JPH0547630A - Fine pattern projection aligner - Google Patents

Abstract

PURPOSE:To control the resolution at will in the direction from the optical axis to a light source on a plane vertical to the optical axis, in an oblique incident illumination method wherein a prism and a grating are employed. CONSTITUTION:When seeing in a plane vertical to an optical axis, this device is provided with a device for oblique incident illumination from one direction out of the optical axis or from two directions outside the optical axis which are symmetrical about the optical axis and a special diaphragm 18 having an aperture 19 around a straight line which is located at right angles with a straight line to connect the one direction or the two directions and the optical axis that passes the optical axis. Therefore, the resolution of an L and an S pattern which cross at right angles can be controlled at will by combining the device for oblique incident illumination from one or two directions outside the optical axis and the special diaphragm 18 and by selecting the requirements for oblique incident illumination for these two devices.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called projection exposure apparatus for forming a fine pattern of an LSI or the like on a wafer (substrate) using a mask and a projection lens.

[0002]

2. Description of the Related Art Conventionally, a projection exposure apparatus for forming a fine pattern such as an LSI is required to have a high resolution. Therefore, the projection lens of the recent projection exposure apparatus has a resolution close to the theoretical limit determined by the wavelength of light.
Nevertheless, in order to cope with the recent miniaturization of LSI patterns, higher resolution is required. In order to meet this demand, in recent years, it has been necessary to add 1 to the adjacent light transmitting parts on the reticle.
A phase shift method has been proposed in which a phase difference close to 80 degrees is provided to bring the light intensity in the light-shielding portion close to zero, and it has been shown that the resolution is improved.

However, in the phase shift method, a high miniaturization effect can be obtained in a pattern such as an L & S pattern (line and space pattern) which can easily provide a phase difference of 180 degrees between adjacent light transmitting portions. On the other hand, in the case of a random pattern, it is difficult to satisfy this condition, so the effect is reduced, that is, the effect of improving the resolution differs depending on the type of pattern. For this reason, there are drawbacks such as an effective shifter placement method for random patterns, technical difficulties in shifter fabrication, inspection, and correction, and a large increase in reticle fabrication cost.

On the other hand, the same applicant applies the phase shift method by irradiating the light incident on the reticle in the fine pattern projection exposure apparatus at an angle corresponding to the numerical aperture of the projection optical system from the optical axis. A method for achieving equivalent resolution has been proposed (Japanese Patent Application No. 3-135317). Unlike the phase shift method, this method has a great advantage over the phase shift method because the improvement in resolution does not depend on the type of pattern and the conventional mask can be used as it is.
This method will be briefly described with reference to FIG.

FIG. 10 (a) shows the above-mentioned oblique incidence projection method (Japanese Patent Application No. 3-135317) proposed by the same applicant, and FIG. 10 (b) shows a conventional projection method. In the conventional projection method, as shown in FIG.
The (wave number k ₀ ) enters perpendicularly to the surface of the reticle 31 and produces diffracted light (wave number k ₁ ) on both sides of the optical axis. Due to the aperture stop (aperture) 32 below the reticle 31, the maximum wave number that can pass through the projection system is k ₁ , which blocks light with a large wave number, that is, diffracted light with a pattern shorter than 2π / k _1. I will end up. Where the diffraction angle is α

K ₁ = k ₀ · sin α (1)

Therefore, the minimum resolution dimension is 2π / (k ₀
・ It becomes 1/2 of sin α). On the other hand, in the grazing incidence projection method shown in FIG. 10A, when the 0th-order light obtained by going straight on the incident light I (wave number k ₀ ) has an inclination such that it passes through the outermost periphery of the projection system aperture stop 32, As shown in the figure, the diffracted light having the diffraction angle 2α and the 0th-order light give the highest resolution. The wave number of this diffracted light is

K ₁ ′ = k ₀ · sin (2α) ≈ 2k ₀ · sin (α) (2)

Therefore, the minimum resolution dimension is 2π /
Half of (2k ₀ · sin α), that is, half the size of the conventional exposure method can be resolved. Here, since sin α is the numerical aperture of the projection lens: NA,
This oblique-incidence illumination system can increase the resolution by inclining the irradiation light by an angle corresponding to NA with respect to the optical axis to allow light having a larger diffraction angle to pass therethrough.
As a specific method of realizing this oblique incidence illumination, an optical element such as a prism or a grating is disclosed in Japanese Patent Application No. 3-142782 “Mask illumination optical system and projection exposure apparatus and method using the same” filed by the same applicant. Is shown in a part of the illumination optical system. Before describing this method, the configuration of a conventional typical fine pattern projection exposure apparatus, that is, the optical system of a stepper will be described with reference to FIG.

In FIG. 2, the light source lamp 1 is placed at the first focal point of the elliptical reflecting mirror 2, and the luminous flux is once collected near the second focal point 3 of the elliptic reflecting mirror 2 via the cold mirror 12. Then, the light flux is converted into a parallel light flux by the input lens 4 which shares a focus substantially with the second focus 3. The light rays that have passed through the filter 10 enter the optical integrator 6 that collects the light flux at the central portion by the cone lens 5 to make the light intensity distribution uniform and makes the irradiation intensity distribution on the reticle surface uniform. The light emitted therefrom uniformly illuminates the reticle 9 by the output lens 7, the cold mirror 13 and the condenser lens group 8. An aperture stop 11 is placed on the exit side of the optical integrator 6 to determine the exit dimension. Reticle 9
The light irradiating the laser beam passes through the projection optical system 14, and the image of the fine pattern on the reticle 9 is projected and exposed on the resist on the wafer 15. In the projection optical system 14, there is a diaphragm 1 that determines the numerical aperture.
There are six.

FIG. 11 is an example in which the above-mentioned Japanese Patent Application No. 3-142782 is applied, and the optical element 1 is provided on the reticle 9 in FIG.
7 is a case where a one-sided prism having an inclination angle of 9.2 ° is mounted as 7 and a case where the aperture stop 11 having a coherence factor σ = 0.2 is applied and the contrast of the conventional method are obtained by simulation. In the figure, the horizontal axis is the spatial frequency normalized by the wave number of the illumination light, and the vertical axis is the contrast: M
Represents TF. As is clear from FIG. 11, the resolution of the L & S pattern P: L (Y) perpendicular to the tilt direction of the one-sided prism is significantly improved, but the parallel L & S pattern P: L is reduced.
The resolution of (X) is S: L (X), S: L (Y) of the conventional method.
It is lower. The former is the effect of the grazing incidence illumination described above, but the reason for the lower resolution in the latter is that in the pupil space,
Since the light source is near the pupil circumference, the NA in the direction perpendicular to the light source-optical axis becomes small.

[0012]

As described above, in the grazing incidence illumination system from one direction using the prism including one prism, both prisms or a grating consisting of L & S patterns, or from two directions symmetrical with the optical axis on a plane perpendicular to the optical axis. The L & S pattern, which is parallel to the direction connecting the optical axes on the plane perpendicular to the optical axis, has a drawback that the resolution is significantly deteriorated.

The present invention has been made in view of the above points, and in the oblique incidence illumination system using a prism or a grating, when the direction connecting the optical axis and the light source is taken on a plane perpendicular to the optical axis, the L & S parallel to this is taken. L & S orthogonal to the pattern
It is an object of the present invention to provide a fine pattern projection exposure apparatus capable of arbitrarily controlling the resolving ability of the pattern even though the resolving ability is improved and deteriorated.

[0014]

In order to achieve the above-mentioned object, the present invention is directed to an inclination of an angle corresponding to the numerical aperture of a projection lens with respect to an optical axis of a light beam irradiating an object surface mask on which a pattern is drawn. In a projection exposure apparatus having a means for providing the light, when viewed in a plane perpendicular to the optical axis, oblique incidence illumination is performed from one direction from the outside of the optical axis or from two directions from the outside of the optical axis that are axially symmetric with respect to the optical axis. The means and the straight line connecting the optical axis to these one or two directions are equipped with a special diaphragm having an opening on the periphery of the straight line passing through the optical axis at right angles.

[0015]

According to the present invention, by combining oblique incidence illumination from one direction or two directions off the optical axis and a special diaphragm, and selecting the oblique incidence illumination conditions of both, the resolution of orthogonal L & S patterns can be improved. It can be controlled arbitrarily.

[0016]

EXAMPLES The present invention will be described in detail below with reference to examples.
Oblique incidence illumination by an optical element causes directionality in the effect of improving resolution because the illumination direction is specified when viewed in a plane perpendicular to the optical axis. For ease of explanation, here, an X-axis and a Y-axis that are orthogonal to each other with the optical axis as the origin are set on a plane perpendicular to the optical axis, and the oblique incidence illumination is a prism having an inclination in the X-axis direction or the Y-axis. A grating consisting of parallel L & S patterns is used. This is equivalent to illumination with oblique incidence from the direction on the X axis, which is off the optical axis. Further, the evaluation pattern will be described by using the L & S pattern parallel to the X axis and the Y axis as a representative in the following description. L (X): L & S pattern parallel to the X axis L (Y): L & S pattern parallel to the Y axis

In such a system, the normalized incident angle R
X, RY and the spread angle σ _D of incident light are defined as follows. RX = m · sin αx / NA RY = m · sin αy / NA σ _D = m · sin β / NA where m is the reduction magnification, NA is the numerical aperture of the projection lens, β
Is the divergence angle of the reticle illumination light beam, αx is the angle between it and the optical axis of the light beam center line projected on the plane containing the optical axis and the X coordinate, and αy is the optical axis of the light beam center line projected on the plane containing the optical axis and the Y coordinate. Is an angle.

Since the special diaphragm according to the present invention has an opening around the Y-axis, RX is determined by the tilt angle of the prism or the L & S pattern pitch of the grating, and RY is determined by the opening position of the special diaphragm. .. Further, σ _D is determined by the size of the aperture of the special diaphragm. Hereinafter, using these parameters, some embodiments will be described with reference to the drawings.

FIG. 1 shows an example of a special diaphragm 18 according to the present invention, which has a circular aperture 19 at a position symmetrical with respect to the optical axis on the Y axis when viewed in a plane perpendicular to the optical axis. This special diaphragm 18
, The light source used is the g-line, and the numerical aperture of the projection lens NA = 0.
54, and a projection exposure apparatus having a reduction ratio m = 5. In practice, the special diaphragm 18 was replaced with the aperture diaphragm 11 of the projection exposure apparatus shown in FIG. 2 and the optical element 17 was applied.

FIGS. 3 to 5 show the position and size of the light source 21 in the pupil space 20 obtained by variously changing the conditions of the prism or the grating and the special diaphragm in this embodiment. The values of RX, RY and σ _D for each are listed together in Table 1.

[0021]

[Table 1]

Further, in FIG. 3 and Table 1, the conventional method S (FIG. 3 (a)) with RX coherence factor σ = 0.5 and RX =
An example of the oblique incidence illumination method P (FIG. 3 (b)) described in Japanese Patent Application No. 3-142782 having a ratio of 0.9 is also shown, and the simulation result of the contrast obtained from both is shown in FIG.

Pupil condition A (FIG. 3 (c)) in this embodiment,
B (FIG. 3 (d)) and C (FIG. 4 (a)) are the cases where the light source 21 is arranged to circumscribe the pupil periphery at the positions of 30 °, 45 °, and 60 ° with respect to the X axis. The obtained contrast simulation result is shown in FIG. In FIG. 6, A
In Fig. 3 (c), compared to the oblique incidence illumination method P in Fig. 11, L
It can be seen that the resolution is greatly improved in (X).
Further, in B, the resolution just opposite to A is obtained for L (X) and L (Y).

Next, using this embodiment, a wafer coated with a resist of 0.5 μm was exposed and developed with L & S patterns having various dimensions, and the formed pattern was observed with a scanning electron microscope to determine the limit. The resolution pattern size was determined. The critical resolution pattern size is the smallest L / S pattern size among the normally formed patterns with no L- and S-patterns and no resist residue between the patterns. The results are shown in Table 1. Good correspondence with the simulation results. Table 1 shows the conventional method S obtained in the same manner (Fig. 3 (a)).
The results obtained with the oblique incidence illumination method P (FIG. 3B) are also shown.

As described above, in the present embodiment, if appropriate RX and RY are combined with the oblique incidence illumination and the special diaphragm, L
It is shown that the resolution of (X) and L (Y) can be controlled arbitrarily. Pupil condition A (FIG. 3 (c)) in this embodiment,
D (FIG. 4 (b)) and E (FIG. 4 (c)) circumscribe the light source 21 around the pupil at a position of 30 ° with respect to the X axis, and the size thereof is σ _D = 0.1, FIG. 7 shows a simulation result of the contrast obtained by changing σ _D = 0.3, and Table 1 shows the limit resolution obtained by actually exposing and developing the pattern by the same method as described above. Shown in. It can be seen that as the size of the light source 21 is increased, the resolution of both L (Y) and L (X) decreases, but this shows that the effects of the present invention are not lost. There is.

In the conventional projection exposure apparatus,
Generally, a coherence factor of around σ = 0.5 is used to obtain the optimum resolution. The pupil conditions F, G and H (FIG. 5) in the present invention are such a conventional σ = 0.
This is an embodiment applied to a projection exposure apparatus having a coherent factor of 5. Pupil condition F (Fig. 5 (a)) and G (Fig. 5 (b))
Is the pupil condition H (FIG. 5 (c)) when the light source 21 is arranged at positions of 30 ° and 45 ° with respect to the X-axis and circumscribes a circle of 1/2 the size of the pupil. Is 1 in the Y-axis direction
When the light source is arranged so that the X-axis direction circumscribes the circle of 1 in the circle of No. 2, the simulation result of the contrast obtained by this is shown in FIGS. Table 1 shows the limit resolution obtained by exposure and development.
Shown in. The rate of change in resolution is small compared to the result of FIG. 6, but the effect of the present invention is confirmed. Further, in FIG. 9, in comparison with the result of FIG. 11 which is the conventional oblique incidence illumination system, L
The resolution of (X) can be significantly improved.

Although the special diaphragm 18 having a circular aperture is arranged immediately after the secondary light source surface in the above-mentioned embodiment, this special diaphragm has a point symmetrical with respect to the optical axis. The same can be done with an opening having two congruent circles or two congruent polygons.

[0028]

As described above, the projection exposure apparatus of the present invention combines oblique incidence illumination from one or two directions off the optical axis with a special diaphragm and selects both oblique incidence illumination conditions. In comparison with the conventional projection exposure apparatus, the resolution of orthogonal L & S patterns can be arbitrarily controlled. Therefore, according to the projection exposure apparatus of the present invention, the resolution can be distributed in the X direction and the Y direction. Therefore, from a pattern such as a grating or a surface acoustic wave element that requires high resolution in one direction, an LSI or the like can be obtained. In forming a fine pattern, optimum resolution distribution can be performed especially when the same resolution is not necessarily required for orthogonal patterns such as gate patterns and wiring patterns. Therefore, the degree of integration of the LSI and the like and the device performance can be significantly improved.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a special diaphragm according to the present invention.

FIG. 2 is a diagram showing a specific example when the special diaphragm of FIG. 1 is applied to a normal projection exposure apparatus and an example of a normal projection exposure apparatus.

FIG. 3 is an explanatory diagram showing the present embodiment, where (a) and (b) show the position and size of the light source in the pupil space of the conventional method S and the oblique incidence illumination method P used for comparison, (c) and (d) show the positions and sizes in the pupil spaces A and B obtained when the conditions of the prism or the grating and the special diaphragm are changed.

4 (a), 4 (b) and 4 (c) are also explanatory views showing the present embodiment, where the positions in the pupil spaces C, D and E obtained when the conditions of the prism or the grating and the special diaphragm are changed. And the size is shown.

5 (a), 5 (b) and 5 (c) are positions in the pupil spaces F, G and H obtained by changing the conditions of the prism or the grating and the special diaphragm. And the size is shown.

FIG. 6 is a diagram showing a simulation result of contrasts obtained from a conventional projection exposure apparatus used for comparison with pupil conditions A, B and C in the present invention.

FIG. 7 is a diagram showing simulation results of contrasts obtained from a conventional projection exposure apparatus used for comparison with pupil conditions A, D and E in the present invention.

FIG. 8 is a diagram showing a simulation result of the pupil conditions F and G in the present invention and the contrast obtained from the conventional projection exposure apparatus used for comparison.

FIG. 9 is a diagram showing a simulation result of a pupil condition H in the present invention and a contrast obtained from a conventional projection exposure apparatus used for comparison.

FIG. 10A is an explanatory diagram showing reticle irradiation by an oblique incident exposure method proposed by the same applicant, and FIG. 10B is an explanatory diagram of reticle irradiation by a conventional method for comparison with this.

FIG. 11 is a diagram showing a result of simulation determination of a resolution limit in the case where the conventional projection exposure apparatus and the oblique incidence illumination method are applied.

[Explanation of symbols]

 1 Light Source Lamp 4 Input Lens 5 Cone Lens 6 Optical Integrator 7 Output Lens 8 Condenser Lens Group 9 Reticle 14 Projection Optical System 15 Wafer 17 Optical Element 18 Special Aperture 19 Circular Aperture 20 Pupil Space 21 Light Source

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Emi Tamekichi 1-6, Uchiyukicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Inventor Kazuhiko Komatsu 1-1-6, Uchiyuki-cho, Chiyoda-ku, Tokyo No. Japan Telegraph and Telephone Corp. (72) Inventor Yoshiaki Mimura 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp.

Claims (3)

[Claims] 1. A projection exposure apparatus having means for imparting a tilt of a light beam illuminating an object surface mask with a pattern drawn with respect to the optical axis, the angle being corresponding to the numerical aperture of a projection lens. When viewed inside, means for obliquely illuminating from one direction from the outside of the optical axis or two directions from the outside of the optical axis that are axially symmetric with respect to the optical axis, and a straight line connecting the one or two directions to the optical axis Is a fine pattern projection exposure apparatus having a special aperture having an opening on the periphery of a straight line passing through a right-angled optical axis. 2. The optical system according to claim 1, wherein the special diaphragm is on a straight line passing through an optical axis perpendicular to a straight line connecting one direction or two directions of the oblique incidence illumination and the optical axis, and a point symmetrical to the optical axis. A fine pattern projection exposure apparatus having an opening formed of two congruent circles or two congruent polygons. 3. The fine pattern projection exposure apparatus according to claim 1, wherein the special diaphragm can be mounted immediately after the secondary light source surface.