JPH06168880A - Method and system for forming dielectric thin film - Google Patents

Abstract

PURPOSE:To enhance electric characteristics by irradiating a perovskite-type composite compound with a pulse laser beam under innert gas atmosphere to evaporate the perovskite-type composite compound and deposite on a substrate and then performing oxidation thereby componsating for deficiency of oxygen. CONSTITUTION:Multielement targets 6, 7 are irradiated with laser beams emitted from a pulse laser 1 and branched through optical paths thus performing laser abrasion and deposition on a substrate 9 with high compositional controllability. Furthermore, inert gas such as argon gas is employed in the atmosphere at the time of forming film and oxidation is performed using an ion source 11 or the like immediately after formation of film thus enhancing crystallinity while compensating for deficiency of oxygen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film manufacturing method and apparatus. In particular, it relates to the production of dielectric thin films.

[0002]

2. Description of the Related Art Thin film technology is used in the electronics field,
In particular, it has been developed mainly in the semiconductor manufacturing process and has progressed along with the development of new materials. These thin films are extremely rare in the case of a simple element, and in many cases, they are generally alloys or compounds, and their characteristics remarkably change depending on the forming method. The creation of these new materials and their deviceization are mostly due to the improvement of thin film technology, as represented by artificial lattice materials.

ABO ₃ is a thin-film material that has been receiving attention in recent years.
There is a dielectric material having a perovskite structure composed of Here, the A site contains at least one element of Pb, Ba, Sr, or La, and the B site contains at least one element of Ti and Zr. For example (Pb _1-x L
a _x ) (Zr _y Ti _1-y ) _{1-x / 4} O ₃ system, BaTiO ₃ system, and other ferroelectric materials have excellent ferroelectricity, piezoelectricity, pyroelectricity, electro-optical characteristics, etc. And various functional devices utilizing the same have been studied. In particular, in the field of semiconductor ICs, application to new devices and non-volatile memories is expected. In addition, although SrTiO ₃ system does not show ferroelectricity, it is an ultra high density DR as a high dielectric constant material.
The application of AM to capacitor insulating films is expected.

In order to improve the characteristics of these materials or to integrate them, it is very important to reduce the film thickness.
It is important to develop a technology for manufacturing a semiconductor substrate such as i on a semiconductor substrate. From the viewpoint of improving its performance, it is desirable that it is a single crystal thin film or an oriented film, and development of heteroepitaxial technology is important. Research on these has been conducted in many research institutes based on various thin film deposition methods.
However, it is generally not easy to obtain a thin film having desired characteristics by controlling the composition, crystal structure and the like. The crystallinity of the thin film is basically controlled by the substrate material, the chemical composition and the forming temperature. Generally, a crystalline coating can be obtained at low temperature if the chemical composition is matched by using a highly active deposition method with less lattice mismatch with the substrate.

In the sputtering method which has hitherto been most commonly used for thinning an oxide dielectric, a chemical composition is likely to shift between an oxide sintered body which is a target material and a formed film. Moreover, it largely depends on the sputtering conditions. Due to the highly active, non-thermal equilibrium process, the formation temperature was significantly reduced, but still 600 ° C. to obtain a good crystalline coating.
High front and back substrate temperatures are required, so that mutual diffusion with the substrate and pinholes due to columnar growth are likely to occur.
Furthermore, since it is an oxide, an oxidizing atmosphere is required, but the composition, crystallization temperature, etc. are significantly affected by the selection of the conditions. In order to obtain a dense and highly crystalline film, it is necessary to form the film at a lower temperature by using a deposition method having good composition controllability and higher activity.

An oxide superconductor having a perovskite structure similar to the oxide dielectric according to the present invention as a basic structure has the same problem in thinning the film, but a so-called laser ablation method causes considerable problems. It is improving. This method irradiates a strong pulse laser such as an excimer laser with a sintered body as a target,
A film is formed on the opposing substrates. It is said that there is no compositional deviation between the sintered target and the formed film, and it has advantages such as being able to be formed under a high oxygen partial pressure or at a low substrate temperature as compared with other thin film forming methods.

[0007]

However, as the research on the laser ablation method for these oxide dielectrics has been advanced recently, some problems have appeared. There is a problem that the composition, crystallinity, and oxygen deficiency of the formed thin film are significantly affected by the forming atmosphere. Further, there is a problem that it is difficult and unstable to prepare a target, and it is impossible to flexibly select the chemical composition even though they are solid solutions.

In order to solve the above-mentioned conventional problems, it is an object of the present invention to provide a method and apparatus for manufacturing a perovskite type oxide dielectric thin film having high electric characteristics with good controllability and stability.

[0009]

In order to achieve the above object, the first method for producing a dielectric thin film according to the present invention comprises ABO ₃
A method of manufacturing a dielectric thin film using a perovskite-type composite compound, comprising: irradiating the perovskite-type composite compound with pulsed laser light in an inert gas atmosphere to evaporate and deposit a film on a substrate. And an oxidation treatment is then performed. (Here, A site is
At least one element selected from Pb, Ba, Sr, and La, and the B site contains at least one element selected from Ti and Zr. In the above configuration, it is preferable that the treatment for depositing the coating film on the substrate and the oxidation treatment are performed in the same forming tank.

Next, a first method for producing a dielectric thin film of the present invention is a method for producing a dielectric thin film using a perovskite type composite compound composed of ABO ₃ , wherein oxidation of an A site or B site element is performed. It is characterized in that pulsed laser light is applied to at least two targets made of an object or a complex oxide to evaporate them and deposit a film on the substrate. (Here, A site is Pb, Ba, Sr and L
At least one element selected from a and B site is Ti
And at least one element selected from Zr. In the above structure, as the target, a main target made of a composite oxide of A site and B site elements, and a composite oxide having a different composition ratio from that of the main target, or at least one sub-target made of an oxide may be used. preferable.

Next, the apparatus for producing a dielectric thin film of the present invention is
A dielectric thin film manufacturing apparatus using a perovskite-type composite compound composed of BO ₃ , comprising A site or B
A pulsed laser beam is generated by using a means for disposing at least two target materials composed of oxides of site elements or complex oxides at positions facing the substrate, and at least two laser light sources or at least two branched optical paths. It is characterized by comprising means for irradiating to vaporize the target material and deposit a film on the substrate. (A here
The site contains at least one element selected from Pb, Ba, Sr and La, and the B site contains at least one element selected from Ti and Zr. In the above structure, it is preferable to provide a means capable of individually setting the light energy density per pulse on the surface of the target material for each target material.

Further, in the above structure, at least two pulse laser light sources or choppers are arranged on a branched optical path, and the repetition frequency of the pulse laser light for irradiating the target material is set individually for each target. It is preferable to have means for obtaining.

[0013]

According to the structure of the first method for producing a dielectric thin film of the present invention, the perovskite-type composite compound is
By irradiating with pulsed laser light in an inert gas atmosphere to evaporate the film to deposit a film on the substrate and then perform an oxidation treatment, oxygen vacancies can be compensated and electrical characteristics can be improved.

According to the second method for producing a dielectric thin film of the present invention, a perovskite type oxide dielectric thin film, which has been conventionally difficult to control its composition, can be realized with good controllability and stability.

According to the structure of the thin film manufacturing apparatus of the present invention, the chemical composition of the multi-element perovskite type oxide dielectric is changed by irradiating a plurality of targets composed of the constituent elements with laser. Control and selection can be facilitated, and the crystallinity of the thin film can be improved by using an inert gas atmosphere during formation, and oxygen deficiency can be compensated by an oxidative post-treatment.

[0016]

EXAMPLES The present invention will be described in more detail with reference to the following examples. The present inventors have examined the effects on the composition, crystallinity, and oxygen deficiency of thin films formed under various formation atmospheres, and have found a process capable of realizing high quality dielectric thin films. In the method for producing a thin film according to the present invention, an atmosphere of an inert gas such as Ar is found as an atmosphere for obtaining a thin film having excellent crystallinity, and an oxygen treatment is performed immediately after the film formation to compensate for oxygen deficiency, thereby electrically It has been found that the improvement of characteristics can be realized. In addition, by diversifying the laser ablation method, that is, by facilitating the control and selection of multiple chemical compositions, the perovskite oxide dielectric thin film, which had been difficult to control in composition, was realized with good controllability and stability. I found what I could do.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the thin film forming apparatus used in this example.
In FIG. 1, the pulse laser 1 uses, for example, an excimer laser. In this case, a carbon dioxide laser or the like is also effective, but an excimer laser having an oscillation wavelength in the ultraviolet region is more effective. In the case of the configuration shown in FIG. 1, the laser light is
The light is split into two optical paths via the half mirror 2 and the mirror 3, and is condensed on the targets 6 and 7 by the lenses 4 and 5, respectively. This laser light irradiation evaporates the target material and deposits it as a thin film 10 on the substrate 9 heated by the heater 8. The light energy density per pulse on the target surface due to evaporation of the target material is 1 J / cm ² ·
There is a threshold of about shot, and the deposition rate of the thin film increases by increasing the light energy density. The deposition rate can also be improved by increasing the laser repetition frequency, but the upper limit is up to about 20 Hz, and at higher frequencies, the temperature of the target rises and compositional deviation of the elements composing the target is induced. there's a possibility that. Further, the manufacturing apparatus of the present embodiment is provided with a bucket type ion source as the ion source 11 so that the formed thin film can be oxidized.

First, the lens 4 and the target 6 shown in FIG.
Oxide ferroelectric Pb _0.9 L
The case of forming a _0.1 Ti _0.975 O ₃ will be described. As the target 6, a stoichiometric ratio sintered body was used, but the target whose density was increased by HIP (hot isostatic pressing) or the like was excellent in terms of deposition rate and stability. As the substrate 9, in order to evaluate the characteristics in the film thickness direction, for example, a substrate on which platinum is previously vapor-deposited as a lower electrode is used. A single crystal substrate is effective for forming the thin film 10 having high crystallinity, and a single crystal such as magnesium oxide, sapphire (α-Al ₂ O ₃ ), or strontium titanate is effective. Also, the electrode material itself is preferably crystalline, and in the case of platinum, the substrate temperature is 6
What was sputter-deposited at 00 ° C. was used.

The atmosphere of the forming tank during film formation is (a) an oxidizing atmosphere of 100% oxygen gas and (b) 100% of argon gas.
% And an inert gas atmosphere was selected for comparative examination. Film formation was performed in the pressure range of 1 to 10 ^-3 Pa when the distance between the substrate and the target was 4.5 cm. A XeCl excimer laser (wavelength 308 nm) was used as the pulse laser 1, focused on the target to obtain a power density of about 1 joule per cm ² in one shot, and a repetition frequency of 10 Hz and 3 × 10 ⁴ pulse irradiation. A film having a thickness of 0.3 μm was obtained. We have
In order to form the oxide thin film 10 having high crystallinity, it was confirmed that the temperature range of the substrate is 300 to 750 ° C. When the substrate temperature is set to 450 ° C., although the film composition of the thin film 10 does not depend on the atmospheric gas species as shown in FIG. 2, it depends significantly on the gas pressure and a thin film having a stoichiometric ratio can be obtained. A vacuum of about 0.1 Pa was suitable. At this time,
The crystallinity of the coating was analyzed by X-ray diffractometry and found to be perovskite structure irrespective of the atmospheric gas species. However, when confirmed by RHEED pattern by electron diffraction, (a) oxidation of 100% oxygen gas Although a spot pattern derived from a single crystal was observed in a neutral atmosphere, (b) a streak pattern suggesting better crystallinity was also observed in an inert gas atmosphere of 100% argon gas.

In order to prevent reduction and re-evaporation of the oxide thin film to be formed as a gas atmosphere necessary for the production of oxide superconductors and dielectric thin films, O ₂ , O ₃ , and N have been used so far.
_Although it has been performed under an atmosphere of an oxidizing gas such as ₂ O,
As shown in the above examples, it was revealed that an inert gas atmosphere is preferable in terms of improving crystallinity.

Next, gold was vacuum-deposited as an upper electrode using a mask having a diameter of 0.5 mm, and electrical characteristics were measured. As a result of evaluating the dielectric constant ε and the leakage current density I at an electric field strength of 100 KV, (b) the thin film prepared in an inert gas atmosphere of 100% argon gas has good crystallinity, but ε is ~ 170. And I is ~ 10 ^-4 A / cm
^It was as high as ² , and the electrical characteristics were rather inferior to (a) in the oxidizing atmosphere of 100% oxygen gas. It is considered that the electrical characteristics were lowered due to the introduction of oxygen defects although the crystallinity was improved by the production in the inert gas atmosphere.

In order to improve this, after completion of film formation
Post-treatment was performed. That is, at least the
Immediately after the film formation, oxygen gas was introduced to³Below Pascal
Performing an oxidative treatment by gradually cooling under the above pressure
Oxygen deficiency is compensated for, and electrical characteristics are improved.
I was sure that. In particular, the bucket type ion source of FIG.
The electrical characteristics of ε is ~
200, I is ~ 10^-6A / cm ²I was able to improve.
In this case, if the acceleration voltage of oxygen ions is too high, crystallinity will be
300 V or less is appropriate because it may worsen
It was

Next, an attempt was made to multipleize the laser ablation method using a plurality of targets. Although FIG. 1 shows a binary system consisting of two targets and two branched optical paths, the number of dimensions can be increased by a similar configuration.
Instead of splitting the optical path, an independent optical path using a plurality of pulsed lasers can be used. The evaporation rate from each target can be set individually for each target by controlling the light energy density per pulse on the target surface or the repetition frequency for irradiating the target. The former can be controlled by controlling the laser power and the degree of focusing by a lens, and the latter can be controlled by arranging a laser repetition frequency and a chopper on the optical path. The deposition process does not need to be simultaneous vapor deposition in a strict sense, and may be periodic so that the composition distribution after film formation is considered to be constant in the depth direction.

In laser ablation, due to pluralization
First, (Pb _1-xLa_x) (Zr
_yTi_1-y)_{1-x / 4}O₃(PLZT) system Pb, BaT
i₃System Ba, SrTiO 3₃Vapor pressure such as Sr of the system
It is high and it is possible to compensate for elements that are likely to be lost in the film. This
This is as shown in Table 1, target combinations 1, 2, and 3.
A stoichiometric target and an oxide of an element that is apt to be lost.
Achieved by setting each as the main and sub target
To be done.

[0025]

[Table 1]

For example, in the case of combination 1, Pb _0.9 La
_When only a target with a stoichiometric ratio of _0.1 Ti _0.975 O ₃ (target A; main target) is used, the film composition changes with the atmospheric pressure as shown in FIG. In order to obtain a thin film having a specific ratio, it is necessary to control the atmospheric pressure, although there is a balance with other film forming conditions such as the substrate temperature. However, when PbO was used together as a sub-target (target B) for multidimensionalization, the pressure dependence of the film composition could be changed as shown in FIG.
That is, the present inventors have found that when only a stoichiometric target is used, under the condition that the atmospheric gas pressure is low or the substrate temperature is high, an element with a high vapor pressure is formed in the formed film. Although defects were often observed, it was confirmed that a thin film of good stoichiometric ratio could be obtained by using the oxide of the element which is apt to be lost together as a sub-target for multi-factorization. In the conventional method using a single target, compensation for these elements that tend to be deficient has been done by adding 10 to 20% excess of these oxides at the time of making the target. There were problems such as lack of flexibility and difficulty in making targets. In the multi-factorization according to this example, the compensation amount of these elements that are likely to be lost could be optimized by the repetition frequency and energy density of the laser according to the film forming conditions.

The functions provided by the pluralization are as follows.
(Pb _1-x La _x ) (Zr _y Ti _{1- y} ) _{1-x / 4} O ₃ , 0
≦ x ≦ 0.4, 0 ≦ y ≦ 1) system or (Ba _1-x Sr _x ) Ti
The point is that a solid solution such as an O ₃ (0 ≤ x ≤ 1) system can be easily realized. Since the characteristics of these oxide dielectrics vary greatly depending on the composition, that is, the solid solution ratio, strict control of the solid solution ratio is necessary to obtain an oxide thin film having desired characteristics. This is because in the multi-factorization according to the present embodiment, as shown in the target combinations 4 and 5 in Table 1, a system in which a matrix is used as a main target and an oxide of an element to be substituted as a sub-target, or a target combination is used. As shown in 6 and 7, this is realized by a configuration in which a target is used in combination with systems corresponding to the minimum and maximum solid solution ratios of the respective solid solutions.

For example, in the configuration of combination 6, (Pb _1-x L
a _x ) Ti _{1-x / 4} O ₃ (hereinafter abbreviated as PLT, 0 ≦ x ≦ 0.
4) In order to realize the system, it was possible to use a binary target of PbTiO ₃ and Pb _0.6 La _0.4 Ti _0.9 O ₃ corresponding to the solid solution limit. In this case, PbTi
As for the O ₃ increases the deposition rate of the _{Pb 0.6 La 0.4 Ti 0.9 O 3} , as shown in FIG. 4, La content in the thin film to be formed is increased, even tetragonal lattice constant which can be read from the X-ray diffraction pattern Cubic P from the value of PbTiO ₃
It was found that the value changed to b _0.6 La _0.4 Ti _0.9 O ₃ systematically. That is, it was confirmed that the oxide dielectric thin film, whose solid solution ratio was difficult to control, could be realized with good stability and controllability by the multi-factorization according to this example.
In the previous methods that used a single target, these solid solution targets were used, but there is a compositional deviation between the target and the formed thin film, there is no flexibility, and the crystallization temperature is greatly different, making it difficult to make a target. There was such a problem. In the pluralization according to this embodiment,
The solid solution ratio could be controlled to a desired value by the laser repetition frequency and energy density according to the film forming conditions.

[0029]

As described above, according to the present invention, a manufacturing apparatus and process for making an oxide dielectric into a thin film are provided, which is of great industrial value. The dielectric used is a multi-element oxide, and its characteristics are greatly affected by its chemical composition and crystallinity, but the present invention can realize a highly precise thin film. It is possible to obtain a thin film conforming to the stoichiometric ratio by selecting the forming atmosphere and making it multi-dimensional.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a basic configuration of a thin film manufacturing apparatus according to an embodiment of the present invention.

FIG. 2 is a dielectric thin film Pb _0.9 La according to one embodiment of the present invention.
It is a diagram showing an atmospheric pressure dependency of the composition ratio of _0.1 Ti _0.975 O _3.

FIG. 3 is a dielectric thin film Pb _0.9 La according to an embodiment of the present invention.
It is a diagram showing an atmospheric pressure dependency of the composition ratio of _0.1 Ti _0.975 O _3.

FIG. 4 shows a dielectric thin film (Pb _1-x La according to one embodiment of the present invention.
It is a diagram illustrating a change in lattice constant and the composition ratio of _{x) Ti 1-x / 4} O 3.

[Explanation of symbols]

 1 pulse laser 2 half mirror 3 mirror 4 condenser lens 5 condenser lens 6 target 7 target 8 heater 9 substrate 10 coating 11 ion source

Claims (7)

[Claims] 1. A method for producing a dielectric thin film using a perovskite-type composite compound composed of ABO ₃ , wherein the perovskite-type composite compound is irradiated with pulsed laser light in an inert gas atmosphere for evaporation. A method of manufacturing a dielectric thin film, comprising depositing a film on a substrate, and then performing an oxidation treatment. (Here, A site is Pb, B
at least one element selected from a, Sr and La,
The B site contains at least one element selected from Ti and Zr. ) 2. The method for producing a dielectric thin film according to claim 1, wherein the treatment for depositing the coating film on the substrate and the oxidation treatment are performed in the same forming tank. 3. A method for producing a dielectric thin film using a perovskite-type composite compound composed of ABO _3.
A method for producing a dielectric thin film, which comprises irradiating pulse laser light to at least two targets made of an oxide of a site or B site element or a complex oxide to evaporate and deposit a film on a substrate. (Here, the A site contains at least one element selected from Pb, Ba, Sr, and La, and the B site contains at least one element selected from Ti and Zr.) 4. A main target made of a composite oxide of A site and B site elements and a composite oxide having a different composition ratio from this, or at least one sub-target made of an oxide is used as a target.
A method for producing a dielectric thin film according to item 4. 5. An apparatus for producing a dielectric thin film using a perovskite type composite compound composed of ABO _3.
A means for arranging at least two target materials composed of oxides or complex oxides of site or B-site elements at positions facing the substrate, and using at least two laser light sources or at least two branched optical paths,
An apparatus for producing a dielectric thin film, comprising means for irradiating a pulsed laser beam to vaporize the target material and deposit a film on a substrate. (Here, A site is P
At least one element selected from b, Ba, Sr, and La, and the B site contains at least one element selected from Ti and Zr. ) 6. The dielectric thin film manufacturing apparatus according to claim 5, further comprising means for individually setting the light energy density per pulse on the surface of the target material for each target material. 7. A means for arranging a chopper on at least two pulse laser light sources or a branched optical path so that a repetition frequency of pulse laser light for irradiating a target material can be individually set for each target. An apparatus for manufacturing a dielectric thin film according to claim 5.