DE4421053A1 - Illumination device esp. for microlithographic projection exposure - Google Patents

Abstract

A Hg arc lamp (1) emitting at 365 nm is placed at the focus of an ellipsoidal mirror (12). An iris (13) beyond the second focus (121) passes the light to a zoom lens system (2) including concave and convex axicons (22,23) with adjustable spacing which pref. can be reduced to zero. A glass rod (5) transmits the light between second and third lens systems (4,6), the latter having an intermediate plane (62) for filters or irises and a deflecting mirror (64) for a horizontal reticle (7).

Description

The invention relates to a lighting device for a optical system, especially a microlithographic Projection exposure system with two axicons.

From W.N. Partlo et al., SPIE Vol. 1927, Optical / Laser Microlithography VI (1993), pp. 137-157 (Fig. 19, 20) is one Generic lighting device known in the collimated beam path between two lenses in the area two axicons between light source and light integrator are arranged, a concave, a convex, with flat second Interfaces. For optimal illumination of various Ring field diaphragms their distance can be varied from zero, conventional lighting can also be used.

From EP 0 564 264 A1 it is known to generate a Ring field illumination with wafer steppers a conical lens - to use an axicon, or to generate one Multipole lighting pyramid prisms (Fig. 7, 8). Also the Arrangement of two axicons is known (Fig. 17, 19) that however, two axicons are through different optical elements Cut. The conical or pyramidal surfaces are both convex.

The usability of concave conical components in this Connection is disclosed in JP 5/251 308 A.

EP 0 346 844 A1 shows the use of pairs convex conical lenses, the tips of which are opposite to each other are directed to the lighting beam splitting for the Dot mapping with over-resolution.

From US 5 208 629 is for the illumination of a wafer stepper the use of pyramid or cone axicon lenses, too as a convex concave shape, for low-loss provision of a  symmetrical oblique lighting (multipole lighting) known. A zoom function is not connected to it.

Zoom systems for varying the degree of coherence are shown in Lighting systems for wafer steppers with honeycomb condensers ASM-L company from the Netherlands has been in use since 1987.

From US 5 237 367 is the use of a zoom in the Illumination device of a wafer stepper for lossless Setting the degree of coherence σ is known, namely at conventional lighting.

From US 5 245 384 is an afocal zoom system for the Illumination in wafer steppers known with which Coherence factor σ can be adjusted with little loss. An axicon is not scheduled.

EP 0 297 161 A1 provides for a projection exposure system Optical fiber glass rod in the illumination beam path indicates that after a gradient filter can be attached to the glass rod. This apparently serves the further homogenization, not the Dimming.

The ever advancing approach to the resolution limits optical projection for lithographic Microstructuring entails the requirement that the Illumination according to the structures of the individual templates must be optimized, that is, optimized ring field or Quadrupole lighting and others need to be set can.

It is therefore the object of the invention to be particularly flexible indicate changeable lighting device by Adjusting elements, without exchange, and with as much as possible high efficiency, a variety of lighting modes enables.  

The task is solved by a generic Lighting device in which the two axicons in one Zoom lens are integrated and their distance is adjustable.

The flexibility achieved in the design of the The cross section of the light beam is created by the execution of the axicons with the same tip angle and the possible reduction of the Distance between the two axicons up to the contact according to the Sub-claims 2 and 3 optimized. In particular, the Borderline case of conventional lighting can be shown.

If the axicons are conical, the arrangement is suitable especially for ring field lighting. With pyramid-shaped Axicons, on the other hand, optimize multipole lighting.

It is particularly advantageous if according to claims 6 and 7 the second interfaces of the axicons have a lens effect and so the zoom lens is more compact and easier to assemble becomes.

Claim 8 describes the particular advantage of Lighting device according to the invention, namely conventional, ring field or multipole lighting very much are variably adjustable.

Advantageous in the lighting device according to the invention is integrated according to claim 8 and 9, a glass rod as Light integrator with a masking system at the exit is arranged. A reticle masking system right on Reticle, which is especially there when it should be adjustable is problematic, or your own intermediate mapping system for a reticle masking system are saved and the construction effort is reduced while maintaining high quality.

The arrangement of the usual shutter outside the focus of the Lamp mirror is a general additional measure for Improving the homogeneity of the lighting, which is reflected in  Combination with the other features of the invention particularly proven.

With the described lighting device it is possible set the various types of lighting mentioned above, completely without apertures to form the light beam after the Light integrator for different types of lighting should be adjustable or changeable. The whole formation happens by adjusting the zoom axicon lens what is optimally suited to from a computer to be done programmatically. The quality achieved here the individual lighting modes can be increased effort significantly increased for the Zoom / Axicon assembly become.

Fixed screens to suppress stray light and the like are of course at every advantageous point in the beam path possible.

The invention is explained in more detail with reference to the drawing.

Show it:

Figure 1 is a schematic representation of a preferred embodiment of a lighting device according to the invention.

FIG. 2a shows an embodiment of the zoom axicon objective contained in FIG. 1 as a lens section with axicons moved together at a distance of zero;

Fig. 2b the same as Fig. 2a, but with separate axicons;

Fig. 3 shows the intensity variation as a function of the radius in the pupil plane intermediate for different zoom and axicon positions of the assembly of Figure 2a and 2b.

FIG. 4a shows another embodiment schematically;

FIG. 4b shows another embodiment schematically;

Fig. 4c another embodiment schematically;

Fig. 4d schematically shows another embodiment.

Fig. 1 shows an example of an illumination device according to the invention for projection lithography at resolutions up to fractions of 1 micron, z. B. for the manufacture of integrated circuits.

A lamp ( 1 ), a mercury short-arc lamp for the i-line of 365 nm wavelength, is arranged in the focal point of an elliptical mirror ( 12 ), which collects the emitted light in the second focal point ( 121 ).

Deviating from the rule, the shutter ( 13 ) is arranged outside the focal point ( 121 ), namely the distance from the apex of the elliptical mirror ( 12 ) is approximately 5% to 20%, preferably 10%, greater than the distance from the focal point ( 121 ) to the crown. It is thereby achieved that the secondary light source formed here becomes more homogeneous and the partially coherent effect of the illumination on the optical image is improved. An extra mixing system for this purpose can be saved. This measure is also useful in an otherwise conventional lighting device.

The following objective ( 2 ) consists of a first lens group ( 21 ), the concave first axicon ( 22 ), the convex second axicon ( 23 ) and a second lens group ( 24 ). Adjustment means ( 231 ) and ( 241 ) allow the axial displacement of an axicon ( 23 ) and an element of the second lens group ( 24 ). This allows both the distance between the axicons ( 22 , 23 ) to be adjusted and thus the character of the ring field to be changed, as well as a zoom effect to change the illuminated pupil diameter, i.e. the degree of coherence (sigma).

After the interpupillary plane ( 3 ) there follows a second objective ( 4 ), with which the light is coupled into the glass rod ( 5 ) of about 0.5 m in length. The output of the glass rod ( 5 ) is an intermediate field level, in which a masking system ( 51 ) is arranged, which is used instead of conventional REMA (reticle masking) systems. The otherwise usual creation of an additional intermediate field level for the REMA system with complex lens groups is saved.

The following objective ( 6 ) images the intermediate field plane with the masking system ( 51 ) onto the reticle ( 7 ) (mask, lithography template) and contains a first lens group ( 61 ), an intermediate pupil plane ( 62 ), into which filters or diaphragms are inserted second and third lens groups ( 63 and 65 ) and in between a deflecting mirror ( 64 ), which makes it possible to install the large lighting device (approx. 3 m in length) horizontally and to store the reticle ( 7 ) horizontally.

The part of the lighting device common to all embodiments is the objective ( 2 ), which is shown in FIG. 2a for an embodiment. Table 1 shows the lens data for this.

The first lens group ( 21 ) contains two lenses with the surfaces ( 211 , 212 , 215 , 216 ) and two flat plates with the surfaces ( 213 , 214 and 217 , 218 ), which can be designed as filters.

The two axicons ( 22 and 23 ) have the same cone angle α and can therefore be pushed together as shown in this Fig. 2a until they touch. In this position, the axicons ( 22 , 23 ) have no effect on the conical surfaces ( 222 , 231 ) and together form a simple lens, since their second boundary surfaces ( 221 , 232 ) are curved. This lens is important for the correction of the objective 2 , the beam path on the axicon ( 22 , 23 ) is not collimated. The lens ( 24 ) is axially displaceable and makes the arrangement a conventional zoom lens. Conventional illumination with a variable pupil diameter in the pupil plane ( 3 ), that is to say with a variable coherence factor a, can thus preferably be represented in the range 0.3 to 0.8. But of course it is provided that the two axicons ( 22 , 23 ) are moved apart by the adjusting means ( 231 ) to a desired distance.

Such a case is shown in FIG. 2b, which otherwise corresponds entirely to FIG. 2a.

The second lens group ( 24 ) is designed as a single biconcave lens with the surfaces ( 241 and 242 ). The focal plane ( 121 ) of the light source ( 1 , 12 ) and the pupil plane ( 3 ) are also shown in FIGS. 2a, 2b.

Fig. 3 shows the intensity curve (I) of the light as a function of r / r₀ in the pupil plane ( 3 ) for different positions of the axicon ( 23 ) and the lens ( 24 ). The curve A applies to the position according to FIG. 2a, the curve B applies to a position in which, starting from FIG. 2a, the lens ( 24 ) is largely moved towards the axicon ( 23 ). Curve C applies to the position of FIG. 2b shaped by the axicons ( 22, 23 ). The distance d23 ( 222 - 231 ) - i.e. the distance between the axicons ( 22 , 23 ) - determines the strength of the ring field lighting with a central dark disc. The latter grows with increasing distance. The distance d24 ( 242-3 ) determines the zoom effect, i.e. the total diameter of the illumination spot in the pupil plane ( 3 ). The ring field lighting has a high degree of efficiency because it is generated without hiding the middle pane. A (small) dark spot on the axis usually remains even with completely combined axicons ( 22 , 23 ) due to the design of the lamp ( 1 ) and the concave mirror ( 12 ). This is deliberately wanted and creates space for the accommodation of auxiliary systems, for example for focusing and positioning systems.

To multipole lighting (symmetrical oblique lighting device) one arrives when a multi-hole aperture is inserted into the pupil plane ( 3 ) or an equivalent plane of the lighting device, which from the ring field z. B. only lets four bundles through.

Special lighting geometries can also be achieved by deviating the shape of the axicons ( 22 , 23 ). B. Quadrupole lighting can be pyramid-shaped with a square base, achieve and support.

Further variants of lighting devices according to the invention are shown in FIGS . 4a to 4d. The same parts have the same reference numerals as in FIG. 1.

Fig. 4a shows an embodiment in which the glass rod ( 5 ) of Fig. 1 is replaced by a honeycomb condenser ( 50 ). This is an alternative that, among other things, reduces the overall length. However, the option for the REMA system described above does not apply. The objective ( 6 ) consists of the two lens groups ( 66 ) and ( 65 ) with an intermediate deflecting mirror ( 64 ) (schematic illustration based on the continuous optical axis).

FIG. 4b shows in comparison with FIG. 4a an additional glass rod (15) in the manner of the glass rod (5) of Fig. 1, disposed between the shutter (13) and the zoom axicon lens (2). The illumination of the pupil plane on the honeycomb condenser ( 50 ) can thus be homogenized even further. The zoom axicon lens ( 2 ) has more lenses here and is correspondingly longer.

FIG. 4c shows an arrangement according to FIG. 1, but with the additional glass rod ( 15 ) and the longer zoom axicon ( 2 ) from FIG. 4b.

Fig. 4d shows a variant of the illumination device according to the invention, serving as a light source, a laser beam (10) in the. This is preferably an excimer laser beam with a wavelength in the deep UV range. The shape of the laser beam ( 10 ) is typically a narrow rectangle. With a beam shaping device ( 14 ), for. B. according to DE 41 24 311 A1, the laser beam ( 10 ) is cheaper, typically square, shaped and at the same time reduced in coherence. After the shutter ( 13 ) follows a modified zoom axicon lens ( 2 '), which is designed here as a beam expansion telescope. After a diffusing screen or a diffraction element ( 8 ) as a further coherence-reducing secondary light source follows, adapted accordingly, as in FIGS . 4a and 4b, the honeycomb condenser ( 50 ) and the objective. ( 6 ) to the reticle ( 7 ). Of course, a glass rod according to FIGS. 1 and 4c can also be provided with the laser light source.

The variants presented are only a selection of typical ones Examples. Nor is the application of the invention to that Projection microlithography limited. In simpler Execution is suitable for. B. also as a variable Microscope lighting or as lighting for apparatus for Pattern recognition.  

Table 1

Claims (13)

1. Illumination device for an optical system, in particular a microlithographic projection exposure system, with two axicons ( 22 , 23 ), characterized in that a zoom lens ( 2 ) is provided for adjusting the degree of coherence (σ) and the two axicons ( 22 , 23 ) are arranged in this zoom lens ( 2 ) and their distance (d23) is adjustable. 2. Lighting device according to claim 1, characterized in that the axicons ( 22 , 23 ) as far as feasible in terms of production technology and functionally effective have the same tip angle (α). 3. Lighting device according to claim 1 or 2, characterized in that the distance (d23) of the two axicons ( 22 , 23 ) can be reduced to the point of contact. 4. Lighting device according to at least one of claims 1-3, characterized in that the axicons ( 22 , 23 ) are conical. 5. Lighting device according to at least one of claims 1-3, characterized in that the axicons ( 22 , 23 ) are pyramid-shaped. 6. Lighting device according to at least one of claims 1-5, characterized in that at least one axicon ( 22 , 23 ) as the second interface ( 221 , 232 ) has a curved surface. 7. Lighting device according to at least one of claims 1-6, characterized in that the axicons ( 22 , 23 ) are not arranged in a collimated beam. 8. Lighting device according to at least one of claims 1-7, characterized in that by adjusting the distance (d23) of the two axicons ( 22 , 23 ) or the position of at least one zoom lens element ( 24 ) both conventional lighting and ring field - or multi-pole lighting of different geometries can be set. 9. Lighting device according to at least one of claims 1-8, characterized in that it contains a glass rod ( 5 ) as a light integrator. 10. Lighting device according to claim 9, characterized in that a masking system ( 51 ) is arranged at the outlet of the glass rod ( 5 ). 11. Lighting device according to at least one of claims 1-10, characterized in that an aperture ( 13 ) forming a secondary light source is arranged outside the focus ( 121 ) of a lamp mirror ( 12 ). 12. Lighting device according to at least one of claims 1-11, characterized in that after the light integrator ( 5 ) no diaphragms are arranged to form the light beam. 13. Lighting device according to at least one of the Claims 1-12, including claim 8, characterized characterized in that the setting is programmatically via a computer is done.