JPH01300226A - Matrix array substrate and its manufacture - Google Patents

Abstract

PURPOSE:To reduce the resistance of a wiring electrode by putting the pattern of a base conduction diagram behind the pattern of lower metal at the part where an MIM element is present, and further making an insulator layer at the periphery of the base conduction diagram thicker than the insulator of the MIM element. CONSTITUTION:The lower metal 14 of a nonlinear resistance element in electrically connected metal-insulator-metal(MIM) element structure on a side closer to a substrate 10 is formed by interposing a base conductive layer 15 which is lower in specific resistance than the lower metal 14 between the lower metal and substrate 10, the pattern of this base conductive layer 15 is put behind the pattern of the lower metal 14 at the part where the MIM element is present, and the insulator layer 17 is formed at the periphery of the lower conductive layer 15. The insulator layer 17 is thicker than the insulator 16 of the MIM element. Therefore, a current which flows through the insulator layer 17 at the periphery of the base conductive layer 15 becomes extremely small. Consequently, the resistance of the wiring electrode for applying a signal from outside is reducible without spoiling the current-voltage characteristics of the MIM element.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) This invention uses MIM()let as a switching element.
The present invention relates to a matrix array substrate using an al-1nsulator-)tetal) element and a method for manufacturing the same.

(Prior Art) In recent years, display devices using liquid crystal displays have been used for everything from relatively simple devices such as watches, calculators, and measuring instruments to personal computers, word processors, and even terminal equipment for office automation and TV images. It has been used for displaying large amounts of information such as displays. In such large-capacity liquid crystal display devices, a matrix display multiplex driving method is generally adopted. However, due to the essential characteristics of the liquid crystal itself, this method is insufficient in terms of contrast ratio between display areas (on pixels) and non-display areas (off pixels) even when it has about 200 scanning lines. Furthermore, when performing large-scale matrix driving with approximately 500 or more scanning lines, the deterioration of contrast is fatal.

Developments to solve the drawbacks of this liquid crystal display device are actively being carried out in various places. One direction is to directly switch drive individual pixels. Thin film transistors are used as switching elements in this case. Various materials such as single crystal silicon, polycrystalline silicon, cadmium selenide, and tellurium have been proposed as semiconductors constituting thin film transistors, but amorphous silicon is currently being studied the most. However, in manufacturing this type of liquid crystal display, several microfabrication steps are required, which may result in complicated steps and poor yield. As a result, product costs have increased and manufacturing of large-scale liquid crystal displays has become extremely difficult.

Another way to use a switching element array is to use a nonlinear resistance element.

A nonlinear resistance element basically has two terminals and has a simpler structure than a thin film transistor, which has two terminals, and is easier to manufacture. Therefore, an improvement in product yield can be expected, and there is an advantage in cost reduction.

Nonlinear resistance elements are made of the same materials as thin film transistors, such as diode type junctions, varistor types using zinc oxide, and metal insulating layers with an insulator sandwiched between electrodes.
Metal (MIM) type, and even semiconductive layer (
Molds using MSI) have been developed.

This Ura MIM type has one of the simplest structures,
At present, it can be said that this is the closest to practical application. FIG. 7 is a cross-sectional view showing an example of a pixel portion of an array substrate having MIM elements. To explain this according to the manufacturing process, first, a tantalum (Ta) film 2 is formed on a glass substrate 1 by a thin film forming method such as a sputtering method or a vacuum evaporation method, and a desired pattern is formed by a photolithography method. As a result, wiring and an electrode on one side of the MIM are formed.

Next, the Ta film 2 is chemically converted by an anodic oxidation method using a citric acid aqueous solution or the like to form an oxide film 3. Furthermore, a chromium (Cr) film 4 is formed as the other electrode of the MIM by a thin film formation method, thereby completing the MIM element. Furthermore, a transparent electrode 5 for image display may be formed on this bond. This basic manufacturing technology was published in Japanese Patent Application Laid-Open No. 55-1612.
It was disclosed in Japanese Patent Publication No. 73, and its improved technology was published in Japanese Unexamined Patent Publication No. 58-1.
This is shown in JP-A No. 78320 and the like.

(Problems to be Solved by the Invention) In the conventional MIM element, as described in Japanese Unexamined Patent Publication No. 55-161273, the metal constituting the electrode on one side of the MIM element is also used for wiring. For this reason, it is not necessarily possible to use a material with low electrical resistance, and the commonly used materials such as tantalum (β-Ta) have relatively high resistance. Reducing the resistance of wiring electrodes is an essential issue in increasing the display area.

This invention was made in view of the above circumstances,
It is an object of the present invention to provide a matrix array substrate and a method for manufacturing the same that can reduce the resistance of wiring electrodes without increasing the number of photolithography steps compared to conventional ones.

[Structure of the Invention] (Means for Solving the Problems) In the matrix array substrate of the invention according to claim 1, the lower metal on the side closer to the substrate in the MIM element as a nonlinear resistance element has a gap between the lower metal and the substrate. A base conductive layer with low specific resistance is interposed, and the pattern of this base conductive layer is set back from the lower metal pattern in the area where the MIM element is present, and the thickness of the insulating layer around the base conductive layer is is set to be much larger than the thickness of the insulator of the MIM element.

In addition, in the method for manufacturing a matrix array substrate of the invention as claimed in claim 2, the lower metal and wiring electrodes of the nonlinear resistance element are formed on the substrate with relatively low resistance (at least β-T).
Form a metal pattern (resistivity lower than that of a) on the entire surface of the metal pattern and other plugging plates (meaning almost the entire surface, taking into account the parts that are removed as necessary during film formation or in the process),
An insulating layer that is to become an insulator constituting a nonlinear resistance element is formed. Thin film formation methods include vapor deposition, sputtering, and CVD.
(Chemical Vapor Deposit
There are various methods such as on) and coating, but in this invention, an anodic oxide film obtained by anodization of a metal, which is preferable in terms of characteristics, is used. Therefore, in terms of process, it is sufficient to form a thin metal over the entire surface and then completely oxidize it to form an insulating layer. Therefore, we investigated the optimal current density for anodizing this thin metal, and found that if the current density was low, the formation time would take a long time, but if the current density was high, the formation would not be uniform over the entire surface, and no formation would occur. There was a problem in that the metal remained in dots and the transmittance did not decrease. The present inventor investigated formation current density conditions that can achieve both uniformity over the entire surface and a practical formation time, and found that a current density o, in the range of oi to 0.1 mA/cri is preferable. Furthermore, since there is a possibility that the lower metal in the underlying layer may also be partially oxidized, it is preferable that the oxide of the lower metal can also be used to some extent as an insulating layer of the MIM element. Next, by forming the upper metal pattern of the MIM cable and forming the display pixel electrode made of a transparent conductive film, it is possible to realize a matrix array substrate in which the resistance of the wiring electrodes is lowered.

(Function) In the matrix array substrate of the invention as claimed in claim 1, the pattern of the base conductive layer is set back from the lower metal pattern of the MIM element, and the thickness of the insulator layer formed around the base conductive layer is Since it is thicker than the insulator of the MIM element portion, the current flowing through the insulator layer around the base conductive layer is extremely small. As a result, the resistance of the wiring electrode for applying a signal from the outside can be reduced without impairing the current-voltage characteristics of the MIM element.

In order to obtain this matrix array substrate, the following method is used in the present invention.

That is, before forming a Ta film on a substrate, AI, Cr,
At least one base conductive layer of Ti, Ni, Mo, Nb, W, etc. is formed. After this, Ta is patterned, but it is necessary to prevent the underlying conductive layer below from coming out of the Ta pattern.

This can be achieved by selectively etching only this conductive layer after patterning Ta. For example, if A1 or Mo is selected as the underlying conductive layer, HCL-HNO3
If a series etchant is used, only the underlying conductive layer is etched without changing Ta. Furthermore, even in the dry etching method, combinations and conditions that allow selective etching can be found by carefully examining the reactivity of various gases.

Next, the 1q metal double layer pattern thus obtained is anodized. Anodic oxidation produces a variety of coatings depending on the metal being treated. Here, a combination of materials and anodization conditions are selected so that the thickness of the anodic oxide film formed by the base conductive layer is thicker than that of the lower metal anodic oxide film forming the original MIM element. In general, the insulator layer of an MIM element is a dense film through which a constant current flows, that is, a barrier film, and an anodized film of Ta falls under this category. On the other hand, the A1 coating, except when the electrolyte is extremely neutral,
It becomes a porous film. In terms of the formation process, the barrier film has a thickness that is uniquely determined by a constant formation voltage, and the formation time saturates the thickness within a certain length. On the other hand, porous films tend to increase in film thickness over time. This invention is realized by skillfully combining these. FIG. 3 is a diagram showing the growth-time dependence of a positive #A oxide film of Ta and A1. You can read it from the same figure.
When the electrolytic solution was 5% citric acid and the formation voltage was 36 V, the Ta anodic oxide film reached saturation with a thickness of 0.06 μm after 15 minutes, whereas the A1 anodic oxide film had a thickness of 0.3 μm after 1 hour.
m, and its speed increased in proportion to time. and 3
After some time, the film thickness difference was 0.84 μm, and it was found that the original Ta pattern and the A1 pattern had almost the same boundary when the difference was 0.9 μm.

Here, if, for example, Cr is formed as the upper metal of the MIM element, the distance between Cr and Ta is 0.06 μm, and the distance between Cr and A is 0.06 μm.
The distance between I is 0.9 μm, and when a voltage is applied between the upper electrode (Cr) and the lower electrode (Ta/A
(Nonlinear characteristics do not occur in such a configuration), the current is extremely large, and it is possible to reduce the resistance of the wiring part and exhibit good I-■ characteristics, even switching characteristics. can.

On the other hand, in relation to the invention described in claim 2, N of various composition ratios
A sample of the b-choa alloy film was prepared and its resistivity was investigated, as shown in FIG. 4.

That is, it has been found that when the composition ratio of Ta is 90% or less, the specific resistance is considerably smaller than that of tetragonal Ta, which is 180 to 200 μΩ·cm. Therefore, we performed patterning and anodic oxidation of the alloy film on various samples.
Furthermore, an MIM element was formed by forming an electrode on this. When we measured the current-voltage characteristics of these elements, we found that the Ta composition ratio was 20 to 90.
% showed good properties. Note that here, the symmetry of the current with respect to the polarity of the applied voltage and the magnitude of the current density at a constant voltage (for example, 2 V, 10 V) were taken into consideration. Therefore, by using these alloys, it is possible to lower the electrode wiring resistance and suppress, for example, distortion of the applied voltage waveform inside the liquid crystal device and reduction in the effective voltage value, thereby enabling a larger display.

Here, the electrode material according to the present invention will be described in detail. Originally, the preferable characteristics for an MIM cord are largely based on the oxide of one electrode metal, mainly Ta. From this point of view, Ta, W, Nb, Mo, AI, Ti, Zr, etc., or alloys thereof are recommended as the metal oxide for forming the insulator of the MIM element. In particular, Ta and Wang a-W, Ta-MO, Ta-Nb, Ta-Ti
, Ta-7-r and other Ta-based alloys are good M
Experiments conducted by the present inventor have revealed that it exhibits IM characteristics (sufficient current-voltage characteristics). There are various methods for forming these oxide layers, and any of them can be applied to the present invention, but the above-mentioned film obtained by anodizing a metal with a predetermined electrolyte is particularly preferable in terms of characteristics. In anodic oxidation, the Ta and its alloy films change into oxides having about 2.5 times the volume.

Therefore, by forming the metal layer in advance to a thickness of 0.004 to 0.4 μm, an oxide film of 0.01 to 0.1 μm in thickness can be obtained. Oa
A thickness of μm is preferable.

Conventionally, in order to convert the surface layer of a metal film (Ta, etc.) into an anodic oxide film, a forming voltage (0.00167 μm/V in the case of Ta, according to the inventor's experiments) corresponding to a predetermined thickness was selected. , constant current density (typically 0.1-10 mA/ct
it), chemical conversion was performed until the residual current became below a certain level. However, the inventors have discovered that when anodizing the entire thin metal film, a uniform oxide film cannot be formed within a practical time unless the current density is limited to a certain range.

Next, the experimental results that led to this invention will be described.

FIG. 5 is a diagram showing the relationship between anodic oxidation current density and transmittance. As can be seen from the figure, when the current density is 0.1 mA/crA or less, more preferably 0.08 mA/ri or less, unconverted metal remains in dots,
This lowered the transmittance, resulting in a deterioration of the appearance and, ultimately, the characteristics. Further, FIG. 6 is a diagram showing the relationship between anodizing current density and anodizing time. As can be seen from the figure, when the current density is low, the formation time becomes long and long. Practically, it is not preferable that the formation time takes more than 2 hours, and within this limit, the current density is determined to be 0.01 mA/cff1 or more.

Therefore, as a result of studying the optimal current density for anodizing thin metals, the current density during anodization is 0.01~0.1m^/
It turns out that d is good.

Further, it is preferable in terms of characteristics that the lower metal of the nonlinear resistance element is formed of a material having a lower resistivity than the metal used to form the oxide. The reason for this is that the lower metal also serves as a wiring electrode for power supply, and lowering the resistance of this part prevents uneven signal and scanning waveforms and potential drops, making it possible to drive a larger number of lines. This makes it possible to meet technological demands for increased display capacity and larger screens. However, the types of metals are limited due to the characteristics of MIM elements. In this invention, a part of the metal that should be converted into an insulator may remain and become part of the lower metal, but in many cases, a part of the lower metal that is selected and used with the intention of low resistance is used. is likely to be oxidized and form part of the insulator of the MIM device. For this reason, it is preferable that the lower metal selected for its low resistance is also a material that can be converted into an insulator of the MIM element. For example, when the insulator layer is Ta205,
As the lower metal, a material such as an alloy of 1-a and MO, an alloy of Ta and W, and an alloy of 1-a and Nb, which has a significantly lower resistance than Ta, can be selected. In addition, the insulator layer is an alloy of 1'-a and MO (Ta in weight %:
Mo=80:20), the lower metal is Ta and MO
alloy (Ta:M in weight %).

= 20:80), a similar effect can be expected, and there are many different combinations.

(Example) The details of this invention will be explained below with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the invention as claimed in claim 1, and will be explained according to the manufacturing process. First, Figure 1(a)
As shown, a substrate 10 made of borosilicate glass, for example
A thin film 11 made of A1 with a thickness of 0.5 .mu.m and a thin film 12 made of Ha with a thickness of 0.1 .mu.m are successively formed thereon by sputtering. Next, as shown in FIG. 1(b), a resist is applied over the entire surface of the thin film 12, exposed using a mask, and developed to form a resist pattern 13.

Next, the thin film 12 is formed using a chemical dry etching method.
Perform etching. Here, etching is performed in a plasma containing equal amounts of C4 and 02 gases, and a Taber shape is formed around the pattern periphery (edge).Next, the first
As shown in Figure (C), when the thin film 11 is slightly over-etched using a hydrochloric acid-nitric acid based etching solution, the thin film 11 is recessed compared to the pattern of the thin film 12. Here, similar processing is also possible by dry etching using a gas containing chlorine groups. In this way, the lower metal 14 on the side closer to the substrate 10 of the nonlinear resistance element and the base conductive layer 15 interposed between the lower metal 14 and the substrate 10 are obtained. Next, as shown in FIG. 1 (d>), with the resist pattern 13 removed, chemical formation is performed in an acidic electrolyte (5% by weight citric acid aqueous solution) using the lower metal 14 as an anode, and the voltage at this time is The insulator 16 of the nonlinear resistance element and the insulator layer 17 are formed on the surface and side surfaces of the lower metal 14 and the base conductive layer 15, respectively, by controlling the In the lower metal 14 and the underlying conductive layer 15, a Ta film with a thickness of 0.024 μm is used.
changes to Ta205 with a film thickness of 0.06 μm, and the film thickness becomes 0.2 μm.
A1 with a thickness of 0.3 μm changes to Al2O3 with a thickness of 0.3 μm.

Next, as shown in FIG. 1(e), a film with a thickness of 0.14 mm was applied to the entire surface.
After forming a thin film 18 made of Cr by sputtering, a resist is applied again, and exposure and development using a mask are performed to form a resist pattern 19. continue,
As shown in FIG. 1(f), the thin film 19 is etched using a Cr etching solution prepared by dissolving 173 ceric ammonium nitrate and 5 cc of perchloric acid in 100 cc of water, thereby etching the substrate of the nonlinear resistance element. 10 is formed with an upper metal 20 on the far side and a lead-out portion (not shown) therefrom. Next, after forming a transparent conductive rpA 21 made of ITO over the entire surface, a resist is applied again, and exposure and development using a mask are performed to form a resist pattern 22. Subsequently, as shown in FIG. 1(g), the transparent conductive film 21 is etched into a predetermined pattern using hydrochloric acid, and then the resist pattern 22 is peeled off. In this way, the display pixel section 2
A part of the display pixel portion 23 is overlapped with the upper metal 20 so that the upper metal 20 is electrically connected to the upper metal 20.

In this embodiment, the display pixel section 23 is made of ITO as in the conventional case.
Under the lower metal 14 of the MIM element, which is a nonlinear resistance element, a base conductive layer 15 made of a thin film 11 of a material with lower resistance is provided, and the wiring portion is It is composed of these multiple layers.

Therefore, the resistance of the wiring electrode can be lowered compared to the case where the wiring is made of only the lower metal 14. Further, after sequentially laminating the Begin R film 11 that will become the base conductive layer 15 and the thin film 12 that will become the lower metal 14, these thin films 11
．． When etching 12 into a predetermined pattern, the pattern of the underlying conductive layer 15 is etched so as to be recessed in the portion where the nonlinear resistance element is present, compared to the pattern of the lower metal 14, and the insulating layer of the lower metal 14 is etched. Since the film thickness of the conductive layer 17 is smaller than that of the insulating layer 16 of the underlying conductive layer 15, the current-voltage characteristics of the MIM element are not impaired. Furthermore, since the base conductive layer 15 is formed at the same time as the lower metal 14 is formed, the photolithography process only needs to be performed three times.

FIG. 2 is a diagram showing an embodiment of the invention according to claim 2. First, on a substrate 30 made of borosilicate glass, for example,
An alloy film of MO-Ta alloy (MO:Ta weight ratio 40:60, specific resistance 40 μΩ·cm) with a thickness of 0.15 μm was formed by sputtering. Then, as shown in FIG. 2(a). As shown, this alloy film is patterned on the wiring electrode 31 and the lower metal 32 of the nonlinear resistance element section.For this purpose, after coating the entire surface with resist,
A resist pattern is formed by light exposure using a mask and development, and then the alloy film is etched by a chemical dry etching method. Note that this etching is performed in a plasma containing a mixture of equal amounts of CF4 and 02 gases.

Next, after peeling off the resist, a Ta film having a resistivity higher than that of the lower metal 32 is formed to a thickness of 0.02 μm by sputtering. Then, the substrate 30 is inserted into a citric acid aqueous solution, the chemical formation voltage is set to 30 V, and the current density is set to 0.02 mA/c.
The above-mentioned Ta film is entirely converted by the anodic oxidation method described in i, and a 0.05 μm Ta oxide film is formed as the insulator 33 of the nonlinear resistance element portion, as shown in FIG. 2(b). Since this Ta oxide film is transparent, it exists as a transparent insulator on the substrate 30 except for the nonlinear resistance element. Next, after forming a Cr film to a thickness of 0.15 μm,
Using a photolithography process, the upper metal 34 of the nonlinear resistance element portion is formed as shown in FIG. 2(C).

Subsequently, ITO is formed by sputtering and patterned using a photolithography process into a display pixel section 35 connected to the upper metal 34 of the nonlinear resistance element section, as shown in FIG. 2(d).

In this embodiment, a pattern of relatively low resistance metal that will become the lower metal 32 of the nonlinear resistance element portion and the wiring electrode 31 is formed on the substrate 30, and a thin metal suitable for the lower metal 32 is formed on the entire surface. This is completely oxidized to obtain the insulator 33 of the nonlinear resistance element portion. As a result, as in the previous embodiments, the resistance of the wiring electrode 31 is lower than before, and the current-voltage characteristics of the nonlinear resistance element are also good. In addition, the wiring electrode 31 and the lower metal 32
Since an insulating film is to be coated on top so as to cover these, when the upper metal 34 is formed on top of it,
The wiring portion of the upper metal 34 is laminated gently at the pattern edge portion, improving step coverage. That is,
It is possible to eliminate factors that cause defects such as step breaks in the wiring portion of the upper metal 34, which helps improve yield.

Note that, in order to form a matrix type liquid crystal display device from the obtained matrix array substrate, the following may be performed, for example. An alignment film made of polyimide resin is further coated on the nonlinear resistance element forming surface of the 1q matrix array substrate, baked, and rubbed to regulate the liquid crystal alignment direction. - For each direction, a counter substrate is prepared in which a common electrode made of ITO is formed on a substrate made of Pyrex glass, and the liquid crystal alignment direction is regulated by an alignment film made of polyimide resin and rubbing, and the long axis direction of the liquid crystal molecules is an open substrate. The liquid crystal is injected into the liquid crystal cell while maintaining a spacing of 5 to 20 degrees so that the polarization axis is twisted by about 90 degrees. Just place it.

[Effects of the Invention] The matrix array substrate and the manufacturing method thereof according to the present invention can easily reduce the resistance of wiring electrodes without impairing the characteristics of nonlinear resistance elements.
It is very effective for the practical application of 1-Rix type liquid crystal display devices.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the manufacturing process of an embodiment of the invention as claimed in claim 1, FIG. 2 is a sectional view showing an embodiment of the invention as claimed in claim 2, and FIG. 3 is an anode in Ta and A1. Figure 4 shows the relationship between oxide film thickness and formation time, Figure 4 shows the relationship between Ta composition ratio and specific resistance in Nb-Cata alloy, and Figure 5 shows the relationship between anodizing current density and the transmittance of the formed film. FIG. 6 is a diagram showing an example of the relationship between anodizing current density and formation time. FIG. 7 is a cross-sectional view showing an example of a pixel portion of a conventional matrix array substrate. 40, '30... Substrate 14, 32... Lower metal 15... Base conductive layer 16, 33... Insulator 17... Insulator layer 20, 34... Upper metal 23, 35... ...Display Pixel Department Representative Patent Attorney Nori Chika Yudo Kikuo Takehana (a) (b) (c)
(d) (e) (f) 2θ - Figure 1 Figure 2 θ3ρ and ρ1? ρ12ρMe S1ρfjEh Kuihi〃♀1
Tankaku (association) Fig. 3 Ikso ratio j3%) Fig. 4 Fig. 6 Fig. 7

Claims (2)

[Claims] (1) In a matrix array substrate in which a plurality of display pixel portions and nonlinear resistance elements having a metal-insulator-metal (MIM) element structure electrically connected to each of the display pixel portions are formed on the substrate, The lower metal on the side closer to the substrate is interposed with a base conductive layer having a lower resistivity than the lower metal, and the pattern of this base conductive layer is formed so that the lower metal is closer to the base metal in the area where the nonlinear resistance element is present. is set back from the pattern, and an insulator layer is formed around the base conductive layer, and the thickness of the insulator layer is thicker than the thickness of the insulator of the nonlinear resistance element. Matrix array substrate. (2) In a method for manufacturing a matrix array substrate in which a plurality of display pixel portions and nonlinear resistance elements having a metal-insulator-metal (MIM) element structure electrically connected to each of the display pixel portions are formed on the substrate, the nonlinear resistance The insulator of the element is formed over the entire surface of the substrate, and is made of a metal having a higher resistivity than the lower metal on the side of the nonlinear resistance element closer to the substrate at a current density of 0.01 to 0.1 mA/cm^. 2. A method for manufacturing a matrix array substrate, characterized in that the matrix array substrate is converted by an anodic oxidation method using chemical formation conditions selected from the range of 2.