JP2000243924A - Ferroelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the influence of an active hydrogen to a ferroelectric and to obtain a ferroelectric element with less machining damage by setting an upper electrode formed on the ferroelectric layer of the ferroelectric element to a conductive nitride. SOLUTION: A field oxide film 2 is formed on the surface of a substrate 1, and a lower electrode 4 is formed on it. Further, a ferroelectric film 5 is formed on the lower electrode 4. Further, a gallium nitride thin film that is a conductive nitride is formed as an upper electrode 7 by the DC sputtering method. Also, in a conductive nitride thin film used for the upper electrode 7, a conductive nitride thin film such as gallium nitride and aluminum nitride or their mixed crystals or impurities are mixed, thus extremely reducing the active characteristic function of hydrogen, thus obtaining a reliable ferroelectric element without any damage due to an active hydrogen and with a high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ferroelectric device, and more particularly, to a structure of a ferroelectric device having a highly reliable upper electrode.

[0002]

2. Description of the Related Art Recently, as one type of nonvolatile memory, a ferroelectric memory which has a high operation speed and can take a large number of rewrites has appeared. This is a structure in which a DRAM capacitor is replaced with a ferroelectric capacitor.
It can be found as M (Ferroelectric Random Access Memory) in JP-A-2-113496 (Ramtron Corporation) and the like. This element is a non-volatile memory in which information is not lost even when power is cut off, and operates in a D
Attention has been paid to the high speed of a RAM.

[0003] In the device, a Pt (platinum) electrode is generally used as an upper electrode on a ferroelectric layer, and the Pt electrode is activated by hydrogen generated in the manufacturing process or outside. As a result, there is a problem that the Pt electrode functions as a hydrogen activation catalyst and damages the ferroelectric layer which is a composite oxide.

[0004]

The damage to the ferroelectric layer is that the Pt upper electrode activates hydrogen,
It is said that this has a serious effect of reducing ferroelectrics and mainly breaking weak metal-oxygen bonds. Therefore, it is considered that the use of a material having no oxygen activity as the upper electrode can dramatically reduce the damage to such a ferroelectric. However, it is difficult to select an electrode material that does not have a hydrogen activation function, resists annealing in an oxidizing atmosphere, and is easily dry-etched. The present invention has been made to solve such an unsolved problem of the conventional technology, and has as its object to solve the problem of deterioration of a ferroelectric caused by active hydrogen.

[0005]

Means for Solving the Problems The present inventor has found that a conductive nitride is effective as an upper electrode for solving the above-mentioned problems, and has reached the present invention. That is, claim 1
The ferroelectric element described in (1) is a ferroelectric element having an upper electrode on a ferroelectric layer, wherein the upper electrode is a conductive nitride. The ferroelectric element according to a second aspect is the ferroelectric element according to the first aspect, wherein the conductive nitride is a compound comprising a Group 3 metal and nitrogen, or an impurity mixed into the compound. It is characterized by the following.

According to a third aspect of the present invention, in the ferroelectric element according to the first aspect, the conductive nitride is gallium nitride or aluminum nitride, or a mixed crystal of gallium nitride and aluminum nitride, or They are characterized by being mixed with impurities. According to a fourth aspect of the present invention, there is provided the ferroelectric element according to the first aspect, wherein the ferroelectric layer includes at least PbTi.
O ₃ , PZT (PbZrTiO ₃ ), PLZT (Pb
_1-x La _x Zr _1-y Ti _y O ₃ ), Bi ₂ SrTa ₂ O
₉ , Bi _{2 -X} Nb _X SrTa ₂ O ₉ , Bi ₂ VO _5-6
It is a thin film.

According to a fifth aspect of the present invention, in the ferroelectric element according to any one of the first to fourth aspects, the ferroelectric layer functions as a gate insulating film of a field effect transistor. Or provided on a gate insulating film.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A ferroelectric element is a ferroelectric capacitor.
Pasters and ferroelectric capacitors and field-effect transistors
Combination of ferroelectrics with field-effect transistors
Refers to devices used for the gate insulating layer. Field effect type
A transistor has a structure in which a semiconductor and an insulator are joined.
Conductor electrodes called source and drain on both sides of the gate
Transistor, for example, MOS (Meta
l / Oxide / Semiconductor)-FET (Field Effect Tran)
sistor), TFT (Thin Film Transistor), etc.
Hit. A ferroelectric substance means that even if the applied voltage is removed,
Dielectric (insulator) with partial poles remaining (remanent polarization)
For example, PbTiO_Three, PZT (PbZrTiO_Three),
PLZT (Pb_1-xLa_xZr_1-yTi_yO_Three), Bi
_TwoSrTa_TwoO ₉, Bi_2-XNb_XSrTa_TwoO₉, B
i_TwoVO_5-6Use a thin film or the like. With ferroelectric capacitors
Is a thin film composed of the above ferroelectrics as a lower electrode.
Platinum, iridium, iridium oxide, upper electrode
Conductive thin film electrodes such as gallium nitride and aluminum nitride
It is sandwiched between poles to form a capacitance (capacitor).

The conductive nitride thin film used for the upper electrode is
For example, a conductive nitride thin film such as gallium nitride or aluminum nitride, or a mixed crystal of these, or a mixture of these with impurities, has no or very small hydrogen active characteristic function. With these features, a highly reliable ferroelectric element free from damage by active hydrogen can be obtained.

[0010]

Embodiment 1 Hereinafter, an embodiment of the present invention will be described with reference to the drawings. A ferroelectric device as shown in FIG. 1 was manufactured. As the substrate 1, a p-type Si (100) single crystal substrate having a resistivity of 2 Ωcm is used, and a field oxide film 2 is formed on the surface by a thermal oxidation method.
Having a thickness of 400 nm was used. On this, the lower electrode 4
As a result, titanium 20 nm and Pt 150 nm were formed by DC sputtering. The substrate temperature when forming Pt was 300 ° C.
Further, as a ferroelectric thin film 5 on the lower electrode, PL
ZT was produced by a sol-gel method. The composition of the ferroelectric is Pb
1.15, La0.03, Zr0.30, Ti0.70 were used. The coating was performed five times to obtain a film thickness of 250 nm. RT for each application
A (rapid heating method) annealing at 600 ° C for 30 seconds, 5
After the first coating, annealing was performed in oxygen for 20 minutes. Further, as the upper electrode 7, a GaN (gallium nitride) thin film having a thickness of 150 nm was obtained by using a DC sputtering method. At this time, conductive sintered GaN was used as the target, and the substrate temperature was set at 30 ° C.
The temperature was set to 0 ° C. This is sequentially dry-etched to form a ferroelectric capacitor.
After forming a TEOS film of 400nm and opening a contact hole,
Recovery annealing was performed in an oxygen atmosphere at 650 ° C. for 20 minutes.

Further, an Al wiring 6 was formed and processed by dry etching. The Al wiring was formed into a 0.1 mm square pad so that electrical characteristics could be evaluated with a stylus. Finally, annealing was performed at 400 ° C. for 20 minutes in a nitrogen atmosphere. Further, in order to evaluate the electric characteristics, a metal layer 9 for substrate contact was formed on the back surface. After the back surface was treated with diluted hydrofluoric acid, aluminum was formed by vacuum evaporation.

As a comparative example, a comparative element similar to that of Example 1 was also prepared except that the upper electrode 7 was Pt. Samples of the comparative device and the device of Example 1 were diluted in 1% hydrogen (diluted with nitrogen).
Annealing was performed at 150 ° C. for 20 minutes, and the presence or absence of deterioration was observed in relation to applied voltage and polarization intensity. When the relationship between the applied voltage and the polarization intensity was measured using a circuit as shown in the schematic diagram of FIG. 2, a result as shown in FIG. 3 was obtained. In the case where the upper electrode was made of Pt, the polarization intensity was severely deteriorated, whereas GaN was
It can be seen that the sample that had been hardly deteriorated. Similar superiority was obtained when Ga0.9Al0.1N1 was used as the upper electrode.

[0013]

Embodiment 2 Another embodiment will be described below. MFIS (Metal-Ferroelectrics-Insulator-Semicon) as shown in FIG.
A ductor type device was produced (however, in this case, the conductive nitride layer corresponds to the Metal layer). As the substrate 1, a p-type Si (100) single crystal substrate having a resistivity of 2 Ωcm was used, and a gate insulating film 8 SiON insulating film having a thickness of 4 nm was formed on the surface. This SiON film is formed by ion implantation of nitrogen and annealing at 800 ° C. for 15 minutes in an oxygen atmosphere. Further, an SBT (SrBi) is formed thereon as a ferroelectric thin film 5.
₂ Ta ₂ O ₉ ) was prepared by a coating method. The composition of the coating solution used was Sr0.80, Bi2.20, Ta2.0. The coating was performed five times to obtain a film thickness of 400 nm. Annealing was performed 20 times at 700 ° C. in an atmosphere of oxygen after each application, and annealing was performed in oxygen at 700 ° C. for 30 minutes after applying 5 times.

Further, as the upper electrode 7, a GaN thin film was formed by DC sputtering to a thickness of 150
got m. Dry etching of the upper electrode, MFIS
Structure formed. Further, as the interlayer insulating film 3, ozone TEOS
After forming a film of 400 nm and opening a contact hole, recovery annealing was performed in an oxygen atmosphere at 700 ° C. for 20 minutes. further,
An Al wiring 6 was formed and processed by dry etching. The Al wiring was formed into a 0.1 mm square pad so that electrical characteristics could be evaluated with a stylus. Finally, annealing was performed at 400 ° C. for 20 minutes in a nitrogen atmosphere.

As a comparative example, a comparative device similar to that of Example 2 except that the upper electrode 7 was made of Pt was also manufactured. A sample of the comparative device and the device of Example 2 were diluted with 1% hydrogen (diluted with nitrogen).
Annealing was performed at 150 ° C. for 20 minutes, and the presence or absence of deterioration was observed in relation to applied voltage and polarization intensity. When the relationship between the applied voltage and the capacitance was measured using a circuit as shown in the schematic diagram of FIG. 5, the result as shown in FIG. 6 was obtained. In the case where the upper electrode was made of Pt, the polarization intensity was severely deteriorated, whereas GaN was
It can be seen that the sample that had been hardly deteriorated. Similar superiority was obtained when Ga0.9Al0.1N1 was used as the upper electrode.

[0016]

As described above, according to the present invention,
The influence of active hydrogen on the ferroelectric can be significantly reduced, and a ferroelectric element with less processing damage can be provided. In addition, the conductive nitride thin film can be easily formed by a sputtering method or the like, can be dry-etched, and is easier to process than platinum or iridium. For this reason, there are effects that a high yield and a highly reliable ferroelectric element can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross section of a ferroelectric element of the present invention manufactured in Example 1.

FIG. 2 is a diagram showing a circuit for measuring electric characteristics of the ferroelectric element manufactured in Example 1.

FIG. 3 is a view showing the results of evaluating the electric characteristics of the ferroelectric element manufactured in Example 1.

FIG. 4 is a diagram showing a cross section of the ferroelectric element of the present invention manufactured in Example 2.

FIG. 5 is a diagram showing a circuit for measuring electric characteristics of the ferroelectric element manufactured in Example 2.

FIG. 6 is a diagram showing the results of evaluating the electrical characteristics of the ferroelectric element manufactured in Example 2.

[Explanation of symbols]

 1 ... Substrate 2 ... Field oxide film 3 ... Interlayer insulating film (ozone TEOS silicon oxide film) 4 ... Lower electrode (Pt / Ti thin film) 5 ... Ferroelectric Thin film (PLZT) 6 Metal wiring layer (aluminum) 7 Upper electrode 8 Gate insulating film 9 Metal layer for substrate contact 10 Metal stage

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H01L 21/8247 29/788 29/792

Claims (5)

[Claims] 1. A ferroelectric device having an upper electrode on a ferroelectric layer, wherein the upper electrode is a conductive nitride. 2. The ferroelectric device according to claim 1, wherein
A ferroelectric element, wherein the conductive nitride is a compound comprising a Group 3 metal and nitrogen, or an impurity mixed with the compound. 3. The ferroelectric element according to claim 1, wherein said conductive nitride is gallium nitride, aluminum nitride, a mixed crystal of gallium nitride and aluminum nitride, or an impurity mixed therein. Characteristic ferroelectric element. 4. The ferroelectric device according to claim 1, wherein
The ferroelectric layer is at least PbTiO_Three, PZT (P
bZrTiO_Three), PLZT (Pb_1-xLa_xZr_1-y
Ti_yO_Three), Bi_TwoSrTa_TwoO₉, Bi_2-XNb_X
SrTa _TwoO₉, Bi_TwoVO_5-6One of the thin films
A ferroelectric element characterized in that: 5. The ferroelectric element according to claim 1, wherein the ferroelectric layer functions as a gate insulating film of a field effect transistor or is provided on the gate insulating film. A ferroelectric element characterized by the above-mentioned.