JP2004273496A - System and method for electron beam exposure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system and a method for electron beam exposure by which strain correction can be made appropriately at the time of performing exposure by accurately measuring deflection strains and the heights of wafers. <P>SOLUTION: In the method, a factor acquiring mark which is disposed on a sample and the position of which is premeasured is measured by fixing a stage on which the sample is placed and only deflecting an electron beam. Then deflection strains and the height of the sample are made to be measured accurately by removing error factors related to the stage by acquiring a deflection strain correction factor by means of a correcting section 4 based on the information obtained by the measurement. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electron beam exposure apparatus and an electron beam exposure method, and more particularly, to correction of deflection distortion in electron beam exposure.
[0002]
[Prior art]
When manufacturing a semiconductor device such as an LSI, there is an electron beam exposure apparatus as one of exposure apparatuses for exposing a pattern on a semiconductor wafer (hereinafter, simply referred to as “wafer”). In the field / subfield connection in the electron beam exposure, generally, distortion due to the deflection of the field and the subfield (hereinafter, referred to as “deflection distortion”) is measured, and then the distortion is corrected in accordance with the height of the wafer. Beam exposure must be performed. Therefore, by accurately measuring the deflection distortion and the height of the wafer, the field / subfield connection accuracy is improved.
[0003]
Hereinafter, conventional methods for measuring deflection distortion and wafer height will be described.
(Method of measuring deflection distortion)
FIG. 6 is a diagram for explaining a conventional deflection distortion measuring method. The deflection distortion is measured using a measurement mark 62 fixed to a mark area of the stage 61 as shown in FIG. The mark area is an area different from the area where the wafer 63 is placed on the stage 61. The measurement mark 62 is a single embedded mark, a convex mark, or a concave mark formed using tantalum (Ta), tungsten (W), silicon (Si), or the like.
[0004]
The measurement of the deflection distortion is performed for each of the field and the subfield. In the measurement of the deflection distortion in the field, the measurement mark is sequentially moved to the positions of points PF1 to PF25 in the field by moving the stage as shown in FIG. 6B, and the measurement mark is detected by electron beam deflection. To measure the position of each point. Then, the shift amount between the position measured by the electron beam and the position moved by the stage is calculated, and fitting is performed using a higher-order correction formula to obtain a correction coefficient.
[0005]
Similarly, the measurement of the deflection distortion in the subfield is performed for each subfield, and the measurement mark is sequentially moved to the position of each point PS1 to PS16 of each subfield by stage movement as shown in FIG. The position of each point is measured by an electron beam to obtain a correction coefficient.
[0006]
(Method of measuring wafer height)
Methods for measuring the height of the wafer include a method of measuring the wafer by irradiating the wafer with laser light, and a method of detecting and measuring a mark arranged on the wafer with an electron beam.
FIG. 7 is a diagram for explaining a conventional method of measuring the height of a wafer using an electron beam. The height of the wafer is measured by using one of the alignment marks TM (for example, the lower left mark 72 of each chip) of each chip 71 arranged on the wafer to be exposed as shown in FIG.
[0007]
In the measurement of the height, the mark 72 is detected by an electron beam, and the lens condition is changed so that the detection signal waveform of the mark becomes steep. By performing this for a plurality of chips 71, a focus map is obtained, and the focus map is fitted by a higher-order equation to obtain a focus value for each chip.
[0008]
Further, a method of performing correction according to the height of a wafer in an electron beam exposure apparatus is also disclosed in Patent Document 1 and the like.
[0009]
[Patent Document 1]
JP-A-9-34122
[Problems to be solved by the invention]
However, in the above-described conventional measurement of deflection distortion, since the stage is sequentially moved, the error due to the stoppage of the stage or the distortion of the mirror used for measuring the position of the stage is included in the displacement amount. . In the conventional wafer height measurement, since the height of each chip is measured at only one location, the height of the wafer may not be accurately measured.
[0011]
Here, when the height of the wafer is not accurately measured, as shown in an example in FIG. 8, the accuracy of the connection between the field and the subfield is reduced due to the shift of the focus. FIG. 8 is a diagram showing an example of a decrease in field / subfield connection accuracy due to focus fluctuation, and FIG. 8B shows a case of just focus. On the other hand, FIG. 8A shows the case of overfocus, and FIG. 8C shows the case of underfocus. The deflecting field (subfield) is rotated or scaled, Field / subfield connection accuracy is low. In FIG. 8, reference numeral 81 denotes a mark, 82 denotes a portion of the mark 81 scanned by an electron beam, 83 denotes a subfield, and 84 denotes one pattern.
[0012]
As described above, in the electron beam exposure using the electron beam exposure apparatus, the deflection distortion and the height of the wafer are not accurately measured, and if the correction of the deflection distortion and the focus (focus value) are not appropriate, the exposure on the wafer is performed. Pattern accuracy is reduced.
The present invention has been made in view of such circumstances, and it is an object of the present invention to accurately measure deflection distortion and wafer height, and to appropriately perform distortion correction at the time of exposure. I do.
[0013]
[Means for Solving the Problems]
The electron beam exposure apparatus according to the present invention includes a correction processing unit that obtains a deflection distortion correction coefficient, fixes a stage on which a sample on which a plurality of coefficient acquisition marks are arranged is mounted, and obtains a coefficient acquisition mark whose position is measured in advance. A deflection distortion correction coefficient is obtained based on information obtained by measurement performed only by electron beam deflection.
According to the present invention, when performing measurement on a plurality of coefficient acquisition marks using an electron beam, the stage is fixed, so that error factors relating to the stage are removed, and deflection distortion and the height of the sample are accurately measured. Will be able to do it.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0015]
FIG. 1 is a block diagram showing a configuration example of an electron beam exposure apparatus according to one embodiment of the present invention.
The electron beam exposure apparatus according to the present embodiment includes an electron beam irradiation unit 1, a measurement unit 2, a storage unit 3, a correction processing unit 4, a control unit 5, and an exposure data input unit 6.
[0016]
The electron beam irradiator 1 irradiates the sample 7 with an electron beam according to a control instruction (including lens conditions and the like) from the controller 5. The measurement unit 2 measures the intensity of the electron beam reflected from the sample 7 of the electron beam irradiated from the electron beam irradiation unit 1. The storage unit 3 is for storing position measurement data relating to the position (may include the height) of a measurement mark for obtaining a coefficient arranged on the sample 7, a deflection distortion correction coefficient, and the like.
[0017]
The correction processing unit 4 performs processing related to deflection distortion correction, and includes a position comparison unit 8 and a correction coefficient calculation unit 9. The position comparing unit 8 compares the position of the measurement mark measured based on the intensity of the backscattered electrons from the sample 7 with the position of the measurement mark based on the position measurement data stored in the storage unit 3 to determine the amount of positional deviation. calculate. The correction coefficient calculation unit 9 calculates a deflection distortion correction coefficient based on the position shift amount calculated by the position comparison unit 8, or calculates a relational expression between the calculated deflection distortion correction coefficient and the focus value.
[0018]
The control unit 5 controls the electron beam irradiation unit 1 based on data input from the exposure data input unit 6, a request from the correction processing unit 4, and the like. The exposure data input unit 6 is for inputting data of a pattern to be exposed on a wafer.
[0019]
Next, the operation will be described.
FIG. 2 is a flowchart showing an operation example of the electron beam exposure apparatus shown in FIG.
[0020]
In step S1, the position measurement data is stored in the storage unit 3. The position measurement data is data relating to the positions of a plurality of measurement marks for coefficient acquisition arranged on the sample 7 for measuring deflection distortion, and is measured in advance by a position measurement device using a light wave or the like, for example. In the present embodiment, a plurality of measurement marks M1 to M25 for obtaining coefficients are arranged on a wafer (measurement chip, calibration chip) 31 as shown in FIG. The shape of the measurement marks M1 to M25 is arbitrary, and may be an embedded mark, a convex mark or a concave mark.
[0021]
In step S2, the positions of the measurement marks M1 to M25 for coefficient acquisition are measured by an electron beam, and the deflection distortion correction coefficients for the field and the subfield are calculated.
[0022]
First, the positions of the measurement marks in the field are measured as shown in FIG. 3, and the deflection distortion correction coefficient of the field is calculated.
Specifically, the center of the measurement chip 31 placed on the movable stage (the position of the measurement mark M13 in FIG. 3) coincides with the deflection center position of the electron beam irradiated from the electron beam irradiation unit 1. As described above, the control unit 5 drives the stage to move the measurement chip 31.
[0023]
Next, as indicated by an arrow in FIG. 3, the electron beam is deflected to one of the measurement marks M1 to M25 whose absolute value is measured in advance, and the reflected electron intensity is measured by the measurement unit 2 to measure the measurement mark M1. The position of ~ M25 is measured. Here, the electron beam is deflected by a deflector for the field (main deflection), for example, when the electron beam exposure apparatus is a two-stage deflector, the first stage deflector. The position measurement of the measurement marks M1 to M25 is performed on all the measurement marks M1 to M25, respectively, by merely deflecting the electron beam without moving the stage.
[0024]
The position comparing unit 8 calculates a shift amount (difference) between the measured positions of the measurement marks M1 to M25 and the positions of the measurement marks M1 to M25 based on the position measurement data stored in the storage unit 3. The correction coefficient calculation unit 9 calculates a deflection distortion correction coefficient for the field based on the positional deviation calculated by the position comparison unit 8. Here, the deflection distortion correction coefficient includes, for example, rotation related to angle (rotation), gain related to length, trapezoid related to deformation, and the like.
[0025]
Next, as shown in FIG. 4, the positions of the measurement marks in the subfield are measured, and the deflection distortion correction coefficient of the subfield is calculated. In FIG. 4, a rectangular area having the measurement marks M1, M2, M7, and M6 as vertices is one subfield, and similarly, an area having the measurement marks M2, M3, M8, and M7 as vertices, and a measurement mark M6. , M7, M12, and M11 as vertices, and areas having the measurement marks M7, M8, M13, and M12 as vertices are subfields.
[0026]
A description will be given of an example of a subfield having the measurement marks M1, M2, M7, and M6 as vertices.
First, the control unit 5 deflects the electron beam to the center position SC1 of the subfield by the deflector related to the field. Next, the electron beam is deflected by a deflector related to the subfield, for example, in the case of two-stage deflection, as indicated by an arrow in FIG. The positions of M1, M2, M7, and M6 are respectively measured. Thereafter, the correction processing unit 4 calculates the deviation amount of the position of each of the measurement marks M1, M2, M7, and M6 in the same manner as the case of calculating the deflection distortion correction coefficient of the field, and calculates the deflection distortion correction coefficient for the subfield. Is calculated.
[0027]
In the other subfields, similarly, after deflecting the electron beam to the center position SC2, SC3, SC4 of each subfield, the position of the measurement mark is measured, and the deflection distortion correction coefficient for each subfield is calculated. In this way, the deflection distortion correction coefficients for the subfields are calculated for all the subfields.
[0028]
As described above, in the present embodiment, when calculating the deflection distortion correction coefficient for the field and the subfield, the stage is first moved only once, and the stage is moved while the deflection distortion correction coefficient is being calculated. Instead, the position of each measurement mark is measured by deflecting the electron beam. Therefore, in the present embodiment, it is possible to accurately measure the deflection distortion (position measurement) by eliminating the error factors of the stage system such as the stop error due to the stage movement, and to improve the accuracy of the deflection distortion correction.
[0029]
In the above description, when calculating the deflection distortion correction coefficient of the field and the subfield, the center of the measurement chip and the center position of each subfield are made to coincide with the deflection center of the electron beam with the reference point as the reference point. The position of the measurement mark is not limited to the center and the center of each subfield, but may be any position as long as the position of the measurement mark can be measured by deflecting the electron beam.
[0030]
Returning to FIG. 2, in step S3 and subsequent steps, a correction coefficient is calculated based on the difference in wafer height. The calculation of the correction coefficient based on the difference in the height of the wafer is performed by measuring the measurement mark 51 on each surface (each step) having a different height as shown in FIG. Is performed using a stepped wafer (measurement chip, calibration chip) on which each is arranged. The heights H1 to H5 of the measurement marks 51 arranged on each stage are measured in advance and stored in the storage unit 3.
[0031]
Although FIG. 5 shows an example in which five stages are provided, the number of stages provided on the wafer is arbitrary. Further, in order to improve the measurement accuracy, a plurality of measurement marks 51 are arranged at each stage, but the number of the measurement marks 51 is arbitrary, and the measurement marks 51 may be embedded marks, convex marks or It may be a concave mark. It is desirable that the position in the height direction of the measurement mark 51 at the center, that is, the height H3, is the same as the height of the wafer surface to be actually exposed.
[0032]
In step S3, a correction coefficient in the just focus state is calculated for each stage of the wafer. The focus value that is in the just-focused state is determined based on the detection signal waveform of the measurement mark based on the reflected electron intensity measured by the measurement unit 2, and the deflection distortion at the focus value is determined in the same manner as the calculation of the deflection distortion correction coefficient described above. The correction coefficient is calculated by the correction processing unit 4. The calculated correction coefficient for each stage is stored in the storage unit 3 in step S4.
[0033]
In step S5, the correction processing unit 4 refers to a relational expression between the correction coefficient calculated and stored in steps S3 and S4 and the focus value at which the focus is set to the just focus state (hereinafter, referred to as “A coefficient relational expression” for convenience of description). ) Is calculated.
[0034]
Next, in step S6, control is performed such that the wafer is brought into the just-focused state at the center of the wafer (height H3 in FIG. 5). The coefficients are calculated by the correction processing unit 4 respectively. In other words, the correction coefficient is calculated for each stage other than the center stage when the stage is not in the just-focus state (the stage is at a height H1 or H2, and the stage at the heights H4 and H5 is underfocus). The calculated correction coefficient for each stage is stored in the storage unit 3 in step S8.
[0035]
In step S9, the correction processing unit 4 calculates a relational expression between the correction coefficient and the focus value (hereinafter, referred to as a “B coefficient relational expression” for convenience of description) in the same manner as in step S5.
As described above, in steps S3 to S9, the deflection distortion correction coefficient for the focus value and the deflection distortion correction coefficient when the focus is shifted are obtained.
[0036]
In steps S5 and S9, the relational expression between the correction coefficient and the focus value is calculated, but a table (table model) in which the correction coefficient and the focus value are associated with each other is generated. Is also good.
[0037]
In step S10, measurement is performed using a coefficient measurement chip provided on a wafer (chip) to be actually exposed, and each deflection distortion correction coefficient is obtained. Specifically, the position of an alignment mark (measurement mark) arranged on a coefficient measurement chip is measured, and each correction coefficient such as rotation, gain, and trapezoid is obtained based on the measured position.
[0038]
In step S11, the height is calculated and an appropriate focus value is calculated based on each deflection distortion correction coefficient and the A coefficient relational expression acquired in step S10. Further, in step S12, an appropriate deflection distortion correction coefficient for the focus value calculated in step S11 is calculated using a B coefficient relational expression.
In step S12, the pattern is exposed on the wafer based on the appropriate deflection distortion correction coefficient calculated in step S11.
[0039]
As described above, according to the present embodiment, when calculating the deflection distortion correction coefficient of the field and the subfield, the position of each measurement mark is measured only by electron beam deflection while the stage is fixed, and the deflection distortion correction is performed. Calculate the coefficient. Thereby, the influence of the error factor of the stage system can be removed, and the deflection distortion can be accurately measured.
[0040]
Further, a deflection distortion correction coefficient in a focus state and a defocus state is calculated using measurement marks respectively arranged on a plurality of surfaces (steps) having different heights, and a relational expression between the deflection distortion correction coefficient and the focus value is calculated. And so on, it is possible to calculate an appropriate deflection distortion correction coefficient and a focus value according to the height of the wafer, and prevent the accuracy of the exposed pattern from being degraded due to the focus blur. Therefore, when a fine pattern is formed on a wafer, it is possible to avoid occurrence of pattern separation, overlap, and the like at a field / subfield connection portion.
[0041]
The above embodiment is not limited to the two-stage deflection electron beam exposure apparatus, but can be applied to an electron beam exposure apparatus which is deflected by an arbitrary number of stages.
Further, each of the embodiments described above is merely an example of a concrete example for carrying out the present invention, and the technical scope of the present invention should not be interpreted in a limited manner. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features.
Various aspects of the present invention are shown below as supplementary notes.
[0042]
(Supplementary Note 1) By fixing the stage on which the sample is mounted and deflecting the electron beam, measurement using the electron beam is performed on a plurality of coefficient acquisition marks placed on the sample and measured in advance. An electron beam exposure apparatus comprising: a correction processing unit that obtains a deflection distortion correction coefficient based on information obtained by measurement using a beam.
(Supplementary Note 2) The apparatus further includes storage means for storing position measurement information obtained by previously measuring the positions of the plurality of coefficient acquisition marks,
The correction processing unit acquires the deflection distortion correction coefficient based on difference information between position measurement information stored in the storage unit and information obtained by measurement using the electron beam. The electron beam exposure apparatus according to claim 1.
(Supplementary Note 3) The correction processing unit compares the position measurement information with information obtained by measurement using the electron beam, and outputs the difference information;
3. The electron beam exposure apparatus according to claim 2, further comprising: a correction coefficient calculating unit configured to calculate the deflection distortion correction coefficient from the difference information.
(Supplementary note 4) The electron beam exposure apparatus according to any one of Supplementary notes 1 to 3, wherein the coefficient acquisition marks are respectively arranged on a plurality of surfaces of the sample having different heights.
(Supplementary note 5) The electron beam exposure apparatus according to supplementary note 4, wherein a plurality of the coefficient acquisition marks are arranged on each surface of the sample.
(Supplementary note 6) The supplementary note 4 or 5, wherein the coefficient acquisition mark arranged on one of a plurality of surfaces of the sample has the same height as an exposure surface of the sample on which the pattern is exposed. Electron beam exposure equipment.
(Supplementary Note 7) The electron beam is focused on the coefficient acquisition mark arranged on one of a plurality of surfaces of the sample, and the measurement using the electron beam is performed on the coefficient acquisition mark arranged on each surface. 7. The electron beam exposure apparatus according to claim 4, wherein the electron beam exposure apparatus obtains the deflection distortion correction coefficient.
(Supplementary Note 8) The electron beam is focused on the coefficient acquisition mark, and measurement using the electron beam for the coefficient acquisition mark is performed on each surface of the sample to acquire the deflection distortion correction coefficient. The electron beam exposure apparatus according to any one of supplementary notes 4 to 6, wherein
(Supplementary note 9) The electron according to supplementary note 7 or 8, wherein at least one of a relational expression of the deflection distortion correction coefficient with respect to a focus value related to the focus of the electron beam and a correspondence table of the deflection distortion correction coefficient is generated. Beam exposure equipment.
(Supplementary Note 10) The positions of the plurality of coefficient acquisition marks arranged on the sample are measured in advance, and the electron beam for the plurality of coefficient acquisition marks is measured by deflecting the electron beam while fixing the stage on which the sample is mounted. Perform the measurement using
Obtain a deflection distortion correction coefficient based on information obtained by the measurement using the electron beam,
An electron beam exposure method, comprising: exposing a pattern in which deflection distortion has been corrected using the deflection distortion correction coefficient.
(Supplementary note 11) The electron beam exposure according to supplementary note 10, wherein the deflection distortion correction coefficient is acquired based on information on the position and height of the coefficient acquisition mark obtained by the measurement using the electron beam. Method.
[0043]
【The invention's effect】
As described above, according to the present invention, the stage is fixed, and the deflection distortion correction coefficient is obtained based on information obtained by performing measurement with the electron beam on a plurality of coefficient acquisition marks whose positions are measured in advance. . As a result, an error factor relating to the stage can be removed, the deflection distortion and the height of the wafer can be accurately measured, and an appropriate deflection distortion correction coefficient can be obtained. Therefore, distortion correction can be performed while improving the accuracy of distortion correction during exposure.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration example of an electron beam exposure apparatus according to an embodiment of the present invention.
FIG. 2 is a flowchart showing an operation example of the electron beam exposure apparatus shown in FIG.
FIG. 3 is a diagram for explaining measurement (field) of deflection distortion.
FIG. 4 is a view for explaining measurement (sub-field) of deflection distortion.
FIG. 5 is a diagram for explaining a method of obtaining a deflection distortion correction coefficient for height.
FIG. 6 is a diagram for explaining a conventional method of measuring deflection distortion of a field and a subfield.
FIG. 7 is a diagram for explaining a conventional wafer height measuring method.
FIG. 8 is a diagram illustrating an example of a decrease in field / subfield connection accuracy due to a focus change.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electron beam irradiation part 2 Measurement part 3 Storage part 4 Correction processing part 5 Control part 6 Exposure data input part 8 Correction coefficient calculation part 9 Position comparison part

Claims (5)

By fixing the stage on which the sample is mounted and deflecting the electron beam, measurement using the electron beam was performed for a plurality of coefficient acquisition marks which were arranged on the sample and were measured in advance, and the electron beam was used. An electron beam exposure apparatus comprising: a correction processing unit that obtains a deflection distortion correction coefficient based on information obtained by measurement. 2. The electron beam exposure apparatus according to claim 1, wherein the coefficient acquisition marks are respectively arranged on a plurality of surfaces of the sample having different heights. The electron beam is focused on the coefficient acquisition mark arranged on one of the plurality of surfaces of the sample, and the measurement is performed using the electron beam for the coefficient acquisition mark arranged on each surface, and the deflection is performed. 3. The electron beam exposure apparatus according to claim 2, wherein a distortion correction coefficient is obtained. 3. The method according to claim 2, wherein an electron beam is focused on the coefficient acquisition mark, and measurement using the electron beam for the coefficient acquisition mark is performed on each surface of the sample to acquire the deflection distortion correction coefficient. 3. The electron beam exposure apparatus according to claim 1. Preliminarily measure the positions of a plurality of coefficient acquisition marks arranged on the sample,
By performing the measurement using the electron beam for the plurality of coefficient acquisition marks by fixing the stage on which the sample is mounted and deflecting the electron beam,
Obtain a deflection distortion correction coefficient based on information obtained by the measurement using the electron beam,
An electron beam exposure method, comprising: exposing a pattern in which deflection distortion has been corrected using the deflection distortion correction coefficient.

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