Reflective mask blank and process for producing the reflective mask blank
View Patent ↗To provide a reflective mask blank having pseudo defects significantly excluded. The reflective mask blank comprises a substrate, a reflective layer for reflecting EUV light, formed on the substrate, and an absorber layer for absorbing EUV light, formed on the reflective layer, wherein S sk <1.0 is satisfied, where S sk is skewness in a region of 1 μm×1 μm on the absorber layer side surface.
1. A reflective mask blank comprising:
a substrate,
a reflective layer for reflecting extreme Ultra-Violet (EUV) light, formed on the substrate, and
an absorber layer for absorbing EUV light, formed on the reflective layer,
wherein S sk <1.0 is satisfied, where S sk is skewness in a region of 1 μm×1 μm on the absorber layer side surface, or S ku <10 is satisfied, where S ku is kurtosis in a region of 1μm×1 μm on the absorber layer side surface,
wherein the skewness S sk is represented by the following formula (3):
S
sk
=
1
S
q
3
[
1
A
∫
∫
A
z
3
(
x
,
y
)
dxdy
]
,
Formula
(
3
)
wherein the skewness S sk represents a symmetry of concaves and convexes to a standard height S q , wherein S q is represented by the following formula (2):
S
q
=
1
A
∫
∫
A
z
2
(
x
,
y
)
dxdy
,
Formula
(
2
)
wherein A represents a standard area of a surface to be evaluated, and
wherein the kurtosis S ku is represented by the following formula (4):
S
ku
=
1
S
q
4
[
1
A
∫
∫
A
z
4
(
x
,
y
)
dxdy
]
,
Formula
(
4
)
wherein the kurtosis S ku represents a peaked state of convexes or concaves to the standard height S q .
2. The reflective mask blank according to claim 1 , wherein on the absorber layer, a low reflective layer against inspection light for inspecting a pattern, having a wavelength of from 190 nm to 260 nm, is formed.
3. The reflective mask blank according to claim 2 , wherein the low reflective layer comprises tantalum, nitrogen and oxygen.
4. The reflective mask blank according to claim 1 , which has an additional layer between the reflective layer and the absorber layer.
5. The reflective mask blank according to claim 1 , wherein the absorber layer comprises tantalum and nitrogen.
6. The reflective mask blank according to claim 1 , wherein the substrate is a glass substrate.
7. A process for producing a reflective mask blank, comprising:
(1) forming a reflective layer for reflecting extreme Ultra-Violet (EUV) light, on a substrate, and
(2) forming an absorber layer for absorbing EUV light, on the reflective layer, wherein S sk <1.0 is satisfied, where S sk is skewness in a region of 1μm×1μm on the surface of the absorber layer obtained in (2), or S ku <10 is satisfied, where S ku is kurtosis in a region of 1 μm×1 μm on the surface of the absorber layer obtained in (2),
wherein the skewness S sk is represented by the following formula (3):
S
sk
=
1
S
q
3
[
1
A
∫
∫
A
z
3
(
x
,
y
)
dxdy
]
,
Formula
(
3
)
wherein the skewness S sk represents a symmetry of concaves and convexes to a standard height S q ,wherein S q is represented by the following formula (2):
S
q
=
1
A
∫
∫
A
z
2
(
x
,
y
)
dxdy
,
Formula
(
2
)
wherein A represents a standard area of a surface to be evaluated, and
wherein the kurtosis S ku is represented by the following formula (4):
S
ku
=
1
S
q
4
[
1
A
∫
∫
A
z
4
(
x
,
y
)
dxdy
]
,
Formula
(
4
)
wherein the kurtosis S ku represents a peaked state of convexes or concaves to the standard height S q .
8. A process for producing a reflective mask blank, the process comprising:
(1) forming a reflective layer for reflecting extreme Ultra-Violet (EUV) light, on a substrate,
(2) forming an absorber layer for absorbing EUV light, on the reflective layer, and
(3) forming a low reflective layer against inspection light for inspecting a pattern, having a wavelength of from 190 nm to 260 nm, on the absorber layer, wherein S sk <1.0 is satisfied, where S sk is skewness in a region of 1 μm×1 μm on the surface of the low reflective layer obtained in (3), or S ku <10 is satisfied, where S ku is kurtosis in a region of 1μm×1μm on the surface of the low reflective layer obtained in (3),
wherein the skewness S sk is represented by the following formula (3):
S
sk
=
1
S
q
3
[
1
A
∫
∫
A
z
3
(
x
,
y
)
dxdy
]
,
Formula
(
3
)
wherein the skewness S sk represents a symmetry of concaves and convexes to a standard height S q , wherein S q is represented by the following formula (2):
S
q
=
1
A
∫
∫
A
z
2
(
x
,
y
)
dxdy
,
Formula
(
2
)
wherein A represents a standard area of a surface to be evaluated, and
wherein the kurtosis S ku is represented by the following formula (4):
S
ku
=
1
S
q
4
[
1
A
∫
∫
A
z
4
(
x
,
y
)
dxdy
]
,
Formula
(
4
)
wherein the kurtosis S ku represents a peaked state of convexes or concaves to the standard height S q .
9. The process for producing a reflective mask blank according to, claim 8 , wherein the low reflective layer comprises tantalum, nitrogen and oxygen.
10. The process for producing a reflective mask blank according to claim 7 , further comprising forming an additional layer on the reflective layer before the forming of the absorber layer.
11. The process for producing a reflective mask blank according to claim 8 , further comprising forming an additional layer on the reflective layer before the forming of the absorber layer.
12. The process for producing a reflective mask blank according to claim 7 , wherein the absorber layer comprises tantalum and nitrogen.
13. The process for producing a reflective mask blank according to claim 8 , wherein the absorber layer comprises tantalum and nitrogen.
14. The process for producing a reflective mask blank according to claim 7 , wherein the substrate is a glass substrate.
15. The process for producing a reflective mask blank according to claim 8 , wherein the substrate is a glass substrate.
16. The process for producing a reflective mask blank according to claim 7 , wherein the absorber layer is formed under a gas pressure of at most 0.28 Pa.
17. The process for producing a reflective mask blank according to claim 8 , wherein the absorber layer is formed under a gas pressure of at most 0.28 Pa.