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Patent Issued for Lithographic Apparatus for Transferring Pattern from Patterning Device onto Substrate, and Damping Method

June 4, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Butler, Hans (Best, NL); Oude Nijhuis, Marco Hendrikus Hermanus (Eindhoven, NL), filed on October 25, 2011, was published online on May 20, 2014.

The patent's assignee for patent number 8730451 is ASML Netherlands B.V. (Veldhoven, NL).

News editors obtained the following quote from the background information supplied by the inventors: "A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the 'scanning'-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

"Lithographic apparatus commonly comprise a support frame which is supported by a base via a vibration isolation system, and a projection system arranged to transfer a pattern from a patterning device onto a target portion of a substrate, wherein the projection system comprises a first frame which is spring-supported by the support frame. Spring-supported in this context refers to a resilient support which may alternatively be referred to as spring-mounted, and does not require the actual presence of a spring. Any element having a resilient or spring-like behavior, such as air-mounts may form a spring-support as mentioned in this application.

"The mentioned vibration isolation system is used to isolate the support frame from vibrations in the base and may therefore use elements having a resilient or spring-like behavior. Therefore, a mass can be spring-supported by another mass using a vibration isolation system that is arranged in between the two masses, or in other words, the vibration isolation system may form a spring-support. Vibration isolation systems and spring-support are well known to a person skilled in the art and will therefore not be described in more detail.

"The first frame may interact with other parts of the projection system such as optical elements, e.g. lens element, mirrors, etc. As the optical elements of the projection system are critical in the imaging performance of the lithographic apparatus, it is desired that the interaction between the first frame and the optical elements minimally disturbs the optical elements. However, it has been found that first frame movements cause disturbances of the optical elements. These movements may originate from movement of the support frame, which in turn may be caused by movement of other masses supported by the support frame, so that movement of e.g. a second frame of the projection system excites movement of the first frame. This effect may be worsened by the fact that resonance frequencies of the first frame can be close to other resonance frequencies of masses connected to the first frame via the support frame. As a result, the imaging performance of the lithographic apparatus is not satisfactory.

"Additionally, movement of the first frame may induce deformations of the frame. As the first frame is commonly used to support sensors measuring the optical element positions, these frame deformations may induce position errors in the optical element, again leading to a deteriorated imaging performance of the lithographic apparatus."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "It is desirable to provide an improved lithographic apparatus, in particular an apparatus having an improved imaging performance.

"According to an embodiment of the invention, there is provided a lithographic apparatus comprising: a support frame supported by a base via a vibration isolation system; a projection system arranged to transfer a pattern from a patterning device onto a substrate, wherein the projection system comprises a first frame which is spring-supported by the support frame; and an active damping system configured to damp movement of the first frame, the active damping system comprising: a first sensor system configured to provide a first sensor output representative of absolute movement of the first frame, a first actuator system arranged to apply a force between the first frame and the support frame, and a controller configured to provide a drive signal to the first actuator based on the first sensor output.

"According to another embodiment of the invention, there is provided a method for damping movement of a first frame of a lithographic apparatus, wherein the first frame is spring-supported by a support frame which in turn is supported by a base via a vibration isolation system, the method comprising: a) measuring the absolute movement of the first frame; b) applying a force between the first frame and the support frame based on the measured movement of the first frame."

For additional information on this patent, see: Butler, Hans; Oude Nijhuis, Marco Hendrikus Hermanus. Lithographic Apparatus for Transferring Pattern from Patterning Device onto Substrate, and Damping Method. U.S. Patent Number 8730451, filed October 25, 2011, and published online on May 20, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=61&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=3034&f=G&l=50&co1=AND&d=PTXT&s1=20140520.PD.&OS=ISD/20140520&RS=ISD/20140520

Keywords for this news article include: ASML Netherlands B.V.

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Source: Journal of Engineering


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