JPH0370329B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a low-resistance transparent conductive film on a transparent substrate and a method for producing the same. The present invention provides a transparent conductive film formed on a light-transmitting substrate that has a low sheet resistance of 35Ω/□ or less (high conductivity) and a low absorption coefficient of 6% or less (transmittance of 80% or more). It is characterized by having high acid resistance and plasma reaction treatment resistance. The present invention proposes a transparent conductive film having many contradictory characteristics, including an indium oxide film to which tin oxide is added (hereinafter simply referred to as ITO), and a tin oxide film to which 2.5 to 7.5% of antimony oxide is added. The present invention is characterized in that the two-layer film is formed by stacking them using the same vacuum evaporation apparatus. Conventionally, ITO has been known as an excellent transparent conductive film due to its low sheet resistance. However, it takes ITO
When considering acid resistance or plasma reactivity resistance, it is an extremely weak film. For example, when a film formed by depositing ITO on a glass plate with a thickness of 500 to 1000 Å is immersed in 100% hydrochloric acid, It dissolved away in seconds and was completely useless. Furthermore, indium oxide is an oxygen-deficient transparent conductive film and has an acceptor conductivity type, and because the bond between indium oxide and oxygen is strong, the plasma gas phase reaction can be carried out at 100 to 400℃ in a reducing atmosphere.
If the process was carried out at a temperature of For this reason, tin oxide is applied to the top surface of this blocking layer at a temperature of 200%.
It was required to be formed to a thickness of ±100 Å.
However, since this tin oxide alone cannot sufficiently lower the sheet resistance, the inventor added antimony oxide in an amount of 7.5% or less, preferably 2.5 to 7.5%. As a result, when this tin oxide is formed in the same reactor, in order to promote recombination current at the interface between ITO and tin oxide, if the thickness of tin oxide is less than ~300 Å, it is practically the only The equivalent sheet resistance is
It was possible to obtain 50Ω/□ or less, typically 15 to 30Ω/□. Furthermore, in the hydrochloric acid immersion test mentioned above, 60~
I was able to withstand 1.5 to 2 minutes, which is 100 times longer. In addition, when forming a two-layer film of ITO as the first transparent conductive film of the present invention and tin oxide as the second transparent conductive film, ITO can be made into an oxidation-deficient type by performing a vacuum treatment between them. , the variation in sheet resistance is extremely small, and the value is less than 35Ω/□ when ITO is 400 to 650 Å thick and tin oxide is 100 to 300 Å thick, and the absorption rate of the film is less than 6%. was completed. Furthermore, in the present invention, this tin oxide film is
After forming at ~200°C, the ITO and tin oxide films are densified by increasing and holding the temperature at 250~450°C in a vacuum atmosphere in the same vacuum evaporation equipment; Furthermore, oxidation was promoted by supplying oxygen only to the tin oxide film at the same temperature of 250 to 450°C. As a result, the acid resistance of this film was 5 to 20 times longer than the time required for dissolution in a hydrochloric acid test of 10 to 40 minutes, and 100 to 400 times longer than the IT-only film. Additionally, if this oxidation is performed excessively, the ITO itself will accept oxygen and its sheet resistance will increase, so it was found that the oxidation treatment has a certain condition: oxidation temperature x oxidation time. As described above, the present invention is capable of producing 200 to 400
ITO was then kept in a vacuum atmosphere and then lowered to a substrate temperature of 50 to 200 degrees Celsius to form tin oxide, and then heated to 250 to 450 degrees Celsius in a vacuum atmosphere in the same vacuum evaporator. A large number of processes such as processing to densify the coating and further oxidation treatment at 250 to 450°C can be performed continuously and automatically under the control of a microcomputer in the same vacuum evaporation equipment. It is characterized by The details are described below according to the drawings. In FIG. 1, A indicates a first transparent conductive film of ITO2 and a second transparent conductive film 3 mainly composed of tin oxide on a transparent substrate 1 used in the present invention (the downward direction is shown). are laminated to have a two-layer structure. In the drawing, an auxiliary electrode 4 made of metal such as copper, nickel or aluminum is closely connected to these transparent conductive films, and an external lead electrode 4 is provided.
It is provided with a thickness of 0.5 to 3μ. The main purpose of the present invention is to use such a substrate and apply it to a photoelectric conversion device shown in FIG. 1B. Figure 1B is outlined. In FIG. 1B, a first transparent conductive film 2 and a second transparent conductive film 3 are formed on a light-transmitting substrate 1 by electron beam evaporation, and then on the top surface by plasma vapor deposition at a temperature of preferably 100 to 400°C. A non-single crystal semiconductor is formed using a glow discharge method at 200-300°C. That is, a P-type non-single-crystal semiconductor layer 5 in which hydrogen or a halogen element represented by Si _X C _1-X (0<x<1) is added to neutralize recombination centers is formed on a transparent conductive film.
or Si ₃ N _4-X (0<x<4), Si _X Ge _1-X (0<x<4)
1) An intrinsic or substantially intrinsic non-single-crystal semiconductor layer in which the recombination center neutralizing agent described above is added to Si _X Sn _1-X (0<x<1), and a similar semiconductor material on the upper surface thereof. A PIN-type photoelectric conversion semiconductor device is provided, which is formed by laminating N-type semiconductor layers 7 made of the following. In the drawing, a back electrode 8 is made of aluminum on the upper surface, and a front electrode for incident light 10 is formed of the transparent conductive film of the present invention. When trying to fabricate this photoelectric conversion semiconductor device, the plasma vapor phase method uses hydrogen or silane (SiH ₄ ).
Methane (CH ₄ ), ammonia (NH ₃ ) and other valent impurities for P-type (B ₂ H ₆ , Ga(CH ₃ ) ₃ ) or V-valent impurities for N-type (PH, Sb(CH ₃ ) ₃ ) is 0.1
~50MHz Typically, _non -single-crystal silicon, _Si is formed. However, these plasma reactions are reducing reactions, and an extremely large amount of plasma energy is applied to the formation surface, so the transparent conductive film that constitutes the formation surface is strongly required to have acid resistance and plasma reactivity resistance. ing. When considering the application of the present invention to such photoelectric conversion devices, emphasis is placed on high light transmittance (low absorption), low electrical resistance, as well as strong oxidation resistance and plasma reactivity resistance. Therefore, the present invention is characterized in that it satisfies all of these contradictory characteristics to the extent possible industrially and provides an unprecedented membrane. FIG. 2 shows the relative relationship between these three characteristics. As can be seen from the drawing, the electrical resistance can be reduced by increasing the film thickness. However, if the thickness is increased, the absorption rate (absorption loss) in this film increases and the transparency deteriorates. Further, in order to increase the plasma resistance, the tin oxide film may be made thinner, but in that case, the current flowing in the direction of the arrow in FIG. 1B will be prevented, and the electrical resistance will increase. The present invention provides a first method containing indium oxide as a main component.
a step of vacuum baking the first transparent conductive film; a step of forming a second transparent conductive film containing tin oxide as a main component on the film; The method includes a step of densifying the film by baking it in a vacuum, and a step of oxidizing it by baking it in air or an oxidizing atmosphere. The second transparent conductive film has a thickness of 400 Å or less, preferably 100 Å or less
The thickness was 300 Å, and the conductive film was extremely dense and oxygen-rich. Further, in order to form a donor type, antimony may be added in an amount of 7.5% or less, typically 2.5 to 7.5%, particularly 5%, and the first transparent conductive film is dense and oxygen-deficient, Tin oxide may be added in an amount of 2.5 to 7.5% to form an acceptor type. Furthermore, at the interface, if at least one of each is made 10% or more, the amount to prevent the formation of an InSb compound semiconductor and devitrification, that is, the amount of tin oxide added in the first conductive film, and the amount of tin oxide added in the second conductive film are increased. It is also preferable that the amounts of antimony added to the conductive film are both 7.5% or less. As a result, an excessive recombination current flows between the donor type and acceptor type at the interface of the film, and as a result, the sheet resistance in tin oxide is reduced by itself.
For a film of 100 to 300 Å, the value is 2 to 10 KΩ/□, and for a thick film, for example, 0.5 to 1μ, a value of 20 to 50 Ω/□ can be obtained.
Values of less than 35 Ω/□ were obtained in the complex at a thickness of 100 to 300 Å, similar to that obtained with that thick film. Examples thereof will be described below with reference to the drawings. EXAMPLE FIG. 3 shows an outline of a program chart for forming a transparent conductive film of the present invention. The vacuum evaporation equipment is an electron beam type, and BMC
A fully automatic type (vacuum equipment industry type) controlled by a -700 microcomputer was used. The thickness of the deposited film and the deposition rate were controlled using a crystal oscillation system, and an HP-85 computer was used to feed back the electron beam (control the emission current). In FIG. 3, after the glass substrate is inserted, the first conductive film is deposited in the region 11, the first conductive film is annealed (baked) in the region 12, the second conductive film is deposited in the region 13, and the second conductive film is deposited in the region 14. , 15 and 16, the second conductive film was annealed (baked). Arrows indicate the deposition temperature and annealing temperature range. Typical processing steps are shown in the table below.

[Table] FIG. 4 shows the characteristics of the transparent conductive film obtained according to the present invention. In drawings A and B, the annealing in the region indicated by 12 in Fig. 3 is performed using oxygen (2.5×10 ^-4 torr).
Curve 19 shows the characteristics obtained by annealing in an atmosphere.
24, and the characteristics obtained in the case of nitrogen (1×10 ^-4 torr) atmosphere are shown by curves 20 and 25, vacuum (5×
Curve 1 shows the characteristics obtained in the case of 10 ^-6 torr) atmosphere.
8,23. As is clear from the drawing,
As the amount of antimony oxide in tin oxide increases, the sheet resistance decreases and the absorption rate K increases,
The opposite characteristics are obtained. In Figure 4A, 22 has a sheet resistance of 35Ω/
26 in FIG. 4B indicates the amount of antimony oxide where the absorption rate is 6% or less. However, when the area 12 in FIG. 3 is processed in a vacuum, the sheet resistance also has small variations and is all 35 Ω/□ or less, preferably 30 Ω/□ or lessq. This is a major feature of the present invention. Moreover, an absorption rate of 6% or less can be obtained. This absorption rate was calculated using the following formula using a wavelength of 500 nm as a reference. K=100-(T+αR)% where K: Absorption rate of two-layer film (%) T: Measured transmittance R: Measured reflectance α: Correction value (0.918) Note that a Hitachi 350 monochromator was used for the measurement. However, if oxygen or air is used for this annealing, a resistance layer is formed at the interface with antimony oxide formed by vapor deposition, and sufficient recombination current does not flow at the interface, resulting in a resistance of 40Ω/□ or more. . Furthermore, when the amount of antimony oxide in the second transparent conductive film is increased to 7.5% or more, especially 10% or more,
Due to the reaction between this antimony and indium,
A compound semiconductor made of InSb was created, and as a result, the absorption loss of light in this film increased. Furthermore, in order to satisfy these two characteristics at the same time, the recombination current at the boundary (interface) between the first conductive film and the second conductive film is actively utilized, and the InSb compound semiconductor is without making
ITO was also achieved for the first time by making it oxygen-deficient and increasing its density through vacuum annealing. As mentioned above, ITO alone devitrified due to the plasma reaction, and in the hydrochloric acid test, even a film with a thickness of 500 to 1000 Å was dissolved away in 1 to 2 seconds, and was extremely weak. Furthermore, if a tin oxide film is formed on this, 30~
It was able to obtain acid resistance in a hydrochloric acid test for 1.5 to 2 minutes, which is 100 times longer. This example is intended to further improve the plasma reactivity resistance or acid resistance of the two-layer transparent conductive film. Vacuum firing was performed in an oxidizing atmosphere as follows. Figure 5A shows the change in sheet resistance in the chart of Figure 3 when vacuum firing is performed in area 15 after passing through vacuum heating area 14, and when firing is performed in air without performing this step at all. Shown against firing time. That is, curves 27 and 27' represent the case where the transparent conductive film is densified by vacuum annealing. curve 2
Curve 7 was conducted at 350°C for 30 minutes, and curve 27' was conducted at 450°C for 10 minutes. Curve 28 is the case where such vacuum firing was not performed at all. In other words, this is the case when all of these were fired in the atmosphere at 350°C. As is clear from FIG. 5A, it can be seen how this vacuum firing reduces the deterioration of sheet resistance. That is, this vacuum baking makes the second transparent conductive film highly dense (densified) and prevents the oxygen in the air from reaching the level of oxygen-deficient ITO. From the above, it can be seen that vacuum firing is important for this two-layer film. On the other hand, FIG. 5B shows how the hydrochloric acid resistance changed by firing in the atmosphere. In other words, after performing vacuum firing at 350℃ for 30 minutes, as shown in area 16 of the chart in Fig.
Firing was performed at a temperature of 31° C. between M shown on the horizontal axis. From this, it can be seen from FIG. 5B that acid resistance, that is, plasma resistance, is improved by performing baking in the atmosphere at a higher temperature for a longer time. However, if such firing in the atmosphere is performed, the first
Oxygen diffusion into the layer occurs, resulting in an increase in sheet resistance as shown in FIG. 5A. As a result, although this baking in the atmosphere makes the second transparent conductive film an oxygen-rich type and improves acid resistance and plasma reactivity resistance, the second transparent conductive film itself is We learned the importance of firing in a vacuum to achieve high density. The present invention combines such a two-layer film with vacuum firing and firing in air or an oxidizing atmosphere, and as a result of a chlorine test, it can withstand elution for 10 to 30 minutes instead of 1.5 to 2 minutes. It is characterized by the development of a manufacturing method that makes it into a film. For this reason, if the sheet resistance is to be 35Ω/□ or less, firing in air or an oxidizing atmosphere is 30 minutes to 2 hours at 250℃, 5 to 30 minutes at 350℃, and 5 to 30 minutes at 450℃. 1 to 10 minutes was optimal. This is because there is a condition that oxygen is supplied only to the second transparent conductive film to make it an oxygen-excess type, and that oxygen is not delivered to the first transparent conductive film. FIG. 6 corresponds to curve 27 in FIG. 5A for a two-layer film in which a second transparent conductive film was formed after forming the first transparent conductive film and then vacuum baking the film. The transmittance of the transparent film was investigated by firing it in the atmosphere. As shown in the drawing, total film thickness = 750Å
(first film = 550 Å, second film = 200 Å)
Curve 33 was formed only in the wavelength range of 400 to 800 nm when the firing time was 10 minutes 34, 30 minutes 35, and 60 minutes.
Minute 36, 120 minute 37 was added. This shows that firing in the atmosphere is extremely important for improving transmittance. However, it was found that this increase in transmittance has an optimum range; when fired at 350°C, the transmittance is 85% for 10 to 30 minutes, and that firing for 60 minutes or more is rather poor. Curve 33' has an ITO film thickness of 3000 Å and a SnO ₂ film thickness of 200 Å.
This is the characteristic when Å. If this film thickness is simply increased, the transmittance decreases, making it impossible to maintain the transmittance of 75% or more, preferably 80% or more, as required in the present invention. In the transparent conductive film of the present invention, the first transparent conductive film is made of indium oxide (also referred to as ITO) mixed with 2.5 to 7.5% tin oxide, and the second transparent conductive film is formed on the upper surface of the indium oxide (ITO) containing 7.5% or less of ammothine oxide. Even if the film is formed from a film containing added tin oxide as a main component, a transparent conductive film having a sheet resistance of 35Ω/□ or less and an absorption rate of 6% or less can be obtained. A photoelectric conversion device having a vertical cross-sectional view of the structure shown in FIG. 1B was manufactured using the transparent conductive film of the present invention manufactured according to the example. Then, its efficiency is 10-12
%/ ^cm2 , Voc=0.9~0.93V, Isc=17~26mA/
cm ² could be made with an area of 2 cm □. Further, when forming the P-type non-single crystal semiconductor layer 5, only 0.5 to 1 W could be obtained using ITO alone.
Beyond that, devitrification was observed. In addition, in the two-layer film, no devitrification was observed at the output of the high frequency power source (7.56MHz) up to 5W. Furthermore, no devitrification was observed even at 30W. Therefore, the transparent conductive film of the present invention obtained in the example has extremely large flexibility in the plasma CVD method, and as a result, the P-type semiconductor layer can also be formed as a high-output film, so that the energy band width of the conventional one is 1.5 to 1.7. We were able to increase the ev to 2.2~2.4ev. As is clear from the above description, the present invention makes it possible to form a transparent conductive film on a glass substrate that is as thin as possible, has low resistance, and has acid resistance and plasma reactivity resistance.

[Brief explanation of drawings]

In FIG. 1, A shows a substrate on which the transparent conductive film of the present invention is formed, and B shows a vertical sectional view of a photoelectric conversion device to which the same is applied. FIG. 2 shows the relative relationship of characteristics that the transparent conductive film of the present invention should have. FIG. 3 is a program chart for forming the transparent conductive film of the present invention. FIG. 4 shows sheet resistance A and absorption rate B using the amount of antimony oxide added to the second transparent conductive film on the first transparent conductive film of the present invention as a parameter. FIG. 5 shows the deterioration of the characteristics of the transparent conductive film of the present invention upon firing. 6th
The figure shows the change in transmittance due to firing of the transparent conductive film of the present invention.

Claims (1)

[Scope of Claims] 1. A step of forming a first transparent conductive film containing indium oxide as a main component, a step of vacuum baking the first transparent conductive film, and a step of forming a first transparent conductive film containing tin oxide as a main component on the film. forming a second transparent conductive film;
A step of performing film densification treatment on the second transparent conductive film by vacuum baking, and after the step,
A method for producing a low-resistance transparent conductive film, comprising the step of oxidizing the second transparent conductive film by firing in air or an oxidizing atmosphere. 2 In claim 1, the vacuum firing for high density is performed at a substrate temperature of 250 to 450°C in an atmosphere evacuated to 5 × 10 ^-5 torr or less, and at a temperature of 250 to 450°C. A method for producing a low-resistance transparent conductive film, characterized in that the second transparent conductive film is oxidized in the air or in an oxidizing atmosphere. 3 In claim 2, the firing in an oxidizing atmosphere is performed at 250°C for 30 minutes to 2 hours, and at 350°C for 5 to 30 minutes.
1. A method for producing a low-resistance transparent conductive film, characterized in that the process is performed at 450° C. for 1 to 10 minutes.