JP2658878B2 - Ferroelectric thin film capacitor and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small-sized electronic circuit device, and more particularly to a ferroelectric thin film capacitor used for a nonvolatile semiconductor memory device.

[0002]

2. Description of the Related Art Conventionally, a thin film capacitor using a ferroelectric thin film has been developed. In particular, ferroelectric thin film capacitors using lead zirconate titanate (PZT) as a ferroelectric have been widely studied. However, it has been pointed out that the so-called fatigue phenomenon in which the characteristics of PZT deteriorate when repeated polarization inversion is repeated. Therefore, when a PZT thin film capacitor is applied to a nonvolatile semiconductor memory device, the number of read / write operations is limited to 10 ⁸ (Nikkei Microdevice 199).
June 2002 P.M. 80).

[0003] Bismuth-based oxides have also been studied as ferroelectric materials other than PZT. For example, Japanese Journal of Applied Physics, Vol. 32, 4
Page 086 (JAPANESE JOURNAL O
F APPLIED PHYSICS, VOL. 3
2, P. 4086) by CVD of bismuth titanate thin film
It describes a thin film capacitor fabricated by the method. International Publication Number W
O93 / 12542 (INTERNATIONAL P
UBLICATION NUMBER WO93 / 12
No. 542) describes a nonvolatile semiconductor memory device using a memory cell composed of a bismuth-based oxide thin film capacitor such as SrBi ₂ Ta ₂ O ₉ and a transistor for charge transfer, and the fatigue characteristics of the bismuth-based oxide are extremely high. It is pointed out that it is excellent.

[0004]

In this conventional bismuth-based oxide thin film capacitor, the bismuth-based oxide exhibits remarkable anisotropy. There is a problem that the characteristic varies. That is, the bismuth-based oxide has a layered structure and has a large spontaneous polarization in the a-axis or b-axis direction, but has a very small spontaneous polarization in the c-axis direction. Therefore, when the orientation of the thin film is not uniform, the amount of spontaneous polarization changes in the plane of the substrate on which the thin film capacitor is manufactured or for each substrate.
Therefore, it becomes a serious obstacle to realize a nonvolatile memory that stores information 1 and 0 according to the amount of spontaneous polarization.

[0005]

SUMMARY OF THE INVENTION The present invention provides a ferroelectric thin film capacitor applicable to a nonvolatile semiconductor memory circuit without variation in electrical characteristics within a substrate and between substrates, and a method of manufacturing the same. is there. Therefore thin film capacitor of the present invention, by being a pair of electrodes sandwiching the predominantly <105> thin and thin film of SrBi ₂ the axis is oriented in the thickness direction _{(Ta x Nb 1-x)} 2 O 9 The above objective has been achieved.

[0006] Further, as a method for producing the same, a lower electrode layer is formed on a substrate, and a solution made of an alkoxide of strontium, bismuth, tantalum or niobium or an organic metal salt is applied on the electrode, dried, and dried. Film thickness of 20 to
Repeat crystallized at 600 to 850 ° C. in the range of _{80nm SrBi 2 (Ta x Nb 1} -x) 2 O 9 (x =
It is characterized in that a thin film of 0-1) is formed, and an upper electrode is further formed.

[0007]

FIG. 1 is a sectional view of a semiconductor memory device showing one embodiment of the thin film capacitor of the present invention. 1 is a silicon substrate, 2 is a field oxide film for element isolation, 3 is a gate insulating film, 4 is a word line of polysilicon or the like, 5 and 5 'are impurity diffusion regions serving as sources or drains of charge transfer transistors, 6 Is an interlayer insulating film, 7 is polysilicon, 8 is a titanium nitride layer serving as a silicon diffusion barrier metal layer, and 9 is a platinum layer. The platinum layer is patterned to become one electrode of each individual ferroelectric capacitor.

Next, a method of forming a ferroelectric thin film layer 10 of SrBi ₂ Ta ₂ O ₉ on this substrate will be described. 0.1 mol of diisopropoxystrontium, 0.2 mol of bismuth nitrate and 0.2 mol of tetraethoxytantalum are dissolved in 100 ml of glacial acetic acid, and heated and stirred at 100 ° C. for 24 hours. After diluting this solution to 0.1 M with xylene, the substrate is spin-coated at 3000 rpm for 1 minute and dried at 250 ° C. for 10 minutes. The film thickness after drying is about 30 nm. If the thickness is within the range of 80 nm or less, the film can be formed without generating cracks or the like. If the film thickness is less than 20 nm, the film becomes discontinuous and is not practical.
After drying, heat treatment is performed at 800 ° C. for 10 minutes in an oxygen atmosphere. If the temperature of the heat treatment is lower than 600 ° C., crystallization does not occur, and if the temperature is higher than 850 ° C., bismuth is volatilized (the melting point of bismuth oxide is 830 ° C.), which is not preferable. This heat treatment crystallizes the thin film. At this time, since crystallization occurs from the interface with the substrate, a film in which the crystal grows epitaxially and is oriented in <105> can be obtained. If the film thickness during crystallization exceeds 80 nm, crystallization occurs randomly in the film, and an oriented film cannot be obtained. By repeating this application and heat treatment, the orientation obtained initially can be maintained, and a film having a larger thickness can be obtained. In this embodiment, a total of about 200 nm is repeated 6 times.
An SrBi ₂ Ta ₂ O ₉ film 10 oriented in <105> was prepared. By adding bismuth in excess of 5% to 15%, it is possible to crystallize more densely. In addition to such a normal heat treatment method, heat treatment can be performed by rapid heating using an infrared lamp. An upper electrode platinum layer 11 is formed thereon.

FIG. 2 shows SrBi ₂ Ta ₂ obtained by the above method.
FIG. 4 is a curve diagram showing X-ray diffraction of an O ₉ thin film. Thus, a film almost completely oriented to <105> can be obtained.

FIG. 3 shows the spontaneous polarization of the thin film capacitor formed by the alignment film according to the present invention and the conventional non-alignment film formed on ten 8-inch silicon wafer substrates, respectively, at 10 points randomly selected for each substrate. FIG. 3 is a distribution diagram showing distribution of measured values, that is, measured values at a total of 100 points, with the average of the measured values being 100. As described above, the distribution of spontaneous polarization in the plane of the substrate and between the substrates of the thin film capacitor according to the present invention is very small.

Although this embodiment has been described for SrBi ₂ Ta ₂ O ₉ , the same effect can be applied to SrBi ₂ Nb ₂ O ₉ and a solid solution of both SrBi ₂ (Ta, Nb) ₂ O ₉ in the same manner. Obtainable.

[0012]

As described above, according to the thin-film capacitor and the method of manufacturing the same of the present invention, the thin-film capacitor applicable to a nonvolatile semiconductor memory circuit without variation in electrical characteristics within a substrate surface and between substrates. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor memory device according to an embodiment of the present invention.

FIG. 2 is an X-ray diffraction image of a ferroelectric thin film according to an example of the present invention.

FIG. 3 is a distribution diagram illustrating a distribution of measured values of spontaneous polarization of a thin film capacitor according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Field oxide film 3 Gate oxide film 4 Word line 5, 5 'Impurity diffusion region 6 Interlayer insulating film 7 Polysilicon 8 Lower electrode barrier metal layer 9 Lower electrode 10 Ferroelectric 11 Upper electrode 12 Interlayer insulating film

Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location H01L 27/108

Claims (6)

(57) [Claims] 1. A predominantly <105> SrBi ₂ the axis is oriented in the thickness direction _{(Ta x Nb 1-x)} 2 O 9 (x = 0~1)
And a pair of electrodes sandwiching the thin film. 2. Strontium, bismuth, tantalum, d
Solution made from alkoxide or organometallic salt of
Is dried after coating on an electrode, and the film thickness after drying is 20 to 80 nm.
In an oxygen atmosphere at 600 to 850 ° C for about 10 minutes
Repeated heat treatment and crystallization
_{SrBi 2 (Ta x Nb 1-} x) 2 O 9 was (x = 0 to
The thin film of 1) and a pair of electrodes sandwiching the thin film
A thin film capacitor characterized by the above-mentioned. (3) Bi should be 5-15% excess
3. The thin film capacity according to claim 1, wherein:
Ta. 4. A lower electrode layer is formed on a substrate, and a solution containing strontium, bismuth, tantalum, niobium alkoxide or an organic metal salt as a raw material is applied on the electrode and dried. 600 to 85 in the range of 80 nm
SrBi ₂ (Ta _x Nb _1-x ) is repeatedly heated and crystallized in an oxygen atmosphere at 0 ° C. for about 10 minutes.
_A method for manufacturing a thin film capacitor, comprising forming a thin film of ₂ O ₉ (x = 0 to 1) and further forming an upper electrode. (5) The solution is diisopropoxystronic
0.1 mol, bismuth nitrate 0.2 mol, tetra
Dissolve 0.2 mol of ethoxy tantalum in 100 ml of glacial acetic acid
The mixture was heated and stirred at 100 ° C for 24 hours.
The solution is diluted to 0.1 M with
5. The method for manufacturing a thin film capacitor according to 4. 6. Hand when crystallizing at 600-850 ° C
Step is by infrared lamp A contract characterized by that
6. The method for manufacturing a thin film capacitor according to claim 4 or 5.