JP2007108780A - Contact hole formation method for active matrix substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a contact hole formation method of an active matrix substrate in which a low contact resistance can be obtained. <P>SOLUTION: The contact hole formation method includes (1) a process for forming an insulating film by covering a first electrode provided on a substrate and the substrate, (2) a process for forming a contact hole by patterning the insulating film by dry etching, and (3) a process for forming a second electrode and obtaining contact between the second electrode and the first electrode. After the contact hole is formed by dry etching in the process (2), the contact hole has its surface treated by plasma etching using oxygen gas. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for forming a contact hole in an insulating film or a semiconductor film formed on an insulating substrate. More specifically, the present invention relates to a hole (hereinafter referred to as a contact hole) for electrical contact between an electrode made of chromium or a chromium compound and an upper electrode formed on an insulating substrate as an active matrix substrate used in a liquid crystal display device. ) And a processing method after dry etching.

  In a matrix type liquid crystal display device, a liquid crystal is usually sandwiched between two substrates, a substrate provided with a thin film transistor (hereinafter referred to as TFT) made of a semiconductor thin film and a counter substrate. On the other hand, a voltage is selectively applied to each pixel. On the counter substrate, a counter electrode, a color filter, and a black matrix are provided. A liquid crystal display (hereinafter referred to as LCD) using such a TFT array substrate is hereinafter referred to as TFT-LCD.

  The TFT array substrate is provided with at least TFTs and pixel electrodes in a matrix for each pixel on an insulating substrate made of glass or the like. In addition, an alignment film and a storage capacitor as necessary are provided, and gate wiring and source Signal lines such as wiring are provided.

  In order to manufacture a liquid crystal display device using such a TFT array substrate, TFTs, gate wirings, source wirings and other common wirings are formed in an array on a glass substrate to form a display area, and input terminals, spares Wiring and driving circuits are arranged around the display area. At this time, a conductive film or an insulating film is provided as necessary in order to develop each function. A counter electrode is provided on the counter substrate, and a color filter and a black matrix are provided.

  After producing the TFT array substrate and the counter substrate, the two substrates are bonded together around the two substrates in a state having a desired gap so that the liquid crystal material can be injected between the two substrates. After that, a liquid crystal display device is manufactured by injecting a liquid crystal material into a gap between two substrates.

  Various semiconductor devices and solid-state devices are provided on TFT array substrates and counter substrates used in liquid crystal display devices by utilizing so-called thin film technology. In these semiconductor devices and solid-state devices, semiconductor films, insulating films, and conductive films are used.

In a liquid crystal display device, in order to contact a pixel and a gate wiring, to contact a pixel and a source wiring, to contact a pixel and a drain wiring, and to contact each other In addition, a contact hole is provided at a necessary location via an interlayer insulating film. A dry etching method is used to form a contact hole that penetrates the interlayer insulating film. As a gas for dry etching, SF ₆ gas, CF ₄ gas, or a mixed gas of these gases with oxygen gas or inert gas is often used. Of these, a combination of sulfur hexafluoride gas and oxygen gas is the most common from the viewpoint of etching rate and selectivity with the underlying film.

  Regarding the formation of the contact hole, a contact hole having a tapered hole shape is usually formed by controlling the ratio of the etching rate of the photoresist to the target film.

  At this time, a gas in which oxygen gas is mixed with fluorine gas is used. However, if the flow ratio of oxygen gas is increased, the resist is etched faster, and the contact hole size may increase or the resist pattern may disappear during etching. The oxygen gas flow rate is suppressed to be equal to or lower than the flow rate of other mixed gases. Also, immediately after etching, oxygen plasma treatment is generally performed to remove the damaged layer on the resist surface.

  A film made of chromium (hereinafter referred to as a chromium film) is hardly etched under the etching conditions of the insulating film (SiN). For this reason, gas is adsorbed on the surface of the chromium film, and reaction products due to etching are reattached. Therefore, when a conductive film made of ITO was formed on the contact hole, good contact between the chromium film and the ITO film could not be obtained.

  When another film made of the same chromium is formed on the chromium film, the electrical resistance value is often low when the same material is contacted through the contact hole. Depending on the device, the resistance value may be several kΩ. Therefore, it has not been a problem until now. However, when a chrome film wiring is formed and an ITO film is formed at the end through another process, and contact is made, the contact resistance is about several MΩ by simply applying the conventional dry etching conditions. It becomes extremely high and cannot be used. Also, due to problems with the panel characteristics, such as improving display characteristics, it has become necessary to reduce the resistance value by several digits from several kΩ.

  As a result of the investigation by the inventors, among the combinations of wiring materials to be contacted through the contact hole, the lower layer side is a material that is hardly etched under the etching conditions for the insulating film, such as chromium, and the upper layer side is made of ITO or aluminum. Thus, it has been found that the contact resistance is particularly high when different materials are combined on the upper layer side and the lower layer side.

  It is an object of the present invention to provide a method for forming a contact hole in an active matrix substrate that can solve such a conventional problem and obtain a low contact resistance.

  In particular, as a result of studies for reducing the contact resistance between the chromium film and the ITO film, it has been found that the contact resistance can be significantly reduced depending on the etching conditions and post-treatment conditions after etching.

  It has been found that plasma treatment with oxygen after etching is effective as one of such post-treatment conditions. The effect of the plasma treatment is characterized by a strong dependence on the treatment pressure. It has been found that conventional resist ashing conditions often involve increasing the resistance because only the peeling of the damaged resist surface layer is considered. Therefore, it is necessary to review the resist ashing conditions. In particular, once the oxygen plasma treatment is performed to increase the contact resistance, it is very difficult to restore or lower the resistance value by using a dry etching apparatus alone.

  As means for not controlling the contact resistance by dry etching (for example, when the contact resistance is increased), there is a case where the wet treatment is effective. However, it has also been found that even when wet processing is performed, it is not possible to obtain a favorable result by processing with an etching solution in which chromium is etched, and an etching solution containing an oxidizing agent must be used.

  Further, when the above-described means cannot be taken due to restrictions such as the number of processed sheets in the mass production process, the problem can be solved by increasing the oxygen gas flow rate among the dry etching conditions. However, there are restrictions due to reasons such as hole size and taper angle, and it may be better to add oxygen plasma treatment.

  By performing the plasma treatment in this way, the gas or product adhering to the surface of the chromium electrode is reduced or eliminated, and good contact with the ITO film on the upper layer side and other conductors can be obtained.

In another contact hole forming method according to the present invention, the contact hole forming method according to claim 1 comprises:
(1) a step of forming an insulating film so as to cover the first electrode provided on the substrate and the substrate;
(2) a step of dry etching and patterning the insulating film to form a contact hole;
(3) A method for forming a contact hole in an active matrix substrate comprising a step of forming a second electrode and making a contact between the second electrode and the first electrode,
In the step (2), after forming the contact hole, by treating the electrode surface of the contact hole with a mixed solution of cerium ammonium nitrate and nitric acid, the number of steps increases, but the contact resistance can be reduced. The effect is great.

  According to the present invention, a good contact can be realized even when silicon nitride as an insulating film is formed on a chromium film, contact holes are formed by dry etching, and an ITO film is formed.

  In another contact hole forming method according to the first aspect of the present invention, in the step (2), after forming the contact hole, the contact hole is wetted with a mixed solution of cerium ammonium nitrate and nitric acid. When processed, the contact resistance can be lowered regardless of plasma processing conditions such as dry etching and resist ashing.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Embodiment 1
First, an active matrix substrate and a method for forming a contact hole in the active matrix substrate according to an embodiment of the present invention will be described. FIG. 1 is an explanatory cross-sectional view showing the structure of a contact hole in an active matrix substrate. In the figure, 1 is an insulating substrate, 2 is a gate electrode of a chromium film as a first electrode, 3 is an insulating film provided as a gate insulating film, and 4 is a transparent conductive film. The film is patterned to form a pixel electrode which is a second electrode. Note that in this embodiment mode, a structure in which a semiconductor film is not provided over an insulating film or the like has been described. In this case, the contact hole may also penetrate the semiconductor film. However, the contact hole forming method described below can be applied to the case of penetrating the semiconductor film.

  Next, a method for forming the contact hole shown in the contact portion will be described according to the manufacturing process of the contact portion.

  First, as a first step, a gate insulating film is formed on the gate electrode 2 formed on the insulating substrate 1. The insulating substrate 1 is, for example, a glass plate, and has a size of 370 mm × 470 mm and a thickness of about 0.7 mm. The gate electrode 2 is provided for inputting a scanning signal to the pixel, and is made of, for example, chromium or a chromium compound. Thus, a thickness of about 400 nm is formed at a desired position by sputtering. The gate insulating film 3 is made of, for example, silicon nitride, and is formed to a thickness of about 400 nm by CVD to cover the entire surface of the insulating substrate 1 where the gate electrode and the gate electrode are not formed. As a material for the gate insulating film, silicon oxide or the like can be similarly used instead of silicon nitride.

  Next, as a second step, a contact hole is formed by a so-called photolithography technique.

  Next, as a third step, the conductive film 4 is formed and further patterned by photolithography technique to make contact between the gate electrode and the pixel electrode through the contact hole. The conductive film is, for example, ITO, and is formed to a thickness of about 100 nm by sputtering.

  In this embodiment, the case where the second electrode is a transparent conductive film made of ITO has been described. However, even when chromium or aluminum is used as the material of the second electrode, it is lower than before. Contact resistance can be obtained.

Embodiment 2
In the method of the second embodiment, after the usual dry etching, the substrate subjected to dry etching is put into a mixed solution of cerium ammonium nitrate and nitric acid to clean the chromium surface. In this case, it is usually performed immediately after dry etching, but there is no particular problem even after the resist is removed. Note that it is impossible to reduce contact resistance with a mixed solution of cerium ammonium nitrate and perchloric acid, which is generally used as an etching solution for chromium. However, if a mixed solution of cerium ammonium nitrate and nitric acid is used, the deposits can be removed. Although the detailed mechanism is not known, among other etchants that can etch the chromium film, there are some that can remove deposits and surface layers and ensure good contact.

  In this case, since the chromium film is etched, it must be controlled to remove only the surface layer so as not to disappear.

Embodiment 3
The active matrix substrate manufactured according to the contact hole forming method described in Embodiments 1 and 2 and a liquid crystal display device using the active matrix substrate are described above.

  The configuration and manufacturing method of the active matrix substrate and the liquid crystal display device using the active matrix substrate are the same as those according to the prior art.

  For example, a chromium film is formed on an insulating substrate and patterned. A silicon nitride film as a gate insulating film and a silicon film as a semiconductor layer are formed thereon by CVD, and the silicon film is patterned so that it exists only in the TFT portion and the vicinity thereof. A chromium film as a source / drain electrode is formed thereon and patterned. An insulating film is formed thereon, and a contact hole is formed by one of the methods described in the first and second embodiments. Then, an ITO film that is a pixel electrode is formed and patterned to complete an active matrix substrate. Since the contact holes are formed using the methods of the first and second embodiments, the contact resistance is low, and a process for manufacturing an active matrix substrate with a structure in which an ITO film or the like is directly contacted on a chromium film is possible. The effect that resistance was realizable was acquired. In addition, the liquid crystal display device using the active matrix substrate according to the present invention has an effect that it has excellent quality free from the occurrence of defects related to contact resistance.

FIG. 3 is a cross-sectional explanatory view showing a contact portion of an active matrix substrate according to the present invention. It is a schematic cross-sectional explanatory view showing a contact portion when the gate insulating film and the insulating film on the source electrode are etched at once. It is a graph which shows the relationship between an oxygen plasma processing pressure and contact resistance. It is a graph which shows the relationship between oxygen plasma processing time and contact resistance.

Explanation of symbols

  1 insulating substrate, 2 gate electrode, 3 gate insulating film, 4 conductive film, 5 source electrode, 6 insulating film.

Claims (1)

(1) a step of forming an insulating film so as to cover the first electrode made of a chromium film or a chromium compound film provided on the substrate and the substrate;
(2) a step of dry etching and patterning the insulating film to form a contact hole;
(3) A method for forming a contact hole in an active matrix substrate comprising a step of forming a second electrode and making a contact between the second electrode and the first electrode,
In the step (2), after forming the contact hole, the contact hole forming method for an active matrix substrate, wherein the electrode surface of the contact hole is treated with a mixed solution of cerium ammonium nitrate and nitric acid.

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