JP2009065088A - Manufacturing method of ferroelectric memory device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a ferroelectric memory device capable of simplifying a process of forming a contact hole. <P>SOLUTION: This manufacturing method of a ferroelectric memory device includes processes of: forming a ferroelectric capacitor 3 on a semiconductor substrate; forming a hydrogen barrier film 12 covering the ferroelectric capacitor 3; forming an interlayer insulation film 13 covering the hydrogen barrier film 12; forming a through-hole 22 penetrating the interlayer insulation film 13 by etching using a mixture gas containing C<SB>4</SB>F<SB>8</SB>gas and O<SB>2</SB>gas; and forming, continuously to the through-hole 22, a through-hole 21 penetrating the hydrogen barrier film 12 by etching using the mixture gas. The ratio of the flow rate of the C<SB>4</SB>F<SB>8</SB>gas to the sum of the flow rate of the C<SB>4</SB>F<SB>8</SB>gas and the flow rate of the O<SB>2</SB>gas in the formation process of the through-hole 22 is smaller than that in the formation process of the through-hole 21. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a ferroelectric memory device having a ferroelectric capacitor.

A ferroelectric memory device (FeRAM) is a nonvolatile memory capable of low voltage and high speed operation utilizing spontaneous polarization of a ferroelectric material, and a memory cell can be composed of one transistor / one capacitor (1T / 1C). . Therefore, since it can be integrated in the same manner as a DRAM, it is expected as a large-capacity nonvolatile memory.
Here, as the ferroelectric material, a perovskite oxide such as lead zirconate titanate (Pb (Zr, Ti) O ₃ : PZT) or a bismuth layer such as bismuth strontium tantalate (SrBi ₂ TaO ₉ : SBT) is used. Compound etc. are mentioned.

A hydrogen barrier film that blocks reducing species such as hydrogen entering from the outside is provided around the ferroelectric capacitor that constitutes the ferroelectric memory device. As a result, oxygen deficiency occurs in the ferroelectric material, and the electrical characteristics of the ferroelectric capacitor are prevented from deteriorating.
In addition, the ferroelectric capacitor is electrically connected to the wiring formed on the interlayer insulating film covering the hydrogen barrier film and the plug formed in the contact hole penetrating the hydrogen barrier film and the interlayer insulating film ( For example, see Patent Document 1).
The contact hole is formed using a dry etching method. Here, the gas used during etching is changed between the step of forming contact holes in the interlayer insulating film and the step of forming contact holes in the hydrogen barrier film.
JP 2006-108268 A

  However, the following problems remain in the conventional method for manufacturing a ferroelectric memory device. That is, since the gas used at the time of etching is changed between the interlayer insulating film and the hydrogen barrier film, there is a problem that the manufacturing process becomes complicated.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a method for manufacturing a ferroelectric memory device in which a contact hole forming process is simplified.

  The present invention employs the following configuration in order to solve the above problems. That is, a method of manufacturing a ferroelectric memory device according to the present invention includes a step of forming a ferroelectric capacitor on a substrate, a step of forming a hydrogen barrier film covering the ferroelectric capacitor, and the hydrogen barrier film. Forming a first through hole penetrating the insulating film by etching using a mixed gas containing a fluorocarbon gas and an oxygen gas, and etching using the mixed gas Forming a second through-hole penetrating the hydrogen barrier film continuously with the first through-hole, and with respect to the sum of the flow rate of the fluorocarbon gas and the flow rate of the oxygen gas in the formation step of the first through-hole The ratio of the flow rate of the fluorocarbon gas is smaller than the ratio of the flow rate of the fluorocarbon gas in the step of forming the second through hole. And features.

In the present invention, since the insulating film and the hydrogen barrier film can be selectively etched only by changing the gas flow rate, the manufacturing process can be simplified.
That is, when the ratio of the flow rate of the fluorocarbon gas to the oxygen gas is reduced during etching, the etching rate of the hydrogen barrier film with respect to the etching rate of the insulating film is lowered. Therefore, by reducing the ratio of the flow rate of the fluorocarbon gas to the oxygen gas when forming the first through hole, it is possible to prevent the hydrogen barrier film from being etched through the insulating film when forming the first through hole. it can. Further, by increasing the ratio of the flow rate of the fluorocarbon gas to the oxygen gas when forming the second through hole, the etching rate of the hydrogen barrier film is increased and the time for forming the second through hole can be shortened. As described above, selective etching can be performed only by changing the flow rates of the fluorocarbon gas and the oxygen gas in the mixed gas, thereby simplifying the process of forming the first and second through holes.
In addition, since the insulating film and the hydrogen barrier film can be selectively etched, even when the film thickness of the insulating film varies, the hydrogen barrier film can be prevented from being etched when the first through hole is formed. Accordingly, the ferroelectric capacitor is prevented from being etched when the second through hole is formed, and the electrical characteristics of the ferroelectric capacitor are prevented from being deteriorated.

In the method for manufacturing a ferroelectric memory device according to the present invention, the sum of the flow rate of the fluorocarbon gas and the flow rate of the oxygen gas in the step of forming the first through hole is the same as in the step of forming the second through hole. The flow rate is preferably larger than the sum of the flow rate of the fluorocarbon gas and the flow rate of the oxygen gas.
In this invention, the sum of the flow rate of the fluorocarbon gas and the flow rate of the oxygen gas at the time of forming the first through hole is made larger than that at the time of forming the second through hole, so that the insulating film is formed in the first through hole forming step. It can suppress more reliably that the hydrogen barrier film penetrates and is etched.

In the method of manufacturing a ferroelectric memory device according to the present invention, it is preferable that the high frequency bias power in the first through hole forming step is larger than the high frequency bias power in the second through hole forming step.
According to the present invention, the high frequency bias power at the time of forming the first through-hole is made larger than that at the time of forming the second through-hole, so that the hydrogen barrier film is further hardly etched in the first through-hole forming step.

In the method for manufacturing a ferroelectric memory device according to the present invention, the fluorocarbon gas is preferably a perfluorocarbon gas.
In the present invention, by using a perfluorocarbon gas that does not contain hydrogen as a constituent element for the ferroelectric material as a constituent element, oxygen deficiency can be prevented from occurring in the ferroelectric material.

In the method for manufacturing a ferroelectric memory device according to the present invention, it is preferable that the first through hole forming step and the second through hole forming step are continuously performed in the same chamber.
In the present invention, since mixed gases having different flow ratios are used, the first and second through holes can be formed continuously in the same chamber. Thereby, the manufacturing process of the ferroelectric memory device can be shortened.

In the method for manufacturing a ferroelectric memory device according to the present invention, the mixed gas preferably contains carbon monoxide gas.
In the present invention, the resist layer used as a mask is less likely to be etched when the first and second through holes are formed. Thereby, the processing accuracy of the first and second through holes can be maintained.

  Hereinafter, an embodiment of a method for manufacturing a ferroelectric memory device according to the present invention will be described with reference to the drawings. In each drawing used in the following description, the scale is appropriately changed to make each member a recognizable size. Here, FIG. 1 is an enlarged cross-sectional view schematically showing a ferroelectric memory device manufactured by the method for manufacturing a ferroelectric memory device, and FIG. 2 is a process diagram showing the method for manufacturing the ferroelectric memory device.

[Ferroelectric memory device]
First, a ferroelectric memory device manufactured by the method for manufacturing a ferroelectric memory device in this embodiment will be described with reference to FIG.
The ferroelectric memory device 1 is a stack type having a 1-transistor / 1-capacitor (1T / 1C) type memory cell structure. As shown in FIG. 1, a semiconductor substrate (substrate) 2 and a semiconductor substrate 2 The ferroelectric capacitor 3 and the transistor 4 are provided.

The semiconductor substrate 2 is made of, for example, Si (silicon), and a first interlayer insulating film 11, a hydrogen barrier film 12, and a second interlayer insulating film (insulating film) 13 are sequentially stacked on the upper surface.
The first interlayer insulating film 11 is made of, for example, SiO ₂ (silicon oxide) and covers the transistor 4 formed on the semiconductor substrate 2. A through hole 15 is formed on the drain region 42 described later of the first interlayer insulating film 11 and is filled with a plug 16.
The plug 16 is made of a conductive material filled in the through hole 15, and is formed of, for example, W (tungsten), Mo (molybdenum), Ta (tantalum), Ti (titanium), Ni (nickel), or the like. Yes.

The hydrogen barrier film 12 is made of, for example, AlOx (alumina). The hydrogen barrier film 12 covers the upper surface and side surfaces of the ferroelectric capacitor 3 formed on the first interlayer insulating film 11. Further, a through hole (second through hole) 21 is formed in the hydrogen barrier film 12.
As shown in FIG. 1, the second interlayer insulating film 13 is made of, for example, SiO ₂ , like the first interlayer insulating film 11. The second interlayer insulating film 13 covers the hydrogen barrier film 12. In addition, a through hole (first through hole) 22 is formed in the second interlayer insulating film 13. The through hole 22 is formed continuously with the through hole 21.
The upper surface of the second interlayer insulating film 13, the inner wall surfaces of the through holes 21 and 22, and the region exposed by the through holes 21 and 22 on the upper surface of the ferroelectric capacitor 3 are connected to the plug 23. An adhesion layer (not shown) for improving adhesion is formed. The adhesion layer is formed of a material having a hydrogen barrier property such as TiN, TiAlN, or a laminated film thereof.

The plug 23 is made of, for example, W, Mo, Ta, Ti, Ni or the like.
A wiring 24 that is electrically connected to the plug 23 is formed on the second interlayer insulating film 13. The wiring 24 is formed integrally with the plug 23. An antireflection film (not shown) is formed on the surface of the wiring 24.

The ferroelectric capacitor 3 is formed on the first interlayer insulating film 11 and the plug 16. A conductive film 31, an oxygen barrier film 32, a lower electrode 33, a ferroelectric film 34, and an upper electrode 35 are sequentially formed from the lower layer. It has a laminated structure.
The conductive film 31 is made of, for example, a conductive material such as TiN, and the plug 16 and the ferroelectric capacitor 3 are electrically connected.
The oxygen barrier film 32 is formed of a material having an oxygen barrier property such as TiAlN, TiAl, TiSiN, TiN, TaN, TaSiN.

  The lower electrode 33 is made of, for example, at least one of Ir (iridium), Pt (platinum), Ru (ruthenium), Rh (rhodium), Pd (palladium), Os (osmium), an alloy thereof, or an oxide thereof. Consists of. Here, the lower electrode 33 is preferably made of Ir or Pt, and more preferably made of Ir. The lower electrode 33 may be a single layer film or a laminated multilayer film.

When the lower electrode 33 is crystalline, it is preferable that the crystal orientation of the lower electrode 33 and the crystal orientation of the oxygen barrier film 32 have an epitaxial orientation relationship at the interface where they are in contact with each other, as shown in FIG. . At this time, it is preferable that the crystal orientation of the lower electrode 33 and the crystal orientation of the ferroelectric film 34 have an epitaxial orientation relationship at the interface contacting each other.
For example, when the oxygen barrier film 32 belongs to a cubic system and its crystal orientation is (111) orientation, or the oxygen barrier film 32 belongs to a hexagonal system and its crystal orientation is (001) orientation, The crystal orientation of the lower electrode 33 is preferably (111) orientation. According to this configuration, when the ferroelectric film 34 is formed on the lower electrode 33, the crystal orientation of the ferroelectric film 34 can be easily set to the (111) orientation.

The ferroelectric film 34 is formed of a ferroelectric material having a perovskite crystal structure represented by a general formula of A _{1 -b} B _{1 -a} X _a O ₃ . Here, A in the above general formula consists of Pb, and a part of Pb may be substituted with La. B is made of at least one of Zr (zirconium) and Ti. X is composed of at least one of V (vanadium), Nb (niobium), Ta, Cr (chromium), Mo, W, Ca (calcium), Sr (strontium), and Mg (magnesium). At this time, as a ferroelectric material constituting the ferroelectric film 34, for example, a known material such as PZT, SBT, (Bi, La) ₄ Ti ₃ O ₁₂ (bismuth lanthanum titanate: BLT) is used. Among them, PZT is preferable.

Here, when using PZT as the ferroelectric material, it is preferable to use Ir as the lower electrode 33 from the viewpoint of the reliability of the ferroelectric capacitor 3.
Further, when PZT is used as the ferroelectric material, in order to obtain a larger spontaneous polarization amount, it is preferable to make the Ti content in the PZT larger than the Zr content as described above. Furthermore, when the ferroelectric film 34 is composed of PZT and the Ti content in the PZT is greater than the Zr content, the hysteresis orientation is good, and the crystal orientation of the PZT is (111) orientation. Preferably there is.

  The upper electrode 35 is made of the same material as that of the lower electrode 33 described above, Al, Ag (silver), Ni, or the like. The upper electrode 35 may be a single layer film or a laminated multilayer film. Here, the upper electrode 35 is preferably made of a multilayer film of Pt or IrOx and Ir.

As shown in FIG. 1, the transistor 4 includes a source region 41, a drain region 42 and a channel region (not shown) formed on the surface layer of the semiconductor substrate 2, a gate insulating film 43 formed on the channel region, a gate And a gate electrode 44 formed on the insulating film 43. The transistor 4 is electrically connected to the plug 16 formed on the drain region 42.
In addition, a plurality of transistors 4 are formed at intervals in the semiconductor substrate 2 and are insulated from each other by an element isolation region 45 provided between the other adjacent transistors 4.

[Manufacturing Method of Ferroelectric Memory Device]
Next, a manufacturing method of the above-described ferroelectric memory device 1 will be described with reference to FIG.
First, the transistor 4 is formed on the semiconductor substrate 2 and the first interlayer insulating film 11 covering the transistor 4 is formed. Then, a through hole 15 penetrating the first interlayer insulating film 11 is formed, and the through hole 15 is filled with a plug 16.
Next, the ferroelectric capacitor 3 is formed on the first interlayer insulating film 11 (FIG. 2A). Here, a film made of a constituent material of the conductive film 31, a film made of a constituent material of the oxygen barrier film 32, a film made of a constituent material of the lower electrode 33, and the ferroelectric film 34 on the first interlayer insulating film 11. And a film made of the constituent material of the upper electrode 35 are laminated. Then, these are patterned by a photolithography technique or the like. Thereby, the ferroelectric capacitor 3 is formed. At this time, the oxygen barrier film 32 is electrically connected to the plug 16.

Subsequently, a hydrogen barrier film 12 covering the ferroelectric capacitor 3 is formed (FIG. 2B). Here, an AlOx film is formed by CVD so as to cover the first interlayer insulating film 11 and the ferroelectric capacitor 3.
In addition to the CVD method, an AlOx film may be formed by a sputtering method.
Further, the ferroelectric film 34 in the ferroelectric capacitor 3 may cause oxygen vacancies depending on the film forming conditions. Therefore, after the hydrogen barrier film 12 is formed, heat treatment may be performed in an oxygen atmosphere as necessary, and oxygen may be supplied to the ferroelectric film 34 through the hydrogen barrier film 12 to compensate for oxygen vacancies. Here, as temperature of heat processing, it is 550 to 750 degreeC, for example, and it is preferable that it is 600 to 750 degreeC.

Then, a second interlayer insulating film 13 that covers the hydrogen barrier film 12 is formed (FIG. 2C). Here, the SiO ₂ film is formed by a plasma CVD method (plasma TEOS method) using TEOS (tetraethoxysilane) as a raw material, which is a film forming method in which damage to the ferroelectric capacitor 3 is sufficiently small. Thereafter, the upper surface of the SiO ₂ film is flattened by CMP treatment. In addition to the plasma TEOS method, the SiO ₂ film may be formed by sputtering.

Subsequently, a through hole 22 is formed in the second interlayer insulating film 13 (FIG. 2D), and a through hole 21 is formed in the hydrogen barrier film 12 (FIG. 2E). Here, the through holes 21 and 22 are formed by dry etching using a resist layer (not shown) formed on the upper surface of the second interlayer insulating film 13 and having openings in the formation regions of the through holes 21 and 22 as a mask. As an etching apparatus, for example, Alliance4520XL (Lamb Research) is used.
Here, the etching rate of the SiO ₂ film that constitutes the second interlayer insulating film 13 and the etching rate of the AlOx film that constitutes the hydrogen barrier film 12 when the gas flow rate and high-frequency bias power are changed during dry etching, respectively. Table 1 shows.

As shown in Table 1, the mixed gas introduced into the chamber during etching is a mixture of C ₄ F ₈ gas, O ₂ gas, CO gas, Ar gas, and N ₂ gas, which are perfluorocarbon gases. It is gas.
Then, as shown in the condition 2 in Table _1, reducing the ratio of _C 4 _{F 8} gas to C 4 _{F 8} gas and _{O 2} gas, the etching rate of the SiO ₂ film constituting the second interlayer insulating film 13 Becomes higher than the etching rate of the AlOx film constituting the hydrogen barrier film 12.
Further, as shown in Conditions 1 and 4, when the flow rates of C ₄ F ₈ gas and O ₂ gas are increased, the etching rate of the SiO ₂ film becomes higher than the etching rate of the AlO x film.
Further, as shown in Conditions 3 and 4, when the high frequency bias power is increased, the etching rate of the SiO ₂ film becomes higher than the etching rate of the AlOx film.
Therefore, in this embodiment, the dry etching conditions at the time of forming the through holes 22 and 21 are the conditions 1 and 2, respectively.

When the through-hole 22 is formed by etching the second interlayer insulating film 13 under the condition shown in the condition 1, the through-hole 22 is formed because the ratio of the etching rate of the second interlayer insulating film 13 to the hydrogen barrier film 12 is high. Sometimes the hydrogen barrier film 12 is not etched excessively. Thereby, the hydrogen barrier film 12 functions as an etch stop layer when the through hole 22 is formed.
Further, when the through-hole 21 is formed by etching the hydrogen barrier film 12 under the condition shown in the condition 2, the ratio of the etching rate of the hydrogen barrier film 12 to the second interlayer insulating film 13 is increased, and thus the through-hole 21 is formed in a short time. Is formed. At this time, even if in-plane variation occurs in the film thickness of the second interlayer insulating film 13 in the same semiconductor substrate 2, the hydrogen barrier film 12 is not excessively etched when the through hole 22 is formed. The variation in the film thickness of the hydrogen barrier film 12 is reduced. This suppresses etching of the upper electrode 35 of the ferroelectric capacitor 3 when the through hole 21 is formed.
The step of forming the through hole 22 and the step of forming the through hole 21 are performed by changing the flow rate of the mixed gas in the same chamber.

As described above, by forming the through holes 22 and 21, a part of the upper surface of the ferroelectric capacitor 3 is exposed.
Thereafter, the plug 23 and the wiring 24 filling the through hole 22 are integrally formed. As described above, the ferroelectric memory device 1 as shown in FIG. 1 is manufactured.

As described above, according to the method for manufacturing the ferroelectric memory device 1 in the present embodiment, the second interlayer insulating film can be formed when the through hole 22 is formed only by changing the flow rates of the C ₄ F ₈ gas and the O ₂ gas. 13 can be selectively etched to prevent the hydrogen barrier film 12 from being etched. Thereby, the formation process of the through-holes 22 and 21 can be simplified.
Here, by using a C ₄ F ₈ gas that does not contain hydrogen as a reducing species as a fluorocarbon gas, it is possible to prevent oxygen deficiency from occurring in the ferroelectric film 34 when the through hole 21 is formed.

Further, the flow rate of C ₄ F ₈ gas and the flow rate of O ₂ gas at the time of forming the through hole 22 are made larger than those at the time of forming the through hole 21, and the high frequency bias power at the time of forming the through hole 22 is increased. By making it larger than at the time of formation, it is possible to more reliably prevent the hydrogen barrier film 12 from being etched at the time of forming the through hole 22.
Since the mixed gas contains CO gas, the etching selectivity of the resist layer when forming the through holes 22 and 21 can be improved.

In addition, this invention is not limited to the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention.
For example, the ferroelectric capacitor is not limited to the stack type structure, but may be another structure such as a planar type.
Further, the fluorocarbon gas is not limited to C ₄ F ₈ gas, which is a perfluorocarbon gas, and may be other perfluorocarbon gas such as C ₄ F ₆ gas or C ₅ F ₈ gas, for example, CHF ₃ gas. Other fluorocarbon gas containing hydrogen as a constituent element may be used.

The flow rate of the fluorocarbon gas with respect to the sum of the flow rate of the fluorocarbon gas and the flow rate of the oxygen gas in the step of forming the through hole in the second interlayer insulating film is equal to the flow rate of the fluorocarbon gas in the step of forming the through hole in the hydrogen barrier film. Any other ratio may be used as long as it is smaller than the ratio of the flow rate of the fluorocarbon gas to the sum of the flow rate of the oxygen gas.
Further, the sum of the flow rate of the fluorocarbon gas and the flow rate of the oxygen gas in the step of forming the through hole in the second interlayer insulating film is equal to the flow rate of the fluorocarbon gas and the flow rate of the oxygen gas in the step of forming the through hole in the hydrogen barrier film. Or less than the sum of
Further, the high frequency bias power in the step of forming the through hole in the second interlayer insulating film may be equal to or lower than the high frequency bias power in the step of forming the through hole in the hydrogen barrier film.
The mixed gas only needs to contain at least a fluorocarbon gas and an oxygen gas, and if a sufficient etching selectivity for the resist layer is obtained, the carbon monoxide gas is not included. Also good.

It is a schematic sectional drawing of the ferroelectric memory device manufactured with the manufacturing method of this invention. It is process drawing which shows the manufacturing method of the ferroelectric memory device of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ferroelectric memory device, 2 Semiconductor substrate (substrate), 3 Ferroelectric capacitor, 12 Hydrogen barrier film, 13 2nd interlayer insulation film (insulation film), 21 Through-hole (2nd through-hole), 22 Through-hole ( 1st through hole)

Claims (6)

Forming a ferroelectric capacitor on the substrate;
Forming a hydrogen barrier film covering the ferroelectric capacitor;
Forming an insulating film covering the hydrogen barrier film;
Forming a first through hole penetrating the insulating film by etching using a mixed gas containing a fluorocarbon gas and an oxygen gas;
Forming a second through-hole penetrating the hydrogen barrier film by etching using the mixed gas continuously with the first through-hole,
The ratio of the flow rate of the fluorocarbon gas to the sum of the flow rate of the fluorocarbon gas and the flow rate of the oxygen gas in the first through-hole forming step is higher than the ratio of the flow rate of the fluorocarbon gas in the second through-hole forming step. A manufacturing method of a ferroelectric memory device characterized by being small.   The sum of the flow rate of the fluorocarbon gas and the flow rate of the oxygen gas in the step of forming the first through hole is the sum of the flow rate of the fluorocarbon gas and the flow rate of the oxygen gas in the step of forming the second through hole. 2. The method of manufacturing a ferroelectric memory device according to claim 1, wherein the number of the ferroelectric memory devices is larger.   3. The method of manufacturing a ferroelectric memory device according to claim 1, wherein a high-frequency bias power in the first through-hole forming step is larger than a high-frequency bias power in the second through-hole forming step. .   The method for manufacturing a ferroelectric memory device according to claim 1, wherein the fluorocarbon gas is a perfluorocarbon gas.   5. The ferroelectric memory according to claim 1, wherein the step of forming the first through hole and the step of forming the second through hole are continuously performed in the same chamber. 6. Device manufacturing method.   The method for manufacturing a ferroelectric memory device according to claim 1, wherein the mixed gas contains carbon monoxide gas.

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