JP4055935B2 - Method for producing iridium thin film using chemical vapor deposition - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an iridium thin film using chemical vapor deposition. More specifically, the present invention relates to a method of forming an iridium thin film on a substrate using an organic iridium compound as a raw material by a metal organic chemical vapor deposition method (MOCVD method).
[0002]
[Prior art]
The electrode material of the ferroelectric capacitor that constitutes the nonvolatile memory element is required to have heat resistance to a high temperature process necessary for forming the ferroelectric material. For this reason, it was normal to use Pt (platinum) as an electrode material at the beginning. However, when a Pt electrode is used, particularly in PZT, fatigue characteristics and imprint characteristics are very poor, which is a serious problem in terms of device reliability. Thus, Ir (iridium) or its oxide IrO ₂ has attracted attention as an electrode material that can be used as a Pt electrode. These Ir or IrO ₂ materials have heat resistance against high-temperature processes and, at the same time, have an effect of improving fatigue characteristics and imprint characteristics of PZT capacitors. Furthermore, it also serves as an oxygen barrier during high temperature processes. In particular, in a stacked memory cell structure necessary for high integration of a nonvolatile memory element, it is used to prevent oxidation of a diffusion barrier film for preventing mutual diffusion between a polysilicon plug and a capacitor electrode material. it can. Therefore, these Ir or IrO ₂ materials are actively studied not only for PZT but also for ferroelectric capacitors using SBT, and are expected to become mainstream as future electrode materials.
[0003]
These Ir or IrO ₂ materials were originally formed by sputtering. However, in the sputtering method, the step coverage in the three-dimensional structure of the capacitor is insufficient, and considering the future high integration, the chemical vapor deposition method (CVD method), which is excellent in the step coverage, particularly the organometallic chemical vapor. Thin film formation by the phase growth method (MOCVD method) is required. Advantages of forming a thin film by the MOCVD method include not only that the step coverage is excellent as described above, but also that the base substrate is not exposed to plasma unlike the case of the sputtering method. In particular, if the thin film formation technology by MOCVD is used to form the intermediate electrode of the ferroelectric gate-transistor, which is the next-generation ferroelectric device, plasma damage to the transistor channel can be suppressed, and good transistor characteristics can be obtained. It is thought that.
[0004]
In recent years, several MOCVD raw materials have been developed for this iridium, and studies on thin film formation by the MOCVD method have begun. For example, in Japanese Patent Application Laid-Open Nos. 06-290789 and 08-260148, Ir (acac) 3 and Ir (DPM) 3 which are solid raw materials are sublimated at a temperature of about 200 ° C. A technique for forming an iridium thin film by supplying on a substrate is disclosed. However, since the vapor pressure of these raw materials (solid raw materials) is sensitive to temperature fluctuations, it is difficult to keep the vapor pressure constant with high accuracy at a temperature of about 200 ° C. required for sublimation of the raw materials. There is a problem that it is difficult to supply a stable raw material, for example, vapor gas is solidified in a pipe and causes clogging. On the other hand, several liquid raw materials have been developed and are being studied. For example, JP-A-11-292888 discloses a raw material iridium-ethylcyclopentadienyl-1,5-cyclooctadiene (Ir (C ₅ H ₄ C ₂ H ₅ ) (1,5-C ₈ H ₁₂ ) or Ir (EtCp) (cod).) And a method for forming an iridium thin film using the raw material by MOCVD. However, although the publication describes that the iridium thin film was formed under the conditions of the substrate temperature of 300 ° C. and the low oxygen partial pressure, there is no description regarding the film quality of the formed iridium thin film.
[0005]
[Problems to be solved by the invention]
When an iridium thin film is formed by the MOCVD method, there is generally a problem that the surface shape of the thin film is rough. Usually, an organic iridium compound is used as a CVD raw material, and oxygen gas or hydrogen gas is used as a reaction gas to cause vapor phase growth on a substrate maintained at a temperature of about 250 ° C. to 500 ° C. Unless the conditions are selected, the film surface becomes a porous film with severe irregularities or many gaps. For example, if the oxygen partial pressure is too high at a certain substrate temperature, the crystallinity is good and the resistivity is low, but the grain size tends to be large and the film unevenness tends to be severe. On the other hand, if the oxygen partial pressure is too low, the flatness of the film is improved by reducing the grain size, but the resistivity tends to increase due to a decrease in crystallinity due to residual carbon.
[0006]
Further, when the iridium thin film is formed by the MOCVD method, there is a problem that it is generally difficult to obtain a dense iridium film. When the oxygen partial pressure is low and the crystallinity is not good, fine grains are not connected to each other and a porous film tends to be formed. Conversely, even when the oxygen partial pressure is high and the crystallinity is good, the film tends to be a film with many gaps due to the increase in grains. In particular, in the case of such a film having a loose grain boundary, the following problem occurs. That is, when this iridium film is used as a ferroelectric base electrode and a ferroelectric thin film forming process at 600 ° C. or higher is performed, the film condenses and the characteristics of the ferroelectric capacitor are remarkably deteriorated. Even if the film is dense, if the surface unevenness is large, a portion where the thickness of the ferroelectric thin film is thin is generated, which causes deterioration of the breakdown voltage of the ferroelectric capacitor.
[0007]
As a technique for improving the flatness of an iridium thin film, Japanese Patent Application Laid-Open No. 2001-181841 discloses that a liquid source Ir (EtCp) (cod) is used, and a substrate temperature after exposing a SiO ₂ / Si substrate in a hydrogen atmosphere. It is disclosed that a flat iridium thin film can be obtained by a method of forming a film in a reduced pressure oxygen atmosphere at 250 ° C. to 400 ° C. However, when such a hydrogen atmosphere is used, it is expected that metal oxides, metal nitrides, and the like used as the base film deteriorate due to reduction or decomposition. For this reason, this method has a problem that its application is limited.
[0008]
Accordingly, an object of the present invention is to provide a method for producing an iridium thin film using chemical vapor deposition which is suitable for a wide range of applications and can form a dense and flat iridium thin film.
[0009]
[Means for Solving the Problems]
In order to solve the above-described problem, the method for producing an iridium thin film using the chemical vapor deposition method of the present invention accommodates a substrate in a reaction chamber, and Ir (which is an iridium compound in the reaction chamber while the substrate is heated ). In the method for producing an iridium thin film using a chemical vapor deposition method in which a carrier gas containing EtCp) (cod) and an oxygen gas are introduced to form an iridium thin film on the substrate, the pressure in the reaction chamber is set to 1 Torr. 10 to Torr, the substrate temperature is set to 450 ° C. to 550 ° C., and the oxygen partial pressure in the reaction chamber is set to 0.05 Torr to 0.5 Torr.
[0010]
As will be described later, the iridium thin film formed by the manufacturing method of the present invention is dense and flat and has a low resistivity. Therefore, when the manufacturing method of the present invention is applied to the formation of the electrode material (lower electrode or upper electrode) of the ferroelectric capacitor, good characteristics of the ferroelectric can be extracted. In addition, since the film is formed by the CVD method, the step coverage is good, which is very useful for forming a three-dimensional capacitor. In addition, the production method of the present invention uses oxygen instead of hydrogen as a reaction gas, and thus is suitable for a wide range of applications.
[0011]
In one embodiment of the method for producing an iridium thin film using the chemical vapor deposition method, a carrier gas containing the Ir (EtCp) (cod) iridium compound is generated by a bubbling method.
[0012]
Moreover, the manufacturing method of the iridium thin film using the chemical vapor deposition method of one Embodiment uses argon (Ar) as said carrier gas.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.
[0014]
FIG. 1 shows the configuration of an MOCVD apparatus used in the method for producing an iridium thin film of the present invention. The MOCVD apparatus includes a reaction chamber 5 for accommodating a substrate 9 on which a film is to be formed, and a CVD material cylinder 3 for accommodating a liquid material Ir (EtCp) (cod) 4.
[0015]
The reaction chamber 5 is provided with a heater block 13 containing a substrate heater 7. A substrate 9 is placed horizontally on the heater block 13 via a substrate susceptor 8. A gas inlet 17 is formed in the ceiling wall of the reaction chamber 5. A gas shower head 6 is disposed between the gas inlet 17 and the substrate susceptor 8. The gas shower head 6 functions to supply the gas introduced through the gas introduction port 17 substantially uniformly to the substrate surface.
[0016]
Pipes 14A and 14B are attached to the CVD raw material cylinder 3 through the cylinder wall surface. In the cylinder 3, in order to perform the bubbling method, the end of the upstream pipe 14A is disposed in the liquid raw material 4, and the end of the downstream pipe 14B is disposed above the liquid surface of the liquid raw material 4. Yes. A carrier gas made of argon (Ar) flows through the upstream pipe 14A, and this Ar carrier gas passes through the liquid raw material 4 in the form of bubbles to become an Ar carrier gas containing the vapor of the liquid raw material 4 ( Bubbling method). The Ar carrier gas containing the vapor of the liquid raw material 4 is supplied into the reaction chamber 5 through the downstream pipe 14 </ b> B and the gas inlet 17. At the same time, oxygen (O ₂ ) gas is supplied into the reaction chamber 5 through the pipe 15. The flow rates of these Ar carrier gas and O ₂ gas are determined by an Ar carrier gas flow meter 2 and an O ₂ gas flow meter 1 (both comprising a mass flow controller (MFC)) inserted in the pipes 14A and 15 respectively. Be controlled.
[0017]
A gas (such as unreacted gas) in the reaction chamber 5 is exhausted by a vacuum pump 12 through a gas exhaust pipe 16. The flow rate of this exhaust gas is controlled by a pressure control valve 11 inserted in the gas exhaust pipe 16. The pressure in the reaction chamber 5 is monitored by a pressure gauge 10.
[0018]
When an iridium thin film is formed using this apparatus, liquid source material Ir (EtCp) (cod) 4 is filled in a cylinder container 3, and vapor of the source gas is supplied into the reaction chamber by bubbling using Ar as a carrier gas. Carry to 5. On the other hand, O ₂ gas is introduced into the reaction chamber 5 as a reaction gas for decomposing the raw material. At this time, it is appropriate to heat the cylinder container 3 to about 80 ° C. to 140 ° C. in order to increase the vapor pressure. The heating method may be anything such as immersing the cylinder container 3 in a constant temperature oil tank or heating the cylinder container 3 by winding a ribbon heater. Similarly, the pipe 14 </ b> B from the cylinder 3 to the reaction chamber 5 is preferably heated to a temperature equal to or higher than the heating temperature of the cylinder container 3 in order to prevent the raw materials from aggregating on the way. In general, the Ar carrier gas flow rate and the O ₂ gas flow rate are each set in the range of about 0 sccm to 1000 sccm.
[0019]
The substrate 9 on which the film is formed may be any element such as an element such as a transistor, a silicon substrate on which an interlayer insulating film, a polysilicon plug, a metal wiring, or the like is formed. In the following example, a substrate in which SiO ₂ is formed as a base film on a Si substrate (this is referred to as “SiO ₂ / Si substrate”) is used.
[0020]
FIG. 2 shows that the pressure in the reaction chamber 5 (meaning the total pressure of the mixed gas of Ar carrier gas and O ₂ gas in the reaction chamber 5; hereinafter referred to as “reaction chamber pressure”) is set to 5 Torr. 3 shows the result (scatter diagram) of evaluating the denseness of the surface of the iridium film at a ratio including gaps (this is referred to as “gap content ratio”). In the figure, a circle indicates a film with a gap content of less than 0.1%, a triangle indicates a film with a gap content of 0.1% to 1%, a square indicates a film with a gap content of 1% to 10%, The mark ◆ indicates a film having a gap content of 1% to 10%. From FIG. 2, the substrate temperature is 450 ° C. to 550 ° C., the oxygen partial pressure in the reaction chamber 5 (hereinafter, simply referred to as “oxygen partial pressure”) is 0.05 Torr to 0.5 Torr, and the gap content is 1% or less. It can be seen that a dense film is obtained. The same results were obtained when the reaction chamber pressure was in the range of 1 Torr to 10 Torr.
[0021]
As an example of the conditions in such a range, the iridium thin film is formed when the substrate temperature is set to 500 ° C., the reaction chamber pressure is set to 5 Torr, the oxygen partial pressure is set to 0.25 Torr, and the film is formed on the SiO ₂ / Si substrate. A surface SEM photograph and a cross-sectional SEM photograph are shown in FIGS. 3A and 3B that this film is a dense and flat film. The resistivity of this film was 8.7 μΩcm, and the root mean square surface roughness was 3.0 nm. On the other hand, as an example of the condition for increasing the gap content, when the substrate temperature is set to 300 ° C., the reaction chamber pressure is set to 5 Torr, and the oxygen partial pressure is set to 1.5 Torr, the film is formed on the SiO ₂ / Si substrate. FIGS. 4A and 4B show a surface SEM photograph and a cross-sectional SEM photograph of the iridium film, respectively. 4 (a) and 4 (b), it can be seen that this film is a sparse film with very many gaps. The resistivity of this film was 20.5 μΩcm, and the root mean square surface roughness was 7.7 nm.
[0022]
The reason why such a film quality difference occurs is explained as follows. That is, when the substrate temperature at the time of film formation is as low as about 300 ° C. as shown in FIGS. 4A and 4B, the decomposition of the raw material mainly contributes to the decomposition by oxygen, and the best possible film quality is obtained. Requires a relatively high oxygen partial pressure. However, carbon still tends to remain in the film, and when oxygen is introduced excessively, oxygen is taken into the film, which adversely affects the morphology. Therefore, there is little or no oxygen partial pressure range in which a good film quality of denseness and flatness can be obtained. On the other hand, when the substrate temperature at the time of film formation is as high as about 500 ° C. as shown in FIGS. 3A and 3B, both oxygen and heat contribute to the decomposition of the raw material. Conceivable. Therefore, even if the oxygen partial pressure is kept relatively low, carbon is unlikely to remain in the film, and an iridium film with good film quality can be obtained.
[0023]
【The invention's effect】
As is clear from the above, according to the method for producing an iridium thin film using the chemical vapor deposition method of the present invention, a dense and flat iridium thin film can be formed.
[Brief description of the drawings]
FIG. 1 is a diagram showing the configuration of an MOCVD apparatus used in a method for producing an iridium thin film according to the present invention.
FIG. 2 is a graph showing a gap content on a film surface of a film formed at each substrate temperature and oxygen partial pressure when an iridium thin film is formed by MOCVD.
3A is a surface SEM photograph in the case where an iridium thin film is formed on a SiO ₂ / Si substrate at a substrate temperature of 500 ° C., a reaction chamber pressure of 5 Torr, and an oxygen partial pressure of 0.25 Torr. FIG. (B) is a cross-sectional SEM photograph when the substrate temperature is 500 ° C., the reaction chamber pressure is 5 Torr, and the oxygen partial pressure is 0.25 Torr, and an iridium thin film is formed on the SiO ₂ / Si substrate.
4A is a surface SEM photograph in the case where an iridium thin film is formed on a SiO ₂ / Si substrate at a substrate temperature of 300 ° C., a reaction chamber pressure of 5 Torr, and an oxygen partial pressure of 1.5 Torr. FIG. (B) is a cross-sectional SEM photograph in which the substrate temperature is 300 ° C., the reaction chamber pressure is 5 Torr, the oxygen partial pressure is 1.5 Torr, and an iridium thin film is formed on the SiO ₂ / Si substrate.
[Explanation of symbols]
1 O ₂ gas flow meter 2 Ar carrier gas flow meter 3 CVD raw material cylinder 4 Liquid raw material Ir (EtCp) (cod)
5 reaction chamber 6 gas shower head 7 heater for substrate heating 8 susceptor for substrate 9 substrate 10 pressure gauge 11 pressure control valve 12 vacuum pump

Claims (3)

A substrate is accommodated in the reaction chamber, and a carrier gas containing oxygen (Ir (EtCp) (cod) , which is an iridium compound, and oxygen gas are introduced into the reaction chamber while the substrate is heated, and an iridium thin film is formed on the substrate. In the method of manufacturing an iridium thin film using chemical vapor deposition to form
The pressure in the reaction chamber is set in the range of 1 Torr to 10 Torr, the temperature of the substrate is set in the range of 450 ° C. to 550 ° C., and the oxygen partial pressure in the reaction chamber is set in the range of 0.05 Torr to 0.5 Torr. A method for producing an iridium thin film using chemical vapor deposition. In the manufacturing method of the iridium thin film using the chemical vapor deposition method of Claim 1,
A method for producing an iridium thin film using chemical vapor deposition, wherein a carrier gas containing Ir (EtCp) (cod) is generated by a bubbling method. In the manufacturing method of the iridium thin film using the chemical vapor deposition method of Claim 1 or 2 ,
A method for producing an iridium thin film using chemical vapor deposition, wherein argon (Ar) is used as the carrier gas.

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