System and method for custom-polarized photolithography illumination
In one embodiment, a system for custom-polarized photolithography illumination includes an illuminator operable to generate an illumination pattern of light, a polarizer unit operable to variably polarize the light, and a mask pattern defining photolithographic pattern features in two dimensions. The mask pattern is associated with a mask capable of transmitting at least a portion of the variably polarized light through the mask pattern.
This invention relates generally to photolithography systems and more particularly to a system and method for custom-polarized photolithography illumination.
BACKGROUND OF THE INVENTIONAchieving increasingly smaller line resolutions in semiconductor photolithography requires exposure tool systems with increasingly larger numerical apertures. As the numerical aperture increases, light transmitted through the lens illuminates the semiconductor wafer at Brewster's angle, which prevents light polarized parallel to the plane of incidence from coupling to the photoresistive material on the wafer. Conventional photolithography systems use unpolarized, circularly polarized, or linearly polarized illumination. In the case of unpolarized or circularly polarized illumination, interference of electrical fields exacerbated by Brewster angle effects can lead to a significant reduction in contrast for the resulting photolithographic image, decreasing the resolution of the system. In systems where light is linearly polarized, significant contrast loss may prevent geometry from being printable on the wafer.
SUMMARY OF THE INVENTIONIn one embodiment, a system for custom-polarized photolithography illumination includes an illuminator operable to generate an illumination pattern of light, a polarizer unit operable to variably polarize the light, and a mask pattern defining photolithographic pattern features in two dimensions. The mask pattern is associated with a mask capable of transmitting at least a portion of the variably polarized light through the mask pattern.
In another embodiment, a method is provided for custom-polarized photolithography illumination. The method includes generating an illumination pattern, varying the polarization of the light in the illumination pattern, and transmitting the variably polarized light through a mask pattern associated with a mask and defining photolithographic pattern features in two dimensions.
In yet another embodiment, a system for custom-polarized photolithography illumination includes a means for generating an illumination pattern having linearly polarized light and a means for separating the illumination pattern into a plurality of light beams. The system also includes a means for varying the polarization of the light across the illumination pattern by rotating the polarization of at least a portion of the light to generate tangentially polarized light and a means for transmitting the variably polarized light through a mask pattern associated with a mask and defining photolithographic pattern features in two dimensions. The system further includes a means for directing the variably polarized light through a medium onto at least a portion of a photoresistive material disposed on a wafer and a means for exposing the photosensitive material to at least a portion of the variably polarized light to form a photolithographic pattern.
Technical advantages of one or more embodiments of the present invention may include the ability to vary the polarization of light specific to a desired illumination pattern to be projected onto the wafer. The polarization may be variable with respect to different light beams in the illumination pattern and/or different portions of a single light beam. Another technical advantage of one embodiment of the present invention is to provide for variable polarization of light to provide optimum line and space printing of a photolithographic image, thereby allowing for smaller images to be printed than are possible using conventional photolithography techniques. Still another technical advantage of the present invention is the ability to print photolithographic images in two directions using a single mask during a single exposure to the variably polarized light.
Certain embodiments may provide all, some, or none of these technical advantages. Certain embodiments may provide one or more other technical advantages, one or more of which may be readily apparent to those skilled in the art from the figures, description, and claims included herein.
BRIEF DESCRIPTION OF THE DRAWINGSTo provide a more complete understanding of the present invention and certain features and advantages thereof, reference is made to the following description taken in conjunction with the accompanying drawings, in which:
Illuminator 20 may also include polarizer 24. Polarizer 24 may include any device or combination of devices operable to pass light along a polarization axis associated with polarizer 24 or block light along a direction associated with polarizer 24. In the illustrated example, polarizer 24 is operable to receive light 70 from light source 22 and linearly polarize light 70 to generate linearly polarized light 72. Although polarizer 24 is illustrated as a distinct component from light source 22, in certain embodiments, polarizer 24 may be integral to light source 22, such that light source 22 generates linearly polarized light 72. Illuminator 20 also includes prism system 26. Prism system 26 may comprise any device or combination of devices operable to separate linearly polarized light 72 into one or more light beams 74. In the illustrated embodiment, prism system 26 is capable of separating linearly polarized light 72 into four light beams 74a-74d.
In certain embodiments, polarizer unit 27 may be contained within illuminator 20. In other embodiments, as illustrated in
In certain embodiments, one or more polarization rotators 28 are capable of rotating the polarization at least a portion of linearly polarized light beams 74 to vary the polarization of light across illuminator 20 to create custom-polarized photolithography illumination. For example, in the illustrated embodiment, the polarizations of linearly polarized light beams 74a, 74b are rotated by polarization rotators 28a, 28b, respectively, while linearly polarized light beams 74c, 74d do not have their polarizations rotated. In this manner, the polarization of light 70 may be varied across illuminator 20 specific to the desired illumination pattern to be projected onto wafer 60. Example illumination patterns of variably polarized light are illustrated in
System 10 also includes a mask 30. Mask 30 may comprise any device or combination of devices operable to allow the transmission of at least a portion of linearly polarized light beams 74c, 74d and/or rotated, linearly polarized light beams 76a, 76b through a mask pattern 32 of mask 30. In certain embodiments, mask pattern 32 defines a photolithographic image with features in two dimensions that can be projected onto wafer 60. As an example only, mask pattern 32 may compromise a patterned emulsion of metal film. The light beams 74, 76 that are incident upon mask 30 and that are transmitted through mask pattern 32 are illustrated in
System 10 also includes a lens system 40. Lens system 40 may comprise any device or combination of devices operable to receive and focus light 78 and project the focused light 80 through medium 50 onto wafer 60. System 10 may also include a medium 50 disposed between lens system 40 and wafer 60. In certain embodiments, medium 50 may include air. In other embodiments, when implementing a technique known as immersion lithography, wafer 60 may be immersed in a liquid medium 50, such as water, having an index of refraction greater than one to improve photolithographic image resolution.
In certain embodiments, wafer 60 may comprise a semiconductor wafer. Wafer 60 comprises a thin layer of photoresistive material 65 disposed on a surface of wafer 60. In certain embodiments, photoresistive material 65 may comprise a photosensitive polymeric material disposed on at least a portion of a surface of wafer 60. Exposing photoresistive material 65 to light 80 enables the creation of the photolithographic image on wafer 60. For example, when light 80 is projected onto wafer 60, photoresistive material 65 may undergo wavelength-specific, radiation-sensitive chemical reactions which cause the portions of photoresistive material 65 exposed to light 80 to become either more or less acidic. If the portions of photosensitve material 65 exposed to light 80 become more acidic, photoresistive material 65 is referred to as a “positive photoresist,” while if the portions of photoresistive material 65 becomes less acidic, photoresistive material 65 is referred to as a “negative photoresist.” After exposure to light 80, photoresistive material 65 is exposed to a development solution, such as tetramethyl ammonium hydroxide, which removes either the exposed (positive photoresist) or the unexposed (negative photoresist) photoresistive material 65. For positive photoresist, the portions of photoresistive material 65 exposed to light 80 are washed away by the development solution, leaving a substantially exact copy of mask pattern 32 on the surface of wafer 60. If a negative photoresist is used, the portions of the negative photoresistive material exposed to light 80 remain on the surface of wafer 60 and the development solution removes only the portions of photoresistive material 65 that were unexposed to light 80.
By variably polarizing light 70 specific to the desired illumination pattern to be projected onto wafer 60, thereby creating custom-polarized photolithography illumination, a photolithographic image associated with mask pattern 32 can be projected onto the surface of wafer 60 using a single mask 30 during a single exposure of wafer 60 to light 80, advantageously eliminating the need for multiple masks 30 associated with a particular direction of photolithographic image features and multiple exposures of wafer 60 to light 80. Such custom polarization specific to the desired illumination pattern provides improved image and optimum line and space printing, thereby allowing for smaller images to be printed than are possible using conventional photolithography techniques. The properties of this custom polarization that provide these advantages are described below.
As light 278 is transmitted through lens system 240, it is focused and redirected to emerge as light 280 projected onto wafer 260. The structure and function of lens system 240 and wafer 260 can be substantially similar to the structure and function of lens system 40 and wafer 60, respectively, of
As light 378 is transmitted through lens system 240, it is focused and redirected to emerge as light 380 projected onto wafer 260. Light 380a comprises an associated electrical field 394a parallel to the direction of propagation light 390a, while light 380b comprises an associated electrical field 394b parallel to the direction of propagation of light 380b. In the illustrated example, electrical fields 394a, 394b, associated with light 380a, 380b are parallel to each other. Because the electrical fields 394 are parallel to each other, they act cumulatively to increase the contrast of the photolithographic image projected onto wafer 260. Therefore, the image deterioration that occurs when the electrical fields at least partially cancel each other, as illustrated in
In certain embodiments, the ability to vary the polarization of the light incident upon the mask, such as mask 30, specific to the illumination pattern, enables photolithographic image features to be printed in two dimensions without a loss of contrast that usually occurs due to electrical field interference between different light beams.
The polarizations of light beam portions 442a-442h may be rotated using appropriate polarization rotators 28 such that symmetrically opposed light beam portions have the same direction of polarization. For example, linearly polarized light beam portions 442c, 442g have linear polarizations 444c, 444g, which are orientated in the same direction. In the illustrated embodiment, light beam portions 442c, 442g are not transmitted through polarization rotators 28. Light beam portions 442a, 442e comprise rotated, linear polarizations 444a, 444e resulting from light beam portions 442a, 442e being transmitted through polarization rotators 28. Illumination pattern 440 also comprises light beam portions 442b, 442d, 442f, and 442h which have rotated, linear polarizations 444b, 444d, 444f, and 444h, respectively, resulting from light beam portions 442b, 442d, 442f, and 442h being transmitted through additional polarization rotators 28.
Although specific examples of custom polarizations are described above, any custom polarization of one or more light beams, or portions thereof, of an illumination pattern may be variably polarized (and not limited to tangential polarization) such that electrical field interference among corresponding light beams or light beam portions is substantially reduced, thereby improving the quality of the projected image.
Although an example method is illustrated, the present invention contemplates two or more steps taking place substantially simultaneously or in a different order. In addition, the present invention contemplates using methods with additional steps, fewer steps, or different steps, so long as the steps remain appropriate for custom-polarized photolithographic illumination.
Although the present invention has been described with several embodiments, a multitude of changes, substitutions, variations, alterations, and modifications may be suggested to one skilled in the art, as it is intended that the invention encompass all such changes, substitutions, variations, alterations, and modifications as fall within the spirit and scope of the appended claims.
Claims
1-20. (canceled)
21. A method for patterning photoresist on a semiconductor wafer, comprising:
- forming a photoresist layer on a semiconductor wafer;
- generating an illumination pattern comprising a quadrupole illumination pattern having a first and second set of symmetrically opposed light beams, the method further comprising rotating the polarization of at least a portion of the illumination pattern such that the first set of symmetrically opposed light beams have polarizations in the same direction and the second set of symmetrically opposed light beams have polarizations in the same direction, wherein the polarization direction of the first set of light beams is perpendicular to the polarization direction of the second set of light beams; and
- transmitting the illumination through a mask pattern associated with a mask unto said photoresist layer to define a photolithographic pattern in said photoresist.
22. The method of claim 21 further comprising varying the polarization of a different portion of the light using a different polarization rotator.
23. The method of claim 21 wherein at least one polarization rotator comprises a half-wave plate.
24. The method of claim 21 wherein the illumination pattern comprises a dipole illumination pattern having two symmetrically opposed light beams, the method further comprising rotating the polarization of at least a portion of the illumination pattern such that the two symmetrically opposed light beams have polarizations in the same direction.
25. The method of claim 21 further comprising developing said photoresist and processing said semiconductor wafer.
Type: Application
Filed: Jun 24, 2005
Publication Date: Oct 27, 2005
Inventor: James Blatchford (Richardson, TX)
Application Number: 11/166,006