PHOTO RESIST AS OPAQUE APERTURE MASK ON MULTISPECTRAL FILTER ARRAYS

Abstract

An apparatus (e.g., a multi-spectral optical filter array, an optical wafer, an optical component) has an aperture mask printed directly thereon, the aperture mask including a positive or negative photoresist. The apparatus includes a substrate having the aperture mask printed on at least one of a light entrance surface or a light exit surface of the substrate so as to provide an aperture over a portion of the substrate. The photoresist from which the aperture mask is formed is photo-definable or non-photo-definable, and is deposited/printed to form the aperture mask on the substrate.

Claims

1. A method comprising: depositing a first photoresist layer directly on a first surface of an optical substrate; exposing portions of the first photoresist layer to light; and developing the first photoresist layer to form a first aperture mask on the first surface of the optical substrate, wherein no optical coating is placed between the first surface of the optical substrate and the first photoresist layer.

2. The method of claim 1, wherein the first aperture mask is opaque.

3. The method of claim 1, further comprising: depositing a second photoresist layer directly on a second surface of the optical substrate that is opposite to the first surface of the optical substrate; exposing portions of the second photoresist layer to light; and developing the second photoresist layer to form a second aperture mask on the second surface of the optical substrate.

4. The method of claim 1, further comprising: forming the optical substrate, wherein the optical substrate is formed by: forming a first filter element comprising a first stack of filter layers arranged on a first filter element substrate; forming a second filter element comprising a second stack of filter layers arranged on a second filter element substrate; and bonding a sidewall of the first filter element to a sidewall of the second filter element.

5. The method of claim 4, wherein an adhesive is used to bond the sidewall of the first filter element to the sidewall of the second filter element.

6. The method of claim 5, wherein the first aperture mask is arranged directly over the adhesive.

7. A method comprising: forming a first photoresist layer over a light entrance surface of a substrate; removing portions of the first photoresist layer to form a first aperture mask defining entrance apertures on the light entrance surface of the substrate; forming a second photoresist layer over a light exit surface of the substrate; and removing portions of the second photoresist layer to form a second aperture mask defining exit apertures on the light exit surface of the substrate, wherein no optical coating is present between the substrate and the first aperture mask.

8. The method of claim 7, wherein the first photoresist layer is a positive photoresist or a negative photoresist.

9. The method of claim 7, wherein at least one of the first or second photoresist layers are opaque.

10. The method of claim 7, wherein the first photoresist layer is photo-definable.

11. The method of claim 7, wherein the first photoresist layer is non-photo-definable.

12. The method of claim 7, wherein the substrate comprises an optical filter array that comprises optical filter elements bonded to one another along sidewalls of the optical filter elements.

13. The method of claim 12, wherein the second aperture mask is arranged directly below the sidewalls of the optical filter elements, and wherein the first aperture mask is arranged directly above the sidewalls of the optical filter elements.

14. A method comprising:. forming a multi-spectral optical filter array comprising a plurality of optical filter elements bonded together along sidewalls of the optical filter elements; forming a first photoresist layer over a first surface of the multi-spectral optical filter array; and developing the first photoresist layer to remove portions of the first photoresist layer arranged directly on the multi-spectral optical filter array, thereby forming a first. aperture mask comprising portions arranged over the sidewalls of the optical filter elements.

15. The method of claim 14, wherein each optical filter elements comprises a filter layer stack, and wherein the first photoresist layer is formed directly on the filter layer stack.

16. The method of claim 14, further comprising: forming a second photoresist layer over a second surface of the multi-spectral optical filter array, wherein the second surface is opposite to the first surface of the multi-spectral optical filter array; and developing the second photoresist layer to remove portions of the second photoresist layer arranged directly on the multi-spectral optical filter array, thereby forming a second aperture mask comprising portions arranged over the sidewalls of the optical filter elements.

17. The method of claim 14, wherein the multi-spectral optical filter array comprises a light entrance surface and a light exit surface, and wherein the first photoresist layer is formed on the light entrance surface.

18. The method of claim 17, wherein the first aperture mask defines an entrance aperture on the light entrance surface of the multi-spectral optical filter array.

19. The method of claim 14, wherein the multi-spectral optical filter array comprises a light entrance surface and a light exit surface, and wherein the first photoresist layer is formed on the light exit surface.

20. The method of claim 19, wherein the first aperture mask defines an exit aperture on the light exit surface of the multi-spectral optical filter array.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The following is a brief description of the drawings, which are presented for the purposes of illustrating the exemplary embodiments disclosed herein and not for the purposes of limiting the same.

[0021] FIG. 1 diagrammatically show a side view of a first exemplary filter array having an aperture mask that includes or is formed from a photoresist, which can be printed thereon.

[0022] FIG. 2 diagrammatically show a perspective view of the filter array of FIG. 1.

[0023] FIG. 3 diagrammatically show a method of manufacturing the filter array.

DETAILED DESCRIPTION

[0024] A more complete understanding of the components, processes and apparatuses disclosed herein can be obtained by reference to the accompanying drawings. These figures are merely schematic representations based on convenience and the ease of demonstrating the present disclosure, and are, therefore, not intended to indicate relative size and dimensions of the devices or components thereof and/or to define or limit the scope of the exemplary embodiments.

[0025] Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of the embodiments selected for illustration in the drawings, and are not intended to define or limit the scope of the disclosure. In the drawings and the following description below, it is to be understood that like numeric designations refer to components of like function.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent can be used in practice or testing of the present disclosure. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and articles disclosed herein are illustrative only and not intended, to be limiting.

[0027] The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0028] As used in the specification and in the claims, the term “comprising” may include the embodiments “consisting of” and “consisting essentially of.” The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that require the presence of the named ingredients/steps and permit the presence of other ingredients/steps. However, such description should be construed as also describing compositions or processes as “consisting of” and “consisting essentially of” the enumerated ingredients/steps, which allows the presence of only the named ingredients/steps, along with any unavoidable impurities that might result therefrom, and excludes other ingredients/steps.

[0029] Numerical values in the specification and claims of this application should be understood to include numerical values which are the same when reduced to the same number of significant figures and numerical values which differ from the stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value.

[0030] All ranges disclosed herein are inclusive of the recited endpoint and independently combinable (for example, the range of “from 2 grams to 10 grams” is inclusive of the endpoints, 2 grams and 10 grams, and all the intermediate values).

[0031] The terms “about” and “approximately” can be used to include any numerical value that can vary without changing the basic function of that value. When used with a range, “about” and “approximately” also disclose the range defined by the absolute values of the two endpoints, e.g. “about 2 to about 4” also discloses the range “from 2 to 4.” Generally, the terms “about” and “approximately” may refer to plus or minus 10% of the indicated number.

[0032] The present disclosure may refer to temperatures for certain process steps. It is noted that these generally refer to the temperature at which the heat source (i.e., furnace, oven, etc.) is set, and do not necessarily refer to the temperature that must be attained by the material being exposed to the heat.

[0033] The term “room temperature” as used herein refers to a temperature in the range of 20° C. to 25° C.

[0034] It is noted that the coefficient of thermal expansion is typically reported as the average between a starting temperature and a reported temperature.

[0035] It is further noted that as used herein, “aperture mask,” “mask,” and “opaque coating” may be used interchangeably, unless understood by the context in which they are used below to refer to distinct embodiments. For example, an “aperture mask” may comprise other coatings besides “opaque”, and the use herein is intended solely to assist the reader and not to limit application of the subject disclosure to only aperture masks of opaque coating materials.

[0036] As explained in greater detail below, the present disclosure provides exemplary embodiments of methods and apparatuses including the application of an opaque aperture mask that includes or is formed from a photoresist on a variety of optical components (e.g., filter arrays). According to several embodiments set forth herein, the application may be performed on one or both faces of the filter creating an aperture mask on the entrance and/or the exit face. It will be appreciated that the non-limiting examples of the present disclosure describe and illustrate embodiments wherein the aperture mask may be offset from the entrance face and/or the exit face, taking into account the incident angle of a light ray.

[0037] As shown in FIG. 1, a preexisting or prefabricated optical filter array (i.e., the substrate) is provided. The substrate is, in particular illustrative embodiments, a multi-spectral optical filter array. The substrate may comprise an optical wafer. The substrate of FIG. 1 corresponds to an angled array. The perspective view of FIG. 2 shows the “stick” geometry of the optical filter elements of this one-dimensional filter array. As seen in both FIG. 1 and FIG. 2, the filter elements have slanted sidewalls 140 (labeled only in FIG. 1). However, the outermost optical filter elements of the filter array (those identified with numbers “1” and “4”) have straight “outer” sidewalls 141 forming the edges of the assembled filter array. This can be advantageous insofar as the assembled filter array has the shape of a right-angled parallelepiped. An alternative (not shown) is to employ optical filter elements with both sidewalls slanted, and to include additional triangular-shaped fill elements to provide the assembled filter geometry with straight outermost sidewalls. The filter array depicted in FIG. 1 is shown as being an angled filter array. However, the substrates/filter arrays of the present disclosure can generally be of any desired structure and are only limited by the apertures masks which are applied thereon.

[0038] With reference to FIG. 1, an improved filter array is shown in side-sectional view. In this diagrammatic illustrative example, a filter array includes four filter elements labeled “1” to “4”. (This is merely illustrative—in general the filter array may have dozens or hundreds of filter elements). Each filter element is diced from a filter plate on which a filter layers stack was deposited having a different optical characteristic (e.g., different pass band or stop band, in terms of center wavelength and/or bandwidth). As shown in FIG. 1, each filter element can thus include a filter layers stack 112 supported by a filter element substrate 114. The filter layers stack 112 is, for example, embodied as multiple layers of optical coatings forming interference filters, disposed on the filter element substrate 114.

[0039] Typically, each filter element is diced from a single filter plate. The filter elements may, in general, be designed for any pass band or stop band in the ultraviolet, visible, or infrared wavelength range. By way of illustrative example, a filter element operating in the visible range may include a filter element substrate 114 of glass, sapphire, or another material having suitable transparency in the optical range, and the filter stack 112 may include alternating layers of tantalum oxide (Ta.sub.2O.sub.5) and silicon dioxide (SiO.sub.2), or more generally alternating layers of two (or more) materials with different refractive index values. By way of another illustrative example, the layers may be metal/metal oxide layers such as titanium/titanium dioxide (Ti/TiO.sub.2). Known techniques for designing interference filter optical stacks can be employed to design the layer thicknesses for a given pass-band or notch filter stop-band, or to provide desired high pass or low pass filtering characteristics. The diced filter elements are bonded together using an adhesive or other bond 116. The bonded optical filter elements may comprise a plurality of optical filter elements defined by different interference filters. The interference filters of the optical filter elements may comprise pass-band filters or notch filters operating in (in various embodiments) the visible spectrum, the ultraviolet spectrum, and/or the infrared spectrum.

[0040] With continuing reference to FIG. 1, the illustrative filter array is designed to be illuminated by light. Again, the filter array depicted in FIG. 1 is shown as being an angled filter array, such that the light would enter the array at an angle. As explained above, as will be appreciated by those skilled in the art, the substrates/filter arrays of the present disclosure can generally be of any desired structure and are only limited by the apertures masks which are applied thereon.

[0041] In use, light impinges on a light entrance surface 123 of the filter array. Printed on the light entrance surface 123 of the filter array are entrance apertures 120. The entrance apertures 120 define an aperture mask on the light entrance surface 123 of the filter array. In accordance with the present disclosure, the aperture mask defined by the entrance apertures 120 includes a photoresist, with the apertures applied at predetermined locations on the array. The entrance apertures 120 reduce optical cross-talk (e.g. block stray light) at the light entrance surface 123 of the filter array.

[0042] The light then passes through the filter layers stack 112 of the filter element and through the filter element substrate 114, and exits from a light exit surface 124 of the filter array. Printed on the light exit surface 124 are exit apertures 122. The exit apertures 122 define an aperture mask on the light exit surface 124 of the filter array. In accordance with the present disclosure, the aperture mask defined by the exit apertures 122 includes a photoresist, with the apertures applied at predetermined locations on the array. The exit apertures 122 reduce optical cross-talk (e.g. block stray light) at the light exit surface 124 of the filter array.

[0043] The light output from the light exit surface of each filter element is filtered by the filter layers stack 112 of that filter element, and thus includes only the spectral component of the incident light in the pass-band (or only the spectral component outside of the stop-band, in the case of a notch filter; or only the spectral component above the cut-off wavelength in the case of a high-pass filter element; or only the spectral component below the cut-off wavelength in the case of a low-pass filter element; or so forth). In FIG. 1, the filter layers stack 112 of each filter element is disposed on the light entrance surface of the filter element (or, more precisely, on the light entrance surface of the filter element substrate 114). It is alternatively possible to have the filter layers stack disposed on the light exit surface, or to have filter layers stacks disposed on both the light entrance and exit surfaces (either of the same type to provide sharper spectral bandwidth or cutoff, or of different types to provide more complex filter characteristics, e.g., two stop-bands in a two-band notch filter).

[0044] As explained above, the entrance and exit apertures 120, 122, define apertures masks on the light entrance surface 123 and light exit surface 124 of the filter array, respectively, and are patterned opaque coatings deposited onto the boundaries between optical filter elements after assembly of the filter elements. In particular, the aperture mask includes a photoresist, or in other words is formed from the photoresist. Due to the use of a photoresist, the aperture mask can be printed directly on the light entrance or exit surfaces 123, 124 of the filter array (i.e., without an optical coating applied between the apertures and the light entrance surface or light exit surface). This advantageously eliminates the need for optical coatings between the aperture mask and the substrate, and further eliminates certain conditions required for coatings, such as temperature and stress as well as the long lift-off process in chemicals. It will also be appreciated that such an implementation will assist in the elimination of stray light and crosstalk between optical bands.

[0045] Again, the aperture mask(s) includes or is formed from a photoresist, which advantageously obviates the need to apply optical coatings to the substrate. Depending on the desired application of the filter array, the photoresist can be negative or positive. Similarly, again depending on the desired application of the filter array, the photoresist can be photo-definable or non-photo-definable (e.g., a polyimide that is not light sensitive, i.e. is not a positive photoresist and is not a negative photoresist). Suitable examples of positive photoresists capable of functioning as set forth above include, for exemplary purposes only and not for purposes of limiting the same: SK-9010, S-1813, or S-1818. Suitable examples of negative photoresists capable of functioning as set forth above include, for exemplary purposes only and not for purposes of limiting the same: AZ P4620, AZ NLof 2020, or AZ NLof 2070. Suitable examples of non-photo-definable photoresists capable of functioning as set forth above include, for exemplary purposes only and not for purposes of limiting the same: polyimides.

[0046] As will be appreciated by those skilled in the art, application of an aperture mask including a photoresist to a substrate in accordance with the present disclosure can be achieved by any suitable means. For purposes of example and not for purposes of limiting the same, the aperture mask can be applied in any desired pattern using additive manufacturing techniques, such as printing via an inkjet-type additive manufacturing printer, printing via an extrusion-type printer (i.e., a fused filament fabrication printer), printing via any other 3-D printing technique, fused deposition modeling, or any standard photolithography technique, including but not limited to contact printing, spray applications, or any other exposure or development method. A separate mask is then used to expose the photoresist to light. The photoresist can then be developed by application of a developer, which removes the undesired portion of the photoresist layer, leaving the desired portion behind as an aperture mask. In other words, the photoresist is used to form the aperture mask, rather than used as a means of forming the desired aperture mask pattern in an optical DMC coating and then being removed from the optical DMC coating.

[0047] Thus, in some embodiments an optical device comprises a multi-spectral optical filter array comprising a plurality of optical filter elements bonded together to form the multi-spectral optical filter array, and an aperture mask formed on a light entrance surface and/or on a light exit surface of the multi-spectral optical filter array wherein the aperture mask comprises a photoresist or a non-photo-definable polyimide. In some embodiments, each optical filter element comprises a filter element substrate and a filter layers stack forming an interference filter having a pass band or stop band, the filter layers stack supported by the filter element substrate. In some embodiments each optical filter element has a different pass band or stop band.

[0048] With continuing reference to FIGS. 1 and 2 and with further reference to FIG. 3, an illustrative method of manufacturing the aperture mask of a filter array is described. In an operation S1, a photoresist layer is deposited on a surface of the optical substrate, that is, on the preexisting or prefabricated optical filter array. For fabricating the entrance apertures 120, the photoresist layer is suitably deposited on the light entrance surface 123 of the filter array. For fabricating the exit apertures 124, the photoresist layer is suitably deposited on the light exit surface 124 of the filter array. In an operation S2, portions of the photoresist layer are exposed to light. In an operation S3, the photoresist layer is developed to form the aperture mask (e.g. entrance apertures 120 and/or exit apertures 122) on the surface of the optical substrate.

[0049] The apparatuses (e.g., a multi-spectral optical filter array, an optical wafer, an optical component) of the present disclosure can be manufactured by any suitable means, as will be appreciated by those skilled in the art. For example, manufacture of the filter array of FIG. 1 and FIG. 2 can include fabrication of a filter plate on a bulk substrate for each filter element 1-4. Typically, this entails disposing the substrate (e.g. a glass substrate for some visible-range designs) in a deposition system and depositing the filter layers stack by sputtering, vacuum evaporation, plasma deposition, or another technique, with the thicknesses of the constituent layers of the filter stack of each filter plate designed to provide filter characteristics of the corresponding filter type. The result of this processing is a set of filter plates, e.g. four filter plates corresponding to filter elements 1, 2, 3, and 4, for fabricating the illustrative filter array of FIG. 1 and FIG. 2. Filter elements of the desired types can then be mounted in a bonding jig and glued together at the sidewalls (e.g., slanted sidewalls for an angled array, such as that depicted in FIG. 1 and FIG. 2) using adhesive or are otherwise bonded together to form the multispectral filter array. Finally, other components, such as the entrance and/or exit apertures 120, 122 and other components (e.g., light detectors) are added to the filter array to form a complete multispectral optical system.

[0050] The present specification has been set forth with reference to exemplary embodiments. Modifications and alterations will occur to others upon reading and understanding the present specification. It is intended that the present disclosure be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.