JPH02285628A - Lighting optical system - Google Patents

Abstract

PURPOSE:To enable a lighting region to be arbitrarily changed corresponding to an objective region without changing NA of a lighting optical system as well as the lighting intensity to be augmented especially in smaller lighting region for making the lighting effective by a method wherein the lighting range in a specific surface is changed by changing the refractive power of an optical integrator. CONSTITUTION:When a light flux 5 from a laser 1 is adjusted to specific size through an adjusting optical system 2a so as to be entered as parallel light flux into an optical integrator 2b comprising multiple fine lenses for lighting a specific surface 4 using the light flux emitted from the optical integrator 2b, the lighting range on the specific surface 4 is to be changed by changing the refractive power of the integrator 2b. For example, the said optical integra tor 2b is composed of three each of lens units 7-9 comprising multiple fly-eye lenses. In such a constitution, the lighting range phi on the lighted surface 4 is to be changed by changing the focal length of the whole optical integrator 2b by shifting the lens units 8, 9 on an optical axis.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to an illumination optical system, and in particular to an illumination optical system used in an exposure apparatus for manufacturing semiconductor devices, for illumination surfaces exclusively used for masks and reticles on which fine patterns such as electronic circuits are formed. This invention relates to an illumination optical system for efficiently illuminating.

(Conventional technology) Recent semiconductor manufacturing technology includes high integration of electronic circuits.
There is a need for lithography technology that can form high-density electronic circuit patterns.

As an exposure device that can perform relatively high-precision printing in lithography technology, a reticle formed m times larger than the required size of an electronic circuit pattern is illuminated by an illumination optical system, and the reticle is transferred onto a wafer by a projection optical system. 17 on the surface
There is a so-called reduction projection exposure apparatus that reduces projection by m times.

FIG. 7 is a schematic diagram of an illumination optical system for illuminating a reticle used in a reduction projection exposure apparatus.

In the figure, reference numeral 10 denotes a light source, such as a mercury lamp or a halogen lamp. 11 is an elliptical mirror and a light source lO
In order to efficiently condense the luminous flux from the light source 10, the light emitting surface of the light source 10 is arranged at its first focal point, and the luminous flux from the light source 10 is condensed near the second focal point. 12 is an optical integrator that forms a secondary light source with uniform light distribution characteristics and multiple microlenses (fly's eye lens) to obtain the optimal NA.
It is arranged near the second focal point of the elliptical mirror 2. A condenser lens 13 condenses the light beam from the optical integrator 12, which is a secondary light source, and uniformly illuminates a reticle 14, which is a surface to be illuminated.

(Problems to be Solved by the Invention) A reticle on which an electronic circuit pattern is formed generally has a rectangular shape, and the pattern area has various dimensions.

The effective illumination range of the illumination optical system that illuminates the reticle surface in a reduction projection exposure apparatus is generally circular. When performing projection exposure on the wafer, a part of the effective illumination range is shielded from light by a masking mechanism or the like, so that only the light beam within a rectangle similar to the reticle pattern shape is used.

However, currently used reticle patterns have various sizes, and in order to accommodate all four reticles, it is necessary to configure the effective illumination range of the illumination optical system to target the reticle of the largest size. When a reticle having only these four small pattern areas is used, there is a large amount of unused light flux, which causes a decrease in illumination efficiency.

For example, if an illumination optical system that guarantees a circular area with a diameter of 100 mm on the reticle is used for a reticle that targets a circular area with a diameter of 70 mm, unnecessary areas will be illuminated, resulting in a very poor illumination efficiency. There was a problem.

According to the present invention, the illumination area can be arbitrarily changed according to the target area without changing the NA of the illumination optical system, and especially when the illumination area is small, the illuminance can be increased and efficient illumination can be achieved. The purpose is to provide an illumination optical system.

(Means for Solving the Problems) The illumination optical system of the present invention shapes the light beam from a laser into a predetermined size through a shaping optical system, and makes it enter an optical integrator consisting of a plurality of microlenses as a parallel light beam. , when illuminating a predetermined surface using the light beam emitted from the optical integrator, the illumination range on the predetermined surface is changed by changing the refractive power of the optical integrator.

(Embodiment) FIGS. 1A and 1B are schematic diagrams of essential parts of an embodiment in which the illumination optical system of the present invention is applied to a reduction projection exposure apparatus.

In the figure, 1 is a laser that emits highly directional light, for example, λ=
It is a 248.4 nm excimer laser. 5 is laser 1
The luminous flux emitted from the laser beam 5 is a luminous flux adjusting means, which will be described later, in order to form a secondary light source surface with uniform light distribution characteristics in conjunction with a beam shaping system such as a beam expander that shapes the luminous flux diameter of the laser beam 5. It has an optical integrator consisting of multiple fly-eye lenses. 3 is a condensing optical system, and 4 is a reticle surface which is an irradiated surface. Reference numeral 6 denotes an image-side focal plane of the light flux adjusting means 2 which condenses the light beam emitted from the light flux adjusting means 2, and this point also serves as a pupil plane of the condensing optical system 3. A projection optical system 101 projects the pattern on the four surfaces of the reticle onto the surface of the wafer 102 at a predetermined reduction magnification. Each lens constituting the light flux adjustment means 2 is constructed of a sinusoidal lens, and efficiently transmits excimer laser light.

In this embodiment, the light beam 5 from the laser 1 is made into a light beam having a predetermined opening angle by the light beam adjustment means 2, and is focused on the image side focal plane 6. A condensing optical system 3 whose pupil plane is the image-side focal plane 6
The illuminated surface 4 is uniformly illuminated.

Of these, FIG. 1(A) shows the optical path in the standard state,
This is a case where the entire target area Φl is illuminated by the projection optical system 101. FIG. 1 (B,) shows a case where the area Φ2 targeted by the projection optical system 101 is smaller than that in FIG. .

Next, a method of changing the illumination area in this embodiment will be explained.

FIGS. 2(A) and 2(B) respectively show the luminous flux adjusting means 2 of this embodiment.
FIG. 2 is an explanatory diagram of an optical arrangement showing the relationship between a beam shaping optical system 2a and an optical integrator 2b.

The beam shaping optical system 2a uses a light beam 5 with good directionality such as a laser.
The beam diameter of the beam is shaped, and the beam is made incident on the optical inch grater 2b as a parallel beam. The optical inch grater 2b consists of three lens units 7.8.9 each consisting of a plurality of fly-eye lenses.

In the figure, when the beam shaped by the beam shaping optical system 2a enters the optical inch grater 2b, the diameter of the beam incident on each fly's eye lens is d, the focal length of the optical inch grater 2b is fl, and the focusing optical system 3 Let r2 be the focal length of the illumination area 4, and Φ be the irradiation diameter of the illumination area 4, then Φ=(f2/fl)·d.

For example, d=10mm, fl=lomrn, f235mm
Then, Φ=35mm.

In this embodiment, the illumination area Φ is determined by changing the focal length of the optical inch grater 2b.

That is, while fixing the position of the image-side focal plane 6 of the optical inch grater 2b, the lens unit 8.9 is moved along the optical axis and displaced as shown in FIG. 2(B) to determine the focal length of the entire objective integrator 2b. Changing f1. Thereby, the illumination range on the irradiated surface 4 is changed based on the above-mentioned formula Φ-(f2/fl)d.

For example, the focal length f1 of the optical inch grater 2b
When changing fl=50mm, the illumination area Φ becomes Φ=7m
m.

Next, a concrete explanation will be given using a formula.

Now, the powers (reciprocal of the focal length) of lens units 7, 8, and 9 are respectively φ1, φ2, and φ3, the distance between the principal points of lens units 7 and 8 is e l , and the distance between the principal points of lens units 8 and 9 is C2, when the distance between the principal points of the lens unit 9 and the rear focal plane 6 is Sk, the total power φ of the optical inch grater 2b constituted by the lens unit 7.8.9 is ψ・φ1+φ2+φ5−eIφeffectφ2÷ φ3) C2φ,
(φ, +φ2)÷e+e2φ, φ, φ.

becomes. Also, Sk-φ = l-e+ φ 1-C2φ 1-C2φ
There is a relationship: 2◆e+e2φ 1φ2. In this embodiment, the value of Sk is fixed, and the lens unit 8.9 is moved along the optical axis so that the overall power φ becomes the desired power.

For example, φ+ =0.04 (f=25mm)φ! =
-〇, 05 (f=-20mm),
φs0.04 (f = 25mm), S, = 12mm,
When e+ = 12.43 mm, ex = to, and 77 mm, φ = 0.0286 (f = 35 mm).

Here, in order to narrow the illumination range, for example, φ0.02 (f
=50mm), set e, =10.2, e
Lens units 7 and 8 may be moved so that x=33.85.

In this embodiment, the power φ of the optical inch grater 2b was changed by moving the lens unit 7.8.
The lens unit to be moved is not limited to the lens unit 7.8, and any lens unit may be moved.

The refractive power of the lens unit 7.8.9 can be arbitrarily set as long as the power of the entire optical inch grater 2b can be changed by movement of a predetermined lens unit.

In this embodiment, a case is shown in which the power of the objective integrator 2b as a whole is positive, but as shown in FIG. 3, the power as a whole may be negative. In this case, the image side focal point position 6 in FIGS. 2(A) and 2(B) is simply displaced to the left position 29 of the lens unit 9, and basically the image side focal position 6 in FIGS. The case is exactly the same.

In the embodiments shown in FIGS. 2(A) and 2(B), the optical inch grater 2b is composed of three lens units 7, 8, and 9 having a predetermined refractive power.
), as shown in (B), it may be composed of two lens units 13 and 14 with positive and negative refractive powers.
By moving the two lens units 13 and 14, the power of the entire optical inch grater 2b can be changed while the position of the image-side focal plane 6 is fixed.

FIGS. 5(A) and 5(CB) are schematic diagrams of main parts of another embodiment of the optical integrator according to the present invention, and FIGS.
A) shows the basic state, and (3) in the same figure shows a case where the illumination range is smaller than that in the same figure (A).

In this embodiment, the optical integrator 2b is
The two parts, bl and rear group 2b2, constitute an afocal system with the front group. Then, by changing the afocal magnification of the front group 2bl, the power of the entire optical integrator 2b is changed, and the irradiated surface 4 is changed in the same manner as described above.
changing the lighting range.

FIG. 6 shows an optical integrator 2b according to the present invention.
FIG. 2 is a schematic diagram of main parts of another embodiment.

In this embodiment, the optical integrator shown in FIG. 5 is used, and in order to make the secondary light source surface more uniform, an optical element 25 having a diffusion effect, such as a diffusion plate or a very fine fly's eye lens, is placed on the front side of the lens unit 24. It is placed in the focal plane. This forms a uniform secondary light source surface. In addition, 26 is N of the luminous flux emitted from the optical element 25.
This is a diaphragm that regulates A, and is placed at the pupil plane position of the entire system.

(Effects of the Invention) According to the present invention, a highly directional laser is used as a light source,
By changing the refractive power of the optical integrator that constitutes the luminous flux adjustment means, the illumination range on the illuminated surface can be arbitrarily changed while preventing loss of light quantity.
For example, when a reticle with a small illumination range is used, the illumination intensity can be increased, so it is possible to achieve an illumination optical system that has features such as being able to shorten the exposure time per shot.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a main part of an embodiment when the present invention is applied to a reduction projection exposure apparatus, and FIG. 2 is a light flux adjusting means 2 of FIG. 1.
The explanatory diagrams of Figure 3, Figure 4, Figure 5, and Figure 6 are respectively
FIG. 7 is a schematic view of a main part of another embodiment of the luminous flux adjustment means 2 shown in the figure, and FIG. 7 is a schematic view of a main part of a conventional illumination optical system. In the figure, 1 is a laser, 2 is a light] 2 East adjustment means, 3 is a condensing optical system, 4 is an irradiated surface, 2a is an enlargement system, 2b is an optical integrator, 7.8.9
．． 30.31.32.13.14.21 to 24 are lens units, 25 is an optical element, and 26 is an aperture.

Claims (1)

[Claims] (1) The light beam from the laser is shaped into a predetermined size via a shaping optical system, and is made to enter an optical integrator consisting of a plurality of microlenses as a parallel light beam, and the light beam emitted from the optical integrator is used to form a predetermined size. An illumination device characterized in that when illuminating a surface, the illumination range on the predetermined surface is changed by changing the refractive power of the optical integrator.