Cross quadrupole double lithography method and apparatus for semiconductor device fabrication using two apertures

Provided is a lithography system operation to include a first aperture or a second aperture. Each of the first and second apertures has two pairs of radiation-transmitting regions where one pair of radiation-transmitting regions are larger than a second pair. For an aperture, each pair of radiation-transmitting regions are on different diametrical axis. In an embodiment, one aperture is used for x-dipole illumination and the second aperture is used for y-dipole illumination.

BACKGROUND

Semiconductor integrated circuit (IC) technology has experienced rapid progress including the continued minimization of feature sizes and the maximization of packing density. The minimization of feature size relies on improvement in photolithography and its ability to print smaller features or critical dimensions (CD). Various techniques have been developed to enhance the resolution of optical lithography. An example of such a technique is off-axis illumination (OAI). OAI illumination may include any radiation that reduces and/or eliminates the “on-axis” (on the optical axis) component of the radiation. For OAI however, the shape and size of the illumination must be optimized for the specific pattern that is to be printed on a substrate. Another RET technique used is double dipole lithography (DDL) or double patterning which can use a strong OAI. DDL requires decomposition of patterns into a vertical pattern and a horizontal pattern, which in turn requires two (double) exposure processes. However, the process window to perform DDL may be limited. Therefore, improvement of one or more of these disadvantages is needed.

SUMMARY

In an embodiment, a lithography system is provided. A first aperture is operable to be incorporated in the lithography system. The first aperture has a first pair of radiation-transmitting regions and a second pair of radiation-transmitting regions. The first pair of radiation-transmitting regions are along a first diametrical axis and the second pair of radiation-transmitting regions are along a second diametrical axis. The first pair of radiation-transmitting regions are larger than the second pair of radiation-transmitting regions. A second aperture is complementary to the first aperture and operable to be incorporated in the lithography system. The second aperture has a third pair of radiation-transmitting regions and a fourth pair of radiation-transmitting regions. The third pair of radiation-transmitting regions are along a third diametrical axis and the fourth pair of radiation-transmitting regions are along a fourth diametrical axis. The third pair of radiation-transmitting regions are larger than the fourth pair of radiation-transmitting regions. In an embodiment, the first and second diametrical axis are substantially perpendicular. In an embodiment, the third and fourth diametrical axis are substantially perpendicular.

In another embodiment, a method of photolithography is provided. In the method, a lithography system is provided. A first aperture is coupled to the lithography system. The first aperture includes a first pair and a second pair of radiation-transmitting regions. The first pair is larger than the second pair. An x-dipole illumination process is performed to form a first pattern on a substrate using the first aperture. A second aperture to the lithography system is coupled to the lithography system. The second aperture includes a third pair and a fourth pair of radiation-transmitting regions. The third pair is larger than the fourth pair. A y-dipole illumination process is performed using the second aperture to form a second pattern on the substrate.

In another embodiment, a lithography system is provided. The system includes a radiation source for providing a radiation energy and an imaging system configured to direct the radiation energy onto a substrate to form an image thereon. The system further includes a first aperture operable to be incorporated with the imaging system. The first aperture has a first pair of radiation-transmitting regions positioned along a first diametrical axis and a second pair of radiation-transmitting regions positioned along a second diametrical axis substantially perpendicular to the first diametrical axis. The first pair of radiation-transmitting regions allow a greater energy of radiation to transmit the first aperture than the second pair of radiation-transmitting regions. The system further includes a second aperture operable to be incorporated with the imaging system. The second aperture has a third pair of radiation-transmitting regions positioned along the first diametrical axis and a fourth pair of radiation-transmitting regions positioned along the second diametrical axis. The fourth pair of radiation-transmitting regions allow a greater energy of radiation to transmit the second aperture than the third pair of radiation-transmitting regions. The first and second apertures are interchangeable in the imaging system.

DETAILED DESCRIPTION

Referring toFIG. 1, in one embodiment, a lithography system100includes a radiation source (or source)110. The radiation source110may be any suitable radiation source. For example, the source110may be a mercury lamp having a wavelength of 436 nm (G-line) or 365 nm (I-line); a Krypton Fluoride (KrF) excimer laser with wavelength of 248 nm; an Argon Fluoride (ArF) excimer laser with a wavelength of 193 nm; a Fluoride (F2) excimer laser with a wavelength of 157 nm; or other radiation sources having a desired wavelength (e.g., below approximately 100 nm). The radiation source may include an optical source selected from the group consisting of ultraviolet (UV) source, deep UV (DUV) source, extreme UV (EUV) source, and X-ray source. The radiation source may alternatively include a particle source selected from the group consisting of electron beam (E-Beam) source, ion beam source, and plasma source.

It is understood that in the above description of radiation sources, each radiation source may have a certain wavelength distribution, or line width, rather than an exact single wavelength. For example, the I-line (e.g., 365 nm) wavelength of the mercury lamp may not be exactly 365 nm, but may be centered at approximately 365 nm with a range of varying wavelengths extending above and below 365 nm. This range may be used to determine a minimum possible line width during photolithography, with less variation from the desired 365 nm wavelength resulting in a thinner line width.

The lithography system100includes an illumination system (e.g., a condenser)120. The illumination system120may comprise a single lens or a lens system having multiple lenses and/or other lens components. For example, the illumination system120may include microlens arrays, shadow masks, and/or other structures designed to aid in directing light from the radiation source110onto a photomask.

During a lithography patterning process, a photomask (also referred to as a mask or a reticle)130may be included in the lithography system100. The photomask130may include a transparent substrate and a patterned absorption layer. The transparent substrate may use fused silica (SiO2) relatively free of defects, such as borosilicate glass and soda-lime glass. The transparent substrate may use calcium fluoride and/or other suitable materials. The patterned absorption layer may be formed using a plurality of processes and a plurality of materials, such as depositing a metal film made with chromium (Cr) and iron oxide, or an inorganic film made with MoSi, ZrSiO, SiN, and/or TiN. A radiation beam may be partially or completely blocked when directed on an absorption region. The absorption layer may be patterned to have one or more openings through which a radiation beam may travel without being absorbed by the absorption layer. The mask may incorporate other resolution enhancement techniques such as phase shift mask (PSM) and/or optical proximity correction (OPC).

The lithography system100includes an objective lens140. The objective lens140may have a single lens element or a plurality of lens elements. Each lens element may include a transparent substrate and may further include a plurality of coating layers. The transparent substrate may be a conventional objective lens, and may be made of fused silica (SiO2), calcium-fluoride (CaF2), lithium fluoride (LiF), barium fluoride (BaF2), or other suitable material. The materials used for each lens element may be chosen based on the wavelength of light used in the lithography process to minimize absorption and scattering. The illumination system120(e.g., lens) and the objective lens140are collectively referred to as an imaging lens. The imaging lens may further include additional components such as an entrance pupil and an exit pupil to form an image defined in the photomask130on a substrate to be patterned.

The lithography system100may further include a substrate stage150capable of securing and moving a substrate in translational and rotational modes such that a target substrate may be aligned with the photomask130.

In the present example, a substrate160may be provided in the lithography system100for receiving a lithography process. The substrate160may be a semiconductor wafer comprising an elementary semiconductor such as crystal silicon, polycrystalline silicon, amorphous silicon, germanium, and diamond, a compound semiconductor such as silicon carbide and gallium arsenic, an alloy semiconductor such as SiGe, GaAsP, AlInAs, AlGaAs, and GaInP, or any combination thereof. The substrate160may have a photosensitive coating layer (e.g., photoresist) formed thereon during the lithography process. An exemplary photoresist includes chemical amplification resist (CAR).

The lithography system100includes an aperture170having a plurality of radiation-transmitting regions (also referred to as illumination poles or poles) to transmit radiation energy from the radiation source110. The aperture170may be positioned between the radiation source110and the condenser120in the lithography system100and/or other possible locations. The radiation-transmitting regions are defined by and surrounded by, an opaque blocking material. Each radiation-transmitting region may be designed to be in various shapes, sizes, and/or angles. Each radiation-transmitting region may be disposed away from the optical axis for off-axis illumination. The plurality of radiation-transmitting regions are defined along radial axis perpendicular to the optical axis. Examples of apertures are described inFIGS. 2a,2b,3a,3b,4a, and4c. The lithography system100may be configurable such that the aperture170may be removed (manually or automatically) and a differently configured aperture placed in the system100.

The lithography system100may also incorporate other techniques and components. For example, a photomask stage135configured for securing and aligning the photomask130. For example, the lithography system may also include components and mechanism to implement an immersion lithography process.

FIG. 2aillustrates an exemplary embodiment of an aperture200. The exemplary aperture may be incorporated in the lithography system100. The aperture200may be an aperture of a set of complementary apertures used in double patterning or DDL illumination. The aperture200includes a plate210being opaque to the radiation so that the radiation illuminated on the plate210will be blocked from transmitting through. The plate210may be made of a metal, metal alloy, or other proper material. The plate210may include proper coating materials. The plate210may have a circular perimeter defining a center to be aligned with the optical axis during a lithography process. A plurality of diametrical axis can be defined crossing the center (e.g., crossing perpendicular to the optical axis) an in the plane of the plate210.

The aperture200further includes a pair of radiation-transmitting regions defined in the plate210. A pair of radiation-transmitting regions220are positioned in a first diametrical axis and on opposite sides of the optical axis. For example, the pair of radiation-transmitting regions220are mirror-images of one another on the optical axis. In an embodiment, the aperture200is used for an x-dipole illumination (e.g., illumination of an x-dipole oriented pattern). In an embodiment, x-dipole oriented patterns include vertical lines. The radiation-transmitting regions may include transparent or translucent materials, an opening, and/or other suitable material.

FIG. 2billustrates an exemplary embodiment of an aperture230. The exemplary aperture may be incorporated in the lithography system100. The aperture230may be an aperture of a set of complementary apertures for use in double patterning or DDL illumination. In an embodiment, the aperture230and the aperture200are complementary apertures. For example, in an embodiment, the aperture200may be positioned in the lithography system100and used to expose a first pattern on the substrate160(e.g., x-dipole illumination). Thereafter, the aperture230may be positioned in the lithography system100and used to expose a second pattern on the substrate160(e.g., y-dipole illumination). The complementary apertures may be used to form an aggregate pattern on a layer of a substrate by providing two illuminations of two decomposed portions of the aggregate pattern.

The aperture230may be substantially similar to the aperture200including the plate210. However, the configuration of radiation-transmitting regions may be different, as illustrated. In the aperture230, a pair of radiation-transmitting regions240are on a second diametrical axis and positioned on opposite sides of the optical axis. For example, the pair of radiation-transmitting regions240are mirror-images of one another on the optical axis. In an embodiment, the aperture200is used for an y-dipole illumination (e.g., illumination of an y-dipole oriented pattern). In an embodiment, a y-dipole oriented pattern includes horizontal lines. The second diametrical axis is substantially perpendicular to the first diametrical axis, illustrated inFIG. 2a. Both diametrical axis are substantially perpendicular to the optical axis of the lithography system.

A system including apertures such as the complementary apertures200and230may include disadvantages. In an embodiment, the apertures200and230may be used in a double dipole lithography system or method. The DDL process provides for a photolithography process exposing a pattern having a first directional orientation (e.g., x-dipole). This is followed by a photolithography process exposing a pattern having a second directional orientation (e.g., y-dipole). Following both exposures, an etch process may be performed to provide the final pattern (e.g., x and y oriented patterns combined) on the substrate. However, the DLL process window of this process may be small. Therefore, the lithography performance many not be well controlled and the optimization of the process is fairly restricted. An example issue is image overlay. There may be a small margin for error in overlaying the first exposure and the second exposure patterns. Additionally, the process may not produce 2D patterns sufficiently. Furthermore, heavy use of optical proximity correction (OPC) for sufficient resolution enhancement may be required. One or more of these disadvantages may be improved by one or more embodiments described below.

Referring now toFIGS. 3aand3billustrated are an embodiment of a complementary pair of apertures300and330. The apertures300and330may be used in a cross quadrupole double lithography (CQDL) process such as described below with reference toFIG. 5. The apertures300and/or330may be used in the lithography system100, for example, as the aperture170.

The aperture300includes a plate310being opaque to the radiation so that the radiation illuminated on the plate310will be blocked from transmitting through. The plate310may be made of a metal, metal alloy, or other proper material. The plate310may include proper coating materials. The plate310may have a circular perimeter defining a center to be aligned with the optical axis during a lithography process. A plurality of diametrical axis can be defined crossing the center (e.g., crossing perpendicular to the optical axis) of the plate310.

The aperture300further includes two pair of radiation-transmitting regions defined in the plate310(e.g., quadrupole). A first pair of radiation-transmitting regions320are positioned in a first diametrical axis and on opposite sides of the optical axis. The first pair of radiation-transmitting regions320may be mirror-images of one another about the optical axis. A second pair of radiation-transmitting regions325are positioned on a second diametrical axis. Each of the radiation-transmitting regions325may be mirror-images of one another about the optical axis. The first and second diametrical axis may be substantially perpendicular (as illustrated); however, numerous other configurations are possible. The first diametrical axis is labeled ‘a’ and the second diametrical axis is labeled ‘b.’

The radiation-transmitting regions320allow a greater amount of radiation to pass the aperture300than the radiation-transmitting regions325. In an embodiment, the radiation-transmitting regions320are larger in size than the radiation-transmitting regions325. The radiation-transmitting regions320and325may include transparent or translucent materials, an opening, and/or other suitable material. In an embodiment, the aperture300is used for an x-dipole illumination (e.g., illumination of an x-dipole oriented pattern). In an embodiment, x-dipole illumination exposes a pattern including vertical features (e.g., lines).

Either or both pairs of radiation-transmitting regions, such as the first pair320or second pair325, may be symmetrically designed for transmittance symmetrical relative to the optical axis. For example, each pair of radiation-transmitting regions may be designed to have a same geometrical shape, have a same size, be equally distanced from the center of the aperture, and have a same transmittance. Each radiation-transmitting region may be provided at any pole angle (e.g., diametrical axis). Each radiation-transmitting region may include a pole width (e.g., open angle) between approximately 0 degrees and 90 degrees.

In an embodiment, the radiation-transmitting regions325are at a pole angle of approximately 90 degrees. In an embodiment, the radiation-transmitting regions325have a width (e.g., open angle) of approximately 25 degrees. In an embodiment, the radiation-transmitting regions320are at a pole angle of approximately 0 degrees. In an embodiment, the radiation-transmitting regions320have a width (e.g., open angle) of approximately 45 degrees.

FIG. 3billustrates an exemplary embodiment of an aperture330. The exemplary aperture may be incorporated in the lithography system100. The aperture330may be an aperture of a set of complementary apertures for use in CQDL illumination processes. In an embodiment, the aperture330and the aperture300are complementary apertures. For example, in an embodiment, the aperture300may be positioned in the lithography system100and used to expose a first pattern on the substrate160(e.g., x-dipole illumination). Thereafter, the aperture330may be positioned in the lithography system100and used to expose a second pattern on the substrate160(e.g., y-dipole illumination). The first and second pattern may be formed on the same layer of a target substrate.

The aperture330includes a plate310which may be substantially similar to the plate310of the aperture300described above. The aperture330further includes two pair of radiation-transmitting regions defined in the plate310(e.g., quadrupole). A first pair of radiation-transmitting regions340are positioned in a first diametrical axis and on opposite sides of the optical axis. The first pair of radiation-transmitting regions340may be mirror-images of one another about the optical axis. A second pair of radiation-transmitting regions345are positioned on a second diametrical axis. Each of the radiation-transmitting regions345may be mirror-images of one another about the optical axis. The first and second diametrical axis may be substantially perpendicular (as illustrated); however, numerous other configurations are possible. The first and second diametrical axis ofFIG. 3bare labeled “c” and “d.” The radiation-transmitting regions340allow a greater amount of radiation to pass the aperture330than the radiation-transmitting regions345. In an embodiment, the radiation-transmitting regions340are larger in size than the radiation-transmitting regions345. The radiation-transmitting regions340and345may include transparent or translucent materials, an opening, and/or other suitable material. In an embodiment, the aperture330is used for an y-dipole illumination (e.g., illumination of an y-dipole oriented pattern). In an embodiment, y-dipole illumination includes exposing a pattern including horizontally oriented features (e.g., lines).

Either or both pairs of radiation-transmitting regions, such as the first pair340or second pair345, may be symmetrically designed for transmittance symmetrical relative to the optical axis. For example, each pair of radiation-transmitting regions may be designed to have a same geometrical shape, have a same size, be equally distanced from the center of the aperture, and have a same transmittance. Each radiation-transmitting region may be provided at any pole angle (e.g., diametrical axis). Each radiation-transmitting may include a pole width (e.g., open angle) between approximately 0 degrees and 90 degrees. In an embodiment, a greater amount of radiation is allowed to be transmitted by increasing the number of radiation-transmitting regions in lieu of or in addition to increasing the size of the radiation-transmitting regions.

In an embodiment, the radiation-transmitting regions340are at a pole angle of approximately 90 degrees. In an embodiment, the radiation-transmitting regions340have a width (e.g., open angle) of approximately 45 degrees. In an embodiment, the radiation-transmitting regions345are at a pole angle of approximately 0 degrees. In an embodiment, the radiation-transmitting regions345have a width (e.g., open angle) of approximately 25 degrees.

During a lithography exposing process (e.g., CQDL process), a first pair of radiation beams illuminates through the first pair of radiation-transmitting regions320and a second pair of radiation beams illuminates through the second pair of radiation-transmitting regions325. The aperture is designed and configured such that the first pair of radiation beams and the second pair of radiation beams are not equal in terms of intensity. During a second exposure of the lithography process (e.g., CQDL process), a first pair of radiation beams illuminates through the first pair of radiation-transmitting regions345and a second pair of radiation beams illuminates through the second pair of radiation-transmitting regions340. It is noted that in the complementary apertures, the radiation transmitting region320and345are substantially aligned (e.g., fall on the same diametrical axis (a=d) relative to an optical axis or pole angle) and the radiation regions325and340are substantially aligned (e.g., fall on the same diametrical axis relative to an optical axis (b=c)).

Referring now toFIGS. 4aand4b, illustrated are additional exemplary embodiment of an aperture400and430that can be incorporated in the lithography system100. The aperture400and430may be complementary apertures used in a CQDL process. For example, the aperture400may provide an x-dipole illumination and the aperture430may provide a y-dipole illumination such that when used together (e.g., two exposure processes) a complete pattern is formed. The apertures400and430may include a plate310, substantially similar to the one illustrated inFIGS. 3aand3b. The aperture400and430are provided to illustrate another embodiment of configuration and shape of the radiation-transmitting regions.

The aperture400includes a first pair of radiation-transmitting regions410and a second pair of radiation-transmitting regions420. The radiation-transmitting regions410lie on a first diametrical axis and the second pair of radiation-transmitting regions420lie on a second diametrical axis. The radiation-transmitting regions410and420may be substantially similar to the radiation-transmitting regions320and325, except that the vary in size, shape, and position (e.g., diametrical axis). The aperture400may be used to expose patterns of a first orientation.

The aperture430includes a first pair of radiation-transmitting regions440and a second pair of radiation-transmitting regions450. The radiation-transmitting regions440lie on a first diametrical axis and the second pair of radiation-transmitting regions450lie on a second diametrical axis. The radiation-transmitting regions440and450may be substantially similar to the radiation-transmitting regions340and345, except that the vary in size, shape, and position (e.g., diametrical axis). The aperture430may be used to expose patterns of a second orientation that differs from the orientation exposed by the aperture400.

It is noted that the diametrical axis of radiation-transmitting regions410and440may be the same or substantially similar. The diametrical axis of radiation-transmitting regions420and450may be the same or substantially similar.

The configuration, size, open angles, and diametrical axis of the radiation-transmitting regions described above are exemplary only and not intended to be limiting in any manner. The configuration, sizes, angles, quantity, or similar features of the radiation-transmitting regions may be varied to provide optimization for the lithography process being performed. Specifically, the configuration, sizes, angles or the like may be varied such as to optimize the sigma provided by the lithography process. One of ordinary skill in the art would recognize varying the configuration, size, or angles of the poles of the exemplary apertures would effect the variability and optimization of sigma values for cross-quadrupole lithography. Variables such as the numerical aperture (NA), wavelength of radiation, properties (e.g., pitch, size) of pattern to be exposed, and the like, would be recognized as applicable to the selection of the configuration, size, shape, or angle of poles.

In an embodiment, a pair of complementary apertures may include a first aperture for x-dipole illumination and a second aperture for y-dipole illumination. In the embodiment, the aperture for x-dipole illumination may include four radiation-transmission regions (four poles or quadrupole) the regions providing the x-dipole being larger in size than the y-dipole. The aperture for the y-dipole illumination may include two radiation-transmission regions (two poles or dipole), providing radiation-transmission regions just in the y-dipole direction (e.g.,FIG. 2b). Other embodiments may include other combinations of quadrupole and dipole apertures.

FIG. 5illustrates a method500to implement cross quadrupole double lithography (CQDL) illumination. The method500may be used to implement CQDL in the lithography system100. The system100may include apertures such as those depicted inFIGS. 3a,3b,4a, and4b. In an embodiment, the method500may be used for a 22 nanometer technology node process; however, numerous other technologies may benefit.

The method begins at step510where a semiconductor substrate is provided. The semiconductor substrate may be coating with a photosensitive material (e.g., photoresist such as a chemical amplification resist (CAR)). The substrate may be substantially similar to the substrate160, described above with reference toFIG. 1.

The method500then proceeds to step520where the lithography system is configured to provide x-dipole illumination. The lithography system may be substantially similar to the lithography system100, described above with reference toFIG. 1. The lithography system may be configured to illuminate a part of a pattern that is finally formed on the substrate (e.g., the pattern is decomposed into a first part). Step520may be performed by configuring the lithography system to include an aperture providing a greater portion of radiation in an x-dipole direction. The aperture may be substantially similar to the aperture400, described above with reference toFIG. 4a.

The method500then proceeds to step530where the illumination, using the lithography system configured in step520, is performed. The illumination may be described as a x-dipole illumination. The x-dipole illumination may include illuminating (patterning or exposing) a set of features of a pattern onto the substrate. In an embodiment, the features patterned are vertical lines.

The method500then proceeds to step540where the lithography system is configured to provide y-dipole illumination. The lithography system may be substantially similar to the lithography system100, described above with reference toFIG. 1. The lithography system may be configured to illuminate a part of a pattern that is finally formed on the substrate (e.g., the pattern is decomposed into a second part). Step540may be performed by configuring the lithography system to include an aperture providing a greater portion of radiation in a y-dipole direction. The aperture may be substantially similar to the aperture430, described above with reference toFIG. 4b.

The method500then proceeds to step550where the illumination, using the lithography system configured in step540, is performed. The illumination may be described as a y-dipole illumination. The y-dipole illumination may include illuminating (patterning or exposing) a set of features of a pattern onto the substrate. In an embodiment, the features patterned are horizontal lines. The illumination may include a strong off-axis illumination. The illumination may provide a pattern on the same photosensitive layer as the pattern of step530. The step550may include further processes such as, baking, developing, rinsing, drying, and/or other suitable processes.

The method500then proceeds to step560where an etch process is performed. The etch process may use the pattern provided by the illumination of step530and step550as a masking element to etch one or more layers of the substrate. The etched pattern is referred to as an aggregate pattern being the pattern resulting from the aggregation of first pattern features (e.g., vertical lines) and second pattern features (e.g., horizontal lines). The etching may include wet etching, plasma etching, reactive ion etching (RIE), and/or other suitable processes.

Advantages of certain embodiments of CQDL including embodiments of the method500and/or embodiments using of the apertures ofFIGS. 3a,3b,4a, or4b, include increasing process margins that allows for increased illumination optimization. Embodiments may allow the process window to be enlarged. The OPC loading on the second pattern to be imaged may be decreased. Furthermore, the overlay window (e.g., process margin) of the first image to be patterned and the second image to be patterned may be increased. In another embodiment, 2D patterns may be more accurately formed. These exemplary advantages related to one or more embodiments described herein, but may not be present in each embodiments discussed herein.

The present disclosure has been described relative to one or more preferred embodiments. Improvements or modifications that become apparent to persons of ordinary skill in the art only after reading this disclosure are deemed within the spirit and scope of the application. It is understood that several modifications, changes and substitutions are intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.