JPH0547636A - Projection aligner - Google Patents

Abstract

PURPOSE:To improve the quality of an image at the time of exposure by means of a projection optical system by reducing the ASE light which, without being narrowed, leaks into the narrowed laser light from an excimer laser light source by a polarization selecting device such as a polarization beam splitter. CONSTITUTION:The spectrum-narrowed beam emitted from a KrF excimer laser light source 1 is narrowed down to a specified beam intensity through a polarization selecting device 2, a polarization cancelling device 3 and a variable attenuator for adjusting the beam intensity 4. The beam illuminates a reticle R through a beam quality unification optical system 5, a splitter 6, a variable blind mechanism 7, a mirror 8 and a condensing lens 9. At the same time, spectrum-narrowed beam including a background component as the ASE light is emitted from the laser light source 1. Since the ASE light has no specific polarized light, the narrowed main spectrum having specific polarized light is taken out without being attenuated and at the same time the intensity of the ASE light lowers to nearly half.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus for transferring circuit patterns such as ULSI and VLSI.

[0002]

2. Description of the Related Art In promoting miniaturization of LSI, it is essential to improve the resolution performance of a projection exposure apparatus (stepper) that transfers a circuit pattern. The excimer stepper of the type that narrows the oscillation spectrum of the KrF excimer laser and prevents the chromatic aberration of the projection lens system is the 1986 ATT.
Since the company's announcement, efforts have been made to put it into practical use. This type of device uses a light source of a shorter wavelength than a stepper using a g-line or i-line of a conventional mercury lamp, so that the resolution is high and the fidelity of transfer of a pattern formed on a reticle as a mask is high. High, so LSI with 0.35 μm rule
It is considered to be the most suitable exposure apparatus for.

[0003]

In the excimer stepper of the above type, the spectrum is narrowed.
Recent experiments have revealed that, in addition to the originally narrowed spectrum, there is a background spectrum that is emitted as it is without being narrowed. This background spectrum causes a large chromatic aberration in the image forming optical system (projection lens system), and it becomes as if flare occurs with respect to the regular transfer pattern image, thus lowering the contrast of image formation. Due to this decrease in contrast, not only the minimum resolution line width becomes large, but also the depth of focus becomes shallow in a 0.35 μm line width pattern larger than the minimum resolution line width.

The present invention has been made in order to solve such a conventional problem, and an object thereof is to obtain an excellent image with high contrast.

[0005]

According to the present invention, a laser light source (excimer laser light source 1) that emits an output beam having a narrowed spectral width and a spatial uniformity of the output beam are improved. An illumination system (2 to 2) for irradiating the first substrate (reticle R) having the transferred pattern with a uniform intensity distribution.
9) and a projection system (projection lens PL) for imaging and projecting the transferred pattern onto the second substrate (wafer W). Further, in the present invention, between the laser light source (1) and the projection system (PL), a component (AS) other than the main polarized light in the output beam (LB) from the laser light source (1) is further added.
A polarization selecting means (element 2 such as a polarization beam splitter and a quartz plate having Brewster's angle) for attenuating E light) by a predetermined amount is provided.

[0006]

In the present invention, since the polarization selection element that allows the linearly polarized light having a strong polarization direction to pass with respect to the output light of the excimer laser whose polarized light is polarized, the linearly polarized light orthogonal to this polarized light is shielded. To be done. Most of the background light that remains with a wide spectrum width even if the wavelength band is narrowed is ASE
Since it is (Amplified Spontaneous Emission) and it is not polarized, the intensity is attenuated to about half by the polarization selection element.

[0007]

FIG. 1 is a diagram showing the structure of an excimer stepper according to an embodiment of the present invention, the basic structure of which is 198.
Proc. of SPIE vol. 1088, pages 434-440, "Excimer Laser Stepper fo
r Sub-half Micron Lithography ”.

In FIG. 1, the KrF excimer laser light source 1 has a mechanism for narrowing the oscillation spectrum and stabilizing the absolute value of the narrowed center wavelength.
The emitted beam from this laser light source 1 is a polarization selection element 2,
The beam passes through the depolarizer 3 and is incident on the variable attenuator 4 for adjusting the beam intensity, and the beam is focused to a predetermined beam intensity. The beam from the attenuator 4 is made uniform in the cross-sectional intensity distribution of the beam by the beam quality equalizing optical system 5. Most of the beams emitted from the homogenizing optical system 5 are transmitted through the beam splitter 6 and have a variable blind mechanism (variable illumination field diaphragm).
It is incident on 7. The illumination beam whose cross-sectional shape is defined by the variable blind mechanism 7 is reflected by the mirror 8 and reaches the condenser lens 9 to illuminate the pattern area of the reticle R with a uniform illuminance distribution. The light flux that has passed through the pattern area of the reticle R enters the projection lens PL and forms an image of the pattern area on the wafer W as a photosensitive substrate.

On the other hand, a part of the beam divided by the beam splitter 6 is received by a photoelectric sensor (integrator sensor) 11 for monitoring the integrated exposure amount,
The exposure amount control unit 10 uses the output of the sensor 11 to determine the actual exposure amount for one shot area on the wafer W and the light amount (or peak value) of the excimer beam per pulse.
To monitor. The exposure amount control unit 10 is also connected to the main control computer of the stepper and controls the laser light source 1 and the variable attenuator 4. Control unit 1
The control with the laser light source 1 of 0 includes generation of a trigger pulse for oscillation, driving of an internal shutter, monitoring of gas in the laser chamber, gas exchange control, and the like.

Further, in this embodiment, a polarization beam splitter or a flat synthetic quartz plate arranged at Brewster's angle with respect to the beam is used as the polarization selection element 2. These optical elements are set so as to pass one of the emitted beams from the laser light source 1 having a large linear polarization component, which has a stronger polarization component. Further, as the depolarization element 3, a quarter wavelength plate (λ / 4 plate) can be used, but ideally, it is desirable to use a depolarization prism using quartz. In this way, the depolarizing element 3 is provided in order to prevent the light flux passing through the optical system, especially the projection lens PL, from being affected by the polarization characteristics of the lens elements in the projection lens PL, specifically, a plurality of lens elements. This is to prevent a decrease in the amount of light due to the polarization effect of the optical element and the like, and the occurrence of uneven illuminance on the image plane. Therefore, the polarization selection element 2 and the depolarization element 3 are connected to the condenser lens 9 from the laser light source 1.
It is desirable to provide it in a position as close as possible to the laser light source 1 in the illumination optical system up to, but it is not necessarily limited to that depending on the configuration of the device, and where it is before the illumination beam is incident on the projection lens PL. It may be. Furthermore, the polarization selection element 2 and the depolarization element 3 do not necessarily have to be arranged adjacent to each other, and may be separated in some cases.

It should be noted that, except for the polarization selection element 2 and the depolarization element 3 in each block in FIG. 1, the previous paper (Proc. Of
SPIE, Vol. 1088, pp. 434-440), it functions exactly the same as the stepper disclosed in U.S. Pat. FIG. 2 shows an example of the internal configuration of the excimer laser light source 1 shown in FIG.
A gain part (laser chamber) 14 that seals a mixed gas of (fluorine) and Ne (neon) at a predetermined pressure ratio and performs optical amplification by discharge, a beam splitter 17 that acts as a partial mirror for output, and a spectroscope. The laser oscillation narrowed by the (narrowing) prism 15 and the grating 16 is performed. A part of the beam LB emitted from the beam splitter 17 on the output side is split by the beam splitter 18, and the beam 1 for monitoring is
It becomes 9 and enters the wavelength monitor 20. The wavelength monitor 20 detects the absolute value of the center wavelength of the output beam LB and the spectral width, and sends the detection information to the wavelength controller 21.
When the central wavelength deviates from a predetermined value, the wavelength control unit 21 controls the driving unit 22 for finely adjusting the incident angle of the grating 16 with respect to the beam so as to restore it. The narrowed central wavelength of the output beam LB is stabilized to a constant value by servo-controlling the rotational fine movement of the grating 16 every oscillation of the output beam LB or every predetermined number of oscillations.

FIG. 3 shows a band narrowed by the laser light source of FIG.
Is a graph showing the state of the spectrum, where the horizontal axis is wavelength
represents λ, and the vertical axis represents the intensity I of the spectrum. In Figure 3
The narrowing prism 15 and grating 16
Instead, a mere total reflection mirror does not interfere with the beam from the gain unit 14.
The spectrum of the output beam LB when arranged directly is broken.
It is broad like line 13. Spec at this time
Torr width Δλg (FWHM) is 300 to 400 pm
It On the other hand, the prism 15 and the grating 16
The spectrum of the output beam LB when narrowed by inserting
Half-width Δλ as shown by solid line 12₀Is about 3 pm, narrow band
It is 1/100 or less compared to when it is not converted. In Figure 3
The central wavelength of the band narrowing is λ₀And the narrowed space
The cuttle is biased to a specific polarization (eg linear polarization).
The output beam LB of the spectrum narrowed in this way is
By using it, the chromatic aberration of the projection lens PL is almost
You can ignore it. However, in reality, the spectrum
Background component of is emitted at the same time as ASE light
ing. The intensity I of this ASE light (background light) _BG
Is the central wavelength λ₀Compared to the peak value of the main spectrum of
Though it is much lower, consider a higher resolution with the projection lens PL.
When the intensity of ASE light I_BGIs zero if possible
It is desirable to be suppressed by.

Now, it was found that the ASE light does not have a specific polarization, unlike the narrowed spectrum (solid line 12 in FIG. 3). Therefore, by the polarization selection element 2 in FIG. 1, the main spectrum (wavelength λ ₀ ) having a specific polarization and having a narrow band is extracted with almost no attenuation, and at the same time, the intensity I _{BG of the} ASE light is attenuated to almost half. .. Therefore,
The beam emitted from the polarization selection element 2 contains ASE light as an impure component, but the intensity of ASE light is reduced to about half as compared with the conventional case (without the elements 2 and 3). Therefore, the resolution and image quality of the fine pattern by the projection lens PL are improved as compared with the conventional one. In particular, when a negative resist is used, the effect of improving the image quality by reducing the ASE light is great, and the effect of increasing the depth of focus is great.

In the above description, as the depolarizer 3, it is preferable to use a birefringent crystal prism (quartz prism) as disclosed in, for example, Japanese Patent Laid-Open No. 3-16114. In the above embodiments, the laser light source 1 is supposed to be polarized to linearly polarized light, but when it is polarized to circularly polarized light, the polarization selection element 2 allows only either clockwise or counterclockwise circular polarization to pass. It should have a property. Specifically, a combination of a λ / 4 plate and a polarization beam splitter can be considered.

Although the KrF excimer laser is used in the above embodiment, the present invention can be applied to other excimer lasers such as ArF and F ₂ laser. Furthermore, Y
When the high frequency of a solid state laser such as AG or a free electron laser is used, the purity of the spectrum is improved by applying the present invention.

[0016]

As described above, according to the present invention, it is possible to reduce the impure spectrum intensity that is not narrowed, and therefore the second
This has the effect of increasing the contrast of the pattern image formed on the surface of the substrate (wafer). By increasing the contrast of the image, a finer pattern can be transferred, and not only can the density of the LSI be increased, but the line width control accuracy of the LSI can be expected to be improved by increasing the depth of focus.
This is useful because it can achieve an improvement in the product rate.

[Brief description of drawings]

1 is a block diagram of an apparatus according to the present invention.

FIG. 2 is a block diagram of an excimer laser light source used in an embodiment of the present invention.

FIG. 3 is an explanatory diagram of spectrum narrowing.

[Explanation of symbols for main parts]

 1 Excimer Laser Light Source 2 Polarization Selector 3 Depolarizer 4 Variable Attenuator 15 Prism 16 Grating R Reticle PL Projection Lens W Wafer

Claims (3)

[Claims] 1. A laser light source that emits an output beam having a narrowed spectral width, and a spatial uniformity of the output beam is improved so that the first substrate having a transferred pattern has a uniform intensity. In a projection exposure apparatus including an illumination system for irradiating with a distribution and a projection system for image-forming and projecting the transferred pattern onto a second substrate, an output from the laser light source is provided between the laser light source and the projection system. A projection exposure apparatus comprising a polarization selection means for attenuating a component of the beam other than the main polarization by a predetermined amount. 2. The projection exposure apparatus according to claim 1, further comprising a depolarization element for eliminating the polarization characteristic of the output beam between the polarization selection unit and the projection system. 3. The illumination system includes an illumination field diaphragm that narrows an irradiation area of the output beam with respect to a transferred pattern area of the first substrate, and a spatially uniform output beam that passes through the illumination field diaphragm. Beam uniformizing optics to improve the
3. The apparatus according to claim 2, wherein the polarization selecting means and the depolarizing element are arranged between the laser light source and the beam uniformizing optical system.