Source: https://patents.google.com/patent/US7107573?oq=5708422
Timestamp: 2018-05-24 14:52:10
Document Index: 785574952

Matched Legal Cases: ['arts 41', 'art 42', 'art 16', 'art 16', 'art 17', 'art 17', 'Application No. 10', 'Application No. 10']

US7107573B2 - Method for setting mask pattern and illumination condition - Google Patents
Method for setting mask pattern and illumination condition Download PDF
US7107573B2
US7107573B2 US10251581 US25158102A US7107573B2 US 7107573 B2 US7107573 B2 US 7107573B2 US 10251581 US10251581 US 10251581 US 25158102 A US25158102 A US 25158102A US 7107573 B2 US7107573 B2 US 7107573B2
US10251581
US20030198872A1 (en )
A method for setting a mask pattern and an illumination condition suitable for an exposure method for using plural kinds of light to illuminate a mask that arranges a predetermined pattern and an auxiliary pattern smaller than the predetermined pattern, so as to resolve the predetermined pattern without resolving the auxiliary pattern on a target via a projection optical system includes the steps of forming data for the predetermined pattern, forming data for the auxiliary pattern, and setting the illumination condition for defining an effective light source of illumination using the plural kinds of light.
The present invention relates generally to methods for setting a mask pattern and an illumination condition optimal to the mask pattern, and more particularly to a method for setting a mask pattern and its illumination condition suitable for an exposure method for illuminating a mask that arranges a desired pattern and an auxiliary pattern or dummy pattern (these terms are used interchangeably in this application) smaller than the desired pattern, using plural kinds of light so as to resolve the desired pattern without resolving the auxiliary pattern on a target via a projection optical system.
Although the resolution generally improves with the shorter exposure wavelength and the larger NA, the projection exposure apparatus has, from its nature, patterns that are easily resolved and patterns that are hard to be resolved. Generally speaking, a line and space pattern (“L/S pattern” hereinafter) is more easily resolved than a contact hole pattern (“C/H pattern” hereinafter), and thus the C/H pattern is usually made wider than the L/S pattern for use with semiconductor chips. Therefore, there has been a problem to manufacture a minute C/H pattern in the fine lithography.
The instant inventors have discovered that the way of inserting the dummy C/H pattern would change an imaging state of a desired C/H pattern. The instant inventors have also discovered an insertion rule of a dummy C/H pattern based on a size, period, arrangement of a desired C/H pattern, etc. The instant inventors further discovered that a certain insertion method of a dummy pattern would improve not only the depth of focus but also the resolution, and that the optimal illumination system is neither the annular illumination nor the quadrupole illumination. In particular, according to the experiences of the instant inventors, the quadrupole illumination is seldom useful when k1 is 0.25×√2 or smaller, where k1 corresponds to a half pitch of a mask pattern that arranges the dummy pattern. Here, k1 is a factor expressed by k1=R·NA/λ, where R is the resolution, NA is a numerical aperture, and λ is a wavelength of an exposure light source. In addition, the prior art has inserted a dummy pattern into a desired pattern only when the desired pattern has a certain period. However, desired patterns do not always have certain periods in an actual mask pattern, and thus the prior art has limited applicability. The instant inventors have also discovered that a desired pattern on a mask is sometimes not successfully reproduced even when a dummy C/H pattern follows the insertion rule and the illumination system is set to be suitable for the mask pattern. In this case, the desired pattern should be corrected.
Accordingly, it is an exemplary object of the present invention to provide a method for comparatively easily setting a mask pattern and its illumination condition to improve the resolution.
The plural kinds of light may include light for resolving the predetermined pattern, and light for preventing the auxiliary pattern from being resolved. The step of obtaining the illumination condition may convert, before using the minimum pitch, the minimum pitch into k1 expressed by k1=R·NA/λ, where R is the resolution, NA is a numerical aperture, and λ is a wavelength of an exposure light source. The step of obtaining the illumination condition may obtain the illumination condition by referring to a database that correlates the minimum pitch with the illumination condition.
A mask manufacturing method of another embodiment is suitable for the above exposure method, and includes the steps of setting a size of the predetermined pattern, setting a size of the auxiliary pattern, and adjusting the size of the auxiliary pattern, utilizing a relationship between the size of the auxiliary pattern and at least one of a mask error enhancement factor, a critical dimension error, a depth of focus, a location error of the auxiliary pattern, a size error of the auxiliary pattern, and an exposure dose for the size of the predetermined pattern, whereby the at least one may fall within a permissible range. The adjusting step may change the size of the auxiliary pattern within a range of ±10% of the size of the auxiliary pattern. The adjusting step may make smaller the size of the auxiliary pattern so as to improve the mask error enhancement factor, the location error or the size error. The adjusting step may make larger the size of the auxiliary pattern so as to improve the critical dimension, the depth of focus or the exposure dose.
A mask manufacturing method of another embodiment is suitable for the above exposure method, and includes the steps of forming the predetermined pattern in first and second areas spaced by a non-interfering distance, and setting the auxiliary pattern as a different pattern for each of the first and second areas. The non-interfering distance may be 2 or greater when converted into k1 expressed by k1=R·NA/λ, where R is the resolution, NA is a numerical aperture, and λ is a wavelength of an exposure light source. A minimum pitch in the first area may be smaller than that in the second area, and the step of forming the predetermined pattern may increase a size of the predetermined pattern in the second area. An exposure method for illuminating a mask manufactured by this method using an illumination system optimized by the minimum pitch in the first area is also another aspect of the present invention. The step of forming the predetermined pattern may correct the predetermined pattern in the first area. An exposure method for illuminating a mask manufactured by this method, using an illumination system optimized by the minimum pitch in the second area is also another aspect of the present invention.
A mask manufacturing method of another embodiment is suitable for the above exposure method, and includes the step of arranging, when an interval between two minimum vertexes of two auxiliary patterns to be inserted is 0.20 or smaller when converted into k1 expressed by k1=R·NA/λ, where R is the resolution, NA is a numerical aperture, and λ is a wavelength of an exposure light source, one auxiliary pattern that has a center of gravity that accords with a center of gravity of the two auxiliary patterns instead of inserting the two auxiliary patterns.
The step of arranging the auxiliary pattern for the periodic pattern may include the steps of determining a size of the auxiliary pattern based on a minimum pitch of the predetermined pattern, and determining a period of the auxiliary pattern based on a hole diameter of the predetermined pattern and the period as the interval. The step of determining the size of the auxiliary pattern may include the first step of determining whether the minimum pitch of the predetermined pattern is 0.25×√2 or smaller when converted into k1 expressed by k1=R·NA/λ, where R is the resolution, NA is a numerical aperture, and λ is a wavelength of an exposure light source, the step of setting the size of the auxiliary pattern to a predetermined ratio of the predetermined pattern, when the first step determines that the minimum pitch is 0.25×√2 or smaller, and the step of setting the size of the auxiliary pattern to a size corresponding to 0.25 or smaller when converted into k1, when the first step determines that the minimum pitch is not 0.25×√2 or smaller. The predetermined ratio may be between 70% and 85%.
The step of determining the period of the auxiliary pattern may include the first step of determining whether a hole diameter of the predetermined pattern is below a first threshold, and the step of terminating the method with an abnormal operation when the first step determines that the hole diameter is below the first threshold. The first threshold may be between 0.25 and 0.25×√2. The method further include the second step of determining, when the first step determines that the hole diameter is not below the first threshold, whether the hole diameter of the predetermined pattern is between the first threshold and a second threshold, the third step of determining whether the period of the periodic pattern is a third threshold or greater when converted into k1 expressed by k1=R·NA/λ, where R is the resolution, NA is a numerical aperture, and λ is a wavelength of an exposure light source, where the second step determines that the hole diameter is between the first and second thresholds, and the step of arranging the auxiliary pattern with the period of the periodic pattern when the third step determines that the period of the periodic pattern is not the third threshold or greater. The method may further include the step of arranging the auxiliary pattern with a first value obtained by dividing the period of the periodic pattern by a second value when the third step determines that the period of the periodic pattern is the third threshold or greater. The first threshold may be between 0.25 and 0.25×√2, the second threshold may be between 0.25×√2 and 0.5, and the third threshold may be between 1.0 and √2.
The method may further include the fourth step of determining whether the period of the periodic pattern is a fourth threshold or greater when converted into k1, where the second step determines that the period of the periodic pattern is not between the first threshold and the second threshold, and the fifth step of determining whether a third value obtained by subtracting the hole diameter of the predetermined pattern from a fourth value of the period of the periodic pattern converted into k1 is a fifth threshold or smaller, when the fourth step determines that the period of the periodic pattern is the fourth threshold or greater, the auxiliary pattern being not inserted when the fifth determining step determines that the third value is a fifth threshold or smaller. The method may further include the fourth step of determining whether the period of the periodic pattern is a fourth threshold or greater when converted into k1, where the second step determines that the period of the periodic pattern is not between the first threshold and the second threshold, and the step of arranging the auxiliary pattern with the period of the periodic pattern, when the fourth step determines that the period of the periodic pattern is not the fourth threshold or greater. The first threshold may be between 0.25 and 0.25×√2, the second threshold may be between 0.25×√2 and 0.5, and the fourth threshold may be between 1.0 and √2. The step of arranging the auxiliary pattern for the isolated pattern may include the steps of determining whether the periodic pattern exists within a predetermined range from the isolated pattern, arranging the auxiliary pattern in accordance with the period of the periodic pattern when the determining step determines that the periodic pattern exists, and arranging the auxiliary pattern using a size of the isolated pattern for a half pitch of the auxiliary pattern when the determining step determines that the periodic pattern does not exist.
FIG. 1 is a flowchart for explaining a setting method of the present invention.
FIG. 41B is an illustrative view in which a dummy pattern is inserted into an area “s” in FIG. 41A.
FIG. 41C is an illustrative view in which a dummy pattern is inserted into an area “t” in FIG. 41A.
FIG. 41D is an illustrative view in which a dummy pattern is inserted into an area “s” in FIG. 41A with the optical proximity correction.
A description will be given with reference to accompanying drawings. Here, FIG. 1 is a flowchart for explaining a method for setting a mask pattern and illumination condition of the instant embodiment. A mask is formed which includes a desired C/H pattern, a dummy C/H having a hole diameter smaller than that of the desired C/H pattern. An exposure method is referred to as an exposure method I that resolves only the desired C/H pattern.
DUMMY HOLE CRITICAL DIMENSION
DIAMETER CONTRAST ERROR [nm]
96 0.69751 7.79325
94.8 0.702352 8.05575
93.6 0.70737 8.304
92.4 0.71256 8.53875
91.2 0.71791 8.76225
90 0.723416 8.97225
88.8 0.729068 9.1695
87.6 0.734858 9.3555
86.4 0.740778 9.5295
85.2 0.746816 9.70575
84 0.752966 9.8745
This database correlates the contrast with the critical dimension (“CD”) error for each value corresponding to 1% of the dummy hole diameter of 120 nm. As the dummy hole diameter becomes smaller, the contrast improves but the CD error becomes large. The proper dummy hole may be determined by providing the permissible contrast and CD error.
DUMMY NOTE CRITICAL DIMENSION
90.5 0.7385725 8.54175
89.4 0.7418475 8.80875
88.3 0.74446 9.15075
87.2 0.7471675 9.4635
86.1 0.74499725 9.7725
85 0.7528675 10.07625
83.9 0.755855 10.37475
82.8 0.75893 10.6695
81.7 0.76209 10.94175
80.6 0.7653325 11.22825
79.5 0.768215 11.505
This database correlates the contrast with the critical dimension (“CD”) error for each value corresponding to 1% of the dummy hole diameter of 110 nm. As the dummy hole diameter becomes smaller, the contrast improves but the CD error becomes large. The proper dummy hole may be determined by providing the permissible contrast and CD error.
The following method may define Oi. It is desirable to illuminate a binary mask with an illumination system having an effective light source distribution typically shown in FIG. 16 in which imaging performance is changeable by varying the light cross shielding area, more specifically, values of “a” and “b”. It is also effective to change a value of the maximum coherence factor σ in FIG. 16. It is desirable to illuminate a phase-shift mask shown in FIG. 17 and it is effective to change the light shielding area, i.e., values of “a” and “b” even in this case in FIG. 17. It is also effective to change a value of the maximum coherence factor σ in FIG. 17. FIG. 18 includes small coherence factor σ illumination and large coherence factor σ illumination. It is effective to change a ratio of strength between the small coherence factor σ illumination and the large coherence factor σ illumination, or to change a position of the large coherence factor σ illumination. An insertion of Dum clearly changes a pseudo-period of the mask pattern in the longitudinal and lateral directions. It is not necessary to use illumination systems of rotational symmetry with respect to an angle of 90° typified in FIGS. 16-18, and an illumination system of rotational symmetry with respect to an angle of 180° may be used as shown in FIG. 19.
The desired pattern is not always transferred with accuracy even when Fpd and Oi are obtained. When a pattern to be transferred does not meet the specific standard, original Dpd should be corrected. This is so-called optical proximity correction (“OPC”) (step 1012). The following method may transfer the desired pattern with accuracy. Basically, as shown in FIG. 15, when the pattern size to be transferred is smaller than a desired value, OPC is provided so as to make large Dpd (FIG. 15A), while when the pattern size to be transferred is greater than a desired value, OPC is provided so as to make small Dpd (FIG. 15D). As a change of Dpd also affects the resolution of the desired pattern, when the desired pattern size is smaller than the desired value, Dum is made large or its period is made small near Dpd. On the other hand, the desired pattern size is larger than the desired value, Dum is made small or its period is made large near Dpd. The number of Dums near Dpd may be changed to affect the resolution of the desired pattern. As the number of Dums decreases, the light amount of the desired pattern may be made small, whereas as the number of Dums increases the light amount of the desired pattern may be made large. The illumination system may be changed. For example, although the illumination by the illumination system having the effective light source distribution shown in FIG. 16 is effective to a binary mask, a change of the size of the light shielding area would make the hole shape circular, and change the resolving power and depth of focus.
Accordingly, the illumination is required to enable the diffracted beams 11-18 to enter the pupil. For example, in order for two diffracted beams 10 and 15 as an example to enter a diagonal area on the pupil plane shown in FIG. 63, the oblique incidence illumination is set for a dark and rectangular area “a” on the effective light source plane in FIG. 64. Thereby, the diffracted beams labeled by 10′ and 15′ respectively move to areas b1 and b2 depicted by a cross line and a diagonal, and enter both ends on the pupil in the projection optical system. Two diffracted beams enter the pupil with the effective light source shown by one rectangle, and result in interference, forming interference infringes at a regular interval in an wafer. Similarly, the oblique incidence illumination may be set even for two diffracted beams 10 and 17 as described for the beams 10 and 15. Four rectangular effective light source areas “a” are combined as shown in FIG. 65, and linear interference infringes, which has a line shape with a regular pitch in longitudinal and transverse directions, cause part having strong intensity and part having weak intensity to appear two-dimensionally and periodically at intersections of overlapping light intensity on the wafer. The effective light source at this time has, as shown in FIG. 68A, a crossed four-rectangle shape that extends in a direction orthogonal to the radial direction of the pupil.
Accordingly, as shown in FIG. 63, except an area “c” that is defined by linearly connecting positions of two diffracted beams on the pupil plane, an effective light source distribution is added which enables only one diffracted beam, since an oblique incidence angle may be made small. FIG. 67 shows one example of the effective light source distribution. Such illumination is available, for example, by enabling one diffracted beam 10′ to enter the dark and sector area “a” in the effective light source plane. Thereby, the diffracted beam labeled by 10′ moves to a bright and sector area b, and thus the diffracted light enters the pupil plane. There are four pieces corresponding to these conditions, forming an effective light source as shown in FIG. 68B.
The exposure apparatus used for this example has a wavelength of the exposure light of 248 nm and an NA of 0.73. A binary mask shown in FIG. 20A is used which has a dummy hole diameter for each C/H of 120 nm on a wafer, a lateral pitch of 120 nm, and a longitudinal pitch of 360 nm. This corresponds to a lateral period of 240 nm and a longitudinal period of 480 nm. As shown in FIG. 20B, dummy holes are inserted with periods of 240 nm in the longitudinal and lateral directions. Dummy patterns of three circumferences are inserted around the desired pattern. An illumination system has the maximum coherence factor σ of 0.92 in FIG. 16, and FIG. 21A shows an experimental result with a=0.7 and b=0.5, while FIG. 21B shows an experimental result with a=0.6 and b=0.5. It is understood that an either case forms an image clearly. The resist at this time uses TOK-DP746HC, but it has been discovered that other resists including JSA-KRFM170, UV6-SL, etc. may also form an image.
The wavelength of the exposure light in the exposure apparatus used for this example has 248 nm, and an NA of 0.73. An attenuated PSM (or a half tone mask) having the transmittance of 6% of light strength uses the structure of the mask shown in FIG. 20A. It has a hole diameter for each C/H of 120 nm on a wafer, a lateral pitch of 120 nm, and a longitudinal pitch of 360 nm. This corresponds to a lateral period of 240 nm and longitudinal period of 480 nm. As shown in FIG. 20B, dummy holes are inserted with periods of 240 nm in the longitudinal and lateral directions. Dummy patterns of three circumferences are inserted around the desired pattern. An illumination system has the maximum coherence factor σ of 0.92 in FIG. 16, and FIG. 22 shows a simulation result with a=0.7 and b=0.5. It is understood that the result forms an image successfully.
The wavelength of the exposure light in the exposure apparatus used for this example has 248 nm, and an NA of 0.73. A phase-shift mask a phase difference of 180° between adjacent holes uses the structure of the mask shown in FIG. 20A. It has a hole diameter for each C/H of 120 nm on a wafer, a lateral pitch of 120 nm, and a longitudinal pitch of 360 nm. This corresponds to a lateral period of 240 nm and longitudinal period of 480 nm. As shown in FIG. 20B, dummy holes are inserted with periods of 240 nm in the longitudinal and lateral directions so that adjacent holes have a phase difference of 180°. Dummy patterns of three circumferences are inserted around the desired pattern. An illumination system has the maximum coherence factor σ of 0.92 in FIG. 17, and FIG. 23 shows a simulation result with a=0.2 and b=0.1. It is understood that the result forms an image successfully.
The wavelength of the exposure light in the exposure apparatus used for this example has 248 nm, and an NA of 0.73. A binary mask shown in FIG. 24A is used which blends holes with a hole diameter “s” of various periods. As a result, there are at least two periods P and P′″ in the lateral direction and at least two periods P′ and P″ in the longitudinal direction. The present invention is effective to such a mask, and a dummy pattern shown in FIG. 24B may be inserted. The principal of the dummy hole insertion combines those stated in the embodiment. In addition to the insertion of these dummy holes, a pattern that is not resolved usually was resolved by changing values for “a” and “b” in the illumination system shown in FIG. 16. More specifically, when p=240 nm, p″=280 nm, p′=260 nm, and p′″=220 nm using the annular illumination without any dummy hole, an image is not clearly formed since the isolated hole has a weak light strength. As shown in FIG. 24B, all the images are clearly resolved when the dummy holes was inserted and the illumination system shown in FIG. 16 was used with a=0.7 and b=0.5.
As shown in FIG. 25A, a mask that arranges a pattern with a period of “p” and a pitch 2p+p′, where p is a period corresponding to 0.5<k1<1.0 and p′ is a period corresponding to 1.0<k1<1.5. Here, k1 is expressed by k1=R·NA/λ, where R is the resolution, NA is a numerical aperture, and λ is a wavelength of an exposure light source. As the dummy holes of two circumferences is inserted with a period of “p” around each pattern, an area with a dummy hole interval of p′−p appears. These dummy holes would possibly expose the resist due to their mutual proximity effect. Accordingly, in order to avoid the problem, dummy holes are arranged partially having a period of p′/2 as shown in FIG. 25B. It has been confirmed that thus arranged dummy holes caused proximity effect to the adjacent dummy holes, and had an indirect affect of this effect on the desired pattern. In particular, the depth of focus has appeared to improve.
This example determines dummy holes by operation(s). Given the desired pattern shown in FIG. 3, the lateral period p is 240 nm, the longitudinal period is 2p, and the hole diameter “s” is p/2. Like the desired pattern, the mask pattern is setup so that an area that does not have the mask data is provided with the transmittance of zero and an area that has the mask data is provided with the transmittance of one. FIG. 4A is the thus produced mask pattern.
The arrangement of the dummy pattern may be determined by the desired pattern. There are various rules for the arrangement of the dummy pattern, as discussed above, and the inventors have also obtained an empirical rule shown in FIG. 6. FIG. 6A is a flowchart showing a method for setting a hole diameter of the dummy hole from the desired pattern. First, it is determined whether k1 corresponding to the minimum half pitch p′ of the desired pattern is 0.25×√2 or smaller (step 2002), and if so the size of the dummy hole is set to be 75% of p′ (step 2004). If not, the size of the dummy hole is set so that its k1 may become 0.25 or smaller (step 2006). A description will now be given of the reason of the empirical rule. In exposing a binary mask having usual dense contact holes, the diffracted light is generated as shown in FIG. 28. Two dimensionally distributing diffracted light is referred to as shown in FIG. 28. More, the maximum coherence factor σ is one for simplicity purposes. In order for (0, 1)-order light or (1, 0)-order light to enter the pupil plane, k1 corresponding to p should be 0.25 or greater. On the other hand, in order for (1, 1)-order light to enter the pupil plane, k1 corresponding to p′ is 0.25×√2 or greater. Therefore, when k1 corresponding to p′ becomes 0.25×√2 or smaller, the resolution becomes extremely difficult. Therefore, a boundary condition that uses 0.25×√2 for k1 corresponding to p′, is not necessarily incorrect. When k1 corresponding to p′ becomes 0.25×√2 or smaller, the resolution becomes extremely difficult and thus the dummy holes are difficult to be resolved even when the size of the dummy hole is set to be as relatively large as 75% of p′. On the other hand, when k1 corresponding to p′ becomes 0.25×√2 or larger, the size of the dummy hole is set so that k1 as an index of difficulty of resolution becomes 0.25 or smaller. This is true when the maximum coherence factor σ is 1 in the illumination system. In an actual exposure apparatus, the maximum coherence factor σmax is usually less than 1. As a result, the resolution becomes extremely difficult when k1 corresponding to p′ becomes 0.25×√2/σmax or smaller. Therefore, it is proper to require as a boundary condition that k1 corresponding to p′ is 0.25×√2/σmax or smaller.
FIG. 6B is a flowchart for explaining a method for determining a period of the dummy hole pattern. In FIG. 6B, a user may determine g1, g2, g3 and g4. Theoretically, it is preferred that g1=0.25, g2=0.50, g3=2×g2, and g4=2×g2. A description will now be given of theoretical meanings of g1, g2, g3 and g4. g1 is set to be 0.25 due to the resolution limit. g2 is set to be 0.5 due to a requirement for which the first order diffracted light enters the pupil plane, and the larger pattern would relatively easily be resolved. g3 indicates a pattern period, and g3 larger than g2 times 2 would result in comparatively easy resolution. g3 may be set to be g2 times 2 since the dummy holes are inserted so that the pseudo-period may be obtained between g2 and g3 by dividing a certain integer. The same reason as g3 is applied to g4. Of course, these values are variable by considering the past experience and exposure apparatus performance. For example, as a result of using an exposure apparatus Canon FPA-5000ES3 (with a wavelength of 245 nm and a NA of 0.73) and resist TOK-DP746HC, the convergence solutions are obtained with g1=0.30, g2=0.45, g3=1.2 and g4=0.9. The arrangement of the dummy pattern is determined even at an area that has the desired pattern by considering the above. FIG. 4B shows thus determined grids for the dummy hole arrangement. More specifically, the hole diameter in this example is 120 nm, and does not lead to the abnormal termination. k1 of the minimum hole diameter 120 nm is about 0.35, and thus it is between g1 and g2. Since the pattern period P1 is 240 nm, P2 is also 240. Since the pattern period P3 is about 0.70 when converted into k1, it does not correspond to g3 or greater. As a result, the dummy holes may be inserted with a period P2=240 nm. The size of the dummy hole may be set to be 90 nm as 75% of 120 nm since the minimum half pitch is 0.25×√2 or smaller.
This example determines the dummy holes using a table. Given the desired pattern shown in FIG. 3, the lateral period p corresponding to k1 where 0.5<k1<1.0, the longitudinal period is 2p, and the hole diameter “s” is p/2. FIG. 6 shows a method for determining a size and period of a dummy hole obtained by the empirical rule, and a sized dummy pattern is inserted in accordance with this rule, although the mask for the desired pattern is not considered at this stage. There is a method for producing the desired pattern and dummy hole pattern at one time corresponding to the minimum pitch of the desired pattern from the insertion table of the dummy hole prepared in accordance with the rule shown in FIG. 6. Such a method may provide the mask pattern shown in FIG. 4B, and the desired pattern may be exposed by properly selecting the illumination system suitable for the mask.
This example determines the illumination system by operation(s). Given mask data into which the dummy holes have been inserted using an operation or table, the illumination system in the instant exposure method includes illumination portions that serve to resolve the desired pattern typically shown in FIG. 7A and to prevent the dummy pattern typically shown in FIG. 7B from being resolved. The illumination portion shown in FIG. 7A and the illumination shown in FIG. 7B are added by operation, and any overlapping portion adopts one of illumination systems. FIG. 7D is the illumination system obtained by excluding the area by operation larger than the maximum coherence factor σ shown in FIG. 7C in thus obtained illumination system. The illumination system thus obtained could resolve the desired pattern successfully.
This example determines the illumination system utilizing a table that has been obtained experimentally. For example, the illumination system suitable for the instant exposure method that uses a binary mask may be the illumination system shown in FIG. 16. However, the instant inventors have discovered that a value of “a” is close to a solution when set to be ((1/k1)/2−0.1)/2 after k1 corresponding to the minimum half pitch is obtained. This is understood from the first example. “b” serves to prevent the dummy pattern from being resolved. The inventors have experimentally discovered that “b” is suitably set to be 0.5 or greater when k1 corresponding to the minimum half pitch is 0.25×√2 or smaller. When k1 corresponding to the minimum half pitch is 0.25×√2 or greater, the desired pattern is relatively easily resolved, and a value of “b” does not have to be concerned. Therefore, “b” may be ((1/k1)/2−0.1)/2 or smaller and usually be ((1/k1)/2−0.1)/2−0.1. The desired pattern was successfully resolved using the illumination system obtained by referring to values of “a” and “b” from a table that has been prepared based on the above rule. Tables shown in FIGS. 29 and 30 may also be utilized. Although this table data was obtained by simulation, the experimentally obtained data may be used for the table data. The table data in FIGS. 29 and 30 are obtained by checking a change of contrast depending upon the values of “a” and “b” in patterns with hole diameters of 120 nm and 110 nm. The desired pattern was successfully resolved by selecting the illumination system suitable for the mask pattern from the table that has been prepared in this way.
This example forms dummy holes after determining the illumination system for a certain desired pattern. The wavelength of the exposure light in the exposure apparatus used for this example has 248 nm, and an NA of 0.73.
FIG. 1 shows a flowchart of a method for producing mask pattern data and illumination system data relating to this example.
Given a desired pattern typically shown in FIG. 26, and the wavelength of the exposure light in the exposure apparatus used for this example has 248 nm and an NA of 0.73. The desired pattern blends, as shown in FIG. 26A, mask data 26 d that has a hole diameter of 110 nm, a pattern half pitch of 110 nm in the lateral direction, and a pattern half pitch of 220 nm in the longitudinal direction, and mask data 26 e that has a hole diameter of 120 nm, a pattern half pitch of 120 nm in the lateral direction, and a pattern half pitch of 240 nm in the longitudinal direction. The desired mask data was divided into 26 d and 26 e, and dummy data was independently inserted. First, dummy holes were inserted only for the mask data 26 d, and then inserted only for the mask data 26 e. Then, the illumination system common to them was determined. As a result, it was found that there are a difference in exposure dose between the mask data 26 d and the mask data 26 e. This is because the mask data 26 e has the larger hole diameter.
A difference in exposure dose between the mask data 26 d and 26 e was successfully eliminated by changing the number and size of dummy holes. As shown in FIG. 26B, the final mask pattern includes the mask pattern 26 d with dummy holes of 80 nm arranged by three circumferences around the desired pattern with a period of 110 nm in the longitudinal and lateral directions, and the mask pattern 26 e with dummy holes of 80 nm arranged by three circumferences around the desired pattern with a period of 120 nm in the longitudinal and lateral directions. The illumination system used a=0.7 and b=0.5 in FIG. 16. TOK-DP746HC used for the resist could resolve the desired pattern with the exposure dose of 460 J/m2. FIG. 27 shows the result. FIG. 27A shows an exposure result corresponding to the mask pattern 26 d, while FIG. 27B shows an exposure result corresponding to the mask pattern 26 e.
A description will now be given another embodiment of the present invention. Unless otherwise specified, the exposure apparatus used for the following description is an exposure apparatus that uses a wavelength of a light source of 248 nm and a NA of its projection optical system of 0.73. The projection exposure apparatus generally provides demagnification projection exposure. In case of demagnification projection exposure, the pattern size to be produced is different from a mask pattern by a demagnification in the exposure apparatus. The demagnification of the exposure apparatus depends upon its machine type, and this application converts the pattern size on the mask into the size on the wafer or an object to be exposed. For example, in order to form a pattern of 120 nm on the wafer, when the demagnification on the projection exposure apparatus is 0.25, a pattern of 480 nm should be actually formed on the mask, and when the demagnification on the projection exposure apparatus is 0.20, a pattern of 600 nm should be formed on the mask. However, for simplicity purposes, the instant application converts the size of the mask pattern into the size on the wafer or object to be exposed, and calls the pattern of 120 nm. Although each pattern includes one or more contact holes, the term “pattern” sometimes means part of the pattern or one contact hole.
A change of the illumination system would correct the desired pattern. For example, although the illumination by the illumination system having the effective light source distribution shown in FIG. 16 is effective to a binary mask, a change of the size of the light shielding area (“a” and “b” in FIG. 16) would make the hole shape circular, and change the resolving power and depth of focus.
The illumination system may use effective light sources shown in FIGS. 16, 17 and 34 and. The quadrupole illumination shown in FIG. 34 and illumination shown in FIGS. 16 and 17 are typically implemented as an aperture stop located just after a light exit plane of an optical integrator. The optical integrator is located at a position conjugate with a pupil plane in the projection optical system of the exposure apparatus (not shown), and an aperture shape of the aperture stop corresponds to an effective light source shape on the pupil plane in the projection optical system. Therefore, the effective light source shape shown in FIG. 34 is implemented, for example, as an aperture stop 40 having light transmitting parts 41 and a light shielding part 42. The effective light source shape shown in FIG. 16 is implemented as an aperture stop having a light shielding part 16 a and a light transmitting part 16 b. The effective light source shape shown in FIG. 17 is implemented as an aperture stop having a light shielding part 17 a and a light transmitting part 17 b.
FIG. 35A shows a result of exposure experiment using the mask pattern 50 shown in FIG. 33 and the illumination system that uses the quadrupole illumination shown in FIG. 34. As understood from FIG. 35A, the desired pattern 41 is not resolved well.
It is assumed that the desired pattern 41 shown in FIG. 32A, in which has p=220 nm. Since the desired pattern is arranged at lattice points, the auxiliary pattern 32 is added as shown in FIG. 33 for successful exposure with the effective light source shape having a cross light shielding part.
A provision for a database that considers the characteristics of each resist would handle such a case. The database of the instant embodiment stores a table or graph indicative of a relationship between a contrast to the developer for the resist and a corresponding bias to the desired pattern. Here, the contrast to the developer is defined as a subtraction of the solution velocity before exposure from the solution velocity after the exposure. This difference is set to be large in the hole-use resist and small in the line-use resist. In accordance with the above, a graph is drawn as a simply decreasing graph shown in FIG. 61 is obtained in which as the contrast of the resist to the developer decreases the bias to the desired pattern increases, and as the contrast of the resist to the developer increases the bias to the desired pattern decreases, where a longitudinal axis indicates a bias to the desired pattern and a lateral axis indicates a contrast of the resist to the developer. The “bias to the desired pattern” is a magnification of the desired pattern to the basic dimension. As noted, the “basic dimension of the desired pattern” is an initial size converted into the size on the wafer in this embodiment.
One performance index in the exposure method I is a mask error enhancement factor (“MEFF”). MEFF is defined herein as a ratio of an error on the mask pattern to an error that occurs accordingly on a wafer. In general, MEFF is preferably close to 1. For example, a roadmap tends to be produced while it is assumed that MEFF is preferably 1.4 or smaller in an isolated line binary mask, about 1 in an isolated line phase-shift mask, 2 or smaller in a L/S pattern, and 3 or smaller in a hole. Although the exposure method I has relatively small MEFF, some cases require smaller MEFF. A provision for a MEFF database that stores a relationship between the size of the dummy pattern and MEFF would handle such a case. For example, it is assumed that the mask shown in FIG. 32A has p of 220 nm and the hole diameter of 110 nm. When the dummy pattern is inserted with a period of 220 nm in the lateral and longitudinal directions, the mask pattern is completed as shown in FIG. 33. FIG. 57A shows MEFF when the dummy pattern includes an error in the lateral direction. In FIG. 57A, the lowest line indicates the size of the desired pattern, and leftmost column indicates the size of the dummy pattern. Similarly, FIG. 57B shows MEFF with p of 240 nm and the hole diameter of 110 nm. The instant inventors have discovered that as the size of the dummy pattern is reduced, MEFF also becomes small. This is confirmed in view of FIG. 57 as an example, which shows that as the dummy pattern is small MEFF becomes small accordingly for any size of the desired pattern. It is understood that as the desired pattern is made larger, MEFF may be made small.
It is assumed that the desired pattern 41 shown in FIG. 32A has the size of 110 nm, and the auxiliary pattern 52 is added as shown in FIG. 33. The size of the auxiliary pattern 52 is set to be 85 nm (which corresponds to 77% of the desired pattern). The illumination system is set to have the effective light source shape shown in FIG. 16 with the maximum coherence factor σ of 0.92, “a” of 0.7, and “b” of 0.5. FIG. 37 shows MEFF (which assumes two-dimensional errors and appears different at sight from the result in FIG. 57 that assumes one-dimensional errors, but both are the same essentially) in which the pattern half pitch is changed while each hole diameter of the desired pattern 41 is maintained to be 110 nm. It is understood that the pattern half pitch is changed to obtain certain CD error or below. This method changes the desired pattern itself, but is an index of a mask pattern to be designed.
One performance index in the exposure method I is a CD error. The CD error is defined herein as a ratio of difference in size between an actual pattern on a wafer and the desired pattern 41. In general, the CD error is preferably close to 0.
It is assumed that the desired pattern 41 shown in FIG. 32A has the size of 110 nm, and the auxiliary pattern 52 is added as shown in FIG. 33. The size of the auxiliary pattern 52 is set to be 85 nm. The used illumination system is set to have the effective light source shape shown in FIG. 16 with the maximum coherence factor σ of 0.92, “a” of 0.7, and “b” of 0.5. FIG. 38 shows the CD error in which the pattern half pitch is changed while each hole diameter of the desired pattern 41 is maintained to be 110 nm. It is understood that the pattern half pitch is changed to obtain certain MEFF or below. This method changes the desired pattern itself, but is an index of a mask pattern to be designed.
One performance index in the exposure method I is a depth of focus (“DOF”). The DOF provides a permissible range within which a wafer may be offset from a focus position in an optical axis direction of an exposure apparatus. The permissible range is usually determined so that the size of the desired pattern 41 may be fallen within 10% of a desired size. In general, the DOF is preferably large.
Although the exposure method I is considered to expose the pseudo-dense pattern and thus has a relatively large DOF, some cases require larger DOF. Although the lower limit to the DOF is different according to users, Photo Mask Japan (“PMJ”) as a symposium held over three days of Apr. 23-25, 2002, announced that the DOF of 0.4 μm or greater is preferable in the near future in the opening speech “Lithography Strategy for 65 nm Node”. A provision for a DOF database that stores a relationship between the size of the dummy pattern and the DOF would handle such a case. For example, it is assumed that the mask shown in FIG. 32A has p of 220 nm and the hole diameter of 110 nm. When the dummy pattern is inserted with a period of 220 nm in the lateral and longitudinal directions, the mask pattern is completed as shown in FIG. 33. FIG. 59 shows the DOF. In FIG. 59, the lowest line indicates the size of the desired pattern, and leftmost column indicates the size of the dummy pattern. The result shown in FIG. 59 indicates the DOF under such a relatively strict condition with the CD between 108 nm and 120 nm. It is understood in view of FIG. 59 that as the size of the dummy pattern is enlarged, the DOF also becomes large. FIG. 60 shows the simulation result about this. It is assumed that the mask shown in FIG. 32A has p of 220 nm and the hole diameter of 110 nm. When the dummy pattern is inserted with a period of 220 nm in the lateral and longitudinal directions, the mask pattern is completed as shown in FIG. 33. When the dummy pattern having the size of 79.5 nm is inserted, the aerial image for each defocus is as shown in FIG. 60(i). When the dummy pattern having the size of 90.5 nm is inserted, the aerial image for each defocus is as shown in FIG. 60(ii). As the dummy pattern becomes large, the DOF becomes large visually.
In an attempt to form an ellipse hole in the exposure method I, for example, when there is a desired rectangular pattern 33 shown in FIG. 40A, such a pattern 33 is often resolved as an ellipse hole actually. Therefore, a square dummy hole 34 is inserted into a desired pattern 30A in accordance with its pitch and a mask pattern 30B is formed as shown in FIG. 40B. A symbol attached to each arrow means that the same symbol indicates the same length of the arrow. The desired pattern 33 may be resolved by optimizing an illumination system for the mask pattern 30B shown in FIG. 40B. Although the larger OPC is needed when the ellipse hole should be made longer, it was discovered that the ellipse hole corresponding to the desired pattern 33 is easily producible when a rectangular hole 35 is inserted instead of the dummy pattern 34, like the mask pattern 30C shown in FIG. 40C.
A description will now be given of a case where there are a plurality of desired patterns having plural pitches apart so far from each other to ignore interference between these patterns. FIG. 41A shows desired patterns 130A and 130B in areas “s” and “t” encircled by two dot lines on one mask 130. The desired pattern 130A includes one square hole 132 and two rectangular holes 134. The desired pattern 130B includes three square holes 136.
The desired pattern 130A in the area “s” has a narrow pattern interval D1, while the desired pattern 130B in the area “t” has a wide pattern interval D2. The area “t” has k1 corresponding to a pattern period P2 slightly smaller than 1. When the period P1 in the area “s” is compared with the period P2 in the area “t”, P1 is smaller. Therefore, it is difficult to resolve the pattern in the area “s” with accuracy. Moreover, the normal exposure cannot resolve both patterns 130A and 130B at the same time because the light strength reaching the wafer is different between the areas “s” having a dense pattern and the area “t” having a sparse pattern.
Nevertheless, the exposure I is effective even in this case. As shown in FIG. 41B, a dummy pattern 140A is inserted into the area “s”. As shown in FIG. 41B, the desired pattern 130A has holes 132 and 134 having two different shapes, and the dummy pattern 140A includes dummy holes 142 and 144 accordingly.
Therefore, this example devises the way of inserting the dummy pattern 140A. As introduced by the seventeenth example, the desired rectangular pattern is congenial to a similar rectangular dummy pattern, while the desired square pattern is congenial to a similar square dummy pattern. Therefore, dummy pattern having two kinds of shapes is included in the area “s”.
As shown in FIG. 41C, the dummy pattern 140B is inserted into the area “t”. As shown in FIG. 41C, the dummy pattern 140B includes dummy holes 146, and there is no dummy pattern 146 inserted between two holes 136 in the desired pattern 130B. If the dummy hole 146 is inserted, k1 corresponding to the pattern period becomes smaller than 0.5 below the theoretical resolution limit. For example, this is so when the hole diameter D2 is 110 nm and the hole interval D3 is 220 nm. As discussed above, the exposure apparatus has a wavelength of the light source of 248 nm and a NA of 0.73, and thus k1 corresponding to the period P2 of 330 nm is about 0.97 and k1 corresponding to the half period is about 0.48, which is below the theoretical resolution limit.
Thus, when the dummy patterns 140A and 140B are inserted, the illumination condition was optimized in accordance with a pitch P1 in the area “s” since a pitch P1 in the area “s” is smaller than the pitch P2 in the area “t”. As a result, the pattern was transferred satisfactorily. In this course, the size of the dummy pattern was adjusted between these areas so that the desired pattern 130B in the area “t” is enlarged.
A description will now be given of the way of improving the depth of focus in the area “t” as well as the better resolution in the desired patterns 130A and 130B. In the above example, the DOF in the area “t” sometimes becomes small. This is because the pitch P2 in the area “t” is excessively large and so-called forbidden pitch phenomenon occurs in the illumination system corresponding to the area “s”. The forbidden pitch phenomenon is a phenomenon in which the DOF is remarkably reduced with a certain pitch or greater. This is because the second or higher order diffracted light contributes to the pattern formation with the excessively large pattern period although the normal imaging uses 0th order light, 1st order light and −1st-order light. The illumination system should be optimized so as to match the area “t”. As a result of this case, the pattern in the area “s” was not resolved properly. This rests in the contradictory principal in which the preference of the resolving power would deteriorate the DOF and the preference of the DOF would deteriorate the resolving power. FIG. 41A shows one example of the contradictory patterns. On the contrary, the instant inventors have discovered that it is possible to prevent the lowering resolving power by changing the pattern in the area “s” using the OPC as shown in FIG. 41D. In FIG. 41D, the OPC partially reduces the desired pattern 130A in the area “s”. More specifically, the desired hole 132 indicated by a broken line is changed to a desired hole 132A indicated by a solid line. The desired hole 134 indicated by a broken line is changed to a desired hole 134A indicated by a solid line. This is because the mask data is increased since the DOF has made larger. A user may determine which takes preference among the DOF and the size of the mask data.
A description will now be given of characteristics of a binary mask, an attenuated PSM and a phase-shift mask. It is assumed that the desired pattern 41 shown in FIG. 32A has p of 220 nm and a pitch of 110 nm. Since the desired pattern 41 is arranged on lattice points, the dummy pattern 52 shown in FIG. 33 is inserted to form the mask pattern 30. In case of binary and half tone masks, the illumination system shown in FIG. 16 is used for exposure with the maximum coherence factor σ of 0.92, a=0.7, and b=0.5. In case of a phase-shift mask as the mask shown in FIG. 33 in which adjacent holes are different in phase by 180°, the illumination system having the effective light source shape shown in FIG. 17 is used with a=0.2 and b=0.1.
When two inserted dummy patterns are fallen within a predetermined distance, the way of insertion should be reviewed because these dummy patterns are highly likely to be resolved.
A mask for use with the exposure method I is characterized in that a dummy pattern is inserted into a desired pattern. Therefore, it is necessary to investigate the influence by the dummy pattern on the desired pattern. This example addresses a so-called location error. Here, the location error is a slight offset among centers 172 of mask patterns 171 which are expected to be aligned with one another as shown in FIG. 45. The current mask preparing technique usually associates with a few nanometers.
A mask for use with the exposure method I is characterized in that a dummy pattern is inserted into a desired pattern. Therefore, it is necessary to investigate the influence by the dummy pattern on the desired pattern. This example addresses a so called size error. Here, the size error is an offset of a dummy pattern 182 drawn in a solid line, as shown in FIG. 46, from a predetermined size of a dummy pattern 181 originally prepared as a design value indicated by a broken line.
In case of a pattern 190 that includes plural periods as shown in FIG. 47A, it has conventionally been impossible to insert a dummy pattern into this desired pattern 190 because the premise that a dummy pattern is periodically inserted is unavailable. However, the present invention may insert a dummy pattern into such a pattern 190 in accordance with the flowchart shown in FIG. 48.
FIG. 48 is a flowchart to determine the size of a dummy pattern. FIG. 48A determines the size of the dummy hole in the above example. A creator may freely set “v” in FIG. 48A. First, it is determined whether k1 corresponding to the minimum half pitch p of the desired pattern is 0.25×√2 or smaller (step 3102). When the step 3102 determines so, then the size of a dummy hole is set to be v % of a desired pattern (step 3104). On the other hand, when the step 3104 determines not, then the size of the dummy hole is set to be 0.25 or smaller when converted into k1 (step 3106).
FIG. 48B is a flowchart to determine a period of the dummy pattern when the desired pattern is a periodic pattern. In FIG. 48B, a creator may freely set g1, g2, g3 and g4. It is theoretically preferable to set g1=0.25, g2=0.50, g3=2×g2, and g4=2×g2, although these values may be changed taking the past experience and performance of the exposure apparatus into consideration.
First, it is determined whether the hole diameter of the desired pattern (i.e., “s” in FIG. 47A) is below g1 as a first threshold (step 3202). If the step 3202 determines so, the process ends with an abnormal operation (step 3204). On the other hand, if the step 3202 determines not, it is determined whether the hole diameter of the desired pattern is between g1 as the first threshold and g2 as a second threshold (step 3206). Here, the periodic pattern has a period of P1.
In case of a pattern 200 shown in FIG. 49, the pattern 200 forms a lattice at a certain interval and a center 212 of the pattern 210 is arranged on each lattice point, but only one pattern 220 does not have its center on the lattice point. In addition, the center 222 of the pattern 220 is slightly offset from the lattice point.
A description will now be given of a relationship between the size of a dummy pattern and the exposure dose. It is assumed that the desired pattern 41 shown in FIG. 32A has p of 220 nm. Since the desired pattern 41 is arranged on lattice points, the dummy pattern 52 is inserted, as shown in FIG. 33, to form the mask pattern 30.
A description will now be given of an example that follows the flowchart shown in FIG. 48. Here, the description addresses FIGS. 48A and 48B for simplicity purposes. A program that the instant inventors have created assumes an exposure apparatus with a wavelength of 248 nm and a NA of 0.73.
The resolving power in the projection exposure apparatus often changes at 0.25 and √2 as a boundary. Therefore, it was been discovered that a period of a dummy pattern may be determined for almost all the patterns by setting g1 between 0.25 and 0.25×√2, g2 between 0.25×√2 and 0.5, g3 between 1.0 and √2, g4 between 0.5×√2 and 1.0, g5 between 0.25 and 0.25×√2.
illuminating the mask using an effective light source that has a shape adjusted based on a period of a pattern that consists of the auxiliary pattern and the contact hole pattern,
wherein the effective light source includes a cross-shaped light shielding area, and the shape of the effective light source is adjustable by changing a shape of the cross-shaped light shielding area.
2. An exposing method according to claim 1, wherein said contat hole pattern and auxiliary pattern are arranged on the mask along at least a first direction, and the cross-shaped light shielding area has axes in the first direction and in the second direction that is orthogonal to the first direction.
preparing data for the auxiliary pattern based on data of the contact hole pattern;
adjusting a shape of an effective light source for illuminating the mask based on a period of a pattern that consists of the auxiliary and the contact hole pattern;
evaluating a resolution state of the contact hole and auxiliary patterns when the mask is illuminated by the effective light source; and
correcting data of the contact hole pattern and/or the auxiliary patterns based on the resolution state,
wjerein the effective light source includes a cross-shaped light shielding area, and the shape of the effective light source is adjustable by changing a shape of the cross-shaped light shielding area.
6. A mask designing method according to claim 5, wherein said correcting step includes the step of changing a size of the auxiliary pattern.
arranging the contact hole pattern with at least two periods in each of a lateral direction and a longitudinal direction; and
arranging the auxiliary pattern at a position apart from the contact hole pattern according to the at least two periods in each of one lateral directio or a longitudinal direction.
14. A mask designing method suitable for an exposure method for illuminating a mask that has a contact hole pattern and an auxiliary pattern smaller than the contact hole pattern by using light that enables the contact hole pattern to resolve and prevents the auxiliary pattern from resolving, and for exposing an object using the light from the mask, said mask designing method comprising the step of:
arranging, when two auxiliary pattern overlap each other or are adjacent to each other, only one auxiliary pattern having a center of gravity that cooresponds to a center of gravity of the two auxiliary patterns.
15. A mask designing method according to claim 14, wherein a form of the auxiliary pattern is similar to a form of the contact hole pattern.
arranging, only one auxiliary pattern having a center of gravity that cooresponds to a center of gravity of two centers of gravity of two auxiliary patterns to be inserted which have an interval of a vertex distance between the two auxiliary patterns smaller than a predetermined value, instead of providing the two auxiliary patterns,
wherein the predetermined value is 0.20 when standardized by λ/NA, where λ is a wavelength of the exposure light, and NA is a numerical aperture of the projection optical system.
17. A mask designing method according to claim 16, wherein the auxiliary pattern is similar to a form of the contact hole pattern.
preparing data of the auxiliary pattern to be arranged so that the isolated contact hole pattern and the auxiliary pattern formn a periodic pattern having a predetermined period, wherein the predetermined period is twice as large as a hole diameter of the isolated contact hole pattern in either one of a lateral direction or a longitudinal direction.
19. A mask designing method according to claim 18, wherein a form of the auxiliary pattern is similar to a form of the contact hole pattern pattern.
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JP2002160741A JP3754934B2 (en) 2002-04-23 2002-04-23 Setting a mask pattern and illumination condition
JP160741/2002(PAT.) 2002-04-23
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US20030198872A1 true US20030198872A1 (en) 2003-10-23
US7107573B2 true US7107573B2 (en) 2006-09-12
ID=28793638
US10251581 Active US7107573B2 (en) 2002-04-23 2002-09-20 Method for setting mask pattern and illumination condition
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