JP2005195548A - Scanning probe microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scanning probe microscope capable of stable and highly reliable operation in inspections on wafers etc. without operation halts in an inspection apparatus or any damage to a probe even if samples are charged in an inline automatic inspection process of wafers etc. <P>SOLUTION: The scanning probe microscope is provided with a measuring unit 1 provided with a probe 20 at a tip of a cantilever 21 for acquiring information on sample surfaces by bringing the probe close to the samples 12, destaticizing devices (301 and 302) for removing electrostatic charges of the samples, an electrostatically charged state determining part 311 for detecting the state of electrostatic charges of the samples based on displacements of the cantilever, and an additional destaticizing control part 312 for additionally removing electricity in the case that the state of electrostatic charge of the samples exceeds a threshold value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a scanning probe microscope, and more particularly to a scanning probe microscope provided with a charge removal device for reliably removing the charge of a sample.

  A scanning probe microscope is conventionally known as a measurement apparatus having a measurement resolution capable of observing a fine object of atomic order (grade) or size. In recent years, scanning probe microscopes have been applied to various fields such as measurement of fine irregularities on the surface of a substrate or wafer on which a semiconductor device is made. There are various types of scanning probe microscopes depending on the detected physical quantity used for measurement. For example, there are a scanning tunnel microscope using a tunnel current, an atomic force microscope using an atomic force, a magnetic force microscope using a magnetic force, etc., and their application range is expanding.

  Among these, the atomic force microscope is suitable for detecting fine irregularities on the surface of the sample with high resolution, and has a proven record in the fields of semiconductor substrates and disks. Recently, it has also been used for in-line automatic inspection processes.

  The atomic force microscope includes a measuring device portion based on the principle of the atomic force microscope as a basic configuration. Usually, a tripod type or tube type XYZ fine movement mechanism formed using a piezoelectric element is provided, and a cantilever having a probe tip formed at the tip is attached to the lower end of the XYZ fine movement mechanism. The tip of the probe faces the surface of the sample. For example, an optical lever type optical detection device is provided for the cantilever. That is, laser light emitted from a laser light source (laser oscillator) disposed above the cantilever is reflected by the back surface of the cantilever and detected by the photodetector. When the cantilever is twisted or bent, the incident position of the laser beam in the photodetector changes. Therefore, when a displacement occurs between the probe and the cantilever, the direction and amount of the displacement can be detected by the detection signal output from the photodetector. As for the configuration of the above atomic force microscope, a comparator and a controller are usually provided as a control system. The comparator compares the detection voltage signal output from the photodetector with the reference voltage and outputs a deviation signal. The controller generates a control signal so that the deviation signal becomes zero, and gives this control signal to the Z fine movement mechanism in the XYZ fine movement mechanism. In this way, a feedback servo control system that maintains a constant distance between the sample and the probe is formed. With the above configuration, the probe can be scanned while following the fine irregularities on the sample surface, and the shape of the probe can be measured (see, for example, Patent Document 1).

  At the time when the atomic force microscope was invented, measurement of surface fine shapes on the order of nm (nanometer) or less was a central issue by utilizing its high resolution. However, at present, the scanning probe microscope has been expanded in its range of use to in-line automatic inspection in which inspection is performed at an intermediate stage of an in-line manufacturing apparatus for semiconductor devices. In such a situation, in the actual inspection process, it is required to inspect the surface of the substrate or wafer at predetermined intervals. For this reason, automatic measurement for rapidly detecting the surface of a substrate or wafer is also being demanded. Further, there are various processes before the actual inspection process, and a sample such as a substrate or a wafer processed in these processes may be charged.

  In general, in the atomic force microscope, when the sample to be observed is charged, the cantilever receives an attractive force (or repulsive force) due to static electricity from the charged sample, making it impossible to access the sample, resulting in an inability to measure. It has been.

  In general, it is known that a sample can be charged by exposing the sample to a charge removal device (charge removal device). For this reason, in a conventional atomic force microscope, a neutralization device is provided inside and outside the device, and the sample is neutralized before inspection (Patent Document 2). However, if the tip at the tip of the cantilever is forcibly approached with insufficient charge removal from the sample, a microspark occurs between the probe and the sample at the first contact between the probe and the sample. However, even if the probe is damaged and measurement becomes impossible, or measurement can be performed, there is a high possibility that noise will occur in the measurement data. Therefore, the atomic force microscope has a problem that the probe cannot be approached when the charge amount of the sample is large, and the probe is damaged if the measurement is interrupted or forcedly approached.

  According to the in-line automatic inspection described above, the atomic force microscope (AFM) is used for sampling inspection (line QC) in each process, condition determination of the manufacturing apparatus, and the like in the manufacturing line of the semiconductor factory.

  In the semiconductor manufacturing line, the wafer may be charged by the manufacturing process as described above. For example, the wafer is often charged immediately after the scrub cleaning process.

Furthermore, conditions may change due to partial changes in the manufacturing process or defects in the manufacturing apparatus, and the amount of charge on the wafer may increase. In this case, the static elimination time set at the initial stage is insufficient for static elimination, and the wafer cannot be completely eliminated. As a result, the probe cannot be approached and the inspection apparatus stops. The semiconductor production line is operated for 24 hours, and the stoppage of the apparatus affects the line schedule, and the worst case is the line stoppage. Since there is not always an administrator who is familiar with the atomic force microscope (AFM) at the site when the apparatus is stopped, there is a high possibility that the static elimination time cannot be reset again.
Japanese Patent No. 3364531 JP 2000-171471 A (for example, paragraph 0046)

  An object of the present invention is to prevent the inspection apparatus from being stopped or the probe from being damaged in the inspection of a charged wafer or the like based on the scanning probe microscope in the operating environment as described above. It is in.

  In view of the above-described problems, the object of the present invention is to inspect the wafer or the like, even if the sample is charged in the in-line automatic inspection process of the wafer or the like, the inspection apparatus does not stop operating, and the probe is damaged. It is an object of the present invention to provide a scanning probe microscope capable of stable and reliable operation without being subjected to the above.

  In order to achieve the above object, a scanning probe microscope according to the present invention is configured as follows.

  The first scanning probe microscope (corresponding to claim 1) is provided with a probe at the tip of the cantilever, and the probe is brought close to the sample to obtain information on the sample surface, and the sample is charged. A scanning probe microscope equipped with a static eliminator for removal, and means for knowing the charged state of the sample from the displacement of the cantilever (charged state determination unit), and additional static elimination if the charged state of the sample is above a threshold value And a means for performing (additional charge removal control unit).

In the second scanning probe microscope (corresponding to claim 2), in the first apparatus configuration described above, preferably, the static elimination apparatus applies positive and negative ions from the electrode needle by applying a voltage to the electrode needle. It is characterized by static eliminators that are generated alternately.
Further, in the first scanning probe microscope (corresponding to claim 3), in the first apparatus configuration described above, preferably, the static eliminator ionizes gas in the vicinity of the sample by irradiating with X-rays or ultraviolet rays. It is characterized by a static eliminator that generates positive and negative ions.

  In the fourth scanning probe microscope (corresponding to claim 4), preferably, the means for knowing the charged state of the sample from the displacement of the cantilever is configured to charge the sample based on the output signal of the photodetector. Characterized by knowing the state.

  The fifth scanning probe microscope (corresponding to claim 5) is characterized in that, in the above-described apparatus configuration, preferably, when additional static elimination is performed, the display means has information for displaying information related to the additional static elimination. It is attached.

  The scanning probe microscope according to the present invention is equipped with a static eliminator for removing the charge of the sample, and further includes means for knowing the charged state of the sample and when the charged state of the sample is equal to or greater than a threshold value. It is possible to provide a means for performing additional static elimination, thereby determining the charged state of the sample and removing the charged sample according to the charged state of the sample. In conventional scanning probe microscopes, there is no means to repeatedly remove static electricity depending on the charged state of the sample.If the sample to be measured is charged, additional static electricity cannot be removed depending on the charged state. Is not discharged, the probe may not be able to approach the sample surface. On the other hand, in the present invention, the charge of the sample can be reliably removed based on the above configuration. That is, when the cantilever and the sample start approaching from a state where they are several mm apart by the approaching means, even at this distance, the cantilever is displaced by the electrostatic force depending on the charged state of the sample, and the cantilever when approaching a minute section From the displacement, the cantilever displacement when the next minute section is approached, that is, the surface potential of a sample such as a wafer can be predicted. If the predicted value exceeds the threshold value, additional static elimination is performed. By repeating this process as necessary, the approach is completed with a displacement equal to or less than the threshold value, and it is possible to continue the inspection without requiring manual labor.

  According to the present invention, in an in-line automatic inspection process of semiconductor devices, it is possible to prevent the inspection from being interrupted due to sudden wafer charging or the like and to prevent the probe from being damaged. Inspection can be performed with a force microscope (AFM) or the like. In addition, by accumulating charge amount information for each wafer or the like by an additional charge removal process, it is possible to optimize the preliminary charge removal for each wafer or the like.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  A scanning probe microscope (SPM) according to a representative embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows an external view of the entire apparatus of a scanning probe microscope and a perspective view of a schematic structure inside the apparatus. This scanning probe microscope assumes an atomic force microscope (AFM) as a typical example.

  As shown in FIG. 1, the scanning probe microscope according to the present embodiment includes a measurement unit 1 and a transport unit 2. The measurement unit 1 includes a sample stage 11, an AFM sensor unit 3, a first control device 33, a second control device 34, a display device 35, an input device 36, a static eliminator (ionizer) 301, and a static eliminator control device 302. A device (charge removing device) is provided. The transport unit 2 includes a transport robot 303, an aligner 304, and a load port 305.

  FIG. 2 is a diagram illustrating a configuration of the measurement unit 1. A sample stage 11 is provided below the AFM sensor unit 3 and the static eliminator 301. The sample 12 transported by the transport robot 303 is placed on the sample stage 11. The sample stage 11 is a mechanism for changing the position of the sample 12 in a three-dimensional coordinate system 13 composed of orthogonal X, Y, and Z axes. The sample stage 11 includes an XY stage 14, a Z stage 15, and a sample holder 16. The sample stage 11 is normally configured as a coarse movement mechanism that causes displacement (position change) on the sample side. On the upper surface of the sample holder 16 of the sample stage 11, the sample 12 having a relatively large area and a thin plate shape is placed and held. The sample 12 is, for example, a substrate or a wafer on which a semiconductor device is manufactured on the surface. The sample 12 is fixed on the sample holder 16. The sample holder 16 includes a sample fixing chuck mechanism. The sample stage 11 operates so as to place the sample 12 immediately below the static eliminator 301 when removing the sample 12, and to place the sample 12 directly below the AFM sensor unit 3 when performing AFM measurement. To do. In FIG. 2, the sample holder 16 is shown in an arrangement state at the time of AFM measurement.

  A specific configuration example of the sample stage 11 will be described with reference to FIG. In FIG. 3, 14 is an XY stage, and 15 is a Z stage. The XY stage 14 is a mechanism for moving the sample on the horizontal plane (XY plane), and the Z stage 15 is a mechanism for moving the sample 12 in the vertical direction. The Z stage 15 is mounted and mounted on the XY stage 14, for example.

  The XY stage 14 includes two Y-axis rails 201 arranged in parallel in the Y-axis direction, a Y-axis motor unit composed of a Y-axis motor 202 and a Y-axis driving force transmission mechanism 203, and an X-axis direction. The X-axis mechanism unit includes two parallel X-axis rails 204, an X-axis motor 205, and an X-axis driving force transmission mechanism 206. By the XY stage 14, the Z stage 15 is arbitrarily moved in the X-axis direction or the Y-axis direction. The Z stage 15 is provided with a drive mechanism for raising and lowering the sample holder 16 in the Z-axis direction. In FIG. 3, the drive mechanism is hidden and not shown. A chuck mechanism 207 for fixing the sample 12 is provided on the sample holder 16. As the chuck mechanism 207, a mechanical type or a mechanism using an action such as adsorption or electrostatic is usually used.

  In FIG. 2 again, the AFM sensor unit 3 is provided with an optical microscope 18 having a drive mechanism 17. The optical microscope 18 is supported by a drive mechanism 17. The drive mechanism 17 includes a focus Z-direction moving mechanism 17a for moving the optical microscope 18 in the Z-axis direction and an XY-direction moving mechanism 17b for moving in the XY axial directions. As an attachment relationship, the Z-direction moving mechanism 17a moves the optical microscope 18 in the Z-axis direction, and the XY-direction moving mechanism 17b moves the units of the optical microscope 18 and the Z-direction moving mechanism 17a in the respective XY axes. Although the XY direction moving mechanism portion 17b is fixed to the frame member, the frame member is not shown in FIG. The optical microscope 18 is disposed with its objective lens 18a facing downward, and is disposed at a position facing the surface of the sample 12 from directly above. A camera 19 is attached to the upper end of the optical microscope 18. The camera 19 captures and acquires an image of a specific area of the sample surface captured by the objective lens 18a, and outputs image data.

  On the upper side of the sample 12, a cantilever 21 having a probe 20 at the tip is arranged in a close state. The cantilever 21 is fixed to the attachment portion 22. For example, the attachment portion 22 is provided with an air suction portion (not shown), and the air suction portion is connected to an air suction device (not shown). The cantilever 21 is fixed and mounted by adsorbing the base portion having a large area by the air suction portion of the mounting portion 22.

  The attachment portion 22 is attached to a Z fine movement mechanism 23 that causes a fine movement operation in the Z direction. Further, the Z fine movement mechanism 23 is attached to the lower surface of the cantilever displacement detection unit 24.

  The cantilever displacement detector 24 has a configuration in which a laser light source 26 and a light detector 27 are attached to a support frame 25 in a predetermined arrangement relationship. The cantilever displacement detector 24 and the cantilever 21 are held in a certain positional relationship, and the laser light 28 emitted from the laser light source 26 is reflected by the back surface of the cantilever 21 and enters the photodetector 27. The cantilever displacement detector constitutes an optical lever type optical detector. When the cantilever 21 undergoes deformation such as twisting or bending by the optical lever type optical detection device, the deformation can be detected.

  The cantilever displacement detector 24 is attached to an XY fine movement mechanism 29. The XY fine movement mechanism 29 moves the cantilever 21, the probe 20 and the like at a minute distance in the XY axial directions. At this time, the cantilever displacement detector 24 is moved simultaneously, and the positional relationship between the cantilever 21 and the cantilever displacement detector 24 is unchanged.

  In the above description, the Z fine movement mechanism 23 and the XY fine movement mechanism 29 are usually composed of piezoelectric elements. The Z fine movement mechanism 23 and the XY fine movement mechanism 29 cause displacement of the probe 20 by a minute distance (for example, several to 10 μm, maximum 100 μm) in each of the X axis direction, the Y axis direction, and the Z axis direction.

  In the above mounting relationship, the observation field of view by the optical microscope 18 includes the surface of a specific region of the sample 12 and the tip (back) of the cantilever 21 including the probe 20.

  In FIG. 2, the above-described static eliminator (ionizer) 301 is disposed above the sample stage 11. As will be described later, a static eliminator 301 and a static eliminator control device 302 for controlling the static eliminator 301 constitute a static eliminator.

  FIG. 4 is a diagram illustrating the configuration and operation of the static eliminator. As shown in FIG. 4A, the static eliminator includes a static eliminator 301 and a static eliminator control device 302. The static eliminator 301 includes a plurality of ion generators 301a, and each ion generator 301a has an electrode needle 301b. As shown in FIG. 4B, a high voltage is applied to the electrode needle 301b by the power supply 301c, and a corona discharge is generated between the electrode needle 301b and the ground surface to generate a large number of positive ions 301d and negative ions 301e. With these ions, the charged sample is electrically neutralized and neutralized. Here, the static eliminator 301 is an AC type static eliminator, and as shown in FIG. 4C, an AC voltage indicated by a curve C10 is applied to the electrode needle 301b. As a result, positive ions are generated when the voltage is equal to or higher than the positive threshold voltage (eg, 3 kV) indicated by the dotted line L11, and the voltage is equal to or lower than the negative threshold voltage (eg, −3 kV) indicated by the dotted line L12. When it becomes, negative ions are generated. In this way, positive ions and negative ions are generated alternately from the electrode needle 301b. In FIG. 4C, the vertical axis indicates the applied voltage (V), and the horizontal axis indicates time (t). Usually, an AC power supply of 50 Hz or 60 Hz is used, and positive ions and negative ions are alternately generated at 50 Hz or 60 Hz. The charge removal process is controlled by the charge removal time, that is, the time during which the AC voltage is applied to the electrode needle 301b.

  Next, referring to FIG. 2 again, the control system of the scanning probe microscope will be described. As a configuration of the control system, a comparator 31, a controller 32, a first control device 33, a second control device 34, and a static eliminator control device 302 are provided. The controller 32 is a controller for realizing in principle a measurement mechanism using, for example, an atomic force microscope (AFM). The first control device 33 is a control device for driving control of each of a plurality of drive mechanisms, the static eliminator control device 302 is a device that controls the operation of the static eliminator 301, and the second control device 34 is a host device. It is a control device.

  The comparator 31 compares the voltage signal Vd output from the photodetector 27 with a preset reference voltage (Vref) and outputs a deviation signal s1 (s1 = Vref−Vd). Usually, when no force is applied to the probe, Vd indicates a voltage in the vicinity of 0 V, and the reference voltage (Vref) is set to a plus number V in the normal measurement state. When a repulsive force is applied to the probe and the cantilever is deformed to the anti-sample side, Vd is displaced to the plus side. When an attractive force is applied to the probe and the cantilever is deformed to the sample side, Vd is deformed to the minus side. The controller 32 generates a control signal s2 so that the deviation signal s1 becomes 0, and gives this control signal s2 to the Z fine movement mechanism 23. Upon receiving the control signal s2, the Z fine movement mechanism 23 adjusts the height position of the cantilever 21, and keeps the distance between the probe 20 and the surface of the sample 12 at a constant distance. The control loop from the photodetector 27 to the Z fine movement mechanism 23 detects the deformation state of the cantilever 21 with the optical lever type optical detection device while scanning the sample surface with the probe 20. This is a feedback servo control loop for maintaining the distance to the sample 12 at a predetermined constant distance determined based on the reference voltage (Vref). By this control loop, the probe 20 is kept at a constant distance from the surface of the sample 12, and when the surface of the sample 12 is scanned in this state, the uneven shape of the sample surface can be measured.

  Next, the first control device 33 will be described. The first control device 33 includes the following functional units.

  The position of the optical microscope 18 is changed by a driving mechanism 17 including a focusing Z-direction moving mechanism 17a and an XY-direction moving mechanism 17b. The first control device 33 includes a first drive control unit 41 and a second drive control unit 42 for controlling the operations of the Z direction moving mechanism unit 17a and the XY direction moving mechanism unit 17b.

  The sample surface and the image of the cantilever 21 obtained by the optical microscope 18 are picked up by the camera 19 and taken out as image data. Image data obtained by the camera 19 of the optical microscope 18 is input to the first control device 33 and processed by the internal image processing unit 43.

  In the feedback servo control loop including the controller 32 and the like, the control signal s2 output from the controller 32 means a height signal of the probe 20 in the scanning probe microscope (atomic force microscope). . Information related to the change in the height position of the probe 20 can be obtained by the height signal of the probe 20, that is, the control signal s2. The control signal s2 including the height position information of the probe 20 is given to the Z fine movement mechanism 23 for driving control as described above, and is taken into the data processing unit 44 in the control device 33.

  The voltage signal Vd output from the photodetector 27 of the cantilever displacement detection unit (displacement detection device) 24 is monitored by the monitor unit 49.

  The scanning of the sample surface with the probe 20 in the measurement region on the surface of the sample 12 is performed by driving the XY fine movement mechanism 29. The drive control of the XY fine movement mechanism 29 is performed by an XY scanning control unit 45 that provides the XY fine movement mechanism 29 with an XY scanning signal s3.

  The XY stage 14 and the Z stage 15 of the sample stage 11 are driven by an X drive control unit 46 that outputs an X direction drive signal, a Y drive control unit 47 that outputs a Y direction drive signal, and a Z direction that outputs a Z direction drive signal. It is controlled by the drive control unit 48.

  The first control device 33 includes a storage unit that stores and saves the set control data, the input optical microscope image data, the data related to the height position of the probe, and the like as necessary.

  The static eliminator control device 302 is a device that controls the operation of the static eliminator 301 based on a command from the second control device 34.

  A second control device 34 positioned above the first control device 33 and the static eliminator control device 302 is provided. The second control device 34 stores and executes a normal measurement program and sets and stores a normal measurement condition, stores and executes an automatic measurement program and sets and stores the measurement condition, stores measurement data, and displays an image of the measurement result. Processing such as processing and display on the display device (monitor) 35 is performed. In particular, in the case of the present invention, a program for realizing a function of knowing the charged state of a sample, a function of repeatedly performing additional static elimination when the charged state of the sample is equal to or greater than a threshold value, and a function of driving a static elimination device. Prepare. That is, after the sample is set directly under the AFM sensor unit 3, the detection signal output from the photodetector is monitored, the charged state of the sample is determined by the monitored detection signal, and the charged state of the sample is equal to or greater than the threshold value. In this case, a program for repeatedly performing additional static elimination is provided. In addition, a program for performing a series of processes from the conveyance of the sample after the sample cassette 307 is set to the AFM measurement is provided. Furthermore, it can be configured to have a communication function, and can have a function to communicate with an external device.

  Since the second control device 34 has the above function, the second control device 34 includes a CPU 51 that is a processing device and a storage unit 52. The storage unit 52 stores and saves the above programs, condition data, and the like. In addition, the CPU 51 and the storage unit 52 monitor the detection signal output from the photodetector after the sample is set directly under the AFM sensor unit, determine the charged state of the sample based on the monitored detection signal, and charge the sample. A function of repeatedly performing additional static elimination when the value is equal to or greater than a threshold value and a function of performing a series of processes from sample conveyance after setting the sample cassette to AFM measurement are realized. Further, the second control device 34 includes an image display control unit 53 and a communication unit. In addition, an input device 36 is connected to the second control device 34 via an interface 54 so that programs, conditions, data, and the like stored in the storage unit 52 can be set and changed by the input device 36. It has become. In addition, a transport robot 303 is connected to the second control device 34 via an interface 56.

  The CPU 51 of the second control device 34 provides higher-level control commands and the like to each functional unit of the first control device 33 via the bus 55, and the image processing unit 43, the data processing unit 44, and the monitor unit 49. Image data, data related to the height of the probe, and the like. Further, a higher-level control command for preliminary static elimination and additional static elimination is provided to the static eliminator control device 302.

  Next, the transport unit 2 will be described with reference to FIGS. 1 and 5. The transport unit 2 includes a load port 305, an aligner 304, and a transport robot 303. The load port 305 is for installing a sample cassette. The aligner 304 adjusts the direction of the wafer. The transfer robot 303 transfers a sample (wafer) from the load port 305 to the aligner 304 and the sample stage 11. The operation of the transport unit 2 will be described with reference to FIG. 5. The sample 12 as the subject is set in the load port 305 of the apparatus in a state where it is in the cassette 307. The sample 12 set in the load port 305 is taken out from the sample cassette 307 by a robot hand 308 having a transfer robot 303 attached to the tip. The sample 12 taken out is once placed on the aligner 304, and the angle and the alignment in the XY plane are performed. After placing the sample on the aligner 304 and adjusting the position of the sample as described above, the sample 12 is transferred from the aligner 304 to the sample holder 16 of the sample stage 11 of the measurement unit 1 by the robot hand 308. The chuck mechanism 207 adsorbs the sample 12 with negative air pressure.

  Next, the operation of the apparatus in the measurement unit 1 will be described. The sample 12 transported by the transport robot 303 is moved to a position immediately below the static eliminator 301, and before the inspection by the AFM sensor unit 3 starts, the static eliminator 301 first performs static elimination (preliminary static elimination) for a predetermined time. .

  When the preliminary charge removal is completed, the XY stage 11 is driven to move the chuck mechanism 207 and the sample 12 to the position of the AFM sensor unit 3. At this time, the probe 20 and the sample 12 are separated by several mm or more in the Z direction. For the inspection by the AFM sensor unit 3, the probe 20 must be brought close to the sample 12 until it reaches a predetermined distance. Therefore, the Z stage 16 of the sample stage 11 is driven to bring them closer together. At this time, if the sample 12 is charged, the cantilever 21 receives displacement due to electrostatic force, and the displacement amount increases as the distance between the two approaches and the charge amount increases. This is shown in FIG. The electrostatic force is a long-distance force that is inversely proportional to the square of the distance, and even if it is several hundred microns away, the cantilever 21 is subject to a large displacement and may be mistaken for the end of the approach.

  The vertical axis in FIG. 6 is the absolute value of the output signal Vd of the photodetector 27, and the horizontal axis represents the distance between the probe 20 and the sample 12. A curve C20 indicates the relationship between the output signal and the distance when the sample 12 is highly charged, and a curve C21 indicates the relationship between the output signal and the distance when the sample 12 is smallly charged. The electrostatic force includes repulsive force and attractive force, and which one works depends on the charged state of the sample 12. For this reason, LVdl, which is the absolute value of Vd, is used as an index of the sample charge amount.

  The photodetector 27 converts a minute displacement (deflection) of the cantilever 21 due to the interatomic force acting on the probe 20 into an electric signal, but it cannot be distinguished from the signal due to the cantilever displacement due to the electrostatic force. There is a problem in that it is erroneously determined that the contact has been received by the contact 12, that is, the approach has been completed, and the approach has been interrupted, leading to no inspection by the AFM sensor unit 3. Even when the offset of Vd due to electrostatic force is canceled and the approach is continued, when the probe 20 really reaches a predetermined distance from the sample 12, the charge charged on the sample 12 passes through the probe 20. Microsparks that are discharged at a time are generated, and the probe 20 may be greatly damaged.

  The former requires human intervention to continue, which is a bad situation for an inline automatic inspection device. The latter has even worse results because the test appears to continue.

  In the present embodiment, a function of automatically performing additional static elimination when the amount of charge is large and static elimination is insufficient only by preliminary static elimination is realized. The mechanism will be described with reference to FIGS.

  FIG. 7 is a block diagram of the additional static elimination control mechanism described above. The additional charge removal control mechanism 309 includes an approach end determination unit 310, a charged state determination unit 311, and an additional charge removal control unit 312. The approach end determination unit 310 is realized as a functional unit in the second control device 33, and an atomic force acting between the probe 20 and the sample 12 based on an output signal from the monitor unit 49 is set to a set value (= Judgment is made based on whether or not Vref has been reached. Information about the end of the approach is output to the charging state determination unit 311. The charged state determination unit 311 compares the absolute value of the output signal Vd with the threshold value Vt, and outputs information on the magnitude relationship between the absolute value of Vd and Vt to the additional static elimination control unit 312. The additional static elimination control unit 312 stops static elimination when receiving a signal that the absolute value of Vd is smaller than Vt, and executes the additional static elimination program when receiving a signal that the absolute value of Vd is larger than Vt. . In the additional static elimination program, first, the XY stage 15 is moved so that the sample 12 is disposed immediately below the static eliminator 301, and then the static eliminator 301 is driven to perform static elimination, and the XY stage 15 is driven again. This is a program for causing the sample 12 to move directly below the AFM sensor unit 3.

  FIG. 8 shows changes in the distance between the probe 20 and the sample 12 and the absolute value of the output signal Vd when actual additional static elimination is performed. The horizontal axis indicates the distance between the probe 20 and the sample 12, and the vertical axis indicates the absolute value of the output signal Vd. The straight line L30 is the threshold value Vt, and is a value that does not affect the inspection by the AFM sensor unit 3 and does not damage the probe if the charge amount is less than this. First, according to the curve C30, the absolute value of the output voltage Vd gradually increases as the probe 20 approaches the sample 12. Then, when the threshold value Vt is reached at the distance d1, additional static elimination is performed, the absolute value of the output voltage Vd becomes VL, and changes as shown by the curve C31 when the probe 20 further approaches. A dotted line C32 indicates a change in the absolute value of Vd when static elimination is not performed. Assuming that the change in Vd when the probe approaches dZ is dVd, the increase in Vd due to the approach in the next section (= dZ) can be predicted to be approximately dVd. If this predicted value exceeds Vt, the approach is temporarily interrupted, the sample is moved to a position directly below the static eliminator (charge removal device) 301, and after additional static elimination, the original position is returned and approached. continue.

  An algorithm relating to the above-described pre-static elimination and additional static elimination processes will be described with reference to the flowchart of FIG. First, pre-charge elimination is performed (step S11), and then the probe 20 is approached on the sample 12 immediately below the AFM sensor unit 3 (step S12). In step S12, it is determined whether or not the approach is completed. The determination of the end of the approach is made based on whether or not the atomic force acting between the probe 20 and the sample 12 has reached a set value (= Vref). There is a relationship of Vref> Vt between Vref and Vt. This determination is performed by the approach end determination unit 310 of FIG. In the case of the end of approach, this step ends, and the process of AFM measurement by the AFM sensor unit 3 starts. If the approach is not complete, the probe 20 approaches the sample 12 (step S13). In step S14, the determination of LVdl> Vt in FIG. 9 is performed by the charged state determination unit 311 in FIG. When the absolute value of Vd is smaller than Vt, step S12 is executed. This is the case in FIG. 8, and the potential of the sample 12 is lowered by one additional static elimination until the approach is completed. When the absolute value of Vd is larger than Vt, that is, when the amount of charged sample still remains and exceeds the threshold value Vt due to the approach even after static elimination, additional static elimination is repeated (step S15). The number of additional static elimination required until the end of the approach is recorded in the storage unit 52 of the second control device 34 and output to the display device 35. In step S16, it is determined whether or not the number of static eliminations is greater than the set value. If the number of additional static eliminations exceeds the set value, an error (step S17) is issued and sufficient access is not possible, and the approaching operation is stopped. To do.

  Further, when approaching the probe 20 to the sample 12, in order not to reduce the throughput, the probe 20 is approached by a large step (unit moving distance: for example, dZ = 100 μm in this embodiment) halfway. Switch to a small step (eg dZ = 10 μm). The exact distance between the probe 20 and the sample 12 is not known at the start of approach. That is, the exact approach end position is not known. This step change point is determined in consideration of variations in the thickness of the wafer and the like.

  According to the present embodiment, the charge amount of a sample such as a wafer is increased due to a sudden cause (correction of a manufacturing process, a defect of a manufacturing apparatus, etc.), and the charge removal cannot be sufficiently performed in the pre-static charge time set by the apparatus administrator. Even in this case, additional static elimination can be automatically performed and the inspection by AFM can be continued. If neutralization is not possible even after the set number of additional neutralizations, an error is generated and the probe stops, so there is little possibility of damage to the probe due to microsparking, etc. Contributes to improving data reliability.

  Further, by storing / accumulating data related to the implementation status of the additional static elimination, and further displaying the implementation status, it is possible to notify the apparatus manager that there has been a change in the manufacturing process. In response to this, the device manager determines whether to extend the pre-charge removal time or review the charge removal process.

  In the inspection by AFM, usually, several places are measured for one wafer or the like. For example, in the case of five places, it is usual to measure symmetrically with the wafer center, left end, right end, upper end, and lower end. According to the present embodiment, since it is possible to know the implementation status of additional static elimination at each measurement point, it is possible to know the balance of charging on the wafer or the like.

  When the additional static elimination process as described above is completed, the Z-axis direction fine movement portion of the AFM sensor unit 3 and the Z stage 15 are driven with respect to the sample holder 16 and the sample 12 in the sample stage 11, Inspection based on AFM measurement is performed.

  Next, the basic operation of the scanning probe microscope (atomic force microscope) will be described.

  The tip of the probe 20 of the cantilever 21 is made to face a predetermined region on the surface of the sample 12 such as a semiconductor substrate placed on the sample stage 11. Normally, the probe 20 is brought close to the surface of the sample 12 by the Z stage 15 which is a probe approach mechanism, and an atomic force is applied to cause the cantilever 21 to bend and deform. The amount of bending due to the bending deformation of the cantilever 21 is detected by the optical lever type optical detection device described above. In this state, the sample surface is scanned (XY scan) by moving the probe 20 relative to the sample surface. The XY scanning of the surface of the sample 12 by the probe 20 is performed by moving (finely moving) the probe 20 side by the XY fine movement mechanism 29 or by moving (coarsely moving) the sample 12 side by the XY stage 14. This is done by creating a relative movement relationship in the XY plane between the sample 12 and the probe 20.

  The movement on the probe 20 side is performed by giving an XY scanning signal s3 related to XY fine movement to an XY fine movement mechanism 29 including a cantilever 21. The scanning signal s3 related to the XY fine movement is given from the XY scanning control unit 45 in the first control device 33. On the other hand, the movement on the sample side is performed by giving drive signals from the X drive control unit 46 and the Y drive control unit 47 to the XY stage 14 of the sample stage 11.

  The XY fine movement mechanism 29 is configured using a piezoelectric element, and can perform scanning movement with high accuracy and high resolution. Further, the measurement range measured by the XY scanning by the XY fine movement mechanism 29 is limited by the stroke of the piezoelectric element, and therefore is a range determined by a distance of about 100 μm at the maximum. According to the XY scanning by the XY fine movement mechanism 29, a minute range is measured. On the other hand, since the XY stage 14 is usually configured using an electromagnetic motor as a drive unit, the stroke can be increased to several hundred mm. According to the XY scanning by the XY stage 14, the measurement is performed in a wide range.

  As described above, while the predetermined measurement area on the surface of the sample 12 is scanned with the probe 20, the amount of bending of the cantilever 21 (the amount of deformation due to bending) is controlled based on the feedback servo control loop. I do. The amount of bending of the cantilever 21 is controlled so as to always coincide with the reference target amount of bending (set by the reference voltage Vref). As a result, the distance between the probe 20 and the surface of the sample 12 is maintained at a constant distance. Accordingly, the probe 20 moves while tracing the fine uneven shape (profile) on the surface of the sample 12, and the fine uneven shape on the surface of the sample 12 can be measured by obtaining the probe height signal.

  For example, as shown in FIG. 10, the scanning probe microscope as described above is incorporated as an automatic inspection process 92 for inspecting a wafer or a substrate at an intermediate stage of an in-line manufacturing apparatus of a semiconductor device (LSI). When a wafer (sample 12) to be inspected is unloaded from the manufacturing process step 91 in the previous stage by a substrate transfer device (not shown) and placed on the substrate holder 16 of the scanning probe microscope (SPM) in the automatic inspection step 92, scanning is performed. A microprotrusion shape of a predetermined area on the substrate surface is automatically measured by a scanning probe microscope, and the pass / fail of the processing of the substrate manufacturing in the previous stage is determined. Thereafter, the substrate is transported again to the subsequent manufacturing processing step 93 by the substrate transfer device. The

  It should be noted that, when performing static elimination beforehand, by knowing the type of sample in advance, a certain level of static elimination conditions can be set, and even when static elimination is performed, by performing additional static elimination as described above, The sample can be surely neutralized. Furthermore, in the description of the above embodiment, an example of a type having an electrode needle as a static eliminator has been described. However, as another type of static eliminator, X-rays or ultraviolet rays are irradiated to ionize a gas in the vicinity of the sample to generate ions. A generated type can also be used.

  The configurations, shapes, sizes, and arrangement relationships described in each of the above embodiments are merely schematically shown to the extent that the present invention can be understood and implemented, and the numerical values and the compositions (materials) of the respective configurations. Is just an example. Therefore, the present invention is not limited to the above-described embodiment, and can be modified in various forms without departing from the scope of the technical idea shown in the claims.

  INDUSTRIAL APPLICABILITY The present invention is an in-line automatic inspection process for wafers and the like, which is used as an inspection apparatus that operates stably and highly reliably without damaging the probe even when charged wafers are inspected. Is done.

It is a block diagram which shows the whole structure (an apparatus is a schematic internal structure) of the scanning probe microscope which concerns on typical embodiment of this invention. It is a figure which shows the detailed structure of a measurement unit. It is a perspective view which shows the specific structure of a sample stage. It is a figure which shows a structure and operation | movement of a static elimination apparatus, (a) shows a structure of a static elimination apparatus, (b) shows a mode that ion discharge | releases from an electrode needle, (c) is a time change of an applied voltage, and ion It is a figure which shows generation | occurrence | production. It is a figure explaining the operation | movement by a conveyance unit. It is a graph which shows the relationship between the absolute value of the output signal of a photodetector, and the distance between a probe and a sample. It is a block block diagram of an additional static elimination control mechanism. It is a graph which shows the relationship between the absolute value of an output signal when additional static elimination is performed, and the distance between a probe and a sample. It is a flowchart which shows the process of static elimination. It is the block diagram which showed the structure by which the scanning probe microscope which concerns on this invention is used as an in-line automatic test process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measurement unit 2 Conveyance unit 3 AFM sensor unit 11 Sample stage 12 Sample 16 Sample holder 17 Drive mechanism 18 Optical microscope 19 Camera 20 Probe 21 Cantilever 22 Mounting part 23 Z fine movement mechanism 29 XY fine movement mechanism 33 1st control apparatus 34 2nd Control device 301 Static eliminator 302 Static eliminator control device 303 Transfer robot 304 Aligner 305 Load port 310 Approach end determination unit 311 Charged state determination unit 312 Additional static elimination control unit

Claims (5)

In a scanning probe microscope provided with a probe at the tip of a cantilever and bringing the probe close to a sample to obtain information on the surface of the sample, and a static eliminator for removing the charge of the sample ,
Means for knowing the charged state of the sample from the displacement of the cantilever;
Means for performing additional static elimination when the charged state of the sample is equal to or greater than a threshold;
A scanning probe microscope comprising:   2. The scanning probe microscope according to claim 1, wherein the static eliminator is a static eliminator that alternately generates positive and negative ions from the electrode needle by applying a voltage to the electrode needle.   2. The scanning probe microscope according to claim 1, wherein the static eliminator is a static eliminator that generates positive and negative ions by ionizing a gas in the vicinity of the sample by irradiating with X-rays or ultraviolet rays.   The scanning according to any one of claims 1 to 3, wherein the means for knowing the charged state of the sample from the displacement of the cantilever knows the charged state of the sample based on an output signal of a photodetector. Type probe microscope.   5. The scanning probe microscope according to claim 1, further comprising a display unit configured to display information related to the additional static elimination when the additional static elimination is performed.