JP2816172B2 - MIM element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a MIM (metal-insulating film-conductor) type switching element applicable to a high-capacity flat panel display for OA, TV, etc., particularly for driving a liquid crystal. It relates to a switching element.

[Technology]

Conventionally, as a MIM element, an element in which an insulating film is formed of an anodic oxide film or an element formed of SiNx or SiOx formed by a gas phase synthesis method (for example, a plasma CVD method) is known.

FIGS. 1 (a) and 1 (b) show schematic diagrams of MIM elements using these insulating films and particularly suitable as liquid crystal display switching elements. (A) is a perspective view, (b) is a cross-sectional view, 1 is a substrate, 2 is a lower electrode (transparent electrode),
Reference numeral 3 denotes an insulating film (for example, SiNx), and reference numeral 4 denotes an upper electrode. First
As is clear from FIG. 2B, since the cross-sectional shape of the lower electrode 2 has a rectangular outer shape, the insulating film 3 formed by a gas phase synthesis method (for example, a plasma CVD method) or the like is not There are drawbacks such as a thinner or non-uniform film thickness as compared to the upper surface. Therefore, when a voltage is applied, particularly when the voltage is continuously applied for a long time, a characteristic failure or a short circuit is likely to occur in that portion. Also, since the lower electrode 2 has a corner,
The concentration of the electric field then occurs, causing the same drawbacks as above.

Although the above is a structural defect of the conductor in the conventional MIM element, there is also a material defect of the insulating film.

That is, in the case of a MIM element in which the insulating film is formed of an anodic oxide film, (1) the insulating film is limited to the anodic oxide film of the lower metal,
It is impossible to arbitrarily control the physical property values and, consequently, control the MIM element characteristics. (2) Since a heat treatment at about 300 to 500 ° C. is required, the substrate material used is limited to one having high heat resistance. (3) Since the dielectric constant is high, when used as a switching element of a liquid crystal display device, the element area needs to be reduced due to the constraint of MIM capacitance / liquid crystal capacitance <1/10, and advanced fine processing is required. It has drawbacks such as

On the other hand, those using an insulating film (or a semi-insulating film) such as SiNx or SiOx are formed by a vapor phase synthesis method.
There is no such disadvantage as described above, and there is an advantage that property control can be performed in a wide range. However, the deposition temperature is as high as 300 ° C,
In addition to the problem that the material of the substrate is limited or that it is difficult to form a film having uniform characteristics over a large area, there is a problem that pinholes are easily generated by dust and the like, and the yield is reduced. I have.

[Problems to be solved by the invention]

A first object of the present invention is to provide a MIM element that can operate stably for a long period of time by eliminating a structural defect of a conductor in a conventional MIM element.

A second object of the present invention is to provide a low-cost and high-reliability MIM element which solves the problem of the material of the insulating film in the conventional MIM element and is particularly suitable for use in a liquid crystal display device. .

[Configuration and operation of the invention]

The MIM element of the present invention is characterized in that, in the MIM element in which an insulating film is interposed between a lower electrode and an upper electrode, the cross-sectional shape of the lower electrode is a continuous curve having no corners.

Hereinafter, an example of a method for manufacturing a MIM element according to the present invention will be described with reference to FIG.

First, Al, Ta, T is formed on a transparent substrate 1 such as glass, plastic plate or plastic film as a thin film 2 'for a lower electrode.
i, Cr, Ni, Cu, Au, Ag, W, Mo, Pt, ITO, ZnO: Al, In 2 O 3, sputtering a conductive thin film of SnO ₂ or the like, by a method such as vapor deposition, several hundreds to several thousands成膜 and a photoresist 5
Is formed in a thickness (height of the highest part) of several hundreds of m to several μm so that the cross-sectional shape becomes a continuous curved shape having no corners, for example, a substantially semicircular shape or a semielliptical shape [FIG. a)]. In order to form such a shape, in the case of a positive resist, a highly sensitive resist may be used or the dissolving ability of a developer may be increased. The cross-sectional shape of the resist is not limited to the illustrated one, but may be a tapered shape having a relatively gentle inclination.

Next, the lower electrode 2 is formed by etching using a dry etching method such as a reactive ion etching method (RIE) or an ion beam etching method (FIG. 2B). At this time, in order to make the lower electrode 2 substantially semi-circular or semi-elliptical as shown in the figure, for example, in the case of RIE, anisotropic etching is performed, and the condition that the selectivity with the resist is small, that is, What is necessary is just to perform by making gas pressure low and RF power high.

Next, a SiNx film, a hard carbon film, or the like is formed as the insulating film 3 to a thickness of several hundred to several thousand square meters by a plasma CVD method, an ion beam method, a sputtering method, or the like, and then a wet etching method, a dry etching method, or a lift-off method. To pattern a predetermined pattern [FIG. 2 (c)]. Finally, Pt, Ni, Ag, Au, Cu, Cr,
Ti, Au, W, Mo, Ta, ITO, ZnO: Al, by forming a conductive thin film such as In ₂ O _3, SnO ₂ sputtering, to a thickness of several hundreds to several thousands Å by a method such as vapor deposition, Etch to a predetermined pattern [Second
Figure (d)]. Since the MIM element manufactured in this manner has a gentle curved surface on the side of the lower electrode, when the insulating film is formed by a vapor phase synthesis method, the film thickness and physical properties become relatively uniform, and the corners are formed. Since it does not have an electric field, the electric field does not concentrate when a voltage is applied. Therefore, it operates stably for a long time, and the first object of the present invention can be achieved.

On the other hand, it is preferable to use a hard carbon film as the insulating film in order to solve various problems in the material of the conventional insulating film, which is the second object of the present invention.

This insulating film is composed of a hard carbon film (i-C film, diamond-like carbon film, amorphous diamond film, diamond thin film, etc.) containing at least one of amorphous and microcrystalline materials using carbon atoms and hydrogen atoms as main structure forming elements. Called.) One of the characteristics of the hard carbon film is that it is a vapor-grown film, so that its physical properties can be controlled over a wide range by film formation conditions as described later. Therefore, the resistance value of the insulating film covers from the semi-insulator to the insulator region, and in this sense, the MIM element of the present invention is an MSI element (Metel- Semi-Ins
ulator).

To form such a hard carbon film, an organic compound gas, particularly a hydrocarbon gas, is used. The phase state of this raw material does not necessarily need to be a gas phase at normal temperature and normal pressure, and any material that can be vaporized through melting, evaporation, sublimation, etc. by heating or decompression can be used in a liquid phase or a solid phase. is there.

For example, CH ₄ ,
Paraffin hydrocarbons such as C ₂ H ₆ , C ₃ H ₈ , C ₄ H ₁₀ , acetylene hydrocarbons such as C ₂ H ₄ , olefin hydrocarbons, diolefin hydrocarbons, and aromatic hydrocarbons Gases containing all hydrocarbons can be used.

Further, other than hydrocarbons, for example, alcohols,
Any compound containing a carbon element such as ketones, ethers, esters, and CO and CO ₂ can be used.

As a method for forming a hard carbon film from a source gas in the present invention, a method in which a film forming active species is formed through a plasma state generated by a plasma method using a direct current, a low frequency, a high frequency, or a microwave or the like However, a method using a magnetic field effect is more preferable because deposition is performed at a low pressure for the purpose of increasing the area, improving uniformity, and forming a film at a low temperature.

The active species can also be formed by high-temperature pyrolysis.
In addition, it may be formed through an ion state generated by an ionization evaporation method, an ion beam evaporation method, or the like, or may be formed from neutral particles generated by a vacuum evaporation method, a sputtering method, or the like. And, furthermore,
It may be formed by a combination of these.

An example of the deposition conditions of the hard carbon film thus produced is generally as follows in the case of the plasma CVD method.

RF output: 0.1 to 50 W / cm ² Pressure: 10 ^{-3 to} 10 Torr Deposition temperature: room temperature to 950 ° C. The raw material gas is decomposed into radicals and ions by this plasma state and reacts with it to form carbon atoms C on the substrate. A hard carbon film containing at least one of amorphous (amorphous) composed of hydrogen atoms H and microcrystalline (crystal size is several tens to several μm) is deposited. Table 1 shows various properties of the hard carbon film.

As a result of analysis by the IR absorption method and the Raman spectroscopy, the hard carbon film thus formed shows that carbon atoms form hybrid orbitals of SP ³ and SP ² as shown in FIGS. 3 and 4, respectively. It is clear that the interatomic bonds are mixed. The ratio between SP ³ and SP ² bonds can be roughly estimated by separating peaks in the IR spectrum. In the IR spectrum, spectra of many modes are overlapped and measured at 2800 to 3150 cm ^-1 , but the assignment of peaks corresponding to each wave number is clear, and as shown in FIG. Separate and calculate each peak area,
By calculating the ratio, SP ³ / SP ² can be known.

According to X-ray and electron diffraction analyses, it is known that it is in an amorphous state (a-C: H) and / or an amorphous state containing fine crystal grains of about 50 ° to several μm.

In the case of plasma CVD which is generally suitable for mass production, RF
The lower the output, the higher the specific resistance and hardness of the film, and the lower the pressure, the longer the life of the active species. Therefore, the substrate temperature can be lowered, the uniformity over a large area can be achieved, and the specific resistance and hardness increase. Tend to. Furthermore, since the plasma density decreases at low pressure, the method using the magnetic field confinement effect is particularly effective for improving the film quality.

Further, this method has a feature that a high-quality hard carbon film can be similarly formed even at a relatively low temperature condition of about room temperature to about 150 ° C., so that it is most suitable for lowering the MIM element manufacturing process. Therefore, there is a feature that the degree of freedom in selecting a substrate material to be used is widened and a uniform film can be obtained over a large area in order to easily control the substrate temperature.
Also, the structure and physical properties of the hard carbon film are as shown in Table 1,
Since control is possible over a wide range, there is an advantage that device characteristics can be freely designed. Furthermore, since the dielectric constant of the film is 3-5, which is smaller than Ta ₂ O ₅ , Al ₂ O ₃ , and SiNx used for the conventional MIM element, when making an element having the same electric capacity, Since the element size can be large, fine processing is not so required, and the yield is improved.
The capacitance ratio between the LCD and the MIM element needs to be about C _LCD : C _MIM = 10: 1.

Further, since the hardness of the film is high, the damage due to the rubbing step at the time of enclosing the liquid crystal material is small, and the yield is improved from this point as well.

In the hard carbon film as described above, in order to further expand the property control range as necessary, as an impurity in the periodic table III.
A group element, a group IV element, a group V element, an alkali metal element, an alkaline earth metal element, a nitrogen atom, an oxygen atom, a chalcogen element, or a halogen atom can be contained. This impurity doping further increases the stability of the device and the degree of freedom in device design. Usually, the amount of these impurities is 5 atomic% or less based on all the constituent atoms of the group III element of the periodic table, the amount of the group IV element is 35 atomic% or less, and the amount of the group V element is 5 atomic%. Hereinafter, the amount of the alkali metal element is 5 atom% or less, the amount of the alkaline earth metal element is 5 atom% or less, the amount of nitrogen element is 5 atom% or less, the amount of oxygen atom is 5 atom% or less, chalcogen element. The amount is 35
Atomic% or less, and the amount of halogen element is 35 atomic% or less. The amounts of these elements or atoms can be measured by a conventional method of elemental analysis, for example, Auger analysis. Also, this amount can be adjusted by the amount of other compounds contained in the source gas, film forming conditions, and the like.

Note that the range of the thickness of the insulating film and the like is 100 mm as a hard carbon film suitable for a liquid crystal driving MIM element, depending on driving conditions.
It is desirable that the specific resistance is in the range of Å to 8000Å and the specific resistance is in the range of 10 ⁶ to 10 ¹³ Ωcm. Considering the margin between the driving voltage and the withstand voltage (dielectric breakdown voltage), the film thickness is desirably 200 mm or more, and color unevenness due to a step (cell gap) between the pixel portion and the MIM element portion is practically impossible. In order not to cause a problem, it is desirable that the film thickness be 6000 mm or less. Therefore, the thickness of the hard carbon film is 200 to 6000 mm, and the specific resistance is 5 × 10 ^6.
More preferably, it is about 10 ¹² Ωcm. In addition, the number of defects in the element due to pinholes in the hard carbon film increases as the film thickness decreases, and becomes particularly remarkable at 300 ° or less (the defect rate exceeds 1%), and the in-plane distribution of the film thickness is uniform. (Thus, the accuracy of film thickness control is limited to about 30 mm, and the variation in film thickness exceeds 10%), so that the film thickness is more preferably 300 mm or more. . Further, in order to make the hard carbon film hardly exfoliated due to stress and to drive at a low duty ratio (preferably 1/1000 or less), the film thickness is more preferably 4000 ° or less. Therefore, it is more preferable that the hard carbon film has a thickness of 300 to 4000 ° and a specific resistance of 10 ⁷ to 10 ¹¹ Ωcm.

 Hereinafter, the present invention will be described with reference to examples.

Example 1 As shown in FIG. 6, ITO was deposited to a thickness of 1000 mm on a Pyrex glass substrate as a transparent substrate by a sputtering method, and then patterned to form a pixel electrode 6. Next, a MIM element was provided as an active element as follows. First, Al was deposited on the pixel electrode of the substrate to a thickness of 1000 mm by a vapor deposition method, and then patterned to form the lower electrode 2. At this time, the resist film thickness was set to 5000 mm at the highest part. Etching was performed using parallel plate RIE with CCl ₄ gas at a pressure of 0.02 Torr and RF power.
The test was performed at 0.3 W / cm ² .

A hard carbon film 2 was deposited thereon as an insulating film to a thickness of 800 mm by a plasma CVD method, and then patterned by dry etching. The film forming conditions at this time are as follows.

Pressure: 0.035 Torr CH ₄ Flow rate: 20 SCCM RF power: 0.2 W / cm ² Further, Ni is deposited on this hard carbon insulating film by a vapor deposition method at 1000 Å.
After the thick deposition, the upper electrode 4 was formed by patterning.

Example 2 A MIM device as shown in FIG. 7 was manufactured as follows. First, an Al thin film having a thickness of 1000 mm was formed on a glass plate by a vapor deposition method, and was patterned to obtain a lower metal electrode 2.

At this time, the resist film thickness and the etching conditions were the same as those in Example 1 except that CCl ₄ + O ₂ was used as an etching gas.

Next, a hard carbon film 3 having a thickness of 600 mm is coated thereon, and is patterned by dry etching to form an insulating film. An ITO film having a thickness of 1000 mm is further coated on the hard carbon film by an EB vapor deposition method, and is patterned by etching. The upper transparent pixel electrode 4 was formed. The conditions for forming the hard carbon film are as follows.

Pressure: 0.05 Torr CH ₄ Flow rate: 10 SCCM RF power: 0.1 W / cm ² [Effects of the Invention] The MIM element of the present invention has a continuous curve with no corners between the lower electrode and the upper electrode sandwiching the insulating film. With such a cross-sectional shape having the outer shape, there is an effect that reliability is high, stable operation is performed for a long time, and defects due to electrode disconnection are greatly reduced.

When a hard carbon film is used as the insulating film, this film is manufactured by 1) a gas phase synthesis method such as a plasma CVD method.
Physical properties can be controlled in a wide range depending on the film formation conditions, so that there is a large degree of freedom in device design. 2) Since it is hard and thick, it is hard to be damaged by mechanical damage. 3) Because there is no restriction on the material of the substrate, since a good quality film can be formed even at a low temperature around room temperature, 4) It is suitable for thin film devices because of its excellent uniformity of film thickness and film quality. Since the dielectric constant is low, it does not require advanced microfabrication technology, and is therefore advantageous for increasing the area of the device.
The M element is suitable as a switching element for a liquid crystal display.

[Brief description of the drawings]

1 (a) and 1 (b) are a perspective view and a sectional view of a conventional preferred MIM element, respectively. FIG. 2 is an explanatory view of a manufacturing process of an example of the MIM element of the present invention. Are the MIs of the present invention, respectively.
FIG. 5 shows an IR spectrum and a Raman spectrum of a hard carbon film based insulating film used for the M element. FIG. 5 shows a Gaussian distribution of the hard carbon film. FIGS. 6 and 7 show Example 1 respectively.
FIG. 3 is a perspective view of the MIM element manufactured in FIGS. DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Lower electrode (transparent electrode) 3 ... Insulating film, 4 ... Upper electrode 5 ... Resist, 6 ... Pixel electrode

Claims (2)

(57) [Claims] 1. A MIM device in which an insulating film is interposed between a lower electrode and an upper electrode, wherein the cross-sectional shape of the lower electrode is a continuous curved shape having no corners. 2. The MIM device according to claim 1, wherein the insulating film is made of a hard carbon film.