Abstract:
The present invention provides a light beam measuring instrument that can securely receive light reflected by a sample. The light beam measuring instrument  1  includes an optical axis tilting mechanism  13  that includes a first tilting mechanism  131  and a second tilting mechanism  132 . From the optical axis A 1  of irradiation light beam emitted from a light beam source  112 , the first tilting mechanism  131  tilts the optical axis A 1  about the first tilting axis T 1 . The second tilting mechanism  132  tilts the optical axis A 1  about the second tilting axis T 2 . The light beam measuring instrument  1  can receive the light reflected by the semiconductor chip C by means of operation of the optical axis tilting mechanism  13  even if the light reflected by the semiconductor chip C is tilted. Accordingly, this apparatus can securely perform measurement or inspection using the light beam.

Description:
TECHNICAL FIELD 
     The present invention relates to a measuring instrument using light beam (which will be referred to as “light beam measuring instrument”) that irradiates a sample with a light beam, such as laser light beam, detects the light beam reflected by the sample, and performs measurement or inspection based on the detection. 
     BACKGROUND ART 
     Light beam measuring instruments are used in various situations. Among them are included, for instance, quality inspections of semiconductor products, in which semiconductor chips are inspected whether they are correctly formed or whether wiring is correctly made, and reverse engineering of a competitor&#39;s semiconductor circuit. An end-point detector (EPD) can be regarded as a type of light beam measuring instrument for determining whether etching reaches a desired depth or not by means of light reflected from the bottom surface of etching or of interference of the lights reflected from the top surface and reflected from the bottom surface of etching during etching by plasma or the like. 
     CITATION LIST 
     Patent Literature 
     
         
         [Patent Literature 1] JP 2006-330210 A 
       
    
     Non Patent Literature 
     
         
         [Non Patent Literature 1] Ramdane Benferhat, “Plasma dry etch end-point monitor, DIGILEM”, [online], Horiba, Ltd., [searched Jun. 4, 2014], Internet 
         [Non Patent Literature 2] “Optical end-point detectors”, [online], Oxford Instruments plc, [searched Jun. 4, 2014], Internet 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     It is not always possible to visually confirm beforehand or predict the position of the part of a sample to be irradiated with a light beam. For instance, in the case of inspecting or measuring a surface of a semiconductor chip molded in a resin package, the resin mold of the package is etched by plasma or other means to reveal the semiconductor chip, which is then irradiated with a light beam. If the semiconductor chip is tilted in the package, the reflected light deviates, and the light beam may not return to the light beam measuring instrument. Normally in such an instrument for etching a resin package, the light beam is delivered from outside of the etching chamber (vacuum chamber) through a small window of the etching chamber. This inevitably leads to an elongated distance between the light beam source and the semiconductor chip (sample), and even a slight tilt of the semiconductor chip surface and the resultant deviation of the reflected light prevent the reflected light beam from returning to the light beam measuring instrument. 
     In view of such a problem in the conventional light beam measuring instrument, the present invention has an object to provide a light beam measuring instrument that can securely receive the light beam reflected by a sample. 
     Solution to Problem 
     A device according to the present invention made to solve the problem is a light beam measuring instrument including a light beam source for emitting a light beam toward an object, and a light beam detector for detecting the light beam reflected by a surface of the object, the light beam measuring instrument further including: 
     a first optical-axis-tilting mechanism configured to tilt the light beam source about a first tilting axis lying in a plane unparallel to the optical axis of the light beam emitted from the light beam source; and 
     a second optical-axis-tilting mechanism configured to tilt the light beam source about a second tilting axis lying in the plane and unparallel to the first tilting axis. 
     The light beam measuring instrument according to the present invention can tilt, in any degree, the light beam source by means of the first optical-axis-tilting mechanism and the second optical-axis-tilting mechanism. Accordingly, the direction of the light beam emitted from the light beam source, i.e., the direction of the optical axis, can be tilted as necessary, and the light beam reflected by the object can be correctly returned to the light beam detector. 
     Preferably, the light beam measuring instrument according to the present invention includes not only the mechanism of tilting the optical axis but also a translation mechanism configured to translate (or laterally move) the optical axis of the light beam emitted from the light beam source. If the direction of the optical axis is tilted by the optical axis tilting mechanism, the position on the object irradiated with the light beam moves. Even in this case, the translation mechanism can restore the irradiation position, or can fix the irradiation position on the object. The translation mechanism may be either a mechanism that translates (or moves) the light beam source, or a mechanism that translates (or moves) the object. 
     It is preferred that, in order to perform the fixation of the irradiation position automatically, an irradiation position controller be provided to drive the translation mechanism. The irradiation position controller may perform the control by analyzing the position or shape of the irradiated light beam on the object using an image, or by detecting the irradiation (tilting) angle of the light beam. In the analysis and determination of the irradiation position using an image, specifically, an intensity of the light in the image can be analyzed. 
     The optical-axis-tilting mechanism may be a cylindrical type two-axis gonio-stage including two sets of sliding partial cylindrical surfaces for the first tilting axis and the second tilting axis. Alternatively, the mechanism may be a plane tilting type two-axis gonio-stage in which a plane is tilted in two directions by moving two points other than a pivot of the plane vertically (or parallel to the optical axis) while fixing the pivot. Otherwise, a tilting mechanism using a ball joint or a universal joint may be employed. 
     Advantageous Effects of Invention 
     The light beam measuring instrument according to the present invention can always return and receive the light beam reflected by a surface of the object, even if the surface is tilted. Accordingly, this instrument can securely perform proper measurement or inspection. 
     When a mechanism for translating the light beam source is used, the object need not be moved when tilting the optical axis of a light beam in the light beam measuring instrument according to the present invention. In this case, light beam measurement or inspection can be performed while the object is undergoing a process, such as etching or the like. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an overall configuration diagram of a surface inspection apparatus according to a first embodiment of the present invention. 
         FIG. 2  is a perspective view of a main part of the surface inspection apparatus according to the first embodiment of the present invention. 
         FIG. 3  is a schematic view of the surface inspection apparatus where reflected light correctly returns to a main body tilted by a cylindrical type two-axis gonio-stage. 
         FIG. 4  is a perspective view of a main part of a surface inspection apparatus according to a second embodiment of the present invention. 
         FIG. 5  is a schematic view of the surface inspection apparatus where a main body is tilted by a plane tilting type two-axis gonio-stage. 
         FIG. 6  is an overall configuration diagram of a surface inspection apparatus of a third embodiment of the present invention. 
         FIG. 7  is an overall configuration diagram of a surface inspection apparatus according to a fourth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A first embodiment is hereinafter described where a light beam measuring instrument according to the present invention is applied to an apparatus of inspecting a surface of a semiconductor device or the like with reference to  FIG. 1  to  FIG. 3 . 
       FIG. 1  is a schematic overall configuration diagram of a surface inspection apparatus  1  according to this embodiment. The surface inspection apparatus  1  includes a main body  11 , an XY stage  12 , a cylindrical type two-axis gonio-stage  13 , a laser light condenser  14 , a control device  15  and a vacuum chamber  16 . The cylindrical type two-axis gonio-stage  13  (hereinafter, simply referred to as “two-axis gonio-stage  13 ”) is an optical axis tilting mechanism of the present invention. A sample stage  161  on which a resin package semiconductor sample S to be inspected is mounted is provided at the bottom of the vacuum chamber  16 . On the ceiling of the vacuum chamber  16  above the stage, a sample window  162  for projecting light to the sample S and receiving light reflected by the sample S is provided. In actuality, the vacuum chamber  16  forms a part of a plasma processing apparatus (plasma processing chamber). This surface inspection apparatus  1  inspects the surface of a semiconductor chip C while gradually etching the resin package of the sample S and the semiconductor chip C molded in the package. 
     The main body  11  is mounted on the XY stage  12  which is, in turn, mounted on the two-axis gonio-stage  13 , both of which are disposed aside of the sample window  162  of the vacuum chamber  16 . Though, in  FIG. 1 , the XY stage  12  is shown mounted on the two-axis gonio-stage  13 , the two-axis gonio-stage  13  may be alternatively mounted on the XY stage  12 . The control device  15  may be integrated with the main body  11 , or it may be provided separately. In the separately provided case, the control device  15  can be constructed by dedicated software installed in a personal computer. An input unit (not shown) and an output unit (not shown) are connected to the main body  11 . Alternatively, the input unit and the output unit may be connected to the control device  15 . 
     The main body  11  includes a CCD camera  111 , a laser light source  112  consisting of a laser diode, a laser light detector  113 , a visible light source  114 , and half mirrors  115 ,  116  and  117 . The half mirrors  115  to  117  are disposed in series just above the laser light condenser  14 . The visible light source  114  is disposed behind the half mirrors  115 ,  116  and  117  (on the opposite side of the laser light condenser  14 ). The CCD camera  111 , the laser light source  112  and the laser light detector  113  are disposed so as to face the reflective surfaces of the half mirrors  115 ,  116  and  117 , respectively. The laser light condenser  14  includes a condenser lens  141 . 
       FIG. 2  shows a perspective view of the main body  11 , the XY stage  12 , the two-axis gonio-stage  13  and the laser light condenser  14  of the surface inspection apparatus  1  according to this embodiment. 
     The XY stage  12  includes an X stage  121  and a Y stage  122 . The X stage  121  and the Y stage  122  are provided with an X direction translation handle  121   a  and a Y direction translation handle  122   a , respectively. Rotating the X direction translation handle  121   a  causes the main body  11  to translate in the X direction. Rotating the Y direction translation handle  122   a  causes the main body  11  to translate in the Y direction. 
     The two-axis gonio-stage  13  includes a first gonio-stage  131  and a second gonio-stage  132 . The first gonio-stage  131  and the second gonio-stage  132  include a first rotation handle  131   a  and a second rotation handle  132   a . The first gonio-stage  131  and the second gonio-stage  132  have a mechanism for sliding cylindrical surfaces centered on a first tilting axis T 1  parallel to the Y axis and a second tilting axis T 2  parallel to the X axis, respectively. The first tilting axis T 1  and the second tilting axis T 2  are depicted at upper parts of  FIG. 1  and  FIG. 2 . Rotating the first rotation handle  131   a  causes the main body  11  to pivot about the axis T 1 . Rotating the second rotation handle  132   a  causes the main body  11  to pivot about the axis T 2 . 
     The control device  15  includes a light source controller  151  and a data processor  152 . The light source controller  151  is connected to the laser light source  112  and the visible light source  114 . The data processor  152  is connected to the CCD camera  111  and the laser light detector  113 . 
     The light source controller  151  controls the laser light source  112  and the visible light source  114 . With visible light emitted from the visible light source  114 , a wide area including the sample S is irradiated. An image of the sample S observed through the sample window  162  is taken by the CCD camera  111 , and sent through the data processor  152  to the output unit. Laser light beam emitted from the laser light source  112  is reflected by the half mirror  116 , condensed by the condenser lens  141 , and passes through the sample window  162 , thereby causing the sample S to be irradiated. More specifically, the revealed surface of the semiconductor chip C of which the resin package of the sample S has been removed is irradiated with the laser light beam, and causes a bright spot on the sample S. If the surface of the semiconductor chip C is not tilted, the image of the sample S taken by the CCD camera  111  includes a clear image of the bright spot, and the light beam reflected by the surface of the semiconductor chip C returns along the same axis as that of the incident light, passes through the sample window  162  and the laser light condenser  14 , is reflected by the half mirror  117  and detected by the laser light detector  113  as the largest luminance. The signal of the largest luminance detected by the laser light detector  113  is sent to the data processor  152 . If the surface of the semiconductor chip C is tilted, the bright spot in the image of the sample S taken by the CCD camera  111  is distorted and the luminance decreases, which is detected by the data processor  152  as the sign of the tilt. For example, if the laser light beam has a circular cross-sectional shape, the bright spot is detected as a circle when there is no tilt of the sample S. When, on the contrary, there is a tilt of the sample S, the bright spot is detected as an ellipse and the luminance decreases. 
     Hereinafter, a method of correcting the tilt of the optical axis A 1  is described with reference to  FIG. 1  and  FIG. 3 . The control device  15  is not shown in  FIG. 3  for simplicity. 
     In  FIG. 1 , the exposed surface of the semiconductor chip C is tilted after the resin package of the sample S has been removed with plasma. In this case, an optical axis A 2  of the laser light beam reflected by the surface of the semiconductor chip C deviates from the optical axis A 1  of the incident laser light beam, and the surface inspection apparatus  1  is unable to receive the reflected light beam. 
     To address this, an operator rotates the rotation handles  131   a  and/or  132   a  of the first gonio-stage  131  and/or the second gonio-stage  132  to gradually tilt optical axis A 1  of the incident light while observing an image in a point irradiated by the light beam on the surface of the semiconductor chip C, and which is sent to the output unit, to thereby cause the optical axis A 2  of the reflected light beam to return to the main body  11  (see  FIG. 3 ). The fact that the optical axis A 2  of the reflected light beam returns to the main body  11  can be determined by observation of a bright light spot of the reflected light beam through the CCD camera  111 , or by observation of the shape of the bright spot in the image or the luminance of the bright spot as described before. Further fine adjustment allows the optical axis A 2  of the reflected light beam to coincide with the optical axis A 1  of the incident light, thereby correctly guiding the reflected light beam to the laser light detector  113 . 
     If the optical axis A 1  of the incident light beam is tilted, the irradiation point with the laser light beam on the semiconductor chip C moves. However, the XY stage  12  can bring the irradiation point to the original position. As a result, the optical axis A 2  of the reflected light substantially coincides with the optical axis A 1  of laser light emitted from the laser light source  112 , and the target point can be continuously inspected. 
       FIG. 4  shows a perspective view of a surface inspection apparatus  2  according to a second embodiment of the present invention. The surface inspection apparatus  2  of this embodiment includes a plane tilting type two-axis gonio-stage  23  as the optical axis tilting mechanism. The main body  11  and other parts of the surface inspection apparatus  2  other than the plane tilting type two-axis gonio-stage  23  are the same as those of the surface inspection apparatus  1  of the first embodiment, and the explanation about them is thus omitted. 
     The plane tilting type two-axis gonio-stage  23  (hereinafter, simply referred to as “two-axis gonio-stage  23 ”) of the surface inspection apparatus  2  of this embodiment includes a lower-disposed first stage  231 , an upper-disposed second stage  232 , a pivot  233  sandwiched between them, and a first liner motion mechanism  234  and a second liner motion mechanism  235  which are oppositely arranged at 90 degrees centered on the pivot  233 . The first liner motion mechanism  234  and the second liner motion mechanism  235  are screws that change the distance between the first stage  231  and the second stage  232 . 
     The lower end of the pivot  233  is fixed onto the first stage  231 , and its distal end (upper end) is formed in a spherical shape so as to fit into a spherical recess provided in a bottom surface of the second stage  232 . Changing the distance between the first stage  231  and the second stage  232  by the first liner motion mechanism  234  causes the main body  11  to tilt about the first tilting axis T 1  with the contact portion of the distal end of the pivot  233  and the second stage  232  being as a pivot. Similarly, by the second liner motion mechanism  235 , the main body  11  is tilted about the second tilting axis T 2 . A hydraulic or a pneumatic actuator may be employed instead of the liner motion mechanisms  234  and  235 .  FIG. 5  shows a result in which the first liner motion mechanism  234  and the second liner motion mechanism  235  tilt the optical axis A 1  to enable the surface inspection apparatus  2  to receive the reflected light beam. 
       FIG. 6  shows a schematic overall configuration diagram of a surface inspection apparatus  3  according to a third embodiment of the present invention. The basic mechanism of the surface inspection apparatus  3  of this embodiment is the same as that of the surface inspection apparatus  1  of the first embodiment. Differing from the surface inspection apparatus  1  of the first embodiment, an XY stage  32  and a two-axis gonio-stage  33  are not manually driven but are automatically driven according to signals from the outside, and a control device  35  is provided with a translation driver  353  and a tilting driver  354 . An X stage  321  and a Y stage  322  of the XY stage  32  are provided with an X direction driver  321   a  and a Y direction driver  322   a , which translate the main body  11  according to signals from the translation driver  353  in the X direction and the Y direction, respectively. A first gonio-stage  331  and a second gonio-stage  332  of the two-axis gonio-stage  33  are provided with a first axis driver  331   a  and a second axis driver  332   a , which rotate the main body  11  according to signals from the tilting driver  354  about a first tilting axis T 1  and a second tilting axis T 2 , respectively. 
     Operations of the control device  35  in the surface inspection apparatus  3  of this embodiment are described. A light source controller  351  of the control device  35  causes the laser light source  112  to emit laser light, and causes the visible light source  114  to emit visible light. The sample S is irradiated with both lights passing through the sample window  162 . An image in a wide area including the sample S inside the vacuum chamber, which is formed by reflected light of the visible light is taken by the CCD camera  111 , is sent to a data processor  352 , and subjected to the image analysis. The data processor  352  detects a portion of the taken image having a luminance larger than a first predetermined value. This identifies the point on the semiconductor chip C revealed from the sample S at which the laser light beam is irradiated. The irradiation point may be identified based not only on the luminance but also on the color (wavelength) of the laser light beam. Of course, they may be simultaneously used. 
     Laser light beam emitted from the laser light source  112  is reflected by the surface of the semiconductor chip C, and returns to the main body  11 . However, as shown in  FIG. 6 , in the case where the surface of the semiconductor chip C is not perpendicular to the optical axis A 1  of the incident laser light beam, the reflected light beam passes along an optical axis A 2  deviating from the optical axis A 1 , which prevents the light beam from being detected by the laser light detector  113 . In this case, the luminance of the point irradiated with the laser light in the image taken by the CCD camera  111  is larger than the first predetermined value but lower than a second predetermined value that is set in consideration of the luminance when the laser light beam reflected by the sample directly enters the CCD camera  111 . The control device  35  drives the two-axis gonio-stage  33  through the tilting driver  354  and drives the XY stage  32  through the translation driver  353 , thereby causing the luminance at the point irradiated with the laser light beam to have a value higher than the second predetermined value. When the luminance of the point irradiated with the laser light becomes higher than the second predetermined value, the control device  35  stops driving the two-axis gonio-stage  33  and the XY stage  32  judging that the optical axis A 2  coincides with the optical axis A 1  and the reflected light of the laser light beam from the surface of the sample S enters the laser light detector  113 . 
       FIG. 7  shows a schematic overall configuration diagram of a surface inspection apparatus  4  according to a fourth embodiment of the present invention. The surface inspection apparatus  4  of this embodiment is the same as the surface inspection apparatus  3  of the third embodiment in that a two-axis gonio-stage  43  is automatically driven according to signals from the outside. Differing from the surface inspection apparatus  3  of the third embodiment, an automatically driven XY stage  42  that is driven according to the signals from the outside is equipped not with the main body  11  but with the sample stage  161 . An X stage  421  and a Y stage  422  of the XY stage  42  are provided with an X direction drive input terminal  421   a  and a Y direction drive input terminal  422   a  respectively, and the both stages translate the sample stage  161  according to signals from the translation driver  453  in the X direction and the Y direction, respectively. A first gonio-stage  431  and a second gonio-stage  432  of the two-axis gonio-stage  43  are provided with a first axis driver  431   a  and a second axis driver  432   a , which rotate the main body  11  according to signals from a tilting driver  454  about a first tilting axis T 1  and a second tilting axis T 2 , respectively. 
     Operations of a control device  45  in the surface inspection apparatus  4  of this embodiment are described. A light source controller  451  of the control device  45  causes the laser light source  112  to emit laser light, and causes the visible light source  114  to emit visible light. The sample S is irradiated with the both lights passing through the sample window  162 . An image in a wide area including the sample S taken by the CCD camera  111  with the visible light is sent to a data processor  452 , and subjected to an image analysis. The data processor  452  detects a portion of the taken image having a luminance larger than the first predetermined value. This identifies the point on the semiconductor chip C revealed from the sample S at which the laser light beam is irradiated. The irradiation point may be identified based not only on the luminance but also on the color (wavelength) of the laser light beam. Of course, they may be simultaneously used. 
     Laser light beam emitted from the laser light source  112  is reflected by the surface of the semiconductor chip C, and returns to the main body  11 . However, as shown in  FIG. 7 , in the case where the surface of the semiconductor chip C is not perpendicular to the optical axis A 1  of the incident laser light beam, the reflected light beam passes along an optical axis A 2  deviating from the optical axis A 1 , which prevents the light beam from being detected by the laser light detector  113 . In this case, the luminance of the point irradiated with the laser light beam in the image taken by the CCD camera  111  is at least the first predetermined value but lower than the second predetermined value that is set taken into account the luminance when the laser light beam reflected by the sample S directly enters the CCD camera  111 . The control device  45  drives the two-axis gonio-stage  43  through the tilting driver  454  as well as driving the XY stage  42  through the translation driver  453 , thereby causing the luminance at the point irradiated with the laser light to have a value higher than the second predetermined value. At the point when the luminance of the point irradiated with the laser light becomes higher than the second predetermined value, the control device  45  stops driving the two-axis gonio-stage  43  and the XY stage  42  judging that the optical axis A 2  coincides with the optical axis A 1 , and the reflected light beam of the laser light from the surface of the sample S enters the laser light detector  113 . 
     The surface inspection apparatuses  3  and  4  of the third and fourth embodiments tilt the optical axis A 1  of the laser light beam by analyzing the image of the sample. Alternatively, the tilt of the optical axis A 1  of the laser light beam may be directly measured. In one of such methods, the stages  331  and  332  of the axes of the two-axis gonio-stage  33  are provided with respective rotating position sensors. According to another method, a sensor for detecting the tilt degree from a vertical line or a horizontal plane is provided for the main body  11 . 
     Four embodiments have been described above. However, the present invention is not limited to these embodiments. It is apparent that configurations appropriately added or modified within a scope of the gist are encompassed in the claims of the present patent application. 
     REFERENCE SIGNS LIST 
     
         
           1 ,  2 ,  3 ,  4  . . . Surface Inspection Apparatuses 
           11  . . . Main Body 
           111  . . . CCD Camera 
           112  . . . Laser Light Source 
           113  . . . Laser Light Detector 
           114  . . . Visible Light Source 
           115 ,  116 ,  117  . . . Half Mirror 
           12 ,  32 ,  42  . . . XY Stage 
           121 ,  321 ,  421  . . . X Stage 
           121   a  . . . X direction translation handle 
           321   a ,  421   a  . . . X Direction Driver 
           122 ,  322 ,  422  . . . Y Stage 
           122   a  . . . Y direction translation handle 
           322   a ,  422   a  . . . Y Direction Driver 
           13 ,  33 ,  43  . . . Cylindrical Type Two-Axis Gonio-Stage 
           131 ,  331 ,  431  . . . First Gonio-Stage 
           131   a  . . . First rotation handle 
           331   a ,  431   a  . . . First Axis Driver 
           132 ,  332 ,  432  . . . Second Gonio-Stage 
           132   a  . . . Second rotation handle 
           332   a ,  432   a  . . . Second Axis Driver 
           14  . . . Laser Light Condenser 
           141  . . . Condenser Lens 
           15 ,  35 ,  45  . . . Control Device 
           151 ,  351 ,  451  . . . Light Source Controller 
           152 ,  352 ,  452  . . . Data Processor 
           353 ,  453  . . . Translation Driver 
           354 ,  454  . . . Tilting Driver 
           16  . . . Vacuum Chamber 
           161  . . . Sample Stage 
           162  . . . Sample Window 
           23  . . . Planar Tilt Type Two-Axis Gonio-Stage 
           231  . . . First Stage 
           232  . . . Second Stage 
           233  . . . Pivot 
           234  . . . First Liner motion mechanism 
           235  . . . Second Liner motion mechanism 
         A 1 , A 2  . . . Optical Axis 
         T 1  . . . First Tilting Axis 
         T 2  . . . Second Tilting Axis 
         S . . . Sample 
         C . . . Semiconductor Chip