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Thin gold and indium films on Si(111) surface
Surface Science Letters 273 (1992) L449-L452 North-Holland
surface science letters
Surface Science Letters
Thin gold and indium films on Si( 111) surface O.V. Bekhtereva,
B.K. Churusov
and V.G. Lifshits
Institute of Automation and Control Processes, The Russian Academy of Sciences, Vladivostok 690032, Russia
Received 22 October 1991; accepted for publication 18 March 1992
A 3-component system (Au-In-Si) and thin indium and gold film interactions on the Si(111)7 x 7 surface were examined using Auger electron spectroscopy @ES) and low energy electron diffraction (LEED). A new surface phase Si(llU3 X 1-(Au, In) was detected at submonolayer metal coverages. Gold and indium were deposited under UHV conditions with further annealing at 300-500°C. It was shown that the agglomeration of gold atoms into islands covered by indium atoms takes place upon deposition of In onto the Si(lllj5 X l-Au surface phase with further annealing. This explains the absence of the gold Auger-peak (69 eV). Indium atoms in excess with respect to the Si(lll)l x l-In surface phase are responsible for the Si-Au surface phase decay and for the formation of gold islands covered by indium.
1. Introduction Deposition of metals (Au, In) onto Si(lllI7 X 7 surfaces leads to the formation of a set of ordered surface phases (SP’s), namely, Si(lll)6 X ~-AU, Si(lll)fi X &-Au, Si(111)5 X l-Au Si(lll)l X l-In, and Si(lll)n-41, 4 X l-In, Si(lll)J31 X J31-In, Si(lll)fi X a-In [5-81. The role of such 2D structures in surface processes is similar to that of bulk phases in bulk processes [91. One can expect the formation of 3-component SP’s upon deposition of two metals (Au and In) onto Si surface by analogy with the well-known formation of 3-component bulk phases. The present study deals with the investigation of 3-component (Au-In-S8 W’s and thin indium and gold film interactions on the silicon surface. The Si(111)5 x l-Au SP was examined under indium deposition.
2. Experimental The experiments were performed in a RIBER LAS-600 UHV system under a base pressure of 2 x 10-i’ Torr. To obtain a clean surface, the 7.5 0039-6028/92/$05.00
0. cm n-type Si(ll1) samples were cleaned in toluene and then annealed in situ at 1250°C for several minutes. The temperature was controlled by a pyrometer and by the current value. The cleaned samples displayed sharp (7 x 7) LEED patterns and no contamination was detected by AES. Gold and indium were deposited from tungsten baskets onto the clean Si(111)7 x 7 substrate held at room temperature with further annealing at 300-500°C. The indium coverage for the Si(lll)l X l-In phase was calculated to be 1.1 ML which is consistent with the data of refs. [6,7]. The gold coverage for the Si(111)5 x l-Au phase was 0.4 ML [lo]. The composition of the Si-Au-In system was controlled by AES (Si LVV 92 eV, InMNN 404 eV and AuOVV 69 eV>. Structure changes were controlled by LEED.
3. Results and discussion ABS measurements showed that the deposition of thin (l-2 monolayer) gold films onto Si(lll)l X l-In with 3D indium islands causes an increase of the indium AES-peak instead of the decrease that should be expected due to a “shadowing” effect (fig. la). The annealing of
0 1992 - Elsevier Science Publishers B.V. All rights resewed
0. V. Bekhrerec’a Edal. / Thin gold and indium films on Sic1 I I) surface
cl
b
1
I
#J----L
mm
mm
Fig. 1. Si(lll)-In SP with 1 mm wide deposited with Au strip: (a) before annealing, (b) after annealing (3OO”C, 1 min).
this system at 300-500°C leads initially to the disappearance of the gold Auger-peak (69 eV), while the indium peak (404 eV> continues to increase slightly. Optical microscopy of this surface showed the presence of a great number of 3D indium islands (fig. 2). The deposition of several In monolayers onto Si(lllj5 x l-Au or Si(lll)& x O-Au followed by annealing at the same temperatures (300-
Fig. 2. Optical
microphotograph
500°C) also causes a disappearance of the gold Auger-peak. AES analysis showed that the thickness of the In film corresponds to the composition of the SXlllll x l-In SP. Such a behavior was observed at any Au and In deposition sequence. LEED observations confirmed the presence of the Si(lll)l x I-In structure. It is well-known that gold diffusion into a silicon substrate does not occur at 300-500°C. On the other hand, gold desorption from the silicon surface becomes noticeable only beyond 850°C [ill. The above facts may be interpreted as follows. Agglomeration of gold atoms into islands, covered by indium atoms takes place on Si surfaces upon annealing of deposited Au and In films. The gold islands serve as additional centers of 2D In gas condensation. This explains the absence of the gold Auger-peak. However, deposition of “thin” indium films (without 3D islands and “on-phase” indium atoms) onto a Si-Au surface phase does not induce the gold Auger-peak disappearance or amplitude decrease. Hence, “onphase” atoms (i.e., atoms in excess with respect to the Si(lll)l X l-In SP) are responsible for the Si-Au SP decay and for formation of gold islands covered by indium.
of the edge region of a Au strip deposited
on a Si(lll)-In
SP.
ia et al. / 1rhin! gold and
0.V. Bek
Isothermal desorption experiments of such a 3-component system confirm the presence of gold on the silicon surface. As an example, AES data of In desorption are shown in fig. 3. The 3-component system was produced by In deposition onto the Si(111)5 x l-Au SP. The annealing causes the evaporation of the indium atoms from the islands [8]. Then migration of gold atoms from the islands along the surface takes place. This leads to the restoring of the initial gold peak amplitude. After the disappearance of the islands, 8,” begins to decrease according to the exponential law e(t) = 8, exp( -L/T), where B0 is the initial In coverage and r is the mean lifetime of an In atom on the sample surface. As indium evaporates, the Au Auger-peak appears; its amplitude increases rapidly up to the initial level corresponding to the Si(111)5 x l-Au SP. Structural transitions, i.e., Si(lll)l X l-In + Si(111)3 X 1-(Au,In) + Si(111)4 X 1 + 5 X l(Au,In) + Si(111)5 x l-Au are observed by LEED with decreasing indium coverage. A new SP, named Si(11113 X 1-(Au, In) was detected (fig. 4). This phase is not formed on Si(lllj7 x 7 surfaces upon In or Au deposition. One can see from region II of the desorption curve (fig. 3), where the (3 X 1) structure was observed by LEED, that the Au coverage corresponds to the Si(111)5 x l-Au phase and the
Fig. 4. LEED pattern of Si(111)3 X 1-(Au,In).
indium coverage is inferior to that of the Si(lll)1 X l-In SP. One can see from the indium desorption experiments of the 3-component system that the In atom lifetime (7) is practically unchanged when the surface phases are changing. From the T(T) dependence T( 7) =
To
eXp
I?/(
/CT),
the binding energy of the In atoms in the 3-component system was determined: 1.4 + 0.2 eV; it is nearly the same as that for Si(111)4 X l-In WI. The presence of the gold atoms is supposed to affect only the lateral In-In interactions for the formation of the Si(111)3 x 1-(Au&r) SP but it has a weak effect on the In-substrate bonding.
References Williams, R.S. Daley, J.H. Huang and R.M. Charatan, Appl. Surf. Sci. 41/42 (1989) 70. [2] G. Le Lay and J.P. Faurie, Surf. Sci. 69 (1977) 295. [3] Ph. Dumas, A. Humbert, G. Mathieu, P. Mathiez, C. [l] R.S.
. . 01 0
’
5
10
15
20
time
‘qmin)JO
35
40
Fig. 3. Isothermal desorption of In from the ES-Au-In at 500°C: I - Si(lll)l X l-In, II - %(111)3X Si(111)4X1+5Xl-(Au,In),IV-Si(111)5Xl-Au.
1-(Au,In),
45
1 50
system III -
Mouttet, R. Rolland, F. Salvan, F. Thibaudau and S. Tosch, Phys. Ser. 38 (1988) 244. [4] V.G. Lifshits, V.B. Akilov and Y.L. Gavriljuk, Solid State Commun. 40 (1981) 429. [5] J. Lander and J. Morrison, Surf. Sci. 2 (1964) 533.
0. V. Bekhtereva et al. / Thin gold and indium films on Sic11 I) surface H. Hirayama, S. Baba and A. Kinbara, Appt. Surf. Sci. 33/34 (1988) 193. [71 Sang-i1 Park, J. Nogami and CF. Quate, J. Microsc. 152 (1988) 727. V.B. Akilov, B.K. Churusov and Y.L. 181 V.G. Lifshits, Gavriljuk, Surf. Sci. 222 (1989) 21.
[9] V.G. Lifshits, Modern Problems of Physical Chemistry of Semiconductor Surface (Nauka, Novosibirsk, 1988). [lo] A.A. Baski, J. Nogami, and CF. Quate, Phys. Rev. B 41 (1990) 10247. [ll] G. Le Lay, M. Manneville and R. Kern, Surf. Sci. 65 (1977) 261.
surface science letters
Surface Science Letters
Thin gold and indium films on Si( 111) surface O.V. Bekhtereva,
B.K. Churusov
and V.G. Lifshits
Institute of Automation and Control Processes, The Russian Academy of Sciences, Vladivostok 690032, Russia
Received 22 October 1991; accepted for publication 18 March 1992
A 3-component system (Au-In-Si) and thin indium and gold film interactions on the Si(111)7 x 7 surface were examined using Auger electron spectroscopy @ES) and low energy electron diffraction (LEED). A new surface phase Si(llU3 X 1-(Au, In) was detected at submonolayer metal coverages. Gold and indium were deposited under UHV conditions with further annealing at 300-500°C. It was shown that the agglomeration of gold atoms into islands covered by indium atoms takes place upon deposition of In onto the Si(lllj5 X l-Au surface phase with further annealing. This explains the absence of the gold Auger-peak (69 eV). Indium atoms in excess with respect to the Si(lll)l x l-In surface phase are responsible for the Si-Au surface phase decay and for the formation of gold islands covered by indium.
1. Introduction Deposition of metals (Au, In) onto Si(lllI7 X 7 surfaces leads to the formation of a set of ordered surface phases (SP’s), namely, Si(lll)6 X ~-AU, Si(lll)fi X &-Au, Si(111)5 X l-Au Si(lll)l X l-In, and Si(lll)n-41, 4 X l-In, Si(lll)J31 X J31-In, Si(lll)fi X a-In [5-81. The role of such 2D structures in surface processes is similar to that of bulk phases in bulk processes [91. One can expect the formation of 3-component SP’s upon deposition of two metals (Au and In) onto Si surface by analogy with the well-known formation of 3-component bulk phases. The present study deals with the investigation of 3-component (Au-In-S8 W’s and thin indium and gold film interactions on the silicon surface. The Si(111)5 x l-Au SP was examined under indium deposition.
2. Experimental The experiments were performed in a RIBER LAS-600 UHV system under a base pressure of 2 x 10-i’ Torr. To obtain a clean surface, the 7.5 0039-6028/92/$05.00
0. cm n-type Si(ll1) samples were cleaned in toluene and then annealed in situ at 1250°C for several minutes. The temperature was controlled by a pyrometer and by the current value. The cleaned samples displayed sharp (7 x 7) LEED patterns and no contamination was detected by AES. Gold and indium were deposited from tungsten baskets onto the clean Si(111)7 x 7 substrate held at room temperature with further annealing at 300-500°C. The indium coverage for the Si(lll)l X l-In phase was calculated to be 1.1 ML which is consistent with the data of refs. [6,7]. The gold coverage for the Si(111)5 x l-Au phase was 0.4 ML [lo]. The composition of the Si-Au-In system was controlled by AES (Si LVV 92 eV, InMNN 404 eV and AuOVV 69 eV>. Structure changes were controlled by LEED.
3. Results and discussion ABS measurements showed that the deposition of thin (l-2 monolayer) gold films onto Si(lll)l X l-In with 3D indium islands causes an increase of the indium AES-peak instead of the decrease that should be expected due to a “shadowing” effect (fig. la). The annealing of
0 1992 - Elsevier Science Publishers B.V. All rights resewed
0. V. Bekhrerec’a Edal. / Thin gold and indium films on Sic1 I I) surface
cl
b
1
I
#J----L
mm
mm
Fig. 1. Si(lll)-In SP with 1 mm wide deposited with Au strip: (a) before annealing, (b) after annealing (3OO”C, 1 min).
this system at 300-500°C leads initially to the disappearance of the gold Auger-peak (69 eV), while the indium peak (404 eV> continues to increase slightly. Optical microscopy of this surface showed the presence of a great number of 3D indium islands (fig. 2). The deposition of several In monolayers onto Si(lllj5 x l-Au or Si(lll)& x O-Au followed by annealing at the same temperatures (300-
Fig. 2. Optical
microphotograph
500°C) also causes a disappearance of the gold Auger-peak. AES analysis showed that the thickness of the In film corresponds to the composition of the SXlllll x l-In SP. Such a behavior was observed at any Au and In deposition sequence. LEED observations confirmed the presence of the Si(lll)l x I-In structure. It is well-known that gold diffusion into a silicon substrate does not occur at 300-500°C. On the other hand, gold desorption from the silicon surface becomes noticeable only beyond 850°C [ill. The above facts may be interpreted as follows. Agglomeration of gold atoms into islands, covered by indium atoms takes place on Si surfaces upon annealing of deposited Au and In films. The gold islands serve as additional centers of 2D In gas condensation. This explains the absence of the gold Auger-peak. However, deposition of “thin” indium films (without 3D islands and “on-phase” indium atoms) onto a Si-Au surface phase does not induce the gold Auger-peak disappearance or amplitude decrease. Hence, “onphase” atoms (i.e., atoms in excess with respect to the Si(lll)l X l-In SP) are responsible for the Si-Au SP decay and for formation of gold islands covered by indium.
of the edge region of a Au strip deposited
on a Si(lll)-In
SP.
ia et al. / 1rhin! gold and
0.V. Bek
Isothermal desorption experiments of such a 3-component system confirm the presence of gold on the silicon surface. As an example, AES data of In desorption are shown in fig. 3. The 3-component system was produced by In deposition onto the Si(111)5 x l-Au SP. The annealing causes the evaporation of the indium atoms from the islands [8]. Then migration of gold atoms from the islands along the surface takes place. This leads to the restoring of the initial gold peak amplitude. After the disappearance of the islands, 8,” begins to decrease according to the exponential law e(t) = 8, exp( -L/T), where B0 is the initial In coverage and r is the mean lifetime of an In atom on the sample surface. As indium evaporates, the Au Auger-peak appears; its amplitude increases rapidly up to the initial level corresponding to the Si(111)5 x l-Au SP. Structural transitions, i.e., Si(lll)l X l-In + Si(111)3 X 1-(Au,In) + Si(111)4 X 1 + 5 X l(Au,In) + Si(111)5 x l-Au are observed by LEED with decreasing indium coverage. A new SP, named Si(11113 X 1-(Au, In) was detected (fig. 4). This phase is not formed on Si(lllj7 x 7 surfaces upon In or Au deposition. One can see from region II of the desorption curve (fig. 3), where the (3 X 1) structure was observed by LEED, that the Au coverage corresponds to the Si(111)5 x l-Au phase and the
Fig. 4. LEED pattern of Si(111)3 X 1-(Au,In).
indium coverage is inferior to that of the Si(lll)1 X l-In SP. One can see from the indium desorption experiments of the 3-component system that the In atom lifetime (7) is practically unchanged when the surface phases are changing. From the T(T) dependence T( 7) =
To
eXp
I?/(
/CT),
the binding energy of the In atoms in the 3-component system was determined: 1.4 + 0.2 eV; it is nearly the same as that for Si(111)4 X l-In WI. The presence of the gold atoms is supposed to affect only the lateral In-In interactions for the formation of the Si(111)3 x 1-(Au&r) SP but it has a weak effect on the In-substrate bonding.
References Williams, R.S. Daley, J.H. Huang and R.M. Charatan, Appl. Surf. Sci. 41/42 (1989) 70. [2] G. Le Lay and J.P. Faurie, Surf. Sci. 69 (1977) 295. [3] Ph. Dumas, A. Humbert, G. Mathieu, P. Mathiez, C. [l] R.S.
. . 01 0
’
5
10
15
20
time
‘qmin)JO
35
40
Fig. 3. Isothermal desorption of In from the ES-Au-In at 500°C: I - Si(lll)l X l-In, II - %(111)3X Si(111)4X1+5Xl-(Au,In),IV-Si(111)5Xl-Au.
1-(Au,In),
45
1 50
system III -
Mouttet, R. Rolland, F. Salvan, F. Thibaudau and S. Tosch, Phys. Ser. 38 (1988) 244. [4] V.G. Lifshits, V.B. Akilov and Y.L. Gavriljuk, Solid State Commun. 40 (1981) 429. [5] J. Lander and J. Morrison, Surf. Sci. 2 (1964) 533.
0. V. Bekhtereva et al. / Thin gold and indium films on Sic11 I) surface H. Hirayama, S. Baba and A. Kinbara, Appt. Surf. Sci. 33/34 (1988) 193. [71 Sang-i1 Park, J. Nogami and CF. Quate, J. Microsc. 152 (1988) 727. V.B. Akilov, B.K. Churusov and Y.L. 181 V.G. Lifshits, Gavriljuk, Surf. Sci. 222 (1989) 21.
[9] V.G. Lifshits, Modern Problems of Physical Chemistry of Semiconductor Surface (Nauka, Novosibirsk, 1988). [lo] A.A. Baski, J. Nogami, and CF. Quate, Phys. Rev. B 41 (1990) 10247. [ll] G. Le Lay, M. Manneville and R. Kern, Surf. Sci. 65 (1977) 261.