Method for manufacturing an oxide TFT and a protective layer thereof

Abstract

A method for manufacturing an oxide TFT and its protective layer, comprising the steps of: (1) disposing an oxide TFT on a substrate; (2) coating a positive transparent first photosensitive resin layer on the TFT and pre-curing; (3) coating a negative black second photosensitive resin layer on the first photosensitive resin layer and pre-curing; (4) exposing the second photosensitive resin layer to form a light-shielding surface layer in a part of the first region; (5) developing the second photosensitive resin layer to dissolve a part of it in the second region and expose the first photosensitive resin layer at its bottom; (6) exposing the first photosensitive resin layer so that a part of it in the second region is irradiated with ultraviolet light; (7) developing the first photosensitive resin layer to dissolve a part of it in the second region and leaving a laminate in the first region; (8) post-curing the laminate to form a protective layer. The present invention can reduce the adverse effects of ultraviolet light on the active layer during the process of manufacturing the TFT and its protective layer.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor devices, and particularly to a manufacturing method of an oxide TFT and its protective layer. Background Art

[0002] A TFT (abbreviation for thin film transistor) is a driving part of an active matrix display screen (such as active LCD, OLED, mini-LED), and generally includes a gate, a gate insulating layer, a source electrode, a drain electrode, and an active layer. Conventional TFTs generally use amorphous silicon as the active layer, which faces problems such as low electron mobility and insufficient driving ability. Oxide TFTs (thin film transistors) with an oxide semiconductor film (such as an IGZO film) as the active layer have the advantages of high electron mobility, good driving performance, and suitability for large-area production, and are increasingly favored by display manufacturers.

[0003] However, when the oxide semiconductor film is irradiated with short-wavelength light, it is easy to excite defect states such as oxygen vacancies, causing a negative shift in the threshold voltage of the TFT, and it is difficult to recover after the light irradiation stops; especially when the oxide semiconductor film is irradiated with ultraviolet light with a shorter wavelength, it can form a larger density of internal defect states, resulting in irreversible permanent defects. Oxide TFTs generally need to be covered with a protective layer, and the protective layer needs to be patterned through photolithography processes such as exposure and development. During the exposure process, a large amount of ultraviolet light will irradiate into the TFT, resulting in the above-mentioned defects in its active layer.

[0004] Therefore, someone has proposed a manufacturing method of an oxide TFT and its protective layer using a positive photosensitive resin. During its patterning process, when the positive photosensitive resin forms a pattern, the mask plate needs to block its remaining part and make the ultraviolet light irradiate its removed part. The protective layer is the remaining part of the photosensitive resin, which covers the TFT. Therefore, the ultraviolet light does not need to irradiate the TFT, and the above-mentioned defects in the active layer can be reduced. However, due to generally using non-contact exposure, there is still a large gap between the mask plate and the TFT, and part of the ultraviolet light can still irradiate the active layer of the TFT through reflection, diffraction and other ways, making the TFT still at risk of the above-mentioned defects in the active layer. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a manufacturing method of an oxide TFT and its protective layer, which can reduce the adverse effects of ultraviolet light on the active layer during the manufacturing process of the oxide TFT and its protective layer. The technical solution adopted is as follows:

[0006] A manufacturing method of an oxide TFT and its protective layer includes the following steps:

[0007] (1)Provide a substrate, and an oxide TFT is disposed on the surface of the substrate. The oxide TFT includes a gate, a gate insulating layer, a source, a drain, and an active layer, and the active layer is formed of an oxide semiconductor film;

[0008] It is characterized in that the following steps are further included:

[0009] (2)Coat a positive transparent first photosensitive resin coating on the surface of the oxide TFT and pre-cure it;

[0010] (3)Coat a negative black second photosensitive resin coating on the surface of the pre-cured first photosensitive resin coating and pre-cure it;

[0011] (4)Perform a first exposure on the second photosensitive resin coating, and irradiate the second photosensitive resin coating in the first region where the active layer is located through ultraviolet light in cooperation with a mask plate, so as to form a cured light-shielding surface layer at least in the part of the second photosensitive resin coating in the first region;

[0012] (5)Perform a first development on the second photosensitive resin coating, and use a developer to dissolve the part of the second photosensitive resin coating in the second region outside the active layer to expose the first photosensitive resin coating at its bottom;

[0013] (6)Perform a second exposure on the first photosensitive resin coating. The part of the first photosensitive resin coating in the first region is blocked by the light-shielding surface layer and is not irradiated by ultraviolet light, while the part of the first photosensitive resin coating in the second region is irradiated by ultraviolet light;

[0014] (7)Perform a second development on the first photosensitive resin coating, and use a developer to dissolve the part of the first photosensitive resin coating in the second region, and leave a laminate composed of the first photosensitive resin coating and the second photosensitive resin coating in the first region;

[0015] (8)Perform post-curing on the laminate, so that the laminate is completely cured under the action of heat to form a protective layer covering the oxide TFT.

[0016] Generally speaking, exposure is a process of irradiating a photosensitive resin coating with ultraviolet light, and development is a process of immersing the photosensitive resin coating in a developer after exposure. Irradiating ultraviolet light can cause a chemical reaction inside the photosensitive resin and change its solubility with respect to the developer. In order to form a desired pattern, a mask plate is generally used for exposure, so that some regions (exposed parts) of the photosensitive resin are irradiated by ultraviolet light, while some other regions (unexposed parts) are not irradiated by ultraviolet light, and thus a pattern of the photosensitive resin coating can be developed.

[0017] Generally speaking, the photosensitive resin presents a transparent state, while incorporating carbon particles (especially nano-carbon particles) into the photosensitive resin can make the photosensitive resin appear black. During exposure, the carbon particles can absorb ultraviolet light. Therefore, when the black photosensitive resin is exposed, a cured layer (i.e., a light-shielding surface layer) is more likely to form on its surface layer, while the inside of the second photosensitive resin coating remains uncured or semi-cured.

[0018] In the manufacturing method of the present invention, in the step (1), the substrate can be a glass substrate, a quartz substrate, a silicon oxide substrate, or a plastic film such as PI (polyimide) or CPI (colorless polyimide); the oxide semiconductor film can be an amorphous IGZO thin film (indium gallium zinc oxide thin film); in the steps (2) and (3), the first photosensitive resin coating and the second photosensitive resin coating can be coated by methods such as slit-coating. Pre-curing is to bake at a lower temperature (≤100 °C) after coating the photosensitive resin to remove the solvent in the photosensitive resin, which can make the photosensitive resin coating present a solid state, so as to facilitate the processing of more coatings; in the steps (4) and (5), the second photosensitive resin coating is composed of a negative black photosensitive resin. During mask exposure, the carbon particles inside the second photosensitive resin coating can absorb ultraviolet light. Therefore, when the black second photosensitive resin coating is exposed, a cured light-shielding surface layer is more likely to form on its surface layer, while the inside of the second photosensitive resin coating remains uncured or semi-cured; the exposed part of the second photosensitive resin coating is cured (generally a cross-linking reaction occurs), and its solubility in the developer is reduced compared to the unexposed part, so that after development, a pattern is formed in which the exposed part is retained and the unexposed part is selectively removed; in the steps (6) and (7), the first photosensitive resin coating is composed of a transparent positive photosensitive resin. After exposure, the solubility of the exposed part of the first photosensitive resin coating in the developer is higher than that of the unexposed part, so that after development, a pattern is formed in which the exposed part is selectively removed and the unexposed part is retained; in the step (8), post-curing is to bake the photosensitive resin at a higher temperature, which can cause cross-linking curing of the photosensitive resin (whether exposed or not), thereby obtaining a stronger film layer.

[0019] As a preferred embodiment of the present invention, the oxide TFT has a coplanar structure. Its manufacturing process is generally as follows: (1) Deposit a metal film (such as a molybdenum-aluminum-molybdenum thin film, a chromium thin film) on the surface of the substrate and pattern it to form a gate (and its external circuit); (2) Deposit a layer of silicon oxide or silicon nitride as a gate insulating layer at the position where the oxide TFT is located by processes such as magnetron sputtering; (3) Deposit a metal film (such as a molybdenum-aluminum-molybdenum thin film) on the gate insulating layer and pattern it to form a source electrode and a drain electrode arranged oppositely, with a channel gap between the source electrode and the drain electrode; (4) Deposit an oxide semiconductor film (such as an IGZO thin film) and pattern it to form an active layer, and the active layer straddles the channel gap between the source electrode and the drain electrode and is respectively lapped with the source electrode and the drain electrode. Since the last process of forming the oxide TFT is the fabrication of its active layer, and then the fabrication of the protective layer is carried out, it can avoid the active layer being irradiated by ultraviolet light during other processes (if the oxide TFT is a staggered structure, after the active layer is fabricated, the source and drain electrodes still need to be fabricated, and the active layer may also be affected during this process).

[0020] As a preferred embodiment of the present invention, the thickness of the first photosensitive resin coating is 1-2 μm. With the first photosensitive resin coating of this thickness, it can more effectively prevent part of the ultraviolet light from still irradiating the active layer through reflection, diffraction and other ways of the first photosensitive resin coating, and at the same time, it can also reduce the influence of the first photosensitive resin coating on the stack thickness.

[0021] As a preferred embodiment of the present invention, the optical density of the second photosensitive resin coating with respect to ultraviolet light is not less than 3. The optical density (OD value) is the logarithm of the ratio of the incident light to the transmitted light or the logarithm of the reciprocal of the light transmittance, and can be used to represent the light-shielding performance of the film layer. Its calculation formula is OD = log 10 (incident light / transmitted light). By setting the optical density of the second photosensitive resin coating to be not less than 3, the transmission of ultraviolet light can be effectively reduced.

[0022] As a preferred embodiment of the present invention, the thickness of the second photosensitive resin coating is 4-8 μm. With the second photosensitive resin coating of this thickness, it can more effectively block ultraviolet light and at the same time avoid the stack being too thick.

[0023] As a preferred embodiment of the present invention, the second photosensitive resin coating is a photosensitive resin coating doped with nano-carbon particles. Thus, the carbon particles can more effectively absorb ultraviolet light.

[0024] As a further preferred embodiment of the present invention, the diameter of the carbon particles is 50-500 nm.

[0025] As a further preferred embodiment of the present invention, the volume ratio of the carbon particles to the second photosensitive resin coating is 10%-40%. Thus, the carbon particles can more effectively absorb ultraviolet light.

[0026] The manufacturing method of the present invention has the following advantages in the process of fabricating the oxide TFT and its protective layer:

[0027] (1) The second photosensitive resin coating and the first photosensitive resin coating closely and completely cover the active layer of the oxide TFT. When ultraviolet light irradiates the second photosensitive resin coating in the first region, due to the absorption of ultraviolet light by the second photosensitive resin coating, it has good light-shielding properties. Moreover, the second photosensitive resin coating and the first photosensitive resin coating are closely attached to the active layer, and there is no gap between the second photosensitive resin coating and the active layer. Therefore, it can effectively prevent ultraviolet light from irradiating into the active layer, avoid ultraviolet light from irradiating the active layer of the TFT, and prevent internal defect states from occurring in its active layer;

[0028] (2) The first photosensitive resin coating can avoid the influence of carbon particles inside the second photosensitive resin coating on the conductivity of the active layer;

[0029] (3) By selecting the first photosensitive resin coating as positive and the second photosensitive resin coating as negative, when the first photosensitive resin coating is patterned, the second photosensitive resin coating is irradiated by secondary ultraviolet light and is further cured (generally increasing its curing depth). The first photosensitive resin coating uses the second photosensitive resin coating as a mask, and it can form an accurate laminate with consistent patterns without the need to add an additional mask exposure process, and will not significantly increase the manufacturing cost;

[0030] (4) The second photosensitive resin coating can also serve as a shielding layer for the active layer to avoid interference from external light during the subsequent operation of the oxide TFT. Description of the Drawings

[0031] Figure 1 is a schematic flow chart of the manufacturing method of the preferred embodiment of the present invention.

[0032] Figure 2 is a schematic structural diagram of the oxide TFT and its protective layer fabricated according to the preferred embodiment of the present invention. Embodiment

[0033] As Figure 1 、 Figure 2 shown, this manufacturing method of the oxide TFT and its protective layer includes the following steps:

[0034] (1) Provide a substrate 1, and dispose an oxide TFT 2 on the surface of the substrate 1. The oxide TFT 2 includes a gate 21, a gate insulating layer 22, a source 23, a drain 24, and an active layer 25, and the active layer 25 is composed of an oxide semiconductor film;

[0035] (2) A positive transparent first photosensitive resin coating 3 is coated on the surface of the oxide TFT2 and pre-cured (pre-curing is to bake at a lower temperature (≤100 °C) to remove the solvent in the photosensitive resin).

[0036] (3) A negative black second photosensitive resin coating 4 is coated on the surface of the pre-cured first photosensitive resin coating 3 and pre-cured.

[0037] (4) The second photosensitive resin coating 4 is subjected to a first exposure, and the second photosensitive resin coating 4 in the first region 100 where the active layer 25 is located is irradiated with ultraviolet light in cooperation with a mask plate 5, so that at least a cured light-shielding surface layer 41 is formed in the part of the second photosensitive resin coating 4 in the first region 100.

[0038] (5) The second photosensitive resin coating 4 is subjected to a first development, and the part of the second photosensitive resin coating 4 in the second region 200 outside the active layer 25 is dissolved by the developer to expose the first photosensitive resin coating 3 at its bottom.

[0039] (6) The first photosensitive resin coating 3 is subjected to a second exposure. The part of the first photosensitive resin coating 3 in the first region 100 is blocked by the light-shielding surface layer and is not irradiated with ultraviolet light, while the part of the first photosensitive resin coating 3 in the second region 200 is irradiated with ultraviolet light.

[0040] (7) The first photosensitive resin coating 3 is subjected to a second development, and the part of the first photosensitive resin coating 3 in the second region 200 is dissolved by the developer, and a laminate 6 composed of the first photosensitive resin coating 3 and the second photosensitive resin coating 4 is left in the first region 100.

[0041] (8) The laminate 6 is post-cured (post-curing is to bake the photosensitive resin at a higher temperature, which can cause the photosensitive resin (whether exposed or not) to crosslink and cure, thereby obtaining a stronger film layer), so that the laminate 6 is completely cured under the action of heat to form a protective layer covering the oxide TFT2.

[0042] In this embodiment, the substrate 1 can be a glass substrate, a quartz substrate, a silicon oxide substrate, or a plastic film such as PI (polyimide) or CPI (colorless polyimide); the oxide semiconductor film can be an amorphous IGZO thin film (indium gallium zinc oxide thin film).

[0043] In this embodiment, the first photosensitive resin coating 3 is composed of a transparent positive photosensitive resin, and the second photosensitive resin coating 4 is composed of a negative black photosensitive resin. The first photosensitive resin coating 3 and the second photosensitive resin coating 4 are coated by methods such as slit-coating. Generally, the photosensitive resin is in a transparent state, and adding carbon particles to the photosensitive resin can make the photosensitive resin appear black. During exposure, the carbon particles can absorb ultraviolet light. Therefore, when the black photosensitive resin is exposed, a light-shielding surface layer is more easily formed on its surface layer, while the inside of the second photosensitive resin coating 4 remains uncured or semi-cured. The exposed part of the second photosensitive resin coating 4 is cured (generally a cross-linking reaction occurs), and its solubility in the developer is reduced relative to the unexposed part, so that after development, a pattern is formed in which the exposed part is retained and the unexposed part is selectively removed.

[0044] In this embodiment, the oxide TFT 2 has a coplanar structure, and its manufacturing process is as follows: (1-1) Deposit a metal film (such as a molybdenum-aluminum-molybdenum thin film) on the surface of the substrate 1 and pattern it to form the gate 21 and its external circuit; (1-2) Deposit a layer of silicon oxide or silicon nitride as the gate insulating layer 22 at the position where the oxide TFT 2 is located by processes such as magnetron sputtering; (1-3) Deposit a metal film (such as a molybdenum-aluminum-molybdenum thin film) on the gate insulating layer 22 and pattern it to form the relatively arranged source electrode 23 and drain electrode 24, and there is a channel gap between the source electrode 23 and the drain electrode 24; 1- (4) Deposit an oxide semiconductor film (such as an IGZO thin film) and pattern it to form the active layer 25, and the active layer 25 straddles the channel gap between the source electrode 23 and the drain electrode 24 and is respectively lapped with the source electrode 23 and the drain electrode 24. Since the last process of forming the oxide TFT 2 is the production of its active layer 25, and then the production of the protective layer is carried out, the active layer 25 can be prevented from being irradiated by ultraviolet light during other processes (if the oxide TFT 2 is a staggered structure, after the production of the active layer 25, the production of the source and drain electrodes 24 is also required, and the active layer 25 may also be affected during this process).

[0045] In this embodiment, the thickness of the first photosensitive resin coating 3 is 1 to 2 μm. Using the first photosensitive resin coating 3 with this thickness can more effectively prevent part of the ultraviolet light from irradiating the active layer 25 through reflection, diffraction, etc. of the first photosensitive resin coating 3, and at the same time, it can also reduce the influence of the first photosensitive resin coating 3 on the thickness of the stack 6.

[0046] In this embodiment, the optical density of the second photosensitive resin coating 4 with respect to ultraviolet light is not less than 3. The optical density (OD value) is the logarithm of the ratio of the incident light to the transmitted light or the logarithm of the reciprocal of the light transmittance, and can be used to represent the light-shielding performance of the film layer. Its calculation formula is OD = log 10(Incident light / Transmitted light), by setting the optical density of the second photosensitive resin coating 4 to be not less than 3, the transmission of ultraviolet light can be effectively reduced.

[0047] In this embodiment, the thickness of the second photosensitive resin coating 4 is 4-8 μm. With the second photosensitive resin coating 4 having this thickness, ultraviolet light can be blocked more effectively while avoiding the laminate 6 from being too thick.

[0048] In this embodiment, the second photosensitive resin coating 4 is a photosensitive resin coating doped with nano-carbon particles, the diameter of the carbon particles is 50-500 nm, and the volume ratio of the carbon particles to the second photosensitive resin coating 4 is 10%-40%. Thus, the carbon particles can absorb ultraviolet light more effectively.

[0049] In addition, it should be noted that for the specific embodiments described in this specification, the names of their respective parts and the like can be different. Any equivalent or simple changes made according to the structure, features, and principles described in the inventive concept of this invention patent are included within the protection scope of this invention patent. Those skilled in the technical field to which this invention pertains can make various modifications or supplements to the described specific embodiments or use similar methods for substitution, as long as they do not deviate from the structure of this invention or exceed the scope defined by this claim book, they should all fall within the protection scope of this invention.

Claims

1. A method for manufacturing an oxide TFT and its protective layer, comprising the following steps: (1) providing a substrate, and disposing an oxide TFT on the surface of the substrate, the oxide TFT including a gate, a gate insulating layer, a source electrode, a drain electrode, and an active layer, the active layer being composed of an oxide semiconductor film; characterized in that: The oxide TFT has a coplanar structure; the following steps are further included: (2) Coating a positive transparent first photosensitive resin coating on the surface of the oxide TFT and pre-curing; (3) Coating a negative black second photosensitive resin coating on the surface of the pre-cured first photosensitive resin coating and pre-curing; (4) Conducting a first exposure on the second photosensitive resin coating, irradiating the second photosensitive resin coating in the first region where the active layer is located through ultraviolet light in cooperation with a mask plate, so as to form a cured light-shielding surface layer at least in the part of the second photosensitive resin coating in the first region; (5) Conducting a first development on the second photosensitive resin coating, using a developer to dissolve the part of the second photosensitive resin coating in the second region outside the active layer, exposing the first photosensitive resin coating at its bottom; (6) Conducting a second exposure on the first photosensitive resin coating, the part of the first photosensitive resin coating in the first region is blocked by the light-shielding surface layer and not irradiated by ultraviolet light, and the part of the first photosensitive resin coating in the second region is irradiated by ultraviolet light; (7) Conducting a second development on the first photosensitive resin coating, using a developer to dissolve the part of the first photosensitive resin coating in the second region, and leaving a laminate composed of the first photosensitive resin coating and the second photosensitive resin coating in the first region; (8) Conducting post-curing on the laminate, so that the laminate is completely cured under the action of heat to form a protective layer covering the oxide TFT.

2. The manufacturing method of an oxide TFT and its protective layer according to claim 1, characterized in that: The thickness of the first photosensitive resin coating is 1 to 2 μm.

3. A method for manufacturing an oxide TFT and its protective layer according to claim 1, characterized in that: The optical density of the second photosensitive resin coating to ultraviolet light is not less than 3.

4. A method for manufacturing an oxide TFT and a protective layer thereof according to claim 1, characterized in that: The thickness of the second photosensitive resin coating is 4 to 8 μm.

5. A method for manufacturing an oxide TFT and its protective layer according to any one of claims 1-4, characterized in that: The second photosensitive resin coating is a photosensitive resin coating doped with nano-carbon particles.

6. The manufacturing method of an oxide TFT and its protective layer according to claim 5, characterized in that: The diameter of the carbon particles is 50 to 500 nm.

7. A method for manufacturing an oxide TFT and its protective layer according to claim 5, characterized in that: The volume ratio of the carbon particles to the second photosensitive resin coating is 10% to 40%.

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