JP2005181044A - Coordinate measurement accuracy calibration method, coordinate measurement accuracy evaluation method, program, and mask - Google Patents

Abstract

A coordinate measuring accuracy calibration method capable of easily grasping an error of a coordinate measuring instrument and performing accurate calibration and a program for executing the calibration method are provided.
An absolute position of a plurality of marks formed on a measured object is measured by a coordinate measuring instrument (step ST3), and a relative position between the marks is measured by an overlay accuracy measuring instrument (step ST4). Based on the absolute position of the mark measured in step ST3, the relative position between the marks is obtained. Then, the consistency between the measured value of the relative position between the marks measured by the overlay accuracy measuring instrument and the calculated value of the relative position between the marks calculated based on the absolute position of the mark is determined (step ST6) When it is determined that there is no consistency, the coordinate measuring device is calibrated (step ST7).
[Selection] Figure 1

Description

  The present invention relates to a coordinate measurement accuracy calibration method, a coordinate measurement accuracy evaluation method, and a program for executing the calibration method and the evaluation method, for example, for calibration of a coordinate measuring instrument that measures the coordinates of a mark formed on a mask or a wafer. , And masks.

  Since the design rule 65nm generation, the resolution of photolithography is approaching its limit, and instead of the conventional KrF laser (wavelength 248nm) and ArF laser (wavelength 193nm), shorter wavelength electron beam (EB) and extreme ultraviolet light Development of next generation lithography technology (NGL) using (EUV light) is underway.

  These next-generation lithography technologies are not applied to all layers of the device from the beginning, but are expected to be applied sequentially from the so-called critical layers, such as gate layers and contact layers, which have strict design rules. . This is because using a new technique for a non-critical layer that can be processed by photolithography is disadvantageous in terms of cost.

  Conventionally, the critical layer is usually processed consistently with a single exposure apparatus. This is because there are inherent systematic errors (specifically, systematic errors such as lens aberration and stage accuracy) that each exposure apparatus has. If each layer is processed using a different exposure apparatus, overlay errors or line errors will occur. This is because there is a high possibility that a width defect will occur.

  As described above, mix-and-match exposure, in which each layer of the same device is processed with different exposure apparatuses, is generated as next-generation lithography technology using EB and EUV light is sequentially introduced. To do.

  Even if the next-generation exposure technology is not used, in the integrated production using a single exposure apparatus, there is a problem that when the apparatus is stopped due to a failure or maintenance, the production of the device is simultaneously stopped. Furthermore, the productivity of the factory is improved by performing mix-and-match exposure using different exposure apparatuses according to the idle time of the apparatus.

  In order to perform mix and match exposure from the viewpoint of resolution and productivity, it is necessary to grasp the systematic error of the exposure apparatus in the previous process. In particular, the positional accuracy due to lens aberration and stage accuracy in the previous process has a great influence on the overlay accuracy in the next process. Therefore, accurate evaluation of the positional accuracy of the substrate processed in the previous process is indispensable for estimating the overlay error in the next process (needed to determine whether to perform mix-and-match exposure) and developing an error correction method. It is.

The position accuracy of the substrate can be measured by a coordinate measuring instrument represented by LMS IPRO (LEICA) and light wave XY-6i (Nikon) on the mark processed on the wafer in the previous process. These coordinate measuring instruments are routinely used all over the world for guaranteeing the positional accuracy of the photomask, and can generally be said to be extremely reliable long dimension measuring means.
JP-A-8-297014

  However, when the present inventors evaluate a wafer or a next-generation exposure mask manufactured from the wafer, there are various error factors in the measurement by the coordinate measuring instrument, and the reliability is not necessarily high and the accuracy is high. I found out that it was necessary to pay close attention to data acquisition. Although different from the coordinate measuring instrument, a technique for correcting an error of the position measurement system is disclosed (see Patent Document 1).

The material of the photomask is ultra-low expansion glass (expansion coefficient 7.5 × 10 ⁻⁷ / K or less), the thickness is 6.25 mm, and the rigidity is high. Therefore, deformation due to temperature change or device chucking is small. On the other hand, the expansion coefficient of the silicon wafer is 2.6 × 10 ⁻⁶ / K and the thickness is only 725 μm. That is, the deformation due to temperature is larger than that of the photomask, and the rigidity is much lower.

  FIG. 13 is a diagram for explaining the systematic error of the coordinate measuring device. FIG. 13A shows the result of measuring the positional accuracy of the wafer processed by the ArF scanner with the light wave XY-6i at the wafer orientation of 0 °. FIG. 13B is a diagram showing a result of measurement with a light wave XY-6i at a wafer orientation of 180 °. As shown in FIG. 13A, it can be seen that a systematic error occurs at the X position of 5000 μm. If this systematic error is due to the ArF scanner when the wafer is rotated 180 °, it should appear rotated 180 °. However, as shown in FIG. 13B, since an error appears at the same position as 0 ° in FIG. 13A, this systematic error is a so-called TIS (tool induced shift) caused by the measuring instrument. It turns out that it is.

  As described above, when the pattern position accuracy of a wafer or a next-generation exposure mask manufactured from the wafer is measured by a coordinate measuring device, it is not easy to perform highly accurate position accuracy measurement equivalent to that of a photomask. However, since there is no method other than evaluating the resist pattern transferred on the wafer or the digging pattern obtained by etching it with a coordinate measuring instrument, it is desirable to establish a highly reliable measurement method. It is.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to easily grasp an error of a coordinate measuring instrument and to perform accurate calibration and a calibration method of the coordinate measurement accuracy and the calibration method. It is to provide a program that implements.

  Another object of the present invention is to provide a coordinate measurement accuracy evaluation method capable of easily and accurately evaluating the accuracy of a coordinate measuring instrument and a program for executing the evaluation method.

  Furthermore, another object of the present invention is to provide a mask capable of accurately performing coordinate measurement with a coordinate measuring instrument.

  In order to achieve the above object, the coordinate measurement accuracy calibration method according to the present invention includes a step of measuring the absolute positions of a plurality of marks formed on a measured object by a coordinate measuring instrument and a relative position between the marks. A step of measuring by an accuracy measuring device, a step of obtaining a relative position between the marks based on an absolute position of the mark, an actual value of the relative position between the marks measured by the overlay accuracy measuring device, Determining the consistency between the calculated relative position between the marks calculated based on the absolute position of the mark, and calibrating the coordinate measuring instrument when it is determined that there is no consistency A step of performing.

  In the coordinate measurement accuracy calibration method of the present invention described above, the overlay accuracy measuring device can measure only the relative position of the mark, but attention is paid to the high measurement reliability. Therefore, in the present invention, when determining the accuracy of the coordinate measuring device, the relative position between the marks is calculated based on the absolute position of the mark measured by the coordinate measuring device, and the calculated value and the overlay accuracy measuring device are calculated. The consistency with the actual measurement value measured by the method is determined. If the accuracy of the coordinate measuring machine is high, they should match. If it is determined that the results of the two are not consistent, the coordinate measuring device is calibrated so that the results are consistent.

  In order to achieve the above object, the coordinate measurement accuracy calibration method of the present invention includes a step of forming a plurality of first marks for coordinate measurement and a plurality of second marks for overlay accuracy measurement on a measurement object; Measuring the absolute position of the first mark with a coordinate measuring instrument, measuring the relative position of the second mark with an overlay accuracy measuring instrument to obtain an overlay error, and the first mark from a design value Calculating a first linear distortion and a first nonlinear distortion of the object to be measured based on the absolute position shift of the measurement object, and using the first linear distortion of the object to be measured, A step of obtaining a linear distortion-derived component due to the first linear distortion of the measured object, a step of subtracting the linear distortion-derived component from the overlay error to obtain a second nonlinear distortion of the measured object, Previous If it is determined that there is no the consistency and determining consistency between the first nonlinear distortion and the second non-linear distortion of the object to be measured, and a step of calibrating the coordinate measuring machine.

In the coordinate measurement accuracy calibration method of the present invention described above, the coordinate measuring instrument has low measurement accuracy of the non-linear distortion of the measured object, but can measure the linear distortion of the measured object almost accurately, while measuring the overlay accuracy. While the instrument can only measure the relative position of the mark, it pays attention to its high measurement reliability.
Therefore, in the present invention, the first linear distortion and the first nonlinear distortion of the measured object are calculated based on the deviation from the design value of the absolute position of the first mark measured by the coordinate measuring instrument, and the measured object Using the first linear distortion of the body, a linear distortion-derived component resulting from the first linear distortion of the measured object is obtained from the overlay error.
Then, the linear distortion-derived component is subtracted from the overlay error to obtain the second nonlinear distortion of the measured object, and the consistency between the first nonlinear distortion and the second nonlinear distortion of the measured object is determined. If the accuracy of the coordinate measuring machine is high, they should match. If it is determined that the results of the two are not consistent, the coordinate measuring device is calibrated so that the results are consistent.

  In order to achieve the above object, the coordinate measurement accuracy evaluation method of the present invention superimposes the step of measuring the absolute positions of a plurality of marks formed on a measured object with a coordinate measuring instrument and the relative positions between the marks. A step of measuring by an accuracy measuring device, a step of obtaining a relative position between the marks based on an absolute position of the mark, an actual value of the relative position between the marks measured by the overlay accuracy measuring device, Determining a consistency with a calculated value of a relative position between the marks calculated based on an absolute position of the mark.

  In the coordinate measurement accuracy evaluation method of the present invention described above, the overlay accuracy measuring device can measure only the relative position of the mark, but attention is paid to the high measurement reliability. Therefore, in the present invention, when determining the accuracy of the coordinate measuring device, the relative position between the marks is calculated based on the absolute position of the mark measured by the coordinate measuring device, and the calculated value and the overlay accuracy measuring device are calculated. The consistency with the actual measurement value measured by the method is determined. If the accuracy of the coordinate measuring machine is high, they should match.

  In order to achieve the above object, the coordinate measurement accuracy evaluation method of the present invention includes a step of forming a plurality of first marks for coordinate measurement and a plurality of second marks for overlay accuracy measurement on a measurement object; Measuring the absolute position of the first mark with a coordinate measuring instrument, measuring the relative position of the second mark with an overlay accuracy measuring instrument to obtain an overlay error, and the first mark from a design value Calculating a first linear distortion and a first nonlinear distortion of the object to be measured based on the absolute position shift of the measurement object, and using the first linear distortion of the object to be measured, A step of obtaining a linear distortion-derived component due to the first linear distortion of the measured object, a step of subtracting the linear distortion-derived component from the overlay error to obtain a second nonlinear distortion of the measured object, Previous And a determining consistency between the second nonlinear distortion and the first non-linear distortion of the object to be measured.

In the coordinate measurement accuracy evaluation method of the present invention described above, the coordinate measuring instrument has low measurement accuracy of the non-linear distortion of the measured object, but can measure the linear distortion of the measured object almost accurately, while measuring the overlay accuracy. While the instrument can only measure the relative position of the mark, it pays attention to its high measurement reliability.
Therefore, in the present invention, the first linear distortion and the first nonlinear distortion of the measured object are calculated based on the deviation from the design value of the absolute position of the first mark measured by the coordinate measuring instrument, and the measured object Using the first linear distortion of the body, a linear distortion-derived component resulting from the first linear distortion of the measured object is obtained from the overlay error.
Then, the linear distortion-derived component is subtracted from the overlay error to obtain the second nonlinear distortion of the measured object, and the consistency between the first nonlinear distortion and the second nonlinear distortion of the measured object is determined. If the accuracy of the coordinate measuring machine is high, they should match.

  In order to achieve the above object, the present invention relates to a measurement object in which a plurality of first marks for coordinate measurement and a plurality of second marks for overlay accuracy measurement are formed by a coordinate measuring instrument. An absolute position of one mark is measured, a relative accuracy of the second mark is measured by an overlay accuracy measuring device to obtain an overlay error, and based on the input absolute position of the first mark and the overlay error. A program for causing a computer to execute a correction process of a measurement value by the coordinate measuring device, and based on a deviation of the absolute position of the first mark from a design value, A step of calculating a first nonlinear distortion, and a step of obtaining a linear distortion-caused component resulting from the first linear distortion of the device under test from the overlay error using the first linear strain of the device under test. When, Subtracting the linear distortion-derived component from the registration error to obtain a second nonlinear distortion of the object to be measured; and measuring by a coordinate measuring device so that the first nonlinear distortion matches the second nonlinear distortion. And a step of setting a correction value to the value, and causing the computer to execute.

In the above-described present invention, the coordinate measuring instrument has low measurement accuracy of the non-linear distortion of the measured object, while the linear distortion of the measured object can be measured almost accurately, while the overlay measuring instrument can measure the relative position of the mark. Although it can only measure, it pays attention to the high reliability of measurement.
Therefore, in the program of the present invention, the first linear distortion and the first nonlinear distortion of the measured object are calculated based on the deviation from the design value of the absolute position of the first mark measured by the coordinate measuring instrument, Using the first linear distortion of the measured object, a process for obtaining a linear distortion-derived component resulting from the first linear distortion of the measured object among the overlay errors is executed.
Then, a process for determining the consistency between the first nonlinear distortion and the second nonlinear distortion of the measured object is obtained by subtracting the linear distortion-derived component from the overlay error to obtain the second nonlinear distortion of the measured object. Let If the accuracy of the coordinate measuring device is high, the two match each other. Therefore, a correction value is set to the measurement value obtained by the coordinate measuring device so that they match.

  In order to achieve the above object, the present invention relates to a measurement object in which a plurality of first marks for coordinate measurement and a plurality of second marks for overlay accuracy measurement are formed by a coordinate measuring instrument. An absolute position of one mark is measured, a relative accuracy of the second mark is measured by an overlay accuracy measuring device to obtain an overlay error, and based on the input absolute position of the first mark and the overlay error. A program for causing a computer to execute processing for evaluating the accuracy of the coordinate measuring instrument, wherein the first linear distortion of the object to be measured is determined based on a deviation of the absolute position of the first mark from a design value. A step of calculating a first nonlinear distortion, and a step of obtaining a linear distortion-caused component resulting from the first linear distortion of the device under test from the overlay error using the first linear strain of the device under test. And before Subtracting the linear distortion-derived component from an overlay error to obtain a second nonlinear distortion of the object to be measured; and determining whether the first nonlinear distortion and the second nonlinear distortion match. Are executed by a computer.

In the above-described present invention, the coordinate measuring instrument has low measurement accuracy of the non-linear distortion of the object to be measured, while the linear distortion of the object to be measured can be accurately measured, whereas the overlay measuring instrument can only measure the relative position of the mark. Although it cannot be measured, it pays attention to the high reliability of measurement.
Therefore, in the program of the present invention, the first linear distortion and the first nonlinear distortion of the measured object are calculated based on the deviation from the design value of the absolute position of the first mark measured by the coordinate measuring instrument, Using the first linear distortion of the measured object, a process for obtaining a linear distortion-derived component resulting from the first linear distortion of the measured object among the overlay errors is executed.
Then, a process for determining the consistency between the first nonlinear distortion and the second nonlinear distortion of the measured object is obtained by subtracting the linear distortion-derived component from the overlay error to obtain the second nonlinear distortion of the measured object. Let If the accuracy of the coordinate measuring machine is high, they should match.

  In order to achieve the above object, the mask of the present invention has a pattern forming film in which a pattern is formed by an opening, and a reinforcing portion that partitions the pattern forming film and reinforces the pattern forming film, A strain measurement mark that can measure an absolute position with a coordinate measuring device and a relative position with an overlay accuracy measuring device is formed on the reinforcing portion.

In the mask of the present invention described above, a strain measurement mark capable of measuring an absolute position with a coordinate measuring instrument and a relative position with an overlay accuracy measuring instrument is formed on the reinforcing portion.
Therefore, in the measurement of mask distortion, the absolute position of the distortion measurement mark is measured by a coordinate measuring instrument, and the relative position is measured by the overlay accuracy measuring instrument as verification of whether the absolute position measurement result is correct. The strain measurement mark is configured so that
That is, since the coordinate measuring device is calibrated based on the measurement result of the relative position by the overlay accuracy measuring device, a correct mask distortion measurement result can be obtained. By obtaining a correct measurement result of the mask distortion, the mask distortion can be corrected and exposed in the exposure using the mask, and the mask pattern is accurately exposed on the object to be exposed.

According to the coordinate measurement accuracy calibration method and the program for executing the calibration method of the present invention, the error of the coordinate measuring device can be easily grasped, and accurate calibration can be performed.
Moreover, according to the coordinate measurement accuracy evaluation method and the program for executing the evaluation method, the accuracy of the coordinate measuring device can be evaluated easily and accurately.
The coordinate measuring instrument calibrated as described above or evaluated to have good accuracy can accurately measure the transfer position accuracy by the exposure apparatus and the position accuracy of the pattern formed on the mask.
Furthermore, according to the mask of the present invention, coordinate measurement can be accurately performed by a coordinate measuring instrument. By obtaining an accurate coordinate measurement result, the mask distortion can be corrected and exposed in exposure using the mask. As a result, it is possible to realize a mask that can accurately expose the pattern onto the object to be exposed.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a flowchart showing a procedure of a coordinate measurement accuracy calibration method and a coordinate measurement accuracy evaluation method according to this embodiment. In the present embodiment, a wafer on which a mark is transferred by a mask is used as a measurement object for calibrating the coordinate measuring device.

(Step ST1)
First, in order to calibrate the coordinate measuring device, a mask for transferring a mark to a wafer is produced. A mask suitable for an exposure apparatus whose position accuracy is to be evaluated by a coordinate measuring device is used. For example, a photolithography stepper or scanner is a normal photomask in which a pattern is formed of chromium on a glass substrate. For EB transfer lithography such as EPL (electron-beam projection lithography) and LEEPL (low-energy electron-beam proximity-projection lithography), it is a stencil mask in which an opening pattern is formed in a thin film membrane. In the case of EUV lithography, a Mo / Si multilayer film is formed on a low expansion glass substrate similar to a photomask, and a pattern is formed thereon by an EUV light absorber. The present invention can also be applied to laser direct drawing and EB direct drawing that do not use a mask.

  There are two mask configurations. FIG. 2A is a schematic configuration diagram of a first type mask. As shown in FIG. 2A, in the first type mask M, a plurality of coordinate measurement marks (first marks) 11 are arranged at the mask central portion, and an overlay accuracy measurement mark ( The second mark) is arranged. The mask M shown in FIG. 2A corresponds to the size of one chip, for example. The overlay accuracy measurement mark includes a main scale 21 arranged along two sides of the mask peripheral part and a vernier 22 arranged along the other two sides of the mask peripheral part. For example, 100 to 200 coordinate measuring marks 11 are arranged in the center of the mask. As shown in FIG. 2B, by repeatedly exposing this single mask M onto the wafer W, the main scale 21 and the sub-scale 22 are transferred on the wafer in an overlapping manner.

  3A and 3B are diagrams for explaining a second type mask using two masks. FIG. 3A shows the first mask M1, and FIG. 3B shows the second mask M2. is there. As shown in FIG. 3, an overlay accuracy measurement mark main ruler 21 is arranged on the first mask M1, and an overlay accuracy measurement mark auxiliary ruler 22 is placed on the second mask M2. It is arranged. Masks M1 and M2 shown in FIGS. 3A and 3B are examples corresponding to four chip sizes, respectively. By sequentially exposing with these two masks, the main scale 21 and the sub-scale 22 are transferred in an overlapping manner on the wafer.

(Step ST2)
Next, the mask mark manufactured in step ST1 is exposed on the wafer by an exposure apparatus whose position accuracy is to be evaluated.

  When the mark is transferred onto the wafer with the first type mask M, the coordinate measurement mark 11 is transferred to the center of each chip J as shown in FIG. The alignment mark main scale 21 and sub-scale 22 are transferred in an overlapping manner. However, the main scale 21 and the sub-scale 22 belong to two adjacent chips J. In the case of EB direct drawing, the chip width may be designed to match the field width of EB deflection, and the main scale 21 and the sub-scale 22 at the boundary may be drawn in separate fields.

  On the other hand, when the two masks M1 and M2 of the second type shown in FIG. 3 are sequentially exposed, the main scale 21 and the sub-scale 22 overlap on the wafer. Also in this method, as in the case shown in FIG. 2B, the main mark 21 and the sub-scale 22 of the overlay mark are transferred in an overlapping manner at the chip boundary portion. In the case of EB direct drawing, two pieces of data may be separately exposed twice.

(Step ST3)
When a resist pattern is formed by developing after exposure in step ST2, and a mark is transferred using a single mask shown in FIG. 2A to a wafer etched using the resist pattern The position of the coordinate measurement mark at the center of each chip of the wafer W is measured with a coordinate measuring device. When the mark is transferred using the two masks M1 and M2 shown in FIG. 3, the position of at least one of the overlapping main measure 21 and sub measure 22 is measured by a coordinate measuring instrument. The reliability of the coordinate measuring device is verified using this data.

(Step ST4)
The relative position of the main scale 21 and the vernier 22 is measured by an overlay accuracy measuring instrument. Unlike the coordinate measuring instrument that measures the absolute position of the mark with respect to the stage coordinate system of the apparatus, the overlay accuracy measuring instrument measures only the relative position of the main scale 21 and the sub-scale 22 that are close to each other. Hard to be affected by deformation, its reliability is extremely high. This overlay accuracy measurement data is used to verify the reliability of the coordinate measuring instrument.

(Step ST5)
From the data obtained in steps ST3 and ST4, the reliability of the coordinate measuring device is verified by data processing as described below. FIG. 4 is a diagram for explaining the relationship between the measurement data obtained by the coordinate measuring device and the measurement data obtained by the overlay accuracy measuring device.

As shown in FIG. 4, the absolute positions R _in and R _out measured by the coordinate measuring instrument with respect to a set of main scale 21 and sub scale 22 existing at the boundary between adjacent chips J and J + 1, and overlay accuracy If the measurement by the coordinate measuring device is correct, the relationship R _OL = R _in −R _out should be established between the relative position R _OL measured by the measuring device. In FIG. 4, dotted lines indicate a case where the chips J and J + 1 are ideal lattices, and a solid line indicates a case where the chips J and J + 1 are distorted. As shown in FIG. 4, when there is no distortion, the central coordinates of the main scale 21 and the sub-scale 22 are the same and R _OL = 0, but when there is distortion, the main scale 21 ′. And the coordinates of the center of the vernier 22 'do not match and R _OL = 0.

  In this embodiment, the coordinate measuring instrument has low measurement accuracy of the nonlinear distortion of the chip, but the linear distortion of the chip can be measured almost accurately. On the other hand, the overlay measuring instrument can only measure the relative position of the main scale and the vernier scale. Although it cannot be measured, it pays attention to the high reliability of the measurement and evaluates the accuracy of the coordinate measuring instrument as follows.

In the broadest sense, it is calculated based on the actual measurement value R _OL of the relative position (overlay error) between the main scale 21 and the sub-scale 22 measured by the overlay accuracy measuring instrument and the absolute position of the mark by the coordinate measuring instrument. The accuracy of the coordinate measuring device can be evaluated by determining the consistency of the R _in −R _out values (overlay error).

  However, as described above, if it is assumed that the coordinate measuring instrument can accurately measure the linear distortion of the chip, the nonlinear distortion of the chip is determined based on the absolute coordinates of the mark measured by the coordinate measuring instrument. And the consistency between the nonlinear distortion of the chip and the nonlinear distortion extracted from the overlay error measured by the overlay accuracy measuring device may be evaluated.

  Therefore, in the present embodiment, the following data processing is performed. FIG. 5 is a detailed flowchart of the data processing in step ST5 of FIG.

  First, the first linear distortion and the first nonlinear distortion of the chip are calculated based on the deviation from the ideal position of the coordinate measuring mark whose position is measured by the coordinate measuring instrument (step ST11).

When attention is paid to a certain chip on the wafer, the displacement ΔR (dX, dY) from the ideal position R (X ₀ , Y ₀ ) of the coordinate measurement mark in the chip is as follows. It can be represented by the sum of the distortion and the first nonlinear distortion.

Here, (μ _{X ,} μ _Y ) is a magnification change in the X / Y direction, and θ and ψ represent the rotation and non-orthogonality of the chip. (T _X , T _Y ) represents the translation error (shift) of the chip. These parameters give the first linear distortion (L _X , L _Y ) of the chip. On the other hand, the first nonlinear distortion (σ _X , σ _Y ) is a residual term that cannot be fitted with the matrix of the above equation.

  In step ST11, the first linear distortion and the first nonlinear distortion of each chip are obtained by fitting the above equation to the absolute coordinates of the coordinate measurement mark measured by the coordinate measuring instrument. In the present embodiment, the reliability of the coordinate measuring device is verified by verifying whether the value of the first nonlinear distortion obtained here is valid.

  Next, using the first linear distortion described above, a linear distortion-derived component resulting from the first linear distortion of the chip is obtained from the overlay error of the main scale 21 and the sub-scale 22 measured by the overlay accuracy measuring instrument. (Step ST12).

When the first type mask is used, the relative position R _OL = (X _OL , Y _OL ) of the main scale and the sub-scale at the chip boundary by the overlay accuracy measuring instrument is the difference between the absolute coordinates, Using equation (1), it is given as follows.

  In the above equation (2), the first term is a linear distortion-induced component of the overlay error, which is the difference between the first linear distortions at the boundary between adjacent chips J and J + 1. The second term is a non-linear distortion-induced component of the overlay error, which is a difference between the first non-linear distortions of the adjacent chips J and J + 1. In step ST12, the first term of the above equation (2) is calculated from the first linear distortion of each adjacent chip measured by the coordinate measuring device.

  Then, when the calculated value of the first term is subtracted from the overlay error, the second term of the above equation, that is, the nonlinear distortion-caused component (nonlinear distortion difference) of the overlay error is obtained (step ST13). The standard deviation of the difference in nonlinear distortion is √2 times the standard deviation of nonlinear distortion. Therefore, the obtained standard deviation is divided by {square root over (2)} and converted into a standard deviation of nonlinear distortion (referred to as second nonlinear distortion) (step ST14).

(Step ST6)
In step ST6 of FIG. 1, the standard deviation of the second nonlinear distortion extracted from the overlay error measured by the overlay accuracy measuring instrument and the standard deviation of the first nonlinear distortion obtained from the measurement data of the coordinate measuring instrument are calculated. By comparing, the reliability of the coordinate measuring instrument is verified. That is, the coordinate measuring instrument is reliable if the two substantially match each other and needs to be calibrated if they are separated by a predetermined value or more. In addition, the above-described data processing is performed on the assumption that the linear distortion of the chip measured by the coordinate measuring instrument is accurate, but as a confirmation of whether this linear distortion can be measured accurately, the coordinate measuring instrument It is confirmed that there is no correlation between the obtained linear distortion-derived component of the first term of the above formula (2) and the non-linear distortion-derived component of the second term after subtracting this. This is because most nonlinear distortions are randomly generated errors, which should not correlate with linear errors. Finally, this is confirmed, and if there is no correlation, the coordinate measuring instrument is considered to be reliable.

(Step ST7)
If the reliability of the coordinate measuring device cannot be obtained in step ST6, it is considered that there are problems in the temperature management of the coordinate measuring device, the wafer holder, the stage accuracy, the wafer backside foreign matter, and the like. Therefore, as one method for calibrating the coordinate measuring device, the temperature management of the coordinate measuring device, optimization of the suction force / flatness of the wafer holder, stage accuracy, removal of foreign matter adhering to the back surface of the wafer, etc. are performed. . If the coordinate measuring instrument is improved, the process returns to step ST3 to verify the reliability. Steps ST3 to ST7 described above are continued until the reliability can be confirmed.

  As another method of calibrating the coordinate measuring device, the above-described improvement is not performed, and a correction value for a systematic error depending on the position on the wafer is given to the coordinate measuring device so as to achieve consistency in step ST6. After setting the correction value, the process returns to step ST3 to verify the reliability. Steps ST3 to ST7 described above are continued until the reliability can be confirmed. In the specification of the present application, the calibration of the coordinate measuring instrument is to improve the temperature management and stage accuracy as described above so that reliability can be obtained, and to correct the measurement value by setting a correction value without improving them. To include.

  The coordinate measurement accuracy calibration method and the evaluation method according to the present embodiment are realized by causing a computer to execute a program in which a data processing procedure for performing steps ST5 and ST6 of FIG. 1 described above is written.

FIG. 6 is a diagram for explaining an example of an apparatus configuration for evaluating and calibrating the coordinate measurement accuracy by reading the program according to the present embodiment.
As shown in FIG. 6, the above coordinate measurement accuracy evaluation and calibration method can be performed by the data processing device 3 connected to the coordinate measurement device 1 and the overlay accuracy measurement device 2. In the data processing device 3, the built-in CPU 5 performs the above-described data processing on the measurement data from the coordinate measuring instrument 1 and the measurement data from the overlay accuracy measuring instrument 2 based on the program 4 according to the present embodiment. And the accuracy of the coordinate measuring instrument 1 is evaluated. In the apparatus configuration, when it is determined by the data processing apparatus 3 that the coordinate measuring instrument is not reliable, the coordinate measuring instrument is improved.

FIG. 7 is a diagram for explaining another example of an apparatus configuration for evaluating and calibrating the coordinate measurement accuracy by reading the program according to the present embodiment.
In the example shown in FIG. 7, the CPU 5 in the coordinate measuring instrument 1 performs calibration by evaluating measurement data and setting correction values based on the program 4. In the example shown in FIG. 7, the overlay accuracy measurement data D previously measured using the overlay accuracy measuring device is provided, and the above-described data processing is performed on the measurement data by the coordinate measuring device 1 to perform the overlay accuracy measurement data D. The CPU 5 sets a correction value for correcting the systematic error for each wafer position.

  Hereinafter, the present invention will be described with reference to more detailed examples. The present invention is not limited to the following examples.

(Example)
The accuracy of the wafer coordinate measuring device was evaluated using the photomask shown in FIG. The exposure area of the photomask is a 22.5 mm square corresponding to one chip, and the main scale 21 is arranged on the left side and the lower side, and the sub-scale 22 is arranged on the upper side and the right side. In addition, a coordinate measurement mark 11 is arranged at the center of the chip. The main scale 21 is a square of 6 μm square, and the sub-scale 22 has a box shape surrounding it. This photomask was mounted on an ASMF ArF scanner PASS5500 / 1100, and the pattern was transferred to a 200 mm silicon wafer coated with resist ZEP520 (thickness 50 nm). The transferred wafer was developed with a coating and developing machine MARK8 manufactured by Tokyo Electron, and a resist pattern was formed. Using this pattern as a mask, the silicon wafer was etched to process the coordinate measurement mark and the overlay accuracy measurement mark.

  The coordinates of the coordinate measurement mark at the center of the chip were measured with a coordinate measuring instrument LMS IPRO manufactured by Leica. The wafer was vacuum-sucked by a special holder and automatically transferred to a measurement chamber maintained at 23 ° C. The stage moves to the mark position registered in advance in the measurement recipe, and the optical image of the mark is read by the CCD camera. The coordinates of the coordinate measurement mark are measured by a highly accurate laser interferometer installed on the stage system.

  FIG. 8A is a diagram showing measurement data of a coordinate measurement mark measured by a coordinate measuring device, and FIG. 8B is measurement data after the magnification correction of the entire wafer. In order to correct the magnification error caused by the change in the wafer temperature during exposure and the wafer temperature in the coordinate measuring instrument, the magnification was corrected by -3.2 ppm in FIG. 8B.

  The coordinate measurement data was separated into the first linear distortion and the first nonlinear distortion by fitting the above equation (1) to the data of FIG. 8B. FIG. 9A is a diagram showing the first linear distortion of the coordinate measurement data thus separated, and FIG. 9B is a diagram showing the first nonlinear distortion of the coordinate measurement data. Thereafter, the reliability of the coordinate measuring device is confirmed by verifying the validity of the first nonlinear distortion shown in FIG.

  Next, the chip boundary overlay accuracy was measured. The apparatus used was Hitachi LA3200. FIG. 10A is a diagram showing overlay accuracy measurement data obtained by the overlay accuracy measuring instrument. In addition, the linear distortion-derived component of the chip boundary overlay accuracy was calculated from the linear distortion coefficients (shift, magnification, non-orthogonality) of each chip obtained when separating the measurement data of the coordinate measuring device. FIG. 10B is a diagram showing a linear distortion-derived component with superimposition accuracy obtained in this way.

  From the data shown in FIG. 10 (a) and the data shown in FIG. 10 (b), the above-described equation (2) is used to calculate the nonlinear distortion-derived component, and its standard deviation is divided by √2 to calculate the nonlinear distortion standard. Converted to deviation. FIG. 11 is a diagram illustrating the nonlinear distortion-derived component with the obtained overlay accuracy. In the results shown in FIG. 11, the standard deviation of the non-linear distortion was 16.6 nm in the X direction and 12.4 nm in the Y direction. On the other hand, the values calculated only from the coordinate measuring instrument were 16.4 nm in the X direction and 12.6 nm in the Y direction (see FIG. 9B).

  From this, it seems that the agreement between the two is good, and the reliability of the coordinate measuring machine has been verified. However, as described later, it is necessary not only to match the standard deviation values but also to confirm that the correlation between the linear distortion-derived component and the nonlinear distortion-derived component of the overlay accuracy measurement data is low. This is because most nonlinear distortions are randomly generated errors, which should not correlate with linear errors. In order to confirm this, when the correlation between the data shown in FIG. 10B and the data shown in FIG. 11 was calculated, the correlation coefficient was 0.92, and the nonlinear distortion-derived component shown in FIG. Is low. That is, the coordinate measuring instrument used this time cannot measure the linear distortion accurately. Possible causes include temperature change and wafer deformation due to chucking. For this reason, it is necessary to calibrate the coordinate measuring instrument by improving the wafer holder of the coordinate measuring instrument.

As described above, according to the present embodiment, the measured value R _OL of the relative position (superposition error) between the main measure 21 and the sub measure 22 measured by the overlay accuracy measuring instrument, and the mark measured by the coordinate measuring instrument. By determining the consistency of the R _in -R _out value (superposition error) calculated based on the absolute position, the accuracy of the coordinate measuring instrument can be easily evaluated.

  In a more detailed method, assuming that the coordinate measuring instrument can accurately measure the linear distortion of the chip, the nonlinear distortion of the chip is calculated based on the absolute coordinates of the mark measured by the coordinate measuring instrument. By extracting and determining the consistency between the nonlinear distortion of the chip and the nonlinear distortion extracted from the overlay error measured by the overlay accuracy measuring instrument, the accuracy of the coordinate measuring instrument can be easily and accurately evaluated.

  Then, the coordinate measuring instrument can be calibrated accurately by improving the coordinate measuring instrument so as to achieve the above-mentioned consistency or by setting a correction value for each wafer position so as to correct the systematic error. Can do.

  The coordinate measuring instrument calibrated as described above or evaluated to have good accuracy can accurately measure the transfer position accuracy by the exposure apparatus and the position accuracy of the pattern formed on the mask.

(Second Embodiment)
The coordinate measurement by the coordinate measuring device is used not only for measuring a wafer but also for measuring the positional distortion of a mask manufactured on the basis of a silicon wafer such as EPL and LEEPL.

  As a method for transferring a mask pattern used in LEEPL or EPL to a wafer with high accuracy, it is conceivable to measure the distortion of the mask and correct it at the time of transfer. In lithography using charged particles such as LEEPL and EPL, incident particles can be deflected with high accuracy and high speed by an electrostatic / magnetic field lens, and it is considered that more advanced correction can be performed. In the case of LEEPL, the main deflection lens scans the EB over the mask area, but the mask distortion can be corrected by changing the incident angle of the EB in real time using the sub deflection lens.

  In order to correct the mask distortion in this way, it is important to first accurately measure the mask distortion. FIG. 12 is a diagram showing a configuration of a mask according to the present embodiment that is preferably used in the coordinate measurement accuracy calibration method according to the first embodiment and can accurately measure the mask distortion. The mask shown in FIG. 12 is used for LEEPL and EPL.

  As shown in FIG. 12, the mask according to this embodiment is divided into membranes 31 of small sections (typically about 1 mm square). For example, in LEEPL, an opening pattern corresponding to a device pattern is formed in a membrane 31 having a thickness of several hundred nm. In order to prevent the mask pattern from being distorted by its own weight when the membrane is enlarged and the mask pattern being distorted by internal stress, the membrane 31 in a small section is reinforced by a thick film beam 32.

  In the present embodiment, a plurality of overlay accuracy measurement marks (distortion measurement marks) formed by double exposure are formed on the beams 32 between the membranes 31 unlike the normal coordinate measurement marks. The overlay accuracy measurement mark is configured with a main scale 33 and a vernier 34 as a pair. Since the mark on the beam 32 is not transferred onto the wafer, the number of measurement points can be increased and the strain measurement accuracy can be improved.

  Then, by measuring the coordinates of the main scale 33 with the coordinate measuring instrument and simultaneously measuring the relative position of the main scale 33 and the vernier 34 with the overlay accuracy measuring instrument, the coordinate measurement is performed by the method described in the first embodiment. The instrument can be calibrated. Thereby, the distortion of the mask can be accurately measured, and the accuracy of distortion correction is improved.

  On the other hand, when a conventional coordinate measurement mark is arranged on the beam 32, when the absolute position of the coordinate measurement mark formed on the beam 32 is measured by the coordinate measurement device, the coordinate measurement mark is used. An error occurs and the mask distortion cannot be measured accurately.

The present invention is not limited to the description of the above embodiment.
For example, the measurement object used in the coordinate measurement accuracy evaluation method and the coordinate measurement accuracy calibration method according to the present embodiment is not limited to a wafer or a mask manufactured from the wafer, but also has a large thermal expansion coefficient and rigidity. Low ones can also be suitably used. In addition, the coordinate measuring device may have a function as an overlay accuracy measuring device. In this case, verification of the measurement data measured by the coordinate measuring function is performed using the overlay accuracy measuring function. The alignment accuracy measurement data can be used by the same method as in this embodiment.
In addition, various modifications can be made without departing from the scope of the present invention.

It is a flowchart which shows the procedure of the coordinate measurement accuracy calibration method and coordinate measurement accuracy evaluation method which concern on this embodiment. (A) is a schematic block diagram of a 1st type mask, (b) is a schematic block diagram of the wafer transferred by repeatedly exposing the mask of (a) to a wafer. It is a figure for demonstrating the 2nd type mask which uses two masks, (a) is a 1st mask, (b) is a figure which shows a 2nd mask. It is a figure for demonstrating the relationship between the measurement data by a coordinate measuring device, and the measurement data by an overlay accuracy measuring device. It is a detailed flowchart of the data processing in step ST5 of FIG. It is a figure for demonstrating an example of the apparatus structure for evaluating and calibrating a coordinate measurement precision by the program concerning this embodiment being read. It is a figure for demonstrating the other example of the apparatus structure for evaluating and calibrating a coordinate measurement precision by the program which concerns on this embodiment being read. (A) is a figure which shows the measurement data of the mark for coordinate measurements measured with the coordinate measuring device, (b) is the measurement data after the magnification correction of the whole wafer. (A) is a figure which shows the 1st linear distortion of coordinate measurement data, (b) is a figure which shows the 1st nonlinear distortion of coordinate measurement data. (A) is a figure which shows the overlay precision measurement data by an overlay precision measuring device, (b) is a figure which shows the linear distortion origin component of overlay precision measurement data. It is a figure which shows the nonlinear distortion origin component of overlay accuracy measurement data. It is a figure which shows the structure of the mask which concerns on this embodiment. It is a figure for demonstrating the system | strain error of a coordinate measuring device, (a) shows the measurement result of wafer orientation 0 degree, (b) shows the measurement result of wafer orientation 180 degrees.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Coordinate measuring device, 2 ... Overlay accuracy measuring device, 3 ... Data processing device, 4 ... Program, 5 ... CPU, 11 ... Coordinate measuring mark, 21 ... Main scale, 22 ... Sub-scale, 31 ... Membrane, 32 ... Beam part, 33 ... Main scale, 34 ... Sub-scale, D ... Overlay accuracy measurement data, M ... Mask, M1 ... First mask, M2 ... Second mask

Claims (11)

Measuring absolute positions of a plurality of marks formed on the measurement object with a coordinate measuring instrument;
Measuring a relative position between the marks with an overlay accuracy measuring instrument;
Obtaining a relative position between the marks based on the absolute position of the marks;
The consistency between the measured value of the relative position between the marks measured by the overlay accuracy measuring instrument and the calculated value of the relative position between the marks calculated based on the absolute position of the mark is determined. Steps,
A coordinate measurement accuracy calibration method comprising: calibrating the coordinate measuring device when it is determined that the consistency is not obtained. Forming a plurality of first marks for measuring coordinates on a measurement object and a plurality of second marks for measuring overlay accuracy;
Measuring the absolute position of the first mark with a coordinate measuring instrument;
Measuring a relative position of the second mark with an overlay accuracy measuring instrument to obtain an overlay error;
Calculating a first linear distortion and a first nonlinear distortion of the measured object based on a deviation of the absolute position of the first mark from a design value;
Using the first linear strain of the device under test to determine a linear strain-caused component due to the first linear strain of the device under test of the overlay error;
Subtracting the linear distortion-derived component from the overlay error to obtain a second nonlinear distortion of the measured object;
Determining the consistency between the first nonlinear distortion and the second nonlinear distortion of the object to be measured, and calibrating the coordinate measuring instrument when it is determined that the consistency is not present. Coordinate measurement accuracy calibration method. If it is determined that there is consistency, after determining the consistency,
Determining whether there is a correlation between the second nonlinear distortion and the first linear distortion;
The coordinate measurement accuracy calibration method according to claim 2, further comprising a step of calibrating the coordinate measuring device when it is determined that the correlation exists. In the step of obtaining the second nonlinear distortion of the measured object, the nonlinear distortion-derived component of the overlay error is obtained by subtracting the linear distortion-derived component from the overlay error, and the nonlinear distortion-derived component is determined as The coordinate measurement accuracy calibration method according to claim 2, wherein the coordinate measurement accuracy is converted into non-linear distortion. The coordinate measurement accuracy calibration method according to claim 2, wherein the first mark is selected from a plurality of the second marks. Measuring absolute positions of a plurality of marks formed on the measurement object with a coordinate measuring instrument;
Measuring a relative position between the marks with an overlay accuracy measuring instrument;
Obtaining a relative position between the marks based on the absolute position of the marks;
The consistency between the measured value of the relative position between the marks measured by the overlay accuracy measuring instrument and the calculated value of the relative position between the marks calculated based on the absolute position of the mark is determined. A coordinate measurement accuracy evaluation method comprising: Forming a plurality of first marks for measuring coordinates on a measurement object and a plurality of second marks for measuring overlay accuracy;
Measuring the absolute position of the first mark with a coordinate measuring instrument;
Measuring a relative position of the second mark with an overlay accuracy measuring instrument to obtain an overlay error;
Calculating a first linear distortion and a first nonlinear distortion of the measured object based on a deviation of the absolute position of the first mark from a design value;
Using the first linear strain of the device under test to determine a linear strain-caused component due to the first linear strain of the device under test of the overlay error;
Subtracting the linear distortion-derived component from the overlay error to obtain a second nonlinear distortion of the measured object;
A coordinate measurement accuracy evaluation method comprising: determining consistency between the first nonlinear strain and the second nonlinear strain of the measured object. If it is determined that there is consistency, after determining the consistency,
The coordinate measurement accuracy evaluation method according to claim 7, further comprising a step of determining whether or not there is a correlation between the second nonlinear distortion and the first linear distortion. An absolute position of the first mark is measured by a coordinate measuring instrument on a measurement object on which a plurality of first marks for coordinate measurement and a plurality of second marks for overlay accuracy measurement are formed. The relative position of the second mark is measured by a measuring device to obtain an overlay error, and based on the input absolute position of the first mark and the overlay error, the measured value is corrected by the coordinate measuring device. A program for causing a computer to execute
Calculating a first linear distortion and a first nonlinear distortion of the measured object based on a deviation of the absolute position of the first mark from a design value;
Using the first linear strain of the device under test to determine a linear strain-caused component due to the first linear strain of the device under test of the overlay error;
Subtracting the linear distortion-derived component from the overlay error to obtain a second nonlinear distortion of the measured object;
A program for causing a computer to execute a step of setting a correction value to a measurement value by a coordinate measuring device so that the first nonlinear distortion matches the second nonlinear distortion. An absolute position of the first mark is measured by a coordinate measuring instrument on a measurement object on which a plurality of first marks for coordinate measurement and a plurality of second marks for overlay accuracy measurement are formed. A process of measuring the relative position of the second mark by a measuring device to obtain an overlay error, and evaluating the accuracy of the coordinate measuring device based on the input absolute position of the first mark and the overlay error A program for causing a computer to execute
Calculating a first linear distortion and a first nonlinear distortion of the measured object based on a deviation of the absolute position of the first mark from a design value;
Using the first linear strain of the device under test to determine a linear strain-caused component due to the first linear strain of the device under test of the overlay error;
Subtracting the linear distortion-derived component from the overlay error to obtain a second nonlinear distortion of the measured object;
A program for causing a computer to execute a step of determining whether or not the first nonlinear distortion and the second nonlinear distortion match. A pattern forming film in which a pattern is formed by an opening;
A reinforcing portion that partitions the pattern forming film and reinforces the pattern forming film;
Have
A mask in which a strain measurement mark is formed on the reinforcing portion so that the absolute position can be measured by a coordinate measuring instrument and the relative position can be measured by an overlay accuracy measuring instrument.

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