Vaporizer apparatus

Abstract: Heat can be supplied effectively to a porous member of a vaporizer apparatus so that the vaporizing operation can be carried out smoothly and efficiently. The vaporizer apparatus comprises a vaporizer section (B) having a porous member (9) including a liquid receiving surface and a vapor discharge surface; a feed supply section (A) for supplying a liquid feed material to the liquid receiving surface of the porous member; a heating medium passage (P1) in thermal contact with the porous member; and a heating medium supply system for flowing a heating medium (L2) of a temperature higher than a vaporization temperature of the liquid feed material, through the heating medium passage.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates in general to a vaporizer apparatus which is used, for example, in chemical vapor deposition of thin films from liquid feed material, and relates in particular to a liquid feed vaporizer apparatus for vaporizing such high dielectric thin film forming materials as barium/strontium titanate. Description of the Related Art In recent years, significant progress has been made in the field of high density integration of semiconductor electronic circuits in anticipation of achieving giga-bit-capacity DRAMs to overtake the currently available mega-bit-capacity DRAMs. For obtaining the high capacity dielectric thin films necessary to produce such DRAM circuits, the currently used dielectric materials such as silicon oxide and silicon nitride films having dielectric constant less than 10 are to be superseded by metallic thin film materials such as tantrum pentaoxide (Ta 2 O 5 ) having a dielectric constant in the range of 20, barium titanium oxide (BaTiO 3 ) or strontium titanium oxide (SrTiO3) having a dielectric constant in the range of 300, or barium strontium titanate which is an admixture of the afore-mentioned compounds. As a method of growing thin films from such materials, chemical vapor deposition (CVD) is being favored. In this case, it is necessary that, in the event, a gas-phase feed material be supplied steadily on a substrate material held in a reaction chamber. In order to stabilize the vaporization characteristics, the feed gas is derived by heating for vaporization a liquid source produced by dissolving materials such as Ba(DPM) 2 or Sr(DPM) 2 , which are solid at normal temperature, in some organic solvent such as THF. It is extremely difficult to stably vaporize feed materials of highly dielectric materials described above because: (1) vaporization and decomposition temperatures are close together; (2) a difference exists in the vaporization temperatures between the film material and the organic solvent; and (3) the vapor pressures are all very low. For example, for a liquid feed made by dissolving Ba(DPM) 2 or Sr(DPM) 2 in THF, the liquid phase of the solvent ranges in the region marked as "a" in Figure 6, and the liquid or solid phase of the material ranges in "a+c". Therefore, when raising the temperature of the liquid through the region marked "c" to vaporize the liquid feed which is in "a", there is a danger that only the solvent is evaporated, causing the film material to precipitate out and resulting in plugging of the passage or degradation in the feed quality due to compositional changes. Therefore it is generally considered that, when vaporizing a liquid feed material, it is necessary to rapidly heat the liquid to bring it quickly to the high temperature region. A known type of vaporizer apparatus utilizes a technology of first preparing atomized mist with the use of ejector nozzle or ultrasonic vibrator, and then heating the mist in a high temperature region to produce a vapor. However, in the conventional type of vaporizer apparatus presented above, the porous member loses heat due to the heat of vaporization of the liquid feed dispersed therein, and if a local low temperature zone should be created, it may cause a clogging of the porous member. Therefore, it is necessary that a fairly large amount of excess heat be supplied to the porous member. In the conventional vaporizer apparatus, the heat to the porous member is supplied externally, and the center of the porous member is heated primarily by the heat conducted through the porous member itself. Therefore, the supply of heat to the interior of the porous member tends to be insufficient, and consequently the vaporizing efficiency is lowered due to such problems as clogging in the interior of the porous member. For the type of vaporizing process in which only the lower temperature limit is important, the exterior temperature of the porous member is heated to a sufficiently high temperature so that the interior region of the porous member can reach the required temperature. However, for certain types of liquid feed material, excessive raising of the external temperature may cause a possible decomposition or degradation of the liquid or evaporated feed material. For such materials, the present method is inapplicable because the required range between the upper and lower temperature limits is too narrow. Further, attention is drawn to US 5,224,202 which discloses a heated evaporator housing having at its inlet an ultrasonic atomizer for reducing monomers to small droplets and a permeable porous body completely occupying a cross section of the housing between the inlet and the outlet. US 5,204,314 describes a process and apparatus for delivering an involatile reagent in gaseous form, wherein an involatile reagent source liquid is flash vaporized on a vaporization matrix structure at elevated temperature. A carrier gas may be flowed past the flash vaporization matrix structure to yield a carrier gas mixture containing the flash vaporized source reagent. The matrix structure preferably has a high surface-to-volume ratio, and may suitably comprise a foraminous matrix element such as screen mesh onto which the reagent source liquid is distributed for flash vaporization. SUMMARY OF THE INVENTION According to the present invention a vaporizer apparatus is provided as set forth in claim 1. Preferred embodiments are disclosed in the dependent claims. The object of this invention is to resolve the problem outlined above so that heat can be supplied effectively to a porous member of a vaporizer apparatus so that the vaporizing operation can be carried out smoothly and efficiently. The object has been achieved in a vaporizer apparatus comprising: a vaporizer section having a porous member including a liquid receiving surface and a vapor discharge surface; a feed supply section for supplying a liquid feed material to the liquid receiving surface of the porous member; a heating medium passage in thermal contact with the porous member; and a heating medium supply system for flowing a heating medium of a temperature higher than a vaporization temperature of the liquid feed material, through the heating medium passage. Accordingly, the porous member is heated directly by the heat sufficiently provided by the heating medium flowing through the heating medium passage so that the vaporization process is efficiently conducted by utilizing the whole section of the porous member. The heating medium passage is usually defined by a suitable casing of a proper material and a dimension such as diameter or thickness so as to construct an independent and closed system against the material passage including the porous member. The heat of vaporization is transferred by conduction from the heating medium through the casing to the porous member. The heating medium is usually selected from high heat capacity materials such as oil so that temperature variation is minimized and stable temperature control can be achieved. When a heating medium of high heat capacity is used, there is no need to circulate the heating medium at a high flow rate, if the bore of the heating medium passage is of a sufficient size. It is evident that in addition to the heating medium passage, some external source of heat can be utilized to provide heat to the porous member. The heating medium passage may include an outer heating medium passage which surrounds a side surface of the porous member and/or an inner heating medium passage which passes through the porous member. The inner heating medium passage may include a transverse path which extends in a direction to cross an axis of the porous member and/or a longitudinal passage which extends in a direction parallel to an axis of the porous member and/or a stagnant section which enlarges in a central region of the porous member. The heating medium passage may be provided so as to surround an edge section of at least one of the liquid receiving section or the vapor discharge section and/or comprised by a jacket device constructed as split members so as to clamp an edge section of the porous member. A second outer heating medium passage may be provided to surround a central part of at least one of the liquid receiving surface or the vapor discharge surface. The porous member may be formed in a columnar shape or a disc shape or may include a cross section which enlarges towards a downstream direction. The speed of the vapor produced within the porous member from the feed fluid is determined by the cross sectional area of the fluid passage, and if the velocity is too high, there is a pressure increase at the fluid inlet side. By increasing the size of the downstream region of the porous member, pressure loss can be maintained below a suitable value. The feed material supply section may be thermally separated from the vaporizer section and is provided with a temperature maintaining device for maintaining a temperature of the liquid feed supply route to a temperature not more than a vaporization temperature of the liquid feed material. It becomes possible to prevent heat transfer from the vaporizer section at a high temperature to the feed material supply route, and furthermore, the temperature maintaining device is able to prevent the heat effect through radiation for example from the vaporizer section. The temperature should be selected to be the lowest temperature of the various temperature elements for the liquid feed material such as vaporization and decomposition temperatures of the components of the liquid feed material. Accordingly, the composition of the feed material can be kept stable until just prior to its entry into the vaporization region. The feed material supply section may be provided with a pressure adjustment section disposed immediately upstream of the vaporizer section for adjusting a pressure of the liquid feed material. The pressure adjustment section may comprise pressure valves, orifice or spring-loaded one-way valve for enabling to adjust the flow pressure. Accordingly, it becomes possible to maintain the pressure of the liquid feed material to immediately prior to its entering the vaporizer section so as to prevent separation of the most volatile components from the liquid feed material. The apparatus may be provided with a temperature maintaining device for heating or cooling the pressure adjustment section. The pressure adjustment section has usually a constriction and is particularly vulnerable to clogging. By controlling the temperature in this vulnerable section, it becomes possible to prevent clogging of the section. The temperature maintaining device may perform heating or cooling of the pressure adjustment section by way of a liquid heating medium. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross sectional view of a first embodiment of the vaporizer apparatus of this invention. Figure 2(a) is a cross-sectional view of the porous member of Figure 1 along the line II; Figure 2(b) is a cross-sectional view of the porous member of another embodiment along the line II. Figure 3 is a cross sectional view of another embodiment of the vaporizer apparatus according to the invention. Figure 4 is a cross sectional view of the main sections of the embodiment shown in Figure 3. Figure 5 is a cross sectional view of the main sections of another embodiment of the vaporizer apparatus according to the invention. Figure 6 is a graph showing the properties of a liquid feed material. DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the invention will be explained with reference to the drawings. Figures 1 and 2 show a first embodiment of this invention comprising, sequentially from top, a liquid feed supply section A; a vaporizer section B for contacting and heating the liquid feed material to be vaporized; and a discharge pipe C for discharging the feed gas vaporized by the vaporizer section B to a next processing station. The liquid supply section A comprises a liquid feed supply pipe 1 which extends through the center region vertically, and the top section of the supply pipe is connected to a feed pipe while the bottom section opens to an upper section of the vaporizer section B. In the vicinity of the bottom section, there is a pressure adjustment valve 2 for releasing the feed liquid when the upstream pressure is higher than a given pressure, and a feed material discharge opening (nozzle) 3 further downstream. A thermal insulation jacket 4 is provided to maintain the temperature of the feed supply pipe 1 including the pressure adjustment valve 2. There are also cooling provisions having an inlet pipe 5 and an outlet pipe 6 for circulating a cooling medium L 1 such as water. In this embodiment, the thermal insulation jacket 4 is separable vertically by way of a flange 7 for facilitating maintenance work such as exchanging of the pressure adjustment valve 2. The inlet pipe 5 of the feed supply section A is extended to near the bottom section of the jacket 4 so as to provide smooth circulation of the cooling medium L 1 therein. The vaporizer section B is provided with a porous member 9 inside a cylindrical casing 8 which is surrounded by a jacket heater 10 for defining an outer heating medium passage P 1 around the casing 8. The jacket heater 10 is provide with an inlet port 11 and an outlet port 12 for flowing the heating medium L 2 therethrough. It is desirable to use a liquid heating medium L 2 having a large heat capacity, and the usual practice is to use a suitable oil. In this embodiment, the jacket heater 10 extends to a thermal insulation jacket 4 surrounding the feed supply pipe 1 located above. These elements, together with a ceiling plate 13, define a space 14 which tightly surrounds the nozzle 3 at the lower end of the feed supply pipe 1. The ceiling plate 13 is provided with a carrier gas inlet for introducing carrier gas such as Ar into the space 14 for facilitating the vaporization or the substitution of the liquid feed. The lower tip end of the nozzle 3 is placed to maintain a predetermined narrow gap between the upper surface (liquid receiving surface) 9a, so that even a small amount of liquid feed is smoothly delivered to the porous member 9. The porous member 9 is made of a thermally conductive material and is formed into a porous member having a specific void content so as to generate a suitable liquid and gas permeability. For example, the porous member may be made of a solid material in the form of powder, particulate, wire, aciculate, fiber or other irregular shaped pieces which are packed into a gas permeable container, or it may also be made by pressing or heating the solid material into a porous member or mesh form. It is desirable that the diameter of the void in the porous member be in a range of several tens of micrometers to 100 µm. It is also permissible to make a porous member from a non-porous material member by forming fine slits or holes therein. The solid material is usually a metal, but other materials having suitable thermal resistance and conductivity such as ceramic and plastic materials may also be used. As illustrated in Figure 2(a), there is a horizontal through hole 16 in the vertically middle section of the porous member 9, and at a position corresponding with the through hole 16, a through pipe 17 is provided on the cylindrical casing 8 for defining an inner heating medium passage P 2 . The lower surface (vapor discharge surface) 9b of the porous member 9 opens to the discharge pipe C connected to the lower section of the vaporizer section B, which is also provided with jacket 18 defining another outer heating medium passage P 3 to maintain the temperature of the porous member 9 and the exhausted feed material gas above its vaporization temperature. The feed material supply pipe 1 is connected to a feed material supply source having a flow rate controller and a pump to supply the feed at a given rate and pressure. The discharge pipe C is connected, for example, to a vacuum chamber for carrying out CVD process, consequently, the internal pressure is fairly low. The thermal insulation jacket 4 of the feed material supply pipe 1 is maintained at a temperature below the vaporization temperature of the liquid feed material by circulating coolant such as cold water therein, and the outer and inner heating medium passages P 1 , P 2 , P 3 within the jackets 10, 18 are maintained above the vaporization temperature by circulating hot oil. When the pressure of the liquid feed material increases beyond a certain value set on the pressure adjustment valve 2 by the operation of the pump provided in the feed material supply source, the pressure adjustment valve 2 opens, and the liquid feed material is supplied to the upper surface of the vaporizer section B. The supplied feed liquid contacts the upper surface 9a of the porous member 9 to be absorbed into the bulk of the porous member 9 by such effects generated by the lower pressure in the lower section and capillary actions, and is vaporized by gaining the heat of vaporization while flowing through the porous member 9. In this embodiment, the liquid feed material transfers instantly from the supply section A, which is at a low temperature, to the vaporizer section B which is at a high temperature, and therefore, temperature transition region is virtually eliminated. It follows then that such undesirable events as separation of the solvent from the feed material and the precipitation of constituents from the feed material are effectively prevented. In this embodiment, because the heated medium passage 17 is disposed so as to pass through the center section of the porous member 9, the heat is supplied effectively to the interior of the porous member 9 which has experienced a lowering of temperature due to the absorption of the heat of vaporization by the infiltrating liquid feed material. Thus even in the interior of the porous member 9, non-uniformity in temperature distribution is kept low. Therefore, the vaporization efficiency is improved by utilizing the entire region of the porous member 9. It is obvious that a plurality of heating medium passages 17 passing through the porous member 9 may be provided as illustrated in Figure 2(b). Another embodiment is shown in Figure 3, in which the porous member 19 is tapered so as to be progressively wider towards the bottom section. The larger downstream radius is meant to prevent an increase in the pressure loss at the inlet side caused by an increasing downstream vapor velocity as the vaporization process progresses. In this case, to produce a temperature uniformity between the interior and exterior sections in the enlarged section, an inner heating medium passage P 4 in the lower center section of the porous member 19 is provided. In this embodiment, the inner heating medium passage P 4 is formed to have a vertical path 20 and transverse paths 21, 22 provided at the upstream and downstream thereof. However, as shown in Figure 4, it is permissible to provide an inlet passage P 5 having transverse paths 21, 22 at the same height. In such a case, the vertical path 20a is formed to have wider sectional areas than the transverse paths 21, 22, and heating medium circulates by convection within the vertical path 20a. Figure 5 shows another embodiment of the present invention, in which the porous member 23 is a disc in comparison to the pervious embodiments. This porous member 23 does not have any inner heating medium passage, instead, a split jacket members 24a, 24b are in contact with the side surfaces as well as the outer peripheries of the top and bottom surfaces 23a, 23b of the porous member 23 for constituting a first outer heating medium passage P 6 . The jacket members 24a, 24b are constructed so that the ring-shaped depression sections 25a, 25b thereof receive and clamp the edge section of the porous member 23. Another jacket device 26, constituting a second outer heating medium passage P 7 , protrudes out in the center of the discharge pipe C so that its top surface contacts the center section of the vapor discharge surface 23b. In the vaporizer of such a construction, the liquid feed material is supplied from the nozzle 3 to the center of the liquid receiving surface 23a of the porous member 23, and flows radially in the interior of the porous member 23, due to the effects of negative pressure below and capillary actions, and vaporizes on the way by gaining the heat of vaporization. The vaporized gas flows from the annular vapor discharge surface 23b into the discharge pipe C to be supplied to the next step in the process. Because the porous member 23 is a disc, it can be heated sufficiently by heat supplied from the edge section and the bottom surfaces so that stable vaporization can be achieved without plugging. The shape is simple and the manufacturing cost is low. Also, in this embodiment, because the external jacket devices 24a, 24b are split into vertical members to fix the porous member 23 thereberween, they can easily be detached from the porous member 23 for cleaning and replacement thereof. As explained above, according to this invention, the porous member is heated from its core by the heating medium flowing in the passage so as to promote vaporization from the interior of the porous member, thereby producing highly efficient vaporizer action by enabling to utilize the whole area of the porous member. Furthermore, by providing a feed material supply section separate from the vaporizer section and providing a temperature maintaining device for maintaining a temperature of the feed material supply route to a given temperature, it is possible to prevent the conduction of heat from the vaporizer section at a high temperature to the feed material supply section at a lower temperature, thereby enabling to produce efficient operation of the vaporizer apparatus. Further, by providing a pressure adjustment valve directly upstream of the vaporizer section to adjust the internal pressure of the liquid feed material, it is possible to prevent degradation of the liquid feed before reaching the vaporizer section. The overall result of such improvement is that a liquid feed material having a complex set of properties may be processed effectively and efficiently in the vaporizer apparatus of this invention.

Claims: A vaporizer apparatus comprising: a vaporizer section (B) having a three dimensional porous member (9; 19; 23) including a liquid receiving surface (9a; 23a) and a vapor discharge surface (9b; 23b); a feed supply section (A) for supplying a liquid feed material to said liquid receiving surface (9a; 23a) of said porous member (9; 19; 23); a heating medium passage (P 1 , P 2 ; P 1 , P 4 ; P 5 ; P 6 , P 7 ) in thermal contact with said porous member (9; 19; 23); and a heating medium supply system (10, 11, 12; 24a, 24b, 26, 11, 12, 11a, 12a) for flowing a heating medium of a temperature higher than a vaporization temperature of said liquid feed material, through said heating medium passage (P 1 , P 2 ; P 1 , P 4 ; P 6 , P 7 ). An apparatus according to claim 1, wherein said heating medium passage (P 1 , P 2 ; P 1 , P 4 ; P 5 ; P 6 , P 7 ) includes an outer heating medium passage (P 1 ; P 3 ; P 6 ) which surrounds a side surface of said porous member (9; 19; 23). An apparatus according to claim 1, wherein said heating medium passage (P 1 , P 2 , P 3 ; P 4 ; P 5 , P 6 , P 7 ) includes an inner heating medium passage (P 1 , P 4 ; P 5 ; P 7 ) which passes through said porous member (9, 19). An apparatus according to claim 3, wherein said inner heating medium passage (P 2 ) includes a transverse path (17) which extends in a direction to cross an axis of said porous member (9; 19). An apparatus according to claim 3, wherein said inner heating medium passage (P 4 ) includes a longitudinal passage (20) which extends in a direction parallel to a vertical axis of said porous member (19). An apparatus according to claim 3, wherein said porous member (19) includes a central region said inner heating medium passage (P 5 ) includes a stagnant section (20a) which enlarges in a central region of said porous member (19). An apparatus according to claim 1, wherein said heating medium passage (P 6 ) is provided so as to surround an edge section defined by a periphery of at least one of said liquid receiving section (23a) or said vapor discharge section (23b). An apparatus according to claim 2, wherein said outer heating medium passage (P 6 ) is comprised by a jacket device constructed as split members (24a, 24b) so as to clamp an edge section defined by a periphery of at least one of said liquid receiving section (23a) or said vapor discharge section (23b) of said porous member (23). An apparatus according to claim 2, wherein said apparatus is provided with a second outer heating medium passage (P 7 ) to surround a central part of at least one of said liquid receiving surface (23a) or said vapor discharge surface (23b). An apparatus according to claim 1, wherein said porous member (9) is formed in a columnar shape. An apparatus according to claim 1, wherein said porous member (23) is formed in a disc shape. An apparatus according to claim 1, wherein said porous member (19) includes a cross section which enlarges towards a downstream direction. An apparatus according to claim 1, further comprising a carrier gas supply passage (15) for supplying a carrier gas towards said liquid receiving surface (9a, 23a). An apparatus according to claim 1, wherein said feed material supply section (A) is thermally separated from said vaporizer section (B), and includes a temperature regulation device (4, 5, 6) to maintain said heating medium passage at a temperature not exceeding a vaporization temperature of said liquid feed material. An apparatus according to claim 1, wherein said feed material supply passage (1) includes a pressure regulation section (2) for adjusting a pressure of said liquid feed material, disposed adjacently upstream of said vaporizer section (B). An apparatus according to claim 15, wherein said pressure regulation section (2) includes a temperature regulation device (4, 5, 6) to heat or cool said pressure regulation section (2). An apparatus according to claim 16, wherein said temperature regulation device (4, 5, 6) comprises a thermal transfer medium (L 1 ) of a fluid nature for heating or cooling. . An apparatus according to claim 16, wherein said temperature regulation device (4, 5, 6) maintains said pressure regulation section (2) at a temperature not exceeding a vaporization temperature of liquid feed material.

Inventors: FUKUNAGA YUKIO, HONGO AKIHISA, HORIE KUNIAKI, OGURE NAOAKI, FUKUNAGA, YUKIO, HONGO, AKIHISA, HORIE, KUNIAKI, OGURE, NAOAKI
Applicants: EBARA CORP, EBARA CORPORATION
Application year: 1997
Main classification: C23C16
IPC codes: C23C16, B01D1