- Email: [email protected]
Vanadium oxide thin films deposited onto Cu buffer layer by RF magnetron sputtering
Thm Solid Films
?J?-314
(1999)
165-170
Vanadium oxide thin films deposited onto Cu buffer layer by RF magnetron sputtering Hidetoshi Miyazaki’.
Masayuki Kamei, Itaru Yasui
Imrimre ofImllfs!).iol Scimce. (i,liWJif~ of 7d,Yo. 7-?2- I Roppmsi.
hliw~roku.
To!a o. Jqwn
Abstract Vanadium osidc films were deposited by RF magnetron sputtering onto silica glass substrates or silica glass substrate, coated with Cu metal thin film buffer layer. If the vanadium oxide film was deposited onto the Cu thin film bufkr layer, tilm deprxition was carried out invacuum. and the valence of vanadium in the deposited films were reduced From the depth profiles of dcpobikxl films. the films deposited onto Cu buffer layer showedCu at the film surface.However.Cu did not exist in the vanadiumoxide layer ThusCu did nor diffusethrough vanadium oxide films. From the surface morphology analysis by AFI4. it was proved that nucleation density was decreased by presence of Cu buffer layer. G 1999 Elsevier Science S.A. All rights reserved. Kc.~ro&:
Vanadium oxide; RF mngnrrron sputterin 9: Buffer layer; .Atomic force microxopy; KucleAon in-wcuum deposition
1. Introduction
2. Experimental
Vanadium takes various valence states. and vanadium oxide exists a number of oside forms. Among the vanadium oxides. VzO3, VOZ. and Vz0.j films have widely beenstudied for optical. electrical. electrochemical. thermochromic. and thermal switching materials [l-6]. Single phaseV20! films are preparedeasily by various methods.But the other. single phaseof stoicbiometric vanadium oxide films were difficult to prepare [7]. In previous study. we depositedvanadium oxide films by RF magnetron sputtering [8], and the deposition rate of the VO, films depositedat a substratetetnperature of 100°C is shown in Fig. 1. When the oxygen partial flow rates were higher than that of the transition region. VIOi lilms kvere deposited. V:O;. VO?. and V,O,; films were deposited by controlling the oxygen partial flow ratio among the transition region. but they were very narrow in the region of the oxygen partial flow ratio. In this paper. vanadium oxide films were depositedonto a silica glassand those coated with Cu thin film as a buffer layer. The stoichiometry of depositedvanadium oxide films could be controlled by Cu buffer layer thickness. The surface tnorphology of deposited films were observed by U’M and it was obvious that probability of nucleation was decreasedby existence of Cu buffer layer [S-IO].
Thin films of VO, (.Y= 1.5-2.5) were depositedby reactive RF magnetron sputtering using an Anelva SPF332H with a three inch diameter 99.7% metallic vanadium target. Vanadium oxide films were deposited onto Cu and silica glass substrate, and the substrate temperature T> was JOO’C. The total sputtering pressureduring film growth was 1 Pa of an Ar and O1 gas mixture and the OjAr ratio was 1.5%. The RF power applied to the cathode was 100 W. theseconditions were maintained during the deposition. When the film was deposited onto the Cu substrate. it was electrically isolated from the chamber in order to prevent from Ar ion bombardment causeddamages Vanadium oxide films were also deposited onto Cu thin film in-vacuum. and the thickness of Cu films were 50 and 100 nm. The film thickness was measuredby a probe contact method using a Sloan Technology Dektak-3 and the structure of the films was investigated by XRD measurements using a Rigaku-Rint 2100. The copper/vanadium radio of the depositedfilms was determined by XPS measurements using a Phi quantum 2000. and we alsocarried out the depth profiles of Cu/V ratio of ones.The surfacemorphologiesof depositedfilms were obserliedby AFM measurementswith Jeol JSTM42OOD/A/S. When the AFM measurementswere carried out. the AFM chamberwas evacuated down to IO-’ Pa.
- Correqondmg author. Tel.: - Sl-331016231: fax: i 51-331595012. E-~ril acllft,ess;[email protected] IH. Miyazakir
@NO-6090/99/% see front matter *C 1999 Elsevier Science S.A. All rights reserved PTI: SOO10-6090(9S’10
I655-
1
H. Miwrakc
ei al. / 7%
Mid
Fihzs 343-344
ii999j
165-170
169
0.6 G d
0.4’5
d g ‘S .z
0.2
v
0
I g
1
i.75
1.25
1.5
Oxygen partial flow ratio (%) Fig. I. The depktion rare.
rate ofV0,
films as a function
of the O2 partial flow
3. Resuits and discussion XRD profiles of vanadium oxide films onto various thickness of Cu film are shown in Fig. 2. The film which deposited without Cu buffer layer showed VzOj structure. When vanadium oxide fihns were deposited onto the Cu buffer layer, the V30, film was deposited under Cu layer thickness of 50 nm, and the VZ03 film was deposited under a Cu layer thickness of 100 nm, respectively, and the VZO; film was deposited onto Cu substrate. These results indicated that the stoichiometry of vanadium oxide films could be controlled by the Cu layer thickness, however x in VO,, were 1.5, 2.3 and 2.5. In order to investigate the Cu buffer Iayer thickness dependent of films surface morphology, AFM m&surements were carried out for these films, and the AFM photographs are shown in Fig. 3. The SEM photographs of Cu buffer layers (not shown in this paper) were taken, the difference between various Cu films was not observed in the small area, and a smooth inciinarion was observed in the large area on the Cu film thickness of 100 nm. This indicates that the
o ho3 l W7 00
Fig. 3, The AFM images (4 X 1 pm! of the VO, films deposited onto: ia) silicaglass. (b) Cu buffer layer of 50 nm, and (cl Cu buffer layer of 100 MI.
30
50
70
2 8 (degree) (b) CLI buffer substrate.
XRD patterns of the VO, films deposited onto:(al silica glass, layer of 50 nm, (cl Cu buffer layer of 100 nm, and (dj Cu
preferential nucleation or film growth did not occur on steps on the various buffer layers. According to the Fig. 3, a lot of nucleuswere observedon the film which was depositedonto silica glass.As thicknessof Cu buffer layer was thick, nuclei number decreased:nucleation frequency decreasedcorresponding to nucleusesnumber. It was natura1 rhat when the nucleus number was small, each grain size became large, and the samephenomenawere observed. CuN ratio at various deoth in obtained vanadium oxide
170
stable. These results indicate that V;O; or V:O,. crystal growth energies are lou.er than that of fhe V.O- 3 nucleation energy under the condition \vhich V&?T films are deposited stable.
4. Conclusion
0
25
50
75
100
sputtering time (mm) FIN. 4. The depth profiles or’XPS sqnrli iur etch element of Cu/V in tilmb \\ hrch \\ere depncited onro: ~a) Cu buffer layer of 50 run. and (bl Cu bufier layer oi 100 nm.
films are shoan in Fig 1. The films deposited onto Cu buffel layer of 50 and 100 nm shoued Cu at the film surface. In the vanadium oxide layer. however. Cu did not esist. that ~vas. Cu did not dissolve into vanadium oxide films. Co-existence of Cu and V was obser\,ed at the deep level in the film in the Cu buffer layer of 100 nm. this ~vas caused by a smooth inclination on the Cu buffer layer. From these results. Cu esisted on the grooving films as a surfactant. It was assumed that grooving film surface was covered with Cu by surfaclant effects, and oxygen u’as not supplied to vanadium oxide films very much. Because of existence of Buffer layer. nucleation was hard to occur. and instead of’ a V;Oj film deposited. V;O: or V:O,, films were deposited by the surfactant effects. From Fig. 1. it was obvious VyOj films uere deposited in these conditions. however. the bthrr stoichiometry films uere deposited
Vanadium oxide films were deposited onto Cu buffet layer under the V;Oi deposition condition. V,
References [II
J hl. Coscianrelli. hf. .\Ienemer. C. Dctmar. J.P. Coumerc. M. Pouch&d. 11 Broussely. 1. L.~b~t. SOW Swte tonics 78 (1995) 143. B.B. Ouew N.H. Smyrl. I. 1’1 D.B. Le. S. P.:,benm. J. Guo. J. Reskr. Elecrruchrm. SW. l-l3 1n7) I 1996) 2099. 171S I. Pyun. J.S. Bae, Elecrrochimrca Acra 41 (n6) (1996) 919. 141F. Cardillo Cnx. J. Vas. Sci. Technut. A 2 (JI (19511 1509. P. Jln. S. Tanemura. Jpn J. Appl Phy,. 33 ( 199-1, 147s. Ia; I. Tnkahdbhl. 51. Hlbino. T. Kudo. Jpn J. Appl Phyb. Pan 2 35 (1996) L-13S. Krihhn:. Y. Devauge. A.K. Bharrxharya. Thin solid 171 .\I Gh.math)am Films !l (19981 116. 181H. hli>azaki. F Lwno. Y. ShigehJru. I. Yawi. Tbln Solid Films Xl I 1996)
116.
[91 R.P. Michet. .A. Chaikcn 37 1n5) (19961 4651. A. Yokowaw.~. H. Wakma. Y. KJhhiwabs. 1101 0. XlIchlkrlml. Appl. Ph>>. !6 (199;) 36-16.
Jpn. J
?J?-314
(1999)
165-170
Vanadium oxide thin films deposited onto Cu buffer layer by RF magnetron sputtering Hidetoshi Miyazaki’.
Masayuki Kamei, Itaru Yasui
Imrimre ofImllfs!).iol Scimce. (i,liWJif~ of 7d,Yo. 7-?2- I Roppmsi.
hliw~roku.
To!a o. Jqwn
Abstract Vanadium osidc films were deposited by RF magnetron sputtering onto silica glass substrates or silica glass substrate, coated with Cu metal thin film buffer layer. If the vanadium oxide film was deposited onto the Cu thin film bufkr layer, tilm deprxition was carried out invacuum. and the valence of vanadium in the deposited films were reduced From the depth profiles of dcpobikxl films. the films deposited onto Cu buffer layer showedCu at the film surface.However.Cu did not exist in the vanadiumoxide layer ThusCu did nor diffusethrough vanadium oxide films. From the surface morphology analysis by AFI4. it was proved that nucleation density was decreased by presence of Cu buffer layer. G 1999 Elsevier Science S.A. All rights reserved. Kc.~ro&:
Vanadium oxide; RF mngnrrron sputterin 9: Buffer layer; .Atomic force microxopy; KucleAon in-wcuum deposition
1. Introduction
2. Experimental
Vanadium takes various valence states. and vanadium oxide exists a number of oside forms. Among the vanadium oxides. VzO3, VOZ. and Vz0.j films have widely beenstudied for optical. electrical. electrochemical. thermochromic. and thermal switching materials [l-6]. Single phaseV20! films are preparedeasily by various methods.But the other. single phaseof stoicbiometric vanadium oxide films were difficult to prepare [7]. In previous study. we depositedvanadium oxide films by RF magnetron sputtering [8], and the deposition rate of the VO, films depositedat a substratetetnperature of 100°C is shown in Fig. 1. When the oxygen partial flow rates were higher than that of the transition region. VIOi lilms kvere deposited. V:O;. VO?. and V,O,; films were deposited by controlling the oxygen partial flow ratio among the transition region. but they were very narrow in the region of the oxygen partial flow ratio. In this paper. vanadium oxide films were depositedonto a silica glassand those coated with Cu thin film as a buffer layer. The stoichiometry of depositedvanadium oxide films could be controlled by Cu buffer layer thickness. The surface tnorphology of deposited films were observed by U’M and it was obvious that probability of nucleation was decreasedby existence of Cu buffer layer [S-IO].
Thin films of VO, (.Y= 1.5-2.5) were depositedby reactive RF magnetron sputtering using an Anelva SPF332H with a three inch diameter 99.7% metallic vanadium target. Vanadium oxide films were deposited onto Cu and silica glass substrate, and the substrate temperature T> was JOO’C. The total sputtering pressureduring film growth was 1 Pa of an Ar and O1 gas mixture and the OjAr ratio was 1.5%. The RF power applied to the cathode was 100 W. theseconditions were maintained during the deposition. When the film was deposited onto the Cu substrate. it was electrically isolated from the chamber in order to prevent from Ar ion bombardment causeddamages Vanadium oxide films were also deposited onto Cu thin film in-vacuum. and the thickness of Cu films were 50 and 100 nm. The film thickness was measuredby a probe contact method using a Sloan Technology Dektak-3 and the structure of the films was investigated by XRD measurements using a Rigaku-Rint 2100. The copper/vanadium radio of the depositedfilms was determined by XPS measurements using a Phi quantum 2000. and we alsocarried out the depth profiles of Cu/V ratio of ones.The surfacemorphologiesof depositedfilms were obserliedby AFM measurementswith Jeol JSTM42OOD/A/S. When the AFM measurementswere carried out. the AFM chamberwas evacuated down to IO-’ Pa.
- Correqondmg author. Tel.: - Sl-331016231: fax: i 51-331595012. E-~ril acllft,ess;[email protected] IH. Miyazakir
@NO-6090/99/% see front matter *C 1999 Elsevier Science S.A. All rights reserved PTI: SOO10-6090(9S’10
I655-
1
H. Miwrakc
ei al. / 7%
Mid
Fihzs 343-344
ii999j
165-170
169
0.6 G d
0.4’5
d g ‘S .z
0.2
v
0
I g
1
i.75
1.25
1.5
Oxygen partial flow ratio (%) Fig. I. The depktion rare.
rate ofV0,
films as a function
of the O2 partial flow
3. Resuits and discussion XRD profiles of vanadium oxide films onto various thickness of Cu film are shown in Fig. 2. The film which deposited without Cu buffer layer showed VzOj structure. When vanadium oxide fihns were deposited onto the Cu buffer layer, the V30, film was deposited under Cu layer thickness of 50 nm, and the VZ03 film was deposited under a Cu layer thickness of 100 nm, respectively, and the VZO; film was deposited onto Cu substrate. These results indicated that the stoichiometry of vanadium oxide films could be controlled by the Cu layer thickness, however x in VO,, were 1.5, 2.3 and 2.5. In order to investigate the Cu buffer Iayer thickness dependent of films surface morphology, AFM m&surements were carried out for these films, and the AFM photographs are shown in Fig. 3. The SEM photographs of Cu buffer layers (not shown in this paper) were taken, the difference between various Cu films was not observed in the small area, and a smooth inciinarion was observed in the large area on the Cu film thickness of 100 nm. This indicates that the
o ho3 l W7 00
Fig. 3, The AFM images (4 X 1 pm! of the VO, films deposited onto: ia) silicaglass. (b) Cu buffer layer of 50 nm, and (cl Cu buffer layer of 100 MI.
30
50
70
2 8 (degree) (b) CLI buffer substrate.
XRD patterns of the VO, films deposited onto:(al silica glass, layer of 50 nm, (cl Cu buffer layer of 100 nm, and (dj Cu
preferential nucleation or film growth did not occur on steps on the various buffer layers. According to the Fig. 3, a lot of nucleuswere observedon the film which was depositedonto silica glass.As thicknessof Cu buffer layer was thick, nuclei number decreased:nucleation frequency decreasedcorresponding to nucleusesnumber. It was natura1 rhat when the nucleus number was small, each grain size became large, and the samephenomenawere observed. CuN ratio at various deoth in obtained vanadium oxide
170
stable. These results indicate that V;O; or V:O,. crystal growth energies are lou.er than that of fhe V.O- 3 nucleation energy under the condition \vhich V&?T films are deposited stable.
4. Conclusion
0
25
50
75
100
sputtering time (mm) FIN. 4. The depth profiles or’XPS sqnrli iur etch element of Cu/V in tilmb \\ hrch \\ere depncited onro: ~a) Cu buffer layer of 50 run. and (bl Cu bufier layer oi 100 nm.
films are shoan in Fig 1. The films deposited onto Cu buffel layer of 50 and 100 nm shoued Cu at the film surface. In the vanadium oxide layer. however. Cu did not esist. that ~vas. Cu did not dissolve into vanadium oxide films. Co-existence of Cu and V was obser\,ed at the deep level in the film in the Cu buffer layer of 100 nm. this ~vas caused by a smooth inclination on the Cu buffer layer. From these results. Cu esisted on the grooving films as a surfactant. It was assumed that grooving film surface was covered with Cu by surfaclant effects, and oxygen u’as not supplied to vanadium oxide films very much. Because of existence of Buffer layer. nucleation was hard to occur. and instead of’ a V;Oj film deposited. V;O: or V:O,, films were deposited by the surfactant effects. From Fig. 1. it was obvious VyOj films uere deposited in these conditions. however. the bthrr stoichiometry films uere deposited
Vanadium oxide films were deposited onto Cu buffet layer under the V;Oi deposition condition. V,
References [II
J hl. Coscianrelli. hf. .\Ienemer. C. Dctmar. J.P. Coumerc. M. Pouch&d. 11 Broussely. 1. L.~b~t. SOW Swte tonics 78 (1995) 143. B.B. Ouew N.H. Smyrl. I. 1’1 D.B. Le. S. P.:,benm. J. Guo. J. Reskr. Elecrruchrm. SW. l-l3 1n7) I 1996) 2099. 171S I. Pyun. J.S. Bae, Elecrrochimrca Acra 41 (n6) (1996) 919. 141F. Cardillo Cnx. J. Vas. Sci. Technut. A 2 (JI (19511 1509. P. Jln. S. Tanemura. Jpn J. Appl Phy,. 33 ( 199-1, 147s. Ia; I. Tnkahdbhl. 51. Hlbino. T. Kudo. Jpn J. Appl Phyb. Pan 2 35 (1996) L-13S. Krihhn:. Y. Devauge. A.K. Bharrxharya. Thin solid 171 .\I Gh.math)am Films !l (19981 116. 181H. hli>azaki. F Lwno. Y. ShigehJru. I. Yawi. Tbln Solid Films Xl I 1996)
116.
[91 R.P. Michet. .A. Chaikcn 37 1n5) (19961 4651. A. Yokowaw.~. H. Wakma. Y. KJhhiwabs. 1101 0. XlIchlkrlml. Appl. Ph>>. !6 (199;) 36-16.
Jpn. J