colsep="0" rowsep="0">

Cr
Ti
W
Zr
Ir
Ni
Co
V
Y
Hf

Interstitial
Cr₃C₂
TiC
W₂C
ZrC
Ir₅C₃
Ni₃C
Co₃C
V₄C₃
Y₂C
HfC

Compound
Cr₇C₃
TiB₂
W₂N
ZrC₂
Ir₄C₅
Ni₃N
Co₂C
VN
YN
HfN

Cr₂₃C₆
TiN
W₃N₂
ZrB₂
IrC₂

Co₂N
VSi₂
YB₂

Cr₄C
TiSi₂

ZrN
Ir₃C₇

Co₃N
V₃Si
YSi₂

Cr₂N

ZrSi₂
IrC₃

Co₄C

YC₂

Cr₂B

IrC₄

Co₂Si

CrB₂

IrN₂

Ir₃Si

In some embodiments, the interstitial compound is comprised of a matrix alloy of two or more transitional metals and an interstitial element occupying interstitial sites of the alloy. In some embodiments, the alloy is a binary alloy of Cr and Ta, and the interstitial element is N. In some embodiments, the alloy is a ternary alloy of Cr, Ta, and V, and the interstitial element is N.

In some embodiments, the absorber layer 130 includes the transitional metal in a concentration ranging from about 20% by weight to about 95% by weight. In some embodiments, the absorber layer 130 includes the transitional metal in a concentration about 20% by weight, about 25% by weight, about 30% by weight, about 35% by weight, about 40% by weight, about 45% by weight, about 50% by weight, about 55% by weight, about 60% by weight, about 65% by weight, about 70% by weight, about 75% by weight, about 80% by weight, about 85% by weight, about 90% by weight, about 92% by weight, about 93% by weight, about 94% by weight, or about 95% by weight.

In some embodiments, the absorber layer 130 includes the interstitial element in a concentration ranging from about 5% by weight to about 80% by weight. In some embodiments, the absorber layer 130 includes the interstitial element in a concentration about 5% by weight, about 10% by weight, about 15% by weight, about 20% by weight, about 25% by weight, about 30% by weight, about 35% by weight, about 40% by weight, about 45% by weight, about 50% by weight, about 55% by weight, about 60% by weight, about 65% by weight, about 70% by weight, about 75% by weight, or about 80% by weight.

Because the interstitial compounds of the present application have high extinction coefficients in the EUV wavelength range, a thin absorber layer 130 with a thickness less than 50 nm can be used to provide sufficient EUV absorption, while reducing the mask 3D effects. In some embodiments, the absorber layer 130 may have a thickness ranging from about 30 nm to about 40 nm.

The absorber layer 130 is formed by deposition techniques such as PVD, CVD, ALD, RF magnetron sputtering, DC magnetron sputtering, or IBD. The deposition process is carried out in the presence of interstitial elements, such as B, C, N, Si, or P. Carrying out the deposition in the presence of the interstitial elements results in the interstitial elements being incorporated into the interstitial sites of the absorber layer 130.

In embodiments of the present disclosure, by using interstitial compounds having a high extinction coefficient κ as the absorber material, the mask 3D effects caused by EUV phase distortion can be reduced. As a result, the best focus shifts and pattern placement errors can be reduced, while the normalized image log-slope (NILS) can be increased.

Referring to FIGS. 2 and 3D, the method 200 proceeds to operation 208, in which a hard mask layer 140 is deposited over the absorber layer 130, in accordance with some embodiments. FIG. 3D is a cross-sectional view of the structure of FIG. 3C after depositing hard mask layer 140 over the absorber layer 130, in accordance with some embodiments.

Referring to FIG. 3D, the hard mask layer 140 is disposed over the absorber layer 130. The hard mask layer 140 possesses different etching characterizes from the absorber layer 130, and thereby serves as an etch stop layer to prevent damages to the absorber layer 130 during the photolithography process. In some embodiments, the hard mask layer 140 serves as an anti-reflection layer for reducing a reflection of the EUV radiation. In some embodiments, the hard mask layer 140 includes a dielectric material such as, for example, SiN, TaBO, TaO, CrO, or CrON.

In some embodiments, the hard mask layer 140 is formed using a deposition process such as, for example, CVD, PECVD, or PVD.

Additionally or alternatively, in some embodiments, a buffer layer (not shown) is formed on the capping layer 120 as an etch stop layer for patterning the absorber layer 130 and a sacrificial layer during a subsequent focused ion beam defect repair process for the absorber layer 130. The buffer layer may include silicon dioxide (SiO₂), silicon oxynitride (SiON), or other suitable materials.

FIG. 4 is a cross-sectional view of an EUV mask 400 that is formed by patterning the absorber layer 130 of the EUV mask blank 100, in accordance with a second embodiment of the present disclosure. Referring to FIG. 4, the EUV mask 400 includes a substrate 102, a reflective multilayer stack 110 over a front surface of the substrate 102, a capping layer 120 over the reflective multilayer stack 110, and a patterned absorber layer 130P over the capping layer 120. The EUV mask 400 further includes a conductive layer 104 over a back surface of the substrate 102 opposite the front surface.

The patterned absorber layer 130P contain a pattern of openings 152 that correspond to circuit patterns to be formed on a semiconductor wafer. The pattern of openings 152 is located in a pattern region 400A of the EUV mask 400, exposing a surface of the capping layer 120. The pattern region 400A is surrounded by a peripheral region 400B of the EUV mask 400. The peripheral region 400B corresponds to a non-patterned region of the EUV mask 400 that is not used in an exposing process during IC fabrication. In some embodiments, the pattern region 400A of EUV mask 400 is located at a central region of the substrate 102, and the peripheral region 400B is located at an edge portion of the substrate 102. The pattern region 400A is separated from the peripheral region 400B by trenches 154. The trenches 154 extend through the patterned absorber layer 130P, the capping layer 120, and the reflective multilayer stack 110, exposing the front surface of the substrate 102.

FIG. 5 is a flowchart of a method 500 for fabricating an EUV mask, for example, EUV mask 400, in accordance with some embodiments. FIG. 6A through FIG. 6G are cross-sectional views of the EUV mask 400 at various stages of the fabrication process, in accordance with some embodiments. The method 500 is discussed in detail below, with reference to the EUV mask 400. In some embodiments, additional operations are performed before, during, and/or after the method 500, or some of the operations described are replaced and/or eliminated. In some embodiments, some of the features described below are replaced or eliminated. One of ordinary skill in the art would understand that although some embodiments are discussed with operations performed in a particular order, these operations may be performed in another logical order.

Referring to FIGS. 5 and 6A, the method 500 includes operation 502, in which a photoresist layer 610 is deposited over the hard mask layer 140, in accordance with some embodiments. FIG. 6A is a cross-sectional view of a structure after depositing the photoresist layer 610 over the hard mask layer 140, in accordance with some embodiments.

Referring to FIG. 6A, the photoresist layer 610 is disposed over the topmost surface of the EUV mask blank 100, i.e., the hard mask layer 140. The photoresist layer 610 includes a photosensitive material operable to be patterned by radiation. In some embodiments, the photoresist layer 610 includes a positive-tone photoresist material, and a negative-tone photoresist material or a hybrid-tone photoresist material. In some embodiments, the photoresist layer 610 is applied to the surface of the hard mask layer 140, for example, by spin coating.

Referring to FIGS. 5 and 6B, the method 500 proceeds to operation 504, in which the photoresist layer 610 is lithographically patterned to form a patterned photoresist layer 610P, in accordance with some embodiments. FIG. 6B is a cross-sectional view of the structure of FIG. 6A after lithographically patterning the photoresist layer 610 to form the patterned photoresist layer 610P, in accordance with some embodiments.

Referring to FIG. 6B, the photoresist layer 610 is patterned by first subjecting the photoresist layer 610 to a pattern of irradiation. Next, the exposed or unexposed portions of the photoresist layer 610 are removed depending on whether a positive-tone or negative-tone resist is used in the photoresist layer 610 with a resist developer, thereby forming the patterned photoresist layer 610P having a pattern of openings 612 formed therein. The openings 612 expose portions of the hard mask layer 140. The openings 612 are located in the pattern region 400A and correspond to locations where the pattern of openings 152 are present in the EUV mask 400 (FIG. 4).

Referring to FIGS. 5 and 6C, the method 500 proceeds to operation 506, in which the hard mask layer 140 is etched using the patterned photoresist layer 610P as an etch mask to form a patterned hard mask layer 140P, in accordance with some embodiments. FIG. 6C is a cross-sectional view of the structure of FIG. 6B after etching the hard mask layer 140 to form the patterned hard mask layer 140P, in accordance with some embodiments.

Referring to FIG. 6C, portions of the hard mask layer 140 that are exposed by the openings 612 are etched to form openings 142 extending through the hard mask layer 140. The openings 142 expose portions of the underlying absorber layer 130. In some embodiments, the hard mask layer 140 is etched using an anisotropic etch. In some embodiments, the anisotropic etch is a dry etch such as, for example, reactive ion etch (RIE), a wet etch, or a combination thereof. The etch removes the material providing the hard mask layer 140 selective to the material providing the absorber layer 130. The remaining portions of the hard mask layer 140 constitute the patterned hard mask layer 140P. If not completely consumed during the etching of the hard mask layer 140, after etching the hard mask layer 140, the patterned photoresist layer 610P is removed from the surfaces of the patterned hard mask layer 140P, for example, using wet stripping or plasma ashing.

Referring to FIGS. 5 and 6D, the method 500 proceeds to operation 508, in which the absorber layer 130 is etched using the patterned hard mask layer 140P as an etch mask to form a patterned absorber layer 130P, in accordance with some embodiments. FIG. 6D is a cross-sectional view of the structure of FIG. 6C after etching the absorber layer 130 to form the patterned absorber layer 130P, in accordance with some embodiments.

Referring to FIG. 6D, portions of the absorber layer 130 that are exposed by the openings 142 are etched to form openings 132 extending through the absorber layer 130. The openings 132 expose portions of the underlying capping layer 120. The openings 132 in the patterned absorber layer 130P define the pattern of openings 152 in the EUV mask 400. In some embodiments, the absorber layer 130 is etched using an anisotropic etching process. In some embodiments, the anisotropic etch is a dry etch such as, for example, RIE, a wet etch, or a combination thereof that removes the material providing the absorber layer 130 selective to the material providing the underlying capping layer 120. For example, in some embodiments, the absorber layer 130 is dry etched with a gas that contains chlorine, such as Cl₂or BCl₃, or with a gas that contains fluorine, such as NF₃. Argon (Ar) may be used as a carrier gas. In some embodiments, oxygen (O₂) may also be included as the carrier gas. The etch rate and the etch selectivity depend on the etchant gas, etchant flow rate, power, pressure, and substrate temperature. After etching, the remaining portions of the absorber layer 130 constitute the patterned absorber layer 130P.

Referring to FIGS. 5 and 6E, the method 500 proceeds to operation 510, in which a patterned photoresist layer 620P comprising a pattern of openings 622 is formed over the patterned hard mask layer 140P and the capping layer 120, in accordance with some embodiments. FIG. 6E is a cross-sectional view of the structure of FIG. 6D after forming the patterned photoresist layer 620P comprising openings 622 over the patterned hard mask layer 140P and the capping layer 120, in accordance with some embodiments.

Referring to FIG. 6E, the openings 622 expose portions of the patterned hard mask layer 140P at the periphery of the patterned absorber layer 130P. The openings 622 correspond to the trenches 154 in the peripheral region 400B of the EUV mask 400 (FIG. 4). To form the patterned photoresist layer 620P, a photoresist layer (not shown) is applied over the patterned hard mask layer 140P and the capping layer 120. The photoresist layer fills the openings 142 within the patterned hard mask layer 140P and the openings 132 within the patterned absorber layer 130P. In some embodiments, the photoresist layer includes a positive-tone photoresist material, a negative-tone photoresist material, or a hybrid-tone photoresist material. In some embodiments, the photoresist layer includes a same material as the photoresist layer 610 described above in FIG. 6A. In some embodiments, the photoresist layer includes a different material from the photoresist layer 610. In some embodiments, the photoresist layer is formed, for example, by spin coating. The photoresist layer is subsequently patterned by exposing the photoresist layer to a pattern of radiation, and removing the exposed or unexposed portions of the photoresist layer using a resist developer depending on whether a positive or negative resist is used. The remaining portions of the photoresist layer constitute the patterned photoresist layer 620P.

Referring to FIGS. 5 and 6F, the method 500 proceeds to operation 512, in which the patterned hard mask layer 140P, the patterned absorber layer 130P, the capping layer 120, and the reflective multilayer stack 110 are etched using the patterned photoresist layer 620P as an etch mask to form trenches 154 in the peripheral region 400B of the substrate 102, in accordance with some embodiments. FIG. 6F is a cross-sectional view of the structure of FIG. 6E after etching the patterned hard mask layer 140P, the patterned absorber layer 130P, the capping layer 120, and the reflective multilayer stack 110, to form the trenches 154 in the peripheral region 400B of the substrate 102, in accordance with some embodiments.

Referring to FIG. 6F, the trenches 154 extend through the patterned hard mask layer 140P, the patterned absorber layer 130P, the capping layer 120, and the reflective multilayer stack 110 to expose the surface of the substrate 102. The trenches 154 surround the pattern region 400A of the EUV mask 400, separating the pattern region 400A from the peripheral region 400B.

In some embodiments, the patterned hard mask layer 140P, the patterned absorber layer 130P, the capping layer 120, and the reflective multilayer stack 110 are etched using a single anisotropic etching process. The anisotropic etch can be a dry etch such as, for example, RIE, a wet etch, or a combination thereof that removes materials of the respective patterned hard mask layer 140P, patterned absorber layer 130P, capping layer 120, and reflective multilayer stack 110, selective to the material providing the substrate 102. In some embodiments, the patterned hard mask layer 140P, the patterned absorber layer 130P, the capping layer 120, and the reflective multilayer stack 110 are etched using multiple distinct anisotropic etching processes. Each anisotropic etch can be a dry etch such as, for example, RIE, a wet etch, or a combination thereof.

Subsequently, the patterned photoresist layer 620P is removed from the pattern region 400A and the peripheral region 400B of the substrate 102, for example, by wet stripping or plasma ashing. The removal of the patterned photoresist layer 620P from the openings 142 in the patterned hard mask layer 140P and the openings 132 in the patterned absorber layer 130P re-exposes the surfaces of the capping layer 120 in the pattern region 400A.

Referring to FIGS. 5 and 6G, the method 500 proceeds to operation 514, in which the patterned hard mask layer 140P is removed, in accordance with some embodiments. FIG. 6G is a cross-sectional view of the structure of FIG. 6F after removing patterned hard mask layer 140P, in accordance with some embodiments.

Referring to FIG. 6G, the removal of the patterned hard mask layer 140P exposes the surfaces of the patterned absorber layer 130P. In some embodiments, the patterned hard mask layer 140P is removed by an etching process which can be an anisotropic etch or an isotropic etch. In some embodiments, the etch can be a dry etch such as RIE or a wet chemical etch that removes the patterned hard mask layer 140P selected to the patterned absorber layer 130P, the capping layer 120, the reflective multilayer stack 110, and the substrate 102.

After removal of the patterned hard mask layer 140P, the EUV mask 400 may be cleaned to remove any contaminants therefrom. In some embodiments, the EUV mask