Active matrix addressing liquid-crystal display device

An active matrix addressing LCD device having an active matrix substrate on which conductive lines are formed is provided, which suppress the AI hillock without complicating the structure of the lines and which decreases the electrical connection resistance increase at the terminals of the lines, thereby improving the connection reliability. The device comprises an active matrix substrate having a transparent, dielectric plate, thin-film transistors (TFTs) arranged on the plate, and pixel electrodes arranged on the plate. Gate electrodes of the TFTs and scan lines have a first multilevel conductive structure. Common electrodes and common lines may have the first multilevel conductive structure. Source and drain electrodes of the TFTs and signal lines may have a second multilevel conductive structures. Each of the first and second multilevel conductive structures includes a three-level TiN/Ti/Al or TiN/Al/Ti structure or a four-level TiN/Ti/AI/Ti structure. Each of the TiN film of the first and second structures has a nitrogen concentration of 25 atomic % or higher. The Al file may be replaced with an Al alloy.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an active-matrix addressing Liquid-Crystal Display (LCD) device having a so-called active-matrix substrate on which pixel electrodes and Thin-Film Transistors (TFTs) are arranged in a matrix array.

More particularly, the invention relates to an active-matrix addressing LCD device with an active-matrix substrate on which multilayer-structured conductive lines are formed along with pixel electrodes and TFTs, which suppresses effectively aluminum (Al) hillocks without any complicated conductive line structure to thereby decreasing the connection resistance increase of the lines due to heat or moisture and improving their connection reliability.

2. Description of the Related Art

The active-matrix addressing LCD device has a typical configuration as follows.

The LCD device of this type comprises an active matrix substrate and an opposite substrate coupled to each other in parallel to form a specific gap between them with a sealing member. The gap between the substrates forms a closed space for confining a specific liquid crystal. Thus, the space (and the liquid crystal) is sandwiched by the substrates.

Pixel areas are arranged in a matrix array on the active matrix substrate. TFTs are arranged on the active matrix substrate to correspond to the respective pixel areas, which are to control the voltages applied to the corresponding pixel electrodes. Opposing electrodes are arranged on the opposite substrate. Specific voltages are applied across the electrodes arranged on these two substrates to drive the liquid crystal, thereby displaying images on the screen of the LCD device.

If the LCD device is of the vertical electric-field type where electric fields are generated to be approximately vertical to the substrates in the closed space (i.e., in the liquid crystal) on operation, the active matrix substrate comprises a transparent glass plate. Scan lines extending in the first direction are arranged at equal intervals on the surface of the glass plate in the second direction, where the second direction is perpendicular to the first direction. Signal lines extending in the second direction are arranged at equal intervals on the surface of the glass plate in the first direction. The pixel electrodes are arranged at the respective pixel areas defined by the scan lines and the signal lines thus intersected. The TFTs are arranged in the respective pixel areas, The gate electrodes, the drain electrodes, and the source electrodes of the TFTs are connected to the scan lines, the signal lines, and the pixel electrodes, respectively.

Accordingly, when specific electric currents are supplied to one of the scan lines and one of the signal lines, respectively, the TFT located at the intersection of these scan and signal lines are turned on, allowing a specific voltage to be applied to the relating pixel electrode to the TFT in question. This operation is conducted for all the necessary pixels. Thus, a desired image is displayed on the screen of the device

Each of the scan lines has a scan-line terminal at its end. Each of the signal lines has a signal-line terminal at its end. These scan- and signal-line terminals are used to connect a tape-shaped cable for interconnecting the scan and signal lines with a specific driver circuit unit. The cable includes a set of conductive or wiring lines previously connected to the driver circuit unit. Thus, the scan and signal lines are connected to the unit by way of the corresponding lines of the cable.

With the active-matrix substrate of this type, there is the need to decrease the size of the pixel electrodes and to decrease the electrical resistance of the scan and signal lines themselves by using any other conductive material of lower electrical resistance and any other structure. This is responsive to the recent requirement of enlarging the LCD device and of raising the density of the elements or components used in the device.

Moreover, since the scan and signal lines need to be connected to the conductive lines of the tape-shaped flat cable at their terminals, these terminals need to be made of a reliable material or materials to prevent the connection reliability at the terminals from degrading due to invasion of moisture.

To meet the above-described need, various improvements have been made and disclosed so far.

For example, the Japanese Non-Examined Patent Publication No. 7-120789, which was published in 1995, discloses a multi-level conductive structure applicable to the scan and signal lines of the LCD device This structure includes a lower aluminum (Al) film and an upper titanium nitride (TiN) film. The Al film is used to lower the electrical resistance of the structure or the lines. The TiN film is used to prevent the underlying Al film from being exposed to various chemicals during the fabrication processes and therefore, corrosion of the TiN firm can be avoided. This means that a highly reliable connection structure is possible.

However, the multi-level conductive structure disclosed by the Publication No. 7-120789 has a problem that hillocks tend to occur on the Al film. As known well, “Al hillocks” are small hills or protrusions formed on the surface of the Al films which are caused by the fact that a compressive stress is applied to the Al film in a heat treatment process and then, the stress is relaxed or decreased with time to thereby diffuse the Al atoms of the film outwardly. The Al hillocks will cause various defects (e.g., inter-level short-circuit) and as a result, the fabrication yield degradation will be more likely.

A technique to prevent the Al hillocks is disclosed by, for example, the Japanese Non-Examined Patent Publication No. 7-58110 published in 1995. This technique includes a multilevel conductive structure with TiN, Ti, Al, TiON, and Ti films. In other words, this technique includes a TiN/Ti/Al/TiON/Ti structure. The top-level TiN film is used to prevent reflection of light and to ensure desired etch selectivity in the contact-hole formation process. The upper Ti film is to decrease the electrical connection resistance. The middle-level Al film is used as a conductor material. The TiON film is used as a diffusion barrier film against silicon (Si) The bottom-level or lower Ti film is to decrease the electrical connection resistance.

With the technique disclosed by the Publication No. 7-58110, the Al film is sandwiched by the top-level TiN film and the underlying TiON film to prevent the Al hillocks (and alloy pits). However, the Publication No. 7-58110 discloses only the TiN/Ti/Al/TiON/Ti structure and fails to disclose other conductive or wiring structures that are effective to prevent the Al hillocks. Therefore, it is not clear that whether or not the TiN/Ti/Al/TiON/Ti structure disclosed therein is effective or advantageous to the case where the conductive or wiring structure is not contacted with a semiconductor layer. For example, if the disclosed structure is applied to the gate electrodes of the TFTs of the LCD device described above, the gate electrodes are not contacted with a semiconductor layer but a dielectric glass plate. In this case, it is not clear whether or not the disclosed structure is effective or advantageous.

In particular, the TiON film of the disclosed structure, which is used as the diffusion barrier film against Si, is unnecessary for the LCD device, because the gate electrodes are not contacted with a semiconductor layer. The TiON film only makes the structure complicated.

Furthermore, according to the information disclosed by the Publication No. 7-58110, it is seen that the combination of the TiN film and the Ti film located above the Al film and the combination of the TiON film and the Ti film located below the Al film are effective to the cases disclosed therein. However, it is not clear whether or not the disclosed advantages in the Publication No. 7-58110 are expected as well even if some of the constituent films of the TiN/Ti/Al/TiON/Ti structure is/are cancelled.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide an active matrix addressing LCD device with an active matrix substrate on which specific conductive lines are arranged along with pixel electrodes and TFTs, in which the Al hillock is effectively suppressed without complicating the line structure and at the same time, the electrical connection resistance increase at the terminals of the lines is decreased to thereby improve the connection reliability.

Another object of the present invention is to provide an active matrix addressing LCD device with an active matrix substrate on which specific conductive lines are arranged along with pixel electrodes and TFTs, in which the size of the pixel electrodes can be decreased.

Still another object of the present invention is to provide an active matrix addressing LCD device with an active matrix substrate on which specific conductive lines are arranged along with pixel electrodes and TFTs, in which the LCD device can be enlarged and the density of the elements used in the device can be raised.

The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.

According to a first aspect of the invention, an active matrix addressing LCD device is provided. This device comprises:

an active matrix substrate having a transparent, dielectric plate, TFTs arranged on the plate, and pixel electrodes arranged on the plate;

gate electrodes of the TFTs having a first multilevel conductive structure;

scan lines connected to the corresponding gate electrodes and having the first multilevel conductive structure;

the first multilevel conductive structure including a TiN film located at a top of the structure, an Al-based film located below the TiN film, and at least one Ti film located at at least one of an upper position and a lower position with respect to the Al-based film; and

the TiN film of the first multilevel conductive structure having a nitrogen concentration of 25 atomic % or higher.

In a preferred embodiment of the device of the first aspect, the device further comprises:

common electrodes formed on the plate to be opposite to the corresponding pixel electrodes; and

common lines formed on the plate to be connected to the corresponding common electrodes;

the common electrodes and the common lines having a second multilevel conductive structure;

the second multilevel conductive structure including a TiN film located at a top of the structure, an Al-based film located below the TiN film, and at least one Ti film located at at least one of an upper position and a lower position with respect to the Al-based film; and

the TiN film of the second multilevel conductive structure having a nitrogen concentration of 25 atomic % or higher.

In another preferred embodiment of the device of the first aspect, each of the scan lines has a terminal at its end for electrical connection to an external circuit The TiN film is exposed from the first multilevel conductive structure at the terminal.

In still another preferred embodiment of the device of the first aspect, each of the common lines has a terminal at its end for electrical connection to an external circuit. The TiN film is exposed from the second multilevel conductive structure at the terminal.

According to a second aspect of the invention, another active matrix addressing LCD device is provided. This device comprises:

an active matrix substrate having a transparent, dielectric plate, TFTs arranged on the plate, and pixel electrodes arranged on the plate;

source electrodes of the TFTs having a first multilevel conductive structure;

drain electrodes of the TFTs having the first multilevel conductive structure;

signal lines connected to the corresponding source electrodes and having the first multilevel conductive structure;

the first multilevel conductive structure including a TiN film located at a top of the structure, an Al-based film located below the TiN film, and at least one Ti film located at at least one of an upper position and a lower position with respect to the Al-based film; and

the TiN film of the first multilevel conductive structure having a nitrogen concentration of 25 atomic % or higher.

In a preferred embodiment of the device of the second aspect, the pixel electrodes have the first multilevel conductive structure.

In another preferred embodiment of the device of the second aspect, each of the signal lines has a terminal at its end for electrical connection to an external circuit. The TiN film is exposed from the first multilevel conductive structure at the terminal.

According to a third aspect of the invention, still another active matrix addressing LCD device is provided. This device comprises:

an active matrix substrate having a transparent, dielectric plate, TFTs arranged on the plate, and pixel electrodes arranged on the plate;

gate electrodes of the TFTs having a first multilevel conductive structure;

scan lines connected to the corresponding gate electrodes and having the first multilevel conductive structure;

the first multilevel conductive structure including a TiN film located at a top of the structure, an Al-based film located below the TiN film, and at least one Ti film located at at least one of an upper position and a lower position with respect to the Al-based film; and

the TiN film of the first multilevel conductive structure having a nitrogen concentration of 25 atomic % or higher;

source electrodes of the TFTs having a second multilevel conductive structure;

drain electrodes of the TFTs having the second multilevel conductive structure;

signal lines connected to the corresponding source electrodes and having the second multilevel conductive structure;

the second multilevel conductive structure including a TiN film located at a top of the structure, an Al-based film located below the TiN film, and at least one Ti film located at an upper position or both an upper position and a lower position with respect to the Al-based film; and

the TiN film of the second multilevel conductive structure having a nitrogen concentration of 25 atomic % or higher.

In a preferred embodiment of the device of the third aspect, common electrodes formed on the plate to be opposite to the corresponding pixel electrodes and common lines formed on the plate to be connected to the corresponding common electrodes are additionally provided The common electrodes and the common lines have the first multilevel conductive structure.

In another preferred embodiment of the device of the third aspect, the pixel electrodes have the first multilevel conductive structure.

In still another preferred embodiment of the device of the third aspect, each of the scan lines has a terminal at its end for electrical connection to an external circuit. The TiN film is exposed from the first multilevel conductive structure at the terminal.

In a further preferred embodiment of the device of the third aspect, each of the common lines has a terminal at its end for electrical connection to an external circuit. The TiN film is exposed from the second multilevel conductive structure at the terminal.

According to a fourth aspect of the invention, a further active matrix addressing LCD device is provided. This device comprises:

an active matrix substrate having a transparent, dielectric plate, TFTs arranged on the plate, and pixel electrodes arranged on the plate;

gate electrodes of the TFTs having a first multilevel conductive structure;

scan lines connected to the corresponding gate electrodes and having the first multilevel conductive structure;

the first multilevel conductive structure including a TiN film located at a top of the structure, an Al-based film located below the TiN film, and at least one Ti film located at at least one of an upper position and a lower position with respect to the Al-based film; and

the TiN film of the first multilevel conductive structure having a nitrogen concentration of 25 atomic % or higher;

source electrodes of the TFTs having a second multilevel conductive structure;

drain electrodes of the TFTs having the second multilevel conductive structure;

signal lines connected to the corresponding source electrodes and having the second multilevel conductive structure;

the second multilevel conductive structure including a TiN film located at a top of the structure, an Al-based film located below the TiN film, and at least one Ti film located at an upper position or both an upper position and a lower position with respect to the Al-based film; and

the TiN film of the second multilevel conductive structure having a nitrogen concentration of 25 atomic % or higher

In a preferred embodiment of the device of the fourth aspect, common electrodes formed on the plate to be opposite to the corresponding pixel electrodes and common lines formed on the plate to be connected to the corresponding common electrodes are additionally provided. The common electrodes and the common lines have the first multilevel conductive structure.

In another preferred embodiment of the device of the fourth aspect, the pixel electrodes have the second multilevel conductive structure.

In still another preferred embodiment of the device of the fourth aspect, each of the scan lines has a terminal at its end for electrical connection to an external circuit. The TiN film is exposed from the first multilevel conductive structure at the terminal.

In a further preferred embodiment of the device of the fourth aspect, each of the signal lines has a terminal at its end for electrical connection to an external circuit. The TiN film is exposed from the second multilevel conductive structure at the terminal.

In a still further preferred embodiment of the device of the fourth aspect, each of the common lines has a terminal at its end for electrical connection to an external circuit. The TiN film is exposed from the first multilevel conductive structure at the terminal.

In the devices of the first to fourth aspects of the invention, preferably, for example, each of the first and second multilevel conductive structures is a three-level structure of TiN/Ti/Al or TiN/Al/Ti. Alternately, it is preferred that each of the first and second multilevel conductive structures is a four-level structure of TiN/Ti/Al/Ti.

As the Al-based film, not only a substantially pure Al film but also an Al alloy film may be used.

With the active matrix addressing LCD devices according to the first to fourth aspects of the invention, since the Ti film is contacted with the Al-based film in each of the first and second multilevel conductive structures, generation of Al hillocks on the Al-based film is effectively suppressed.

For the drain electrode, the Ti film is located below the Al-based film in the second multilevel conductive structure and therefore, the Ti film is located between the Al-based film and an underlying semiconductor island. Thus, generation of alloy pits is suppressed for the drain electrode.

Moreover, since the TIN film is located at the top of the first or second multilevel conductive structure, corrosion at the terminals of the scan, signal, and common lines is prevented. Thus, the electrical connection resistance increase at the terminals of these lines can be decreased, thereby enhancing or improving the connection reliability at the same terminals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

An active matrix addressing LCD device according to a first embodiment of the invention is shown inFIG. 1andFIGS. 2A to 2D. This device is of the vertical electric-field type.

As shown inFIG. 1, the LCD device according to the first embodiment comprises an active matrix substrate1and an opposite substrate (not shown) coupled to each other in parallel to form a specific gap between them with a sealing member (not shown). The gap between the substrates forms a closed space in which a specific liquid crystal is confined. This configuration itself is known well and therefore, no further explanation is presented here.

Since the feature of the invention resides in the active matrix substrate1, the following explanation will be mainly made with respect to the substrate1. The substrate1has the following configuration.

As shown inFIG. 1, the active matrix substrate1comprises a transparent glass plate10. Scan lines11extending in the first direction (in the horizontal direction inFIG. 1) are arranged at equal intervals on the surface of the plate10in the second direction (in the vertical direction inFIG. 1) perpendicular to the first direction.

Signal lines12extending in the second direction are arranged at equal intervals on the surface of the plate10in the first direction Thus, the scan lines11intersect perpendicularly with the signal lines12.

Pixel areas13are formed in the rectangular areas formed on the surface of the plate10by the respective scan and signal lines11and12. Thus, the areas13are arranged in a matrix array on the surface of the plate11.

TFTs14are arranged on the surface of the plate11which are located in the respective pixel areas13. The TFTs14, which are of the inverted-staggered type, are used to control the voltages applied to the corresponding areas13.

As clearly shown inFIG. 2B, each of the TFTs14has a gate electrode15, a gate insulating film16, an island-shaped semiconductor layer (i.e., a semiconductor island)17, a source electrode18, and a drain electrode19. The gate electrode15is located on the same level as the scan lines11on the surface of the glass plate10. The gate insulating film16is formed on the surface of the plate10to cover the scan lines11and the gate electrode15. The semiconductor island17is formed on the gate insulating film16to be opposite to the gate electrode15by way of the film16. The source electrode18and the drain electrode19are formed on the same level as the signal lines12on the surface of the plate10. The source electrode18is located on one side of the island17and the drain electrode19is located on the other side thereof. A passivation film20is formed to cover the TFTs14.

The gate insulating film16and the passivation film20are commonly used by all the TFTs14.

Each of the pixel areas13comprises a transparent pixel electrode21made of a transparent conductive material, such as ITO (Indium Tin Oxide). Most of the electrode21is exposed through a corresponding opening (i.e., display window)21aof the passivation film20. The exposed part of the electrode21serves as part of the display area.

The gate electrode15is connected to a corresponding one of the scan lines11. The drain electrode19is connected to a corresponding one of the signal lines12. The source electrode19is connected to a corresponding one of the pixel electrodes21.

Each of the scan lines11has a connection terminal22at its end, as shown inFIGS. 1 and 2A. The connection terminal22of the line11is exposed from the gate insulating film16and the passivation film20through a corresponding opening22a, as clearly shown inFIG. 2C. Similarly, each of the signal lines12has a connection terminal23at its end, as shown inFIGS. 1 and 2A. The connection terminal23of the line12is exposed from the gate insulating film16and the passivation film20through a corresponding opening23a, as clearly shown inFIG. 2D.

The gate electrodes15and the scan lines11are formed by the same multilevel conductive film. In other words, they are formed by a common conductive film with a multilevel structure. Specifically, as seen fromFIGS. 2B and 2C, the common conductive film is formed by an Al film (thickness: 100 nm)101located at the bottom, a Ti film (thickness: 50 nm)102located at the middle, and a TiN film (thickness: 200 nm)103located at the top Therefore, it is said that the common conductive film has the three-level TiN/Ti/Al structure.

The source and drain electrodes18and19and the signal lines12are formed by the same multilevel conductive film. In other words, they are formed by a common conductive film with a multilevel structure. Specifically, as seen fromFIGS. 2B and 2D, the common conductive film is formed by an ITO film (thickness: 50 nm)111located at the bottom, and a Cr (chromium) film (thickness: 200 nm)112located at the top. Therefore, it is said that the common conductive film has the two-level Cr/ITO structure.

Next, a method of fabricating the active matrix substrate1of the first embodiment is explained below with reference toFIGS. 3A to 3D,4A to4D,5A to5D, and6A to6D.

First, as shown inFIGS. 3A to 3D, the Al film101with a thickness of 200 nm, the Ti film102with a thickness of 50 nm, and the TiN film103with a thickness of 100 nm are successively formed on the surface of the glass plate10by a sputtering method. Thus, the three-level TiN/Ti/Al structure is formed.

Then, the first photolithography process is carried out for the three-level TiN/Ti/Al structure thus formed. Specifically, a first photoresist film (not shown) is formed on the structure and then, exposed to specific light and developed, thereby pattering the first photoresist film. Thereafter, using the patterned first photoresist film as a mask, the TiN/Ti/Al structure is patterned by a dry etching method, thereby forming the gate electrodes15and the scan lines11on the surface of the plate10. The state at this stage is shown inFIGS. 3A to 3D.

The TiN film103is formed by a reactive sputtering method in such a way that the nitrogen concentration of the film103is 25 atomic % or higher while controlling the flow rate ratio of Ar and N2gases. This is easily realized under the condition that the pressure in the sputtering chamber is 0.8 Pa, the flow rate of Ar gas is 225 sccm, the flow rate of N2gas is 150 sccm, the DC discharge power is 16 kW, the substrate temperature is 150° C., and the sputtering gap is 115 mm, for example.

Thereafter, as shown inFIGS. 4A to 4D, a SiN (silicon nitride) film with a thickness of 400 nm is formed over the whole surface of the plate10as the gate insulating film16. The SiN film16covers entirely the patterned TiN/Ti/Al structure. An intrinsic amorphous silicon (i-type a-Si) film121with a thickness of 250 nm is formed on the SiN film16and then, an n+-type a-Si film122with a thickness of 50 nm is formed on the i-type a-Si film121. The film122is doped with phosphorus (P) as a n-type impurity. The n+-type a-Si film122, which serves as an ohmic layer, is used to ensure ohmic contact with the drain and source electrodes18and19. These two films121and122are formed by a plasma-enhanced CVD (Chemical Vapor Deposition) method.

Next, the second photolithography process is carried out in the following way. A second photoresist film (not shown) is formed on the n+-type a-Si film122and then, exposed to specific light and developed, thereby pattering the second photoresist film. Thereafter, using the patterned second photoresist film as a mask, the a-Si films121and122are successively patterned by a dry etching method, thereby forming the semiconductor islands17on the gate insulating film (i.e., the SiN film)16to be opposite to the corresponding gate electrodes15. The state at this stage is shown inFIGS. 4A to 4D.

Subsequently, the ITO film111with a thickness of 50 nm, which is transparent, is formed on the n+-type a-Si film122over the whole surface of the glass plate10and then, the Cr film112with a thickness of 200 nm is formed on the film111. These two films111and112are deposited by a sputtering method.

Next, the third photolithography process is carried out in the following way. A third photoresist film (not shown) is formed on the Cr film112and then, exposed to specific light and developed, thereby pattering the third photoresist film. Thereafter, using the patterned third photoresist film as a mask, the Cr film112and the ITO film111are successively patterned by a wet etching method. Thus, the pixel electrodes21, the source electrodes18united with the corresponding pixel electrodes21, the drain electrodes19, and the signal lines12united with the corresponding drain electrodes19are formed.

Using the source and drain electrodes18and19as a mask, the underlying n+-type a-Si film122is selectively removed by a dry etching method. Thus, “channel gaps” are formed between the corresponding pairs of the electrodes18and19. The remaining film122forms the ohmic layer located just below the electrodes18and19. As a result, the TFTs14are formed to be arranged in a matrix array on the surface of the plate10. The state at this stage is shown inFIGS. 5A to 5D.

Subsequently, a SiN film, which serves as the passivation film20, is formed to cover the TFTs14, the scan and signal lines11and12, and the pixel areas13over the entire surface of the plate10by a plasma-enhanced CVD method. Then, the fourth photolithography process is carried out in the following way. A fourth photoresist film (not shown) is formed on the SiN film20and then, exposed to specific light and developed, there by pattering the fourth photoresist film. Thereafter, using the patterned fourth photoresist film as a mask, the SiN film20is patterned by an etching method. Thus, the film20is selectively removed at the pixel electrodes21, the terminals22of the scan lines11, and the terminals23of the signal lines12. Moreover, the gate insulating film16also is selectively removed at the terminals22while the Cr film112is selectively removed at the terminals23and the pixel areas13. In this way, the windows or openings21a,22a, and23aare formed.

As a result, as shown inFIGS. 2A to 2D, the scan lines11are exposed from the passivation film20and the gate insulating film16by way of the openings22aat the scan-line terminals22. The signal lines12(i.e., their ITO film111) are exposed from the passivation film20and the Cr film112by way of the openings23aat the signal-line terminals23. The pixel areas13(i.e., their ITO film111) are exposed from the passivation film20and the Cr film112by way of the openings21a.

Furthermore, although not illustrated here, an alignment layer is formed on the passivation film20. Thus, the active matrix substrate1according to the first embodiment is completed.

On the other hand, an opposite substrate (not shown) is placed to be opposed to the active matrix substrate1at a specific gap and then, these two substrates are coupled together with a sealing member so as to confine a liquid crystal in the gap. Thus, the LCD panel is completed.

Thereafter, one end of a flat cable of a driver circuit unit is connected to the scan and signal lines11and12at their terminals22and23. Thus, the conductive lines combined in the cable are connected to the respective scan and signal lines11and12, resulting in electrical interconnection of the driver circuit unit with the LCD panel. This makes it possible to supply electric power to the LCD panel and to drive all the pixels on the active matrix substrate1, thereby displaying images on the screen of the device. In this way, the active matrix addressing LCD device of the first embodiment is finally fabricated.

With the LCD device according to the first embodiment, the active matrix substrate1employs the three-level TiN/Ti/Al structure to form the gate electrodes15and the scan lines11. Therefore, the effect to suppress Al hillocks is enhanced or raised without complicating the structure of the lines11, compared with the prior-art TiN/Al structure of the of the Publication No. 7-120789.

Moreover, since the TiN film103has a nitrogen concentration of 25 atomic % or higher, the increase of the electrical connection resistance at the terminals22of the scan lines11is suppressed. This improves the connection reliability at the terminals22.

FIG. 7shows the correlation of the number of induced Al hillocks with the three-level TiN/Ti/Al structure used in the first embodiment of the invention and the two-level TiN/Al structure used in the prior-art wiring structure disclosed by the Publication No. 7-120789. The data shown inFIG. 7were obtained by the inventors' test conducted in the following way.

After the inventive TiN/Ti/Al structure and the prior-art TiN/Al structure were formed, they were subjected to a heat treatment process at 300° C. for one hour in a nitrogen atmosphere. Thereafter, the inventors observed Al hillocks induced on the Al films of the inventive and prior-art structures and then, they counted the total number of the hillocks existing in the square area of 1 mm×1 mm of the Al films with the naked eye.

In the prior-art TiN/Al structure (Sample No.1inFIG. 7) of the Publication No. 7-120789, the total number of the Al hillocks was 6410 pieces/mm2. On the other hand, in the inventive TiN/Ti/Al structure (Sample No.3inFIG. 7) of the first embodiment, the total number of the Al hillocks was limited to approximately 4 pieces/mm2Thus, it was seen that the inventive structure of the first embodiment is much fewer in the Al hillock number than the prior-art structure. This means that Al hillocks can be effectively suppressed at the terminals22of the scan lines11without making their structure complicated.

The sample Nos.2and4shown inFIG. 7are variations of the inventive TiN/Ti/Al structure of the first embodiment. The sample No.2, which has the TiN film thickness of 50 nm, the Ti film thickness of 50 nm, and the Al film thickness of 200 nm, has an Al hillock number of 26 pieces/mm2. The sample No.4, which has the TiN film thickness of 100 nm, the Ti film thickness of 100 nm, and the Al film thickness of 200 nm, has an Al hillock number of approximately 1 piece/mm2.

It is seen from the sample Nos.2and4that the inventive structure of the first embodiment is much fewer in the Al hillock number than the prior-art structure, even if the constituent film thickness is changed.

The inventors presumed that the advantage of the inventive structure of the first embodiment was generated by the placement that the Ti film102was located between the TiN and Al films103and101, in other words, the effect of the TiN film103to physically suppress the hillocks was enhanced by the TiN/Ti/Al placement. Moreover, it is seen from the sample Nos.2and4that the hillock suppressing effect can be enhanced if the thickness of the TiN film103is increased. It is seen from the sample Nos.2and4that the hillock suppressing effect can be enhanced if the thickness of the Ti film102is increased as well.

With the inventive TiN/Ti/Al structure of the first embodiment, the TiN film103located at the top improves the reliability of electrical interconnection at the scan-line terminals22. This is shown inFIG. 8andFIGS. 9A to 9C.

FIG. 8shows the correlation of the nitrogen concentration of the TiN film103with the electrical resistance increase of the TiN/Ti/Al and TiN/Al structures used in the first embodiment and the prior-art. The data inFIG. 8was obtained by the following test conducted by the inventors.

As shown inFIGS. 9A and 9B, testing terminal units201of first to third types, each of which had 2000 dummy scan-line terminals22A arranged along a straight line at equal intervals, were prepared. The dummy terminals22A, which were connected to each other in series by way of conductive connection lines204, had the same TiN/Ti/Al structure as that of the scan-line terminals22of the active matrix substrate1of the first embodiment. The dummy terminals22A formed the first type of the units201had a nitrogen concentration of 15 atomic %. The dummy terminals22A formed the second type of the units201had a nitrogen concentration of 25 atomic %. The dummy terminals22A formed the third type of the units201had a nitrogen concentration of 35 atomic %.

Dummy Tape carrier packages (TCPs)206, each of which had 2000 wiring or conductive lines arranged on a dielectric base sheet in the same way as that of the dummy terminals22A of each unit201, was prepared. These dummy TCPs206were a typical tape-shaped flat cable used for interconnection of the LCD panel and the driver circuit unit thereof. The wiring lines of each TCP206were mechanically and electrically connected to the dummy terminals22A of the corresponding unit201with metallic bonding members207through their openings22Aa, as shown inFIG. 9B. The reference symbols10A and16A inFIG. 9Bdenote the glass plate and the gate insulating film, respectively.

Two measuring terminals202and203were formed on each unit201at its either end. The measuring terminal202was electrically connected to the terminal22A by way of the line204at the corresponding end (i.e., the left-side end inFIG. 9A) of the unit201. The measuring terminal203was electrically connected to the terminal22A by way of the line204at the corresponding end (i.e., the right-side end inFIG. 9A) of the unit201. A resistance meter (RM)205was electrically connected across the measuring terminals202and203of each unit201in order to measure the electrical resistance of the 2000 dummy terminals22A and the TCPs206connected in series.

The electrical resistance between the measuring terminals202and203of each unit201was measured with the resistance meter205at the start of this test. Thereafter, each unit201was subjected to a heat treatment Process along with the corresponding dummy TCP206under the process condition that the temperature was 85° C., the humidity was 85%, and the heating period was 1000 hours. When the heat treatment process was finished, the electrical resistance between the measuring terminals202and203was measured again with the resistance meter205.

As shown inFIGS. 9B and 9C, some deformation was caused in the bonding members207due to the heat treatment process. Typically, defective connection of the member207to the terminal22A will start at their peripheries. Therefore, when the heat treatment process was finished, the members207were turned into the undesired state, as shown inFIG. 9C. As a result, the connection length TL of the members207with the terminals22A decreased from the value shown inFIG. 9Bto the value shown inFIG. 9C.

In this test, the acceptable value of the connection length TL was set at 0.1 mm, where the electrical resistance increase was set at “2” (arbitrary unit), as shown inFIG. 8. If the electrical resistance increase thus measured did not exceed the value of “2” after the above-described heat treatment process, the testing terminal unit201in question was judged as good or non-defective.

The measured electrical resistance increase of the testing terminal units201with three different nitrogen concentrations of 15, 25, and 35 atomic % in this test was plotted inFIG. 8. If the three circular dots are interconnected with a broken, continuous curve, it was found that the threshold value of the nitrogen concentration of the TiN film103was 25 atomic %. This means that if the nitrogen concentration of the TiN film103is equal to or higher than 25 atomic %, the electrical resistance increase can be limited to the reference value of “2” or lower, including fluctuation or deviation of the measured value. In other words, the electrical resistance increase is suppressed against corrosion and accordingly, the connection reliability at the scan-line terminals22is improved.

As explained above, the signal lines12and the source and drain electrodes19and20are formed by the two-level Cr/ITO conductive structure in the first embodiment. However, the signal lines12and the source and drain electrodes19and20may be formed by the three-level TiN/Ti/Al structure used for the gate electrodes15and the scan lines11.

Second Embodiment

FIG. 10andFIGS. 11A to 11Eshow the configuration of an active matrix substrate1A used in an active matrix addressing LCD device according to a second embodiment of the invention. Unlike the first embodiment, this device is of the lateral electric-field type. This device comprises the active matrix substrate1A and an opposite substrate (not shown) coupled to each other in parallel to form a specific gap between them-with a sealing member (not shown) The gap between the substrates forms a closed space in which a specific liquid crystal is confined. This configuration is the same as the first embodiment.

The same reference numerals or symbols are attached to the same or corresponding elements as those of the first embodiment inFIG. 10andFIGS. 11A to 11E.

As shown inFIGS. 10 and 11A, the active matrix substrate1A of the second embodiment comprises a transparent glass plate10. Scan lines11extending in the first direction (in the horizontal direction inFIG. 10) are arranged at equal intervals on the surface of the plate10in the second direction (in the vertical direction inFIG. 10) perpendicular to the first direction.

Common lines30extending in the first direction are arranged at specific intervals on the surface of the plate10in the second direction. The common lines30are parallel to the scan lines11and arranged between the adjacent scan lines11.

Signal lines12extending in the second direction are arranged at equal intervals on the surface of the plate10in the first direction Thus, the scan lines11and common lines30intersect perpendicularly with the signal lines12.

Pixel areas13are formed in the rectangular areas formed on the surface of the plate10by the respective scan, common, and signal lines11,30, and12. Thus, the areas13are arranged in a matrix array on the surface of the plate11.

TFTs14are arranged on the surface of the plate11, which are located in the respective pixel areas13. The TFTs14, which are of the inverted-staggered type, are used to control the voltages applied to the corresponding areas13.

As clearly shown inFIG. 11B, each of the TFTs14has a gate electrode15, a gate insulating film16, a semiconductor island17, a source electrode18, and a drain electrode19. The gate electrode15is located on the same level as the scan and common lines11and30on the surface of the glass plate10. The gate insulating film16is formed on the surface of the plate10to cover the scan and common lines11and30and the gate electrode15. The semiconductor island17is formed on the gate insulating film16to be opposite to the gate electrode15by way of the film16. The source electrode18and the drain electrode19are formed on the same level as the signal lines12on the surface of the plate10. The source electrode18is located on one side of the island17and the drain electrode19is located on the other side thereof. A passivation film20is formed to cover the TFTs14over the entire surface of the plate10.

The gate insulating film16and the passivation film20are commonly used by all the TFTs14.

Each of the pixel areas13comprises a comb- or frame-shaped common electrode32formed in the same level as the gate electrode13, and a comb- or frame-shaped pixel electrode33formed in the same level as the source electrode18. The level of the source electrode18is higher than that of the pixel electrode33. The pixel electrode33is laterally shifted or staggered in the first direction (i.e., in the horizontal direction inFIG. 11A) with respect to the common electrode32along the surface of the plate10, as clearly shown inFIGS. 11A and 11B. The common and pixel electrodes32and33are made of a transparent conductive material such as ITO.

The gate electrode15is connected to a corresponding one of the scan lines11. The drain electrode19is connected to a corresponding one of the signal lines12. The source electrode19is connected to a corresponding one of the pixel electrodes33. The common electrode32is connected to a corresponding one of the common lines30.

Each of the scan lines11has a connection terminal22at its end, as shown inFIGS. 10 and 11A. The connection terminal22of the line11is exposed from the gate insulating film16and the passivation film20through a corresponding opening22a, as clearly shown inFIG. 11C. Similarly, each of the signal lines12has a connection terminal23at its end, as shown inFIGS. 10 and 11A. The connection terminal23of the line12is exposed from the gate insulating film16and the passivation film20through a corresponding opening23a, as clearly shown inFIG. 11D. Each of the common lines30has a connection terminal31at its end, as shown inFIGS. 10 and 11A. The connection terminal31of the line30is exposed from the gate insulating film16and the passivation film20through a corresponding opening32a, as clearly shown inFIG. 11E.

The gate electrodes15, the scan lines11, the common electrodes32, and the common lines30are formed by the same multilevel conductive film. In other words, they are formed by a common conductive film with a multilevel structure. Specifically, as seen fromFIGS. 11B and 11C, the common conductive film is formed by a Ti film (thickness: 50 nm)104located at the bottom, an Al film (thickness: 200 nm)101located at the lower middle, a Ti film (thickness: 50 nm)102located at the upper middle, and a TiN film (thickness: 50 nm)103located at the top. Therefore, it is said that the common conductive film has the four-level TiN/Ti/Al/Ti structure.

The drain electrodes19, the signal lines12, the source electrodes18, and the pixel electrodes33are formed by the same multilevel conductive film. In other words, they are formed by a common conductive film with a multilevel structure. Specifically, as seen fromFIGS. 11B and 11D, the common conductive film is formed by a Ti film (thickness: 50 nm)134located at the bottom, an Al film (thickness: 200 nm)131located at the lower middle, a Ti film (thickness: 50 nm)132located at the upper middle, and a TiN film (thickness: 50 nm)133located at the top. This configuration is the same as that of the common conductive film for the gate electrodes15, the scan lines11, the common electrodes32, and the common lines30. Therefore, it is said that the common conductive film for the drain electrodes19, the signal lines12, the source electrodes18, and the pixel electrodes33has the four-level TiN/Ti/Al/Ti structure as well. This point is unlike the first embodiment.

Next, a method of fabricating the active matrix substrate1A of the second embodiment is explained below with reference toFIGS. 12A to 12E,13A to13E,14A to14E, and15A to15E.

First, as shown inFIGS. 12A to 12E, the Ti film104with a thickness of 50 nm, the Al film101with a thickness of 200 nm, the Ti film102with a thickness of 50 nm, and the TiN film103with a thickness of 50 nm are successively formed on the surface of the glass plate10by a sputtering method. Thus, the four-level TiN/Ti/Al/Ti structure is formed.

Then, the first photolithography process is carried out for the four-level TiN/Ti/Al/Ti structure thus formed, forming a patterned first photoresist film. Using the patterned first photoresist film as a mask, the TiN/Ti/Al/Ti structure is patterned by a dry etching method, thereby forming the gate electrodes15, the scan lines11connected to the gate electrodes15, the common electrodes32, and the common lines30connected to the common electrodes32an the surface of the plate10. The state at this stage is shown inFIGS. 12A to 12E.

Like the first embodiment, the TiN film103is formed by a reactive sputtering method in such a way that the nitrogen concentration of the film103is 25 atomic % or higher while controlling the flow rate ratio of Ar and N2gases. This is easily realized under the same condition as shown in the first embodiment

Thereafter, as shown inFIGS. 13A to 13E, a SiN film with a thickness of 400 nm is formed on the whole surface of the plate10as the gate insulating film16. The SiN film16covers entirely the patterned TiN/Ti/Al/Ti structure. An i-type a-Si film121with a thickness of 250 nm is formed on the SiN film16and then, an n+-type a-Si film122with a thickness of 50 nm is formed on the i-type a-Si film121. The film122is doped with phosphorus (P) as a n-type dopant. The n+-type a-Si film122is to ensure ohmic contact with the drain and source electrodes18and19. These two films121and122are formed by a plasma-enhanced CVD method.

Next, the second photolithography process is carried out to form a patterned second photoresist film. Using the patterned second photoresist film as a mask, the a-Si films121and122are successively patterned by a dry etching method, thereby forming the semiconductor islands17on the gate insulating film (i.e., the SiN film)16to be opposite to the corresponding gate electrodes15. The state at this stage is shown inFIGS. 13A to 13E.

The Ti film134with a thickness of 50 nm, the Al film131with a thickness of 200 nm, the Ti film132with a thickness of 50 nm, and the Ti film133with a thickness of 50 nm are successively formed on the n+-type a-Si film122over the whole surface of the glass plate10by a sputtering method. Thus, the TiN/Ti/Al/Ti structure is formed to have the same height as that of the above-described TiN/Ti/Al/Ti structure for the gate electrodes15, the scan lines11, the common electrodes32, and the common lines30.

Next, the third photolithography process is carried out to form a patterned third photoresist film. Using the patterned third photoresist film as a mask, the TiN/Ti/Al/Ti structure is patterned by a wet etching method. Thus, the drain electrodes19, the signal lines12united with the corresponding drain electrodes19, the source electrodes18, and the pixel electrodes33united with the corresponding source electrodes18are formed.

Like the above-described step of forming the TiN film103, the TiN film133is formed by a reactive sputtering method in such a way that the nitrogen concentration of the film133is 25 atomic % or higher while controlling the flow rate ratio of Ar and N2gases. This is easily realized under the same condition as shown in the first embodiment.

Using the source and drain electrodes18and19as a mask, the n+-type a-Si film122is selectively removed by a dry etching method. Thus, “channel gaps” are formed between the corresponding pairs of the electrodes18and19. The remaining film122forms the ohmic layers located just below the electrodes18and19. As a result, the TFTs14are formed to be arranged in a matrix array on the plate10. The state at this stage is shown inFIGS. 14A to 14E.

Subsequently, a SiN film, which serves as the passivation film20, is formed to cover the TFTs14, the scan, common, and signal lines11,30, and12, and the pixel areas13over the entire surface of the plate10by a plasma-enhanced CVD method, Then, the fourth photolithography process is carried out to form a patterned fourth photoresist film. Thereafter, using the patterned fourth photoresist film as a mask, the SiN film20and the gate insulating film16are patterned by an etching method. The SiN or passivation film20and the gate insulating film16are selectively removed at the terminals22of the scan lines11and the terminals31of the common lines30. The SiN film20is selectively removed at the terminals23of the signal lines12. Thus, the windows or openings22a,23a, and31aare formed at the terminals22,23, and31, respectively.

As a result, as shown inFIGS. 11A to 11E, the scan lines11are exposed from the passivation film20and the gate insulating film16by way of the openings22aat the scan-line terminals22. The signal lines12are exposed from the passivation film20by way of the openings23aat the signal-line terminals23. The common lines30are exposed from the passivation film20and the gate insulating film16by way of the openings31aat the common-line terminals31.

Furthermore, although not illustrated here, an alignment layer is formed on the passivation film20. Thus, the active matrix substrate1A according to the second embodiment is completed.

On the other hand, an opposite substrate (not shown) is placed to be opposed to the active matrix substrate1at a specific gap and then, these two substrates are coupled together with a sealing member so as to confine a liquid crystal in the gap. Thus, the LCD panel is completed.

Thereafter, one end of a flat cable of a driver circuit unit is connected to the respective scan, common, and signal lines11,30, and12at their terminals22,31, and23. Thus, the conductive lines combined in the cable are connected to the scan, common, and signal lines11,30, and12, resulting in electrical interconnection of the driver circuit unit with the lines11,30, and12in the LCD device. This makes it possible to supply electric power to the LCD panel and to drive the pixels on the active matrix substrate1A, thereby displaying images on the screen of the device. In this way, the active matrix addressing LCD device of the second embodiment is finally fabricated.

With the LCD device according to the second embodiment, the active matrix substrate1A employs the four-level TiN/Ti/Al/Ti structure to form the gate electrodes15, and the scan, common, and signal lines11,30, and12and therefore, the effect to suppress Al hillocks is enhanced or raised without complicating the structure of the lines11, compared with the prior-art TiN/Al structure of the of the Publication No. 7-120789. This is the same as the first embodiment.

Moreover, since the Ti film104or134is additionally formed below the Al film101or131, there is an additional advantage that the crystallinity of the Al film101or131is improved, thereby suppressing the migration phenomenon. This enhances the effect of the TiN/Ti/Al structure to suppress the Al hillock.

The inventors conducted the same test for measuring the electrical connection resistance as shown in the first embodiment with respect to the scan-line terminals22, the common-line terminals31, and the signal-line terminals23. As a result, the same result to represent the improvement of connection reliability as shown inFIG. 8was obtained if the TiN film103or133has a nitrogen concentration of 25 atomic % or higher.

It was found from the same test as above that substantially no change was observed about the effect to suppress the Al hillock even if the thickness of the TiN film was changed.

Third Embodiment

Although not illustrated here, an active matrix substrate used in an active matrix addressing LCD device according to a third embodiment has a three-level TiN/Al/Ti structure. Examples of the thickness of these Ti, Al, and TiN films are shown by the sample Nos.5and6inFIG. 7. The other configuration of the active matrix substrate of the third embodiment is the same as the substrate1of the first embodiment.

As seen fromFIG. 7, the substrate of the third embodiment has an additional advantage that the number of Al hillocks can be made substantially zero, in other words, Al hillocks can be prevented approximately completely.

Variations

Needless to say, the invention is not limited to the above-described first to third embodiments. Any change or modification may be added to these embodiments within the spirit of the invention. For example, although a substantially pure Al film is used in the first to third embodiments, the invention is not limited to this. Any Al alloy film may be used instead of a substantially pure Al film to get the advantages of the invention.

While the preferred forms of the present invention has been described, it is to be understood that modifications will be apparent to those skilled in the art without departing from the spirit of the invention. The scope of the present invention, therefore, is to be determined solely by the following claims.