Patent Application
20100062175
This application claims priority to German Patent Application 10 2008 046 579.8, which was filed Sep. 10, 2008 and is incorporated herein by reference.
The invention relates to a method for manufacturing an optical waveguide layer.
Layers having waveguide properties are particularly required for what are known as biochips, in particular, for applications in medical diagnostics, for example, for DNA analysis or for the determination of antibodies, and in genetic engineering. An optical waveguide can, in particular, be created by applying a layer that has a higher refractive index to a substrate.
Optical waveguide layers should favorably exhibit low attenuation. When growing such layers on glass, layers having a high refractive index and low attenuation are achieved by applying the coating while the substrate is at a high temperature, so that the natural columnar growth of the layers, which hinders light propagation through the layer, is minimized.
The coating methods used to create optical waveguide layers on glass are generally associated with a high energy input into the substrate, as a result of which the substrate temperature can easily exceed a value of 100° C.
Substrate temperatures of more than 100° C., however, are not suitable for some temperature-sensitive plastic substrates. It would, on the other hand, be desirable to fabricate optical waveguide layers on plastic substrates, as these are considerably more economical to manufacture than glass substrates. In particular, thermoplastics can be processed by hot stamping or injection molding, and the microstructures required for application as biochips can be formed directly.
In one aspect, the invention discloses a method for the fabrication of an optical waveguide layer on a substrate permitting manufacturing waveguide layers of high quality with low attenuation on temperature-sensitive substrates, in particular, on plastic substrates.
According to at least one embodiment of the method for the fabrication of an optical waveguide layer, a substrate is prepared, and a first part-layer of the waveguide layer is grown on the substrate. Subsequently a second part-layer of the waveguide layer, comprising or consisting of the same material as the first part-layer, is grown on top of the first part-layer, wherein the second part-layer is bombarded with ions as it grows.
The optical waveguide layer is thus grown on the substrate in two partial steps. During the first partial step of the method, a first part-layer of the waveguide layer is applied to the substrate, and this is favorably not bombarded with ions as it grows. In this way, damage to the substrate, in particular, a plastic substrate, resulting from ion bombardment and the excessive increase in the temperature of the substrate surface that could result from this, is avoided. Only during the second stage of the process during which the second part-layer of the waveguide layer, which comprises or consists of the same material as the first part-layer, is grown, energy is introduced into the growing second part-layer by ion bombardment. The input of energy into the growing layer by means of ion bombardment creates a high quality layer, so that in this way an optical waveguide layer with low attenuation can be fabricated. In particular, attenuation values of less than 5 dB, preferably less than 3 dB, can be achieved on a variety of substrate materials. A composite of substrate and optical waveguide layer manufactured in this way exhibits, furthermore, low intrinsic fluorescence.
Favorably, the ions with which the second part-layer is bombarded during its growth have an energy of between 50 eV and 90 eV inclusive. Ions having energy in this range yield a layer of good quality; in particular, the growing layer is compacted by the ion bombardment, which allows a waveguide layer having low attenuation to be created. The ion energy is, on the other hand, still sufficiently low that damage to the substrate caused by the ion bombardment or by an excessive rise in the substrate temperature does not occur.
The ions with which the second part-layer is bombarded as it grows can, in particular, be ions of argon or oxygen.
Favorably, the temperature of the substrate during the growth of the first part-layer and of the second part-layer does not rise above 80° C. It is particularly favorable if the temperature of the substrate during the growth of the two part-layers of the waveguide layer does not rise above even 60° C.
The method is therefore particularly suitable for growing an optical waveguide layer on a temperature-sensitive substrate. In particular, the substrate may be a polymer substrate. Favorably, the substrate incorporates a cyclo-olefine polymer. Cyclo-olefine polymers feature, in particular, low intrinsic fluorescence, which is advantageous for optical measurement processes in biochip applications. Zeonex and Zeonor are examples of cyclo-olefine polymers. Cyclo-olefine polymers of this sort are temperature-sensitive, and cannot therefore easily be coated with an optical waveguide layer using conventional coating methods.
The waveguide layer that comprises the two part-layers applied one after the other favorably comprises or consists of an inorganic material. In particular, the waveguide layer can contain tantalum pentoxide (Ta2O5) or can consist of it. Owing to its relatively high refractive index and its transparency, tantalum pentoxide is very suitable as a material for optical waveguide layers.
The first part-layer of the waveguide layer, which is favorably manufactured without ion bombardment, favorably has a thickness of at least 5 nm, particularly favorably of at least 10 nm. In this way it is possible to ensure that the first part-layer protects the substrate underneath from ion bombardment while the second part-layer is being grown.
It is furthermore favorable if the second part-layer is thicker than the first part-layer, so that the greater proportion of the waveguide layer is manufactured under the influence of energy input through ion bombardment. In this way, a high layer quality is achieved, thus yielding a waveguide layer with low optical attenuation. The thickness of the first part-layer that is manufactured without ion bombardment is favorably selected in such a way that it is sufficient to protect the substrate from ion bombardment while the second part-layer is being grown. Favorably the second part-layer is at least ten times as thick as the first part-layer. The second part-layer can, in particular, have a thickness of 100 nm or more.
The first part-layer of the waveguide layer is favorably grown by thermal evaporation. In particular, it has been found advantageous for the first part-layer of the waveguide layer not to be grown with the aid of electron beam evaporation, as in that case a higher intrinsic fluorescence results in the substrate with the applied waveguide layer than in the case of purely thermal evaporation.
The second part-layer can be grown with the aid of thermal evaporation and/or electron beam evaporation. Favorably, the second part-layer, like the first part-layer, is grown using only thermal evaporation.
The optical waveguide layers manufactured by means of the present method are characterized by good adhesion and by a good resistance to temperatures in the range from −25° C. to +60° C. The waveguide layers also exhibit high resistance to polar solvents.
The invention is explained in more detail below with the aid of an exemplary embodiment and in association with
Elements that are the same, or that have the same effect, are in each case referred to using the same reference numbers. Neither the elements illustrated nor the relative sizes of the elements should be thought of as being to scale.
In the first intermediate step illustrated in
The substrate 4 is favorably a polymer substrate. In particular, the polymer substrate 4 may be a substrate comprising or consisting of a cyclo-olefine polymer, since cyclo-olefine polymers exhibit low intrinsic fluorescence, which is advantageous for applications in biochips.
The optical waveguide layer, of which the first part-layer 1 is applied during the first intermediate step illustrated in
The material of the first part-layer 1 is favorably applied to the substrate 4 from an evaporation source 6, as suggested by the arrow. The coating process is advantageously carried out in high-vacuum coating equipment, e.g., in coating equipment that permits plasma ion assisted deposition (PIAD). During the coating process, the equipment is favorably evacuated down to a pressure in the range less than 1×10−6 mbar.
The material that is to be applied is evaporated in the evaporation source 6 from, e.g., a crucible, for instance, a tungsten boat. The crucible is heated for this purpose by, for instance, resistance heating.
The first part-layer 1 is favorably grown by means of thermal evaporation up to a thickness of at least 5 nm on the substrate 4. The first part-layer 1 can, for example, have a thickness of about 10 nm.
In the second partial step of the method, illustrated in
The ion bombardment is provided by a plasma ion source (not illustrated). A suitable plasma ion source is, for instance, the APS (Advanced Plasma Source) plasma ion source manufactured by the company Leybold Optics. The ions are accelerated in the direction of the substrate 4 by an adjustable bias voltage. A bias voltage is favorably set to between 50 V and 90 V, in order to bombard the substrate with ion energies of between 50 eV and 90 eV. In particular a value of 80 V, can be set for the bias voltage.
The ions 5 can, for example, be argon and/or oxygen ions. In order to generate the ions, the plasma ion source is supplied with argon or oxygen gas, for instance argon at a flow rate of 14 sccm and oxygen at a flow rate of 20 sccm.
The substrate 4 is protected from the ion bombardment during the growth of the second part-layer 2 by the previously applied first part-layer 1. The temperature of the substrate, furthermore, only rises slightly during the coating process, so that the substrate is also not damaged by a rise in temperature. For example, a temperature of 28° C. is measured at the substrate 4 at the beginning of the coating process, and a temperature of 55° C. at the end.
Like the first part-layer 1, the second part-layer 2 can be created by thermal evaporation from a crucible, for instance from a tungsten boat. The second part-layer 2 can, alternatively, be grown by means of electron beam evaporation. Favorably, however, both the first part-layer 1 and the second part-layer 2 are deposited with the aid of thermal evaporation.
The thickness of the second part-layer 2 is favorably greater than the thickness of the first part-layer 1. In particular, the second part-layer 2 can be at least ten times as thick as the first part-layer 1. The first part-layer 1 can, for example, be grown to a thickness of about 10 nm, while the second part-layer 2 is applied to a thickness of more than 100 nm. The growth rate can, for instance, be 0.23 nm/s. As a result of the ion bombardment during growth of the second part-layer 2, a comparatively dense layer is achieved, characterized by a low attenuation of 5 dB or less.
The method is thus particularly suitable for manufacturing optical waveguide layers having low attenuation on temperature-sensitive substrates.
The invention is not restricted to the description that refers to the example embodiments. The invention, rather, comprises every new feature and every combination of features, and, in particular, any combination of features in the patent claims, even if this feature or this combination itself is not explicitly described in the patent claims or in the exemplary embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 046 579.8 | Sep 2008 | DE | national |
