JP2004111991A - Contact hole formation method for active matrix substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a contact hole formation method for an active matrix substrate that can obtain a low contact resistance. <P>SOLUTION: The contact hole formation method for an active matrix comprises the steps of (1) forming an insulating film by coating a first electrode provided on a substrate as well as the substrate, (2) forming a contact hole by dry-etching the insulating film for patterning, and (3) forming a second electrode, and bringing the second electrode into contact with the first electrode. The step (2) enables the formation of the contact hole by dry-etching, and then, a surface-treatment for the contact hole by the plasma etching using oxygen gas. <P>COPYRIGHT: (C)2004,JPO

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

In a matrix type liquid crystal display device, a liquid crystal is sandwiched between a substrate provided with a thin film transistor (hereinafter, referred to as a TFT) composed of a semiconductor thin film and a counter substrate, and a liquid crystal is sandwiched between the substrates. In contrast, the configuration is such that a voltage is selectively applied to each pixel. A counter electrode, a color filter, and a black matrix are provided on the counter substrate. A liquid crystal display (LCD) using such a TFT array substrate is hereinafter referred to as a 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, and further includes an alignment film and, if necessary, a storage capacitor, a gate wiring and a source. A signal line such as a wiring is provided.

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 and spares. Wiring and driving circuits are arranged around the display area. At this time, a conductive film or an insulating film is provided as needed in order to exert each function. Further, a counter electrode is provided on the counter substrate, and a color filter and a black matrix are provided.

(4) After manufacturing the TFT array substrate and the counter substrate, the two substrates are bonded together in a state having a desired gap so that a liquid crystal material can be injected between the two substrates. After that, a liquid crystal material is injected into a gap between the two substrates to manufacture a liquid crystal display device.

ＴＦＴVarious semiconductor devices and solid-state devices are provided on a TFT array substrate and a counter substrate used for a liquid crystal display device using a so-called thin film technology. Semiconductor films, insulating films, and conductive films are used in these semiconductor devices and solid-state devices.

In a liquid crystal display device, in order to make a contact between a pixel and a gate wiring, to make a contact between a pixel and a source wiring, to make a contact between a pixel and a drain wiring, and to make a wiring contact. Then, a contact hole is provided at a necessary place via an interlayer insulating film. A dry etching method is used to form a contact hole penetrating the interlayer insulating film. As a gas for dry etching, SF ₆ gas, CF ₄ gas, or a mixed gas of these gases with an oxygen gas or an inert gas is often used. Among them, a combination of a sulfur hexafluoride gas and an oxygen gas is most common from the viewpoints of an etching rate and selectivity with respect to a base film.

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

At this time, a gas in which oxygen gas is mixed with fluorine gas is used, but if the flow rate ratio of oxygen gas is increased, the resist is quickly etched, and the contact hole size may be increased or the resist pattern may be lost during etching. In addition, the flow rate of the oxygen gas is controlled to be lower than the flow rate of the other mixed gas. Immediately after etching, oxygen plasma treatment is generally performed to remove a damaged layer on the resist surface.

膜 A film made of chromium (hereinafter, referred to as a chromium film) is hardly etched under the etching condition of the insulating film (SiN). Therefore, a gas is adsorbed on the surface of the chromium film, or a reaction product by etching is re-adhered to the chromium film. 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.

(4) In the case where the same material is contacted through a contact hole as in the case of forming another film made of the same chromium on the chromium film, the electric resistance value is often low. Further, the resistance value may be several kΩ depending on the device. Therefore, it has not been a problem in particular. However, if a chromium film wiring is formed, an ITO film is formed at the end of another process, and a contact is made, a contact resistance of about several MΩ can be obtained by simply applying the conventional dry etching conditions. It becomes extremely high and cannot be used. Further, from the viewpoint of the characteristics of the panel, such as increasing the display characteristics, it is necessary to reduce the resistance value from several kΩ to one or more digits.

As a result of the investigations by the inventors, among the combinations of wiring materials contacted through the contact holes, the lower layer is a material which is hardly etched under the etching conditions for the insulating film, such as chromium, and the upper layer is a material such as ITO or aluminum. As described above, it was found that the contact resistance was particularly high when a combination of different materials was used on the upper layer side and the lower layer side.

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

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

プ ラ ズ マ It was found that plasma treatment with oxygen after etching was effective as one of such post-treatment conditions. The effect of the plasma processing is characterized by a strong dependence on the processing pressure. It was also found that the conventional resist ashing conditions often increase 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 reduce the resistance value by using the dry etching apparatus alone.

し な い As a means of not controlling the contact resistance by dry etching (for example, when the contact resistance is increased), there is a case where wet processing is effective. However, it has also been found that even in the case of wet treatment, favorable results cannot be obtained even if the treatment is carried out simply by using an etching solution for etching chromium, and that an etching solution containing an oxidizing agent must be used.

あ い In addition, if the above means cannot be taken due to restrictions on the number of processed wafers in the mass production process, the problem can be solved by increasing the oxygen gas flow rate in the dry etching conditions. However, there is a restriction due to reasons such as a hole size and a taper angle, and in some cases, it is better to add an oxygen plasma treatment.

プ ラ ズ マ By the plasma treatment, gas or products adhering to the surface of the chromium electrode is reduced or eliminated, and good contact with the upper ITO film or other conductor is obtained.

The contact hole forming method according to claim 1 of the present invention comprises:
(1) forming an insulating film over the first electrode provided on the substrate and the substrate;
(2) 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 the steps of: forming a second electrode and making contact between the second electrode and the first electrode;
In the step (2), after the contact hole is formed, a gas or a reaction product adsorbed on the surface of the first chromium electrode can be removed by plasma etching using an oxygen gas, and a good contact can be obtained. Become like

In the contact hole forming method according to claim 2 of the present invention, 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. If the vacuum is lower than 400 Pa, the apparatus is not at a practical level at which oxygen plasma can be obtained on the apparatus. Therefore, the processing pressure P is preferably set to 50 Pa ≦ P ≦ 400 Pa.

In the contact hole forming method according to the third aspect of the present invention, it is preferable that the processing pressure P of the oxygen gas is about 150 Pa ≦ P ≦ 250 Pa because the surface treatment effect is easily obtained in practical use.

In the contact hole forming method according to claim 4 of the present invention, the surface treatment can be performed in the same processing chamber as the processing chamber of the processing apparatus in which the step (2) is performed.

In the contact hole forming method according to claim 5 of the present invention, the surface treatment may be performed in a processing chamber different from or in a processing chamber of a processing apparatus in which the step (2) is performed.

Further, the method for forming a contact hole according to claim 6 of the present invention includes:
(1) forming an insulating film over the first electrode provided on the substrate and the substrate;
(2) 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 the steps of: forming a second electrode and making contact between the second electrode and the first electrode;
In the step (2), after the contact hole is formed, the contact hole is formed by reactive ion etching (hereinafter, also abbreviated as RIE) with an oxygen gas at a processing pressure P of 100 Pa ≦ P ≦ 400 Pa. Can also lower the contact resistance.

に お い て In the contact hole forming method according to claim 7 of the present invention, it is preferable to perform the treatment with the oxygen gas at a processing pressure P of 150 Pa ≦ P ≦ 250 Pa, since the effect is high, and thus it is preferable.

In the contact hole forming method according to claim 8 of the present invention, even when the surface treatment is performed by reactive ion etching, the surface treatment can be performed in the processing chamber of the processing apparatus in which the step (2) is performed.

In the contact hole forming method according to the ninth aspect of the present invention, the surface treatment may be performed in a processing chamber different from or in a processing chamber of a processing apparatus in which the step (2) is performed.

In another method for forming a contact hole according to the present invention, the method for forming a contact hole according to claim 10 is characterized in that:
(1) forming an insulating film over the first electrode provided on the substrate and the substrate;
(2) 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 the steps of: forming a second electrode and making contact between the second electrode and the first electrode;
In the step (2), after forming the contact hole, the electrode surface of the contact hole is treated with a mixed solution of cerium ammonium nitrate and nitric acid, thereby increasing the number of steps but reducing contact resistance. The effect is great.

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

According to the first aspect of the present invention, there is provided a method for forming a contact hole according to the present invention, comprising the steps of: (1) forming a first electrode provided on a substrate and forming an insulating film over the substrate; (2) a step of forming a contact hole by dry-etching and patterning the insulating film; and (3) forming a second electrode to make contact between the second electrode and the first electrode. Forming a contact hole in the active matrix substrate in the step (2). After forming the contact hole in the step (2), the contact hole is subjected to plasma processing in an oxygen gas at a suitable processing pressure in a plasma etching mode. In addition, it is possible to remove deposits on the surface of the chromium electrode formed by dry etching at the time of forming a contact hole, and obtain an effect that a good contact can be obtained. To.

According to the second aspect of the present invention, since the processing pressure P with the oxygen gas is 50 Pa ≦ P ≦ 400 Pa, there is an effect that oxygen plasma can be easily obtained and surface treatment can be performed.

According to the third aspect of the present invention, since the processing pressure P with the oxygen gas is 150 Pa ≦ P ≦ 250 Pa, the effect of the surface treatment can be easily obtained.

According to the invention described in claim 4 of the present invention, the surface treatment can be performed in the same processing chamber as the processing chamber of the processing apparatus in which the step (2) is performed, and the effect of obtaining a low-resistance contact can be obtained. Play.

According to the invention described in claim 5 of the present invention, the surface treatment can be performed in one of a processing chamber different from the processing chamber of the processing apparatus in which the step (2) is performed and another processing apparatus. And has the effect of obtaining a low-resistance contact.

Another contact hole forming method according to the invention described in claim 6 of the present invention is as follows.
In the step (2), after forming the contact hole, the surface of the chromium electrode formed by dry etching at the time of forming the contact hole is subjected to plasma processing in a reactive ion etching mode at an appropriate processing pressure in oxygen gas. This has the effect of removing adhering substances and providing good low contact.

According to the invention of claim 7 of the present invention, when the processing pressure P with the oxygen gas is 150 Pa ≦ P ≦ 250 Pa, there is an effect that surface treatment can be performed with high efficiency.

According to the invention of claim 8 of the present invention, the surface treatment can be performed in the same processing chamber as the processing chamber of the processing apparatus in which the step (2) is performed, and the effect of obtaining a low-resistance contact can be obtained. Play.

According to the ninth aspect of the present invention, the surface treatment may be performed in one of a processing chamber different from the processing chamber of the processing apparatus in which the step (2) is performed and another processing apparatus. And has the effect of obtaining a low-resistance contact.

According to another method for forming a contact hole according to claim 10 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 the treatment is performed, there is an effect that the contact resistance can be reduced 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 of forming contact holes in the active matrix substrate according to one embodiment of the present invention will be described. FIG. 1 is an explanatory sectional view showing a 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, 4 is a transparent conductive film, and The film is patterned to form a pixel electrode as a second electrode. Note that in this embodiment, a structure in which a semiconductor film is not provided over an insulating film or the like is described; however, a semiconductor film may be provided in consideration of the design of a TFT array substrate. In this case, the contact hole may also penetrate the semiconductor film. However, the method for forming the contact hole described below can be applied to the case where the contact hole also penetrates the semiconductor film.

Next, a method for forming the contact hole shown in the contact portion will be described in accordance with 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 about 370 mm × 470 mm and a thickness of about 0.7 mm. The gate electrode 2 is provided for inputting a scanning signal to a pixel. In this manner, a film is formed at a desired position with a thickness of about 400 nm by a sputtering method. The gate insulating film 3 is made of, for example, silicon nitride, and is formed to a thickness of about 400 nm by a CVD method so as 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 used instead of silicon nitride.

Next, as a second step, a contact hole is formed by a so-called photolithography technique. That is, a contact pattern 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 to a desired position to a thickness of about 1.6 μm, dried, and baked at 160 ° C. The dry etching is performed using, for example, 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 2,000 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 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 a sputtering method. During the dry etching process for forming the contact hole, the surface of the chromium film is constantly exposed to the plasma. If this surface can be etched to some extent with an etching gas, the reaction gas is also immediately removed from the surface of the chromium film.However, since chromium is hardly etched under general dry etching conditions for silicon and silicon nitride, It is difficult to remove gas or reaction products by dry etching (hereinafter also referred to as adsorbed substances) adsorbed on the surface of the chromium film. These adsorbed substances cause poor contact with the ITO film, resulting in an increase in contact resistance.

考 え 方 There are roughly two ways to reduce the amount of adsorbed substances on the surface of the chromium film. Either do not adhere during etching or remove the adhered matter later.

{Circle around (1)} First, as a method for preventing adhesion during the etching, there is a method in which the ratio of oxygen gas in the etching gas is increased to combine with an unnecessary reaction gas and exhaust the gas to the outside of the chamber. This method is a seemingly simple method because the flow rate ratio of the oxygen gas originally contained in the etching gas is slightly increased. However, if the flow rate ratio of the oxygen gas is increased, the etching rate of the resist increases, and the pattern shift (the deviation between the dimensions of the resist pattern and the etched pattern) increases, or the resist pattern itself disappears during the etching. Therefore, it is not applicable unless the insulating film is very thin, that is, if the etching time is short. Further, the fluorine-based gas in the mixed gas is not a commonly used sulfur hexafluoride gas but a carbon tetrafluoride gas because 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.

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

In the first embodiment, 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 higher than the flow rate of carbon tetrafluoride gas. The flow rate of the oxygen gas is preferably 50% or more and 95% or less of the total flow rate. Here, the reason for limiting to 50% or more is that the critical ratio at which the amount of adsorption increases is this level, and the reason for limiting to 95% or less is that when the ratio of the flow rate of oxygen gas increases, the etching rate of silicon nitride decreases. At the same time, the etching rate of the resist increases, and the etching is at a possible limit. Further, the content is preferably set to 70% or more and 95% or less in that the adsorption hardly occurs.

In addition, in the case of Embodiment 1, if 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 uniformity of the etching can be improved. As the inert gas, for example, an argon gas or a helium gas or both of them can be used, and the uniformity of etching can be improved by using an easily available gas. When the inert gas is mixed, the flow 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, the second electrode is lower than before. Contact resistance can be obtained.

Embodiment 2
Embodiment 2 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: processing pressure of mixed gas of carbon tetrafluoride gas / 50 sccm and oxygen gas / 60 sccm: 5 Pa
Electrode plate interval: 65mm
Electrode plate temperature: 25 ° C

(4) Manufacturing conditions other than the etching conditions shown here, the types of electrode materials to be used, and the like are the same as those of the first embodiment, and the same effects as those of 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 condition having a large selectivity with respect to the resist. Second-stage etching and over-etching are performed by increasing the flow rate of oxygen gas. Here, the reason why the etching amount is limited to 50% or more is that if the switching is performed at less than 50%, the resist may not be etched in the second step, and the chromium surface may be reduced to 50% from the viewpoint of uniformity of etching. There is almost no risk of leaving. The reason for limiting the content to 100% or less is to prevent adsorbed substances from being formed on the chromium electrode. The two-stage etching can solve the problems of pattern shift and pattern disappearance.

The conditions such as the etching gas for the two-step etching are first second 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 mixed gas with 80 sccm: 5 Pa 5 Pa
Electrode plate interval: 65mm 65mm
Electrode plate temperature: 25 ° C 25 ° C
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 an etching rate so as to be a desired amount, for example, an over-etching amount of about 20%.

(4) Manufacturing conditions other than the etching conditions shown here, the types of electrode materials to be used, and the like are the same as those of the first embodiment, and the same effects as those of the first embodiment can be obtained.

Note that any gas may be used for the first condition, but the amount of the reaction product adhering to the chromium surface depends on the first dry etching condition. For example, when the first etching is performed under etching conditions mainly containing sulfur hexafluoride gas, it is difficult to obtain a good contact without post-processing. On the other hand, if the second etching time is too long, the resist will be lost or the amount of pattern shift will increase.

{Circle around (2)} By such two-stage dry etching, an effect is obtained in which etching can be performed without loss of the resist pattern even when the insulating film is thick.

Embodiment 4
As described above, in the first to third embodiments, the reaction product is not adsorbed on the chromium film during the etching. However, depending on the processing conditions, it is quite difficult to prevent the reaction product from being adsorbed on the chromium film. There is. For example, there is a case where the gate insulating film and the insulating film on the source wiring are etched at one time, and FIG. 2 is a schematic sectional explanatory view showing the contact portion. The reference numerals shown in FIG. 2 are the same as 1 to 4 shown in FIG. 1, 5 is a source electrode, 6 is an insulating film, 11 is a gate terminal, and 12 is a source terminal. . For example, when a contact hole is formed simultaneously in the lowermost gate electrode and an electrode such as a source wiring further above the insulating film, a hole is opened in the upper source wiring electrode, and so on. Furthermore, the chromium film of the upper source wiring is exposed to the plasma of the etching gas only for the time required to make a hole on the lowermost chromium film (almost twice as long). In such a case, post-processing is required.

In the contact hole forming methods described in the fourth and fifth embodiments, oxygen plasma treatment is further performed after etching. The conditions of the oxygen plasma treatment are shown below.
Etching mode: PE
High frequency voltage power supply: 13.56 MHz, 1500 W
Etching gas: oxygen gas / 500 sccm
Gas processing pressure: 200 Pa
Electrode plate interval: 65mm
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 conventionally performed. Conventionally, the oxygen plasma treatment is performed for the purpose of removing a part of the surface layer of the resist damaged during the dry etching. In this case, since the conditions were determined only by the ashing amount of the resist, there were many cases where the contact resistance was increased.

In this embodiment, after a contact hole is formed by dry etching, oxygen plasma is generated by introducing oxygen gas in the same device or another device, and oxygen plasma is used for surface treatment of an electrode of the contact hole. do. In addition to the oxygen plasma processing conditions described in the present embodiment, in this embodiment, dry etching for forming a contact hole may be performed under any conditions. The other manufacturing conditions and the types of electrode materials to be used are the same as in the first embodiment.

At this time, it is preferable that the processing pressure P in the oxygen plasma is 50 Pa ≦ P ≦ 400 Pa. The reason for limiting the vacuum to higher than 400 Pa is the limit that can be easily realized by the apparatus, and the reason for limiting the vacuum to lower than 50 Pa is to reduce the contact resistance. Within this range, oxygen plasma can be obtained without the need for modification of conventional equipment, and the contact resistance can be reduced. Even 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 reduced.

In addition, this processing may be performed continuously after etching in the same processing chamber of the same processing apparatus, or may be performed in another processing chamber of the same processing apparatus, or once in a vacuum and transferred to another processing apparatus. And the same effect can be obtained.

Embodiment 5
In the fourth embodiment, the oxygen plasma processing is performed in the plasma etching mode, but the processing 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 in the fourth embodiment. An example of processing conditions in the RIE mode will be described.
Etching mode: RIE
High frequency voltage power supply: 13.56 MHz, 1000 W
Etching gas: oxygen gas / 500 sccm
Gas processing pressure: 200 Pa
Electrode plate interval: 135mm
Electrode plate temperature: 25 ° C
Processing time: 30 sec

At this time, it is preferable that the processing pressure P with the oxygen gas is 100 Pa ≦ P ≦ 400 Pa. The processing pressure determines an optimum value according to other parameters such as the RF power of the power supply and the ashing rate of the resist. The reason why the vacuum is limited to higher than 400 Pa is the limit that can be easily realized by the apparatus, and the reason that the vacuum is set to be lower than 100 Pa is to reduce the contact resistance. Furthermore, it is particularly preferable that the contact resistance can be reduced by setting the processing pressure P in the oxygen plasma to 150 ≦ P ≦ 250 Pa. By treating the surface of the electrode in the contact hole with the oxygen plasma in this manner, a 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 oxygen gas treatment pressure on the contact resistance between the chromium film and the ITO film at 35 μm square after oxygen plasma treatment in the RIE mode. According to FIG. 3, the contact resistance varies considerably depending on the oxygen plasma conditions, and a lower vacuum results in a lower resistance. FIG. 4 shows the relationship between the oxygen plasma processing time and the contact resistance. According to FIG. 4, there is a case where a sufficient effect cannot be obtained in a short time, and it is understood that a process of about 30 seconds is necessary. Note that the required time varies depending on the etching conditions when forming the contact hole. The contact property 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 if additional plasma treatment is performed. Care must be taken in the conditions of the oxygen plasma treatment. It is. In addition, this processing can be continuously performed after etching in the same processing chamber of the same processing apparatus, or can be performed in another processing chamber of the same processing apparatus or once out of the vacuum and transferred to another processing apparatus. The same effect can be obtained.

In the fourth and fifth embodiments, the case where the chromium film surface is exposed to the etching for a long time is used. However, the case where the insulating film is thin is also effective.

Embodiment 6
Further, when the countermeasures described in Embodiments 1 to 5 cannot be taken due to the conditions of dry etching or the number of substrates to be processed, and when the adhered substances cannot be removed, the surface is wet-etched. Another method is to remove the layer. Embodiment 4 is the same as Embodiment 4 except that the surface layer is removed by wet etching instead of dry etching.

According to the method of the sixth embodiment, the substrate which has been dry-etched is put in a mixed solution of cerium ammonium nitrate and nitric acid after the usual dry etching to clean the chromium surface. In this case, the etching is usually performed immediately after the dry etching, but there is no problem after removing the resist. Note that it is impossible to reduce the 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, it is possible to remove deposits. Although the detailed mechanism is unknown, some of the other etchants that can etch the chromium film can remove the deposits and the surface layer and ensure good contact.

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

Embodiment 7
As described above, an active matrix substrate manufactured according to the contact hole forming methods described in Embodiments 1 to 6 and a liquid crystal display device using the active matrix substrate will be described.

The structure of the active matrix substrate and the liquid crystal display device using the active matrix substrate and the method of manufacturing the same 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 as to be present only in the TFT portion and its vicinity. 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 of the methods described in the first to sixth embodiments. Then, an ITO film as a pixel electrode is formed and patterned to complete an active matrix substrate. Since the contact holes are formed using the methods of Embodiments 1 to 6, the contact resistance is low, and a process of manufacturing an active matrix substrate by directly contacting an ITO film or the like on a chromium film becomes possible. The effect that the contact resistance can be realized was obtained. Further, the liquid crystal display device using the active matrix substrate according to the present invention has an effect of having excellent quality without occurrence of a defect relating to contact resistance.

FIG. 3 is an explanatory sectional view showing a contact portion of an active matrix substrate according to the present invention. FIG. 3 is a schematic sectional view showing a contact portion when a gate insulating film and an insulating film on a source electrode are etched at a time. 4 is a graph showing a relationship between oxygen plasma processing pressure and contact resistance. 5 is a graph showing the relationship between oxygen plasma processing time and contact resistance.

Explanation of reference numerals

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

Claims (10)

(1) forming an insulating film over the first electrode provided on the substrate and the substrate;
(2) 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 the steps of: forming a second electrode and making contact between the second electrode and the first electrode;
In the step (2), a method of forming a contact hole in an active matrix substrate, wherein the contact hole is formed by dry etching and then the contact hole is surface-treated by plasma etching with oxygen gas. 2. The method for forming a contact hole in an active matrix substrate according to claim 1, wherein the processing pressure P with the oxygen gas is 50 Pa ≦ P ≦ 400 Pa. 2. The method for forming a contact hole in an active matrix substrate according to claim 1, wherein the processing pressure P with the oxygen gas is 150 Pa ≦ P ≦ 250 Pa. 2. The method according to claim 1, wherein the surface treatment is performed in the same processing chamber of a processing apparatus in which the step (2) is performed. The method for forming a contact hole in an active matrix substrate according to claim 1, wherein the surface treatment is performed in one of a processing chamber different from a processing chamber of a processing apparatus in which the step (2) is performed and another processing apparatus. (1) forming an insulating film over the first electrode provided on the substrate and the substrate;
(2) 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 the steps of: forming a second electrode and making contact between the second electrode and the first electrode;
In the step (2), after forming the contact hole, forming a contact hole on the active matrix substrate, the surface of which is treated in a reactive ion etching mode at a processing pressure P of 100 Pa ≦ P ≦ 400 Pa in oxygen gas. Method. 7. The contact hole forming method according to claim 6, wherein the processing pressure P with the oxygen gas is 150 Pa ≦ P ≦ 250 Pa. 7. The method for forming a contact hole in an active matrix substrate according to claim 6, wherein the surface treatment is performed in the same processing chamber as the processing chamber of the processing apparatus in which the step (2) is performed. 7. The method for forming a contact hole in an active matrix substrate according to claim 6, wherein the surface treatment is performed in one of a processing chamber different from a processing chamber of the processing apparatus in which the step (2) is performed and another processing apparatus. (1) forming an insulating film over the first electrode provided on the substrate and the substrate;
(2) 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 the steps of: forming a second electrode and making contact between the second electrode and the first electrode;
In the step (2), a method for forming a contact hole in an active matrix substrate, wherein after forming the contact hole, an electrode surface of the contact hole is treated with a mixed solution of cerium ammonium nitrate and nitric acid.

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