JPH05129156A - Ferroelectric capacitor and its manufacture - Google Patents

Abstract

PURPOSE:To form a plurality of ferroelectric capacitors connected in series or parallel on a semiconductor substrate easily. CONSTITUTION:A silicon oxide film 102 is made as an insulating film on a silicon substrate 100, and a lower electrode 104 of Pt is made. A PZT ferroelectric film 106 is made on this lower electrode 104, and further a silicon nitride film 108 is made as an insulating film. A contact hole 108a is made on the PZT ferroelectric film of this silicon sandwiched between the lower electrode 104 and the upper electrode 110 functions as a ferroelectric capacitor, and they can be connected in series or parallel by making the upper electrode 110 or the lower electrode 104 common.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric capacitor and a method of manufacturing the same, and more particularly to a method of manufacturing a ferroelectric capacitor suitable for connecting a large number of ferroelectric capacitors in series or in parallel.

[0002]

2. Description of the Related Art Optical sensors, heat sensors, pressure sensors, wind sensors, and the like generate electric potentials according to the amount of light, heat, or pressure to be measured. To monitor, for example, a comparator 10 as shown in FIG. 9 is used. Comparator 1
0 is a normal current mirror circuit 10a and a differential circuit 10b
And a voltage corresponding to the difference between the non-inverting input terminal and the inverting input terminal is taken out as an output. Then, by connecting a device that generates a potential such as an optical sensor or a thermal sensor to the non-inverting input terminal and applying a reference voltage to the inverting input terminal, the external voltage of the optical sensor or the thermal sensor becomes higher than the reference voltage. Whether or not it is monitored.

However, the conventional voltage measuring device such as a comparator has a problem that it cannot operate unless the power source 10c is supplied from the outside, and in order to constantly monitor the maximum voltage, an external memory is further connected to the output of the comparator. There is a problem in that the device structure must be complicated.

Therefore, it has been proposed to measure the voltage using a non-volatile ferroelectric capacitor without using a comparator. As is well known, a ferroelectric substance is a dielectric substance having spontaneous polarization based on a permanent dipole moment, whose polarization direction can be reversed by applying an electric field, and is very similar to the BH curve of a ferromagnetic substance. It is known to exhibit characteristics (P-E hysteresis loop of ferroelectric).

It is known that when the ferroelectrics have different thicknesses, the value of the coercive electric field necessary for reversing the spontaneous polarization increases in proportion to the thickness.

Therefore, by utilizing such a property of the ferroelectric substance and applying an external voltage to a plurality of ferroelectric elements having different thicknesses and measuring whether or not the inverted polarization is generated, it is possible to operate without a power source. It is possible to measure the maximum voltage.

[0007]

As described above, in the voltage measuring device using the ferroelectric capacitors, the maximum voltage can be measured with no power supply and in a nonvolatile manner, but a plurality of ferroelectric capacitors having different thicknesses can be used. Is difficult to form, and particularly when PZT (lead zirconate titanate) having excellent physical properties is used as a ferroelectric substance, its processing is difficult, which leads to an increase in device cost. It was

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to minimize the number of ferroelectric processing steps when manufacturing a plurality of ferroelectric capacitors, and to reduce yield and cost. It is an object of the present invention to provide a ferroelectric capacitor that can be lowered and a method for manufacturing the same.

[0009]

In order to achieve the above object, a method of manufacturing a ferroelectric capacitor according to claim 1 is
A first insulating film forming step of forming a first insulating film on a semiconductor substrate; a first metal film forming step of forming a first metal film on the first insulating film; and a first metal film Forming a plurality of lower electrodes, forming a ferroelectric film on the lower electrode, forming a ferroelectric film on the lower electrode, and forming a second insulating film on the ferroelectric film. A second insulating film forming step, a contact hole forming step of etching the second insulating film to form a contact hole with the ferroelectric film, and a second metal on the second insulating film. A second metal film forming step of forming a film; and an upper electrode forming step of etching the second metal film to form a plurality of upper electrodes on the contact holes.

In order to achieve the above object, a ferroelectric capacitor according to a second aspect of the invention is formed with a semiconductor substrate, a plurality of lower electrodes formed on the semiconductor substrate, and these lower electrodes. A ferroelectric film, an insulating film formed on the ferroelectric film and having a contact hole on the ferroelectric film, and a plurality of upper electrodes formed on the insulating film and connecting the contact holes, , Are included.

[0011]

As described above, when measuring the maximum voltage by using, for example, a ferroelectric capacitor, it is necessary to use a plurality of ferroelectric capacitors having different thicknesses, but a ferroelectric capacitor having almost the same thickness is used. The film thickness can be substantially changed by connecting the dielectric capacitors in series and changing the number of the ferroelectric capacitors connected in series. The present invention pays attention to this fact and forms a large number of ferroelectric capacitors having substantially the same layer on a semiconductor substrate.

That is, the ferroelectric capacitor is composed of two metal films and a ferroelectric material disposed between the metal films. In the present invention, the lower electrode is first formed on the semiconductor substrate, and then the lower electrode is formed. A ferroelectric film is formed on. The ferroelectric film can be formed on the lower electrode by forming the ferroelectric film on the entire surface of the semiconductor substrate and then removing the unnecessary portion by etching.

Then, an insulating film having a contact hole is formed in a region where the ferroelectric capacitor is to be formed, and a plurality of upper electrodes are formed on the contact hole to form a ferroelectric film sandwiched between the upper electrode and the lower electrode. A large number of ferroelectric capacitors composed of body films can be formed.

When connecting a large number of these ferroelectric capacitors in series or in parallel, it suffices to connect the upper electrode or the lower electrode to an adjacent ferroelectric capacitor as required.

As described above, in the present invention, the area is not changed to change the capacitance of the capacitor, but the film thickness is changed by changing the number of the series ferroelectrics in order to obtain the difference in the coercive electric field. The difference in coercive electric field can be achieved only by forming the upper electrode on the contact hole.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for manufacturing a ferroelectric capacitor according to the present invention will be described below with reference to the drawings.

FIG. 1 shows an explanatory view of the manufacturing method of this embodiment. First, as shown in FIG. 1A, a silicon oxide film 1 is formed as a first insulating film on a silicon substrate 100.
02 is formed by thermal oxidation. Then, a Pt metal film is formed as a first metal film on the silicon oxide film 102 by a sputtering method, and an unnecessary portion is removed by etching to form a lower electrode 104.

Next, as shown in FIG. 1B, the PZT
A ferroelectric film is formed by a sputtering method, baking is performed at a predetermined temperature, and an unnecessary portion is removed by etching to form a PZT ferroelectric film 106 on the lower electrode 104.

Then, as shown in FIG.
A silicon oxide film 108 is formed as an insulating film by a CVD method or the like, and the PZT ferroelectric film 106 formed in the above step is removed by etching to remove the contact hole 10.
8a is formed.

Finally, as shown in FIG. 1D, a Pt film is formed as a second metal film on the silicon oxide film 108 by a sputtering method or the like, and an unnecessary portion is removed by etching to form an upper electrode 110. To do. Then contact hole 1
In the region where 08a is formed, the PZT ferroelectric film 106
Is sandwiched between the upper electrode 110 and the lower electrode 104, and thus this portion functions as a ferroelectric capacitor. Then, as shown in FIG. 1 (D), the adjacent upper electrode 11 has a common ferroelectric capacitor.
By forming the upper electrode 110 to the lower electrode 104 so as to have 0 or have the common lower electrode 104, it is possible to connect the ferroelectric capacitors in series (in the present embodiment, 3). Two ferroelectric capacitors are connected in series).

By forming a plurality of ferroelectric capacitors having substantially the same thickness on the silicon substrate 100 and connecting a desired number of these ferroelectric capacitors in series, the ferroelectric capacitors are substantially strengthened. The thickness of the dielectric can be changed, and the maximum voltage measuring device described later can be easily manufactured.

FIG. 2 shows an application example of a ferroelectric capacitor manufactured by using the manufacturing method of this embodiment, taking a maximum voltage measuring device as an example.

A plurality of ferroelectric element rows (three ferroelectric element rows in FIG. 2) manufactured by the above-described manufacturing method are connected in parallel to each other to form a ferroelectric unit 20.
Here, the first ferroelectric element row is an individual ferroelectric element F.
Consists of _1, the second ferroelectric element row two ferroelectric elements F _1, F ₂ are formed by connecting in series. The third ferroelectric element row is composed of three ferroelectric element rows F ₁ , F ₂ and F ₃ connected in series.
Then, the switches S _{1 to} S are serially connected to each ferroelectric element array.
₃ is connected.

Further, the reset circuit 22 is provided for causing the spontaneous polarization of the ferroelectric unit 20, via the Pt electrode of the ferroelectric elements F ₁ to F ₃ by the DC power supply 22a of the reset circuit 22 PZT ferroelectric 20b
A direct current voltage is applied to to generate maximum spontaneous polarization Pr. Here, since the first ferroelectric element array is composed of one ferroelectric element F ₁ , the film thickness of the ferroelectric element is the film of the PZT ferroelectric 20a of the ferroelectric element F _1. Will be equal to the thickness. On the other hand, since the second ferroelectric element array is composed of two ferroelectric elements F ₁ and F ₂ , the total thickness of the ferroelectric material is the PZT ferroelectric material 20b of the ferroelectric element F _1. Of 2
Double the film thickness. Furthermore, since the third ferroelectric element row is composed of three ferroelectric elements F ₁ , F ₂ , and F ₃ , the thickness of the ferroelectric substance is the same as that of the PZT ferroelectric substance 20b. 3 times.

FIG. 5 shows the PE hysteresis loop of each ferroelectric element array. In the figure, the first and second
The values of the maximum spontaneous polarization Pr of the third ferroelectric element array are almost the same value, but the electric field necessary for reversing the polarization, that is, the value of the coercive electric field increases as the total film thickness of the ferroelectric increases. I understand that Therefore, when the maximum spontaneous polarization Pr is generated by the DC power source 22a of the reset circuit 22, it is necessary to apply an electric field sufficient to generate the maximum spontaneous polarization to the third ferroelectric element array having the largest film thickness. ..

In this way, after the maximum spontaneous polarization Pr is generated in all the ferroelectric elements in the ferroelectric unit 20 by the reset circuit 22, the external voltage to be measured is reversed in polarity to the ferroelectric unit 20. Connect so as to measure the maximum value of external voltage. The maximum voltage value calculation process will be described below by taking the case of measuring the voltage from the wind sensor as an example.

FIG. 3 shows a flow chart of the measurement process of this embodiment. First, it causes maximum spontaneous polarization Pr to each ferroelectric element F ₁ to F ₃ of the ferroelectric unit 20 using the reset circuit 22 described above in S101. Next, the ferroelectric unit 2 is controlled so that the voltage output from the wind sensor has a polarity opposite to that of the reset circuit 22.
Connect to 0. At this time, all the switches S _{1 to} S ₃ connected in series to each ferroelectric element array are turned on. FIG. 4 shows an example of output voltage characteristics from the wind sensor, where the horizontal axis represents time and the vertical axis represents output voltage. In this embodiment, the output voltage from the wind sensor is time t ₁ ,
The peak values d, e, and f are output at t ₂ and t ₃ , respectively.
The external voltage having such characteristics is applied to the ferroelectric unit 2
When applied to each of the ferroelectric elements F _{1 to} F ₃ within 0, the spontaneous polarization of each ferroelectric element changes along its PE hysteresis loop.

Here, as shown in FIG. 6, as the film thickness of the PZT ferroelectric increases, the coercive electric field that causes the reversal polarization also increases substantially in proportion to the film thickness. When the voltage reaches the maximum value f and the electric field corresponding to this f is equal to or higher than the coercive electric field, reversal polarization occurs. In the present embodiment, as described above, the first ferroelectric element row has the smallest film thickness and the third ferroelectric element row has the largest film thickness. Therefore, depending on the value of the output voltage f, 3 modes will appear.

(1) Inversion polarization does not occur in any of the first, second, and third ferroelectric element arrays.

(2) Any one of the first, second, and third ferroelectric element rows (the first, second, and third ferroelectric element rows are less likely to be domain-inverted in this order) is domain-inverted. ..

(3) The polarization of all the first, second, and third ferroelectric element arrays is inverted.

Therefore, the output terminal of the ferroelectric unit is next connected to the polarization measuring circuit 24, the switches S _{1 to} S ₃ are sequentially turned on, and it is checked whether or not the polarization is reversed, whereby the wind sensor is detected. The maximum output voltage value of can be detected.

FIG. 7 shows the polarization measuring circuit 2 in this embodiment.
4 is a circuit diagram and a polarization measurement principle explanatory diagram. The polarization measuring circuit 24 is composed of a DC power supply 24a and a resistor 24b that cause the ferroelectric element to generate maximum spontaneous polarization.
Remanent polarization is detected by monitoring the voltage or current across it.

That is, when a voltage is applied between AB to cause the ferroelectric element to have maximum spontaneous polarization and the voltage variation between BC at that time is measured, the ferroelectric element undergoes polarization reversal and already has the maximum spontaneous polarization Pr. 7B, the change is as shown in FIG. 7B, but when the remanent polarization of the ferroelectric element is not completely inverted, the change is as shown in B. This is because the ferroelectric element shows a change on the PE hysteresis loop when it already has the maximum spontaneous polarization, and otherwise changes without following the PE hysteresis loop.

Therefore, when a residual polarization other than the maximum spontaneous polarization occurs, a voltage (or current) change like the one shown in (b) is shown. Therefore, a predetermined voltage is applied twice between AB, and
The value of remanent polarization can be measured by obtaining the difference in voltage (or current) change (shaded area in the figure) between times (if the maximum spontaneous polarization Pr is already present, the difference becomes 0; Will show a difference depending on the polarization).

As described above, the DC power source 24a for producing the maximum spontaneous polarization in each ferroelectric element array needs to be changed according to the film thickness of the ferroelectric material, and therefore the polarization measurement of this embodiment is performed. The voltage of the DC power supply 24a of the circuit 24 may be the same voltage as the DC power supply 22a of the reset circuit 22,
For example, as shown in FIG. 8, the second ferroelectric element array and the third ferroelectric element array
Switches T ₁ and T ₂ are provided in each of the ferroelectric element rows, and when measuring the inverted polarization of the first ferroelectric element row, S ₁ is closed and a DC voltage is applied to the ferroelectric element F _1. Then
When measuring the inverted polarization of the second ferroelectric element array, the switches S ₂ and T ₁ are turned on and the inverted polarization of only the ferroelectric element F ₁ is measured. When measuring the reverse polarization of the third ferroelectric element array, the switches S ₃ and T ₂ are turned on and the reverse polarization of only the ferroelectric element F ₁ is measured.

As described above, when measuring the inversion polarization of each ferroelectric element array, the DC voltage is not applied to all the ferroelectric elements in the ferroelectric element array, but all the ferroelectric elements are arranged. By paying attention to only the ferroelectric element F ₁ common to the columns and measuring the inversion polarization, the DC power supply 2 of the polarization measuring circuit 24 is measured.
4a requires a low voltage, which facilitates measurement.

In the above-mentioned embodiment, the case where there are three ferroelectric element rows is shown, but the number of rows may be appropriately increased if necessary, and the number of ferroelectric elements connected in series is also increased. It goes without saying that the number may be increased appropriately.

[0039]

As described above, according to the ferroelectric capacitor and the method of manufacturing the same according to the present invention, a plurality of ferroelectric capacitors connected in series or in parallel can be easily formed on the semiconductor substrate. Therefore, the yield can be improved and the cost can be reduced. Further, it becomes possible to measure the maximum voltage with no power supply and in a nonvolatile manner by using the ferroelectric capacitor formed by the manufacturing method of the present invention.

[Brief description of drawings]

FIG. 1 is an explanatory view of a ferroelectric capacitor of the present invention and a method of manufacturing the same.

FIG. 2 is an overall configuration diagram of a maximum voltage measuring device using a ferroelectric capacitor of the present invention.

FIG. 3 is a measurement flow chart of the same example.

FIG. 4 is an output characteristic diagram of the wind sensor of the same embodiment.

FIG. 5 is a PE hysteresis loop diagram of each ferroelectric element array of the example.

FIG. 6 is a graph showing the relationship between the thickness of the ferroelectric substance and the coercive electric field in the same example.

FIG. 7 is an explanatory diagram of remanent polarization measurement in the same example.

FIG. 8 is a configuration diagram of another embodiment of the present invention.

FIG. 9 is a circuit diagram of a conventional device.

[Explanation of symbols]

 100 Silicon substrate 102 Silicon oxide film 104 Lower electrode 106 PZT ferroelectric film 108 Silicon oxide film 110 Upper electrode

Claims (2)

[Claims] 1. A first insulating film forming step of forming a first insulating film on a semiconductor substrate; a first metal film forming step of forming a first metal film on the first insulating film; A step of forming a lower electrode by etching the first metal film to form a plurality of lower electrodes; a step of forming a ferroelectric film on the lower electrode; a step of forming a ferroelectric film on the ferroelectric film; A second insulating film forming step of forming a second insulating film; a contact hole forming step of etching the second insulating film to form a contact hole with the ferroelectric film; and a second insulating film on the second insulating film. A second metal film forming step of forming a second metal film on the upper surface, and an upper electrode forming step of etching the second metal film to form a plurality of upper electrodes on the contact holes. Ferroelectricity Method of manufacturing a capacitor. 2. A semiconductor substrate, a plurality of lower electrodes formed on the semiconductor substrate, a ferroelectric film formed on the lower electrodes, and a ferroelectric film formed on the ferroelectric film. A ferroelectric capacitor comprising: an insulating film having a contact hole on the film; and a plurality of upper electrodes formed on the insulating film and connecting the contact holes.