Patent Application
20240363307
This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2023-071315 filed on Apr. 25, 2023 in Japan, the entire contents of which are incorporated herein by reference.
An embodiment of the present invention relates to a mark position measurement apparatus, a charged particle beam writing apparatus, and a mark position measurement method, and, for example, to a method for measuring a position of an alignment mark on a writing target object.
The lithography technique which advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is becoming increasingly finer year by year. The electron beam writing technique, which intrinsically has excellent resolution, is used for writing or “drawing” on a wafer and the like with electron beams.
For example, as a known example of employing the electron beam writing technique, there is a writing apparatus using multiple beams. Since it is possible for multi-beam (multiple beam) writing to apply multiple beams at a time, the writing throughput can be greatly increased in comparison with single electron beam writing. For example, a writing apparatus employing the multiple beam system forms multiple beams by letting an electron beam emitted from an electron gun pass through a mask having a plurality of holes, performs blanking control for each beam, reduces each unblocked beam by an optical system, and deflects it by a deflector to irradiate a desired position on a target object or “sample”.
In electron beam writing including multi-beam writing, when a writing target substrate is disposed on the stage, an alignment mark formed on the substrate is detected with an electron beam. Using a detected alignment mark as a reference, alignment of a writing region is performed. In electron beam writing, there is a case where a writing position on a mask is highly accurately specified so as to execute writing. For example, when a phase shift mask is formed by multiple layers, it is necessary to align the relative position between the first and second layers. Since the relative position between patterns in respective layers affects the performance of lithography writing using the mask, the relative position should be formed with a high precision of about several nanometers. Further, in an EUV mask, the substrate for which a defect inspection has been performed in advance is used, and patterns are written circumventing coordinates of defects. Then, the mark formed on the mask substrate is measured to be used as a reference for alignment in writing so as to highly accurately specify writing positions.
The line width of current alignment marks has become finer than that of conventional ones. Therefore, when marks are irradiated with electron beams, the electron yield is low, thereby being difficult to acquire contrast. Consequently, there is a problem that since an S/N ratio is low, an alignment mark on the substrate is difficult to find. As a countermeasure for this problem, it is examined to increase the dose of an electron beam in order to acquire contrast. However, according to this method, because a high dose electron beam is applied to a resist in a wide area, the resist is dispersed (scattered) to contaminate the inside of the writing chamber.
Regarding some methods for finding an alignment mark, a method is used which scans a laser beam over a mark, and detects a reflected light to calculate a mark position based on a change of the reflected light from the mark. However, according to this method, there is a case where a plurality of mark candidate signals are measured in the vicinity of the mark due to an influence of a configuration except for the mark, a resist unevenness, a noise, or the like, resulting in a problem that it is difficult to determine which one in the plurality of mark candidate signals is the one of the true mark.
According to one aspect of the present invention, a mark position measurement apparatus includes
According to another aspect of the present invention, a charged particle beam writing apparatus includes
According to yet another aspect of the present invention, a mark position measurement method includes
Embodiments of the present invention provide an apparatus and method that can highly accurately specify a desired mark signal in a plurality of mark candidate signals of a plurality of mark formed on a target object.
Embodiments below describe a configuration using an electron beam as an example of a charged particle beam. The charged particle beam is not limited to the electron beam, and other charged particle beam such as an ion beam may also be used. Embodiments below describe a writing apparatus using multiple beams. However, it is not limited thereto, and is also preferable to employ a writing apparatus using a single beam. For example, embodiments can be applied to a variable shaped beam (VSB) type writing apparatus.
In the writing chamber 103, an XY stage 105 is disposed. On the XY stage 105, there is placed a target object or “sample” 101 such as a mask serving as a writing target substrate when writing (exposure) is performed. The target object 101 is, for example, an exposure mask used when fabricating semiconductor devices, or a semiconductor substrate (silicon wafer) for fabricating semiconductor devices. Further, the target object 101 may be, for example, a mask blank on which a resist has been applied and nothing has yet been written. On target object 101, a plurality of alignment marks (concave-convex marks) whose concave (recessed) surface and convex (projected) surface are made of the same material, to be described later, are formed.
Further, on the XY stage 105, a mirror 210 for measuring the position of the XY stage 105 is arranged.
On the writing chamber 103, a Z sensor 220 (an example of a sensor) is disposed. The Z sensor 220 includes, for example, an irradiator 222 which generates a visible laser beam, and a photoreceiver 224 which receives a reflected light from a target object irradiated with the laser beam. The irradiator 222 generates a laser beam in oblique incidence on the surface of the target object 101 arranged on the XY stage 105 in the writing chamber 103. Thus, the irradiator 222 irradiates the target object 101 with laser beams. The laser beam emitted from the irradiator 222 has a light intensity distribution of normal distribution. Further, the laser beam emitted from the irradiator 222 has a diameter larger than the width of the alignment mark formed on the target object 101. This is due to the beam diameter at the emission, and the optical element for guiding beams, and is largely affected by the phenomenon that the beam extends in an incident direction because of the oblique incidence on the target object. For example, a laser beam with a diameter of 10-300 μm on the surface of the target object 101 is used. For example, it is preferable to use a laser beam with a diameter of about 200 μm on the surface of the target object 101. The photoreceiver 224 receives a reflected light from the target object 101 along with irradiation of the laser beam, and outputs information on the height of the surface of the target object 101. As the photoreceiver 224, an optical position sensor is used, for example. The photoreceiver 224 receives a reflected light, measures the height position of the surface of the target object 101 based on a deviation of the light-receiving position on the surface which received the light, and outputs information on the measured position.
The control system circuit 160 includes a control computer 110, a memory 112, a deflection control circuit 130, digital-analog converter (DAC) amplifier units 132 and 134, a detection circuit 135, a lens control circuit 136, a stage control mechanism 138, a stage position measuring instrument 139, and storage devices 140 and 142 such as magnetic disk drives. The control computer 110, the memory 112, the deflection control circuit 130, the detection circuit 135, the lens control circuit 136, the stage control mechanism 138, the stage position measuring instrument 139, and the storage devices 140 and 142 are connected to each other through a bus (not shown). The DAC amplifier units 132 and 134 and the blanking aperture array mechanism 204 are connected to the deflection control circuit 130. The deflector 209 is composed of at least four electrodes (or “at least four poles”), and controlled by the deflection control circuit 130 through the DAC amplifier unit 132 disposed for each electrode. The deflector 208 is composed of at least four electrodes (or “at least four poles”), and controlled by the deflection control circuit 130 through the DAC amplifier unit 134 disposed for each electrode. Electromagnetic lenses such as the illumination lens 202, the reducing lens 205, and the objective lens 207 are controlled by the lens control circuit 136. The detector 226 is connected to the detection circuit 135.
The position of the XY stage 105 is controlled by the drive of each axis motor (not shown) which is controlled by the stage control mechanism 138. Based on the principle of laser interferometry, the stage position measuring instrument 139 measures the position of the XY stage 105 by receiving a reflected light from the mirror 210.
In the control computer 110, there are arranged a height position distribution average calculation unit 50, a mark region specification unit 52, a height position distribution calculation unit 54, a mark candidate signal position calculation unit 56, a combination generation unit 58, a relative position information calculation unit 60, an index calculation unit 64, a selection unit 66, a mark position calculation unit 68, a determination unit 69, a shot data generation unit 70, a data processing unit 72, a transmission processing unit 74, and a writing control unit 76. Each of the “ . . . units” such as the height position distribution average calculation unit 50, the mark region specification unit 52, the height position distribution calculation unit 54, the mark candidate signal position calculation unit 56, the combination generation unit 58, the relative position information calculation unit 60, the index calculation unit 64, the selection unit 66, the mark position calculation unit 68, the determination unit 69, the shot data generation unit 70, the data processing unit 72, the transmission processing unit 74, and the writing control unit 76 includes processing circuitry. The processing circuitry includes, for example, an electric circuit, computer, processor, circuit board, quantum circuit, semiconductor device, or the like. Each “ . . . unit” may use common processing circuitry (the same processing circuitry), or different processing circuitry (separate processing circuitry). Information input/output to/from the height position distribution average calculation unit 50, the mark region specification unit 52, the height position distribution calculation unit 54, the mark candidate signal position calculation unit 56, the combination generation unit 58, the relative position information calculation unit 60, the index calculation unit 64, the selection unit 66, the mark position calculation unit 68, the determination unit 69, the shot data generation unit 70, the data processing unit 72, the transmission processing unit 74, and the writing control unit 76, and information being operated are stored in the memory 112 each time.
The XY stage 105, the Z sensor 220, the deflector 209, the detector 226, the detection circuit 135, the height position distribution average calculation unit 50, the mark region specification unit 52, the height position distribution calculation unit 54, the mark candidate signal position calculation unit 56, the combination generation unit 58, the relative position information calculation unit 60, the index calculation unit 64, the selection unit 66, the mark position calculation unit 68, the determination unit 69, and the like are used not only as configuration elements of the writing apparatus 100 but also as those of the mark position measurement apparatus according to the first embodiment.
Writing operations of the writing apparatus 100 are controlled by the writing control unit 76. Processing of transmitting irradiation time data of each shot to the deflection control circuit 130 is controlled by the transmission control unit 74.
Writing data (chip data) is input from the outside of the writing apparatus 100, and stored in the storage device 140. Chip data defines information on a plurality of FIG. patterns configuring a chip pattern. Specifically, for example, a figure code, coordinates, a size, and the like are defined for each figure pattern.
In the control circuit 41, an amplifier (not shown) (an example of a switching circuit) is arranged. As an example of the amplifier, a CMOS (Complementary MOS) inverter circuit serving as a switching circuit is disposed. In regard to inputs (IN) to the CMOS inverter circuit, either an L (low) potential (e.g., ground potential) lower than a threshold voltage, or an H (high) potential (e.g., 1.5 V) higher than or equal to the threshold voltage is applied as a control signal. According to the first embodiment, in a state where an L potential is applied to the input (IN) of the CMOS inverter circuit, the output (OUT) of the CMOS inverter circuit, which is to be applied to the control circuit 41, becomes a positive potential (Vdd), and then, a corresponding beam is deflected by an electric field due to a potential difference from the ground potential of the counter electrode 26, and is controlled to be in a beam OFF condition by being blocked by the limiting aperture substrate 206. In contrast, in a state (active state) where an H potential is applied to the input (IN) of the CMOS inverter circuit, the output (OUT) of the CMOS inverter circuit becomes a ground potential, and therefore, since there is no potential difference from the ground potential of the counter electrode 26, a corresponding beam is not deflected, and is controlled to be in a beam ON condition by passing through the limiting aperture substrate 206. Blanking control is provided by such deflection.
Next, operations of the writing mechanism 150 will be described. The electron beam 200 emitted from the electron gun 201 (emission source) almost perpendicularly (e.g., vertically) illuminates the whole of the shaping aperture array substrate 203 by the illumination lens 202. A plurality of rectangular holes 22 (openings) are formed in the shaping aperture array substrate 203. The region including all of the plurality of holes 22 is irradiated with the electron beam 200. For example, rectangular multiple beams (a plurality of electron beams) 20 are formed by letting portions of the electron beam 200 applied to the positions of the plurality of holes 22 individually pass through a corresponding one of the plurality of holes 22 in the shaping aperture array substrate 203. The multiple beams 20 individually pass through corresponding blankers of the blanking aperture array mechanism 204. The blanker provides blanking control such that a corresponding beam individually passing becomes in an ON condition during a set writing time (irradiation time).
The multiple beams 20 having passed through the blanking aperture array mechanism 204 are reduced by the reducing lens 205, and travel toward the hole in the center of the limiting aperture substrate 206. Then, the electron beam which was deflected by the blanker of the blanking aperture array mechanism 204 deviates (shifts) from the hole in the center of the limiting aperture substrate 206 and is blocked by the limiting aperture substrate 206. In contrast, the electron beam which was not deflected by the blanker of the blanking aperture array mechanism 204 passes through the hole in the center of the limiting aperture substrate 206 as shown in
In addition to multiple beam writing, for example, in electron beam writing including single beam writing using the VSB method, an alignment mark formed on a target object is detected when the writing target substrate is disposed on the stage. Then, using a detected alignment mark as a reference, alignment of the writing region is carried out. Current alignment marks are formed with a micro line width compared with that of conventional alignment marks.
The size of the large mark 12 is formed to be large, such as about 4000 μm, and mainly used, as a temporary alignment mark, for searching for the alignment mark region 10 in the wide range region on the surface of the target object 101, for example. The size of the small mark 14 is formed to be small, such as about 400 μm, and used as an alignment mark serving as a position reference. The large mark 12 may be used as an alignment mark serving as a position reference. The small mark 14 may be used as a mark for searching for the alignment mark region 10 in the wide range region on the surface of the target object 101.
For the large mark 12 and the small mark 14, patterns of the same line width are used, for example. Each of the large mark 12 and the small mark 14 is formed by a cross pattern acquired by crossing a line pattern having a line width of 2-200 μm and in the x direction, and a line pattern having a line width of 2-200 μm and in the y direction. The line width of the concave (recessed) portion of each of the large mark 12 and the small mark 14 is formed to be 4-5 μm. Detailed configurations are described below.
Conventionally, an alignment mark on the surface of the target object 101 is detected (searched for) using electron beams, and the position of the alignment mark is measured with the electron beams. However, with respect to a mark of the concave-convex configuration of the same material, if scanning an electron beam over the mark, since difference in electron yields is small, contrast is difficult to obtain. As a result, there is a problem that since the S/N ratio is small, the alignment mark on the target object 101 cannot be found easily. To cope with this problem, it is examined to increase the dose (irradiation amount) of an electron beam in order to acquire contrast. However, this method has a problem that because a high dose electron beam is applied to a resist in a wide area, the resist is dispersed (scattered) to contaminate the inside of the writing chamber. Then, according to the first embodiment, using a laser beam by which no resist or a negligible level of resist may be dispersed, an alignment mark is searched for in a wide range region on the surface of the target object 101, and the center position of the alignment mark is measured. After specifying the center position of an alignment mark, the center position is measured by an electron beam to obtain a more accurate measurement value than that in the case of using a laser beam.
In
When a mark portion is convex, an output signal is a convex signal. In that case, a plurality of concave-convex signals showing a convex portion are detected. Therefore, according to the first embodiment, when a mark portion is concave, concave-convex signals are measurement signals indicating a concave portion. When a mark portion is convex, concave-convex signals are measurement signals indicating a convex portion.
According to the first embodiment, when a plurality of concavo-convex signals indicating a concave portion in each aliment mark are measured by scanning over the plurality of alignment marks (concave-convex marks), a true alignment mark is specified by using a relation with a concavo-convex signal indicating a concave portion of the other alignment mark. Detailed operations are described below.
In the mark search step (S102), using the Z sensor 220, the large mark 12 is searched for in the wide range region on the target object 101. The position of the alignment mark region 10 on the target object 101 has been set in the design. However, the relative positional relationship between the XY stage 105 and the target object 101 having been transferred into the writing chamber 103 and placed on the XY stage 105 is not necessarily in accordance with the design positional relationship perfectly. For example, arrangement deviation of the target object 101 may occur. Accordingly, there may possibly be a case in which the large mark 12 does not exist at the position where the large mark 12 should exist in the design. Then, an actual large mark 12 is searched for based on the design position of the large mark 12. Specifically, the XY stage 105 is moved to a design position where the large mark 12 should be irradiated with a laser beam from the Z sensor 220. Regarding this position as a reference, the XY stage 105 is moved, for example, in the −x direction by a predetermined pitch from a position where an irradiation position of a laser beam is sufficiently far, for example, in the −x direction from the reference position. By this method, the height position of the target object 101 is measured at a plurality of measurement positions. Thereby, the height position can be measured at a plurality of measurement positions which are relatively in the x direction on the surface of the target object. Information on measured height positions is output to the control computer 110. Further, instead of moving the XY stage 105 to the design position where the large mark 12 should be irradiated with a laser beam, it is also preferable to move the irradiator 222 and the photoreceiver 224 in conjunction with each other in order to apply a laser beam to the surface of the target object 101. Alternatively, while changing the direction of radiation of a laser beam from the irradiator 222, and making the light receiving position of the photoreceiver 224 be in conjunction with the change, a laser beam may be applied to the surface of the target object 101.
The height position distribution calculation unit 54 inputs measured height position information, and calculates a height position distribution. The mark region specification unit 52 searches for a position whose height position is lower than that of the surrounding outer position, and specifies the position as the alignment mark region 10. Details on a height position distribution acquired from the Z sensor 220 will be described later.
In the mark rough search step (S104), while moving the target object 101 placed on the XY stage 105, a height position distribution of the surface of the target object 101 is measured which is obtained by scanning a laser beam, using the Z sensor 220, such that the laser beam intersects the small mark 14 (or large mark 12) (concave-convex mark) in the specified alignment mark region 10. If the alignment mark region 10 is located at each of four corners of the target object 101, the mark rough search step (S104) for the small mark 14 (or large mark 12) (concave-convex mark) is performed in each of the specified alignment mark regions 10 at the four corners.
In the height position distribution calculation step (S106), the height position distribution calculation unit 54 inputs information on the measured height position, and calculates a height position distribution. As shown in
If the small mark 14 (or large mark 12) exists at each of the four corners of the target object 101, the height position distribution calculation step (S106) is performed for each small mark 14 (or large mark 12) (concave-convex mark).
In the examples described above, the height position of the surface of the target object 101 is measured by the Z sensor. However, it is not limited thereto.
In the case of measuring the height position on the surface of the target object by using the white confocal displacement sensor 300, the height position can be calculated by multiplying the wavelength of the received reflected light by a height conversion coefficient. Needless to say, the height conversion coefficient to be multiplied by a measurement value of the Z sensor 220 is different from that to be multiplied by a measurement value of the white confocal displacement sensor 300. Hereinafter, the case of measuring using the Z sensor 220 is mainly described.
The center of gravity position of the reflected light 9 is affected by a light intensity of each light receiving position on the light receiving surface of the photoreceiver 224. Therefore, change of the center of gravity position can be made larger in the case of acquiring height information on the concave bottom by a portion with a high light intensity compared with the case of acquiring it by a portion with a low light intensity. Consequently, as shown in
According to the first embodiment, not only the case where the peak position indicates the upward maximum height position of a convex signal but also the case of indicating the downward minimum position of a concave signal is included. The peak position described herein indicates the downward minimum height position.
The height position distribution described above is calculated at each of the upper, lower, right, and left positions of the small mark 14 (or large mark 12).
In the mark candidate signal position calculation step (S108), the mark candidate signal position calculation unit 56 (position calculation unit) calculates, for each small mark 14 (or large mark 12) (concave-convex mark), a position of a mark candidate signal acquired in a scanned region, by using a height position distribution of the surface of the target object 101, which is for each small mark 14 (or large mark 12) (concave-convex mark) and obtained by scanning a laser beam over a plurality of small marks 14 (or large marks 12) (concave-convex marks) in a manner intersected with a small mark 14, etc. of the plurality of small marks 14 (or large marks 12) (concave-convex marks). The position of a mark candidate signal is represented, for each small mark 14 (or large mark 12) (concave-convex mark), by either a concave signal or a convex signal obtained in a scanned region.
If the small mark 14 (or large mark 12) exists at each of the four corners of the target object 101, the position of a mark candidate signal acquired in a scanned region is calculated for each small mark 14 (or large mark 12) (concave-convex mark). Specifically, it operates as follows:
The mark candidate signal position calculation unit 56 inputs a height position distribution of each of the upper, lower, right, and left positions of the small mark 14 (or large mark 12) (concave-convex mark), as height information on the surface of the target object 101. Then, the mark candidate signal position calculation unit 56 calculates, using the height position distribution on the surface of the target object 101, a position of each mark candidate signal shown in a height position distribution measured at each position. If there are a plurality of mark candidate signals in the same scanning direction in each of height position distributions, obtained at the upper, lower, right, and left positions of the small mark 14 (or large mark 12) (concave-convex mark), the positions of all the mark candidate signals are calculated. Specifically, calculation is performed as follows:
The mark candidate signal position calculation unit 56 calculates, as a position of a mark candidate signal, a peak position of a normal distribution acquired by approximating a mark candidate signal, which is a portion of a height position distribution of the surface of the target object 101, by using a density function of normal distribution (hereinafter referred to as a normal distribution function).
Alternatively, it is also preferable that the mark candidate signal position calculation unit 56 calculates the center of gravity position of a height position distribution of the surface of the target object 101, and obtains the center of gravity position as a position of a mark candidate signal. The center of gravity position, g, can be calculated by the following equation (1) using a coordinate mi and a height position hi of measurement data. i indicates an index.
g=Σ(mi·hi)/Σhi (1)
Alternatively, it is also preferable that the mark candidate signal position calculation unit 56 calculates, as a position of a mark candidate signal, the position of the minimum height measurement value of a height position distribution of the surface of the target object 101. The minimum height measurement value in measurement data on a plurality of measurement positions shown in
Using any of the above methods, an error of an acquired position of a mark candidate signal can be within an acceptable range.
The mark candidate signal position calculation unit 56 can obtain the x position (x coordinate) of the center of a mark candidate signal by calculating an average value between the x position measured at the upper position of the small mark 14 (or large mark 12) and the x position measured at the lower position of the small mark 14 (or large mark 12). Also, the y position (y coordinate) of the center of a mark candidate signal can be obtained by calculating an average value between the y position measured at the right position of the small mark 14 (or large mark 12) and the y position measured at the left position of the small mark 14 (or large mark 12). If a plurality of mark candidate signals are measured by scanning in the x direction, a plurality of x positions are acquired. In such a case, the x position (x coordinate) of the center of the plurality of mark candidate signals can be obtained. Also, if a plurality of mark candidate signals are measured by scanning in the y direction, a plurality of y positions are acquired. In such a case, the y position (y coordinate) of the center of the plurality of mark candidate signals can be obtained. Thus, by combining a plurality of x coordinates and a plurality of y coordinates, positions (x, y) of a plurality of mark candidate signals can be calculated.
In the combination generation step (S110), when a plurality of mark candidate signals are acquired in a scanning direction with respect to at least one of a plurality of small marks 14 (or large marks 12) (concave-convex marks), the combination generation unit 58 generates a plurality of combinations by combining mark candidate signals selected one by one from the plurality of small marks 14 (or large marks 12) (concave-convex marks).
In the relative position information (distance/angle) calculation step (S112), the relative position information calculation unit 60 calculates relative position information between positions of the mark candidate signals in the same combination.
The relative position information includes a distance between positions of mark candidate signals, and an angle between two straight lines each connecting positions of two mark candidate signals, while treating one position of them as being common, in three mark candidate signals.
The relative position information calculation unit calculates an angle between two straight lines each connecting positions of two mark candidate signals, while treating one position of them as being common, in three mark candidate signals in the same combination. For example, an angle θ between a straight line connecting mark candidate signals with respect to the marks A and B and a straight line connecting mark candidate signals with respect to the marks A and C is calculated while treating the position of the mark candidate signal of the mark A as being common. If, for example, three alignment marks are arranged on the target object 101, three angles are calculated per combination. Therefore, when there are n combinations, 3n angles are calculated. If there are four alignment marks, twelve angles are calculated per combination. Therefore, when there are n combinations, 12n angles are calculated. Calculated angles are stored, in relation to a combination identifier, in the storage device 142.
In the mark selection (rough detection) step (S114), the selection unit 66 selects a combination of mark candidate signals, which are mark signals of a plurality of marks, from a plurality of combinations, by comparing, with a predetermined reference value, relative position information regarding mark candidate signals in the same combination in a plurality of combinations. It is preferable to use a design value as the reference value. Specifically, the selection unit 66 selects a combination of mark candidate signals serving as mark signals of a plurality of small marks 14 (or large marks 12) (concave-convex marks) from a plurality of combinations, by comparing, with a design value, at least one of a distance between positions of mark candidate signals in the same combination, and an angle between two straight lines each connecting positions of two mark candidate signals, while treating one position of them as being common, in three mark candidate signals in the same combination. Then, the selection unit 66 outputs the position of each mark candidate signal configuring a selected combination, as a position of a mark signal.
When scanning over two small marks 14 (or large marks 12) (concave-convex marks) as a plurality of small marks 14 (or large marks 12) (concave-convex marks), the selection unit 66 selects, by comparing distances, a combination of mark candidate signals serving as mark signals of the two small marks 14 (or large marks 12) (concave-convex marks) from a plurality of combinations.
Alternatively, when scanning over three or more small marks 14 (or large marks 12) (concave-convex marks) as a plurality of small marks 14 (or large marks 12) (concave-convex marks), the selection unit 66 selects, by comparing both distances and angles, a combination of mark candidate signals serving as mark signals of the three or more small marks 14 (or large marks 12) (concave-convex marks) from a plurality of combinations.
Therefore, the index calculation unit 64 calculates a distance index for comparing distances, and an angle index for comparing angles.
For example, when a plurality of distances are calculated for each combination, a sum of squares of a difference between a measured distance and a distance design value is calculated as a distance index, for example. It is preferable to increase the priority along with a decrease in the distance index, namely, the smallest distance index has the highest priority. Also, when a plurality of angles are calculated for each combination, a sum of squares of a difference between a measured angle and an angle design value is calculated as an angle index, for example. It is preferable to increase the priority along with a decrease in the angle index, namely, the smallest angle index has the highest priority.
Alternatively, when a plurality of distances are calculated for each combination, it is preferable to increase the priority along with a decrease in a statistical value, such as an average, median, minimum, or maximum value of a difference between a measured distance and a distance design value. Also, when a plurality of angles are calculated for each combination, it is preferable to increase the priority along with a decrease in a statistical value, such as an average, median, minimum, or maximum value of a difference between a measured angle and an angle design value.
In the case of scanning over two small marks 14 (or large marks 12) (concave-convex marks), since no angle information is acquired, the priority of each combination is determined such that the priority increases as the distance becomes closer to the design value.
With respect to a plurality of combinations, the selection unit 66 gives a priority sequentially to a combination in which at least one of the distance and the angle is closer to the design value, one by one starting from the closest, and selects a combination with a higher priority, one by one starting from the highest, in the plurality of combinations. In the case of
Although, in the examples described above, the position is calculated for all the measured mark candidate signals to make them be elements of combinations, it is not limited thereto. For example, the mark candidate signal position calculation unit 56 approximates a plurality of mark candidate signals by using a normal distribution which employs the same parameter as that used in another normal distribution having previously been used for a target object with the same configuration of the small mark 14 (or large mark 12) (concave-convex mark) formed. Then, the combination generation unit 58 generates a plurality of combinations excluding mark candidate signals which have not been approximated because of unmatched distribution shapes. Thereby, the number of mark candidate signals can be narrowed down. Consequently, the load of calculation processing can be reduced and the processing time can be shortened.
As described above, the center position of an alignment mark (here, the small mark 14) can be measured by the Z sensor 220. Thus, even when a plurality of mark candidate signals are measured close to a concave-convex mark, it is possible to highly accurately select and detect the signal of the true mark in a plurality of mark candidate signals. Next, the center position of an alignment mark is measured, with high accuracy, using an electron beam. Specifically, using information on the position of each mark candidate signal configuring a combination selected in the mark selection (rough detection) step (S114), in the state in which the XY stage 105 has been moved to a position where the small mark 14 (concave-convex mark) can be irradiated with an electron beam, the position of the small mark 14 (concave-convex mark) is measured by scanning an electron beam over the small mark 14 (concave-convex mark).
In the mark scan step (S120), first, using information on the position of each concave-convex mark configuring a combination selected in the mark selection (rough detection) step (S114), the XY stage 105 is moved to a position where the small mark 14 (concave-convex mark) can be irradiated with an electron beam. Then, in the state in which the XY stage 105 has been moved to the position where the small mark 14 (concave-convex mark) can be irradiated with an electron beam, scanning over the small mark 14 (concave-s mark) is performed by deflecting an electron beam by the deflector 209. For example, as described above with reference to
Secondary electrons emitted from the target object when the small mark 14 (concave-convex mark) was scanned are detected by the detector 226. Detected data is converted into digital data from analog data by the detector 226 and is amplified to be output from the detector 226 to the control computer 110.
In the mark position calculation (fine detection) step (S122), the mark position calculation unit 68 calculates the center position of the small mark 14 (concave-convex mark) by using secondary electron image data, obtained at each of the upper, lower, right, and left positions of the small mark 14, generated based on a second electron in the mark scan step (S120). For example, both the edge positions which configure each of a vertical line width and a lateral line width of the small mark 14 in a secondary electron image are measured. Then, an average value of the center positions of vertical line widths and an average value of the center positions of lateral line widths are obtained as x and y coordinates of the small mark 14.
According to the first embodiment, by performing a fine search using an electron beam after performing a rough search using a laser beam by which no resist or a negligible level of resist may be dispersed, the region scanned with electron beams can be reduced. Since an approximate position of the small mark 14 has already been known by a rough search, it is possible to acquire, with an electron beam, the concave-convex configuration of the small mark 14 even when a concave-convex mark is made of the same material. Therefore, resist dispersion can be prevented or reduced. Further, even when increasing an incident dose amount (dose) of an electron beam, resist dispersion can be reduced.
In the determination step (S126), first, the relative position information calculation unit 60 calculates a distance between calculated positions of a plurality of small marks 14. Also, the relative position information calculation unit 60 calculates an angle between two straight lines each connecting two positions of small marks, while treating one position of them as being common, in a plurality of calculated small marks 14. Then, the determination unit 69 compares a calculated distance with a distance design value, and determines whether a comparison result difference (or a sum of squares of a comparison result difference) is within a threshold. Also, the determination unit 69 compares a calculated angle with an angle design value, and determines whether a comparison result difference (or a sum of squares of a comparison result difference) is within a threshold. If the difference exceeds the threshold, it is treated as an error. Then, it returns to the mark selection step (S114), and selects a combination with a next priority. Until the difference (or a sum of squares of the difference) is determined to be within the threshold, each step from the mark selection step (S114) to the determination step (S126) is repeated.
As described above, highly accurate x and y coordinates of the small mark 14 serving as an alignment mark are obtained.
With respect to the large mark 12 and the small mark 14, a mark opposite to the one described above can also be used. What is necessary is just to properly use marks in each step according to a required accuracy, a configured mark kind, or the number. Although, in the above examples, the case of using a concave alignment mark is described, the case of using a convex alignment mark may also be applied. In that case, the direction of a concavo-convex signal detected as a mark candidate signal is reversed.
First, the XY stage 105 is moved to make an adjustment such that the irradiation region 34 of the multiple beams 20 is located at the left end, or at a position further left than the left end, of the first stripe region 32, and then writing of the first stripe region 32 is performed. When writing the first stripe region 32, the XY stage 105 is moved, for example, in the −x direction, so that the writing may relatively proceed in the x direction. The XY stage 105 is moved, for example, continuously at a constant speed. After writing the first stripe region 32, the stage position is moved in the −y direction by the width of the stripe region 32.
Next, an adjustment is made so that the irradiation region 34 of the multiple beams 20 can be located at the left end, or at a position further left than the left end, of the second stripe region 32. Then, writing of the second stripe region 32 is performed by moving the XY stage 105, for example, in the −x direction to proceed the writing relatively in the x direction.
Although
In the shot data generation step (S130), first, the shot data generation unit 70 generates shot data for each pixel 36. Specifically, it operates as follows: First, the shot data generation unit 70 reads writing data from the storage device 140, and calculates, for each pixel 36, a pattern area density ρ′ in the pixel 36 concerned. This processing is performed for each stripe region 32, for example.
Next, the shot data generation unit 70, first, virtually divides the writing region (here, for example, stripe region 32) into a plurality of proximity mesh regions (mesh regions for proximity effect correction calculation) by a predetermined size. The size of the proximity mesh region is preferably about 1/10 of the influence range of the proximity effect, such as about 1 μm. The shot data generation unit 70 reads writing data from the storage device 140, and calculates, for each proximity mesh region, a pattern area density p″ of a pattern arranged in the proximity mesh region concerned.
Next, the shot data generation unit 70 calculates, for each proximity mesh region, a proximity effect correction irradiation coefficient Dp(x) (correction dose) for correcting a proximity effect. An unknown proximity effect correction irradiation coefficient Dp(x) can be defined by a threshold value model for proximity effect correction, which is the same as the one used in a conventional method, where a backscatter coefficient rl, a dose threshold value Dth of a threshold value model, a pattern area density ρ″, and a distribution function g(x) are used.
Next, the shot data generation unit 70 calculates, for each pixel 36, an incident dose D(x) (amount of dose) with which the pixel 36 concerned is irradiated. The incident dose D(x) can be calculated, for example, by multiplying a base dose Dbase by a proximity effect correction irradiation coefficient Dp and a pattern area density ρ′. The base dose Dbase can be defined by Dth/(1/2+η), for example. Thereby, it is possible to obtain an incident dose D(x) for each pixel 36, for which a proximity effect has been corrected, based on layout of a plurality of figure patterns defined by the writing data.
Next, the shot data generation unit 70 calculates an irradiation time for each pixel 36. The irradiation time for each pixel 36 can be obtained by diving an incident dose D(x) of the pixel concerned by a current density J.
In the data processing step (S132), the data processing unit 72 rearranges obtained irradiation time data for each pixel 36 in order of shot, and stores it in the storage device 142. The transmission processing unit 74 transmits, in order of shot, the irradiation time data to the deflection control circuit 130.
In the writing step (S140), under the control of the writing control unit 76, the writing mechanism 150 writes, with the multiple beams 20, a pattern on the target object 101 on the XY stage 105 while moving the XY stage 105. In the multiple beam writing, in parallel with performing the writing processing, the writing mechanism 150 generates shot data for a region in which later writing processing is to be performed. For example, while writing the k-th stripe region 32, shot data for the k+2 stripe region 32 is generated in parallel. Repeating this operation, all the stripe regions 32 are written.
In the writing operation shown in
As described above, according to the first embodiment, a concave-convex mark whose concave (recessed) surface and convex (projected) surface are made of the same material can be specified highly accurately in a plurality of detection signals, and thus to be detected. Further, according to the first embodiment, even when a plurality of mark candidate signals are measured due to an influence of a configuration in the vicinity of the mark except for itself, of resist unevenness, a noise or the like, it is possible to highly accurately select and detect a true mark signal in the plurality of mark candidate signals.
As described above, according to the first embodiment, a desired mark can be specified in detection signals of a plurality of marks formed on the target object.
Embodiments have been explained referring to specific examples described above. However, the present invention is not limited to these specific examples. For example, in the above example, a case has been described in which uneven marks on the same material are measured, but the cases to which the present invention is applied are not limited to this, and may be a case in which marks whose mark portions are made of different materials are measured. Note that the present technique can be used not only for measurement with a z sensor but also measurement with other sensors such as a white confocal displacement sensor.
While the apparatus configuration, control method, and the like not directly necessary for explaining the present invention are not described, some or all of them can be appropriately selected and used on a case-by-case basis when needed. For example, although description of the configuration of the control unit for controlling the writing apparatus 100 is omitted, it should be understood that some or all of the configuration of the control unit can be selected and used appropriately when necessary.
Further, any position measurement apparatus, charged particle beam writing apparatus, and mark position measurement method that include elements of the present invention and that can be appropriately modified by those skilled in the art are included within the scope of the present invention.
Additional advantages and modification will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-071315 | Apr 2023 | JP | national |
