JPS62111228A - Light source for reduction projection - Google Patents

Abstract

PURPOSE:To oscillate a laser light suitable for reduction projection by constituting a light source with a means which oscillates an incoherent ultraviolet laser light and a wavelength selecting means which narrows the spectrum line width of the ultraviolet laser light and narrowing the spectrum line width while keeping the incoherent property. CONSTITUTION:A solid etalon 4 is placed on the outside of the cavity of an excimer laser provided with a resonator consisting of a total reflection mirror 1 and an output mirror 2, and the laser light oscillated by the resonator is allowed to pass the solid etalon 4. The spectrum line width of the laser light which passes the solid etalon 4 as the wavelength selecting element is narrowed by the transmission characteristic of the solid etalon 4. A mixed gas of argon and fluorine, a mixed gas of krypton and fluorine, or the like is filled up in a chamber 3. This excimer laser has a short wavelength (193mm for ArF and 248mm ultraviolet for KrF) and has the incoherent property essentially.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a reduction projection light source used in reduction projection exposure such as lithography.

[Conventional technology]

Conventional light sources for this mallet are those that generate light in the ultraviolet region in order to improve the resolution of nine turns, and an excimer laser may be one of them.

This excimer laser will be explained using a product from Lambda Fisox as an example. As shown in FIG. 17, this innoex-lock type laser includes a resonator consisting of a total reflection mirror tt% and an output mirror IQ, a dispersion prism 13q disposed within this resonator, and an aperture 14Q.
, 15 and the oscillator section 10 consisting of electrodes 16 and optically connected via mirrors 17ζ and 18q, mirrors 21%, 22 sections and 'jt@23Q,
It has an amplifier section 20Q consisting of.

In this laser, wavelengths are separated by a dispersion prism 13Q in an armature radar section 101$H1, and an annular armature 14Q, 1
The 5Q acts to narrow down the beam, thereby providing a laser signal with a narrow spectral linewidth and coherent beam characteristics.

This signal is injection-locked to the Ang part 20tl forming the unstable resonator, and is forced to oscillate in the cavity mode.

[Problem that the invention seeks to solve]

An excimer laser with the above configuration can obtain laser light with a narrow spectral linewidth, but at the same time it becomes a single mode (higher coherency), so when used as a reduction projection light source, However, there is a problem in that speckles (stripes) occur and high resolution cannot be obtained.

Furthermore, since the antennas 14Q and 15Q are used, there is also a drawback that the laser output is significantly reduced.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a light source for reduction projection that can oscillate a laser beam suitable for reduction projection.

[Means and effects for solving the problems] The present invention
, a means for oscillating incoherent ultraviolet laser light, and a wavelength selection means for narrowing the spectral line width of the ultraviolet laser light.

With this configuration, incoherence remains.

The spectral linewidth is narrowed.

〔Example〕

The present invention will now be described in detail with reference to the accompanying drawings.

1 to 10 are schematic configuration diagrams showing embodiments of a light source for reduction projection according to the present invention.

In each figure, parts having the same function are given the same number.

The light source for reduction projection shown in FIG. The oscillated laser beam is made to pass through the solid etalon 4.

The laser beam that has passed through the solid etalon 4, which is one of the wavelength selection elements, has a narrow cis vector linewidth due to the transmission characteristics of the solid etalon 4.

The chamber 3 is filled with, for example, a mixed gas of argon and fluorine or a mixed gas of krypton and fluorine. This excimer laser has a short wavelength (193 cm for ArF and 248 cm for KrF).
(ultraviolet light of gourd), and is essentially incoherent.

1&, regarding the intensity of laser light, solid etalon 4
0 If the incident cross-sectional area is made sufficiently large compared to the cross-sectional area of the laser beam, the loss is only due to reflection and diffusion, so 1
The decrease in strength is small.

FIG. 2 shows a ninth embodiment in which a window 5 is disposed at one end of the chamber 3, and a solid etalon 4 is disposed between the window 5 and the output mirror 2.

That is, the solid etalon 4 is placed in a cavity between the total reflection mirror 1 and the output mirror 2-2, and in this case as well, the spectral line width can be narrowed in the same manner as above. In addition, in this type of arrangement, only the light that has passed through the solid etalon 4 is amplified, so the laser oscillation efficiency is improved.

FIG. 3 shows an embodiment in which an air gap etalon 6 is arranged in place of the solid etalon 4 in FIG.
The figures each show an embodiment in which an air gap etalon 6 is arranged in place of the solid etalon 4 in FIG. 2, and both perform the same function as described above. Note that there are two types of air gap etalon: fixed type (same as solid etalon in this case) and variable type.If the latter is used, it can be made adjustable.

FIG. 5 shows an embodiment in which a total reflection mirror 1 and an output mirror 2 form a cavity, and a prism 7 is arranged between the total reflection mirror 1 and the window 5. In this case, wavelength selection is performed by the prism 7. Comparing this embodiment with the conventional one shown in FIG. 11, this embodiment differs in that no aperture is provided, which allows the spectral linewidth to be narrowed while maintaining incoherence.

FIG. 6 shows an embodiment in which a cavity is formed by a single diffraction grating 8 and a total reflection mirror 1, and wavelength selection is performed by a prism 7 and a diffraction grating 8.

In this case, the light is expanded by the prism 7 and one diffraction grating 8
Because wavelength selection is performed at , a much narrower spectral linewidth can be obtained.

FIG. 7 shows an embodiment in which a cavity is formed by one diffraction grating 8 and an output mirror 2, and an air gap etalon 6 and a prism beam expander 9 are arranged between one diffraction grating 8 and the window 5. In this case, Since wavelength selection is performed by the diffraction grating 8, the air gap etalon 6, and the prism beam expander 9, a very narrow spectral linewidth can be obtained.

FIG. 8 shows an embodiment in which a total reflection mirror 1 and an output mirror 2 form a cavity, and a diffraction grating 8 is arranged between the total reflection mirror 1 and the window 5. In this case, wavelength selection is performed by one diffraction grating 8.

FIG. 9 shows a cavity formed by one diffraction grating 8 and an output mirror 2, and a prism 7 between one diffraction grating 8 and the window 5.
This figure shows an example in which .

In this case, wavelength selection is performed using the single diffraction grating 8 and the prism 7.

FIG. 10 shows a case where a cavity is formed by one diffraction grating 8 and an output mirror 2, and at the same time wavelength selection is performed by the diffraction grating 8. This is simple in construction and easy to implement.

Note that the wavelength selection means is not limited to the above-mentioned embodiment, and various other means can be considered, and in short, any means may be used as long as it narrows the spectral line width of the laser beam.

Next, a more specific embodiment in which the air gap etalon 6 is used as a wavelength selection means will be described with reference to FIGS.

Etalon fleece vector range FSR to narrow the line width of excimer laser.

1.00 cIN ~ 1203'' in gold bias 1 half price width 503
~70crn″″1 is required. Therefore, the optimum fleece vector range FSR of this etalon is: FSR=50cWI to 120cm-'.

When using the Air Yatsuno Etalon 6 as an etalon, the air gap space d of this etalon 6 and the fleece vector range FSR (!-1c FSR=
1/2 nd ・= ・” (1) However, no
;Since there is a relationship between the air gap and the refractive index of the etalon, the range of the air gap d to obtain the above-mentioned optimum fleece vector range is:

By setting n k n −1 in equation (1), d −1
72.1FSR = 42 μm to 100 μm -*-...' (2).

On the other hand, the etalon's width F and line width (half width) Δσ,
F=
It is calculated as 25-60.

By the way, the finesse F of the air gap etalon 6 is the finesse F due to the surface accuracy within the air gap of the etalon,
and finesse F8 due to reflection. Therefore, in the case of air gap etalon 6, finesse F due to surface precision, and finesse FB due to reflection are
All you have to do is set .

FIG. 11 shows an example in which one air gap etalon 6 is disposed within the cavity of the excimer laser.

In this example, the window 5' provided on the total reflection mirror 1 side
An etalon 6 is interposed between the total reflection mirror 1 and the total reflection mirror 1. In this case, the specifications of the etalon 6 to obtain a line width of 2 cfr1 are as follows.

■ Fleece vector range 50 cm-' ~ 120
cm-' (air gap space di42μF-100
(Set to μm) ■ Effective diameter 2- or more ■ Total finesse 25 to 60 Fr-7'h2) In this embodiment, if the etalon 6 is placed between the window 5 on the output mirror 2 side and the mirror 2, This is equivalent to the configuration shown in FIG. and.

Even in such a case, the specifications of the etalon 6 may be the same as above.

FIG. 12 shows an embodiment in which the etalon 6t excimer laser is disposed outside the cavity, that is, on the outside of the output mirror, and this embodiment corresponds to the embodiment shown in FIG.

(7) The specifications of the etalon 6 in the embodiment shown in FIG. 12 are the same as those in the embodiment shown in FIG.

FIG. 13 shows an embodiment in which an etalon 6 is arranged outside the output mirror 2 of the embodiment shown in FIG.

This figure shows an embodiment in which the configurations shown in FIGS. 11 and 12 are combined. In this example, if the etalon 6 placed inside the cavity is called the internal etalon, and the etalon 6 placed outside the cavity is called the external etalon, then the internal etalon and the external etalon are combined to obtain a line width of 2cfn-'. The specifications are as follows.

[Internal etalon] ■ Fleece vector range 50 countries ~120crII
(Set the air gap space d to 42 μm to 100 μm) ■ Effective diameter 2 ■ or more ■ Total finesse be 5 or more and less than 60.

(5≦(F; 2+F',, 2) = (Set F, , F, to fill 60) [External etalon] ■ Fleece (cuttle range 10m-' to 20tMI-
'(Air gap space d is 208μm~2500
(set to μm) ■ Effective diameter 2 wIR or more ■ Total finesse Fin of internal etalon (!: Overall finesse FaL, which is the product of total finesse F0□ of this external etalon = Fin・Fout,
25≦Fin”out≦60.

(Set F, FR so as to satisfy 25≦(F;2+F,:2)=・F, n≦60) In addition, in the example shown in this @13 figure, the internal x I
Of course, it is also possible to provide the ann 6 in the cavity on the output mirror side.

FIG. 14 shows an embodiment in which m internal etalons 6 (m≧2) are arranged in multiple stages on a total reflection mirror l@ (the figure shows the case where m=2).

As shown in FIG. 17, there are m air gap etalons 6 and 9. ! In case of membrane arrangement, @1st etalon 6 h
Based on the formula (1), FSR1 = V2nd, · old · (5), and that of the th (k = 2 to m) etalon 6 is , the finesse of the first etalon is F,
If the @th etalon is Fk, then FSRk”
1/(F,・F2 ””F' y-,) X 1
/2nd 1 ”' (6) and 2nd
To obtain a line width of m-1, set n = 1 and use (5
) The fleece vector range FSR shown in the formula is 50ay
It is sufficient if it is within the range of +N120, and for the second fleece vector range from formula (6), 50cm-'≦FSRk・(F,・F2・～・Fm)≦
12oz-'... (7) It is sufficient if the relationship t is satisfied.

On the other hand, the O/J-all finesse Fat due to the finesse of each etalon is FmF-F・～・F... (7) al 1
It is expressed as 2 m and 2 c! In order to obtain a line width of n''-', the overall finesse Fml should be in the range of 25 to 60.

Therefore, the specifications of the m etalons 6 in the embodiment of FIG. 14 are as follows.

(2) Set the fleece vector range for the first etalon to 50≦FSR4≦120, and set the fleece vector range for the second etalon so as to titrate the relationship of equation (7).

(Set the air gap space for the first etalon to 42≦d,≦100)■ Each etalon 6
■ Set the overall finesse 'ml to 25≦F,・F2・～・Fm≦60.In this example, the oscillation light is incident on the first etalon to the mth etalon. Although the etalons are arranged sequentially from the side, this is for the convenience of explanation, and the order in which the individual etalons are arranged is random. That is, as long as the above specifications are satisfied for each etalon, the arrangement order does not matter.

Further, in this embodiment, each internal etalon 6 may be arranged in a cavity on the output mirror 5 side.

FIG. 15 shows an embodiment in which m (m≧2) external etalons 6 are arranged in multiple stages (the case where m=2 is shown in the figure). The specifications of each etalon 6 in this embodiment are shown in FIG. 14 and are the same as those in the hypothetical embodiment, and if the specifications are fulfilled, the arrangement and order of each etalon will be random as described above. FIG. 16 shows an embodiment using m internal etalons 6 and external etalons 6 (the case where m = 2 is shown in the figure), and the internal etalons 6 and external etalons in this embodiment are The specifications of each etalon are shown in FIG. 14 and are the same as those of the embodiment.

Also in this embodiment, the arrangement order of each internal etalon and the arrangement order of each external etalon do not matter as long as the above specifications are satisfied. In this embodiment, it is also possible to arrange the internal etalon 6 in the cavity on the output mirror 2 side.

Table 1 shown below is specification example 1 of air gap etalon 6.
A shows ~12.

In the above table, the surface accuracy is expressed using the oscillation wavelength λ-632.8 nmt- of the He-N laser.

Table 2 below shows the experimental values of the line width and output ratio of the laser beam when the specification examples shown in Table 1 are appropriately selected and combined as the internal etalon 6 shown in Figure 13 and the external etalon 6. ing.

Note that the above output ratio means the ratio of the oscillation output when the etalon is used to the oscillation output when the etalon 6 is not used at all.

As shown in the table above, in combination example 0, the reflectance of the internal etalon is 95 cm, so the throughput is small and oscillation is impossible, but for other combination examples, the line width is about 251 cm. is obtained. As a result of passing the laser beam obtained from this combination example through a pinhole and examining its interference, no interference fringes were observed.
Therefore, it was found that the obtained laser beam was multimode, that is, it had a sufficiently large number of transverse modes.

Note that the above-mentioned throughput is the ratio of the intensity of output light to the intensity of input light when light of a selected wavelength is transmitted through the etalon, and is defined by the following equation.

The following Table 3 shows the above results when the number of internal etalons is 2 in the embodiment shown in FIG. Similar experimental results are shown.

As shown in the above table, a line width of about 2 crn-' was obtained for all of the combinations ① to 0. As is clear from the comparison with that of the garment 2, this experimental data shows that the configuration shown in FIG. 14 has less power loss than the configuration shown in FIG. 13. Note that a sufficient transverse mode was also obtained in this combination example.

Table 4 below shows similar experimental results when the number of external etalons is two in the embodiment shown in FIG.

As shown in Table 4 above, a line width of 2 sub-1 was obtained for all combinations ■ to 0, but the output ratio was low at 1 to 3 inches compared to the experimental data in Tables 2 and 3. It has become. This shows that when the line width is made smaller by using an external etalon, the loss is large.

In addition, in the embodiments shown in FIGS. 11 to 16, whether the air ear lug etalon 6 is used as the etalon can be determined by referring to FIG.
Of course, it is also possible to apply the solid etalon 4 shown in FIG. However, in that case, it is necessary to use one with the same specifications as the air ear lugs 6.

Further, in each of the above embodiments, the length of the excitation region of the excimer laser is preferably set to 2 m or more, and the effective diameter of the windows 5, 5' is set to 2 m or more. Furthermore, no slit (aperture) smaller than 2 is provided within the excimer laser cavity.

FIG. 1 shows that the light projected from the reduction projection light source 30 is transferred to an integrator 31, a mirror 32, a condenser lens 33,
A reduction projection exposure apparatus is conceptually shown in which a wafer 36 is reached through a reticle (thick plate) 34 and a reduction projection lens 35, thereby projecting the image of the reticle 34 onto the wafer 36.

In this device, for example, when a high-pressure mercury lamp is used as the light source 30, the resolution is up to 1.0μ.
Since the thickness is about m, it is impossible to expose fine patterns. In addition, since the mercury Lang's line width is wide, it is necessary to correct chromatic aberration, and therefore, the reduction projection lens 35 must be of a complicated construction combining glasses with different refractive indexes. This not only makes designing the lens 35 difficult, but also increases its cost.

According to the embodiment shown in FIGS. 11 to 16, 2 scratches-1
Since laser light with a relatively narrow line width can be obtained, chromatic aberration correction is not required, and therefore the projection lens 35 can be constructed using only quartz. This facilitates the design of the lens 35 and reduces costs.

Furthermore, according to each of the above embodiments, the line width can be narrowed without reducing the number of transverse modes.

No problems such as speckles occur during projection,
Therefore, a projection device with high resolution can be constructed.

〔Effect of the invention〕

According to the present invention, projection light with a narrow spectral linewidth can be obtained without reducing the number of transverse modes, and therefore reduction projection with high resolution can be performed.

[Brief explanation of drawings]

1 to 10 are schematic configuration diagrams showing embodiments of a light source for reduction projection according to the present invention, and FIGS. 11 to 1
Fig. 6 is a schematic configuration diagram showing an example in which air gap etalons are used, Fig. 17 is a conceptual diagram showing a state in which a plurality of air gap etalons are arranged in multiple stages, and Fig. 18 is a diagram showing the configuration of a reduction projection exposure apparatus. FIG. 19 is a conceptual diagram showing an example of the configuration of a conventional excimer laser. 1... Total reflection mirror, 2... Output mirror, 3...
Chamber, 4... Solitu etalon, 5. D... Wind, 6... Air gap etalon, 7... Prism, 8... Diffraction grating, 9... Prism beam expander. Figure 1 Figure 3 Figure 4 Alice 1m Figure 5 r',! Figure 7, Figure 8, Figure 10, Figure 11, Figure 12, Figure 13, Figure 14, Figure 15, Figure 16, Figure 17, Figure 1.

Claims (3)

[Claims] (1) A light source for reduction projection comprising means for oscillating incoherent ultraviolet laser light and wavelength selection means for narrowing the spectral line width of the ultraviolet laser light. (2) The light source for reduction projection according to claim (1), wherein the means for oscillating the ultraviolet laser beam is an excimer laser. (3) The reduction according to claim (1), wherein the wavelength selection means comprises at least one of an air gap etalon, a solid etalon, a dispersion prism, a total reflection mirror, a diffraction grating, and a prism beam expander. Projection light source.