Image sensor and apparatus for image sensor

Abstract

Embodiments of the present disclosure relate to image sensors and apparatuses for image sensors. An apparatus for an image sensor is provided. The apparatus includes a semiconductor device including a photosensitive region and a metallization stack for electrically contacting the photosensitive region. The photosensitive region is configured to generate an electrical signal based on incident light. Further, the apparatus includes an optical stack formed on a surface of the semiconductor device for directing the incident light towards the photosensitive region. The optical stack includes a plurality of regions stacked on top of each other. The plurality of regions includes a filter region configured to selectively transmit the incident light only in a target wavelength range.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a structure for an image sensor. In particular, examples relate to an apparatus for an image sensor. Further examples relate to an image sensor. BACKGROUND

[0002] In optical cameras, light is captured by an optical sensor. The performance of such systems improves as the optical sensor becomes more and more sensitive. However, as the sensitivity improves, the sensitivity to ambient light interference (signal-to-noise ratio, SNR) also increases.

[0003] In a conventional structure, the filter is integrated with the optical sensor in one package. The filter is only transparent for light in a wavelength range of interest. As a result of the package solution, the distance between the filter and the optical sensor is large. Furthermore, the package solution allows light rays to hit the filter at large angles. This increases the amount of ambient light that can still reach the optical sensor through the filter.

[0004] Therefore, there can be a need for improvements in the guidance of incident light towards the light-sensitive area. SUMMARY

[0005] This requirement can be met by the content of the present application.

[0006] One example relates to an apparatus for an image sensor. The apparatus comprises a semiconductor device comprising a light-sensitive area and a metallization stack for electrically contacting the light-sensitive area. The light-sensitive area is configured to generate an electrical signal based on incident light. Furthermore, the apparatus comprises an optical stack formed on a surface of the semiconductor device for guiding incident light towards the light-sensitive area. The optical stack comprises a plurality of regions stacked on top of each other. The plurality of regions comprises a filter region configured to selectively transmit incident light only in a target wavelength range.

[0007] Another example relates to an image sensor for an optical camera. The image sensor comprises an array of light-sensitive pixels. At least one light-sensitive pixel of the array of light-sensitive pixels comprises an apparatus as presented herein. BRIEF DESCRIPTION OF DRAWINGS

[0008] Some examples of apparatuses and / or methods will hereinafter be described by way of example only, and with reference to the drawings, in which

[0009] Figure 1 A first example of an apparatus for an image sensor is shown,

[0010] Figure 2 A second example of an apparatus for an image sensor is shown,

[0011] Figure 3 An example transmission characteristic of a filter region is shown,

[0012] Figure 4 A first example of a prism region is shown,

[0013] Figure 5 A second example of a prism region is shown,

[0014] Figure 6 An example of a lens region is shown,

[0015] Figure 7 A third example of an apparatus for an image sensor is shown,

[0016] Figure 8 A fourth example of an apparatus for an image sensor is shown,

[0017] Figure 9 A fifth example of an apparatus for an image sensor is shown,

[0018] Figure 10 A sixth example of an apparatus for an image sensor is shown,

[0019] Figure 11 A seventh example of an apparatus for an image sensor is shown,

[0020] Figure 12 An eighth example of an apparatus for an image sensor is shown,

[0021] Figure 13 A ninth example of an apparatus for an image sensor is shown,

[0022] Figure 14 A tenth example of an apparatus for an image sensor is shown,

[0023] Figure 15 An eleventh example of an apparatus for an image sensor is shown, and

[0024] Figure 16 An example of an optical camera is shown. DETAILED DESCRIPTION

[0025] Various examples will now be described more fully with reference to the accompanying drawings in which some examples are illustrated. The other possible examples can, however, be deviated from the specific embodiments which are described in the detailed description. The examples can include modifications and equivalents of the features and concepts described herein. It will be appreciated that embodiments including the features of the application can be used as alternatives. Furthermore, terminology used for describing particular examples is not intended to be limiting and is used solely for illustration of the aspects.

[0026] Throughout the description of the drawings, same or similar reference numerals can refer to the same or similar elements and / or features, which can be implemented identically or by modifications thereof, and which can perform the same or similar functions. In the drawings, the thicknesses of lines, layers, and / or regions can be exaggerated for clarity.

[0027] If two elements A and B are combined using an "or," it is understood that other alternatives (for example only A, or only B) can also be expressly stated. As a further alternative to the same combination, "at least one of A and B" or "A and / or B" can be used. This applies similarly to combinations of more than two elements.

[0028] If a singular form such as "one" is used and it is not explicitly stated or implied that the use of only a single element is mandatory, additional examples can also implement the same functionality using multiple elements. If a functionality is subsequently described as implemented using multiple elements, additional examples can implement the same functionality using a single element or processing entity. It will be further understood that the terms "comprises" and / or "comprising," when used, specify the presence of stated features, integers, steps, operations, processes, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, processes, elements, components, and / or groups thereof.

[0029] Figure 1 An apparatus 100 for an image sensor of an optical camera is shown. The apparatus 100 comprises a semiconductor apparatus 110 comprising a photosensitive region 111 and a metallization stack 112 for electrically contacting the photosensitive region 111.

[0030] The photosensitive region 111 is configured to generate an electrical signal based on incident (incoming) light 101. When the incident light 101 hits the semiconductor material of the photosensitive region 111, the photosensitive region 111 emits electrons or other charge carriers based on the internal photoelectric effect. The emitted electrons or other charge carriers cause an electrical signal that is related to the incident light 101. The photosensitive region 111 can be sensitive to incident light 101 of any desired wavelength range. For example, the photosensitive region 111 can be sensitive to one or more of infrared light, visible light, or ultraviolet light. The photosensitive region 111 (and other parts of the semiconductor material 112) can be composed of any desired semiconductor material, such as silicon or gallium arsenide.

[0031] The metallization stack 112 comprises a plurality of metal layers for electrically contacting the photosensitive region 111. For example, the metallization stack 112 can be used to couple readout circuitry and / or drive circuitry (e.g., providing a bias or modulation signal for the photosensitive region 111) of the image sensor to the photosensitive region 111.

[0032] For example, the light-sensitive region 111 can be formed in a semiconductor material of the semiconductor device 110, and the metallization stack 112 can be formed in a non-semiconductor (e.g., silicon dioxide SiO2) of the semiconductor device 110. However, the proposed device 100 is not limited thereto. In other examples, the light-sensitive region 111 can be part of the metallization stack 112. That is, the light-sensitive region 111 can be formed of a semiconductor material within the metallization stack 112. For example, the light-sensitive region 111 can be formed on a surface of a semiconductor wafer of the semiconductor device 110 as part of the metallization stack 112.

[0033] One or more semiconductor structures, such as diodes or transistors, can optionally be formed in the semiconductor material of the semiconductor device 110. In particular, one or more semiconductor structures can be formed in or around the light-sensitive region 111.

[0034] Furthermore, the device 100 comprises an optical stack 120 (directly) formed on a surface of the semiconductor device 110 for directing the incident light 101 towards the light-sensitive region 111. In Figure 1 In an example, the optical stack 120 is formed on the front surface 113 of the semiconductor device 110. In other words, the metallization stack 112 is arranged between the light-sensitive region 111 and the optical stack 120 along a thickness direction z of the optical stack 112. For example, the optical stack 120 can be deposited on the metallization stack 112 of a wafer of the semiconductor device 110. The device 100 can be used for front-side illumination of the light-sensitive region 111.

[0035] Alternatively, the optical stack can be formed on a backside of the semiconductor device. This is shown in Figure 2 In an example, an alternative device 200 for an image sensor is shown. The device 200 differs from the device 100 shown in Figure 1 In other words, along a thickness direction z of the optical stack 112, the light-sensitive region 111 is arranged between the metallization stack 112 and the optical stack 120. The device 200 can be used for back-side illumination of the light-sensitive region 111. For example, the optical stack 120 can be deposited on the backside 114 of a backside-thinned wafer (made of Si or another semiconductor material) of the semiconductor device 110, over the area of the light-sensitive region 111. For example, the wafer can be a single-crystal wafer thinned to a thickness of 1 pm to 725 pm along the thickness direction z of the optical stack 112.

[0036] From Figure 1 and Figure 2It can be seen that the optical stack comprises a plurality of regions 121-1, …, 121-n stacked on top of each other along a thickness direction z of the optical stack 112. The plurality of regions 121-1, …, 121-n can comprise any number of regions n > 2. Each of the plurality of regions 121-1, …, 121-n can be formed by one or more layers of material. Different regions of the plurality of regions 121-1, …, 121-n can be formed by different materials. The plurality of regions 121-1, …, 121-n can serve different (optical) functions in the process of directing the incident light 101 towards the light-sensitive region 111. Two or more regions of the plurality of regions 121-1, …, 121-n can serve the same function in the process of directing the incident light 101 towards the light-sensitive region 111.

[0037] The plurality of regions 121-1, …, 121-n comprises at least a filter region configured to selectively transmit the incident light 101 only in a target wavelength range (e.g. region 121-2 can be the filter region). In other words, the filter region is configured to selectively filter out (block) a light portion of the incident light 101 outside the target wavelength range. This is exemplarily shown in Figure 3 Figure 3 A first phase 310 of the transmittance of the filter region and a second phase 320 of the transmittance of the filter region are shown. The abscissa represents the wavelength of the incident light, the ordinate represents the transmittance of the filter region.

[0038] The first phase 310 of the transmittance of the filter region can for example be a desired (target) transmittance / filtering behavior (property) of the filter region. In the first phase 310, the filter region does not transmit at all the incident light outside the target wavelength range between 830 and 900 nm. On the other hand, the filter region transmits all the incident light within the target wavelength range. From Figure 3 It can be seen from that the transmittance of the filter region drops abruptly at the edges of the target wavelength range in the first phase 310.

[0039] The second phase 320 of the transmittance of the filter region can for example be a minimum desired or required behavior (property) of the filter region. In the second phase 320, the filter region suppresses the incident light outside the target wavelength range. However, a small amount (e.g. less than 5% in the example of Figure 3 ) of light is still transmitted by the filter region. On the other hand, the filter region transmits almost all the incident light within the target wavelength range (e.g. more than 95% in the example of Figure 3 ). It can be seen from that the transmittance of the filter region in the second phase 320 drops more gently (i.e. with a smaller gradient) at the edges of the target wavelength range compared to the first phase 310. Figure 3

[0040] ​​In other words, the filtering region is used to allow the incident light to pass with high transmission in a specific wavelength range (e.g. 940 nm + / - 25 nm, with a transmission of at least 95%) and to suppress the incident light in other wavelength ranges (e.g. others, with a transmission < 5%).

[0041] The filtering region can for example be formed as an optical interference filter or a Bragg filter. For example, the optical filtering region can comprise a stack of layers with layers of materials with high and low refractive index alternating (e.g. silicon Si and silicon monoxide SiO). In other words, the filtering region can comprise a plurality of stacked layers with different refractive indices. The thickness of the filtering region along the thickness direction z of the optical stack 112 can for example be between 1 pm and 20 pm.

[0042] Thanks to the minimization of the distance between the optical stack 120 and the photosensitive region 111 (i.e. the optical sensor) in the devices 100 and 200, the illumination of the photosensitive region 111 is improved compared to traditional approaches. Moreover, the filtering region in the optical stack allows to filter out unwanted light portions from the incident light 101.

[0043] Referring back to Figure 1 and Figure 2 , the plurality of regions 121-1,..., 121-n can also comprise a prismatic region. For example, the region 121-3 can be a prismatic region. An exemplary prismatic region 400 is illustrated in Figure 4 . The prismatic region 400 comprises a prism 410 comprising a first surface 411 for receiving the incident light 101 and a second surface 412 opposite the first surface 411 and turning towards the filtering region. In other words, in the example of Figure 4 , the filtering region would be arranged below the prismatic region. The incident light 101 first passes through the prismatic region 400 before reaching the filtering region. In other words, the filtering region is arranged between the prismatic region and the semiconductor device.

[0044] The first surface 411 and the second surface 412 are inclined with respect to each other by an inclination angle g, modifying the propagation direction of the incident light 101 passing through the prism 400 to be parallel to the thickness direction z of the optical stack 120.

[0045] The prism 410 is embedded in an embedding material 420 of the prismatic region 400. The prism exhibits a refractive index n2 and the embedding material exhibits a refractive index nl. The refractive indices nl and n2 of the prism 410 and the embedding material 420 are different from each other. Embedding the prism 410 in a layer of embedding material 420 can allow forming the prismatic region 400 in a way that the prismatic region 400 is free of topography at the top and bottom surfaces contacting the adjacent regions of the optical stack 120.

[0046] In Figure 4In the example of FIG. 4, the first surface 411 is perpendicular to the thickness direction z of the optical stack 120, while the angle between the second surface 412 and the thickness direction z of the optical stack is 90° - γ. In other examples, the second surface 412 can be perpendicular to the thickness direction z of the optical stack 120, and the angle between the first surface 411 and the thickness direction z of the optical stack 120 can be 90° - γ.

[0047] The angle a1 of the received incident light 101 to the normal of the first surface 411 within the prism 410 is given by:

[0048]

[0049] The angle a represents the angle of the incident light to the thickness direction z of the optical stack into the embedding material 420. The angle a2 of the incident light 101 to the normal of the second surface 412 within the prism 410 is given by:

[0050] a2 = a1 - γ (2).

[0051] The angle a3 of the exiting incident light 101 to the normal of the second surface 412 into the embedding material 420 is given by:

[0052]

[0053] The angle a4 of the exiting incident light 101 to the thickness direction z of the optical stack into the embedding material 420 is given by:

[0054] a4 = a3 + γ (4).

[0055] The prism 410 is oriented with respect to the filtering region and the photosensitive region 111 so as to achieve a uniform illumination of the photosensitive region 111. The geometry (dimensions, inclination angle γ) of the prism 410 as well as the material of the prism 410 (refractive index n2 versus the refractive index n1 of the embedding material 420) are chosen so that the light rays impinging on the underlying layer are parallel to each other and perpendicular to the surface of the semiconductor device (i.e. parallel to the thickness direction z of the optical stack).

[0056] In other words, the inclination angle γ as well as the refractive indices n1 and n2 can be chosen so that |a4| < |a|. In particular, the inclination angle γ as well as the refractive indices n1 and n2 can be chosen so that |a4| « 0°.

[0057] In some examples, the prism region can comprise more than one prism. In general, the prism region can comprise any number m > 1 of prisms. Figure 5 An exemplary prism region 500 is shown, which comprises three prisms 510-1, 510-2 and 510-3 embedded in an embedding material 520.

[0058] As above for the prism region 400, the prism region 500 can be used to achieve a uniform illumination of the photosensitive region 111.Figure 4 Similar to the example described, the first prism 510-1 includes a first surface 511-1 for receiving incident light 101 and a second surface 512-1 opposite to the first surface 511-1 and oriented toward the filtering region (i.e., facing the filtering region). Figure 4 As in the example, in Figure 5 In the example, the filtering region will be arranged below the prism region 500. The first surface 511-1 and the second surface 512-1 are tilted relative to each other by a first tilt angle γ1, thereby modifying the propagation direction of the incident light 101 passing through the first prism 510-1 to be (substantially) parallel to the thickness direction z of the optical stack.

[0059] Similarly, the second prism 510-2 includes a third surface 511-2 for receiving incident light 101 and a fourth surface 512-2 opposite to the third surface 511-2 and directed toward the filtering region. The third surface 511-2 and the fourth surface 512-2 are tilted relative to each other by a second tilt angle γ2, thereby modifying the propagation direction of the incident light 101 passing through the second prism 510-2 to be (substantially) parallel to the thickness direction z of the optical stack.

[0060] The third prism 510-3 includes a fifth surface 511-3 for receiving incident light 101 and a sixth surface 512-3 opposite to the fifth surface 511-3 and directed toward the filtering region. The fifth surface 511-3 and the sixth surface 512-3 are tilted relative to each other by a third tilt angle γ3, thereby modifying the propagation direction of the incident light 101 passing through the third prism 510-3 to be (substantially) parallel to the thickness direction z of the optical stack.

[0061] Incident light 101 strikes the first to third prisms 510-1 to 510-3 at different incident angles α1 to α3. This is achieved by selecting the refractive index n2 of the first to third prisms 510-1 to 510-3, the refractive index n1 of the embedded material 520, and the corresponding tilt angle γ of each prism in the first to third prisms 510-1 to 510-3. x The propagation direction of the incident light 101 passing through the corresponding prisms 510-1, 510-2, and 510-3 can be changed to be (substantially) parallel to the thickness direction z of the optical stack. The first tilt angle γ1 to the third tilt angle γ3 can be adjusted individually. In particular, the first tilt angle γ1 to the third tilt angle γ3 can be different from each other.

[0062] like Figure 5 As shown, the prisms in the prism region can be in contact with each other (i.e., forming a single integral element). Alternatively, the prisms in the prism region can be far apart from each other (i.e., not in contact). Furthermore, the prisms in the prism region can exhibit characteristics similar to those in… Figure 5 The different refractions shown.

[0063] The use of prism regions such as prism regions 400 and 500 described above in the optical stack 120 of the devices 100 and 200 can allow to modify the propagation direction of the incident light 101 so that the incident light 101 hits the filter region substantially at a right angle. In other words, the prism regions can allow to modify the propagation direction of the incident light 101 so that the incident light 101 is substantially perpendicular to the filter region when reaching the filter region. If the incident light 101 hits the filter region at a substantially right angle, a narrower target wavelength range of the filter region to transmit the incident light 101 can be achieved. In other words, the prism regions can guarantee that only a very small angle (with respect to the surface normal of the filter region) of light can impinge on the filter region, so that the transmitted wavelength range is ideal in terms of specification. As the distance between the optical stack and the photosensitive region is minimal, there is less interference and the illumination of the photosensitive region is optimal.

[0064] Referring back to Figure 1 and Figure 2 The plurality of regions 121-1,..., 121-n can also comprise lens regions. For example, region 121-1 can be a lens region. A lens region comprises at least one lens configured to converge the incident light 101 reaching the respective lens into a cross-section smaller than the cross-section of the respective lens (the cross-section in a plane perpendicular to the lens thickness direction z of the optical stack 120). In other words, each lens focuses the incident light into a smaller cross-section.

[0065] An exemplary lens region 600 is illustrated in Figure 6 The lens region 600 comprises three lenses 610-1, 610-2 and 610-3, each lens being configured to converge the incident light 101 reaching the respective lens into a cross-section smaller than the cross-section of the respective lens. The lenses 610-1, 610-2 and 610-3 are embedded in an embedding material 620 of the lens region 600. The refractive indices of the embedding material 620 and the lenses 610-1, 610-2 and 610-3 are different from each other. For example, the refractive index n3 of the embedding material 620 can be smaller than the refractive index n4 of the lenses 610-1, 610-2 and 610-3.

[0066] As Figure 6As shown, lenses 610-1, 610-2, and 610-3 can be formed as hemispherical converging lenses embedded in a layer of embedding material 620. Alternatively, lenses 610-1, 610-2, and 610-3 can be formed as spherical lenses. The ratio of the refractive indices of the lens material and the embedding material 620 can be chosen such that lenses 610-1, 610-2, and 610-3 concentrate the incoming light 101 hitting the spherical surface onto a smaller area underneath the flat side of the respective lens. The lens areas can allow focusing the incoming light 101 of the upper layer of the optical stack 120 from a larger cross section to a smaller cross section (in the lower optical stack 120). The lenses can be arranged with respect to the light sensitive area 111 such that an optimal illumination of the light sensitive area 111 is achieved.

[0067] The optical stack 120 can comprise one or more of the above-described regions. The optical stack 120 can also comprise regions different from the above-described regions. For example, the optical stack 120 can comprise one or more non-optically active transition regions (or layers) that are required for manufacturing the optical stack (e.g. planarization regions / layers). The stacking order of the various regions can vary depending on the targeted (desired) performance of the overall system consisting of the optical stack 120 and the semiconductor device 110.

[0068] Furthermore, the optical stack 120 can be at least partially covered with one or more layers of film. For example, the optical stack 120 can be at least partially covered with a passivation film to protect the optical stack from environmental influences. For example, the passivation film can be a SiO2coating. However, it is to be noted that any other suitable coating can also be used. Alternatively or additionally, the optical stack 120 can be at least partially covered with an anti-reflective film (coating) to suppress reflection of the incoming light 101 at the surface of the optical stack 120. For example, the anti-reflective film can be a nitride coating. However, it is to be noted that any other suitable anti-reflective coating can also be used.

[0069] In the following, some exemplary stacking orders of the various regions in the proposed optical stack will be described with reference to Figures 7 to 13 Figures 1 and 2. Figures 7 to 9 Exemplary devices for front-side illuminated image sensors are shown, whereas Figures 10 to 13 Exemplary devices for back-side illuminated image sensors are shown. In the following, only the stacking order of the various layers within the respective optical stack will be highlighted. The features / inner structure of the individual regions are as explained above with respect to Figures 1 to 6 Figures 1 and 2. Similarly, the features / inner structure of the semiconductor device are as explained above with respect to Figures 1 to 6 Figures 1 and 2. In particular, in the example of Figures 7 to 13 the light sensitive area 111 is formed in the semiconductor material 116 of the semiconductor device 110, whereas the metallization stack 112 is formed in a non-semiconductor material (e.g. SiO2) of the semiconductor device 110.

[0070] In Figure 7 the optical stack 720 includes a lens region 721-1, a filter region 721-2, and a prism region 721-3. In Figure 7 the example, the filter region 721-2 and the prism region 721-3 are immediately adjacent to each other in the optical stack 720. Further, the filter region 721-2 and the lens region 721-1 are immediately adjacent to each other in the optical stack 720. The lens region 721-1 is closest to the photosensitive region 111 formed in the semiconductor material 116 of the semiconductor device 110. In other words, the filter region 721-2 is disposed between the prism region 721-3 and the photosensitive region 111. Additionally, the lens region 721-1 is disposed between the filter region 721-2 and the photosensitive region 111.

[0071] In Figure 8 the optical stack 820, the filter region 721-2 and the prism region 721-3 are separated by an intermediate region 721-5 in the optical stack 820. The intermediate region 721-5 is optically transparent to the incident light. Similarly, the filter region 721-2 and the lens region 721-1 are separated by an intermediate region 721-4 in the optical stack 820. Again, the intermediate region 721-4 is optically transparent to the incident light. The intermediate regions 721-4 and 721-5 can be, for example, planarization layers or other non-optically active regions. The lens region 721-1 is again closest to the photosensitive region 111 formed in the semiconductor material 116 of the semiconductor device 110. The filter region 721-2 is again disposed between the prism region 721-3 and the photosensitive region 111. Additionally, the lens region 721-1 is disposed between the filter region 721-2 and the photosensitive region 111.

[0072] In Figure 9 the example, the filter region 721-2 and the prism region 721-3 are immediately adjacent to each other in the optical stack 920. Further, the prism region 721-3 and the lens region 721-1 are immediately adjacent to each other in the optical stack 920. In comparison to the example of Figure 7 the lens region 721-1 is now the topmost region of the optical stack rather than the lowermost region. In other words, the prism region 721-3 is disposed between the lens region 721-1 and the photosensitive region 111. Further, the filter region 721-2 is disposed between the prism region 721-3 and the photosensitive region 111.

[0073] It is noted that in alternative examples, respective intermediate regions that are optically transparent to the incident light can be formed between the lens region 721-1, the filter region 721-2, and the prism region 721-3. For example, the filter region 721-2 and the prism region 721-3 can be separated by an intermediate region in the optical stack. Similarly, the prism region 721-3 and the lens region 721-1 can be separated by an intermediate region in the optical stack.

[0074] Figures 7 to 9 Examples of the first aspect focus on front-side illumination implementations, such that the metallization stack 112 is arranged between the photosensitive region 111 and the respective optical stack, while Figures 10 to 13 Examples of the second aspect focus on back-side illumination implementations, such that the photosensitive region 111 is arranged between the metallization stack 112 and the respective optical stack.

[0075] In the example of FIG. 10A, the filter region 721-2 and the prism region 721-3 are immediately adjacent to each other in the optical stack 1020. Further, the filter region 721-2 and the lens region 721-1 are immediately adjacent to each other in the optical stack 1020. The lens region 721-1 is closest to the photosensitive region 111 formed in the semiconductor material 116 of the semiconductor device 110. In other words, the filter region 721-2 is arranged between the prism region 721-3 and the photosensitive region 111. In addition, the lens region 721-1 is arranged between the filter region 721-2 and the photosensitive region 111. Figure 10 In the example of FIG. 10B, the filter region 721-2 and the prism region 721-3 are separated by an intermediate region 721-5 in the optical stack 1120. The intermediate region 721-5 is transparent to incident light. Similarly, the filter region 721-2 and the lens region 721-1 are separated by an intermediate region 721-4 in the optical stack 1120. Again, the intermediate region 721-4 is transparent to incident light. The intermediate regions 721-4 and 721-5 can be, for example, planarization layers or other non-optically active regions. The lens region 721-1 is again closest to the photosensitive region 111 formed in the semiconductor material 116 of the semiconductor device 110. The filter region 721-2 is arranged between the prism region 721-3 and the photosensitive region 111. Further, the lens region 721-1 is arranged between the filter region 721-2 and the photosensitive region 111.

[0076] Figure 11 In the example of FIG. 10B, the filter region 721-2 and the prism region 721-3 are separated by an intermediate region 721-5 in the optical stack 1120. The intermediate region 721-5 is transparent to incident light. Similarly, the filter region 721-2 and the lens region 721-1 are separated by an intermediate region 721-4 in the optical stack 1120. Again, the intermediate region 721-4 is transparent to incident light. The intermediate regions 721-4 and 721-5 can be, for example, planarization layers or other non-optically active regions. The lens region 721-1 is again closest to the photosensitive region 111 formed in the semiconductor material 116 of the semiconductor device 110. The filter region 721-2 is arranged between the prism region 721-3 and the photosensitive region 111. Further, the lens region 721-1 is arranged between the filter region 721-2 and the photosensitive region 111.

[0077] In the example of FIG. 10C, the filter region 721-2 and the prism region 721-3 are immediately adjacent to each other in the optical stack 1220. Further, the prism region 721-3 and the lens region 721-1 are immediately adjacent to each other in the optical stack 1220. In contrast to the example of FIG. 10A, the lens region 721-1 is now the lowermost region of the optical stack rather than the topmost region. In other words, the prism region 721-3 is arranged between the lens region 721-1 and the photosensitive region 111. Further, the filter region 721-2 is arranged between the prism region 721-3 and the photosensitive region 111. Figure 12 Figure 10 In the example of FIG. 10C, the filter region 721-2 and the prism region 721-3 are immediately adjacent to each other in the optical stack 1220. Further, the prism region 721-3 and the lens region 721-1 are immediately adjacent to each other in the optical stack 1220. In contrast to the example of FIG. 10A, the lens region 721-1 is now the lowermost region of the optical stack rather than the topmost region. In other words, the prism region 721-3 is arranged between the lens region 721-1 and the photosensitive region 111. Further, the filter region 721-2 is arranged between the prism region 721-3 and the photosensitive region 111.

[0078] In the example of FIG. 10D, the filter region 721-2 and the prism region 721-3 are separated by an intermediate region 721-5 in the optical stack 1220. The intermediate region 721-5 is transparent to incident light. Similarly, the prism region 721-3 and the lens region 721-1 are separated by an intermediate region 721-4 in the optical stack 1220. Again, the intermediate region 721-4 is transparent to incident light. The intermediate regions 721-4 and 721-5 can be, for example, planarization layers or other non-optically active regions. The lens region 721-1 is again closest to the photosensitive region 111 formed in the semiconductor material 116 of the semiconductor device 110. The filter region 721-2 is arranged between the prism region 721-3 and the photosensitive region 111. Further, the lens region 721-1 is arranged between the filter region 721-2 and the photosensitive region 111. Figure 13 ​​In the illustrated example, the filter region 721-2 and the prism region 721-3 are separated by an intermediate region 721-5 in the optical stack. Similarly, the prism region 721-3 and the lens region 721-1 are separated by an intermediate region 721-6 in the optical stack 1320. The filter region 721-2 is closest to the photosensitive region 111 formed in the semiconductor material 116 of the semiconductor device 110. The prism region 721-3 is again arranged between the lens region 721-1 and the photosensitive region 111. Moreover, the filter region 721-2 is arranged between the prism region 721-3 and the photosensitive region 111.

[0079] It should be noted that according to some examples, more than one intermediate region can also be arranged between respective pairs of the lens region 721-1, the filter region 721-2 and the prism region 721-3.

[0080] In Figures 7 to 13 In each of the illustrated examples, the filter region 721-2 is arranged between the prism region 721-3 and the semiconductor device 111 such that the propagation direction of the incident light is modified by the prism region 721-3 to be substantially perpendicular to the surface of the filter region 721-2 (i.e. substantially parallel to the thickness direction z of the respective optical stack) before reaching the filter region 721-2. Thus, the incident light hits the surface of the filter region 721-1 at a substantially right angle, thereby improving the filtering function of the filter region 721-1.

[0081] Figure 14 Another example of a device 1400 for an image sensor is illustrated. The device 1400 is similar to the device 100 described above. The main difference between the device 1400 and the device 100 is that the optical stack 1420 of the device 1400 is embedded in the metallization stack 120. In particular, a recess 118 is formed in the non-semiconductor material 115 of the metallization stack 112. The optical stack 1420 is formed on the surface 117 of the recess 118 such that the optical stack 1420 is embedded in the metallization stack 112. Moreover, the recess 118 is partially filled with an embedding material 119 to embed the optical stack 1420 in the metallization stack 112. Thus, the optical stack 1420 does not protrude from the metallization stack 112 along the thickness direction z of the optical stack 1420.

[0082] It is considered Figure 1 and Figure 14 According to the proposed architecture, the optical stack of a device can be arranged on, or embedded in, the metallization stack of a semiconductor device such that the optical stack is arranged on top of the photosensitive region of the semiconductor device.

[0083] In Figure 14In the example of FIG. 14A, the filter region 1421-2 and the prism region 1421-3 are next to each other in the optical stack 1420. Further, the filter region 1421-2 and the lens region 1421-1 are next to each other in the optical stack 1420. The lens region 1421-1 is closest to the photosensitive region 111 formed in the semiconductor material 116 of the semiconductor device 110.

[0084] Figure 15 Another device 1500 for backside illumination is shown in FIG. 15A. In the example of FIG. 15A, the optical stack 1520 is formed on the backside 114 of the semiconductor device 110. The filter region 1421-2 and the prism region 1421-3 are again next to each other in the optical stack 1420. Further, the filter region 1421-2 and the lens region 1421-1 are next to each other in the optical stack 1420. The lens region 1421-1 is closest to the photosensitive region 111 formed in the semiconductor material 116 of the semiconductor device 110. Figure 15 In the above examples, the optical stack with improved ambient light robustness is provided directly on a semiconductor device holding an optical sensor (e.g., a photosensitive region). Thus, the above examples can provide improved ambient light robustness for the optical sensor due to the optimized optical stack.

[0085]

[0086] A schematic example of an optical camera 1600 using the proposed technology is shown in FIG. 16. The optical camera 1600 comprises an image sensor 1610. The image sensor 1610 comprises an array of photosensitive pixels (elements). At least one photosensitive pixel of the array of photosensitive pixels comprises a device 1611 with a semiconductor device and an optical stack according to the proposed technology (e.g., according to one or more of the above examples). According to some examples, each pixel of the array of photosensitive pixels can comprise a respective device according to the proposed technology. Figure 16 Further, the optical camera comprises an objective with at least one objective group 1620 configured to focus incoming light 1601 on the image sensor 1610. The objective can comprise further objective groups for focusing the incoming light 1601 on the image sensor 1610.

[0087] The optical camera 1600 can further comprise other hardware - conventional and / or custom. For example, the optical camera 1600 can comprise circuitry for processing electrical signals output by the photosensitive regions of the individual pixels of the image sensor 1610, or circuitry for driving (e.g., biasing or gating) the individual pixels of the image sensor 1610.

[0088]

[0089] ​The optical camera 1600 can be used for any kind of two-dimensional or three- dimensional image capture. For example, the image sensor 1610 can be a two- dimensional imager for visible or infrared light. In other examples, the image sensor 1610 can be a three-dimensional imager for time-of-flight measurements. In case the optical camera 1600 is a time-of-flight camera, the target wavelength range of the light-sensitive area for a pixel and the corresponding filter area of the optical stack can for example be between 830 nm and 1600 nm or any sub-range thereof (e.g. 940 nm + / - 25 nm).

[0090] Due to the optimized optical stack according to the proposed technology, the image sensor 1610 and the optical camera 1600 can exhibit improved ambient light robustness.

[0091] Examples as described herein can be summarized as follows:

[0092] Some examples relate to an apparatus for an image sensor. The apparatus comprises a semiconductor device comprising a light-sensitive area and a metallization stack for electrically contacting the light-sensitive area. The light-sensitive area is configured to generate an electrical signal based on incident light. Further, the apparatus comprises an optical stack formed on a surface of the semiconductor device for directing the incident light towards the light-sensitive area. The optical stack comprises a plurality of regions stacked on top of each other. The plurality of regions comprises a filter region configured to selectively transmit the incident light only within a target wavelength range.

[0093] In some examples, the filter region comprises a plurality of stacked layers having different refractive indices.

[0094] According to some examples, the plurality of regions comprises a prism region, wherein the prism region comprises at least a first prism comprising a first surface for receiving the incident light and a second surface opposite to the first surface and turning towards the filter region, wherein the first surface and the second surface are tilted with respect to each other by a first tilt angle, thereby modifying a propagation direction of the incident light passing through the first prism to be parallel to a thickness direction of the optical stack.

[0095] In some examples, the prism region further comprises a second prism comprising a third surface for receiving the incident light and a fourth surface opposite to the third surface and turning towards the filter region, wherein the third surface and the fourth surface are tilted by a second tilt angle, thereby modifying a propagation direction of the incident light passing through the second prism to be parallel to the thickness direction of the optical stack, wherein the first tilt angle is different from the second tilt angle.

[0096] According to some examples, the first prism is embedded in an embedding material of the prism region, wherein the refractive indices of the first prism and the embedding material are different from each other.

[0097] In some examples, the filter region is arranged between the prism region and the semiconductor device.

[0098] According to some examples, the filter region and the prism region are next to each other in the optical stack.

[0099] In alternative examples, the filter region and the prism region are separated by an intermediate region in the optical stack, wherein the intermediate region is transparent to the incident light.

[0100] According to some examples, the plurality of regions comprises a lens region, wherein the lens region comprises at least one lens configured to converge the incident light reaching the respective lens to a cross-section smaller than a cross-section of the respective lens.

[0101] In some examples, the at least one lens is embedded in an embedding material of the lens region, wherein the at least one lens and the embedding material differ from each other in refractive index.

[0102] According to some examples, the filter region and the lens region are next to each other in the optical stack.

[0103] In alternative examples, the filter region and the lens region are separated by an intermediate region in the optical stack, wherein the intermediate region is transparent to the incident light.

[0104] According to some examples, the prism region and the lens region are next to each other in the optical stack.

[0105] In alternative examples, the prism region and the lens region are separated by an intermediate region in the optical stack, wherein the intermediate region is transparent to the incident light.

[0106] According to some examples, the optical stack is at least partially covered with at least one of a passivation film and an anti-reflection film.

[0107] In some examples, a metallization stack is arranged between the light-sensitive region and the optical stack.

[0108] According to some examples, a surface of the semiconductor device is a surface of a recess formed in the metallization stack, such that the optical stack is embedded in the metallization stack.

[0109] In some examples, the light-sensitive region is arranged between the metallization stack and the optical stack.

[0110] Other examples relate to an image sensor for an optical camera. The image sensor comprises an array of light-sensitive pixels. At least one light-sensitive pixel in the array of light-sensitive pixels comprises a device as set forth herein.

[0111] According to some examples, the image sensor is an image sensor for a time-of-flight camera, wherein the boundaries of the target wavelength range are between 830 nm and 1600 nm.

[0112] Due to the optimized optical stack, examples according to the proposed technology can provide improved ambient light robustness for optical sensors.

[0113] Aspects and features described with respect to one or more examples can be combined with one or more other examples, either for replacement of like features or additionally thereto. Figure 1 Aspects and features described with respect to one or more examples can be combined with one or more other examples, either for replacement of like features or additionally thereto.

[0114] It can be appreciated that the disclosure of multiple steps, processes, operations, or functions disclosed in the specification and claims can not be construed as an implied

[0115] Further, the claims are hereby incorporated into the detailed description, where each claim can stand on its own as a separate example. While each claim can stand on its own as a separate example, it is to be noted that, although a dependent claim can refer in the claims to a specific combination with one or more other claims, other examples can also include a combination of each of the dependent claims with the subject of each of the other dependent claims or independent claims. Such combinations are specifically included herein unless it is explicitly stated to the contrary. In addition, features of a claim can be included in any other independent claim, even if that claim is not directly dependent on the independent claim.

Claims

1. An apparatus (100, 200) for an image sensor, comprising: a semiconductor device (110) comprising a photosensitive area (111) and a metallization stack (112) for electrically contacting the photosensitive area (111), wherein the photosensitive area (111) is configured to generate an electrical signal based on an incident light (101); and an optical stack (120) formed on a surface of the semiconductor device (110) for directing the incident light (101) towards the photosensitive area (111), wherein the optical stack (120) comprises a plurality of areas (121-1,..., 121-n) stacked on top of each other, and wherein the plurality of areas (121-1,..., 121-n) comprises a filter area configured to selectively transmit the incident light (101) only in a target wavelength range, wherein the surface of the semiconductor device (110) is a surface of a recess formed in the metallization stack (112) such that the optical stack (120) is embedded in the metallization stack (112).

2. The apparatus according to claim 1, wherein the filter area comprises a plurality of stacked layers having different refractive indices.

3. The apparatus according to claim 1, wherein the plurality of areas (121-1,..., 121-n) comprises a prism area (400, 500), wherein the prism area (400, 500) comprises at least a first prism (410, 510-1) comprising a first surface (411, 511-1) for receiving the incident light (101) and a second surface (412, 512-1) opposite to the first surface (411, 511-1) and turning the incident light (101) towards the filter area, wherein the first surface (411, 511-1) and the second surface (412, 512-1) are inclined with respect to each other by a first inclination angle, thereby modifying a propagation direction of the incident light (101) passing through the first prism (410, 510-1) to be parallel to a thickness direction of the optical stack (120).

4. The apparatus according to claim 3, wherein the filter area is arranged between the prism area (400, 500) and the semiconductor device (110).

5. The apparatus according to claim 3, wherein the filter area and the prism area (400, 500) are next to each other in the optical stack (120).

6. The apparatus according to claim 3, wherein the filter area and the prism area (400, 500) are separated by an intermediate area in the optical stack (120), wherein the intermediate area is transparent for the incident light (101).

7. The apparatus according to any one of claims 3 to 6, wherein the plurality of regions (121-1,..., 121-n) comprises a lens region (600), wherein the lens region (600) comprises at least one lens (610-1) configured to converge the incident light (101) arriving at the respective lens to a cross section smaller than a cross section of the respective lens.

8. The apparatus according to claim 7, wherein the filter region and the lens region (600) are next to each other in the optical stack (120).

9. The apparatus according to claim 7, wherein the filter region and the lens region (600) are separated by an intermediate region in the optical stack (120), wherein the intermediate region is transparent for the incident light (101).

10. The apparatus according to claim 7, wherein the prism region (400, 500) and the lens region (600) are next to each other in the optical stack (120).

11. The apparatus according to claim 7, wherein the prism region (400, 500) and the lens region (600) are separated by an intermediate region in the optical stack (120), wherein the intermediate region is transparent for the incident light (101).

12. The apparatus according to claim 1, wherein the metallization stack (112) is arranged between the light-sensitive region (111) and the optical stack (120).

13. The apparatus according to claim 1, wherein the light-sensitive region (111) is arranged between the metallization stack (112) and the optical stack (120).

14. An image sensor (1610) for an optical camera (1600), wherein the image sensor (1610) comprises an array of light-sensitive pixels, and wherein at least one light-sensitive pixel of the array of light-sensitive pixels comprises an apparatus (1611) according to any one of claims 1 to 13.

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