JP4289908B2 - Atomizer for forming ceramic thin film and thin film manufacturing method using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thin film manufacturing apparatus, and more particularly to a raw material liquid atomizer used therein and a thin film manufacturing method using the apparatus.
[0002]
[Prior art]
With the advent of the multimedia era, research and development of next-generation non-volatile memory to replace conventional DRAM has been actively conducted in recent years. Among them, non-volatile memories using ferroelectric thin films are capable of retaining information and rewriting at high speeds by utilizing their remanent polarization. It has become.
[0003]
These ferroelectric thin films are currently produced by chemical solution method (CSD method), sputtering method, metal organic chemical vapor deposition method (MOCVD method), laser ablation method and the like. In particular, a liquid mist chemical deposition (LSMCD) method is known as a method for producing a ceramic thin film. Patent Document 1 proposes that in this LSMCD method, a thin film is manufactured by adhering to a substrate a mist-like material whose particle size is controlled by moving between electrodes.
[0004]
[Patent Document 1]
JP-T-2001-523889 Publication [0005]
[Problems to be solved by the invention]
Each of the above-mentioned various methods for producing a thin film has advantages and disadvantages, and no particularly advantageous one has been established. Under such circumstances, the LSMCD (Liquid Source Misted Chemical Deposition) method has attracted attention because it has the following advantages.
(1) Composition stability
(2) Large area film formability
(3) Step coverage (required for future high integration)
(4) Raw material selectivity (There are already a wide variety of relatively inexpensive raw materials, and the selection range is wide)
(5) Industriality (low operating cost)
[0006]
The LSMCD method with these advantages is one of the most promising for establishing a full-scale process for manufacturing ferroelectric thin film memories. In order to realize these advantages reliably, It is important to make the mist fine and uniform. As described above, Patent Document 1 attempts to solve this problem by moving the mist between the electrodes. The average particle diameter of the droplet particles in the mist generated there is about 0.5 μm, and 1 μm. The thing of the above big particle size is also mixed. However, because submicron order pattern formation is performed in high-density integrated circuits, the presence of particles exceeding 1 μm is not preferable to ensure step coverage, and if possible, the average particle size should be 0.5 μm or less. Is preferred.
[0007]
The present invention has been made to solve such problems, and the object of the present invention is to provide a ceramic capable of producing a mist having an average particle size of 0.5 μm or less and not containing large particles of 1 μm or more. It is providing the manufacturing method of the thin film by the atomizer for thin film formation, and the thin film manufacturing apparatus using the atomizer.
[0008]
[Means for Solving the Problems]
An atomizer for forming a ceramic thin film according to the present invention, which has been made to solve the above problems,
a) a first ultrasonic vibrator for atomizing the raw material liquid;
b) a sorting chamber having a predetermined volume for passing the raw material mist atomized by the first ultrasonic transducer;
c) a vibrator provided with a second ultrasonic transducer provided in the sorting chamber;
It is characterized by providing.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
As shown in FIG. 1, the liquid mist chemical deposition apparatus (thin film production apparatus) equally atomizes the raw material liquid and the mist of the raw material liquid produced by the atomizer 10 on the substrate 11 to be processed. And a chamber 12 for spraying and forming a thin film. The present invention relates to the atomizer 10.
[0010]
Since the thin film manufacturing apparatus including the atomizer according to the present invention has the above-described configuration, the liquid raw material supplied to the apparatus is first misted by the first ultrasonic vibrator. This mist collides with a vibrating body (hereinafter referred to as “stem”) that vibrates with ultrasonic waves emitted from the second ultrasonic transducer in the sorting chamber. At this time, the mist having a large particle size collides with the stem by its own inertial force and falls, while the mist having a small particle size suppresses the enlargement of the particle size due to recombination by the ultrasonic space, The average particle size of the mist is reduced. Furthermore, since the particles having a large particle size gradually settle while passing through the sorting chamber, the mist supplied from the sorting chamber is composed only of components having a fine particle size.
[0011]
Two or more sorting rooms may be provided. In this case, it is not necessary to provide a stem in each chamber, and the effect of atomization can be obtained only by providing one or more chambers. This is because the effect that large particles are eliminated by sedimentation while the mist passes is obtained even when there is no stem.
Further, in order to further promote the sedimentation of the large-diameter particles in the sorting chamber, it is effective to increase the mist passage distance in the sorting chamber.
[0012]
【The invention's effect】
In the atomizer according to the present invention, after the mist is generated by the first ultrasonic transducer, the average particle size of the mist is reduced by the action of the stem in the selection chamber, and the particles having a large diameter are formed by flight sedimentation. To eliminate. Due to these effects, the mist supplied from the atomizer according to the present invention has an average particle size smaller than that produced by the conventional atomizer and a large particle size is excluded. . As a result, by appropriately setting the flow rate of the carrier gas and the operating condition of the ultrasonic transducer as will be described later, a mist that has an average particle size of 0.5 μm or less and does not contain large particles of 1 μm or more is manufactured. Is possible.
[0013]
For this reason, the thin film produced by the thin film manufacturing apparatus provided with the atomizer according to the present invention has a good step coverage, and is not limited to the ferroelectric thin film, but can form patterns on the order of submicrons such as a high dielectric thin film. It can be suitably used for a required high-density integrated circuit manufacturing process and other fine thin film manufacturing processes.
[0014]
【Example】
An embodiment of an atomizer for forming a ceramic thin film according to the present invention will be described. 2A is a horizontal cross-sectional view of the atomizer for forming a ceramic thin film, and FIG. 2B is a cross-sectional view of FIG. 2A taken along the line II-II. The atomizer 10 of the present embodiment includes an atomization chamber 21 and first to third selection chambers 22 to 24. The atomizing chamber 21 is provided with three ultrasonic transducers 25a to 25c, and the first selection chamber is provided with a stem 26 provided with one ultrasonic transducer 27. In this embodiment, the second selection chamber 23 is not provided with a stem having an ultrasonic transducer, and the mist simply passes therethrough. The third selection chamber 24 has a configuration in which elongated small flight chambers 24a to 24d are arranged in parallel as shown in FIG. 2 (a), and the communication holes are alternately provided between them, As a result, the flight path of the mist is folded in a zigzag shape. The mist is finally supplied from a mist supply port 28 provided downstream of the third selection chamber 24 to the chamber 12 of the thin film manufacturing apparatus (FIG. 1).
[0015]
A liquid raw material feeder is provided at the upper part of the atomizing chamber 21 (the front side in FIG. 2A) (not shown), and the side of the atomizing chamber 21 (upward in FIG. 2A). Is provided with a carrier gas inlet 29 for transporting mist.
[0016]
In the present embodiment having such a configuration, the fine particle mist is generated as follows. First, after supplying the liquid raw material from the liquid raw material supply unit above the atomizing chamber 21 to the atomizing chamber 21 so that the liquid raw material has a predetermined height above the ultrasonic vibrator, the ultrasonic vibrators 25a to 25c are set to 2.4 MHz. Operate (Fig. 2 (b)). Thereby, the liquid raw material is first atomized roughly from the liquid surface. This mist is carried toward the first selection chamber 22 by the nitrogen gas introduced from the carrier gas introduction port 29.
[0017]
A communication hole 30 having a diameter of 2 mm and a length of 5 mm is provided between the atomization chamber 21 and the first selection chamber 22, and the mist generated in the atomization chamber 21 passes through the communication hole 30 to form a first hole. 1 is introduced into the selection chamber 22. FIG. 4 shows a cross section of the communication hole 30 used in this example. It is desirable that the communication hole 30 has an acute angle around both ends so that the communication hole 30 is not easily blocked by mist droplet particles.
[0018]
In the first selection chamber 22, a vibration surface of a stem 26 provided with an ultrasonic transducer 27 is provided at a position 15 mm away from the communication hole 30, and the ultrasonic transducer 26 operates at 40 kHz. Of the raw material mist introduced from the atomization chamber 21, particles having a large diameter fall by the action of the stem 26, and the mist particle size distribution is further refined. Further, particles having a relatively large diameter settle while the raw material mist passes through the first selection chamber 22 and are not introduced into the second selection chamber 23.
[0019]
A circular communication hole 31 having a diameter of 2 mm is also provided between the first selection chamber 22 and the second selection chamber 23, and the particle size distribution of the mist introduced from here into the second selection chamber 23 is the atomization chamber. The mist generated at 21 moves to the smaller diameter side than that of the mist. That is, the average particle size is reduced and the large particle size portion is excluded.
[0020]
Although the stem is not provided in the second selection chamber 23, large particles gradually settle down as in the first selection chamber 22 while the mist rides on the carrier gas and passes through the carrier gas. The selection room 24 is not reached. That is, sedimentation sorting is performed.
[0021]
In the third selection chamber 24, the mist rides on the carrier gas and flies over a long distance in a zigzag manner as described above, and the communication holes between the small flight chambers 24a to 24d (both of which have a diameter of 2 mm). While passing through, large particles are eliminated. Accordingly, the mist supplied from the atomizer 10 excludes large-diameter particles, and the distribution is sufficiently small in average particle diameter.
[0022]
In addition, the large diameter particle | grains which did not pass through each selection chamber 22-24 adhere to the floor and side wall of each selection chamber 22-24, and are finally collect | recovered from a predetermined drain.
[0023]
The particle size distribution of the mist generated by the atomizer 10 depends on the flow rate of the carrier gas. FIG. 5 shows the result of examining the relationship between the flow rate of the carrier gas and the particle size of the mist obtained when no ultrasonic transducer is provided in the selection chambers 22 and 23 in the apparatus of FIG. Here, the particle diameter of the mist is represented by the number of particles (unit: pieces / minute) in the mist supplied from the atomizer 10 with a constant flow rate of the raw material liquid. The number of particles was measured with a commercially available particle counter (manufactured by Anerva: DM100). FIG. 5 (a) shows the change in the total number of particles, and FIG. 5 (b) shows the change in the number of particles for each particle size (0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm).
[0024]
The total number of particles does not change much until the carrier gas flow rate is about 0.2 L / min (Fig. 5 (a)), but as the carrier gas flow rate increases, the number of large diameter particles of 0.5 µm or more decreases. (FIG. 5B). When the carrier gas flow rate exceeds that, the average particle diameter begins to decrease. When the carrier gas flow rate is about 0.45 L / min, the number of particles captured by the particle counter is saturated at 100,000 particles / min. Among them, those with a particle size of 0.2 μm are the most frequent at about 35,000 pieces / min, and the average particle size is about 0.33 μm.
[0025]
However, when the flow rate of the carrier gas exceeds 0.4 L / min, the total number of particles does not change, but the number of large diameter particles starts to increase. This is presumably because the large-diameter particles pass through the atomizer as they are without settling in the selection chamber due to an increase in the flow rate of the carrier gas.
[0026]
Next, FIG. 6 shows the relationship between the number of mist raw material particles obtained and the flow rate of the carrier gas when the stem 26 is provided in the first selection chamber 22. The relationship between (a) and (b) is the same as in FIG. When the stem 26 of the selection chamber 22 is operated at 40 kHz, when the carrier gas flow rate is 0.2 L / min, the total number of particles captured by the particle counter reaches the first saturation point at 100,000 particles / min. . Among them, those with a particle size of 0.2 μm are the largest at about 40,000 particles / min, and the average particle size is about 0.34 μm. Compared with the case where the selection chamber 22 is not provided with the stem 26, the total number of particles is saturated at a low carrier gas flow rate, and fine particles are selected. This is presumably because mist having a large particle diameter falls due to the collision with the stem 26, and enlargement of the particles due to recombination of the small diameter particles by the ultrasonic waves is reduced. In this case, even if the carrier gas flow rate is increased, the total number of particles and the composition of the particles hardly change for a while, but when the carrier gas flow rate becomes 0.4 L / min, the total number of particles and the number of large diameter particles increase. At first, the effect of the stem decreased.
[0027]
FIG. 7 shows the relationship between the particle diameter and the number of particles at a carrier gas flow rate of 0.1 to 0.4 L / min. In this case, in the first selection chamber 22, the vibration surface of the stem 26 is provided at a position 30 mm away from the communication hole 30. As shown in FIG. 7, at any carrier gas flow rate, the particle size distribution of mist is maximum at a particle size of 0.2 μm in the range of particle size of 0.2 to 0.5 μm. Although it is not certain because it exceeds the measurement lower limit of the measuring instrument, extrapolating this distribution curve to 0.2 μm or less suggests that the peak is 0.2 μm or less.
[0028]
From the above, it can be seen that the flow rate of the carrier gas needs to be appropriately set according to the desired mist particle diameter, the operating frequency of the ultrasonic vibrator, and the like. The range is approximately 0.1 to 0.5 L / min.
[0029]
In the atomizer 10 of FIG. 2, no ultrasonic transducer is provided in the second selection chamber 23, but as shown in FIG. 3, a stem 32 having an ultrasonic transducer 33 may also be provided here. Good. Thereby, refinement | miniaturization of a particle | grain is promoted more.
[0030]
The ferroelectric thin film was formed using the thin film manufacturing apparatus provided with the atomizer 10 shown in FIG. As a raw material for forming a thin film, a MOD coating material in which Pb (Zr, Ti) O ₃ (hereinafter referred to as “PZT”) is a 4 wt% methyl ethyl ketone solution is used. A μm mist was generated. The mist was sent from the mist supply port 28 to the chamber 12. Here, the flow rate of the carrier gas in the atomizer 10 is 0.2 L / min.
[0031]
As shown in FIG. 1, a Pt / TiO ₂ / SiO ₂ / Si substrate 11 was placed in advance in a chamber 12 in a chamber 12, and a raw material mist was sprayed from a mist spreader 13 for 60 seconds. The mist may be evenly spread on the substrate 11 by slowly rotating the substrate mounting table 14. As a result, a PZT film containing methyl ethyl ketone having a thickness of about 0.1 μm was formed. Then, after passing through a drying process at 100 ° C for 1 minute and then at 300 ° C for 3 minutes, annealing is performed at 650 ° C for 30 minutes in an oxygen atmosphere, or rapid heat treatment (RTP) is performed under the same conditions, and PZT A thin film was obtained (FIG. 8).
[0032]
FIG. 9 shows an SEM cross-sectional image of the PZT thin film formed on the substrate 11 having a groove width of 2 μm and a depth of 1 μm. The raw material mist was sprayed from the mist sprayer 13 for 120 seconds, whereby a PZT film containing methyl ethyl ketone was formed. Then, after passing through a drying process at 110 ° C. for 3 minutes and then at 300 ° C. for 3 minutes, annealing was performed at 650 ° C. for 5 minutes in an oxygen atmosphere to obtain a PZT thin film having a thickness of about 0.15 μm.
As shown in FIG. 9, the PZT thin film produced by using the thin film production apparatus for the atomizer according to this example has a good step coverage and can sufficiently cope with the production of high-density integrated circuits. is there.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a thin film manufacturing apparatus.
2A is a horizontal cross-sectional view of an atomizer for forming a ceramic thin film according to an embodiment of the present invention, and FIG. 2B is a cross-sectional view taken along line II-II of FIG.
FIG. 3 is a horizontal sectional view of an atomizer for forming a ceramic thin film according to another embodiment of the present invention.
FIG. 4 is a cross-sectional view of a passage hole used for an entrance / exit of a selection chamber.
FIG. 5 is a relationship diagram of the carrier gas flow rate and the number of mist particles when no vibrating body is installed in the selection chamber.
FIG. 6 is a relationship diagram between the carrier gas flow rate and the number of mist particles when a vibrating body is installed in the selection chamber.
FIG. 7 is a relationship diagram between the mist particle diameter and the number of mist particles when a vibrating body is installed in the selection chamber.
8 is an SEM image showing a cross section of a PZT thin film manufactured by a thin film manufacturing apparatus including the atomizer shown in FIG.
9 is an SEM image showing a cross section of a PZT thin film produced on a substrate having grooves by a thin film manufacturing apparatus including the atomizer of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Atomizer 11 ... Substrate 12 ... Thin film formation chamber 13 ... Mist spreader 14 ... Substrate mounting table 21 ... Atomization chamber 22 ... First selection chamber 23 ... Second selection chamber 24 ... Third selection chamber 24a- 24d ... Small flight chambers 25a to 25c, 27 ... Ultrasonic vibrator 26 ... Vibrating body (stem)
28 ... Mist supply port 29 ... Carrier gas introduction port 30, 31 ... Communication hole

Claims (8)

a) a first ultrasonic vibrator for atomizing the raw material liquid;
b) a sorting chamber having a predetermined volume for passing the raw material mist atomized by the first ultrasonic transducer;
c) a vibrator provided with a second ultrasonic transducer provided in the sorting chamber;
An atomizer for forming a ceramic thin film, comprising: 2. The atomizer for forming a ceramic thin film according to claim 1, wherein two or more sorting chambers are provided. The atomizer for forming a ceramic thin film according to claim 1 or 2, wherein the sorting chamber is composed of a plurality of small chambers connected in a zigzag manner. The atomizer for forming a ceramic thin film according to any one of claims 1 to 3, wherein a tip of a mist passage hole provided at an entrance and / or an exit to the sorting chamber has an acute angle. . a) Mist the raw material liquid with the first ultrasonic vibrator,
b) Sorting the mist further by passing it through a sorting chamber in which a vibrating body having a second ultrasonic transducer is installed.
A method for atomizing a raw material liquid for forming a ceramic-based thin film. a) Mist the raw material liquid with the first ultrasonic vibrator,
b) Sorting the mist further by passing it through a sorting chamber in which a vibrating body having a second ultrasonic transducer is installed,
c) Disperse the mist refined by sorting on the heated substrate.
A method for producing a thin film, comprising a step. The thin film manufacturing method according to claim 6, wherein the flow rate of the carrier gas for conveying the mist is 0.1 to 0.5 L / min. The thin film manufacturing method according to claim 6, wherein the substrate is moved during the dispersion.

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