Optical: systems and elements – Lens – Telecentric system
Reexamination Certificate
2000-02-16
2001-10-23
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Lens
Telecentric system
C359S619000, C359S676000
Reexamination Certificate
active
06307682
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to photolithographic illumination systems.
2. Related Art
Photolithography (also called microlithography) is a semiconductor device fabrication technology. Photolithography uses ultraviolet or visible light to generate fine patterns in a semiconductor device design. Many types of semiconductor devices, such as diodes, transistors, and integrated circuits, can be fabricated using photolithographic techniques. Exposure systems or tools are used to implement photolithographic techniques, such as etching, in semiconductor fabrication. An exposure system typically includes an illumination system, a reticle (also called a mask) containing a circuit pattern, a projection system, and a wafer alignment stage for aligning a photosensitive resist covered semiconductor wafer. The illumination system illuminates a region of the reticle with a preferably rectangular slot illumination field. The projection system projects an image of the illuminated region of the reticle circuit pattern onto the wafer.
As semiconductor device manufacturing technology advances, there are ever increasing demands on each component of the photolithography system used to manufacture the semiconductor device. This includes the illumination system used to illuminate the reticle. For example, there is a need to illuminate the reticle with an illumination field having uniform irradiance. In step-and-scan photolithography, there is also a need to continuously vary a size of the illumination field in a direction perpendicular to a wafer scan direction, so that the size of the illumination field can be tailored to different applications. One factor often limiting wafer processing throughput is the amount of energy available from the illumination system. Therefor, there is a need to vary the size of the illumination field without a loss of energy.
As the size of the illumination field is varied as mentioned above, it is important to preserve the angular distribution and characteristics of the illumination field at the reticle. To achieve this goal, the illumination system must maintain telecentric illumination at a substantially fixed numerical aperture at the reticle as the size of the illumination field is varied. Some illumination systems include an array or diffractive scattering optical element positioned before the reticle. The scattering optical element produces a desired angular light distribution that is subsequently imaged or relayed to the reticle. In such an illumination system, there is a need to maintain telecentric illumination at a substantially fixed numerical aperture at the scattering optical element, and correspondingly, at the reticle as the size of the illumination field is varied.
A standard zoom lens can vary the size of the illumination field. However, in the standard zoom lens, image magnification, and correspondingly the size of the illumination field, is inversely proportional to angular magnification. Thus, a standard zoom lens that increases the size of an image by a factor M, disadvantageously decreases the numerical aperture by a factor 1/M, and fails to preserve the angular distribution of the illumination field.
Therefor, there is a need to vary the size of the illumination field (that is, magnify the illumination field) without a loss of energy, and to maintain telecentric illumination at a substantially fixed numerical aperture as the size of the illumination field is varied.
SUMMARY OF THE INVENTION
The present invention is directed to an illumination system for varying the size of an illumination field incident upon a reticle and/or a scattering optical element while maintaining telecentric illumination at a substantially fixed numerical aperture. The illumination field is subsequently imaged to a reticle in a photolithographic process. In one embodiment, the illumination system includes, in series along an optical axis of the illumination system, an optical source, a beam conditioner, a first optical integrator, a first or input collimating lens, a unique zoom array integrator (ZAI), a second or output collimating lens, the optical scattering element, and the reticle. The ZAI includes an assembly of fixed and moveable lens components arranged to vary the size of the illumination field throughout a zoom range of the ZAI while maintaining telecentric illumination at a substantially fixed numerical aperture. Illumination telecentricity and substantially fixed numerical apertures are maintained at both the scattering optical element and the reticle throughout the zoom range.
In one example, the ZAI includes two fixed lens arrays spaced apart from each other along an optical axis of the ZAI. The two fixed lens arrays are arranged in a fly's eye configuration and include optical power in an X-direction. The two fixed lens arrays are referred to as X-arrays. The ZAI also includes a fixed front lens array and three moveable lens arrays that are moveable along the optical axis between the two fixed arrays. The fixed front lens array and the three moveable lens arrays have optical power in a Y-direction perpendicular to the X-direction, and are referred to as Y-arrays. Each of the moveable Y-arrays is moved along the optical axis to vary a focal length and thus magnification of the ZAI in the Y-direction. This correspondingly varies the size of the illumination field in the Y-direction while maintaining telecentric illumination and substantially fixed numerical apertures at the scattering optical element and the reticle. The fixed front Y-array prevents light under- or over-filling at an input to the ZAI, to thereby reduce a variation in an illumination uniformity at the scattering optical element and the reticle.
FEATURES AND ADVANTAGES
The system of the present invention advantageously produces an illumination field having uniform irradiance and that is suitable for use in photolithography.
The system of the present invention advantageously varies the size of the illumination field at a reticle and/or scattering optical element and maintains the angular properties of the illumination field as the size of the illumination field is varied. To achieve this, the system of the present invention maintains telecentric illumination at a substantially fixed numerical aperture while the system varies the size of the illumination field.
The system of the present invention advantageously varies or zooms the size of the illumination field throughout a zoom range without reducing energy efficiency, that is, without a loss of energy.
According to one feature of the present invention, the system advantageously uses easily manufactured and readily/commercially available lens components, and includes a minimal number of moving lens components.
The system of the present invention can either continuously or discretely vary the size of the illumination field throughout the zoom range. In other words, the size of the illumination field represents a continuum of sizes throughout the zoom range.
Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.
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patent: 5724122 (1998-03-01), Oskotsky
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International Search Report for International Application No. PCT/US00/03896 dated Oct. 12, 2000.
Hoffman Jeffrey M.
Kunick Joseph M.
Oskotsky Mark
Ryzhikov Lev
Silicon Valley Group Inc.
Sterne Kessler Goldstein & Fox P.L.L.C.
Sugarman Scott J.
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