GB2192644A

GB2192644A - Transparent conductive film and the production thereof

Info

Publication number: GB2192644A
Application number: GB08713076A
Authority: GB
Inventors: Yukio Ide; Teruyuki Ohnuma; Narihito Kojima
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1986-06-04
Filing date: 1987-06-04
Publication date: 1988-01-20
Also published as: GB8713076D0; DE3718789A1; JPS62287513A

Description

1 GB2192644A 1 SPECIFICATION pound or during the heat treatment, thereby

to obtain a film mainly containing In, 0 and C. In Transparent conductive filrn and the pro- a modification of this method the heat treat duction thereof ment step is replaced by a plasma annealing 70 treatment step.

This invention relates to a transparent conduc- In the following description, reference will tive film having good transparency and electri- be made to the accompanying drawings, in cal conductivity and to a method for the pro- which:

duction thereof. Figure I is a schematic drawing illustrating a Transparent conductive films have found 75 plasma CVD device for use in the preparation utility as transparent conductive glasses, tran- of a film of the invention; sparent conductive films, transparent elec- Figures 2A and 2B are, respectively, IR trodes, antistatic films or electromagnetic shi- spectra of a film before and after heat treat elds. They have been used, for instance, in ment; displays, photosensors, solar batteries, light- 80 Figure 3 is a thermal- decomposition mass emitting elements, permselective membranes spectrum of a film before heat treatment; and transparent heaters. Figure 4 shows X-ray diffraction spectrum Known transparent conductive films include of a film before and after heat treatment, and the ITO film [ln2O,(Sn)] and the NESA film Figure 5 shows the spectral transmittance of [Sn02(Sb)]. However, each of these suffers 85 a film before and after heat treatment.

from some drawbacks from a technical point The atomic ratio of In, 0 and C in the tran of view. sparent conductive film of the invention prefer The ITO film does not have fully satisfactory ably falls in the range given by the formula:

transparency and is expensive. It has insuffici ent chemical stability so that it unavoidably 90 In,OYC, succumbs to loss of conductivity due to diffu sion of alkali metal ions, such as Nal- and K1, in which the sum of x, y, and z is 1; from the glass substrate. Since it is vulnerable x is from 0.1 to 0.6 (inclusive), more prefera to a reducing atmosphere, the conductive film bly from 0.2 to 0.6 (inclusive); will be, during the fabrication of an a-Si:H 95 y is from 0.2 to 0.6 (inclusive), more prefera solar battery by the plasma CVD method us- bly from 0.3 to 0.6 (inclusive); and ing SiH4 gas, reduced by the atomic hydrogen z is from 0.005 to 0.5 (inclusive), more pre (HO) in the plasma and consequently the film ferably from 0.01 to 0.3 (inclusive).

will suffer from a loss of conversion effici- The structure of the transparent conductive ency. 100 film may be crystalline or amorphous; how The NESA film is better in terms of chemi- ever, a transparent conductive film of a poly cal stability than ITO film, but inferior in terms crystalline or partially microcrystalline texture of conductivity and transparency. It is rela- possesses higher conductivity than one having tiveiy difficult to etch chemically, and, there- an amorphous texture.

fore, it has the disadvantage that the pattern- 105 The transparent conductive film may also ing treatment required for the formation of an contain other elements, such as Si, Ge, Sn, H, electrode and the like cannot be easily ef- F, Cl, Br and 1, if necessary, to further, im fected. prove conductivity. The film can also contain The transparent conductive films of the con- hydrogen, derived from the alkyl indium com ventional type mentioned above have been 110 pound, to satisfy or partlially satisfy unsatu produced, for instance, by the spattering rated (free claying) bonds.

method, ion beam deposition method or the The thickness of the transparent conductive CVD method. Since these conventional film is suitably approximately from 50 to methods require relatively high substrates tem15,000 A, preferably 100 to 8,000 A and peratures to give desirable characteristics, 115 more preferably from 100 to 3,000 A.

they have the disadvantages that their applica- The transparent conductive film of the in tion to plastic films as substrate is limited. vention may be deposited on any suitable The transparent conductive film of the presubstrate. Examples of such substrates include sent invention is characterized by the fact that various glasses, quartz glasses, ceramics, of it is formed mainly from indium, oxygen and 120 high molecular materials, weight materials, and carbon as constituent elements. papers which have been generally used as The film of the invention is suitably pre- substrates. The transparent conductive film pared by introducing an alkyl In compound may, of course, be directly formed onto a into a vacuum vessel; causing the alkyl com- functional device such as, for example, and a pound to be deposited by the plasma CVD 125 Si solar battery or a-Si sensor.

method in the form of a film on to a substrate The transparent conductive film of the in previously placed in the vacuum vessel; and vention may be formed by any one of various subsequently subjecting the deposited film to film-forming processes such as the CVD a heat treatment; an oxygen source being pre- method, the plasma CVID method, the reactive sent during the deposiiiion of the alkyl com- 130 spattering method, the reactive vacuum evapo- 2 GB2192644A 2 ration method and the cluster ion beam be produced at a relatively low temperature method. When the film is desired to be and the film produced is both transparent and formed at a low temperature or on a sub- electrically conductive. The film produced may strate of large surface area, the plasma CVD be rendered more electrically conductive and method, particularly, the plasma CVD method 70 transparent by being subjected to heat treat using the phenomenon of glow discharge, can ment to a plasma annealing treatment.

be advantageous used to provide a conductive When a heat or plasma annealing treatment film on a substrate formed of a high molecular is employed, the starting materials for the de weight film (such as a polyethylene terephtha- position may include the alkyl In compound as late or polyimide film) and to make possible 75 In source and partial C source but does not the direct formation of the conductive film on necessarily include 0 source. The 0 source functional devices in the form of an electrode may be added in a suitable amount to the or window member. deposited film during the course of the heat The formation of the conductive film by the treatement or plasma annealing treatment. The plasma CVID method using-glow discharge will 80 alkyl In compound may be deposited to serve now be described with reference to Fig. 1 of as In and C source, and then the deposited the drawings. film is oxidized to give the ln,,O Y C, film during The plasma CVD device shown in Fig. 1 the heat treatment or plasma annealing treat comprises a vacuum reaction vessel (vacuum ment. The conditions for the plasma CVID in vessel) 11 having counter electrodes 13 and 85 this case are the same as those already de disposed therein. A substrate 17, on scribed above except for the omission of the which a transparent conductive film is to be use of the 0 source. When the CVD is carried deposited, is disposed on electrode 13. out by simultaneously feeding the alkyl In An evacuation system 19 connected to va- compound and the oxygen source, there is the cuum vessel 11 is used to exhaust air from 90 possibility that the two substances may and reduce the pressure in the interior of the chemically react with each other on the sub vacuum vessel. A series of gas cylinders 35 strate before they reach the atmosphere of are connected to vacuum reaction vessel 11 plasma. This unfavourable chemical reaction suppling reaction. gases thereto in combination can be avoided by effecting the CVD deposi with a carrier gas such as Ar, if necessary; 95 tion of the film by feeding only the alkyl In with the flow rates of the gases being con- compound and subsequently subjecting the trolled by flow meters 33. A bubbler 31 deposited film to oxidation by plasma anneal serves to introduce a liquid raw material, such ing.

as ln(C,HI)3, into the vacuum vessel 11 in Though the heat treatment may be carried combination with - a carrier gas. Electric power 100 out under a vacuum, it is preferably effected is supplied to electrodes 13 and 15 from a in air or in the presence of oxygen. The tem high frequency power source 21 to induce RF perature of the heat treatment is suitably from discharge and consequently the generation of 150'C to 600'C, preferably from 200'C to plasma, with the result that a transparent con- 450'C. The duration of the heat treatment is ductive film is formed on substrate 17. In the 105 suitably from 30 seconds to 2 hours, prefera Fig. 1, reference number 23 referred to a cyl- bly 1 minute to 1 hour inder for nitrogen gas to be used for purging, It is believed that the hpat treatment prob to a vacuum gauge, 33 to gas piping and ably gives rise to the effects described below 41 to a carrier gas cylinder. and that these cooperate to improve transpar- Typical conditions under which the film is 110 ency and electric conductivity in great mea deposited by the plasma CVD method are as sure.

shown below. (1) Before heat treatment hydrocarbon (1) Reaction gases: groups, such as -CH3 groups, are present In source (partial C source): In(CH36 within the deposited film, and they themselves ln(C,H,),, IN(C3HI)3, ln(C,H,),, etc. 115 are one cause for lowering transparency and 0 source (possible partial C source): 0, CO, electric conductivity. The heat treatment CO, etc. serves in the thermal elimination of these hy C source: CH, C,H,, etc. drocarbon groups from the film.

(2) Carrier gas: Ar, He, Ne, N2, etc. (2) Owing to the oxygen present in the at- (3) Glow discharge device: DC glow dis- 120 mosphere, the oxidation is induced.

charge device or AC glow discharge device (3) Crystallization proceeds further in the de (capacitive coupling type or inductive coupling posited film.

type). The plasma annealing treatment consists in (4) Reaction gas pressure: 0.01 to several exposing the deposited film to a relatively Torr (optimally 0.05 to 2 Torrs). 125 weak plasma of an inert gas or an active gas (5) Substrate temperature: O'C to 350C and may be distinguished from the plasma (optimally 20'C to 200'C) CVD by the fact that it involves substantially (6) Electric power: 0.01 to 3 W/cm2 (opti- no further accumulation of the film. Typical mally 0.05 to 1 W/CM2) conditions under which the plasma annealing Using the plasma CVD method, the film can 130 treatment is carried are as follows.

3 GB2192644A (1) Gas for plasma annealing treatment: He, valve. A high-frequency electric power of Ar, Ne, Kr, Xe, N2, 02, H2, etc. 13.56 MHz and 50 W was then fed to effect (2) Flow volume of gas: 0. 1 to 1,000 SCCM a plasma discharge for 10 minutes, thereby (optimally 1 to 100 SCCM). completing the cleaning of the substrate and (3) Pressure: 0.01 to 10 Torr (optimally 70 the electrode.

0.05 to 2 Torr) (4) The plasma discharge and introduction of (4) Electric power for discharging: 0.01 to 5 Ar were temporarily suspended and the in W/CM2 (optimally 0.01 to 1 W/CM2). terior of the vacuum reaction vessel was again (5) Substrate temperature: O'C to 400C evacuated to not more than 10-3 Torrs.

(optimally O'C to 250'C). 75 (5) Oxygen was introduced into the vacuum (6) Annealing time: 10 seconds to 10 hours reaction vessel at a flow rate of 20 SCCM (optimally 30 seconds to 3 hours). until its partial pressure reached 0.3 Torrs.

The mechanism of the plasma annealing is Then, ln(C2H5)3 was introduced into the vessel not understood in detail but is believed to be while bubbling with Ar until its partial pressure the same as that of the heat treatment. To be 80 of 0. 1 Torrs.

specific, the plasma annealing is believed to (6) When the flow volume and pressure possibly eliminate hydrocarbon groups such as reached constant levels, a high-frequency elec -CH, group, present. in the deposited film, to tric power of 13.56 MHz and 50 W was fed induce the oxidation with the minute amount to effect the reaction for 15 minutes.

of oxygen present in the plasma or with the 85 The transparent conductive film thus pro oxygen-containing reaction gas intentionally duced was a colorless transparent membrance supplied and to allow the crystallization to having a film thickness of 1, 800 A and show proceed, thereby improving electric conductiv- ing a spectral transmittance of not less than ity. 85 % at 400 to 800 nm.

In accordance with the present invention, a 90 The surface resistance measured by the four transparent Conductive film of low resistance point probe method was about 500 0/0.

and high permeability to light is obtained When this film was tested for the etching pro which mainly contains In, 0 and C as the con- perty and the resistance to environment, the stituent element. This transparent conductive results were highly satisfactory. It showed film has good chemical stability, affects high 95 high stability to withstand environmental reliability and is readily etched to permit easy changes (in terms of temperature and humi patterning. dity) and offered high resistance to various The transparent conductive film of the in- organic solvents. Further, it exhibited stability vention may be produced by the plasma CVD to withstand the reducing atmosphere of method. Since the plasma CVID method pos- 100 plasma. It permits safe adoption of the acid sible film formation at low temperatures, the etching which has been conventionally used to transparent conductive film may be formed on date, and accordingly it may be easily pat a high molecular plastic film or on a functional terned.

device vulnerable to heat, The spectral transmittance of the NESA film The improvement of electric conductivity 105 is in the range of 75 to 80 % at 400 to 800 and transparency acquired by the film which is nm and that of the ITO film in the range of obtained by the plasma CVD method using as 78 to 89 % at 400 to 800 nm. This fact the starting material an alkyl compound of in- indicates the outstanding light-transmitting pro dium can be further enchanced by subjecting perty of the transparent conductive film of the this film to heat treatment to a plasma anneal- 110 present invention. The NESA film and the ITO ing treatment. film were tested for the etching property and In order that the invention may be well un- the resistance to the environment. The results derstood the following Examples are given by indicate that the NESA film was deficient in way of illustraton only. the etching property and could not be easily 115 given fine patterning by the conventional acid Example 1 etching method and the ITO film was deficient A transparent conductive film was produced in the adaptability to the environment and suc by the following procedures using a plasma cumbed to deterioration in a reducing atmos CVD device as illustrated in Fig. 1. phere of plasma containing H atom and so on.

(1) A glass substrate or silicon wafer sub- 120 strate cleaned and dried in advance was set in Example 2 position on the upper electrode inside the va- A transparent conductive film was produced cuum vessel. by following the procedures shown below (2) The interior of the reaction vessel was subsequently to the steps (1) through (4) of evacuated to not more than 10-3 Torrs and 125 Example 1.

then the substrate was heated to and kept at (5) The Ar gas was introduced at p flow 1 50C. rate of 10 SCCM into the vacuum reacton (3) The Ar gas was introduced at a flow vessel until its partial pressure reached 0.3 rate of 20 SCCM, and the pressure was kept Torrs. Then, ln(C,H,).3 bubbled with Ar was at 0.3 Torrs by manipulation of the evacuation 130 introduced therein until its partial pressure 4 GB2192644A 4 reached 0. 1 Torrs. to effect the reaction for 15 minutes.

(6) When the flow volume and pressure (7) After suspending the plasma discharge reached constant levels, a high-frequency elec- and the introduction of gas, the interior of the tric power of 13.56 MHz and 50 W was fed reaction vessel was again evacuated to va to effect the reaction for 15 minutes and con- 70 cuum of not more than 10-3 Torrs. Subse sequently the deposition of film. quently Ar was introduced at a flow rate of (7) After completion of the reaction, the 10 SCCM and 02 at a flow rate or 1 SCCM plasma discharge, introduction of gas and followed by keeping the pressure at 0.3 heating of the substrate were suspended and Torrs. A high-frequency electric power of the vessel was evacuated to varuum. 75 13.56 MHz and 10 W was fed and the film (8) The deposited film was left to cool and was subjected to a plasma annealing for 60 then removed from the vessel. It was then minutes.

subjected to a heat treatment at 250 'C for The transparent conductive film thus ob 1 minutes in an atmosphere. tained showed the spectral transmittance of The transparent conductive film thus ob- 80 not less than 85 % at 400 to 800 nm and tained was a colorless transparent membrance possessed a film thickness of 1,500 A. The having the spectral transmittance of not less etching property and other various properties than 85 % at 400 to 800 rim and of about were as satisfactory as those of the film of 1,600 A in film thickness. The surface resis- Example 1.

tance of this film was 300 Q/[11. The stability 85

Claims

to withstand the acid etching and other vari- CLAIMS ous properties were

the same as those of the 1. A transparent conductive film formed film obtained in Example 1. mainly from indium, oxygen and carbon as constituent elements.

Example 3 90
2. A transparent conductive film as claimed A film was produced by following the pre- in claim 1, in which the atomic ratio of the cedures of Example 1, except that the sub- constituent elements is represented by the strate temperature during the deposition of the formula:

film by the plasma CVID method was changed to 140'C. The deposited film obtained was 95 In,,OYC, subjected to the heat treatment at 250'C for minutes. The properties of the film before in which the sum of x, y and z is 1; and after the heat treatment were compared. X is from 0. 1 to 0.6; Fig. 2A and Fig. 213 are FT-IR spectra of y is from 0.2 to 0.6; and the film before and after the heat treatment, 100 z is from 0.005 to 0.5.

espectively. Those two]R spectra clearly
3. A transparent coductive film as claimed show that the absorption of the alkyl group in claim 1 or claim 2 which is at least partially was disappeared owing to the heat treatment. crystallized.

Fig. 3 is a thermal-deconposition mass spec-
4. A transparent conductive film as claimed trum of the film before the heat treatment, 105 in any one of the preceding claims also con which shows the presence of hydrocarbon taining a further element selected from Si, Ge, groups in the deposited film. Sn, H, F, Cl, Br and 1.

Fig. 4 is an X-ray diffraction spectra of the
5. A transparent conductive film as claimed film before and after the heat treatment, which in any one of the preceding claims having a indicates that the crystallization was occured 110 spectral transmittance of not less than 85% at by the heat treatment. 400 to 800 nm.

Fig. 5 is a spectral transmittance of the film
6. A transparent conductive film as claimed before and after the heat treatment, which in- in claim 1 substantially as hereinbefore de dicates that the spectral transmittance is scribed with reference to the Examples.

greatly enhanced after the heat treatment. 115
7. A method for the production of a tran sparent conductive film as claimed in any one Example 4 of the preceding claims which comprises intro A transparent conductive film was produced ducing an alkyl indium compound into a va by following the procedures shown below cuum vessel; causing the alkyl compound to subsequently to the steps (1) through (4) of 120 be deposited by a plasma CVID method in the Example 1. form of a film on a substrate placed within (5) The Ar gas was introduced into the va- the vacuum vessel; and subjecting the deposi cuum reaction vessel at a flow rate of 10 ted film to heat treatment, an oxygen source SCCM until its partial pressure reached 0.3 being present during the deposition of the al- Torrs. Then, In(C,HJ, bubbled with Ar was 125 kyl compound or during the heat treatment.

introduced therein until its partial pressure
8. A method as claimed in claim 7, reached 0.1 Torrs. wherein the heat treatment is continued for 30 (6) After the flow volume and pressure seconds to 2 hours, at a temperature of from reached constant levels, a high-frequency elec- 150 to 6000C.

tric power of 13.56 MHz and 50 W was fed 130
9.A modification of the method claimed in GB2192644A 5 claim 7 in which the heat treatment step is replaced by a plasma annealing treatment, the oxygen source being present during the deposition of the alkyl compound or during the 5 plasm a annealing treatment.
10. A treatment as claimed in any one of claims 7-9 in which the alkyl indium compound is ln(CH,),. IN (CA)3, ln(C3HI)3 or ln(C4H9)3.
11. A method as claimed in any one of claims 7-10 in which the temperature of the substrate is maintained at from 0 to 350T.
12. A method as claimed in any one of claims 7-11 in which the oxygen source is present during the heat treatment or plasma annealing treatment.
13. A method a claimed in any one of claims 7-12 in which the deposited film of the alkyl compound is oxidized during the heat treatment or plasma annealing treatment.
14. A method as claimed in claim 7 or claim 9 substantially as hereinbefore described with reference to the Examples.

Published 1988 at The Patent Office, State House, 66/71 High Holborn, London WC 1 R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.