JPH05190425A - Irradiation apparatus - Google Patents

Abstract

PURPOSE:To remove a beam of background light having a narrow-band spectrum and to radiate a laser beam whose spectral is narrower by a method wherein only a fundamental light flux is extracted spatially out of the fundamental light flux and a noise component and an extraction means is adjusted according to the spatial position of the noise component with respect to the fundamental light flux. CONSTITUTION:A laser beam whose band has been made narrow is emitted from an excimer laser 1 together with a beam of background light whose band has not been made narrow. A slit 24 limits the beam of background light; only a spectrum whose band has been made narrow is passed through an opening part in the slit 24. The opening part has a structure wherein its width both in the longitudinal direction and the transverse direction can be changed freely by using a drive part 23. One part of the laser beam which has been passed through the slit 24 is reflected by using a beam splitter 22; it is incident on a detector 3. A beam reference is always compared with a detection result; the width of the slit 24 is controlled by using the drive part 23. Thereby, it is possible to obtain the spectrum which does not contain any beam of background light and which has been made narrow.

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 used for manufacturing a ULSI circuit pattern, for example.

[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 that transfers a circuit pattern. The excimer stepper of the type in which the oscillation spectrum of the KrF excimer laser is narrowed and the chromatic aberration of the projection lens system is not generated has been continuously put into practical use since the announcement by ATT in 1986. This type of device uses a shorter wavelength than an exposure device using a g-line or i-line of a conventional mercury lamp, and thus has a high resolution and a high fidelity of transfer of a reticle pattern. LS
It is considered to be the most suitable exposure apparatus for I.

For narrowing the oscillation spectrum of an excimer laser that has been conventionally performed, for example, a light source device having a structure as shown in FIG. 8 is used. This laser light source is Kr, F
A gain section 31 and an output side beam splitter 34 for enclosing a mixed gas of 2, Ne and the like and amplifying the light generated by the discharge.
And a prism 32 for narrowing the spectrum and a grating 33.

Part of the narrowed output light is split by the beam splitter 35 and is incident on the wavelength monitor 36.
Information about the center wavelength and the spectrum width of the spectrum is sent from the wavelength monitor 36 to the wavelength controller 37.
Controls the rotation angle of the grating 33 based on this information to stabilize the center wavelength of the output beam at a substantially constant value. The prism 32 and the grating 33
In some cases, etalon may be used instead of, or they may be used in an appropriate combination. However, the control range of the wavelength control unit 37 was only management of the central wavelength.

[0005]

In the excimer laser light source as described above, the oscillation spectrum of the laser is narrowed as shown by the solid line A in FIG. In the figure, the broken line B shows the spectrum of the laser light in which there is no narrowing element such as the prism 32 and the grating 33 but only a total reflection mirror, that is, the laser light is not narrowed. The spectrum width Δλ _G (FWHM) at this time is 300 to 400 pm, and the half width Δλ ₀ of the spectrum A in the case where the band is narrowed.
Is 100 times larger than the value of about 3 pm.

By narrowing the spectrum in this way, the chromatic aberration of the projection lens of the exposure optical system can be almost ignored. However, in fact, in addition to the originally narrowed spectrum, the ASE (Amplified Spontaneous Emissi
It is generally known that a small amount of (on) light is output from a laser light source as background light of intensity I _BG .

Most of the intensity of the background light appears as flare on the image plane of the beam and is affected by the chromatic aberration of the image forming optical system to lower the contrast of image formation. This decrease in contrast not only increases the minimum resolution line width, but also increases the minimum resolution line width of 0.
There was a problem that the depth of focus, which should be deeper, becomes shallower at a line width of 35 μm.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to obtain an illuminating device which eliminates background light having a narrowed spectrum and emits laser light having a narrower spectral width.

[0009]

In order to achieve the above object, in the illuminating device according to the invention described in claim 1, in the illuminating device including a laser light source that narrows the spectrum of laser light and emits the laser light, The light source simultaneously emits the basic light flux of the first spectrum to be emitted due to the narrowing and the noise component of the second spectrum which passes along the basic light flux and is displaced around the cross section of the basic light flux. And is arranged in the optical path of the laser beam emitted from the laser light source, of the basic light flux and the noise component, the extraction means for spatially extracting only the basic light flux, and the space of the noise component with respect to the basic light flux. The adjusting means is provided so that the extracting means can be adjusted according to the desired position.

According to a second aspect of the present invention, there is provided the illumination device according to the first aspect, wherein the extraction means includes at least one of a slit and a pinhole.

According to a third aspect of the present invention, there is provided an illuminating device according to the first aspect, wherein in the exposure apparatus according to the first aspect, a detecting means for detecting the relationship between the spectrum and the intensity of the laser beam that has passed through the extracting means. , Determining means for determining the presence or absence of the noise component by obtaining a logarithmic value of the intensity of the previous period based on the relationship, and control means for adjusting the adjusting means based on the result of the determining means.

[0012]

The present invention is an exposure apparatus provided with an extracting means for limiting a light beam from a laser light source in a predetermined region of the light beam cross section and extracting only a fundamentally necessary basic light beam narrowed. Background light emitted without being narrowed by the light source can be removed. Further, the presence or absence of background light is determined based on the result of the detection unit that detects the relationship (spectral characteristic) between the wavelength and intensity of the laser light, and the determination result is fed back to operate the adjustment unit via the control unit. By adjusting the extraction means.

Now, the operation of the present invention will be described with reference to the case where a slit is used as the extraction means. In the detection of the spectral characteristics of the laser light, the intensity of the background light is much smaller than that of the narrowed spectrum in the normal output, so that it is difficult to determine the presence or absence of the background light. ..

However, since the shape of the spectral characteristic of the excimer laser light is generally expressed by Gaussian or Laurentian, it can be expressed by a quadratic function by logarithmizing it. Therefore, in the present invention, as shown in FIG. 7, the logarithmic value of the energy intensity value of the detected spectral characteristic data is obtained. As a result, the background light appears at the skirt of the peak in FIG. 7 as shown by the curve BG, which allows the presence or absence of the background light to be easily determined.

That is, if the data of the spectral characteristic without background light as shown by the broken line in FIG. 7 is used as a reference, by comparing it with the detection data as shown by the solid line in FIG. Ground light B
The presence or absence of G can be easily determined. By feeding back the result and operating the adjusting means to adjust the slit width, it is possible to obtain the laser light from which the background light is removed.

As described above, in the present invention,
The presence or absence of background light can be easily detected by logarithmizing the spectral characteristics of the detected laser light, and the background light can be removed by adjusting the extraction means according to the detection result.

[0017]

EXAMPLES Examples of the present invention will be described below. In Figure 1,
The schematic block diagram of the projection exposure apparatus suitable for using the illuminating device which is one Example of this invention is shown. The configuration of this embodiment is
A KrF excimer laser light source 1 having a narrow spectrum and wavelength stabilization, an extraction member 2 having a driving device, a spectral characteristic detector 3, a variable attenuator 4 for changing the intensity of laser light, and an intensity distribution in the cross-sectional direction of the beam. Beam homogenizing element 5 for homogenizing, beam splitter 6, variable blind 7 for defining the illumination area of the beam, mirror 8, condenser lens 9, reticle R, projection lens PL, wafer W, light amount detector 11, exposure amount control And part 10.

The extraction member 2 removes flare of the output of the laser light source 1, that is, background light. The detection result of the detector 3 is fed back to the driving device,
The extraction member 2 is controlled. The extraction member will be described below.

FIG. 2 shows an embodiment in which a light shielding member having a slit-shaped opening (hereinafter simply referred to as a slit) is used as the extraction member. In the figure, the excimer laser 1
The narrowed laser light is emitted together with the background light which is not narrowed. The slit 24 limits the background light that appears as flare, and only the narrowed spectrum that is originally required for exposure is slit 24.
Pass through the opening. The opening has a structure in which the width can be freely changed in both the vertical and horizontal directions by the drive unit 23.

A part of the laser light passing through the slit 24 is reflected by the beam splitter 22 and is incident on a detector 3 for detecting a spectral characteristic, for example, a spectroscope.
The detection result by the detector 3 is represented by logarithmically converting the energy intensity on the vertical axis as shown in FIG. A spectral characteristic without background light as shown by a broken line in FIG. 7 is given as a reference to the operation comparison section in the computer 21, and this is constantly compared with the detection result to determine whether the background light BG exists or not. Make a decision.

When the background light is confirmed, the control unit in the computer 21 controls the drive unit 23 so as to narrow the width of the slit 24 based on the result. By repeating this operation, it is possible to obtain a desired narrow band spectrum having high purity (narrow spectral width) without background light.

FIG. 3 is a flow chart showing the above-mentioned sequence. That is, the spectral characteristic of the laser light is detected (step 101), and the logarithm of the intensity value at each wavelength is obtained (step 102). The presence or absence of background light is judged from this result (step 10
3, 104), in the presence of background light,
Stop accepting oscillation from the stepper (step 10
5).

In a normal exposure apparatus, cooperative control is performed between the laser side and the stepper side by an interface signal. If background light is detected by detecting the spectral characteristics, it informs the stepper that oscillation cannot be accepted, and the laser light is emitted from the stepper (especially on the wafer) by means such as closing the shutter in the illumination optical system.
Not reach. After that, the drive unit is controlled to adjust the shape of the opening of the slit.

While the background light is being detected, this routine is repeated to adjust the slits, but if it is determined that the background light has been removed as a result of the detection of the spectral characteristics, then the suspension of oscillation acceptance is canceled. If there is an oscillation command from the stepper side (step 107), the laser beam is oscillated according to the instruction (steps 108, 10).
9).

Next, FIG. 4 shows a case where a lens system and a slit are used in combination as an extracting member. A lens system 25 having a driving unit 23 is disposed between the excimer laser unit 1 and the slit 24, and each optical element of the lens system 25 is moved to change the cross-sectional shape of the laser light with which the slit 24 is irradiated. Removes background light that appears as flares.

When only the slit is used as in the case of FIG. 2, the cross-sectional shape of the beam light after passing through the slit may be smaller than desired by changing the shape of the slit opening. Therefore, if the lens system 25 is used and the shape of the opening of the slit 24 is not changed as described above, the sectional shape of the laser light incident on the attenuator 4 shown in FIG. 1 can be made desired. ..
Therefore, it is not necessary to change or adjust the configuration of the device after the attenuator 4.

FIG. 5 shows a structure in which the laser light applied to the slit is condensed. For example, the lens system 27a including a cylindrical lens or the like focuses the laser light on the slit 24a arranged in the vicinity of the focal position, and removes flare in the direction orthogonal to the longitudinal direction of the slit.

The laser light passing through the slit 24a is condensed by the lens system 27b in a direction substantially orthogonal to the above direction, and the flare in that direction is removed by the slit 24b arranged near the focal position of the lens system 27b. It Since the laser light that has passed through the slit 24b is divergent, it is possible to arrange the optical system in the optical path after the slit 24b to make the cross-sectional shape of the light beam a desired shape.

The slits 24a and the slits 24b are moved along the optical axis of the laser light by the driving portions 23a and 23b, respectively, and change the flare limiting (shielding) area. Alternatively, the positions of the slits 24a and 24b may be fixed, and the lens systems 27a and 27b may be moved. In the figure, the state of light collection is shown in a plane for the sake of convenience in two directions that are substantially orthogonal to each other.

Further, it is not particularly necessary to remove the flare in two times by using the two slits 24a and 24b, and one focusing optical system may be used to focus the laser light on the slits. It has the same effect. In each of the embodiments shown in FIGS. 2, 4 and 5, the flare is removed by the slit, but the same effect can be obtained by replacing the slit with a pinhole.

In FIG. 6, an etalon is used as the extraction member. Background light is emitted by irradiating the etalon 29 with a laser beam that has been narrowed and oscillated from the laser light source 1 and controlling the inclination of the etalon 29, that is, by controlling the incident angle of the laser beam with respect to the etalon 29. Remove. This uses the etalon 29 as a filter.

By limiting the laser light transmitted through the etalon 29 with the slit 24, the background light can be further removed. However, the slit 24 need not be provided in particular. It goes without saying that the etalon can be applied to each of the embodiments shown in FIGS. 1, 4 and 5 described above.

In the above embodiments, the spectroscope is used as an example of the means for detecting the relationship between the wavelength and the intensity of the laser light after the background light is removed. However, the fringe of the laser light is used by using an etalon. May be detected. Also in this case, the presence or absence of the background light can be determined by obtaining the logarithm of the intensity value as in the above embodiment.

As the laser light source, an ArF excimer laser, an F ₂ laser or the like may be used instead of the KrF excimer laser. Further, when the harmonic of a solid-state laser such as a YAG laser or a free electron laser is used, the purity of the spectrum is improved by applying the present invention.

[0035]

As described above, according to the present invention, unnecessary background light other than the originally necessary spectrum of the narrowed laser light can be removed, so that the contrast of the image formed on the wafer surface can be improved. Has the effect of improving. In addition, the spectrum width can be controlled, and a narrower spectrum width can be obtained, which can similarly contribute to the improvement of image contrast.

Further, by improving the contrast of the image,
Not only can a finer pattern be transferred, the density of the LSI can be increased, but the depth of focus is increased and the line width control accuracy of the LSI is improved, so that the yield is also improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a projection exposure apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a background light removal system when a slit is used as the limiting means of the present invention.

FIG. 3 is a flowchart showing a sequence of a background light removing mechanism of the present invention.

FIG. 4 is an explanatory diagram of a background light removal system when a lens and a slit are used as the extraction means of the present invention.

FIG. 5 is an explanatory diagram of another example of the background light removal system when the lens and the slit are used as the extraction means of the present invention.

FIG. 6 is an explanatory diagram of a background light removal system when an etalon is used as the extraction means of the present invention.

FIG. 7 is a diagram showing a spectrum intensity for explaining the operation of the present invention.

FIG. 8 is a schematic configuration diagram of a laser light source unit of a conventional projection exposure apparatus.

FIG. 9 is an explanatory diagram of spectrum narrowing.

[Explanation of symbols]

 1: Excimer laser light source 2: Extraction member 3: Detector 4: Variable attenuator R: Reticle PL: Projection lens W: Wafer 11: Excimer laser 32: Prism 33: Grating 22: Beam splitter 23: Driving unit 24, 24a, 24b: Slit 25: Lens system 27a, 27b: Lens system 29: Etalon 21: Computer

Claims (3)

[Claims] 1. A lighting device including a laser light source that narrows the spectral width of laser light and emits the laser light, wherein the laser light source emits light by the narrowing.
In the optical path of the laser light emitted from the laser light source, the basic light flux of the spectrum and the noise component of the second spectrum passing along the basic light flux and passing through a position displaced around the cross section of the basic light flux are simultaneously emitted. Of the basic light flux and the noise component, the extraction means spatially extracting only the basic light flux, and the extraction means can be adjusted according to the spatial position of the noise component with respect to the basic light flux. A lighting device, comprising: 2. The lighting device according to claim 1, wherein the extraction unit includes at least one of a slit and a pinhole. 3. The presence or absence of the noise component is determined by detecting means for detecting the relationship between the spectrum and the intensity of the laser beam that has passed through the extracting means, and obtaining the logarithmic value of the previous intensity based on the relationship. The lighting device according to claim 1, further comprising: a determination unit and a control unit that adjusts the adjustment unit based on a result of the determination unit.