JPWO2018177747A5 - - Google Patents

Description

1 is a schematic representation of a measuring apparatus for inspecting the surface of a mask blank or wafer for microlithography, in particular for particle detection; FIG. 1 shows a plane of a mask or wafer with partial areas irradiated with measuring radiation by a measuring device; FIG. 2 shows a schematic representation of measurement radiation used to illuminate a surface and scattered at the surface into a detection angular range; 1 shows a schematic representation of a surface to be inspected with particles deposited on the surface; FIG. 1 shows a schematic diagram of a test object with an antireflection coating applied to the test object surface; FIG. 1 shows a schematic diagram of a test object with an antireflection coating applied to the test object surface; FIG. 1 shows a schematic representation of a test object with surface structures that reduce the reflectance of the test surface; FIG. Figure 3 shows a schematic representation of the frequency distribution of the scattered light intensity recorded during inspection of a conventional surface or during inspection of the surface shown in Figures 3a-3c; Fig. 3b shows a schematic representation of the reflectance of the surface of Fig. 3a with two different antireflection coatings within the detection angle range of the measuring device;

FIG. 4 shows what is known as the "defect count" (D.C.) of the scattered light intensity I, which consists of a first portion called the defect signal 17 and a second portion called the haze signal 18. have The haze signal 18 represents the frequency distribution of the measuring radiation 9 scattered over the surface 11, i.e. of the total measuring radiation 9 detected during the movement of the subregion T over the surface 11, the surface 11 being e.g. can be divided into Correspondingly, the defect signal 17 is the scattered light intensity I measured in a partial region T (eg corresponding to a grid element of the measurement grid). As can be seen in FIG. 4 the defect signal 17 has its maximum at a higher scattered light intensity I than the haze signal 18 .

As can be seen in FIG. 4, the haze signal 18 has a relatively large full width at half maximum (FWHM) and the right edge of the substantially Gaussian haze signal 18 probably overlaps the defect signal 17 . Although the right end of the haze signal 18 constitutes only a relatively small portion of the frequency distribution, the haze signal 18 alone may cause the scattered light intensity I to exceed the intensity threshold IS, which is due to particles _P in a subregion of the surface 11. It means that a particle P is detected there even though it is not there. As such, the intensity threshold I _S , and thus the minimum detectable particle size D _S , cannot be arbitrarily small to avoid erroneous detection of the particles P.

Claims (19)

A method for detecting deposited particles (P) on a surface (11) of an object (2, 3, 14), comprising:
irradiating a subregion (T) of the surface (11) of the object (2, 3, 14) with measuring radiation (9);
detecting the scattered measurement radiation (9) in the illuminated partial area (T);
detecting said particles (P) on said surface (11) of said object (2, 3, 14) based on said detected measuring radiation (9), said irradiating and said measuring radiation ( 9), an antireflection coating (13) on said surface (11) of said object (2, 3, 14) that reduces the reflectance (R) of said surface (11) with respect to said measuring radiation. and/or a surface structure (15) is provided, and the antireflection coating (13) and/or the surface structure (15) lowers the particle detection limit,
The antireflection coating (13) and/or the surface structure (15) reduce the haze scattered light intensity due to the roughness of the surface (11) to lower the particle detection limit based on the intensity threshold (Is). A method provided to reduce the FWHM of a power distribution (18) compared to not providing said antireflection coating (13) and/or said surface structure (15) . A method according to claim 1, wherein said particles (P) are detected on said surface (11) of an object in the form of a wafer (3) or mask blank (2) for microlithography. 3. Method according to claim 1 or 2, wherein the measuring radiation (9) has a predetermined measuring wavelength ([lambda] _M ). A method according to any one of claims 1 to 3, characterized in that the scattered measuring radiation (9) is arranged at a first scattering angle (α ₁ ) to a second scattering angle (α 1 ) with respect to the incident measuring radiation (9). A method of detecting in the detection angle range of α ₂ ). A method according to any one of claims 1 to 4, wherein the antireflection coating (13) is formed as a multi-layer coating. A method according to claim ₄ , wherein said antireflection coating (13) is such that said reflectance ₍ R) A method having an angle dependent reflectance (R) for said measuring radiation (9) wherein the difference between the maximum value of (R _MAX ) and the minimum value (R _MIN ) of said reflectance (R) is less than 5%. A method according to any one of the preceding claims, wherein the reflectivity (R) of the antireflection coating (13) with respect to the measuring radiation (9) is less than 15%. A method according to any one of the preceding claims, wherein the surface structures (15) are formed as acicular microstructures. A method according to any one of claims 1 to 8, wherein said object (3) is made of silicon. 10. The method of claim 9, wherein the surface structure (15) is formed as black silicon. A method according to any one of claims 1 to 8, wherein said object (14) is formed from an optical filter glass for filtering said measuring radiation (9). A method according to any one of claims 1 to 11, wherein said object (2, 3, 14) is made of a material having an absorption coefficient of more than 1 x 10 ⁴ 1/cm with respect to said measuring radiation (9). way. A method according to any one of the preceding claims, wherein said objects (2, 3, 14) have a thickness (d ₁ , d ₂ ) between 500 μm and 3 mm. Method according to any one of the preceding claims, characterized in that the particle A method for detecting (P) in said illuminated partial area (T). A method according to any one of the preceding claims, in which the steps of illuminating at least the object (2, 3, 14) with the measuring radiation (9) and detecting the scattered measuring radiation (9) with a measuring device (1) for measuring mask blanks (2) or wafers (3) for microlithography. A wafer for microlithography, the reflectance (R) of the surface (11) of the wafer (3) for measuring radiation (9) of at least one measuring wavelength (λ _M ) in the visible or UV wavelength range An antireflection coating (13) and/or a surface structure (15) is provided on the surface (11), which reduces the intensity threshold. In order to reduce the particle detection limit based on (Is), the FWHM of the frequency distribution (18) of the haze scattered light intensity due to the roughness of the surface (11) is measured by the antireflection coating (13) and/or the surface Wafer for microlithography provided to reduce structure (15) compared to not provided . Mask blank (2) for microlithography, in particular for EUV lithography, for measuring radiation (9) of at least one measuring wavelength (λ _M ) in the visible or UV wavelength range characterized in that said surface (11) is provided with an antireflection coating (13) and/or a surface structure (15) that reduces the reflectivity (R) of the surface (11), said antireflection coating (13) and/or Alternatively, the surface structure (15) reduces the FWHM of the frequency distribution (18) of the haze scattered light intensity due to the roughness of the surface (11) to reduce the particle detection limit based on the intensity threshold (Is). A mask blank for microlithography, which is provided with an antireflection coating (13) and/or said surface structure (15) to be reduced compared to the case without it . 17. A microlithographic wafer according to claim 16, wherein said wafer (3) comprises a substrate. 18. The mask blank for microlithography according to claim 17, wherein said mask blank (2) comprises a substrate.