Target for Oxide Semiconductor Sputtering and Method for Manufacturing Thin Film Transistor Using the Same

Abstract

To provide a sputtering target used in a sputtering process for depositing a thin film, specifically an active layer of a thin film transistor.SOLUTION: There is provided a sputtering target used in a sputtering process for depositing an active layer of a thin film transistor, the sputtering target being an oxide semiconductor sputtering target that contains a material based on a composition of In, Sn, Ga, Zn, and O. Further, the oxide semiconductor sputtering target contains indium oxide, tin oxide, gallium oxide and zinc oxide. The In, Sn, Ga, and Zn contents are in ranges of 60-80%, 0.5-8%, 5-15%, and 10-30% by weight with respect to the weight of (In+Sn+Ga+Zn), respectively. There is also provided a method of fabricating a thin film transistor, the method including depositing an active layer using the oxide semiconductor target.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a target for oxide semiconductor sputtering and a method for manufacturing a thin film transistor using the same. More specifically, the present invention relates to a target for oxide semiconductor sputtering for depositing a thin film having high electron mobility and element driving reliability, and a method for manufacturing a thin film transistor using the same.

Background Art

[0002] Generally, thin film transistors (TFTs) are applied to SRAMs and ROMs, but are mainly used as pixel switching elements of active matrix flat panel displays. For example, they are used as switching elements and current driving elements of liquid crystal displays and organic electroluminescent displays. Here, the thin film transistor used as a switching element serves to independently control each pixel so that each pixel can represent other electrical signals.

[0003] Currently, liquid crystal displays and organic light emitting displays mainly use thin film transistors having a silicon-based active layer. However, in the case of amorphous silicon (a-Si) used in displays, there is a limit to realizing large area high resolution / high speed drive displays due to low operating speed and unstable characteristics due to a low electron mobility of approximately 0.5 cm 2 / Vs. And in the case of polycrystalline silicon (poly-Si) mainly used in organic electroluminescent displays, since it is crystallized through an excimer laser, the TFT element characteristics including electron mobility show better performance than amorphous silicon, but there is a disadvantage that large area manufacturing is impossible.

[0004] Recently, as a solution to this problem, thin film transistors having an indium gallium zinc oxide-based active layer have been partially applied as driving elements of display devices. However, due to their lower electron mobility compared to polycrystalline silicon, there is a limit to their application to next-generation large-area / high-resolution / high-speed driving displays.

[0005] In addition, oxide-based active layers with a high indium content have been developed to improve mobility. However, when the indium content is high, characteristics differences such as the mobility of thin film transistors may occur due to temperature dispersion that can occur in the post-heat treatment process. As a result, there is a limit to their application to large-area substrates of 8th generation and above.

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made to solve the problems of the prior art as described above. The object of the present invention is to provide an oxide semiconductor sputtering target for depositing a thin film having high electron mobility, element driving reliability, and high uniformity during large-area manufacturing, and a method for manufacturing a thin film transistor using the same.

Means for Solving the Problems

[0007] For this purpose, one aspect of the present invention provides a target used in a sputtering process for depositing a thin film, particularly an active layer of a thin film transistor, the target comprising a substance based on the composition of In, Sn, Ga, Zn, and O, for oxide semiconductor sputtering.

[0008] In one embodiment, the target for oxide semiconductor sputtering may include indium oxide, tin oxide, gallium oxide, and zinc oxide, and may be composed of In at 60 - 80 wt%, Sn at 0.5 - 8 wt%, Ga at 5 - 15 wt%, and Zn at 10 - 30 wt% with respect to (In + Sn + Ga + Zn).

[0009] On the one hand, another aspect of the present invention provides a method for manufacturing a thin film transistor by depositing an active layer using the above-described target for oxide semiconductor sputtering. Such a thin film transistor can be used in a display device, for example, a liquid crystal display device, an organic light emitting display device, a display device using field emission, and the like.

Effects of the Invention

[0010] According to the present invention, a target is formed of a five-component semiconductor material based on the composition of In, Sn, Ga, Zn, and O, and by depositing an active layer of a thin film transistor through this, it is possible to exhibit higher electron mobility and element drive reliability than an active layer formed of a four-component semiconductor material based on the composition of conventional In, Ga, Zn, and O. There are few characteristic differences due to the temperature of the subsequent process, and the performance of the thin film transistor and the display device including the same can be improved. When manufacturing a large area, the manufacturing yield can also be improved by improving the uniformity of the thin film transistor.

Brief Description of the Drawings

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Figure 1

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Embodiments for Carrying Out the Invention

[0012] Hereinafter, with reference to the attached drawings, an oxide semiconductor sputtering target according to an embodiment of the present invention, a thin film transistor having an active layer deposited through this, and a display device including the same will be described in detail.

[0013] In addition, in describing the present invention, when it is determined that a specific description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

[0014] FIG. 1 is a cross-sectional view showing a thin film transistor according to an embodiment of the present invention.

[0015] The oxide semiconductor sputtering target according to an embodiment of the present invention is a target used in a sputtering process for depositing the active layer 130 of the thin film transistor 100 as shown in FIG. 1. Here, it is a method of colliding sputtering plasma particles with the target at a high speed and depositing the ejected target particles on a substrate on the opposite side of the target.

[0016] In an embodiment of the present invention, such an oxide semiconductor target contains a substance based on the composition of In, Sn, Ga, Zn, and O, and for example, can contain gallium oxide, tin oxide, zinc oxide, and indium oxide. At this time, In can be contained in a content ratio of 60 to 80% by weight, Sn can be 0.5 to 8% by weight, Ga can be 5 to 15% by weight, and Zn can be 10 to 30% by weight with respect to (In + Sn + Ga + Zn).

[0017] FIG. 1 illustrates a thin-film transistor with a bottom gate structure, but the present invention is not necessarily limited thereto.

[0018] For example, the sputtering target of the present invention can be used for thin-film deposition of thin-film transistors with various structures such as thin-film transistors with a top gate structure.

[0019] FIG. 2 is a graph showing the on current according to the gate voltage of a thin-film transistor according to an embodiment of the present invention and a thin-film transistor according to the prior art.

[0020] As described above, if an oxide semiconductor target is formed of a substance based on the composition of In, Sn, Ga, Zn, and O, and the active layer 130 of the thin-film transistor 100 is deposited through a sputtering process using this, as shown in FIG. 2, the thin-film transistor (a) in which the active layer is deposited through an oxide semiconductor target containing a substance based on the composition of In, Sn, Ga, Zn, and O has a drain current that is approximately 10 times higher in the high voltage region (Vg > Vth) compared to the thin-film transistor (b) having an active layer formed of a conventional four-component semiconductor substance based on the composition of In, Ga, Zn, and O. It can be confirmed that a high on-off switching ratio is exhibited, and the thin-film transistor can be switched faster due to the low subthreshold swing (V / dec), which is a main characteristic of the switching element.

[0021] FIG. 3 is a graph showing the electron mobility of thin-film transistors according to the indium content of the target in the present invention, and FIG. 4 is a drawing showing the result of classifying the characteristics of the thin film of FIG. 3. Further, FIG. 5 is a drawing showing the change in Id with respect to Vg in a thin-film transistor in which a conductor thin film and a thin film having semiconductor characteristics but poor characteristics and unsuitable for use as an active layer of a thin-film transistor and a semiconductor thin film having excellent characteristics are used as the active layer.

[0022] As shown, although the thin film deposited using a target with In less than 60 wt% may exhibit semiconductor characteristics, its electron mobility is low and it is not suitable for use in the active layer of a thin film transistor. Also, the thin film deposited using a target with In exceeding 80 wt% has low electron mobility or exhibits conductor characteristics and cannot be used in the active layer of a thin film transistor. On the contrary, the thin film deposited using a target with In of 60 - 80 wt% shows excellent electron mobility. From this, it can be seen that it is desirable that the In content of the target for forming the active layer of the present invention is 60 - 80 wt%. The thin film of the present invention desirably has an electron mobility value of at least 30 cm 2 / V·s.

[0023] When the active layer exhibits conductor characteristics, a high drain current is measured regardless of the gate voltage in the thin film transistor, and it is impossible to realize the characteristics of a semiconductor element that performs on-off switching based on the threshold voltage.

[0024] For a thin film transistor using a thin film unsuitable for use in a semiconductor as the active layer, there is a change in the drain current depending on the gate voltage, but the difference is not large, and a high leakage current is generated at a gate voltage below the threshold voltage, showing poor performance as a switching element. On the other hand, a thin film transistor using a thin film showing excellent semiconductor characteristics as the active layer shows a large difference in drain current change depending on the gate voltage, and thus shows excellent performance as a switching element.

[0025] Figure 6 is a drawing showing the etching rate of the thin film according to the tin content of the target in the present invention.

[0026] As shown, it can be seen that when the tin content of the target exceeds 8 wt% with respect to (In + Sn + Ga + Zn), the etching rate of the thin film formed therefrom decreases rapidly.

[0027] Thin film transistors come to be fabricated using photolithography processes. In the case of the active layer, patterning in a constant shape is necessary through wet etching after deposition. At this time, for wet etching, an etching rate higher than a certain rate is required, and desirably, an etching rate of 200 Å / min or more is required.

[0028] FIG. 7 is a graph showing the electron mobility of TFT elements according to the tin content ratio with respect to indium of the target in the present invention.

[0029] As shown in the figure, if the tin content ratio (weight ratio) with respect to indium of the target is 0.03 to 0.15 (indium weight: tin weight = 1: 0.03 to 0.15), the thin film formed therefrom exhibits excellent electron mobility. From this, it can be seen that it is desirable that the tin content ratio with respect to indium of the target for forming the active layer of the present invention is 0.03 to 0.15.

[0030] FIG. 8 is a graph showing the mobility dispersion depending on the temperature of TFT elements according to the gallium content ratio with respect to the gallium and zinc contents of the target in the present invention.

[0031] As shown in the figure, if the gallium content ratio (weight ratio) with respect to the gallium and zinc contents of the target is 0.6 or less, the thin film formed therefrom exhibits excellent mobility dispersion. From this, it can be seen that it is desirable that the gallium content ratio with respect to the gallium and zinc contents of the target for forming the active layer of the present invention is 0.6 or less.

[0032] In the present invention, the mobility dispersion is the difference in mobility of each TFT element fabricated by heat-treating the thin film at 200 ° C and 400 ° C after depositing the active layer, and desirably has a mobility dispersion value of 30% or less.

[0033] The target composed of such a composition and content ratio can be manufactured by mixing gallium oxide powder, tin oxide powder, zinc oxide powder, and indium oxide powder according to the content ratio, followed by cold pressing, slip casting, filter pressing, cold isostatic pressing, gel casting, centrifugal sedimentation, gravimetric sedimentation, or other forming methods, and then sintering it. In addition, the target manufactured in this way can be used in a sputtering process in a state where it is joined and supported to a backing plate composed of a metal material, for example.

[0034] On the other hand, the thin film transistor 100 including the active layer 130 deposited using the oxide semiconductor target according to the embodiment of the present invention is used as a switching element or a current driving element for a liquid crystal display or an organic light emitting display. Such a thin film transistor 100 is formed including a gate electrode 110, a gate insulating film 120, an active layer 130, a source electrode 140, and a drain electrode 150.

[0035] On the other hand, as the substrate 10, glass, a semiconductor wafer, a metal oxide, a ceramic material, plastic, or the like that can satisfy the thermodynamic and mechanical requirements for the thin film transistor 100 can be used. In particular, the substrate 10 is preferably glass or plastic, but is not limited thereto.

[0036] The gate electrode 110 is formed on the substrate 10. When applied to a display device, it is formed by branching from a gate line (not shown) arranged along a first direction, for example, the horizontal direction, on the substrate 10. A voltage for turning on / off the thin film transistor 100 is applied to such a gate electrode 110. For this purpose, the gate electrode 110 can be formed of a conductive material such as a metal or a metal oxide. For example, the gate electrode 110 can be formed of a metal such as Pt, Ru, Au, Ag, Mo, Al, W, or Cu, or a metal such as IZO (Indium Zinc Oxide) or ITO (Indium Tin Oxide), or a conductive oxide. That is, the gate electrode 110 is formed by depositing the above-mentioned conductive material in a thin film on the substrate 10 and then patterning it, but is formed simultaneously with the gate line (not shown) through one process.

[0037] Such a gate electrode 110 can be made of a structure of a diffusion prevention film (not shown) and a copper film deposited on the diffusion prevention film (not shown). The diffusion prevention film (not shown) is for preventing copper atoms from diffusing into the substrate 10 and improving the bonding force and electrical characteristics of copper, and can be made to contain any one of titanium, tantalum, molybdenum, chromium, nickel, or platinum.

[0038] The gate insulating film 120 can be formed of an insulating material used for ordinary semiconductor elements, and in particular, can be formed of silicon oxide or silicon nitride. For example, the gate insulating film 120 can be made of SiO2 or a High-K material having a higher dielectric constant than SiO2, such as HfO2, Al2O3, Si3N4, or a mixture thereof.

[0039] The active layer 130 is formed on the gate insulating film 120 corresponding to the gate electrode 110 and has a channel region (CH).

[0040] In the embodiment of the present invention, the active layer 130 is formed by depositing and patterning on the gate insulating film 120 through a sputtering process using a target for sputtering an oxide semiconductor according to the embodiment of the present invention described above, that is, a target containing In in a content ratio of 60 to 80% by weight, Sn in a content ratio of 0.5 to 8% by weight, Ga in a content ratio of 5 to 15% by weight, and Zn in a content ratio of 10 to 30% by weight with respect to (In + Sn + Ga + Zn).

[0041] In this way, the active layer 130 can exhibit higher electron mobility and reliability than the active layer formed of a conventional four-component semiconductor material based on the composition of In, Ga, Zn, and O, which is composed of a thin film having the above composition and content ratio, and the performance of the thin film transistor 100 including the same can be improved.

[0042] The source electrode 140 and the drain electrode 150 are arranged separately on the active layer 130. Such source electrode 140 and drain electrode 150 can be composed of a conductive material such as a metal, or can be formed in a structure of a copper film deposited on a diffusion prevention film (not shown) and a diffusion prevention film (not shown) like the gate electrode 110.

[0043] The source electrode 140 is connected to a data line (not shown) arranged along a second direction, for example, a vertical direction, orthogonal to a gate line (not shown) on the substrate 10. And the drain electrode 150 is connected to a pixel electrode (not shown).

[0044] On the other hand, an ohmic contact layer 135, which is an impurity semiconductor layer, can be formed between the active layer 130 and the source electrode 140 and the drain electrode 150.

[0045] Also, although not shown in FIG. 1, the thin film transistor can include a protective layer (not shown) formed on the source electrode and the drain electrode, etc. As the protective layer, substances such as SiO2 and SiNx and other oxides can be used.

[0046] The thin film transistor 100 according to an embodiment of the present invention is used as a switching element or a current driving element in various display devices. For example, although not shown, when the thin film transistor 100 is used in a liquid crystal display device (LCD) including upper and lower substrates facing each other, a liquid crystal layer interposed therebetween, and a backlight disposed on the back surface of the lower substrate to irradiate light forward, the thin film transistor 100 is formed in a pixel region defined by the intersection of a plurality of gate lines and data lines arranged on the lower substrate. At this time, a color filter is provided on the upper substrate corresponding to the pixel region. And an optical film that compensates for the optical characteristics of the liquid crystal display device can be disposed on the upper surface of the upper substrate.

[0047] In addition, the thin film transistor 100 according to the embodiment of the present invention can be used not only in a liquid crystal display device but also in an organic light emitting display device (OLED). In this case, the thin film transistor 100 is formed in a pixel region defined by the intersection of a plurality of gate lines and data lines on a lower substrate. At this time, an organic light emitting element is formed on the lower substrate. The lower substrate and the upper substrate are combined to form an organic light emitting panel of the organic light emitting display device. Here, the organic light emitting element includes an anode electrode, a cathode electrode, and a hole transporting layer, an emission layer, and an electron transporting layer located therebetween. At this time, in order to inject holes and electrons more efficiently, a hole injection layer can be included between the anode electrode and the hole transporting layer, and an electron injection layer can be included between the electron transporting layer and the cathode electrode. As a result, holes injected from the anode electrode through the hole injection layer and the hole transporting layer into the emission layer and electrons injected from the cathode electrode through the electron injection layer and the electron transporting layer into the emission layer form excitons, and these excitons emit light corresponding to the energy gap between the holes and the electrons. At this time, the anode electrode is made of a material such as indium-tin oxide (ITO) or indium-zinc-oxide (IZO) that has a high work function and is transparent, and the cathode electrode can be made of a material such as aluminum (Al), calcium (Ca), or an aluminum alloy that has a low work function and is chemically stable.

[0048] On the other hand, an optical film that compensates for the optical characteristics of the organic light emitting display device can be disposed on the upper surface of the upper substrate.

[0049] As described above, although the present invention has been described by way of limited embodiments and drawings, the present invention is not limited to the above embodiments, and various modifications and variations are possible from such descriptions for those having ordinary knowledge in the field to which the present invention pertains.

[0050] Therefore, the scope of the present invention should not be determined only by the described embodiments, but should be determined not only by the appended claims, but also by equivalents of the claims.

Explanation of Reference Numerals

[0051] 100 Thin film transistor 110 Gate electrode 120 Gate insulating film 130 Active layer 135 Ohmic contact layer 140 Source electrode 150 Drain electrode 10 Substrate CH Channel region

Claims

1. A sputtering target used in a sputtering process for depositing an active layer of a thin film transistor, the sputtering target containing a substance based on a composition of In, Sn, Ga, Zn, and O, containing gallium oxide, tin oxide, zinc oxide, and indium oxide, wherein In is 60 to 80 wt% with respect to (In + Sn + Ga + Zn), Sn is 0.5 to 8 wt%, Ga is 5 to 15 wt%, and Zn is 10 to 30 wt%, an oxide semiconductor sputtering target.

2. The oxide semiconductor sputtering target according to claim 1, wherein In is 65 to 75 wt% with respect to (In + Sn + Ga + Zn), Sn is 1 to 5 wt%, Ga is 7 to 13 wt%, and Zn is 10 to 20 wt%.

3. The oxide semiconductor sputtering target according to claim 1, wherein the weight ratio of Sn to In is 0.03 to 0.

15.

4. The oxide semiconductor sputtering target according to claim 1, wherein the total content of Ga and Zn is 20 to 40 wt% with respect to (In + Sn + Ga + Zn).

5. The oxide semiconductor sputtering target according to claim 1, wherein the weight ratio of Ga to (Ga + Zn) is 0.6 or less.

6. A method for manufacturing a thin film transistor, comprising depositing an active layer using the oxide semiconductor sputtering target according to any one of claims 1 to 5.

7. Depositing an active layer using the oxide semiconductor sputtering target according to any one of claims 1 to 5, and after depositing the active layer, heat-treating the active layer at 200 to 400 °C, a method for manufacturing a thin film transistor.

8. A method for manufacturing a thin film transistor provided in a liquid crystal display device or an organic light emitting display device, comprising depositing an active layer using the oxide semiconductor sputtering target according to any one of claims 1 to 5, a method for manufacturing a thin film transistor.

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