JP4927506B2 - Charged particle beam device and imaging method of charged particle beam device - Google Patents

Description

  The present invention relates to a charged particle beam apparatus such as an electron microscope and an ion beam machining / observation apparatus, and an imaging method for the charged particle beam apparatus.

  In recent years, the degree of integration of semiconductor products has been further improved, and further refinement of circuit patterns has been demanded. In a sample on which a circuit pattern typified by a semiconductor wafer is formed, various inspection means are used for the purpose of quality control and yield improvement.

  For example, a scanning electron microscope (hereinafter referred to as a length measurement SEM) that irradiates a charged particle beam as an inspection means and measures the dimensional accuracy of a circuit pattern, or a circuit pattern defect or adhered foreign matter that is also irradiated with a charged particle beam. Examples include a scanning electron microscope to be evaluated (hereinafter referred to as a review SEM).

  Also, in order to meet the demand for higher definition of circuit patterns, for example, in order to correspond to the 35 nm node design rule as the line width rule of the circuit pattern, a secondary with less noise at an observation magnification of 300,000 times or more. Obtaining an electronic image has become an important issue.

  In addition, in order to draw a high-definition circuit pattern, it is necessary to suppress vibration and drift in the order of nm on the stage on which the sample wafer is mounted and held in order to improve the contrast by overlaying multiple images. .

  At present, the wafer size is mainly 300 mm, and the stage for that is considerably large. At the same time, a high output drive mechanism for increasing the speed of the stage is required from the viewpoint of improving the throughput, and the temperature rises due to the heat generated by the motor and the drive shaft.

  Conventionally, as a technique for avoiding the stage drift due to the thermal expansion and contraction, Japanese Patent Laid-Open No. 2002-126964 monitors the position of a stage on which a wafer is mounted and held in real time, and follows the behavior of the table. A so-called servo control technique that feeds back the control amount of the motor and the deflection amount of the electron beam is disclosed.

  Japanese Patent Application Laid-Open No. 2000-57985 also measures the position of the stage on which the sample wafer is placed, and adjusts the deflection amount of the charged particle beam applied to the sample by the deflector based on the measurement result. A technique configured to do this is disclosed.

  On the other hand, Japanese Patent Laid-Open No. 2004-134155 discloses a pulse in which a gap of 20 μm to 100 μm is provided between a moving stage on which a sample is placed and a driving shaft, and the driving shaft is disconnected when the moving stage is stopped. A technique for performing control by an open loop using a motor is disclosed.

  Japanese Patent Laid-Open No. 2000-57985 discloses a column for generating charged particles, a deflector for charged particles, a stage for moving a sample, a length measuring device for measuring the position of the stage, a column and a deflector. And a control unit that controls the stage, and a charged particle beam that corrects the irradiation direction of the charged particles by operating the deflector based on the displacement of the stage detected by the sensor, and irradiates the sample with charged particles to image the sample. Device technology is disclosed.

JP 2002-126964 A JP 2004-134155 A JP 2000-57985 A

  In order to improve the throughput of sample imaging, it is effective to reduce the time required to move the stage on which the sample wafer is mounted and held. However, shortening the stage moving time reduces the stage moving stage. It means an increase in speed and stage acceleration.

  Needless to say, in the charged particle beam apparatus technology described in Japanese Patent Laid-Open Nos. 2002-126964, 2004-134155, and 2000-57985, the stage speed and the stage acceleration are increased. Although the stage moving time is shortened, the establishment time Ts, which is the time required for the stage 21 moved due to the increase in the stage speed and the stage acceleration to converge within the deflectable region of the electron beam, becomes longer. As a result, the effect of reducing the overall measurement time is not so great.

  This means that if priority is given to shortening the overall measurement time, the accuracy of the captured image (distortion, blur, etc.) deteriorates.

  An object of the present invention is to provide charged particles that ensure the image accuracy obtained by imaging a sample and shorten the establishment time associated with the movement of a stage on which the sample is mounted, thereby greatly improving the throughput of imaging the sample. An object of the present invention is to provide an imaging method for a beam apparatus and a charged particle beam apparatus.

A charged particle beam apparatus according to the present invention includes an electron gun that generates a charged particle beam, a column including a deflector that can deflect the charged particle beam generated from the electron gun to a desired position, and a charged particle generated from the electron gun. A sample chamber in which a stage configured to be movable by placing a sample irradiated with a line is placed inside, a length measuring device capable of measuring the position of the stage in the sample chamber, and the deflection amount of the column deflector In a charged particle beam apparatus for imaging a sample by irradiating a charged particle beam with a column control unit for controlling and a position control unit for controlling the position of the stage in the sample chamber, the state of the stage measured by the length measuring device A deviation processing unit that calculates a deviation value from the target position of the sample irradiated with the charged particle beam based on the information, determination criterion information constituted by stage position information and velocity information, and current stage position information Compare with speed information Positional deviation of the then stage, at least the image pickup hours or more samples, by determining whether it is possible to have remained deflectable region of the charged particle beam during the imaging time of the sample stage state A deflection control unit that instructs a deflector that adjusts the deflection amount of the charged particle beam based on the deviation value calculated by the deviation processing unit. In addition, the present invention is characterized in that a specimen is photographed by irradiating a charged particle beam.

Further, the charged particle beam apparatus imaging method of the present invention causes a charged particle beam generated by generating a charged particle beam from an electron gun provided in a column to be deflected to a desired position by a deflector provided in the column. In the imaging method of a charged particle beam apparatus that images a sample by irradiating the charged particle beam to a sample placed on a stage that is movably installed inside the sample chamber, the position of the stage on which the sample is placed is measured. The charged particle beam irradiated based on the stage state information measured by the instrument calculates a deviation value from the target position of the sample, and includes judgment reference information composed of stage position information and velocity information, by positional deviation of comparing the current position information and velocity information stage, it determines whether it is possible to at least imaging hours or more samples, remains deflectable region of the charged particle beam During the imaging time for imaging the sample, the stage state determines whether or not the sample can be imaged. If it is determined that the sample can be imaged, the charged particle beam is deflected based on this deviation value. The sample is photographed by controlling the amount so as to approach the target position.

  According to the present invention, charged particles that ensure the image accuracy obtained by imaging the sample and shorten the establishment time associated with the movement of the stage on which the sample is placed, thereby significantly improving the throughput of the sample imaging. An imaging method for a beam apparatus and a charged particle beam apparatus can be realized.

  A scanning electron microscope will be described with reference to the drawings as a charged particle beam apparatus and an imaging method of the charged particle beam apparatus according to an embodiment of the present invention.

  A scanning electron microscope as a charged particle beam apparatus according to an embodiment of the present invention will be described with reference to FIG.

  In FIG. 1, a mount 4 for isolating floor vibration is attached to the upper part of a plurality of mounts 6 installed on the floor, and the sample chamber 2 is supported by the mount 6 via the mounts 4. Yes.

  A column 1 for generating and controlling an electron beam is provided above the sample chamber 2, and a load lock 3 containing a transfer robot 31 for transferring the sample is attached to the side of the sample chamber 2.

  The inside of the sample chamber 2 is constantly evacuated by a vacuum pump 5 installed on the lower side of the material chamber 2 to maintain the vacuum state, and the inside of the column 1 is also evacuated by a vacuum pump (not shown) to a high degree of vacuum. It is kept.

  Inside the sample chamber 2, a stage 21 for mounting and holding the sample 10 is installed so as to be movable within the sample chamber 2. An electrostatic chuck 24 is attached to the top of the stage 21, and the sample 10 is electrostatically attracted by the electrostatic chuck 24 and is strongly held on the stage 21.

  A bar mirror 22 is also attached to the upper part of the stage 21, and the position of the stage 21 is measured by measuring the relative distance between the interferometer 23 attached to the sample chamber 2 and the bar mirror 22 by laser measurement. Thus, the position of the sample 10 mounted and held on the stage 21 is managed.

  On the other hand, an atmosphere-side gate valve 33 is provided on the atmosphere side of the load lock 3 through an opening through which the sample 10 is taken in and out, and is isolated from the atmosphere. A vacuum-side gate valve 32 that isolates the sample chamber 2 is attached.

  Next, the transport path of the sample 10 in the scanning electron microscope of the present embodiment will be briefly described below. First, the atmosphere side gate valve 33 of the load lock 3 is opened, and the transport robot 31 is operated to introduce the sample 10 into the load lock 3 through the opening from the atmosphere side.

  Next, the atmosphere side gate valve 33 of the load lock 3 is closed, and the inside of the load lock 3 is evacuated by a vacuum pump (not shown) to be in a vacuum state.

  When the degree of vacuum inside the load lock 3 becomes about the same as the degree of vacuum inside the sample chamber 2, the vacuum side gate valve 32 of the load lock 3 is opened and opened from the load lock 3 by the operation of the transfer robot 31. The sample 10 is transported onto the stage 21 contained in the sample chamber 2 through the through-hole.

  After the sample 10 is processed inside the sample chamber 2, the sample 10 is conveyed from the sample chamber 2 to the load lock 3 in the reverse flow, and further returned from the load lock 3 to the atmosphere.

  Inside the sample chamber 2, the sample 10 is electrostatically attracted by the electrostatic chuck 24 attached to the stage 21 and is strongly held on the stage 21. Further, a bar mirror 22 is mounted on the stage 21, and by measuring the relative distance change with the interferometer 23 mounted in the sample chamber 2 and measuring the position of the stage 21, The position of the sample 10 on the stage 21 can be managed.

  The position information of the stage 21 laser-measured by the interferometer 23 is created as a position data signal by the position control unit 71, and this position data signal is moved by the stage 21 that holds and holds the sample 10 inside the sample chamber 2. Is input to a stage control unit 72 that controls.

  The stage control unit 72 compares the current position data signal of the stage 21 input from the position control unit 71 with target position data serving as preset target coordinates, and calculates a deviation signal between the two, and calculates the calculated deviation. Feedback control is performed to move and control the position of the stage 21 so that there is no deviation value from the target position data as a signal.

  As feedback control for controlling the movement of the stage 21, there is a control performed only with simple position feedback, a PID control for improving response speed and positioning accuracy by adding speed information of the stage 21 and integration information of the position deviation of the stage 21. It is done.

  On the other hand, for the column 1 of the scanning electron microscope of the present embodiment, an electron beam 12 is generated from an electron gun 11 installed in the column 1, and this electron beam 12 is placed in the column 1 below the electron gun 11. It passes through the installed electron lens 13 and electron lens 16 having a convergence effect.

  A deflector 14 is provided between the electron lens 13 and the electron lens 16 in the column 1, and the electron beam 12 traveling in the column 1 is deflected to a desired trajectory by the deflector 14. The sample 10 mounted and held on the stage 21 inside the sample chamber 2 communicating with the sample chamber 2 is irradiated.

  Reflected electrons or secondary electrons generated by irradiating the electron beam 12 to the sample 10 on the stage 21 in the sample chamber 2 from the electron gun 11 installed in the column 1 are detected by a detector 15 installed in the column 1. Detected.

  A detection signal of reflected electrons or secondary electrons detected by the detector 15 is input to the image control unit 73 together with control information of the electron beam 12 by the deflector 14.

  The image control unit 73 draws an image of the sample 10, for example, a wafer as the sample 10, based on the control information of the electron beam 12 by the deflector 14 and the detection signal of the reflected electrons or the secondary electrons detected by the detector 15. Image data such as an enlarged image of the circuit pattern is generated, and the image data is displayed on the monitor 74 as an image.

  In the scanning electron microscope of the present embodiment, an optical Z sensor 25 for detecting the height of the sample 10 is attached above the sample chamber 2 communicating with the column 1, and the height of the sample 10 is constantly monitored. Is possible.

  The height signal of the sample 10 obtained by the Z sensor 25 is input to the position controller 71 and converted into a signal, and then transmitted to the column controller 70.

  The column control unit 70 changes the optical conditions of the electron lens 13 and the electron lens 16 as necessary based on the height information of the sample 10 input from the position control unit 71, so that the height of the sample 10 changes. Control is performed so that the focus of the electron beam 12 applied to the sample 10 does not shift.

  The above-described position information of the stage 21 on which the sample 10 is mounted and held is also transmitted to the column control unit 70 that controls various devices installed in the column 1 to correct the deflection control signal of the electron beam 12.

  The deflector 14 is divided into a position deflector 14A that positions the deflection center of the electron beam 12 that irradiates the position of the sample 10, and a scanning deflector 14B that scans the target field at a high speed for imaging. The position deflector 14A and the scanning deflector 14B are controlled by operating the deflection controller 17 based on a command signal from the column controller 70.

  For example, when the position data signal that is the current position of the stage 21 is displaced within the deflection range (for example, within 10 μm) from the target position serving as the target coordinates, the position data of the current position of the stage 21 detected by the interferometer 23. A deviation signal between the signal and the target position data of the target coordinate is calculated by the position controller 71, and this deviation signal is transmitted from the position controller 71 to the column controller 70 as an input signal.

  The column controller 70 controls the position deflector 14A and the scanning deflector 14B based on the deviation value of the deviation signal calculated and input by the position controller 71 so that the deviation value of the deviation signal is eliminated. The deflection amount of the beam of the electron beam 12 irradiated on the sample 10 placed on the stage 21 is adjusted.

  That is, the column control unit 70 calculates a deflection correction command value obtained by adding the deviation value as a correction amount to the deflection command value for the deflection control unit 17, and commands the deflection control command value to the deflection control unit 17 to give a position deflector. 14A and the scanning deflector 14B are controlled to adjust the deflection amount of the beam of the electron beam 12.

  In this case, the control system can be configured relatively easily if correction is controlled based on only the position information of the deflection center of the electron beam 12 as the correction target.

  This is because the control speed of the position deflector 14A is slower than the control speed required for the scanning deflector 14B. The scanning deflector 14B requires a high-speed deflection operation (for example, 20 KHz or more), and in order to control the feedback of the deflection command value, a correction circuit that can be operated at high speed as hardware must be added. Will also increase significantly.

  On the other hand, since the position deflector 14A is configured to constantly feed back the deviation between the target coordinates of the stage and the current position of the stage 21 in this embodiment, even if residual vibration or drift occurs in the stage 21, for example, Imaging of the sample 10 can be started without waiting until these phenomena are established.

  At this time, the deviation caused by the mechanical vibration of the stage 21 or the control vibration of the stage 21 is not a very fast frequency (for example, 500 Hz or less). Therefore, the correction to the deflection command value by software can be sufficiently performed, and it is very inexpensive. It becomes feasible.

  Further, even if a circuit is added as hardware, high-speed computation is not required at all, and a general transistor circuit can sufficiently satisfy the functions, so that it can be realized at a small cost.

  FIG. 2 shows a velocity profile that is an example of the moving speed of the stage 21 when the stage 21 on which the sample 10 is mounted and held is controlled by the stage controller 72 in the scanning electron microscope of the present embodiment.

  In FIG. 2, the vertical axis represents the moving speed of the stage 21, and the horizontal axis represents time. In the movement of the stage 21 shown in FIG. 2, the stage controller 72 moves the stage 21 at a constant speed increase rate from the stop state to increase the speed, and when the predetermined speed is reached, the predetermined speed is kept for a while. This represents a state of control in which the stage 21 is decelerated from a predetermined speed at a constant speed deceleration rate after that.

  In FIG. 2, Tm is a stage moving time required to move the stage 21, Ts is an established time required for the moved stage 21 to converge within the range of the deflectable region, Tc is an imaging time required for imaging the sample, T is the total measurement time (T = Tm + Ts + Tc), W is the deflectable region, and X is the amount of overshoot outside the deflectable region.

  When the control according to the embodiment as described above is applied, as shown in the speed profile of FIG. 2, the stage 21 is subjected to the residual vibration after the stage is stopped, but the position of the stage 21 is deflected after the stage establishment time Ts. If the position of the stage 21 is within the deflection range of the beam of the electron beam 12 within the possible region W (for example, within target coordinates ± 10 μm), it is possible to shift to imaging of the imaging time Tc for irradiating the sample 10 with the electron beam 12. The overall measurement time T can be greatly shortened.

  Further, in the movement control of the stage 21 according to the present embodiment, if the position of the stage 21 is within the range of the deflectable region W, there is no obstacle to the photographing of the sample 10, so that it is particularly necessary to completely stop the stage 21. No.

  In FIG. 3, as another example of the movement control of the stage 21 according to the present embodiment, when the stage 21 is decelerated at a constant speed reduction rate from a state where a predetermined speed is maintained, the rapid speed reduction rate is initially set. After that, an example of a speed profile with a two-stage speed reduction rate in which the vehicle is decelerated at a gradual speed reduction rate is shown. In this case, the stage establishment time Ts can be eliminated.

  As shown in the example of the speed profile of the stage 21 shown in FIG. 3, the stage establishment time Ts can be eliminated even if the positioning operation when the stage is stopped is delayed by adopting a two-stage speed reduction rate. The specimen 10 placed on the stage 21 can be imaged from the point in time 21 within the deflection range of the beam of the electron beam 12 by the deflector 14 in the deflectable region W.

  Therefore, in the example of the speed profile of the stage 21 shown in FIG. 3, the movement control of the stage 21 can be accommodated in the total measurement time T which is substantially the same time as the speed profile of FIG.

  The advantage of the example of the speed profile of the stage 21 shown in FIG. 3 is that vibration acceleration of the column 1 and the like can be reduced because the acceleration at the time of deceleration of the stage 21 can be kept small. That is, it is possible to obtain an image with higher accuracy by reducing the adverse effect on the image quality caused by the vibration of the column 1 that is not included in the position information of the stage 21.

  In addition, as an action device for moving the stage 21, an actuator with friction, such as a ball screw or an ultrasonic motor, which is usually adopted, stops the control when the stage is close to the target position and uses a braking force by the friction force. However, in the case of a linear motor, since a braking force does not work, vibration and drift occur.

  In the present embodiment having the above-described configuration, even if the stage 21 does not stop completely, if the position of the stage 21 falls within the deflectable region W, it is possible to take an image, so that a linear motor that is an actuator without friction is relatively easy. Applicable to.

  Next, the detailed structure of the position control unit 71 in the scanning electron microscope of the present embodiment shown in FIG. 1 will be described with reference to FIG.

  In FIG. 4, the position control unit 71 converts the detection signal of the current position of the stage 21 detected by the interferometer 23 into position information data by the position converter 80, and simultaneously differentiates the speed information data by the speed converter 81 with respect to time. The position information data of the stage 21 converted by the position converter 80 and the speed information data of the stage 21 converted by the speed converter 81 are input to the determination unit 82.

  The determination unit 82 compares the input position information data and velocity information data of the stage 21 with the determination criteria stored in the memory 83, and the sample placed on the stage 21 within a predetermined imaging time Tc. It is determined whether or not irradiation of the electron beam to the sample within the range of the deflectable region W of the electron beam 12 irradiated by the position 10, that is, the position of the stage 21 is possible.

  The memory 83 of the position control unit 71 stores the determination reference value shown in FIG. 5 as a determination reference for the stage position and the stage speed of the stage 21, and can be read from the determination unit 82 at any time.

  Then, in the determination unit 82, the deflectable region is determined by the determination unit 82 only when both of the determination reference values including both the “threshold deviation” of the stage position and the “speed” which is the stage speed shown in FIG. It is determined that the sample 10 within the range of W can be irradiated with the electron beam 12.

  That is, when the stage position is 15 μm or more and less than 20 μm and the stage speed is 0.02 mm / s or less, or when the stage position is 10 μm or more and less than 15 μm and the stage speed is 0.015 mm / s or less, the stage position When the condition is 5 μm or more and less than 10 μm and the stage speed is 0.01 mm / s or less, and when the stage position is 0 μm or more and less than 5 μm and the stage speed is 0.005 mm / s or less, the respective conditions are satisfied It is determined that only the sample 10 can be irradiated with the electron beam 12.

  The position information data of the stage 21 converted by the position converter 80 is input to the deviation processing unit 85 of the position control unit 71, and a deviation signal between the detected position information data of the stage 21 and the target value is calculated.

  The deviation signal calculated by the deviation processing unit 85 is input to the low-pass filter 84, and the deviation signal passing through the low-pass filter 84 is transmitted to the column control unit 70 as input data.

  Since the deviation signal is passed through the low-pass filter 84, the high-frequency noise component contained in the converted deviation signal is removed. Therefore, mechanical vibration of the stage 21 or vibration caused by controlling the movement of the stage 21 is caused. It is possible to correct by narrowing down.

  Here, the determination criterion composed of the stage position and the stage speed stored in the memory 83 read by the determination unit 82 of the position control unit 71 as needed is that the sample 10 placed on the stage 21 is irradiated with a shift in the position of the stage 21. Whether or not the position deviation of the stage 21 remains within the deflectable region W for at least a time longer than the imaging time Tc of the sample 10 when it is within the deflectable region W of the beam of the electron beam 12 This is a threshold value serving as a reference value for determining whether or not, and a specific example thereof is as shown in FIG.

  If it is determined by the determination unit 82 that the position and speed of the stage 21 deviate from the determination standard shown in FIG. 5 and the sample 10 cannot be irradiated with the electron beam 12, the position of the stage 21 is again determined. The speed is measured, and the determination by the determination unit 82 is repeated until these measured values satisfy the determination criteria.

  The determination criteria stored in the memory 83 can be stored in the memory 83 as a function expression of the stage position and the stage speed other than the table shown in FIG. Further, specific numerical values of the stage position and the stage speed, which are the determination criteria, may be determined and stored by performing a preliminary evaluation for collecting the speed and position when the stage is stopped.

  Since it is expected to vary depending on the output of the driving actuator that moves the stage 21, the movable mass of the stage 21, and the resistance of the stage 21, it is desirable to set for each movement axis (two horizontal axes) of the stage 21. .

  Next, with reference to the position deviation at the time of positioning of the stage 21 shown in FIG. 6, the relationship between the position and moving speed of the stage in this embodiment and the determination result will be described below.

  The vertical axis in FIG. 6 indicates the stage position of the stage 21, and the horizontal axis indicates the passage of time of the stage position. A on the vertical axis indicates the upper limit value of the stage position, and B indicates the lower limit value of the stage position.

  In FIG. 6, as an example of a typical moving method of the stage 21 on which the wafer of the sample 10 is mounted and held, a method called step-and-repeat that repeats the moving profile of the stage consisting of stage movement, stage stop, and sample imaging The stage moving speed when controlled by is shown.

  That is, after the stage moving time Tm required for moving the stage, the specimen is irradiated with an electron beam after a set time Ts until the stage is stopped and the residual vibration and drift of the stage are allowed to fall within the deflectable region W. 10 images are captured (imaging time: Tc). Therefore, the total measurement time at one location of the sample 10 is T (T = Tm + Ts + Tc), which is a major factor related to the sample processing speed (hereinafter referred to as throughput).

  In the movement profile in which the stage 21 passes from the stage position P1 before the stage position P6 to the stage position P6, the stage position deviation at the stage position P1 is gradually deflected in the process of gradually approaching the deviation 0 from the + side of the stage position deviation. It enters the range of the deflectable region W through the upper limit value A (+20 μm).

  Information on the state of the stage immediately after passing through the stage position P1 is that the stage position is 20 μm and the moving speed is 0.03 mm / s. Therefore, referring to the determination criteria stored in the memory 83 shown in FIG. In particular, the position is 15 μm or more and less than 20 μm, and the stage speed is greatly deviated from the reference value of 0.02 mm / s or less. Therefore, it is determined that the sample 10 placed on the stage is in an NG state. .

  Information on the state of the stage immediately after passing the next stage position P2 is that the stage position is near 0 μm and the moving speed is 0.02 mm / s. The speed is significantly different from the reference value of 0 μm or more and less than 5 μm and the stage speed is 0.005 mm / s or less. Therefore, it is determined that the sample 10 placed on the stage is in an NG state.

  Information on the state of the stage immediately after passing through the next stage position P3 is that the stage position is about 15 μm and the moving speed is 0.018 mm / s. The stage position is 10 μm or more and less than 15 μm, and the stage speed is particularly deviated from the reference value of 0.015 mm / s or less. Therefore, it is determined that the sample 10 placed on the stage is in an NG state. .

  The stage 21 passes through the stage position P2 and the stage position P3 and reaches the stage position P4. Information on the state of the stage immediately after passing through the stage position P4 is the lower limit B of the range where the stage position can be deflected. Since (−20 μm) is exceeded, the stage position deviates from the upper limit of 20 μm of the reference value, and the imaging of the sample 10 is determined to be NG.

  After that, the stage 21 reaches the stage position P5, but the stage position immediately enters the range of the lower limit value B (−20 μm) in the stage state information immediately after passing through the stage position P5. Further, the stage speed is also reduced to 0.01 mm / s, and referring to the judgment standard stored in the memory 83, the judgment standard for the stage position of 15 μm to less than 20 μm and the stage speed of 0.02 mm / s or less. Therefore, it is determined that the imaging of the sample 10 is OK.

  Similarly, the stage state information immediately after passing through the stage position P6 indicates that the stage position is near 0 μm, the stage speed is also reduced to 0.005 mm / s, and the stage position is determined by referring to the determination criteria stored in the memory 83. Is 0 μm or more and less than 5 μm, and the stage speed satisfies the criterion of 0.005 mm / s or less, so that even after passing through the stage position P6, it is determined that the sample 10 is in an OK state.

  The above-described determination method of this embodiment is an effective technique that can shorten the processing time of the sample 10 by reducing the determination time as much as possible and executing the early start of the imaging start time of the sample 10.

  If it is desired to determine whether or not the sample can be irradiated with the electron beam more reliably, the above-described determination is continuously performed, and if the determination result is OK for a certain number of times (or time). For example, the sample 10 may be imaged.

  Further, in this determination of whether or not the sample can be irradiated with the electron beam, the positional deviation and speed with respect to the target value of the stage 21 have been used as indices, but the absolute coordinates (position) and acceleration of the stage 21 are parameters. Can also be used.

  For example, when the absolute coordinates of the stage 21 are different, when the natural frequency of the stage 21 changes, the time that falls within the deflection range changes, or when the time that falls within the deflection range changes because the amount of shaking of the main body changes. This is effective.

  The acceleration can be determined with higher accuracy if it is used as a parameter when the acceleration is not constant due to the use time, the stage position, the use temperature, or the like on the stage 21 using the brake mechanism. Here, it is preferable to set a value obtained by giving a certain degree of likelihood to the actual speed upper limit value as the speed upper limit value at each stage position, and aim at a stable apparatus operating state.

  FIG. 7 shows an image acquisition sequence of the sample 10 mounted and held on the stage 21 according to the present embodiment. Steps S1 to S7 are roughly divided into one process.

  At the start of target coordinate movement in step S1, the target coordinate movement of the stage 21 is started, and in the next target position setting of step S2, the target position of the stage 21 is set, so that a drive profile according to drive parameters such as speed and acceleration is obtained. Is generated.

  In step S3, the stage 21 starts moving along the generated drive profile.

  In the determinable range of step 4, when the position of the stage 21 enters the determinable range near the target position due to the movement of the stage 21, the position of the stage 21, which is a determination parameter, is determined by the position converter 80 and the speed converter 81 of the position controller 71. Information on the current stage coordinate position and information on the current stage speed at which the stage 21 moves are read.

  In step S5 within the next allowable determination parameter range, information on the stage current coordinate position and stage current speed read in step S4 by the determination unit 82 of the position control unit 71 and the memory 83 of the position control unit 71 are stored in advance. The determination reference value is compared with the stage coordinate position and the stage speed.

  If the determination unit 82 of the position control unit 71 determines that the image can be captured, the process proceeds to the start of image acquisition in step S6, and the image control unit 73 is operated by an instruction from the column control unit 70 to capture the sample 10. To start.

  If there is no particular problem with the imaging result of the sample 10, the process proceeds to the end of image acquisition in step S7 and the imaging of the sample 10 is terminated.

  If the determination unit 82 of the position control unit 71 determines that imaging is not possible in step S5 within the determination parameter allowable range, the process returns to step S4 again, and the current stage position information and stage speed are read again. Imaging determination is performed in the same sequence until it is determined by the unit 82 that imaging is possible.

  Of course, there is a possibility that imaging may not be performed for a long time due to an erroneous setting of the judgment reference value or a malfunction of the stage. Therefore, an upper limit of the number of determinations or an upper limit of the determination time may be set in this sequence.

  If it is determined by the determination unit 82 of the position control unit 71 in step S5 that imaging is possible, the process proceeds to the start of image acquisition in step S6 and the current position information of the stage measured by laser is taken into the position control unit 71 and the column control unit 70 is acquired. Then, the deflection control unit 17 calculates based on the deviation value of the electron beam 12 from the target position, and images the sample 10 while feeding back to the deflection command value of the beam of the electron beam 12 that operates the deflector 14.

  When the imaging of the sample 10 is completed for a desired time, the process proceeds to the end of image acquisition in step S7, the stage 21 is moved toward the next target position for acquiring the image, and the image acquisition of the sample 10 is performed in the same sequence. Do.

  FIG. 8 shows the movement profile of the stage 21 with respect to the positional deviation at the time of positioning the stage 21 as in FIG. 6, but the major difference from FIG. 6 is that the overshoot amount with respect to the target is within the deflection range (upper limit value A˜ It is to converge toward zero deviation without exceeding the lower limit B).

  That is, in FIG. 8, the relationship between the overshoot amount and the speed at the stage position P1 is examined in advance, and the limit speed Vm at the stage position P1 at which the overshoot amount does not exceed the lower limit value B is obtained. If the relationship of v ≦ Vm with respect to the speed v at the stage position P1 in FIG.

  That is, by determining the movement profile of the stage 21 or the gain coefficient of the stage 21 so that the movement speed of the stage 21 at the P1 point is always kept below Vm, the imaging judgment operation of the sample 10 for each stage movement becomes unnecessary. The control system of the apparatus can be simplified.

  In general, in the movement profile of the stage 21, the setting gain of the stage 21 tends to be low and the response speed tends to be slow. However, the rising gain when moving to the next measurement position is set high, By setting the gain to a low gain, the throughput can be improved efficiently.

  Of course, for the purpose of stable apparatus operation, it is desirable that the moving speed v of the stage 21 at P1 is set to a threshold with a certain margin with respect to Vm.

  Here, in order to correctly manage the position of the sample 10 even when the stage 21 is vibrated, the sample is held so that the relationship between the position of the sample 10 on the stage 21 and the installation position of the bar mirror 22 is kept constant. Means are needed.

  With a mechanical sample holding means having a weak holding force, there is a high possibility that the sample 10 will be displaced or deformed when acceleration is applied to the stage 21.

  In such a state, a slight variation of about several nanometers occurs in the distance between the bar mirror 22 on the stage 21 and the sample 10 to cause a measurement error in the sample position. Based on the laser measurement value including this error, If the beam deflection is corrected, the image of the sample 10 is blurred or distorted, leading to a reduction in image quality.

  Therefore, in this embodiment, as shown in FIGS. 1 and 4, the electrostatic chuck 24 is used as a holding means for holding the sample 10 on the stage 21 to solve the above-described problems.

  In the mechanical sample 10 holding means, it is common to suppress the periphery of the sample 10 at several places. However, in the sample 10 holding means employing the electrostatic chuck 24 of this embodiment, the back surface of the sample 10 is almost the entire surface. By adsorbing to the holding means over a long period of time, it is possible to strongly hold the sample, and thus it is possible to realize an apparatus configuration in which a length measurement error hardly occurs.

  In other words, even when the amount of displacement that occurs when the material 10 placed on the stage 21 is displaced from the surface of the stage 21 due to stage vibration caused by the movement of the stage 21 is typically about 10 μm, for example, as a holding means for the sample 10. If the electric chuck 24 is employed, the amount of deviation can be suppressed to 1 μm or less.

  As a result, it is possible to improve the image quality of an image for photographing a sample by irradiating an electron beam with higher accuracy.

  In general, a sequence in which an optimum image state is obtained through a focus operation in which the wafer height is detected before imaging the wafer as the sample 10 and the optical condition of the column 1 is changed based on the detected value. It has become.

  Since this focus operation can absorb the warp and bend of the wafer (for example, 100 μm), it is necessary to secure the focus swing width to about 200 μm. However, the larger the swing width, the longer the time required. It is desirable to be.

  Therefore, the electrostatic chuck 24 of this embodiment is used for holding the wafer of the sample 10 to correct wafer warping and bending (for example, 100 μm) and to form a flatter processing plane, thereby reducing the focus operation with a narrow swing width ( For example, 50 μm) can be set, and a secondary effect leads to an improvement in throughput.

  In order to facilitate maintenance of the electrostatic chuck 24, the electrostatic chuck 24 configured as a detachable holder type (not shown) from the stage 21 is desirable. In this case, the detachable holder and the sample 10, and the detachable holder and the stage 21 are fixed by adsorption by the electrostatic chuck 24, respectively, so that a high holding force of the sample 10 can be realized, and the stage 21 and the holder are interposed. The sample 10 is almost free from relative displacement.

  The holder is automatically ejected from the sample chamber by the transfer robot 31, so that it can be removed from the apparatus and maintenance such as cleaning can be performed. Thereby, it becomes the structure which can ensure both a highly accurate measurement and the ease of a maintenance.

  As described above, according to the embodiment of the present invention, it is possible to secure the image accuracy obtained by imaging the sample and shorten the establishment time associated with the movement of the stage on which the sample is placed, It is possible to realize a charged particle beam apparatus and a charged particle beam apparatus imaging method that greatly improve throughput.

  The present invention can be applied to a charged particle beam apparatus such as an electron microscope and an ion beam processing / observation apparatus and an imaging method of the charged particle beam apparatus.

The top view which shows the whole structure of the scanning electron microscope which is one Example of this invention. FIG. 3 is an explanatory diagram illustrating an example of a stage moving speed in the embodiment of the scanning electron microscope of FIG. 1. Explanatory drawing which shows the other example of the moving speed of the stage in the Example of the scanning electron microscope of FIG. The detailed block diagram which shows the structure of the position control part in the Example of the scanning electron microscope of FIG. The data table showing the threshold value which shows an example of the criterion in the determination part of the position control part of FIG. FIG. 3 is an explanatory diagram illustrating a determination result based on a position and a moving speed of a stage and a determination criterion in the embodiment of the scanning electron microscope of FIG. 1. The block diagram showing the imaging sequence of the sample in the Example of the scanning electron microscope of FIG. FIG. 3 is an explanatory diagram illustrating an example of a determination result based on a position and a moving speed of a stage at a stage position P1 and a determination criterion in the embodiment of the scanning electron microscope of FIG.

Explanation of symbols

  1: column, 2: sample chamber, 3: load lock, 4: mount, 5: vacuum pump, 6: mount, 10: sample, 11: electron gun, 12: electron beam, 13: electron lens, 14: deflector 14A: Position deflector, 14B: Scanning deflector, 15: Detector, 16: Electron lens, 17: Deflection controller, 21: Stage, 22: Bar mirror, 23: Interferometer, 24: Electrostatic chuck, 25: Z sensor, 31: transfer robot, 32: vacuum side gate valve, 33: vacuum side gate valve, 70: column control unit, 71: position control unit, 72: stage control unit, 73: image control unit, 74: monitor, 80: position converter, 81: speed converter, 82: determination unit, 83: memory, 84: low-pass filter.

Claims (9)

A column equipped with an electron gun for generating a charged particle beam, a deflector capable of deflecting the charged particle beam generated from the electron gun to a desired position, and a sample irradiated with the charged particle beam generated from the electron gun are placed. A sample chamber in which a movable stage is arranged, a length measuring device capable of measuring the position of the stage in the sample chamber, a column control unit for controlling the deflection amount of the column deflector, and a sample chamber A charged particle beam apparatus that images a sample by irradiating a charged particle beam with a position control unit that controls the position of the stage,
Criteria composed of a deviation processing unit that calculates a deviation value from a target position of a sample irradiated with a charged particle beam based on stage state information measured by a length measuring instrument, and stage position information and velocity information Compare the information with the current position information and velocity information of the stage, and check whether the stage position deviation can remain in the deflectable region of the charged particle beam for at least the time required for imaging the sample. A determination unit that determines whether or not the stage is capable of imaging the sample during the imaging time of the sample, and the charged particle beam is based on the deviation value calculated by the deviation processing unit. A charged particle beam apparatus comprising: a deflection control unit that commands a deflector that adjusts the amount of deflection of the sample; and configured to irradiate a charged particle beam and take a sample.   The charged particle beam apparatus according to claim 1, wherein the determination unit determines whether or not the target position of the sample can remain in the deflectable region.   The charged particle beam apparatus according to claim 1, wherein the determination unit includes determination criterion information configured by the current position information and speed information of the stage and the position information and speed information of the stage stored in advance in the position control unit; A charged particle beam apparatus that determines whether or not imaging of a sample is possible based on the comparison of the above.   2. The charged particle beam apparatus according to claim 1, wherein the deflector for adjusting the deflection amount of the charged particle beam includes a position deflector for positioning a deflection center of the charged particle beam at a desired position of the sample, and a charged particle for imaging. A charged particle beam + device comprising: a scanning deflector that scans a line within a target field of view; and a deviation value calculated by a deviation processing unit is used as a command value of a position deflector.   The charged particle beam apparatus according to claim 1, wherein the stage is provided with an electrostatic chuck capable of electrostatic adsorption for holding a sample on the stage.   2. The charged particle beam apparatus according to claim 1, wherein the deviation value calculated by the deviation processing unit is input to the deflection control unit that commands the deflection amount of the charged particle beam after passing through the low-pass filter. Charged particle beam device characterized by the above. A charged particle beam generated by generating a charged particle beam from an electron gun provided in the column is deflected to a desired position by a deflector provided in the column, and the deflected charged particle beam is movably installed inside the sample chamber. In the imaging method of the charged particle beam apparatus that irradiates the sample placed on the stage and images the sample,
The charged particle beam irradiated based on the stage state information obtained by measuring the position of the stage on which the sample is placed with the length measuring device calculates the deviation value from the target position of the sample, and the stage position information, velocity information, The position information of the stage remains within the deflectable region of the charged particle beam for at least the imaging time of the sample. If it is determined that the sample can be imaged during the imaging time for imaging the sample, the stage state is determined whether the sample can be imaged. An imaging method for a charged particle beam apparatus, wherein a specimen is imaged by controlling a deflection amount of the charged particle beam to approach a target position based on the deviation value.   The charged particle beam apparatus imaging method according to claim 7, wherein the determination unit determines whether or not the target position of the sample can remain in the deflectable region. Wire device.   8. The charged particle beam apparatus according to claim 7, wherein the sample is photographed such that the sample is held on a stage by an electrostatic chuck capable of electrostatic attraction. Imaging method.

Images