JP2006250637A - Scanning probe microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scanning probe microscope capable of controlling accurately the probe length by measuring the length of the probe mounted on a device, estimating accurately the abrasion state of the probe, keeping excellently the tip state of the probe during measurement, elongating the using lifetime of the probe, and keeping excellently accuracy of measuring/inspection. <P>SOLUTION: This scanning probe microscope is equipped with a probe part (21, 22 or the like) having the probe 20 facing to a sample 12, a probe moving mechanism 14, 15, 23, 29 for moving the probe, a measuring part 63 (24, 31, 32) for measuring a physical quantity generated between the probe and the sample, and a sample stage 11 where the sample is placed. The scanning probe microscope for measuring the sample surface by scanning the sample surface by the probe has a constitution equipped with a probe length measuring mechanism 62 for measuring the length in the axial direction of the probe 20. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a scanning probe microscope, and more particularly to a scanning probe microscope suitable for improving the measurement accuracy by managing the length of a probe in continuous automatic measurement 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 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 scanning tunneling microscopes (STM) that use tunnel current, atomic force microscopes (AFM) that use atomic force, and magnetic force microscopes (MFM) that use magnetic force. It's getting on.

  Of these, the atomic force microscope is particularly suitable for detecting fine irregularities on the surface of a 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.

When an atomic force microscope or the like is used in an in-line automatic inspection process, a large number of samples that are semiconductor products must be sequentially and sequentially measured to inspect the semiconductor products. The measurement accuracy of an atomic force microscope greatly depends on the degree of wear of the tip of the probe. Therefore, if measurement / inspection of a large number of samples is continued, the tip of the probe is gradually worn, the length of the probe is shortened, and the sharp state is deteriorated. When the length of the probe is shortened and the tip of the probe becomes dull in proportion to it, the resolution decreases and the measurement accuracy decreases, conventionally, the probe is usually replaced (for example, a patent) Reference 1).
JP 2002-323430 A

  In an atomic force microscope or the like used in an in-line automatic inspection process or the like, the tip shape of the probe is an important element in measurement and needs to be managed. In the current wear management of the probe tip, the travel distance management and the number of contacts with the measurement sample are managed for the probe in use. The tip shape of the probe is estimated using these management data, and the lifetime of the probe is estimated. Therefore, at present, the degree of wear of the probe is only estimated by indirect data, and the wear of the probe is not directly monitored. In addition, since there is no device for directly monitoring the wear of the probe, in practice, it is mostly known to know the tip wear of the probe from the abnormality of the data being measured. Therefore, the reliability as a measuring apparatus is low. Furthermore, the wear of the tip of the probe has individual differences among the probes, but it is more dependent on the sample than that. Therefore, it is difficult to accurately estimate the wear state of the probe tip based simply on indirect management data such as the travel distance and the number of contacts.

  The object of the present invention is to accurately control the length of the probe by measuring the length of the probe mounted on the apparatus and accurately estimate the wear state of the probe, and to measure the tip of the probe during measurement. An object of the present invention is to provide a scanning probe microscope capable of maintaining a good state, extending the service life of a probe, and maintaining a good measurement / inspection accuracy.

  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) includes a probe unit having a probe facing the sample, a probe moving mechanism for moving the probe, and a physical quantity generated between the probe and the sample. Measures the length of the probe in the axial direction in a scanning probe microscope that includes a measurement unit for measurement and a sample stage on which the sample is placed, and measures the surface of the sample by scanning the surface of the sample with a probe. A probe length measuring mechanism is provided.

  The above-described scanning probe microscope is deployed, for example, in an in-line automatic inspection process during a semiconductor manufacturing process, and continuously measures and inspects a large number of semiconductor substrates and the like. According to the scanning probe microscope, in the measurement / inspection of this sample, the length in the axial direction of the probe before or during use is measured by the probe length measurement mechanism at an appropriate timing at the time of measurement, In addition, by recording and managing data related to the probe length in a memory or the like, it is possible to always use the probe in a good tip wear state.

  In the second scanning probe microscope (corresponding to claim 2), in the configuration of the scanning probe microscope described above, preferably, the probe length measuring mechanism includes a reference base and a tip of the probe on the reference base. The difference between the first position and the second position, the measuring unit for measuring the first position when the probe is positioned and the second position when the proximal end of the probe is positioned on the reference base, and the length of the probe It is characterized by having a length calculation unit for calculating the length.

  The third scanning probe microscope (corresponding to claim 3), in the configuration of the scanning probe microscope described above, preferably, after the probe is mounted on the probe portion, the probe length measuring mechanism is used before use. Measure the length of the probe.

  In the fourth scanning probe microscope (corresponding to claim 4), preferably, in the configuration of the scanning probe microscope described above, a recording unit for recording the probe length measured by the probe length measuring mechanism is provided. It is characterized by providing.

  According to the scanning probe microscope of the present invention, when the measurement probe is deployed in an in-line automatic inspection process or the like in the semiconductor manufacturing process, the length of the mounted probe is measured to Since the length is managed accurately, the wear state of the probe in use is accurately estimated, the tip state of the probe is maintained well during measurement, the service life of the probe is extended, The accuracy of the inspection can be improved and kept well.

  DESCRIPTION OF EMBODIMENTS Preferred embodiments (examples) of the present invention will be described below with reference to the accompanying drawings.

  Based on FIG. 1, the whole structure of the scanning probe microscope (SPM) based on this invention is demonstrated. This scanning probe microscope assumes an atomic force microscope (AFM) as a typical example.

  A sample stage 11 is provided in the lower portion of the atomic force microscope apparatus. The sample stage 11 is arranged on the reference surface 10 so as to be able to move smoothly and freely. The sample stage 11 itself is an XY moving unit, and has a Z stage 15 inside thereof. The XY stage mechanism 14 fixed on the reference surface 10 moves the sample stage 11 on the reference surface 10 as an XY moving unit. The XY stage mechanism 14 includes an X stage mechanism 14a and a Y stage mechanism 14b. The sample stage 11 and the XY stage mechanism 14 are connected by a connecting portion 14c.

  A sample 12 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 the XY stage mechanism 14 and the Z stage 15 as described above, and further includes the 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 an integrated circuit pattern of a semiconductor device is manufactured on the surface. The sample 12 is fixed on the sample holder 16. The sample holder 16 has a sample fixing chuck mechanism on the upper surface portion thereof.

  In FIG. 1, an optical microscope 18 having a drive mechanism 17 is disposed above the sample 12. 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 TV camera (imaging device) 19 is attached to the upper end of the optical microscope 18. The TV 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 accordingly.

  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 a base portion having a large area by an 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 is deformed such as torsion or bending by the optical lever type optical detection device, the displacement due to 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. 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. The XY fine movement mechanism 29 is fixed to the frame member (not shown).

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

  Next, the control system of the atomic force microscope will be described. As a configuration of the control system, a comparator 31, a controller 32, a controller (first control device) 33, and a host control device (second control device) 34 are provided. The controller 32 is a controller for realizing in principle a measurement mechanism using an atomic force microscope (AFM). The controller 33 is a control device for driving control of each of a plurality of drive mechanisms and the like, and the host control device 34 is a control device that issues commands to the controller 33 and processes data from the controller 33.

  The comparator 31 compares the voltage signal Vd output from the photodetector 27 with a preset reference voltage (Vref) and outputs the deviation signal s1. The controller 32 generates a control signal s2 so that the deviation signal s1 becomes zero, 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 controller 33 is a control device for driving each part of the atomic force microscope, and 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 controller 33 includes a first drive control unit 41 and a second drive control unit 42 for controlling the operations of the Z-direction movement mechanism unit 17a and the XY-direction movement mechanism unit 17b.

  The sample surface and the image of the cantilever 21 obtained by the optical microscope 18 are picked up by the TV camera 19 and taken out as image data. Image data obtained by the TV camera 19 of the optical microscope 18 is input to the controller 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 the height signal of the probe 20 in the 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 controller 33.

  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 mechanism 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 drive signal. It is controlled by the Z drive control unit 48.

  The controller 33 includes a storage unit (not shown) 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.

  A host controller 34 is provided for the controller 33. The host controller 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 performs image processing of the measurement result. Further, processing such as display on the display device (monitor) 35 is performed. Particularly in the case of the present invention, control related to the measurement of the length of the probe in automatic measurement is performed. Conditions relating to automatic measurement are stored and managed in a setting file. Furthermore, it can be configured to have a communication function, and can have a function to communicate with an external device.

  Since the host controller 34 has the above functions, the host controller 34 includes a CPU 51 that is a processing device and a storage unit 52. The storage unit 52 stores and stores the above-described program, condition data, and the like. The control device 34 includes an image display control unit 53 and a communication unit. In addition, an input device 36 is connected to the host control device 34 via an interface 54 so that a measurement program, measurement conditions, data, and the like stored in the storage unit 52 can be set and changed by the input device 36. It has become.

  The CPU 51 of the host controller 34 provides host control commands and the like to each functional unit of the controller 33 via the bus 55, and image data and probe data from the image processor 43 and the data processor 44. Provide data on height position.

  Next, the basic operation of the atomic force microscope apparatus 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. In the XY scanning of the surface of the sample 12 by the probe 20, the probe 20 side is moved (finely moved) by the XY fine movement mechanism 29, or the sample 12 side is moved (coarsely moved) by the XY stage mechanism 14. Thus, a relative movement in the XY plane is created 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. A scanning signal s 3 related to XY fine movement is given from an XY scanning control unit 45 in the controller 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 mechanism 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. In addition, the measurement range measured by XY scanning by the XY fine movement mechanism 29 is limited by the stroke of the piezoelectric element, and is a range determined by a distance of about 10 μm at the maximum. According to the XY scanning by the XY fine movement mechanism 29, the measurement is performed in a minute narrow range. On the other hand, since the XY stage mechanism 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 mechanism, a wide range can be measured.

  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 kept constant. Therefore, for example, the probe 20 moves (scans) 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 is obtained by obtaining the height signal of the probe. It can be measured.

  In the scanning probe microscope having the above configuration, a reference table 61 is further provided on the sample stage 11. The reference base 61 is preferably formed with a height reference surface whose height position is set as known as the “reference height” on the upper surface thereof. The height of the reference table 61 is not necessarily known. For example, any one can be used as long as the difference between the first height position and the second height position can be measured.

  Further, the storage unit 52 of the host controller 34 stores a program for measuring the length of the probe 20 (length in the axial direction) and measurement data relating to the length of the probe 20. Measurement data relating to the length of the probe 20 is recorded in the probe recording area of the storage unit 52.

  Next, an operation for measuring and managing the length of the probe 20 will be described with reference to FIGS. FIG. 2 is a flowchart of a program for measuring the length of the probe, and FIG. 3 is a diagram showing the positional relationship between the probe 20 and the reference table 61.

  In the first step S <b> 11, the probe 20 is attached to the attachment portion 22 before the measurement by the scanning probe microscope is started. Next, the sample stage 11 is moved by the X stage mechanism 14a and the Y stage mechanism 14b, and the probe 20 is positioned above the reference table 61 (step S12). Thereafter, the probe 20 is lowered, and the tip of the probe 20 is brought into contact with the height reference surface of the reference table 61 (step S13). FIG. 3A shows this state. The Z-direction height position (Z1) of the probe 20 is measured from the amount of movement of the probe 20 lowered at that time (step S14). Data relating to the measured height position (Z1) in the Z direction is recorded in the probe recording area of the storage unit 52 (step S15).

  Next, the probe 20 is raised (step S16), and the positional relationship between the probe 20 and the reference table 61 is changed (step S17).

  The probe 20 is lowered again, and the edge portion of the proximal end of the probe 20 (the root portion of the cantilever 21) is brought into contact with the height reference surface of the reference table 61 (step S18). FIG. 3B shows this state. The Z-direction height position (Z2) of the probe 20 is measured from the amount of movement of the probe 20 lowered at that time (step S19). Data relating to the measured height position (Z2) in the Z direction is recorded in the probe recording area of the storage unit 52 (step S20).

  Next, the length (L1 = Z1-Z2) of the probe 20 is calculated based on the height position data Z1, Z2 recorded in the probe recording area of the storage unit 52 (step S21). The calculated length data of the probe 20 is recorded in the probe recording area of the storage unit 52.

  In the flowchart of FIG. 2, steps S22 and S23 exist, but these processes are not executed in the initial probe length measurement process.

  According to the above procedure, the length (L1) of the probe 20 at the stage before use which is mounted on the attachment portion 22 of the probe 20 and starts measurement is measured. Thereafter, measurement with a scanning probe microscope is started. After the measurement is started, the measurement of the length of the probe 20 based on the above procedure is periodically and repeatedly executed at a required timing. Therefore, the length of the new probe 20 is first measured and recorded, and thereafter, the length of the probe is periodically measured and recorded. In the subsequent process of measuring the length of the probe 20, each time the length of the probe 20 is measured, the length of the probe 20 is compared with the length of the probe 20 before use (step S22), and the state of the probe 20 is changed. The information is displayed on the display device 35 (step S23). When a certain amount of length difference is generated by this display, warning information such as replacement is notified to the operator or the like on the assumption that wear of the tip of the probe 20 has increased.

  When the scanning probe microscope shown in FIG. 1 is deployed and used in an in-line automatic inspection process in the semiconductor manufacturing process, the above warning information is notified to the host computer.

  A probe length measuring mechanism realized by the above-described program for measuring the probe length is shown in FIG. The probe length measuring mechanism 72 includes the reference table 61 having a reference height position, the first height position (Z1) when the tip of the probe 20 is positioned on the reference table 61, and the reference table 61. A difference between the measurement unit 63 that measures the second height position (Z2) when the proximal end of the probe 20 is positioned, and the first height position (Z1) and the second height position (Z2). And a length calculation unit 64 that calculates the length of the probe 20 as a length. Data relating to the probe length calculated by the length calculation unit 64 is supplied to the recording unit 65 where it is recorded.

  In the probe length measurement process according to the above embodiment, the length of the probe 20 is accurately obtained as an absolute value every time the length measurement is performed. However, only steps S12 to S15 are periodically performed. By performing the above, it is possible to perform a simple measurement process for obtaining a change in the probe length relatively based on the measurement state of FIG.

  The configurations, shapes, sizes, and arrangement relationships described in the above embodiments are merely 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 are as follows. It is only an example. Therefore, the present invention is not limited to the described embodiments, and can be variously modified without departing from the scope of the technical idea shown in the claims.

  In the above description of the embodiment, the example using the reference table 61 has been described. However, it is not necessary to provide a special one for the reference table 61. For example, a specific place such as a part of the sample or the sample holder 16 is used. Of course you can.

  INDUSTRIAL APPLICABILITY The present invention is used for managing the probe tip wear level in a scanning probe microscope to manage the wear degree of the tip of the probe, and to effectively use the probe to increase the measurement / inspection accuracy.

It is a block diagram which shows embodiment of the scanning probe microscope which concerns on this invention. It is a flowchart which shows the probe length measurement process implemented with the scanning probe microscope which concerns on this embodiment. It is a figure which shows the positional relationship of the probe in the case of measurement of probe length, and a reference stand. It is a block diagram which shows the structure of the probe length measurement mechanism which performs the probe length measurement process which concerns on this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Reference surface 11 Sample stage 12 Sample 14 XY stage mechanism 15 Z stage 16 Sample holder 20 Probe 21 Cantilever 23 Z fine movement mechanism 29 XY fine movement mechanism 61 Reference stand

Claims (4)

  A probe unit having a probe facing the sample, a probe moving mechanism for moving the probe, a measuring unit for measuring a physical quantity generated between the probe and the sample, and the sample are mounted A scanning probe microscope that measures the surface of the sample by scanning the surface of the sample with the probe, and a probe length measuring mechanism that measures the axial length of the probe A scanning probe microscope, comprising:   The probe length measuring mechanism includes a reference table, a first position when the tip of the probe is positioned on the reference table, and a second position when the proximal end of the probe is positioned on the reference table. 2. The scanning according to claim 1, further comprising measuring means for measuring a position, and length calculating means for calculating a difference between the first position and the second position as a length of the probe. Type probe microscope.   3. The scanning probe microscope according to claim 1, wherein after the probe is attached to the probe portion, the length of the probe before use is measured by the probe length measuring mechanism. The scanning probe microscope according to claim 1, further comprising recording means for recording the length of the probe measured by the probe length measuring mechanism.

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