JPH1140748A - Manufacture of thin film capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a conductor film without causing abnormal grain deposition or sharp ruggedness, suppress the current leakage and avoid reduction of a dielectric film at forming of this film, by oxidizing the surface of electrode layers under the condition that an oxidation and disproportionation reactions occur at the same time. SOLUTION: At an Si substrate 1 heated at a low pressure in a closed vessel, an Rh oxide conductor layer 5 is formed on the surface of an electrode film 4 such that a part of the conductor layer 5 being formed on the film 4 evaporates from this film 4 by a disproportionation reaction as RuO4 in a gaseous form, and hence the internal stress of the conductor layer 5 is relaxed in the compressing direction to form a flat surface of the layer 5 without causing large grain precipitates thereon, thus suppressing the current leak and avoiding reduction of a dielectric film 6 at forming thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thin film capacitor used for a high density semiconductor memory or the like.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become more sophisticated, high-capacity memories have been required. Therefore, in order to realize a gigabit class DRAM, attempts to manufacture a thin film capacitor using a thin film made of a high dielectric material as a dielectric layer have been actively made. For example, semiconductor, integrated circuits Technology Symposium As reviewed in [p103-p108 (1992)] , a high dielectric constant and Ba _x Sr ₁ -xTiO ₃ having both paraelectric (hereinafter, referred to as BST) To
Attempts have been made to use a dielectric layer of a DRAM by using a sputtering or CVD technique.

[0003] However, the BST film has a gigabit DR.
When the thickness is reduced for application to AM, there arises a problem that the relative dielectric constant decreases and the leak current increases significantly. Hereinafter, the reason will be described.

A thin film capacitor is formed on a lower electrode layer made of Al or the like by a chemical vapor deposition (hereinafter, referred to as M) method using an organic metal.
A dielectric layer made of BST is formed by OCVD, and an upper electrode layer made of Al or the like is formed on the dielectric layer, followed by annealing. Here, MOCVD is a heat treatment performed in a thermal environment of about 400 ° C., and the annealing treatment is also a heat treatment.

When such a heat treatment (MOCVD, annealing) is performed, a dielectric layer (BST) and an electrode layer (particularly,
A low dielectric constant layer is formed at the interface with the lower electrode layer). The low dielectric constant layer is believed to be formed as follows. That is, when heat of MOCVD or annealing treatment is applied to the dielectric layer (BST), the heat oxidizes the electrode layer (Al ₂ O ₃ is formed near the interface), and at this time, the dielectric layer near the electrode interface is formed. The layer is reduced to generate oxygen vacancies, and a low dielectric constant layer is formed at the site where oxygen vacancies have occurred.

The formation of such a low dielectric constant layer at the interface between the dielectric layer and the electrode layer causes a decrease in relative dielectric constant and an increase in leak current. In particular, in a thin film capacitor in which a dielectric material having a high relative dielectric constant (such as BST) is formed in a thin film having a thickness of about several hundred degrees, the formation of a low dielectric constant layer causes
The relative permittivity and the leak current are significantly deteriorated. Therefore, it has been required to prevent the occurrence of such a low dielectric constant layer.

On the other hand, it is conceivable to form the electrode layer from platinum (Pt) having excellent oxidation resistance to suppress the formation of a low dielectric constant layer. However, platinum (Pt) is a material that is difficult to finely process, so that gigabit D
It is difficult to apply to a highly integrated thin film capacitor such as a RAM.

Conventionally, metals such as ruthenium (Ru) and iridium (Ir), which do not have the same oxidation resistance as platinum (Pt), but have a certain degree of oxidation resistance and can be finely processed. Thus, an inconvenience was solved by forming an electrode layer (particularly, a lower electrode layer). However, since ruthenium (Ru) and iridium (Ir) are more oxidizing than platinum (Pt), they may slightly reduce the dielectric layer near the electrode interface to cause oxygen defects. Therefore, conventionally, attention was paid to the fact that oxides of ruthenium (Ru) and iridium (Ir) have conductivity and an oxygen shielding function, and the occurrence of oxygen deficiency was prevented as follows. That is, after an electrode made of ruthenium (Ru) or iridium (Ir) is formed, a conductor layer made of an oxide of the electrode layer, such as RuO ₂ or IrO ₂ , is formed on the surface of the electrode layer. In addition to performing the function described above, oxygen was prevented from permeating from the dielectric layer toward the electrode layer.

[0009] RuO ₂ or IrO ₂ exhibiting such a function.
Conventionally, the conductive layer is formed mainly by a so-called reactive sputtering method in which oxygen is introduced into a sputtering gas such as Ar after using a single metal such as Ru or Ir or a target such as RuO ₂ or IrO _2. I was

[0010]

However, the method of forming the conductor layer in this manner has the following disadvantages. That is, irregularities are formed on the surface of the conductor layer (RuO ₂ , IrO ₂ ) formed by the reactive sputtering method. Although the size of the unevenness is relatively small, it has a feature that the tip of the convex portion tends to be sharp. Therefore, when a dielectric layer is formed on a conductor layer having such irregularities, a problem arises in that a projection on the surface of the conductor layer penetrates through the dielectric layer and causes current leakage. A capacitor having a relatively thick dielectric layer is unlikely to cause current leakage even with a conductive layer having a sharp pointed protruding portion. Such a problem is conspicuous in a thin film capacitor having a dielectric layer which is thinned accordingly.

On the other hand, a sputtering process is utilized by making use of the characteristic of the reactive sputtering method that the size of the irregularities on the product surface can be suppressed to some extent by lowering the film forming temperature (substrate temperature). It is conceivable to solve the above problem by lowering the temperature. However, even if the above problem is avoided in this way, there is a fear that the size of the irregularities increases after passing through the subsequent steps, which again causes a current leak. This will be described below.

The particles of the conductor layer (RuO ₂ , IrO ₂ ) include:
The characteristic is that the particle diameter at which the shape is stabilized is uniquely determined with respect to the environmental temperature at that time, and the particle diameter at which the shape is stabilized increases in proportion to the rise in temperature. for that reason,
Step of forming dielectric layer (MOCVD) performed after formation of conductive layer
Etc., and the processing temperature is about 400 to 600 ° C.)
Annealing process after upper electrode formation (processing temperature is about 4
(Approximately 100 to 600 ° C.), the particles of the conductor layer (RuO ₂ , IrO ₂ ) grow due to the temperature rise associated with such treatment, and the size of the irregularities on the surface of the conductor layer also increases. Oops.

By directly oxidizing the electrode layer (Ru, Ir) instead of the reactive sputtering method having such disadvantages,
There is a method of forming a conductor layer (RuO ₂ , IrO ₂ ) (hereinafter, referred to as a direct oxidation method). However, such a direct oxidation method also has the following disadvantages. That is, R
The electrode layer made of u and Ir is usually formed by a sputtering method. However, in the Ru or Ir electrode layer formed by the sputtering method, it is inevitable that a compressive stress remains due to the manufacturing method. On the other hand, the direct oxidation method is characterized in that if compressive stress remains in the oxide to be formed, the formed oxide undergoes volume expansion and the oxide particles grow abnormally. for that reason,
When the conductive layer (RuO ₂ , IrO ₂ ) is formed by oxidizing the electrode layer (Ru, Ir) formed by the sputtering method, abnormal growth of particles due to volume expansion of the conductive layer causes the surface of the conductive layer to become abnormal. However, although sharp projections are not formed, irregular and large irregularities are formed, which makes it impossible to form a dielectric layer on the conductor layer with high accuracy, and is thin in terms of shape. It becomes inappropriate as a component of the capacitor.

Therefore, an object of the present invention is to improve the method of forming a conductive layer by a direct oxidation method and to solve the above-mentioned problems.

[0015]

The present invention relates to a method of manufacturing a thin film capacitor in which a conductor layer is formed on an electrode layer by oxidizing the electrode layer, and then a dielectric layer is formed on the conductor layer. A conductive material that causes a disproportionation reaction is used as a material for the electrode layer, and the conductor layer is formed under conditions in which an oxidation reaction and a disproportionation reaction occur simultaneously in the electrode layer. By doing so, the above problem is solved.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the first aspect of the present invention, after a conductor layer formed by oxidizing the electrode layer is formed on the electrode layer, a dielectric layer is formed on the conductor layer. A method of manufacturing a thin film capacitor to be formed, wherein a conductive material that causes a disproportionation reaction is used as a material of the electrode layer, and the oxidation reaction and the disproportionation reaction are performed on the conductor layer in the electrode layer. Formed under conditions that occur simultaneously,
This has the following operation. That is, after the surface of the electrode layer is oxidized, a part of the oxide becomes an evaporating component due to the disproportionation reaction and evaporates from the electrode layer surface, so that the compressive stress remaining in the electrode layer is dissipated. .

According to a second aspect of the present invention, in the method for manufacturing a thin film capacitor according to the first aspect, the conductive layer is formed under a reduced-pressure aerobic environment, so that an oxidation reaction occurs in the electrode layer. And a disproportionation reaction are simultaneously satisfied, thereby having the following effects. That is, the condition in which an oxidation reaction and a disproportionation reaction are simultaneously generated is satisfied by a relatively simple operation of forming a conductor layer under a reduced-pressure aerobic environment, so that the present invention can be easily implemented. Become like

According to a third aspect of the present invention, in a method for manufacturing a thin film capacitor according to the first or second aspect,
The invention is characterized in that a conductive material containing at least one element of Ru and Ir is used as a material of the electrode layer, and has the following effects. That is,
Ru and Ir have the property that an oxidation reaction and a disproportionation reaction occur simultaneously, and the oxide has the property of being conductive. Therefore, a conductive material containing at least one of these elements is used. If the material is used as the material of the electrode layer,
The present invention can be easily implemented.

According to a fourth aspect of the present invention, in the method of manufacturing a thin film capacitor according to the second aspect, after the conductor layer is formed, an evaporation component generated by the formation of the conductor layer is reduced by the conductor layer. It is characterized in that the pressure on the atmosphere on the conductor layer is increased in a state where it is prevented from diverging from the atmosphere above, thereby having the following effects. That is, if the pressure is increased in a state in which the divergence of the evaporation component is prevented, a reaction opposite to the disproportionation reaction occurs, and a part of the evaporation component is deposited on the conductor layer. Therefore, the thickness of the conductor layer can be adjusted by changing the timing of the start of the pressure increase to adjust the amount of the evaporated component deposited.

According to a fifth aspect of the present invention, in the method for manufacturing a thin film capacitor according to the fourth aspect, the evaporation component is prevented from escaping from the atmosphere on the conductor layer, and further, the evaporation component is prevented. It is characterized in that a gas having a component equivalent to the component is supplied to the atmosphere on the conductor, thereby having the following effects. That is, the supply amount of the gas (having a component equivalent to the evaporation component) to be supplied when the reaction opposite to the disproportionation reaction is caused by increasing the pressure while preventing the divergence of the evaporation component is adjusted. Thus, the amount of the evaporated component can be controlled with high accuracy.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, a case where a capacitor is formed on the silicon substrate 1 will be described as an example.

Embodiment 1 As shown in FIG. 1, a capacitor C includes a silicon substrate 1, an insulating layer 2 provided on the silicon substrate 1, a contact 3 provided in the insulating layer 2, It comprises an electrode layer 4 and a conductor layer 5 sequentially laminated on the insulating layer 2 and a dielectric layer 6 provided on the conductor layer 5.

Next, a method of manufacturing the capacitor C will be described.

[0024] First, after forming the insulating layer 2 made of SiO ₂ on a silicon substrate 1, to form a contact 3 in the insulating layer 2. Polycrystalline silicon is suitable for the contact 3, and CVD is suitable for its production method.

The electrode layer 4 is formed on the insulating layer 2 on which the contact 3 has been formed. In the present embodiment, the electrode layer 4 has a multilayer structure of Ru / TiN / Ti (Ru / TiN / Ti) containing Ru as a main component.
Is the uppermost layer), and the electrode layer 4 having such a multilayer structure is
Is manufactured by a sputtering method. The thickness of the electrode layer 4 is 200 nm (Ru), 100 nm (TiN), and 25 nm (T
i) is appropriate. The reason why the electrode layer 4 has a multilayer structure instead of a single Ru layer is as follows. That is, the Ti layer functions as an adhesion layer to silicon and a layer for reducing the resistance with the contact 3,
This is because the TiN layer functions as a layer for preventing mutual diffusion between the Ru layer and silicon.

In the present embodiment, the Ru layer forming the electrode layer 4 is formed by sputtering gas (Ar) and a target (R
u) Under a condition of a substrate temperature of 250 ° C. and a sputtering pressure of 8 mTorr, it is formed by a DC magnetron sputtering method.

The surface (Ru film) of the electrode film 4 thus obtained has a Ru (110) orientation, and internal stress in a compressed state is accumulated inside the electrode film 4. Such an internal stress can be obtained by comparing the warpage of the silicon substrate 1 before and after the formation of the electrode film 4.

Next, the conductor film 5 is formed by directly oxidizing the electrode film 4 (specifically, the Ru film constituting the electrode layer 4).

Here, the electrode film 4 (Ru film) in which the internal stress of the compression is accumulated is directly thermally oxidized in the atmosphere or in an oxygen atmosphere at normal pressure at a processing temperature of 600 ° C. and a processing time of 30 minutes to obtain Ru0. _It is assumed that the conductor layer 5 made of 2 is formed. In this case, due to the internal stress state of the electrode film 4 and the difference in volume between the conductor film 5 (RuO ₂ ) and the electrode film 4 (Ru), the formed conductor layer 5 (RuO ₂ ) In addition to the precipitation of particles of about 1 μm, sharp irregularities are formed on the surface of the conductor layer 5 even in portions other than the particle precipitation portions.
Therefore, when the dielectric film 6 is formed on the conductor layer 5 formed in this manner, there is a possibility that a leak current is generated.

Therefore, in the present embodiment, the electrode film 4
By performing the oxidation process under reduced pressure, the surface of the conductor layer 5 is flattened to suppress the leak electrode. This will be described below.

As shown in FIG. 2, a sealed container A is prepared. A vacuum pump B is connected to the sealed container A, and an argon gas and oxygen gas injection pipe D is connected to the sealed container A. Further, a substrate heating unit E is disposed in the sealed container A.

After the insulating layer 2, the contact 3, and the electrode film 4 are formed on the silicon substrate 1, the silicon substrate 1 is placed on the substrate heating section E in the sealed container A, and the sealed container A is sealed. Then, the vacuum pump B is operated to evacuate the inside of the sealed container A to 10 ^-8 Torr, and then argon gas (Ar) and oxygen gas (O ₂ ) are injected through the injection pipe D.
Inject until the internal pressure of the sealed container A becomes 1 mTorr.

In this state, the silicon substrate is heated to 700 ° C. by the substrate heating section B, and held in this state for 30 minutes.

As described above, when the silicon substrate 1 is heated in a reduced oxygen atmosphere, a conductor layer 5 of RuO ₂ is formed on the electrode layer 4 to a thickness of about 20 nm. At this time, although a slight unevenness (an unevenness of several nm) is formed on the surface of the conductor layer 5, a sharp shape is not observed. Hereinafter, the reason will be described.

Ruthenium (Ru) causes an oxidation reaction when heated in an aerobic environment, like a general oxidizing substance.
It is known that when such heating is performed in a reduced pressure environment, a disproportionation reaction occurs at the same time. When ruthenium (Ru) is heated in a reduced-pressure aerobic environment, specifically, the following reaction occurs.

Ru + O ₂ → RuO ₂ (oxidation reaction) RuO ₂ → Ru + RuO ₄ (disproportionation reaction) In the above reaction, ruthenium (Ru) forms an oxide film RuO ₂ on its surface by an oxidation reaction. A portion of the oxide film (RuO ₂ ) formed by the subsequent reaction causes a disproportionation reaction, and the Ru film takes a gaseous form in the reaction environment.
It becomes O ₄ and evaporates. At this time, even if the internal stress is accumulated in the ruthenium (Ru) film, the ruthenium (Ru)
The internal stress accumulated when a part of the Ru element constituting the film is evaporated as RuO ₄ is dissipated.

According to the above principle, the following phenomenon occurs on the surface of the electrode film 5. That is, in the silicon substrate 1 heated (700 ° C.) under a reduced pressure environment (1 mTorr) in the sealed container A, the conductor layer 5 made of ruthenium oxide (RuO ₂ ) is formed on the surface (Ru) of the electrode film 4. Is formed. At this time, a part of the conductor layer 5 (RuO ₂ ) generated and being formed on the electrode film 4 becomes RuO ₄ which takes a gaseous form in the reaction environment due to the disproportionation reaction, and from above the electrode film 4. Evaporates. This means that part of the ruthenium element (Ru) constituting the surface of the electrode film 4 is diverged as RuO _4, and such a ruthenium element (Ru)
With the divergence, the internal stress in the compression direction accumulated in the electrode film 4 is dissipated. Therefore, the conductor layer 5 (RuO ₂ ) has the electrode film 5 in which the internal stress in the compression direction has been eliminated.
The conductor layer 5 is formed on the surface (Ru).
Is formed in a flat state without causing large particle precipitation on its surface.

However, even under the same pressure condition (1 mTorr), when the temperature condition is about 800 ° C., the disproportionation reaction proceeds too quickly, and the reaction occurring on the surface (Ru) of the electrode film 4 is almost RuO. ₄ until the formation reaction of the conductive layer 5
(RuO ₂ ) is hardly formed. Therefore, in order to form the flat electrode layer 5, it is important not to raise the temperature condition to about 800 ° C.

As described above, by oxidizing the surface (Ru) of the electrode layer 4 under the condition that the oxidation reaction and the disproportionation reaction occur simultaneously, abnormal particle precipitation and sharp irregularities are caused. This makes it possible to form the conductor layer 5 (RuO ₂ ) without suppressing current leakage and to prevent reduction of the dielectric film 6 when the dielectric film 6 is formed.

Embodiment 2 The manufacturing method of this embodiment can be similarly implemented by the apparatus shown in FIG. 2 referred to in the above-described embodiment, and the following description will be made with reference to FIG.

After the same insulating layer 2, contact 3, and electrode layer 4 as in the first embodiment are formed on silicon substrate 1, silicon substrate 1 is housed in sealed container A, and the temperature is set to 700 ° C. In an oxygen-containing atmosphere at a pressure of about 1 mTorr, a disproportionation reaction occurs on the surface (Ru) of the electrode layer 4, whereby ruthenium (Ru) is formed on the electrode film 4 as an oxide film (RuO ₂ ) and RuO is formed. Volatilize as ₄ . The above steps are the same as in the first embodiment.

Next, the steps which characterize the present embodiment will be described. In the present embodiment, during the period in which the disproportionation reaction occurs on the surface of the electrode layer 4, the sealed container A by the vacuum pump B is used.
Is stopped, and the evaporated RuO ₄ is retained in the sealed container A (in the vicinity of the silicon substrate 1) with the vapor pressure increased. Then, in this state, the inert gas Ar is injected into the sealed container A from the injection pipe D until the pressure in the sealed container A returns to a pressure equivalent to the atmospheric pressure. Then, the RuO ₄ vapor sealed in the sealed container A and staying near the silicon substrate 1 reaches a saturated vapor pressure as the pressure rises,
A part of the oxide R
It is deposited on the conductor layer 5 (RuO ₂ ) as uO ₂ (conductor layer 5). Thus, the thickness of the conductor layer 5 is the sum of the thickness obtained by the oxidation reaction and the thickness obtained by deposition, and the thickness of the conductor layer 5 is further increased. In addition, the amount of oxide (RuO ₂ ) deposited can be adjusted by changing the timing of the start of pressure increase, so that the film thickness of the conductor layer 5 obtained in this way adjusts the timing of start of pressure increase. Can be controlled.

By the way, in this embodiment, (Ru
O ₄ → RuO ₂ ) deposition step is added to make the conductor layer 5
The reason why the film thickness is increased is as follows. That is, a homogeneous conductor layer (R
In the case of forming uO ₂ ), a part of the surface (Ru) of the electrode layer 4 must be converted to RuO ₄ and evaporated, and even if the conductor layer 5 is formed on the electrode layer 4, Surface (R
It is inevitable that the combined film thickness of u) and the conductor layer 5 (RuO ₂ ) is reduced to some extent. On the other hand, in the present embodiment, a part of the evaporated RuO ₄ is converted to RuO ₂ and is deposited on the surface of the conductor layer 5, so that such a film loss can be compensated.

In the second embodiment, the RuO ₄ in the sealed container A is stopped by stopping the exhaust of the sealed container A.
Of had increased vapor pressure, the other, by supplying into the sealed container A the RuO ₄ from the outside in terms of stopping the exhaust of RuO _4, may be increasing the vapor pressure of RuO _4. Then, the vapor pressure of RuO ₄ in the sealed container A can be further increased to approach a saturated state. The amount of RuO ₂ deposited depends on the vapor pressure of RuO ₄ in the sealed container A. If RuO ₄ is supplied to increase the vapor pressure of RuO ₄ ,
The amount of RuO ₂ deposited increases, and the above-described film reduction (electrode layer 4
(Thickness reduction of film thickness combining surface (Ru) and conductor layer 5)
Can be suppressed more reliably. Moreover, by varying the supply amount of RuO _4, since the precipitation amount of volatile components (RuO ₄₎ can be adjusted accurately, it is possible to further accurately control the thickness of the conductor layer 5.

In each of the above-described embodiments, the conductor layer 5 is formed on the surface of the electrode layer 4 from its oxide, and the above-described effect (flattening of the conductor layer 5) is exhibited. As an example, ruthenium (Ru) has been mentioned as an example.
Examples of the conductor include at least one of ruthenium (Ru) and iridium (Ir). In short, any oxide may be used as long as the oxide has conductivity and causes a disproportionation reaction.

[0046]

As described above, according to the present invention, the surface of the electrode layer is oxidized under conditions in which an oxidation reaction and a disproportionation reaction occur simultaneously, thereby preventing abnormal particle precipitation and sharp irregularities. This makes it possible to form a conductor layer without causing such a phenomenon, and it is possible to prevent reduction of the dielectric film during formation of the dielectric film while suppressing current leakage. This has made it possible to manufacture thin-film capacitors suitable for high-density semiconductor memories such as gigabit DRAMs.

[Brief description of the drawings]

FIG. 1 is a sectional configuration view of a thin film capacitor according to the present invention.

FIG. 2 is a diagram illustrating a configuration of a manufacturing apparatus used in the manufacturing methods according to the first and second embodiments of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Insulating layer 3 Contact 4 Electrode layer 5 Conductor layer 6 Dielectric layer A Sealed container B Substrate heating part D Vacuum pump

Claims (5)

[Claims] 1. A method of manufacturing a thin film capacitor, comprising: forming a conductor layer formed by oxidizing an electrode layer on an electrode layer; and forming a dielectric layer on the conductor layer. A conductive material that causes a disproportionation reaction is used as the material, and the conductive layer is formed under conditions in which an oxidation reaction and a disproportionation reaction occur simultaneously in the electrode layer. A method for manufacturing a thin film capacitor. 2. The method for manufacturing a thin film capacitor according to claim 1, wherein the conductive layer is formed in a reduced-pressure aerobic environment,
A method for manufacturing a thin film capacitor, wherein a condition in which an oxidation reaction and a disproportionation reaction occur simultaneously in an electrode layer is satisfied. 3. The method for manufacturing a thin film capacitor according to claim 1, wherein a conductive material containing at least one element of Ru and Ir is used as a material of the electrode layer. A method for manufacturing a capacitor. 4. The method for manufacturing a thin film capacitor according to claim 2, wherein after the formation of the conductor layer, evaporation components generated by the formation of the conductor layer diverge from an atmosphere on the conductor layer. A method of manufacturing a thin film capacitor, comprising increasing the pressure of an atmosphere on a conductor layer in a state where the pressure is blocked. 5. The method for manufacturing a thin film capacitor according to claim 4, wherein the vapor component is prevented from escaping from the atmosphere on the conductor layer, and further has a component equivalent to the vapor component. Is supplied to the atmosphere above the conductor.