Abstract:
A measurement system is provided to measure a hole of a target, including a light source generation unit, a capturing unit and a processing unit. The light source generation unit generates a light source and focuses the light source on a plurality of different height planes. The capturing unit captures a plurality of images scattered from the plurality of different height planes. The processing unit obtains boundaries of the hole on the plurality of different height planes according to the plurality of images, samples image intensities of different azimuth angles on the boundaries of the hole on each of the plurality of different height planes to generate a plurality of sampling values, and develops a sidewall image of the hole according to the plurality of sampling values, the plurality of different height planes and the different azimuth angles.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority of Taiwan Patent Application No. 101134870, filed on Sep. 24, 2012, the entirety of which is incorporated by reference herein. 
     BACKGROUND 
     1. Technical Field 
     The disclosure relates to measurement systems and measurement methods, and relates to a measurement system for measuring the boundary of a hole. 
     2. Description of the Related Art 
     Fabrication of 3D ICs via stacking has increased due to development and demand for more advanced and complex ICs. One type of IC packaging staking method is through-silicon via. The yield rates of ICs are affected by the accuracy of measuring through-silicon vias. 
     However, through-silicon vias have a high depth-width ratio. Thus, depth and sidewalls thereof cannot be measured by an optical microscope. Therefore, a measurement system and a measurement method for measurement by an optical microscope are needed. 
     SUMMARY 
     An embodiment of a measurement system to measure a hole of a substrate is provided, and the measurement system comprises a light source generation unit, a capturing unit and a processing unit. The light source generation unit is used to generate a light source and focus the light source, respectively, on a plurality of different height planes of a hole, along a height axis direction of the hole. The capturing unit captures a plurality of images scattered by the plurality of different height planes. The processing unit obtains boundaries of the hole on the plurality of different height planes according to the plurality of images thereby sampling image intensities of different azimuth angles on the boundaries of the hole on each of the plurality of different height planes to generate a plurality of sampling values, and developing a sidewall image of the hole according to the plurality of sampling values, heights of the plurality of different height planes and the different azimuth angles. 
     An embodiment of a measurement method to measure a hole of a substrate is provided, the measurement method comprises focusing a light source, respectively, on a plurality of different height planes of a hole, along a height axis direction of the hole, capturing a plurality of images scattered by the plurality of different height planes, obtaining boundaries of the hole on the plurality of different height planes according to the plurality of images, sampling image intensities of different azimuth angles on the boundaries of the hole on each of the plurality of different height planes to generate a plurality of sampling values, and developing a sidewall image of the hole according to the plurality of sampling values, heights of the plurality of different height planes and the different azimuth angles. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The disclosure can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is the schematic diagram of a measurement system in accordance with an exemplary embodiment; 
         FIG. 2  is the schematic diagram of an image of a hole received by the measurement system in accordance with an exemplary embodiment; 
         FIG. 3  is another image of a hole captured by the capturing unit  120 ; 
         FIG. 4  is a schematic diagram of the relation between the image intensity and radial in accordance with an exemplary embodiment; 
         FIG. 5  is a measurement system in accordance with another exemplary embodiment; 
         FIG. 6  is a schematic diagram of the relation between the image intensity and height in accordance with an exemplary embodiment; 
         FIG. 7  is the sidewall image of a hole in accordance with an exemplary embodiment; 
         FIG. 8A  and  FIG. 8B  are sidewall images of a hole obtained by a scanning electron microscope; and 
         FIG. 9  is a flowchart of a measurement method in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is made for the purpose of illustrating the general principles of the disclosure and should not be taken in a limiting sense. The scope of the disclosure is best determined by reference to the appended claims. 
       FIG. 1  is the schematic diagram of a measurement system in accordance with an exemplary embodiment. Referring to  FIG. 1 , the measurement system  100  includes a light source generation unit  110 , a capturing unit  120  and a processing unit  130 . Specifically, each point of the sidewall of a hole can be expressed by the cylindrical system and written in the form of (R, θ, Z). The light source generation unit  110  is arranged to generate a light source, and to respectively focus the light source on a plurality different height of planes (such as planes PZ 1 ˜PZ 4 ) of a hole, along the height axis direction (also called z axis) of the hole HL. The capturing unit  120  captures a plurality of images (as shown in  FIG. 2 ) scattered from the plurality of different height planes PZ 1 ˜PZ 4 . The processing unit  130  is arranged to sample image intensities of different azimuth angles on boundaries of the hole on each of the plurality of different height planes, thereby generating a plurality of sampling values and developing a sidewall image of the hole HL according to the plurality of sampling values and heights of the plurality of different height planes and the different azimuth angles. In some embodiments, the capturing unit  120  and the processing unit  130  can be arranged within the light source generation unit  110 , but, the disclosure is not limited thereto. 
       FIG. 2  is the schematic diagram of an image of a hole received by the measurement system in accordance with an exemplary embodiment. Referring to  FIG. 2 , when the light source is focused on planes PZ 1 , PZ 2 , PZ 3  and PZ 4  of the plurality of different heights Z 1 , Z 2 , Z 3  and Z 4 , the plurality of images I 1 , I 2 , I 3  and I 4  are respectively obtained. To further explain, circle B 1 , B 2 , B 3  and B 4  are boundaries of the hole on the plurality of different height planes PZ 1 , PZ 2 , PZ 3  and PZ 4 . The magnification ratio of the plurality of different height planes PZ 1 ˜PZ 4  are 
                 M   ⁢           ⁢   1     =       D   ⁢           ⁢   0       D   ⁢           ⁢   1         ,       M   ⁢           ⁢   2     =       D   ⁢           ⁢   0       D   ⁢           ⁢   2         ,       M   ⁢           ⁢   3     =           D   ⁢           ⁢   0       D   ⁢           ⁢   3       ⁢           ⁢   and   ⁢           ⁢   M   ⁢           ⁢   4     =       D   ⁢           ⁢   0       D   ⁢           ⁢   4           ,         
respectively, wherein lengths D 1 , D 2 , D 3  and D 4  are the distances from the light source generation unit  110  to the plurality of different height planes PZ 1 , PZ 2 , PZ 3  and PZ 4  respectively, and D 0  is the distance from the light source generation unit  110  to the capturing unit  120 . Because D 1 &lt;D 2 &lt;D 3 &lt;D 4 , therefore M 1 &gt;M 2 &gt;M 3 &gt;M 4 . Accordingly, the captured images of the boundaries of the hole on the plurality of different height planes PZ 1 , PZ 2 , PZ 3  and PZ 4  do not overlap.  FIG. 3  is an image of a hole captured by the capturing unit  120 . Referring to  FIG. 3 , the boundaries of the hole on each of the plurality of different height planes do not overlap.
 
     Therefore, when the light source is focused on the plurality of different height planes PZ 1 , the change in image intensity of the circle B 1  increases in sensitivity. For example, the image intensity outside of the circle B 1  is very weak, but the image intensity within the circle B 1  is strong. Therefore, the boundary of the hole can be determined by the variations of the image intensity of the radical coordinate. Similarly, when the light source is focused on the plane PZ 2 , circle B 2  can be determined as the boundary of the hole of the plane PZ 2  from the image I 2 . When the light source is focused on the plane PZ 3 , circle B 3  can be determined as the boundary of the hole of the plane PZ 3  from the image I 3 . When the light source is focused on the plane PZ 4 , circle B 4  can be determined as the boundary of the hole of the plane PZ 4  from the image I 4 . 
       FIG. 4  is a schematic diagram of the relation between the image intensity and radial in accordance with an exemplary embodiment. As shown in  FIG. 4 , an intensity curve is along the radial coordinate r at a predetermined azimuth angle θ 1 . The intensity curve CV 1  is differentiated by the radial coordinate to obtain the differential curve CV 2 . The processing unit  130  obtains a radial point R 1  according to the maximum limit value of the differential curve CV 2  and obtains the mean value VA 1  of the image intensity in the region between R 1 +δ and R 1 −δ, and regards the mean value VA 1  of the radial point R 1  as the plurality of sampling values (image intensity) of the coordinate (R 1 , θ 1 , Z 2 ). Referring to  FIG. 2  again, in other words, the closed curve composed of the radial points at the azimuth angles can be regarded as the boundary of the hole in accordance with the plane PZ 2 . 
       FIG. 5  is a measurement system in accordance with another exemplary embodiment. Referring to  FIG. 5 , the measurement system  500  includes a light source generation unit  510 , a capturing unit  520 , a processing unit  530  and a platform  540 . In the embodiment of the present disclosure, the light source generation unit  510  can be a dark field optical microscope. A light source is transmitted through a ring mirror  511  to a ring condenser lens  512 , and through the ring condenser  512  to a target  550 . The light scattered by the target  550  is transmitted through the objectives  513  to the capturing unit  520 , but the light transmitted to the capturing unit  520  doesn&#39;t include the mirror reflected light transmitted to the target  550 . The dark field device is different from the bright field device. Instead of observing illuminated light directly, the dark field device observes the scattered light from the target. Therefore, the viewing field is a dark background, but the target displays a bright image. The dark microscope is suitable for observing a figure and profile of tiny structures which can not be observed by the bright microscope. In the embodiment of the present disclosure, the target  550  is placed on the platform  540 . By fixing the focal length and moving the platform  540  along the height axis direction of a hole, the light source can focus on the plurality of different heights of the hole. 
       FIG. 6  is a schematic diagram of the relation between the image intensity and height in accordance with an exemplary embodiment. Referring to  FIG. 6 , the horizontal axis is the height Z, and the vertical axis is the standardized image intensity. When fixing the azimuth angle and the radial length, the image intensity changes corresponding to the focus positions (height). By observation, it can be realized that there are periodical notches and bumps on the boundary of the hole. 
       FIG. 7  is the sidewall image of a hole in accordance with an exemplary embodiment.  FIG. 8A  and  FIG. 8B  are sidewall images of a hole obtained by a scanning electron microscope. Referring to  FIG. 7 , the horizontal axis is the azimuth angle θ, and the vertical axis is the height Z. The sidewall image of the hole HL in  FIG. 7  is developed according to the plurality of sampling values and the corresponding height Z and the azimuth angle θ. By observation, it can be realized that the sidewall of the hole has a scallop-type structure which is the same as that shown in  FIGS. 8A and 8B . 
       FIG. 9  is a flowchart of a measurement method in accordance with an exemplary embodiment. Referring to  FIG. 9 , the measurement method includes the following steps. 
     In step S 91 , the light source is focused, respectively, on a plurality of different height planes (such as planes PZ 1 ˜PZ 4 ) of a hole, along the height axis direction (also called z axis) of the hole HL. In step S 92 , a plurality of images scattered by the plurality of different height planes are captured. In step S 93 , boundaries of the hole on the plurality of different height planes are obtained according to the plurality of images. In step S 94 , image intensities of different azimuth angles on boundaries of the hole on each of the plurality of different height planes are sampled to generate a plurality of sampling values. In step S 95 , a sidewall image of the hole HL is developed according to the plurality of sampling values and heights of the plurality of different height and the different azimuth angles. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.