Using ellipsometry methods for depth analyzing the optical disc data layer relief structures
We studied the relief depth of the data layer formed in a glass disk by ion beam etching process with using classical ellipsometry at the constant wavelength 632.8 nm for different angles of incidence. It was found that for 0° and 90° azimuth angles, a pair of ellipsometric parameters Ψ and ∆ is...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2008
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| Цитувати: | Using ellipsometry methods for depth analyzing the optical disc data layer relief structures / V.G. Kravets, I.V. Gorbov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2008. — Т. 11, № 1. — С. 11-15. — Бібліогр.: 8 назв. — англ. |
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Kravets, V.G. Gorbov, I.V. 2017-05-30T17:02:34Z 2017-05-30T17:02:34Z 2008 Using ellipsometry methods for depth analyzing the optical disc data layer relief structures / V.G. Kravets, I.V. Gorbov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2008. — Т. 11, № 1. — С. 11-15. — Бібліогр.: 8 назв. — англ. 1560-8034 PACS 42.79.Vb https://nasplib.isofts.kiev.ua/handle/123456789/118596 We studied the relief depth of the data layer formed in a glass disk by ion beam etching process with using classical ellipsometry at the constant wavelength 632.8 nm for different angles of incidence. It was found that for 0° and 90° azimuth angles, a pair of ellipsometric parameters Ψ and ∆ is sufficient to characterize the changes in light reflection for various structure depths. The depth of optical disc data layer relief structures was estimated via experimental dependences of ellipsometric parameters. The estimated data layer depths were found to be in good agreement with independent tunnelling electron microscopy measurements. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics Using ellipsometry methods for depth analyzing the optical disc data layer relief structures Article published earlier |
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Using ellipsometry methods for depth analyzing the optical disc data layer relief structures |
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Using ellipsometry methods for depth analyzing the optical disc data layer relief structures Kravets, V.G. Gorbov, I.V. |
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Using ellipsometry methods for depth analyzing the optical disc data layer relief structures |
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Using ellipsometry methods for depth analyzing the optical disc data layer relief structures |
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Using ellipsometry methods for depth analyzing the optical disc data layer relief structures |
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Using ellipsometry methods for depth analyzing the optical disc data layer relief structures |
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using ellipsometry methods for depth analyzing the optical disc data layer relief structures |
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Kravets, V.G. Gorbov, I.V. |
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Kravets, V.G. Gorbov, I.V. |
| publishDate |
2008 |
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English |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Article |
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We studied the relief depth of the data layer formed in a glass disk by ion beam
etching process with using classical ellipsometry at the constant wavelength 632.8 nm for
different angles of incidence. It was found that for 0° and 90° azimuth angles, a pair of
ellipsometric parameters Ψ and ∆ is sufficient to characterize the changes in light
reflection for various structure depths. The depth of optical disc data layer relief
structures was estimated via experimental dependences of ellipsometric parameters. The
estimated data layer depths were found to be in good agreement with independent
tunnelling electron microscopy measurements.
|
| issn |
1560-8034 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/118596 |
| citation_txt |
Using ellipsometry methods for depth analyzing the optical disc data layer relief structures / V.G. Kravets, I.V. Gorbov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2008. — Т. 11, № 1. — С. 11-15. — Бібліогр.: 8 назв. — англ. |
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| first_indexed |
2025-11-25T22:33:23Z |
| last_indexed |
2025-11-25T22:33:23Z |
| _version_ |
1850566796319391744 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2008. V. 11, N 1. P. 11-15.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
11
PACS 42.79.Vb
Using ellipsometry methods for depth analyzing
the optical disc data layer relief structures
V.G. Kravets1, I.V. Gorbov2
Institute for Information Recording, National Academy of Science of Ukraine
2, M. Shpaka str., 03113 Kyiv, Ukraine
1 Phone: (38-044) 454-21-19, fax: (38-044) 241-72-33, e-mail: vasyl_kravets@yahoo.com
2 Phone: (38-044) 454-22-09, fax: (38-044) 241-72-33, e-mail: ivan-gorbov@list.ru
Abstract. We studied the relief depth of the data layer formed in a glass disk by ion beam
etching process with using classical ellipsometry at the constant wavelength 632.8 nm for
different angles of incidence. It was found that for 0° and 90° azimuth angles, a pair of
ellipsometric parameters Ψ and ∆ is sufficient to characterize the changes in light
reflection for various structure depths. The depth of optical disc data layer relief
structures was estimated via experimental dependences of ellipsometric parameters. The
estimated data layer depths were found to be in good agreement with independent
tunnelling electron microscopy measurements.
Keywords: data layer, optical disc, relief depth, ellipsometry, scatterometry, effective
medium theory, effective refractive indices.
Manuscript received 13.12.07; accepted for publication 07.02.08; published online 31.03.08.
1. Introduction
Scatterometry is an attractive metrological technique for
determining the grating parameters, such as the line-
width and thickness from optical measurements.
Previous researches have demonstrated the use of reflec-
tion scatterometry for characterizing 100 to 400 nm
grating lines with a 100 to 500 nm pitch (or depth) [1, 2].
These characteristics were determined within a
computational resolution of 10 nm. Classical scattero-
metry is limited to reflectance measurements for two
configurations, in which the azimuth angle φ between
the plane of incidence and the grating vector is 0° or 90°.
In this work, we extended this method by performing
ellipsometry-type measurements of a surface relief
structure. This technique involves extracting the phase
in addition to the measured amplitude of a reflected
laser beam. For 0° or 90° azimuth angles, a pair of
ellipsometric parameters Ψ and ∆ is sufficient to
characterize the reflection. A grating or compact-disc
relief structure should be considered as anisotropic
media due to their anisotropic geometry [3–5]. To
describe this anisotropic media, we have employed the
effective medium theory (EMT) [6, 7]. Within the scope
of this theory, the relief structure is approximated as
anisotropic medium that have effective refractive
indices. Although the grating diffraction is rigorously
described by RCWA for rapid analysis of the relief
structure in a technological process, the EMT is more
convenient. In this work, we have used the second order
EMT to estimate geometrical parameters of the CD-disc
relief structure.
2. Theory
By using ion beam etching, the grating structures on the
surface of glass were fabricated with various depth
thicknesses. Fig. 1 displays the dependence of the
surface profile depth for ion etched glass disc. Used for
optical media data coding (EFM for CD, EFM+ for
DVD, ETM for HD-DVD and 17PP for Blu-Ray)
provides presence of 50 % pits and 50 % lands on every
tracks. Then disc relief structure can be presented by the
1_D binary profile, which is illustrated in Fig. 2. It is
assumed that grating profile is square, the geometry is
completely defined by the depth thickness d, periodicity
Λ, and profile width b. The period Λ was not considered
as a fitting parameter, because the period value is very
accurate with laser-beam lithography. Moreover, we
could experimentally check the period accuracy with
both AFM measurements and angular positions of higher
diffraction orders at normal incidence of light. The hole
walls of recorded bits were assumed to be perfectly
vertical, and their shape was approximated by rounded
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2008. V. 11, N 1. P. 11-15.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
12
Fig. 1. The structure of data layer on the glass substrate surface.
squares. Any surface roughness of the glass substrate
was neglected. The refractive index of the glass was
taken from experimental values determined by
spectroscopic ellipsometry. Finally, the depth and width
of the holes were the only two adjustable parameters in
the simulations used to fit the ellipsometric data. This
structure (Fig. 2) can be treated as effective medium
sandwiched between two homogeneous dielectrics. The
second-order EMT theory is employed to analyze the
disc structure. The medium of light incidence is air
(ni = 1), the filling factor f of the profile is equal to the
ratio b/Λ, and the profile depth is d.
We will analyze only the zeroth order of scattered
light to calculate the ellipsometric parameters: phase
shift ∆ and restored angle Ψ. It was shown in literature
that the gratings of dielectric material act as homo-
geneous birefringent materials. In this case, there exists a
difference between effective indices of refraction np for
light polarized in the plane parallel to the grating and ns
– perpendicular to the layers of gratings.
The interaction of light with grating is accurately
described by the rigorous coupled-wave analysis
(RCWA) developed by Moharam and Gaylord [2-5].
According to this model, nanostructured surface of the
disc is represented by an uniaxial anisotropic layer
described by the effective parameters. In the second-
order in the period-to-wavelength ratio Λ/λ, we can
represent the effective dielectric function of the top layer
in Fig. 2b that can be expressed as in [6, 7]:
Fig. 2. The disc relief structure profile (a) and its view as
effective medium sandwiched between two homogeneous
dielectrics (b).
,)0()()1(
3
1
)0(
2
eff
eff
222
2
2
effeff
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
εε
ε
ε−−
β
π
+×
×ε=ε
si
p
s
is
pp
nnff
(1)
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
ε
−
−
β
π
+ε=ε
)0(
)(
)1(
3
1)0(
eff
2
22
2
2
effeff s
isss nn
ff , (2)
where the filling factor f is given by
Λ
=
bf . (3)
The design constant β describes how much smaller
the ratio Λ/λ is relatively to the ratio 1/(ni + ns).
)( si nn +Λ
λ
=β , (4)
where ni = 1 is the refractive index of air, and ns = 1.5 is
the refractive index of glass, while 2
ii n=ε and 2
ss n=ε .
The effective dielectric function for the zeroth
order is given by [6, 7]:
is
p
ff
ε
−
+
ε
=
ε
1
)0(
1
eff
, (5)
is
p ff ε−+ε=ε )1()0(eff . (6)
Using these parameters and formulas (1)-(6), we
can calculate neff , which is represented at Fig. 2b for two
polarizations of reflected light:
⎪⎭
⎪
⎬
⎫
ε=
ε=
2/1
effeff
2/1
effeff
)(
)(
ss
pp
n
n
. (7)
After this procedure, we have all the refractive
indexes (Fig. 2b) to calculate the Fresnel reflection
coefficients.
2/122
eff
2
eff
2/122
eff
2
eff
01 ]sin)/[(cos)/(
]sin)/[(cos)/(
θ−+θ
θ−−θ
=
i
p
i
p
i
p
i
p
p
nnnn
nnnn
r , (8)
2/122
eff
2/122
eff
01 ]sin)/[(cos
]sin)/[(cos
θ−+θ
θ−−θ
=
i
s
i
s
s
nn
nn
r , (9)
2/1
1
22
eff1
2
eff
2/1
1
22
eff1
2
eff
12 ]sin)/[(cos)/(
]sin)/[(cos)/(
θ−+θ
θ−−θ
= p
s
p
s
p
s
p
sp
nnnn
nnnn
r , (10)
2/1
1
22
eff1
2/1
1
22
eff1
12
]sin)/[(cos
]sin)/[(cos
θ−+θ
θ−−θ
=
s
s
s
ss
nn
nn
r , (11)
where θ is the angle of incidence of the laser beam, and
θ1 is determined from the Snell law;
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2008. V. 11, N 1. P. 11-15.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
13
ni sin θ = ns sin θ1,
where ni = 1, ns = 1.5.
We can write the equations for the total Fresnel
reflection coefficients [9]:
)2exp(1
)2exp(
1201
1201
p
pp
p
pp
p
irr
irr
r
δ−+
δ−+
= , (12)
)2exp(1
)2exp(
1201
1201
s
ss
s
ss
s irr
irr
r
δ−+
δ−+
= , (13)
where
1eff cos2 θ⎟
⎠
⎞
⎜
⎝
⎛
λ
π=δ p
p nd , (14)
1eff cos2 θ⎟
⎠
⎞
⎜
⎝
⎛
λ
π=δ s
s nd , (15)
where d is the grating thickness (Fig. 2).
If we have the Fresnel reflection coefficients rp and
rs, we can write the main ellipsometry law [8]:
)exp()tan( ∆Ψ= i
r
r
s
p . (16)
We carried out theoretical simulation for a CD-type
disc structure to verify the diffraction sensitivity of the
ellipsometric technique. Our parameters for calculation
were as follows: Λ = 1500 nm, b= 1500–600 = 900 nm,
λ = 632.8 nm, ni = 1, ns = 1.5. We performed the theo-
retical simulations of disc relief structures with the path
line either parallel (φ = 0°, Ψ0, ∆0) or normal (φ = 90°,
Ψ90, ∆90) to the incident plane. Fig. 3 shows the Ψ0, ∆0
variations versus the angle of incidence for various
profile depths in glass. Second-order EMT predicts the
minimum for the function of Ψ around Brewster angles.
On the other hand, this theory predicts that the function
of ∆ must cross 90 deg. for these angles of incidence. As
expected, both ellipsometric parameters Ψ0, ∆0 are very
sensitive to the depth d in the region of the Brewster
angle of incidence for pure glass substrate (θ ≈ 57°).
These simulations were performed to characterize the
changes in d of 10 nm. We can note that changes in the
diffracted light parameters Ψ0 and ∆0 are sufficient to
detect 10-nm variations in depth of the disc profile.
3. Experiment
The ellipsometric parameters Ψ0, ∆0 and Ψ90, ∆90 at
λ = 632.8 nm of 7 disc profile structures were measured.
He-Ne laser was used as the source of illumination. The
incident beam passed through the polarizer and
compensator and illuminated the disc structure. The
glass disc was rotated about the vertical axis to provide φ
variations. The ellipsometric parameters were measured
for angles of incidence θ ranging from 50 to 65 degrees.
This allowed us to determine the ellipsometric functions,
as well as the minimum of the restored angle Ψ, which
corresponds to the Brewster angle.
50 55 60 65
2
4
6
8
10
12
14
16
18
20
22
24
Ψ
0 (d
eg
.)
θ (deg.)
d=30 nm
d=40 nm
d=50 nm
d=70 nm
d=90 nm
50 55 60 65
0
20
40
60
80
100
120
140
160
180
θ (deg.)
d=30 nm
d=40 nm
d=50 nm
d=70 nm
d=90 nm
∆ 0 (d
eg
.)
Fig. 3. The theoretical dependences of ellipsometrical
parameters Ψ0, ∆0 as a function of the angles of incidence for
various profile depths of a glass CD disc.
Fig. 4 shows the experimental measurements of the
functions Ψ0 and ∆0 for different values of the depth d.
The experimental result shows the polarization effect
from subwavelength profile features. Different depths, d,
give different angle dependences of Ψ0 and ∆0. The
region in the vicinity of the Brewster angle θBr ≈57° can
be used as sensitive signatures of the depth d.
Comparison of the experimental (Fig. 3) and
theoretical (Fig. 4) curves gives that angle dependences
of the ellipsometric parameters Ψ and ∆ for different
profile depth disc structures agree rather well with the
second-order EMT calculations in predicting the
thickness d for which the minimum of Ψ is reached and
approximate homogeneous layer models provide a
reasonable estimate of the thickness of the profile depth.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2008. V. 11, N 1. P. 11-15.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
14
48 50 52 54 56 58 60 62
0
2
4
6
8
10
12
14
16
glass
1
2
3
4
5
6
7
Ψ
0 (d
eg
.)
θ (deg.)
48 50 52 54 56 58 60 62
0
25
50
75
100
125
150
175
200 glass
1
2
3
4
5
6
7
∆
0 (d
eg
.)
θ (deg.)
Fig. 4. The experimental dependences of ellipsometrical
parameters Ψ0, ∆0 as a function of the angles of incidence for
various profile depths of a glass CD disc.
We performed measurements of disc relief
structures with the path line either parallel (φ = 0°, Ψ0,
∆0) or normal (φ = 90°, Ψ90, ∆90) to the plane of inci-
dence. It is difficult to estimate the profile depth d
directly from the data for Ψ and ∆, because it is difficult
to determine values of minimums for functions Ψ and ∆.
Then, to estimate the structure depth we have used
diagrams (∆0–∆90) versus the angle of incidence θ for
various values of d (Fig. 5).
The dimensions of the disc profile were also
measured before the optical measurements by atomic
force microscopy. The agreement between these both
measurements is reasonably good, although the value of
d from optical measurements for small thicknesses is
larger than the expected ones (Table).
48 50 52 54 56 58 60 62 64
-10
-8
-6
-4
-2
0
2
glass
1
2
3
4
5
6
7
∆ 90
−∆
0 (d
eg
.)
θ (deg.)
Fig. 5. Variations of (∆0–∆90) versus the angle of incidence θ
for different values of d for CD disc.
Table. Estimated value of the depth, d, for CD profiles in
the case of width b = 600 nm.
Number of Test Estimated depth,
d (nm) AFM, d (nm)
Test 120 30 30
Test 127 40 38
Test 130 45 45
Test V1 55 56
Test 155 70 75
Test 001 80 82
Test 011 90 93
4. Conclusion
We have demonstrated the feasibility of ellipsometric
scatterometry for the metrology of the depth by
analyzing the optical disc data layer relief structures
within the accuracy of 5 nm. For correct reading optical
discs by the standard player, the depth of relief
structures must be 125±30 nm, then the accuracy of
proposed estimations is enough to control disc
manufacture. Therewith, because material of substrate
may consist of many components, the difference of
even neighbour pit depth can reach 5 nm after ion beam
etching. The diameter of scanning laser beam is about
3 mm, then almost 2000 data tracks get in the scanned
area. It means that the averaged depth is estimated in
contrast to analysis of a single pit by atomic-force
microscope. Obtained results are extremely useful in
the context of optical disc fabrication due to monitoring
and controlling the depth of etching into a glass
(dielectric) wafer in real time (in situ) by using ellipso-
metric measurements.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2008. V. 11, N 1. P. 11-15.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
15
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