TWI546944B - Image sensor and method for fabricating the same - Google Patents

Description

Image sensor and manufacturing method thereof

The invention relates to an optical microstructure and a manufacturing method and application thereof, and in particular to an optical microstructure applied to an image sensor and a manufacturing method and application thereof.

With the continuous development and growth of electronic products such as digital cameras and scanners, the demand for semiconductor image sensors in the consumer market has continued to increase. Currently used semiconductor image sensors include front side illuminated image sensors and backside illuminated image sensors.

Since the sensor array of the front-illuminated image sensor is formed on the front surface of the semiconductor substrate, and a plurality of inner-metal layers stacked on each other are formed over the sensing array. The incident light must first pass through the stacked inner metal layer to reach the sensing array. Blocked by the inner metal layer, the photon efficiency of the image sensor is reduced.

Compared to the front-illuminated image sensor, the back-illuminated image sensor light is incident from the back side of the semiconductor substrate and does not have to pass through the inner metal layer to reach the sensing array. Therefore, the entire sensing array can be used to sense photons, so the back-illuminated image sensor has better photon efficiency than the front-illuminated image sensor.

However, preparing back-illuminated image sensors typically requires thinning the semiconductor substrate. In addition to having to additionally attach a handle wafer to the semiconductor substrate, the presence of the carrier wafer also blocks the formation of the inner metal layer from the pads. Therefore, it is necessary to form a Through-Silicon Via (TSV) in the carrier wafer for subsequent wiring package. And the process steps are relatively complicated, and the process cost is more This is high.

At present, there is a conventional technique in which a color filter layer is embedded in a sensing region layer by layer in a typical lithography process by forming an alcove in a sensing region of a front-illuminated image sensing element to shorten incident light. The propagation distance is combined with the microlens structure to increase the photon efficiency, so that at the lower process cost, the optical effect is substantially the same as that of the back-illuminated image sensor.

However, the color filter layer embedded in the sensing region has a problem of poor surface flatness, which may affect the subsequent process yield. Therefore, the depth of the color filter layer embedded in the sensing region is limited. As the demand for image sensor resolution increases, the color pixels shrink and the process difficulty increases.

Therefore, there is a need to provide a novel optical microstructure suitable for an image sensor and a manufacturing method and application thereof, which can reduce the cross-talk phenomenon of the image sensing component and improve the light quantum efficiency at a low process cost. purpose. At the same time, the process of the entire image sensor can be shortened by the stand-alone color filter layer and the microlens process.

In view of the above, an object of the present invention is to provide a method for preparing an image sensor. The image sensor includes: a plurality of color filter units, a plurality of micro lenses, and an image sensing device. element. The microlenses are correspondingly formed on the color filter units; the image sensing elements have a sensing area combined with the color filter unit.

In an embodiment of the invention, the color filter unit is embedded in the inner dielectric material layer of the sensing region, the depth of which exceeds the bottom metal layer around the sensing region. However, in another embodiment of the invention, the color filter unit is adjacent to the back side of the substrate of the sensing region. In still another embodiment of the present invention, image sensing The device further includes a flat layer between the color filter unit and the microlens.

In one embodiment of the invention, the image sensor is a circular structure that can be cut into a plurality of image sensor chips.

In an embodiment of the invention, the image sensor further includes: a working substrate, and a transparent substrate on the working substrate, wherein the transparent substrate has a plurality of recesses for accommodating the microlenses correspondingly In it.

In an embodiment of the invention, the image sensor further includes a passive layer on the transparent substrate opposite to one side of the microlenses.

Another object of the present invention is to provide a method for fabricating an image sensor, comprising the steps of: forming a transparent substrate on a working substrate; and forming a plurality of microlenses in the transparent substrate to make the micro The lens has a different refractive index than the transparent substrate. Then, color filters are formed on these microlenses. The working substrate is flipped and the color filter is combined with the image sensing element.

In an embodiment of the invention, the step of combining the color filter and the image sensing component comprises: forming a recess in the sensing region of the image sensing component; and then arranging the color filter adjacent to the bottom surface of the recess . In another embodiment of the invention, the step of combining the color filter and the image sensing element comprises: locating the color filter adjacent to the back surface of the substrate of the sensing region of the image sensing element.

In an embodiment of the invention, the step of forming a color filter includes forming a color filter unit on each of the microlenses. In another embodiment of the invention, the step of forming a color filter includes first forming a planar layer over the microlenses; and forming a plurality of color filter units on the planar layer.

In an embodiment of the invention, after combining the color filter and the image sensing element, the planarizing working substrate is further included as a passivation layer for protecting the color filter.

In an embodiment of the invention, wherein the color filter and the image sense are combined After the measuring component, further comprising removing the working substrate; and forming a passivation layer on the transparent substrate with respect to one side of the microlens.

Another object of the present invention is to provide a method for fabricating an image sensor, comprising the steps of: first providing a color filter wafer having a plurality of color filters; and providing a plurality of image sensing An image sensing wafer of components, wherein each image sensing component has a sensing region corresponding to one of the color filters. Then, the color filter wafer is combined with the image sensing wafer, so that each color filter is embedded in the inner dielectric material layer of the sensing region to have a depth exceeding the bottom metal of the sensing region. Floor.

In an embodiment of the present invention, after combining the color filter wafer and the image sensing wafer, a wafer cutting process is further included to form at least one microlens, at least one color filter, and at least one A plurality of image sensor dies of the image sensing element.

The invention provides an improved image sensor and a preparation method thereof. Different from the prior art, the color filter layer is formed without being attached to the image sensing element, but separately formed on another transparent substrate and then combined with the image sensing element. It can be used simultaneously to prepare front-illuminated image sensors or back-illuminated image sensors, which has the advantage of simplifying the packaging process.

In particular, when used in the preparation of a front-illuminated image sensor, the surface flatness of the color filter layer can be improved in advance, and the depth limit of the color filter layer embedded in the sensing region can be eliminated, thereby shortening the propagation distance of the incident light and increasing the image. Sensing the optical quantum efficiency of the component and solving the problem of crosstalk interference. Therefore, the optical effect substantially the same as that of the back-illuminated image sensor can be achieved by a lower process cost.

The above and other objects, features and advantages of the present invention will become more <RTIgt;

It is an object of the present invention to provide an image sensor and method of fabricating an image sensor having an optical microstructure 100.

Please refer to Figures 1A to 1E. 1A through 1E are schematic cross-sectional views showing a process structure for fabricating an optical microstructure 100 in accordance with a preferred embodiment of the present invention.

First, the working substrate 101 is provided (as shown in FIG. 1A). In some embodiments of the present invention, the working substrate 101 may be a light transmissive glass substrate, a germanium substrate, or a germanium wafer.

Next, a transparent substrate 102 is provided adjacent to the working substrate 101 (as shown in FIG. 1B). In some embodiments of the present invention, the transparent substrate 102 may be a transparent material layer that is pre-formed and directly adjacent to the working substrate 101; or may be deposited, plated, spin-coated, embossed, or the like. The transparent layered structure formed by the process.

The material constituting the transparent substrate 102 may be a material similar to the working substrate 101 or another material having a refractive index different from that of the working substrate 101. The material of the transparent substrate 102 is preferably made of ruthenium, glass, resin, Propylene Glycol Methyl Ether Acetate (PGMEA), or poly-Glycidyl Methyl Acrylate (PGMA). Or any combination of the above materials.

Then, at least one recess 103 is formed on the upper surface 102a of the transparent substrate 102 (as shown in FIG. 1C). The method of forming the recess 103 is preferably an etching pattern having a specific depth of a plurality of recesses 103 on the upper surface 102a of the transparent substrate 102 by etching. In some embodiments of the present invention, the cross-sections of the bottom portions 103a of the recesses 103 may be curved or other geometric patterns; the recesses 103 may be coupled to each other or may be separated from each other. In this embodiment Among these, the recesses 103 are coupled to each other to form an array pattern, and each of the recesses 103 has a hemispherical bottom portion 103a.

Thereafter, a microlens 104 is formed in each of the recesses 103 so as to be embedded in the recess 103 (as shown in FIG. 1D). The microlens 104 is preferably made of glass, a polymer plasticized material (for example, resin, propylene glycol methyl ether acetate, polymethacryl propylene oxide), a semiconductor material (for example, ruthenium), or any combination of the above materials.

In the embodiment of the present invention, the microlens 104 is formed by filling a transparent colloid material at the bottom 103a of the recess 103, conforming the transparent colloid material to the bottom 103a of the recess 103, and then curing the transparent colloid material to complete Preparation of microlens 104. Wherein, the microlens 104 is a hemispherical transparent lens structure.

It is worth noting that in order to achieve the optical effect of concentrating light, the microlens 104 must have a different refractive index than the transparent substrate 102. The refractive index of the microlens 104 is preferably greater than the refractive index of the transparent substrate 102.

Thereafter, a color filter unit 105a is formed over each of the microlenses 104 (as shown in FIG. 1E). The color filter unit 105a may be a single color, such as a red, green, blue, yellow, magenta or cyan filter element, which in turn may constitute a color filter with a single color. Slice 105. However, in other embodiments, the color filter 105 can include a color filter unit 105a having a plurality of different colors.

In the preferred embodiment of the present invention, the color filter 105 is formed by sequentially forming patterned photoresist layers of different colors on the microlens 104, thereby forming various kinds on the microlens 104. Color color filter unit 105a.

In some embodiments of the present invention, the color filter unit 105a is only partially filled in the recess 103, so that the color filter unit 105a in the recess 103 is A specific space remains between the upper surfaces 102a of the transparent substrate 102. In still other embodiments of the present invention, the color filter unit 105a fills the recess 103 beyond the upper surface 102a of the transparent substrate 102.

In order to take into account the surface flatness of the color filter 105, after the color filter 105 is formed, a planarization process (not shown) is further performed to make the color filter 105 and the upper surface 102a of the transparent substrate 102. Coplanar.

As shown in FIG. 1E, the optical microstructure 100 prepared by the above steps includes at least a working substrate 101, a transparent substrate 102, a plurality of microlenses 104, and color filters composed of a plurality of color filter units 105a. Slice 105. The transparent substrate 102 is adjacent to the working substrate 101, and the transparent substrate 102 has an upper surface 102a including a plurality of recesses 103. Each of the microlenses 104 is correspondingly disposed in one of the recesses 103 and conformed to the bottom 103a of the corresponding recess 103. The color filter unit 105a is correspondingly located on the plurality of microlenses 104 and fills each of the recesses 103 such that the color filter 105 is coplanar with the upper surface 102a of the transparent substrate 102.

In addition, please refer to FIG. 2, which is a cross-sectional view of an optical microstructure 200 according to another preferred embodiment of the present invention. In the present embodiment, the optical microstructures 200 are substantially similar to the optical microstructures 100 (the same elements will be denoted by the same reference numerals), with the difference that, prior to forming the color filter 105 of the optical microstructure 200, it will be micro An additional flat layer 206 is additionally formed between the lens 104 and the color filter 105.

Hereinafter referred to as a color filter wafer 300). The color filter wafer 300 includes a color filter array 35 composed of a plurality of color filters 305 separated from each other and a plurality of microlenses 304a.

Subsequently, the working wafer 301 can be cut according to the arrangement of the color filter array 35, thereby forming a plurality of colors including at least one color. Filter wafer 300). The color filter wafer 300 includes a color filter array 35 composed of a plurality of color filters 305 separated from each other and a plurality of microlenses 304a.

Subsequently, the working wafer 301 can be cut according to the arrangement of the color filter array 35, thereby forming a plurality of single dies including at least one color filter 305, and then combining a single image sensing component to form a complete Image sensor. However, in other embodiments, the color filter wafer 300 that has not been cut may be directly combined with an image sensing wafer (not shown) having a plurality of image sensing elements, and then subjected to a wafer cutting process. And forming a plurality of image sensor chips including at least a plurality of microlenses, a color filter and an image sensing element. For the sake of clarity, the image sensor will be described in detail below with reference to the fabrication of a single optical microstructure 100 in conjunction with a single image sensing element.

4A to 4D are cross-sectional views showing a series of process structures of the front-illuminated image sensor 40 according to another preferred embodiment of the present invention.

The method of fabricating the image sensor 40 includes the steps of first providing an image sensing element 400 and an optical microstructure 100 as shown in FIG. 1E.

As shown in FIG. 4A, the image sensing element 400 is a front-illuminated image sensing element including a tantalum substrate 411. A sensing region 411a and a peripheral region 411b can be formed and defined on the substrate 411 by a front-end process (Front-End-Of-Line; FEOL). Wherein, the sensing region 411a includes at least one photodiode 410 and at least one transfer gate structure 408. The sensing region 411a and the peripheral region 411b are sequentially covered with at least one inner dielectric material layer 412 and a protective layer 414; and the inner dielectric material layer 412 covered by the peripheral region 411b is embedded with a plurality of layers He This stacked inner metal layer 413.

In some embodiments of the present invention, the sensing region 411a includes an array structure (not shown) composed of a plurality of photodiodes 410, and is located between the shallow trench isolation layer (STI) 407. The peripheral region 411b is located over the shallow trench isolation layer in the germanium substrate 411 with the inner metal layer 413 stacked thereon.

Next, the transparent substrate 102 of the optical microstructure 100 is combined with the image sensing element 400 such that the color filter 105 and the sensing region 411a of the image sensing element 400 are adjacent to each other.

In some embodiments of the present invention, before the transparent substrate 102 of the optical microstructure 100 is combined with the image sensing element 400, it must be removed in whole or in part by the etching or other similar manner over the sensing region 411a. The protective layer 414 or the inner dielectric material layer 412 is formed on the sensing region 411a to form a recess 415 (as shown in FIG. 4B).

The recess 415 can be designed to match the optical requirements of the image sensor, and extends from the protective layer 414 down to the inner dielectric material layer 412. The depth of the recess 415 preferably exceeds at least one of the inner metal layers 413 of the peripheral region 411b; even the sensing region 411a of the tantalum substrate 411 may be exposed. In the present embodiment, the recessed portion 415 extends downward from the protective layer 414 to the inner dielectric material layer 412 by lithography, and extends beyond the highest metal layer 413a of the inner metal layer 413. That is, the so-called bottom metal in the field.

After the recess 415 is formed, the optical microstructure 100 is flipped, and the color filter 105 of the optical microstructure 100 is embedded in the image sensing together with the transparent substrate 102 for preparing the color filter 105. Among the recessed portions 415 of the element 400, the color filter 105 and the bottom surface 415a of the recessed portion 415 are provided. Adjacent. Thereby, a front-illuminated image sensor 40 as shown in FIG. 4C is formed.

It should be noted that the optical micro-structure 100 described above is not only suitable for preparing the front-illuminated image sensor 40, and is of course also suitable for fabricating a back-illuminated image sensor. Referring to FIG. 5, FIG. 5 is a cross-sectional view showing the structure of a back-illuminated image sensor 50 according to another preferred embodiment of the present invention.

This embodiment employs a back-illuminated image sensing element 500 for bonding to the optical microstructure 100. Like the front-illuminated image sensing element 400, the back-illuminated image sensing element 500 also includes a germanium substrate 511; a sensing region 511a and a peripheral region 511b formed by a front-end process (including the photodiode 510) And an inner metal layer 513 and an inner dielectric material 512 formed by a back end-end process (Back-End-Of-Line; BEOL). The back-illuminated image sensing component 500 differs from the front-illuminated image sensing component 400 only in that the back-illuminated image sensing component 500 further includes an inner metal layer 513 and an inner dielectric material 512 attached thereto. The wafer 516 is carried; and the back surface 511c of the tantalum substrate 511 of the back-illuminated image sensing element 500 has been thinned.

The combination of the optical microstructure 100 and the image sensing component 500 only needs to align the color filter 105 of the optical microstructure 100 with the sensing region 511a of the image sensing component 500, and the transparent substrate 102 of the optical microstructure 100. The upper surface 102a is attached to the back surface 511c of the image sensing element 500, the substrate 511, and the working substrate 101 is removed. Subsequent to the wiring and packaging process, the through-holes 509 and the pads 517 are formed to connect the inner metal layer 513 to form the image sensor 50 as shown in FIG.

In addition, after the transparent substrate 102 of the optical microstructure 100 is combined with the image sensing element 400 (or 500), the entire removed portion of the working substrate 101 of the optical microstructure 100 can be removed or retained. In some embodiments of the invention, the working substrate 101 is retained as a color filter 105 and micro A protective layer of the lens 104. In some embodiments of the present invention, the working substrate 101 and between there is a release film (not shown), which can be used to strip the working substrate 101, and the removed working substrate 101 is preferably reusable.

In other embodiments of the invention, the working substrate 101 and a portion of the transparent substrate 102 are removed by grinding. After the working substrate 101 is removed, the transparent substrate 102 exposed to the outside also functions to protect the color filter layer. Preferably, however, a further encapsulation or planarization step is performed over the transparent substrate 102 to form a planarization layer or passivation layer 418 (passivation layer 518) as depicted in FIG. 4D (FIG. 5). In some embodiments of the present invention, after removing the working substrate 101, a passivation layer 418 (518) made of glass or germanium is additionally formed over the transparent substrate 102 by a packaging step.

According to the above embodiment, the present invention provides an image sensor comprising a separately configurable color filter layer and microlens. Different from the prior art, the image sensor of the present invention has a color filter layer required for preparing an image sensor, and does not need to be attached to the image sensing element, but is separately formed on another transparent base. Above the material, combined with the image sensing element. It can be used simultaneously to prepare front-illuminated image sensors or back-illuminated image sensors, which has the advantage of simplifying the packaging process.

In addition, when applied to a front-illuminated image sensor, the surface flatness of the color filter layer can be improved in advance during the preparation of the color filter layer and the microlens. The depth limitation when the color filter layer is embedded in the sensing region is excluded, thereby shortening the propagation distance of the incident light, increasing the optical quantum efficiency of the image sensing element, and solving the problem of crosstalk interference. Therefore, the optical effect substantially the same as that of the back-illuminated image sensor can be achieved by a lower process cost.

While the present invention has been described in its preferred embodiments, the present invention is not intended to limit the invention, and the present invention may be modified and modified without departing from the spirit and scope of the invention. Scope of protection The scope defined in the patent application is subject to change.

40‧‧‧ Front-illuminated image sensor

50‧‧‧Back-illuminated image sensor

100‧‧‧Optical microstructure

101‧‧‧Working substrate

102‧‧‧Transparent substrate

102a‧‧‧ Upper surface of transparent substrate

103‧‧ ‧ alcove

103a‧‧‧ bottom of the alcove

104‧‧‧Microlens

105‧‧‧Color filters

105a‧‧‧Color Filter Unit

200‧‧‧Optical microstructure

206‧‧‧flat layer

300‧‧‧Optical microstructure

301‧‧‧Semiconductor wafer

304‧‧‧Microlens array

304a‧‧‧microlens

35‧‧‧Color Filter Array

305‧‧‧Color Filters

400‧‧‧ Front-illuminated image sensing components

407‧‧‧Shallow trench isolation

408‧‧‧Transition gate structure

410‧‧‧Photoelectric diode

411‧‧‧矽 substrate

411a‧‧‧Sensing area

411b‧‧‧ surrounding area

412‧‧‧ Inner dielectric material layer

413‧‧‧Inner metal layer

413a‧‧‧The highest metal layer

414‧‧‧protection layer

415‧‧‧Depression

415a‧‧‧ underside of the recess

418‧‧‧passivation layer

500‧‧‧Back-illuminated image sensing components

509‧‧‧through through hole

510‧‧‧Photoelectric diode

511‧‧‧矽 substrate

511a‧‧‧Sensing area

511b‧‧‧ surrounding area

511c‧‧‧矽Back side of the substrate

512‧‧‧ Inner dielectric material

513‧‧‧Inner metal layer

516‧‧‧bearing wafer

517‧‧‧ solder pads

518‧‧‧ Passivation layer

Please refer to Figures 1A to 1E. 1A through 1E are cross-sectional views showing a process structure for fabricating an optical microstructure in a series according to a preferred embodiment of the present invention.

2 is a schematic cross-sectional view of an optical microstructure according to another preferred embodiment of the present invention.

3 is a schematic cross-sectional view of an optical microstructure according to another preferred embodiment of the present invention.

4A to 4D are cross-sectional views showing a series of process structures of a front-illuminated image sensing element according to still another preferred embodiment of the present invention.

FIG. 5 is a cross-sectional view showing the structure of a back-illuminated image sensor according to still another preferred embodiment of the present invention.

40‧‧‧ Front-illuminated image sensor

100‧‧‧Optical microstructure

101‧‧‧Working substrate

102‧‧‧Transparent substrate

104‧‧‧Microlens

105‧‧‧Color filters

400‧‧‧ Front-illuminated image sensing components

407‧‧‧Shallow trench isolation

408‧‧‧Transition gate structure

410‧‧‧Photoelectric diode

411‧‧‧矽 substrate

411a‧‧‧Sensing area

411b‧‧‧ surrounding area

412‧‧‧ Inner dielectric material layer

413‧‧‧Inner metal layer

413a‧‧‧The highest metal layer

414‧‧‧protection layer

Claims (15)

An image sensor includes: a plurality of color filter units; a plurality of micro lenses are correspondingly formed on the color filter units; and an image sensing element has a sensing area, and the image sensor a plurality of color filter units; a working substrate; and a transparent substrate on the working substrate, having a plurality of recesses for receiving the microlenses, wherein the microlenses are correspondingly embedded in the recesses in. The image sensor of claim 1, wherein the color filter unit is embedded in an inner dielectric material layer of the sensing region, the depth of which exceeds a bottom metal of the sensing region Bottom metal. The image sensor of claim 1, further comprising a flat layer between the color filter units and the microlenses. The image sensor of claim 1, wherein the color filter unit is adjacent to a back surface of a substrate of the sensing region. The image sensor of claim 1, wherein the image sensor is a wafer level structure that can be cut into a plurality of image sensor chips. The image sensor of claim 1, further comprising a passive layer on the transparent substrate opposite to one side of the microlenses. A method for preparing an image sensor, comprising: forming a transparent substrate on a working substrate; forming a plurality of microlenses in the transparent substrate, the microlenses having a different refractive index from the transparent substrate; Forming a color filter on the microlenses; and flipping the working substrate and combining the color filter with an image sensing element. The method for preparing an image sensor according to claim 7, wherein the step of combining the color filter and the image sensing element comprises: forming a sensing region in the sensing region of the image sensing device a recessed portion; and a color filter adjacent to a bottom surface of the recessed portion. The method for preparing an image sensor according to the seventh aspect of the invention, wherein the step of combining the color filter and the image sensing element comprises: locating the color filter adjacent to the image sensing element A back side of a substrate in a sensing area. The method for preparing an image sensor according to claim 7, wherein the step of forming the color filter comprises: forming a color filter unit on each of the microlenses. The method for preparing an image sensor according to claim 7, wherein the step of forming the color filter comprises: forming a flat layer on the microlenses; and forming a plurality of layers on the flat layer Color filter unit. The method for preparing an image sensor according to claim 7, wherein after combining the color filter and the image sensing element, further comprising planarizing the working substrate to protect the color filter a passivation layer. The method for preparing an image sensor according to claim 7, wherein after combining the color filter and the image sensing element, the method further comprises: removing the working substrate; and on the transparent substrate, A passivation layer is formed with respect to one side of the microlenses. A method for preparing an image sensor, comprising: providing a color filter wafer having a plurality of color filters; providing an image sensing wafer having a plurality of image sensing elements, and each of the images The sensing component has a sensing region corresponding to one of the color filters; and the color filter wafer is combined with the image sensing wafer to embed each of the color filters In an inner dielectric material layer of the sensing region, the depth exceeds a bottom metal layer around the sensing region. The method for preparing an image sensor according to claim 14, wherein after combining the color filter wafer and the image sensing wafer, a wafer cutting process is further included to form a plurality of images. Sensor die, and each The image sensor dies include at least one of the microlenses, at least one of the color filters, and at least one of the image sensing elements.