is found to be smaller than the oxidation rate of the top of the silicon film, which is controlled by 0, diffusion through the growing SiO, layer. The thickness of the interface Si02 layer has been found to vary by a factor of four from batch to batch for a given set of oxygen pressure and oxidation time. As we have not found any correlation between the yttria content and the interface oxidation rate, the observed variations of the latter would be related to the
0
8
s
8
x
+B <
**
3
x
8
I:
BACKSCATTERING YIELD ICOUNTS) Y E 6 ci? 8 :
d
6 f
Volume 2, number 6A&B
MATERIALS LETTERS
(uncontrolled) presence within the substrates of impurities that favor hole conductivity. Fig. 3 shows a RBS spectrum (2.2 MeV 4He+) obtained in random geometry on a (100) YSZ substrate (9.5 m/o Y203). The oxidation has been performed in a N,-0, mixture with an oxygen partial pressure of lo- 2 atm. The Si02 layers are clearly evidenced by the shoulders at both the surface and the interface. In both cases the height of the plateaux is typical of thermal SiO,. The interface SiO, thickness deduced from the integrated number of Si atoms into the interface shoulder is ~1500 A, which is in agreement with SEM observations performed on the same sample. Finally, we would like to point out that the adhesion of the Si films after oxidation was excellent and that no cracking or blistering have been observed.
5. Conclusions
We have shown that a buried SiO, layer could be grown at the interface between epi-Si layers and YSZ substrates, resulting in a SiO,-Si-SiO,/YSZ structure in which the most defective region of the epiSi layer has been replaced by a SiO, film. It seems that the high-temperature electronic properties of the YSZ substrates control the kinetics of interface silicon oxidation. It is worth pointing out that the uncontrolled doping of these substrates is likely to play a signiiicant role in electron-hole conductivity; this may explain
528
September 1984
the scatter of our experimental results for the SGYSZ interface oxidation rate.
Acknowledgement
The authors would like to thank N. Nouailles for the SEM work, S. Ries for the crystal orientations, C. Bussac and A. Penot for the polishing work and A. Sollier for assistance in the epi-deposits. One of the authors (DP) would also like to thank J. Fouletier for helpful discussions. A DRET grant in aid is gratefully acknowledged.
References [I] I. Golecki, H.M. Manasevit, L.A. Moudy, J.J. Yang and J.E. Mee, Appl. Phys. Letters 42 (1983) 501. [2] V.A. Loebs, T.W. Haas and J.S. Solomon, J. Vacuum Sci. Technol. Al (1983) 596. [3] H.M. Manasevit, I. Golecki, L.A. Moudy, J.J. Yang and J.E. Mee, J. Electrochem. Sot. 130 (1983) 1752. (41 L.M. Mercandali, D. Pribat, M. Croset, D. Dieumegard, M. Dupuy and J. Siejka, M.R.S. Conference, Boston, 1984, submitted for publication. [S] R.C. Buchanam and S. Pope, .I. Electrochem. Sot. 130 (1983) 962. [6] M. Kleitz, E. Fernandez, J. Fouletier and P. Fabry, in: Advances in ceramics, Vol. 3. Science and technology of zirconia (American Ceramic Society, Columbus, 198 1) p. 337. [7] M. Croset, L.M. Mercandalli, J.Ph. Schnell, S. Khanfir and J. Siejka, Rev. Tech. ThomsonCSF 16 (1984) 235.