Image contrast enhancement in sample inspection

Abstract

SUMMARY OF THE INVENTION A method and apparatus for inspecting (eg, viewing, measuring, and imaging) samples such as wafers and masks used in device manufacturing processes, such as integrated circuit (IC) manufacturing, is disclosed. [Solution] Disclosed herein is a method comprising depositing a first amount of charge in a region of a sample for a first time period, depositing a second amount of charge in the region for a second time period, and scanning a probe spot created on the sample by the charged particle beam while recording a signal from the probe spot representative of the interaction of the charged particle beam with the sample, wherein the average deposition rate during the first time period is different from the average deposition rate during the second time period.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS)

[0001] This application claims priority to U.S. Application No. 62 / 566,195, filed September 29, 2017, which is incorporated by reference in its entirety herein.

[0002] This disclosure relates to methods and apparatus for inspecting (eg, viewing, measuring, imaging) samples such as wafers and masks used in device manufacturing processes, such as the manufacture of integrated circuits (ICs). [Background technology]

[0003]

[0003] A device manufacturing process may include applying a desired pattern to a substrate. A patterning device, alternatively referred to as a mask or reticle, may be used to generate the desired pattern. This pattern may be transferred onto a target portion (e.g. comprising part of one or several dies) on the substrate (e.g. a silicon wafer). Transfer of the pattern is typically achieved by imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. A substrate may contain a network of adjacent target portions which are successively patterned. A lithographic apparatus may be used for this transfer. One type of lithographic apparatus is called a stepper, in which each target portion is irradiated by exposing the entire pattern onto the target portion in one go. Another type of lithographic apparatus is called a scanner, in which each target portion is irradiated by scanning a beam of radiation in a given direction while synchronously scanning the substrate parallel or anti-parallel to the given direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004]

[0004] To monitor one or more steps of a device manufacturing process (e.g., exposure, resist treatment, etching, developing, baking, etc.), a sample, such as a substrate patterned by the device manufacturing process or a patterning device used therein, may be inspected to measure one or more parameters of the sample. The one or more parameters may include, for example, edge placement error (EPE), which is the distance between an edge of a pattern on the substrate or patterning device and the corresponding edge of the intended design of the pattern. Inspection may also find pattern defects (e.g., poor connection or separation) and extraneous particles.

[0005]

[0005] Inspection of substrates and patterning devices used in device manufacturing processes can help improve yield. Information gained from inspection can be used to identify defects or to adjust the device manufacturing process. Summary of the Invention

[0006]

[0006] Disclosed in this specification is a method comprising depositing a first amount of charge in a region of a sample for a first time period, depositing a second amount of charge in the region for a second time period, and scanning a probe spot created on the sample by the charged particle beam while recording a signal from the probe spot representative of an interaction of the charged particle beam with the sample, wherein an average deposition rate for the first time period differs from an average deposition rate for the second time period.

[0007]

[0007] According to one embodiment, the method further includes repeating depositing a first amount of charge in the region for a first period of time and depositing a second amount of charge in the region for a second period of time.

[0008] According to one embodiment, the first amount or the second amount is zero.

[0009] According to one embodiment, the first amount and the second amount are different.

[0010] According to one embodiment, the length of the first period and the length of the second period are different.

[0011] According to one embodiment, the region has a non-uniform spatial distribution of a chemical or physical property.

[0012]

[0012] According to one embodiment, the chemical or physical property is selected from the group consisting of composition, doping level, electrical resistance, electrical capacitance, electrical inductance, thickness, crystallinity, and dielectric constant.

[0013] According to one embodiment, depositing the first amount of charge or depositing the second amount of charge is performed using a beam of charged particles.

[0014]

[0014] According to one embodiment, depositing the first amount of charge or depositing the second amount of charge is not performed using a beam of charged particles, but using a separate beam comprising an electric charge.

[0015] According to one embodiment, the other beam has a cross-sectional area at least twice the cross-sectional area of ​​the beam of charged particles.

[0016]

[0016] According to one embodiment, the region comprises a first subregion and a second subregion, and a rate of change of the amount of charge dissipated from the first subregion is different from a rate of change of the amount of charge dissipated from the second subregion.

[0017]

[0017] According to one embodiment, the region comprises a first subregion and a second subregion, and the rate of change of the amount of charge deposited in the first subregion is the same as the rate of change of the amount of charge deposited in the second subregion.

[0018]

[0018] According to one embodiment, the region comprises a first subregion and a second subregion, and a net rate of change of the amount of charge in the first subregion is different from a net rate of change of the amount of charge in the second subregion.

[0019]

[0019] According to one embodiment, the region comprises a first subregion and a second subregion, and the net rate of change of the amount of charge in the first subregion or the net rate of change of the amount of charge in the second subregion is negative.

[0020]

[0020] According to one embodiment, the region comprises a first subregion and a second subregion, and the difference between the amount of charge in the first subregion and the amount of charge in the second subregion increases over time.

[0021] According to one embodiment, the region comprises sub-regions, and the amount of charge in the sub-regions is zero during a portion of the second period.

[0022]

[0022] Disclosed herein is a computer program product comprising a non-transitory computer readable medium having instructions recorded thereon which, when executed by a computer, perform any of the methods described above.

[0023]

[0023] Disclosed herein is an apparatus configured to inspect a sample, the apparatus including a source of charged particles, a stage, optical components configured to direct a beam of charged particles toward a sample supported on the stage, and a controller configured to control the source and optical components, where the source, optical components, and controller are collectively configured to deposit a first amount of charge in a region of the sample during a first time period and to deposit a second amount of charge in that region during a second time period, wherein an average deposition rate for the first time period differs from the average deposition rate for the second time period.

[0024]

[0024] According to one embodiment, the apparatus further comprises a detector configured to record a signal representative of the interaction of the beam with the sample.

[0025] According to one embodiment, the source, optical components and controller are collectively configured to generate a signal.

[0026]

[0026] According to one embodiment, the optical component is configured to scan a probe spot formed on the sample by the beam relative to the sample.

[0027]

[0027] According to one embodiment, the stage is configured to move the sample. [Brief description of the drawings]

[0028] [Figure 1] 1 illustrates generally an apparatus capable of performing charged particle beam inspection. [Figure 2A]

[0029] 1 shows a schematic representation of an apparatus capable of performing charged particle beam inspection using multiple beams of charged particles, the charged particles of the multiple beams originating from a single source (a "multi-beam" apparatus); [Figure 2B]

[0030] 1 illustrates diagrammatically an alternative multi-beam device; [Figure 2C]

[0031] 1 illustrates diagrammatically an alternative multi-beam device; [Diagram 3]

[0032] A region of the sample is shown diagrammatically as an example. [Figure 4]

[0033] 1 illustrates a schematic of an example in which the chemical and physical properties of a sample are used to generate spatial contrast in a signal representative of the interaction of a beam of charged particles with the sample. [Figure 5A]

[0034] 1 shows a schematic example for illustrating the influence of charge deposition characteristics on the inspection. [Figure 5B]

[0034] An example is shown diagrammatically to illustrate the influence of charge deposition characteristics on the inspection. [Figure 5C]

[0034] An example is shown diagrammatically to illustrate the influence of charge deposition characteristics on the inspection. [Figure 5D]

[0034] An example is shown diagrammatically to illustrate the influence of charge deposition characteristics on the inspection. [Figure 6A]

[0034] An example is shown diagrammatically to illustrate the influence of charge deposition characteristics on the inspection. [Figure 6B]

[0034] An example is shown diagrammatically to illustrate the influence of charge deposition characteristics on the inspection. [Figure 6C]

[0034] An example is shown diagrammatically to illustrate the influence of charge deposition characteristics on the inspection. [Figure 6D]

[0034] An example is shown diagrammatically to illustrate the influence of charge deposition characteristics on the inspection. [Figure 7A]

[0034] An example is shown diagrammatically to illustrate the influence of charge deposition characteristics on the inspection. [Figure 7B]

[0034] An example is shown diagrammatically to illustrate the influence of charge deposition characteristics on the inspection. [Figure 7C]

[0034] An example is shown diagrammatically to illustrate the influence of charge deposition characteristics on the inspection. [Figure 7D]

[0034] An example is shown diagrammatically to illustrate the influence of charge deposition characteristics on the inspection. [Figure 8]

[0035] 1 shows a flow chart of a method for inspecting a sample using a beam of charged particles, according to one embodiment. [Figure 9]

[0036] 1 illustrates a schematic component diagram of an apparatus configured to inspect a sample using a beam of charged particles, according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029]

[0037] There are various techniques for inspecting samples (e.g. substrates and patterning devices). One type of inspection technique is optical inspection, in which a light beam is directed at the substrate or patterning device and signals representative of the interaction of the light beam with the sample (e.g. scattering, reflection, diffraction) are recorded. Another type of inspection technique is charged particle beam inspection, in which a beam of charged particles (e.g. electrons) is directed at the sample and signals representative of the interaction of the charged particles with the sample (e.g. secondary emission and backscattered emission) are recorded.

[0030]

[0038] The term "or" as used herein includes all possible combinations unless specifically specified otherwise and unless impracticable. For example, if it is stated that a database may comprise A or B, the database may comprise A, or B, or A and B, unless specifically specified otherwise or unless impracticable. As a second example, if it is stated that a database may comprise A, B, or C, the database may comprise A, or B, or C, or A and B, or A and C, or B and C, or A and B and C, unless specifically specified otherwise or unless impracticable.

[0031]

[0039] 1 shows a schematic diagram of an apparatus 100 capable of performing charged particle beam inspection. The apparatus 100 may include components configured to generate and control a beam of charged particles, such as a source 10 capable of generating charged particles in free space, a beam extraction electrode 11, a focusing lens 12, a beam blanking deflector 13, an aperture 14, a scanning deflector 15, and an objective lens 16. The apparatus 100 may also include components configured to detect signals representative of the interaction of the beam of charged particles with a sample, such as an E×B charged particle diversion device 17, a signal detector 21, and the like. The apparatus 100 may also include components, such as a processor, configured to process the signals or to control other components.

[0032]

[0040] In one example of an inspection process, a beam of charged particles 18 is directed at a sample 9 (e.g., a wafer or mask) positioned on a stage 30. A signal 20 representative of the interaction of the beam 18 with the sample 9 is directed by an E×B charged particle diversion device 17 to a signal detector 21. A processor may move the stage 30 or cause the beam 18 to scan.

[0033]

[0041] Charged particle beam inspection can have higher resolution than optical inspection because it uses charged particles with shorter wavelengths than those used in optical inspection. As device manufacturing processes evolve, charged particle beam inspection becomes more widely used as the dimensions of features on substrates and patterning devices become smaller and smaller.

[0034]

[0042] In some examples, multiple beams of charged particles will scan multiple regions on the sample simultaneously. The scanning of the multiple beams may be synchronized or independent. The multiple regions may have overlap with each other, may be tilted to cover a contiguous area, or may be isolated from each other. Signals generated from the interaction of the beams with the sample may be collected by multiple detectors. The number of detectors may be less than, equal to, or greater than the number of beams. The multiple beams may be individually or collectively controlled.

[0035]

[0043] Multiple beams of charged particles may form multiple probe spots on the surface of the sample. The probe spots may scan multiple areas on the surface individually or simultaneously. The charged particles of the beam may generate a signal from the location of the probe spot. One example of a signal is a secondary electron. Secondary electrons typically have an energy less than 50 eV. Another example of a signal is a backscattered electron when the charged particles of the beam are electrons. Backscattered electrons typically have an energy close to the landing energy of the electrons of the beam. The signal from the location of the probe spot may be collected by multiple detectors individually or simultaneously.

[0036]

[0044] The multiple beams may each originate from multiple sources or may originate from a single source. If the beams originate from multiple sources, multiple columns may scan and focus the beams onto the surface, and the signals generated by the beams may be detected by detectors in each column. An apparatus using beams from multiple sources may be referred to as a multi-column apparatus. The columns may be independent or may share a multi-axis magnetic or electromagnetic compound objective lens. See U.S. Pat. No. 8,294,095, the disclosure of which is incorporated herein by reference in its entirety. The probe spots generated by a multi-column apparatus may be spaced apart by distances on the order of 30-50 nm.

[0037]

[0045] If the beam originates from a single source, multiple virtual or real images of the single source may be formed using a source conversion unit. Each of the images and the single source may be considered as an emitter of the beam (may be referred to as a "beamlet" since all of the beamlets originate from the same source). The source conversion unit may have a conductive layer with multiple apertures that can split the charged particles from the single source into multiple beamlets. The source conversion unit may have optical elements that can affect the beamlets to form multiple virtual or real images of the single source. Each of the images may be considered as a source that emits one of the beamlets. The beamlets may be spaced apart by a distance of several micrometers. A single column, which may have a projection system and a deflection scanning unit, may be used to scan and focus the beamlets on multiple areas of the sample. Each signal generated by the beamlet may be detected by multiple detection elements of a detector in a single column. An apparatus using a beam from a single source may be referred to as a multi-beam apparatus.

[0038]

[0046] There are at least two ways to form an image of a single source. In the first way, each optical element has an electrostatic microlens that focuses one beamlet, thereby forming one real image. See, for example, U.S. Pat. No. 7,244,949, the disclosure of which is incorporated herein by reference in its entirety. In the second way, each optical element has an electrostatic microdeflector that deflects one beamlet, thereby forming one virtual image. See, for example, U.S. Pat. No. 6,943,349 and U.S. Patent Application No. 15 / 065,342, the disclosures of which are incorporated herein by reference in their entirety. Because the real image has a higher current density, the interaction between charged particles (e.g., Coulomb effect) in the second way will be weaker than that in the first way.

[0039]

[0047] FIG. 2A shows a schematic diagram of an apparatus 400 capable of performing charged particle beam inspection using multiple beams of charged particles, the charged particles in the multiple beams originating from a single source. That is, the apparatus 400 is a multi-beam apparatus. The apparatus 400 has a source 401 capable of generating charged particles in free space. In one example, the charged particles are electrons, and the source 401 is an electron gun. The apparatus 400 has an optical system 419 capable of generating multiple probe spots on the surface of a sample 407 with the charged particles and scanning the probe spots on the surface of the sample 407. The optical system 419 may have a condenser lens 404 and a main aperture 405 upstream or downstream with respect to the condenser lens 404. The expression "component A is upstream with respect to component B" as used herein means that during normal operation of the apparatus, the beam of charged particles will reach component A before reaching component B. The expression "component B is downstream with respect to component A" as used herein means that during normal operation of the device, the beam of charged particles will reach component B after reaching component A. The optical system 419 comprises a source conversion unit 410 configured to form a plurality of virtual images of the source 401 (e.g., virtual images 402 and 403). The virtual images and the source 401 may each be considered as emitters of beamlets (e.g., beamlets 431, 432, and 433). The source conversion unit 410 may comprise a conductive layer 412 with a plurality of apertures capable of splitting the charged particles from the source 401 into a plurality of beamlets, and an optical element 411 capable of influencing the beamlets to form a virtual image of the source 401. The optical element 411 may be a micro-deflector configured to deflect the beamlets. The current of the beamlets may be influenced by the size of the aperture of the conductive layer 412 or the focusing power of the focusing lens 404. The optical system 419 includes an objective lens 406 configured to focus the multiple beamlets and thereby form multiple probe spots on the surface of the sample 407 .The source transformation unit 410 may also include a micro-compensator configured to reduce or eliminate aberrations of the probe (eg, field curvature and astigmatism).

[0040]

[0048] FIG. 2B shows a schematic representation of an alternative multi-beam device. The condenser lens 404 collimates the charged particles from the source 401. The optical element 411 of the source conversion unit 410 may comprise a micro-compensator 413. The micro-compensator 413 may be separate from the micro-deflector or may be integral with the micro-deflector. If separate, the micro-compensator 413 may be positioned upstream of the micro-deflector. The micro-compensator 413 is configured to compensate for off-axis aberrations (e.g. field curvature, astigmatism and distortion) of the condenser lens 404 or the objective lens 406. The off-axis aberrations may adversely affect the size or position of the probe spot formed by the off-axis (i.e. not along the primary optical axis of the device) beamlets. The off-axis aberrations of the objective lens 406 will not be completely eliminated by deflection of the beamlets. The microcompensators 413 may compensate for residual off-axis aberrations of the objective lens 406 (i.e., the portion of the off-axis aberrations that cannot be eliminated by deflecting the beamlets) or non-uniformity in the size of the probe spot. Each of the microcompensators 413 is aligned with one of the apertures in the conductive layer 412. The microcompensators 413 may each have four or more poles. The current of the beamlets may be influenced by the size of the apertures in the conductive layer 412 and / or the position of the focusing lens 404.

[0041]

[0049] 2C shows a schematic representation of an alternative multi-beam device. The optical element 411 of the source conversion unit 410 may comprise a pre-bending micro-deflector 414. The pre-bending micro-deflector 414 is a micro-deflector configured to bend the beamlets before passing through the apertures in the conductive layer 412.

[0042]

[0050] Further description of devices using multiple beams of charged particles from a single source may be found in U.S. Patent Application Publication Nos. 2016 / 0268096, 2016 / 0284505, and 2017 / 0025243, U.S. Patent No. 9,607,805, U.S. Patent Application Nos. 15 / 365,145, 15 / 213,781, 15 / 216,258, and 62 / 440,493, and PCT Application No. PCT / US17 / 15223, the disclosures of which are incorporated herein by reference in their entireties.

[0043]

[0051] When an area of ​​a sample (e.g., a substrate or a patterning device) is probed with a beam of charged particles, a signal representative of the interaction of the beam with the sample is recorded from a probe spot formed by the beam in that area. The interaction represented by the signal may include an interaction of the charged particles of the beam with charges of the sample. The charges that may interact with the charged particles of the beam may be internal to the sample. Thus, the spatial distribution of charges in the sample may be used to create a spatial contrast of the signal.

[0044]

[0052] The spatial distribution of charge can vary significantly within a sample. The spatial distribution of chemical and physical properties in a sample can affect the spatial distribution of charge. Examples of these properties may include composition, doping level, electrical resistance, electrical capacitance, electrical inductance, thickness, crystallinity, dielectric constant, etc. FIG. 3 shows a schematic representation of a region 1000 of a sample as an example. The region 1000 includes several subregions 1010-1070 that may differ in one or more chemical and physical properties. In this example, the subregions 1010-1070 have different electrical resistances. In this example, the subregion 1070 is a thick metal layer, the subregions 1050 and 1060 are thin metal layers, the subregion 1040 is a lightly doped semiconductor layer, the subregion 1030 is a thin dielectric layer, and the subregions 1020 and 1010 are thick dielectric layers. The electrical resistivity ordering of the sub-regions 1010-1070 is shown diagrammatically in Figure 3. Differences in electrical resistivity between the sub-regions 1010-1070 can give rise to spatial contrast in the signal representative of the interaction of the beam of charged particles with the sample.

[0045]

[0053] In one example, charge may dissipate more quickly from a subregion with a lower electrical resistance than from a subregion with a higher electrical resistance. If a subregion with a lower electrical resistance and a subregion with a higher electrical resistance start with the same amount of charge, the subregion with the lower electrical resistance will have less charge than the subregion with the higher electrical resistance after a finite period of time. Thus, after that finite period of time, the interaction of the beam of charged particles with the subregion with the higher electrical resistance may be different from the interaction of the beam of charged particles with the subregion with the lower electrical resistance. Thus, spatial contrast in the signal representative of these interactions may result.

[0046]

[0054] One use of electrical resistance to create spatial contrast in the signal representing the interaction of the beam of charged particles with the sample is to detect certain defects. For example, a deep via with a bad conductive path has a higher electrical resistance than a similar deep via with a normal conductive path. Thus, the signal contrast can reveal defects such as a deep via with a bad conductive path.

[0047]

[0055] FIG. 4 shows a schematic example of using the chemical and physical properties of a sample (e.g. electrical resistance as in FIG. 3) to generate spatial contrast of a signal representative of the interaction of a beam of charged particles with the sample. Charges can be deposited on an area 1000, for example, using an expanded beam 1999 containing the charges. The expanded beam 1999 may or may not be large enough to encompass the entire area 1000. The expanded beam 1999 can be scanned across the area 1000. The charge of the expanded beam 1999 can be carried by the same or different particles as the charged particles of the beam for inspecting the sample. The current carried by the expanded beam 1999 can be modulated as shown in FIG. 4. For example, the current carried by the expanded beam 1999 can be a high value C1 during a period T1 and a low value C2 during a period T2 following the period T1. Although a square waveform is shown in this example, the current carried by the expanded beam 1999 can have any other suitable waveform. After charge is deposited on region 1000, the amount of charge in the sub-regions will differ over time due to differences in the electrical resistance of the sub-regions. The difference in the amount of charge in the sub-regions will be affected by the characteristics of the modulated charge deposition such as C1, C2, T1, and T2.

[0048]

[0056] Figures 5A to 5D, 6A to 6D and 7A to 7D show schematic examples to explain the influence of charge deposition characteristics on the test. These figures are simplified and may not show all the physical mechanisms behind the deposition and dissipation of charge on the sample. For example, the dissipation rate is approximated to be independent of the amount of charge on the sample.

[0049]

[0057] 5A shows the rate of change 5011 of the amount of charge deposited in the two sub-regions 1050 and 1070 of region 1000, the rate of change 5012 of the amount of charge dissipated from sub-region 1070, and the rate of change 5013 of the amount of charge dissipated from sub-region 1050. The rate of change 5012 of the amount of charge dissipated from sub-region 1070 is higher in absolute value than the rate of change 5013 of the amount of charge dissipated from sub-region 1050 because sub-region 1070 has a lower electrical resistance than sub-region 1050 as shown in FIG. 3. FIG. 5B shows the net rate of change 5022 of the amount of charge in sub-region 1070 and the net rate of change 5023 of the amount of charge in sub-region 1050. The net rate of change 5022 is the sum of the rates of change 5011 and 5012. The net rate of change 5023 is the sum of the rates of change 5011 and 5013. FIG. 5C shows the amount of charge 5033 for subregion 1050 as a function of time T, and the amount of charge 5032 for subregion 1070 as a function of time T, assuming that subregions 1050 and 1070 have zero charge when T is zero. The amounts of charge 5032 and 5033 may be derived by integrating the net rates of change 5022 and 5023 with respect to time T. FIG. 5C also shows a maximum value 5035 for the amount of charge for each of subregions 1050 and 1070. If the amount of charge for subregion 1050 or subregion 1070 exceeds the maximum value 5035, undesirable effects may occur (e.g., the structure of subregion 1050 or subregion 1070 may be damaged). FIG. 5D shows the difference 5046 between the amount of charge in subregion 1050 and the amount of charge in subregion 1070 as a function of time T. FIGS. 5C and 5D show that the difference 5046 can increase with time T as a result of modulation of the rate of change 5011 of the amount of charge deposited in subregions 1050 and 1070 and the disparity between the rate of change 5012 of the amount of charge dissipated from subregion 1070 and the rate of change 5013 of the amount of charge dissipated from subregion 1050. The presence of the maximum 5035 limits the length of time of charge deposition in subregions 1050 and 1070, and thus the difference 5046 between the amount of charge in subregion 1050 and the amount of charge in subregion 1070. The expanded beam 1999 shown in FIG. 4 can be used to produce the rate of change 5011 of FIG. 5A.For example, when C2 is about half the length of C1 and T2 is about half the length of T1, the expanded beam 1999 can produce the rate of change 5011 of Figure 5A. In the example shown in Figures 5A-5D, the difference 5046 can reach about 2 / 5 of the maximum value 5035.

[0050]

[0058] 6A shows the rate of change 6011 of the amount of charge deposited in the two sub-regions 1050 and 1070 of region 1000, the rate of change 6012 of the amount of charge dissipated from sub-region 1070, and the rate of change 6013 of the amount of charge dissipated from sub-region 1050. The rate of change 6012 of the amount of charge dissipated from sub-region 1070 is higher in absolute value than the rate of change 6013 of the amount of charge dissipated from sub-region 1050 because sub-region 1070 has a lower electrical resistance than sub-region 1050 as shown in FIG. 3. FIG. 6B shows the net rate of change 6022 of the amount of charge in sub-region 1070 and the net rate of change 6023 of the amount of charge in sub-region 1050. The net rate of change 6022 is the sum of the rates of change 6011 and 6012. The net rate of change 6023 is the sum of the rates of change 6011 and 6013. FIG. 6C shows the amount of charge 6033 for subregion 1050 as a function of time T and the amount of charge 6032 for subregion 1070 as a function of time T, assuming that subregions 1050 and 1070 have zero charge when T is zero. The amounts of charge 6032 and 6033 may be derived by integrating the net rates of change 6022 and 6023 with respect to time T. FIG. 6C shows that the net rates of change 6022 and 6023 may be negative (i.e., the amount of charge for subregions 1050 and 1070 may decrease). FIG. 6C also shows a maximum value 6035 for the amount of charge for each of subregions 1050 and 1070. If the amount of charge in subregion 1050 or subregion 1070 exceeds the maximum value 6035, undesirable effects may occur (e.g., the structure of subregion 1050 or subregion 1070 may be damaged). Figure 6D shows the difference 6046 between the amount of charge in subregion 1050 and the amount of charge in subregion 1070 as a function of time T. Figures 6C and 6D show that the difference 6046 may increase over time T as a result of modulation of the rate of change 6011 of the amount of charge deposited in subregions 1050 and 1070 and the disparity between the rate of change 6012 of the amount of charge dissipated from subregion 1070 and the rate of change 6013 of the amount of charge dissipated from subregion 1050.The presence of the maximum 6035 limits the length of time for charge to accumulate in the subregions 1050 and 1070, and thus the difference 6046 between the amount of charge in the subregion 1050 and the amount of charge in the subregion 1070. The expanded beam 1999 shown in FIG. 4 may be used to produce the rate of change 6011 of FIG. 6A. For example, the expanded beam 1999 may produce the rate of change 6011 of FIG. 6A when C2 is about zero and T2 is about half the length of T1. In the example shown in FIGS. 6A-6D, the difference 6046 may reach about 3 / 5 of the maximum 6035. In the example shown in Figures 6A-6D, no charge is deposited during T2, and thus the length of time of charge deposition in sub-regions 1050 and 1070 before exceeding maximum value 6035 is longer than the length of time of charge deposition in sub-regions 1050 and 1070 before exceeding maximum value 5035 in Figures 5A-5D. Difference 6046 and difference 5046 increase monotonically with time T. Thus, with longer deposition, difference 6046 is greater than difference 5046.

[0051]

[0059] 7A shows the rate of change 7011 of the amount of charge deposited in the two sub-regions 1050 and 1070 of region 1000, the rate of change 7012 of the amount of charge dissipated from sub-region 1070, and the rate of change 7013 of the amount of charge dissipated from sub-region 1050. The rate of change 7012 of the amount of charge dissipated from sub-region 1070 is higher in absolute value than the rate of change 7013 of the amount of charge dissipated from sub-region 1050 because sub-region 1070 has a lower electrical resistance than sub-region 1050 as shown in FIG. 3. FIG. 7B shows the net rate of change 7022 of the amount of charge in sub-region 1070 and the net rate of change 7023 of the amount of charge in sub-region 1050. The net rate of change 7022 is the sum of the rates of change 7011 and 7012. The net rate of change 7023 is the sum of the rates of change 7011 and 7013. Figure 7C shows the amount of charge 7033 for subregion 1050 as a function of time T, and the amount of charge 7032 for subregion 1070 as a function of time T, assuming that subregions 1050 and 1070 have zero charge when T is zero. The amounts of charge 7032 and 7033 may be derived by integrating the net rates of change 7022 and 7023 with respect to time T. Figure 7C also shows a maximum value 7035 for the amount of charge for each of subregions 1050 and 1070. If the amount of charge for subregion 1050 or subregion 1070 exceeds the maximum value 7035, undesirable effects may occur (e.g., the structure of subregion 1050 and subregion 1070 may be damaged). FIG. 7D shows the difference 7046 between the amount of charge in subregion 1050 and the amount of charge in subregion 1070 as a function of time T. FIGS. 7C and 7D show that the difference 7046 can increase with time T as a result of modulation of the rate of change 7011 of the amount of charge deposited in subregions 1050 and 1070 and the disparity between the rate of change 7012 of the amount of charge dissipated from subregion 1070 and the rate of change 7013 of the amount of charge dissipated from subregion 1050. The presence of the maximum 7035 limits the length of time of charge deposition in subregions 1050 and 1070, and thus the difference 7046 between the amount of charge in subregion 1050 and the amount of charge in subregion 1070. The expanded beam 1999 shown in FIG. 4 can be used to produce the rate of change 7011 of FIG. 7A.For example, when C2 is about zero and T1 is about half the length of T2, the expanded beam 1999 can produce the rate of change 7011 of FIG. 7A. In the example shown in FIGS. 7A-7D, the difference 7046 can reach about 7 / 8 of the maximum value 7035. In the example shown in FIGS. 7A-7D, all of the charge deposited on the subregion 1070 during T1 dissipates from the subregion 1070 during T2, and thus the amount of charge on the subregion 1070 is zero during part of T2. Meanwhile, the amount of charge on the subregion 1050 increases with the number of periods of T1 and T2, eventually approaching the maximum value 7035. Thus, the difference 7046 can reach nearly the full magnitude of the maximum value 7035. Because the difference 7046 is greatest among the examples of Figures 5A to 5D, 6A to 6D, and 7A to 7D, the example of Figures 7A to 7D will produce the greatest spatial contrast of the signal representing the interaction of the beam of charged particles with the sample.

[0052]

[0060] FIG. 8 shows a flow chart of a method for inspecting a sample using a beam of charged particles, according to one embodiment. In step 810, a modulated charge is deposited in a region of the sample. The modulated deposition includes at least a first time period and a second time period. Step 810 includes sub-step 811, in which a first amount of charge is deposited in the region during the first time period. Step 810 includes sub-step 812, in which a second amount of charge is deposited in the region during the second time period. Sub-steps 811 and 812 may be repeated. The average deposition rate in the first time period (i.e., the first amount divided by the length of the first time period) is different from the average deposition rate in the second time period (i.e., the second amount divided by the length of the second time period). The first amount or the second amount may be zero. The first amount and the second amount may be different. The length of the first time period and the length of the second time period may be different. The region may have a non-uniform spatial distribution of one or more chemical or physical properties. In step 820, the beam of charged particles is scanned across the area and a signal representative of the interaction of the charged particles with the sample is recorded. The modulated deposition of procedure 810 may be performed with the same beam of charged particles used in step 820. The modulated deposition of procedure 810 may be performed with a different beam of charged particles than the beam of charged particles used in step 820, in which case the different beam may have a cross-sectional area at least twice the cross-sectional area of ​​the beam of charged particles used in step 820.

[0053]

[0061] FIG. 9 illustrates a schematic component diagram of an apparatus 9000 configured to inspect a sample using a beam of charged particles, according to one embodiment. The apparatus 9000 includes a source 9001 of charged particles, a stage 9003, and optics 9002 configured to direct the beam of charged particles to a sample supported on the stage 9003. The stage 9003 may be configured to move the sample. The optics 9002 may be configured to scan a probe spot formed on the sample by the beam relative to the sample. The apparatus 9000 includes a controller 9010 configured to control the source 9001 and the optics 9002. The apparatus 9000 also includes a detector 9004 configured to record a signal representative of an interaction of the beam of charged particles with the sample. The source 9001, the optics 9002, and the controller 9010 may be configured to generate a signal to be recorded and may also be configured to perform a modulated deposition of charge into the sample. In one embodiment, the apparatus 9000 optionally includes a separate source 9101 dedicated to modulated deposition of charge into the sample, separate optics 9102 and a controller 9110.

[0054]

[0062] The embodiments may be further described using the following clauses.

[0055] 1. depositing a first amount of charge in an area of ​​a sample for a first period of time; depositing a second amount of charge in the region for a second period of time; scanning a probe spot created on the sample by the beam of charged particles while recording a signal from the probe spot representative of an interaction of the beam of charged particles with the sample; A method comprising: The method, wherein the average deposition rate during the first time period is different from the average deposition rate during the second time period.

[0056] 2. The method of clause 1, further comprising repeating depositing a first amount of charge in the region for a first period of time and depositing a second amount of charge in the region for a second period of time.

[0057] 3. The method of any one of clauses 1 to 2, wherein the first amount or the second amount is zero.

[0058] 4. The method of any one of clauses 1 to 3, wherein the first amount and the second amount are different.

[0059] 5. The method of any one of clauses 1 to 4, wherein the length of the first period and the length of the second period are different.

[0060] 6. The method of any one of clauses 1 to 5, wherein the region has a non-uniform spatial distribution of a chemical or physical property.

[0061] 7. The method of clause 6, wherein the chemical or physical property is selected from the group consisting of composition, doping level, electrical resistivity, electrical capacitance, electrical inductance, thickness, crystallinity, and dielectric constant.

[0062] 8. The method of any one of clauses 1 to 7, wherein depositing the first amount of charge or depositing the second amount of charge is performed using a beam of charged particles.

[0063] 9. The method of any one of clauses 1 to 8, wherein depositing the first amount of charge or depositing the second amount of charge is not performed using a beam of charged particles but using a separate beam comprising an electric charge.

[0064] 10. The method of clause 9, wherein the separate beam has a cross-sectional area at least twice the cross-sectional area of ​​the beam of charged particles.

[0065] 11. The method of any one of clauses 1 to 10, wherein the region comprises a first sub-region and a second sub-region, and the rate of change of the amount of charge dissipated from the first sub-region is different from the rate of change of the amount of charge dissipated from the second sub-region.

[0066] 12. The method of any one of clauses 1 to 11, wherein the region comprises a first sub-region and a second sub-region, and the rate of change of the amount of charge deposited in the first sub-region and the rate of change of the amount of charge deposited in the second sub-region are the same.

[0067] 13. The method of any one of clauses 1 to 12, wherein the region comprises a first sub-region and a second sub-region, and the net rate of change of the amount of charge in the first sub-region is different from the net rate of change of the amount of charge in the second sub-region.

[0068] 14. The method of any one of clauses 1 to 13, wherein the region comprises a first subregion and a second subregion, and the net rate of change of the amount of charge in the first subregion or the net rate of change of the amount of charge in the second subregion is negative.

[0069] 15. The method of any one of clauses 1 to 14, wherein the region comprises a first subregion and a second subregion, and the difference between the amount of charge in the first subregion and the amount of charge in the second subregion increases over time.

[0070] 16. The method of any one of clauses 1 to 15, wherein the region comprises a subregion, and the amount of charge in the subregion is zero during a portion of the second time period.

[0071] 17. A computer program product comprising a non-transitory computer readable medium having instructions recorded thereon, the instructions, when executed by a computer, performing any of the methods of clauses 1 to 16.

[0072] 18. An apparatus configured to inspect a sample, comprising: a source of charged particles; Stage and an optical component configured to direct the beam of charged particles toward a sample supported on a stage; a controller configured to control the source and the optical components; It is equipped with The source, optics and controller depositing a first amount of charge within an area of ​​the sample for a first period of time; collectively configured to deposit a second amount of charge within the region for a second period of time; The apparatus, wherein the average deposition rate in the first time period is different from the average deposition rate in the second time period.

[0073] 19. The apparatus of clause 18, further comprising a detector configured to record a signal representative of an interaction of the beam with the sample.

[0074] 20. The apparatus of clause 19, wherein the source, the optical components and the controller are collectively configured to generate a signal.

[0075] 21. An apparatus according to clause 19, wherein the optical component is configured to scan a probe spot formed on the sample by the beam relative to the sample.

[0076] 22. The apparatus of clause 19, wherein the stage is configured to move the sample.

[0077]

[0063] Although the concepts disclosed in this specification may be used for inspection of samples such as silicon wafers or patterning devices such as chrome on glass, it should be understood that the concepts disclosed may be used with any type of sample, for example samples other than silicon wafers.

[0078]

[0064] The above description is intended to be illustrative and not limiting. Thus, it will be apparent to one skilled in the art that modifications as described may be made without departing from the scope of the claims below.

Claims

1. 1. A method for enhancing contrast in a sample image, comprising: depositing a first net amount of charge in an area of ​​a sample by directing a first beam of charged particles into the area for a first time period; depositing a second net amount of charge in the region by irradiating the region with the first beam of charged particles for a second period of time; and repeating depositing the first net amount of charge in the region for the first time period and depositing the second net amount of charge in the region for the second time period; after said repeating, scanning a probe spot created on the sample with a second beam of charged particles while recording a signal from the probe spot representative of an interaction of the second beam of charged particles with the sample; A method for providing the above.

2. The method of claim 1 , wherein the first net amount and the second net amount are different.

3. The method of claim 1 , wherein the first period of time and the second period of time are different in length.

4. The method of claim 1 , wherein the region has a non-uniform spatial distribution of a chemical or physical property.

5. The method of claim 4 , wherein the chemical property or the physical property is selected from the group consisting of composition, doping level, electrical resistivity, electrical capacitance, electrical inductance, thickness, crystallinity, and dielectric constant.

6. The method of claim 1, wherein the first beam of charged particles is identical to the second beam of charged particles.

7. The method of claim 1, wherein the first beam of charged particles is not a beam of the second charged particles but a separate beam having an electric charge.

8. The method of claim 7 , wherein the first beam of charged particles has a cross-sectional area at least twice that of the second beam of charged particles.

9. the region comprises a first sub-region and a second sub-region; The method of claim 1 , wherein a rate of change of an amount of charge dissipated from the first sub-region and a rate of change of an amount of charge dissipated from the second sub-region are different.

10. the region comprises a first sub-region and a second sub-region; The method of claim 1 , wherein a rate of change of the amount of charge deposited in the first sub-region and a rate of change of the amount of charge deposited in the second sub-region are the same.

11. the region comprises a first sub-region and a second sub-region; The method of claim 1 , wherein the rate of change of the net amount of charge in the first sub-region or the rate of change of the net amount of charge in the second sub-region is negative.

12. the region comprises a first sub-region and a second sub-region; The method of claim 1 , wherein the difference between the net amount of charge in the first sub-region and the net amount of charge in the second sub-region increases over time.

13. 1. An apparatus configured to enhance contrast of a sample image, comprising: a source of the first or second charged particles; Stage and an optical component configured to direct the first beam of charged particles or the second beam of charged particles from the source onto a sample supported on the stage; a controller configured to control the source and the optical component; Equipped with The source, the optical component, and the controller depositing a first net amount of charge in an area of ​​the sample by directing a first beam of charged particles into the area for a first time period; depositing a second net amount of charge in the region by irradiating the region with the first beam of charged particles for a second period of time; repeating depositing the first net amount of charge in the region for the first time period and depositing the second net amount of charge in the region for the second time period; after said repeating, the apparatus is collectively configured to: scan a probe spot created on the sample with the second beam of charged particles while recording a signal from the probe spot indicative of an interaction of the second beam of charged particles with the sample.

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