JP4112842B2 - Mask defect correction method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a defect correction technique such as a semiconductor photomasks relates to defect correction method for a mask used to correct the black-based defects, especially along the pattern edge.
[0002]
[Prior art]
When correcting defects along the pattern edge of a photomask, an apparatus using FIB (focused ion beam) may cause an edge position error due to insufficient position accuracy of the irradiation beam or end point detection. There is. Even if a laser correction device is used, edge position deviation due to correction accuracy frequently occurs. In such a case, re-correction is required unless the correction standard by AIMS (image quality evaluation apparatus) or the like is reached.
[0003]
Conventionally, re-correction has been performed by a method of forming a minute cut by moving the laser irradiation position in small steps while observing in real time with a laser correction device. With this method, it is impossible to process a minute width that is below the resolution limit that cannot be observed with a laser correction device. In the current state of the art, there is no apparatus that can stably form a cut with a width of 10 nm to 20 nm. Similarly, in the FIB apparatus, it is impossible to control the beam irradiation more accurately than the correction accuracy. Under the circumstances that require re-correction with a very small width, as long as the conventional method is used, Even if an apparatus is used, it is difficult to correct a minute width below the resolution limit.
[0004]
Further, when such re-correction is performed using conventional techniques, the position corresponding to the boundary between the defective portion and the normal portion may be protruded and scraped off depending on the case. In other words, this means that a new dent defect (hereinafter referred to as a white defect) is created, but in a phase shift mask such as a halftone mask, it is more difficult to correct a white defect than a black defect. That is, it is very difficult to reach a correction standard by AIMS (image quality evaluation apparatus) or the like. This is because the deposition film deposited at the dent position does not have a phase shift effect. Therefore, the generation of white defects in the correction of black defects must be reduced as much as possible. However, with the current technology, within the range of correction accuracy, it will be the same probability whether it will be finished as a bulge or a dent.
[0005]
The above description is after a standard black defect has been corrected once. For example, in a stripe pattern in which lines and spaces are arranged, the line portion is locally slightly thick (referred to as a CD error defect). ), The same situation occurs from the first correction.
[0006]
[Problems to be solved by the invention]
As described above, when correcting a black defect generated in a photomask with a focused ion beam, if the beam irradiation position for defect correction shifts to the pattern side, the originally required pattern is scraped and a new white defect is generated. There was a problem that occurred. In addition, there is a problem that it is difficult to correct a minute width below the resolution limit.
[0007]
The present invention has been made in consideration of the above circumstances, and the object of the present invention is to create new defects due to excessive cutting even when the irradiation position of the focused ion beam for defect correction is shifted. An object of the present invention is to provide a mask defect correction method capable of satisfactorily correcting pattern defects such as a photomask without causing occurrence.
[0008]
[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 method for correcting a protrusion defect existing on an edge of a mask pattern or a minute protrusion defect remaining after the protrusion defect is corrected, and the defect is detected in advance by a dimension measuring device. A step of measuring the tension length, and irradiating the edge portion on the opposite side of the pattern of the defect with a focused ion beam under a condition that is less than the dose amount necessary for cutting the pattern, so that the edge portion is more than the center portion of the pattern Using the phenomenon in which etching proceeds faster, and performing a cutting corresponding to the measured protrusion length, and the focused ion beam can be scanned in units of pixels arranged in a matrix, The pixel that scans the focused ion beam is linear in a direction parallel to the pattern edge where the defect exists, and corresponds to the edge portion of the defect opposite to the pattern. A two-row configuration on the pattern side with respect to the position of the pattern, and selected in a checkered lattice shape in the two-row configuration, and the amount of cutting is controlled by controlling the beam irradiation amount of the focused ion beam It is characterized by controlling.
[0012]
(Function)
According to the present invention, the irradiation amount (dose amount) of the focused ion beam for defect correction is set to be smaller than the irradiation amount necessary for cutting the original pattern, and the edge portion is etched faster than the central portion of the pattern. It is possible to correct a defect with a small irradiation amount by performing the cutting using the phenomenon (edge effect etching) in which the amount of light advances. In this case, even if the beam irradiation position is shifted to the pattern side, a new defect due to excessive shaving does not occur.
[0013]
In addition, by devising the beam irradiation method for defects (two-column configuration of pixels, checkered lattice, etc.), it becomes possible to control the cutting width by controlling the irradiation amount, so that the defect is below the resolution limit. Can also be modified.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The details of the present invention will be described below with reference to the illustrated embodiments.
[0015]
(First embodiment)
FIG. 1 is a schematic configuration diagram showing a focused ion beam (FIB) correction apparatus used in the first embodiment of the present invention. In the figure, 1 is a gallium ion source, 2 is a magnifying lens, 3 is a deflector, 4 is an objective lens, 5 is an ion beam column including 1-4, 6 is a charge neutralizer, 7 is a secondary particle detector, and 8 is A photomask (sample), 9 is a sample stage, 10 is a chamber containing 6 to 9, 11 is a gas introduction tube for supplying gas to the sample surface, and 12 is an exhaust port for exhausting the inside of the ion beam column 5 , 13 indicate exhaust ports for exhausting the inside of the chamber 10.
[0016]
The ion beam column 5 is provided in the upper part of the chamber 10, and the ions emitted from the ion source 1 are focused on the surface of the photomask 8 by the electro-optical components 2 to 4.
[0017]
The FIB correcting apparatus having such a configuration blows gas onto the photomask 8 by the gas introduction tube 11 and irradiates the portion with an ion beam, and removes a part of the mask pattern by gas assist etching or deposition, Alternatively, the mask pattern is corrected by partially depositing a film. Each part of this apparatus is controlled by a dedicated or general-purpose computer.
[0018]
In the FIB correction apparatus, the correction work is usually performed through the following procedure. First, the focused ion beam that has passed through the ion beam column 5 is scanned on an appropriate area including a defect on the mask surface. At this time, secondary electrons or secondary ions emitted from the pattern portion of the photomask 8 or the substrate portion are detected in units of scanning pixels to form an image. Next, the exact position and size of the defect, the shape that should be a normal pattern, etc. are recognized on this image. Next, a focused ion beam is irradiated onto the defect portion while flowing a gas having an etching effect on the pattern material of the photomask 8 into the chamber 10. Defects are removed by irradiating a certain amount of beam.
[0019]
FIG. 2 shows how defects are removed. FIG. 2A shows a state before processing, in which a protruding defect 22 exists in a part of the original pattern 21. FIG. 2B shows a state in which the defect 22 is removed by irradiation with a focused ion beam after processing, but the defect 22 is not completely removed, and a micro defect 23 remains. When the protrusion defect is corrected in this way, the defect 23 may remain as a small step as shown in FIG. If this minute defect 23 becomes a problem during wafer transfer, it must be corrected again.
[0020]
Whether or not the minute defect 23 has a problem in the wafer transfer is confirmed by measuring the portion with another measuring device such as an image quality evaluation device. FIG. 3B shows the light intensity distribution obtained on the wafer when exposure light is irradiated to the mask pattern as shown in FIG. ). On the other hand, FIG. 3C shows a broken line B portion (correction portion) where a minute defect exists. The half-value width A1 of the intensity distribution in the normal part A is compared with the half-value width B1 in the correction part B, and it is determined whether or not the difference or ratio is within an allowable value. Become.
[0021]
In the present embodiment, when such a small level difference is corrected by the FIB correction apparatus, correction with a higher success rate than usual is possible by using the following method.
[0022]
As shown in the upper diagram of FIG. 4, pixels 25 for scanning the focused ion beam with respect to the pattern 21 and the defect 23 are defined. The pixel 25 is a minimum unit when the focused ion beam is irradiated. As shown in the drawing, the pixels 25 made up of rectangular regions are arranged in a matrix.
[0023]
In this embodiment, as shown in FIG. 4A, the focused ion beam 27 is irradiated to a position corresponding to the edge on the opposite side of the pattern 21 of the defect 23. The dose amount of the focused ion beam at this time is set to be smaller (for example, 50%) than the dose amount necessary for removing the pattern 21. Unlike the solid film portion, the edge portion has a high etch rate, so that etching with a low dose is possible. This etching method is called edge effect etching. It has been found that the end point is usually reached at about 30% of the dose when the solid film portion is etched to the base substrate (for example, glass substrate) 20.
[0024]
Therefore, according to the present embodiment, the defect 23 can be removed using edge effect etching, and the pattern can be corrected. In this case, since the dose is small, even if the beam irradiation position is shifted by one dot toward the glass substrate as shown in FIG. Furthermore, as shown in FIG. 4C, even when the pattern is shifted by one dot, the damage to the pattern is very small. That is, by using edge effect etching, damage can be reduced even when the beam irradiation position is shifted to the pattern side or the glass substrate side.
[0025]
Incidentally, in the micro-cutting using the laser correction device, although there is little damage to the glass substrate, there is a case where the pattern is cut too much and, on the contrary, white defects may be caused, but according to this embodiment, this is prevented beforehand. be able to.
[0026]
(Second Embodiment)
Next, a photomask defect correcting method according to the second embodiment of the present invention will be described. As the FIB correction apparatus, the apparatus shown in FIG. 1 is used as in the first embodiment described above.
[0027]
In the first embodiment, as shown in FIG. 5A, when the amount of overlap between the defect 23 and the focused ion beam 27 is small, the amount of shaving of the defect 23 is small. On the other hand, as shown in FIG. 5B, when the amount of overlap between the defect 23 and the focused ion beam 27 is large, the amount of shaving of the defect 23 is large. That is, the edge finishing position changes depending on the beam irradiation position. In this case, it is relatively difficult to control the cutting width. In addition, there is a limit in reducing the cutting width.
[0028]
Note that it is only necessary that the beam irradiation position can be optimally set with respect to the edge position of the defect 23. However, when the width of the defect 23 is equal to or less than the resolution limit of the FIB correction apparatus, the beam irradiation position is always set with respect to the edge position of the defect 23. It is difficult to set the optimal position.
[0029]
Therefore, in the present embodiment, the irradiation position of the focused ion beam 27 for defect correction is set to two lines of the edge position pixel and the adjacent pixel as shown in FIG. ). The pitch interval P at this time is φ≈P where φ is the beam diameter effective for etching. FIGS. 6A and 6B show a case where the beam irradiation position is shifted in the left-right direction by about half a dot (1/2 pixel).
[0030]
In the initial state of FIG. 6A, the edge effect etching proceeds predominantly in the outer dot row 32, and then the inner dot row 31 is gradually shifted to the edge effect etching. When the etching in the outer dot row 32 reaches the end point, the edge effect etching in the inner dot row 31 proceeds with maximum efficiency. These etching processes are illustrated in time series as (a) → (b) → (c) → (d) in FIG. 7, and the cutting width can be controlled by controlling the dose. . Note that the unevenness of the edge is less than the resolution limit and is not a problem.
[0031]
In FIG. 6B, edge effect etching is performed in the outer dot row 32 in the initial state, but not so in the inner dot row 31. However, even in this case, if the beam irradiation is continued, it is expected that the state (b) temporarily shifts to the state (a), and thereafter, etching is performed through the same process. Therefore, in either case, the edge position can be adjusted by the dose amount.
[0032]
Here, if the protrusion length of the defect 23 is measured in advance using an image quality evaluation apparatus or the like as described above, accurate recorrection can be performed by irradiating a beam dose amount corresponding thereto. In the example of FIG. 6, the edge has a concavo-convex finish, but the concavo-convex is very fine and has little influence on the wafer transfer image. And the position which averaged the unevenness will contribute to the dimensional variation at the time of wafer transfer.
[0033]
As described above, according to this embodiment, when the focused ion beam for defect correction is irradiated, the margin of the beam irradiation position can be expanded by adopting a two-row zigzag beam scanning method. . As a result, it becomes possible to improve the processing reproducibility of micromachining. Further, the edge position can be controlled by the irradiation amount by proceeding stepwise with a process having a high etch rate occurring on the corner of the edge. This means that even a defect having a protrusion length less than the resolution limit can be cut by a necessary amount, which is an extremely effective effect for defect correction. Furthermore, there is an advantage that the minimum scraping width can be made smaller than when the adjacent pixels are irradiated with the beam.
[0034]
(Third embodiment)
In the first and second embodiments, a case is assumed in which it is not achieved with the aim of satisfying the correction criteria in the first correction. However, you may try for the purpose of satisfying the standard with two corrections from the beginning. In other words, it is possible to increase the correction accuracy in a total sense by deliberately leaving the first correction slightly and performing highly accurate edge position control using edge effect etching in the second correction. .
[0035]
In such an embodiment, by dividing the correction into two steps from the beginning, it is possible to reduce the probability of a correction error in which the edge position shifts to the dent side during the first correction. Further, the correction accuracy in the two-step total is better than the single correction accuracy.
[0036]
(Modification)
The present invention is not limited to the above-described embodiments. The configuration of the FIB correction device is not limited to that shown in FIG. 1 and may be any device that can deflect and turn on / off the focused ion beam. Furthermore, the gas used when scraping off the defects can be appropriately changed according to the material of the defects. Further, all processing in the FIB correction apparatus may be performed under computer control based on a program in which software is described. Further, the dose amount of the focused ion beam at the time of cutting the defect may be appropriately determined within a range smaller than the dose amount necessary for removing the original pattern.
[0037]
In addition, various modifications can be made without departing from the scope of the present invention.
[0038]
【The invention's effect】
As described above in detail, according to the present invention, the defect edge portion is irradiated with the focused ion beam under the condition that the beam irradiation amount is small, and the defect is utilized by utilizing the phenomenon that the etching proceeds faster in the edge portion than in the center portion of the pattern. By performing the cutting corresponding to the projecting length of the film, even if the beam irradiation position is shifted, it is possible to satisfactorily correct pattern defects such as a photomask without causing new defects due to excessive cutting. be able to.
[0039]
In addition, according to the present invention, by using a two-row zigzag beam scanning method, the edge position can be controlled by the amount of beam irradiation, and the processing reproducibility of micromachining can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an FIB correction apparatus used in a first embodiment.
FIG. 2 is a diagram showing a state in which defects are removed by irradiation with a focused ion beam.
FIG. 3 is a schematic diagram when measuring uncut residue with an image quality evaluation apparatus.
FIG. 4 is a view for explaining the first embodiment and showing a state of edge effect etching;
FIG. 5 is a diagram illustrating a state in which a correction position is shifted by edge effect etching using a pattern in one row.
FIG. 6 is a diagram illustrating edge effect etching using a zigzag pattern for explaining a second embodiment;
FIG. 7 is a diagram showing a time-series change in edge effect etching by a zigzag pattern.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Gallium ion source 2 ... Magnifying lens 3 ... Deflector 4 ... Objective lens 5 ... Ion beam column 6 ... Charge neutralizer 7 ... Secondary particle detector 8 ... Mask (sample)
DESCRIPTION OF SYMBOLS 9 ... Sample stage 10 ... Chamber 11 ... Gas introduction pipes 12, 13 ... Exhaust port 20 ... Glass substrate 21 ... Mask pattern 22 ... Black type defect (defect before correction)
23 ... Black defects (small defects after correction)
25 ... Pixel unit for scanning the ion beam 27 ... Focused ion beam 31 ... Inner irradiation position in the two-row irradiation 32 ... Outer irradiation position in the two-row irradiation

Claims (4)

A method for correcting a protrusion defect existing on an edge of a mask pattern, or a minute protrusion defect remaining after correcting the protrusion defect,
Measuring the protrusion length of the defect with a dimension measuring device in advance;
A phenomenon in which a focused ion beam is irradiated on an edge portion of the defect opposite to the pattern on the opposite side to a dose amount necessary for cutting the pattern, and etching proceeds faster at the edge portion than at the pattern central portion. A step of cutting corresponding to the measured projecting length, using
Including
The focused ion beam can be scanned in units of pixels arranged in a matrix,
The pixel that scans the focused ion beam is linear in a direction parallel to the pattern edge where the defect exists, and a position corresponding to the edge portion of the defect opposite to the pattern and 2 on the pattern side of the position. It is a column configuration and is selected in a checkered pattern in the two column configuration,
A mask defect correcting method, wherein the amount of cutting is controlled by controlling a beam irradiation amount of the focused ion beam. A process in which a projecting defect existing on the edge of the mask pattern is previously cut by a correction device using an ion beam or a laser beam at a position about a beam radius away from the edge of the normal pattern, and after being corrected by the process Necessary for minimizing the dimensional difference between the repaired part and the normal part by measuring the projecting length of the remaining projecting defects with a dimension measuring device, and newly cutting the remaining projecting defects. defect correction method of a mask according to claim 1, characterized in that it comprises the steps of determining the amount of narrowing shaving, the. The focusing when irradiating the ion beam, the defect correcting method of a mask according to claim 1, wherein the supplying gas having an etching effect on the defect. As a step of measuring the lugs length of the defect by the dimension measuring device, defect correction method of a mask according to claim 1, wherein the detecting the secondary charged particle image from the mask by scanning the focused ion beam .

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