JPH0959089A - Growing of chemical vapor phase - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable formation of film at a sufficient deposition rate and control of the composition and enable improvement of coating property to difference in level by using a gas containing one or more kinds of ozone, N2 O and NO2 as an oxidizing gas in a chemical vapor phase growing method introducing a raw material gas and an oxidizing gas into a reaction vessel and depositing a bismuth compound. SOLUTION: An oxidizing gas is produced by introducing oxygen gas into an ozonizer to produce about several wt.% ozone gas. Tripheylbismuth and dipivaloylstrontium, etc., are respectively selected as Bi source and Sr source in MOCVD method. The source material is dissolved in an organic solvent and put in a source bottle and Ar gas is made to flow and the source is introduced into a mixing pipe in a liquid state and each source is mixed. Formation of the film is typically carried out at 400-700 deg.C substrate temperature under 0.01-50Torr reacting gas pressure. As necessary, after forming the film, the film is annealed at a temperature higher than the film-forming temperature in an oxidative atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical vapor deposition method of a bismuth compound which is useful for an electronic device such as a ferroelectric memory.

[0002]

2. Description of the Related Art Bismuth compounds, for example, bismuth layered compounds that are complex oxides, are a group of compounds that are extremely important in industry, such as bismuth-based superconducting oxides having a critical temperature of 110 K, or materials for ferroelectric memories. I am doing it. When applying these compounds to electronic devices, development of a thin film process is indispensable.

This bismuth layer compound such as Bi ₂ S
A ferroelectric memory using rTa ₂ O ₉ as a ferroelectric material is PZT (PbZ) which is a conventional ferroelectric memory material.
Recently, it has been drawing attention because it does not exhibit the phenomenon that remanent polarization is reduced by repeated rewriting, which is a disadvantage of the (rTi oxide) type material, that is, the so-called fatig phenomenon.

Attempts are currently being made to apply this bismuth layered compound to electronic devices. Among them, a thin film of a bismuth layered compound exhibiting good ferroelectricity is MOD.
It is obtained by a spin coating method such as the (Metal Organic Deposition) method.

[0005]

However, the demand for cleanliness is strict in an actual semiconductor process, and the above-mentioned film forming method by spin coating cannot satisfy this demand.

Therefore, it is necessary to develop a new film forming process, but it is difficult to perform an oxidation reaction on an oxide thin film by an ultrahigh vacuum process (for example, molecular beam epitaxy method or laser ablation). Therefore, in order to promote the oxidation reaction and crystallize the thin film, introduction of a strong oxidizing gas such as ozone, N ₂ O or NO ₂ has been attempted in addition to oxygen gas.

Further, as post-treatment after film formation, heat treatment in an oxidizing gas is also performed to improve crystallinity.

On the other hand, in the MOCVD method (metalorganic chemical vapor deposition method) which is often used in semiconductor processes, complicated multi-step elementary processes between sources in the raw material supply process,
In addition, there are many factors causing compositional deviations such as various reactions on the substrate and re-evaporation, and when the oxidizing property of the atmosphere is strong, the composition of the deposited film before crystallization is greatly affected. In particular, bismuth is a metal having a low melting point, and when it is deposited as a metal, it is extremely likely to be re-evaporated, and in the conventional film forming process using only oxygen as an oxidant, a high reaction gas pressure of, for example, 10 to 20 torr was required.

The greatest feature of the MOCVD method is the step coverage, which is formed on the stepped lower electrode for the purpose of increasing the effective capacitor area in the manufacturing process of a highly integrated ferroelectric memory, for example. This is an indispensable characteristic when forming a ferroelectric film. However, in general, in order to obtain a good step coverage and further obtain the uniformity of the thin film, the reaction gas pressure in MOCVD is preferably as low as possible within the range in which the gas retains the property of viscous flow, and is as high as about 10 torr. It is difficult to obtain sufficient step coverage with gas pressure.

In order to solve the above-mentioned problems, the present invention provides a method for producing a bismuth compound excellent in both film composition and step coverage by setting an oxidizing atmosphere during film formation by MOCVD. It is a thing.

[0011]

The present invention is a chemical vapor deposition method in which a source gas and an oxidizing gas are introduced into a reaction vessel to deposit a bismuth compound, and ozone, N ₂ O, and At least 1 selected from NO ₂
A gas containing a seed is used.

According to the above-described structure of the present invention, by introducing a strong oxidizing agent such as ozone during the film forming process by the chemical vapor deposition method (CVD method), a low melting point metal which is easily re-evaporated can be obtained. The composition of certain bismuths can be controlled. At the same time, it is possible to manufacture a bismuth compound having excellent step coverage by taking advantage of the characteristics of the CVD method.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the chemical vapor deposition method for bismuth compounds of the present invention, a source gas and a strongly oxidizing gas selected from ozone, N ₂ O and NO ₂ as an oxidizing gas are placed in a reaction vessel. , More preferably diluted with oxygen gas etc.
By introducing the bismuth compound while controlling the flow rate, it is possible to obtain a bismuth compound having a desired composition, which is useful for electronic devices such as a highly integrated ferroelectric memory and excellent in step coverage.

The outline of the method for producing a bismuth compound by the chemical vapor deposition method according to the present invention will be described.

In the chemical vapor deposition method of the present invention, an oxidizing gas is introduced during the film forming process. This oxidizing gas is manufactured by introducing oxygen gas into, for example, a commercially available ozonizer to generate ozone gas of about several wt%. At this time, if ozone gas is introduced into the reactor as it is, the oxidizing effect may be too strong to obtain stable results. Therefore, either the discharge power of the ozonizer may be reduced, or the gas discharged from the ozonizer may be diluted with an inert gas or an oxygen gas having a relatively weak oxidizing power, but the latter is relatively Easy to control. Therefore, the concentration of ozone is adjusted by diluting with oxygen gas to obtain oxidizing gas.

The apparatus of the CVD method may be of any type, but in order to prevent the source gas from being oxidized before it reaches the substrate, the oxidizing gas is directly fed to the reaction chamber without passing through the source gas mixer. The piping will be introduced.

As the MOCVD source, for example, Bi
BiPh ₃ (triphenylbismuth) as the source, Sr (DPM) ₂ (dipivaloyl-strontium) as the Sr source, Ta (OCH ₃ ) ₅ as the Ta source are selected.
Then, it is introduced into the reactor by a technique such as bubbling using argon gas as a carrier, and preferably brought into contact with an oxidizing gas in the vicinity of the substrate.

Regarding the concentration of the oxidizing gas, it is preferable to analyze the composition of the trial-produced thin film with an EPMA (electron probe microanalyzer), a fluorescent X-ray device, etc., and compare it with the target composition, and based on that, Set the correct mixing ratio and concentration of oxidizing gas. If the film forming conditions are appropriate, a sufficient deposition rate of bismuth can be obtained at a pressure far lower than that in a normal process using oxygen as an oxidant.

Next, specific examples of the method for producing a bismuth compound according to the present invention will be described. In this example, bismuth oxide (Bi ₂ O ₃ ), which is extremely difficult to form a film when only oxygen gas is used as an oxidant, or tantalum.
It is an example of forming a thin film of an oxide having a sufficient excess of bismuth with respect to strontium.

FIG. 1 shows an example of the structure of an apparatus for carrying out the MOCVD method according to the present invention in this case. This device is an example of a device that combines a so-called flash MOCVD and an oxidizing gas pipe.

This apparatus is roughly classified into a reactor, for example, a portion including a quartz reaction tube Q for performing reaction and film formation, a portion for supplying a raw material (MOCVD source) to the reactor, and an oxidizing gas for the reactor. And the part that supplies it to.

In the portion for supplying the raw material to the reactor, the Ar gas supply port G ₁ , the source bottles S ₁ , S ₂ , S ₃ in which the respective sources (raw materials) for MOCVD are placed, and the MOCVD source are mixed and adjusted. It comprises a mixing tube M, a liquid injection pump P for injecting a MOCVD source, and a vaporizer V for vaporizing the MOCVD source into a source gas, and an Ar gas supply port G.
Ar gas from ₁ passes through a mass flow controller (MFC) for flow rate adjustment, vaporizer V, each source bottle S ₁ ,
It is designed to be supplied to S ₂ and S ₃ .

The portion for supplying the oxidizing gas is provided with respective oxidizing gas supply ports G ₂ and G ₃ for oxygen gas and N ₂ O,
The oxygen gas is supplied to the ozonizer OZ to generate ozone gas by oxidation of the oxygen gas. Further, the oxygen gas from the oxygen gas supply port G ₂ and the ozone gas from the ozonizer OZ,
N ₂ O gas from the N ₂ O gas supply port G ₃ are respectively adapted to be supplied to the quartz reaction tube Q via a mass flow controller (MFC).

A portion including a reactor for performing reaction and film formation is a film forming chamber R provided with a quartz reaction tube Q for performing an oxidation reaction.
₁ , RF coil C for heating the inside of quartz reaction tube Q, load chamber R ₁ separated from film forming chamber R ₁ by gate valve GV
_In this reactor, a transfer rod TR for loading and unloading the susceptor SC made of graphite on the support of the substrate Sub on which a film is formed by the MOCVD method is arranged. In addition, it has an exhaust pipe D connected to an exhaust system such as a vacuum pump.

As the substrate Sub, for example, one obtained by sequentially depositing Ti and Pt on silicon by a sputtering method is used.

As the MOCVD source, Bi source is used as Bi source.
Ph ₃ (triphenylbismuth), Bi (O-Tol)
Similarly, other suitable elements such as Sr and Ta are selected using _{3 and the} like.

[0027] After these source materials were placed in the source bottle S _1, S _2, S ₃ dissolved like in an organic solvent, by flowing Ar gas to each source bottle source bottle S ₁ source in the liquid state, S ₂ , S ₃ to the mixing tube M and mix the respective sources. At this time, the mixing ratio is adjusted by adjusting the flow rate of Ar gas flowing into each source bottle with a valve.

The mixed MOCVD source is conveyed to the vaporizer V in a liquid state by the liquid injection pump P. It is vaporized in the vaporizer V together with the Ar carrier gas that has passed through the MFC and introduced into the quartz reaction tube Q. At this time, the source solution is vaporized by rapidly reducing the pressure in the vaporizer V, preferably to about 0.1 to 10 torr, and transported in the vapor phase state onto the substrate Sub in the quartz reaction tube Q. At this time, the vaporizer V is appropriately heated so that the source material does not deposit and adhere to the inner wall of the vaporizer V.

As for the oxidizing gas, oxygen gas is introduced into the ozonizer OZ to generate ozone gas of about several wt%, which is diluted with oxygen gas or N ₂ O gas. The flow rate of these oxidizing gases is adjusted by the mass flow controller MFC so that the partial pressure of the oxygen gas to be diluted + the output gas from the ozonizer is about 50% of the total pressure (the remaining 50% is the partial pressure of the argon carrier gas). Adjust and supply.

The film forming conditions are typically a substrate temperature of 400.
-700 degreeC and reaction gas pressure are 0.01-50 torr.

If necessary, after film formation, annealing (heat treatment) is performed at a temperature equal to or higher than the film formation temperature in an oxidizing atmosphere.

Conventional CVD using only oxygen as oxidant
In film formation, it is impossible to produce a CVD film having a sufficient bismuth composition regardless of temperature at a pressure of about 5 torr or less, and to deposit bismuth oxide alone (not containing strontium or tantalum). Was also difficult. On the other hand, by performing CVD film formation in an oxidizing atmosphere containing ozone of several percent or more, bismuth is introduced into the film by several tens of times (tantalum ratio) as compared with oxygen only,
It also becomes possible to form a film of bismuth oxide.

FIG. 2 shows the relationship between the partial pressure of ozone gas in the reaction gas and the composition of the film. Here, the oxidizing gas output from the ozonizer (oxygen gas containing 10 wt% ozone)
Is diluted with oxygen, and the total flow rate of the diluted oxidizing gas (ozone + oxygen) and the flow rate of the argon gas of the carrier are kept at 900 sccm. That is, the partial pressures of both the diluted oxidizing gas and the argon gas are kept at 50%. Further, the composition of the film is standardized with the tantalum composition being 2, and shows the bismuth composition (● mark) and the strontium composition (∘ mark), respectively.

It can be seen from FIG. 2 that the bismuth composition rapidly increases even when the ozone gas having a partial pressure of about 0.4% is introduced, and reaches tens of times that of tantalum at a partial pressure of 0.8%. From this, it is considered that the introduction of ozone gas produces bismuth oxide containing almost no strontium or tantalum. When the partial pressure of ozone gas is 1.5% or more, bismuth in the composition of the film is saturated, whereas tantalum continues to increase. Therefore, the proportion of bismuth gradually decreases as the oxygen partial pressure increases. It can be seen that bismuth is increased as compared with the case of only oxygen without addition (0% in the figure).

The partial pressure of ozone gas is preferably in the range of 0.01 to 20% of the total pressure. If it is less than 0.01%, the effect of adding ozone gas does not appear. When the partial pressure is 20% or more, ozone gas has a strong oxidizing property and is dangerous in handling.

The X-ray diffraction pattern of the thin film formed under the condition that the partial pressure of the oxidizing gas is 50% is shown in FIG. Almost the same diffraction pattern is exhibited even when the partial pressure of the oxidizing gas is about 6%. In FIG. 3, the peak described as Pt (111) is the peak due to Pt of the substrate under the thin film, and the other peaks are those of the bismuth compound (δ-Bi ₂ O ₃ ) having an oxygen-deficient fluorite structure. It is a peak. The number attached to the peak indicates the crystal plane to which the peak corresponds. From FIG. 3, (111), (200), (220), (31
The peaks due to the reflection of each surface of 1) and (222) are observed, which clearly shows the characteristics of the fluorite structure.

Next, another specific example of the method for producing a bismuth compound according to the present invention will be described. In this example Bi
This is an example in the case of producing a bismuth composite oxide thin film represented by -Sr-Ta-O. The CVD apparatus can be applied in the same manner as the apparatus shown in FIG.

A substrate Sub is formed by sequentially depositing 100 nm each of Ti and Pt on the (100) plane of naturally oxidized silicon by a sputtering method at room temperature.

As source materials for the MOCVD method, for example, BiPh ₃ as a Bi source and Sr as an Sr source, respectively.
(DPM) ₂ , Ta (O-iPr) ₃ or the like is selected as a Ta source, these source materials are dissolved in an organic solvent such as THF (tetrahydrofuran), and each is 0.1 M / l.
A solution having a certain concentration is prepared.

This solution was mixed at an appropriate liquid volume ratio,
It is carried by Ar gas and introduced into the vaporizer V. Regarding the mixing ratio of each source, the composition of the thin film produced as described above is analyzed, the composition is compared with the target composition, and the correct mixing ratio is set based on that.

The vaporized source solution is fed from the vaporizer V to Ar.
Introduce to the reactor with carrier gas. The inside of the vaporizer V and the quartz reaction tube Q is decompressed to about 0.2 torr to vaporize the source solution. Then, the vaporized source solution is transported and deposited on the substrate Sub in a vapor phase state. At this time, the substrate Su
The temperature of b is set to about 700 ° C.

On the other hand, oxidizing gas such as ozone, N ₂ O and NO _{2 is} directly introduced into the quartz reaction tube Q without passing through the vaporizer V. The Ar carrier gas and the oxidizing gas are supplied by adjusting their flow rates to about 900 sccm by the mass flow controller MFC.

In this way, the so-called as depos state where the film is not annealed as it is
Bi-Sr-T with pyrochlore structure
A bismuth composite oxide thin film represented by aO can be obtained.

The X-ray diffraction pattern of this thin film is shown in FIG. In FIG. 4, peaks described as Pt (111) and Pt (200) are peaks due to Pt of the substrate under the thin film, and other than that, bismuth compound oxide (Bi-Sr-Ta) having a pyrochlore structure is used. -O) peak. Also, the number attached indicates the crystal plane to which the peak corresponds. From FIG. 4, (111), (222), (40
0), (440), and (622) surface reflection peaks are observed, which clearly shows the characteristics of the pyrochlore structure.

In this way, a bismuth composite oxide thin film represented by Bi-Sr-Ta-O having a pyrochlore structure in the as-deposited state could be obtained. With respect to the bismuth layer compound having other composition, a thin film having a desired composition can be obtained by adjusting the film forming conditions in the same manner.

Since the reaction pressure can be lowered by introducing the oxidizing gas, a thin film having good uniformity and step coverage can be formed, and the cleanliness of the thin film can be improved and the productivity can be improved.

The composite oxide having a pyrochlore structure produced at this time may have a cubic crystal pyrochlore structure, or a structure having a slightly different crystal system or a similar structure due to lattice distortion or the like. Further, since the composite oxide having a pyrochlore structure has a slight nonstoichiometry, the composition or structure may be slightly deviated from the pyrochlore structure.

The above embodiment is an example of the present invention.
Various other configurations are possible without departing from the scope of the present invention.

[0049]

According to the above-described chemical vapor deposition method for bismuth compounds according to the present invention, a method of using normal oxygen as an oxidant by introducing a strong oxidizing gas such as ozone during film formation Bismuth, which is difficult to deposit, can be deposited at a sufficient deposition rate.

Further, according to the production method of the present invention, the composition of the film can be adjusted by adjusting the flow rate of each gas.
When a bismuth compound such as a bismuth composite oxide is formed, its composition can be easily controlled.

Furthermore, by using a strong oxidizer such as ozone, the reaction pressure can be suppressed to a low level, and therefore the step coverage can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a manufacturing apparatus by a MOCVD method.

FIG. 2 is a diagram showing the relationship between the partial pressure of ozone gas in a reaction gas and the composition of a film.

FIG. 3 is an X-ray diffraction pattern of a thin film of bismuth oxide having an oxygen-deficient fluorite structure according to the present invention.

FIG. 4 is an X-ray diffraction pattern of a thin film of a bismuth composite oxide having a pyrochlore structure obtained in the as-deposited state according to the present invention.

[Explanation of symbols]

G ₁ Ar gas supply port G ₂ Oxygen gas supply port G ₃ N ₂ O gas supply port OZ Ozonizer MFC Mass flow controller S ₁ , S ₂ , S ₃ Source bottle M Mixing tube P Liquid injection pump V Vaporizer Q Quartz reaction tube C RF coil SC Susceptor Sub Substrate TR Transfer rod R ₁ Film forming chamber R ₂ Load lock chamber GV Gate valve D Exhaust pipe

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical indication location H01L 27/04 H01L 27/10 451 21/822 27/04 C 27/10 451 27/10 651 27 / 108 21/8242

Claims (7)

[Claims] 1. A chemical vapor deposition method in which a source gas and an oxidizing gas are introduced into a reaction vessel and a bismuth compound is deposited, wherein the oxidizing gas is at least one selected from ozone, N ₂ O and NO _2. A chemical vapor deposition method using a gas containing a seed. 2. The chemical vapor deposition method according to claim 1, wherein the oxidizing gas contains oxygen gas. 3. The partial pressure of the ozone gas is 0.0 of the total pressure.
2. The range of 1 to 20% is selected.
The chemical vapor deposition method described in. 4. The chemical vapor deposition method according to claim 1, wherein the oxidizing gas is directly introduced into the reaction vessel. 5. The chemical vapor deposition method according to claim 1, wherein the bismuth compound is a bismuth composite oxide. 6. The chemical vapor deposition method according to claim 5, wherein the bismuth composite oxide contains a bismuth composite oxide having a pyrochlore structure. 7. The deposition of the bismuth compound is 0.01
The chemical vapor deposition method according to claim 1, wherein the chemical vapor deposition is performed under a reaction pressure of -50 torr.