JP4634563B2 - Electron beam exposure apparatus and focus detection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electron beam exposure apparatus and a focus detection method. In particular, the present invention relates to a method for detecting whether or not the focal position of an electron lens matches the position where an electron beam that has passed through a mask is imaged on the wafer surface, and an electron beam that detects the focal position by this focus detection method. The present invention relates to an exposure apparatus.
[0002]
[Prior art]
FIG. 1 shows a method for detecting the focal position of a conventional electron lens. The electron gun 300 emits an electron beam. The mask 302 has a rectangular transmission area and generates a detection pattern beam 315. The electron beam that has passed through the mask 302 is formed in a rectangular shape. The electron lens 304 adjusts the focal position so that the detection pattern beam 315 forms an image on the surface of the mark 306. The deflector 305 deflects the detection pattern beam 315 and scans the surface of the mark 306 with the detection pattern beam 315. The reflected electron detector 310 detects the reflected electrons 314 reflected by scanning the mark 306 with the detection pattern beam 315, and outputs a detection signal to the focus determination unit 316. The focus determination unit 316 determines whether or not the focus position is correct based on the detection signal supplied from the backscattered electron detection unit 310. The focus determination unit 316 requests the electronic lens control unit 12 to change the focal position of the electronic lens 304. The electronic lens control unit 12 changes the focal position of the electronic lens 304 by controlling the amount of current supplied to the electronic lens 304.
[0003]
For example, the focus determination unit 316 determines that the focus position where the inclination of the detection signal is the largest is the focus position. For example, the focus determination unit 316 determines that the focus position where the inclination of the detection signal is the largest among the detection signals at a plurality of different focus positions is in focus.
[0004]
[Problems to be solved by the invention]
However, the method of determining whether or not the focal position is based on the reflected electrons 314 obtained by scanning the mark 306 with the rectangular detection pattern beam 315 cannot be accurately determined.
[0005]
Therefore, an object of the present invention is to provide an electron beam exposure apparatus and a focus detection method that can solve the above-described problems. This object is achieved by a combination of features described in the independent claims. The dependent claims define further advantageous specific examples of the present invention.
[0006]
[Means for Solving the Problems]
The inventor of the present invention pays attention to the fact that the amount of change in reflected electrons due to the shift of the focal position is extremely small, and that the shape of the conventional detection pattern beam is different from the shape of the exposure pattern beam during exposure. I came to do.
[0007]
In order to solve the above-mentioned problem, a first aspect of the present invention is a focus detection method for detecting whether or not an image by an electron beam is formed on a desired imaging plane, and irradiates the electron beam. A generation step for generating a detection pattern beam having a plurality of irradiation areas, and a mark in a scanning period by scanning the detection pattern beam so as to pass a mark provided on a surface substantially the same as a desired imaging plane And a detection step of detecting whether or not an image is formed on a desired imaging plane based on a change in the amount of reflected electrons due to the focus detection method.
[0008]
According to another aspect of the present invention, when the detection pattern beam is scanned, the generation step is performed so that the amount of reflected electrons in a part of the scanning period changes by substantially the same amount in a predetermined period. May be generated. Further, the generation step may generate detection pattern beams having the same size of the plurality of irradiation regions. Further, the generation step may generate a detection pattern beam having an irradiation area larger than the number of irradiation areas simultaneously irradiated on the mark. Further, the generation step may generate detection pattern beams having rectangular irradiation areas having substantially the same shape in the scanning direction at substantially the same intervals. In the detection step, the detection pattern beam may be scanned so that the longitudinal direction of the mark and the longitudinal direction of the irradiation region are parallel to each other.
[0009]
The generation step may generate a detection pattern beam in which the interval between the irradiation regions is equal to the length of the irradiation region in the short direction. Further, a determination step for determining whether an image is formed on a desired imaging surface based on the amount of reflected electrons, an intensity adjustment step for performing the determination step while adjusting the lens strength of the electronic lens, And a step of determining the lens strength when the determination value uniquely determined based on the amount of reflected electrons takes an extreme value as a desired lens strength. Further, the determination value is different from the maximum value to the maximum value from the first fluctuation range Imax obtained by dividing the minimum value different from the minimum value from the maximum value obtained by differentiating the amount of reflected electrons in the scanning period. It may be a value obtained by dividing a value obtained by dividing the maximum value by subtracting the second fluctuation range Imin by a value obtained by adding the first fluctuation range Imax and the second fluctuation range Imin.
[0010]
According to a second aspect of the present invention, there is provided an electron beam exposure apparatus for irradiating a wafer with a predetermined electronic circuit pattern by irradiating the electron beam, wherein the exposure pattern irradiates the electron beam in the same shape as the predetermined electronic circuit pattern. An exposure pattern beam generating unit for generating a beam, a detection pattern beam generating unit for generating a detection pattern beam having a plurality of irradiation regions for irradiating an electron beam, and an electron lens for forming an image on the wafer by the exposure pattern beam and the detection pattern beam A mark that reflects the detection pattern beam, a reflected electron detection unit that detects the amount of reflected electrons of the electron beam reflected by the mark, and a reflected electron during the scanning period when the detection pattern beam is scanned over the mark Focus detection that detects whether the focus position of the electron lens is aligned with the mark based on the change in the amount With the door, when it is detected that the focus position, an exposure pattern beam is irradiated to the wafer to expose a predetermined pattern on the wafer
An electron beam exposure apparatus is provided.
[0011]
In another aspect of the second aspect of the present invention, the detection pattern beam generation unit may include an electron gun that generates an electron beam and a detection pattern beam generation mask having a plurality of transmission regions that transmit the electron beam. Good. Further, the detection pattern beam generation mask may have a plurality of transmission regions so that when the detection pattern beam is scanned, the amount of reflected electrons during the scanning period changes by substantially the same amount at a predetermined period. . Further, the detection pattern beam generation mask may have transmission regions at the same interval in a predetermined direction. Further, the detection pattern beam generation mask may have a plurality of transmission regions of the same size. Further, the detection pattern beam generation mask may have a plurality of transmission regions at intervals equal to the length of the transmission region in a predetermined direction.
[0012]
In addition, the mark may have a size that can simultaneously reflect the electron beams in a smaller number of irradiation regions than the number of irradiation regions included in the detection pattern beam. Further, the length in the predetermined direction of the mark may be an odd multiple of the length in the predetermined direction in the transmission region. The detection pattern beam generation mask may be formed such that the width of the irradiation region of the detection pattern beam formed on the wafer passing through the transmission region is substantially equal to the minimum line width of the predetermined electronic circuit pattern. .
[0013]
The above summary of the invention does not enumerate all the necessary features of the present invention, and sub-combinations of these feature groups can also be the invention.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described through embodiments of the invention. However, the following embodiments do not limit the claimed invention, and all combinations of features described in the embodiments are the solution of the invention. It is not always essential to the means.
[0015]
FIG. 2 is a block diagram of an electron beam exposure apparatus 100 according to one embodiment of the present invention. The electron beam exposure apparatus 100 includes an exposure unit 150 for performing a predetermined exposure process on the wafer 64 with an electron beam, and a control system 140 for controlling the operation of each component of the exposure unit 150.
[0016]
The exposure unit 150 deflects the electron beam irradiated from the electron beam irradiation system 110 and the electron beam irradiation system 110 inside the housing 10 and forms an image of the electron beam in the vicinity of the mask 30. A mask projection system 112 for adjusting the position, a focus adjustment lens system 114 for adjusting the imaging position of the electron beam in the vicinity of the wafer 64, and the electron beam passing through the mask 30 on the wafer 64 placed on the wafer stage 62. An electron optical system that includes a wafer projection system 116 that deflects a predetermined region and adjusts the orientation and size of the pattern image transferred to the wafer 64 is provided.
[0017]
The exposure unit 150 also includes a mask stage 72 on which a mask 30 having a plurality of blocks each formed with a pattern to be exposed on the wafer 64 is mounted, a mask stage driving unit 68 that drives the mask stage 72, and a pattern. A stage system including a wafer stage 62 on which a wafer 64 to be exposed is placed and a wafer stage driving unit 70 for driving the wafer stage 62 is provided. Further, the exposure unit 150 includes an electron detector 60 that detects electrons scattered from the wafer stage 62 side and converts them into an electrical signal corresponding to the amount of scattered electrons for adjusting the electron optical system. The wafer stage 62 is a focal point used to detect whether or not the target mark member 160 used for adjusting the deflection amount and / or the beam shape of the electron beam and the focal position of the focusing lens system 114 are in alignment. And a detection mark 162. For example, the target mark member 160 and the focus detection mark 162 are formed of heavy metals such as platinum, gold, tungsten, and tantalum having a large amount of electrons.
[0018]
The electron beam irradiation system 110 includes a first electron lens 14 that determines a focal position of an electron beam by an electron gun 12 that generates an electron beam, and a slit portion 16 in which a rectangular opening (slit) that allows the electron beam to pass is formed. And have. Since the electron gun 12 takes a predetermined time to generate a stable electron beam, the electron gun 12 may always generate an electron beam during the exposure processing period. The slit is preferably formed in accordance with the shape of a block including a predetermined pattern formed on the mask 30. In FIG. 2, the optical axis of the electron beam when the electron beam irradiated from the electron beam irradiation system 110 is not deflected by the electron optical system is represented by a one-dot chain line A.
[0019]
The mask projection system 112 includes a first deflector 18, a second deflector 22, and a third deflector 26 as mask deflection systems that deflect an electron beam, and a mask focus system that adjusts the focus of the electron beam. The second electron lens 20 and the first blanking electrode 24 are provided. The first deflector 18 and the second deflector 22 perform deflection by irradiating a predetermined region on the mask 30 with an electron beam. For example, the predetermined area may be a block having a pattern to be transferred to the wafer 64. When the electron beam passes through the pattern, the cross-sectional shape of the electron beam becomes the same shape as the pattern. An image of an electron beam that has passed through a block on which a predetermined pattern is formed is defined as a pattern image. The third deflector 26 deflects the trajectory of the electron beam that has passed through the first deflector 18 and the second deflector 22 substantially parallel to the optical axis A. The second electron lens 20 has a function of forming an image of the opening of the slit portion 16 on the mask 30 placed on the mask stage 72. The mask 30 includes an exposure pattern mask for generating an exposure pattern beam for exposing a predetermined pattern on the wafer 64 and a detection pattern beam generation mask for generating a detection pattern beam for detecting a focal position. 250.
[0020]
The focus adjustment lens system 114 includes a third electron lens 28 and a fourth electron lens 32. The third electron lens 28 and the fourth electron lens 32 focus the electron beam on the wafer 64. The wafer projection system 116 includes a fifth electron lens 40, a sixth electron lens 46, a seventh electron lens 50, an eighth electron lens 52, a ninth electron lens 66, a fourth deflector 34, A fifth deflector 38, a sixth deflector 42, a main deflector 56, a sub deflector 58, a second blanking electrode 36, and a round aperture unit 48.
[0021]
The pattern image rotates depending on the set value of the lens intensity. The fifth electron lens 40 adjusts the amount of rotation of the pattern image of the electron beam that has passed through a predetermined block of the mask 30. The sixth electron lens 46 and the seventh electron lens 50 adjust the reduction ratio of the pattern image transferred to the wafer 64 with respect to the pattern formed on the mask 30. The eighth electron lens 52 and the ninth electron lens 66 function as an objective lens. The fourth deflector 34 and the sixth deflector 42 deflect the electron beam in the direction of the optical axis A downstream of the mask 30 with respect to the traveling direction of the electron beam. The fifth deflector 38 deflects the electron beam so as to be substantially parallel to the optical axis A. The main deflector 56 and the sub deflector 58 deflect the electron beam so that a predetermined region on the wafer 64 is irradiated with the electron beam. In the present embodiment, the main deflector 56 is used to deflect an electron beam between subfields including a plurality of regions (shot regions) that can be irradiated with one shot of an electron beam, and the subdeflector 58 is used as a subfield. Is used for deflection between shot areas.
[0022]
The round aperture 48 has a circular opening (round aperture).
The first blanking electrode 24 and the second blanking electrode 36 can turn on and off the electron beam in synchronization with each other at high speed. Specifically, the first blanking electrode 24 and the second blanking electrode 36 have a function of deflecting the electron beam so as to strike the outside of the round aperture. Have. That is, the first blanking electrode 24 and the second blanking electrode 36 can control the amount of the electron beam that reaches the wafer 64 without causing displacement of the pattern image formed on the wafer 64. . Therefore, the first blanking electrode 24 and the second blanking electrode 36 can prevent the electron beam from traveling downstream from the round aperture 48 with respect to the traveling direction of the electron beam. Since the electron gun 12 always irradiates an electron beam during the exposure processing period, the first blanking electrode 24 and the second blanking electrode 36 further expose the pattern when changing the pattern to be transferred to the wafer 64. When changing the region of the wafer 64, it is desirable to deflect the electron beam so that the electron beam does not travel downstream from the round aperture 48.
[0023]
The control system 140 includes an overall control unit 130 and an individual control unit 120. The individual control unit 120 includes an electron beam current control unit 94, a deflection control unit 82, a mask stage control unit 84, a shot control unit 86, an electron lens control unit 88, a backscattered electron processing unit 90, and a wafer stage control. Part 92. The overall control unit 130 is a workstation, for example, and performs overall control of each control unit included in the individual control unit 120. The electron beam current control unit 94 controls the amount of current of the electron beam emitted from the electron gun 12. The electron gun 12 can adjust the amount of current by a control signal supplied from the electron beam current control unit 94. The deflection control unit 82 includes the first deflector 18, the second deflector 22, the third deflector 26, the fourth deflector 34, the fifth deflector 38, the sixth deflector 42, the main deflector 56, and the sub-deflector. The device 58 is controlled. The mask stage control unit 84 controls the mask stage driving unit 68 to move the mask stage 72.
[0024]
The shot control unit 86 controls the first blanking electrode 24 and the second blanking electrode 36. In the present embodiment, the first blanking electrode 24 and the second blanking electrode 36 are controlled so as to irradiate the wafer 64 with an electron beam at the time of exposure, and not to reach the wafer 64 at times other than the exposure. Is desirable. The electron lens control unit 88 includes the first electron lens 14, the second electron lens 20, the third electron lens 28, the fourth electron lens 32, the fifth electron lens 40, the sixth electron lens 46, the seventh electron lens 50, The current supplied to the eighth electron lens 52 and the ninth electron lens 66 is controlled. The backscattered electron processing unit 90 detects digital data indicating the amount of electrons based on the electrical signal detected by the electron detection unit 60.
[0025]
The wafer stage control unit 92 moves the wafer stage 62 to a predetermined position by the wafer stage driving unit 70.
[0026]
An operation of the electron beam exposure apparatus 100 according to the present embodiment will be described. The electron beam exposure apparatus 100 performs adjustment processing for adjusting the configuration of the electron optical system and the like in advance before performing exposure processing. In the following, first, the adjustment process of the electron optical system before the exposure process will be described. The wafer stage 62 includes a target mark member 160 that is used to adjust the focus and the degree of deflection of the electron beam. The target mark member 160 is preferably provided on the wafer stage 62 at a location other than the area where the wafer is placed.
[0027]
First, in order to focus the electron beam, the mask projection system 112 performs deflection so that the detection pattern beam generation mask 250 that generates the detection pattern beam is irradiated with the electron beam. The wafer stage control unit 92 moves the focus detection mark 162 provided on the wafer stage 62 to the vicinity of the optical axis A by the wafer stage driving unit 70. Next, the overall control unit 130 adjusts the focal position of each lens to a predetermined position. Further, the overall control unit 130 deflects the detection pattern beam generated by the detection pattern beam generation mask 250 and scans the focus detection mark 162. The electron detector 60 outputs an electrical signal corresponding to the reflected electrons generated when the focus detection mark 162 is irradiated with the electron beam. The reflected electron processing unit 90 performs predetermined processing on the electrical signal supplied from the electron detector 60 to detect the amount of reflected electrons and notify the overall control unit 130. The overall control unit 130 determines whether or not the lens system is in focus based on the detected amount of reflected electrons. The overall control unit 130 controls the current supplied to each electron lens so that the differential value of the detection waveform of the reflected electrons is maximized.
[0028]
For example, when the coordinate system of the electron beam exposure apparatus 100 is configured with a laser interferometer or the like as a reference in order to perform highly accurate exposure processing, there are an electron beam deflection coordinate system and an orthogonal coordinate system based on the laser interferometer. It must be strictly calibrated. Therefore, in order to adjust (calibrate) the deflection amount after focusing the electron beam, the wafer stage control unit 92 uses a predetermined mark for adjusting the deflection amount provided on the wafer stage 62 by the wafer stage driving unit 70. The target mark member 160 formed with is moved to the vicinity of the optical axis A.
[0029]
The deflector scans the deflection amount adjustment mark of the target mark member 160 with the electron beam a plurality of times, and the electron detector 60 detects the change of the reflected electrons reflected from the target mark member 160, and controls the overall control unit 130. Notify The overall control unit 130 can determine the edge of the mark and obtain the center position of the mark coordinate based on the detection waveform of the reflected electrons. By performing the above mark detection, calibration of the deflection coordinate system and the orthogonal coordinate system can be realized, and the deflector can irradiate a predetermined region on the wafer with an electron beam with high accuracy.
[0030]
Next, the operation of each component when the electron beam exposure apparatus 100 performs an exposure process will be described. On the mask stage 72, a mask 30 having a plurality of blocks on which a predetermined pattern is formed is placed, and the mask 30 is fixed at a predetermined position. On the wafer stage 62, a wafer 64 to be exposed is placed. The wafer stage control unit 92 moves the wafer stage 62 by the wafer stage driving unit 70 so that the area to be exposed of the wafer 64 is positioned in the vicinity of the optical axis A. Further, since the electron gun 12 always irradiates the electron beam during the exposure processing period, the shot control unit 86 performs the first control so that the electron beam that has passed through the opening of the slit portion 16 is not irradiated onto the wafer 64 before the exposure is started. The first blanking electrode 24 and the second blanking electrode 36 are controlled. In the mask projection system 112, the electron lens 20 and the deflectors (18, 22, and 26) are adjusted so that the electron beam can be irradiated onto the block on which the pattern to be transferred to the wafer 64 is formed. In the focus adjustment lens system 114, the electron lenses (28, 32) are adjusted so that the electron beam is focused on the wafer 64. In the wafer projection system 116, the electron lens (40, 46, 50, 52, 66) and the deflector (34, 38, 42, 56, 58) can transfer the pattern image to a predetermined area of the wafer 64. To be adjusted.
[0031]
After the mask projection system 112, the focus adjustment lens system 114, and the wafer projection system 116 are adjusted, the shot control unit 86 stops the deflection of the electron beam by the first blanking electrode 24 and the second blanking electrode 36. Thereby, as shown below, the electron beam is irradiated onto the wafer 64 through the mask 30. The electron gun 12 generates an electron beam, and the first electron lens 14 adjusts the focal position of the electron beam to irradiate the slit portion 16. Then, the first deflector 18 and the second deflector 22 deflect the electron beam that has passed through the opening of the slit portion 16 so as to irradiate a predetermined region on the mask 30 where the pattern to be transferred is formed. The electron beam that has passed through the opening of the slit portion 16 has a rectangular cross-sectional shape. The electron beams deflected by the first deflector 18 and the second deflector 22 are deflected by the third deflector 26 so as to be substantially parallel to the optical axis A. The electron beam is adjusted by the second electron lens 20 so that an image of the opening of the slit portion 16 is formed in a predetermined region on the mask 30.
[0032]
Then, the electron beam that has passed through the pattern formed on the mask 30 is deflected in a direction approaching the optical axis A by the fourth deflector 34 and the sixth deflector 42, and substantially the same as the optical axis A by the fifth deflector 38. It is deflected to be parallel. The electron beam is adjusted by the third electron lens 28 and the fourth electron lens 32 so that the pattern image formed on the mask 30 is focused on the surface of the wafer 64, and the pattern image is formed by the fifth electron lens 40. , And the reduction rate of the pattern image is adjusted by the sixth electron lens 46 and the seventh electron lens 50. Then, the electron beam is deflected by the main deflector 56 and the sub deflector 58 so as to irradiate a predetermined shot area on the wafer 64. In the present embodiment, the main deflector 56 deflects the electron beam between subfields including a plurality of shot regions, and the subdeflector 58 deflects the electron beam between shot regions in the subfield. The electron beam deflected to a predetermined shot area is adjusted by the electron lens 52 and the electron lens 66 and irradiated onto the wafer 64. As a result, the image of the pattern formed on the mask 30 is transferred to a predetermined shot area on the wafer 64.
[0033]
After a predetermined exposure time has elapsed, the shot controller 86 controls the first blanking electrode 24 and the second blanking electrode 36 so that the electron beam does not irradiate the wafer 64 to deflect the electron beam. By the above process, the pattern formed on the mask 30 is exposed to a predetermined shot area on the wafer 64. In order to expose the pattern formed on the mask 30 to the next shot region, the electron lens 20 and the deflectors (18, 22, 26) in the mask projection system 112 are blocks having a pattern to be transferred to the wafer 64. It is adjusted so that it can be irradiated with an electron beam. In the focus adjustment lens system 114, the electron lenses (28, 32) are adjusted so that the electron beam is focused on the wafer 64. In the wafer projection system 116, the electron lens (40, 46, 50, 52, 66) and the deflector (34, 38, 42, 56, 58) can transfer the pattern image to a predetermined area of the wafer 64. To be adjusted.
[0034]
Specifically, the sub deflector 58 adjusts the electric field so that the pattern image generated by the mask projection system 112 is exposed to the next shot area. Thereafter, the pattern is exposed to the shot area in the same manner as described above. After exposing the pattern to all of the shot areas to be exposed in the subfield, the main deflector 56 adjusts the magnetic field so that the pattern can be exposed in the next subfield. The electron beam exposure apparatus 100 can expose a desired circuit pattern onto the wafer 64 by repeatedly executing this exposure process.
[0035]
FIG. 3A is an example of the detection pattern beam generation mask 250. The detection pattern beam generation mask 250 has a plurality of transmission regions 252 that transmit electron beams at a predetermined interval a. For example, the detection pattern beam generation mask 250 has a plurality of transmission regions 252 such that when the detection pattern beam is scanned, the amount of reflected electrons during the scanning period changes by substantially the same amount at a predetermined period. For example, the detection pattern beam generation mask 250 alternately includes transmission regions 252 and non-transmission regions that do not transmit electron beams in a predetermined direction. The predetermined direction is a direction in which the detection pattern beam is scanned. For example, each of the plurality of transmission regions 252 has the same size. Further, it is preferable that the interval between the first transmission region and the second transmission region in a predetermined direction is formed to be substantially equal to the narrowest interval between the irradiation regions included in the exposure pattern mask included in the mask 30.
[0036]
For example, the interval between the first transmission region 252 and the second transmission region 252 included in the detection pattern beam generation mask 250 is preferably set based on the shape of the pattern exposed on the wafer 64. For example, the interval between the first transmission region 252 and the second transmission region 252 included in the detection pattern beam generation mask 250 is substantially the same as the narrowest interval between the transmission region and the transmission region included in the exposure pattern mask. Is preferred.
[0037]
When the pattern is exposed on the wafer 64 by setting the interval between the first transmission region 252 and the second transmission region 252 of the detection pattern beam generation mask 250 based on the shape of the pattern exposed on the wafer 64 The focus position can be adjusted in situations close to. The electron beam is blurred due to the Coulomb force acting between the electrons. By setting the interval between the transmission regions 252 based on the shape of the pattern exposed on the wafer 64, the focal position can be adjusted including the influence of the Coulomb force acting between the electron beams transmitted through the transmission regions 252.
[0038]
FIG. 3B is an example of the transmissive region 252. When the transmission region 252 has a width w and a length l, for example, the width w of the transmission region 252 is the same width w as the interval a in which the plurality of transmission regions 252 described with reference to FIG. is there. Therefore, the detection pattern beam generation mask 250 can generate detection pattern beams having alternating regions (line: space = 1: 1) that are irradiated with electron beams having substantially the same size. The electron beam exposure apparatus 100 determines whether or not the focus position is in accordance with the detection pattern beam generated using the detection pattern beam generation mask 250.
[0039]
FIG. 4 shows a temporal positional relationship between the focus detection mark 162 and the detection pattern beam during a period in which the detection pattern beam is scanned on the focus detection mark 162. In FIG. 4, the detection pattern beam has irradiation regions (253a, 253b, 253c, 253d, 253d, and 253e) that irradiate four electron beams. Further, in FIG. 4, each irradiation region has a width Bw, and the interval between the irradiation regions is Sw. The detection pattern beam is scanned so that the longitudinal side of the irradiation region 253 is parallel to the longitudinal side of the focus detection mark 162.
[0040]
FIG. 4A shows the positional relationship between the focus detection mark 162 and the detection pattern beam at time t = t0. Since the irradiation area of the detection pattern beam does not irradiate the focus detection mark 162 at time t0, the electron detector 60 does not detect the reflected electrons.
[0041]
FIG. 4B shows the positional relationship between the focus detection mark 162 and the detection pattern beam at time t = t1. At time t1, since the irradiation region 253a is irradiating the focus detection mark 162, the electron detector 60 detects reflected electrons from the irradiation region 253a.
[0042]
FIG. 4C shows the positional relationship between the focus detection mark 162 and the detection pattern beam at time t = t2. At time t2, since the irradiation region 253a and the irradiation region 253b irradiate the focus detection mark 162, the electron detector 60 detects the reflected electrons from the irradiation region 253a and the irradiation region 253b. Since the detection pattern beam is scanned at a constant speed, the amount of reflected electrons increases until time t2 after the irradiation region 253a starts to irradiate the focus detection mark 162.
[0043]
FIG. 4D shows the positional relationship between the focus detection mark 162 and the detection pattern beam at time t3. At the time t3, the irradiation area 253a is deviated from the focus detection mark 162, and only the irradiation area 253b is irradiating the focus detection mark 162, so the electron detector 60 detects the reflected electrons from the irradiation area 253b. From time t2 to time t3, the amount of reflected electrons decreases as the irradiated region 253a moves away from the focus detection mark 162.
[0044]
FIG. 4E shows the positional relationship between the focus detection mark 162 and the detection pattern beam at time t4. At time t4, since the irradiation region 253b and the irradiation region 253c irradiate the focus detection mark 162, the electron detector 60 detects reflected electrons from the irradiation region 253b and the irradiation region 253c. The irradiation area 253a deviates from the focus detection mark 162, and the irradiation area 253c starts to irradiate the focus detection mark 162. From time t3 to time t4, the irradiation area 253c increases as the focus detection mark 162 is irradiated.
[0045]
Accordingly, by scanning the detection pattern beam having the irradiation regions 253 alternately, the electron detector 60 outputs an electrical signal that repeats fluctuations by the amount of reflected electrons by one irradiation region. Moreover, since the detection pattern beam has the irradiation regions 253 at the same interval, the amount of reflected electrons detected by the electron detector 60 repeatedly fluctuates at a constant interval. Therefore, the electron detector 60 outputs an electrical signal that fluctuates at a predetermined period to the reflected electron processing unit 90.
[0046]
FIG. 5 is an example of a detailed functional block diagram of the backscattered electron processing unit 90. The reflected electron processing unit 90 includes an amplification unit 220, a differentiation processing unit 222, an averaging processing unit 224, and a signal output unit 226. The amplification unit 220 amplifies the electric signal supplied from the electron detector 60 and outputs the amplified signal 230 to the differentiation processing unit 222. The differential processing unit 222 performs differential processing on the amplified signal 230 supplied from the amplification unit 220 and outputs the differential signal 232 to the averaging processing unit 224. The averaging processing unit 224 is, for example, a filter and averages the differential signal 232 supplied from the differential processing unit 222 and outputs the averaged signal to the signal output unit 226. For example, the averaging processing unit 224 may be a band pass filter. The signal output unit 226 converts the electrical signal supplied from the averaging processing unit 224 so that it can be processed by the overall control unit 130 and outputs the converted signal to the overall control unit 130. For example, the signal output unit 226 may be an A / D converter that converts an analog signal into a digital signal.
[0047]
FIG. 6A is an example of the amplified signal 230 output from the amplification unit 220 described with reference to FIG. In FIG. 6A, the horizontal axis indicates time, and the vertical axis indicates the amount of reflected electrons. FIG. 6A will be described with reference to FIG. At time t0, the irradiation region 253a does not irradiate the focus detection mark 162, and therefore the amount of reflected electrons is almost zero. The amount of reflected electrons increases to the maximum amount of reflected electrons N until time t2 after the irradiation region 253a starts irradiating the focus detection mark 162. From time t2 to time t3, the amount of reflected electrons decreases by the amount of reflected electrons S as the irradiation region 253a moves away from the focus detection mark 162. From time t3 to time t4, the amount of reflected electrons increases to the maximum amount of reflected electrons N as the irradiation region 253c irradiates the focus detection mark 162. Thereafter, the fluctuation of the amount of reflected electrons S is repeated until the irradiation region 253d irradiates the focus detection mark 162. When the entire irradiation area 253e irradiates the focus detection mark 162, the amount of reflected electrons continues to decrease and becomes almost zero.
[0048]
The size of the focus detection mark 162 is preferably set based on the detection performance of the reflected electrons of the electron detector 60. The electron detector 60 is saturated when the amount of electrons by the focus detection mark 162 is excessive. As a result, the detection sensitivity decreases. Therefore, it is preferable that the focus detection mark 162 has such a size that the amount of reflected electrons reflected by the focus detection mark 162 does not decrease the detection sensitivity of the electron detector 60. In addition, it is preferable that the size of the focus detection mark 162 is set so that the ratio of the variable reflected electron amount S to the maximum reflected electron amount N is larger than a predetermined value. By setting the size of the focus detection mark 162 so as to be larger than a predetermined value, it becomes easy to detect the variation in the amount of reflected electrons due to each of the irradiation regions 253. Since it is easy to detect fluctuations in the amount of reflected electrons due to each of the irradiation regions 253, it is easy to detect blurring of the electron beam due to a shift in the focal position.
[0049]
For example, it is preferable that the focus detection mark 162 has a size capable of simultaneously reflecting the electron beams in a smaller number of irradiation regions than the number of irradiation regions included in the detection pattern beam. Further, when the amount of reflected electrons by one irradiation region is defined as the unit reflected electron amount, the focus detection mark 162 may be sized so that the maximum reflected electron amount is an integral multiple of the unit reflected electron amount. preferable. In particular, the length in the predetermined direction of the focus detection mark 162 is preferably an odd multiple of the length in the predetermined direction in the transmission region. The size of the focus detection mark 162 is set based on the detection performance of the electron detector 60, the number of irradiation regions included in the detection beam, and the ratio of the variable reflected electron amount S to the maximum reflected electron amount N. Therefore, the focus detection mark 162 is fine. By making the focus detection mark 162 finer, it becomes easier to measure the amount of reflected electrons from each irradiation region 253, and it is possible to accurately determine whether or not the focus position is correct.
[0050]
FIG. 6B is an example of the differential signal 232 output from the differential processing unit 222. The differential signal 232 is a signal obtained by differentiating the amplified signal 230 and is an increment of the amount of reflected electrons for each time of the amplified signal 230. Accordingly, the differential value increases immediately after the irradiation region 253a starts irradiating the focus detection mark 162, and the differential value becomes 0 when the amount of reflected electrons is an extreme value. The differential value takes the maximum value Max between time t0 and time t2. The differential value takes a minimum value Min ′ that is different from the minimum value Min from time t2 to time t3 when the amount of reflected electrons decreases when the irradiation region 253 deviates from the focus detection mark 162. Further, the differential value takes a maximum value Max ′ different from the maximum value Max between time t3 and time t4 when the amount of reflected electrons increases when the irradiation region 253 starts to irradiate the focus detection mark 162. Over the period in which the reflected electrons fluctuate with the variable electron quantity S, the differential value also fluctuates between the minimum value Min ′ and the maximum value Max ′. The entire area of the irradiation area 253e irradiates the focus detection mark 162, and the differential value takes the minimum value Min while the amount of reflected electrons continues to decrease and becomes almost zero.
[0051]
The overall control unit 130 determines whether or not the focus position is correct based on the variation amount of the differential value. When the focal position is correct, the amount of variation in the differential value increases. When the focal position is not correct, the amount of change in the differential value is smaller than that when the focal position is correct. The overall control unit 130 may calculate a determination value that is uniquely determined from the differential value, and determine whether the focus is achieved based on the determination value. For example, when the value obtained by subtracting the minimum value Min ′ from the maximum value Max is the first fluctuation range Imax, and the value obtained by subtracting the maximum value Max ′ from the maximum value Max is the second fluctuation range Imin, the overall control unit 130 determines You may calculate a value with following Formula.
[0052]
Determination value = (Imax−Imin) / (Imax + Imin)
The determination value increases as the focal position is matched. The overall control unit 130 outputs a focus setting value for adjusting the focus position to the electronic lens control unit 88. The overall control unit 130 calculates a determination value for each focus position adjusted based on the focus setting value. The overall control unit 130 determines that the focal position where the determination value is maximized is in focus. In addition, for example, the overall control unit 130 may store a focus setting value for adjustment to a focus position that is determined to be in focus. By storing the focus setting value that is determined to be in focus, the overall control unit 130 can adjust the focus position based on the stored focus setting value.
[0053]
FIG. 7A shows the current distribution in each irradiation region 253 of the detection pattern beam when the focal position is in focus. When the focal position is in alignment, the amount of current changes abruptly between the non-irradiated area and the irradiated area 253. FIG. 7B shows a current distribution of each irradiation region 253 included in the detection pattern beam when the focal position is out of focus. When the focal position is not matched, the amount of current gradually changes between the non-irradiated area and the irradiated area 253.
[0054]
FIG. 8 (a) shows an amplified signal 230 when the focal position is correct and an amplified signal 230 ′ when the focal position is not correct. The variable reflected electron amount S of the amplified signal 230 is larger than the variable reflected electron amount S ′ of the amplified signal 230 ′. FIG. 8B shows a differential signal 232 when the focal position is correct and a differential signal 232 ′ when the focal position is not correct. When the focal position is correct, the differential signal 232 changes rapidly. When the focal position is not correct, the differential signal 232 ′ changes slowly. The overall control unit 130 determines whether or not the focus position is correct based on the amount of change in the differential value.
[0055]
FIG. 9 is a flowchart of the focus adjustment method for a predetermined amount of electron beam current. The overall control unit 130 outputs, to the electron beam current control unit 94, a current value setting value that specifies that the current amount of the electron beam emitted from the electron gun 12 is set to a predetermined current amount (S10). The electron beam current control unit 94 adjusts the amount of electron beam current emitted from the electron gun 12 based on the current setting value.
[0056]
The overall control unit 130 outputs a lens control value designating adjustment of the focal position of the electronic lens to the electronic lens control unit 88 (S12). The electronic lens control unit 88 adjusts the focal position of the electronic lens based on the lens control value. For example, the electronic lens control unit 88 adjusts the amount of current supplied to the electronic lens based on the lens control value. The mask projection system 112 deflects the electron beam and irradiates the detection pattern beam generation mask 250. The wafer projection system 116 deflects the detection pattern beam generated by passing through the detection pattern beam generation mask 250 and scans the focus detection mark 162. The electron detector 60 detects the amount of reflected electrons reflected by scanning the detection pattern beam (S14).
[0057]
The reflected electron processing unit 90 generates a differential signal 232 based on the electrical signal supplied from the electron detector 60 and outputs the differential signal 232 to the overall control unit 130. The overall control unit 130 calculates a determination value based on the differential signal supplied from the backscattered electron processing unit 90 (S16). The overall control unit 130 determines whether or not all lens control values that can adjust the focal position of the electronic lens are set in the electronic lens control unit 88 (S18). If not all lens control values are set, the overall control unit 130 sets a new lens control value (S12). When all the lens control values are set, the overall control unit 130 finds the lens control value at which the determination value is maximized, and the focal position of the electronic lens adjusted by the lens control value matches the focal position. Determine (S20). The overall control unit 130 stores the current setting value output to the electron beam current control unit 94 and the lens control value output to the electronic lens control unit 88 in association with each other. Therefore, the overall control unit 130 can store the lens control value for each predetermined amount of current.
[0058]
Since the Coulomb force acts between the electrons, the focal position at which the pattern image is formed near the surface of the wafer 64 by the exposure pattern beam varies depending on the aperture ratio of the transmission region that transmits the electron beam included in each pattern of the mask 30. . Therefore, in order to accurately expose the pattern on the wafer 64 in the electron beam exposure apparatus 100, the total current amount of the electron beam passing through the objective lens changes according to the aperture ratio of the pattern to be exposed. It is necessary to change the focal position according to the amount of current from the focal position. The focus position changed according to the aperture ratio is defined as refocus. The distance from the reference focal position to the refocus is defined as a refocus amount Rf. The refocus amount Rf is
[0059]
Rf = rfc × S
Given in. Here, rfc is a refocus coefficient and is uniquely determined by the amount of current of the electron beam emitted from the electron gun 12. S is the area of the opening of the pattern. The electron beam exposure apparatus 100 adjusts the refocus amount Rf according to the opening area of the pattern to be exposed. The wafer projection system 116 described with reference to FIG. 2 has a highly responsive refocus lens in order to adjust the refocus amount Rf for each pattern. For example, it may be an electron lens that adjusts the focus by an electric field. The overall control unit 130 calculates the refocus amount Rf according to the opening area of the pattern exposed on the wafer 64, and adjusts the refocus lens so that the focal position is adjusted to the calculated refocus amount Rf.
[0060]
According to the present invention, the refocus coefficient rfc can be determined with high accuracy. When the refocus coefficient rfc is determined, the refocus coefficient rfc is determined based on the opening area S of the detection pattern beam generation mask 250 and the focus position when it is determined that the focus position is matched. According to the present invention, it is possible to accurately determine whether or not the focus position is in alignment, so that the refocus amount Rf can be determined with high accuracy. Therefore, the refocus coefficient rfc can be determined with high accuracy. Since the refocus coefficient rfc can be determined with high accuracy, the refocus amount Rf can be set with high accuracy according to the opening area of the pattern. Further, since the refocus coefficient rfc is a value uniquely determined by the amount of electron beam current emitted from the electron gun 12, the refocus coefficient rfc is determined for each amount of electron beam current used for exposure. Therefore, according to the present invention, the refocus coefficient rfc can be determined for each current amount.
[0061]
As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. Various changes or improvements can be added to the above embodiment. It is apparent from the description of the scope of claims that embodiments with such changes or improvements can be included in the technical scope of the present invention. Examples of such changes include:
[0062]
As a first modification, the overall control unit 130 adjusts the focal position based on the distance between the inflection point and the inflection point of the differential signal portion that periodically changes with substantially the same amplitude included in the differential signal 232. It may be determined whether or not. FIG. 10 shows an example of the differential signal 232. For example, the overall control unit 130 determines whether or not the focus position is correct based on the distance d between the arrangement points shown in FIG. The overall control unit 130 determines that the focal position when the distance d is the smallest is the position where the focal position is in alignment.
[0063]
As a second modification, the overall control unit 130 may measure the reduction rate of the pattern image of the wafer projection system 116 based on the differential signal 232. For example, the overall control unit 130 calculates the reduction ratio based on the distance between the extreme value and the extreme value of the differential signal portion that periodically changes with substantially the same amplitude included in the differential signal 232. Since the interval between the first transmission region 252 and the second transmission region 252 included in the detection pattern beam generation mask 250 is determined in advance, the interval between the first transmission region 252 and the second transmission region 252 and the differential signal 232. The reduction rate of the wafer projection system 116 can be calculated based on the extreme value and the interval between the extreme values. For example, the overall control unit 130 is based on the distance between the maximum value and the maximum value shown in FIG. 10 and the distance between the first transmission region 252 and the second transmission region 252 formed on the detection pattern beam generation mask 250. Measure the reduction rate. Therefore, the overall control unit 130 can accurately adjust the reduction rate of the wafer projection system 116 based on this measurement.
[0064]
As a third modification, when the detection pattern beam is scanned, a plurality of detection pattern beam generation masks 250 are provided so that the amount of reflected electrons in a part of the scanning period changes by substantially the same amount in a predetermined cycle. It suffices to have an irradiation region. FIG. 11 shows another form of the detection pattern beam generation mask 250. The detection pattern beam generation mask 250 includes a plurality of transmission regions 254, transmission regions 256a, and transmission regions 256b. The transmission area of the transmission region 256 a and the transmission region 256 b is half of the transmission area of the transmission region 254. The transmissive region 256a and the transmissive region 256b are formed so as to irradiate the focus detection mark 162 at the same time. The transmissive region 254 and the transmissive regions 256a and 256b are formed at regular intervals. Therefore, when the detection pattern beam generated by the detection pattern beam generation mask 250 shown in FIG. 11 is scanned, the amount of reflected electrons in a part of the scanning period changes by substantially the same amount at a predetermined period. It is obvious to those skilled in the art that the detection pattern beam generation mask 250 can be considered in various ways other than the mask having the transmissive regions 252 alternately described with reference to FIG.
[0065]
As a fourth modification, the electron beam exposure apparatus 100 may store a refocus coefficient rfc for each amount of electron beam current emitted by the electron gun 12. Further, a pattern used for exposure and a refocus amount Rf calculated based on the aperture ratio of the pattern may be stored in association with each other.
[0066]
【The invention's effect】
As is clear from the above description, according to the present invention, it can be determined whether or not the focal position of the electron lens is in alignment.
[Brief description of the drawings]
FIG. 1 shows a method for detecting a focal position of a conventional electron lens.
FIG. 2 is a block diagram of an electron beam exposure apparatus 100 according to an embodiment of the present invention.
3 is an example of a detection pattern beam generation mask 250. FIG.
FIG. 4 is a diagram showing a temporal positional relationship between a focus detection mark 162 and a detection pattern beam.
FIG. 5 is an example of a detailed functional block diagram of a backscattered electron processing unit 90;
6 is an example of an amplified signal 230. FIG.
7 shows a current distribution in an irradiation region 253. FIG.
FIG. 8 shows an amplified signal 230 when the focal position is correct and an amplified signal 230 ′ when the focal position is not correct.
FIG. 9 is a flowchart of a focus adjustment method for a predetermined amount of current of an electron beam.
FIG. 10 is an example of a differential signal 232;
11 shows an example of a detection pattern beam generation mask 250. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Housing | casing, 12 ... Electron gun, 14 ... 1st electron lens, 16 ... Slit part, 18 ... 1st deflector, 20 ... 2nd electron lens, 22. ..Second deflector, 24 ... first blanking deflector, 26 ... third deflector, 28 ... third electron lens, 30 ... mask, 32 ... fourth electron lens 34 ... 4th deflector, 36 ... 2nd blanking deflector, 38 ... 5th deflector, 40 ... 5th electron lens, 42 ... 6th deflector, 46. .. Sixth electron lens 48... Round aperture 50. Seventh electron lens 52. Eighth electron lens 56... Main deflector 58 .. sub deflector 60. ..Electron detector, 62 ... wafer stage, 64 ... wafer, 66 ... 9th electron lens, 68 ... mask stay Driving unit, 70 ... wafer stage driving unit, 72 ... mask stage, 82 ... deflection control unit, 84 ... mask stage control unit, 86 ... blanking electrode control unit, 88 ... Electron lens control unit, 90 ... backscattered electron processing unit, 92 ... wafer stage control unit, 100 ... electron beam exposure apparatus, 110 ... electron beam irradiation system, 112 ... mask projection system, 114: Focus adjustment lens system, 116: Wafer projection system, 120 ... Individual control unit, 130 ... Overall control unit, 140 ... Control system, 150 ... Exposure unit, 220 ..Amplifying unit, 222... Differential processing unit, 224... Averaging processing unit, 226... Signal output unit, 230... Amplified signal, 232. Beam generation mask 252, Transmission region, 300 ... electron gun, 302 ... mask, 304 ... electron lens, 306 ... mark, 308 ... table, 310 ... backscattered electron detector, 312 ... electron Lens control unit, 314 ... backscattered electron, 315 ... rectangular beam, 316 ... focus determination unit

Claims (13)

A focus detection method for detecting whether an image by an electron beam is connected to a predetermined imaging plane,
Generating a detection pattern beam having a plurality of irradiation regions for irradiating the electron beam; and
The detection pattern beam is scanned on a mark provided on substantially the same plane as the predetermined imaging plane, and the image is based on a change in the amount of reflected electrons by the mark during the scanning period. A detection step for detecting whether or not the image is connected on a predetermined imaging plane,
The detection pattern beam has rectangular irradiation areas having substantially the same shape at substantially the same interval in the scanning direction,
The focus detection method according to claim 1, wherein the mark has a size capable of simultaneously reflecting a smaller number of electron beams in the irradiation region than the number of the irradiation regions included in the detection pattern beam.   The generation step generates the detection pattern beam so that when the detection pattern beam is scanned, the amount of reflected electrons in a part of the scanning period changes by substantially the same amount in a predetermined cycle. The focus detection method according to claim 1.   The focus detection method according to claim 1, wherein the generation step generates the detection pattern beams having the same size of the plurality of irradiation areas.   4. The focus detection method according to claim 1, wherein in the detection step, the detection pattern beam is scanned so that a longitudinal direction of the mark is parallel to a longitudinal direction of the irradiation region. 5. .   5. The focus detection method according to claim 1, wherein the generation step generates the detection pattern beam in which an interval between the irradiation regions is equal to a length in a short direction of the irradiation regions. . A determination step of determining whether or not the image is formed on the predetermined imaging plane based on the amount of reflected electrons;
An intensity adjustment step for performing the determination step while adjusting the lens intensity of an electron lens that forms an image on the imaging plane;
The focus detection method according to claim 1, further comprising a step of determining the lens intensity when a determination value uniquely determined based on the amount of reflected electrons takes an extreme value. The judgment value is
From the first fluctuation range Imax obtained by dividing the minimum value different from the minimum value from the maximum value obtained by differentiating the amount of reflected electrons in the scanning period,
A value obtained by subtracting the second fluctuation range Imin obtained by dividing the maximum value different from the maximum value from the maximum value,
The focus detection method according to claim 6, wherein the focus detection method is a value obtained by dividing the first variation width Imax and the second variation width Imin by a value obtained by adding the first variation width Imax and the second variation width Imin. An electron beam exposure apparatus that irradiates a wafer with a predetermined electronic circuit pattern by irradiating an electron beam,
An exposure pattern beam generator for generating an exposure pattern beam for irradiating the electron beam in the same shape as the predetermined electronic circuit pattern;
A detection pattern beam generating unit that generates a detection pattern beam having a plurality of irradiation regions for irradiating the electron beam;
An electron lens that forms an image on the wafer by the exposure pattern beam and the detection pattern beam;
A mark that reflects the detection pattern beam;
A reflected electron detector that detects the amount of reflected electrons of the electron beam reflected by the mark;
A focus detection unit configured to detect whether or not a focal position of the electron lens is aligned with the mark based on a change in the amount of reflected electrons during the scanning period when the mark is scanned with the detection pattern beam; With
The detection pattern beam generator is
An electron gun that generates an electron beam;
A detection pattern beam generation mask having a plurality of transmission regions that transmit the electron beam,
The detection pattern beam generation mask includes a plurality of transmission regions having the same interval in a predetermined direction,
The mark is of a size that can simultaneously reflect the number of electron beams in the irradiation region smaller than the number of the irradiation regions included in the detection pattern beam,
An electron beam exposure apparatus, wherein, when it is detected that the focal position is in alignment, the wafer is irradiated with the exposure pattern beam to expose the predetermined pattern onto the wafer. The detection pattern beam generation mask is
The plurality of transmission regions are provided so that when the detection pattern beam is scanned, the amount of reflected electrons during the scanning period is changed by substantially the same amount at a predetermined period. Electron beam exposure equipment.   10. The electron beam exposure apparatus according to claim 8, wherein the detection pattern beam generation mask includes a plurality of the transmission regions having the same size. 10.   11. The electron beam exposure apparatus according to claim 8, wherein a length of the mark in the predetermined direction is an odd multiple of a length of the transmission region in the predetermined direction.   The detection pattern beam generation mask is formed so as to pass through the transmission region and the width of the irradiation region of the detection pattern beam imaged on the wafer is substantially equal to the minimum line width of the predetermined electronic circuit pattern. The electron beam exposure apparatus according to claim 8, wherein the electron beam exposure apparatus is provided.   13. The electron beam exposure apparatus according to claim 8, wherein the detection pattern beam is scanned so that a longitudinal direction of the mark and a longitudinal direction of the irradiation region are parallel to each other.

Images