KR20080111736A - Oxide semiconductor and thin film transistor comprising the same - Google Patents

Abstract

An oxide semiconductor and a thin film transistor having the same are provided to prevent hysteresis of the oxide thin film transistor, and improve the movement and on/off current characteristic. A gate(13) is formed on a substrate(11). A gate isolation layer(14) is formed on a substrate, and the gate. An oxide layer(12) is formed on the substrate if the substrate is Si substrate by the thermal oxidation process. A channel(15) is formed on the gate isolation layer corresponding to the gate. A source(16a) and a drain(16b) are formed on two part and gate isolation layer of channel.

Description

Oxide semiconductor and thin film transistor comprising same

1 is a cross-sectional view illustrating an oxide thin film transistor according to an exemplary embodiment of the present invention.

2A to 2E illustrate a method of manufacturing an oxide thin film transistor according to an exemplary embodiment of the present invention.

Figure 3a is a graph showing the XRD (X-ray Diffraction: X-ray diffraction) measurement results for the specimen added Ta to ZnO and InZnO.

Figure 3b and Figure 3c shows the results of the Rutherford Backscattering Spectroscopy (RBS) composition for the specimen of Figure 3a.

4 is a graph illustrating a result of a performance test of an oxide thin film transistor according to an exemplary embodiment of the present invention, and illustrates a change in gate voltage (Vg) and drain current (Id) for each source-drain voltage (0.1V, 5V, and 10V). to be.

5 is a graph showing the drain current value with respect to the drain voltage of the oxide thin film transistor according to an embodiment of the present invention.

6A to 6C are graphs showing the results of measuring optical reactivity of an oxide thin film transistor according to an exemplary embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

11 ... substrate 12 ... insulating layer

13 ... gate 14 ... gate insulation

15 ... Channel 16a ... Source

16b ... drain

The present invention relates to an oxide semiconductor and a thin film transistor including the same, and more particularly, to a semiconductor material in which a new material is added to a Zn oxide and an oxide thin film transistor including the same.

Currently, thin film transistors are used in various applications, and in particular, they are used as switching and driving elements in display fields, and are used as selection switches of cross-point type memory elements.

Currently, liquid crystal displays (LCDs) are mainly used as TV panels, and organic light emitting displays are also being researched for application to TVs. The development of display technology for TVs is evolving to meet the demands of the market. Market demands include large-sized TVs or digital information displays (DIDs), low cost, and high quality (video expression, high resolution, brightness, contrast ratio, and color reproduction). In order to cope with such requirements, a thin film transistor (TFT) to be applied as a switching and driving element of a display having excellent performance along with an enlargement of a substrate such as glass is required.

As a driving and switching element of a display, there is an amorphous silicon thin film transistor (a-Si TFT). It is a device that can be uniformly formed on a large substrate of more than 2 m at low cost and is the most widely used device at present. However, with the trend toward larger displays and higher image quality, device performance is also required, and the existing a-Si TFT with a mobility of 0.5 cm ² / Vs is expected to reach its limit. Therefore, there is a need for a high performance TFT and a manufacturing technology having higher mobility than a-Si TFT.

Poly-Si TFTs, which have significantly higher performance than a-Si TFTs, have high mobility from tens to hundreds of cm ² / Vs, and thus can be applied to high-definition displays that were difficult to realize in conventional a-Si TFTs. Has the performance to In addition, the problem of deterioration of device characteristics is very small compared to a-Si TFT. However, in order to manufacture poly-Si TFTs, a complicated process is required compared to a-Si TFTs, and the additional cost is increased accordingly. Therefore, the p-Si TFT is suitable to be applied to products such as high-definition display and OLED, but in terms of cost is inferior to the existing a-Si TFT has a disadvantage in that the application is limited. In the case of the p-Si TFT, due to technical problems such as limitations of manufacturing equipment and poor uniformity, the manufacturing process using a large substrate of more than 1 m has not been realized until now, and therefore, application to a TV product is difficult.

Accordingly, there is a need for a new TFT technology having both the advantages of a-Si TFT and the advantages of poly-Si TFT. Research on this is being actively conducted, an example of which is an oxide semiconductor device.

Recently, ZnO-based thin film transistors have been spotlighted as oxide semiconductor devices. Currently, Zn oxide and Ga-In-Zn oxide have been introduced as ZnO-based materials. The ZnO-based semiconductor device can be manufactured by a low temperature process and has an advantage of large area because it is amorphous. In addition, the ZnO-based semiconductor film is a highly mobile material and has very good electrical properties such as polycrystalline silicon. Currently, research is being conducted to use an oxide semiconductor material layer having a high mobility, that is, a ZnO-based material layer, in a channel region of a thin film transistor. Zn oxide, Ga-In-Zn oxide, etc. have been introduced as ZnO-based materials.

It is an object of the present invention to provide an oxide semiconductor in which a new material is added to Zn oxide.

In addition, the present invention is to provide an oxide thin film transistor having high integration and excellent electrical characteristics by using the oxide semiconductor in the channel region.

In order to achieve the above object, the present invention provides an oxide semiconductor in which a Zn oxide or an In—Zn composite oxide is doped with an element having an electronegativity of 1.0 to 1.6.

In the present invention, in the oxide thin film transistor,

gate;

A channel formed at a position corresponding to the gate and including an oxide semiconductor doped with a Zn oxide or an In—Zn composite oxide with an element having an electronegativity of 1.0 to 1.6;

A gate insulator formed between the gate and the channel; And

An oxide thin film transistor including a source and a drain formed in contact with both sides of the channel, respectively, is provided.

In the present invention, the doping element is characterized in that the ion radius is similar to Zn.

In the present invention, the ion radius of the doping element is characterized in that 0.050 ~ 0.095nm.

In the present invention, the doping element is characterized in that at least one selected from the group consisting of Ta, Cr, Hf, Y and Ti.

In the present invention, the doping element is characterized in that at least one selected from the group consisting of Ta, Hf and Ti.

In the present invention, the doping element is characterized in that Ta.

In the present invention, the oxide semiconductor is a composite oxide of ZnO and Ta ₂ O ₃ , the atomic ratio of Zn and Ta is characterized in that 3 to 5: 1.

In the present invention, the atomic ratio of Zn and Ta is 4: 1.

In the present invention, the oxide semiconductor is characterized in that it comprises nanocrystals.

In the present invention, the oxide semiconductor is a composite oxide of ZnO, In ₂ O ₃ and Ta ₂ O ₃ , and Zn: In: Ta (atomic ratio) is 1 to 3: 2 to 4: 1.

In the present invention, the Zn: In: Ta (atomic ratio) is 2: 3: 1.

In the present invention, the oxide semiconductor is characterized in that it comprises nanocrystals.

In the present invention, the source or drain is characterized in that formed of a metal or a conductive metal oxide.

Hereinafter, an oxide semiconductor and an oxide thin film transistor including the same according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. For reference, it should be noted that the thickness and width of each layer shown in the drawings are somewhat exaggerated for explanation.

1 is a cross-sectional view illustrating a structure of a thin film transistor including an oxide semiconductor according to an exemplary embodiment of the present invention. In FIG. 1, a bottom gate type thin film transistor is illustrated, but the thin film transistor according to an exemplary embodiment of the present invention may be applied to both a top gate type and a bottom gate type thin film transistor.

Referring to FIG. 1, an oxide thin film transistor according to an exemplary embodiment of the present invention may include a gate 13 formed on one surface of a substrate 11, a gate insulating layer formed on a substrate 11, and a gate 13. 14). When the substrate 11 is Si, the oxide layer 12 may be formed on the surface thereof by a thermal oxidation process. The channel 15 is formed on the gate insulating layer 14 corresponding to the gate 13, and the source 16a and the drain 16b are formed on both sides of the channel 15 and the gate insulating layer 14. Formed.

Referring to the forming material of each layer forming the oxide thin film transistor according to an embodiment of the present invention. The substrate 11 may be a substrate commonly used in a semiconductor device, for example Si, glass or an organic material may be used. The insulating layer 12 formed on the substrate surface may be, for example, SiO ₂ formed by thermally oxidizing a Si substrate. The gate 13 may use a conductive material, for example, may be a metal or a metal oxide. The gate insulating layer 14 may be formed using an insulating material used in a conventional semiconductor device, and may use silicon oxide or nitride. Specifically, HfO ₂ , Al ₂ O ₃ , Si ₃ N _4, which are higher dielectric constants than SiO ₂ or SiO ₂ , or a mixture thereof may be used. Source 16a and drain 16b may be formed using a conductive material, for example a metal such as Pt, Ru, Au, Ag, Mo, Al, W, or Cu or IZO (InZnO) or AZO (AlZnO). Metal or conductive oxides such as

An oxide semiconductor according to an embodiment of the present invention is characterized in that the Zn oxide is formed by including a material having an electronegativity of 1.2 to 1.6. The oxide thin film transistor according to the embodiment of the present invention is characterized in that the channel 15 is formed of Zn oxide including a material having an electronegativity of 1.2 to 1.6. In addition, the oxide semiconductor according to the embodiment of the present invention may be formed into a nanocrystalline phase.

In the oxide thin film transistor according to the embodiment of the present invention, the reason why the ionic bondability of the channel material is important will be described. Ion coupling is important to secure the reliability of the oxide thin film transistor. For example, in the case of a-Si: H, a covalent bond is formed. When the bond is in an amorphous state by a sp3 coordination bond with a directivity, the electron cloud that is in the oxygen bond is distorted. This results in weak bonds. When a TFT having such a coupling structure is driven for a long time, when electrons or holes accumulate in the coupling region, the coupling is broken, resulting in a problem in reliability due to the shift of the threshold voltage. On the other hand, in the case of ionic bonds, the size of the cation electron cloud is large, so it becomes overlab regardless of the bond of oxygen anions, so that weak bonds, whether crystalline or amorphous, do not exist and thus, a highly reliable thin film transistor can be manufactured. Therefore, the channel material of the oxide thin film transistor according to the embodiment of the present invention has an electronegativity smaller than that of oxygen, and an element having a difference of 1.9 or more is added to the Zn oxide. Since the electronegativity of oxygen is about 3.5, in order for the electronegativity difference to be 1.9 or more, the cation atom has an element having an electronegativity of about 1.6 or less. However, it is preferable that the ion radius is similar when ZnO and In2O3-ZnO structures are used for the purpose of substitution with Zn without bringing about a large change in the structure. Therefore, it is preferable that the electronegativity is 1.0 or more. This is because the ion radius is 0.093 nm for elemental yttrium, and the electronegativity is 1.2. Atoms that can be selected on this principle are Ta (electronegativity: ion radius = 1.5: 0.07 nm), Y (1.2: 0.093), Ti (1.5: 0.068), Cr (1.6: 0.052), Hf (1.3: 0.078) and the like. For reference, Zn has an ion radius of 0.074 nm and electronegativity of 1.6.

For example, when Ta is doped in ZnO, the channel 15 is formed of a composite oxide of ZnO and Ta ₂ O ₃ , and the atomic ratio of Zn and Ta is 3 to 5: 1, and preferably 4: 1. Do. When the channel 15 is formed of a composite oxide of ZnO, In ₂ O _3, and Ta ₂ O ₃ , Zn: In: Ta (atomic ratio) is 1 to 3: 2 to 4: 1, and 2: 3: It is preferable that it is 1.

Hereinafter, a method of manufacturing an oxide thin film transistor according to an exemplary embodiment of the present invention will be described with reference to FIGS. 2A to 2E.

Referring to FIG. 2A, a substrate 11 is prepared. Si, glass or organic materials can be used. When using a Si substrate, the insulating layer 12 can be formed in the surface by a thermal oxidation process. A conductive material 13a such as a metal or a conductive metal oxide is coated on the substrate 11.

Referring to FIG. 2B, the gate 13 is formed by patterning the conductive material 13a. Referring to FIG. 2C, the gate insulating layer 24 is formed by coating and patterning an insulating material on the gate 13.

Referring to FIG. 2D, the channel 15 is formed by applying a channel material on the gate insulating layer 14 corresponding to the gate 13 by a process such as PVD, CVD, or ALD, and then patterning the channel material. The channel material may be formed by adding at least one element selected from the group consisting of Ta, Y, Ti, Cr, and Hf to the Zn oxide. In addition, In can be further added thereto. Specifically, a sputtering process may be performed by mounting a target formed of ZnO or InZnO and a target formed of at least one of Ta, Y, Ti, Cr, and Hf in a process chamber by using a sputtering process. It can form using. In addition, a single target further including at least one of Ta, Y, Ti, Cr, or Hf may be used for ZnO or InZnO.

Referring to FIG. 2E, a material such as a metal or a conductive metal oxide is applied on the channel 25 and the gate insulating layer 14, and then patterned to be connected to both sides of the channel 15 to drain the source 16a and the drain. (16b) is formed.

Finally, a heat treatment process is carried out using a general furnace, rapid thermal annealing (RTA), laser or hot plate at a temperature of 400 ° C. or lower, for example 300 ° C.

Figure 3a is a graph showing the X-ray diffraction (XRD) measurement results for the oxide thin film according to an embodiment of the present invention.

A 150 watt current was applied to the ZnO target and 35 watt was added to the Ta target, and the first thin film specimen was formed by coping with the conditions adjusted to Ar: O 2 = 190 sccm: 2.5 sccm. Also, except that the InZnO (In: Zn = 1: 1) target was used instead of the ZnO target, the second thin film specimen was formed by coping with the same conditions. After the heat treatment was performed on the two formed specimens XRD (X-ray Diffraction: X-ray diffraction) was measured and shown in FIG. Referring to FIG. 3, it can be seen that a peak appearing around 30 degrees has an amorphous phase. In addition, it is determined that the pick appeared between 50 and 60 degrees has a nanocrystalline phase.

3b and 3c show the results of the Rutherford Backscattering Spectroscopy (RBS) composition of the thin film specimen formed as described above.

According to the RBS analysis of FIG. 3B, Ta: Zn (atomic ratio) = 1: 4 in the first sample, and Ta: In: Zn (atomic ratio) = 1 in the second sample according to the RBS analysis of FIG. 3C. The result was 3: 3.

4 is a graph illustrating a result of a performance test of an oxide thin film transistor according to an exemplary embodiment of the present invention, and illustrates a change in gate voltage (Vg) and drain current (Id) for each source-drain voltage (0.1V, 5V, and 10V). to be. In the oxide thin film transistor, the channel material was formed under the same conditions as the second thin film specimen, the source and the drain were formed of Ti and Pt, and Mo was used as the gate electrode. The formed oxide thin film transistor was heat treated at 300 degrees Celsius for 1 hour.

Referring to FIG. 4, it can be seen that the On current is about 10 ⁻⁴ A, the off current is 10 ⁻¹² A or less, and the On / Off current ratio is 10 ⁸ or more. The channel mobility was 1,5 cm ² / Vs and the gate swing voltage was about 280 mV / dec. As a result, it shows a high On / Off current ratio and a low Off current, it can be seen that there is no hysteresis and excellent characteristics as an oxide thin film transistor.

FIG. 5 illustrates drain current Id values according to drain voltage Vd when gate voltages of 0.1, 4, 8, 12, 14, and 20V are applied to the oxide thin film transistor according to the exemplary embodiment of the present invention. Output graph.

Referring to FIG. 5, it can be seen that when the gate voltage is applied to 0.1V, the drain current value does not change even when the drain voltage is increased. However, it can be seen that when the gate voltage is applied above 4V, the drain current value gradually increases as the drain voltage is increased.

6A to 6C are diagrams illustrating gate voltages Vg and drain currents of source and drain voltages 0.1V, 5V, and 10V according to respective states in order to confirm optical reactivity of an oxide thin film transistor according to an exemplary embodiment of the present invention. Id) Graph showing change. FIG. 6A illustrates a measurement result in a light off state of the specimen, and FIG. 6B illustrates a measurement result in a state in which only the gate region is exposed to light, and FIG. 6C illustrates the entire specimen. It shows the light on.

6A to 6C, it can be seen that the oxide thin film transistor according to the exemplary embodiment of the present invention exhibits almost no change in operating characteristics when no light is exposed or only a gate region is exposed to light. In the case of FIG. 6C exposed to light as a whole, the Off current value is slightly increased, but it can be seen that the state remains below 10 ⁻¹¹ A. That is, it turns out that it is enough to use as a thin film transistor for a display.

Through the above embodiments, those skilled in the art will be able to manufacture various electronic devices such as displays or cross-point memory devices using oxide thin film transistors according to the spirit of the present invention. Could be. The oxide thin film transistor according to the embodiment of the present invention may be used as a bottom gate type or a top gate type. As a result, the scope of the present invention should not be defined by the described embodiments, but should be determined by the technical spirit described in the claims.

According to the present invention, the following effects are obtained.

First, it is possible to provide an oxide thin film transistor having excellent mobility, on / off current characteristics, and no hysteresis using the new material.

Second, it is possible to provide an oxide thin film transistor which operates stably even in an environment exposed to light due to very low sensitivity to external light.

Claims (27)

An oxide semiconductor in which a Zn oxide or an In—Zn composite oxide is doped with an element having an electronegativity of 1.0 to 1.6. The method of claim 1, The doping element is an oxide semiconductor, characterized in that the ion radius is similar to Zn. The method of claim 2, The ion radius of the doping element is an oxide semiconductor, characterized in that 0.050 ~ 0.095nm. The method of claim 3, wherein The doping element is an oxide semiconductor, characterized in that at least one selected from the group consisting of Ta, Cr, Hf, Y and Ti. The method of claim 4, wherein The doping element is an oxide semiconductor, characterized in that at least one selected from the group consisting of Ta, Hf and Ti. The method of claim 5, The doping element is an oxide semiconductor, characterized in that Ta. The method of claim 6, The oxide semiconductor is a composite oxide of ZnO and Ta ₂ O ₃ , the atomic ratio of Zn and Ta is 3 to 5: 1, characterized in that. The method of claim 7, wherein An oxide semiconductor, characterized in that the atomic ratio of Zn and Ta is 4: 1. The method of claim 7, wherein And the oxide semiconductor comprises nanocrystals. The method of claim 6, The oxide semiconductor is a composite oxide of ZnO, In ₂ O ₃ and Ta ₂ O ₃ , Zn: In: Ta (atomic ratio) is 1-3: 2 to 4: 1 oxide oxide. The method of claim 10, The Zn: In: Ta (atomic ratio) is 2: 3: 1 oxide semiconductor. The method of claim 10, And the oxide semiconductor comprises nanocrystals. In an oxide thin film transistor, gate; A channel formed at a position corresponding to the gate and including an oxide semiconductor doped with a Zn oxide or an In—Zn composite oxide with an element having an electronegativity of 1.0 to 1.6; A gate insulator formed between the gate and the channel; And And a source and a drain formed in contact with both sides of the channel, respectively. The method of claim 13, And a doping element of the channel material has an ion radius similar to that of Zn. The method of claim 14, The ion radius of the doping element is an oxide thin film transistor, characterized in that 0.050 ~ 0.095nm. The method of claim 15, The doping element is an oxide thin film transistor, characterized in that at least one kind selected from the group consisting of Ta, Cr, Hf, Y and Ti. The method of claim 16, The doping element is an oxide thin film transistor, characterized in that at least one selected from the group consisting of Ta, Hf and Ti. The method of claim 17, And the doping element is Ta. The method of claim 18, Wherein the oxide semiconductor is a composite oxide of ZnO and Ta ₂ O ₃ , and an atomic ratio of Zn and Ta is 3 to 5: 1. The method of claim 19, Wherein the atomic ratio of Zn and Ta is 4: 1. The method of claim 19, And the oxide semiconductor comprises nanocrystals. The method of claim 18, The oxide semiconductor is a composite oxide of ZnO, In ₂ O ₃ and Ta ₂ O ₃ , Zn: In: Ta (atomic ratio) is 1 to 3: 2 to 4: 1, characterized in that. The method of claim 22, Wherein the Zn: In: Ta (atomic ratio) is 2: 3: 1. The method of claim 22, And the oxide semiconductor comprises nanocrystals. The method of claim 13, And the gate is formed of a metal or a conductive metal oxide. The method of claim 13, And the gate insulating layer is formed of a mixture of silicon oxide, nitride, hafnium (Hf) oxide, aluminum oxide or hafnium oxide, and aluminum oxide. The method of claim 13, And the source or drain is formed of a metal or a conductive metal oxide.

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