Patent Description:
Electron beam inspection systems often utilize a micro-lens array (MLA) in order to split primary electron beams into multiple primary electron beamlets. Due to the large field of view (FOV) of multi-electron beam systems and mechanical tolerances of each micro-lens, astigmatisms within each electron beamlet are inevitable. Larger FOVs result in larger astigmatism aberrations. These focusing aberrations (e.g., fourth-order focusing aberrations, sixth-order focusing aberrations) must be corrected and/or eliminated in order to enable efficient inspection performance. Micro-stigmator arrays (MSA) are one technique which have been incorporated within MLAs in order to correct and/or remove astigmatism aberrations within multi-electron beam systems. Conventional multi-electron beam systems have utilized quadrupole electrostatic stigmators in order to eliminate aberrations within each electron beamlet. However, conventional quadrupole electrostatic stigmators are unable to completely eliminate fourth-order and/or sixth-order focusing aberrations, thereby generating strong octupole (forth-order) and dodecapole (sixth-order) electrostatic fields. Therefore, it would be desirable to provide a system and method that cure one or more of the shortfalls of the previous approaches identified above.

<CIT> discloses a multi-beam inspection apparatus.

<CIT> describes a corrector for axial aberrations of a particle-optical lens.

<CIT> discloses a charged particle beam system and method of aberration correction.

A system as recited in claim <NUM> is disclosed.

The present disclosure has been particularly shown and described with respect to certain embodiments and specific features thereof. The embodiments set forth herein are taken to be illustrative rather than limiting. It should be readily apparent to those of ordinary skill in the art that various changes and modifications in form and detail may be made without departing from the spirit and scope of the disclosure.

Embodiments of the present disclosure are directed to a dodecapole electrostatic stigmator configured to eliminate both fourth-order and sixth-order focusing aberrations. Additional embodiments of the present disclosure are directed to a multi-electron beam apparatus including a multi-stigmator array (MSA) including a plurality of dodecapole electrostatic stigmators. Further embodiments of the present disclosure are directed to a micro-stigmator array (MSA) including a plurality of electrostatic stigmators.

As noted previously herein, electron beam inspection systems often utilize a micro-lens array (MLA) comprising hundreds of micro-lenses in order to split primary electron beams into multi-primary electron beamlets. The size of each electron beamlet is in the order of tens of microns, and the beamlets are typically separated by a spacing distance in the order of tens of microns. Due to the large field of view (FOV) of multi-electron beam systems (e.g., ~<NUM>µm) and mechanical tolerances of each micro-lens, astigmatisms within each electron beamlet are inevitable. Larger FOVs result in larger astigmatism aberrations. These focusing aberrations (e.g., fourth-order focusing aberrations, sixth-order focusing aberrations) must be corrected and/or eliminated in order to enable efficient inspection performance.

Micro-stigmator arrays (MSA) are one technique which have been incorporated within MLAs in order to correct and/or remove astigmatism aberrations within multi-electron beam systems. Conventional multi-electron beam systems have utilized quadrupole electrostatic stigmators in order to eliminate aberrations within each electron beamlet. These quadrupole electrostatic stigmators include four conductive plates in a circular configuration, exhibiting a quadrupole bore size. However, conventional quadrupole electrostatic stigmators are unable to completely eliminate fourth-order and/or sixth-order focusing aberrations, thereby generating strong octupole (forth-order) and dodecapole (sixth-order) electrostatic fields. This is partially due to the fact that the size of the electron beamlets exhibit a size which is similar to that of the bore size of each quadrupole electrostatic stigmator (e.g., within <NUM>-<NUM>% of bore size).

Conventional electrostatic stigmators have taken various forms, including quadrupole electrostatic stigmators. These may be further understood with reference to <FIG>.

<FIG> illustrates a dual-polarity quadrupole electrostatic stigmator <NUM>. It is contemplated herein that a brief discussion of conventional quadrupole electrostatic stigmators <NUM> (illustrated in <FIG>) will provide a base understanding, against which attendant advantages of the present disclosure may be compared.

The quadrupole electrostatic stigmator <NUM> is provided as an example of a conventional stigmator used to correct astigmatism aberrations. In particular, the quadrupole electrostatic stigmator <NUM> may be used to correct astigmatism aberrations which may be generated in either a focused or a shaped electron beam apparatus due to mechanical element misalignments, elliptic fabrications, electronic deflections, or projection image-formations. As shown in <FIG>, a conventional quadrupole electrostatic stigmator <NUM> may include four conductive plates (e.g., a first conductive plate 104a, a second conductive plate 104b, a third conductive plate 104c, and a fourth conductive plate 104d).

The quadrupole electrostatic stigmator <NUM> may be configured to apply voltages to the second conductive plate 104b and the fourth conductive plate 104d in order to generate an electronic focusing force along a first direction (e.g., along the y-axis). Conversely, the quadrupole electrostatic stigmator <NUM> may be configured to apply voltages to the first conductive plate 104a and the third conductive plate 104c in order to generate an electronic de-focusing force along a second direction (e.g., along the x-axis). In this regard, the quadrupole electrostatic stigmator <NUM> may be configured to correct astigmatism blurs in am imaging plane of an electron beam apparatus by selectively adjusting the voltages (e.g., ±1V) applied on the various conductive plates 104a-104d.

In practice, correcting astigmatisms within an electron beam apparatus may require two separate quadrupole electrostatic stigmators <NUM> illustrated in <FIG> to be deployed along the optical z-axis with a rotation angle of <NUM>°. For example, a first quadrupole electrostatic stigmator <NUM> may be arranged along the optical z-axis as illustrated in <FIG>, and a second quadrupole electrostatic stigmator <NUM> may be arranged along the optical z-axis, wherein the second quadrupole electrostatic stigmator <NUM> is rotated <NUM>° with respect to the first quadrupole electrostatic stigmator <NUM>.

The conductive plates 104a-104d of the quadrupole electrostatic stigmator <NUM> may be arranged about a radius R, such that a diameter (bore size) of the quadrupole electrostatic stigmator <NUM> is characterized by 2R, which may be on the order of tens of microns. In practice, each electron beamlet of a multi-electron beam apparatus would require an individual quadrupole electrostatic stigmator <NUM> for aberration correction.

As shown in <FIG>, the first conductive plate 104a and third conductive plate 104c may exhibit a first voltage (+1V), whereas the second conductive plate 104b and fourth conductive plate 104d may exhibit a second voltage (-1V). In order to provide the distinct focusing/de-focusing voltages from voltage sources to the various conductive plates 104a-104d, the quadrupole electrostatic stigmator <NUM> would require two separate voltage connecting lines: one for the +1V on the first and third conductive plates 104a, 104c, and a second for the -1V on the second and fourth conductive plates 104b, 104d. However, in multi-electron beam apparatuses with hundreds of electron beamlets, requiring two separate voltage connecting lines for every quadrupole electrostatic stigmator <NUM> (e.g., every beamlet) complicates the fabrication process, adds unnecessary expenses, and slows down production.

In order to reduce the number of voltage connecting lines required for each quadrupole electrostatic stigmator <NUM>, some conventional multi-electron beam apparatuses have utilized one-power quadrupoles. For example, <FIG> illustrates a single-polarity quadrupole electrostatic stigmator <NUM>. As opposed to the dual-polarity quadrupole electrostatic stigmator <NUM> of <FIG>, which utilized two separate focusing/de-focusing voltages (±1V), the single-polarity quadrupole electrostatic stigmator <NUM> of <FIG> utilizes only a single de-focusing voltage (+1V) on the first and third conductive plates 104a, 104c.

As a result, the quadrupole electrostatic stigmator <NUM> of <FIG> requires only a single voltage connecting line coupling the first and third conductive plates 104a, 104c to a voltage source. The second and fourth conductive plates 104b, 104d are grounded. While this configuration reduces the number of required voltage connecting lines, the focusing/de-focusing sensitivity of the quadrupole electrostatic stigmator <NUM> of <FIG> is half that of the quadrupole electrostatic stigmator <NUM> of <FIG>. Thus, the quadrupole electrostatic stigmator <NUM> of <FIG> is still not suitable for some multi-electron beam apparatuses.

A mathematical derivation of the potential distributions of the quadrupole electrostatic stigmator <NUM> of <FIG> may prove to be helpful. Let ϕ(r,θ) define the electrostatic potential distributions in r ≤ R for the quadrupole electrostatic stigmator <NUM> of <FIG>. Expanding ϕ(r,θ) into a Fourier series yields Equation <NUM>: <MAT> wherein A<NUM>, Ak, and Bk define the Fourier coefficients, as defined by the boundary condition ϕ(R,θ).

Equation <NUM> is an obvious solution of the Laplace equation which defines the electrostatic potential distributions within the bore (e.g., for r ≤ R) of the quadrupole electrostatic stigmator <NUM> illustrated in <FIG>. The Fourier coefficients A<NUM>, Ak, and Bk in Equation <NUM> may be defined by Equation <NUM>, Equation <NUM>, and Equation <NUM>, respectively: <MAT> <MAT> <MAT>.

The symmetrical relations over (r,θ) with a voltage V applied within the quadrupole electrostatic stigmator <NUM> may be defined by Equation <NUM> and Equation <NUM>: <MAT> <MAT>.

In meeting the symmetrical conditions of Equation <NUM> and Equation <NUM>, Equation <NUM> may be simplified to yield Equation <NUM>: <MAT> wherein Ak may be defined according to Equation <NUM>: <MAT>.

The term Ck in Equation <NUM> is the constants defined by the boundary, and may be defined by Equation <NUM>: <MAT> wherein e defines the electron charge.

Accordingly, the electrostatic force (F) in the direction along which the electrical power (V) is applied (e.g., along the x-axis in <FIG>) may be defined by Equation <NUM>: <MAT> wherein F<NUM> defines the quadrupole field force, F<NUM> defines the octupole field force, and F<NUM> defines the dodecapole field force, which may respectively be defined according to Equation <NUM>, Equation <NUM>, and Equation <NUM>: <MAT> <MAT> <MAT>.

The electrostatic quadrupole field force described in Equation <NUM> may represent an ideal quadrupole force, within which the astigmatism of an electron optical apparatus has been completely corrected/removed. However, the electrostatic octupole and dodecapole field forces described in Equation <NUM> and Equation <NUM> represent high-order electrostatic fields which generate the fourth-order and sixth-order focusing/de-focusing aberrations.

In a conventional single-electron beam apparatus, the size of the electron beam (2r, on the order of sub-millimeter) is relatively small compared to the inner diameter (bore size) of the quadrupole electrostatic stigmator <NUM> (2R, on the order of tens of millimeters) shown in <FIG>. For example, in a conventional single-electron beam apparatus, the ratio of r to R is commonly much less than <NUM> (e.g., <MAT>). Due to the significant differences in size between the electron beam and the bore size of the quadrupole electrostatic stigmator <NUM>, the octupole and dodecapole field forces described in Equation <NUM> and Equation <NUM> typically do not result in significant degradation of image-forming resolutions in the context of a conventional single-electron beam apparatus.

However, the same may not be said for conventional multi-electron beam apparatuses. In conventional multi-electron beam apparatuses with hundreds of beamlets, the inner diameter (bore size) of the quadrupole electrostatic stigmator <NUM> (2R) is on the order of tens of microns. In order to maximize the utilization rate (η=BC%) of the electron-source-emitted beam currents (BC) (e.g., <MAT>), the electron beamlet size (2r) is required to be greater than <NUM>% of the inner diameter (2R) of each quadrupole electrostatic stigmator <NUM> (e.g., <MAT>). In such a case, the electrostatic octupole and dodecapole field forces described in Equation <NUM> and Equation <NUM> generate significant high-order aberrations (e.g., fourth-order focusing aberrations, sixth-order focusing aberrations).

Accordingly, embodiments of the present disclosure are directed to electrostatic stigmators which are configured to eliminate fourth-order and sixth-order focusing aberrations, as described in Equation <NUM> and Equation <NUM>. In order to remove the high-order focusing aberrations and keep high utilization rate of beam currents (η=BC%), the octupole and dodecapole field coefficients (A<NUM>, A<NUM>) should be reduced or eliminated. Additionally and/or alternatively, driving the integrations of C<NUM> and C<NUM> would theoretically also eliminate the fourth and sixth-order focusing aberrations. The attendant advantages of the present disclosure may be further shown and described with reference to <FIG>.

<FIG> illustrates a multi-electron beam apparatus <NUM>, in accordance with one or more embodiments of the present disclosure. The multi-electron beam apparatus <NUM> may include, but is not limited to, an electron source <NUM>, an electron gun lens <NUM>, a micro-aperture array <NUM> (e.g., MAA <NUM>), a beam-limiting aperture <NUM> (e.g., BLA <NUM>) a micro-lens array <NUM> (e.g., MLA <NUM>), a micro-stigmator array <NUM> (e.g., MSA <NUM>), a transfer lens <NUM>, and an objective lens <NUM>.

In one embodiment, the electron source <NUM> is configured to emit a source electron beam <NUM>. The electron source <NUM> may include any type of electron gun or electron emitter known in the art including, but not limited to, thermal field emission (TFE) sources. In another embodiment, the BLA <NUM> may be configured to select the primary electron beam <NUM> from the source electron beam <NUM>, and the gun lens <NUM> may be configured to accelerate and/or focus the primary electron beam <NUM>. The gun lens <NUM> may be further configured to direct the primary electron beam <NUM> to the MAA <NUM>.

In another embodiment, the primary electron beam <NUM> is directed through the MAA <NUM> to a micro-lens array <NUM> (e.g., MLA <NUM>). In embodiments, the MLA <NUM> is configured to receive the primary electron beam and split the primary electron beam <NUM> into a plurality of electron beamlets <NUM>. For example, the MLA <NUM> may be configured to split the primary electron beam <NUM> into hundreds of primary electron beamlets <NUM>. The MLA <NUM> may be further configured to focus the primary electron beamlets <NUM> at a crossover plane <NUM>. In this regard, the crossover plane <NUM> may be regarded as the image plane of the MLA <NUM>/MSA <NUM>. In some embodiments, as will be discussed in further detail herein, the MLA <NUM> may include an integrated micro-stigmator array <NUM> (MSA <NUM>). In one embodiment, the MSA <NUM> may include a plurality of electrostatic stigmators configured to eliminate high-order aberrations from the primary electron beamlets <NUM>.

Subsequently, the transfer lens <NUM> and the objective lens <NUM> may be configured to receive the plurality of primary electron beamlets <NUM> and focus the plurality of primary electron beamlets <NUM> to a wafer plane. Optical components from the electron source <NUM> to the crossover plane (e.g., electron source <NUM>, electron gun lens <NUM>, BLA <NUM>, MAA <NUM>, MLA <NUM>, MSA <NUM>, and the like) may be regarded as "illumination optics" of the multi-electron beam apparatus <NUM>. Conversely, the transfer lens <NUM> and the objective lens <NUM> may be regarded as "projection optics" of the multi-electron beam apparatus <NUM>. In addition to serving as the image plane of the MLA <NUM>/MSA <NUM>, it is noted herein that the crossover plane <NUM> may be regarded as the object plane of the projection optics (e.g., transfer lens <NUM> and the objective lens <NUM>).

In another embodiment, the objective lens <NUM> is configured to focus and direct the primary electron beamlets <NUM> to a wafer plane <NUM>. In this regard, the wafer plane <NUM> may be regarded as the image plane of the projection optics (e.g., transfer lens <NUM>, objective lens <NUM>, and the like). The projection optics may be configured to project the primary electron beamlets <NUM> to the wafer plane <NUM> with a defined optical demagnification. In one embodiment, the wafer plane <NUM> may correspond to the surface of a sample, such that the projection optics are configured to direct and focus the primary electron beamlets <NUM> to the surface of a sample.

In another embodiment, the MLA <NUM>/MSA <NUM> may be configured to simultaneously and independently scan each of the primary electron beamlets <NUM> at the wafer plane <NUM>. Primary electron beamlets <NUM> at the wafer plane <NUM> may be used for any characterization processes known in the art including, but not limited to, inspection, review, image-based metrology, and the like.

As noted previously herein, in some embodiments, the MLA <NUM> may include an integrated micro-stigmator array <NUM> (e.g., MSA <NUM>). In one embodiment, the MSA <NUM> may include hundreds of micro electrostatic stigmators configured to remove fourth-order focusing aberrations and/or sixth-order focusing aberrations. For example, the MSA <NUM> may include a plurality of dodecapole electrostatic stigmators, which may be further shown and described with reference to <FIG>.

<FIG> illustrates a dodecapole electrostatic stigmator <NUM> of a micro-stigmator array <NUM> (MSA <NUM>), in accordance with one or more embodiments of the present disclosure.

In some embodiments, the dodecapole electrostatic stigmator <NUM> may include twelve individual conductive plates <NUM> (e.g., a first conductive plate 322a, a second conductive plate 322b. and a twelfth conductive plate 322I). It is contemplated herein that the dodecapole electrostatic stigmator <NUM> illustrated in <FIG> may effectively and efficiently eliminate fourth-order and sixth-order focusing/de-focusing aberrations of primary electron beamlets <NUM>. In this regard, it is further contemplated herein that an MSA <NUM> including a plurality of dodecapole electrostatic stigmators 320a-320n may be utilized to eliminate focusing aberrations within a multi-electron beam apparatus <NUM>.

In embodiments, the dodecapole electrostatic stigmator <NUM> may be operated with two separate focusing voltages. For example, as shown in <FIG>, the first conductive plate 322a, the third conductive plate 322c, the fifth conductive plate 322e, the seventh conductive plate <NUM>, the ninth conductive plate 322i, and the eleventh conductive plate <NUM> may be applied with a first focusing voltage of 1V. Conversely, the second conductive plate 322b, the fourth conductive plate 322d, the sixth conductive plate 322f, the eighth conductive plate <NUM>, the tenth conductive plate 322j, and the twelfth conductive plate 322I may be applied with a second focusing voltage of 0V. The conductive plates <NUM> which do not exhibit a focusing voltage (e.g., focusing voltages of 0V) may be regarded as "grounded" plates. In embodiments, the focusing voltages may be selectively adjusted in order to selectively reduce and/or eliminate high-order focusing/de-focusing aberrations within the primary electron beamlets <NUM>.

As compared to the dual-polarity quadrupole electrostatic stigmator <NUM> illustrated in <FIG>, which requires two separate voltage connecting lines and two voltage sources, each dodecapole electrostatic stigmator <NUM> requires only a single voltage connecting line and a single voltage source. The fewer number of voltage sources and voltage connecting lines allows the dodecapole electrostatic stigmator <NUM> to provide numerous spatial and cost advantages over dual-polarity quadrupole electrostatic stigmator <NUM>.

In some embodiments, the plurality of conductive plates 322a-322I may be arranged about a radius R. In embodiments, a first set of the conductive plates <NUM> may be defined by a plate angle <NUM>α, whereas a second set of the conductive plates <NUM> may be defined by a plate angle β. For example, the first, fourth, seventh, and tenth conductive plates 322a, 322d, <NUM>, 322j may be defined by a plate angle <NUM>α (e.g., defined by a plate angle α per quadrant). Similarly, the second, third, fifth, sixth, eighth, ninth, eleventh, and twelfth conductive plates 322b, 322c, 322e, 322f, <NUM>, 322i, <NUM>, 322Imay be defined by a plate angle β. In embodiments, each conductive plate 322a-322I of the twelve conductive plates <NUM> are separated by a gap angle δ, as shown in <FIG>.

It has been found that proper selection of the plate angles α, β gap angle δ of the dodecapole electrostatic stigmator <NUM> may reduce and/or eliminate the octupole and/or dodecapole fields, and thereby reduce/eliminate the fourth-order and/or sixth-order focusing aberrations. A mathematical analysis of the dodecapole electrostatic stigmator <NUM> may prove to be illustrative.

The electrostatic potential distributions (ϕ(r,θ)) in r ≤ R for the dodecapole electrostatic stigmator <NUM> may again be described by Equation <NUM> above. Due to the symmetry of the boundary ϕ(R,θ) in <FIG>, the Fourier series coefficient Ak in Equation <NUM>, as applied to the dodecapole electrostatic stigmator <NUM>, may be defined by Equation <NUM>: <MAT> wherein Ak<NUM> and Ak<NUM> may be defined by Equation <NUM> and Equation <NUM>, respectively: m <MAT> <MAT>.

It is noted herein that, when k = <NUM> (e.g., fourth-order), the Fourier series coefficient A<NUM> is equal to zero (e.g., A<NUM> = <NUM> when k = <NUM>). Conversely, when k = <NUM>, the Fourier series coefficient A<NUM> may be defined by Equation <NUM>: <MAT>.

Furthermore, when k = <NUM> (e.g., fourth-order), the Fourier series coefficient A<NUM> is equal to zero (e.g., A<NUM> = <NUM> when k = <NUM>). Conversely, when k = <NUM>, the Fourier series coefficient A<NUM> may be defined by Equation <NUM>: <MAT>.

Further derivations may yield Equation <NUM> and Equation <NUM>: <MAT> <MAT>.

Subsequently, Equation <NUM> may follow according to the gap angle δ definition in <FIG>: <MAT>.

Substituting Equation <NUM> into Equation <NUM> yields Equation <NUM>: <MAT> wherein f(α) may be defined by Equation <NUM>: <MAT>.

A review of Equation <NUM> and Equation <NUM> reveals that, for a given gap angle δ, the Fourier series coefficient A<NUM> may be equal to zero due to f(α) being zero at certain plate angles α. In other words, the Fourier series coefficient A<NUM>, and therefore sixth-order focusing aberrations, may be eliminated by careful selection of the plate angle α of the dodecapole electrostatic stigmator <NUM>. This may be further understood with reference to <FIG>.

<FIG> depicts a graph <NUM> illustrating a relationship of plate angle (α) of a dodecapole electrostatic stigmator <NUM> on sixth-order focusing aberrations, in accordance with one or more embodiments of the present disclosure.

Curves <NUM>-<NUM> illustrate the relationship of f(α) and plate angle α for varying gap angles δ (e.g., δ<NUM>, δ<NUM>, δ<NUM>, δ<NUM>, δ<NUM>, δ<NUM>). As shown in graph <NUM>, there exists only one plate angle α within the range of <NUM>~<NUM>° for each respective gap angle δ which makes the function f(α) (and therefore the Fourier series coefficient A<NUM>) equal to zero. For example, for a first given gap angle δ<NUM>, there exists only one plate angle α within the range of <NUM>~<NUM>° which makes the Fourier series coefficient A<NUM> equal to zero by making the function f(α) equal to zero. By way of another example, for a second given gap angle δ<NUM>, there exists only one plate angle α within the range of <NUM>~<NUM>° which makes the Fourier series coefficient A<NUM> equal to zero by making the function f(α) equal to zero.

Continuing with the derivation of the dodecapole electrostatic stigmator <NUM>, and according to Equation <NUM>, the plate angle β may be selected according to Equation <NUM>: <MAT>.

Assuming that the plate angle β is greater than zero (e.g., β > <NUM>), the gap angle δ may be given by Equation <NUM>: <MAT>.

Accordingly, in some embodiments, and in order to eliminate fourth-order focusing aberrations and/or sixth-order focusing aberrations of the primary electron beamlets <NUM>, the respective plate angles α, β and gap angles δ of the dodecapole electrostatic stigmator <NUM> may be selected according to Equation <NUM> and Equation <NUM>.

<FIG> illustrates a simplified view of a micro-aperture array <NUM> (MAA <NUM>) of the multi-electron beam apparatus <NUM>, in accordance with one or more embodiments of the present disclosure.

In embodiments, the MAA <NUM> may include a plurality of aperture holes 330a-330n disposed within an aperture membrane <NUM>. The plurality of aperture holes 330a-330n may be arranged in any arrangement or configuration known in the art. For example, as shown in <FIG>, the plurality of aperture holes 330a-330ns may be arranged on the aperture membrane <NUM> in a hexagonal configuration. It is noted herein that a hexagonal configuration may comprise the closest configuration to achieving rotational symmetry, and may provide a number of optical advantages.

It is further noted herein that the number of aperture holes 330a-330n within the MAA <NUM> may define the number of primary electron beamlets <NUM> generated within the multi-electron beam apparatus <NUM>. For example, the electron source <NUM> may be configured to generate a source electron beam <NUM>, and the BLA <NUM> may direct a primary electron beam <NUM> to the MAA <NUM>. The source electron beam <NUM> incident upon the MAA <NUM> may then be split into a plurality of primary electron beamlets <NUM>, wherein the number and configuration of the primary electron beamlets <NUM> are at least partially defined by the number and configuration of the aperture holes 330a-330n.

The BLA <NUM> may be selectively adjusted in order to selectively adjust a diameter of the primary electron beam <NUM>, which is illustrated as 2R in <FIG>. The size of the BLA <NUM> may be optimized to allow the primary electron beam <NUM> to sufficiently illuminate the MAA <NUM> (e.g., eliminate each respective aperture hole 330a-330n). Additionally, the size of the BLA <NUM> may be selected in order to reduce and/or eliminate various optical blurs generated by the gun lens <NUM>, the MLA <NUM>, and by Coulomb interactions between electrons.

In embodiments, the aperture holes may exhibit a diameter d of <NUM>a (e.g., d = <NUM>a), and the pitch between adjacent aperture holes 330a-330n may be defined by a pitch p. The pitch may be measured from the centers of each of the aperture holes 330a-330n.

<FIG> illustrates a simplified view of a first layer of a micro-lens array <NUM> (MLA <NUM>) including a plurality of micro lenses 334a-334n, in accordance with one or more embodiments of the present disclosure.

In embodiments, the MLA <NUM> may include a plurality of micro-lenses 334a-334n disposed within a conductive membrane <NUM>. The of micro-lenses 334a-334n may include any micro-lenses known in the art including, but not limited to, micro Einzel lenses. In embodiments, each of the micro-lenses 334a-334n may be applied with focusing voltages. In one embodiment, the voltages applied to each of the micro-lenses 334a-334n may be controlled independently of one another. In one embodiment, the applied voltages may be configured to be equal for each micro-lens 334a-334n.

The conductive membrane <NUM> may be on the order of tens of microns thick. The plurality of micro-lenses 334a-334n may be arranged in any arrangement or configuration known in the art. In some embodiments, the plurality of micro-lenses 334a-334n may be arranged in a configuration which substantially conforms or matches to the configuration of aperture holes 330a-330n of the MAA <NUM>. For example, as shown in <FIG>, the plurality of micro-lenses 334a-334n may be arranged on the conductive membrane <NUM> in a hexagonal configuration which maps to (e.g., corresponds to) the hexagonal configuration of the aperture holes 330a-330n, as illustrated in <FIG>. In this regard, the plurality micro-lenses 334a-334n may exhibit a circular shape with the same diameters/bore size (e.g., d = <NUM>a), pitch p, and configuration/arrangement as the aperture holes 330a-330n.

It is noted herein that the micro-lens array <NUM> illustrated in <FIG> pictures only one conductive membrane <NUM>. It is further noted herein, however, that the MLA <NUM> may include three separate membranes with gaps on the order of tens of microns between each of the conductive membranes. For example, the MLA <NUM> may include a first conductive membrane <NUM>, one or more insulating layers, one or more focusing electrodes, and one or more additional conductive membranes. In this regard, the MLA <NUM> may include a uni-potential lens (e.g., Einzel lens). In embodiments, a middle membrane of the MLA <NUM> may be used as a focusing element on which a global voltage is applied to image the primary electron beamlets <NUM> onto the crossover plane <NUM>. Conversely, if two different voltages are applied on two conductive membranes of the MLA <NUM> (e.g., conductive membrane <NUM>), the MLA <NUM> may be used as an acceleration MLA and/or a deceleration MLA.

<FIG> illustrates a simplified elevation view of a first layer <NUM> of a dodecapole electrostatic stigmator <NUM> of a MSA <NUM>, in accordance with one or more embodiments of the present disclosure. <FIG> illustrates a simplified cross-sectional view of a dodecapole electrostatic stigmator <NUM> of an MSA <NUM>, in accordance with one or more embodiments of the present disclosure. <FIG> illustrates a simplified elevation view of an insulator layer <NUM> of a dodecapole electrostatic stigmator <NUM> of an MSA <NUM>, in accordance with one or more embodiments of the present disclosure.

In embodiments, a dodecapole electrostatic stigmator <NUM> may include a first layer <NUM> coupled to a second insulator layer <NUM>. For example, as shown in <FIG>, the conductive plates 322a-322I may be fabricated on the first layer <NUM>, wherein the first layer <NUM> is coupled to the insulator layer <NUM>, as shown in <FIG>. In this regard, the plurality of conductive plates 322a-322I may be said to be disposed and/or fabricated on the insulator layer <NUM>. The plurality of conductive plates 322a-322I may be fabricated on the insulator layer <NUM> via any fabrication techniques known in the art including, but not limited to, micro-electro-mechanical systems (MEMS) fabrication techniques.

It is noted herein that the dodecapole electrostatic stigmator <NUM> illustrated in <FIG> is rotated <NUM>° with respect to the dodecapole electrostatic stigmator <NUM> illustrated in <FIG>. In embodiments, the zero-voltage conductive plates <NUM> (e.g., conductive plates 322b, 322d, 322f, <NUM>, 322j, 322I) may be connected together as grounded plates.

As noted previously herein, there is a desire to reduce the number of voltage connecting lines and the number of voltage sources required for the dodecapole electrostatic stigmators <NUM> and MSA <NUM>. Accordingly, in some embodiments, each dodecapole electrostatic stigmator <NUM> may include a plurality of connecting pins 344a-344f configured to electrically couple at least some of the conductive plates <NUM> to a voltage source via at least one voltage connecting line <NUM>. In this regard, the plurality of conductive plates <NUM> may be electrically coupled to one or more voltage sources via the connecting pins 344a-344f and one or more voltage connecting lines <NUM>. For example, the plurality of voltage-enabled conductive plates <NUM> (e.g., conductive plates 322a, 322c, 322e, <NUM>, 322i, <NUM>) may be electrically coupled to a single voltage connecting line <NUM> via a plurality of connecting pins 344a-344f. The voltage connecting line <NUM> may be configured to electrically couple each of the conductive plates 322a, 322c, 322e, <NUM>, 322i, <NUM> to one another, as well as electrically couple the conductive plates 322a, 322c, 322e, <NUM>, 322i, <NUM> to a voltage source.

In embodiments, the one or more voltage sources are configured to apply one or more focusing voltages to each dodecapole electrostatic stigmator <NUM> of the plurality of dodecapole electrostatic stigmators <NUM> of the MSA <NUM>. In particular, a controller including one or more processors and a memory may be coupled to the voltage sources, and may be configured to cause the voltage sources to selectively apply/adjust focusing voltages applied to the conductive plates <NUM>. For example, the focusing voltages applied to the dodecapole electrostatic stigmators <NUM> of the MSA <NUM> may be selectively adjusted in order to selectively adjust one or more characteristics of the plurality of primary electron beamlets <NUM>. For instance, the focusing voltages applied to the dodecapole electrostatic stigmators <NUM> of the MSA <NUM> may be selectively adjusted in order to selectively remove an octupole field and a dodecapole field of each primary electron beamlet of the plurality of primary electron beamlets. In this regard, focusing voltages may be selectively adjusted in order to eliminate fourth-order focusing aberrations and/or sixth-order focusing aberrations. By way of another example, the focusing voltages applied to the dodecapole electrostatic stigmators <NUM> of the MSA <NUM> may be selectively adjusted in order to individually adjust a position of each primary electron beamlet <NUM> at the crossover plane <NUM> and/or the wafer plane <NUM>.

<FIG> illustrates a simplified view of a first layer <NUM> of a micro-stigmator array <NUM> (MSA <NUM>) including a plurality of dodecapole electrostatic stigmators 320a-320n, in accordance with one or more embodiments of the present disclosure. <FIG> illustrates a simplified view of an insulator layer <NUM> of the MSA <NUM> including the plurality of dodecapole electrostatic stigmators 320a-320n, in accordance with one or more embodiments of the present disclosure.

In embodiments, the MSA <NUM> may include a plurality of dodecapole electrostatic stigmators 320a-320n. The plurality of dodecapole electrostatic stigmators 320a-320n may be arranged in any arrangement or configuration known in the art. In some embodiments, the plurality of dodecapole electrostatic stigmators 320a-320n may be arranged in a configuration which substantially conforms or matches to the configuration of aperture holes 330a-330n of the MAA <NUM> and/or the plurality of micro-lenses 334a-334n of the MLA <NUM>. For example, as shown in <FIG>, the plurality of dodecapole electrostatic stigmators 320a-320n may be arranged in a hexagonal configuration which maps to (e.g., corresponds to) the hexagonal configuration of the aperture holes 330a-330n and/or micro-lenses 334a-334n, as illustrated in <FIG>.

In embodiments, the pitch between each of the dodecapole electrostatic stigmators 320a-320n may be on the order of hundreds of microns. For example, the dodecapole electrostatic stigmators 320a-320n may be spaced from one another by a pitch of approximately <NUM>µm. As shown in <FIG>, each dodecapole electrostatic stigmator 320a-320n may be individually addressable (e.g., coupled to a voltage source) via a single voltage connecting line 346a-346n.

It is noted herein that astigmatism blurs within the plurality of primary electron beamlets <NUM> may be characterized by elliptic spots. For each primary electron beamlet <NUM>, the direction of the elliptic spot (e.g., the long axis or shot axis of an elliptic spot) may be randomly varied. In order to correct the astigmatisms with a random direction for each respective primary electron beamlet <NUM>, the multi-electron beam apparatus <NUM> may include two separate MSAs 310a, 310b arrange in the optical axis, wherein the two separate MSAs 310a, 310b are arranged at a rotation angle of <NUM>° with respect to one another.

For example, <FIG> illustrates a simplified view of a first micro-stigmator array 310a (MSA 310a) in a first orientation, and <FIG> illustrates a simplified view of a second micro-stigmator array 310b (MSA 310b) in a second orientation. Comparing the first MSA 310a to the second MSA 310b, it may be seen that the second MSA 310b is rotated <NUM>° with respect to the first MSA 310a. In embodiments, the first MSA 310a and the second MSA 310b may be coupled to one another. Additionally, the first MSA 310a and the second MSA 310b may be separated by one or more insulator membranes. The insulator membranes may exhibit a thickness on the order of tens of microns.

Maximizing the utilization rate of the illuminating beam current (BC) is an important aspect of a multi-electron beam system (e.g., multi-electron beam apparatus <NUM>). The utilization rate η may be defined according to Equation <NUM>: <MAT> wherein N is the total number of primary electron beamlets <NUM>, a is the radius of the aperture holes 330a-330n, and BLA is the diameter of the BLA <NUM> (e.g., BLA = 2R in <FIG>).

For example, assume that the primary electron beam <NUM> (selected by the BLA <NUM>) is directed to the MAA <NUM> such that it telecentrically illuminates the MAA <NUM>. In this example, the primary electron beam <NUM> is split up into <NUM> primary electron beamlets <NUM> (e.g., N = <NUM>) which are arranged according to the hexagonal configuration of the MAA <NUM>, as shown in <FIG>. The pitch p between the aperture holes 330a-330n may be <NUM>µm, which may be necessary for a <NUM>µm inner bore diameter of the micro-lenses 334a-334n of the MLA <NUM>. Further assume that the size of the primary electron beam <NUM> (e.g., diameter of the BLA <NUM>) is <NUM>% greater than the max corner-to-corner beamlet distance for a reasonable illumination margin, as illustrated in <FIG> (e.g., BLA = (<NUM> + <NUM>%) * <NUM> * p = <NUM>µm). Applying Equation <NUM> to this example, it may be found that the illuminating BC utilization rate is η = <NUM>%, η = <NUM>%, and η = <NUM>% for aperture hole 330a-330n radiuses of a = <NUM> µm, a = <NUM> µm, and a = <NUM> µm, respectively.

As may be seen in the example above, the radius a of the aperture holes 330a-330n dominates the BC utilization rate η strongly. However, optically, the radius a of the aperture holes 330a-330n can not be designed to be similar in size to the bore size R of the dodecapole electrostatic stigmators <NUM> due to the octupole and dodecapole field effects defined in Equation <NUM> and Equation <NUM>, respectively. In order to address these shortfalls of previous techniques, the dodecapole electrostatic stigmator <NUM> of the present disclosure breaks through these limitations defined above by eliminating the terms of the octupole and dodecapole fields through careful selection of the plate angles α, β and gap angles δ. In effect, it is contemplated herein that embodiments of the present disclosure may enable improved BC utilization rates η, thereby increasing throughput in a multi-electron beam apparatus <NUM> or system.

<FIG> illustrates a full-square quadrupole electrostatic stigmator <NUM> of a micro-stigmator array <NUM> (MSA <NUM>), in accordance with one or more embodiments of the present disclosure.

Additional and/or alternative embodiments of the present disclosure are directed to a MSA <NUM> including one or more full-square quadrupole electrostatic stigmators <NUM>. A full-square quadrupole electrostatic stigmator <NUM> may include a first conductive plate 352a, a second conductive plate 352b, a third conductive plate 352c, and a fourth conductive plate 352c. In embodiments, each of the conductive plates 352a-352d may be separated by gaps 354a-354d. The full-square quadrupole electrostatic stigmator <NUM> may include a dual-polarity electrostatic stigmator, or a single-polarity electrostatic stigmator, as shown in <FIG>.

As opposed to the dodecapole electrostatic stigmator <NUM> which includes an inner bore in the shape of a circle (or substantially in the shape of a circle), the full-square quadrupole electrostatic stigmator <NUM> may include an inner bore which is characterized by a square. For example, as shown in <FIG>, the full-square quadrupole electrostatic stigmator <NUM> may include an inner bore including four sides, wherein two opposing sides are of length X, two opposing sides are length Y, and wherein X=Y. In additional and/or alternative embodiments, the quadrupole electrostatic stigmator <NUM> illustrated in <FIG> may include a rectangular-shaped quadrupole electrostatic stigmator <NUM>, wherein the inner bore is rectangular shaped such that X≠Y.

It has been found that the full-square quadrupole electrostatic stigmator <NUM> illustrated in <FIG>, as well as a rectangular-shaped quadrupole electrostatic stigmator may effectively eliminate both octupole fields and dodecapole fields. In this regard, some embodiments of the MSA <NUM> of the present disclosure may include a rectangular-shaped and/or a full-square quadrupole electrostatic stigmator <NUM>. Accordingly, any discussion associated with the dodecapole quadrupole electrostatic stigmator <NUM> may be regarded as applying to the quadrupole electrostatic stigmator <NUM> of <FIG>, unless noted otherwise herein.

<FIG> illustrates a quadrupole electrostatic stigmator <NUM> including conductive plates <NUM> with hyperbolic protrusions <NUM>, in accordance with one or more embodiments of the present disclosure. It is noted herein that any discussion associated with the rectangular-shaped and/or full-square quadrupole electrostatic stigmator <NUM> of <FIG> and/or the dodecapole electrostatic stigmator <NUM> may be regarded as applying to the quadrupole electrostatic stigmator <NUM> of <FIG>, unless noted otherwise herein.

Additional and/or alternative embodiments of the present disclosure are directed to a quadrupole electrostatic stigmator <NUM> including hyperbolic protrusions <NUM>. In embodiments, one or more conductive plates 362a-362d of the quadrupole electrostatic stigmator <NUM> may include a hyperbolic protrusion <NUM>. The hyperbolic protrusions <NUM> may be configured to extend from the conductive plates 362a-362d inward toward the bore of the quadrupole electrostatic stigmator <NUM> (e.g., toward the optical axis of the quadrupole electrostatic stigmator <NUM>). In embodiments, the hyperbolic protrusions 366a-366d may extend approximately <NUM>µm inward toward the center of the bore of the quadrupole electrostatic stigmator <NUM>. It has been found that the fu quadrupole electrostatic stigmator <NUM> may effectively minimize both the octupole fields and dodecapole fields.

<FIG> illustrates a simplified schematic diagram of an optical characterization system <NUM>, in accordance with one or more embodiments of the present disclosure.

The optical characterization system <NUM> may include any characterization system known in the art including, but not limited to, an inspection system, a review system, an image-based metrology system, and the like. In this regard, system <NUM> may be configured to perform inspection, review, or image-based metrology on a sample <NUM>. The optical characterization system <NUM> may include, but is not limited to, multi-electron beam apparatus <NUM>, a sample <NUM> disposed on a sample stage <NUM>, a detector assembly <NUM>, and a controller <NUM> including one or more processors <NUM> and a memory <NUM>.

In one embodiment, the electron beam apparatus <NUM> of system <NUM> is configured to direct the primary electron beamlets <NUM> to the sample <NUM>. The multi-electron beam apparatus <NUM> may form an electron-optical column. In another embodiment, multi-electron beam apparatus <NUM> includes one or more additional and/or alternative electron-optical elements configured to focus and/or direct the primary electron beamlets <NUM> to the surface of the sample <NUM>. In another embodiment, system <NUM> includes one or more electron-optical elements <NUM> configured to collect secondary electrons <NUM> emanated from the surface of the sample <NUM> in response to the primary electron beamlets <NUM>. It is noted herein that the one or more electron-optical elements of multi-electron beam apparatus <NUM> and the one or more electron-optical elements <NUM> may include any electron-optical elements configured to direct, focus, and/or collect electrons including, but not limited to, one or more deflectors, one or more electron-optical lenses, one or more condenser lenses (e.g., magnetic condenser lenses), one or more objective lenses (e.g., magnetic condenser lenses), and the like.

Sample <NUM> may include any sample known in the art including, but not limited to, a wafer, a reticle, a photomask, and the like. In one embodiment, sample <NUM> is disposed on a stage assembly <NUM> to facilitate movement of sample <NUM>. In another embodiment, the stage assembly <NUM> is an actuatable stage. For example, the stage assembly <NUM> may include, but is not limited to, one or more translational stages suitable for selectably translating the sample <NUM> along one or more linear directions (e.g., x-direction, y-direction and/or z-direction). By way of another example, the stage assembly <NUM> may include, but is not limited to, one or more rotational stages suitable for selectively rotating the sample <NUM> along a rotational direction. By way of another example, the stage assembly <NUM> may include, but is not limited to, a rotational stage and a translational stage suitable for selectably translating the sample <NUM> along a linear direction and/or rotating the sample <NUM> along a rotational direction. It is noted herein that the system <NUM> may operate in any scanning mode known in the art.

It is noted that the electron optical assembly of the multi-electron beam apparatus <NUM> and/or system <NUM> is not limited to the electron-optical elements depicted in <FIG>, which are provided merely for illustrative purposes. It is further noted that the system <NUM> may include any number and type of electron-optical elements necessary to direct/focus the primary electron beamlets <NUM> onto the sample <NUM> and, in response, collect and image the emanated secondary electrons <NUM> onto the detector assembly <NUM>.

For example, the system <NUM> may include one or more electron beam scanning elements (not shown). For instance, the one or more electron beam scanning elements may include, but are not limited to, one or more electromagnetic scanning coils or electrostatic deflectors suitable for controlling a position of the primary electron beamlets <NUM> relative to the surface of the sample <NUM>. Further, the one or more scanning elements may be utilized to scan the primary electron beamlets <NUM> across the sample <NUM> in a selected pattern.

In another embodiment, secondary electrons <NUM> are directed by deflectors <NUM> to one or more sensors <NUM> of a detector assembly <NUM>. The deflectors <NUM> may include any optical elements known in the art for directing secondary electrons <NUM> including, but not limited to, Wien filters. The detector assembly <NUM> of the system <NUM> may include any detector assembly known in the art suitable for detecting multiple secondary electrons <NUM> from the surface of the sample <NUM>. In one embodiment, the detector assembly <NUM> includes an electron detector array. In this regard, the detector assembly <NUM> may include an array of electron-detecting portions. Further, each electron-detecting portion of the detector array of the detector assembly <NUM> may be positioned so as to detect an electron signal from sample <NUM> associated with one of the incident primary electron beamlets <NUM>. In this regard, each channel of the detector assembly <NUM> may correspond to a particular primary electron beamlet <NUM> of the multi-electron beam apparatus <NUM>. The detector assembly <NUM> may include any type of electron detector known in the art. For example, the detector assembly <NUM> may include a micro-channel plate (MCP), a PIN or p-n junction detector array, such as, but not limited to, a diode array or avalanche photo diodes (APDs). By way of another example, the detector assembly <NUM> may include a high-speed scintillator/PMT detector.

While <FIG> illustrates the system <NUM> as including a detector assembly <NUM> comprising only a secondary electron detector assembly, this is not to be regarded as a limitation of the present disclosure. In this regard, it is noted that the detector assembly <NUM> may include, but is not limited to, a secondary electron detector, a backscattered electron detector, and/or a primary electron detector (e.g., an in-column electron detector). In another embodiment, system <NUM> may include a plurality of detector assemblies <NUM>. For example, system <NUM> may include a secondary electron detector assembly <NUM>, a backscattered electron detector assembly <NUM>, and an in-column electron detector assembly <NUM>.

In another embodiment, detector assembly <NUM> is communicatively coupled to a controller <NUM> including one or more processors <NUM> and memory <NUM>. For example, the one or more processors <NUM> may be communicatively coupled to memory <NUM>, wherein the one or more processors <NUM> are configured to execute a set of program instructions stored on memory <NUM>. In one embodiment, the one or more processors <NUM> are configured to analyze the output of detector assembly <NUM>. In one embodiment, the set of program instructions are configured to cause the one or more processors <NUM> to analyze one or more characteristics of sample <NUM>. In another embodiment, the set of program instructions are configured to cause the one or more processors <NUM> to modify one or more characteristics of system <NUM> in order to maintain focus on the sample <NUM> and/or the sensor <NUM>. For example, the one or more processors <NUM> may be configured to adjust one or more characteristics of the multi-electron beam apparatus <NUM>, objective lens <NUM>, or one or more optical elements <NUM> in order to focus primary electron beamlets <NUM> from multi-electron beam apparatus <NUM> onto the surface of the sample <NUM>. By way of another example, the one or more processors <NUM> may be configured to adjust the objective lens <NUM> and/or one or more optical elements <NUM> in order to collect secondary electrons <NUM> from the surface of the sample <NUM> and focus the collected secondary electrons <NUM> on the sensor <NUM>. By way of another example, the one or more processors <NUM> may be configured to adjust one or more focusing voltages applied to one or more electrostatic deflectors of multi-electron beam apparatus <NUM> in order to independently adjust the position or alignment of one or more primary electron beamlets <NUM>.

It is noted herein that the one or more components of system <NUM> may be communicatively coupled to the various other components of system <NUM> in any manner known in the art. For example, the one or more processors <NUM> may be communicatively coupled to each other and other components via a wireline (e.g., copper wire, fiber optic cable, and the like) or wireless connection (e.g., RF coupling, IR coupling, data network communication (e.g., WiFi, WiMax, Bluetooth and the like). By way of another example, the one or more processors may be communicatively coupled to one or more components of the multi-electron beam apparatus <NUM> (e.g., electron source <NUM>, MLA <NUM>, MSA <NUM>, and the like), the one or more voltage sources, and the like.

In one embodiment, the one or more processors <NUM> may include any one or more processing elements known in the art. In this sense, the one or more processors <NUM> may include any microprocessor-type device configured to execute software algorithms and/or instructions. In one embodiment, the one or more processors <NUM> may consist of a desktop computer, mainframe computer system, workstation, image computer, parallel processor, or other computer system (e.g., networked computer) configured to execute a program configured to operate the system <NUM>, as described throughout the present disclosure. It should be recognized that the steps described throughout the present disclosure may be carried out by a single computer system or, alternatively, multiple computer systems. Furthermore, it should be recognized that the steps described throughout the present disclosure may be carried out on any one or more of the one or more processors <NUM>. In general, the term "processor" may be broadly defined to encompass any device having one or more processing elements, which execute program instructions from memory <NUM>. Moreover, different subsystems of the system <NUM> (e.g., multi-electron beam apparatus <NUM>, MLA <NUM>, MSA <NUM>, detector assembly <NUM>, controller <NUM>, and the like) may include processor or logic elements suitable for carrying out at least a portion of the steps described throughout the present disclosure. Therefore, the above description should not be interpreted as a limitation on the present disclosure but merely an illustration.

The memory <NUM> may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors <NUM>. For example, the memory <NUM> may include a non-transitory memory medium. For instance, the memory <NUM> may include, but is not limited to, a read-only memory (ROM), a random access memory (RAM), a magnetic or optical memory device (e.g., disk), a magnetic tape, a solid state drive and the like. It is further noted that memory <NUM> may be housed in a common controller housing with the one or more processors <NUM>. In an alternative embodiment, the memory <NUM> may be located remotely with respect to the physical location of the processors <NUM>, controller <NUM>, and the like. In another embodiment, the memory <NUM> maintains program instructions for causing the one or more processors <NUM> to carry out the various steps described through the present disclosure.

<FIG> illustrates a flowchart of a method <NUM> of inspection using a multi-stigmator array <NUM> (MSA <NUM>), in accordance with one or more embodiments of the present disclosure. It is noted herein that the steps of method <NUM> may be implemented all or in part by system <NUM> and/or multi-electron beam apparatus <NUM>. It is further recognized, however, that the method <NUM> is not limited to the system <NUM> and/or multi-electron beam apparatus <NUM> in that additional or alternative system-level embodiments may carry out all or part of the steps of method <NUM>.

In a step <NUM>, a primary electron beam is generated. For example, an electron source <NUM> may generate a primary electron beam <NUM>. The electron source <NUM> may include any electron source known in the art including, but not limited to, thermal field emission (TFE) sources.

In a step <NUM>, the primary electron beam is split into a plurality of primary electron beamlets. For example, as shown in <FIG>, the MAA <NUM> may be configured to receive the primary electron beam <NUM> and split the primary electron beam <NUM> in to a plurality of primary electron beamlets <NUM>.

In a step <NUM>, the plurality of primary electron beamlets are directed to a micro-lens array <NUM> (MLA <NUM>) and a micro-stigmator array <NUM> (MSA <NUM>). In embodiments, the MLA <NUM> may include a plurality of micro-lenses 334a-334n. Similarly, the MSA <NUM> may include a plurality of electrostatic stigmators. For example, the MSA <NUM> may include a plurality of dodecapole electrostatic stigmators <NUM>. By way of another example, the MSA <NUM> may include a plurality of full-square quadrupole electrostatic stigmators <NUM>, rectangular-shaped quadrupole electrostatic stigmators, and/or quadrupole electrostatic stigmators with hyperbolic protrusions.

In a step <NUM>, fourth-order focusing aberrations and/or sixth-order focusing aberrations are eliminated from the plurality of electron beamlets with the MSA. For example, each dodecapole electrostatic stigmator <NUM> of the MSA <NUM> may be configured to receive a single primary electron beamlet <NUM> and eliminate fourth-order focusing aberrations and/or sixth-order focusing aberrations from the primary electron beamlet <NUM>. In embodiments, a controller may be configured to cause one or more voltage sources to selectively adjust focusing voltages applied to the electrostatic stigmators of the MSA <NUM> in order to reduce and/or eliminate focusing aberrations.

In a step <NUM>, the plurality of primary electron beamlets are directed to a wafer plane. For example, projection optics of the multi-electron beam apparatus <NUM> may be configured to direct primary electron beamlets <NUM> to a wafer plane <NUM>. The projection optics may include, but are not limited to, a transfer lens <NUM> and an objective lens <NUM>. In embodiments, the plurality of electron beamlets <NUM> may be directed to a sample <NUM> in order to carry out one or more characterization processes of the sample <NUM>.

One skilled in the art will recognize that the herein described components (e.g., operations), devices, objects, and the discussion accompanying them are used as examples for the sake of conceptual clarity and that various configuration modifications are contemplated. Consequently, as used herein, the specific exemplars set forth and the accompanying discussion are intended to be representative of their more general classes. In general, use of any specific exemplar is intended to be representative of its class, and the non-inclusion of specific components (e.g., operations), devices, and objects should not be taken as limiting.

Those having skill in the art will appreciate that there are various vehicles by which processes and/or systems and/or other technologies described herein can be effected (e.g., hardware, software, and/or firmware), and that the preferred vehicle will vary with the context in which the processes and/or systems and/or other technologies are deployed. For example, if an implementer determines that speed and accuracy are paramount, the implementer may opt for a mainly hardware and/or firmware vehicle; alternatively, if flexibility is paramount, the implementer may opt for a mainly software implementation; or, yet again alternatively, the implementer may opt for some combination of hardware, software, and/or firmware. Hence, there are several possible vehicles by which the processes and/or devices and/or other technologies described herein may be effected, none of which is inherently superior to the other in that any vehicle to be utilized is a choice dependent upon the context in which the vehicle will be deployed and the specific concerns (e.g., speed, flexibility, or predictability) of the implementer, any of which may vary.

The previous description is presented to enable one of ordinary skill in the art to make and use the invention as provided in the context of a particular application and its requirements. As used herein, directional terms such as "top," "bottom," "over," "under," "upper," "upward," "lower," "down," and "downward" are intended to provide relative positions for purposes of description, and are not intended to designate an absolute frame of reference. Various modifications to the described embodiments will be apparent to those with skill in the art, and the general principles defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the particular embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features herein disclosed.

The various singular/plural permutations are not expressly set forth herein for sake of clarity.

All of the methods described herein may include storing results of one or more steps of the method embodiments in memory. The results may include any of the results described herein and may be stored in any manner known in the art. The memory may include any memory described herein or any other suitable storage medium known in the art. After the results have been stored, the results can be accessed in the memory and used by any of the method or system embodiments described herein, formatted for display to a user, used by another software module, method, or system, and the like. Furthermore, the results may be stored "permanently," "semi-permanently," temporarily," or for some period of time. For example, the memory may be random access memory (RAM), and the results may not necessarily persist indefinitely in the memory.

It is further contemplated that each of the embodiments of the method described above may include any other step(s) of any other method(s) described herein. In addition, each of the embodiments of the method described above may be performed by any of the systems described herein.

The herein described subject matter sometimes illustrates different components contained within, or connected with, other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. Likewise, any two components so associated can also be viewed as being "connected," or "coupled," to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being "couplable," to each other to achieve the desired functionality. Specific examples of couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components.

Claim 1:
A system, comprising:
an electron source (<NUM>);
a micro-lens array (<NUM>), MLA, configured to receive one or more primary electron beams from the electron source and split the one or more primary electron beams into a plurality of primary electron beamlets;
a micro-stigmator array (<NUM>), MSA, comprising a plurality of dodecapole electrostatic stigmators, wherein the MSA is configured to eliminate at least one of fourth-order focusing aberrations or sixth-order focusing aberrations of the plurality of primary electron beamlets; and
projection optics (<NUM>, <NUM>) configured to receive the plurality of primary electron beamlets and focus the plurality of primary electron beamlets onto a surface of a sample;
wherein each dodecapole electrostatic stigmator of the plurality of dodecapole electrostatic stigmators comprises twelve conductive plates,
wherein each conductive plate of the twelve conductive plates are separated by a gap angle δ,
wherein a first conductive plate, a fourth conductive plate, a seventh conductive plate, and a tenth conductive plate are defined by a plate angle <NUM>α, wherein α is in the range of <NUM>° ~<NUM>°, and
wherein a second conductive plate, a third conductive plate, a fifth conductive plate, a sixth conductive plate, an eighth conductive plate, a ninth conductive plate, an eleventh conductive plate, and a twelfth conductive plate are defined by a plate angle β, such that β = <NUM>° - α - (<NUM>δ/<NUM>).