JPH04171976A - capacitor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates primarily to a capacitor insulating film used in a dynamic memory, and is concerned with stabilizing its physical properties.

[Conventional technology]

FIG. 3(a) shows Pb as an example of a ferroelectric material. (Z
r x Ti tl-x+ ) Ox (hereinafter,
The dependence of the dielectric constant of PZT on the Zr mole fraction is shown. As is clear from the figure, a very large dielectric constant is exhibited at a Zr mole fraction of 0.52.

Conventionally, when a thin film with a high dielectric constant is required, a method such as Pb+, s (
Using a uniform target such as Zro4Tio,s)Os, and using the (111) plane of Pt as the substrate, Pt)+',o(Zre , 5tTi.

,,) A film with a uniform composition of Os was obtained. In addition, in the above sputtering, the target contains Pb+, s (Zro, s*
Tio, 41) Using Os, input power is 300
W, gas pressure 20 m Torr, gas composition A r /
O! = 1/l, substrate-target distance 7c
It is set to m.

This film forming method is not limited to the sputtering method, but may also be other methods. In the Zolnigel method, the raw material solution composition, firing temperature, etc.
In the method, this is possible by controlling the raw material gas flow rate 9 and the corresponding conditions.

The resulting Pb in the above-example. (Z r
O,62T i 0.41) 03 film has a relative dielectric constant ε,
= 1000 to 10000, so for example 64MD
When used in RAM, the film thickness is 0.5 even if the thickness is 3000.
A capacitor area of about .mu.m2 is sufficient, and considering a cell area of 2 to 3 .mu.m2, complicated techniques such as stacking and trenching are unnecessary, and an extremely simple cell structure can be realized.

Also, Pb+, o (Zrx Ti n-x+ )Ox
Since is a ferroelectric material, it exhibits residual polarization as shown in FIG.

In other words, when ten electric fields are applied, the domains arranged in the applied electric field increase rapidly, and the song #! Draw A-B. Next, when the electric field is decreased, when the external electric field is 0, the charge +P due to residual polarization (point C)
r remains. When an electric field is further applied, the polarization is reversed and reaches point D. Further, when the external electric field is set to 0, negative residual polarization occurs (charge -Pr).

A nonvolatile memory as shown in FIG. 7, for example, utilizes this as a memory.

7(a) and 7(b) show the write operation of data "0" and "1", and FIG. 7(C) shows the read operation. Lead
After both the write word line WL becomes H (3,3V), the drive line DL or L (OV) becomes H (3,3V).
), the operation is completed.

That is, in FIG. 7, the write operation of "0" occurs when WL exceeds a certain voltage 2, for example 3.3V, and the capacitor upper electrodes z, z' of the hit/bit line (BL/BL)
are respectively GND and 3.3V.

In FIG. 7, when DL is at GND level, BL/BL
The polarization of the ferroelectric material above is A and D in Figure 6, and DL=
At 3.3V (7), the polarization moves to A-+B and D-9-E. Therefore, even if the external electric field due to DL becomes 0, the data "0" is +Pr at point C on the BL side and -Pr at point E on the BL side.
Accumulate Pr. Conversely, when it is "l", -Pr is applied to the BL side.
, +Pr is accumulated on the BL side and data is held in a non-volatile manner.

When reading, first set B L/B L to GND level. Next, when WL is set to 3.3V or higher, Z.

Z' are both at the GND level. 3. From DL or GND.
When reading “0” data by changing to 3v,
Charges of BL move from C to B, and charges of BL move from E to B. “
1”, BL moves from E to B, and BL moves to C-4-B.The sense amplifier for BL/BL L moves from BL to BL
Senses the charge difference between them and outputs it to the outside. In a nonvolatile memory that operates in this way, Pb+, o (Z
The amount of residual polarization of rx T 1 ++−x+ ) 02 is an important factor, and the Zr fraction may take a value different from that of the dielectric constant.

[Problem to be solved by the invention]

However, in the capacitor insulating film of conventional capacitors, slight variations in the insulating material, such as dielectric constant,
There were problems such as extremely large variations in physical property values such as residual polarization.

For example, as shown in Figure 3 (al), Ptz, o (Z
rxT i (+-X) ) The relative dielectric constant of Os is very critical to the Zr fraction. Therefore, if a homogeneous film is produced by aiming at the maximum point of the dielectric constant of Zr as in the past, the dielectric constant of Zr A slight variation results in a very large variation in the dielectric constant. For example, if the Zr fraction deviates from 0.52 by ±10%, the dielectric constant (permittivity) will decrease significantly. The same can be said about residual polarization.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain a capacitor having a capacitor insulating film with small variations in physical properties.

[Means to solve the problem]

The capacitor according to the present invention is one in which the composition of the capacitor insulating film is changed to continuously change its physical property values in the film thickness direction6. Since the physical property values are continuously changed in the film thickness direction, a certain range of physical property values is created in the insulating film, and the film physical properties are averaged. Therefore, changes in film physical properties due to variations in physical property values are reduced, thereby making it possible to obtain a capacitor insulating film with small variations in physical property values.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram for explaining a capacitor according to an embodiment of the present invention, and shows a cross-sectional structure of a capacitor insulating film.

In the figure, l is Pb+, o (Zrx 'ri n
-x+ )03 thin film (hereinafter referred to as PZT thin film) X≦
0°52, 2 is a portion of the thin film where x>0.52, and 3 is the substrate. Figure 2 shows the Z of the above PTZ thin film.
It is a graph in which the r fraction is plotted against the film thickness direction.

The Zr fraction of the PZT thin film is x = 0, where the dielectric constant is maximum.
．． It changes continuously between the maximum value F and the minimum value G around 52.

Next, FIG. 3(a) shows the relationship between the dielectric constant and the Zr fraction.

The relative permittivity of the films in FIGS. 1 and 2 is expressed by the area of the shaded area 4 in FIG. 3(a), but in FIG. 3(b), the Zr fraction is shifted overall. The shaded area 4 represents the case where the Zr fraction is ideal, and the shaded area 5 represents the case where the Zr fraction is deviated. Of the shaded areas 4°5, 4a and 5a are common to both, so the parts to be compared are the shaded areas 4b and 5.
This is the area of b.

When the relative dielectric constants are equal to each other in the Zr fractions given by F and G, the areas of the shaded regions 4b and 5b are almost equal, and the area change, that is, the change in the relative permittivity, can be virtually ignored.
The resulting film can be stabilized.

However, the interval between the maximum value F and the minimum value G should be narrower in order to remove the tail part of the peak, that is, the part with poor physical properties. It is most efficient to keep the variation to the same level as the film variation. Note that here, the width is set to 1% or more and 20% or less in terms of Zr fraction.

Next, an example of a method for manufacturing such a film will be described.

FIG. 4 is a top view of a target in the sputtering method. In FIG. 4, 6 is metal pb, 7 is metal Zr, and 8 is metal Ti. In such a mosaic target, the Zr fraction can be changed by changing the area ratio of Ti and Zr depending on the location. Also,
Pb1 with low Zr. (Z r x T i ++-x+
) The Zr fraction can also be changed by placing metal Zr or ZrO2 on the fired body of Os. As shown in FIG. 5, sputtering is performed without rotating the substrate 9 over the target IO. When the substrate passes through a place with a high Zr fraction on the tarp/soto, Z
T when passing through an r-rich film or a place with a high Ti fraction.
An i-rich film is formed, and a film as shown in FIG. 1 can be formed. In the CVD method, since it is only necessary to change the gas flow rate of the Zr raw material, the film shown in FIG. 1 can be obtained more easily.

In this example, since the Zr fraction of the PTZ insulating film changes continuously, the physical property values and the dielectric constant are shown in the shaded area as shown in FIG. 3(a). It can be expressed by the area of 4. That is, by giving a range to the Zr fraction,
It can be said that the average is taken.

At this time, if the Zr fraction includes a peak in the width of the Zr fraction as in this example, the Zr fraction deviates, for example, as shown in FIG.
), since only the area with low physical property values is affected, the area of the shaded area, that is, the overall physical property value is stable as a whole.

In addition, in the above example, Pb+, o (Zrx Tl
(1-,,)0. Did you only explain about Pb, Zr?
.

The Ti oxide may contain La and Fe. Alternatively, other insulating materials may be used. In addition, as a physical property value, the dielectric constant depending on the Zr fraction is taken as an example, or other physical property values such as residual polarization, coercive electric field, etc. may be used.

〔Effect of the invention〕

As described above, according to the present invention, since the composition of the capacitor insulating film is continuously changed in the film thickness direction, the physical property values that depend on the composition can be averaged, and the physical property values in the capacitor insulating film can be It is possible to obtain a capacitor with small variations in .

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view for explaining a capacitor according to an embodiment of the present invention, FIG. 2 is a graph showing a graph plotting the Zr fraction of the capacitor insulating film in the film thickness direction, and FIG.
a) is Pb+, o (Zrx T 1(1-,,>
0. Figure 3 (b) shows the Zr fraction dependence of the dielectric constant of
) is a diagram showing the change in relative permittivity due to a shift in the Zr fraction, Figure 4 is a diagram showing an example of a target when forming a capacitor insulating film according to the present invention by sputtering, and Figure 5 is a diagram showing a substrate during sputtering. , a diagram showing the positional relationship of targets, FIG. 6 a diagram showing hysteresis of a ferroelectric material, and FIG. 7 a diagram showing the operation of a ferroelectric memory. In the figure, 1 is Pb1. o CZrx Tl n-x+
)03 The part of the thin film where X≦0.52, 2 is Pb,...
(Zr x Ti, +-x+) x of Ox thin film>
0.52, 3 is the substrate, 4, 4a, 4b are regions showing the dielectric constant of the film, 5, 5a, 5b are Z during film formation.
A region showing the dielectric constant when the r fraction deviates, 6 is the metal p
b, 7 is metal Zr, 8 is metal Ti, 9 is substrate, IO is target, F is the maximum value of Zr fraction in the film, G is Z in the film
This is the minimum value of r fraction. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (2)

[Claims] (1) A capacitor used in a dynamic memory having a capacitor insulating film, characterized in that the capacitor insulating film has physical properties that vary continuously in the film thickness direction by changing its composition. . (2) The capacitor insulating film is made of oxides of lead, zirconium, and titanium, and the molar fraction of zirconium changes continuously in the film thickness direction, and the width of the change is 1% or more, 2% or more.
2. The capacitor according to claim 1, wherein the mole fraction of zirconium is 0% or less and includes a mole fraction of zirconium corresponding to the maximum dielectric constant as the physical property value.