WO2009122381A1 - Spectrally-sensitive light filter arrangement and approach therefor - Google Patents

Spectrally-sensitive light filter arrangement and approach therefor

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Publication number
WO2009122381A1
WO2009122381A1 PCT/IB2009/051425 IB2009051425W WO2009122381A1 WO 2009122381 A1 WO2009122381 A1 WO 2009122381A1 IB 2009051425 W IB2009051425 W IB 2009051425W WO 2009122381 A1 WO2009122381 A1 WO 2009122381A1
Authority
WO
Grant status
Application
Patent type
Prior art keywords
filter
light
arrangement
different
conductive
Prior art date
Application number
PCT/IB2009/051425
Other languages
French (fr)
Inventor
Vitali Souchkov
Original Assignee
Nxp B.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

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Classifications

    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength, or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144Devices controlled by radiation
    • H01L27/146Imager structures
    • H01L27/14601Structural or functional details thereof
    • H01L27/1462Coatings
    • H01L27/14621Colour filter arrangements
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength, or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144Devices controlled by radiation
    • H01L27/146Imager structures
    • H01L27/14601Structural or functional details thereof
    • H01L27/14625Optical elements or arrangements associated with the device

Abstract

Ambient light is sensed using a filtering approach. According to an example embodiment of the present invention, conductive structures (e.g., 120) are used to filter light at different wavelengths for different regions of a light sensor (e.g., 110). The filtered light is sensed or detected, and is used together with known filtering aspects (e.g., knowledge of a wavelength range of incident light) for one or more of a variety of purposes.

Description

SPECTRALLY-SENSITIVE LIGHT FILTER ARRANGEMENT AND APPROACH THEREFOR

This patent document relates to light filters, and more particularly, to light filters for applications including color imaging and selection of spectral regions above and below the visible spectrum.

Digital imaging devices generally use a set of optics to focus an image onto an image sensor that is responsive to incident light by generating an electrical output. Many digital image sensors employ charge-coupled devices (CCDs) or complementary metal- oxide semiconductor (CMOS) devices, and circuitry to process the electrical output of these sensors for generating an image. These techniques are also used in the detection of electromagnetic radiation in spectral regions different from visible light, while imaging is useful for illustration.

Color images are digitally obtained using a variety of approaches. In many applications, sensors corresponding to certain pixels are used to selectively detect light of a certain color (or wavelength), which can be effected using a color filter to filter certain types of light, such that the output of the pixel(s) correspond to the unfiltered light. One approach involves using what is often referred to as a color filter array (CFA), which is an array of filters having different wavelength-filtering characteristics. For instance, a red, green and blue (RGB) array of interleaved color mosaics has been used for a variety of applications.

Digital imaging approaches have been challenging to implement for a variety of reasons. For example, many filters are complex, expensive and/or have a limited lifetime. In addition, manufacturing approaches for certain filters are not readily implemented with other manufacturing techniques, which can contribute to the expense of the filters and the devices in which they are implemented. Where CMOS sensors are used, many filtering approaches result in inefficient light capture due to the filter location relative to in- substrate sensor location.

Addressing the aforesaid difficulties in accurately and economically sensing light has been challenging. Manufacturing costs, size limitations, packaging difficulties, process integration and other issues relating to various approaches have been a source of difficulty in effectively and efficiently generating spectrally resolved (or colored) digital images. The present invention is directed to overcoming the above-mentioned challenges and others related to the types of applications discussed above and in other applications, such as those that may combine both visible and invisible radiation detection. These and other aspects of the present invention are exemplified in a number of illustrated implementations and applications, some of which are shown in the figures and characterized in the claims section that follows.

According to an example embodiment of the present invention, conductive layers within a semiconductor device, with conductive features to selectively filter visible and close to visible radiation spectra to selectively pass radiation to an underlying sensor. The conductive layers can be formed on the sub-micrometer scale, and can be tailored to filter select radiation at different locations in the device to facilitate the detection of different radiation at different sensor locations. This filtering approach can be implemented for the selective detection of different types of radiation (e.g., different wavelengths of light), without necessarily involving the use of external optics or sophisticated packages otherwise often used to achieve desired spectral selectivity, addressing issues including those discussed in the background above.

According to another example embodiment of the present invention, a spectrally- sensitive light sensor arrangement includes a semiconductor substrate, a light sensor array and a conductive filter arrangement having various conductive features. The light sensor array includes a plurality of light sensors, and the conductive filter arrangement that is located over the sensor array (i.e., between the sensor array and light sources). The filter arrangement includes a plurality of differently-arranged conductive structures (features) to filter different wavelengths of light at different locations, and to control the wavelengths of incident light that reach different light sensors in the sensor array. The above summary is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and detailed description that follow more particularly exemplify these embodiments.

The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:

FIG. 1 shows a semiconductor sensor using a filter arrangement to filter incident light, according to an example embodiment of the present invention; FIG. 2 shows a conductive filter arrangement having conductive features with hexagonal cross-sections to filter incident light, according to another example embodiment of the present invention;

FIG. 3 A shows a cross-sectional view of a multi-layer filter arrangement, according to another example embodiment of the present invention;

FIG. 3B shows an example plot of a transfer function of non-polarized light as may be implemented with the filter arrangement of FIG. 3A, according to another example embodiment of the present invention;

FIGS. 4A and 4B show transfer functions for a metal strip-based filter arrangement, according to another example embodiment of the present invention; and

FIG. 5 shows a cross-sectional view of a conductive strip-based optical filter structure, according to another example embodiment of the present invention.

While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention, including that defined by the claims.

The present invention is applicable to a variety of sensor arrangements and approaches, and particularly to sensor arrangements for selectively detecting visible light. While the present invention is not necessarily limited to such applications, an appreciation of various aspects of the invention is best gained through a discussion of examples in such an environment.

According to an example embodiment of the present invention, a spectrally- sensitive semiconductor sensor includes a conductive filter arrangement that uses different conductive features to filter ambient light that reaches underlying sensors. The filter arrangement can be formed as part of a semiconductor layer and, accordingly, integrated with semiconductor manufacturing approaches (e.g., to filter light reaching CMOS-based sensors). In these contexts, conductive material used to form the filter can be patterned or otherwise arranged using semiconductor manufacturing processes to define features on the sub-micron scale. For certain embodiments, the sensor employs a dielectric layer to filter incoming radiation to limit the range of wavelengths of incoming radiation that reaches the conductive filter arrangement. In some applications, the filter arrangement facilitates the extraction of a visible portion of background radiation in sensing ambient light, such that a resulting signal from detected (filtered) light is predominantly generated in response to photons in the visible spectrum. In other applications, the filter arrangement facilitates the separation of spectra for a variety of different kinds of light and radiation detection approaches, and for use in a variety of different types of instrumentation. In addition, these filters and filtering approaches may be implemented, for example, without electrical connection to the conductive filter arrangements.

The conductive filter arrangement is arranged and/or manufactured in one or more of a variety of manners, and can be tailored as such to suit a variety of different applications. In some embodiments, the filter arrangement includes a combination of apertures having different shape characteristics and/or having a different spatial arrangement to suit particular applications, devices or environments with which the filter arrangement is expected to be used. In some embodiments, the filter arrangement has different apertures with different shapes that facilitate different filtering characteristics at different filter locations (pertaining to the apertures). In some applications, the shapes are arranged in a pattern that, relative to an underlying sensor, facilitates the detection of different wavelengths of light at different sensor locations. For instance, where the sensor includes an array of individual sensors, the filter arrangement can be tailored to selectively filter light differently for each individual sensor.

In other embodiments, the filter arrangement includes apertures that are spatially arranged (i.e., laterally and/or at different depths) relative to an underlying sensor to achieve specific filtering characteristics. For instance, the apertures can be formed in a conductive material and spaced laterally to align with a particular underlying sensor to filter light for that sensor. The relative depths of the apertures can be set to facilitate different filtering characteristics for different underlying sensors as may be attributable, for example, to a thickness of material between the apertures and the underlying filter or a thickness of material over the apertures. In some embodiments, a dielectric material layer is used over the apertures to effectively pre-filter select wavelengths of incoming light to shorten or narrow the range of wavelengths of light that reach the underlying filter arrangement. In one implementation, a dielectric layer having a refractive index of about 1.46 is used to filter incoming visible radiation having wavelengths in the 400-80OnM range, to pass wavelengths of radiation in the 274-548nM range to an underlying filter arrangement. This passive pre-filtering approach facilitates the use of conductive-based filters having relatively small design features, and in many implementations, having small design features exhibiting apertures having feature distances of about 200-50OnM. Turning now to the figures, FIG. 1 shows a semiconductor sensor 100 using a filter arrangement employing one or more of the above approaches to filter incident light 105, according to another example embodiment of the present invention. The sensor 100 includes a photosensor layer 110 that senses light 105 filtered by a conductive filter layer 120 having apertures therein. In some embodiments, the sensor 100 includes a dielectric layer 130 over the filter layer 120 to pre-filter light 105 incident upon an upper surface 135 of the sensor 100.

The filter layer 120 employs conductive filters in accordance with one or more of the above example embodiments. In one implementation, the filter layer 120 includes two-dimensional lattices located in a plane that is perpendicular to incident light to facilitate desirable transparency and suppress oscillations of a transfer function of the filter for a particular spectral region (e.g., several layers of laterally spread lattices may be used). In another implementation, the filter layer 120 uses multiple metal layers with differently sized and shaped openings in sequential layers that are positioned perpendicularly to incident light 105 to control variations of the optical transfer function of the filter. In still another implementation, the filter layer 120 includes conductive apertures that polarize the (non-polarized) incident light 105 prior to wavelength filtering.

FIG. 2 shows a conductive filter arrangement 200 having conductive (e.g., metal) features with hexagonal cross-sections to filter incident light 205, according to another example embodiment of the present invention. The conductive features are made of conductive material layer 210 (or layers) that is/are embedded in a dielectric layer 220, which interfaces air at an upper surface 225 and a silicon layer 230 at a lower surface. Transferred power that enters the silicon layer 230 is simulated at the surface that is perpendicular to the incident beam direction. The composition and arrangement of the conductive layer 210, dielectric layer

220 and silicon 230 are set to suit different applications. For instance, the dielectric layer 220 may exhibit a refractive index of about n=l .8 to facilitate certain filtering characteristics. In one embodiment, the indicated thicknesses and hexagonal cross- sections are geometrically spaced as follows: tl=5000nM, t2=550nM, t3=1000nM, t4=12uM, a=170nM, b=550nM. Other embodiments are directed to the use of different thicknesses, feature dimensions and shapes to filter light in different manners, and to control the response of a sensor to which the filter arrangement 200 passes light, such as by setting the transfer function and related cutoff of the filter arrangement 200. As discussed above, one or more metal layers can be combined to set filtering characteristics for an underlying sensor. FIG. 3A shows a cross-sectional view of a filter arrangement 300 employing one such approach, according to another example embodiment of the present invention. FIG. 3B shows a plot of the transfer function of non-polarized light for the light filter arrangement 300 of FIG. 3A. The filter arrangement 300 includes three layers of conductors 310, 320 and 330 arranged vertically, relative to incident light and an underlying sensor, respectively having openings (e.g., square apertures) 312, 322 and 332 that are progressively smaller from top-down. Each of the conductors 310, 320 and 330 respectively include openings with sizes 32OnM, 38OnM and 44OnM and filter light differently, such that the combination of the three results in a net filtering characteristic suited for a particular application.

Incident non-polarized light may be treated as a combination of polarized components along the axis of symmetry 305 of the openings 312, 322 and 332.

In some applications, the filter arrangement 300 is part of a layer of conductive apertures that filter light passed to an underlying array of photosensors, which differently-shaped and/or positioned apertures filtering light to different photosensors. By implementing such an approach with sub-micron semiconductor technologies, different filtering characteristics can be set for different regions in a particular sensor (e.g., different sensors in a sensor array, or different pixels) to control the response the sensors relative to the wavelength of light incident thereupon.

FIG. 4A and 4B show transfer functions for a metal strip-based filter arrangement, according to another example embodiment of the present invention. The functions are achieved using 32OnM wide and 535 nM thick strips of Aluminum embedded in a dielectric with refraction index of about n=1.46, similar to the approach shown in FIG. 2.

The transfer functions for parallel or perpendicular polarizations (i.e., the electric field being either parallel or perpendicular to the strips) are shown separately. As arranged, the transfer function of the strip system with electric field perpendicular to the strips has more oscillations in the transmission region and slow decay at longer wavelength, while the long wave cutoff is strong for polarization conditions involving the use of an electric field vector that is parallel to the strips.

Results such as those shown in FIG. 4A and in FIG. 4B can be achieved using strips having a pitch to suit particular applications, with the particular results shown respectively using pitches of 640, 720 and 80OnM. Variation in the cutoff wavelength is proportional to the gap width between strips, with the proportionality coefficient equal to that of the refraction index of the dielectric in which the strips are embedded. Attenuation in the cutoff region as strong as about 0.25-0.30db/nM can be reached for light polarized linearly along the strips. FIG. 5 shows a cross-sectional view of a conductive strip-based optical filter structure 500, according to another example embodiment of the present invention. An absorbing material at portions 510 and 520 absorbs the incident radiation 505. Dielectric material 530 and 532 is transparent and, in some instances, are the same material. The material 540 is conductive material such as metal, poly-silicon or a combination including metal and/or poly-silicon. In some instances the openings where light propagates are filled with dielectric material having a refractive index that is close to the refractive index of air. The combination of absorbing, dielectric and conductive materials in the filter structure 500 facilitate sharp attenuation in a selected spectral region by polarizing the incident light prior to filtering with conductive strips system. The upper portion of the filter structure 500, including the absorbing materials

(510, 520) and the dielectric material 530, polarizes the incident light 505 by capturing light polarized in a direction that is perpendicular to the plane as shown, using reflection at Brewster's angle φ (or around φ in relatively wide range). This upper polarizing portion can be formed, for example, by micro-machining using methods similar to those used in fabrication of MEMS pressure sensors and micro mirrors. In some applications, a dielectric material is located or formed on top of the filter structure 500 to collimate incident light, which can desirably affect the filtering of the light.

The various embodiments described above and shown in the figures are provided by way of illustration only and should not be construed to limit the invention. Based on the above discussion and illustrations, those skilled in the art will readily recognize that various modifications and changes may be made to the present invention without strictly following the exemplary embodiments and applications illustrated and described herein. For example, conductive filters with features as described herein may be implemented with a variety of different metal-based and other non-metallic materials. The spatial arrangement of the filters, and the physical arrangement of filter features (apertures and/or others), are also modified to suit various implementations. For example, highly symmetrical structures, such as a honeycomb structure, of different sizes and/or placed at different depths can be used to suppress oscillatory behavior in a filter transmission region. Arrays of openings of polygon shapes with variations of shape, size and/or depth can be used to increase filter transparency in a desired spectral region, and suppress oscillations of the transfer function. These approaches can be implemented using common CMOS technologies. Such modifications and changes do not depart from the true scope of the present invention.

Claims

What is claimed is:
1. A spectrally-sensitive light sensor arrangement comprising: a semiconductor substrate (e.g., 100); a light sensor array (e.g. , 110) in the substrate and including a plurality of light sensors; a conductive-feature filter arrangement (e.g., 120) over the sensor array, the filter arrangement including a plurality of differently-arranged conductive structures to filter different wavelengths of light at different locations, and to control the wavelengths of incident light that reach different light sensors.
2. The arrangement of claim 1, wherein the conductive structures are arranged in shape, symmetry and location to facilitate, at each structure, transparency in a selected spectral region and suppression of transfer function oscillations of the incident light.
3. The arrangement of claim 1, wherein the filter arrangement filters non- visible background radiation to facilitate ambient light sensing at the light sensor array.
4. The arrangement of claim 1 , further including a dielectric material over the filter arrangement to limit the amount of incident light of certain wavelengths that reach the filter arrangement.
5. The arrangement of claim 1, wherein the filter arrangement includes multiple layers of conductors, each layer having openings of different sizes, shapes and spatial arrangement to filter incident light of different wavelengths at different locations in the filter.
6. The arrangement of claim 1 , wherein the filter arrangement includes multiple layers of conductive-feature lattices in a dielectric material and arranged perpendicular to an incident light direction, relative to the sensor array.
7. The arrangement of claim 1, wherein the filter arrangement includes multiple conductive layers arranged perpendicular to an incident light direction, relative to the sensor array, the conductive layers having differently-arranged openings therein to filter the incident light.
8. The arrangement of claim 1, wherein the filter arrangement includes a conductive layer having a plurality of differently-spaced openings.
9. The arrangement of claim 1 , wherein the filter arrangement is embedded in a dielectric material.
10. The arrangement of claim 1, wherein the filter arrangement includes a two- dimensional lattice of conductive material, the lattice having an array of openings arranged in size and shape to filter different wavelengths of light at different locations in the lattice.
11. The arrangement of claim 1, wherein the filter arrangement includes a polarization filter including a dielectric structure that captures light of select polarization using Brewster's angle reflections.
12. An optical filter arrangement for spectrally filtering incident light, the filter arrangement comprising: a semiconductor substrate(e.g., 100); and a plurality of differently-arranged conductive structures (e.g., 120) in the semiconductor substrate, the conductive structures being adapted to filter different wavelengths of incident light at different locations in the filter arrangement.
13. The arrangement of claim 12, further including a dielectric material in the substrate to filter the incident light.
14. The arrangement of claim 12, further including a dielectric material in the substrate and over the conductive structures to filter the incident light reaching the conductive structures.
15. The arrangement of claim 12, wherein the conductive structures are arranged in a dielectric material layer in the substrate.
16. The arrangement of claim 12, further including a polarization arrangement to polarize the incident light before it reaches the conductive structures.
17. The arrangement of claim 12, wherein the conductive structures define openings of different sizes, shapes and spatial arrangement to filter incident light of different wavelengths at different locations in the filter.
18. The arrangement of claim 12, wherein the conductive structures are arranged in shape, symmetry and location to facilitate, at each structure, transparency in a selected spectral region and suppression of transfer function oscillations, for light incident thereupon.
19. A method for filtering light, the method comprising: using a plurality of differently-arranged conductive structures (e.g., 120) in a semiconductor substrate (e.g., 100) to filter different wavelengths of incident light at different locations, and to control the wavelengths of incident light that are passed.
20. The method of claim 19, further comprising: arranging and using the conductive structures to vary the transfer function of filtered incident light at different filter locations.
PCT/IB2009/051425 2008-04-03 2009-04-03 Spectrally-sensitive light filter arrangement and approach therefor WO2009122381A1 (en)

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US61/042,101 2008-04-03

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20030103150A1 (en) * 2001-11-30 2003-06-05 Catrysse Peter B. Integrated color pixel ( ICP )
US6852562B1 (en) * 2003-12-05 2005-02-08 Eastman Kodak Company Low-cost method of forming a color imager
US20050121599A1 (en) * 2003-12-03 2005-06-09 Chandra Mouli Metal mesh filter-comprising semiconductor image sensor
WO2007118895A1 (en) * 2006-04-19 2007-10-25 Commissariat A L'energie Atomique Microstructured spectral filter and image sensor

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20030103150A1 (en) * 2001-11-30 2003-06-05 Catrysse Peter B. Integrated color pixel ( ICP )
US20050121599A1 (en) * 2003-12-03 2005-06-09 Chandra Mouli Metal mesh filter-comprising semiconductor image sensor
US6852562B1 (en) * 2003-12-05 2005-02-08 Eastman Kodak Company Low-cost method of forming a color imager
WO2007118895A1 (en) * 2006-04-19 2007-10-25 Commissariat A L'energie Atomique Microstructured spectral filter and image sensor

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