JPH10200060A - Method for manufacturing ferroelectric capacitor - Google Patents

Abstract

(57) [Problem] It is desired to provide a method for manufacturing a ferroelectric capacitor capable of suppressing the occurrence of a polarization offset and making it usable. A method of manufacturing a ferroelectric capacitor in which a crystallized oxide ferroelectric material is annealed with an activated oxygen-containing gas. Preferably, the activated oxygen is ozone or plasma oxygen. In the case of ozone or oxygen in the form of plasma, the annealing temperature in the annealing process is set to 300 ° C.
As described above, the temperature is preferably set to 500 ° C. or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric capacitor used for a nonvolatile memory and the like.
The present invention relates to a method for manufacturing a ferroelectric capacitor capable of suppressing the polarization offset.

[0002]

2. Description of the Related Art A ferroelectric capacitor is formed by providing a lower electrode and an upper electrode on a thin film made of a ferroelectric material. For example, a ferroelectric capacitor is incorporated and used as a constituent element in a nonvolatile memory or the like. ing.

[0003] By the way, such a ferroelectric capacitor is, for example, MRS BU by William L. Warren and the like.
As introduced on pages 40 to 45 of LLETIN, Volume 21, No. 7 (July 1996), a phenomenon called polarization offset often occurs in the ferroelectric hysteresis characteristics. That is, in the ferroelectric capacitor, the ferroelectric thin film has a hysteresis curve indicating the relationship between the applied voltage and the amount of polarization charge with respect to the applied voltage. It must be in a state of spreading. In this case, the center of the hysteresis curve may not be located on the reference line and may be largely shifted upward or downward, and such a phenomenon is called the polarization offset. is there.

Although such a polarization offset has not been elucidated exactly, it is a phenomenon that occurs due to oxygen deficiency or the like generated at an oxide ferroelectric, particularly at an interface between the ferroelectric and an electrode. It is considered. In other words, the polarization offset is a phenomenon related to the characteristics of the ferroelectric itself, and is caused by a difference in structure between the upper electrode and the lower electrode in the ferroelectric capacitor and a difference in adhesion between the ferroelectric and the electrode. It is different from the phenomenon.

[0005]

By the way, conventionally, for example, when a nonvolatile memory is manufactured, when a characteristic test of the ferroelectric capacitor is performed and the above-mentioned polarization offset occurs in the capacitor, this is corrected. Since it is very difficult to return to a normal state for the following reasons, the nonvolatile memory itself incorporating this capacitor is
Treated as defective. That is, when a polarization offset occurs, a high temperature (6
(00 to 800 ° C.) for a long time (30 to 60 minutes), this can be suppressed to some extent.

However, such a high-temperature and long-time annealing treatment not only damages the ferroelectric capacitor itself but also causes a large damage to the nonvolatile memory itself incorporating the ferroelectric capacitor. However, even if this is improved, another inconvenience will result. Further, if the annealing process is performed for a long time, the throughput is reduced, and it is extremely difficult at present to perform such a process.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method of manufacturing a ferroelectric capacitor capable of suppressing the occurrence of polarization offset and making it usable. Is to do.

[0008]

In the method of manufacturing a ferroelectric capacitor according to the present invention, the method comprises annealing the crystallized oxide ferroelectric material with an activated gas containing oxygen. This was the solution to the problem. As the activated oxygen, ozone or plasma oxygen is preferable. When the ozone or the plasma oxygen is used as the activated oxygen, the annealing temperature in the annealing process is set to 300 ° C. or more,
The temperature is preferably set to 00 ° C. or lower.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for manufacturing a ferroelectric capacitor according to the present invention will be described in detail based on an embodiment.

(Embodiment 1) A ferroelectric capacitor is
It was produced as follows. First, on a silicon substrate,
An SiO ₂ film was formed to a thickness of about 300 nm by a thermal oxidation method, and a Ti (titanium) film serving as an adhesion layer was formed to a thickness of 30 nm on the SiO ₂ film by a sputtering method. Further, a Pt (platinum) film serving as a lower electrode was formed thereon to a thickness of 200 nm by a sputtering method.

Next, a film having a crystal phase of SrBi ₂ Nb ₂ O ₉ as a main crystal phase as an oxide-based ferroelectric was formed to a thickness of about 200 nm on the Pt film by a sol-gel method. . The oxide ferroelectric (SrBi ₂ Nb ₂ O)
_{As the} film formation method by the sol-gel method of ₉ ), first, the solution composition is Sr; 0.7, Bi; 2.4, Nb;
This is spin-coated using a raw material solution adjusted to a molar ratio of 0, O; 9.0, and then dried to remove the solvent. Next, RTA treatment at 600 to 800 ° C. for 30 seconds is performed in an oxygen atmosphere. Then, such a series of processes is repeated until a film having a desired thickness is obtained, and thereafter, crystallization promotion annealing is performed at 800 ° C. for 1 hour in an oxygen atmosphere.

After an oxide ferroelectric (SrBi ₂ Nb ₂ O ₉ ) film thus crystallized is formed, a Pt film serving as an upper electrode is formed thereon by sputtering to a thickness of 200 nm. Formed. After forming the upper electrode in this manner, annealing was performed in oxygen at 800 ° C. for 15 minutes to strengthen the adhesion of the upper electrode (Pt film) to the oxide ferroelectric film.

The ferroelectric capacitor thus manufactured was measured for ferroelectric hysteresis characteristics. FIG. 2 shows the obtained results. As shown in FIG. 2, in the obtained ferroelectric capacitor, the center of the hysteresis curve is largely shifted downward from the reference line A where the polarization charge amount is zero, and thus the polarization offset is reduced. I knew it was awake.

In order to suppress the polarization offset and obtain the original ferroelectric hysteresis characteristics, the following processing according to the present invention was performed. That is, the ferroelectric capacitor in which the polarization offset has occurred was annealed for 10 minutes by heating the substrate temperature to 400 ° C. in an oxygen atmosphere in which ozone was mixed at a volume ratio of 1%. Then, the ferroelectric hysteresis characteristics of the ferroelectric capacitor after the annealing were measured again. The results obtained are shown in FIG.

As shown in FIG. 1, it was found that the center of the hysteresis curve was substantially on the reference line A, and thus normal ferroelectric hysteresis characteristics without polarization offset were obtained. Therefore, it was confirmed that the annealing treatment of the present invention can improve the ferroelectric hysteresis characteristics of a ferroelectric capacitor in which a polarization offset has occurred.

Embodiment 2 In the same manner as in Embodiment 1, a SiO ₂ film, a Ti film, and a Pt film serving as a lower electrode were formed on a silicon substrate. Next, SrBi ₂ Nb was formed as an oxide ferroelectric on the Pt film by MOCVD.
A film having a crystal phase of ₂ O ₉ as a main crystal phase is approximately 200 nm.
It was formed in thickness. This oxide ferroelectric (SrBi ₂
The film forming conditions of Nb ₂ O ₉ ) by the MOCVD method include:
Substrate temperature 400-500 ° C, oxygen pressure 5-10 Torr
Range. After this film formation, crystallization promotion annealing was performed at 800 ° C. for 1 hour in an oxygen atmosphere.

After the oxide ferroelectric (SrBi ₂ Nb ₂ O ₉ ) film thus crystallized is formed, a Pt film serving as an upper electrode is formed thereon in the same manner as in the first embodiment. Then, annealing was performed at 800 ° C. for 15 minutes in oxygen to strengthen the adhesion of the upper electrode (Pt film) to the oxide ferroelectric film. When the ferroelectric hysteresis characteristics of the ferroelectric capacitor thus manufactured were measured, the same result as that shown in FIG. 2 was obtained, and the formed ferroelectric capacitor had a polarization offset. I understood.

In order to suppress the polarization offset and obtain the original ferroelectric hysteresis characteristic, the first embodiment is explained.
The same processing as described above was performed. That is, the ferroelectric capacitor in which the polarization offset has occurred is heated at a substrate temperature of 400 ° C. in an oxygen atmosphere containing ozone mixed at 1% by volume.
And annealed for 10 minutes. When the ferroelectric hysteresis characteristics of the ferroelectric capacitor after the annealing treatment were measured again, the same result as the result shown in FIG. 1 was obtained. Therefore, also in the second embodiment, it was found that the formed ferroelectric capacitor had normal ferroelectric hysteresis characteristics without polarization offset. Therefore, also in this example, it was confirmed that the annealing treatment of the present invention can improve the ferroelectric hysteresis characteristics of the ferroelectric capacitor in which the polarization offset has occurred.

(Embodiment 3) In the same manner as in Embodiment 1, a SiO ₂ film, a Ti film, and a Pt film serving as a lower electrode were formed on a silicon substrate. Next, SrBi ₂ was formed as an oxide ferroelectric on the Pt film by a plasma CVD method.
A film having Nb ₂ O ₉ crystal as a main crystal phase was formed into a film of about 300
It was formed to a thickness of nm. This oxide-based ferroelectric (SrB
When forming the film of i ₂ Nb ₂ O ₉ ), the substrate temperature was set at 20.
The test was performed at 0 to 400 ° C. Then, after this film formation, RTA processing is performed at 785 ° C. for 30 seconds in an oxygen atmosphere.
After that, crystallization promotion annealing was performed at 800 ° C. for 1 hour in an oxygen atmosphere.

After the oxide ferroelectric (SrBi ₂ Nb ₂ O ₉ ) film thus crystallized is formed, a Pt film serving as an upper electrode is formed thereon in the same manner as in the first embodiment. Then, annealing was performed at 800 ° C. for 15 minutes in oxygen to strengthen the adhesion of the upper electrode (Pt film) to the oxide ferroelectric film. When the ferroelectric hysteresis characteristics of the ferroelectric capacitor thus manufactured were measured, the same result as that shown in FIG. 2 was obtained, and the formed ferroelectric capacitor had a polarization offset. I understood.

Therefore, in order to suppress the polarization offset and obtain the original ferroelectric hysteresis characteristics, the first embodiment will be described.
The same processing as described above was performed. That is, the ferroelectric capacitor in which the polarization offset has occurred is heated at a substrate temperature of 400 ° C. in an oxygen atmosphere containing ozone mixed at 1% by volume.
And annealed for 10 minutes. When the ferroelectric hysteresis characteristics of the ferroelectric capacitor after the annealing treatment were measured again, the same result as the result shown in FIG. 1 was obtained. Therefore, also in the third embodiment, it was found that the formed ferroelectric capacitor had normal ferroelectric hysteresis characteristics without polarization offset. Therefore, also in this example, it was confirmed that by performing the annealing treatment of the present invention, the ferroelectric hysteresis characteristics of a ferroelectric capacitor in which a polarization offset has occurred can be improved.

Embodiment 4 In the same manner as in Embodiment 1, an SiO ₂ film, a Ti film, and a Pt film serving as a lower electrode were formed on a silicon substrate. Next, SrBi ₂ was formed as an oxide ferroelectric on the Pt film by a sputtering method.
A film having a crystal phase of Nb ₂ O ₉ as a main crystal phase is formed by about 200
It was formed to a thickness of nm. This oxide-based ferroelectric (SrB
i ₂ Nb ₂ O ₉ ) was formed by sputtering under the conditions of a substrate temperature of 200 to 400 ° C., an RF power of 5
The film forming pressure was set to 5 to 10 mTorr, and the flow ratio of argon to oxygen was set to 2: 1. After this film formation, crystallization promotion annealing was performed at 800 ° C. for 1 hour in an oxygen atmosphere.

After the oxide ferroelectric (SrBi ₂ Nb ₂ O ₉ ) film thus crystallized is formed, a Pt film serving as an upper electrode is formed thereon similarly to the first embodiment. Then, annealing was performed at 800 ° C. for 15 minutes in oxygen to strengthen the adhesion of the upper electrode (Pt film) to the oxide ferroelectric film. When the ferroelectric hysteresis characteristics of the ferroelectric capacitor thus manufactured were measured, the same result as that shown in FIG. 2 was obtained, and the formed ferroelectric capacitor had a polarization offset. I understood.

Therefore, in order to suppress the polarization offset and obtain the original ferroelectric hysteresis characteristics, the first embodiment will be described.
The same processing as described above was performed. That is, the ferroelectric capacitor in which the polarization offset has occurred is heated at a substrate temperature of 400 ° C. in an oxygen atmosphere containing ozone mixed at 1% by volume.
And annealed for 10 minutes. When the ferroelectric hysteresis characteristics of the ferroelectric capacitor after the annealing treatment were measured again, the same result as the result shown in FIG. 1 was obtained. Therefore, also in the fourth embodiment, it was found that the formed ferroelectric capacitor had normal ferroelectric hysteresis characteristics without polarization offset. Therefore, also in this example, it was confirmed that the annealing treatment of the present invention can improve the ferroelectric hysteresis characteristics of the ferroelectric capacitor in which the polarization offset has occurred.

Fifth Embodiment In the same manner as in the first embodiment, an SiO ₂ film, a Ti film, and a Pt film serving as a lower electrode are formed on a silicon substrate. Next, a laser ablation method was used to form an oxide ferroelectric on the Pt film as S
A film having rBi ₂ Nb ₂ O ₉ crystal as a main crystal phase is
It was formed to a thickness of about 200 nm. The oxide ferroelectric material (SrBi ₂ Nb ₂ O ₉ ) is formed by a laser ablation method using a Kr-F excimer laser with a laser energy density of ² J / cm ² and a frequency of 5 to 10 Hz. The substrate temperature was 200 to 400 ° C., and the oxygen pressure was 20 to 500 mTorr. After this film formation, crystallization promotion annealing was performed at 800 ° C. for 1 hour in an oxygen atmosphere.

After the crystallized oxide ferroelectric (SrBi ₂ Nb ₂ O ₉ ) film is formed, a Pt film serving as an upper electrode is formed thereon in the same manner as in the first embodiment. Then, annealing was performed at 800 ° C. for 15 minutes in oxygen to strengthen the adhesion of the upper electrode (Pt film) to the oxide ferroelectric film. When the ferroelectric hysteresis characteristics of the ferroelectric capacitor thus manufactured were measured, the same result as that shown in FIG. 2 was obtained, and the formed ferroelectric capacitor had a polarization offset. I understood.

Therefore, in order to suppress the polarization offset and obtain the original ferroelectric hysteresis characteristics, the first embodiment will be described.
The same processing as described above was performed. That is, the ferroelectric capacitor in which the polarization offset has occurred is heated at a substrate temperature of 400 ° C. in an oxygen atmosphere containing ozone mixed at 1% by volume.
And annealed for 10 minutes. When the ferroelectric hysteresis characteristics of the ferroelectric capacitor after the annealing treatment were measured again, the same result as the result shown in FIG. 1 was obtained. Therefore, also in the fifth embodiment, it was found that the formed ferroelectric capacitor had normal ferroelectric hysteresis characteristics without polarization offset. Therefore, also in this example, it was confirmed that the annealing treatment of the present invention can improve the ferroelectric hysteresis characteristics of the ferroelectric capacitor in which the polarization offset has occurred.

(Comparative Example 1) Annealing treatment using ozone according to the present invention is performed on a sample which has been subjected to crystallization annealing in Embodiment 1, that is, a ferroelectric capacitor having a polarization offset as shown in FIG. Was performed in an oxygen atmosphere at 800 ° C. for 1 hour. Then, the ferroelectric hysteresis characteristics of the ferroelectric capacitor after the annealing were measured again. The results obtained are shown in FIG. As shown in FIG. 5, it was found that the center of the hysteresis curve was considerably close to the reference line A, and thus the polarization offset was significantly improved. However, it is still insufficient compared with the embodiment of the present invention shown in FIG. 1, and it has been found that the annealing treatment according to the present invention is superior.

(Embodiment 6) A ferroelectric capacitor is
It was produced as follows. First, on a silicon substrate,
An SiO ₂ film was formed to a thickness of about 300 nm by a thermal oxidation method. Subsequently, a Ti (titanium) film serving as an adhesion layer was formed to a thickness of 20 nm on the SiO ₂ film by a sputtering method. Further, a Pt (platinum) film serving as a lower electrode was formed thereon to a thickness of 200 nm by a sputtering method.

Next, Pb (Zr, Ti) O ₃ as an oxide-based ferroelectric substance was formed on the Pt film by a sol-gel method.
Was formed into a film having a thickness of about 300 nm, in which the above-mentioned crystal was used as a main crystal phase. This oxide-based ferroelectric (Pb (Zr, T
i) As a method of forming a film of O ₃ ) by the sol-gel method, first, the solution composition is Pb: 1.0, Zr: 0.53, T
i: The raw material solution adjusted to a molar ratio of 0.47 is spin-coated, and subsequently dried at 200 to 400 ° C. to remove the solvent. Then, these treatments are repeated until the obtained film has a desired thickness.
The crystallization promotion annealing is performed at 50 ° C. for 1 hour. The oxide-based ferroelectric (Pb (Zr, T
i) After the O ₃ ) film was formed, a Pt film serving as an upper electrode was formed thereon to a thickness of 200 nm by a sputtering method. Then, after forming the upper electrode in this manner, annealing was performed in oxygen at 650 ° C. for 10 minutes to strengthen the adhesion of the upper electrode (Pt film) to the oxide-based ferroelectric film.

The ferroelectric hysteresis characteristics of the ferroelectric capacitor thus manufactured were measured, and the results are shown in FIG. As shown in FIG. 4, in the obtained ferroelectric capacitor, the center of the hysteresis curve is largely shifted downward from the reference line A where the polarization charge amount is zero, and thus the polarization offset is reduced. I knew it was awake.

Therefore, in order to suppress the polarization offset and obtain the original ferroelectric hysteresis characteristics, the following processing according to the present invention was performed. That is, the ferroelectric capacitor in which the polarization offset has occurred was annealed for 10 minutes by heating the substrate temperature to 400 ° C. in an oxygen atmosphere in which ozone was mixed at a volume ratio of 1%. Then, the ferroelectric hysteresis characteristics of the ferroelectric capacitor after the annealing were measured again. FIG. 3 shows the obtained results.

As shown in FIG. 3, it was found that the center of the hysteresis curve was substantially on the reference line A, and thus normal ferroelectric hysteresis characteristics without polarization offset were obtained. Therefore, it was confirmed that the ferroelectric capacitor in which polarization offset has occurred can be improved in the ferroelectric hysteresis characteristics also in this embodiment by performing the annealing treatment of the present invention.

In the above embodiment, SrBi ₂ Nb ₂ O is used as the crystallized oxide ferroelectric material.
₉ , an example using Pb (Zr, Ti) O ₃ has been described. However, the present invention is not limited to these examples. For example, Bi ₄ Ti ₃ O ₁₂ , SrBi ₂ Ta ₂ O ₉ , PbT
iO _3, such as BaTiO ₃ can also be used.

In the above embodiment, ozone is used as activated oxygen in the annealing process of the present invention. Alternatively, for example, plasma oxygen may be used. Further, as the annealing atmosphere gas containing such activated oxygen, oxygen was used in the above-described embodiment, but the present invention is not limited thereto.
An inert gas such as nitrogen or argon can be used. However, it is inevitable that oxygen will be contained in the atmosphere due to the need to generate ozone or plasma oxygen as activated oxygen. In other words, when generating ozone, for example, oxygen is generated by passing oxygen through an ozone generator. However, all the oxygen passed through the ozone generator does not become ozone, and the ozone generation efficiency is usually several percent. This is because when this ozone is allowed to flow into the atmosphere, oxygen always flows into the atmosphere.
In addition, when oxygen which is converted into plasma is used, an oxygen atmosphere is naturally formed and plasma conversion is performed there, so that oxygen which is not converted into plasma exists in the atmosphere. Therefore, even when a gas other than oxygen is used as the atmosphere gas, a mixed gas of [activated oxygen, ordinary oxygen, nitrogen] or a mixed gas of [activated oxygen, ordinary oxygen, argon], etc. As described above, this atmospheric gas always contains oxygen.

The concentration of the activated oxygen in the atmosphere gas is not particularly limited. However, if the concentration is low, the annealing time needs to be longer, and if the concentration is higher, the annealing time needs to be shorter. For this reason, it is preferable to set the volume ratio to about 0.1 to 5%. That is, if the content is less than 0.1%, the throughput is reduced due to the longer annealing time, while if it exceeds 5%, the concentration of the activated oxygen is maintained stably. Because it is difficult.

Further, when ozone or plasma oxygen is used as the activated oxygen as described above, the annealing temperature in the annealing process is set to 30.
It is preferable that the temperature be 0 ° C or more and 500 ° C or less. The reason is that ozone and oxygen in the form of plasma are relatively stable in the above-mentioned temperature range, have a long life, and can maintain the activated state for a long period of time. This is because it is easy to stabilize.

[0038]

As described above, the method of manufacturing a ferroelectric capacitor according to the present invention is a method of annealing a crystallized oxide-based ferroelectric material with an activated oxygen-containing gas. Therefore, by using oxygen activated in this way, it is possible to obtain a low
The polarization offset can be suppressed in a short time of about a minute. Therefore, conventionally, at high temperatures (600 to 800)
C) for a long time (30 to 60 minutes), the polarization offset could be suppressed to some extent, but in that case, devices such as nonvolatile memories incorporating the same would be damaged. While this process could not be performed, according to the present invention, when the test revealed that a polarization offset had occurred, the above-described annealing process of the present invention performed the polarization offset. Thus, the original ferroelectric hysteresis characteristics can be easily restored.

Therefore, a ferroelectric capacitor or a device incorporating the ferroelectric capacitor which has been practically impossible to use and has been treated as a defective product can be made a good product by suppressing its polarization offset. The yield of a ferroelectric capacitor or a device incorporating the ferroelectric capacitor can be remarkably improved as compared with the related art. Moreover, as described above, the annealing process according to the present invention can be performed in a short period of time, so that the yield can be effectively improved without lowering the throughput and without increasing the manufacturing cost.

[Brief description of the drawings]

FIG. 1 is a graph showing ferroelectric hysteresis characteristics of a ferroelectric capacitor obtained by performing an annealing process according to the present invention.

FIG. 2 is a graph showing ferroelectric hysteresis characteristics of a ferroelectric capacitor in which polarization offset has occurred before an annealing process according to the present invention is performed.

FIG. 3 is a graph showing ferroelectric hysteresis characteristics of a ferroelectric capacitor obtained by performing an annealing process according to the present invention.

FIG. 4 is a graph showing ferroelectric hysteresis characteristics of a ferroelectric capacitor in which a polarization offset has occurred before an annealing process according to the present invention is performed.

FIG. 5 is a graph showing ferroelectric hysteresis characteristics of a conventional ferroelectric capacitor obtained by performing an annealing process at a high temperature for a long time.

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI H01L 29/792

Claims (3)

[Claims] 1. A method of manufacturing a ferroelectric capacitor, comprising annealing a crystallized oxide-based ferroelectric material with an activated oxygen-containing gas. 2. The method according to claim 1, wherein said activated oxygen is ozone or plasma oxygen. 3. The method for manufacturing a ferroelectric capacitor according to claim 2, wherein an annealing temperature in said annealing treatment is 300 ° C. or more and 500 ° C. or less.