JPH0624180B2 - Projection exposure method and apparatus thereof - Google Patents

Description

The present invention relates to projection exposure illumination using laser light, and more particularly to a projection exposure method using an excimer laser suitable for fine pattern resolution of a semiconductor exposure apparatus, and Regarding the device.

[Conventional technology]

Conventionally, a semiconductor exposure apparatus is a g-line (wavelength 436) of a mercury lamp.
nm) and i-line (wavelength 365 nm) have been used as illumination light. In response to the need for finer semiconductor patterns, the resolution has been improved by increasing the numerical aperture (NA) of the reduction lens. Further, miniaturization has been promoted by the shift from the g-line to the i-line.

[Problems to be solved by the invention]

In each of the above-mentioned conventional techniques, exposure illumination light having a relatively wide spectral width of the light source (several nm or more) is used, and the imaging lens is made of a plurality of types of glass materials that do not cause chromatic aberration with respect to this spectral width. Deep (D
eep) Exposure to light in the UV region is required, but only several types of materials such as quartz and fluorite can be used in this region, and one type of material must be used considering the uniformity of the materials. Disappear. In this case, since it is impossible to correct chromatic aberration, it is necessary to use laser light, which also has a spectral width of 0.01 mn or less. For example, an excimer laser with an injection lock is used.

When such laser light is used for exposure illumination, so-called coherent illumination is obtained because the laser has high directivity. As a result, the pattern exposed on the photosensitive material is MTF ((modulation, transfer, function (Modulation Transfer F
unction)) becomes 1 and the MTF becomes 0 at frequencies higher than this, and the unevenness of the spatial frequency corresponding to this cutoff frequency is superimposed on the pattern, and a good quality image is not formed on the photosensitive material.

An object of the present invention is to solve the above-mentioned conventional problems by effectively reducing the coherency of the laser by using laser light as a light source for exposure to obtain monochromatic light suitable for imaging, and to achieve high brightness. In order to provide a high-resolution projection exposure method and apparatus therefor.

[Means for solving problems]

In the projection exposure apparatus having a light source unit, an illumination system unit, and a projection optical system unit, the light source unit has a laser light source, and the illumination system unit emits a laser beam emitted from the laser light source. Laser beam homogenizing means for making the intensity distribution uniform within a desired region of the laser beam, deflection scanning means for deflecting and scanning the laser beam adjusted to have a uniform intensity distribution by the homogenizing means, and laser beam Of the laser beam which has an aperture stop located at a position conjugate with the entrance pupil of the projection optical system by limiting the deflection scanning range of the projection optical system, and the projection optical system unit irradiates the exposure object through the aperture stop and transmits the exposure object. This is achieved by having projection exposure means for forming an image of the exposed object obtained by the method on the surface of the exposed object. Further, the object of the present invention is particularly to reduce the number of types of glass materials that transmit light.
For a high wavelength range of 50 nm or less, a pulsed laser beam such as an excimer laser is used, and the above-mentioned exposure illumination is applied to the pulsed beam for an imaging optical system made of one or several kinds of glass materials.
By synchronizing the pulse period and the deflection drive, the spatial coherency is similarly reduced.

[Action]

When the present invention is applied to a reduction exposure apparatus, a reticle, which is an exposure object, is uniformly illuminated with laser light. At this time, each circuit pattern on the reticle is illuminated with laser light at a constant incident angle. This direction is illuminated so that the incident light is focused at approximately one point on the entrance pupil plane (in the case of one-telecentric) of the reduction lens. Further, a means for deflecting the laser light is inserted in the middle of reaching the reticle from the laser light source. By deflecting the laser light by the deflecting means, the reticle is illuminated with the uniform laser light, and the incident angle of each circuit pattern changes according to the deflection, and therefore, on the entrance pupil plane of the reduction lens. The incident light is focused on almost one point, but its position changes according to the deflection. By performing such illumination, the exposure light transmitted through the reticle, which is illuminated at a desired plurality of incident angles, is integratedly exposed to the resist on the wafer as the medium to be exposed. In this way, each moment within the exposure time is coherent illumination, but the integrated and exposed illumination is equivalent to incoherent (or partial coherent) illumination, and there is little noise and resolution is high. A high good pattern is formed on the wafer.

〔Example〕

The first embodiment of the present invention will be described below with reference to FIG.
Reference numeral 1 denotes an excimer laser light source, and the pulsed laser light emitted from this light source passes through an exposure illumination device 3 of the present invention and uniformly illuminates a reticle 2 which is an exposure object, and the laser light transmitted through this reticle is a reduction lens 5. And an image of the exposed object is formed on the photosensitive material (resist) applied on the wafer 4 which is the medium to be exposed. The exposure illumination device 3 has the following configuration. The distribution of laser light emitted from the laser light source is
Particularly, in the case of an injection lock type excimer laser, since there is a depression in the central portion, the beam passes through the beam homogenizing means 31 which makes the beam uniform in distribution. This beam homogenizing means does not generate a wavefront of laser light from a spherical surface or a plane wave to a random wavefront, or a wavefront that significantly increases the divergence angle of the beam even if it is not random. It is composed of minute openings and the like.
Therefore, the laser beam that has passed through the beam homogenizing means 31 has a uniform distribution in the desired beam area and has a beam divergence angle as well.
It is about the original spread angle of the excimer laser. This uniform laser beam is narrowed down to point A by the condenser lens 3.
On the way to the point A, there is a galvano mirror 301, which deflects the laser light in the negative plane. A lens 302 having a front focus at point A receives the deflected laser light and is arranged so as to form an image on the galvano mirror surface of 303 on the galvano mirror surface of 303. Therefore, the laser light that has passed through the lens 302 becomes substantially parallel light, and the laser light is applied to the same position on the galvano mirror 303 regardless of the deflection angle of the galvano mirror 301. The galvanometer mirror 303 swings around the axis of rotation. The lenses 33 and 34 form the point A on the aperture stop 35 and the pupil 51 of the reduction lens 5, and at the same time,
The Galvano mirrors 301 and 303 and the drawing surface (lower surface) of the reticle 2 are in a mutually positional relationship. Therefore, the control circuit 7 controls the pulse emission timing of the excimer laser 1 and the deflection control of the galvano mirrors 301 and 303 as shown in FIG.
The point A is imaged as shown in FIG. When the point A is imaged on each of these points, the incident angle of the illumination light on the reticle 2 changes, and in any case, the distribution of the irradiation light on the reticle is uniform. That is,
It is clear from the fact that 301 and 303 and the reticle coexist. FIG. 5 (a) is a diagram showing a drive signal for the galvano mirror 301, FIG. 5 (b) is a diagram showing a drive signal for the galvano mirror 303, and FIG. 5 (c) is a diagram showing an emission pulse of the excimer laser. In this way, as shown in FIG. 5, by controlling the pulsed light of the galvanometer mirror and the excimer laser, a spot is formed on the pupil 51 of the reduction lens in a range in which it spreads like a base in a rectangular shape. In general, the rotationally symmetrical distribution spread on the pupil eliminates the direction dependence of the resolution of the crystal pattern. Therefore, an aperture stop 35 is provided behind the lens 33. This has a circular opening, and the opening diameter can be controlled. The opening diameter can be set arbitrarily according to the type of the circuit pattern on the reticle. This aperture stop is a lens 34
Since the image is formed on the pupil of the reduction lens, it becomes possible to arbitrarily control the spread of the laser spot on the pupil (thus, the range of the reticle illumination angle).

FIG. 3 is a diagram for explaining the state of focusing of laser light on the pupil, the spread of the focusing point, and the partial coherency σ. At each pattern position of B1, B2, B3 of reticle 2,
At a certain moment, pulsed light with high directivity that can be represented by light rays 611, 621, and 631 is incident and is condensed on 361 on the pupil. Of course, since circuit patterns are drawn in B1 to B3, it goes without saying that the light diffracted by this pattern has a spread around 361. Similarly, at other moments, light rays 612, 622, and 632 are incident, and 362 on the pupil.
Focus on the center of the pupil. Similarly, the other pulsed light is 36
Focus on 3. Assuming that the range of the spread of the focused spot on the pupil is d and the diameter of the pupil is D, the partial coherency σ of the illumination light is d / D. d0, the center of the pupil 3
When only 62 is illuminated, it becomes completely coherent illumination, and coherency is lost as d / D approaches 1. Although the value of σ and the resolution of the pattern are already known, when σ = 0 as shown in FIG. 4, the depressions of the imaging pattern appear in both the strength and the resolution pattern shape, and a good pattern is obtained. Not formed on the wafer. A good pattern can be formed by setting σ to 0.4 to 0.8. The dotted line in FIG. 4 indicates ideal image formation.

FIG. 6 shows a second embodiment of the present invention, which has the same basic configuration as that of FIG. 1 but is largely different in the beam homogenizing means 31. FIG. 6 (a) shows the beam homogenizing means 31 in the direction perpendicular to the x-y-z coordinates shown in FIG.
It is a view with an inclination of 45 ° on the axis and an inclination of 135 ° on the x-axis. Since the beam emitted from the excimer laser has a hollow at the center, it is divided into four prisms 310, and the beams are advanced in four directions at right angles to the incident direction and at right angles to each other. FIG. 6 (b) is a view of the cross section B-B of FIG. 6 (a) taken along the g direction, and a beam traveling in four directions is shown. Reference numeral 3101 on the prism is a light-shielding plate that cuts a minute area in the central depressed portion. A beam traveling in four directions (two directions perpendicular to the paper surface are not shown in FIG. 6 (a)),
For example, the beam traveling in the <1, 0, -1> direction will be described. Since the light is once condensed by the lens 3110 and there is a minute circular aperture 3111 at this concentration position, a uniform light is obtained by passing through this aperture. Become. This uniform light is reflected by the lens 31.
The beam becomes almost flat by 12 and the prism 3113
Will be folded back at. This folded state is similar to that of the prism 3123 of FIG. 6 (a). Similarly, the four beams are uniformly parallel and enter the common prism 311.
Here, the four beams are separated by the prism 310, and the optical path lengths until they are incident on the common prism 311 are different, for example, by equal difference, and the beam passing through 3110 having the shortest optical path length is 3120. The optical path of the beam passing through is longer by Δl and the beams passing through 3130 and 3140 are longer by 2Δl and 3Δl, respectively. Moreover, Δl is longer than the coherence length of the excimer laser. For example, when an injection lock type excimer laser is used, the spectral width is 0.003 nm, so Δl is 5
The value is 0 nm or more. Thus, the wedge glasses 3114, 3124, 3134, 31 immediately before the beams whose optical path lengths differ from each other by the coherence length or more enter the prism 311.
44 (3114 and 3134 are not shown), the prism 321, and the lens 32
The galvano mirrors 301 overlap at almost the same position. Since the four overlapping beams do not interfere with each other, uniform light beams are added to each other, and a uniform intensity distribution is obtained on the galvanometer mirror 301. However, since these four beams have different traveling directions, at point A shown in FIG. 1, there are four separated spots as shown in FIGS. 6 (a) and 6 (c). Therefore A
Since the surface of the points is co-located with the surfaces of the aperture stop 35 and the pupil 51 of the reduction lens, there are four spots on the pupil as shown in FIG. 7 (b). Further, as described above, since the surfaces of the galvano mirrors 301 and 303 and the reticle 2 are also intimate, the four superimposed beams having a uniform intensity distribution on the galvano mirror 301 have uniform intensity on the reticle. Distribution, and evenly illuminates the circuit pattern on the reticle. As a result, by deflecting the Galvano mirrors 301 and 303, as shown in FIG. 7A, a large number of spots are formed on the pupil of the reduction lens (compared with the case shown in the embodiment of FIG. 2). Therefore, it is possible to realize partial coherent illumination with little discreteness by minutely changing the illumination angle of the reticle. Further, when realizing the same number of spots on the pupil as in FIG. 1, it is possible to obtain a desired partial coherence with a small (1/4) pulse light. Four more beams are the sixth
3125, 3145 (3115, 3135) shown in FIG.
(Not shown) etc., a transmittance distribution filter having a transmittance as shown in FIG. 8B is arranged at a position such that the reticle illumination light becomes more uniform. For example, as shown in FIG. 8 (a), in order to further improve the uniformity in the effective area for illuminating the circuit pattern of the reticle, a filter having a transmittance characteristic inversely proportional to this distribution in the effective area ( If FIG. 8 (b)) is placed at a position such as 3125, as shown in FIG. 8 (c), the uniformity within the effective area becomes high.
Further, if the four transmittance distribution filters are comprehensively adjusted for transmittance, the reticle illumination can be made more uniform.

FIG. 9 shows a third embodiment of the present invention. Instead of the prisms 310 and 311 shown in FIG. 6, a prism 310 '(311' is not shown) for separating and combining beams in six directions is used. It is a thing. In this case as well, the difference in the optical path length from the separation of the beams to the combination of the beams is kept at a coherence length or more. If an exposure illumination device 3'having a beam homogenizing means using such a prism 310 'is used, as shown in FIGS. 10 (a) and 10 (b), there are 6 spots in one pulse exposure. As a result, the distribution of spots in the entrance pupil 51 becomes more dense, and partial coherent illumination can be realized. Further, since the desired number of spots is generated on the pupil, the number of pulses required for the exposure of the pulse laser can be effectively reduced, and the exposure time can be shortened and the reticle illumination light can be made uniform more easily.

In the present invention, the light deflecting means is not limited to the galvano mirror shown in the above-mentioned embodiment, but a polygon mirror, an A / O deflector or the like can be used, and thereby it is possible to increase the speed. . Further, the laser light source is not limited to the excimer laser, and it is obvious that a laser having a wavelength suitable for other exposure may be used.

〔The invention's effect〕

According to the present invention, compared with the conventional reduction lens, using a laser such as an excimer laser light whose exposure wavelength is significantly shortened,
Moreover, in a reduction projection exposure apparatus that has a narrow spectral width and is capable of sufficiently resolving even one type of glass material, it is possible to uniformly illuminate the reticle and to achieve the optimum partial coherency of the illumination. It has become possible to resolve a pattern having a line width of 0.5 μm or less with good image quality by photolithography.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention, FIG. 2 is a diagram showing a laser spot distribution on a pupil of a reduction lens, FIG. 3 is a diagram showing a laser illuminating beam, and FIG. 4 is a diagram showing the present invention. FIG. 5 is a diagram showing the pulse timings of the galvanometer mirror and the excimer laser, FIG. 6 is a diagram showing the uniform exposure means in the second embodiment of the present invention, and FIG. The figure which shows the spot on the pupil in the example of a figure, FIG. 8 is the figure which shows the effect of the transmittance distribution filter in the 2nd Example of this invention, FIG.
FIG. 10 and FIG. 10 are views showing a third embodiment of the present invention. 1 ... Excimer laser, 2 ... Reticle, 3 ... Exposure illuminator, 4 ... Wafer, 5 ... Reduction lens, 301, 3
03 …… Galvano mirror, 35 …… Aperture stop, 31 ……
Uniform exposure means, 51 ... Entrance pupil, 310, 311, 31
0 '... Prism for beam separation or combination, 7 ... Control circuit.

Claims (9)

[Claims] 1. A projection exposure apparatus having a light source section, an illumination system section, and a projection optical system section, wherein the light source section has a laser light source, and the illumination system section emits laser light from the laser light source. The laser beam homogenizing means for uniformizing the intensity distribution within a desired region of the laser beam, and the laser beam adjusted to have a uniform intensity distribution by the homogenizing means are deflected and scanned. Deflection scanning means and an aperture stop that limits the deflection scanning range of the laser beam and is located at a position conjugate with the entrance pupil of the projection optical system, and the projection optical system section exposes the exposure object through the aperture stop. A projection exposure apparatus, comprising: projection exposure means for forming an image of the exposure object, which is obtained by the laser beam irradiated onto the object and transmitted through the exposure object, on the surface of the object to be exposed. 2. The laser beam generating means has a pulse laser light source for generating a pulse laser, and the variable deflecting means deflects and scans the laser beam in synchronization with an emission pulse of the pulse laser. The projection exposure apparatus according to claim 1. 3. The projection exposure apparatus according to claim 1, wherein the laser beam generating means has an excimer laser light source. 4. The projection exposure apparatus according to claim 1, wherein the excimer laser light source is an injection lock system. 5. The projection exposure apparatus according to claim 1, wherein the aperture stop has a variable stop amount. 6. The laser beam generating means makes the laser beam emitted from the laser light source have a uniform intensity distribution in a desired region of the laser beam, and separates the laser beam into a plurality of beams. 2. The projection exposure apparatus according to claim 1, wherein the plurality of separated beams are recombined with an optical path length difference of at least a coherence distance and then are incident on the deflection scanning means. 7. A laser beam emitted from a laser light source has a uniform intensity distribution within a desired region, the laser beam adjusted to have the uniform intensity distribution is deflected and scanned, and the deflected and scanned. Irradiate the exposed object through the aperture stop means for limiting the area for deflecting and scanning the laser beam,
Projection exposure, characterized in that an image of the exposure object obtained by the laser beam transmitted through the exposure object is formed on the surface of the exposure object by projection exposure means provided at a position conjugate with the aperture stop means. Method. 8. The laser beam emitted from the laser light source is separated into a plurality of beams, the separated beams are combined again with an optical path difference of a coherence length or more, and then the deflected beam is deflected. 8. The projection exposure method according to claim 7, wherein images of the plurality of exposed objects are simultaneously formed on the surface of the exposed object by scanning. 9. The partial coherency of the laser beam imaged on the surface of the object to be exposed is between 0.4 and 0.8.
The projection exposure method according to the item.