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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to photolithography which is applied for precise processing when semiconductor devices are produced, and more particularly relates to an optical exposure method used for photolithography.
When semiconductor devices such as ultra-LSIs are highly integrated and precise processing is required, manufactures greatly rely on improvements in lithographic technology. Photolithography using light is suitable for mass production.
Therefore, it is adopted for economical reasons.
2. Description of the Related Art
In order to improve resolution in optical exposure technology, it is important to increase the numerical aperture (NA) and to reduce the wavelength of light generated by a light source. On the other hand, the focal depth is reduced as NA is
increased. Recently, attention has been given to a deformation illumination method (an oblique incident illumination method) which improves the critical resolution and focal depth (for example, shown in pages 28-37 of "Nikkei Micro Device" No. 82,
April, 1992).
For holes in the diaphragm (the apertures) in the deformation illumination method, zonal holes and four holes symmetrical with respect to a point are well known. In a conventional illumination method, a ray, of illumination light sent from a
circular hole, coinciding with an optical axis, to a photomask (reticule) is vertically incident and an image is formed by three beams of light of 0, +1, and -1. However, with this deformation illumination method, the position of the diaphragm is
shifted from the optical axis, so that illumination light sent from the hole is obliquely incident on the photomask, and image formation is conducted by two beams of light of 0 and +1 sent from the photomask. In a focal position, higher contrast can be
provided by the conventional illumination method, however, in a defocal position, higher contrast can be provided by the deformation illumination method, so that the focal depth and resolution can be considerably improved.
In the conventional deformation illumination method, i.e., only for a simple line and space pattern, a pattern of the photomask is projected and exposed on a register with a diaphragm having the aforementioned general type of diaphragm holes.
Accordingly, the illumination system does not meet the requirement of each pattern, so that the effect of oblique incidence of the deformation illumination method is not sufficient.
Also, recently, attention has been given to a lithographic technology using a phase shift mask, and the following pattern forming method has been reported to be an effective technology: an unexposed portion (pattern) is used that is accompanied
by a sharp decrease of optical intensity generated by a step portion (the phase of exposure light is changed by 180.degree. by this step portion) of a phase shifter of a phase shift mask.
However, when a pattern is formed by this technology, the unexposed portion (pattern) is formed in all step portions of the phase shifter. Therefore, in many applicable fields, it is necessary to provide a process to inhibit the formation of a
pattern generated by the unexposed portion generated by an unnecessary step portion of the phase shifter.
Therefore, the following techniques have been conventionally proposed to ease the sharp decrease of optical intensity: another exposure mask is put on the unnecessary unexposed portion so as to conduct an exposure operation (double exposure); and
a multi-shifter (step of 90.degree.) is provided stepwise in a step portion of the phase shifter, the pattern formation of which is not necessary.
However, in the double exposure method that has been conventionally proposed as a method to remove an unnecessary unexposed portion, it is necessary to manufacture a plurality of masks so as to conduct multi-exposures. Accordingly, it is
necessary to increase the number of the mask manufacturing processes. On the other hand, it is also necessary to ensure an alignment of the double exposure, so that the throughput is lowered.
Moreover, when a multi-shifter is manufactured, a complicated and difficult process technique is required in order to provide an optically accurate multi-shifter, and further a big problem is caused when a manufactured phase shift is inspected
and corrected.
In order to meet the demand of forming minute patterns, for example, attention is given to an oblique incidence illumination method disclosed in the official gazette of Japanese Unexamined Patent Publication No. 2-142111 (1990). According to
this method, a ray of light that is vertically incident on a lens is incident being oblique at a predetermined angle, so that focusing is conducted using interference of light.
However, in the aforementioned conventional method, the same light source is used for any device patterns without giving attention to the profile of the light source. Accordingly, problems are caused.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a projection exposure method with a deformation illumination system optimal for a device pattern (photomask pattern).
It is another object of the present invention to provide a method by which an unnecessary unexposed portion can be easily removed without using the aforementioned multi-exposure method or relying on the technique in which the phase shift mask
having a multi-shifter is used, in the case where a pattern is formed using the unexposed portion accompanied by a sharp decrease of optical intensity caused by a step portion of the phase shifter.
It is another object of the present invention to provide an optimization method for a light source profile to obtain an optimal light source profile in accordance with a device pattern.
It is another object of the present invention to realize an optical projection exposure in which resolving power can be provided that is higher than that of the conventional phase shift mask or oblique incidence illumination.
The aforementioned object can be accomplished by an optical exposure method by which a pattern on a photomask is projected and exposed on a register on a base plate with an exposure device including a deformation illumination system composed of a
light source, a diaphragm and a condenser lens, and also including a photomask and a projection lens, wherein the optical exposure method uses a ray of linear light for illumination that is parallel with a photomask pattern in a position separate from an
optical axis of the exposure device (or the optical exposure method uses two rays of linear light for illumination that are symmetrical with respect to the optical axis) when the photomask pattern is a line and space pattern.
The aforementioned object can be accomplished by an optical exposure method, wherein the optical exposure method uses a ray of first linear light for illumination that is parallel with a first pattern portion in a position separate from the
optical axis of the exposure system (or the optical exposure method uses two rays of first linear light for illumination that are parallel with the first pattern portion symmetrical with respect to the optical axis), the optical exposure method also uses
a ray of second linear light for illumination that is parallel with a second pattern portion in a position separate from the optical axis of the exposure system (or the optical exposure method also uses two rays of second linear light for illumination
that are parallel with the second pattern, two rays of second linear light being symmetrical with respect to the optical axis), when the first pattern portion of line and space, and the second pattern portion of similar line and space make a right angle
with each other in the photomask pattern.
Moreover, it is preferable to use an optical exposure method in which the first linear light and the second linear light are oblique by an angle .phi. with respect to the optical axis in a position on the photomask, and an equation
2p.multidot.sin .phi.=.lambda. is satisfied (where p is a setting pitch of the line and space pattern on the projection surface, and .lambda. is a wavelength of light).
The object of the present invention can be accomplished by an optical exposure method by which a pattern on a photomask is projected and exposed on a register on a base plate with an exposure device including a deformation illumination system
composed of a light source, a diaphragm and a condenser lens, and also including a photomask and a projection lens, wherein the optical exposure method uses a ray of first block light for illumination that is parallel with the bottom surface of the
triangular wave in a position separate from the optical axis of the exposure device (or the optical exposure method uses two rays of first block light for illumination that are symmetrical with respect to the optical axis and parallel with the bottom
surface of the triangular wave), and the optical exposure method also uses a ray of second block light for illumination that is perpendicular to the bottom surface of the triangular wave (or the optical exposure method also uses two rays of second block
light for illumination that are symmetrical with respect to the optical axis and perpendicular to the bottom surface of the triangular wave), when the photomask pattern is a line and space pattern of a triangular shape, the bottom angle of which is
.theta..
Moreover, it is preferable to adopt an optical exposure method in which the optical exposure method characterized in that: the first block light is oblique by an angle .phi..sub.x with respect to the optical axis in a position on the photomask,
an equation 2p.multidot.sin .phi.=.lambda.sin .theta. being satisfied (p is a setting pitch of line and space pattern in a register, and .lambda. is a wavelength of light); the second block light is oblique by an angle .phi..sub.y with respect to the
optical axis in a position on the photomask, an equation 2p.multidot.sin .phi.=.lambda.cos .theta. being satisfied; and a ratio of the illumination area of the first block light to that of the second block light is sin .theta.:cos .theta..
In the optical exposure method of the present invention, the most appropriate illumination light shape and oblique incident angle .phi. are set in accordance with each photomask pattern, so that the resolution and focal depth and improved for
each pattern. Especially when the pitch of line and space of a photomask pattern is close to 1:1, the optical exposure method of the invention is especially effective. In this connection, a pattern of line and space corresponds to a plurality of linear
shading (or transmission) stripes of a photomask that are disposed in parallel at regular intervals on a developed register pattern.
In the aforementioned equation 2p.multidot.sin .phi.=.lambda., wavelength .lambda. becomes constant for g ray (434 nm), i ray (365 nm) or excimer laser beam (254 nm for KeF excimer laser beam), and incident angle .phi. is determined in
accordance with pattern pitch width p.
According to another aspect of the present invention, there is provided a projection exposure method of the present invention comprising the steps of: irradiating an exposure mask with exposing light having an optical intensity distribution
extending in a primary direction in its section; and projecting the light transmitted through the exposure mask on a surface to be exposed, wherein exposure is carried out with exposure characteristics relying on a direction of the mask pattern of the
exposure mask.
Moreover, the present invention is to provide a projection exposure method comprising the steps of: irradiating a phase shift exposure mask with exposing light having an optical intensity distribution extending in a primary direction in its
section; and projecting the light transmitted through the phase shift exposure mask on a surface to be exposed, wherein exposure is carried out with exposure characteristics relying on a direction of the mask pattern of the phase shift exposure mask.
Especially, an exposing process is adopted in which exposure is carried out with non-symmetrical exposure characteristics including one direction of a step in which an unexposed portion is formed having a sharp decrease of optical intensity caused close
to an edge portion of the phase shifter of the phase shift exposure mask, and also including the other direction of a step in which an unexposed portion is not formed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of an exposure device of deformation illumination (oblique incidence illumination);
FIG. 2 is a partial plan view of a pattern of line and space;
FIG. 3 is a plan view of a diaphragm provided with two linear through-holes;
FIGS. 4(a)-4(d) are a set of graphs showing the optical intensity in perpendicular directions in accordance with the pattern of FIG. 2 on a projection surface when the diaphragm of FIG. 3 is used. FIG. 4(a) is a graph showing the optical
intensity in the case where an image is in focus, FIG. 4(b) is a graph showing the optical intensity in the case where an image is out of focus, wherein the focus slippage is 0.5 .mu.m, FIG. 4(c) is a graph showing the optical intensity in the case where
an image is out of focus, wherein the focus slippage is 1.0 .mu.m, and FIG. 4(d) is a graph showing the optical intensity in the case where an image is out of focus, wherein the focus slippage is 1.5 .mu.m;
FIGS. 5(a)-5(d) are a set of graphs showing the optical intensity in perpendicular directions on projection surfaces in accordance with the pattern of FIG. 2 when a conventional circular hole diaphragm is used. FIG. 5(a) is a graph showing the
optical intensity in the case where an image is in focus, FIG. 5(b) is a graph showing the optical intensity in the case where an image is out of focus, wherein the focus slippage is 0.5 .mu.m, FIG. 5(c) is a graph showing the optical intensity in the
case where an image is out of focus, wherein the focus slippage is 1.0 .mu.m, and FIG. 5(d) is a graph showing the optical intensity in the case where an image is out of focus, wherein the focus slippage is 1.5 .mu.m;
FIG. 6 is a plan view of a diaphragm provided with one linear through-hole;
FIG. 7 is a partial plan view of a combination pattern in which a pair of patterns are combined, wherein the patterns make a right angle with each other;
FIG. 8 is a plan view of a diaphragm provided with two pairs of parallel linear through-holes, wherein the pairs of parallel linear through-holes make a right angle with each other;
FIGS. 9(a)-9(f) are a set of graphs showing three dimensional optical intensity distributions on the projection surface in accordance with the pattern of FIG. 7 when the diaphragm of FIG. 8 is used. In FIG. 9(a), the optical intensity
distribution is shown in the case of image formation conducted in a focal position (in focus). In FIG. 9(b), the optical intensity distribution is shown in the case of image formation conducted out of focus, wherein the amount of focus slippage is 0.2
.mu.m. In FIG. 9(c), the optical intensity distribution is shown in the case of image formation conducted out of focus, wherein the amount of focus slippage in 0.4 .mu.m. In FIG. 9(d), the optical intensity distribution is shown in the case of image
formation conducted out of focus, wherein the amount of focus slippage is 0.6 .mu.m. In FIG. 9(e), the optical intensity distribution is shown in the case of image formation conducted in a position out of focus, wherein an amount of focus slippage is
0.8 .mu.m. In FIG. 9(f), the optical intensity distribution is shown in the case of image formation conducted out of focus, wherein the amount of focus slippage is 1.0 .mu.m;
FIGS. 10(a)-10(f) are a set of graphs showing three dimensional optical intensity distributions on the projection surface in accordance with the pattern of FIG. 7 when a conventional circular diaphragm is used. FIG. 10(a) is a graph showing the
optical intensity distribution in the case of image formation conducted in a focal position (in focus). FIG. 10(b) is a graph showing the optical intensity distribution in the case of image formation conducted out of focus, wherein the amount of focus
slippage is 0.2 .mu.m. FIG. 10(c) is a graph showing the optical intensity distribution in the case of image formation conducted out of focus, wherein the amount of out of focus is 0.4 .mu.m. FIG. 10(d) is a graph showing the optical intensity
distribution in the case of image formation conducted out of focus, wherein the amount of focus slippage is 0.6 .mu.m. FIG. 10(e) is a graph showing the optical intensity distribution in the case of image formation conducted in a position out of focus,
wherein an amount of focus slippage is 0.8 .mu.m. FIG. 10(f) is a graph showing the optical intensity distribution in the case of image formation conducted out of focus, wherein the amount of focus slippage is 1.0 .mu.m;
FIG. 11 is a plan view of a diaphragm provided with linear through-holes making a right angle with each other;
FIG. 12 is a partial plan view of a triangular wave line and space pattern;
FIG. 13 is a plan view of a diaphragm provided with two pairs block through-holes, wherein each pair includes two block through-holes separate from an optical axis;
FIG. 14 is a partial plan view of a triangular wave line and space pattern utilized in a DRAM activation region;
FIG. 15 is a plan view of a diaphragm provided with two pairs rectangular through-holes, wherein each pair includes two rectangular through-holes separate from an optical axis;
FIGS. 16(a)-16(c) are a set of graphs showing three dimensional optical intensity distributions on a projection surface in accordance with the pattern of FIG. 14 when the diaphragm of FIG. 15 is utilized. FIG. 16(a) is a graph showing the
optical intensity distribution in the case of image formation conducted in a focal position (in focus). FIG. 16(b) is a graph showing the optical intensity distribution in the case of image formation conducted out of focus, wherein the amount of focus
slippage is 0.2 .mu.m. FIG. 16(c) is a graph showing the optical intensity distribution in the case of image formation conducted out of focus, wherein the amount of focus slippage is 0.4 .mu.m;
FIGS. 17(a)-17(d) are a set of graphs showing three dimensional optical intensity distributions on a projection surface in accordance with the pattern of FIG. 14 when the diaphragm of FIG. 15 is used. FIG. 17(a) is a graph showing the optical
intensity distribution in the case of image formation conducted out of focus, wherein the amount of focus slippage is 0.6 .mu.m. FIG. 17(b) is a graph showing the optical intensity distribution in the case of image formation conducted in a position out
of focus, wherein an amount of focus slippage is 0.8 .mu.m. FIG. 17(c) is a graph showing the optical intensity distribution in the case of image formation conducted out of focus, wherein the amount of focus slippage is 1.0 .mu.m. FIG. 17(d) is a graph
showing the optical intensity distribution in the case of image formation conducted out of focus, wherein the amount of focus slippage is 1.2 .mu.m;
FIG. 18 is a plan view of a diaphragm provided with a through-hole corresponding to a conventional circular hole;
FIGS. 19(a)-19(c) are a set of graphs showing three is dimensional optical intensity distributions on a projection surface in accordance with the pattern of FIG. 14 when the conventional diaphragm of FIG. 19 is used. FIG. 19(a) is a graph
showing the optical intensity distribution in the case of image formation conducted in a focal position. FIG. 19(b) is a graph showing the optical intensity distribution in the case of image formation conducted out of focus, wherein the amount of focus
slippage is 0.2 .mu.m. FIG. 19(c) is a graph showing the optical intensity distribution in the case of image formation conducted out of focus, wherein the amount of focus slippage is 0.4 .mu.m;
FIGS. 20(a)-20(d) are a set of graphs showing three dimensional optical intensity distributions on a projection surface in accordance with the pattern of FIG. 14 when the conventional diaphragm of FIG. 19 is used. FIG. 20(a) is a graph showing
the optical intensity distribution in the case of image formation conducted out of focus, wherein the amount of focus slippage is 0.6 .mu.m. FIG. 20(b) is a graph showing the optical intensity distribution in the case of image formation conducted out of
focus, wherein the amount of focus slippage is 0.8 .mu.m. FIG. 20(c) is a graph showing the optical intensity distribution in the case of image formation conducted out of focus, wherein the amount of focus slippage is 1.0 .mu.m. FIG. 20(d) is a graph
showing the optical intensity distribution in the case of image formation conducted out of focus, wherein the amount of focus slippage is 1.2 .mu.m;
FIG. 21 is a plan view showing a diaphragm provided with two sets of block through-holes separate from an optical axis;
FIG. 22 is a sectional view schematic of a fly-eye lens and a liquid crystal plate diaphragm;
FIG. 23 is a schematic illustration of an optical projection exposure device of deformation illumination system;
FIG. 24 is a plan view of a deformation illumination diaphragm provided with 4 holes;
FIG. 25 is a partial plan view of a line pattern of a photomask;
FIG. 26 is a partial plan view of a register line pattern provided by a conventional optical projection exposure device;
FIG. 27 is a partial plan view of a register line pattern in the deformation illumination system;
FIG. 28 is a schematic illustration showing a relation between a photomask and a diaphragm in the case of incident light of three directions in the deformation illumination system;
FIG. 29 is a schematic illustration showing a relation between a photomask and a diaphragm in the case of incident light of two directions (in the case of excellent resolution) in the deformation illumination system;
FIG. 30 is a partial plan view schematic of a pattern in a DRAM (dynamic random access memory);
FIG. 31 is partial plan view schematic of a pattern in an activation region of a DRAM;
FIG. 32 is a plan view showing a configuration of common illumination;
FIG. 33 is a plan view showing a configuration of division illumination;
FIGS. 34(a) and 34(b) are plan views showing the rotation of division illumination in the case where they do not make a right angle with each other;
FIG. 35 is a schematic illustration showing the structure of a projection exposure device used for the projection exposure method;
FIGS. 36(a) and 36(b) are schematic illustrations of the diaphragm of the projection exposure device used for the projection exposure method;
FIG. 37 is an optical intensity distribution diagram of exposure light transmitted through the phase shifter step portion parallel with the primary direction of the exposure light;
FIG. 38 is an optical intensity distribution diagram of exposure light transmitted through the phase shifter step portion perpendicular to the primary direction of the exposure light;
FIGS. 39(a) and 39(b) are schematic illustrations of the projection exposure method of the embodiment 8;
FIGS. 40(a) and 40(b) are schematic views of a pattern showing the effect of the embodiment 8;
FIGS. 41(a) and 41(b) are schematic illustrations of the projection exposure method of the embodiment 9;
FIG. 42 is a schematic illustration of the projection exposure method of the embodiment 10;
FIGS. 43(a) to 43(c) are schematic illustrations of the projection exposure method of the embodiment 11;
FIG. 44 is a schematic illustration of the projection exposure method of the embodiment 12;
FIG. 45 is a view showing the principle of the optimization method for a light source profile of the embodiment 13;
FIG. 46 is a flow chart showing an outline of processing of the embodiment 13;
FIG. 47 is a flow chart showing primary processing of the embodiment 13;
FIG. 48 is a view showing an example of the optimized light source profile of the embodiment 13;
FIG. 49 is a view showing an example of the optimized light source profile of the embodiment 13;
FIGS. 50(a)-50(f) are a set of views showing pattern images for each focal position obtained by the light source shown in FIG. 48;
FIGS. 51(a)-51(f) are a set of views showing pattern images for each focal position obtained by the light source shown in FIG. 49;
FIG. 52 is a flow chart showing primary processing of the embodiment 14;
FIGS. 53(a) and 53(b) are views showing examples of mask patterns;
FIGS. 54(a)-54(c) are a set of views showing spectral distributions of the pattern shown in FIG. 53(a);
FIGS. 55(a-55(c) are a set of views showing spectral distributions of the pattern shown in FIG. 53(b);
FIG. 56 is a view showing examples of a conventional light source profile;
FIGS. 57(a)-57(f) are a set of views showing pattern images for each focal position obtained by the light source shown in FIG. 56;
FIGS. 58(a)-58(f) are a set of views showing pattern images for each focal position obtained by the light source shown in FIG. 56;
FIG. 59 is a perspective view for explaining an outline of projection exposure according to the embodiment 15;
FIG. 60 is a schematic illustration showing a profile of an experimental pattern of exposure of the embodiment shown in FIG. 59;
FIGS. 61(a) and 61(b) are schematic views showing experimental results;
FIG. 62 is a perspective view for explaining projection exposure of the embodiment 16;
FIGS. 63(a)-63(d) are a set of schematic illustrations for explaining a exposure technique in which the phase difference is utilized;
FIGS. 64(a) and 64(b) are a pair of diagrams showing an outline of a phase shift mask;
FIGS. 65(a) and 65(b) are a pair of diagrams showing an outline of oblique incidence illumination exposure; and
FIGS. 66(a) and 66(b) are a pair of diagrams showing an outline of the difference of image formation capacity caused by polarization.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIGS. 1 through 22, the first aspect of the present invention will now be explained in detail with embodiments and comparative examples.
FIG. 1 is a schematic illustration of an exposure device (stepper). The exposure device comprises: a deformation illumination system 4 including a light source 1 composed of a mercury lamp (excimer laser), a diaphragm 2 provided with a
through-hole, and a condenser lens 3; a photomask (reticule) 5 having a predetermined pattern; a projection lens 6; and a register film (projection surface) 7 coated on a base plate. This structure is the same as that of a conventional exposure device,
and only a configuration of the through-hole of the diaphragm 2 is different from that of the conventional exposure device. In this connection, a compound eye condenser lens (fly eye lens) may be provided between the light source 1 and the diaphragm 2
in the same manner as the conventional exposure device.
In this embodiment, the configuration of the light source is determined by the configuration of the diaphragm through-hole. However, the individual single eyes may be disposed to be a target configuration of the light source using a fly eye
lens. In order to change the light source configuration in accordance with the object of use, in the case where a diaphragm is used, the diaphragm may be replaced with another one having a through-hole of different configuration. Alternatively, the
individual single eyes 51a to 51f of the fly eye lens 51 (FIG. 22) may be provided with opening and closing function. For example, a liquid crystal plate 52 is disposed at the exit or entrance of the single eye of the fly eye lens, and voltage is
impressed upon an electrode 53 located in a position corresponding to the single eye so that the light can be transmitted or not.
Embodiment 1
A line and space pattern 13 composed of opaque stripes 11 and transmitting stripes 12 shown in FIG. 2 is formed on the photomask 5 by a conventional method. The photomask 5 is made when a chrome shading film of this pattern is provided on a
quartz glass plate. Pitch A of the line and space corresponds to setting pitch p of the register pattern to be obtained. In order to provide illumination of the present invention, as shown in FIG. 3, two linear through-holes (or light transmission
apertures) 16 are formed in the diaphragm 15 in parallel with each other, wherein the two linear through-holes 16 are disposed symmetrically with respect to an optical axis of the exposure device. Consequently, two slits are formed in the shading
diaphragm, so that the light emitted from the light source 1 passes through these slits and is incident on the condenser lens 3. In this connection, the diaphragm 15 is disposed so that these linear through-holes 16 can be in parallel with the line and
space pattern 13 of the photomask. Then, the photomask 5 is illuminated with light sent from the condenser lens 3, wherein the incident angle of light is .phi.. In this case, the incident angle is an angle formed between the light and the optical axis
of the exposure device in a position on the photomask. Next, the diffraction light of 0 and +1 orders sent from the photomask 5 is projected on the projection lens 6, and the diffraction light is collected by the lens, so that a pattern image is formed
on the register film 7 on the projection surface. The pattern 13 of the photomask 5 is projected and exposed on the register film 7 on a base plate of a semiconductor wafer, and then the projected image is developed so as to obtain a register pattern.
In the case where optical exposure was conducted under the following conditions, optical intensity in a direction perpendicular to the line and space pattern is shown in FIGS. 4(a) to 4(d), wherein the projection surface of the register film is
located in a focal position of the projection lens or in a position shifted from the focal position (defocus).
Wavelength (.lambda.) of light source . . . i ray (0.365 .mu.m)
Numerical aperture of lens (NA) . . . 0.5
Coherence factor (.sigma.) . . . 0.5
Setting pitch (p) of line and space . . . 0.35 .mu.m
Incident angle (.phi.) . . . 31.4.degree.
(calculated from 2.times.0.35.times.sin .phi.=0.365)
In FIG. 4(a), the optical intensity is shown in the case of image formation conducted in a focal position (in focus). In FIG. 4(b), the optical intensity is shown in the case of image formation conducted out of focus, wherein the amount of
defocus is 0.5 .mu.m. In FIG. 4(c), the optical intensity is shown in the case of image formation conducted out of focus, wherein the amount of defocus is 1.0 .mu.m. In FIG. 4(d), the optical intensity is shown in the case of image formation conducted
out of focus, wherein the amount of defocus is 1.5 .mu.m. As can be seen in FIGS. 4(a) to 4(d), the profiles of optical intensity are approximately the same, and the focal depth is large.
As a comparative example, optical exposure was conducted with the same optical exposure device using a conventional circular diaphragm (.sigma.=0.5). The optical intensity on the projection surface on the register film in the focal and non-focal
positions are shown in FIGS. 5(a) to (d).
In FIG. 5(a), the optical intensity is shown in the case of image formation conducted in a focal position (in focus). In FIG. 5(b), the optical intensity is shown in the case of image formation conducted out of focus, wherein the amount of focus
slippage is 0.5 .mu.m. In FIG. 5(c), the optical intensity is shown in the case of image formation conducted out of focus, wherein the amount of focus slippage is 1.0 .mu.m. In FIG. 5(d), the optical intensity is shown in the case of image formation
conducted out of focus, wherein the amount of focus slippage is 1.5 .mu.m. As can be seen in FIGS. 5(a) to 5(d), concerning the profile of optical intensity, the larger the amount of focal slippage is, the smaller the contrast of optical intensity
becomes, so that the resolution is deteriorated. Naturally, the focal depth is smaller than that of the device of the present invention.
Embodiment 2
In the above-mentioned embodiment, the optical exposure device and the photomask 5 of embodiment 1 were used. In the embodiment 2, the diaphragm was replaced with a diaphragm 17 shown in FIG. 6, wherein the number of the linear through-holes 16
was one. The diaphragm 17 was disposed so that the linear through-hole 16 could be parallel with the pattern 13 of the line and space of the photomask. In this case, the light emitted from the light source 1 passed through the linear through-hole 16,
and was incident on the condenser lens 3, so that the photomask 5 was illuminated with the light, the incident angle of which was .phi.. Next, the diffraction light of 0 and +1 orders sent from the photomask 5 was projected on the projection lens 6, and
the diffraction light was collected by the lens, so that a pattern image was formed on the register film 7 on the projection surface. The pattern 13 of the photomask 5 was projected and exposed on the register film 7, and then the projected image was
developed so as to obtain a register pattern. In the case of embodiment 1, the photomask was illuminated with light from both the right and left, however, in the case of embodiment 2, the photomask was illuminated with light in one direction.
Therefore, as compared with the results of embodiment 1, the pattern profile was more deteriorated by the slippage of focus. However, as compared with the aforementioned comparative example, the focal depth was large and resolution was high.
Embodiment 3
A pattern 23 was formed on the photomask 5 by a well known method as shown in FIG. 7, wherein the pattern 23 was composed of a square shading region 21 in which squares were cyclically disposed at regular intervals, and a through-hole region 22
surrounding the square shading region 21. In this pattern 23, the line and space pattern shown in FIG. 2 and the same line and space pattern disposed perpendicular to it are combined. Pitch A of the line and space (the interval of the width of the
shading region 21) corresponds to setting pitch p of the line and space of the register pattern to be obtained. In order to provide illumination of the present invention, as shown in FIG. 8, two linear through-holes 25, which are the same as those of
embodiment 1, are formed in the diaphragm 24 in parallel with each other, wherein the two linear through-holes 25 are disposed symmetrically with respect to an optical axis of the optical exposure device. Moreover, two linear through-holes 26
perpendicular to these linear through-holes 25 are disposed in parallel with each other symmetrically with the optical axis. The two linear through-holes 25 compose the first linear light, and another pair of linear through-holes 26 compose the second
linear light, and these two pairs of through-holes 25 and 26 are disposed in the same position when one of them is rotated around the optical axis by angle 90.degree.. Accordingly, four slits are formed in the shading diaphragm, and the light emitted
from the light source 1 passes through these slits and is incident on the condenser lens 3. In this connection, the diaphragm 24 is disposed so that these linear through-holes 25 and 26 can be in parallel with the line and space pattern 23 of the
photomask. Then, the photomask 5 is illuminated with light sent from the condenser lens 3, wherein the incident angle of light is .phi.. In this case, the incident angle is an angle formed between the light and the optical axis of the exposure device
in a position on the photomask. Next, the diffraction light of 0 and +1 orders sent from the photomask 5 is projected on the projection lens 6, and the diffraction light is collected by the lens, so that a pattern image is formed on the register film 7
on the projection surface. The pattern 23 of the photomask 5 is projected and exposed on the register film 7 on a base plate of a semiconductor wafer, and then the projected image is developed so as to obtain a register pattern.
An exposure simulation was carried out with the exposure device of embodiment 1 under the following conditions, wherein the projection surface of the register film was disposed in a focal position of the projection lens and also disposed in a
position out of focus. The three dimensional optical intensity distribution is shown in FIGS. 9(a) to 9(f) illustrated with equal intensity lines.
Wavelength (.lambda.) of light source . . . i ray (0.365 .mu.m)
Numerical aperture of lens (NA) . . . 0.5
Coherence factor (.sigma.) . . . 0.5
Setting pitch (p) of line and space . . . 0.35 .mu.m
Incident angle (.phi.) . . . 31.40.degree.
(calculated from 2.times.0.35.times.sin .phi.0.365)
In FIG. 9(a), the optical intensity distribution is shown in the case of image formation conducted in a focal position (in focus). In FIG. 9(b), the optical intensity distribution is shown in the case of image formation conducted out of focus,
wherein the amount of focus slippage is 0.2 .mu.m. In FIG. 9(c), the optical intensity distribution is shown in the case of image formation conducted out of focus, wherein the amount of focus slippage is 0.4 .mu.m. In FIG. 9(d), the optical intensity
distribution is shown in the case of image formation conducted out of focus, wherein the amount of focus slippage is 0.6 .mu.m. In FIG. 9(e), the optical intensity distribution is shown in the case of image formation conducted in a position out of
focus, wherein an amount of focus slippage is 0.8 .mu.m. In FIG. 9(f), the optical intensity distribution is shown in the case of image formation conducted out of focus, wherein the amount of focus slippage is 1.0 .mu.m. As can be seen in FIGS. 9(a) to
(f), the profiles of optical intensity distributions are approximately the same, and the focal depth is large.
As a comparative example, exposure was conducted with the same exposure device using a conventional circular diaphragm (.sigma.=0.5). The optical intensity distribution on the projection surface on the register film in the focal and non-focal
positions are shown in FIGS. 10(a) to (f).
In FIG. 10(a), the optical intensity distribution is shown in the case of image formation conducted in a focal position (in focus). In FIG. 10(b), the optical intensity distribution is shown in the case of image formation conducted out of focus,
wherein the amount of focus slippage is 0.2 .mu.m. In FIG. 10(c), the optical intensity distribution is shown in the case of image formation conducted out of focus, wherein the amount of focus slippage is 0.4 .mu.m. In FIG. 10(d), the optical intensity
distribution is shown in the case of image formation conducted out of focus, wherein the amount of focus slippage is 0.6 .mu.m. In FIG. 10(e), the optical intensity distribution is shown in the case of image formation conducted out of focus, wherein the
amount of focus slippage is 0.8 .mu.m. In FIG. 10(f), the optical intensity distribution is shown in the case of image formation conducted out of focus, wherein the amount of focus slippage is 1.0 .mu.m. As can be seen in FIGS. 10(a) to 10(f), the more
the focus slippage is increased, the more gentle the difference of optical intensity distribution becomes, and the distribution spreads to the non-exposure portion, so that the contrast of optical intensity distribution is reduced and the resolution is
deteriorated. Naturally, the focal depth is smaller than that of the device of the present invention.
Embodiment 4
In this embodiment, the optical exposure device and the photomask 5 of embodiment 3 were used, but the diaphragm was replaced with a diaphragm 27 shown in FIG. 11, wherein the number of the linear through-holes 25 and 26 was two. The diaphragm
27 was disposed so that the linear through-holes 25 and 26, which made a right angle with each other, could be disposed in parallel with the pattern 23 of the square shading region 21 on the photomask in which squares were cyclically disposed at regular
intervals. In this case, the light emitted from the light source 1 passed through the linear through-holes 25 and 26, and was incident on the condenser lens 3, so that the photomask 5 was illuminated with the light, the incident angle of which was
.phi.. Next, the diffraction light of 0 and +1 orders sent from the photomask 5 is projected on the projection lens 6, and the diffraction light is collected by the lens, so that a pattern image is formed on the register film 7 on the projection
surface. The pattern 13 of the photomask 5 is projected and exposed on the register film 7, and then the projected image is developed so as to obtain a register pattern. In the case of embodiment 3, the photomask was illuminated with light from both
the right and left, however, in the case of embodiment 4, the photomask was illuminated with light in one direction. Therefore, as compared with the results of embodiment 3, the pattern profile was more deteriorated by the slippage of focus. However,
as compared with the aforementioned comparative example, the focal depth is large and the resolution is high.
In embodiments 1 to 4, a ray of light passes through a linear through-hole in which the width of the slit is selected from 5 to 10 mm. Therefore, when the slit is too narrow, an amount of light (that is, .sigma.) is reduced so that the exposure
time is extended. When the slit is too wide, noise components pass through the slit, so that sufficient effect cannot be provided. Preferably, the slit is 5 to 10 mm wide.
Embodiment 5
A pattern 33 of line and space composed of shading stripes 31, the bottom angle of which is 0 as shown in FIG. 12, and also composed of through-hole stripes 32, is formed on the photomask 5 by a well known method. Pitch A of the line and space
corresponds to setting pitch p of the line and space of a register pattern to be obtained. In order to provide illumination of the present invention, as shown in FIG. 13, the first block through-holes 35 of the same configuration as the diaphragm 34,
the number of which is two, are formed in a position separate from the optical axis of the exposure device, wherein the first block through-holes 35 are disposed in parallel with the longitudinal direction of the stripe symmetrically with respect to the
optical axis. Moreover, the second block through-holes 36 of the same configuration, the number of which is two, are formed in a position separate from the optical axis of the exposure device, wherein the second block through-holes 36 are disposed in
parallel with the longitudinal direction of the stripe symmetrically with respect to the optical axis (that is, four through-holes are provided in total). The two block through-holes 35 compose the first block of light, and another pair of block
through-holes 36 compose the second block of light. The areas of these through-holes are set so that a ratio of the illumination area of the first block light to that of the second block light can be sin .theta.:cos .theta.. The configuration of each
block through-hole is either rectangular, circular, oval, lozenge-shaped or triangular, and the necessary through-hole area must be ensured. Accordingly, four through-holes are formed in the shading diaphragm, and a ray of light emitted from the light
source 1 passes through these through-holes, and is incident on the condenser lens 3. Illumination is conducted on the photomask 5 by the light passing through the condenser lens 3, wherein the incident angle of the block through-hole 35 is .phi..sub.x
and the incident angle of the block through-hole 35 is .phi..sub.y. In this case, these incident angles are defined as an angle formed between the ray of light and the optical axis of the optical exposure device. Concerning incident angle .phi..sub.x,
an equation 2p.multidot.sin .phi..sub.x =.lambda.sin .theta. is satisfied (where p is a setting pitch of the line and space pattern, and .lambda.is a wavelength of light.) Concerning incident angle .phi..sub.y, an equation 2p.multidot.sin .phi..sub.y
=.lambda.cos .theta. is satisfied. Next, the diffraction light of 0 and +1 orders sent from the photomask 5 is projected on the projection lens 6, and the diffraction light is collected by the lens, so that a pattern image is formed on the register
film 7 on the projection surface. The pattern 33 of the photomask 5 is projected and exposed on the register film 7 on a base plate of a semiconductor wafer, and then the projected image is developed so as to obtain a register pattern.
In the case of a triangular wave stripe-shaped pattern 38 utilized in a DRAM activation region shown in FIG. 14, the photomask block through-holes 39 and 40 shown in FIG. 15 are adopted, and then optical exposure simulation is carried out under
the following conditions. The projection surface is set at a focal position and at a position out of focus. In this way, three dimensional optical intensity distributions expressed by equal intensity lines are provided that are shown in FIGS. 16(a) to
16(c) and FIGS. 17(a) to 17(d).
The conditions of the triangular wave stripe-shaped pattern 38 are as follows.
Setting pitch (p) of line and space . . . 0.35 .mu.m
Bottom angle (.theta.) of triangular wave stripe . . . i ray (0.365 .mu.m)
Numerical aperture of lens (NA) . . . 0.5
Coherence factor (.sigma.) . . . 0.5
Incident angle (.phi.) of block through-hole 39 . . . 74.8.degree.
Incident angle (.phi..sub.y) of block through-hole 40 . . . 26.8.degree.
Ratio of the area of block through-hole 39 and that of block-through hole 39 . . . 0.5:0.866
In FIG. 16(a), the optical intensity distribution is shown in the case of image formation conducted in a focal position (in focus). In FIG. 16(b), the optical intensity distribution is shown in the case of image formation conducted out of focus,
wherein the amount of focus slippage is 0.2 .mu.m. In FIG. 16(c), the optical intensity distribution is shown in the case of image formation conducted out of focus, wherein the amount of out of focus is 0.4 .mu.m. In FIG. 17(a), the optical intensity
distribution is shown in the case of image formation conducted out of focus, wherein the amount of focus slippage is 0.6 .mu.m. In FIG. 17(b), the optical intensity distribution is shown in the case of image formation conducted in a position out of
focus, wherein an amount of focus slippage is 0.8 .mu.m. In FIG. 17(c), the optical intensity distribution is shown in the case of image formation conducted out of focus, wherein the amount of focus slippage is 1.0 .mu.m. In FIG. 17(d), the optical
intensity distribution is shown in the case of image formation conducted out of focus, wherein the amount of focus slippage is 1.2 .mu.m. As can be seen in FIGS. 16 and 17, the profiles of optical intensity distributions are approximately the same when
the focal slippage is not more than 1.0 .mu.m, and the focal depth is large.
As a comparative example, optical exposure was conducted with the same optical exposure device using a conventional circular diaphragm (.sigma.=0.5) provided with a conventional circular hole 41 shown in FIG. 18. The optical intensity
distribution on the projection surface in the focal and non-focal positions are shown in FIGS. 19(a) to 19(c) and in FIGS. 20(a) to 20(d).
In FIG. 19(a), the optical intensity distribution is shown in the case of image formation conducted in a focal position (in focus). In FIG. 19(b), the optical intensity distribution is shown in the case of image formation conducted out of focus,
wherein the amount of focus slippage is 0.2 .mu.m. In FIG. 19(c), the optical intensity distribution is shown in the case of image formation conducted out of focus, wherein the amount of focus slippage is 0.4 .mu.m. In FIG. 20(a), the optical intensity
distribution is shown in the case of image formation conducted out of focus, wherein the amount of focus slippage is 0.6 .mu.m. In FIG. 20(b), the optical intensity distribution is shown in the case of image formation conducted out of focus, wherein the
amount of focus slippage is 0.8 .mu.m. In FIG. 20(c), the optical intensity distribution is shown in the case of image formation conducted out of focus, wherein the amount of focus slippage is 1.0 .mu.m. In FIG. 20(d), the optical intensity
distribution is shown in the case of image formation conducted out of focus, wherein the amount of focus slippage is 1.2 .mu.m. As can be seen in FIGS. 19 and 20, the more the focus slippage is increased, the more gentle the difference of optical
intensity distribution becomes, and the distribution spreads to the non-exposure portion, so that the contrast of optical intensity distribution is reduced and the resolution is deteriorated. Naturally, the focal depth is smaller than that of the device
of the present invention.
Embodiment 6
In this embodiment, the optical exposure device and photomask 5 of embodiment 5 are used, but the diaphragm is replaced with a diaphragm 45 provided with block through-holes 35 and 36 in FIG. 21, each number of which is respectively one. The
diaphragm 45 is disposed so that the block through-hole 35 can be parallel with the bottom surface of the triangular wave of the triangular wave stripe, and so that the block through-hole 36 can make a right angle with the bottom surface of the
triangular wave. In this case, the light emitted from the light source 1 passes through the block through-holes 35 and 36, and is incident on the condenser lens 3, so that the photomask 5 is illuminated with the light, the incident angle of which is
.phi..sub.x and .phi..sub.y. Next, the diffraction light of 0 and +1 orders sent from the photomask 5 is projected on the projection lens 6, and then the diffraction light is collected by the lens, so that a pattern image is f | | |
