JP2000200781A - Apparatus and method for gasification of liquid raw material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an apparatus and a method in which a liquid raw material can be gasified in a wide flow-rate range and stably irrespective of whether the supply amount of the liquid raw material is increased or decreased, by a method wherein the heating temperature of a heating flow passage is controlled according to the liquid raw material which is supplied to a vaporizer provided with the heating flow passage. SOLUTION: A solvent container 13 which stores a solvent identical to, or different from, a solvent used to create a liquid raw material is installed so as to join a liquid-raw-material conveyance flow passage 14, Then, a control part 40 which controls the temperature of the heating part 30 of a vaporizer 16 according to the supply flow rate of the liquid raw material, calculated on the basis of the output of a flowmeter inside a flow-rate regulating device 28 is installed. The control part controls the temperature and the flow rate of a heating medium when the heating part 30 is constituted of a jacket which circulates the heating medium. The control part controls a current to an electric heater so as to control the temperature of the heating part 30 when the heating part 30 is constituted of the heater. When a film is formed, a substrate W is placed on a substrate holding base 32, the substrate W is maintained at a prescribed temperature, a source gas and a mixed gas are jetted from the nozzle hole 36 of a gas supply head 34, and a thin film is grown on the surface of the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for vaporizing a liquid raw material, and more particularly to a method for supplying a vaporized raw material to a thin film vapor phase growth apparatus for forming a high dielectric or ferroelectric thin film such as barium / strontium titanate. The present invention relates to an apparatus and method for vaporizing a liquid raw material used for vaporizing a liquid raw material.

[0002]

2. Description of the Related Art In recent years, the degree of integration of integrated circuits in the semiconductor industry has been remarkably improved, and research and development of DRAMs from the current megabit order to the future gigabit order have been conducted. In order to manufacture such a DRAM, a capacitor element capable of obtaining a large capacity in a small area is required. As a dielectric thin film used for manufacturing such a large-capacity element, a tantalum pentoxide (Ta ₂ O ₅ ) thin film having a dielectric constant of about 20 is used instead of a silicon oxide film or a silicon nitride film having a dielectric constant of 10 or less. Or, a metal oxide thin film material such as a barium titanate (BaTiO ₃ ) thin film having a dielectric constant of about 300, strontium titanate (SrTiO ₃ ), or barium strontium titanate which is a mixture thereof is considered to be promising. Further, ferroelectric thin film materials such as PZT, PLZT, and Y1 having a higher dielectric constant are also expected to be promising.

As a method for forming a film of such a material,
Chemical vapor deposition (CVD) is promising. FIG.
FIG. 1 is a view showing an overall configuration of a film forming apparatus for forming a high-dielectric or ferroelectric thin film of barium / strontium titanate or the like of this type, and includes a liquid source container 10 for storing a liquid source and a carrier gas supply. A vaporizer 16 is connected to a downstream side of the liquid source transport path 14 connected to the passage 12, and a film forming chamber (chamber) 20 that can be hermetically sealed via the source gas transport path 18 downstream of the vaporizer 16. Is provided, and a vacuum pump 24 is disposed in the exhaust passage 22 on the downstream side. A flow controller (mass flow controller) 28 for adjusting the flow rate of the liquid raw material to be sent to the vaporizer is provided in the liquid raw material transport passage 14, and the oxidizing gas for supplying an oxidizing gas such as oxygen is supplied to the film forming chamber 20. A gas pipe 26 is connected.

A liquid raw material container 10 contains a solid Ba at room temperature.
In order to liquefy (DPM) ₂ , Sr (DPM) _{2, and the} like, and further stabilize the vaporization characteristics, for example, a liquid raw material in which an organic solvent such as tetrahydrofuran (THF) is mixed is stored. When a plurality of raw materials are used, a plurality of liquid raw material containers may be merged downstream. These raw materials have stable vaporization, such as the vaporization temperature and decomposition temperature are close, the reaction products are likely to stick, there is a difference between the vaporization temperature and the vaporization temperature of the organic solvent, and the vapor pressure is very low. It has properties that inhibit it.

[0005] As the vaporizer 16, for example, as the applicant of the present invention previously filed Japanese Patent Application No. 10-195013, a jacket (heating unit 30) for circulating a heat medium around a narrow tube of a fixed length. The one provided with is used. The heating temperature of the vaporizer 16 is set to a predetermined value so that the liquid material at a predetermined flow rate can be provided with latent heat necessary for vaporization thereof and decomposition of the liquid material can be prevented. It is controlled by adding the value.

[0006] The substrate W
Is placed on a substrate holder 32, the substrate W is maintained at a predetermined film forming temperature by a heater provided on the substrate holder 32, and a mixed gas of a source gas and an oxidizing gas is supplied through a nozzle hole 36 of a gas supply head 34. Is sprayed toward the substrate W to grow a thin film on the surface of the substrate W.

[0007]

In the prior art as described above, the structure of the internal flow path of the vaporizer is constant.
If the flow rate of the liquid raw material flowing through the vaporizer becomes smaller than the set flow rate, the liquid raw material receives more heat in the vaporizer and is overheated, or the heating time becomes longer than necessary, increasing the proportion of the raw material to be decomposed. I do. Decomposition products cause problems such as adhesion to the flow path, causing internal obstruction, and generation of particles to deteriorate the quality of film formation. Conversely, when the flow rate of the liquid raw material flowing in the vaporizer increases, the heat transfer amount of the vaporizer becomes insufficient, and the liquid raw material flows downstream without vaporization, and is condensed in the flow path to hinder stable operation. Alternatively, problems such as inhibition of the reaction in the film formation chamber and reduction of the yield of the raw material occur.

For example, a plurality of vaporization channels are provided in parallel to change the number of channels used in accordance with the flow rate of the liquid raw material,
Although measures such as making the length of the vaporization flow path variable are conceivable,
It is not a practical means in consideration of the property that the raw material is easily precipitated.

The present invention has been made in view of the above problems, and provides an apparatus and a method for vaporizing a liquid raw material capable of performing stable vaporization in a wide flow rate range regardless of an increase or decrease in the supply amount of the liquid raw material. The purpose is to do.

[0010]

According to a first aspect of the present invention, there is provided a vaporizer having a heating flow path and a supply means for supplying a liquid raw material to the vaporizer, wherein the liquid raw material vaporizes the liquid raw material. In the apparatus, a heating temperature of the heating flow path is controlled in accordance with a flow rate of the liquid raw material.

[0011] Thus, the amount of heat supplied to the liquid source can be appropriately controlled within the time when the liquid source passes through the heating flow path of the vaporizer having a certain structure. Therefore,
Even if it is a liquid raw material for forming a high- and ferroelectric film having a narrow range of vaporization temperature and decomposition temperature, it can be vaporized stably without decomposition or condensation over a wide flow rate range according to the situation. Can be.

According to a second aspect of the present invention, there is provided a liquid material vaporizer for vaporizing a liquid material, comprising a vaporizer having a heating flow path and a supply means for supplying the liquid material to the vaporizer. A liquid raw material vaporizer characterized by controlling a heating temperature of the heating flow path in accordance with a raw material concentration in the liquid raw material. Raw materials have properties such as higher latent heat of vaporization than solvents, easy polymerization and multimerization, and easy azeotropic phenomenon with solvents, etc., so that even at the same flow rate, the amount of heat required for vaporization depends on the concentration of the raw materials. , Temperature and residence time in the vaporizer vary greatly. Therefore, by taking this into account, more appropriate control can be performed.

According to a third aspect of the present invention, when the flow rate of the liquid raw material to be supplied is smaller than a predetermined value, a solvent is added to the liquid raw material to reduce the raw material concentration. The liquid raw material vaporizer described in 1 above. That is, in the case where the concentration of the raw material is too high, the supply speed of the raw material is too low, the residence time of the raw material is too long, or the like, the solvent is added to the liquid raw material to reduce the raw material concentration. As a result, even when the flow rate is small, a predetermined flow rate is secured, and an excessive temperature change of the liquid raw material or the vaporized raw material is suppressed. Alternatively, even when the raw material concentration is too high, addition of a solvent can prevent polymerization, multimerization and azeotropic phenomenon of the raw material.

According to a fourth aspect of the present invention, there is provided a liquid material vaporizing apparatus according to any one of the first to third aspects, and an airtight film forming chamber disposed downstream of the vaporizer. It is a film forming apparatus.

According to a fifth aspect of the present invention, there is provided a method for vaporizing a liquid raw material by passing the liquid raw material through a vaporizer having a heating flow path, wherein the flow rate of the liquid raw material and / or the concentration of the raw material in the liquid raw material are determined. Wherein the heating temperature of the heating flow path is controlled in accordance with the method. Here, when the flow rate of the supplied liquid raw material is smaller than a predetermined value, it is preferable to add a solvent to the liquid raw material to reduce the raw material concentration.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a film forming apparatus according to this embodiment. The basic configuration is the same as the conventional film forming apparatus shown in FIG. In this embodiment, a solvent container 13 for storing the same or a different solvent as used for preparing the liquid raw material is provided so as to be joined to the liquid raw material transport flow path 14.

The vaporizer 16 is operated in accordance with the supply flow rate of the liquid raw material calculated from the output of the flow meter in the flow controller 28.
A control unit 40 for controlling the temperature of the heating unit 30 is provided. When the heating unit is formed of a jacket through which the heating medium flows, the control unit controls the temperature and the flow rate of the heating medium, so that the heating unit is formed of an electric heater. In this case, the temperature of the heating unit 30 is controlled by controlling the current to the heater. As shown in FIG. 2A, the relationship between the flow rate and the target heating temperature when a specific liquid material is vaporized is stored in the control unit in advance. Of course, a flow rate sensor may be provided in the liquid raw material transport channel 14 and the output thereof may be input to the control unit. The control unit 40 includes a sensor 40a
The raw material concentration in the liquid raw material is measured through the control unit, and the temperature of the heating unit 30 and the opening of the flow controller are controlled as described later.

In order to form a film in the film forming apparatus having such a structure, the substrate W is placed on the substrate holding table 32, and the substrate W is maintained at a predetermined temperature while the nozzle W of the gas supply head 34 is opened. A mixed gas of a source gas and an oxidizing gas is jetted toward the substrate W to grow a thin film on the surface of the substrate W. At this time, the control unit 40 calculates the flow rate of the liquid raw material to be supplied to the vaporizer 16 from the flow meter in the flow rate controller (mass flow controller) 28, and based on the preset and stored relationship, the vaporizer 16 The heating temperature of the heating unit 30 is controlled.

The relationship between the flow rate and the heating temperature will be described below. In this example, the lower-limit heating temperature Tmin and the upper-limit heating temperature Tmax of the vaporizer 16 are set corresponding to the minimum flow rate Qmin and the maximum flow rate Qmax, and the correlation in this region is set. Such a relationship can be experimentally determined according to the type of the raw material, the type of the vaporizer, and the like. This will be described more specifically below.

The liquid material is to initiate vaporization at a given vaporization temperature T _0, in order to continue the vaporization is required to compensate for the latent heat of vaporization. Therefore, heat transfer governing the vaporization rate will depend on the temperature difference ΔT between the temperature T of the vaporizer which is a heat source and the vaporization temperature T _0. The amount of heat transfer is the temperature difference ΔT
As shown in FIG. 3, the vaporization rate depends on the heating temperature of the vaporizer, and as a result, as shown in FIG. By setting such a relationship, the raw material can be vaporized without giving an excessive change in sensible heat or heating for a long time. In this case, the temperature for obtaining the minimum vaporization rate necessary to vaporize the liquid raw material having the minimum flow rate Qmin within the time in which the liquid raw material stays in the vaporizer is the heating lower limit temperature Tmin.

Meanwhile, the decomposition of the raw material is started when the material reaches the decomposition temperature T _1, with increasing temperature higher than this is considered to decomposition rate increases rapidly. Therefore,
Tmax should be smaller than T _1. Further, for example, if the raw material is not sufficiently purified and impurities are present, O ₂ ,
Due to slight disturbance such as mixing of CO ₂ and H ₂ O,
As shown by the two-dot chain line in FIG. 3, it is considered that a small amount of decomposition of the raw material occurs even at a decomposition start temperature T1 or lower. In such a case, Tmax should be set even smaller than T _1.

Considering the above-described disturbance in the vaporizer, the decomposition rate is considered to depend on time. That is, as shown in FIG. 4, the decomposition rate increases almost in proportion to the residence time in the vaporizer, and the inclination of this straight line becomes steeper as the heating temperature of the vaporizer 16 increases as described above. Conceivable.

Therefore, when the raw material is not sufficiently purified and the vaporization is performed at a relatively low flow rate,
The decomposition temperature T ₁ is is likely to decrease, the flow rate that is a long time staying in slowed by the vaporizer 16, further, the reasons such that the ratio of temperature change for certain heat quantity is increased Since the liquid material tends to be easily decomposed, it is preferable to give priority to preventing the decomposition and to set the temperature such that the temperature is lowered on the low flow rate side as shown by the dashed line in FIG. On the high flow rate side, the heating unit 30 is controlled to have a high temperature in order to prevent the liquid material from flowing downstream in an unvaporized state.

Accordingly, an appropriate vaporization rate can be set without causing an excessive temperature change of the raw material regardless of the flow rate, and when the flow rate is large, the raw material is prevented from flowing unvaporized. When the amount is small, decomposition of the raw material can be suppressed.

In the above description, the case where the concentration of the raw material excluding the solvent in the liquid raw material detected by the sensor 40a is a constant value (n ₀ %), but when this concentration changes, the liquid raw material is vaporized. The temperature range suitable for causing the temperature to change relatively. That is, when the concentration of the raw material in the liquid raw material is high, the temperature range suitable for vaporizing the liquid raw material relatively increases, and conversely, when the concentration is low, the temperature range relatively decreases. This is probably because the raw material has a higher latent heat of vaporization than the solvent. Therefore, when the concentration of the raw material changes, as shown by a broken line in FIG.
Higher molarity (n ₁ %), lower molarity (n ₂
%) Is preferably prepared in advance and the control unit 40 controls the temperature of the heating unit 30 of the vaporizer 16.

When the flow rate of the liquid raw material is small, as described above, the flow velocity in the vaporizer decreases, and the liquid raw material is easily affected by temperature fluctuation. There is a case where stable vaporization cannot be performed only by reduction. In order to maintain the predetermined flow rate, the controller 40 controls the flow controller 28 to increase the solvent content by adding a solvent, as indicated by hatching in FIG. Reduce the molarity of the raw materials. Thus, stable vaporization can be performed while maintaining the heating temperature of the vaporizer 16 at the lower limit temperature Tmin.

[0027]

As described above, according to the present invention,
The amount of heat supplied to the liquid material can be appropriately controlled within the time that the liquid material passes through the heating flow path of the vaporizer with a fixed structure, so it is stable without decomposition or condensation in a wide flow rate range Vaporization can be performed. Therefore, even a liquid material for forming a high- and ferroelectric film having a narrow temperature range for maintaining a gas phase can be smoothly vaporized and a high-quality film can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a film forming apparatus to which the present invention is applied.

FIG. 2 is a diagram illustrating an example of a control diagram stored in a control unit.

FIG. 3 is a diagram showing a relationship between a heating temperature of a vaporizer, a flow rate of a liquid raw material, and a decomposition rate of a raw material.

FIG. 4 is a diagram showing a relationship between a decomposition rate of a raw material and a residence time of a liquid raw material in a vaporizer.

FIG. 5 is a diagram for explaining the addition of a solvent when the vaporizer heating temperature deviates from a set temperature.

FIG. 6 is a view showing a conventional film forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Liquid raw material container 12 Carrier gas supply path 13 Solvent container 14 Liquid raw material transport path 16 Vaporizer 18 Raw material gas transport path 20 Film formation chamber 28 Flow rate controller 30 Heating part 32 Substrate holder 34 Gas supply head 40 Control part

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yuji Abe 11-1, Haneda Asahimachi, Ota-ku, Tokyo Inside Ebara Corporation (72) Inventor Takeshi Murakami 11-1, Haneda Asahi-cho, Ota-ku, Tokyo EBARA F term (reference) 4D074 AA01 BB01 FF06 FF14 4K030 BA42 BA46 EA01 KA25 KA41 LA01 LA15 5F045 AB40 DP03 EE03 EE12 EE14 EE18 GB05 GB07

Claims (5)

[Claims] 1. A liquid source vaporizer for vaporizing a liquid source, comprising: a vaporizer having a heating flow path; and a supply unit for supplying a liquid source to the vaporizer, wherein the heating is performed according to a flow rate of the liquid source. A liquid raw material vaporizer, wherein a heating temperature of a flow path is controlled. 2. A liquid source vaporizer for vaporizing a liquid source, comprising: a vaporizer having a heating flow path; and a supply unit for supplying a liquid source to the vaporizer. A liquid raw material vaporizer, wherein a heating temperature of the heating flow path is controlled. 3. The liquid material vaporizer according to claim 1, wherein when the flow rate of the supplied liquid material is smaller than a predetermined value, a solvent is added to the liquid material to reduce the concentration of the material. . 4. A film forming apparatus comprising: the liquid source vaporizing apparatus according to claim 1; and an airtight film forming chamber disposed downstream of the vaporizer. 5. A method for vaporizing a liquid raw material by passing the liquid raw material through a vaporizer having a heating flow path, wherein the heating flow path is adjusted according to a flow rate of the liquid raw material and / or a raw material concentration in the liquid raw material. A method for vaporizing a liquid raw material, comprising controlling a heating temperature of a liquid.