JP2591582B2 - Projection type exposure equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus used in a semiconductor manufacturing process, and more particularly to a projection exposure apparatus for projecting and transferring a photomask pattern onto a wafer.

[0002]

2. Description of the Related Art In a lithography process in the process of manufacturing a semiconductor device, a resist is applied to one wafer.
The steps of alignment-exposure-chemical process are repeated plural times. In recent years, as the integration density of semiconductor devices has increased, reduction projection type exposure apparatuses have been increasingly used in the alignment and exposure steps during the lithography step. In this reduced projection type exposure apparatus,
In particular, a projection lens having a high resolution is required, and the image of a pattern on a photomask (hereinafter referred to as a “reticle”) can be formed on a wafer having a diameter of 75 mm to 150 mm placed on a moving stage by the high resolution projection lens. To 10
Projection is performed in an exposure field of mm square to 20 mm square, and stage movement and exposure are repeatedly performed. In this case, not only rapid alignment, exposure, and stage movement, but also high alignment accuracy corresponding to the resolution is required.

[0003] In a reduction projection type exposure apparatus, an alignment mark formed on a wafer through a chemical process after being projected and exposed through a projection lens is aligned with an alignment mark on a reticle in the next step for each exposure. Let
So-called die-by-die alignment is performed. In this case, it is desirable that the overlay of the alignment mark between the reticle and the wafer performed through the projection optical system in which the aberration is corrected can be confirmed simultaneously with the printing exposure.

[0004]

In a conventional TTL type alignment optical system for performing alignment through a projection lens, an exposure light as alignment illumination light for illuminating alignment marks on both a reticle and a wafer is used. Light having a wavelength close to the wavelength has often been used. For this reason, it has been found that the following problems occur in relation to the resist (photosensitive agent) on the wafer and the alignment wavelength. In other words, since the normal resist has a wide photosensitive area and has photosensitivity even near the exposure wavelength, if the alignment wavelength is close to the exposure wavelength, the resist on the alignment mark is exposed at the time of alignment, and the alignment mark is printed for each process. There is trouble to change. For this reason, the replacement of the alignment mark has been one of the causes of lowering the alignment accuracy.

Further, when observing the alignment mark on the wafer through the resist, before and after the exposure of the resist by the alignment light, the observation situation (mainly the contrast of the alignment mark) changes due to the qualitative change of the resist. There is a disadvantage that the detection signal becomes unstable. Further, in the case of a multilayer resist or a die-containing resist CEL (contrast, enhanced, layer) having an absorption layer set so as to be non-reflective by an interference condition at an exposure wavelength, an alignment mark on a wafer is used at an alignment wavelength close to the exposure wavelength. There was a drawback that observation became difficult.

Accordingly, the present invention is to solve the above-mentioned drawbacks of the conventional apparatus, and to provide an exposure apparatus capable of detecting an alignment signal satisfactorily without being affected by a resist on a wafer and having high accuracy and high throughput. With the goal.

[0007]

In order to achieve the above object, as shown in FIGS. 1 and 2, for example, a projection type exposure apparatus according to the present invention uses a reticle (3) with exposure light in a predetermined wavelength range. An illumination optical system (1) for illuminating, and a projection optical system for projecting a pattern on a reticle illuminated by the illumination optical system onto a wafer (5), use an alignment light in a wavelength range different from the exposure light to align the reticle and the wafer. the alignment optical system for detecting the alignment state through the projection optical system _{(10 L ~18 L, 10 R} ~18 R) and reflects arranged and exposure light in an optical path on the exit side of the illumination optical system Arai <br / > Dichroic mirror means (2) for transmitting the ment light
And Then, the alignment optical system, the aberration correcting means for correcting the coma generated by the alignment light through the dichroic mirror means (15 _L to 17 _L,
15 has a _R to 17 _R), as configured to detect the alignment through the dichroic mirror means and the projection optical system.

[0008]

In the projection type exposure apparatus according to the present invention as described above, since the exposure light and the alignment light are in different wavelength ranges, the resist on the wafer is not exposed to the alignment light. Therefore, a good alignment detection signal is always obtained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the accompanying drawings.
Will be described in detail. FIG. 1 shows an optical system according to an embodiment of the present invention.
FIG. 2 is a front view of the optical system shown in FIG.
You. In FIG. 1, a core supplied from a light source (not shown)
The exposure light beam passing through the condenser lens 1 is a dichroic light.
The light is reflected by the mirror 2 and the pattern on the reticle 3 is leveled.
Light up at once. Reticks illuminated by the exposure beam
The pattern on the wafer 3 is projected onto the wafer 5 by the projection lens 4.
Projected. On the other hand, oscillates light of a different wavelength from the exposure light beam
Left and right alignment illumination light source 10_L, 10_Rfrom
As shown in FIG._L, 1
1_RThrough the second objective lens 12 for alignment.
_L, 12_R, Reflector 13_L, 13_RAnd alignment
First objective lens, 14_L, 14_RThrough the aberration correction plate
Fifteen_L, 15_R, 16_L, 16 _RAnd 17_L, 17_R
Pass through. Further, the laser beam is described in detail later.
After passing through the dichroic mirror 2
Left and right alignment mark P_L, P_REach
Lighting. Furthermore, the alignment mark P _R, P
_LIlluminating beam for alignment that illuminates
Substantially passes through the center of the diaphragm 4a by the projected projection lens 4.
Mark Q on wafer 5_R, Q_LEach
It is epi-illuminated. The aperture 4a is located on the rear side of the projection lens 4.
It is at the point position.

Alignment on epi-illuminated wafer 5
Mark Q_R, Q_LReflected by the laser beam from the
Of the wafer 5 on the reticle 3
Ment mark Q_R, Q_LThe image of the alignment
Tomark Q_RIs the alignment mark P on the reticle 3._L
And the alignment mark Q_L, Q_ROn reticle 3
Alignment mark P_RAnd each is superimposed. So
Alignment mark P on reticle 3 with superimposed
_L, P_RImage and alignment mark Q on wafer 5_R,
Q_LIs the image after passing through the dichroic mirror 2
Aberration correction plate 17 _L, 17_R, 16_L, 16_R, 15_L,
Fifteen_RAnd the first objective lens 1 for alignment
4_L, 14_R, Reflector 13_L, 13_RFor alignment
Second objective lens 12_L, 12_RThrough, and translucent
Hyperscope 11_L, 11_RAt the ITV imaging tube (or imaging element)
Child) 18_L, 18_RTo the respective light receiving surfaces
Is imaged.

By the way, when light is transmitted through a plane-parallel plate having a thickness, and when the transmitted light is a parallel light beam, the light beam simply shifts laterally without affecting the aberration. If the transmitted light is convergent or divergent light, it affects astigmatism and coma. Therefore, reticle 3
Coma and astigmatism are generated when light traveling from the first to the first objective lenses for alignment 14 _L and 14 _R passes through the dichroic mirror 2 in the alignment optical path. Therefore, coma aberration is corrected by the aberration correction plates 17 _R and 17 _L arranged at an angle of 90 ° with respect to the dichroic mirror 2, and the dichroic mirror 2 is centered on the alignment optical axis.
Is rotated by 90 ° with respect to the alignment optical axis, and the astigmatism is reduced by a pair of aberration correction plates 16 _L , 15 _L , 16 _R , and 15 _R which are arranged in the opposite direction by an equal angle with respect to the alignment optical axis. It is configured to correct. When the numerical aperture (NA) of the alignment light beam is small or the dichroic mirror 2 is thin and does not adversely affect aberration, no aberration correction plate is required. 15 _L , 16 _L , 1
5 _R and 16 _R are extremely important in correcting astigmatism.
Further, as a method of alignment, a laser beam is formed into a slit shape orthogonal to the optical axis by a cylindrical lens (not shown), and the alignment mark is scanned by the slit light beam to perform alignment. On the other hand, aberration correction plates 17 _L and 17
_R is extremely important for coma aberration correction.

[0012] Figure 3 shows an optical characteristic of the dichroic mirrors 2 which are used in Figure 1, the wavelength lambda ₁ of the light 10
With respect to the light of wavelength λ ₂ , which reflects 0%, the polarization component in the P direction that vibrates in a plane perpendicular to the mirror surface is transmitted by 100%,
The polarization component in the S direction oscillating in a plane perpendicular to this is 100
The dichroic mirror 2 is designed to be a thin film so as to reflect%. The polarization component in the S direction is 100
% For a wavelength λ ₃ longer than the% transmission region.
The transmitted light is 0%. In this case, a light beam having a predetermined numerical aperture (NA) on the reticle 3 side with respect to the projection lens 4 must be uniformly reflected or transmitted through the dichroic mirror 2.

A projection lens used in a reduction projection type exposure apparatus usually has a reduction magnification of 5 to 10 times. For example, a projection lens 4 having an NA = 0.35 on the wafer side has a reduction ratio of 0.07 to 7 on the reticle side. It becomes NA of 0.035. For this reason, the dichroic mirror 2 has a NA = NA in consideration of the half width of the spectrum of the exposure wavelength and the alignment wavelength.
It is necessary to have uniform characteristics for light having a wavelength in the wavelength shift range Δλ corresponding to 0.1. Specifically, since NA = 0.1 corresponds to a wavelength shift of about ± 3 nm from the viewpoint of the characteristics of the thin film, in FIG. 3, light having a wavelength shifted from the wavelength λ ₁ by Δλ ₁ = ± 3 nm is also substantially used. 100% is reflected, and almost 100% is transmitted for light having a wavelength shifted by Δλ ₃ = ± 3 nm from wavelength λ ₃ , and further, wavelength λ ₂ which is close to λ ₁ is shifted by Δλ ₂ = ± 3 nm. The dichroic mirror 2 shown in FIG. 1 is designed to have a thin-film design so as to transmit substantially 100% of the polarization component in the P direction and to reflect substantially 100% of the polarization component in the S direction.

FIGS. 4 to 6 are diagrams for explaining the state of chromatic aberration correction with respect to the exposure wavelength and the alignment wavelength of each of the different projection lenses 4 used in the embodiment of FIG. λ, the vertical axis indicates the amount of axial chromatic aberration of the projection lens 4, and the portion d sandwiched by the broken line indicates the allowable range of chromatic aberration. FIG. 4 shows a state of chromatic aberration correction seen in a normal projection lens showing an axial chromatic aberration state of a quadratic curve having one extreme value, and a relatively wide half-value width (spectral value) b within the chromatic aberration allowable range d. an exposure wavelength lambda ₁ having a includes a laser light lambda ₂ of the alignment wavelength. In the present invention, this is referred to as a “collective achromatism type”. In the projection lens 4 using a normal glass material incorporated in a conventional exposure apparatus, etc., since the allowable range of chromatic aberration is narrow, the exposure wavelength λ ₁ and the alignment wavelength λ ₂ are close to each other as shown in FIG. Is often used. Table 1 shows an example of a combination of an exposure wavelength λ ₁ and an alignment wavelength λ ₂ used via the dichroic mirror 2 for the projection lens 4 of the collective achromatic type.

[0015]

[Table 1]

A typical exposure wavelength λ ₁ is 436 nm, 365 nm of the spectrum of an Hg lamp (high pressure mercury lamp).
And 313 nm, and the wavelength half width is relatively wide,
Here, it is uniformly ± 2 nm. Also, similarly, the exposure wavelength λ
As for the excimer laser selected as ₁ , the relatively wide half width of XeCl and KrF is set to ± 0.5 nm. A high-brightness light source is desirable as the alignment light, and He-Cd: 442 nm, He
-Cd: 325 nm or the like is selected. Further, since the alignment wavelength λ ₂ is close to the exposure wavelength λ ₁ , the dichroic mirror 2 uses a region that transmits the P component and reflects the S component as shown by the wavelength λ ₂ in FIG.

FIG. 5 has one extremum like FIG.
In a projection lens having an axial chromatic aberration showing a quadratic curve,
The wavelength λ on the short wavelength side sandwiching the extreme value 0₁And longer wavelength
λ_ThreeThe chromatic aberration was corrected for
This is referred to as a “narrow band two-color achromatic type”. This type of investment
When a shadow lens is used in an exposure apparatus, the exposure wavelength λ₁Is
Chromatic aberration tolerance because it is far away from extreme value 0 to the short wavelength side
d₁For exposing an excimer laser with a narrow half width
Used as light source, alignment wavelength λ_ThreeAs a projection
Various types are selected depending on the design of the lens 4. like this
Dichroic for projection lens with chromatic aberration correction
Exposure wavelength λ used via mirror 2 ₁And Alignmen
Wavelength λ_ThreeTable 2 shows examples of combinations with.

[0018]

[Table 2]

As the excimer lasers in Table 2 above, those having a narrow half width such as an injection locking state are used. Note that the alignment wavelength λ ₃ is the exposure wavelength λ
Because it is far away from ₁ , dichroic mirror 2
Are used in the entire transmission region (the region of λ _{3 in} FIG. 3). In the collective achromatic type as described above, only the wavelength close to the exposure wavelength can be used as the alignment wavelength, and in the narrow band two-color achromatic type, a laser beam with a narrow wavelength width is required for both exposure and alignment. Further, it is impossible to use a plurality of alignment wavelengths. However, if chromatic aberration correction is performed using an optical material exhibiting anomalous dispersion, such as fluorite (CaF ₂ ) or lithium fluoride (LiF), among components of the projection lens 4, an axis having a wavelength as a function is obtained. As shown in FIG. 6, the behavior of the upper chromatic aberration is represented by at least two extreme values 0 _1.
And a cubic curve with 0 ₂ .

In the longitudinal chromatic aberration curve shown in FIG. 6, when the horizontal axis X is substantially in contact with the extreme value 0 ₁ on the short wavelength side,
The axial chromatic aberration can be corrected to 0 (zero) for the wavelength λ ₁ (wavelength approximately equal to the extreme value 0 ₁ ) and the wavelength λ _{3 in} the long wavelength region exceeding the extreme value 0 ₂ on the long wavelength side. . In this case, it is possible to widen the wavelength width in the chromatic aberration tolerance in the vicinity of extreme values 0 _1, an excimer laser, of course, for example, Hg lamp spectrum use wide light source, such as (ultra high pressure mercury lamp) is It becomes possible. Therefore, here, this is referred to as "broad band two-color achromatic type". The wavelength λ _{3 in} the long wavelength range exceeding the extreme value 0 ₂ is used as alignment light, and the wavelength λ ₂ slightly longer than λ ₁ can be used for both exposure and alignment. Tables 3 and 4 show examples of combinations of the exposure wavelength λ ₁ and the alignment wavelengths λ ₂ and λ ₃ used via the dichroic mirror 2 for the projection lens 4 of the wide band two-color achromatic type as described above. Shown in

[0021]

[Table 3]

Table 3 shows the exposure wavelength λ.₁Hg lamp
Specs of 436nm, 365nm, 313nm etc.
XeCl excimer laser
Is a wavelength of 249 ± 0.5 nm, and KrF excimer laser is
Used at length 249 ± 0.5 nm. Also, alignment
Each of the luminous fluxes has an extreme value 0 on the long wavelength side in FIG. _Two
Wavelength λ in the region beyond_ThreeOnly the dichroic
In FIG. 3 of the mirror 2, the total transmission region (the S component is also completely transmitted region)
Area).

Further, in the case of the wide band two-color achromatic type, Table 4
2 wavelengths can be selected as alignment wavelength as shown in
It is. In this case, the dichroic mirror 2 is shown in FIG.
At λ _TwoAnd λ_Three, The exposure wavelength λ₁Close to
Alignment wavelength λ_TwoIs transmitted through the P component.
At the exposure wavelength λ.₁From
Far alignment wavelength λ_ThreeIs completely transmitted.

[0024]

[Table 4]

When alignment is performed on a wafer coated with a resist (photosensitive agent), at one wavelength, a detection signal of an alignment mark on the wafer cannot be obtained due to interference conditions such as the resist thickness and the refractive index. Or may be very noisy. In such a case, if two different wavelengths of light are used for alignment, a sufficient detection signal is often obtained at the other wavelength even if the detection signal at one wavelength is insufficient, and improvement in detection capability can be expected. .

Although not described in Table 4 above, in FIG. 6, two wavelengths of exposure (for example, λ ₁ and λ
₂ ) using one wavelength (eg λ ₃ )
It is also possible to carry out. In this case, when exposure is performed at _one wavelength (for example, λ ₁ ), a standing wave is generated at the pattern edge on the wafer due to the reflected light on both the upper surface of the resist and the upper surface of the wafer, which hinders the formation of a fine pattern. However, if the exposure is performed at two wavelengths (for example, λ ₁ and λ ₂ ), the standing wave can be reduced.
An improvement in the control of the printing line width can be expected.

In the above embodiment, the dichroic mirror 2 is formed of a plane parallel plate. However, the dichroic mirror 2 may be formed by laminating two right-angle prisms so that the oblique side becomes a reflection surface. In this case, aberration does not occur in the transmitted light of the prism, the aberration correction plate 15 _R ~17 _R, 15 _L
~ 17 _L can be deleted. On the other hand, as a characteristic of the dichroic mirror, a cold mirror type that reflects a short wavelength and transmits a long wavelength is advantageous in manufacturing. Usually, when a high-intensity laser is used for the alignment light beam,
Although an alignment optical system having low noise and high detection capability can be configured, many stable lasers have a wavelength longer than the exposure wavelength. Therefore, the embodiment of FIG. 1 employs a dichroic mirror 2 that reflects the exposure wavelength and transmits the alignment wavelength. But,
Depending on the combination of the alignment wavelength and the exposure wavelength, an exposure light beam may be selected on the transmission side of the dichroic mirror 2 and an alignment light beam on the reflection side.

[0028]

According to the present invention as described above, since alignment can be performed under an alignment wavelength in a wavelength range different from the exposure wavelength, a multilayer resist having an absorption band at the exposure wavelength, a die-containing resist, a CEL, etc. , An alignment signal with a good SN ratio can be obtained, and the detection capability can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a side view of an optical system showing one embodiment of the present invention.

FIG. 2 is a front view of the optical system shown in FIG.

FIG. 3 is an optical characteristic diagram of the dichroic mirror shown in FIG.

FIG. 4 is an explanatory diagram showing a chromatic aberration correction state of a collective achromatic projection lens.

FIG. 5 is an explanatory diagram showing a chromatic aberration correction state of a narrow band two-color achromatic projection lens.

FIG. 6 is an explanatory diagram showing a chromatic aberration correction state of a wide band two-color achromatic projection lens.

[Explanation of symbols]

1 ... condenser lens, (illumination optical system) 2 ... dichroic mirror (dichroic mirror means) 3 ... reticle, 4 ... projection lens (projection optical system) 5 ... wafer, 12 _L, 12 _R ... first objective lens for alignment , 14 _L, 14 _R ... second objective lens for _{alignment, 15 L ~17 L, 15 R} ~17 R ... aberration correction plate, 10 _L, 10 _R ... alignment illumination source, 18 _L, 18 _R ... ITV camera tube,

Continued on the front page Judge Kunio Kobayashi Judge Judge Yoshihiro Samura Judge Yoshiaki Aida (56) References JP-A-58-162954 (JP, A) JP-A 60-177625 (JP, A) -23276 (JP, B2)

Claims (2)

(57) [Claims] An illumination optical system for illuminating a reticle with exposure light in a predetermined wavelength range, a projection optical system for projecting a pattern on the reticle illuminated by the illumination optical system onto a wafer, and the exposure light An alignment optical system that detects an alignment state between the reticle and the wafer through the projection optical system by alignment light in different wavelength ranges, and is disposed in an optical path on an emission side of the illumination optical system, and reflects the exposure light , and and a die <br/> Kuroikkumira means for transmitting an alignment beam, the alignment optical system has an aberration correcting means for correcting the coma generated by the alignment light through the dichroic mirror means, said It is characterized in that the alignment is detected through dichroic mirror means and the projection optical system. And the projection type exposure apparatus. (2) The aberration correction unit includes the dichroic
Generated by the alignment light via mirror means
2. The method according to claim 1, wherein the astigmatism is further corrected.
Projection type exposure apparatus.