JP2012248733A - Charged particle beam device and electrostatic chuck device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charged particle beam device which operates normally to hold even a warped sample in place.SOLUTION: A charged particle beam device 1 of the present invention is designed to be the one which irradiates an electron beam 12 upon a sample 101 held on a sample stage 21 to generate an image of the sample 101. For this purpose, it includes a warp amount measurement unit 35 which measures the amount of a warp in the sample 101, an electrostatic chuck having a plurality of suction units 221 which take in the sample 101 by suction, lifting units 222 capable of moving up and down which are installed at the bottoms of each of the plural suction units 221, and a lifting control unit 633 which lifts or lowers the lifting units 222 according to the amount of a warp in the sample 101 measured by the warp amount measurement unit 35.

Description

  The present invention relates to a technology of a charged particle beam device and an electrostatic chuck device.

  In recent years, the degree of integration of semiconductor integrated products has been further improved, and further refinement of circuit patterns has been demanded. In addition, semiconductor wafers (hereinafter referred to as “wafers”) on which circuit patterns are formed have a diameter of Φ300 mm, which is currently the mainstream, but in order to reduce mass production costs, an increase in diameter to Φ450 mm is being studied.

In this field, if the circuit pattern formed on the wafer has been created with a predetermined shape and dimensions, or there is no foreign matter attached, the manufacturing status is inspected and measured in each manufacturing process. It is very important to investigate the cause and take countermeasures. Various apparatuses using charged particle beams are used as apparatuses for inspecting and measuring the state of circuit patterns.
For example, a CD-SEM (Critical Dimension-Scanning Electron Microscope) is used to measure the width of the circuit pattern, and a SEM (Scanning Electron Microscope) type visual inspection device, defect observation / Review SEM etc. are used for classification, and these are all devices based on scanning electron microscope technology.

Here, as a wafer holding mechanism in the above-mentioned apparatus, an electrostatic chuck method can be applied instead of a mechanical method in which two reference pins are provided on the outer periphery of the sample and held by a pressing force by a movable pin from opposite directions. It is expanding. The electrostatic chuck system is roughly classified into those using Coulomb force and Johnson Rabeck force.
The former Coulomb force is an electrostatic adsorption force generated between the sample placed on the surface of the dielectric layer of the electrostatic chuck and the electrode of the electrostatic chuck. The latter Johnson-Rahbek force is an electrostatic adsorption force generated between the sample placed on the surface of the dielectric layer of the electrostatic chuck and the surface of the dielectric layer. Both types do not require pins on the outer periphery of the sample, so that it is possible to take measures against foreign matters generated on the surface of the wafer near the pins, which has been a problem in the mechanical method described above. In addition, since it is fixed to the chucking surface of the electrostatic chuck by the electrostatic chucking force, it also has the effect of reducing the bending and warping of the wafer.

However, due to diversification of wafer manufacturing processes, it is difficult to realize a stable suction operation under various conditions, and various inventions corresponding to these have been made.
The technique disclosed in Patent Document 1 enables a stable holding operation over a wide range of ambient temperatures. The change in the ambient temperature causes a change in the volume resistivity of the material of the electrostatic chuck, which causes problems such as deterioration in adsorption / desorption characteristics and an increase in load on the drive power supply. As a countermeasure, a plurality of electrostatic chucks having different volume resistivity are used, and the electrostatic chuck to be used is switched according to the ambient temperature.
In the technique disclosed in Patent Document 2, by arranging a plurality of electrostatic chucks along the ring shape or along the outer periphery of the wafer, the contact area with the back surface of the wafer is suppressed, and foreign matter adheres to the back surface of the wafer. Is suppressed. Furthermore, by supporting this electrostatic chuck with a leaf spring, the wafer has high rigidity in the surface direction and elasticity in the vertical direction, and even a wafer with bending or warping (hereinafter referred to as “warping wafer”). Stable and flexible holding operation is possible.

JP 2009-135527 A JP 2008-85290 A

However, the technique disclosed in Patent Document 1 is basically configured on the premise that the wafer is flat. Therefore, when the amount of warpage of the wafer is large (for example, 100 μm or more), sufficient adsorption is performed. Power cannot be obtained, suction becomes impossible, it is recognized as a fatal error, and the apparatus stops.
Although the technique disclosed in Patent Document 2 may attract a warped wafer, for example, in a shape where the center of the wafer is recessed, it is assumed that the wafer does not contact or approach the attracting surface of the electrostatic chuck. Therefore, it cannot be said that it can sufficiently cope with a warped wafer.

Further, as a countermeasure for a warped wafer, it is possible to strengthen the suction force by increasing the voltage supplied to the electrostatic chuck and suck the wafer, but there are the following problems.
First, in order to cope with a warp of, for example, several hundred micrometers, a high voltage of several kilovolts or more is required, and the risk of discharge that damages the wafer and the apparatus increases.
Second, there is a problem of residual adsorption. Residual adsorption is a state in which, even if the voltage is applied to the electrostatic chuck and returned to 0 volts, the charge induced on the wafer surface or the like is not relaxed and an unintended adsorption force remains. The residual adsorption force also tends to increase in proportion to the voltage. In the worst case, the sample chamber is opened to the atmosphere and manually taken out, and the downtime of the apparatus increases.
Third, because force is applied to the wafer to force it to flatten, the problem is that the circuit pattern dimensions on the wafer change or deform or the circuit pattern breaks due to the suction operation. It is thought that it becomes obvious by further miniaturization of the pattern. Further, as described above, there is a concern about an increase in the amount of warpage of the wafer accompanying an increase in the diameter of the wafer, and it is considered that the above problem appears more remarkably.

  The present invention has been made in view of such a background, and an object thereof is to perform a normal holding operation even on a warped sample.

In order to solve the above problems, a charged particle beam apparatus according to the present invention is a charged particle beam apparatus that generates an image of the sample by irradiating a sample held on a sample stage with an electron beam, wherein the sample warps. A warp amount measuring unit for measuring the amount; an electrostatic chuck having a plurality of suction units for sucking the sample; a lift unit that can be moved up and down provided at each lower part of the plurality of suction units; and the warp amount measurement. And a lift control unit that lifts and lowers the lift unit in accordance with the amount of warp of the sample measured by the unit.
Other solutions will be described as appropriate in the embodiments.

  According to the present invention, it is possible to perform a normal holding operation even on a warped sample.

It is a block diagram which shows the structure of the charged particle beam apparatus which concerns on 1st Embodiment. It is a top view of a sample room and a load lock room, and is a figure for explaining measurement of the amount of curvature of a wafer. It is a figure for demonstrating the upper surface and A-A 'cross section of a wafer holding part. It is a flowchart which shows operation | movement of the charged particle beam apparatus which concerns on 1st Embodiment. It is the schematic which shows the mode from the initial state of a wafer holding part to wafer adsorption | suction, (a) is a figure which shows the initial state of a wafer holding part. (B) is a figure which shows the state which raised / lowered several Z stage of the wafer holding part according to the curvature amount of the sample. (C) is a figure which shows the state which mounted the sample in the wafer holding part. (D) is a figure which shows the state which applied the voltage to the electrostatic chuck and made the sample adsorb | suck. It is a flowchart which shows operation | movement of the charged particle beam apparatus which concerns on 2nd Embodiment. It is a figure which shows an example of a wafer holding status screen.

<First Embodiment>
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. In each figure, common portions are denoted by the same reference numerals, and redundant description is omitted.
[Configuration of Charged Particle Beam Device 1]
FIG. 1 is a diagram illustrating a configuration of a charged particle beam apparatus 1 according to the first embodiment.
The charged particle beam apparatus 1 includes a column 10, a sample chamber 20, and a load lock chamber 30. The sample chamber 20 is supported on a pedestal 26 installed on the floor via a vibration isolation mount 27 that removes floor vibration. The column 10 is above the sample chamber 20 and the load lock chamber is on the side. 30 is attached.

  First, sample conveyance will be described. First, the atmosphere side gate 31 is opened, and the wafer 101 is carried into the load lock chamber 30 from a wafer transfer device (not shown) outside the apparatus. After the atmosphere side gate 31 is closed, the load lock chamber 30 is evacuated by the vacuum pump 33. The Thereafter, the sample chamber side gate 34 is opened, and the wafer 101 is carried into the sample chamber 20 by the vacuum transfer robot 32. Note that the inside of the sample chamber 20 is always evacuated by the vacuum pump 25, and the inside of the column 10 is also maintained at a high degree of vacuum by a vacuum pump (not shown). The components related to the vacuum evacuation and wafer conveyance are controlled by the evacuation conveyance control unit 65.

Next, the operation in the sample chamber will be described. The wafer 101 carried into the sample chamber 20 is placed on the wafer holder 22 on the sample stage 21. The sample stage 21 is controlled by the stage control unit 63 using, for example, a conveyance unit that combines a ball screw and a pulse motor, or a conveyance unit that combines a linear motor, an ultrasonic motor, or the like. A bar mirror 23 is attached on the sample stage 21, and the position of the sample stage 21 is measured by measuring the relative distance between the interferometer 24 attached to the sample chamber 20 and the bar mirror 23 by laser measurement. The position controller 62 performs processing. The position control unit 62 manages the position of the wafer 101 mounted and held on the sample stage 21. Here, in order to detect the position of the sample stage 21, position detecting means such as a linear scale may be used.
The acceleration limit table 50 will be described later.

  Next, the observation operation using the electron beam 12 will be described. An electron beam 12 is emitted from an electron gun 11 in the column 10, and the electron beam 12 is converged by an electron lens 13 and an objective lens 17. Further, the electron beam 12 is deflected to a predetermined trajectory by the deflection coils 14 and 15 and is irradiated onto the wafer 101. When the electron beam 12 is irradiated onto the wafer 101, reflected electrons and secondary electrons are generated and detected by the detector 16. The detection signals of reflected electrons and secondary electrons detected by the detector 16 are input to the image control unit 64 together with the control information of the electron beam 12 by the deflection coils 14 and 15. The image control unit 64 generates image data based on the control information, and the image is displayed on the display device 42 via the control unit 60. The control unit 60 plays a role of overseeing each of the above components. The operator can execute desired observation by inputting observation conditions and the like using the input unit 41. Note that the scanning electron microscope in the present embodiment is equipped with a height detection sensor (height detection unit) 18, which detects the detailed height of the wafer 101, and the column control unit 61 based on the detected height. The deflection amount and convergence rate of the electron beam 12 are determined.

  A glass window (not shown) is provided on the upper surface of the load lock chamber 30, and a two-dimensional laser displacement meter (warpage amount measuring unit) 35 is provided thereon. The two-dimensional laser displacement meter 35 measures the distance with a laser, and can measure the amount of warpage of the wafer 101 with micron order accuracy.

FIG. 2 is a plan view of the sample chamber 20 and the load lock chamber 30 for explaining the measurement of the amount of warpage of the wafer 101.
As shown in FIG. 2, the two-dimensional laser displacement meter 35 measures the amount of warpage of the wafer 101 before placing the wafer 101 on the wafer holder 22. The two-dimensional laser displacement meter 35 has a linear measurement area, and is installed so that the measurement area is perpendicular to the traveling direction of the wafer 101. For this reason, the amount of warpage of the entire surface of the wafer 101 can be measured during the transfer operation toward the sample chamber 20, and a reduction in the throughput of the apparatus (the number of wafers 101 that can be processed per unit time) is prevented. The stage control unit 63 is provided with a warp amount measurement control unit 631 for controlling the two-dimensional laser displacement meter 35. Although the two-dimensional laser displacement meter 35 is used here, spot-shaped measurement is performed in consideration of cost, necessary measurement position interval (interval between measurement positions perpendicular to the traveling direction of the wafer 101), and the like. A plurality of laser displacement meters having regions may be arranged.

(Configuration of wafer holding unit 22)
FIG. 3 is a view for explaining the upper surface of the wafer holding unit 22 and the AA ′ cross section.
As shown in FIG. 3, the wafer holding unit 22 is divided into twelve pieces, each having an electrostatic chuck chucking unit 221 and a Z stage (lifting unit) 222. In addition, the wafer holding unit 22 includes lift pins (not shown) having a lifting / lowering function stored in the opening 223.
The adsorbing unit 221 adsorbs a sample by applying a voltage to the chuck electrode.
The Z stage 222 adjusts the height of the suction part 221 independently of the other suction parts 221. The Z stage 222 is composed of, for example, a piezo stage that can be positioned with high accuracy and has low dust generation.
The lift pins are raised and temporarily support the wafer 101 when the vacuum transfer robot 32 carries the wafer 101 in and out.

The stage control unit 63 includes an electrostatic chuck control unit 632 and a Z stage control unit (elevation control unit) 633.
The electrostatic chuck control unit 632 performs ON / OFF of the adsorption operation of each adsorption unit 221 of the electrostatic chuck and detects the adsorption state.
The Z stage control unit 633 controls the position of each Z stage 222.
The wafer holding unit 22 in the present embodiment is merely an example, and the number of divisions is increased in order to deal with the more complicated warped wafer 101, or the divided shape corresponding to a characteristic warpage state is used. Also good. For example, the wafer holding unit 22 may have a lattice shape, a strip shape, or a donut shape. Further, the wafer holding unit 22 may reduce the number of divisions in view of manufacturing costs.

  In the present specification and the like, the electrostatic chuck device includes the above-described warpage amount measurement unit, an electrostatic chuck, an elevating unit, and an elevating control unit.

[Operation of Charged Particle Beam Device 1 (1)]
Next, the operation of the charged particle beam apparatus 1 will be described with reference to FIGS. 4 and 5 (configurations are appropriately FIGS. 1 to 3).
FIG. 4 is a flowchart showing the wafer observation operation by the charged particle beam apparatus 1 according to the first embodiment.
As shown in the flowchart of FIG. 4, in step S <b> 101, the vacuum transfer robot 32 takes out the wafer 101 from a wafer transfer case (not shown) and loads it into the load lock chamber 30. At this time, as shown in FIG. 5A, the wafer holding unit 22 is in an initial state.
In step S102, the two-dimensional laser displacement meter 35 (see FIG. 2) measures the amount of warpage of the entire surface of the wafer 101 and acquires position data. The warpage amount measurement control unit 631 calculates target position data of each Z stage 222. The target position data is, for example, an average value of the position data for each region that is handled by each chucking part 221 and Z stage 222 of the electrostatic chuck.

In step S103, the Z stage control unit 633 (see FIG. 3) moves the plurality of Z stages 222 up and down according to the calculated target position data of each Z stage. At this time, as shown in FIG. 5B, the wafer holding unit 22 is in a state where the plurality of Z stages 222 are moved up and down in accordance with the warpage amount of the wafer 101. In FIG. 5B, warping of the wafer 101 is emphasized.
In step S104, the vacuum transfer robot 32 carries the wafer 101 into the sample chamber. That is, the vacuum transfer robot 32 places the wafer 101 on lift pins (not shown) of the sample stage 21, and then the lift pins descend to leave the wafer 101 and place the wafer 101 on the wafer holding unit 22. At this time, as shown in FIG. 5C, the wafer holding unit 22 is in a state where the wafer 101 is placed.

In step S <b> 105, the electrostatic chuck control unit 632 (see FIG. 3) applies a voltage to the electrostatic chuck suction unit 221 to cause the wafer 101 to be suctioned to the suction unit 221. At this time, as shown in FIG. 5D, the wafer holding unit 22 is in a state where a voltage is applied to the chucking unit 221 of the electrostatic chuck and the wafer 101 is chucked.
In step S <b> 106, the electrostatic chuck control unit 632 determines whether the suction state of the wafer 101 is normal for all of the suction units 221. For example, the electrostatic chuck control unit 632 measures a leakage current that flows instantaneously during the suction operation, and makes a determination by comparison with a preset threshold value.

When it is determined that the suction state of the wafer 101 is normal for all the suction portions 221 (Yes in step S106), in step S109, the charged particle beam apparatus 1 determines that the wafer 101 Perform observation. For example, the charged particle beam apparatus 1 performs an operation of acquiring an SEM image of a pattern defect portion.
In step S <b> 110, the electrostatic chuck control unit 632 stops the voltage applied to the electrostatic chuck suction unit 221, and detaches the wafer 101 from the suction unit 221.
In step S111, the vacuum transfer robot 32 carries out the wafer 101.

On the other hand, when it is determined that at least a part of the suction state of the wafer 101 is not normal (step S106 / No), in step S107, the stage control unit 63 adds the suction force of the suction unit 221 whose suction state is normal. To calculate the total attractive force. Note that the suction force of the suction part 221 in which the suction state is normal is known.
In step S108, the stage control unit 63 refers to the acceleration restriction table 50 (see FIG. 1), and restricts the acceleration when the sample stage 21 moves. Here, the acceleration limit table 50 is a table in which the maximum allowable acceleration of the sample stage 21 with respect to the total adsorption force is set. The maximum allowable acceleration indicates a limit acceleration that does not cause displacement due to an inertial force applied to the wafer 101 when the sample stage 21 moves. Thereafter, the processing from step S109 to step S111 described above is executed.

According to the present embodiment, a normal holding operation can be performed even for a wafer with a large amount of warpage, and deformation of the wafer due to the holding operation can be minimized.
In addition, even when an abnormality occurs in the electrostatic chuck adsorption operation, the charged particle beam apparatus does not stop, and the acceleration when the sample stage moves can be automatically limited to perform a desired observation operation. it can.

Second Embodiment
Next, a second embodiment of the present invention will be described.
[Operation of Charged Particle Beam Device 1 (2)]
The operation (2) in the second embodiment of the charged particle beam apparatus 1 will be described with reference to FIGS. 6 and 7 (the configuration is appropriately shown in FIG. 1).
FIG. 6 is a flowchart showing an operation of wafer observation by the charged particle beam apparatus 1 according to the second embodiment. In this flowchart, the processes in steps S101 to S106 and S109 to S111 are the same as the processes in steps S101 to S106 and S109 to S111 in the flowchart of FIG. Here, the processing of steps S201 and S202 will be described.

As shown in the flowchart of FIG. 6, in step S201, the control unit 60 displays a wafer holding status screen.
Here, the wafer holding status screen will be described.
FIG. 7 is a diagram illustrating an example of a wafer holding status screen.
The wafer holding status screen 421 includes a holding state detail display unit 422, a total attractive force display unit 423, a stage acceleration display unit 424, an observation completion delay time display unit 425, a wafer holding unit outline display unit 426, and a Yes button. 427 and a No button 428.

The holding state detail display unit 422 indicates the suction state of the plurality of suction units 221 and the position of the Z stage 222. The item “No.” is a number for identifying each of the divided wafer holding units 22, and corresponds to the number shown in the wafer holding unit outline display unit 426 described later. The item “ESC (ElectroStatic Chuck)” is “OK” when the adsorption state of the adsorption unit 221 is normal. The item “Z [μm]” is position data of the Z stage 222 in the Z direction.
The total attraction force display unit 423 indicates the sum of the attraction forces of the attraction unit 221 in which the attraction state is normal.

The stage acceleration display unit 424 indicates the acceleration of the sample stage 21 when all the suction states are normal as 100%.
The observation completion delay time display unit 425 indicates the delay time of the observation operation time associated with the acceleration limitation.
The wafer holding unit outline display unit 426 displays an outline of the divided wafer holding unit 22 and a number for identifying each of the divided wafer holding units 22.
When the wafer holding status screen 421 is displayed, the operator presses the Yes button 427 or the No button 428.

Returning to FIG. 6, in step S <b> 202, the control unit 60 determines whether the operator has pressed the Yes button 427.
When it is determined that the operator has pressed the Yes button 427 (step S202 / Yes), in step S109, the charged particle beam apparatus 1 is in a state in which the acceleration of the sample stage 21 is limited based on conditions preset by the operator. The wafer 101 is observed.
On the other hand, when it determines with the No button 428 having been pressed by the operator (step S202 * No), the charged particle beam apparatus 1 stops observation operation. (Steps S110 and S111).

  According to the present embodiment, the processing of the charged particle beam apparatus 1 can be selected based on the operator's judgment.

<Modification>
As mentioned above, although one Embodiment of this invention was described, this invention is not limited to this, It can change in the range which does not deviate from the meaning of this invention.

For example, a height detection sensor 18 that detects the height of the sample is provided, and the Z stage control unit 633 moves the Z stage 222 up and down so that the height of the sample detected by the height detection sensor 18 is constant. It is good as well.
Thereby, even if it is a sample with a curvature, it can respond to a highly accurate measurement by making the height of a sample constant.

Further, the output voltage variable function is provided in the electrostatic chuck control unit 632, and the control unit 60 obtains a voltage to be applied to each suction unit 221 of the electrostatic chuck according to the amount of warp of the sample (for example, referring to a table, It is good also as giving an instruction | indication to the electrostatic chuck control part 632.
Thereby, a larger voltage can be applied to the adsorption portion 221 of a part of the sample with a large amount of warpage, and even a sample with a warp can cope with high-precision measurement by flattening. .

  In the embodiment of the present invention, the steps of the flowchart show an example of processing performed in time series according to the described order. However, the steps of the flowchart are not necessarily processed in time series, but are executed in parallel or individually. It also includes processing.

  In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

DESCRIPTION OF SYMBOLS 1 Charged particle beam apparatus 12 Electron beam 18 Height detection sensor (height detection part)
21 Sample stage 22 Wafer holder 30 Load lock chamber 35 Two-dimensional laser displacement meter (warp measurement unit)
DESCRIPTION OF SYMBOLS 50 Acceleration restriction table 60 Control part 61 Column control part 62 Position control part 63 Stage control part 64 Image control part 65 Exhaust conveyance control part 101 Wafer (sample)
221 Suction unit 222 Z stage (lifting unit)
421 Wafer holding status screen (screen showing sample holding status)
631 Warpage measurement control unit 632 Electrostatic chuck control unit 633 Z stage control unit (elevation control unit)

Claims (6)

A charged particle beam apparatus that irradiates a sample held on a sample stage with an electron beam and generates an image of the sample,
A warpage amount measuring unit for measuring the warpage amount of the sample;
An electrostatic chuck having a plurality of suction portions for sucking the sample;
An elevating part capable of ascending and descending provided at a lower part of each of the plurality of adsorption parts;
A lifting control unit that raises and lowers the lifting unit according to the amount of warping of the sample measured by the warping amount measuring unit,
A charged particle beam apparatus comprising:   When it is determined that the suction state is not normal in at least a part between each suction portion of the electrostatic chuck and the sample, the sample stage moves based on a preset acceleration limit table. The charged particle beam device according to claim 1, further comprising a control unit that limits acceleration at the time.   And a control unit that displays a screen indicating a holding state of the sample when it is determined that the suction state is not normal in at least a part between each suction unit of the electrostatic chuck and the sample. The charged particle beam apparatus according to claim 1 or 2, wherein A charged particle beam apparatus that irradiates a sample held on a sample stage with an electron beam and generates an image of the sample,
An electrostatic chuck having a plurality of suction portions for sucking the sample;
An elevating part capable of ascending and descending provided at a lower part of each of the plurality of adsorption parts;
A height detector for detecting the height of the sample;
An elevating control unit for elevating the elevating unit so that the height of the sample detected by the height detecting unit is constant;
A charged particle beam apparatus comprising: A charged particle beam apparatus that irradiates a sample held on a sample stage with an electron beam and generates an image of the sample,
A warpage amount measuring unit for measuring the warpage amount of the sample;
An electrostatic chuck having a plurality of suction portions for sucking the sample;
An electrostatic chuck control unit that controls a voltage applied to the electrostatic chuck in accordance with the amount of warpage measured by the warp amount measurement unit;
A charged particle beam apparatus comprising: An electrostatic chuck device for adsorbing a sample,
A warpage amount measuring unit for measuring the warpage amount of the sample;
An electrostatic chuck having a plurality of suction portions for sucking the sample;
An elevating part capable of ascending and descending provided at a lower part of each of the plurality of adsorption parts;
A lifting control unit that raises and lowers the lifting unit according to the amount of warping of the sample measured by the warping amount measuring unit,
An electrostatic chuck device comprising:

Images