Patent Publication Number: US-7585204-B2

Title: Substrate polishing apparatus

Description:
This is application is a divisional of U.S. patent application Ser. No. 11/806,445, filed May 31, 2007 now U.S. Pat. No. 7,510,460, which is a divisional of U.S. patent application Ser. No. 11/169,797, filed Jun. 30, 2005, now U.S. Pat. No. 7,241,202, issued Jul. 10, 2007, which is a divisional of U.S. patent application Ser. No. 10/854,250, filed May 27, 2004, now U.S. Pat. No. 6,942,543, issued Sep. 13, 2005, which is a divisional of U.S. patent application Ser. No. 10/329,424, filed Dec. 27, 2002, now U.S. Pat. No. 6,758,723, issued Jul. 6, 2004. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a substrate polishing apparatus for polishing a substrate to be polished, including a semiconductor wafer and so on. More particularly, the present invention relates to a substrate polishing apparatus having a film thickness monitor device for continuously monitoring a state of a film thickness of a thin film on a surface to be polished of the substrate (including but not being limited to the state of the film thickness and a state of the film thickness remaining on the surface) in real time during polishing with the substrate polishing apparatus. 
     Conventional techniques for monitoring a film thickness of a thin film on a substrate for use with a substrate polishing apparatus include, for example, a film thickness monitor device for monitoring a film thickness of the thin film on a substrate, as disclosed in JP-A-2001-235311 (Japanese Patent Public Disclosure). This apparatus is configured to monitor a film thickness of a thin film on the surface of a substrate on the basis of an intensity of reflected light. Water flows in a columnar form along the surface of the substrate to be polished, and the surface thereof is irradiated with an irradiation light, and the irradiated light is reflected from the surface through the flow of water to be received by an optical fiber. 
     One aspect of a conventional substrate polishing apparatus is constructed as described above. However, a problem exists with such an apparatus in that water flowing in columnar form over a surface to be polished is not stable at a contact point with the surface and tends to vary, thus making it difficult to reliably and accurately monitor a film thickness of a thin film on the surface of the substrate film using reflected irradiated light. 
     As a similar technique, there is proposed a polishing-end-point detection mechanism as disclosed in JP-A-2001-88021. This mechanism is composed of an optical fiber mounted in a depression in the surface of the table so as to face a light-irradiating and light-receiving surface at one end thereof, and a flow path for feeding a washing liquid, the path having one end opening in the depression. By this configuration, while the washing liquid is being fed into the depression through the flow path, the surface to be polished of a wafer is irradiated with light through the washing liquid in the depression from the optical fiber, and the light reflected on the surface is received through the washing liquid and the optical fiber in the depression. The polishing-end-point is then detected on the basis of surface information about the surface of the substrate obtained from the reflected light. 
     However, a problem also exists in this art in that a washing liquid may flow in the depression in an irregular way when fed through the flow path. This is a particular problem when the washing liquid is fed through a porous member. In such a case, polishing grains contained in a polishing liquid, polished chips of the wafer, polished chips of a polishing pad, and so on enter the depression, and obstruct transmission and reception of irradiated light. Thus, information about the surface of the substrate cannot be obtained with high accuracy. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to overcome the stated problems of the conventional arts, and to provide a substrate polishing apparatus with a film-thickness monitoring device capable of monitoring a state of a film thickness of a thin film on a surface of a substrate to be polished with high accuracy and reliability during a polishing operation. 
     To achieve the stated object, the present invention in a first aspect provides a substrate polishing apparatus for polishing a substrate to be polished by means of a relative movement between the substrate and a polishing member, which comprises a table, the polishing member being fixed on top of the table. A substrate support member presses the substrate to be polished onto the polishing member. An optical system is composed of an optical fiber for irradiating the surface of the substrate with a light through a through-hole disposed in the polishing member, and an optical fiber for receiving the reflected light reflected from the irradiated light on the surface through the through-hole. 
     The substrate polishing apparatus further comprises an analysis system for analyzing the reflected light received by the optical system and a film-thickness monitoring device for monitoring a film thickness of a thin film formed on the surface of the substrate and a state of progress of polishing the thin film on the surface thereof on the basis of an analysis of the reflected light by means of the analysis system. The table is provided with a liquid-feeding opening for feeding a translucent liquid to the through-hole disposed in the polishing member. The liquid-feeding opening is disposed so that the translucent liquid fed to the through-hole through the liquid-feeding opening flows in a direction roughly perpendicular to the surface of the substrate, i.e., to form a perpendicular flow which fills the through-hole, with the optical fiber being disposed such that the irradiated light and the reflected light pass through a flow portion of the translucent liquid flowing in the direction generally perpendicular to the surface. 
     Thus, in the configuration of the substrate polishing apparatus in the first aspect of the invention, the surface of the substrate is irradiated with light through a flow portion of the translucent liquid flowing in the direction generally perpendicular to the surface, and the irradiated light reflected from the surface is received through the perpendicular flow of the translucent liquid. Accordingly, particles of foreign materials, including polishing grains contained in the polishing liquid, polished chips of the polishing member or the substrate, etc., cannot enter the perpendicular flow portion of the translucent liquid from a gap between the polishing member and the surface so that the film thickness of the thin film on the substrate can be observed with high accuracy and stability without intervention from those particles. 
     It is to be noted herein that the translucent liquid to be fed through the liquid-feeding opening may include, but is not limited to, a transparent liquid having a high transparency which is highly transparent immediately after the supply into the through-hole but may become turbid while flowing due to contamination with a polishing liquid. Therefore, the translucent liquid as referred to herein may include, but is not limited to, any transparent or translucent liquid ranging from a transparent liquid having a high degree of transparency to a translucent liquid having a low degree of transparency. 
     In a second aspect of the invention, the substrate polishing apparatus in the first aspect of the invention is further constructed such that the through-hole has a section extending in a direction perpendicular to a flow of the translucent liquid that is equal in size to the liquid-feeding opening and in fluid communication therewith. 
     As the through-hole and the liquid-feeding opening have equal sections extending in the direction perpendicular to the liquid flow and are communicated with each other, the translucent liquid fed from the liquid-feeding opening into the through-hole flows in the direction perpendicular to the surface of the substrate to be polished up to the surface. Therefore, even in a small amount, the flow of the translucent liquid is able to serve as a suitable optical path for passage of the irradiated light and the reflected light. 
     The substrate polishing apparatus in a third aspect of the invention is characterized in that the substrate polishing apparatus in the first or second aspect of the invention is further provided with a liquid-discharging groove on the surface of the polishing member, the liquid-discharging groove being for discharging the translucent liquid rearward from the inner side face of the through-hole in the direction of movement of the table. 
     As the liquid-discharging groove is provided on the upper surface of the polishing member for discharge of the translucent liquid from the inner side faces of the through-hole rearward, and in the direction of movement of the table, the translucent liquid filled in the closed space of the through-hole can be withdrawn readily from the inner side face of the through-hole without the need for any special system. 
     The substrate polishing apparatus in a fourth aspect of the invention is constructed such that the substrate polishing apparatus in the first aspect of the invention is further provided with a liquid-discharging opening for discharging the translucent liquid in the through-hole, which is located behind the liquid-feeding opening in the direction of movement of the table and has an opening at the side face of the through-hole opposite to the substrate to be polished. 
     As the substrate polishing apparatus in the fourth aspect of the invention has the liquid-discharging opening behind the liquid-feeding opening in the direction of movement of the table and has an opening at the side of the through-hole opposite the substrate, in the manner as described above, the translucent liquid within the through-hole can be withdrawn into a gap between the substrate and the polishing member without diluting the polishing liquid present therein. Further, the provision of the liquid-discharging opening behind the liquid-feeding opening in the direction of movement of the table enables a flow to form of the translucent liquid fed from the liquid-feeding opening into the through-hole, that is, it allows the translucent liquid to flow in the direction perpendicular to the surface of the substrate, in a manner as will be described hereinafter in more detail. 
     In a fifth aspect of the invention, the substrate polishing apparatus is characterized in that the substrate polishing apparatus in the fourth aspect of the invention is further arranged such that the middle point of a line segment connecting the center of the liquid-feeding opening and the center of the liquid-discharging opening is located before the central point of the through-hole in the direction of movement of the table. 
     As a result, the translucent liquid fed from the liquid-feeding opening into the through-hole is able to form a flow perpendicular to the surface of the substrate in a manner as will be described hereinafter in more detail. 
     The substrate polishing apparatus in a sixth aspect of the invention is constructed such that the substrate polishing apparatus in the fourth or fifth aspect of the invention is further provided with the through-hole in a generally elliptic section in such a manner that a circumference of the external end thereof is disposed so as to enclose the end faces of the liquid-feeding opening and the liquid-discharging opening. 
     As the generally elliptic section of the through-hole for the substrate polishing apparatus in the sixth aspect of the invention is disposed to enclose the end faces of the liquid-feeding opening and the liquid-discharging opening in the manner as described above, the area of the through-hole can be minimized to thereby reduce its influence upon polishing characteristics. 
     In a seventh aspect of the invention, the substrate polishing apparatus is characterized in that the substrate polishing apparatus in any one aspect of the fourth to sixth aspects of the invention is further provided with a forced liquid discharge mechanism to thereby enable forced discharge of liquid from the liquid-discharging opening. 
     Accordingly, the translucent liquid can be withdrawn reliably from the liquid-discharging opening without using a liquid-feeding tube or a liquid-discharging tube or without an application of a resistance between the polishing member and the surface of the substrate to be polished. 
     Further, the substrate polishing apparatus in this aspect is able to form an optical path through which the irradiated light and the reflected light can pass, as well as reduce any influence on polishing characteristics, and further avoids the need for a complicated control mechanism, because an amount of the translucent liquid to be fed can be increased by providing an appropriate valve mechanism in combination with the liquid supply system. Thus, in a case where the through-hole is covered by a substrate thereby decreasing an amount of translucent liquid supplied, or in a case that the amount of the liquid is otherwise reduced, a force for generating a negative pressure in the through-hole can be generated through the through-hole. Moreover, a constant liquid discharge effect can be exerted on the translucent liquid fed to the through-hole, and an influence upon polishing characteristics can be reduced, even in a state where the through-hole is not closed with the substrate to be polished. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration showing one example of a configuration of a substrate polishing apparatus according to the present invention. 
         FIG. 2  is a schematic illustration showing one example of a configuration of a sensor part of the substrate polishing apparatus according to the present invention. 
         FIG. 3  is a schematic illustration showing another example of a configuration of a sensor part of the substrate polishing apparatus according to the present invention. 
         FIG. 4  is a diagram showing a flow state of the translucent liquid within the through-hole of the sensor part as illustrated in  FIGS. 2 and 3 , in which  FIG. 4(   a ) illustrates a side flow of the translucent liquid within the through-hole and  FIG. 4(   b ) illustrates a plane flow thereof above it. 
         FIG. 5  is a schematic illustration showing another example of the configuration of a sensor part of the substrate polishing apparatus according to the present invention. 
         FIG. 6  is a diagram showing a flow state of the translucent liquid within the through-hole of the sensor part as illustrated in  FIG. 5 , in which  FIG. 6(   a ) illustrates a side flow of the translucent liquid within the through-hole and  FIG. 6(   b ) illustrates a plane flow thereof above it. 
         FIG. 7  is an illustration showing an example of a plane configuration of the through-hole of the sensor part for the substrate polishing apparatus according to the present invention. 
         FIG. 8  is a schematic diagram showing another example of the configuration of a sensor part of the substrate polishing apparatus according to the present invention. 
         FIG. 9  is an illustration showing a side flow of the translucent liquid at the side of the through-hole in the sensor part as illustrated in  FIG. 8 . 
         FIG. 10  is an illustration showing a side flow of the translucent liquid at the side of the through-hole in the sensor part as illustrated in  FIG. 8  (as a comparative example). 
         FIG. 11  is a schematic illustration showing another example of the configuration of a sensor part of the substrate polishing apparatus according to the present invention, in which  FIG. 11(   a ) is a plan view and  FIG. 11(   b ) is a side view in section. 
         FIG. 12  is an illustration showing a flow at the side of the through-hole in the sensor part as illustrated in  FIG. 11 . 
         FIG. 13  is an illustration showing a side flow of the translucent liquid at the side of the through-hole in the sensor part as illustrated in  FIG. 11 . 
         FIG. 14  is an illustration showing an example of a plane configuration of the through-hole of the sensor part for the substrate polishing apparatus according to the present invention. 
         FIG. 15  is an illustration showing an example of a specific configuration of the sensor part for the substrate polishing apparatus according to the present invention. 
     
    
    
     EXPLANATION OF REFERENCE NUMERALS 
       10  is a fixed table;  11 , an axis;  12 , a polishing member;  14 , a table station;  15 , a sensor-mounting bracket;  16 , a bolt;  17 , a sensor main body;  18 , a bolt;  20 , a substrate support member;  21 , a substrate;  22 , an axis;  23 , a liquid-discharging groove;  30 , a monitoring section;  31 , a spectrometer;  32 , a light source;  33 , a personal computer;  34 , an electrical signal system;  40 , a sensor part;  41 , a through-hole;  42 , a liquid-feeding opening;  43 , an optical fiber for irradiating;  44 , an optical fiber for receipt of the reflected light;  45 , an optical fiber for use with irradiation and reflection;  46 , a liquid-discharging opening;  50 , a liquid feed supply-discharge system;  51 , a liquid feed supply-discharge system; and  52 , a liquid-discharging tube. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described in more detail with reference to the accompanying drawings.  FIG. 1  is an illustration showing a configuration of a substrate polishing apparatus according to the present invention, which is equipped with a film-thickness monitoring device for monitoring a film thickness of a thin film on a substrate to be polished.  FIG. 2  is an illustration showing an example of a detailed configuration of a sensor part  40 . 
     In  FIG. 1 , reference numeral  10  denotes a fixed table rotating about an axis  11  as a rotational center, and reference numeral  20  denotes a substrate support member holding a substrate  21  to be polished, such as a semiconductor wafer or the like, and rotating about an axis  22  as a rotational center. Reference numeral  30  denotes a monitoring section that may be composed of a sensor part  40 , a spectrometer  31 , a light source  32  and a personal computer  33  for data processing. 
     The polishing apparatus having the above configuration is arranged such that a polishing member  12 , including, but not limited to, fixed polishing grains (e.g., polishing stone, fixed abrasive) or a polishing pad, is put on top of the table  10  so as to polish a surface of the substrate  21  to be polished by means of a relative movement between the polishing member  12  and the substrate  21  to be polished. The sensor part  40  functions to irradiate the surface to be polished of the substrate with light from the light source  32  and receive the light reflected from the substrate surface in a manner as will be described hereinafter in more detail. 
     The spectrometer  31  measures the spectra of a ray of the reflected light received by the sensor part  40  to yield surface information on the surface of the substrate  21  to be polished. The data-processing personal computer  33  obtains the surface information on the surface from the spectrometer  31  through an electrical signal system  34  and processes the surface information to provide information on the film thickness of the thin film on the surface of the substrate and to transmit the information on the film thickness to a controller of a polishing apparatus (not shown). The controller of the polishing apparatus carries out various controls over the polishing apparatus, including but being not limited to continuation and stop controls of the polishing operations, on the basis of the film-thickness information. In  FIG. 1 , reference numeral  50  denotes a liquid feed supply-discharge system for feeding and discharging a translucent liquid to and from the sensor part  40 . 
       FIG. 2  is a schematic illustration of an embodiment of the configuration of the sensor part  40  in the first aspect of the invention. As illustrated therein, the polishing member  12 , such as the fixed polishing grains or polishing pad, put on top of the table  10  is provided with a through-hole  41 , and a liquid-feeding opening  42  for feeding a liquid is provided at the part of the table  10  corresponding to the bottom portion of the through-hole  41 . The top portion of the through-hole  41  is closed with the substrate  21  upon polishing the substrate  21  and a translucent liquid Q (light-passing liquid) is fed through the liquid-feeding opening  42  to fill the through-hole  41  with the translucent liquid Q. The translucent liquid Q can be discharged through a gap between the polishing member  12  and the surface  21   a  of the substrate  21  to be polished. 
     The liquid-feeding opening  42  is disposed in the table  10  in such a manner that its central axis is located at a position perpendicular to a surface  21   a  of the substrate  21  to be polished. In other words, the liquid-feeding opening  42  is disposed such that the translucent liquid Q fed from the substrate  21  flows in a direction roughly perpendicular to the surface  21   a  of the substrate  21 . An optical fiber  43  for irradiating the surface  21   a  of the substrate  21  with a light of irradiation and an optical fiber  44  for receipt of the reflected light reflected on the surface  21   a  from the irradiated light are disposed within the liquid-feeding opening  42  in such a manner that their central axes are positioned in parallel to the central axis of the liquid-feeding opening  42 . 
     By the above configuration, the sensor part  40  allows the translucent liquid Q discharged from the liquid-feeding opening  42  to flow in the direction generally perpendicular to the surface  21   a  of the substrate  21 , i.e., to form a perpendicular flow with respect to the surface  21   a , in the manner as described above. The irradiation light from the optical fiber  43  is able to reach the surface  21   a  of the substrate  21  through the flow portion of the translucent liquid Q perpendicular to the surface  21   a , and the light reflected from the surface  21   a  can reach the optical fiber  44  through the flow portion of the translucent liquid Q perpendicular to the surface  21   a.    
     The flow of the translucent liquid Q passing in the direction roughly perpendicular to the surface  21   a  of the substrate  21  acts to wash the surface  21   a  as well as to prevent entry of foreign matter, including polishing grains in the polishing liquid, polished chips of the polishing member  12 , polished chips of the substrate  21  to be polished, etc., into a gap between the polishing surface  21   a  and the top surface of the polishing member  12 . Therefore, it functions appropriately as a passageway for the irradiation light and the reflected light, and enables reliable and accurate observation of a state of a thin film on the polishing surface  21   a  of the substrate  21  to be performed. 
     A liquid passageway (although not shown) communicated with the liquid-feeding opening  42  may be provided with an electromagnetic valve  47  that may be controlled to stop or regulate a supply of the translucent liquid Q when the through-hole  41  is not covered by the substrate  21  to be polished, thereby lessening any influence on polishing characteristics. Further, the sensor part  40  having the above configuration is able to work effectively in a situation where the through-hole  41  is covered with a substrate to be polished or where the table  10  is arranged so as to define a planar movement, allowing each point of the table to draw a circular locus having an identical radius without rotating the table about one axis as a rotational center. 
       FIG. 3  is a brief illustration of another embodiment of the construction of the sensor part  40  according to the first aspect of the invention. As illustrated therein, the sensor part  40  of  FIG. 3  is different from the sensor part  40  of  FIG. 2  in that it uses only one optical fiber  45  for irradiation and reflection of light in place of respective optical fibers for irradiation and reception of irradiated light. The other elements, however, are constructed in substantially the same manner as in the case of the sensor part  40  of  FIG. 2 . Using this construction, the sensor part  40  of this aspect of the invention can demonstrate substantially the same action and effects as that of  FIG. 2 . 
       FIG. 4  illustrates the state of a flow of the translucent liquid at the sensor part  40  as illustrated in  FIGS. 2 and 3 . As illustrated in this figure, the flow state of the translucent liquid Q is drawn on the basis of the results of numerical analysis of the flow which has been made on the assumption that a flow of the translucent liquid Q occurs, together with a movement of the surface  21   a  of the substrate  21 , at the portion nearest to the surface  21   a . This is true of  FIGS. 6 ,  9 ,  10 ,  12 , and  13 , each of which illustrates the state of each flow of the translucent liquid at other portions. 
       FIG. 4(   a ) illustrates a side flow of the translucent liquid at the side of the through-hole  41 , and  FIG. 4(   b ) illustrates a plane flow thereof at the top of the through-hole  41  (at a position spaced apart by approximately 0.03 mm above the polishing surface). Here, it is calculated that there is a clearance (CL) of 0.1 mm between the surface of the substrate  21  and the top surface of the polishing member  12 . The side flow of the translucent liquid Q at the side of the through-hole  41  constitutes a flow of the translucent liquid Q discharged from the liquid-feeding opening  42  flowing in the direction perpendicular to the polishing surface  21   a  of the substrate  21 , as indicated by the arrows in  FIG. 4(   a ). 
     On the other hand, the plane flow of the translucent liquid Q at the top of the through-hole  41  passes generally in the direction of movement of the polishing substrate  21  (opposite to the direction of movement of the table  10 ), as indicated by the arrows in  FIG. 4(   b ). Although a portion of the plane flow passes above the tip portion of the optical fiber  45 , such a flow is not sufficiently large to cause any interference with the formation of an optical path because the flow occurs only at a limited location close to the surface  21   a  of the substrate  21  to be polished. In  FIG. 4 , the arrow A indicates the direction of movement of the substrate  21 . 
       FIG. 5  is a schematic illustration of another embodiment of the sensor part  40  in the second aspect of the invention. The sensor part  40  of  FIG. 5  is different from the sensor part  40  of  FIG. 4  in that the sensor part  40  of  FIG. 5  comprises the through-hole  41  and the liquid-feeding opening  42 , in which the through-hole  41  has a section extending in a direction perpendicular to the flow of the translucent liquid Q, and is equal in size to the liquid-feeding opening  42 , and is communicated with the latter. Further, the optical fiber  43  for the irradiating light and the optical fiber  44  for the reflected light are disposed within the through-hole  41  at the sensor part  40  of  FIG. 5  such that the central lines of the optical fiber  43  and the optical fiber  44  extend in parallel to the central line of the liquid-feeding opening  42  in substantially the same manner as in  FIG. 2 . 
     As indicated in  FIG. 5 , the through-hole  41  is disposed so as to have a section positioned perpendicular to the flow of the translucent liquid Q, and is substantially equal in size to the liquid-feeding opening  42 ; and the through-hole  41  is communicated with the liquid-feeding opening  42  in the manner as described above, so that the translucent liquid Q fed through the liquid-feeding opening  42  into the through-hole  41  flows in the direction perpendicular to the surface  21   a  of the substrate  21  and flows up to the surface  21   a . In other words, the translucent liquid Q appropriately constitutes an optical path through which the irradiated light and the reflected light can pass, even in a case that the liquid exists only in a small amount. Therefore, any influence of the translucent liquid Q upon polishing of the substrate with the polishing apparatus can be minimized. 
     For the sensor part  40  of  FIG. 5 , it is possible to use only one optical fiber  45  for the irradiated light and for the reflected light, as opposed to using respective fibers, as indicated in  FIG. 3 . 
       FIG. 6  is a schematic illustration indicating a flow state of the translucent liquid Q in the through-hole  41  of the sensor part  40  in the embodiment of  FIG. 5 .  FIG. 6(   a ) illustrates a side flow of the translucent liquid Q within the through-hole  41  and  FIG. 6(   b ) illustrates a plane flow of the translucent liquid Q at the top portion of the through-hole  41  (at the position apart by about 0.03 mm from the surface in a manner similar to the case of  FIG. 4) . It is computationally assumed that there is a clearance (CL) of 0.1 mm between the surface of the substrate  21  and the top surface of the polishing member  12 . The side flow of the translucent liquid Q within the through-hole  41  is constituted as a flow in which the translucent liquid Q fed through the liquid-feeding opening  42  flows in the direction perpendicular to the substrate  21  to be polished, as indicated by the arrows in  FIG. 6(   a ). 
     As indicated by the arrows in  FIG. 6(   b ), the plane flow of the translucent liquid Q on top of the through-hole  41  flows toward outside from the inside of the through-hole  41 , so that there is no flow component that flows toward the position of the optical fiber. Therefore, as compared with the case illustrated in  FIG. 4 , it is not likely that the polishing liquid will flow in a reverse direction into the through-hole  41  through a gap between the surface  21   a  of the substrate  21  and the top of the polishing member  12 . In  FIG. 6(   a ), the arrow B indicates a direction of movement of the substrate  21  to be polished. 
       FIG. 7  indicates an embodiment of a plane disposition of the through-hole  41  of the sensor part  40  in the third aspect of the invention. In this embodiment, the polishing member  12  is provided on the surface with a liquid-discharging groove  23  for discharging the translucent liquid from the inner side of the through-hole  41  rearward in the direction of movement of the table  10 , as indicated by the arrow C of  FIG. 7 . The disposition of the liquid-discharging groove  23  can ensure easy discharge of the translucent liquid Q that may be filled in the closed space of the through-hole  41  without the provision of a special system. This embodiment is effective to transfer the substrate in the generally identical direction relative to the through-hole, including rotating the table about one axis, or the like. In particular, the liquid-discharging groove can be provided easily in the case where a groove in the form of a lattice is formed on the surface of the polishing member. 
       FIG. 8  is a schematic illustration showing another embodiment of the sensor part  40  in the fourth aspect of the invention. In this embodiment, the sensor part  40  is provided with a liquid-discharging opening  46  for discharging the translucent liquid Q filled in the through-hole  41  behind the liquid-feeding opening  42  in the direction of movement of the table  10  (in the direction as indicated by the arrow D) and has an opening at the edge face of the through-hole  41  opposite to the substrate  21 . 
     The optical fiber  43  for irradiation of light and the optical fiber  44  for reflection of irradiated light are disposed in the liquid-feeding opening  42  in such a manner that each of their central lines is positioned in parallel to the central line of the liquid-feeding opening  42  in substantially the same manner as in the case of  FIG. 2 . It can also be noted herein that the optical fiber  43  for irradiation of light and the optical fiber  44  for reflection of irradiated light may be replaced with a single optical fiber  45  for both of irradiation and reflection in a similar manner as indicated in  FIG. 3 . 
     As the liquid-discharging opening  46  is disposed in the manner as described above, the translucent liquid Q filled in the through-hole  41  can be withdrawn easily into a gap between the substrate  21  and the polishing member  12 , and further the translucent liquid Q can be withdrawn without dilution of the polishing liquid such as slurry and so on present therein. 
       FIGS. 9 and 10  illustrate each a side flow of the translucent liquid Q travelling inside the through-hole  41  of the sensor part  40  of  FIG. 8 . In  FIGS. 9 and 10 , the arrow D indicates the direction of movement of the table and the arrows E and F indicate each direction of movement of the substrate  21  to be polished. 
     As the liquid-discharging opening  46  is provided behind the liquid-feeding opening  42  in the direction of movement of the table  10  (as indicated by the arrow D) in the manner as shown in  FIG. 9 , the translucent liquid Q fed into the through-hole  41  from the liquid-feeding opening  42  collides against the surface  21   a  of the substrate  21  and then is smoothly withdrawn through the liquid-discharging opening  46 . Therefore, the translucent liquid Q fed into the through-hole  41  from the liquid-feeding opening  42  can form a flow perpendicular to the surface  21   a  of the substrate  21 . 
     However, if the liquid-feeding opening  42  and the liquid-discharging opening  46  are disposed in the direction of movement of the table  10  (as indicated by the arrow D therein) in this order as shown in  FIG. 10 , a majority of the flow of the translucent liquid Q struck against the surface  21   a  of the substrate  21  is returned upon colliding against the side wall of the through-hole  41 , with the effect that turbulence may be generated in the flow of the translucent liquid Q in the through-hole  41 . The configuration of this embodiment is also effective, however, when the substrate to be polished can be disposed so as to move in generally the same direction relative to the through-hole, for example, by rotating a table, such as a turntable, about one axis. 
       FIG. 11  is a schematic illustration of another embodiment of the sensor part  40 , as the fifth and sixth aspects of the invention, in which  FIG. 11(   a ) is a plan view and  FIG. 11(   b ) is a side view in section. As shown therein, the liquid-feeding opening  42  and the liquid-discharging opening  46  are disposed before the middle point of the line segment connecting the central point of the liquid-feeding opening  42  and the central point of the liquid-discharging opening  46  in the direction of movement of the table  10 , as indicated by the arrow D therein. More specifically, the liquid-feeding opening  42  and the liquid-discharging opening  46  are disposed in this order, that is, the liquid-feeding opening  42  is located before the liquid-discharging opening  46 , in the direction of movement of the table  10 . 
     Further, the through-hole  41  has a lateral section in a generally elliptic form so as for an outer circumference of the bottom side face thereof to enclose the upper edges of the liquid-feeding opening  42  and the liquid-discharging opening  46 . This arrangement of the through-hole  41  can form a flow of the translucent liquid Q fed into the through-hole  41  from the liquid-feeding opening  42  as a flow travelling perpendicularly to the surface  21   a  of the substrate  21  to be polished. Moreover, the formation of the through-hole  41  in a generally elliptic section minimizes the area of the through-hole  41 , thereby reducing any influence on polishing characteristics. 
     In this embodiment, too, the optical fiber  43  for irradiation of light and the optical fiber  44  for reflection of light are disposed in the liquid-feeding opening  42  such that their central lines extend in parallel to the central line of the liquid-feeding opening  42  in substantially the same manner as in the case of  FIG. 2 . It is to be noted herein, however, that the optical fibers  43  and  44  can be replaced with a single optical fiber  45  for use with both irradiation and reflection in the manner shown in  FIG. 3 . 
       FIG. 12  is a schematic illustration showing a side flow of the translucent liquid Q in the through-hole  41  in the case where the liquid-feeding opening  42  and the liquid-discharging opening  46  are disposed in such a way that the middle point of the line segment connecting the center of the liquid-feeding opening  42  and the center of the liquid-discharging opening  46  is located before the central point of the through-hole  41  in the direction of movement of the table  10  (as indicated by the arrow D). 
     Although the through-hole  41  has a circular section in each of the embodiments, as indicated in the previous figures and  FIG. 12 ,  FIG. 13  further illustrates a side flow of the translucent liquid Q in the through-hole  41  in the case where the through-hole  41  is formed in a generally elliptic section so that the outer circumference of the bottom edge encloses the side faces of the liquid-feeding opening  42  and the liquid-discharging opening  46 . 
     When the liquid-feeding opening  42  and the liquid-discharging opening  46  are disposed in the direction of movement of the table  10  (as indicated by the arrow D) with respect to the through-hole, as shown in  FIGS. 12 and 13 , the translucent liquid Q existing in the through-hole  41  at a position rearward in the direction of movement of the table  10  can be withdrawn in a smoother way than in the case of  FIG. 9 , so that the translucent liquid Q fed into the through-hole  41  from the liquid-feeding opening  42  can flow in the direction perpendicular to the surface  21   a  of the substrate  21  and form a perpendicular flow with respect to the surface  21   a.    
     The sensor part as shown in each of  FIGS. 8 and 11  may be provided with a forced liquid discharge mechanism, although not shown in the drawings, for performing a forced discharge of the translucent liquid from the liquid-discharging opening  46 . The forced liquid discharge mechanism can ensure reliable discharge of the translucent liquid Q from the liquid-discharging opening  46  without use of a liquid-feeding tube communicating with the liquid-feeding opening  42  or a liquid-discharging tube communicating with the liquid-discharging opening  46  or without an application of resistance between the surface  21   a  of the substrate  21  and the polishing member  12 . 
     Further, a supply amount of the translucent liquid Q can be increased by combining a liquid supply system with a valve mechanism having an appropriate pressure adjustment mechanism because the force may act to generate a negative pressure within the through-hole  41  in a case where the through-hole  41  is disposed and brought into a closed state, even if the supply amount of the translucent liquid Q is reduced in such a state where the through-hole  41  is not covered by the substrate  21  to be polished. 
     Therefore, in this embodiment of the present invention an optical path is formed which allows passage of irradiated light of and reflected irradiated light, as well as reducing any influence on polishing characteristics, without the need for a complex control mechanism. Moreover, this embodiment allows a constant effect to be attained in the discharge of the translucent liquid Q fed into the through-hole  41  to be expected in a state where the through-hole  41  is not closed with the substrate  21  and, at the same time, is able to reduce any influence on polishing characteristics. 
       FIG. 14  is a plan view showing an embodiment of a plane configuration of the through-hole  41  of the sensor part  40 . As indicated therein, the through-hole  41  is disposed so as to cause no interference with a groove  12   c  formed on the surface of the polishing member  12 . The provision of the groove  12   c  in this way can ensure a close engagement between the substrate  21  to be polished and the polishing member  12  and improve closing properties within the through-hole  41 , thereby preventing particles, including material grains of the polishing liquid, polished chips of the polishing member and the substrate, etc., into the through-hole  41  as well as preventing leakage of the translucent liquid Q into a gap between the substrate  21  to be polished and the polishing member  12 . 
       FIG. 15  illustrates a specific embodiment of the sensor part  40 . As indicated therein, the table  10  is fixed on a table station  14  and provided underneath with a sensor-mounting depression  12   a  for mounting a sensor. An edge portion of a sensor-mounting bracket  15  is inserted into the sensor-mounting depression  12   a  and a base portion of the sensor-mounting bracket  15  is mounted on the table station  14  through bolts  16 . 
     At a central portion of the sensor-mounting depression  12   a  is formed a hole  12   b  into which a tip portion of a sensor main body  17  of the sensor part, with the liquid-feeding opening  42  and the liquid-discharging opening  46  formed therein, is inserted. Further, the sensor-mounting bracket  15  is provided with an opening  15   a  for receiving the sensor main body  17 . By the above configuration, the sensor main body  17  is inserted into the opening  15   a  of the sensor-mounting bracket  15  and the base portion of the sensor main body  17  is in turn fixed to the sensor-mounting bracket  15  through bolts  18 . 
     Moreover, the polishing member  12 , such as a polishing stone (fixed polishing grains), a polishing pad or the like, put on the top surface of the table  10 , is provided with the through-hole  41  having an opening so as to communicate with the top ends of the liquid-feeding opening  42  and the liquid-discharging opening  46  formed in the sensor main body  17 . In addition, the liquid-feeding opening  42  and the liquid-discharging opening  46  formed in the sensor main body  17  are connected to a liquid-feeding tube  51  and a liquid-discharging tube  52 , respectively. 
     In the above embodiments, the present invention has been described in detail by taking as an example the polishing apparatus having a configuration arranged in such a manner that the surface of the substrate  21  to be polished is polished by a relative movement between the polishing member  12  and the substrate  21  in such a state that the substrate  21  supported by the substrate support member  20  is pressed onto the polishing member  12  put on the top surface of the table  10  disposed underneath. 
     It is to be noted, however, that the present invention should not be interpreted in any respect as being limited to the above embodiments, and it is to be understood that any number of modifications of such a substrate polishing apparatus are conceivable. Such modifications substrate polishmay include, but are not limited to, a configuration in which the table may be disposed above and the substrate support member may be disposed underneath. 
     EFFECTS OF THE INVENTION 
     The substrate polishing apparatus according to the embodiments of each aspect of the invention as described above, and including any appropriate conceivable modifications, can exhibit remarkable effects as described below. 
     The substrate polishing apparatus according to the embodiment in the first aspect of the invention is constructed in such a manner that the liquid-feeding opening for feeding the translucent liquid is disposed so as for the translucent liquid fed into the through-holethrough-hole to flow in the direction roughly perpendicularly to the polishing surface of the substrate to be polished, i.e., to form a perpendicular flow with respect to the polishing surface thereof, and to fill in the through-holethrough-hole and, further, that the polishing surface of the substrate is irradiated with a light of irradiation through a flow portion of the translucent liquid travelling in the roughly perpendicular direction and receives the light of reflection. 
     Therefore, a state of a film thickness on the polishing surface of the substrate can be observed with high accuracy and stability without causing any particles including polished chips of the polishing member and the substrate, etc., to be contaminated with the translucent liquid and to penetrate into a gap between the polishing member and the substrate, and without causing any interference with such particles. 
     The present invention in the second aspect can form an optical path from a small amount of the translucent liquid, which is appropriate for allowing the light of irradiation and the light of reflection to pass therethrough, because the through-hole has the same section extending in the direction perpendicular to the flow of the translucent liquid as the liquid-feeding opening and the through-hole is communicated with the liquid-feeding opening. Therefore, the translucent liquid fed from the liquid-feeding opening can flow in the direction perpendicular to the polishing surface of the substrate to be polished up to the polishing surface thereof. 
     In the third aspect of the invention, the translucent liquid filled in the closed space within the through-hole can be readily withdrawn without using any special system because the polishing member is provided on top thereof with the liquid-discharging groove rearward from the inner side face of the through-hole in the direction of movement of the table. 
     For the substrate polishing apparatus according to the embodiment in the fourth aspect of invention, the liquid-discharging opening is disposed behind the liquid-feeding opening in the direction of movement of the table and it has an opening at the edge of the through-hole opposite to the substrate to be polished. Therefore, the translucent liquid in the through-hole can be withdrawn into a gap between the substrate and the polishing member without dilution of the polishing liquid present therein. Moreover, the liquid-discharging opening is disposed in the position behind the liquid-feeding opening in the direction of movement of the table in the manner as described above, so that the translucent liquid fed into the through-hole from the liquid-feeding opening can flow in the direction roughly perpendicular to the polishing surface of the substrate to be polished, i.e., form a perpendicular flow with respect to the polishing surface thereof. 
     The present invention according to the embodiment in the fifth aspect allows the translucent liquid fed into the through-hole from the liquid-feeding opening to flow in the direction perpendicular to the polishing surface of the substrate to be polished, i.e., to form a perpendicular flow with respect to the polishing surface thereof, because the liquid-feeding opening and the liquid-discharging opening are disposed at the forward side of the through-hole in the direction of movement of the table. 
     The substrate polishing apparatus according to the embodiment in the sixth aspect of the invention can reduce an influence upon polishing characteristics because the area of the through-hole can be minimized by forming the section of the through-hole in a generally elliptic shape so as for the outer circumference of the side face thereof to enclose the edge faces of the liquid-feeding opening and the liquid-discharging opening. 
     In the seventh aspect of the invention, the translucent liquid can be withdrawn from the liquid-discharging opening with certainty without using the liquid-feeding tube or the liquid-discharging tube or without applying a resistance between the polishing surface of the substrate and the polishing member because the translucent liquid can be withdrawn in a forced way by means of the forced liquid discharge mechanism. 
     Further, this embodiment of the present invention can form an optical path appropriate for allowing a passage of the light of irradiation and the light of reflection without the provision of any complex control mechanism, while decreasing an impact on polishing characteristics, because a supply amount of the translucent liquid can be increased by combination of the liquid supply system with an appropriate valve mechanism due to the action of a force for making the pressure within the through-hole a negative pressure when the through-hole is blocked with the substrate into a closed state, even in the case where the supply amount of the translucent liquid is decreased in a state where the through-hole is not closed with the substrate to be polished. Moreover, the embodiment of the present invention can perform a constant liquid discharge effect of discharging the translucent liquid fed into the through-hole and decrease an influence upon polishing characteristics.