Effects of layer sequence and postdeposition annealing temperature on performance of La2O3 and HfO2 multilayer composite oxides on In0.53Ga0.47As for MOS capacitor application

(1)

This content has been downloaded from IOPscience. Please scroll down to see the full text.

Download details:

IP Address: 140.113.38.11

This content was downloaded on 25/12/2014 at 03:22

Please note that terms and conditions apply.

Effects of layer sequence and postdeposition annealing temperature on performance of

La2O3 and HfO2 multilayer composite oxides on In0.53Ga0.47As for MOS capacitor

application

View the table of contents for this issue, or go to the journal homepage for more 2014 Appl. Phys. Express 7 031201

(http://iopscience.iop.org/1882-0786/7/3/031201)

(2)

Effects of layer sequence and postdeposition annealing temperature on performance

of La

2

O

3

and HfO

2

multilayer composite oxides on In

0.53

Ga

0.47

As for MOS capacitor application

Wen-Hao Wu1_{, Yueh-Chin Lin}1_{, Ting-Wei Chuang}1_{, Yu-Chen Chen}1_{, Tzu-Ching Hou}1_{, Jing-Neng Yao}1_,

Po-Chun Chang1_{, Hiroshi Iwai}2_{, Kuniyuki Kakushima}2_{, and Edward Yi Chang}1,3

1_{Institute of Materials Science and Engineering, National Chiao-Tung University, Hsinchu 30010, Taiwan, R.O.C.} 2_{Tokyo Institute of Technology, Meguro, Tokyo 152-8550, Japan}

3_{Department of Electronics Engineering, National Chiao-Tung University, Hsinchu 30010, Taiwan, R.O.C.} E-mail: [email protected]

Received November 20, 2013; accepted January 29, 2014; published online February 13, 2014

In this paper, we report on high-k composite oxides that are formed by depositing multiple layers of HfO2and La2O3on In0.53Ga0.47As for MOS device application. Both multilayer HfO2(0.8 nm)/La2O3(0.8 nm)/In0.53Ga0.47As and La2O3(0.8 nm)/HfO2(0.8 nm)/In0.53Ga0.47As MOS structures were investigated. The effects of oxide thickness and postdeposition annealing (PDA) temperature on the interface properties of the composite oxide MOS capacitors were studied. It was found that a low CET of 1.41 nm at 1 kHz was achieved using three-layer composite oxides. On the other hand, a small frequency dispersion of 2.8% and an excellent Dit of 7.0' 1011cm%2&eV%1 can be achieved using multiple layers of La2O3(0.8 nm) and HfO2(0.8 nm) on the In0.53Ga0.47As MOS capacitor with optimum thermal treatment and layer thickness.

R

ecently, In_xGa_1¹xAs metal–oxide–semiconductor ﬁeld-effect transistors (MOSFETs) have been widely investigated owing to the high electron mobility of the In_xGa_1¹xAs material and the much lower turn-on voltage of In_xGa_1¹xAs devices than of conventional Si devices.1–4)

Rare-earth oxides (REOs) exhibit high dielectric constant and high conduction band offset with respect to silicon and are currently being investigated as high-k gate dielectrics for future ultrascaled devices.5–9) Among the binary REOs, La2O3 is considered as one of the most promising gate

dielectric materials owing to its high ¬ and high band-gap energy. However, strong interdiffusion between InGaAs and La2O3 occurs after postdeposition annealing (PDA) when

La2O3is in direct contact with the InxGa1¹xAs material.10)In

recent years, several groups have studied composite oxides such as HfO2/Al2O3,11) CeO2/Al2O3,12) and CeO2/HfO213)

on InGaAs for next-generation device applications.

In this work, high-k composite oxides of La2O3and HfO2

are investigated for n-In0.53Ga0.47As MOS capacitor

applica-tion. HfO2 is chosen because it has ak of 25 and an energy

band gap of 5.5 eV, and is known to demonstrate inversion behavior with In_xGa_1¹xAs.14–18) _{An in situ molecular beam}

deposition (MBD) system was used to deposit the multiple layers of HfO2(0.8 nm) and La2O3 (0.8 nm) on n-In0.53

-Ga0.47As. The effects of PDA temperature and annealing gas

atmosphere on the interface properties and device perform-ances of HfO2/La2O3/n-In0.53Ga0.47As and La2O3/HfO2/

n-In0.53Ga0.47As MOS capacitors are studied.

The device structure includes a 100 nm In0.53Ga0.47As layer

with 5© 1017cm¹3 Si doping grown on the n-InP substrate by molecular beam epitaxy (MBE). The device process can be divided into four parts: surface treatment, oxide deposi-tion, gate metal deposideposi-tion, and ohmic contact formation. The wafers were ﬁrst cleaned in 4% HCl solution for 3 min, followed by an (NH4)2S solution dip for 30 min at room

temperature. Then, the wafers were loaded into the MBD system to deposit the HfO2(0.8 nm)/La2O3(0.8 nm)

multi-layers on n-In0.53Ga0.47As at 300 °C. The 10 layers of HfO2

(0.8 nm) and La2O3(0.8 nm) MOS capacitors were fabricated

and annealed at temperatures ranging from 400 to 550 °C in N2for 5 min. Then, Ni/Au was deposited on the front side of

the wafer as the gate contact metal and Au/Ge/Ni/Au was

deposited on the back side of the n+ InP substrate as ohmic metal; both were deposited using an e-beam evaporator and the ohmic metal was annealed at 250 °C for 30 s for optimum contact resistance.

Figure 1 shows the X-ray photoelectron spectros-copy (XPS) spectra of the HfO2(0.8 nm)/La2O3(0.8 nm)/

n-In0.53Ga0.47As and La2O3 (0.8 nm)/HfO2(0.8 nm)/n-In0.53

-Ga0.47As composite oxide structures annealed at 400, 500,

and 550 °C in N2for 5 min. The As 3d, Ga 2p3/2, In 3d5/2,

and O 1s XPS spectra of the samples with different PDA temperatures were analyzed to determine the ﬁlm composi-tions and interface properties. In general, with increasing PDA temperature, more interactions between oxides and semiconductors occur, and the number of As–As bonds is reduced owing to the high-temperature annealing, as indi-cated by As 3d in Fig. 1. When the PDA temperature was increased to 500 °C, the amounts of As-, Ga-, and In-related oxides decreased for both composite oxide structures. The amount of La2O3 increased for the La2O3/HfO2/n-In0.53

-Ga0.47As structure, as indicated by the XPS O 1s peak in

Fig. 1. The slight reduction of the native oxides could be explained by the conversion of As–O, Ga–O, and In–O bonds to InAs, GaAs, and La2O3 during thermal annealing for

the La2O3/HfO2/n-In0.53Ga0.47As structure. However, the

amount of La2O3 that diffused into InGaAs increased with

temperature for the HfO2/La2O3/n-In0.53Ga0.47As structure.

The 500 °C annealing not only converted the As–O, Ga–O, and In–O bonds to InAs and GaAs bonds but also resulted in the increase in the amount of La2O3diffusing into InGaAs

for the HfO2/La2O3/n-In0.53Ga0.47As structure. Furthermore,

the amounts of As-, Ga-, and In-related oxides increased signiﬁcantly for both composite oxide structures when the PDA temperature was increased to 550 °C, as indicated by the As 3d, Ga 2p_3/2, and In 3d_5/2 spectra in Fig. 1. This indicates that at the PDA temperature of 550 °C, the diffusions of As, Ga, and In into the oxide layers were quite signiﬁcant for both composite oxide structures.

Figure 2 shows the comparison of capacitance–voltage (C–V) curves at 1 MHz for the ﬁve layers of HfO2(0.8 nm)/

La2O3(0.8 nm) and the ﬁve layers of La2O3(0.8 nm)/

HfO2(0.8 nm) composite oxides on n-In0.53Ga0.47As MOS

capacitors, and the HfO2 (8 nm)/n-In0.53Ga0.47As MOS http://dx.doi.org/10.7567/APEX.7.031201

(3)

capacitor. The electrical characteristics of the composite oxide MOS capacitor were markedly improved when the devices were annealed at the PDA temperature of 500 °C in N2 for 5 min. The dielectric constants of 15.2 and 14.8

were estimated for the ﬁve layers of the La2O3(0.8 nm)/

HfO2(0.8 nm) and HfO2 (0.8 nm)/La2O3(0.8 nm) composite

oxides on n-In0.53Ga0.47As MOS capacitors, respectively.

Some reports show that the semiconductor elements will diffuse into the oxide after annealing, resulting in the decrease in the oxide dielectric constant and the increase in the device capacitance equivalent thickness (CET).19)In this case,

CET ¼ "0"SiO2

Cðaccum:@ f ¼ 1 kÞ;

where C(accum.@ f = 1 kHz) is the capacitance of the accumulation region at frequency= 1 kHz, ¾0is the vacuum

permittivity, and ¾SiO2 is relative permittivity of SiO2. A

CET of 2.2 nm at 1 kHz with a low interface trap den-sity (Dit) of 7.0© 1011cm¹20eV¹1was achieved, as estimated

by the conductance method20) _for _the _La

2O3/HfO2/

n-In0.53Ga0.47As capacitor, as shown in Fig. 3(a). A higher

Ditand a lower CET were obtained for the HfO2(0.8 nm)/

La2O3(0.8 nm)/n-In0.53Ga0.47As device owing to the strong

interaction between La2O3 and n-In0.53Ga0.47As. When the

PDA temperature was increased, the interaction between the oxide and the semiconductor increased. The Gp/wqA vs frequency plot and Dit vs energy plot for the 5 layers

of La2O3(0.8 nm)/HfO2 (0.8 nm) and HfO2(0.8 nm)/

La2O3(0.8 nm) on n-In0.53Ga0.47As MOS capacitors with

PDA at 500 °C are shown in Figs. 4(a) and 4(b), respec-tively. From Fig. 4(b), the lowDitof 7.0© 1011–1.0 © 1012

cm¹20eV¹1 in the energy range of 0.47–0.44 eV above the In0.53Ga0.47As valence band maximum was obtained for

the La2O3 (0.8 nm)/HfO2 (0.8 nm)/n-In0.53Ga0.47As device.

When the PDA temperature was increased to 550 °C, the capacitance decreased from 1.46 (500 °C) to 1.39 µF/cm2

(550 °C) and 1.44 (500 °C) to 1.20 µF/cm2 _{(550 °C) for}

the La2O3/HfO2/n-In0.53Ga0.47As structure and HfO2/La2O3/

n-In0.53Ga0.47As structure, respectively. The larger

capaci-tance decrease, particularly for the HfO2(0.8 nm)/La2O3

(0.8 nm)/n-In0.53Ga0.47As capacitor, was due to the strong

interdiffusion between La2O3and InGaAs after

high-temper-ature annealing. The C–V characteristics of the composite oxide capacitors with PDA temperatures of 400, 500, and 550 °C and different oxide thicknesses are compared in Table I.

Fig. 1. As 3d, Ga 2p3/2, In 3d5/2, and O 1s XPS spectra of La2O3(0.8 nm)/HfO2(0.8 nm)/n-In0.53Ga0.47As and HfO2(0.8 nm)/La2O3(0.8 nm)/

n-In0.53Ga0.47As with postdeposition annealing temperatures of 400, 500, and 550 °C in nitrogen gas for 5 min.

Fig. 2. Comparison ofC–V characteristics of HfO2(8 nm)/

n-In0.53Ga0.47As, La2O3(0.8 nm)/HfO2(0.8 nm)/n-In0.53Ga0.47As and

HfO2(0.8 nm)/La2O3(0.8 nm)/n-In0.53Ga0.47As MOS capacitors.

Appl. Phys. Express 7, 031201 (2014) W.-H. Wu et al.

(4)

Furthermore, the device performance was further improved by forming gas (5% H2+ 95% N2) annealing. Figure 5

shows theC–V characteristics of the 5 layers of La2O3(0.8

nm)/HfO2 (0.8 nm) and the 5 layers of La2O3(0.8 nm)/

HfO2(0.8 nm) on n-In0.53Ga0.47As MOS capacitors with

PDA at 500 °C in forming gas for 5 min. Frequency dis-persion was improved owing to H2 treatment,21) especially

for the La2O3/HfO2/n-In0.53Ga0.47As structure. The

fre-quency dispersions were reduced from 3.5 to 2.9% and 2.8

to 2.6% for the La2O3/HfO2/n-In0.53Ga0.47As structure and

HfO2/La2O3/n-In0.53Ga0.47As structure, respectively.

How-ever, the capacitances of both devices decreased after forming (a)

(b)

Fig. 3. _{C–V characteristics of 5 layers of (a) La}2O3(0.8 nm)/

HfO2(0.8 nm) and (b) HfO2(0.8 nm)/La2O3(0.8 nm) on n-In0.53Ga0.47As

MOS capacitors with PDA at 500 °C in N2gas for 5 min.

Table I. Comparison ofC–V characteristics of HfO2(8 nm)/n-In0.53Ga0.47As, La2O3(0.8 nm)/HfO2(0.8 nm)/n-In0.53Ga0.47As and HfO2(0.8 nm)/

La2O3(0.8 nm)/n-In0.53Ga0.47As MOS capacitors.

Device oxide structure

CET at 1 kHz (nm) Accumulation capacitance (µF/cm2₎ Frequency dispersion (%) Dit (1012_cm¹2_0eV¹1₎ at 1 kHz at 1 MHz 8 nm HfO2PDA at 500 °C in N2 2.71 1.30 1.07 5.1 2.58

(La2O3/HfO2)© 5 PDA at (°C)

400 N2 — — — — 25.10 500 N2 2.21 1.60 1.46 3.5 0.70 Forming gas 2.34 1.51 1.42 2.9 1.05 550 N2 2.23 1.58 1.39 3.5 0.90

400 N2 2.26 1.56 1.35 4.2 2.91 500 N2 2.25 1.57 1.44 2.8 0.97 Forming gas 2.50 1.41 1.32 2.6 1.12 550 N2 2.52 1.40 1.20 4.2 1.80 (a) (b)

gate biases and (b)Ditvs energy curves after 500 °C PDA for 5 layers of

La2O3(0.8 nm)/HfO (0.8 nm) and HfO2(0.8 nm)/La2O3(0.8 nm) on

n-In0.53Ga0.47As MOS devices.

(5)

gas annealing. The device CET was improved for the 3 and 4 layers of the La2O3(0.8 nm)/HfO2(0.8 nm) structure on the

n-In0.53Ga0.47As device after PDA at 500 °C for 5 min in N2

atmosphere. TheC–V curves for the 3-layer device are shown in Fig. 6; for the composite oxide with 3 and 4 layers of the La2O3 (0.8 nm)/HfO2(0.8 nm) structure, the CETs were

reduced to 1.77 and 1.41 nm, respectively, after 500 °C annealing, as measured at 1 kHz.

In summary, high-k composite dielectrics composed of La2O3 and HfO2 layers on n-In0.53Ga0.47As for MOS

capacitor application are investigated. Overall, the La2O3/

HfO2 structure on the n-In0.53Ga0.47As MOS capacitor

demonstrates better performance than the HfO2/La2O3

structure on the n-In0.53Ga0.47As MOS capacitor after thermal

treatment owing to the interaction between the composite oxides and InGaAs materials. A low CET of 1.41 nm at 1 kHz for 3 layers, a small frequency dispersion of 2.6%, and an excellentDitof 7.0© 1011cm¹20eV¹1can be achieved using

multiple layers of La2O3(0.8 nm) and HfO2(0.8 nm) on

In0.53Ga0.47As MOS capacitors with PDA at 500 °C. Acknowledgment The authors would like to thank the Ministry of Education and the National Science Council of the Republic of China for supporting this research under contract Nos. 102-2911-I-009-302 and 101-2221-E-009-173-MY2.

1) Y. Xuan, Y. Q. Wu, H. C. Lin, T. Shen, and P. D. Ye,IEEE Electron Device Lett.28, 935 (2007).

2) N. Goel, P. Majhi, C. O. Chui, W. Tsai, D. Choi, and J. S. Harris,Appl. Phys. Lett._{89, 163517 (2006).}

3) Y. Xuan, Y. Q. Wu, and P. D. Ye,IEEE Electron Device Lett.29, 294 (2008).

4) Y. Xuan, H. C. Lin, P. D. Ye, and G. D. Wilk,Appl. Phys. Lett.88, 263518 (2006).

5) C.-H. Chen, I. Y.-K. Chang, J. Y.-M. Lee, and F.-C. Chiu,Appl. Phys. Lett. 92, 043507 (2008).

6) W.-H. Kim, W. J. Maeng, M.-K. Kim, J. Gatineau, and H. Kim,

J. Electrochem. Soc.158, G217 (2011).

7) W.-H. Kim, M.-K. Kim, W. J. Maeng, J. Gatineau, V. Pallem, C. Dussarrat, A. Noori, D. Thompson, S. Chu, and H. Kim,J. Electrochem. Soc.158, G169 (2011).

8) M. S. Rahman, E. K. Evangelou, I. I. Androulidakis, and A. Dimoulas,

Electrochem. Solid-State Lett.12, H165 (2009).

9) Y. Nishikawa, N. Fukushima, N. Yasuda, K. Nakayama, and S. Ikegawa,

Jpn. J. Appl. Phys.41, 2480 (2002).

10) Y.-C. Lin, C.-H. Chang, K. Kakushima, H. Iwai, T.-E. Shie, G.-N. Huang, P.-C. Lu, T.-C. Lin, and E. Y. Chang,ECS Trans.35 [3], 397 (2011).

11) R. Suzuki, N. Taoka, M. Yokoyama, S. Lee, S. H. Kim, T. Hoshii, T. Yasuda, W. Jevasuwan, T. Maeda, O. Ichikawa, N. Fukuhara, M. Hata, M. Takenaka, and S. Takagi,Appl. Phys. Lett.100, 132906 (2012).

12) L. Yan, L. B. Kong, Q. Li, and C. K. Ong,Semicond. Sci. Technol._{18, L39} (2003).

13) K. Karakaya, B. Barcones, Z. M. Rittersma, J. G. M. van Berkum, M. A. Verheijen, G. Rijnders, and D. H. A. Blank,Mater. Sci. Semicond. Process. 9, 1061 (2006).

14) H.-D. Trinh, Y.-C. Lin, H.-C. Wang, C.-H. Chang, K. Kakushima, H. Iwai, T. Kawanago, Y.-G. Lin, C.-M. Chen, Y.-Y. Wong, G.-N. Huang, M. Hudait, and E. Y. Chang,Appl. Phys. Lett.97, 042903 (2010).

15) É. O’Connor, S. Monaghan, R. D. Long, A. O’Mahony, I. M. Povey, K. Cherkaoui, M. E. Pemble, G. Brammertz, M. Heyns, S. B. Newcomb, V. V. Afanas_{’ev, and P. K. Hurley,}Appl. Phys. Lett._{94, 102902 (2009).}

16) Y. Xuan, Y. Q. Wu, T. Shen, T. Yang, and P. D. Ye,IEDM Tech. Dig., 2007, p. 637.

17) F. Zhu, H. Zhao, I. Ok, H. S. Kim, M. Zhang, S. Park, J. Yum, S. Koveshnikov, V. Tokranov, M. Yakimov, S. Oktyabrsky, W. Tsai, and J. C. Lee,IEEE CSIC Symp., 2008, p. 100.

18) H.-D. Trinh, Y.-C. Lin, H.-C. Wang, C.-H. Chang, K. Kakushima, H. Iwai, T. Kawanago, Y.-G. Lin, C.-M. Chen, Y.-Y. Wong, G.-N. Huang, M. Hudait, and E. Y. Chang,Appl. Phys. Express5, 021104 (2012).

19) L. Sambuco Salomone, J. Lipovetzky, S. H. Carbonetto, M. A. García Inza, E. G. Redin, F. Campabadal, and A. Faigón,J. Appl. Phys._{113, 074501} (2013).

20) E. H. Nicollian and A. Goetzberger,Appl. Phys. Lett.7, 216 (1965).

21) H. D. Trinh, E. Y. Chang, P. W. Wu, Y. Y. Wong, C. T. Chang, Y. F. Hsieh, C. C. Yu, H. Q. Nguyen, Y. C. Lin, K. L. Lin, and M. K. Hudait,Appl. Phys. Lett._{97, 042903 (2010).} -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 0.5 1.0 1.5 2.0 2.5 3.0 Capacitance (uF/cm 2 ) Gate Voltage (V) 1kHz 1MHz

Fig. 6. C–V characteristics of three layers of La2O3(0.8 nm)/

HfO2(0.8 nm) on n-In0.53Ga0.47As MOS capacitors with PDA at 500 °C in

nitrogen gas for 5 min.

(a)

(b)

Fig. 5. C–V characteristics of the ﬁve layers of (a) La2O3(0.8 nm)/

HfO2(0.8 nm) and (b) HfO2(0.8 nm)/La2O3(0.8 nm) on n-In0.53Ga0.47As

MOS capacitors with PDA at 500 °C in forming gas for 5 min.

Appl. Phys. Express 7, 031201 (2014) W.-H. Wu et al.