JP2000068464A - Ferroelectric thin film, method of evaluating the same, ferroelectric memory and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To nondestructively and efficiently obtain the orientation of crystal grains in a ferroelectric thin film and the magnitude of the polarization by obtaining the spectral intensity of Raman scattered lights radiated from the ferroelectric film according to an exciting light irradiated on this film. SOLUTION: A linearly polarized exciting light 31A is irradiated on a ferroelectric film 39. According to the exciting light 31A, Raman scattered lights 31B radiated from the ferroelectric film 39 are detected. C-axis orientation of a tetragonal provskite ferroelectric crystal in the ferroelectric film 39 is obtd. from the spectrum intensity of a Raman scattered light 31B obtd. by a spectroscope 44. Thus the ferroelectric film 39 can be evaluated nondestructively and efficiently, even if the ferroelectric film 39 is a fine pattern. From the Raman scattering intensity, the magnitude of the spontaneous polarization of the ferroelectric film 39 can also be measured nondestructively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a semiconductor device, and more particularly to a method of manufacturing a semiconductor memory device using a ferroelectric thin film. Semiconductor storage devices such as so-called DRAM or SRAM are widely used as high-speed main storage devices in information processing devices such as computers.
These are volatile storage devices, and stored information is lost when the power is turned off. On the other hand, a nonvolatile magnetic disk device has conventionally been used as a large-capacity auxiliary storage device for storing programs and data.

However, magnetic disk drives have the disadvantages of being large and mechanically fragile, consuming large amounts of power, and having low access speeds when reading and writing information. On the other hand, recently, as a nonvolatile auxiliary storage device, an EEPP which stores information in the form of electric charges in a floating gate electrode has been developed.
ROMs or flash memories are often used. In particular, since a flash memory has a cell configuration similar to that of a DRAM, it can be easily formed at a large integration density, and is expected as a large-capacity storage device comparable to a magnetic disk device.

On the other hand, in an EEPROM or a flash memory, information is written by injecting hot electrons into a floating gate electrode through a tunnel insulating film.
Further, there has been a problem that the tunnel insulating film is deteriorated when information is repeatedly written and erased. If the tunnel insulating film is deteriorated, the writing or erasing operation becomes unstable.

On the other hand, there has been proposed a ferroelectric memory device (hereinafter referred to as FeRAM) for storing information in the form of spontaneous polarization of a ferroelectric film. In such an FeRAM, each memory cell transistor is formed of a single MOSFET as in the case of a DRAM, and the dielectric film in the memory cell capacitor is formed of PZT (Pb (Zr, Ti) O ₃ ) or PL.
It has a configuration in which it is replaced with a ferroelectric such as ZT (Pb (Zr, Ti, La) O ₃ ), and integration at a high integration density is possible. In addition, since FeRAM controls spontaneous polarization of a ferroelectric capacitor by applying an electric field, an EEPROM is used to perform writing by injecting hot electrons.
Write speed is 1000 times or more faster than that of flash memory and flash memory, and power consumption is about 1/10
It has the advantageous feature of being reduced to Furthermore, since it is not necessary to use a tunnel oxide film, the lifetime is long, and it is considered that 100,000 times the number of rewrites of the flash memory can be secured.

Although many of the currently realized FeRAMs are designed with relatively loose design rules of about 1 μm, they can be mixed with recent high-speed CMOS logic circuits down to submicron on integrated circuits. Like,
There is research into further miniaturization of FeRAM.

[0006]

2. Description of the Related Art FIG. 1 shows a configuration of a conventional FeRAM 10. Referring to FIG. 1, a FeRAM 10 is formed on a p-type Si substrate 11, and an active region is defined on a surface of the Si substrate 11 by a field oxide film 12. A gate electrode 13 of a memory cell transistor is formed in the active region via a gate oxide film (not shown) corresponding to a word line of FeRAM. ⁺ Type diffusion regions 11A _, 11
B is formed as a source region and a drain region of the memory cell transistor, respectively. Further, the substrate 1
In 1, a channel region is formed between the diffusion regions 11A and 11B.

The gate electrode 13 is covered with a CVD oxide film 14 covering the surface of the Si substrate 11 in the active region, and the CVD oxide film 14 is covered with a planarizing interlayer insulating film 15. A contact hole 15A exposing the diffusion region 11B is formed in the interlayer insulating film 15, and the contact hole 15A is filled with a plug 16 made of polysilicon or WSi.

Further, an adhesion layer 17 having a Ti / TiN structure is formed on the interlayer insulating film 15 so as to cover an exposed portion of the plug 16, and a lower electrode 18 made of Pt or the like is formed on the adhesion layer 17. It is formed. Further, a ferroelectric film 19 made of PZT or PLZT is formed on the lower electrode 18, and an upper electrode 20 made of Pt or the like is formed on the ferroelectric film 19.

The side wall surface of the ferroelectric capacitor composed of the lower electrode 18, the ferroelectric film 19 and the upper electrode 20 is C
The ferroelectric capacitor is entirely covered with an interlayer insulating film 22. A contact hole 22A that exposes the diffusion region 22A is formed in the interlayer insulating film 22, and a bit line made of Al or an Al alloy that contacts the diffusion region 22A in the contact hole 22A on the interlayer insulating film 22. A pattern 23 is formed.

FIG. 2 shows a PZT unit cell used as the ferroelectric film 19 in the FeRAM 10 of FIG. Referring to FIG. 2, PZT has a perovskite crystal structure, and Pb or Ti atoms coordinated by oxygen atoms are displaced in the c-axis direction by an external electric field. As a result, PZT shows the spontaneous polarization characteristics shown in FIG. That is, in the FeRAM 10 of FIG. 1, by applying a predetermined write voltage between the lower electrode 18 and the upper electrode 20, the spontaneous polarization in the PZT film forming the ferroelectric film 19 is inverted, and Is written in the ferroelectric film 19.

In order to read the binary information written in the FeRAM 10 of FIG. 1, the word line, that is, the gate electrode 13 is activated, and the voltage appearing at the bit line electrode 23 through the channel region is detected. FIG.
In an amount width field strength at zero in the hysteresis loop called Q _SW, FERA larger the value
The holding of information by M10 is ensured. The value of the electric field required for writing also tends to decrease, and as a result, F
The eRAM 10 can be driven with low power. In other words,
In the FeRAM 10 of FIG. 1, it is desirable to maximize the value of Q _SW of the ferroelectric film 19.

[0012]

Conventionally, it has been known that a thin film of PZT or PLZT exhibits a maximum Q _SW near a phase boundary between a rhombohedral phase and a tetragonal phase. The body film 19 is generally often used in such a composition near the phase boundary. FIG.
FIG. 2 shows a phase equilibrium diagram of ZT, that is, the PbZrO ₃ —PbTiO ₃ system (B. Jaffe, et al., Piezoelectric Ceramics,
Academic Press, 1971).

Referring to FIG. 4, the PbZrO ₃ -P
In the bTiO ₃ system, the PbTiO ₃ component has a molar ratio of 6-7.
% Cold rhombohedral (rhombohedral) phase and tetragonal phase (Tetragonal) phase and appeared exceeds, phase boundary MPB between the rhombohedral phase region and tetragonal phase region, approximately in the composition of PbTiO ₃ components It can be seen that it is located at 48 mol%. It can also be seen that a cubic (Cubic) phase region appears on the high temperature side of the rhombohedral phase and the tetragonal phase region. In the rhombohedral phase region, F _{R (HT)} indicates a high temperature phase region, and F _{R (LT)} indicates a low temperature phase region.

As described above, in order to maximize the Q _SW of the ferroelectric film 19 in the FeRAM 10, the composition of the ferroelectric film 19 is set near the phase boundary MPB. Such a multiphase ferroelectric film 19 is generally a polycrystalline film, and it is inevitable that the direction of individual crystal grains in the film varies in various directions. On the other hand, the square phase PZT or PLZT has the maximum Q _SW in the c-axis direction, and thus the square phase PZT or PZT in the ferroelectric film 19 of the FeRAM 10.
It is preferable that the LZT is oriented in such a direction that the c-axis is substantially perpendicular to the main surface of the film 19. For this reason, various studies have been made to control the orientation direction of crystal grains in such a polycrystalline ferroelectric film according to sample preparation conditions.

On the other hand, conventionally, the identification of the PZT or PLZT crystal grains in the polycrystalline ferroelectric film formed in this manner and the evaluation of the orientation direction are carried out by using a ferroelectric film uniformly formed on a substrate. Has been performed by applying X-ray diffraction, but in X-ray diffraction, a sample having a size of several mm square or more is required for measurement. However, with such a method, it is impossible to evaluate the characteristics of a fine ferroelectric film 19 like the FeRAM 10 of FIG. FeR
In order to evaluate the orientation of the crystal grains of the ferroelectric film 19 in the AM 10, analysis means having a spatial resolution of 1 μm or less is required. In addition, a method for obtaining the magnitude of the polarization of the ferroelectric film 19 from information on the orientation of the crystal grains is required.

Accordingly, it is a general object of the present invention to provide a new and useful method of manufacturing a ferroelectric memory device which solves the above-mentioned problems. A more specific object of the present invention is to use a method for evaluating a ferroelectric thin film for obtaining orientation and polarization of crystal grains in a ferroelectric thin film with fine spatial resolution, and an evaluation method for such a thin film. An object of the present invention is to provide a method of manufacturing a ferroelectric memory device.

[0017]

According to the present invention, there is provided a method for evaluating a ferroelectric film containing a tetragonal perovskite-type ferroelectric crystal according to the present invention.
Irradiating the ferroelectric film with excitation light, detecting Raman scattered light emitted from the ferroelectric film in response to the excitation light, and from the spectral intensity of the Raman scattered light, Determining the c-axis orientation of the tetragonal perovskite ferroelectric crystal in the ferroelectric film, the method for evaluating a ferroelectric film,
Or as described in claim 2, the step of irradiating the excitation light includes a step of polarizing the excitation light formed by a light source to a first polarization plane, the step of detecting the Raman scattered light, 2. The method according to claim 1, further comprising a step of detecting a polarized light component having a second polarization plane orthogonal to the first polarization plane in the backscattered Raman light emitted from the dielectric film. The step of detecting the Raman scattered light by a method of evaluating a dielectric film or as described in claim 3 includes a step of determining the intensity of a Raman scattered light component having a Raman shift of about 600 cm ^-1. Claim 1
Or in the step of determining the c-axis orientation according to the method for evaluating a ferroelectric film according to 2 or as described in claim 4, wherein the Raman shift is determined from a peak intensity of a Raman scattered light component of about 600 cm ^−1. The ferroelectric film evaluation method according to claim 3, wherein the c-axis orientation is determined. Further, as described in claim 5, the ferroelectric film is further obtained from the spectral intensity of the Raman scattered light. The method for evaluating a ferroelectric film according to any one of claims 1 to 4, wherein the method includes a step of calculating the magnitude of spontaneous polarization of the film, or as described in claim 6, in the ferroelectric film containing the tetragonal phase perovskite ferroelectric crystal, the ferroelectric film, and wherein the Raman shift component of about 600 cm ^-1 is not substantially contained in the Raman scattering spectrum Tsuyo誘The body film, or as described in claim 7, in the manufacturing method of a ferroelectric memory device,
Forming a ferroelectric film containing a tetragonal perovskite ferroelectric crystal on the lower electrode, evaluating the ferroelectric film, and forming an upper electrode on the ferroelectric film The step of evaluating the ferroelectric film, the step of irradiating the ferroelectric film with excitation light, and Raman scattered light emitted from the ferroelectric film in response to the excitation light A ferroelectric memory, comprising: a step of detecting; and a step of obtaining a c-axis orientation of the tetragonal perovskite ferroelectric crystal in the ferroelectric film from the spectral intensity of the Raman scattered light. The step of irradiating the excitation light by a method of manufacturing a device or as described in claim 8 includes a step of polarizing the excitation light formed by a light source to a first polarization plane, wherein the Raman scattered light is emitted. The step of detecting 8. The ferroelectric material according to claim 7, further comprising a step of detecting a polarized light component having a second polarization plane orthogonal to the first polarization plane in the backscattered Raman light emitted from the body film. By the manufacturing method of the storage device,
Alternatively, the step of detecting the Raman scattered light includes a step of obtaining an intensity of a Raman scattered light component having a Raman shift of about 600 cm ^-1 as described in claim 9. According to the method of manufacturing a ferroelectric memory device of the above, or in the step of obtaining the c-axis orientation, the Raman shift is about 600
The method of manufacturing a ferroelectric memory device according to claim 9, wherein the c-axis orientation is obtained from a peak intensity of a Raman scattered light component of cm ⁻¹ , or as described in claim 11, 11. The ferroelectric memory device according to claim 7, further comprising a step of calculating the magnitude of spontaneous polarization of the ferroelectric film from the spectral intensity of the Raman scattered light. After the step of evaluating the ferroelectric film and before the step of forming the upper electrode, the pass / fail based on the magnitude of the spontaneous polarization is further determined by a manufacturing method or as described in claim 12. The method of manufacturing a ferroelectric memory device according to claim 11, further comprising the step of: determining the quality of the upper electrode after the pass / fail determination step. Process The method further includes a step of heat-treating the ferroelectric film determined to be defective in the pass / fail determination step, and a step of performing the evaluating step again on the heat-treated ferroelectric film. The method of manufacturing a ferroelectric memory device according to claim 12, or claim 14.
As described in the above, in a ferroelectric memory device including an active element formed on a substrate and a ferroelectric capacitor formed on the substrate and electrically connected to the active element, The body capacitor includes a lower electrode, a ferroelectric film including a tetragonal perovskite ferroelectric crystal formed on the lower electrode, and an upper electrode formed on the ferroelectric film. The ferroelectric film is about 600 cm
^The problem is solved by a ferroelectric memory device characterized in that a Raman shift component of ^-1 is substantially not included in a Raman scattering spectrum.

[0018]

FIG. 5 shows a schematic configuration of a micro-Raman spectrometer 30 used in the first embodiment of the present invention. Referring to FIG. 5, the argon laser 3
A laser beam 31A having a wavelength of 488 nm and an output of 30 mW emitted from 1 is reflected by a mirror 32 and then converted by a polarizer 33 into linearly polarized light having a first polarization plane.
Further, after being reflected by the holographic mirror 34, the light enters the optical microscope 35. Incident laser beam 31
A is reflected by the half mirror 36, and then the objective lens 37
As a result, the light enters the ferroelectric film 39 held on the XYZ stage 38.

The laser beam reflected by the ferroelectric film 39 passes through the half mirror 36, and then passes through the eyepiece 40.
Then, the light enters the camera 41, and the image of the ferroelectric film 39 is displayed on the display device 42. Further, by driving the XYZ stage based on the image displayed on the display device 42, it is possible to irradiate the laser beam 31A to a desired position on the ferroelectric film 39. become. The laser beam 31A is focused on the ferroelectric film 39 to a beam spot of about 0.6 μm close to the diffraction limit.

On the other hand, the ferroelectric film 39 reflects the laser beam 31A by being irradiated with the laser beam 31A, and also emits backward Raman scattered light 31B. The reflected laser beam 31A and the Raman scattered light 3
1B is reflected by the half mirror 36 and then enters the holographic mirror 34. The holographic mirror 34 selectively cuts the reflected laser beam 31A, and passes only the Raman scattered light 31B. The Raman scattered light 31B further passes through the analyzer 43, and
A polarization component having a polarization plane perpendicular to the polarization plane enters a spectroscope 44 having a CCD device 45.

FIG. 6 shows the spectrum of the Raman scattered light 31B obtained by the spectroscope 44 for the samples A to C.
However, the samples A to C are obtained by sputtering P on the substrate.
The ZT film was heat-treated at 700 ° C. in different oxygen atmospheres. However, the Raman spectrum in FIG. 6 is normalized at the peak of the wave number of about 280 cm ⁻¹ .

Referring to FIG. 6, the observed Raman spectrum is substantially changed in samples A, B, and C. In particular, a peak appearing at a wave number position of about 600 cm ^-1 is observed in samples A, B, and C.
It should be noted that there is a large change in B and C.
In Samples A, B, and C, as will be described later, it is considered that the orientation direction of the PZT crystal grains in the tetragonal phase is different due to the difference in the heat treatment conditions. This is considered to reflect the change in the orientation direction of the PZT crystal grains in B and C.

[0023] Figure 7, with respect to a Raman spectrum obtained by the apparatus of FIG. 5, the wave number is subjected to a linear correction in the range of 400cm ^-1 ~800cm ^-1, further wavenumber of about 520cm
¹ shows the results of approximation with three Gaussian curves of ⁻¹ , about 600 cm ⁻¹ and 700 cm ⁻¹ . Referring to FIG. 7, it can be seen that the Raman spectrum is approximated with very high accuracy by the above three Gaussian curves. Of the Gaussian curves in FIG. 7, the height of the Gaussian curve having a wave number of 600 ^-1 changes greatly in Samples A, B and C corresponding to the results in FIG. 6, and the direction of the c-axis in the PZT sample is changed. It is thought that it reflects sensitively.

FIG. 8 shows Freire, JD (Freire, JD, Ph
ys. Rev. B37, pp. 2074, 1988) Tetragonal PbT by others
4 shows a relationship between a Raman spectrum of an iO ₃ crystal and a lattice vibration mode. From the relationship of FIG. 8, the 600 cm ⁻¹ shown in FIG.
Of the Gaussian peak of Ab in the tetragonal PbTiO ₃ crystal
It is identified as corresponding to the ₁ (TO ₃ ) mode lattice vibration.

Incidentally, the Raman scattering intensity I of the PZT crystal grains when the orientation is rotated in the ferroelectric film 39 is as follows.
When the orientation of the coordinate system fixed to the crystal grain is defined as shown in FIG.

[0026]

(Equation 1)

## EQU2 ## However, in FIG. 8, the coordinate system x ₁
−x ₂ −x ₃ is a coordinate system fixed to the ferroelectric film 39, and a coordinate system x ₁ ′ −x ₂ ′ −x ₃ ′ is PZ in the ferroelectric film 39.
The coordinate system fixed to the T crystal grains, the angle θ is the angle formed by the c-axis of the PZT crystal grains with respect to the film thickness direction, the angle φ is the rotation angle of the PZT crystal grains around the c-axis, and the angle γ is The azimuthal angles formed by the c-axis in the plane of the ferroelectric film 39 are shown. Further, in Equation (1), E _I is the incident laser beam 3
1A is the electric field vector of E, E _s is the electric field vector of the Raman light to be formed, T is the Raman tensor in a coordinate system fixed to the crystal grains, and R is the three-dimensional rotation of the crystal grains by the angles θ, φ, and γ. Represents a matrix corresponding to. Also,
In equation (1), A is a proportional constant.

In the measuring apparatus shown in FIG. 5, the incident laser beam is linearly polarized on the first polarization plane, and the detected Raman light is linearly polarized on the second perpendicular polarization plane. In such a system, the electric field vectors E _I , E _S and A
The Raman tensor T of ₁ (TO ₃ ) mode is given by the following equation (2)

[0029]

(Equation 2)

When the equation (2) is substituted into the equation (1), the Raman scattered light intensity I is given by the following equation (3)

[0031]

(Equation 3)

Is given by Further, assuming that the direction of the c-axis of the PZT crystal grains in the plane of the ferroelectric film 39 is random, the equation (3) is further simplified, and the following equation (4) is obtained.

[0033]

(Equation 4)

As shown in FIG. That is, as shown in FIG. 10, the Raman scattered light intensity I is proportional to the fourth power of the sine of the angle θ formed by the c-axis of the PZT crystal grains in the ferroelectric film 39 with respect to the surface of the film 19. I understand. FIG.
0, PZT in the ferroelectric film 39
When the c-axis direction of the crystal grains is orthogonal to the film 19, or when the angle θ is within about 20 °, the Raman scattering peak at the Raman shift of 600 cm ⁻¹ does not substantially appear. On the other hand, when the c-axis of the PZT crystal grains is inclined and increases beyond the value of the angle of about 20 °, the Raman scattering peak at the Raman shift of 600 ^-1 sharply increases.

The results of FIG. 10 show that the manufactured ferroelectric film was subjected to Raman spectroscopy using the microscopic Raman spectrometer having the configuration of FIG.
By selecting a Raman scattering peak having a low m- ¹ intensity or substantially no Raman scattering peak, the PZ in the ferroelectric film can be reduced.
This means that it is possible to select a sample in which the orientation direction of the T or PLZT crystal is substantially perpendicular to the plane of the ferroelectric film. The comparison of the intensity of the Raman scattering peak at the Raman shift of 600 cm ⁻¹ may be performed on Raman spectrum data normalized to a specific Raman shift peak, for example, a peak of 280 cm ⁻¹ as shown in FIG.

FIG. 11 shows PZT subjected to various heat treatments.
The relationship between the magnitude of the spontaneous polarization Q _SW obtained for the ferroelectric film and the Raman scattered light intensity at a Raman shift of 600 cm ⁻¹ is shown. Referring to FIG. 11, the 600 cm ^-1
PZT as the intensity of the Raman scattered light at
It can be seen that the value of Q _SW of the ferroelectric film increases. This is, for example, considering the result of FIG.
In forming the PZT or PLZT ferroelectric film 19 at 0, a film having a Raman shift of 600 cm ^{-1 and} a low intensity of Raman scattered light is selected and used. Indicates that the ratio of those oriented substantially perpendicular to the film is high, and thus a film exhibiting a large spontaneous polarization is obtained.

The relationship shown in FIG. 11 is obtained experimentally.

[0038]

(Equation 5)

Can be approximated by However, in Equation (5), Q _SW is expressed in units of μC / cm ² . In FIG. 11, the solid line is obtained by plotting the equation (5). Therefore, in the present invention, the spontaneous polarization of the ferroelectric film formed on the substrate is selected by using the microscopic Raman spectrometer of FIG. 5 and selecting a sample having a Raman shift of 600 cm ⁻¹ and a large Raman scattering intensity. It becomes possible to remove a small ferroelectric film. [Second Embodiment] FIG. 12 is a flowchart showing a method of manufacturing a ferroelectric capacitor according to a second embodiment of the present invention.

Referring to FIG. 12, a lower electrode such as Pt is formed on a substrate in step S1, and PZT or PLZ is formed on the lower electrode in step S2.
A ferroelectric film made of T is formed by sputtering or a sol-gel method. The ferroelectric film thus formed is subjected to rapid thermal processing (RTA) at a temperature of about 700 to 750 ° C. for 1 to 2 minutes in step S3, and the ferroelectric film is crystallized.

Next, in the step S4, the c-axis orientation of the tetragonal phase PZT or PLZT crystal grains in the crystallized ferroelectric film is inspected by the method described in the first embodiment. As a result of inspection, Raman shift was 600
If the Raman scattering intensity at cm ^-1 is low or substantially not detected as described in FIG. 10, c of the square phase PZT or PLZT crystal grains in the obtained ferroelectric film is obtained.
It is concluded that the axial direction is substantially orthogonal to the substrate, and an upper electrode is formed on the ferroelectric film in step S5. Further, in step S6, a good capacitor is obtained by performing a rapid heat treatment on the obtained structure in an oxidizing atmosphere, typically at 650 ° C.

On the other hand, in the inspection step of step S4,
If the value of the Raman scattering intensity at the Raman shift of 600 cm ^-1 is large, the ferroelectric film is discarded as defective in step S7. On the other hand, in the inspection step of step S4, if the Raman scattering peak at 600 cm ^-1 is detected but the size is not large, the upper electrode is formed in step S8, and further in step S9, step S6 is performed. A similar rapid heat treatment is performed, and an electrical test is performed in step S10 to determine pass / fail.

The inspection according to the present invention in step S4 is a non-destructive inspection, and therefore, 100% inspection is possible. Also,
By performing the electrical test in step S10 only on the sample whose quality is suspected in step S4, the yield can be improved and the manufacturing throughput can be improved. This is because the sample suspected in step S4 may be recovered in the heat treatment step in step S9. [Third Embodiment] FIGS. 13A to 15H are views showing a manufacturing process of an FeRAM according to a third embodiment of the present invention.

Referring to FIG. 13A, a memory cell region is formed on a p − type Si substrate 51 by a field oxide film 52. Further, a gate insulating film 53 is formed on the Si substrate 51 so as to cover the memory cell region, and a gate electrode 54 is formed on the gate insulating film 53 in the same manner as a normal MOS transistor. Gate electrode 54 forms a part of a word line crossing the memory cell region. Further, in the substrate 51, n-type diffusion regions 55 and 56 are formed on both sides of the gate electrode 54 using the gate electrode 54 as a self-alignment mask.

After the MOS transistor is formed in this manner, an SiO ₂ film 57 is formed on the substrate 51 so as to cover the gate electrode 54, and the SiO ₂ film 57 is formed in the SiO ₂ film 57 by a well-known photolithography method. Then, a contact hole exposing the diffusion region 55 is formed. After the formation of the contact hole, a WSi layer is deposited on the SiO ₂ film 57 so as to include the contact hole. As a result, the WSi layer contacts the diffusion region 55 in the contact hole. By patterning this WSi layer, FIG.
Are formed as shown in FIG.

Next, in the step of FIG. 13B, an interlayer insulating film 59 typically made of SiO ₂ is formed as shown in FIG.
After being planarized using, for example, a CMP (chemical mechanical polishing) method, a deep contact hole 60 exposing the diffusion region 56 is formed in the interlayer insulating film 59 by high-resolution photolithography. . Next, FIG.
In the step of (C), a polysilicon film 61 doped n ⁺ type with P is formed on the structure of FIG.
According to Method D, the polysilicon Si film 61 is deposited so as to fill the contact hole 60.
In the step 4 (D), the polysilicon film 61 is etched back by dry etching until the surface of the interlayer insulating film 59 is exposed, whereby a structure in which the contact holes are filled with polysilicon plugs 62 is obtained.

In the step of FIG. 14D, a Ti film (not shown) is further formed on the interlayer insulating film 59 by a PVD method.
A TiN film (not shown) is formed on the polysilicon plug 62 as a diffusion barrier layer by reactive sputtering. Further thereon, a conductor layer 63 containing Pt, Ir or IrO ₂ is formed. Further, in the step of FIG. 14D, a ferroelectric film 64 made of PZT or PLZT is formed on the conductor layer 63 by sputtering in an oxidizing atmosphere. The deposited ferroelectric film 64 is typically crystallized by rapid heat treatment at about 700 ° C. in an inert atmosphere, and further subjected to rapid heat treatment in an oxidizing atmosphere to form a ferroelectric film. Oxygen vacancies that are easily formed in 64 are eliminated.

Next, in the step of FIG. 14E, the PZT film 64 is patterned into a desired pattern by a photolithography method, and furthermore, a conductor layer 63 thereunder is formed.
Are patterned into a corresponding pattern by an ion milling method. As a result of the patterning of the conductor layer 63, the lower electrode 65 of the ferroelectric capacitor is formed, and as a result of the patterning of the PZT film 24, the capacitor insulating film 6 is formed.
6 are formed.

In the present embodiment, the structure of FIG.
Is held as a substrate 19 on an XYZ stage 38 of a micro-Raman spectrometer 30 of the type described above, and a laser beam 31A formed by the light source 31 is irradiated on the ferroelectric capacitor insulating film 66, thereby forming PZT or PLZT in the film 66. The c-axis orientation direction of the crystal grains is evaluated. That is,
Raman shift of 6 in the observed Raman scattering spectrum
If the peak at 00 cm ^-1 is not substantially detected, it is determined to be a good product, and the process proceeds to the step of FIG. On the other hand, 60
If a Raman shift of 0 cm ^-1 is observed, it is determined that there is a possibility of a defective product.

In the step of FIG. 14F, SiO 2 is formed on the structure of FIG.
₂ film 67 is deposited by a CVD method,
A contact hole 68 exposing the capacitor insulating film 66 is formed in the _second film 67. Further, FIG.
In the step (1), a Pt pattern 69 is formed as an upper electrode of the ferroelectric capacitor so as to cover the capacitor insulating film 66 exposed on the SiO ₂ film 67.
In the step 5 (H), an interlayer insulating film 70 is formed on the SiO ₂ film 67 so as to cover the upper electrode 69. A wiring pattern 71 is formed on the interlayer insulating film 70.
Is formed.

In the FeRAM of FIG. 15H, except that the Raman shift peak at 600 cm ^-1 is not substantially observed in the ferroelectric capacitor insulating film 66, FIG.
Has the same configuration as the conventional FeRAM described in FIG. In the present embodiment, in the inspection process of FIG. 14E, a sample having a possibility of failure can be eliminated by the nondestructive inspection, so that the inspection process of the finished product is simplified, and the manufacturing throughput of the FeRAM can be improved. . Fourth Embodiment FIG. 16 shows the configuration of a micro Raman spectrometer 80 according to a fourth embodiment of the present invention. However, FIG.
The parts described above in the middle are denoted by the same reference numerals, and description thereof is omitted.

Referring to FIG. 16, the microscopic Raman spectrometer 80 sets the center of the transmittance coincident with the Raman shift of 280 cm ⁻¹ on the optical path of the Raman scattered light 31 B and on the downstream side of the analyzer 43. A band-pass optical filter 81 having a band-pass optical filter 81 and a band-pass optical filter 82 having a center of transmittance matching the Raman shift of 600 cm ^-1 is disposed so as to be freely inserted into and removed from the optical path of the Raman scattered light 31B. The Raman scattered light 31B that has passed through the optical filter 81 or 82 inserted in the optical path is focused on a two-dimensional CCD array 84 by a lens 83, and the obtained image signal is sent to an image processing device 85.

[0053] In the present embodiment, first, the optical filter 81 is inserted in the optical path of the Raman scattered light 31B, two-dimensional distribution I ₁ (x peak intensities of Raman shift of 280 cm ^-1 using the image processing apparatus 85, y) is measured on the surface of the ferroelectric film 39. Next, the filter is switched from 81 to 82, and a similar two-dimensional distribution I ₂ (x, y) is measured for a Raman shift of 600 cm ⁻¹ . Further, in the image processing device 85, the standardized operation I ₂ (x, y) / I
₁ By performing (x, y), Raman shift 280
Raman shift 600 normalized with a peak intensity of cm ^-1
A two-dimensional distribution of the peak intensity at cm ^-1 is determined. Baseline correction is performed on each point of the normalized Raman peak intensity distribution obtained in this manner, and Gaussian curve fitting is performed, whereby the c-axis of the square phase PZT or PLZT crystal in the ferroelectric film 39 is obtained. The azimuth can be evaluated.

In the above description, the ferroelectric film is made of PZT.
Alternatively, PLZT is used, but the present invention is not limited to such a specific material system, and the present invention relates to PbTiO ₃ ,
PbZrO ₃ , BaTiO ₃ , SrTiO ₃ , KNbO
_{The present} invention can be applied to a Raman scattering peak derived from lattice vibration having a tetragonal A ₁ symmetry, composed of ₃ , KTaO ₃ , or a mixed crystal thereof.

Although the present invention has been described with reference to the preferred embodiments, the present invention is not limited to such specific embodiments, and various modifications and changes may be made within the scope of the present invention described in the appended claims. Is possible.

[0056]

According to the first to fifth aspects of the present invention, in the method for evaluating a ferroelectric film made of a perovskite-type ferroelectric crystal containing a tetragonal phase, a straight line is formed on the ferroelectric film. Irradiating polarized excitation light, detecting Raman scattered light emitted from the ferroelectric film according to the excitation light,
By determining the spectral intensity of the Raman scattered light, the c-axis orientation of the tetragonal perovskite type ferroelectric crystal in the ferroelectric film is non-destructively, even when the ferroelectric film is a fine pattern. Can be evaluated efficiently. In particular, the Raman shift is 600 cm ^-1
The intensity of the Raman scattering peak clearly reflects the c-axis orientation. Therefore, as described in claims 3 and 4, by measuring the intensity of the Raman scattering peak at 600 cm ⁻¹ , Advantageously, an evaluation of the membrane is performed. Further, it is possible to non-destructively measure even the magnitude of the spontaneous polarization of the ferroelectric film from the Raman scattering intensity.

According to a sixth aspect of the present invention, in the ferroelectric film including the tetragonal phase perovskite type ferroelectric crystal, the ferroelectric film has a Raman shift component of about 600 cm ^-1 substantially in the Raman scattering spectrum. , The square phase PZT or PLZT crystal in the ferroelectric film is c
The axis is oriented substantially perpendicular to the film surface and shows the maximum spontaneous polarization.

According to a feature of the present invention, there is provided a method of manufacturing a ferroelectric memory device including, as a capacitor insulating film, a ferroelectric film made of a perovskite ferroelectric crystal containing a tetragonal phase. By irradiating the ferroelectric film with linearly polarized excitation light, detecting Raman scattered light emitted from the ferroelectric film in response to the excitation light, and determining the spectral intensity of the Raman scattered light. A c-axis orientation of the tetragonal perovskite-type ferroelectric crystal in the ferroelectric film is aligned in a direction substantially perpendicular to a main surface of the ferroelectric film, and has a spontaneous polarization maximum ferroelectric film. The ferroelectric memory device can be inspected and sorted without damaging the ferroelectric memory device. In particular, the intensity of the Raman scattering peak at a Raman shift of 600 cm ^-1 clearly reflects the c-axis orientation, and therefore the intensity of the Raman scattering peak at 600 cm ^-1 as described in claims 9 and 10. It is advantageous to evaluate the ferroelectric film by measuring

According to the feature of the present invention described in claim 14,
In a ferroelectric memory device using a ferroelectric film containing a tetragonal perovskite ferroelectric crystal as a ferroelectric capacitor, the ferroelectric capacitor is about 600 cm.
The spontaneous polarization of the ferroelectric capacitor can be maximized by using a ferroelectric film that does not substantially include the Raman shift component of ^{-1 in} the Raman scattering spectrum. Accordingly, even if such a ferroelectric memory device is miniaturized, the operation does not become unstable.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a conventional ferroelectric memory device.

FIG. 2 is a diagram showing a crystal structure of a ferroelectric film used in the ferroelectric memory device of FIG.

FIG. 3 is a diagram illustrating polarization characteristics of the ferroelectric film of FIG. 2;

FIG. 4 is a diagram showing a phase equilibrium diagram of a ferroelectric film used in the ferroelectric memory device of FIG. 1;

FIG. 5 is a diagram illustrating a configuration of a microscopic Raman spectrometer used in the first embodiment of the present invention.

FIG. 6 is a diagram showing an example of a Raman scattering spectrum obtained by using the apparatus of FIG. 5;

FIG. 7 is a diagram showing an approximation of the Raman scattering spectrum of FIG. 6 using a Gaussian curve.

FIG. 8 is a diagram showing a relationship between a lattice vibration mode in a ferroelectric film and a Raman scattering spectrum.

FIG. 9 is a diagram that defines the orientation of a ferroelectric crystal in a ferroelectric film.

FIG. 10 is a diagram illustrating a relationship between a peak intensity of a Raman shift of 600 cm ⁻¹ in a PZT film and an orientation angle of a ferroelectric crystal in the film.

FIG. 11 is a diagram showing the relationship between the peak intensity of the Raman shift at 600 cm ⁻¹ in the PZT film and the magnitude of spontaneous polarization of the ferroelectric film.

FIG. 12 is a flowchart showing a manufacturing process of a ferroelectric film according to a second embodiment of the present invention.

FIGS. 13A to 13C are diagrams (part 1) illustrating the steps of manufacturing the ferroelectric memory device according to the third embodiment of the present invention.

FIGS. 14 (D) to (F) are views (No. 2) showing the steps of manufacturing the ferroelectric memory device according to the third embodiment of the present invention.

FIGS. 15G to 15H are views (No. 3) showing the steps of manufacturing the ferroelectric memory device according to the third embodiment of the present invention.

FIG. 16 is a diagram showing the configuration of a microscopic Raman spectrometer used in the third embodiment of the present invention.

[Explanation of symbols]

10 ferroelectric memory device 11, 51 substrate 11A, 11B, 55, 56 diffusion region 12, 52 a field insulating film 13,54 gate electrode 14,21,57,67 SiO ₂ film 15,22,59,70 interlayer insulating film 16, 62 conductor plug 17 adhesion layer 18, 63, 65 lower electrode 19, 64, 66 ferroelectric film 20, 69 upper electrode 22A contact hole 23 bit line electrode 30, 80 microscopic Raman spectrometer 31 light source 31A laser beam 31B Back Raman scattered light 32 Mirror 33 Polarizer 34 Holographic mirror 35 Microscope 36 Half mirror 37 Objective lens 38 XYZ stage 39 Sample 40 Eyepiece 41 Camera 42 Display device 43 Analyzer 44 Spectroscope 45, 84 CCD array 53 Gate insulating film 60 conductor layer 68 opening 1 wiring patterns 81 and 82 band-pass filter 83 lens 85 image processing apparatus

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Koichiro Honda 4-1-1, Kamidadanaka, Nakahara-ku, Kawasaki-shi, Kanagawa F-term within Fujitsu Limited (reference) 5F083 AD21 FR02 JA14 JA15 JA38 JA43 PR33 PR34 PR40

Claims (14)

[Claims] 1. A method for evaluating a ferroelectric film including a tetragonal perovskite ferroelectric crystal, comprising: irradiating the ferroelectric film with excitation light; Detecting the Raman scattered light emitted from the film; and determining the c-axis orientation of the tetragonal perovskite ferroelectric crystal in the ferroelectric film from the spectral intensity of the Raman scattered light. A method for evaluating a ferroelectric film, comprising: 2. The step of irradiating the excitation light includes a step of polarizing the excitation light formed by a light source to a first plane of polarization, and the step of detecting the Raman scattered light includes the step of: 2. The evaluation of the ferroelectric film according to claim 1, further comprising a step of detecting a polarized light component having a second polarization plane orthogonal to the first polarization plane in the emitted backscattered Raman light. Method. 3. The method according to claim 1, wherein the step of detecting the Raman scattered light includes the step of determining the intensity of a Raman scattered light component having a Raman shift of about 600 cm ^−1.
The evaluation method of the ferroelectric film described in the above. 4. The method according to claim 3, wherein in the step of determining the c-axis orientation, the c-axis orientation is determined from a peak intensity of a Raman scattered light component having a Raman shift of about 600 cm ^−1. Evaluation method of dielectric film. 5. The method according to claim 1, further comprising a step of calculating the magnitude of spontaneous polarization of the ferroelectric film from the spectral intensity of the Raman scattered light. Evaluation method of ferroelectric film. 6. A ferroelectric film containing a tetragonal phase perovskite ferroelectric crystal, wherein the ferroelectric film has a Raman shift component of about 600 cm ⁻¹ substantially not included in a Raman scattering spectrum. Characteristic ferroelectric film. 7. A method of manufacturing a ferroelectric memory device, comprising: forming a ferroelectric film including a tetragonal perovskite ferroelectric crystal on a lower electrode; and evaluating the ferroelectric film. And forming an upper electrode on the ferroelectric film, wherein the step of evaluating the ferroelectric film includes: irradiating the ferroelectric film with excitation light; and Detecting the Raman scattered light emitted from the ferroelectric film in response to the c-axis orientation of the tetragonal phase perovskite ferroelectric crystal in the ferroelectric film from the spectral intensity of the Raman scattered light And a method for manufacturing a ferroelectric memory device. 8. The step of irradiating the excitation light includes the step of polarizing the excitation light formed by a light source to a first plane of polarization, and the step of detecting the Raman scattered light comprises the step of: 8. The ferroelectric memory device according to claim 7, further comprising a step of detecting, from the emitted backscattered Raman light, a polarization component having a second polarization plane orthogonal to the first polarization plane. Production method. 9. The method according to claim 7, wherein the step of detecting the Raman scattered light includes the step of determining the intensity of a Raman scattered light component having a Raman shift of about 600 cm ^−1.
The manufacturing method of the ferroelectric memory device according to the above. 10. The method according to claim 9, wherein in the step of determining the c-axis orientation, the c-axis orientation is determined from a peak intensity of a Raman scattered light component having a Raman shift of about 600 cm ^−1. A method for manufacturing a dielectric storage device. 11. The method according to claim 7, further comprising a step of calculating the magnitude of spontaneous polarization of the ferroelectric film from the spectral intensity of the Raman scattered light. A method for manufacturing a ferroelectric memory device. 12. The method according to claim 11, further comprising, after the step of evaluating the ferroelectric film and before the step of forming the upper electrode, a step of judging pass / fail based on the magnitude of the spontaneous polarization. The method of manufacturing a ferroelectric memory device according to claim 11. 13. A heat treatment process for the ferroelectric film determined to be defective in the pass / fail determination step after the pass / fail determination step and before the step of forming the upper electrode,
Performing the evaluating step on the heat-treated ferroelectric film again.
3. The method for manufacturing a ferroelectric memory device according to item 2. 14. A ferroelectric memory device comprising: an active element formed on a substrate; and a ferroelectric capacitor formed on the substrate so as to be electrically connected to the active element. The capacitor includes a lower electrode, a ferroelectric film including a tetragonal perovskite-type ferroelectric crystal formed on the lower electrode, and an upper electrode formed on the ferroelectric film. The ferroelectric memory device, wherein the ferroelectric film has substantially no Raman shift component of about 600 cm ^{-1 in} the Raman scattering spectrum.