JPH04302473A - Manufacture of electrode having oxide film - Google Patents

Abstract

PURPOSE:To provide a method of producing an electrode, in which oxide film is formed on part of the electrode constantly in good condition without causing the degradation of the electrode. CONSTITUTION:An electrode 12 is formed on a substrate 11, and it is entirely anodized to form an oxide film 12a. The substrate is immersed in reductive electrolyte solution with the oxide film 12a covered with a selective resist mask 13. The electrode 12 serves as the cathode for cathode reduction in which the oxide film is selectively reduced to metal with the remaining part left as oxide.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electrode having an oxide film on a portion of its surface, for example, in the process of manufacturing a thin film transistor.

0002

2. Description of the Related Art There is a technique in which an electrode is formed on a substrate, an oxide film is formed on the entire surface of the electrode by anodic oxidation, and a portion of the oxide film is left as an insulating part. Such technology is used, for example, in the process of manufacturing thin film transistors, and an example of its use will be described as follows.

First, the general structure of a thin film transistor will be explained. As shown in FIG. 2, this type of transistor has a gate electrode 2 formed on an insulating substrate 1 made of glass or the like; a covering gate insulating film 3; an i-type semiconductor layer 4 formed on this gate insulating film 3 to face the gate electrode 2; and this i-type semiconductor layer 4.
A source electrode 6s and a drain electrode 6d are formed on both sides of the electrode with an n-type semiconductor layer 5 interposed therebetween.

Note that 7 is a blocking insulating film formed on the channel region of the i-type semiconductor layer 4, and this blocking insulating film 7 is used to remove the i-type semiconductor layer during etching to separate the n-type semiconductor layer 5 at a portion corresponding to the channel region. This is provided to prevent the surface of No. 4 from being etched.

[0005] Such a thin film transistor is manufactured by the following steps. First, a metal film is formed on the substrate 1, and this metal film is patterned by photoetching to form the gate electrode 2. And this gate electrode 2
A gate insulating film 3, an i-type semiconductor layer 4, and a blocking insulating film 7 are sequentially formed thereon, and the blocking insulating film 7 is patterned into a shape corresponding to the channel region of the i-type semiconductor layer 4. The semiconductor layer 4 is patterned into a predetermined shape.

After this, an n-type semiconductor layer 5 is formed on the i-type semiconductor layer 4, and a metal film that will become the source and drain electrodes 6s and 6d is further formed on this n-type semiconductor layer 5. The metal film is patterned to form source and drain electrodes 6s,
6d is formed, and the n-type semiconductor layer 5 is patterned into a shape corresponding to the source and drain electrodes 6s and 6d to complete a thin film transistor.

Since the gate electrode 2 is formed by patterning the metal film formed on the substrate 1 by photo-etching as described above, the periphery of the gate electrode 2 has a pattern corresponding to the film thickness. A difference in height occurs.

[0008] Due to such a step difference, the deposited thickness of the gate insulating film 3 formed on the gate electrode 2 becomes thinner in a portion corresponding to the peripheral edge of the gate electrode 2, and as a result, the insulation in this portion becomes thinner. The breakdown voltage decreases and the gate electrode 2
There is a problem in that short circuits easily occur between the source and drain electrodes 6s and 6d.

Therefore, an insulating oxide film is formed in advance on the peripheral edge of the gate electrode 2. The process of forming such an oxide film will be explained with reference to FIG. 3. First, as shown in FIG. 3(a), a gate electrode 2 is formed on a substrate 1, and then the substrate 1 is placed in an electrolytic solution. Figure 3 (b)
), an oxide film 2a is formed on the entire outer surface of the gate electrode 2.

Next, as shown in FIG. 3C, a resist mask 8 is formed on the substrate 1 and the gate electrode 2 by photolithography except for the central part of the gate electrode 2. The periphery of the gate electrode 2 is covered with. Then, as shown in FIG. 3(d), the oxide film 2a in the central part of the gate electrode 2 is removed by photo-etching, and then, as shown in FIG. 3(e), the resist mask 10 is peeled off. do.

If the gate electrode 2 is subjected to such a treatment, the thickness of the gate insulating film 3 formed on the gate electrode 2 will be equal to that of the peripheral edge of the gate electrode 2, as shown in FIG. Even if it becomes thinner in a portion corresponding to
Short circuits between the two are reliably prevented. In addition, gate electrode 2
Since the portion where the oxide film 2a is removed is exposed, it is possible to connect to the terminal at this portion.

0012

[Problem to be solved by the invention] However, in this way,
In the method of removing the oxide film on the surface of the electrode by photo-etching and leaving a part of it, it is necessary to use a strong acid etching medium for the etching process, as shown in Figs. 2(d) and (e). Thus, during etching, not only the oxide film but also the non-oxidized portion of the electrode underneath the oxide film is etched, and as a result, the characteristics of the electrode may deteriorate.

[0013] The present invention has been made with attention to these points, and its purpose is to maintain a proper state at all times without deteriorating the characteristics of the electrode and to apply it to a part of the surface of the electrode. An object of the present invention is to provide a method of manufacturing an electrode having an oxide film on a part of its surface, which allows the oxide film to remain.

[0014]

[Means for Solving the Problems] In order to achieve the above object, the present invention forms an electrode on a substrate, immerses the substrate in an oxidizing electrolyte, and uses the electrode as an anode. An oxide film is formed on the entire surface of the electrode by anodic oxidation treatment, and then the surface of the oxide film is covered with a resist mask except for a certain area, and in this state, the substrate is placed in a reducing electrolyte. The metal oxide in the oxide film in the certain range is reduced to metal by a cathodic reduction treatment using the electrode as a cathode.

[0015]

[Operation] In this method, the metal oxide in a certain range of the oxide film formed on the entire surface of the electrode is reduced to metal by cathodic reduction treatment, so that only a certain part of the electrode is oxidized. A film remains. Furthermore, since no etching treatment is required, the characteristics of the electrodes will not deteriorate.

[0016]

Embodiment An embodiment of the present invention will be described below with reference to FIG. This example is an example in which an oxide film is formed on a part of the gate electrode of a thin film transistor.

[Step 1] First, as shown in FIG. 1(a),
A metal film such as Ta (tantalum), Ta-Mo (molybdenum) alloy, Cr (chromium), etc. is formed on a substrate 11 made of glass or the like by a sputtering method, and this metal film is patterned by a photoetching method to form an electrode. form 12.

[Step 2] Next, as shown in FIG. 1(b), the substrate 11 is immersed in an oxidizing electrolyte to form an electrode 12.
An oxide film 12a is formed on the entire outer surface of the electrode 12 by performing anodic oxidation using the electrode as an anode.

[Step 3] After this, as shown in FIG. 1(c), a resist mask 13 is formed on the substrate 11 and the electrode 12 except for the central part of the electrode 2, and the resist mask 13 is used to form the electrode. Cover the periphery of 12.

[Step 4] Next, as shown in FIG. 1(d), the substrate 11 is immersed in a reducing electrolyte, and the electrode 1
Cathode reduction treatment is performed under the following reduction conditions using No. 2 as the cathode.

Reduction conditions Electrolyte: Weakly acidic or weakly alkaline solution (for example, citric acid, ammonium borate) Concentration: Below several % Current density: Several mA/cm2 Applied voltage: Determined according to the film thickness of the reduced metal Such a cathode When the reduction treatment is performed, the metal oxide constituting the oxide film 12a is reduced to metal in the part of the oxide film 12a formed on the outer surface of the electrode 12 that is not covered with the resist mask 13, and therefore The oxide film 12a remains only on the peripheral edge of the electrode 12.

[Step 5] Thereafter, as shown in FIG. 1(e), the resist mask 13 is peeled off and removed.

In such a method, the metal oxide in a certain range of the oxide film 12a formed on the entire surface of the electrode 12 is reduced to metal by cathodic reduction treatment, and the electrode 12 is reduced by such reduction treatment. The oxide film 12a is left in some required areas, so unlike the conventional method in which a certain range of the oxide film is removed by etching using a strong acid etching medium, the electrode on the lower layer side of the oxide film is removed. There is no inconvenience such as etching of the electrode, and therefore the characteristics of the electrode can always be kept appropriate and an oxide film can be left on a part of the surface of the electrode.

In the above embodiment, an oxide film is formed on the peripheral edge of the electrode of a thin film transistor. The present invention can be similarly applied to a case where an insulating oxide film is formed on the surface of the electrode except for a certain range.

[0025]

As described above, according to the present invention, the metal oxide in a certain range of the oxide film formed on the entire surface of the electrode is reduced to metal by cathodic reduction treatment, and the electrode Since the oxide film is left on a part of the surface of the electrode, the oxide film can be formed on a part of the surface of the electrode without deteriorating the characteristics of the electrode and always maintaining appropriate characteristics.

[Brief explanation of drawings]

FIG. 1 is a manufacturing process diagram of an electrode according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a conventional thin film transistor.

FIG. 3 is a diagram showing the manufacturing process of a conventional electrode.

[Explanation of symbols]

11...Substrate 12...electrode 12a...Oxide film 13...Resist mask

Claims (1)

[Claims] 1. Forming an oxide film on the entire surface of the electrode by forming an electrode on a substrate and anodizing treatment in which the substrate is immersed in an oxidizing electrolyte and the electrode is used as an anode. a step of covering the surface of the oxide film with a resist mask except for a certain area; and a step of immersing the substrate in a reducing electrolytic solution and performing cathodic reduction treatment using the electrode as a cathode. 1. A method for producing an electrode having an oxide film on a part of its surface, the method comprising the step of reducing the metal oxide of the oxide film in the area to a metal.