JP2003282826A - Ferroelectric thin film memory and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a ferroelectric thin film capacitor is damaged by the hydrogen caused by a process during the course of manufacturing a ferroelectric memory. <P>SOLUTION: After the ferroelectric thin film capacitor is formed, the capacitor is coated with an MgO thin film. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric thin film memory and its manufacturing method.

[0002]

2. Description of the Related Art A non-volatile memory device (ferroelectric memory device) utilizing spontaneous polarization peculiar to a ferroelectric substance is not limited to a conventional non-volatile memory because of its features such as high-speed writing / reading and low voltage operation. , SRAM (static RAM) or D
It has the potential to replace most memory such as RAM. Lead zirconate titanate (PZ
T) and other perovskite type oxides and SrBi2Ta2O
Bismuth layered compounds such as 9 have attracted attention.

Generally, 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 the 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 such reduction deterioration of the ferroelectric capacitor due to hydrogen, a method of forming a ferroelectric thin film capacitor and then forming a protective film so as 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.

[0005]

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. Electrochem. Soc. 136,1740 (1989) and Surface Sc
In ience 144, 451 (1984), resistance to a reducing atmosphere was investigated between IrOx films prepared by different film forming methods. 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, it is stated that the IrOx thin film obtained by oxidizing the surface of single crystal Ir is not reduced even in a hydrogen atmosphere at a high temperature 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. However, since IrOx has conductivity, it needs to be formed only on the upper electrode of the capacitor. In order to prevent hydrogen from penetrating from the side wall of the capacitor, an insulating hydrogen barrier film that covers the side wall is required.

As the insulating hydrogen barrier film, various oxides have been studied as promising materials. For example, JP 10
-321811 has titanates, zirconates, niobates,
Tantalate, stannate, hafnate and manganate are applied. However, since these oxides come into contact with the ferroelectric on the side wall of the capacitor, it is necessary to pay attention to mutual element diffusion at both interfaces. In particular, if a thermal process is performed after forming these oxides as a hydrogen barrier film, a reaction may occur at the interface, and the crystallinity of the ferroelectric thin film may be destroyed in this region. It was necessary to select a material having a function as a hydrogen barrier and a compatibility with the ferroelectric thin film.

The method of manufacturing a ferroelectric thin film element according to the present invention comprises:
The purpose is to prevent the characteristic deterioration of the ferroelectric thin film due to the process by coating the thin film material that has a good compatibility with the ferroelectric thin film and has a sufficient barrier effect against hydrogen on the ferroelectric capacitor. There is.

[0008]

According to another aspect of the present invention, there is provided a ferroelectric thin film memory in which a semiconductor substrate and a lower electrode, an oxide ferroelectric thin film, and an upper electrode are sequentially laminated on the substrate. In a ferroelectric thin film memory comprising a configured ferroelectric thin film capacitor and an insulating film and a wiring layer coated on the surface of the capacitor, the insulating film contains magnesium as a main component. According to the above configuration, since the insulating film functions as an excellent hydrogen barrier film, it has an effect of preventing deterioration of the ferroelectric during the process.

According to another aspect of the ferroelectric thin film memory of the present invention,
The insulating film contains magnesium oxide. According to the above configuration, there is an effect that the hydrogen barrier performance of the insulating film is further improved.

According to another aspect of the ferroelectric thin film memory of the present invention,
An oxide is continuously coated on the insulating film. According to the above configuration, the insulating film is not exposed to the atmosphere during the process, and thus the insulating film itself can be prevented from being deteriorated by moisture.

According to another aspect of the ferroelectric thin film memory of the present invention,
A nitride is continuously coated on the insulating film. According to the above configuration, the insulating film is not exposed to the atmosphere during the process, and thus the insulating film itself can be prevented from being deteriorated by moisture.

According to a fifth aspect of the ferroelectric thin film memory,
It is characterized in that the oxide contains aluminum as a main component. According to the above configuration, the oxide itself also exhibits the hydrogen barrier performance, so that the capacitor can be protected more effectively.

According to another aspect of the ferroelectric thin film memory of the present invention,
The nitride contains aluminum as a main component. According to the above configuration, the nitride itself also exhibits the hydrogen barrier performance, so that the capacitor can be protected more effectively.

According to a seventh aspect of the present invention, there is provided a method of manufacturing a ferroelectric thin film memory, in which a lower electrode, an oxide ferroelectric thin film and an upper electrode are sequentially laminated on a semiconductor substrate to form a ferroelectric thin film capacitor. And a method of manufacturing a ferroelectric thin film memory including a step of coating an oxide film containing magnesium as a main component as an insulating film on the ferroelectric thin film capacitor,
After the oxide film is formed, the oxide film is annealed. According to the above method, the crystallinity of the oxide containing magnesium as a main component is improved, and the hydrogen barrier performance is remarkably improved.

A method of manufacturing a ferroelectric thin film memory according to an eighth aspect of the present invention is characterized in that a temperature of the annealing treatment is equal to or lower than a firing temperature of the oxide ferroelectric thin film. According to the above method, the crystallinity of the oxide ferroelectric thin film is not impaired, and therefore, the performance of the capacitor can be prevented from deteriorating.

The ferroelectric thin film memory manufactured by the manufacturing method of the present invention has a strong hydrogen barrier formed without affecting the crystallinity of the oxide ferroelectric thin film. After that, excellent capacitor performance is promised and excellent memory blocking function is demonstrated.

[0017]

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

(Embodiment 1) First, the stacking process of a ferroelectric thin film element will be schematically described with reference to FIG. Switching transistor 102 on single crystal silicon substrate 101
Then, a MOS transistor and an element isolation region 103 are formed, and a boron phosphorus-doped silicon oxide film (BPSG) 104 is further formed as an interlayer insulating film.

Next, a resist pattern for forming a contact hole was formed by a lithography process, and then the contact hole was opened by a dry etching method. After depositing the polysilicon film, phosphorus was doped. Subsequently, the polysilicon film was polished by chemical mechanical polishing to form a polysilicon plug 105 in the contact hole.

Next, a titanium nitride film was formed as a barrier metal layer 106 for the lower electrode and the polysilicon plug 105 by the sputtering method. Platinum 107 was formed as a lower electrode on this. The laminated structure obtained by the above steps is shown in FIG.

An organic solution containing strontium, bismuth and tantalum was applied onto platinum 107 by spin coating 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, by performing oxygen annealing treatment at 700 ° C for 1 hour, SrBi2Ta2 which is a crystalline thin film is formed.
O9 (hereinafter referred to as SBT) 108 was obtained. Platinum 109 was formed as an upper electrode on this by a sputtering method.

Next, the lower electrode, the SBT thin film and the upper electrode were patterned to a desired size to form an SBT thin film capacitor. After performing annealing treatment in oxygen atmosphere again, cover the surface of this capacitor.
The MgO thin film 110 was formed by the sputtering method.
On top of this, TEOS (Tet
A raethylorthosilicate) film 111 was deposited. After forming an opening for making electrical contact with the upper electrode of the ferroelectric thin film capacitor, a metal wiring 112 was formed. The resulting device structure is shown in FIG. This is especially called the stack type and is one of the memory cell structures aimed at high integration (Sample 1). On the other hand, for comparison, a TEOS film was directly formed without forming an MgO thin film on the surface of the SBT thin film capacitor to fabricate a memory cell (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.

FIG. 3 shows the hysteresis loop immediately after forming the SBT capacitor. 4 and 5 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,
It can be seen that in Sample 2, 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 varies depending on the presence or absence of the MgO thin film formed 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 is a major factor causing deterioration of the characteristics of the capacitor.
In Sample 2, since the TEOS film is formed right above the ferroelectric thin film capacitor, hydrogen is considered to easily enter the inside of the capacitor. Due to the reduction of the SBT thin film, the original ferroelectric property of the film was greatly impaired, and the hysteresis property was significantly deteriorated. On the other hand, in Sample 1, the MgO thin film is formed on the ferroelectric thin film capacitor before the TEOS film is formed. It is considered that this MgO thin film blocks hydrogen generated in the TEOS film formation process and prevents hydrogen from entering the inside of the SBT thin film. Forming a MgO thin film with good hydrogen barrier performance on a ferroelectric thin film capacitor is extremely important for blocking hydrogen generated due to the subsequent process. The body thin film memory promises excellent device performance because it fully exhibits the original film performance.

(Example 2) Similar to the method described in Example 1, an SBT thin film capacitor was produced on a circuit board incorporating a switching transistor. MgO on this
A thin film was formed by the sputtering method. Further, an oxide or nitride film was continuously formed thereon. In this example, a sample (Sample 3) on which TiOx was formed and Al
A sample (Sample 4) on which N was deposited was prepared.

A TEOS (Tetraethylorthosilicate) film was further deposited thereon by plasma chemical vapor deposition. After forming an opening for making electrical contact with the upper electrode of the ferroelectric thin film capacitor, metal wiring was formed. The resulting device structure is shown in FIG.

In order to evaluate the electric characteristics of the ferroelectric thin film capacitor, the hysteresis characteristics were examined by the same method as that described in Example 1. For the purpose of quantitative discussion, here we decided to compare the polarization charge amounts when the applied voltage is zero in the hysteresis loop. This is called the remanent polarization amount, and the positive / negative value corresponds to the stored information “1” or “0”. Simply speaking, the larger the absolute value of this value, the more advantageous it is to use as a memory element. In this example, the residual polarization amount was investigated from the hysteresis loop obtained with an applied voltage of ± 3V. The results of Sample 1 (described in Example 1) are summarized in Table 1.

[0029]

[Table 1]

As is clear from Table 1, the remanent polarization amount is larger in Samples 3 and 4 than in Sample 1. It can be said that Samples 3 and 4 exhibit more excellent ferroelectric characteristics.

In Sample 1 and Sample 3 or Sample 4,
The difference in structure is only the film structure on MgO formed as a hydrogen barrier film. Samples 3 and 4 are Ti on MgO.
Ox or AlN is formed. On the other hand, the sample 1 is only MgO. This difference is
It greatly affects the atmosphere to which gO is exposed.

In each of Sample 1, Sample 3, and Sample 4, the next step is TEOS film formation. After the hydrogen barrier film is formed, when the substrate is exposed to the atmosphere at the stage of shifting to the next step,
Moisture in the atmosphere is adsorbed on the sample surface. In Sample 1, moisture is adsorbed on the outermost surface of MgO. However, M
Since gO is unstable with respect to moisture, the crystallinity of the surface is significantly impaired by the chemical reaction. Also, TEO
Even in the atmosphere for forming the S film, water is generated as a by-product, which may adversely affect the MgO thin film. The MgO thin film with disordered crystallinity cannot exhibit the original hydrogen barrier performance. On the other hand, in Samples 3 and 4, TiOx and AlN are continuously formed on MgO, respectively. When the sample is exposed to the atmosphere or T
These films act as a barrier film against moisture generated during EOS film formation. Since the MgO thin film does not come into direct contact with water, the crystallinity of MgO is not disturbed. Therefore, sufficient barrier performance for hydrogen is maintained throughout the process. This appears as an electric characteristic of the capacitor as shown in Table 1. TiO on the MgO surface
The capacitor formed with x or AlN has better characteristics, and it is considered that the hydrogen barrier performance of MgO was exhibited more stably.

Example 3 Similar to the method described in Example 1, an SBT thin film capacitor was produced on a circuit board incorporating a switching transistor. MgO on this
A thin film of 20 nm was formed by the sputtering method. Further, an Al2O3 film having a thickness of 20 nm was continuously formed thereon (Sample 5).
On the other hand, for comparison, only Al2O3 instead of MgO 40
A sample having a film thickness of nm was prepared (Sample 6). On top of this, TEOS (Tetraethylorthosi
licate) film was deposited. After forming an opening for making electrical contact with the upper electrode of the ferroelectric thin film capacitor, metal wiring was formed.

In order to evaluate the electrical characteristics of the ferroelectric thin film capacitor, in this example, the residual polarization amount was examined from the hysteresis loop obtained with an applied voltage of ± 3V. The results are summarized in Table 2.

[0035]

[Table 2]

As is clear from Table 2, the remanent polarization amount of the sample 5 is larger than that of the sample 6, and it can be said that the sample 5 exhibits more excellent ferroelectric characteristics. It was found that sample 5 had less deterioration of characteristics due to hydrogen.

In both samples, the film thickness of the insulating film formed on the capacitor is the same. It is considered that the difference in hydrogen barrier performance between the two samples depends not on the film thickness of the barrier film but on the material and configuration.

In sample 6, Al 2 O 3 was used as the hydrogen barrier film.
Only the film was formed. As compared with Sample 1 in Example 1, it can be seen that the hydrogen barrier performance itself is almost the same as that of MgO. It can be said that the function as hydrogen barrier performance can be fully expected. However, the sample 5 in which MgO and Al 2 O 3 are laminated has better capacitor characteristics than the sample in which the individual films are used as hydrogen barriers. M
It can be seen that the laminated structure of gO and Al2O3 further improves the hydrogen barrier performance.

As shown in Example 2, forming an appropriate insulating film on the MgO thin film is effective in preventing the crystallinity deterioration of MgO itself due to moisture.
In this example, it is considered that Al2O3 played a role of protecting MgO from moisture. A sufficient hydrogen barrier performance was maintained without disturbing the crystallinity of MgO. Further, Al2O3 itself used in this example also has an excellent hydrogen barrier performance. MgO fully exhibits the original hydrogen barrier performance, and the protective film Al2
Since O3 also exhibits the hydrogen barrier performance, extremely excellent capacitor characteristics were secured even after the process.

Example 4 Similar to the method described in Example 1, an SBT thin film capacitor was produced on a circuit board incorporating a switching transistor. MgO on this
A thin film was formed by the sputtering method. Here once
The substrate was annealed in an oxygen atmosphere. The annealing temperature was set lower than the crystallization temperature of SBT so that compositional deviation would not occur due to element evaporation from SBT. Next, TEOS (Tetraethylortho
silicate) film was deposited. Subsequently, after forming an opening for making electrical contact with the upper electrode of the ferroelectric thin film capacitor, a metal wiring was formed (Sample 7).

In order to evaluate the electrical characteristics of the ferroelectric thin film capacitor, in this example, the residual polarization amount was examined from the hysteresis loop obtained with an applied voltage of ± 3V. The results are summarized in Table 3.

[0042]

[Table 3]

As is apparent from the table, the remanent polarization amount is larger in the sample 7 which is heat-treated after forming the MgO film than in the sample 1 (described in Example 1). It was found that in sample 7, reduction deterioration during the process was suppressed.

The difference between Sample 7 and Sample 1 lies only in the presence or absence of heat treatment after forming the MgO thin film. It is considered that there was a difference in hydrogen barrier performance depending on the presence or absence of heat treatment. When the crystallinity of MgO was examined for both samples, it was found that the sample subjected to the heat treatment had better crystallinity. This seems to greatly influence the resistance of MgO to moisture or hydrogen. It was suggested that MgO, which has improved crystallinity by heat treatment, is more resistant to moisture adsorbed during the process and is also excellent in hydrogen barrier performance. It is considered that MgO exhibits an extremely excellent hydrogen barrier performance by heat treatment after film formation.

[0045]

As described above, since the ferroelectric thin film memory of the present invention is provided with the MgO thin film having an extremely excellent hydrogen barrier performance on the ferroelectric thin film capacitor, it is caused by the process. It is possible to suppress the reduction deterioration of the ferroelectric substance from the generated hydrogen. The reliability as a memory device has been remarkably improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a substrate structure in Sample 1.

FIG. 2 is a diagram showing a cross-sectional structure of Sample 1.

FIG. 3 shows initial hysteresis characteristics measured in Sample 1 or Sample 2.

FIG. 4 shows the hysteresis characteristics after metal wiring measured in Sample 1.

FIG. 5 shows hysteresis characteristics after metal wiring measured in Sample 2.

FIG. 6 is a diagram showing a sectional structure of Sample 3 or Sample 4;

[Explanation of symbols]

101. Silicon substrate 102. Switching transistor 103. Element isolation region 104. Interlayer insulating film 105. Polysilicon plug 106. Barrier metal layer 107. Platinum 108. SBT thin film 109. Platinum 110. MgO thin film 111. SiO2 112. Metal wiring 601. Silicon substrate 602. Switching transistor 603. Element isolation region 604. Interlayer insulating film 605. Polysilicon plug 606. Barrier metal layer 607. Platinum 608. SBT thin film 609. Platinum 610. MgO thin film 611. Sample 3 is a TiOx thin film, and Sample 4 is an AlN thin film 612. SiO2 613. Metal wiring

Claims (9)

[Claims] 1. A semiconductor substrate and a semiconductor substrate provided on the substrate,
A ferroelectric memory comprising a ferroelectric thin film capacitor formed by sequentially laminating a lower electrode, an oxide ferroelectric thin film, and an upper electrode, and an insulating film and a wiring layer coated on the surface of the capacitor. A ferroelectric thin film memory characterized in that an insulating film contains magnesium as a main component. 2. The ferroelectric thin film memory according to claim 1, wherein the insulating film contains magnesium oxide. 3. The ferroelectric thin film memory according to claim 2, wherein an oxide is continuously coated on the insulating film. 4. The ferroelectric thin film memory according to claim 2, wherein the insulating film is continuously covered with a nitride. 5. The ferroelectric thin film memory according to claim 3, wherein the oxide contains aluminum as a main component. 6. The ferroelectric thin film memory according to claim 4, wherein the nitride contains aluminum as a main component. 7. A step of forming a ferroelectric thin film capacitor by sequentially laminating a lower electrode, an oxide ferroelectric thin film, and an upper electrode on a semiconductor substrate, and magnesium as an insulating film on the ferroelectric thin film capacitor. A method of manufacturing a ferroelectric thin film memory, which comprises a step of coating an oxide film containing as a main component, wherein the oxide film is annealed after the formation of the oxide film. . 8. The method of manufacturing a ferroelectric thin film memory according to claim 7, wherein the annealing temperature is equal to or lower than the firing temperature of the oxide ferroelectric thin film. 9. A ferroelectric thin film memory manufactured by the manufacturing method according to claim 7.