Abstract:
A pattern inspection method includes: generating a charged particle beam to irradiate the charged particle beam to a sample having a surface on which a pattern to be inspected is formed; detecting at least one of a secondary charged particle, a reflection charged particle and a back scattering charged particle emitted from the sample due to the irradiation of the charged particle beam, and acquiring a first two-dimensional image showing a state of the surface of the sample; using a previously prepared reference image to detect a pattern similar to the reference image within the first two-dimensional image, and storing information on a position of the detected pattern as information on the position of the pattern to be inspected; moving a measurement position from the position of the detected pattern by a predetermined distance in a predetermined direction to focus the charged particle beam; moving the measurement position by the predetermined distance in a direction opposite to the predetermined direction to irradiate the charged particle beam, and acquiring a second two-dimensional image magnified higher than the first two-dimensional image to measure the detected pattern as a first measurement; and automatically moving the measurement position to an area other than an area on the sample to which the charged particle beam has been already irradiated to again carry out a measurement in the case of carrying out a remeasurement of the pattern to be inspected.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims benefit of priority under 35USC §119 to Japanese patent application No. 2006-032433, filed on Feb. 9, 2006, the contents of which are incorporated by reference herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a pattern inspection method, a pattern inspection apparatus, a semiconductor device manufacturing method, and a program, and is directed to the measurement and inspection of, for example, a semiconductor pattern using a charged particle beam.  
         [0004]     2. Related Background Art  
         [0005]     When a semiconductor pattern is automatically measured using a scanning electron microscope, automatic focusing processing or pattern recognition processing, for example, may fail in the middle of the measurement, so that a measurement value results in an abnormal value. In such a case, if the measurement is judged to be an error and remeasurement is automatically carried out when the measurement value exceeds a certain range, the automatic measurement can be continued without troubling an operator.  
         [0006]     However, if a measurement point where the measurement error has occurred is remeasured as it is, an electron beam is irradiated twice, which is a significant problem in the case of measuring a pattern made of a material greatly damaged (volume shrinkage due to the desorption of a protecting group) by the irradiation of the electron beam such as a resist for ArF excimer laser exposure devices or a low-k material. Moreover, even in the case of a material which is not damaged by the irradiation of the electron beam, the shape of the pattern changes due to a contrast change caused by a charge-up and contamination caused by the irradiation of the electron beam, so that it is impossible to accurately measure the pattern.  
       SUMMARY OF THE INVENTION  
       [0007]     According to a first aspect of the present invention, there is provided a pattern inspection method comprising:  
         [0008]     generating a charged particle beam to irradiate the charged particle beam to a sample having a surface on which a pattern to be inspected is formed;  
         [0009]     detecting at least one of a secondary charged particle, a reflection charged particle and a back scattering charged particle emitted from the sample due to the irradiation of the charged particle beam, and acquiring a first two-dimensional image showing a state of the surface of the sample;  
         [0010]     using a previously prepared reference image to detect a pattern similar to the reference image within the first two-dimensional image, and storing information on a position of the detected pattern as information on the position of the pattern to be inspected;  
         [0011]     moving a measurement position from the position of the detected pattern by a predetermined distance in a predetermined direction to focus the charged particle beam;  
         [0012]     moving the measurement position by the predetermined distance in a direction opposite to the predetermined direction to irradiate the charged particle beam, and acquiring a second two-dimensional image magnified higher than the first two-dimensional image to measure the detected pattern as a first measurement; and  
         [0013]     automatically moving the measurement position to an area other than an area on the sample to which the charged particle beam has been already irradiated to again carry out a measurement in the case of carrying out a remeasurement of the pattern to be inspected.  
         [0014]     According to a second aspect of the present invention, there is provided a program which causes a pattern inspection method to be executed by a computer connected to a charged particle beam apparatus, the charged particle beam apparatus being equipped with: a charged particle beam source which generates a charged particle beam to irradiate the charged particle beam to a sample having a surface on which a pattern to be inspected is formed; a focal position adjuster which adjusts the focal position of the charged particle beam; a beam position controller which adjusts a positional relation between the sample and the charged particle beam so that the charged particle beam is irradiated to a desired position on the sample; a detector which detects at least one of a secondary charged particle, a reflection charged particle and a back scattering charged particle emitted from the sample due to the irradiation of the charged particle beam to output data on a two-dimensional image showing a state of the surface of the sample; and a pattern recognizer which detects the pattern to be inspected within the two-dimensional image, the pattern inspection method comprising:  
         [0015]     generating a charged particle beam to irradiate the charged particle beam to a sample having a surface on which a pattern to be inspected is formed;  
         [0016]     detecting at least one of a secondary charged particle, a reflection charged particle and a back scattering charged particle emitted from the sample due to the irradiation of the charged particle beam, and acquiring a first two-dimensional image showing a state of the surface of the sample;  
         [0017]     using a previously prepared reference image to detect a pattern similar to the reference image within the first two-dimensional image, and storing information on a position of the detected pattern as information on the position of the pattern to be inspected;  
         [0018]     moving a measurement position from the position of the detected pattern by a predetermined distance in a predetermined direction to focus the charged particle beam;  
         [0019]     moving the measurement position by the predetermined distance in a direction opposite to the predetermined direction to irradiate the charged particle beam, and acquiring a second two-dimensional image magnified higher than the first two-dimensional image to measure the detected pattern as a first measurement; and  
         [0020]     automatically moving the measurement position to an area other than an area on the sample to which the charged particle beam has been already irradiated to again carry out a measurement in the case of carrying out a remeasurement of the pattern to be inspected.  
         [0021]     According to a third aspect of the present invention, there is provided a semiconductor device manufacturing method comprising executing a process of manufacturing a semiconductor device on a substrate when a pattern to be inspected on the substrate for fabrication of the semiconductor device is judged to satisfy required specifications of the semiconductor device as a result of an inspection by a pattern inspection method, the pattern inspection method including:  
         [0022]     generating a charged particle beam to irradiate the charged particle beam to a sample having a surface on which a pattern to be inspected is formed;  
         [0023]     detecting at least one of a secondary charged particle, a reflection charged particle and a back scattering charged particle emitted from the sample due to the irradiation of the charged particle beam, and acquiring a first two-dimensional image showing a state of the surface of the sample;  
         [0024]     using a previously prepared reference image to detect a pattern similar to the reference image within the first two-dimensional image, and storing information on a position of the detected pattern as information on the position of the pattern to be inspected;  
         [0025]     moving a measurement position from the position of the detected pattern by a predetermined distance in a predetermined direction to focus the charged particle beam;  
         [0026]     moving the measurement position by the predetermined distance in a direction opposite to the predetermined direction to irradiate the charged particle beam, and acquiring a second two-dimensional image magnified higher than the first two-dimensional image to measure the detected pattern as a first measurement; and  
         [0027]     automatically moving the measurement position to an area other than an area on the sample to which the charged particle beam has been already irradiated to again carry out a measurement in the case of carrying out a remeasurement of the pattern to be inspected.  
         [0028]     According to a fourth aspect of the present invention, there is provided a pattern inspection apparatus comprising:  
         [0029]     a charged particle beam source which generates a charged particle beam to irradiate the charged particle beam to a pattern to be inspected formed on a surface of a sample;  
         [0030]     a focal position adjuster which adjusts the focal position of the charged particle beam;  
         [0031]     a beam position controller which adjusts a positional relation between the sample and the charged particle beam so that the charged particle beam is irradiated to a desired position on the sample;  
         [0032]     a detector which detects at least one of a secondary charged particle, a reflection charged particle and a back scattering charged particle emitted from the sample due to the irradiation of the charged particle beam to output data on a first two-dimensional image showing a state of the surface of the sample;  
         [0033]     a pattern recognizer which uses a previously prepared reference image to detect a pattern similar to the reference image within the first two-dimensional image, and outputting information on the position of the detected pattern as information on the position of the pattern to be inspected; and  
         [0034]     a controller which controls the charged particle beam source, the focal position adjuster, the beam position controller, the detector and the pattern recognizer so that a measurement position is moved from the position of the detected pattern by a predetermined distance in a predetermined direction to focus the charged particle beam, the measurement position is then moved by the predetermined distance in a direction opposite to the predetermined direction to irradiate the charged particle beam, a second two-dimensional image magnified higher than the first two-dimensional image is acquired to measure the detected pattern, and then the measurement position is automatically moved to an area other than an area on the sample to which the charged particle beam has been already irradiated in the case of carrying out a remeasurement of the pattern to be inspected. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]     In the accompanying drawings:  
         [0036]      FIG. 1  is a block diagram showing a schematic configuration in one embodiment of a pattern inspection apparatus according to the present invention;  
         [0037]      FIG. 2  is a flowchart showing schematic procedures in one embodiment of a pattern inspection method according to the present invention;  
         [0038]      FIG. 3  is an explanatory diagram of automatic length measurement; and  
         [0039]      FIG. 4  is a diagram explaining the movement of a field of view to the vicinity of a measurement point. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0040]     Several embodiments of the present invention will hereinafter be described with reference to the drawings. It is to be noted that a case will be described below where an electron beam is used as a charged particle beam, but the present invention is not limited thereto and is also applicable to a case where, for example, an ion beam is used.  
         [0041]     (1) Pattern Inspection Apparatus  
         [0042]      FIG. 1  is a block diagram showing a schematic configuration in one embodiment of a pattern inspection apparatus according to the present invention. A pattern inspection apparatus  1  shown in  FIG. 1  is a scanning electron microscope which scans a semiconductor pattern with a converged electron beam EB to measure the dimensions of the semiconductor pattern.  
         [0043]     The pattern inspection apparatus  1  comprises an electron beam column  10 , various electron-optical system control circuits  32 ,  34 ,  36  and  38 , an X-Y stage  22  for supporting a wafer W which is a sample having a pattern to be inspected formed therein, a motor  24 , a stage control circuit  44 , a detector  26 , an image memory  46 , a pattern recognition unit  52 , a monitor  48 , a control computer  60 , a communication circuit  58 , and various recording media MR 2  and MR 4  previously incorporated in or detachable from the apparatus.  
         [0044]     The control computer  60  is connected to the various electron-optical system control circuits  32 ,  34 ,  36  and  38 , the stage control circuit  44  and the pattern recognition unit  52  as well as the recording media MR 2  and MR 4 , and the control computer  60  controls the whole apparatus via these circuits, etc., and carries out a pattern inspection described later on the basis of a recipe file stored in the recording medium MR 2 .  
         [0045]     In the present embodiment, the recording media MR 2  and MR 4  respectively store the recipe file in which a series of procedures of a pattern inspection method described later is written, and a measurement condition file. These files are previously stored in these recording media, or can also be loaded for every measurement from an external recording medium or another apparatus via the communication circuit  58  connected to a private circuit or a public circuit and via the control computer  60 , and then stored in the above-mentioned recording media.  
         [0046]     The recording medium MR 4  stores design data regarding the pattern to be inspected, and a reference image for pattern detection described later.  
         [0047]     The electron beam column  10  includes an electron beam gun  12 , a condenser lens  14 , a scan lens  16  and an objective lens  18 . The electron beam gun  12  is connected to the control computer  60  via the electron beam gun control circuit  32 , and generates the electron beam EB in response to a control signal from the electron beam gun control circuit  32  and irradiates the electron beam EB to the wafer W. The condenser lens  14  is connected to the control computer  60  via the condenser lens control circuit  34 , and excites a magnetic field or an electric field in response to a control signal from the condenser lens control circuit  34 , and then converges the electron beam EB so that it has a proper beam diameter. The objective lens  18  is connected to the control computer  60  via the objective lens control circuit  38 , and excites a magnetic field or an electric field in accordance with a control signal from the objective lens control circuit  38 , and then again converges the electron beam EB so that the electron beam is irradiated just focus onto the wafer W. In the present embodiment, the objective lens  18  and the objective lens control circuit  38  correspond to, for example, a focal position adjuster. The scan lens  16  is connected to the control computer  60  via the scan lens control circuit  36 , and excites an electric field or a magnetic field for deflecting the electron beam EB in response to a control signal from the scan lens control circuit  36 , thereby two-dimensionally scanning the wafer W with the electron beam EB. The motor  24  is connected to the X-Y stage  22  and also connected to the control computer  60  via the stage control circuit  44 , and the motor  24  operates in response to a control signal from the stage control circuit  44 , and moves the X-Y stage  22  within an X-Y plane. In the present embodiment, the scan lens  16  and the scan lens control circuit  36  as well as the X-Y stage  22 , the motor  24  and the stage control circuit  44  correspond to, for example, a beam position controller.  
         [0048]     The detector  26  detects at least one of a secondary electron, a reflection electron and a back scattering electron generated from the wafer W by the irradiation of the electron beam EB. The detector  26  is connected to the image memory  46 . Output signals of the detector  26  constitute a two-dimensional image showing the state of the surface of the wafer W, and data on this two-dimensional image is sent to and stored in the image memory  46 .  
         [0049]     The image memory  46  is connected to the pattern recognition unit  52  and the monitor  48 . The two-dimensional image data from the detector  26  is output from the image memory  46  to the monitor  48  on which the two-dimensional image is displayed so that it serves in the observation of the surface of the wafer, and the two-dimensional image data is also output to the pattern recognition unit  52 .  
         [0050]     The pattern recognition unit  52  uses the reference image loaded and sent from the recording medium MR 4  by the control computer  60  to carry out pattern recognition by comparison with the two-dimensional image supplied from the image memory  46 , and supplies information on the position of the detected pattern to the control computer  60  when the pattern recognition is achieved.  
         [0051]     The operation of the pattern inspection apparatus  1  shown in  FIG. 1  will be described below as embodiments of the pattern inspection method according to the present invention.  
         [0052]     (2) Pattern Inspection Method  
       (i) FIRST EMBODIMENT  
       [0053]      FIG. 2  is a flowchart showing schematic procedures in a first embodiment of the pattern inspection method according to the present invention, and  FIG. 3  is an explanatory diagram of automatic length measurement. The present embodiment provides a method suitable for an inspection of a simple repetitive pattern such as a line-and-space pattern shown in  FIG. 3 .  
         [0054]     First, a measurement condition file is read from recording media MR 2  and MR 4 , from which measurement conditions are read, such as position coordinates of measurement points 1 to n (n is a natural number), a threshold value for acceptability judgment for use in pattern recognition, a reference image, and offsets (step S 1 ).  
         [0055]     Next, a count n of a counter (not shown) incorporated in a control computer  60  is set to 1 (step S 2 ), an X-Y stage  22  is driven on the basis of information on the position of the read first measurement point, thereby moving a wafer W so that the first measurement point is positioned in the center of an observation field (step S 3 ). An electron beam EB is irradiated at this position, and a two-dimensional image having a low magnification of, for example, 15 k× and an observation field of 10 μm is acquired and loaded into an image memory  46  (step S 4 ). A two-dimensional image FVL shown in  FIG. 3  is one example of the two-dimensional image obtained in this manner. This two-dimensional image corresponds to, for example, a first two-dimensional image in the present embodiment.  
         [0056]     Since the accuracy in stopping the stage in a pattern inspection apparatus  1  shown in  FIG. 1  is ±2 μm, it is impossible to precisely decide the measurement point and the position for performing automatic focusing only by the operation of the X-Y stage  22  conforming to step S 3 . Therefore, position search using the reference image is executed for the measurement point.  
         [0057]     More specifically, for example, a reference image Imr shown in  FIG. 3  is read (step S 5 ), and a place Pr corresponding to the reference image Imr within the image FVL loaded earlier into the image memory  46  is searched for by a pattern recognition unit  52  (step S 6 ). When there is the place Pr corresponding to the reference image Imr within the observation field, more specifically, when the level of correspondence of the patterns exceeds the threshold value, the pattern recognition is successful (step S 7 ). In that case, an original point of the scanning with the electron beam EB by a scan lens  16  is then changed, and the electron beam EB is moved to a pattern for automatic focusing which is separated by a predetermined distance (an offset OFS in  FIG. 3 ) in a predetermined direction from the place where the pattern recognition has been successful and which is located at a position Pf outside an observation field FVh (step S 8 ), and then an exciting current of an objective lens  18  is controlled to carry Out the automatic focusing within a field of view for automatic focusing FVf (step S 9 ). The direction and amount (distance) of this offset OFS are preset as one of the measurement conditions. The measurement and focusing are carried out at different positions in this manner to prevent damages due to the irradiation of the electron beam EB from concentrating on one place. On the other hand, when the pattern recognition is unsuccessful, the X-Y stage  22  is driven to move the wafer W to a position in the vicinity of the current measurement point (step S 14 ), thus shifting to a sequence for remeasurement described later.  
         [0058]     When the automatic focusing is finished, the electron beam EB is moved from the above-mentioned position to a position for measurement Pr separated by the same distance as the above-mentioned predetermined distance in a direction opposite to the above-mentioned predetermined direction (step S 10 ), and a high-magnification two-dimensional image is acquired to measure the line width of the pattern (step S 11 ). In the present embodiment, the two-dimensional image at this point corresponds to, for example, a second two-dimensional image. The movement of the electron beam EB in the procedures in steps S 8  and S 10  is electrically controlled by a scan lens control circuit  36 , and the movement is therefore possible with an accuracy of about 10 nm.  
         [0059]     Next, whether the length measurement value of the line width meets a standard is judged to assess whether the measurement has been correctly carried out (step S 13 ). If the length measurement value meets the standard, whether any measurement points to be measured remain is judged (step S 16 ). When there still remain points to be measured, the count of a counter (not shown) is only incremented by one (step S 15 ), thus returning to step S 3  to repeat the operations described above.  
         [0060]     On the other hand, when the length measurement value does not meet the standard, it is presumed that an error has occurred in the procedure of at least one of the judgment of the acceptance of the pattern recognition (step S 7 ), the movement processing of the electron beam EB (steps S 8  and S 10 ), the automatic focusing processing (step S 9 ), and the line width measurement processing (step S 11 ). Thus, the processing for moving the measurement point (step S 14 ) is passed through to shift to the remeasurement sequence.  
         [0061]     The sequence for the remeasurement will be described with reference to  FIG. 4  as well. When the remeasurement is carried out, the redundant irradiation of the electron beam EB has to be avoided. Therefore, as shown in  FIG. 4 , there is decided a range in which the electron beam EB has been irradiated in the first measurement, that is, a position MPr for the remeasurement outside the filed of view in which the two-dimensional image FVL has been acquired with low magnification. When the length measurement value does riot meet the standard as a result of the remeasurement, it is presumed that the dimensions of the pattern to be inspected as such do not meet the standard, without any error in one of the judgment of the acceptance of the pattern recognition (step S 7 ), the movement processing of the electron beam EB (steps S 8  and S 10 ), the automatic focusing processing (step S 9 ), and the line width measurement processing (step S 11 ). Therefore, in the case of the remeasurement (step S 12 ), whether the length measurement value meets the standard is not judged, thus moving to the procedure in step S 15  for incrementing the count of the counter (not shown). It is to be noted that the remeasurement is carried out up to one time in the present embodiment, but the remeasurement may be carried out any number of times as long as measurement time allows.  
         [0062]     Thus, according to the present embodiment, the measurement position is automatically moved to the outside of the area to which the charged particle beam has already been irradiated, even when the remeasurement is needed due to, for example, an error, such that it is possible to minimize the change in the shape of the pattern due to the charged particle beam and accurately measure the pattern targeted for measurement.  
       (ii) SECOND EMBODIMENT  
       [0063]     The present embodiment provides an inspection method suitable for the measurement of a particular place in a random pattern such as a logic circuit. When a pattern to be inspected is a random pattern, a remeasurement point may not at all be anywhere as long as it is outside a range in which an electron beam has been irradiated in the first measurement, and the pattern has to have the same shape as that of the pattern for which the first measurement has been carried out. Thus, in the present embodiment, a plurality of positions for the remeasurement are decided in advance on the basis of design data for the pattern to be inspected, and incorporated in a measurement recipe as candidates for the remeasurement point. This makes it possible to achieve an accurate measurement with a minimum change in the patter shape due to a charged particle beam even if the pattern to be inspected is a complicated pattern. A remeasurement point is selected from these candidates at the time of the remeasurement. These candidates may be automatically decided using a technique of pattern recognition, or may be decided by an operator on the basis of the design data.  
       (iii) THIRD EMBODIMENT  
       [0064]     The position of a remeasurement point is decided in advance on the basis of design data in the second embodiment described above, but the present invention is not limited thereto, and the technique of pattern recognition described above may be used so that the periphery of a first measurement point may be searched as a remeasurement point every time remeasurement is needed.  
         [0065]     (4) Program  
         [0066]     A series of procedures of the pattern inspection method described above may be may be stored, for example, in the form of the above-mentioned recipe file in a recording medium such as a flexible disk or a CD-ROM as a program to be executed by a computer, and may be read into and executed by the computer. This makes it possible to achieve the pattern inspection method according to the present invention by use of a control computer connected to a scanning electron microscope. The recording medium is not limited to a portable medium such as a magnetic disk or an optical disk, and may be a fixed recording medium such as a hard disk drive or a memory. Further, the program incorporating the series of procedures of the pattern inspection method described above may be distributed via a communication line (including wireless communication) such as the Internet. Moreover, the program incorporating the series of procedures of the pattern inspection method described above may be distributed in an encrypted, modulated or compressed state via a wired line such as the Internet or a wireless line or in a manner stored in a recording medium.  
         [0067]     (5) Semiconductor Device Manufacturing Method  
         [0068]     If the pattern inspection method in the embodiments described above is used in a process of manufacturing a semiconductor device, the movement of a measurement position to the outside of an area to which a charged particle beam has been already irradiated can be automatically made without depending on the level of skill of an operator, and the problem of a change in the pattern shape due to the re-irradiation of the charged particle beam is solved, such that it is possible to rapidly and accurately measure the pattern to be inspected for fabrication of the semiconductor device on a substrate. This enables, for example, a dimensional measurement with high accuracy and at a high speed, so that it is possible to manufacture a semiconductor device with a high throughput and a high yield if the above-mentioned process of manufacturing the semiconductor device on the substrate is executed when it is judged that required specifications of products are satisfied as a result of the pattern inspection described above.