US2007201136A1PendingUtilityA1
Thin Film Interference Filter and Bootstrap Method for Interference Filter Thin Film Deposition Process Control
Est. expirySep 13, 2024(expired)· nominal 20-yr term from priority
Inventors:Michael L. Myrick
G01N 21/8422G01N 2021/8438G02B 5/28G01N 21/55
55
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Claims
Abstract
A thin film interference filter system includes a plurality of stacked films having a determined reflectance; a modeled monitor curve; and a topmost layer configured to exhibit a wavelength corresponding to one of the determined reflectance or the modeled monitor curve. The topmost layer is placed on the plurality of stacked films and can be a low-index film such as silica or a high index film such as niobia.
Claims
exact text as granted — not AI-modified1 . A method using experimental measurements to determine reflectance phase and complex reflectance for arbitrary thin film stacks, the method comprising the steps of:
determining reflectance of a stack of a plurality of films before depositing a topmost layer; considering a modeled monitor curve for a wavelength of a high-index layer; and discarding a plurality of monitor curves without maxima in their reflectance during the topmost layer deposition.
2 . The method as in claim 1 , wherein the topmost layer is a niobia layer.
3 . The method as in claim 2 , further comprising the steps of determining an anticipated standard deviation in φk for a plurality of monitor wavelengths in the niobia layer and discarding any with σ greater than 0.9 degrees.
4 . The method as in claim 3 , further comprising the step of computing expected error in δ for wavelengths with σ less than 0.9 degrees at a target thickness of the niobia layer.
5 . The method as in claim 4 , further comprising the step proceeding with a full model deposition of the niobia layer when no wavelengths have an error less than 0.9 degrees.
6 . The method as in claim 1 , further comprising the step of using only the modeled monitor curve during the topmost layer deposition when there is no maxima in the reflectance of each of the plurality of monitor curves.
7 . The method as in claim 1 , further comprising the step of computing a value of δ for all wavelengths based on a value calculated for the monitor wavelength.
8 . The method as in claim 1 , further comprising the step of computing two possible values of phase angle for each wavelength other than the monitor wavelength.
9 . The method as in claim 1 , further comprising the steps of using information extracted from the model for r k at each wavelength and the computed best value of δ, and computing an estimated standard deviation of phase at all wavelengths except the monitor.
10 . The method as in claim 9 , further comprising the steps of using the computed phase closest to the model phase for r k at each wavelength, measured R f and R k values and the computed best value of δ, and computing the estimated standard deviation of phase at all wavelengths for which the magnitude of r k was estimated other than the monitor.
11 . The method as in claim 9 , further comprising the steps of determining if a phase error estimate is less than about 1.3 degrees and averaging calculated and modeled reflectance and phase values to obtain a new value for use in subsequent modeling at that wavelength.
12 . The method as in claim 1 , wherein the topmost layer is a silica film.
13 . The method as in claim 12 , further comprising the step of replacing the magnitude of the amplitude reflectance at each wavelength with √{square root over (R k )} whenever measuring a latest depositing silica film having an intensity reflectance greater than 9%.
14 . The method as in claim 13 , further comprising the step of determining if a phase error estimate is less than about 1.3 degrees when the magnitude of the amplitude reflectance at each wavelength has been replaced with √{square root over (R k )} and averaging calculated and modeled reflectance and phase values to obtain a new value for use in subsequent modeling at that wavelength.
15 . A method for correcting thin film stack calculations for accurate deposition of complex optical filters, the method comprising the steps of:
determining phase angle φk at a monitor wavelength from |r′ k | and Rk using a first equation expressed as: cos ( ± ϕ k ) = r k ′ 2 ( 1 + R k r 2 2 ) - r 2 2 - R k 2 r 2 R k ( 1 - r k ′ 2 ) ; and estimating r′ k using a second equation r k ′ = r k - r 2 1 - r 2 r k ; and obtaining a value for phase at a monitor wavelength.
16 . A method for automated deposition of complex optical interference filters, the method comprising the steps of:
determining from a measurement of intensity reflectance at a topmost interface a phase angle φ at an interface k according to an equation expressed as: cos ( ϕ k ) = ( A ( 1 + r 2 2 ) sin ( δ ) ± B cos ( δ ) C ) A = R f + r 2 4 ( R f - R k ) - R k + 2 r 2 2 ( ( 1 - R f ) ( 1 + R k ) cos ( 2 δ ) - ( 1 - R f R k ) ) B = D ( 1 + r 2 12 ) + F ( r 2 2 + r 2 10 ) + G ( r 2 4 + r 8 2 ) + H r 6 2 C = sin ( δ ) ( 4 r 2 ( 1 - R f ) R k 1 / 2 ( 2 r 2 2 cos ( 2 δ ) - 1 - r 2 4 ) ) D = - ( R f - R k ) 2 F = 2 ( R k ( 2 + R k ) + R f 2 ( 1 + 2 R k ) + 2 R f ( 1 - 5 R k + R k 2 ) - 2 ( 1 - R f ) ( 1 - R k ) ( R f + R k ) cos ( 2 δ ) ) G = - 6 - 4 R f - 5 R f 2 - 4 R k + 38 R f R k - 4 R f 2 R k - 5 R k 2 - 4 R f R k 2 - 6 R f 2 R k 2 + 8 ( 1 - R f 2 ) ( 1 - R k 2 ) cos ( 2 δ ) - 2 ( 1 - R f ) 2 ( 1 - R k ) 2 cos ( 4 δ ) H = 4 ( 3 + 2 R f 2 - 10 R f R k + 2 R k 2 + 3 R f 2 R k 2 - 2 ( 1 - R f ) ( 1 - R k ) ( 2 + R f + R k + 2 R f R k ) cos ( 2 δ ) + ( 1 - R f ) 2 ( 1 - R k ) 2 cos ( 4 δ ) )
17 . The method as in claim 16 , wherein a process control for a deposition system is bootstrapped by detaching the deposition system from all but the topmost interface.
18 . The method as in claim 16 , further comprising the step of validating two resultant solutions according to the expression:
R
f
=
2
r
2
2
+
R
k
(
1
+
r
2
4
)
+
2
r
2
Q
1
+
r
2
4
+
2
r
2
2
R
k
+
2
r
2
Q
Q
=
r
2
2
R
k
1
/
2
cos
(
2
δ
+
ϕ
k
)
+
R
k
1
/
2
cos
(
2
δ
-
ϕ
k
)
-
r
2
(
1
+
R
k
)
cos
(
2
δ
)
-
(
1
+
r
2
2
)
R
k
1
/
2
cos
19 . The method as in claim 16 , further comprising the step of averaging calculated and modeled reflectance and phase values to obtain a new value to be used in all future modeling at a given wavelength.
20 . A thin film interference filter system, comprising:
a plurality of stacked films having a determined reflectance; a modeled monitor curve; and a topmost layer configured to exhibit a wavelength corresponding to one of the determined reflectance or the modeled monitor curve, the topmost layer being disposed on the plurality of stacked films.
21 . The thin film interference filter system as in claim 20 , wherein the topmost layer is a silica film.
22 . The thin film interference filter system as in claim 20 , wherein the topmost layer is a niobia film.Cited by (0)
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