KR20000014388A - Ferroelectric memory capacitor and forming method thereof - Google Patents

Abstract

PURPOSE: A ferroelectric memory capacitor and forming method thereof are provided to compensate a negative electric charge reduced according to oxygen vacancy. CONSTITUTION: The capacitor comprises a lower electrode, a ferroelectric layer formed on the lower electrode and an upper electrode formed on the ferroelectric layer. A first doping layer is formed between the lower electrode and the ferroelectric layer and having an atom to compensate a negative electric charge according to oxygen vacancy generated in the ferroelectric layer. A second doping layer is formed between the ferroelectric layer and the upper layer and having an atom to compensate a negative electric charge according to oxygen vacancy generated in the ferroelectric layer.

Description

Ferroelectric Memory Capacitors and Method of Manufacturing the Same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric memory device and a method of manufacturing the same, and more particularly, to a capacitor using a ferroelectric as a dielectric film and a method of manufacturing the same.

A ferroelectric RAM (hereinafter referred to as "FRAM") is a nonvolatile memory device capable of performing a read operation and a write operation with a single power supply voltage while exhibiting a high operating speed.

FRAM devices can be classified into two types according to the elements of unit cells. One is a unit cell composed of one transistor using a ferroelectric film as a gate insulating film, and the other has the same structure as a DRAM cell composed of one cell capacitor and one access transistor, while the dielectric film of the cell capacitor is a ferroelectric film. Formed. Here, in the former FRAM, the silicon substrate and oxygen atoms react at the interface between the silicon substrate as the channel region and the ferroelectric film as the gate insulating film to form an unwanted silicon oxide film when the annealing of the ferroelectric film is performed. There is a problem in that it is difficult to form a ferroelectric film having excellent film quality due to the lattice constant difference or the thermal expansion coefficient difference between the ferroelectric films. Therefore, in recent years, a ferroelectric film is used to form a dielectric film of a cell capacitor having the same structure as that of the latter FRAM, i.e., a DRAM cell, having fast operating speed and low operating voltage characteristics, and having non-polarity characteristics with residual polarization characteristics of ferroelectrics. FRAM devices are being actively researched.

The polarization characteristics of ferroelectrics appear when they have the ABO ₃ type perovskite crystal structure. The crystal structure of ABO ₃ has a cubic structure, and the corner of the cubic lattice is occupied by a monovalent or divalent positively charged A ion. In addition, a B atom having a tetravalent or pentavalent positive charge is located at the center of the octahedron, in which six oxygen ions having a divalent anion are present in each face. The B atom forms a dipole in the up and down direction by interaction with oxygen ions. Thus, when an electric field is applied, the electrical dipoles are arranged in the electric field direction. This polarization state has only a small amount of depolarization even when the electric field is removed, and has a residual polarization amount, which is used for storing data.

However, when the dielectric film is formed of ferroelectric material, oxygen vacancy occurs at the interface with the electrode material. As the number of read and write operations increases, the oxygen vacancies are locally generated at the interface between the electrode and the ferroelectric film, thereby lowering the polarization characteristics of the ferroelectric film. As such, when the polarization characteristics of the ferroelectric film are degraded, malfunctions are caused during read and write operations. In addition, when oxygen vacancies are locally generated, a strong electric field is formed in a predetermined region of the ferroelectric film, so that the breakdown voltage of the ferroelectric film is lowered and the leakage current increases, thereby reducing the reliability of the ferroelectric film. Therefore, in order to improve the reliability of the ferroelectric film, oxygen vacancies must be reduced.

As a method for preventing the deterioration of characteristics due to oxygen vacancies, a method of doping lanthanum (La) and the like together when forming a ferroelectric film is known. However, when the ferroelectric film is formed, the lanthanum source gas is used together and doped, so that the lanthanum atoms are distributed not only at the interface between the ferroelectric film and the electrode but also throughout the ferroelectric film. Therefore, there is a problem of lowering the ferroelectricity and the dielectric constant than the original ferroelectric film.

The technical problem to be achieved by the present invention is to solve the oxygen vacancies in the ferroelectric film, the ferroelectric memory with improved characteristics by having a doping film containing atoms that can compensate for negative charges reduced by the oxygen vacancies in the lower or upper portion of the ferroelectric film To provide a capacitor.

Another object of the present invention is to provide a method of manufacturing the ferroelectric memory capacitor.

1 to 3 are cross-sectional views illustrating a capacitor manufacturing method and a capacitor manufactured by the method according to an embodiment of the present invention.

Figure 4 is a graph showing the results of measuring the leakage current of a capacitor having a doping film made of a lanthanum titanium oxide film (LaTiO ₃ ) prepared in accordance with the present invention and a doped film according to the prior art.

In order to achieve the above technical problem, a ferroelectric memory capacitor according to an aspect of the present invention includes a doping film including atoms capable of compensating negative charge loss due to oxygen vacancies generated in the ferroelectric film in the lower and / or upper portion of the ferroelectric film. It is provided.

According to a method of manufacturing a ferroelectric memory capacitor according to an aspect of the present invention for achieving the above another technical problem, after forming the lower electrode of the capacitor, before forming the ferroelectric film on the lower electrode, oxygen vacancies generated in the ferroelectric film A first doping film containing an atom capable of compensating negative charge loss due to the present invention is formed on the lower electrode. Next, after the ferroelectric film is formed on the first doping film, heat treatment is performed to crystallize the ferroelectric film, and the atoms in the first doping film are doped into the ferroelectric film.

Prior to the heat treatment step, it is preferable to further form on the ferroelectric film a second doping film containing atoms capable of compensating negative charge loss due to oxygen vacancies generated in the ferroelectric film.

According to another aspect of the present invention, a doping film including an atom capable of compensating negative charge loss due to oxygen vacancies generated in the ferroelectric film may be formed only on the ferroelectric film.

In the present invention, the lower electrode and the upper electrode are formed using any one selected from the group consisting of a resistive metal film, a conductive metal oxide film, and a composite film of the resistive metal film and the conductive metal oxide film, respectively.

And first doped yongmak and second doped film lanthanum titanium oxide (LaTiO _3), barium titanium oxide (BaTiO _3), calcium titanium oxide (CaTiO _3), strontium titanium oxide (SrTiO _3), and a group consisting of a composite film for Form using any one selected from.

Ferroelectric films include strontium titanium oxide film (SrTiO ₃ ), barium titanium oxide film (BaTiO ₃ ), barium strontium titanium oxide film ((Ba, Sr) TiO ₃ ), lead zirconium titanium oxide film (Pb (Zr, Ti) 0 ₃ ), strontium bismuth tantalum Any one selected from the group consisting of an oxide film (SrBi ₂ Ta ₂ O ₉ ), a lead lanthanum zirconium titanium oxide film ((Pb, La) (Zr, Ti) O ₃ ) and a bismuth titanium oxide film (Bi ₄ Ti ₃ O ₁₂ ) To form.

According to the present invention, the oxygen pores can be effectively reduced while maintaining the properties of the ferroelectric film by providing a doping film including atoms capable of compensating for the reduction of negative charge due to oxygen vacancies, respectively, in the lower and / or upper portions of the ferroelectric film. .

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 to 3 are cross-sectional views illustrating a capacitor manufacturing method and a capacitor manufactured by the method according to an embodiment of the present invention.

Referring to FIG. 1, a transistor including a gate insulating film 102, a gate electrode 104, a source region 106, and a drain region 107 is formed on a semiconductor substrate 100 using a conventional method. Subsequently, an insulating material selected from PSG, BPSG, TEOS, and USG is deposited on the entire surface of the resultant and then planarized to form the interlayer insulating film 108.

Subsequently, the interlayer insulating layer is patterned to form a contact hole exposing the source region 106. Next, a conductive film filling the contact hole on the entire surface of the product in which the contact hole is formed, such as a silicon film Si, a tungsten film W, a tantalum film Ta, a ruthenium film Ru, and an iridium film doped with impurities (Ir), an osmium film (Os), a tungsten silicide film (WSi), a tungsten nitride film (WN), or a combination thereof, and then etched back to form a source region 106 in the contact hole. And a plug 110 in contact with it. In this case, the plug 110 may be formed by a selective deposition method in which a conductive film is selectively formed only inside the contact hole.

Next, a material for forming the lower electrode of the capacitor is deposited on the resultant on which the conductive plug 110 is formed, and then patterned using a conventional photolithography process to form the lower electrode 112 of the capacitor. At this time, the lower electrode 112 of the capacitor is formed by using a oxidation resistant metal film, a conductive metal oxide film, or a composite film of the oxidation resistant metal film and the conductive metal oxide film. As the oxidation resistant metal film, any one selected from the group consisting of platinum film (Pt), iridium film (Ir) and ruthenium film (Ru), rhodium film (Rh), osmium film (Os) and palladium film (Pd) is used. , a conductive metal oxide film of ruthenium oxide (RuO _2), iridium oxide (IrO _2), strontium ruthenium oxide (SrRuO _3), from the group consisting of calcium, strontium ruthenium oxide (CaSrRuO ₃₎ and barium strontium ruthenium oxide (BaSrRuO ₃₎ Any one selected may be used.

Referring to FIG. 2, the first doping film 114, the ferroelectric film 116, and the second doping film 118 are sequentially formed on the resultant product on which the lower electrode 112 is formed.

The first doping film 114 and the second doping film 118 are formed using a film containing atoms capable of compensating negative charge loss due to oxygen vacancies generated in the ferroelectric film 116. Thus, lanthanum titanium oxide (LaTiO _3), barium titanium oxide (BaTiO _3), calcium titanium oxide (CaTiO _3), strontium titanium oxide (SrTiO _3), and using these composite membrane first doping yongmak 114 and the second The doping film 118 is formed. Lanthanum (La ¹⁺ ), barium (Ba ²⁺ ), calcium (Ca ²⁺ ), or strontium (Sr ²⁺ ) in the first and second doping films 114 and 118 compensate for negative charge loss due to oxygen vacancies. Act as an atom to do

The first doped film 114 and the second doped film 118 use an atomic layer deposition method, a sputtering method, a metal organic chemical vapor deposition (MOCVD) method, or a sol-gel method. Can be formed.

Since the first doped film 114 and the second doped film 118 do not dop the entire ferroelectric film 116 but only at the interface, they are formed as thin as possible.

The ferroelectric film 116 includes a strontium titanium oxide film (SrTiO ₃ ), a barium titanium oxide film (BaTiO ₃ ), a barium strontium titanium oxide film ((Ba, Sr) TiO ₃ ), and a lead zirconium titanium oxide film (Pb (Zr, Ti) 0 ₃ ) , Strontium bismuth tantalum oxide film (SrBi ₂ Ta ₂ O ₉ ), lead lanthanum zirconium titanium oxide film ((Pb, La) (Zr, Ti) O ₃ ) and bismuth titanium oxide film (Bi ₄ Ti ₃ O ₁₂ ) Form using either.

The ferroelectric film 116 is also formed by a sputtering method, a metal organic chemical vapor deposition method, or a sol-gel method.

After forming the second doping film 118, the entire surface of the resultant is heat-treated to crystallize and stabilize the perovskite structure of the ferroelectric film 116. The heat treatment is carried out in an oxygen atmosphere at a temperature of 700 to 750 ° C.

Atoms contained in the first doping film 114 and the second doping film 118 by heat treatment, and capable of compensating the loss of negative charges due to oxygen vacancies in the ferroelectric film, have A atoms in the ferroelectric film 116 of the ABO ₃ structure. The ferroelectric film 116 is stabilized by binding to the atom or B atom site instead. Therefore, the fatigue characteristics and the retention characteristics of the ferroelectric film 116 are improved, and the leakage current is reduced. In addition, since doping does not occur over the entire ferroelectric film 116 but only on the upper and lower surfaces of the ferroelectric film 116, the polarization characteristics and the high dielectric constant of the ferroelectric film 116 can be maintained.

For example, a PZT film is formed of the ferroelectric film 116 and a lanthanum titanium oxide film (LaTiO ₃ ) is formed of the first and second doping films 114 and 118. ) In more detail.

When oxygen vacancies are generated in the PZT ferroelectric film 116, negative charges decrease due to the loss of oxygen, and the total charge of the PZT ferroelectric film 116 represents a positive value. Therefore, when the heat treatment after forming the doped yongmak 114 and 118 on the upper or lower portion consisting of a lanthanum-titanium oxide film of the PZT ferroelectric film 116, constituting the doping yongmak (114, 118) and band a monovalent positive electric charge is La ^{+ 1} instead binds to the bivalently charged Pb ²⁺ site. That is, the positive charge is also reduced by the amount of negative charge which decreases as oxygen vacancies are generated in the PZT ferroelectric film 116, resulting in the total charge of the PZT ferroelectric film 116 being zero. Therefore, the fatigue characteristics and the retention characteristics of the PZT ferroelectric film 116 are improved, and the leakage current is reduced. In addition, since the substitution reaction of La ^{+ 1} occurs only on the surface of the PZT ferroelectric film 116, the entire film maintains the state of the PZT film as it is, and thus has high polarization characteristics and dielectric constant.

Referring to FIG. 3, after forming an upper electrode conductive film on the second doping film 118, the upper electrode 118, the second doping film 118, and the ferroelectric film 116 through a conventional photolithography process. And the first doping film 114 is patterned on a cell basis to complete the capacitor cell unit.

In the present embodiment, the doping film is formed on both the upper and lower portions of the ferroelectric film 116. However, the doping film is formed only at the interface between the lower electrode 112 and the ferroelectric film 116 or the ferroelectric film 116 and the upper electrode as necessary. It may be formed only at the interface of 120. When the doping film is formed only at the interface between the lower electrode 112 and the ferroelectric film 116, the heat treatment should be performed immediately after the ferroelectric film 116 is formed.

The present invention is described in more detail with reference to the following experimental examples, which are not intended to limit the present invention.

Experimental Example

A platinum film to be used as the lower electrode was formed on the semiconductor substrate by using a sputtering method using argon plasma under a 4 mTorr pressure and 400 ° C. temperature. Next, a lanthanum titanium oxide film was formed on the platinum film to a thickness of 10 Å using an atomic layer deposition method. Subsequently, a PZT film was formed on the lanthanum titanium oxide film by a sol-gel method, and then a lanthanum titanium oxide film having a thickness of 10 Å was formed. Next, the PZT film was stabilized and heat-treated for 30 minutes under an oxygen atmosphere at a temperature of 700 to 750 ° C. to dope the lanthanum atoms of the lanthanum titanium oxide film into the PZT film. A platinum film was formed on the heat-treated result as the upper electrode. The leakage current was measured about the sample thus obtained. The results are shown in graph 1 of FIG.

As a control for comparison with the results of the present invention, a capacitor consisting of a platinum film-PZT film-platinum film was formed according to a conventional method, and leakage current was also measured. The results are also shown in graph 2 in FIG. 4.

From the results of FIG. 4, when lanthanum atoms are doped only on the upper and lower surfaces of the PZT film according to the present invention, lead lanthanum zirconium titanium oxide films ((Pb, La) (Zr, Ti) O ₃ ) are formed only on the upper and lower surfaces of the PZT film. As a result, leakage current was much reduced.

According to the present invention, a ferroelectric memory capacitor is formed at an interface between a ferroelectric film and an electrode by having a doping film including atoms capable of compensating for the reduction of negative charges due to oxygen vacancies in the ferroelectric film, respectively, in the lower and / or upper portion of the ferroelectric film. Effectively reducing the oxygen vacancies. Therefore, while maintaining the characteristics of the ferroelectric film, it is possible to solve the problem of oxygen vacancies to implement a FRAM device having excellent reliability.

Claims (13)

A ferroelectric memory capacitor comprising a lower electrode, a ferroelectric film formed on the lower electrode, and an upper electrode formed on the ferroelectric film, A first doping film including atoms capable of compensating negative charge loss due to oxygen vacancies generated in the ferroelectric film between the lower electrode and the ferroelectric film and / or between the ferroelectric film and the upper electrode in the ferroelectric film A ferroelectric memory capacitor comprising a second doping film containing an atom capable of compensating negative charge loss due to oxygen vacancies generated. The ferroelectric memory of claim 1, wherein each of the lower electrode and the upper electrode is made of any one selected from the group consisting of a metal oxide film, a conductive metal oxide film, and a composite film of an oxide resistant metal film and a conductive metal oxide film. Capacitors. The metal oxide film of claim 2, wherein the metal oxide film is formed of a platinum film (Pt), an iridium film (Ir), a ruthenium film (Ru), a rhodium film (Rh), an osmium film (Os), and a palladium film (Pd). The conductive metal oxide layer may be any one selected from among ruthenium oxide (RuO ₂ ), iridium oxide (IrO ₂ ), strontium ruthenium oxide (SrRuO ₃ ), calcium strontium ruthenium oxide (CaSrRuO ₃ ), and barium strontium ruthenium oxide (BaSrRuO ₃ ). Ferroelectric memory capacitor, characterized in that any one selected from the group consisting of. The method of claim 1, wherein the first doping film and the second doping film is a lanthanum titanium oxide film (LaTiO ₃ ), barium titanium oxide film (BaTiO ₃ ), calcium titanium oxide film (CaTiO ₃ ), strontium titanium oxide film (SrTiO ₃ ) and A ferroelectric memory capacitor, characterized in that composed of any one selected from the group consisting of a composite film. The ferroelectric film of claim 1, wherein the ferroelectric film includes a strontium titanium oxide film (SrTiO ₃ ), a barium titanium oxide film (BaTiO ₃ ), a barium strontium titanium oxide film ((Ba, Sr) TiO ₃ ), and a lead zirconium titanium oxide film (Pb (Zr, Ti). 0 ₃ ), strontium bismuth tantalum oxide film (SrBi ₂ Ta ₂ O ₉ ), lead lanthanum zirconium titanium oxide film ((Pb, La) (Zr, Ti) O ₃ ) and bismuth titanium oxide film (Bi ₄ Ti ₃ O ₁₂ ) A ferroelectric memory capacitor, characterized in that consisting of any one selected from the group. A method of manufacturing a ferroelectric memory capacitor, comprising forming a lower electrode on a semiconductor substrate and forming a ferroelectric film on the lower electrode, Before forming the ferroelectric film, forming a first doping film on the lower electrode, the first doping film including atoms capable of compensating negative charge loss due to oxygen vacancies generated in the ferroelectric film; And And heat-treating the resultant ferroelectric film formed after the forming of the ferroelectric film to crystallize the ferroelectric film and doping atoms in the first doping film into the ferroelectric film. According to claim 6, Before the heat treatment step, And forming a second doping film on the ferroelectric film, the second doping film including atoms capable of compensating negative charge loss due to oxygen vacancies generated in the ferroelectric film. The heat treatment step is a step of crystallizing the ferroelectric film by heat-treating the resultant material on which the second doping film is formed, and doping the atoms in the first doping film and the atoms in the second doping film into the ferroelectric film, And forming the upper electrode after the heat treatment step. The method of claim 6 or 7, wherein the lower electrode and the upper electrode using any one selected from the group consisting of a metal oxide film, a conductive metal oxide film, and a composite film of a metal oxide film and a conductive metal oxide film, respectively. Forming a ferroelectric memory capacitor. The metal oxide film of claim 8, wherein the metal oxide film is formed of a platinum film (Pt), an iridium film (Ir), a ruthenium film (Ru), a rhodium film (Rh), an osmium film (Os), and a palladium film (Pd). The conductive metal oxide layer may be any one selected from among ruthenium oxide (RuO ₂ ), iridium oxide (IrO ₂ ), strontium ruthenium oxide (SrRuO ₃ ), calcium strontium ruthenium oxide (CaSrRuO ₃ ), and barium strontium ruthenium oxide (BaSrRuO ₃ ). The method of manufacturing a ferroelectric memory capacitor, characterized in that any one selected from the group consisting of. The method of claim 6 or 7, wherein the first doping film and the second doping film is a lanthanum titanium oxide film (LaTiO ₃ ), barium titanium oxide film (BaTiO ₃ ), calcium titanium oxide film (CaTiO ₃ ), strontium titanium oxide film ( SrTiO ₃ ) and a method for manufacturing a ferroelectric memory capacitor, characterized in that formed using any one selected from the group consisting of a composite film. The method of claim 6 or 7, wherein the ferroelectric film is a strontium titanium oxide film (SrTiO ₃ ), barium titanium oxide film (BaTiO ₃ ), barium strontium titanium oxide film ((Ba, Sr) TiO ₃ ), lead zirconium titanium oxide film (Pb ( Zr, Ti) 0 ₃ ), strontium bismuth tantalum oxide film (SrBi ₂ Ta ₂ O ₉ ), lead lanthanum zirconium titanium oxide film ((Pb, La) (Zr, Ti) O ₃ ) and bismuth titanium oxide film (Bi ₄ Ti ₃ O ₁₂ ) A method of manufacturing a ferroelectric memory capacitor, characterized in that formed using any one selected from the group consisting of. A method of manufacturing a ferroelectric memory capacitor, comprising: forming a lower electrode on a semiconductor substrate, forming a ferroelectric film on the lower electrode, and forming an upper electrode on the ferroelectric film, Forming a doping film on the ferroelectric film including an atom capable of compensating negative charge loss due to oxygen vacancies generated in the ferroelectric film before forming the upper electrode; And And heat-treating the resultant material on which the doping film is formed to crystallize the ferroelectric film and doping atoms in the doping film into the ferroelectric film. The method of claim 12, wherein a film for the doped lanthanum titanium oxide (LaTiO _3), barium titanium oxide (BaTiO _3), calcium titanium oxide (CaTiO _3), strontium titanium oxide (SrTiO _3), and from the group consisting of a composite film A method of manufacturing a ferroelectric memory capacitor, characterized in that formed using any one selected.