Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1996-08-26
2003-01-14
VerSteeg, Steven H. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192150, C204S192270
Reexamination Certificate
active
06506288
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is generally directed to optical layer materials, especially for optical wavequide applications, and to the technique of producing such layers.
2. Description of Prior Art
The following prior art is considered:
(1) “Integrated Optics; Theory and Technology”, R. G. Hunsperger, Springer-Verlag 1984;
(2) Arnold et al., “Thin solid films”, 165, (1988), p. 1 to 9, “Ion beam sputter deposition of low loss Al
2
O
3
films for integrated optics”;
(3) Goell & Stanley, “Sputtered Glass Waveguides for Integrated Optical Circuits”, in Bell Syst. Tech. J. 48, 3445 (1969);
(4) M. D. Himel et al., “IEEE Photonics Technology Letters” 3(10), (1991), p. 921 ff.;
(5) C. Henry et al., Appl. Optics, 26(13), 1987, 2621, “Low Loss Si
3
N
4
—SiO
2
Optical Waveguides on Si”;
(6) J.Appl.Phys. 71(9), (1992), p. 4136, Gräupner et al.;
(7) D-E-A-41 37 606;
(8) “Plasma-Impulse CVD Deposited TiO
2
Waveguiding Films: Properties and Potential Applications in Integrated Optical Sensor Systems”, Mat.Res.Soc., Spring Meeting San Francisco, 1992, Conference publication;
(9) “Magnetron sputtering deposited AlN waveguides: Effect of the structure on optical properties”, A. Cachard et al., Vacuum 41
umbers 4-6/p. 1151 to 1153/1990;
(10) Applied Optics, Vol. 14, No. 9, September 1975, New York, US, p. 2194-2198, Ingrey et al., “Variable Refractive Index and Birefringent Waveguides by Sputtering Tantalum in O2/N2 Mixtures”;
(11) Journal of Vacuum Science and Technology, Vol. 11, No. 1, January 1974, New York, US, p. 381-384, Westwood et al., “Effect of Pressure on the Properties of Reactively Sputtered Ta2O5”;
(12) Journal of Electronic Materials, Vol. 3, No. 1, 1974, US, p. 37-50, Cheng et al., “Losses in Tantalum Pentoxide Waveguides”;
(13) Proceedings of the Spie: Hard Materials in Optics, Vol. 1275, Mar. 14, 1990, The Hague, NL, p. 75-79, Howson et al., “The Reactive Sputtering of Hard Optical Films of Tin Oxide”;
(14) Journal of Vacuum Science and Technology: Part A, Vol. 2, No. 2, April 1984, New York US, p. 1457-1460, Demiront et al., “Effects of Oxygen in Ion/Beam Sputter Deposition of Titanium Oxides”;
(15) Surface and Coatings Technology, Vol. 49, No. 1-3, Dec. 10, 1991, Lausanne, p. 239-243, Martin et al., “Deposition of TiN, TiC, and TiO2 Films by Filtered Arc Evaporation”.
It is known from (9) to deposit metal nitride layers or films by means of reactive DC-sputtering, namely layers of AlN. As optical waveguiding layers such layers are reported to have optical losses of about 11 dB/cm at minimum, at a wave-length of light of 633 nm and in the TE
0
-mode. Such layers are also reported to show optical losses down to 5 dB/cm.
It is known from (4) to manufacture TiO
2
which, applied as material of a waveguiding layer, exhibits optical losses lower than 10 dB/cm. Thereby it is not specified for which wave-mode and for which wave-length of light such losses are valid. From this reference it is further known to apply Ta
2
O
5
for waveguiding layers which exhibit optical losses of less than 5 dB/cm, which losses are again neither specified with respect to wave-lengths of light nor with respect to propagation mode. The layers are here produced by an ion plating technique.
In agreement with the contents of (4), even in the year 1991, the reference (7) teaches that TiO
2
would be most suited as a material to produce thin film optical waveguides due to its physical and chemical properties. In spite of titanium oxide exhibiting a very high index of refraction, a good chemical resistance and being very hard, it is reported that no method had been known in the literature for producing a low loss titanium oxide thin film waveguide, because of, the fact that titanium oxide exhibits a high tendency toward crystallization during manufacturing.
Therefore the reference (7) proposes to deposit TiO
2
as a material suited as optical waveguiding material by means of a pulsed micro-wave plasma CVD-method. When applied as a material for waveguiding purpose, the TiO
2
produced by the method proposed in (7) exhibits for TE
01
-waves of a wave-length, optical losses of about 2.5 dB/cm.
With respect to wave-lengths it is principally valid that the optical losses become the larger, the shorter the wave-length selected.
From the reference (2) it is further known to produce Al
2
O
3
-layers by ion beam sputtering, exhibiting low optical losses, lower than 1 dB/cm, with no propagation mode and no wavelength of light specified. Due to the proposed ion beam technology, the proposed manufacturing method is not suited for large areal coating and exhibits a relatively low coating rate. This in combination results in an accordingly uneconomic layer production.
The reference (3) proposes to use as a material for optical waveguiding layers, Rf-sputtered glass. The reference (5) further proposes to produce a material which is suited for waveguiding applications by means of low pressure plasma CVD followed by a heat treatment annealing step.
The reference, (8) further proposes to produce TiO
2
by means of plasma impulse CVD, which material, applied for monomode waveguiding in the TE
0
-mode, exhibits optical losses of 2.4 dB/cm or of 5.1 dB/cm in the TM
0
-mode, each referred to the wave-length of light of 633 nm.
In spite of the knowledge out of reference (9), the reference (6) still describes that reactive sputtering of metal nitride layers, namely of AlN, from metallic target results in layers which, applied as optical waveguiding layers, exhibit very high optical losses of 300 dB/cm at propagation conditions which are not specified. Such a material is, in fact, not any more an optical layer material due to its extremely high optical losses and may especially not be said to be suited for optical waveguiding.
Other metal oxides such as TiO
2
in reference (7), would be suited as optical layer material, whereby known methods for producing layers of such materials, as e.g. ion beam sputtering according to reference (2), micro-wave plasma CVD according to reference (7), plasma impulse CVD according to reference (8), low pressure plasma CVD according to reference (5) or ion plating methods according to (4), are disadvantageous especially with respect to large areal coating and deposition rate, so that the wide-spread production of such layer materials is very difficult to reduce to practice in a commercially feasible manner.
The recognition published in reference (7), according to which TiO
2
has the tendency of crystallization during its production, is made, with respect to tantalum pentoxide, in reference (10), i.e. in the year 1975. According to (10), already in that year, reactive DC-diode sputtered optical waveguiding layers were proposed, sputtered in N
2
- and O
2
-gas mixture atmosphere. Thus in fact, some sort of tantalum oxinitride layers were proposed.
For deposition rates of approx. 0.4 Å/sec and at temperatures of about 200° C., there are reported optical losses in the TE
0
- and the TM
0
-modes. lower than or equal to 1 dB/cm at a wavelength of light of approx. 633 nm. Such results are attributed to the nitride addition to the sputtering atmosphere.
From the reference (11) of 1974, which is referred to in reference (10), it is known to produce Ta
2
O
5
-layers for thin film capacitors and for optical waveguides by means of reactive DC-diode sputtering in an O
2
/Argon atmosphere. Different sputtering parameters are varied and losses of approx. 1 dB/cm are reported from the best layers thus produced. Thereby, the following dependencies are reported:
With rising sputtering pressure:
increase of the optical losses;
increase of coating rate;
reduction of coating temperature.
The temperatures reported in reference (11) are in a range between 160° C. and 350° C. at lower pressure of approx. 1.6·10
−2
mbar operating pressure and are about 180° C. at higher operating pressure of about 8·10
−2
mbar.
In reference (12), which is referred to in (10) as well as in (11) and which has in parts the same authors, comparisons are made between Ta
2
O
Edlinger Johannes
Kügler Eduard
Rudigier Helmut
Notaro & Michalos P.C.
Unaxis Balzers Aktiengesellschaft
VerSteeg Steven H.
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