JPH0722103B2 - Projection type exposure system - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a projection exposure apparatus used in a semiconductor manufacturing lithography process.

BACKGROUND OF THE INVENTION In general, a semiconductor manufacturing lithography process consists of resist coating, alignment, exposure and development processes.
When manufacturing a semiconductor, a plurality of lithography processes including etching and deposition for each wafer are required.

The projection type exposure apparatus is provided with an alignment optical system for performing an alignment step in such a semiconductor manufacturing lithography step and an exposure illumination optical system for performing an exposure step.

Alignment here means that a key mark is printed on the wafer as an alignment mark during the first exposure, and an image of the alignment mark on the reticle and an image of the alignment mark on the wafer are exposed during the second and subsequent exposures. It means an operation of aligning the images of the marks by superposing and relatively moving the reticle and the wafer, and arranging the reticle and the wafer in a predetermined relationship.

In the projection type exposure apparatus, the light source of the exposure illumination optical system is, for example, g-line (436 nm) or i-line (365 n).
A projection objective lens that transfers the pattern on the reticle onto the wafer is used with a mercury lamp that emits a bright line spectrum such as m), and a g-line (436 nm), i-line (365 nm), or other exposure wavelength It is designed with chromatic aberration correction so as to have high optical performance only in the vicinity of the spectrum.

Therefore, it is desirable that the TTL alignment optical system that aligns the reticle and the wafer via the projection objective lens uses light in the wavelength range that is the same as the exposure wavelength or is chromatic aberration corrected as the alignment light.

Further, in order to improve the yield (throughput), it is desirable that the alignment mark on the reticle is provided near the outer periphery of a pattern (hereinafter, referred to as a shot) on the reticle that constitutes a semiconductor circuit or within the shot.

Due to these conditions, as a conventional projection type exposure apparatus,
As shown in FIG. 3, the mirror retraction type in which the mirror of the alignment optical system retracts at the time of exposure is predominant.

In the conventional projection type exposure apparatus shown in FIG. 3, the objective lenses 4L and 4R and the epi-illumination mirrors 5L and 5R of the alignment optical system for aligning the reticle 2 and the wafer 3 through the projection objective lens 1 and the reticle 2 are arranged. A main condenser 6 of an exposure illumination optical system that transfers and exposes a pattern onto a wafer 3 via a projection objective lens 1, and the alignment optical system observes an alignment mark provided near the outer circumference of the shot or within the shot. When aligning with each other, the incident-light mirrors 5L and 5R are the main condenser 6
The projection mirrors 5L and 5R are located at a projecting position that blocks a part of the illumination light flux from, and are configured to be retracted from the projecting position in the direction of the arrow in the figure during exposure.

However, in such a conventional projection type exposure apparatus,
At the time of alignment, the epi-illumination mirrors 5L and 5R are inserted into the projecting position, and at the time of exposure, the epi-illumination mirrors 5L and 5R need to be retracted from the projecting position, resulting in poor work efficiency and poor throughput. Since a mechanism for sliding 5R in the direction of the arrow in the figure is required, the overall structure of the device becomes complicated, and after the alignment is completed, the incident-light mirror 5
The device is required to have rigidity enough to keep the reticle 2, the projection objective lens 1 and the wafer 3 in an aligned positional relationship from the evacuation of L and 5R to the completion of exposure, and this requirement is satisfied. If it is not done, complete die-by-die-point TTL alignment cannot be performed, and further, the movement of the epi-illumination mirrors 5L and 5R may cause dust and the like to fall on the reticle 2, increasing the incidence of defective products. There was a problem that it did.

(Object of the Invention) The present invention has been made in view of such a conventional problem, and eliminates the need to retract a part of the alignment optical system out of the light flux of the exposure illumination optical system at each exposure. Accordingly, it is an object of the present invention to provide a projection type exposure apparatus in which the throughput is improved and the configuration of the entire apparatus is simplified.

(Summary of the Invention) An object of the present invention to achieve such an object is to provide an exposure illumination optical system for transferring a pattern on a reticle onto a wafer by a first wavelength light through a projection objective lens, and an exposure illumination optical system. In a projection type exposure apparatus having an alignment optical system for aligning a reticle and a wafer through the projection objective lens with a second wavelength light having a wavelength longer than one wavelength light, the reticle and the exposure illumination optical system. A wavelength-separating reflective optical member having a surface that reflects the first wavelength light and transmits the second wavelength light is provided between the system and
The exposure illumination optical system is arranged on the reflection optical path of the wavelength division reflection optical member, the alignment optical system is arranged on the transmission light path thereof, and the alignment optical system between the wavelength division reflection optical member and the alignment optical system is arranged. An astigmatism correction member that corrects the astigmatism generated by the reflection and classification reflection optical member is provided on the reflection optical path, and the alignment optical system is movable in a direction perpendicular to the optical axis of the projection objective lens. The projection objective lens is present in a projection type exposure apparatus characterized in that chromatic aberration is corrected for the first wavelength light and the second wavelength light.

Then, in the projection type exposure apparatus, the second wavelength light from the alignment optical system is transmitted through the wavelength selective reflection optical member and is irradiated onto the reticle, and the alignment optical system is irradiated with the second wavelength light by the reticle and the wafer. And the first wavelength light from the exposure illumination optical system is reflected by the wavelength-separating reflection optical member and is irradiated onto the reticle during exposure, and the exposure illumination optical system uses the first wavelength light. The pattern on the reticle is transferred onto the wafer by.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

1 and 2 show an embodiment of the present invention.

The projection type exposure apparatus shown in FIG. 1 has a first wavelength light (wavelength is λ
Exposure light optical system 10 for transferring the pattern on the reticle 2 onto the wafer 3 via the projection objective lens 1 by the first light) and the second wavelength light (wavelength) longer than the first wavelength light. Is a light having a wavelength of λ2), an alignment optical system 20 for moving the reticle 2 and the wafer 3 away from the projection objective lens 1, and a wavelength for reflecting the first wavelength light and transmitting the second wavelength light. It is composed of a dichroic mirror 30 as a separate reflection optical member.

The dichroic mirror 30 is provided at an angle of 45 degrees with respect to the optical axis of the projection objective lens 1, and the main condenser 11 of the exposure illumination optical system 10 is arranged on the reflection optical path of the dichroic mirror 30. The dichroic mirror
Objective lenses 21L, 21R and parallel plane plates 22L, 22R for astigmatism correction, which form the alignment optical system 20, are arranged on the transmitted optical path of 30 °.

The plane-parallel plates 22L and 22R have an equal angle (45 °) opposite to the dichroic mirror 30 with respect to the optical axis in order to cancel the astigmatism generated in the dichroic mirror 30 obliquely installed in the non-parallel optical path. ) Is arranged with an inclination.

The projection objective lens 1 is corrected for chromatic aberration with respect to the first wavelength light and the second wavelength light.

FIG. 2 is a graph showing the optical performance of the dichroic mirror 30. As shown in FIG. 2, the dichroic mirror 30 reflects 100% of the first wavelength light of λ1 nm and transmits 100% of the polarization component in the P direction with respect to the second wavelength light of λ2 nm, and The thin film design of the dichroic mirror 30 is made so as to reflect 100% of the polarized component.

Further, a light beam having a predetermined numerical aperture (NA) on the side of the reticle 2 with respect to the projection objective lens 1 is evenly dichroic mirror.
30 must be transmitted or reflected. Specifically, since NA = 0.1 corresponds to a wavelength shift of approximately ± 3 nm due to the thin film characteristics, light with a wavelength shifted ± 3 nm from λ1 is almost 1
The thin film design of the dichroic mirror 30 is made so that about 100% of the light having a wavelength which is reflected by 00% and is shifted ± 3 nm from λ2 is transmitted by almost 100% of the polarization component in the P direction. The projection lens used in the reduction projection type exposure apparatus usually has a reduction ratio of 5 to 10 times and NA = 0.35 on the wafer side.
This is because the reticle has an NA of 0.07 to 0.035 on the reticle side, and the dichroic mirror is required to have uniform characteristics even for a light ray corresponding to NA = 0.1. As shown in the characteristic diagram of the dichroic mirror shown in FIG. 2, both the width Δλ1 for the exposure light λ1 and the width Δλ2 for the alignment light λ2 are wavelength shift ranges relative to NA = 0.1, and even in such a range. The characteristics are stable.

As the first wavelength light, specifically, light having a first wavelength as shown in the left column of Table 1, Hg lamp as a light source,
An excimer laser or the like can be used. Further, as the second wavelength light, specifically, light having a second wavelength as shown in the right column of Table 1, HeCd laser, dye laser, as the light source,
Hg lamp etc. can be used.

The operation will be described below.

When the reticle 2 and the wafer 3 are aligned through the projection objective lens 1, the second wavelength light emitted from the light source (not shown) of the alignment optical system 20 is the objective lens 21.
After passing through L, 21R and the plane-parallel plates 22L, 22R, it is sent to the dichroic mirror 30. Here, the P-direction polarization component of the second wavelength light causes the dichroic mirror 30 to have a polarization component of about 100.
%To Penetrate.

The second wavelength light transmitted through the dichroic mirror 30 is incident on the reticle 2 and the wafer 3 via the projection objective lens 1, and the second wavelength light reflected by the wafer 3 and the reticle 2 is again dichroic mirror 30. Through. Also at this time, the polarization component in the P direction of the second wavelength light is transmitted through the dichroic mirror 30 by almost 100%. The second wavelength light transmitted through the dichroic mirror 30 has a plane-parallel plate 22.
Returning to L, 22R and objective lenses 21L, 21R, by observing the image of the alignment mark on the reticle and the image of the alignment mark on the wafer by the alignment optical system 20, by moving the reticle and the wafer relatively, The images of both marks are matched, and the reticle and the wafer are arranged in a predetermined relationship.

With the alignment thus completed, the alignment optical system 20 as in the conventional example described above is used prior to exposure.
Part of the objective lens 21L, 21R or parallel plane plates 22L, 2L
It is not necessary to retract 2R and the like out of the light flux from the exposure illumination optical system 10, and the alignment optical system 20 may remain at the position at the time of alignment.

When transferring and exposing the pattern on the reticle 2 onto the wafer 3 via the projection objective lens 1, the first wavelength light emitted from a light source (not shown) of the exposure illumination optical system 10 is dichroic by the main condenser 11. Sent to mirror 30.
Here, the first wavelength light is almost 100% reflected by the dichroic mirror 30 according to the characteristics of FIG. 2 and is irradiated onto the reticle 2, and the pattern on the reticle 2 is transferred onto the wafer 3 by the projection objective lens 1. To be done.

As described above, when the alignment and the exposure are repeated, it is not necessary to retract a part of the alignment optical system 20 out of the light flux of the first wavelength light from the exposure illumination optical system 10, and the work efficiency is extremely high. good.

In the above embodiment, in order to improve the alignment detection capability, it is desirable to use a laser as the second wavelength light, but in principle, the second wavelength light may be normal light source light.

Further, in the above embodiment, the alignment optical system 20
The objective lenses 21L and 21R and the plane parallel plates 22L and 22R are movable in a direction perpendicular to the optical axis of the projection objective lens 1 so that the alignment optical system 20 can observe an alignment mark at an arbitrary position. You may comprise.

In the above embodiment, the alignment optical system 20 is provided with two sets of objective lenses 21L and 21R and parallel plane plates 22L and 22R. However, the number of the objective lenses 21L and 21R and the plane parallel plates 22L and 22R is two sets. It is not limited to.

Further, the dichroic mirror 30 is arranged so that the optical axis of the exposure illumination optical system has an incident angle of 45 °, but the invention is not limited to this. It is possible to reduce the difference in characteristics between the S-polarized light and the P-polarized light. Even in such a case, the plane parallel plates 22L and 22R may be arranged so as to be symmetrical to the dichroic mirror with respect to the plane perpendicular to the optical axis.

Further, in the above embodiment, when a dichroic prism is used instead of the dichroic mirror 30 as the wavelength division reflection optical member, the parallel plane plates 22L and 22R are used.
Is unnecessary, and the configuration can be simplified.

(Effect of the Invention) According to the projection type exposure apparatus of the present invention, it is not necessary to retract a part of the alignment optical system to the outside of the light flux of the exposure illumination optical system during each exposure, so that the work efficiency is improved and the throughput is improved. Since the mechanism for retracting a part of the alignment optical system is unnecessary, the configuration of the entire apparatus is simplified and alignment is always possible during the exposure time. Therefore, the reticle, projection objective lens and wafer Even if the relative positional relationship shifts, it is possible to perform exposure while correcting the shift amount, complete die-by-die-TTL alignment is possible, and further, since the optical member does not move above the reticle, Dust is less likely to fall on the reticle, and the incidence of defective products can be reduced accordingly.

[Brief description of drawings]

1 and 2 show one embodiment of the present invention,
FIG. 1 is a schematic layout diagram of an optical system showing a projection type exposure apparatus, FIG. 2 is a graph showing optical characteristics of a wavelength division reflective optical member, and FIG. 3 is an optical system showing a conventional projection type exposure apparatus. It is a schematic layout. 1 ... Projection objective lens, 2 ... Reticle 3 ... Wafer, 10 ... Exposure illumination optical system 20 ... Alignment optical system 30 ... Dichroic mirror (wavelength selective reflection optical member)

Claims (1)

[Claims] 1. An exposure illumination optical system for transferring a pattern on a reticle onto a wafer through a projection objective lens by a first wavelength light, and a second illumination light system having a wavelength longer than the first wavelength light.
In a projection type exposure apparatus having an alignment optical system for aligning a reticle and a wafer through the projection objective lens with wavelength light, the first wavelength is provided between the reticle and the exposure illumination optical system. A wavelength division reflection optical member having a surface for reflecting light and transmitting the second wavelength light is provided, and the exposure illumination optical system is arranged on the reflection light path of the wavelength division reflection optical member, and is provided on the transmission light path. The alignment optical system is arranged, and an astigmatism correction member for correcting astigmatism generated by the reflection / separation reflection optical member is provided on the reflection optical path between the wavelength division reflection optical member and the alignment optical system, The alignment optical system is movable in a direction perpendicular to the optical axis of the projection objective lens, and the projection objective lens has the first wavelength and the second wavelength. Projection exposure apparatus characterized by correcting chromatic aberration is made to the wavelength light.