JP4603305B2 - Exposure method, pattern dimension adjustment method, and focal blur amount acquisition method - Google Patents

Description

  The present invention relates to an exposure method, and more particularly to proximity effect correction in electron beam exposure, and more particularly to a pattern size adjustment method in electron beam exposure using a mask subjected to proximity effect correction, or a focus blur amount acquisition method used in pattern size adjustment.

Lithography technology, which is responsible for the progress of miniaturization of semiconductor devices, is an extremely important process for generating a pattern among semiconductor manufacturing processes. Conventionally, optical exposure technology has been used in the production of semiconductor devices, but in recent years, the pattern dimensions of advanced devices are approaching the limit resolution, and the development of high-resolution exposure technology has become an urgent task.
Electron beam exposure technology has excellent resolution, and is used for the development of state-of-the-art devices such as DRAM (Dynamic random access memory) and for the production of some ASIC (application specific integrated circuit). Yes. However, in the conventional variable shaping exposure method, the pattern is drawn in the manner of one stroke, so the wafer processing capacity per unit time, that is, the throughput is low, which is not suitable for mass production of devices.
At present, an electron beam projection (EPL) technique has been proposed as a next-generation exposure technique, and its research and development is being conducted recently.

FIG. 14 is a conceptual diagram for explaining the operation of the EPL exposure apparatus.
First, on a mask stage in an EPL exposure apparatus, a subfield mask 350 on which a subfield pattern for projecting and transferring a subfield 320 serving as an exposure unit region for one semiconductor chip is formed in a grid pattern. A mask 340 is disposed. The subfield 320 is an area corresponding to one shot when the electron beam 330 (charged particle beam) is irradiated. The subfield mask 350 is formed with various subfield patterns through which the electron beam 330 is transmitted. Then, the electron beam 330 irradiated from the charged particle source is deflected by a deflector and irradiated with a pattern of a predetermined subfield mask 350, and the transmitted electron beam 330 is reduced by the electron lens and divided on the wafer 300. Of the plurality of semiconductor chip regions 310, the subfield pattern formed on the subfield mask 350 is projected and transferred by irradiating the subfield 320 serving as an exposure unit region in one semiconductor chip region. Next, the subfield pattern of the subfield mask 350 located next to the column is deflected by a deflector so that the electron beam 330 irradiates, and similarly, the adjacent subfield 320 for the one semiconductor chip is changed. By irradiation, the subfield pattern formed on the subfield mask 350 is projected and transferred to the adjacent subfield 320. This is repeated in sequence, and after the irradiation of the subfield pattern of the subfield mask 350 in that column is completed, the mask stage and the wafer stage are moved to a position where the top of the subfield mask 350 in the second column can be projected and transferred to the wafer 300. Then, various subfield patterns of the subfield mask 350 in the second column are sequentially irradiated. In this way, exposure of one semiconductor chip region 310 is completed by irradiating the subfield pattern of the subfield mask 350 of all rows. Such an operation is performed on all the semiconductor chip regions 310 divided on the wafer 300. In addition, the EPL exposure apparatus is described in the following documents (for example, see Patent Document 1, Non-Patent Documents 1 and 2).

FIG. 15 is a diagram for explaining the EPL exposure principle.
In FIG. 15, for example, an electron accelerated at 100 kV is irradiated onto a stencil mask 100 as an example of a scattering mask in which an opening pattern is formed by an opening 150 penetrating. As a material for the stencil mask 100, silicon (Si) having a thickness of about 2 μm is usually used. The electron beam 330 that has entered the portion of the stencil mask 100 that is not the opening 150 is greatly scattered by the portion that is not the opening 150. Most of the scattered mask scattered electrons 331 are blocked by the limiting aperture 370 placed in the rear focal plane of the objective lens 380. On the other hand, since the image forming electrons 332 that have passed through the opening 150 freely pass through the opening 150, most of the electrons of the image forming electrons 332 that are projected by the projection lens 360 and deflected by the deflector pass through the limiting aperture 370. can do. The contrast of the mask image is formed on the wafer 300 due to the difference in aperture transmittance. This is called scattering contrast. When the negative resist applied on the wafer 300 is developed thereafter, a resist image 301 shown in FIG. 14 is formed. In addition to the stencil, a membrane mask in which the entire mask pattern is held by a thin membrane can be used as the mask. A mask used for an EPL exposure apparatus is disclosed in literature (for example, see Patent Documents 2 and 3).

FIG. 16 is a diagram showing an example of a stencil mask and a membrane mask manufactured with typical materials.
In FIGS. 16 (a) and 16 (b), only the pattern portion is particularly shown and the others are omitted. FIG. 16A shows an example in which the stencil mask 100 is formed of Si having a thickness of 2 μm, for example. Further, in FIG. 16B, the membrane mask 200 is an example in which a DLC scattering layer having a thickness of about 600 nm in which a pattern is formed on a diamond like carbon (DLC) membrane having a thickness of 30 to 50 nm is formed. (For example, refer nonpatent literature 3). Here, since the image is formed by the scattering contrast in the EPL technique as described above, the structure of the scattering mask is determined in consideration of electron scattering.

Here, in the currently developed exposure apparatus, the irradiation area of the electron beam as a subfield is about 0.25 mm square on the wafer, and this transfer area is sequentially reduced and transferred by the step-and-repeat method.
FIG. 17 is a diagram for explaining electron scattering in the substrate.
As shown in FIG. 17, in electron beam exposure, when electrons enter the resist, energy is given to the resist while colliding with the resist (forward scattering). It rebounds by scattering with atoms and enters the resist again as backscattered electrons.
FIG. 18 is a diagram showing the relationship between the exposure intensity and the energy accumulation range in a resist.
As described above, in electron beam exposure, electrons enter the resist again as backscattered electrons, so that energy is accumulated in the resist over a wide range other than the electron incident point as shown in FIG. If the distance from the electron incident point is r and the exposure intensity is f (r), it can be approximated as the sum of two Gaussians. This f (r) is called an exposure intensity (EID: Exposure Intensity Distribution) function, and is often used in proximity effect correction. The spread of the Gaussian distribution due to forward scattering and backward scattering is called the forward scattering diameter (βf) and the backward scattering diameter (βb). The ratio between the total amount of energy accumulated by forward scattering and the total amount of energy accumulated by backscattering is called the reflection coefficient (η). In practice, the beam blur is incorporated as a square sum into the forward scattering diameter.

FIG. 19 is a diagram for explaining the proximity effect correction by the mask bias.
Due to the spread of the Gaussian distribution due to forward scattering and back scattering, energy is given in addition to the incident point, and a proximity effect peculiar to electron beam exposure occurs. In particular, since the energy accumulation by backscattered electrons covers a wide range, the exposure intensity varies depending on the pattern density. Incidentally, the backscattered diameter of electrons accelerated at 100 kV in silicon (Si) is about 30 microns. A mask bias method is used as a method for correcting the proximity effect (see, for example, Non-Patent Document 4). This method is effective because the exposure amount cannot be corrected when the area exposed at one time is larger than the backscattering diameter. In the mask bias method, the proximity effect is corrected by adjusting the mask size (mask bias) for a pattern dimension that changes due to a difference in pattern density. The bias amount is obtained by a calculator so that the exposure intensity is calculated using an EID function and the pattern has a dimension as designed.

  In addition, with regard to proximity effect correction, a method for obtaining a resize (bias) amount from an energy accumulation amount due to backscattered electrons and beam blur is described in the literature (for example, see Patent Documents 4 and 5).

Further, regarding proximity effect correction by the GHOST method, a method for forming an auxiliary exposure beam and a method for determining the optimum blur amount are described in the literature (see, for example, Patent Documents 6 and 7).
JP 2001-319872 A JP 2002-75842 A JP 2003-68616 A JP 2002-15976 A JP 2004-63546 A JP-A-9-260242 Japanese Patent Laid-Open No. 7-254548 “Nikon Nikon Technology: EPL”, http://www.nikon.co.jp/main/jpn/profile/technology/epl/index.htm ”Stencilreticle development for electron beam projection systems S. Kawata, N. Katakura, S. Takahashi, and K. Uchikawa, J. Vac. Sci. Technol. B 17, 2864 (1999) “Fabrication of a continuous diamondlike carbon membrane mask for electron lithography”, I. Amemiya, H. Yamashita, S. Nakatsuka, M. Tsukahara, and O. Nagarekawa, J. Vac. Sci. Technol. B 21, 3032 (2003) “Proximity effect correction by pattern modified stencil mask in large-field projection electron-beamlithography”, H. Kobinata, H. Yamashita, E. Nomura, K. Nakajima and Y. Kuroki, Jpn. J. Appl. Phys. 37, 6767 ( 1998)

  In proximity effect correction by the mask bias method, an exposure intensity is calculated using an EID function, a bias amount is obtained in advance, and a dimensionally biased mask is used. Therefore, once a mask is manufactured, the correction amount can be adjusted. Can not. Actually, in many cases, the bias amount obtained by the proximity effect correction is not appropriate, or a desired correction result cannot be obtained depending on the type of resist. Therefore, it is necessary to recreate the mask many times when the correction amount is not appropriate or when a desired correction result cannot be obtained. However, since the mask fabrication requires enormous time and cost, it becomes a big problem in terms of time and cost.

  An object of the present invention is to overcome the conventional problems described above and to perform exposure so that a desired pattern can be obtained without changing the mask. Furthermore, it aims at providing the method of adjusting the pattern dimension to expose so that a desired pattern may be obtained.

The exposure method of the present invention comprises:
An exposure method for performing electron beam exposure using a mask provided with a means for correcting a proximity effect,
When exposure is performed, exposure is performed using an electron beam with a blurred focus.

  As will be described later, the pattern width is changed by changing the beam blur by defocusing. Therefore, even if the means for correcting the proximity effect applied to the mask is not appropriate, the desired pattern width can be obtained by changing the beam blur by blurring the focal point.

  Here, the mask according to the present invention is characterized in that means for correcting the proximity effect by a mask bias method is applied.

  When the proximity effect is corrected by the mask bias method, the correction amount cannot be adjusted once the mask is manufactured as described above. Therefore, the present invention is particularly effective when a mask whose adjustment amount cannot be adjusted is used.

  The exposure method according to the present invention is characterized by using the mask in which the proximity effect is overcorrected.

  As will be described later, when the focus blur is changed and the beam blur is changed, the pattern width becomes smaller in the region where the pattern width becomes smaller due to the proximity effect, and the pattern width becomes larger in the region where the pattern width becomes larger due to the proximity effect. Can be changed. Therefore, the amount of overcorrection can be adjusted by using the mask in which the proximity effect is overcorrected. Furthermore, intentionally, for example, by applying the bias amount larger than the optimum value and using the mask in which the proximity effect is overcorrected, the correction amount is not appropriate or a desired correction result is obtained. In addition to the effect as a post-adjustment function for taking advantage of the mask in the absence of the mask, the present invention can be adjusted to an appropriate dimension from the beginning.

The pattern dimension adjusting method of the present invention is
A best focus exposure step of exposing the substrate with a focused electron beam using a mask biased in a predetermined area;
As a result of the best focus exposure step, when the pattern width of the pattern exposed on the biased predetermined region and formed on the substrate does not become a desired pattern width because the bias amount of the bias is too large. A defocus exposure step of performing exposure on the next substrate while blurring the focal point, and obtaining a focal blur amount corresponding to the desired pattern width;
With
The substrate to be exposed after the focal blur amount is acquired by the defocus exposure step is subjected to exposure with the focal point being blurred in accordance with the focal blur amount, and is exposed after the focal blur amount is acquired. The size of the pattern formed on the substrate is adjusted.

  When the pattern width does not become a desired pattern width because the bias amount is too large, the next pattern can be exposed to the desired pattern width while blurring the focus. Further, by obtaining the focal blur amount by the defocus exposure step, the biased mask as described above can be used without being discarded.

  Further, in the defocus exposure step according to the present invention, the pattern of the pattern formed is a region in which the pattern density of the pattern formed on the substrate exposed from the biased predetermined region is relatively small. When the width is larger than a desired pattern width, the next substrate is exposed using the electron beam having a blurred focus.

  As will be described later, when the beam blur is changed by defocusing the focus, the pattern width is reduced in a region where the pattern density of the pattern is relatively reduced. Therefore, when the pattern width of the pattern formed in such a region is larger than the desired pattern width, the next pattern is adjusted to the desired pattern width by performing electron beam exposure on the next substrate using the focused electron beam. be able to.

  Similarly, in the defocus exposure step according to the present invention, the pattern exposed to the biased predetermined area and formed on the substrate has a relatively high pattern density, and When the pattern width is smaller than the desired pattern width, the next substrate is exposed using the electron beam with the focus being blurred.

  As will be described later, when the beam blur is changed by defocusing, the pattern width increases in a region where the pattern density of the pattern is relatively large. Therefore, when the pattern width of the pattern formed in such a region is smaller than the desired pattern width, the next pattern is adjusted to the desired pattern width by performing electron beam exposure on the next substrate using the focused electron beam. be able to.

Further, in the best focus exposure step according to the present invention, the mask is biased to the predetermined region with reference to a predetermined exposure intensity,
In the defocus exposure step, exposure is performed with the focus being defocused without changing the predetermined exposure intensity as the reference.

  By not changing the predetermined exposure intensity based on the reference, it is possible to avoid affecting an area where an appropriate dimension can be obtained with the predetermined exposure intensity based on the reference when the exposure is performed with the focus being blurred. it can.

The focal blur amount acquisition method of the present invention is:
A best focus exposure step of exposing the substrate using a focused electron beam;
As a result of exposure performed on the substrate by the best focus exposure step, when a pattern width of a relatively small pattern density formed on the substrate is larger than a desired pattern width, a focused electron beam is Using a defocus exposure step of exposing a substrate different from the substrate,
With
In the defocus exposure step, the blurring amount of the focal point at which a pattern width of a region having a relatively small pattern density formed on a substrate different from the substrate becomes the desired pattern width is obtained.

  As will be described later, when the beam blur is changed by defocusing the focus, the pattern width is reduced in a region where the pattern density of the pattern is relatively reduced. Therefore, when the pattern width of the pattern formed in such a region is larger than the desired pattern width, it is possible to adjust the desired pattern width for the substrate to be subsequently exposed by obtaining the focal blur amount. it can.

In addition, the method of acquiring the focal blur amount according to the present invention is
A best focus exposure step of exposing the substrate using a focused electron beam;
As a result of exposure performed on the substrate by the best focus exposure step, when a pattern width of a relatively high pattern density region formed on the substrate is smaller than a desired pattern width, a focused electron beam is generated. Using a defocus exposure step of exposing a substrate different from the substrate,
With
In the defocus exposure step, the blurring amount of the focal point where the pattern width of a region having a relatively high pattern density formed on a substrate different from the substrate becomes the desired pattern width is obtained.

  As will be described later, when the beam blur is changed by defocusing, the pattern width increases in a region where the pattern density of the pattern is relatively large. Therefore, when the pattern width of the pattern formed in such a region is smaller than the desired pattern width, it is possible to adjust the desired pattern width for the substrate to be subsequently exposed by obtaining the focal blur amount. it can.

  As described above, according to the present invention, when the pattern width of an area having a relatively low pattern density is larger than the desired pattern width, or the pattern width of an area having a relatively high pattern density is desired. If smaller, the pattern width dimension can be adjusted for the substrate to be exposed later. Since the pattern width dimension can be adjusted, an optimum pattern width dimension can be obtained. Furthermore, since the pattern width dimension can be adjusted, a mask whose correction amount is not appropriate or a mask where a desired correction result cannot be obtained can be used as it is. Since it can be used as it is, it is not necessary to re-create the mask many times. Since it is not necessary to remanufacture the mask, enormous time and cost can be reduced.

Embodiment 1 FIG.
FIG. 1 is a flowchart for explaining a pattern dimension adjusting method according to the first embodiment.
In the first embodiment, the beam blur at the best focus is obtained from the pattern information. Alternatively, it is handled as a constant blur. As the beam current increases due to the Coulomb effect, the blur increases. Then, the exposure intensity is calculated using the EID function and the beam blur information at the best focus obtained from the pattern information, and the bias amount of each region is obtained so that any pattern becomes the design dimension in the calculation. An amount of dimensional biased mask is made. The beam blur information is obtained in advance by simulation. Alternatively, the relationship between the beam current and the beam blur may be obtained in advance, and the beam blur may be obtained from the pattern aperture ratio of the mask. In general, the value δ of the beam blur can be taken into the forward scattering diameter βf as a sum of squares. Actually, if the value of beam blur information including the beam blur used for calculating the exposure intensity is βf ′, βf ′ = √ (βf ² + δ ² )
It is represented by

  In step S (step) 102, a mask having means for correcting the proximity effect is set in the EPL exposure apparatus. For example, here, a mask to which an appropriate bias is applied by the mask bias method is set.

  In S104, the first wafer is carried into the wafer stage. Although not shown, it is assumed that an electron beam resist is applied on the first wafer.

  In S106, as a first exposure process which is an example of a best focus exposure process, exposure (pattern drawing) is performed on the first wafer using a focused (best focus) electron beam. By the best focus exposure, it is possible to obtain a sample for inspecting later whether the proximity effect correction applied to the manufactured mask is appropriate.

FIG. 2 is a diagram for explaining a configuration example of a main part of the EPL exposure apparatus.
In FIG. 2, a large number of subfield masks are formed on the mask 210, and the electron beam 204 uniformly irradiates each subfield mask in the field of view of the optical system. For example, the mask 210 forms one semiconductor chip pattern over the plurality of subfield masks. Of course, the pattern may be divided into a plurality of masks. The mask 210 is set on the mask stage 212. The mask stage 212 is movable, and can irradiate the electron beam 204 with a subfield mask positioned in a wider range than the field of view of the optical system. The electron beam 204 that has passed through the mask 210 passes through the deflectors 214 and 218 and the projection lens 216, blocks scattered electrons with the aperture 220, passes through the projection lens 222, and forms an image at a predetermined position on the wafer 224. Is done. Then, a dose is given to the electron beam resist on the wafer 224, and the pattern on the mask is transferred. The projection lens 216 is controlled by being excited by a coil, and the coil power supply is controlled by the controller 280 via the control unit 266. The projection lens 222 is similarly controlled by the control unit 272, the deflector 214 is controlled by the control unit 264, and the deflector 218 is controlled by the control unit 268.

  In S108, the first wafer is unloaded from the wafer stage. Although not shown, the unloaded first wafer is developed and washed. Thereby, a resist pattern is formed.

  In S110, the first wafer is inspected.

  In S112, it is confirmed whether or not the pattern width (pattern line width) dimension of the first wafer that has been subjected to the best focus exposure using a mask that has been appropriately biased is formed to a desired design dimension. If it is formed to the desired design dimension, in other words, if the proximity effect correction of the mask is optimal, no further dimension adjustment is necessary, so that the subsequent wafer using the exposure conditions in the best focus exposure Can be processed. If the desired design dimension is not formed, the process proceeds to S114.

  In S114, when the pattern width dimension of the first wafer that has been subjected to the best focus exposure using a mask that is appropriately biased for calculation is not formed in a desired design dimension, the method of the first embodiment It is determined whether or not defocus adjustment is possible.

FIG. 3 is a diagram showing the relationship between the resist line width, exposure intensity, and beam blur.
FIG. 4 is a diagram showing the relationship among the line width shift amount, beam blur, and exposure intensity.
As shown in FIG. 3, when the beam blur is increased, the waveform indicating the exposure intensity gradually becomes dull. The vertical axis represents the normalized exposure intensity. In actual exposure, the exposure amount is determined by changing the irradiation time. Assuming that resist development follows a critical energy model, the resist size after development is determined by the width of the waveform traversed at an energy level. For example, when an appropriate exposure amount is given, the critical energy level becomes E _{0 in the} figure, and the dimensions hardly change even if the blur changes. However, when an exposure amount smaller than the appropriate exposure amount is given, the critical energy level moves relatively upward (E ₋ ), and as a result, the line width decreases as the blur increases. On the other hand, when an exposure amount larger than the appropriate exposure amount is given, the critical energy level is relatively lowered (E ₊ ), and the pattern line width increases as the blur increases. If the blur is large, the line width changes depending on the exposure amount. This relationship is summarized as shown in FIG.

FIG. 5 is a diagram showing the relationship between the line width and the exposure intensity when the beam blur is sufficiently smaller than the pattern dimension.
In FIG. 5, it is assumed that the line and space pattern extends in a direction perpendicular to the paper surface. FIG. 5 shows a case where the beam blur is sufficiently smaller than the pattern dimension (ideal distribution), and it can be seen that the line width which is the pattern dimension does not change much even if the pattern density and the exposure amount change.

FIG. 6 is a diagram showing the relationship between the line width and the exposure intensity when the beam blur is approximately equal to or smaller than the minimum processing dimension.
FIG. 5 shows an ideal distribution. However, since the beam blur is actually equal to or smaller than the minimum processing dimension, the exposure intensity is dull as shown in FIG. For this reason, the exposure intensity of the pattern differs depending on the pattern density, and the pattern size is smaller in the vicinity of the small (low) pattern density than in the central portion having the large (high) pattern density. That is, the dimensional variation due to the proximity effect increases.

In order to correct this proximity effect, the mask 210 is biased in advance according to the pattern density. The bias amount can be obtained by calculation by convolving the EID function and the pattern. For backscattering with a wide scattering region, a method such as a pattern density method is used. A bias is applied to the mask so that all patterns have the design dimensions based on the obtained exposure intensity, but the exposure intensity serving as a reference for the bias can be arbitrarily set. That is, in FIG. 6, the exposure intensity at which the central pattern having a large pattern density becomes the desired pattern line width is defined as the reference (I _C ) of the exposure intensity. Become. On the other hand, if the exposure intensity at which the peripheral pattern having a low pattern density becomes a desired pattern line width is used as the reference (I _P ) of the exposure intensity and zero bias is applied, the central pattern having a high pattern density becomes a negative bias.

FIG. 7 is a diagram showing an example of proximity effect correction by the bias method when the exposure intensity of a portion with a high pattern density is used as a reference.
When the exposure intensity of a portion with a high pattern density is used as a reference, a dotted line waveform can be made larger (thicker) like a solid line waveform by applying a positive bias to a peripheral pattern with a low pattern density. Here, the exposure intensity at the best focus is shown.

FIG. 8 is a diagram showing an example in which exposure is performed by defocusing from the exposure conditions of FIG.
As shown by a solid line in FIG. 8, defocusing is performed from the exposure conditions of FIG. 7, and exposure is performed with a larger beam blur, thereby further reducing the waveform from the dotted waveform. For this reason, the pattern of the portion with a high pattern density based on the exposure intensity has little dimensional variation from the principle shown in FIG. 3, but the size can be reduced (thinned) in the pattern of the portion with a low pattern density. If the bias amount is not appropriate for some reason, in other words, even when the mask with the proximity effect overcorrected is used, the correction amount can be adjusted without recreating the mask by changing the beam blur. It becomes possible.

FIG. 9 is a diagram showing an example of proximity effect correction by the bias method when the exposure intensity of a portion having a small pattern density is used as a reference.
When the exposure intensity of a portion having a low pattern density is used as a reference, the waveform of the dotted line can be reduced to the waveform of the solid line by applying a negative bias to the pattern of the central portion having a high pattern density. Here, the exposure intensity at the best focus is shown.

FIG. 10 is a diagram showing an example in which exposure is performed by defocusing from the exposure conditions of FIG. 9 and increasing the beam blur.
As indicated by a solid line in FIG. 10, the waveform is further dulled from the dotted waveform by defocusing from the exposure condition of FIG. For this reason, the pattern having a small pattern density based on the exposure intensity has almost no dimensional variation from the principle shown in FIG. 3, but can be increased in the pattern having a high pattern density. If the bias amount is not appropriate for some reason, in other words, even when the mask with the proximity effect overcorrected is used, the correction amount can be adjusted without recreating the mask by changing the beam blur. It becomes possible.

  As described above, the pattern density of the pattern formed on the substrate exposed by using the biased mask 210 is relatively small, and the pattern width of the formed pattern is a desired pattern width. Defocus adjustment is possible if the pattern density is larger or the pattern density of the pattern formed on the substrate is relatively large and the pattern width of the formed pattern is smaller than the desired pattern width. I understand.

  Therefore, in the pattern formed on the first wafer, the region not formed in the desired design dimension is a region where the pattern density is relatively small, and the pattern width of the formed pattern is larger than the desired pattern width. If it is larger, it can be determined that the defocus adjustment which is the method of the first embodiment is possible. In the pattern formed on the first wafer, the region not formed in the desired design dimension is a region having a relatively high pattern density, and the pattern width of the formed pattern is larger than the desired pattern width. If it is smaller, it can be determined that the defocus adjustment which is the method of the first embodiment is possible. In the exposure with the manufactured mask, if the bias amount is insufficient and the above condition is not satisfied, it is determined that the defocus adjustment is impossible, and the mask is remanufactured.

  In S116 of FIG. 1, when the defocus adjustment is possible, the second wafer to be the next substrate is carried into the wafer stage. Although not shown, it is assumed that an electron beam resist is applied on the second wafer, as in the first wafer.

In S118, as a second exposure process which is an example of a defocus exposure process, exposure (pattern drawing) is performed on the second wafer using a defocused electron beam. Here, the optimum defocus amount (focus blur amount) r for obtaining a desired pattern line width is searched. The EPL exposure apparatus uses the apparatus shown in FIG. A pattern is drawn in a state where the excitation of the dynamic focus lens of the EPL exposure apparatus is changed and the electron beam is defocused. Usually, defocusing is performed by changing the excitation of a plurality of lenses. There is no limitation on the combination of the lenses, and a lens whose excitation is changed may be selected as necessary. In the second exposure step, first, the focus and the exposure amount are changed to be adjusted to a predetermined defocus amount r ₁ , and the second wafer is exposed using the defocused electron beam.

  In S120, the second wafer is unloaded from the wafer stage. Although not shown, the unloaded second wafer is developed and cleaned. Thereby, a resist pattern is formed.

  In S122, the second wafer is inspected.

Whether or not the pattern width (pattern line width) dimension of the second wafer subjected to the defocus exposure with the defocus amount r ₁ is formed in a desired design dimension using a mask that has been appropriately biased in S124. Confirm. If it is formed to have a desired design dimension, in other words, if the defocus amount r ₁ is optimal, no further dimension adjustment is necessary, and the subsequent wafers are processed with the optimal defocus amount r _1. That's fine.

In S126 to S134, when the desired design dimension is not formed in S124 described above, the nth (n> 2) wafer is carried into the exposure apparatus, and the defocus amount r is used using the nth wafer. _{The nth} exposure is performed at _n-1 , and the exposed wafer is unloaded and inspected to check whether it is formed to a desired design dimension. This process is repeated until the optimum defocus amount is acquired.

  As described above, the pattern dimension is designed to be the design dimension at any pattern density by drawing the pattern while changing the excitation of the lens of the exposure apparatus and defocusing the electron beam using the mask to which the dimension bias is applied. An optimal defocus amount can be acquired. If the subsequent wafer is exposed with the acquired optimum defocus amount, the pattern dimension of the design dimension can be obtained without remanufacturing the mask. According to the present embodiment, for example, with regard to proximity effect correction by the mask bias method, the blur of an electron beam having pattern shape information is intentionally changed (defocused), and this is applied to a biased mask. By irradiating and changing the dimensional correction amount obtained on the wafer, the dimensional variation due to the proximity effect can be accurately corrected. As a result, even if the bias amount of the mask once manufactured with a certain bias amount is inappropriate, it is possible to eliminate the need for mask re-preparation.

Embodiment 2. FIG.
In the first embodiment, a mask biased with a bias amount such that the pattern dimension becomes the design dimension at any pattern density is used for calculation. In such a case, regardless of whether a portion with a high pattern density or a portion with a low pattern density is selected as a reference for the exposure amount, the pattern size of the portion with a low pattern density is only relatively smaller than the pattern size of a portion with a high pattern density. Adjustment is not possible. Therefore, as a result of manufacturing the mask, when a portion having a high pattern density is used as a reference for the exposure amount, a portion having a low pattern density is insufficient because a positive bias amount to a predetermined area of the mask corresponding to a portion having a low pattern density is insufficient. If the pattern dimension is smaller than the design dimension, the first embodiment cannot adjust the dimension. Conversely, when the mask is manufactured and the portion with a low pattern density is used as a reference for the exposure amount, the negative bias amount to the predetermined area of the mask corresponding to the portion with the high pattern density is insufficient, and the pattern density In the case where the pattern dimension of the large part is larger than the design dimension, the dimension adjustment cannot be performed in the first embodiment.

  Therefore, in the second embodiment, first, an exposure intensity is calculated from the EID function and pattern information, and a mask having a bias larger than the bias amount that any pattern becomes the design dimension is manufactured. In other words, a mask on which an overcorrection bias is intentionally applied is calculated. Then, using the mask, the excitation of the lens of the exposure apparatus is changed to draw the pattern while defocusing the electron beam, and the optimum defocus amount is obtained so that the pattern dimension becomes the design dimension at any pattern density. If the portion with high pattern density is used as the standard for exposure, the pattern size at the portion with low pattern density is larger at the best focus, but it becomes smaller as the beam blur is defocused and becomes smaller. An appropriate correction amount can be obtained in terms of points. That is, the range of adjustment can be further expanded.

FIG. 11 is a flowchart for explaining the pattern dimension adjusting method according to the second embodiment.
In the second embodiment, as described above, first, the exposure intensity is calculated using the beam blur information at the best focus obtained from the EID function and the pattern information, and each pattern is calculated to have a design dimension. A bias amount of the region is obtained, and a mask having a dimensional bias larger than the bias amount obtained by calculation is manufactured.

  In S102, a mask having a bias amount larger than the appropriate bias is set in the EPL exposure apparatus.

Steps S104 to S112 are the same as those in FIG. Here, in FIG. 1, it is necessary to determine whether or not defocus adjustment is possible. However, in the second embodiment, since the mask is overcorrected in advance with a bias, when a portion with a large pattern density is used as a reference for the exposure amount, the pattern size of the portion with a small pattern density is larger than the design size. It is getting bigger. On the other hand, when a portion having a low pattern density is used as a reference for the exposure amount, the pattern size of the portion having a high pattern density is smaller than the design size. Therefore, by overcorrecting the mask with a bias, it is possible to make a state where defocus adjustment is possible. Therefore, in the second embodiment, it is unnecessary to determine whether or not defocus adjustment is possible. In S112, if the desired design dimensions are not formed, the process may proceed to S116.
The subsequent steps S116 to S134 in FIG. 11 are the same as those in FIG.

  As described above, when a mask having a bias correction larger than the optimum bias amount obtained from the exposure intensity calculation in advance is prepared and used for exposure, exposure is performed with a mask having the bias correction of the optimum bias amount. In comparison, it is possible to relatively increase the pattern dimension of a portion having a low pattern density, and the width of the dimension correction amount is widened. In other words, since the correction amount is larger than the appropriate correction amount at the best focus, the pattern dimension becomes larger, and when defocusing from there, the pattern dimension gradually decreases, and an appropriate dimension is obtained at a certain point. Can do.

Embodiment 3 FIG.
In the first embodiment, the optimum defocus amount is searched using a plurality of wafers. However, conditions are determined by performing test exposure with a focus and an exposure amount on one wafer, and desired design dimensions are obtained. Alternatively, the optimum defocus amount formed may be obtained.
FIG. 12 is a flowchart for explaining the pattern dimension adjusting method according to the third embodiment.
Steps up to S104 are the same as those in the first embodiment, and a description thereof will be omitted.

  In S106, the exposure is performed under one kind of condition in the first embodiment. However, in the third embodiment, the exposure is performed with a plurality of focus and exposure amounts.

In S108, the first wafer is unloaded from the wafer stage. Although not shown, the unloaded first wafer is developed and washed as in the first or second embodiment. Thereby, a resist pattern is formed.

  In S110, the first wafer is inspected.

  In S112, it is confirmed whether or not the pattern width (pattern line width) dimension of the first wafer that has been subjected to the best focus exposure using a mask that has been appropriately biased is formed to a desired design dimension. If it is formed to the desired design dimension, in other words, if the proximity effect correction of the mask is optimal, no further dimension adjustment is necessary, so that the subsequent wafer using the exposure conditions in the best focus exposure Can be processed. If the desired design dimension is not formed, the process proceeds to S114.

  In S114, when the pattern width dimension of the first wafer that has been subjected to the best focus exposure using a mask that is appropriately biased for calculation is not formed in a desired design dimension, a plurality of focus and exposure amounts are set. It is determined whether there is a condition in which the pattern width dimension of the first wafer is formed in a desired design dimension among the conditions exposed by shaking. When there is a condition formed in a desired design dimension, the defocus amount that is the method of the third embodiment is possible, and the defocus amount under such condition is acquired as the optimum defocus amount.

  By configuring as described above, the steps after S116 in FIG. 1 can be omitted.

Embodiment 4 FIG.
Similarly in the second embodiment, the optimum defocus amount is searched using a plurality of wafers. However, as in the third embodiment, the test exposure is performed by changing the focus and the exposure amount on one wafer. Thus, the conditions may be determined, and the optimum defocus amount formed to a desired design dimension may be obtained.
FIG. 13 is a flowchart for explaining the pattern dimension adjusting method according to the fourth embodiment.
Since S102 to S110 are the same as those in FIG. 12 except that an overcorrected bias mask is used, description thereof is omitted.

  In S1314, a condition is determined in which the pattern width dimension of the first wafer is formed to a desired design dimension. Then, the defocus amount under such conditions is acquired as the optimum defocus amount.

  By configuring as described above, the steps after S116 in FIG. 11 can be omitted.

  As described above, according to each of the above embodiments, the proximity effect correction that adjusts the dimensional correction amount of the resist pattern formed on the wafer by combining the proximity effect correction means such as the mask bias method and the defocus exposure. A method can be provided.

  In the above description, when the means for correcting the proximity effect is based on the mask bias method, as a result of the exposure process at the best focus, the pattern of the pattern formed on the substrate exposed from the predetermined region to which the bias is applied is described. Defocus adjustment can be performed when the pattern width does not become the desired pattern width because the bias amount of the bias is too large. Even if the means for correcting the proximity effect is another means, for example, a mask in which the influence of the proximity effect has been corrected in advance when forming the mask pattern, as a result of the exposure process at the best focus, When the pattern density of the pattern formed on the substrate is relatively small and the pattern width of the formed pattern is larger than the desired pattern width, or the pattern density of the pattern formed on the substrate is relatively When the pattern width of the formed pattern is smaller than the desired pattern width, the defocus adjustment can be performed.

  In the above description, as a method of changing the beam blur, the electron beam is defocused by changing the excitation of the lens and the beam blur is changed. However, by changing the beam current density, the beam blur is changed. Also good. Alternatively, the beam blur may be changed by changing the focus by changing the height of the wafer.

  In the above description, the description is made on the assumption that the silicon (Si) wafer is exposed, but the present invention is not limited to this, and other substrates may be used. Further, not limited to EPL exposure, any charged particle beam exposure apparatus using a charged particle beam including an electron beam and an ion beam may be used.

FIG. 3 is a flowchart for explaining a pattern dimension adjusting method in the first embodiment. It is a figure for demonstrating the structural example of the principal part of an EPL exposure apparatus. It is a figure which shows the relationship between the line width of a resist, exposure intensity, and beam blur. It is a figure which shows the relationship between a line | wire width shift amount, beam blur, and exposure intensity. It is a figure which shows the relationship between line | wire width and exposure intensity in case a beam blur is sufficiently smaller than a pattern dimension. It is a figure which shows the relationship between line | wire width and exposure intensity in case a beam blur exists to the extent which is equal to or smaller than the minimum processing dimension. It is the figure which showed the example of the proximity | contact effect correction | amendment by the bias method when the exposure intensity of a part with a large pattern density is made into a reference | standard. It is the figure which showed the example at the time of defocusing from the exposure conditions of FIG. 7, and exposing by enlarging a beam blur. It is the figure which showed the example of proximity | contact effect correction | amendment by the bias method when the exposure intensity of the part with a small pattern density is made into a reference | standard. It is the figure which showed the example at the time of defocusing from the exposure conditions of FIG. 9, and exposing by enlarging a beam blur. FIG. 10 is a flowchart for explaining a pattern dimension adjusting method in the second embodiment. FIG. 10 is a flowchart for explaining a pattern dimension adjusting method in the third embodiment. FIG. 10 is a flowchart for explaining a pattern dimension adjusting method in the fourth embodiment. It is a conceptual diagram for demonstrating operation | movement of an EPL exposure apparatus. It is a figure for demonstrating the exposure principle of EPL. It is a figure which shows the example of the stencil mask and membrane mask which were manufactured with typical material. It is a figure for demonstrating scattering of the electron in a board | substrate. It is a figure which shows the relationship between the exposure intensity | strength in a resist, and the range in which energy is accumulate | stored. It is a figure for demonstrating the proximity effect correction by a mask bias.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Stencil mask 150 Opening part 200 Membrane mask 202 Electron gun 204 Electron beam 206 Condenser lens 208,214,218 Deflector 210,340 Mask 212 Mask stage 216,222,360 Projection lens 220 Aperture 224,300 Wafer 256,258,264 , 266, 268, 272 Controller 280 Controller 301 Resist image 310 Semiconductor chip region 320 Subfield 330 Electron beam 331 Mask scattered electron 332 Image forming electron 350 Subfield mask 370 Limiting aperture 380 Objective lens

Claims (8)

An exposure method for performing electron beam exposure using a mask provided with means for overcorrecting the proximity effect,
An exposure method, wherein exposure is performed using an electron beam with a blurred focus when performing exposure.   2. An exposure method according to claim 1, wherein said mask is provided with means for correcting a proximity effect by a mask bias method. A best focus exposure step of exposing the substrate with a focused electron beam using a mask biased in a predetermined area;
As a result of the best focus exposure step, when the pattern width of the pattern exposed on the biased predetermined region and formed on the substrate does not become a desired pattern width because the bias amount of the bias is too large. A defocus exposure step of performing exposure on the next substrate while blurring the focal point, and obtaining a focal blur amount corresponding to the desired pattern width;
With
The substrate to be exposed after the focal blur amount is acquired by the defocus exposure step is subjected to exposure with the focal point being blurred in accordance with the focal blur amount, and is exposed after the focal blur amount is acquired. A pattern dimension adjusting method comprising adjusting a dimension of a pattern formed on a substrate. A pattern in which the pattern density of the pattern formed in the defocus exposure process is a region where the pattern density of the pattern exposed from the predetermined region to which the bias is applied and formed on the substrate is relatively small, and the pattern width of the formed pattern is desired 4. The pattern dimension adjustment method according to claim 3 , wherein when the width is larger than the width, the next substrate is exposed using the electron beam with the focus being blurred. A pattern in which the pattern density of the pattern formed in the defocus exposure step is a relatively high pattern density exposed from the biased predetermined area and formed on the substrate, and the pattern width of the formed pattern is desired 4. The pattern dimension adjusting method according to claim 3 , wherein, when the width is smaller than the width, the next substrate is exposed by using the electron beam having a blurred focus. In the best focus exposure step, the mask is biased to the predetermined area with reference to a predetermined exposure intensity,
4. The pattern dimension adjusting method according to claim 3 , wherein, in the defocus exposure step, exposure is performed with the focus being defocused without changing the predetermined exposure intensity used as the reference. A best focus exposure step of exposing the substrate using a focused electron beam;
As a result of exposure performed on the substrate by the best focus exposure step, when a pattern width of a relatively small pattern density formed on the substrate is larger than a desired pattern width, a focused electron beam is Using a defocus exposure step of exposing a substrate different from the substrate,
With
In the defocus exposure step, a focus blur amount in which a pattern width of a region having a relatively small pattern density formed on a substrate different from the substrate becomes the desired pattern width is acquired. How to get the blur amount. A best focus exposure step of exposing the substrate using a focused electron beam;
As a result of exposure performed on the substrate by the best focus exposure step, when a pattern width of a relatively high pattern density region formed on the substrate is smaller than a desired pattern width, a focused electron beam is generated. Using a defocus exposure step of exposing a substrate different from the substrate,
With
In the defocus exposure step, a focus blur amount is obtained in which a pattern width of a region having a relatively high pattern density formed on a substrate different from the substrate becomes the desired pattern width. How to get the blur amount.

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