CURVED IMAGE SENSOR
An image sensor includes a plurality of photodiodes arranged in an array and disposed in a semiconductor material with pinning wells disposed between individual photodiodes in the plurality of photodiodes. The image sensor also includes a microlens layer. The microlens layer is disposed proximate to the semiconductor material and is optically aligned with the plurality of photodiodes. A spacer layer disposed between the semiconductor material and the microlens layer. The spacer layer has a concave cross-sectional profile across the array, and the microlens layer is conformal with the concave cross-sectional profile of the spacer layer.
This disclosure relates generally to image sensor fabrication, and in particular but not exclusively, relates to curved image sensors.BACKGROUND INFORMATION
Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as, medical, automobile, and other applications. The technology used to manufacture image sensors has continued to advance at a great pace. For example, the demands of higher resolution and lower power consumption have encouraged the further miniaturization and integration of these devices. While advances in pixel design have dramatically improved image sensor performance, several optical limitations have proved difficult to overcome by optimizing pixel circuitry alone.
Chemical mechanical polishing (CMP) is integral to semiconductor device fabrication. It can be used to thin wafers, remove excess deposition flux, and planarize surfaces. Further, the polish rate is selective to the composition of the films on the surface. Since CMP may be less precise than other fabrication techniques and is generally rougher on the semiconductor wafers, CMP may induce defects into electronic devices if not properly controlled. Defects may include pitting of the wafer, scratches on the wafer surface, and the destruction of layers of device architecture. Accordingly, optimizing the CMP process is desirable in electrical device fabrication.
Non-limiting and non-exhaustive examples of the invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.DETAILED DESCRIPTION
Examples of an apparatus and method for a curved image sensor are described herein. In the following description, numerous specific details are set forth to provide a thorough understanding of the examples. One skilled in the relevant art will recognize, however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects.
Reference throughout this specification to “one example” or “one embodiment” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present invention. Thus, the appearances of the phrases “in one example” or “in one embodiment” in various places throughout this specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more examples.
Throughout this specification, several terms of art are used. These terms are to take on their ordinary meaning in the art from which they come, unless specifically defined herein or the context of their use would clearly suggest otherwise. It should be noted that element names and symbols may be used interchangeably through this document (e.g., Si vs. silicon); however, both have identical meaning.
In one example, plurality of photodiodes 203 is arranged into an array including rows and columns (see infra
In operation, plurality of photodiodes 203 will absorb image light to generate image charge. Image light is focused onto semiconductor material 201 (and corresponding optical structures, e.g., microlens layer 261, color filter layer 241, and optical grid layer 231) via optical lens 281. In conventional image sensors, the lens focal plane is curved but the semiconductor device stack is flat, resulting in image sensor edges that are blurred because they are out of focus (nonconforming with the curvature of the lens). Here, curved image sensor 200 may receive focused image light from optical lens 281 along the edges of curved image sensor 200 because the radius of curvature of curved image sensor 200 now approximates that of optical lens 281. Image light received along the edges of curved image sensor 200 may then be efficiently passed through microlens layer 261 and color filter layer 241 into plurality of photodiodes 203.
In the depicted example, dye-edge structures 371 are disposed above the edges of scribe lines. While forming dye-edge structures 371, semiconductor material 301 may be still part of a larger wafer including multiple image sensors (see e.g.,
It is worth noting that for all semiconductor, oxide, and/or metal formation processes depicted in
In one example, after each image sensor photodiode/pixel in pixel array 405 has acquired its image data or image charge, the image data is readout by readout circuitry 411 and then transferred to function logic 415. Readout circuitry 411 may be coupled to readout image data from the plurality of photodiodes in pixel array 405. In various examples, readout circuitry 411 may include amplification circuitry, analog-to-digital (ADC) conversion circuitry, or otherwise. Function logic 415 may simply store the image data or even alter/manipulate the image data by applying post image effects (e.g., crop, rotate, remove red eye, adjust brightness, adjust contrast, or otherwise). In one example, readout circuitry 411 may readout a row of image data at a time along readout column lines (illustrated) or may readout the image data using a variety of other techniques (not illustrated), such as a serial readout or a full parallel readout of all pixels simultaneously.
In one example, control circuitry 421 is coupled to pixel array 405 to control operation of the plurality of photodiodes in pixel array 405. Control circuitry 421 may be configured to control operation of the pixel array 405. For example, control circuitry 421 may generate a shutter signal for controlling image acquisition. In one example, the shutter signal is a global shutter signal for simultaneously enabling all pixels within pixel array 405 to simultaneously capture their respective image data during a single acquisition window. In another example, the shutter signal is a rolling shutter signal such that each row, column, or group of pixels is sequentially enabled during consecutive acquisition windows. In another example, image acquisition is synchronized with lighting effects such as a flash.
In one example, imaging system 400 may be included in a digital camera, cell phone, laptop computer, or the like. Additionally, imaging system 400 may be coupled to other pieces of hardware such as a processor, memory elements, output (USB port, wireless transmitter, HDMI port, etc.), lighting/flash, electrical input (keyboard, touch display, track pad, mouse, microphone, etc.), and/or display. Other pieces of hardware/software may deliver instructions to imaging system 400, extract image data from imaging system 400, or manipulate image data supplied by imaging system 400.
The above description of illustrated examples of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific examples of the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.
These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific examples disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.
1. An image sensor, comprising:
- a plurality of photodiodes arranged in an array and disposed in a semiconductor material, wherein pinning wells are disposed between individual photodiodes in the plurality of photodiodes to electrically isolate the individual photodiodes;
- a microlens layer disposed proximate to the semiconductor material, wherein the microlens layer is optically aligned with the plurality of photodiodes; and
- a spacer layer disposed between the semiconductor material and the microlens layer, wherein the spacer layer has a concave cross-sectional profile across the array, and wherein the microlens layer is conformal with the concave cross-sectional profile of the spacer layer.
2. The image sensor of claim 1, further comprising a color filter layer and an optical grid layer, wherein the optical grid layer is disposed between the color filter layer and the spacer layer, and the color filter layer is disposed between the optical grid layer and the microlens layer, and wherein the optical grid layer is optically aligned with the plurality of photodiodes such that the optical grid layer directs light into the plurality of photodiodes.
3. The image sensor of claim 2, wherein the optical grid layer and the color filter layer are conformal with the concave cross-sectional profile of the spacer layer.
4. The image sensor of claim 1, wherein the pinning wells include doped semiconductor material.
5. The image sensor of claim 1, wherein a vertex of the concave cross-sectional profile of the spacer layer is located at a center of the array of the plurality of photodiodes.
6. The image sensor of claim 1, further comprising an optical lens disposed between a source of image light and the semiconductor material, wherein the optical lens is positioned to direct image light into the semiconductor material.
7. The image sensor of claim 6, wherein a radius of curvature of the concave cross-sectional profile of the spacer layer approximates a radius of curvature of the optical lens.
8. The image sensor of claim 1, further comprising control circuitry coupled to the plurality of photodiodes and readout circuitry coupled to the plurality of photodiodes, wherein the control circuitry controls operation of the plurality of photodiodes, and the readout circuitry reads out image data from the plurality of photodiodes.
9. The image sensor of claim 8, further comprising function logic, wherein the readout circuitry transfers the image data to the function logic to alter the image data.
10. A method of image sensor fabrication, comprising:
- providing a semiconductor material including a plurality of photodiodes arranged in an array;
- depositing a spacer layer disposed proximate to a surface of the semiconductor material;
- forming dye-edge structures on a surface of the spacer layer, wherein the dye-edge structures encircle the plurality of photodiodes, and wherein the dye-edge structures are elevated on the surface of the spacer layer; and
- polishing the spacer layer and dye-edge structures, wherein polishing results in a concave cross-sectional profile of the spacer layer across the array of the plurality of photodiodes.
11. The method of claim 10, further comprising removing the dye-edge structures from the surface of the spacer layer.
12. The method of claim 10, further comprising forming a color filter layer and a microlens layer, wherein the color filter layer is disposed between the microlens layer and the spacer layer, and wherein the color filter layer and the microlens layer are optically aligned with the plurality of photodiodes.
13. The method of claim 12, further comprising forming an optical grid layer disposed between the spacer layer and the color filter layer.
14. The method of claim 10, further comprising forming control circuitry and readout circuitry disposed in the semiconductor material.
15. The method of claim 10, wherein depositing a spacer layer includes etching an isolation trench in the semiconductor material, and depositing the spacer layer in the isolation trench and on the surface of the semiconductor material.
16. The method of claim 10, wherein forming dye-edge structures on the spacer layer includes:
- depositing a dye-edge layer on the spacer layer; and
- etching the dye-edge layer to form dye-edge structures.
17. The method of claim 16, wherein the dye-edge layer includes silicon nitride and the spacer layer includes silicon oxide.
18. The method of claim 10, wherein polishing the spacer layer and dye-edge structures includes removing a portion of the spacer layer to form the concave cross-sectional profile of the spacer layer.
19. The method of claim 10, wherein providing a semiconductor material includes forming a plurality of photodiodes in a backside of the semiconductor material.
20. The method of claim 19, further comprising forming pinning wells between individual photodiodes in the plurality of photodiodes.
Filed: Dec 18, 2015
Publication Date: Jun 22, 2017
Inventors: Yuanwei Zheng (San Jose, CA), Gang Chen (San Jose, CA), Duli Mao (Sunnyvale, CA), Dyson Tai (San Jose, CA), Arvind Kumar (Manchester, MA), Hung Chih Chang (Newark, CA), Chih-Wei Hsiung (San Jose, CA)
Application Number: 14/974,362