KR20130136537A - Oxide-type semiconductor material and sputtering target - Google Patents

Abstract

The present invention provides an oxide semiconductor material composed of Zn oxide and Sn oxide, which is equivalent to IGZO or higher, has a high carrier mobility of about 10 cm 2 / Vs, and does not require high temperature heat treatment. ZTO: Zn-Sn-O-based oxide). The present invention relates to an oxide semiconductor material containing Zn oxide and Sn oxide, wherein Zr is contained as a dopant, and the Zr content is an atomic ratio of the dopant to the sum of the number of atoms of Zn, Sn, and Zr as metal elements is 0.005 or less. It is characterized by.

Description

Oxide-type Semiconductor Materials and Sputtering Targets {OXIDE-TYPE SEMICONDUCTOR MATERIAL AND SPUTTERING TARGET}

TECHNICAL FIELD The present invention relates to a semiconductor material for forming a semiconductor element constituting a display device such as a liquid crystal display, and more particularly relates to an oxide semiconductor material containing Zn oxide and Sn oxide and containing Zr as a dopant.

Background Art In recent years, display devices such as thin televisions represented by liquid crystal displays have a remarkable tendency of increased production and large screens. As the display device, an active matrix liquid crystal display using a thin film transistor (hereinafter, referred to as TFT) as a switching element is widely used.

In a display device using such a TFT as a switching element, an oxide semiconductor material is used as the constituent material. As this oxide type semiconductor material, IGZO (In-Ga-Zn-O type oxide) which is a kind of transparent oxide semiconductor material attracts attention (refer patent document 1). This IGZO is widely used as a promising semiconductor material since it has a high carrier mobility following polycrystalline Si (silicon) conventionally used and a small characteristic variation in TFT characteristics like a-Si (amorphous silicon). Getting started.

By the way, in the liquid crystal displays, such as a thin television, the change of a display system has arisen. Specifically, in addition to flat display 2D, a liquid crystal display capable of stereoscopic display 3D is provided. In this three-dimensional display (3D) type liquid crystal display, it is realized by making an image different from right and left of a display screen by control using a switch liquid crystal. Therefore, for such a three-dimensional display type liquid crystal display, the switching element which can implement | achieve a faster response speed is calculated | required.

In order to cope with such a change in the display method of a liquid crystal display, development of oxide type semiconductor material like IGZO is performed variously. As for TFT which becomes this high response speed, it is important that carrier mobility is high. For example, in IGZO, it is 1 to 2 digits larger than a-Si, and the carrier mobility is about 5-10 cm <2> / Vs. Therefore, with this IGZO, although it can be used as a constituent material of TFT which is a switching element of a stereoscopic display type liquid crystal display, in order to implement | achieve a high spec liquid crystal display, the constituent material of TFT which can implement | achieve a faster response speed is It is requested.

In addition, since IGZO requires annealing at 350 ° C. or higher when forming a TFT, it is pointed out that it is difficult to use it for a display device that cannot be subjected to high temperature heat treatment such as an organic EL panel or an electronic paper using a flexible substrate or the like. have.

In addition, an oxide semiconductor material that does not use In or Ga is desired because of a resource problem and the influence on the human body and the environment, and development of an alternative material for IGZO is also required in this regard.

As an alternative material of this IGZO, the oxide type semiconductor material (ZTO: Zn-Sn-O type oxide) which consists of Zn oxide and Sn oxide, for example is proposed (patent document 2, patent document 3, patent document 4, Patent document 5). These prior art ZTOs have been developed to realize high carrier mobility. In these prior arts, it has been found that high carrier mobility can be realized, but the heat treatment temperature at the time of TFT formation has not been sufficiently examined, and the applicability to organic EL panels, electronic papers and the like has not been found.

In particular, Patent Document 5, In, Zn, and large and 1 × 10 in the oxide semiconductor material containing Sn, than by incorporating a number of elements including the Zr as the dopant, the electron carrier density of 1 × 10 ¹⁵ / ㎤ to ¹⁸ / Although oxide type semiconductor material which becomes less than cm <3> is proposed, this patent document 5 is also examined about sheet resistance, but examination of the heat treatment temperature at the time of TFT formation, content of the dopant at that time, etc. is not fully performed. The sheet resistance and carrier density in this patent document 5 have a relationship of the following formula.

Rs = ρ / t

ρ = 1 / (eNμ)

(Rs: sheet resistance, ρ: specific resistance (volume resistivity), N: carrier density, μ: carrier mobility, t: film thickness)

That is, as in Patent Document 5, when only the sheet resistance value is unknown, the carrier density cannot be specified unless the film thickness or the carrier mobility can be specified. In this regard, the present situation is that further improvement is required regarding ZTO as an alternative material for IGZO.

Japanese Patent No. 4164562 Japanese Patent Application Laid-Open No. 2009-123957 Japanese Patent Application Laid-Open No. 2010-37161 Japanese Patent Application Laid-Open No. 2010-248547 Japanese Patent Application Laid-Open No. 2009-123957

The present invention has been made on the basis of the above circumstances, and as a substitute material for IGZO, the carrier mobility is equivalent to that of IGZO or more, high carrier mobility of about 10 cm 2 / Vs, and does not require high temperature heat treatment of 300 ° C. or higher. Instead, an object of the present invention is to provide an oxide semiconductor material (ZTO: Zn-Sn-O-based oxide) containing Zn oxide, Sn oxide, and Zr as a dopant.

MEANS TO SOLVE THE PROBLEM In order to solve the said subject, the present inventors earnestly examined about the case where Zr is contained as a dopant in the oxide type semiconductor material which consists of Zn oxide and Sn oxide, and has high carrier mobility in the dopant content of a predetermined range. It was found that ZTO film can realize a TFT that can be driven without requiring a high temperature heat treatment.

The present invention relates to an oxide semiconductor material containing Zn oxide and Sn oxide, wherein Zr is contained as a dopant, and the Zr content is an atomic ratio of the dopant to the sum of the number of atoms of Zn, Sn, and Zr as metal elements is 0.005 or less. It is characterized by.

In the oxide semiconductor material according to the present invention, the carrier mobility is equal to or greater than IGZO, and carrier mobility of about 10 cm 2 / Vs can be realized, and a switching element such as TFT is formed by heat treatment at 250 ° C. or lower. It becomes possible. Moreover, since it does not contain In and Ga, there is no resource problem and the influence on a human body and an environment is also small.

Zr of the dopant in the oxide semiconductor material of the present invention sets the atomic ratio of the dopant to the sum of the number of atoms of Zn, Sn, and Zr as metal elements to be 0.005 or less. Specifically, when the number of atoms of Zn as the metal element is x, the number of Sn is y and the number of atoms of Zr is z, the dopant is contained so that z / (x + y + z) ≦ 0.005. When this atomic ratio exceeds 0.005, when 300 degreeC heat processing is performed, a carrier density will become less than 1 * 10 <^15> cm <^-3> , and it becomes impossible to maintain favorable semiconductor characteristics. If the atomic ratio is 0.005 or less, the carrier density becomes less than 1 × 10 ¹⁸ cm ^-3 , and therefore, a carrier density equal to or less than that of the IGZO film after 350 ° C. heat treatment can be realized. As long as the lower limit of the dopant content can realize a carrier density equal to or less than IGZO, and a switching element such as TFT can be formed by heat treatment at 250 ° C. or lower, the numerical value is not limited. The present inventors have confirmed that even if the Zr content of the dopant is 0.000085 (8.5 × 10 ⁻⁵ ) in atomic ratio, it can be employed as the oxide semiconductor material of the present invention.

In the oxide semiconductor material of the present invention, A / (A + B) = 0.4 to 0.8 when Zn and Sn assume the atomic number of the metal element of Zn to A and the atomic number of the metal element of Sn to B; It is preferable to contain in ratio, and the ratio of 0.6-0.7 is more preferable. When this A / (A + B) is less than 0.4, the ratio of Sn becomes high. Therefore, when patterning the thin film formed at the time of element formation by etching, the etching rate in the oxalic acid-based etching solution is extremely slow, and the production process It is not suitable. In addition, when the ratio exceeds 0.8, the ratio of Zn becomes high, so that the resistance to water of the oxide semiconductor material is lowered, and the stripping solution of the resist in the patterning step of the wiring or semiconductor layer which is generally used at the time of TFT element formation. Under the influence of pure water cleaning, the ZTO film itself is damaged and the original TFT device characteristics cannot be realized, and in some cases, the ZTO film can be dissolved and dropped from the substrate to form a TFT device. There will be no.

The oxide semiconductor material of the present invention is very effective for a bottom gate type or top gate type thin film transistor. As described above, the oxide semiconductor material of the present invention can realize carrier mobility equal to or greater than IGZO and can be used by low temperature heat treatment at 250 ° C. or lower, so it is suitable for a stereoscopic display type liquid crystal display requiring high response speed. It is applicable also when forming switching elements, such as an organic EL panel and an electronic paper, which use a flexible board | substrate.

When the switching element is formed of the oxide semiconductor material of the present invention, it is effective to use a thin film formed of the oxide semiconductor material, and in order to form the thin film, it is preferable to use a sputtering method.

And when forming the thin film of the oxide type semiconductor material of this invention by this sputtering method, it consists of Zn oxide and Sn oxide, contains Zr, and Zr content is each atom of Zn, Sn, Zr as a metal element It is preferable to use the sputtering target whose atomic ratio of the dopant with respect to the number sum is 0.005 or less. And Zn and Sn are targets containing A / (A + B) = 0.4-0.8 when the atomic number of the metallic element of Zn is A, and the atomic number of the metallic element of Sn is B desirable. In this case, a DC power supply, a high frequency power supply, or a pulsed DC power supply can be used at the time of sputtering film formation. In particular, when a target is used, the use of a pulsed DC power supply suppresses the formation of nodules and surface high resistance layers generated on the target surface and enables stable film formation, which is suitable for mass production processes.

When forming an element using the oxide semiconductor material of the present invention, the film can be formed by the above sputtering method. In addition, a film forming method other than sputtering such as a pulse laser deposition method can be adapted. Moreover, the element formation using the oxide type semiconductor material of this invention can also be formed by the circuit formation by the method of apply | coating the dispersion liquid in which the nanoparticle of the semiconductor material disperse | distributed to the solvent, or the inkjet method.

According to the oxide semiconductor material of the present invention, carrier mobility equal to or higher than that of IGZO can be realized, and switching elements such as TFTs can be formed by low temperature heat treatment at 250 ° C or lower. Moreover, since it does not contain In and Ga, there is no resource problem and it becomes possible to reduce the influence on a human body and an environment.

1 is a device schematic diagram of a TFT.
2 is a graph of measurement of TFT characteristics (Example 1, 200 ° C).
3 is a graph of measurement of TFT characteristics (Example 1, 220 ° C).
4 is a measurement graph of TFT characteristics (Example 1, 250 ° C.).
5 is a measurement graph of TFT characteristics (Example 1, 300 ° C).
6 is a measurement graph (comparative example 1, 200 degreeC) of TFT characteristic.
7 is a measurement graph of TFT characteristics (Comparative Example 2, 200 ° C).

Hereinafter, an embodiment of the present invention will be described. First, preparation of the sputtering target with respect to the oxide type semiconductor material of this embodiment is demonstrated.

Target production: A predetermined amount of ZnO powder plasticized at 500 ° C. in the air atmosphere, SnO ₂ powder plasticized at 1050 ° C. and ZrO ₂ powder not calcined in the air atmosphere, respectively. It weighed, it injected into the resin pot (capacity 4L), and mixed in the ball mill. In this ball mill, mixing of rotation speed 130 rpm and mixing time 12 hours was performed. Then, the mixture was sieved with an opening of 500 µm and a line diameter of 315 µm. The mixed powder below the sieve from which the granulated powder was removed was filled into the 100 mm carbon press type, and the sintered compact was produced by hot press. The hot press conditions made Ar gas flow volume 3 L / min, heated up to 1050 degreeC under 9.4 Mpa pressurization, hold | maintained for 90 minutes under 25 Mpa pressurization, naturally cooled, and took out the sintered compact. By the above procedure, the sintered compact target for forming the thin film used as each atomic ratio shown in Table 1 was formed.

Next, the film-forming method using the sputtering target of the produced sintered compact, and its film | membrane evaluation are demonstrated. It formed into a film using the commercially available single | leaf type | mold sputtering apparatus (SML-464 made from SK Corporation | KK). Sputtering condition was a degree of vacuum reached 1 × 10 ^-5 Pa, and a, as a sputter gas using the Ar / O ₂ mixed gas, and the sputtering gas pressure is set to 0.4Pa, and, on the oxygen partial pressure 0.01Pa, a glass at room temperature (25 ℃) On the substrate (Nihon Denki Glass Co., Ltd. product: OA-10), film formation of about 100 nm thickness was performed by DC sputtering of 150W.

This film formation was carried out using an ICP (inductively coupled plasma) emission spectroscopy apparatus (SIA INano Technology Co., Ltd. product: Vista Pro). Table 1 calculates and describes the value of the atomic ratio of Zn / (Zn + Sn) and Zr / (Zn + Sn + Zr) from the measured value of Zn, Sn, Zr. Moreover, when used for elements, such as a thin film transistor (TFT), the composition of the oxide type semiconductor material cut | disconnects an element and observes the element cross section with a transmission electron microscope (TEM), etc. It can be specified by specifying the part and EDX analysis.

Each sample formed into a film was treated with annealing at 200 ° C., 220 ° C., 250 ° C., and 300 ° C. for 1 hour in an air atmosphere, and the Hall effect measurement was performed. The specific resistance, carrier mobility, and carrier density of each sample were measured. Saved. This Hall effect measurement was performed using each sample cut out in 10 mm x 10 mm squares by the commercially available Hall effect measuring apparatus (manufactured by Nanometrics Japan Co., Ltd .: HL5500PC). Table 1 shows the results of the specific resistance, carrier mobility, and carrier density of each sample. In addition, unlike the substrate temperature at the time of film formation (at the time of sputtering), the heat treatment after film formation is to form a film and apply thermal energy to a stable film once fixed. For example, the substrate temperature in patent document 5 is heat | fever provided at the time of film-forming, and when the atom | scattered by sputtering adheres to a board | substrate, this board | substrate temperature rises, and the place which the atom adhered to a board | substrate is more stable place The phenomenon occurs. That is, the control of the substrate temperature at the time of film formation is the total of the energy at the time of sputtering and the thermal energy of the substrate temperature, and the rearrangement of atoms proceeds to determine the crystal state, orientation, and the like of the film. Is different.

TFT evaluation: The said film | membrane was made into the channel layer, and the thin film transistor (TFT) was produced using the metal mask. 1, the cross-sectional schematic A and the planar dimension schematic B of the formed TFT element are shown. As shown in FIG. 1 (A), in the formation of the TFT, an Al alloy (thickness of 2000 kPa) was first formed on the glass substrate 10 as the gate electrode 20. Sputter gas pressure here was 0.4 Pa, and DC sputter | spatter of 1000W of input electric power was performed. Next, SiNx (thickness: 3000 kPa) was formed as a gate insulating film 30. Here, film formation was performed by a plasma CVD apparatus (PD-2202L manufactured by samco), and plasma CVD with a power of 250 W was performed at a substrate temperature of 350 ° C. The flow rate of the source gas was SiH ₄ : NH ₃ : N ₂ = 100cc: 10cc: 200cc. Subsequently, the ZTO-ZrO ₂ film (thickness 300 GPa) was formed as a channel layer 40. The sputter gas pressure here performed DC sputter | spatter of 0.4 Pa and input power 150W. W / L of the channel was set to 22. Finally, the source electrode 50 (thickness 2000 kPa) and the drain electrode 51 (thickness 2000 kPa) were formed by ITO. The sputter gas pressure here was 0.4 Pa, and DC sputter | spatter of 600W of input electric power was performed. The element dimensions of the TFT thus produced are shown in Fig. 1B. The numerical unit of each width | variety of this FIG. 1 (B) is mm.

About the produced TFT, the transmission characteristic was measured by the semiconductor analyzer (Semiconductor Device Analyzer B1500A by Agilent Technologies). The drain voltage Vds applied at the time of the measurement was 1-5V, and the measurement width of the gate voltage Vgs was -10-20V. 2-7, the result of having measured the transfer characteristic of TFT is shown. When FIGS. 2-5 is Example 1 (each heat processing temperature), FIG. 6 has shown TFT characteristics in the comparative example 1 (heat processing 200 degreeC), and FIG. 7 in the comparative example 2 (heat processing). 2 to 6, the left side of the vertical axis represents the large axis of the drain current: Ids (A) value, and the right side of the vertical axis represents the decimal point display axis of the? Ids value.

[Table 1]

As shown in Table 1, when the Zr content is an atomic ratio of 0.000085 (8.5 × 10 ⁻⁵ ) to 0.00312 (3.12 × 10 ⁻³ ), the carrier density of the film after 200 ° C. heat treatment is 1 × 10 ¹⁵ cm ^−3. It became clear that it entered the range below 1 * 10 <^18> cm <^-3> or more. Moreover, about the comparative example 2, it was 300 degreeC of heat processing, and the carrier density of the film | membrane became less than 1 * 10 <^15> cm <^-3> .

In addition, in the case of Example 1, TFT characteristics in each heat processing temperature were the results shown in FIGS. In addition, the result of each TFT characteristic value in FIGS. Moreover, electrolytic effect mobility (micro) is a value obtained from the result of forming a TFT element and measuring TFT characteristic, and carrier mobility of Table 1 is a value obtained from the Hall effect measurement of the film formed into a film. In addition, S value is a subthreshold swing value which shows the characteristic of a transistor.

[Table 2]

As shown in FIGS. 2-5 and Table 2, in Example 1, it turned out that the on / off ratio becomes 5 digits at all the heat processing temperatures, and shows favorable TFT characteristic. However, at the heat processing temperature of 200 degreeC of Example 1, the inclination of the straight line in on / off became slightly smooth like FIG. Moreover, it turned out that it is the same TFT characteristic also about Examples 2-5. On the other hand, in the case of the non-doped comparative example 1 (200 degreeC), as shown in FIG. 6, it turns into an element which does not turn on / off and does not turn off, and cannot function as a channel layer of a switching element. Confirmed. And as shown in FIG. 7, in the case of the comparative example 2 (200 degreeC), the effect | action of on / off is very weak, and it turned out that it cannot function as a channel layer.

The oxide semiconductor material of the present invention is extremely effective as a constituent material of a TFT requiring a higher response speed, such as a switching element of a stereoscopic display liquid crystal display. Moreover, since the oxide type semiconductor material of this invention can be used by low temperature heat processing, it is suitable for the organic electroluminescent panel and electronic paper which use a flexible board | substrate, etc., and is used industrially also from a viewpoint of a resource problem, an influence on a human body, or an environment. High value

Claims (3)

An oxide semiconductor material containing Zn oxide and Sn oxide,
Zr is contained as a dopant, and Zr content is the oxide type semiconductor material characterized by the atomic ratio of the dopant with respect to the sum total of each atomic number of Zn, Sn, Zr as a metal element being 0.005 or less. The bottom gate type or top gate type thin film transistor formed using the oxide type semiconductor material of Claim 1. As a sputtering target for film-forming the thin film formed of the oxide type semiconductor material of Claim 1,
Zn oxide and Sn oxide,
Zr is contained, and Zr content is the sputtering target characterized by the atomic ratio of the dopant with respect to the sum total of each atomic number of Zn, Sn, and Zr as a metal element.

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