KR100496078B1 - Lighting system used in scanning lithography - Google Patents

Abstract

Illumination for scanning lithography systems used in the manufacture of semiconductor devices, having multiplex arrays or multiple image arrays resulting in pattern noise reduced by spatial frequency modulation multiplex arrays or by frequency modulating the pulse rate of a pulsed laser source System is disclosed. A pulsed laser source is used to illuminate a reticle containing thereon a pattern to be reproduced on a semiconductor. Lighting systems that use multiplex arrays or multiple image arrays to achieve large-scale uniformity of lighting slots or fields introduce fixed pattern noise that results in microscopic inhomogeneities or undesirable image characteristics that result in undesirable pattern noise. . The undesirable effect of the pattern noise is eliminated or substantially eliminated by spatially modulating the multiplex array in the scanning direction such that the periodic pattern has a linear magnification according to the positioning. In another embodiment, the pulse rate of the pulsed laser source is frequency modulated. The present invention improves linewidth control, linewidth variation, and edge roughness.

Description

Lighting system used in scanning lithography

Related application

This application claims the privilege of U.S. Provisional Application No. 60 / 031,746, filed November 25, 1996.

Field of invention

The present invention relates generally to lighting systems used for the manufacture of semiconductor devices in photolithography techniques, and more particularly to lighting systems using multiplex arrays or multiple image optics.

Background of the Invention

In the manufacture of semiconductor devices, photolithographic techniques are used to reproduce an image of a reticle on a semiconductor wafer coated with a photosensitive resist. The reticle includes a pattern in which an image is formed on a wafer to which photosensitive resist is applied. After a series of exposure and subsequent processing steps, a semiconductor device including a circuit pattern on top is manufactured. An illumination system is used to provide a flux of electromagnetic radiation for projecting an image of the reticle onto a semiconductor wafer. The image of the reticle is formed by an optical projection system that collects the electromagnetic radiation after passing through the reticle and projects the image of the reticle onto a semiconductor wafer coated with a photosensitive resist. As semiconductor device manufacturing techniques improve, the demand for each component of the photolithography system used to manufacture semiconductor devices is further increased. This includes the lighting system used to illuminate the reticle. There are many prior art lighting systems that improve the uniformity of illumination and minimize the loss of light. One such lighting system is disclosed in US Pat. No. 5,300,971, incorporated herein by reference and entitled "Projection Exposure Apparatus" and issued under the name Kudo of April 5, 1994. The patent describes an illumination system having a pulsed light source with a rotating deflection prism used to direct pulsed light to a fly's eye lens separate from the optical axis. The condenser lens is then used to focus light from the fly's eye lens to illuminate the reticle. Another lighting system is incorporated herein by reference in US Pat. No. 5,296,892, entitled "Illuminating Apparatus and Projection Exposure Apparatus Provided with Such Illumination Apparatus," published in the name of Mori on March 22, 1994. The patent discloses an illumination system having an optical integrator or fly's eye lens placed before the condenser lens. The optical integrator or fly's eye lens is designed to be arranged such that the numerical aperture on the radiation side of the illumination system can be varied. Another lighting system is incorporated herein by reference in US Pat. No. 5,245,384, entitled "Illuminating Optical Apparatus and Exposure Apparatus Having The Same," published in Mori on Sep. 14, 1993. The patent discloses an illumination system having an afocal zoom optical system disposed before an optical integrator or fly's eye lens to vary the size of a plurality of auxiliary light sources. Another lighting system, which is incorporated herein by reference, is disclosed in US Pat. No. 5,237,367, entitled “Illuminating Optical System and Exposure Apparatus Utilizing The same,” published in Kudo on August 17, 1993. The patent discloses an illumination system having a first optical integrator or fly eye lens and a first condenser lens followed by a second optical integrator or fly eye lens and a second condenser lens. The second condenser lens then provides illumination to the reticle. The first optical integrator or fly eye lens and the first condenser lens have a variable focal length. Another lighting system is incorporated herein by reference in U.S. Patent No. 4,939,630, entitled "Illumination Optical Apparatus" and published under the name of kukuchi and its colleagues dated July 3, 1990. The patent discloses an illumination system having a second optical integrator following a first optical integrator or means for forming a plurality of light source images, or a condenser lens for directing illumination on a reticle after a third light source forming means. . Another lighting system is disclosed in US Pat. No. 5,534,970, issued July 9, 1996, in the name of Nakashima and its colleagues, which is incorporated herein by reference. The patent discloses an illumination system that uses a scanning pivot mirror to scan for interference fringes to achieve the desired illumination in a scanning exposure apparatus. In addition, moving diffusers and other established techniques have been used in the past in an effort to achieve more desirable lighting characteristics.

While many of these prior art lighting systems have provided improved lighting for specific applications, still light source scans are available that can be easily manufactured, provide uniform illumination, and have coherence properties such as lasers. When used in lithographic systems, there is a need to provide an illumination system that eliminates or reduces pattern noise effects that may occur in such prior art illumination systems.

Accordingly, it is an object of the present invention to reduce the pattern noise effects caused by using multiplex arrays or multiple image optics used in lighting systems, in particular lighting systems using pulsed laser sources.

Summary of the Invention

The present invention can be used in lighting systems using multiplex arrays or multiple image optics as part of an illumination system that forms a scanning lithography system used to project a portion of a reticle onto a photosensitive resist coated wafer. An illumination system according to the invention may include an illumination source such as a pulsed laser, and an optical component such as a beam conditioner, (at least one) multiplex array or multiple image optics, a condenser lens, and a relay. The spatial frequency modulator is combined with the (at least one) multiplex array or multiple image optics. The spatial frequency modulator effectively moves the multiplex array or multiple image optics in the spatial direction of the scanning direction of the scanning lithography system. The multiplex array can also have a pattern that is spatial frequency modulated to a scanning state. Such modulation is sufficient for the periodic pattern to have a form of linear magnification modulation with position. In another embodiment of the invention, the pulse rate of the laser is frequency modulated. The frequency modulation range and ratio are chosen to have several cycles during only one scan.

These and other objects, advantages, and features will become apparent from the following detailed description.

Example

1 illustrates one embodiment of the present invention. The illumination source 10 directs electromagnetic radiation to the beam conditioner 12. The term "light source" is used to mean any electron emission source regardless of wavelength. Thus, the illumination source 10 may be a laser having a wavelength that is not in the visible region. In addition, the illumination source may be a pulsed laser or a continuous wave laser. The beam conditioner 12 enlarges or modifies the electromagnetic radiation beam from the illumination source 10. This may be accomplished by a beam expander, such as a refractive optical system, or a reflective optical system. The state-controlled electromagnetic radiation goes directly to the multiplex array or multiple image optics 14. The multiplex array or multiple image optical element 14 may be a microlens array composed of a plurality of refractive lens elements or one diffractive optical element. Multiple image optics 14 direct light to condensing lens 16. In the case of a scanning optical lithography system, the condensing lens 16 is preferably an anamorphic condensing lens in that a rectangular slit illumination field is formed by the condensing lens 16. The condenser lens 16 collects light from the multiple image optics 14 and directs it to the array optics 18. The array optics 18 may not be used in any lighting system. However, the use of the array optical element 18 is hereby incorporated by reference and pointed out in US Patent Application No. 08 / 449,301, filed May 24, 1995, entitled "Hybrid Illumination System for use in Photolithography". It may be desirable in some applications as described. The illumination plate 20 is formed after the condenser lens 16 and any array optics 18. The relay 22 is simply used to conjugate the lighting plate 20 with the reticle 24. The image of the reticle 24 is projected onto the wafer 28 by projection optics 26. Reticle 24 is disposed on reticle stage 32 and moved by reticle stage 32. The stage controller 34 controls the movement of the reticle stage 24 and the wafer stage 30. Movement of the reticle stage 24 and the wafer stage 30 is generally synchronized with the magnification of the system. The modulator 36 is connected to a multiplex array or multiple image optics 14. The modulator 36 spatially modulates the multiplex array or multiple image optics in a scanning state such that the periodic pattern has a linear magnification with position. When such a pattern is multi-printed in the scanning process, such a pattern can be formed without aliasing. The present invention is not limited to the exemplary lighting system described, but is multiplexed to control large scale uniformity, to control the numerical aperture of the lighting system, or to control the partial coherence of the lithographic system. It should be understood that it can be applied to any lighting system using arrays or multiple image optics. Such a system may have any number of residual patterns (or standard illumination variations) by having multiple spatial displacement illumination “patches” in small amounts so that multiple displacement fields overlap and multiple pattern patterns reach average lines over multiple exposures. Causes coherence to be eliminated

2 illustrates another embodiment of the present invention. In FIG. 2, the pulsed laser source 110 sequentially transmits electromagnetic radiation to the beam state conditioner 12, the multiplex array or multiple image optics 14, the condenser lens 16, and the array optics 18. To form an illumination plate 20. The lighting plate 20 is conjugated by the relay 22 to illuminate the reticle 24. The image of the reticle 24 is projected on the wafer 28 to which the photosensitive resist is applied by the projection optics 26. The position of the reticle 24 is controlled by the reticle stage 32, the wafer stage 20, and the stage controller 34. The embodiment illustrated in FIG. 2 is similar to the embodiment illustrated in FIG. 1, but a frequency modulator 136 is coupled to the pulse laser source 110. The frequency modulator 136 modulates the pulse rate of the pulse laser source 110. The frequency modulation range and frequency modulation rate are selected such that several cycles of the frequency modulation range can be equipped during a scan time or with only one scan. This causes no aliasing to occur. Each pulse is periodic space modulated in this regard. If the pulse rate varies over a particular exposure time, these patterns do not overlap in a certain space, leading to an average line. That is, as the pulse rate changes, the patterns have different positions to move relative to the exposed wafer to be scanned to prevent any overlapping and, consequently, any cumulative effect that may degrade the formation of the image.

3 more clearly illustrates a scanning illumination slot or field formed in accordance with the present invention. Reticle frame 38 holds reticle 24. The rectangular illumination slot or field 40 is formed to be W wide. The illumination slot or field 40 is scanned in the longitudinal direction across the reticle 24, in the X direction indicated by arrow 41. Typically, the reticle frame 38 is attached to an unillustrated reticle stage to move the reticle 24 relative to the illumination slot or field 40.

4 graphically illustrates a profile of illumination intensity across the width of the illumination slot or field. Waveform 42 represents the illumination intensity in the width or X direction. Although the illumination intensity appears to be relatively uniform, there are often minor nonuniformities as needed.

FIG. 5 is an enlarged cross sectional view of a portion of the waveform 42 illustrated in FIG. 4 showing a slight non-uniformity of the illumination intensity. Waveform 44 illustrates the unique spatial non-uniformity from the lower limit set by the spatial frequency pass band of the projection optics being used. Higher spatial frequencies may exist, but are generally out of interest. 0.2 μm is typical for high numerical apertures, but 0.60 in systems where the magnification is scaled down as needed. Such minor nonuniformities are undesirable because they often lead to image formation problems such as lack of linewidth control, linewidth variations, edge roughness, and other phenomena known to those skilled in the art.

FIG. 6 graphically illustrates the intensity as a function of the frequency of the minute non-uniformity illustrated in FIG. 5. Peak waveform portion 46 represents a fixed or periodic component and waveform portion 48 represents an arbitrary pattern. It is based on pulsed laser sources, but is used in continuous oscillating gas sources with some limitations. In a scanning lithography system, any component illustrated by the waveform portion 48 reaches an average line as the change in noise or illumination microscopic nonuniformity is reduced by the square root of the number of pulses used per unit exposure position. The periodic complex component may or may not be reduced in size due to aliasing between scan rate, pulse rate, and pattern frequency.

FIG. 7 graphically illustrates a first pulse pattern represented by waveform 52 and a second pulse pattern represented by waveform 54. In FIG. 7 an unfavorable phase aliasing state is illustrated. Since the occurrence of such an aliasing portion is complicated, a look up table that does not operate the scanning stage with a predetermined velocity component is inconvenient and unreliable. The present invention eliminates aliasing and consequently ensures higher reliability of the lithographic system. Since any small part of the scan field can be exposed from multiple pulses, such periodic composite components may overlap and not reach an average line. This impairs exposure and the quality of the image.

FIG. 8 schematically illustrates a multiplex array with a spatial frequency modulation pattern that may be used at the location of the multiplex array 14 and / or 18 illustrated in FIGS. 1 and 2. However, when the multiplex array illustrated in FIG. 8 is used in the position of the multiplex array 14 and / or 18, it is generally not necessary that the modulator 36 illustrated in FIG. 1 and the frequency modulator illustrated in FIG. It must be understood. The standard pattern or component 46 illustrated in FIG. 6 is generally the result of the periodic structure of the multiplex array. By providing a spatial frequency modulation pattern composed of elements on the multiplex array of the present invention, any resulting pattern has a different linear magnification for positioning. That is, the scan direction intervals between the waveforms of the resultant pattern are not equal. 9 is a graph illustrating inequality intervals between adjacent waveforms forming the resultant pattern. When such a pattern is multi-printed in the scanning process, the patterns may be formed so that aliasing does not occur. As illustrated in FIG. 8, the multiplex array has elements consisting of four different cross sections 60, 62, 64, 66. Each cross section 60, 62, 64, 66 is composed of elements different from adjacent cross sections. For example, cross section 60 may be composed of elements having dimensions of 100 units, cross section 62 may be composed of elements having dimensions of 110 units, and cross section 64 may be composed of 120 units of dimensions. It may be composed of elements having dimensions, and cross section 66 may be composed of elements having dimensions of 130 units. The units are provided only to indicate relative sizes and may be any typical unit dimensions for a multiplex array. Thus, the multiplex array has a spatial frequency modulation pattern. This spatial frequency modulation pattern is only needed to be modulated in the scanning direction. Arrow 76 indicates the scanning direction. In addition, the spatial frequency modulation pattern illustrated in FIG. 8 in cross sections 60, 62, 64, 66 is only intended to schematically represent a multiplex array. The elements 68, 70, 72, 74 are schematically illustrated as different circular sizes, but may be any shape or pattern commonly used for one element of the multiplex array. The elements 68, 70, 72, 74 extend along the entire length of the respective cross sections 60, 62, 64, 66. In addition, although only four cross sections 60, 62, 64, 66 are illustrated in FIG. 8, there may be multiple cross sections. Also, the cross sections can be repeated. That is, a group of cross sections can be repeated to form multiple circles in a single multiplex array. FIG. 10 illustrates a form of spatial frequency modulation of the multiplex array. In FIG. 10, the multiplex array is formed with repeating longitudinal sections 80, 82, 84. Each of the cross sections 80, 82, 84 includes elements 86, 88, 90 each having a different dimension. The longitudinal sections 80, 82, 84 form one cycle of the pattern repeated in the scanning direction. Therefore, three cycles are illustrated. The scanning direction is preferably substantially perpendicular to the length dimension of the cross sections 80, 82, 84.

Thus, the present invention helps to eliminate pattern noise effects in lighting systems using multiplex arrays or multiple image arrays. As a result, the present invention better provides illumination for use in a scanning lithography system to increase linewidth control, edge roughness, and other image characteristics.

In addition, while the invention has been illustrated with reference to a specific lighting system, it should be understood that the invention can be applied to other lighting systems having multiplex arrays or multiple image arrays. Therefore, it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention.

An advantage of the present invention is that it can be used to improve most lighting systems using multiplex arrays or multiple image optics.

One feature of the present invention is that the modulator is combined with a multiplex array or multiple image optics.

Another feature of the invention is that the multiplex array has a pattern that is spatial frequency modulated in the scan direction.

Another feature of the invention is that the pulse rate of the laser source is frequency modulated.

1 schematically illustrates one embodiment of the invention;

2 schematically illustrates another embodiment of the invention.

3 is a perspective view of a reticle illustrating a lighting slot or field.

4 is a graph illustrating the contour of intensity along the width of an illumination slot or field.

FIG. 5 is an enlarged graph illustrating some of the contours of intensity illustrated in FIG. 4. FIG.

6 is a power spectral graph illustrating a standard pattern and random noise.

7 is a graph illustrating a first laser pulse pattern and a second laser pulse pattern.

8 is a schematic illustration of a haltplex array with a spatial frequency modulation pattern.

9 is a graph illustrating a pattern with unequal spacing.

10 is a schematic illustration of a multiplex array with another form of spatial frequency modulation pattern.

Claims (15)

In illumination systems used in scanning lithography, An illumination source providing electromagnetic radiation; An optical system for receiving electromagnetic radiation from the illumination source, the optical system forming an illumination slot for projecting an image of a reticle onto a photocoated resist coated wafer, the illumination slot scanning the reticle in a scanning direction; And A multiplex array formed as part of the optical system, the multiplex array having a spatial frequency modulation pattern of elements that change in the scanning direction while providing magnification according to position; An illumination system used in scanning lithography which prevents aliasing due to periodic complex components and reduces pattern noise generated by the multiplex array. The method of claim 1, And wherein said illumination source is a pulsed source. The method of claim 1, And wherein said illumination source is coherent. The method of claim 1, The complex component resulting from the multiplex array is multiplexed upon scanning so that aliasing does not occur. In illumination systems used in scanning lithography, A pulsed illumination source providing electromagnetic radiation and having a pulse rate; An optical system for receiving the electromagnetic radiation from the pulsed illumination source, the optical system forming an illumination slot for projecting an image of the reticle onto a photosensitive resist coated wafer, the optical slot scanning the reticle in a scanning direction ; And A multiplex array formed as part of the optical system, the multiplex array having a spatial frequency modulated periodic pattern of elements varying in the scanning direction and providing linear magnification with position; Lighting system used in scanning lithography, characterized in that the pattern noise is reduced. The method of claim 5, And wherein said multiplex array is formed of a plurality of sections, each adjacent section of said plurality of sections being formed of one element having a different dimension. The method of claim 6, And wherein each of the plurality of cross-sections extends in the longitudinal direction along the length of the multiplex array. The method of claim 7, wherein And the length of the multiplex array is perpendicular to the scanning direction. In illumination systems used in scanning lithography, A pulsed illumination source providing electromagnetic radiation and having a pulse rate; An optical system for receiving the electromagnetic radiation from the pulsed illumination source, the optical system forming an illumination slot for projecting an image of the reticle onto a photosensitive resist coated wafer, the optical slot scanning the reticle in a scanning direction ; And A multiplex array formed as part of the optical system, the multiplex array having a spatial frequency modulation pattern in a scanning direction; The multiplex array is formed of a plurality of cross sections, each adjacent cross section of the plurality of cross sections is formed of one element having a different dimension, and each of the plurality of cross sections extends in the longitudinal direction along the length of the multiplex array. Wherein the length of the multiplex array is perpendicular to the scanning direction and the different dimensions increase from one end to the other end of the multiplex array, Lighting system used in scanning lithography, characterized in that the pattern noise is reduced. The method of claim 9, And the plurality of cross sections are repeated to form a plurality of circles. In illumination systems used in scanning lithography, A pulsed illumination source providing electromagnetic radiation and having a pulse rate; An optical system for receiving the electromagnetic radiation from the pulsed illumination source, the optical system forming an illumination slot for projecting an image of the reticle onto a photosensitive resist coated wafer, wherein the illumination slot scans the reticle in the scanning direction. system; A multiplex array formed as part of the optical system; And A modulator coupled to the illumination source, the modulator having a frequency modulation range and a frequency modulation rate such that the pulse rate of the pulsed illumination source is frequency modulated, such that at least one cycle of the frequency modulation range is implemented in a single scan of the reticle; Include, And the pattern noise generated by the multiplex array is reduced. The method of claim 9, At least 30 pulses are used to expose a given portion of the wafer, wherein the illumination system is used in scanning lithography. A pulsed laser illumination source having a pulse rate; Coupled to the pulsed laser illumination source, frequency modulating the pulse rate of the pulsed laser illumination source and having a frequency modulation range and a frequency modulation rate such that at least one cycle of the frequency modulation range is implemented in a single scan of one reticle. Frequency modulator; A beam conditioner positioned to receive electromagnetic radiation from the pulsed laser illumination source; A multiplex array positioned to receive electromagnetic radiation from the beam conditioner; A condenser lens positioned to receive electromagnetic radiation from the multiplex array; An illumination plate disposed after the condenser lens and having a rectangular illumination slot formed thereon; A relay for conjugating a rectangular lighting slot illuminating a portion of the reticle with one reticle; Projection optics for forming an image of the reticle on a photosensitive resist coated wafer; A reticle stage coupled with the reticle; A wafer stage coupled with the wafer; And A stage control coupled to the reticle stage and the wafer stage, the stage control controlling the movement of the wafer stage and the reticle such that the reticle and the wafer are synchronously scanned to expose a portion of the wafer with an image of the reticle And a stage control unit. In the illumination system used in a scanning lithography system, At least 30 pulses are used to expose a given portion of the wafer. The method of claim 1, And said magnification is linear.

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