Patent Document

This application is based on an application number 2002-069111 filed in Japan, the content of which is hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a liquid material evaporation apparatus for use in semiconductor manufacturing. 
   2. Description of Related Art 
     FIG. 5  shows the structure of the main portion of a conventional liquid material evaporation apparatus including a gas-liquid mixing chamber, a flow control portion, and a nozzle portion formed into one block for improved evaporation of a liquid material when the block is heated. In this drawing, the main body block  51  is in the shape of a rectangular parallelepiped. 
   Three flow passages  52 ,  53 ,  54  are formed inside the main body block  51 . A gas-liquid mixing chamber  55  is formed in the upper surface. 
   The flow passage  52  is for introducing a liquid material LM (not shown) into the gas-liquid mixing chamber  55 , and this liquid material introduction passage  52  is provided in a direction vertical to the surface of the drawing in the shape of a reverse-L character so that one end of the flow passage is opened to the front surface side of the main body block  51  and the other end is opened to the upper surface of the main body block  51 . The flow passage  53  is for introducing a carrier gas CG into the gas-liquid mixing chamber  55 . The carrier gas introduction flow passage  53  is in the shape of an L character so that one end is opened to the left side surface of the main body block  51  and the other end thereof is opened to a recess portion  51   a  of the upper surface of the main body block  51 . The flow passage  54  functions as a gas discharge passage, with one end opened to the right side surface of the main body block  51 , the other end is connected vertically up to an appropriate position of the main body block  51 , and the upper end side is coupled to the gas-liquid mixing chamber  55  via a nozzle portion  56 . 
   The gas-liquid mixing chamber  55  is formed so that the recess portion  51   a  formed on the upper surface of the main body block  51  is covered by a diaphragm  57  as a valve member. The diaphragm  57  is accommodated in a valve block  58  arranged on the upper surface of the main body block  51  and is driven downward towards the mixing chamber by means of a piezo actuator  59  extending upward on the upper portion of the valve block  58 . Spring  60  constantly biases the diaphragm  57  upwardly. Heater  61  is for heating the main body block  51 . 
   The nozzle portion  56  is dimensioned so that the diameter and length are 1.0 mm or smaller. The nozzle is located in close proximity to the end of the gas discharge passage  54  closest to the gas-liquid mixing chamber  55 . The mixture of the liquid material and carrier gas passes through the nozzle portion  56  into the discharge passage  54  thereby becoming depressurized and evaporating into a mixed gas. This mixed gas flows to the downstream end of the discharge passage  54 . 
   In the liquid material evaporation apparatus of the above-described structure, the liquid material LM and the carrier gas CG are mixed in the gas-liquid mixing chamber  55  provided in the main body block  51  which is heated to an appropriate temperature while the flow of the liquid material LM is controlled, and this gas-liquid mixture is passed through the nozzle portion  56  formed adjacent to the gas-liquid mixing chamber  55  inside the main body block  51 . Thus, the liquid material LM contained in the gas-liquid mixture is quickly evaporated by depressurization in a stable state. 
   However, in a conventional liquid material evaporation apparatus, if the flow rate of the carrier gas CG into the gas-liquid mixing chamber  55  is too low, or if the flow rate of the liquid material LM to the gas-liquid mixing chamber  55  is too high, there is a possibility of backflow of the liquid material LM in which the liquid material LM flows into the carrier gas introduction passage  53  and the liquid material LM cannot be evaporated smoothly at high speeds. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a liquid material evaporation apparatus in which backflow of the liquid material toward the carrier gas supply passage side is prevented, so that the liquid material can be evaporated smoothly at high speeds. 
   In order to achieve the above-described object, the liquid material and carrier gas are mixed in a gas-liquid mixing chamber with a control valve providing a flow control function that discharges the gas-liquid mixture through a nozzle portion formed in close proximity to the end of the discharge passage near the gas-liquid mixing chamber. After passing through the nozzle into the discharge passage, the liquid material and carrier gas mixture is depressurized and becomes evaporated. The present invention includes a nozzle for preventing backflow of the liquid material into the carrier gas flow passage. 
   Since backflow of the liquid material to the carrier gas supply passage side is prevented, and the flow rate of the carrier gas is increased immediately prior the gas-liquid mixing, the gas-liquid mixing is performed more efficiently, and the liquid material is evaporated more smoothly at high speeds. The liquid material is evaporated efficiently, in real time, using the liquid material evaporation apparatus of the present invention. 
   When the nozzle of the discharge passage and the nozzle of the carrier gas passage have the same dimensions, the structures are symmetrical and it is possible to use the carrier gas supply passage as a gas discharge passage and, conversely, to use the gas discharge passage as a carrier gas supply passage. This symmetry simplifies field installation and may reduce the cost of the apparatus. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The exact nature of this invention will be readily apparent from consideration of the following detailed description in conjunction with the accompanying drawings, wherein: 
       FIG. 1  schematically illustrates one example of the entire structure of a liquid material evaporation apparatus, wherein (A) is a top view and (B) is a front view; 
       FIG. 2  is an enlarged longitudinal cross-sectional view schematically illustrating the structure of the main portion of the liquid material evaporation apparatus according to the present invention; 
       FIG. 3  is an enlarged longitudinal cross-sectional view schematically illustrating the gas-liquid mixing chamber of the liquid material evaporation apparatus. 
       FIG. 4  is a perspective view schematically illustrating the structure of the gas-liquid mixing chamber. 
       FIG. 5  is a longitudinal cross-sectional view schematically illustrating the prior art. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Details of the present invention are explained in reference to the attached drawings that are meant not to limit the disclosure, but rather to illustrate various features.  FIGS. 1–4  illustrate one embodiment of the present invention. In reference to  FIG. 1 , the control valve  1  provides a liquid flow control function. The structure of the control valve  1  is explained referring to  FIG. 2  to  FIG. 4 . The main body block  2  is in the shape of a rectangular parallelepiped constructed from a material with good heat conductivity and corrosion resistance, such as stainless steel. Three flow passages  3 ,  4 ,  5  are formed inside the main body block, and a gas-liquid mixing chamber  6  is formed in the upper surface  2   a.    
   The flow passage  3  is for introducing the liquid material LM into a gas-liquid mixing chamber  6 , and this liquid material introduction passage  3  is in the shape of an L character so that one end is opened to a front side surface  2   b  of the main body block  2  and the other end is opened to the gas-liquid mixing chamber  6  in an upper surface  2   a  of the main body block  2 . 
   The flow passage  4  is for introducing a carrier gas CG into the gas-liquid mixing chamber  6 , and this carrier gas introduction passage  4  is in the shape of a reverse-L character so that one end is opened to a left side surface  2   c  of the main body block  2  and the other end is opened to the gas-liquid mixing chamber  6 . A nozzle  7  is formed between the end of the carrier gas introduction passage  4  and the gas-liquid mixing chamber  6 , in close proximity to the mixing chamber. The term nozzle includes any narrowing of the conduit, but especially a narrow conduit that has a longer dimension along the direction of flow. The nozzle  7 , also called a backflow prevention nozzle, prevents backflow of the liquid material LM into the carrier gas introduction passage  4 . 
   The gas discharge passage  5  is in the shape of an L character so that one end is opened to the right side surface  2   d  of the main body block  2  and the other end is opened to the gas-liquid mixing chamber  6 . A nozzle  8  is formed between the end of the gas discharge passage  5  and the gas-liquid mixing chamber  6 , in close proximity to the mixing chamber. This nozzle  8 , also called a jetting nozzle, is for evaporating the liquid material LM contained in the gas-liquid mixture by depressurization. 
   The backflow prevention nozzle portion  7  and the jetting nozzle portion  8  each have the same shape. The inner diameters of the nozzles are considerably small compared with the inner diameters of the carrier gas introduction passage  4  and the gas discharge passage  5 , and the lengths are also considerably short. For example, the inner diameters of the nozzles are 1.0 mm or smaller, and the lengths are approximately 1.0 mm. 
   Heater  9  is for heating the entire main body block  2  to an appropriate temperature and may be composed of a cartridge heater or other suitable heating element. Heating the main body block  2  conducts heat to the mixing chamber, the carrier gas introduction passage  4  and the gas discharge passage  5 . 
   In reference to  FIGS. 1–2 , a coupling member  10  is provided on the introduction end of the liquid material introduction passage  3 , a coupling member  11  is provided on the introduction end of the carrier gas introduction passage  4 , and the coupling member  12  is provided on the discharge end of the gas discharge passage  5 . Outside cover  13  covers the liquid material evaporation apparatus  1 . 
   In reference to  FIG. 2  and  FIG. 4 , the structure of the upper surface  2   a  of the main body block  2  is explained. The valve block  14  is placed on the upper surface  2   a  via a suitable seal member (not shown). The valve block  14  is made of a material with excellent heat conductivity and corrosion resistance, such as stainless steel. A valve main body  15  having a liquid flow control function is formed between the valve block  14  and the upper surface  2   a . That is, the gas-liquid mixing chamber  6  is formed between the diaphragm  16  and the upper surface  2   a , in an inside space  14   a  of the valve block  14 . 
   The gas-liquid mixing chamber  6  is constructed as follows. A recessed region  17  is formed in the upper surface  2   a . A vertical conduit  3   a  of the liquid material introduction passage  3  is opened to the recessed region  17 . A valve sheet  18 , which is slightly higher than the recessed region  17 , is formed in the center of the recessed region  17 . A mixing groove  19  forms the part of the mixing chamber to which the nozzle  7  of the carrier gas introduction passage  4  and the nozzle  8  of the gas discharge passage  5  are connected. 
   The diaphragm  16  is made of a material with excellent heat and corrosion resistance, with an appropriate elasticity, and is structured in such a manner that a valve  16   b , which alternately makes contact with and flexibly moves away from the upper surface of the valve sheet  18 , is formed under a shaft portion  16   a . A thin wall portion  16   c  is provided in the periphery of the valve portion  16   b , and a heavy wall portion  16   d  is provided in the periphery of the thin wall portion  16   c . In one position, the diaphragm  16  is biased upwardly by means of a spring  20  so that the valve portion  16   b  is opened and not contacting the valve sheet  18 . However, when the piezo actuator  21  is activated, the diaphragm moves to the other position. In this case, when the piezo actuator moves against the shaft portion  16   a,  the valve  16   b  is displaced toward the channel groove  19  and the valve  16   b  contacts the valve sheet  18 . 
   In the present embodiment, a piezo stack  23  formed by layering a plurality of piezoelectric elements in a housing  22  which is extended upwardly on the upper portion of the valve block  14 . The piezo actuator is constructed by allowing a pressing portion  23   a  of a lower portion of this piezo stack  23  to make contact with the upper end of the shaft portion  16   a  of the diaphragm  16  via a spherical element  24 . 
   The liquid material LM is introduced at a predetermined flow rate into the mixing groove  19  through the liquid material introduction passage  3 , and is controlled by the diaphragm  16  driven by the piezo actuator  21 . The carrier gas CG is introduced into the mixing groove  19  through the carrier gas introduction passage  4 . In this case, since the nozzle  7  is formed near the end of the carrier gas introduction passage  4  in close proximity to the mixing chamber, the carrier gas CG having a predetermined flow velocity is vigorously introduced into the mixing groove  19 . Since the mixing groove  19  is a long and narrow groove, and since the carrier gas CG merges with the liquid material LM with great force, the liquid material LM and the carrier gas CG are vigorously mixed in the mixing groove  19  so that both the liquid material and the carrier gas are sufficiently mixed to become a gas-liquid mixture. 
   Even when the flow rate of the carrier gas CG supplied to the gas-liquid mixing chamber  6  is small, or even when the flow rate of the liquid material LM supplied to the gas-liquid mixing chamber  6  is large, since the backflow prevention nozzle portion  7  is formed in the most downstream end of the carrier gas introduction passage  4 , the liquid material LM does not flow into the carrier gas introduction passage  4  side. In this case, the inflow of the liquid material LM into the gas-liquid mixing chamber  6  is not adversely affected. 
   The carrier gas is supplied at a predetermined pressure. The pressure in the carrier gas introduction passage  4  and the reduced size of the backflow prevention nozzle  7  prevent the backflow of liquid material into the carrier gas introduction passage  4 . 
   The gas-liquid mixture is discharged from the jetting nozzle  8  directly down from the gas-liquid mixing chamber  6  into the gas discharge passage  5 . At this time, the liquid material LM and the carrier gas in the gas-liquid mixture are quickly depressurized and become a mixed gas. This mixed gas continues to flow in the gas discharge passage  6  in a direction away from the end of the gas discharge passage that is closest to the mixing chamber. The gas discharge passage  5  is appropriately heated by the heater  9  so that dewfall or condensation does not occur. 
   The pressure of the carrier gas CG increases in the upstream side of the nozzle  8 , and the carrier gas introduction passage  4  is efficiently heated to an appropriate temperature by the heater  9 . Thus, not only does the heating efficiency of the carrier gas CG itself increase, but also the liquid material LM is more forcibly mixed with the carrier gas CG through nozzle  8 , and the heat transfer from the carrier gas CG to the liquid material LM is efficiently performed. As a result, since the heat transfer efficiency from the heater  9  to the liquid material LM increases, the evaporation efficiency of the liquid material LM also increases. Thus, it becomes possible to increase the flow rate of the evaporated liquid material LM, to decrease the temperature necessary for evaporating the liquid material LM, and to reduce the energy cost of evaporating the liquid material. 
   Further, in the process of the gas-liquid mixture moving from the gas-liquid mixing chamber  6  to the downstream side of the gas discharge passage  5 , the gas concentration of the discharged mixed gas decreases due to the existence of the carrier gas CG. Since the temperature necessary for preventing condensation in the gas discharge passage  5  decreases, the energy cost for heating the gas discharge passage  5  can be reduced. Since the discharged mixed gas is adiabatically expanded, and thus loses heat, usually the evaporation efficiency also decreases. However, in the present embodiment, since the heat that the liquid material LM loses in the adiabatic expansion is compensated by the increased heat of the carrier gas CG that is mixed with the liquid material LM, an improvement in the evaporation efficiency of the liquid material LM is achieved. 
   When the nozzle of the discharge passage and the nozzle of the carrier gas passage have the same dimensions, the structures are symmetrical and it is possible to use the carrier gas supply passage as a gas discharge passage and, conversely, to use the gas discharge passage as a carrier gas supply passage. This symmetry simplifies field installation and may reduce the cost of the apparatus. However, it is not necessary that the sizes of the nozzle portions  7 ,  8  are the same dimensions. Different dimensions are acceptable if one flow passage nozzle  7  prevents the backflow of the liquid material LM while other flow passage nozzle  8  evaporates the liquid material LM in the gas-liquid mixture reliably.

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