Abstract:
A trap apparatus is optimum for trapping a material gas discharged from a vapor deposition apparatus for depositing in a vapor phase thin films of high-dielectric or ferroelectric such as barium/strontium titanates on substrates. The trap apparatus is disposed downstream of a vacuum process chamber. The vacuum process chamber is for processing a substrate. The trap apparatus is for trapping a component having a low vapor pressure contained in a gas discharged from the vacuum process chamber. The trap apparatus includes a trap container for introducing the gas discharged from the vacuum process chamber, and a cooling device provided in the trap container for cooling the gas to a temperature equal to or lower than a condensing temperature of a gas component which is contained in the gas and easily liquidized.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a trap apparatus, and more particularly to a trap apparatus optimum for trapping a material gas discharged from a vapor deposition apparatus for depositing in a vapor phase thin films of high-dielectric or ferroelectric such as barium/strontium titanates on substrates. 
     2. Description of the Related Art 
     Recently, in the semiconductor manufacturing industry, the integration of integrated circuits has been improved remarkably, and the research and development activities of DRAM are being intensively carried out in anticipation of gigabit order DRAMs which will replace current megabit order DRAMs. The capacitor element having a large capacity per unit area is needed to produce such DRAMs. As a dielectric thin-film material for producing elements having such a large capacity per unit area, in place of silicon oxide or silicon nitride having dielectric constant less than 10, a metallic oxide film material such as tantalum pentaoxide (Ta 2 O 5 ) having dieelectric constant of approximately 20, or barium titanate (BaTiO 3 ) or strontium titanate (SrTiO 3 ) or barium strontium titanate having dielectric constant of approximately 300 is considered to be a promising thin-film material. Further, a ferroelectric material having a higher dielectric constant is also considered to be a promising thin-film material. 
     In addition to the above, as a wiring material, copper which has a value of resistance lower than aluminum and a superior resistance against electromigration is considered to be a promising material. As a material for gate insulating film, BiVO, Bi 4 Ti 4 O 12 , YMnO 3 , ZnO, ZnS, and CdS are considered to be a promising material. As an electrode material having a perofskite structure, SrRuO 3 , BaRuO 3 , IrO, and CaRuO 3  are considered to be a promising material. As a material for a barrier layer or a buffer layer, MgO, Y 2 O 3 , YSZ, and TaN are considered to be a promising material. As a superconductivity material, La—Ba—Cu—O, La—Sr—Cu—O, Y—Ba—Cu—O, Bi—Sr—Ca—Cu—O, Tl—Ba—Ca—Cu—O, and Hg—Ba—Ca—Cu—O are considered to be a promising material. 
     As a process for depositing thin films of such material, a chemical vapor deposition (CVD) process is expected to have a good prospect. 
     FIG. 6 shows a chemical vapor deposition apparatus for depositing thin films of high-dielectric or ferroelectric such as barium/strontium titanates. The vapor deposition apparatus comprises a vaporizer  10  for vaporizing a liquid material, a hermetically sealable reaction chamber  14  disposed downstream of the vaporizer  10  and connected to the vaporizer  10  through a material gas passage  12 , and a vacuum pump  18  disposed downstream of the reaction chamber  14  and provided in an evacuation passage  16 . An oxidizer gas pipe  20  for supplying an oxidizer gas such as oxygen is connected to the reaction chamber  14 . 
     In the vapor deposition apparatus having the above structure, a substrate W is placed on a stage  22  for holding and heating the substrate W, and a mixture of material gas and oxidizer gas is ejected over the substrate W from nozzles  26  of a gas supply head  24  while keeping the substrate W at a predetermined temperature, thereby depositing a thin film on a surface of the substrate W. In this case, it is necessary to supply the material gas stably to the substrate W in the reaction chamber  14 . The material gas is produced by liquidizing Ba(DPM) 2 , Sr(DPM) 2  or the like which is solid at room temperature, mixing the liquidized substance with organic solvent such as tetrahydrofuran (THF), and vaporizing the obtained mixture by the vaporizer  10 . 
     Gases discharged from the reaction chamber  14  contain unconsumed material and reaction by-product having a high sublimation temperature, and hence the unconsumed material and the reaction by-product are solidified during pressure rise and deposited on the interior of the vacuum pump  18 , resulting in a malfunction of the vacuum pump  18 . In order to prevent this deposition on the interior of the vacuum pump, as shown in FIG. 6, a trap apparatus  30  is provided at the upstream side of the vacuum pump  18  in the evacuation passage  16  to remove components, in the discharged gases, having a high sublimation temperature and a low vapor pressure. The pipe interconnecting the reaction chamber  14  and the trap apparatus  30  is provided with a temperature adjusting device  28  comprising a mantle heater or the like in the same manner as the material gas supply passage  12 . 
     Conventionally, as shown in FIG. 7, the trap apparatus  30  comprises a trap unit  34  having a spiral baffle plate  32  for forming a spiral fluid passage, a trap container  36  for housing the trap unit  34 , an inlet pipe  38  connected to the upper end of the trap container  36 , and an outlet pipe  40  connected to the bottom of the trap container  36 . The trap apparatus  30  is connected to the evacuation passage  16  by quick couplings  42   a  and  42   b . The trap apparatus  30  has a cooling medium flow passage  44 , at the central part thereof, through which a cooling medium cooled to a temperature lower than the condensing temperature of the components, to be trapped, having a low vapor pressure flows. Thus, the components having a low vapor pressure in the discharged gases which have entered the trap container  36  through the inlet pipe  38  are trapped and removed by the trap unit  34  while the discharged gases flow along the baffle plate  32 , and hence only the components having a high vapor pressure are led to the vacuum pump  18  through the outlet pipe  40  and the evacuation passage  16  (see FIG.  6 ). 
     However, in this trap apparatus, the components having a low vapor pressure such as the unconsumed material are condensed to become powdery substances in the trap container, and the produced powdery substances are gradually deposited on the surface of the trap unit. These deposited solid substances, if counterflow occurs, or the supply amount from the upstream side is abruptly decreased or is stopped under change of conditions in the evacuation system, form particles which will flow into the reaction chamber and deposit on the substrate, resulting in deteriorating quality of a produced film. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a trap apparatus which can reliably trap components having a low vapor pressure in gases discharged from a processing apparatus such as a chemical vapor deposition apparatus and prevent the trapped components from being scattered around. 
     According to a first aspect of the present invention, there is provided a trap apparatus disposed downstream of a vacuum process chamber. The vacuum process chamber is for processing a substrate. The trap apparatus is for trapping a component having a low vapor pressure contained in a gas discharged from the vacuum process chamber. The trap apparatus comprises a trap container for introducing the gas discharged from the vacuum process chamber, and a cooling device provided in the trap container for cooling the gas to a temperature equal to or lower than a condensing temperature of a gas component which is contained in the gas and easily liquidized. 
     According to the present invention, the discharged gas introduced into the trap container is cooled by the cooling device, and a gas such as a solvent gas (gas generated from solvent by vaporization), which is contained in the material gas and easily liquidized, is condensed in the trap container, and thus the condensed substances are contained in deposited substances in the trap container. Therefore, the deposited substances in the trap container are moistened, and hence adhesion between the deposited substances and the inner surface of the trap container and cohesion of the deposited substances are heightened. Thus, the deposited substances are prevented from being removed from the inner surface of the trap container and the like, thus preventing generation of particles. 
     According to a second aspect of the present invention, there is provided a trap apparatus disposed downstream of a vacuum process chamber. The vacuum process chamber is for processing a substrate. The trap apparatus is for trapping a component having a low vapor pressure contained in a gas discharged from the vacuum process chamber. The trap apparatus comprises a trap container for introducing the gas discharged from the vacuum process chamber, and a solvent supply device for supplying a solvent, which is hard to be volatilized, into the trap container. 
     According to the present invention, by supplying the solvent to the deposited substances in the trap container, the deposited substances in the trap container are moistened, and hence adhesion between the deposited substances and the inner surface of the trap container and cohesion of the deposited substances are heightened. Thus, the deposited substances are prevented from being removed from the inner surface of the trap container and the like, thus preventing generation of particles. As the solvent which is hard to be volatilized, such material as to be liquid under vacuum in the trap container and as to keep a desired degree of vacuum in the processing chamber is selected. By spraying the solvent or scattering the solvent in the trap container, absorption reaction between gas and liquid may be accelerated. 
     According to a third aspect of the present invention, there is provided a trap apparatus wherein the solvent which is hard to be volatilized is selected from a solvent which is used as a solvent of material including butyl acetate, tetrahydrofrane, or lutidine, a solvent which is used as adduct of material including tetraglymes, toluenes, or tetraenes, or a solvent which is used as a ligand of material including dipivaloylmethane. 
     According to the present invention, a component having a low vapor pressure in the discharged gas introduced into the trap container is trapped in the liquid solvent stored in the solvent storage, and hence scattering of the trapped substances can be prevented. 
     In a preferred aspect, the solvent which is hard to be volatilized is selected from a solvent which is used as a solvent of material including butyl acetate, tetrahydrofrane, or lutidine, a solvent which is used as adduct of material including tetraglymes, toluenes, or tetraenes, or a solvent which is used as a ligand of material including dipivaloylmethane. Thus, even if the solvent flows back to the reaction chamber, it does not affect adversely quality of the deposited film. 
     According to a fourth aspect of the present invention, there is provided a thin-film vapor deposition apparatus comprising: a vaporizer for vaporizing a liquid material; a reaction chamber disposed downstream of the vaporizer; a vacuum pump disposed downstream of the reaction chamber; and a trap apparatus provided in an evacuation passage extending from the reaction chamber to the vacuum chamber, the trap apparatus comprising: a trap container for introducing the gas discharged from the vacuum process chamber; and a cooling device provided in the trap container for cooling the gas to a temperature equal to or lower than a condensing temperature of a gas component which is contained in the gas and easily liquidized. 
     According to another aspect of the present invention, there is provided a thin-film vapor deposition apparatus comprising: a vaporizer for vaporizing a liquid material; a reaction chamber disposed downstream of the vaporizer; a vacuum pump disposed downstream of the reaction chamber; and a trap apparatus provided in an evacuation passage extending from the reaction chamber to the vacuum chamber, the trap apparatus comprising: a trap container for introducing the gas discharged from the vacuum process chamber; and a solvent supply device for supplying a solvent, which is hard to be volatilized, into the trap container. 
     According to still another aspect of the present invention, there is provided a thin-film vapor deposition apparatus comprising: a vaporizer for vaporizing a liquid material; a reaction chamber disposed downstream of the vaporizer; a vacuum pump disposed downstream of the reaction chamber; and a trap apparatus provided in an evacuation passage extending from the reaction chamber to the vacuum chamber, the trap apparatus comprising: a trap container for introducing the gas discharged from the vacuum process chamber; and a solvent storage provided in the trap container for storing a solvent, which is hard to be volatilized, in a liquid condition. 
     The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrates preferred embodiments of the present invention by way of example. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a trap apparatus according to a first embodiment of the present invention; 
     FIG. 2 is a schematic view of a trap apparatus according to a second embodiment of the present invention; 
     FIG. 3 is a schematic view of a trap apparatus according to a third embodiment of the present invention; 
     FIG. 4 is a schematic view of a trap apparatus according to a fourth embodiment of the present invention; 
     FIG. 5 is a schematic view of a trap apparatus according to a fifth embodiment of the present invention; 
     FIG. 6 is a schematic diagram of a thin-film vapor deposition apparatus to which the present invention is applied; and 
     FIG. 7 is a schematic view of a conventional trap apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Next, a trap apparatus according to the present invention will be described below with reference to the drawings. The trap apparatus according to the present invention is applied to the thin-film vapor deposition apparatus shown in FIG. 6, and will be described with reference to FIGS. 1 through 3. The components or elements shown in FIGS. 1 through 3 which are identical or similar to the components or elements in the conventional apparatus shown in FIG. 7 are designated using the same reference numerals. 
     FIG. 1 shows a trap apparatus according to a first embodiment of the present invention. The trap apparatus  30  in this embodiment comprises a trap container  36  having a cylindrical cup-shaped body for defining a trap chamber therein, an inlet pipe  38  connected to the side surface of the trap container  36 , and an outlet pipe  40  connected to the other side surface of the trap container  36 . A cooling device  50  is disposed in the trap container  36  to cool an interior atmosphere of the trap container  36 , and the upper open end of the trap container  36  is closed by a lid  52 . The cooling device  50  serves not only to solidify components having a low vapor pressure such as unreacted material gas but also to cool components which are relatively easily liquidized to a temperature so as to be condensed or lower. 
     The cooling device  50  uses liquid nitrogen in this embodiment, and has a vessel  54  for storing liquid nitrogen, a liquid nitrogen supply pipe  56  for supplying liquid nitrogen into the vessel  54 , and a discharge pipe  58 . The vessel  54  has a number of fins  60  on the outer surface thereof. In the cooling device  50 , the fins  60  are cooled to a temperature of approximately −176° C. corresponding to a boiling point of liquid nitrogen. As shown in FIG. 6, the trap apparatus  30  is provided in the evacuation passage  16  which interconnects the reaction chamber  14  and the vacuum pump  18 , and gases discharged from the reaction chamber  14  are introduced into the trap container  36 . 
     Next, the operation of the trap apparatus having the above structure will be described below. 
     The material gas supplied to the vapor deposition apparatus is produced by liquidizing Ba(DPM) 2 , Sr(DPM) 2  or the like which is solid at room temperature, adding an adduct for accelerating vaporization, mixing the liquidized substance with organic solvent, and vaporizing the obtained mixture. Therefore, gases discharged from the reaction chamber  14  contain components having a low vapor pressure such as unconsumed material or reaction by-product, a solvent gas contained in the material gas, an adduct gas of material, and a carriage gas. As a solvent, butyl acetate, tetrahydrofuran, lutidine, or the like is used, and as an adduct, tetraglymes, toluenes, tetraenes, or the like is used. 
     The discharged gases containing various substances are introduced into the trap container  36 , and the components having a low vapor pressure such as the unconsumed material or the reaction by-product are solidified and deposited on the inner surface of the trap container  36  and the outer surfaces of the fins  60  of the cooling device  50 . At the same time, gas components such as a solvent or an adduct which are easily liquidized are condensed, and hence they are also contained in the deposited substances. Thus, the deposited substances in the trap container  36  become moist. Therefore, adhesion between the deposited substances and the inner surface of the trap container and cohesion of the deposited substances are heightened, and hence the deposited substances are prevented from being removed from the inner surface of the trap container  36  and the surfaces of the fins  60 , thus preventing generation of particles. 
     FIG. 2 shows a trap apparatus according to a second embodiment of the present invention. The trap apparatus in the second embodiment is different from the trap apparatus in the first embodiment in that the cooling device  50  using liquid nitrogen is replaced with a GM (Gifford-McMahon) cycle helium refrigerator  62 . The GM cycle helium refrigerator  62  has such a structure that cold panels  68  provided in a refrigerating unit  64  are cooled by supplying liquid helium from the compressor  66  to the refrigerating unit  64 . The open end of the trap container  36  is closed by a flange  70  of the refrigerating unit  64 . 
     Since the cold panels  68  are cooled to a temperature of approximately −150° C. in the GM cycle helium refrigerator  62 , the interior atmosphere in the trap container  36  can be cooled to a temperature equal to or lower than the condensing temperature of the solvent gas contained in the material gas or the adduct gas of material. 
     FIG. 3 shows a trap apparatus according to a third embodiment of the present invention. The trap apparatus in the third embodiment has a two-stage trap structure. This structure is applicable to the case where material itself has a low vapor pressure and can be trapped by natural heat dissipation. In this embodiment, the trap container  36  in the trap apparatus  30  has a solvent storage  76  disposed at a lower portion thereof for storing a solvent  74 , which is hard to be volatilized, in a liquid state. The solvent storage  76  is enclosed by a cooling jacket  72  through which cooling medium flows. In the solvent storage  76 , there are provided a liquid level sensor  78  for detecting a liquid level of the solvent  74 , and a temperature sensor  80  for detecting a temperature of the solvent  74 . 
     The solvent  74  may use a solvent such as butyl acetate which is used as a solvent of material, a solvent such as tetraglymes which is used as an adduct of material, or a solvent such as dipivaloylmethane which is used as a ligand of material. 
     The interior of the trap container  36  is divided by a partition plate  82  having a lower end extending to a position lower than the liquid level of the solvent  74 . The partition plate  82  divides the trap container  36  into a first chamber  84   a  and a second chamber  84   b . An inlet pipe  38  is connected to the upper end of the first chamber  84   a  and an outlet pipe  40  is connected to the upper end of the second chamber  84   b . The inlet pipe  38  has a lower end connected to an inner pipe  86  which extends downwardly in the first chamber  84   a . The partition plate  82  has a communication opening  82   a , at an upper portion thereof, where a communication pipe  88  extending downwardly in the second chamber  84   b  is connected to the partition plate  82 . Thus, there is provided a discharge gas passage in which the discharged gases flow downwardly in the inlet pipe  38  and the inner pipe  86 , flow upwardly in the first chamber  84   a , and flow downwardly in the communication pipe  88 , and then flow upwardly again and are discharged from the outlet pipe  40 . 
     The trap apparatus  30  includes a solvent supply device  90  for supplying the solvent  74  into the trap container  36  periodically or irregularly. The solvent supply device  90  comprises a solvent tank  92  for storing the solvent  74 , and a solvent supply line  96  extending from the solvent tank  92  and having a solvent supply pump  94  thereon. The solvent supply line  96  is branched into a line extending to the first chamber  84   a  and a line extending to the second chamber  84   b , and both of the lines are connected to respective sprayers  98  located in the first chamber  84   a  and the second chamber  84   b , respectively. The solvent tank  92  is connected to the solvent storage  76  in the trap container  36  through a recovery line  102  having a valve  100  thereon. Thus, by operating the solvent supply pump  94 , the solvent  74  stored in the solvent tank  92  is supplied from the sprayers  98  into the first chamber  84   a  and the second chamber  84   b  in the trap container  36 . 
     In the trap apparatus of this embodiment, gases discharged from the reaction chamber  14  are introduced into the first chamber  84   a  in the trap container  36  through the inlet pipe  38 , and flow upwardly in the first chamber  84   a . During this upward flow, components having a low vapor pressure such as unconsumed material are cooled by natural heat dissipation and condensed, and fall due to inertia of the flow, and are then trapped by the solvent  74  stored in the solvent storage  76 . The gases which have flowed upwardly in the first chamber  84   a  flow downwardly in the communication pipe  88 , and then are introduced into the second chamber  84   b . In the second chamber  84   b , during the upward flow, components having a low vapor pressure such as unconsumed material are cooled by natural heat dissipation and trapped by the solvent  74  stored in the solvent storage  76 . The temperature of the solvent  74  in the solvent storage  76  is controlled to a value so as not to progress vaporization of components having a low vapor pressure. 
     The components having a low vapor pressure solidified in the first chamber  84   a  and the second chamber  84   b  are deposited partly on the inner surface of the trap container  36 , and the surfaces of partition plate  82 , the inner pipe  86  and the communication pipe  88 . Therefore, the solvent supply pump  94  of the solvent supply device  90  is operated periodically or irregularly, and the solvent  74  stored in the solvent tank  92  is sprayed from the sprayers  98  into the first chamber  84   a  and the second chamber  84   b . Thus, the components having a low vapor pressure and deposited on the inner surface of the trap container  36 , the surface of the partition plate  82  and the like are moistened by the solvent  74 , and hence adhesion between the deposited substances and the inner surface of the container and the like and cohesion of the deposited substances are heightened, and the deposited substances are prevented from being removed from the inner surface of the trap container  36 , the surface of the partition plate  82  and the like. 
     At this time, the liquid level of the solvent  74  in the solvent storage  76  can be adjusted by adjusting the amount of the solvent  74  supplied from the sprayers  98  and the amount of the solvent  74  discharged from the solvent storage  76 . Further, if the concentration of material in the solvent  74  stored in the solvent storage  76  becomes high, then the solvent  74  in the solvent storage  76  is replaced with a new one, and trapping operation can be continued. 
     As the solvent  74 , in the case where a solvent such as butyl acetate which is used as a solvent of material, a solvent such as dipivaloylmethane which is used as a ligand of material, or a solvent such as tetraglymes which is used as an adduct of material is utilized, even if the solvent  74  is vaporized and flows back into the reaction chamber  14 , the solvent is prevented from being contained in the thin film deposited on the substrate, thus preventing detrioration of quality of the film. 
     FIG. 4 shows a modified version of the third embodiment shown in. FIG.  3 . The solvent  74 , which is hard to be volatilized, is supplied directly to the solvent storage  76  without passing through the sprayers  98 . In this embodiment, the solvent supply pump  94  is controlled by a controller (not shown) so that the liquid level of the solvent  74  is kept to form a clearance δ having a certain small value between the liquid level, and the inner pipe  86  and the communication pipe  88 . This structure allows the discharged gases to collide with solvent  74 , and the components having a low vapor pressure in the gases are trapped directly by the solvent  74 . According to the trap apparatus of this embodiment, it is difficult for scattering of the deposited substances to occur, compared with the conventional trap apparatus incorporating the baffle plate  32  shown in FIG.  7 . 
     FIG. 5 shows a trap apparatus according to still another embodiment of the present invention. In this embodiment, a plurality of trays  100   a ,  100   b ,  100   c ,  100   d  and  100   e  whose diameters are gradually larger downwardly are provided in a multi-stage manner. The solvent  74 , which is hard to be vaporized, is supplied to the uppermost tray  100   a  from a storage tank  92  by a pump  94  through a supply pipe  104  extending upwardly at a central portion of the container  36 , and then supplied to the lower trays  100   b  to  100   e  in sequence in order of height by overflow, thus constructing multi-stage cascades. The discharged gases are introduced into the container  36  through the inlet pipe  38  provided at the central and upper portion of the trap container, pass through a discharge opening  106  positioned at the outer circumferential portion of the trap container  36  and immediately above the liquid level of the solvent  74 , and are then discharged from the trap container  36  through the outlet pipe  40 . The solvent  74 , which is hard to be vaporized, is circulated between the interior of the trap container  36  and the external storage tank  92 , and purified by filters  108  and reused. 
     According to this embodiment, liquid levels and cascades are provided in a multi-stage manner to increase trap efficiency, and the trapped substances are removed with the filter  108  by circulating the solvent  74  and discharged to the exterior of the system. The timing of replacement of the filter  108  may be judged by detecting a rise of the liquid level of the solvent in the trap apparatus  30  for thereby estimating resistance of the filter. 
     As described above, according to the present invention, gases, which are easily liquidized, such as a solvent gas contained in a material gas are condensed in the trap container, or substances which are hard to be volatilized are supplied to the trap container, and deposited substances in the trap container are moistened, and hence adhesion between the deposited substances and the inner surface of the trap container and cohesion of the deposited substances are heightened. Thus, the deposited substances are prevented from being removed from the inner surface of the trap container and the like, thus preventing generation of particles. Therefore, components having a low vapor pressure in the discharge gases can be trapped reliably and scattering of the trapped substances can be prevented. As a result, in a process chamber such as a reaction chamber positioned at the preceding stage, a process such as deposition can be carried out smoothly and in a high quality, and hence the present invention offers a useful technology in the semiconductor manufacturing industry. 
     Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.