JP2004063891A - Method for manufacturing ferroelectric memory - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a ferroelectric memory by which an appropriate alumina protection film can be formed, even with respect to a refined FeRAM structure. <P>SOLUTION: This method is used to form a protective film for FeRAM, and it includes a step, wherein a capacitor structure comprising a lower electrode, a ferroelectric film and an upper electrode film is formed on a semiconductor board and a step for forming the protective film. The step for forming the protective film includes a temperature rise step, wherein an object subject to film formation including a capacitor structure is introduced into a reaction furnace for plasma CVD and is heated to a specified temperature; a deposition step, wherein an alumina material made of aluminium alkoxide and and oxygen are introduced into the reaction furnace in a condition of high-output plasma power; and oxidation step, wherein an oxygen is introduced, without introducing the alumina material into the reaction furnace in a condition of high-output plasma power. The deposition and oxidation steps are repeated plural number of times, forming the protective film, having the desired thickness on the object of film formation. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention generally relates to the technical field of semiconductor memories, and more particularly, to a method of manufacturing a ferroelectric memory (Ferro-Electrical Random Access Memory).
[0002]
[Prior art]
As nonvolatile memories in this type of technical field, flash memories and FeRAMs are known. A flash memory has a floating gate embedded in a gate insulating film of an insulated gate field effect transistor (IGFET: Insulated Gate Field Effect Transistor), and stores information by accumulating charges in the floating gate. Remember. A flash memory has a cell configuration similar to that of a dynamic random access memory (DRAM), and thus is advantageous for large-scale integration.
[0003]
The FeRAM stores information using the polarization hysteresis characteristics of a ferroelectric. The ferroelectric film provided between the capacitor electrodes of the FeRAM generates polarization according to the voltage applied between the electrodes, and maintains spontaneous polarization even when the applied voltage is removed. When the polarity of the applied voltage is reversed, the polarity of the spontaneous polarization is also reversed. By detecting the direction of the spontaneous polarization, it becomes possible to read and write information. FeRAM operates at a lower voltage and consumes less power than a flash memory, and can write at high speed.
[0004]
The ferroelectric film of FeRAM is made of a PZT-based material such as lead zirconate titanate (PZT), La-doped PZT (PLZT), or SrBi. ₂ Ta ₂ O ₉ (SBT, Y1), SrBi ₂ (Ta, Nb) ₂ O ₉ It is formed of a Bi layer structure compound such as (SBTN, YZ). Conventionally, an amorphous ferroelectric film was formed on the lower electrode of a capacitor of FeRAM by, for example, a sputtering method or a sol-gel method, and then heat-treated to crystallize into a perovskite structure. This ferroelectric film has a property of being easily reduced by hydrogen, and when it is reduced, its polarization characteristics are deteriorated (that is, it is difficult or difficult to polarize). After the formation of the capacitor structure, there is a step of generating hydrogen as in the step of growing the interlayer insulating film. Therefore, it is necessary to form a protective film functioning as a hydrogen barrier on the capacitor structure (particularly on the ferroelectric film). An alumina film is used as the protective film. This is because the alumina film has various desirable properties such as a high dielectric constant, thermal and chemical stability, and a low interface state density.
[0005]
Japanese Patent Application Laid-Open No. 2001-44357 discloses a technique of forming an alumina film having a predetermined film density by using a sputtering method so as to cover the entire capacitor structure formed stepwise. Such a method is relatively effective for a device of about 0.35 μm FeRAM. The capacitor structure formed in a step shape is, for example, as shown in FIG. 1A, and a transistor portion (not shown) is arranged on a base substrate along with the capacitor structure.
[0006]
However, in a next-generation FeRAM such as a 0.18 μm FeRAM with further miniaturization, it is no longer appropriate to form an alumina film by a normal sputtering method. This is because, at such a fine dimension, the capacitor structure is different from the above-mentioned step-like structure, for example, the capacitor structure is etched at a time, and the stacked capacitor structure (the capacitor structure is replaced with a transistor portion (shown in FIG. 1)). (FIG. 1B), which is located at the upper part of FIG. For this reason, the aspect ratio becomes larger than before, and there is a concern that sufficient coverage cannot be obtained with an alumina film formed by a normal sputtering method. For example, there is a concern that a protective film having a sufficient thickness is not formed on the side surface of the capacitor structure.
[0007]
An alumina film may be formed by a CVD method instead of the sputtering method. In the case of performing the CVD method, trimethyl aluminum (TMA: Tri-methyl aluminum, Al (CH) is formed by CVD using an organic metal. ₃ ) ₃ ) And water (H ₂ O) is generally used. In this method, water (steam) is adsorbed on the substrate surface, and vacuum evacuation is performed to remove excess water (purge). Then, TMA is introduced, and a hydroxyl group (OH) group adsorbed on the substrate is reacted with TMA to remove excess TMA. By repeating this series of steps, an alumina film having a desired thickness can be obtained. According to this method, since the deposition is performed at an atomic layer level by a method called an atomic layer deposition method (ALD: Atomic Layer Deposition), it is possible to overcome the problem of the coverage which is a problem in the sputtering method.
[Problems to be solved by the invention]
However, the present inventor has discovered that the use of TMA and water to form an alumina protective film of FeRAM can degrade the characteristics (particularly, polarization characteristics) of the ferroelectric film. The reason is that a large amount of water is used when forming the alumina protective film, so that hydrogen (H) is adsorbed on a ferroelectric film such as PZT, or hydrogen is contained in the alumina protective film. It is conceivable that the ferroelectric film remains and causes a reducing action of the ferroelectric film by a heat treatment step or the like performed later. Further, since the ignitability of TMA is very high, even slight contact with the surrounding air causes explosive combustion. Such dangerous TMA is disadvantageous from the viewpoint of mass productivity where safety is required. Therefore, it is not always appropriate to form an alumina protective film using TMA.
[0008]
A general object of the present application is to provide a method of manufacturing a ferroelectric memory capable of forming a good alumina protective film even on an FeRAM structure with a finer structure.
[0009]
A specific object of the present application is to provide a method for forming an alumina protective film that enables film formation without deteriorating the polarization characteristics of a ferroelectric substance for FeRAM.
[0010]
A specific object of the present application is to provide a method for forming an alumina protective film that enables safe film formation.
[0011]
[Means for Solving the Problems]
According to the solution according to the invention,
A method of manufacturing a ferroelectric memory, comprising: a step of forming a capacitor structure for the ferroelectric memory; and a step of forming the protective film,
The step of forming the capacitor structure includes a step of forming a lower electrode film on a semiconductor substrate, a step of forming a ferroelectric film on the lower electrode, and a step of forming an upper electrode film on the ferroelectric film. ,
The step of forming the protective film,
A temperature increasing step of introducing a film formation target including the capacitor structure into a reaction furnace for performing plasma CVD, and heating the film formation target to a predetermined temperature;
A deposition step of introducing an alumina raw material comprising aluminum alkoxide and oxygen into the reactor under low-power plasma power conditions;
An oxidation step of introducing oxygen under high-power plasma power conditions without introducing the alumina raw material into the reactor;
A protective film having a desired thickness is formed on the object to be formed by repeating the deposition step and the oxidation step a plurality of times. .
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
(Manufacture of FeRAM)
FIG. 2 shows a part of a manufacturing process for forming a ferroelectric memory. As shown in FIG. 2A, a MOS transistor 20 is formed on a semiconductor substrate 10. The MOS transistor 20 is created using an existing semiconductor process. As an example, an element formation region is defined on the semiconductor substrate 10 by a field oxide film. A gate electrode is formed in the element formation region, source and drain regions are formed using the gate electrode as a mask, and the entire surface is covered with an oxide film. Further, an interlayer insulating film 22 is deposited, and the upper surface thereof is etched and flattened. A contact hole is formed where the electrode is taken out. A glue film (TiN (50 nm) / Ti (30 nm)) functioning as an adhesion layer is formed inside the contact hole. Thereafter, the first plug 30 is formed by filling tungsten (W) by CVD.
[0013]
At the stage shown in FIG. 2B, a lower electrode film 40, a ferroelectric film 50, and an upper electrode film 60 are sequentially deposited on the interlayer insulating film 22 and the first plug 30.
[0014]
The lower electrode film 40 is made of, for example, iridium (Ir) and can be formed by a sputtering method under the following conditions:
Film thickness: 200 nm
Argon gas pressure: 0.11 Pa
DC power: 0.5kW
Film formation time: 335 seconds
Film formation temperature: 500 ° C
The ferroelectric film 50 is made of, for example, PZT and can be formed by MOCVD under the following conditions:
Film thickness: 120 nm
Film formation pressure: 5 Torr
Film formation time: 420 seconds
Film formation temperature: 580 ° C
In the MOCVD method, since a film is formed by vapor phase growth, solid materials such as lead (Pb), zirconium (Zr), and titanium (Ti) for forming a ferroelectric film are dissolved in an organic solvent. This solution is vaporized to form a source gas. The source gas is introduced into a reaction furnace to form, for example, a PZT film. The raw materials and the supply amount can be supplied, for example, under the following conditions:
Organic solvent: THF (Tetra HydroFuran: C ₄ H ₈ O)
Flow rate of organic solvent: 0.474 ml / min
Pb (DPM) ₂ : 0.326ml / min
Zr (dmhd) ₄ : 0.200ml / min
Ti (O-iPr) ₂ (DPM) ₂ : 0.200ml / min
(All are dissolved in THF at a concentration of 0.3 mol / l)
The upper electrode 60 is made of, for example, iridium oxide (IrO). ₂ ), A film can be formed by the sputtering method under the following conditions:
Film thickness: 200 nm
Argon gas flow rate: 100 sccm
Oxygen gas flow rate: 100sccm
DC power: 0.5kW
Film formation time: 79 seconds
Here, iridium oxide (IrO) was used without using platinum (Pt) as the upper electrode. ₂ ) Is mainly used to improve the resistance to hydrogen degradation. In the case of a Pt electrode, since this has a catalytic action on hydrogen molecules, hydrogen radicals are generated, and the PZT film is easily reduced (polarization characteristics are easily deteriorated). In contrast, IrO ₂ Since the electrode does not have such a catalytic action, the hydrogen deterioration resistance of the PZT film 50 is improved as compared with the case of the Pt electrode.
[0015]
After the upper electrode 60 is formed by the sputtering method, recovery annealing for recovering damage (particularly, dropout of oxygen) applied to the ferroelectric film 50 by sputtering is performed. This is performed, for example, by supplying oxygen at 650 ° C. for 60 minutes in a furnace (electric furnace).
[0016]
At the stage shown in FIG. 2C, a ferroelectric capacitor structure having a stack structure is formed by patterning and etching. Here, three layers of the upper electrode film 60, the ferroelectric film 50, and the lower electrode film 40 are collectively etched using the plasma TEOS / TiN as a hard mask.
[0017]
At the stage shown in FIG. 3A, a 50 nm-thick alumina protective film 70 is formed on the capacitor structure. The film forming method will be described later. After depositing the alumina protective film 70, furnace annealing at 650 ° C. is performed for 60 minutes while supplying oxygen. Then, an interlayer insulating film 80 is deposited, and planarization is performed by chemical mechanical polishing (CMP: Chemical Mechanical Polishing). The remaining film thickness after polishing is, for example, 300 nm on the upper electrode film 60 of the ferroelectric capacitor.
[0018]
In the step shown in FIG. 3B, the interlayer insulating film 80 is patterned and etched to form a contact hole for connecting to the first plug 30 made of tungsten. A glue film made of, for example, 50 nm titanium nitride (TiN) is formed inside the contact hole, filled with tungsten, and the upper surface is polished by chemical mechanical polishing (CMP) to form a second plug 90. Is done. After polishing, the substrate is reacted with nitrogen plasma at 350 ° C. for 120 seconds.
[0019]
At the stage shown in FIG. 3C, for example, a tungsten antioxidant film of SION (100 nm) is formed. By patterning and etching the interlayer insulating film 80, a contact hole 94 for the upper electrode film 60 of the ferroelectric capacitor structure is formed. Then, recovery annealing is performed by performing furnace annealing for 60 minutes while introducing oxygen at 550 ° C. After that, the tungsten oxidation preventing film is etched back.
[0020]
Next, a metal wiring 92 for the upper electrode film 60 and the second plug 90 is formed. In this embodiment, the metal wiring 92 is composed of TiN (70 nm) / Ti (5 nm) / Al-Cu (400 nm) / TiN (30 nm) / Ti (60 nm). Also, SION (30 nm) is used as an antireflection film. Thereafter, although not shown, contact plugs are formed between the second and subsequent metal wirings, and finally a cover film made of TEOS and SIN is formed. Thus, an FeRAM having a ferroelectric capacitor structure is formed.
[0021]
Electrical connection from the metal wiring 92 to the substrate can be realized by via-to-via contact by coupling the second plug 90 and the previously formed first plug 30. Will be possible. Compared with a normal semiconductor device, the FeRAM has an extra step corresponding to the ferroelectric capacitor structure, so that the aspect of the contact from the metal wiring 92 to the substrate increases. If an attempt is made to form a contact with this large aspect by a single etching, it may be difficult to embed the glue film in addition to the difficulty in etching itself. Forming the via-to-via contact as in this embodiment makes it possible to avoid such a problem.
[0022]
(Formation of alumina protective film)
Hereinafter, a method of forming the alumina protective film 70 referred to in FIG. 3A will be described. The alumina protective film 70 is formed using a CVD device using helicon wave plasma.
[0023]
FIG. 4 is a schematic sectional view of such a CVD apparatus 100. The CVD apparatus 100 includes a helicon wave plasma generation source 104 composed of a bell jar 102, a reaction furnace 106 coupled to the helicon wave plasma generation source 104, and a material supply unit 108 that supplies a film formation material to the reaction furnace 106.
[0024]
The helicon wave plasma source 104 has a dome-shaped bell jar 102 made of, for example, quartz. Around the bell jar 102, a helicon wave antenna 110 coupled to a helicon wave plasma power supply 109 is provided. Further, the bell jar 102 is surrounded by a solenoid coil 113. The solenoid coil 113 includes an inner coil that contributes to the propagation of the helicon wave and an outer coil that contributes to transport of the generated plasma. The helicon wave plasma source 104 is provided with a matching box 116 for adjusting electrical conditions for generating plasma in the bell jar 102.
[0025]
A substrate stage 118 is provided in the reaction furnace 106 so as to be coaxial with the bell jar 102. A substrate to be processed (film formation target) such as a semiconductor wafer is arranged on the substrate stage 118. The substrate stage 118 is also provided with a heater and a temperature detector for raising the temperature of the film formation target (not shown). A film formation target is carried in or out of the load lock chamber 124 through the gate valve 122. Further, a turbo molecular pump 128 is connected to the reactor 106 for exhausting gas inside through a gate valve 126.
[0026]
The raw material supply unit 108 is provided with a bottle container 130 containing a film forming raw material such as aluminum alkoxide. The bottle container 130 is placed in a thermostat 132 and is heated so as to obtain a constant temperature and vapor pressure. The raw material in the bottle container 130 is introduced into the reaction furnace 106 through the raw material gas introduction line 134 and the first gas introduction part 136 after being vaporized. In this case, the source gas introduction line 134 is heated by the heater 138 so that the gas is not liquefied during the transfer of the gas. The bottle container 130 is also provided with a carrier gas introduction line 140, only a part of which is shown, and adjusts the pressure in the bottle container 130 as needed. As the carrier gas, for example, argon gas is used.
[0027]
The source gas conveyed by the source gas introduction line 134 is introduced into the reaction furnace through the first gas introduction unit 136 by a vent line mechanism (not shown), or is exhausted without being introduced into the reaction furnace 106. Destroyed. The reason why the source gas is continuously supplied even in the case of discarding is to stabilize the flow rate of the source gas. Oxygen from the oxygen cylinder 142 is introduced into the reactor 106 through the oxygen introduction line 144 and the second gas introduction unit 146.
[0028]
The helicon wave plasma source 104 of the CVD apparatus configured as described above generates a helicon wave (Heusler wave) by the helicon wave antenna 110 and the solenoid coil 113, and ¹¹ -10 ¹³ / Cm ³ It is possible to generate a high density plasma. In addition, high-density plasma can be generated over a wide range of RF power (applied power). The plasma density of a parallel plate type plasma apparatus, which is a general plasma generation source, is 10 ⁹ / Cm ³ That is, the CVD apparatus 100 can obtain a plasma density as large as two to four orders of magnitude. This high-density plasma propagates along the magnetic field created by the solenoid coil 113 and supplies high-density reactive species onto the substrate 120 with ion bombardment. Therefore, the organic component is more efficiently decomposed and removed from the substrate to be processed as compared with the high-temperature CVD.
[0029]
FIG. 5 shows an alumina film (Al film) using the CVD apparatus 100 shown in FIG. 4 according to the first embodiment of the present invention. ₂ O ₃ 2) shows a flowchart 200 for forming a film. In step 202, the silicon substrate (substrate to be processed) 120 loaded from the load / lock chamber 124 is set on the substrate stage 118. As a film forming material, aluminum tri-secondary butoxide (Al (O-sec-C ₄ H ₉ ) ₃ ). In this embodiment, film formation is performed under the following conditions.
[0030]
(Common conditions)
Film forming material: aluminum tri-secondary butoxide
Temperature of bottle container 130: 145 degrees Celsius
Gas pressure: 5 mTorr
Substrate temperature: 320 degrees Celsius
Number of repetitions: 40
(Deposition conditions)
Carrier gas flow rate: 0 sccm
Helicon wave plasma power output: 60W (13.56MHz)
Processing time: 8 seconds
Oxygen flow rate: 80 sccm
(Oxidation conditions)
Helicon wave plasma power supply output: 2000W (13.56MHz)
Processing time: 15 seconds
Oxygen flow rate: 100 sccm
Here, the common condition is a condition common to all processes, the deposition condition is a condition relating to the deposition process, and the oxidation condition is a condition relating to the oxidation process.
[0031]
In the temperature raising step 204, the silicon substrate is heated to a predetermined temperature such as 320 degrees Celsius. Note that this temperature is much lower than the temperature used in thermal CVD (eg, 700 degrees Celsius). In this embodiment, the temperature is raised to 320 ° C. over about 2 minutes.
[0032]
In the deposition step 206, an alumina film is deposited under the above-mentioned common conditions and deposition conditions. In this step, the plasma power output is set very low, such as 60 W. The aluminum tri-secondary butoxide introduced from the first gas introduction part 136 is poured down onto the silicon substrate 120 in a molecular state, or a precursor such as a partially-condensed dimer or trimer is formed. It is formed and becomes a seed, which is poured onto the silicon substrate 120. Note that the carrier gas flow rate is 0 sccm. In this embodiment, the temperature of the bottle container 130 is set to 145 degrees Celsius by the constant temperature bath 132, and a vapor pressure of about 1 Torr is obtained. This is because the raw material can be supplied by the pressure difference from the reaction furnace (the raw material gas introduction line 134 is heated to 170 degrees Celsius by the heater 138). Therefore, when the temperature conditions are changed or when the pressure difference with the reaction furnace is not sufficient, a carrier gas such as an argon gas having a flow rate of 5 sccm may be introduced.
[0033]
On the other hand, oxygen introduced from the second gas introduction unit 146 is dissociated by high-density plasma generated in the bell jar 102 and becomes an active species such as an oxygen radical. This active species is transferred onto the silicon substrate 120 due to the magnetic field generated by the solenoid coil 113. On the silicon substrate 120, aluminum oxide is deposited by the active species and the film forming raw material. From the viewpoint of preventing aluminum tri-secondary butoxide from decomposing in the gas phase and becoming particles (contaminant particles) and falling on the silicon substrate, the plasma power is reduced to 200 W or less, for example. In particular, it is desirable to set it to about 60 W. However, in the deposited film, in addition to alumina, extra components such as hydrogen and carbon generated by the reaction between the active species and the film forming raw material remain. The deposition step 206 is performed for 8 seconds.
[0034]
In the oxidation step 208, the valve of the reaction furnace 106 is closed to stop the supply of the raw material from the first gas introduction unit 136, and the gas from the raw gas introduction line 134 is exhausted by a vent line mechanism. In the oxidation step 208, the plasma power is set to a high output of 2000W. Oxygen is subsequently introduced from the second gas introduction unit 146 and dissociated by high-density plasma to become active species such as oxygen radicals. The flow rate of the supplied oxygen may be the same as or different from the flow rate in the deposition step, and is a value that can be appropriately adjusted. This active species is transferred onto the silicon substrate 120 due to the magnetic field generated by the solenoid coil 113. Since the plasma power is high power, the amount of active species generated increases, and reacts with hydrogen and carbon in the deposited alumina film to form CO 2. ₂ And H ₂ O is formed and vaporized to promote the densification of the alumina film. As described above, from the viewpoint of promoting the densification by oxidation, the plasma power in the oxidation step should be set to a high output of, for example, 1000 W or more, and particularly preferably about 2000 W. Oxidation step 208 is performed for 15 seconds.
[0035]
The deposition step 206 and the oxidation step 208 are repeated a predetermined number of times to form an alumina film having a desired thickness. In this embodiment, these steps are repeated 40 times to form a 50 nm alumina film. Therefore, the film formation amount per time is about 1.25 nm. By forming such a very thin film 40 times, it is possible to form a film with very dense coverage and excellent coverage, in addition to performing film formation safely at low temperature. Thereafter, the silicon substrate 120 on which the film forming process has been performed is taken out of the load lock chamber 124, and the film forming process ends (210).
[0036]
FIG. 6 shows an alumina film (Al) using the CVD apparatus 100 shown in FIG. 4 according to the second embodiment of the present invention. ₂ O ₃ 3) shows a flowchart 300 for forming a film. The introduction of the silicon substrate 120 and the heating step 304 of the silicon substrate in the step 302 are the same as the step 202 and the heating step 204 described with reference to FIG. However, conditions in the deposition step 306 and the oxidation step 308 are different. In this embodiment, film formation is performed under the following conditions.
[0037]
(Common conditions)
Material for film formation: aluminum, tri, iso, proxide
Temperature of bottle container 130: 115 degrees Celsius
Gas pressure: 5 mTorr
Substrate temperature: 320 degrees Celsius
Number of repetitions: 5 times
(Deposition conditions)
Carrier gas flow rate: 5 sccm
Helicon wave plasma power output: 200W (13.56MHz)
Processing time: 60 seconds
Oxygen flow rate: 100 sccm
(Oxidation conditions)
Helicon wave plasma power supply output: 2000W (13.56MHz)
Processing time: 60 seconds
Oxygen flow rate: 100 sccm
Unlike the first embodiment, in the second embodiment, aluminum tri-isoproxide (Al (O-i-C) ₃ H ₇ ) ₃ ). That is, the raw material gas is formed by sublimating the raw material in the bottle container 130. When this raw material is used, the amount of hydrogen and carbon is smaller than that of the raw material used in the first embodiment (the number of C and H per Al is smaller), so that the hydroxyl groups (OH) in the alumina film tend to decrease. Is advantageous. In addition, the solid source can supply more source gas than the liquid source. For example, if the temperature of the bottle container 130 is the same, it is possible to supply a source gas at a larger flow rate for the solid source than for the liquid source. Therefore, it is preferable to use a solid raw material from the viewpoint of quickly performing the film forming process. On the other hand, the liquid raw material has an advantage that the flow rate and the remaining amount are easier to control than the solid raw material.
[0038]
The thickness of the alumina film formed in both the first embodiment and the second embodiment is 50 nm. In the second embodiment, the number of repetitions of the deposition step and the oxidation step is only five times, but the deposition time is as long as 60 seconds, and the film formation amount per time is 10 nm. It is formed thick. Although it is possible to form the film safely and at a low temperature even if the film is formed thick at a time in this way, from the viewpoint of improving the film density, a cycle of forming the film thin as in the first embodiment is performed many times. Is preferred.
[0039]
(Evaluation)
The inventor of the present application evaluated the effect of hydrogen contained in the alumina protective film on the ferroelectric film in the research that forms the basis of the present invention. A ferroelectric capacitor structure is formed, and a 50 nm alumina protective film is formed under various conditions listed in FIG. Then, a heat treatment at 650 ° C. was performed for 60 minutes to diffuse hydrogen (H) in the alumina protective film out of the protective film. Although H also diffuses into the gas phase, it also diffuses into the ferroelectric film, so that the reduction action caused by hydrogen causes deterioration of polarization. Thereafter, the entire surface was etched to evaluate how the ferroelectric characteristics changed. Specifically, the capacitor structure includes a Pt / Ti lower electrode with a thickness of 175 nm / 20 nm, a ferroelectric film of PLZT with a thickness of 200 nm, and an IrO film with a thickness of 200 nm. ₂ Are formed in order by sequentially depositing the upper electrodes by a sputtering method. Then, the upper electrode was processed into a 50 × 50 μm square, and the PLZT film was also etched.
[0040]
FIG. 7 shows film forming conditions for ten types of test samples A to J as shown in the leftmost column. The second column from the left of this chart indicates that the film is formed by sputtering, and only the sample J complies with this condition (this sample corresponds to a protective film by a conventional method). Other samples are formed by CVD using helicon wave plasma as in the present embodiment. The third and fourth columns show the substrate temperature and the carrier gas flow rate in the deposition process. The fifth and sixth columns (rightmost column) from the left show the oxidation time and plasma power in the oxidation step. Other film forming conditions are common to all test samples A to J except sample I. For example, the final film thickness is 50 nm, and the number of times of deposition and oxidation is 5 times. That is, the plasma power in the deposition step is 200 W, and the film forming material is aluminum tri-iso-proxyd which is solid at room temperature.
[0041]
FIG. 8 shows the switching charge (μC / cm) when a voltage of 3 volts is applied between the capacitor electrodes for these test samples A to J. ² ) Is shown in a box-whisker diagram. This switching charge amount indicates the magnitude of the polarization (the height of the hysteresis). That is, when the ferroelectric is reduced and deteriorated due to the hydrogen diffused by the heat treatment at 650 ° C., the measured switching charge is also reduced. Desirably, the median is large and the variation is small. As is clear from the figure, the median value of sample B is lower than the other samples. Therefore, it turns out that an oxidation time of 30 seconds is not enough, and a longer time (for example, 60 seconds) is required. In addition, since the sample D is not preferable because the variation between the maximum value and the minimum value is large, it is found that the plasma power should be larger than 1000 W (for example, 2000 W). Thus, optimization can be achieved by changing various film forming conditions. In this example, the number of repetitions of the deposition and oxidation steps is five, but it is also possible to change and evaluate the number of repetitions.
[0042]
Next, the evaluation of the alumina film made by the present inventors will be described. First, in order to evaluate the denseness of the alumina film, the density of the alumina film was measured by using the XRR (X-ray reflectivity film thickness measurement) method. An alumina film having a thickness of 50 nm formed on a silicon substrate by using the helicon wave plasma CVD apparatus described above is used.
[0043]
FIG. 9 shows the relationship between the plasma power and the alumina film density in the deposition process. A graph 402 corresponds to a case where a 50 nm-thick alumina film is formed by repeating the deposition step and the oxidation step five times. As shown, the plasma power and the alumina film density are in a proportional relationship. Therefore, the film density increases or decreases according to the magnitude of the plasma power. From the viewpoint of suppressing particle particles in the deposition step, it is preferable that the plasma power be low. However, a certain amount of plasma power is required from the viewpoint of plasma stabilization. On the other hand, when the plasma power is fixed and the number of repetitions is changed, a film density of a value as shown by coordinates 404 in the case of 15 times and a value of coordinates 406 in the case of 30 times is obtained. That is, as the number of repetitions increases, the film density also increases. From the above results, it can be seen that it is effective to increase the number of repetitions with a low plasma power of 200 or less (especially about 60 W) in order to improve the density while suppressing the generation of particles.
[0044]
FIG. 10 shows the relationship between the oxidation time and the film density in the oxidation step. By examining this relationship, it is possible to find the minimum time required for oxidation. The evaluation target is an alumina film formed to a thickness of 50 nm on a silicon substrate. The plasma power in the deposition step prior to oxidation is 60W. Since the film density for oxidation for 15 seconds or more has not changed, it can be seen that the film is saturated in about 15 seconds. In addition, since there is no change in the graph when the number of repetitions is set to 30 or 35, it can be seen that the number of repetitions is saturated at about 30. In consideration of such saturation, the film formation amount per one time is 50/30 = 1.67 nm, which can be said to be about 2 nm or less.
[0045]
As described above, according to the embodiment of the present invention, it is possible to form an alumina protective film having good step coverage even for a finer FeRAM structure. Specifically, it is possible to perform film formation while suppressing deterioration of the polarization characteristics of the ferroelectric substance for FeRAM. That is, the alumina protective film can be formed while maintaining a high switching charge amount. Further, since a safe aluminum alkoxide is used without using a dangerous raw material such as TMA, it is possible to form a film safely.
[0046]
According to the embodiment of the present application, due to the good coverage characteristics of the alumina protective film to be formed, it is possible to form a good film even on the capacitor structure which is etched at once.
[0047]
According to the embodiment of the present application, since helicon wave plasma is used, high-output and low-output plasma can be satisfactorily generated.
[0048]
According to the embodiment of the present application, aluminum tri-secondary butoxide (Al (O-sec-C ₄ H ₉ ) ₃ Since a liquid material such as that described in (1) is used, for example, the supply amount of the material can be accurately controlled.
[0049]
According to the embodiment of the present application, aluminum tri-isoproxide (Al (OiC) ₃ H ₇ ) ₃ Since a solid material such as that described in (1) is used, it is possible to improve the film formation rate by, for example, quickly supplying the raw material.
[0050]
Although the present invention has been described with reference to particular embodiments, the invention is not limited thereto. For example, it is possible to use a Pt / Ti laminated structure instead of Ir as the lower electrode. Further, instead of PZT and PLZT, SBT and SBTN can be used as the ferroelectric material. Furthermore, instead of forming the ferroelectric film by MOCVD, a sol-gel method or a sputtering method can be used.
[0051]
Hereinafter, means taught by the present invention will be listed.
[0052]
(Supplementary Note 1) A method for manufacturing a ferroelectric memory, comprising: a step of forming a capacitor structure for the ferroelectric memory; and a step of forming the protective film.
The step of forming the capacitor structure includes a step of forming a lower electrode film on a semiconductor substrate, a step of forming a ferroelectric film on the lower electrode, and a step of forming an upper electrode film on the ferroelectric film. ,
The step of forming the protective film,
A temperature increasing step of introducing a film formation target including the capacitor structure into a reaction furnace for performing plasma CVD, and heating the film formation target to a predetermined temperature;
A deposition step of introducing an alumina raw material comprising aluminum alkoxide and oxygen into the reactor under low-power plasma power conditions;
An oxidation step of introducing oxygen under high-power plasma power conditions without introducing the alumina raw material into the reactor;
A method of manufacturing a ferroelectric memory, wherein a protective film having a desired thickness is formed on the object to be formed by repeating the deposition step and the oxidation step a plurality of times.
[0053]
(Supplementary Note 2) In the manufacturing method according to Supplementary Note 1, the step of forming the capacitor structure further includes a step of collectively etching the upper electrode film, the ferroelectric film, and the lower electrode film. Manufacturing method.
[0054]
(Supplementary Note 3) The method according to Supplementary Note 1, wherein a film formation amount per one time of the deposition step and the oxidation step, which is repeated a plurality of times, is 2 nm or less.
[0055]
(Supplementary Note 4) The method according to Supplementary Note 1, wherein the plasma used is helicon wave plasma.
[0056]
(Supplementary Note 5) In the production method according to Supplementary Note 1, the alumina raw material may be aluminum tri-secondary butoxide (Al (O-sec-C ₄ H ₉ ) ₃ ).
[0057]
(Supplementary Note 6) In the production method according to Supplementary Note 1, the alumina raw material may be aluminum tri-isoproxide (Al (OiC). ₃ H ₇ ) ₃ ).
[0058]
(Supplementary note 7) The method according to supplementary note 1, wherein the ferroelectric film is made of a material selected from the group consisting of PZT, PLZT, SBT, and SBTN.
[0059]
(Supplementary Note 8) The method according to supplementary note 1, wherein the lower electrode has a Pt / Ti laminated structure.
[0060]
【The invention's effect】
As described above, according to the present invention, it is possible to form an excellent alumina protective film even on a FeRAM structure with a finer structure.
[0061]
[Brief description of the drawings]
FIG. 1 shows a schematic diagram of a ferroelectric capacitor structure.
FIG. 2 is a diagram (part 1) illustrating a manufacturing process of the ferroelectric memory;
FIG. 3 is a diagram (part 2) illustrating a step of manufacturing the ferroelectric memory;
FIG. 4 is a schematic view of a helicon wave plasma CVD apparatus used in the embodiment of the present invention.
FIG. 5 is a flowchart for forming an alumina protective film according to the embodiment of the present invention.
FIG. 6 shows another flowchart for forming an alumina protective film according to the embodiment of the present invention.
FIG. 7 is a chart showing conditions for forming an alumina protective film.
FIG. 8 is a diagram showing a switching charge amount for each sample.
FIG. 9 is a graph showing the relationship between plasma power and alumina film density in a deposition step.
FIG. 10 is a graph showing a relationship between an oxidation time and an alumina film density.
[Explanation of symbols]
10 Semiconductor substrate
20 MOS transistors
22 Interlayer insulating film
30 first plug
40 lower electrode
50 Ferroelectric
60 upper electrode
70 Alumina protective film
80 Interlayer insulation film
90 Second plug
92 metal wiring
94 Contact Hole
100 CVD equipment
102 Belja
104 Helicon Wave Plasma Source
106 reactor
108 Raw material supply unit
110 Helicon wave antenna
113 solenoid coil
116 Matching Box
118 Substrate stage
120 Substrate to be processed
122 Gate valve
124 Road Lock Room
126 Gate valve
128 turbo molecular pump
130 bottle container
132 constant temperature bath
134 Source gas introduction line
136 First gas inlet
138 heater
140 Carrier gas introduction line
142 oxygen cylinder
144 Oxygen introduction line
146 Second gas inlet

Claims (5)

A method of manufacturing a ferroelectric memory, comprising: a step of forming a capacitor structure for the ferroelectric memory; and a step of forming the protective film,
The step of forming the capacitor structure includes a step of forming a lower electrode film on a semiconductor substrate, a step of forming a ferroelectric film on the lower electrode, and a step of forming an upper electrode film on the ferroelectric film. ,
The step of forming the protective film,
A temperature increasing step of introducing a film formation target including the capacitor structure into a reaction furnace for performing plasma CVD, and heating the film formation target to a predetermined temperature;
A deposition step of introducing an alumina raw material comprising aluminum alkoxide and oxygen into the reactor under low-power plasma power conditions;
Under high-power plasma power conditions, without introducing the alumina raw material into the reactor, comprises an oxidation step of introducing oxygen, and by repeating the deposition step and the oxidation step a plurality of times, a desired thickness is obtained. A method of manufacturing a ferroelectric memory, characterized in that a protective film is formed on the object to be formed. 2. The manufacturing method according to claim 1, wherein the step of forming the capacitor structure further comprises a step of etching the upper electrode film, the ferroelectric film, and the lower electrode film all at once. Method. 2. The method according to claim 1, wherein the plasma used is helicon wave plasma. Manufacturing process in the production method of Claim 1, wherein the alumina raw material, characterized in that made of aluminum tri-secondary butoxide _{(Al (O-sec-C} 4 H 9) 3). Manufacturing process in the production method of Claim 1, wherein the alumina raw material, characterized in that made of aluminum tri-iso-Purokishido _{(Al (O-i-C} 3 H 7) 3).

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