JPH0794608A - Ferroelectric material and field-effect transistor using the material as a gate - Google Patents

Abstract

(57) [Summary] (Modified) [Objective] When an oxide of Pb and Ti is used as a ferroelectric thin film material to be formed on a gate, the material is further added by adding a specific element to the material. Instability is reduced, and the operation as a device is stabilized and improved. [Structure] Oxide of Pb and Ti (hereinafter referred to as PTO)
And an element that can be an acceptor when the PTO is n-type, and an element that can be a donor when the PTO is p-type, and the addition amount of the element is 3% by weight per element. The following ferroelectric material is used as a field effect transistor (MFSF) including a conductive layer (M), a ferroelectric thin film 2 (F) as a gate, and a semiconductor layer (S).
ET) used as a gate material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric material and a field effect transistor (hereinafter also referred to as MFSFET) using the material as a gate.

[0002]

2. Description of the Related Art A ferroelectric thin film is used as a MOSFET (Metal-ox
ide-semiconductor field-effect-transistor) gate, which can control the surface potential of the channel by the electric polarization accompanied by the hysteresis phenomenon of the film to change the drain current and produce the non-volatile memory effect. . This element is MFS (Metal-ferroelectric-semi
conductor) FET, whose outline is introduced by the following two documents.

"Nonvolatile memory FET using ferroelectric thin film" Yasushi Matsui, Keihiro Hamakawa et al. Technical Report of IEICE Technical Report CPM 78-46 p. 1-8 (1978) US Patent 2,791,758 (195)
7)

[0004]

The MFSFET has advantages over the EPROM in that the structure is simple and the response speed of the element is as fast as several nanoseconds, but it has been delayed to be a device so far. . One of the causes is
The stability of the crystal structure and electrical properties of the dielectric thin film related to the material composition has not reached the level at which it can be made into a device. For example, although there are many examples of studying PZT (Pb, Zr, Ti oxide) as a ferroelectric thin film material on the gate, when the polarization inversion is repeated, the value of the residual polarization (Pr) is about 10 ⁹ times. The drop in is noticeable. It is considered that this deterioration phenomenon is caused by movement of ions and lattice defects in the thin film, and research is continuing toward improvement. Further, among the dielectric properties of the thin film, the values of the operating electric field strength (E _R ), the coercive electric field (Ec), the leak current, etc. are important characteristic parameters, but as described above, they change with the number of reversal repetitions. Is known, and this is also an obstacle to deviceization. The change in these characteristic parameters is
Not to say, it depends on the original properties of the material, but rather, it is thought that it is due to defects in the crystal lattice of nonuniform composition introduced during film formation.

An object of the present invention is to use an oxide of Pb and Ti as a ferroelectric thin film material formed on a gate in an MFSFET by further adding a specific element to the material as described above. It is to reduce the instability of the material and stabilize and improve the operation as a device.

[0006]

According to the present invention, firstly, an oxide of Pb and Ti (hereinafter referred to as PTO) and P
When TO is n-type, at least one element that can be an acceptor is added, and when PTO is p-type, at least one element is added, and the addition amount of the element is 3% by weight. % Ferroelectric material is provided.

Secondly, in the first structure, the additive elements in the case of the p-type PTO are V, Nb, Ta, Cr and M.
There is provided a ferroelectric material which is at least one selected from the group consisting of o, W, Se, Te, Re, Ru, Os, Sc, Y, lanthanoid elements and actinoid elements.

Thirdly, in the second configuration, the n-type P
In the case of TO, the additive elements are Cu, Ag, Au, Na,
K, Rb, Cs, Zn, Cd, Hg, B, Al, Ga,
In, Fe, Co, Ni, Rh, Pd, Pt and Ir
A ferroelectric material is provided that is at least one selected from the group consisting of:

Fourthly, in any one of the first to third structures, the above-mentioned additional element is added by an ion implantation method, and the addition amount is 10 ^-2 % by weight or less per element. Will be provided.

Fifth, an MFS having a conductive layer (M), a ferroelectric thin film (F) as a gate, and a semiconductive layer (S).
In the FET, the ferroelectric thin film is an MFS composed of any one of the ferroelectric materials described in the first to fourth aspects.
An FET is provided. FIG. 1 is a cross-sectional structure example of the MFSFET.
Shown in.

It is known that the PTO thin film has p-type or n-type properties depending on the manufacturing conditions. In addition, P-E curve of PTO and P-E after reversal fatigue
The curves are as shown in FIGS. 2 and 3, respectively.

When an element that can serve as a donor is added to the p-type PTO thin film, carrier compensation occurs and the leak current is reduced. Further, in this case, it is considered that vacancies are generated at the position of the ions for charge compensation, and the polarization vector is easily moved to reduce the EC.

Further, in the case of an n-type PTO thin film, when an element that can serve as an acceptor is added, the ion forms a dipole, and pinning of the polarization wall is performed, so that there is an effect of reducing a change with time.

Furthermore, addition of the above-mentioned element that can be a donor or acceptor can not only reduce the leak current and EC as described above, but also other parameters of the ferroelectric such as the polarization reversal rate. And PTO as a ferroelectric memory
The characteristics of the thin film can be improved.

Therefore, with respect to PTO, by adding an element acting as a donor or an acceptor to Pb and Ti, it is possible to bring about the above-described effects such as a decrease in leak current and EC. Such Pb
And an element capable of acting as a donor or an acceptor on Ti are A of the perovskite structure PTO.
-Site Pb has a valence of 2, and B-
Since Ti of the site has a valence of 4, it is suitable to have a valence as shown in Table 1 below.

[Table 1]

The elements that can be the donor and acceptor include the following. <Donor> V, Nb, Ta (group V) Cr, Mo, W, Se, Te (group VI) Re (group VII) Ru, Os (group VIII) Sc, Y, lanthanoid element, actinide element (III)
Group) <Acceptor> Cu, Ag, Au, Na, K, Rb, Cs (group I) Zn, Cd, Hg (group II) B, Al, Ga, In, Tl (group III) Fe, Co, Ni, Rh, Pd, Pt, Ir (Group VIII)

The addition of the above-mentioned element to the PTO thin film is carried out, for example, at the time of forming the PTO thin film by sputtering with a sputtering target mixed with the oxide of the element, or by an appropriate method. After forming the film, the desired element can be ion-implanted into the PTO thin film. The addition amount is 3% by weight or less per element because the stoichiometric composition of the main component is not significantly changed. Also, in the case of ion implantation, the local effect can be increased, so 10 ^-2 % by weight
It is the following.

[0018]

EXAMPLES Next, specific examples and comparative examples of the present invention will be shown.

[Comparative Example] Si having a P-type resistance value of 10 Ωcm ^-1
A PTO film (PbTiO ₃ ) was formed on a (110) substrate by an rf sputtering method to a film thickness of 0.04 to 1.0 μm. The PTO film can also be formed by a dc sputtering method, a multi-source evaporation method, a laser ablation method, a sol-gel method, a MOCVD method, or the like. PT
After forming the O film, a gate electrode film was deposited and an electrode pattern was formed by photolithography and etching. At this time, the reactive ion etching method was adopted for the etching in consideration of anisotropy. Next, about 3 × 10 ¹³ pieces / cm ² of arsenic (A
s) was injected at an acceleration voltage of 160 eV and activated by lamp annealing to form a source and a drain.
Subsequently, a metallization process and a passivation film formation process are performed, and aluminum wiring is further formed by a sputtering method using Al-2% Si.
ET (1)) was produced. With respect to this FET (1), a repeated cycle test of polarization reversal and a leak current were measured.

Example 1 The PTO used in the above Comparative Example was used as a sputtering target, and Y oxide (Y ₂₎ was added to the sputtering target for the purpose of adding Y as an example of the additive donors described above. By mixing O ₃ ), 1.
The above FET except that a PTO film containing 75 wt% Y is used.
In the same manner as (1), MFSFET (hereinafter, FET (2)
Called). A durability test was conducted on this FET (2) in the same manner as in the comparative example.

The test results of the FET (1) and the FET (2) are shown below. Number of repetitions 1 × for FET (1)
The value of the remanent polarization started to decrease from 10 ⁹ times, and at 8 × 10 ¹⁰ times, it became difficult to distinguish the FET as a switching operation due to the decrease of the polarization value and the flattening of the hysteresis curve. Corresponding to this, the leakage current value was 5 × 1 of the initial value.
It increased from 0 ^-8 Amp / cm ² to 7 × 10 ^-6 Amp / cm ² . On the other hand, in FET (2), the reduction of the remanent polarization value started from 4 × 10 ¹⁰ times, but the switching operation could be confirmed up to 3 × 10 ¹³ times. However, at 1 × 10 ¹⁴ times, similarly to the above, the hysteresis curve was flattened, and it was difficult to identify the switching operation. Also, the corresponding leakage current is initially 2 × 10 ⁻⁸ Amp.
/ Cm ² and 5 × 10 even after 8 × 10 ¹³ times
It was a good value of ⁻⁷ Amp / cm ² .

[Embodiment 2] In the process of manufacturing the FET (1), after PTO film formation by rf sputtering,
Ion implantation was performed to the portion of the PTO film for the purpose of adding La ions. The acceleration voltage at this time is 200e
After the implantation, lamp annealing was performed at a V ion concentration of 6 × 10 ⁻³ wt%. MFSFET (hereinafter referred to as FET (3)) manufactured by the same process as FET (1)
Was prepared and a durability test was conducted in the same manner as in Comparative Example.

According to the result of the durability test of the FET (3), the remanent polarization starts to decrease from the repetition number of 1 × 10 ¹⁰ to 2 × 10 10.
^It was no longer recognized as a switching operation after about ¹² times. The initial value of the leakage current is 5 × 10 ^-7 Amp / cm
² that also maintains 8 × 10 ¹³ times the post-inversion was observed.

[0024]

The MFSFET using the ferroelectric material in which the specific element is added to the PTO having the stoichiometric composition provided by the present invention is a PTO in which the specific element is not added.
In comparison with the MFSFET using the above, the number of polarization reversals and the leakage current value were improved by almost two digits.
Therefore, such an improvement makes it possible to manufacture an element that satisfies the product specifications of the MFSFET, which has been conventionally difficult.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a cross-sectional structure of an MFSFET.

FIG. 2 is a model view showing a PE curve of a ferroelectric PTO.

FIG. 3 is a model view showing a PE curve of a ferroelectric PTO after inversion fatigue.

[Explanation of symbols]

 1 P-Si substrate 2 Ferroelectric thin film 3 Metal electrode 4 Passivation film

Claims (5)

[Claims] 1. An oxide of Pb and Ti containing an element that can serve as an acceptor when the oxide is n-type,
In the case of the type, a ferroelectric material composed of at least one element that can serve as a donor is added, and the added amount of the element is 3% by weight or less per element. 2. The additive element when the oxide is p-type,
V, Nb, Ta, Cr, Mo, W, Se, Te, Re,
The ferroelectric material according to claim 1, which is at least one selected from the group consisting of Ru, Os, Sc, Y, a lanthanoid element, and an actinoid element. 3. The additive element when the oxide is n-type is C
u, Ag, Au, Na, K, Rb, Cs, Zn, Cd,
Hg, B, Al, Ga, In, Fe, Co, Ni, R
The ferroelectric material according to claim 1, which is at least one selected from the group consisting of h, Pd, Pt, and Ir. 4. The additive element is added by an ion implantation method, and the added amount is 10 ^-2 % by weight per element.
It is the following, The ferroelectric material as described in any one of Claims 1-3. 5. A field effect transistor comprising a conductive layer (M), a ferroelectric thin film (F) as a gate and a semiconductive layer (S), wherein the ferroelectric thin film is any one of claims 1 to 4. A field-effect transistor made of the ferroelectric material as described in 1 above.