JPH02271579A - Mim element - Google Patents

Abstract

PURPOSE:To enable it to operate stably for a long time by putting the sectional form of at least one conductor between the first and second conductors in continuous curvature free from angles. CONSTITUTION:A conductive film is formed as a film 2' for lower electrode on a transparent substrate 1, and a photoresist 5 is formed thereon so that the sectional form may be continuous curvature free from angles. Next, this is etched by reactive ion etching method, etc., so as to form a lower electrode 2. Next, an SiNx film, a hard carbon film, or the like is formed as an insulating film 3, and then it is patterned into a specified pattern, and lastly a conductive film is formed as an upper electrode 4, and is etched into a specified pattern. In the MIM element, which is manufactured this way, the side of the lower electrode 2 has a slow curved surface, so the film thickness and the physical property become uniform when the insulating film 3 is formed by a vapor phase composing method, and it does not have angles, so electric fields are never concentrated at voltage application. Hereby, it becomes the one which operates stably for a long time.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an MIM (metal-insulating film-metal) that can be applied to high-capacity flat panel displays for OA, TV, etc.
The present invention relates to switching elements, particularly switching elements for driving liquid crystals.

[Technology]

Conventionally, MIM elements are known in which the insulating film is made of an anodic oxide film or made of SiNx or SiOx formed by a vapor phase synthesis method (for example, plasma CVD method).

A schematic diagram of an MIM element using these insulating films and particularly suitable as a liquid crystal display switching element is shown in Figure 1 (
As shown in a) and (b). (a) is a perspective view, (b) is a cross-sectional view, and 1 is a substrate, 2 is a lower electrode (transparent electrode), and 3
is an insulating film (for example, 5iNx), and 4 is an upper electrode. As is clear from FIG. 1(b), since the cross-sectional shape of the lower electrode 2 has a rectangular outer shape, the insulating film 3 formed by a vapor phase synthesis method (for example, plasma CVD method) is formed on the side of the lower electrode 2. There are drawbacks such as the film thickness being thinner or non-uniform in some parts than in the upper surface part. Therefore, when voltage is applied, especially when applied continuously for a long period of time, poor characteristics or short circuits tend to occur in that part. Furthermore, since the lower electrode 2 has corners, electric field concentration occurs there, resulting in the same drawbacks as described above.

The above are disadvantages in terms of the structure of the conductor in the conventional MIM element, but there are also disadvantages in the material of the insulating film.

In other words, in the case of an MIM element whose insulating film is an anodic oxide film, (
1) Since the insulating film is limited to the anodic oxide film of the lower metal, it is impossible to control its physical properties and, by extension, the characteristics of the MIM element. (2) Heat treatment at about 300 to 500°C is necessary. (3) Because the dielectric constant is high, the substrate material used is limited to one with high heat resistance.
When used as a switching element of a liquid crystal display device, M
Due to the constraint of IM capacitance/liquid crystal capacitance<1/10, it is necessary to reduce the element area, and it has drawbacks such as requiring advanced microfabrication.

On the other hand, an insulating film (or semi-insulating film) such as SiN or SiOx
Since it is formed by a vapor phase synthesis method, it does not have the drawbacks mentioned in (1) above, and has the advantage that physical properties can be controlled over a wide range.

However, the film formation temperature is high at around 300°C, and there are problems such as limited substrate materials and difficulty in forming a film with uniform characteristics over a large area.In addition, pinholes are likely to occur due to dust etc. However, there is a problem in that the yield is reduced.

[Problem to be solved by the invention]

A first object of the present invention is to eliminate the structural defects of conductors in conventional MIM elements and to provide an MIM element that operates stably for a long time.

A second object of the present invention is to eliminate the disadvantages of the insulating film material in conventional MIM elements, and to provide a low-cost and highly reliable MIM element that is particularly suitable for use in liquid crystal display devices. .

[Structure and operation of the invention]

The MIM element of the present invention is an MIM element in which an insulating film is interposed between a first conductor and a second conductor, in which the cross-sectional shape of at least one of the first and second conductors is a continuous curved shape without corners. It is characterized by:

An example of the method for manufacturing the MIM element of the present invention will be explained below based on FIG. 2.

First, a thin film 2' for a lower electrode is formed on a transparent substrate 1 such as glass, a plastic plate, or a plastic film.
a, Ti, Cr, Ni, Cu.

Au, Ag, W, Mo, Pt, ITO, Zn○:Afl
A conductive thin film of , In2O, SnO, etc. is formed to a thickness of several hundred to several thousand layers by sputtering, vapor deposition, etc., and a photoresist 5 is applied on top of the conductive thin film with a continuous cross-sectional shape without corners. Form into a curved shape, for example, approximately semicircular or semielliptical, with a thickness of several hundred to several micrometers (height at the highest point) [
In order to form such a shape as shown in FIG. 2(a), in the case of a positive resist, a highly sensitive resist may be used or the dissolving ability of the developer may be increased. Note that the cross-sectional shape of the resist is not limited to that shown in the drawings, and may be a tapered shape with a relatively gentle slope.

Next, etching is performed using a dry etching method such as reactive ion etching (RIE) or ion beam etching to form the lower electrode 2 [FIG. 2(b)]. At this time, the lower electrode 2 is formed as shown in the figure. In order to obtain a substantially semicircular or semielliptical shape, for example, in the case of RIE, anisotropic etching is performed and the selectivity with the resist is small, that is, the gas pressure ζ is low and the RF power is high. Just do it.

Next, as the insulating film 3, a SiNx film, a hard carbon film, etc. is formed to a thickness of several hundred to several thousand layers by plasma CVD, ion beam, sputtering, etc., and then wet etching, dry etching, or lift-off is performed. patterning into a predetermined pattern [Figure 2 (
C)].

Finally, as the upper electrode 4, P t HN i+ Ag t
Au, Cu, Cr, Ti, Au, W, Mo, Ta.

A conductive thin film of ITO, ZnO:AQ, In2O, Sn○2, etc. is formed to a thickness of several hundred to several thousand layers by sputtering, vapor deposition, etc., and then etched into a predetermined pattern [Fig. d)]. Since the MIM element manufactured in this way has a gently curved side of the lower electrode,
When the insulating film is formed by vapor phase synthesis, the film thickness and physical properties are relatively uniform, and since there are no corners, the electric field does not concentrate when voltage is applied. Therefore, it can operate stably for a long time, and the first object of the present invention can be achieved.

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

This insulating film is a hard carbon film (i-C film, diamond-like carbon film, amorphous diamond film) containing carbon atoms and hydrogen atoms as main structure-forming elements and at least one of amorphous and microcrystalline properties.

Also called diamond thin film. ), one of the characteristics of the hard carbon film is that since it is a vapor phase grown film, its physical properties can be controlled over a wide range by changing the film forming conditions, as will be described later. Therefore, even though it is called an insulating film, its resistance value covers the range from semi-insulator to insulator region, and in this sense, the MIM element of the present invention is
MSI device shown in No. 9 (Metel-3emi-I
nsulator).

In order 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 have to be a gas phase at room temperature and normal pressure; it can be used in either a liquid phase or the same phase as long as it can be vaporized through melting, evaporation, sublimation, etc. by heating or reduced pressure. .

Regarding hydrocarbon gas as raw material gas, for example, C1-1
4,C2H,,C,I+. , C4H Eng. paraffinic hydrocarbons such as, acetylenic hydrocarbons such as C, H, olefinic hydrocarbons, diolefinic hydrocarbons.

Furthermore, gases containing all hydrocarbons such as aromatic hydrocarbons can be used.

Furthermore, other than hydrocarbons, compounds containing carbon elements such as alcohols, ketones, ethers, esters, co, and co□ can be used.

The method of forming a hard carbon film from a raw material gas in the present invention is a method in which the film-forming active species is formed through a plasma state generated by a plasma method using direct current, low frequency, high frequency, microwave, etc. However, since deposition is performed under low pressure for the purpose of increasing the area, improving uniformity, and forming a film at a low temperature, a method using a magnetic field effect is more preferred.

This active species can also be formed by high temperature pyrolysis. In addition, it may be formed through an ionic state generated by ionization vapor deposition, ion beam vapor deposition, etc., or may be formed from neutral particles generated by vacuum vapor deposition, sputtering, etc. However, it may also be formed by a combination of these.

An example of the deposition conditions for the hard carbon film produced in this way is approximately as follows in the case of plasma CVD method.

RF output 0.1 to 50 V/ca + "pressure to -" 10 Torr Deposition temperature: room temperature to 950°C Due to this plasma state, the raw material gas is decomposed into radicals and ions and reacts, thereby forming carbon atoms on the substrate. C
A hard carbon film containing at least one of amorphous (amorphous) and microcrystalline (crystal size is several tens of micrometers to several micrometers) consisting of hydrogen atoms H is deposited. The physical properties of the hard carbon film are shown in Table 1.

Table-1 Note) Measurement method: Specific resistance (ρ): I- by coplanar cell
Determined from V characteristics.

Optical bandgap: Obtain the absorption coefficient (α) from the spectral characteristics, (Egopt) (αhv)””:β
(h v-Egopt).

Amount of hydrogen in the film (CH): Obtained by integrating the peak around 2900 as-' from the infrared absorption spectrum and multiplying it by the absorption cross section A. That is, C8 α(w) cH=A5-・dw SP3/SP' ratio: SP infrared absorption spectrum
3/SP'' into Gaussian functions, respectively, and find it from the area ratio.

Vickers hardness (11): Based on micro Vickers meter.

Refractive index (n): By ellipsometer.

Defect density: Based on ESR.

The hard carbon film thus formed was analyzed by IR absorption method and Raman spectroscopy, and it was found that the carbon atoms formed an SP3 hybrid orbital and an sp'' hybrid orbital, as shown in Figures 3 and 4, respectively. It has become clear that there are interatomic bonds.

The ratio of SP3 bonds to SP2 bonds can be approximately estimated by peak-separating the IR spectrum. The IR spectrum has 2800-3150C! Although the spectra of many modes are measured overlapping in m-', the attribution of the peak corresponding to each wave number is clear, and as shown in Figure 5, the peaks are separated using a Gaussian distribution, and each peak is Calculate the area.

By finding the ratio, SP"/SP" can be found.

Also, according to X-ray and electron diffraction analysis, it is in an amorphous state (
a-C:H) and/or in an amorphous state containing microcrystalline grains of about 50 to several μm in size.

In the case of plasma CVD method, which is generally suitable for mass production, R
The smaller the F output, the more the specific resistance value and hardness of the membrane increase,
The lower the pressure, the longer the life of the active species, the lower the temperature of the substrate, the more uniform it can be over a large area, and the more specific resistance and hardness tend to increase. Furthermore, since the plasma density decreases at low pressure, a method using the magnetic field confinement effect is particularly effective in improving film quality.

Furthermore, this method has the feature that it can form a hard carbon film of good quality even under relatively low temperature conditions of about room temperature to 150° C., so it is optimal for lowering the temperature of the MIM element manufacturing process. Therefore, the degree of freedom in selecting the substrate material to be used increases, and in order to make it easier to control the substrate temperature,
It has the characteristic that a uniform film can be obtained over a large area. Furthermore, the structure and physical properties of the hard carbon film can be controlled over a wide range, as shown in Table 1.

Another advantage is that device characteristics can be designed freely.

Furthermore, the dielectric constant of the film is 3 to 5, compared to Ta, 0= I AQ * Oz * SiN, which is used in conventional MIM devices.
Since it is small compared to The capacity ratio is CLco:C
MIM=10:1 is required.

Furthermore, since the film has high hardness, there is little damage caused by the rubbing process when filling the liquid crystal material, which also improves the yield.

In order to further widen the control range of physical properties as necessary, the hard carbon film described above may contain impurities such as elements from Group ■ of the periodic table, elements from Group ■, elements from Group ■, alkali metal elements,
It can be doped with alkaline earth metal elements, nitrogen atoms, oxygen atoms, chalcogen elements, or halogen atoms. This impurity doping further increases the stability of the element and the degree of freedom in device design.

The amount of these impurities is usually 5 atomic % or less of the total constituent atoms for Group Ⅰ elements of the Periodic Table, 35 yK % or less for Group Ⅰ elements, and 5 atomic % for Group Ⅰ elements. Below, the amount of alkali metal elements is 5 at% or less, the amount of alkaline earth metal elements is 5 at% or less, and the amount of nitrogen photons is 5 at% or less.
The amount of oxygen atoms is 5H% or less, the amount of chalcogen elements is 35% or less, and the amount of halogen elements is 35% or less. Note that the amounts of these elements or atoms can be measured by a conventional method of elemental analysis, for example, Auger analysis. Further, this amount can be adjusted by adjusting the amount of other compounds contained in the source gas, film forming conditions, etc.

Note that the range of the film thickness of the insulating film is such that the film thickness is 10 mm depending on the driving conditions as a hard carbon film suitable for an MIM element for driving a liquid crystal.
It is desirable that the resistivity is in the range of 0 to 8000 people and the specific resistance is in the range of 10' to 1013 Ωl. In addition, considering the margin between drive voltage and withstand voltage (dielectric breakdown voltage), it is desirable that the film thickness is 200 Å or more, and color unevenness due to the step (cell gap) between the pixel part and the MIM element part is not practical. To avoid problems, it is desirable that the film thickness be 6,000 Å or less, so the thickness of the hard carbon film should be 200 to 6,000 Å or less.
It is more desirable that the specific resistance is between 5X10'' and 1012Ω1, and the number of device defects due to pinholes in the hard carbon film increases as the film thickness decreases.
This is particularly noticeable below Å (the defect rate exceeds 1%), and the uniformity of the in-plane distribution of the film thickness (and therefore the uniformity of the device characteristics) cannot be ensured (the accuracy of film thickness control is approximately 30 people). (with a variation in film thickness exceeding 10%), it is more desirable that the film thickness be 300 Å or more. In addition, in order to prevent the hard carbon film from peeling off due to stress, and to reduce the duty ratio (preferably 1/
1000 Å or less), it is more desirable that the film thickness be 4000 Å or less. Therefore, the thickness of the hard carbon film should be 300 to 4000 Å, and the specific resistance should be 10' to 11.
It is more preferable that the opening is Ω.

The present invention will be explained below by way of examples.

Embodiment 1 As shown in FIG. 6, ITO was deposited on a Pyrex glass substrate as a transparent substrate to a thickness of about 100 cm by sputtering, and then patterned to form a pixel electrode 6. A MIM element was used as a zero-order active element as follows. It was set up like this. First, An was deposited to a thickness of 1000 nm on the pixel electrode of the substrate by vapor deposition, and then patterned to form the lower electrode 2. The resist film thickness at this time was 5000 at the highest point. Etching was performed using CCQ4 gas by parallel plate type RIE.
The test was carried out at a pressure of 0.02 Torr and an RF power of 0.3 W/d.

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

Pressure Crab 0.035Torr CH4 flow rate: 203CCM RF power: 0.2W/cd Furthermore, Ni was deposited on this hard carbon insulating film by evaporation to 100%
After being deposited to a thickness of zero, it was patterned to form the upper electrode 4.

Example 2 A MIM device as shown in FIG. 7 was fabricated as follows. First, a deposited thin film with a thickness of 1,000 layers was formed on a glass plate by vapor deposition, and patterned to form the lower metal electrode 2.

The resist film thickness and etching conditions at this time were Ca2. The procedure was the same as in Example 1 except that +02 was used.

Next, a hard carbon film 3 with a thickness of 600 mm is coated thereon, and patterned by dry etching to form an insulating film.Furthermore, a deposited O film 3 with a thickness of 1000 mm is coated on the hard carbon film by E, B, and vapor deposition methods. Then, the upper transparent pixel electrode 4 was formed by patterning by etching. The conditions for forming the hard carbon film are as follows.

Pressure crab 0.05TorrCH, flow rate:
IO5ccM RF power: 0.1W/cd [Operations and Effects of the Invention] The MIM element of the present invention has a cross-sectional shape in which at least one of the first conductor and the second conductor sandwiching the insulating film has a continuous curved outline without corners. As a result, it is highly reliable and operates stably for a long time.

This has the effect of significantly reducing defects due to electrode disconnection.

In addition, when a hard carbon film is used as an insulating film, this film is manufactured by a vapor phase synthesis method such as plasma CVD, so the physical properties can be controlled over a wide range by changing the film formation conditions, and therefore there is greater freedom in device design. 2) It is hard and can be made into a thick film, so it is less susceptible to mechanical damage, and a thicker film can also be expected to reduce pinholes. 3) A high-quality film can be formed even at low temperatures near room temperature. , there are no restrictions on the substrate material; 4) it has excellent uniformity in film thickness and film quality, making it suitable for thin film devices; 5) it has a low dielectric constant, so it does not require advanced microfabrication technology; This is advantageous for increasing the area of the device.

Therefore, MI using such an insulating film
The M element is suitable as a switching element for liquid crystal display.

[Brief explanation of drawings]

1(a) and 1(b) are respectively a perspective view and a sectional view of a conventional preferred MIM element, FIG. 2 is an explanatory diagram of the manufacturing process of an example of the MIM element of the present invention, and FIGS. 3 and 4. 5 shows the IR spectrum and Raman spectrum of the hard carbon film-based insulating film used in the MIM device of the present invention, FIG. 5 shows the Gaussian distribution of the hard carbon film, and FIGS. 6 and 7 show the results of the embodiment, respectively. FIG. 2 is a perspective view of the MIM device manufactured in Examples 1 and 2. 1... Substrate 2... Lower electrode (transparent electrode) 3
... Insulating film 4 ... Upper electrode 5 ... Resist 6 ... Pixel electrode Patent applicant Rico Co., Ltd. - Agent Patent attorney Sa 1) Mamoru Otori Figure 3 Figure 4 Raman spectrum (wave number) Figure 2 Figure 5 Figure 6

Claims (1)

[Claims] 1. MIM with an insulating film interposed between the first conductor and the second conductor
1. A MIM device, wherein the cross-sectional shape of at least one of the first and second conductors is a continuous curved shape without corners. 2. The MIM device according to claim 1, wherein the insulating film is made of a hard carbon film.