JP2003282830A - Ferroelectric thin film memory - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a ferroelectric thin film is not protected sufficiently from hydrogen caused by a process even when the thin film is made of a material having excellent hydrogen barrier ability, because the thin film is difficult to be formed on a capacitor with high crystallinity. <P>SOLUTION: The capacitor is isolated from a hydrogen atmosphere by catching the hydrogen caused by a process by providing a material having a hydrogen storing property on the capacitor instead of a hydrogen barrier film. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION A non-volatile memory device (ferroelectric memory device) utilizing spontaneous polarization peculiar to a ferroelectric substance is
Due to its features such as high-speed writing / reading and low-voltage operation, it has the possibility of replacing not only conventional non-volatile memory but also most memories such as SRAM (static RAM) and DRAM. Ferroelectric materials include lead zirconate titanate (PZT) and other perovskite oxides and S.
Bismuth layered compounds such as rBi2Ta2O9 are receiving attention.

In general, when the above oxide material is used as a capacitor insulating layer, it is covered with an interlayer insulating film such as SiO 2 for the purpose of electrical insulation between memory elements after the upper electrode is formed. As the film forming method, C having excellent step coverage is used.
The VD (Chemical Vapor Deposition) method is generally used. However, when such a film forming method is used, hydrogen is generated as a reaction by-product. In particular, when activated hydrogen permeates SiO 2 and the upper electrode and reaches the ferroelectric thin film, the reducing action thereof causes the ferroelectric characteristics to be significantly deteriorated. Also, as a switching element
Since the characteristics of the MOS transistor deteriorate due to lattice defects in the silicon single crystal generated in the device manufacturing process, it is necessary to perform heat treatment in hydrogen-mixed nitrogen gas at the final stage. However, the hydrogen concentration in this step is higher than when the interlayer insulating film is formed, and the damage to the ferroelectric thin film becomes more serious.

In order to overcome the reduction degradation of the ferroelectric capacitor due to hydrogen, a method of forming a ferroelectric thin film capacitor and then forming a protective film to cover the ferroelectric thin film capacitor to prevent the invasion of hydrogen is tried. Has been. This protective film is generally called a hydrogen barrier film.

[0004]

2. Description of the Related Art Oxide materials have been vigorously studied as promising candidates for hydrogen barrier films. IrOx is a typical example, and reduction resistance is investigated. For example, J. Electr
ochem.Soc.136,1740 (1989) and Surface Science 144,451
In (1984), between IrOx films produced by different film formation methods,
Resistance to reducing atmosphere has been investigated. According to these reports, the easiness of reduction varies greatly depending on the difference in crystallinity, and IrOx with better crystallinity has better hydrogen resistance. As an example, Ir obtained by oxidizing the surface of single crystal Ir
It is published that the Ox thin film is not reduced even in a high temperature hydrogen atmosphere near 700 ° C. When such an IrOx thin film having good crystallinity is formed on the capacitor, IrOx itself is less likely to be reduced even in a hydrogen atmosphere, and a sufficient hydrogen barrier effect can be expected. In addition, various oxides have been studied as potential materials for the hydrogen barrier film. For example, in JP-A-10-321811, titanate, zirconate, niobate, tantalate, stannate, hafnate, and manganate are applied.

[0005]

In order for the above-mentioned various materials to exhibit excellent hydrogen barrier performance, it is premised that all of them have good crystallinity. Although a sputtering method or the like is generally used for film formation, the above-mentioned oxide materials generally have a high melting point. Even if a film is formed using these materials as a target, the thin film usually becomes amorphous. Post-annealing treatment is effective for obtaining a dense crystalline thin film, but treatment at a temperature higher than the crystallization temperature of the ferroelectric material is not preferable. This is because the crystallinity of the ferroelectric substance is deteriorated and the original ferroelectric characteristics are impaired. Even if there are materials with excellent hydrogen barrier performance,
Since it is difficult to form a film with good crystallinity, the problem is that the expected hydrogen barrier effect cannot be obtained.

According to the present invention, a new material replacing the conventional hydrogen barrier film is provided in the periphery of the capacitor,
The purpose is to protect the ferroelectric from hydrogen generated due to the process and guarantee the performance as a memory device.

[0007]

A ferroelectric thin film memory according to claim 1 is a ferroelectric thin film formed by sequentially laminating a lower electrode, an oxide ferroelectric thin film and an upper electrode on a semiconductor substrate. A capacitor, a protective film layer covering the surface of the capacitor, an opening provided on the upper electrode of the protective film layer, and a wiring layer formed on the protective film layer and in the opening. In the ferroelectric thin film memory described above, a thin film having a hydrogen storage property is deposited as the protective film layer. According to the above configuration, hydrogen generated due to the process is captured by the protective film of the capacitor, so that the capacitor can be isolated from the hydrogen atmosphere.

According to another aspect of the ferroelectric thin film memory of the present invention,
A hydrogen barrier film is formed between the ferroelectric capacitor and the hydrogen storage thin film. According to the above configuration, it is possible to prevent hydrogen released from the material having a hydrogen storage property from reaching the ferroelectric substance.

According to a third aspect of the ferroelectric thin film memory,
The area of the opening provided in the thin film having the hydrogen storage property is larger than the area S1 of the opening provided in the hydrogen barrier film.
S2 is large, and the wiring layer is not in contact with the thin film having a hydrogen storage property. According to the above configuration, there is an effect that a conductive material can be used as the thin film having a hydrogen storage property.

According to another aspect of the ferroelectric thin film memory of the present invention,
The hydrogen barrier film is an oxide containing any one of aluminum, magnesium and titanium. According to the above configuration, the hydrogen barrier film has an effect of exhibiting excellent hydrogen barrier performance.

A method of manufacturing a ferroelectric thin film memory according to a fifth aspect of the present invention is characterized in that the thin film having a hydrogen storage property is composed of a compound containing lanthanum and nickel. According to the above configuration, since the hydrogen storage property of the protective film is improved, it is possible to reduce the amount of hydrogen reaching the capacitor.

A method of manufacturing a ferroelectric thin film memory according to a sixth aspect of the present invention is characterized in that the thin film having a hydrogen storage property is composed of a compound containing magnesium and palladium. According to the above configuration, since the hydrogen storage property of the protective film is improved, it is possible to reduce the amount of hydrogen reaching the capacitor.

A method of manufacturing a ferroelectric thin film memory according to a seventh aspect is characterized in that the thin film having a hydrogen storage property is a laminated film in which magnesium and lanthanum are alternately deposited. According to the above configuration, the protective film stores hydrogen more efficiently, so that hydrogen reaching the capacitor can be further reduced.

In a method of manufacturing a ferroelectric thin film memory according to an eighth aspect, in the laminated film in which the magnesium and the lanthanum are alternately deposited, the thickness of the magnesium layer is represented by M and the thickness of the lanthanum layer is represented by L. At this time, M: L = 8: 1. According to the above configuration, since the protective film stores hydrogen most efficiently, it has an effect that hydrogen reaching the capacitor can be completely blocked.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) First, a process of forming a ferroelectric thin film element will be schematically described with reference to the drawings.

A drive circuit portion (102) of a ferroelectric memory device is formed on the substrate 101 in advance. Next, after forming a film of platinum or iridium on the entire surface by using a sputtering method or the like, this was patterned into a desired shape by etching. Here, the lower electrodes 10 arranged in parallel with each other
Formed 3. An organic solution containing strontium, bismuth, and tantalum was applied onto this by a spin coating method, and dried to obtain a precursor film. The steps of spin coating and drying were repeated until the precursor film reached the desired film thickness. Finally, an oxygen annealing treatment was performed at 700 ° C for 1 hour to form a crystalline thin film of SrBi2Ta2O9.
(Hereinafter referred to as SBT) was obtained. In addition, as a film forming method of SBT, a MOCVD method, a sputtering method, or the like can also be used. The SBT was removed by etching except the region covering the lower electrode 103 (104). Subsequently, platinum or iridium was deposited by the sputtering method. This platinum or iridium was patterned by etching to form the upper electrode 105 arranged in the direction orthogonal to the lower electrode 103 (FIG. 3). A region where the lower electrode 103 and the upper electrode 105 intersect is arranged in a matrix as shown in FIG. 3, and this intersecting region corresponds to a ferroelectric capacitor.

Al2O as a hydrogen barrier film 106 is formed on the ferroelectric capacitors arranged in a matrix as described above.
3 was deposited. As shown in FIG. 4, this Al2O3 was removed from the drive circuit portion by etching. On top of this, an alloy represented by the chemical formula of La5Ni was formed as a material 107 having a property of storing hydrogen by a sputtering method (FIG. 5). TEOS (Tetraethylort) is used as the interlayer insulating film 108.
A hosilicate) film was formed (FIG. 6), and contact holes 109 were formed on the lower electrode 103 and the upper electrode 105 (FIG. 7). Aluminum was deposited here, and wiring (110) between the ferroelectric capacitor and the drive circuit portion was performed (FIG. 8). A cross-sectional view taken along the line AB of FIG. 8 is shown in FIG. 9 (Sample 1). On the other hand, for comparison, a sample was prepared by forming an oxide film of iridium instead of La5Ni (Sample 2).

It was decided to compare the characteristics of the memory devices obtained by the respective manufacturing methods. Here, we decided to focus on the ferroelectric characteristics of the ferroelectric thin film capacitor. When an appropriate AC voltage is applied between the upper and lower electrodes, a certain amount of electric charge is induced in the upper and lower electrodes depending on the magnitude and direction of the applied voltage. To monitor this state, plotting the applied voltage on the horizontal axis and the charge amount on the vertical axis, a hysteresis loop resulting from the inversion of the polarization axis is obtained. The results are shown in FIGS. 10 to 12.

FIG. 10 shows the hysteresis loop immediately after forming the SBT capacitor. This is as shown in FIG.
Is a hysteresis loop obtained by selecting one lower electrode 103 and one upper electrode 105 and applying a voltage between these electrodes. Similarly, FIGS. 11 and 12 show the hysteresis loops obtained in Sample 1 and Sample 2, respectively. As is clear from the figure, in Sample 1, the ferroelectric characteristics are less deteriorated as compared with immediately after the formation of the SBT capacitor. On the other hand, in Sample 2, it can be seen that the hysteresis loop is thin and the characteristics are significantly deteriorated. It was clarified that a large difference in characteristics appears after the processing process due to the structural difference between the two samples. That is, it is considered that the degree of process deterioration greatly differs due to the presence or absence of La5Ni having the property of storing hydrogen deposited on the ferroelectric thin film capacitor.

In the method of manufacturing the ferroelectric memory described in this embodiment, hydrogen generated in the TEOS film forming step or the passivation film forming step is a major factor causing deterioration of the characteristics of the capacitor. In Sample 2, Al2O3 and an iridium oxide film were formed as a hydrogen barrier film on the ferroelectric thin film capacitor. However, it is considered that sufficient hydrogen barrier performance could not be obtained, and hydrogen could not be completely blocked from entering the capacitor portion. SB
Due to the partial reduction of the T thin film, the original ferroelectric properties were significantly impaired, and the hysteresis properties were significantly degraded. On the other hand, in Sample 1, before forming the TEOS film, an Al2O3 thin film was formed on the ferroelectric thin film capacitor, and La5Ni was formed thereon. It is considered that almost all hydrogen generated in the passivation film formation step is stored in La5Ni. Hydrogen stored once is not released in the subsequent process temperature range. As a result, hydrogen penetration into the capacitor part was completely prevented, and the crystallinity of the ferroelectric did not deteriorate.
Excellent ferroelectric characteristics were obtained without changing the ferroelectric characteristics from the initial state.

Capturing hydrogen by utilizing the hydrogen storage property of the specific material as in this embodiment is a very effective method for protecting the ferroelectric capacitor from hydrogen deterioration due to the process. is there. La5Ni used in this example
Is an alloy used as a hydrogen storage material in the field of fuel cells. Its hydrogen storage capacity is overwhelmingly larger than the hydrogen generated in the process. Therefore, if such a material is placed around the capacitor with an appropriate film thickness,
All process-derived hydrogen is captured. Since hydrogen intrusion into the ferroelectric capacitor is completely blocked, the conventional passivation process can be applied.

(Embodiment 2) Hydrogen barrier film 1 in FIG.
An MgO thin film was formed as No. 06. For this film formation, MgO was used as an oxide target, and reactive sputtering was used. That is, a mixed gas of argon and oxygen was used as the process gas. Further, the composition ratio in the film thickness direction was made to have a gradient by changing the mixing ratio of this process gas in the film forming process. In this example, MgO in a completely oxidized state was first formed, and MgO (1-x) having a partial oxygen deficiency was formed on the upper portion of the film. Further, palladium was deposited as a material 107 having a property of storing hydrogen on the sample to prepare a sample (Sample 3). The ferroelectric capacitor of Sample 3 was examined for electrical characteristics.
A hysteresis curve as shown in (3) was obtained. It can be seen that there is no difference when compared with the sample 1 produced in Example 1 for comparison. It was found that the ferroelectric characteristics of the capacitor maintained the initial state even after the passivation process.

In this embodiment, palladium is used as the material for storing hydrogen. This film itself has the property of absorbing hydrogen very easily. Also. This palladium is deposited on MgO as described above. Since a portion of this MgO upper portion was formed in a state of oxygen deficiency, metallic Mg was mixed. In addition, MgO itself is also unstable and easily releases oxygen and forms a compound with other materials. Here Mg
It is considered that an interface layer formed by alloying palladium with palladium was formed. This alloy of magnesium and palladium has a higher hydrogen storage performance than palladium alone. Above the capacitor, MgO originally having a hydrogen barrier performance
This means that a thin film, an alloy of magnesium and palladium having a high hydrogen storage capacity, and a simple substance of palladium are laminated on the thin film. All the hydrogen generated in the interlayer insulating film or the passivation film forming process is captured by the palladium or the alloy of palladium and magnesium and does not reach the ferroelectric capacitor. As a result, the crystallinity was maintained in the initial state without the reduction deterioration of the ferroelectric thin film. Since the capacitor performance can maintain the initial characteristics, it can be said that the reliability as a memory element is significantly improved.

Example 3 A sample was prepared by forming a laminated film of lanthanum and magnesium as the material 107 having the property of storing hydrogen in FIG. 9 (Sample 4). Sputtering was used for film formation. Here, two targets of lanthanum and magnesium were used, and the films were alternately formed by sputtering. Each film thickness can be adjusted arbitrarily. Here, we decided to deposit about 5 nm for both materials. 10 in total
After forming the film as a laminated film of about layers, the capacitor characteristics were examined after the passivation process was completed as in Example 1 or 2. The results are shown in Fig. 14.

As is apparent from the figure, no characteristic difference is recognized as compared with Sample 1 or Sample 3. It was confirmed that the capacitor characteristics equivalent to those of both samples were secured.

In this example, it is considered that the laminated structure of lanthanum and magnesium provided on the capacitor efficiently occluded hydrogen generated in the step of forming the interlayer insulating film or the passivation. Since the hydrogen that reached the capacitor was blocked, the crystallinity of the ferroelectric did not deteriorate. It is considered that excellent capacitor characteristics were obtained because the ferroelectric characteristics inherent in the film were sufficiently exhibited. This greatly contributes to improving the reliability of the memory device.

Example 4 A sample was prepared by forming a laminated film of lanthanum and magnesium as the material 107 having the property of storing hydrogen in FIG. 9 (Sample 5). Here, what is different from Sample 4 of Example 3 is the film thickness ratio of lanthanum and magnesium. In this embodiment, the layers are laminated so that the magnesium film thickness and the lanthanum film thickness are 8: 1. The actual film thickness was 8 nm for magnesium and 1 nm for lanthanum. This lamination was repeated about 10 layers to obtain a desired film thickness.
After the final passivation process, the ferroelectric characteristics of the capacitor were examined. The results are shown in Fig. 15.

As compared with the hysteresis loop measured with the capacitor of Sample 4 (FIG. 14), it is understood that Sample 5 has a more excellent ferroelectric characteristic. It was revealed from the initial characteristics that this sample did not deteriorate at all.

The difference between Sample 4 and Sample 5 is the film thickness ratio of the laminated film of magnesium and lanthanum formed in the expectation of hydrogen storage. In Sample 4, the film thickness ratio of magnesium to lanthanum was 1: 1. On the other hand, in sample 5, the film thickness ratio of magnesium to lanthanum is 8: 1. It can be said that even in the laminated structure of the same material, a difference appears in the hydrogen storage capacity depending on the film thickness ratio of each material. That is, it is considered that the film thickness ratio of magnesium to lanthanum set in the present example is more excellent in hydrogen storage capacity, so that hydrogen could be captured more reliably. By optimizing the film thickness ratio of magnesium and lanthanum, it became possible to completely prevent hydrogen from entering the capacitor.
The crystallinity of the ferroelectric did not deteriorate at all, and the initial characteristics were maintained.

[0031]

As described above, in the structure of the ferroelectric thin film memory of the present invention, the material having a hydrogen storage property is thinly arranged on the capacitor. Since all the hydrogen generated due to the process is captured by this hydrogen storage material, it does not reach the capacitor. Since the reduction deterioration of the ferroelectric substance can be prevented, the obtained memory device promises high reliability.

[Brief description of drawings]

FIG. 1 is a plan view showing the structure of a sample at the time when the lower electrode patterning process is completed in the sample 1 manufacturing process.

FIG. 2 is a plan view showing the structure of a sample at the time when a ferroelectric thin film is formed in the manufacturing process of sample 1.

FIG. 3 is a plan view showing the structure of a sample at the time when the formation of the upper electrode is completed in the manufacturing process of sample 1.

FIG. 4 is a plan view showing the sample structure at the time when the hydrogen barrier film is formed in the manufacturing process of sample 1.

FIG. 5 is a plan view showing a sample structure at the time when a material having a property of storing hydrogen is formed in the manufacturing process of sample 1.

FIG. 6 is a plan view showing the structure of a sample at the time when an interlayer insulating film is formed in the manufacturing process of sample 1.

FIG. 7 is a plan view showing a sample structure at the time when a contact hole is formed in the manufacturing process of sample 1.

FIG. 8 is a plan view showing a sample structure at the time when a wiring layer is formed in the manufacturing process of sample 1.

9 is a diagram showing a cross section of Sample 1 taken along the line AB in FIG. 8. FIG.

10 is an initial hysteresis loop measured with the ferroelectric thin film capacitor of Sample 1. FIG.

FIG. 11 is a hysteresis loop after formation of passivation measured in the ferroelectric thin film capacitor of Sample 1.

FIG. 12 is a hysteresis loop after formation of passivation measured in a ferroelectric thin film capacitor of Sample 2.

FIG. 13 is a hysteresis loop after formation of passivation measured in a ferroelectric thin film capacitor of Sample 3.

FIG. 14 shows a hysteresis loop after formation of passivation measured in a ferroelectric thin film capacitor of Sample 4.

15 is a hysteresis loop after formation of passivation measured in a ferroelectric thin film capacitor of Sample 5. FIG.

[Explanation of symbols]

101. Substrate 102. Drive circuit 103. Lower electrode 104. SBT thin film 105. Upper electrode 106. It is a hydrogen barrier film and is Al2O in Example 1.
3 thin films. In Example 2, a MgO thin film. 107. It is a material having a property of storing hydrogen, and is La5Ni in Example 1. Palladium in Example 2. A laminated film of magnesium and lanthanum in Example 3 and Example 4.

Claims (8)

[Claims] 1. A ferroelectric thin film capacitor formed by sequentially stacking a lower electrode, an oxide ferroelectric thin film and an upper electrode on a semiconductor substrate, a protective film layer coated on the surface of the capacitor, and a protective film. A ferroelectric thin film memory comprising an opening provided on the upper electrode of a film layer, and a wiring layer formed on the protective film layer and in the opening,
A ferroelectric thin film memory, wherein a thin film having a hydrogen storage property is deposited as the protective film layer. 2. The ferroelectric thin film memory according to claim 1, wherein a hydrogen barrier film is formed between the ferroelectric capacitor and the hydrogen storage thin film. 3. The area S2 of the opening provided in the thin film having the hydrogen storage property is larger than the area S1 of the opening provided in the hydrogen barrier film, and the wiring layer has the storage property of the hydrogen. The thin film does not come into contact with the thin film.
A ferroelectric thin film memory according to. 4. The ferroelectric thin film memory according to claim 1, wherein the hydrogen barrier film is an oxide containing any of aluminum, magnesium and titanium. 5. The ferroelectric thin film memory according to claim 1, wherein the thin film having a hydrogen storage property is composed of a compound containing lanthanum and nickel. 6. The ferroelectric thin film memory according to claim 1, wherein the thin film having a hydrogen storage property is composed of a compound containing magnesium and palladium. 7. The ferroelectric thin film memory according to claim 1, wherein the thin film having a hydrogen storage property is a laminated film in which magnesium and lanthanum are alternately deposited. 8. In the laminated film in which magnesium and lanthanum are alternately deposited, when the film thickness of the magnesium layer is represented by M and the film thickness of the lanthanum layer is represented by L, M: L = 8: 1. The ferroelectric thin film memory according to claim 7.