Patent Application
20210207266
The present invention relates to a vaporizer for vaporizing a liquid material without using an atomizing carrier gas for atomizing the liquid material to be vaporized, and more particularly to a vaporizer in which a supply tube (a capillary tube) for introducing the liquid material into the vaporizer is disposed in contact with or in close proximity to a porous member (a sintered filter) to minimize pressure fluctuations in the course of vaporization.
A semiconductor device fabrication process includes various steps such as deposition (film formation), etching, and diffusion. Gases are used as source materials in most of these steps. In recent years, however, most of the gaseous materials have been replaced by liquid materials.
A liquid material is converted into a gas by a vaporizer and then subjected to a reaction step. In the case of a gaseous material, its flow rate is very stable because it is controlled by a mass flow controller.
On the other hand, in the case of a liquid material, it is introduced into the vaporizer at a controlled flow rate, atomized into a mist by an atomizing gas in the vaporizer, and then the mist is vaporized by heating. In this case, the pressure fluctuates more widely than in the case of the gaseous material. In order to produce uniform films stably, these pressure fluctuations must be reduced as much as possible.
In the state-of-the-art semiconductor deposition processes, the use of carrier gases has decreased. In a vaporization step performed without using such an atomizing gas or a carrier gas, the pressure fluctuates much more widely than in the case where an atomizing gas or a carrier gas is used, for the reasons described below.
[PTL 1] Japanese Patent No. 3650543
[PTL 2] Japanese Patent No. 4601535
As a conventional method for vaporizing a liquid material efficiently and stably, the liquid material is atomized into a mist using an atomizer and then the mist is introduced into a vaporization chamber, as described above. With this method, the vaporization is performed stably and the pressure fluctuations in the vaporization chamber can be reduced.
However, in a state-of-the-art method, a liquid material is not atomized using an atomizer but is dropped through a narrow supply tube and the resulting large droplets are introduced directly into the vaporization chamber. The droplets thus introduced hit the heated inner wall of the vaporization chamber one after another and are vaporized instantaneously. As a result, bumping occurs in succession on the inner wall of the vaporization chamber and the pressure in the vaporizer (the internal pressure of the vaporization chamber) fluctuates widely. These fluctuations cause the uneven concentration of the source gas to be supplied to a film forming apparatus. This uneven concentration of the source gas, which is fatal to the film forming apparatus, prevents uniform deposition in the apparatus. This is a serious problem in the vaporization step performed without using an atomizer.
The present invention has been made in view of the above conventional problem, and its object is to provide a vaporizer capable of reducing the occurrence of bumping which occurs when a liquid material comes in contact with a heated surface and thereby minimizing the pressure fluctuations in the vaporizer, when a method not using an atomizer is employed.
The invention according to claim 1 is a vaporizer 1 including:
a tank body 10 having a vaporization space 5 therein;
a porous member 30 disposed in the vaporization space 5 and heated;
a supply tube 40 inserted into the vaporization space 5 from outside and configured to supply a liquid material L to the porous member 30; and
a gas discharge passage 7 configured to discharge, from the vaporization space 5 to the outside, a source gas G produced by vaporizing the liquid material L through the porous member 30.
In this vaporizer 1, an outlet 41 of the supply tube 40 is disposed in contact with or in close proximity to the porous member 30, and
when the outlet 41 is disposed in close proximity to the porous member 30, a separation distance H between the outlet 41 and the porous member 30 is not greater than a distance from the outlet 41 to a bottom of a droplet of the liquid material L formed and suspended at the outlet 41 by surface tension.
The invention according to claim 2 is the vaporizer 1 according to claim 1, wherein the supply tube 40 is provided with a micro through-hole 45 on a side wall thereof near the outlet 41.
The invention according to claim 3 is the vaporizer 1 according to claim 1 or 2, wherein the porous member 30 has a recess 34 formed on a top surface thereof to allow the outlet 41 of the supply tube 40 to be inserted into the recess 34.
The invention according to claim 4 is the vaporizer 1 according to any one of claims 1 to 3, wherein the porous member 30 is made of a sintered metal, a ceramic, a sintered metal mesh laminate, or a sintered metal fiber fabric.
The invention according to claim 5 is the vaporizer 1 according to claim 1 or 2, wherein the porous member 30 is formed of a stack of two or more porous plates 30a and 30b.
The invention according to claim 6 is the vaporizer 1 according to claim 3, wherein the porous member 30 is formed of a stack of two or more porous plates 30a and 30b, a porous plate 30a located closer to the outlet 41 of the supply tube 40 is provided with a through-hole 34a serving as the recess 34, and a porous plate 30b located farther from the outlet 41 is a flat plate.
The invention according to claim 7 is the vaporizer 1 according to claim 1, wherein an edge 42 of the outlet 41 of the supply tube 40 is cut to form a notch 48 near the outlet 41.
In the vaporizer 1 of the present invention, the outlet 41 of the supply tube 40 is disposed in contact with the porous member 30 or in close proximity to the porous member 30 at a separation distance H within the range as described above. Therefore, upon contact with the porous member 30, the liquid material L discharged through the outlet 41 penetrates into the porous member 30 before evaporating and then rapidly spreads in all directions from a point corresponding to the outlet 41.
The liquid material L evaporates gradually and continuously from an area of the surface of the porous member 30 around the point corresponding to the outlet 41 of the supply tube 40. As a result, the pressure fluctuations in the vaporizer 1 is significantly reduced.
Hereinafter, the present invention will be described with reference to the drawings.
The tank body 10 includes an outer block 11 and an inner block 21, which are made of a corrosion-resistant material resistant to a liquid material L. The outer block 11 has a bottom-open storage space 12 formed therein and an insertion hole 13 extending from its top surface to the ceiling surface of the storage space 12. One or a plurality of heaters 50a are embedded in the side wall 14 of the outer block 11 that surrounds the storage space 12 to heat the outer block 11 to a predetermined temperature. A thermocouple 60a for measuring the temperature of the outer block 11 is embedded in the ceiling wall of the outer block 11. The thermocouple 60a is inserted into the ceiling wall so that the tip thereof is located in close proximity to the ceiling surface to accurately measure the temperature of a vaporization space 5 in contact with that ceiling surface.
The inner block 21 includes a base portion 22 and a stand portion 23 mounted in the center of the top surface of the base portion 22. One or a plurality of heaters 50b are embedded in the inner block 21 from the bottom of the inner block 21 to the vicinity of the top surface of the stand portion 23.
A space, which is formed between the top surface of the stand portion 23 and the ceiling surface of the storage space 12 of the outer block 11, is referred to as a vaporization space 5. An annular gap, which is formed between the inner circumferential surface of the storage space 12 and the outer circumferential surface of the stand portion 23, is referred to as a gas discharge gap 17 serving as a portion of a gas discharge passage 7.
A bottom-open central cavity 24 extending from the bottom of the inner block 21 upward into the stand portion 23 is formed in the inner block 21. The bottom of the central cavity 24 is closed by a lid member 27. A gas inlet hole 25 is formed in the side surface of the upper end portion of the central cavity 24 to communicate with the gas discharge gap 17, and a gas outlet hole 26 is formed in the side surface of the central cavity 24 near its bottom and connected to the tip of a gas discharge nozzle 29 formed in the side surface of the base portion 22. The gas discharge gap 17, the gas inlet hole 25, the central cavity 24, and the gas outlet hole 26 form the gas discharge passage 7. In this case, a thermocouple 60b is inserted from the bottom of the inner block 21 to the vicinity of the top surface of the stand portion 23 so as to measure the temperature in the vicinity of the top surface of the stand portion 23 and thereby detect the temperature in the vaporization space 5.
In the case where only the heater 50a in the outer block 11 can maintain the vaporization space 5 at a temperature suitable for vaporization, the heater 50b in the inner block 21 is omitted. On the other hand, in the case where only the heater 50b in the inner block 21 can maintain the vaporization space 5 at a temperature suitable for vaporization, the heater 50a in the outer block 11 is omitted.
The porous member 30 is a thick disk-shaped member. Examples of the material suitable for the porous member 30 include sintered particles 31 of alloys such as highly corrosion-resistant stainless steels, Hastelloys, and Permalloys, sintered particles 31 of other metals such as copper, aluminum, and iron, for certain types of the liquid material L, and even sintered particles 31 of ceramics.
Pores (voids) 38 formed between the particles 31 of the porous member 30 communicate with each other (a so-called “open-cell” member), and numerous pores open to the surface of the porous member 30 (and further to the inner circumferential surface and bottom surface of a recess 34 to be described later). The thickness of the porous member 30 is smaller than the height of the vaporization space 5 (i.e., the height from the stand portion 23 to the ceiling surface of the storage space 12). The maximum size of the porous member 30 is equal to the size of the top surface of the stand portion 23 to cover the entire top surface thereof. The size of the porous member 30 may be smaller than the size of the top surface of the stand portion 23 as long as the vaporization of the liquid material L penetrated into the porous member 30 is not inhibited.
Other examples of the material suitable for the porous member 30 include a sintered metal mesh laminate 32 having high corrosion resistance and chemical resistance, as shown in
In a modification of the shape of the porous member 30, a recess 34 is formed in the center of the top surface of the porous member 30, as shown in
The top porous plate 30a is more likely to clog than the lower porous plate(s) 30b. Therefore, only the top porous plate 30a can be replaced by a new one, if it clogs.
The supply tube 40 is a capillary tube leading from a device like, for example, a liquid flow control valve 9, and is configured to supply the liquid material L from above the vaporizer 1 to the downstream vaporizer 1 at a predetermined mass flow rate. In
This supply tube 40 may be a single capillary tube in its entirety, or may be provided with micro through-holes 45 on the side wall of its tip, as shown in
The supply tube 40 is disposed in such a manner that the outlet 41 of the supply tube 40 at its tip is in contact with the surface of the porous member 30, as shown in
The separation distance H is usually about 0.5 mm to 1.0 mm. The maximum separation distance H is a distance from the outlet 41 to the bottom of a droplet of the liquid material L formed and suspended at the outlet 41. If the separation distance H is too large, the droplet of the liquid material L suspended at the outlet of the supply tube 40 detaches from the outlet 41, transforms into a spherical shape, and then hits the top surface of the porous member 30. Upon collision between the droplet and the top surface, bumping occurs and the pressure in the vaporization space 5 fluctuates greatly. The maximum separation distance H is determined to prevent this pressure fluctuations. More specifically, when the separation distance H is equal to the length of the droplet of the liquid material L, the droplet of the liquid material L suspended at the outlet 41 comes into contact with the surface of the porous member 30 before it detaches from the outlet 41, and upon contact with the porous member 30, the liquid material L penetrates into the porous member 30. Thus, bumping as described above is prevented.
Next, an operation example of the vaporizer 1 of the present invention will be described. When the heater 50a for the outer block 11 of the vaporizer 1 is turned on, the outer block 11 is heated to a predetermined temperature. The temperature is controlled by the thermocouple 60a mounted in the outer block 11 by feedback control. Thereby, the interior of the vaporization space 5 is maintained at a temperature suitable for vaporization and thus the porous member 30 is also maintained at that temperature.
In the case of
In this state, when the liquid material L is supplied through the supply tube 40 toward the porous member 30 at a mass flow rate controlled by the liquid flow control valve 9, the liquid material L that has reached the outlet 41 of the supply tube 40 does not vaporize but instantaneously penetrates into the pores 38 of the porous member 30 through its surface and rapidly spreads around in the porous member 30.
The porous member 30 is fixed to the top surface of the stand portion 23 of the inner block 21 and maintained at a predetermined temperature, as described above. Therefore, the liquid material L that has penetrated into the porous member 30 is heated in the porous member 30. The heated liquid material L is vaporized successively and steadily, without any bumping, through the pores 38 exposed to the surface of the porous member 30 around the supply tube 40. As a result, the pressure fluctuations in the vaporization space 5 are reduced to a very low level and stable vaporization is performed. The source gas G thus vaporized is delivered to the next step through the gas discharge passage 7 composed of the gas discharge gap 17 between the outer block 11 and the inner block 21, the gas inlet hole 25, the central cavity 24, and the gas outlet hole 26. Thus, high-precision deposition can be achieved.
In the above case, only the heater 50a of the outer block 11 is used. However, in the case where the amount of the liquid material L to be supplied is larger than that the heater 50a can heat or the liquid material L is less likely to vaporize due to its properties, the heater 50b of the inner block 21 is additionally used. Since the porous member 30 is fixed to the top surface of the stand portion 23 of the inner block 21, when the heater 50b of the inner block 21 is turned on, its heat is transferred to the porous member 30.
It should be understood that since the heaters 50a and 50b are thermally controlled by the thermocouples 60a and 60b, both the heaters 50a and 50b may be used in combination even in the above first case.
When vaporization continues for a long time, even if the liquid material L is less likely to produce a reaction product, the reaction product may be deposited at the outlet 41 of the supply tube 40 and eventually clog the outlet 41. In this case, the liquid material L is forced out of the supply tube 40 through the micro through-holes 45 on the side surface near the outlet 41, steadily flows down the outer surface of the supply tube 40, and penetrates into the porous member 30 upon contact therewith. Thus, with the use of the supply tube provided with the micro through-holes 45 near its outlet, even if the outlet 41 is clogged, vaporization operation can be continued without interruption.
The notch 48 shown in
In contrast,
In this case, even if the reaction product is gradually deposited in the pores 38 of the porous member 30 and on the porous member 30 up to the level of the outlet 41 of the supply tube 40, a space large enough for the liquid material L to flow through is provided between the deposit 70 and the outlet 41 of the supply tube 40, and therefore vaporization operation can be continued without interruption. The flowing liquid material L is absorbed into the porous member 30 before being vaporized and then vaporized from the porous member 30 in a steady manner, as in the case of the supply tube 40 located at no distance from the porous member 30.
Here, the separation distance H between the outlet of the supply tube 40 and the porous member 30 is described. When the separation distance H between the outlet of the supply tube 40 and the porous member 30 is too large, the liquid material L flowing from the outlet 41 is pulled into a spherical shape by surface tension and the resulting droplets drop onto the surface of the porous member 30. Upon hitting the surface of the porous member 30, the droplets are vaporized instantaneously and cause bumping, resulting in great pressure fluctuations in the vaporization space 5. Therefore, the separation distance H is an important factor in achieving the steady vaporization operation.
The separation distance H is usually determined in a range of 0.5 mm to 1.0 mm. The separation distance H is at most the distance from the outlet 41 to the bottom of the droplet suspended at the outlet 41. The value of this distance depends on the surface tension of the liquid material L, but a value less than the value of this distance can be selected. A value in the above-mentioned range is selected in practice. In this sense, the values mentioned above are significant in the present invention.
In this case, when the porous plate 30a as the top layer (or the porous plates 30a as the upper layers including the top layer) is sparser than the porous plate(s) 30b as the lower layer(s), the liquid material L penetrates into the porous plate 30a as the top layer (or the porous plates 30a as the upper layers including the top layer) at a higher rate. As a result, the occurrence of bumping can be further reduced.
In an example of this case, when the porous member 30 is composed of two or more porous plates 30a and 30b, the porous plate(s) 30a provided with a through-hole 34a serving as the recess 34 and the flat porous plate 30b as the top layer of the flat porous plates 30b without a through-hole 34a serving as the recess 34 may be made of a sparse material as described above while the lower flat porous plate(s) 30b may be made of a denser material as described above. In this example, the liquid material L penetrates into the sparser layers at a higher rate, and the occurrence of bumping can be further reduced, as in the case described above.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-138837 | Jul 2018 | JP | national |
| 2019-076185 | Apr 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/016959 | 4/22/2019 | WO | 00 |
