Semiconductor device and method for manufacturing the same

Abstract

To suppress an increase in contact resistance.SOLUTION: A semiconductor device comprises: a ferroelectric capacitor Ca including a lower electrode 40, a ferroelectric film 42, and an upper electrode 44; an insulation film 62 that covers the ferroelectric capacitor Ca; and a conductive plug 64 that penetrates the insulation film 62 and in which a bottom part is embedded into the upper electrode 44. The upper electrode 44 includes: an electrode film 58 of the upper most layer containing an oxide of a first metal element; and an electrode film 56 that is provided under the electrode film 58, and contains an oxide of the first metal element of which an oxygen composition ratio is higher than that of the electrode film 58. The conductive plug 64 contains: an adhesion film 66 that is provided in a manner to reach the electrode film 56 while penetrating the electrode film 58, is in contact with the electrode films 56 and 58, and contains a second metal element; and a conductive film 68 on the adhesion film 66. An oxidation concentration of a bottom part 66b positioned on a bottom surface of the conductive plug 64 of the adhesion film 66 is lower than that of a sandwiched part 66a sandwiched between the electrode films 58 and 68.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device. [Background technology]

[0002] Ferroelectric random access memories (FeRAMs) are known that store data in ferroelectric capacitors by utilizing polarization reversal of ferroelectrics. The ferroelectric capacitors include a lower electrode, a ferroelectric film provided on the lower electrode, and an upper electrode provided on the ferroelectric film. A conductive plug is provided on the upper electrode, connecting to the upper electrode.

[0003] Ferroelectric capacitors are formed by patterning them into a desired shape using techniques such as etching, but a recovery annealing process (heat treatment) is performed in an oxygen atmosphere to repair process damage. This recovery annealing process oxidizes the upper electrode, which can increase the contact resistance between the conductive plug and the upper electrode. To prevent this increase in contact resistance, it is known to provide a conductive layer between the upper electrode and the conductive plug, containing a conductive material that remains conductive even when oxidized (see, for example, Patent Document 1). It is also known to make the upper layer of the upper electrode an iridium oxide layer with a lower oxygen concentration than the lower layer, so that the conductive plug stops at the upper layer of the upper electrode and does not reach the lower layer (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-206213 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-344684 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the methods described in Patent Documents 1 and 2 still have room for improvement in terms of suppressing an increase in contact resistance between the conductive plug and the upper electrode.

[0006] In one aspect, an object is to suppress an increase in contact resistance. [Means for solving the problem]

[0007] In one aspect, a ferroelectric capacitor includes a first electrode, a ferroelectric film provided on the first electrode, and a second electrode provided on the ferroelectric film, an insulating film covering the ferroelectric capacitor, and a conductive plug penetrating the insulating film and having a bottom portion embedded in the second electrode, wherein the second electrode includes a first layer that is an uppermost layer containing an oxide of a first metal element, and a second layer that is provided below the first layer and contains an oxide of the first metal element and has a higher oxygen composition ratio than the first layer, and the conductive plug is provided penetrating the first layer to reach the second layer, and includes an adhesive film that is in contact with the first layer and the second layer and contains a second metal element, and a conductive film on the adhesive film, and a first portion of the adhesive film located on a bottom surface of the conductive plug has a lower oxygen concentration than a second portion sandwiched between the first layer and the conductive film. The oxide of the first metal element is iridium oxide, and the iridium oxide contained in the first layer is IrO z (z<1.0), and the iridium oxide contained in the second layer is IrO β (β>z) , a semiconductor device.

[0008] In one aspect, the method includes the steps of: forming a film to be a first electrode; forming a ferroelectric film on the film to be the first electrode; forming a film to be a second electrode on the ferroelectric film, the film including a first layer as an uppermost layer which is a metal layer of a first metal element and a second layer provided below the first layer and which is an oxide layer of the first metal element; patterning the film to be the first electrode, the ferroelectric film, and the film to be the second electrode to form a ferroelectric capacitor having the first electrode, the ferroelectric film, and the second electrode; performing a heat treatment on the ferroelectric capacitor in an oxygen atmosphere; forming an insulating film covering the ferroelectric capacitor after the heat treatment; and forming a conductive plug penetrating the insulating film and the first layer to reach the second layer, in contact with the first layer and the second layer, the conductive plug including an adhesive film containing a second metal element and a conductive film on the adhesive film, an oxide of the first metal element having a lower oxygen composition ratio than that of the second layer is formed in the first layer by the heat treatment; A first portion of the adhesive film located on the bottom surface of the conductive plug has a lower oxygen concentration than a second portion sandwiched between the first layer and the conductive film. The oxide of the first metal element is iridium oxide, and after the heat treatment, the iridium oxide contained in the first layer is IrO z (z<1.0), and the iridium oxide contained in the second layer is IrO β (β>z) , a method for manufacturing a semiconductor device. [Effects of the Invention]

[0009] As one aspect, an increase in contact resistance can be suppressed. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view of a semiconductor device according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the ferroelectric capacitor and its vicinity in the embodiment. [Figure 3] 3(a) to 3(c) are cross-sectional views (part 1) showing a method for manufacturing a semiconductor device according to an embodiment. [Figure 4] 4(a) and 4(b) are cross-sectional views (part 2) showing the method for manufacturing a semiconductor device according to the embodiment. [Figure 5]5(a) and 5(b) are cross-sectional views (part 3) showing a method for manufacturing a semiconductor device according to an embodiment. [Figure 6] 6(a) and 6(b) are cross-sectional views showing a method for manufacturing a semiconductor device according to a comparative example. [Figure 7] 7(a) and 7(b) are cross-sectional views of the vicinity of the ferroelectric capacitor of the first and second samples on which the experiment was conducted. [Figure 8] FIG. 8 shows the results of measuring the contact resistance between the conductive plug and the upper electrode in the first and second samples. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Example]

[0012] Fig. 1 is a cross-sectional view of a semiconductor device 100 according to an embodiment. As shown in Fig. 1, the semiconductor device 100 is formed on a semiconductor substrate 10, which is, for example, a P-type silicon substrate. An element isolation region 12 made of an insulator such as silicon oxide (SiO2) is formed in a surface layer portion of the semiconductor substrate 10, and defines a formation region of the transistor Ta. Also, a source region S and a drain region D of the transistor Ta are formed in the surface layer portion of the semiconductor substrate 10. The source region S and the drain region D are made of, for example, an N-type semiconductor.

[0013] A gate electrode G is provided on a semiconductor substrate 10 via a gate insulating film 14. The gate insulating film 14 is made of, for example, SiO2, and the gate electrode G is made of, for example, polysilicon. The gate electrode G functions as a word line. Sidewalls 16 made of an insulator such as SiO2 are provided on the sides of the gate electrode G. Silicide layers 18 are provided on the surfaces of the source region S, the drain region D, and the gate electrode G to reduce contact resistance. The transistor Ta is a field-effect transistor.

[0014] A cover film 20, an interlayer insulating film 22, an etch stopper film 24, an interlayer insulating film 26, an oxidation prevention film 28, and a buffer film 30 are stacked in this order on the transistor Ta. The cover film 20 is approximately 50 nm to 100 nm thick and is made of an insulator such as silicon nitride (SiN). The interlayer insulating film 22 is approximately 300 nm to 400 nm thick and is made of SiO2 or the like. The etch stopper film 24 is approximately 20 nm to 50 nm thick and is made of an insulator such as SiN. The interlayer insulating film 26 is approximately 200 nm to 300 nm thick and is made of SiO2 or the like. The oxidation prevention film 28 is approximately 50 nm to 150 nm thick and is made of an insulator such as SiN. The buffer film 30 is approximately 200 nm to 300 nm thick and is made of an insulator such as SiO2.

[0015] Conductive plugs 32, 34 penetrate the interlayer insulating film 22 and the cover film 20 and are connected to the source region S and the drain region D, respectively. The conductive plugs 32, 34 are made of a conductor such as tungsten (W). A wiring 38 that functions as a bit line is provided, penetrating the interlayer insulating film 26 and the etch stopper film 24. The wiring 38 is electrically connected to the drain region D of the transistor Ta via the conductive plug 34. The wiring 38 is made of a conductor such as W. A conductive plug 36 is provided, penetrating the buffer film 30, the oxidation suppression film 28, the interlayer insulating film 26, and the etch stopper film 24, and is connected to the conductive plug 32. The conductive plug 36 is made of a conductor such as W.

[0016] A ferroelectric capacitor Ca is provided on the buffer film 30. The ferroelectric capacitor Ca has a laminated structure in which a lower electrode 40, a ferroelectric film 42, and an upper electrode 44 are laminated. The lower electrode 40 is electrically connected to the source region S of the transistor Ta via conductive plugs 36 and 32.

[0017] The lower electrode 40 has an adhesive film 46, an oxygen barrier conductive film 48, and an electrode film 50 stacked in this order. The adhesive film 46 has a thickness of about 1 nm to 10 nm and is made of a conductor such as titanium nitride (TiN). The adhesive film 46 functions to improve adhesion between the conductive plug 36 and the buffer film 30 and the oxygen barrier conductive film 48. The oxygen barrier conductive film 48 has a thickness of about 50 nm to 100 nm and is a film with low oxygen permeability, and functions to suppress oxygen diffusion into the conductive plug 36. The oxygen barrier conductive film 48 has lower oxygen permeability than the adhesive film 46 and the electrode film 50. The oxygen barrier conductive film 48 is made of, for example, titanium aluminum nitride (TiAlN), titanium aluminum oxynitride (TiAlON), titanium silicon nitride (TiSiN), tantalum aluminum nitride (TaAlN), tantalum aluminum oxynitride (TaAlON), or tantalum silicon nitride (TaSiN). The electrode film 50 has a thickness of about 10 nm to 100 nm, and is made of a conductor such as iridium (Ir).

[0018] The ferroelectric film 42 is formed containing a ferroelectric oxide having a perovskite crystal structure, such as PZT (Pb(Zr,Ti)O3) or SBT (SrBi2Ta2O9), etc. The thickness of the ferroelectric film 42 is about 50 nm to 150 nm.

[0019] The upper electrode 44 is formed by laminating an electrode film 52, an electrode film 54, an electrode film 56, and an electrode film 58 in this order. The electrode film 52 has a thickness of, for example, about 10 nm to 40 nm and is made of IrO x The electrode film 52 is formed of iridium oxide having a composition of (1.3≦x≦1.9). Note that x may be 1.5≦x≦1.9 or 1.8≦x≦1.9. The electrode film 52 is provided to suppress interdiffusion of iridium oxide between the ferroelectric film 42 and the upper electrode 44 at the interface between the upper electrode 44 and the ferroelectric film 42 and to control the thickness of the dead layer (interface layer with no ferroelectric properties). The electrode film 54 has a thickness of, for example, about 50 nm to 100 nm and is made of IrO αThe electrode film 56 is made of iridium oxide having a composition of (x<α). The electrode film 56 has a thickness of, for example, about 50 nm to 125 nm and is made of IrO β The electrode film 58 is made of iridium oxide having a composition (x<β, α≠β). The electrode film 54 and the electrode film 56 are provided to prevent hydrogen penetration and to suppress damage to the ferroelectric capacitor Ca due to a reducing atmosphere. Furthermore, the two-layer structure of the electrode film 54 and the electrode film 56 can suppress the generation of foreign matter during film formation and the occurrence of abnormal oxidation during film formation, compared to a single layer structure. The electrode film 58 has a thickness of, for example, about 20 nm to 70 nm and is made of IrO z The electrode film 58 is made of iridium oxide having a composition of (z<1.0). The electrode film 58 is provided to enable the thickness of the insulating film 62 to be measured after polishing. The electrode film 58 is made of IrO z As long as the layer contains iridium oxide having a composition of (z<1.0), it is not limited to an iridium oxide layer, and may contain, for example, metallic iridium in addition to iridium oxide.

[0020] The side surfaces of the lower electrode 40, the ferroelectric film 42, and the upper electrode 44 are continuous and do not have discontinuous protruding portions. The widths of the lower electrode 40, the ferroelectric film 42, and the upper electrode 44 may be gradually narrowed from the lower electrode 40 toward the upper electrode 44, or may be substantially the same width.

[0021] A protective film 60 is provided to cover the ferroelectric capacitor Ca. The protective film 60 has a thickness of, for example, about 20 nm to 70 nm and is made of aluminum oxide (Al x O y ), magnesium oxide (Mg x O y ), aluminum nitride (Al x N y ), or magnesium nitride (Mg x N y The protective film 60 has the function of preventing hydrogen and moisture from penetrating into the ferroelectric capacitor Ca.

[0022] An insulating film 62 made of SiO2 or the like is provided on the protective film 60. The insulating film 62 has a thickness of approximately 1000 nm to 1800 nm. A conductive plug 64 is provided, penetrating the insulating film 62 and the protective film 60, with its bottom embedded in the upper electrode 44. The conductive plug 64 includes an adhesive film 66 in contact with the insulating film 62, the protective film 60, and the upper electrode 44, and a conductive film 68 provided on the adhesive film 66. The adhesive film 66 functions to improve adhesion between the conductive film 68 and the insulating film 62, the protective film 60, and the upper electrode 44. The adhesive film 66 has a thickness of, for example, approximately 2 nm to 100 nm, and is mostly made of titanium nitride (TiN) and partially made of titanium oxynitride (TiON). This will be described in detail later. The conductive film 68 is made of, for example, tungsten (W).

[0023] An interconnection 70 functioning as a plate line is provided on the insulating film 62. The interconnection 70 has a layered structure in which a barrier film 72, an interconnection film 74, and a barrier film 76 are stacked. The barrier films 72 and 76 are made of, for example, Ti or TiN. The interconnection film 74 is made of a conductor such as an aluminum-copper alloy. The interconnection 70 is electrically connected to the upper electrode 44 of the ferroelectric capacitor Ca via a conductive plug 64.

[0024] 2 is a cross-sectional view of the vicinity of a ferroelectric capacitor Ca in the embodiment. As shown in FIG. 2, the conductive plug 64 is provided with its bottom located within the upper electrode 44. The conductive plug 64 penetrates the electrode film 58, which is the uppermost layer of the upper electrode 44, and reaches the electrode film 56, which is provided in contact with the lower surface of the electrode film 58. Therefore, the bottom surface of the conductive plug 64 is in contact with the electrode film 56.

[0025] A large amount of TiON is formed in a sandwiched portion 66a of the adhesion film 66, which is sandwiched between the electrode film 58 and the conductive film 68. The portion where a large amount of TiON is formed is shown with dark hatching (the same applies to similar figures below). The other portions of the adhesion film 66 are formed almost entirely of TiN, with little TiON formed. Therefore, the bottom portion 66b of the adhesion film 66, which is located on the bottom surface of the conductive plug 64, has a lower oxygen concentration than the sandwiched portion 66a, which is sandwiched between the electrode film 58 and the conductive film 68. The oxygen concentration is the ratio of the number of oxygen atoms to the total number of atoms contained per unit area.

[0026] [Manufacturing method] 3(a) to 5(b) are cross-sectional views showing a manufacturing method of a semiconductor device 100 according to an embodiment. FIG. 5(b) is an enlarged view of region A in FIG. 5(a). As shown in FIG. 3(a), an isolation region 12 is formed in a surface layer of a semiconductor substrate 10, which is, for example, a P-type silicon substrate, using shallow trench isolation (STI) technology. Next, a SiO2 film for forming a gate insulating film 14 is formed on the surface of the semiconductor substrate 10 using thermal oxidation, and then a polysilicon film for forming a gate electrode G is deposited using chemical vapor deposition (CVD). Thereafter, the SiO2 film and polysilicon film are patterned using photolithography and etching to form the gate insulating film 14 and the gate electrode G.

[0027] Next, an insulating film such as SiO2 is formed using a CVD method to cover the gate electrode G, and then the insulating film is etched back to form sidewalls 16 that cover the side surfaces of the gate electrode G. Next, using the gate electrode G and the sidewalls 16 as a mask, ion implantation is performed to form the source region S and the drain region D. After that, heat treatment is performed to activate the N-type impurity diffusion regions that constitute the source region S and the drain region D. Next, a salicide process is used to form silicide layers 18 on the surfaces of the source region S, the drain region D, and the gate electrode G to reduce contact resistance. This completes the formation of the transistor Ta on the semiconductor substrate 10.

[0028] As shown in FIG. 3(b), a cover film 20 is formed by depositing an insulating film such as SiN on the surface of the transistor Ta using the CVD method. Next, an interlayer insulating film 22 such as SiO2 is formed on the cover film 20 using the CVD method, and the surface of the interlayer insulating film 22 is then planarized using the CMP (chemical mechanical polishing) method. Next, contact holes reaching the source region S and the drain region D are formed in the interlayer insulating film 22 and the cover film 20 using the photolithography method and the etching method. Next, an adhesive film such as Ti is formed on the side and bottom surfaces of the contact holes using the sputtering method or the CVD method, and the contact holes are then filled with a conductive film such as W using the CVD method. Next, the excess adhesive film and conductive film deposited on the interlayer insulating film 22 are removed using the CMP method, thereby forming conductive plugs 32 and 34.

[0029] As shown in FIG. 3(c), an insulating film such as SiN is deposited on the interlayer insulating film 22 using the CVD method to form an etch stopper film 24. Next, an interlayer insulating film 26 such as SiO2 is formed on the etch stopper film 24 using the CVD method. Next, photolithography and etching are used to form linear trenches in the interlayer insulating film 26 and the etch stopper film 24 in the regions where the wiring 38 will be formed. Next, an adhesive film such as Ti is formed on the side and bottom surfaces of the linear trenches using the sputtering method or the CVD method, and then a conductive film such as W is filled into the linear trenches using the CVD method. Next, excess adhesive film and conductive film deposited on the interlayer insulating film 26 are removed using the CMP method to form the wiring 38.

[0030] Next, an insulating film such as SiN is deposited on the interlayer insulating film 26 using the CVD method to form an oxidation prevention film 28. Next, an insulating film such as SiO2 is deposited on the oxidation prevention film 28 using the CVD method to form a buffer film 30. Next, photolithography and etching are used to form contact holes that penetrate the buffer film 30, the oxidation prevention film 28, the interlayer insulating film 26, and the etch stopper film 24 and reach the conductive plug 32. Next, an adhesion film such as Ti is formed on the side and bottom surfaces of the contact hole using the sputtering method or the CVD method, and then the contact hole is filled with a conductive film such as W using the CVD method. Next, excess adhesion film and conductive film deposited on the buffer film 30 are removed using the CMP method to form a conductive plug 36. The conductive plug 36 is connected to the conductive plug 32.

[0031] As shown in FIG. 4( a), an adhesion film 46 made of, for example, TiN is formed on the buffer film 30 by PVD (Physical Vapor Deposition). An oxygen barrier conductive film 48 made of, for example, TiAlN is formed on the adhesion film 46 by PVD. An electrode film 50 made of, for example, Ir is formed on the oxygen barrier conductive film 48 by PVD. A ferroelectric film 42 made of, for example, PZT is formed on the electrode film 50 by PVD or CVD. Thereafter, the ferroelectric film 42 is subjected to rapid thermal processing, which is a heat treatment in an oxygen atmosphere. This causes desorption and oxidation of excess elements in the ferroelectric film 42, completing the crystallization of the ferroelectric film 42.

[0032] Next, a layer of, for example, IrO is deposited on the ferroelectric film 42 by using a PVD method. x An electrode film 52, which is an iridium oxide layer having a structure of (1.3≦x≦1.9), is formed on the electrode film 52 by using a PVD method. α An electrode film 54, which is an iridium oxide layer having a structure of (x<α), is formed on the electrode film 54 by using a PVD method. βAn electrode film 56 is formed as an iridium oxide layer having a structure in which x<β, α≠β. An electrode film 58 is formed as a metal layer made of, for example, Ir on the electrode film 56. The oxygen composition ratio of the iridium oxide layer can be controlled by the film formation conditions. For example, when the iridium oxide layer is formed by sputtering, the oxygen composition ratio can be controlled by the DC power and / or the film formation temperature.

[0033] 4(b), photolithography and etching are used to pattern the electrode film 58, the electrode film 56, the electrode film 54, the electrode film 52, the ferroelectric film 42, the electrode film 50, the oxygen barrier conductive film 48, and the adhesive film 46. As a result, a ferroelectric capacitor Ca is formed, which has a lower electrode 40 including the adhesive film 46, the oxygen barrier conductive film 48, and the electrode film 50, and an upper electrode 44 including the ferroelectric film 42, the electrode film 52, the electrode film 54, the electrode film 56, and the electrode film 58.

[0034] After the ferroelectric capacitor Ca is formed, the ferroelectric capacitor Ca is subjected to a recovery annealing treatment, which is a heat treatment in an oxygen atmosphere, to remove process damage such as etching. In this recovery annealing treatment, the top and side surfaces of the electrode film 58 are exposed to the oxygen atmosphere. Therefore, the Ir contained in the electrode film 58 is oxidized to IrO y Here, Ir is a noble metal element, so it is oxidized by heat treatment to become IrO y When IrO is formed, y becomes an unsaturated oxide with an oxygen composition ratio lower than the theoretical value, and y is y<1.0. Note that y may be y<0.5 or y<0.2.

[0035] As shown in FIG. 5(a) and FIG. 5(b), a CVD method or a PVD method is used to form a film, for example, Al, so as to cover the ferroelectric capacitor Ca. x O y , Mg x O y , Al x N y , or Mg x N yA protective film 60 made of IrO is formed. An insulating film 62 containing, for example, mainly SiO2 is formed on the protective film 60 using a CVD method. Thereafter, the surface of the insulating film 62 is planarized using a CMP method. After this, a remaining film measurement is performed to confirm whether the insulating film 62 remains with an appropriate thickness. The electrode film 58 is made of IrO, an unsaturated oxide with a small oxygen composition ratio. y Therefore, the thickness of the insulating film 62 can be measured using the electrode film 58. For example, the thickness of the insulating film 62 can be measured by irradiating light onto the insulating film 62 and utilizing the reflection of the light from the electrode film 58.

[0036] Next, photolithography and etching are used to form contact holes that penetrate the insulating film 62 and the protective film 60 and reach the inside of the upper electrode 44. The contact holes are formed to penetrate the electrode film 58, which is the top layer of the upper electrode 44, and reach the electrode film 56 below the electrode film 58. Next, an adhesion film 66 made of, for example, TiN is formed on the side and bottom surfaces of the contact holes using a sputtering method. Thereafter, a conductive film 68 made of, for example, W is filled into the contact holes using a CVD method. Next, CMP is used to remove excess adhesion film 66 and conductive film 68 deposited on the insulating film 62, thereby forming conductive plugs 64.

[0037] Here, the adhesive film 66 is formed in contact with the electrode film 58 and the electrode film 56. The electrode film 56 is made of IrO β (x<β), and the electrode film 58 is IrO y (y<1.0), and the oxygen composition ratios are different from each other. β Since (x<β) is 1.3≦x≦1.9 as described above, β is at least greater than 1.3. Therefore, the electrode film 58 has a lower oxygen composition ratio than the electrode film 56. When the oxygen composition ratio is low, the bond between Ir and O is weak, and when the oxygen composition ratio is high, the bond between Ir and O is strong. Note that the upper layer portion 23B of the upper electrode 23 in FIG. 6 of Japanese Patent Laid-Open Publication No. 2006-344684, which is described in the prior art document, is an iridium oxide layer formed by sputtering, and is made of IrO 1.4Since the electrode film 58 has the above composition, the bonding state of Ir and O is different from that of the electrode film 58.

[0038] In the electrode film 58 in which the bond between Ir and O is weak, oxygen (O) contained in the electrode film 58 is likely to undergo solid-phase diffusion into the adhesive film 66 due to the temperature rise during the manufacturing process of the conductive plug 64. For example, when the conductive film 68 is formed using a CVD method, the temperature rises to approximately 400°C, which makes it easy for oxygen contained in the electrode film 58 to undergo solid-phase diffusion into the adhesive film 66. Furthermore, the metal contained in the adhesive film 66 is Ti, and the metal contained in the electrode film 58 is Ir. Ti has a greater ionization tendency than Ir, so this also makes it easy for oxygen contained in the electrode film 58 to diffuse into the adhesive film 66. Therefore, TiN reacts with the diffused oxygen to form TiON in the sandwiched portion 66a of the adhesive film 66, and this results in a portion with a large amount of TiON. Note that, as oxygen diffuses into the adhesive film 66, the electrode film 58 becomes IrO z (z <y<1.0)となる。

[0039] On the other hand, the electrode film 56 has a stronger bond between Ir and O than the electrode film 58, so even if the temperature rises during the manufacturing process of the conductive plug 64, the oxygen contained in the electrode film 56 is less likely to diffuse into the adhesion film 66. Therefore, the oxygen concentration is lower in the bottom portion 66b of the adhesion film 66 than in the sandwiched portion 66a. Therefore, TiON is less likely to form in the bottom portion 66b of the adhesion film 66 than in the sandwiched portion 66a.

[0040] 1, a barrier film 72, a wiring film 74, and a barrier film 76 are laminated on the surface of the insulating film 62. Next, this laminated film is patterned using photolithography and etching to form wiring 70. The wiring 70 is electrically connected to the upper electrode 44 of the ferroelectric capacitor Ca via the conductive plug 64. Through the above steps, the semiconductor device 100 of the embodiment is formed.

[0041] [Comparative Example] The semiconductor device according to the comparative example differs from the semiconductor device 100 of the embodiment in that the conductive plug 64 does not penetrate the electrode film 58 of the upper electrode 44, and the bottom of the conductive plug 64 remains within the electrode film 58 and does not reach the electrode film 56. The other configurations are the same as those of the semiconductor device 100 of the embodiment.

[0042] 6(a) and 6(b) are cross-sectional views showing a semiconductor device manufacturing method according to a comparative example. FIG. 6(b) is an enlarged view of region A in FIG. 6(a). First, the same manufacturing process as that shown in FIGS. 3(a) to 4(b) of Example 1 is performed. Note that the electrode film 58 is thicker than in the example. Then, as shown in FIGS. 6(a) and 6(b), a protective film 60 is formed to cover the ferroelectric capacitor Ca. An insulating film 62 is formed on the protective film 60. Next, photolithography and etching are used to form contact holes that penetrate the insulating film 62 and protective film 60 and reach the interior of the upper electrode 44. The contact holes are limited to the electrode film 58, which is the top layer of the upper electrode 44, and do not reach the electrode film 56. Next, a TiN adhesion film 66 is formed on the side and bottom surfaces of the contact holes using a sputtering method. Then, a W conductive film 68 is filled into the contact holes using a CVD method. Next, the excess adhesive film 66 and conductive film 68 deposited on the insulating film 62 are removed by CMP, thereby forming conductive plugs 64.

[0043] In the comparative example, the bottom of the conductive plug 64 is located within the electrode film 58 of the upper electrode 44 and is in contact with the electrode film 58. As described above, the electrode film 58 has a weak bond between Ir and O, so oxygen contained in the electrode film 58 is likely to diffuse into the adhesion film 66. Therefore, the bottom portion 66b of the adhesion film 66 is a portion where TiN reacts with the diffused oxygen and TiON is likely to be formed, and contains a large amount of TiON. Therefore, a large amount of TiON is formed between the bottom surface of the conductive film 68 and the upper electrode 44.

[0044] Thereafter, although not shown, similarly to the semiconductor device 100 of the embodiment, a barrier film 72, a wiring film 74, and a wiring 70 including a barrier film 76 are formed on the surface of the insulating film 62.

[0045] In the comparative example, the bottom of the conductive plug 64 is formed and located within the electrode film 58 of the upper electrode 44. As described above, the electrode film 58 has a weak bond between Ir and O. Therefore, oxygen in the electrode film 58 is likely to diffuse into the adhesion film 66 due to the temperature rise when forming the conductive plug 64, and the bottom portion 66b of the adhesion film 66 comes to contain a large amount of TiON, which is oxidized TiN. The formation of a large amount of TiON between the bottom of the conductive film 68 and the upper electrode 44 increases the contact resistance between the conductive plug 64 and the upper electrode 44.

[0046] In contrast, in Example 1, as shown in FIGS. 5( a) and 5(b), the conductive plug 64 is formed penetrating the electrode film 58, and the bottom of the conductive plug 64 is in contact with the electrode film 56. As described above, the electrode film 56 has a strong bond between Ir and O. Therefore, oxygen contained in the electrode film 56 is less likely to diffuse into the adhesion film 66 even when the temperature rises during the formation of the conductive plug 64, and TiON is less likely to form on the bottom surface portion 66b of the adhesion film 66. This can suppress an increase in contact resistance between the conductive plug 64 and the upper electrode 44. Note that the sandwiched portion 66a of the adhesion film 66 contains a large amount of TiON. However, even if a large amount of TiON is formed on the sandwiched portion 66a, the effect on the increase in contact resistance between the conductive plug 64 and the upper electrode 44 is small.

[0047] As described above, according to the embodiment, the upper electrode 44 (second electrode) is made of IrO z and an uppermost electrode film 58 (first layer) including IrO βand an electrode film 56 (second layer) including the above. The conductive plug 64 is provided so as to penetrate the electrode film 58 and reach the electrode film 56. The bottom portion 66b (first portion) of the adhesive film 66 constituting the conductive plug 64 has a lower oxygen concentration than the sandwiched portion 66a (second portion). As a result, TiON is less likely to be formed in the bottom portion 66b of the adhesive film 66. Therefore, the bottom portion 66b of the adhesive film 66 has less TiON than the sandwiched portion 66a. This suppresses an increase in contact resistance between the conductive plug 64 and the upper electrode 44. In order to keep the contact resistance between the conductive plug 64 and the upper electrode 44 low, the oxygen concentration of the bottom portion 66b of the adhesive film 66 is preferably 0.5 times or less, more preferably 0.3 times or less, and even more preferably 0.1 times or less, of the oxygen concentration of the sandwiched portion 66a.

[0048] In this embodiment, as shown in FIG. 4(a), an adhesion film 46, an oxygen barrier conductive film 48, and an electrode film 50 are formed to form the lower electrode 40. A ferroelectric film 42 is formed on the electrode film 50. Electrode films 52 to 58 are formed on the ferroelectric film 42 to form the upper electrode 44, including a top electrode film 58, which is an Ir metal layer, and an electrode film 56, which is an Ir oxide layer, provided below the electrode film 58. As shown in FIG. 4(b), the electrode films 58, 56, 54, 52, ferroelectric film 42, electrode film 50, the oxygen barrier conductive film 48, and the adhesion film 46 are patterned to form a ferroelectric capacitor Ca, which is then heat-treated in an oxygen atmosphere. Thereafter, as shown in FIGS. 5(a) and 5(b), an insulating film 62 is formed to cover the ferroelectric capacitor Ca, and a conductive plug 64 is formed that penetrates the insulating film 62 and the electrode film 58 and reaches the electrode film 56. As a result, the oxygen concentration is lower in the bottom portion 66b of the adhesion film 66 constituting the conductive plug 64 than in the sandwiched portion 66a. Therefore, TiON is less likely to be formed in the bottom portion 66b of the adhesion film 66, and an increase in contact resistance between the conductive plug 64 and the upper electrode 44 is suppressed.

[0049] In the embodiment, the iridium oxide contained in the electrode film 58 of the upper electrode 44 is IrO z (z<1.0), and the iridium oxide contained in the electrode film 56 is IrOβ The electrode film 58 has a composition where β>z. In this case, the bond between Ir and O in the electrode film 58 is weak, and oxygen in the electrode film 58 is more likely to diffuse into the adhesive film 66 due to the temperature rise when the conductive plug 64 is formed. Therefore, TiN in the adhesive film 66 is oxidized, and TiON is more likely to be formed. However, even in this case, by forming the conductive plug 64 to penetrate the electrode film 58 and reach the electrode film 56, TiON is less likely to be formed on the bottom portion 66b of the adhesive film 66, and an increase in contact resistance between the conductive plug 64 and the upper electrode 44 is suppressed. In addition, if the iridium oxide contained in the electrode film 58, which is the top layer of the upper electrode 44, is replaced with IrO z By setting the composition to (z<1.0), the thickness of the insulating film 62 after polishing can be measured using the electrode film 58. Note that the iridium oxide contained in the electrode film 56 is preferably IrO β In the composition, β is preferably β>1.3, more preferably β>1.6, and even more preferably β>1.8.

[0050] In the embodiment, the adhesion film 66 contains TiN. In this case, when oxygen in the electrode film 58 diffuses into the adhesion film 66, highly resistant TiON is formed. However, even in this case, by forming the conductive plug 64 to penetrate the electrode film 58 and reach the electrode film 56, TiON is less likely to be formed on the bottom surface portion 66b of the adhesion film 66. Therefore, an increase in contact resistance between the conductive plug 64 and the upper electrode 44 is suppressed. Furthermore, since the adhesion film 66 contains TiN, the adhesion between the conductive film 68 and the insulating film 62 and between the conductive plug 64 and the upper electrode 44 is improved.

[0051] In the embodiment, the adhesion film 66 is not limited to containing TiN and may contain metal Ti. That is, the adhesion film 66 may contain at least one of metal Ti and TiN. When the adhesion film 66 contains metal Ti, titanium oxide (TiO) is formed when oxygen diffuses into the adhesion film 66. Even in this case, if a large amount of TiO is formed on the bottom surface portion 66b of the adhesion film 66, the contact resistance between the conductive plug 64 and the upper electrode 44 increases. However, by forming the conductive plug 64 to penetrate the electrode film 58 and reach the electrode film 56, TiO is less likely to be formed on the bottom surface portion 66b of the adhesion film 66, and therefore the increase in contact resistance between the conductive plug 64 and the upper electrode 44 is suppressed.

[0052] 1, the upper electrode 44 includes an uppermost electrode film 58, an electrode film 56 provided below the electrode film 58, an electrode film 54 (third layer) provided below the electrode film 56, and an electrode film 52 (fourth layer) provided below the electrode film 54. The electrode film 58 is made of IrO y The electrode film 56 contains IrO having a higher oxygen composition ratio than the electrode film 58. β The electrode film 54 has an oxygen composition ratio higher than that of the electrode film 58 and different from that of the electrode film 56. α The electrode film 52 has an oxygen composition ratio higher than that of the electrode film 58 and lower than that of the electrode films 56 and 54. x The upper electrode 44 includes the electrode film 52, which suppresses interdiffusion of iridium oxide between the ferroelectric film 42 and the upper electrode 44 at the interface between the upper electrode 44 and the ferroelectric film 42, and makes it possible to control the thickness of the dead layer (a non-ferroelectric interfacial layer). The upper electrode 44 includes the electrode films 54 and 56, which suppress damage to the ferroelectric capacitor Ca due to a reducing atmosphere. The upper electrode 44 includes the electrode film 58, which makes it possible to measure the thickness of the insulating film 62 provided to cover the ferroelectric capacitor Ca after polishing. Furthermore, the upper electrode 44 includes iridium oxide, which makes it difficult for the properties of the ferroelectric film 42 to deteriorate because iridium has a relatively weak catalytic action, and oxygen is supplied from the iridium oxide to the ferroelectric film 42, thereby suppressing deterioration of the properties.

[0053] [experiment] 7(a) and 7(b) are cross-sectional views of the ferroelectric capacitor Ca of the first and second samples used in the experiment. As shown in FIG. 7(a), in the first sample, the bottom surface of the conductive plug 64 was aligned with the interface between the electrode film 56 and the electrode film 58 of the upper electrode 44. Therefore, the distance between the bottom surface of the conductive plug 64 and the interface between the electrode film 56 and the electrode film 58 was 0 nm. As shown in FIG. 7(b), in the second sample, the bottom surface of the conductive plug 64 was positioned closer to the electrode film 56 than the interface between the electrode film 56 and the electrode film 58. Therefore, the bottom portion 66b of the adhesive film 66 was positioned closer to the electrode film 56 than the interface between the electrode film 56 and the electrode film 58 and was provided within the electrode film 56. The distance L between the bottom portion 66b of the adhesive film 66 and the interface between the electrode film 56 and the electrode film 58 was 10 nm.

[0054] The films of the first and second samples were made of the materials shown in the examples, and were fabricated by the manufacturing methods shown in Figures 3(a) to 5(b).

[0055] A plurality of first samples and a plurality of second samples were fabricated, and the contact resistance between the conductive plug 64 and the upper electrode 44 was measured for each. FIG. 8 shows the measurement results of the contact resistance between the conductive plug 64 and the upper electrode 44 for the first and second samples. The horizontal axis of FIG. 8 represents the measured sample, and the vertical axis represents the contact resistance. As shown in FIG. 8, some of the first samples had high contact resistance, but all of the second samples had low contact resistance.

[0056] Therefore, in order to suppress an increase in contact resistance between the conductive plug 64 and the upper electrode 44, it is preferable that the bottom portion 66b of the adhesive film 66 be located closer to the electrode film 56 than the lower surface of the electrode film 58 and be provided inside the electrode film 56. Furthermore, the distance L between the bottom portion 66b of the adhesive film 66 and the lower surface of the electrode film 58 is preferably 10 nm or more, more preferably 15 nm or more, and even more preferably 20 nm or more. From the viewpoint of ease of manufacturing the conductive plug 64, the distance L is preferably 30 nm or less, more preferably 25 nm or less, and even more preferably 20 nm or less.

[0057] In the embodiment, the electrode films 52, 54, 56, and 58 of the upper electrode 44 contain iridium oxide as an oxide of a metal element, but this is not limited to this case and may contain oxides of other metal elements as long as they are conductive. For example, they may contain oxides of strontium, ruthenium, or lanthanum. The adhesion film 66 contains at least one of metal Ti and TiN, i.e., Ti as a metal element, but it may also contain other metal elements whose resistivity increases upon reaction with oxygen. For example, it may contain chromium (Cr).

[0058] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0059] 10. Semiconductor substrate 40 Lower electrode (1st electrode) 42 Ferroelectric film 44 Upper electrode (second electrode) 46 Adhesion Film 48 Oxygen barrier conductive film 50 Electrode membrane 52 Electrode film (4th layer) 54 Electrode film (3rd layer) 56 Electrode film (2nd layer) 58 Electrode film (1st layer) 60 Protective film 62 insulating film 64 Conductive plug 66 Adhesion Film 66a Clamped part (second part) 66b Bottom part (1st part) 68 Conductive Film 100 Semiconductor device Ca ferroelectric capacitor

Claims

1. a ferroelectric capacitor having a first electrode, a ferroelectric film provided on the first electrode, and a second electrode provided on the ferroelectric film; an insulating film covering the ferroelectric capacitor; a conductive plug that penetrates the insulating film and has a bottom portion embedded in the second electrode, the second electrode includes a first layer as an uppermost layer containing an oxide of a first metal element, and a second layer provided below the first layer and containing an oxide of the first metal element having a higher oxygen composition ratio than the first layer; the conductive plug is provided to penetrate the first layer and reach the second layer, and includes an adhesive film in contact with the first layer and the second layer and containing a second metal element, and a conductive film on the adhesive film; a first portion of the adhesion film located on a bottom surface of the conductive plug has a lower oxygen concentration than a second portion sandwiched between the first layer and the conductive film; the oxide of the first metal element is iridium oxide, the iridium oxide contained in the first layer has a composition of IrO z (z<1.0); In the semiconductor device, the iridium oxide contained in the second layer has a composition of IrO β (β>z).

2. 2. The semiconductor device according to claim 1, wherein the first portion of the adhesive film contains less oxide and / or oxynitride of the second metal element than the second portion of the adhesive film.

3. 3. The semiconductor device according to claim 1, wherein said second metal element is titanium.

4. 4. The semiconductor device according to claim 1, wherein the first portion of the adhesive film is located on the second layer side of a lower surface of the first layer and is provided inside the second layer.

5. 5. The semiconductor device according to claim 4, wherein the distance between the first portion of the adhesive film and the lower surface of the first layer is 10 nm or more.

6. 6. The semiconductor device according to claim 1, wherein the second electrode includes: the first layer, which is an uppermost layer; the second layer, which is provided below the first layer; a third layer, which is provided below the second layer and contains an oxide of the first metal element, having a higher oxygen composition ratio than the first layer and a different oxygen composition ratio than the second layer; and a fourth layer, which is provided below the third layer and contains an oxide of the first metal element, having a higher oxygen composition ratio than the first layer and a lower oxygen composition ratio than the second layer and the third layer.

7. a step of forming a film to be a first electrode; forming a ferroelectric film on the film that will become the first electrode; forming a film to be a second electrode on the ferroelectric film, the film including a first layer as an uppermost layer which is a metal layer of a first metal element, and a second layer provided below the first layer and which is an oxide layer of the first metal element; a step of patterning the film to be the first electrode, the ferroelectric film, and the film to be the second electrode to form a ferroelectric capacitor having the first electrode, the ferroelectric film, and the second electrode; a step of subjecting the ferroelectric capacitor to a heat treatment in an oxygen atmosphere; forming an insulating film covering the ferroelectric capacitor after the heat treatment; forming a conductive plug that penetrates the insulating film and the first layer to reach the second layer, is in contact with the first layer and the second layer, and includes an adhesion film containing a second metal element and a conductive film on the adhesion film; an oxide of the first metal element having a lower oxygen composition ratio than that of the second layer is formed in the first layer by the heat treatment; a first portion of the adhesion film located on a bottom surface of the conductive plug has a lower oxygen concentration than a second portion sandwiched between the first layer and the conductive film; the oxide of the first metal element is iridium oxide, After the heat treatment, the iridium oxide contained in the first layer has a composition of IrO z (z<1.0), and the iridium oxide contained in the second layer has a composition of IrO β (β>z).

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