JP4918738B2 - ITO sputtering target and manufacturing method thereof - Google Patents

Description

【発明の効果】
本発明により、アーキング発生が少なく、基板上へのパーティクルの付着が少なくなるＩＴＯスパッタリングターゲットを提供することができる。
【図面の簡単な説明】
【図１】 実施例１で得られたＩＴＯスパッタリングターゲットの表面構造を示す図である。
【図２】 図１における中間化合物粒子に相当する部分を黒く示した図である。
【図３】 比較例１で得られたＩＴＯスパッタリングターゲットの表面構造を示す図である。
【図４】 図３における中間化合物粒子に相当する部分を黒く示した図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sputtering target for forming an ITO transparent conductive film and a method for producing the same.
[0002]
[Prior art]
The manufacturing method of ITO (Indium Tin Oxide) thin film, which is a transparent conductive film, is roughly divided into chemical film-forming methods such as spray pyrolysis and CVD, and physical film-forming methods such as electron beam evaporation and sputtering. Can do. In particular, the sputtering method using an ITO target is easy to increase in area, has little change over time in the resistance value and transmittance of the obtained film, and can easily control the film formation conditions in various fields. in use.
[0003]
The ITO thin film has characteristics such as high conductivity and high transmittance, and can be easily finely processed. Therefore, it covers a wide range of fields such as display electrodes for flat panel displays, window materials for solar cells, and antistatic films. It is used. In particular, in the field of flat panel displays such as liquid crystal display devices, the increase in size and definition has progressed in recent years, and there is an increasing demand for lower particles in the ITO thin film that is the display electrode.
[0004]
The amount of particles adhering to the substrate is deeply related to the frequency of arcing during sputtering, and it is effective to reduce arcing to reduce particles.
[0005]
For reducing arcing, it is effective to improve the density of the ITO sintered body used for the sputtering target, and as a method for improving the density, for example, a method of performing oxygen pressure sintering such as JP-A-3-207858, A method using fine tin oxide powder is known as disclosed in JP-A- 9-25567 .
[0006]
Also disclosed is a method for reducing the intermediate compound phase (a complex oxide phase of indium oxide and tin oxide, which is different from the indium oxide phase in which tin is dissolved) after being densified. ing. For example, Japanese Patent Laid-Open Nos. 06-158308 and 07-166341 have a relative density of 90% or more and a single-phase structure (the SnO ₂ phase and the intermediate compound phase are 10% or less in area ratio), An ITO sputtering target having a specific resistance of 1 × 10 ⁻³ Ω · cm or less is disclosed.
[0007]
This target is aimed at preventing deterioration of film property uniformity due to arcing and preventing increase in thin film resistance due to blackening of the target surface formed due to arcing. The amount of tin is reduced to 2 to 6% by weight. It is obtained by press-molding an indium oxide-tin oxide composite powder having an average particle size of 0.1 μm or less and then sintering at 1500 to 1700 ° C. in a pressurized oxygen atmosphere of 1 to 10 atm.
[0008]
[Problems to be solved by the invention]
However, the performance required for the ITO thin film is increasing day by day, and further improvement is required as the cost reduction requirement becomes stronger.
[0009]
[Means for Solving the Problems]
The present inventors have intensively studied measures for reducing the arcing frequency of an ITO sputtering target composed of a sintered body having a relative density of 99% or more, and the arcing frequency is strongly correlated with the shape of the intermediate compound phase. By making the elliptical long / short axis ratio of the intermediate compound particles observed with a scanning electron microscope (SEM) an arbitrary cross section of 2.1 or more, and making the shape a polygonal shape including a concave surface It has been found that the frequency of occurrence can be reduced.
[0010]
That is, the present invention is a sputtering target made of an ITO sintered body obtained by mixing, molding and firing indium oxide powder and tin oxide powder, the relative density of which is 99% or more, and the sintered body is cubic. (1) Ellipse long and short axes of intermediate compound particles observed with an SEM in an arbitrary cross section of a sintered body comprising a two-phase structure of a parent phase composed of indium oxide and an intermediate compound phase of indium oxide and tin oxide An ITO sputtering target having a ratio of 2.1 or more, or (2) an ITO sputtering target in which 80% or more of intermediate compound particles observed using an SEM on an arbitrary cross section of the sintered body have a polygonal shape including a concave surface And (3) Indium oxide powder and tin oxide powder are mixed and molded, sintered in a pure oxygen stream at 1550 ° C. or higher and lower than 1650 ° C., and then held at a sintering holding temperature. From the cooling rate of up to at least 1300 ° C., a method of manufacturing an ITO sputtering target characterized in that a 200 ° C. / time or more.
[0011]
Hereinafter, the present invention will be described in detail.
[0012]
The ITO sputtering target of this invention can be manufactured with the following method, for example. First, indium oxide powder and tin oxide powder are put into a ball mill pot at a desired ratio, and dry or wet mixed to prepare a mixed powder. The average particle size of the powder used is preferably 1.5 μm or less, more preferably more than 0.1 μm and 1.5 μm or less. By using such a powder, the effect of increasing the density of the sintered body can be obtained.
[0013]
In the present invention, the content of tin oxide in the mixed powder is preferably 8 wt% or more and less than 15 wt% in SnO ₂ / (In ₂ O ₃ + SnO ₂ ). By doing so, the resistivity of the thin film obtained when the film is formed by the sputtering method is lowered.
[0014]
The powder thus obtained is molded by a molding method such as a pressing method or a casting method to produce an ITO molded body. In the case of producing a molded body by press molding, the mixed powder is filled into a mold having a predetermined size, and then pressed at a pressure of 100 to 300 kg / cm ² using a press machine to obtain a molded body. At this time, a binder such as PVA may be added as necessary. On the other hand, when a molded body is produced by a casting method, the mixed powder is mixed with water, a binder, and a dispersing agent to form a slurry, and the slurry having a viscosity of 50 to 5000 centipoise thus obtained is cast for molding. To form a molded body.
[0015]
Next, the molded body thus obtained is treated by cold isostatic pressing (CIP) as necessary. At this time, since the pressure of the CIP to obtain a sufficient compaction effect 1 ton / cm ² or more, it is desirable that preferably is 2~5ton / cm ^2.
[0016]
When molding is performed by a casting method, a drying process and a debinding process are performed at a temperature of 300 to 500 ° C. for about 5 to 20 hours in order to remove moisture and organic substances such as a binder remaining in the molded body after CIP. It is preferable to apply. Even when the molding is performed by the press method, it is preferable to perform the same debinding process when a binder is used during the molding.
[0017]
Next, the molded body thus obtained is sintered. The temperature raising rate is not particularly limited, but is preferably 10 to 400 ° C./hour from the viewpoint of shortening the sintering time and preventing cracking.
[0018]
In the present invention, the subsequent temperature profile is important.
[0019]
The sintering holding temperature is 1550 ° C. or higher and lower than 1650 ° C., preferably 1580 ° C. or higher and 1620 ° C. or lower. By doing so, the solid solution of tin oxide in the indium oxide lattice is promoted beyond the solid solution limit at low temperature.
[0020]
The holding time is 5 hours or more, preferably 5 to 30 hours. By doing so, it becomes easy to obtain a high-density sintered body.
[0021]
The temperature is decreased at a temperature decrease rate of 200 ° C./hour or more until at least 1300 ° C. Preferably it is 250 degreeC / hour or more, More preferably, it is 300 degreeC / hour or more. The rate of temperature decrease here is not the set value of the temperature pattern of the furnace during sintering, but the temperature in the furnace. The upper limit of the temperature lowering rate is not particularly defined, but is preferably 500 ° C./hour or less in consideration of prevention of cracking of the sintered body. Tin oxide, which has been dissolved in the high temperature range above the solid solution limit at low temperature, precipitates during this temperature lowering process to form an intermediate compound. By setting the temperature decreasing rate as described above, the amount of precipitation is reduced. The intermediate compound phase particles observed when an arbitrary cross section is observed with an SEM has an elliptical major axis ratio of 2.1 or more, and has a polygonal shape including a concave surface.
[0022]
The result of examining the surface structure of the ITO sputtering target of the present invention by SEM is shown in FIG. 1, and the portion corresponding to the intermediate compound particles extracted from the SEM image in black is shown in FIG. The particle | grains containing the concave surface as used in this invention mean that the concave surface is included in at least one part of the outline of particle | grains, as shown in FIG.1 and FIG.2. The ITO sputtering target having a polygonal shape including a concave surface of the present invention means that 80% (number conversion) or more of intermediate compound particles include a concave surface.
[0023]
By making the intermediate compound phase into such a shape, it is possible to effectively suppress arcing during sputtering. Although the mechanism of this phenomenon has not been clarified, it is possible to suppress arcing with good reproducibility by firing rapidly at a high temperature as described above and then rapidly cooling to form an intermediate compound phase of the above shape. Is possible.
[0024]
When sintering is not performed at 1550 ° C. or higher, the shape of the intermediate compound observed by SEM is mainly circular and has no concave surface, and the ellipse major axis ratio is also smaller than 2.1. In addition, in the case where rapid cooling at 200 ° C./hour or more is not performed, the intermediate compound having a concave surface with an elliptical major axis ratio of 2.1 or more is not main, and the amount of precipitation of the intermediate compound phase increases. Since the average cross-sectional area of the intermediate compound particles exceeds 5 μm ² , the effect of reducing arcing cannot be obtained.
[0025]
The temperature lowering rate after the temperature becomes less than 1300 ° C. is preferably 100 ° C./hour or less in order to prevent cracking of the sintered body. It is more preferable to lower the temperature lowering rate after the temperature becomes 1200 ° C. or lower. The setting of the temperature for lowering the temperature decrease rate and the selection of the temperature decrease rate may be appropriately determined in consideration of the capacity of the sintering furnace, the size and shape of the sintered body, the ease of cracking, and the like.
[0026]
The atmosphere during sintering is in an oxygen stream, and the ratio of the oxygen flow rate (L / min) and the charged amount of the compact (kg) when introducing oxygen into the furnace during sintering (charge weight / oxygen flow rate), 1.0 or less. By doing so, it becomes easy to obtain a high-density sintered body.
[0027]
The method for measuring the ellipse major axis minor axis ratio, shape and average cross-sectional area of the intermediate compound particles according to the present invention may be performed, for example, as follows. First, the ITO sintered body is cut to an appropriate size, and then surface polishing is performed. While taking a photograph of the surface of the sintered body using FE (Field Emission) -SEM or the like, each individual particle is quantitatively analyzed and classified into an indium oxide phase in which Sn is dissolved and an intermediate compound phase.
[0028]
Next, the SEM image with the crystal phase classified is taken into a computer and image analysis is performed. In the present invention, the measurement was performed using the software name “Image-Pro Plus” manufactured by Media Cybernetics.
[0029]
The ratio of the major axis to the minor axis of the intermediate compound phase is the ratio of the major axis length to the minor axis length of the corresponding ellipse of the measured symmetric particle (the ellipse having the same area as the symmetric particle and equal to the first and second moments in physics). (Axis / short axis).
[0030]
As for the polygonal shape including the concave surface, the shape of the particles identified as the intermediate compound as a result of quantitative analysis was visually observed on the SEM photograph.
[0031]
The average cross-sectional area was obtained by dividing the sum (S) of the areas of particles identified as intermediate compounds by the number of particles (n) as a result of quantitative analysis.
[0032]
In the present invention, as the relative density is higher, the effect of reducing arcing is obtained, so 99.5% or more is preferable. More preferably, it is 99.7% or more, and particularly preferably 99.8% or more.
[0033]
The relative density in the present invention and (D) shows the relative values with respect to the theoretical calculated from the true density of the arithmetic mean of In ₂ O ₃ and SnO ₂ Density (d). The theoretical density (d) obtained from the arithmetic mean is the true density of 7.18 and 6.g when the mixing amount of In ₂ O ₃ and SnO ₂ powder is a and b (g) in the target composition. 95 (g / cm ³ )
d = (a + b) / ((a / 7.18) + (b / 6.95))
Is required. When the measured density of the sintered body is d1, the relative density is
Formula: D = d1 / d × 100 (%)
Is required.
[0034]
Next, after grinding the obtained sintered body into a desired shape, the ITO sputtering target of the present invention is bonded to a backing plate made of oxygen-free copper or the like using indium solder or the like as necessary. Obtainable.
[0035]
The obtained target is placed in a sputtering apparatus, and sputtering is performed by applying a dc or rf electric field using an inert gas such as argon and, if necessary, an oxygen gas as a sputtering gas. In this case, an ITO thin film can be formed. At this time, the effect of the present invention that the amount of arcing is reduced is exhibited.
[0036]
【Example】
Example 1
90 parts by weight of indium oxide powder having an average particle diameter of 0.5 μm and 10 parts by weight of tin oxide powder having an average particle diameter of 0.5 μm were placed in a polyethylene pot and mixed by a dry ball mill for 72 hours to prepare a mixed powder. The tap density of the mixed powder was measured and found to be 2.0 g / cm ³ .
[0037]
This mixed powder was put into a mold and pressed at a pressure of 300 kg / cm ² to obtain a molded body. This molded body was treated with CIP at a pressure of 3 ton / cm ² . Next, this compact was placed in a pure oxygen atmosphere sintering furnace and sintered under the following conditions.
(Sintering conditions)
Temperature increase rate: 100 ° C./hour, sintering temperature: 1600 ° C., sintering time: 6 hours, atmosphere: pure oxygen gas in the furnace from 800 ° C. during temperature increase to 400 ° C. during temperature decrease (feed weight / oxygen flow rate) ) = 0.8, temperature drop rate: From 1600 ° C. to 1200 ° C., the density of the sintered body obtained by 400 ° C./hour and thereafter 50 ° C./hour was measured by Archimedes method. The results are shown in Table 1.
[0038]
From this sintered body, a 5 × 7 inch 6 mm thick target sintered body and a sample for SEM analysis were cut out by wet processing.
[0039]
The result of measuring the surface structure of this sample by SEM is shown in FIG. 1, and the intermediate compound portion in FIG. 1 shown in black is shown in FIG. Table 1 shows the results of measuring the density, the elliptical long / short axis ratio, the shape, and the average cross-sectional area of the intermediate compound particles.
[0040]
On the other hand, the target sintered body was bonded to an oxygen-free copper backing plate using indium solder to obtain a target. This target was continuously discharged under the following sputtering conditions to examine the amount of arcing.
(Sputtering conditions)
DC power: 300 W, gas pressure: 7.0 mTorr, sputtering gas: Ar + oxygen, oxygen gas concentration in sputtering gas (O ₂ / Ar): 0.05%, discharge time: 66 hours (remaining target thickness is about 1 mm) ) Here, the oxygen gas concentration was set to a value at which the resistivity of the obtained thin film was most reduced.
[0041]
Table 1 shows the total number of arcing occurrences when the battery is continuously discharged for 66 hours. The cumulative number of arcing occurrences was very small.
[0042]
(Example 2)
An ITO target and a sample for analysis were prepared in the same manner as in Example 1 except that the cooling rate from 1600 ° C. to 1200 ° C. was 350 ° C./hour.
[0043]
Table 1 shows the results of measurement of the density, the ellipse major axis ratio, the shape, and the average cross-sectional area of the intermediate compound particles.
In addition, Table 1 shows the results of conducting a continuous discharge test similar to Example 1. The cumulative number of arcing occurrences was very small.
[0044]
(Example 3)
An ITO target and a sample for analysis were prepared in the same manner as in Example 1 except that the rate of temperature decrease from 1600 ° C. to 1200 ° C. was set to 300 ° C./hour.
[0045]
Table 1 shows the results of measurement of the density, the elliptical long / short axis ratio, the shape, and the average cross-sectional area of the intermediate compound particles.
In addition, Table 1 shows the results of conducting a continuous discharge test similar to Example 1. The cumulative number of arcing occurrences was very small.
[0046]
Example 4
An ITO target and a sample for analysis were prepared in the same manner as in Example 1 except that the temperature lowering rate from 1600 ° C. to 1200 ° C. was 200 ° C./hour.
[0047]
Table 1 shows the results of measurement of the density, the ellipse major axis ratio, the shape, and the average cross-sectional area of the intermediate compound particles.
In addition, Table 1 shows the results of conducting a continuous discharge test similar to Example 1. The cumulative number of arcing occurrences was very small.
[0048]
(Example 5)
An ITO target and an analytical sample were produced in the same manner as in Example 1 except that the temperature lowering rate from 1600 ° C. to 1300 ° C. was changed to 400 ° C./hour and thereafter 50 ° C./hour.
[0049]
Table 1 shows the results of measurement of the density, the ellipse major axis ratio, the shape, and the average cross-sectional area of the intermediate compound particles.
In addition, Table 1 shows the results of conducting a continuous discharge test similar to Example 1. The cumulative number of arcing occurrences was very small.
[0050]
(Comparative Example 1)
An ITO target and an analytical sample were produced in the same manner as in Example 1 except that the sintering temperature was 1500 ° C., and the temperature decrease rate from 1500 ° C. to 1200 ° C. was 400 ° C./hour.
[0051]
The result of measuring the surface structure of this analytical sample by SEM is shown in FIG. 3, and the intermediate compound portion in FIG. 3 shown in black is shown in FIG. Table 1 shows the results of measuring the density, the elliptical long / short axis ratio, the shape, and the average cross-sectional area of the intermediate compound particles. Further, Table 1 shows the results of carrying out a continuous discharge test similar to that in Example 1. A lot of arcing occurred.
[0052]
(Comparative Example 2)
An ITO target and a sample for analysis were prepared in the same manner as in Example 1 except that the rate of temperature decrease from 1600 ° C. to 1200 ° C. was set to 100 ° C./hour.
[0053]
Table 1 shows the results of measurement of the density, the ellipse major axis ratio, the shape, and the average cross-sectional area of the intermediate compound particles. In addition, Table 1 shows the results of conducting a continuous discharge test similar to Example 1. A lot of arcing occurred.
[0054]
(Comparative Example 3)
An ITO target and an analytical sample were produced in the same manner as in Example 1 except that the sintering temperature was 1500 ° C., and the temperature decrease rate from 1500 ° C. to 1200 ° C. was 100 ° C./hour.
[0055]
Table 1 shows the results of measurement of the density, the ellipse major axis ratio, the shape, and the average cross-sectional area of the intermediate compound particles. In addition, Table 1 shows the results of conducting a continuous discharge test similar to Example 1. A lot of arcing occurred.
[0056]
[Table 1]

【Effect of the invention】
According to the present invention, it is possible to provide an ITO sputtering target with less arcing and less adhesion of particles on the substrate.
[Brief description of the drawings]
1 is a view showing the surface structure of an ITO sputtering target obtained in Example 1. FIG.
FIG. 2 is a diagram in which a portion corresponding to intermediate compound particles in FIG. 1 is shown in black.
3 is a view showing a surface structure of an ITO sputtering target obtained in Comparative Example 1. FIG.
FIG. 4 is a diagram in which a portion corresponding to intermediate compound particles in FIG. 3 is shown in black.

Claims (7)

A sputtering target made of an ITO sintered body obtained by mixing, molding and firing indium oxide powder and tin oxide powder, the relative density of which is 99% or more, and the sintered body is made of cubic indium oxide An ellipse major axis ratio of the intermediate compound phase particles having a two-phase structure consisting of a matrix phase and an intermediate compound phase of indium oxide and tin oxide, and an arbitrary cross section of the sintered body observed using a scanning electron microscope Is an ITO sputtering target characterized by being 2.1 or more. A sputtering target made of an ITO sintered body obtained by mixing, molding and firing indium oxide powder and tin oxide powder, the relative density of which is 99% or more, and the sintered body is made of cubic indium oxide 80% or more of the number of particles of the intermediate compound phase, which has a two-phase structure of a parent phase and an intermediate compound phase of indium oxide and tin oxide, and is observed with a scanning electron microscope in an arbitrary cross section of the sintered body Is a polygonal shape including a concave surface. 3. The ITO sputtering target according to claim 1, wherein an average cross-sectional area of the intermediate compound phase particles is 5 μm ² or less. The tin content in the sintered body was Sn / (In + Sn) × 100%, and 7.7 wt% or more 14. The sputtering target according to claim 1, wherein the sputtering target is less than 3 % by weight. Indium oxide powder and tin oxide powder are mixed and molded, sintered in a pure oxygen stream at 1550 ° C. or higher and lower than 1650 ° C., and then the temperature decreasing rate from the sintering holding temperature to at least 1300 ° C. is 200 ° C./hour. The manufacturing method of the ITO sputtering target characterized by the above. 6. The method for producing an ITO sputtering target according to claim 5, wherein the indium oxide powder and the tin oxide powder are mixed at a ratio such that tin oxide is 8 wt% or more and less than 15 wt% in terms of oxide. The ratio (charge weight / oxygen flow rate) of the oxygen flow rate (L / min) and the charged amount of the compact (kg) when introducing oxygen into the furnace during sintering is 1.0 or less. The manufacturing method of the ITO sputtering target of Claim 5 or Claim 6.

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