KR101331293B1 - Sintered oxide and oxide semiconductor thin film - Google Patents

Abstract

An object of the present invention is to provide an oxide sintered body which does not contain expensive gallium (Ga) and has a small bulk resistance. Another object is to provide an oxide semiconductor thin film having the same composition as the oxide sintered body. As an oxide sintered body consisting of indium (In), zinc (Zn), metal element X (where X represents at least one element selected from Al and Ti), and oxygen (O), indium (In), An oxide sintered body in which the atomic ratio of zinc (Zn) and the metal element X satisfies 0.2 ≦ In / (In + Zn + X) ≦ 0.8, 0.1 ≦ Zn / (In + Zn + X) ≦ 0.5, and 0.1 ≦ X / (In + Zn + X) ≦ 0.5, respectively. And an oxide semiconductor film having the same composition as this.

Description

Oxide sintered body and oxide semiconductor thin film {SINTERED OXIDE AND OXIDE SEMICONDUCTOR THIN FILM}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide sintered body and a transparent oxide semiconductor thin film which are useful for fabricating a thin film transistor or a transparent electrode in a display device.

Transparent oxide semiconductors are used as transparent electrodes such as solar cells and touch panels in addition to active layers of thin film transistors in display devices such as liquid crystal display devices, plasma display devices and organic EL display devices. Conventionally, an In—Ga—Zn—O system (hereinafter referred to as “IGZO system”) is known as a transparent oxide semiconductor (see Non-Patent Document 1), and tin (Sn) is added for intention of improving characteristics. There is also a report regarding the system (see Patent Documents 1 and 2). However, gallium (Ga), which is an essential component of these systems, is a rare element and, due to its high price and the like, has a large limitation in the industrial and large-scale use.

As a transparent oxide semiconductor which does not use Ga, there is a report regarding an In—Zn—Sn—O system (see Patent Document 3). In patent document 3, it contains indium, tin, zinc, and oxygen, the number of atoms of indium (= [In]), the number of atoms of tin (= [Sn]), and the number of atoms of zinc (= [Zn] When the atomic ratio of the above-mentioned [Sn] to the sum of N) is more than 0.1 and less than 0.2, the following atomic ratio 1 is satisfied, and when it is 0.2 or more and less than 0.3, the following atomic ratio 2 is described.

Atomic ratio 1

0.1 <[In] / ([In] + [Sn] + [Zn]) <0.5

0.1 <[Sn] / ([In] + [Sn] + [Zn]) <0.2

0.3 <[Zn] / ([In] + [Sn] + [Zn]) <0.8

Atomic ratio 2

0.01 <[In] / ([In] + [Sn] + [Zn]) <0.3

0.2 ≤ [Sn] / ([In] + [Sn] + [Zn]) <0.3

0.4 <[Zn] / ([In] + [Sn] + [Zn]) <0.8

Japanese Patent Application Laid-Open No. 2008-280216 Japanese Laid-Open Patent Publication No. 2010-118407 Japanese Patent Application Laid-Open No. 2008-243928

 Nature 432, p488-492, October 2004

However, in the In-Zn-Sn-O system described in Patent Document 3, there is a problem that abnormal discharge is likely to occur at the time of sputtering because the bulk resistance is high.

Then, an object of this invention is to provide the oxide sintered compact which is a scarce resource and does not contain expensive gallium (Ga) and can make a bulk resistance small. Another object of the present invention is to provide an oxide semiconductor thin film having the same composition as the oxide sintered body.

The inventors found out that aluminum (Al), a trivalent metal element such as gallium, and titanium (Ti), a tetravalent metal element, are promising as alternative elements of gallium (Ga), which is a rare and expensive element, and these elements are promising. The atomic ratio, the sintered compact, the manufacturing conditions of a film | membrane, etc. were earnestly examined, and this invention was completed.

In an aspect, the present invention provides an oxide composed of indium (In), zinc (Zn), metal element X (where X represents at least one element selected from Al and Ti), and oxygen (O). As the sintered body, the atomic ratios of indium (In), zinc (Zn), and metal element X are 0.2 ≦ In / (In + Zn + X) ≦ 0.8, 0.1 ≦ Zn / (In + Zn + X) ≦ 0.5, and 0.1 ≦ X / (In + Zn + X, respectively). ) Is an oxide sintered body that satisfies?

In one embodiment, the oxide sintered body according to the present invention has a relative density of 98% or more.

In another embodiment, the oxide sintered body according to the present invention has a bulk resistance of 3 mΩcm or less.

In another aspect of the present invention, indium (In), zinc (Zn), metal element X (where X represents at least one element selected from Al and Ti) and oxygen (O) In the oxide semiconductor thin film formed, the atomic ratio of indium (In), zinc (Zn), and metal element X is 0.2 ≦ In / (In + Zn + X) ≦ 0.8, 0.1 ≦ Zn / (In + Zn + X) ≦ 0.5, 0.1 ≦ X / (In + Zn + X ) Is an oxide semiconductor thin film satisfying?

In one embodiment, the oxide semiconductor thin film according to the present invention is amorphous.

In another embodiment, the oxide semiconductor thin film according to the present invention has a carrier concentration of 10 ¹⁶ to 10 ¹⁸ cm ^-3 .

In yet another embodiment, the oxide semiconductor thin film according to the present invention has a mobility of 1 cm 2 / Vs or more.

In yet another aspect, the present invention is a thin film transistor including the oxide semiconductor thin film as an active layer.

In yet another aspect, the present invention is an active matrix driving display panel including the thin film transistor.

According to this invention, the oxide sintered compact which does not contain gallium (Ga) and can make a bulk resistance small can be provided. This oxide sintered compact is useful as a sputtering target. By sputter film-forming using this target, a transparent oxide semiconductor film can be manufactured.

(Composition of oxide-sintered body)

The oxide sintered body according to the present invention includes indium (In), zinc (Zn), metal element X (where X represents at least one element selected from Al and Ti), and oxygen (O) as constituent elements. . However, it is usually necessary to contain an element which is inevitably contained in the raw material refining process or an impurity element that is inevitably mixed in the oxide sintered manufacturing process, for example, up to about 10 ppm of each element. It is contained in the sintered compact which concerns on this invention.

It is preferable that ratio [In] / ([In] + [Zn] + [X]) of the number of atoms of indium to the total number of atoms of indium, zinc and the metal element X is 0.2-0.8. If [In] / ([In] + [Zn] + [X]) is less than 0.2, the relative density at the time of target manufacture becomes small, bulk resistance becomes high, and abnormal discharge at the sputter | spatter becomes easy to generate | occur | produce. . On the contrary, when [In] / ([In] + [Zn] + [X]) exceeds 0.8, the carrier concentration of the film obtained by sputtering the target of the composition becomes too high, and the on-off ratio becomes small as the channel layer of the transistor. . [In] / ([In] + [Zn] + [X]), More preferably, it is the range of 0.25-0.6, More preferably, it is the range of 0.3-0.5. Here, [In] represents the number of atoms of indium, [Zn] represents the number of atoms of zinc, and [X] represents the number of atoms of the metal element X, respectively.

It is preferable that ratio [Zn] / ([In] + [Zn] + [X]) of the number of atoms of zinc with respect to the total number of atoms of indium, zinc, and the metal element X is 0.1-0.5. If [Zn] / ([In] + [Zn] + [X]) is less than 0.1, the carrier concentration of the film becomes too large. On the contrary, when [Zn] / ([In] + [Zn] + [X]) exceeds 0.5, the carrier concentration of the film becomes too small. The relative density at the time of manufacture of a target becomes small. [Zn] / ([In] + [Zn] + [X]), More preferably, it is the range of 0.15-0.4, More preferably, it is the range of 0.2-0.35.

It is preferable that ratio [X] / ([In] + [Zn] + [X]) of the total number of atoms of the metal element X with respect to the total number of atoms of indium, zinc, and the metal element X is 0.1-0.5. When [X] / ([In] + [Zn] + [X]) is less than 0.1, the carrier concentration of the film obtained by sputtering the target of the composition becomes too high, and the on-off ratio becomes small as the channel layer of the transistor. On the contrary, when [X] / ([In] + [Zn] + [X]) exceeds 0.5, the carrier concentration of the film becomes too small, the relative density at the time of target production becomes small, the bulk resistance becomes high, and sputtering Abnormal discharge easily occurs. [X] / ([In] + [Zn] + [X]), More preferably, it is the range of 0.15-0.4, More preferably, it is the range of 0.2-0.35.

Relative Density of Oxide Sintered Body

The relative density of the oxide sintered body has a correlation with the occurrence of Joules on the surface during sputtering. If the oxide sintered body is low density, when the oxide sintered body is processed into a target and sputtered into film, the lower oxide of indium is formed on the surface as the sputter film is formed. The high-resistance part called a nodule of a processus | protrusion generate | occur | produces, and it becomes easy to become a starting point of abnormal discharge in the subsequent sputter | spatter. In this invention, the relative density of an oxide sintered compact can be made into 98% or more, and if it is a high density of this grade, there is little adverse effect by the nodule at the time of sputtering. The relative density is preferably 99% or more, and more preferably 99.5% or more.

In addition, the relative density of an oxide sintered compact can be calculated | required by dividing the density computed from the weight and external dimension after processing an oxide sintered compact in a predetermined shape by the theoretical density of the oxide sintered compact.

(Bulk resistance of oxide-sintered body)

The bulk resistance of the oxide sintered body has a correlation with the extent to which abnormal discharge during sputtering is likely to occur. When the bulk resistance is high, abnormal discharge easily occurs during sputtering. In the present invention, the bulk resistance can be made 3 mΩcm or less by the appropriate range of the composition and the optimization of the manufacturing conditions, and there is little adverse effect on the occurrence of abnormal discharge during sputtering if the low bulk resistance is about this level. The bulk resistance is preferably 2.7 mΩcm or less, and more preferably 2.5 mΩcm or less.

In addition, a bulk resistance can be measured using a resistivity meter by the four probe method.

(Manufacturing Method of Oxide Sintered Body)

Oxide sinters of various compositions according to the present invention include, for example, a blending ratio of raw material powders such as indium oxide and zinc oxide as raw materials, particle diameters of raw material powders, grinding time, sintering temperature, sintering time, and sintering atmosphere. It can obtain by adjusting conditions, such as a gas kind.

It is preferable that raw material powder is an average particle diameter of 1-2 micrometers. When the average particle diameter exceeds 2 m, the density of the sintered compact becomes difficult to be improved. Therefore, the fine particle may be wetly pulverized or the like as the raw material powder alone or as a mixed powder, and the average particle size may be reduced to about 1 m. It is also effective to preliminarily sinter for the purpose of improving the sinterability before wet mixing and grinding. On the other hand, a raw material of less than 1 µm is difficult to obtain, and when too small, aggregation between particles easily occurs and difficult to handle, so the average particle diameter of the mixed powder before sintering is preferably 1 to 2 µm. Here, the average particle diameter of raw material powder points out the median diameter in the volume distribution measured by the laser diffraction type particle size distribution measuring apparatus. Moreover, in the range which can be interpreted as the equivalent of this invention, you may add other components which have an effect, such as improving a sinterability, without adversely affecting sintered compact characteristics other than predetermined raw material powder. It is preferable to shape | mold after mixing the raw material mixed powder after grinding | pulverization with a spray dryer, etc., to improve fluidity | liquidity and moldability. The molding can be carried out by a conventional method such as press molding or cold isostatic pressing.

Thereafter, the molded product is sintered to obtain a sintered body. It is preferable to sinter 2 to 20 hours at 1400-1600 degreeC. Thereby, relative density can be made into 98% or more. If the sintering temperature is less than 1400 ° C., the density is hardly improved. On the contrary, if the sintering temperature is more than 1600 ° C., the composition of the sintered body may change due to volatilization of constituent elements or the like, causing a decrease in density due to void generation due to volatilization. Sometimes. Atmosphere can be used for the atmosphere gas at the time of sintering, the oxygen deficiency with respect to a sintered compact can be increased, and bulk resistance can be made small. However, depending on the composition of the sintered compact, even if the atmospheric gas is oxygen, a sufficiently high density sintered compact can be obtained.

(Sputter Deposition)

The oxide sintered body obtained as mentioned above can be made into the sputtering target by performing grinding | polishing, grinding | polishing, etc., and can form an oxide film which has the same composition as the said target by film-forming using this. At the time of processing, it is preferable to make surface roughness Ra into 5 micrometers or less by grinding a surface by methods, such as surface grinding. By reducing the surface roughness, it is possible to reduce the starting point of nodule generation which causes anomalous discharge.

The sputtering target is affixed to a backing plate made of copper or the like and installed in the sputtering device, and sputtered under suitable conditions such as an appropriate degree of vacuum, atmospheric gas, sputter power, and the like, thereby obtaining a film having substantially the same composition as the target.

In the case of the sputtering method, it is preferable that the attained vacuum degree in the chamber before film formation is 2 × 10 ^-4 Pa or less. If the pressure is excessively high, there is a possibility that the mobility of the obtained film is lowered due to the influence of the impurities in the residual atmosphere gas.

As the sputter gas, a mixed gas of argon and oxygen can be used. As a method of adjusting the oxygen concentration in the mixed gas, for example, using a gas cylinder of 100% argon and a gas cylinder of 2% oxygen in argon, the supply flow rate from each gas cylinder to the chamber is changed to the mass flow. It can implement by setting suitably. Here, the oxygen concentration in the mixed gas means oxygen partial pressure / (oxygen partial pressure + argon partial pressure), which is also the same as dividing the flow rate of oxygen by the sum of the flow rates of oxygen and argon. The oxygen concentration may be appropriately changed in accordance with the desired carrier concentration, but may typically be 1 to 3%, more typically 1 to 2%.

The total pressure of the sputter gas is about 0.3 to 0.8 Pa. If the total pressure is lower than this, plasma discharge becomes difficult to start, and plasma starts to become unstable even when started. In addition, when the total pressure is higher than this, problems such as slowing the film formation speed and adversely affecting productivity occur.

Sputter | spatter power forms into a film about 200-1200 W when target size is 6 inches. If the sputter power is too small, the film formation speed is small, the productivity is lowered. On the contrary, if the sputter power is too large, problems such as splitting of the target occur. 200-1200 W is 1.1 W / cm <2> -6.6 W / cm <2> in conversion with sputter power density, It is preferable to set it as 3.2-4.5 W / cm <2>. Here, the sputter power density is obtained by dividing the sputter power by the area of the sputtering target, and the power applied to the sputtering target is different because the power actually received by the sputtering target and the deposition rate are different depending on the sputtering target size even for the same sputtering power. It is an index for unifying expression.

As a method of obtaining a film from an oxide sintered body, a vacuum vapor deposition method, an ion plating method, a PLD (pulse laser deposition) method, etc. can also be used, but what is easy to use industrially is that it satisfies requirements such as large area, high speed film formation, and discharge stability. DC magnetron sputtering.

There is no need to heat the substrate at the time of sputtering. This is because relatively high mobility can be obtained without heating the substrate, and there is no need to add time or energy for raising the temperature. When the substrate is sputtered without heating, the resulting film becomes amorphous. However, since the same effect as the annealing after room temperature film-forming can be expected by heating a board | substrate, you may form into a film by board | substrate heating.

(Carrier concentration of oxide film)

The carrier concentration of the oxide film has a correlation with various characteristics of the transistor when the film is used for the channel layer of the transistor. If the carrier concentration is too high, a small leakage current is generated even when the transistor is turned off, and the on-off ratio is lowered. On the other hand, if the carrier concentration is too low, the current flowing through the transistor becomes small. In the present invention, the carrier concentration of the oxide film is changed from 10 ¹⁶ to the appropriate range of the composition or the like. It can be 10 ¹⁸ cm ^-3, and if it is this range, the transistor with a favorable characteristic can be manufactured.

(Mobility of oxide film)

Mobility is one of the most important characteristics among the transistors, and it is preferable that the oxide semiconductor is 1 cm 2 / Vs or more, which is the mobility of amorphous silicon, which is a competition material used as the channel layer of the transistor. Basically, the higher the mobility, the better. The oxide film according to the present invention may have a mobility of 1 cm 2 / Vs or more, preferably 3 cm 2 / Vs or more, and more preferably 5 cm 2 / Vs or more, depending on an appropriate range of composition. It can have This results in superior characteristics than amorphous silicon, resulting in higher industrial applicability.

The oxide semiconductor thin film according to the present invention can be used, for example, as an active layer of a thin film transistor. In addition, the thin film transistor obtained by using the above manufacturing method can be used as an active element and used in an active matrix drive display panel.

Example

Examples of the present invention will now be described in conjunction with comparative examples, which are provided for a better understanding of the present invention and its advantages and are not intended to be limiting. Therefore, this invention includes all the aspects or modifications other than an Example within the scope of the technical idea of this invention.

In the following Examples and Comparative Examples, the physical properties of the sintered compact and the film were measured by the following method.

(A) Relative density of sintered body

It calculated | required from the measurement result of a weight and an external dimension, and the theoretical density from a structural element.

(B) Bulk resistance of sintered body

It was calculated | required by the four probe method (JIS K7194) using the model Σ-5 + apparatus manufactured by NPS (NPS).

(C) Composition of sintered body and film

It was calculated | required by ICP (High Frequency Inductively Coupled Plasma) analysis using the model SPS3000 by SII Nanotechnology.

(D) Thickness

It calculated | required using the step | diometer (made by Veeco, model Dektak8 STYLUS PROFILER).

(E) Carrier concentration and mobility of the film

The glass substrate formed into a film was cut out to about 10 mm in width | variety, the indium electrode was attached to the four corners, it was set in the hall measuring apparatus (Toyo Technica make, model Resitest8200), and it measured.

(F) Crystals or amorphous structures of membranes

Crystallinity was determined using a RINT-1100 X-ray diffractometer manufactured by Rigaku Corporation. If no significant peak above background level was recognized, it was determined to be amorphous.

(G) Average particle size of powder

The average particle diameter was measured by SALD-3100 by Shimadzu Corporation.

&Lt; Example 1 >

The indium oxide powder (average particle diameter 1.0 mu m), the zinc oxide powder (average particle diameter 1.0 mu m), and the aluminum oxide powder (average particle diameter 1.0 mu m) had an atomic ratio of the metal element (In: Zn: Al) of 0.4: 0.3: 0.3 Weighed as desired, and the wet mixed grinding was performed. The average particle diameter of the mixed powder after grinding was 0.8 µm. After this mixed powder was granulated with a spray dryer, it filled into a metal mold | die and pressure-molded, and it sintered for 10 hours at 1450 degreeC high temperature in air | atmosphere. The obtained sintered compact was processed into the disk shape of diameter 6 inch and 6 mm in thickness, it was ground-grinded, and it was set as the sputtering target. About the said target, it was 99.8% when the relative density was computed from the measurement result and theoretical density of a weight and an external dimension. In addition, the bulk resistance of the sintered compact measured by the probe probe method was 2.1 m (ohm) cm. As a result of sintered body composition analysis by ICP (high frequency inductively coupled plasma) analysis, In: Zn: Al = 0.4: 0.3: 0.3 (atomic ratio).

The sputtering target produced above was affixed on the copper backing plate using indium as a solder | pewter, and it installed in the DC magnetron sputtering apparatus (SPL-500 sputtering apparatus made by ANELVA). The glass substrate used Corning 1737, and sputter | spatter conditions were: substrate temperature: 25 degreeC, reaching pressure: 1.2 * 10 <^-4> Pa, atmospheric gas: Ar 99%, oxygen 1%, sputter pressure (total pressure): 0.5 Pa, A thin film having a film thickness of about 100 nm was produced with an input power of 500 W. At the time of film-forming of the oxide semiconductor thin film, abnormal discharge was not recognized.

As a result of performing the hole measurement of the obtained film | membrane, carrier density | concentration 5.0 * 10 <^17> cm <^-3> and mobility 5.1cm <2> / Vs were obtained. As a result of membrane composition analysis by ICP (High Frequency Inductively Coupled Plasma) analysis, In: Zn: Al = 0.4: 0.3: 0.3 (atomic ratio). As a result of the measurement by X-ray diffraction, the film was amorphous.

<Example 2-Example 6>

An oxide sintered body and an oxide semiconductor thin film were obtained in the same manner as in Example 1 except that the composition ratio of the raw material powders was set to the respective values shown in Table 1. Each relative density, bulk resistance, carrier concentration, and mobility were as listed in Table 1. In addition, the composition of the sintered compact and the film | membrane was the same as the composition ratio of raw material powder, respectively.

<Comparative Example 1- Comparative Example 13>

An oxide sintered body and an oxide semiconductor thin film were obtained in the same manner as in Example 1 except that the composition ratio of the raw material powders was set to the respective values shown in Table 1. Each relative density, bulk resistance, carrier concentration, and mobility were as shown in Table 1. In addition, the composition of the sintered compact and the film | membrane was the same as the composition ratio of raw material powder, respectively.

As can be seen from the results shown in Table 1, the oxide sintered body according to the embodiment of the present invention has a high relative density and a small bulk resistance. In addition, when the oxide sintered body according to the present invention is formed as a sputtering target, an oxide semiconductor thin film having an appropriate carrier concentration and high mobility is obtained.

Claims (10)

As an oxide sintered body consisting of indium (In), zinc (Zn), metal element X (where X represents Ti), and oxygen (O), indium (In), zinc (Zn), and metal element X Oxide ratios satisfying 0.2 ≦ In / (In + Zn + X) ≦ 0.6, 0.1 ≦ Zn / (In + Zn + X) ≦ 0.5, and 0.2 ≦ X / (In + Zn + X) ≦ 0.5, and the bulk resistance is 3 mΩcm or less, respectively. Sintered body. The method of claim 1,
Oxide sintered compact whose relative density is 98% or more. 3. The method according to claim 1 or 2,
Oxide sintered compact whose 0.2 (except 0.2) <= X / (In + Zn + X) <0.35 and whose bulk resistance is 2.5 m (ohm) cm or less. An oxide semiconductor thin film composed of indium (In), zinc (Zn), metal element X (where X represents Ti), and oxygen (O), and includes indium (In), zinc (Zn), and metal element X The atomic ratio of satisfies 0.2 ≦ In / (In + Zn + X) ≦ 0.6, 0.1 ≦ Zn / (In + Zn + X) ≦ 0.5, 0.2 (excluding 0.2) ≦ X / (In + Zn + X) ≦ 0.35, and is amorphous. , Oxide semiconductor thin film. 5. The method of claim 4,
The carrier concentration is 10 ¹⁶ ~ 10 ¹⁸ ㎝ ^-3 of the oxide semiconductor thin film. The method according to claim 4 or 5,
Wherein the mobility is at least 1 cm 2 / Vs. A thin film transistor comprising the oxide semiconductor thin film according to claim 4 or 5 as an active layer. The thin film transistor provided with the oxide semiconductor thin film of Claim 6 as an active layer. An active matrix drive display panel comprising the thin film transistor according to claim 7. An active matrix drive display panel comprising the thin film transistor according to claim 8.