Color Filter Array and Micro-Lens Structure for Imaging System
A color filter array and micro-lens structure for imaging system and method of forming the color filter array and micro-lens structure. A micro-lens material is used to fill the space between the color filters to re-direct incident radiation, and form a micro-lens structure above a top surface of the color filters.
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Digital cameras and other digital imaging devices use arrays of millions of tiny photodetectors or pixels to record an image. For example, when a cameraman or camerawoman presses his or her camera's shutter button and exposure begins, each photodetector in the array is uncovered to detect the presence or absence of photons at the individual array locations. To end the exposure, the camera closes its shutter, and circuitry in the camera assesses how much light (e.g., how many photons) fell into each photodetector while the shutter was open. The relative quantity or intensity of photons that struck each photodetector are then stored according to a bit depth (0-255 for an 8-bit pixel). The digital values for all the pixels are then stored and are used to form a resultant image.
The description herein is made with reference to the drawings, wherein like reference numerals are generally utilized to refer to like elements throughout, and wherein the various structures are not necessarily drawn to scale. In the following description, for purposes of explanation, numerous specific details are set forth in order to facilitate understanding. It will be appreciated that the details of the figures are not intended to limit the disclosure, but rather are non-limiting embodiments. For example, it may be evident, however, to one of ordinary skill in the art, that one or more aspects described herein may be practiced with a lesser degree of these specific details. In other instances, known structures and devices are shown in block diagram form to facilitate understanding.
Individual photodetectors are often, in-and-of themselves, unable to differentiate between different colors of light. Therefore a color filter array (CFA) with color filter elements for different colors is often aligned over a photodetector array so that photodetectors detect light intensity of different colors. Traditionally, indexes of refraction of the different color filter elements are similar, such that when an incident light ray has a large angle of incidence, the light could easily pass through one color filter into other neighboring color filters and/or other neighboring photodetectors underneath the color filters. In this way, crosstalk can happen between photodetectors for different color filters, ultimately causing noise that distorts the resultant digital images.
In general, the present disclosure is related to an optimized semiconductor color filter array and micro-lens structure that alleviates crosstalk between neighboring photodetectors underlying different color filters. These disclosed techniques improve signal-to-noise ratios (SNR) for imaging systems. More particularly, a sidewall waveguide structure is formed between neighboring color filter elements and works in conjuction with a color filter element and a micro-lens structure to limit crosstalk. In some embodiments, the sidewall waveguide structure and micro-lens structure can be made of the same material to limit the number of manufacturing steps. In some embodiments, when incident radiation reaches a waveguide structure between two neighboring color filter elements, the waveguide re-directs the incident radiation back to one of the color filter elements and away from the other color filter element. With some incident angles, for example, total internal reflection happens at the contact surface of the color filter element and the sidewall waveguide structure, which prevents light from passing through neighboring color filter elements. With other incident angles, for example, the sidewall waveguide structure refracts light between neighboring photodetector elements so the light does not inadvertently strike a neighboring photodetector. As a result, larger portion of the incident radiance strikes a photodiode underneath its corresponding color filter element and less light “strays” to neighboring photodiodes, such that SNR is improved.
When incident radiance (see e.g., incident rays 112, 116) strikes this structure, the incident radiance is focused by a micro-lens structure towards its corresponding color filter element, and is re-directed when reaching an internal contact surface 114 at which the color filter element 102 meets the micro-lens material 110. In some embodiments, the micro-lens material 110 could be photo resist or oxide with an index of refraction (nr) smaller than the index of refraction of the color filter elements 102, 104 (ncf). In an embodiment, the index of refraction of the micro-lens material is between 1.1 and 1.8. If the incident radiance has an angle of incidence that is less than some critical angle (see incident ray 112), the incident radiance experiences total internal reflectance at the internal contact surface 114 and is therefore bounced back into the color filter element 102. On the other hand, if the incidence radiance has an angle of incidence that is larger than the critical angle (see incident ray 116), the incident radiance is refracted at the internal surface 114 and therefore is re-directed closer to the color filter element 102. In some embodiments, the critical angle for total internal reflection at the internal contact surface 114 can be larger than 30 degrees.
An array of photodetectors 202, which is made up of individual photodetectors (e.g., 202a, 202b, 202c, 202d), is arranged as a matrix of pixels to collect incident radiance coming through an array of color filter elements 204, which is made up of individual color filter elements (e.g., 204a, 204b, 204c, 204d). As shown, the individual color filter elements are vertically aligned with the individual photodetectors. The color filter array 204 comprises color filter elements for different colors. It could comprise primary color filter elements arranged in a matrix. For example, first color filter element 204a could be a blue filter and second color filter element 204b could be a green filter. Sidewall waveguide structure 206 is arranged between neighboring color filter elements. Similar as previously described with regards to
Advantageously, in either case of total internal reflection or refraction by the sidewall waveguide structure 206, the sidewall waveguide structure 206 diverts the incident light away from neighboring photodetectors (e.g., away from photodetector 202b). Thus, in cases of total internal reflection such as shown by incident ray 210, the sidewall waveguide structure 206 is helpful in that it improves the collection efficiency of photodetector 202a, but also helps to limit cross-talk experienced by the neighboring photodetector 202b. Further, even in cases of refraction as shown by incident ray 212 which do not necessarily improve the collection efficiency of photodetector 202a, by refracting the incident ray 212 away from the neighboring photodetector 202b, the sidewall waveguide structure 206 still helps to limit cross-talk between neighboring photodetectors.
In an embodiment, in order to have total internal reflection at an internal contact surface at which the sidewall waveguide structure 206 meets a color filter element, a first index of refraction of the sidewall waveguide structure (n1) and a second index of refraction of the micro-lens structure (n2) are smaller than a third index of refraction of the color filter element (n3). In an embodiment, the index of refraction of the sidewall waveguide structure, micro-lens structure, and the color filter element are different. In an embodiment, the material of the photodetector 202 could be or contains silicon. The color filter element 204 could be formed by photo resist with index of refraction n3, which can be between 1.6 and 2.0. The micro-lens structure 208 and the sidewall waveguide structures 206 could be formed by transparent photo resist or oxide. The ratio of a height of color filter element to a space between two adjacent color filter elements (or a distance between at least one of the opposing surfaces of two adjacent color filter elements, e.g. 202a and 202b) could be around 1:7.
Further, as will be appreciated in more detail herein, the micro-lens structure 208 and the sidewall waveguide structure 206 could be formed by same manufacturing step and/or made of same material.
At 402, a photodetector array is patterned.
At 404, a color filtering array is patterned onto the photodetector array. The color filter elements are patterned separately wherein a space exists between two color filter elements. The color filter elements are patterned so that a ratio of a height of a color filter element to a distance between two color filter elements is about 1:7. The color filter array comprises primary color filter elements arranged in a matrix. The primary colors could be red, green and blue.
At 406, a micro-lens material is applied above the color filter array. In an embodiment, a height of the micro-lens material is larger than a sum of a height and width of the color filter element. The micro-lens material could be coated for example by either spin-on method or deposition.
At 408, a micro-lens shape is patterned above the micro-lens material. Varies methods could be used to pattern micro-lens shape. For example, a photo resist could be exposed, developed and baked to form a rounding shape which will be utilized as micro-lens shape in following steps.
At 410, a back etching is performed to form micro-lens.
One example of FIG. 4's method is now described with regards to a series of cross-sectional views as shown in
At
Space 506 exists between neighboring color filter elements 502, 504. In some embodiments, this space 506 extends downward from an upper surface of the color filter elements to the substrate. In some embodiments, this space 506 can be formed by performing an etch when a mask is placed or disposed over the color filter elements. In other embodiments, the color filter elements can be selectively grown over the photodetector array such that the space 506 is a result of the selective growth.
At
At
At
At
Thus, some embodiments relate to a semiconductor device. The device includes a first color filter element on a semiconductor substrate. A second color filter element is formed on the semiconductor substrate and spaced apart from the first color filter element. A micro-lens structure is arranged over a top surface of the first color filter element. A sidewall waveguide structure is arranged between neighboring sidewalls of the first and second color filter elements. The sidewall waveguide structure and micro-lens structure are made of the same material.
Other embodiments relate to a semiconductor imaging system. The semiconductor imaging system includes a photodetector array including a matrix of individual photodetectors. A color filter array is arranged over the photodetector array and includes a matrix of color filter elements which are arranged vertically over respective photodetectors in the photodetector array. An array of micro-lenses are arranged over the color filter array and includes a matrix of micro-lens structures which are arranged vertically over, or overlap, respective color filter elements of the color filter array. A sidewall waveguide structure laterally surrounds a color filter element. The sidewall waveguide structure re-directs incident radiation striking a micro-lens structure with a first angle of incidence, which is less than a predetermined angle of incidence, toward an individual photodetector that corresponds vertically to the color filter element and the micro-lens structure. In an embodiment, the micro-lens structure is configured to focus a first incident ray with an angle of incidence that is less than a predetermined angle of incidence, and a second incident ray with an angle of incidence that is greater than the predetermined angle of incidence, through a color filter element. In another embodiment, the sidewall waveguide structure is configured to reflect the focused first incident ray to strike the photodetector and further configured to refract the focused second incident ray to pass between neighboring photodetectors.
Still another embodiment relates to a method of forming a semiconductor imaging system structure. In this method, a photodetector array is patterned on a semiconductor substrate. A color filter array is patterned over the photodetector array. The color filter array, after being patterned, has spaces between neighboring color filter elements of the color filter array. A micro-lens material is applied to the patterned color filter array. The micro-lens material fills the spaces between neighboring color filter elements to establish sidewall waveguide structures and also covers upper surfaces of the color filter elements to establish micro-lens structures.
It will be appreciated that while reference is made throughout this document to exemplary structures in discussing aspects of methodologies described herein (e.g., the structure presented in
Also, equivalent alterations and/or modifications may occur to those skilled in the art based upon a reading and/or understanding of the specification and annexed drawings. The disclosure herein includes all such modifications and alterations and is generally not intended to be limited thereby. For example, although the figures provided herein, are illustrated and described to have a particular doping type, it will be appreciated that alternative doping types may be utilized as will be appreciated by one of ordinary skill in the art.
In addition, while a particular feature or aspect may have been disclosed with respect to only one of several implementations, such feature or aspect may be combined with one or more other features and/or aspects of other implementations as may be desired. Furthermore, to the extent that the terms “includes”, “having”, “has”, “with”, and/or variants thereof are used herein, such terms are intended to be inclusive in meaning—like “comprising.” Also, “exemplary” is merely meant to mean an example, rather than the best. It is also to be appreciated that features, layers and/or elements depicted herein are illustrated with particular dimensions and/or orientations relative to one another for purposes of simplicity and ease of understanding, and that the actual dimensions and/or orientations may differ substantially from that illustrated herein.
Claims
1. An imaging device comprising:
- a first color filter element on a semiconductor substrate;
- a second color filter element on the semiconductor substrate and spaced apart from the first color filter element;
- a micro-lens structure arranged over a top surface of the first color filter element; and
- a sidewall waveguide structure arranged between neighboring sidewalls of the first and second color filter elements, the sidewall waveguide structure and micro-lens structure being made of the same material.
2. The imaging device of claim 1, the material of the micro-lens structure and the sidewall waveguide structure being transparent and having an index of refraction which is lower than that of the first color filter element.
3. The imaging device of claim 1, wherein the material of the sidewall waveguide structure and the micro-lens structure is photo resist or oxide and has an index of refraction that is between 1.1 and 1.8.
4. The imaging device of claim 1, further comprising:
- a first photodetector arranged under the first color filter element; and
- a second photodetector arranged under the second color filter element;
- the micro-lens structure being configured to focus both a first incident ray, which has a first angle of incidence that is less than a predetermined angle of incidence, and a second incident ray, which has a second angle of incidence that is greater than the predetermined angle of incidence, through the first color filter element, and
- the sidewall waveguide structure being configured to reflect the focused first incident ray to strike the first photodetector and further configured to refract the focused second incident ray to pass between the first and second photodetectors.
5. A semiconductor imaging system comprising:
- a photodetector array including a matrix of individual photodetectors;
- a color filter array arranged over the photodetector array and including a matrix of color filter elements which are arranged vertically over respective photodetectors in the photodetector array;
- an array of micro-lenses arranged over the color filter array and including a matrix of micro-lens structures which are arranged vertically over respective color filter elements of the color filter array; and
- a sidewall waveguide structure laterally surrounding a color filter element and configured to re-direct incident radiation striking a micro-lens structure with a first angle of incidence, which is less than a predetermined angle of incidence, toward an individual photodetector that corresponds vertically to the color filter element and the micro-lens structure.
6. The semiconductor imaging system of claim 5, the sidewall waveguide structure being further configured to re-direct incident radiation striking the micro-lens structure with a second angle of incidence, which is greater than the predetermined angle of incidence, to pass between neighboring photodetectors.
7. The semiconductor imaging system of claim 5, wherein the sidewall waveguide structure has a first index of refraction, the micro-lens structure has a second, different index of refraction, and the color filter element has a third index of refraction that is larger than the first index of refraction and larger than the second index of refraction.
8. The semiconductor imaging system of claim 5, wherein the sidewall waveguide structure and the micro-lens structure are made of the same material.
9. The semiconductor imaging system of claim 8, wherein the material of the sidewall waveguide structure and the micro-lens structure is photoresist or oxide and has an index of refraction that is between 1.1 and 1.8.
10. The semiconductor imaging system of claim 5, wherein the color filter array comprises primary color filter elements arranged in a matrix.
11. The semiconductor imaging system of claim 10, wherein the primary color filter elements include a red color filter, a green color filter, and a blue color filter.
12. The semiconductor imaging system of claim 5, wherein the individual photodetectors are made of a silicon-containing material.
13. The semiconductor imaging system of claim 5, wherein the color filter element is made of photoresist and has an index of refraction that is between 1.6 and 2.0.
14. The semiconductor imaging system of claim 5, wherein a ratio of a height of a color filter element to a space between neighboring color filter elements is about 1:7.
15. The semiconductor imaging system of claim 5, wherein the individual photodetectors are complementary metal-oxide-semiconductor (CMOS) photodetectors.
16-20. (canceled)
21. An imaging device disposed over a semiconductor substrate comprising:
- first and second photodetectors arranged at least partially in the semiconductor substrate;
- first and second color filter elements disposed above the first and second photodetectors, respectively;
- first and second micro-lens structures covering top surfaces of the first and second color filter elements, respectively; and
- a sidewall waveguide structure separating the first and second color filter elements;
- wherein the sidewall waveguide structure has an index of refraction that is smaller than that of the first and second color filter elements.
22. The imaging device of claim 21, wherein the material of the sidewall waveguide structure is photoresist.
23. The imaging device of claim 21, wherein the material of the sidewall waveguide structure is silicon dioxide.
24. The imaging device of claim 21, wherein the sidewall waveguide structure has an index of refraction that is between 1.1 and 1.8.
25. The imaging device of claim 21, wherein the sidewall waveguide structure and the first and second micro-lens structures are made of the same material.
Type: Application
Filed: Nov 20, 2013
Publication Date: May 21, 2015
Applicant: Taiwan Semiconductor Manufacturing Co., Ltd. (Hsin-Chu)
Inventors: Szu-Ying Chen (Toufen Township), Dun-Nian Yaung (Taipei City), Chen-Jong Wang (Hsin-Chu), Tzu-Hsuan Hsu (Kaohsiung City)
Application Number: 14/084,758
International Classification: H01L 27/146 (20060101);