Abstract:
Disclosed is a device capable of probing with minimal effect from electron beams. Rough probing is made possible using a lower magnification than the magnification usually viewed. When target contact of semiconductor is detected, measurement position is set in the center of picture usually to move probe without moving stage. With the miniaturization, contact can be confirmed only at high magnification, although probe can be confirmed at low magnification on the contrary but it is necessary to display it in real time. Static image obtained at high magnification once is combined with image obtained at low magnification in real time from target contact required for probing and characteristic of probe to be displayed, so that probing at low magnification can be realized to reduce the effects of electron beams and obtain accurate electrical characteristics.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a semiconductor inspection device and method and more particularly to a semiconductor inspection method and device that perform inspection or defect analysis to get electrical characteristics of semiconductor while reducing damage caused to semiconductor by electron beams of a scanning electron microscope (SEM). 
       BACKGROUND ART 
       [0002]    In recent years, miniaturization of 45-nm devices and semiconductors are advanced, so that distance and height between contacts of transistor become very short. Accordingly, when semiconductor is inspected by the device as described in Patent Literature 1, it is getting difficult to get accurate transistor characteristics because of effects of electron beams absorbed by semiconductor. 
         [0003]    Accordingly, in the pre-processing of semiconductor, oxide layer is left as large as possible so as to make the oxide layer thicker, so that semiconductor is processed to escape from the effects of electron beams even a little. Further, acceleration voltage of electron beams and emission current are reduced to thereby decrease the effects of electron beams although there is obtained an image having low contrast and difficult to understand. 
       CITATION LIST 
     Patent Literature 
       [0004]    Patent Literature 1: JP-A-2002-343843 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    However, with the miniaturization, invasion area affects contacts, oxide layer, gate, source and drain due to influence of electrification of electron beams, so that electrical characteristics cannot be obtained accurately (refer to  FIG. 2 ). In order to get electrical characteristics accurately, it is necessary to probe contacts accurately while observing the contacts in SEM image at high magnification in detail, although this causes large damage to sample and there is a trade-off relationship therebetween. 
         [0006]    When accurate electrical characteristics cannot be obtained, it is not understood which characteristic is defective when some electrical characteristics of transistor are obtained and one defect is found and accordingly there arises a problem. Further, there is a possibility that absolutely accurate electrical characteristics cannot be obtained even if relative electrical characteristics can be obtained. 
         [0007]    Moreover, the fact that the effects of electron beams are reduced requires some restriction on observation of contact. If a probe is not put on correct contact, accurate electrical characteristics cannot be measured naturally. An apparatus requiring probing is described in Patent Literature 1. 
         [0008]    With the miniaturization, when contact at the tip of probe is to be viewed without using a scanning electron microscope having the magnification of twenty to thirty thousands, the presence of the contact cannot be viewed and naturally it cannot be probed. Further, in order to reduce the effects of electron beams, acceleration voltage is reduced to 0.5 kV and emission current is reduced to 5 μA. Clear SEM image cannot be obtained and in the existing circumstances probing is made in the state that contact is viewed dimly. Moreover, since electric charges of electron beams are easily accumulated when scanning mode of electron beams is slow, TV mode (about 20 msec. per picture) is utilized as much as possible. 
         [0009]    It is an object of the present invention to reduce the effects of electron beams and get accurate electrical characteristics so that defective position is made clear. Furthermore, it is an object of the present invention to view contact sufficiently and put a probe on contact sufficiently even if electron beams are restricted. 
       SOLUTION TO PROBLEM 
       [0010]    As measures for solving the above problem, a stage is fixed and a contact to be probed is decided. Then, an image of the contact is obtained at high magnification once. Further, a probe is displayed in real time at low magnification so as to show where the probe is. The contact image obtained at high magnification once is combined with the probe image expressed in real time at low magnification and the combined image is expressed. 
         [0011]    If the tip position of the probe is understood from low-magnification image, where the tip position of the probe exists in high-magnification image can be calculated. The probe position calculated from low-magnification image is expressed in real time in high-magnification image obtained once, so that damage to sample can be reduced. 
         [0012]    When the effects of electron beams are analyzed from many different angles, sample is damaged upon probing requiring handling extremely. Further, contact of sample cannot be viewed unless magnification of tens of thousands is used, although it is not necessary to move stage during probing. Moreover, since probe is large, it can be viewed from several times, although the probe collides with adjacent probe unless it is viewed in real time upon probing, so that probe is damaged. 
         [0013]    A stage is fixed and a contact to be probed is decided. Then, an image of the contact is obtained at high magnification once. Further, a probe is displayed in real time at low magnification so as to show where the probe is. In brief, a combined image of the contact image obtained at high magnification once with the probe image expressed in real time at low magnification is expressed, so that both of static contact and dynamic contact can be expressed and sample is not damaged since processing can be made at low magnification usually. 
       ADVANTAGEOUS EFFECTS OF INVENTION 
       [0014]    According to the present invention, since defective position can be probed rapidly and accurately and furthermore the effects of electron beams can be suppressed slightly, measurement of electrical characteristics and the like of semiconductor and realization of a semiconductor inspection device can be attained and user&#39;s usefulness is improved. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS  
         [0015]      FIG. 1  is a schematic diagram illustrating a semiconductor inspection device; 
           [0016]      FIG. 2  is a diagram showing the effects of electron beams on transistor in semiconductor; 
           [0017]      FIG. 3  is a diagram illustrating an embodiment of the present invention; 
           [0018]      FIG. 4  is a diagram illustrating an embodiment of the present invention; 
           [0019]      FIG. 5  is a diagram illustrating an embodiment of the present invention; 
           [0020]      FIG. 6  is a diagram illustrating an embodiment of the present invention; and 
           [0021]      FIG. 7  is a diagram illustrating an embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0022]    An embodiment of the present invention is now described with reference to the accompanying drawings. 
         [0023]      FIG. 1  is a schematic diagram illustrating a semiconductor inspection device to which an embodiment of the present invention is applied. 
         [0024]    In  FIG. 1 , the semiconductor inspection device irradiates a thin sample  103  in a vacuum chamber partition wall  105  with primary electron beams  101  of an SEM (scanning electron microscope). Second electron beams  102  are detected by a secondary electron detector  104  and an SEM image of semiconductor is displayed in a display unit  133  through by means of a control computer  134 . This SEM image is utilized when a probe  127  is put on the sample  103 . 
         [0025]    The control computer  134  utilizes a first image processing system  131 , a memory means  132  and the display unit  133  to perform operation control of the whole semiconductor inspection device such as SEM image, movement of stage, change of magnification and the like. 
         [0026]    An electron beam irradiation optical system  118  generates primary electron beams  101  from an electron gun  111  through condensing lenses  112 ,  113 , diaphragm  114 , scan deflector  115 , image shift deflector  116  and objective lens  117 . Sometimes, only one condensing lens is provided. The scan deflector  115  decides direction and magnification of scan. 
         [0027]    In stage, large stage  122 , sample stand driving means  123 , sample stand  124 , probe driving means  125 , probe attachment  136  and probe  127  are mounted on base  121 . 
         [0028]    The present invention can be implemented by SEM which can change magnification and edit image basically. 
         [0029]      FIG. 2  shows the effects of electron beams on transistor in general semiconductor. Sample  202  is irradiated with primary electron beams  201 . The sample is polished and upper layer part thereof is scraped. Oxide layer  204  is formed on substrate  203  and drain  205 , source  206  and gate  207  constituting transistor are connected to contacts  208 . Probe is put on contact part and electrical characteristics of transistor is obtained to thereby understand which transistor is defective. 
         [0030]    However, when sample is irradiated with primary electron beams, electron beam invasion area  209  can be formed to a large or small extent. When the electron beam invasion area  209  extends to drain  205 , source  206  and gate  207 , important electrical characteristics is affected, so that it cannot be understood which transistor is defective. For example, rising of Vth characteristic indicating voltage with which drain current flows suddenly when gate voltage exceeds a certain value is affected. With the miniaturization in recent years, distance between contacts is shorter and thickness of oxide layer is thinner gradually, so that electrical characteristics are apt to be affected by thinner oxide layer even if electron beam invasion area is the same. 
         [0031]    In order to make the electron beam invasion area  209  as small as possible and not to extend the electron beam invasion area  209  to drain  205 , source  206  and gate  207 , it is considered that acceleration voltage (1.0 kV or less) of primary electron beams  201  is reduced and emission current (5 μA or less) of primary electron beams  201  is reduced. Furthermore, there are countermeasures that observation is made at as low magnification as possible, focusing of electron beams on sample is reduced to the lowest minimum, fast scanning mode is used to make it difficult to accumulate electric charges, observation is made within as short a time as possible and so on. 
         [0032]    However, any of them is unnecessary item for probing and when probing is made in clear SEM image, damage to sample is increased. There is a tradeoff relationship between probing and low damage. 
         [0033]    Accordingly, 2 kinds of images of high and low magnifications are used to solve probing and low damage. Referring now to  FIGS. 3 to 7 , description is made. When a plurality of probes  303  are now to be concentrated on target contact  302  in the state that target contact  302  and probes  303  are displayed in picture  301  of high magnification, image in picture  301  of high magnification is obtained once. 
         [0034]    Next, the picture is changed to picture  401  of low magnification. At this time, it is effective that focusing is changed from sample to probe. When magnification is changed to be low, probe  404  distant from the center can be viewed but the whole contact cannot be sometimes viewed. Moreover, position of target contact  402  is not clear also. 
         [0035]    Accordingly, as shown in  FIG. 5 , data is reduced to display high-magnification picture  301  within high-magnification original picture area  504  in the center of low-magnification picture  401 . 
         [0036]    That is, target contact  502  and probes  503  and  505  are displayed within low-magnification reference picture  501  and image only in high-magnification original picture area  504  is easier to understand. It is a matter of course that since this image is obtained at high magnification only once and thereafter obtained at low magnification, damage is reduced. Magnification is changed to thereby change size of the high-magnification original picture area  504 , so that image can be obtained at lower magnification than magnification of high-magnification original picture. Consequently, since magnification can be changed to be low to position that probe can be viewed and high-magnification original picture area can be interlocked with magnification changed while probing where target contact  502  is, operation can be made easily. 
         [0037]    Further, when focusing is made on probe instead of sample, electron beams are not focused or concentrated on sample because of difference in height between probe and sample and accordingly damage to sample can be reduced. Since only probe information is required in low-magnification picture, information of clearer probe can be obtained and this is a bright idea that makes it possible to kill two birds with one stone. In editing of image within high-magnification original picture area  504  of  FIG. 5 , integration can be made to judge both of low-magnification probe and high-magnification target contact  502 . 
         [0038]    Next, as shown in  FIG. 6 , high-magnification picture is displayed as a base notwithstanding that processing is being made at low magnification and low-magnification image data is displayed in the high-magnification picture on an enlarged scale in a superposition manner. Probe  604  displayed newly is obtained by enlarging low-magnification image. The image is slightly rough, although position of probe can be understood clearly. 
         [0039]    Further, even if probe  303  displayed originally in high-magnification picture  301  is moved, probe  303  is displayed in original image and accordingly both of probe  303  at original position and newly moved probes  303  and  403  are displayed. However, it can be easily imagined that probe distant from center is probe of previous original image and accordingly there is no problem. 
         [0040]    When probing is made, it is considered that it is meaningless to make probing in accurate image and it is effective that measured result of electrical characteristics after probing is accurate. 
         [0041]    Moreover, as another method of  FIG. 6 , picture obtained in real time at low magnification in  FIG. 4  is searched for the tip of probe by means of image processing and where its position is in high-magnification picture  301  is calculated to display probe  604 . This method is illustrated in  FIG. 7 . 
         [0042]    A picture  701  of high magnification is obtained once. Target contact  702  and probe  703  are contained in high-magnification picture  701 . 
         [0043]    Next, the picture is changed to picture  704  of low magnification. Target contact  702  of high magnification corresponds to target contact  705  of low magnification and probe  703  of high magnification corresponds to probe  706  of low magnification. 
         [0044]    At this time, image can be displayed at high magnification by changing picture by user, although actual electron beam irradiation optical system is left to be low magnification as it is. When probe  707  is moved in movement direction  709  by user&#39;s operation, the device understands that probe considered beforehand to be moved is moved and accordingly the tip position  708  of probe is detected from low-magnification image. Where the tip position  708  in low-magnification picture  704  is in high-magnification picture  710  is calculated to be displayed. High-magnification picture  701  is combined with high-magnification picture  710  in which the tip position of probe is detected to display picture  712  to user. 
         [0045]    Target contact  713  and probes  714  and  715  are displayed, so that user can view image as if high-magnification picture is handled notwithstanding that sample is irradiated at low magnification. 
         [0046]    At that time, there are 3 display methods of probe  715 . 
         [0047]    In the first method, images of probes prepared beforehand as system are superposed. 
         [0048]    In the second method, images cut out from high-magnification picture are combined. 
         [0049]    In the third method, marker indicating picture or drawing of probe is displayed at tip position. This method is also effective. In case of superposition of images, in order to improve quality of image, when low magnification is set to divisor of high magnification, expansion/reduction result of image is satisfactory and image is not distorted. 
         [0050]    Since image is not expanded and reduced when marker is displayed, influence due to difference of magnification between high magnification and low magnification is reduced. 
         [0051]    In the foregoing description, for simplification of description, operation at the time that single probe is moved has been described, although even if a plurality of probes are moved, the same way of thinking can be used to cope with it. 
         [0052]    When marker is displayed, expression of thickness of probe at high magnification is apt to be unclear and accordingly breakage of probe due to contact or collision between probes is considered. However, picture or drawing of marker is expressed by 2 lines extending from tip of probe as shown by  403  and lines of probe having sufficiently safe thickness are drawn, so that contact can be avoided. 
         [0053]    High-magnification picture  301  of original image and low-magnification picture  401  are subjected to image editing such as contrast emphasis, color display and outline emphasis, so that difference between current data and past data is clear. Further, when image editing of high-magnification picture  301  is performed once, it is not necessary to perform the image editing upon combination of low-magnification picture with high-magnification picture in real time. Accordingly, processing time is not required and contact can be emphasized. It is possible to perform editing in which probe in past position is not emphasized, so that difference between the probe in past position and latest probe expressed in low-magnification picture  401  can be expressed effectively. 
         [0054]    The system of  FIG. 5  is used in early stage of rough probing so that operation can be made while confirming distant probe and when probes are collected to some extent, the system of  FIG. 6  can be used to approach probe to appropriate position. In this manner, the system can be used in accordance with convenient case, so that probing can be made without damaging sample. 
       REFERENCE SIGNS LIST 
       [0055]      101  primary electron beams 
         [0056]      102  secondary electron beams 
         [0057]      103 ,  202  sample 
         [0058]      104  secondary electron detector 
         [0059]      105  vacuum chamber partition wall 
         [0060]      110 ,  118  electron beam irradiation optical system 
         [0061]      111  electron gun 
         [0062]      112  condensing lens  1   
         [0063]      113  condensing lens  2   
         [0064]      114  diaphragm 
         [0065]      115  scan deflector 
         [0066]      116  image shift deflector 
         [0067]      117  objective lens 
         [0068]      121  base 
         [0069]      122  large stage 
         [0070]      123  sample stand driving means 
         [0071]      124  sample stand 
         [0072]      125  probe driving means 
         [0073]      126  probe attachment 
         [0074]      127 ,  303 ,  403 ,  404 ,  503 ,  505 ,  603 ,  604 ,  703 ,  706 ,  707  probe 
         [0075]      128  electrical characteristic measuring instrument 
         [0076]      131  first image processing system 
         [0077]      132  memory means 
         [0078]      133  display unit 
         [0079]      134  control computer 
         [0080]      201  primary electron beams 
         [0081]      203  substrate 
         [0082]      204  oxide layer 
         [0083]      205  drain 
         [0084]      206  source 
         [0085]      207  gate 
         [0086]      208  contact 
         [0087]      209  electron beam invasion area 
         [0088]      301 ,  701  high-magnification picture 
         [0089]      302 ,  402 ,  502 ,  602 ,  702 ,  705  target contact 
         [0090]      401 ,  704  low-magnification picture 
         [0091]      501  low-magnification reference picture 
         [0092]      504  high-magnification original picture area 
         [0093]      601  high-magnification reference picture 
         [0094]      708  tip position of probe 
         [0095]      709  probe movement direction 
         [0096]      710  high-magnification picture calculated at low magnification 
         [0097]      711  calculated probe 
         [0098]      712  high-magnification picture combined 
         [0099]      713  target contact combined 
         [0100]      714  probe combined 
         [0101]      715  probe combined after calculation of movement