Optical Properties of Crystalline Ta2o5 Thin Films

Optical Properties of Crystalline Ta2O5 Thin Films

H. Darmasetiawan1, M. Nur Indro1, S. G. Sukaryo1, Irzaman1, M Hikam2, Na Peng Bo2, M. Barmawi3

1Department of Physics, FMIPA IPB, Jl. Raya Pajajaran Bogor, Indonesia Telp. : 62-(0251)-326166, fax. : 62-(0251)-326166,e-mail : [email protected] 2Department of Physics, FMIPA University Indonesia, Kampus Depok, Indonesia Telp. : 62-(021)-9137323, fax. : 62-(021) 7863441,e-mail : [email protected] 3Department of Physics, FMIPA ITB, Jl. Ganesha 10 Bandung, Indonesia Telp. 62-(022) 251 1848, fax. : 62-(022) 7863441

ABSTRACT

Thin tantalum oxide (Ta2O5) films on Si(100) using The Chemical Solution Deposition (CSD) method.

X-ray diffraction (XRD), Scanning electron microscopy (SEM), Spectrophotometer UV-VIS analysis measurement were employed to characterise the films. The growth condition to obtain enough quality epitaxial of Ta2O5 carried out by spin coating at 2000 and 3000 rpm for 30 seconds, and then annealing at 900oC for 15 hours. The microstructure and crystallinity of thin films were investigated by XRD preffered orientation (001), (010), (200); surface analysis and thickness films by SEM, thin films were

heterogen; optical characterization Ta2O5 by Spectrophotometer ( = 400 – 800 nm) carried out refractive index (n) was 1.53.

Keywords : Ta2O5, thin films, CSD method, spectrophotometer, refractive index.

I. INTRODUCTION

Tantalum oxide (Ta2O5) films are of considerable interest for a range of application, including optical waveguide devices, high temperature resistors, and oxygen sensors.[1] Because of their high dielectric constant, in recent years they have received increasing attention as a possible alternative dielectric to replace thin SiO2 layers as capacitor insulators in high density dynamic random access memories, such as DRAM and in ultra large scale integrated (ULSI) devices[1].

Tantalum oxide films can be formed by various methods, such as Chemical Solution Deposition (CSD)

[1,2,3,], Metal Organic Chemical Vapor Deposition (MOCVD)[4], Plasma Enhanced Chemical Vapor

Deposition (PECVD)[5,6], Low Pressure Chemical Vapor Deposition (LPCVD)[7], Reactive

Magnetron Sputtering [8].

------Presented in ICMAT 2001, 1 – 6 July 2001, Singapore 1 CSD Method is of particular interest because of its good control of stoichiometry, ease of fabrication and low temperature synthesis. It is relatively new and requires a greater understanding to optimize film quality. Crystallization mechanisms in CSD-derived thin films are different from phenomena associated with vapor phase epitaxy. It was reported that CSD derived thermodinamically stable.

II. METHODOLOGY

Procedural Ta2O5 thin films were fabricated by CSD methods using 1.0156 gram tantalum ethoxide

[Ta(OC2H5)5, 99.98 %] as precursor in 5 ml 2-methoxyethanol [H3COOCH2CH2OH, 99.9 %] was used as solvent was introduced under mixing by Ultrasonic Model Branson 2210 at 1 hour. A clear liquid resulted. After 20 mintues of standing at room temperature, this solution acquired a milky appearance.

1 drop of acetic acid was intoduced into the solution and mixed. The cloudy appearance disappeared. It contained equivalent 0.5 M Ta2O5. After 2 hours of aging, the solution described above was applied on a silicon (100) substrate with measure 25 mm x 25 mm with a spin coating 2000 and 3000 rpm for 30 seconds. The coated was then baked at 900oC for 15 hours on air atmosphere in Furnace Model

Nabertherm Type 27. The structure of the films was analyzed by x-ray diffraction (XRD). The XRD pattern were recorded on a Diano type 2100E diffractometer using CuK radiation at 30 KV and 30 mA (900 watt). The surface morphology and thickness of the films was examined by SEM JEOL type

JSM-35C. The optical characterization Ta2O5 by Spectrophotometer ( = 400 – 800 nm) type Varian

Cary 2415. Step by research to explain within flow diagram in Figure 1.

Primary goal of this experiment is to present some refractive index (n) is Eq. (1) namely : [9] 2 n 1 R  , (1) n 1 where R = reflectance (%).

Presented in ICMAT 2001, 1 – 6 July 2001, Singapore 2 1.0156 gram Tantalum ethoxide 5 ml 2-methoxyethanol [Ta(OC H ) , 99.98 %] [H COOCH CH OH, 99.9 %] 2 5 5 3 2 2

Mixing by Ultrasonic Model Branson 2210 at 1 hour

1 drop of acetic acid

0.5 M Ta O precursor 2 5

Spin coating at 2000 and 3000 rpm for 30 seconds on to Si(100) substate with measure 25 mm x 25 mm

Post-deposition annealing at 900oC for 15 hours on air atmosphere in Furnace Model Nabertherm Type 27 to get crystalline Ta O thin films 2 5

Ta O Thin films 2 5

Analyze and characterization : the structure and crystallinity of the films (XRD Diano type 2100E), surface morphology and thickness (SEM JEOL type JSM-35C), refractive index (Spectrophotometer type Varian Cary 2415)

Figure 1. Flow diagram of Step by Step Research

III. RESULT AND DISCUSSION

Figure 2 shows the structure and crystallinity of Ta2O5 thin films were investigated by XRD, increase angular velocity from 2000 rpm to 3000 rpm preffered orientation Ta2O5 (201) and (002) disappeared,

 ωR ν θ  because influence the velocity deviation factor on Coriolis Effect   . Figure 3 and  ωR 

Presented in ICMAT 2001, 1 – 6 July 2001, Singapore 3 Figure 4 shows the morphology film by SEM magnification x10000 surface thin films were heterogen

and cross section carried out thickness (1) was 2100 nm for film  = 2000 rpm and 2 was 1400 nm

for  = 3000 rpm, 1 > 2 because increase angular velocity to give increase vapour solution. Plot thickness films () versus angular velocity () shows in Figure 5. Figure 6 shows The R (%) versus - wavelength of spectrophotometer (nm) characteristics of T2O5, R maximum was 4.44 % at 400 nm, with formula (1) carried out refractive index (n) = 1.53.

2000 ) 1800 ) 0 u ) 0 .

1600 ) 0 1 ( 1 1 a )

i 0 0 ( 1

1400 ) ( 0

S 0 0 ( 5

2 y 0 5 ) O 1200 ( t 2 2 0 O a 5 ( i 2 2 a T 5 O 0 s 1000 2 T ( a O

2 5 n a T

800 O T e 2 a t

600 T 3000 rpm n I 400 200 2000 rpm 0 5 15 25 35 45 55 65 75 Diffraction angle (degree)

Figure 2. The structure and crystallinity by XRD of Ta2O5 thin films on Si (100) substrate influence angular velocity

(a) (b)

Figure 3. (a) The morphology Ta2O5 film by SEM magnification x10000 for  = 2000 rpm,

(b) Cross section film thickness (1) was 2100 nm.

Presented in ICMAT 2001, 1 – 6 July 2001, Singapore 4 (a) (b)

Figure 4. (a) The morphology Ta2O5 film by SEM magnification x10000 for  = 3000 rpm,

(b) Cross section film thickness (2) was 1400 nm.

) 2500 m n (

s 2000 m l i f

1500 s s e

n 1000 k c i

h 500 T

0 1750 2000 2250 2500 2750 3000 3250 Angular velocity (rpm)

Figure 5. Plot thickness films () versus angular velocity ()

) 4.4 % (

c 4 n a t 3.8 c e l

f 3.6 e

R 3.4 3.2 3 400 450 500 550 600 650 700 750 800 wavelength spectrophotometer (nm)

Presented in ICMAT 2001, 1 – 6 July 2001, Singapore 5 Figure 6. The R (%) versus -wavelength of spectrophotometer (nm) characteristics of T2O5 films.

Presented in ICMAT 2001, 1 – 6 July 2001, Singapore 6 IV. CONCLUSIONS

The growth condition to obtain enough quality of Ta2O5 thin films carried out by spin coating at 1

o = 2000 and 2 = 3000 rpm for 30 seconds, and then annealing at 900 C for 15 hours. Increase angular velocity from 2000 rpm to 3000 rpm to improve crystallinity films, finally preffered orientation Ta 2O5

(201) and (002) disappeared, and decrease thickness films (1 > 2). Optical characterization Ta2O5 by

Spectrophotometer ( = 400 – 800 nm) carried out refractive index was 1.53.

ACKNOWLEDGMENT

This work was supported by DCRG URGE Project, The Ministry of Education, The Republic of

Indonesia, under contract No. 011/DCRG/URGE/2000.

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