Abstract:
In semiconductor surface inspection apparatus, foreign matter that sticks to the wafer can reduce the quality of the wafer. The present invention is directed to improving the internal cleanliness of the apparatus. Specifically, during rotation of a semiconductor wafer, foreign matter suspended in an atmosphere surrounding the wafer is attracted to a central section of the wafer, and that while heading from the central section of the wafer, towards an outer edge thereof, the foreign matter is most likely to stick to the wafer. In conventional techniques, sufficient consideration is not given to such likelihood of foreign matter sticking This invention supplies a medium from two directions to an inner circumferential section of a substrate. In accordance with the invention, foreign matter that sticks to a wafer can be reduced more significantly than in the conventional techniques.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a surface inspection apparatus that inspects foreign substances, flaws, and other defects present on surfaces of objects such as semiconductor wafers or ceramic substrates. 
         [0003]    2. Description of the Related Art 
         [0004]    If foreign substances, flaws, or other defects are present on the surface of a semiconductor wafer, semiconductor devices fabricated using such semiconductor wafer will be defective. Accordingly, the wafer needs inspection by a surface inspection apparatus to scan for defects. The surface inspection apparatus irradiates the wafer surface with laser light, receives the light reflected from the wafer, and compares the light signal with a threshold value to determine whether the wafer is nondefective. At this time, the wafer is fixed by a substrate-holding jig and rotated at a predetermined speed by a spindle. Simultaneously with the rotation by the spindle, the wafer is moved rectilinearly by a stage. The rotation by the spindle and the linear movement by the stage make the laser light helically scan the wafer surface in relative form. The entire wafer surface is inspected during the scan. In manufacturing lines, the inspection apparatus may also be used with a view to monitoring an occurrence status of dust raised from manufacturing apparatuses. 
         [0005]    With the miniaturization of semiconductor circuit width in recent years, the foreign substances, flaws, and other surface defects becoming a problem if they stick to wafers are also being miniaturized in size. The dimensional miniaturization of these defects is, in turn, increasing the number of defects likely to become a problem, and this tendency is bringing about a call for further improvement of the internal cleanliness of apparatuses. 
         [0006]    Among existing techniques relating to the cleaning of an inspection apparatus are those described primarily in JP-2011-75351-A, JP-2010-236948-A, and JP-1995-230037-A. JP-2011-75351-A discloses a technique in which multiple fan-filtering units, each of which comprises a fan and exhaust unit for supplying clean air, are disposed and flow rates of air in each of the fans and exhaust units are controlled to suppress a disturbance in the apparatus internal air flow and reduce the volume of foreign matter likely to stick to a wafer. 
         [0007]    JP-2010-236948-A discloses suppressing a disturbance in an air flow near a semiconductor wafer by incorporating louver and exhaust unit structural design considerations for reduced sticking of foreign matter to the wafer. 
         [0008]    JP-1995-230037-A discloses adopting a downward flow scheme and exhaust unit structure for reduced sticking of foreign matter to a wafer. 
         [0009]    Other related techniques include those proposed in JP-2000-230910-A, U.S. Pat. No. 7,420,668, U.S. Pat. No. 7,372,559, and U.S. Pat. No. 6,005,660. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention is based upon the inventors&#39; findings that during rotation of a semiconductor wafer, foreign matter suspended in an atmosphere surrounding the wafer is attracted to a central section of the wafer, and that while heading from the central section of the wafer, towards an outer edge thereof, the foreign matter is most likely to stick to the wafer. 
         [0011]    More specifically, this event is accounted for as follows. (1) While the semiconductor wafer is rotating at several thousands of revolutions per minute (rpm), inspection is conducted and friction between the wafer and the air resulting from the rotation generates an airflow similar to that formed by a disc fan. (2) The airflow near the rotating wafer increases in circumferential flow velocity as it moves closer to the outer edge of the wafer. Thus, the airflow gains a speed by an action of centrifugal force to move to radial outside of the wafer and move further outward from the wafer surface. Compared with a circumferential section of the wafer, therefore, the central section thereof assumes a negative pressure and moves the airflow to the central section of the wafer. (3) The airflow that has moved to the central section of the wafer moves away therefrom, towards the outer edge and then moves to the outside of the wafer. (4) For this reason, the foreign matter that sticks to the rotating wafer is considered to stick while traveling along a route similar to that of the airflow. 
         [0012]    The rotational airflow generated by the rotation of the wafer spinning at several thousands of rpm has a higher flow velocity than an airflow supplied from the fan-filtering unit disclosed in Patent Document 1, and tends to become a ruling flow inside the inspection unit. A risk of the atmosphere being stirred up or disturbed by the rotational airflow, therefore, cannot be completely eliminated by merely adopting the method disclosed in JP-2011-75351-A. 
         [0013]    JP-1995-230037-A discloses the downward flow scheme in which clean air is supplied downward from a direction above the wafer. However, parts of an optical system which serves as a core of inspection are usually arranged above the wafer and no consideration is given to in what form the system for supplying the airflow is to be disposed. Even after the layout of the optical system parts has been changed to enable the application of the downward flow scheme, if parts exist above the wafer, a disturbance in the airflow at rear of the parts may cause foreign matter to stem from the parts. If this actually happens, the foreign matter is most likely to stick to the wafer. 
         [0014]    The present invention is intended to reduce the volume of foreign matter likely to stick to a wafer. 
         [0015]    The present invention features supplying a medium to an inner circumferential section of a substrate from two directions. 
         [0016]    In accordance with the present invention, the volume of foreign matter likely to stick to the wafer can be reduced as compared with conventional techniques. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a schematic diagram of an inspection apparatus according to a first embodiment; 
           [0018]      FIG. 2  is a top view showing a schematic configuration of the inspection apparatus according to the first embodiment; 
           [0019]      FIGS. 3A and 3B  are front views showing the schematic configuration of the inspection apparatus according to the first embodiment; 
           [0020]      FIG. 4  is a schematic diagram of an airflow formed around a substrate when no duct is used; 
           [0021]      FIG. 5  is a schematic diagram of an airflow formed around the substrate when duct is used; 
           [0022]      FIG. 6  is a flowchart that shows an operational sequence of the inspection apparatus according to the first embodiment; 
           [0023]      FIG. 7  is a top view showing a schematic configuration of an inspection apparatus according to a second embodiment; 
           [0024]      FIG. 8  is a schematic diagram of an airflow supplied from the inspection apparatus according to the second embodiment; 
           [0025]      FIG. 9  is a flowchart that shows an operational sequence of the inspection apparatus according to the second embodiment; 
           [0026]      FIG. 10  is a top view showing a schematic configuration of an inspection apparatus according to a third embodiment; 
           [0027]      FIGS. 11A ,  11 B, and  11 C are detailed views of an airflow supply system according to the third embodiment; 
           [0028]      FIG. 12  is a diagram illustrating an example of supplying an airflow at an average flow velocity of 5 m/s from two ducts,  1201  and  1202 , to a substrate  1203 ; 
           [0029]      FIG. 13  is a diagram illustrating an example of supplying an airflow at an average flow velocity of 1 m/s from the two ducts,  1201  and  1202 , to the substrate  1203 ; 
           [0030]      FIGS. 14(   a ) and  14 ( b ) are explanatory diagrams of a fourth embodiment; and 
           [0031]      FIGS. 15(   a ) and  15 ( b ) are additional explanatory diagrams of the fourth embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    Hereunder, embodiments of the present invention will be described using the accompanying drawings. 
       First Embodiment 
       [0033]    A schematic diagram of an inspection apparatus according to a first embodiment is shown in  FIG. 1 . A laser light emitter  104  emits laser light  107  towards a substrate  101 . After the emission of the laser light  107 , backscattered light  108  from the substrate  101  is received by an optical system  105  for detection. The detected signal is compared with a threshold level by a processing unit  106 , and if the detected signal level is higher than the threshold level, the signal is determined to indicate presence of foreign matter or a surface defect such as a flaw. If the signal level is lower than the threshold level, on the other hand, the signal is determined to be a false report. In the detection step, the substrate  101  is fixed by a substrate-holding jig  102  and rotated by a spindle  103 . During substrate rotation, an illumination region that the laser light emitter  104  has formed upon the substrate  101  is scanned in a circumferential direction. Various control described later herein is conducted by the processing unit  106 . 
         [0034]      FIG. 2  is a top view of the inspection apparatus existing when viewed from a direction above the substrate  101  in the present embodiment. The substrate  101  is retained by the substrate-holding jig  102 . The substrate-holding jig  102  is mounted on the spindle  103 . The spindle  103  is mounted on a moving stage  201 . The moving stage  201  moves the substrate  101  rectilinearly in a direction of arrow  204 , along a surface of a stage  202  disposed on a stage  203 . Since the substrate  101  is rotated by the spindle  103  and moved by the moving stage, the laser light  107  causes the illumination region  2001  on the substrate  101  to draw a helical path in relative form with respect to the substrate  101 . 
         [0035]    In a moving zone of the moving stage  201 , ducts  211  to  218  for supplying an airflow, one example of a medium, are arranged in a moving direction of the stage  201 . The medium may be a nitrogen gas, an argon gas, or any other appropriate inert gas, instead of air. A distance between the ducts  212  and  214  is expressed in terms of D 1  (this also applies to a distance between the ducts  211  and  213 ), a distance between the ducts  214  and  216  is expressed in terms of D 2  (this also applies to a distance between the ducts  213  and  215 ), and a distance between the ducts  216  and  218  is expressed in terms of D 3  (this also applies to a distance between the ducts  215  and  217 ), where D 1 =D 2 =D 3 . 
         [0036]      FIGS. 3A and 3B  are diagrams representing a relationship between an optical system  301  and the ducts  211  to  218 .  FIG. 3A  shows the inspection apparatus existing when viewed from an x direction in the present embodiment. The optical system  301  includes an illumination optical system such as the laser light emitter  104 , and the detection optical system  105 . The optical system  301  is disposed above the substrate  101 , and the ducts  211  to  218  are disposed around the optical system  301 . 
         [0037]      FIG. 3B  shows the inspection apparatus existing when viewed from a y direction in the present embodiment. The detection optical system  105  includes a lens  3001  that converges the light backscattered from the substrate  101 , and a photoelectric conversion element  3002  that conducts a photoelectric conversion of the converged light. The lens  3001  is provided to acquire the light from the substrate  101  in a certain zone  3003 , and the duct  212 , for example, is disposed outside the zone  3003  so as not to trouble or inconvenience the detection of the light from the substrate  101  (the same also applies to the other ducts). The detection optical system in the present embodiment may include a plurality of combinations of the lens  3001  and photoelectric conversion element  3002  shown in  FIG. 3B . 
         [0038]    Next, layers of clean air that the ducts  211  to  218  form on the substrate  101  in the present embodiment are described below. An example of not using the ducts  211  to  218  is first described below.  FIG. 4  is a diagram illustrating an airflow formed around the substrate  101  when the ducts  211  to  218  are not used. The substrate  101  is supported by the substrate-holding jig  102 , and when viewed from above, the substrate is rotated counterclockwise by the spindle  103 . The rotation of the substrate  101  generates an airflow  402  heading downward from the direction above the substrate  101 , towards a central section of the substrate, and then near the surface of the substrate  101 , the airflow  402  next heads from the central section of the substrate, towards an outer edge thereof. Additionally, as the airflow  402  approaches the outer edge of the substrate  101 , it decreases in circumferential velocity and increases in disturbance. Much of the foreign matter considered to exist in the airflow  402  moves along substantially the same route as that of the airflow, and sticks to the substrate  101  in a course of the movement. 
         [0039]    An example of using the ducts  211  to  218  is next described below.  FIG. 5  is a diagram illustrating an airflow formed around the substrate  101  when the ducts  211  to  218  are used. The ducts  211  and  212 , especially, lines of projection onto the substrate  101 , are arranged in mutually opposed form to face an inner circumference, more specifically the central section  401 , of the substrate  101 , and supply airflows  511  and  512 , respectively, that are cleaner than an atmosphere surrounding the substrate  101 , towards the central section of the substrate  101 . The clean airflows  511 ,  512  are created as a result of cleaning with a filter or the like inside the ducts  211 ,  212 . 
         [0040]    During the rotation of the substrate  101 , the clean airflows  511  and  512  become clean airflows  521  and  522  each heading from the central section  401  of the substrate  101 , towards the outer edge thereof. The clean airflows  521 ,  522  stream near the entire surface of the substrate  101 . That is to say, highly clean layers of air are formed on or directly near the substrate  101 . The airflow  402  lower than the airflows  521 ,  522  in cleanliness streams externally to the airflows  511 ,  512 ,  521 ,  522 , thus allowing the volume of foreign matter likely to stick to the substrate  101 . 
         [0041]    When the clean airflows  511 ,  512  are supplied, their flow velocities can also be controlled. This characteristic is described below using  FIGS. 12 and 13 .  FIG. 12  is a diagram illustrating an example of supplying an airflow at an average flow velocity of 5 m/s from two ducts,  1201  and  1202 , to a substrate  1203  mounted on a substrate-holding jig  1202 .  FIG. 13  is a diagram illustrating an example of supplying an airflow at an average flow velocity of 1 m/s from the two ducts,  1201  and  1202 , to the substrate  1203  mounted on the substrate-holding jig  1204 .  FIG. 12 , which shows airflows supplied at higher flow velocities than the airflow shown in  FIG. 13 , indicates that flow lines  1211  and  1212  that pass through a neighborhood of the substrate  1203  move from the ducts  1201  and  1202 , respectively, onto the substrate  1203 . Meanwhile,  FIG. 13 , which shows the airflow of a lower flow velocity, indicates that a flow line  1301  moves from a non-duct region, onto the substrate  1203 . These facts indicate that if the flow velocities of cleaner airflows are appropriately controlled to a fixed level as in  FIG. 12 , the cleaner airflows can be supplied to the central section of the substrate  1203  for improved cleanliness in the neighborhood of the wafer. 
         [0042]    Referring back to  FIG. 5 , when air is supplied from the ducts  211 ,  212  at a fixed flow velocity or more, the clean airflow  511  and the clean airflow  512  collide against each other and also against the substrate  101 , thus causing a pressure of the air near the central section of the substrate  101  to rise relative to a pressure of its surrounding region. This prevents entry of the low-cleanliness airflow  402  more reliably and maintains the neighborhood of the substrate surface at a high level of cleanliness. 
         [0043]    Additionally, if the airflows  511 ,  512  supplied from the ducts  211 ,  212  are controlled to increase in both flow velocity and flow rate, this increases thickness of the clean layers of airflow that the airflows  511 ,  512  form on the substrate  101 , thus further reduces the volume of foreign matter stirred up from the outside of the clean layers of airflow by a disturbance in the airflows at the outer edge, and results in a further reduced volume of foreign matter sticking to the wafer. Furthermore, the increase in the flow rates of the airflows  511 ,  512  increases the flow velocities at which the airflows move in a radially outward direction of the substrate  101 , at the outer edge thereof. The foreign matter that has been stirred up by the disturbance is therefore discharged from the surface of the substrate  101  more rapidly, with the result that the volume of foreign matter likely to stick is also further reduced. 
         [0044]    Since the clean airflows  511 ,  512  need only to be supplied towards the central section of the substrate  101 , it is unnecessary for the ducts  211 ,  212  to completely face each other. If both face each other, however, the central section of the substrate  101  can be boosted in pressure effectively and for the reason described above, such orientations of the ducts  211 ,  212  are more effective for reducing the amount of contamination with foreign matter. 
         [0045]    The opposed layout of the ducts  211 ,  212  further yields the following advantageous effect. That is, during slow spindle rotation at several tens of rpms or several hundreds of rpm, the airflow by the rotation of the substrate  101  is not a ruling one. Instead, airflows from the ducts  211 ,  212  become ruling ones. As shown in  FIG. 5 , when the ducts  211 ,  212  are arranged to face each other for collisions between the airflows  511 ,  512 , these clean airflows have a relatively uniform density on or directly near the surface of the substrate  101 , compared with the airflow formed when the ducts are not in opposed arrangement. The result is that the amount of contamination with foreign matter can also be reduced during slow rotation. 
         [0046]    Next, an operational sequence of the inspection apparatus according to the present embodiment is described below using a flowchart of  FIG. 6 . First, the substrate  101  is mounted on the substrate-holding jig  102  (step  600 ). The processing unit  106  activates the spindle  103  to rotate the substrate  101  (step  601 ). After confirming that the rotation of the substrate  101  has reached a fixed rotating speed for inspection, the processing unit  106  moves the moving stage  201  (step  602 ). The processing unit  106  next detects any ducts arranged near the surface of the substrate  101  (step  603 ). The ducts that have been determined to be present near the surface of the substrate  101  open respective internal valves to supply clean airflows (step  604 ). If no ducts are determined to be present near the surface of the substrate  101 , the respective internal valves are closed so as not to supply a clean airflow (step  605 ). Inspection takes place between steps  601  and  604 . After the inspection of the entire substrate surface, next substrate is inspected (step  606 ). 
         [0047]    Step  603  is described in further detail below. Constantly changing central positions of the substrate  101  are defined in an internal program of the processing unit  106  beforehand from a horizontal moving speed and other factors of the substrate  101 , and ducts present near the surface of the substrate  101  are detected from a relationship between the central position thereof at a specific time and previously saved positions of each duct. 
         [0048]    To be more specific, if the horizontal moving speed of the moving stage  201  is expressed as “v”, a distance through which the center of the substrate  101  moves while a time “t” elapses from a start of the horizontal movement can be expressed as “vt” in the x-axis direction represented in  FIG. 2 . If the distances between the ducts arranged in the moving direction of the substrate  101  are expressed here in terms of D 1  and D 2  as shown in  FIG. 2 , the ducts above the substrate  101  can be detected by setting the program as follows: 
         [0000]      0 ≦vt&lt;D   1 /2→Supply from ducts 211, 212   (1)
 
         [0000]        D   1 /2≦ vt &lt;( D   1   +D   2 /2)→Supply from ducts 213, 214   (2)
 
         [0000]      ( D   1   +D   2 /2)≦ vt &lt;( D   1   +D   2   +D   3 /2)→Supply from ducts 214, 216   (3)
 
         [0000]      ( D   1   +D   2   +D   3 /2)≦ vt ≦( D   1   +D   2   +D   3 )→Supply from ducts 217, 218   (4)
 
         [0049]    Ideally, while the substrate  101  is moving horizontally, a clean airflow keeps the pressure near the center of the substrate  101  higher than its surroundings at all times. Supply of the clean airflow, however, is not limited to the above-described control method. During the inspection time (this time can also be expressed as a time during which the moving stage  201  is moving), a substantially clean layer of air needs only to be present on or directly near the surface of the substrate  101 . In addition, while the number of opposed duct pairs in the present embodiment is four, the number of ducts is not limited to the embodiment and any other number suffices if a substantially clean layer of air is formed on or directly near the surface of the substrate  101 . 
         [0050]    In accordance with the present embodiment, the volume of foreign matter likely to stick to the substrate  101  can be reduced as compared with the conventional techniques discussed earlier herein. 
       Second Embodiment 
       [0051]    The following describes a second embodiment. The second embodiment has the following two differences from the first embodiment: (1) ducts are arranged more densely than in the first embodiment, and (2) a temperature of airflows supplied from the ducts is changed (controlled). 
         [0052]      FIG. 7  is a top view illustrating an inspection apparatus according to the present embodiment. In the present embodiment, the ducts  701  to  712  are arranged so that distance D between any two ducts, in a direction of arrow  204 , is shorter than D w /2, a radius of a substrate  101 . 
         [0053]    The airflows supplied in the present embodiment are described below using  FIG. 8 . In the present embodiment, the ducts  703 ,  704  are oriented towards a central section  401  of the substrate  101 , and the ducts  701 ,  702 ,  706  are arranged externally to the ducts  703 ,  704  and oriented towards an outer edge of the substrate  101 . 
         [0054]    When viewed from above, the substrate  101  is rotating counterclockwise by an action of a spindle  103 . In the present embodiment, a clean airflow is supplied only from the ducts  701 ,  703 ,  704 ,  706 , and no clean airflow is supplied from the ducts  702 ,  705 . 
         [0055]    Clean hot airflows  801  and  802  that have been heated by a heater or the like to a temperature higher than an ambient temperature, and passed through the filter at least once, are supplied from the ducts  703 ,  704 . The rotation of the substrate  101  causes the hot airflows  801 ,  802  to head from the central section of the substrate  101 , towards the outer edge of the substrate, and become clean hot airflows  811 ,  812  that stream near the substrate surface. 
         [0056]    On the other hand, clean cold airflows  821  and  822  that have been cooled by a cooler or the like to a temperature equal to or lower than the ambient temperature, and passed through the filter at least once, are supplied from the ducts  701 ,  706 . The clean airflows  821 ,  822  stream above the clean hot airflows  811 ,  812 . Forming these airflows causes the clean hot airflows to stream near the surface of the substrate  101 , and forms a flow field in which the clean cold airflows stream externally to the clean hot airflows. 
         [0057]    Operational actions of the present embodiment are accounted for as follows: if a temperature gradient exists around microscopic foreign matter as small as nearly submicrons (submicrometers) in diameter, heat migration exerts upon the foreign matter a force making it move to lower-temperature regions, such that the foreign matter moves to the lower-temperature regions. In  FIG. 8 , warmer airflows exist at sections closer to the substrate  101 , cooler airflows exist at sections more distant from the substrate  101 , and hence even when the foreign matter is present in the clean hot airflows  811 ,  812  or the clean cold airflows  821 ,  822 , the foreign matter undergoes the force to move away from the substrate  101  and leave the neighborhood thereof, which in turn allows reduction in the amount of contamination with foreign matter. 
         [0058]    Next, an operational sequence of the inspection apparatus according to the present embodiment is described below using a flowchart of  FIG. 9 . First, the substrate  101  is mounted on a substrate-holding jig  102  (step  900 ). A processing unit  106  activates the spindle  103  to rotate the substrate  101  (step  901 ). After confirming that the rotation of the substrate  101  has reached a fixed rotating speed for inspection, the processing unit  106  moves a moving stage  201  (step  902 ). The processing unit  106  next detects any ducts arranged near the surface of the substrate  101  (step  903 ). Of all ducts present on or near the surface of the substrate  101 , only those closest to the central section  401  are detected (step  904 ). A clean hot airflow is supplied from each duct closest to the central section  401  (step  906 ). Supply of an airflow from ducts other than those which have been determined to be present near the surface of the substrate  101  is stopped (step  905 ). A clean cold airflow is supplied from the remaining ducts present near the surface of the substrate  101  (step  907 ). At this time, an airflow is supplied from the ducts facing in the same direction as a tangent direction with respect to the rotation of the substrate  101 , and the supply of the airflow from the ducts facing in an opposite direction is stopped. 
         [0059]    More specifically, as shown in  FIG. 8 , the present embodiment supplies the clean hot airflows  801 ,  802  from the ducts  703 ,  704 , and supplies the clean cold airflows  821 ,  822  only from the ducts  701 ,  706  whose airflow supply directions match the tangent direction with respect to the rotation of the substrate  101 . 
         [0060]    In the present embodiment, when the substrate  101  rotates counterclockwise in  FIG. 7 , airflows are supplied in the following time-series timing with a progress of the movement of the substrate  101 :
   (1) Supply a clean hot airflow from the ducts  703 ,  704 , and supply a clean cold airflow from the ducts  701 ,  706     (2) Supply a clean hot airflow from the ducts  705 ,  706 , and supply a clean cold airflow from the ducts  703 ,  708     (3) Supply a clean hot airflow from the ducts  707 ,  708 , and supply a clean cold airflow from the ducts  705 ,  710     (4) Supply a clean hot airflow from the ducts  709 ,  710 , and supply a clean cold airflow from the ducts  707 ,  712     
 
         [0065]    In accordance with the present embodiment, foreign matter can be prevented from sticking. Although an example in which an airflow of a different temperature is supplied above the substrate  101  has been described in the present embodiment, an airflow of much the same temperature, not an airflow of a different temperature, may be used to supply an airflow that streams in the same direction as the tangent direction with respect to the rotation of the substrate  101 . Advantageous effects obtained in this case are substantially the same as in the first embodiment. 
       Third Embodiment 
       [0066]    Next, a third embodiment is described below. In the third embodiment, a system configuration that supplies airflows differs from those of the first and second embodiments. While the first and second embodiments have used a plurality of ducts arranged spatially apart from one another, the present embodiment uses substantially one airflow supply system fitted with a plurality of blowout ports. 
         [0067]      FIG. 10  is a top view illustrating an inspection apparatus existing when viewed from a direction above a substrate  101  in the present embodiment. In the present embodiment, airflow supply systems  1001  and  1002  are arranged in a direction, indicated by arrow  204 , where the substrate  101  is carried by a moving stage  201 . The airflow supply systems  1001 ,  1002  supply airflows to a neighborhood of the substrate surface while the moving stage  201  carries the substrate  101 . 
         [0068]    The airflow supply system  1001  is next described in detail below using  FIGS. 11A ,  11 B, and  11 C.  FIG. 11A  is a perspective view of the airflow supply system  1001 .  FIG. 11B  is an external view of the airflow supply system  1001  as viewed from an airflow supply direction, and  FIG. 11C  is a sectional view of the airflow supply system  1001 , at a section  1103  shown in  FIG. 11B . The airflow supply system  1002  is of the same structure as that of the system  1001 . 
         [0069]    The airflow supply system  1001  has a structure with a plurality of ducts adjacent to each other, the ducts each including a blowout port  1200  having a width “d”. 
         [0070]    As shown in  FIG. 11C , each duct forms an independent flow channel around the blowout port  1200 . On the inside distant from the blowout port  1200 , however, all ducts are coupled to one flow channel  1210 . 
         [0071]    A belt  1101  with a hole  1102 , and two belt take-up mechanisms,  1111  and  1112 , are provided inside the airflow supply system  1001 . The belt take-up mechanism  1111 ,  1112  allow a position of the hole  1102  in the belt  1101  to be controlled. In this case, width of the belt  1101  and that of the belt  1102  are set to be nearly equal to the width “d” of the blowout port  1200  of the airflow supply system  1001 . 
         [0072]    In the airflow supply system  1001 , central coordinates of the substrate  101  in  FIG. 10  and those of the hole  1102  in the belt  1101  of  FIG. 11  can be matched in the direction of arrow  204  shown in  FIG. 10 , and thus the center of the substrate  101  and a clean airflow supply position can be matched. As a result, even when the substrate  101  is moving horizontally, clean airflows can always be supplied to the center of the substrate  101 , for suppressed sticking of foreign matter. To obtain these favorable effects, if the number of ducts with the width “d” is taken as N and the distance through which the moving stage  201  moves is taken as L, then the three parameters are desirably set to satisfy a relationship of d·N&gt;L. 
         [0073]    In addition, providing a filter over an entire surface of the blowout port  1200  in the airflow supply system  1001  allows clean airflows to be supplied from the airflow supply system  1001 , even if friction occurs between the belt  1101  and the airflow supply system  1001  and/or foreign matter arises from the belt take-up mechanisms  1111 ,  1112 . 
       Fourth Embodiment 
       [0074]    Next, a fourth embodiment is described below. Depending upon a rotating speed of a spindle, the present embodiment changes at least one of a flow rate and flow velocity of a medium supplied to a substrate. 
         [0075]    How the flow rate of the medium supplied to the substrate is changed according to the particular spindle speed is first described below.  FIGS. 14(   a ) and  14 ( b ) are explanatory diagrams of the present embodiment,  FIG. 14(   a ) representing a relationship between time and the rotating speed of the spindle  103  in one of the first to third embodiments, and  FIG. 14(   b ) representing a relationship between time and the flow rate “v” of an airflow supplied to the substrate  101  in one of the first to third embodiments. 
         [0076]    Time T 1  denotes a time required for the spindle to reach a desired rotating speed for inspection, time T 2  denotes a time during which the inspection is ongoing at the desired spindle speed, and time T 3  denotes a time required for the substrate  101  to complete the rotation from an end of the inspection. 
         [0077]    During time periods of T 1 , T 2 , foreign matter may stick to the substrate  101  more significantly than during any other time periods. In the present embodiment, therefore, a flow rate “s 1 ” within time T 1  and a flow rate “s 3 ” within time T 3  are set to be higher than a flow rate “s 2 ” within time T 2 . This helps prevent foreign matter from sticking, even during a non-inspection time. 
         [0078]    How the flow velocity of the medium supplied to the substrate is changed according to the particular spindle speed is next described below.  FIGS. 15(   a ) and  15 ( b ) are other explanatory diagrams of the fourth embodiment,  FIG. 15(   a ) representing a relationship between time and the rotating speed of the spindle  103  in one of the first to third embodiments, and  FIG. 15(   b ) representing a relationship between time and the flow velocity “v” of an airflow supplied to the substrate  101  in one of the first to third embodiments. 
         [0079]    Time T 1  denotes a time required for the spindle to reach a desired rotating speed for inspection, time T 2  denotes a time during which the inspection is ongoing at the desired spindle speed, and time T 3  denotes a time required for the substrate  101  to complete the rotation from an end of the inspection. 
         [0080]    During time periods of T 1 , T 2 , foreign matter may stick to the substrate  101  more significantly than during any other time periods. In the present embodiment, therefore, a flow velocity “v 1 ” within time T 1  and a flow velocity “v 3 ” within time T 3  are set to be higher than a flow velocity “v 2 ” within time T 2 . This helps prevent foreign matter from sticking, even during a non-inspection time. 
         [0081]    While embodiments of the present invention have been described above, contents of the embodiments may also be applied to inspection apparatuses that move the substrate  101  in an X-Y plane direction.