JPH01321618A - Ceramic capacitor - Google Patents

Abstract

PURPOSE:To improve frequency characteristics of capacitor capacity and its temperature dependency so as to improve increase of surface resistance and occurrence of cracks, etc., by constituting a dielectric film of Ba2Ti9O20 or BaTi5O11 or their mixed phase, and laminating a lower electrode in the order of an SiOX layer, a Cr layer, an Ni layer, and a Pt layer from the substrate side. CONSTITUTION:A dielectric film 6 contains at least Ba2Ti9O20 or BaTi5O11 or these mixed phase, and a lower electrode 12 is constituted by laminating a chromic layer 16, a nickel layer 18, a platinum layer 20 in this order on a silicon oxide layer 14 formed on the surface of a silicon substrate 2. Hereby, the frequency characteristics of capacitor capacity becomes favorable and its temperature dependency becomes small. A ceramic capacitor can be obtained which has the lower electrode 12 that surface resistance does not increase even by heat treatment at high temperature when manufacturing the ceramic capacitor, and cracks, etc., do not occur, either, and the planeness is maintained, and further the fear of separation from the substrate 2, etc., is small.

Description

[Detailed Description of the Invention] The present invention has excellent frequency characteristics of capacitor capacitance, small temperature dependence of capacitor capacitance, and excellent durability with no peeling or cracking of electrodes. related to ceramic capacitors.

In general, in a ceramic capacitor, a dielectric layer is formed between electrodes, and electric charge is stored between the electrodes. Conventionally, this ceramic capacitor had a film thickness of 20μ.
Multilayer capacitors in which m or more dielectric layers are stacked are known. Conventionally, the dielectric layer of this capacitor is
A typical example is one using barium titanate having a structure of BaTiO3. Ceramic capacitors using barium titanate as a dielectric layer have the advantage that the capacitor capacity can be increased because barium titanate has a higher dielectric constant than other materials.

However, the above-mentioned ceramic capacitor using ordinary barium titanate as a dielectric layer has problems in that the frequency characteristics of the capacitor capacitance are insufficient and the temperature dependence of the capacitor capacitance is large.

Also, has it been proposed to increase the capacitance by thinning the dielectric layer of a ceramic capacitor? , it has the following disadvantages.

Thin film ceramic capacitor 10 as shown in Figure 2
To manufacture this, first, a film-like lower electrode 4 is formed on a substrate 2 by means such as vapor deposition. Thereafter, a dielectric layer pA6 is formed on the surface of the lower electrode 4, and this is heat-treated together with the lower ionization layer 4 and the substrate 2 at a temperature of about 1200° C. to bake the dielectric thin film 6. Thereafter, an upper electrode 8 is formed on the surface of this dielectric thin film 6 by means such as vapor deposition, thereby completing the ceramic capacitor 10. Note that the reason why the substrate 2 is required in the ceramic capacitor 10 is to improve the validity of the ceramic capacitor 10 as a whole.

Such a conventional ceramic capacitor 10 requires heat treatment at a high temperature of about 1200° C. during its manufacturing process, and it is required that the lower electrode 4 does not change in quality due to the heat treatment. Therefore, the lower type f
Materials constituting li4 include Pt, Pd, W, Ni,
High melting point materials such as Ti and Cr are used.

However, in the conventional lower electrode 4 made of a high melting point material such as Pd, W, Ni, Ti, Cr, etc., the surface is oxidized during the heat treatment for firing the dielectric layer M6, resulting in an increase in sheet resistance. There was a risk.

Note that when PT is used as the lower electrode 4, there is almost no change in sheet resistance, but due to the difference in thermal expansion coefficients of the substrate 2, the lower electrode 4, and the dielectric layers 115 and 6, peeling and cracking may occur. There was a problem that this could occur. If such peeling or cracking occurs, do not use a high melting point material other than PT for lower mold iF! A similar spread occurred when f:14 was used.

Therefore, there has been a desire for a ceramic capacitor having a lower electrode that does not change in quality even when subjected to high-temperature heat treatment, does not cause peeling or cracking, and can maintain flatness as an electrode.

The present invention has been made in order to solve the problems of the prior art, and to manufacture a ceramic capacitor that has good frequency characteristics of capacitor capacitance and small temperature dependence. To provide a ceramic capacitor having a lower electrode which does not increase sheet resistance, does not generate cracks, maintains flatness, and has less risk of peeling off from a substrate etc. even when subjected to high-temperature heat treatment. The purpose is

In order to achieve these objects, the present invention provides a ceramic capacitor in which a dielectric thin film is formed between a lower electrode and an upper electrode formed on a silicon substrate, comprising: The thin film is Ba2Ti90□. Or Ba T
i 5011 or a mixed phase thereof, and the lower electrode includes a chromium layer, a nickel layer, and a platinum layer stacked in this order on a silicon oxide layer formed on the surface of the silicon substrate. It is characterized by being composed of

According to such a ceramic capacitor according to the present invention, the dielectric film is made of BaTi902o or BaTi5O1.
1 or a mixed phase thereof, the frequency characteristics of the capacitor capacitance are improved and its temperature dependence is also reduced.

Further, according to the lower electrode used in the ceramic capacitor according to the present invention, the electrode has a multilayer structure, and a silicon oxide layer, a chromium layer, a nickel layer, and a platinum layer are laminated in this order from the substrate side. As the silicon oxide layer exhibits extremely good adhesion, the p-
Because the T-layer has good oxidation resistance, even if heat treatment is performed at a relatively high temperature, the surface will not oxidize and the sheet resistance will not increase, and cracks will not occur. The flatness of the electrode is maintained, and the electrode does not peel off from the substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments shown in the drawings.

FIG. 1 is a schematic cross-sectional view of a ceramic capacitor according to an embodiment of the present invention.

The ceramic capacitor 3o shown in FIG. 1 is a thin film capacitor in which the capacitance is increased by reducing the thickness of the dielectric thin film 6a, and a lower electrode 12, a dielectric thin film 6a and an upper electrode 8 are formed on the surface of the substrate 2 in this order. It is laminated with.

The substrate 2 is preferably made of a heat-resistant material that can withstand the temperature at which the dielectric thin film 6a is fired, and a member whose at least the surface is made of silicon is used. Specifically, a silicon wafer is used. It will be done. As silicon wafers, it is possible to use commercially available silicon wafers of any type, such as non-doped, P-type, or N-type, and there is no need for surface treatment such as surface etching.0 Flatness can be maintained without surface treatment. This is because it is retained.

Note that the reason why the surface of the substrate 2 is required to be flat is to maintain the flatness of the ceramic capacitor 30 formed thereon. The thickness of the substrate 2 must be sufficient to impart appropriate rigidity to the entire ceramic capacitor 30, and is preferably 50 to 5000 μm.

Note that the substrate is not necessarily limited to a flat plate shape, but may be cylindrical or cylindrical. When the substrate is cylindrical or columnar, the electrodes and dielectric thin film formed thereon also follow the shape of the substrate.

The lower electrode 12 used in the ceramic capacitor 30 according to the present invention is a silicon oxide formed by oxidizing the surface of the substrate 2 (the valence of silicon in the silicon oxide does not matter). layer (hereinafter referred to as rs
A chromium layer (referred to as "io layer") 14 made of chromium is on top of the chromium layer (referred to as
A nickel layer (hereinafter referred to as "rNi layer") 18 made of nickel (hereinafter referred to as "rcr layer") 16 and a platinum layer (hereinafter referred to as "rpt layer") 20 made of platinum are laminated in this order. It is made up of the following:

The thickness of the Si0 layer 14 on the surface of the substrate 2 is 100 to 5000
number of people, preferably 500 to 1000 people. Also, cr
The thickness of layer 16 is between 50 and 20 mm, preferably between 80 and 1 mm.
There are 50 people. The thickness of the Ni layer 18 is 200 to 2000
number of people, preferably 300 to 1000 people. pt layer 20
The thickness is 1000 to 1000, preferably 200
0 to 6000 people. By setting the thickness of each layer 14, 16, 18, 20 within such a range, the lower electrode 1
The flatness of 2 is maintained, and cracks, yaws, #J#, etc. can be prevented.

The lower electrode 12 is formed on the substrate 2, for example, as follows.

First, the substrate 2 is cleaned as necessary to remove dust etc. adhering to the surface, and then the substrate 2 is heated in an oxygen or air atmosphere at a temperature of 1000 to 1200°C for 30 to 12'
A heat treatment is performed for 0 minutes to form a Si0 layer 14 on the surface of the substrate 2. This Si0 layer 14 can also be formed by a sputtering method, a vapor deposition method, or the like. Next, this Si0 layer 14
A Cr layer is formed on the surface by a film forming method such as a sputtering method, a vapor deposition method, or a plating method. Specifically, this Cr layer is preferably formed by sputtering using Cr as a target and an inert atmosphere such as argon in the system. Form. Note that sputtering or vapor deposition may be used as a film forming method, but both sputtering and vapor deposition do not require Cr.
It is desirable that the layer 16, the Ni layer 18, and the PT layer 20 are formed continuously. This is to prevent these layers 16 and 18 from being oxidized.

In the ceramic capacitor according to the present invention, the dielectric thin film 6a is formed on the surface of the lower electrode 12 formed by such a method, and the upper electrode 8 is formed on the surface of this dielectric thin film 6a. 30 are configured.

The upper electrode 8 includes Ag, Cu, Au, AJ,
Known materials such as pt can be used. As a means for forming this upper electrode 8 on the surface of the dielectric thin film 6a,
A sputtering method, a plating method, etc. are used. The thickness of the upper electrode is preferably 100 OA to 1.0 μm.

In the present invention, the dielectric thin film 6a is made of Ba 2 'ri 9
The film is composed of a crystalline phase containing at least O2O, BaTi5O11, or a mixed phase thereof. dielectric weight g
The thickness of 6 a is 2000 to 20.1. m, especially 2
000 to 3.0 μm. As a means for forming such a dielectric thin film 6a on the surface of the lower electrode 12, a sol-gel method, a sputtering method, a vapor deposition method, etc. are used.

B a 2 T on the surface of the lower electrode 12! A specific means for forming the dielectric weight M6a having a crystalline phase of 9020 by the sol-gel method is shown below.

[Barium acetate, barium hydroxide, or barium alkoxide may be used alone or in combination as the barium source on the Natsuboshi.

Specifically, barium alkoxide includes barium methoxide, barium ethoxide, barium n-globoxide, barium isopropoxide, and the like.

Among these, barium isopropoxide is preferred.

Furthermore, titanium alkoxide is used as a titanium source. Specifically, such titanium alkoxides include titanium methoxide, titanium ethoxide, titanium n-
Propoxide, titanium isopropoxide, titanium butoxide, etc. are used, and among these, titanium isopropoxide is preferred.

In addition to the barium source and titanium source described above, it is preferable to add a tin source or a zirconium source to the reaction raw materials.

As the tin source, tin alkoxide is used. As such tin alkoxide, specifically, tin methoxide, tin ethoxide, tin n-propoxide, tin isopropoxide, tin butoxide, etc. are used, and among these, tin n-propoxide or tin isopropoxide is preferable. .

Zirconium alkoxide is used as the zirconium source.

Specific examples of such zirconium alkoxides include zirconium methoxide, zirconium ethoxide, zirconium n-10 boxoxide, zirconium isopropoxide, and zirconium butoxide, among which zirconium n-propoxide or zirconium isopropoxide Propoxide is preferred.

In order to hydrolyze the above alkoxides, it is necessary to coexist water in the reaction system.

As described below, this water may be water added to the reaction system, or may be moisture in the air, depending on the case.

The above barium compounds, titanium alkoxides, tin alkoxides or zirconium alkoxides are
Each is used in the following amounts. That is, the barium compound is used in an amount that corresponds to the composition of the target barium titanate. Furthermore, the titanium alkoxide, tin alkoxide, or zirconium alkoxide is such that the total amount of titanium and tin or zirconium corresponds to the composition of barium titanate, and 1 to 10 mol% of the titanium alkoxide is substituted with the tin alkoxide or zirconium alkoxide. used in large quantities.

When the amount of tin alkoxide or zirconium alkoxide is used within this range, B a 2 can be obtained without losing the original properties of barium titanium.
The firing temperature of barium titanate having a crystal phase shown by T j 9020 can be lowered.

Note - 1 In the present invention, the reactions of each component as described above are carried out using an ethylene glycol monomethyl ether solvent or a mixed solvent of ethylene glycol monomethyl ether and alcohol containing 10% by volume or more of ethylene glycol monomethyl ether. Examples of the alcohol used at this time include methanol, ethanol, n-propanol, isopropanol, n-butanol, 5ec-butanol, and t-butanol. Among these, ethanol or isopropanol is preferred.

[At least one barium compound selected from barium acetate, barium hydroxide, or barium alkoxide;
Titanium alkoxide and tin alkoxide or zirconia alkoxide are uniformly mixed in ethylene glycol monomethyl ether or a mixed solvent of ethylene glycol monomethyl ether and alcohol containing 10% by volume or more of ethylene glycol monomethyl ether, and then the obtained The mixture is hydrolyzed to form a gel.

Hydrolysis of the mixture as described above can be carried out, for example, by uniformly mixing the mixture by heating and refluxing the mixture, and then adding water to the system.

The water required for hydrolysis may be water added to the reaction system as described above, or water that has absorbed moisture in the air.

Such water is preferably 0.001 to 4 times the total number of moles of titanium and tin or zirconium.
It is desirable that the amount is ~4 times the weight, particularly preferably 1~21Δ.

If the amount of water added is less than 4 times the molar amount of the total amount of titanium and tin or zirconium, a sol suitable for deimping can be obtained, but if it exceeds 4 times the molar amount, it easily changes to a gel. It is not desirable because

The sol thus obtained is applied to the surface of the lower electrode 12 shown in FIG. 1 by means such as dipping, and then dried and fired. Drying is usually done by drying the obtained gel for 2
This is done by keeping the temperature between 5 and 70°C.

The thus dried gel is heated in air together with the substrate 2 and the lower electrode 12 at a temperature of 800°C or higher, preferably 900°C.
When the dielectric film 6a is fired at a temperature of 800 to 1300°C for 30 minutes to 5 hours, a dielectric thin film 6a made of barium titanate crystals having a crystal phase represented by Ba2T j 9020, for example, is obtained.

This calcination may be carried out under oxygen conditions, but it can also be carried out in air. When a small amount of tin source or zirconium source is added to the reaction raw materials as described above, even if the gel as described above is fired in air, the firing temperature at that time must be 1100°C or less, preferably 1000°C or less. It can be done with

In addition, in the conventional manufacturing method of barium titanate, a firing temperature of 1150° C. or higher is required even when firing in oxygen. Therefore, when forming the dielectric thin film 6a by the above-described method, the firing temperature can be lowered compared to the conventional method, so cracks and peeling of the lower electrode 12 during firing can be effectively prevented. I can do it.

Further, even if a zirconium source is not added to the reaction raw materials as described above, unlike a small amount of a tin source, the lower electrode 12 according to the present invention has a laminated structure as described above, so that the conventional barium titanate Like the manufacturing method of about 1
Even when heat-treated at a firing temperature of 150° C. or higher, the lower electrode 12 showed less change in sheet resistance than before heat treatment, maintained flatness, and was confirmed to have almost no peeling or cracking.

In addition, the dielectric weight ff having a crystal phase of BaTi5O11
! A6a is also B a T I ta O2of)
a-body NM In the same manner as above, the raw material composition is adjusted by the sol-gel method, and the firing temperature is adjusted (for example, 700
~1000°C).

Note that the present invention is not limited to the method of forming the dielectric thin film 6a by the sol-gel method as described above, and
Known means can be employed to form a film made of a crystalline phase containing at least O, BaTi5O11, or a mixed phase thereof.

Further, according to the present invention, a chromium oxide layer or other oxide film layer consisting of chromium oxide (however, the valence of chromium in the chromium oxide does not matter) is provided between the Si0 layer 14 and the CR layer 16. may be formed to have a predetermined thickness.

As explained above, according to the present invention, the dielectric thin film is made of Ba 2 Tl 9020 or Ba Ti 5
Since it is composed of O11 or a mixed phase thereof, it has the excellent effect of improving the frequency characteristics of the capacitor capacitance and reducing its temperature dependence.

Furthermore, according to the present invention, the lower electrode is a multilayer supplement, and the SiO layer, Cr layer, Ni layer, and PT layer are laminated in this order from the substrate side, so that the 5 inch layer has extremely good adhesion. In addition, because the Pt layer has good oxidation resistance, even if heat treatment is performed at a relatively high temperature, the surface will not oxidize and the sheet resistance will not increase, and cracks will not occur. Moreover, the flatness of the electrode is maintained, and the electrode does not peel off from the substrate, which is an excellent effect.

Hereinafter, the present invention will be explained based on more specific examples, but the present invention is not limited to these examples.

Example [Substrate and Lower Electrode] A commercially available silicon wafer (P type, specific resistance 10Ω) was used as a substrate, and its surface was oxidized to form a Si0 layer. Oxidation was carried out using an infrared image furnace with oxygen at 0.2j/
This was carried out by heat treating the substrate at 1000° C. for 3 hours while introducing a heat treatment for 3 hours.

Next, this was subjected to ultrasonic cleaning in trichlene.

On this substrate, Cr, N! , Pj were formed in this order. The conditions are shown below.

■Chrome 11! (Cr layer) After evacuating the chamber to a pressure of 1.0 x 10'torr or less, argon was evacuated to 1.0XIO-3 torr.
rr, then squeeze the main valve and let the system cool down to 5
, OX 10-3 torr. Using 99.9% chromium (Cr) as a target, high frequency output 10
After press sputtering was performed for 10 minutes at 0 W, the shutter was opened for 20 seconds to form a chromium film on the SiO film. The film thickness was approximately 80 people.

■Ni gel film (Ni layer) Next, use 99.9% N1 as the target and apply pressure 1
, Ox 10-2torr, output 300W
After sputtering for 10 minutes, close the shutter for 2 minutes.
Approximately 300 N1 films were formed after opening for a few seconds.

■Platinum film (Pt layer) Next, using 99.9% platinum as the target, press sputtering was performed for 10 minutes at a pressure of 5 x 10'torr and an output of 200W, and then the shutter was opened for 6 minutes.
Approximately 6,000 people formed platinum films.

In particular, in order to prevent oxidation of the formed Cr layer and Ni layer, steps 1, 2, and 2 were continuous steps. After this process,
Si0 layer and Cr layer on silicon wafer substrate (80 people)
, Ni layer (300 A), and PT layer (6000 A) were formed in this order.

[Weighed 28.42 g and 5.68 g of dielectric thin film cotitanium isopropoxide and barium isopropoxide so that the Ti/Ba (atomic ratio) was 4.5, respectively, and added them to methoxyethanol as a solvent. 30ml, ethanol 80ml
was added to the mixture. Next, the obtained mixture was refluxed using an oil bath while maintaining the bath temperature at 150°C to prepare a homogeneous solution.

Even after returning to room temperature, this solution does not readily gel. This homogeneous solution was applied onto the above electrode by a dipping method to form a dielectric thin film. This thin film contains organic matter.

Next, the silicon wafer with the lower electrode and the dielectric thin film attached thereto was heat treated at 1200°C under the following conditions to scatter the organic matter in the dielectric film and to reduce B a 2
A crystalline phase of T j 9020 was produced.

A dielectric thin film with a thickness of 500 mm is formed by this one-time dipping and heat treatment operation.

By repeating this operation 8 times, a 0.4 μm thick Ba
Ti90□. A dielectric thin film having a crystalline phase of

The heat treatment conditions are described below.

[Heat treatment conditions] Heat treatment is performed in an infrared image furnace or boxes, and in the infrared image furnace, the temperature is 1200°C at 5°C/sec.
After raising the temperature to
Temperature should not be lowered at °C/SeC. During this period, only oxygen should be used at 0.2J
/minute was supplied. This operation was repeated 8 times. For boxes, after raising the temperature to 1200°C at 70°C/hour,
This temperature was maintained for an hour and returned to room temperature at 70'C/hour. During this time, only oxygen was supplied at 0.2J/min. This operation is 8
Repeat several times.

In order to observe changes in the surface resistance of the lower electrode before and after heat treatment, a portion of the lower electrode that was not covered with the dielectric thin film was provided, and the surface resistance of this portion was measured. As a result, the surface resistance of the lower electrode before heat treatment was 0.3 Ω/mouth, but after heat treatment (image furnace, box furnace), it was 0.2 for both.
The resistance value was 3Ω/mouth, and there was no increase in resistance value. Furthermore, no cracks or discoloration occurred in the film.

It also had excellent surface smoothness.

[Upper Electrode] A thin gold film having a thickness of 2000 nm was formed on the above dielectric film by sputtering.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of a ceramic capacitor according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of a conventional ceramic capacitor. 2... Substrate 4, 12... Lower electrode 6.6
a... Dielectric thin film 8... Upper electrode 14/5
in2 layer 16・Cr layer 18...Ni layer
20...PT layer agent Patent attorney Kazuo Suzuki

Claims (1)

[Claims] A ceramic capacitor in which a dielectric thin film is formed between a lower electrode and an upper electrode formed on a silicon substrate, wherein the dielectric thin film contains at least Ba_2Ti_9O_2_0, BaTi_5O_1_1, or a mixed phase thereof. The lower electrode is configured by laminating a chromium layer, a nickel layer, and a platinum layer in this order on a silicon oxide layer formed on the surface of the silicon substrate. ceramic capacitor.