The assignee for this patent application is
Reporters obtained the following quote from the background information supplied by the inventors: "Mask inspection, or photo mask inspection, is an operation of checking the correctness of the fabricated photo masks (e.g., used for semiconductor device fabrications). Modern technologies for locating defects in photo masks are automated systems that involve scanning electron microscopy and other advanced tools. Existing optical systems in the market for mask inspection employ ultra-violet light at or above 193 nm that are not sufficient to resolve the features and defects below the 22 nm node. In order to resolve features and defects below 22 nm node, light of shorter wavelength in the EUV (e.g., 13.5 nm) region needs to be used.
"Laser produced plasma (LPP) is a good candidate light source for extreme ultraviolet (EUV) mask inspection. LPP light source may use Xenon as fuel and Nd:YAG laser at wavelength near 1030 nm as driver laser. It has been observed that a few percent of the driver laser may enter the inspection system and cause enough detrimental thermal damage and image flare, and thus its intensity needs to be significantly reduced. Out of band radiation with wavelength from a few nm to 1000 nm also exists in the light source and needs to be suppressed.
"While there are some Spectral Purity Filter (SPF) methods available, they are developed for EUV lithography which use CO2 laser of wavelength 10.6 um on Sn target. That is, these SPF methods are not developed specifically for mask inspection using Xenon LPP source with 1030 nm light, and due to the significant difference in laser wavelength (e.g., ten times the difference) and different use cases between inspection and lithography, the existing SPF methods are not applicable for EUV mask inspection.
"Therein lies a need for providing phase grating for mask inspection without the aforementioned shortcomings."
In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventors' summary information for this patent application: "The present disclosure is directed to phase grating on a near normal incidence mirror. The mirror comprising a substrate; a plurality of continuous base bilayers positioned on the substrate; and a plurality of gratings positioned on the plurality of continuous base bilayers, wherein each of the plurality of gratings is formed using between 10 and 200 bilayers.
"An additional embodiment of the present disclosure is directed to phase grating on a grazing incidence mirror. The mirror comprising a substrate; a continuous Ru base layer positioned on the substrate; and a plurality of Ru gratings positioned on the continuous Ru base layer, wherein a depth of the gratings is determined based on an angle of incidence.
"A further embodiment of the present disclosure is directed to a mirror. The mirror comprising: a substrate, the substrate having a grated surface defining a plurality of gratings, wherein each of the plurality of gratings having a depth of approximately (laser wavelength)/4/cos(angle of incidence), a pitch of the gratings is a predetermined value between 5 and 1000 um, and a duty ratio of the gratings is a predetermined value between 0.7 and 1.5; and a coating layer deposited on the reflective substrate, the coating layer covering the entirety of the grated surface.
"A further embodiment of the present disclosure is directed to a mask inspection system. The mask inspection system includes a laser configured for driving an EUV light source, a collector configured for collecting the EUV light and delivering the EUV light via an illumination module to an EUV mask, and a light sensor configured for receiving imaging of the EUV mask. The collector and the illumination module each include at least one mirror with phase grating. If the mirror is a normal incidence mirror, the phase grating includes a plurality of gratings formed using between 10 and 200 bilayers. Otherwise, if the mirror is a grazing incidence mirror, the phase grating includes a plurality of Ru gratings.
"It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the present disclosure. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate subject matter of the disclosure. Together, the descriptions and the drawings serve to explain the principles of the disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
"The numerous advantages of the disclosure may be better understood by those skilled in the art by reference to the accompanying figures in which:
"FIG. 1 is a block diagram depicting a mask inspection system;
"FIG. 2 is a side view depicting a normal incidence mirror;
"FIG. 3 is a front view of the normal incidence mirror having a plurality of radial gratings;
"FIG. 4 is a cross-sectional view of the normal incidence mirror having a plurality of radial gratings;
"FIG. 5 is an illustration depicting the ray footprint at IF1 of the mask inspection system of FIG. 1;
"FIG. 6 is a front view of a normal incidence mirror having a plurality of parallel gratings;
"FIG. 7 is a chart illustrating dependence of grating IR (1030 nm) suppression factor on the number of top bilayers, where the number of base bilayers is 37, the pitch is 20 um, the duty ratio is 1, the plane of incidence is parallel to the groove, the angle of incidence is 0.degree. and the period of Mo/Si bilayer is 6.96 nm;
"FIG. 8 is a chart illustrating dependence of grating IR (1030 nm) suppression factor on the number of base bilayers, where the number of base bilayers is 37, the pitch is 20 um, the duty ratio is 1, the plane of incidence is parallel to the groove, the angle of incidence is 0.degree. and the period of Mo/Si bilayer is 6.96 nm;
"FIG. 9 is an illustration depicting a grazing incidence mirror having a plurality of gratings;
"FIG. 10 is a cross-sectional view of the grazing incidence mirror of FIG. 9;
"FIG. 11 is a cross-sectional view of a coating deposited on a grated substrate;
"FIG. 12 is a cross-sectional view of a mirror having more than one type of phase gratings;
"FIG. 13 shows examples of thin film Be and Zr coatings on light sensor to achieve the transmission ratio (13.5 nm/1030 nm) of 200;
"FIG. 14 is a chart illustrating suppression of reflectivity in the wavelength range .about.130 to .about.400 nm; and
"FIG. 15 is another chart illustrating suppression of reflectivity in the wavelength range .about.130 to .about.400 nm."
For more information, see this patent application: Wang, Daimian; Khodykin, Oleg; Wack, Daniel; Wang, Li; Liu, Yanwei. Phase Grating for Mask Inspection System. Filed
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