JP6015893B2 - Thin film transistor manufacturing method - Google Patents

Description

  The present invention relates to a manufacturing method of an electronic device having a transparent conductive film such as a touch panel, electronic paper, a display, an image scanner, an image sensor array, a solar cell, a transparent antenna, and a flexible device, and a thin film transistor manufactured by the manufacturing method. In particular, it is suitable for the production of a transparent thin film transistor produced by processing a transparent conductive film through a plurality of exposure steps using a plurality of masks.

  Conventionally, a crystalline transparent conductive film having a large electrical conductivity is generally used for an electronic device having a transparent conductive film. In manufacturing an electronic device, methods for processing a transparent conductive film include a lift-off method and an etching method.

  The lift-off method has an advantage that an etching process is eliminated, but has a disadvantage that a relatively large number of processes are required to form a transparent conductive film. Moreover, there is a limit in forming a transparent conductive film pattern of 1 μm or less.

  As a method for etching the transparent conductive film, there are wet etching and dry etching.

  In wet etching, the end point is time-controlled, so that etching residue and overetch defects frequently occur. In addition, since etching proceeds isotropically, the amount of side etching is large, and when processing into a concavo-convex shape, the processing accuracy for processing into a desired shape deteriorates. Also, nanoscale fine pattern formation is not easy.

  Since the adhesive force between the photoresist pattern and the transparent conductive film is weakened, a photoresist pattern peeling phenomenon occurs during the etching process, and the peeled photoresist pattern contaminates the etching tank. is there.

  Further, the etching rate in wet etching remarkably depends on the crystallinity. Near the crystallization temperature, the film quality is a mixture of amorphous and crystalline, and the etching characteristics become extremely unstable.

  Furthermore, since the amorphous oxide thin film has a higher etching rate than the crystalline oxide thin film, if the crystalline oxide thin film deposited on the amorphous oxide thin film is etched by wet etching and separated, As soon as the material thin film is etched and the underlying amorphous oxide thin film is exposed, the underlying amorphous oxide is greatly etched, and in the worst case, the underlying amorphous oxide thin film is completely lost.

For example, in Patent Document 1, in the case of wet etching using an acid, the etching rate of amorphous In—Ga—ZnO ₄ (also referred to as IGZO) is higher than that of tin-doped indium oxide (also referred to as ITO) of the transparent conductive film. Also shows that it is much larger. When the crystalline ITO deposited on the amorphous IGZO using such an acid is etched within a practical time, the underlying amorphous IGZO cannot be processed without greatly etching.

  In dry etching, there are a method of milling by a physical etching mechanism using ions such as rare gas, and a method of etching by the effects of both a physical etching mechanism using a halogen-based gas or an organic gas and a chemical etching mechanism. is there.

  In the method of milling by a physical etching mechanism using ions such as a rare gas, the etching rate is generally slow, and there is a problem that the etched non-volatile substance is reattached to the side wall, which is not suitable for mass production. There is a problem.

  The dry etching method using a halogen gas has the following problems.

  That is, in the case of a transparent conductive film containing indium or zinc, chemical etching hardly occurs in the fluorine-based gas because the vapor pressure of the fluorine compound of indium or zinc is low. Moreover, even if the etching progresses by physical etching, there arises a problem that many nonvolatile substances are generated.

  Similarly, in the case of a transparent conductive film containing indium or zinc, etching with a chlorine-based gas is difficult because the vapor pressure of a chlorine compound of indium or zinc is low. In addition to the problem that many non-volatile substances are generated, the extremely high etching rate of the organic resist used as a mask, the contamination of the organic product in the chamber caused by the organic resist, the corrosion of the apparatus by corrosive chlorine gas, etc. Various problems arise.

  Research and development has been conducted on dry etching methods using organic gases, and prior art studies have been conducted. As a result, techniques such as Patent Documents 2 and 3 are known. Patent Document 2 discloses carbonization as a stable dry etching method without generating a nonvolatile substance during dry etching of an oxide semiconductor film formed of In—Ga—Zn—O formed on a substrate. A technique using an etching gas containing hydrogen is described. Further, in Patent Document 3, in an etching method for patterning a transparent conductive film, etching is expressed by hydrogen and the general formula CnHm while heating the transparent conductive film (heating the base to 50 ° C. to 200 ° C.). A technique for performing reactive dry etching using a mixed gas of hydrocarbons is described.

JP 2008-041695 A JP 2007-335505 A JP-A-3-77209

In conventional dry etching using organic gas, chemical etching is possible not only by physical etching but also by generation of organic compounds with high vapor pressure, but often non-volatile organometallic compounds are generated during etching, Induces low etch rate and non-volatile re-deposition problems. Therefore, in Patent Document 2, for example, a high power density of 0.1 W / cm ² or more and 20 W / cm ² or less is used in order to prevent adhesion of a nonvolatile organometallic compound when dry etching an oxide semiconductor film with an organic gas. The reaction pressure conditions of 0.6 Pa to 3.5 Pa are described, particularly 2 W / cm ² or more is described as being most preferable, and high power density and reaction pressure conditions are required.

  Moreover, in the technique of patent document 3 which dry-etches a transparent conductive film using the conventional organic type gas, it is described that a board | substrate must be heated to 50 to 200 degreeC, and when it does not heat, it cannot etch. Has been.

  For these reasons, it has been difficult to produce an electronic device by depositing a transparent conductive film on an amorphous oxide semiconductor. Therefore, using the aforementioned lift-off, or forming a protective film on the amorphous oxide semiconductor first and then making a hole in the protective film, a transparent conductive film is deposited so that the wet etching solution does not penetrate into the protective film. There was only a method of performing wet etching while paying close attention.

  A method of depositing a protective film, then depositing a transparent conductive film, and etching the transparent conductive film on the protective film is often performed by dry etching.

  In the method in which a protective film is deposited on these amorphous oxide semiconductors, a hole is made in the protective film, and a transparent conductive film is deposited on the protective film, an exposure process is required for drilling the protective film. The number of sheets increases and the cost increases, and an increase in the exposure process causes a decrease in yield due to dust and the like.

  The present invention is intended to solve these problems, and realizes a method capable of directly depositing and processing a transparent conductive film without depositing and processing a protective film on an amorphous oxide semiconductor. It is the purpose. It is another object of the present invention to provide a thin film transistor having excellent electrical characteristics at low cost.

  As a result of conducting extensive research, the present inventors have found the following facts. That is, an amorphous oxide semiconductor and a crystalline transparent conductive film are etched by 100 to 250 angstroms per minute with a power density of about 0.33 watts per square centimeter even with a dilute organic gas diluted by 2 to 16 mol% diluted with hydrogen gas. Etching at a speed. That is, etching can be performed at an etching rate of 300 to 750 angstroms per minute per watt per square centimeter. At that time, the dilute organic gas does not emit plasma unless the pressure is raised, and a pressure of 5 Pascals or more is required for plasma generation. According to X-ray photoelectron spectroscopy (XPS measurement), there is little carbon element on the surface of the transparent conductive film etched with dilute organic gas diluted with hydrogen, and there is very little or almost no accumulation of non-volatile organic matter on the etched surface. Absent. Also, the lower the organic gas (methane gas, etc.) concentration, the less effective the physical etching, so the lower the organic gas concentration, the lower the etching rate. However, a thick and strong non-volatile organic substance is formed on the resist or silicon oxide film. In order to reduce the non-volatile organic matter deposited on the resist or silicon oxide film after etching the crystalline transparent conductive film, and for cleaning the non-volatile organic matter adhering to the device. The time required can be shortened.

  The etching rate between the crystalline transparent conductive film and the amorphous oxide semiconductor in dry etching using a hydrocarbon / hydrogen mixed gas containing 16% or less of hydrocarbon is not significantly different from wet etching. Therefore, when the crystalline transparent conductive film is etched and separated, there is no problem like wet etching in which the underlying amorphous oxide thin film is largely etched and completely disappears. Therefore, the upper crystalline transparent conductive film can be separated and processed while maintaining the performance of the amorphous oxide semiconductor only by time control without using a protective film.

  Note that oxygen gas or hydrogen gas can be used to clean the nonvolatile organic substances. Pure hydrogen gas containing no organic gas is more difficult to emit plasma than dilute organic gas, but plasma can be generated even with pure hydrogen gas by increasing the pressure. In particular, pure hydrogen gas has an etching action for non-volatile organic substances and is effective for cleaning and the like.

  The present invention has the following features in order to achieve the above object.

  The method of the present invention is a method of manufacturing an electronic device having a laminated structure in which a polycrystalline transparent conductive film made of an oxide containing indium or tin is directly formed on an amorphous oxide semiconductor containing indium and gallium, The polycrystalline transparent conductive film is dry-etched to form an etching groove reaching the amorphous oxide semiconductor. The electronic device is a thin film transistor including a plurality of electrodes made of the polycrystalline transparent conductive film separated by the etching groove and a channel of the amorphous oxide semiconductor between the electrodes. In the dry etching of the present invention, it is preferable to use a mixed gas containing a hydrocarbon containing no halogen and hydrogen. The dry etching of the present invention is preferably reactive ion etching. In addition, the present invention is a bottom-gate thin film transistor manufactured by these manufacturing methods.

  The amorphous oxide semiconductor containing indium and gallium of the present invention may contain any one or more elements of tin, titanium, zirconium, hafnium, niobium, tantalum, copper, iron, and zinc in addition to indium and gallium. . For example, there are an In—Ga—Zn—O system, an In—Ga—O system, and the like.

  The polycrystalline transparent conductive film made of an oxide containing In or Sn according to the present invention is any one of ITO, tin oxide, and indium oxide. Gallium, tin, titanium, zirconium, hafnium, niobium, tantalum, copper, iron, Any one or more elements of zinc may be included.

  In the present invention, the crystalline transparent conductive film is dry-etched to separate the crystalline transparent conductive film into two or more island-like structures, and each island-like structure is used as an electrode.

  In the mixed gas composed of hydrocarbon gas and hydrogen gas used in the dry etching of the present invention, ethane, propane, butane, ethylene, propylene, acetylene, etc. can be used as the carbon hydrogen gas, in addition to methane gas.

  The dry etching of the present invention preferably has an etching rate of 300 to 750 angstroms per minute per watt per square centimeter.

  According to the present invention, since the transparent conductive film can be directly deposited and processed on the amorphous oxide semiconductor without depositing and processing the protective film, the number of masks can be reduced and the manufacturing cost can be reduced. According to the present invention, the manufacturing process of an electronic device can be performed by an all dry process.

  According to the present invention, since the exposure process can be reduced, a decrease in yield due to dust or the like can be suppressed.

  In addition, the thin film transistor obtained by the manufacturing method of the present invention is low in cost and has excellent electric characteristics such as electric field mobility.

1 is a conceptual diagram illustrating a bottom gate channel etch thin film transistor of the present invention. 8A and 8B illustrate a manufacturing process of a bottom-gate channel etched thin film transistor of the invention. The figure which shows the relationship between the methane density | concentration of methane-hydrogen mixed gas, and the pressure which plasma discharge starts. The figure which shows the methane density | concentration dependence of the etching rate of a polycrystal ITO transparent conductive film. The figure which shows the methane concentration dependence of the etching rate of an amorphous indium gallium zinc oxide thin film. The figure which shows the relationship between the pressure and the etching rate in the dry etching of a polycrystal ITO transparent conductive film and an amorphous indium gallium zinc oxide thin film. The figure explaining the methane concentration dependence of the recovery time until oxygen plasma recovers from white to light yellow. The figure which shows the electrical property of the channel etch type bottom gate transparent thin-film transistor of a present Example.

  Embodiments of the present invention will be described below with reference to the drawings. The present invention provides an electronic device having a laminated structure in which a polycrystalline transparent conductive film made of an oxide containing indium or tin is formed on an amorphous oxide semiconductor containing indium and gallium, and a recess is formed in the transparent conductive film. This is an effective method for electronic device structures that need to be performed. By forming recesses, grooves, and holes in the polycrystalline transparent conductive film, the polycrystalline transparent conductive film can be separated and a plurality of electrodes can be formed.

(First embodiment)
As an embodiment of the present invention, a bottom gate channel etch thin film transistor will be described as an example. FIG. 1 shows a bottom gate channel etch type thin film transistor. As shown in FIG. 1, a bottom gate thin film transistor includes a gate electrode 101, an insulating film 102, an amorphous oxide semiconductor thin film 103, a transparent conductive film 104, and a transparent conductive film 105 sequentially stacked on a substrate (for example, a glass substrate) 100. With a structure. In this embodiment, the transparent conductive films 104 and 105 are separated by an etching groove formed by etching to form a plurality of electrodes, and the amorphous oxide semiconductor 103 between the electrodes functions as a channel region in the bottom gate thin film transistor. Therefore, it can be called a bottom gate channel etch thin film transistor.

  Next, a method for manufacturing the bottom-gate channel-etched thin film transistor of this embodiment is described with reference to FIGS.

  A substrate 100 (for example, a glass substrate) is prepared (FIG. 2A). The glass substrate only needs to be a light-transmitting substrate, and quartz glass, barium borosilicate glass, or alumino borosilicate glass can be used. In addition, a light-transmitting substrate such as a plastic substrate can also be used.

  As shown in FIG. 2B, a transparent conductive film 101 is deposited on the glass substrate 100 by a sputtering method. As the transparent conductive material, for example, ITO (tin-added indium oxide), tin oxide, indium oxide, zinc oxide, or a compound thereof can be used. As shown in FIG. 2C, a desired photoresist 110 is formed using a first photomask. As shown in FIG. 2D, the transparent conductive film 101 is etched using a photoresist 110 to form a gate electrode 101 and a gate wiring. The gate electrode 101 and the gate wiring can also be formed of a low-resistance metal conductive material such as aluminum (Al) or copper (Cu). When the metal conductive material is used, the translucency of the gate electrode and the gate wiring portion is lost, but a desired resistance is obtained with a thickness smaller than that of the transparent conductive film, and an electronic device having excellent electrical operation performance can be obtained. When a metal conductive material is used, it may be formed in combination with a plurality of metal materials in consideration of heat resistance and corrosion resistance, or an alloy may be used. Thereafter, the photoresist is peeled off.

  As shown in FIG. 2E, an insulating film 102, an amorphous oxide semiconductor thin film 103, and a transparent conductive film 104 are sequentially formed on the gate electrode 101. For example, ITO, tin oxide, or indium oxide can be used as the transparent conductive material. The insulating film 102 is a gate insulating film, and is formed of a single layer such as a silicon oxide film or an alumina film or a laminated structure thereof. Of course, the gate insulating film is not limited to such a material, and other insulating films such as a tantalum oxide film and a hafnia film may be used to form a single layer or a laminated structure made of these materials. The insulating film 102 is formed by a CVD method. You may deposit by ALD. When deposited by ALD, a dense and highly insulating thin film can be deposited at a low temperature, so that it can also be deposited on a substrate having poor heat resistance such as plastic. The amorphous oxide semiconductor thin film 103 and the transparent conductive film 104 form a channel region, a source region, and a drain region, respectively. The amorphous oxide thin film 103 is a high resistance thin film with a low carrier concentration, and the transparent conductive film 104 is a crystalline low resistivity thin film having a high concentration of an impurity element imparting conductivity. The amorphous oxide thin film and the crystalline transparent conductive film are formed by a sputtering method. By using a multi-chamber apparatus, an insulating film, an amorphous oxide semiconductor thin film, and a crystalline transparent conductive film can be successively formed. By not exposing to the atmosphere, contamination of impurities can be prevented. In this embodiment mode, an amorphous oxide semiconductor or a crystalline transparent conductive film is formed by a sputtering method, but an evaporation method, a PLD method, a CVD method, an ALD method, or the like can also be used.

  As shown in FIG. 2F, a desired photoresist 111 is formed using a second photomask in order to separate the amorphous oxide semiconductor in the channel region into islands. As shown in FIG. 2G, the amorphous oxide semiconductor and the crystalline transparent conductive film on the gate electrode 101 covered with the insulating film 102 are dry-etched by using the photoresist 111 to form an island-shaped amorphous oxide. The physical semiconductor 103 and the island-like crystalline transparent conductive film 104 are obtained. Note that in the case of the gate electrode 101 and the gate wiring using a metal conductive material, a photoresist formed on the amorphous oxide semiconductor and the crystalline transparent conductive film by back exposure from the back surface of the substrate using the metal film as a photomask. By selectively exposing, a photoresist having a desired pattern can be formed. In this case, since light passes through the thin film by backside exposure and the photoresist is exposed, the amorphous oxide semiconductor and the crystalline transparent conductive film other than the gate wiring are desirably transparent at the exposure wavelength of the photoresist. When a photoresist pattern formed by backside exposure is used, self-alignment eliminates the need for alignment of the photomask in the gate electrode region and the channel region, and dry etching can be performed in a self-aligned manner. If the amorphous oxide semiconductor and the crystalline transparent conductive film absorb at the exposure wavelength of the photoresist, the amorphous oxide semiconductor and the crystalline transparent conductive film must be thin enough to make the photoresist photosensitive. It is. Thereafter, the photoresist is peeled off.

  As shown in FIG. 2H, a transparent conductive film 105 is formed on the entire surface of the substrate. For example, ITO, tin oxide, or indium oxide can be used as the transparent conductive material. The transparent conductive film 105 serves as a source electrode, a drain electrode, and a source wiring. As shown in FIG. 2I, a photoresist 121 is formed using a third photomask. As shown in FIG. 2J, dry etching is performed using a photoresist 121 to form wiring, and the source region and the drain region are separated. In addition, when the said back surface exposure is performed, you may form the photoresist which has different thickness using a halftone exposure technique. In that case, after the dry etching of the wiring portion, the thin resist portion is removed by an ashing process, and dry etching for separating the source region and the drain region is performed. Thereafter, the photoresist 121 is peeled and removed.

  As shown in FIG. 2K, an insulating film is formed on the entire surface of the substrate to form a protective film 106. The insulating film serving as the protective film 106 may be a silicon oxide film, an alumina film, a gallium oxide film, or a laminated film thereof.

  Thereafter, a hole for electrical contact may be further formed in the protective film 106, and a transparent conductive material such as a pixel electrode may be deposited, or a transparent conductive material for wiring may be deposited. For example, ITO, tin oxide, indium oxide, nickel oxide, zinc oxide, or a compound thereof may be used as the transparent conductive material.

  Next, dry etching of the amorphous oxide semiconductor and the polycrystalline transparent conductor will be described in detail.

  Dry etching was performed using amorphous indium gallium zinc oxide as the amorphous oxide semiconductor and ITO as the polycrystalline transparent conductor. FIG. 3 shows the relationship between the methane concentration of the methane-hydrogen mixed gas and the pressure at which plasma discharge starts when a dry etching apparatus (RIE-200L manufactured by Samco) is used. A cross indicates that plasma was not generated, and a circle indicates that plasma was generated. As can be seen from FIG. 3, since the pressure at which plasma discharge starts increases with decreasing methane concentration, reactive ion etching (RIE) is performed at a pressure of 5 Pascal or less at a methane concentration of 16% or less, particularly 10% or less. It turns out that cannot be done.

  FIG. 4 is a graph showing the methane concentration dependence of the etching rate of a polycrystalline ITO transparent conductive film performed at a pressure of 11 Pascal and a power density of 0.33 watts per square centimeter (power of 150 watts). FIG. 5 is a graph showing the methane concentration dependence of the etching rate of an amorphous indium gallium zinc oxide thin film performed at a pressure of 11 Pascal and a power density of 0.33 watts per square centimeter. Even at low methane concentrations below 16%, both polycrystalline ITO transparent conductive films and amorphous indium gallium zinc oxide thin films achieve an etching rate of 100 angstroms per minute to 250 angstroms at a low power density of 0.33 watts per square centimeter. It turns out that you can. That is, etching can be performed at an etching rate of 300 to 750 angstroms per minute per watt per square centimeter. Even at low methane concentrations of 10% or less, an etch rate of 150 angstroms per minute or higher is obtained with a low power density of 0.33 watts per square centimeter. This is a result of diluting methane with hydrogen and performing the pressure at 5 Pascals or higher.

  The present invention focuses on dry etching a polycrystalline ITO transparent conductive film and an amorphous indium gallium zinc oxide thin film under the same conditions. As described above, polycrystalline ITO does not have an order of magnitude faster etching than amorphous indium gallium zinc oxide as in wet etching in Patent Document 1, and is approximately the same etching rate. It has been found. As a result, the polycrystalline ITO deposited on the amorphous indium gallium zinc oxide can be separated and processed without disappearance due to excessive etching of the amorphous indium gallium zinc oxide.

  FIG. 6 is a diagram showing the relationship between the pressure and the etching rate for the polycrystalline ITO transparent conductive film and the amorphous indium gallium zinc oxide thin film. In both cases, the methane concentration of the mixed gas is 2%. When the pressure is about 18 Pa, the etching rates of IGZO and ITO are the same, and when the pressure is lower than that, the etching rate of ITO is larger than the etching rate of IGZO.

  As a result of examining the surface composition of the etched amorphous indium gallium zinc oxide by X-ray photoelectron spectroscopy (XPS), the outermost surface composition is most gallium up to a methane concentration of 2 to 16%. It became clear that zinc became the most when it was large. In amorphous indium gallium zinc oxide semiconductors, the more zinc, the weaker the moisture, the more likely it is to deteriorate, and the more zinc, the more likely the leak current flows. The more gallium, the more chemically stable, the less leak current flows. Tend.

  It has been found that dry etching at a low organic gas concentration in this embodiment is also suitable for electrical characteristics of an electronic device using an amorphous indium gallium zinc oxide semiconductor.

  In this embodiment, hydrocarbons are used to dilute the organic gas, and the concentration of the organic gas is set to a low concentration of 16% or less, so that there is almost no generation of nonvolatile organic substances. According to XPS measurement, there is little carbon element on the surface of the transparent conductive film etched with dilute organic gas diluted with hydrogen, including the possibility that the sample surface was contaminated with atmospheric carbon after etching. It was found that there was very little or no non-volatile organic deposition on the top. It has been found that the non-volatile organic material is deposited on the surface of a material such as a resist material or silicon oxide, which is hardly dry-etched by RIE using an organic gas, rather than on the surface of the oxide being etched. .

  In this embodiment, since the effect of physical etching is reduced, the lower the organic gas concentration, the lower the etching rate. However, the lower the concentration, the thicker and stronger non-volatile organic material is generated on the resist and the silicon oxide film. Because it is difficult, the cleaning time for reducing the non-volatile organic material deposited on the resist and the silicon oxide film after the etching of the crystalline transparent conductive film, and the time required for cleaning the non-volatile organic material adhering in the apparatus Can be shortened.

  FIG. 7 shows a dry etching apparatus (RIE-200L manufactured by Samco) using a silicon oxide holder for an 8-inch wafer for 5 minutes using a mixed gas of methane-hydrogen for 5 minutes, and then on the holder. The accumulated non-volatile organic matter is cleaned by RIE with 100% oxygen, pressure 5 Pascals, power density 0.22 watts per square centimeter (100 watts), and the time until the oxygen plasma recovers from white to light yellow It is the result of having investigated. As shown in FIG. 7, when the methane concentration was 2 to 16 mol%, it was found that the lower the methane concentration, the more the accumulation of non-volatile organic substances on the holder was suppressed. In addition, although oxygen plasma was used for the cleaning of FIG. 7, hydrogen plasma may be used.

  When dry etching is performed on a polycrystalline oxide or an amorphous oxide using an organic gas-hydrogen mixed gas, the total process time can be optimized in consideration of the cleaning time.

  The dry etching according to the present invention is preferably performed at a hydrocarbon gas concentration of 2 to 16% and a pressure of 5 Pa to 30 Pa in a mixed gas of hydrocarbon and hydrogen. In this embodiment mode, dry etching is performed without heating by a heating source. In addition, in order to improve the reactivity, it may be heated by a heating source in the range from room temperature to about 200 ° C. or less, or may be cooled by a cooling source in order to suppress resist damage.

(Example)
A channel-etched bottom gate thin film transistor was manufactured using the dry etching method of this embodiment.

  A polycrystalline ITO thin film was deposited on a quartz glass substrate at a substrate temperature of 277 ° C. by DC sputtering at 400 Å. A desired photoresist was formed using the first photomask, and the polycrystalline ITO thin film was dry-etched to form a gate electrode and a gate wiring. Dry etching was performed using a RIE-200L dry etching apparatus manufactured by Samco Co., Ltd. for 4 minutes at a methane concentration of 2% -hydrogen 98% mixed gas, a pressure of 11 Pascal, and a power of 150 W. Thereafter, a cleaning process was performed for 4 minutes at 100% hydrogen, a pressure of 15 Pascals, and a power of 150 W, and then the wafer was taken out from the dry etching apparatus and subjected to 300 W oxygen ashing for 10 minutes. Thereafter, the photoresist was peeled off with an organic solvent (Tokyo Ohka Kogaku 104, isopropyl alcohol).

  A silicon oxide film is formed on the gate electrode and the gate wiring by CVD using tetraethoxysilane (TEOS) as an insulating film at 1230 angstroms at 400 ° C., and an amorphous indium gallium zinc oxide thin film is formed thereon. A 520 Å film was formed at room temperature using a DC sputtering method. Note that it was confirmed that a silicon oxide film may be deposited at 350 ° C. by a CVD method using TEOS as an insulating film, and an alumina thin film may be deposited by an ALD method using trimethylaluminum (TMA).

  Next, in order to separate the amorphous indium gallium zinc oxide thin film in the channel region into islands, a desired photoresist is formed using a second photomask, and the ITO gate electrode covered with the silicon oxide insulating film is formed. The amorphous indium gallium zinc oxide thin film was dry etched. Dry etching was performed for 6 minutes using a RIE-200L dry etching apparatus manufactured by Samco Corporation at a methane concentration of 2% -hydrogen 98% mixed gas, a pressure of 11 Pascal, and a power of 150 W. Thereafter, a cleaning process was performed for 4 minutes at 100% hydrogen, a pressure of 15 Pascals, and a power of 150 W, and then the wafer was taken out from the dry etching apparatus and subjected to 300 W oxygen ashing for 10 minutes. Thereafter, the photoresist was peeled off with an organic solvent (Tokyo Ohka Kogaku 104, isopropyl alcohol).

  Next, a polycrystalline ITO transparent conductive film was formed on the entire surface of the substrate at 700 ° C. at 277 ° C. A photoresist was formed using a third photomask, and wiring was formed by dry etching, and the source region and the drain region were separated. Dry etching was performed for 6 minutes and 20 seconds using a RIE-200L dry etching apparatus manufactured by Samco Co., Ltd. with a mixed gas of methane concentration 2% -hydrogen 98%, pressure 11 Pascal, power 150 W. Thereafter, ashing or the like was performed to remove and remove the photoresist.

Next, a silicon oxide thin film as a protective film was deposited on the entire surface of the substrate by 700 Å at 400 ° C. by a CVD method using TEOS. Finally, after removing the insulating film of the electrode pad portion for applying a voltage to the gate electrode, the source electrode, and the drain electrode by reactive ion etching using CHF ₃ using a RIE-200L dry etching apparatus manufactured by Samco Then, annealing was performed at 400 ° C. in an oxygen atmosphere to prepare a channel-etched bottom gate thin film transistor.

  The produced thin film transistor was transparent in the visible light region. FIG. 8 shows an example of electrical characteristics of the channel-etched bottom gate transparent thin film transistor fabricated. FIG. 8 shows the gate voltage dependence of the drain current of a channel-etched bottom gate transparent thin film transistor having a channel length of 20 microns and a channel width of 20 microns. The source-drain voltage is 10 volts. An on / off ratio of 7 digits or more is obtained, with a gate voltage of -12 volts and a minus 13th power amperage of 10 and a gate voltage of 23 volts and a minus 6th power of amperage. An excellent bottom gate thin film transistor having an electric field mobility of 3 square centimeters per volt per second was obtained.

  Note that an ozone-containing gas may be used for the annealing at 400 ° C. in the oxygen atmosphere. When ozone is used, the hydrogen concentration in the amorphous indium gallium zinc oxide thin film can be efficiently reduced, and a thin film transistor with excellent electrical characteristics can be obtained by low-temperature annealing treatment. If necessary, a thin film transistor having excellent electrical characteristics at a lower temperature than the oxygen annealing treatment can be obtained by using high-purity ozone treatment, pure ozone treatment, oxygen plasma treatment, UV treatment, or the like.

  Although the bottom gate channel etch type thin film transistor has been described, the manufacturing method of the present invention can be similarly used for electronic devices such as a rectifier diode, a light emitting diode, and a light detection element.

  In addition, the example shown by the said embodiment etc. was described in order to make invention easy to understand, and is not limited to this form.

100 Substrate 101 Gate electrode 102 Insulating film 103 Amorphous oxide semiconductor thin film 104, 105 Transparent conductive film 110, 111, 121 Photoresist

Claims (2)

A method of manufacturing a thin film transistor having a laminated structure in which a polycrystalline transparent conductive film made of an oxide containing indium or tin is directly formed on an amorphous oxide semiconductor containing indium and gallium,
The polycrystalline transparent conductive film, and a reactive ion etching using a mixed gas containing a hydrocarbon and hydrogen containing no halogen, by forming the etching groove reaching the amorphous oxide semiconductor, etched the The outermost surface composition of the amorphous oxide semiconductor has the largest amount of gallium , and includes a plurality of electrodes made of the polycrystalline transparent conductive film separated by the etching groove, and a channel of the amorphous oxide semiconductor between the electrodes. A method of manufacturing a thin film transistor, which is characterized.   2. The method of manufacturing a thin film transistor according to claim 1, wherein the halogen-free hydrocarbon and hydrogen-containing mixed gas is performed at a hydrocarbon gas concentration of 2% to 16% and a pressure of 5 Pa to 30 Pa. 3. .

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