JPS6312135A - Lighting optical system - Google Patents

Abstract

PURPOSE:To light the surfaces to be lighted of a mask, a reticle and the like efficiently, in a lighting optical system utilizing luminous flux from an optical integrator, by making the refractive index of said integrator variable. CONSTITUTION:Luminous flux from a light source 1 is converged with an elliptical mirror 2 and reaches an optical integrator 3. The optical integrator 3 comprises a plurality of minute lenses and forms a secondary light source having uniform light projecting characteristics. The integrator 3 is constituted with a variable power system. The emitting angle of the emitted luminous flux can be changed. In this constitution, the printing range of a reticle 5 can be internally contacted all the time within the circle of the effective range provided by the lighting optical system. Therefore, the luminous flux, which is not used, is decreased, and the lighting efficiency can be improved.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an illumination optical system, and in particular to an illumination optical system that efficiently illuminates the irradiated surface of a mask or reticle on which a fine pattern such as an electronic circuit is formed in semiconductor manufacturing equipment. This invention relates to an illumination optical system for illumination.

(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.

Among these, a so-called reduction projection exposure apparatus, which uses a reticle formed with an electronic circuit pattern enlarged m times larger than the required size and projects it onto the wafer surface using a projection optical system at a reduced size of 1/m, is relatively effective. They are currently attracting attention because of their high resolution.

With this reduced projection exposure system, the effective area of the projection optical system that can be exposed at once on the wafer surface is smaller than the size of a sea urchin, so when one projection exposure is completed, the wafer stage is moved a certain amount and the next A step-and-beat method is used to repeatedly expose the area.

The reticle on which the electronic circuit pattern is formed is generally rectangular, and the projection exposure range on the wafer surface is a rectangle ranging from several millimeters to more than ten millimeters, and one to several chips of elements are arranged within this range. has been done.

On the other hand, the effective illumination range of the illumination optical system that illuminates the reticle surface in a reduction projection exposure apparatus is circular. When performing projection exposure on a surface of a sea urchin, a part of the effective illumination range is blocked by a masking mechanism or the like, so that only the light beam within a rectangular shape similar to the reticle shape is used.

For this reason, the luminous flux from the light source can be used most effectively if the reticle surface is illuminated in a rectangular shape that is always inscribed within the circle of the effective illumination range of the illumination optical system.

However, the exposure range currently used varies depending on the user, and if the exposure range is smaller than the effective illumination range of the illumination optical system, there will be a large amount of unused luminous flux, which may cause a reduction in illumination efficiency. .

In addition, in semiconductor manufacturing equipment that uses the contact method, in which a mask with a circuit pattern formed thereon is directly placed on the wafer and baked, and the proximity method, in which the mask and wafer are printed a predetermined distance apart, illumination on the mask surface is also used. There are also problems similar to those described above depending on the inch size of the wafer used.

(Problems to be Solved by the Invention) By configuring the optical integrator used in a part of the illumination optical system as a variable magnification system, the present invention can be used even when the size of the exposure range is smaller than the effective illumination range. An object of the present invention is to provide an illumination optical system that is particularly suitable for semiconductor manufacturing equipment and is capable of uniform illumination and can always efficiently use the luminous flux from a light source.

(Means for Solving the Problems) In an illumination optical system that makes a light beam from a light source enter an optical integrator consisting of a plurality of minute lenses, and illuminates a predetermined surface using the light beam emitted from the optical integrator, This is because the refractive power of the optical integrator is made variable.

Other features of the invention are described in the Examples.

(Embodiment) FIG. 1 is a schematic diagram of an optical system of an embodiment when the present invention is applied to a reduction projection exposure apparatus. In the figure, reference numeral 1 denotes a light source, for example, a mercury lamp or a halogen lamp. Reference numeral 2 denotes an elliptical mirror, and in order to efficiently condense the luminous flux from the light source 1, the light emitting surface of the light [1 is arranged at its first focal point, and the luminous flux from the light source 1 is condensed near the second focal point. Reference numeral 3 denotes an optical integrator, which is made up of a plurality of minute lenses and is arranged near the second focal point of the elliptical mirror 2 in order to form a secondary light source with uniform light distribution characteristics. A condenser lens 4 condenses a light beam from an optical integrator 3, which is a secondary light source, arranged near its front focal point, and uniformly illuminates a reticle 5, which is a surface to be illuminated. 6
is a projection optical system that projects the reticle 5 onto the wafer 7 in a reduced size.

In this embodiment, in the case of the contact method or the proximity method, the projection optical system 6 is not necessary, and the mask 5 and the wafer 7, which are the surfaces to be irradiated, are placed in close contact with each other or are spaced apart by a predetermined distance.

In this embodiment, the printing range of the reticle 5 is square, while the effective illumination range by the light beam from the condenser lens of the illumination optical system is circular. For this reason, as shown in FIG. 2(A), if the printing range 20 of the reticle 5 is configured to be a square inscribed within the circle of the effective illumination range 21 of the illumination optical system, the luminous flux from the light source can be used most efficiently. It can be used in many ways. However, in reality, depending on various specification conditions, the burning range 20 may be smaller than the effective illumination range 21, as shown in FIG. 2B. For this reason, depending on the specification conditions, there may be a large amount of unused illumination luminous flux, causing a reduction in illumination efficiency.

Therefore, in this embodiment, the optical integrator 3 is configured with a variable magnification system, and by changing the exit angle of the light beam emitted from the optical integrator 3, the printing range of the reticle 5 is set within the circular effective illumination range by the illumination optical system. is always inscribed to reduce unused illumination flux,
Efforts are being made to improve lighting efficiency.

FIG. 3(A) is an enlarged view of the optical integrator 3 shown in FIG. 1, where 30 is the optical axis of the illumination optical system, 31,
32 and 33 are microlens groups each consisting of a plurality of microlenses.

FIG. 3(B) is a cross-sectional view of one microlens group shown in FIG. 3(A), and each microlens is constructed by processing one or both surfaces of hexagonal prism glass into a convex surface.

Note that the microlens group may be constructed from a glass mold in which a plurality of convex surfaces are formed on one or both sides of a large piece of glass. Further, as shown in FIG. 2C, the lens barrel may be provided with microlenses one by one.

FIGS. 4(A) and 4(B) are explanatory diagrams of three microlens groups constituting the optical integrator 3, for example, three microlenses on the optical axis 30 in FIG. 3(A). In the figure, 41, 42, and 43 are micro lens groups 31 and 32, respectively.
．． 33 is a microlens, and L is an illumination light flux.

Now, if the refractive power of the microlens 41 is Φ1, and the refractive power of the composite lens 44 of the microlens 42 and 43 is Φ23, the maximum exit angle α of the light beam from the microlens 43 is the refractive power Φ
It is proportional to 23.

Therefore, by changing the distance between the two microlenses 42 and 43 and changing the refractive power Φ23, the maximum exit angle α can be arbitrarily changed to the exit angle α′ as shown in FIG.

FIG. 4(C) is an explanatory diagram of the refractive power arrangement at this time.

The distance d from the position 45 of the secondary light source to the rear principal point position of the composite lens group 44 of the optical integrator is d=
1/Φ2 (1-Φ1/Φ23).

Also, the length l from the principal point of the microlens 41 to the secondary light source 45
is l=1/Φ23 (2-Φ1/Φ23).

In this embodiment, the position of the secondary light source associated with the variable magnification system remains unchanged, and the entire optical integrator is moved in the optical axis direction so that, for example, the imaging position of the secondary light source does not deviate from the pupil position of the projection lens.

In this embodiment, when changing the refractive power of the optical integrator, the principal ray of the emitted light beam from the optical integrator in each state is always emitted approximately parallel to the optical axis of the illumination optical system, so that it enters the center of the reticle. As a result, the range of illumination on the reticle by the light beams from each point on the exit surface of the optical integrator matches, making efficient illumination possible and uniform illumination on the reticle surface. That is, the distance between the principal points of the microlens 31 and the composite lens group 44 is set to 1/Φ23 in each state, that is, to match the focal length of the composite lens group 44, so that the reticle surface is uniformly illuminated. .

FIG. 5 is an explanatory diagram showing the relationship between the effective illumination range on the surface of the reticle 5 and the two exit angles α and α' of the light beam emitted from the optical integrator 3.

In the figure, when the exit angles are α and α゛, the radii of the illumination range on the 5th surface of the reticle are R and R'', respectively.As is clear from the figure, there is a relationship of α°/α=R'/R. .

In this embodiment, by utilizing this relationship, the distance between the two microlens groups 32 and 33 is changed, that is, the refractive power of the optical integrator is changed, and the exit angles α and α゛ of the light beam are changed. The lighting range can be controlled arbitrarily.

In this case, the angle of incidence β of the incident light beam onto the surface of the reticle 5 is an amount that affects the projection resolution, but this angle β is an invariant that does not change as the optical integrator changes magnification. This is the same even when the contact method or proximity method is used.

As a result, in this embodiment, even if the exposure range becomes small, efficient illumination is always achieved by making the effective illumination range into a circle that inscribes the printing range 20 of the reticle as shown in FIG. 2(A).

For example, if the length of one side of the burning area 20 is reduced by 10% by changing the magnification, the illuminance can be increased by about 23%.

Furthermore, in a contact type or proximity type illumination optical system, by changing the illumination range from 6'' to 5'', the illuminance can be increased by approximately 44%.

In this example, the optical integrator 3 is composed of three microlens groups, and the illumination range is changed by moving two of these microlens groups along the optical axis and moving the entire integrator along the optical axis. The micro lens group may be composed of four or more, and the interval between at least two of these lens groups may be changed.

The magnification change of the optical integrator may be performed automatically when the Schottreiald is manually operated from the console. That is, the illumination range on the reticle surface may be calculated by a computer from the shot layout, and a predetermined microlens group of the optical integrator may be automatically driven by a drive mechanism based on the calculated value.

The above-described embodiments can also be successfully applied to contact-type or broximity-type illumination optical systems.

(Effects of the Invention) According to the present invention, the effective illumination range can be changed by changing the magnification by moving at least two microlens groups that constitute the optical integrator in the illumination optical system according to the effective screen size of the illuminated surface. As a result, an illumination optical system capable of efficient illumination with little loss of luminous flux can be achieved. Furthermore, by automatically performing magnification changes manually using the console, it is possible to perform the changes with high precision and quickly.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an optical system of an embodiment when the present invention is applied to a minute projection exposure apparatus, and FIG. 2 (A). (B) and (G) are explanatory diagrams showing the relationship between the irradiated surface and the effective illumination range, respectively, and Fig. 3 (A), (B), (
C) is an explanatory diagram of a part of FIG. 1, FIG. 4(A),
(B). (C5) is an explanatory diagram of magnification change of the optical integrator according to the present invention, and FIG. 5 is an explanatory diagram showing the relationship between the emitted light flux from the optical integrator and the effective illumination range. In the figure, 1 is a light source, 2 is an elliptical mirror, 3 is an optical integrator, 4 is a condenser lens, 5 is a surface to be illuminated,
6 is a projection optical system, and 7 is a wafer. Patent applicant: Canon Co., Ltd. 1 Zutsuri ro (△) (B) (G) Kabuto 3 times (A) (B) (C) 夷
4 times 91 φ23

Claims (3)

[Claims] (1) In an illumination optical system that makes a light beam from a light source enter an optical integrator consisting of a plurality of minute lenses and illuminates a predetermined surface using the light beam emitted from the optical integrator, the refractive power of the optical integrator is variable. An illumination optical system characterized by: (2) At least three optical integrators
2. The illumination optical system according to claim 1, wherein the illumination optical system is comprised of a lens group having two refractive surfaces. (3) The illumination optical system according to claim 1, wherein the magnification of the optical integrator is automatically changed by an input signal from a console.