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MICRON Ex.1017 p.1

THIN SOLID FILMS VOLUM E 249, N U MBER 2, SEPTEMBER 15, 1994

Contents

Synthesis and Characterization

Solution growth of As2S3 thin films from a thioacetamide bath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 J. D. Desai and C. D. Lokhande ( Kolhapur, India)

Electron spectroscopy fo r chemical analysis studies on electron beam evaporated CuOx thin films .. ... . .. .. .. . .. . . . . 140 G. P. Kothiyal, K. P. Muthe, J. C . Vyas, D . P. Gandhi, V. K. Handu, K. D. Singh, S. C. Sabha rwal and M . K . Gupta (Bombay, India)

Controlled growth of tin dioxide thin films by atomic layer epitaxy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 H. Viirola and L. Niinisto (Espoo, Finland)

Structural behaviour of direct-current sputtered and termally evaporated molybdenum thin films . . .... . ... .. .. . . ... . 150 S. Kacim ( Marrakech, Morocco), P. Delcambe, L. Binst , M. Jardinier-Offergeld and F . Bouillon (Bruxelles, Belgium)

Surface roughness reduction in a tomic layer epitaxy growth of titanium dioxide thin films . . . . . . . . . . . . . . . . . . . . . . . . . 155 M. Ritala, M. Leskelii ( Helsinki, Finland), L. Niinisto (Espoo, Finland), T. Prohaska, G . F riedbacher and M. Grasserbauer (Vienna, Austria)

Research on YSZ thin films prepared by plasma-CVD process . .. . .. .. .. .. . . .......... .. .. . .. . ... .. .. ... . . . ... .. 163 C.-B. Cao, J.-T. Wang (Shanghai, China), W.-J . Yu, D.-K. Peng and G .-Y. Meng (Hefei, China)

Surfaces, Interfaces and Colloidal Behaviour

Room temperature fo rmation and stability of compounds in metal couples of bulk-film type . . . . . . . . . . . . . . . . . . . . . . . 168 V. Simic and Z. Marinkovic (Zemun-Beograd, Yugoslavia)

Metallurgical, Protective and Hard Layers

The mechanism of interaction between Cl-containing gaseous phase and cemented carbides in the chemical vapour deposition process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 4

I. Yu. Konyashin ( Moscow, Russian Federation)

Ion beam mixing modification of sputter-deposited molybdenum fi lms on Si3N4 ceramics . . . . . . . . . . . . . . . . . . . . . . . . . . 183 M. Bai and X. Zhang (Lanzhou, China)

Electronics, Optics and Opto-electronics

In-situ X-ray diffraction measurements of silicide formation in the Co- Si system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 S. Zalkind , J. Pelleg, L. Zevin ( Beer Sheva, Israel) and B. M . Ditchek (Waltham, MA, USA)

Optical properties of Sb and SbOx films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 J. C. G. de Sande, F . Vega, C. N . Afo nso (Madrid, Spain), C. Ortega and J. Siejka (Paris, France)

The interaction kinetics and compound formation between electroless Ni - P and solder ... . .. . . . . . ... ... .. .. . .. . . . . 201 C.-Y. Lee and K .-L. Lin (Tainan, Taiwan)

Dispersive optical bistability in ZnS- ZnTe strained-layer superlattices grown on transparent substra tes Ba F2 by MOCVD 207 Y. M. Lu, X. W. Fan, L. C. Chen, Z . P. Guan and B. J. Yang (Changchun , China)

Langmuir-Blodgett, Biological and Related Films

Physical properties of a mixed conducting Langmuir- Blodgett film based on tetrathiafulvalene derivative with or without iodine oxidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210

Y. Xiao, Z. Yao and D. J in ( Lanzhou, China)

Plasma desorption mass spectrometry of Langmuir- Blodgett film s: dependence of salt form ation of arachidic acid monolayers on the subphase parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215

D. Brandl, Ch. Schoppmann, Ch. Tomaschko and H. Voit (Erlangen, Germany)

Elsevier Science S.A.

MICRON Ex.1017 p.2

11

Thin Film Devices, Sensors and Actuators

Effect of temperature on photoconduction and low frequency capacitance measurements on fJ-CuPc photovoltaic cells . 219 A. S. Riad (Minia, Egypt), S. M. Khalil (Alexandria, Egypt) and S. Darwish (Minia, Egypt)

Grain growth of laser-recrystallized polycrystalline and amorphous si licon films. . ...... . . . . ... .. . .. . . . .. .. . . .. . .. . 224 M.-J. Tsai and H.-C. Cheng (Hsinchu, Taiwan)

Condensed Matter Film Behaviour

Structure and photoelectrical behaviour of vacuum-evaporated metal-free phthalocyanine films . . . . . . . . . . . . . . . . . . . . . 230 S. Nespurek (Prague, Czech Republic), H. Podlesak and C. Hamann (Chemnitz, Germany)

Grand canonical ensemble Monte Carlo simulations of adsorption in energetically heterogeneous slit-like pores . . . . . . . 236 K. Karykowski , W. R:.i:ysko, A. Patrykiejew and S. Sokolowski (Lublin, Poland)

Effect of blend composition on the pyroelectric behaviour of cellulose acetate - polyvinyl acetate polymer blend films. . 241 D. S. Sagar and A. K. Sharma (Tirupati , India)

A method for the measurement of the thermal conductivity tensor in thin layers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 N. Gluzman and M . Auslender (Beer-Sheva, Israel)

Characterization of WNx metallization prepared by ion implantation of nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 D . Gregufova, T. Lalinsky, Z. Mozolova, D. Machajdik, I. Pochaba, I. Vavra and M. Porges (Bratislava, Slovakia)

The effect of ion bombardment on some properties of a-Si0.8Ge0.2 :H alloys prepared by ion beam-assisted reactive evaporation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254

K. Rajesh and D. E. Brodie (Waterloo, Ont. , Canada)

In situ characterization of ra re earth - CdTe heterostructures by ion beam analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 P. Gros, G . Fiat, D . Brun, B. Daudin, J . Eymery, E. Ligeon and A. C. Chami (Grenoble, France)

Author Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271

Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273

The publisher encourages the submission of a rticles in electronic form thus saving time and avoiding rekeying errors. A leaflet describing our requirements is ava ilable from the publisher upon request.

MICRON Ex.1017 p.3

144 Thin Solid Films, 249 ( 1994) 144- 149

Controlled growth of tin dioxide thin films by atomic layer epitaxy*

H. Viirola and L. Niinisto Laboratory of Inorganic and Analylical Chemislry, Helsinki Universily of Technology, FIN-02150 Espoo, Finland

(Received October 28, 1993; accepted March I)

Abstract

Tin dioxide thin films were deposited on glass substrates by atomic layer epitaxy using SnCl4 and H20 as reactants. The growth experiments were carried out in the temperature range of 300- 600 °C. The effect of growth parameters on the growth rate and crystal texture was studied . Spectrophotometry, X-ray diffraction, Rutherford backscattering spectroscopy, secondary ion mass spectrometry and sheet resistance measurements were used to characterize the films . The films were transparent and highly uniform with only small thickness variations. The films were polycrystalline with their crystallites having a preferred orientation, which depended on the growth temperature and film thickness .

1. Introduction

Tin dioxide is a frequently studied material for tech-nical applications. Sn02 is an n-type, wide-bandgap metal oxide semiconductor. Doped Sn02 films have high conductivity while retaining optical transparency in the visible region and a high reflectivity for infrared radiation. Because of their high stability, hardness and adherence to many types of substrates, these films are widely used in optoelectronics, e.g. as transparent con-ductive layers in liquid crystal and electroluminescent displays and in solar cells. Sn02 films are also used as antireftective and antistatic coatings. All these applica-tions of Sn02 require uniform coatings over large sub-strate areas.

Sn02 is also an important gas sensor material for the detection of combustible and toxic gases. Commercial sensors typically use Sn02 sintered powders. With the aid of thin film technology more cost-effective and reproducible devices can be constructed simultaneously minimizing device size and maximizing the speed of response.

Several methods including evaporation, sputtering, spray pyrolysis and chemical vapor deposition (CVD) have been used to deposit pure or doped Sn02 films. In addition to SnC14 [ 1- 3), different organic tin( IV) com-pounds [ 1, 4 - 7) are the most common precursors used in CVD. The earlier preparative approaches and prod-ucts obtained therewith have been reviewed by Jarzeb-ski and Marton [8 - 10) while Chopra et al. [ 11) have

*Presented in part at the 2nd International Symposium on Atomic Layer Epitaxy in Raleigh, NC, June 2- 5, 1992.

0040-6090/94/$7 .00 SSDI 0040-6090(94)06122-2

discussed, besides Sn02, the preparation techniques and properties of other transparent conductors as well. The various thin film techniques for depositing Sn02 gas sensors have been presented by Sberveglieri [ 12) and current trends in the development of ceramic, thick film and thin film Sn02 sensors have been summarized by Schierbaum et al. [ 13).

Atomic layer epitaxy (ALE) is a novel deposition technique which allows controlled growth of thin films [14). It has been applied mainly to grow II - VI and III - V semiconductors but considerable work has also been done in growing oxide thin films [ 15). Even when the films are deposited on polycrystalline or amorphous substrates the resulting polycrystalline films usually have crystallites with preferred orientation.

In order to assess the applicability of the ALE pro-cess for the growth of Sn02 thin films of controlled microstructure and texture, a systematic, applications-oriented study was undertaken involving several start-ing materials and characterization techniques as well as bulk samples for reference. Here we are presenting the results of Sn02 thin film growth by using the exchange reaction:

2. Experimental details

The Sn02 films were grown in a flow type ALE reactor described elsewhere [ 16). The reactant source materials SnC14 and H 20 were alternately introduced by pulsed doses into the reactor and their doses were separated by inert (99.999% N 2) purge gas pulsed doses. Deposition took place at a reduced pressure (approx. 2 mbar) in the

© 1994 - Elsevier Science S.A. All rights reserved

MICRON Ex.1017 p.4

H. Viiro/a , L. Niinisto / Tin dioxide thin film controlled growth by ALE 145

temperature range 300- 600 °C. The source temperatures of SnC14 and H 20 were from - 1 to 22 °C and 24 °C, respectively. SnC14 and H 20 were contained in ther-mostated glass reservoirs and they were introduced into the reactor through capillaries by means of their own vapor pressure. SnCl4 used was an analytically pure commercial reagent from Fluka. The pulse durations were 100- 900 ms for the reactants and 400 ms - 3 s for the purge gas. Soda lime glass (for T ~ 500 °C) and Corning 7059 glass (for T ~ 600 °C) were used as sub-strates; their size was 5 x 5 cm2 • The reactor chamber was made of Pyrex glass (for T ~ 500 °C) or quartz (for T = 500-600 °C).

Thicknesses and refractive indices of the films were evaluated by fitting measured transmittance curves ac-cording to the method developed and described by YWammi and Ranta-aho [ 17]. Transmittance spectra were recorded by a Hitachi U-2000 double beam spec-trophotometer controlled by a microcomputer. The measurement wavelength range was 370- 1000 nm. Profilometry was also used for thickness measurements (Veeco Instruments Dektak 3030 profilometer) . Steps were etched in the films with a slurry of zinc and hydrochloric acid. Crystal structure and crystallite ori-entation were determined by X-ray diffraction measure-ments with a Philips powder diffractometer MPD 1880 using Cu K cx radiation and () - 2() scans. Depth profiling was performed with secondary ion mass spectrometry (SIMS). The analysis was made using a VG IX70S double focusing magnetic sector secondary ion mass spectrometer with a Cs + primary beam at 10 keV en-ergy. The ion current was 20 nA and the pressure in the analytical chamber was 10- 7 Pa. The primary beam was focused to less than 10 µm in diameter and the beam was raster-scanned over an area of 400 x 300 µm 2 . A mass resolution of 1000 was used in this study. Negative secondary ions of 160 -, 37Cl -, and 120sn -were depth profiled. Film stoichiometry and chlorine residues were determined by Rutherford backscattering spectroscopy (RBS) with a 2.0 MeV 4He + beam at the Accelerator Laboratory of the University of Helsinki. The sheet resistances were measured by the four-point probe method in air at room temperature.

3. Results and discussion

3.1. Optimization of growth parameters As a result of preliminary studies at 500 °C the source

temperatures of H 20 and SnC14 were chosen to be 24 and 8 °C, respectively. The purge pulse durations ( 1- 3 s) were not observed to affect the growth rate in these studies. In order to avoid the mixing of reactant pulses during the optimization of pulse durations , the purge pulse of 3 s was used in the subsequent experiments.

Growth rate (A/cycle) 0.6 .-----------------

0.5

0.4

0.3

0.2

0.1

100 200 300 400 500 600

SnCl4 pulse duration (ms)

Fig. 1. Dependence of the growth rate a t 500 °C on the SnC14 pulse duration. H 20 pulse 300 ms ( • , both soda lime and Corning 7059 glass substrate).

Growth rate (A/cycle) 0.6 .----------------~

0.5

0.4

0.3

0.2

0. 1

0 100 200 300 400 500 600 700 800 900 1000 11 00

H20 pulse duration (ms)

Fig. 2. Dependence of the growth rate at 500 °C on the H 20 pulse duration. SnC14 pulse 200 ms ( • , both soda lime and Corning 7059 glass substrate).

After the preliminary studies the effect of reactant and purge pulse durations on the film growth rate at 500 °C was studied. The number of cycles used was 9000 for reactant pulse optimization and 3000 for purge pulse optimization.

The dependence of the growth rate on the SnCl4 pulse (H20 pulse 300- 600 ms) is presented in Fig. 1. The growth rate was the same on both substrate materi-als and was found to be independent of the SnC14 pulse between 100 and 500 ms indicating that enough SnC14 was flowing into the reactor to cover the entire surfaces of the substrates. In contrast, the growth rate increased with the increasing H 20 pulse (SnC14 pulse 200 ms) obtaining a constant value at 600 ms (Fig. 2). This indicates that a certain minimum pulse duration is needed to obtain a full coverage of the substrate.

The effect of the N 2 purge gas pulse duration on the growth rate was studied in the range of 400 ms- 3 s and 750 ms - 3 s for SnCl4 and H 20 pulses, respectively . No effect on the growth rate was observed.

The dependence of the growth rate on the growth temperature in the range 300- 600 °C is shown in Fig. 3. The number of cycles used was 5000. The growth rate increased with increasing temperature , namely from 0.14 or 0.11 A per cycle at 300 °C to 0.33 or 0.34 A per cycle at 500 °C for films deposited on soda lime glass or

MICRON Ex.1017 p.5

146 H. Viirola , L. Niinisto / Tin dioxide thin film controlled growth by A LE

Growth rate (A/cycle) 0.5

0.4

0.3

0.2

0.1

200 250 300 350 400 450 500 550 600 650 700

Temperature iCJ

Fig. 3. Growth rates on soda lime ( e ) and Corning 7059 ( D , ~ 500 °C, Pyrex glass chamber; • , ;;:> 500 °C, quartz chamber) glass substrates as a function of temperature. SnC14 , H 20 and purge pulse duration 200, 600 and 3000 ms, respectively.

Corning 7u59 glass, respectively. There was no signifi-cant difference between the growth rates at 500 and 550 °C indicating a narrow plateau of self-controlled growth. At 600 °C the growth rate decreased slightly. The slightly lower growth rate (approx. 0.30 A per cycle) in the quartz chamber compared with that in the Pyrex glass chamber was attributed to the small dimen-sional differences between the two chambers.

3.2. Dependence of the film thickness on reaction cycles

Film thickness as a function of the number of reac-tion cycles at 500 °C is presented in Fig. 4. It shows a linear relation with growth rate of 0.35 A per cycle on both substrate materials. This growth rate was much lower than that of a theoretical monolayer growth mode, which would correspond with 1.6- 2.3 A per cycle depending on the crystal orientation of the film [ 18). On the basis of theoretical studies of ALE with the ZnC12 + H 2S --.ZnS + 2HC1 reaction [19, 20) , it is plau-sible to assume that the reaction mechanism in the present case is complicated leading also to a growth rate which is only a fraction of that of the monolayer growth mode.

500

400

300

200

100

2000 4000 6000 8000 10000 12000 14000 16000

Number of reaction cycles

Fig. 4. Dependence of the film thickness on the number of cycles at 500 °C with the same pulse rates as for Fig. 3 ( • , both soda lime and Corning 7059 glass substrate).

3.3. Crystal texture X-ray diffraction (XRD) measurements made on

films grown on both substrates were almost identical and indicated that the films were polycrystalline and composed of tetragonal, rutile-type Sn02 [21). The rela-tive intensities of the reflections found differed from those reported for a Sn02 powder indicating a preferred orientation. This orientation was observed to depend on the film thickness and growth temperature.

The XRD patterns of films with various thicknesses (50 - 420 nm) grown at 500 °C are depicted in Figs. 5( a) - 5( d) . The (110) reflection was the most intense in films up to 110 nm thick. This reflection is also the most intense reported for a powder sample [21) . For 150 and 420 nm thick films the (211) reflection became domi-nant. In the 420 nm thick films the relative intensity of the ( 110) reflection was much reduced and the (301) reflection became intense.

The ( 110) reflection was also the most intense in the 55 - 145 nm and 140- 155 nm thick films deposited in the temperature range of 300- 450 °C and 550- 600 °C, respectively. At 550 and 600 °C the (110) line was particularly strong compared with other reflections ob-served, namely (211), (220) and (321) (Fig. 6).

3.4. Other properties The films were uniform showing only small thickness

variations (typically less than ± 2%) both in and per-pendicular to the gas flow direction, within the sub-strate length of 5 cm.

SIMS depth profile of a 205 nm thick Sn02 film deposited on a Corning 7059 glass substrate is pre-sented in Fig. 7 showing a uniform distribution of Sn, 0 and Cl atoms.

Stoichiometry and chlorine residues were quantita-tively determined by RBS. The RBS spectrum of a 300 nm thick Sn02 film deposited on a silicon ( 100) substrate (covered with a native oxide layer) is pre-sented in Fig. 8. The film was stoichiometric ( ± 2-3%). There was no difference in the stoichiometry between an as-prepared sample and an annealed one ( 12 h in 0 2 at 700 °C). The amount of chlorine was below the detection limit (approx. 0.2 at.%) of RBS. The amount of atoms (expressed in atoms cm- 2) was con-verted to geometrical thickness using the density of bulk Sn02 ( 6.95 g cm - 3) [22) . The calculated thickness was 320 nm and it was verified by fitting [ 17) the measured reflectance curve of the film. This indicated that the growth rate on silicon was the same as on glass substrates. Also the XRD pattern of the film deposited on silicon was almost similar to those of 300 nm thick films deposited on glass substrates. The difference was observed in the relative intensities of ( 310) and (321) reflections which were higher in the film deposited on silicon.

MICRON Ex.1017 p.6

H. Viiro/a , L. Niinistii / Tin dioxide thin fi lm controlled growth by ALE 147

1000 ~~~~~~~~~~~~~~~~~~~~~~

[co u n t s J

900

BOO

700

6 00

500

4 0 0

[count s]

900

BO O

700

60 0

500

4 0 0

300

f 11 O I

2 0 40

( 1 1 0 l

120 OJ

2 0 40

a

60 12 8 I B O

c

121 1 )

( 30 1 )

60 12 0 1 B O

1000 ~~~~~~~~~~~~~~~~~~~~·~~~

{counts J

900

BOO

700

600

500

400

300

20

( 110 )

( 20 0 )

40

b

I 211 l

60 [ 2 9 ] 80

1000 ,-~~~~~~~~~~~~~~~~~~~~~~

[ counts ]

900

800

7 00

600

500

4 00

3 0 0 I 11 O I

( 2 1 1 ) d

( 30 1 )

( 20 O J

Fig. 5. XRD patterns of Sn02 fi lms grown at 500 °C on Corning 7059 glass substrates: (a) 50 nm ; (b) 110 nm; (c) 150 nm; (d) 420 nm th ick.

{cou n ts ] ( 11 0)

3 000

25 00

2 000

15 00

1000

( 211 l

( 2 20) ( 321 l 5 00

A

20 40 60 [ 2 8 ] 80

Fig. 6. XRD pattern of a 150 nm thick Sn02 film grown at 550 °C on Corning 7059 glass substrate.

The resistivity as a function of the number of reac-tion cycles and the corresponding film thickness is presented in Table I. In general , the n-type conductivity of undoped Sn02 is primarily due to its non-stoi-chiometry, but in the present films deposited from SnC14 the incorporation of chlorine ions into the lattice may also contribute to the conductivity. The resistivity

106

0

105

Sn

104

~ Cl

Q.

~ 103 ;; c:

.2P

"' 102

101

JOO 0 10 20 30 40 50

Time (min)

Fig. 7. SIMS depth profile of a 205 nm thick Sn02 film deposited on Corning 7059 glass substrate.

of undoped Sn02 films is usually in the range of 10- 3 _ 10- 2 ncm[ll].

The refractive index at the wavelength 580 nm had a constant value of 2.0. Neither film thickness nor deposi-tion temperature was observed to have an effect on the refractive index.

MICRON Ex.1017 p.7

148 H. Viirola, L. Niinisto / Tin dioxide thin fi lm controlled growth by ALE

7000

8000

"il ~ 6000

.Q

~4000 ., ... § 3000 0

~ ~ 2000

~ 1000

0 100

2.0 MeV 'He Sn02 on Si

Si

0

Sn

200 800 400 500 600 Channel number

Fig. 8. RBS spectrum of a 300 nm thick Sn02 film deposited on silicon substrate ( e , experimental data; - , theoretical spectrum).

TABLE I. Resist ivity of Sn02 films as a function of number of reaction cycles and film thickness at 500 °C

Number of reaction cycles

Film thickness (nm)

Resistivity (!1 cm)

1500 3000 4500 6000

12500

T%

50 11 0 150 205 420

Soda lime glass

0.09 0.09 0.13 0.18 0.20

100,--~~~-;;;~~~----,;,--...;;;o-~~-----,

90

80 70

60 50

40

30 20

10

300 400 500 600 700 800 900 1000 1100

Wavelength {nm)

Corning 7059 glass

0.06 0.09 0.13 0.18 0. 17

Fig. 9. Transmittance spectrum of a Sn02-coated soda lime glass substra te relative to that of an uncoated substrate. Sn02 film thick-ness is 415 nm .

Highly transparent films in the visible region were produced under a ll reaction conditions. The transmit-tance spectrum of a Sn02-coated substrate relative to that of an uncoated substrate is presented in Fig. 9. The thickness of the Sn02 film on a soda lime substrate is 415 nm. The absolute transmittance of the Sn02 film was calculated by multiplying the relative transmittance of Fig. 9 by the transmittance of an uncoated substra te surface [23]. The absorption coefficient was then ob-tained at transmission maxima from an expression [23] for the transmittance of weakly absorbing films . For a 415 nm film on a soda lime glass substrate the calcu-lated absorption coefficients were 1520 and 480 cm - 1 at

the wavelengths of 428 and 556-561 nm, respectively. For a 418 nm film on a Corning 7059 glass substrate the calculated absorption coefficients were 1860 and 690 cm - 1 at the wavelengths of 432 and 561 - 566 nm, respectively.

4. Conclusions

Transparent layers of Sn02 can be reproducibly de-posited on glass substrates by an ALE process from SnCl4 and H20. The films were highly uniform with only small thickness variations (typically less than ± 2%) over a substrate a rea of 5 x 5 cm2 • The crystal-lites in the polycrystalline films showed a preferred orientation which depended on the film thickness and growth temperature. At 500 °C the ( 110) reflection was the most intense in thinner films ( ~ 110 nm thick). With increasing film thickness (;:;::: 150 nm) the (2 11) reflection became dominant. RBS measurement indi-cated that the film grown at 500 °C was stoichiometric and the amount of chlorine was below the detection limit of RBS. The resistivities of films deposited at 500 °C were in the range 0.06 - 0.20 Q cm.

Acknowledgments

The authors wish to thank Dr Eero Ristolainen for the SIMS analysis and Dr Eero Rauhala for the RBS measurements. The assistance of Ms Heini Moisa and Mr Pekka Soininen is gratefully acknowledged.

References

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( 1989), 3820. 7 J. Proscia and R. G. Gordon, Thin Solid Films , 2 14 ( 1992) 175. 8 Z. M. Jarzebski and J. P. Marton, J. Electrochem . Soc., 123

( 1976) I 99C. 9 Z. M. Ja rzebski and J. P. Marton, J. Electrochem. Soc., 123

( 1976) 299C. 10 Z. M. Jarzebski and J. P. Marton, J. Electrochem. Soc., 123

( 1976) 333C. 11 K. L. Chopra, S. Major and D. K. Pandya, Thin Solid Films, 102

( 1983) I. 12 G. Sberveglieri, Sensors A ctuators B, 6 ( 1992) 239. 13 K. D. Schierbaum, U . Weimar and W. Gopel , S ensors Actuators

B, 7( 1992) 709.

MICRON Ex.1017 p.8

H. Viirola, L. Niinisto / Tin dioxide thin film controlled growth by ALE 149

14 M. Leskelii and L. Niinisto, in T. Suntola and M. Simpson (eds.), Atomic Layer Epitaxy, Blackie, Glasgow, 1990, p. I.

15 L. Niinisto and M. Leskela, Thin Solid Films , 225 ( 1993) 130. 16 T. Suntola and J. Hyvarinen, Ann. Rev. Mater. Sci., 15 (1985)

177. 17 M. Ylilammi and T. Ranta-aho, Thin Solid Films , 232 ( 1993) 56. 18 M. Ylilammi, M.Sc. Thesis , Helsinki University of Technology,

Espoo, 1979.

19 T. A. Pakkanen, V. Nevalainen , M. Lindblad and P. Makkonen , Swf Sci. , 188 ( 1987) 456.

20 P. Hirva, Ann. A cad. Sci. Fenn. , Ser. A2, 239 ( 1992) 1. 21 Joint Committee on Powder Diffraction Standards, Card 21-1250. 22 CRC Handbook of Chemistry and Physics, CRC Press, Boca

Raton , FL, 69th edn. , 1988, p. B-140. 23 J. C. Manifacier, J. Gasiot and J. P. Fillard , J. Phys. E, 9 ( 1976)

1002.

MICRON Ex.1017 p.9