JPH0665223B2 - Capacitor and manufacturing method thereof - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to capacitors. More specifically, the present invention relates to a capacitor having a structure in which an insulating film is sandwiched between conductor layers, particularly a capacitor having a very large capacitor per unit area.

2. Description of the Related Art With the progress of semiconductor device manufacturing technology, it has become possible to achieve high capacity, high speed operation, and low cost. Bipolar memory has been put to practical use, and its application as a main memory of electronic computers is spreading due to the large capacity of MOS dynamic memory.

As described above, the progress of electronic devices centering on semiconductor devices has been remarkable, and accordingly, the requirements for each constituent element and element have become increasingly severe. In order to meet these requirements, it is important to improve the semiconductor-related part, that is, the active element part. On the other hand, the improvement of passive elements such as resistors and capacitors is also in parallel with that of the active element. This is an important task that must be done.

Therefore, in MOSIC and the like, it is necessary to improve passive elements such as resistors and capacitors in parallel with improving active elements.

For example, for a capacitor, as shown in FIG. 4, a metal layer 1, an insulating film 2 provided thereon, and an upper electrode 3 are provided.
One having a three-layer structure in which an insulating film is sandwiched between the two is known.

At present, one of the capacitors that require a very large capacitor per unit area is a charge storage capacitor for a MOS dynamic memory. That is, the area of the capacitor must be reduced in order to increase the integration of the memory. However, the capacitance of the capacitor cannot be reduced so much in terms of circuit operation. Therefore, a large capacitor per unit area is required.

Conventionally, such a capacitor uses an insulating film made of a metal oxide having a high dielectric constant, such as tantalum oxide, niobium oxide, titanium oxide, hafnium oxide, or zirconium oxide. In this case, in a capacitor obtained by forming a metal oxide insulating film as described above on a silicon substrate and then forming a metal electrode thereon, which is conventionally used, the insulating film formation is performed. At times, a silicon oxide film is inevitably formed at the interface between the silicon substrate and the insulating film.

By the way, in order to increase the size of the capacitor, it is necessary to reduce the thickness of the insulating film. However, due to the above reasons, the ratio of the film thickness of the silicon oxide film to the insulating film becomes large, and the effective dielectric constant decreases. For example, the relationship between the tantalum oxide film thickness and the effective relative permittivity when tantalum oxide is used as the insulating film is shown by the curve a in FIG. 5, but the effective relative permittivity decreases sharply as the film thickness decreases. I understand.

In order to avoid such inconvenience, a material that does not form an oxide or the like at the interface with the insulating film at the time of forming the insulating film, or if a slight oxide or the like is formed, the oxide or the like Materials that have conductivity or high dielectric constant,
It must be used as the lower electrode of the capacitor.

That is, first, in order to prevent the metal oxide (AOx), which is an insulating film, from reacting with the lower electrode material (B) to form an oxide (BOy), the Gibbs free energy change in the reaction formula of AOx + B → A + BOy is It must be a positive material. Examples of such a material include molybdenum and tungsten for tantalum oxide.

Next, as a material in which the oxide has conductivity, there are molybdenum, tungsten, and the like in which the oxide serves as a semiconductor, and in this case, any insulating film may be used.

Furthermore, titanium is a material whose oxide has a high dielectric constant.
There are tantalum, niobium, hafnium, zirconium, and the like, and in this case as well, the insulating film may be any.

The relationship between the tantalum oxide film thickness and the effective relative dielectric constant when molybdenum is used as the lower electrode is shown by the curve b in FIG. From this curve, it can be seen that the effective relative permittivity does not decrease even when the tantalum oxide film reaches 100 Å.

However, when a metal film is formed by a normal sputtering method, a vapor deposition method, a chemical vapor deposition method, or the like, the obtained film is polycrystalline, and its surface is considerably uneven. In particular, refractory metal films such as molybdenum and tungsten become columnar crystals and
The crystal grains of the book are obtained as being fine and having a highly uneven surface. This is shown in FIG. As described above, this is composed of the metal layer 1 formed by the usual sputtering method, the insulating film 2, and the upper electrode 3, and this functions as a capacitor. As shown in FIG. 4, since the unevenness of the surface of the metal layer as the lower electrode is severe, the insulating film 2 is formed unevenly by reflecting the unevenness of the surface of the metal layer 1. Therefore, when a voltage is applied to the capacitor, the electric field concentrates on the thin portion of the insulating film 2, and the leak current becomes extremely large. For example, the leak current characteristics of the capacitor when the metal layer 1 is formed by sputtering using 3000 Å molybdenum, the insulating film 2 is 100 Å tantalum oxide, and the upper electrode 3 is molybdenum are shown in FIG. It was shown to. From this figure, it is apparent that such a structure has a leak current level that is not practically usable.

Problems to be Solved by the Invention As described above, even in the MOSIC, which is expected as a large-capacity dynamic memory for electronic computers, reduction of the capacitor area is required for high integration, and as a result, it is extremely large. Capacitors with different capacitors per unit area would be needed.

However, there are some problems that must be solved in order to increase the capacitor per unit area of the capacitor. In particular, the presence of irregularities on the surface of the metal film forming the capacitor causes the electric field to concentrate in the thin portion of the insulating film, resulting in a significant increase in leakage current, which is not practical.

Therefore, the development of capacitors that can solve this problem
It is of great significance and highly desired in achieving high integration of S dynamic memory, downsizing, and increasing capacity of computers.

Therefore, a first object of the present invention is to provide a capacitor having a large capacitor per unit area and a small leak current.

A second object of the present invention is to provide a method for manufacturing the above-mentioned capacitor as a passive element, which is suitable for the trend of large scale integration or miniaturization of electronic devices.

Means for Solving the Problems As a result of various studies to develop a capacitor capable of achieving the above-mentioned object, the present inventors found that the unevenness of the metal film which is an obstacle in increasing the capacitance per unit area of the capacitor is Based on the idea that there is a problem in the structure (columnar crystal state), the manufacturing method of the metal film is examined, and the structure of the lower electrode is made to be a stone wall shape other than the columnar shape, an amorphous shape, etc. The present invention has been completed by finding that it is effective in achieving the property.

That is, a capacitor as a first object of the present invention is a thin film capacitor having a sandwich structure of a first conductor layer, an insulating film, and a second conductor layer, the first conductor layer having a predetermined thickness. It is a layer with a stone wall structure, a layer with an amorphous structure, or a thin layer made of a material with low layer resistance, and the unevenness of the surface on the insulating film side is It is characterized in that it is smaller than the film thickness of the insulating film.

Here, first, as the material of the first conductor layer, molybdenum,
Tungsten, niobium, titanium, tantalum, hafnium, zirconium and the like can be used. on the other hand,
The second conductor layer can be formed of any conventionally known material and is not particularly limited.

Further, as the insulator film material, any of tantalum oxide, niobium oxide, titanium oxide, hafnium oxide, zirconium oxide and the like can be used. This may be a single layer structure of a single material, or a composite layer or multilayer structure of different materials.

In such a capacitor of the present invention, the film thickness of each constituent layer is not special and is similar to the conventionally known one,
There is no particular limitation, but in general, the first conductor layer is several thousand liters, the second conductor layer is several thousand liters, and the intermediate insulating film is about 10 liters.
It is about 0 to 1000Å. However, when the first conductor layer is a thin layer of a material having a low layer resistance value, it is preferably thinner than the thickness of the insulating film. In this case, the lower limit varies depending on the material, but the thickness is such that the layer resistance value is 10 ⁴ Ω / □ or less. If this condition is not satisfied, it will not function as a capacitor and there is a risk of fusing or the like. It is not preferable because it exists.

According to the first aspect of the present invention, the first conductor layer has a stone wall-shaped crystal structure, which is obtained by once using a vapor deposition method,
For example, it can be realized by forming a film by a sputtering method, a vacuum deposition method, a chemical vapor deposition method or the like, and then performing a heat treatment. Although this treatment varies somewhat depending on the material used, it generally comprises treatment at a temperature in the range of ⅕ to about the melting point of the material. This heat treatment is performed in an inert gas atmosphere, for example, a nitrogen gas atmosphere.

The heat treatment can be performed simultaneously with the film formation by raising the substrate temperature to a temperature within the above range during the film forming operation. In any case, it suffices to be able to shift from a structure having severe irregularities such as the conventional columnar crystal shown in FIG. 4 to a flat structure such as a stone wall crystal.

In addition, in the second aspect of the present invention, the first conductor layer has an amorphous structure. With such a non-structure, surface irregularities can be significantly reduced, and this amorphous state can be achieved by the following method.

That is, it can be formed by first performing the reactive sputtering method in an argon gas containing impurities such as oxygen.
In this case, the crystal structure of the film does not necessarily have to be amorphous, and it is effective even if the crystal grain size is small.

For example, FIG. 7 shows the relationship between the oxygen concentration in the molybdenum film and the crystal grain size. It can be understood that the effect of reducing the crystal grain size is remarkable when the oxygen concentration is about 10 atomic% or more. Therefore, in this case, the oxygen concentration is
The concentration can be 10 atomic% or more, and the concentration is such that oxide crystals are not formed, that is, the concentration is equal to or lower than the stoichiometry of the oxide.

In addition to the above oxygen, nitrogen or the like can be used as the impurity, and the concentration thereof is the same as that of the above oxygen. Further, as the film forming method, in addition to the reactive sputtering method, a film is formed by a reactive vapor deposition method or a normal film forming method, and then an impurity is injected by an ion injection method to destroy the crystal and reduce the crystal grain size. Or can be made amorphous. That is, any method can be used as long as it can reduce the crystal grain size or can amorphize.

Furthermore, according to the third aspect of the present invention, the first conductor layer is formed as a thin layer of a material having a low layer resistance. As the material, any of the above materials can be used. The insulating film and the second conductor layer are the same as those in the first and second modes, and the thickness is as described above.

Action In order to meet the demands for high integration, miniaturization, and large capacity of various electric devices such as semiconductor ICs and LSIs, miniaturization of capacitors, which is one of the passive elements, is required.
Therefore, a large capacitor per unit area has been required, but in the conventional three-layer structure as shown in FIG. 4, when an insulating film is formed on a silicon substrate, these interfaces are formed. However, there is a problem that a silicon oxide film is formed on the surface and the effective dielectric constant is lowered. This problem can be solved by selecting a metal material having a specific property such as not forming an oxide at the interface with the insulating film as the lower electrode of the capacitor, as described above in detail. Due to the upper limit, considerable unevenness occurs on the surface, which increases the leakage current of the capacitor and causes a short circuit,
This has been a cause of greatly impairing the yield and reliability of the capacitor.

It is considered that this problem can be overcome by smoothing the surface of the lower electrode. Therefore, in the present invention, the structure of the lower electrode is selected from the group consisting of special materials, particularly molybdenum, tungsten, niobium, titanium, tantalum, hafnium, and zirconium, and a layer having a stone wall structure or By using a layer having a crystalline structure or a thin layer made of a material having low layer resistance, the unevenness on the surface on the insulating film side can be made smaller than the thickness of the insulating film. We have found that the purpose can be achieved.

According to the first aspect, as shown in FIG. 1, the above results were achieved by making the crystal form a stone wall. The example shown in FIG. 1 is a lower electrode 4 having a crystal structure of a stone wall and an insulating film 5.
And the upper electrode 6, the stone wall structure is realized by once forming columnar large crystals as in the conventional case and then performing heat treatment.

Further, according to the second aspect, as shown in FIG. 2, the lower electrode layer 7 is made amorphous in order to reduce the crystal grain size. This does not necessarily need to be amorphous, and merely reducing the crystal grain size is sufficient. Therefore, impurities such as oxygen are added in a predetermined amount.

Furthermore, according to the third aspect, as shown in FIG. 3, the particle size can be reduced by reducing the thickness of the lower electrode layer 8, and the same effect can be achieved in this case as well. can do.

Thus, according to the present invention, the surface smoothing of the capacitor lower electrode can be achieved, a capacitor having a large capacitance per unit area can be obtained, and a passive element that meets recent demands of various electronic devices can be advantageously provided. .

EXAMPLES The present invention will be described in more detail with reference to Examples below, and the effects thereof will be demonstrated. However, the scope of the present invention is not limited by these examples.

Example 1 In this example, a capacitor according to the first aspect of the present invention as shown in FIG. 1 was produced. First, the lower electrode 4 is a 3000 Å molybdenum film which is formed by a sputtering method known per se and then heat-treated in nitrogen at 1000 ° C. The insulating film 5 is a 100Å tantalum oxide film formed by a known sputtering method, and the upper electrode 6 is a 3000Å molybdenum film formed by a known sputtering method. By subjecting the molybdenum film to a heat treatment at a high temperature, a columnar crystal such as the metal layer 1 in FIG. 4 changes into a stone-wall-shaped crystal with a very flat surface like the molybdenum film 4 in FIG. Therefore, as compared with the film before the heat treatment, the unevenness on the surface is reduced and the number of the unevenness is reduced due to the increase in the crystal grain size. Therefore, the capacitor of this structure is a capacitor in which the unevenness of the surface of the lower electrode is smaller than the thickness of the insulating film. The leakage current characteristic of this capacitor is shown as a curve d in FIG. It is clear that the leakage current is significantly reduced as compared with the conventional capacitor (curve c in the same figure).

Example 2 In this example, a capacitor according to the second aspect of the present invention as shown in FIG. 2 was produced. First, the lower electrode 7 is a 3000-liter amorphous molybdenum film containing oxygen, which is formed by a reactive sputtering method in argon gas containing oxygen, which is known per se. The insulating film 5 and the upper electrode 6 are the same as in the first embodiment. Since the molybdenum film 7 is amorphous, the surface unevenness is extremely small. Therefore, the capacitor of this structure is a capacitor in which the unevenness of the surface of the lower electrode is smaller than the thickness of the insulating film. The leakage current characteristic of this capacitor is shown as a curve e in FIG. It is clear that the Cooke current is significantly reduced compared to the conventional capacitor.

Example 3 In this example, a capacitor according to the third aspect of the present invention as shown in FIG. 3 was produced. Here, the lower electrode 8 is a 20Å molybdenum film formed by a sputtering method known per se. The insulating film 5 and the upper electrode 6 are the same as in the first embodiment.
Although the molybdenum film 8 is as thin as 20Å, it has a sufficiently low layer resistance value as shown in FIG. 8 and forms a good conductor layer. In the structure shown in FIG. 3, since the surface roughness of the molybdenum film 8 is at most 20 Å or less, the surface roughness of the lower electrode is a capacitor smaller than the thickness of the insulating film. The leakage current characteristic of this capacitor is shown in FIG. It is clear that the leakage current is remarkably reduced as compared with the conventional capacitor.

As described above, according to the present invention, since the unevenness of the lower electrode can be reduced, the leakage current can be reduced, and the capacitor per unit area can be very large, and a capacitor having excellent insulation can be obtained. it can.

Therefore, by using such a capacitor, various electronic devices such as a MOS dynamic memory of an electronic computer can be downsized, highly integrated, or have a large capacity.

Furthermore, according to the method of the present invention, the capacitor can be manufactured with high reliability and high yield.

[Brief description of drawings]

1 is a sectional view of a capacitor according to the first aspect of the present invention, FIG. 2 is a sectional view of a capacitor according to the second aspect of the present invention, and FIG. 3 is a sectional view of a capacitor according to the third aspect of the present invention. FIG. 4 is a cross-sectional view of a conventional capacitor, FIG. 5 is a characteristic diagram showing the relationship between the tantalum oxide film thickness and the effective relative dielectric constant of a capacitor using tantalum oxide as an insulating film, and FIG. FIG. 7 is a characteristic diagram showing the relationship between the molybdenum crystal grain size and the oxygen concentration in the molybdenum film when molybdenum containing oxygen is formed by the reactive sputtering method. FIG. 8 is a characteristic diagram showing the relationship between the layer resistance value and the molybdenum film thickness when molybdenum is formed by the sputtering method. (Main reference numbers) 1 ... metal layer, 2 ... insulating film, 3 ... upper electrode, 4,6,7,8 ... molybdenum film, 5 ... tantalum oxide film

Claims (7)

[Claims] 1. A capacitor having a three-layer laminate structure including a first conductor layer, an insulating film formed on the first conductor layer, and a second conductor layer provided on the insulating film. The first conductor layer has a stone wall crystal structure composed of one selected from the group consisting of molybdenum, tungsten, niobium, titanium, tantalum, hafnium and zirconium, and the surface of the first conductor layer The unevenness of is smaller than the thickness of the insulating film. 2. A capacitor having a three-layer laminated structure including a first conductor layer, an insulating film formed on the first conductor layer, and a second conductor layer provided on the insulating film. Wherein one conductor layer is an amorphous layer containing oxygen or nitrogen as an impurity composed of one selected from the group consisting of molybdenum, tungsten, niobium, titanium, tantalum, hafnium and zirconium, The above capacitor, wherein surface irregularities are smaller than the thickness of the insulating film. 3. A capacitor having a three-layer structure including a first conductor layer, an insulating film formed on the first conductor layer, and a second conductor layer provided on the insulating film. The film has a thickness of 1000 Å or less, and the first conductor layer is composed of one kind selected from the group consisting of molybdenum, tungsten, niobium, titanium, tantalum, hafnium and zirconium, and the unevenness of the surface thereof is the insulation. The above capacitor, which is smaller than the thickness of the film and is not less than the thickness that gives a layer resistance of 10 ⁴ Ω / □ or less and not more than the thickness of the insulating film. 4. The insulating film comprises tantalum oxide, niobium oxide,
A single layer of at least one kind selected from the group consisting of titanium oxide, hafnium oxide and zirconium oxide, or a laminated structure consisting of a plurality of layers, characterized in that any one of claims 1 to 3. The described capacitor. 5. A method of manufacturing a capacitor having a three-layer laminated structure by laminating a first conductor layer, an insulating film and a second conductor layer in this order by a vapor deposition method, the method comprising the steps of: Is formed by a vapor deposition method using molybdenum, tungsten, niobium, titanium, tantalum, hafnium and zirconium to form a layer having a predetermined thickness, and then the melting point of the conductor material. The method for producing a capacitor is characterized in that it is formed by heat treatment at a temperature of less than ⅕ and at least ⅕ of the melting point, and the surface irregularities are smaller than the thickness of the insulating film. 6. A method of manufacturing a capacitor having a three-layer laminated structure by laminating a first conductor layer, an insulating film, and a second conductor layer in this order by a vapor deposition method, the method comprising the steps of: The conductive layer of 10 atomic% formed by vapor deposition of one selected from the group consisting of molybdenum, tungsten, niobium, titanium, tantalum, hafnium and zirconium in the presence of oxygen or nitrogen as impurities. ~ A capacitor characterized by being an amorphous layer containing oxygen or nitrogen having a stoichiometry of oxide or nitride of a conductive material and having surface irregularities smaller than the thickness of the insulating film. Manufacturing method. 7. The method of manufacturing a capacitor according to claim 6, wherein the impurity is added to the first layer by an ion implantation method.