JP2000277705A - Reforming method for ferroelectric film and manufacture of capacitor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of a bond defect in a ferroelectric film in an amorphous state by performing oxidation after the formation of a ferroelectric film in an amorphous state, and then heat-treating and crystalizing the oxidation-treated ferroelectric film. SOLUTION: After the formation of a base SiO2 film 11 by thermal oxidation of the surface of a silicon substrate, a Ti film 12 and a Pt lower electrode 13 are deposited successively on the SiO2 film 11, to make a lower electrode for a ferroelectric capacitor in an amorphous state. Following this, a sputtered PZT film 14 is formed under 0.02 Torr obtained by flowing a process gas of Ar and O2 having PbZrTiO3 composition. On this PZT film 14, hydrogen peroxide water 15 is applied, and removed one second later. Following this, heat treatment is performed in an atmospheric oxygen atmosphere of 650 deg.C, and the PZT film 14 is crystalized as an perovskite oxide into a crystalized PZT film 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for modifying a ferroelectric film and a method for manufacturing a capacitor, and more particularly to a 2Tr + 2C type or 1Tr + 1C type FeRAM.
The present invention relates to a method for improving a ferroelectric film and a method for manufacturing a capacitor element, which are characterized by a method for improving electrical characteristics such as hysteresis characteristics and leak characteristics of a ferroelectric film used for (Ferroelectric RAM).

[0002]

2. Description of the Related Art Conventionally, DR for recording various kinds of information has been used.
AM (dynamic random access memory),
Semiconductor storage devices such as SRAM (static random access memory) or FLASH (flash memory) are used. Among them, DRAM has the characteristics of high read / write speed and long service life. However, since it is volatile, a refresh operation is required. Therefore, it must be always connected to the power supply voltage. No.

An SRAM has a feature that the contents of the memory are not erased as long as it is connected to a power supply voltage and that the reading and writing speeds are high, but the DRAM has a large cell area.
3 to 4 times as large as the above, which is not suitable for high integration.

[0004] On the other hand, FLASH is a non-volatile memory and does not require a refresh operation. However, there is a problem that the writing speed is slow and the service life is short. For example, for a writing speed of about 100 nsec of DRAM, 1
It takes 10 to 10 milliseconds, and the service life is 10 times that of DRAM.
Against ¹⁵ times, it made much shorter and about 10 ^five times.

In recent years, a ferroelectric memory (FeRAM: Ferroelectric R) has been proposed as a memory that solves all of these problems, that is, a memory that does not require a refresh operation, has a high operating speed, and has a long service life.
AM) is attracting attention.

The FeRAM is a non-volatile memory utilizing the polarization characteristics of the ferroelectric film, so that it does not require a refresh operation, has the same write and read speeds as the DRAM, and has a long service life. 10 ¹² times or more and FLAS
There is a feature that it is longer than H.

As a ferroelectric film material used for this FeRAM, PZT (PbZr _x Ti _{1 -x} O ₃ ) or PL
A perovskite oxide containing Pb such as ZT (La-doped PZT) or a Bi-based layered perovskite oxide such as SBT is used. Since a ferroelectric thin film used for such a ferroelectric capacitor is formed by a sputtering method, a sol-gel method, or the like,
A conventional ferroelectric thin film forming flow will be described with reference to FIG.

First, after a lower electrode is formed on a base insulating film, an amorphous ferroelectric thin film is formed by a sputtering method, a sol-gel method, or the like.
The basic configuration of the ferroelectric capacitor is completed by forming a polycrystalline perovskite structure that can be crystallized by heat treatment at a temperature of about 800 ° C., for example, about 700 ° C. and that can be inverted, and finally form an upper electrode. I do.

As described above, since it is necessary to perform high-temperature oxygen annealing in the crystallization step, the lower electrode and the upper electrode do not oxidize even in a high-temperature oxygen atmosphere, or their electrical conductivity is impaired even if they are oxidized. No Pt, Ru,
A platinum group oxide such as Ir or a platinum group oxide such as RuO ₂ or IrO ₂ is used.

Next, an example of a manufacturing process of an FeRAM using such a ferroelectric capacitor will be described with reference to FIG. FIG. 6 is a schematic cross-sectional view of the FeRAM. First, a p-type well region 22 is formed in a predetermined region of an n-type silicon substrate 21, and element isolation oxidation is performed by selectively oxidizing the n-type silicon substrate 21. After the film 23 is formed, a gate electrode 25 is formed in the element forming region via the gate oxide film 24, and ions such as As are implanted using the gate electrode 25 as a mask to thereby form an n ^- type LDD (Lightly).
A Doped Drain region 26 is formed. Next, a SiO ₂ film or the like is deposited on the entire surface, and a sidewall 27 is formed by performing anisotropic etching. Then, ion implantation of As or the like is performed again to thereby form an n ⁺ -type drain region 28 and an n ⁺ -type source region. 29 are formed.

Next, after forming a first interlayer insulating film 30 made of a thick SiO ₂ film or the like, a Ti film as an adhesion improving layer is formed on the first interlayer insulating film 30 on the element isolation oxide film 23 by a sputtering method. Then, a Pt lower electrode 32 is formed on the Ti film 31.

Next, after depositing an amorphous sputtered PZT film by using a sputtering method, 700 to 80
The sputtered PZT film is crystallized as perovskite oxide by performing low-speed heating and long-time heat treatment in an atmospheric oxygen atmosphere at 0 ° C. to form a crystallized PZT film 33.

Next, the PZT is formed by a mask sputtering method using a metal mask having an opening having a predetermined area.
After forming the Pt upper electrode 34 on the film 33, the PZT film 33 is subjected to a heat treatment at 500 to 650 ° C. for about 30 minutes in an atmosphere of oxygen under atmospheric pressure to recover the damage of the PZT film 33,
Finally, after a second interlayer insulating film 35 is newly formed on the entire surface, a connection electrode 36 for connecting the n ⁺ type source region 29 and the Pt upper electrode 34 is provided, and the Pt lower electrode 31
Forming a ground electrode 37 connected to the N ⁺ -type drain region 28 and a bit line 38 connected to the n ⁺ -type drain region 28.
The basic structure of one memory cell of M is completed.

[0014]

However, such a PZ
In the case of the T film forming process, there are the following problems.
That is, it is necessary to reduce the thickness of the ferroelectric film of the ferroelectric capacitor portion in accordance with the demand for higher integration and higher performance of the FeRAM. However, when the PZT film is reduced to 150 nm or less, the leakage current is reduced. However, there is a problem that good hysteresis characteristics cannot be obtained.

The leak current in such a PZT film is as follows:
Generally, PZT is influenced by impurity levels and mobile ions caused by oxygen defects and Pb defects, and therefore, it is ideal that PZT has few crystal defects in order to reduce leakage current.
However, when the film thickness is 150 nm or less, the amorphous PZT film formed by any of various film forming methods is in a state where defects are easily generated.

For example, it has been reported that when Ar sputtering is performed on a PZT thin film, the Pb—O bond in the PZT thin film is broken to become metal Pb (if necessary, Mater. Res. Soc. Symp. .Proc
c. , Vol. 200, pp. 267-274,199
0).

Since this metal Pb can easily move in the PZT thin film, it can be easily inferred that Pb deficiency occurs in the PZT thin film, particularly near the electrode interface during the crystallization annealing step. If the thickness of this PZT film is large, PZT
Since the ratio of the surface defect portion to the entire film is reduced, the margin for leakage is improved. However, when the film is made thinner, the margin is reduced.

The high dielectric constant film CVD-Ta ₂ O
_In order to remove oxygen vacancies and residual carbon in Step 5, it is proposed to carry out a reforming treatment at a temperature of 600 ° C. or lower after crystallization (if necessary, see JP-A-10-13523).
No. 3).

For example, an annealing process in a gas atmosphere containing O ₃ , an annealing process while spraying an aerosol containing H ₂ O ₂ , or an annealing process after application of an H ₂ O ₂ solution has been proposed. , These reforming processes are processes after crystallization, and P
In the case of a ZT film, Pb-
Since defects such as O-bond defects have already occurred, PZT
No modification effect can be expected even when applied to a film.

On the other hand, in the FeRAM, as is apparent from FIG. 6, after forming the thick first interlayer insulating film 30 and the second interlayer insulating film 35, a through hole is formed, and
The wiring connecting the transistor portion and the ferroelectric capacitor portion is formed by using TiN or TiN, but when the film thickness of the ferroelectric capacitor portion is large, the aspect ratio of the through hole formed in the transistor portion increases. Therefore, there is a problem that it is difficult to form an electrode wiring layer.

Therefore, for high integration of the FeRAM, it is desired to reduce the thickness of the PZT film constituting the ferroelectric capacitor. In addition, due to the requirement of low-voltage operation of 3 V or less, it is essential to reduce the coercive voltage V _{c of} hysteresis, that is, the minimum voltage required for the occurrence of polarization inversion. since anti voltage V _c with a decrease also becomes small, thin is desired from this point of view. However, when the PZT film is made thinner, the above-mentioned leak current increases, and there is a problem that good hysteresis characteristics cannot be obtained.

Accordingly, an object of the present invention is to prevent the occurrence of coupling defects in a ferroelectric film in an amorphous state, or to remarkably improve the film quality by repairing the defects.

[0023]

FIG. 1 is a process flow showing the basic configuration of the present invention, and the means for solving the problems in the present invention will be described with reference to FIG. See FIG. 1. (1) The present invention relates to a method for modifying a ferroelectric film, in which an amorphous ferroelectric film is formed, an oxidation process is performed, and then the ferroelectric film after the oxidation process is heat-treated. And crystallized.

As described above, by oxidizing the amorphous ferroelectric film before the crystallization step,
Generation of defects due to release of metal elements constituting the ferroelectric film can be suppressed, whereby the electrical characteristics of the ferroelectric film after crystallization can be improved.

(2) The present invention is characterized in that, in the above (1), the oxidation treatment is an oxidation treatment using a hydrogen peroxide solution.

As described above, by using the hydrogen peroxide solution as the oxidizing treatment, it is possible to suppress the occurrence of coupling defects on the surface of the amorphous ferroelectric film.

(3) The present invention is characterized in that, in the above (2), the concentration of the hydrogen peroxide solution is 20% by volume or more.

As described above, by using 20% by volume or more of hydrogen peroxide as the hydrogen peroxide, it is possible to effectively suppress the occurrence of the bonding defects on the surface of the amorphous ferroelectric film. . In the case of 100% by volume, pure hydrogen peroxide (H ₂ O ₂ ) is obtained.

(4) Further, according to the present invention, in any one of the above (1) to (3), the ferroelectric film after crystallization is
It is a perovskite oxide containing Pb.

Such a bonding defect in the amorphous state is remarkable in an oxide containing Pb such as PZT. In order to exhibit ferroelectric characteristics after crystallization, the ferroelectric film after crystallization must be made of perovskite. Must be a structure. When the ferroelectric film after crystallization has a pyrochlore structure, it does not show good ferroelectric characteristics.

(5) Further, according to the present invention, in the method for manufacturing a capacitive element, amorphous Pb is contained on a lower electrode made of a platinum group oxide, a platinum group oxide, or a laminated structure thereof. After forming the oxide film, a hydrogen peroxide solution treatment is performed, and then the hydrogen peroxide-treated oxide containing Pb is heat-treated and crystallized to form a perovskite oxide containing Pb, and then an upper electrode is formed. It is characterized by the following.

As described above, the ferroelectrics of the above (1) to (4)
Capacitor element, that is, ferroelectric capacitor
Low leakage current by applying
Ferroelectric capacitor with good hysteresis characteristics
Can be manufactured, and in that case, the lower electrode and
To prevent oxidation or to maintain electrical conductivity after oxidation
In order not to impair the platinum group (Pt, Ru, Ir), white
Gold oxide (RuO) _Two, IrO_Two) Or these
Laminated structure (Pt / IrO_TwoEtc.)
Is desirable.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a first embodiment of the present invention will be described with reference to FIGS. 2 and 3. First, a first embodiment of the present invention will be described with reference to FIG. 4A and 4B are explanatory diagrams of a manufacturing process according to the embodiment, and then with reference to FIG. 3, illustrating characteristics of the crystallized PZT film according to the first embodiment of the present invention. Referring to FIG. 2A, first, the surface of a silicon substrate (not shown) is thermally oxidized,
After forming an underlying SiO ₂ film 11 having a thickness of, for example, 500 nm, a Ti film 12 having a thickness of 20 nm and a thickness of 2 nm are formed on the underlying SiO ₂ film 11 by sputtering.
A 00 nm Pt lower electrode 13 is sequentially deposited to form a lower electrode of a ferroelectric capacitor.

[0034] Then, diameter Pb _1.1 Zr _0.53 Ti _0.47 O ₃ composition with a disc of 50mm as a target,
With a flow rate of Ar: O ₂ = 8: _{2 and} a flow rate of Ar: O _{2 of} 0.02 Torr, 50 W of R
The F power is applied to form a sputtered PZT film 14 having a thickness of 70 nm and 110 nm at room temperature. This sputtered PZT film 14 is in an amorphous state when formed.

Next, referring to FIG. 2B, a hydrogen peroxide solution 15 having a concentration of 20 to 100% by volume is applied to the surface of the sputtered PZT film 14 at room temperature (24 ° C.), and is removed after one second. . The concentration at this time was 20% by volume, 30% by volume, 50% by volume,
00% by volume was adopted.

Next, as shown in FIG. 2 (c), the sputtered PZT film 14 is crystallized as a perovskite oxide by performing a heat treatment for 30 minutes in an atmospheric oxygen atmosphere at 500 to 800 ° C., for example, 650 ° C. The PZT film 16 is used.

Next, although not shown, a diameter of 0.2 to
A Pt upper electrode having a thickness of, for example, 200 nm is formed on the crystallized PZT film 16 by using a mask sputtering method using a metal mask having an opening of 0.5 mm. By performing a heat treatment for 30 minutes in the inside, the damage of the crystallized PZT film 16 in the deposition step of the Pt upper electrode is recovered, thereby completing the basic configuration of the ferroelectric capacitor.

The crystallized PZT film 16 thus formed
When the surface was observed using a reflection microscope, almost no defects were found, but for comparison, when crystallized without hydrogen peroxide solution treatment, a convex shape with a size of about several μm was observed. Many defects were observed.

FIG. 3A is a diagram showing the relationship between the concentration of hydrogen peroxide and the defect density in the treatment with aqueous hydrogen peroxide. For comparison, FIG.
Crystallized without hydrogen peroxide treatment, and 0
Also shown are the results obtained when a volume%, that is, pure water, and a hydrogen peroxide solution treatment at a concentration of 10% by volume are performed.
As is clear from the figure, the effect of reducing the defect density is apparent when the hydrogen peroxide concentration is 20% by volume or more.

FIG. 3B is an explanatory diagram of the hysteresis characteristics of the crystallized PZT film. In the case where the hydrogen peroxide solution treatment is not performed, the hysteresis expands due to a large leak current. But
It can be seen that when the treatment with the aqueous solution of hydrogen peroxide at a concentration of 30% by volume is performed, the leak current is small and the sharp hysteresis is obtained.

As described above, the amorphous sputter PZ
By performing an oxidation treatment using a hydrogen peroxide solution after forming the T film, it is possible to suppress the occurrence of defects such as a Pb-O bond defect, thereby reducing a leak current. A ferroelectric capacitor having good hysteresis characteristics can be formed.

Next, a second embodiment of the present invention using a laminated structure of Pt / IrO ₂ as the lower electrode will be described. The structure of the second embodiment is the same as that of the first embodiment except for the structure of the lower electrode. Therefore, the illustration is omitted. First, the surface of a silicon substrate is thermally oxidized to form an underlayer S having a thickness of, for example, 500 nm.
After forming the iO ₂ film, an IrO ₂ film having a thickness of 50 nm and a Pt lower electrode having a thickness of 150 nm are sequentially deposited on the underlying SiO ₂ film by sputtering, thereby forming a lower electrode of the ferroelectric capacitor. And

[0043] Thereafter, similarly to the first embodiment described above, using a Pb _1.1 Zr _0.53 Ti _0.47 O ₃ as a target, the flow rate ratio of Ar and O ₂ is Ar: O ₂ = 8: 2 Process With the gas flowing to 0.02 Torr, 5
At room temperature by applying 0 W RF power,
A sputtered PZT film having a thickness of 140 nm is formed.

Next, an aqueous solution of hydrogen peroxide having a concentration of 20 to 100% by volume is applied on the surface of these sputtered PZT films at room temperature (24 ° C.), and after 1 second, it is removed.
By performing a heat treatment for 30 minutes in an atmospheric oxygen atmosphere at 00 to 800 ° C., for example, 650 ° C., the sputtered PZT film is crystallized as a perovskite oxide to form a crystallized PZT film.

Then, the thickness of the crystallized PZT film is set to, for example, 200 nm by using a mask sputtering method using a metal mask having an opening having a diameter of 0.2 to 0.5 mm.
m Pt upper electrode is formed, and then a heat treatment is performed for 30 minutes in an atmospheric pressure oxygen atmosphere at 500 ° C., so that crystallized PZT
By recovering the damage from the film, the basic structure of the ferroelectric capacitor is completed.

FIG. 4 (a) shows the crystallization of a sputtered PZT film formed to a thickness of 140 nm for crystallization annealing without performing hydrogen peroxide treatment for comparison. FIG. 4 is a graph showing hysteresis characteristics of a PZT film. When the film thickness is 140 nm, good characteristics are obtained without performing an oxidation treatment.

FIG. 4 (b) also shows, for comparison, the crystallization when the sputtered PZT film formed to a thickness of 70 nm is subjected to crystallization annealing without performing hydrogen peroxide treatment. FIG. 4 is a diagram showing hysteresis characteristics of the PZT film, and it is understood that an increase in defect density results in a leaky capacitor.

Referring to FIG. 4C, FIG. 4C shows a sputter PZ formed to a thickness of 70 nm.
FIG. 9 is a diagram showing the hysteresis characteristics of the crystallized PZT film when the T film is oxidized with a hydrogen peroxide solution having a concentration of 30% by volume, and excellent hysteresis characteristics are obtained. In the figure, the applied voltage is 2 V, 3 V, 5 V
3 shows hysteresis characteristics when three voltages are used.

Also in the second embodiment, even when the PZT film is thinned, defects such as Pb-O bond defects are reduced and the number of leak paths is reduced by performing the oxidation treatment with the hydrogen peroxide solution. The leakage current decreases,
And it was confirmed that good hysteresis characteristics were obtained.

The embodiments of the present invention have been described above. However, the present invention is not limited to the configuration shown in each embodiment, and various modifications are possible. For example, in each of the above embodiments, PZT is used as the ferroelectric film. However, the present invention is not limited to PZT, but PZT, PT,
The present invention is generally applied to perovskite oxides containing Pb such as PLZT.

In addition to the perovskite oxide containing Pb, the following general formula (Bi ₂ O ₂ ) ²⁺ (A _n-1 B _n O _{3n + 1} ) ^2- such as SBT, where A = Bi, Pb, Ba, Sr, Ca, Na, B = Ti, Ta, Nb, W, Mo, Fe, Co, Cr, Bi Bi-layered perovskite oxides represented by P in perovskite oxide containing
Since it behaves similarly to b, it is effective to perform an oxidation treatment on such a Bi-based layered perovskite oxide before the crystallization annealing step.

In the description of each of the above embodiments, the PZT film is formed by the sputtering method, but the PZT film formed by the sol-gel method or the MOCVD method is used.
The present invention is also applied to a film, and in any case, an oxidation treatment may be performed before the crystallization annealing step.

The oxidation treatment with the hydrogen peroxide solution is not limited to the application of the hydrogen peroxide solution.
The silicon substrate on which the ZT film has been formed may be brought into contact with the substrate by immersing it in a hydrogen peroxide solution, and further, an aerosol containing hydrogen peroxide may be sprayed.

Such an oxidation treatment is not necessarily limited to an oxidation treatment using a hydrogen peroxide solution.
It may be exposed to an atmosphere containing ozone (O ₃ ).

In each of the above embodiments, Pt or Pt / IrO ₂ is used as the lower electrode. However, a substance that does not oxidize in the crystallization process in a high-temperature oxygen atmosphere, or an electric substance that does not oxidize. Any material that does not impair the conductivity may be used, for example, Ru, Ir, or RuO.
₂ or the like may be used. That is, the platinum group (Pt,
Ru, Ir), oxides of the platinum group (RuO ₂ , Ir)
O ₂ ) or a laminated structure of these (Pt / IrO)
₂ ) is desirable.

In the description of the above embodiment, the information storage capacitor of the 2Tr + 2C type ferroelectric memory is described, but the present invention is also applied to the information storage capacitor of the 1Tr + 1C type ferroelectric memory. Further, the present invention is not limited to such a capacitor for a ferroelectric memory, but may be used as a small capacitor having a large capacitance in a normal semiconductor integrated circuit device, or
It is also applied as a capacitor for other electronic devices.

[0057]

According to the present invention, since the oxidation treatment is performed on the amorphous ferroelectric film before the crystallization annealing step, good characteristics can be obtained even when the ferroelectric film is thinned. This makes it possible to reduce the thickness of the ferroelectric film used for the ferroelectric capacitor.
M can achieve high integration, high performance, and high reliability, greatly contributing to the realization of a FeRAM with a logic circuit mixed therein.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a basic configuration of the present invention.

FIG. 2 is an explanatory diagram of a manufacturing process according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of characteristics of a crystallized PZT film according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram of characteristics of a crystallized PZT film according to a second embodiment of the present invention.

FIG. 5 is a view showing a flow of forming a conventional ferroelectric thin film.

FIG. 6 is a schematic sectional view of a conventional FeRAM.

[Explanation of symbols]

REFERENCE SIGNS LIST 11 base SiO ₂ film 12 Ti film 13 Pt lower electrode 14 sputtered PZT film 15 hydrogen peroxide 16 crystallized PZT film 21 n-type silicon substrate 22 p-type well region 23 element isolation oxide film 24 gate oxide film 25 gate electrode 26 n ^- -type LDD region 27 the sidewalls 28 n ⁺ -type drain region 29 n ⁺ -type source region 30 first interlayer insulating film 31 Ti film 32 Pt lower electrode 33 PZT film 34 Pt upper electrode 35 the second interlayer insulating film 36 connection electrode 37 grounded Electrode 38 bit line

Claims (5)

[Claims] 1. A ferroelectric film, comprising: forming an amorphous ferroelectric film, performing an oxidation treatment, and then heat-treating the oxidized ferroelectric film for crystallization. Reforming method. 2. The method for modifying a ferroelectric film according to claim 1, wherein the oxidation treatment is an oxidation treatment using a hydrogen peroxide solution. 3. The concentration of the hydrogen peroxide solution is 20% by volume.
3. The method for modifying a ferroelectric film according to claim 2, wherein: 4. The method for modifying a ferroelectric film according to claim 1, wherein the ferroelectric film after crystallization is a perovskite oxide containing Pb. . 5. An oxide containing Pb in an amorphous state is formed on a lower electrode made of a platinum group oxide, a platinum group oxide, or a laminated structure of any of these, and then treated with a hydrogen peroxide solution. Performing a heat treatment of the oxide containing Pb, which has been subjected to hydrogen peroxide treatment, and then crystallizing the resultant to form a perovskite oxide containing Pb, and then forming an upper electrode.