JP2000200885A - Fabrication of capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an oxide dielectric thin film excellent in coverage and characteristics by facing a substrate and a deposition source at an appropriate angle when an oxide dielectric thin film is formed on an electrode of three- dimensional structure by physical film deposition and turning the substrate continuously during film deposition. SOLUTION: Ti0.7Al0.3N excellent in oxidation resistance is grown epitaxially as a buffer layer on an Si substrate by reactive deposition employing nitrogen plasma. Subsequently, Ru is deposited thereon as a metal layer 3 by sputtering and a metal oxide thin film layer 4 of RuO2 is formed by laser abrasion using R2O2, as a target. Furthermore, dry etching is performed and a three-dimensional lower electrode structure is formed by machining the RuO2/Ru before a capacitor 5 is formed by physical film deposition. In this regard, an angle α is set between the normal direction of the substrate 11 and the position of the deposition source 12, i.e., the target.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for forming a capacitor made of an oxide dielectric thin film of a gigabit-class DRAM having a three-dimensional electrode structure, and more particularly, to a method of manufacturing a capacitor using a physical film forming method. It is about.

[0002]

2. Description of the Related Art Large-scale integration of DRAMs has been realized by miniaturization of memory cells accompanying reduction in design dimensions. Even if the memory cell size is reduced, it is necessary to keep the capacitance value of the capacitor above a certain value for stable operation of the DRAM. Therefore, in the megabit generation, the capacitance electrode structure has been made three-dimensional. However, in the gigabit generation, it is difficult to obtain a required capacitor capacitance value by a combination of a conventional SiON-based capacitance insulating film and a three-dimensional structure. Therefore, a high-dielectric-constant thin film having a higher relative dielectric constant is required, and among them, (Ba, Sr)
TiO ₃ (BST) is considered promising. However,
Even if BST is used, it is difficult to apply a planar capacitor structure in the gigabit generation, and a three-dimensional electrode structure using a side surface such as a thick film stack is required. Oxide dielectric thin films such as BST are formed by various methods. Among them, Jpn. J. Appl. Phys
s. 33 , 5129 (1994) and Jpn. J. App
l. Phys. 35 , 5089 (1996), there is a method using a CVD method which also extends to the side surface of the electrode structure.
It is attracting attention as a technology for forming a two-dimensional capacitor.

[0003]

However, the capacitor forming technique using the conventional film forming method has the following problems.

First, conventional physical film forming methods such as a sputtering method, a vapor deposition method, and a laser ablation method cannot simply be applied to the formation of a capacitor on a three-dimensional electrode structure because they do not go around the side as described above. .

[0005] On the other hand, there are a thermal CVD method and a plasma CVD method as CVD methods which are supposed to reach the side surface of the three-dimensional structure, but have the following problems. In the thermal CVD method, 80
%, A high coverage (a film thickness ratio between the upper surface and the side surface) of about 700% is obtained.
The above heat treatment is required. This heat treatment is not preferable in terms of process because it not only complicates the process but also affects the lower electrode. In the case where BST is formed by a thermal CVD method, the composition greatly changes depending on the film forming temperature, or the in-plane distribution has large non-uniformity. Since the composition affects the relative dielectric constant and the leakage current characteristics, a change in the composition is not preferable. Further, there is a problem that the film thickness on the side surface is not uniform.

On the other hand, in the plasma CVD method, a BST film having good crystallinity can be obtained even at a relatively low temperature as compared with the thermal CVD method, the composition change is small even in a wider substrate temperature range, and the in-plane distribution is uniform. Further, the film thickness on the side surface is also uniform. However, the coverage when the film is formed by plasma CVD is 50.
%, Which is inferior to thermal CVD. Furthermore, thermal CVD
Despite the better crystallinity than the BST method, the BST t _eq (2
SiO ₂ equivalent thickness of the dielectric film required to obtain a 5 fF) is 0.4nm just under real thickness 30 nm, which is inferior to _t eq 0.2 nm stand BST films prepared by sputtering . Also, the leakage current is 10 at the actual film thickness of 30 nm.
⁻⁹ to 10 ⁻⁸ A / cm ² , and the leak current increases and the dielectric constant decreases as the film thickness is further reduced. Furthermore, the CVD method uses a dangerous gas, which is not good for environmental health.

The present invention solves the above-mentioned problems and comprises an oxide dielectric thin film having high coverage and good characteristics on a three-dimensional electrode by using a safe and simple physical film formation method. An object of the present invention is to provide a technology for forming a capacitor for a gigabit DRAM.

[0008]

The capacitor forming technique of the present invention solves the above-mentioned problems, and is a technique of forming a capacitor comprising an oxide dielectric thin film on an electrode having a three-dimensional structure by a physical film forming method. In the above, the substrate and the evaporation source are opposed at an appropriate angle, and the substrate is continuously rotated during film formation. Further, the appropriate angle at which the substrate and the evaporation source face each other depends on the position of the evaporation source with respect to the normal direction of the substrate. Is 30 to 80
°.

Further, the capacitor forming technique of the present invention
In a technology for forming a capacitor composed of an oxide dielectric thin film on a three-dimensionally structured electrode by a physical film forming method, the angle between the substrate and the evaporation source facing the film is continuously changed during film formation, and the substrate is continuously formed. The angle between the substrate and the vapor deposition source, which is continuously changed during film formation, is characterized in that the position of the vapor deposition source with respect to the normal direction of the substrate is within −90 ° to 90 °.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments.

(Embodiment 1) FIG. 1 is a view showing a sectional structure of a capacitor used in Embodiment 1 of the present invention. Substrate 1,
It comprises a lower electrode structure composed of a buffer layer 2, a metal layer 3, and a metal oxide film layer 4, a capacitor 5 composed of an oxide dielectric, and an upper metal electrode 6.

Hereinafter, a method of manufacturing the present structure will be described. An Si substrate is used as the substrate 1, and Ti _0.7 Al _0.3 N having excellent oxidation resistance is epitaxially grown on the Si substrate as a buffer layer 2 by reactive deposition using nitrogen plasma. At this time, the substrate temperature is 600 ° C. Next, Ru is formed thereon as the metal layer 3 by sputtering. Subsequently, a RuO ₂ film of the metal oxide film layer 4 is further formed thereon by a laser ablation (PLD) method using RuO ₂ as a target. At this time, the substrate is irradiated with oxygen radicals by an RF radical beam gun during film formation. Thereafter, RuO ₂ / Ru is processed as shown in FIG. 1 by dry etching using O ₂ + CF ₄ to form a three-dimensional lower electrode structure.

Subsequently, the capacitor 5 is formed by using a physical film forming method. Here, as the physical film forming method, PL
D is used. PLD is an effective method for forming a multi-component oxide film because the target composition and the thin film composition are almost the same over a wide substrate temperature range if the film formation conditions are adjusted.
SBT is used as an oxide dielectric for forming the capacitor 5.
Is used. The composition of the SBT is (Ba _0.3 Sr _0.7 ) T
iO ₃ is used, and a single target of SBT having the composition is used as an evaporation source. FIG. 2 is a diagram schematically showing a positional relationship between the substrate 11 and the evaporation source 12. As shown in FIG. The angle between the normal direction of the substrate 11 and the position of the target as the evaporation source 12 is defined as α. In this case, the substrate 11 is made of RuO ₂ from the Si substrate in FIG.
Up to the layer, source 12 refers to a single target of SBT. Here, the position of the target is fixed, and the angle of the substrate 11 is changed. When a multi-component oxide thin film is formed by PLD, the composition ratio of the thin film depends on the laser energy. Using KrF excimer laser as laser, α
The laser energy is set so that the composition ratio of cations in the thin film is within ± 2% when = 0 °. Substrate temperature 500 ℃
Is fixed, and the substrate is continuously rotated for 20 n
FIG. 3 shows the relationship between the coverage of BST and α when the m film was formed.
Shown in Note that the substrate is irradiated with oxygen radicals during film formation and cooling. As can be seen, α is 70 ° C.
, Changes linearly until reaching approximately 100% coverage at 60 ° C. When α is 45 to 50 °, the same coverage as that of thermal CVD is obtained, and when α is 30 °, the same coverage as that of plasma CVD is obtained. When α is 50 ° or more, a coverage that cannot be obtained by thermal CVD is obtained. The value of this coverage is almost independent of the height of the lower electrode structure of RuO ₂ / Ru and is constant. The thickness of the side surface of the BST is substantially uniform, and both the upper surface and the side surface are flat independently of α. Furthermore, the composition ratio of both the upper surface region and the side region hardly changes from the composition ratio of the target.

[0014] Here, _{t eq} flat RuO ₂ of the formed film thickness 20nm on the electrode BST was 0.15nm about almost constant until α is 0 to 80 °. However, it was higher at 80 ° and above. Also, the leak current density J _L
Up to 80 °, 10 ^-10 A / cm ² units (＠ 1V)
And a good value. On the other hand, _{t eq} of the side of the BST film thickness of the side and the electrode on the three-dimensional structure has a 20nm is
It decreased as α increased, and became almost saturated at 50 ° or more. α is 30 ° or more and 0.25 nm or less, and α is 5
It was about 0.18 nm at 0 ° or more. Also, J _L is t
_It shows the same tendency as _eq, and 10 ⁻⁹ A / c at 30 ° or more.
m ² units (＠ 1V) or less, 10 ⁻¹⁰ A / c at 50 ° or more
^Two m and (@ 1V) showed good values. Further, the relative dielectric constant ε has a value exceeding 400 at the maximum. Also by reducing the real thickness up to 10nm, _{J L} and ε is hardly deteriorated. These results indicate that the crystallinity of the dielectric thin film is good.

[0015] The above _coverage, t eq, from the results of _{J L,} alpha is preferably 30 to 80 °, more preferably alpha
Is 50 to 80 °, and the coverage is higher than CVD,
t _{e q, J L} is obtained, 4Gb DRAM
And the required capacitance value can be realized. Here,
Although BST was used as the oxide dielectric, other materials may be used, and the structure and material of RuO ₂ or less are not limited to the above-described embodiment. In addition, there is no problem with a physical film forming method other than the laser ablation method, such as a sputtering method or a vapor deposition method. (Embodiment 2) Details of a capacitor forming technique in Embodiment 2 of the present invention will be described below with reference to FIGS.

The cross-sectional structure of the capacitor to be manufactured is shown in FIG.
Is the same as That is, the lower electrode structure includes the substrate 1, the buffer layer 2, the metal layer 3, and the metal oxide film layer 4, the capacitor 5 formed of an oxide dielectric, and the upper metal electrode 6. The materials used are the same as those in FIG. The manufacturing method of the above structure is the same as that of the first embodiment up to the formation of the three-dimensional lower electrode structure. The formation of the capacitor 5 on the three-dimensional lower electrode using the physical film forming method is as follows.

PLD is used as a physical film forming method. P
LD is an effective method for forming a multi-component oxide film because the target composition and the thin film composition are almost the same over a wide substrate temperature range if the film forming conditions are adjusted. Capacitor 5
SBT is used as an oxide dielectric for forming the semiconductor. SB
The composition of T is (Ba _0.3 Sr _0.7 ) TiO _3, and a single target of SBT having the composition is used as a vapor deposition source.
As shown in FIG. 2, the angle between the normal direction of the substrate 11 and the position of the target which is the evaporation source 12 is defined as α. In this case, the substrate 11 indicates from the Si substrate to the RuO ₂ layer in FIG. 1, and the deposition source 12 indicates a single target of SBT. Here, the position of the target is fixed, and the angle of the substrate 11 is changed. When a multi-component oxide thin film is formed by PLD, the composition ratio of the thin film depends on the laser energy.
Using KrF excimer laser as the laser, α = 0
The laser energy is set so that the composition ratio of the cations in the thin film is within ± 2% at the time of °. Before forming the BST film on the three-dimensional structure, the substrate temperature is set to 500 ° C. on the flat electrode, and α is continuously changed in the range of −90 ° to 90 °,
The substrate 11 was also continuously rotated to form a 20 nm BST film. During the film formation and during the cooling, the substrate is irradiated with oxygen plasma. As a result, t _eq is 0.20 nm, J _L
Showed a good value of 10 ⁻¹⁰ A / cm ² units (＠ 1 V). Then, during film formation on the three-dimensional electrode, α is also -90 °.
The BST, which is a capacitor, was formed by continuously changing the substrate in the range of ９０90 ° and continuously rotating the substrate. As a result, it was found that the coverage of BST depends on the speed of changing α. That is, the coverage can be controlled by adjusting the speed at which α is changed. Therefore, the speed of changing α was adjusted, and BST was formed so that the coverage became about 100%. _{T eq} of BST side at that time is good and 0.22 nm, _{J L} also ^{10 -10} A as capacitor
/ Cm ² (＠ 1 V). These values are
It shows better results than the case of forming with. Note that even if the coverage is 80%, which is almost the same as that of CVD, t
_{eq, J L} is better than the case of CVD. As for ε, a value exceeding 400 at the maximum was obtained as in the case of Example 1. Even when the actual film thickness is reduced to 10 nm, almost no deterioration in characteristics is observed. That is, a BST film having uniformity and good crystallinity is obtained by continuously changing α. As described above, continuously changing α during film formation and continuously rotating the substrate are effective in forming a capacitor on the three-dimensional electrode structure. It is possible to obtain a capacitance value required for a gigabit DRAM. Further, not only the speed at which α is changed, but also the angle range at which α is changed is from −90 ° to 9 °.
The coverage can also be controlled by changing the angle within 0 °, and the same effect can be obtained.

Here, BS is used as an oxide dielectric.
T was used, but other materials may be used.
The structures and materials of ₂ or less are not limited to the above-described embodiment. In addition, there is no problem with a physical film forming method other than the laser ablation method, such as a sputtering method or a vapor deposition method.

[0019]

As described above, according to the present invention, in a technology for forming a capacitor comprising an oxide dielectric thin film on an electrode having a three-dimensional structure by a physical film forming method, an appropriate substrate and an evaporation source are used. An appropriate angle at which the substrate and the deposition source face each other is such that the position of the deposition source with respect to the normal direction of the substrate is 30 degrees.
When the angle is 80 °, it is possible to provide a capacitor forming technique which has high coverage and can be applied to a gigabit-class DRAM even with a safe and simple physical film forming method.

According to the present invention, in a technology for forming a capacitor comprising an oxide dielectric thin film on an electrode having a three-dimensional structure by a physical film forming method, the angle between a substrate and a deposition source during film formation may be changed. Continuously changing, and also rotating the substrate continuously, furthermore, the angle between the substrate and the vapor deposition source that is continuously changed during the film formation is such that the position of the vapor deposition source with respect to the normal direction of the substrate is -90 ° or more. By being within 90 °,
It is possible to provide a capacitor formation technique having a high coverage and a property applicable to a gigabit-class DRAM even by a safe and simple physical film formation method.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross-sectional structure of a capacitor used in Example 1 of the present invention.

FIG. 2 is a diagram schematically showing a positional relationship between a substrate and an evaporation source in Embodiment 1 of the present invention.

FIG. 3 is a diagram illustrating a relationship between an angle α formed by a normal direction of a substrate, a position of an evaporation source, and coverage in Example 1 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Buffer layer 3 Metal layer 4 Metal oxide film layer 5 Capacitor 6 Upper metal electrode 11 Substrate 12 Evaporation source

Claims (4)

[Claims] In a method of manufacturing a capacitor comprising an oxide dielectric thin film on an electrode having a three-dimensional structure by a physical film forming method, a substrate and an evaporation source are opposed at an appropriate angle, and A method for manufacturing a capacitor, comprising continuously rotating the capacitor. 2. An appropriate angle at which the substrate and the evaporation source face each other is as follows:
2. The method according to claim 1, wherein the position of the evaporation source with respect to the normal direction of the substrate is 30 to 80 [deg.]. 3. A method of manufacturing a capacitor comprising an oxide dielectric thin film on an electrode having a three-dimensional structure by a physical film forming method, wherein a facing angle between a substrate and a deposition source is continuously changed during film formation. A method for manufacturing a capacitor, wherein the substrate is also continuously rotated. 4. The method according to claim 1, wherein the angle between the substrate and the evaporation source which is continuously changed during the film formation is within a range of -90 ° to 90 ° with respect to the normal direction of the substrate. 4. The method for producing a capacitor according to 3.