JP4589489B2 - Pupil filter, pattern forming method, and projection exposure apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pattern forming method for forming a fine pattern of various solid-state elements such as LSI, and a pupil filter and a projection exposure apparatus used therefor.
[0002]
[Prior art]
In order to improve the degree of integration and operation speed of solid-state elements such as LSI, circuit patterns have been miniaturized. For the formation of these fine patterns, a reduction projection exposure method excellent in mass productivity and resolution performance is widely used.
[0003]
A conventional reduced projection exposure apparatus used in this reduced projection exposure method is shown in FIG. In the figure, 1 is a light source (here, the light source is a secondary light source obtained by shaping light emitted from a light source through a predetermined aperture), 2 is an illumination optical system such as a condenser lens, and 3 is an arbitrary shape. 4 is a reduction projection optical system such as a projection lens, and 6 is a semiconductor substrate (substrate to be exposed) whose surface is coated with a photoresist.
[0004]
In this reduction projection exposure apparatus, the exposure light emitted from the light source 1 is irradiated onto the mask 3 via the condenser lens 2, and the pattern on the mask 3 is projected onto the semiconductor substrate 6 via the reduction projection lens 4. -A pattern is transferred and formed on the photoresist by exposure.
[0005]
[Problems to be solved by the invention]
In general, the limit resolution δ of the projection exposure optical system is expressed by the following equation (1) (Rayleigh equation).
δ = k1 · λ / NA (1)
Here, k1 is a constant depending on the process such as the characteristics, thickness, developing conditions, degree of coherence and shape of illumination light of the photosensitive material attached to the substrate to be exposed, and is generally about k1 = 0.6. λ is the wavelength of the exposure light, and NA is the numerical aperture of the projection optical system.
[0006]
As can be seen from the equation (1), the limit resolution δ is proportional to the exposure wavelength λ and inversely proportional to the numerical aperture NA of the projection lens (projection optical system). The limit resolution has been improved by NA. However, miniaturization has progressed to the point where the pattern dimension is smaller than the exposure wavelength, and it has become difficult to improve resolution by shortening the wavelength and increasing the NA. For this reason, in addition to shortening the wavelength and increasing the NA, it is essential to introduce a so-called super-resolution technique that further improves the resolution.
[0007]
For example, there is a modified illumination method in which a reticle (mask) is illuminated obliquely as one of the techniques for improving the resolution in addition to shortening the wavelength and increasing the NA. This modified illumination method greatly improves the limit resolution and depth of focus of dense patterns (periodic patterns). There is also a method of exposing using a halftone phase shift mask that reverses the phase of the transmitted light of the reticle translucent portion with respect to the phase of the transmitted light of the reticle opening. This method greatly improves the limit resolution and depth of focus of the isolated contact hole pattern due to the edge enhancement effect and the defocus aberration compensation effect.
[0008]
However, as can be seen from FIG. 10, an isolated light-shielding pattern, for example, a positive type isolated line pattern (isolated in the translucent substrate 70) shown in FIG. 8 ((a) is a plan view and (b) is a front view). The above-described super-resolution method is not effective in principle for the existing line-shaped opaque (light-shielding) pattern 71), and there is no method for effectively improving the limit resolution. Currently. FIG. 10 shows the relationship between the positive isolated line pattern width and the optical image contrast of the positive isolated line pattern when the positive isolated line pattern is exposed by the conventional method (projection exposure apparatus of FIG. 8). It is a figure. As the exposure conditions at this time, the light source is a KrF excimer laser (wavelength λ = 248 nm), the coherent coefficient σ is 0.75, normal illumination, a so-called circular light source, and the NA of the projection optical system is 0.6.
[0009]
The present invention solves the above-described problems, and a pattern forming method and projection exposure for improving the resolution of an isolated light-shielding pattern in which a dark opaque pattern exists in a bright field of view, that is, a so-called positive type isolated pattern. An object of the present invention is to provide a pupil filter used in the apparatus and the projection exposure apparatus.
[0010]
[Means for Solving the Problems]
The pupil filter of the present invention irradiates a mask with light emitted from a light source via an illumination optical system, and projects the pattern on the mask onto the exposure substrate via the projection optical system. A pupil filter used, wherein a central portion is formed of a semi-transparent portion, has a ring-shaped light shielding portion outside the semi-transparent portion adjacent to the semi-transparent portion, and the outer side of the light shielding portion is a transparent portion. It is characterized by being. Here, the effect is large when the radius of the translucent portion is 0.2 to 0.5 times the pupil radius and the radius outside the annular light shielding portion is 0.5 to 0.85 times the pupil radius. More preferably, the relationship between the radius R1 of the translucent part, the outer radius R2 of the annular light shielding part, and the pupil radius NA is R1: R2: NA≈1: 2: 3. The transmissivity of the translucent part should be as low as possible. However, if the transmittance T is too low (for example, a transmittance of 1%), the reduction of the frequency 0 component representing the information of the transmitted light in the background is large, and the significance of providing the semitransparent portion is diminished. The transmittance is desirably about 5% to 20%.
[0011]
The pattern forming method of the present invention is a pattern forming method in which light emitted from a light source is irradiated onto a mask via an illumination optical system, and the pattern on the mask is projected and exposed onto an exposed substrate via a projection optical system. Thus, when projecting and exposing a positive isolated pattern in which a dark opaque pattern that is isolated in a bright field of view exists, projection exposure is performed by a projection optical system provided with the above-mentioned pupil filter on the pupil plane. At this time, it is preferable that the coherent coefficient σ is the same as, substantially the same as, or less than the radius of the semi-transparent portion of the pupil filter.
[0012]
The projection exposure apparatus of the present invention includes an illumination optical system that illuminates a mask on which a positive type isolated pattern in which an isolated dark opaque pattern exists in a bright field of view, and an image of the mask pattern on an exposed substrate. A projection exposure apparatus having a projection optical system for projection exposure, wherein the pupil filter is provided on the pupil plane of the projection optical system. At this time, it is preferable that the coherent coefficient σ is the same as, substantially the same as, or less than the radius of the semi-transparent portion of the pupil filter.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a schematic view of a projection exposure apparatus of the present invention. In the figure, 1 is a light source (here, the light source is a secondary light source obtained by shaping light emitted from a light emitting source through a predetermined aperture), 2 is an illumination optical system such as a condenser lens, and 3a is a positive type isolation. A mask on which a light-shielding pattern is drawn, 4 is a projection optical system such as a projection lens, 5 is a pupil filter disposed on the pupil plane of the projection optical system 4, and 6 is a semiconductor substrate (substrate to be exposed) coated with a photoresist. It is.
[0014]
In this projection exposure apparatus, the exposure light emitted from the light source 1 is irradiated to the mask 3a via the illumination optical system 2 such as a condenser lens, and the pattern on the mask 3a is passed through the projection optical system 4 and the pupil filter 5. The pattern is transferred and formed on the photoresist by reducing projection and exposure on the semiconductor substrate 6.
[0015]
As shown in FIG. 2, the pupil filter 5 has two parts, a translucent part 5a and a ring-shaped light shielding part 5b, in the light transmitting part 5c. The central part is a translucent part 5a, the transmittance is 5 to 20%, and the radius R1 is 0.2 to 0.5 times the pupil radius (NA). The outer portion adjacent to the semi-transparent portion 5a is a light shielding portion 5b, and the outer radius R2 of the light shielding portion 5b is 0.5 to 0.85 times NA. More desirably, R1: R2: NA = 1: 2: 3 is preferable. As shown in FIG. 1, this pupil filter is inserted into the pupil plane of the projection optical system when a positive type isolated line pattern is exposed. At this time, the coherence coefficient σ is set to a value substantially equal to or less than the radius R1 of the translucent portion.
[0016]
The resolution improvement effect of the present invention will be described by optical image simulation.
[0017]
The simulation condition is that the light source is a KrF excimer laser (wavelength 248 nm), normal illumination with σ = 0.3, a so-called circular light source, and the pupil radius (NA) of the projection optical system is NA = 0.6. Under this condition, a conventional method (σ = 0.75, normal illumination) in which exposure is performed without using a pupil filter to form a pattern, and the method of the present invention in which exposure is performed using the pupil filter in FIG. The numerical value of each part of the pupil filter is the radius R1 = 0.3 NA of the translucent part 5a, the transmittance T = 10% of the translucent part 5a, and the outer radius R2 of the annular light shielding part 5b = 0.6 NA). FIG. 3 shows the light intensity distribution of an optical image of an isolated line pattern having a width of 120 nm. As can be seen from FIG. 3, the curve 31 (light intensity distribution according to the method of the present invention) has a larger light intensity change than the curve 32 (light intensity distribution according to the conventional method), and the spread outward of the pattern is small. That is, according to the present invention, it can be seen that the optical image is very sharp and the image contrast is improved as compared with the conventional method. For this reason, the limit resolution of the present invention is greatly improved as compared with the prior art.
[0018]
4A to 4I show the pattern size dependence of the image contrast according to the conventional method and the present invention under the above conditions, with the radius (R1) of the translucent part and the outer radius (R2) of the annular light shielding part. ) Are variously simulated (black circle (●) indicates the result of the present invention, and white circle (◯) indicates the result of the conventional method). Here, the image contrast is defined as (Ie−Ic) / Ie using the light intensity Ic at the center of the pattern (point A in FIG. 3) and the light intensity Ie at the pattern edge (point B in FIG. 3). The The numerical values of each part of the used pupil filter are as follows: R1 = 0.3NA and R2 = 0.6NA in FIG. 4A, R2 = 0.75NA and R1 in FIGS. 4B to 4E are 0, respectively. .1NA, 0.3NA, 0.5NA, 0.7NA, FIGS. 4 (f) to (i) are R1 = 0.35NA, R2 is 0.4NA, 0.6NA, 0.7NA, 0.9NA, respectively. It is. In FIG. 4B, the image contrast according to the present invention is very poor and cannot be displayed, so the result of the present invention is not entered.
[0019]
As can be seen from FIG. 4, if the resolution contrast limit is 45%, the limit resolution is 0.145 μm in the conventional method, but the limit resolution is 0.100 μm in the case of the present invention, for example, FIG. Greatly improved. This means that the limit resolution δ = k1 × λ / NA of the Rayleigh equation is achieved, and an ultrahigh resolution of k1 = 0.24 is achieved.
[0020]
4 (a), (c), (d), (g), and (h) show that the result of the present invention (black circle (●)) is higher than the result of the conventional method (white circle (◯)). The invention has better image contrast than the conventional method. 4E and 4F, the image contrast deteriorates as the pattern dimension increases. 4B and 4I, the image contrast of the present invention is entirely inferior. Based on the results shown in FIG. 4, the relationship between the image contrast, the radius R1 of the semi-transparent portion, and the radius R2 of the ring-shaped light shielding portion is shown in FIG. FIG. 6 shows the relationship between (R2−R1) and the width W2 (W2 = NA−R2) of the transparent portion. In the figure, “◯” indicates that the image contrast is improved compared to the conventional method (for example, as shown in FIGS. 4A and 4C), and “X” indicates that the image contrast is worse than that of the conventional method. A thing (for example, a thing like FIG.4 (b), (i)) is shown. Cases as shown in FIGS. 4E and 4F are classified as “×”. The hatched area in the upper right corner of the diagonal line in FIG. 5 is an area that cannot be constituted by the pupil filter of the present invention.
[0021]
According to FIGS. 4, 5, and 6, in order to improve the image contrast, the semitransparent portion radius R1 of the pupil filter is approximately 0.2NA to 0.5NA, and the outer radius R2 of the annular light shielding portion is approximately 0.5NA to 0.85NA. I find it good to do. If the width of any one of the translucent part, the light-shielding part, and the transparent part of the pupil filter (radius R1 in the translucent part) is 0.1 NA or less, the image contrast is worse than the conventional one. In the translucent portion, the radius R1) is 0.15 NA or more, preferably 0.2 NA or more. Also, if the width of any of the semi-transparent part, the light-shielding part, and the transparent part is extremely narrow, the contrast tends to deteriorate, and the widths of the semi-transparent part, the light-shielding part, and the transparent part are approximately the same. A pupil filter having a well-balanced width has improved image contrast. Accordingly, it can be seen that it is desirable that R1: R2: NA = 1: 2: 3 or so.
[0022]
7A to 7H, the same conditions as in FIG. 3 (light source is KrF excimer laser (wavelength 248 nm), normal illumination (circular light source), projection optical system pupil radius NA = 0.6, half of pupil filter. The coherence coefficient σ is 0 from 0.1 to 0.8 under the radius R1 = 0.3 NA of the transparent portion, the transmittance T = 10% of the translucent portion, and the outer radius R2 of the annular light shielding portion = 0.6 NA) Shows the change in image contrast when changing in increments of 1. As can be seen from FIG. 7, when σ is equal to or less than R1, the image contrast is improved. When σ is larger than R1, the image contrast is significantly deteriorated. Note that the results of the present invention are not entered in FIGS. 7E and 7F because the image contrast is very poor under the conditions of FIGS. 7E and 7F and may be entered in the figure. This is because it is impossible.
[0023]
Although the above embodiment has been described with respect to an isolated line, the present invention can be applied not only to an isolated line but also to a positive type isolated pattern in general, such as an isolated dot or an isolated island pattern. The present invention can also be applied to contact hole patterns. Even in these cases, the limit resolution can be effectively improved as in the above embodiment.
[0024]
【The invention's effect】
In pattern information transmission from the reticle surface (mask surface) to the wafer surface, the finer the pattern, the greater the contribution of the high-frequency diffracted light located on the outer peripheral portion on the pupil plane (Fourier transform plane) of the projection optical system. The more this is emphasized for low frequency components, the higher the contrast of the aerial image and the better the resolution limit. Therefore, when a light shielding part is provided in the pupil central area, the light shielding part plays a role of cutting low frequency components and the limit resolution is improved. However, in the case of a positive type isolated line, since transmission of a frequency 0 component representing information of transmitted light in the background is essential, the center of the pupil is not completely shielded, but is halfway around the center of the shield in the center of the pupil. A transparent part is provided to attenuate the zero frequency component to about 10% and then transmitted to the wafer surface. In this way, it is possible to improve the limit resolution by effectively cutting the low frequency component and emphasizing the high frequency component.
[0025]
The present invention provides a pupil filter provided on the pupil plane of the projection optical system, the central portion being a semi-transparent portion, an annular light-shielding portion that is adjacent to the semi-transparent portion and outside the semi-transparent portion, and outside the light shielding portion. The above operations and effects are realized as a configuration in which is a transparent portion. That is, the ring-shaped light shielding portion plays a role of cutting low frequency components, and the semi-transparent portion at the center plays a role of attenuating and transmitting a frequency 0 component representing information of transmitted light in the background. By installing this pupil filter on the pupil plane of the projection optical system, low frequency components can be cut and high frequency components can be emphasized, and the limit resolution is improved.
[Brief description of the drawings]
FIG. 1 is a schematic view of a projection exposure apparatus of the present invention.
FIG. 2 is a plan view of a pupil filter of the present invention.
FIG. 3 is a diagram showing a light intensity distribution of an optical image of an isolated line pattern.
FIG. 4 is a diagram showing pattern size dependence of image contrast according to a conventional method and the present invention.
FIG. 5 is a diagram showing a relationship between image contrast and a semi-transparent radius R1 of a pupil filter and an outer radius R2 of an annular light shielding portion.
FIG. 6 is a diagram showing the relationship between the image contrast and the semi-transparent radius R1 of the pupil filter, the width of the annular light shielding portion, and the width of the transparent portion.
FIG. 7 is a diagram showing the relationship between the pattern size dependence of image contrast and the coherence coefficient σ according to the present invention.
FIG. 8 is a diagram showing an example of a positive type isolated pattern.
FIG. 9 is a schematic view of a conventional projection exposure apparatus.
FIG. 10 is a diagram showing pattern size dependence of image contrast according to a conventional method without a pupil filter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Light source 2 Illumination optical system 3 Mask 3a Mask 4 Projection optical system 5 Pupil filter 5a Translucent part 5b Light shielding part 5c Light transmission part 6 Semiconductor substrate 31 Light intensity distribution curve 32 Light intensity distribution curve 70 Light transmission board 71 Light shielding pattern

Claims (11)

A pupil filter used in a projection optical system when light emitted from a circular light source is irradiated onto a mask via an illumination optical system and a pattern on the mask is projected and exposed onto an exposed substrate via a projection optical system. And
A pupil filter characterized in that a central part is formed of a semi-transparent part, an annular light shielding part is provided outside the semi-transparent part adjacent to the semi-transparent part, and the outer side of the light shielding part is a transparent part. . The translucency of the translucent part is 5 to 20%, the radius of the translucent part is 0.2 to 0.5 times the pupil radius, and the outer radius of the annular light shielding part is 0.5 to 0.85 times the pupil radius. The pupil filter according to claim 1. 3. The pupil filter according to claim 1, wherein the relationship between the radius R1 of the translucent part, the radius R2 outside the annular light shielding part, and the pupil radius NA is R1: R2: NA≈1: 2: 3. A pattern forming method of irradiating a mask with light emitted from a circular light source via an illumination optical system, and projecting and exposing a pattern on the mask onto a substrate to be exposed via a projection optical system,
When projecting and exposing a positive type isolated pattern having an isolated dark opaque pattern in a bright field onto a substrate to be exposed, a central portion is formed of a semi-transparent portion, and the semi-transparent portion is adjacent to the semi-transparent portion. A pattern forming method comprising: projecting exposure by a projection optical system having a pupil filter having a ring-shaped light shielding part outside and a transparent part outside the light shielding part.   The transmittance of the translucent part of the pupil filter is 5 to 20%, the radius of the translucent part is 0.2 to 0.5 times the pupil radius, and the outer radius of the annular light shielding part is 0.5 to 0 of the pupil radius. The pattern forming method according to claim 4, which is .85 times.   6. The pattern according to claim 4, wherein the relationship between the radius R1 of the translucent part of the pupil filter, the radius R2 outside the annular light shielding part, and the pupil radius NA is R1: R2: NA≈1: 2: 3. Forming method.   The pattern forming method according to claim 4, wherein the coherent coefficient σ of the light source is the same as, substantially the same as, or less than the radius of the semi-transparent portion of the pupil filter. An illumination optical system that illuminates a mask with a positive isolated pattern in which a dark opaque pattern is isolated in a bright field of view using light emitted from a circular light source, and an image of the pattern on the mask is exposed A projection exposure apparatus having a projection optical system for projecting exposure onto a substrate,
The pupil plane of the projection optical system has a semi-transparent portion at the center, an annular light-shielding portion outside the semi-transparent portion adjacent to the semi-transparent portion, and a transparent portion outside the light-shielding portion. A projection exposure apparatus provided with a pupil filter as described above.   The transmittance of the translucent part of the pupil filter is 5 to 20%, the radius of the translucent part is 0.2 to 0.5 times the pupil radius, and the outer radius of the annular light shielding part is 0.5 to 0 of the pupil radius. 9. The projection exposure apparatus according to claim 8, wherein the projection exposure apparatus has a magnification of .85.   The projection according to claim 8 or 9, wherein the relationship between the radius R1 of the translucent part of the pupil filter, the radius R2 outside the annular light shielding part, and the pupil radius NA is R1: R2: NA≈1: 2: 3. Exposure device.   The projection exposure apparatus according to any one of claims 8 to 10, wherein the coherent coefficient σ of the light source is the same as, substantially the same as, or less than the radius of the semitransparent portion of the pupil filter.

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