JP2009094200A - Semiconductor device and method of manufacturing thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable semiconductor device with improved resistance characteristic against processing damage. <P>SOLUTION: The semiconductor device has a semiconductor substrate 101, and a capacitor which is provided on the upper side of the semiconductor substrate and composed by placing a dielectric film 116 in between a lower electrode 115 and an upper electrode 117. The upper electrode has a first MOx type conductive oxide film ("M" is a metal element, "O" is an oxygen element, and x>0) 117b having a crystal structure, and a second MOx type conductive oxide film ("M" is a metal element, "O" is an oxygen element, and x>0) 117c which is formed on the first MOx type conductive oxide film, has a crystal structure, and has a smaller oxygen ratio than the first MOx type conductive oxide film. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a semiconductor device and a manufacturing method thereof.

A ferroelectric memory (FeRAM: Ferroelectric Random Access Memory) is a capacitor portion _{PZT (Pb (Zr x Ti 1} -x) O 3), BIT (Bi 4 Ti 3 O 12), SBT (SrBi 2 Ta 2 O 9 This is a nonvolatile memory that uses a ferroelectric film such as) and retains data by utilizing the residual polarization. For the film formation process of the ferroelectric film, a sputtering method, a MOCVD (Metal Organic Chemical Vapor Deposition) method, a sol-gel method, or the like that can be consistent with the semiconductor memory manufacturing process is used.

  Since ferroelectrics such as PZT are oxides, they are reduced when a gas mainly containing hydrogen enters and the crystal characteristics are lost, or space charges due to hydrogen contamination are formed at the electrode interface, and the ferroelectric characteristics are reduced. to degrade. As the capacitor size becomes smaller, the influence of hydrogen becomes larger. Since many semiconductor device manufacturing processes are performed in an atmosphere containing hydrogen, it is necessary to prevent hydrogen from entering the ferroelectric film.

  In order to solve such a problem, a lower electrode, a ferroelectric film formed on the lower electrode, and an upper electrode formed on the ferroelectric film are provided. A ferroelectric capacitor having a first layer and a second layer formed on the first layer and made of an oxide and having a higher oxidation rate than the first layer has been proposed (see, for example, Patent Document 1). . The oxide is, for example, IrOx.

  This ferroelectric capacitor suppresses deterioration of the characteristics of the ferroelectric film due to hydrogen intrusion due to the process damage resistance of the second layer (upper layer) of the upper electrode having a high oxidation rate.

On the other hand, the first layer (lower layer) of the upper electrode is a film containing a small amount of oxygen deficiency and a large amount of oxygen vacancies. Defects such as oxygen vacancies at the interface between the ferroelectric film and the upper electrode are caused by reduced resistance to reducing process damage in the capacitor manufacturing process, deterioration of fatigue characteristics, deterioration of retention characteristics, imprint characteristics (polarization written in one direction (Phenomenon that stabilizes in that direction) This causes problems such as deterioration and decreases reliability.
Japanese Patent No. 3661850

  SUMMARY OF THE INVENTION An object of the present invention is to provide a highly reliable semiconductor device and a method for manufacturing the same that improve process damage resistance.

  A semiconductor device according to an aspect of the present invention includes a semiconductor substrate and a capacitor provided above the semiconductor substrate and sandwiching a dielectric film between a lower electrode and an upper electrode, and the upper electrode includes a crystal A first MOx-type conductive oxide film (M is a metal element, O is an oxygen element, x> 0) and a first MOx-type conductive oxide film having a crystal structure, And a second MOx type conductive oxide film (M is a metal element, O is an oxygen element, x> 0) having an oxygen ratio smaller than that of the first MOx type conductive oxide film.

According to an aspect of the present invention, there is provided a method for manufacturing a semiconductor device, comprising: forming a lower electrode film constituting a capacitor above a semiconductor substrate; forming a dielectric film constituting the capacitor on the lower electrode film; A first MOx type conductive oxide film (M is a metal element, O is an oxygen element, x> 0) is formed on the dielectric film by reactive sputtering using a metal M target, and the first MOx type conductive oxide film is formed. A target containing metal M is used on the MOx type conductive oxide film, and the ratio of the O ₂ flow rate to the Ar flow rate is smaller or the sputtering power is higher than when forming the first MOx type conductive oxide film. A second MOx type conductive oxide film (M is a metal element, O is an oxygen element, x> 0) is formed by the reactive sputtering method.

  According to the present invention, process damage resistance can be improved and reliability can be increased.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  (First Embodiment) FIG. 1 shows a schematic configuration of a ferroelectric memory according to a first embodiment of the present invention. A trench type element isolation (not shown) is formed on the semiconductor substrate 101, and a gate insulating film 103 and a gate electrode to be a word line (for example, a polycide structure including a polysilicon film 104 and a tungsten silicide film 105). A MOS transistor is formed by the gate cap film and gate sidewall film 106 made of a silicon nitride film and the source / drain diffusion layer 102.

  The interlayer insulating film 107 (silicon oxide film) formed so as to surround the MOS transistor is planarized, and further, the interlayer insulating films 108 (silicon oxide film), 109 (silicon nitride film), and 110 (silicon oxide film) are further formed thereon. Film) is formed.

  In these interlayer insulating films 107, 108, 109 and 110, contact plugs 111 and tungsten plugs 113 connecting the source / drain diffusion layers 102 of the MOS transistors and the barrier layers 114 of the capacitors are formed. Further, a diffusion prevention film (contact barrier film) 112 is formed so as to surround the tungsten plug 113.

  A capacitor is formed on interlayer insulating film 110. The capacitor includes a barrier layer (capacitor barrier film) 114, a lower electrode 115, a capacitor dielectric film 116, and an upper electrode 117 that are sequentially stacked.

  Furthermore, a hydrogen prevention film 118 of, for example, an AlOx film is formed so as to surround the entire capacitor. A contact 119 for connecting the upper electrodes of adjacent capacitors is formed in an interlayer insulating film (silicon oxide film) 120 formed thereon.

  The barrier layer 114 includes a TiAl film 114a and a TiAlN film 114b.

  The lower electrode 115 is, for example, an Ir film. The capacitor dielectric film 116 is a PZT film, for example.

  The upper electrode 117 is an SRO film (ABOx perovskite type conductive oxide (A and B are metal elements, O is an oxygen element, x> 0)) 117a, IrOx film (MOx type conductive oxide (M is Metal element, O includes oxygen element, x> 0)) 117b, and IrOx film 117c.

The IrOx film 117b has an IrO ₂ crystal structure, and is rich in oxygen in the composition ratio and has an O / Ir ratio larger than 2. The density is about 10.5 g / cm ³ and consists of fine particles having a size of about 100 A or less.

The IrOx film 117c formed on the IrOx film 117b has an IrO ₂ crystal structure with high crystallinity, the composition is close to the stoichiometric composition, and the O / Ir ratio is about 2. The density is higher than that of the IrOx film 117b and is about 11.5 g / cm ³ , and has a dense microstructure.

  The IrOx film 117b formed on the SRO film 117a has a high oxygen content and can supply sufficient oxygen to the SRO film 117a portion or the SRO film 117a / PZT film 116 interface. Therefore, an upper electrode with few defects can be formed at the interface.

  Thereby, polarization amount deterioration, imprint characteristic deterioration, and retention characteristic deterioration can be prevented. In addition, the IrOx film 117c formed on the IrOx film 117b can block hydrogen intrusion in the treatment in the hydrogen atmosphere and suppress reductive damage.

  Thus, the semiconductor device according to the present embodiment has improved process damage resistance and high reliability.

  Next, a method for manufacturing such a semiconductor device will be described with reference to FIGS.

  As shown in FIG. 2, a transistor T is formed on a silicon substrate 201 by a known process to form a CMOS structure. Then, a silicon oxide film 202, a silicon oxide film 203, a silicon nitride film 204, and a silicon oxide film 205 are deposited by CVD (chemical vapor deposition) and CMP (chemical mechanical polishing) to form an interlayer insulating film. .

  Here, in order to connect the capacitor and the active area (source, drain) of the transistor using a plug made of tungsten or polysilicon, the plug 206 is formed in advance.

  The plug 206 includes a contact plug 207, a tungsten plug 208, and a contact barrier film 209 formed so as to surround the tungsten plug 208. The formation of the plug 206 uses both blanket CVD and CMP.

  As shown in FIG. 3, a barrier metal layer 300 is formed on the silicon oxide film 205 and the plug 206. The barrier metal layer 300 has a laminated structure of a TiAl film 301 and a TiAlN film 302. A TiAl film 301 having a thickness of 5 nm and a TiAlN film 302 having a thickness of 30 nm are formed by DC magnetron sputtering.

  The barrier metal layer 300 prevents the surface of the plug 206 from being oxidized during the formation of the ferroelectric film or the subsequent annealing process in oxygen for securing the capacitor characteristics.

  As shown in FIG. 4, an Ir film 401 having a thickness of 100 nm to be a lower electrode is formed on the barrier metal layer 300 by a sputtering method.

As shown in FIG. 5, a 100-nm-thick PZT film 501 serving as a capacitor dielectric film is formed on the Ir film 401 by sputtering. In this case, an RF magnetron sputtering method is used. Here, a PZT ceramic target in which the amount of Pb is increased by about 10% is used. The composition of the target is Pb _1.10 La _0.05 Zr _0.4 Ti _0.6 O ₃ . A high-density PZT ceramic target has a high sputtering rate and good environmental resistance against moisture and the like, and therefore a ceramic sintered body having a theoretical density of 98% or more is used.

  At the time of sputtering, since there is an increase in substrate temperature due to plasma and bombardment due to flying particles, evaporation of Pb from the Si substrate and re-sputtering easily occur, and loss of the amount of Pb in the film tends to occur.

  Excess Pb in the target is added to compensate for this and promote crystallization of the PZT film 501 during RTA (Rapid Thermal Annealing). Since elements such as Zr, Ti, and La are incorporated into the film in substantially the same amount as the target composition, elements having a desired composition ratio may be used.

  Then, the PZT film 501 is crystallized using RTA.

As shown in FIG. 6, the upper electrode 600 is formed on the PZT film 501. The upper electrode has a laminated structure of an SRO film 601, an IrOx film 602, and an IrO ₂ film 603.

  First, DC magnetron sputtering was performed on an SRO ceramic target having a diameter of 300 mm under the conditions of sputtering power 1 kW, room temperature, pressure 0.5 Pa, argon / oxygen mixed gas, oxygen flow rate ratio 50%, and SRO film 601 having a film thickness of 10 nm. Form.

  After the formation of the SRO film 601, a crystallization process is performed at 550 to 650 ° C. by RTO (Rapid Thermal Oxidation) or the like.

Next, DC magnetron sputtering was performed on an Ir target having a diameter of 300 mm under the conditions of sputtering power 0.2 kW, room temperature, pressure 0.5 Pa, and argon / oxygen mixed gas (Ar / O ₂ = 20/80). An IrOx film 602 having a thickness of 30 nm is formed.

The IrOx film 602 is formed by sputtering with a high oxygen concentration (high oxygen partial pressure) and a low sputtering power density so as to be oxygen-rich. Preferably, the sputtering power density is 0.1 to 1 W / cm ² , and the proportion of the O ₂ flow rate in the total sputtering gas flow rate is 50% or more and less than 100%.

If the sputtering power density is less than 0.1 W / cm ² , it is not practical because the discharge is stably prevented and the deposition rate becomes very slow.

Further, when the sputtering power density is larger than 1 W / cm ² , the particle size becomes large, and a large amount of oxygen needs to be introduced to form an oxygen-rich IrOx film, so that the film characteristics (film thickness, resistance, etc.) Variability increases.

Subsequently, an IrO ₂ film 603 is formed by sputtering with a higher sputtering power and a smaller amount of oxygen than when the IrOx film 602 is formed. For example, DC magnetron sputtering is performed on an Ir target having a diameter of 300 mm under the conditions of a sputtering power of 2 kW, a room temperature, a pressure of 0.5 Pa, and an argon / oxygen mixed gas (Ar / O ₂ = 50/50). An IrO ₂ film 603 is formed.

The IrOx film 602 has an IrO ₂ crystal structure after the heat treatment, is oxygen-rich in composition ratio, and has an O / Ir ratio larger than 2. On the other hand, the IrO ₂ film 603 has an IrO ₂ crystal structure with high crystallinity after the heat treatment, the composition is close to the stoichiometric composition, and the O / Ir ratio is about 2. Further, the IrO ₂ film 603 has a finer fine structure and a higher density than the IrOx film 602.

As shown in FIG. 7, the upper electrode 600, the PZT film 501, the Ir film 401, and the barrier metal layer 300 are RIE processed using a hard mask (not shown) to form a capacitor structure. After removing the mask, an AlOx film (for example, an Al ₂ O ₃ film) 701 serving as a hydrogen prevention film is formed so as to cover the capacitor structure.

  Thereafter, an interlayer insulating film (silicon oxide film) 702 is formed, and a contact 703 for connecting the upper electrodes of adjacent capacitors is formed in the interlayer insulating film 702.

  The IrOx film 602 has a high oxygen content and can supply sufficient oxygen to the SRO film 601 part or the SRO film 601 / PZT film 501 interface. Further, since the sputtering power at the time of film formation is low, sputtering damage caused by element implantation on the SRO film 601 can be reduced. As a result, generation of defects at the ferroelectric film / upper electrode interface can be suppressed.

Further, the IrO ₂ film 603 having a fine microstructure prevents capacitor deterioration and hydrogen diffusion due to a hard mask CVD film formation process, a capacitor processing RIE process, reductive annealing, or the like.

  Thus, process damage resistance is improved, and a highly reliable semiconductor device can be manufactured.

  The above-described embodiment is an example and should not be considered as limiting.

For example, as shown in FIG. 8, the upper electrode 117 does not include an SRO film, has an IrO ₂ crystal structure, has an oxygen rich composition, and has an O / Ir ratio greater than 2, and an IrO ₂ film having high crystallinity. It may have a laminated structure with an IrO ₂ film 117c having a crystal structure, a composition close to the stoichiometric composition, an O / Ir ratio of about 2, a density higher than that of the IrOx film 117b, and a fine microstructure.

  Since the oxygen-rich IrOx film 117 b is formed on the PZT film 116, sufficient oxygen is supplied to the interface between the PZT film 116 and the upper electrode 117. Therefore, generation of defects such as oxygen vacancies can be prevented, and a highly reliable semiconductor device can be obtained.

  In the above embodiment, IrOx is used for the MOx type conductive oxide of the upper electrode, but RuOx, OsOx, RhOx, and PdOx may be used.

In addition to SRO (SrRuO ₃ ), LNO (LaNiO ₃ ), LSCO ((La, Sr) CoO ₃ ), YBCO (superconductor), or the like can be used as the ABOx type conductive oxide.

  In the above embodiment, as shown in FIG. 5, the PZT film to be the capacitor dielectric film is formed by sputtering, but it may be formed by MOCVD. The MOCVD method has good step coverage for the electrode structure, excellent composition controllability, a uniform high quality film can be obtained over a large area, the film formation speed is fast, and the ferroelectric film is thinned. Has the advantage that it can be operated (low voltage operation is possible).

The raw materials for PZT used in the MOCVD method are typical, Pb (dpm) ₂ as the Pb source, Zr (dpm) ₄ or Zr (O-tC ₄ H ₉ ) _{4 as} the Zr source, and Ti (O) as the Ti source. -iC ₃ H _{7) 4} and _{Ti (O-iC 3 H 7} ) 2 (dpm) 2 include, be used as a solution vaporization method by mixing with THF (tetrahydrofuran) and butyl acetate.

  There are many types of vaporizers, and the source material is vaporized using a device that atomizes the solution with ultrasonic waves, a device that sprays the solution on a hot plate, or a device that uses an atomizer.

Although the substrate temperature depends on the raw material, approximately 600 ° C. is appropriate. N ₂ O and O ₂ are simultaneously supplied as an oxidizing agent. Crystallization occurs in-situ, and a PZT <111> oriented crystal film can be obtained on the Ir film 401.

Further, RTO treatment may be performed at 500 ° C. after the IrO ₂ film 603 is formed. Thereby, the IrO ₂ film 603 becomes denser, and the reducing damage suppressing effect can be increased.

  The technical scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is a schematic configuration diagram of a semiconductor device according to an embodiment of the present invention. It is process sectional drawing explaining the manufacturing method of the semiconductor device which concerns on embodiment of this invention. FIG. 8 is a process cross-sectional view illustrating the manufacturing method of the semiconductor device according to the embodiment. FIG. 8 is a process cross-sectional view illustrating the manufacturing method of the semiconductor device according to the embodiment. FIG. 8 is a process cross-sectional view illustrating the manufacturing method of the semiconductor device according to the embodiment. FIG. 8 is a process cross-sectional view illustrating the manufacturing method of the semiconductor device according to the embodiment. FIG. 8 is a process cross-sectional view illustrating the manufacturing method of the semiconductor device according to the embodiment. It is a schematic block diagram of the semiconductor device by a modification.

Explanation of symbols

101 Semiconductor substrate 102 Source / drain diffusion layer 103 Gate insulating film 104 Polysilicon film 104
105 Tungsten silicide film 106 Gate cap film and gate sidewall films 107, 108, 109, 110, 120 Interlayer insulating film 111 Contact plug 112 Diffusion prevention film 113 Tungsten plug 114 Capacitor barrier film 115 Lower electrode 115
116 Capacitor dielectric film 117 Upper electrode 117a SRO film 117b, 117c IrOx film 118 Hydrogen prevention film 119 Contact

Claims (5)

A semiconductor substrate;
A capacitor provided above the semiconductor substrate and having a dielectric film sandwiched between a lower electrode and an upper electrode;
The upper electrode is
A first MOx type conductive oxide film having a crystal structure (M is a metal element, O is an oxygen element, x>0);
A second MOx type conductive oxide film (M is a metal element, formed on the first MOx type conductive oxide film, having a crystal structure and having an oxygen ratio smaller than that of the first MOx type conductive oxide film) O is an oxygen element, x> 0),
A semiconductor device comprising:   The upper electrode further includes an ABOx type conductive oxide film (A and B are metal elements, O is an oxygen element, and x> 0) having a crystal structure below the first MOx type conductive oxide film. The semiconductor device according to claim 1.   3. The semiconductor device according to claim 1, wherein the first MOx type conductive oxide film contains a number of oxygens having a composition ratio larger than a stoichiometric composition ratio. 4. Forming a lower electrode film constituting the capacitor above the semiconductor substrate;
Forming a dielectric film constituting the capacitor on the lower electrode film;
A first MOx type conductive oxide film (M is a metal element, O is an oxygen element, x> 0) is formed on the dielectric film by a reactive sputtering method using a target of metal M,
Using a target containing the metal M on the first MOx type conductive oxide film, the ratio of the O ₂ flow rate to the Ar flow rate is smaller than that at the time of forming the first MOx type conductive oxide film, or sputtering is performed. A method for manufacturing a semiconductor device, wherein a second MOx type conductive oxide film (M is a metal element, O is an oxygen element, x> 0) is formed by a reactive sputtering method under a high power condition.   5. The method of manufacturing a semiconductor device according to claim 4, wherein the metal M is Ir.

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