DEVICE FOR AN IMAGE SENSOR, IMAGE SENSOR FOR AN OPTICAL CAMERA AND OPTICAL CAMERA

Description

Field

[0001] The present disclosure relates to imaging. In particular, examples relate to a device for an image sensor, an image sensor for an optical camera and an optical camera.Background

[0002] In an optical camera, the individual pixels in a pixel array are illuminated by light coming from an objective lens. The light from the objective lens is not reaching all pixels at the same angle. In particular, the light is not reaching each pixel at an angle of 90 °. The Chief Ray Angle (CRA) of the light is transferred into the photo-sensitive part of the pixel (e.g. silicon material). Due to the CRA, the light reaches the photo-sensitive part of a neighboring pixel and causes crosstalk. Moreover, in case of front side illumination of the pixel array, the light needs to pass the dielectric stack for wiring the photo-sensitive part of the pixel such that the light is shadowed by wiring lines and does not completely reach the photo-sensitive part of the pixel.

[0003] Document KR 2010 0067982 A proposes an image sensor and a manufacturing method thereof to solve the difficulty of a wiring design by vertically inputting light to all pixels by changing the path of light passing through a prism array on the lower side of a color filter array. A substrate comprises a pixel array. An image sensor is formed on the substrate. The image sensor comprises a prism array which becomes larger from the center to the outer side of the substrate. The prism array corresponds to the pixel.

[0004] In document US 2007 / 069109 A1, an image sensing device for receiving an incident light having an incident angle and photo signals formed thereby is proposed. The image sensing device includes a micro prism and a micro lens for adjusting the incident angle and converging the incident light, respectively, a photo sensor for converting the photo signals into electronic signals, and an IC stacking layer for processing the electronic signals.

[0005] Document US 2010 / 188537 A1 proposes a solid-state imaging device. Light-splitting elements are arranged in at least two columns and two rows to form two pairs. Each element splits incident light into light rays and makes them fall on a portion of a photosensing section right under itself and an adjacent photosensitive cell. A first one of the elements splits the incident light so that a first primary color ray and its complementary color ray enter first adjacent cell and a first underlying cell, respectively. A second one of the elements makes a second primary color ray and its complementary color ray enter a second underlying cell and a second adjacent cell respectively. A third one of the elements does the same as the second one of the elements. And fourth one of the elements makes a third primary color ray and its complementary color ray enter a third adjacent cell and a third cell, respectively. These photosensitive cells perform photoelectric conversion, thereby outputting an electrical signal representing the intensity of the incident light. By carrying out simple calculations between the outputs of these cells, a color signal and a luminance signal are generated.

[0006] In document JP 2003 243639 A, an image pickup element and an image pickup device are proposed. The image pickup element is provided with a photoelectric conversion part, a wavelength selecting part which is formed on a light incidence side to the photoelectric conversion part and transmits a light in a prescribed wavelength range, a first region which is formed on a light incidence side to the wavelength selecting part and has a prescribed refractive index, and a second region which is formed on a light incidence side to the first region and has a prescribed refractive index. The refractive index of the first region is higher than that of the second region.

[0007] Document US 2007 / 053037 A1 proposes an image sensor and method for fabricating the same. The image sensor includes a substrate in which photoelectric elements have been formed, and an array of optical path conversion elements formed at a light so that the optical path converted light may be incident on the substrate, wherein each of the optical path conversion elements has different tangent line gradients on the corresponding parts of incident surfaces according to distances from the center of the image sensor in order to compensate for differences of incident angles of incident light according to the distances from the center of the image sensor. In addition, a method for fabricating the image sensor fabricates the optical path conversion elements according to a photolithography process using a gray scale mask, combinations of the photolithography process and a reactive ion etching process, or combinations of the photolithography process, the reactive ion etching process, and an UV-molding process.

[0008] In document WO 2007 / 097062 A1, a solid-state imaging device is proposed. The solid-state imaging device comprises a semiconductor substrate, a plurality of pixels having a light receiving sensor part formed on the semiconductor substrate, element isolation formed between the pixels in the semiconductor substrate, and an insulating film formed on the upper portion of the pixels and the element isolation. The relationship between the refractive index n1 of the insulating film and the refractive index n2 of the element isolation is n1 < n2. This suppresses the occurrence of a color mixture due to the arrival of light at the element isolation with a large incident angle.

[0009] Document 2019 / 074318 A1 proposes a solid-state imaging device that features a pixel region with multiple pixels, each having a photoelectric conversion section and a pixel transistor. The device also includes an on-chip color filter, an on-chip microlens, and a multilayer interconnection layer with various interconnections formed via an interlayer insulating film. Additionally, the device incorporates a light-shielding film situated through an insulating layer at the pixel boundary on the light-receiving surface where the photoelectric conversion section is located.

[0010] Document US 2017 / 077163 A1 proposes an image sensor designed for high angular response discrimination, which includes both phase detection autofocus (PDAF) pixels and image capture pixels. The pixels have sensors arranged in a semiconductor substrate, surrounded by a grid structure. Microlenses are positioned over this grid structure, including a PDAF microlens with greater optical power or an asymmetric profile compared to the image capture microlens.

[0011] Document US 2019 / 096930 A1 proposes a semiconductor image sensor, specifically a backside-illuminated (BSI) image sensor. This sensor includes a substrate with a front side and an opposite back side, where multiple pixel sensors are arranged in an array. Each pixel sensor contains a photo-sensing device within the substrate, a color filter positioned over the pixel sensor on the back side, and an optical structure also located on the back side above the color filter. The optical structure features a first sidewall that forms an angle greater than 0° with a plane that is substantially parallel to the front surface of the substrate.

[0012] Document US 9 935 146 B1 proposes phase detection pixels with optical structures designed to improve or customize their response to incident light. These optical structures, positioned between a microlens and photodiodes, serve to redirect light effectively. They may consist of multiple layers with varying refractive indices, such as silicon dioxide and silicon nitride, which can form a concave lens to enhance angular response. The optical structures can be tailored to have any shape to optimize the photodiodes' response to incoming light.Summary

[0013] Hence, there may be a demand for improved guidance of incident light towards a photo-sensitive region.

[0014] The demand may be satisfied by the subject matter of the appended claims.

[0015] An example relates to a device for an image sensor. The device comprises a semiconductor device comprising a photo-sensitive region formed in semiconductor material of the semiconductor device and configured to generate an electric signal based on incident light. The semiconductor device further comprises a metallization stack formed in a non-semiconductor material of the semiconductor device for electrically contacting the photo-sensitive region. Additionally, the device comprises an optical element comprising a first surface for receiving the incident light and a second surface opposite the first surface and turned towards the photo-sensitive region. The first surface and the second surface are tilted by a tilt angle relative to each other so as to modify a direction of propagation of the incident light passing through the optical element towards a center of the photo-sensitive region to compensate for a chief ray angle of the incident light. The device comprises further comprises a microlens configured to focus the incident light onto the first surface of the optical element. In addition, the device comprises an oxide layer formed on the semiconductor device. The optical element is at least in part formed in the oxide layer such that the oxide layer at least partially encloses the optical element. The photo-sensitive region is arranged between the metallization stack and the optical element.

[0016] Another example relates to an image sensor for an optical camera. The image sensor comprises an array of photo-sensitive pixels, wherein the array of photo-sensitive pixels comprises a first pixel comprising a first device according to the proposed technology, and a second pixel comprising a second device according to the proposed technology. The first pixel is located at a smaller lateral distance to a center of the array than the second pixel. The tilt angle of the optical element of the first pixel is smaller than the tilt angle of the optical element of the second pixel.

[0017] A further examples relates to an optical camera comprising an image sensor according to the proposed technology. Additionally, the optical camera comprises one or more obj ective lenses configured to focus the incident light on the image sensor.Brief description of the Figures

[0018] Some examples of apparatuses and / or methods will be described in the following by way of example only, and with reference to the accompanying figures, in which Fig. 1 illustrates a first example of a device for an image sensor; Fig. 2 illustrates a second example of a device for an image sensor; Fig. 3 illustrates a third example of a device for an image sensor; Fig. 4 illustrates a fourth example of a device for an image sensor; Fig. 5 illustrates a fifth example of a device for an image sensor; Figs. 6a and 6b illustrate examples of the optical element; Fig. 7 illustrates a sixth example of a device for an image sensor; Fig. 8 illustrates an example of an image sensor; and Fig. 9 illustrates an example of an optical camera. Detailed Description

[0019] The scope of protection is defined in the claims.

[0020] Various examples will now be described more fully with reference to the accompanying drawings in which some examples are illustrated. In the figures, the thicknesses of lines, layers and / or regions may be exaggerated for clarity.

[0021] Accordingly, while further examples are capable of various modifications and alternative forms, some particular examples thereof are shown in the figures and will subsequently be described in detail. However, this detailed description does not limit further examples to the particular forms described. Further examples may cover all modifications, equivalents, and alternatives falling within the scope of the disclosure. Same or like numbers refer to like or similar elements throughout the description of the figures, which may be implemented identically or in modified form when compared to one another while providing for the same or a similar functionality.

[0022] It will be understood that when an element is referred to as being "connected" or "coupled" to another element, the elements may be directly connected or coupled via one or more intervening elements. If two elements A and B are combined using an "or", this is to be understood to disclose all possible combinations, i.e. only A, only B as well as A and B, if not explicitly or implicitly defined otherwise. An alternative wording for the same combinations is "at least one of A and B" or "A and / or B". The same applies, mutatis mutandis, for combinations of more than two Elements.

[0023] The terminology used herein for the purpose of describing particular examples is not intended to be limiting for further examples. Whenever a singular form such as "a", "an" and "the" is used and using only a single element is neither explicitly nor implicitly defined as being mandatory, further examples may also use plural elements to implement the same functionality. Likewise, when a functionality is subsequently described as being implemented using multiple elements, further examples may implement the same functionality using a single element or processing entity. It will be further understood that the terms "comprises", "comprising", "includes" and / or "including", when used, specify the presence of the stated features, integers, steps, operations, processes, acts, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, processes, acts, elements, components and / or any group thereof.

[0024] Unless otherwise defined, all terms (including technical and scientific terms) are used herein in their ordinary meaning of the art to which the examples belong.

[0025] Fig. 1 illustrates a device 100 for an image sensor of an optical camera. The device 100 comprises a semiconductor device 110 comprising a photo-sensitive region 111 formed in semiconductor material 112 of the semiconductor device 110. The photo-sensitive region 111 is configured to generate an electric signal based on incident (incoming) light 101. The photo-sensitive region 111 emits electrons or other charge carriers based on the inner photoelectric effect when the incident light 101 hits the semiconductor material of the photo-sensitive region 111. The emitted electrons or other charge carriers cause an electric signal, which depends on the incident light 101. The photo-sensitive region 111 may be sensitive to incident light 101 of any desired (target) wavelength. For example, the photo-sensitive region 111 may be sensitive to one or more of infrared light, visible light or ultraviolet light. The photo-sensitive region 111 (and also other parts of the semiconductor material 112) may be made up of any desired semiconductor material such as silicon or gallium arsenide.

[0026] In addition to the semiconductor material 112, the semiconductor device 100 comprises further layers or regions such as non-semiconductor material 114 illustrated in Fig. 1. A metallization stack 113 comprising multiple metal layers M1, ..., MQ is formed in the non-semiconductor material 114 for electrically contacting the photo-sensitive region 111. For example, the metallization stack 113 may be used to couple a read-out circuit and / or a driver circuit (e.g. providing a bias or modulation signal for the photo-sensitive region 111) to the photo-sensitive region 111.

[0027] The incident light 100 is coming from an objective of the optical camera comprising one or more objective lenses. The optical axis of the optical camera / objective is indicated in Fig. 1 by dotted line 102. The optical axis of the optical camera is parallel to a thickness direction y of the semiconductor device 110. As can be seen from Fig. 1, the incident light 101 reaches the device 100 at an angle with respect to the optical axis 102. The angle of the incident light 101 with respect to the optical axis 102 is the CRA of the incident light 101.

[0028] In order to compensate for the CRA, the device 100 additionally comprises a dedicated optical element 120. The optical element 120 comprises a first surface 121 for receiving the incident light. Further, the optical element 120 comprises a second surface 122 opposite (to) the first surface 121. The second surface 122 is turned towards the photo-sensitive region 111. In other words, the second surface 122 faces the photo-sensitive region 111. As can be seen from Fig. 1, the second surface 122 is for emitting the incident light 101 towards the photo-sensitive region 111.

[0029] The first surface 121 and the second surface 122 are tilted by a tilt angle α relative to each other so as to modify a direction of propagation of the incident light 101 passing through the optical element 120 towards a center C of the photo-sensitive region 111 in order to compensate (at least in part) for the CRA of the incident light 101.

[0030] The optical element 120 allows to modify the direction of propagation of the incident light 101 towards the thickness direction y of the semiconductor device 110 such that the incident light 101 passing through the optical element 120 is focused to the center C of the photo-sensitive region 111. Accordingly, the direction of propagation of the incident light 101 is substantially parallel to the thickness direction y of the semiconductor device 110. Consequently, propagation of the incident light 101 to neighboring photo-sensitive regions may be avoided. Therefore, crosstalk between the photo-sensitive region 111 and neighboring photo-sensitive regions may be reduced. Furthermore, measures for suppressing crosstalk such as trenches in the semiconductor device 110 may be omitted. This allows reduced complexity and costs. Additionally, a thickness of the photo-sensitive region 111 (i.e. an extension along the thickness direction y of the semiconductor device 110) may be increased. This may allow to further reduce crosstalk between the photo-sensitive region 111 and neighboring photo-sensitive regions. In addition, shadowing by wiring lines of the metallization stack 113 may be avoided since the direction of propagation of the incident light 101 is substantially parallel to the thickness direction y of the semiconductor device 110 in the metallization stack 113 as well.

[0031] In the example of Fig. 1, the optical element 120 is arranged on a front surface 115 of the of the semiconductor device 110. In particular, the second surface 122 of the optical element 120 is formed on the surface 115 of the semiconductor device 110 such that the second surface 122 of the optical element 120 is parallel to the surface 115 of the semiconductor device 110.

[0032] As can be seem from Fig. 1, a lateral position of the optical element 120 is substantially equal to a lateral position of the photo-sensitive region 111. The lateral extension of the optical element 120 partly overlaps with the lateral extension of the photo-sensitive region 111.

[0033] The refractive indexes of the optical element 120 and material contacting the optical element 120 are different from each other such that the optical element 120 changes the direction of propagation of the incident light 101 towards the center C of the photo-sensitive region 111 by optical refraction. In the example of Fig. 1, the semiconductor device 110 and an oxide layer 130 formed on the semiconductor device 110 are contacting the optical element 120. Therefore, the refractive index η OE of the optical element 120 is different from the refractive index η SD of the semiconductor device 110 and the refractive index η OL of the oxide layer 130. For example, the oxide layer 130 partially enclosing the optical element 120 may be made up of silicon oxide such that η OL = 1.46. The optical element 120 may, e.g., be made up of material exhibiting a higher refractive index than silicon oxide such as silicon nitride, polysilicon, amorphous silicon, monocrystalline silicon or polymer materials. For example, the optical element 120 may be made up of amorphous silicon such that η OE = 3.6. In other examples, material exhibiting a lower refractive index than silicon oxide (or any other material enclosing the optical element 120) may be used. In alternative examples, the optical element 120 may enclose a cavity (not illustrated in Fig. 1) which is evacuated (empty, under vacuum) or filled with a predefined gas (air or other gases).

[0034] The tilt angle α is related to the CRA and the refractive indexes of the material contacting the optical element 120. The angle β shown in Fig. 1 indicates the angle of the incident light 101 with respect to a surface normal 123 of the first surface 121 and is defined as follows: β = CRA + α

[0035] Taking into account the above definition of the angle β, the tilt angle α may be determined as follows using Snell's law: η OL ⋅ sin β = η OE ⋅ sin α η OL ⋅ sin CRA + α = η OE ⋅ sin α α = arcsin η OL / η OE 1 − arcsin η OL / η OE ⋅ CRA

[0036] In the example of Fig. 1, the optical element 120 is in part formed in the oxide layer 120 and arranged between the semiconductor device 110 and a microlens 140 for focusing the incident light 101 onto the first surface 121 of the optical element 120. The microlens 140 is a small lens with a diameter that is at maximum ten, five, three or less times the lateral extension of the photo-sensitive region 111. In the example of Fig. 1, the microlens 140 is formed by structuring the oxide layer 120, i.e. the microlens 140 is formed in the oxide layer 120. However, it is to be noted that the microlens 140 may alternatively be formed separate from the oxide layer 120. Further, it is to be noted that in other examples, the microlens 140 may be formed between the optical element 120 and the photo-sensitive region 111. In other words, the optical element 120 may be arranged above the microlens 140 according to some examples.

[0037] The optical element 120 may at least partly be covered with an antireflective film (coating) in order to suppress reflections of the incident light at the surface of the optical element 120.

[0038] The device 100 described above in connection with Fig. 1 is for front side illumination such that the metallization stack 113 is arranged between the photo-sensitive region 111 and the optical element 120 along the thickness direction y of the semiconductor device 110. However, the proposed technology for compensating the CRA of incident light may as well be used for back side illumination. This is shown in Fig. 2 illustrating another device 200 for an image sensor of an optical camera. In the example of Fig. 2, the optical element 120 is arranged (formed) on a back surface 116 of the of the semiconductor device 110. In contrast to the example of Fig. 1, the photo-sensitive region 111 is arranged between the metallization stack 113 and the optical element 120 in the device 200.

[0039] The oxide layer 130 is formed on the back surface 116 of the semiconductor device 110 and partially encloses the optical element 120, which is formed directly on top (e.g. as part) of the detector semiconductor material forming the photo-sensitive region 111 by tilting the surface of the photo-sensitive region 111.

[0040] In the examples of Fig. 1 and Fig. 2, the second surface 122 of the optical element 120 is parallel to the surface 115, 116 of the semiconductor device 110, whereas the first surface 121 of the optical element 120 is tilted with respect to the respective surface 115, 116 of the semiconductor device 110. However, the proposed technology is not limited thereto. Fig. 3 illustrates another device 300 for an image sensor of an optical camera according to the proposed technology. In contrast to the examples of Fig. 1 and Fig. 2, the first surface 121 of the optical element 120 is parallel to the surface 115 of the semiconductor device 110, whereas the second surface 122 of the optical element 120 is tilted with respect to the surface 115 of the semiconductor device 110.

[0041] Additionally, the optical element 120 is fully formed in the oxide layer 130 such that the oxide layer 130 fully encloses the optical element 120. The optical element 120 is arranged distant from the surface 115 of the semiconductor device 110 along the thickness direction y of the semiconductor device 110 contrary to the examples of Fig. 1 and Fig. 2 in which the optical element 120 is formed on the respective surface 115, 116 of the semiconductor device 110. Also the example of Fig. 3 allows to change to the direction of propagation of the incident light to the thickness direction y of the semiconductor device 110 in order to focus the incident light 101 passing through the optical element 120 towards the center C of the photo-sensitive region 111 for compensating the CRA of the incident light 101.

[0042] Fig. 4 illustrates a further device 400 for an image sensor of an optical camera according to the proposed technology. The first surface 121 and the second surface 122 of the optical element 120 are both tilted with respect to the surface 115 of the semiconductor device 110 in the example of Fig. 4, i.e. none of the first surface 121 and the second surface 122 of the optical element 120 is parallel to the surface 115 of the semiconductor device 110. Similar to the example of Fig. 3, the optical element 120 is fully formed in the oxide layer 130 such that the optical element 120 is arranged distant from the surface 115 of the semiconductor device 110 along the thickness direction y of the semiconductor device 110.

[0043] Similar to the examples of Fig. 1 and Fig. 2, the lateral position of the optical element 120 is substantially equal to the lateral position of the photo-sensitive region 111 in the examples of Fig. 3 and Fig. 4. Again, the lateral extension of the optical element 120 partly overlaps with the lateral extension of the photo-sensitive region 111.

[0044] Fig. 5 illustrates another device 500 for an image sensor of an optical camera according to the proposed technology. The device 500 is for back side illumination. The optical element 120 compensating the CRA of the incident light 101 is arranged distant from the back surface 116 of the semiconductor device 110. The metallization stack is arranged at the front surface 115 of the semiconductor device, which is covered by another oxide layer 150.

[0045] In the above examples, the optical element 120 was used together with the microlens 140 for focusing the incident light towards the center C of the photo-sensitive region 111 for compensating the CRA of the incident light 101. This is illustrated schematically in Fig. 6a. An alternative example implementing the functionality of the microlens 140 into the optical element 120 is illustrated in Fig. 6b. While the first surface 121 is a plane (even) surface in the example of Fig. 6a, the first surface 121 is a curved surface serving as a microlens in the example of Fig. 6b.

[0046] Fig. 7 illustrates another device 700 for an image sensor of an optical camera according to the proposed technology. In the device 700, the optical element 120 is partially formed in a recess 117 in the front surface 115 of the semiconductor device 110. Accordingly, the second surface 122 of the optical element 120 extends partially in the recess 117 and partially in the oxide layer 130 formed on the front surface 115 of the semiconductor device 110.

[0047] Further, the optical element 120 is covered with an antireflective film 117 in order to mitigate reflections of the incident light at the surface of the optical element 120. In the example of Fig. 7, the antireflective film 117 is a nitride coating. However, it is to be noted that any other suitable antireflective coating may be used as well. Further, it is to be noted that according to some examples only part of the optical element 120 may be covered with the antireflective film 117.

[0048] Further illustrated are two passivation films 118-1 and 118-2 of nitride material for passivating the device 100. The passivation film 118-1 partially covers the front surface 115 of the semiconductor device 110, wherein the surface 115 is not covered by the passivation film 118-1 at the lateral position of the metallization stack 113, i.e. the lateral position of the photo-sensitive region (not illustrated). The passivation film 118-2 extends laterally between the optical element 120 and the microlens 120.

[0049] Fig. 7 further indicates the electrical contacting of the photo-sensitive area from the outside. A multilayer contact structure 160 coupling to the metallization stack 113 is illustrated in the right part of Fig. 7. The multilayer contact structure 160 is coupled to logic and driver circuitry for reading-out and driving (e.g. biasing or gating) the photo-sensitive region of the device 700.

[0050] The above described tilted surfaces of the optical element 120 may be generated using various processes of semiconductor fabrication. For example, for generating a tilted surface within resist material, grey-scale lithography may be used. Alternatively, a mechanical stamp technique may be used. Further, the tilted surfaces may be transferred to other materials by etch processes. Etch processes may allow to adjust (tune) the tilt angle. Further, more than one of the above described optical elements may be used for modifying the direction of propagation of the incident light towards the center of the photo-sensitive region in order to compensate for the CRA of the incident light.

[0051] An example of an image sensor 800 using the proposed technology is illustrated in Fig. 8. The image sensor 800 comprises an array of photo-sensitive pixels 810-1, 810-2, ..., 810-25. It is to be noted that the proposed technology is not limited to arrays comprising 25 photo-sensitive pixels as illustrated in Fig. 8. The number of photo-sensitive pixels illustrated in Fig. 8 is merely illustrative. In general, any number N ≥ 2 of photo-sensitive pixels may be used.

[0052] Two or more of the photo-sensitive pixels 810-1, 810-2, ..., 810-25 use devices according to the proposed technology. In the example of Fig. 8, all of the photo-sensitive pixels 810-1, 810-2, ..., 810-25 use a respective device according to the proposed technology.

[0053] Further details of the image sensor 800 will be described in the following with reference to the photo-sensitive pixels 810-14 and 810-15, to which it is referred to as a first pixel and a second pixel.

[0054] The first pixel 810-14 comprise a first device as described above, whereas the second pixel 810-15 comprise a second device as described above.

[0055] The first pixel 810-14 and the second pixel 810-15 are located at different lateral distances to a center C' of the array. The CRA of the incident light reaching the first pixel 810-14 and the second pixel 810-15 generally depends on the position of the pixel within the array. In other words, the pixels 810-14 and 810-15 are illuminated with a different CRA. Therefore, the tilt angles of the first pixel 810-14 and the second pixel 810-15 are chosen different from each other. In particular, the tilt angles of the first pixel 810-14 and the second pixel 810-15 depend on the position of the respective pixel within the pixel array. As the first pixel 810-14 is located at a smaller lateral distance to the center C' of the array than the second pixel 810-15, the tilt angle α 1 of the optical element 820 of the first pixel 810-14 is smaller than the tilt angle α 2 of the optical element 820 of the second pixel 810-15. The refractive indexes of the optical elements of the first device and the second device are equal. In other words, the image sensor 800 uses an arrangement of tilted surfaces within the optical stack in order to transfer the incident light into the vertical direction by optical refraction.

[0056] The image sensor 800 may thus allow to compensate for the CRA of the incident light.

[0057] The optical elements 820 of individual pixels of the pixel array are oriented towards the center C of the array. Therefore, a thickness of the respective optical element increases for each of the first pixel 810-14 and the second pixel 810-14 with decreasing lateral distance to the center C' of the array as illustrated in Fig. 8. In other words, a distance between the first and second surface of the optical along the thickness direction of the semiconductor device holding the photo-sensitive area increases for each of the first pixel 810-14 and the second pixel 810-14 with decreasing lateral distance to the center C' of the array.

[0058] The pixel 810-13 located at the center C' of the array comprises an optical element 820' with a bottom surface and a top surface parallel to the surface of the below semiconductor device holding the photo-sensitive region as the CRA of the incident light is assumed to be 0° in the center C' of the array.

[0059] A schematic example of an optical camera 900 using the proposed technology for compensating the CRA is illustrated in Fig. 9.

[0060] The optical camera 900 comprises an image sensor 920 as described above. Additionally, the optical camera comprises an objective with at least one objective lens 911 configured to focus incident light 901 on the image sensor 920. As indicated in Fig. 9, the optical camera 900 may comprise further objective lens 912, 913, ... for focusing the incident light 901 on the image sensor 920.

[0061] The optical camera 900 may further comprise other hardware - conventional and / or custom. For example, the optical camera 900 may comprises circuitry for processing the electric signals output by the photo-sensitive regions of the individual pixels of the image sensor 920, or circuitry for driving (e.g. biasing or gating) the individual pixels of the image sensor 920.

[0062] The proposed technology may allow effective and cheap handling of large CRAs of the incident light focused on the image sensor 920 by compensating the CRA with optical refraction at the tilted surfaces of the optical elements. Conventional expensive approaches such as trenches for crosstalk suppression or back side illumination may be omitted. However, it is to be noted that the proposed technology may as well be used with back side illumination.

[0063] The optical camera 900 may be used for any kind of two-dimensional or three-dimensional image capturing. For example, the image sensor 920 may be a two-dimensional imager for visible or infrared light. In other examples, the image sensor 920 may be a three-dimensional imager for time-of-flight measurements.

[0064] The camera 900 may be of smaller size than conventional cameras because a higher CRA may be enabled without disadvantages such as crosstalk. For example, the available space, in particular the available height, for a camera is strictly limited in smartphones. Accordingly, the camera 900 may be suitable for smartphones as it may be built with small size. Moreover, the camera 900 may allow increased sensitivity as the thickness of the photo-sensitive region may be increased (see above). For example, if silicon is used as detector material for the photo-sensitive region and infrared light is to be detected, increasing the thickness of the photo-sensitive region may be beneficial because of the height penetration depth of infrared light in silicon.

Claims

1. A device for an image sensor, comprising: a semiconductor device (110) comprising: a photo-sensitive region (111) formed in semiconductor material (112) of the semiconductor device (110) and configured to generate an electric signal based on incident light (101); and a metallization stack (113) formed in a non-semiconductor material (114) of the semiconductor device (110) for electrically contacting the photo-sensitive region (111); an optical element (120) comprising a first surface (121) for receiving the incident light (101) and a second surface (122) opposite the first surface (121) and turned towards the photo-sensitive region (111), wherein the first surface (121) and the second surface (122) are tilted by a tilt angle relative to each other so as to modify a direction of propagation of the incident light (101) passing through the optical element (120) towards a center of the photo-sensitive region (111) to compensate for a chief ray angle of the incident light (101); a microlens (140) configured to focus the incident light (101) onto the first surface (121) of the optical element (120); and an oxide layer (130) formed on the semiconductor device (110), wherein the optical element (120) is at least in part formed in the oxide layer (130) such that the oxide layer (130) at least partially encloses the optical element (120), wherein the photo-sensitive region (111) is arranged between the metallization stack (113) and the optical element (120).

2. The device of claim 1, wherein one of the first surface (121) and the second surface (122) of the optical element (120) is parallel to a surface (115, 116) of the semiconductor device (110).

3. The device of claim 1, wherein the first surface (121) and the second surface (122) of the optical element (120) are both tilted with respect to a surface (115, 116) of the semiconductor device (110).

4. The device of any of claims 1 to 3, wherein the optical element (120) is arranged on a surface (115, 116) of the of the semiconductor device (110), or wherein the optical element (120) is arranged distant from the surface (115, 116) of the of the semiconductor device (110).

5. The device of any of claims 1 to 4, wherein a lateral extension of the optical element (120) at least partly overlaps with a lateral extension of the photo-sensitive region (111).

6. The device of any of claims 1 to 5, wherein refractive indexes of the optical element (120) and material contacting the optical element (120) are different from each other.

7. The device of any one of claims 1 to 6, wherein the optical element (120) is fully formed in the oxide layer (130) such that the oxide layer (130) fully encloses the optical element (120).

8. The device of any one of claims 1 to 6, wherein the optical element (120) is partially formed in a recess in a surface (115, 116) of the semiconductor device (110) such that the second surface (122) of the optical element (120) extends partially in the recess and partially in the oxide layer (130).

9. The device of any one of claims 1 to 6, wherein the second surface (122) of the optical element (120) is formed on a surface (115, 116) of the semiconductor device (110).

10. The device of any of claims 1 to 9, wherein refractive indexes of the optical element (120) and the oxide layer (130) are different from each other.

11. An image sensor (800) for an optical camera, wherein the image sensor comprises an array of photo-sensitive pixels (810-1, ..., 810-25), and wherein the array of photo-sensitive pixels (810-1, ..., 810-25) comprises: a first pixel (810-14) comprising a first device according to any of claims 1 to 10; and a second pixel (810-15) comprising a second device according to any of claims 1 to 10, wherein the first pixel (810-14) is located at a smaller lateral distance to a center of the array than the second pixel (810-15), and wherein the tilt angle of the optical element (820) of the first pixel (810-14) is smaller than the tilt angle of the optical element (820) of the second pixel (810-15).

12. The image sensor (800) of claim 11, wherein refractive indexes of the optical elements (120) of the first pixel (810-14) and the second pixel (810-15) are equal13. An optical camera (900) comprising: an image sensor (920) according to claim 11 or claim 12; and one or more objective lenses (911) configured to focus the incident light (101) on the image sensor (920).