JP3277097B2 - Manufacturing method of ferroelectric thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ferroelectric memory device,
The present invention relates to a ferroelectric thin film used for a pyroelectric sensor element, a piezoelectric element, and the like, a method for manufacturing the same, and a capacitor structure element using the ferroelectric thin film.

[0002]

2. Description of the Related Art Ferroelectric materials have many functions such as spontaneous polarization, high dielectric constant, electro-optic effect, piezoelectric effect and pyroelectric effect, and are widely used in capacitors, oscillators, optical modulators and infrared sensors. It is applied to the development of various devices. Conventionally, these applications are based on ferroelectric materials such as single crystals such as glycine sulfate (TGS), LiNbO ₃ , LiTaO _{3 and the} like.
aTiO ₃ , PbTiO ₃ , Pb (Zr _1-x Ti _x ) O ₃
(PZT), cutting sintered ceramics such as PLZT,
It was processed to a thickness of about 50 μm by polishing. However, large single crystals are difficult and expensive to make,
In addition, processing is difficult due to cleavage. In addition, ceramics are generally brittle, and may be cracked during the processing process.
Since it is difficult to process to a thickness of 0 μm or less,
It takes a lot of time and increases production costs.

On the other hand, with the development of thin film forming technology, application fields of these ferroelectric thin films are currently expanding. As one of them, by applying the high dielectric constant characteristics to capacitors of various semiconductor devices such as DRAMs, high integration of devices and improvement of reliability by reducing the capacitor area are being attempted. In particular, in recent years, ferroelectric nonvolatile memories (FRAMs) that operate at high density and at high speed have been actively developed in combination with semiconductor memory elements such as DRAMs. The ferroelectric nonvolatile memory uses a ferroelectric characteristic (hysteresis effect) of a ferroelectric to eliminate the need for a backup power supply. To develop such a device, the residual spontaneous polarization (Pr) is large and the coercive electric field (E
It is necessary to use a material having characteristics such as low c), low leakage current, and high resistance to repetition of polarization reversal. Furthermore, in order to reduce the operating voltage and adapt to the semiconductor microfabrication process, it is desired to realize the above characteristics with a thin film having a thickness of 200 nm or less.

At present, for the purpose of application to FRAM and the like,
Attempts have been made to reduce the thickness of oxide ferroelectrics having a perovskite structure such as PbTiO ₃ , PZT, and PLZT by a thin film forming method such as a sputtering method, a vapor deposition method, a sol-gel method, and an MOCVD method.

Of the above ferroelectric materials, Pb (Zr
_1-X Ti _x ) O ₃ (PZT) has been most intensively studied recently, and a thin film having good ferroelectric properties has been obtained by a sputtering method or a sol-gel method. Spontaneous polarization Pr is 10 μC / cm ² to 26 μC
Some have a large value of / cm ² . However, despite the fact that the ferroelectric properties of PZT largely depend on the composition x, it contains Pb having a high vapor pressure, so that the film composition tends to change during film formation, heat treatment, etc. As a result, generation of a low dielectric constant layer due to the reaction between the underlying electrodes Pt and Pb, and the like, there is a problem that a reduction in film thickness (thinning) results in deterioration of leakage current and polarization inversion resistance. For this reason, the development of another material having excellent ferroelectric properties and polarization reversal resistance has been desired. In addition, in consideration of application to an integrated device, the thin film must be dense enough to cope with microfabrication.

As a material having good ferroelectric properties and excellent polarization reversal resistance, a Bi-based layered oxide material represented by SrBi ₂ Ta ₂ O ₉ has attracted attention. This thin film of SrBi ₂ Ta ₂ O ₉ is manufactured by the MOD method. The MOD method is a film forming method including the following steps. That is, as in the case of the sol-gel method, the organometallic raw materials are mixed so as to have a predetermined film composition, and a raw material solution for coating whose concentration and viscosity are adjusted is prepared. This is spin-coated on a substrate, dried, and then temporarily sintered to remove organic components. This is repeated until a predetermined film thickness is reached, and finally crystallization by main sintering is performed. Therefore,
The control of the film thickness is limited to the thickness of one coating film. (1
The most important problem of SrBi ₂ Ta ₂ O ₉ as a ferroelectric material is that the sintering temperature is extremely high, from 750 ° C. to 800 ° C., and more than one hour. That is, a long sintering time is required. It is thus 650 ° C. in the manufacturing process
When processes such as film formation and heat treatment are performed at the above temperatures for a long time, the interdiffusion reaction between the underlying platinum electrode and the ferroelectric, and furthermore, the silicon or silicon oxide under the underlying electrode and the electrode or the ferroelectric This causes a change in the film composition due to the volatilization of the constituent elements from the ferroelectric thin film, which makes application to an actual device fabrication process difficult. Also,
At present, only a film having a surface morphology of about 0.3 μm and a large particle diameter is obtained, so that it cannot be applied to sub-micron fine processing required for development of a highly integrated device. Further, since the film is formed by coating, the step coverage is poor and there is a problem such as disconnection of the wiring. Therefore, SrB
Although i ₂ Ta ₂ O ₉ is excellent in ferroelectric properties and polarization inversion resistance, it still has a serious problem as a ferroelectric thin film material.

At present, in order to realize high integration of a ferroelectric nonvolatile memory, the use of polycrystalline silicon for a wiring between a MOS transistor and a ferroelectric capacitor has been studied. _In the case of producing a ferroelectric thin film by a long-time high-temperature process such as ₂ Ta ₂ O ₉ , there is a problem that characteristic deterioration occurs due to mutual diffusion between polycrystalline silicon for wiring and the ferroelectric thin film. . In order to solve such a problem, a structure in which various diffusion barrier layers are inserted has been studied. However, the film formation temperature of the ferroelectric thin film is still within an allowable range up to 650 ° C. If the time is short, about 700 ° C. is considered to be the limit. However, at present, the aforementioned SrBi
_{In the case of 2} Ta ₂ O ₉ and other ferroelectric thin films, generally, the higher the film formation temperature, the better the crystallinity and the ferroelectric characteristics.
If the film forming temperature is lowered, the crystallinity and the ferroelectric properties deteriorate, and it is difficult to achieve both the improvement of the ferroelectric properties of the ferroelectric thin film and the low-temperature film forming.

On the other hand, Bi ₄ Ti ₃ O ₁₂ having a layered perovskite structure is an oxide ferroelectric containing no Pb that adversely affects leakage current and polarization reversal resistance. This Bi ₄ Ti ₃ O ₁₂ has a layered perovskite structure with strong anisotropy (orthogonal system / lattice constant: a = 5.411Å, b = 5.
448 °, c = 32.83 °)
The ferroelectricity of the single crystal is based on the residual spontaneous polarization Pr =
It has the largest spontaneous polarization among the above-mentioned bismuth-based oxide ferroelectrics at 50 μC / cm ² and coercive electric field Ec = 50 kV / cm, and shows excellent characteristics. Therefore, in order to apply the large spontaneous polarization of Bi ₄ Ti ₃ O _{12 to} a ferroelectric nonvolatile memory or the like, it is desirable to have a large number of a-axis components of the crystal in a direction perpendicular to the substrate.

Although thinning of Bi ₄ Ti ₃ O ₁₂ has been attempted by the MOCVD method or the sol-gel method, most of them have a c-axis whose spontaneous polarization is smaller than that of the a-axis oriented film. It is an alignment film. Further, in the conventional sol-gel method, a heat treatment at 650 ° C. or more is required to obtain good ferroelectric properties, and the film surface morphology is 0.5 μm
It is difficult to apply to a highly integrated device requiring fine processing because it is composed of crystal grains of the order of magnitude. On the other hand, MOC
By the VD method, a c-axis oriented Bi ₄ Ti ₃ O ₁₂ thin film is formed on a Pt / SiO ₂ / Si substrate or a Pt substrate at a substrate temperature of 600 ° C. or higher. It is not applicable to the structure. That is, like a Pt / Ti / SiO ₂ / Si substrate, an adhesive layer such as a Ti film for securing the adhesive strength between the Pt electrode layer and the underlying SiO ₂ is required. However, when a Bi ₄ Ti ₃ O ₁₂ thin film is formed by MOCVD on a Pt electrode substrate provided with such an adhesive layer, the film surface morphology is composed of coarse crystal grains and a pyrochlore phase (Bi ₂ Ti ₂ O ₇ ) is reported to be more likely to occur (Jpn. J. Appl. Phys., 32, 19).
93, p. 4086; Ceramic So
c. Japan, 102, 1994 pp. 512). If the film surface morphology is composed of coarse crystal grains, it cannot be applied to a highly integrated device requiring fine processing, and if the film thickness is small, it causes a pinhole and causes a leakage current. Therefore, it is difficult to realize a ferroelectric thin film having good ferroelectric properties with a thin film thickness of 200 nm or less in such a conventional technique.

[0010]

As described above, in the above prior art, in order to apply a ferroelectric thin film to a highly integrated device, the fineness of the surface of the thin film required for fine processing and low leakage current is reduced. There is a problem that one that sufficiently satisfies various conditions such as flatness, large residual spontaneous polarization, and low-temperature film forming process has not been obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a ferroelectric thin film having a dense and flat surface, excellent leakage current characteristics, and exhibiting a sufficiently large residual spontaneous polarization. It is an object of the present invention to provide a ferroelectric thin film substrate capable of producing a body thin film by a low-temperature process, a method of manufacturing the same, and a capacitor structure element using the ferroelectric thin film.

[0012]

In order to solve the above-mentioned problems, in the present invention, the ferroelectric thin film is constituted by a film in which a ferroelectric and a paraelectric are mixed.

Further, according to the present invention, in the above-mentioned ferroelectric thin film, the ferroelectric has a perovskite structure or a layered perovskite structure.

Further, in the present invention, in the above ferroelectric thin film, the constituent elements of the paraelectric are the same as some or all of the constituent elements of the ferroelectric.

Further, in the present invention, in the above-mentioned ferroelectric thin film, the composition of the material constituting the ferroelectric thin film is different from the stoichiometric composition of the ferroelectric material.

[0016] In the present invention, the strength in the ferroelectric thin film and the dielectric and paraelectric become mixed, the ferroelectric is made of bismuth titanate Bi ₄ Ti ₃ 0 _12, wherein the paraelectric pyrochlore structure this made from mixed bismuth titanate of bismuth titanate Bi ₂ Ti ₂ O ₇ and <br/> amorphous structure
And features.

In the present invention, a ferroelectric thin film including a ferroelectric substance and a paraelectric substance is formed on a substrate at a substrate temperature of 400 ° C. to 500 ° C. by MOCVD. It is a method of manufacturing a dielectric thin film.

Further, the production of the ferroelectric thin film according to the present invention.
The method uses the MOCVD method using the first raw material,
The temperature was set from 500 ° C to 650 ° C,
A ferroelectric thin film with a site structure or layered perovskite structure
After forming, the same material as the first material is formed on the ferroelectric thin film.
Substrate temperature from 400 ° C by MOCVD method using
Perovskite structure or layered perovska at 500 ° C
And ferroelectric with pyrochlore or
A ferroelectric thin film composed of a mixture of
It is characterized by including the step of forming .

Further, a lower electrode made of a conductive material is arranged on a substrate, the ferroelectric thin film is arranged on the lower electrode, and an upper electrode made of a conductive material is arranged on the ferroelectric thin film. Thus, a capacitor structure element is formed.

[0020]

According to the ferroelectric thin film of the present invention, by mixing a ferroelectric and a paraelectric, sufficient ferroelectricity is maintained, and the ferroelectric thin film has excellent smoothness and denseness. A body thin film can be obtained.

That is, in a ferroelectric thin film made of only a normal ferroelectric substance, a gap is generated between the crystal grains during the formation of the ferroelectric substance in the growth of the ferroelectric substance due to the coarsening of the crystal grains. This deteriorates the smoothness and denseness of the thin film. In an element using such a ferroelectric thin film, pinholes occur in the ferroelectric thin film, which causes an increase in leak current. Therefore, by interposing a paraelectric substance in the ferroelectric substance so as to fill the gap between the crystal grains of the ferroelectric substance with a dense normal conductor,
The smoothness and denseness of the thin film can be improved without deteriorating the ferroelectricity of the ferroelectric thin film, and an element having excellent leakage current characteristics can be realized.

As described above, according to the ferroelectric thin film of the present invention, since the thin film is excellent in smoothness and denseness, it can be finely processed and can be applied to various highly integrated devices. Furthermore, since the thin film is excellent in smoothness and denseness, if a device element is formed using the ferroelectric thin film of the present invention, an element having excellent leakage current characteristics can be realized.

The film thickness of the ferroelectric thin film of the present invention is set to a value lower than that of the conventional one by 40.degree.
This can be realized by a manufacturing method in which the temperature is set from 0 ° C to 500 ° C.

That is, in film formation by the MOCVD method, a ferroelectric thin film in which a ferroelectric substance and a paraelectric substance are mixed can be formed by setting the substrate temperature lower than the conventional one. Since the substrate temperature is low, the paraelectric phase does not form coarse crystal grains. The paraelectric phase may include not only fine crystal grains but also an amorphous structure.

According to such a method of manufacturing a ferroelectric thin film of the present invention, a ferroelectric thin film can be formed by a low-temperature process of 500 ° C. or less. The device can be applied to a highly integrated device without damaging the element, and the degree of freedom in design can be significantly improved.

In the film formation using the MOCVD method, the substrate temperature is raised from 500 ° C. to 650 using the MOCVD method.
After forming a ferroelectric thin film on a substrate at a temperature of 400 ° C., a ferroelectric material comprising a mixture of a ferroelectric and a paraelectric is formed on the ferroelectric thin film by MOCVD using a substrate temperature of 400 ° C. to 500 ° C. The above-described ferroelectric thin film of the present invention can also be obtained by a manufacturing method of forming a thin film.

According to the manufacturing method of the present invention, the ferroelectric thin film can have higher ferroelectricity than the above-described manufacturing method. It is considered that since a part of the body thin film is formed, the growth of the ferroelectric can be promoted, and the ferroelectricity of the ferroelectric thin film can be further enhanced.

Although the substrate temperature of this manufacturing method is slightly higher than that described above, it can be applied to a sufficiently highly integrated device. Acceptable and effective for those requiring higher ferroelectricity.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing the structure of a capacitor element according to a first embodiment of the present invention. As shown in FIG. 1, this capacitor structure element is made of silicon (Si).
On a substrate 1, a silicon oxide (SiO ₂ ) layer 2, an adhesive layer 3, a lower electrode 4, a ferroelectric thin film 5 in which a ferroelectric and a paraelectric are mixed, and an upper electrode 6 are sequentially formed, respectively. It is.

In the first embodiment, a silicon single crystal wafer was used as the silicon substrate 1, and a silicon oxide thin film obtained by thermally oxidizing the surface of the silicon single crystal wafer was used as the SiO ₂ layer 2. A tantalum (Ta) thin film is used as the adhesive layer 3, and platinum (Pt) is used as the lower electrode 4.
As the thin film, a bismuth titanate thin film was used as the ferroelectric thin film 5 in which a ferroelectric substance and a paraelectric substance were mixed, and a platinum (Pt) thin film was used as the upper electrode 6.

Next, a method of manufacturing the capacitor element of the first embodiment shown in FIG. 1 will be described. First, Pt / T
The fabrication of the a / SiO ₂ / Si substrate will be described. The surface of the silicon single crystal wafer (100), which is the silicon substrate 1, is thermally oxidized to form a 200 nm-thick SiO 2 film.
_Two layers 2 are formed. Then, a Ta thin film serving as the adhesive layer 3 is formed to have a thickness of 30 nm, and Pt (1
11) A thin film having a thickness of 200 nm was formed by a sputtering method.

Here, these materials and film thickness are not limited to the present embodiment, and a polycrystalline silicon substrate or a GaAs substrate may be used instead of the silicon single crystal substrate. In addition, the adhesive layer is for preventing peeling of the film due to a difference in the coefficient of thermal expansion between the substrate and the lower electrode layer during film formation, and the film thickness only needs to be large enough to prevent peeling of the film. As for the material, titanium (Ti) or the like can be used other than Ta, but in the case of this embodiment, it is preferable to use Ta because an alloy of Ti and Pt is formed. Further, the SiO ₂ layer used for the insulating layer may not be formed by thermal oxidation, but may be formed by a sputtering method, a vacuum deposition method,
An SiO ₂ film, a silicon nitride film, or the like formed by an OCVD method or the like can be used, and any material and thickness may be used as long as they have sufficient insulating properties.

The lower electrode may have a thickness sufficient to function as an electrode layer. The material is not limited to Pt, but may be a conductive material used for ordinary electrode materials. It can be appropriately selected in relation to other thin films. Further, the film formation method is not limited to the silicon thermal oxidation or the sputtering method so far, but may be performed by using a normal thin film forming technique such as a vacuum evaporation method. Further, the substrate structure is not limited to the above.

Next, the thus prepared Pt / T
On a / SiO ₂ / Si substrate, a bismuth titanate thin film, which is a ferroelectric thin film in which a ferroelectric
It was formed by the OCVD method. Table 1 shows the supply conditions of the raw materials in the film formation by the MOCVD method at this time.

[0035]

[Table 1]

As shown in Table 1, the bismuth titanate thin film was formed by using triortho tolyl bilyl bismuth (Bi (o-OC ₇ H ₇ ) ₃ ) as a bismuth raw material and titanium isopropoxide (Ti ( i-OC
_{Using 3} H ₇ ) ₄ ), these raw materials were heated and vaporized to the raw material temperatures shown in Table 1, respectively (bismuth raw material 16).
(0 ° C., titanium raw material 50 ° C.), an argon (Ar) gas as a carrier gas, and an oxygen (O ₂ ) gas as a reaction gas were supplied into the film formation chamber. Here, the flow rate at the time of supplying the Ar gas was set to 200 sccm for the Bi raw material and 50 sccm for the Ti raw material, and the flow rate at the time of supplying the O ₂ gas was 1000 s.
ccm. Note that, in these film forming steps, the degree of vacuum in the film forming chamber is set to 5 Torr because a gas phase reaction easily occurs when the pressure is 10 Torr or more.

Under these conditions, the film formation temperature, that is, the substrate temperature is set to 420 ° C., and the film formation is performed for about 1 hour.
A bismuth titanate thin film having the following film thickness was formed.

Observation of the crystallinity of the bismuth titanate thin film thus formed by X-ray diffraction and SEM
The surface morphology was observed by (scanning electron microscope). FIG. 2 shows the observation result by X-ray diffraction at this time.
FIG. 3 shows the results of observation by SEM.

In FIG. 2, the vertical axis represents the X-ray diffraction intensity (a.
u.), and the horizontal axis is the diffraction angle 2θ (deg).
(00n) (n is an integer) is the c of Bi ₄ Ti ₃ O ₁₂
(117) indicates a Bi ₄ T
It is a diffraction peak due to random orientation including the a-axis component of i ₃ O ₁₂ , and (nnn) is Bi ₂ Ti ₂ of (111) orientation.
Represents a diffraction peak due to O ₇ (pyrochlore phase), and represents 2θ
= The diffraction peak around 40 degrees (deg) is the Pt of the lower electrode.
It is due to. Note that Bi ₄ Ti ₃ O ₁₂ is a ferroelectric material having a layered perovskite structure, and Bi ₄ Ti ₃ O ₁₂ has a pyrochlore phase of Bi.
₂ Ti ₂ O ₇ is a paraelectric.

According to the X-ray diffraction pattern shown in FIG.
Among the bismuth titanate thin films prepared according to the present embodiment, there are a ferroelectric Bi ₄ Ti ₃ O ₁₂ having a c-axis orientation and a random orientation, ie, a random orientation, and a paraelectric (pyrochlore) having a (111) orientation. It can be seen that both Bi ₂ Ti ₂ O ₇ are present.

As a result of the composition analysis by the composition analyzer EPMA, the Bi / Ti composition ratio was changed to the ferroelectric Bi ₄ Ti ₃ O.
_The stoichiometric composition of the stoichiometric composition should be 1.3 for the stoichiometric composition of ₁₂ and 1.0 for the stoichiometric composition of the paraelectric (pyrochlore) Bi ₂ Ti ₂ O _7. The Bi / Ti composition ratio of the thin film was 0.8, which was shifted from the stoichiometric composition of the ferroelectric Bi ₄ Ti ₃ O ₁₂ . Thus, Bi
The reason why the / Ti ratio is smaller than 1.3 of the ferroelectric Bi ₄ Ti ₃ O ₁₂ and 1.0 of the paraelectric (pyrochlore) Bi ₂ Ti ₂ O ₇ is that the ferroelectric Bi It is conceivable that not only the paraelectric substance Bi ₂ Ti ₂ O ₇ but also amorphous bismuth titanate exhibiting paraelectric property is mixed in addition to ₄ Ti ₃ O ₁₂ .

FIG. 3 shows that the surface of this bismuth titanate thin film is a dense thin film having a particle size of about 0.1 μm, which is extremely excellent in smoothness. This is clear from comparison with a comparative example described later.

Next, as described above, Pt / Ta /
On a bismuth titanate ferroelectric thin film formed on a SiO ₂ / Si substrate, a Pt electrode (100
μm) was formed by a vacuum evaporation method to produce a capacitor structure element as shown in FIG. 1, and its electrical characteristics were evaluated. Note that the upper electrode 6 formed here also needs to have a thickness enough to function as an electrode similarly to the lower electrode 2, and the material is not limited to Pt.
A conductive material used for a normal electrode material may be used, and a film forming method such as a vacuum evaporation method and a sputtering method can be used.

A voltage was applied between the lower electrode 4 and the upper electrode 6 shown in FIG. 1 to evaluate the ferroelectric characteristics. As a result, a ferroelectric hysteresis curve as shown in FIG. 4A was obtained. . That is, in the capacitor structure element of the present embodiment, 3
When V is applied, the residual spontaneous polarization Pr = 7.5 μC / cm
^2. The characteristic of coercive electric field Ec = 70 kV / cm was shown.
The value of Pr is almost twice as large as Pr = 4 μC / cm ² in the c-axis direction reported for the Bi ₄ Ti ₃ O ₁₂ single crystal (bulk).

This is because Pr _{4 in} the a-axis direction of Bi ₄ Ti ₃ O ₁₂
Is known to be larger than that in the c-axis direction,
Further, since the ferroelectric material Bi ₄ Ti ₃ O ₁₂ of random orientation was shown from the X-ray diffraction observation of this example, this 7.5 μC /
The large Pr of the present embodiment of cm ² is Bi ₄ Ti ₃ O ₁₂
It is considered that the a-axis orientation component of the ferroelectric greatly contributed.

Further, as a result of measuring the leak current density Il of this sample, the applied voltage dependency becomes as shown in FIG. 5, and at an applied voltage of 3 V, Il = 8 × 10 ⁻⁷ A / cm ²
And small good values were obtained. It is considered that, as described above, since a dense bismuth titanate thin film having excellent smoothness was obtained, pinholes were suppressed, and the leakage current characteristics were greatly improved.

In the above embodiment, the substrate temperature was 420 ° C. when the bismuth titanate thin film was formed by MOCVD.
However, in this case, when the substrate temperature was in the range of 400 ° C. to 500 ° C., the same good results as in the above example were obtained.

Next, in the above embodiment, the substrate temperature was 420 ° C. when the bismuth titanate thin film was formed by the MOCVD method. However, the substrate temperature at this time was 600 ° C., and the others were manufactured in the same manner as in the above embodiment. The results of observation of a bismuth titanate thin film and measurement of electrical characteristics will be described for a comparative example. In addition, since the film formation time of the bismuth titanate thin film of the comparative example was higher than the substrate temperature in the above example,
In order to obtain the same film thickness of 200 nm, the film formation time was about 40 minutes, which was shorter than that of the above example.

FIG. 6 shows the results of X-ray diffraction of the bismuth titanate of the comparative example, and FIG. 7 shows the results of SEM observation of the bismuth titanate thin film of the comparative example.

According to FIG. 6, the X-ray diffraction pattern of the bismuth titanate thin film of the comparative example shows only the diffraction peak of the ferroelectric Bi ₄ Ti ₃ O _{12 having} c-axis orientation or random orientation, that is, random orientation. No existence of paraelectric (pyrochlore) Bi ₂ Ti ₂ O ₇ can be confirmed. As a result of the composition analysis by the composition analyzer EPMA, the Bi / Ti composition ratio is 1.3 if the stoichiometric composition of the ferroelectric Bi ₄ Ti ₃ O ₁₂ , and the paraelectric (pyrochlore) Bi ₂ Ti ₂ If the stoichiometric composition of O ₇ is supposed to be 1.0, the Bi / Ti composition ratio of the bismuth titanate thin film of the comparative example indicates the stoichiometric composition of the ferroelectric Bi ₄ Ti ₃ O _12. 1.3 matched
And only the ferroelectric Bi ₄ Ti ₃ O ₁₂ is present,
It is considered that paraelectric (pyrochlore) Bi ₂ Ti ₂ O ₇ is not mixed.

According to FIG. 7, the surface of the bismuth titanate thin film of the comparative example was composed of coarse crystal grains having a particle size of about 0.5 μm or more. In comparison with this, it can be seen that the surface of the thin film of the above example is formed of crystal grains having a grain size of about 0.1 μm, and is a dense thin film having extremely excellent smoothness.

The electrical characteristics of the capacitor element of the comparative example were measured under the same conditions as in the above example. As a result, in the comparative example, the applied voltage was 3 V and the leak current density was 1
The value was as large as 0 ^-4 A / cm ² . In comparison with this, it can be seen that the capacitor structure element of the above example is superior to the comparative example by three orders of magnitude in leakage electric characteristics.

Next, a second embodiment will be described. In the second embodiment, the same substrate as in the first embodiment was used, and a bismuth titanate thin film was formed thereon by MOCVD. However, in the above-described first embodiment, the substrate temperature was set to 420 ° C. and the 200-nm bismuth titanate thin film was formed. Subsequently, the substrate temperature was set to 420 ° C., and a 50 nm-thick bismuth titanate film was formed to form a 100 nm-thick bismuth titanate thin film.

With respect to the bismuth titanate thin film of the second embodiment, the crystallinity was observed by X-ray diffraction and the surface morphology was observed by SEM (scanning electron microscope).
FIG. 8 shows an observation result by X-ray diffraction and FIG. 9 shows an observation result by SEM at this time.

According to the X-ray diffraction pattern of FIG. 8, the bismuth titanate thin film of the second embodiment has c-axis orientation and random orientation, that is, high intensity of random orientation, as in the first embodiment. It can be seen that both dielectric Bi ₄ Ti ₃ O ₁₂ and (111) oriented paraelectric (pyrochlore) Bi ₂ Ti ₂ O ₇ are mixed. In addition, each diffraction peak is set to the first
As compared with the embodiment of the present invention, in the second embodiment, the ferroelectric B
The thickness due to i ₄ Ti ₃ O ₁₂ is large, and the thickness due to paraelectric (pyrochlore) Bi ₂ Ti ₂ O ₇ is small. This is because the mixing ratio between the ferroelectric Bi ₄ Ti ₃ O ₁₂ and the paraelectric (pyrochlore) Bi ₂ Ti ₂ O ₇ is larger in the ferroelectric Bi ₄ Ti ₃ O _12. Can be

As a result of the composition analysis by the composition analyzer EPMA, the Bi / Ti composition ratio was 1.0 in the Bi / Ti composition ratio of the bismuth titanate thin film of the second embodiment. The value was larger than 0.8. This is considered to be because the mixing ratio of the paraelectric Bi ₂ Ti ₂ O ₇ or the amorphous bismuth titanate showing the paraelectric is small, which is consistent with the observation result of the X-ray diffraction.

According to FIG. 3, the surface of this bismuth titanate thin film has a particle size of about 0.1 as in the first embodiment.
It can be seen that a dense thin film having an excellent smoothness of μm was formed.

Next, similarly to the first embodiment, the upper electrode 6 was formed, and the electrical characteristics of the capacitor element as shown in FIG. 1 were evaluated.

The ferroelectric characteristics of the capacitor element of the second embodiment were measured in the same manner as in the first embodiment. As a result, a ferroelectric hysteresis curve as shown in FIG. 4B was shown. That is, in the capacitor structure element of the second embodiment, the residual spontaneous polarization Pr = 5 μC / c when 3 V is applied.
m ² and coercive electric field Ec = 100 kV / cm. The value of Pr is 200 nm in the second embodiment, whereas the thickness of the bismuth titanate thin film in the first embodiment is 100 nm, which is half of that in the first embodiment. Regardless, it shows a sufficiently large value. This is presumably because the mixing ratio of the ferroelectric Bi ₄ Ti ₃ O ₁₂ was increased and the ferroelectricity was enhanced, as described above.

As for the leakage electric characteristics, as in the first embodiment, as a result of the measurement, the dependency of the leakage current density Il on the applied voltage is as shown in FIG. A good value of Il = 6 × 10 ⁻⁸ A / cm ² , which is smaller than that of the first embodiment, was obtained.

In the second embodiment, the MOCVD
The substrate temperature at the time of forming the bismuth titanate thin film by the method
600 ° C. when forming a part of the ferroelectric thin film first
The temperature was set to 420 ° C. when a ferroelectric thin film in which a ferroelectric substance and a paraelectric substance were mixed was formed thereafter. However, these substrate temperatures are in the range of 500 ° C. to 650 ° C. when a part of the ferroelectric thin film is first formed, and the ferroelectric thin film in which the ferroelectric and paraelectric are mixed later is used. When forming the film, the temperature was in the range of 400 ° C. to 500 ° C., and the same good effects as in the above example were obtained.

The bismuth titanate thin film Bi / Ti
Regarding the composition ratio, when the stoichiometric composition of the ferroelectric Bi ₄ Ti ₃ O ₁₂ was shifted from 0.5 to 1.1, good characteristics were obtained by the effect of the present invention.

In the above embodiment, bismuth titanate Bi ₄ Ti ₃ O ₁₂ was used as the ferroelectric substance. However, the present invention is not limited to this, and the same result can be obtained with a perovskite structure such as PZT or PLZT. Obtained, and as a layered perovskite structure, the Bi ₄ Ti ₃
O _{12 addition, SrBi 2 Nb 2 O 9,} SrBi 2 Ta 2 O 9,
BaBi ₂ Nb ₂ O ₉ , BaBi ₂ Ta ₂ O ₉ , Pb ₂ Bi ₂ N
b ₂ O ₉ , PbBi ₂ Ta ₂ O ₉ , SrBi ₄ Ti ₄ O ₁₅ , B
aBi ₄ Ti ₄ O ₁₅ , PbBi ₄ Ti ₄ O ₁₅ , Na _0.5 Bi
_4.5 Ti ₄ O ₁₅ , K _0.5 Bi _4.5 Ti ₄ O ₁₅ , Sr ₂ Bi ₄ T
_{i 5 O 18, Ba 2 Bi} 4 Ti 5 O 18, Pb 2 Bi 4 Ti 5 O 18
Are also applicable to the present invention.

In the above embodiment, Pt /
Although a capacitor structure element using a Ta / SiO ₂ / Si substrate is used, the invention is not limited to this. For example, S
An integrated circuit is formed on an i or GaAs substrate, the surface of the integrated circuit is covered with an interlayer insulating film such as silicon oxide or silicon nitride, and the integrated circuit is formed through a contact hole formed in a part of the interlayer insulating film. An electrode layer electrically connected to the element may be formed on the interlayer insulating film, and the ferroelectric thin film of the present invention may be formed on the electrode layer. That is, the present invention is applicable to an integrated circuit element electrically connected to the elements of the integrated circuit such as the capacitor structure and the transistor structure of the above embodiment, and various highly integrated devices.

[0065]

As described above, according to the ferroelectric thin film of the present invention, a ferroelectric film having sufficient ferroelectric properties and excellent in smoothness and denseness even at a film thickness of 200 μm or less. Since a thin film can be realized, the leak current characteristics can be greatly improved. Further, it is applicable to various microfabrication processes and is effective for application to highly integrated devices.

Further, according to the method of manufacturing a ferroelectric thin film of the present invention, a ferroelectric thin film can be formed by a low-temperature process, so that it can be applied to a highly integrated device. Furthermore, since the MOCVD method is used instead of the conventional MOD method or the sol-gel method for coating and film formation, a large-area thin film can be manufactured with good film thickness controllability and high speed. It can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of a capacitor structure element using a ferroelectric thin film of the present invention.

FIG. 2 is a view showing an observation result of a bismuth titanate thin film of a first example by X-ray diffraction.

FIG. 3 shows S of the bismuth titanate thin film surface of the first embodiment.
It is a photograph which shows the observation result by EM.

FIG. 4 is a diagram showing a ferroelectric hysteresis curve (a) of the capacitor structure element of the first embodiment and a ferroelectric hysteresis curve (b) of the capacitor structure element of the second embodiment.

FIG. 5 is a diagram showing the applied voltage dependence of the leakage current density Il of the capacitor structure element of the first embodiment.

FIG. 6 is a diagram showing observation results by X-ray diffraction of a bismuth titanate thin film of a comparative example.

FIG. 7 is a photograph showing the result of observation of the bismuth titanate thin film surface of the comparative example by SEM.

FIG. 8 is a diagram showing an observation result by X-ray diffraction of a bismuth titanate thin film of a second example.

FIG. 9 shows S of the bismuth titanate thin film surface of the second embodiment.
It is a photograph which shows the observation result by EM.

FIG. 10 is a diagram showing the applied voltage dependency of the leak current density Il of the capacitor structure element of the second embodiment.

[Explanation of symbols]

 Reference Signs List 1 silicon substrate 2 silicon oxide layer 3 adhesive layer 4 lower electrode 5 ferroelectric thin film 6 upper electrode

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI H01L 27/04 H01L 27/04 C 27/10 451 (72) Inventor Masayoshi Kiba 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka, Sharp JP-A-4-132615 (JP, A) JP-A-3-141146 (JP, A) JP-A-6-329497 (JP, A) JP-A-6-29462 (JP, A A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 27/04 H01L 21/822 C01G 29/00 C30B 29/32 H01L 21/31 H01L 21/316 H01L 27/10 451

Claims (1)

(57) [Claims] An MOCVD method using a first raw material .
Ri, Bae on the substrate at a substrate temperature of 650 ° C. from 500 ° C.
After forming a ferroelectric thin film having a lobskite structure or a layered perovskite structure, a first raw material is formed on the ferroelectric thin film.
The substrate temperature was set to 40 by the MOCVD method using the same raw material.
Perovskite structure or layered
A ferroelectric with a lobskite structure and a pyrochlore structure or
A method of manufacturing a ferroelectric thin film, comprising a step of forming a ferroelectric thin film in which a paraelectric having an amorphous structure is mixed.