JPH06313964A - Mask and pattern forming method - Google Patents

Abstract

PURPOSE:To obtain fine and highly precise patterns by forming auxiliary patterns having sizes which are not resolvable on the peripheries or the inside of the desired patterns. CONSTITUTION:This mask consists of a translucent type phase shift mask set with the transmittance and phase different of not 0 transmittance and not 0 phase difference from the light transmission parts in at least one points thereof and has the auxiliary patterns 12a which are not resolvable exclusive of the desired patterns 11. Namely, the auxiliary pattern groups 12 consisting of the auxiliary patterns 12a are arranged at the ends where periodicity ends to create the conditions under which the periodicity continues, by which the strains of the exposing light intensity profile appearing at the terminal of the period of a diagonal incident illumination system are decreased. The two compatible requirements in such a case are that the auxiliary patterns 12a is so arranged as to allow the periodicity of the desired patterns 11 to continue even at the ends and that the auxiliary patterns is the auxiliary patterns 12a or auxiliary pattern groups 12 which do not remain after development and are not resolvable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mask and a pattern forming method used in a projection exposure method using a grazing incidence illumination system for forming a fine pattern such as an LSI on a substrate such as a wafer using a projection optical system. It is a thing.

[0002]

2. Description of the Related Art Conventionally, a projection exposure apparatus for forming a fine pattern such as an LSI has been required to have high resolution, and recently, it has reached a resolution close to a theoretical limit determined by the wavelength of light. In recent years, in order to deal with further miniaturization of LSI patterns, a phase difference close to 180 ° is provided between adjacent light transmitting portions on a mask (reticle) to improve the resolution by making the light intensity in the light shielding portion close to zero. A phase shift method has been proposed to improve the resolution. However, in the phase shift method, a large miniaturization effect can be obtained in a pattern having a high periodicity such as an L & S pattern (line and space pattern) in which a phase difference of 180 ° can be obtained between adjacent light transmitting portions. It is difficult to satisfy this condition with a random pattern, and the effect is also reduced. That is, the effect of improving the resolution differs depending on the type of pattern and the way of arrangement. For this reason, the phase shift method has many technical difficulties such as effective shifter placement method, defect-free shifter fabrication technology and its inspection, repair technology, etc. There were drawbacks such as increasing the number.

On the other hand, Japanese Patent Application No. 3-99822 “fine pattern projection exposure apparatus” irradiates light incident on a mask at an angle corresponding to the numerical aperture of the projection optical system from the optical axis. It is an invention that realizes resolution equivalent to that of the phase shift method. This method has a great advantage over the phase shift method because the conventional mask can be used as it is. In order to illuminate the mask illuminating light by inclining it from the optical axis, Japanese Patent Application No. 3-157401 "Fine pattern projection exposure method" invents and provides a light source such as a ring, four points, or multiple points.

Since only one side of the diffracted light diffracted by the mask pattern is used for image formation in such oblique incidence illumination, the 0th-order diffracted light is approximately doubled as compared with the conventional method using both-side diffracted light. Since this extra 0th-order light causes a reduction in contrast, in Japanese Patent Application No. 3-157401 “fine pattern projection exposure method”, a portion corresponding to the shape of the light source that forms an image at the aperture stop position when there is no mask and A method of arranging a 0th-order light adjustment filter around it,
In Japanese Patent Application No. 3-177816 "Mask and projection exposure method using the same", the light-shielding portion of the mask is semitransparent, and the light transmitted through the light-shielding portion has a phase difference of approximately 180 ° with the light transmitted through the transparent portion. The 0th-order light adjustment masks are used to adjust the 0th-order light respectively to improve the contrast. Kamon et al. Also reported at the 39th Joint Lecture on Applied Physics 30a-NA-7 that a similar contrast improvement effect can be obtained by combining the grazing incidence illumination method and a shifter shading type phase shift mask.

First, the light sources used in the above-described oblique incidence illumination system and the conventional illumination system will be described. FIG. 14 shows an example of typical light source shapes and typical optical parameters for conventional illumination and various oblique incidence illumination systems. The shaded area in the figure is the light source. Here, the radius of the aperture stop normalized by the numerical aperture (NA) of the projection lens is set to 1. The radius of the circular light source in the conventional illumination method is σ. For a circular light source, the radius to the center of the circular ring is R, and the width of the circular ring is 2σΔ
And In a four-point light source, the distance to the center of each point light source having a finite size was R, and the diameter of each point light source was 2σΔ.

FIGS. 15 (a), 15 (b), and 15 (c) illustrate a zero-order light adjustment mask for improving image contrast in combination with the grazing incidence illumination method. In the figure, 1 is a mask substrate, 2 is a light transmitting portion, and 3 is a transmittance adjusting phase shift portion (corresponding to a light shielding portion of a normal mask). The 0th order light adjustment mask is
In the conventional mask, the light-shielding portion 3 is used as a semi-transmissive film, and its transmittance is adjusted so as to improve the contrast (a typical amplitude transmittance is t = 0.35 (intensity transmittance about 12).
%), But the most effective transmittance differs depending on the light source shape, pattern shape, and the like. ) And semi-transmissive part 3
The phase difference between the light that has passed through and the light that has passed through the transmissive portion 2 is adjusted to be close to 180 °. The use of the grazing incidence illumination in combination with this 0th order light adjustment mask improves the image contrast, and as a result, further improves the resolution and the depth of focus. In addition, the 0th-order light adjustment mask has a large tolerance for phase shift and can obtain an effect in a wide range of phase difference as compared with the case where it is used as a so-called phase shift mask for an ordinary light source. Here, this mask is called a 0th order light adjustment mask for the purpose of use, but even in a phase shift mask generally called a shifter light shielding type or a halftone type, if the light shielding portion is semitransparent and has a phase difference. , Can bring about the same effect. Therefore, the drawbacks to be described hereinafter also appear, and the effects of the present invention can be obtained in the same manner. Therefore, masks that produce similar effects in combination with these oblique incidence illumination methods are generically referred to as 0th-order light adjustment masks, When combined with illumination, it will be called a halftone phase shift mask. In both cases, the original light-shielding portion is semi-transparent, so this portion will be referred to as a semi-transmissive portion in distinction from a general light-transmitting portion or a light-shielding portion.

In both of the above-described exposure methods that combine the oblique incidence illumination method and the zero-order light adjustment mask, a phase difference is imparted between adjacent patterns by oblique irradiation to improve resolution similar to the phase shift method. Since the effect of is obtained, high resolution can be obtained in a pattern with high periodicity,
There is a problem that the resolution is lowered or the imaging pattern is distorted in a random pattern having a low periodicity, an end portion of a period of a periodic pattern, an isolated pattern having no periodicity or a large pattern.
In order to explain this problem in detail, in the following description, the unit of U and Z standardized as follows for the size of the pattern, the distance in the mask, and the defocus amount is used. Unit of pattern size and distance in mask ・ ・ ・ U = λ / 2 (NA) Unit of defocus amount ・ ・ ・ Z = λ / 2 (NA) 2 The parameters shown in FIG. 3 for the system were used as standard values. In addition, the defocus amount in the light intensity distribution is 0, 1, 1.5 of Z and 4 times that of Z.
The level was set.

In the exposure using the halftone type phase shift mask or the 0th order light adjustment mask described above, light is transmitted to the semi-transmissive portion. Therefore, there is a problem that an area that should not be exposed is exposed depending on the transmittance and the exposure intensity, and an unnecessary pattern due to this exposure is transferred onto the resist (photosensitive material) depending on the strength of development. there were. In other words, in other words, since the unnecessary pattern is not transferred, the margin for the developing condition becomes very small.

Next, the exposure method in which the grazing incidence illumination method and the zero-order light adjustment mask are combined will be described by comparing the location of problems such as pattern distortion with the conventional illumination method. FIG.
(A), (B), (C), and (D) show simulation results of exposure intensity profiles for typical periodic patterns, and (E) and (F) show exposure intensity profiles for non-periodic patterns. It is a thing. The periodic pattern is an L & S pattern (line and space pattern) consisting of 16 lines of infinite length, and the width of each line and space is U. The horizontal axis represents the distance in the mask expressed in U, and the vertical axis represents the exposure intensity. The design value of the pattern edge is from 4 to 35 in the unit of U, and the defocus amount is shown by a solid line, a short solid line, a long broken line and a dash-dotted line for four levels of 0, 1, 1.5 and 2 times of Z, respectively. is there. (A), (C),
(E) is the case of the conventional method using the conventional illumination and the conventional mask, and (B), (D), and (F) is the case of using the exposure method combining the oblique incidence illumination method and the zero-order light adjustment mask. Is.

In ordinary development, a pattern is formed when the exposure intensity is around 0.3 level. Therefore, the amount of lateral displacement between the point where the exposure intensity profile intersects the level of the exposure intensity of 0.3 and the design edge is small, that is, the pattern distortion is small, and how much the region where this amount of displacement is small is above and below. It is important that the development margin is large and that this margin does not become small even if the defocus amount becomes large. Comparing FIG. 16 (A) and (B),
The conventional illumination method shows that the resolution decreases as the defocus amount increases, the development margin decreases, and pattern formation is difficult. On the other hand, it can be seen that the 0th-order light adjustment mask method shows good resolution even when the defocus amount is large, and can form a pattern with a large depth of focus. However, comparing the exposure intensity profiles of the 16 patterns, the conventional illumination method shows almost the same over all patterns, whereas the 0th-order light adjustment mask method shows a large change in the exposure intensity especially at the end of the periodic pattern. These appear as a result that the pattern width is different between the central portion and the end portion in the actual pattern formation, or the end pattern is not formed during defocusing. (C) and (D) are (A),
It is an enlarged view of a part of (B). In the 0th-order light adjustment mask method, the exposure intensity profile is prominently projected due to defocusing at the rightmost pattern. This means that in the actual pattern formation, it appears as a positional deviation of the pattern edge or a distortion of the pattern shape, and if the development fluctuates, a large dimensional variation occurs.

The non-periodic patterns shown in FIGS. 16E and 16F are infinite length patterns having design edges 4 and 16 in units of U. The defocus condition is the same as the periodic pattern. In the exposure intensity profile (E) by the conventional illumination method, there is almost no deviation due to defocus at the intersection of the standardized exposure intensity 0.3 and the design edge, whereas in the 0th order light adjustment mask method (F), the defocus amount is The larger the position, the larger the displacement. This is the actual pattern formation,
It appears as a thin pattern (for positive resist) or a thick pattern (for negative resist).

Regarding the problem of excessive light transmission in the semi-transmissive portion, which was pointed out above regarding the exposure method using the 0th-order light adjusting mask combined with the grazing incidence illumination method, the location of the problem is compared with the case of using a conventional mask. While explaining. FIG. 17 (A),
(B) is a simulation of the light intensity distribution on the X axis for the same pattern in which the light transmitting portion is an isolated line. Three
The solid line is the case where the solid line is in focus, and the other two lines are in the case where the focus amount is sequentially increased. The light source is an oblique incidence illumination of an annular zone, (A) is a conventional Cr mask, and (B) is a 0-order adjustment mask having an intensity transmittance of 12%. When a resist exposed with such an exposure intensity distribution is developed in a normal process, the light intensity is set to a threshold value of about 0.3, and a portion exposed further is dissolved (in the case of a positive resist). At this time, this value is always 0.degree. Depending on the properties and thickness of the resist and the developing conditions (the strength of the developing solution and the developing time).
However, the larger the difference in light intensity between the exposed portion and the unexposed portion, the closer the pattern-shaped cross section after development is to a rectangular shape, which is a desirable shape. When exposure is performed with a conventional mask as shown in (A), the light intensity of the surroundings is substantially equal to 0 because the portion other than the isolated line is the light shielding portion. Therefore, the peripheral portion is not exposed to light, and after the resist development, a groove is formed only in the pattern portion (in the case of a positive type resist), and the resist is left as it is in the peripheral portion to form a pattern. On the other hand, when the 0th-order light adjustment mask of (B) is used, the peripheral portion of the pattern has a transmittance of 12%, so that the influence also appears on the exposure intensity distribution, and the light intensity at the peripheral portion is increased. Is over 0.1. Therefore, in some cases, this portion is exposed to light, and after development, the resist in the peripheral portion other than the groove in the pattern portion is dug or the film is reduced. Further, in the pattern formation with a resist, usually, the contrast of the light intensity between the exposed portion and the unexposed portion is used as the maximum intensity Imax and the minimum intensity Imin. MTF = (Imax-Imin) / (Imax + Imi
n), which means that the higher the contrast, the more marginal the development conditions are, and the more advantageous the pattern formation is. In the case of FIG. 17, since Imin≈0 in (A), the contrast is close to 100%, but in (B), the contrast is only about 50% when Imin is set at the highest point in the peripheral portion.

[0013]

As described above,
In the oblique-incidence illumination method, there is a drawback that unevenness of exposure intensity or deformation of exposure intensity profile occurs at the end of the cycle of non-periodic pattern or periodic pattern, which results in pattern distortion or positional deviation, which lowers accuracy. there were. Further, in the halftone type phase shift mask and the 0th order light adjustment mask in the oblique incidence illumination method, since light is transmitted to the semi-transmissive portion, the development margin at the time of forming the resist pattern is small, and the film loss of the non-patterned portion occurs. It had the drawback of being easy.

The present invention has been made in view of the conventional problems as described above, and an object thereof is to form a pattern by projection exposure using an oblique incidence illumination system.
Mask and pattern formation that makes it possible to obtain fine and highly precise patterns by removing or reducing pattern distortions and positional deviations that occur at the end of the periodic pattern and the edge of the aperiodic pattern, and also improving the contrast. To provide a method. Further, in the pattern formation using the mask having the semi-transmissive portion, the present invention can suppress the light intensity on the wafer surface in the region corresponding to the semi-transmissive portion without impairing the effect thereof, and thus the high contrast can be obtained accurately. It is an object of the present invention to provide a mask capable of obtaining a pattern and a pattern forming method.

[0015]

In order to achieve the above object, the first aspect of the present invention is directed to oblique incidence illumination for improving the resolution and the depth of focus by arranging the main part of the light source at a position displaced from the optical axis. In the mask used in the method, the mask is a transflective phase shift mask having a transmittance and a phase difference which are not 0 and have a non-zero phase difference with respect to the light transmitting portion in at least one place. In addition to that pattern, it has auxiliary patterns that cannot be resolved. Second
In the first invention, in the first invention, when the target pattern arrangement has periodicity, an unresolvable auxiliary pattern or auxiliary pattern group is formed so as to preserve the periodicity. In the third invention, in the first invention, when the arrangement of the target pattern has no periodicity, the unresolvable auxiliary pattern or the auxiliary pattern group is formed so as to impart the periodicity to the target pattern. It was done. In a fourth aspect based on the second aspect, when λ is the wavelength of the illumination light and NA is the numerical aperture of the projection lens, the width of the target pattern formed of the light transmitting portion (or the transmittance adjusting portion) is λ / (2N
In the vicinity of A) or more, 0.8 × λ / (2NA) or more from the mask transmission part (or transmittance adjustment part) edge where the cycle ends
One or more unresolvable auxiliary patterns composed of light transmitting portions (or transmittance adjusting portions) are formed at a pitch of 1.4 × λ / (2NA). In a fifth aspect based on the third aspect, when the target pattern is a pattern composed of an isolated light transmitting portion having no periodicity and the width is about λ / (2NA) or more, one side or both sides, One non-resolvable auxiliary pattern consisting of a light transmitting part (or a transmittance adjusting part) at a distance of 0.8 × λ / (NA) to 1.2 × λ / (NA) from the target pattern edge. The above is formed. Sixth
The invention of No. 1 is to form a target pattern by using the mask according to any one of the first to fifth inventions. A seventh invention is a phase shift mask, wherein at least one semi-transmissive portion having a transmissivity greater than 0 and a transmissivity of the transmissive portion and having a phase difference greater than 0 with the transmissive portion is greater than 0. The auxiliary pattern other than the target pattern is provided in at least one place on the whole or part of the semi-transmissive portion. In an eighth aspect based on the sixth aspect, the auxiliary pattern is a line pattern that cannot be resolved. A ninth invention is a checkered pattern or a lattice pattern in which the auxiliary pattern is unresolvable in the seventh invention. A tenth invention is any one of the seventh to ninth inventions, and an oblique incidence illumination method for improving resolution and depth of focus by arranging a main part of a light source at a position displaced from an optical axis. The target pattern is formed by combining the mask described in 1).

[0016]

The auxiliary pattern which cannot be resolved promotes the periodicity of the target pattern or imparts the periodicity, so that the distortion of the exposure intensity profile of the imaging pattern is reduced and the contrast is improved. This allows for finer,
It is possible to form a pattern with high accuracy. In the semi-transmissive shift mask, an unresolvable auxiliary pattern is arranged in the semi-transmissive portion. The light intensity of the semi-transmissive part is suppressed by the auxiliary pattern.By arranging a fine pattern with a pattern size that cannot be resolved in the semi-transmissive region, the diffraction angle of the reticle diffracted light is increased and the light of this part is imaged. Try not to reach the surface.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the drawings. FIG. 1 is a diagram showing a basic arrangement of an auxiliary pattern group or an auxiliary pattern according to the present invention. (A) is a periodic pattern, (B) is an end portion of a large area pattern, and (C) is an example of auxiliary pattern arrangement for an isolated line pattern. Is. In (A),
Reference numeral 11 is a target pattern including a light transmitting portion, 12 is an auxiliary pattern group including the light transmitting portion according to the present invention, and 12a is an auxiliary pattern forming the auxiliary pattern group 12. For example, when the target pattern 11 is a light-transmitting portion, the white portion represents the light-transmitting portion and the hatched portion represents the transmittance adjusting semi-transmitting portion, but the same auxiliary pattern is used when the light-transmitting portion and the semi-transmitting portion are opposite. Shows the effect. Distortion of the exposure intensity profile appearing at the end of the period of the oblique incidence illumination system is reduced by arranging the auxiliary pattern group 12 made up of the auxiliary patterns 12a at the end of the periodicity and creating the condition that the periodicity continues. Is. In this case, the auxiliary pattern 12a is arranged such that the periodicity of the target pattern 11 is maintained even at the end portion, and it is an unresolvable auxiliary pattern 12a or auxiliary pattern group 12 that does not remain as a pattern after development. is necessary. For the former, it is more effective to arrange the auxiliary patterns 12a as large as possible so that the width Lo of the auxiliary patterns 12a is as large as possible. However, with respect to the latter, conversely, Lo is as small as possible, and the smaller the number of auxiliary patterns 12a is, the larger the development margin is. Therefore, it is necessary to optimize. Further, as can be seen from FIG. 16B, since the exposure intensities of the first and second patterns from the cycle end are greatly affected, the number of auxiliary pattern groups 12 is about two. Is most suitable, but the effect of the present invention can be obtained with only one or three. In addition, the auxiliary pattern 12 in the auxiliary pattern group 12
If the number of a is also 1 or more, the effect of the present invention can be exhibited. In the case of a pattern having no periodicity such as a large area pattern or an isolated line pattern, the contrast improving effect appears by newly providing the periodicity. Therefore, FIG.
As in (B), it is advisable to locate the periodic pattern groups on both sides of the large area pattern end. In addition, 13 is a target pattern, 14 is an auxiliary pattern formed of a light shielding portion, and 15 is an auxiliary pattern formed of a light transmitting portion. In this case, λ / NA, which is a period peculiar to the exposure light, is effective as the period, and in particular in the sense that this period is given, the first auxiliary patterns 14 and 15 from the end
The distance to Pb-Lo / 2 is 1U = λ / (2NA)
Above, and when Pb + Lo / 2 is 2U = λ / NA or less, the effect is high. Here, an example is shown in which two auxiliary pattern groups each consisting of one auxiliary pattern 14 and 15 are arranged on both sides, but this auxiliary pattern group can also be composed of several, and the number of auxiliary pattern groups themselves can be set. Also, it is sufficient that the number is one or more, and the effect can be obtained by the method of arranging the auxiliary pattern only on one side. FIG. 1C shows an example in which an auxiliary pattern that gives periodicity is similarly applied to the isolated line pattern. 16 is a target pattern consisting of a transmission type isolated pattern, 17
Is an auxiliary pattern group, and 17a is an auxiliary pattern including a light transmitting portion. It is effective to set the arrangement period Pa of the auxiliary pattern 17a to a value close to λ / NA. However, the transmitting portion and the light shielding portion may be reversed.

FIG. 2A is an example to which the present invention shown in FIG. 1A is applied. L = same as in FIGS. 16A and 16B
Pa = 2 × U, Lo = at both ends of the 1 × U L & S pattern
2 auxiliary patterns consisting of 2 0.3xU auxiliary patterns
These are arranged one by one, and show the exposure intensity profile by the 0th-order light adjustment mask method (amplitude transmittance t = 0.35, phase difference 180 °). In order to clarify the location of the auxiliary pattern 26 (corresponding to the auxiliary pattern 12a in FIG. 1), the light-shielding portion 27 (hatched portion in FIG. 1) is shown in black at the upper part of the drawing (hereinafter, the exposure intensity profile including the auxiliary pattern). (This display is included in all figures except FIG. 5). 25 (1 in FIG. 1
(Corresponding to 1) is a target pattern composed of a light transmitting portion. Figure 2
(B) is an exposure intensity profile by the 0th-order light adjustment mask method when the present invention is not shown, which is shown for comparison. From the comparison between the two, it can be seen that the unevenness of the exposure intensity at the end of the cycle is improved, and the exposure intensity profile of the outermost pattern is almost completely eliminated. Further, since the exposure intensity of the auxiliary pattern group 26 is 0.2 or less, the auxiliary pattern group 26 does not remain as a pattern after development. The display of the defocus amount is the same as in FIG.

Next, an embodiment in which the basic arrangement of FIG. 1A is modified or applied will be described. FIG. 3A shows an arrangement example of auxiliary patterns in the case where a target periodic pattern is composed of a light transmission adjusting portion (a light shielding portion in a normal mask, hereinafter referred to as a light shielding portion for convenience), and is similar to FIG. 1A. An example in which an auxiliary pattern group including one auxiliary pattern 19 including a light shielding portion is arranged with respect to a target pattern 18 including a light shielding portion,
1B is an example in which an auxiliary pattern 21 including a light transmitting portion is arranged on only one side of a target pattern 20 including a light transmitting portion similar to FIG. 1B, and FIG. 1C is an isolated pattern including a light transmitting portion. 2 shows an example in which an auxiliary pattern 23 formed of a single light transmitting portion is arranged when the target pattern 22 is set. In this case, by arranging an auxiliary pattern or a group of auxiliary patterns each including a light shielding portion at the end of the cycle,
The same effect as (A) can be obtained.

FIG. 4A shows the embodiment shown in FIG.
Similarly to the above, one auxiliary pattern (26a) consisting of a light-shielding portion of Lc = 0.2 × U is provided on the right side of the L & S pattern 25 of infinite length consisting of five lines of the dimension of L = 1 × U, and also on the left side. Lc
Is an exposure intensity profile by the 0th-order light adjustment mask method in the case where one auxiliary pattern (26b) made of 0.3 × U is arranged. For comparison, FIG. 4B shows an example in which the auxiliary pattern according to the present invention is not applied to the same pattern. Focusing on the vicinity of an exposure intensity of 0.3 at which a pattern is formed after development, when the present invention is not applied, the phenomenon in which the pattern edge squeezes inward as the defocus amount increases is remarkable. It can be seen that the application improves this. Further, although the light-shielding (transmittance adjustment) auxiliary patterns 26a and 26b reduce the exposure intensity,
Since the exposure intensity of the formed pattern is larger than 0.3, it does not remain as a pattern after development. Further, from the comparison of the left and right, it is understood that the thinner the auxiliary patterns 26a and 26b, the smaller the decrease in strength. The display of the defocus amount is shown in FIG.
Is the same as.

FIG. 5 is a modification of the basic arrangement of FIG. 1A, in which the number of auxiliary patterns in the auxiliary pattern group and the auxiliary pattern group is one. Lo = at both ends of 5 infinite length L & S
One auxiliary pattern consisting of 0.3 × U and 0.5 × U of Sa
To 1.5 × U, the exposure intensity by the 0th-order light adjustment mask method is shown. (A) shows the case where there is no auxiliary pattern, and the exposure intensity is uneven, and the exposure intensity profile is projected outside the patterns at both ends.
Comparing (B) to (F), the correction effect is greatest in (D) of Sa = 1 × U. In (D), the exposure intensities of the respective patterns are substantially equal, and in particular, the contrast of the patterns at both ends is improved and the protrusion of the exposure intensity profile is reduced. It can be seen that this is a position where the distance Sa between the pattern ends of the target patterns and the auxiliary patterns is equal to the distance between the target patterns (1/2 of the period P), and the periodicity of the target patterns is maintained. Further, since (C) and (E) also show relatively good effects, it can be seen that although the position of the auxiliary pattern has an optimum value, the effect of the present invention can be obtained even in the vicinity thereof. In the auxiliary pattern arrangement according to the present invention, it is effective to arrange so as to maintain the periodicity of the target pattern. As a method thereof, Wa is equal to the target pattern width W as shown in FIG. In addition to the case of holding it by the close auxiliary pattern group, there is also a case of holding it by the auxiliary pattern group consisting of one auxiliary pattern as shown in FIG. In the latter case, the pitch does not necessarily have to be equal to or close to the target pattern, and it is important that the distance Sa from the end of the target pattern is closer to the pattern interval of the target pattern, and this is S (Sa = S- Expressed as Lo / 2), the effect of the present invention is recognized in the range of S = W to S = 2W.

FIG. 6A is a light intensity distribution chart of an example when the present invention is applied to a large area pattern. 4 to 1 on the horizontal axis
Between 6 is a target pattern 25 composed of a light transmitting portion. Figure 1
In FIG. 3B, an example in which the auxiliary pattern 26 is applied to both the inside and outside of the target pattern is shown, but here, an example is shown in which it is applied only to the outside as shown in FIG. Which one is selected has not only the effect size but also the exposure amount margin problem. Therefore, an effective one may be selected depending on the conditions such as the properties of the resist. For comparison, FIG. 5B shows an exposure intensity profile by the 0th-order light adjustment mask method when the present invention is not applied to the same large area pattern. According to the present invention, when the exposure intensity is around 0.3, the exposure intensity profile is prevented from protruding due to an increase in defocus, and the edge position shift is reduced. According to the basic arrangement rule of the present invention, in the case of a pattern which originally has no periodicity, 2U =
λ / NA is effective, and therefore the arrangement is as shown in FIG. 1 (B), but as a modified application example, if the distance from the large area pattern edge is close to U as in the case of FIG. 6 (A). In this case, the effect of the present invention can be obtained. In this case, an auxiliary pattern group consisting of three auxiliary patterns 26 is arranged, but if this is one or more, the effect is substantially the same. The display of the defocus amount is the same as in FIG.

FIG. 7 shows an exposure intensity profile of the 0th-order light adjustment mask system in the case where the target pattern 25 is a light transmission isolated pattern, and a case where an auxiliary pattern group consisting of two auxiliary patterns 26 is applied. ) Is an example. A case where the auxiliary pattern 26 of the present invention is arranged is shown in (A), and a case where the auxiliary pattern is not arranged is shown in (B) for comparison. In (A), for the light transmission isolated line pattern 25 having a target pattern width of 1U, two light transmission auxiliary patterns are provided at a distance of 1U from the end of the target pattern in order to have a periodicity of 2U which is a period peculiar to the exposure light. An auxiliary pattern group 26 consisting of
It can be seen that the peak intensity is higher than that in (B), the exposure intensity profile is kept from protruding when defocusing, and the contrast is remarkably improved. The intensity is set to 0.3 at the development point and the slope of the intensity profile at that time is LOG
-Comparing by SLOPE value, (B)
It improved from 1.28 to 2.33 in (A) and from 0.22 to 1.15 when the defocus was 2.0 × Z. The display of the defocus amount is the same as in FIG.

FIG. 8 shows an exposure intensity profile of the 0th-order light adjustment mask method in the case where the target pattern is a light-shielding isolated pattern, which corresponds to the embodiment of FIG. 3C in which one auxiliary pattern is provided on each side. A case where the auxiliary pattern according to the present invention is arranged is shown in (A), and a case where the auxiliary pattern is not arranged is shown in (B) for comparison. For the light shielding (transmittance adjustment) isolated line pattern 25 with a target pattern width of 1 U, in (A), 1 from the target pattern end.
One light-shielding auxiliary pattern 26 was placed at a distance of U.
As a result, it can be seen that the exposure intensity profile is prevented from approaching the inside of the exposure intensity profile due to an increase in defocus near the exposure intensity of 0.3, and the contrast is improved. In the case where the background portion (the other portion that becomes the background with respect to the target pattern) is the transmissive portion 28 as in this example, if many light-shielding auxiliary patterns (semitransmissive phase inversion auxiliary patterns) are arranged in the transmissive portion 28, the original light will be emitted. Since the exposure intensity of the portion to be transmitted is lowered, it is impossible to arrange a large number of auxiliary patterns 26. One on each side is suitable. The display of the defocus amount is the same as in FIG.

Next, the case where the present invention is implemented in a two-dimensional suitable pattern will be described. 9 and 10 show examples of arrangement of light-shielding auxiliary patterns and light-shielding bands according to the present invention. In all the pattern layouts of the mask, the pattern portion is a light transmitting portion and the ground portion other than the pattern is a semi-transmissive portion (corresponding to a normal light shielding portion).

FIG. 9 shows a two-dimensional arrangement example of a part of the mask pattern. Reference numeral 31 is a target pattern corresponding to a hole pattern, 32 and 33 are line target patterns, 34 is a linear auxiliary pattern, and 35 is a line-shaped auxiliary pattern. Is an auxiliary pattern of a checkered lattice, and 36 is an auxiliary pattern of other shapes such as a broken line, a dot pattern, a lattice, and an oblique line. (A) is an example in which only auxiliary patterns consisting of line patterns are used to shield the semi-transparent portion, (B) is an example in which line patterns and checkered grid patterns are used together, and (C) is various light-shielding auxiliary patterns. It is a figure which extracts the peripheral part of each pattern about a case and explains one-dimensional arrangement in detail.

FIGS. 10A and 10B are examples of light-shielding auxiliary pattern arrangements when another pattern does not exist in the peripheral portion of the isolated line, where 41 is the object pattern of the isolated line and 42 is the object of L / S. Patterns 43 are auxiliary patterns. (A)
In order to improve the intensity profile at the edge of the target pattern due to interference, the auxiliary pattern group has periodicity. (B) is an example in which line patterns are simply spread. In the figure, the case where the line and the space are equal is shown, but it is not always necessary. If the width of the line pattern becomes too thick, the line pattern will be resolved.Therefore, the line pattern needs to have a fine dimension to some extent. Considering the ease of mask fabrication, it is more convenient to have a wider interval than the line pattern.
For example, taking a numerical example in the case where the wavelength of the light source is 365 nm and NA = 0.6, the line pattern is not resolved at an interval of 0.3 μm with respect to the line pattern width of 0.1 μm, and there is a light shielding effect.
This value is an example, and it is effective even if the interval is wider than this. The width of the resolvable line pattern varies depending on the optical system and the exposure and development conditions, but in the above example, the realistic pattern width is about 0.1 μm to 0.2 μm. Further, regarding the interval, it is effective that the pitch added to the line width is λ / NA (0.5 μm in the above example) or less. In (C), if there are free areas on both sides of the L / S (line / space pattern) pattern, it is better to arrange more auxiliary patterns. In that case, it may be arranged at an intermediate interval as in (A) or at even intervals as in (B). However, FIG.
In all cases, it is better to make a space near Sa in the figure near the target pattern 42. This is because if the auxiliary pattern 43 is placed too close to the target pattern 42, it will be difficult to resolve the space. A certain amount of space is required to increase the contrast of the target pattern 42, and the optimum value of Sa is about 0.4λ / NA (0.24 μm in the above example), although it depends on the pattern width and the like.

Next, the effect of using the above-mentioned light-shielding auxiliary pattern will be described with reference to simulation results.
In FIG. 11, the target pattern (light transmitting portion) has a dimension of 0.5λ / NA.
Is an exposure intensity distribution in the case of L / S consisting of 5 lines.
The horizontal axis is the distance normalized by λ / NA, the vertical axis is the exposure intensity,
The four lines in the figure correspond to the case where the focus position is changed. When the defocus amount is represented by a value z standardized by .lambda. / 2NA2, the solid line shows the case of z = 0 at the time of focusing, and the following is the case of z = 1, 1.5, 2 in the order of the dotted line, the broken line, and the alternate long and short dash line.
(A) is a case where a 0th-order light adjustment mask in which a light-shielding auxiliary pattern according to the present invention is arranged is used for the oblique incidence of a ring type, and both ends of L / S are the same as the auxiliary pattern group of FIG. 10 (A). From each other with a space Sa = 0.5λ / NA and a width of 0.
15λ / NA auxiliary pattern, 0.2λ / NA space,
In this example, the 0.15λ / NA auxiliary pattern, the 0.5λ / NA space, the 0.15λ / NA auxiliary pattern, the 0.2λ / NA space, and the 0.15λ / NA auxiliary pattern are arranged in this order. (B) is a case where a zero-order light adjustment mask without auxiliary patterns is used for the annular oblique illumination, and (C) is a case where a conventional Cr mask is used for the normal illumination. In (C), the pattern does not resolve when defocused, whereas
In (B), when the oblique incidence illumination is used, the pattern of the same size is resolved, but there is a maximum light intensity of about 0.15 at the semi-transmissive portion of the 0th-order light adjustment mask, and transfer is possible. On the other hand, in (A), the exposure intensity of the transmissive part is suppressed to 0.1 or less by the light-shielding auxiliary pattern.
The contrast of the pattern at the edge is also improved due to the presence of a. As a result, a highly accurate pattern can be formed with a relatively large development margin without the semi-transparent portion being transferred.

Next, the case of the isolated pattern will be described with reference to FIGS. 12 and 13. FIG. 12 shows a case where a 0th order light adjustment mask is used for the oblique incidence illumination method, and FIG. 13 shows a case where a halftone type phase shift mask is used for normal illumination.
The exposure intensity distribution for an isolated line pattern having a thickness of λ / NA (corresponding to an isolated space in a positive resist) is shown. The solid line is in focus (z = 0), the short dashed line is approximately z = 0.7
5, the long dashed line represents z = 1.5. (Wavelength 365 nm,
When NA = 0.52, defocus amounts 0, 0.5, 1.
This corresponds to 0 μm. )

FIG. 12A shows the case where the 0th order light adjustment mask is used as it is, and FIG. 12B shows the case where the light shielding auxiliary pattern is desired to be arranged. The pattern is arranged such that the space Sa = 0.36λ / with respect to the target pattern 0.5λ / NA.
NA, auxiliary pattern width 0.14λ / NA, and next to it, also leave a space of 0.36λ / NA, and a width of 0.14λ / NA.
This is a case where three NA auxiliary patterns are arranged.
In (A), the light intensity around the pattern is reduced, and the contrast is generally improved. In this figure, there are three auxiliary patterns, so the light intensity rises to the outside again,
Such an excess light portion can be eliminated by further arranging an auxiliary pattern according to the state of surrounding patterns.

FIG. 13A shows the case where the halftone phase shift mask is used as it is, and FIG. 13B shows the case where the light shielding auxiliary pattern is arranged therein, and the pattern arrangement is the same as in FIG. In the case of normal illumination as shown in FIG. 6A, the influence of the phase change at the target pattern edge is large, so that the intensity sharply decreases at the pattern edge, but a relatively large secondary peak occurs outside it. Since this light intensity peak is larger than that in the case of grazing incidence illumination and exceeds 0.2, there is a high possibility that this peak will be transferred, and it is considered that the margin for development becomes more severe. On the other hand, (B)
Then, this secondary peak is significantly suppressed, and even at the time of defocusing, it is suppressed to 0.1 or less, and it can be said that there is almost no possibility of peripheral exposure.

Although the case where all the light shielding patterns are simple line patterns is shown here, when considering a two-dimensional arrangement as shown in FIG. 9, not only simple line patterns but also polygons and grids are used. A light shielding pattern or the like may be used. Similar to the line pattern, the lattice pattern is made unresolvable by making the pattern size fine, and serves as a light shielding portion.

Up to now, the case where the pattern portion is the light transmitting portion and the peripheral portion is the semi-transmissive portion has been described. Conversely, when the peripheral portion is the light transmitting portion and the pattern portion is the semi-transmissive portion, the peripheral light transmitting portion is transmitted. It is not necessary to place a light-shielding auxiliary pattern in the area, but when the area of the pattern portion is large, the light-shielding auxiliary pattern as described above should be placed in the pattern portion to reduce the exposure intensity of the semi-transmissive portion. Is also possible.

As described in the section of the prior art, the conventional transflective phase shift mask is composed of a light transmissive portion and a semitransmissive portion having a lower transmittance than that, and the semitransmissive portion is usually formed in the mask. Since it coincides with the light-shielding portion, the exposure intensity on the image plane of the semi-transmissive portion needs to be low enough not to expose the resist. Therefore, the transmissivity of the semi-transmissive portion is usually 20.
It was set below%. However, when the light-shielding auxiliary pattern according to the present invention is used, even if the transmittance of the semi-transmissive portion is large, the light-shielding effect of the unresolvable auxiliary pattern is similarly obtained, so that the transmittance of the semi-transmissive portion is not necessarily required to be small. Absent. For convenience, it is called a semi-transmissive portion, but it may have the same transmittance as the transmissive portion. Even in that case, a space of Sa that enhances the effect of the phase shift is required near the pattern, and the arrangement is the same as that shown in FIGS. 9 and 10.

Although the case of the normal illumination and the annular oblique incidence illumination has been described here, the present invention can be similarly applied to the oblique incidence illumination method such as four-point illumination. As explained above,
The present invention relates to an exposure method in which a grazing incidence illumination method using a so-called modified light source such as ring illumination or four-point illumination and a zero-order light adjustment mask method are combined, and an exposure in which normal illumination and a halftone type phase shift mask are combined. It is effective in the law.

[0036]

The mask and pattern forming method according to the present invention relates to a mask used in projection exposure by a method combining a grazing incidence illumination system and a zero-order light adjusting mask. In the grazing incidence illumination system, the higher the periodicity of the pattern, the higher the pattern periodicity. Focusing on obtaining high resolution, the periodicity of the target pattern is disrupted so that the periodicity is maintained at the end of the cycle, and the periodicity is added when the target pattern has no periodicity. As described above, since the auxiliary pattern having a size that cannot be resolved is formed around or inside the target pattern, as a result, the pattern forming accuracy can be improved. If the auxiliary pattern or the auxiliary pattern group does not affect the performance or function of the LSI or the like, it is possible to increase Lo and Lc described above to obtain a high effect.

Further, the present invention solves this problem by arranging an auxiliary mask which cannot be resolved, with respect to the problem of overexposure in the semi-transmissive portion which occurs in the exposure using the semi-transmissive side phase shift mask. Is. If there is overexposure in the semi-transmissive portion, unnecessary patterns may be transferred onto the resist, resulting in a small development margin. On the other hand, when exposure is performed using the mask of the present invention, a highly accurate pattern can be formed with a large development margin.

[Brief description of drawings]

1 (A), (B) and (C) are diagrams showing an example of basic arrangement of an auxiliary pattern group or an auxiliary pattern according to the present invention,
(A) when the target pattern has periodicity (L & S pattern), (B) when the target pattern is non-periodic (at the end of the large area pattern), (C) is isolated when the target pattern is non-periodic. This is the case for patterns.

FIG. 2A is an example in which the present invention is applied to a periodic pattern, and FIG. 2B is a case where the present invention is not applied to the same pattern shown for comparison.

FIG. 3 is a diagram showing an example of application arrangement of an auxiliary pattern group or an auxiliary pattern according to the present invention, where (A) has periodicity (L & S pattern), and (B) has aperiodicity (large area pattern (End part) and (C) are cases of non-periodic isolated patterns.

FIG. 4A is an example in which the present invention is applied to a periodic pattern, and FIG. 4B is a case where the present invention is not applied to the same pattern shown for comparison.

5 (B) to (F) are examples using FIG. 2 (A) which is an auxiliary pattern group arrangement according to the present invention, and (A) is the same pattern shown for comparison and the present invention is not applied. This is the case.

FIG. 6A shows an example for a large area pattern,
(B) is a case where the present invention is not applied with the same pattern shown for comparison.

7A is an auxiliary pattern arrangement according to the present invention when the target pattern is aperiodic and is an isolated pattern. FIG.
(B) is a case where the present invention is not applied with the same pattern shown for comparison.

8A is an example of the present invention in the case of an isolated pattern in which black and white is inverted from FIG. 8, and FIG. 8B is the same pattern shown for comparison and the present invention is not applied.

FIG. 9A is an arrangement example using mainly a line pattern as a light-shielding auxiliary pattern, and FIG. 9B is an arrangement example using a line pattern and a checkerboard lattice pattern as a light-shielding auxiliary pattern.
(C) is an arrangement example using various patterns as the light-shielding auxiliary patterns.

10A is a layout example (1) for an isolated pattern, FIG. 10B is a layout example (2) for an isolated pattern, FIG.
(C) is an arrangement example for the L / S pattern.

FIG. 11 is an exposure intensity distribution of an application example of the present invention to an L / S pattern, where (A) shows a case where the auxiliary pattern of the present invention is arranged in an oblique incident illumination + 0th order light adjustment mask, and (B) shows the same oblique pattern. When the auxiliary pattern of the present invention is arranged in the incident illumination + 0th order light adjustment mask, (C) is a case where a conventional (Cr) mask is used in the conventional illumination method.

FIG. 12 is an exposure intensity distribution for an isolated line pattern using a grazing incidence illumination + zero-order light adjustment mask, where (A) shows a case where no auxiliary pattern is arranged and (B) shows a case where an auxiliary pattern is arranged.

FIG. 13 is an exposure intensity distribution for an isolated line pattern using normal illumination and a halftone type phase shift mask, (A).
Shows the case where the auxiliary pattern is not arranged, and (B) shows the case where the auxiliary pattern is arranged.

FIG. 14 is a diagram showing a light source shape and a transmittance arrangement in an aperture stop in a conventional illumination method and various oblique incidence illumination methods used for explaining the present invention.

FIG. 15 is a diagram illustrating a 0th-order light adjustment mask method used in the present invention.

16A and 16B are exposure intensity distribution charts (simulations) for explaining the problems of the conventional technique. FIG. 16A is a conventional method (L & S pattern), and FIG. 16B is a grazing incidence illumination method using a zero-order light adjustment mask method ( L & S pattern), (C) is an enlarged view of a conventional illumination method: L & S pattern (A), (D) is an enlarged view of an oblique incidence illumination method: L & S pattern (B) using the 0th-order light adjustment mask method,
(E) is a conventional illumination method (large area pattern), and (F) is a grazing incidence illumination method using a 0th-order light adjustment mask method (large area pattern).
Is.

17A is an exposure intensity distribution for an isolated line pattern using a normal mask in oblique incidence illumination, and FIG. 17B is an exposure intensity distribution for an isolated line pattern using a zero-order light adjustment mask in oblique incidence illumination. .

[Explanation of symbols]

 11 Objective Pattern 12 Auxiliary Pattern Group 12a Auxiliary Pattern 13 Objective Pattern 14 Auxiliary Pattern 15 Auxiliary Pattern 16 Objective Pattern 17 Auxiliary Pattern Group 17a Auxiliary Pattern 25 Objective Pattern 26 Auxiliary Pattern (Group) 31 Hole Pattern 32, 33 Objective Pattern 34 Auxiliary Pattern 35 Checkered grid pattern 36 Other auxiliary patterns

Claims (10)

[Claims] 1. A mask used for an oblique illumination system in which a main portion of a light source is arranged at a position displaced from an optical axis to improve resolution and depth of focus, wherein the mask has a transmittance of 0 at least at one position. It is composed of a semi-transmissive phase shift mask that has a transmittance and a phase difference that are not present and has a phase difference with the light transmitting portion which is not 0, and is provided with an unresolvable auxiliary pattern other than the target pattern. Mask to do. 2. The mask according to claim 1, wherein when the desired pattern arrangement has periodicity, an unresolvable auxiliary pattern or group of auxiliary patterns is formed so as to preserve the periodicity. And the mask. 3. The mask according to claim 1, wherein when the arrangement of the target pattern has no periodicity, an unresolvable auxiliary pattern or a group of auxiliary patterns is provided so as to impart periodicity to the target pattern. A mask characterized by being formed. 4. The mask according to claim 2, wherein when λ is the wavelength of the illumination light and NA is the numerical aperture of the projection lens, the width of the target pattern composed of the light transmitting portion (or the transmittance adjusting portion) is , Λ / (2NA) or more, 0 .. from the edge of the mask transmission part (or the transmittance adjustment part) where the cycle ends.
A mask characterized in that one or more unresolvable auxiliary patterns composed of a light transmitting portion (or a transmittance adjusting portion) are formed at a pitch of 8 × λ / (2NA) to 1.4 × λ / (2NA). . 5. The mask according to claim 3, wherein when the target pattern is a pattern composed of an isolated light transmitting portion having no periodicity and the width thereof is around λ / (2NA) or more, one or both sides are formed. , 0.8 × from the target pattern edge
A mask characterized by forming one or more non-resolvable auxiliary patterns composed of a light transmitting portion (or a transmittance adjusting portion) at a distance of λ / (NA) to 1.2 × λ / (NA). . 6. A pattern forming method, which comprises forming a target pattern by using the mask according to claim 1. 7. A phase shift mask, comprising a transmissive part,
A semi-transmissive portion having a phase difference of greater than 0 and less than or equal to that of the transmissive portion and greater than 0 with respect to the transmissive portion is provided at least at one location, and the semi-transmissive portion is wholly or partially except the target pattern. A mask having at least one auxiliary pattern of. 8. The mask according to claim 7, wherein the auxiliary pattern is a non-resolvable line pattern. 9. The mask according to claim 7, wherein the auxiliary pattern is an unresolvable checkerboard pattern or a lattice pattern. 10. The oblique incidence illumination system for improving resolution and depth of focus by arranging a main part of the light source at a position displaced from the optical axis, and the method according to claim 7. A pattern forming method comprising forming a desired pattern by combining with a mask.