KR20120050565A - Metal-doped oxide semiconductor thin film transistor - Google Patents

Abstract

PURPOSE: A metal doped oxide semiconductor thin film transistor is provided to easily control device properties according to a process condition by suppressing carrier generation due to oxygen deficiency. CONSTITUTION: A gate electrode(12) is formed on a substrate(10). A gate insulating film(14) is formed on the upper part of the substrate. An oxide semiconductor layer(16) is formed on the gate insulating film. The oxide semiconductor layer provides a channel region, a source region, and a drain region. Source and drain electrodes(18a,18b) are respectively formed on the oxide semiconductor layer.

Description

Metal doped oxide semiconductor thin film transistors {METAL-DOPED OXIDE SEMICONDUCTOR THIN FILM TRANSISTOR}

The present invention relates to an oxide semiconductor thin film transistor doped with a metal so as to effectively control an internal carrier to have excellent characteristics.

Thin film transistors (TFTs) are used in a variety of applications and are used as switching and driving devices, particularly in the display field. Currently, liquid crystal displays are mainly used as TV panels, and as a late runner, many researches are being conducted for application to organic light emitting displays. The development of TV display technology is being made in accordance with the market demand direction such as large area, low price and high quality. In order to meet such requirements, the enlargement of substrates such as glass is fundamental, and it is necessary to develop a thin film transistor that can be applied as a switching and driving element of a display having excellent performance.

Currently used as driving and switching elements of displays are amorphous silicon thin film transistors. This is the most widely used device because it not only facilitates large area deposition but also has advantages of low cost process. However, with the trend toward ultra-large and high-definition displays, device performance is also required, and the existing amorphous silicon thin film transistors having a mobility of less than 1 cm ² / Vs are considered to have reached the limit of their applicability. Therefore, there is a need for a high performance TFT and a manufacturing technology having higher mobility characteristics than amorphous silicon thin film transistors.

Polycrystalline silicon thin film transistors, which have higher performance than amorphous silicon thin film transistors, have high mobility of tens to hundreds of cm ² / Vs, and thus can be applied to high-definition displays that were difficult to realize in conventional thin film transistors. In addition, the deterioration of device characteristics is less than that of the amorphous silicon thin film transistor. However, in the case of polycrystalline silicon thin film transistors, the manufacturing process is complicated and additional costs are incurred.

Therefore, the polycrystalline silicon thin film transistor is suitable for application to a product such as an OLED that requires a high image quality of a small area, but has a limitation such as manufacturing cost and uniformity to apply to a large area.

Accordingly, there is an increasing demand for a technology of a new thin film transistor having all the advantages of an amorphous / polycrystalline silicon thin film transistor. While research on this is being actively conducted at home and abroad, a representative technique is a thin film transistor device based on an oxide semiconductor.

Recently, ZnO-based thin film transistors have been spotlighted as oxide semiconductor devices. Currently, Zn oxide and In-Ga-Zn oxide are mainly ZnO-based materials. In the case of a ZnO-based semiconductor device, a low temperature process is possible and the amorphous phase has an advantage of easy large area. In addition, the ZnO-based semiconductor thin film is a material having high mobility characteristics and has very good electrical properties such as polycrystalline silicon.

Since the outstanding performance of IGZO TFT was announced in 2004, numerous articles related to oxide semiconductors have been published and cited. In particular, papers related to IGZO have been the main source, and the number of publications has been exploding since 2007.

Research activities on oxide channel materials as well as the IGZO are active, and IZO, SZO, IGO, etc. are emerging as candidates. The number of citations also increased sharply in recent years, indicating that interest in oxide thin film transistors has increased at home and abroad.

However, since the ZnO-based multi-element oxide thin film transistor mainly uses a ternary oxide semiconductor containing In, it is difficult to control complex compositions first, and thus, it is difficult to secure a reproducible process necessary for commercialization. In addition, the price increases due to the addition of In, and the supply thereof is not expected to be smooth. Therefore, development of next-generation oxide semiconductor materials based on dioxide is essential.

SnO ₂ In the case of the oxide semiconductor based, since the first thin film transistor was fabricated in 1964, many research groups have tried to improve the characteristics, but the biggest problem was the difficulty of controlling the carrier inside the SnO ₂ . To improve this, the thickness of the thin film can be adjusted, the process pressure can be adjusted [Myung Soo Huh et. al ., Improving the Performance of Tin Oxide Thin-Film Transistors by Using Ultralow Pressure Sputtering, Journal of The Electrochemical Society, 157 (4) H425-H429 (2010)], adding transition elements such as Al [Myung Soo Huh et. al ., Improvement in the Performance of Tin Oxide Thin-Film Transistors by Alumina Doping, Electrochemical and Solid - State Letters , 12 (10) H385-H387 (2009)], but the results have not been satisfactory.

Myung Soo Huh et al., Improving the Performance of Tin Oxide Thin-Film Transistors by Using Ultralow Pressure Sputtering, Journal of The Electrochemical Society, 157 (4) H425-H429 (2010) Myung Soo Huh et al., Improvement in the Performance of Tin Oxide Thin-Film Transistors by Alumina Doping, Electrochemical and Solid-State Letters, 12 (10) H385-H387 (2009)

In order to solve the above problems, the present inventors fabricated a bottom gate type thin film transistor using a metal doped SnO ₂ thin film as an oxide semiconductor layer, and as a result of examining the transition characteristics, the mobility increases as the content of the doped metal increases. In spite of the small amount of doping, it is possible to suppress the generation of carriers due to oxygen deficiency and to check the possibility of adjusting the device characteristics according to the process conditions. It was confirmed.

Accordingly, an object of the present invention is to provide an oxide semiconductor thin film transistor having excellent characteristics by effectively controlling an internal carrier.

In order to achieve the above object,

An oxide semiconductor thin film transistor comprising a semiconductor oxide thin film as a channel layer,

The semiconductor oxide thin film provides an oxide semiconductor thin film transistor which is a SnO ₂ thin film doped with one metal selected from the group consisting of Hf, Zr, Al, Ga, Ti, and combinations thereof.

The oxide semiconductor thin film transistor according to the present invention has excellent characteristics by effectively controlling the internal carrier.

1 is a schematic diagram for explaining a theory of improving the electrical properties of a metal doped (typically Hf) SnO ₂ thin film according to the present invention.
2 is a cross-sectional view illustrating an oxide semiconductor thin film transistor according to an exemplary embodiment of the present invention.
3 is a graph showing a change in carrier concentration and a resistance value in a thin film according to the doping amount of Hf.
4 is a voltage of the device (Device 1), the device (Device 2, 3) including a Hf undoped SnO ₂ films containing Hf-doped SnO ₂ thin film according to the present invention - a graph showing the current characteristics change.
5 is a graph showing a change in voltage-current characteristics of the device according to the doping amount of the Hf-doped SnO ₂ thin film according to the present invention.
6 is a graph showing a change in voltage-current characteristics of the device according to the thickness of the Hf-doped SnO ₂ thin film according to the present invention.
7 is a voltage of the device (Device 2) containing the device (Device 6), Hf undoped SnO ₂ films containing Hf-doped SnO ₂ thin film according to the present invention - a graph showing the current characteristics change.

The present invention relates to a non-ZnO-based oxide semiconductor transistor that can replace ZnO as a material of a semiconductor oxide thin film, and uses SnO ₂ instead of ZnO. The SnO ₂ thin film has a very high electrical conductivity with a carrier concentration of 10 ¹⁹ or more, which is suitable as a transparent electrode. However, the SnO ₂ thin film is difficult to drive when applied as an oxide semiconductor layer of a thin film transistor. The lower the carrier concentration in the 10 ^14? 10 ¹⁹ level required for the thin film transistor, according to the process variable, the control thereof is very difficult, there is a problem that change to the characteristics markedly when exposed to the environment.

This requires the production of SnO ₂ thin film to easily control the carrier concentration and to lower the electrical conductivity, there is a problem that the electrical conductivity is too high when introducing a SnO ₂ thin film concept of metal doping, such as ITO. Therefore, the doping should be made to lower the electrical conductivity, and the present inventors have secured such characteristics in some metal elements as a result of various experiments.

The doped metal that can be used may be one selected from the group consisting of Hf, Zr, Al, Ga, Ti, and combinations thereof, and preferably Hf may be used. Such metals control the oxygen-related defects in the SnO ₂ thin film to effectively reduce the carrier concentration to control the electrical conductivity, and in particular, Hf can also reduce the amount of SnO ₂ characteristic change exposed to the outside by using a strong oxidation power.

1 is a schematic diagram for explaining a theory of improving the electrical properties of a metal doped (typically Hf) SnO ₂ thin film according to the present invention. In this case, (a) of FIG. 1 corresponds to an Hf undoped SnO ₂ thin film, and (b) corresponds to an Hf doped SnO ₂ thin film.

Referring to FIG. 1, Hf may be doped to reduce ionized V _o ⁺ , thereby reducing carrier concentration. Mobility can also be improved by reducing the overall trap (including interface and bulk range) in the SnO ₂ thin film. As a result, I _DS increases, the active energy decreases, and the falling rate increases.

In particular, the metal is essentially limited in its doping amount, which is used in a much smaller range of atomic% compared to conventional metal doping amounts.

Doping amount is 1-10 atomic%, Preferably it is used in the range of 1.23-2.70 atomic%. If the content is less than the above range, the doping effect is weak and the carrier concentration is not easily controlled. On the contrary, if the content exceeds the above range, the charge mobility is greatly reduced due to excessive decrease of the carrier concentration. Becomes difficult.

The metal-doped SnO ₂ thin film may be formed in a typical thickness range when applied as an oxide semiconductor layer, for example, 0.5 to 500 nm, preferably 1 to 150 nm, and more preferably 40 to 100 nm. It is possible to obtain good results in thin film transistor characteristics such as carrier mobility and on / off ratio. If the thickness is thinner than the above range, it is difficult to form an industrially uniform film. On the contrary, if the thickness is too thick, the film forming time becomes long and cannot be employed industrially.

Formation of the metal-doped SnO ₂ thin film according to the present invention is not particularly limited in the present invention and is preferably prepared by a conventional physical vapor deposition (PVD) method.

As a specific PVD method, sputtering method, resistance heating vapor deposition method, electron beam vapor deposition method, ion beam deposition method, etc. can be applied, but sputtering is performed in order to make film formation on a large area substrate easy. At this time, in order to make the film thickness distribution even, it is more preferable to carry out by DC magnetron sputtering method.

As mentioned above, the target in sputtering uses the sintered compact of Sn oxide as a target, or sputters, while making the metal target of Sn react with oxygen.

The sputtering conditions may be appropriately changed by those skilled in the art according to various parameters such as a chamber apparatus, and in this embodiment, 0.25 to 1.25 W / cm 2, oxygen partial pressure 5 to 80%, and pressure of 5 mTorr or less at a temperature of room temperature to 100 ° C. Perform on

In particular, the amount of Hf, Zr, Al, Ga, Ti during the sputtering is added by controlling the content of the metal element to control the doping amount, sputtering gas may be used N ₂ , He, Ne, Ar, Kr, Xe and the like.

After film formation by sputtering, heat treatment is performed to increase the field effect mobility.

Specifically, after the oxide semiconductor layer is formed, in the air or in a nitrogen atmosphere, the heat treatment is performed at 150 ° C. or higher and 600 ° C. or lower, preferably at 180 ° C. to 250 ° C., more preferably at 200 ° C. for 1 minute to 1 hour, and more preferably for 3 minutes. Do

The low heat treatment temperature may lower the thermal stability or heat resistance, or the mobility may be lowered. On the contrary, the high heat treatment temperature is limited to the use of a substrate having no cost or heat resistance. At this time, the heat treatment time may vary depending on the heat treatment temperature.

By transferring the metal-doped SnO ₂ thin film to the oxide semiconductor layer of the thin film transistor, it is possible to secure excellent electrical characteristics.

2 is a cross-sectional view illustrating an oxide semiconductor thin film transistor according to an exemplary embodiment of the present invention. The structure of FIG. 2 shows a bottom gate shape but includes a top gate structure if necessary, and may further include a known layer such as a buffer layer between each layer.

2, an oxide semiconductor thin film transistor includes a substrate 10; The gate electrode 12 is formed on the substrate 10. A gate insulating layer 14 is formed on the gate electrode 12, and an oxide semiconductor layer 16 is formed on the gate insulating layer 14 as an active layer providing a channel region, a source region, and a drain region. The source and drain electrodes 18a and 18b are formed on the oxide semiconductor layer 12 so as to be connected to the source and drain regions, respectively.

The material and formation method of the substrate 10, the gate electrode 12, the gate insulating film 14, and the source / drain electrodes 18a and 18b are not particularly limited in the present invention and are well known.

The substrate 10 may be a glass substrate such as alkali silicate-based glass, alkali-free glass, quartz glass or the like, a resin substrate such as silicon substrate, acrylic, polycarbonate, polyethylene naphthalate (PEN), or polyethylene terephthalate (PET). , Polymers such as polyamide may be used. The thickness is also used within the conventional range, and for example, 0.1 to 10 mm and 0.3 to 5 mm are preferable.

A gate insulating film 14 is _{SiO 2, SiNx, Al 2 O} 3, Ta 2 O5, TiO 2, MgO, ZrO 2, CeO 2, K 2 O, Li 2 O, Na 2 O, Rb 2 O, Sc 2 O Metal oxides such as ₃ , Y ₂ O ₃ , CaHfO ₃ , PbTi ₃ , BaTa ₂ O ₆ , SrTiO ₃ , AlN or organic insulating films such as poly (4-vinylphenol) (PVP) and perylene are possible, and these may be used alone. Or it can be formed in the multilayered structure laminated | stacked two or more layers.

There is no restriction | limiting in particular in the material which forms each electrode of the gate electrode 12 and the source / drain electrodes 18a and 18b, What is generally used in the range which does not lose the effect of this invention can be arbitrarily selected. For example, transparent electrodes such as indium tin oxide (ITO), indium zinc oxide, ZnO, metal electrodes such as Al, Ag, Cr, Ni, Mo, Au, Ti, Ta, Cu, or metal electrodes of alloys containing them Can be used. Moreover, it is preferable to laminate | stack two or more layers, and to reduce contact resistance or to improve interface strength.

When the metal-doped SnO ₂ thin film according to the present invention is used as the oxide semiconductor layer 16 in the oxide semiconductor thin film transistor having the above structure, the carrier concentration is about 10 ^{12 to} 10 ¹⁷ / cm 3, and the mobility (μ _FE ) is When used as a thin film transistor at 0.5 cm <2> / Vs or more, the balance of mobility and an on / off ratio is favorable, and it is preferable. In addition, as a result of measuring the light transmittance, it was confirmed that the transparent film had a high transmittance of 60% or more at 400-700 nm.

As such, the metal-doped SnO ₂ thin film according to the present invention can be preferably applied to a transistor to replace ZnO and thus can be used as a non-ZnO-based oxide semiconductor transistor. In addition, low temperature process application, large-area process can be easily applied, and thus low-cost manufacturing can be applied to a wide range of applications.

In addition, it contributes to the development of transparent smart windows in economic and industrial aspects (high value-added glass products, functional auto parts, security electronic devices, outdoor advertising display products, solar cells, game consoles, electronic photo frames, etc.). In addition to eliminating spatial and visual constraints, it is possible to manufacture ultra-thin, high-quality products, thereby fostering high value-added industries. In addition, since low-cost manufacturing is possible, the existing TFT LCD market may be shared first, and then may cause a sudden change in display president.

Furthermore. It can be applied to large area OLED market based on uniformity, reliability, and excellent device characteristics.As a type oxide semiconductor can be realized, transparent logic IC is expected to replace part of the existing silicon-based IC market. It is possible to develop.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention may be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

[Example]

Experimental Example 1

As shown in the cross-sectional view of Fig. 2, the device structure of the TFT was fabricated in a bottom gate type. DC sputtering was performed using Sn and Hf as targets on a substrate that was not heated by mixing Ar and O ₂ gas, and then heat-treated at 200 ° C. for 3 minutes to form a channel layer.

In this case, a substrate using a n-type silicon wafer having a high doping concentration coated with a thermally oxidized silicon film (100 nm thick), an insulating film includes SiO ₂ (100 nm), and a source / drain electrode includes Mo (300 nm). It formed using the photolithographic method of.

3 is a graph showing a change in carrier concentration and a resistance value in a thin film according to the doping amount of Hf.

Referring to FIG. 3, there was no change in carrier concentration and resistance up to a certain level according to the doping amount of Hf, but the carrier concentration in the thin film decreased from 0.059 ppm (1.23 atomic%) and, on the contrary, the specific resistance tended to increase. These results predict that Hf can reduce the number of carriers by selectively reducing traps or defects inside the thin film.

Experimental Example 2

Figure 4 is the device (Device 1), Hf undoped voltage of the device (Device 2, 3) comprising a SnO ₂ films containing Hf-doped SnO ₂ thin film according to the present invention and a graph showing the current characteristics change, the device characteristics Was measured and shown in Table 1 below.

Device 1 Device 2 Device 3
Thin film structure Channel layer / thickness Hf Doped SnO ₂ Thin Films / 40nm SnO ₂ Thin Films / 40nm SnO ₂ Thin Films / 40nm Doping amount 1.23 atomic% - - Insulation film / thickness SiO ₂ / 100nm Si ₃ N ₄ / SiO _2, (100 / 10nm), Si ₃ N ₄ / 100nm Source / Drain Electrode / Thickness Mo / 300nm Mo / 300nm Mo / 300nm
Electrical characteristics Mobility (μ _FE ) 0.50 0.16 0.011 On / Off Current (I _{ON / OFF} ) 3.04 × 10 ⁵ 1.53 × 10 ⁵ 3.84 × 10 ⁴ SS (V / decade) 1.68 3.743 0.93 Von (V) -28 -28 2

According to Table 1 and FIG. 4, the Hf undoped element exhibits a very low characteristic even though the SnO ₂ transition characteristic is exhibited, and the drain current is improved despite the improvement of the characteristic by applying a buffer film to the insulator. It is very low. In addition, when the SnO ₂ TFT is manufactured, there is a disadvantage in that it exhibits low mobility.

In contrast, it can be seen that the Hf doping element according to the present invention exhibits a high drain current and greatly improves characteristics.

Experimental Example 3

5 is a graph showing a change in the voltage-current characteristics of the device according to the doping amount of the Hf-doped SnO ₂ thin film according to the present invention, Device 1 shows the Hf doping amount 1.23 atomic%, Device 4 is 2.70 atomic%. In this case, the properties of the devices are measured and shown in Table 2 below.

Device 1 Device 4
Thin film structure
Channel layer / thickness Hf Doped SnO ₂ Thin Films / 40nm Hf Doped SnO ₂ Thin Films / 40nm Doping amount 1.23 atomic% 2.70 atomic% Insulation film / thickness SiO ₂ / 100nm SiO ₂ / 100nm Source / Drain Electrode / Thickness Mo / 300nm Mo / 300nm
Electrical characteristics
Mobility (μ _FE ) 0.50 0.51 On / Off Current (I _{ON / OFF} ) 3.04 × 10 ⁵ 1.31 × 10 ⁵ SS (V / decade) 1.68 1.52 Von (V) -2.8 -9

Referring to FIG. 5 and Table 2, as the content of Hf increases, the internal carriers decrease, which is consistent with the characteristics analyzed through hole measurement. In addition, it can be seen that the carrier voltage inside the SnO ₂ thin film is effectively reduced by Hf doping because the operating voltage shifts positively.

Experimental Example 4

6 is a graph showing the voltage-current characteristics of the device according to the thickness of the Hf-doped SnO ₂ thin film according to the present invention, in which the characteristics of the devices are measured and shown in Table 3 below.

Device 1 Device 5
Thin film structure
Oxide semiconductor layer / thickness Hf Doped SnO ₂ Thin Films / 40nm Hf Doped SnO ₂ Thin Films / 100nm Doping amount 1.23 atomic% 1.23 atomic% Insulation film / thickness SiO ₂ / 100nm SiO ₂ / 100nm Source / Drain Electrode / Thickness Mo / 300nm Mo / 300nm
Electrical characteristics
Mobility (μ _FE ) 0.50 4.28 On / Off Current (I _{ON / OFF} ) 3.04 × 10 ⁵ 2.16 × 10 ⁴ SS (V / decade) 1.68 1.222 Von (V) -28 -38

Referring to FIG. 6 and Table 3, as the thickness of the oxide semiconductor layer increases, the mobility increases about 9 times or more, so that the carrier concentration can be effectively controlled by controlling the thickness of the thin film.

Experimental Example 5

7 is a device including a Hf-doped SnO ₂ thin film according to the present invention (Device 6), Hf undoped voltage of the device (Device 2) containing SnO ₂ thin film - a graph showing the current characteristics change, measuring the device characteristics It is shown in Table 4 below.

Device 6 Device 2
Thin film structure
Channel layer / thickness Hf Doped SnO ₂ Thin Films / 40nm SnO ₂ Thin Films / 40nm Doping amount 2.70 atomic% - Insulation film / thickness Si ₃ N ₄ / SiO _2, (100 / 10nm), Si ₃ N ₄ / SiO _2, (100 / 10nm), Source / Drain Electrode / Thickness Mo / 300nm Mo / 300nm
Electrical characteristics
Mobility (μ _FE ) 0.66 0.16 On / Off Current (I _{ON / OFF} ) 6.09 × 10 ⁷ 1.53 × 10 ⁵ SS (V / decade) 0.704 1.364 Von (V) -5 -3

According to FIG. 7 and Table 4, in the case of the Hf doping device according to the present invention, it can be seen that the drain current is greatly increased and the electrical characteristics are also improved.

10 substrate 12 gate electrode
14: gate insulating film 16: oxide semiconductor layer
18a: source electrode 18b: drain electrode

Claims (1)

An oxide semiconductor thin film transistor comprising a semiconductor oxide thin film as a channel layer,
And the semiconductor oxide thin film is a SnO ₂ thin film doped with one metal selected from the group consisting of Hf, Zr, Al, Ga, Ti, and combinations thereof.

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