ATOMIZING APPARATUS FOR FILM FORMATION AND FILM FORMING APPARATUS USING THE SAME

An atomizing apparatus for film formation enabling high-quality thin film formation with suppressed particle adhesion, including: a raw-material container accommodating a raw-material solution; a cylindrical member connecting inside the raw-material container to an outer unit, and disposed so a lower end of the cylindrical member does not touch a liquid surface of the raw-material solution in the container; an ultrasound generator having at least one source emitting ultrasound; and a liquid tank where the ultrasound propagates the raw-material solution through a middle solution. The generation source is outside the liquid tank and has a center between a plane extending from an inner side wall of the raw-material container and a plane extending from an outer side wall of the cylindrical member. A center line of an ultrasound-emitting surface of the ultrasound generation source is designated as u, wherein the center line u does not intersect the cylindrical member side wall.

TECHNICAL FIELD

The present invention relates to an atomizing apparatus for film formation and a film forming apparatus using the atomizing apparatus.

BACKGROUND ART

Mist Chemical Vapor Deposition (Mist CVD. Hereinafter, also referred to as “mist CVD method”) has been developed in which a thin film is formed on a substrate by using a raw material atomized into a mist form. This method has been utilized to prepare oxide semiconductor film etc. (Patent Document 1, 2). In film formation according to the mist CVD method, mist is obtained with ultrasound as a general technique.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, a method for atomizing a raw material to form high-quality film has not been established yet, and there is a problem that numerous particles reflecting the raw-material mist quality adhere to the prepared film. Moreover, it is known that when the film-formation speed is increased, for example, if mist is supplied in larger amount, such particles adhere more noticeably. It has been desired to achieve both high film quality and productivity.

The present invention has been made to solve the above problems. An object of the present invention is to provide: an atomizing apparatus for film formation which enables efficient formation of a high-quality thin film with particle adhesion suppressed; and a film forming apparatus for forming a high-quality film in high productivity by using this atomizing apparatus.

Solution to Problem

The present invention has been made to achieve the object, and provides an atomizing apparatus for film formation, comprising:

a raw-material container configured to accommodate a raw-material solution;

a cylindrical member configured to spatially connect inside of the raw-material container to an outer unit, and disposed such that a lower end of the cylindrical member does not touch a liquid surface of the raw-material solution in the raw-material container;

an ultrasound generator having at least one ultrasound generation source configured to emit ultrasound; and

a liquid tank where the ultrasound propagates to the raw-material solution through a middle solution, wherein

the ultrasound generation source is located outside the liquid tank,

the ultrasound generation source has a center between a plane extending from an inner side wall of the raw-material container and a plane extending from an outer side wall of the cylindrical member, and

provided that a center line of an ultrasound-emitting surface of the ultrasound generation source is designated as u, the ultrasound generation source is provided such that the center line u does not intersect the side wall of the cylindrical member.

Such an atomizing apparatus for film formation makes it possible to stably obtain favorable, high-quality and high-density mist, which is suitable for film formation. Thus, the atomizing apparatus for film formation enables efficient formation of high-quality film with fewer particles.

In this case, the ultrasound generation source is preferably provided such that a distance d between the outer wall of the cylindrical member and a straight line which passes through the center of the ultrasound generation source and is parallel to the outer wall of the cylindrical member is 5 mm or more.

In this manner, mist with higher density can be obtained more stably.

In addition, the present invention provides a film forming apparatus comprising at least:

an atomizer configured to atomize a raw-material solution to form a raw-material mist; and

a film-forming unit configured to supply the mist to a substrate to form a film on the substrate, wherein the film forming apparatus comprises the above-described atomizing apparatus for film formation as the atomizer.

Such an apparatus is capable of forming high-quality film with high productivity.

Advantageous Effects of Invention

As described above, the present invention makes it possible to provide an atomizing apparatus with which high-quality and high-density mist is stably obtained for film formation. Moreover, the present invention makes it possible to provide a film forming apparatus capable of forming high-quality film in high productivity.

DESCRIPTION OF EMBODIMENTS

As noted above, there have been demands for: an atomizing apparatus for film formation which enables formation of high-quality thin film with particle adhesion suppressed; and a film forming apparatus for forming high-quality film in high productivity by using this atomizing apparatus.

The present inventors have earnestly studied the above problems and consequently found that high-quality thin films with suppressed particle adhesion can be formed in high productivity by using an atomizing apparatus for film formation, including: a raw-material container configured to accommodate a raw-material solution; a cylindrical member configured to spatially connect inside of the raw-material container to an outer unit, and disposed such that a lower end of the cylindrical member does not touch a liquid surface of the raw-material solution in the raw-material container; an ultrasound generator having at least one ultrasound generation source configured to emit ultrasound; and a liquid tank where the ultrasound propagates to the raw-material solution through a middle solution. In the atomizing apparatus for film formation, the ultrasound generation source is located outside the liquid tank, the ultrasound generation source has a center between a plane extending from an inner side wall of the raw-material container and a plane extending from an outer side wall of the cylindrical member, and provided that a center line of an ultrasound-emitting surface of the ultrasound generation source is designated as u, the ultrasound generation source is provided such that the center line u does not intersect the side wall of the cylindrical member. This finding has led to the completion of the present invention.

Hereinbelow, description will be given with reference to the drawings.

(Atomizing Apparatus for Film Formation)

FIG.1shows an atomizing apparatus100for film formation according to the present invention. The atomizing apparatus100for film formation includes: a raw-material container111configured to accommodate a raw-material solution114; a cylindrical member113configured to spatially connect the inside of the raw-material container111to an outer unit, and disposed such that a lower end of the cylindrical member113does not touch a liquid surface of the raw-material solution114in the raw-material container111; an ultrasound generator120having at least one ultrasound generation source (ultrasonic vibration plate)121configured to emit ultrasound; and a liquid tank122, where ultrasound propagates to the raw-material solution114through a middle solution123.

In the raw-material container111, a carrier gas inlet112for entry of a carrier gas131is disposed. The shapes of the raw-material container111and the cylindrical member113are not particularly limited, but these members having columnar shape enable smooth flow of a gas mixture133of the carrier gas131and a mist132. The carrier gas inlet112is preferably provided higher than the lower end of the cylindrical member113inside the raw-material container111. In this manner, the carrier gas131and the mist132can be sufficiently mixed. Additionally, although unillustrated, the raw-material container111may include a mechanism for replenishing the raw-material solution114depending on the consumption.

The members constituting atomizing apparatus for film formation are not particularly limited, as long as the materials and structures are chemically stable with respect to the raw-material solution114and have sufficient mechanical strength. It is possible to utilize, for example, metal, plastic material, glass, metal materials whose surfaces are coated with plastic material, etc.

The ultrasound generator120includes at least the ultrasound generation source(s)121. Moreover, an oscillator or the like provided to the ultrasound generator120can drive the ultrasound generation source121. Meanwhile, the liquid tank122accommodates the middle solution123through which ultrasound emitted from the ultrasound generation source121is propagated to the raw-material solution114. The ultrasound generation source121has an ultrasound-emission surface with a flat shape, and the emission direction may be fixed after inclining this emission surface, or may be adjustable by inclining the emission surface with an angle adjusting mechanism121a. In addition, the ultrasound generation source121includes at least one ultrasonic vibration plate which may be a vibration plate alone or may be constituted in combination with means for controlling ultrasound emission direction. Moreover, the number of the ultrasound generation sources121to be provided may be one or more, depending on desired mist density, the size of the raw-material container111, etc. The frequency of ultrasound emitted from the ultrasound generation source121is not limited, as long as the mist132to be generated has desired particle diameter and particle size. The frequency to be utilized may be, for example, 1.5 MHz to 4.0 MHz. Thereby, the raw-material solution114is formed into mist of droplets with a micron size, which is suitable for film formation.

Further, each ultrasound generation source121is disposed outside the liquid tank122such that the center of the ultrasound generation source121is located between a plane extending from an inner side wall of the raw-material container111and a plane extending from an outer side wall of the cylindrical member113. A distance between the outer wall of the cylindrical member113and a straight line which passes through the center of the ultrasound generation source121and is parallel to the outer wall of the cylindrical member113is here designated as “d”. The distance d is preferably 5 mm or more, more preferably 10 mm or more. This makes it possible to more stably obtain mist with higher concentration. Note that the upper limit value of “d” can be set within a range that is less than a distance between the outer wall of the cylindrical member113and the inner wall of the raw-material container111. For example, “d” can be 100 mm or less.

The middle solution123accommodated in the liquid tank122is not particularly limited, as long as ultrasound is not inhibited. For example, water, an alcohol, an oil, and so forth may be used. The liquid tank122and the like are not particularly limited, as long as the materials and structures are chemically stable with respect to the middle solution123and have certain mechanical strength. It is possible to utilize, for example, metal, plastic material, glass, metal materials whose surfaces are coated with plastic material, etc. Additionally, although unillustrated, the liquid tank122may further include means for detecting and controlling the liquid amount and temperature of the middle solution123.

FIG.2is a diagram for explaining a mist generation section of the inventive atomizing apparatus for film formation.FIG.2is an enlarged diagram corresponding to a section A of a dashed line frame inFIG.1, and schematically showing a state near the liquid surface of the raw-material solution when ultrasound is emitted. A center line of an ultrasound-emitting surface of an ultrasound generation source221is designated as “u”. When ultrasound is emitted from the ultrasound generation source221below a raw-material solution214in a direction of the center line u, a liquid column214pis formed on the raw-material solution214along the ultrasound emission direction, and a mist is formed simultaneously.

In this event, the ultrasound generation source221is inclined with an angle adjusting mechanism221asuch that the center line u does not intersect the side wall of a cylindrical member213. Meanwhile, the center line u and a line c passing through the center of the cylindrical member213may intersect at any point, or may form skew lines. Further, in this event, a distance D from the center of the ultrasound generation source221to a plane extending from a side wall of a raw-material container211is preferably such that the liquid column214pis not significantly blocked by the side wall of the raw-material container211. Thereby, the gas mixture is supplied to the outside of the atomizing apparatus for film formation without blocking the flow of the gas mixture, enabling more efficient film formation. Simultaneously, the gas mixture is prevented from mixing with droplets of relatively large particle diameter which possibly cause unreacted materials and particles. Consequently, film with higher quality can be formed. Incidentally, the descriptions of the same members as inFIG.1are omitted as appropriate.

Note that, in the present invention, the term “particle” refers to ones observed as particles when semiconductor film surface is observed, and includes ones incorporated in the film and integrated with the film and ones attached as foreign matter on the semiconductor film surface. Additionally, the particle diameter is a value based on the particle size measured with a particle measurement instrument according to light scattering. The particle size is determined through calibration of the measurement instrument with reference particles of multiple sizes. Specifically, the particle size is a classified value, and a measurement value of particles measured with a measurement instrument is compared with measurement values of reference particles having been measured. Particles on semiconductor film surface can be measured, for example, with a laser scattering-based particle counter.

The present invention further provides a film forming apparatus which employs the atomizing apparatus for film formation described inFIGS.1and2.

FIG.3is a diagram for explaining one embodiment of a configuration of the inventive film forming apparatus. The inventive film forming apparatus300includes at least: an atomizer320configured to atomize a raw-material solution321to form a raw-material mist322; and a film-forming unit330configured to supply the mist322to a substrate334to form a film on the substrate334. The film forming apparatus300includes, as the atomizer320, the inventive atomizing apparatus100for film formation described with reference toFIG.1andFIG.2. Further, a carrier-gas supplier311, the atomizer320, and the film-forming unit330are connected with pipes313,324.

The carrier-gas supplier311may be, for example, an air compressor, various gas cylinders or nitrogen gas separators, etc., and may include a mechanism for controlling the supply flow amount of gas.

The pipes313,324are not particularly limited, as long as the pipes have sufficient stability with respect to the raw-material solution321and temperature near the film-forming unit330and so forth. It is possible to widely use pipes made of quartz or common resins, such as polyethylene, polypropylene, vinyl chloride, silicon resin, urethane resin, and fluorine resin.

Moreover, although unillustrated, another pipe from the carrier-gas supplier311bypassing the atomizer320may be connected to the pipe324so as to allow dilution-gas supply to a gas mixture352.

Multiple atomizers320may be provided depending on the materials for film formation, etc. Moreover, in this case, gas mixtures352supplied from the multiple atomizers320to the film-forming unit330may be independently supplied to the film-forming unit330, or may be mixed in the pipe324or another container for mixing (not shown) that is provided additionally.

The film-forming unit330may include a film forming chamber331, a susceptor332disposed in the film forming chamber331and configured to hold the substrate334where a film is formed, and a heater333configured to heat the substrate334.

The structure and so forth of the film forming chamber331are not particularly limited. For example, a metal such as aluminum and stainless steel may be employed, or quartz or silicon carbide may be employed when a film is formed at higher temperature.

The heater333can be selected depending on the materials and structures of the substrate334, the susceptor332and the film forming chamber331. For example, a resistance heating heater or a lamp heater is suitably used.

A carrier gas351is mixed with the mist322formed in the atomizer320. The resulting gas mixture352is conveyed to the film-forming unit330to form a film.

Further, the inventive film forming apparatus may further include a discharge unit340. The discharge unit340may be connected to the film-forming unit330with a pipe or the like, or may be disposed with a space in between. Moreover, the structure and configuration of the discharge unit340are not particularly limited, as long as the discharge unit340is made of a material that is stable with respect to heat, gas, and product discharged from the film-forming unit330. It is possible to use known common exhaust fan or exhaust pump. Further, depending on the nature of the gas and product to be discharged, for example, a mist trap, a wet scrubber, a bag filter, a purifier, or the like may be installed.

FIG.3explains the embodiment of the film-forming unit330in which the substrate334is disposed inside the film forming chamber331. Nevertheless, the inventive film forming apparatus is not limited thereto, and may be a film forming apparatus400as shown inFIG.4. A nozzle431configured to eject a gas mixture452containing a mist422may be used as a film-forming unit430to directly blow the gas mixture452onto a substrate434disposed on a susceptor432for film formation.

In this case, a driver configured to drive one or both of the nozzle431and the susceptor432in a horizontal direction may be provided, so that a film is formed by changing relative positions of the substrate434and the nozzle431in the horizontal direction. Moreover, the susceptor432may include a heater433configured to heat the substrate434. Further, the film-forming unit430may include a discharge unit435. The discharge unit435may be integrated with the nozzle431, or may be separately disposed. Note that the descriptions of the same members as inFIGS.1to3are omitted as appropriate.

EXAMPLE

Hereinafter, the present invention will be described in detail by showing Examples, but the present invention is not limited thereto.

The atomizing apparatus for film formation shown inFIGS.1and2and the film forming apparatus shown inFIG.3were used to form an α-gallium oxide film.

In the atomizing apparatus for film formation, the raw-material container and cylindrical member used were both made of borosilicate glass, and a film forming chamber made of quartz was prepared. A gas cylinder filled with nitrogen gas was used to supply carrier gas. The gas cylinder and the atomizing apparatus for film formation were connected with a urethane resin tube, and the atomizing apparatus for film formation was further connected to the film forming chamber with a quartz pipe.

An aqueous solution containing 0.02 mol/L of gallium acetylacetonate was mixed with hydrochloric acid with a concentration of 34% such that the volume ratio of the latter was 1%. The mixture was stirred with a stirrer for 60 minutes to prepare a raw-material solution, and the raw-material container was filled therewith. The atomizing apparatus for film formation used had two ultrasonic vibration plates (frequency: 2.4 MHz, emission angle: 80°). Each ultrasonic vibration plate was disposed such that the center of the ultrasonic vibration plate was located 10 mm apart outwardly from the side wall of the cylindrical member, and the center line u did not intersect the side wall of the cylindrical member as inFIG.2.

Next, a c-plane sapphire substrate with a thickness of 0.6 mm and a diameter of 4 inches (approximately 10 cm) was placed on a quartz susceptor disposed in the film forming chamber, and heated such that the substrate temperature reached 500° C.

Next, with the ultrasonic vibration plates, ultrasonic vibration was propagated through water to the precursor in the raw-material container to atomize the raw-material solution (mist was formed).

Next, a nitrogen gas was added to the raw-material container at a flow rate of 5 L/min. A gas mixture of the mist and the nitrogen gas was supplied to the film forming chamber for 60 minutes to form a film. Immediately thereafter, supplying the nitrogen gas was stopped, and supplying the gas mixture to the film forming chamber was stopped.

In the X-ray diffraction measurement, the peak appeared at 2θ=40.3°. This verified that the prepared crystal layer of the laminate was α-phase Ga2O3.

Then, the film thickness of the prepared film was measured by the light reflectance analysis, and the growth rate was calculated. Moreover, the concentration of particles (diameter: 0.5 μm or more) on the film was evaluated with a substrate inspector (KLA candela-CS10).

A film was formed as in Example 1, except that the nitrogen gas flow rate was 10 L/min.

In the X-ray diffraction measurement, the peak appeared at 2θ=40.3°. This verified that the prepared crystal layer of the laminate was α-phase Ga2O3.

Then, the film was evaluated as in Example 1.

An α-gallium oxide film was formed using the same apparatus and raw-material solution as those in Example 1, except the film forming apparatus used was the film forming apparatus shown inFIG.4. A mist-ejecting nozzle made of quartz was used. An aluminum hot plate was used as the susceptor, and the substrate was heated to 450° C. Next, the susceptor was reciprocally driven in the horizontal direction at a speed of 10 mm/s below the mist-ejecting nozzle. Further, the gas mixture was supplied from the mist-ejecting nozzle to the substrate on the susceptor at 5 L/min for 60 minutes to form a film.

In the X-ray diffraction measurement, the peak appeared at 2θ=40.3°. This verified that the prepared crystal layer of the laminate was α-phase Ga2O3. Then, the film was evaluated as in Example 1.

Comparative Example 1

A film was formed as in Example 1, except that ultrasound was emitted toward the side wall of the cylindrical member.

In the X-ray diffraction measurement, the peak appeared at 2θ=40.3°. This verified that the prepared crystal layer of the laminate was α-phase Ga2O3. Then, the film was evaluated as in Example 1.

Comparative Example 2

A film was formed as in Example 2, except that ultrasound was emitted toward the side wall of the cylindrical member.

In the X-ray diffraction measurement, the peak appeared at 2θ=40.3°. This verified that the prepared crystal layer of the laminate was α-phase Ga2O3. Then, the film was evaluated as in Example 1.

Table 1 shows the growth rates and the particle concentrations of the films obtained in Examples 1, 2, 3 and Comparative Examples 1, 2.

As can be seen from Table 1 and shown by Examples 1, 2, 3, the inventive film forming apparatuses were excellent and capable of forming high-quality films at high growth rate with fewer particles. In contrast, in Comparative Examples 1, 2 using the atomizing apparatus for film formation of the conventional technique, the growth rates were low, and a large number of particles adhered.

A film was formed under the same conditions as in Example 1, except that the film-formation time, that is, the time during which the gas mixture of the mist and nitrogen gas was supplied to the film forming chamber, was 120 minutes. A semiconductor film having a film thickness of 1 μm or more was formed. Then, the concentration of particles (diameter: 0.3 μm or more) on the film surface obtained by the film formation was evaluated with a substrate inspector (KLA candela-CS10).

A film was formed under the same conditions as in Example 2, except that the film-formation time was 120 minutes. The film was evaluated under the same conditions as in Example 4.

A film was formed under the same conditions as in Example 3, except that the film-formation time was 120 minutes. The film was evaluated under the same conditions as in Example 4.

Comparative Example 3

A film was formed under the same conditions as in Comparative Example 1, except that the film-formation time was 120 minutes. The film was evaluated under the same conditions as in Example 4.

Comparative Example 4

A film was formed under the same conditions as in Comparative Example 2, except that the film-formation time was 120 minutes. The film was evaluated under the same conditions as in Example 4.

Table 2 shows the growth rates and the particle concentrations of the films obtained in Examples 4, 5, 6 and Comparative Examples 3, 4.

As can be seen from Table 2 and shown by Examples 4, 5, 6, when the inventive film forming apparatuses were used for the film formation, high-quality films were successfully formed at high growth rate with fewer particles. Particularly, the semiconductor films were obtained such that the particle concentration with the diameter of 0.3 μm or more was 50/cm2or less. In contrast, in Comparative Examples 3, 4 using the atomizing apparatus for film formation of the conventional technique, the growth rates were low, and a large number of particles adhered.