Beam grid layout
A sub-beam aperture array for forming a plurality of sub-beams from one or more charged particle beams. The sub-beam aperture array comprises one or more beam areas, each beam area comprising a plurality of sub-beam apertures arranged in a non-regular hexagonal pattern, the sub-beam apertures arranged so that, when projected in a first direction onto a line parallel to a second direction, the sub-beam apertures are uniformly spaced along the line, and wherein the first direction is different from the second direction. The system further comprises a beamlet aperture array with a plurality of beamlet apertures arranged in one or more groups. The beamlet aperture array is arranged to receive the sub-beams and form a plurality of beamlets at the locations of the beamlet apertures of the beamlet array.
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This application is a reissue of U.S. Pat. No. 9,934,943 B1, issued on Apr. 3, 2018, from U.S. patent application Ser. No. 14/787,775, filed Oct. 29, 2015, which is a 35 U.S.C. 371 National Phase Entry Application from PCT/EP2014/059106, filed May 05, 2014, which claims the benefit of US Provisional Patent Application No. 61/818,919, filed on May 3, 2013, the disclosure of which is incorporated herein in its entirety by reference.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to an aperture array and a charged particle lithography system using an aperture array.
2. Description of the Related Art
In the charged particle lithography field, various aperture pattern schemes for a multi-beam pattern definition device are known. For example, U.S. Pat. No. 5,369,282 to Arai discloses an electron-beam lithography system using a blanking aperture array (BAA) as the pattern definition device. The BAA has a number of rows of apertures, and the images of the apertures are scanned over a stripe of the substrate in a controlled, continuous motion.
Arai teaches to group aperture rows of the BAA by exposure order. The substrate stripe is first exposed using a full dosage, as delivered by a first group, and then subsequently exposed to compensate for proximity effects exhibited by the substrate stripe, as delivered by a second group. In some embodiments, corresponding apertures of the first and second groups are offset from each other in relation to an electron scanning direction and/or to a mechanical scanning direction. Further, within each group, apertures on every other row align in the electron-scan direction and all rows align in the mechanical-scan direction.
U.S. Patent Application No. 2011-0073782 to Wieland discloses an electron-beam lithography system with a beamlet blanker array with apertures for generating 16 sub-beams arranged in a square 4×4 array, where each sub-beam is divided into 9 beamlets arranged in a square 3×3 array. Wieland teaches various writing strategies using such beamlet arrangements to achieve exposure of a wafer surface when the wafer is moved with respect to the beamlet blanker array and the beamlets are deflected over the surface of the wafer.
Among other deficiencies, the system of Arai lacks sufficient throughput for commercial viability and neither system provides an optimum arrangement of sub-beams or beamlets for uniform exposure of the wafer. Thus there is a need for alternative aperture pattern schemes that improve throughput and distribution of the writing beams on the wafer surface.
BRIEF SUMMARY OF THE INVENTIONThe invention aims to address these problems. In one aspect the invention provides a sub-beam aperture array for forming a plurality of sub-beams from one or more charged particle beams. The sub-beam aperture array comprises one or more beam areas, each beam area comprising a plurality of sub-beam apertures arranged in a non-regular hexagonal pattern, the sub-beam apertures arranged so that, when projected in a first direction onto a line parallel to a second direction, the sub-beam apertures are uniformly spaced along the line, and wherein the first direction is different from the second direction.
In the non-regular hexagonal pattern of the sub-beam apertures of each beam area, each aperture has six neighbouring apertures, but these six neighbours are not arranged in the shape of a regular hexagon. The hexagonal pattern is non-regular in the sense that an aperture is not equi-distant from all of its six neighbouring apertures, but the aperture array preferably repeats the same non-regular hexagonal pattern uniformly within each beam area so that every aperture within a beam area is arranged in the same non-regular hexagonal pattern. The uniform spacing of sub-beam apertures when they are projected onto a line parallel to the second direction, results in evenly spaced writing paths when a plurality of sub-beams are formed using the sub-beam aperture array, and a target such as a wafer is moved perpendicular to the second direction relative to the sub-beam aperture array. The uniform spacing of projected apertures preferably applies for all of the sub-beam apertures in all of the beam areas. The preferred arrangement enables each sub-beam to form a separate writing path which does not coincide with the writing path of any other sub-beam and is equidistant from the writing paths of adjacent sub-beams.
Within each of the one or more beam areas of the sub-beam aperture array, the sub-beam apertures may be arranged in a plurality of columns regularly spaced in the second direction, with the sub-beam apertures in each column offset by a same amount, in the second direction, from each adjacent sub-beam aperture in the same column. Furthermore, the columns of sub-beam apertures may extend generally in the first direction, the columns being spaced apart with uniform spacing in the second direction. Within each column, adjacent apertures may be offset from each other in the second direction by a uniform offset. This uniform offset results in the sub-beam apertures being uniformly spaced, when projected in the first direction onto a line parallel to the second direction. This offset also results in the columns of apertures not extending exactly in the first direction but at a slight angle to the first direction.
The offset between sub-beam apertures within each column may be the same as an offset between a sub-beam aperture in one beam area and an adjacent sub-beam aperture in a corresponding column of another beam area. The offset of adjacent sub-beam apertures in a single column may be equal to a fraction of a diameter of the sub-beam apertures. Also, within each of the one or more beam areas, the sub-beam apertures in each column may be staggered, in the first direction, with respect to the sub-beam apertures of a neighbouring column. This stagger of apertures of adjacent columns results in the apertures being not aligned in the second direction. In one arrangement, the sub-beam apertures of neighbouring columns are not aligned in the second direction but the sub-beam apertures of every other column are be aligned in the second direction.
In the sub-beam aperture array, the second direction may be substantially perpendicular to the first direction. The first and second directions may be exactly perpendicular, but also may be close to perpendicular but not exactly perpendicular. This may be done, for example, to compensate for movement of the target in the first direction while the sub-beams are being scanned across the surface of the target in the second direction.
In a second aspect the invention provides a beamlet aperture array for forming a plurality of beamlets from one or more charged particle sub-beams. The beamlet aperture array comprises a plurality of beamlet apertures arranged in one or more groups, wherein the beamlet apertures are arranged so that, when projected in a fourth direction onto a line parallel to a third direction, the sub-beam apertures of each group are uniformly spaced along the line, and wherein the third direction is different from the fourth direction. The beamlets may be formed from a single charged particle sub-beam, or from multiple separate sub-beams, where each group of beamlet apertures corresponds with a separate charged particle sub-beam projected onto the beamlet aperture array. The sub-beams may be formed by a separate sub-beam array as described above and herein.
The uniform spacing of beamlet apertures when they are projected onto a line parallel to the third direction, results in evenly spaced writing paths when a plurality of beamlets are formed using the beamlet aperture array, and the beamlets are scanned across a target such as a wafer perpendicular to the third direction. The uniform spacing of projected apertures preferably applies for all of the beamlet apertures in each group. The preferred arrangement enables each beamlet to form a separate writing path which does not coincide with the writing path of any other beamlet and is equidistant from the writing paths of adjacent beamlets.
The beamlet apertures may be arranged in rows and columns, each beamlet aperture within a row of the beamlet aperture array being uniformly offset in the third direction from adjacent beamlet apertures in the row. In the beamlet aperture array, the fourth direction may be substantially perpendicular to the third direction. The third and fourth directions may be exactly perpendicular, but also may be close to perpendicular but not exactly perpendicular. This may be done, for example, to compensate for movement of the target in the third direction while the sub-beams are being scanned across the surface of the target in the fourth direction. The beamlet aperture apertures within a column of each group may be aligned in the fourth direction.
In another aspect the invention provides a beamlet aperture array for forming a plurality of beamlets from one or more charged particle sub-beams, the beamlet aperture array comprising a plurality of beamlet apertures arranged in one or more groups, each group corresponding to a sub-beam, wherein the positions of the beamlet apertures within each group form an unbalanced array.
The beamlet apertures neighboring within a row of the beamlet aperture array may be offset from each other by a uniform amount with respect to the third direction. The offset may be equal to a fraction of the pitch between the neighboring beamlet apertures. This fraction may be equal to the pitch between the neighboring beamlet apertures divided by the number of beamlet apertures within the row. The beamlet apertures in each group of the beamlet aperture array may be arranged in the form of a skewed square array.
The beamlet apertures in each group may be all offset from the center of a beam spot formed by the group of beamlet apertures. In a beamlet aperture array with forty-nine beamlet apertures arranged within the beam spot, each beamlet aperture may be associated with an aperture number, and the offset in an X direction of each beamlet aperture from the center of the beam spot is defined by the formula: appxoffset=(int[(aperture number−1)/7)]−3)*pitch, where int is a floor function. The offset in a Y direction of each beamlet aperture from the center of the beam spot may be defined by the formula: appyoffset=(−pitch/2)+[(6−[(aperture number−1)mod 7]+int(aperture number/29)−3)*pitch]−[(pitch/7)* (int[(aperture number−1)/7)]−3)], where int is a floor function.
In yet another aspect, the invention provides a charged particle lithography system for exposing a target using a plurality of charged particle sub-beams. The system comprises a charged particle generator for generating a charged particle beam, a sub-beam aperture array as described above and herein arranged to receive the charged particle beam and form a plurality of sub-beams at the locations of the apertures of the sub-beam array, and a projection lens system configured to project the sub-beams onto the surface of the target.
The charged particle lithography system may further comprise a deflector arranged to deflect the sub-beams in the first direction, and may further comprise a moveable stage for moving the target in the second direction. The first direction may correspond to a scanning direction of the plurality of sub-beams and the second direction to a mechanical-scan direction of the target.
The charged particle lithography system may also comprise a beamlet aperture array as described above and herein, the beamlet aperture array arranged to receive the sub-beams and form a plurality of beamlets at the locations of the beamlet apertures of the beamlet array. The first direction (for the sub-beam array) may be the same as the third direction (for the beamlet array), and the second direction (for the sub-beam array) may be the same as the fourth direction (for the beamlet array).
In yet another aspect, the invention provides a method for exposing a field of a target using a plurality of charged particle beamlets, the field having a length in a first direction and a width in a second direction. The method comprises forming the charged particle beamlets into a plurality of discrete groups, the groups being equally spaced across the width of the field, and moving the target in the first direction and simultaneously scanning each group of beamlets across a width of a corresponding stripe of the field so that each beamlet follows a writing path on the surface of the target, wherein the writing paths of the beamlets of each group are evenly spaced in the first direction. Each group of beamlets is assigned to a single stripe of the field, and is deflected across the width of the field as the target is moved. The writing paths of separate groups of beamlets do not substantially overlap (there may be some small overlap of the writing paths where stitching is performed at the boundary between two stripes). Similarly, the writing paths of the individual beamlets with each group are evenly spaced in the first direction.
The first direction may be substantially perpendicular to the second direction. The first and second directions may be exactly perpendicular, but also may be close to perpendicular but not exactly perpendicular. This may be done, for example, to compensate for movement of the target in the first direction while the beamlets are being scanned across the field.
Various aspects of the invention will be further explained with reference to embodiments shown in the drawings wherein:
The following is a description of various embodiments of the invention, given by way of example only and with reference to the drawings. Further, unless noted otherwise, the drawings are not drawn to scale.
In this description the following definitions are used:
Unbalanced array: an array or matrix with at least one row and/or column that has a different number of elements than another row or column of the array or matrix; a sub-set of unbalanced arrays include arrays with “shifted” columns, wherein the patterning scheme shifts one or more columns in relation to the other columns of the array.
Offset: the distance between one feature of an aperture, beam spot, or other object with respect to a corresponding feature of another object or other reference point. The distance may be with respect to (e.g. perpendicular to) a mechanical scan direction and/or an electron scan direction. For example, features of an aperture include the midpoint and centerline of an aperture.
Stagger: objects arranged in a zig-zag or other misalignment pattern.
Column: a sub-group of elements that align with the least deviation from the Y-axis or mechanical scan direction compared with alternative alignments of the elements of a group.
Row: a sub-group of elements that align with the least deviation from the X-axis or an electron scan direction compared with alternative alignments of the elements of a group.
Corresponding beam: A beam or group of beams arranged to pass through an aperture, projection lens, or deflector. Corresponding beams may have a one-to-one, one-to-many, or many-to-one relationship with an aperture, projection lens, or deflector.
Sub-beam: a charged particle beam projected by an aperture array that will be further divided into a plurality of beams known as beamlets.
The electron beam 20 from the electron source 1 passes a collimator lens 3 to produce a collimated electron beam 21, which impinges on sub-beam aperture array 4. The aperture array 4 blocks part of the beam and emits a plurality of sub-beams 22. The system generates a large number of sub-beams 22, e.g. about 10,000 to 1,000,000 beamlets.
The sub-beams pass through a condenser lens array 5, which focuses the sub-beams approximately in the plane of beam stop array 8 and towards a corresponding opening in beam stop array 8. In principle each sub-beam can be focused either at the corresponding opening in beam stop array 8, or at the effective lens plane of the corresponding projection lens system. In practice it is preferred to focus the sub-beams somewhere between these two points. This results in the aperture array 4 being imaged onto the target 11.
The condenser lens array may comprise a single condenser lens array or a set of condenser lens arrays, as would be known to a person of skill in the field of electron-optics.
The sub-beams 22 are intercepted by multiple aperture array 6 which includes a number of apertures in the path of (i.e., corresponding to) each sub-beam, producing a group of beamlets 23 from each sub-beam 22. The groups of beamlets, formed from the sub-beams, are also focused approximately in the plane of beam stop array 8 and each group of beamlets is directed towards a corresponding opening in beam stop array 8.
These beamlets 23 then pass through beamlet blanker array 7. Blanked beamlets are blocked by beam stop array 8, while unblanked beamlets in each group pass through a corresponding opening in beam stop array 8 and are subsequently projected onto the target by projection lens arrangement 10. In the example shown in
The beamlet blanker array 7 may deflect individual beamlets 23 in a group of beamlets at certain times in order to blank them. This is illustrated in
Subsequently, the electron beamlets 23 enter the end module. The end module may be constructed as an insertable, replaceable unit which comprises various components or a discreet combination of individual components. The end module includes a beam stop array 8, a beam deflector array 9, and a projection lens arrangement 10. The end module will, amongst other functions, provide a demagnification of about 25 to 500 times. Additionally, the end module may be configured to deflect the beamlets 23. After leaving the end module, the beamlets 23 impinge on a surface of a target 11 positioned at a target plane. For lithography applications, the target usually comprises a wafer provided with a charged-particle sensitive layer or resist layer.
In the end module, the electron beamlets 23 first pass beam stop array 8. This beam stop array 8 largely determines the opening angle of the beamlets. In an embodiment, the apertures in beam stop array 8 are round, resulting in beamlets with a generally uniform opening angle.
The passages of the beam stop array 8 may be aligned with the elements of the beamlet blanker array 7. The beamlet blanker array 7 and beam stop array 8 then operate together to block or let pass the beamlets 23 in the following way. If beamlet blanker array 7 deflects a beamlet, it will not pass through the corresponding aperture in beam stop array 8. Instead, it will be blocked by the substrate of beam stop array 8. However, if beamlet blanker array 7 does not deflect a beamlet, it will pass through the corresponding aperture in beam stop array 8, and will then be projected as a spot on the surface of target 11. In this way the individual beamlets 23 may be effectively switched on and off.
Next, the beamlets 23 pass through a beam deflector array 9 which provides for deflection of each beamlet 23 in a direction substantially perpendicular to the direction of the undeflected beamlets 23. Next, the beamlets 23 pass through projection lens arrangement 10 and are projected onto a target 11 to be exposed, typically a wafer, located in a target plane.
The projection lens arrangement 10 in the embodiment of the end module shown in
The plates may be coated with an electrically conductive coating to form electrodes. A metal with a conductive native oxide may be used for the electrode, such as molybdenum, deposited onto the plate using techniques well known in the art. An electrical voltage is applied to each electrode to control the shape of the electrostatic lenses formed at the location of each aperture. Each electrode is controlled by a single control voltage for the complete array. Thus, in the embodiment shown in
The three control voltages V1, V2, and V3 create an array of uniform electrostatic lenses which focus and demagnify the large number of electron beamlets 23. The characteristics of the electrostatic lenses are controlled by the three control voltages, so that the amount of focusing and demagnification of all of the beamlets can be controlled by controlling these three voltages. In this way, a single common control signal can be used to control a whole array of electrostatic lenses for demagnifying and focusing a very large number of electron beamlets. A common control signal may be provided for each plate or as a voltage difference between two or more plates. The number of plates used in different projection lens arrangements may vary, and the number of common control signals may also vary.
The voltages V1, V2, and V3 may be set so that the difference in voltage between the second and third plates (13 and 14) is greater than the difference in voltage between first and second plates (12 and 13). This results in stronger lenses being formed between plates 13 and 14 so that the effective lens plane of each projection lens system is located between plates 13 and 14, as indicated in
The multiple aperture plate 6 above the deflector array 9 may comprise a multiplicity of apertures 24 as depicted, i.e. may have a patterned opening to accommodate the multiple beamlets 23 that correspond to a single lens system associated with on opening in beam stop array 8. Note that in a real design, the beam angle is much smaller than shown in
Because part or all of the plurality of beamlets directed through to a each projection lens system may be blanked at any point in time during operation, a system encompassing aforementioned principle may in this description be referred to as a patterned beamlet system. Such a patterned beamlet system may also be regarded as a multiplicity of miniaturized imaging systems arranged side by side.
Referring back to
Further, the patterned beamlets are scanned across the surface of the target 11 by the deflector array 9. This movement of the beamlets is performed in a second direction, the second direction being different than the first direction. This second direction is referred to variously in this description as a second direction or X-direction or deflection scan direction. In one embodiment of the invention, the first direction is substantially perpendicular to the second direction, i.e. nearly perpendicular but not exactly perpendicular, as explained below. Please note that the movement of the beamlets in the second direction is generally a repetitive movement, i.e. a beamlet is scanned from a starting position over a certain distance until an end position and then moved back again to the starting position. Hence, the movement of the beamlets in the second direction may be performed with a certain predetermined frequency.
As mentioned previously, for lithography applications, the target usually comprises a wafer provided with a charged-particle sensitive layer or resist layer. The current industry standard is a 300 mm wafer, although new systems accommodating 450 mm wafers are already being designed. Wafers are typically divided into fixed size fields with a maximum dimension of 26 mm×33 mm, although other sized fields may also be used. Each field may be processed to produce multiple integrated circuits (i.e. the layout for multiple chips may be written into a single field) but the ICs usually do not cross a field border. With a maximum size of 26 mm×33 mm there are 63 fields available on a single standard 300 mm wafer. Smaller fields are possible and will result in a higher number of fields per wafer.
In one embodiment of the lithography machine, the machine generates 13,260 sub-beams and each sub-beam is split into 49 beamlets arranged in a 7×7 unbalanced array, resulting in 649,740 beamlets (i.e. 13,260×49). Of the 13,260 sub-beams, 260 sub -beams may be used for a redundancy scan, i.e. for use during a second scan of each field to take the place of faulty beamlets. Other embodiments are also possible using a subset of sub-beams for a first scan and another (different) sub-set of sub-beams for a second scan of the same area of the wafer, in order to divide the total heat loading of the beamlets striking the wafer across two scans and to reduce the data path capacity needed for each scan by reducing the number of active sub-beams per scan. In a similar way, the sub-beams can be used in three or more subsets over three or more scans of the same area of the wafer.
When this arrangement is applied in the machine of
The wafer is preferably written on (exposed) by the lithography machine in both a backward and forward Y-direction, as shown in
When the width of a field 27 is chosen to be smaller than the width 29A of the electron-optical (EO) slit 29 (i.e. the size of the complete array of sub-beams as projected onto the wafer) (e.g. smaller than the maximum size of 26 mm), then more fields can be placed on the wafer, but not all of the sub-beams will be used to write on the wafer. The EO slit will need to cross the wafer more often to write all fields and the overall throughput will decrease. Therefore, the EO slit 29 preferably has a writing width 29A that coincides with the width of a field 27.
The arrangement of sub-beams 510 in the EO slit 29 is determined by the pattern of apertures in the aperture array (e.g. aperture array 4 in the system of
The aperture array may be tilted by an angle 513 selected so that the writing paths 511 of adjacent sub-beams in each column are separated by a desired distance, e.g. by the stripe width 28A. For example, all of the sub-beams 510 positioned along column 514A of the aperture array will have writing paths 511A separated by equal distances, and all of the sub-beams 510 along column 514B will have writing paths 511B separated by equal distances. The desired result is that all of the writing paths 511 of all of the sub-beams 501 are evenly distributed across the width 29A of the EO-slit 29, i.e. each writing path is equi-distant from adjacent writing paths.
However, due to the geometry of a regular hexagonal pattern, the distance separating adjacent writing paths of sub-beams on adjacent columns will not be uniform for all of the sub-beams. For example, in
These uneven distances between adjacent writing paths results in a non-uniform distribution of sub-beams across the width 29A of the EO slit 29. This will result in uneven exposure of the wafer fields unless corrected, but correcting the uneven distribution of sub-beams will result in a more complex and difficult to control lithography system. Alternative arrangements of apertures are described below to overcome this problem.
Beam areas may be designated by the letters P, Q, R, S, T. Although this embodiment includes five beam areas it may include fewer or more than five beam areas, and may comprise only a single beam area. In some embodiments, each beam area 500 includes an array of 204 columns by 13 rows of apertures, as shown in
The apertures in all of the beam areas 500 are preferably distributed so that they are all spaced evenly when projected onto a line parallel with the X-direction, i.e. there is an equal distance between all adjacent apertures when projected onto this line. This arrangement results in forming sub-beams 510 (one sub-beam generated by each aperture 520) with equally spaced writing paths which are distributed evenly across the surface of a wafer when it is moved in the Y-direction (or more generally, when the wafer and sub-beams move relatively to each other). In one embodiment, the apertures 520 in the set of beams areas 500 are arranged to form an array of sub-beams 510, thus forming an EO slit 29 with equally spaced writing paths 511 which are distributed evenly across the width 27A of the field 27 of wafer 26. As the wafer 26 is moved in the Y-direction, each sub-beam 510 of the array traces a writing path 511 along the length of a stripe 28 on the surface of the wafer. This results in the EO slit 29 having a writing width 29A, equal to the field width 27A (e.g. 26 mm).
In some embodiments, the centerlines of row A apertures and row M apertures in the same numbered columns of neighboring beam areas have the same spacing 506, e.g. 4.225 mm, in the Y-direction, as shown in
In some embodiments, the diameter of apertures 520 varies and in others it is constant. In some embodiments, the smallest diameter is approximately 2.7 μm. Equally-sized apertures and other diameter sizes are within the scope of the invention.
In some embodiments, the apertures 520 are arranged in a plurality of columns oriented in the Y-direction, and adjacent columns are regularly spaced with a fixed pitch in the X-direction. The apertures 520 of every other column of the aperture array may be aligned in the X-direction and have a fixed pitch (e.g. distance 521 between apertures L202 and L204, equal to 260 μm in some embodiments). In some embodiments, apertures in adjacent columns of the aperture array are staggered by a fixed amount in the Y-direction (e.g. distance 522 between apertures M202 and M203, equal to 75 μm in some embodiments) and have a uniform aperture column pitch (e.g. pitch 523 between apertures M202 and L202, equal to 150 μm in some embodiments). Thus, in the embodiment shown in
Further still, in some embodiments, neighboring apertures within the same numbered column of a beam area are offset in the X-direction by a uniform amount (e.g. offset 525, equal to 2 μm in some embodiments). That is, in the embodiment shown in
As can be seen in
One aspect of the invention is based on the insight that a skewed or offset hexagonal pattern e.g. as described above obtains most of the benefits of a regular hexagonal pattern regarding aperture density and mutual beam influence, but maintains uniform spacing of writing paths and avoids or minimizes other disadvantages of a tilted regular hexagonal pattern.
In the embodiment shown in
A further aspect of the invention includes offsetting apertures within a column of apertures to skew the array and provide slanting rows (at an angle with respect to the X-direction in
In some embodiments, the intra-row offset 625 is equal to the pitch 624 between beamlet apertures 620 of neighboring columns divided by the number of apertures within the row. This results in all of the apertures 620 within a group/beam spot 621 being equally spaced when projected onto a line parallel to the Y-direction. This arrangement results in forming beamlets (e.g. one beamlet 610 generated by each aperture 620) with equally spaced writing paths 611 which are distributed evenly on the surface of a wafer when the group of beamlets 621 is moved in the X-direction (e.g. by the deflection scan of the beamlets). For example, the beamlet apertures 620 in
Another aspect of the arrangement includes patterning an array such that the group of beamlet apertures 620 are offset from center point 710 of beam spot 621. In embodiments including forty-nine apertures that are arranged within each beam spot, each aperture may be associated with an aperture number, and the offset of each aperture from the center of the beam spot may be defined by the following formulas:
appxxoffset=(int[(num−1)/7)]−3)*pitch;
appyoffset=(−pitch/2)+[(6−[(num−1)mod 7]+int(num/29)−3)*pitch]−[(pitch/7)*(int[(num−1)/7)]−3)];
where appxoffset and appyoffset express the X and Y-axis offset from center point 710, num=aperture number, and int[ ] is a floor function that maps a real number to the largest previous integer, including 0.
It should be noted that this arrangement may be used without actually forming any sub-beams. The groups of beamlets 610 may be formed in a single aperture array, in which the groups form beam spots 621 which are evenly spaced and distributed in one direction (e.g. in the X-direction across the width of the field 27). The multiple beamlets 610 in each group/beam spot 621 are arranged with writing paths 611 evenly spaced and distributed in a different direction (e.g. in the Y-direction along the length of the field 27), where the two directions are preferably exactly or nearly perpendicular to each other.
To explain further, a beamlet group is projected from the multiple aperture array potion 6a and towards beam stop array portion 8a. The beamlet group crosses over at or near beam stop array portion. This crossover results in a translated image being projected on wafer portion 11a.
On the right, a group of beamlets 610′ are shown, as projected on wafer portion 11a. The two groups of beamlets 610 and 610′ show, for example, that beamlet numbers 1, 7, 43, and 49 are translated into a different position, along with the other beamlets not numbered in
As further exampled below, one advantage of the present invention is minimizing overscan.
A scan line is the path of a sub-beam or beamlet on the surface of the wafer during the scan phase. A scan line (see
It is therefore desirable to arrange the apertures of the aperture plate to minimize overscanning. Embodiments of the present invention minimize this problem, as can be seen in
As explained in
Although the figures show a particular lithography system, sub-beam array 4 and multiple aperture array 6 are beneficial in a number of different configurations upstream and downstream of the arrays, including the use of either array 4 or 6 individually and with other arrays not within the scope of the invention. Arrays 4 and 6 may be implemented in either parallel or perpendicular writing strategies. Further, the beamlets may be focused individually or in groups.
Thus, it will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention, which is defined in the accompanying claims.
Claims
1. A sub-beam aperture array for forming a plurality of sub-beams from one or more charged particle beams, the sub-beam aperture array comprising one or more beam areas, each beam area comprising a plurality of sub-beam apertures arranged in columns in a non-regular hexagonal pattern of neighboring sub-beam apertures, the sub-beam apertures arranged so that, when projected in a first direction onto a line parallel to a second direction, the sub-beam apertures in each column are uniformly spaced along the line, and wherein the first direction is different from the second direction,
- wherein, within each of the one or more beam areas, the sub-beam apertures in each column are staggered, in the first direction, with respect to the sub-beam apertures of a neighboring column, and
- wherein the sub-beam apertures of every other column are aligned in the second direction.
2. The sub-beam aperture array of claim 1, wherein, within each of the one or more beam areas, the sub-beam apertures are arranged in a plurality of columns regularly spaced in the second direction, and the sub-beam apertures in each column are offset by a same amount, in the second direction, from each adjacent sub-beam aperture in the same column.
3. The sub-beam aperture array of claim 2, wherein the offset between sub-beam apertures within each column is the same as an offset between a sub-beam aperture in one beam area and an adjacent sub-beam aperture in a corresponding column of another beam area.
4. The sub-beam aperture array of claim 3, wherein the offset of adjacent sub-beam apertures in a single column is equal to a fraction of a diameter of the sub- beam apertures.
5. The sub-beam aperture array of claim 1, wherein, within each of the one or more beam areas, the sub-beam apertures in each column are staggered, in the first direction, with respect to the sub-beam apertures of a neighboring column.
6. The sub-beam aperture array of claim 1, wherein the sub-beam apertures of every other column are aligned in the second direction.
7. The sub-beam aperture array of claim 1, wherein the second direction is substantially perpendicular to the first direction.
8. A charged particle lithography system for exposing a target using a plurality of charged particle sub-beams, the system comprising:
- a charged particle generator for generating a charged particle beam;
- a sub-beam aperture array for forming a plurality of sub-beams from one or more the charged particle beams beam, the sub-beam aperture array comprising one or more beam areas, each beam area comprising a plurality of sub-beam apertures arranged in columns in a non-regular hexagonal pattern of neighboring sub-beam apertures, the sub-beam apertures arranged so that, when projected in a first direction onto a line parallel to a second direction, the sub-beam apertures in each column are uniformly spaced along the line, and wherein the first direction is different from the second direction; and
- a projection lens system configured to project the sub-beams onto a surface of the target;
- wherein the system further comprises a beamlet aperture array comprising a plurality of beamlet apertures arranged in one or more groups, the beamlet aperture array arranged to receive the sub-beams and form a plurality of beamlets at the locations of the beamlet apertures of the beamlet array,
- wherein the sub-beam apertures in each column are staggered, in the first direction, with respect to the sub-beam apertures of a neighboring column, and
- wherein the sub-beam apertures of every other column are aligned in the second direction.
9. The system of claim 8, further comprising a beamlet aperture array comprising a plurality of beamlet apertures arranged in one or more groups and arranged to receive the sub-beams, and wherein each group of beamlet apertures corresponds with a separate charged particle sub-beam projected onto the beamlet aperture array.
10. The system of claim 8, further comprising a beamlet aperture array comprising a plurality of beamlet apertures arranged in one or more groups and arranged to receive the sub-beams, and wherein the beamlet apertures are arranged so that, when projected in a fourth direction onto a line parallel to a third direction, the sub-beam beamlet apertures of each group are uniformly spaced along the line, and wherein the third direction is different from the fourth direction.
11. The system of claim 10, wherein the first direction is the same as the third direction, and the second direction is the same as the fourth direction.
12. The system of claim 10, wherein the beamlet apertures are arranged in rows and columns, and each beamlet aperture within a row of the beamlet aperture array is uniformly offset in the third direction from adjacent beamlet apertures in the row.
13. The system of claim 10, wherein the beamlet apertures within a column of each group align in the fourth direction.
14. The system of claim 8, further comprising a beamlet aperture array comprising a plurality of beamlet apertures and arranged to receive the sub-beams, and wherein the beamlet apertures are arranged in a plurality of groups, each group corresponding to a sub-beam, wherein the positions of the beamlet apertures within each group positioned to form an unbalanced array.
15. The system of claim 14, wherein beamlet apertures neighboring within a row of the beamlet aperture array are offset from each other by a uniform amount with respect to the a third direction.
16. The system of claim 15, wherein the offset is equal to a fraction of the pitch between the neighboring beamlet apertures.
17. The system of claim 16, wherein the fraction is equal to the pitch between the neighboring beamlet apertures divided by the number of beamlet apertures within the row.
18. The system of claim 8, further comprising:
- a beamlet aperture array comprising a plurality of beamlet apertures arranged to receive the sub-beams and to form a plurality of beamlets at the locations of the beamlet apertures of the beamlet aperture array,
- wherein the beamlet apertures in each group form a skewed square array.
19. The system of claim 8, further comprising a beamlet aperture array comprising a plurality of beamlet apertures and arranged to receive the sub-beams, and wherein the plurality of beamlet apertures in each group are all offset from the center of a beam spot formed by the group of beamlet apertures.
20. The system of claim 19, wherein forty-nine beamlet apertures are arranged within the beam spot, each beamlet aperture is associated with an aperture number, and the offset in an X direction of each beamlet aperture from the center of the beam spot is defined by the formula: appxoffset=(int[(aperture number−1)/7)]−3)*pitch, where int is a floor function.
21. The system of claim 19, wherein the offset in a Y direction of each beamlet aperture from the center of the beam spot is defined by the formula: appyoffset =(−pitch/2)+[(6−[(aperture number−1) mod 7]+int(aperture number/29)−3)*pitch]−[(pitch/7)*(int[(aperture number−1)/7)]−3)], where int is a floor function.
22. The system of claim 8, further comprising a deflector arranged to deflect the sub-beams in the first direction and a moveable stage for moving the target in the second direction.
23. A beamlet aperture array for forming a plurality of beamlets from charged particle sub-beams, the beamlet aperture array comprising consisting of a plurality of beamlet apertures arranged in a plurality of groups, each group corresponding to a sub-beam, wherein the plurality of groups are arranged in a non-regular hexagonal pattern of neighboring groups and wherein the positions of the beamlet apertures within each group form an unbalanced array.
24. The beamlet aperture array of claim 23, wherein beamlet apertures neighboring within a row of the beamlet aperture array are offset from each other by a uniform amount with respect to a third direction.
25. The beamlet aperture array of claim 24, wherein the offset is equal to a fraction of the pitch between the neighboring beamlet apertures.
26. The beamlet aperture array of claim 25, wherein the fraction is equal to the pitch between the neighboring beamlet apertures divided by the number of beamlet apertures within the row.
27. The beamlet aperture array of claim 23, wherein the beamlet apertures in each group form a skewed square array.
28. The beamlet aperture array of claim 23, wherein the beamlet apertures in each group are all offset from the center of a beam spot formed by the group of beamlet apertures.
29. The beamlet aperture array of claim 28, wherein forty-nine beamlet apertures are arranged within the beam spot, each beamlet aperture is associated with an aperture number, and the offset in an X direction of each beamlet aperture from the center of the beam spot is defined by the formula: appxoffset=(int[(aperture number−1)/7)]−3)*pitch, where int is a floor function.
30. The beamlet aperture array of claim 28, wherein the offset in a Y direction of each beamlet aperture from the center of the beam spot is defined by the formula: appyoffset=(−pitch/2)+[(6−[(aperture number−1)mod 7]+int(aperture number/29)−3)*pitch]−[(pitch/7)*(int[(aperture number−1)/7)]3)], where int is a floor function.
31. The beamlet aperture array of claim 23, wherein the groups are arranged in a non-regular hexagonal array.
32. The beamlet aperture array of claim 23, further comprising one or more beam areas, each beam area comprising a plurality of groups of beamlet apertures, wherein in each beam area the groups are arranged in a non-regular hexagonal array.
33. A method for exposing a field of a target using a plurality of charged particle beamlets, the field having a length in a first direction and a width in a second direction, the method comprising:
- forming the charged particle beamlets into a plurality of discrete groups arranged in columns in a non-regular hexagonal pattern of neighboring discrete groups, the groups being equally spaced across the width of the field; and moving the target in the first direction and simultaneously scanning each group of beamlets across a width of a corresponding stripe of the field so that each beamlet follows a writing path on a surface of the target; wherein the writing paths of the beamlets of each group in each column are evenly spaced in the first direction,
- wherein the plurality of discrete groups arranged such that discrete groups in each column are staggered, in the first direction, with respect to the discrete groups of a neighboring column, and
- wherein the discrete groups of every other column are aligned in the second direction.
34. The method of claim 33, wherein the discrete groups are arranged in a plurality of columns regularly spaced in the second direction, and the discrete groups in each column are offset by a same amount, in the second direction, from each adjacent discrete group in the same column.
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Type: Grant
Filed: Apr 2, 2020
Date of Patent: Apr 30, 2024
Assignee: ASML Netherlands B.V. (Veldhoven)
Inventors: Vincent Sylvester Kuiper (The Hague), Erwin Slot (Zoetermeer)
Primary Examiner: Kenneth Whittington
Application Number: 16/838,976
International Classification: H01J 37/317 (20060101); H01J 37/09 (20060101); H01J 37/30 (20060101);