JP2004087754A - Forming method of ferroelectric film and ferroelectric memory - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a ferroelectric film for stably forming the ferroelectric film having a large amount of polarized charge. <P>SOLUTION: A wafer 20 is fixed to a supporting table main body 40 with a curved upper surface by a clamp 41. Next, the wafer is inserted into an MOCVD (metal organic chemical vapor deposition) device to form the ferrodielectric film on the wafer 20. Subsequently, the wafer is left until reaching a temperature not higher than the curie temperature of the ferroelectric film and, thereafter, the clamp 41 is removed and the configuration of the wafer 20 is returned to the initial state of the same. According to this method, a compressive force is applied on the ferroelectric film whereby the amount of polarized charge of the ferroelectric film is increased by the piezo-electric effect. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of forming a ferroelectric film exhibiting a spontaneous polarization phenomenon, and a ferroelectric memory using a ferroelectric film as a capacitor for holding data.
[0002]
[Prior art]
Some semiconductor memories lose data when the power is turned off, and others do not lose data when the power is turned off. The former is called a volatile memory, and the latter is called a nonvolatile memory.
[0003]
A system LSI having a built-in nonvolatile memory is used for an IC card and a smart card. In recent years, a ferroelectric memory (FeRAM: Ferroelectric random access memory) having a ferroelectric capacitor has been used as a nonvolatile memory for this type of system LSI. The ferroelectric memory has a high rewriting speed of several tens of ns, low read / write voltage, and 1 × 10 ¹⁰ ~ 1 × 10 ¹² This has the advantage that rewriting can be performed once.
[0004]
A ferroelectric capacitor used for a data holding unit of a ferroelectric memory has PZT (PbZr) between a pair of electrodes. _x Ti _1-x O ₃ ), PLZT (Pb _y La _1-y Zr _x Ti _1-x O ₃ ) Or SBT (SrBi ₂ Ta ₂ O ₉ ) Etc. are sandwiched between thin films made of a ferroelectric material. The ferroelectric thin film exhibits a spontaneous polarization phenomenon in which a polarization state is maintained even when no electric field is applied. When an electric field is applied, the polarization direction changes according to the direction of the electric field. In a ferroelectric memory, data is stored by associating two polarization states having different polarization directions with “1” and “0”. The polarity inversion operation of a ferroelectric capacitor using PZT is described in, for example, SEIKE et al. : JOURNAL OF APPLIED PHYSICS VOL. 88, No. 9 2000.15. sep. pp. 3445-3447.
[0005]
[Problems to be solved by the invention]
By the way, since IC cards and smart cards are often used for systems handling money information and personal information, it is required to maintain high reliability for a long period of time. For example, in order to realize a service life of 10 years or more, the polarization charge amount of the ferroelectric film is 30 μC / cm. ² Above, more preferably 35 μC / cm ² There is a need to be more than that.
[0006]
Conventionally, a ferroelectric film is generally formed by a sputtering method or an MOCVD method. However, in a ferroelectric capacitor manufactured by the conventional method, the amount of polarization charge of the ferroelectric film is 20 to 25 μC / cm. ² Occupy the majority, 30μC / cm ² The ratio of the above capacitors is about 20 to 30%. Therefore, there is a demand for a method of forming a ferroelectric film capable of stably forming a ferroelectric film having a large polarization charge.
[0007]
As described above, an object of the present invention is to provide a method for forming a ferroelectric film capable of stably forming a ferroelectric film having a large amount of polarization charge.
[0008]
Another object of the present invention is to provide a ferroelectric memory capable of maintaining high reliability for a long period of time.
[0009]
[Means for Solving the Problems]
The above-described problems include a first step of bending the substrate within a range of elastic deformation, a second step of forming a ferroelectric film on the curved substrate, and a step of returning the substrate to the original shape. The third method is performed in this order, and the problem is solved by a method of forming a ferroelectric film.
[0010]
In addition, the above-mentioned problems are solved by a semiconductor substrate, a transistor formed on the semiconductor substrate, a first interlayer insulating film formed on the semiconductor substrate and covering the transistor, and a first interlayer insulating film formed on the first interlayer insulating film. A ferroelectric capacitor formed by laminating a lower electrode, a ferroelectric film, and an upper electrode, wherein one of the lower electrode and the upper electrode is electrically connected to the transistor; A second interlayer insulating film formed on the insulating film and covering the ferroelectric capacitor, wherein a compressive stress or a tensile stress is applied to the ferroelectric film. Solving with memory.
[0011]
It is known that when compressive stress is applied to a ferroelectric crystal material, the amount of polarization charge increases due to a piezo effect. The present invention utilizes this phenomenon to form a ferroelectric film having a large polarization charge.
[0012]
That is, in the present invention, the substrate is deformed by applying a stress within the range of elastic deformation, a ferroelectric film is formed on the substrate in that state, and the stress applied to the substrate is released to return to the original shape. return. According to this method, no stress is applied to the ferroelectric film immediately after film formation, but the ferroelectric film is in a state in which stress is applied by returning the substrate to its original shape. Thus, a ferroelectric film having a large amount of polarization charge is obtained.
[0013]
When a ferroelectric film is formed on a substrate by bending the substrate in a convex shape, a compressive stress is applied to the ferroelectric film when the shape of the substrate returns to flat. As described above, when a compressive stress is applied to the ferroelectric film, the amount of polarization charge of the ferroelectric film increases significantly as compared to when no stress is applied. Conversely, if a ferroelectric film is formed on a substrate by curving the substrate into a concave shape, a tensile stress is applied to the ferroelectric film when the shape of the substrate returns to flat. Also in this case, the amount of polarization charge of the ferroelectric film increases compared to when no stress is applied. However, the rate of increase in the amount of polarization charge is smaller than in the case where a compressive stress is applied. Therefore, it is preferable to deform the wafer so that a compressive stress is applied to the ferroelectric film.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in more detail. In the following description, “compressive stress” is a stress that compresses the ferroelectric thin film, and “tensile stress” is a stress that pulls the ferroelectric thin film.
[0015]
The inventors of the present application cleave a wafer having a PZT film (ferroelectric film) formed on its surface to obtain a test piece, and apply a stress (tensile stress or compressive stress) within a range of elastic deformation to the test piece. Thus, the polarization charge 2Pr of the ferroelectric film was measured. FIG. 1 shows the result. However, first, the polarization charge was measured without stress, and then the polarization charge when tensile stress was applied, the polarization charge when the stress was released (no stress), and when the compression stress was applied. The polarization charge amount and the polarization charge amount when the stress is released (no stress) are measured in order.
[0016]
The application of the tensile stress to the PZT film is performed by placing a plate 11 below the center of the test piece 10 and fixing both ends of the test piece 10 to a table with an adhesive tape 12 as shown in FIG. Was. Thereafter, the probe 13 was brought into contact with the center of the test piece 10 to measure the amount of polarization charge of the PZT film. In addition, as shown in FIG. 2B, the compressive stress is applied to the PZT film by placing a plate 11 under both ends of the test piece 10 and fixing the vicinity of the center of the test piece 10 to a table with an adhesive tape 12. Was done by doing. Thereafter, the probe 13 was brought into contact with the center of the test piece 10 to measure the amount of polarization charge of the PZT film.
[0017]
As shown in FIG. 1, the polarization charge amount 2Pr of the ferroelectric film measured without stress first is 31 μC / cm. ² However, the polarization charge amount 2Pr measured in a state where a tensile stress was applied was 32.5 μC / cm. ² Has increased. Once the stress is released and then a compressive stress is applied to the ferroelectric film, the polarization charge 2Pr becomes 35 μC / cm. ² Increased.
[0018]
FIG. 3 shows a test piece obtained by cleaving a wafer on which a PZT ferroelectric film is formed, bending the test piece by applying a stress within the range of elastic deformation, and then releasing the ferroelectric film in a state where the stress is released. It is a figure which shows the result of having measured 2Pr of polarization electric charges. That is, first, the polarization charge of the ferroelectric film is measured in the state of no stress, then the stress is released after applying the tensile stress 50 times, the polarization charge is measured, and the compressive stress is further applied 50 times. After the stress was released, the polarization charge was measured. However, the tensile stress was applied by turning the surface on which the PZT film was formed as shown in FIG. 4 (a) upward, and from a flat state to both ends of the test piece 10 as shown in FIG. 4 (b). This was performed by applying stress. The compressive stress was applied from the flat state with the surface on which the PZT film was formed as shown in FIG. 4A upward to both ends of the test piece 10 as shown in FIG. 4C. This was performed by applying stress.
[0019]
As can be seen from FIG. 3, the polarization charge 2Pr of the ferroelectric film to which no stress is applied is 33.5 μC / cm. ² However, the polarization charge amount 2Pr after applying a compressive stress was 38 μC / cm. ² Showed a large value.
[0020]
Thus, it was confirmed that the amount of polarization charge increases when stress is applied to the ferroelectric film. Therefore, in the present invention, a ferroelectric film is formed with the substrate deformed, and then the substrate is returned to a flat state. As a result, stress is applied to the ferroelectric film, and the amount of polarization charge increases.
[0021]
Assuming that the increase in the polarization charge is due to the piezo effect, it is necessary to bend the substrate so that a compressive stress is applied to the ferroelectric film before forming the ferroelectric film. However, as can be seen from FIG. 1, the amount of polarization charge also increases when a tensile stress is applied to the ferroelectric film. This is presumably because even when a tensile stress is applied to the ferroelectric film, there is a portion to which a compressive stress is applied in the film. Therefore, the ferroelectric film may be formed after bending the substrate so that a tensile stress is applied.
[0022]
(MOCVD equipment)
FIG. 5 is a schematic diagram showing a configuration of an MOCVD apparatus used for forming a ferroelectric film (PZT).
[0023]
The raw material tank 21a stores a Pb-based liquid raw material, the raw material tank 21b stores a Zr-based liquid raw material, the raw material tank 21c stores a Ti-based liquid raw material, and the raw material tank 21d stores a THF solvent. I have. The pipes 22a to 22d coming out of the raw material tanks 21a to 21d join the pipe 24. A mass flow controller 23a is provided in the middle of the pipe 22a, a mass flow controller 23b is provided in the middle of the pipe 22b, a mass flow controller 23c is provided in the middle of the pipe 22c, and a mass flow controller 23d is provided in the middle of the pipe 22d. Thus, the flow rate of each liquid source can be adjusted.
[0024]
For example, N is used as a carrier gas in the pipe 24. ₂ Is supplied. The liquid raw material is transferred to the vaporizer 25 by the carrier gas. The vaporizer 25 is provided with a heater (not shown) for heating the internal space and a nozzle (not shown) for injecting the liquid material sent through the pipe 24 into the internal space. The liquid raw material is gasified in the vaporizer 25 to become a raw material gas.
[0025]
A pipe 26 coming out of the vaporizer 25 is branched on the way, and one of the branched pipes 26a is connected to the MOCVD apparatus 30 via a valve 27a. The other branched pipe 26b is connected to an exhaust device 28 via a valve 27b.
[0026]
The MOCVD apparatus 30 includes a gas mixing chamber 31, a shower head 32, and a reaction chamber 33. In the gas mixing chamber 31, the source gas sent through the pipe 26a and the oxidizing gas (eg, O ₂ ) Are mixed. The gas mixed in the gas mixing chamber 31 is introduced from the shower head 32 into the reaction chamber 33.
[0027]
In the reaction chamber 33, a support table 34 for supporting the wafer (substrate) and a plate 35 for heating the wafer together with the support table 34 are provided. The gas introduced into the reaction chamber 33 undergoes a chemical reaction on the surface of the heated wafer to form a ferroelectric film on the wafer.
[0028]
The gas exhausted from the reaction chamber 33 is transferred to the exhaust device 28 through the pipe 29. Then, after the exhaust device 28 performs processing such as decomposition, the exhaust gas is exhausted.
[0029]
(Support)
FIGS. 6A and 6B are diagrams illustrating an example of the support base 34. FIG. As shown in FIG. 6A, the support table 34 includes a support table main body 40 having a convex (cylindrical) curved upper surface, and two clamps 41. The wafer 20 is placed on the support base body 40, the edge of the wafer 20 is pressed by the clamp 41, and the wafer 20 is fixed on the support base body 40 in a curved state as shown in FIG. 6B. .
[0030]
Each of the support base body 40 and the clamp 41 is made of a material coated with SiC or pBN (Pyrolytic Boron Nitride: Pyrolytic Boron Nitride), or a material having a high oxidation resistance such as AlN. Oxidation and corrosion are prevented even when exposed to an oxidizing atmosphere at a temperature of ° C.
[0031]
(Method of forming ferroelectric film)
In the present embodiment, the wafer 20 is fixed to the support table 34 in a curved state, and the support table 34 is placed on the plate 35 in the reaction chamber 33. Then, the wafer 20 is heated to 550 to 650 ° C., and a gas of an organometallic raw material of Pb, Zr and Ti and an oxidizing gas are introduced into the reaction chamber 33. Thereby, PZT is deposited on the wafer 20, and a PZT film is formed. After the PZT film is formed to a desired thickness, the supply of the source gas and the oxidizing gas is stopped.
[0032]
Next, the support 34 is taken out of the reaction chamber 33 and left until the temperature becomes lower than the Curie temperature of the ferroelectric material (PZT). Thereafter, the clamp 41 is removed to return the wafer 20 to its original flat shape. If the clamp 41 is removed to return the wafer 20 to a flat shape at a temperature higher than the Curie temperature of the ferroelectric material, the effect of applying stress to the ferroelectric film is lost. Although the Curie temperature of the ferroelectric material varies depending on the composition, it is generally about 280 to 300 ° C., so it is preferable to remove the clamp 41 after the temperature reaches 100 ° C. or lower.
[0033]
When there is a step in which the temperature becomes higher than the Curie temperature of the ferroelectric film after the formation of the ferroelectric film, it is preferable to remove the wafer 20 from the support table 34 after completing these steps.
[0034]
In the ferroelectric film thus formed, a compressive stress is applied to the ferroelectric crystal constituting the ferroelectric film, and as a result, the amount of polarization charge increases. As a result, the polarization charge amount becomes 30 μC / cm. ² Or 35μC / cm ² The above ferroelectric film can be formed stably, and the reliability of the ferroelectric memory can be improved.
[0035]
The method of forming a ferroelectric film according to the present embodiment is the same as the conventional method except that the wafer is fixed to a jig (support table) in a curved state, so that equipment other than the jig is updated. It is not necessary and can be implemented at low cost.
[0036]
In the above-described embodiment, the case where the ferroelectric film is a PZT film has been described. However, the present invention provides another ferroelectric film containing Pb (lead), Zr (zirconium), and Ti (titanium) as main components. The present invention can also be applied to the formation of a ferroelectric film mainly containing Sr (strontium), Bi (bismuth), and Ta (tantalum), and a ferroelectric film mainly containing Bi, La (lanthanum), and Ta. it can. For example, Pb (Zr, Ti) _0.3 , (Pb, La) (Zr, Ti) _0.3 , (Pb, La, Ca) (Zr, Ti) _0.3 , (Pb, La, Sr) (Zr, Ti) _0.3 And (Pb, La, Ca, Sr) (Zr, Ti) _0.3 There is. The ferroelectric material containing Sr, Bi, and Ta as main components includes, for example, SrBi. ₂ Ta ₂ O ₉ There is. Further, ferroelectrics containing Bi, La, and Ta as main components include, for example, (Bi, La) ₄ Ti ₃ O ₁₂ There is.
[0037]
In the present embodiment, the wafer 20 is curved in a cylindrical shape, but may be curved in a spherical shape or a conical surface. Further, in the present embodiment, the wafer 20 is fixed in a curved state by the support table 34 having the clamp 41, but the wafer 20 may be fixed on the curved surface of the support table by electrostatic force.
[0038]
Further, in the present embodiment, the wafer 20 is fixed on the support table 34 and placed on the heating plate 35. However, the wafer is fixed on the susceptor using a susceptor having a convex upper surface. You may make it.
[0039]
(FeRAM)
FIG. 7 is a sectional view showing an example of the FeRAM. An element isolation insulating film 51 for isolating an element region is formed on the semiconductor substrate 50. In each element region, a transistor 52 forming a memory cell is formed. Then, a first interlayer insulating film 53 covering the transistor 52 is formed on the semiconductor substrate 50. This interlayer insulating film 53 is made of SiO ₂ Alternatively, it is made of an insulating material such as SiN.
[0040]
On the interlayer insulating film 53, a ferroelectric capacitor formed by laminating a lower electrode 54, a ferroelectric film 55, and an upper electrode 56 is formed. This ferroelectric capacitor is covered by a second interlayer insulating film 57 formed on the first interlayer insulating film 53.
[0041]
Wirings 59a, 59b, 59c are formed on the interlayer insulating film 57. In this example, the wirings 59a and 59b are electrically connected to the impurity diffusion layers of the transistor 52 via the via contacts 58a and 58b embedded in the insulating films 53 and 57. The wiring 59b is also electrically connected to the upper electrode 56 of the ferroelectric capacitor via a contact hole formed in the insulating film 57, and the wiring 59c is strongly connected via a via contact 58c embedded in the insulating film 57. It is electrically connected to the lower electrode 54 of the dielectric capacitor.
[0042]
The lower electrode 54 and the upper electrode 56 are made of, for example, one of noble metals of Pt (platinum), Ir (iridium) and Ru (ruthenium), or Pt, Ir, Ru, Sr (strontium) and Co (cobalt). It is formed with any one kind of conductive noble metal oxide as a main component.
[0043]
Further, the ferroelectric film 55 is formed of a dielectric material such as PZT, PLZT or SBT, and is formed by using the MOCVD apparatus shown in FIG.
[0044]
The interlayer insulating film 57 is made of, for example, SiO ₂ , TEOS (Tetraethyl orthosilicate): Si (OC ₂ H ₅ ) ₄ ), SiN, FSG (Fronrite doped Silicate Glass), HSG (trade name of Hitachi Chemical), SiLK (trade name of Dow Chemical, a kind of organic polymer), BCB (Dow Chemical, a kind of organic polymer) And NCS (Nano Cavity Silicon: nanocavity silica) as the main component.
[0045]
In the FeRAM, one ferroelectric capacitor is formed for one memory cell. In this case, if the compression direction (or the tensile direction) is not uniform for a plurality of ferroelectric films in the same chip, the characteristics of the ferroelectric capacitor may vary. Therefore, it is preferable to align the directions of the ferroelectric films in the same wafer or the same chip in one direction. For example, as shown in FIG. What is necessary is just to make the direction of the short side or the long side of the ferroelectric film 45 of the ferroelectric capacitor coincide with the X direction.
[0046]
This makes it possible to obtain a ferroelectric memory in which the amount of polarization charge of the ferroelectric film is large and uniform, and high reliability can be maintained for a long period of time.
[0047]
(Other embodiments)
In the above-described embodiment, the wafer is curved by the support main body and the clamp, but the method of bending the wafer is not limited to this. For example, as shown in FIG. 9, SiO 2 is formed on the back side of the wafer 60 by a thermal oxidation method or a CVD method. ₂ By forming the film 61, the wafer 60 can be curved in a convex shape. In the case of a wafer having a thickness of 0.3 mm and a diameter of 6 to 8 inches, an SiO having a thickness of 100 nm to 1 μm ₂ When the film 61 is formed, the wafer 60 can be curved in a convex shape.
[0048]
A ferroelectric film is formed on the wafer 60 while the wafer 60 is curved as described above. Then, the SiO ₂ When the film 61 is removed, the wafer 60 returns to its original flat shape, and a compressive stress is applied to the ferroelectric film. Thereby, a ferroelectric film having a large amount of polarization charge can be obtained.
[0049]
In the above-described embodiment, the ferroelectric film is formed by the MOCVD method. However, the method of forming the ferroelectric film in the present invention is not limited to this. Any method can be used as long as a thin film can be formed with good reproducibility. Such methods include CVD (including MOCVD), sputtering, and sol-gel methods.
[0050]
(Supplementary Note 1) A first step of bending the substrate within a range of elastic deformation, a second step of forming a ferroelectric film on the curved substrate, and a third step of returning the substrate to its original shape. And (c) are performed in this order.
[0051]
(Supplementary Note 2) The method for forming a ferroelectric film according to Supplementary Note 1, wherein in the second step, the ferroelectric film is formed by an MOCVD method.
[0052]
(Supplementary Note 3) The method for forming a ferroelectric film according to Supplementary Note 1, wherein in the first step, the substrate is curved in a convex shape.
[0053]
(Supplementary Note 4) The method for forming a ferroelectric film according to supplementary note 1, wherein in the first step, the substrate is curved in a concave shape.
[0054]
(Supplementary Note 5) The method for forming a ferroelectric film according to Supplementary Note 1, wherein the third step is performed after the temperature of the substrate becomes equal to or lower than the Curie temperature of the ferroelectric film.
[0055]
(Supplementary note 6) The method for forming a ferroelectric film according to supplementary note 1, wherein the ferroelectric film formed in the second step includes Pb, Zr, and Ti as main components.
[0056]
(Supplementary note 7) The method for forming a ferroelectric film according to supplementary note 1, wherein the ferroelectric film formed in the second step includes Sr, Bi, and Ta as main components.
[0057]
(Supplementary note 8) The method for forming a ferroelectric film according to supplementary note 1, wherein the ferroelectric film formed in the second step includes Bi, La, and Ta as main components.
[0058]
(Supplementary note 9) The method for forming a ferroelectric film according to supplementary note 1, wherein in the first step, the substrate is fixed to a curved surface of a jig having a curved surface.
[0059]
(Supplementary note 10) The method for forming a ferroelectric film according to supplementary note 1, wherein the substrate is a silicon substrate, and in the first step, an oxide film is formed on a back surface side of the silicon substrate.
[0060]
(Supplementary Note 11) A semiconductor substrate, a transistor formed on the semiconductor substrate, a first interlayer insulating film formed on the semiconductor substrate to cover the transistor, and a lower electrode on the first interlayer insulating film. A ferroelectric capacitor formed by laminating a ferroelectric film and an upper electrode, wherein one of the lower electrode and the upper electrode is electrically connected to the transistor; and And a second interlayer insulating film which covers the ferroelectric capacitor and is formed with a compressive stress or a tensile stress applied to the ferroelectric film.
[0061]
(Supplementary note 12) The ferroelectric memory according to supplementary note 11, wherein the direction of the compressive stress or the tensile stress applied to the ferroelectric film is the same for all the ferroelectric films on the substrate. .
[0062]
(Supplementary Note 13) The supplementary note 11, wherein at least one of the lower electrode and the upper electrode is formed with one kind of noble metal selected from the group consisting of Pt, Ir, and Ru as a main component. Ferroelectric memory.
[0063]
(Supplementary Note 14) At least one of the lower electrode and the upper electrode is formed mainly of an oxide of one metal selected from the group consisting of Pt, Ir, Ru, Sr, and Co. 13. The ferroelectric memory according to claim 11, wherein
[0064]
(Supplementary Note 15) The ferroelectric memory according to supplementary note 11, wherein the ferroelectric film is formed mainly of Pb, Zr, and Ti.
[0065]
(Supplementary note 16) The ferroelectric memory according to supplementary note 11, wherein the ferroelectric film is formed mainly of Sr, Bi, and Ta.
[0066]
(Supplementary Note 17) The ferroelectric memory according to supplementary note 11, wherein the ferroelectric film is formed mainly of Bi, La, and Ta.
[0067]
(Supplementary Note 18) The second interlayer insulating film is made of SiO ₂ 12. The ferroelectric memory according to claim 11, wherein the ferroelectric memory is formed using, as a main component, one kind of insulator selected from the group consisting of TEOS, SiN, FSG, HSG, SiLK, BCB, and NCS.
[0068]
【The invention's effect】
As described above, according to the ferroelectric film forming method of the present invention, the ferroelectric film is formed in a state where the substrate is curved, and then the substrate is returned to the original shape. Is subjected to a compressive stress or a tensile stress, and as a result, the polarization charge of the ferroelectric film increases. As a result, a ferroelectric film having a large amount of polarization charge can be formed stably, and a ferroelectric memory capable of maintaining high reliability for a long period of time can be obtained.
[0069]
Further, according to the ferroelectric memory of the present invention, since the compressive stress or the tensile stress is applied to the ferroelectric film constituting the ferroelectric capacitor, the polarization charge of the ferroelectric film is large. Thus, high reliability can be maintained for a long period of time, so that the present invention can be applied to an IC card or a smart card that handles money information or personal information.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a test piece obtained by cleaving a wafer having a PZT film formed on a surface thereof, and applying a stress within a range of elastic deformation to the test piece to obtain a polarization charge amount 2Pr of a ferroelectric film. It is a figure showing the result of measurement.
FIGS. 2A and 2B are diagrams showing a method of applying a compressive stress and a tensile stress to a PZT film.
FIG. 3 is a diagram illustrating a test piece obtained by cleaving a wafer on which a PZT ferroelectric film is formed, bending the test piece by applying a stress within a range of elastic deformation, and then strengthening the test piece with the stress released. It is a figure showing the result of having measured 2Pr of polarization electric charges of a dielectric film.
FIGS. 4A to 4C are diagrams showing a method of applying a compressive stress and a tensile stress to a PZT film.
FIG. 5 is a schematic diagram showing a configuration of an MOCVD apparatus used for forming a ferroelectric film.
FIGS. 6A and 6B are diagrams illustrating an example of a support base.
FIG. 7 is a cross-sectional view illustrating an example of an FeRAM.
FIG. 8 shows an example in which the direction of the short side or the long side of the ferroelectric film of each of the plurality of ferroelectric capacitors formed on the wafer is made to coincide with the compression direction of the ferroelectric film. FIG.
FIG. 9 is a cross-sectional view showing an example in which the wafer is curved by forming an oxide film on the back surface side of the wafer.
[Explanation of symbols]
10 ... test piece,
12 ... adhesive tape,
13 ... probe,
20 ... wafer,
21a-21d ... raw material tank,
23a to 23d: mass flow controller,
25 ... vaporizer,
28 ... exhaust device,
30 ... MOCVD equipment,
31 ... gas mixing chamber,
32 ... shower head,
33 ... Reaction chamber,
34 ... Support,
40 ... support base body,
41… Clamp,
50: semiconductor substrate,
51 ... element isolation insulating film,
52 ... transistor,
53, 57 ... interlayer insulating film,
54 ... Lower electrode,
55 ... ferroelectric film,
56: upper electrode,
58a to 58c: Via contact,
59a59c ... wiring.

Claims (8)

A first step of bending the substrate within a range of elastic deformation;
A second step of forming a ferroelectric film on the curved substrate;
And a third step of returning the substrate to its original shape in this order. 2. The method according to claim 1, wherein in the first step, the substrate is curved in a convex shape. 2. The method according to claim 1, wherein the third step is performed after the temperature of the substrate becomes equal to or lower than the Curie temperature of the ferroelectric film. A semiconductor substrate;
A transistor formed on the semiconductor substrate;
A first interlayer insulating film formed on the semiconductor substrate and covering the transistor;
A ferroelectric layer formed by stacking a lower electrode, a ferroelectric film, and an upper electrode on the first interlayer insulating film, wherein one of the lower electrode and the upper electrode is electrically connected to the transistor; A capacitor,
A second interlayer insulating film formed on the first interlayer insulating film and covering the ferroelectric capacitor;
A ferroelectric memory, wherein a compressive stress or a tensile stress is applied to the ferroelectric film. The ferroelectric memory according to claim 4, wherein the direction of the compressive stress or the tensile stress applied to the ferroelectric film is the same for all ferroelectric films on the substrate. 5. The ferroelectric substance according to claim 4, wherein at least one of the lower electrode and the upper electrode is formed with one kind of noble metal selected from a group consisting of Pt, Ir, and Ru as a main component. memory. At least one of the lower electrode and the upper electrode is formed mainly of an oxide of one kind of metal selected from the group consisting of Pt, Ir, Ru, Sr and Co. 5. The ferroelectric memory according to 4. The second interlayer insulating film is formed mainly of one kind of insulator selected from the group consisting of SiO ₂ , TEOS, SiN, FSG, HSG, SiLK, BCB and NCS. The ferroelectric memory according to claim 4.

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