UV LIGHT SENSOR WITH STRAY LIGHT SUPPRESSION, AND A METHOD FOR DETECTING UV LIGHT

Abstract

The invention relates to a UV light sensor produced in a CMOS method, comprising a substrate that has a surface, one or more sensor elements that detect radiation and are designed in said substrate, at least one passivation layer arranged over said substrate surface, and a functional layer that is arranged over said passivation layer and designed in the form of at least one filter. The problem addressed by the invention of providing a UV light sensor which is sensitive exclusively within the UV wavelength range is solved, in terms of arrangement, by means of filters designed directly on a planar passivation layer, and stray light suppressing means around said at least one sensor element and/or around the UV light sensor. In terms of the method, the problem is solved by measuring two output signal from at least two photo diodes fitted with different filters, and by determining a mathematical relationship between the two output signals.

Claims

1. UV light sensor produced by a CMOS process, comprising a substrate that has a surface, one or more sensor elements that detect radiation and are designed in the substrate, at least one passivation layer arranged over the substrate surface, and a functional layer that is arranged over the passivation layer, wherein the functional layer is designed as at least one filter, characterized in that the passivation layer has a planar design, and the filter is designed directly on the planar passivation layer, and stray light suppressing means are designed around the at least one sensor element and/or around the UV light sensor.

2. The UV light sensor according to claim 1, characterized in that the stray light suppressing means are formed at least partially by the filter.

3. The UV light sensor according to claim 1, characterized in that the stray light suppressing means is formed at least partially by a metal layer arranged over the entire surface of the UV light sensor, leaving the sensor elements uncovered.

4. The UV light sensor according to claim 1, characterized in that the stray light suppressing means are formed at least partially by light barriers bordering the UV light sensor laterally.

5. The UV light sensor according to claim 1, characterized in that the stray light suppressing means are formed at least partially by an embedding of the UV light sensor (1) in an opaque material, wherein the opaque material encloses the margin of the UV light sensor.

6. The UV light sensor according to claim 1, characterized in that the stray light suppressing means are formed at least partially by an opaque material on the back side of the UV light sensor.

7. The UV light sensor according to claim 1, characterized in that the stray light suppressing means are formed at least partially by trenches filled with opaque material that laterally border the respective sensor element.

8. The UV light sensor according to claim 1, characterized in that the stray light suppressing means are formed at least partially by light barriers, which are vertical with respect to the substrate surface, in the CMOS wiring planes above the sensor elements designed in the substrate.

9. The UV light sensor according to claim 8, characterized in that the vertical light barriers in the CMOS vertical wiring planes are formed by closed contact rings and/or by via rings designed offset extending into a top metal plane of the CMOS process.

10. The UV light sensor according to claim 1, characterized in that the radiation detecting sensor elements are arranged in a matrix.

11. The UV light sensor according to claim 1, characterized in that, over the radiation detecting sensor elements, filters are formed from different filter materials, wherein the filters partially overlap one another and/or the two filters are designed so that they partially overlap the active sensor element surface.

12. The UV light sensor according to claim 1, characterized in that the sensor elements are designed as photodiodes or/and ALS sensors or/and dark current compensating sensors.

13. The UV light sensor according to claim 1, characterized in that several sensor elements are arranged in a matrix, wherein the sensor elements comprise at least one photodiode with UV filter, an ALS sensor, and a photodiode with a polysilicon coating and a UV filter.

14. The UV light sensor according to claim 13, characterized in that the matrix is designed as 44 matrix with optimized half-space sensitivity, consisting of four different sensor elements.

15. The UV light sensor according to claim 14, characterized in that the optimized half-space sensitivity is set in that different sensor elements meet the following arrangement criteria: each sensor element is arranged once in the corner of the diode matrix, each sensor element is arranged twice on the side edge of the diode matrix each sensor element is arranged once per row of the diode matrix, each sensor element is arranged once per column of the diode matrix, each sensor element is arranged once in the 4 22 sub quadrants of the diode matrix.

16. A method for detecting UV light with a UV light sensor, wherein the one or more sensor elements detect light and in response thereto generate a signal, characterized in that a first output signal of a sensor element, which is designed as a photodiode, is measured, that a second output signal of a sensor element, which is designed as a photodiode with a polysilicon coating, is measured and weighted by a factor, and a mathematical relationship between the first and second output signals is determined.

17. The method according to claim 16, characterized in that, as mathematical relationship, the difference between the first and second output signals is calculated.

18. The method according to claim 17, characterized in that the first output signal is formed by a UV component, a VIS/IR component, and a leakage current component.

19. The method according to claim 17, characterized in that the second output signal is formed by a weighted VIS/IR component and a weighted leakage current component.

20. A method for detecting UV light with a UV light sensor, wherein the one or more sensor elements can detect light and in response thereto generate a signal, according to the preceding claims, characterized in that a first output signal of a sensor element, which is designed as a photodiode, is measured, that a second output signal of a sensor element, which is designed as a dark diode, is measured, wherein the dark diode is coated with an opaque metal and weighted by a factor, and a mathematical relationship between the first and second output signals is determined.

21. The method according to claim 16, characterized in that, as mathematical relationship, the difference between the first and second output signals is calculated.

22. (canceled)

23. The method according to claim 20, characterized in that, as mathematical relationship, the difference between the first and second output signals is calculated.

24. The method according to claim 23, characterized in that the first output signal is formed by a UV component, a VIS/IR component, and a leakage current component.

25. The method according to claim 23, characterized in that the second output signal is formed by a weighted VIS/IR component and a weighted leakage current component.

Description

[0035] In the associated drawings

[0036] FIG. 1 shows the spectral sensitivity of known IC structures;

[0037] FIG. 2 shows the penetration depth of radiation in silicon as a function of the wavelength of the incident radiation;

[0038] FIG. 3 shows a passivation process a) according to the prior art, b) according to the present invention;

[0039] FIG. 4 shows a top view of an IC with UV light sensor, wherein the entire IC with UV filter (hatched), pads removed, and, if applicable, other filter positions (dense hatching), is coated;

[0040] FIG. 5 shows the overlapping of the filters, in order to allow as little stray light as possible to penetrate at the boundary sites; in the process, the UV filter is brought as close as possible to the optical opening of the other sensor element, in order to maximize the degree of coverage of the UV filter; a) top view, b1) the second filter material covers the UV filter, b2) the UV filter covers the second filter material;

[0041] FIG. 6 shows the extension of the UV filter (hatched) into the optical opening of the ALS sensor, a) top view, b) side view;

[0042] FIG. 7 shows a top view of an IC with UV light sensor coating of the entire IC with metal, except for the sensor elements;

[0043] FIG. 8 shows a diagrammatic representation of an IC with UV light sensor in a housing a) without and b) with stray light suppressing means, with, among other things, the light barriers that laterally border the IC;

[0044] FIG. 9 shows a diagrammatic representation of an IC with UV light sensor in a housing with light barriers, embedding in opaque molding material, arrangement of opaque molding material on the IC back side;

[0045] FIG. 10 shows a diagrammatic representation of stray light suppressing means that are formed by closed contact rings and/or by via rings arranged offset, as a result of which the penetration of stray light by light guiding or by reflections is prevented;

[0046] FIG. 11 shows a diagrammatic representation of the compensation with a photodiode, which is coated with poly Si for case a) without UV filter and b) with UV filter;

[0047] FIG. 12 shows a diagrammatic representation of a matrix of diodes with different filters and thus with different functions.

[0048] FIG. 4 shows a design of the invention in which the filter 4 is formed over the entire surface of the IC 2 with the integrated UV light sensor 1 with associated signal processing 20. As a result, a vertical penetration of light outside of one or more sensor elements 13 can be prevented. In the process, the contact pads 3 for the IC are not covered by the filter 4. It is also possible to arrange different filters 4, 5 over individual sensor elements 13, wherein different radiation components can then be detected with the sensor elements 13. In a design, several sensor elements can be designed as dark diodes DD, on which no radiation at all is incident.

[0049] If different filters 4, 5 are used within a UV light sensor 1, then, on the transitional areas of the filters 4, 5, no interfering radiation should reach the sensor elements 13 either. In order to prevent this, the different filter materials in the transition areas are designed with overlap, as represented diagrammatically in FIG. 5 b1), b2).

[0050] FIG. 6 shows a design of the invention in which the stray light suppressing means are formed by two different filter materials 4, 5. On the one hand, they are formed by a UV filter 4 and, on the other hand, by a second filter material 5. The filters are arranged over a matrix of sensor elements 13, wherein the sensor elements 13 comprise UV and ALS sensor elements. The two filter materials 4, 5 are arranged so that the UV filter 4 is positioned above the UV sensor elements, and the second filter material 5 is positioned above the ALS sensor elements. In the process, it is particularly advantageous if the extension of the UV filter 4 reaches into the optical opening 9 of the ALS sensor element (FIG. 6b). In the process, the aperture or orifice or optical opening of the ALS sensor element is decreased by the UV filter 4, and thus the sensitivity thereof is reduced, for example, surface corresponds to a decrease in the sensitivity of the ALS sensor element 13 by . However, the reduced sensitivity can be tolerated, since, as a result of the overlapping, a clear reduction of the stray light coupling on the adjacent UV sensor elements 13 can be achieved. Indeed, due to the expansion of the UV filter 4 into the active sensor surface 14 of the ALS sensor element (i.e., in a projection above the active sensor surface 14), clearly less stray light passes through the ALS filter 5 onto the top metal. At the top level, the coupled in stray light 7 would in fact again be able to move on, as in a light guide, to the UV sensor element 13. This can be clearly reduced by the described design.

[0051] FIG. 7 shows a large-surface metal coating 6 of the entire IC 2 with the integrated UV light sensor 1. As a result, the progression of light to the silicon surface can be prevented at the sites that cannot be covered by filters (for example, surfaces around the bond pads 31 (not represented) of the individual sensor elements). Moreover, in this way any residual light that would penetrate into the IC 2, due to a limited stop band suppression of the filter, can be screened from hitting the silicon surface.

[0052] FIG. 8 shows a diagrammatic representation of an IC 2 with UV light sensor 1 in a housing 8. Here, FIG. 8a shows the interfering radiation penetrating the UV light sensor 1 due to the absence of stray light suppressing means, whereas, in FIG. 8b, light barriers 10 that laterally border the IC 2 are arranged, in order to prevent the penetration of the interfering radiation into the UV light sensor 1 outside of the sensitive sensor surface 1.

[0053] FIG. 9 shows a kind of summary of the possible stray light suppressing means. The vertical penetration of light 7 from the back side of the IC 2 or UV light sensor 1, can be prevented by an encapsulation with an opaque material 11, for example, with a suitable molding material, in the packing process. Moreover, the horizontal penetration of light 7 via the IC chip edges can be achieved by the covering of the chip margin with appropriate light-screening materials 11 during the packing process, wherein, for example, light barriers 10 that laterally border the IC 2 are arranged, or the entire IC 2 is embedded in an opaque molding material 11.

[0054] FIG. 10 shows a diagrammatic representation of stray light suppressing means that are formed by closed contact rings 12 and/or by via rings arranged offset, as a result of which the penetration of stray light due to reflections or light guiding into the intermetallic dielectric materials in the metallization complex of the IC 2 (oxides between wiring planes) or passivation planes is prevented.

[0055] FIG. 11 shows a diagrammatic representation of the result of the compensation of the VIS/IR sensitivity of a Si photodiode by the compensation with a photodiode which is coated with poly-Si, for case a) without UV filter and b) with UV filter, for the purpose of which the method according to the invention is used for the detection of UV light with a UV light sensor 1. For example, in a UV light sensor 1 consisting of at least one photodiode with UV filter (UV diode) or at least one polysilicon layer-coated photodiode with UV filter (UV poly diode), the VIS/IR sensibility of the Si diodes is suppressed by the following exemplary method steps: the output signal of the UV diode is measured. This output signal consists of UV+VIS/IR stray light+leakage current components. With the poly UV diode, a second output signal is measured. This second output signal consists of the a1*VIS/IR stray light+a2*leakage current components. The stray light of the two diodes is not identical, represented by the factor a1 which is not equal to 1. Thus, the difference would not exactly be the desired UV component, that is to say the compensation would not be optimal. The optimization is achieved in that a weighted difference is determined, for example, the UV poly diode is first weighted by 1/(a1) and then the difference is determined. The leakage currents are compensated for the case in which a2 is equal (approximately) to 1.

[0056] For the suppression of the VIS/IR sensitivity of the Si diodes, vertically stacked PN transitions (pinched Si diodes) can also be used, in order to eliminate the VIS/IR sensitivity from the photocurrent used.

[0057] Here occurs in principle a division of the photocurrents resulting from charge carrier generation into components that are generated by long-wave light at greater depth in the silicon, and components that are generated by short-wave light on the surface.

[0058] In an additional embodiment example, in order to suppress temperature-dependent and fabrication-caused leakage currents, a compensation method is also used, wherein, in a UV light sensor (1) consisting of at least one photodiode with UV filter (UV diode) and at least one dark diode (DD) coated with a metal layer, the temperature-dependent and fabrication-caused leakage currents of the Si diodes are suppressed by the following exemplary method steps: the output signal of the UV diode is measured. This output signal consists of the UV+leakage current components. With the dark diode, a second output signal is measured. This second output signal comprises the a2*leakage current component. Subsequently, for example, a compensation is carried out by determining the difference between the two measured output signals. In the case in which a2 is not equal to 1, the optimization is achieved in that a weighted difference is determined, for example, the dark diode is first weighted by 1/(a2), and then the difference is determined. For example, storage of trim values can also occur, in order to carry out a chip- and diode-based programmable dark current calibration.

[0059] If the UV light sensor 1 consists of at least one photodiode with UV filter (UV diode), at least one a polysilicon layer-coated photodiode with UV filter (UV poly diode), and at least one dark diode DD coated with a metal layer, then a compensation of the VIS/IR sensitivity and of the leakage currents of the Si photodiodes can occur at the same time. If, for example, the UV light sensor 1 comprises a photodiode with UV filter (D1), a photodiode with UV filter which is coated with a polysilicon layer (D2), and a UV dark diode (D3) coated with metal, then the output signals of the three diodes have the following composition:

D1=UV+VIS/IR stray+leakage current;

D2=a1*VIS/IR stray+a2_2*leakage current;

D3=+a2_3*leakage current.

[0060] In a first step, a weighted compensation of the leakage currents occurs by calculation of D13=(D1x1*D3) and D23=(D2x2*D3) and determination of x1 and x2 taking into consideration a2_2 and a2_3.

[0061] In a second step, the weighted compensation of the VIS/IR sensitivity occurs by calculation of UV=D13x3*D23 and determination of x3 taking into consideration a1. The homogenization of the leakage currents can also occur by optimized healing in the fabrication process.

[0062] If the UV light sensor 1 consists of a matrix of several sensor elements (FIG. 12), then, by means of a filter arrangement composed in accordance with certain arrangement criteria, wherein the filters consist of function-dependent filter materials, remaining stray light, or different leakage current effects, can be homogenized. For example, in this way, an optimal half-space sensitivity of the UV light sensor 1 and, under some circumstances, a suppression of particles or fabrication residues on the UV light sensor 1 can also be compensated. Here, the sensor elements 13 forming the UV light sensor 1 are arranged in a matrix structure, wherein, by means of a geometric center-of-gravity formation, an equal-value averaging of light components from all spatial directions above the UV light sensor occurs. If, in a 44 matrix arrangement with a total of 16 photodiodes, four different filter materials are associated with these 16 photodiodes, i.e., the photodiodes perform different functions in accordance with their associated filters, then the filter arrangement must meet the following criteria: The four different filters are arranged once in the corner, twice on the side edge, once per row, once per column, and once in the four 22 sub quadrants. The four different filters are then also associated with different measurement channels. FIG. 12 shows such an arrangement of different filters. Here, it is particularly advantageous that, stray light arriving in the array, for example, when the filter marked G is covered not with UV filters, but instead with another filter, for example, a photo-optical filter, visible light intendedly arrives through these filters, visible light which can then scatter towards the UV diodes and UV poly diodes. In order not to negatively influence the stray light compensation thereof, these diodes should see to the extent possible the identical stray light components, even in the case of different incidence angles of the light.

LIST OF REFERENCE NUMERALS

[0063] 1 UV light sensor [0064] 2 IC (integrated circuit) [0065] 3 Contact pads [0066] 31 Vias, bond pads of the sensor elements [0067] 4 UV filter [0068] 5 Second filter material [0069] 6 Metal layer [0070] 7 Incident radiation [0071] 8 Housing [0072] 9 Optical opening [0073] 10 Light barrier [0074] 11 Opaque material [0075] 12 Closed contact rings [0076] 13 Sensor element [0077] 14 Active sensor element surface [0078] 15 Substrate [0079] 16 Substrate surface [0080] 17 Passivation layer [0081] 18 Functional layer [0082] 19 Stray light suppressing means [0083] 20 Processing unit of the IC [0084] DD Dark diode