Image sensor and method for forming the same

Abstract

An image sensor and a method for forming the same, the image sensor comprising: a semiconductor substrate; a plurality of photodiodes located in the semiconductor substrate; a plurality of microlens arrays located on the surface of the semiconductor substrate, each microlens array corresponding to a photodiode, each microlens array consisting of n rows and n columns of microlenses, n ≥ 2; wherein the microlenses arranged in the same row or in the same column or on the same diagonal line in the microlens array are of the same size. The scheme of the present invention can provide an improved image sensor that meets marketing and market requirements and ensures the performance of the pixel unit.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to an image sensor and a method for forming the same. Background Art

[0002] Image sensors are semiconductor devices that convert optical image signals into electrical signals. Among the various types of image sensors, complementary metal oxide semiconductor (CMOS) image sensors (CIS) are widely used due to their small size, low power consumption and low price.

[0003] Existing CMOS image sensors (can be referred to as image sensors) mainly include front-side illumination (FSI) CMOS image sensors and back-side illumination (BSI) CMOS image sensors. Among them, back-side illumination CMOS image sensors are more widely used due to their better photoelectric conversion effect. The back-side illumination CMOS image sensors can also be called back-illuminated CMOS image sensors.

[0004] At present, high-pixel image sensor chips are popular in the market. From the perspective of market sales and marketing, portable electronic device manufacturers and smartphone manufacturers often use the performance parameters and pixel count of the camera as the main selling points. When launching new products, they highlight the high pixel count of the image sensor chip from the perspective of advertising benefits. In recent years, the number of pixels in smartphones has increased from 16 million pixels to 48 million, 64 million pixels, and even 100 million pixels. The increase in the number of pixels corresponds to a smaller pixel unit size, from 1.75 microns (um) to the current 0.7um. When the pixel unit size is small, the amount of light entering the pixel unit becomes smaller, the received signal becomes weaker, and the optical signal crosstalk problem between the microlenses on the pixel unit is aggravated. In order to achieve the functional requirements of PD and solve the crosstalk problem of optical signals, deep isolation (DTI) will be introduced during pixel design. In addition, small-sized pixel units will lead to a decrease in the full well capacity of the image sensor and poor performance of the image sensor. If large-sized pixel units are still used, the size of the image sensor chip will become larger and the module height will become higher, which is inconsistent with the application demand direction of thin and light smartphones. Therefore, how to compatibly market high-pixel image sensor chips while taking into account the performance of image sensor chips has become an urgent problem to be solved.

[0005] Patent CN106257678B provides a CMOS image sensor, which achieves the technical effect of increasing light flux and improving photosensitivity by setting a microlens array corresponding to a photodiode one by one, and setting a plurality of microlenses in the microlens array, and in the microlens array, the size of the microlens corresponding to the edge area of ​​the photodiode is smaller than the size of the microlens corresponding to the central area of ​​the photodiode. The inventor simulates and verifies the technical solution and technical effect proposed in patent CN106257678B, and takes a microlens array containing three microlenses, with a large central microlens and a small edge microlens as an example, and verifies and compares it with the traditional structure of a single microlens corresponding to a pixel unit. Figure 1 This is the result of the comparison and verification between the technical solution in patent CN106257678B and the traditional microlens solution. Figure 1 As shown, the light sensitivity of the central microlens area and the edge microlens area of ​​the image sensor in a single microlens and a microlens array is compared. For a single microlens, the central microlens area is the central area of ​​the single microlens, and the edge microlens area is the edge area of ​​the single microlens. It can be seen from the figure that the light sensitivity of the pixel unit corresponding to a single lens is about 78%, and the light sensitivity of the pixel unit corresponding to the microlens array is about 60%. When the microlens is set to a microlens array composed of multiple microlenses, the light sensitivity cannot be improved, but will cause a decrease in the light sensitivity. Obviously, after technical verification, the technical solution proposed by patent CN106257678B cannot achieve the technical effect of increasing luminous flux and providing light sensitivity. Summary of the invention

[0006] The technical problem solved by the present invention is to provide an improved image sensor and a method for forming the same.

[0007] To solve the above technical problems, an embodiment of the present invention provides an image sensor, comprising: a semiconductor substrate; a plurality of photodiodes located in the semiconductor substrate; a plurality of microlens arrays located on the surface of the semiconductor substrate, each microlens array corresponding to a photodiode, each of the microlens arrays consisting of n rows and n columns of microlenses, n≥2; wherein the microlenses arranged in the same row, the same column, or the same diagonal line in the microlens array have the same size.

[0008] Optionally, the microlenses in each of the microlens arrays have the same size.

[0009] Optionally, each of the microlens arrays is composed of four microlenses in two rows and two columns, and sizes of the microlenses located on the same diagonal line are the same.

[0010] Optionally, each of the microlens arrays is composed of four microlenses in two rows and two columns, and sizes of two microlenses in the same row are the same.

[0011] Optionally, each of the microlens arrays is composed of four microlenses in two rows and two columns, and sizes of two microlenses in the same column are the same.

[0012] Optionally, each of the microlens arrays is composed of 9 microlenses in 3 rows and 3 columns, and the three microlenses in the same row have the same size.

[0013] Optionally, each of the microlens arrays is composed of 9 microlenses in 3 rows and 3 columns, and the three microlenses in the same column have the same size.

[0014] Optionally, the microlens is in the shape of a convex lens, and the bottom surface of the convex lens is flat.

[0015] The present invention also provides a method for forming an image sensor, comprising: providing a semiconductor substrate, wherein a photodiode is provided in the semiconductor substrate; arranging a plurality of microlens arrays on the surface of the semiconductor substrate, wherein each microlens array corresponds to one of the photodiodes, and each microlens array is composed of n rows and n columns of microlenses, where n≥2; wherein the microlenses in the same row, the same column, or the same diagonal arranged in the microlens array have the same size.

[0016] Optionally, the method further includes forming a filter between the semiconductor substrate and the microlens array.

[0017] Optionally, forming the microlens array includes the following steps: forming a fence on a filter corresponding to each of the photodiodes, the fence consisting of a plurality of mutually spaced strip structures, with gaps between adjacent strip structures, each of the gaps corresponding to a predetermined microlens; depositing microlens material to fill the gaps; removing the fence; and reflowing the microlens material to form a plurality of microlenses.

[0018] Optionally, the fence is composed of a plurality of rows or columns of intersecting strip structures, and there are square gaps between adjacent strip structures.

[0019] Optionally, the microlens is in the shape of a convex lens, and the bottom surface of the convex lens is flat.

[0020] Compared with the prior art, the technical solution of the embodiment of the present invention has the following beneficial effects:

[0021] By setting the microlens array to microlenses of multiple sizes, the number of pixels is multiplied, thereby meeting the market demand for high pixels, while avoiding the problem of weak photosensitivity and chip performance degradation caused by too small pixel size, which not only meets marketing and market needs but also ensures the imaging performance of pixel units;

[0022] By corresponding a microlens array with multiple microlenses to a photosensitive diode, the area of ​​the photosensitive unit is increased while meeting the number of pixels, thereby improving the sensitivity of the pixel and solving the loss of signal-to-noise ratio caused by the decrease in unit area due to resolution requirements of a single pixel. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the result of the comparison and verification between the technical solution in patent CN106257678B and the traditional microlens solution.

[0024] Figure 2 is a partial top view of the image sensor provided by the first embodiment of the present invention;

[0025] Figure 3 yes Figure 2 A schematic diagram of the cross-sectional structure of the image sensor along the dotted line shown;

[0026] Figure 4 is a flow chart of a method for forming an image sensor according to an embodiment of the present invention;

[0027] Figure 5 is a partial top view of an image sensor provided by Embodiment 2 of the present invention;

[0028] Figure 6 is a partial top view of an image sensor provided by Embodiment 3 of the present invention;

[0029] Figure 7 is a partial top view of an image sensor provided by Embodiment 4 of the present invention;

[0030] Figure 8 is a partial top view of an image sensor provided by Embodiment 5 of the present invention;

[0031] Fig. 9 It is a partial top view of the image sensor provided in the sixth embodiment of the present invention. DETAILED DESCRIPTION

[0032] In order to solve the above problems in the prior art, the present invention provides an image sensor and a method for forming the same. By disposing a plurality of micro lenses on a pixel unit, the marketing and market demands are met while ensuring the effectiveness and performance of the pixel unit.

[0033] In the following specific description of the preferred embodiments, reference will be made to the attached drawings which constitute a part of the present invention. The attached drawings show by way of example specific embodiments that can implement the present invention. The illustrative embodiments are not intended to be exhaustive of all embodiments according to the present invention. It will be appreciated that other embodiments may be utilized, and structural or logical modifications may also be made without departing from the scope of the present invention. Therefore, the following specific description is not restrictive, and the scope of the present invention is limited by the appended claims.

[0034] The present invention is further described below in conjunction with specific embodiments.

[0035] Embodiment 1

[0036] like Figure 2 As shown, the present invention provides an image sensor, comprising: a semiconductor substrate 10; a plurality of photodiodes (not shown), located in the semiconductor substrate 10; a plurality of microlens arrays 11, located on the surface of the semiconductor substrate 10, each microlens array 11 corresponds to a photodiode, and each of the microlens arrays is composed of n rows and n columns of microlenses, n ≥ 2; wherein the microlenses arranged in the same row or the same column or the same diagonal line in the microlens array 11 have the same size.

[0037] The microlenses in the microlens array are arranged in rows and columns, including at least two rows and two columns, which can be reasonably selected according to actual conditions. Figure 2 As shown, the microlens array is composed of 2 rows and 2 columns of microlenses, that is, the microlens array 11 includes microlenses 111, 112, 113 and 114. Among them, the microlens 111 and the microlens 113 are located on the same diagonal line, the microlens 112 and the microlens 114 are located on the same diagonal line, the microlens 111 and the microlens 113 have the same size, the microlens 112 and the microlens 114 have the same size, and the microlenses 111, 113 and the microlenses 112, 114 have different sizes. Of course, the sizes of the microlenses 111, 112, 113 and 114 can also be the same, that is, the sizes of the microlenses in each microlens array are the same, and can also be designed according to actual needs.

[0038] Furthermore, the edges of the microlenses in the microlens array are connected, which can reduce light loss. The microlenses are in the shape of convex lenses, and the bottom surface of the convex lenses is flat.

[0039] Figure 4 is a flow chart of a method for forming an image sensor provided by the present invention. Specifically, referring to Figure 2 and Figure 3 , the method for forming the image sensor may include the following steps:

[0040] First, a semiconductor substrate 10 is provided, wherein a photodiode 12 is provided in the semiconductor substrate 10;

[0041] Then, a plurality of microlens arrays 11 are arranged on the surface of the semiconductor substrate 10, each of the microlens arrays 11 corresponds to a photodiode 12, and each of the microlens arrays 11 is composed of n rows and n columns of microlenses, where n≥2; wherein the microlenses in the same row, the same column, or the same diagonal line arranged in the microlens array 11 have the same size.

[0042] Furthermore, before forming the microlens, the method may further include: arranging a filter on the surface of the semiconductor substrate. The position of the filter corresponds to the position of the photodiode. The filter may be arranged as a Bayer array or a 4C array to filter light within each wavelength range.

[0043] As an example, forming a microlens array includes the following steps: first, a fence is formed on the surface of the semiconductor substrate corresponding to each photodiode 12, the fence is composed of a plurality of mutually spaced strip structures, adjacent strip structure supports have gaps, each gap corresponds to a predetermined microlens, the strip structure can be composed of any material with a larger etching selectivity relative to the microlens material deposited later, and the strip structure has a certain height. In order to ensure that the process operation is simple when the fence is removed later, and in order to ensure that there is no gap between the predetermined microlenses, the width of the strip structure can be controlled to have a relatively narrow width. Afterwards, the microlens material is deposited to fill the gap. Next, the fence is removed, and a suitable removal method is selected according to the material of the fence, such as an etching method, which has a larger etching selectivity of the fence material than the microlens material, and no etching loss is caused to the microlens material while removing the fence. The microlens material is reflowed to form a plurality of microlenses, and the reflow is achieved by heating. For example, the temperature is heated to above the glass softening temperature of the microlens material, and under the action of surface tension, the surface of the microlens material is transformed into a hemispherical shape. The specific reflow temperature can be reasonably selected according to the microlens material actually used, and is not specifically limited here. Finally, the formed microlens is in the shape of a convex lens. The bottom surface of the microlens is flat and located on the substrate. The appropriate fence can be selected according to the number, size, height, etc. of microlenses actually produced.

[0044] Furthermore, if the microlens array to be formed is composed of several rows and columns of microlenses, the fence is composed of several rows and columns of intersecting strip structures, and there are square gaps between adjacent strip structures. Further, the square can be a square or other shapes such as a rectangle.

[0045] According to the above method, the image sensor provided by the present invention is formed.

[0046] Embodiment 2

[0047] This embodiment provides an image sensor such as Figure 5 As shown, the technical solution is similar to that of the first embodiment, but different from the first embodiment in that the size arrangement of the micro lenses is different.

[0048] For details, please refer to Figure 5 In the image sensor provided in this embodiment, the microlens array 20 is composed of 2 rows and 2 columns of microlenses, and includes microlenses 211, 212, 213 and 214. Among them, the microlens 211 and the microlens 212 are located in the first row, the microlens 213 and the microlens 214 are located in the second row, the microlens 211 and the microlens 212 have the same size, the microlens 213 and the microlens 214 have the same size, and the microlenses 211 and 212 are different from the microlenses 213 and 214.

[0049] Other technical solutions are the same as those in the first embodiment and will not be described in detail here.

[0050] Embodiment 3

[0051] This embodiment provides an image sensor such as Figure 6 As shown, the technical solution is similar to that of the first embodiment, but different from the first embodiment in that the size arrangement of the micro lenses is different.

[0052] For details, please refer to Figure 6 In the image sensor provided in this embodiment, the microlens array 30 is composed of 2 rows and 2 columns of microlenses, namely, microlenses 311, 312, 313 and 314. Among them, microlenses 311 and 313 are located in the first column, microlenses 312 and 314 are located in the second column, the sizes of microlenses 311 and 313 are equal, the sizes of microlenses 312 and 314 are the same, and the sizes of microlenses 311 and 313 are different from those of microlenses 312 and 314.

[0053] The other technical solutions are the same as those of Embodiment 1 and Embodiment 2 and will not be described in detail here.

[0054] Embodiment 4

[0055] This embodiment provides an image sensor such as Figure 7 As shown, the technical solution is similar to that of the first embodiment, but different from that of the first embodiment in that the number and size arrangement of the micro lenses are different.

[0056] For details, please refer to Figure 7In the image sensor provided in this embodiment, the microlens array 40 is composed of 3 rows and 3 columns of microlenses, namely, microlenses 411, 412, 413, 414, 415, 416, 417, 418 and 419. Among them, the microlens 411 and the microlenses 415 and 419 are located on the same diagonal line, the microlens 413 and the microlenses 415 and 417 are located on another diagonal line, the microlenses 411, 415, 419, 413 and 417 have the same size, the microlenses 412, 414, 416 and 418 have the same size, and the microlenses 411, 415, 419, 413 and 417 have different sizes from the microlenses 412, 414, 416 and 418.

[0057] Other technical solutions are the same as those in the first embodiment and will not be described in detail here.

[0058] Embodiment 5

[0059] This embodiment provides an image sensor such as Figure 8 As shown, the technical solution is similar to that of the fourth embodiment, but different from the fourth embodiment in that the size arrangement of the micro lenses is different.

[0060] For details, please refer to Figure 8 In the image sensor provided in this embodiment, the microlens array 50 is composed of 3 rows and 3 columns of microlenses, namely, microlenses 511, 512, 513, 514, 515, 516, 517, 518 and 519. Among them, the microlens 511 and the microlenses 514 and 517 are located in the first column, the microlens 512 and the microlenses 515 and 518 are located in the second column, and the microlenses 513, 516 and 519 are located in the third column. The sizes of the microlenses 511, 514 and 517 are the same, the sizes of the microlenses 512, 515 and 518 are the same, and the sizes of the microlenses 513, 516 and 519 are different from each other.

[0061] The other technical solutions are the same as those in the fourth embodiment and will not be described in detail here.

[0062] Embodiment 6

[0063] This embodiment provides an image sensor such as Fig. 9 As shown, the technical solution is similar to that of the fourth embodiment, but different from the fourth embodiment in that the size arrangement of the micro lenses is different.

[0064] For details, please refer to Fig. 9In the image sensor provided in this embodiment, the microlens array 60 is composed of 3 rows and 3 columns of microlenses, namely, microlenses 611, 612, 613, 614, 615, 616, 617, 618 and 619. Among them, the microlens 611 and the microlenses 612 and 613 are located in the first row, the microlens 614 and the microlenses 615 and 616 are located in the second row, and the microlens 617 and the microlenses 618 and 619 are located in the third row. Among them, the microlenses in the same row have the same size, that is, the size of the microlenses 611, 612, 613 is the same, the size of the microlenses 614, 615, 616 is the same, the size of the microlenses 617, 618, 619 is the same, and the size of the microlenses 611, 612, 613 is different from the microlenses 614, 615, 616 and the microlenses 617, 618, 619.

[0065] The other technical solutions are the same as those in the fourth embodiment and will not be described in detail here.

[0066] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. An image sensor, characterized in that: include: Semiconductor substrate; A plurality of photodiodes are located in the semiconductor substrate; A plurality of microlens arrays are located on the surface of the semiconductor substrate, each microlens array corresponds to a photodiode, and each microlens array is composed of n rows and n columns of microlenses, where n≥2; The sizes of microlenses arranged in the same row of the microlens array are the same, while the sizes of microlenses in different rows are different; or, the sizes of microlenses arranged in the same column of the microlens array are the same, while the sizes of microlenses in different columns are different; or, the sizes of microlenses arranged on the same diagonal line of the microlens array are the same, while the sizes of microlenses adjacent to the diagonal microlenses are different from the sizes of the diagonal microlenses.

2. The image sensor according to claim 1, characterized in that Each of the microlens arrays is composed of four microlenses in two rows and two columns, and the sizes of the microlenses located on the same diagonal line are the same.

3. The image sensor according to claim 1, characterized in that Each of the microlens arrays is composed of four microlenses in two rows and two columns, and the sizes of the microlenses in the same row are the same.

4. The image sensor according to claim 1, characterized in that Each of the microlens arrays is composed of four microlenses in two rows and two columns, and the sizes of the microlenses in the same column are the same.

5. The image sensor according to claim 1, characterized in that Each of the microlens arrays is composed of 9 microlenses in 3 rows and 3 columns, and the three microlenses in the same row have the same size.

6. The image sensor according to claim 1, characterized in that: Each of the microlens arrays is composed of 9 microlenses in 3 rows and 3 columns, and the three microlenses in the same column have the same size.

7. The image sensor according to claim 1, characterized in that: The microlens is in the shape of a convex lens, and the bottom surface of the convex lens is flat.

8. A method for forming an image sensor, characterized in that: include: providing a semiconductor substrate having a photodiode therein; A plurality of microlens arrays are arranged on the surface of the semiconductor substrate, each of the microlens arrays corresponds to one of the photodiodes, and each of the microlens arrays is composed of n rows and n columns of microlenses, where n≥2; wherein the sizes of the microlenses arranged in the same row in the microlens array are the same, and the sizes of the microlenses in different rows are different; or, the sizes of the microlenses arranged in the same column in the microlens array are the same, and the sizes of the microlenses in different columns are different; or, the sizes of the microlenses arranged on the same diagonal line in the microlens array are the same, and the sizes of the microlenses adjacent to the diagonal microlenses are different from the sizes of the diagonal microlenses.

9. The method for forming an image sensor according to claim 8, wherein: The method also includes the step of forming a filter between the semiconductor substrate and the microlens array.

10. The method for forming an image sensor according to claim 8, wherein: Forming the microlens array comprises the following steps: Forming a fence on the filter corresponding to each of the photodiodes, wherein the fence is composed of a plurality of strip structures spaced apart from each other, and there is a gap between adjacent strip structures, and each of the gaps corresponds to a predetermined microlens; depositing a microlens material to fill the gap; removing said fence; The microlens material is reflowed to form a plurality of microlenses.

11. The forming method according to claim 10, characterized in that: The fence is composed of a plurality of rows or columns of intersecting strip structures, and there are square gaps between adjacent strip structures.

12. The forming method according to claim 8, characterized in that: The microlens is in the shape of a convex lens, and the bottom surface of the convex lens is flat.

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