JPH06337440A - Mim type nonlinear element and manufacture thereof - Google Patents

Abstract

PURPOSE:To reduce element capacity as well as wiring resistance, heighten image quality of a liquid crystal display panel, and enable enlargement by forming a scanning line and a metal electrode layer as a specific multilayer structure, and thickening a film thickness of an insulating film of an upper layer metal side wall part. CONSTITUTION:In a metal - insulator - metal(MIM) type nonlinear element having such a structure as the first metal electrode layer, an insulating film and the second metal electrode layer to be connected electrically to a scanning circuit through a scanning line are laminated in order upon each other, the scanning line and the first metal electrode layer are constituted as a two-layer structure of lower layer metal 202 composed of tantalum or alloy mainly composed of tantalum and upper layer metal 203 composed of aluminium or alloy mainly composed of aluminium. A film thickness of an insulating film (Al postive electrode oxide film) 204 of an upper layer metal side wall part is made thicker than a film thickness of an insulating film (Ta positive electrode oxide film) of a lower layer metal side wall part. A chrome layer 207 having a prescribed film thickness is formed above these.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a MIM used for a switching element such as an active matrix type liquid crystal display panel.
Type non-linear element structure, material composition and manufacturing method.

[0002]

2. Description of the Related Art Generally, in an active matrix type liquid crystal display panel, it is arranged between a substrate on one side on which a non-linear element is provided in each pixel region to form a matrix array and a substrate on the other side on which a color filter is formed. Is filled with liquid crystal and the alignment state of the liquid crystal is controlled for each pixel area to display predetermined information. Here, as the non-linear element, a three-terminal element such as a thin film transistor (TFT) or a metal-
A two-terminal element such as an insulator-metal (MIM) type non-linear element is used, but in order to meet the demand for a larger screen and a lower cost for a liquid crystal display panel, the element structure is simple and the process is short. A method using a non-linear element is advantageous. Further, when the MIM type non-linear element is used,
Since the scanning line can be provided on the substrate on one side where the matrix array is formed and the signal line can be provided on the substrate on the other side,
There is also an advantage that a crossover short circuit between the scanning line and the signal line does not occur.

In the active matrix type liquid crystal display panel using the MIM type non-linear element, as shown in FIG. 6, the MIM type non-linear element is provided between each scanning line 601 and each signal line 602 for each pixel region 603. 604 (indicated by a varistor symbol in the figure) and a liquid crystal display element 605 (indicated by a capacitor symbol in the diagram) are connected in series, and based on signals applied to the scanning lines and the signal lines. The display operation is controlled by switching the liquid crystal display element to the display state, the non-display state or an intermediate state thereof.

As shown by 701 in FIG. 7A, the MIM
In the non-linear element, the applied voltage V _NL and the current I _NL have a non-linear relationship. Assuming that the threshold voltage of the MIM type non-linear element is V _th , the threshold voltage of the liquid crystal display element is V _b , and the potential in the display state is (V _b + ΔV), FIG.
As shown in (b), in the selection period, a predetermined pixel area 60
By setting the potential difference V (voltage applied to the unit pixel) between the scanning line 601 and the signal line 602 in (3) to (V _b + V _th ), the liquid crystal display element 605 can be brought into a non-display state, and scanning is performed. By setting the potential difference V between the line 601 and the signal line 602 to be (V _b + V _th + ΔV), the liquid crystal display element 605 can be brought into a display state. On the other hand, in the non-selection period, the voltage V applied to the unit pixel is set to be close to the potential remaining in the liquid crystal display element 605, and if the difference is V _th or less, the MIM is performed in the non-selection period.
The non-linear element 604 is always in a cutoff state, and the state defined in the selection period is maintained as it is.

The above is an ideal M in which the element capacitance is sufficiently smaller than the liquid crystal capacitance and the nonlinearity of the voltage-current characteristic is sufficiently high.
This is the most basic operation example when the IM nonlinear element 604 can be obtained. In practice, there are problems such as a small capacitance ratio between the MIM type non-linear element 604 and the liquid crystal display element 605 and insufficient non-linearity of the voltage-current characteristic, and therefore, a very complicated driving method (application Voltage waveform) has been devised and used.

As shown in FIG. 5, a conventional MIM type non-linear element is formed on the surface of an insulating substrate 501 and has a tantalum layer 502 which is conductively connected to a scanning circuit via a scanning line and an insulation formed on the surface. A film (Ta anodic oxide film) 503,
The chrome layer 504 is formed on the surface thereof and is conductively connected to the pixel electrode 505. In addition, the insulating film (Ta
The anodic oxide film 503 is formed by anodic oxidation of the tantalum layer 502 so that it is formed uniformly on the surface of the tantalum layer 502 without pinholes.

A general process example for realizing this structure is as follows.

1. By depositing a tantalum film on a glass substrate by sputtering and performing thermal oxidation, about 100
1. a step of forming a 0Å tantalum oxide film; Next, sputter the tantalum film to 3000 Å
2. Deposit and pattern. Next, a step of forming a tantalum oxide film by performing anodic oxidation at 30 V using, for example, an aqueous citric acid solution as a chemical conversion solution, and 4. Next, a step of depositing and patterning a chromium film to be the second metal electrode layer of the MIM type non-linear element by a 1500Å sputtering method, and 5. Next, a step of depositing an ITO film to be a pixel electrode by 1000 Å by a sputtering method and patterning it.

[0009]

In the conventional MIM type non-linear element, all the intersections of the first metal electrode layer and the element insulating film and the second metal electrode layer are used as elements, and the capacitance with the liquid crystal element is used. Since the ratio is small, it has been an obstacle to the high definition of the liquid crystal display panel using the MIM type non-linear element.

To solve this, the '91 IDRC
Digest P. In 247, a method of laterally disposing the MIM type non-linear element by using the side surface portion of the first metal electrode layer is introduced.

According to this method, the element area of the MIM type non-linear element can be reduced and the liquid crystal display panel can be made finer.

However, when tantalum is used for the scanning line, the delay of the electric signal from the scanning circuit due to the high specific resistance of tantalum becomes a problem, and in order to solve this, there is a means of increasing the pattern width of the scanning line. It is necessary to take measures, which causes a problem that the effective display area is reduced.

In addition, the '91 IDRC Digest
P. In the manufacturing method introduced in No. 247, it is necessary to increase the photolithography process more than in the past, and the process becomes complicated, and the cost merit which is the characteristic of the MIM type non-linear element is sacrificed.

[0014]

Means for Solving the Problems In order to solve the above-mentioned problems, the means taken in the present invention is to provide a scanning line and a first metal electrode layer with tantalum or an alloy containing tantalum as a main component of a lower layer metal, aluminum or The alloy having aluminum as a main component has a two-layer structure in which it is an upper metal layer.

When patterning the scan line and the first metal electrode layer, after patterning the upper layer metal, anodic oxidation is performed and the lower layer metal is etched using this anodic oxide film as a mask, or the upper layer metal is previously formed. By etching the upper layer metal and the lower layer metal using the selectively formed anodic oxide film as a mask, the number of photolithography steps can be suppressed to the same number as the conventional number.

[0016]

EXAMPLES A method of manufacturing a MIM type non-linear element according to the present invention will be described below with reference to the drawings.

FIG. 1A is a sectional view of a MIM type non-linear element according to the first embodiment of the present invention, FIG. 1B is a sectional view of an MIM type non-linear element according to the second embodiment of the present invention, and FIG. Example 1 of
3 is a cross-sectional view showing the manufacturing process of the MIM type non-linear element of FIG. 3, FIG. 3 is a cross-sectional view showing the manufacturing process of the MIM type non-linear element of Example 2 of the present invention, and FIG. FIG. 5 is a plan view showing a state before the element insulating film is formed.

Among the metals forming the scanning line and the first metal electrode layer, tantalum was used as the lower layer metal and aluminum was used as the upper layer metal. The lower layer metal was an alloy containing tantalum as a main component, and the upper layer metal was mainly aluminum. You may use the metal as a component.

Example 1 A 2000 Å tantalum layer 202 is formed on the surface of an insulating substrate 201 such as glass or ceramics.
And 1000 Å aluminum layer 203 are continuously formed by sputtering, and then a photoresist pattern is formed by photolithography technique.
Is etched and patterned. At this time, the aluminum layer 203 may be etched by either a dry etching method or a wet etching method.

The thickness of the tantalum layer 202 is 1500 to 2000 in consideration of the reduction of the thickness of the metal due to anodic oxidation.
Å, the thickness of the aluminum layer 203 is 800 to 1300Å
Decide between

Next, using an electrolytic solution such as an ammonium tartrate aqueous solution whose pH is adjusted to 6.5 to 7.5, which does not form a porous aluminum oxide film, 40 to 8 is used.
An insulating film (Al anodic oxide film) 204 and an insulating film (Ta anodic oxide film) are formed on the surfaces of the patterned aluminum layer 203 and the tantalum layer 202 exposed by the etching of the aluminum layer 203 by performing anodic oxidation at a voltage of about 0 V, respectively. ) 205 is formed, and the state shown in FIG.

Next, using the previously formed insulating film (Al anodized film) 204 as a mask, the insulating film (Ta anodized film) 205 and the tantalum layer 202 are chemically dry-etched using carbon tetrafluoride. Etched by
The shape is as shown in FIG. In this method, the aluminum layer 203 and the insulating film (Al anodic oxide film) 20 are used.
Since No. 4 is not etched, it is not necessary to newly provide a photoresist pattern. A plan view of these patterns after etching is as shown in FIG.

Next, anodic oxidation is performed at a voltage of 25 to 40 V to form an insulating film (Ta anodic oxide film) 206 having a predetermined thickness. Regarding the electrolytic solution used at this time, since the aluminum layer 203 is not exposed, there is no particular limitation on the pH value as in the first anodic oxidation, and the anodic oxidation may be performed using an electrolytic solution such as citric acid or phosphoric acid. It is possible.

Here, when the second anodic oxidation is performed, a portion which will be a terminal is covered with an organic insulating film 401 such as a photoresist as shown in FIG. 4B, and the tantalum layer 2 of the terminal portion is covered.
02 The side wall is not anodized.

Further, the insulating film (Ta anodic oxide film) 206 is thinner than the insulating film (Al anodic oxide film) 204.

Next, after forming a chromium layer 207 having a predetermined thickness by sputtering, patterning is performed to form the chromium layer 207 as shown in FIG. 2 (f). Here, as the second metal electrode layer, titanium, molybdenum, or the like may be used instead of chromium.

Here, the terminal portion is, as shown in FIG.
It should be completely covered by the chrome layer 207.
Accordingly, when etching the pixel electrode 208, IT
It is possible to prevent aluminum from being corroded by an etching solution of O, and conductively connect the first metal electrode layer and the second metal electrode layer to reduce the wiring resistance by using the scanning line as two layers of aluminum and tantalum. The effect is not lost.

Next, an ITO film having a predetermined thickness is formed by sputtering, and then patterning is performed, as shown in FIG.
The pixel electrode 208 is formed as in (f).

At this time, if the terminal portion is not anodized, the second metal electrode layer and the pixel electrode 208 must be formed in this order in order to prevent corrosion of aluminum by the ITO etching solution. When the entire surface is also anodized, the second metal electrode layer and the pixel electrode 2
It does not matter which of the 08 is formed first.

Further, the second metal electrode layer and the pixel electrode 208
It is also possible to apply a simpler process by using the same material as the photolithography technique and etching once.

Example 2 On the surface of the insulating substrate 301, 2
After continuously forming a 000 Å tantalum layer 302 and a 1000 Å aluminum layer 303 by sputtering, a photoresist pattern 309 is formed by a photolithography technique so that the photoresist in the scan line and the portion to be the first metal electrode layer is removed. After that, selective anodic oxidation is performed to form an insulating film (Al anodic oxide film) 304. At this time, an anodic oxidation is performed at a voltage of about 40 to 80 V using an electrolytic solution such as an ammonium tartrate aqueous solution whose pH is adjusted to 6.5 to 7.5 that does not form a porous aluminum oxide film.

Here, the film thicknesses of the tantalum layer 302 and the aluminum layer 303 are determined for the same reason as in the first embodiment.

Next, the photoresist pattern 309 is peeled off, and the formed insulating film (Al anodic oxide film) 304 is used as a mask to form the aluminum layer 303 and the tantalum layer 302.
Is etched into a shape as shown in FIG. At this time, the aluminum layer 303 is wet-etched using a mixed acid of nitric acid and phosphoric acid, and the tantalum layer 302 is etched by a chemical dry etching method using carbon tetrafluoride as an etching gas. A plan view of these patterns after etching is as shown in FIG.

Next, using an electrolyte solution such as an ammonium tartrate aqueous solution whose pH is adjusted to 6.5 to 7.5, which does not form a porous aluminum oxide film, 25 to 40 V is used.
Are again anodized at a voltage of 3 .mu.m, and an insulating film (Al anodized film) 305 and an insulating film (Ta anodized film) are formed on the side wall of the aluminum layer 303 and the side wall of the tantalum layer 302, respectively.
306 is formed, and the state as shown in FIG.

Here, when the second anodic oxidation is performed, the terminal portion is covered with an organic insulating film 401 such as a photoresist as shown in FIG. 4B, and the side wall portion of the terminal portion is not anodized. To do so.

Further, the insulating film (Al anodized film) 304 is formed on the side wall of the insulating film (Al anodized film) 304.
5 is thinner, and insulating film (Ta anodic oxide film) 3
06 is 10 compared with the insulating film (Al anodic oxide film) 305.
It is about 0 to 150Å thicker. This is because the growth rate of the tantalum anodic oxide film is 18 to 19Å / V, whereas that of aluminum is 13 to 14Å / V.

The subsequent steps are the same as in the first embodiment.

The sheet resistance is 6.4 to 6.5 Ω / □ when the film thickness of tantalum is 3000 Å.

The sheet resistance when the upper layer is aluminum and the lower layer is tantalum is almost determined by the film thickness of aluminum. For example, the film thickness of the upper aluminum is 100
The sheet resistance is 0.3 to 0.4 Ω / □ when 0 Å and the thickness of the lower tantalum film is 2000 Å.
The wiring resistance can be reduced to about 7%. As an extreme example, if the film thickness of aluminum is 100
Even with Å, the wiring resistance is smaller than before.

Comparing the example with the conventional MIM type non-linear element, in the example, among the insulating films, the upper surface of the first metal electrode layer is an aluminum oxide film, and the side wall is an aluminum oxide film and a tantalum oxide film. The conventional insulating film is a tantalum oxide film.

Since the relative permittivity of the aluminum oxide is 1/2 to 1/4 of the relative permittivity of the tantalum oxide, even if the element areas are the same, the MIM type non-linear element of the embodiment. The device capacitance can be made smaller than that of the conventional MIM type nonlinear device.

For example, the film thickness of the first metal electrode layer is 300.
0 Å, the taper angle of the first metal electrode layer is 45 degrees, and the element area of the MIM type non-linear element when viewed in a plane is 16 μ.
Assuming that m ² is 600 Å and the thickness of the insulating film is 600 Å, the element capacitance is 6.9 × 10 ^-14 F when the first metal electrode layer is a single tantalum layer as in the conventional case.

The element capacitance in the case of Example 1 will be taken as an example.

The tantalum layer 202 has a thickness of 2000 Å, the aluminum layer 203 has a thickness of 1000 Å, and the insulating film (Al
Anodized film 204 has a film thickness of 1000Å and an insulating film (Ta
If the thickness of the anodic oxide film) 206 is 600 Å and the device area is the same as the conventional one, the device capacity is 1.9 × 1.
It becomes 0 ^-14 F, and it is possible to reduce the element capacitance to about 30% of the conventional value.

Even in the case of Example 2, the insulating film (A
The influence of the thin (1 anodic oxide film) 305 is small, and the same effect as in the case of the first embodiment can be obtained.

Even if the first metal electrode layer is made of a single aluminum layer as in the conventional structure, the wiring resistance is lowered and the element capacitance is also reduced. However, if the insulating film is only aluminum oxide, the threshold voltage Vth of the MIM type non-linear element shown in FIG. 7A becomes high, which makes it necessary to increase the drive voltage of the liquid crystal display panel, resulting in power consumption. Growing is not realistic. Further, if the film thickness of aluminum oxide is reduced in order to reduce Vth, the element capacitance increases correspondingly, and the effect of reducing the element capacitance is halved.

By using tantalum oxide and aluminum oxide at the same time for the insulating film, Vth can be set to an appropriate value, and at the same time, an effect can be obtained in reducing the element capacitance.

[0048]

As described above, in the present invention, the first metal electrode layer forming the scanning line and the MIM type non-linear element is mainly composed of tantalum or an alloy containing tantalum as a lower layer metal, aluminum or aluminum. The alloy as a component has a two-layer structure in which the upper layer metal is patterned. After patterning the upper layer metal, anodic oxidation is performed, and the lower layer metal is etched using this anodic oxide film as a mask, or an anode of the upper layer metal that is selectively formed in advance. Using the oxide film as a mask,
By etching the upper metal and the lower metal,
It is characterized in that the scan line and the first metal electrode layer are formed.

According to the present invention, the following effects can be obtained.

By forming the scanning line and the first metal electrode layer into a two-layer structure in which aluminum is the upper metal and tantalum is the lower metal, the MIM type non-linear element with reduced wiring resistance and reduced element capacitance is obtained. Can be realized.

By reducing the element capacitance and wiring resistance,
It is possible to improve the image quality and increase the size of the liquid crystal display panel.

By patterning the scanning line and the first metal electrode layer using the aluminum anodic oxide film as a mask, a MIM type non-linear element having a small wiring resistance and a small element capacitance can be formed by the same number of photolithography steps as the conventional one. It can be manufactured.

[Brief description of drawings]

FIG. 1A is a sectional view of a MIM type non-linear element according to a first embodiment of the present invention. (B) is sectional drawing of Example 2 of this invention.

2A to 2F are MIMs of Embodiment 1 of the present invention.
6A and 6B are cross-sectional views showing the manufacturing process of the non-linear element.

3A to 3E are MIMs of Embodiment 2 of the present invention.
6A and 6B are cross-sectional views showing the manufacturing process of the non-linear element.

4 (a) and 4 (b) are plan views showing a process before the second anodic oxidation in the manufacturing process of the MIM type nonlinear device of the present invention. FIG. 6C is an enlarged plan view of the terminal portion after the second metal electrode layer is formed.

FIG. 5 is a cross-sectional view of a conventional MIM type nonlinear element.

FIG. 6 is an equivalent circuit diagram of an active matrix type liquid crystal display panel using a MIM type nonlinear element.

FIG. 7A is a relationship diagram between an applied voltage and a current of a MIM type non-linear element forming a matrix array of a liquid crystal display panel. (B) is a relationship diagram showing the relationship between the applied voltage to the unit pixel and the brightness of the display.

[Explanation of symbols]

201, 301, 501 ... Insulating substrate 202, 302, 502 ... Tantalum layer 203, 303 ... Aluminum layer 204, 304, 305 ... Insulating film (Al anodized film) 205, 206, 306, 503 ... Insulating film (Ta anodic oxide film) 207, 307, 504 ... Chrome layer 208, 308, 505 ... Pixel electrode 309 ... Photoresist pattern 401 ... Organic insulating film 601 ... Scanning line 602 ... Signal line 603 ... Pixel region 604 ... MIM type non-linear element 605 ... Liquid crystal display element 701 ... Typical voltage-current characteristic of MIM type non-linear element

Claims (6)

[Claims] 1. A MIM type non-linear element having a structure in which a first metal electrode layer, an insulating film, and a second metal electrode layer, which are conductively connected to a scanning circuit via a scanning line, are sequentially laminated, The first metal electrode layer has a two-layer structure of a lower metal layer made of tantalum or an alloy containing tantalum as a main component and an upper metal layer made of aluminum or an alloy containing aluminum as a main component. The MIM type non-linear element is characterized in that the film thickness of the insulating film is thicker than the film thickness of the insulating film on the side wall of the lower metal layer. 2. A method for manufacturing a MIM type non-linear element, comprising: (1) a first step of forming a lower metal layer made of tantalum or an alloy containing tantalum as a main component; and (2) aluminum or an aluminum containing as a main component. Second, forming an upper metal layer made of an alloy on the lower metal layer
And (3) forming a photoresist pattern, patterning the upper layer metal into a predetermined shape, and removing the photoresist pattern; (4) exposing the upper layer metal by patterning A fourth step of forming a first anodic oxidation film on the lower layer metal to form an anodic oxide film, and (5) forming the anodic oxide film on the lower layer metal surface using the anodic oxide film formed on the upper layer metal surface as a mask. A fifth step of etching the anodic oxide film and the lower metal layer and patterning them into a predetermined shape; and (6) performing a second anodic oxidation to form an anodic oxide film on the side wall portion of the lower metal layer. The manufacturing method of the MIM type | mold nonlinear element characterized by including the process of. 3. The M according to claim 2, wherein the second anodic oxidation for forming the anodic oxide film on the side wall of the lower metal layer is performed at a voltage equal to or lower than the voltage of the first anodic oxidation.
IM-type non-linear element manufacturing method. 4. An MIM type non-linear element having a structure in which a first metal electrode layer, an insulating film, and a second metal electrode layer, which are conductively connected to a scanning circuit via a scanning line, are sequentially laminated, The first metal electrode layer has a two-layer structure of a lower metal layer made of tantalum or an alloy containing tantalum as a main component and an upper metal layer made of aluminum or an alloy containing aluminum as a main component. And the insulating film of the lower metal side wall portion are simultaneously formed. 5. A method of manufacturing a MIM type non-linear element, comprising: (1) a first step of forming a lower layer metal made of tantalum or an alloy containing tantalum as a main component; and (2) aluminum or an aluminum containing as a main component. Second, forming an upper metal layer made of an alloy on the lower metal layer
And (3) forming a photoresist pattern, and selectively performing the first anodic oxidation on the upper layer metal only with the scanning line and the portion to be the first metal electrode layer using the photoresist pattern as a mask. A third step of forming an anodic oxide film on the upper surface of the upper metal layer, and then removing the photoresist pattern, and (4) etching the upper metal layer and the lower metal layer using the anodic oxide film as a mask to obtain a predetermined pattern. A fourth step of patterning into a shape; and (5) a second anodic oxidation to simultaneously form an anodic oxide film on the upper metal side wall and the lower metal side wall.
The manufacturing method of the MIM type | mold nonlinear element characterized by including the process of. 6. The second anodic oxidation for simultaneously forming an anodic oxide film on the upper metal side wall and the lower metal side wall is performed at a voltage equal to or lower than the voltage of the first anodic oxidation. Item 6. A method of manufacturing a MIM type non-linear element according to item 5.