JPH11330408A - Method for manufacturing thin film capacitor - Google Patents

Abstract

(57) [Problem] To provide a thin film capacitor having a small occupation area and a large capacity. SOLUTION: Ta ₂ O formed on a TiN lower electrode is formed.
₅ By heat treating the dielectric film in a nitrogen atmosphere, T
A method for producing a thin film capacitor, characterized in that a relative dielectric constant is improved by diffusing i into a Ta ₂ O ₅ dielectric film, and the dielectric film is crystallized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention has a small occupied area,
The present invention also relates to a method of manufacturing a thin film capacitor for a semiconductor device having a large capacity.

[0002]

2. Description of the Related Art With the high integration of semiconductor integrated circuits such as DRAMs, there is a demand for a capacitor having a required capacity and a smaller area. Various countermeasures have been taken to address this requirement, such as: The capacitance per unit area is inversely proportional to the thickness of the capacitance film. Therefore, reducing the thickness of the capacitor film is one of the methods. For example, 80 nm is used for a 16K DRAM.
A SiO ₂ capacitor film having a thickness of 10 nm has been used.
An O ₂ capacitance film is used. However, there is a problem that the required withstand voltage cannot be secured because the leakage current increases with the thinning.

As another method, there is a method of increasing the actual area per unit area by making the shape of the capacitor uneven. Trench structure, crown structure, etc.
This is a typical example, and the HSG (Hemi Spherical Grain) method for increasing the actual area by about 1.5 times by treating the surface of the capacitor film with fine irregularities of about several tens of nm is also based on the idea. .

Further, since the capacitance per unit area is proportional to the relative dielectric constant of the capacitance film, there is a method of applying a dielectric having a high relative dielectric constant to a dielectric material forming the capacitance film. The relative dielectric constant of conventionally used SiO ₂ is about 3.7, but a composite film of Si ₃ N ₄ and SiO ₂ having a higher relative dielectric constant (about 7) is applied to a DRAM of 4M or more. ing. For further integration, Ta ₂ O ₅ , which has a relative dielectric constant as high as 20 or more than Si ₃ N ₄ , or (Ba, Sr) TiO ₃ or (Pb, Zr) having a relative dielectric constant as large as several hundreds or more ) T
Application to a capacitance film such as iO ₃ is being studied.

For the integration of semiconductor circuits, the above-mentioned methods have been studied or used alone or in various combinations. It is also reported that the relative dielectric constant of a ceramic sintered body to which Ti is added for Ta ₂ O ₅ increases (Nature vol. 377 21 september 1995).
p.215). According to this paper, (Ta ₂ O ₅ ) _1-x (Ti
O ₂ ) _x system, when x = 0.08, the relative dielectric constant is 12
It is shown to improve to 6.

[0006]

SUMMARY OF THE INVENTION Ta ₂ O ₅ is used in a DRAM.
In the case of applying such a method, it is desirable to form a film by a CVD method which is excellent in step coverage and mass productivity. However, when the film is formed by the CVD method, the obtained Ta ₂ O
_{5 The} dielectric layer is amorphous and thermally unstable. In addition, there is a disadvantage that a leak current is large because carbon atoms and oxygen atoms in the raw material are contained as impurities.
On the other hand, a method has been proposed in which heat treatment or the like is performed in an oxygen atmosphere or the like after film formation to promote crystallization, remove impurities, and take measures to reduce leakage current. However, at this time, the lower electrode is oxidized, so that a new dielectric layer is formed, and there is a problem that the actual capacitance of the capacitor is reduced. In order to solve this problem, there is a demand for a capacitor structure and a method of manufacturing the same, in which a lower electrode is prevented from being oxidized and a capacity film having a higher relative dielectric constant is applied without lowering the capacity.

To address this problem, a capacitor film and a lower electrode have been used.
Si to prevent interdiffusion between poles _ThreeN_FourSuch as barrier
Method of forming a film, lower electrode is made of RuO_TwoConductive acids such as
Method to prevent the effect of oxidation with the oxide film, lower part
To reduce leak current without impairing electrode performance
Low temperature plasma processing is proposed.
You. Si_ThreeN_FourIs used for the barrier film,_Three
N_FourIs an insulating film, the equivalent film thickness increases,
It is inevitable that the capacity decreases. RuO_TwoIs etch
And the subsequent steps are difficult. Also low temperature plasm
When the processing is performed, Ta_TwoO_FiveDoes not crystallize
Each has its drawbacks.

Further, as described above, an increase in capacity can be expected by adding several percent of Ti to Ta ₂ O ₅ . As a method of adding Ti to Ta ₂ O ₅ of the capacitance film, there is a method of adding Japanese Patent Publication No. Hei 6-27328, but this method uses a plurality of raw materials each containing Ta and Ti when forming the capacitance film by CVD. This is a method, and a plurality of raw materials must be supplied to the CVD, which increases the manufacturing cost.

The present invention has been made in view of the above circumstances, and has as its object to provide a method of manufacturing a thin film capacitor having a small occupied area, a high relative dielectric constant, and a small leak current. .

[0010]

In order to achieve the above object, a method of manufacturing a thin film capacitor according to the present invention comprises, for example, forming a lower electrode layer made of TiN and a dielectric layer made of Ta ₂ O ₅ into an inert layer. By performing heat treatment in a gas atmosphere, for example, a nitrogen atmosphere, the leakage current in the dielectric layer is reduced, and the Ti in the lower electrode layer is not diffused without diffusing O in the dielectric layer and N in the lower electrode layer. Is diffused into the dielectric layer to improve the relative dielectric constant of the dielectric layer.

Thus, a capacitor having a large capacitance per unit area can be obtained. As an inert gas,
It is desirable to use inexpensive and readily available nitrogen.

[0012]

FIG. 1 shows a manufacturing process of a thin film capacitor according to the present invention. First, a film was formed on a silicon substrate by sputtering using Ti as an intermediate layer in order to improve the adhesion of the lower electrode. A TiN film was formed thereon by a CVD method as a lower electrode. This was performed by using TiCl ₄ and NH ₃ as raw materials and forming a film with a thickness of 100 nm at 600 ° C.
In addition, this film formation method may be a method such as a sputtering method, a vapor deposition method, or surface nitridation after forming a Ti film. Next, Ta ₂ O ₅ was formed as a dielectric layer on the lower electrode by MOCVD. FIG. 2 shows the film forming conditions.

The above film was subjected to rapid heat treatment under various conditions. FIG. 3 shows the heat treatment conditions. Examples in which the heat treatment atmosphere is nitrogen are examples of the present invention, and those in which the heat treatment atmosphere is oxygen and those without heat treatment are comparative examples. The heating rate was 5 ° C./sec, and the cooling rate was 10 ° C./sec. In order to evaluate the crystallinity of the obtained film, Ta was analyzed by X-ray diffraction.
The crystallinity of ₂ O ₅ was measured. As a result, 72
It turned out that heat treatment at 5 ° C. or more was necessary. FIG. 4 shows an example of the obtained X-ray diffraction pattern.

Next, in order to evaluate the electric characteristics of the obtained film, an Al film having a diameter of 1 mm was formed as an upper electrode on the film processed under the respective conditions by a vacuum evaporation method, and a capacitor was formed. Produced. The material of the upper electrode is not limited to Al but may be any material having conductivity. Also, the film formation method is not limited to the vacuum evaporation method, but may be a sputtering method, a C method.
A method such as a VD method may be used.

FIGS. 5 and 6 show the obtained SiO ₂ equivalent film thickness and leakage current value of the capacitor. SiO ₂ equivalent thickness is 1M
Hz, and the leak current was measured by measuring the current density when +1.5 V and -1.5 V were applied to the upper electrode.
FIG. 6 shows the larger value of the current density when +1.5 V and -1.5 V are applied. As shown in FIG. 5, the heat treatment in oxygen shown as a comparative example, SiO ₂ equivalent thickness is increased at any temperature. This is because the lower electrode reacts with oxygen to form TiO ₂ , and the generated TiO ₂ is a dielectric, which substantially increases the capacitance film thickness. The result of the secondary ion mass spectrometry shown in FIG. 7 supports this. The distribution in the depth direction of O and Ti when held at 725 ° C. for 30 seconds in oxygen is shown,
O is diffused into the lower electrode. Therefore, it was found that the heat treatment in oxygen increases the equivalent SiO ₂ film thickness, that is, decreases the capacity, which is not desirable.

On the other hand, an embodiment of the present invention is shown.
Distribution of O and Ti in the depth direction of sample heat-treated in nitrogen
Is also shown in FIG. 7 as a result of secondary ion mass spectrometry. This
According to this, O was diffused at 725 ° C in oxygen
On the other hand, despite being kept at 800 ° C for 30 seconds in nitrogen
No diffusion of O was observed._TwoNo layer was formed.
Also, as shown in FIG._TwoThe equivalent film thickness decreased. This
This is because Ti in the lower electrode is Ta._TwoO_FiveDiffused into the capacitive film
Therefore, it is considered that the relative dielectric constant increased.
This is also confirmed from FIG. Spread by XPS
When the amount was measured, 1.5 atm% of Ti was Ta._TwoO_Five
Diffusion into the capacitance film. This is (Ta _TwoO_Five)
_1-x(TiO_Two)_xX is equivalent to 0.099
You. In this case, as shown in FIG.
When held for 30 seconds, the leakage current also decreases.
This indicates that the effect of heat treatment is working effectively.
Was.

From the above, by heat treatment in nitrogen at 725 ° C. or higher, Ti diffuses into the Ta ₂ O ₅ capacitance film, and the capacitance film is crystallized, whereby a high-capacity and stable thin-film capacitor can be obtained. It turns out. In addition, it was found that it is preferable to hold at 800 ° C. in nitrogen for some time, for example, 30 to 60 seconds in order to reduce the leak current density.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the invention. For example, the inert gas is not limited to nitrogen, but may be argon, helium, a mixed gas thereof, or the like.

[0019]

As described above, according to the present invention, a capacitor film having a high relative dielectric constant and a small leak current can be obtained, and the capacitor can be miniaturized.

[Brief description of the drawings]

FIG. 1 is a view showing a manufacturing process of a thin film capacitor of the present invention.

FIG. 2 is a diagram showing film forming conditions of the present embodiment.

FIG. 3 is a diagram showing heat treatment conditions of the present embodiment.

FIG. 4 is an X-ray diffraction diagram of a Ta ₂ O ₅ film heat-treated at 650 to 800 ° C. for 60 seconds in oxygen.

FIG. 5 is a view showing a measurement result of a SiO ₂ equivalent film thickness of a capacitive element.

FIG. 6 is a diagram showing a measurement result of a leakage current density of a capacitor.

FIG. 7: 725 ° C. for 30 seconds in oxygen, 80% in nitrogen
It is a figure which shows the ion intensity profile measurement result of the depth direction by the secondary ion mass spectrometry of the sample hold | maintained at 0 degreeC for 30 second.

Claims (3)

[Claims] 1. A heat treatment of a lower electrode layer made of a conductive nitride containing Ti and a dielectric layer made of tantalum oxide formed on the lower electrode layer in an inert gas atmosphere to reduce Ti in the lower electrode layer. A method for manufacturing a thin film capacitor, characterized in that a dielectric layer is crystallized while being diffused into the dielectric layer. 2. The method according to claim 1, wherein the inert gas is nitrogen. 3. A semiconductor device comprising: a lower electrode layer made of a conductive nitride containing Ti; and a dielectric layer made of tantalum oxide formed thereon, wherein Ti in the lower electrode layer is diffused into the dielectric layer. A thin film capacitor, wherein the dielectric layer is crystallized.