Abstract:
This invention is related to an optical-analysis-type raw material fluid density detector including a detector main body and a light oscillation unit and a light detection unit that are provided on the upper surface or the under surface of the detector main body, in which the detector main body has at least one recess formed in the upper surface and the under surface, a fluid flow path connecting a fluid inlet of the detector main body to the recess, a fluid flow path connecting the recesses to each other, and a fluid flow path connecting the recess to a fluid outlet of the detector main body; the light oscillation unit is disposed in the recess that is closest to the inlet; and light detection units are disposed in the remaining recesses.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an improvement of a process fluid density meter for use in a raw material fluid supply system for a semiconductor manufacturing apparatus and the like, and particularly relates to an in-line optical-analysis-type raw material fluid density detector which achieves a size reduction and an in-line type of a sensor unit of a density meter and also enables maintenance of high transparency of a light transmission window and high cleanliness (resistance to particles) of the inside of a sensor which are stable over a long time period even in the case of a raw material fluid having high deposition properties, high photoreactivity, and corrosiveness. 
       BACKGROUND ART 
       [0002]    The raw material fluid supply system for the semiconductor manufacturing apparatus and the like needs to supply a process raw material fluid with a stable density to a processing device in terms of improving the quality of a semiconductor product. 
         [0003]    Thus, in the former raw material fluid supply system of this type, e.g., in a bubbling type raw material fluid supply system illustrated in  FIG. 9 , an optical-analysis-type density meter  22  is provided in the vicinity of a raw material vapor outlet of a raw material tank  21  of which temperature is controlled, and the temperature of the raw material tank  21 , the flow rate of a carrier gas CG, the vapor pressure Po in the tank, and the like are adjusted by a density detection signal from the density meter  22 , whereby a process gas  24  (for example, a process gas containing organometallic material steam, such as trimethyl gallium TMGa, stored in the tank  21 ) of a predetermined raw material density is supplied to a reactor  23 . 
         [0004]      FIG. 9  includes thermal mass flow controllers  25  and pressure adjusting devices  26  for the pressure in the tank. 
         [0005]    Although density meters  22  having various kinds of configurations are practically used as the optical-analysis-type density meter  22 , as illustrated in  FIG. 10  (Japanese patent Laid-Open No. 9-178652) and  FIG. 11  (Japanese Patent Laid-Open No. 2004-108981), almost the density meters  22  contain an optical cell (gas cell)  27  through which a gas G to be measured flows, a light source  28  which irradiates the inside of the optical cell  27  with light beams, a light receiving device  29  of the light beams passing through the inside of the optical cell  27 , an arithmetic calculation device  30  which determines the absorbance from a signal of the light receiving device  29  to calculate the raw material density, and the like. The reference numeral  31  denotes a main pipe line and  32  denotes a branch pipe line. 
         [0006]    The density meter  22  of  FIG. 10  is configured so that a so-called absorbance of the gas in the optical cell  27  is measured and also the gas density is calculated by applying the Lambert-Beer law to the measurement result of the absorbance. 
         [0007]    In the Japanese Patent Laid-Open No. 2004-108981, as illustrated in  FIG. 11 , an in-line sensor  33  containing an optical cell (light absorption cell) is fixed to the pipeline  31 , and the luminous intensity of light transmitting through the optical cell is measured. 
         [0008]    The optical-analysis-type density meter  22  and the in-line sensor  33  containing the optical cell (light absorption cell)  27  are known, and thus a detailed description thereof is omitted herein. 
         [0009]    Thus, when measuring the raw material gas density, the optical cell  27  first needs to be connected and fixed to the pipeline  32  (or the pipeline  31 ). However, there are problems that it is not easy to secure the airtightness of a connecting portion between the optical cell  27  and the pipeline  32  (or the pipeline  31 ) and, for example, it is not easy to achieve connection and fixation having high airtightness by screw connection and a flange connection method employing usual packing materials and seal materials, which makes it actually impossible to achieve securing of airtightness performance (External leak of 1×10 −1 ° Pa·m 3 /sec or less) demanded in the field of a semiconductor manufacturing apparatus. 
         [0010]    In order to continuously perform stable gas density measurement over a long period of time, the transparency of the light transmission window of the optical cell  27  needs to be stable over a long period of time. When the transparency changes with time, the stable gas density measurement becomes difficult to achieve. 
         [0011]    However, quartz glass has been used as a constituent material of the light transmission window in former density meters in many cases. Thus, when measuring the density of an organic raw material gas having high corrosiveness or high deposition properties, the light transmission window is corroded or the transparency decreases at an early stage due to the deposition of the raw material. Thus, a problem that stable measurement of the raw material gas density cannot be performed has remained unsolved. 
         [0012]    On the other hand, various structures in the optical cell  27  also need to be firmly fixed and held to the main body of the optical cell  27  with high airtightness. Thus, inside the optical cell  27 , various kinds of synthetic resin seal materials, silver brazing, gold brazing, and the like are used. 
         [0013]    However, materials, such as synthetic resin seal materials, silver brazing, and gold brazing, in the optical cell  27  have risk of serving as emission sources which emits gas and particles contained in each material itself into the organic raw material gas, which actually poses a problem of a reduction in gas purity due to the emission of particles. Thus, in the gas supply systems for semiconductor manufacturing, the use of silver brazing or gold brazing is not desirable. 
         [0014]    As described above, the use of the former optical-analysis-type density meter makes it difficult to reduce the size and the cost of facilities and also poses a large number of problems in maintaining gas airtightness, securing of stability of density measurement accuracy, maintenance of high gas purity, and the like. Particularly in the case of an organic raw material gas, the problems, such as the reduction in the transparency of the light transmission window resulting from the corrosiveness thereof, the reduction in the gas purity due to the seal members, the securing of airtightness, and the like, need to be solved as soon as possible. 
       CITATION LIST 
     Patent Literature 
     Patent Document 1: Japanese Laid-Open Patent Publication No. 9-178652 
     Patent Document 2: Japanese Laid-Open Patent Publication No. 2004-108981 
     Patent Document 3: Japanese Laid-Open Patent Publication No. 11-280967 
     SUMMARY OF INVENTION 
     Technical Problem 
       [0015]    A main object of the present invention is to provide an in-line type raw material fluid density detector which solves the above-described problems in a raw material density meter for use in a former raw material fluid supply system and the like, i.e., (I) A simplification of the structure and a reduction in the size and the product cost of a density meter are not easy to achieve, (II) Stable and high-accuracy measurement of the raw material fluid density cannot be performed due to fluctuation of the transparency of a light transmission window, and the like, and which can stably and highly accurately measure the density without causing fluctuation of the transparency of a light transmission window over a long period of time even in the case of an organic raw material fluid with high corrosiveness and also can achieve size reduction and manufacturing at low cost. 
       Solution to Problem 
       [0016]    As the basic configuration of the present invention, a first aspect of a raw material fluid density detector according to the present invention is an optical-analysis-type raw material fluid density detector comprising a detector main body  2  and a light oscillation unit  5   a  and a light detection unit  5   b  provided on the upper surface or the undersurface of the detector main body  2 , wherein the detector main body  2  includes at least one recess  17  formed in the upper surface and the undersurface thereof; a fluid flow path  2   a  connecting a fluid inlet of the detector main body  2  to the recess  17 , a fluid flow path  2   b  connecting the recesses  17  to each other, and a fluid flow path  2   c  connecting the recess  17  to a fluid outlet of the detector main body  2 , the light oscillation unit  5   a  is disposed in at least one recess, and the light detection unit  5   b  is disposed in the remaining recess. 
         [0017]    According to a second aspect of the raw material fluid density detector according to the first aspect of the present invention, the light oscillation unit includes a light transmission plate, a photodiode for light intensity detection, and a light source (optical fiber) for light oscillation, and the light detection unit includes a light transmission plate and a photodiode for light intensity detection in the raw material fluid density detector. 
         [0018]    According to a third aspect of the raw material fluid density detector according to in the second aspect of the present invention, the light transmission plates disposed in the recesses formed in the detector main body are airtightly fixed using gasket type seals in the raw material fluid density detector. 
         [0019]    A fourth aspect of a raw material fluid density detector according to the present invention is an optical-analysis-type raw material fluid density detector comprising a detector main body  2 , a light oscillation unit  5   a  provided on the upper surface of the detector main body  2 , a light detection unit  5   b  provided on the undersurface of the detector main body  2 , recesses  17  provided in the upper surface and the undersurface of the detector main body  2  and connected to each other through a fluid flow path  2   b , gasket type seals  6  attached into the recesses  17 , a first fixing flange  14  and a second fixing flange  16  disposed facing the gasket type seals  6  and airtightly joined and fixed while holding the light transmission plates  11   a , an optical fiber  9  and a photodiode  10  provided in the second fixing flange  16 , and a holding and fixing body  12  airtightly fixing both the joined-and-fixed fixing flanges  14  and  16  into the recesses of the detector main body  2  through the gasket type seals  6 . 
         [0020]    A fifth aspect of a raw material fluid density detector according to the present invention is an optical-analysis-type raw material fluid density detector comprising a detector main body  2 , a light oscillation unit  5   a  provided on the upper surface of the detector main body  2 , and a light detection unit  5   b  provided on the undersurface of the detector main body  2 , wherein the detector main body  2  includes a recess  17  provided in each of the upper surface and the undersurface thereof, a fluid flow path  2   b  connecting both the recesses  17  to each other, a fluid flow path  2   a  connecting a fluid inlet to the recess  17  in the upper surface, and a fluid flow path  2   c  connecting a fluid outlet to the recess  17  in the undersurface; and wherein the light oscillation unit  5   a  and the light detection unit  5   b  each have a gasket type seal  6  attached into a gasket accommodation portion  17   a  linked to the recess  17 , a first fixing flange  14  including an insertion recess  14   b  having an inner circumferential surface having a stepwise narrowed diameter and disposed facing the gasket type seal  6 , a light transmission plate  11   a  disposed at the deepest portion of the insertion recess  14   b  of the first fixing flange  14 , a second fixing flange  16  airtightly joined and fixed to the insertion recess  14   b  while sandwiching the light transmission plate  11   a  by inserting of a projection portion  16   b  having a step-like outer circumferential surface into the insertion recess  14   b  of the first fixing flange  14 , a photodiode  10  for light intensity detection disposed and fixed on the outside of the light transmission plate  11   a  in the second fixing flange  16 , and a holding and fixing body  12  including a flange accommodation portion  12   a  accommodating both the fitted-and-fixed fixing flanges  14  and  16  at the center portion and airtightly fixing both the fixing flanges  14  and  16  accommodated in the flange accommodation portion  12   a  to the detector main body  2  through the gasket type seal  6  by cramping fixation bolts  8 . 
         [0021]    Regarding a sixth aspect of the raw material fluid density detector according to the fifth aspect of the present invention, a tip surface  16   d  of the projection portion  16   b  of the second fixing flange  16  and a bottom surface  14   c  of the insertion recess  14   b  of the first fixing flange  14  serve as a seal surface of the light transmission plate  11   a.    
         [0022]    Regarding a seventh aspect of the raw material fluid density detector according to the fifth aspect of the present invention, a bottom surface  14   e  of the gasket accommodation portion  14   d  of the first fixing flange  14  serves as a gasket seal surface. 
         [0023]    Regarding an eighth aspect of the raw material fluid density detector according to the fifth aspect of the present invention, an optical fiber insertion hole  9   a  is provided in the second fixing flange  16  of the light oscillation unit  5   a , and the photodiode  10  serves as a photodiode for detecting the intensity of reflected light from the light transmission plate  11   a.    
         [0024]    Regarding a ninth aspect of the raw material fluid density detector according to the fifth aspect of the present invention, the photodiode  10  provided in the second fixing flange  16  of the light detection unit  5   b  serves as a photodiode for detecting the intensity of transmission light from the light transmission plate  11   a.    
         [0025]    Regarding a tenth aspect of the raw material fluid density detector according to the fifth aspect of the present invention, another light detection unit  5   b  is provided at an interval on the upper surface of the detector main body  2 ; the recess  17  of the light detection unit  5   b  provided in the undersurface of the detector main body  2  and the recess  17  of the light detection unit  5   b  are connected to each other through the fluid flow path  2   c ; and the intensity of reflected light from the light transmission plate  11   a  of the light detection unit  5   b  provided on the undersurface is detected in the light detection unit  5   b.    
         [0026]    Regarding an eleventh aspect of the raw material fluid density detector according to the fifth aspect of the present invention, the raw material fluid is a depositing, high reactive, or corrosive organic raw material. 
         [0027]    Regarding a twelfth aspect of the raw material fluid density detector according to the fifth aspect of the present invention, the light transmission plate  11   a  is formed of sapphire. 
       Advantageous Effects of Invention 
       [0028]    According to the present invention, at least one recess  17  is formed in the upper surface and the undersurface thereof, a fluid flow path  2   a  connecting a fluid inlet of the detector main body  2  to the recess  17 , a fluid flow path  2   b  connecting the recesses  17  to each other, and a fluid flow path  2   c  connecting the recess  17  to a fluid outlet of the detector main body  2  are provided, the light oscillation unit  5   a  is disposed in at least one recess, and the remaining light detection units  5   b  are disposed in the remaining recesses in the detector main body  2 . Thus, an in-line type raw material density detector with a very simple configuration can be achieved. 
         [0029]    Moreover, the light oscillation unit  5   a  and the light detection unit  5   b  have the gasket type seal  6  attached into the gasket accommodation portion  17   a , the first fixing flange  14  having the insertion recess  14   b  disposed facing the same, the second fixing flange  16  airtightly joined and fixed to the first fixing flange  14  by inserting and press-fitting the projection portion  16   b  into the insertion recess  14   b , the sapphire light transmission plate  11   a  airtightly held between both the flanges, and the holding and fixing body  12  which pressurizes and fixes both the flanges  14  and  16  to the detector main body  2 . Thus, the structure of the light oscillation unit  5   a  and the light detection unit  5   b  can be simplified and also high airtightness can be held. 
         [0030]    Furthermore, the light transmission window  11  is formed of sapphire, and thus, even in the case of a depositing, reactive, and corrosive fluid, the light transmittance does not decrease and stable high-accuracy density measurement can be achieved. 
         [0031]    Moreover, since the gasket type seal is used, mixing of impurities into the fluid can be completely eliminated as compared with other seal structures employing synthetic resin seal materials, silver brazing materials, gold brazing materials, and the like. 
         [0032]    In addition, the light transmission window which is the plate member  11  containing a brittle fracture material is sandwiched between the first fixing flange  14  and the second fixing flange  16  and also both the flanges are airtightly joined and fixed, and further both the joined and fixing flanges, to which the light transmission window is attached, are airtightly inserted into the recess  17  with the holding and fixing body  12  fixed to the main body  2 , and thus the light transmission window can be airtightly, easily, and firmly held and fixed without using a seal material. 
         [0033]    Thus, the raw material fluid density detector of the present invention demonstrates outstanding effects in terms of reducing the size and the cost of facilities, maintaining airtightness, securing of stability of density measurement accuracy, maintaining of high gas purity, and the like. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0034]      FIG. 1  A vertical cross-sectional view of a raw material fluid density detector according to an embodiment of the present invention. 
           [0035]      FIG. 2  A plan view of the raw material fluid density detector of  FIG. 1 . 
           [0036]      FIG. 3  A vertical cross-sectional view of a light oscillation unit of the raw material fluid density detector of  FIG. 1 . 
           [0037]      FIG. 4  A vertical cross-sectional view and a plan view of a holding and fixing body of the light oscillation unit of  FIG. 3 . 
           [0038]      FIG. 5  A vertical cross-sectional view of a second fixing flange of the light oscillation unit of  FIG. 3 . 
           [0039]      FIG. 6  A vertical cross-sectional view of a first fixing flange of the light oscillation unit of  FIG. 3 . 
           [0040]      FIG. 7  A cross-sectional view showing the outline of a gasket type seal of the light oscillation unit of  FIG. 3 . 
           [0041]      FIG. 8  A system diagram showing the outline of a testing system of a density meter according to the present invention. 
           [0042]      FIG. 9  A system diagram for explaining a former raw material gas supply device for semiconductor manufacturing apparatus. 
           [0043]      FIG. 10  A systematic view showing an example of use of a former gas density meter. 
           [0044]      FIG. 11  A systematic view showing an example of use of another former gas density meter. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0045]    Hereinafter, embodiments of the present invention are described in detail with reference to the drawings. 
         [0046]      FIG. 1  and  FIG. 2  illustrate a raw material fluid density detector  1  according to a first embodiment of the present invention, and the raw material fluid density detector  1  is configured from a detector main body  2 , an inlet block  3  and an outlet block  4  fixed to both sides thereof, a light oscillation unit  5   a  and a light detection unit  5   b  provided in parallel on the upper surface side of the detector main body  2 , a light detection unit  5   b  provided on the undersurface side of the detector main body  2 , and the like. 
         [0047]    The detector main body  2 , the inlet block  3 , and the outlet block  4  are formed of stainless steel and the like, and fluid flow paths  2   a ,  2   b ,  2   c ,  3   a , and  4   a  are provided in a communication manner. The inlet block  3  and the outlet block  4  are airtightly fixed to both sides of the detector main body  2  with bolts (not illustrated) via gasket type seals  6 . The reference numerals  3   b  and  4   b  denote coupling portions,  7  denotes leakage inspection holes, and  8  denotes bolts for fixing the light oscillation unit  5   a . The light detection unit  5   b  is also fixed with the fixation bolts  8  (not illustrated) in the same manner as in the light oscillation unit  5   a.    
         [0048]    The light oscillation unit  5   a  and the light detection unit  5   b  are disposed side by side at an interval on the upper surface side of the detector main body  2 . Light of a predetermined wavelength in a visible region or an ultraviolet region from a light source device (not illustrated) containing a light source, a diffraction grating, a mirror, and the like enters a plate member  11  containing a brittle fracture material, i.e., a light transmission plate  11   a  containing a sapphire light transmission plate member, in the light oscillation unit  5   a  through an optical fiber  9 . 
         [0049]    Although a large part of the incident light transmits through the sapphire light transmission plate  11   a  to enter the fluid flow path  2   a , the incident light is partially reflected by the sapphire light transmission plate  11   a , and then the intensity of the reflected light is detected by the photodiode  10 . 
         [0050]    The light detection unit  5   b  is provided at an obliquely downward position with respect to the light oscillation unit  5   a  in such a manner as to face the light oscillation unit  5   a  on the undersurface side of the detector main body  2 . The light entering from the light oscillation unit  5   a  through the fluid flow path  2   b  enters the photodiode  10  in the light detection unit  5   b  through the sapphire light transmission plate  11   a , and then the light intensity of the incident light is detected. 
         [0051]    Also in the sapphire light transmission plate  11   a  in the light detection unit  5   b  on the undersurface side of the detector main body  2 , the incident light is partially reflected. However, the reflected light enters the light detection unit  5   b  on the upper surface side of the detector main body  2  through the fluid flow path  2   c . Then, the intensity of the reflected light from the light detection unit  5   b  on the undersurface side is detected in the light detection unit  5   b.    
         [0052]    The light intensity detected in the light detection unit  5   b  on the undersurface side varies depending on the density and the like of a raw material fluid (fluid for process) which flows in the fluid flow path  2   b . The detected light intensity signal is input into an arithmetic calculation device (not illustrated), and then the raw material density in the raw material fluid is calculated herein. 
         [0053]    Generally, a raw material density C is calculated by the following expression (1) based on an absorbance A determined by a spectrum photometer. 
         [0000]        A =log 10 ( I   0   /I )=ε× C×I   (1)
 
         [0054]    In Expression (1), I 0  represents the incident light intensity from the light oscillation unit  5   a , I represents the transmission light intensity (Intensity of incident light into the photodiode  10  of the light detection unit  5   b ), ε represents the molar absorptivity of the raw material, C represents the raw material density, and A represents the absorbance. 
         [0055]    The light transmission characteristics of the light oscillation unit  5   a  and the light detection unit  5   b  change with time and the like but the changes in these light transmission characteristics appear as the changes in detection values of the photodiode  10  of the light oscillation unit  5   a  on the upper surface side and the photodiode  10  of the light detection unit  5   b  on the upper surface side, the photodiodes  10  which detect reflected light. Thus, the incident light intensity I 0  and the transmission light intensity I in Expression (1) above are compensated using the detection value of each of the photodiodes  10  of the light oscillation unit  5   a  and the light detection unit  5   b  on the upper surface side. 
         [0056]    The light oscillation unit  5   a  and the light detection unit  5   b  are completely the same in the structure and are configured from, as illustrated in  FIG. 3 , a holding and fixing body  12  which is formed of stainless steel and has a flange accommodation hole  12   a  at the center, a first fixing flange  14  provided on the outer surface of the detector main body  2 , a second fixing flange  16 , a sapphire light transmission plate  11   a  which is airtightly sandwiched and fixed between both the flanges  14  and  16 , a photodiode  10  which is located above the light transmission plate  11   a  and is fixed to the second fixing flange  16 , and the like. 
         [0057]    More specifically, by press fitting a projection portion  16   b  of the second fixing flange  16  into the insertion recess  14   b  of the first fixing flange  14  with force of 8 to 12 N as described later, the second fixing flange  16  and the first fixing flange  14  are airtightly integrated in a state where the sapphire light transmission plate  11   a  is sandwiched and fixed therebetween with the tip surface  16   d  of the projection portion  16   b  and the bottom surface  14   c  of the insertion recess  14   b  as a seal surface. 
         [0058]    By inserting the integrated second fixing flange  16  and first fixing flange  14  into the flange accommodation hole  12   a  of the holding and fixing body  12 , and then pressurizing and fixing the holding and fixing body  12  to the detector main body  2  via the gasket type seals  6  with the fixation bolts  8 , the light oscillation unit  5   a  and the light detection unit  5   b  are airtightly fixed to the detector main body  2 . 
         [0059]      FIG. 3  includes a recess  17  formed in the outer surface of the detector main body  2 , a gasket  6   a , a seal surface  13  between both the fixing flanges  14  and  16 , a seal surface  14   e  between the gasket  6   a  and the first fixing flange  14 , and an optical fiber insertion hole  9   a.    
         [0060]    In the embodiment of  FIG. 1 , the light oscillation unit  5   a  and the light detection unit  5   b  are provided at an interval on the upper surface side of the detector main body  2 . However, it is a matter of course that the light detection unit  5   b  on the upper surface side is omitted and the recess  17  of the light detection unit  5   b  on the undersurface side and the fluid outlet side may be directly connected to each other by the fluid flow path  2   c.    
         [0061]    Furthermore, the light detection unit  5   b  can be provided on the upper surface side of the detector main body  2  and the light oscillation unit  5   a  can be provided on the undersurface side, i.e., the light oscillation unit  5   a  can be disposed in another recess in place of disposing the same in a recess closest to the inlet and another material, e.g., quartz glass and the like, can also be used in place of the sapphire light transmission plate  11   a.    
         [0062]    Specifically, in the holding and fixing body  12 , as illustrated in  FIG. 4 , the flange accommodation hole  12   a  is provided in the central portion of a 12 to 15 mm thick square steel plate and insertion holes  12   b  for the fixation bolts  8  are provided in both sides thereof. 
         [0063]    Moreover, a step portion  12   c  which is fitted to the upper surface of the outer circumferential portion of the first fixing flange  14  for pressurizing the same is formed in the lower end portion of the holding and fixing body  12 . The diameter of the lower portion of the flange accommodation hole  12   a  is enlarged and is formed in the accommodation portion of the first fixing flange  14 . 
         [0064]    As illustrated in  FIG. 5 , the second fixing flange  16  is formed in the shape of a short cylinder formed of stainless steel and the central portion on one side thereof is formed in the projection portion  16   b  having a stepwise narrowed diameter by a two-step portion  16   a.    
         [0065]    The tip surface  16   d  of the tip portion of the narrowed projection portion  16   b  serves as the seal surface abutting on the thin light transmission plate  11   a  having a thickness of about 0.8 to 1.5 mm. 
         [0066]    As illustrated in  FIG. 6 , the first fixing flange  14  is formed in a disk shape with stainless steel and is formed in the insertion recess  14   b  having a stepwise narrowed diameter by a three-step portion  14   a  in the central portion. Moreover, the insertion recess  14   b  is formed in such a manner as to penetrate and is connected to the recess  17  of the detector main body  2 . 
         [0067]    Furthermore, the middle portion of the three-step portion  14   a  forms an accommodation portion of the sapphire light transmission plate  11   a , and the sapphire light transmission plate  11   a  is placed and fixed therein. 
         [0068]    The accommodation portion  14   d  for the gasket  6   a  is formed in the undersurface side of the first fixing flange  14 , and the upper half portion of the gasket type seal  6  is inserted and fixed therein. 
         [0069]    As illustrated in  FIG. 7 , the gasket type seal  6  is configured from the gasket accommodation portion  14   d  of the first fixing flange  14 , the gasket accommodation portion  17   a  on the side of the detector main body  2 , the ring-like gasket  6   a , a ring-like retainer  6   b , a ring-like guide ring  6   c , and the like and is configured to be sealed double by the seal surfaces  15  and  15 . 
         [0070]    It is confirmed that the sapphire light transmission plate  11   a  constituting the light transmission window formed of the plate member  11  contains a brittle fracture material is a so-called single crystal of high purity alumina (Al 2 O 3 ) formed with a thickness of 0.8 to 1.5 mm and has excellent abrasion resistance, corrosion resistance (chemical resistance), heat resistance, and the like, and thus the sapphire light transmission plate  11   a  is hardly corroded and degraded by organic raw material gas when used for semiconductor manufacturing and the optical transparency thereof is hardly changed. 
         [0071]    Since the gasket type seal  6 , the sapphire light transmission plate  11   a , the photodiode  10 , and the like are known, a detailed description thereof is omitted herein. 
         [0072]    Next, a density detection test of the raw material fluid density detector  1  according to the present invention and the results thereof are described. 
         [0073]    First, as illustrated in  FIG. 8 , the raw material fluid density detector  1  was connected to a supply pipe line of process gas (Organic raw material TMGa steam) for semiconductor manufacturing apparatus in the in-line shape, and then light was emitted to the light oscillation unit  5   a  through the optical fiber  9  from a light source device  18 . The photodiodes  10  of the light oscillation unit  5   a  and the light detection unit  5   b  are set to a right receiving surface having a size of 1.0 mm×1.1 mm, a diameter of 504 mm, and a height of 3.6 mm. The sapphire light transmission plate  11   a  is set to a thickness of 1.0 mm and a diameter of 8.0 mm. The length of the flow path length  2   b  between the light oscillation unit  5   a  and the light detection unit  5   b  is set to 30 mm and the internal diameter of the flow path is set to 4.0 mmφ. 
         [0074]    Light is emitted to the light oscillation unit  5   a , a detection output from the photodiode  10  of the light oscillation unit  5   a  is input into the arithmetic calculation device  19  through a reflected light detection device  18   a  and also a detection output from the photodiode  10  of the light detection unit  5   b  is input into the arithmetic calculation device  19  through an output photon detection device  18   b , the density of the organic raw material TMGa steam flowing in the fluid flow path  2   a  is calculated herein at predetermined time intervals using Expression (1), and then the results are recorded and displayed. 
         [0075]    The detection output from the reflected light detection device  18   a  is used for compensation of the raw material density detection value in the arithmetic calculation device  19 . Thus, a measurement error of the raw material density due to so-called fluctuation of the incident light from the light source device  18 , changes with time in the light transmittance of the sapphire light transmission plate  11   a , and the like is corrected. 
         [0076]    It is confirmed from the test results that the raw material fluid density detector according to the present invention enables high-accuracy density measurement which is not inferior to a former expensive density detection meter. 
       INDUSTRIAL APPLICABILITY 
       [0077]    The present invention can be used not only for a gas supply system for semiconductor manufacturing but for continuous detection of the fluid density in every fluid supply line and fluid use apparatus treating a depositing, photoreactivity, and corrosive fluid. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  raw material fluid density detector 
           2  detector main body 
           2   a  fluid flow path 
           2   b  fluid flow path 
           2   c  fluid flow path 
           3  inlet block 
           3   a  fluid flow path 
           3   b  coupling portion 
           4  outlet block 
           4   a  fluid flow path 
           4   b  coupling portion 
           5   a  light oscillation unit 
           5   b  light detection unit 
           6  gasket type seal 
           6   a  gasket 
           6   b  ring-like retainer 
           6   c  guide ring 
           7  leakage inspection hole 
           8  fixation bolt 
           9  optical fiber 
           9   an  optical fiber insertion hole 
           10  photodiode 
           11  plate member (light transmission window) containing brittle fracture material 
           11   a  sapphire light transmission plate 
           12  holding and fixing body 
           12   a  flange accommodation portion 
           12   b  bolt insertion hole 
           12   c  step portion 
           13  seal surface 
           14  first fixing flange 
           14   a  step portion 
           14   b  insertion recess 
           14   c  bottom surface (seal surface) of recess 
           14   d  gasket accommodation portion 
           16  second fixing flange 
           16   a  step portion 
           16   b  projection portion 
           16   c  photodiode accommodation recess 
           16   d  tip surface (seal surface) of projection portion 
           17  recess 
           17   a  gasket accommodation portion 
           18  light source device 
           18   a  reflected light detection device 
           18   b  output light detection device 
           19  arithmetic calculation device 
           20  standard density meter