JP2004144885A - Method for correcting laser beam and laser drawing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for correcting laser beams and a drawing method to prevent degradation in dimensional accuracy by compensating the factors of dimensional fluctuation in each beam in a method for correcting laser beams to be used for laser drawing by scanning a mask blank with a plurality of laser beams different from one another at a specified distance to expose to make a unit pattern, repeating the pattern in the scanning direction and in the direction perpendicular thereto to produce a multiple units. <P>SOLUTION: A test pattern having the designed width W in the perpendicular direction is drawn on a mask blank, wherein W is the total designed width W in the perpendicular direction of the above unit pattern and the adjacent pattern drawn with one laser beam. The optical intensity of the laser beam used to draw the end part of the test pattern in the width direction is corrected according to the difference between the designed width W of the test pattern and the width of the drawn test pattern. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for correcting a laser beam used for laser writing for irradiating a laser beam for manufacturing a photomask or the like for manufacturing a semiconductor element to draw a desired pattern, and a laser writing method using the same. In particular, the present invention relates to a laser beam correction method and a drawing method for avoiding a decrease in dimensional accuracy of a drawing pattern due to a dimensional variation between laser beams.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an apparatus that draws a mask blank with a laser beam has been used for manufacturing a photomask used in a semiconductor wafer process. Usually, a mask refers to a substrate made of glass or the like on which multiple patterns of an actual semiconductor LSI are multi-faced or a mask blank having a pattern four times or five times the original size is drawn. The latter is called a reticle. With recent miniaturization, most masks are of the reticle type. The laser beam drawing apparatus uses laser light for photomask production using an electron beam, and the apparatus is simple, for example, a vacuum device is not required.By using a multi-beam, the drawing time is reduced to the electron beam. There are merits such as shorter.
[0003]
In order to use a multi-beam, the laser beam output from the generator is usually divided into a plurality of laser beams. Thereafter, these are collimated by an optical system, and each laser beam is simultaneously scanned and exposed on the mask blank, thereby shortening the drawing time. As an exposure method, first, the mask blank is fixed on a stage that can move in the vertical and horizontal axes. Then, the plurality of laser beams are simultaneously scanned at a certain distance to expose the mask blank. A pattern scanned and exposed at this fixed distance is used as a basic unit. Then, after irradiating the basic unit, the mask blank is moved. The stage of the mask blank is usually moved so that the pattern comes into contact with the area irradiated with the mask blank. Then, the laser beam is scanned again to irradiate the basic unit, and then the mask blank is moved. As described above, the irradiation of each unit is repeated by the scanning of the laser beam and the movement of the mask blank, thereby forming a plurality of surfaces, thereby completing the drawing of the entire mask blank. Therefore, in the mask blank, the basic unit is repeated, and the image is drawn with this cycle.
[0004]
As a method of scanning a beam, there are a method using a rotating mirror and a method using an acousto-optic element. After passing through these mirrors and elements, it passes through an f-Θ lens or a reduction lens, and is subjected to processing such as parallel light, and is then exposed on a mask blank.
[0005]
However, the following problems occur due to the above mask drawing. That is, the dimensions of the pattern exposed by each laser beam vary on the mask blank due to the variation of the optical intensity of each beam and the influence of optical components such as lenses and mirrors.
[0006]
A drawing apparatus that draws using a plurality of laser beams measures the optical intensity of each laser beam and makes it uniform, in order to avoid such a dimensional variation between the beams, so that dimensional variations between the beams can be obtained. Has been reduced. Due to the deterioration of the optical system and the stability of the AOM (Acousto-Optical Modulator acousto-optic modulator, which is used for adjusting the optical intensity, etc.), the intensity between the beams is periodically adjusted to vary. Need to be eliminated.
[0007]
The optical intensity of each beam is converted as a current value of a photodiode, and is adjusted by changing an output applied to the AOM.
[0008]
The pattern size by a laser writer depends on the beam forming the edge of the pattern. The dimensions increase as the optical intensity of the beam increases, and decrease as the optical intensity of the beam decreases.
Therefore, in a pattern in which both edges are drawn with the same beam, the size depends on the specific beam.
[0009]
FIG. 5 is a graph schematically showing a graph of an optical intensity distribution of each beam and a dimension of a pattern drawn by each beam. The figure shows a state in which the beam is irradiated on the photosensitive portion of the photodiode, the vertical axis represents the optical intensity of the beam, and the horizontal axis represents coordinate values along the photosensitive portion of the photodiode. (A) represents a normal distribution, in which the dimension width of the intensity corresponding to the normal dose is represented by a, and the current of the photodiode is represented by Ia. The normal dose is a dose amount at which the dimensions can be designed as designed with a normal distribution. FIG. 7B shows the case where the focus is different. The width of the intensity corresponding to the normal dose is represented by b, and the current of the photodiode is represented by Ib. In this case, the intensity width b is smaller than the width a in the normal state. FIG. 9C shows the case where the spot shapes are different. The width of the intensity corresponding to the normal dose is indicated by c, and the current of the photodiode is indicated by Ic. In this case, the intensity width c is a value smaller than the width a in the normal state. FIG. 4D shows the case where there is scattered light. The width of the intensity corresponding to the normal dose is d, and the current of the photodiode is Id. In this case, the intensity width d is a value smaller than the width a in the normal state. The currents Ia, Ib, Ic, Id of the photodiodes are all the same, and the optical intensities are kept constant. As can be seen, there are differences in the spot size, spot shape, FOCUS, scattered light, etc., depending on the beam, so that the distribution of the optical intensity does not match the distribution of the dimensions.
[0010]
That is, even if the optical intensities of the beams are made constant, the variation in the pattern size depending on each beam is not constant. This is because the dimensional variation factors other than the optical intensity described above are not corrected. For this reason, there is dimensional variation between the beams, leading to a reduction in dimensional accuracy.
[0011]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described problems, and it is an object of the present invention to provide a laser beam correction method and a drawing method that do not reduce the dimensional accuracy by correcting a dimensional variation factor of each beam. .
[0012]
[Means for Solving the Problems]
The present invention is to solve such a problem, and the invention of claim 1 is to expose a mask blank by scanning a plurality of different laser beams at a predetermined distance at a predetermined distance, and to use the same as one unit pattern in a scanning direction and a scanning direction. In the method of correcting a laser beam used for laser drawing for performing multiple drawing by repeatedly drawing in the vertical direction, the one unit pattern and the pattern formed by drawing one adjacent laser beam in the vertical direction may be used. Is drawn on a mask blank with the total design width being W and the vertical design width being W, and the test pattern is determined from the difference between the design width W of the test pattern and the width of the drawn test pattern. And correcting the optical intensity of the laser beam drawn at the width end of the laser beam.
[0013]
The invention of claim 2, the mask blank is exposed by scanning a plurality of different laser beams at a predetermined distance, and repeatedly writing in the scanning direction and the vertical direction as a unit pattern to form a multi-surface, Further, in a laser writing method in which the position of one unit pattern is changed and drawn in a superimposed manner to form a multi-surface, the optical intensity of a laser beam is corrected by the correction method according to claim 1. .
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
In the method of correcting a laser beam according to the present invention, a mask blank is exposed by scanning a plurality of different laser beams at a predetermined distance, and is repeatedly drawn in a scanning direction and a vertical direction as one unit pattern to form a multi-plane. This beam is corrected for the laser beam used for laser writing to be attached. Here, the total design width in the vertical direction of the one unit pattern and the pattern formed by drawing one adjacent laser beam is W. Then, a test pattern having the vertical design width W is drawn on the mask blank, and the optical intensity of the laser beam drawn at the width end of the test pattern is corrected based on the drawn test pattern width. .
[0015]
Further, as a correction method, the optical intensity of the laser beam that has drawn the width end of the test pattern is determined from the difference between the design width W of the test pattern and the width of the test pattern on the drawn mask blank. It is to be corrected.
[0016]
The laser beam writing method of the present invention corrects the optical intensities of a plurality of different laser beams as described above, and scans and exposes a plurality of different laser beams at a predetermined distance on a mask blank. Are repeatedly drawn in the scanning direction and the direction perpendicular thereto as one unit pattern to form a multi-surface, and furthermore, the position of the one unit pattern is changed and drawn to form a multi-surface.
[0017]
In the laser writing method according to the present invention, for example, after uniformly adjusting the optical intensity of each beam using a photodiode, the amount of dimensional variation of each beam by the optical system is obtained by the correction method of the present invention, and the OFFSET of the optical intensity is obtained. And expose and draw on the mask blank.
[0018]
An example of the method for measuring the dimensional variation of each beam by the optical system according to the present invention will be described. First, the total design width in the vertical direction of the one unit pattern and the pattern formed by drawing one adjacent laser beam is defined as W. Then, a test pattern having the vertical design width of W is drawn on the mask blank, so that the same type of beam is used to expose both ends of the test pattern, and the dimensions drawn on the mask blank are measured. . This is similarly performed for all the beams, and the deviation from the design dimension due to each beam is defined as the amount of dimensional variation due to the optical system.
[0019]
FIG. 1 shows an example of a test pattern layout necessary for this. In drawing with a plurality of laser beams, one unit pattern scanned (scanned length) at a predetermined distance is repeatedly drawn, so that in the case of multi-beam drawing, the same beam is periodically repeated. FIG. 1A is a diagram schematically illustrating a state in which a part of the next unit pattern is in contact with one drawn unit pattern. There are n different beams, and the names of the beams are assigned in order from 1 to n, and beams 1, 2, 3,... Therefore, the beam 1 of the next unit pattern is in contact with the beam n. FIG. 6B shows one test pattern, and the width in the vertical direction in the scanning direction is a value obtained by adding the width of one unit pattern (the beam 1 in this case) to the width of one unit pattern (the above W1). 4) is a diagram schematically illustrating a test pattern whose length in the scanning direction is longer than the scanning length. In this case, both ends of the test pattern are drawn by the beam 1. FIG. 3C shows that the width in the scanning direction is the same as that in FIG. 3B and the length in the scanning direction is the same, but the position of the pattern in the scanning direction in FIG. FIG. 3 is a diagram schematically showing a test pattern designed to be shifted in the vertical direction. In this case, both ends of the test pattern are drawn by the beam 2. Similarly, by designing a test pattern of the same size by shifting the position by one beam width in the scanning direction and the vertical direction, the beams for writing both end portions of the width of the test pattern are beams 3, 4, 5,. ... N can be designed.
[0020]
The design dimensions of the width of the test pattern as described above are as follows, where the beam interval is M, and the number of beams necessary for the beams at both ends to be the same is N ((number of beams for writing one unit pattern) +1). , M × N (= W). For example, assuming that the beam interval is 100 nm, when the number of beams is 32 and the pattern has a line width of 3.3 μm, both edges are exposed by the same beam.
[0021]
When a pattern laid out so that the left and right edges become the same beam in this manner is drawn, the dimension after drawing becomes a value depending on the beam on which the edge is drawn. Then, the variation of the width of the test pattern with respect to the design value after the writing is obtained as the dimensional variation of the beam that has drawn the both ends of the width of the test pattern.
[0022]
There is a relationship between the optical intensity of the laser beam and the dimension of the exposed portion that can be increased by increasing the optical intensity and reduced by decreasing the optical intensity. Therefore, the dimensional variation amount of each beam can be corrected by adjusting the optical intensity of each beam.
[0023]
Note that the width of the test pattern also varies in the scanning direction, and therefore, it is preferable to use an average value in the scanning direction for the value.
[0024]
In the above example, the test pattern is drawn only once, but it may be overwritten a plurality of times. In this case, if the overwriting is performed while being shifted in the scanning direction, the variation in the scanning direction is averaged, and the measured width value can be directly used without averaging.
[0025]
Next, an example of the laser writing method of the present invention will be described.
FIG. 4 shows the relationship between the optical intensity of each beam and the size of a pattern on which an edge is drawn by each beam without considering the OFFSET calculated from the dimensions of the optical intensity of each beam. Since the optical intensity affects the dimensions, the distribution of the optical intensity and the distribution of the dimensions are almost the same. The dispersion of the optical intensity is large, and the distribution of the dimensions is also large.
[0026]
FIG. 3 shows the dimensions of the test pattern in which the edge is drawn by each beam at the time when the output applied to the AOM is adjusted so that the optical intensity of each beam becomes the same from the state of FIG. Although the optical intensity is almost constant as compared with FIG. 4, the distribution of the optical intensity does not coincide with the distribution of the dimensions, but varies.
In a state where the dispersion of the optical intensity is adjusted to be almost the same by RANGE / MEAN up to 1.9%, the dispersion of the dimension has a dispersion of 21 nm.
[0027]
FIG. 2 shows a state in which the output applied to the AOM of each beam is corrected with the OFFSET value calculated from the dimension so that the variation in the size of each beam is offset by the optical intensity from the state of FIG. 3 shows the dimensions of the test pattern on which the edge is drawn.
The optical intensity varies by 10.8% in RANGE / MEAN due to the addition of OFFSET. However, the dispersion of the size distribution is reduced to 8 nm by RANGE.
[0028]
The reason why the dimensional variation is improved by individually setting OFFSET in the optical intensity in the above example is as follows.
Even if the optical intensities are the same, there are differences in spot size, spot shape, FOCUS, scattered light, etc. depending on the beam. As described above (prior art), it is considered that these differences cause dimensional variations.
[0029]
In other words, dimensional variations due to differences in spot size, spot shape, FOCUS, scattered light, etc., depending on the beam can be offset by adjusting the optical intensity and conversely causing dimensional variations to reduce dimensional variations. As a result, the optical intensity between the beams varies, but the dimensional variation is improved, and laser drawing can be performed without lowering the dimensional accuracy of the pattern to be drawn.
[0030]
It is important that the optical intensity varies by OFFSET, and a mere variation causes a dimensional change. Therefore, it is necessary to adjust the optical intensity once so as to be constant, and then to vary the optical intensity by adding an offset.
[0031]
Further, the OFFSET amount of each beam depends on the optical system, and the OFFSET amount can be used as a fixed value as long as the optical system does not change. However, it is necessary to periodically check whether the optical system has changed.
[0032]
【Example】
Examples of the present invention will be specifically described below.
ALTA3500 (manufactured by ETEC) was used as a laser drawing apparatus. A test mask consisting of a test pattern for each beam was designed, and writing data was created. The measured test pattern was set so that the beam at the edge portion was shifted as shown in FIG.
[0033]
A mask blank on which a resist for laser light was formed was set in the above apparatus, and the drawing data was overlapped and drawn by four exposures using the same beam. The distribution of dimensional variations in the scanning direction of the line pattern of the developed and created mask is shown below.
[0034]
FIG. 2 shows a distribution of optical intensity and a distribution of dimensions of each beam.
In the figure, for 32 types of line patterns (BEAMs 1 to 32 in FIG. 1), the line graph of the optical intensity is the current value detected by the photodiode, and the line graph of the dimensional variation is the deviation from the average of the whole.
[0035]
The variation of each line pattern (BEAM1 to 32) is 10.8% in R / M when the optical intensity is OFFSET, but the average size difference between the line patterns (BEAM) is 8 nm. small.
[0036]
<Comparative Example 1>
FIG. 3 shows a comparative example of the laser beam writing method of the present invention, and shows the average dimension between line patterns (BEAM) when the optical intensities of the respective beams are adjusted to be the same.
[0037]
The variation in the line patterns (BEAMs 1 to 32) is as small as about 1.9% in R / M when the optical intensity is adjusted to be the same, but the difference in average size between the line patterns (BEAM) is as follows. , 21 nm.
[0038]
<Comparative Example 2>
FIG. 4 shows a comparative example of the laser beam writing method according to the present invention, in which the optical intensity of each beam does not include the OFFSET fed back from the dimensions, and the average size between line patterns (BEAM) when the intensity varies. is there.
[0039]
The variation in the optical intensity of each beam is as large as 13.6% in R / M, and the difference in the average size between the line patterns (BEAMs 1 to 32) is as large as 33 nm.
[0040]
【The invention's effect】
According to the laser beam correction method of the present invention, the influence of each of the plurality of beams on the dimensions can be individually evaluated, so that the correction value of the optical intensity of each beam can be calculated.
[0041]
According to the laser writing method according to the second aspect, dimensional variation between patterns exposed by different beams can be reduced, thereby improving the dimensional accuracy of the drawn pattern.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram schematically showing an embodiment of a test pattern of each beam according to the correction method of the present invention.
FIG. 2 is a diagram showing, in a line graph, a variation in optical intensity of each beam and a distribution of dimensions in a state where the optical intensity of the beam is corrected in the embodiment of the correction method of the present invention.
FIG. 3 is a diagram showing, in a line graph, a conventional variation in optical intensity and a distribution of dimensions of each beam in a state where the beams are adjusted to be the same.
FIG. 4 is a diagram showing, in a line graph, a conventional variation in optical intensity of each beam and a distribution of dimensions in a state where the optical intensity of each beam before the optical intensity is adjusted to be the same is varied. .
FIG. 5 is a graph schematically showing a graph of an optical intensity distribution of each beam and a dimension of a pattern drawn by each beam.

Claims (2)

A laser beam used for laser writing, in which multiple different laser beams are scanned and exposed on a mask blank at a predetermined distance, and the mask blank is repeatedly written in the scanning direction and in the vertical direction as a unit pattern. Wherein the total design width in the vertical direction of the one unit pattern and the pattern formed by drawing one adjacent laser beam is W, and the design width in the vertical direction is W. The method is characterized in that the pattern is drawn on a mask blank, and the optical intensity of the laser beam that has drawn the width end of the test pattern is corrected from the difference between the design width W of the test pattern and the width of the drawn test pattern. Laser beam correction method. A mask blank is exposed by scanning with a plurality of different laser beams at a predetermined distance, and this is repeatedly drawn as a unit pattern in the scanning direction and in the vertical direction to form a multiple pattern, and furthermore, the position of the one unit pattern is determined. A laser drawing method for performing drawing by changing and superimposing, wherein the optical intensity of a laser beam is corrected by the correction method according to claim 1.

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