JP2006344614A - Exposure method and exposure apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exposure method capable of obtaining sufficient resolution by solving the problem that focus or an astigmatism correction condition largely varies depending on a charged state and an exposure image is blurred or a proper line width or shape cannot be formed because a charged particle beam exposure method, in particular, an electron beam exposure method is remarkably influenced by a charged substrate. <P>SOLUTION: A method is disclosed wherein a substrate is exposed while a focusing quantity depending on a charging state or distribution on a substrate or an electric field state or distribution, or the quantity of astigmatism correction depending thereon is fixed during exposure, or the correction condition is fixed for the same exposure substrate. This method has two ways, i.e. one method in which the focusing condition on the wafer or the astigmatism correction quantity distribution is directly measured, and the other in which the charging distribution or the electric field distribution or the magnetic field distribution on the wafer is measured, and the focusing condition or the astigmatism correction condition is calculated in calibration as a correction quantity for the optimized condition on the basis of the measured value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electron beam or charged particle beam exposure method used in a lithography process such as a semiconductor integrated circuit, and more particularly to a beam correction control method during exposure of an electron beam or charged particle beam depending on a substrate to be exposed at the time of main exposure.

  In recent years, high integration of semiconductor integrated circuits has further progressed, and mass production of 90 nm node devices has already been carried out, and it is finally time for mass production of 65 nm devices. Device miniaturization greatly contributes to the advancement of lithography technology, but exposure devices that use ArF (Argon Fluoride) lasers as light sources, which have finally begun mass production from around the 100 nm node, are already required to have a resolution half that wavelength. In the 65nm node, resolution of 1/3 of the exposure wavelength has already been brought out, and for further fine pattern formation, a shorter wavelength light source is used, or reticle phase control is applied. There is a big crossroads, either focusing on further progress in resolution technology or choosing a completely different exposure method. The next exposure method candidate is often referred to as “NGL (Next Generation lithography)”. One of the NGL candidates is an electron beam exposure method using one of charged particle beams and an electron beam as a light source.

  As an electron beam exposure method, the convergent beam classified as a direct drawing method is raster scanned, vector scanned to form a pattern, variable shaping, cell projection exposure method and other second generation technologies aimed at improving throughput, On the other hand, several projection exposure methods such as EPL (Electron Projection Lithography) and LEEPL (Low Energy Electron Projection Lithography) have been developed with the goal of further increasing the throughput.

  In these electron beam exposure apparatuses, calibration is performed in advance before exposure, and adjustment is performed so as to obtain optimum values such as a focus and a stigmator for correcting astigmatism. This method is a general method of an electron beam apparatus.

On the other hand, since the projection exposure method such as EPL can project and transfer only a few mm □ area at a time, the divided transfer method is used, but the pattern in each divided subfield (pattern area that can be exposed and transferred at one time) is used. If the distribution is different, it is necessary to control astigmatism and the like so as to obtain an appropriate exposure image. A method that can make this method highly accurate is disclosed, for example, in (Patent Document 1). In the present invention, an index based on the pattern distribution shape in the subfield is given as exposure information data to the control unit of the exposure apparatus, the correspondence between the optical correction value of the subfield and the index is stored as a table, and the above for each subfield is stored. Data is optically corrected based on a table.
JP 2001-267238 A

  However, in the semiconductor integrated circuit manufacturing process, the substrate to be exposed has a complicated charge distribution on the process substrate, such as the one that has already been charged globally in the manufacturing process or the charging caused by the electron beam itself that is irradiated during exposure. Many have. In particular, the electron beam is easily affected by the charge on the substrate, and depending on the charged state, the focus and astigmatism correction conditions also fluctuate, and the exposed image may be blurred or an appropriate line width or shape cannot be formed as it is. Problem will occur.

  Also, for GSR (magnetic head module formation) processes that require fine pattern formation with a relatively thick film resist of the um order, electron beam exposure with high acceleration voltage includes resolution. Although excellent in controllability, since a magnetic material containing substrate such as Fe is used for the substrate, the electric field distribution in the substrate is not uniform, and astigmatism correction conditions fluctuate within the substrate surface during electron beam exposure It also happens to do. For this reason, when electron beam exposure is performed on the substrate, the focus and astigmatism fluctuate, resulting in a problem that the exposure image is blurred and an appropriate line width or pattern shape cannot be formed.

  Therefore, in view of the above, the present invention provides stable resolution, pattern shape, and pattern line width in charged particle beam exposure such as an electron beam, even for a substrate structure in a semiconductor integrated circuit manufacturing process or a magnetic substrate in a magnetic head manufacturing process. It aims at disclosure of a method which can realize processing.

Hereinafter, the present invention in the charged particle beam exposure apparatus or exposure method will be described by using the electron beam exposure apparatus or the same method.
Before performing electron beam exposure, the exposure apparatus automatically performs the operation, or the user manually performs at least beam optical axis adjustment, focusing, and astigmatism correction. In particular, when these calibrations are performed automatically, for example, a pattern having a high secondary electron emission capability is arranged on the wafer substrate surface, and the shaped electron beam is irradiated thereon to obtain the highest signal. Further, the focus correction lens or astigmatism correction can perform focusing or astigmatism correction using an aerial image. The optical axis can be adjusted using a backscattered electron detector on the reticle for an illumination system or on a wafer for a projection system.

  However, when exposure is performed on a resist on a predetermined substrate after calibration, sometimes sufficient resolution is not obtained, it is greatly deviated from the target dimension, and sometimes the pattern shape is greatly collapsed. Sometimes. This tendency is more conspicuous as the insulating film structure is the base. In recent years, high resolution is also required in GSR (magnetic head process), but there is still a problem that sufficient resolution cannot be obtained even after calibration.

These problems seem to be due to the influence of substrate charging or electric field distribution on the substrate. For example, there is a global charge distribution with a large distribution on the substrate and a local charge distribution with a local charge distribution, but the global charge distribution amount is generally higher, and defocusing when exposed in that state. Alternatively, the astigmatism shift is greatly generated. Therefore, as a result of diligent examination, the charged state / distribution or electric field state / distribution on these substrates is measured in advance, and the exposure on the charged substrate or the magnetic field variation substrate exceeds the allowable charge amount Vac. Devised a method to correct beam correction, that is, at least focusing or astigmatism correction at the right time, just before exposure. The allowable charge amount depends on the acceleration voltage of the exposure light source and the size control of the transferred image. In the exposure method according to the first aspect of the present invention, when a mask pattern or an aperture shape is projected and exposed onto a substrate wafer by using an electron beam or a charged particle beam, charging on the wafer is performed for each underlying structure substrate (layer) to be exposed. When the condition and its distribution are monitored, the allowable charge amount is Vac-ch [V], the exposure light source acceleration voltage is Vacc [V], the transfer pattern dimension control is Lac [nm], and the proportionality coefficient is K, Vac- ch <K · Lac · Vacc ² / 10,000, and when the allowable charge amount Vac-h is exceeded, at least beam correction is performed.

  In addition, in order to perform focusing or astigmatism correction on the substrate immediately before exposure, it is effective to monitor each as an aerial image, and the focus and astigmatism correction values monitored in the aerial image are the values at the time of initial calibration. It is desirable that the exposure is performed with the corrected focus value or astigmatism correction value by feeding back the optical system only when a difference greater than a predetermined value that can be arbitrarily set by the user from the value occurs. According to a second aspect of the present invention, there is provided an exposure method according to the first aspect of the present invention, wherein an aerial image is measured in a timely manner before exposure or during exposure using an exposure substrate on which a beam correction detection pattern has been formed in advance. The astigmatism residual component amount is detected, and feedback to the electron beam or charged particle beam optical system is performed only when the control standard value deviates from an allowable value or more, and at least focusing or astigmatism correction ( (STIGMA correction) Exposure is performed while adjusting.

  Also, charge distribution or electric field distribution for substrate structures of the same structure is treated as almost the same, and a pattern-formed measurement wafer that can measure aerial images for each same substrate structure is prepared and measured timely before exposure, or the same substrate It is also effective to register at least the focus correction amount and astigmatism correction amount in the wafer surface as a table for each structure, and perform exposure by performing correction control based on the correction table for each substrate structure to be exposed. According to a third aspect of the present invention, there is provided an exposure method according to the first aspect, wherein the pattern for beam correction detection is arranged on each underlying structure substrate (layer) to be patterned by exposure so that in-plane distribution measurement can be performed. This wafer is used for beam correction of the layer, and at least the focusing position and astigmatism correction amount are calculated from the aerial image obtained by irradiating the beam on the beam correction detection pattern using this wafer during exposure. The wafer in-plane correction mapping data is provided in the exposure apparatus system as a database, and when the pattern is formed on the same substrate structure in the subsequent exposure, the layer is exposed based on the corresponding database. To do.

In addition, the charge distribution on the substrate is measured in advance by surface potential measurement or a charge amount monitoring method that can be used as an alternative, the focus correction value is calculated from each charge bias amount, and the device has the correction value table as a database. It is also effective to perform correction based on a database of the same substrate structure corresponding to the exposure. In the exposure method according to the fourth aspect of the present invention, the global charge amount distribution in the exposure wafer surface is measured in advance by at least a method capable of measuring the surface potential or monitoring the charge amount in place of the surface potential, and for each charge bias amount Vch. The correction focus amount Fcorr is calculated as Fcorr = F ₀ + k · Vch with respect to the appropriate focus F ₀ at the time of calibration of the exposure apparatus (k is a constant depending on the exposure light source acceleration voltage and the exposure optical system), and this calculation formula The exposure is performed by controlling the projection optical system based on the focus correction value in the wafer surface on the same base substrate obtained from the above.

In addition, the charge distribution on the substrate is measured in advance by surface potential measurement or a charge amount monitoring method that can be used as an alternative. Astigmatism correction values are calculated from the respective charge bias amounts, and the correction value table is used as a database. It is also effective to perform correction based on a database of the same substrate structure corresponding to the exposure. In the exposure method according to the fifth aspect of the present invention, the global charge amount distribution in the exposed wafer surface is measured in advance by at least a method capable of measuring the surface potential or monitoring the charge amount instead. identical to respect to proper correction amount STG ₀ during calibration astigmatism correction amount STGcorr exposure apparatus, and K = constant, and calculates a correction value by _{STGcorr = STG 0 + K · Vch} , obtained from the calculation formula The exposure is performed while controlling the astigmatism correction based on the astigmatism correction value in the wafer surface on the underlying structure substrate.

  In addition, it is effective that the aerial image measurement pattern formed on the substrate during the aerial image measurement improves the aerial image detection S / N by using a substance having a high secondary electron emission ability. The exposure method according to claim 6 of the present invention is the exposure method according to claim 2 or claim 3, wherein the aerial image measurement pattern formed on the substrate at the time of aerial image measurement has a secondary electron or reflected electron emission ability in the background. It is characterized by a material or structure that is 20% or more higher than

  Further, if the reticle aperture ratio is too high when measuring the focus adjustment amount or the astigmatism correction amount in the aerial image, the astigmatism correction value measured depending on the pattern aperture ratio may change. This depends on the space charge effect, and this tendency is particularly strong in the case of non-uniform pattern arrangement. In view of this, it is necessary to detect the focus amount correction or astigmatism correction before exposure using a reticle pattern having a minimum aperture ratio. According to a seventh aspect of the present invention, in the second or third aspect, the aperture ratio of the aerial image measurement reticle pattern is at least 5% or less and the local aperture ratio of the measurement pattern portion is 1% or less. , Which suppresses the influence of the space charge effect.

  According to the present invention, high-precision processing of nano-order fine pattern formation of 100 nm or less is possible, and high-precision exposure is performed on all substrate structures such as pattern formation on a magnetic material used in a magnetic head manufacturing process. be able to.

(First embodiment)
First, as shown in FIG. 4, when the bias amount distribution (133) is not charged on the substrate to be exposed (132), the parameters of the projection optical system (131) are set by the apparatus calibration periodically performed in advance. By optimizing and adjusting the focus position and astigmatism correction amount to optimum values so that the reticle pattern (130) image is appropriately projected onto the exposed substrate (132), the focus or astigmatism within the substrate or within the substrate is adjusted. It is not necessary to correct the aberration distribution, and the focus correction amount (134) is almost 0 (0 in the case of the same as the calibration), and a uniform exposure pattern can always be formed on the wafer surface.

  However, like the focus correction amount (134) in FIG. 4, the focus correction amount may become slightly (+) or conversely (-). When a correction value slightly different from the focusing condition at the time of calibration is detected in this way, a detection error of the detection system is considered as the cause of the error. For example, the aerial image measurement method as shown in FIG. An offset value may be obtained and corrected. Details of this method will be described later.

  Even in such a case, the focus correction value in the wafer surface remains constant, and it is not necessary to perform at least astigmatism correction during or before exposure. As such a substrate whose focus adjustment value does not change in the wafer surface, an unformed silicon substrate, a substrate on which a conductive material is formed, or the like is applicable (however, a conductive material is different from a magnetic material). In this embodiment, only the focusing amount has been described, but astigmatism correction can also be controlled by the same method.

Hereinafter, a charged particle beam exposure method and a charged particle beam exposure apparatus according to a first embodiment of the present invention will be described with reference to FIGS.
The apparatus calibrates at a constant frequency to obtain a focus position and an astigmatism correction amount, but depending on the substrate structure or material, a blurred exposure image can be obtained under those conditions. In such a case, first, as shown in FIG. 1, the charge amount distribution on the wafer substrate is measured by scanning, for example, the charge amount monitor (102) in the diameter direction on the wafer or the exposure substrate (101). To do. Assuming that the wafer substrate (101) is charged, the charge distribution (103) on the wafer substrate at that time has a higher charge amount in the middle, and the charge amount at the wafer center is the highest on the negative side. Since the focus optimized by calibration is under the condition of charge amount = 0, in this embodiment, an appropriate image can be formed on the wafer with the calibration condition at the outermost peripheral portion of the wafer. . However, the amount of charge increases toward the center of the wafer. Therefore, when exposure is attempted at the center, the charge on the wafer substrate has a coulomb repulsive action on the projection beam, and the focus is set above the normal level. In order to correct this, it is necessary to adjust the focus control voltage depending on the charge amount, and it is necessary to increase the focus control voltage as the charge amount increases (104). The focus correction amount at that time increases as the charge amount increases, and when the charge amount increases, focus correction is performed in the wafer direction (105). In many cases, the charge amount, the focus control voltage, and the focus correction amount have symmetrical shapes within the wafer surface, and when they are displayed in respective X / Y, the profiles are almost the same (103, 104, 105).

  In this embodiment, a typical case of charging is shown. For example, a case of a charged substrate or a magnetic substrate will be described with reference to FIG. 2. A bias distribution (111) on the charged substrate (110) is a peripheral portion. Thus, it can be seen that as it goes to the center of the wafer with 0, it becomes a (−) bias and is in a typical globally charged state. In this state, if exposure is performed with the focus correction amount setting obtained by the calibration before exposure, the focus position shifts as the charge amount increases. Defocusing occurs (112). As seen from the optical system diagram, when the focus followability is not corrected on the charged substrate, the electron beam transmitted through the reticle pattern (116a) is reduced by the projection optical system (116b) and calibrated by the projection optical system (116c). Since the focusing is performed with the lens excitation current optimized at the time of the exposure, the focus of the exposure beam is blurred on the wafer substrate (117a). If exposure is performed in this state, the difference (ΔCD) increases toward the wafer center with respect to the pattern size at the periphery of the wafer, leading to problems such as increased roughness. Therefore, the focus correction amount (114) on the same charged substrate (113) is measured while measuring the bias amount or the focus correction amount for each wafer position by aerial image measurement, and exposure is performed while correcting the focus based on the obtained correction amount. As a result, the focus shift amount (115) can be reduced to 0 in the entire surface, and an appropriate exposure image can be obtained on the entire wafer surface. As seen from the optical system diagram, the excitation intensity of the focus control lens 116c is controlled so as to follow the charge amount on the substrate, so that an appropriate focus can be established on the wafer (117b).

Incidentally, the structure of the charged substrates (110 and 113) corresponds to a substrate in which an insulating film such as SiO ₂ or a low-k film is formed on the front surface and back surface of the substrate. The amount tends to increase. When this structure is applied to the device manufacturing process, it corresponds to contact formation, Via, wiring process or the like. There is a magnetic substrate as a substrate structure that behaves similarly to charging. The magnetic body structure includes a magnetic layer such as Fe ₂ O ₃ in the substrate surface layer or film formation structure, and corresponds to a magnetic head manufacturing process.

The focus correction amount may be measured every time exposure is performed, but it is more efficient to perform the measurement only when the charge amount is equal to or larger than a certain amount, which is a result of the charge amount measurement performed before that.
The influence of the charge amount or the magnetic substance on the electron beam is inversely proportional to the acceleration voltage of the electron beam, and the influence of the charge quantity or the magnetic substance is reduced as the acceleration voltage increases. In addition, how much the electron beam optical system can be affected depends on how much dimension control is performed. That is, the charge amount is inversely proportional to the acceleration voltage of the exposure electrons and directly proportional to the control dimension. About the acceleration voltage and the allowable charge amount, it is considered from the experimental results at several acceleration voltages that it is less than 2 V per nm at 100 kV, less than 0.3 V at 50 kV, and less than 0.05 V at 15 kV. For acceleration voltage, Vac-ch to Vacc ² / 10,000
It is thought that this relationship holds. Since the control dimensions are in a proportional relationship, the allowable charge amount Vac-ch [V] is expressed as the acceleration voltage Vacc [kV] and the transfer pattern dimension control Lac [nm]. Vac-ch <Lac · Vacc ² / 10,000 (0)
It can be expressed as

  As a method for detecting the focus or astigmatism correction correction amount on the charge amount distribution on the substrate, an exposure substrate on which a beam correction detection pattern has been formed in advance is used. / and reflected electron distribution) measurement is effective. In general, the aerial image measurement of a Gaussian beam is easy, but it is very difficult to measure the aerial image with a rectangular beam used in a batch transfer method with a certain area as proposed in the next generation EB exposure method. However, as shown in FIG. 3, the alignment pattern (123) having the same repetitive pattern shape as the repetitive pattern of the beam (122) transmitted through the electron beam (120) as the exposure light source illuminated on the reticle (121) is formed in the space. When the pattern on the wafer for image measurement is formed on the wafer (125), the beam (122) of the repetitive pattern transmitted through the reticle pattern portion for measuring the aerial image of the reticle (121) is the alignment pattern on the wafer (125). Only when synchronized with (123), the reflected electron signal (126) with the highest SN can be obtained. If the focus shifts, the reflected electron signal (126), which is the aerial image profile, becomes broad, but if the focus is the best, the sharpest waveform can be obtained and can be easily adjusted. In addition, when the astigmatism is deviated, the waveform becomes broad and asymmetrical, but when the astigmatism is optimized to be minimized with a stigmator, the sharpest and most symmetric waveform can be obtained. it can. If the aerial image measurement method is applied to this method, the optimum focus and astigmatism values depending on the charge distribution, electric field distribution, or magnetic field distribution on the wafer can be obtained. The obtained backscattered electron image is monitored by backscattered electrons or a secondary electron detector (144), and the focus correction value and astigmatism correction can be performed by adjusting the waveform so that the maximum SN can be obtained in real time. Is possible.

A focus and astigmatism adjustment method to which this aerial image measurement method is applied will be described with reference to FIG. 5 in the second embodiment.
The aerial image measurement method in the electron beam transfer exposure method was also reported in 2000 SPIE Microlithography, and it is useful to employ these aerial image measurement methods in the present invention. In the present invention, by applying such an aerial image measurement method, a plurality of grating patterns of about 10 μm □ for aerial image measurement are arranged in the TEG pattern portion in the actual layer pattern, and the aerial image is measured with the pattern. The focus correction amount or astigmatism correction amount of the exposure subfield can be measured.

(Second Embodiment)
A second embodiment will be described with reference to FIG.
An alignment pattern (145) is formed in advance on the wafer (125) as the substrate to be exposed in the same manner as the alignment pattern (123) described with reference to FIG. 3 (145). When an illumination electron beam (140) as an exposure light source is irradiated onto a reticle (141) on which an identical structure pattern of 1 / reduction magnification of the alignment pattern (145) formed on the substrate is irradiated, electrons transmitted through the reticle pattern The line (142) is reduced to an arbitrary size by the projection optical system (143) and projected onto the substrate. On the wafer, a pattern obtained by correcting the pattern cycle of the reticle pattern and reducing the magnification is formed as an alignment pattern (145), and the pattern beam is irradiated onto the alignment pattern. As a result, reflected electrons or secondary electrons emitted from the alignment pattern (145) are always detected by the detector (144), and the aerial image (146) can be monitored. If there is a residual astigmatism component that is in focus, the distribution shape of the monitored aerial image (146) will be a broad distribution, but if the focus is focused and the residual astigmatism component is reduced, it will be monitored accordingly. The secondary electron distribution shape becomes sharp. By adjusting the projection lens system so that the sharpest signal profile can be obtained according to this principle, focus control or astigmatism correction control can be performed. When this operation is performed on each of the alignment patterns (145) formed on the wafer surface, the projection lens set value distribution in the wafer can be acquired. Thus, preparations before exposure are completed, and at the time of actual exposure, the corresponding exposure projection optical system (148) may be controlled by the projection lens setting value (147) obtained above. By doing so, an appropriate pattern can be formed on the entire surface of the substrate. Note that in this adjustment, if the projection lens setting value distribution as described above is acquired in advance for the same substrate, the exposure is performed while controlling the lens by extracting the same lens setting value when processing the same wafer. That's fine. However, if the lens setting value varies from substrate to substrate, it is preferable to perform the adjustment for each exposure substrate.

(Third embodiment)
In the second embodiment, the detection of the charge distribution or electric field distribution on the wafer and the focus position or non-aberration correction value depending on it is directly measured by aerial image measurement or the like to obtain the projection lens correction value, and the exposure accuracy is improved. A method of maintaining was disclosed. On the other hand, a third method is to measure the charge distribution, the electric field distribution, or the magnetic field distribution on the wafer and calculate the focus control or astigmatism correction conditions as correction amounts for the conditions optimized by calibration based on the measured values. This will be described with reference to FIG.

  The charge amount or magnetic strength distribution of the charged wafer or magnetic substrate on the substrate to be exposed (150) is measured with a charge monitor or magnetic strength monitor (151). The charge monitor or magnetic strength monitor can monitor the charge amount or magnetic strength of an area equivalent to or smaller than the exposure area (≤250um for EPL, ≤5um for variable shaping direct drawing device). Therefore, the detection resolution is desirably 1/5 or less of the allowable charge amount or the allowable magnetic body strength in the equation (0). These detections are preferable if they can be performed on the entire surface of the wafer substrate, but those having a general global charge or magnetic distribution have a symmetric distribution from the center of the wafer substrate. It is sufficient to detect the direction. Note that it is necessary to measure in advance a portion that may affect the charge amount or the magnetic material distribution, such as when there is a portion where the underlying structure of the substrate greatly changes in the wafer surface.

For example, in the case of a global charge distribution (152) that is charged toward the center of the wafer, k is a constant depending on the acceleration voltage of the exposure beam and the exposure optical system, and the correction focus amount Fcorr is calculated from the charge amount Vch on each wafer. The appropriate focus F ₀ at the time of calibration of the exposure apparatus can be calculated by the following equation (1).

Fcorr = F ₀ + k · Vch (1)
Each charge amount and each lens setting value distribution (153) on the wafer surface obtained by the equation (1) are stored in the exposure system as a conversion table, and the projection is performed during actual exposure on the wafer. When the optical system (154) is exposed with an optimum lens setting value based on the conversion table, a stable exposure image can be formed. Further, in this method, it is not necessary to form an alignment mark different from the wafer formation pattern on the wafer substrate as in the first or second embodiment, the processing efficiency is high, and the device is more suitable for mass production. Although the lens setting value calculation method based on the charge amount has been described in the present embodiment, the same method can be used for the exposure control on the magnetic substrate used in the magnetic head manufacturing process and the like.

  In addition, this method does not necessarily need to be performed for each exposure wafer. For wafers of the same structure, if a lens setting value for the charge amount or magnetic distribution is measured in advance and exposure is always performed based on the setting value, throughput is also sacrificed. Therefore, a highly accurate exposure image can be obtained.

  The present invention is useful for a method of forming a fine pattern using a charged particle beam.

Schematic diagram showing a method of optical system correction in charge amount distribution measurement according to the first embodiment Schematic diagram showing a method of optical system correction at the time of exposure according to the first embodiment Schematic diagram of aerial image measurement according to the first and second embodiments Schematic diagram explaining exposure control on a substrate with no charge distribution or magnetic field distribution on the substrate Schematic diagram explaining a method of controlling the exposure optical system based on the prior measurement of the focus correction amount or astigmatism correction value and the result according to the second embodiment Schematic diagram illustrating a method for calculating and controlling an exposure optical system lens setting value based on the prior measurement of the charge amount or magnetic field distribution on the substrate and the result according to the third and fourth embodiments

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Wafer or exposure board | substrate 102 Charge amount monitor 103 Charge amount distribution 104 Focus lens control voltage 105 Focus position correction amount 110,113 Charge substrate 111 Bias amount distribution 112 Focus shift amount distribution 114 Focus correction amount distribution 115 Focus shift amount 116a Reticle pattern 116b Reduction magnification control projection optical system 116c Focus control projection optical system 117a Defocus state during focus or astigmatism correction 117b Best focus state during focus or astigmatism correction 120 Electron beam (exposure light source)
121 reticle 122 beam of repetitive pattern transmitted through reticle pattern portion for aerial image measurement 123 aerial image measurement wafer pattern 125 wafer 126 reflected electron signal 130 reticle pattern 131 projection optical system 132 exposed substrate 133 bias amount distribution 134 focus correction amount 140 Illumination electronics (exposure light source)
141 reticle 142 electron beam 143 projection optical system 144 reflection or secondary electron detector 145 aerial image measurement alignment pattern 146 aerial image 147 projection lens setting value 148 exposure projection optical system 150 exposure substrate 151 charge amount or magnetic intensity monitor 152 Charge amount or magnetic intensity distribution 153 Projection lens setting value distribution 154 Exposure projection optical system

Claims (8)

When projecting and exposing a mask pattern or aperture shape using an electron beam or charged particle beam on a substrate wafer,
For each underlying structure substrate (layer) to be exposed, the charge state on the wafer and its distribution are monitored, the allowable charge amount is Vac-ch [V], the acceleration voltage of the exposure light source is Vacc [V], and the transfer pattern dimension control is Lac [nm], where K is the proportionality coefficient
Vac-ch <K ・ Lac ・ Vacc ² / 10,000
An exposure method that performs at least beam correction when the allowable charge amount Vac-ch is exceeded. Using an exposed substrate on which a beam correction detection pattern has been formed in advance, timely aerial image measurement is performed before or during exposure, and at least the focused state and the astigmatism residual component amount are detected. From these control standard values 2. The exposure method according to claim 1, wherein exposure is performed while performing at least focusing or astigmatism correction (STIGMA correction) adjustment by performing feedback to an electron beam or a charged particle beam optical system only when the value exceeds a tolerance. A pattern for beam correction detection is arranged and formed on each underlying structure substrate (layer) to be exposed and patterned so that in-plane distribution measurement can be performed, and this wafer is used for beam correction of the layer. Using the wafer, calculate at least the focus position and astigmatism correction amount from the aerial image obtained by irradiating the beam on the beam correction detection pattern, and have the wafer in-plane correction mapping data as a database in the exposure apparatus system. 2. The exposure method according to claim 1, wherein when a pattern is formed on the same substrate structure in the subsequent exposure, the layer is exposed based on a corresponding database. The global charge amount distribution in the exposure wafer surface is measured in advance by at least a method that can measure the surface potential or monitor the charge amount instead, and the corrected focus amount Fcorr for each charge bias amount Vch is obtained during calibration of the exposure apparatus. For proper focus F _0, F corr = F ₀ + k · Vch
(K is a constant depending on the exposure light source acceleration voltage and the exposure optical system), and exposure is performed by controlling the projection optical system based on the focus correction value within the wafer surface on the same substrate obtained from this calculation formula. Exposure method. Measure the astigmatism correction amount STGcorr for each charge bias amount Vch in advance by calibrating the global charge amount distribution in the exposure wafer surface in advance by at least measuring the surface potential or using an alternative charge amount monitoring method. For the appropriate correction amount STG ₀ at the time of calibration, K = constant and STGcorr = STG ₀ + K · Vch
An exposure method in which a correction value is calculated in step 1 and exposure is performed while controlling astigmatism correction based on the STIGMA correction value in the wafer surface on the same underlying structure substrate obtained from this calculation formula. The aerial image measurement pattern formed on the substrate during aerial image measurement is
4. The exposure method according to claim 2, wherein the exposure method is a material or structure having a secondary electron or reflected electron emission ability higher by 20% or more than the background. The aperture ratio of the aerial image measurement reticle pattern is at least 5% or less and the local aperture ratio of the measurement pattern portion is 1% or less to suppress the influence of the space charge effect. Exposure method.   An exposure apparatus that executes the exposure method according to claim 1.

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