The Sixth International Workshop on Junction Technology (IWJT), May 15-16, 2006, Shanghai, China.

Formation and characterization of aluminum-oxide by stack-layered metal structure Schottky diode

Wen-Chang Huang and Dong-Rong Cai

ConclusionThe electrical characteristic of the double metal, Pt/Al/n-InP structure is better than the conventional single metal/n-InP contact. Moreover, the electrical characteristic can be more improved as the diode was annealed in furnace at 300-400C for 10 min. This is due to the formation of Al2O3 thin film layer at the contact interface which was proved by XRD and SIMS analysis. The formation of thin film, Al2O3, of the Pt/Al/n-InP diode improved the rectified characteristics, and the diode’s barrier height was improved to 0.74eV. The diode also showed a good surface morphology after thermal annealing. It is suitable in

submicron device applications.

半導體元件研究室

Abstract

A double metals structure, Pt/Al/n-InP diode was studied. An Al2O3 thin film was formed at the contact interface of the Pt/Al/InP diode after thermal annealing. It was detected at the diffraction angle of 2=20.4 by X-ray diffraction (XRD) analysis after the diode was annealed at 300C or 400C for 10 min. Also, from secondary ion mass spectrum (SIMS) analysis, it was found that the Al2O3 thin film located at the contact interface of the Pt/Al/n-InP diode. The electrical characteristic was improved due to the formation of aluminum-oxide. The effective barrier height is equal

to 0.74 eV which was measured on the annealed sample.

IntroductionSurface Fermi level pinning, arising from the high density of surface states and other nonstoichiometric defects, make it difficult for n-InP to obtain a Schottky barrier height greater than 0.5 eV. Many researcher proposed some method to improve the electrical characteristic, they including PH3 plasma treatments,[1] growing a thin P3N5 film,[2] a POxNyHz film,[3] a InSb film,[4] an interfacial oxide layer,[5-8] low temperature deposition techniques[9]or stacked metal structure Ag/Al [10], Pt/Al[11, 12], and Ni/Ai/Ni [13]. All the reports showed higher effective barrier height than that of conventional single metal/n-InP diode. In this paper, we discussed the material characteristics of the Pt/Al/n-InP diode. XRD was employed to observe the phase formation after various temperature annealing. SIMS was used to see the distribution of all elements in the diode. Atomic force microscope (AFM) was used to discuss the morphology of the surface.

Diode fabrication and measurementThe diodes were fabricated on (100) n-InP substrate wafers with a free-carrier concentration of 5-91015 cm-3. Ohmic contact with low specific contact resistance on the back side was formed by evaporating an AuGeNi eutectic source ( 84% Au, 12% Ge, 4% Ni by weight ), followed by annealing at 400C for 3 min. Multiple layer of metals Pt/Al were deposited sequentially on the wafers in a vacuum of 410-6 Torr, and metal patterns were obtained by using a lift-off process. The Pt thickness was about 500 Å and the Al thickness is 85 Å. The wafers were then annealed in an N2 gas flow, at various temperatures for a long time.

Results and Discussion

[1] T. Sugino, H. Yamamoto, Y. Sakamoto, H. Ninomiya and J. Shirafuji, Jpn. J. Appl. Phys., 30 (1991) L1439.[2] Y. H. Jeong, G. T. Kim, S. T. Kim, K. I. Kim, and W. J. Chung, J. Appl. Phys., 69 (1991) 6699.[3] D. T. Quan and H. Hbib, Solid-St. Electron., 36 (1993) 339. [4] Z, Benamara, B. Akkal, A. Talbi, B. Gruzza, L. Bideux, Materials Science and Engineering, C2 (2002) 287.[5] H. Yamagishi Jpn. J. Appl. Phys., 25 (1986) 1691.[6] K. Kamimura, T. Suzuki, and A. Kunioka, J. Appl. Phys., 51 (1980) 4905. [7] O. Wada, A. Majerfeld, and P. N. Robson, Solid-St. Electron., 25 (1982) 381. [8] Y. S. Lee and W. A. Anderson, J. Appl. Phys., 65 (1989) 4051. [9] Z. Q. Shi, R. L. Wallace and W. A. Anderson, Appl. Phys. Lett., 59 (1991) 446. [10] J. Dunn and G. B. Stringfellow, Journal of Electronic Material, 17 (1988) 181. [11] W. C. Huang, T. F. Lei and C. L. Lee, Journal of Appl. Phys., 78 (1995) 291. [12] W. C. Huang, T. F. Lei, and C. L. Lee, Jpn. J. Appl. Phys., 42 (2003) 71.[13]S. Miyazaki, M. Saruta, T. Okumura, Applied Surface Science, 117/118 (1997) 357.

AcknowledgmentsThe authors would like to thank the National Science Council of the Republic of China, for financially supporting the research under Contract No. NSC-94-2216-E-168-004.

References

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Al(

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Pt(

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200)

Pt(

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Pt(

111)

InP

(400

)

InP

(200

)

Unannealed Pt/Al/InP

Inte

nsi

ty

Diffraction Angle20 30 40 50 60 70 80 90

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Al 2O

3(11

0) Pt(

31

1)

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200)

InP

(400

)

Pt(

200)

InP

(200

)

Pt(

11

1)

300oC annealed Pt/Al/InP

Inte

nsi

ty

Diffraction Angle

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Al 2O

3(11

0) Pt(

311)

Al(

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200)

InP

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Pt(

200)

Pt(

111)

InP

(200

)

400oC annealed Pt/Al/InP

Inte

nsi

ty

Diffraction AngleXRD— As depositedXRD-- 300C annealed, A new phase corresponds to Al2O3 (110) which centered at 2=20.4. XRD-- 400C annealed, The intensity of the Al2O3 (110) signal peak was stronger than that of the 300C–annealed diode.

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OAlPInPt

Sputtering Time (sec)

O

metal InP substrate

PPt

Al

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SIMS– The elements Pt, Al, In and P were shown in the Figure. An additional element, oxygen, was also found in the SIMS profile. It proved that the Al2O3 thin film was existed at contact interface

10-8

10-6

0.0001

0.01

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100

-3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1

Pt/Al/n-InP

As deposited300C annealed400C annealed

Voltage (V)

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Idea

lity

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tor

Annealed Temperature (oC)

Current-voltage characteristics— Barrier height =0.69eV (as deposited), 0.74eV (300C annealed), 0.73eV (400 C annealed)

Condition As deposited 300C annealed 400C annealed

RMS(nm) 2.376E+01 4.461E+01 5.573E+01