JP2776115B2 - Thin film capacitor and method of manufacturing the same - Google Patents

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 more particularly to the structure of the lower electrode.

[0002]

2. Description of the Related Art With the development of integrated circuit technology, electronic circuits have become increasingly smaller, and the miniaturization of capacitors, which are essential circuit elements for various electronic circuits, has become even more important. However, miniaturization of thin film capacitors is slower than miniaturization of active elements, which is a major factor preventing high integration. Therefore, SiO ₂ or Si ₃ N, which is conventionally used as a technique for reducing the size of a capacitor, is used.
BaTiO ₃ , SrTi having a dielectric constant larger than ₄
It has become important to develop capacitors using ferroelectrics made of O ₃ , PbZrO ₃ , PbTiO ₃ or solid solutions 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 direct sputtering (Japanese Patent Application No. 1-217).
No. 918), or a dielectric layer on a conductive layer composed of a first layer made of at least one kind of refractory metal such as tantalum and titanium on a silicon electrode and a second layer made of at least one kind of material of platinum and palladium. A structure in which a body film and an upper electrode are sequentially formed (Japanese Patent Application No. 1-248484) is used.

Further, for example, IBM Journal of Research and Development, 1969, Vol. 68, pp. 686-695 (IBM Jou
rnal of Research and deve
As described in US Pat. No. 6,086,849, Pt or Pd is deposited on an insulating substrate such as sapphire as a lower electrode, 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 using silicon as a lower electrode, a low dielectric constant layer is formed between the dielectric film and silicon, resulting in a high capacitance density. Can not get. Also,
Even if Pt or Pd is used as the lower electrode, LSI
In order to provide a low dielectric constant, silicon diffusion occurs at the bottom electrode, resulting in a low dielectric constant layer as if a dielectric film was deposited directly on the silicon.

For the above reasons, a thin-film capacitor using a ferroelectric, which is intended to be applied to an LSI, has a two-layer metal structure as a lower electrode as disclosed in Japanese Patent Application No. 1-248484. Attempts with the ones used have become widespread.

[0007]

In order to apply a capacitor having the above structure to an LSI, the lower electrode must be processed to have an appropriate area and 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 one layer and two layers.

However, when depositing a dielectric film on a step formed by etching the lower electrode, if the deposition cannot be performed with good step coverage, the lower electrode may be formed at a thin film thickness or at a place where no dielectric film is provided. And the upper electrode conducts or is broken at a low voltage, and cannot operate sufficiently as a capacitor. As described above, in order to manufacture a capacitor using a 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 depositing a dielectric film with better step coverage by eliminating a step between a lower electrode and a substrate, 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 buried in a contact hole, and a lower electrode, a dielectric film, and an upper electrode are sequentially laminated on an insulating layer.
BaTiO ₃ , SrTiO ₃ , PbTiO ₃ , PbZrO ₃
Consisting of one or a solid solution of these,
The lower electrode on which a dielectric is directly formed has a first layer formed on an insulating film and a second layer made of platinum laminated on a part of the first layer, and a second layer is laminated on the upper layer. The portion of the first layer that is not present is Ta ₂ O ₅ , and the portion of the first layer on which the second layer is stacked is insufficient oxygen having an O / Ta of 2.0 or less from the stoichiometric composition. Conductive tantalum oxide.

In a 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 buried 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 directly formed on the insulating film, and a part of the first layer formed from platinum. Are formed by laminating a second layer, and the portion of the first layer on which the second layer is not laminated is T
a ₂ O ₅ , and the first layer portion on which the second layer is laminated is a conductive tantalum oxide having an O / Ta of 2.0 or less and a stoichiometric oxygen deficiency. In addition, Ta ₂ O ₅ and the conductive tantalum oxide of the first layer of the lower electrode are produced by annealing at a substrate temperature of 500 ° C. or more and 1000 ° C. or less in an oxygen atmosphere.

An insulating layer is formed on a silicon substrate,
A contact hole for establishing conduction with a silicon substrate is opened in an insulating layer, tungsten or polysilicon is buried in the contact hole, and a lower electrode, a dielectric film and an upper electrode are sequentially laminated on the insulating layer. In a manufacturing method, a 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 of the first layer, and a second layer is formed on the upper layer. The portion of the first layer which is not formed is Ta ₂ O ₅ , and the portion of the first layer on which the second layer is laminated is oxygen / O / Ta of 2.0 or less due to lack of oxygen from the stoichiometric composition. Is a conductive tantalum oxide, and Ta ₂ O ₅ of the first layer of the lower electrode and the conductive tantalum oxide are produced by ion implantation of oxygen.

[0013]

The tantalum oxide is used for the first layer of the lower electrode,
The part where the second layer is not formed on the upper part is made of insulating Ta ₂
When the portion where O ₅ and the second layer are formed is made of conductive tantalum oxide, a step corresponding to the thickness of the second layer can be eliminated. This allows the dielectric film to be deposited with better step coverage. Furthermore, 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 the effect of making the lower electrode finer than that of the Ta ₂ O ₅ produced.

[0014]

Next, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG.
_{2. This} is an embodiment of the structure of a thin film capacitor using tungsten as a material for filling a contact hole and BaTiO ₃ as a dielectric film.

In the figure, SiO _{2 is formed} on a silicon substrate 1.
The insulating layer 2 made of is laminated. In the insulating layer 2, a contact hole 3 is formed in order to establish conduction with the silicon substrate 1.
Embedded by On the contact hole 3,
Conductive tantalum oxide 5, else T
a first layer consisting of a ₂ O ₅ 6, on the tantalum oxide 5 conductive layer and the second layer made of platinum (Pt) 7 is formed.
A dielectric film of BaTiO ₃ 8 is laminated on the lower electrode, and a film of Al 9 is laminated on the dielectric material to constitute a thin film capacitor.

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

Tungsten chloride was used as a source gas, and the film formation temperature was 500 ° C. Next, a 50 nm tantalum film was formed by DC magnetron sputtering. The film was formed using a metal tantalum target in an Ar gas atmosphere, 4 × 10 ⁻³ Torr, and a substrate temperature of 50 ° C. Platinum 7 was deposited in a thickness of 50 nm continuously 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 those for forming tantalum. Metallic platinum was used as a target when depositing platinum 7. Next, the platinum layer was processed so that the electrode area became 10 μm □. Platinum etching was performed by ECR dry etching. 10% in chlorine for etching
Using oxygen-added gas at a total pressure of 0.5 μm Torr
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 the tantalum directly touch the oxygen oxidation, insufficient Ta ₂ O ₅ 6 insulating, low degree of part of the platinum 7 on top is oxidized, the oxygen stoichiometry Conductive tantalum oxide 5
(O / Ta = 1.5). Subsequently, a BaTiO ₃ 8 film was deposited at 500 ° on the processed lower electrode. The deposition was performed by a high frequency magnetron sputtering method in an Ar—O ₂ mixed gas under the 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. 5000Å Al9 for the upper electrode
Was deposited by DC sputtering. The target was made of metal Al, in an Ar gas atmosphere, at 4 × 10 ⁻³ Torr, and at a substrate temperature of 50 ° C.

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

Where no film is attached, a short circuit occurs.
Even if it is thin, it works as a capacitor because the film thickness is not uniform, but causes a variation in breakdown voltage. 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.

O / Ta of the conductive tantalum oxide 5;
The relationship with the capacitance density of the capacitor was examined. 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,
1. The resistance of the tantalum oxide gradually increases as O / Ta increases, and changes from a conductive layer to an insulating layer.
If it is 0 or more, it becomes an insulator and the tantalum oxide functions as a low dielectric constant layer. From this, O /
Ta needs to be 2.0 or less.

FIG. 4 shows the results of examining the change in capacitance when the annealing temperature was changed during the fabrication of the lower electrode. The capacitors were fabricated on a 3 inch substrate. Substrate temperature is 50
At 0 ° C. or lower, a value much larger than the capacitance expected from the dielectric constant of the capacitance film is obtained. On the other hand, those manufactured at 1000 ° C. or higher have lower dielectric constants. If the temperature is 500 ° C. or less, the upper portion of the second layer, which does not have platinum, is not sufficiently oxidized, so that it does not become an insulator and insulation from other capacitors cannot be obtained.

As a result, apparently, the capacitor has a large electrode area, so that the capacitance is increased.
On the other hand, the reason why the capacity decreases at 1000 ° C. or more is that the tantalum under the platinum is sufficiently oxidized at 1000 ° C. or more and becomes an insulator, and acts as a low dielectric constant layer, so that the capacity decreases. From the above, the substrate temperature at the time of annealing needs to be 500 ° C. or more and 1000 ° C. or less.

The contact hole is made of polysilicon and (Ba, Sr) TiO ₃ , SrTi as a dielectric film.
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 first layer of the lower electrode was produced by ion implantation. As in the first embodiment, tantalum and platinum are deposited on the insulating film where the contact hole 3 is open.
Masking the area required as an electrode, the first tantalum layer is supplied with oxygen of 40 to 100 KeV and a dose of 10 ¹⁵ to 10 ^18
Implant ions at cm ^-2 . The ion-implanted substrate was subjected to a heat treatment at 400 ° C. for 2 hours in a nitrogen atmosphere, and platinum etching, a dielectric film, and an upper electrode were deposited as in Example 1. As a result, for the obtained capacitor,
The same result as the result shown in FIG. 2 was obtained.

[0028]

As described above, according to the present invention,
Since the step of the lower electrode is reduced, short circuit between the lower electrode and the upper electrode due to poor step coverage is prevented, and there is an effect that a thin film capacitor can be manufactured with good reproducibility.

[Brief description of the drawings]

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

FIGS. 2A and 2B show distributions of breakdown voltage. FIG. 2A shows a case where tantalum of a first layer is etched, and FIG. 2b shows a case where only platinum of a second layer is etched and annealed. is there.

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

FIG. 4 is a diagram showing a change in capacitance of a capacitor when a temperature at which annealing is performed 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)

(57) [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, tungsten or polysilicon is buried in the contact hole, and a lower electrode and a dielectric film are formed. And 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 ,
The lower electrode, which is made of one selected from PbZrO ₃ or a solid solution thereof, and on which a dielectric is directly formed, comprises a first layer formed on an insulating film and platinum laminated on a part of the first layer. The first layer portion, which is composed of the second layer and the second layer is not laminated on the
_The portion of the first layer which is ₂ O ₅ and the second layer is laminated on the upper portion is a conductive tantalum oxide having an O / Ta of 2.0 or less and a stoichiometric oxygen deficiency. A thin film capacitor characterized by the following. 2. An insulating layer is formed on a silicon substrate, a contact hole is formed in the insulating layer to establish conduction with the silicon substrate, and tungsten or polysilicon is buried in the contact hole and is sequentially formed on the insulating layer. Lower electrode,
A method of manufacturing a thin film capacitor comprising a dielectric film and an upper electrode laminated, 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 of the first layer. The portion of the first layer on which the second layer is not laminated is Ta ₂ O ₅
And the portion of the first layer on which the second layer is laminated is O
/ Ta is a conductive tantalum oxide having an oxygen deficiency of 2.0 or less from the stoichiometric composition. Ta ₂ O ₅ of the first layer of the lower electrode and the conductive tantalum oxide have a substrate temperature of A method for producing a thin film capacitor, characterized by being produced by annealing in an oxygen atmosphere at 500 ° C. or more and 1000 ° C. or less. 3. An insulating layer is formed on a silicon substrate, a contact hole is formed in the insulating layer to establish electrical connection with the silicon substrate, and 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 a dielectric film and an upper electrode laminated, 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 of the first layer. The portion of the first layer on which the second layer is not laminated is Ta ₂ O ₅
And the portion of the first layer on which the second layer is laminated is O
/ Ta is a conductive tantalum oxide having an oxygen deficiency of 2.0 or less from the stoichiometric composition, and Ta ₂ O ₅ of the first layer of the lower electrode and the conductive tantalum oxide are A method for producing a thin film capacitor, characterized by being produced by ion implantation.