JP2005123318A - Method and device for evaluating resolution and electron beam exposing system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide resolution evaluating method/device for evaluating resolution of an exposure pattern transferred on a sample such as a semiconductor wafer by quantitative evaluation reference. <P>SOLUTION: An image of the exposure pattern is picked up and two pattern edge positions in a picked-up image are decided based on a threshold on the pixel value of the picked-up image. A distance between the pattern edge positions is measured for a plurality of times by changing the threshold. The parameter of a prescribed approximate expression approximating a relation between the threshold and the distance between the pattern edge positions is decided, and resolution of the exposure pattern is evaluated based on the parameter. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method and an apparatus for evaluating the resolution of a pattern transferred onto a sample by exposure, and in particular, a mask having a fine exposure pattern used in a manufacturing process of a semiconductor integrated circuit or the like is used as a semiconductor wafer. The present invention relates to a method and an apparatus for evaluating the resolution of an exposure pattern exposed on a sample in electron beam proximity exposure in which exposure is performed with an electron beam that is placed close to the surface of the sample and passed through a mask.

  In recent years, with the need for higher integration of semiconductor integrated circuits, further miniaturization of circuit patterns has been demanded. At present, the limits of miniaturization are mainly limited to exposure apparatuses, and new exposure apparatuses such as an electron beam direct writing apparatus and an X-ray exposure apparatus have been developed.

  Recently, an electron beam proximity exposure apparatus that can be used for ultrafine processing at a mass production level has been disclosed as a new type of exposure apparatus (for example, Patent Document 1 and Patent Document 2 corresponding to Japanese Patent Application). .

  FIG. 9 is a view showing a basic configuration of the electron beam proximity exposure apparatus. This electron beam proximity exposure apparatus 10 mainly includes an electron beam source 14 that generates an electron beam 15, a lens 18 that converts the electron beam 15 into a parallel beam, and an electron gun 12 that includes a shaping aperture 16, and main deflectors 21, 22 and The scanning unit 24 includes sub-deflectors 51 and 52 and scans an electron beam parallel to the optical axis, a mask 30, an electrostatic chuck 44, and a wafer stage 46.

The mask 30 is disposed so as to be close to the wafer 40 attracted by the electrostatic chuck 44 (so that the gap between the mask 30 and the wafer 40 is, for example, 50 μm). In this state, when the electron beam is irradiated perpendicularly to the mask 30, the electron beam that has passed through the mask pattern of the mask 30 is irradiated to the resist layer 42 on the wafer 40.
The main deflectors 21 and 22 in the scanning unit 24 control the deflection of the electron beam 15 so that the electron beam 15 scans the entire surface of the mask 30 as shown in FIG. As a result, the mask pattern of the mask 30 is transferred to the resist layer 42 on the wafer 40 at the same magnification.

  The wafer stage 46 moves the wafer 40 adsorbed by the electrostatic chuck 44 in two horizontal orthogonal axes, and moves the wafer 40 by a predetermined amount each time the mask pattern is transferred at an equal magnification. A plurality of mask patterns can be transferred to a single wafer 40. As described above, in the electron beam proximity exposure apparatus, the mask pattern is transferred by being arranged in the vicinity of the mask 30 and the wafer 40 and the electron beam 15 scanning the entire surface of the mask 30. The wafer stage 46 can also adjust the gap between the mask 30 and the sample 40 by raising and lowering the electrostatic chuck 44 in the vertical direction.

If the electron beam 15 applied to the mask 30 and the resist layer 42 on the sample 40 is not a parallel beam, the resolution of the pattern transferred to the resist layer 42 is lowered. The reason for this will be described with reference to FIG.
FIG. 11A shows a state in which the parallel beam 15 ′ and the non-parallel beam 15 pass through the mask 30 and are applied to the resist layer 42 on the sample 40, and FIG. The energy distribution in the pattern line width direction of the energy amount of the electron beam irradiated to the resist layer 42 portion shown in FIG.

As shown in FIG. 11A, the parallel beam 15 ′ is irradiated to the resist layer 42 sharply while maintaining the pattern line width as it is even after passing through the opening of the mask 30. Since the non-parallel beam 15 having a beam travels through the opening of the mask 30 while being slightly dispersed, the pattern edge portion 47 is blurred when the resist layer 42 is irradiated.
Therefore, as shown in FIG. 11B, the energy accumulation amount distribution by the parallel beam 15 ′ has a sharp rise at the pattern edge portion, whereas the energy accumulation by the non-parallel beam 15 indicated by a solid line or a chain line. The quantity distribution forms a distribution curve in which the rise at the pattern edge portion is somewhat gentle.

Here, in the resist layer 42 irradiated with the electron beam 15, only a portion irradiated with the electron beam having a predetermined energy accumulation amount threshold value _Eth is removed or left in a subsequent development process, and a pattern is formed on the sample 40. Form. However, when the rise of the energy accumulation amount distribution at the pattern edge portion becomes gradual as described above, the intensity of the accumulated electron beam varies. As a result, the pattern line width energy exceeding a predetermined threshold E _th is accumulated, so that the resolution is reduced by an error Δw occurs.

The above-described decrease in resolution also occurs when the electron beam 15 has astigmatism. For example, the cross-sectional shape of the electron beam 15 that should be a perfect circle as shown in FIG. 12A on the sample 40 is an electron having an elliptical cross-sectional shape that is long in the Y2 direction as shown in FIG. 12B due to astigmatism. The beam 15 ′ has an oblique component of the electron beam in the Y2 direction. For this reason, as in the case of the non-parallel electron beam 15 described above, the blur in the Y2 direction becomes large and the resolution in the Y2 direction decreases.
Further, when the electron beam 15 ″ has an elliptical cross-sectional shape that is long in the Y1 direction due to astigmatism, the blur in the Y1 direction becomes large and the resolution in the Y1 direction decreases.

  For this reason, the electron beam proximity exposure apparatus 10 changes the cross-sectional shape of the electron beam 15 irradiated onto the sample 40 of the electron beam 15 to correct the astigmatism of the electron beam 15. A coil 9 and an X-axis astigmatism coil 11 are provided. As shown in FIG. 12D, the Y-axis and X-axis astigmatism coils 9 and 11 include coils YC11, YC12, YC21, and YC22 that constitute the Y-axis astigmatism coil 9, and the X-axis astigmatism coil 11, respectively. Are combined with coils XC11, XC12, XC21, and XC22 to form an octupole coil.

  As shown in the figure, the X-axis astigmatism coil 11 is arranged in a state rotated by 45 ° with respect to the Y-axis astigmatism correction coil 9 and is YC11 and YC12, YC21 and YC22, XC11 and XC12, XC21 and XC22. Are arranged opposite to each other. Although the astigmatism correction coils 9 and 11 are generally configured on the same plane, they are shown separately in FIG. 10 for easy explanation of the present invention.

In recent years, the allowable range of variation in pattern line width has become very strict as semiconductor integrated circuits are highly integrated. For example, the allowable range allowed in the current 65 nm node semiconductor integrated circuit is within 6.5 nm.
For this reason, conventionally, a test-exposed pattern is imaged with a scanning electron microscope (SEM) or the like, and its resolution is evaluated, so that the electron beam parallelism, astigmatism, mask, etc. are optimized. The exposure conditions such as the gap between 30 and 40 were adjusted.

US Patent No. 5,831,272 (Overall) Japanese Patent No. 2951947 (Overall)

  However, the conventional evaluation of the resolution of the exposure pattern is performed by means such as measuring the line width of the captured exposure pattern and comparing the measurement result with the desired line width in the design. The standard for grasping the resolution state of was not clear. Further, since the above-described means is performed by a human system, a difference in resolution of captured images due to individual differences among operators is generated, and individual differences occur in setting exposure conditions.

  In view of the above circumstances, in the present invention, a resolution evaluation method and resolution of an exposure pattern transferred onto a sample such as a semiconductor wafer, which can automatically perform resolution evaluation according to a clear evaluation standard. An object is to provide a sex assessment device.

  Still another object of the present invention is to provide an electron beam exposure apparatus capable of setting the best exposure conditions by the resolution evaluation method provided by the present invention.

  In order to achieve the above object, in the resolution evaluation method according to the first aspect of the present invention, an exposure pattern for evaluating the resolution is imaged, and two pattern edge positions in the captured image are determined. This is determined based on the threshold value for the pixel value, the distance between the pattern edge positions is measured multiple times by changing the threshold value, and a parameter of a predetermined approximate expression that approximates the relationship between the threshold value and the distance between the pattern edge positions is The resolution of the exposure pattern is evaluated based on this parameter.

FIG. 1A shows a flowchart of the resolution evaluation method according to the first embodiment of the present invention.
In step S101, an image of a sample having an exposure pattern corresponding to a predetermined mask pattern transferred on the surface is imaged. FIG. 1B illustrates a captured image.

As shown in the figure, the captured image is a grayscale image having brightness information. In the figure, the exposure pattern corresponding to the mask opening is captured as a relatively bright portion, and the other portions are captured as relatively dark portions. Yes.
Further, the pattern edge portion which is the boundary region appears as a gradation.

  In step S102, a threshold relating to the pixel of the captured image used as a reference when determining the pattern edge position in step 103 below is determined. This threshold value is, for example, a threshold value regarding the brightness of the pixel of the captured image.

  In step S103, two pattern edge positions of the imaging pattern in the captured image are determined based on the threshold value. In the example of the captured image shown in FIG. 1B, the position of the boundary where the brightness is 50% or more is determined as the pattern edge portion.

  In step S104, the distance between the two pattern edge positions is measured. The above steps S103 and S104 are repeated while changing the threshold value, and each threshold value and the corresponding measurement distance are stored.

  In step S106, a parameter of a predetermined approximation formula that approximates the relationship between the threshold and the distance between the pattern edge positions is determined based on each measured value and each threshold.

  In step S107, the resolution of the exposure pattern is evaluated based on the determined parameter. If the resolution of the exposure pattern transferred here is high, the change in the length measurement value with respect to the change in the threshold value is small (or the change in the threshold value with respect to the change in the length measurement value is large). It is possible to quantitatively evaluate the resolution based on the property of and the numerical value of the determined approximate parameter.

Further, the resolution evaluation apparatus according to the second embodiment of the present invention includes an imaging unit that images a sample on which an exposure pattern corresponding to a predetermined mask pattern is transferred, and an exposure pattern in an image obtained by imaging. The pattern edge position determining means that determines two pattern edge positions of the imaging pattern corresponding to the image pattern based on a threshold value relating to the pixel value of the image, and the distance between the determined pattern edge positions is measured a plurality of times while changing the threshold value. Length measuring means, and approximating means for determining a parameter of a predetermined approximation formula that approximates the relationship between the threshold value and the distance between the pattern edge positions based on each measured length value and the threshold value. And an evaluation means for evaluating the resolution of the exposure pattern based on this parameter.
Note that a conventional scanning electron microscope may be used as the imaging means.

  Furthermore, an electron beam exposure system according to a third aspect of the present invention includes the resolution evaluation apparatus, an exposure electron beam source that generates an exposure electron beam to be irradiated on a sample, and an exposure electron beam path. A mask having a predetermined mask pattern and an exposure electron beam scanning unit that scans the exposure electron beam on the mask, and corresponds to the mask pattern by the electron beam that has passed through the mask; An electron beam exposure apparatus for transferring the exposure pattern to the sample surface is provided, and the resolution of the exposure pattern is evaluated.

  As described above, according to the present invention, the resolution of an exposure pattern exposed under a certain exposure condition can be handled quantitatively. Therefore, it is possible to optimize the exposure conditions by obtaining the parameter values for each sample obtained by transferring the mask pattern a plurality of times while changing the exposure conditions, and determining the exposure conditions for the samples based on the parameter values.

  By treating the resolution of the exposure pattern quantitatively, it becomes possible to make the resolution uniform between multiple exposures.

  Hereinafter, preferred embodiments of a resolution evaluation method, a resolution evaluation apparatus, and an electron beam exposure system according to the present invention will be described with reference to the accompanying drawings.

  FIG. 2 is a schematic diagram of the configuration of an electron beam proximity exposure system according to the present invention. The electron beam proximity exposure system includes a resolution evaluation device 80 and an electron beam proximity exposure device 10. Since the configuration of the electron beam proximity exposure apparatus 10 has a configuration similar to the configuration shown in FIG. 9, the same functional parts are denoted by the same reference numerals and the description thereof is omitted.

  The resolution evaluation apparatus 80 is an imaging electron beam source 81 that generates an imaging electron beam, and an imaging electron beam scanning unit that scans the electron beam on the sample 40 whose surface is exposed to a predetermined pattern. A certain deflector 84, a deflector controller 86 for controlling the scanning position of the electron beam by the deflector 84, an electron detector 85 for detecting electrons reflected from the surface of the sample 40, and the scanning position of the electron beam. And a signal processing circuit 87 for processing the output signal of the electronic detector and converting it into digital signal information.

The resolution evaluation apparatus 80 includes a computer 89 such as a computer. Each scanning position information and each reflected electron detection amount information of the electron beam are supplied to the data bus of the computer 89 by the deflector controller 86 and the signal processing circuit 87, respectively. The computer 89 generates a two-dimensional reflected electron image of the imaging pattern generated based on each scanning position of the electron beam and each reflected electron detection amount.
The resolution evaluation apparatus 80 includes an imaging unit having the above-described configuration, and the imaging unit may use a normal scanning electron microscope.

  Further, the resolution evaluation device 80 determines the pattern edge position for determining two pattern edge positions of the pattern (imaging pattern) corresponding to the exposure pattern included in the image (captured image) obtained by the imaging unit. Unit 90 and a length measuring unit 91 for measuring the distance between the determined pattern edge positions.

  The pattern edge position determination unit 90 is provided with position information of a partial image including a pattern edge portion in the captured image and a threshold value of the pixel value of each pixel, and pattern the boundary position of the pixel region that satisfies the given threshold value. The edge position is determined.

  For example, in a grayscale captured image as illustrated in FIG. 1B, the threshold value is given with respect to the brightness which is a pixel value. Now, FIG. 3 shows a change in brightness in a predetermined direction (X direction) of a partial pattern in the captured image. For example, when 50% lightness is given as the threshold value, the boundary position between the pixel region having the lightness of 50% or more and the pixel region having the lightness of less than 50% is determined as the pattern edge position. Note that when the captured image is displayed with a change in color as in the case of a color image, the threshold value may be set not only for the brightness but also for each pixel value such as saturation and hue.

Then, the length measuring unit 91 measures the distance between the two pattern edge portions determined by the pattern edge position determining unit 90, as shown in FIG.
The length measuring unit 91 performs length measurement a plurality of times while changing the threshold given to the pattern edge position determining unit 90 with respect to the same captured image obtained by the imaging unit included in the resolution evaluation device 80.

  Furthermore, the resolution evaluation apparatus 80 calculates an approximate parameter of a predetermined approximate expression that approximates the relationship between the threshold value and the distance between the pattern edge positions based on each measured length value and each threshold value. An approximation unit 92 for determining and a parameter evaluation unit 93 for evaluating the resolution of the exposure pattern based on the determined parameters are provided. The parameter evaluation unit 93 includes an exposure condition determination unit 94 that determines the optimum exposure condition of the electron beam proximity exposure apparatus 10 based on the resolution evaluation of the exposure pattern exposed on the sample 40.

  Further, the resolution evaluation apparatus 80 includes a data input / output unit 95 that inputs data related to the exposure conditions of the sample 40 to which the exposure pattern to be subjected to resolution evaluation is transferred from the electron beam proximity exposure apparatus 10. The data input / output unit 95 also outputs the optimum exposure condition determined by the exposure condition determination unit 94 in the parameter evaluation unit 93 to the electron beam proximity exposure apparatus 10. Data input / output by the data input / output unit 95 is stored in the storage unit 96.

  The pattern edge position determination unit 90, the side length unit 91, the approximation unit 92, the parameter evaluation unit 93, the data input / output unit 95, and the storage unit 96 are also connected to the data bus of the computer 89 on the resolution evaluation apparatus 80 side. It is connected.

  On the other hand, the electron beam proximity exposure apparatus 10 controls the irradiation lens 18 to adjust the equilibrium state of the electron beam 15 and the astigmatism coils 9 and 11 to control the astigmatism of the electron beam 15. An astigmatism coil controller 72 that adjusts the aberration state, and a stage controller 73 that controls the wafer stage 46 to adjust the gap between the sample 40 and the mask 30 are provided. These irradiation lens control unit 71, astigmatism coil control unit 72, and stage control unit 73 are connected to the data bus of the computer 74 on the electron beam proximity exposure apparatus 10 side, and can exchange data.

  Further, the electron beam proximity exposure apparatus 10 includes a data input / output unit 75 that outputs to the resolution evaluation apparatus 80 data related to the exposure conditions of the sample 40 to which the exposure pattern to be subjected to resolution evaluation is transferred. The data input / output unit 75 also inputs optimum exposure conditions from the resolution evaluation device 80. Data input / output by the data input / output unit 75 is stored in the storage unit 76 of the electron beam proximity exposure apparatus 10.

  Further, the electron beam proximity exposure apparatus 10 drives the irradiation lens control unit 71, the astigmatism coil control unit 72, and the stage control unit 73 based on the exposure conditions stored in the storage unit 76, respectively. The exposure condition control unit 77 is provided for adjusting the parallelism state and astigmatism state, and the gap between the mask 30 and the sample 40.

  The irradiation lens control unit 71, the astigmatism coil control unit 72, the stage control unit 73, the data input / output unit 75, the storage unit 76, and the exposure condition control unit 77 are included in the computer 74 on the electron beam proximity exposure apparatus 10 side. It is possible to exchange data by being connected to a data bus.

  Data exchange between the data input / output unit 95 on the resolution evaluation apparatus 80 side and the data input / output unit 75 on the electron beam proximity exposure apparatus 10 side may be performed online, or other flexible disks or CD-ROMs. Alternatively, it may be performed offline using a storage medium such as a memory card. In addition, a storage medium such as a non-contact IC chip is attached to the sample 40 to be evaluated, and a reader / writer is provided on the resolution evaluation device 80 side and the electron beam proximity exposure device 10 side to exchange data with the sample 40. May be.

FIG. 4 is an operation flowchart of the electron beam proximity exposure system according to the present invention.
In step S201, the exposure condition control unit 77 of the electron beam proximity exposure apparatus 10 sets the exposure condition to a certain value in order to expose the exposure pattern whose resolution is to be evaluated. Here, the exposure conditions are, for example, a control amount of the irradiation lens control unit 71 that is an adjustment amount of the parallelism of the electron beam 15 and a control of the astigmatism coil 9 or 11 that is an adjustment amount of astigmatism of the electron beam 15. It may be an amount or a gap amount between the sample 40 and the mask 30.

  In step S202, the electron beam proximity exposure apparatus 10 exposes and transfers the mask pattern of the mask 30 to the resist layer 42 applied to the surface of the sample 40 under the exposure conditions determined by the exposure condition control unit 77. .

  In step S203, the exposed sample 40 is placed in the resolution evaluation apparatus 80, and the pattern (exposure pattern) exposed on the resist layer 42 corresponding to the mask pattern is imaged by the imaging unit described above. . That is, the electron beam 82 generated by the imaging electron beam source 81 is irradiated on the sample 40 by being scanned by the deflector 84, and the electrons reflected on the surface of the sample 40 are detected by the electron detector 85. An intensity distribution image of the output signal of the electron detector corresponding to each scanning position is acquired.

  In the resist layer 42, the electron beam 15 is irradiated and charged in the portion irradiated with the electron beam 15, so that the amount of reflected electrons is different from the portion not irradiated with the electron beam 15. Therefore, the acquired image (captured image) is a grayscale two-dimensional reflected electron image as exemplified in FIG. The exposure pattern corresponding to the mask opening is imaged as a relatively bright part, and the other part is imaged as a relatively dark part. The pattern edge portion, which is the boundary region, appears as a gradation.

  In step S204, a threshold value related to the pixel value of the captured image to be given to the pattern edge position determination unit 90 is determined. Here, in order to determine any position in the region where the brightness changes, which is a boundary portion between the bright part and the dark part, as a pattern edge, a threshold value related to the brightness is determined.

  In step S205, the pattern edge position determining unit 90 determines a pattern edge position of a pattern (imaged pattern) imaged corresponding to the exposure pattern in the captured image.

  First, a pattern portion including a pattern edge portion is selected from the captured image as a pattern portion to be a sample for resolution evaluation, and its position information is given to the pattern edge position determination unit 90. The position information may be given by arbitrarily selecting a pattern portion including a pattern edge portion by SEM observation by an operator, and automatically selecting a pattern portion including a pattern edge portion from CAD data of a mask pattern. Also good.

  Here, as shown in FIG. 5A, the two pattern edge portions for which the pattern edge position determining unit 90 determines the pattern edge position do not necessarily need to select the opposite edge portions for one pattern line. However, as shown in FIG. 5B, at least in the direction orthogonal to the pattern edge direction of the imaging pattern (the direction of change in gradation occurring at the boundary between the dark part and the bright part of the pattern, that is, the line width direction of the imaging pattern) It is preferable to select two points on the extending straight line.

  Then, the pattern edge position determining unit 90 determines the boundary position of the pixel region that satisfies the given threshold condition as the pattern edge position in the pattern edge part (the boundary part between the dark part and the bright part of the pattern) as described above. .

In step S206, the distance between the two pattern edge positions determined by the pattern edge position determination unit 90 is measured.
Then, the pattern edge position determination in step S205 and the length measurement in step S206 are repeated a plurality of times while changing the threshold as many times as necessary for the resolution evaluation (step S207).

In step S208, the approximating unit 92 approximates the relationship between the threshold value and the distance between the pattern edge positions using a predetermined approximate expression based on the measured length values and the corresponding threshold values. To do. As this approximation formula, various approximation formulas such as polynomial approximation including linear approximation using a linear function and approximation using a normal distribution curve may be used. At this time, the approximating unit 92 determines approximate parameters included in the approximate expression used for approximation. For example, when linear approximation is used as the approximate expression, the approximate parameter may be the straight line slope a. This approximate parameter quantitatively indicates the change amount of the distance between the pattern edge positions with respect to the change amount of the threshold value.
FIG. 6 illustrates a plurality of measured length values, plot results of the corresponding threshold values, and a graph of an approximate expression obtained based thereon.

  The above steps S202 to S208 are repeated by changing the exposure condition of the electron beam proximity exposure apparatus 10 and changing the threshold value as many times as necessary for the resolution evaluation to cope with a plurality of exposure conditions. A plurality of approximate parameters to be acquired are acquired (step S209). FIG. 7A shows the relationship between the threshold value obtained by changing the exposure condition and the distance between the pattern edge positions, and FIG. 7B shows the relationship between the exposure condition and the approximate parameter.

  At this time, as described above, the approximate parameter quantitatively indicates the change amount of the distance between the pattern edge positions with respect to the change amount of the threshold value. Therefore, as long as exposure is performed with the same intensity over the entire exposure pattern, the same numerical value can be obtained regardless of the portion of the imaging pattern under a certain exposure condition.

  Therefore, when acquiring approximate parameters for exposure patterns exposed under different exposure conditions in steps S202 to S209, the distance between pattern edges measured at the same pattern edge portion between different approximate parameters is measured. There is no need to use long values. That is, for each approximate parameter to be acquired, the approximate parameter may be obtained at different pattern edge portions.

  Further, as described above, the approximate parameter indicates the amount of change in the distance between the pattern edge positions with respect to the amount of change in the threshold. Therefore, the two pattern edge portions that determine the pattern edge position are not necessarily shown in FIG. As shown in Fig. 2, two points on a straight line extending in the direction orthogonal to the pattern edge direction of the image pickup pattern (the change direction of the gradation generated at the boundary between the dark part and the bright part of the pattern, that is, the line width direction of the image pickup pattern) are selected. There is no need, and as shown in FIG. 8 (a), the straight lines connecting the two pattern edge positions should be the same in a predetermined direction defined on the sample for all of the imaging patterns with different exposure conditions. .

  When adjusting astigmatism, it is desirable to evaluate the resolution in each of the 45 °, 90 °, 135 °, and 180 ° directions shown in FIG. Therefore, in this case, therefore, the imaging unit included in the resolution evaluation device 80 captures an isolated pattern extending in each of the directions as shown in FIGS. The determination unit 90 and the length measurement unit 91 measure the length in the line width direction using each of these captured images. Accordingly, it is preferable to evaluate each resolution in the 45 °, 90 °, 135 °, and 180 ° directions.

  As shown in FIG. 4, each time the approximate parameter is determined (S208), the exposure condition is changed (S209), and the exposure (S202) is not repeated. After the sample is exposed, sample imaging (S203) to approximate parameter determination (S208) are repeatedly performed for the exposure pattern exposed under each exposure condition, and a plurality of approximate parameters corresponding to a plurality of exposure conditions are obtained. It is good also as acquiring.

In step S210, the exposure condition determination unit 94 of the parameter evaluation unit 93 determines the exposure condition based on the relationship between the exposure condition and the approximate parameter.
For example, in the case where the adjustment amount of astigmatism that is the exposure condition is changed in step S209 and approximation is performed by linear approximation in step S208, the pattern of the captured image is obtained when the astigmatism amount that has the maximum inclination as the approximation parameter is obtained. It can be seen that the amount of change in brightness difference at the edge portion is the largest (that is, the width of the gradation portion of the pattern edge portion is narrow), that is, the resolution is high, and the amount of astigmatism at this time is optimal. . Thus, it becomes possible to evaluate exposure conditions.

Thereafter, the determined exposure condition data is stored in the storage unit 96, and is output to the electron beam proximity exposure apparatus 10 by the data input / output unit 95.
The data input / output unit 75 of the electron beam proximity exposure apparatus 10 stores the input exposure condition data in the storage unit 76.

  The exposure condition control unit 77 reads the stored exposure condition data, controls the irradiation lens control unit 71, the astigmatism coil control unit 72, or the stage control unit 73, and the parallelism state of the electron beam 15 that is the exposure condition Alternatively, an astigmatism state or a gap adjustment between the sample 40 and the mask 30 is performed. As described above, it is possible to optimize the exposure conditions.

  The amount of change in the distance between pattern edge positions with respect to the amount of change in the pixel value of the captured image (that is, the critical dimension that is the pattern width measurement value) is quantitatively evaluated using the approximate parameters determined by this system. Therefore, it is possible to confirm the uniformity of the resolution between different exposed samples 40.

  Furthermore, it is possible to confirm the uniformity of the resolution of the exposure pattern within the change region (in the shot) of the electron beam by the main deflectors 21 and 22.

  By utilizing the present invention, it is possible to quantitatively evaluate the resolution of a pattern transferred onto a sample in pattern exposure such as electron beam exposure, and it is possible to set the best exposure conditions. .

(A) is a flowchart of the resolution evaluation method according to the present invention, and (b) is an example of a captured image of an exposure pattern. 1 is a basic configuration diagram of an electron beam proximity exposure system according to the present invention. It is a figure explaining the determination method of the pattern edge position by a pattern edge position determination part. 3 is an operation flowchart of the electron beam proximity exposure system of FIG. 2. It is FIG. (1) explaining the determination method of a pattern edge position. FIG. 6 is a relationship diagram between a distance between pattern edge positions and a pixel value threshold value. (A) is a relationship diagram between the distance between pattern edge positions under a plurality of exposure conditions and a pixel value threshold, and (b) is a relationship diagram between exposure conditions and approximate parameters. It is FIG. (2) explaining the determination method of a pattern edge position. It is a basic block diagram of the conventional electron beam proximity exposure apparatus. It is explanatory drawing of control of the electron beam which scans the mask whole surface. (A) is explanatory drawing of the parallel beam and non-parallel beam irradiated to the resist layer on a sample, (b) is a figure which shows energy distribution of the energy amount of the irradiated electron beam. (A)-(b) is a change figure of the electron beam cross-sectional shape by astigmatism, (d) is a block diagram of the astigmatism coil in the electron beam proximity exposure apparatus of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electron beam proximity exposure apparatus 14 ... Exposure electron beam source 15 ... Exposure electron beam 18 ... Irradiation lens 9, 11 ... Astigmatism coil 30 ... Mask 40 ... Sample 46 ... Wafer stage 71 ... Irradiation lens control part 72 ... Astigmatic coil control unit 73 ... stage control unit 77 ... exposure condition control unit 80 ... resolution evaluation device 81 ... imaging electron beam source 82 ... imaging electron beam 84 ... deflector 85 ... electron detector 90 ... pattern edge position Determining unit 91 ... Length measuring unit 92 ... Approximating unit 93 ... Parameter evaluating unit 94 ... Exposure condition determining unit

Claims (9)

Image a sample with an exposure pattern corresponding to a predetermined mask pattern transferred to the surface,
In the image obtained by the imaging, two pattern edge positions of the imaging pattern corresponding to the exposure pattern are determined based on a threshold value regarding the pixel value of the image,
Measuring the distance between the determined pattern edge positions a plurality of times by changing the threshold value,
Based on each measured length value and each threshold value, a parameter of a predetermined approximate expression that approximates a relationship between the threshold value and the distance between the pattern edge positions is determined;
A method for evaluating the resolution of an exposure pattern transferred to a sample, wherein the resolution of the exposure pattern is evaluated based on the determined parameter.   2. The resolution according to claim 1, wherein the parameter value is obtained for each sample obtained by transferring the mask pattern a plurality of times under different exposure conditions, and the exposure condition of the sample is determined based on the parameter value. Evaluation methods.   The imaging is performed by scanning the sample with an electron beam and irradiating the sample, and detecting the electrons reflected on the sample surface, so that the electron beam is detected based on the detected amount of the electron according to each scanning position of the electron beam. The resolution evaluation method according to claim 1, wherein the method is performed by generating a two-dimensional reflected electron image of a pattern. Imaging means for imaging a sample having an exposure pattern corresponding to a predetermined mask pattern transferred to the surface;
Pattern edge position determining means for determining two pattern edge positions of an imaging pattern corresponding to the exposure pattern in an image obtained by the imaging based on a threshold relating to a pixel value of the image;
Length measuring means for measuring the distance between the determined pattern edge positions a plurality of times by changing the threshold value;
Approximating means for determining a parameter of a predetermined approximation formula that approximates a relationship between the threshold value and the distance between the pattern edge positions based on the measured length values and the threshold values;
An evaluation unit for evaluating the resolution of the exposure pattern based on the determined parameter, and a resolution evaluation apparatus for the resolution of the exposure pattern transferred to the sample.   5. An exposure condition determining means for obtaining each of the parameter values for a sample on which the mask pattern has been transferred a plurality of times under different exposure conditions and determining the exposure conditions of the sample based on the parameter values. The resolution evaluation apparatus according to 1. The imaging means includes
An imaging electron beam source for generating an imaging electron beam;
An imaging electron beam scanning means for scanning the imaging electron beam on a sample whose surface is exposed to a predetermined pattern;
An electron detection means for detecting electrons reflected from the surface of the sample;
5. The backscattered electron image generating unit that generates a two-dimensional backscattered electron image of the pattern based on each detection amount of the electron detecting unit corresponding to each scanning position of the electron beam. Resolution evaluation equipment. The resolution evaluation apparatus according to claim 4, and
An exposure electron beam source for generating an exposure electron beam for irradiating the sample;
A mask having a predetermined mask pattern disposed in the path of the exposure electron beam;
Exposure electron beam scanning means for scanning the exposure electron beam on the mask,
An electron beam exposure apparatus that transfers an exposure pattern corresponding to the mask pattern to the sample surface by the electron beam that has passed through the mask;
An electron beam exposure system for evaluating the resolution of the exposure pattern.   8. The electron beam exposure according to claim 7, wherein the parameter value is obtained for each of a plurality of samples to which the mask pattern is transferred under different exposure conditions, and the exposure conditions for the sample are determined based on the parameter values. system.   9. The electron beam exposure according to claim 8, wherein the exposure condition is at least one of a parallelism state or an astigmatism state of the exposure electron beam, or an interval between the mask and the sample. system.

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