JP3133618B2 - Spatial filter used in reduction projection exposure apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reduction projection exposure apparatus used for manufacturing semiconductor devices, liquid crystal devices, dielectric devices, ferroelectric devices, magnetic devices, superconductor devices, and the like.
In particular, the present invention relates to a spatial filter used for improving resolution and depth of focus in the reduction projection exposure apparatus.

[0002]

2. Description of the Related Art With the recent increase in the degree of integration of semiconductor devices, the realization of circuits constituted by finer patterns has been demanded, and further improvements in photolithography technology have been desired. In a reduction projection exposure apparatus called an optical stepper used in photolithography, attempts have been made to improve the limit resolution R and the depth of focus DOF. Heretofore, attempts have been made to use shorter wavelength light to improve the critical resolution R of the projection exposure apparatus,
Accompanying this, improvements in related technologies related to optical lens systems and photoresists have been attempted. As light having a short wavelength, g-line (wavelength: 4
36 nm), i-line (wavelength: 365 nm), and Kr
Deep UV region included in F excimer laser (wavelength:
248 nm).

However, particularly with the rapid increase in the degree of integration in semiconductor devices, the line width included in the circuit is reduced to 0.3.
It is desired that the thickness be equal to or less than μm and further equal to or less than the wavelength of light.

Here, the limit resolution R and the depth of focus DOF of the projection exposure apparatus are generally obtained by the following Rayleigh equations (1) and (2).

R = k ₁ · λ / NA (1) DOF = k ₂ · λ / (NA) ² (2) where k ₁ and k ₂ are constants determined depending on the process. , Λ is the wavelength of the light, and NA represents the numerical aperture of the optical system.

Therefore, from the equation (1), it can be seen that in order to improve the limit resolution R without changing the wavelength of light, it is necessary to increase the numerical aperture NA of the optical system.
However, as can be seen from equation (2), increasing the numerical aperture NA decreases the depth of focus DOF, another important characteristic in photolithography. That is, in order to obtain a preferable combination of the limit resolution R and the depth of focus DOF, it is necessary to optimize the numerical aperture NA.

By the way, increasing the numerical aperture NA involves technical difficulties in manufacturing, and the maximum numerical aperture NA generally obtained at present is about 0.6. In addition, in the case of a quartz-type lens material that is generally used, it is difficult to correct chromatic aberration with respect to short-wavelength light, and furthermore, light absorption by the lens material also increases, and the lens absorbs heat due to the light absorption. Distortion also matters.

In recent years, several attempts have been made to improve the resolution and the depth of focus without necessitating a reduction in the wavelength λ of light or an increase in the numerical aperture NA of an optical system.

FIG. 12 schematically shows a photomask disclosed in JP-A-57-62052. This photomask 1A includes a plurality of transparent portions 1a and a light shielding pattern 2. The plurality of transparent portions 1a correspond to a plurality of parallel lines arranged at a constant pitch. Further, a λ / 2 plate 3a functioning as a phase shifter is provided in every other transparent portion 1a. In the case where such a photomask and coherent illumination light are used in the projection exposure apparatus, the light passing through the phase shifter 3a has a higher light intensity than the light passing through the adjacent transparent portion 1a in FIG.
As shown by the solid curve in the middle, the phase of the amplitude distribution is inverted. Therefore, by the interference of light,
On the image plane, a light intensity distribution as shown by a broken line curve in FIG. 12 is obtained. That is, the width of the light intensity distribution for one projected line is smaller than the width of the amplitude distribution, and the resolution of the projected image is improved.

FIG. 13 shows a cross section of a photomask disclosed in Japanese Patent Application Laid-Open No. 62-67547. The photomask 1B includes a light-shielding pattern 2 formed on a transparent substrate 1.
Contains. The light-shielding pattern 2 includes an isolated linear opening 5a having a width close to the resolution limit. The light-shielding pattern 2 also includes a plurality of linear openings 7 arranged at a constant pitch. When such a mask is used in a projection exposure apparatus, the intensity of light passing through the isolated aperture 5a on the image plane tends to be lower than the intensity of light passing through one of the grouped openings 7. It is in. Therefore, for example, in order to generate a sufficient photochemical reaction in the resist on the semiconductor wafer by the light passing through the isolated opening 5a, it is desired to increase the intensity (dose) of the irradiation light. However, if the dose of the irradiation light is increased, the intensity of the light passing through each of the grouped openings 7 is increased and the width of the intensity distribution is also increased. Therefore, in order to prevent an undesired increase in the intensity of light passing through each of the grouped openings 7, a plurality of light-shielding dots 6a having a size smaller than the resolution limit are provided in each of the openings 7. I have. Further, in order to prevent the intensity distribution of the light passing through each of the grouped openings 7 from spreading, as in the photomask of FIG.
A phase shift layer 8 is provided in every other opening 7.

FIG. 14 is disclosed in JP-A-4-101148.
1 shows a reduced projection exposure apparatus. This exposure device
Is a spatial filter 9, a condenser lens 10, and a light shielding
Photomask 11 having pattern 12 and projection optical system
Another spatial filter 15 arranged in the pupil plane 13
And a semiconductor wafer 17 disposed on the image plane.
You. In such an exposure apparatus, as shown in FIG.
Photomasks 11 are arranged at a constant pitch
Light-shielding pattern 12 including a plurality of parallel lines
The pattern 12 on the Fourier transform plane
A spatial filter 9 is provided. The spatial filter 9 is
As shown in FIG. 15A, as shown in FIG.
Equivalent to the Fourier transform pattern of the shaded pattern 12
Two openings 9a and 9b. Illumination light L_iof
Illumination light passing through two openings 9a and 9b respectively
Wire bundle L_ilAnd L_irIs diffracted by the light shielding pattern 12
You. Light beam L indicated by solid line_l0And L_r0Are
Bright ray bundle L_ilAnd L_irRepresents the zero-order diffraction beam of
The indicated light beam L_l1And L_r1Is the illumination light flux L
_ilAnd L_irOf the first order diffraction beam. Projection optical system
The spatial filter 15 arranged on the pupil plane 14 of FIG.
As shown in (C), the zero-order diffraction beam L _l0And L
_r0And the first-order diffraction beam L_l1And L_r1Only let through
A pair of openings 15a and 15b. But,
The spatial filter 15 in the projection optical system is not always necessary.
Not. In a projection exposure apparatus as shown in FIG.
Shading pattern on photomask and aperture pattern of spatial filter
If a Fourier transform relationship exists between
Improved image resolution and depth of focus are obtained.

As described above, shortening the wavelength of light is effective for improving resolution. However, with the shortening of the wavelength, a light source with a narrow wavelength band and a lens system with little aberration are required, and the development of a photoresist suitable for light of a short wavelength is also required. At present, the development of light sources capable of emitting light of shorter wavelengths and high-performance lens systems is approaching its limits. Also, the development of new light sources, lens systems, photoresists, etc., will increase the cost of photolithography.

On the other hand, a method of improving the resolution and the depth of focus by improving a photomask or installing a spatial filter in a projection exposure apparatus is based on existing light sources, lens systems,
A photoresist or the like can be used, and increase in cost of photolithography can be minimized.

[0014]

By the way, in the photomask according to the prior art as shown in FIG. 12, the improvement of the resolution and the depth of focus can be obtained only for a regular repeating pattern. In addition, a pattern that does not actually exist in the mask pattern may be formed on the image plane due to the phase inversion action of the phase shifter 3a. further,
In the design of laying out complex circuit patterns,
It is necessary to arrange a large number of phase shifters appropriately, which not only complicates the design, but also may cause inconsistencies in the layout of the phase shifter depending on the circuit structure. Furthermore, whether a phase shifter is formed above or below the light-shielding pattern in mask fabrication, an additional high-accuracy overlay step is required for phase shifters not found in conventional mask fabrication processes. And Furthermore, regarding inspection and correction of a defect of a photomask, inspection and correction of a phase shifter made of a transparent film completely different from a conventional Cr film which is a light shielding film must be performed, and such a transparent phase shifter is required. At present, there is no practical method available for inspection and correction of data.

In the prior art photomask as shown in FIG. 13, an attempt has been made to improve the resolution of the isolated minute opening 5 a, but like the photomask in FIG. , There is a problem similar to that of the photomask of FIG. Further, it is difficult to stably form the fine light-shielding dots 6a, and there is a problem that if the light-shielding dots 6a are large, the pattern is formed on the image forming surface.

In the prior art shown in FIG. 14, resolution and depth of focus can be improved only by disposing a spatial filter in an illumination system of a projection exposure apparatus using a conventional ordinary mask not including a phase shifter. Although possible, the improvement depends on the direction of pattern layout, and the improvement is obtained only with respect to a limited layout direction. In a range of a line width larger than the optimized predetermined line width, the depth of focus (DO
F) The properties are much lower than those obtained with normal illumination. Further, regarding a plurality of lines having the same line width, the DOF characteristic depends on the density of the line pattern, and the DOF characteristic does not depend on the fluctuation of the pitch between lines.
There is a problem that the improvement of the F characteristic cannot be obtained.
That is, the prior art spatial filter as shown in FIG. 14 can improve the resolution and the depth of focus only when it has a specific geometric relationship with the pattern on the photomask. There is a problem that resolution and depth of focus cannot be improved for all of various photomasks including size and layout conditions.

In view of the above-mentioned problems in the prior art, it is an object of the present invention to provide a mask having various dimensions and directions without necessity of shortening the wavelength of light or improving a lens system. An object of the present invention is to provide a spatial filter capable of improving the resolution and depth of focus of a projection exposure apparatus with respect to a pattern at a low cost.

[0018]

According to the present invention, an illumination optical system for illuminating a photomask including a fine pattern and a projection optical system for reducing and projecting the fine pattern on an image forming surface are provided. The spatial projection filter arranged near the illumination source included in the illumination optical system includes a central region that transmits light with a transmittance of 45% or less, a substantially transparent peripheral region, and a central region. Includes optical path differences that cause a substantially 180 ° phase difference between light that has passed through the region and light that has passed through the peripheral region.

[0019]

When the spatial filter according to the present invention is used in a reduction projection exposure apparatus, the central area of the spatial filter is set to 45.
%, And the light that has passed through the substantially transparent peripheral region has a phase difference of 180 ° with respect to the light that has passed through the substantially transparent peripheral region, and is superimposed on the projection surface. An excellent resolution and a deep depth of focus can be obtained at a low cost with respect to a mask pattern including various dimensions and directions without a need to shorten a wavelength of light or improve a lens system.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of image formation in a reduction projection exposure apparatus will be briefly described.

Referring to FIG. 16A, a projection using conventional ordinary illumination in a reduced projection exposure apparatus is illustrated in a schematic cross-sectional view. The illumination light that has passed through the condenser lens 19 is diffracted by the pattern on the photomask 20, and the 0th-order diffraction beam L0 and the two ± 1st-order diffraction beams L
It is separated into 1. In this case, the photomask 20 has a relatively large pattern size, as can be seen in the circle 20A which shows the circle 20a in an enlarged manner. Therefore, the diffraction angle formed by the diffracted beams L0 and L1 is not so large, and all three diffracted beams enter the pupil of the projection lens system 21. Then, the pattern on the mask 20 is reduced and projected on the image forming surface such as the semiconductor wafer 22 by the three beams.

However, when the photomask 20 has a fine pattern, as can be seen in the circle 20B obtained by enlarging the area of the circle 20b in FIG.
And the angle formed by the first-order diffracted light L1 increases. If the diffraction angle is large, the first-order diffracted light L1 cannot enter the pupil of the projection lens system 21 and cannot form a fine pattern on the semiconductor wafer 22.

In order to solve such a problem, in the prior art, an off-switch as shown in FIG.
Axis (tilt) illumination methods have been proposed. The prior art projection exposure apparatus of FIG. 14 utilizes such off-axis illumination. That is, in FIG. 17A, a spatial filter 31 similar to that shown in FIG. 15A is arranged above the condenser lens 19.
The light beam that passes through the opening in the spatial filter 31 and is irradiated on the photomask 20 by the condenser lens 19 is inclined with respect to the photomask 20. Therefore, even when the photomask 20 has a fine pattern and a large diffraction angle as shown in a circle 20B, one of the pair of first-order diffraction beams L1 is generated by the projection lens system 21. Even if the beam cannot enter the pupil, the other two beams, the first-order diffraction beam L1 and the 0th-order diffraction beam L0, can enter the pupil. And
A fine pattern on the mask 20 is imaged on the semiconductor wafer 22 by these two beams. At this time, it is possible to improve the phase matching by almost eliminating the optical path difference between the two beams entering the pupil, and to obtain a good resolution and a good depth of focus. On the other hand, FIG.
In the three-beam imaging as shown in FIG. 6A, the phases between the 0th-order diffraction beam L0 and a pair of the 1st-order diffraction beams L1 are mismatched except for the just-focus condition. High depth of focus cannot be obtained.

An off-state as shown in FIG.
In the Axis illumination method, by using an annular (annular) type spatial filter as shown in FIG. 18 instead of the spatial filter as shown in FIG. The resolution and the depth of focus can be improved without depending on the resolution.

However, even in such an off-axis illumination technique, as for a pattern having a size larger than the range of the optimized pattern size, FIG.
The DOF characteristic is greatly reduced as compared with the normal illumination as shown in FIG. 1A, and the DOF characteristic is significantly deteriorated even when the density varies in the pattern.

For example, as shown in a circle 20A in FIG. 17B, if the pattern size increases and the diffraction angle decreases, both of the pair of first-order diffraction beams L1 are projected lenses. It is possible to enter the pupil of the system and the pattern on the mask 20 will be projected onto the semiconductor wafer 22 by three diffracted beams. FIG.
In three-beam imaging in off-axis illumination as shown in (B), compared to three-beam imaging in on-axis (symmetric) illumination as shown in FIG. The phase shift between the beams increases. Therefore, in three-beam imaging by off-axis illumination as shown in FIG.
The DOF characteristic is inferior to that of three-beam imaging by ordinary on-axis illumination as shown in FIG.

FIG. 19A illustrates a method for preventing such a decrease in the DOF characteristic. FIG.
5A, a halftone annular type spatial filter 32 is disposed above the condenser lens 19, and a central region 32A of the spatial filter 32 has a predetermined light transmittance. As indicated by the dashed arrow, the on-axis illumination by the light transmitted through the central region 32A forms the same image as the normal illumination shown in FIG. That is, a balanced three-beam image formed by an on-axis illumination component having reduced light intensity is superimposed on a three-beam image formed by off-axis illumination as shown in FIG. 17B. This makes it possible to suppress the deterioration of the DOF characteristics as compared with normal illumination.

However, when the pattern size is small as shown in a circle 20B in FIG.
The imaging by the three beams of the on-axis illumination having the reduced intensity is superimposed on the imaging by the two beams of the off-axis illumination. At this time, FIG.
As can be seen from the graph representing the amplitude distribution 23 in (A), the main peak of the amplitude distribution due to the two beams of the off-axis illumination has a relatively narrow width, while the on-axis having the reduced light intensity has a small width. The main peak of the amplitude distribution of the three beams of the Axis illumination 24 has a wide width.

A curve 26 in the graph representing the intensity distribution in FIG. 20B represents an intensity distribution obtained by superposing the amplitude distributions 23 and 24 in FIG. 20A. Since the amplitude distributions 23 and 24 have the same sign phase, the light intensity distribution 26 obtained by superimposing the two amplitude distributions is obtained.
Is larger than the width of the main peak of the amplitude distribution 23.

That is, when the pattern size of the mask is small, as shown in FIG.
In a projection method in which an image formed by three beams of on-axis illumination having reduced intensity is superimposed on an image formed by two beams of axis light, and off-axis illumination as shown in FIG. Both the resolution and the DOF characteristics are inferior to the projection method using only two beams.

The present invention provides a spatial filter capable of improving the resolution and DOF characteristics of a reduction projection exposure apparatus without depending on the direction of the pattern and without depending on the size or density of the pattern. The spatial filter according to the present invention comprises:
The central region belongs to an annular type having a predetermined light transmittance, and includes means for generating a phase difference of 180 ° between light passing through the central region and light passing through the peripheral region.

The operation and effect of the spatial filter according to the present invention are as follows.
This will be described with reference to FIG. 1 together with FIGS. 20 (A) and 20 (B). In FIG. 1, the illumination optical system of the projection exposure apparatus is shown in a schematic sectional view. Light from a light source (not shown) is essentially partially coherent light after passing through fly-eye lens 18. That is, as shown in the graph 29 representing the amplitude phase in FIG. 1, there is no large phase difference between the beams that have passed through the respective minute lenses in the fly-eye lens 18. Therefore, the phase can be adjusted by the novel phase / transmittance modulation filter 40 according to the present invention. As can be seen from a comparison of the amplitude and phase graphs 28 and 29A in FIG. 1, the phase of light transmitted through the central region may be shifted by 180 ° with respect to the phase of light transmitted through the peripheral region. The light that has passed through the spatial filter 40 is spatially modulated by the condenser lens 19 into an on-axis component and an off-axis component, and these light components are irradiated onto the mask 20 while maintaining a phase difference of 180 °.

In the case of projecting a fine pattern on the mask 20 onto an image forming plane in an exposure apparatus having an illumination system as shown in FIG. 1, similar to the case of FIG. The imaging by two beams of illumination and the imaging by three beams of on-axis illumination are superimposed. However, in the lighting method of FIG.
As shown in the graph of (A), the imaging by the two beams of the off-axis illumination has a positive phase amplitude distribution as shown by the curve 23, whereas the on-axis imaging has the positive phase amplitude distribution. The image formed by the three beams of the Axis illumination has a negative phase amplitude distribution as shown by a curve 25. Therefore, these two opposite-phase amplitude distributions 23 and 25 cancel each other out of side lobes, resulting in a light intensity distribution as shown by a curve 27 in FIG. 20B. As can be seen from the comparison between the curves 27 and 26, according to the illumination method using the spatial filter according to the present invention as shown in FIG. 1, the illumination method according to the prior art shown in FIG. In comparison, the light intensity of the projected pattern is slightly reduced, but the width of the light intensity distribution is significantly reduced. That is, the projection exposure using the spatial filter according to the present invention as shown in FIG. 1 has a higher resolution than the projection exposure using the prior art spatial filter as shown in FIG. And the depth of focus is improved.

As described above, the phase / transmittance modulation spatial filter according to the present invention can improve the resolution and DOF characteristics of a projection exposure apparatus without depending on the direction, size and density of a mask pattern used. .

As a substrate of the spatial filter according to the present invention,
Quartz or the like may be used. The outer diameter and the inner diameter of the annular aperture in the spatial filter will be represented using a σ factor. The σ factor is defined as σ = NA _i / NA _p , where NA _i represents the numerical aperture of the illumination system and NA _p represents the numerical aperture of the projection system. When the projection exposure apparatus is used, the numerical aperture NA _p of the projection system is generally set to a constant maximum value, the numerical aperture NA _i of the illumination system may vary depending on the size of the aperture to be inserted into the illumination system. The outer diameter of the annular opening of the spatial filter according to the present invention can be set to a value corresponding to σ ₁ = 0.4 to 0.7, and the inner diameter of the annular opening corresponds to σ ₂ = 0.2 to 0.6. Value can be set to

The transmittance modulation in the central region of the spatial filter is
A plurality of minute openings are provided in the light-shielding film in the central region, or Cr, Al, Ta,
Alternatively, it can be realized by using a semi-permeable membrane such as Mo. In addition, a relative 180 ° between the light beam passing through the central portion of the spatial filter and the light beam passing through the peripheral portion.
Can be obtained by changing the thickness of the filter substrate by etching. Such an optical path difference can also be obtained by providing an additional layer such as an SOG (spin-on-glass) film, a sputtered SiO ₂ film, or an organic film having a predetermined thickness. The change amount t of the substrate thickness or the thickness t of the additional layer for generating the phase difference of 180 ° can be obtained by the following equation (3a) or (3b).

N · t−t = m · λ / 2 (3a) t = m · λ / 2 (n−1) (3b) where n is the refractive index of the filter substrate or the refractive index of the laminated material. And m represents a positive odd number.

FIG. 2A is a plan view schematically showing a spatial filter according to the first embodiment of the present invention.
FIG. 2B shows a cross section taken along line 2B-2B in FIG. In the spatial filter according to the first embodiment, a light shielding pattern 2 is formed on a quartz substrate 1. The light-shielding pattern 2 includes an annular opening 3 and a plurality of small openings 4 in a central region. In the region of the annular opening 3, the substrate 1 is reduced in thickness by etching. The amount of change G1 in the thickness of the substrate is determined by equation (3b). For example, a substrate 1 is made of quartz and a KrF excimer laser (λ = 248n) is used as exposure light.
When m) is used, the variation G1 of the substrate thickness is 27
0 nm. In FIG. 2B, the substrate 1 is etched below the region of the annular opening 3,
Alternatively, it goes without saying that the substrate 1 may be etched under the plurality of minute openings 4 in the central region.

FIG. 3 illustrates a process for manufacturing the spatial filter shown in FIG. 2 (B). First, FIG.
3A, a quartz substrate 1 is prepared. In FIG. 3B, a light-shielding film 2 made of an Al layer having a thickness of about 400 nm is formed on the substrate 1. Next, in FIG.
The Al layer 2 is patterned using a normal photolithography technique, and an annular opening 3 is formed. FIG.
In (D), the substrate 1 is formed in a region below the annular opening 3 by a dry process such as RIE (reactive ion etching) or a wet process using HF or the like.
Is etched. In FIG. 3E, the Al layer 2 is patterned again by using a normal photolithography technique, and a plurality of minute openings 4 are formed in a central region inside the annular opening 3. As a result, FIG.
And the phase / transmittance modulation filter shown in (B) is completed.

FIG. 4A is a plan view of a spatial filter according to a second embodiment of the present invention, and FIG.
(A) shows a cross section along line 4B-4B in FIG. In the spatial filter according to the second embodiment, a light-shielding pattern 2 is formed on a transparent substrate 1. The light shielding pattern 2 includes an annular opening 3 and a plurality of minute openings 4 in a central region. The plurality of minute openings 4 are
It is covered by a transparent material film 5. The transparent material film 5 has a phase of light of 1 used in the projection exposure apparatus.
It has a thickness G2 shifted by 80 °. Its thickness G
2 can also be obtained from equation (3b).

FIG. 5 illustrates the manufacturing process of the spatial filter shown in FIG. In FIG. 5A, a quartz substrate 1 is prepared, and in FIG. 5B, a light-shielding film 2 made of an Al layer having a thickness of about 400 nm is formed on the quartz substrate 1. In FIG. 5C, the Al layer 2 is patterned using a normal photolithography technique to form an annular opening 3 and a plurality of minute openings 4 in a central region. In FIG. 5D, the substrate 1 and the light shielding pattern 2 are covered with a layer 5 of a transparent material. This transparent material layer 5 can be formed using SOG, SiO ₂ , or an organic material. In FIG. 5E, the transparent material 5 is removed by patterning in a region above the annular opening 3. As a result, a phase / transmittance modulation filter as shown in FIGS. 4A and 4B is completed.

In the first and second embodiments, the shape of the minute opening 4 in the central region is shown as a circle, but it goes without saying that the shape may be a triangle or another polygon. The thickness of the Al light shielding layer 2 is 400 nm.
Not limited to this, it may be about 150 nm or more.

When a phase / transmittance modulation type spatial filter as shown in the first embodiment or the second embodiment is used in a projection exposure apparatus, the minute aperture 4 in the central area of the spatial filter and the peripheral aperture are used. It is desirable that the arrangement of the annular openings 3 be synchronized with the arrangement cycle of a plurality of microlenses in the fly-eye lens 18 (see FIG. 1). That is, it is desirable that each of the openings 4 and 3 includes the entirety of each of the corresponding microlenses.

In the graph of FIG. 6, the first embodiment and the second embodiment
Using a novel phase / transmittance modulation filter according to the embodiment
The resolution of the projection exposure apparatus is higher than that of the prior art.
In the comparison. In this graph, the horizontal axis is
Represents the designed line width (μm) on the image plane
The vertical axis is the line width actually measured on the image plane.
(Μm). The circle is a new space according to the present invention.
A triangle is shown in FIG. 18 when a filter is used.
Normal annular type according to the prior art as
Corresponding to the spatial filter of the square mark, the center area is translucent
Corresponding to an annular spatial filter of
In contrast to the conventional normal illumination as shown in FIG.
I am responding. In the measurement of FIG. 6, the projection of the projection exposure apparatus
The numerical aperture of the system is NA = 0.45 and λ = 248 nm.
A KrF excimer laser with a wavelength was used. In addition,
These annular type spatial filters also have a σ₁= 0.5
And σ _Two= 0.4 was set. In addition, on a semiconductor wafer
Negative resist is used as a resist layer
I was. Further, the center in the spatial filter of the present invention
The light transmittance of the region was set to 15%.

As can be seen from FIG. 6, in the prior art, the ordinary annular type spatial filter exhibits the best resolution limit of 0.28 μm, whereas the phase / transmittance modulation filter according to the present invention has It shows a resolution limit of 0.25 μm or less. That is, it can be seen from the graph of FIG. 6 that the novel spatial filter according to the present invention can achieve a better resolution limit than any type of spatial filter in the prior art.

FIGS. 7A and 7B show the DOF characteristics of the spatial filters according to the first and second embodiments in comparison with various spatial filters according to the prior art. In each of these figures, the horizontal axis represents the defocus amount (μm), and the vertical axis represents the line width (μm) measured on the image plane. 7A and 7B, the experimental conditions were set in the same manner as in FIG.

As can be seen from FIG.
For projections of lines having small widths, the conventional annular type spatial filter in the prior art shows the best DOF characteristics, and the novel spatial filter according to the present invention has the same spatial quality as the best spatial filter in the prior art. This shows DOF characteristics. However, as can be seen from FIG. 7 (B), for projections of lines having a relatively large width of 0.7 μm, the prior art annular spatial filter has a clearly degraded DOF characteristic. On the other hand, the novel spatial filter according to the present invention has a DOF characteristic equivalent to that of conventional ordinary illumination.
However, as can be seen from FIG. 7A, with respect to the projection of a line having a width of 0.3 μm, the conventional ordinary illumination has a significantly reduced DOF characteristic. That is, it will be understood that the phase / transmittance modulation filter according to the present invention can realize excellent DOF characteristics without depending on the width of a projected line.

FIGS. 8A and 8B show traces of a scanning electron micrograph of a line pattern actually formed on a resist layer on a semiconductor wafer. In FIG. 8A, conventional ordinary illumination is used.
In (B), a phase / transmittance modulation filter according to the present invention is used. In each of FIGS. 8A and 8B, the designed line width is 0.3 μm, and the line pitch is set to 0.6 μm and 1.2 μm.
In FIG. 8A in which normal illumination is used, it can be seen that the line width projected when the line pitch becomes large also becomes large. On the other hand, in FIG. 8B where the novel spatial filter according to the present invention is used, it can be seen that the width of the projected line is substantially constant without depending on the line pitch. That is,
It will be appreciated that the novel spatial filter according to the invention can improve the resolution independently of the pattern density.

FIG. 9A is a plan view showing a phase / transmittance modulation filter according to the third embodiment of the present invention.
(B) shows a cross section along line 9B-9B in FIG. 9 (A). In the spatial filter according to the third embodiment, a light shielding film 2 is formed on a transparent substrate 1. The light-shielding film 2 includes an annular opening 3 and a central opening 3a integrated therewith. In the central opening 3a, a semi-transparent film 6 is formed on the substrate 1. Below the annular opening 3, the substrate 1 is reduced in thickness by etching. That is, between the light passing through the annular opening area 3 and the light passing through the central area 6, 1
The thickness of the substrate 1 is changed by the change amount G1 so as to generate a light phase difference of 80 °.

FIG. 10 illustrates the manufacturing process of the spatial filter shown in FIG. 9 (B). FIG. 10 (A)
In FIG. 10, a quartz substrate 1 is prepared. In FIG. 10B, a light-shielding film 2 made of an Al layer having a thickness of about 400 nm is formed on the quartz substrate 1. In FIG. 10C, the light-shielding film 2 is patterned, and an annular opening 3 is formed. In FIG. 10D, the substrate 1 is etched below the annular opening region 3 in the same manner as in the first embodiment. In FIG. 10E, the light shielding film 2 is removed on the central region surrounded by the annular opening 3. In FIG. 10F, the substrate 1 and the light shielding film 2 are about 70
It is covered with a semi-transparent film 6 made of a Cr layer having a thickness of nm. In FIG. 10 (G), the semi-light-transmitting film 6 is removed on the annular aperture region 3 to complete a phase / transmittance modulation type spatial filter as shown in FIGS. 9 (A) and 9 (B). . It should be noted that the thickness of the Cr film 6 is not limited to 70 nm and may be in a range of about 150 nm or less. It is understood that the novel spatial filter as shown in the third embodiment can also improve the resolution and DOF characteristics of the projection exposure apparatus in the same manner as the spatial filters shown in the first and second embodiments. Like.

FIG. 11 shows the result obtained by simulation of the relationship between the light transmittance in the central region surrounded by the annular opening 3 of the spatial filter according to the present invention and the normalized contrast on the image plane. . That is,
The horizontal axis of this graph represents the light transmittance in the central region surrounded by the annular aperture 3, and the vertical axis represents the normalized contrast in the pattern of 0.25 μm line width and line interval projected on the image plane. (%).
In this graph, the solid line curve indicates that the defocus amount is 1.0 μm.
m, and the broken line curve indicates that the defocus amount is 0.
This corresponds to the case of 6 μm, and the dashed line curve corresponds to the case where the defocus amount is 0 μm. As can be seen from FIG. 11, in the phase / transmittance modulation type spatial filter according to the present invention, it is understood that the transmittance in the central region surrounded by the annular opening 3 is desirably 45% or less.

Although the light shielding film made of Al and the semi-light-transmitting film made of Cr have been described in the above embodiments, the light-shielding film and the semi-light-transmitting film can be formed by appropriately selecting the thickness.
It can also be formed using a material such as l, Cr, Ta, or Mo.

In the above embodiment, the description was made using the illumination light of the KrF excimer laser with λ = 248 nm.
The new spatial filter according to the invention has a g of λ = 436 nm.
It is needless to say that the present invention is also effective for illumination light such as a line, an i-line at λ = 365 nm, and an ArF excimer laser beam at λ = 193 nm.

[0054]

As described above, when the spatial filter according to the present invention is used in the reduction projection exposure apparatus, light passing through the central region of the spatial filter at a transmittance of 45% or less,
The light that has passed through the substantially transparent peripheral region is phase-shifted by 180 ° with respect to each other by means of generating a phase difference and is superimposed on the projection surface, so that the wavelength of light is shortened and the lens system is improved. , And excellent resolution and deep depth of focus can be obtained at low cost with respect to a mask pattern including various dimensions and directions.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an illumination system of a projection exposure apparatus including a spatial filter according to the present invention.

FIG. 2A is a schematic plan view of a spatial filter according to one embodiment of the present invention, and FIG. 2B is a line 2B- in FIG.
It is sectional drawing which followed 2B.

FIG. 3 is a cross-sectional view showing a process of manufacturing the spatial filter of FIG.

FIG. 4A is a plan view showing a spatial filter according to another embodiment of the present invention, and FIG. 4B is a line 4 in FIG.
It is sectional drawing in alignment with B-4B.

FIG. 5 is a cross-sectional view illustrating a process of manufacturing the spatial filter of FIG.

FIG. 6 is a graph showing an improvement in resolution in a projection exposure apparatus using a spatial filter according to the present invention.

7A is a graph showing an improvement in the depth of focus for a fine pattern in a projection exposure apparatus using a spatial filter according to the present invention, and FIG. 7B is a graph showing a comparative example in a projection exposure apparatus including a spatial filter according to the present invention; 7 is a graph showing improvement in depth of focus for large patterns.

FIG. 8A is a plan view showing a line pattern projected on an image plane using conventional ordinary illumination, and FIG. 8B is an image plane of a projection exposure apparatus including a spatial filter according to the present invention. FIG. 4 is a plan view showing a line pattern projected on a line.

FIG. 9A is a plan view showing a spatial filter according to still another embodiment of the present invention, and FIG. 9B is a cross-sectional view taken along line 9B-9B in FIG. 9A.

FIG. 10 is a sectional view showing a process for manufacturing the spatial filter of FIG. 9;

FIG. 11 is a graph showing a relationship between a light transmittance in a central portion of a spatial filter according to the present invention and a contrast of an image formed on an imaging surface.

FIG. 12 is a schematic sectional view showing an example of a photomask according to the prior art.

FIG. 13 is a cross-sectional view showing another example of a photomask according to the prior art.

FIG. 14 is a schematic sectional view showing a reduction projection exposure apparatus according to the prior art.

15A is a plan view showing a spatial filter used in the exposure apparatus of FIG. 14, FIG. 15B is a plan view showing a photomask used in the exposure apparatus of FIG. 14, and FIG. 15C is a plan view showing another spatial filter used in the projection exposure apparatus of FIG.

FIG. 16A is a schematic cross-sectional view illustrating an exposure apparatus when a relatively large pattern on a photomask is projected using conventional ordinary illumination, and FIG. FIG. 9 is a schematic cross-sectional view showing an exposure apparatus when a pattern is projected using conventional ordinary illumination.

FIG. 17A is a schematic cross-sectional view showing an exposure apparatus when a fine pattern on a photomask is projected using off-axis illumination according to the prior art, and FIG. 1 is a schematic cross-sectional view showing an exposure apparatus when a relatively large pattern is projected using off-axis illumination according to the prior art.

FIG. 18 is a plan view showing a conventional annular type spatial filter according to the prior art.

FIG. 19A is a schematic sectional view showing an exposure apparatus when a relatively large pattern on a photomask is projected using a halftone annular type spatial filter according to the prior art, and FIG. FIG. 1 is a schematic cross-sectional view showing an exposure apparatus when projecting a fine pattern on a photomask using a halftone annular type spatial filter.

FIG. 20A is a graph showing an amplitude distribution of light projected on an imaging surface, and FIG. 20B is a graph showing an intensity distribution of light projected on an imaging surface.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Light-shielding layer 3 Annular opening 4 Micro opening 5 Transparent film 6 Semi-translucent film

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-4-179114 (JP, A) JP-A-7-57992 (JP, A) JP-A-7-142327 (JP, A) JP-A-6-142327 196382 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/027 G02B 5/20 G03B 27/32 G03F 7/20 521

Claims (5)

(57) [Claims] 1. A reduction projection exposure apparatus comprising: an illumination optical system for illuminating a photomask including a fine pattern; and a projection optical system for reducing and projecting the fine pattern on an image forming surface. A spatial filter disposed near an illumination source included in an optical system, the spatial filter including: a central region that transmits light with a transmittance of 45% or less; a central region that surrounds the central region and is substantially transparent; A spatial filter, comprising: a peripheral region; and means for producing a substantially 180 ° phase difference between light having passed through the central region and light having passed through the peripheral region. 2. The filter includes a light-shielding layer, and the transmittance of 45% or less in the central region is obtained by a plurality of fine openings formed in the light-shielding layer.
Spatial filter. 3. The spatial filter according to claim 1, wherein the transmittance of 45% or less in the central region is obtained by a semi-permeable uniform layer. 4. The method of claim 1, wherein the spatial filter includes a substantially transparent substrate, and the means for producing the phase difference is obtained by changing a thickness of the substrate by a predetermined amount.
Spatial filter. 5. The spatial filter according to claim 1, wherein said means for producing a phase difference comprises an additional layer having a predetermined thickness.