Thin film transistor manufacturing method using heat treatment and thin film transistor structure

Abstract

The present invention relates to a transistor manufacturing method and a transistor structure, wherein a metal is oxidized using heat treatment, and the oxidized metal is utilized as a gate insulating film. A gate electrode is formed by depositing a first metal, which is not easily thermally oxidized, on a substrate, and then a second metal, which is easily thermally oxidized, is deposited on the gate electrode and oxidized through heat treatment to be converted into a gate insulating film. Through the thermal oxidation process, an existing vacuum deposition process may be replaced, thereby simplifying the manufacturing process and reducing costs, and, if necessary, an additional insulating film may be deposited to enhance leakage current suppression and high-voltage tolerance. The present invention is applicable to transistor designs including Bottom Gate, Top Gate, and modified structures, and can be used in various application fields such as displays, wearable devices, and biosensor platforms. Through this, a technology capable of economically manufacturing a high-performance transistor can be provided, and the electrical characteristics and reliability of devices can be significantly improved.

Description

Method and structure of manufacturing a thin-film transistor using heat treatment

[0001] The present invention relates to a thin-film transistor, and more specifically, to a method and structure for manufacturing a transistor using heat treatment, which simplifies the manufacturing process and reduces costs by forming a metal oxide film as a gate insulating film using heat treatment, thereby enabling its use in high-performance electronic devices and integrated circuits such as display technology, wearable devices, and biosensor platforms.

[0002] The development of the electronics industry and the advancement of integrated circuits have enabled increased device integration and operating speed, but this has led to problems such as increased complexity of manufacturing processes and power consumption. In particular, thin film transistors (TFTs) play a key role in various application fields, including display technology, but the process of forming the gate insulating film, a major component of the transistor, requires expensive equipment and complex manufacturing steps.

[0003] FIGS. 1a to 1d show the structure of a general thin-film transistor. FIG. 1a is a bottom gate structure in which the gate electrode (2) is placed at the very bottom of the substrate (1). Then, an insulating film (3) and a semiconductor layer (4) are formed sequentially on the gate electrode (2). This process is simple and the manufacturing cost is relatively low. It is also frequently used in conventional thin-film transistor fabrication methods. However, an overlap between the gate electrode (2) and the semiconductor layer (4) is required. FIG. 1b is similar to the structure of FIG. 1a, but the source (5) / drain (6) electrodes are located below the semiconductor layer (4). FIG. 1c is a top gate structure in which the gate electrode (2) is placed on the semiconductor layer (4). It is a structure in which the semiconductor layer (4) is formed on the substrate (1), and the insulating film (3) and the gate electrode (2) are formed on top of it. This allows for more precise control of the electric field, thereby improving the performance of the transistor, and reduces damage to the semiconductor layer (4), resulting in high process stability. However, the manufacturing process may be somewhat complex and cost more. Fig. 1d is similar to the structure of Fig. 1c, but the source and drain electrodes are formed on the semiconductor layer.

[0004] In the fabrication of thin-film transistors with such diverse structures, vacuum deposition technologies such as PECVD (Plasma Enhanced Chemical Vapor Deposition), CVD (Chemical Vapor Deposition), or ALD (Atomic Layer Deposition) have been primarily used to form gate insulating films. While these methods provide high-quality insulating films, they act as a major factor in increasing overall manufacturing costs due to the high cost and maintenance burden of vacuum deposition equipment. Furthermore, these processes require multi-step steps, which poses a problem of increasing manufacturing time.

[0005] The present invention was devised to solve such problems and aims to simplify the manufacturing process and reduce costs, support various structures and applications, and expand application fields by improving electrical characteristics and stability, by proposing a transistor manufacturing method and structure that oxidizes a metal using heat treatment and utilizes it as a gate insulating film.

[0006] To achieve the above objective, the present invention comprises the steps of: (a) depositing different first metals and second metals on a substrate; and (b) heat-treating the deposited first metals and second metals to convert the first metal into a gate electrode and the second metal into a gate insulating film.

[0007] The above heat treatment is within a range where the substrate material does not change.

[0008] The above heat treatment is within the range where the second metal is thermally oxidized.

[0009] The above heat treatment is carried out in an atmosphere of oxygen, nitrogen, or a mixture of oxygen and nitrogen.

[0010] The first metal mentioned above is any one selected from the group consisting of titanium (Ti), molybdenum (Mo), or copper (Cu).

[0011] The second metal mentioned above is any one selected from the group consisting of tantalum (Ta), hafnium (Hf), or aluminum (Al).

[0012] The above step (a) comprises: (a1) sequentially stacking the first metal and the second metal on the substrate; (a2) forming a pattern for a gate electrode on the stacked first metal and the second metal; and (a3) ​​heat-treating the patterned first metal and the second metal.

[0013] The above step (a) comprises: (a1) a step of depositing the first metal on the substrate; (a2) a step of forming a pattern for a gate electrode on the deposited first metal; (a3) ​​a step of depositing a second metal on the patterned first metal; and (a4) a step of heat-treating the first metal and the second metal.

[0014] Between the above steps (a3) ​​and (a4), the deposited second metal further includes a step of patterning to cover the first metal.

[0015] The above step (a) comprises: (a1) a step of patterning a semiconductor layer on the substrate; (a2) a step of sequentially stacking a second metal and a conductive oxide electrode on the semiconductor layer; (a3) ​​a step of patterning the stacked second metal and conductive oxide electrodes; and (a4) a step of heat-treating the patterned second metal and conductive oxide electrodes.

[0016] Another feature of the present invention for achieving such an objective comprises: a substrate; a gate electrode formed on the lower or upper part of the substrate; and a gate insulating film formed to be electrically insulated from the gate electrode, wherein the gate insulating film is formed after depositing a second metal that is heat-treatable on the gate electrode formed of a first metal that is heat-treatable.

[0017] The first metal mentioned above is any one selected from the group consisting of titanium (Ti), molybdenum (Mo), or copper (Cu).

[0018] The second metal mentioned above is any one selected from the group consisting of tantalum (Ta), hafnium (Hf), or aluminum (Al).

[0019] The present invention proposes a method and structure for manufacturing a transistor in which a metal is oxidized using heat treatment and utilized as a gate insulating film, thereby overcoming the limitations of existing technology and providing the following effects.

[0020] First, the manufacturing process is simplified and costs are reduced. By replacing expensive vacuum deposition processes such as PECVD, CVD, and ALD with a thermal oxidation process, a gate insulating film can be formed without separate complex equipment. Since the gate insulating film is formed by heat treatment alone, the manufacturing process is simplified, productivity is improved, and since expensive equipment and complex process steps are not required, there is an effect of significantly reducing manufacturing costs.

[0021] In addition, it is useful for supporting various transistor structures and applications, making it suitable for various transistor design requirements such as Bottom Gate, Top Gate, and modified structures. It is effective for use in various application fields, such as display technology (LCD, AMOLED), wearable devices, and biosensor platforms.

[0022] It also improves electrical characteristics and stability. The oxide film formed through thermal oxidation has a high dielectric constant (k) and enhances charge storage capacity, thereby improving transistor performance. Furthermore, the thin, uniform oxide film formed by heat treatment strengthens electrical insulation properties, effectively suppressing leakage current. Additionally, by controlling the thickness of the insulating film or depositing additional insulating films (SiO₂, SiNx, etc.), it is suitable for applications requiring high voltage resistance.

[0023] Furthermore, surface quality and reliability are enhanced. If the surface quality of the oxide film formed by thermal oxidation is insufficient, surface defects (such as microcracks) can be corrected through the deposition of an additional insulating film. This strengthens the reliability of the insulating film, thereby providing a transistor capable of stable operation over a long period.

[0024] FIGS. 1a to 1d show the structure of a typical thin-film transistor.

[0025] FIGS. 2a to 2c are drawings sequentially illustrating a method for manufacturing a thin-film transistor using heat treatment according to a first embodiment of the present invention.

[0026] FIGS. 3a to 3c are drawings sequentially illustrating a method for manufacturing a thin-film transistor using heat treatment according to a second embodiment of the present invention.

[0027] FIGS. 4a to 4c are drawings sequentially illustrating a method for manufacturing a thin-film transistor using heat treatment according to a third embodiment of the present invention.

[0028] FIG. 5 is a diagram showing the results of a top gate method of a thin-film transistor using heat treatment according to the fourth embodiment of the present invention.

[0029] FIG. 6 is a diagram showing the heat treatment results in the method for manufacturing a thin-film transistor using the heat treatment of the present invention.

[0030] Hereinafter, embodiments according to the present invention will be described in detail with reference to the attached drawings. Identical or similar components are assigned identical or similar reference numerals, and redundant descriptions thereof are omitted. In describing the embodiments disclosed in this specification, if it is determined that a detailed description of related prior art may obscure the essence of the embodiments disclosed in this specification, such detailed description is omitted. The attached drawings are intended only to facilitate understanding of the embodiments disclosed in this specification, and the technical concept disclosed in this specification is not limited by the attached drawings; it should be understood that they include all modifications, equivalents, or substitutions that fall within the spirit and technical scope of the present invention.

[0031] Terms containing ordinal numbers, such as first, second, etc., may be used to describe various components; however, these terms are used solely for the purpose of distinguishing one component from another, and the corresponding components are not limited by these terms. A singular expression includes a plural expression unless the context clearly indicates otherwise.

[0032] Terms such as “comprising,” “comprising,” or “having” as used herein should be understood as limiting the existence of the features, steps, components, or combinations thereof described herein, and are not intended to exclude the possibility that one or more other features, steps, components, or combinations thereof may exist or be added.

[0033] When a component is described as being "connected" or "joined" to another component, it should be understood that it may be directly connected or joined to that other component, or that there may be another component in between. On the other hand, when a component is referred to as being "directly connected" or "directly joined" to another component, it should be understood that no other component exists in between.

[0034] FIGS. 2a to 2c are drawings sequentially illustrating a method for manufacturing a thin-film transistor using heat treatment according to a first embodiment of the present invention.

[0035] A method for manufacturing a thin film transistor using heat treatment according to a first embodiment of the present invention comprises the steps of: heat treating different first metals (11) and second metals (12) deposited on a substrate (10); and converting the heat-treated first metal (11) into a gate electrode and the second metal (12) into a gate insulating film.

[0036] A method for manufacturing a thin-film transistor using heat treatment according to the first embodiment of the present invention will be described in detail with reference to FIGS. 2a to 2c.

[0037] First, as shown in FIG. 2a, a substrate (10) is prepared, and a first metal (11) and a second metal (12) are deposited sequentially on the substrate (10). The substrate (10) used here utilizes an insulating material such as glass, a silicon wafer, or plastic. When using a plastic substrate, a buffer layer may be formed before metal deposition to ensure heat treatment stability. The first metal is a metal to be used as a gate electrode, such as titanium (Ti), molybdenum (Mo), or copper (Cu), which does not oxidize easily. The second metal (12) deposited on the first metal (11) utilizes a metal that oxidizes easily due to a low Gibbs-free energy of the oxide, such as tantalum (Ta), hafnium (Hf), or aluminum (Al). Using materials with high dielectric constants of oxide films, such as tantalum (Ta), hafnium (Hf), or aluminum (Al), increases the dielectric constant of the insulating film, which helps improve the characteristics of the transistor. Here, the deposition process of the first metal (11) and the second metal (12) is performed using sputtering or evaporation, which are representative thin film processes, to form an evenly thin layer. At this time, the deposition thickness of the first metal (11) is adjusted to 50 nm to 300 nm to optimize electrode resistance, and the thickness may be increased further when lower resistance is required. The thickness of the second metal (12) can be adjusted to 1 nm to 200 nm, taking into account the thickness of the oxide film to be formed after thermal oxidation.

[0038] Subsequently, as illustrated in FIG. 2b, a gate electrode pattern for a gate electrode is formed using the first metal (11) and the second metal (12), and heat treatment is performed. Here, the pattern is formed by applying a photosensitive material onto a substrate using photolithography (spin coating), performing exposure to a specific pattern, and then removing the unnecessary photosensitive material through development. Alternatively, dry etching or wet etching may be used. When the patterned first metal (1) and the second metal (12) are thermally oxidized, the first metal (11) becomes the gate electrode, and the second metal (12) is converted into a gate insulating film. The heat treatment can be performed at a temperature of 300°C to 1000°C for 10 minutes to 2 hours in an atmosphere of oxygen, nitrogen, or a mixture of oxygen and nitrogen gas, and is carried out within a temperature range where the material of the substrate does not change.

[0039] The insulating film (13) of FIG. 2c can be formed by heat-treating the first metal (11) and the second metal (12) as in FIG. 2b to convert the second metal (12) into an oxide film, and then depositing an additional insulating layer if necessary. This is for enhancing insulating properties, and although the oxide film of the second metal (12) formed through heat treatment is thin and uniform, an additional insulating film layer may be required for certain applications. For example, if more electrical insulation is required or to prevent leakage current, an additional insulating film (SiO₂, SiNx, etc.) can be deposited on the oxide film to increase the insulating thickness. Also, in high-voltage devices, the thickness of the insulating film may need to be increased to improve voltage withstand characteristics. Furthermore, for certain applications to adjust dielectric properties, the dielectric constant (k) characteristics of the insulating film may need to be optimized. For example, depositing high-dielectric (hk) materials (e.g., HfO₂, Ta₂O₂) can improve the dielectric properties of the gate insulating film and enhance device performance (charge storage capacity). Additionally, depositing different dielectric materials over existing thermally oxidized secondary metals can simultaneously improve electrical characteristics and reliability. Furthermore, to complement surface quality, if the surface condition of the oxide film formed by thermal oxidation is imperfect, additional insulating film deposition can correct surface defects (microcracks, defect structures, etc.). Since surface defects can cause increased leakage current, the additional insulating film contributes to enhancing the electrical stability of the transistor. Moreover, to protect the upstream process, the additional insulating film can serve as a protective layer to prevent oxide film damage or contamination during subsequent processes. In particular, when semiconductor layers or source / drain electrodes are formed, it is necessary to deposit a protective insulating layer to prevent the oxide film from being damaged or contaminated. Additionally, structurally, some transistor designs require a composite insulating layer structure. For example, it can be designed to improve insulation performance through a multilayer insulating film structure, or to perform other functions (buffer layer, electron movement blocking, etc.) in specific layers.

[0040] FIGS. 3a to 3c are drawings sequentially illustrating a method for manufacturing a thin-film transistor using heat treatment according to a second embodiment of the present invention.

[0041] The substrate (10) illustrated in FIG. 3a is composed of an insulating material such as glass, a silicon wafer, or plastic. In the case of a plastic substrate, a buffer layer may be additionally formed before metal deposition to increase heat treatment stability. The buffer layer is composed of an insulating material such as SiNx or SiO₂ and is formed through a PECVD or sputtering process. The deposition of the first metal (11) involves depositing the first metal (11) to be used as a gate electrode on the substrate (10). The material of the first metal (11) is a metal that does not easily undergo thermal oxidation (e.g., Ti, Mo, Cu, etc.). The deposition process is performed evenly using a sputtering or evaporation process, and the deposition thickness is adjusted to 1 nm to 500 nm to optimize the electrode resistance.

[0042] Subsequently, as shown in FIG. 3b, the deposited first metal (11) is patterned to form a gate electrode. Then, as shown in FIG. 3c, a second metal (12) is deposited on top of the patterned first metal (11), and the second metal (12) is patterned. At this time, the pattern of the second metal is patterned to completely cover the first metal (11). Here, the second metal (12) is a metal that oxidizes easily (e.g., Ta, Hf, Al, etc.), and the first metal (11) and the second metal (12) are heat-treated. The heat treatment temperature is 300°C to 1000°C and is adjusted according to the oxide film thickness, for about 5 minutes to 2 hours in an atmosphere of oxygen, nitrogen, or a mixture of oxygen and nitrogen gas. As a result of the heat treatment, the first metal (11) is maintained as a gate electrode, and the second metal (12) is oxidized and converted into a gate insulating film. The oxidized gate insulating film is thin and uniform and has high dielectric constant characteristics.

[0043] FIGS. 4a to 4c are drawings sequentially illustrating a method for manufacturing a thin-film transistor using heat treatment according to a third embodiment of the present invention, which is similar to the second embodiment according to FIGS. 3a to 3c, but in FIG. 4c, the second metal (12) is not patterned as in FIG. 3c. An insulating film is formed by heat treatment in oxygen, nitrogen, or an oxygen-nitrogen mixed gas while the second metal is not patterned.

[0044] Figure 5 is a diagram showing the results of a top gate method of a thin-film transistor using heat treatment according to the fourth embodiment of the present invention.

[0045] In the fourth embodiment of FIG. 5, as a result of applying the present invention to a top-gate structure transistor, a semiconductor layer (14) is first patterned on a substrate (10), and if necessary, a buffer layer (not shown) may be formed to suppress contamination from the substrate (10) before the formation of the semiconductor active layer (13). After the semiconductor active layer (14) is formed, a gate insulating film is generally deposited. In the present invention, a second metal (12) that undergoes thermal oxidation is deposited, followed by the deposition of a conductive oxide electrode such as ITO using a first metal (11), and then a pattern is formed simultaneously. Then, when thermal oxidation is performed, the conductive oxide electrode acts as a gate electrode since it is originally an oxide, and the second metal (12) is oxidized to act as a gate insulating film.

[0046] Figure 6 is a diagram showing the heat treatment results in the method for manufacturing a thin-film transistor using the heat treatment of the present invention, and represents the heat treatment results of tantalum (Ta), which is used as the second metal material of the present invention. Tantalum (Ta) was heat-treated for 20 minutes in an oxygen atmosphere at atmospheric pressure, and the oxygen flow rate was 50 sccm. The heat treatment temperature was varied from 400 °C to 600 °C. It is clearly shown that the oxide thickness of Ta gradually increases as the heat treatment temperature increases. Since a nitride film is formed when heat treatment is performed in a nitrogen atmosphere, the composition of the insulating film formed may vary depending on the type of gas in the heat treatment atmosphere. When heat treatment is performed, gas elements and metals react; an oxide film is formed in an oxygen atmosphere, and a nitride film is formed in a nitrogen atmosphere. At this time, metals with a lower Gibbs free energy after the reaction react more readily.

[0047] As described above, although the present invention has been explained by limited embodiments and drawings, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical spirit of the present invention and the equivalent scope of the claims described below by those skilled in the art to which the present invention belongs.

Claims

1. (a) a step of depositing different first metals and second metals on a substrate; and, (b) a step of heat-treating the deposited first metal and second metal to convert the first metal into a gate electrode and the second metal into a gate insulating film. A method for manufacturing a thin-film transistor using a heat treatment including 2. In Claim 1, The above heat treatment is within a temperature range where the substrate material does not change. A method for manufacturing a thin-film transistor using heat treatment characterized by 3. In Claim 1, The above heat treatment is a temperature range in which the second metal is thermally oxidized. A method for manufacturing a thin-film transistor using heat treatment characterized by 4. In Claim 1, The above heat treatment is carried out in an atmosphere of any one of oxygen, nitrogen, or a mixture of oxygen and nitrogen gas. A method for manufacturing a thin-film transistor using heat treatment characterized by 5. In Claim 1, The first metal is any one selected from the group consisting of titanium (Ti), molybdenum (Mo), or copper (Cu). A method for manufacturing a thin-film transistor using heat treatment characterized by 6. In Claim 1, The second metal is any one selected from the group consisting of tantalum (Ta), hafnium (Hf), or aluminum (Al). A method for manufacturing a thin-film transistor using heat treatment characterized by 7. In Claim 1, The above step (a) is, (a1) A step of sequentially stacking the first metal and the second metal on the substrate; (a2) a step of forming a pattern for a gate electrode for the stacked first metal and the second metal; and, (a3) A step of heat-treating the patterned first metal and second metal. A method for manufacturing a thin-film transistor using heat treatment, characterized by including 8. In Claim 1, The above step (a) is, (a1) A step of depositing the first metal on the substrate; (a2) A step of forming a pattern for a gate electrode on the deposited first metal; (a3) A step of depositing a second metal on the patterned first metal; and, (a4) A step of heat-treating the first metal and the second metal. A method for manufacturing a thin-film transistor using heat treatment characterized by including 9. In Claim 8, Between the above steps (a3) ​​and (a4), The step of patterning the deposited second metal to cover the first metal. A method for manufacturing a thin-film transistor using heat treatment characterized by further including 10. In Claim 1, The above step (a) is, (a1) A step of forming a semiconductor layer pattern on the substrate; (a2) A step of sequentially stacking a second metal and a conductive oxide electrode on the semiconductor layer; (a3) a step of patterning the stacked second metal and conductive oxide electrodes; and, (a4) A step of heat-treating the patterned second metal and conductive oxide electrodes. A method for manufacturing a thin-film transistor using heat treatment characterized by including 11. Substrate; A gate electrode formed on the lower or upper part of the substrate; and, A gate insulating film formed to be electrically insulated from the gate electrode. Includes, The above gate insulating film is formed after depositing a second metal that is heat-treatable on the gate electrode formed of a first metal that is heat-treatable. Thin film transistor structure using heat treatment.

12. In Claim 11, The first metal is any one selected from the group consisting of titanium (Ti), molybdenum (Mo), or copper (Cu). Thin film transistor structure using heat treatment characterized by 13. In Claim 11, The second metal is any one selected from the group consisting of tantalum (Ta), hafnium (Hf), or aluminum (Al). Thin film transistor structure using heat treatment characterized by

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