JP2008214697A - Sputtering target - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sputtering target capable of suppressing the occurrence of abnormal discharge even if an IGZO sputtering target is used in DC sputtering. <P>SOLUTION: The sputtering target consists of a compound expressed by InGaZnO<SB>4</SB>as a principal component and contains positive quadrivalent or higher valency metal elements. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sputtering target. More specifically, the present invention relates to an IGZO sputtering target that can suppress abnormal discharge when an oxide semiconductor film is formed.

Oxide semiconductor films composed of several metal complex oxides have high carrier mobility and visible light transmission, so liquid crystal display devices, thin-film electroluminescence display devices, electrophoretic display devices, powder transfer It is used in a wide variety of applications such as switching elements and drive circuit elements for system display devices.
An oxide semiconductor film made of indium oxide-gallium oxide-zinc oxide called IGZO is most popular among oxide semiconductor films made of such metal complex oxides. In addition, indium oxide-zinc oxide (IZO), tin oxide added with zinc oxide (ZTO), indium oxide-zinc oxide-tin oxide added with gallium oxide, and the like are known. Since these are different in ease of manufacture, price, characteristics, etc., they are used as appropriate according to their use.

  Among these, oxides of In, Ga, and Zn (IGZO) or an oxide semiconductor film containing these as a main component have an advantage of higher carrier mobility than an amorphous silicon film. It has attracted attention (see, for example, Patent Document 1-10).

Generally, a sputtering target used for forming an oxide semiconductor film composed of indium oxide-gallium oxide-zinc oxide is mixed with raw material powder, and then calcined, pulverized, granulated, molded, sintered, and reduced. It is manufactured through a process. Thus, since there are many manufacturing processes, it has the fault that productivity is bad and cost increases. Further, although the bulk resistance of the target is reduced by reduction, the conductivity after reduction is 90 S / cm (bulk specific resistance: 0.011 Ωcm) at the most, and a sufficiently low resistance target could not be obtained. .
Therefore, although it is desirable to omit even one of the above steps, the current state is that the process has not been improved and the conventional manufacturing process is followed.

_Also, the _{InGaO 3 (ZnO) 2, InGaO} 3 (ZnO) 3, InGaO 3 (ZnO) 4, InGaO 3 (ZnO) 5 or InGaO _{3 (ZnO) 7,} compound and their preparation, for example, Patent Documents 11-15. However, as for the raw material powder used, it is only described that the particle size is particularly preferably 10 μm or less, and although the formation of each compound has been confirmed, the bulk resistivity value There was no description, and there was a problem in using for a sputtering target.

Further, it is known that the IGZO sputtering target has a compound of InGaZnO ₄ as a main component. However, this target has a problem that an abnormal discharge occurs during DC sputtering, resulting in a defect in the resulting film.
Japanese Patent Application Laid-Open No. 08-295514 Japanese Patent Laid-Open No. 08-330103 Japanese Patent Laid-Open No. 2000-044236 JP 2006-165527 A JP 2006-165528 A JP 2006-165529 A JP 2006-165530 A JP 20061655531 JP 2006-165532 A JP 2006-173580 A JP-A-63-239117 JP 63-210022 A JP 63-210023 A JP 63-21004 A JP-A 63-265818

  An object of this invention is to provide the sputtering target which can suppress generation | occurrence | production of abnormal discharge, even if it uses an IGZO sputtering target by DC sputtering.

  As a result of intensive studies, the present inventors have found that by adding a positive tetravalent metal element to the IGZO sputtering target, the occurrence of abnormal discharge during sputtering can be suppressed, and the present invention has been completed.

According to the present invention, the following sputtering target can be provided.
1. A sputtering target comprising a compound represented by InGaZnO ₄ as a main component and containing a positive tetravalent or higher metal element.
2. 2. The sputtering target according to 1, wherein the content of the positive tetravalent or higher metal element is 100 ppm to 10,000 ppm with respect to all metal elements in the sputtering target.
3. 2. The sputtering target according to 1, wherein the content of the positive tetravalent or higher metal element is 200 ppm to 5000 ppm with respect to all metal elements in the sputtering target.
4). 2. The sputtering target according to 1, wherein the content of the positive tetravalent or higher metal element is 500 ppm to 2000 ppm with respect to all metal elements in the sputtering target.
5. Bulk resistance is less than 1 * 10 < ^-3 > (omega | ohm) cm, The sputtering target in any one of 1-4 characterized by the above-mentioned.
6). The positive tetravalent or higher metal element is one or more elements selected from the group consisting of tin, zirconium, germanium, cerium, niobium, tantalum, molybdenum, and tungsten. The sputtering target described.

  ADVANTAGE OF THE INVENTION According to this invention, the IGZO sputtering target which can suppress generation | occurrence | production of the abnormal discharge at the time of sputtering can be provided.

The sputtering target of the present invention is an IGZO sputtering target produced mainly from indium oxide, gallium oxide and zinc oxide, and contains a compound represented by InGaZnO ₄ as a main component and contains a metal element having a positive tetravalent or higher value. Features. In an IGZO sputtering target to which a positive or tetravalent metal element is added, the bulk resistance value of the target itself can be reduced, and the occurrence of abnormal discharge during DC sputtering can be suppressed.
Furthermore, in the target manufacturing process, it is possible to omit a reduction process for reducing the bulk resistance of the target. Therefore, productivity is high and manufacturing costs can be reduced.
Note that the main component is a compound (crystal) represented by InGaZnO ₄ is a case where a structure other than InGaZnO ₄ is not confirmed in X-ray diffraction analysis or is smaller than the intensity of InGaZnO ₄ even if confirmed. means.

  In the sputtering target of the present invention, the addition amount (weight) of a positive tetravalent or higher metal element with respect to all the metal elements in the target is preferably 100 ppm to 10,000 ppm. If the amount added is less than 100 ppm, the effect of adding a positive tetravalent or higher metal element may be small. On the other hand, if it exceeds 10000 ppm, problems may occur in the stability of the oxide thin film or the carrier mobility may be reduced. is there. The amount of addition of the positive tetravalent or higher metal element is preferably 200 ppm to 5000 ppm, and more preferably 500 ppm to 2000 ppm.

In the sputtering target of the present invention, the bulk resistance of the target is preferably less than 1 × 10 ⁻³ Ωcm. If the bulk resistance is more than 1 × 10 ^-3 Ωcm, when continued long time DC sputtering, or cracking sparking target by abnormal discharge, the particles jumped out from the target to adhere to the film substrate by a spark Thus, the performance of the obtained film as an oxide semiconductor film may be reduced.
The bulk resistance is a value measured by a four-probe method using a resistivity meter.

The sputtering target of the present invention can be produced, for example, by mixing each powder of a material containing indium oxide, gallium oxide, zinc oxide and a metal element having a positive tetravalent or higher, and pulverizing and sintering the mixture.
As a material containing a positive tetravalent or higher metal element, for example, a single metal or an oxide can be used. The positive tetravalent or higher metal element may be appropriately selected from one or more of tin, zirconium, germanium, cerium, niobium, tantalum, molybdenum, and tungsten.

For the raw material powder, the specific surface area 8~10m ² / g of indium oxide powder, the specific surface area of 5 to 10 m ² / g of gallium oxide powder, the specific surface area of the zinc oxide powder be 2 to 4 m ² / g preferable. Alternatively, it is preferable that the median diameter of the indium oxide powder is 1 to 2 μm, the median diameter of the gallium oxide powder is 1 to 2 μm, and the median diameter of the zinc oxide powder is 0.8 to 1.6 μm.
In addition, it is preferable to use the powder whose specific surface area of an indium oxide powder and the specific surface area of a gallium oxide powder are substantially the same. Thereby, it can pulverize and mix more efficiently. Specifically, the difference in specific surface area is preferably 3 m ² / g or less. If the specific surface area is too different, efficient pulverization and mixing cannot be performed, and gallium oxide particles may remain in the sintered body.

In the raw material powder, the mixing ratio of indium oxide powder, gallium oxide powder and zinc oxide powder (indium oxide powder: gallium oxide powder: zinc oxide powder) is approximately 45:30:25 by weight ratio (In: Ga: Zn = 1: 1: 1) and approximately 51:34:15 (in a molar ratio of In ₂ O ₃ : Ga ₂ O ₃ : ZnO = 1: 1: 1).
As described above, the blending amount of the material containing a metal element having a positive tetravalent or higher valence is preferably 100 ppm to 10000 ppm with respect to all metal elements in the target, and the amount of indium oxide powder, gallium oxide powder and zinc oxide powder used. Adjust accordingly.
In addition, as long as the mixed powder containing a material containing a metal element including indium oxide powder, gallium oxide powder, zinc oxide powder and a positive tetravalent or higher metal element is used, other components that improve the characteristics of the sputtering target may be added. .

The mixed powder is mixed and ground using, for example, a wet medium stirring mill. At this time, pulverization is performed so that the specific surface area after pulverization is 1.5 to 2.5 m ² / g higher than the specific surface area of the raw material mixed powder, or the average median diameter after pulverization is 0.6 to 1 μm. It is preferable to do. By using the raw material powder adjusted in this way, a high-density sintered body for an IGZO sputtering target can be obtained without requiring a calcination step at all. Moreover, a reduction process is also unnecessary.
In addition, if the increase in the specific surface area of the raw material mixed powder is less than 1.0 m ² / g or the average median diameter of the raw material mixed powder after pulverization exceeds 1 μm, the sintered density may not be sufficiently increased. On the other hand, if the increase in the specific surface area of the raw material mixed powder exceeds 3.0 m ² / g, or if the average median diameter after pulverization is less than 0.6 μm, contamination from the pulverizer during pulverization (impurity contamination amount) ) May increase.

  Here, the specific surface area of each powder is a value measured by the BET method. The median diameter of the particle size distribution of each powder is a value measured with a particle size distribution meter. These values can be adjusted by pulverizing the powder by a dry pulverization method, a wet pulverization method or the like.

  The raw material after the pulverization step is dried with a spray dryer or the like and then molded. For forming, a known method such as pressure forming or cold isostatic pressing can be employed.

Next, the obtained molded product is sintered to obtain a sintered body. The sintering is preferably performed at 1500 to 1600 ° C. for 2 to 20 hours. As a result, a sintered body for an IGZO sputtering target having a sintered body density of 6.0 g / cm ³ or more can be obtained. When the temperature is less than 1500 ° C., the density does not improve. When the temperature exceeds 1600 ° C., zinc evaporates, the composition of the sintered body changes, or voids (voids) are generated in the sintered body due to evaporation. There is.
Sintering is preferably performed in an oxygen atmosphere by circulating oxygen or under pressure. As a result, transpiration of zinc can be suppressed, and a sintered body that does not have voids (voids) can be obtained.
Since the sintered body manufactured in this way has a high density of 6.0 g / cm ³ or more, the generation of nodules and particles at the time of use is small, and thus an oxide semiconductor film having excellent film characteristics is manufactured. Can do.
InGaZnO ₄ is produced as a main component in the obtained sintered body. This can be confirmed by identification of the crystal structure by X-ray diffraction.

In order to use the sintered body thus manufactured as a sputtering target, the sintered body is ground by, for example, a surface grinder so that the surface roughness Ra is 5 μm or less. Further, the sputter surface of the sputtering target may be mirror-finished so that the average surface roughness Ra is 1000 angstroms or less. For this mirror finishing (polishing), a known polishing technique such as mechanical polishing, chemical polishing, mechanochemical polishing (a combination of mechanical polishing and chemical polishing) can be used. For example, polishing to # 2000 or more with a fixed abrasive polisher (polishing liquid: water) or lapping with loose abrasive lapping (abrasive: SiC paste, etc.), and then lapping by changing the abrasive to diamond paste Can be obtained by: There is no restriction | limiting in particular in such a grinding | polishing method.
By bonding the obtained sputtering target to a backing plate, the sputtering target can be mounted and used.

In addition, air blow, running water washing | cleaning, etc. can be used for the cleaning process of a sputtering target. When removing foreign matter by air blow, it is possible to remove the foreign matter more effectively by suctioning with a dust collector from the opposite side of the nozzle.
In addition to air blow and running water cleaning, ultrasonic cleaning and the like can also be performed. In ultrasonic cleaning, a method of performing multiple oscillations at a frequency of 25 to 300 KHz is effective. For example, it is preferable to perform ultrasonic cleaning by causing multiple oscillations of 12 types of frequencies at intervals of 25 KHz between frequencies of 25 to 300 KHz.

By performing sputtering using the sputtering target after bonding, an IGZO oxide semiconductor film mainly containing oxides of In, Ga, and Zn can be formed on an object such as a substrate.
The oxide thin film obtained from the target of the present invention is an amorphous film, and the added tetravalent or higher-valent metal element does not show a doping effect (an effect of carrier generation). It will be good enough. Therefore, when used as an oxide semiconductor film, the stability is high and the Vth shift is suppressed, so that the operation as a semiconductor is stable.

  Subsequently, the present invention will be described with reference to comparative examples by way of examples. In addition, a present Example shows the suitable example of this invention, and this invention is not restrict | limited to an Example. Therefore, the present invention includes modifications based on the technical idea or other embodiments.

Example 1
A specific surface area of the indium oxide powder and the specific surface area is ^6m 2 / g ^6m 2 / g gallium oxide powder and the specific surface area is as a raw material powder and zinc oxide powder is ^3m 2 / g in a weight ratio of 45:30:25 It was weighed so as to further the SnO ₂ as a positive tetravalent metal elements, the content of Sn element relative to the total metal elements [Sn / (in + Ga + Zn + Sn): weight ratio] was added to a 600 ppm.
The mixed powder of raw materials was mixed and pulverized by a wet medium stirring mill. As the medium, 1 mmφ zirconia beads were used. The specific surface area after pulverization was increased by 2 m ² / g from the specific surface area of the raw material mixed powder, and then dried with a spray dryer.
The mixed powder after pulverization was filled in a mold and pressure-molded with a cold press. Further, sintering was performed at 1550 ° C. for 8 hours in an oxygen atmosphere while oxygen was circulated. Thus, a sintered body for an IGZO sputtering target having a sintered body density of 6.12 g / cm ³ was obtained without performing a calcination step.
The density of the sintered body was calculated from the weight and outer dimensions of the sintered body cut out to a certain size.

This sintered body was analyzed by X-ray diffraction. FIG. 1 is an X-ray diffraction chart of the sintered body. From this figure, it was confirmed that InGaZnO ₄ crystals exist in the sintered body. Moreover, since the peak of metal oxides other than InGaZnO ₄ was not observed, it was confirmed that a sintered body containing InGaZnO ₄ as a main component was obtained.
The bulk resistance of the sintered body was measured by a four probe method using a resistivity meter (manufactured by Mitsubishi Oil Chemical Co., Ltd., Loresta) and found to be 0.95 × 10 ⁻³ Ωcm.

Comparative Example 1
A sintered body was produced in the same manner as in Example 1 except that a metal oxide (tin oxide) containing a metal element having a positive tetravalent or higher value was not added.
As a result, the density of this sintered body was 5.98 g / cm ³ . Further, as a result of analysis by X-ray diffraction, a sintered body containing InGaZnO ₄ as a main component was obtained because of the presence of InGaZnO ₄ crystals and the absence of peaks of metal oxides other than InGaZnO _4. Was confirmed.
The bulk resistance of this sintered body was 0.018 Ωcm.

  FIG. 2 is a graph showing the relationship between the amount of tin element added and the bulk resistance of the sintered body. Except that the addition amount of tin oxide powder was 500 ppm, 800 ppm, and 1000 ppm, bulk resistance was illustrated for a sintered body manufactured in the same manner as in Example 1 and Comparative Example 1 (the addition amount of tin element was 0 ppm). . As apparent from FIG. 2, the bulk resistance of the sintered body can be reduced by adding a tin element which is a positive tetravalent metal element.

Example 2-8
A sintered body was produced in the same manner as in Example 1 except that a predetermined amount of the oxide shown in Table 1 was used instead of tin oxide as the metal oxide containing a metal element having a positive tetravalent or higher valence. Table 1 shows the bulk resistance values of the sintered bodies.

  FIG. 3 is a graph showing the relationship between the amount of addition of a positive tetravalent or higher metal element and the bulk resistance of the sintered body for the results of Example 2-8. As apparent from FIG. 3, the bulk resistance of the sintered body is reduced by adding a metal element having a positive tetravalent or higher value.

  The sputtering target of the present invention is suitable as a raw material for oxide semiconductor films such as switching elements and drive circuit elements in liquid crystal display devices, thin film electroluminescence display devices, electrophoretic display devices, powder transfer display devices, and the like.

2 is an X-ray diffraction chart of a sintered body produced in Example 1. FIG. It is a figure which shows the relationship between the addition amount of a tin element, and the bulk resistance value of a sintered compact. It is a figure which shows the relationship between the addition amount of the metal element more than positive tetravalence and the bulk resistance of a sintered compact.

Claims (6)

A sputtering target comprising a compound represented by InGaZnO ₄ as a main component and containing a positive tetravalent or higher metal element.   2. The sputtering target according to claim 1, wherein the content of the positive tetravalent or higher metal element is 100 ppm to 10,000 ppm with respect to all metal elements in the sputtering target.   2. The sputtering target according to claim 1, wherein a content of the positive tetravalent or higher metal element is 200 ppm to 5000 ppm with respect to all metal elements in the sputtering target.   2. The sputtering target according to claim 1, wherein a content of the positive tetravalent or higher metal element is 500 ppm to 2000 ppm with respect to all metal elements in the sputtering target. Bulk resistance is less than 1x10 < ^-3 > ohm-cm, The sputtering target in any one of Claims 1-4 characterized by the above-mentioned. 6. The positive tetravalent or higher metal element is at least one element selected from the group consisting of tin, zirconium, germanium, cerium, niobium, tantalum, molybdenum, and tungsten. A sputtering target according to claim 1.