The patent's assignee is
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 or part of a substrate. A lithographic apparatus may be used, for example, in the manufacture of integrated circuits (ICs), flat panel displays and other devices or structures having fine features. In a conventional lithographic apparatus, a patterning device, which may be referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of the IC, flat panel display, or other device). This pattern may transferred on (part of) the substrate (e.g. silicon wafer or a glass plate), e.g. via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate.
"Instead of a circuit pattern, the patterning device may be used to generate other patterns, for example a color filter pattern, or a matrix of dots. Instead of a conventional mask, the patterning device may comprise a patterning array that comprises an array of individually controllable elements that generate the circuit or other applicable pattern. An advantage of such a 'maskless' system compared to a conventional mask-based system is that the pattern can be provided and/or changed more quickly and for less cost.
"Thus, a maskless system includes a programmable patterning device (e.g., a spatial light modulator, a contrast device, etc.). The programmable patterning device is programmed (e.g., electronically or optically) to form the desired patterned beam using the array of individually controllable elements. Types of programmable patterning devices include micro-mirror arrays, liquid crystal display (LCD) arrays, grating light valve arrays, arrays of self-emissive contrast devices and the like."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "In a lithographic process, a proportion of the radiation projected onto a resist layer formed on a substrate may be redirected (e.g., reflected) back from the resist layer. For example, some radiation may reflect from the lower surface of the resist, namely at the interface between the resist and the substrate or another layer interposed between the resist and the substrate. The superposition of the incident radiation and the redirected radiation may result in standing waves within the resist layer. This may cause one or more problems.
"For example, the intensity of a standing wave at the surface of the resist layer, and therefore the intensity of the radiation redirected back from the resist layer, may be dependent on the thickness of the resist layer and optionally one or more other layers formed on the substrate. A small change in resist layer thickness may result in the significant change in the intensity of the redirected radiation. Such redirected radiation will not contribute to the exposure dose of the resist. Accordingly a change in the thickness of the resist may result in a change in the exposure dose received by the resist for a given intensity of beam of radiation projected onto the resist layer. This, in turn, may affect the critical dimension (CD) of the features of the pattern being formed. Therefore, a variation in the thickness of the resist layer on the substrate may result in a deterioration of the critical dimension uniformity (CDU), which is undesirable.
"In order to avoid a reduction in the critical dimension uniformity, it may be desirable to reduce the variation in the thickness of a resist layer across the substrate. However, this may be difficult and/or expensive, especially for relatively large substrates.
"Alternatively or additionally, a so-called bottom anti reflection coating (BARC) may be used in order to reduce the reflection of radiation from the lower surface of the resist layer. However, this may result in additional process costs because it is necessary to perform additional processes to a substrate.
"Alternatively or additionally, the problem may be reduced or overcome by use of a radiation source having a relatively broad bandwidth. This is because the redirection of the radiation from the resist layer depends on the thickness of the resist layer relative to the wavelength of the radiation. Therefore, if the radiation source has a relatively broad bandwidth, for any particular thickness of resist layer some wavelengths of the radiation will be redirected relatively strongly and other wavelengths will be redirected relatively weakly. Accordingly, the overall redirection of the broadband radiation may not vary greatly with variations of the thickness of the resist layer. However, it may be desirable to use a relatively narrow bandwidth radiation source, such as a laser diode.
"It is therefore desirable, for example, to provide a system in which the critical dimension uniformity is less sensitive to variation in the thickness of the resist layer.
"According to an embodiment of the invention, there is provided a lithographic apparatus, configured to project a patterned beam of radiation onto a substrate, the apparatus comprising: a measurement system, configured to provide measurement data related to a thickness of a resist layer on the substrate; and a controller, configured to control the operation of the lithographic apparatus such that a radiation intensity level in the patterned beam to be projected onto the substrate is controlled based on the measurement data.
"According to an embodiment of the invention, there is provided a device manufacturing method, comprising: using a lithographic apparatus to project a patterned beam of radiation onto a substrate; obtaining measurement data related to a thickness of a resist layer on the substrate; and controlling the operation of the lithographic apparatus to control the radiation intensity level in the patterned beam to be projected onto the substrate based on the measurement data.
BRIEF DESCRIPTION OF THE DRAWINGS
"Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:
"FIG. 1 depicts a part of a lithographic apparatus according to an embodiment of the invention;
"FIG. 2 depicts a top view of a part of the lithographic apparatus of FIG. 1 according to an embodiment of the invention;
"FIG. 3 depicts a highly schematic, perspective view of a part of a lithographic apparatus according to an embodiment of the invention;
"FIG. 4 depicts a schematic top view of projections by the lithographic apparatus according to FIG. 3 onto a substrate according to an embodiment of the invention;
"FIG. 5 schematically depicts a lithographic apparatus according to an embodiment of the present invention;
"FIG. 6 depicts a variation of the arrangement depicted in FIG. 5; and
"FIG. 7 depicts a portion of a lithographic apparatus according to an embodiment of the invention."
For additional information on this patent application, see: Bleeker,
Keywords for this news article include:
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SEPTEMBER 2, 2014
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