Patent Application
20240234083
This application is based upon and claims benefit of priority from the Japanese Patent Application No. 2022-170017, filed on Oct. 24, 2022, the entire contents of which are incorporated herein by reference.
The present invention relates to a beam detector, a multi-charged-particle-beam irradiation apparatus, and an adjustment method for beam detector.
With high integration of LSI, the circuit line width of semiconductor devices has been further miniaturized. An electron beam writing technique with a superior resolution is used as a method of forming an exposure mask (the one used in a stepper or a scanner is also called a reticle) for forming a circuit pattern on these semiconductor devices.
Writing apparatuses using multiple beams are being developed as electron beam writing apparatuses. The use of multiple beams enables irradiation with a large number of beams as compared with writing using a single electron beam, and thus allows a significant increase in throughput. In a multi-beam writing apparatus, for example, an electron beam emitted from an electron gun passes through an aperture member having multiple apertures, thus forming multiple beams. Each of the beams is subjected to blanking control through a blanking aperture array. The beams that have not been blocked are reduced through an optical system and are then applied to a substrate placed on a movable stage.
For precisely keeping irradiation positions of the multiple beams on the substrate, it is important to precisely determine the position of each of the beams constituting the multiple beams. In a configuration in which a small number of beams, for example, a few beams, are used and in which the pitch of beams, or beam pitch, is sufficiently large, marks equal in number to the beams are arranged on a stage, and each of the beams is caused to scan over the corresponding mark, so that the position of the beam can be determined.
Significantly increasing the throughput for finer circuit patterns requires a larger number of beams, serving as multiple beams. As the number of beams increases, the beams have a smaller diameter, and the beam pitch decreases. As the beam pitch decreases due to an increase in the number of beams as described above, it is more difficult to detect individual beams of the applied multiple beams with the marks arranged on the stage.
A recently developed individual beam detector includes a thin-film aperture member having a single passage hole having a size smaller than the beam pitch of multiple beams and larger than the diameter of each of the multiple beams, and detects a single detection target beam passing through the passage hole with a sensor, such as a photodiode. In such an individual beam detector, scattered electrons caused by beams located in proximity to the detection target beam and transmitted through the thin-film aperture member may be incident on the sensor, serve as a noise source, and reduce the accuracy of detection. To block the scattered electrons, a second aperture member can be disposed between the thin-film aperture member (first aperture member) and the sensor. However, it is difficult to align the hole of the thin-film aperture member with a hole of the second aperture member because both the holes of these aperture members are minute holes.
In one embodiment, a beam detector includes a first aperture plate including a first passage hole, a second aperture plate including a second passage hole that allows a single detection target beam passing through the first passage hole to pass therethrough, and a sensor detecting a beam current of the detection target beam passing through the second passage hole. The second aperture plate includes an electrically conductive material, a plurality of third passage holes are formed around the second passage hole, and the plurality of third passage holes allow light to pass therethrough.
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
This writing apparatus includes a writing unit W, which applies electron beams to a writing target substrate 24 to write a desired pattern on the substrate, and a controller C, which controls an operation of the writing unit W.
The writing unit W includes an electron beam column 2 and a writing chamber 20. The electron beam column 2 contains an electron gun 4, an illumination lens 6, a shaping aperture array plate 8, a blanking aperture array plate 10, a reduction lens 12, a limiting aperture member 14, an objective lens 16, and a deflector 17.
The writing chamber 20 contains an XY stage 22. The writing target substrate 24 is placed on the XY stage 22. Examples of the writing target substrate 24 include a wafer and an exposure mask that is used to transfer a pattern to a wafer with a reduction projection exposure apparatus or an extreme ultraviolet (EUV) exposure apparatus, such as a stepper or a scanner, including an excimer laser as a light source.
A transmission mark type individual beam detector 40 is disposed on the XY stage 22 at a position different from a position at which the substrate 24 is placed. A level at which the individual beam detector 40 is disposed can be adjusted by an adjustment mechanism (not illustrated). The individual beam detector 40 is preferably installed such that its upper surface is at the same level as the surface of the substrate 24.
The controller C includes a control computer 32 and a deflection control circuit 34.
The control computer 32 includes a writing data processing unit 60, a writing control unit 61, and a measurement unit 62. These units of the control computer 32 may be implemented by hardware, such as electric circuitry, or software, such as a program that performs functions of the units. If the units are implemented by software, a program that achieves the functions of the units may be stored in a recording medium, and a computer including a central processing unit (CPU) may be caused to read and execute the program.
A storage device (not illustrated) stores writing data in a format for the writing apparatus converted from design data (layout data). The writing data processing unit 60 reads writing data from the storage device and executes multi-stage data conversion on the writing data to generate shot data. The shot data is generated for each pixel, and writing time (irradiation time) is computed. For example, when no pattern is formed in a target pixel, the target pixel is not irradiated with any beam. In this case, an identification code indicating “zero writing time” or “no beam irradiation” is defined. A maximum writing time T (maximum exposure time) for one multi-beam shot is set in advance. The irradiation time of each beam to be actually applied is preferably determined in proportion to a calculated area density of a pattern. The irradiation time of each beam that is finally calculated is preferably a period of time that corresponds to a dose obtained by correcting, with a dose, the amount of dimensional change resulting from a phenomenon (not illustrated), such as a proximity effect, a fogging effect, or a loading effect, which causes a dimensional change. For the irradiation time of each beam to be actually applied, irradiation time may vary from beam to beam. The writing time (irradiation time) of each beam is computed as a value within the maximum writing time T. The writing data processing unit 60 generates, for each multi-beam shot, irradiation time array data, in which pieces of data indicating computed irradiation periods of time of multiple beams for each pixel are arranged in the order of array of the multiple beams, as data for the beams to be used to write the pixel.
The writing control unit 61 uses the irradiation time array data (shot data) to output a control signal for a writing process to the deflection control circuit 34 and a control circuit (not illustrated) that drives the writing unit W. The writing unit W writes, based on the control signal, a desired pattern on the substrate 24 with multiple beams. Specifically, the writing unit W operates as follows.
The electron gun 4 emits an electron beam 30. The illumination lens 6 causes the electron beam 30 to be applied substantially perpendicular to the entire shaping aperture array plate 8.
The electron beam 30 is applied to an area including all of the apertures 8a of the shaping aperture array plate 8. The electron beam 30 partly passes through these apertures 8a, thus forming multiple beams 30a to 30e as illustrated in
The blanking aperture array plate 10 has through-holes aligned with the respective apertures 8a of the shaping aperture array plate 8. In each of the through-holes, a blanker including two paired electrodes is disposed. Each of the electron beams 30a to 30e passing through the through-holes is independently deflected by a voltage applied by the blanker. This deflection achieves blanking control on the beams. The blanking aperture array plate 10 performs blanking deflection on each of the multiple beams that have passed through the apertures 8a of the shaping aperture array plate 8.
The multiple beams 30a to 30e that have passed through the blanking aperture array plate 10 are reduced in beam size and array pitch by the reduction lens 12 and travel toward a central aperture of the limiting aperture member 14. Electron beams deflected by the blankers of the blanking aperture array plate 10 are changed in trajectory, so that the electron beams are deviated from the central aperture of the limiting aperture member 14 and are accordingly blocked by the limiting aperture member 14. In contrast, electron beams that have not been deflected by the blankers of the blanking aperture array plate 10 pass through the central aperture of the limiting aperture member 14.
The limiting aperture member 14 blocks electron beams deflected in a beam OFF state by the blankers of the blanking aperture array plate 10. The beams passing through the limiting aperture member 14 for a period between the time when the beams enter a beam ON state and the time when the beams are switched to the beam OFF state correspond to electron beams of one shot.
The electron beams 30a to 30e that have passed through the limiting aperture member 14 are focused by the objective lens 16, thus forming a pattern image reduced at a desired reduction ratio on the substrate 24. The electron beams (multiple beams) that have passed through the limiting aperture member 14 are deflected together in the same direction by the deflector 17 and are applied to the substrate 24.
The multiple beams applied at a time are ideally arranged at a pitch obtained by multiplying the array pitch of the apertures 8a of the shaping aperture array plate 8 by the above-described desired reduction ratio. The writing apparatus performs a writing operation in a raster scanning manner such that beam shots are successively and sequentially applied. In writing a desired pattern, the blanking control is performed to cause beams necessary for the pattern to enter the beam ON state. While the XY stage 22 is continuously moving, the deflector 17 performs control such that the beam irradiation positions follow the movement of the XY stage 22.
Such a writing apparatus needs to determine individual irradiation positions of beams constituting the multiple beams to improve the accuracy of writing. For this purpose, the individual beam detector 40 is used to detect the position of each beam.
The first aperture plate 41 (thin film) has, at its central part, a single minute hole 42 (first passage hole). The first aperture plate 41 is formed by a thin film having a thickness that allows the multiple beams to be transmitted through the film. Specifically, the first aperture plate 41 is made of heavy metal and is formed as a thin flat plate having a thickness of, for example, from 300 to 1000 nm. More preferably, the first aperture plate 41 may have a thickness of approximately 500 nm±50 nm. For example, electron beams emitted at an accelerating voltage of 50 keV cannot be absorbed by the first aperture plate 41, and are thus transmitted through the first aperture plate 41.
Such a thin-film structure of the first aperture plate 41 makes it difficult to transfer heat from a heated portion of the first aperture plate 41 to surroundings and thus can reduce heat dissipation. Preferable examples of heavy metal, serving as a material, include platinum (Pt), gold (Au), and tungsten (W). A thin-film structure made of heavy metal can reduce the amount of electrons that are transmitted through the structure when irradiated with the multiple beams.
The minute hole 42 has a diameter φ1, which is larger than a beam diameter of each individual beam of the multiple beams formed by electron beams and is smaller than a beam pitch. In the case where the beam pitch of the multiple beams ranges, for example, from approximately 150 to approximately 200 nm, the minute hole 42 is formed such that the diameter φ1 ranges, for example, from approximately 80 to approximately 120 nm. The diameter of the minute hole 42 is larger than the beam diameter of each individual beam and is smaller than the beam pitch. This prevents some of the multiple beams scanning over the minute hole 42 from simultaneously passing through the minute hole 42.
The first aperture plate 41 is supported by the support 43. The support 43 has an aperture 44, which is located under a portion of the first aperture plate 41 that includes the minute hole 42. In the example of
As a material for the support 43, for example, molybdenum (Mo), platinum (Pt), tantalum (Ta), or silicon (Si) is preferably used. The support 43 is thick enough to block electron beams constituting the multiple beams and applied to the support without transmitting the beams therethrough. For example, a thickness of 15 μm or more enables blockage of electron beams accelerated at 50 key.
The support 43 further has an aperture 45, which is formed by thinning a lower portion of the support 43 that surrounds the edge of the aperture 44 to such an extent that no electrons are transmitted therethrough. This makes it difficult for heat transferred from the first aperture plate 41 to the support 43 around the edge of the aperture 44 to be transferred horizontally. Thus, a reduction in temperature of the portion of the first aperture plate 41 around the minute hole 42 above the aperture 44 can be further suppressed.
The support 43 has a perimeter greater than or equal to, for example, the perimeter of the first aperture plate 41. The support 43 has a bottom supported by the casing 49.
The second aperture plate 50 is disposed between the first aperture plate 41 and the sensor 48. As illustrated in
Observation light, which is used in a process of alignment of the minute hole 42 of the first aperture plate 41 and the minute hole 51 of the second aperture plate 50, may be visible radiation, infrared radiation, or ultraviolet radiation.
The multiple observation light passage holes 52 are circular and have the same dimensions and shape. The centers of the multiple observation light passage holes 52 are located at regular intervals on the same circumference centered on the minute hole 51. The observation light passage holes 52 have a diameter larger than that of the minute hole 51.
The observation light is blocked by a portion of the second aperture plate 50 that is other than the minute hole 51 and the observation light passage holes 52 without being transmitted through the portion. For the second aperture plate 50, a highly electrically resistive, non-magnetic, electrically conductive material is preferably used. Examples of such a material include a titanium alloy, a ceramic material (alumina or SiC) covered with an electrically conductive coating, and an electrically conductive ceramic (a mixture of SiC and Si). The second aperture plate 50 is thick enough to block scattered electrons.
The scattered-electron cover 80 is disposed between the second aperture plate 50 and the sensor 48. The scattered-electron cover 80 is fixed to the casing 49 and has an opening 81 at its central part. The opening 81 has a diameter larger than that of the minute hole 51.
The scattered-electron cover 80 can be made of the same material as that for the above-described second aperture plate 50. The distance between the second aperture plate 50 and the scattered-electron cover 80 and the diameter of the opening 81 of the scattered-electron cover 80 are set so that scattered electrons that have passed through the observation light passage holes 52 do not pass through the opening 81. Since the diameter of the opening 81 is larger than those of the minute hole 42 and the minute hole 51, the opening 81 can be easily aligned with the minute hole 42 and the minute hole 51. The minute hole 42, the minute hole 51, and the opening 81 are preferably located on the same axis.
Although the scattered-electron cover 80 may be disposed directly under and in tight contact with the second aperture plate 50 in the transmission mark type individual beam detector 40, friction caused by contact of the second aperture plate 50 with the scattered-electron cover 80 may displace the second aperture plate 50, thus causing the sensor to malfunction. In assembling the transmission mark type individual beam detector 40, therefore, the second aperture plate 50 is preferably disposed at a predetermined distance from the scattered-electron cover 80.
When the first aperture plate 41 is scanned with the multiple beams, a single detection target beam B1 of a group of beams applied to an area above the aperture 44 passes through the minute hole 42, the minute hole 51, and the opening 81, and is detected by the sensor 48.
The other beams are transmitted through the first aperture plate 41 and scatter from a lower surface of the first aperture plate 41. For example, beams B2 next to the detection target beam B1 may be transmitted through the first aperture plate 41 and scatter from the lower surface of the first aperture plate 41. Most of the scattered electrons are blocked by the second aperture plate 50. Some of the scattered electrons pass through the observation light passage holes 52 of the second aperture plate 50. The scattered electrons that have passed through the observation light passage holes 52 are blocked by the scattered-electron cover 80 and are thus prevented from reaching a light receiving surface of the sensor 48.
Of the multiple beams, a group of beams applied to an area other than the area above the aperture 44 are blocked by the support 43.
The sensor 48 is, for example, a solid-state detector (SSD), and detects a beam current of the detection target beam. Notification of a result of detection by the sensor 48 is provided to the control computer 32. As the first aperture plate 41 is scanned with the multiple beams, the measurement unit 62 acquires a beam current of each beam from the sensor 48. The measurement unit 62 converts the beam current into a brightness, forms a beam image based on the amount of deflection by the deflector 17, and acquires information on, for example, the shape of the whole of the multiple beams. For example, a dose of each beam is corrected based on the information.
As illustrated in
The process of alignment (axial alignment) of the minute hole 42 of the first aperture plate 41 and the minute hole 51 of the second aperture plate 50 will now be described. The alignment process is performed outside the writing apparatus.
As illustrated in
Observation light emitted from the light source 71 is reflected by the semi-transparent mirror 72 disposed at an angle of 45° to the optical axis, passes through the objective lens 73, and is then applied to observation targets (the first aperture plate 41 and the second aperture plate 50). The second aperture plate 50 is located between the objective lens 73 and the first aperture plate 41. The first aperture plate 41 has the support 43 attached thereto.
The light reflected by the observation targets passes through the objective lens 73 and then through the semi-transparent mirror 72, and is imaged on the image sensor 75 by the imaging lens 74. The image sensor 75 is, for example, a complementary metal-oxide-semiconductor (CMOS) image sensor.
First, the position of the objective lens 73 is adjusted, thereby focusing the objective lens 73 on the first aperture plate 41. Observation light passes through the minute hole 51 and the observation light passage holes 52 of the second aperture plate 50. An image detected by the image sensor 75 is observed to determine an image location of the minute hole 42. The determined location is set to a reference mark. For the observation light passage holes 52 of the second aperture plate 50, for example, the size of each hole, the positions of the holes, and the number of holes are set so that visible radiation required to determine the image location of the minute hole 42 can pass through the holes.
Then, as illustrated in
When the image location of the minute hole 51 of the second aperture plate 50 coincides with the reference mark, the minute hole 42 of the first aperture plate 41 is precisely aligned with the minute hole 51 of the second aperture plate 50.
At the completion of alignment, the first aperture plate 41 and the support 43, the second aperture plate 50, the scattered-electron cover 80, and the sensor 48 are fixed to the casing 49, thus forming the individual beam detector 40 in which the minute hole 42 is aligned with the minute hole 51. The individual beam detector 40 is mounted in the writing apparatus.
As described above, according to the present embodiment, the minute holes 42 and 51 of the two aperture plates, or the first aperture plate 41 and the second aperture plate 50, can be aligned with each other with high precision.
The diameter of each observation light passage hole 52 of the second aperture plate 50 and the distance from the minute hole 51 to the observation light passage hole 52 are determined in consideration of the numerical aperture of the objective lens 73 of the epi-illumination unit used in the alignment process, the distance between the objective lens 73 and the first aperture plate 41, and the distance between the objective lens 73 and the second aperture plate 50.
As illustrated in
θ=sin{circumflex over ( )}−1(NA/n)
As illustrated in
The minimum diameter Dmin is calculated by simulation to satisfy a required ratio of blockage of scattered electrons. The blockage ratio is expressed by (1−e)/1, where 1 denotes a situation in which an electron beam having a beam energy of 50 key, a beam diameter of 10 nm, and an intensity distribution regarded as Gaussian distribution is applied to the first aperture plate 41, and e denotes a transmittance at which scattered electrons transmitted through the openings including the minute hole 51 and the observation light passage holes 52 reach the sensor 48. Simulation results yield, for example, a blockage ratio greater than or equal to (1−0.053)/1≈94.7%.
As described above, the diameter of the opening 81 of the scattered-electron cover 80 is preferably greater than or equal to 2×a×L′. Furthermore, the diameter of the opening 81 is preferably smaller than the above-described minimum diameter Dmin so that a reduction in scattered-electron blockage ratio can be avoided.
The shape of the observation light passage holes arranged around the minute hole 51 in the second aperture plate 50 is not limited to that illustrated in
For example, as illustrated in
As illustrated in
For the examples of
In the above-described embodiment, the configuration in which the scattered-electron cover 80 is disposed between the second aperture plate 50 and the sensor 48 has been described. If the second aperture plate 50 is disposed at a large distance from the sensor 48 so that scattered electrons passing through the observation light passage holes 52 fail to reach the sensor 48, the scattered-electron cover 80 may be omitted.
Furthermore, the casing 49 may have tilted side walls so that scattered electrons reflected by the side walls fail to reach the sensor 48.
In the above-described embodiment, the multi-beam writing apparatus has been described as an exemplary apparatus with the individual beam detector mounted therein. The embodiment is not limited to this example. The individual beam detector can similarly be mounted in any apparatus that emits multiple beams, for example, an inspection apparatus that inspects patterns for defects. The individual beam detector can be mounted in an apparatus that emits a single beam.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-170017 | Oct 2022 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| 20240136148 A1 | Apr 2024 | US |
