JPH04341707A - Transparent conductive film - Google Patents

Abstract

PURPOSE:To thin a conductive film, shorten etching time, improve yield, and secure a specified value of light transmittance in a transparent conductive film having indium oxide as a main component by making the film contain hafnium oxide. CONSTITUTION:Respective transparent conductive films having indium oxide In2O3 and ITO(Indiun-Tin Oxide) as main components are made to contain hafnium oxide HfO2. When the HfO2 is added to the In2O3, the In2O3 and the HfO2 are weighted, to which ethanol is added so as to be wet-blended at 50% slurry concentration for 10 hours by a ball mill made of nylon. Resulted slurry is dried at 60 deg. and is calcined at 1400 deg.C in an atmosphere for 15 hours. After dry grinding, being formed into a slurry-like, and after being made into granular, a spattering target is made, and specified spattering gas is led in so as to form a transparent film. Thereby it is possible to lower resistivity to 2X10<-4>OMEGA.cm or less, and to secure at least 80% or more as light transmittance in all visible wave length range.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent conductive film, and more particularly to a transparent conductive film suitable for use in transparent electrodes of liquid crystal displays, electroluminescent displays, electrochromic displays, and the like.

0002

2. Description of the Related Art Transparent conductive films made of metals such as gold or platinum or oxides such as tin oxide or indium oxide formed on a substrate are known. Among these, ITO, which is made by adding tin oxide to indium oxide, is used for liquid crystal displays, etc.
(Indium-Tin Oxide) is the mainstream. This is because ITO has good etching properties, chemical stability, adhesion to substrates, etc., as well as high transparency and low resistance.

[0003] In addition to ITO, there are the following examples of techniques for reducing the resistance of transparent conductive films using a semiconductor formation mechanism based on valence control. In JP-A-59-163707, ruthenium oxide, lead oxide, and copper oxide were added to ITO, and JP-A-59-712
In 05, phosphorus oxide was added to ITO, JP-A-61-29470
3. In JP-A No. 63-78404, indium oxide, IT
Aluminum fluoride for each O, JP-A-63-17
In 8414, tellurium oxide was added to ITO in JP-A-1-283.
In No. 369, selenium oxide or tin fluoride is added to ITO to lower the resistance of the transparent conductive film.

On the other hand, as an example of reducing the resistance of a transparent conductive film by converting it into a semiconductor based on reduction, US Pat. No. 4,399,1
There are 94. In US Pat. No. 4,399,194, 40 to 60 wt % of zirconium oxide is added to indium oxide to obtain characteristics of specific resistance of 4.4 x 10 -4 Ω·cm and light transmittance of 80%. The transparent conductive film is formed by vacuum evaporation,
There are physical vapor deposition methods such as ion plating and sputtering, chemical vapor deposition methods that form a film by chemical reactions such as thermal decomposition, and coating methods such as spraying and dipping. Among these methods, the physical vapor deposition method, especially the sputtering method, has become mainstream because it has good film density and can easily produce a low resistance film.

[0005]

[Problem to be solved by the invention] In recent years, word processors,
BACKGROUND ART As liquid crystal displays have come into widespread use for televisions and the like, and the size of the liquid crystal screens has increased, there has been a need to improve the light transmittance of conventional transparent conductive films without degrading their specific resistance. At this time, by maintaining the specific resistance value at a low resistance, the film thickness of the electrode can be reduced, and therefore good etching performance is also possible. The thickness of the transparent conductive film is 20
If it exceeds 00 Å, the etching time becomes longer, resulting in disconnection of the pattern, nonuniform resistance due to deterioration of the film surface condition, and a decrease in yield. The present invention not only maintains the specific resistance of the conventionally used transparent conductive film of 2 x 10-4 Ωcm, but also aims to achieve a lower specific resistance value.
The purpose of the present invention is to make the conductive film thinner, shorten the etching time, improve the yield, and further secure a light transmittance of at least 80% over the entire visible wavelength range. investigated.

[0006]

[Means for Solving the Problems] The present inventor uses In2O3
As a result of various studies on the addition of metal elements that act as electron donors and increase carrier concentration by adding metal ions to transparent conductive films mainly composed of In2O3 and ITO, we found that the main components were In2O3 and ITO. We have found a transparent conductive film characterized by containing hafnium oxide (HfO2) in each of the transparent conductive films.

Generally, the specific resistance R [Ω·cm] of an n-type semiconductor
is the elementary charge e (=1.602×10-19 C),
The carrier concentration is n [cm-3], and the mobility is μ [cm2].
/V・sec], then R=1/n・e・μ. Since the transparent conductive film whose main component is In2O3 is also an n-type semiconductor, in order to reduce the specific resistance R, the carrier concentration n or This means that it is sufficient to increase the mobility μ.

Considering the present invention, In2O
When HfO2 is added to No. 3, the carrier concentration increases and the resistivity decreases as the addition amount increases compared to a film to which the same amount of SnO2 is added. However, when the amount added is further increased, the mobility decreases and the specific resistance increases. As a result, HfO2 was reduced to 5-2
When added in a range of 5 mol %, the resistance becomes lower than the specific resistance of conventional ITO, which is 2×10 −4 Ω·cm. Outside this addition amount range, the resistivity will be 2 x 10-4 at most or at least
Higher than Ω・cm. From this, Hf4+ is Sn4
It can be seen that it is easier to replace In3+ in the In2O3 crystal than +, and has the effect of lowering the resistance more than in the case of Sn4+.

Similarly, when part of the SnO2 contained in ITO is replaced with HfO2, the carrier concentration increases, resulting in a resistance lower than that of conventional ITO. In this case, SnO2 and HfO
If the total amount of 2 added is in the range of 4 to 30 mol%, the specific resistance will be lower than 2 x 10-4 Ωcm, and outside this added amount range, the specific resistance will be 2 x 10-4 Ω at most or less.・
higher than cm. To further lower the resistivity, use SnO2
and the total amount of HfO2 added is 10 to 25 mol%
The range is more desirable. From this, Hf4
It can be seen that when + is added simultaneously with Sn4+, it has the effect of lowering the resistance more than when Sn4+ is added alone.

Sputtering and electron beam evaporation are commonly used to form transparent conductive films, but there are other methods such as ion plating, chemical vapor deposition, and coating, each of which is suitable for each film formation method. The method is selected as appropriate depending on the raw materials used. In the sputtering method and the electron beam evaporation method, a sintered body of indium and an oxide of an additive element or an alloy thereof is used as the evaporation material.

[0011] The oxide sintered body as a vapor deposition material uses oxides, metals, hydroxides, chlorides, nitrates, sulfates, etc. as raw materials, and compounds containing these indium and additive elements are processed using a ball mill, etc. The mixture mixed with HfO2 is calcined in powder form at 400-1400℃,
Add a binder such as PVA or PVB, and granulate it by spray drying, freeze drying, etc. to a mass of 500 to 2,000 kg/cm.
It is made by molding and sintering. The sintering temperature is 1,
000 to 1,600°C.

[0012] When forming a film by sputtering, after setting the sintered body or alloy as the vapor deposition material and the substrate on which the film is to be formed, and after evacuation to 1 x 10-5 Torr or less,
A mixed gas of Ar and O2 is introduced as a sputtering gas to a temperature of about 1×10 −3 to 5×10 −2 Torr to form a film.

At this time, as the O2 partial pressure in the sputtering gas increases, the transmittance increases and the resistance value decreases, but if it becomes too high, the resistance value increases. In addition, when the vapor deposition material is an oxide sintered body, the optimum O2 partial pressure is 0.5 to 3.
%, but since the amount of O2 gas is very small, O2
It is difficult to control the flow rate, and subtle variations in the O2 flow rate cause variations in membrane properties such as resistivity. Even if only Ar gas is used as the sputtering gas without adding O2 gas, the oxygen in the oxide acts in the same way as the O2 gas in the mixed sputtering gas, so the film properties such as resistance value will not deteriorate, and the delicate O2 gas flow rate will not deteriorate. There is no need for control, and the reproducibility of film properties is good. Therefore, sputtering may be performed using only Ar gas. In this case, the sputtering gas in which only Ar gas is introduced is also introduced to a temperature of about 1.times.10@-3 to 5.times.10@-2 Torr. In the same way, 1×
At a low pressure of less than 10-3 Torr, stable plasma is not generated, and at a high pressure of more than 5 x 10-2 Torr, the resistance value of the film deteriorates.

[0014] When the vapor deposition material is an alloy, the O2:Ar gas ratio of the sputtering gas is 0.5:9.5 to 4.
: A range of 6 is desirable, and a low O2 of less than 0.5:9.5
At partial pressure, transparency is poor, and at O2 partial pressure exceeding 4:6, the specific resistance value deteriorates.

The film is formed at a substrate temperature of 200 to 500° C. and a target power input of 0.5 to 4 W/cm 2 . The input power here refers to the power per 1 cm 2 of the target, and is used to turn the sputtering gas into plasma and accelerate the ions that make up the plasma. The substrate temperature is 2
If the temperature is less than 00°C, the resistance value will be poor, and if it exceeds 500°C, the substrate will deform and become unusable. The input power is 0.
If it is less than 5 W/cm2, the deposition rate will be slow and the production efficiency will be poor, and if it is more than 4 W/cm2, the resistance value will be poor. In addition to the input power, the film formation rate depends on the total pressure of the sputtering gas,
Although it is determined by the distance between the substrates, etc., the characteristics of the film will be superior or inferior even at the same deposition rate.

Considering the above, if the membrane transmittance is 8.
The sputtering conditions that provide the lowest resistance value at 0% or more are selected. In addition, when forming a film by electron beam evaporation, Ar gas is not introduced, but oxygen gas is introduced,
Heating the substrate is similar to sputtering, and the deposition rate is determined by the electron beam voltage, current, and beam diameter. O2
Select partial pressure, substrate temperature, and deposition rate appropriately, and transmittance is 90%.
With the above steps, a film with the lowest resistance value is obtained. The initial vacuum level to be achieved is 1 x 10-5 Torr or less, the subsequent O2 partial pressure is 0.5 x 10-4 to 4 x 10-4 Torr, the substrate temperature is 200 to 400°C, and the deposition rate is 0.5 to 10 Å/ sec
is an appropriate condition. Among film forming methods such as sputtering, electron beam evaporation, chemical vapor deposition, and coating, it is known that sputtering can provide a low-resistance film within the widest range of additive amounts. As the substrate on which the film is to be formed, glass, plastic sheets or films, or those coated with a protective film or a functional film are used.

[0017]

EXAMPLES The present invention will be explained in detail below using examples using sputtering, which is the mainstream method for forming transparent conductive films. Similar results can be obtained using other film forming methods. Examples 1 to 4 Table 1 for adding HfO2 to In2O3
In2O3 and HfO2 were weighed, ethanol was added, and wet-mixed in a nylon ball mill for 10 hours at a slurry concentration of 50% so as to have the composition shown below. The obtained slurry was dried at 60°C and calcined at 1400°C in the air for 15 hours. Next, it is milled in a nylon ball mill.
Dry milling was carried out for 0 hours. For this pulverized powder, 2.5% PV
A 20 wt % aqueous solution was added to form a slurry, and the slurry was granulated by freeze-drying. The granules were press-molded at 1 ton/cm2 to obtain a molded product with a diameter of 80 mmφ and a thickness of about 8 mm. This molded body was fired in the atmosphere at 1400°C for 2 hours,
I made a sputtering target.

This target was set in a high frequency magnetron sputtering device, and the vacuum chamber was heated to 1×10−6 To
After evacuation to rr, the stuttering gas shown in Table 1 was introduced to 1 x 10-3 Torr, and a transparent conductive film was created at the slide glass substrate temperature and input power shown in Table 1.

Properties such as film thickness, light transmittance, and specific resistance of the obtained transparent conductive film were measured, and these are also listed in Table 1. The film thickness was determined by masking during film formation, and after the film was formed, the step difference between the film and the substrate from which the masking had been removed was determined by measuring the step difference using a Talystep manufactured by Rank Taylor Bobson Co., Ltd. The light transmittance is the transmittance of 550 nm light using a spectrometer manufactured by JASCO Corporation. The electrical characteristics were determined by Hall effect measurement at a magnetic flux density of 10,000 Gauss. In addition, EP confirms that the deviation between the target composition and the film composition is within ±1%.
Confirmed with MA.

Examples 5 to 12 Next, sputtering targets were made using the composition of Example 3, which had the lowest resistivity, in the same manner and under the same conditions as Examples 1 to 4.
The characteristics were measured while changing the film deposition conditions, and the results of the film characteristics are shown in Table 1.

[0021]

[Table 1]

Comparative Example 1 Regarding In2O3 without adding HfO2,
Sputtering targets were made under the same conditions as Examples 1 to 4, and films were formed under the conditions shown in Table 1. Other conditions such as the method for measuring film properties were also the same as in Examples 1 to 4, and the results are shown in Table 1.

From Table 1, it can be seen that the higher the substrate temperature, the lower the resistance value. However, under the conditions of Example 5, warping of the substrate glass was observed. A film with better characteristics can be obtained as the input power is smaller, but when comparing Examples 3 and 8, the film deposition speed of Example 8 was half that of Example 3. O
When introduced, the two gases have the effect of lowering the resistivity, but when introduced in excess, the resistivity increases as in Example 12. Figure 1 also shows a substrate temperature of 400°C, input power of 2W/cm2,
The relationship between the amount of HfO2 added and specific resistance at an O2 partial pressure of 0% is shown. Figure 2 shows a substrate temperature of 400℃ and an input power of 2W/cm2.
Figure 3 shows the relationship between the amount of HfO2 added and the carrier concentration at an O2 partial pressure of 0% and a substrate temperature of 400°C and an input power of 2 W/c.
The relationship between the amount of HfO2 added and the mobility at m2 and O2 partial pressure of 0% is shown. It can be seen from FIG. 2 that the carrier concentration increases by adding HfO2. Moreover, from FIG. 3, it can be seen that when the amount added is too large, the mobility decreases. As a result, as shown in FIG. 1, the resistivity decreases as the amount of HfO2 added increases, but it increases if the amount added is too large. Conventional I when the amount of HfO2 added is 5 to 25 mol%.
The resistance is lower than 2×10 −4 Ω·cm, which is the specific resistance value of TO.

Examples 13 to 18 Regarding the addition of HfO2 to In2O3 and SnO2, sputtering targets were prepared by weighing In2O3, SnO2, and HfO2 to have the compositions shown in Table 2. Thereafter, the film was formed and its properties such as light transmittance and specific resistance were measured and are also listed in Table 2. The target manufacturing method, film forming method, film characteristic measurement, etc. were the same as those described in Examples 1 to 4. Furthermore, it was confirmed by EPMA that the compositional deviation between the target and the film was also within ±1%.

[0025]

[Table 2]

Comparative Examples 2 and 3 Table 2 shows ITO with no HfO2 added.
Sputtering targets having the composition shown in Table 2 were prepared under the same conditions as in Examples 1 to 4, and films were formed under the conditions shown in Table 2. The characteristics of the membrane were also measured in the same manner as in Examples 1 to 4, and the results are shown in Table 2.

Examples 19 to 26 Next, Examples 1 to 4 were prepared using the composition of Example 16, which had the lowest specific resistance.
A sputtering target was made using the same method and conditions as above, and the characteristics were measured when the film deposition conditions were changed. Table 3 shows the film deposition conditions and characteristics of light transmittance, carrier concentration, and mobility at that time.

From Table 3, it can be seen that as the substrate temperature decreases, both carrier concentration and mobility deteriorate. Further, at a substrate temperature of 450° C., warping of the substrate glass was confirmed. When the input power is lowered to 1.0 W/cm2, the specific resistance decreases, but
The film deposition speed was halved. As the input power increased, the resistivity increased. When the O2 partial pressure was controlled to 1.0%, the specific resistance decreased, but when it was controlled to 5.0%, the specific resistance increased. In addition, Figure 4 shows that the total of SnO2 and HfO2 is 8, respectively.
．． The relationship between the ratio of the amount of HfO2 added to the amount of SnO2 added and the specific resistance is shown at 84 mol% and 16.99 mol% at a substrate temperature of 400°C, input power of 2 W/cm2, and O2 partial pressure of 0%. Figure 5 shows that the sum of SnO2 and HfO2 is 8.84 mol% and 16.99 mol%, respectively.
1%, substrate temperature 400℃, input power 2W/cm2
, HfO2 with respect to the amount of SnO2 added at O2 partial pressure of 0%
Figure 6 shows the relationship between the addition amount ratio and carrier concentration of SnO.
The amount of HfO2 added relative to the amount of SnO2 added at a substrate temperature of 400°C, input power of 2 W/cm2, and O2 partial pressure of 0% when the total of 2 and HfO2 is 8.84 mol% and 16.99 mol%, respectively. The relationship between ratio and mobility was shown. It can be seen from FIG. 5 that the carrier concentration increases as the ratio of the amount of HfO2 added to the amount of SnO2 added increases. Furthermore, it can be seen from FIG. 6 that as the ratio of the amount of HfO2 added to the amount of SnO2 added increases, the mobility decreases. As a result, as shown in FIG. 4, it can be seen that the specific resistance decreases as the ratio of the amount of HfO2 added to the amount of SnO2 added increases, but increases when the amount added is too large.

[0029]

[Table 3]

[0030]

[Effect of the invention] As stated above, HfO in In2O3
By mixing HfO2 into ITO or by mixing HfO2 into ITO, it is possible to create a film with a high carrier concentration and a low resistance value, which makes the conductive film thinner, shortens the etching time, and improves the yield. This invention has an effect unique to the present invention in that it can be improved.

[Brief explanation of the drawing]

[Figure 1] When HfO2 is added to In2O3, the substrate temperature is 400°C, the input power is 2W/cm2, and the O2 partial pressure is 0%.
FIG. 3 is a diagram showing the relationship between the amount of HfO2 added and specific resistance.

[Figure 2] When HfO2 is added to In2O3, the substrate temperature is 400°C, the input power is 2W/cm2, and the O2 partial pressure is 0%.
FIG. 3 is a diagram showing the relationship between the amount of HfO2 added and the carrier concentration.

[Figure 3] When HfO2 is added to In2O3, the substrate temperature is 400°C, the input power is 2W/cm2, and the O2 partial pressure is 0%.
FIG. 3 is a diagram showing the relationship between the amount of HfO2 added and the mobility.

FIG. 4 shows the relationship between the ratio of the amount of HfO2 added to the amount of SnO2 added and the specific resistance at a substrate temperature of 400°C, input power of 2 W/cm2, and O2 partial pressure of 0% when HfO2 is added to ITO. This is a diagram.

FIG. 5 shows the relationship between the carrier concentration and the ratio of the amount of HfO2 added to the amount of SnO2 added at a substrate temperature of 400°C, input power of 2 W/cm2, and O2 partial pressure of 0% when HfO2 is added to ITO. This is a diagram.

FIG. 6 shows the relationship between the mobility and the ratio of the amount of HfO2 added to the amount of SnO2 added at a substrate temperature of 400°C, input power of 2 W/cm2, and O2 partial pressure of 0% when HfO2 is added to ITO. FIG.

Claims (2)

[Claims] Claim 1: In a transparent conductive film containing indium oxide (In2O3) as a main component, hafnium oxide (Hf
A transparent conductive film characterized by containing O2). 2. A transparent conductive film whose main components are indium oxide (In2O3) and tin oxide (SnO2), and which contains hafnium oxide (HfO2).