Photolithography method for source-drain electrode and method for preparing thin film transistor

Abstract

The present invention belongs to the field of semiconductor technology, and particularly relates to a photolithography method for source-drain electrodes and a method for preparing a thin film transistor. The photolithography method for source-drain electrodes provided by the present invention comprises the following steps: partially coating the surface of a patterned active layer, drying it, and obtaining a patterned active layer partially covered with photoresist; using the uncoated portion of the patterned active layer partially covered with photoresist, focusing the patterned active layer partially covered with photoresist on a photolithography mask for preparing source-drain electrodes, performing ultraviolet light exposure and growth, and forming source-drain electrodes on the surface of the patterned active layer. The present invention partially coats the patterned active layer with photoresist, and the portion not spin-coated with photoresist can be used as an alignment reference, so that the patterned active layer covered with photoresist is accurately focused on the channel position of the photolithography mask for preparing source-drain electrodes.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor technology, and particularly relates to a photolithography method for source-drain electrodes and a method for preparing a thin film transistor. Background Art

[0002] The preparation methods of metal oxide thin film transistors include magnetron sputtering, atomic layer deposition, thermal evaporation and sol-gel methods, which have the advantages of high film quality and mature process. These methods need to rely on photolithography to prepare patterned thin film transistors. As people's requirements for the display field become higher and higher, the application of high light transmittance materials such as fully transparent displays is becoming more and more widespread.

[0003] The existing photolithography method is to first evenly cover the substrate to be etched with photoresist, and then etch or continue to grow materials after ultraviolet exposure and development. The photolithography process can form a patterned active layer and source and drain electrodes. In order for the source and drain electrodes to be accurately covered on the patterned active layer, the photolithography needs to be precisely aligned. However, during the repeated photolithography process, when a high light-transmitting material is used as the material to be photolithography, due to the high transparency of the material to be photolithography itself, under the photolithography microscope, the patterned active layer covered with photoresist is difficult to accurately focus on the photolithography mask for preparing the source and drain electrodes, resulting in deviations in the coverage of the source and drain electrodes, affecting carrier injection and reducing the photoelectric performance of the thin film transistor device. Summary of the invention

[0004] In view of this, an object of the present invention is to provide a photolithography method for source and drain electrodes. The photolithography method provided by the present invention can enable a patterned active layer covered with photoresist to be precisely focused on a photolithography mask for preparing source and drain electrodes.

[0005] In order to achieve the purpose of the above invention, the present invention provides the following technical solutions:

[0006] The present invention provides a source-drain electrode photolithography method, comprising the following steps:

[0007] Partially coating the surface of the patterned active layer, and drying the layer to obtain a patterned active layer partially covered with photoresist;

[0008] By utilizing the uncoated portion of the patterned active layer partially covered with photoresist, the patterned active layer partially covered with photoresist is focused on a photolithography mask for preparing source and drain electrodes, and ultraviolet light exposure and growth are performed to form source and drain electrodes on the surface of the patterned active layer.

[0009] Preferably, the partial coating is: deviating from the center of the surface of the patterned active layer, and coating the photoresist on the surface of the patterned active layer.

[0010] Preferably, the light transmittance of the active layer at 550 nm visible light is 80-85%.

[0011] Preferably, the chemical composition of the active layer is one or more of zinc oxide, indium zinc oxide and indium gallium zinc oxide.

[0012] Preferably, the drying temperature is 85-95° C. and the drying time is 4-6 minutes.

[0013] Preferably, the radiation intensity of the ultraviolet light in the ultraviolet light exposure is 400-450 mW / cm 2 , the exposure time is 3 to 6 seconds.

[0014] The present invention provides a method for preparing a thin film transistor, comprising the following steps:

[0015] Growing a gate dielectric layer on a substrate; and preparing a patterned active layer on the surface of the obtained gate dielectric layer;

[0016] Photolithographically preparing source and drain electrodes on the surface of the patterned active layer to obtain a primary thin film transistor;

[0017] Annealing the primary thin film transistor to obtain the thin film transistor;

[0018] The photolithography method for preparing the source and drain electrodes adopts the photolithography method described in the above technical solution.

[0019] Preferably, the substrate is conductive glass;

[0020] The chemical composition of the gate dielectric layer is hafnium dioxide;

[0021] The chemical composition of the source-drain electrode is aluminum.

[0022] Preferably, the annealing temperature is 250-350° C., the time is 10-20 min, and the annealing atmosphere is air.

[0023] The present invention provides a photolithography method for source-drain electrodes, comprising the following steps: partially coating the surface of a patterned active layer, drying, and obtaining a patterned active layer partially covered with photoresist; utilizing the uncoated portion of the patterned active layer partially covered with photoresist, focusing the patterned active layer partially covered with photoresist on a photolithography mask for preparing source-drain electrodes, performing ultraviolet light exposure and growth, and forming source-drain electrodes on the surface of the patterned active layer. The present invention partially coats the patterned active layer with photoresist, and in the photolithography mask for focusing the patterned active layer covered with photoresist to prepare source-drain electrodes, the uncoated portion of the photoresist can be used as a focus alignment reference, so that the portion of the patterned active layer covered with photoresist is precisely focused on the channel position of the photolithography mask for preparing source-drain electrodes.

[0024] The thin film transistor prepared by the photolithography method provided by the present invention has stable electrical properties; compared with devices with alignment errors and source and drain electrodes that fail to accurately cover the active layer, the thin film transistor provided by the present invention has high mobility, switching ratio and positive and negative bias stability.

[0025] The test results of the embodiment show that the photolithography method provided by the present invention can enable the patterned active layer covered with photoresist to accurately focus on the photolithography mask for preparing the source and drain electrodes; the current switching ratio of the thin film transistor provided by the present invention is 1.4×10 2 ~3.1×10 3 . . BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A picture of gate dielectric hafnium dioxide grown on a conductive glass substrate;

[0027] Figure 2 This is a picture of the active layer zinc oxide grown on the gate dielectric;

[0028] Figure 3 Picture of patterning of active layer;

[0029] Figure 4 This is a picture of some photolithography methods before photolithography.

[0030] Figure 5 This is a picture of partial coating after partial coating by partial coating lithography method;

[0031] Figure 6 This is a picture of the alignment of the photolithography machine microscope after partial coating;

[0032] Figure 7 This is a picture of the source and drain electrodes grown after precise alignment using the partial coating method;

[0033] Figure 8 This is the picture before normal photolithography and coating;

[0034] Fig. 9 This is a picture of the photoresist evenly covering the surface after spin coating. DETAILED DESCRIPTION

[0035] The present invention provides a source-drain electrode photolithography method, characterized in that it comprises the following steps:

[0036] Partially coating the surface of the patterned active layer, and drying the layer to obtain a patterned active layer partially covered with photoresist;

[0037] By utilizing the uncoated portion of the patterned active layer partially covered with photoresist, the patterned active layer partially covered with photoresist is focused on a photolithography mask for preparing source and drain electrodes, and ultraviolet light exposure and growth are performed to form source and drain electrodes on the surface of the patterned active layer.

[0038] In the present invention, unless otherwise specified, all substances in the technical solutions are commercially available products well known to those skilled in the art.

[0039] The present invention performs partial photoresist coating on the surface of the patterned active layer and drying to obtain the patterned active layer partially covered with photoresist.

[0040] The present invention has no special limitation on the patterned active layer, and any patterned active layer well known to those skilled in the art may be used.

[0041] In the present invention, the coating is preferably a photoresist. The present invention has no special limitation on the photoresist used in the coating, and any photoresist known to those skilled in the art can be used. In the present invention, the coating amount of the coating is preferably 20 to 27 μL / cm 2 , more preferably 21 to 26 μL / cm 2 , and preferably 22 to 25 μL / cm 2 .

[0042] In the present invention, the device for glue homogenization is preferably a glue homogenizer. In the present invention, the speed of the glue homogenizer is preferably 2500-3500rpm, more preferably 2600-3400rpm, and more preferably 2800-3200rpm; the time is preferably 25-35s, more preferably 26-34s, and more preferably 28-32s.

[0043] In the present invention, the partial coating is preferably: deviating from the surface center of the patterned active layer, and applying photoresist on the surface of the patterned active layer. In the present invention, the coating is partial coating, that is, the coating area does not completely cover the surface of the patterned active layer. In the present invention, the coating area in the partial coating preferably accounts for 50-70% of the surface area of ​​the patterned active layer, and more preferably 55-67%.

[0044] In the present invention, the light transmittance of the active layer at 550nm visible light is preferably 80-85%, more preferably 81-84%. In the present invention, the chemical composition of the active layer is preferably one or more of zinc oxide, indium zinc oxide and indium gallium zinc oxide.

[0045] After partial coating, the present invention dries the partially coated active layer to obtain a patterned active layer partially covered with photoresist.

[0046] In the present invention, the drying temperature is preferably 85 to 95° C., more preferably 87 to 93° C.; the drying time is preferably 4 to 6 min, more preferably 4.5 to 5.5 min.

[0047] After obtaining a patterned active layer partially covered with photoresist, the present invention uses the uncoated portion of the patterned active layer partially covered with photoresist to focus the patterned active layer partially covered with photoresist on a photolithography mask for preparing source and drain electrodes, performs ultraviolet light exposure and growth, and forms source and drain electrodes on the surface of the patterned active layer.

[0048] After obtaining the patterned active layer partially covered with photoresist, the present invention uses the uncoated portion of the patterned active layer partially covered with photoresist to focus the patterned active layer partially covered with photoresist to prepare a photolithography mask for source and drain electrodes.

[0049] In the present invention, the device for focusing the patterned active layer partially covered with photoresist on the photolithography mask for preparing source and drain electrodes is preferably a photolithography microscope.

[0050] After focusing the patterned active layer partially covered with photoresist on a photolithography mask for preparing source and drain electrodes, the present invention performs ultraviolet light exposure and growth on the obtained system to form source and drain electrodes on the surface of the patterned active layer.

[0051] In the present invention, the radiation intensity of the ultraviolet light in the ultraviolet light exposure is preferably 400-450 mW / cm 2 , more preferably 410 to 440 mW / cm 2 ; The exposure time is preferably 3 to 6 seconds, more preferably 4 to 5 seconds.

[0052] In the present invention, the chemical composition of the source-drain electrode is preferably aluminum.

[0053] The present invention has no special limitation on the growth, and the source and drain electrodes may be grown on the surface of the active layer in a manner well known to those skilled in the art.

[0054] For the surface of the patterned active layer not coated with photoresist, the present invention preferably repeats the photolithography method of the source-drain electrode described in the above technical solution to achieve precise focus photolithography preparation of the source-drain electrode on the entire patterned active layer.

[0055] The present invention also provides a method for preparing a thin film transistor, comprising the following steps:

[0056] Growing a gate dielectric layer on a substrate; and preparing a patterned active layer on the surface of the obtained gate dielectric layer;

[0057] Photolithographically preparing source and drain electrodes on the surface of the patterned active layer to obtain a primary thin film transistor;

[0058] Annealing the primary thin film transistor to obtain the thin film transistor;

[0059] The photolithography method for preparing the source and drain electrodes adopts the photolithography method described in the above technical solution.

[0060] The present invention grows a gate dielectric layer on a substrate.

[0061] In the present invention, the substrate is preferably conductive glass, specifically, ITO conductive glass.

[0062] Before growing the gate dielectric layer, the present invention preferably further comprises pre-treating the substrate; the pre-treating preferably comprises sequentially washing with acetone, washing with alcohol and washing with deionized water. In the present invention, the pre-treating is preferably carried out under ultrasonic conditions. In the present invention, the time for washing with acetone, washing with alcohol and washing with deionized water is preferably 5 to 15 minutes independently.

[0063] In the present invention, the chemical composition of the gate dielectric layer is preferably hafnium dioxide. In the present invention, the thickness of the gate dielectric layer is preferably 90 to 110 nm, more preferably 95 to 105 nm.

[0064] In the present invention, the gate dielectric layer is preferably grown by magnetron sputtering.

[0065] In an embodiment of the present invention, the conditions for growing the gate dielectric layer by magnetron sputtering include: the power is preferably 100-200 W, more preferably 120-180 W; the growth pressure is preferably 6-10 mTorr, more preferably 7-9 mTorr; and the atmosphere gas is preferably argon.

[0066] After the gate dielectric layer is obtained, the present invention prepares a patterned active layer on the surface of the obtained gate dielectric layer.

[0067] In the present invention, the light transmittance of the active layer at 550nm visible light is preferably 80-85%, more preferably 81-84%. The chemical composition of the active layer is preferably a metal oxide, more preferably one or more of zinc oxide, indium zinc oxide and indium gallium zinc oxide. In the present invention, the thickness of the active layer is preferably 30-50nm, more preferably 35-45nm. The present invention has no special limitation on the pattern of the active layer, and a pattern well known to those skilled in the art can be used.

[0068] In the present invention, the active layer is preferably prepared by a magnetron sputtering method or a sol-gel method.

[0069] In an embodiment of the present invention, the conditions for preparing the active layer by magnetron sputtering include: the power is preferably 50-150W, more preferably 70-130W; the growth pressure is preferably 6-10mTorr, more preferably 7-9mTorr; the atmosphere gas is preferably argon and / or oxygen. In the present invention, when the atmosphere includes argon and oxygen, the volume ratio of argon and oxygen is preferably (90-100): (0-10), and oxygen is not 0.

[0070] After obtaining the active layer, the present invention performs patterning on the active layer to obtain a patterned active layer.

[0071] In the present invention, the patterning treatment preferably includes: coating the surface of the active layer with a resin and drying it, then fixing it on a mask with a pattern for ultraviolet light exposure, developing it and then acid etching it to obtain the patterned active layer.

[0072] In the present invention, the coating is preferably a photoresist coating. In the present invention, the coating amount of the coating is preferably 20 to 27 μL / cm 2 , more preferably 21 to 26 μL / cm 2 , and preferably 22 to 25 μL / cm 2 The present invention has no special limitation on the photoresist used for coating the surface of the active layer, and any photoresist well known to those skilled in the art can be used.

[0073] In the present invention, the device for glue homogenization is preferably a glue homogenizer. In the present invention, the speed of the glue homogenizer is preferably 2500-3500rpm, more preferably 2600-3400rpm, and more preferably 2800-3200rpm; the time is preferably 25-35s, more preferably 26-34s, and more preferably 28-32s.

[0074] In the present invention, the drying temperature is preferably 85 to 95° C., more preferably 87 to 93° C.; the drying time is preferably 4 to 6 min, more preferably 4.5 to 5.5 min.

[0075] In the present invention, the radiation intensity of the ultraviolet light in the ultraviolet light exposure is preferably 400-450 mW / cm 2 , more preferably 410 to 440 mW / cm 2 ; The exposure time is preferably 3 to 6 seconds, more preferably 4 to 5 seconds.

[0076] After ultraviolet light exposure, the present invention develops the obtained system and then performs acid etching to obtain the patterned active layer.

[0077] The present invention preferably soaks the system obtained by ultraviolet light exposure in a sodium hydroxide aqueous solution to remove the photoresist irradiated by ultraviolet light and realize development. In the present invention, the mass percentage concentration of sodium hydroxide in the sodium hydroxide aqueous solution is preferably 0.1-0.9%, more preferably 0.2-0.8%. In the present invention, the time for soaking the system obtained by ultraviolet light exposure in the sodium hydroxide aqueous solution is preferably 7-8s.

[0078] After soaking in the sodium hydroxide aqueous solution, the present invention preferably further comprises drying the obtained system with nitrogen and then performing thermal curing. In the present invention, the thermal curing temperature is preferably 80 to 100° C., more preferably 85 to 95° C.; the time is preferably 3 to 7 minutes, more preferably 4 to 6 minutes. The present invention achieves the curing of the photoresist that is not exposed to ultraviolet light by thermal curing.

[0079] In the present invention, the acid etching is preferably performed by soaking the obtained system in acid for etching.

[0080] In the present invention, the acid used for acid etching is preferably hydrochloric acid; the mass percentage concentration of the hydrochloric acid is preferably 0.1-0.9%, more preferably 0.2-0.8%. In the present invention, the soaking time is preferably 3-4 seconds. The present invention etches the exposed active layer through acid etching to achieve patterning of the active layer.

[0081] After acid etching, the present invention preferably further comprises washing the acid etching system with acetone, washing with water and drying with nitrogen. The present invention removes the photoresist that is not exposed to ultraviolet light by washing with acetone.

[0082] After the patterned active layer is obtained, the present invention photolithographically prepares source and drain electrodes on the surface of the patterned active layer to obtain a primary thin film transistor.

[0083] In the present invention, the thickness of the source-drain electrode is preferably 40 to 60 nm, and more preferably 45 to 55 nm.

[0084] In the present invention, the chemical composition of the source-drain electrode is preferably aluminum.

[0085] In the present invention, the photolithography method for preparing the source and drain electrodes adopts the photolithography method described in the above technical solution, which will not be described in detail here.

[0086] When the present invention is aligned under a lithography machine microscope, the patterned active layer in the area not covered by the photoresist is directly exposed under the lithography machine microscope. The channel position of the patterned active layer can be clearly found from the microscope by using the area not covered by the photoresist. If the photoresist mask plate of the area not covered with the photoresist and the corresponding source and drain electrodes are accurately focused, then the area covered with the photoresist and the photoresist mask plate of the corresponding source and drain electrodes are also accurately focused, so that the source and drain electrodes in the area covered with the photoresist can also be accurately covered on the active layer.

[0087] In the photolithography preparation of source and drain electrodes, after ultraviolet light exposure, the present invention preferably immerses the obtained system in a sodium hydroxide solution to remove the photoresist irradiated by the ultraviolet light, grows source and drain electrodes on the surface of the obtained system after drying with nitrogen, and washes with acetone to remove the source and drain electrodes grown on the photoresist, thereby forming source and drain electrodes with channels.

[0088] The present invention preferably uses electron beam evaporation to prepare the source and drain electrodes.

[0089] After obtaining the primary thin film transistor, the present invention anneals the primary thin film transistor to obtain the thin film transistor.

[0090] In the present invention, the annealing temperature is preferably 250-350°C, more preferably 260-340°C, and more preferably 270-320°C; the annealing time is preferably 10-20 min, more preferably 12-18 min, and more preferably 14-16 min; and the annealing atmosphere is preferably air.

[0091] In order to further illustrate the present invention, a photolithography method for source-drain electrodes and a method for preparing a thin film transistor provided by the present invention are described in detail below in combination with embodiments, but they should not be understood as limiting the scope of protection of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0092] Example 1

[0093] Partially coat the surface of the patterned active layer, drop photoresist on the edge of the substrate, partially coat the surface with photoresist after spin coating, heat and dry at 90° C. for 5 minutes to obtain a patterned active layer partially covered with photoresist;

[0094] The substrate is fixed on the electrode patterning mask, and the patterned active layer in the area not covered by the photoresist is directly exposed to the microscope of the photoresist. The position of the active layer can be clearly found from the microscope, and the area not covered by the photoresist is accurately aligned so that the source and drain electrodes in the area covered by the photoresist can also be accurately covered on the active layer;

[0095] After the system is exposed to ultraviolet light for 4 seconds, it is immersed in a 0.5wt.% sodium hydroxide aqueous solution for 7 seconds to wash away the photoresist irradiated by the ultraviolet light, and the substrate is rinsed with deionized water and blown dry with nitrogen; a 50nm aluminum layer is grown as a source and drain electrode using electron beam evaporation technology, and the aluminum grown on the photoresist is stripped with acetone, and finally a source and drain electrode is formed on the surface of the patterned active layer.

[0096] It has been observed that the patterned active layer covered with photoresist can accurately focus on the photolithography mask for preparing source and drain electrodes.

[0097] Example 2

[0098] The ITO substrate was washed with acetone, alcohol and deionized water under ultrasonic conditions for 10 min each to obtain a clean substrate;

[0099] A 100 nm thick HfO2 layer was grown by magnetron sputtering on the cleaned ITO substrate as a gate dielectric layer. The magnetron sputtering conditions were: growth power of 150 W, growth pressure of 8 mTorr, and argon atmosphere gas. Figure 1 A picture of gate dielectric hafnium dioxide grown on a conductive glass substrate;

[0100] A 40 nm thick ZnO layer is grown on the surface of the obtained gate dielectric layer by magnetron sputtering as an active layer. The magnetron sputtering conditions are: growth power of 100 W, growth pressure of 8 mTorr, atmosphere gas of argon and oxygen, and the volume ratio of argon to oxygen is 95:5. Figure 2 This is a picture of the active layer zinc oxide grown on the gate dielectric;

[0101] The photoresist was evenly coated on the entire active layer surface using a 3000 rpm coating machine for 30 seconds. The coating amount was 23 μL / cm 2 , dried on a 90°C hot plate for 5 minutes, fixed on a patterned mask and irradiated with UV light at an intensity of 420 mw / cm 2The substrate was exposed to ultraviolet light for 4 seconds; the substrate was immersed in a 0.5wt.% sodium hydroxide solution for 7 seconds to wash away the photoresist irradiated by the ultraviolet light, and the substrate was rinsed with deionized water and dried with nitrogen; the photoresist not irradiated by the ultraviolet light was cured by heating on a hot plate for 3 minutes, and then immersed in a 0.5wt.% hydrochloric acid solution for 3 seconds to etch the exposed active layer to pattern the active layer, and the photoresist not irradiated by the ultraviolet light was removed with acetone, and the substrate was rinsed with deionized water and dried with nitrogen to obtain a patterned active layer; Figure 3 Picture of patterning of active layer;

[0102] Partially coat the surface of the patterned active layer, drop photoresist on the edge of the substrate, partially coat the surface with photoresist after spin coating, heat and dry at 90° C. for 5 minutes to obtain a patterned active layer partially covered with photoresist; Figure 4 This is a picture of some photolithography methods before photolithography. Figure 5 This is a picture of partial coating after partial coating by partial coating lithography method;

[0103] The substrate is fixed on the electrode patterning mask, and the patterned active layer in the area not covered by the photoresist is directly exposed to the microscope of the photoresist. The position of the active layer can be clearly found from the microscope, and the area not covered by the photoresist is accurately aligned so that the source and drain electrodes in the area covered by the photoresist can also be accurately covered on the active layer; Figure 6 This is a picture of the alignment of the photolithography machine microscope after partial coating; Figure 7 This is a picture of the source and drain electrodes grown after precise alignment using the partial coating method;

[0104] After exposing the system to ultraviolet light for 4 seconds, immerse it in a 0.5wt.% sodium hydroxide aqueous solution for 7 seconds to wash away the photoresist irradiated by ultraviolet light, rinse the substrate with deionized water and blow dry it with nitrogen; use electron beam evaporation technology to grow a 50nm aluminum layer as a source and drain electrode, use acetone to peel off the aluminum grown on the photoresist, and finally form a source and drain electrode on the surface of the patterned active layer to obtain a primary thin film transistor;

[0105] The primary thin film transistor is annealed at 300° C. in air for 15 minutes to obtain the thin film transistor.

[0106] The thin film transistor prepared in Example 2 was subjected to electrical testing using a semiconductor parameter instrument, and data analysis was performed in the following manner: a thin film transistor device with a conductive channel having a source-drain electrode spacing of 100 μm was selected to test the output characteristic curve, that is, at different gate voltages V G Under this condition, the source-drain current I DS As the source-drain voltage V DS The change curve is the output characteristic curve, and the test gate voltage V GThe scanning range is 0V~8V, and the source-drain voltage V DS The scanning range is 0V~5V. G Lower source drain current I DS All have good regulation effect; the transfer characteristic curve is at different source-drain voltages V DS Under this condition, the source-drain current I DS As the gate voltage V G The change curve of the test gate voltage V G The scanning range is -10V~4V, the source-drain voltage V DS The scanning range is 0V~4V, and the current switching ratio of the thin film transistor device can be calculated from the transfer curve to be 3.1×10 3 .

[0107] However, in the traditional method, thin-film transistors are prepared by uniformly spin-coating photoresist. Since the active layer is a material with high light transmittance, the lithography machine microscope cannot observe the position of the patterned active layer through the photoresist. As a result, the prepared source and drain electrodes cannot be accurately covered on the patterned active layer, and the conductive channel is offset, so the field effect performance of the thin-film transistor cannot be tested.

[0108] Comparative Example 1

[0109] Traditional method for preparing source and drain electrodes on the surface of patterned active layer:

[0110] The photoresist is dropped on the center of the patterned active layer surface. After spin coating, the photoresist will evenly cover the entire patterned active layer. Figure 8 This is a picture before normal photolithography, where the photoresist is dripped on the center of the substrate; Fig. 9 This is a picture of the photoresist evenly covering the surface after spin coating; after heating and drying for 5 minutes, the obtained system is fixed on the electrode patterned mask and aligned under the microscope of the photolithography machine so that the electrode aluminum can cover the patterned active layer.

[0111] This photolithography process technology is mature and has good stability. However, when the active layer is made of a material with high light transmittance, the lithography machine microscope cannot observe the position of the patterned active layer through the photoresist. When preparing the source and drain electrodes, they cannot be accurately covered on the surface of the patterned active layer. Poor channel control and carrier injection can be foreseen.

[0112] Example 3

[0113] Partially coat the surface of the patterned active layer, drop photoresist on the edge of the substrate, partially coat the surface with photoresist after spin coating, heat and dry at 90° C. for 5 minutes to obtain a patterned active layer partially covered with photoresist;

[0114] The substrate is fixed on the electrode patterning mask, and the patterned active layer in the area not covered by the photoresist is directly exposed to the microscope of the photoresist. The position of the active layer can be clearly found from the microscope, and the area not covered by the photoresist is accurately aligned so that the source and drain electrodes in the area covered by the photoresist can also be accurately covered on the active layer;

[0115] After the system is exposed to ultraviolet light for 4 seconds, it is immersed in a 0.5wt.% sodium hydroxide aqueous solution for 7 seconds to wash away the photoresist irradiated by the ultraviolet light, and the substrate is rinsed with deionized water and blown dry with nitrogen; a 50nm aluminum layer is grown as a source and drain electrode using electron beam evaporation technology, and the aluminum grown on the photoresist is stripped with acetone, and finally a source and drain electrode is formed on the surface of the patterned active layer.

[0116] It has been observed that the patterned active layer covered with photoresist can accurately focus on the photolithography mask for preparing source and drain electrodes.

[0117] Example 4

[0118] The ITO substrate was washed with acetone, alcohol and deionized water under ultrasonic conditions for 10 min each to obtain a clean substrate;

[0119] A 100 nm thick HfO2 layer was grown by magnetron sputtering on the cleaned ITO substrate as a gate dielectric layer. The magnetron sputtering conditions were: growth power of 150 W, growth pressure of 8 mTorr, and argon atmosphere gas.

[0120] A 60 nm thick ZnO layer was grown on the surface of the obtained gate dielectric layer by magnetron sputtering as an active layer. The magnetron sputtering conditions were: growth power of 100 W, growth pressure of 8 mTorr, atmosphere gas of argon and oxygen, and the volume ratio of argon to oxygen was 95:5.

[0121] The photoresist was evenly coated on the entire active layer surface using a 3000 rpm coating machine for 30 seconds. The coating amount was 23 μL / cm 2 , dried on a 90°C hot plate for 5 minutes, fixed on a patterned mask and irradiated with UV light at an intensity of 420 mw / cm 2 The substrate was exposed to ultraviolet light for 4 seconds; the substrate was immersed in a 0.5wt.% sodium hydroxide solution for 7 seconds to wash away the photoresist irradiated by the ultraviolet light, and the substrate was rinsed with deionized water and dried with nitrogen; the photoresist not irradiated by the ultraviolet light was cured by heating on a hot plate for 3 minutes, and then immersed in a 0.5wt.% hydrochloric acid solution for 3 seconds to etch the exposed active layer to pattern the active layer, and the photoresist not irradiated by the ultraviolet light was removed with acetone, and the substrate was rinsed with deionized water and dried with nitrogen to obtain a patterned active layer;

[0122] Partially coat the surface of the patterned active layer, drop photoresist on the edge of the substrate, partially coat the surface with photoresist after spin coating, heat and dry at 90° C. for 5 minutes to obtain a patterned active layer partially covered with photoresist;

[0123] The substrate is fixed on the electrode patterning mask, and the patterned active layer in the area not covered by the photoresist is directly exposed to the microscope of the photoresist. The position of the active layer can be clearly found from the microscope, and the area not covered by the photoresist is accurately aligned so that the source and drain electrodes in the area covered by the photoresist can also be accurately covered on the active layer;

[0124] After exposing the system to ultraviolet light for 4 seconds, immerse it in a 0.5wt.% sodium hydroxide aqueous solution for 7 seconds to wash away the photoresist irradiated by ultraviolet light, rinse the substrate with deionized water and blow dry it with nitrogen; use electron beam evaporation technology to grow a 50nm aluminum layer as a source and drain electrode, use acetone to peel off the aluminum grown on the photoresist, and finally form a source and drain electrode on the surface of the patterned active layer to obtain a primary thin film transistor;

[0125] The primary thin film transistor is annealed at 300° C. in air for 15 minutes to obtain the thin film transistor.

[0126] According to the method of Example 2, the thin film transistor prepared in Example 4 was subjected to electrical testing using a semiconductor parameter instrument, and data analysis was performed to calculate the current switching ratio of the thin film transistor device to be 1.4×10 2 .

[0127] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a thin film transistor, characterized in that: The following steps are involved: Growing a gate dielectric layer on a substrate; and preparing a patterned active layer on the surface of the obtained gate dielectric layer; Partially coating the surface of the patterned active layer, and drying the layer to obtain a patterned active layer partially covered with photoresist; Using the uncoated portion of the patterned active layer partially covered with photoresist, focusing the patterned active layer partially covered with photoresist on a photolithography mask for preparing source and drain electrodes, performing ultraviolet light exposure and growth, forming source and drain electrodes on the surface of the patterned active layer, and obtaining a primary thin film transistor; Annealing the primary thin film transistor to obtain the thin film transistor; The partial coating is as follows: deviating from the center of the surface of the patterned active layer, and coating the photoresist on the surface of the patterned active layer; The light transmittance of the active layer at 550nm visible light is 80-85%; The chemical composition of the active layer is one or more of zinc oxide, indium zinc oxide and indium gallium zinc oxide; The drying temperature is 85-95°C and the drying time is 4-6 minutes; The radiation intensity of the ultraviolet light in the ultraviolet light exposure is 400-450 mW / cm 2 , the exposure time is 3 to 6 seconds.

2. The preparation method according to claim 1, characterized in that: The substrate is conductive glass; The chemical composition of the gate dielectric layer is hafnium dioxide; The chemical composition of the source and drain electrodes is aluminum.

3. The preparation method according to claim 1, characterized in that: The annealing temperature is 250-350° C., the time is 10-20 min, and the annealing atmosphere is air.

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