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Ion-beam induced orientation growth of PtSi
Vacuum/volume 39/numbers Printed in Great Britain
2-4/pages
Ion-beam
induced
Yang Lijia, Liu Yili and Wang Beijing,
0042-207X/89$3.00+.00 Pergamon Press plc
227 to 229/I 989
Zhonglie,
orientation Institute
growth
of Low Energy Nuclear
of PtSi
Physics, Beijing Normal
University,
PRC
and
Li Hengde,
Qinghua
University,
Beijing,
PRC
Thin films of platinum with thicknesses up to 550 A were deposited onto Si( 1 I 1) substrates. The samples were implanted with 300 keV As’ ions at room temperature and annealed thermally after As’ ion implantation. Preferred orientation growth of PtSi was observed from the X-ray diffraction measurement. On the Si( 7 7 1) substrates the preferred (101) orientation growth of PtSi was obtained. However, it was observed that the orientation of Si substrates strongly affected the orientation growth of PtSi. There is no obvious orientation growth on Si(100) substrates. We propose a possible growth mechanism of the interface Pt-Si on the basis of the Bravais crystal theory and lattice matching conditions.
1. Introduction Metal silicide films grown on silicon substrates’m3 have attracted much attention over the last decade because of their wide application in the semiconductor industry as ohmic or Schottky-bartier contacts and low resistance interconnects. The study of the formation of silicides which involves the reaction between two solid phases in direct contact to form ordered intermetallic compounds at temperatures well below any liquid phase is of both academic interest and metallurgical importance. In this paper, we investigate the crystallographic properties and the structure of the platinum-silicide formed by ion-induced and post annealing. The results of Rutherford backscattering and X-ray analysis of the platinum silicide layers and the observation of the orientation of PtSi formed by ion beams on the (111) Si wafers are described. 2. Experimental procedure
annealed after being implanted. The thickness of PtSi is about 1100 A, which is nearly twice that of the Pt-film. The X-ray diffraction spectra show that for the samples of 550 8, Pt/(l 1l)Si which have been implanted and annealed the PtSi silicide phase was obtained. It was found that the observed intensity distribution of PtSi is different from the PDF standard values4. The strongest diffraction line of PtSi is (101). The PtSi films are oriented. Figure 2 shows the X-ray diffraction spectra of 550 8, Pt/Si(111) samples implanted with 1 x lOI As+ cm-* and annealed. In Figure 2(a), the temperature of post annealing is 450°C the strongest diffraction line of PtSi is (lOl), and the second strongest diffraction line is (020). The rest are weak. When the post annealing temperature rises to 650°C or 8OO”C, as can be seen in Figures 2(b) and (c), the relative intensity of the (101) diffraction line increases with increasing temperature. However, the diffraction line of (020) nearly disappears.
Thin Pt films either 550 A or 350 A thick were sputtered onto chemically cleaned (111) Si and (100) Si substrates at a pressure of 8 x 10m9 bar with an average deposition rate of 120 8, min ‘. Then 300 keV As+ ions were implanted into these samples at room temperature with doses 1 x 10I5 cm-* and 9 x 10” cm-*. The average beam current density was about 1.2 ,uA cm- *. The implanted samples were subsequently annealed for 20 min in a N, flow of 1 1mini ’ at temperatures ranging from 450 to 800°C. Rutherford backscattering of 2 MeV 4He+, was used to measure the composition profile of the intermixed layers. The crystal structure of PtSi films was determined by X-ray diffraction analysis with Cu k, radiation.
Pt
3. Experimental results The backscattering spectra for an As+ implanted series are shown in Figure 1 for PtjSi samples. As can be seen in Figure l(b), a substantial intermixing occurs between the Pt and Si when the samples have been bombarded with energetic ions. However, there is not any well-defined phase formed. In Figure 1(c), all Pt atoms are consumed in forming a PtSi film when the samples were
Channel
number
Figure 1. Backscattering spectra of 2 MeV 4Hef
for Pt-Si thin-film samples that were implanted at RT with 300 keV 1 x 10” cm-’ As ions. (a) ~ unimplanted; (b) ~~~ unannealed after implanted; (c) “’ implanted and annealed (45o”C, 20 min). 227
Yang Ll//a et al: Ion-beam
Induced
orientation
growth
of PtSl
zoo< ial
(a) Phase: (101)
Phase:
Pt Si
(101)
(020)
1.
1001
Pt Si
(121)
loo<
(020)
(121)
(21 ,)fi
1
1
root
I
I
I
(101
(b) Phase:
I
___I____-
2ooi
~1011
!b)
Pt Si
Phase
Pt Si
ii!
is & I’ 2 p:
2 32
lOO(
IOOC
(121)
2 5
,5
-
2002
-‘L
200(
L
‘-,
-
(101
_L
(101 )
(c)
(C) Phase. Phase:
Pt
Pt
SI
Si
IOOC
IOOl
(121) I
---.s C
+-e
0
(002)
(21 I)
Ju
I
30
40
50
6’)
28 (deg)
28 (deg)
dill’raction spectra of samples Pt;Si-( I I I) implanted wth cm ’ at RT and post annealed. (a) 4.50 C. (h) 650 c. (c) x00 (‘.
Figure 3. X-ray dilfraction spectra of samples 550 A Pt. Si( I I I) ~mplanlcd with 300 keV 9 x IO“ As’ cm ’ at RT and post annoalcd. (:I) 450 C (h) 650 (‘. Cc) 1(00 (‘.
t+igurc 3 shows the X-ray diffraclion spectra of Pt:‘Si-( I I I ) specimens implanted with 9 x IO” As- cm ’ and heat treated. For all post annealing tcmpcraturcs, we can set in Figure 3. that the (101) difrraction line of PtSi is very strong. and the others arc weak. The X-ray diffraction spectra I‘or the PtSi on Si-( I I I) prepared mcrcly by unncaling are shown in Figure 4. It was found that the orientation is sornewhat different from that of the ion-bcaminduced case. As Figure 4(a) shows. for the sample annealed at 450 C. the strongest diffraction line of PtSi is (020). This orientation remains unchanged by annealing at 650’ C ; however. at 800 C there is a definite indication of a changeover from (020) to (101). In contrast. Figure 5 shows the X-ray diffraction spectra for the PtSi on Si( 100) substrate lhrmed by the ion induced post anncalcd method. In this case, no prclcrcnlisl oricnlation effect ~\a ohscrvcd. The intensity distribution of the diffraction lines
01‘
Figure 2.
X-ray
300 kcV. I x IO“ 4s’
228
PtSi. on the whole. k ~~nchanged with the tcmpcrxturc ol‘l~c;~t treatment. As shown from the results, the preferred orientation of PtSi depends on the orientation of the silicon substrutc.
4. Discussion The orientation in PtSi films formed nt IOM, annealing temperatures is (020). It can bc intcrprctcd according to the pscudohexagonal symmetry of’ PtSi (010) presented by Sinhu 01 trl‘. There is a close resemblance between the atomic arrangcmcnt on the surtace of (I I I) Si and the (020) planes of PtSi. It appears that these epitaxial forces are of paramount importance at lower temperatures. At higher annealing temperatures the preferred orientation of the PtSi phase varies from (020) at 450 C and 650 C. to (101) at X00 C. In the case of ion-beam induced reactions, the formation ot silicidcs is caused by the penetration or energetic ions through
Yang Luia et a/c Ion-beam
induced
orientation
growth
of PtSi
zoo< (a) Phase:
Pt Si
lOO(
1b 1600°C
200(
(b) Phase:
Pt Si
63 2 2
IOOC
5 I5
I
I
30
40
I 50 28
Figure 5. X-ray diffraction mixing and post annealing.
spectra
I
60
(deg)
for PtSi on (100) Si formed by ion
2ooc
(c’ Phase:
unit surface. For PtSi, which has an orthorhombic B31 (MnP type) structure’, the crystallographic planes in order of importance are the ( 1 IO) and ( IO 1). Also, the atomic layer period of the (101) direction of PtSi is very close to that of the (I 11) direction of Si. The mismatch is only 1.9%. The layer sequence is SiLSi-Pt-Pt. Assuming the Pt atoms move interstitially between Si layers due to the ion mixing, it was easy to form the layer sequence of Si-Si-Pt-Pt. As a result, the polycrystalline films of PtSi tend to grow in the (101) direction.
Pt Si
I001
,
I
I
I
I
30
40
50
60
5. Summary and conclusions
28 (deg) Figure 4. X-ray diffraction spectra for PtSi on (111) Si prepared annealing. (a) 450°C. (b) 650 ‘C. (c) 800°C.
by merely
the interface between a metal film and silicon. The initial growth condition of PtSi is changed due to the deposition of large amounts of energy in localized regions, which overcomes equilibrium constraints and forces atoms to rearrange. The epitaxial forces of the (020) direction are eliminated. The silicide phase is polycrystalline. However, during the sequential heat treatment, the polycrystalline PtSi grows with a preferred orientation. Preferred orientation in polycrystalline films can be modelled in terms of the modified Bravais theory of crystal growth’. According to this theory, the growth velocity of a particular plane is directly proportional to its reticular density. The reticular density of a given plane is defined as the number of lattice points per
In summary, we have demonstrated that the ion-beam-induced epitaxy occurs in a Pt film deposited onto a (11 I) Si substrate, and concluded that this phenomenon can be explained by the formation of polycrystalline PtSi due to the penetration of ions through the Pt-Si interface, followed by the epitaxial growth of the polycrystalline film by sequential heat treatment. The preferred orientation of PtSi induced by ion beams is (101). References
‘K N Tu and J W Mayer, in Thin FilmsInterdt~u.~ion and Reaction (Edited by J M Poate, K N Tu and J W Mayer). Wiley, New York (1978). ‘G Ottaviani, J Vat Sci Technol, 16, 1112 (1979). ‘S P Murarka, J Vuc Sci Technol, 17,775 (1980). 4 Powder Diffraction File, set 7-251. American Society for Testing and Materials (1980). ‘A K Sinha, R B Marcus, J J Sheng and S E Haszka, J appl Phys. 43, 3637 (1972). ‘S S Chao, J Gronzalez-Hernandez, D Martin and R Tsu, Appl Phys Lett, 46, 1089 (1985). ‘M Hansen, in Constitution of Bincrry AIlo,vs, p 1140. McGraw-Hill, New York (1969).
229
2-4/pages
Ion-beam
induced
Yang Lijia, Liu Yili and Wang Beijing,
0042-207X/89$3.00+.00 Pergamon Press plc
227 to 229/I 989
Zhonglie,
orientation Institute
growth
of Low Energy Nuclear
of PtSi
Physics, Beijing Normal
University,
PRC
and
Li Hengde,
Qinghua
University,
Beijing,
PRC
Thin films of platinum with thicknesses up to 550 A were deposited onto Si( 1 I 1) substrates. The samples were implanted with 300 keV As’ ions at room temperature and annealed thermally after As’ ion implantation. Preferred orientation growth of PtSi was observed from the X-ray diffraction measurement. On the Si( 7 7 1) substrates the preferred (101) orientation growth of PtSi was obtained. However, it was observed that the orientation of Si substrates strongly affected the orientation growth of PtSi. There is no obvious orientation growth on Si(100) substrates. We propose a possible growth mechanism of the interface Pt-Si on the basis of the Bravais crystal theory and lattice matching conditions.
1. Introduction Metal silicide films grown on silicon substrates’m3 have attracted much attention over the last decade because of their wide application in the semiconductor industry as ohmic or Schottky-bartier contacts and low resistance interconnects. The study of the formation of silicides which involves the reaction between two solid phases in direct contact to form ordered intermetallic compounds at temperatures well below any liquid phase is of both academic interest and metallurgical importance. In this paper, we investigate the crystallographic properties and the structure of the platinum-silicide formed by ion-induced and post annealing. The results of Rutherford backscattering and X-ray analysis of the platinum silicide layers and the observation of the orientation of PtSi formed by ion beams on the (111) Si wafers are described. 2. Experimental procedure
annealed after being implanted. The thickness of PtSi is about 1100 A, which is nearly twice that of the Pt-film. The X-ray diffraction spectra show that for the samples of 550 8, Pt/(l 1l)Si which have been implanted and annealed the PtSi silicide phase was obtained. It was found that the observed intensity distribution of PtSi is different from the PDF standard values4. The strongest diffraction line of PtSi is (101). The PtSi films are oriented. Figure 2 shows the X-ray diffraction spectra of 550 8, Pt/Si(111) samples implanted with 1 x lOI As+ cm-* and annealed. In Figure 2(a), the temperature of post annealing is 450°C the strongest diffraction line of PtSi is (lOl), and the second strongest diffraction line is (020). The rest are weak. When the post annealing temperature rises to 650°C or 8OO”C, as can be seen in Figures 2(b) and (c), the relative intensity of the (101) diffraction line increases with increasing temperature. However, the diffraction line of (020) nearly disappears.
Thin Pt films either 550 A or 350 A thick were sputtered onto chemically cleaned (111) Si and (100) Si substrates at a pressure of 8 x 10m9 bar with an average deposition rate of 120 8, min ‘. Then 300 keV As+ ions were implanted into these samples at room temperature with doses 1 x 10I5 cm-* and 9 x 10” cm-*. The average beam current density was about 1.2 ,uA cm- *. The implanted samples were subsequently annealed for 20 min in a N, flow of 1 1mini ’ at temperatures ranging from 450 to 800°C. Rutherford backscattering of 2 MeV 4He+, was used to measure the composition profile of the intermixed layers. The crystal structure of PtSi films was determined by X-ray diffraction analysis with Cu k, radiation.
Pt
3. Experimental results The backscattering spectra for an As+ implanted series are shown in Figure 1 for PtjSi samples. As can be seen in Figure l(b), a substantial intermixing occurs between the Pt and Si when the samples have been bombarded with energetic ions. However, there is not any well-defined phase formed. In Figure 1(c), all Pt atoms are consumed in forming a PtSi film when the samples were
Channel
number
Figure 1. Backscattering spectra of 2 MeV 4Hef
for Pt-Si thin-film samples that were implanted at RT with 300 keV 1 x 10” cm-’ As ions. (a) ~ unimplanted; (b) ~~~ unannealed after implanted; (c) “’ implanted and annealed (45o”C, 20 min). 227
Yang Ll//a et al: Ion-beam
Induced
orientation
growth
of PtSl
zoo< ial
(a) Phase: (101)
Phase:
Pt Si
(101)
(020)
1.
1001
Pt Si
(121)
loo<
(020)
(121)
(21 ,)fi
1
1
root
I
I
I
(101
(b) Phase:
I
___I____-
2ooi
~1011
!b)
Pt Si
Phase
Pt Si
ii!
is & I’ 2 p:
2 32
lOO(
IOOC
(121)
2 5
,5
-
2002
-‘L
200(
L
‘-,
-
(101
_L
(101 )
(c)
(C) Phase. Phase:
Pt
Pt
SI
Si
IOOC
IOOl
(121) I
---.s C
+-e
0
(002)
(21 I)
Ju
I
30
40
50
6’)
28 (deg)
28 (deg)
dill’raction spectra of samples Pt;Si-( I I I) implanted wth cm ’ at RT and post annealed. (a) 4.50 C. (h) 650 c. (c) x00 (‘.
Figure 3. X-ray dilfraction spectra of samples 550 A Pt. Si( I I I) ~mplanlcd with 300 keV 9 x IO“ As’ cm ’ at RT and post annoalcd. (:I) 450 C (h) 650 (‘. Cc) 1(00 (‘.
t+igurc 3 shows the X-ray diffraclion spectra of Pt:‘Si-( I I I ) specimens implanted with 9 x IO” As- cm ’ and heat treated. For all post annealing tcmpcraturcs, we can set in Figure 3. that the (101) difrraction line of PtSi is very strong. and the others arc weak. The X-ray diffraction spectra I‘or the PtSi on Si-( I I I) prepared mcrcly by unncaling are shown in Figure 4. It was found that the orientation is sornewhat different from that of the ion-bcaminduced case. As Figure 4(a) shows. for the sample annealed at 450 C. the strongest diffraction line of PtSi is (020). This orientation remains unchanged by annealing at 650’ C ; however. at 800 C there is a definite indication of a changeover from (020) to (101). In contrast. Figure 5 shows the X-ray diffraction spectra for the PtSi on Si( 100) substrate lhrmed by the ion induced post anncalcd method. In this case, no prclcrcnlisl oricnlation effect ~\a ohscrvcd. The intensity distribution of the diffraction lines
01‘
Figure 2.
X-ray
300 kcV. I x IO“ 4s’
228
PtSi. on the whole. k ~~nchanged with the tcmpcrxturc ol‘l~c;~t treatment. As shown from the results, the preferred orientation of PtSi depends on the orientation of the silicon substrutc.
4. Discussion The orientation in PtSi films formed nt IOM, annealing temperatures is (020). It can bc intcrprctcd according to the pscudohexagonal symmetry of’ PtSi (010) presented by Sinhu 01 trl‘. There is a close resemblance between the atomic arrangcmcnt on the surtace of (I I I) Si and the (020) planes of PtSi. It appears that these epitaxial forces are of paramount importance at lower temperatures. At higher annealing temperatures the preferred orientation of the PtSi phase varies from (020) at 450 C and 650 C. to (101) at X00 C. In the case of ion-beam induced reactions, the formation ot silicidcs is caused by the penetration or energetic ions through
Yang Luia et a/c Ion-beam
induced
orientation
growth
of PtSi
zoo< (a) Phase:
Pt Si
lOO(
1b 1600°C
200(
(b) Phase:
Pt Si
63 2 2
IOOC
5 I5
I
I
30
40
I 50 28
Figure 5. X-ray diffraction mixing and post annealing.
spectra
I
60
(deg)
for PtSi on (100) Si formed by ion
2ooc
(c’ Phase:
unit surface. For PtSi, which has an orthorhombic B31 (MnP type) structure’, the crystallographic planes in order of importance are the ( 1 IO) and ( IO 1). Also, the atomic layer period of the (101) direction of PtSi is very close to that of the (I 11) direction of Si. The mismatch is only 1.9%. The layer sequence is SiLSi-Pt-Pt. Assuming the Pt atoms move interstitially between Si layers due to the ion mixing, it was easy to form the layer sequence of Si-Si-Pt-Pt. As a result, the polycrystalline films of PtSi tend to grow in the (101) direction.
Pt Si
I001
,
I
I
I
I
30
40
50
60
5. Summary and conclusions
28 (deg) Figure 4. X-ray diffraction spectra for PtSi on (111) Si prepared annealing. (a) 450°C. (b) 650 ‘C. (c) 800°C.
by merely
the interface between a metal film and silicon. The initial growth condition of PtSi is changed due to the deposition of large amounts of energy in localized regions, which overcomes equilibrium constraints and forces atoms to rearrange. The epitaxial forces of the (020) direction are eliminated. The silicide phase is polycrystalline. However, during the sequential heat treatment, the polycrystalline PtSi grows with a preferred orientation. Preferred orientation in polycrystalline films can be modelled in terms of the modified Bravais theory of crystal growth’. According to this theory, the growth velocity of a particular plane is directly proportional to its reticular density. The reticular density of a given plane is defined as the number of lattice points per
In summary, we have demonstrated that the ion-beam-induced epitaxy occurs in a Pt film deposited onto a (11 I) Si substrate, and concluded that this phenomenon can be explained by the formation of polycrystalline PtSi due to the penetration of ions through the Pt-Si interface, followed by the epitaxial growth of the polycrystalline film by sequential heat treatment. The preferred orientation of PtSi induced by ion beams is (101). References
‘K N Tu and J W Mayer, in Thin FilmsInterdt~u.~ion and Reaction (Edited by J M Poate, K N Tu and J W Mayer). Wiley, New York (1978). ‘G Ottaviani, J Vat Sci Technol, 16, 1112 (1979). ‘S P Murarka, J Vuc Sci Technol, 17,775 (1980). 4 Powder Diffraction File, set 7-251. American Society for Testing and Materials (1980). ‘A K Sinha, R B Marcus, J J Sheng and S E Haszka, J appl Phys. 43, 3637 (1972). ‘S S Chao, J Gronzalez-Hernandez, D Martin and R Tsu, Appl Phys Lett, 46, 1089 (1985). ‘M Hansen, in Constitution of Bincrry AIlo,vs, p 1140. McGraw-Hill, New York (1969).
229