JPH0721585B2 - Illumination optics - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illumination optical system, and more particularly to an irradiation optical system in which a fine pattern such as an electronic circuit is formed using a light source such as an excimer laser having a high brightness in the ultraviolet region. The present invention relates to an illumination optical system suitable for a semiconductor manufacturing apparatus capable of efficiently and uniformly illuminating a mask that is a surface while preventing damage to optical elements.

(Prior Art) Recent semiconductor manufacturing technology has been accompanied by high integration of electronic circuits.
There is a demand for a lingrafie technology capable of forming a high-density circuit pattern.

Generally, when the circuit pattern on the mask or reticle surface is transferred onto the wafer surface, the resolution line width of the circuit pattern transferred onto the wafer surface is proportional to the wavelength of the light source. For this reason, excimer lasers have recently become more bright, monochromatic, instead of conventional ultra-high pressure mercury lamps or xenon mercury lamps that oscillate a short wavelength in the deep ultraviolet (deep UV region) with a wavelength of 200 to 300 nm.
Due to its good directivity, various researches have been conducted on its application to the Lingrafi technology.

Generally, in baking exposure on a wafer surface in semiconductor manufacturing, it is required that the illumination light flux on the mask surface has a constant spread angle for uniform exposure on the entire baking surface and control of the physical-optical effect. Therefore, conventionally, an illumination optical system using a so-called light integrator composed of a lens array called a fly's eye lens, an optical fiber bundle, and a condenser lens is used between the light source and the wafer surface. In the illumination optical system, a so-called contact / proximity exposure method in which a mask and a wafer are closely contacted or separated by several tens of microns to perform printing, a condenser lens is used to form a light integrator image at infinity. Further, in a so-called projection exposure method in which a pattern of a mask such as a stepper is projected and exposed on a wafer surface by using a projection optical system, a so-called projection lens is formed by a condenser lens to form an image of a light integrator on an entrance pupil of the projection optical system. It constitutes the Koehler illumination system.

For example, FIG. 2 is a cross-sectional view of a set of lenses constituting a lens array when a convex lens array is used as a light integrator. One set of lenses is 2 of convex lenses 21 and 22
It consists of two lenses. Both the convex lenses 21 and 22 have the same focal length, and the two lenses are arranged apart by the focal length. Then, the light flux is limited by the diameter of the convex lens 21, that is, a diaphragm is formed, and after parallel light fluxes that have entered the convex lens 21 at various angles are condensed in the vicinity of one lens surface of the convex lens 22, the respective chief rays become parallel to each other. It is ejected to become. At this time, the convex lens 22 functions as a field lens. That is, the convex lenses 21 and 22 collectively constitute a telecentric optical system.

A general excimer laser has a divergence angle of its luminous flux of several milliradians, which is close to parallel light, and has a high output in the ultraviolet region. For this reason, when an excimer laser is used in the optical system shown in FIG. 2, only parallel axial light fluxes are produced, and the energy density becomes enormous at the focal point (F in the figure). Therefore, the coating of the convex lens 22 or the lens material itself may be destroyed. Therefore, it is conceivable to omit the convex lens 22, but even in this case, the laser light flux is condensed in the air, and at that time, the air causes a dielectric breakdown and discharges or emits light to waste the energy of the laser light flux. It may happen.

(Problems to be Solved by the Invention) The present invention eliminates waste of output energy when using an excimer laser as a light source, prevents destruction of optical elements due to focusing of a laser beam, and further provides uniform illumination of a surface to be illuminated. The purpose is to provide a possible illumination optical system.

(Means for Solving the Problems) In an illumination optical system having an optical fiber bundle that receives coherent light from a laser and a condenser lens that directs the light from the optical fiber bundle to an illuminated surface, This is to form a divergent lens surface on the light emitting surface of each optical fiber of the optical fiber bundle by giving a difference of coherence length or more to the length of each optical fiber.

Other features of the present invention are described in the embodiments.

(Embodiment) FIG. 1 is a schematic view of an optical system of an embodiment when the present invention is applied to a contact / proximity exposure apparatus which is one of semiconductor manufacturing methods. In the figure, 1 is an excimer laser as a light source, and 2 is a light flux conversion member for isotropically converting the light flux of a normally rectangular excimer laser. For example, a beam expander including a cylindrical lens is used. It is configured. 3 is a reflector, 4
Is an optical fiber bundle, and the optical fibers that make up the optical fiber bundle are bundled so that there is a difference of at least the coherence length of the laser light, and the exit surface (light exit surface) of each optical fiber is a divergent lens. Forming a surface. In FIG. 1, only the lens surface is shown for simplicity. 5 is a convergent condenser lens, 6
Is a mask, and 7 is a wafer. The mask 6 and the wafer 7 are in close contact with each other (contact) or are arranged at intervals of several microns to several tens of microns (proximity).

The distance between the lens surface formed on the exit surface of the optical fiber bundle 4 and the condenser lens 5 and the distance between the condenser lens 5 and the mask 6 are made substantially equal to the focal length of the condenser lens 5.

The divergence angle of the laser beam emitted from the excimer laser 1 is a few milliradians, which is very small.
For this reason, the light beam is simply shaped by a diaphragm or isotropically expanded by the light beam conversion means 2 and then reflected by a reflecting mirror 3 and then incident on an optical fiber bundle 4.
In this embodiment, a divergent lens surface is formed on the exit surface of each optical fiber forming the optical fiber bundle 4. As a result, a plurality of second lenses corresponding to the number of lens surfaces are
It forms the next light source. Then, the light fluxes from the plurality of secondary light sources are condensed by the condenser lens 5 so as to be parallel to the optical axis and then irradiate the mask surface 6. With such a configuration, the light beams from the plurality of secondary light sources can be overlapped on the mask 6, which is the surface to be illuminated. As a result, an illumination optical system that achieves uniform illuminance distribution on the illuminated surface is achieved.

Further, in this embodiment, the irradiation light beam on the mask 6 surface is a light beam having a constant spread angle α according to the entire size of the optical fiber bundle having a divergent lens surface on the exit surface. In the configuration of this embodiment, there is no point where the parallel light beam emitted from the excimer laser 1 is condensed in the optical system. For this reason, an illumination optical system has been achieved in which problems such as destruction of optical elements such as coating due to focusing of a laser beam and insulation breakdown of air are improved.

In this embodiment, when an optical fiber bundle having a divergent lens surface on the exit surface is used, the front end shape and the rear end shape of the fiber bundle can be formed in any desired shape. There is an advantage that the shape of the light flux can be optimized without using 2. Further, if the oscillation wavelength width is narrowed by the injection locking method using the excimer laser used as the light source, coherency is improved and so-called speckle harmful to fine pattern exposure may occur. Even in such a case, the length of each fiber of the fiber bundle is configured to have a difference of not less than the coherence length with each other, whereby the coherency of the light flux is reduced, and the illumination optical system in which the speckle is well removed is provided. Has achieved.

The illumination optical system of this embodiment can be applied to a projection method such as a stepper.

Further, in the present embodiment, an illumination optical system having a similar effect can be achieved by using a laser that oscillates at a high output as a light source instead of an excimer laser.

(Effect of the Invention) According to the present invention, when a high-power laser such as an excimer laser is used as a light source in a semiconductor exposure apparatus, it is possible to uniformly illuminate a surface to be irradiated, and further, due to damage to optical elements or dielectric breakdown of air An illumination optical system that prevents energy loss can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an optical system of one embodiment when the present invention is applied to a contact / proximity exposure apparatus, and FIG. 2 is an explanatory diagram of a conventional light integrator. In the figure, 1 is a light source, 2 is a light flux conversion member, 4 is an optical fiber bundle, 5 is a condenser lens, 6 is a mask, and 7 is a wafer.

Claims (1)

[Claims] 1. An illumination optical system having an optical fiber bundle for receiving coherent light from a laser and a condenser lens for directing the light from the optical fiber bundle to a surface to be illuminated, the length of each optical fiber in the optical fiber bundle. And a divergent lens surface is formed on the light emitting surface of each optical fiber of the optical fiber bundle.