JPH0578835A - Production of thin film of ferroelectric substance - Google Patents

Abstract

PURPOSE:To obtain a thin PZT film having satisfactory ferroelectric characteristics with high reproducibility by forming an electrode on a silicon substrate with silicon dioxide in-between and depositing a thin PZT film on the electrode by high-frequency sputtering while controlling the potential of the electrode to earth potential or floating potential. CONSTITUTION:An electrode 103 is formed on a silicon substrate 101 with silicon dioxide 102 in-between and a thin PZT film is deposited on the electrode 103 by high-frequency sputtering while controlling the potential of the electrode to earth potential or floating potential.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a ferroelectric thin film mainly used in a non-volatile memory device, and more particularly to a potential of a substrate surface when manufacturing a ferroelectric thin film by using a high frequency sputtering method. Concerning the control of.

[0002]

2. Description of the Related Art Conventionally, for example, IBM J. Res. De
velop. As described in Volume 14, Item 172, the DC bias voltage of the substrate holder is controlled by controlling the substrate impedance in the high frequency sputtering apparatus.

This will be described in detail with reference to the electrical equivalent circuit of the high frequency sputtering apparatus shown in FIG.

Zs, Zt, and Zw are impedances 201, 202, and 202 of the sheath of the substrate, the target, and the vessel wall, respectively.
It is 203. When the target is a dielectric, the target capacitance 204, the substrate capacitance 205, the film capacitance 206 on the wall
Is included.

Vrf is a high frequency power source and Vp is a plasma potential.

Zsg is a substrate impedance 207 for controlling the substrate potential.

Conventionally, the potential of the substrate holder is controlled by controlling the substrate impedance 207, not the potential of the substrate surface.

[0008]

However, when the ferroelectric thin film is formed by the high frequency sputtering method, it is better to control the potential of the substrate surface than to control the potential of the substrate holder, that is, the potential of the back surface of the substrate. is important.

The potential on the surface of the substrate to be deposited has a great influence on the deposition rate, film thickness distribution, and various characteristics of the formed ferroelectric thin film. However, there is a problem that it is difficult to obtain good characteristics with good reproducibility.

The various characteristics referred to here are ferroelectric characteristics such as remanent polarization and anti-electric field, dielectric characteristics such as permittivity and current-voltage characteristics, and crystal composition, orientation, and grain size. Including physical properties such as.

Therefore, the present invention is intended to solve these problems, and an object thereof is to control the potential of the surface of the substrate to be deposited during high frequency sputtering to a ground potential or a floating potential for deposition. This is to ensure the reproducibility of the characteristics of the ferroelectric thin film.

[0012]

The method for producing a ferroelectric thin film of the present invention is (1) a method for producing a ferroelectric thin film on a substrate having electrodes formed on its surface by high frequency sputtering. The ferroelectric thin film is deposited by controlling the potential of the electrode to the ground potential or the floating potential.

(2) The ferroelectric thin film is characterized by being either PZT or PLZT.

[0014]

EXAMPLE A first example of the method for producing a ferroelectric thin film of the present invention will be described with reference to the conceptual diagram of FIG.

As shown in FIG. 1, about 500 inches is formed on a 6-inch size n-type silicon substrate 101 by chemical vapor deposition.
A silicon dioxide film (SiO2) 102 of 0 A and platinum (Pt) of about 2000 A are formed as an electrode 103 by a sputtering method, and Pb (Zr0.5) is formed on the electrode 103.
A Ti0.5) O3, that is, a PZT thin film having a Zr / Ti composition ratio of 1 is formed by a high frequency magnetron sputtering method.

The silicon substrate 101 has a floating potential and is grounded via a certain impedance Z1.

The silicon substrate 101 on which the silicon dioxide film 102 and the electrode 103 are formed is fixed by a ring chuck, and the potential of the surface of the electrode 103 is grounded via the ring chuck and becomes the ground potential. There is.

The sputtering condition for the PZT thin film is that the substrate temperature is 3
Atmosphere gas of 00 ° C. and Ar: O 2 = 9: 1, gas pressure of 20 mTorr, distance between target and silicon substrate of 65 mm, power of 1 kW, and thickness of 3000 A PZ
A T thin film was formed.

A deposition rate of 100 A / min was obtained.

FIG. 3 shows a cross-sectional structure of a sample for evaluating ferroelectric characteristics.

The PZT thin film 104 immediately after sputtering does not show a perfect ferroelectric phase, that is, a perovskite structure.

That is, it is in a mixed state of a perovskite structure and a pyrochlore phase which does not exhibit a ferroelectric phase.

Then, next, in an oxygen atmosphere, at 1 at 750 ° C.
Time annealing is performed to form a complete ferroelectric phase.

Finally, the upper electrode 105 made of Pt having a thickness of 1000 A was formed on the PZT thin film 104 by DC sputtering.
After being formed on the entire upper surface, it was patterned into 100 μm square by using ordinary photolithography.

The ferroelectric characteristics of this ferroelectric thin film were measured by a hysteresis curve by a Sawyer tower circuit.
The measurement was performed at room temperature and a frequency of 50 Hz. Remanent polarization is 3
A good ferroelectric property was obtained with 0 μC / cm ² and an anti-electric field of 30 kV / cm.

FIG. 4 shows changes in the value of remanent polarization when 100 electrodes are continuously flowed when the electrode 103 is set to the ground potential as shown in FIG.

As described above, a high quality PZT thin film can be stably obtained only by setting the potential of the electrode surface to the ground potential.

A second embodiment of the method for manufacturing a ferroelectric thin film of the present invention will be described with reference to the conceptual diagram of FIG.

The difference from the first embodiment is that the electrode 103
That is, the potential of is not dropped to the ground potential via the ring chuck, so that it is grounded via the impedance Z2.

The sputtering condition for the PZT thin film is that the substrate temperature is 3
Atmosphere gas of 00 ° C. and Ar: O 2 = 5: 1, gas pressure of 20 mTorr, distance between target and silicon substrate of 65 mm, power of 1 kW, thickness of 3000 A PZ
A T thin film was formed.

A deposition rate of 150 A / min was obtained.

After forming a sample for evaluating the ferroelectric characteristic according to the same procedure as in Example 1, the ferroelectric characteristic was measured by a hysteresis curve by a Sawyer tower circuit. The measurement was performed at room temperature and a frequency of 50 Hz. The remanent polarization was 45 μC / cm ² , and the anti-electric field was 35 kV / cm, and good ferroelectric properties were obtained.

FIG. 6 shows changes in the value of remanent polarization when the electrode 103 is set to a floating potential as shown in FIG. 5 when 100 wafers are continuously flowed.

As described above, a high quality PZT thin film can be stably obtained only by setting the potential of the electrode surface to the ground potential.

7 (a) to 7 (f) are conceptual views showing a method of manufacturing a ferroelectric thin film showing another embodiment.

In FIG. 7A, the potential of the silicon substrate 101 is ground and the potential of the surface of the electrode 103 is also ground.

In FIG. 7B, the potential of the silicon substrate 101 is ground and the potential of the surface of the electrode 103 is a floating potential because it passes through a certain impedance Z2.

FIGS. 7C to 7F show the silicon substrate 10.
In the case where the electrode 103 is directly formed on the substrate 1, the substrate potential and the electrode potential are as shown below. Z1,
Z2 represents a certain impedance.

Silicon substrate potential Electrode surface potential (c) Floating potential Earth potential (d) Earth potential Earth potential (e) Earth potential Floating potential (f) Floating potential Floating potential In the above examples, Zr was used as the ferroelectric thin film. The explanation was made using PZT with a Ti / Ti composition ratio of 1, but P with other composition ratios.
The thin film may be a ZT thin film, PLZT doped with lanthanum (La) may be used, or calcium (C
Of course, a), barium (Ba), magnesium (Mg), niobium (Nb), strontium (Sr), etc. may be doped.

Furthermore, barium titanate (BaTiO 3
3), lead titanate (PbTiO3), potassium niobate (KNbO3), lithium niobate (LiNbO3), lithium tantalate (LiTaO3) or their compounds.

Although a silicon substrate is used for the description, another substrate such as magnesia (MgO) or sapphire may be used. In the first and second embodiments, a silicon dioxide film is formed between the silicon substrate 101 and the electrode 103. Although the description has been given using the structure sandwiching 102, a silicon nitride film (Si3N4) may be used instead of the silicon dioxide film, and nothing is sandwiched as shown in FIGS. 7 (a) to 7 (c). Alternatively, the electrodes may be formed directly on the substrate.

[0042]

As described above, the method for producing a ferroelectric thin film of the present invention is a method for producing a ferroelectric thin film on a substrate having electrodes formed on its surface by high frequency sputtering. , Controlling the potential of the electrode to a ground potential or a floating potential, and depositing the ferroelectric thin film,
It has the effect of being able to obtain a thin film having good reproducibility and good characteristics and good ferroelectric characteristics.

Further, by using this method for manufacturing a ferroelectric thin film, there is an effect that it can be used as a nonvolatile memory, an optical switch, a capacitor, an infrared sensor and an ultrasonic sensor.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a first embodiment of a method for manufacturing a ferroelectric thin film of the present invention.

FIG. 2 is an electrical equivalent circuit diagram of a high frequency sputtering apparatus for manufacturing a conventional ferroelectric thin film.

FIG. 3 is a cross-sectional view of a sample for evaluating the characteristics of the ferroelectric thin film according to the first embodiment of the present invention.

FIG. 4 is a graph showing reproducibility of remanent polarization of the ferroelectric thin film of Example 1 of the present invention.

FIG. 5 is a conceptual diagram showing a second embodiment of the method for manufacturing a ferroelectric thin film of the present invention.

FIG. 6 is a graph showing reproducibility of remanent polarization of the ferroelectric thin film of Example 2 of the present invention.

FIG. 7 is a conceptual diagram showing a method for manufacturing a ferroelectric thin film of the present invention.

[Explanation of symbols]

 101 Silicon Substrate 102 Silicon Dioxide Film 103 Electrode 104 PZT 105 Upper Electrode 201 Substrate Sheath Impedance 202 Target Sheath Impedance 203 Instrument Wall Sheath Impedance 204 Target Capacity 205 Substrate Capacitance 206 Instrument Wall Film Capacitance 207 Substrate Impedance

Claims (2)

[Claims] 1. A method of manufacturing a ferroelectric thin film on a substrate having an electrode formed on its surface by using a high frequency sputtering method, wherein the potential of the electrode is controlled to a ground potential or a floating potential, and A method of manufacturing a ferroelectric thin film, which comprises depositing a dielectric thin film. 2. The ferroelectric thin film according to claim 1, wherein the ferroelectric thin film is PZ.
A method of manufacturing a ferroelectric thin film, which is either T or PLZT.