JP3947515B2 - Contact hole forming method of active matrix substrate - Google Patents

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.

A contact hole forming method according to claim 1 of the present invention includes:
(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 gas and reaction products adsorbed on the surface of the first chromium electrode can be removed by plasma etching with oxygen gas, and a good contact can be obtained. It becomes like this. Here, in the contact hole forming method, since the processing pressure P of the plasma etching using the oxygen gas is 50 Pa ≦ P ≦ 400 Pa, the effect of the surface treatment is low when the processing pressure is higher than 50 Pa, which is lower than 400 Pa. Since the low vacuum is not at a practical level where oxygen plasma can be obtained on the apparatus, the processing pressure P is preferably 50 Pa ≦ P ≦ 400 Pa.

A contact hole forming method according to claim 2 of the present invention includes:
(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) forming a second electrode and making contact between the second electrode and the first electrode;
A method for forming a contact hole in an active matrix substrate comprising:
In the step (2), after forming the contact hole, the gas and reaction products adsorbed on the surface of the first chromium electrode can be removed by plasma etching with oxygen gas, and a good contact can be obtained. It becomes like this. Here, in the contact hole forming method, the treatment pressure P with the oxygen gas is preferably about 150 Pa ≦ P ≦ 250 Pa because a surface treatment effect is practically easily obtained.

  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.

According to the first aspect of the present invention, there is provided a contact hole forming method according to the present invention, comprising: (1) covering a first electrode made of a chromium film or a chromium compound film provided on a substrate and the substrate; Forming an insulating film; (2) forming a contact hole by dry etching and patterning the insulating film; and (3) forming a second electrode to form the second electrode and the first electrode. A method for forming a contact hole in an active matrix substrate comprising the step of making contact with one electrode, wherein after forming the contact hole in the step (2), plasma is generated in oxygen gas at an appropriate processing pressure. By performing plasma treatment in the etching mode, it is possible to remove deposits on the surface of the chrome electrode resulting from dry etching during contact hole formation. Such contacts take, process pressure P in said oxygen gas is an effect that it surface treatment easily obtained oxygen plasma because it is 50 Pa ≦ P ≦ 400 Pa.

According to the second aspect of the present invention, there is provided a contact hole forming method according to the present invention, comprising: (1) covering a first electrode made of a chromium film or a chromium compound film provided on a substrate and the substrate; Forming an insulating film; (2) forming a contact hole by dry etching and patterning the insulating film; and (3) forming a second electrode to form the second electrode and the first electrode. A method for forming a contact hole in an active matrix substrate comprising the step of making contact with one electrode, wherein after forming the contact hole in the step (2), plasma is generated in oxygen gas at an appropriate processing pressure. By performing plasma treatment in the etching mode, it is possible to remove deposits on the surface of the chrome electrode resulting from dry etching during contact hole formation. Such contacts take, process pressure P in the oxygen gas an effect of easily obtaining an effect of the surface treatment since it is 150 Pa ≦ P ≦ 250 Pa.

  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. That is, a resist hole is formed at a desired position on the gate insulating film 3 and a contact hole is formed by dry etching. The resist is applied at a desired position to a thickness of about 1.6 μm, dried, and baked at 160 ° C. For example, dry etching is performed using a mixed gas of sulfur hexafluoride gas (SF ₆ gas) and oxygen gas under conditions of a pressure of about 16 Pa and a power of about 2000 W, and a hole reaching the gate electrode is formed in the gate insulating film.

  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. During the dry etching process for forming contact holes, the surface of the chromium film is constantly exposed to plasma. If this surface can be etched to some extent with an etching gas, the reactive gas will be removed immediately for the surface of the chromium film, but chromium is hardly etched under the general dry etching conditions for silicon and silicon nitride, Reaction products (hereinafter also referred to as adsorbents) adsorbed on the surface of the chromium film due to gas and dry etching are difficult to remove. These adsorbents cause poor contact with the ITO film and increase contact resistance.

  There are roughly two methods for reducing the amount of adsorbate on the surface of the chromium film. Either to prevent adhesion during etching or to remove the adhering material later.

  First, as a method for preventing adhesion during etching, there is a method in which the ratio of oxygen gas in the etching gas is increased and combined with unnecessary reaction gas and exhausted out of the chamber. This method is simple at first because it only increases the flow rate ratio of the oxygen gas originally contained in the etching gas. However, if the flow rate ratio of oxygen gas is increased, the resist etching rate is increased, resulting in a large pattern shift (deviation between the dimensions of the resist pattern and the etched pattern), or the resist pattern itself disappears during etching. Therefore, it is not applicable unless the insulating film is very thin, that is, when the etching time is short. Also, if the fluorine-based gas in the mixed gas is not a commonly used sulfur hexafluoride gas but a carbon tetrafluoride gas, the amount of adsorption on the surface of the chromium film is small and the contact resistance is 6 This is because the inventors have found that it is about an order of magnitude better than that using sulfur fluoride gas.

When the thickness of the insulating film is about 100 nm, the etching conditions are as follows (RIE indicates reactive ion etching).
Etching mode: RIE
High frequency voltage power supply: 13.56 MHz, 300 W
Etching gas: Treatment pressure of mixed gas of carbon tetrafluoride gas / 30 sccm and oxygen gas / 80 sccm: 5 Pa
Electrode plate interval: 65 mm
Electrode plate temperature: 25 ° C

In Embodiment 1, a mixed gas of carbon tetrafluoride gas (CF ₄ gas) and oxygen gas is used, and the flow rate of oxygen gas is set to be larger than the flow rate of carbon tetrafluoride gas. The flow rate of oxygen gas is preferably 50% to 95% of the total flow rate. Here, the reason for limiting to 50% or more is that the critical ratio for increasing the adsorption amount is this level, and the reason for limiting to 95% or less is that the etching rate of silicon nitride decreases as the ratio of the oxygen gas flow rate increases. At the same time, the etching rate of the resist is increased, and the etching is possible. Furthermore, it is preferable that the content is 70% or more and 95% or less because adsorption hardly occurs.

  In the case of the first embodiment, when an inert gas is further mixed with the mixed gas used for dry etching, the in-plane variation of the etching rate can be reduced and the etching uniformity can be improved. As the inert gas, for example, argon gas or helium gas or both can be used, and the uniformity of etching can be improved by using a readily available gas. When the inert gas is mixed, the flow rate ratio of the oxygen gas in the mixed gas is also 50% or more and 95% or less.

  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
The second embodiment is applied when the thickness of the insulating film made of silicon nitride is about 100 to 400 nm.
Etching mode: RIE
High frequency voltage power supply: 13.56 MHz, 1000 W
Etching gas: Treatment pressure of mixed gas of carbon tetrafluoride gas / 50 sccm and oxygen gas / 60 sccm: 5 Pa
Electrode plate interval: 65 mm
Electrode plate temperature: 25 ° C

  Manufacturing conditions other than the etching conditions shown here and the type of electrode material used are the same as those in the first embodiment, and the same effects as those in the first embodiment can be obtained.

Embodiment 3
In the third embodiment, most of the etching of the insulating film made of silicon nitride, that is, 50% or more and 100% or less of the total etching amount is performed under the conventional etching conditions with a high selectivity to the resist. Second-stage etching and over-etching are performed by increasing the flow rate of oxygen gas. Here, the reason for limiting the etching amount to 50% or more is that if the switching is less than 50%, the resist may not be the second-stage etching, and even from the viewpoint of etching uniformity, the chromium surface is up to 50%. There is almost no risk of getting out. The reason for limiting it to 100% or less is that no adsorbate is deposited on the chromium electrode. This two-stage etching can solve the problems of pattern shift and pattern disappearance.

Conditions such as etching gas for two-stage etching
1st 2nd etching mode (mode): RIE RIE
High frequency voltage power supply: 13.56 MHz, 800 W 13.56 MHz, 300 W
Etching gas: Carbon tetrafluoride gas / Carbon tetrafluoride gas /
250 sccm and oxygen gas / 30 sccm and oxygen gas /
Processing pressure of mixed gas with 110 sccm and mixed gas with 80 sccm: 5 Pa 5 Pa
Electrode plate interval: 65 mm 65 mm
Electrode plate temperature: 25 ° C 25 ° C
As such, the first and second switching points are determined by monitoring the emission intensity of nitrogen with an EPD (end point detector). The second processing time is determined in consideration of the etching rate so as to be a desired amount, for example, an overetching amount of about 20%.

  Manufacturing conditions other than the etching conditions shown here and the type of electrode material used are the same as those in the first embodiment, and the same effects as those in the first embodiment can be obtained.

  Note that any gas may be used as the initial condition, but the amount of reaction product deposited on the chromium surface depends on the initial dry etching conditions. For example, when the first etching is performed under etching conditions mainly composed of sulfur hexafluoride gas, it is difficult to obtain a good contact without post-processing. Also, if the second etching time is too long, the resist will disappear and the amount of pattern shift will increase.

  By such two-stage dry etching, even if the insulating film is thick, the resist pattern is not lost and etching can be performed.

Embodiment 4
As described above, the reaction product is not adsorbed on the chromium film during the etching in the first to third embodiments. However, depending on the processing conditions, it may be difficult to prevent the reaction product from adsorbing on the chromium film. There is. For example, the gate insulating film and the insulating film on the source wiring may be etched at once, and FIG. 2 is a schematic cross-sectional explanatory view showing the contact portion. 2 are the same as those shown in FIG. 1, 5 is a source electrode, 6 is an insulating film, 11 is a gate terminal portion, and 12 is a source terminal portion. . In the case where a contact hole is simultaneously formed in the lowermost gate electrode and an electrode such as a source wiring above the insulating film on the lower layer, after a hole is opened on the upper source wiring electrode, Furthermore, the chromium film of the upper source wiring is exposed to the plasma of the etching gas only for the time for making a hole on the lowermost chromium film (almost double time). In such a case, post-processing is required.

In the contact hole forming method described in Embodiments 4 and 5, oxygen plasma treatment is further performed after etching. The conditions for the oxygen plasma treatment are as follows.
Etching mode: PE
High frequency voltage power supply: 13.56 MHz, 1500 W
Etching gas: Oxygen gas / 500 sccm
Gas processing pressure: 200Pa
Electrode plate interval: 65 mm
Electrode plate temperature: 25 ° C
Processing time: 30 sec

  This oxygen plasma treatment has a different purpose and effect from the so-called light ashing that has been performed conventionally. Conventional oxygen plasma treatment has been performed for the purpose of removing a part of the resist surface layer damaged during dry etching. In this case, since the condition was determined only by the ashing amount of the resist, the contact resistance was often increased.

  At this time, the treatment pressure P with oxygen plasma is preferably 50 Pa ≦ P ≦ 400 Pa. The reason for limiting the vacuum to higher than 400 Pa is that it can be easily realized by the apparatus, and the reason for limiting to a vacuum lower than 50 Pa is to lower the contact resistance. Within this range, oxygen plasma can be obtained without requiring modification of conventional equipment, and contact resistance can be lowered. Within this range, a processing pressure of about 150 Pa ≦ P ≦ 250 Pa is practically easy to obtain a surface treatment effect, so that the contact resistance can be easily lowered.

Embodiment 5
In the fourth embodiment, the oxygen plasma treatment is performed in the plasma etching mode, but the treatment may be performed in a reactive ion etching (hereinafter referred to as RIE) mode instead of the plasma etching mode. Other conditions for processing in the RIE mode are the same as those in the fourth embodiment. An example of processing conditions in the RIE mode will be shown.
Etching mode: RIE
High frequency voltage power supply: 13.56 MHz, 1000 W
Etching gas: Oxygen gas / 500 sccm
Gas processing pressure: 200Pa
Electrode plate interval: 135 mm
Electrode plate temperature: 25 ° C
Processing time: 30 sec

  At this time, the treatment pressure P with oxygen gas is preferably 100 Pa ≦ P ≦ 400 Pa. The optimum processing pressure is determined according to other parameters such as the RF power of the power source and the ashing rate of the resist. The reason for limiting the vacuum to higher than 400 Pa is that it can be easily realized by the apparatus, and the reason for limiting to a vacuum lower than 100 Pa is to reduce the contact resistance. Further, it is particularly preferable that the contact resistance can be lowered by setting the treatment pressure P with oxygen plasma to 150 ≦ P ≦ 250 Pa. By subjecting the electrode surface of the contact hole to surface treatment with oxygen plasma in this way, the reactant formed on the surface can be removed, and a good contact with a low value can be obtained.

  FIG. 3 shows the influence of the treatment pressure of oxygen gas on the contact resistance with respect to the contact resistance between the chromium film and the ITO film at 35 μm square after the oxygen plasma treatment in the RIE mode. According to FIG. 3, the contact resistance varies considerably depending on the oxygen plasma conditions, and lower vacuum results in lower resistance. FIG. 4 shows the relationship between oxygen plasma treatment time and contact resistance. According to FIG. 4, it can be seen that there is a case where a sufficient effect cannot be obtained in a short time, and processing of about 30 seconds is necessary. This required time also varies depending on the etching conditions when forming the contact hole. Contactability is also affected by the RF power of the oxygen plasma. Moreover, once the contact resistance is increased by the oxygen plasma treatment, the contact resistance may not be improved even after the additional plasma treatment. Care must be taken in the conditions of the oxygen plasma treatment here. It is. In addition, this process can be continuously processed after etching in the same processing chamber of the same processing apparatus, or can be performed by moving from another processing chamber of the same processing apparatus or once out of vacuum to another processing apparatus, The same effect can be obtained.

  In Embodiments 4 and 5, it is assumed that the time for which the chromium film surface is exposed to etching is long, but it is of course also effective when the insulating film is thin.

Embodiment 6
The active matrix substrate manufactured according to the contact hole forming method described in Embodiments 1 to 5 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 any one of the methods described in the first to fifth 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 to fifth 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, which is low. The effect that contact 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 (2)

(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 the contact hole is formed by dry etching, the contact hole is surface-treated by plasma etching with oxygen gas ,
(4) A method for forming a contact hole in an active matrix substrate, wherein the processing pressure P with the oxygen gas is 50 Pa ≦ P ≦ 400 Pa . (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 the contact hole is formed by dry etching, the contact hole is surface-treated by plasma etching with oxygen gas ,
(4) A method for forming a contact hole in an active matrix substrate, wherein the processing pressure P with the oxygen gas is 150 Pa ≦ P ≦ 250 Pa .

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