JP7746232B2 - Charge reduction system, device including the same, and charge reduction method - Google Patents

Description

The present invention relates to the reduction of charge on insulating materials, and in particular to a charge reduction system that uses electric field control.

In the manufacture of electronic devices, processing equipment is equipped with a mounting table for placing an object on, which generally includes an electrostatic chuck. A voltage is applied to the electrostatic chuck, and the object is attracted to the electrostatic chuck by the Coulomb force generated by this voltage. If the object is an insulator, an electric charge may build up on the surfaces of the object and the electrostatic chuck, and this charge may not be released even after the application of the voltage is stopped. If the object is removed from the electrostatic chuck while the surfaces of the object and the electrostatic chuck are charged, a load will be applied to the object, which may cause the object to bend or crack. Therefore, it is necessary to discharge the electric charge from the electrostatic chuck and the object.

Furthermore, in charged particle beam devices that handle charged particles, such as electron microscopes, focused ion beam processing devices, and mass spectrometers, charging of the device and the object being observed is an issue, as it affects the control of the charged particles. In particular, in the semiconductor device manufacturing process, in-line inspection and measurement using a scanning electron microscope (SEM) has become an important inspection item with the aim of improving yield. In SEMs, when the surface of the object being inspected is an insulator, charging on the object's surface becomes an issue. Specifically, charging of the object distorts the electric field, changing the trajectory of the charged particles, and in some cases preventing the expected performance from being achieved. Therefore, it is necessary to remove or reduce the charge that accumulates on insulators.

In general electrical equipment, static electricity also accelerates the deterioration of insulators, increasing the incidence of insulation failure. Therefore, it is similarly necessary to remove or reduce the static electricity that accumulates in insulators.

When considering the relaxation (elimination) of charge accumulated in an insulator, there are two possible methods. One is to extract charge from the insulator through a medium other than the insulator, eliminating the charge via light, gas, charged particles (electrons, ions, plasma), etc. Because the charge is relaxed through a separate medium, a device configuration is required to generate the medium and guide it to the insulator, as well as a configuration to appropriately remove the released charge. For example, when using charged particles to relax the charge, it is important that the charged particles introduced for charge relaxation do not charge other areas, which can be expected to result in a complex device configuration.

The other method is to transfer the charge through the insulator itself. Charging is relieved by transferring the charge inside or along the surface of the insulator. Charge accumulated in the insulator is diffused over time according to the electric field formed by the charge itself, and the charge is relieved. The speed at which the charge moves varies depending on the insulator material. It is generally said that the speed at which charge moves inside an insulator is about two orders of magnitude faster on the surface than on the inside. Therefore, charge relaxation through the insulator's surface is conceivable. The speed at which the charge moves can be controlled by applying an electric field in the direction of charge movement, so it is thought that by changing the electric field applied to the object, the charge accumulated in the insulator will move and become neutralized.

Patent Document 1 is a prior art document in this technical field. Patent Document 1 describes a method for promoting the relaxation of accumulated charge on a sample, which is the object of observation with an electron microscope, by reversing the polarity of the voltage applied to the surrounding electrodes.

WO 2018/134870

Patent Document 1 is based on the premise that the polarity of the applied voltage is reversed, but reversing the polarity poses challenges such as increasing the size of the power supply system and speeding up the process until the voltage settles. In particular, for inspection equipment, inspection throughput is an important product value, but the time required for charge relaxation each time directly leads to a decrease in throughput.

In view of the above problems, the present invention aims to provide a charge reduction system that can easily and quickly eliminate charge, an apparatus equipped with the system, and a charge reduction method.

One example of the present invention is a charge reduction system that controls the amount of charge on a target insulator, and is configured to include a pulsed power supply capable of applying a pulsed voltage to the insulator or the electrodes surrounding it, a pulsed power supply control unit that controls the pulsed power supply using parameters that are combinations of the applied voltage width and application time width of the pulsed voltage, an ammeter that measures the amount of charge that flows through the insulator due to the pulsed voltage applied by the pulsed power supply, and a memory unit that stores the relationship between the combination of the applied voltage width and application time width of the pulsed voltage applied to the insulator or the electrodes surrounding it and the amount of charge measured by the ammeter.

The present invention provides a charge reduction system that can easily and quickly eliminate charge, an apparatus equipped with the system, and a charge reduction method.

FIG. 1 is a schematic diagram of a charge relaxation system according to a first embodiment. FIG. 1 is a diagram showing a conventional configuration in which a voltage is applied to an electrostatic chuck. FIG. 2 is a diagram illustrating a configuration for applying a voltage to an electrostatic chuck according to the first embodiment. FIG. 4 is another schematic diagram of the charge relaxation system according to the first embodiment. FIG. 10 is a diagram showing a change in the charge relaxation amount with respect to the voltage application time in Example 1. FIG. 10 is a diagram showing the change in the charge relaxation amount with respect to the applied electric field strength in Example 1. 10 is an operation instruction screen of the charge relaxation system in the first embodiment. 10 is a flowchart of a charge relaxation process in the first embodiment. 1 is a diagram illustrating the configuration of an SEM according to a second embodiment. FIG. 10 is a configuration diagram of another SEM according to the second embodiment. FIG. 11 is a diagram illustrating a configuration for applying a voltage to an object in a film winding process in Example 3.

Embodiments of the present invention will be described below with reference to the drawings. Note that identical components in each drawing will be assigned the same reference numerals, and detailed descriptions of overlapping parts will be omitted.

Figure 1 is a schematic diagram of the charge alleviation system of this embodiment. Figure 1 shows the minimum configuration required to achieve the effects of this embodiment, and in actual use, it is incorporated as part of various products. As shown in Figure 1, a pulsed power supply 130 is connected to an electrode 120 in contact with an insulating object 110, and a pulsed voltage is applied. In other words, Figure 1 shows a configuration in which a pulsed voltage is applied to the electrode in contact with the object, directly applying an electric field to the object. Pulse conditions such as applied voltage, application time, and pulse waveform are controlled by a pulsed power supply control unit 140. In addition, an ammeter 150 is connected to the object 110 to measure the neutralization current. The measured neutralization current data is then integrated with the pulse conditions and stored in a memory unit 160. If the object 110 is an electrostatic chuck, the electrode 120 corresponds to the electrostatic chuck.

The ammeter 150 measures the amount of charge flowing through the insulator using the applied voltage and application time as parameters, and records this as the charge relaxation amount in the memory unit 160. Since the effect of charge relaxation varies depending on the material and shape of the insulator, this evaluation is performed for each material. The conditions for charge relaxation are determined from the resulting charge relaxation amount map, which will be described later. Although this differs depending on the target, if charge relaxation throughput is important, the user can set the conditions, such as increasing the voltage application time.

In Figure 1, when a specific voltage, i.e., a constant potential, is applied to the object, a pulse voltage is applied in addition to it to reduce the charge. For this reason, in this embodiment, the magnitude of the applied voltage is not important, but rather the range of change in the electric field is considered to be the parameter.

Figure 2 shows a conventional configuration in which the electrode 120 in Figure 1 is an electrostatic chuck 121. As shown in Figure 2, a voltage 510 has already been applied to the electrostatic chuck 121 to charge the electrostatic chuck.

Figure 3 shows the configuration in this embodiment when a constant potential is applied to the object. As shown in Figure 3, in order to neutralize the object 110 and the electrostatic chuck 121, a pulse power supply 130 for neutralization is connected in series with a voltage 510.

Figure 4 is another schematic diagram of the charge alleviation system in this embodiment. Figure 4 differs from Figure 1 in that the electrode 120 is not in contact with the object 110. In other words, Figure 4 shows a configuration in which a pulse voltage is applied to an electrode that is not in contact with the object, thereby indirectly applying an electric field to the object. The electrode 120 may be a newly installed neutralization electrode, or an existing electrode may be used. In the case of an SEM, for example, an existing electrode refers to a booster electrode installed in the objective lens to lift up secondary electrons.

Figure 5 shows the relationship between the charge relaxation amount and the voltage application time, i.e., the pulse time width, when a pulse voltage is applied to an insulator in this embodiment. In Figure 5, the applied electric field strength, i.e., the pulse voltage width, is shown as a parameter, and the charge relaxation amount increases in proportion to the voltage application time, and the greater the applied electric field strength, the greater the charge relaxation amount. For example, when a 1 cm x 1 cm _x 1 μm SiO2 is applied with an electric field strength of 20 kV/mm for a voltage application time of 1 second, the charge relaxation amount is approximately 10 nC.

Figure 6 shows the relationship between the applied electric field strength and the amount of charge relaxation in this embodiment. In Figure 6, the voltage application time is shown as a parameter, and the amount of charge relaxation increases in proportion to the applied electric field strength, and the longer the voltage application time, the greater the amount of charge relaxation. Therefore, if you want to speed up throughput, you can set a short voltage application time and then adjust the applied electric field strength to achieve the desired amount of charge relaxation. Alternatively, if there is a limit to the electric field that can be applied, you can fix the applied electric field strength and adjust the voltage application time.

When the electrode on the target is an electrostatic chuck, a charge relaxation amount _Q0 at which detachment abnormalities are eliminated exists for each target, and the voltage application conditions that satisfy _Q0 can be shown as a two-dimensional map of electric field and time. From this, the user can determine the voltage application conditions. Note that since the charge accumulated on the electrostatic chuck is expected to be positive, the electric field is applied in the direction from the electrostatic chuck to the target. If the electrostatic chuck is charged under conditions different from normal and negative charge is accumulated, a reverse electric field can be applied.

Figure 7 shows an operation instruction screen (GUI) for the charge alleviation system in this embodiment. The charge alleviation system shown in Figures 1 and 4 operates under the control of a user via a control device (not shown). The charge alleviation system also has a display device such as a touch panel for displaying an operation screen (not shown) for the user to input control details. Figure 7 shows an example of an operation instruction screen (GUI) for the charge alleviation system on this display device.

7, when a user inputs the name of the object to be neutralized into a neutralization object input section 410, the material and shape of the object to a neutralization object condition input section 420, and the neutralization charge amount _Q0 required for neutralization into a neutralization charge amount input section 430, the control device of the charge relaxation system displays a two-dimensional map of the charge relaxation amount with electric field [kV/mm] and time [sec] as axes in a voltage application condition display section 440. On this map, the user selects voltage application conditions (voltage application time and applied electric field strength) according to the desired charge relaxation amount, inputs the applied electric field strength and voltage application time into a voltage application condition input section 450, and presses an apply button 460 to apply the voltage application conditions selected by the user.

In this case, the name of the object, its material, shape, and the amount of charge to be neutralized may be linked in advance and stored in the storage unit 160 as a database, so that the material, shape, and amount of charge to be neutralized are automatically output simply by entering the name of the material in the neutralization object input unit 410.

Next, an electric field is applied to the object by the pulsed power supply control unit 140 and the pulsed power supply 130, the neutralization current is measured by the ammeter 150, and the amount of charge Q actually neutralized is displayed on the neutralization charge amount output unit 470. If the amount of charge Q matches the neutralization charge _Q0 within an error range specified by the user, neutralization can be completed by pressing the end button 480. If the amount of charge Q differs significantly from the neutralization charge _Q0 , the voltage application conditions can be reselected by pressing the correction button 490.

Figure 8 is a flowchart of the charge reduction process in this embodiment. In Figure 8, a pulse voltage is first applied to the insulator, or the electrodes surrounding it, and the amount of current flowing through the insulator is measured (S610). Next, the pulse voltage conditions, such as the magnitude and duration of the applied pulse voltage, are changed (S620), and S610 and S620 are repeated until measurements are completed under all pulse voltage conditions specified by the user (S630). Once measurements are completed under all pulse voltage conditions, the pulse voltage conditions (magnitude and duration) to be applied to the insulator are determined based on the amount of charge to be reduced (S640). Next, the determined pulse voltage is applied by the pulse power supply (S650), and if the amount of charge reduction calculated from the amount of current flowing through the insulator is equal to or greater than the allowable value (S660), neutralization is completed. If it is equal to or less than the allowable value, the process returns to S640 and the pulse voltage application conditions are redefined.

The pulse voltage magnitude and duration results obtained in steps S610 and S620 of the flowchart in Figure 8 can be stored in a database for each sample, and actual static elimination can start from step S640 of the flowchart.

As described above, according to this embodiment, by controlling the magnitude and duration of the pulse voltage applied depending on the insulator, it is possible to promote the relaxation of the charge on the insulator, and it is possible to provide a charge relaxation system and charge relaxation method that can easily and quickly eliminate charge.

This embodiment describes an example of application of the charge relaxation system shown in Example 1 to an SEM, which is a type of charged particle beam device.

Figure 9 is a diagram of the SEM configuration in this embodiment. In Figure 9, in the SEM 1000, primary electrons 702 emitted from an electron source 701 are imaged onto a sample 706 on a stage 713 by a condenser lens 703, signal electron deflectors 711 and 707, a primary electron deflector 704, and an objective lens 705. The primary electrons on the sample are scanned two-dimensionally by the signal electron deflectors 711 and 707. When the primary electrons 702 irradiate the sample 706, electrons such as secondary electrons and backscattered electrons are emitted from the irradiated area. The emitted electrons are accelerated toward the electron source by an acceleration action based on a negative voltage applied to the sample, and collide with a signal electron aperture 710, generating secondary electrons. The secondary electrons emitted from the signal electron aperture 710 are captured by a detector 709, and the output of the detector 709 changes depending on the amount of captured secondary electrons. The brightness of a display device (not shown) changes depending on this output. For example, when forming a secondary electron image, an image of the scanning area is formed by synchronizing the deflection signals to the signal electron deflectors 711 and 707 with the output of the detector 709.

In this way, SEM irradiates a sample with an electron beam and detects and images the secondary electrons emitted from the sample. Therefore, if the balance between the irradiated electron beam and the emitted secondary electrons is disrupted, the sample will become charged. When the sample becomes charged, the electric field above the sample becomes distorted, causing the electron beam to be deflected or secondary electrons emitted from the sample to be missed. This appears as image distortion and uneven brightness in the detected image, reducing measurement accuracy.

To address this issue, in this embodiment, a pulsed voltage is applied to the stage 713 on which the sample is placed. That is, in FIG. 9, a stage voltage is applied to the sample 706 from the stage power supply 715 to adjust the incident energy of the electron beam, and a pulsed voltage from the pulsed power supply 130 is superimposed on this. The pulsed power supply control unit 140, ammeter 150, and memory unit 160 have the functions described in FIG. 1. In this case, there is no need to reverse the polarity of the voltage applied to the sample; simply apply a voltage that changes the electric field relative to the reference stage voltage. The pulse application duration is on the order of tens of milliseconds to several seconds, allowing charge relaxation to proceed, minimizing the impact on measurement throughput and enabling measurements that eliminate the effects of charge. While FIG. 9 illustrates the application of a voltage to the stage on which the sample is placed, the same effect can be achieved by applying a pulsed voltage to the secondary electron lift electrode 801 in the objective lens directly above the sample 706, as shown in FIG. 10.

In the case of an electron microscope, there is a charge relaxation amount _Q0 at which the sample charge disappears for each object, and the voltage application conditions that satisfy _Q0 can be shown as a two-dimensional map of electric field and time. From this, the user can determine the voltage application conditions.

The SEM operation instruction screen (GUI) in this embodiment is basically the same as in embodiment 1, as shown in Figure 7, but it may also be possible to select the timing of static elimination. Specifically, if the static elimination time exceeds one second, static elimination may be performed after each image capture. Conversely, if static elimination is possible in a short time, such as less than one microsecond, static elimination may be performed after each line of electron beam scanning is completed.

In the case of the SEM in this embodiment, the flowchart for the charge relaxation process is basically the same as that shown in Figure 8. During the first measurement, pulse conditions are created in a database for each specimen/sample (S610-630), and from the next measurement onwards, pulse conditions are identified and used from the database (S640-660). Creating a database of voltage application conditions and static elimination amounts for each object to be observed enables smooth static elimination.

As such, according to this embodiment, by adding a pulsed power supply 130, a pulsed power supply control unit 140, an ammeter 150, and a memory unit 160 to an SEM with a conventional configuration and applying a pulsed voltage to the stage 713, it is possible to provide an SEM that is a charge mitigation system that can easily and quickly eliminate charge, similar to Example 1.

This example describes an application of the charge reduction system shown in Example 1 to a film winding device.

Figure 11 is a diagram of the film winding device in this embodiment. In Figure 11, film 901 is pulled out from roller 902, which has completed winding, by winding roller 903.

Most polymeric materials used in film are excellent insulators, meaning that charges easily accumulate on their surfaces. Charging in film and roller systems can cause problems such as electrostatic discharge, film contamination, and inability to process, reducing the quality of the film. In particular, film take-up rolls are the final step in the film production and processing process, and the charges generated and discharged here are rarely dealt with, directly leading to a reduction in the quality of the film product, which is a major issue.

To solve this problem, in this embodiment, as shown in Figure 11, a static elimination electrode 904 is provided in a position that contacts the pulled-out film 901, and static electricity can be eliminated from the film by applying a pulse voltage.

In the case of a film winding process, a charge relaxation amount _Q0 exists for each object to sufficiently reduce the charge on the film, and the voltage application conditions that satisfy _Q0 can be displayed as a two-dimensional map of electric field and time. From this, the user can determine the voltage application conditions. The operation instruction screen (GUI) and the flowchart of the charge relaxation process are the same as those shown in Example 1.

In this way, this embodiment provides a charge reduction system that can easily and quickly eliminate static electricity, even in a film winding device.

The above describes examples of the present invention, which enable static electricity to be easily and quickly eliminated from objects, thereby resolving the issue of not being able to achieve the expected performance due to static electricity. Therefore, the present invention contributes to achieving a high level of economic productivity through technological improvement and innovation in order to realize the Sustainable Development Goals (SDGs), particularly in goal 8, "Decent Work and Economic Growth."

Furthermore, the present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is also possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

110: Object, 120: Electrode, 121: Electrostatic chuck, 130: Pulse power supply, 140: Pulse power supply control unit, 150: Ammeter, 160: Memory unit, 410: Input unit for object to be neutralized, 420: Input unit for object to be neutralized conditions, 430: Input unit for neutralization charge amount, 440: Display unit for voltage application conditions, 450: Input unit for voltage application conditions, 460: Apply button, 470: Output unit for neutralization charge amount, 48 0: Exit button, 490: Correction button, 510: Voltage, 701: Electron source, 702: Primary electrons, 703, 708: Condenser lens, 704: Primary electron deflector, 705: Objective lens, 706: Sample, 707, 711: Signal electron deflector, 709: Detector, 710: Signal electron aperture, 715: Stage power supply, 801: Secondary electron lift electrode, 904: Neutralization electrode

Claims (9)

A charge mitigation system for controlling the amount of charge on a target insulator,
a pulse power source capable of applying a pulse voltage to the insulator or an electrode surrounding the insulator;
a pulse power supply control unit that controls the pulse power supply using a combination of an applied voltage width and an applied time width of the pulse voltage as a parameter;
an ammeter that measures the amount of charge that flows in the insulator due to the pulse voltage applied by the pulse power supply;
A charge alleviation system characterized by comprising a memory unit that stores the relationship between the combination of the applied voltage width and application time width of the pulse voltage applied to the insulator or the electrodes surrounding it and the amount of charge measured by the ammeter. 10. The charge alleviation system of claim 1,
The pulsed power supply control unit determines the application conditions of the pulsed voltage, ie, the application voltage width and application time width, according to a value obtained by measuring the amount of charge flowing through the insulator due to the application voltage width and application time width of the pulsed voltage applied to the insulator or the electrodes surrounding it, and the amount of charge to be alleviated, and controls the pulsed power supply to apply the pulsed voltage according to the application conditions. 3. The charge alleviation system of claim 2,
a display unit that displays the magnitude of the charge amount relative to the applied voltage width and application time width of the pulse voltage as a two-axis map based on the measured charge amount;
storing the map in the storage unit;
A charge alleviation system characterized by having an input unit in which a user sets application conditions for a pulse voltage based on information from the display unit. 10. The charge alleviation system of claim 1,
the pulse power supply is configured to be capable of applying a pulse voltage superimposed on a specific voltage when a specific voltage is applied to the insulator or an electrode surrounding the insulator in advance,
The pulsed power supply control unit controls the pulsed power supply to apply the pulsed voltage superimposed on the specific voltage, thereby controlling the electric field applied to the insulator or the electrodes surrounding it. 10. The charge alleviation system of claim 1,
The charge alleviation system is characterized in that the pulse power supply control unit changes the application conditions of the pulse voltage to be applied, that is, the applied voltage width and the applied time width, depending on the insulator. 10. The charge alleviation system of claim 1,
the storage unit stores, for each of the insulators, an applied voltage width and an applied time width, which are application conditions of the pulse voltage to be applied;
The pulsed power supply control unit reads and sets the pulsed voltage application conditions stored in the memory unit in accordance with the information on the insulator, and controls the pulsed power supply. A charged particle beam device comprising the charge relaxation system according to any one of claims 1 to 6,
the target insulator is a sample that is a target of the charged particle beam device,
the electrode is a stage on which the sample is placed or an electrode of the charged particle beam device,
A charged particle beam device, characterized in that a pulse voltage is applied from the pulse power supply to a stage on which the sample is placed or to an electrode of the charged particle beam device. A film winding device equipped with the charge alleviation system according to any one of claims 1 to 6,
The target insulator is a film,
the electrode is a static elimination electrode provided at a position where it contacts the film,
A film winding device, characterized in that a pulse voltage is applied to the static elimination electrode by the pulse power supply. A charge alleviation method for controlling the charge amount of a target insulator, comprising:
a pulse power source capable of applying a pulse voltage to the insulator or an electrode surrounding the insulator;
A charge alleviation method characterized by controlling the pulse power supply using parameters that include a combination of the amount of charge flowing into the insulator due to the pulse voltage applied by the pulse power supply, and the applied voltage width and application time width of the pulse voltage.