Method of fast surface particle and scratch detection for EUV mask backside

A method of scanning a substrate and determining scratches of the substrate includes transmitting a converging beam of light that comprises multiple wavelengths to the substrate. Each wavelength of the multiple wavelengths focuses at a different distance in a focus interval around and including a surface of the substrate. The method also includes receiving reflected light from the surface of the substrate and determining a height or depth of the surface of the substrate based on a wavelength of the reflected light having a highest intensity.

BACKGROUND

During an integrated circuit (IC) design, a number of layout patterns of the IC, for different steps of IC processing, are generated. The layout patterns include geometric shapes corresponding to structures to be fabricated on a wafer. The layout patterns may be produced by projecting, e.g., imaging, a mask on the wafer. The mask includes a layout pattern that is produced on a clean (with no pattern) semiconductor substrate or a mask blank. Thus, the masks include a layout pattern of the IC or a layout pattern of a portion of the IC that is created on the mask blank. A lithography process transfers a layout pattern of the mask to the wafer such that etching, implantation, or other steps are applied only to predefined regions of the wafer.

In some embodiments, a reflective mask is used during extreme ultraviolet (EUV) lithography process to form an integrated circuit having smaller feature sizes. Reflective masks are vulnerable to manufacturing/fabrication defects, such as oxidation and particles, and are easily damaged. Therefore, a number of defects may exist on the mask surface that can affect the layout printing that are produced by patterned masks. In addition, the printing error of the layout pattern of the mask may impact the fabricated circuit on the wafer. An efficient mask blank scanning (e.g., mapping) is desirable to detect the defect of the mask blank to avoid the impact of the defects when producing the mask on the mask blank.

In some embodiments, a scratch is on the backside including the backside edge of the mask and the scratch causes defects such as dips or bumps on the front side of the mask or causes a defect, e.g., anomaly, in the thickness of the mask that is desirable to be avoided. Therefore, the backside including the backside edges of the mask blank is scanned (e.g., mapped) for the scratches to determine areas of the mask including edge zones of the mask that is desirable to be avoided when the mask is created on the mask blank.

DETAILED DESCRIPTION

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. In addition, the term “being made of” may mean either “comprising” or “consisting of.” In the present disclosure, a phrase “one of A, B and C” means “A, B and/or C” (A, B, C, A and B, A and C, B and C, or A, B and C), and does not mean one element from A, one element from B and one element from C, unless otherwise described.

In some embodiments, a substrate, e.g., a mask blank, is scanned for bumps and dips. When producing a mask and imaging a layout pattern on the mask blank, the bumps and dips are avoided for wafer printing error concerns. In some embodiments, a scratch on the backside of the mask blank causes dips and/or bumps on the front side of the mask blank where the layout pattern is created. In some embodiments, the scratch on the backside of the mask blank causes some changes in the thickness of the mask blank that although may not be visible on the front side of the mask blank, may degrade the wafer layout pattern that is produced by the mask. Therefore, the backside of the mask blank is examined for scratches and particles, e.g., bump and/or dips, and the areas of the mask blank to be avoided, cleaned, or repaired is mapped. A fast scanning method for inspecting the backside of the mask blank is desirable. In some embodiments, an edge region of the mask blank are more vulnerable for having scratches or particles and thus the edge region of the mask blank is inspected. In some embodiments, the entire backside of the mask blank is inspected.

In some embodiments, an optical system is used for scanning the backside of the mask blank. The optical system has a multi-wavelength light source, e.g., a white light source, and a chromatic lens. The chromatic lens that may include a plurality of lenses, stacked together in series, creates a focal distance for each wavelength of the light source. Thus, when a collimated beam of light is transmitted to the chromatic lens, each component of the collimated beam of light having a different wavelength is focused at a different focal point from the chromatic lens. In some embodiments, a component of the collimated beam of light having a shorter wavelength has a shorter focal point and focuses closer to the chromatic lens than a component of the collimated beam of light having a longer wavelength. Thus, for a collimated beam of white light, the violet component of the white light focuses closer to the chromatic lens than the green component and the green component focuses closer to the chromatic lens than the red component of the white light.

In some embodiments, the collimated beam of light is focused on a substrate. In some embodiments, the substrate has roughness with bumps and dips. Thus, when the collimated beam of white light is focused on the substrate, depending on the height of a bump or depth of a dip, a different color of the components of the white light is focused to a point on the substrate and the other components are not focused and create a blurred and expanded points, e.g., spot, on the substrate. In some embodiments, the reflected light from the substrate goes back through the chromatic lens and then is deflected by a mirror, e.g., a beam splitter, and the reflected and then deflected light is imaged to a pinhole in a plane. The component of the multi-wavelength light that is in-focus on the substrate is thus imaged as a point on the pinhole and passes, e.g., essentially entirely passes, through the pinhole and the other components of the white light that are not in-focus on the substrate are imaged as blurred and expanded points, e.g., spots, on the pinhole and, thus, only a fraction of the other components of the white light passes through the pinhole.

In some embodiments, the components of the white light or any multi-wavelength light source, after passing through the pinhole pass through a focusing lens of a spectrometer and then are detected per wavelength by the detectors of the spectrometer. In some embodiments, the spectrometer creates an output signal that is an intensity of the reflected light that passes through the pinhole as a function of the wavelength of the light. As noted, the component of the light that focuses on the substrate also focuses on the pinhole. Thus, if the output signal of the spectrometer passes through a peak detector, a wavelength of the light having the peak intensity, e.g., having the highest intensity, is determined. The wavelength of the light having the peak intensity is the wavelength of the light that is in-focus on the substrate. As described, each component of the light source that has a different wavelength focuses at a different distance from the chromatic lens. Thus, the wavelength that focuses on the substrate may determine the height or depth of the surface of the substrate. Therefore, the wavelength corresponding to the peak intensity of the output signal of the spectrometer determines the height of the surface of the substrate in some embodiments.

FIGS.1A and1Billustrate optical scanning systems100and180for scanning a substrate in accordance with some embodiments of the present disclosure. The optical scanning system100ofFIG.1Aincludes a light source116and a light source controller135for controlling the light source116. The light source controller135commands the light source116to transmit a beam of light134that includes multiple wavelengths to an optical device114. The optical device114that is controlled by an optical controller118receives the beam of light134and in response transmits beams of light142,144, and146to a surface131of a substrate130. In some embodiments, the substrate130is a mask blank for EUV lithography. In other embodiments, the substrate130is a mask blank for DUV lithography, a glass substrate, or a semiconductor substrate. As shown inFIG.1A, the beams of light142,144, and146focuses, e.g., converges, at different distances from the surface131of the substrate130such that the beam of light142focuses, e.g., converges, at point A before the surface131of the substrate130(i.e., the converging point is between the optical device114and the surface131). The beam of light144focuses, e.g., converges, at point B before the surface131of the substrate130and the beam of light146is converging to point C after, e.g., under, the surface131of the substrate130(i.e., focus point is in the substrate130). In some embodiments, when there is a bump132on the surface of the substrate130, the beam of light144focuses at the point A that is on the bump132and thus the beam of light144converges as the point A on the bump132. The beam of light142that converges at the point A, generates a spot on the surface131of the substrate130that covers the bump132and portions of the surface131of the substrate130in some embodiments. The beam of light146that would be converging to point C after the surface131of the substrate130also generates a spot on the bump132. As noted, the beam of light146is stopped by a top surface of the bump132and, thus, the extensions of the beam of light146inside the bump132and inside the substrate130is shown by broken lines146B. In some embodiments, the optical controller118controls the light source116and commands the light source116, via the light source controller135, to transmit the beam of light134.

In some embodiments, the substrate130is a mask blank that is placed on a stage112and the stage112is moved by a stage controller110such that the beam of light134is transmitted to multiple locations on the surface of the substrate130and a line on the surface131of the substrate130or an area of the surface131of the substrate130is scanned, e.g., mapped. In some embodiments, the optical device114receives the reflected light from the surface of the substrate130and transmits, e.g., images, the reflected light from the surface131of the substrate130to a pinhole structure124that includes a pinhole149. In some embodiments, a position and a size of the pinhole149is controlled by the optical controller118such that a beam from the beams of light142,144, and146that is in-focus on the surface of the substrate130is also in-focus on the pinhole and substantially entirely, e.g., more than 90 percent, passes through the pinhole149but the other beams of light that are not in-focus on the surface131of the substrate130are not also in-focus on the pinhole149and only a small fraction, e.g., less than 30 percent, of the other beams of light pass through the pinhole149. Thus, the optical controller118may adjust a distance117between the pinhole structure124and the optical device114such that the reflected light from the surface of the substrate130is imaged on the pinhole structure124. In some embodiments, the optical controller118moves the pinhole structure124and/or the optical device114to adjust the distance117. In some embodiments, the optical device114is designed such that the reflected light from the beam of light that is focused on the surface of the substrate is focused on the pinhole149. The reflected light from the other beams of light that are not focused on the surface of the substrate do not focus on the pinhole149.

In some embodiments, the beam of light142has a wavelength w1, the beam of light144has a wavelength w2(e.g., w2greater than w1), and the beam of light146has a wavelength w3(e.g., w3greater than w2). In some embodiments, the stage controller110generates the location158of the surface131of the substrate130that is illuminated by the beams of light142,144, and146. Thus, the location158of the surface131is a location that one the beams of light142,144, or146is in-focus. In some embodiments, either the stage controller110moves the stage112up or down, or the optical controller118moves the optical device114up or down to adjust a distance136between the optical device114and the substrate130such that a beam of light with a specific wavelength focuses on the surface131of the substrate130. In some embodiments, the beam of light134is a beam of light that includes a continuous spectrum of wavelengths and thus the wavelength w1, w2, and w3are examples of wavelengths in the beam of light134. In some embodiments, the beam of light134is a white beam of light that includes a continuous spectrum of wavelengths from red to green and thus the wavelength w1, w2, and w3are examples of wavelengths such as violet, green, or red. In some embodiments, the surface131of the substrate130is a backside surface of the substrate130.

As shown inFIG.1A, the beam of light144is in-focus on the bump132and the reflected light from the bump132is also focused at the pinhole149of the pinhole structure124and thus entirely, e.g., more than 90 percent, passes through the pinhole149. The reflected light from the other beams of light142and146that are not in-focus on the surface of the substrate130are not also focused at the pinhole structure124. Thus, only a fraction, e.g., a small fraction less than 30 percent, of the reflected light from the other beams of light142and146pass through the pinhole149.

As noted, in some embodiments, the light source116is a white light source that includes wavelengths of the white light spectrum from red to violet. In some embodiments, the beams of light142,144, or146having the longer wavelength focuses farther from the optical device114and the beams of light142,144, or146having the shorter wavelength focuses closer to the optical device114. Thus, when the light source116is a white light source, the violet beam of light142having the wavelength w1focuses above the surface131of the substrate130and the red beam of light146having the wavelength w3may focus farther inside the substrate130after, e.g., under, the surface131and the green beam of light144having the wavelength w2focuses slightly above the surface131of the substrate130, e.g., about 10 micron above the surface131between where the violet beam of light142and the red beam of light146focus. In some embodiments, the light source116includes a continuous spectrum of color sources, e.g., between red and violet, which produce the white light.

In some embodiments, the beams of light that passes through the pinhole149is imaged with a lens122on one or more light detectors121of a spectrometer120. As shown inFIG.1A, the reflected light that is focused on the pinhole structure124entirely passes through the pinhole149and thus produces a peak intensity in the light detectors121. As shown, the beam of light144(having the wavelength w2) that focuses on the bump132of the substrate also focuses at the pinhole149and creates the peak intensity in the spectrometer. In some embodiments, the light source116includes multiple wavelengths and each light detector121of the spectrometer120, detects the received light intensity in a specific wavelength, e.g., a specific short range of wavelengths. Thus each one of the light detectors121detects one of the wavelengths of the multiple wavelengths and thus creates an intensity141versus wavelength143curve, a spectrum148of the detected light on a display screen140. In some embodiments, the spectrometer120includes a prism (not shown) for splitting the direction of transmission of the multiple wavelengths and thus leading each wavelength, e.g., a short wavelength range, to one of the light detectors121. As shown inFIG.1A, the spectrometer120generates a spectrum data152, which includes intensity141per wavelength143of the received beams of light by the lens122and detected by the light detectors121. In some embodiments, a display controller115receives the spectrum data152and displays the spectrum data152on the display screen140.

In some embodiments, a peak-wavelength detector125determines, e.g., calculates or detects, the peak intensity of the spectrum148and determines a wavelength154corresponding to the peak intensity. As noted each wavelength of the multiple wavelengths of the beam of light134converges at a specific distance from the optical device114. Thus, in some embodiments, a height variation of the substrate, e.g., a height145of the bump132on the substrate130is determined based on the wavelength of the light that converged, e.g., focused, on the bump132and thus produced the peak intensity in the spectrum data152. In some embodiments, a wavelength-to-height converter126receives the wavelength154corresponding to the peak intensity and generates a height156. For example, if the peak intensity is at w2wavelength (e.g., in the green color range), the defect is a bump with a height156of about 10 microns and if the peak intensity is at w3wavelength (e.g., in the red color range), the defect is a dip with a height156of −5 microns (e.g., a depth of about 5 microns).

As shown inFIG.1A, the beam of light144that has the wavelength w2focuses on the substrate130, e.g., on the bump132of the substrate130. In addition, the deflected beam of light144impinging on the pinhole structure124also focuses on the pinhole structure124and thus entirely passes through the pinhole149and thus produces a peak intensity in the light detectors121. Also, the spectrum148produces a peak at the wavelength w2of the beam of light144.

In some embodiments, the multi-wavelength of the light source116includes one or more wavelength corresponding to desired heights and depths of the defects. In some embodiments, the reflected light that goes through the pinhole149is filtered by the spectrometer to select one or more wavelengths corresponding to defects having one or more desired height or depth.

The optical scanning system180ofFIG.1Bis consistent with the optical scanning system ofFIG.1Awith the difference that the spectrometer120of the optical scanning system180in addition to the light detectors121includes the peak-wavelength detector125and wavelength-to-height converter126. Also, the optical scanning system180includes an optical system185. In some embodiments, the optical system185includes the optical device114ofFIG.1Aand transmits the beams of light142,144, and146to the surface of the substrate130.

In addition, the optical system185receives the light reflected from the beams of light142,144, and146from the surface of the substrate130and directs the reflected light from the beam of light that is focused on the surface of the substrate out of an exit pupil187of the optical system185. In some embodiments, the optical system185includes the pinhole149. The optical system185is designed such that the reflected light from the beam of light that is focused on the surface of the substrate is focused on the pinhole149and thus transmits the light through the pinhole. However, the reflected light from the other beams of light that are not focused on the surface of the substrate do not focus on the pinhole149and only a fraction of them transmits through the pinhole149. In some embodiments, the optical system185is designed such that the reflected light from the beam of light that is focused on the surface of the substrate transmits through the exit pupil187out of the optical system185. The reflected light from the other beams of light that are not focused on the surface of the substrate are not transmitted through the exit pupil187out of the optical system185. As shown inFIG.1B, the beam of light144focuses on the surface of the substrate130and thus the reflected light from the beam of light144is transmitted through the exit pupil187out of the optical system185.

FIG.2illustrates an optical scanning system200for scanning a substrate in accordance with some embodiments of the present disclosure.FIG.2, is consistent withFIG.1A. The optical scanning system200shows that the optical device114includes a chromatic lens150that creates the beams of light142,144, and146from the multi-wavelength beam of light134.FIG.2also shows that the optical device114includes a beam splitter160. In some embodiments, a portion of the beam of light134passes through the beam splitter160and hits the chromatic lens150to create the beams of light142,144, and146. The reflected light from the surface of the substrate is transmitted back through the chromatic lens150and is deflected by the beam splitter160to the pinhole structure124. In some embodiments, the chromatic lens150and the beam splitter160are used to image an illuminated surface131of the substrate130onto the pinhole structure124.

FIG.3illustrates an optical scanning system300for scanning a substrate in accordance with some embodiments of the present disclosure.FIG.3is consistent withFIG.1A. As shown inFIG.3, the reflected light that is focused on the pinhole structure124, e.g., the beam of light146, entirely passes through the pinhole149and thus produces a peak intensity in the light detectors121. As shown, the beam of light146(having the wavelength w3) that focuses at a bottom of a dip133on the substrate130also focuses at the pinhole149and creates the peak intensity of the spectrometer120. In some embodiments as described, the light detectors121of the spectrometer120generate an intensity141versus wavelength143curve, e.g., a spectrum147on a display screen140. As shown inFIG.3, the spectrometer120generates a spectrum data152, which includes intensity141per wavelength143of the received beams of light by the lens122and detected by the light detectors121.

As shown inFIG.3, the beam of light146that has the wavelength w3focuses on the substrate130, e.g., at the bottom of the dip133of the substrate130. In addition, the deflected beam of light146impinging on the pinhole structure124also focuses on the pinhole structure124and entirely passes through the pinhole149and thus produces a peak intensity in the light detectors121. Also, the spectrum147produces a peak at the wavelength w3of the beam of light146.

As shown inFIG.3, the reflected light from the surface131of the substrate130is received by the optical device114and is deflected by the optical device114to the pinhole structure124. As shown the beam of lights142and144, having the wavelengths w1and w2, e.g., violet and green lights, do not focus on the surface131of the substrate130. The beam of light146, having the wavelength w3, e.g., the red light, focuses on a bottom surface of the dip133in the substrate130. Thus, the reflected light from the red beam of light also focuses at the pinhole149and entirely passes through the pinhole149. Thus, the intensity versus wavelength, e.g., the spectrum147, has a peak in the red region. In some embodiments the wavelength of the peak intensity in the red region determines that a depth155of the dip133is about 5 microns.

FIGS.4A and4Billustrate substrates that include scratches in accordance with some embodiments of the present disclosure.FIG.4Ashows a backside408of a substrate400with scratches and particles that includes a bump404and a dip402. In some embodiments, the bump404on the backside408of the substrate is caused by or may cause a dip (not shown) on the front side415of the substrate. In some embodiments, the dip402on the backside408of the substrate is caused by or may cause a bump406on the front side415of the substrate. In some embodiments, the backside408of a substrate400is scanned by the optical scanning systems100,200, or300ofFIGS.1-3. In some embodiments, the bump404is scanned along a direction412that is parallel to a Y-direction410and the dip402is scanned along a direction414that is parallel to an X-direction420. In some embodiments, a scratch on the backside408of the substrate400, e.g., the dip402or the bump404, does not have an associated scratch on the front side415of the substrate400, however, the scratch on the backside408of the substrate400may cause a defect or wafer printing error in the thickness413of the substrate400. Thus, the backside408and the front side415of the substrate400is scanned in some embodiments. In some embodiments, an edge region is a region extending 10 percent of the width of the substrate400in the X-direction and extending 10 percent of the length of the substrate400in the Y-direction. The substrate400is more vulnerable to having the scratches in the edge region and the bump404and the dip402may be in the edge region of the substrate400. In some embodiments, the bump has a height of about 5 microns to about 15 microns, e.g., 10 microns.

FIG.4Bshows a backside surface458of a substrate450with scratches that includes bumps452,454,466,468; and dips462,464, and470. As shown, the dip462on the backside surface458of the substrate450is caused by or may cause a bump456on the front side455of the substrate450. In some embodiments, the backside surface458of a substrate450is scanned by the optical scanning systems100,200, or300ofFIGS.1-3. In some embodiments, the dip464follows the bump454in a direction451that is parallel to the Y-direction410and the dip462follows the bump452in a direction453that is parallel to the X-direction420. In some embodiments, the bump454and the dip464are scanned along the direction451and the bump452and the dip462are scanned along the direction453. In some embodiments, an entire backside of the substrate450including the bumps452,454,466,468and the dips462,464, and470are scanned either along multiple parallel lines parallel to the Y-direction, along multiple parallel lines parallel to the X-direction, or both. In some embodiments, the edge region of the backside of the substrate450is scanned.

FIG.5illustrates a detector systems for the optical scanning system in accordance with some embodiments of the present disclosure.FIG.5shows the detector system500that includes the spectrometer120, which receives the beams of light510through the lens122. As described, the spectrometer120includes a prism for splitting the direction of transmission of the multiple wavelengths and thus directing each wavelength, e.g., a short wavelength range, to one of the light detectors121of the spectrometer120. In some embodiments, each light detector121of the spectrometer120includes a filter for selecting a specific wavelength, a specific short wavelength range, of the beam of light510. The output of the spectrometer120is the spectrum data152, which includes intensity141per wavelength143of the received beams of light510. The detector system500also includes a peak detector502, consistent with the peak-wavelength detector125ofFIGS.1A,1B,2, and3, that receives the spectrum data152and generates a peak wavelength154of the spectrum data152corresponding to the peak intensity of the spectrum data152. Thus, the peak intensity of the spectrum data152is at the peak wavelength154.

The detector system500also includes a peak threshold verifier504that receives the spectrum data152and the peak wavelength154having the peak intensity. The peak threshold verifier504may further determine an average value of the spectrum data and a shape of the spectrum data152around the peak intensity. The peak threshold verifier504verifies the peak intensity at the peak wavelength154. In some embodiments, the peak intensity at the peak wavelength154in addition to being the peak value of the spectrum data152, is at least two times greater than the average value of the spectrum data152. In some embodiments, the shape of the spectrum data152around the peak intensity is a bump protruding outward and the peak threshold verifier504verifies that bump has a width within a threshold range. After verifying the peak wavelength154, the peak wavelength154is inputted to the wavelength-to-height converter126. In some embodiments, the wavelength-to-height converter126determines the associated height156of the surface131of the substrate130based on the peak wavelength154. In some embodiments, the peak-wavelength detector125ofFIGS.1A,1B,2, and3, is consistent with the combination of the peak detector502and the peak threshold verifier504.

As noted, based on the height of the substrate, a specific wavelength converges, e.g., focuses, on the surface131of the substrate130. As described above and shown inFIG.1A, the beam of light144having the wavelength w2converges on the bump132when the stage112is at a location, e.g., position, that the bump132is illuminated by the optical device114. As noted, when the wavelength w2converges on the bump132, the deflected beam of light144entirely passes through the pinhole149and thus the peak of the spectrum data152is at wavelength w2, which is the peak wavelength.

In addition, as described above and shown inFIG.3, the beam of light146having the wavelength w3converges at the bottom of the dip133when the stage112is at a location that the dip133is illuminated by the optical device114. When the wavelength w3converges at the bottom of the dip133, the deflected beam of light146entirely passes through the pinhole149and thus the peak of the spectrum data152is at wavelength w3. Thus, based on the peak wavelength154the height156at the surface131of the substrate130is determined.

Thus, the height of the surface131, e.g., the height145of the bump132, is determined based on the wavelength w2and the height of the surface131, a depth at the bottom of the dip133, is determined based on the wavelength w3. In some embodiments, the location of the stage112is provided by the stage controller110. Thus, for each location of the stage112, e.g., a corresponding location158of the surface131of the substrate130, the height156at the surface131of the substrate130is determined by the wavelength-to-height converter126. In some embodiments, a height-vs-location identifier128receives a location158of the surface131of the substrate130as well as the height156at the surface131of the substrate130for multiple points of the surface131of the substrate130and provides a line scan data161, e.g., a map data, of the height of the surface131of the substrate130.

FIGS.6A and6Billustrate line scans through the substrates ofFIG.4Athat include scratches and particle in accordance with some embodiments of the present disclosure. As shown inFIG.6A, a graph600, e.g., a profile, shows a line scan of the backside408of the substrate400having the bump404over the backside surface. In some embodiments, the horizontal coordinate is along the scanning direction412and is in millimeter and the vertical coordinate604is the height of the surface of the substrate130and is in microns. The backside surface of the substrate is displayed with an initial height608. The bump404has a maximum height630, where the maximum height is at location636on the horizontal coordinate that is along the direction412ofFIG.4A. The maximum height630is above the initial height608by a distance634. In some embodiments, the distance634is between 2 microns and 15 microns, e.g., 10 microns. In some embodiments, the height630corresponds to wavelength w2.

As shown inFIG.6B, a graph610, e.g., a profile, shows a line scan of the backside408of the substrate400having the dip402over the backside surface. The backside surface of the substrate is displayed with an initial height618. The dip402has a maximum depth632, where the maximum depth632is at location638on the horizontal coordinate that is along the scanning direction414ofFIG.4A. The maximum depth632is below the initial height618by a distance635. In some embodiments, the distance635is between 2 microns and 10 microns, e.g., 5 microns. In some embodiments, the graphs600and610are generated by the optical scanning system100,200, or300ofFIGS.1-3. In some embodiments, the depth632corresponds to wavelength w3.

FIGS.7A and7Billustrate line scans through the substrates ofFIG.4Bthat include scratches and particle in accordance with some embodiments of the present disclosure. As shown inFIG.7A, a graph700, e.g., a profile, shows a line scan of the backside surface458of the substrate450having the bump454and the dip464over the backside surface458. In some embodiments, the horizontal coordinate is along the scanning direction451and the vertical coordinate604is the height. The backside surface of the substrate is displayed with an initial height725. The graph700shows that the backside scan has a bump around a distance712with a maximum height722at the distance712. The graph700also shows that the backside scan has a dip around a distance714with a minimum height724at the distance714. In some embodiments, the initial height725of the surface131of the substrate130corresponds to locations of the surface131of the substrate130which has no bumps or dips. In some embodiments, the maximum height722has a distance726above the initial height725and the minimum height724has a distance728below the initial height725. In some embodiments, the maximum height722corresponds to the wavelength w2and the minimum height724corresponds to the wavelength w3.

As shown inFIG.7B, a graph710, e.g., a profile, shows a line scan of the backside surface458of the substrate450having the bump452and the dip462over the backside surface458. In some embodiments, the horizontal coordinate is along the scanning direction453and the vertical coordinate604is the height. The backside surface of the substrate is displayed with the initial height725. The graph710shows that the backside scan has a bump around a distance716with a maximum height above the height722at the distance716. The graph710also shows that the backside scan has two dips around distances715and717with two minimum depth below the height724. In some embodiments, the initial height725of the surface131of the substrate130corresponds to locations of the surface131of the substrate130which has no bumps or dips. In some embodiments, the height722corresponds to the wavelength w2and the height724corresponds to the wavelength w3. In some embodiments, the maximum of the bump452corresponds to the wavelength w1. In some embodiments the maximum height of the bump452is between 10 microns and 20 microns, e.g., 15 microns.

FIG.8illustrates an exemplary optical scanning system800for determining scratches including bumps and/or dips of a substrate in accordance with some embodiments of the disclosure. The optical scanning system800includes an analyzer module830and a main controller840coupled to each other. Referring back toFIG.1or3, the analyzer module830receives the wavelength154of the peak intensity of the spectrum data152of the reflected light from the surface of the substrate and determines, e.g., calculates, a height156of the surface of the substrate based on the received wavelength154. The analyzer module830receives the wavelength154of the peak intensity from a peak detector810, which is consistent with the peak-wavelength detector125ofFIGS.1Aand is also consistent with a combination of the peak detector502and the peak threshold verifier504. The peak detector810is either directly coupled to the analyzer module830or is coupled to the analyzer module830via the main controller840.

In some embodiments, the analyzer module830is consistent with a combination of the peak-wavelength detector125and the wavelength-to-height converter126ofFIGS.1A,1B,2, and3. As shown inFIG.8, the main controller840, controls the other controllers, devices, and systems. In some embodiments, a main controller (not shown), consistent with the main controller840, controls the timing and functionality of the optical controller118, light source controller135, the spectrometer120, the stage controller110and the display controller115of the optical scanning systems100and300ofFIGS.1A and3. The main controller enables the optical scanning systems100or300to scan a surface of the substrate130and display a map of the specific range of heights on the surface of the substrate as shown inFIGS.7A and7B. In some embodiments, a main controller (not shown), consistent with the main controller840, controls the timing and functionality of the optical controller118, the spectrometer120, the stage controller110, the display controller115, and the optical system185(via the optical controller118) of the optical scanning system180ofFIG.1B.

In some embodiments, the main controller840is coupled to a light source controller808, a display controller806, an optical controller804, and a stage controller802. In some embodiments and returning back toFIG.1Athe optical controller804is consistent with the optical controller118. The optical controller804, which is controlled by the main controller840, controls the optical device114to perform transmitting a converging beam of light to the surface of the substrate, receiving the reflected light from the surface of the substrate, and transmitting the reflected light from the surface of the substrate to the pinhole structure124. In addition, the optical controller804may control a location of the pinhole structure124and a size of the pinhole149such that the beam of light having the wavelength that focuses on the surface of the substrate focuses at the pinhole structure124and passes, e.g., entirely passes, through the pinhole149and the other beams of light having other wavelengths do not pass through the pinhole149or a fraction passes through the pinhole149. The optical controller804also controls the light source controller808, which is consistent with the light source controller135ofFIG.1A, to control the light source116and to generate the beam of light134that includes a plurality of wavelengths to transmit the beam of light134to the optical device114.

In some embodiments, the main controller840is coupled to and controls the stage controller802, which is consistent with the stage controller110ofFIG.1A, to move the substrate such that the optical device114receives the reflected light from different points on the surface of the substrate. In some embodiments, the main controller840is coupled to and controls the display controller806, which is consistent with the display controller115ofFIG.1A, to display a spectrum of the reflected beam of light from a location of the substrate on the display screen140or to display a scan line of the height of the surface of the substrate on the display screen140.

FIG.9illustrates a flow diagram of an exemplary process for scanning a substrate and determining scratches including bumps and/or dips of the substrate in accordance with some embodiments of the disclosure. The process900may be performed by the optical scanning system ofFIGS.1,2,4, and8. In some embodiments, the process900or a portion of the process900is performed and/or is controlled by the computer system1000described below with respect toFIGS.10A and10B. The method includes the operation S902of transmitting a converging beam of light that comprises multiple wavelengths to a substrate. As shown inFIG.1A, the beam of light134is transmitted by the light source116and the beam of light134is focused by the optical device114. In operation S904, reflected light from the surface of the substrate is received. As shown inFIG.1A, the reflected light is received by the spectrometer120. In operation S906, a height or depth of the surface of the substrate is determined based on a wavelength of the reflected light. As discussed, the height or depth is determined based on the wavelength corresponding to the peak intensity of the detected light from the surface of the substrate. In some embodiments and referring back toFIG.1A, the analyzer module830ofFIG.8determines the wavelength of the peak intensity of the spectrum data152and also determines the height of the surface131of the substrate130based on the determined wavelength.

FIGS.10A and10Billustrate an apparatus for scanning a substrate and determining scratches including bumps and dips of the substrate in accordance with some embodiments of the disclosure.FIG.10Ais a schematic view of a computer system1000that executes the process for determining the bumps and dips of the substrate according to one or more embodiments as described above. All of or a part of the processes, method and/or operations of the foregoing embodiments can be realized using computer hardware and computer programs executed thereon. The operations include converging a multi-wavelength beam of light on a substrate for determining bumps and dips of the substrate. Thus, in some embodiments, the computer system1000provides the functionality of the optical controller804, the analyzer module830, the main controller840, the stage controller802, the light source controller808, the peak detector810, and the display controller806. InFIG.10A, a computer system1000is provided with a computer1001including an optical disk read only memory (e.g., CD-ROM or DVD-ROM) drive1005and a magnetic disk drive1006, a keyboard1002, a mouse1003, and a monitor1004. In some embodiments, the computer system1000provides the functionality of the optical controller118, the light source controller135, the stage controller110, and the display controller115ofFIG.1A. As described, in some embodiments, a main controller, consistent with the main controller840, controls the timing and functionality the other controllers, devices, and systems of the optical scanning systems ofFIGS.1A,1B,2, and3. Thus, the computer system1000also provides the functionality of the main controller.

FIG.10Bis a diagram showing an internal configuration of the computer system1000. InFIG.10B, the computer1001is provided with, in addition to the optical disk drive1005and the magnetic disk drive1006, one or more processors1011, such as a micro-processor unit (MPU), a ROM1012in which a program such as a boot up program is stored, a random access memory (RAM)1013that is connected to the processors1011and in which a command of an application program is temporarily stored and a temporary storage area is provided, a hard disk1014in which an application program, a system program, and data are stored, and a bus1015that connects the processors1011, the ROM1012, and the like. Note that the computer1001may include a network card (not shown) for providing a connection to a LAN.

The program for causing the computer system1000to execute the process for determining the scratches including bumps and/or dips of the substrate in the foregoing embodiments may be stored in an optical disk1021or a magnetic disk1022, which are inserted into the optical disk drive1005or the magnetic disk drive1006, and transmitted to the hard disk1014. Alternatively, the program may be transmitted via a network (not shown) to the computer1001and stored in the hard disk1014. At the time of execution, the program is loaded into the RAM1013. The program may be loaded from the optical disk1021or the magnetic disk1022, or directly from a network. The program does not necessarily have to include, for example, an operating system (OS) or a third party program to cause the computer1001to execute the process for manufacturing the lithographic mask of a semiconductor device in the foregoing embodiments. The program may only include a command portion to call an appropriate function (module) in a controlled mode and obtain desired results.

In some embodiments, implementing the processes and methods mentioned above, increases the throughput of scanning the backside of a substrate such a mask blank. In processes of manufacturing an integrated circuit or a die by EUV lithography process, a substrate, e.g., a mask blank, a backside of a mask or a patterned mask, is scanned for bumps and dips before the lithography process. When detecting a unwanted bump or dip on the mask and imaging a layout pattern on the mask blank by the present disclosure, the mask or region with bumps and dips can be effectively avoided or repaired for wafer printing error concerns. Accordingly, the mask used in the EUV lithography process is qualified by the system and method of the present disclosure.

According to some embodiments of the present disclosure, a method of scanning a substrate includes transmitting a converging beam of light that comprises multiple wavelengths to the substrate. Each wavelength of the multiple wavelengths focuses at a different distance in a focus interval around and including a surface of the substrate. The method also includes receiving reflected light from the surface of the substrate and determining a height or depth of the surface of the substrate based on a wavelength of the reflected light having a highest intensity. In an embodiment, the method further includes irradiating the surface of the substrate with the converging beam of light from a light source located at a first distance from the surface of the substrate. The surface of the substrate is a backside surface of the substrate and the light source is located above the backside surface of the substrate. In an embodiment, the first distance is a perpendicular distance between the light source and a flat portion of the surface of the substrate with no bumps or dips. In an embodiment, the surface of the substrate includes one or more of bumps and dips, wherein a height of a bump or a depth of dip on the surface of the substrate is determined with respect an area having with no bumps or dips surrounding the bump or the dip. In an embodiment, the reflected light from the surface of the substrate is received by a spectrometer, the method further includes detecting the reflected light from a first point on the surface of the substrate, determining a spectrum of the detected reflected light, determining a first wavelength of a peak intensity of the spectrum, and determining the height or depth of the first point on the surface of the substrate based on the first wavelength of the peak intensity. In an embodiment, the spectrometer includes a lens at an input to the spectrometer. The lens focuses the reflected light from the surface of the substrate onto one or more light detectors and each light detector includes a filter to select a specific wavelength range to generate a signal proportional to an intensity of the reflected light in the specific wavelength range. In an embodiment, a portion of the converging beam of light having the first wavelength is configured to focuses on the surface of the substrate. In an embodiment, a pinhole structure having a pinhole is arranged before the lens of the spectrometer. The reflected light with the first wavelength focuses on the pinhole structure and the reflected light with the first wavelength substantially entirely passes through the pinhole. In an embodiment, the reflected light having one or more wavelengths other than the first wavelength does not focus on the pinhole. In an embodiment, a fraction of the reflected light passes through the pinhole when the reflected light has the other than the first wavelength. In an embodiment, the reflected light having a wavelength that does not focus on the surface of the substrate does not focus on the pinhole structure. In an embodiment, the substrate is arranged on a stage and the method further includes configuring the stage to move the substrate in a first direction and receiving the reflected light from the surface of the substrate at one or more different points along the first direction, scanning the surface of the substrate by the converging beam of light, receiving the reflected light from the surface of the substrate in a specific range of wavelengths corresponding to a specific range of heights, and determining a map of the specific range of heights on the surface of the substrate on a scan line along the first direction. In an embodiment, the method further includes moving the stage in parallel lines along the first direction or moving the stage in parallel lines perpendicular to the first direction to scan the substrate, receiving the reflected light from the surface of the substrate in a specific range of wavelength corresponding to a specific range of heights, and determining a map of the specific range of heights on the surface of the substrate. In an embodiment, the light source is a white light source and the multiple wavelengths are in white light spectrum.

According to some embodiments of the present disclosure, a method of scanning a substrate includes receiving reflected light from a first point on a surface of the substrate and configuring the reflected light to pass through a pinhole. The method includes detecting the reflected light from the first point after passing the pinhole and determining a spectrum of the detected reflected light. The method also includes determining a first wavelength of a peak intensity of the spectrum and determining a height or depth of the first point on the surface of the substrate based on the first wavelength of the peak intensity. In an embodiment, the substrate is arranged on a stage and the method further includes configuring the stage to move the substrate in a first direction and receiving the reflected light from the surface of the substrate at one or more different points along the first direction, scanning the surface of the substrate by a converging beam of light, receiving the reflected light from the surface of the substrate in a specific range of wavelength corresponding to a specific range of heights, and determining a map of the specific range of heights on the surface of the substrate on a scan line along the first direction.

According to some embodiments of the present disclosure, a system for scanning a substrate includes a main controller, a light source coupled to the main controller and to transmit a beam of light that includes multiple wavelengths to the substrate, and a stage coupled to the main controller and configured to move the substrate. The system also includes an optical system disposed in a light path between the light source and the substrate and coupled to the main controller and configured for focusing the beam of light on a surface of the substrate, and a spectrometer to receive the beam of light reflected from the surface of the substrate and directed by the optical system and configured for detecting reflected light from a first point on the surface of the substrate, determining a spectrum of the detected reflected light determining a first wavelength of a peak intensity of the spectrum, and determining a height or depth of the first point on the surface of the substrate based on the first wavelength of the peak intensity. In an embodiment, the spectrometer includes a lens for focusing the reflected light onto the one or more light detectors. Each light detector generates a signal proportional to the reflected light in a specific wavelength range. In an embodiment, the light source is a white light source and the multiple wavelengths are in white light spectrum. In an embodiment, the system further includes a pinhole disposed in a light path between the substrate and the spectrometer. The pinhole is arranged before the lens of the spectrometer, the reflected light with the first wavelength focuses on the pinhole and substantially entirely pass through the pinhole, and the reflected light having wavelengths other than the first wavelength does not focus on the pinhole and a fraction of the reflected light passes through the pinhole when the reflected light has other than the first wavelength.