Noise reduction of high voltage supply voltage

Abstract

A method and high voltage (HV) system can include a noise reduction unit (MNRU) and a bias setting unit (BSU). The HV system can receive an HV supply signal on a high voltage supply line from an HV supply unit. The HV supply unit, the MNRU, the BSU, and an HV charged particle system can share a ground. At least the MNRU can detect noise in the HV supply signal and send a noise compensation signal through the ground. The BSU can receive an indication of a requested value for a bias voltage and apply the bias voltage to the noise-compensated HV signal to provide a biased and noise-compensated HV signal to the HV charged particle system.

Description

TECHNICAL FIELD

[0001] The present disclosure claims priority to U.S. Application No. 16 / 885,740, filed May 28, 2020, the disclosure of which is incorporated herein by reference in its entirety and for all purposes.

[0002] A scanning electron microscope (SEM) is a wafer semiconductor foundry tool that produces an image of a sample, such as a wafer, by illuminating the wafer with a focused electron beam (e-beam) and detecting secondary electrons from the wafer. The secondary electrons give information about the wafer topology, defects, and critical dimensions. BACKGROUND

[0003] The SEM can be used for defect review at nanometer resolution, critical dimension measurement, and wafer inspection.

[0004] The high precision of the SEM makes it an attractive tool for monitoring multiple manufacturing stages of a sample, such as a wafer.

[0005] To generate and control the e-beam, high voltage signals should be applied to multiple electrodes and parts in the SEM.

[0006] The increased resolution required by the SEM makes the SEM very sensitive to noise, chatter, and fluctuations in the high voltage supply signals.

[0007] Multiple noise sources can be found in the SEM (e.g., noise from various high voltage modules, cables, and connectors) and outside the SEM.

[0008] There is a need to provide a system and method that is important to overcome the high voltage supply signal stabilization and precision changes to improve tool performance. SUMMARY

[0009] A method and system for noise reduction for high voltage supply signals can be provided to provide a highly stable high voltage supply signal. BRIEF DESCRIPTION OF DRAWINGS

[0010] The subject matter regarded as the embodiments of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. The embodiments, however, can be best understood from the following description in conjunction with the accompanying drawings. Figure One The embodiments of the present disclosure will be best understood by reference to the following detailed description of embodiments when read with the accompanying drawings, in which:

[0011] Figure 1 Examples of a high voltage system, a high voltage supply unit, and a high voltage charged particle system are shown;

[0012] Figure 2 Examples of a noise reduction unit are shown;

[0013] Figure 3 An example of a bias setting unit is shown; and

[0014] Figure 4 An example of a method is shown. DETAILED DESCRIPTION

[0015] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present disclosure.

[0016] However, it will be understood by those skilled in the art that the embodiments of the present disclosure can be practiced without such specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments of the present disclosure.

[0017] What is regarded as the subject matter of the embodiments of the present disclosure is particularly pointed out and distinctly claimed in the conclusion part of the specification. However, both the organization and method of operation, together with objects, features, and advantages thereof, will be best understood from the following detailed description when read in Figure One The embodiments of the present disclosure will be best understood from the following detailed description when read in conjunction with the accompanying drawings.

[0018] It will be understood that, for clarity's sake, the elements shown in the drawings are not necessarily to scale. For example, the dimensions of certain components can be exaggerated relative to other components for clarity. Also, where considered appropriate, reference numerals have been repeated among the figures to indicate corresponding or analogous elements.

[0019] Since the illustrated embodiments of the present disclosure can be mostly implemented using electronic components and circuits known to those skilled in the art, the details will not be explained to a greater extent than the essentials necessary for the understanding and appreciation of the basic concepts of the embodiments of the present disclosure and in order not to obscure or dilute the teachings of the embodiments of the present disclosure.

[0020] Any reference in the specification to a method should be considered as applying also to a system capable of executing the method.

[0021] Any reference in the specification to a system should be considered as applying also to a method that can be executed by the system.

[0022] The word "and / or" means additional or alternative.

[0023] Figure 1 A high voltage system 100, a high voltage supply unit 90 and a high voltage charged particle system 80 are shown.

[0024] The high voltage system 100 can comprise a noise reduction unit 110 and a bias setting unit 120.

[0025] The noise reduction unit 110 and the bias setting unit 120 can be configured to receive the high voltage supply signal 61 from the high voltage supply line 70. The high voltage supply signal 61 can be output from the high voltage supply port 92 of the high voltage supply unit 90.

[0026] The first port 101 of the high voltage system 100 receives the high voltage supply signal 61.

[0027] The noise reduction unit 110 and the bias setting unit 120 can be coupled to the ground 94. The ground 94 can also be shared by the high voltage charged particle system 80 and the high voltage supply unit 90.

[0028] The second port 102 of the high voltage system 100 is connected to the ground 94. The second port 102 is also connected to the output port of the bias setting unit 120.

[0029] The noise reduction unit 110 or the combination of the noise reduction unit 110 and the bias setting unit 120 can be configured to detect noise in the high voltage supply signal 61 and send a noise compensation signal 62 through the ground 94 to compensate for the noise in the high voltage supply signal 61.

[0030] It should be understood that the use of the bias setting unit 120 alone can provide noise compensation. However, the use of the bias setting unit 120 alone provides less effective noise reduction compared to the noise reduction obtained by the combination of the noise reduction unit 110 and the bias setting unit 120.

[0031] Figure 1 The input to the noise reduction unit 110 is shown connected between the high voltage supply unit 90 and the bias setting unit 120. However, the input can be located between the bias setting unit 120 and the high voltage charged particle system 80.

[0032] The bias setting unit 120 can be configured to receive an indication of a requested value for a bias voltage (or receive a bias voltage 63) and to apply the bias voltage (from the first port 101) to the high voltage signal in order to provide a biased and noise compensated high voltage signal 65 to the high voltage input port 81 of the high voltage charged particle system 80. The biased and noise compensated high voltage signal 65 can be output via the third port 103 of the high voltage system 100.

[0033] The high voltage supply signal 61 can exceed one hundred volts, five hundred volts, one thousand volts, five thousand volts, or even higher.

[0034] The bias setting unit 120 can be configured to apply the bias voltage 63 with a precision that can be much smaller than the high voltage supply signal 61. While the high voltage supply signal can exceed one thousand volts, the bias voltage can be provided with a precision (resolution) in the order of millivolts.

[0035] The high voltage system 100 can include an activation port 130 for receiving an ON / OFF signal (activation / deactivation signal) 68 to turn on or off the high voltage system 100. A bypass path can be provided between the first port 101 and the third port 130 and can be selectively applied when deactivating the high voltage system 100.

[0036] The high voltage charged particle system 80 can be configured to generate one or more charged particle beams, such as one or more ion beams, one or more electron beams, etc. The high voltage charged particle system 80 can be a scanning electron microscope, an electron imager, a milling system, etc.

[0037] The noise reduction unit 110 can be configured to compensate for noise over a span of noise frequency ranges between less than one hertz to more than one megahertz.

[0038] Figure 2 An example of the noise reduction unit 110 is shown.

[0039] The noise reduction unit 110 can include an amplifier 112 and a first low pass filter 111. The first low pass filter 111 can be configured to low pass filter the high voltage supply signal 61 to provide a low pass filtered high voltage supply signal 66, and (b) the amplifier 112.

[0040] The amplifier 112 includes a positive input (labeled “+”) and a negative input (labeled “-”). The positive input is configured to receive the high voltage supply signal 61. The negative input is configured to receive the low pass filtered high voltage supply signal 66. The amplifier 112 is further fed by supply voltages 144 and 145.

[0041] The amplifier 112 is configured to compare the high voltage supply signal 61 to the low pass filtered high voltage supply signal 66 and provide a comparator output signal 67.

[0042] The comparator output signal 67 is indicative of the result of the comparison. The result of the comparison can be indicative of the presence of noise in the high voltage supply signal 61.

[0043] The first low pass filter 111 can be formed by an eighth resistor 148 and a first capacitor 150. The noise reduction unit 110 can include other low pass filters.

[0044] A second capacitor 149 is coupled between an output port of the amplifier 112 and the ground 94 (via the second port 102). The amplifier 112 can be coupled to a virtual ground (not shown).

[0045] The noise reduction unit 110 can include one or more additional components (not shown) that can be configured to transform the comparator output signal 67 into the noise compensated signal 62. The transformation can include impedance matching, voltage to current transformation, etc. For example, the comparator output signal 67 can be a voltage signal that can change its value according to changes in the difference between the high voltage supply signal 61 and the low pass filtered high voltage supply signal 66. The voltage change causes a change in the current that flows through the second capacitor 149 and through ground.

[0046] The second capacitor 149 can be replaced by any network of resistors, capacitors, inductors, and / or semiconductors that can be configured to increase the current flow when a higher voltage is applied. For example, the second capacitor 149 can be replaced by a resistor, an inductor, a Zener diode, and a capacitor connected in series with each other.

[0047] The cutoff frequency of the first low pass filter 111 can be any value, for example, the cutoff frequency can be lower than ten Hertz and can even be lower than one Hertz.

[0048] Figure 3 An example of the bias setting unit 120 is shown.

[0049] The bias setting unit 120 can include an amplifier 112, a first resistor 141, a second resistor 142, a third resistor 143, a sixth resistor 146, a seventh resistor 147, an eighth resistor 148, a first capacitor 150, and a second capacitor 149.

[0050] The amplifier 112 includes a positive input (labeled "+") and a negative input (labeled "-"). The bias voltage 63 is provided to the positive input of the amplifier 112. The amplifier 112 is also fed by supply voltages 144 and 145.

[0051] The first resistor 141 is a series resistor that separates the source and the load. The first end of the first resistor is coupled to the first port 101. The second end of the first resistor 141 is connected to the virtual ground 96 and to the third port 103. The second resistor 142 and the third resistor 143 form an amplifier offset compensation network.

[0052] The sixth resistor 146 and the first capacitor 150 form a second low pass filter.

[0053] The seventh resistor 147 and the eighth resistor 148 can be added to improve the high voltage immunity of the bias setting unit 120. The second capacitor 149 and the seventh resistor 147 are between the output port of the amplifier 112 and the ground 94.

[0054] The bias setting unit 120 can perform noise compensation in substantially the same manner as the bias setting unit, resulting in a current flowing through the second capacitor 149.

[0055] The bias setting unit 120 can perform noise compensation by generating a voltage drop across the first resistor 141, which is the correction voltage needed to compensate for the noise, and thus the voltage drop across the first resistor 141 should be equal to or close to the noise.

[0056] The first resistor 141 can be replaced by any network of resistors, inductors, capacitors, and semiconductor elements such as diodes. For example, the first resistor can be replaced by a resistor, a capacitor, and a diode connected in parallel to each other.

[0057] Figure 4 A method 200 for high voltage noise reduction is shown.

[0058] The method 200 can include steps 210, 220, 230, 240, 250, and 260.

[0059] The step 210 can include receiving a high voltage supply signal by a noise reduction unit and a bias setting unit. The high voltage supply signal is received over a high voltage supply line and from a high voltage supply port of a high voltage supply unit. The noise reduction unit and the bias setting unit are coupled to a ground, which is also shared by a high voltage charged particle system and the high voltage supply unit.

[0060] The step 210 can be followed by a step 220 of detecting noise in the high voltage supply signal by at least the noise reduction unit.

[0061] The at least noise reduction unit represents (i) a noise reduction or (ii) a noise reduction and an additional unit, such as a bias setting unit.

[0062] The step 220 can be followed by a step 230 of generating a noise compensation signal for compensating the noise in the high voltage signal.

[0063] The step 230 can be followed by a step 240 of sending the noise compensation signal through the ground.

[0064] The method 200 can further include a step 250 of applying a bias voltage to the high voltage signal (following the step 240 of compensating the noise) to provide a biased and noise compensated high voltage signal.

[0065] Multiple iterations of the steps 210, 220, 230, 240, and 250 can be provided to maintain the high voltage supply signal at a noise compensated value. The repetition can be performed in a continuous manner or in iterations spaced apart.

[0066] Step 250 can be followed by step 260 of providing the biased and noise-compensated high voltage signal to a high voltage input port of the high voltage charged particle system.

[0067] Step 230 can comprise a sequence of steps 231, 233 and 235.

[0068] Step 231 can comprise low-pass filtering the high voltage supply signal by a low-pass filter to provide a low-pass filtered high voltage supply signal.

[0069] Step 233 can comprise comparing the high voltage supply signal to the low-pass filtered high voltage supply signal by a comparator.

[0070] Step 235 can comprise providing a comparator output signal indicative of a result of the compensation, wherein the result of the compensation is an indication of noise in the high voltage supply signal.

[0071] Step 230 can further comprise step 237 of transforming the comparator output signal into a noise compensation signal by one or more additional components of the noise reduction unit.

[0072] The proposed solution is found to provide at least 20 dB noise reduction over a wide range of noise frequencies (e.g. between less than one hertz and higher than one megahertz).

[0073] Although the high voltage supply signal can exceed one hundred volts, the bias voltage can be provided with a precision (resolution) in the order of millivolts. This enables a precise adjustment of the electron beam generated by the SEM supplied with the noise-compensated high voltage supply voltage.

[0074] The solution further provides for an improved high voltage arc immunity.

[0075] In the above specification, the embodiments of the disclosure have been described with reference to specific examples of embodiments of the disclosure. It is clear, however, that various modifications and changes can be made without departing from the broader spirit and scope of the embodiments of the disclosure as set forth in the appended claims.

[0076] Any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermediate components. Likewise, any two components so associated can also be viewed as being "operatively connected", or "operatively coupled", to each other to achieve the desired functionality.

[0077] Moreover, those skilled in the art will appreciate that the functions of the various steps need not be performed in the precise order described. The illustrative embodiments of the present disclosure have been described herein with reference to acts and symbolic representations of operations (e.g., in the form of flowcharts) that are performed by one or more devices, unless indicated otherwise. As such, it will be understood that the various

[0078] Also by way of example, in one embodiment, the examples of icons can be implemented as circuitry located on a single integrated circuit or in the same device. Alternatively, the examples can be implemented as any number of separate integrated circuits or separate devices interconnected with each other in a suitable manner.

[0079] However, other modifications, changes, and substitutions are also possible. The description and the accompanying drawings are therefore to be regarded in an illustrative rather than a restrictive sense.

[0080] In the claims, any reference signs placed between two consecutive dashes ( — ) should not be construed as a limitation on the scope of the claims. The word comprising does not exclude the presence of additional elements or steps than those listed in a claim. Furthermore, the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. It is also understood that an element denoted by a preceded by "each" should not be construed as implying that a limitation is made to a single element but that a plurality of elements can be present. Also, the use of introductory phrases such as "at least one" and "one or more" in

[0081] While certain features of the embodiments of the disclosure have been illustrated and described, many modifications, substitutions, changes, and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended drawings are intended to illustrate and describe, not limit, the true spirit and scope of the embodiments of the disclosure.

[0082] Any combination of any of the modules or units listed in any of the accompanying drawings, the description, and / or any of the claims can be provided. In particular, any combination of any of the claimed features can be provided.

[0083] Any reference to "comprising" or "containing" etc. should be construed as meaning "consisting essentially of" or "consisting of". For example, a method comprising certain steps can respectively include additional steps, can be limited to certain steps, or can include additional steps that do not materially affect the basic and novel characteristics of the method.

[0084] The above description includes specific examples of one or more embodiments. However, it is apparent that various modifications and changes can be made without departing from the spirit and scope of one or more embodiments as set forth in the appended claims.

Claims

1. A high voltage system, the high voltage system comprising: a noise reduction unit; and a bias setting unit; wherein the noise reduction unit and the bias setting unit are configured to receive a high voltage supply signal on a high voltage supply line and from a high voltage supply unit; wherein the noise reduction unit and the bias setting unit are coupled to a ground, the ground also shared by a high voltage charged particle system and the high voltage supply unit; wherein the noise reduction unit is configured to detect noise in the high voltage supply signal and to send a noise compensation signal for compensating the noise through the ground to provide a noise compensated high voltage signal; and wherein the bias setting unit is configured to receive an indication of a requested value for a bias voltage and to apply the bias voltage to the noise compensated high voltage signal to provide a biased and noise compensated high voltage signal to the high voltage charged particle system.

2. The high voltage system of claim 1, wherein the noise reduction unit comprises (a) a low pass filter configured to low pass filter the high voltage supply signal to provide a low pass filtered high voltage supply signal and (b) a comparator configured to compare the high voltage supply signal to the low pass filtered high voltage supply signal and to provide a comparator output signal, the comparator output signal indicating the noise in the high voltage supply signal.

3. The high voltage system of claim 2, wherein a cutoff frequency of the low pass filter is below ten hertz.

4. The high voltage system of claim 2, wherein a cutoff frequency of the low pass filter is below one hertz.

5. The high voltage system of claim 1, wherein the high voltage supply signal exceeds one hundred volts and wherein the bias setting unit is configured to apply the bias voltage with an accuracy of less than ten millivolts.

6. The high voltage system of claim 1, comprising an activation port for receiving an activation signal and a deactivation signal.

7. The high voltage system of claim 1, wherein the high voltage charged particle system is a scanning electron microscope.

8. The high voltage system of claim 1, wherein the noise reduction unit is configured to compensate the noise over a noise frequency range of less than one hertz or more than one megahertz.

9. A method for high voltage noise reduction, the method comprising: receiving, by a noise reduction unit and a bias setting unit, a high voltage supply signal on a high voltage supply line and from a high voltage supply unit; wherein the noise reduction unit and the bias setting unit are coupled to a ground, the ground also shared by a high voltage charged particle system and the high voltage supply unit; detecting, by at least the noise reduction unit, noise in the high voltage supply signal; generating a noise compensation signal for compensating the noise to provide a noise compensated high voltage signal; receiving an indication of a requested value for a bias voltage; sending the noise compensation signal through the ground; applying the bias voltage to the noise compensated high voltage signal to provide a biased and noise compensated high voltage signal; and ​ providing the biased and noise-compensated high voltage signal to the high voltage charged particle system.

10. The method of claim 9, wherein generating the noise-compensated signal comprises: low-pass filtering the high voltage supply signal through a low-pass filter to provide a low-pass filtered high voltage supply signal; comparing the high voltage supply signal to the low-pass filtered high voltage supply signal through a comparator; and providing a comparator output signal indicative of the noise in the high voltage supply signal.

11. The method of claim 10, wherein a cutoff frequency of the low-pass filter is less than ten Hertz.

12. The method of claim 10, wherein a cutoff frequency of the low-pass filter is less than one Hertz.

13. The method of claim 9, wherein the high voltage supply signal exceeds one hundred Volts, and wherein the biasing unit is configured to apply the bias voltage with a precision of less than ten millivolts.

14. The method of claim 9, comprising: selectively activating and deactivating the noise reduction unit based on an activation signal and a deactivation signal.

15. The method of claim 9, wherein the high voltage charged particle system is a scanning electron microscope.

16. The method of claim 9, comprising compensating for the noise over a noise frequency range of less than one Hertz or greater than one Megahertz.

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