JPH05218299A - Thin film capacitor and its manufacture - Google Patents

Abstract

PURPOSE:To eliminate the step-difference between a lower electrode and a substrate, by constituting the part of a first layer on the upper part of which a second layer is laminated, of tantalum oxide wherein O/Ta is lower than or equal to 2.0 and oxygen is short from stoichiometrical composition. CONSTITUTION:An insulating layer 2 composed of SiO2 is laminated on a silicon substrate 1. On a contact hole 3, conductive tantalum oxide 5 is formed. On the other part, a first layer composed of Ta2O5 6 as insulator is formed. On the tantalum oxide 5 as a conducting layer, a second layer composed of platinum (Pt) 7 is formed. On a lower electrode BaTiO3 8 as dielectric is laminated. Thereon a film of Al 9 of an upper electrode is laminated to constitute a thin- film capacitor. Thereby the step-difference of the lower electrode is reduced, the short-circuit between the lower electrode and the upper electrode which short-circuit is due to imperfect step coverage is prevented, and a thin film capacitor can be formed with high reproducibility.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a small electronic circuit (hereinafter referred to as LS).
I)), and particularly the structure of the lower electrode.

[0002]

2. Description of the Related Art With the development of integrated circuit technology, electronic circuits are becoming smaller and smaller, and it is becoming more important to make capacitors, which are circuit elements essential for various electronic circuits, smaller. However, miniaturization of thin-film capacitors is delayed compared to miniaturization of active elements, which is a major factor preventing high integration. Therefore, SiO ₂ and Si ₃ N, which are conventionally used as a method for miniaturizing capacitors, are used.
BaTiO ₃ , SrTi having a dielectric constant larger than ₄
It has become important to develop a capacitor using a ferroelectric substance composed of O ₃ , PbZrO ₃ , PbTiO ₃ or a solid solution thereof.

Conventionally, a thin film capacitor using such a dielectric has a structure in which a dielectric film and an upper electrode are sequentially formed on a silicon electrode by a direct sputtering method (Japanese Patent Application No. 1-217).
No. 918) or a conductive layer composed of a first layer made of at least one refractory metal such as tantalum and titanium on a silicon electrode and a second layer made of at least one material of platinum and palladium. A structure in which a body film and an upper electrode are sequentially formed (Japanese Patent Application No. 1-238484) is used.

Further, for example, 1969 IBM Journal of Research and Development, Vol. 68, pp. 686-695 (IBM Jou
rnal of Research and dev
Lopment, 68, P686-695), a structure is known in which Pt or Pd is deposited as a lower electrode on an insulating substrate such as sapphire, and a dielectric film and an upper electrode are sequentially deposited.

However, when a dielectric film is directly deposited on silicon and a capacitor is manufactured by using silicon as a lower electrode, a low dielectric constant layer is formed between the dielectric film and silicon, resulting in high capacitance density. Can't get Also,
Even if Pt or Pd is used as the lower electrode, the LSI
In order to provide a low dielectric constant layer, silicon diffusion occurs at the bottom electrode, resulting in a low dielectric constant layer as if a dielectric film was deposited directly on silicon.

From the above, a thin film capacitor using a ferroelectric for the purpose of applying to an LSI has a two-layer structure of metal as a lower electrode as in Japanese Patent Application No. 1-238484. Attempts by the ones used have become widespread.

[0007]

In order to apply the capacitor having the above-mentioned structure to an LSI, the lower electrode must be processed in an appropriate area so as not to be electrically connected to other lower electrodes. For that purpose, the lower electrode which is a conductive layer must be removed by etching both the first layer and the second layer.

However, when the dielectric film is deposited on the step formed by etching the lower electrode, if the step coverage cannot be deposited well, the lower electrode is formed in a thin film portion or a portion without the dielectric film. Then, the upper electrode becomes conductive or is broken at a low voltage, and it becomes impossible to sufficiently operate as a capacitor. As described above, in order to manufacture a capacitor using the ferroelectric film for LSI, it is important to minimize the step between the lower electrode and the substrate.

An object of the present invention is to provide a thin film capacitor capable of eliminating a step between the lower electrode and the substrate and depositing a dielectric film with better step coverage, and a method of manufacturing the same.

[0010]

In order to achieve the above object, in a thin film capacitor according to the present invention, an insulating layer is formed on a silicon substrate, and a contact hole for establishing conduction with the silicon substrate is opened in the insulating layer. , A thin film capacitor having a structure in which tungsten or polysilicon is embedded in a contact hole, and a lower electrode, a dielectric film, and an upper electrode are sequentially stacked on an insulating layer, and the dielectric is
BaTiO ₃ , SrTiO ₃ , PbTiO ₃ , PbZrO ₃
Selected from the following, or consisting of these solid solutions,
The lower electrode for directly depositing the dielectric is composed of a first layer formed on the insulating film and a second layer made of platinum laminated on a part thereof, and the second layer is laminated on the upper portion. The part of the first layer which is not present is Ta ₂ O ₅ , and the part of the first layer in which the second layer is laminated on top has oxygen with O / Ta of 2.0 or less from the stoichiometric composition. Conductive tantalum oxide.

In the method of manufacturing a thin film capacitor, an insulating layer is formed on a silicon substrate, a contact hole for establishing conduction with the silicon substrate is opened in the insulating layer, and tungsten or polysilicon is embedded in the contact hole. A method of manufacturing a thin film capacitor, in which a lower electrode, a dielectric film and an upper electrode are sequentially laminated on an insulating layer, wherein the lower electrode comprises a first layer formed directly on the insulating film and platinum on a part of the first layer. The second layer is formed by laminating the second layer, and the first layer portion on which the second layer is not laminated is T
The part of the first layer, which is a ₂ O ₅ and on which the second layer is laminated, is a conductive tantalum oxide in which oxygen with O / Ta of 2.0 or less is insufficient from the stoichiometric composition. The Ta ₂ O ₅ and the conductive tantalum oxide of the first layer of the lower electrode are prepared by annealing in a oxygen atmosphere at a substrate temperature of 500 ° C. or higher and 1000 ° C. or lower.

An insulating layer is formed on the silicon substrate,
A thin film capacitor in which a contact hole for establishing conduction with a silicon substrate is opened in an insulating layer, tungsten or polysilicon is embedded in the contact hole, and a lower electrode, a dielectric film and an upper electrode are sequentially laminated on the insulating layer In the manufacturing method, the lower electrode is formed by laminating a first layer directly formed on the insulating film and a second layer made of platinum on a part of the first layer, and laminating the second layer on the upper part. The part of the first layer that is not formed is Ta ₂ O ₅ , and the part of the first layer on which the second layer is laminated has oxygen with O / Ta of 2.0 or less from the stoichiometric composition. The conductive tantalum oxide, which is Ta ₂ O ₅ and the conductive tantalum oxide in the first layer of the lower electrode, are produced by ion implantation of oxygen.

[0013]

[Function] Using tantalum oxide for the first layer of the lower electrode,
The portion where the second layer is not formed on the upper portion is Ta ₂ of the insulator.
By forming O ₅ and the portion where the second layer is formed from conductive tantalum oxide, it is possible to eliminate steps corresponding to the film thickness of the second layer. This allows the dielectric film to be deposited with better step coverage. Further, Ta ₂ O ₅ can be produced by ion implantation to control the width of the conductive tantalum oxide with high accuracy, and annealing has an effect of making the lower electrode finer than that of Ta ₂ O ₅ produced.

[0014]

Embodiments of the present invention will now be described with reference to the drawings.

(Embodiment 1) FIG. 1 shows SiO as an insulating film.
₂ is an example of the structure of a thin film capacitor using tungsten as the material for filling the contact hole and BaTiO ₃ as the dielectric film.

In the figure, SiO ₂ is deposited on the silicon substrate 1.
The insulating layer 2 made of is laminated. A contact hole 3 is opened in the insulating layer 2 to establish electrical connection with the silicon substrate 1, and the contact hole 3 is filled with tungsten 4 in the contact hole 3.
Embedded by. On the contact hole 3,
Conductive tantalum oxide 5, other parts of insulator T
A first layer of a ₂ O ₅ 6 and a _second layer of platinum (Pt) 7 are formed on the tantalum oxide 5 of the conductive layer.
A thin film capacitor is formed by laminating a dielectric material of BaTiO ₃ 8 on the lower electrode, and laminating a film of Al 9 of the upper electrode thereon.

The method of manufacturing the thin film capacitor will be described below. SiO ₂ was formed on the silicon substrate 1 by steam oxidation at a substrate temperature of 900 ° C. The film thickness was 5000Å. The contact hole 3 was formed by the plasma etching method. Chlorine gas as reaction gas, pressure 0.5mTo
It was performed at rr and 200 W. The tungsten 4 was embedded in the contact hole 3 by the CVD method.

Tungsten chloride was used as the source gas, and the film formation temperature was 500 ° C. Next, a 50 nm tantalum film was formed by the DC magnetron sputtering method. The film formation was performed using a metal tantalum target in an Ar gas atmosphere, 4 × 10 ⁻³ Torr, and a substrate temperature of 50 ° C. 50 nm of platinum 7 was continuously deposited in the apparatus so that the formed tantalum film did not come into contact with the atmosphere.

The film forming conditions were the same as the tantalum film forming. Metallic platinum was used as a target for forming the platinum film 7. Next, the platinum layer was processed so that the electrode area was 10 μm □. The platinum was etched by ECR dry etching. 10% chlorine for etching
Using oxygen-added gas, total pressure 0.5μm Tor
It was performed at r, 200 W, and a substrate temperature of -25 ° C.

The lower electrode processed as described above was annealed at a substrate temperature of 500 ° C. for 2 hours in an oxygen atmosphere.
By annealing, the surface of tantalum which is in direct contact with oxygen is oxidized, and the degree of oxidation of insulating Ta ₂ O ₅ 6 to the part with platinum 7 on top is small, and oxygen is insufficient from the stoichiometric composition. Conductive tantalum oxide 5
(O / Ta = 1.5). Then, a film of BaTiO ₃ 8 was deposited on the processed lower electrode in an amount of 500 Å. The deposition was performed by a high frequency magnetron sputtering method in Ar—O ₂ mixed gas under the film forming conditions of 1 × 10 ⁻² Torr and a substrate temperature of 600 ° C. A powder target having a stoichiometric composition was used as the target. 5000 Å Al9 for the upper electrode
Was deposited by the DC sputtering method. Metal Al was used as a target, and the processing was performed in an Ar gas atmosphere, 4 × 10 ⁻³ Torr, and a substrate temperature of 50 ° C.

Next, FIG. 2 shows the results of examining the distribution of the breakdown voltage for 1000 capacitors each having a lower electrode area of 1 μmm ² in the structure according to the present invention and the structure in which the tantalum layer is etched. In the case where tantalum is etched (FIG. 2A), about half of them are short-circuited.
Also, the variation of the breakdown voltage is large. The short circuit and the large variation of the breakdown voltage are caused by etching up to the first layer, which causes a large step between the lower electrode and the substrate, and the dielectric film is deposited on the step with good step coverage. This is because it is no longer possible.

Where there is no film, short circuit occurs,
Even if it is thin, it works as a capacitor because the film thickness is not uniform, but the breakdown voltage will vary. On the other hand, the capacitor using the lower electrode having the structure of the present invention has almost no breakdown voltage distribution as shown in FIG. 2B, and there is no short circuit.

O / Ta of the conductive tantalum oxide 5,
The relationship with the capacitance density of the capacitor was investigated. The result is shown in FIG. In FIG. 3, when the value of O / Ta is larger than 2.0, the capacity is greatly reduced. this is,
The resistance of the oxide of tantalum gradually increases as O / Ta increases, and changes from a conductive layer to an insulating layer.
This is because when it is 0 or more, it becomes an insulator and tantalum oxide acts as a low dielectric constant layer. From this, O / of tantalum oxide
Ta needs to be 2.0 or less.

FIG. 4 shows the results of examining the capacitance change when the annealing temperature was changed during the production of the lower electrode. The capacitor was manufactured on a 3-inch substrate. Substrate temperature is 50
At 0 ° C. or lower, a value much larger than that expected from the dielectric constant of the capacitance film is obtained. On the other hand, those manufactured at 1000 ° C. or higher have a low dielectric constant. This is because at 500 ° C. or lower, the portion of the second layer without platinum in the upper portion is not sufficiently oxidized and thus does not serve as an insulator and cannot be insulated from other capacitors.

As a result, a capacitor having a large electrode area is apparently formed, so that the capacitance becomes large.
On the other hand, the reason that the capacity decreases at 1000 ° C. or higher is that the tantalum below platinum is sufficiently oxidized at 1000 ° C. or more to become an insulator, and acts as a low dielectric constant layer, so that the capacity decreases. From the above, the substrate temperature during annealing needs to be 500 ° C. or higher and 1000 ° C. or lower.

[0026] In the contact holes, a polysilicon, a dielectric film _{(Ba, Sr) TiO 3,} SrTi
Similar results are obtained when a ferroelectric film made of O ₃ , PbZrO ₃ , PbTiO ₃ or a solid solution thereof is used.

Example 2 In the thin film capacitor of Example 1, Ta ₂ O ₅ of the lower electrode first layer was prepared by ion implantation. As in the first embodiment, tantalum and platinum are deposited on the insulating film having the contact holes 3 open.
The area required for the electrode is masked, oxygen is added to the first tantalum layer at 40 to 100 KeV, and the dose is 10 ¹⁵ to 10 ^18.
Ion implantation is performed at cm ^-2 . The ion-implanted substrate was heat-treated at 400 ° C. for 2 hours in a nitrogen atmosphere, and platinum was etched and a dielectric film and an upper electrode were deposited as in Example 1. As a result, regarding the obtained capacitor,
Results similar to those shown in FIG. 2 were obtained.

[0028]

As described above, according to the present invention,
By reducing the step difference of the lower electrode, short circuit between the lower electrode and the upper electrode due to poor step coverage can be prevented, and the thin film capacitor can be manufactured with good reproducibility.

[Brief description of drawings]

FIG. 1 is a cross-sectional side view of a thin film capacitor according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a distribution of breakdown voltage, where (a) shows a case where tantalum of the first layer is etched, and (b) shows a case where only platinum of the second layer is etched and annealed. is there.

FIG. 3 is a diagram showing a change in permittivity when O / Ta of tantalum oxide in a conductive layer is changed.

FIG. 4 is a diagram showing a change in capacitance of a capacitor when an annealing temperature is changed.

[Explanation of symbols]

1 Silicon 2 SiO ₂ 3 Contact Hole 4 Tungsten 5 Tantalum Oxide 6 Ta ₂ O ₅ 7 Pt 8 BaTiO ₃ 9 Al

Claims (3)

[Claims] 1. An insulating layer is formed on a silicon substrate, a contact hole for establishing conduction with the silicon substrate is opened in the insulating layer, and tungsten or polysilicon is embedded in the contact hole to form a lower electrode and a dielectric film. A thin film capacitor having a structure in which an upper electrode and an upper electrode are sequentially laminated on an insulating layer, wherein the dielectric is BaTiO ₃ , SrTiO ₃ , PbTiO ₃ ,
One of PbZrO ₃ or a solid solution of PbZrO ₃ and a lower electrode for directly forming a dielectric is composed of a first layer formed on an insulating film and platinum laminated on a part thereof. The portion of the first layer that is composed of a second layer and has no second layer stacked on top is Ta.
₂ O ₅ and the second layer is laminated on the upper part of the first layer is a conductive tantalum oxide in which oxygen with O / Ta of 2.0 or less is insufficient from the stoichiometric composition. A thin film capacitor characterized by being present. 2. An insulating layer is formed on a silicon substrate, a contact hole for establishing conduction with the silicon substrate is opened in the insulating layer, tungsten or polysilicon is buried in the contact hole, and the contact layer is sequentially formed on the insulating layer. Lower electrode,
A method of manufacturing a thin film capacitor, comprising laminating a dielectric film and an upper electrode, wherein the lower electrode is formed by laminating a first layer directly formed on an insulating film and a second layer made of platinum on a part thereof. The portion of the first layer on which the second layer is not stacked is Ta ₂ O ₅
And the portion of the first layer on which the second layer is laminated is O
/ Ta is an electrically conductive tantalum oxide in which oxygen of 2.0 or less is insufficient from the stoichiometric composition, and Ta ₂ O ₅ and the electrically conductive tantalum oxide of the first layer of the lower electrode are the same as the substrate temperature. A method of manufacturing a thin film capacitor, which is manufactured by annealing in an oxygen atmosphere at 500 ° C. or higher and 1000 ° C. or lower. 3. An insulating layer is formed on a silicon substrate, a contact hole for establishing electrical connection with the silicon substrate is opened in the insulating layer, tungsten or polysilicon is buried in the contact hole, and the insulating layer is sequentially formed on the insulating layer. Lower electrode,
A method of manufacturing a thin film capacitor, comprising laminating a dielectric film and an upper electrode, wherein the lower electrode is formed by laminating a first layer directly formed on an insulating film and a second layer made of platinum on a part thereof. The portion of the first layer on which the second layer is not stacked is Ta ₂ O ₅
And the portion of the first layer on which the second layer is laminated is O
/ Ta is an electrically conductive tantalum oxide having a oxygen content of 2.0 or less from the stoichiometric composition, and Ta ₂ O ₅ and the electrically conductive tantalum oxide in the first layer of the lower electrode are A method of manufacturing a thin film capacitor, characterized by being manufactured by ion implantation.