JP2001338834A - Method of manufacturing dielectric capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a ferroelectric capacitor which is possessed of a small leakage current, excellent in reliability, and manufactured with its yield high. SOLUTION: A ferroelectric film precursor is deposited on the lower electrode of a capacitor and subjected to a thermal process through a manner in which the film precursor is heated at a high temperature rise rate till it reaches a temperature higher than its crystallization temperature, the precursor is kept at the above temperature for a short time for crystallization. The above thermal process is carried out several times for the crystallization of the film precursor. By these processes, a dense and flat dielectric film having large crystal grains can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric (ferroelectric) used for a storage element such as a semiconductor memory element or a ferroelectric memory element, or other semiconductor integrated circuit elements.
The present invention relates to a method for manufacturing a capacitor.

[0002]

2. Description of the Related Art Ferroelectrics have many functions such as spontaneous polarization, high dielectric constant, electro-optic effect, piezoelectric effect and pyroelectric effect, and are therefore applied to a wide range of device development. For example, the pyroelectricity is used for an infrared linear array sensor, the piezoelectricity is used for an ultrasonic sensor, the electro-optic effect is used for a waveguide type optical modulator, and the high dielectric property is used. Utilizing DRAM and MMIC capacitors,
It is used in various directions.

[0003] Above all, with the development of thin film forming technology in recent years, in combination with semiconductor memory technology, a ferroelectric nonvolatile memory (FRA) operating at high density and high speed has been developed.
M) has been actively developed. A nonvolatile memory using a ferroelectric thin film has characteristics such as high-speed write / read, low-voltage operation, and high write / read durability.
Not only replacement of conventional non-volatile memory, but also SRAM
Research and development are being actively conducted for practical use as a memory that can be replaced with a DRAM. To develop such a device, a material having a large remanent polarization (Pr), a small coercive electric field (Ec), a low leak current, and a high resistance to repetition of polarization reversal is required. Moreover,
In order to reduce the operating voltage and adapt to the semiconductor microfabrication process, it is desirable to realize the above characteristics with a thin film having a thickness of 200 nm or less.

As a ferroelectric or high dielectric material used in these applications, oxide materials having a perovskite structure represented by PZT (lead zirconate titanate, Pb (Ti, Zr) O3) are mainly used. Was. However, PZ
A material containing lead as its constituent element, such as T, has a high vapor pressure of lead or its oxide, so that the lead component evaporates during film formation to cause defects in the film, and in severe cases, a pinhole. To form As a result, there are disadvantages such as an increase in leakage current and a fatigue phenomenon in which the magnitude of spontaneous polarization decreases when the polarization inversion is repeated. In particular, regarding the fatigue phenomenon, considering replacement of a DRAM with a ferroelectric nonvolatile memory, it is necessary to guarantee that there is no change in characteristics even after 10 ¹⁵ polarization inversions. The development of was desired.

On the other hand, in recent years, SBT (SrBi2
Research and development of bismuth layered structure compound materials typified by Ta2O9) have been conducted. The bismuth layer structure compound material is characterized by excellent fatigue properties, in which no change is observed in properties even after polarization reversal more than 10 ¹² times.

[0006] Ferroelectric thin films can be produced by physical methods such as vacuum deposition, sputtering, and laser ablation, or by using organometallic compounds as starting materials and thermally decomposing and oxidizing them to form oxide ferroelectrics. Sol-gel method or MOD method for obtaining a body, MOCVD (Metal Organic)
ic Chemical Vapor Deposit
Chemical methods such as the (ion) method are used.

[0007] Among the above film forming methods, sol-gel method or MO
In method D, the composition control is easy and the reproducibility is excellent by using a homogeneous mixed material solution at the atomic level, and a large area film can be formed at normal pressure without the need for a special vacuum apparatus. It is widely used because of its low industrial cost.

In the process of forming a bismuth layered compound thin film, a ferroelectric thin film or a dielectric thin film is manufactured by the following steps.

1) A step of applying a precursor solution composed of a complex alkoxide or the like on a substrate by spin coating or the like to form a film.

2) In order to release the solvent and the alcohol and residual moisture generated in the step 1) from the film,
Heating and drying the obtained film at 150 ° C. for 30 seconds to several minutes.

3) In order to remove the organic components in the film and to crystallize the film, the temperature is raised at a rate of 0.2 ° C./sec using a firing furnace.
Step c: heating to about 700 ° C. to 800 ° C. in an oxygen atmosphere and holding for 30 minutes.

4) A step of heating and holding at 700 ° C. to 800 ° C. for 30 minutes in an oxygen atmosphere after forming the upper electrode.

In order to obtain a desired film thickness, the steps 1) to 3) are repeated, and finally the step 4) is performed.

As described above, a ferroelectric thin film or a dielectric thin film can be formed.

On the other hand, in the conventional planar type FRAM, a Pt-based material excellent in high temperature resistance is used as a capacitor electrode material. On the other hand, when a memory cell having a stacked capacitor structure (hereinafter referred to as an STC structure) in which a high degree of integration can be obtained by forming a capacitor element on a contact plug connected to a source or a drain of a transistor, Pt is required. However, there is a problem that the contact plug is oxidized due to easy passage of oxygen, causing a contact failure, and mutual diffusion of elements between the ferroelectric and the plug occurs. Accordingly, Ir-based materials having excellent oxygen barrier properties and mutual diffusion prevention properties have been attracting attention as STC structure electrode materials. In recent years, in a capacitor using PZT for a ferroelectric material, when an Ir-based material is used for an electrode,
It has been reported that the fatigue deterioration characteristics of a capacitor are improved (Japanese Patent Laid-Open No. 07-245237).

[0016]

In the above-described conventional method of manufacturing a ferroelectric thin film, the ferroelectric thin film manufactured by performing a crystallization step before forming the upper electrode is annealed. When formed on an integrated circuit, the temperature is extremely high and the annealing time is long, and there is a problem of damage such as contact failure and characteristic deterioration due to mutual diffusion and oxidation between the via hole material and the electrode.

In the case where an Ir-based material is used for the lower electrode of the capacitor, there are the following problems. After the lower electrode is formed, when a heat treatment process for forming a ferroelectric thin film is performed, a large number of precipitates composed of Ir oxide are generated in the ferroelectric thin film. The precipitate short-circuits the lower electrode and the upper electrode of the capacitor to increase the leakage current of the capacitor, resulting in a decrease in capacity and an increase in operating current. In addition, the step due to the precipitate causes a wiring failure in a subsequent wiring process.

When Ir is heated in direct contact with oxygen, segregation of IrO2 occurs. Therefore, when a ferroelectric thin film is formed by a spin coating method, application and baking of a solution are repeated several times. At this time, the thickness of the ferroelectric film formed by one coating and baking process is several tens nm. And thin,
If the ferroelectric film is not sufficiently dense, an oxygen leak path is easily generated from the grain boundary. Further, when the particle diameter of the ferroelectric film is small, the penetration of oxygen from the grain boundary increases, which promotes the formation of precipitates.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and can form a dense and flat dielectric film having a large grain size as compared with a conventional manufacturing method.
In addition, by reducing the crystallization temperature and shortening the crystallization time, damage to contact plugs and electrodes can be reduced, and a highly reliable dielectric capacitor with a small leakage current can be manufactured at a high yield. It is an object of the present invention to provide a method for manufacturing a dielectric capacitor.

[0020]

According to a first aspect of the present invention, there is provided a method of manufacturing a dielectric capacitor comprising a lower electrode, a dielectric film, and an upper electrode. A precursor solution applying step of applying a body solution, and rapidly heating the precursor film coated and formed in the step to a predetermined temperature higher than the crystallization temperature of the dielectric film, and then maintaining the temperature to crystallize. A film forming step including a heat treatment step for changing the thickness is repeated a predetermined number of times to form the dielectric film having a predetermined thickness on the lower electrode.

Further, according to the method of manufacturing a dielectric capacitor of the present invention (second invention), in the method of manufacturing a dielectric capacitor of the first invention, the heating rate in the heat treatment step is 10 ° C.
/ Sec or more. Here, when the heating rate is higher than 200 ° C./sec, the overshoot of the furnace temperature becomes large at the time of heating, and stable temperature control becomes difficult, so the heating rate is 200 ° C./sec.
The following is desirable.

Further, according to the method of manufacturing a dielectric capacitor of the present invention (third invention), in the method of manufacturing a dielectric capacitor of the first or second invention, the heating temperature is equal to the crystallization temperature of the dielectric film. A temperature higher than 50 ° C.
In addition, the holding time is 10 minutes or less. Here, the heating temperature is set at 50 degrees from the crystallization temperature.
If the temperature is higher than 0 ° C., cracks (cracks) due to stress are likely to occur at the time of raising the temperature. Therefore, the heating temperature is desirably equal to or lower than (crystallization temperature + 500 ° C.).

In the method for manufacturing a dielectric capacitor according to the present invention (fourth invention), in the method for manufacturing a dielectric capacitor according to the first to third inventions, the number of repetitions of the film forming step is three or more. It is characterized by the following. Here, if the number of repetitions is more than 10, the process takes too much time. Therefore, the number of repetitions is desirably 10 or less.

The method for manufacturing a dielectric capacitor according to the present invention (fifth invention) is the same as the method for manufacturing a dielectric capacitor according to any one of the first to fourth inventions, except that the one
It is characterized in that the film thickness applied at a time is 10 nm or more and 100 nm or less. Here, when the film thickness applied at one time is smaller than 10 nm, it takes too much time to obtain a ferroelectric film having a sufficient film thickness. Since cracks due to stress tend to occur, the film thickness applied at a time is 1
It is desirable that the thickness be 0 nm or more and 100 nm or less.

Further, in the method of manufacturing a dielectric capacitor according to the present invention (sixth invention), the method of manufacturing a dielectric capacitor according to any of the first to fifth inventions, wherein the lower electrode is an Ir electrode and the dielectric film is Is a ferroelectric film made of a bismuth-based layered compound.

The method of applying the precursor solution is as follows.
For example, a spin coating method or the like can be used.

As the precursor, for example, an organic metal salt containing a metal carboxylate or alkoxide as a component is used.

[0028]

Embodiments of the present invention will be described below in detail.

(First Embodiment) A method for manufacturing a dielectric capacitor according to a first embodiment of the present invention will be described with reference to FIG.

First, as shown in FIG.
A silicon oxide film 102 having a thickness of 300 nm is formed on the silicon oxide film 102 by thermal oxidation, and the Ti adhesion layer 103 and the TaSi
The N barrier metal layer 104 has a thickness of 20 nm and 5 nm, respectively.
It is formed with a thickness of 0 nm. Further, the barrier metal layer 10
4 on the Ir lower electrode 105 by sputtering.
To form

Next, as shown in FIG.
MOD (Metal Organic De)
composition method) to form a ferroelectric thin film 106
Was formed. SBT precursor solution (solution composition ratio: S
r / Bi / Ta = 8/24/20) is applied by spin coating to a thickness of about 30 nm, followed by a drying process at 250 ° C. for 5 minutes, and then a crystallization heat treatment in an oxygen atmosphere (RTA:
Rapid Thermal Annealing) was performed. The heat treatment is performed at a substrate temperature of 700 as a conventional condition.
° C, a heating rate of 0.2 ° C / sec, and a baking time of 30 minutes, and a heating rate of 2 ° C / sec at a substrate temperature of 700 ° C.
The crystallization heat treatment in an oxygen atmosphere was performed for a total of five types, including four types of ℃ / sec, 20 ° C / sec, and 30 ° C / sec, and firing for 5 minutes. This step was repeated a total of five times to obtain an SBT film 106 having a thickness of about 150 nm. Here, the substrate temperature is set to the crystallization temperature (600 in case of SBT).
If the temperature is not higher than 50 ° C. or more, the grains do not grow sufficiently and sufficient ferroelectric characteristics cannot be obtained. Therefore, it is desirable that the substrate temperature be higher than the crystallization temperature by 50 ° C. or more.
Further, if the firing is performed for 10 minutes or more, the three-dimensional growth of the particles proceeds and the flatness of the film is lost.
0 minutes or less is desirable. Further, if the number of repetitions of the precursor solution application to obtain a ferroelectric film of a predetermined thickness is two or less (one applied film thickness becomes large), a rapid temperature increase in the firing step is performed. At times, a large stress is applied to the film, causing cracks, which may cause a breakdown voltage failure of the capacitor.
It is preferable that the film thickness applied at one time be thin (100 nm or less) and the number of repetitions is three or more.

The SBT thin film 106 thus formed
The value of Rmax (maximum level difference of the film) and the particle size of AFM (A
The measurement was performed using a tomical force microscope (atomic force microscope). The result is shown in FIG.

The particle size of SBT is such that the heating rate during heating is 10
When the temperature is slower than ° C / sec, the particle size is 20 equivalent to the conventional condition.
Although the particle diameter is smaller than 0 nm, the particle diameter sharply increases when the heating rate is 10 ° C./sec or more, and a size of 200 nm or more is obtained. In addition, the value of Rmax is almost the same as that of the conventional condition and that of the heating rate of 10 ° C./sec or more, and the surface morphology is not roughened due to the increase in the particle size. . The reason why the value of Rmax is large in a region where the rate of temperature rise is lower than 10 ° C./sec is that the grains did not grow sufficiently and were stacked in an island state with a gap between the grains. From this result, it can be seen that the sample having a temperature rising rate of 10 ° C./sec or more maintains the same surface smoothness as the conventional condition while being composed of large grains.

Next, the surface of the ferroelectric layer of each sample was observed using an optical microscope, and the number of generated foreign substances was examined. The result is shown in FIG.

In a capacitor manufactured at a temperature rising rate of 10 ° C./sec or more, a large amount of precipitates observed under conventional conditions are sufficiently suppressed. This is because the firing process time has been greatly reduced, and because the grains are large and have a dense structure, there are fewer grain boundaries than when the grains are small, and oxygen enters from the grain boundaries. It is due to being suppressed. If the heating rate is lower than 10 ° C./sec, the grains are not sufficiently grown, and there are gaps between the grains, which are leak paths for oxygen. Is not completely suppressed.

Next, a Pt upper electrode 107 was formed on the ferroelectric film thus obtained, and heat treatment was performed again at 700 ° C. to evaluate the ferroelectric characteristics of the capacitor. FIG.
Then, using a known Sawyer tower circuit for each sample, 3V
And the leakage current density also measured at 3V.

For a sample having a temperature rise rate of 10 ° C./sec or more, ΔQ was 11 μC / cm ² and the leak current density was 1 × 1.
0 ^-7 A / cm ² , sufficient characteristics as a ferroelectric capacitor were confirmed. The same ΔQ as before even if the firing time is short
Is obtained because the grains are large. The reason why the value of the leak current density is sufficiently small is that the film is dense and the surface is flat.

From the above results, it was confirmed that a film having a small amount of foreign matter and sufficient ferroelectric characteristics could be formed.

(Second Embodiment) Next, the formation of a ferroelectric memory element using the structure of the first embodiment will be described with reference to FIG.
This will be described with reference to FIG.

First, a LOCOS film 502 having a thickness of about 5000 ° is formed on the surface of a silicon substrate 501 to form an element isolation region. Next, after a select transistor including the gate electrode 503 and the source / drain regions 504a and 504b is formed, a first silicon oxide film 505 is formed as an interlayer insulating film by a CVD method at a thickness of about 5000.degree. A 6 μm contact hole is formed. Next, C
After the polysilicon is buried by the VD method, the surface is flattened by the CMP method to form a polysilicon plug 506. Next, as shown in the first embodiment, after the polysilicon is wet-treated with hydrofluoric acid, the Ti film 50 is formed on the polysilicon plug 506 by DC magnetron sputtering.
7 is formed on the polysilicon plug 506 at 200 °.
Thereafter, a TaxSi1-xNy film 508 as a diffusion barrier film is formed by DC reactive magnetron sputtering.
(0.2 ≦ x ≦ 1, 0 ≦ y ≦ 1) on the Ti film 507 by 5
00 ° is formed. Subsequently, an Ir film 509 serving as a lower electrode was formed thereon by a DC magnetron sputtering method for 200 nm.
m. Next, an SBT film 510 is formed on the Ir film 509 by using a spin-on method. The heat treatment is performed at a temperature rising rate of 10 ° C./sec, and all other conditions are the same as in the first embodiment. Next, after a Pt film 511 having a thickness of 1000 ° is formed by DC magnetron sputtering,
The upper Pt electrode 511 is formed to have a size of 1 to 3 μm square by a dry etching method using Cl 2. The underlying SBT film 510 was processed by dry etching using C2F6 and Ar. Subsequently, the I formed under it
The r lower electrode 509, the TaxSi1-xNy diffusion barrier film 508, and the Ti film 507 are processed by a dry etching method using Cl2 and C2F6.

After that, a second silicon oxide film 512 is formed as an interlayer insulating film by using the CVD method, a contact hole is formed, and an upper Pt of the ferroelectric capacitor is formed.
An aluminum extraction electrode 513 from the electrode 511 is formed by DC magnetron sputtering. Next, a contact hole is formed on the source region 504a, and an aluminum lead electrode 514 is formed. Thus, a ferroelectric memory element as shown in FIG. 5 is finally manufactured.

By applying a triangular wave voltage between the aluminum extraction electrode 513 from the upper Pt electrode 511 and the aluminum extraction electrode 514 from the source region 504a of the dielectric capacitor manufactured by the above-described process. A hysteresis curve was obtained. In addition,
The electric field strength of the applied triangular wave was 150 kV / cm, and the frequency was 75 Hz. The ferroelectric property is ΔQ =
12 μC / cm ² , leak current density 1 × 10 ⁻⁷ A / c
m ² and the withstand voltage were 10 V or more. From these results, ferroelectric characteristics of a sufficient size to be used as a ferroelectric capacitor were obtained. Further, when the surface was observed using an optical microscope, almost no IrO2-like foreign matter was found.

In the above embodiment, SBT is used as the material of the ferroelectric film. However, the present invention is not limited to this, and PZT, SrBi2Nb2O
9, SrBi2 (Ta, Nb) 2O9, Bi4Ti3O
12, SrBi4Ti4O15, SrBi4 (Ti, Z
r) 4O15, CaBi2Ta2O9, BaBi2Ta
2O9, BaBi2Nb2O9, PbBi2Ta2O9
The present invention is applicable to any material that can be formed into a film by a sol-gel method or a MOD method, such as.

[0044]

As described above in detail, according to the method for manufacturing a dielectric capacitor of the present invention, the heat treatment time at the highest attainable temperature which affects the damage of the element has conventionally been at 800 ° C. for 150 minutes or more. However, according to the present invention, sufficient characteristics can be obtained at, for example, a heat treatment temperature of 700 ° C. and a time of 1/6 or less, and the film formation temperature can be lower than that of the conventional manufacturing method. This makes it possible to shorten the film forming time.

In addition, the dielectric thin film formed by the manufacturing method of the present invention can realize the densification and flattening of the film in spite of the large crystal grains, can reduce the leak current, and have the high withstand voltage. It is possible to obtain a dielectric thin film.

As a result of these effects, according to the manufacturing method of the present invention, damage to contact plugs and electrodes can be reduced, and a highly reliable ferroelectric capacitor having a small leak current can be manufactured at a high yield. You can do it.

[Brief description of the drawings]

FIG. 1 is a structural diagram of a dielectric capacitor for explaining a method of manufacturing a dielectric capacitor according to a first embodiment of the present invention.

FIG. 2 is a graph showing a temperature rise rate according to the first embodiment of the present invention;
It is a graph which shows the relationship between Rmax (maximum level | step difference of a film) and a particle size.

FIG. 3 is a graph showing a relationship between a heating rate and the number of foreign substances in the first embodiment of the present invention.

FIG. 4 is a graph showing a temperature rise rate and a temperature increase rate according to the first embodiment of the present invention;
It is a graph which shows the relationship between (DELTA) Q (storage charge amount) and leak current density.

FIG. 5 is a sectional view of a memory element for explaining a method of manufacturing a ferroelectric memory element according to a second embodiment of the present invention.

[Explanation of symbols]

101 Silicon substrate 102 Silicon oxide film 103 Ti adhesion layer 104 TaSiN barrier metal layer 105 Ir lower electrode 106 SrBi2Ta2O9 film 107 Pt upper electrode 501 Silicon substrate 502 Locos film 503 Gate electrode 504a Source region 504b Drain region 505 First silicon oxide film 506 Polysilicon plug 507 Ti film 508 TaxSi1-xNy diffusion barrier film 509 Ir lower electrode 510 SBT film 511 Upper Pt electrode 512 Second silicon oxide film 513 Aluminum lead electrode from upper Pt electrode 514 Aluminum lead electrode from source region

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 27/105 H01L 27/10 444B 27/108 651 21/8242 F-term (Reference) 4G048 AA05 AB02 AB05 AC02 AD02 AE08 5E082 AB03 BB10 BC38 EE05 EE23 EE37 FG03 FG26 FG54 KK01 MM24 PP05 PP06 PP08 PP09 PP10 5F058 BA11 BC03 BD05 BF46 BH01 BH03 BJ02 5F083 AD21 FR02 GA21 JA15 JA17 JA35 JA36 JA38 JA39 PR40 PR03

Claims (6)

[Claims] 1. A method for manufacturing a dielectric capacitor comprising a lower electrode, a dielectric film, and an upper electrode, comprising: a precursor solution application step of applying a precursor solution of the dielectric film; and a precursor coated by the step. The body film is rapidly heated to a predetermined temperature higher than the crystallization temperature of the dielectric film, and thereafter, a film formation step including a heat treatment step of performing crystallization while maintaining the temperature is repeatedly performed a predetermined number of times. A method for manufacturing a dielectric capacitor, comprising forming the dielectric film having a predetermined thickness on the lower electrode. 2. The heating rate of the heat treatment step is 10 ° C./s.
The method of claim 1, wherein the value is at least ec. 3. The method according to claim 1, wherein the heating temperature is higher than the crystallization temperature of the dielectric film by 50 ° C. or more, and the holding time is 10 minutes or less.
3. The method for manufacturing a dielectric capacitor according to item 1. 4. The method for producing a dielectric capacitor according to claim 1, wherein the number of repetitions is three or more. 5. The dielectric capacitor according to claim 1, wherein the thickness of the precursor solution applied at one time is 10 nm or more and 100 nm or less. Production method. 6. The method according to claim 1, wherein the lower electrode is an Ir electrode, and the dielectric film is a ferroelectric film made of a bismuth-based layered compound. Of manufacturing a dielectric capacitor.