WO2010097858A1 - 電子顕微鏡および試料保持方法 - Google Patents
電子顕微鏡および試料保持方法 Download PDFInfo
- Publication number
- WO2010097858A1 WO2010097858A1 PCT/JP2009/005375 JP2009005375W WO2010097858A1 WO 2010097858 A1 WO2010097858 A1 WO 2010097858A1 JP 2009005375 W JP2009005375 W JP 2009005375W WO 2010097858 A1 WO2010097858 A1 WO 2010097858A1
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- Prior art keywords
- sample
- electrostatic chuck
- electron microscope
- contact
- wafer
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/02—Details
- H01J37/20—Means for supporting or positioning the objects or the material; Means for adjusting diaphragms or lenses associated with the support
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/28—Testing of electronic circuits, e.g. by signal tracer
- G01R31/302—Contactless testing
- G01R31/305—Contactless testing using electron beams
- G01R31/307—Contactless testing using electron beams of integrated circuits
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
- H01J37/28—Electron or ion microscopes; Electron or ion diffraction tubes with scanning beams
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/20—Positioning, supporting, modifying or maintaining the physical state of objects being observed or treated
- H01J2237/2007—Holding mechanisms
Definitions
- the present invention relates to a measuring apparatus and an inspection apparatus that perform line width measurement and defect inspection of a semiconductor device using an electron beam.
- An electron microscope is a device that performs image formation, pattern dimension measurement, or defect inspection by detecting electrons obtained by irradiating a sample with a finely focused electron beam.
- the higher the acceleration energy of the electron beam the higher the resolution image can be formed.
- the electron beam with high acceleration energy may damage the sample or damage the sample.
- the retarding technique is a technique for forming a deceleration electric field for an electron beam on a sample by applying a negative voltage to the sample. That is, the electron beam that has passed through the objective lens with high energy is decelerated immediately before reaching the sample. As described above, according to the retarding technique for reducing the energy reaching the sample, it is possible to achieve both high resolution of the image and suppression of damage to the sample.
- Patent Documents 1 and 2 describe a technique for conducting a sample covered with an insulating film.
- Patent Document 1 describes a method of breaking through an insulating layer by pressing a conductive pin against a semiconductor wafer.
- Patent Document 2 describes a technique for reducing the contact resistance between the ground electrode and the sample by cleaning the insulating film by flowing a leak current from the ground electrode in contact with the sample.
- an electrostatic chuck for holding the wafer is used to conduct the wafer in a state where the conduction pins are not in the way.
- a method of providing a plurality of sharp conducting pins with tips that can be projected and retracted from the suction surface is disclosed.
- an elastic member that urges the conductive pin in the protruding direction and a drive mechanism that can vibrate the conductive pin left and right at high speed are provided and attached to the wafer.
- a method of mechanically breaking through an insulating film to establish conduction is also disclosed.
- the tip is sharp in order to securely ground while suppressing the increase of the back surface foreign matter due to the contact between the ground electrode and the wafer.
- a method is disclosed in which a non-ground electrode is brought into contact with the wafer, a voltage is applied to the ground electrode to flow a surface activation current to clean (purge) the insulating film, and lower the contact resistance.
- electrical_connection measuring the surface activation current and measuring the voltage to apply alternately are disclosed, and adjusting an applied voltage until sufficient surface activation current flows is disclosed. It is also disclosed that the polarity of the voltage applied at this time is opposite to the voltage applied to the electrostatic chuck holding the wafer to prevent the adsorption force from being reduced.
- Patent Document 1 According to the methods disclosed in Patent Document 1 and Patent Document 2, it is possible to conduct the ground potential and the sample. However, nothing is described about properly applying the retarding voltage.
- the electron beam is applied by applying a negative voltage to the sample.
- a negative voltage application power source that forms a decelerating electric field with respect to, an electrostatic chuck mechanism that generates an attractive force for the sample by applying a potential difference between the plurality of internal electrodes, and when the sample is placed on the sample support table,
- a contact terminal configured to contact the sample
- the electrostatic chuck mechanism causes a potential difference between the internal electrodes in a state where the contact terminal is in contact with the sample
- the negative voltage application power source is Then, after the potential difference is generated, a negative voltage is applied to the contact terminal, and an electron microscope is proposed.
- Conduction between the contact terminal and the sample is obtained by the potential difference generated between the plurality of electrodes of the electrostatic chuck mechanism. Therefore, depending on the presence of an insulating film or the like by applying a negative voltage to the sample in the conductive state. Therefore, it is possible to stably apply a negative voltage to the sample.
- CD-SEM Crohn's disease senor-Dimension SEM
- SEM scanning electron microscope
- a scanning electron microscope is used for continuity inspection of a wiring deep hole by utilizing potential contrast.
- the basic principle of measurement will be briefly explained. Basically, it is the same as the scanning electron microscope. Primary electrons are emitted from the electron gun and accelerated by applying a voltage. Thereafter, the beam diameter of the electron beam is narrowed down by an electromagnetic lens. This electron beam is scanned two-dimensionally on a sample such as a semiconductor wafer. Secondary electrons generated when the scanned electron beam enters the sample are detected by a detector.
- the fine pattern on the sample can be imaged by synchronizing the scanning of the electron beam and the detection of the secondary electrons and displaying them on the monitor.
- the edge of the pattern is discriminated based on the change in brightness of the obtained image to derive the dimension. The above is the measurement principle of CD-SEM.
- the generation efficiency of the secondary electrons depends on the acceleration energy of the primary electrons incident on the sample.
- the incident energy is relatively large, the secondary electron generation efficiency is less than 1, so that the sample has high insulation. And the surface is negatively charged. If the sample is charged during measurement, it causes image distortion and contrast changes. Further, some materials to be measured are damaged by irradiation with an electron beam having a large incident energy, which also causes a problem.
- the stage is made of the support pin as a conductive material. And a retarding voltage to be applied to the stage.
- wafers flowing in an actual production line have an insulating thin film such as an oxide film or a nitride film on the surface.
- the wafer is simply mounted on the stage or the support pins, it is electrically insulated by the insulating film. Therefore, the wafer cannot be fixed at the retarding voltage, and the wafer potential is not stable.
- an electrostatic chuck has been used for the stage in anticipation of an effect of facilitating focusing by flattening the wafer.
- the surface holding the wafer is usually covered with ceramics having high electrical insulation. Therefore, charging by the electron beam occurs only by loading the wafer on the electrostatic chuck, and the wafer potential cannot be stabilized.
- an electrostatic chuck mechanism capable of ensuring conduction to a sample such as a wafer and applying a retarding voltage in a state where the conduction is ensured, or the electrostatic chuck mechanism.
- a scanning electron microscope equipped with is described.
- a method for holding a sample of a scanning electron microscope capable of observing a sample while ensuring conduction between the contact pin and the wafer and applying a retarding voltage to the wafer via the contact pin will also be described.
- the sample in a scanning electron microscope that measures the surface of a sample using an electron beam, the sample is held by an electrostatic chuck having a plurality of electrodes therein.
- the retarding voltage is applied via a contact pin held by an elastic member so as to protrude from the surface, and the absolute value differs at least before starting the irradiation of the electron beam to a plurality of electrodes of the electrostatic chuck.
- a scanning electron microscope having a configuration for applying a DC voltage will be mainly described.
- the sample is held by an electrostatic chuck having a plurality of electrodes therein, and at least a plurality of contact pins held by an elastic member so as to protrude from the surface of the electrostatic chuck are provided.
- a scanning electron microscope having a configuration in which a retarding voltage is applied to at least one of a plurality of contact pins before starting irradiation of an electron beam will be described.
- the electrostatic beam is irradiated before the sample is irradiated with the electron beam.
- a step of contacting a sample with a contact pin held by an elastic member so as to protrude from the surface of the chuck, a step of applying a DC voltage having a different absolute value to an internal electrode of the electrostatic chuck, and at least for the contact pin A sample holding method having a step of applying a retarding voltage will be described.
- the sample before irradiating the sample with an electron beam, the sample contacts a plurality of contact pins held by an elastic member so as to protrude from the surface of the electrostatic chuck, and at least one of the contact pins is retarded
- a sample holding method having a step of applying a voltage will be described.
- the wafer surface in the scanning electron microscope, the wafer surface can be measured while the wafer potential is maintained at the retarding voltage while the wafer is held flat by the electrostatic chuck, and after the measurement is completed. Since the wafer can be smoothly transported from the electrostatic chuck, there is no change in image distortion or contrast during measurement, high resolution and no damage to the sample surface, and high throughput measurement is possible. .
- Figure 5 shows a schematic diagram of the CD-SEM.
- the electrons emitted from the electron source 1 are accelerated by the primary electron acceleration electrode 2 to which a high voltage is applied by a high voltage power source 3.
- the electron beam 14 is converged by the converging electron lens 4.
- the electron beam is scanned two-dimensionally by the scanning coil 6 after the beam current amount is adjusted by the diaphragm 5.
- the electron beam is focused by an electron objective lens 8 disposed immediately above a semiconductor wafer (hereinafter simply referred to as a wafer) 9 as a sample, and is incident on the wafer.
- Secondary electrons 15 generated as a result of incidence of primary electrons are detected by the secondary electron detector 7.
- the shape of the surface can be imaged based on the information of the secondary electrons.
- the inside of the housing 13 is maintained at a high vacuum.
- the wafer 9 is held on the electrostatic chuck 10 while ensuring a certain flatness, and is fixed on the XY stage 16.
- the casing and its internal structure are described in a cross-sectional view as seen from the lateral direction, but the XY stage, electrostatic chuck, and wafer are described in perspective views so that the operation can be easily imagined.
- the electrostatic chuck is loaded on the Y stage 11 of the XY stage and can move in the Y direction.
- the Y stage is loaded on the X stage 12 and is movable in the X direction. Therefore, the wafer can freely move in both the X direction and the Y direction, and can measure an arbitrary position in the wafer surface.
- the through-hole 18 is provided in the electrostatic chuck serving as the sample support base, and a transfer push-up pin for attaching / detaching the wafer to / from the electrostatic chuck can move up and down.
- Reference numeral 17 denotes a contact pin used for applying a retarding voltage to the wafer. The contact pins function as contact terminals between the retarding power supply and the inside of the wafer covered with an insulating film or the like.
- the scanning electron microscope illustrated in FIG. 5 is controlled by a control device (not shown), and an electrostatic chuck mechanism and a retarding voltage application power source described below are also controlled by the control device.
- Fig. 2 shows the detailed structure of the contact pin.
- a through hole is provided in the electrostatic chuck, and an insulating pipe 19 is packed so as to accept the through hole.
- a contact pin 17 having a conductive diamond tip is inserted into the insulating pipe.
- a flange 20 is provided below the electrostatic chuck of the contact pin, and is supported by a coil spring 23 housed in a cover 22 fixed to the electrostatic chuck with a bolt 21. In this state, the tip of the contact pin 17 is configured to protrude from the surface of the electrostatic chuck. When the wafer is loaded, the contact pin sinks due to the weight of the wafer.
- the contact pins are pressed against the back surface of the wafer by the pushing force of the coil spring, so that even if there is an insulating film such as an oxide film or a nitride film on the back surface of the wafer, the contact pins and the wafer are It becomes easy to obtain electrical conduction between them.
- the proper protrusion amount of the contact pin in a state where the wafer is not loaded is determined from the spring constant of the coil spring and the pressing force to be applied to the contact pin.
- the pressing force is about 20 to 60 gf, which is good from the viewpoint of reproducibility of conduction and low foreign matter.
- the spring constant of the coil spring is 80 gf / mm
- the protrusion amount of the contact pin is 0.5 mm. That is, the pressing force is 40 gf.
- the weights of 8-inch and 12-inch wafers are approximately 50 gf and 120 gf, respectively, and when the wafer is loaded, the contact pins are pushed down by the own weight.
- Fig. 1 shows a schematic diagram of an electrostatic chuck and a circuit for applying a retarding voltage.
- the bulk material of the electrostatic chuck is high-resistance alumina, and two internal electrodes 25 and 26 are built inside. That is, the electrostatic chuck of the present invention is a so-called bipolar type.
- protrusions on dots having a diameter of 1 mm or less and a height of 20 ⁇ m or less are provided at a ratio of less than 10% of the total projected area for the purpose of preventing foreign matter from adhering to the back surface of the wafer. is there.
- DC power supplies 27 and 28 are connected to the internal electrodes 25 and 26.
- the DC power sources 27 and 28 are connected in a floating manner to a retarding power source 29 that applies a retarding voltage to the wafer.
- the contact pins 17 are also connected in a floating manner to the retarding power supply in the same manner as the DC power supply, and the tip is in contact with the wafer 9.
- Reference numeral 30 denotes an ammeter for measuring a leakage current flowing through the contact pin, which can be monitored by an external monitor (not shown).
- FIG. 3 shows an equivalent circuit model of FIG. 1, and FIG. 4 shows a voltage application time chart (first embodiment).
- the retarding switch 31 is for switching between the retarding power source 29 and the ground.
- the DC power supply switches 32 and 33 are used to connect a DC power supply to the internal electrode of the electrostatic chuck.
- the equivalent circuit illustrated in FIG. 3 includes capacitances 34 and 36 of the dielectric film of the electrostatic chuck and resistors 35 and 37 of the dielectric film. Further, the contact resistance 38 of the contact portion between the contact pin and the wafer back surface is included.
- the retarding power switch 39 is used to connect or disconnect the contact pin from the ground or the retarding power source.
- the time chart of FIG. 4 will be described.
- the wafer on the electrostatic chuck is stacked on time T 1.
- the wafer comes into contact with the contact pins.
- the retarding switch 31 in FIG. 3 is connected to the ground.
- the DC power switch is also turned off, that is, the internal electrodes 25 and 26 are grounded.
- the contact pin switch is open, and the wafer is at a floating potential.
- the DC power supply switches 32 and 33 in FIG. 3 are simultaneously turned on, and a DC voltage is applied to the internal electrodes 25 and 26.
- +1020 V is applied to the internal electrode 25
- ⁇ 1000 V is applied to the internal electrode 26.
- the wafer potential is substantially intermediate between the applied voltages, and is +10 V in this embodiment.
- the retarding power switch 39 is switched.
- a voltage of 10 V is applied between the tip of the contact pin and the bulk silicon of the wafer.
- a leakage current flows to ensure conduction between the contact pin and silicon.
- the leak current flowing in the circuit at this time can be measured by the ammeter 30 and the conduction state between the contact pin and the wafer can be monitored. If it is determined that the continuity is insufficient as a result of monitoring, it is possible to increase the difference in the voltage applied to the internal electrode and to ensure the continuity by switching the contact pin switch again. .
- a threshold value is provided for the current amount, and when the current amount detected by the ammeter 30 does not reach the threshold value or is equal to or less than the threshold value, the potential difference between the plurality of internal electrodes is determined. For example, it is conceivable to increase the value by a predetermined value. If the current amount still does not satisfy the predetermined condition, the process of giving a larger potential difference is repeated. According to such a configuration, it is possible to apply a retarding voltage after confirming that conduction is sufficiently ensured. It is also possible to adjust the potential difference according to the amount of current detected by the ammeter 30.
- start measuring the T 5 (applying a beam current) is.
- the measurement is terminated at time T 6 (the beam current is turned off). Since the beam current incident on the wafer surface during measurement flows to the ground via the retarding power source, the wafer can be prevented from being charged up.
- the wafer surface can be measured while the wafer potential is maintained at the retarding voltage while the wafer is held flat by the electrostatic chuck, and the wafer is measured after the measurement is completed. Can be smoothly transported from the electrostatic chuck, so that it is possible to perform measurement with high throughput without changing image distortion and contrast during measurement and with high resolution without damaging the sample surface.
- a potential difference of 20 V is given to the voltage applied to the internal electrode, and this voltage is maintained even during measurement by beam irradiation.
- the present invention is not necessarily limited to this.
- the absolute values of the applied voltages of the two DC power supplies may be adjusted to be the same so that the potential difference between the voltages applied to the internal electrodes is zero.
- the application of the retarding voltage has been described as being performed by switching the switch 31.
- the present invention is not necessarily limited to this, and the retarding voltage is always connected to the ground via the retarding power source. A similar effect can be realized even if the application is continuously adjusted from 0 V to a desired value.
- the dielectric film of the electrostatic chuck is formed of high-resistance alumina, and the electrostatic chuck is a so-called Coulomb electrostatic chuck.
- the dielectric film is not necessarily limited to this.
- a so-called Johnson Rabeck type electrostatic chuck having a specific resistivity of about 1 ⁇ 10 12 ⁇ cm or less and a leakage current of the order of several ⁇ A may be used.
- the internal electrodes of the electrostatic chuck are two so-called bipolar electrostatic chucks, but are not necessarily limited thereto.
- the present invention can also be applied to a case where a larger number of internal electrodes are arranged because it is necessary to adjust the magnitude of the suction force for each area.
- a potential difference is given between the wafer and the contact pin by providing a difference in the absolute value of the voltage applied to the internal electrode of the electrostatic chuck in order to ensure the conduction between the contact pin and the sample.
- the reverse polarity is applied with the applied voltages being +1020 V and ⁇ 1000 V, but it is not always necessary to have the reverse polarity. For example, the same effect can be expected when +1200 V and +200 V are used.
- the contact pin is simply supported by the coil spring, the pressing force between the contact pin and the wafer can be managed with a simple structure.
- the coil spring moves relatively easily in the radial direction of the insulating pipe.
- unnecessarily sliding friction may occur between the contact pins and the wafer, which may increase the amount of foreign matter on the back surface. Therefore, in a case where a slight increase in foreign matter on the back surface is a problem, it is necessary to limit the movement in the lateral direction. Therefore, the occurrence of foreign matter on the back surface was suppressed by reducing the lateral movement of the contact pins.
- FIG. 6 The specific structure of the contact pin is shown in FIG. 6 (second embodiment).
- the spacer 24 is inserted between the back surface of the electrostatic chuck and the contact pin flange, and the coil spring is compressed in advance to give a preload.
- the coil spring was compressed by 0.3 mm. Therefore, the protrusion amount of the tip of the contact pin is 0.5 mm, which is 0.5 mm in the first embodiment.
- the protrusion amount of the contact pin and the pressing force of the contact pin against the wafer can be adjusted by changing the thickness of the spacer. Therefore, by setting the protrusion amount small, when it is necessary to apply a pressing force larger than the wafer's own weight, even if the wafer is lifted from the electrostatic chuck surface only by placing the wafer, The wafer can be reliably chucked by the suction force of the electric chuck, and the pressing force of the contact pins against the wafer can be increased. By doing in this way, it is possible to reliably ensure conduction regardless of the thickness of the wafer with an insulating film.
- FIG. 7 shows another configuration example of the contact pin (third embodiment).
- the compression member 41 having a structure is attached.
- the screwing amount of the compression member by adjusting the screwing amount of the compression member, the compression amount applied to the coil spring, that is, the pressing force of the contact pin can be easily adjusted. Therefore, with this configuration, the pressing force of the contact pins can be adjusted according to the thickness of the insulating film on the back surface of the wafer, and the pressing load can be adjusted according to the wafer. By pressing with a load, it is possible to reliably establish conduction without increasing the number of foreign substances on the back surface.
- a preload can be applied to the coil spring that supports the ground pin.
- the pressing load is adjusted for each wafer. I can't.
- a driving mechanism such as a motor
- the compression member of the third embodiment is rotated to displace the compression member along the female screw of the cover.
- the shaft can be driven by a drive mechanism such as a motor in a state where the coil spring can be expanded and contracted. It is also possible to drive the vertical displacement of the coil spring by combining, for example, a piezo element and a mechanism for enlarging the displacement of the piezo element.
- the ground pin is supported by the coil spring.
- the present invention is not necessarily limited to this, and the same effect can be expected as long as it can be supported elastically.
- FIG. 8 shows another configuration example using the electrostatic chuck mechanism and the retarding method together (fourth embodiment).
- the present embodiment unlike the first embodiment, only the DC power sources 27 and 28 are connected to the internal electrodes 25 and 26, and the retarding power source is not connected.
- a retarding power source 42 is connected to the contact pin 17 via an ammeter 30. The output of the ammeter can be monitored by an external monitor (not shown).
- FIG. 9 shows a time chart of voltage application.
- the wafer on the electrostatic chuck is stacked on time T 1.
- the retarding power supply is switched off, no retarding voltage is applied, and it is not connected to ground.
- the DC power supply switch is connected to the ground, and the internal electrodes 25 and 26 are grounded.
- the DC power source switch is switched, 27 and 28 are simultaneously turned on, and a DC voltage is applied to the internal electrodes 25 and 26.
- +1020 V was applied to the internal electrode 25 and ⁇ 1000 V was applied to the internal electrode 26.
- the wafer potential is substantially intermediate between the applied voltages, and is +10 V in this embodiment.
- the retarding power switch 39 is switched to ground.
- a voltage of 10 V is applied between the tip of the contact pin and the bulk silicon of the wafer, and leakage current flows to ensure conduction between the contact pin and silicon.
- the leak current flowing in the circuit at this time can be measured by the ammeter 30 and the conduction state between the contact pin and the wafer can be monitored. If it is determined that the continuity is insufficient as a result of monitoring, it is possible to increase the difference in the voltage applied to the internal electrode and to ensure the continuity by switching the contact pin switch again. .
- the wafer surface can be measured while the wafer potential is maintained at the retarding voltage while the wafer is held flat by the electrostatic chuck, and the wafer is measured after the measurement is completed. Can be smoothly transported from the electrostatic chuck, so that there is no change in image distortion or contrast during measurement, no damage to the sample surface with high resolution, and high-throughput measurement is possible.
- the voltage of the electrostatic chuck applied at time T 2 was not particularly adjusted even after the retarding voltage was applied to T 3 , but is adjusted according to the value of the retarding voltage. It is also possible. Specifically, for example, when ⁇ 1000 V is applied to the wafer as the retarding voltage, no attracting force is generated on the internal electrode to which a voltage of ⁇ 1000 V is applied. Therefore, for example, if the voltage on the side to which + 1020V is applied is changed to 0V and the voltage on the side to which ⁇ 1000V is applied is changed to ⁇ 2000V, the applied voltage as an electrostatic chuck is ⁇ 1000V even while the retarding voltage is being applied. Therefore, it is possible to maintain the adsorption force in a well-balanced manner.
- FIG. 10 shows still another configuration example in which the electrostatic chuck mechanism and the retarding method are used together (fifth embodiment).
- a second contact pin is added to the fourth embodiment.
- the switch 45 is a switch for switching whether the second contact pin 43 is connected to ground or grounded.
- the voltage is applied to the wafer by utilizing the potential difference between the voltages applied to the internal electrodes, for example, even when +1000 V and 0 V are applied, the voltage that can be applied to the ground pin and the wafer remains at 500 V. .
- this method since it is possible to ensure conduction by using the voltage of the retarding power supply, a larger potential difference can be given, and conduction can be more reliably ensured.
- it is possible to ensure continuity without using the electrostatic chuck power supply it is possible to ensure continuity even when the electrostatic chuck or power supply fails, without having to operate the electrostatic chuck.
- the apparatus can be operated.
- FIG. 11 shows a time chart of voltage application.
- the wafer on the electrostatic chuck is stacked on time T 1.
- the retarding power switch 39 is connected to the ground.
- the DC power supply switches 32 and 33 are connected to the ground, and the internal electrodes 25 and 26 are also grounded.
- the switch 45 of the second contact pin 43 is turned on and connected to the ground.
- the DC power supply switches 32 and 33 are switched, the DC power supplies 27 and 28 are simultaneously turned on, and a DC voltage is applied to the internal electrodes 25 and 26.
- +1020 V was applied to the internal electrode 25 and ⁇ 1000 V was applied to the internal electrode 26.
- the wafer potential is substantially intermediate between the applied voltages, and is +10 V in this embodiment.
- the contact pins and the second contact pins 43 often ensure electrical continuity with the wafer, in which case the wafer potential is 0V.
- the retarding power switch 39 is turned on. Thereby, a retarding voltage is applied from the contact pin to the ground via the second contact pin.
- 100V is applied. This voltage of 100 V is lower than a voltage generally adopted as a retarding voltage.
- the conduction between the contact pin and the silicon is ensured by the leakage current flowing.
- the leak current flowing in the circuit at this time can be measured by the ammeter 30 and the conduction state between the contact pin and the wafer can be monitored.
- start measuring the T 5 (applying a beam current) is.
- the measurement is terminated at time T 6 (the beam current is turned off). Since the beam current incident on the wafer surface during measurement flows to the ground via the retarding power source, the wafer can be prevented from being charged up.
- the wafer surface can be measured while the wafer potential is maintained at the retarding voltage while the wafer is held flat by the electrostatic chuck, and the wafer is measured after the measurement is completed. Can be smoothly transported from the electrostatic chuck, so that there is no change in image distortion or contrast during measurement, no damage to the sample surface with high resolution, and high-throughput measurement is possible.
- a voltage difference of 1020 V and ⁇ 1000 V is applied to the electrostatic chuck.
- a voltage having the opposite polarity and the same absolute value is applied. May be set to 0V.
- the second contact pin is added to the contact pin.
- the present invention is not necessarily limited to this, and a contact pin can be added. In that case, it is possible to ensure conduction more reliably, but if the contact portion is carelessly swollen, an increase in foreign matter on the back surface is caused. Therefore, the number of contact pins should be determined arbitrarily in consideration of the ease of wafer conduction and the viewpoint of backside foreign matter.
- the power supply for applying a voltage to the electrostatic chuck is configured to have one end grounded, but this is not necessarily limited to this, and the floating power supply to the retarding power supply is not necessarily limited to this. It is also possible to connect in the form of a ring.
- Electron source 2 Primary electron acceleration electrode 3 High voltage power source 4
- Electron lens 5 Aperture 6
- Scan coil 7 Secondary electron detector 8
- Electronic objective lens 9 Wafer 10
- Electrostatic chuck 11 Y stage 12
- X stage 13 Case 14
- Electron beam 15 Secondary Electronic 16
- Contact pin 18 Through hole 19
- Insulating pipe 20 ⁇ 21
- Bolt 22 Cover 23 Coil spring 24
- Spacer 25 26
- Retarding power supply 30 Ammeter 31 Retarding switch 32 , 33 DC power supply switch 34, 36 Dielectric film capacitance 35, 37 Dielectric film resistance 38 Contact resistance 39
- Retarding power switch 40 40
- Compression member 43
- Second contact pin 44 Power supply 45 switch
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Abstract
Description
2 一次電子加速電極
3 高圧電源
4 電子レンズ
5 絞り
6 走査コイル
7 2次電子検出器
8 電子対物レンズ
9 ウエハ
10 静電チャック
11 Yステージ
12 Xステージ
13 筐体
14 電子ビーム
15 2次電子
16 X-Yステージ
17 コンタクトピン
18 貫通穴
19 絶縁パイプ
20 鍔
21 ボルト
22 カバー
23 コイルバネ
24 スペーサ
25,26 内部電極
27,28 直流電源
29,42 リターディング電源
30 電流計
31 リターディング用スイッチ
32,33 直流電源用スイッチ
34,36 誘電体膜静電容量
35,37 誘電体膜抵抗
38 接触抵抗
39 リターディング電源用スイッチ
40 カバー
41 圧縮部材
43 第二のコンタクトピン
44 導通用電源
45 スイッチ
Claims (10)
- 電子源から放出された電子ビームを、試料支持台上に配置された試料上にて走査する走査電子顕微鏡において、
試料に負電圧を印加することによって、前記電子ビームに対する減速電界を形成する負電圧印加電源と、
複数の内部電極間に電位差を与えて試料に対する吸着力を発生する静電チャック機構と、
前記試料支持台上に、試料を配置したときに、前記試料に接触するように構成された接触端子とを備え、
前記静電チャック機構は、前記接触端子が前記試料に接した状態で、前記内部電極間に電位差を生じさせ、前記負電圧印加電源は、当該電位差を生じさせた後に、前記接触端子に負の電圧を印加することを特徴とする電子顕微鏡。 - 請求項1において、
前記接触端子と、前記負電圧印加電源との間に流通する電流を検出する電流計を備えたことを特徴とする電子顕微鏡。 - 請求項2において、
前記静電チャック機構は、前記電流計によって検出される電流量が所定の条件を満たさなかった場合に、前記電位差を大きくするように制御されることを特徴とする電子顕微鏡。 - 請求項1において、
前記接触端子は、前記試料に対し、弾性部材によって押圧される構成を備えていることを特徴とする電子顕微鏡。 - 請求項1において、
前記試料に接触する接触端子が2つ設けられることを特徴とする電子顕微鏡。 - 請求項5において、
前記2つの接触端子の内、1の接触端子と試料間に、所定の電流が流通しない場合に、前記2つの接触端子の内、他の接触端子から、前記試料に対し、前記負電圧印加電源から負電圧を印加されることを特徴とする電子顕微鏡。 - 静電チャックにより試料を保持しつつ電子ビームを用いて前記試料表面を計測する走査電子顕微鏡において、
前記静電チャックは内部に複数の電極を備え、前記静電チャックの表面から突出するように弾性部材に保持されたコンタクトピンを備え、少なくとも前記コンタクトピンに対してはリターディング電圧を印加し、前記複数の電極に対して少なくとも前記電子ビームを照射開始する以前に絶対値の異なる直流電圧を印加することを特徴とする走査電子顕微鏡。 - 内部に複数の電極を備えた静電チャックにより試料を保持しつつ電子ビームを用いて前記試料表面を計測する走査電子顕微鏡の試料保持方法であって、
該試料保持方法は前記電子ビームを前記試料に照射する以前に、前記静電チャックの表面から突出するように弾性部材に保持されたコンタクトピンに前記試料が接触するステップと、
前記静電チャックの内部電極に絶対値の異なる直流電圧を印加するステップと、少なくとも前記コンタクトピンに対してはリターディング電圧を印加するステップを有することを特徴とする走査電子顕微鏡の試料保持方法。 - 静電チャックにより試料を保持しつつ電子ビームを用いて前記試料表面を計測する走査電子顕微鏡において、前記静電チャックは内部に複数の電極を備え、前記静電チャックの表面から突出するように弾性部材に保持されたコンタクトピンを少なくとも2個備え、前記電子ビームを照射開始する以前に前記コンタクトピンの少なくとも一方にリターディング電圧を印加することを特徴とする走査電子顕微鏡。
- 内部に複数の電極を備えた静電チャックにより試料を保持しつつ電子ビームを用いて前記試料表面を計測する走査電子顕微鏡の試料保持方法であって、
該試料保持方法は前記電子ビームを前記試料に照射する以前に、前記静電チャックの表面から突出するように弾性部材に保持された複数のコンタクトピンに前記試料が接触するステップと、前記コンタクトピンの少なくとも一方に対してリターディング電圧を印加するステップを有することを特徴とする走査電子顕微鏡の試料保持方法。
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