News Column

Patent Issued for Alignment of Collector Device in Lithographic Apparatus

May 7, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Klaassen, Michel Fransois Hubert (Eindhoven, NL); Van Schoot, Jan Bernard Plechelmus (Eindhoven, NL); Dutartre, Sylvain (Montigny le Bretonneux, FR), filed on July 15, 2009, was published online on April 22, 2014.

The patent's assignee for patent number 8704199 is ASML Netherlands B.V. (Veldhoven, NL).

News editors obtained the following quote from the background information supplied by the inventors: "The present invention generally relates to the field of lithography tools and, more particularly, to alignment of a collector device in a lithographic apparatus.

"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 that instance, a patterning device, which is alternatively referred to as a mask or a reticle, can 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., 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 (e.g., resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus can include so-called 'steppers,' in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time 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.

"In order to be able to project ever smaller structures onto substrates, it has been proposed to use extreme ultraviolet radiation (EUV) having a wavelength, for example, within a range of about 13-14 nm. It has further been proposed that radiation with a wavelength of less than about 10 nm could be used (e.g., about 6.7 nm or 6.8 nm). In the context of lithography, wavelengths of less than about 10 nm are sometimes referred to as 'beyond EUV' or as 'soft x-rays.'

"Extreme ultraviolet radiation and beyond EUV radiation can be produced using, for example, a plasma. The plasma can be created for example by directing a laser at particles of a suitable material (e.g., tin), or by directing a laser at a stream of a suitable gas or vapor (e.g., Xe gas or Li vapor). The resulting plasma emits EUV (or beyond EUV radiation), which is collected using a collector such as a focusing mirror or a grazing incidence collector.

"The orientation and/or position of the collector will determine the direction in which radiation is directed from the collector (e.g., reflected from the collector). Radiation will need to be accurately directed to different parts of the lithographic apparatus, and it is therefore important for the collector to direct radiation in a specific direction. When a lithographic apparatus is constructed and used for the first time, it may be possible to ensure that the collector directs radiation in such specific direction. However, over time it can be difficult to ensure that the radiation beam is always directed in this specific direction. For instance, movement of parts of the lithographic apparatus (e.g., parts of the radiation source) can shift the direction of radiation. Additionally or alternatively, when parts of the lithographic apparatus are replaced (e.g., for maintenance purposes) even a slight misalignment of replacement parts can shift the direction of radiation. It is therefore desirable to align or re-align a collector of a radiation source and parts of the lithographic apparatus located further along the path of the radiation beam. Since an illuminator (hereinafter also referred to as an 'illumination system' or 'illumination arrangement') is a part of the lithographic apparatus that receives radiation directed by the collector, it is desirable to align or re-align the collector of the radiation source with respect to the illuminator.

"A proposed method of aligning the collector with respect to the illuminator involves attaching light emitting diodes (LEDs) to the collector. A measurement of radiation emitted by the LEDs can be used to determine an orientation (e.g., tilt) and/or position of the collector with respect to a default (or reference) position. However, an issue with this method is that the LEDs may not be robust to withstand a harsh environment surrounding the collector. For instance, high temperatures and prolonged exposure to EUV radiation can quickly damage or destroy the LEDs. Furthermore, the LEDs must be attached to the collector with a high degree of accuracy, with little or no drift in the position of the LEDs over time. Given these conditions, an LED-based implementation is difficult to achieve

"A lithographic apparatus and method for alignment of a collector device with respect to an illuminator device is needed to solve the aforementioned issues."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "According to an embodiment of the present invention, an arrangement for a lithographic apparatus can include the following: a radiation source for providing radiation; a radiation collector for collecting radiation from the radiation source; an illumination system configured to condition radiation collected by the collector and to provide a radiation beam; wherein the lithographic apparatus can include: a detector, the detector being disposed in a fixed positional relationship with a part of the illumination system relative to which the collector is to be aligned, and a region of the collector configured to direct a portion of radiation emanating from the radiation source and traversing the region toward the detector, the detector being arranged to detect a change of a characteristic of the portion of radiation, such a change being indicative of a change in a position or orientation of the collector relative to the part of the illumination system relative to which the collector is to be aligned.

"Radiation collected by the collector can traverse a collector surface having a reflectivity, and the region may be, or may be provided with at least one of the group that includes a surface having an increased reflectivity relative to the reflectivity, a surface having a reduced reflectivity relative to the reflectivity, an aperture, or a pattern.

"The region can have a surface which has a shape (or topography) different from a shape (or topography) of the surface of the collector such as, for example, to re-direct radiation in a different direction. The region can be a part of the collector, or may be attached to the collector.

"The detector can be attached to the illumination system, located on or within the illumination system, attached to a part of the illumination system relative to which the collector is to be aligned, or located on or within a part of the illumination system relative to which the collector is to be aligned.

"The illumination system can be provided with an optical element, where the optical element can include raster elements for dividing a radiation beam impinging on those elements, and wherein the detector is attached to the optical element, or forms part of the optical element.

"The arrangement for the lithographic apparatus can also include a plurality of detectors like aforementioned detector and arranged to function similar to aforementioned detector.

"The region of the collector can be arranged to affect an intensity profile of the radiation directed towards the detector or to affect the direction in which radiation is directed towards the detector. The region of the collector can be arranged to affect the radiation directed towards the detector when the position or orientation of the collector changes with respect to a part of the illumination system relative to which the collector is to be aligned.

"According to another embodiment of the present invention, an arrangement for a lithographic apparatus can include the following: a radiation source for providing radiation; a radiation collector for collecting radiation from the radiation source; an illumination system configured to condition radiation collected by the collector and to provide a radiation beam; wherein the arrangement can include: a detector, the detector being disposed in a fixed positional relationship with a part of the illumination system relative to which the collector is to be aligned; and, a further radiation source arranged to direct corresponding further radiation towards a region of the collector, the region being configured to direct the further radiation towards the detector, the detector being arranged to detect a change of a characteristic of the further radiation reflected from the region, such a change being indicative of a change in the position or orientation of the collector relative to the part of the illumination system with respect to which the collector is to be aligned. More than one region can be provided.

"The further radiation source can be attached to the illumination system, located on or within the illumination system, attached to a part of the illumination system relative to which the collector is to be aligned, or located on or within a part of the illumination system relative to which the collector is to be aligned.

"The lithographic apparatus of the arrangement can further include the following: a support constructed to support a patterning device, the patterning device capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; and, a projection system configured to project the patterned radiation beam onto a target portion of the substrate.

"According to yet another embodiment of the present invention, a method of aligning the collector and the part of the illumination system of the arrangement can include the following: detecting radiation directed from the region with which the collector is provided; determining from that detection whether the collector is aligned with the part of the illumination system; and, if the collector is not aligned with the part of the illumination system, moving the collector or the part of the illuminator. After moving the collector or the part of the illuminator, the method can be repeated."

For additional information on this patent, see: Klaassen, Michel Fransois Hubert; Van Schoot, Jan Bernard Plechelmus; Dutartre, Sylvain. Alignment of Collector Device in Lithographic Apparatus. U.S. Patent Number 8704199, filed July 15, 2009, and published online on April 22, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=76&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=3776&f=G&l=50&co1=AND&d=PTXT&s1=20140422.PD.&OS=ISD/20140422&RS=ISD/20140422

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

Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC


For more stories covering the world of technology, please see HispanicBusiness' Tech Channel



Source: Journal of Engineering


Story Tools






HispanicBusiness.com Facebook Linkedin Twitter RSS Feed Email Alerts & Newsletters