JP4112759B2 - Pattern measurement method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a transfer pattern measurement method in a lithography process, and more particularly to a pattern measurement method for examining aberrations of an optical system of an exposure apparatus.
[0002]
[Prior art]
In recent years, in an exposure apparatus that reduces and transfers a pattern formed on a mask onto a wafer, a phenomenon occurs in which a specific pattern is transferred asymmetrically as the LSI device pattern becomes finer. This phenomenon is considered to be mainly due to lens aberration, and therefore a technique for measuring lens aberration is required.
[0003]
2. Description of the Related Art Conventionally, a method for measuring an optical system of an exposure apparatus by measuring a relative positional deviation amount between a reference pattern and a pattern to be measured consisting of a set of a plurality of patterns is known. At this time, in order to accurately obtain the aberration function on the pupil plane of the optical system, it is necessary to use a diffraction grating in which the pattern to be measured continues indefinitely, but this is substantially impossible. For this reason, the pattern to be measured consisting of a plurality of repetitions of the same pattern as the reference pattern is transferred onto the wafer in the first exposure so that it can be regarded as virtually infinite, and then the repeated portion of the pattern to be measured The first and last patterns are erased by the second exposure so that only the inner repeat part remains finally.
[0004]
In this way, the relative position between the reference pattern and the pattern to be measured that is repeated substantially infinitely can be measured. The range in which the first and last patterns of the repeated portion are erased may be one at each end or plural. The size of the pattern to be measured is in the vicinity of the resolution limit of the exposure apparatus, and there have been cases where it is less than ¼ micron with the recent miniaturization of devices.
[0005]
By the way, an optical misalignment inspection apparatus is used for measuring the relative position of this type of pattern, and the resolution of the inspection apparatus is about 1 μm at most. For this reason, when obtaining the position of the pattern to be measured, the position of the pattern set is obtained instead of obtaining the position of each pattern. In order to make a repeated pattern that repeats substantially infinitely as described above, the second exposure must be performed to erase the patterns at both ends. The measuring device measures the position of each pattern to be measured. This is because it does not have as much resolving power as possible.
[0006]
Further, since the measuring apparatus does not have a high resolving power, it is necessary to make the monitor pattern composed of the reference pattern and the pattern to be measured relatively large. The occupied area of the monitor pattern actually used is about 10 to 30 μm square, and cannot be said to be sufficiently small.
[0007]
[Problems to be solved by the invention]
As described above, in the conventional technique, if the aberration function of the optical system in the exposure apparatus is to be obtained with high accuracy, the pattern to be measured cannot be formed by one exposure, and two exposures are necessary. It took. Further, since the area occupied by the pattern to be measured is large, it is difficult to introduce a pattern used for measurement of an optical system as a process inspection pattern in the device manufacturing process.
[0008]
The present invention has been made in consideration of the above circumstances, and the object of the present invention is to form a pattern to be measured with a single exposure and to achieve high accuracy even if the area occupied by the pattern for measurement is reduced. An object of the present invention is to provide a pattern measurement method that can perform measurement and is suitable for measuring an aberration function of an optical system in an exposure apparatus.
[0009]
[Means for Solving the Problems]
(Constitution)
In order to solve the above problems, the present invention adopts the following configuration.
[0010]
That is, the present invention is a pattern measuring method for measuring the relative position between a reference pattern and a pattern to be measured, and the pattern to be measured is composed of a repetitive pattern of a predetermined period, and the line width is larger than this pattern for measurement A step of transferring each of the patterns onto the sample using a projection exposure apparatus using a mask having a reference pattern, and transferring the pattern to each of the patterns formed on the sample by the transfer Measuring the center position of the reference pattern on the sample and the center position of the pattern to be measured using a measuring instrument having a measurement light source or a charged beam source having a wavelength shorter than the exposure wavelength of that is to include a step of measuring the center position of the pattern except the first and last part of the repetition, and a step of obtaining a shift amount of each center position that is the measuring And butterflies.
[0011]
Here, preferred embodiments of the present invention include the following.
[0012]
(1) The mask reference pattern should be arranged symmetrically with respect to the pattern to be measured, or symmetrical with respect to the pattern to be measured.
[0013]
(2) The pattern to be measured on the mask should be formed to imitate a pattern equivalent to the actual circuit pattern to be formed on the sample.
[0014]
(3) To measure the relative position between the reference pattern and the pattern to be measured, use a measuring device (such as SEM) having a charged beam source.
[0015]
(4) A plurality of sets of reference patterns and patterns to be measured are prepared, each set is rotated with respect to each other, and the rotation angle is a value obtained by dividing 360 degrees by an integer.
[0016]
(Function)
According to the present invention, by measuring the relative positional deviation amount between the reference pattern and the pattern to be measured, it is possible to investigate the influence of the aberration or the like on the pattern of the projection optical system. In this case, in order to measure the position of the reference pattern and the pattern to be measured using a measuring device having a measurement light source or a charged beam source having a wavelength shorter than the exposure wavelength, one of the patterns to be measured having a fine pitch 1 The book can be resolved. Therefore, it is possible to perform measurement in a state in which these patterns are optically removed without physically removing the first and last portions of the pattern to be measured, that is, the pattern of the end portion with low dimensional accuracy. it can.
[0017]
Therefore, the position of the pattern to be measured formed by one exposure can be measured with high accuracy, and can be effectively applied to the measurement of the aberration function of the optical system in the exposure apparatus. It becomes possible. In addition, since the measuring instrument has a high resolving power, the area occupied by the pattern to be measured can be reduced, and this can be introduced as a process inspection pattern in the device manufacturing process.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The details of the present invention will be described below with reference to the illustrated embodiments.
[0019]
(First embodiment)
First, as shown in FIG. 1, a mask on which a reference pattern 11 and a measurement pattern 12 are formed is prepared. Here, each of the patterns 11 and 12 is, for example, a light shielding film pattern formed on a transparent substrate. The pattern 12 to be measured is a repeated pattern, and the reference pattern 11 and the pattern 12 to be measured are both arranged in line symmetry. Therefore, the measurement pattern 12 may be arranged on both sides of the reference pattern 11, or the measurement pattern 12 may be sandwiched between the reference patterns 11.
[0020]
The reference pattern 11 includes line patterns 11a and 11b arranged in line symmetry in the X direction with respect to the center point 10, and line patterns 11c and 11d arranged in line symmetry in the Y direction with respect to the center point 10. Each line pattern has a relatively large size (about 1.5 μm in terms of wafer).
[0021]
The pattern 12 to be measured has a large number of line patterns (six for simplicity in the figure) arranged in line with the center point 10 in the X direction, and a line in the Y direction with respect to the center point 10. It consists of a large number of symmetrically arranged line patterns (six lines are shown in the figure for simplicity). Each line pattern is about 0.2 to 0.3 μm in terms of the wafer.
[0022]
Note that the pattern 12 to be measured is obtained by combining the line patterns having the same period as described above, and as a result, a plurality of rectangular annular patterns (six for simplicity in the figure) 12a around the center point 10 are formed. ~ 12f are periodically arranged. The reference pattern 11 surrounds the pattern 12 to be measured from approximately four directions.
[0023]
The mask configured as described above is set in the exposure apparatus, and each pattern of the mask is transferred to the resist on the wafer. Further, development processing is performed to obtain a resist pattern. When the resist on the wafer is a positive type, a reduced image of each of the patterns 11 and 12 formed with a light shielding film on the mask remains as a resist pattern. And it measures with respect to the obtained resist pattern.
[0024]
For measuring the relative position between the reference pattern and the pattern to be measured, a light source having a wavelength shorter than the exposure wavelength is used as a measurement light source. Alternatively, a high-resolution measuring device such as a scanning electron microscope (SEM) using an electron beam is used. That is, a measuring apparatus that can sufficiently resolve each pattern to be measured is used.
[0025]
In this pattern measurement, the center position of the reference pattern on the wafer and the center position of the pattern to be measured are measured, and the relative positions thereof are obtained. At this time, among the repetitive patterns of the pattern to be measured, since the periodicity of the repetition is lost at the beginning and end of the repetition, that portion is not considered when measuring the position of the pattern to be measured. Find the position of the pattern.
[0026]
Specifically, as shown in FIG. 2, with respect to the resist pattern formed on the wafer, an intermediate point Ac between the center positions of the two reference patterns A1 and A2 is obtained and set as the center position of the reference pattern. As the position of the pattern to be measured, the position C of the pattern to be measured is obtained from the average center position of the plurality of patterns to be measured, and the midpoint is obtained as the center position of the pattern to be measured. The relative displacement between the center position of the reference pattern and the center position of the pattern to be measured is not zero after being transferred through the projection optical system. By measuring the amount of deviation, it is possible to measure the influence of aberration or the like on the pattern of the projection optical system.
[0027]
When measuring the position of the reference pattern, if there are four or more measurement edges of the reference pattern, the position of the reference pattern may be obtained as Bc from the two positions B1 and B2 having a line symmetry. . Further, the pattern to be measured is obtained as a pattern position D to be measured from the measurement point positions D1 and D2 of the two pattern edges having a line-symmetric relationship, and the middle point is obtained as the center position of the pattern to be measured. May be.
[0028]
The arrangement of the pattern formed on the mask is not limited to that shown in FIG. 1, and as shown in FIG. 3, the pattern to be measured 32 may surround the reference pattern 31 from approximately four directions. Even in such a case, the positions of the reference pattern and the pattern to be measured formed on the wafer can be obtained as described above. In the case of FIGS. 1 and 3, it is possible to measure not only in the horizontal direction but also in the vertical direction with the same mark. When enclosing approximately four sides, the shape does not necessarily need to be a square, and may be a regular polygon or a circle.
[0029]
Also, in order to measure even higher-order aberrations, a plurality of sets of reference patterns and patterns to be measured as shown in FIGS. 1 and 3 may be prepared and arranged so that each set is rotated with respect to each other. good. The rotation angle in this case is a value obtained by dividing 360 degrees by an integer.
[0030]
As described above, according to this embodiment, when the pattern to be measured is formed on the wafer, it is not necessary to perform the exposure twice, and only one exposure is required, so that the pattern to be measured can be formed very easily and quickly. To be able to. Since the first and last repeated patterns of the pattern to be measured are not included in the measurement, the pattern to be measured can be treated as an infinite repeating pattern, and accurate measurement is possible. Further, by arranging a combination of the reference pattern and the pattern to be measured that are rotated, it is possible to measure even higher-order aberrations when measuring the aberration of the projection optical system.
[0031]
(Second Embodiment)
As a modified example of the pattern to be measured, it can be as shown in FIG. This is such that the relationship between the reference pattern 41 and the pattern for measurement 42 is such that the reference pattern 41 surrounds the pattern for measurement 42 from approximately two directions.
[0032]
The position of the reference pattern 41 is obtained from the position A or B, and the pattern 42 for measurement is obtained from the position F. The details of how to find it are almost the same as in the first embodiment, and will be omitted. Also in this case, the same effect as the first embodiment can be obtained.
[0033]
The reference pattern 41 is not limited to a configuration in which the measurement pattern 42 is surrounded from approximately two sides, and the measurement pattern 42 may be configured to surround the reference pattern 41 from approximately two sides. These patterns 41 and 42 may include not only a horizontal direction but also a vertical pattern. A plurality of sets of the reference pattern 41 and the pattern 42 to be measured may be exposed simultaneously by changing the pattern size and density.
[0034]
Further, in order to measure higher-order aberrations, a plurality of sets of reference patterns and patterns to be measured as shown in FIG. 4 may be prepared and arranged such that each set is rotated with respect to each other. The rotation angle in this case is a value obtained by dividing 360 degrees by an integer. For the relative position measurement between the reference pattern 41 and the pattern to be measured 42, a light source having a wavelength shorter than the exposure wavelength is used as a measurement light source, or a high-resolution measuring device such as an SEM using a charged beam source is used.
[0035]
(Third embodiment)
When the reference pattern and the pattern to be measured are arranged in the original plate for creating a semiconductor device, the semiconductor device pattern can be used as the pattern to be measured. An example is shown in FIG. This figure shows a resist pattern formed on a wafer by exposure using a mask on which a pattern equivalent to a circuit pattern to be actually formed is formed as a pattern to be measured.
[0036]
The method for obtaining the position of the reference pattern is as in the first embodiment. That is, an intermediate point Ac between the center positions of the two reference patterns A1 and A2 is obtained and set as the center position of the reference pattern. Or, when there are four or more measurement edges of the reference pattern when measuring the position of the reference pattern, the position of the reference pattern is obtained as Bc from the two positions B1 and B2 having a line-symmetric relationship. Also good.
[0037]
In measuring the position of the pattern to be measured, the position H of the pattern to be measured is obtained from the average center position of a plurality of patterns to be measured, and the midpoint is obtained as the center position of the pattern to be measured. Alternatively, the length G of the pattern to be measured may be obtained from the measurement point positions G1 and G2 of the two pattern edges that are in a line-symmetric relationship, and the midpoint may be obtained as the center position of the pattern to be measured.
[0038]
The reference pattern and the pattern to be measured are extremely small such that one set fits in a 5 μm square frame, for example. In the relative position measurement between the reference pattern and the pattern to be measured, as in the first embodiment, a light source having a wavelength shorter than the exposure wavelength is used as the measurement light source, or an SEM using a charged beam light source is used. A high-resolution measuring device may be used.
[0039]
According to the present embodiment, the same effects as those of the first embodiment can be obtained, and the influence of aberration specific to the circuit is measured by using the circuit pattern in the pattern to be measured. be able to. In addition, the monitor pattern consisting of the reference pattern and the pattern to be measured is extremely small, about 5 μm square, and the monitor pattern can be formed on the actual exposure mask instead of the measurement-specific mask. It can be introduced as a process inspection pattern in the process.
[0040]
The method for obtaining the pattern position used in the first to third embodiments is not limited to this method, and other methods can be used within the spirit of the invention. The reference pattern does not necessarily need to be formed long as shown in FIGS. 1 to 5, and may be longer than the length required for the measurement in the direction orthogonal to the direction in which the edge position is to be measured. Further, the reference pattern and the pattern to be measured formed on the mask do not necessarily need to be a light-shielding film, and can be formed from a translucent film. In addition, various modifications can be made without departing from the scope of the present invention.
[0041]
【The invention's effect】
As described above in detail, according to the present invention, the reference pattern and the pattern to be measured formed on the sample are measured using a measurement device having a measurement light source or a charged beam source having a wavelength shorter than the exposure wavelength. The center position of the pattern to be measured and the center position of the pattern to be measured are measured, and the center position of the pattern excluding both ends is measured for the pattern to be measured. The relative position between the reference pattern and the pattern to be measured can be accurately measured without having to be removed.
[0042]
Therefore, even when the aberration function of the optical system is to be obtained with high accuracy, the number of exposures required for forming the pattern to be measured can be reduced to one, and the inspection process can be facilitated and speeded up.
[Brief description of the drawings]
FIG. 1 is a diagram showing a pattern arrangement on a mask used in the first embodiment.
FIG. 2 is a view showing a resist pattern formed on a wafer.
FIG. 3 is a diagram showing another example of pattern arrangement on a mask.
FIG. 4 is a diagram showing an example of pattern arrangement on a mask in the second embodiment.
FIG. 5 is a view showing an example of pattern formation on a wafer in a third embodiment.
[Explanation of symbols]
10: Center points 11, 31, 41 ... Reference patterns 12, 32, 42 ... Patterns to be inspected

Claims (3)

A pattern measuring method for measuring a relative position between a reference pattern and a pattern to be measured,
A step of transferring each of the above patterns onto a sample using a projection exposure apparatus using a mask having a pattern to be measured consisting of a repetitive pattern of a predetermined period and a reference pattern having a line width larger than the pattern to be measured When,
For each pattern formed on the sample by the transfer, using a measuring instrument having a measurement light source or a charged beam source having a wavelength shorter than the exposure wavelength when the pattern is transferred, the reference pattern on the sample is Measuring the center position and the center position of the pattern to be measured, and measuring the center position of the pattern excluding the first and last parts of the repetition for the pattern to be measured;
Obtaining a displacement amount of each measured center position;
A pattern measuring method comprising: The reference pattern of the mask is arranged in line symmetry with respect to the pattern to be measured, or arranged symmetrically with respect to the pattern to be measured , and the center positions of the patterns coincide with each other. The pattern measuring method according to claim 1. 3. The pattern measuring method according to claim 1, wherein the pattern to be measured of the mask is formed by imitating a pattern equivalent to an actual circuit pattern to be formed on the sample.

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