TWI521685B - Image sensor and method for fabricating the same - Google Patents

Description

Image sensor and manufacturing method thereof

The present invention relates to a semiconductor device and a method of fabricating the same, and more particularly to an image sensor and a method of fabricating the same.

An image sensor, such as a Metal-Oxide-Semiconductor (MOS) image sensor, is a semiconductor component that converts an optical image into an electronic signal. It has been widely used in consumer electronics, such as digital cameras, personal communications services (PCS), game equipment and other high-resolution products.

In order to meet the consumer's requirements for high image resolution, the pixel density of the image sensor must be increased, that is, a photoelectric transducer device in each unit of pixels, such as a photodiode ( The size of photodiode) will be smaller. However, as the pixel density increases, the corresponding pixel pitch will also shrink, which will lead to a surge in electronic and optical crosstalk between adjacent pixels, and even severely degrade the resolution. The sensed image is distorted.

Since the Shallow Trench Isolation (STI) structure is usually located between adjacent pixels, the conventional technique uses a shallow trench isolation structure to reduce electrical crosstalk. However, due to the limited depth of the shallow trench isolation structure, a satisfactory electrical crosstalk barrier cannot be provided. Especially in the application of back-illuminated image sensors, shallow trench isolation structures are not sufficient to provide effective optical crosstalk interference barriers.

Therefore, there is a need to provide a new type of image sensor and a method of fabricating the same to solve the problem of electronic and optical crosstalk interference between adjacent pixels.

In view of the above, one of the objects of the present invention is to provide an image sensor including a substrate, a plurality of photoelectric transducer devices, an interconnect structure, at least one dielectric isolation structure, and a rear side pair. Alignment mark. Wherein the substrate has a back side surface and a front side surface opposite the back side surface. The interconnect structure is located on the front side surface of the substrate. A photoelectric conversion element is formed on the front side surface. The dielectric isolation structure extends from the rear side surface into the substrate to isolate the plurality of photoelectric conversion elements. The back side alignment mark extends into the substrate from the rear side surface and corresponds to the front side alignment mark previously formed on the front side surface.

In an embodiment of the invention, the dielectric isolation structure comprises a plurality of anti-reflective coatings (ARCs). In an embodiment of the invention, the image sensor further includes an ion doped layer disposed in the substrate and surrounding the dielectric isolation structure.

In an embodiment of the invention, the image sensor further includes a shallow trench isolation structure extending from the front side surface into the interior of the substrate and connected to the dielectric isolation structure. In one embodiment of the invention, the backside alignment marks are aligned with the front side alignment marks or associated with the front side alignment marks in a particular spatial relationship.

In an embodiment of the invention, the image sensor further includes a color filter and a plurality of microlenses on the back side surface of the substrate. In an embodiment of the invention, the image sensor further includes a patterned metal shield layer between the color filter and the dielectric isolation structure. In one embodiment of the invention, the backside alignment mark includes an alcove extending into the substrate from the backside surface. In an embodiment of the invention, the backside alignment mark has a dielectric material layer and the metal shield layer is located at the sidewall and bottom of the recess.

Another object of the present invention is to provide a method of fabricating an image sensor comprising the steps of first forming a plurality of photoelectric conversion elements and interconnect structures on a front side surface of a substrate. At least one dielectric isolation structure is then formed extending from the backside surface of the substrate into the substrate to isolate the photoelectric conversion elements, wherein the back side surface is opposite the front side surface. And forming a back side alignment mark extending from the back side surface of the substrate into the substrate corresponding to the front side alignment mark previously formed on the front side surface.

In one embodiment of the invention, both the dielectric isolation structure and the backside alignment marks are formed simultaneously. The formation of the dielectric isolation structure and the backside alignment marks includes the step of performing an etching process prior to the backside surface to form at least one trench and an recess in the substrate. A layer of dielectric material is then formed on the backside surface to fill the trench and partially fill the recess; a planarization process is performed to remove a portion of the dielectric material layer and expose a portion of the substrate. In an embodiment of the invention, the trenches expose the shallow trench isolation structures formed on the front side surface.

In an embodiment of the invention, after the trenches and the recesses are formed, the trenches and the sidewalls of the recesses are further included in the ion implantation process and the laser annealing process. In an embodiment of the invention, before the etching process is performed, a hard mask layer is further formed on the rear side surface.

In an embodiment of the present invention, after the planarization process, the method further includes the following steps: first surface treating the substrate, the dielectric isolation structure, and the back side alignment mark; and the substrate, the dielectric isolation structure, and A metal layer is formed on the back side alignment mark. The metal layer is then patterned to form a metal shield layer overlying the dielectric isolation structure and the backside alignment marks, respectively. In an embodiment of the invention, the surface treatment comprises: performing an ion doping process and a laser annealing process on the back side surface, the dielectric isolation structure and the back side alignment mark; and the back side surface, the dielectric isolation structure and An anti-reflection layer is formed on the rear side alignment mark.

In one embodiment of the invention, the backside alignment marks are aligned with the front side alignment marks or associated with the front side alignment marks in a particular spatial relationship. In an embodiment of the invention, after forming the dielectric isolation structure and the back side alignment mark, further comprising forming a color filter and a plurality of microlenses on the rear side surface and the dielectric isolation structure.

In an embodiment of the present invention, before forming the dielectric isolation structure, the method further comprises: combining a working wafer with the interconnect structure; and performing a thinning process on the rear surface to thin the substrate.

It is still another object of the present invention to provide a method of fabricating an image sensor comprising the steps of first forming a plurality of photoelectric conversion elements and interconnect structures on a front side surface. An etching process is then performed on the back side surface of the substrate to form at least one trench in the substrate. Thereafter, a dielectric material layer is formed on the rear side surface to fill the trench, and at least one dielectric isolation structure is formed, extending from the rear side surface into the substrate for isolating the photoelectric conversion element and dielectrically The material layer remains as-deposited.

According to the above embodiment, the present invention provides an image sensor and a method of fabricating the same, first forming a photoelectric conversion element and an interconnect structure on a front side surface of the image sensor, and then on a rear side surface opposite to the front side surface Forming at least one dielectric isolation structure extending into the interior of the substrate to isolate the plurality of photoelectric conversion elements. By the arrangement of the dielectric isolation structure, the light incident into the substrate and the photo-carrier generated in the substrate can be sufficiently separated to prevent electronic and optical crosstalk from being generated by adjacent pixels. The problem.

Further, since the process of forming the dielectric isolation structure and the process of forming the photoelectric conversion element and the interconnect structure are performed on opposite sides of the substrate, respectively. Therefore, in the formation of the dielectric isolation structure, even if a high temperature thermal oxide and a gap-fill material densification step are performed, the photoelectric conversion element and the interconnect structure are not The function produces interference. When a planarization step (for example, a chemical mechanical polishing process) is performed, there is no possibility that a U-shaped scratch may be caused on the front side surface of the substrate, which may affect the quality of the subsequent interconnect structure process.

Further, while forming the dielectric isolation structure, a rear side alignment mark may be formed on the rear side surface corresponding to the front side alignment mark originally formed on the front side surface of the substrate for performing the front side process. The manufacturing precision of the overall component can be improved without requiring additional manufacturing costs.

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 a method of fabricating the same that solves the problems of conventional optical and electronic crosstalk interference and at the same time improves process accuracy. The above and other objects, features and advantages of the present invention will become more apparent and understood. , as detailed below.

Referring to FIG. 1A to FIG. 1J, FIG. 1A to FIG. 1J are cross-sectional views showing a process of fabricating a metal-oxide-semiconductor image sensor 100 according to an embodiment of the invention. First, as shown in FIG. 1A, a substrate 101 is provided, and a front side process is performed on a front side surface 101a of the substrate 101, whereby a plurality of photoelectric conversion elements 102 are formed on the front side surface 101a. Thereafter, an interconnect structure 103 is formed on the front side surface 101a to be electrically connected to the photoelectric conversion element 102.

In a preferred embodiment of the invention, substrate 101 is a tantalum substrate. However, in other embodiments, the substrate 101 may also be a silicon-on-insulator (SOI) substrate. A plurality of photoelectric conversion elements 102 are formed on the front side surface 101a, and each of the photoelectric conversion elements 102 is separated by at least one shallow trench isolation structure 111 extending downward from the front side surface 101a into the inside of the substrate 101. Each of the photoelectric conversion elements 102 includes a photodiode structure 102a and a drain structure 102b formed in the substrate 101, and a gate structure 102c formed on the front side surface 101a. The interconnect structure 103 is composed of a plurality of metal wiring layers 103a, a dielectric material layer 103b, and a conductive plug 103c which are sequentially stacked. The dielectric material layer 103b is used to isolate the metal wire layer 103a; the conductive plug 103c passes through the dielectric material layer 103b and turns on the two metal wire layers 103a.

Although FIG. 1A shows only a set of interconnect structures 103 composed of a metal wiring layer 103a, a dielectric material layer 103b and a conductive plug 103c as a representative, it should be understood that the front side process can actually produce a complex array with the same layout density. Or interconnect structures 103 that are different, have the same or different line widths.

Next, one working wafer 104 is bonded to the interconnect structure 103 on the substrate 101, and after the substrate 101 is turned over, a thinning is performed on the rear surface 101b of the substrate 101 (opposite the front side surface 101a). In the process, the thickness of the substrate is thinned to substantially less than 3 μm, preferably substantially between 2 μm and 3 μm (as shown in FIG. 1B). Then, a patterned hard mask layer 107 is formed on the rear side surface 101b. The etching process is performed by patterning the hard mask layer 107 as a mask, thereby forming at least one trench 105 and one recess 106 in the substrate 101.

In some embodiments of the invention, the material forming the hard mask layer 107 is tantalum nitride, hafnium oxide or a combination of the two. In the present embodiment, the groove 105 extends from the rear side surface 101b toward the inside of the substrate 101, and exposes the shallow groove isolation structure 111 to the outside. However, in other embodiments, the trenches 105 are not aligned with the shallow trench isolation structures 111 and are interleaved with the shallow trench isolation structures 111. The recess 106 extends from the rear side surface 101b toward the inside of the substrate 101 and is aligned with the front side alignment mark 113 on the front side surface 101a (as shown in Fig. 1C). The front side alignment mark 113 is formed before the front side process to provide a front side process for the mask alignment step.

Although the front side alignment mark 113 illustrated in FIG. 1C is a single mark formed in the substrate 101. However, in other embodiments of the invention, the front side alignment marks 113 are not necessarily located in the substrate 101, and may include more than one member formed before, during or after the front end process. That is, any mark that can be identified and used as an alignment for the recess 106 can be used as the front side alignment mark 113.

Then, using the hard mask layer 107 as a mask, an ion doping step is performed to implant the P-type dopant into the sidewalls of the trench 105 and the recess 106, and the laser annealing process is performed to make the trench 105. The tantalum substrate and the sidewalls of the sidewalls of the recess 106 are recrystallized and form a P+ doped layer 108 (shown in Figure 1D) surrounding the trenches 105 and the recesses 106.

A layer of dielectric material 109 is formed on the hard mask layer 107, at least filling the trench 105, and partially filling the recess 106, thereby defining another recess 114 inside the recess 106 (as shown in FIG. 1E). ). This is because the size of the recess 106 is much larger than the trench 105, and the recess 106 and the trench 105 are produced by the same etching, so the depth of the recess 106 will be shallower than that of the trench 105. When the recess 106 and the trench 105 are simultaneously filled with the dielectric material layer 109, the trench 105 is first filled without filling the recess 106, leaving only another recess 114 in the recess 106.

In some preferred embodiments of the invention, the dielectric material layer 109 is comprised of a plurality of anti-reflective materials. In the present embodiment, the dielectric material layer 109 is an anti-reflection layer composed of a ceria layer/tantalum nitride layer/cerium oxide layer stacked in sequence, or a layer of ruthenium dioxide and a layer of ruthenium oxynitride. An anti-reflective layer is formed.

Then, a planarization process is selectively performed, for example, chemical mechanical polishing is performed by using the rear side surface 101b of the substrate 101 as a polishing stop layer, thereby removing a portion of the dielectric material layer 109 and a part of the substrate. The 101 is exposed while forming at least one dielectric isolation structure 110 and forming a backside alignment mark 112 in the recess 106.

The dielectric isolation structure 110 extends from the rear side surface 101b of the substrate 101 into the interior of the substrate 101 and is connected to the shallow trench isolation structure 111 for isolating the photoelectric conversion elements 102. The rear side alignment mark 112 includes a portion of the dielectric material layer 109 remaining in the recess 106, extending from the rear side surface of the substrate 101 toward the inside of the substrate 101, and corresponding to the front side surface 101a previously formed. The upper front side is aligned with the mark 113. In the present embodiment, the back side alignment mark 112 is aligned with the front side alignment mark 113 (as shown in FIG. 1F). However, in other embodiments, the back side alignment mark 112 is not aligned with the front side alignment mark 113, and the front side alignment mark 113 is interlaced with each other and aligned with the front side in a specific spatial relationship, such as a coordinate relationship. Tag 113 produces an association.

Subsequently, the substrate 101 and the back side alignment mark 112 are selectively surface-treated, and a selective metal shield layer 115a is formed on the dielectric isolation structure 110 and the back side alignment mark 112. The surface treatment includes first performing a P-type ion doping process and a laser annealing process on the back side surface 101b, the dielectric isolation structure 110, and the back side alignment mark 112, thereby forming a P+ doping in the substrate 101. District (not shown). An anti-reflection layer 119 (shown in FIG. 1G) is formed on the sidewalls and the bottom of the rear side surface 101b, the dielectric isolation structure 110, and the recess 114.

The step of forming the selective metal shield layer 115a includes forming a metal layer 115 on the sidewalls of the back side surface 101b, the dielectric isolation structure 110, and the recess 114 of the back side alignment mark 112, and partially filling the surface The side is aligned with the recess 114 of the indicia 112 (as depicted in Figure 1H). The metal layer 115 is then patterned, a portion of the metal layer 115 is removed, and the remaining metal layer 115 is overlaid on the sidewalls and bottom of the recess 114 of the dielectric isolation structure 110 and the back side alignment mark 112, respectively. (as shown in Figure 1I).

After the selective metal shielding layer 115a is formed, a plurality of color filters 116 and a plurality of microlenses 117 are formed on the rear side surface 101b and the dielectric isolation structure 110 to complete the metal-oxide as shown in FIG. 1J. - Preparation of a semiconductor image sensor 100.

Referring to FIG. 1J again, the metal-oxide-semiconductor image sensor 100 prepared by the above method comprises a substrate 101, a plurality of photoelectric conversion elements 102, an interconnect structure 103, a dielectric isolation structure 110, and a rear side pair. The alignment mark 112, the selective metal shield layer 115a, the color filter 116, and the plurality of microlenses 117. Among them, the photoelectric conversion element 102 is formed on the front side surface 101a of the substrate 101. The interconnect structure 103 is then located on the front side surface 101a of the substrate 101. The dielectric isolation structure 110 extends from the rear side surface 101b of the substrate 101 into the interior of the substrate 101, thereby isolating the plurality of photoelectric conversion elements 102. The rear side alignment mark 112 also extends into the substrate 101 from the rear side surface 101b, and corresponds to the front side alignment mark 113 previously formed on the front side surface 101a. The color filter 116 and the microlens 117 are located on the rear side surface 101b and the dielectric isolation structure 110. The selective metal shield layer 115a is between the dielectric isolation structure 110 and the color filter 116.

Since the embodiment of the present invention is a step of filling the trenches 105, it is arranged after the front side process requiring precise alignment. Therefore, in other embodiments of the present invention, after filling the trenches 105 with the dielectric material layer 109, it is preferred that the dielectric material layer 109 is not planarized, but the dielectric material layer 109 is The state just after deposition is left. After the subsequent processing steps, a metal-oxide-semiconductor image sensor 200 as shown in FIG. 2 is formed. It can further save process costs.

According to the above embodiment, the present invention provides an image sensor and a method of fabricating the same, first forming a photoelectric conversion element and an interconnect structure on a front side surface of the image sensor, and then on a rear side surface opposite to the front side surface Forming at least one dielectric isolation structure extending into the interior of the substrate to isolate the plurality of photoelectric conversion elements. By providing a dielectric isolation structure, it is possible to sufficiently isolate the light incident into the substrate and the photocarriers generated in the substrate to prevent the adjacent pixels from generating electronic and optical crosstalk.

Further, since the process of forming the dielectric isolation structure and the process of forming the photoelectric conversion element and the interconnect structure are performed on opposite sides of the substrate, respectively. Therefore, when the dielectric isolation structure is formed, even if a thermal oxidation and a trenching material densification step which generate a high temperature are performed, the functions of the photoelectric conversion element and the interconnect structure are not disturbed. When a planarization step (for example, a chemical mechanical polishing process) is performed, there is no possibility that a U-shaped alcove may be caused on the front side surface of the substrate, which may affect the quality of the subsequent interconnect structure process.

Further, while forming the dielectric isolation structure, a rear side alignment mark may be formed on the rear side surface corresponding to the front side alignment mark originally formed on the front side surface of the substrate for performing the front side process. The manufacturing precision of the overall component can be improved without requiring additional manufacturing costs.

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. The scope of protection is subject to the definition of the scope of the patent application.

100. . . Image sensor

101. . . Substrate

101a. . . Front side surface of the substrate

101b. . . Back side surface of the substrate

102. . . Photoelectric conversion element

102a. . . Photodiode structure

102b. . . Bungee structure

102c. . . Gate structure

103. . . Inline structure

103a. . . Metal wire layer

103b. . . Dielectric material layer

103c. . . Conductive plug

104. . . Working wafer

105. . . Trench

106. . . Alcove

107. . . Hard mask layer

108. . . P+ doped layer

109. . . Dielectric material layer

110. . . Dielectric isolation structure

111. . . Shallow trench isolation structure

112. . . Back side alignment mark

113. . . Front side alignment mark

114. . . Alcove

115. . . Metal layer

115a. . . Metal shield

116. . . Color filter

117. . . Microlens

119. . . Antireflection layer

200. . . Image sensor

1A-1J are cross-sectional views showing a process of fabricating a metal-oxide-semiconductor image sensor according to an embodiment of the invention.

2 is a cross-sectional view showing the structure of a metal-oxide-semiconductor image sensor according to another embodiment of the present invention.

100. . . Image sensor

101. . . Substrate

101a. . . Front side surface of the substrate

101b. . . Back side surface of the substrate

102a. . . Photodiode structure

102b. . . Bungee structure

102c. . . Gate structure

103. . . Inline structure

103a. . . Metal wire layer

103b. . . Dielectric material layer

103c. . . Conductive plug

104. . . Working wafer

108. . . P+ doped layer

109. . . Dielectric material layer

110. . . Dielectric isolation structure

111. . . Shallow trench isolation structure

112. . . Back side alignment mark

113. . . Front side alignment mark

115a. . . Metal shield

116. . . Color filter

117. . . Microlens

119. . . Antireflection layer

Claims (20)

An image sensor comprising: a substrate having a back side surface and a front side surface opposite the back side surface; an interconnect structure on the front side surface of the substrate; and a plurality of photoelectric conversion elements a (photoelectric transducer device) formed on the front side surface; at least one dielectric isolation structure extending from the rear side surface into the substrate to isolate the photoelectric conversion elements; and a back side alignment mark Marked from the back side surface into the substrate and corresponding to a front side alignment mark previously formed on the front side surface, wherein the back side alignment mark includes an alcove from the rear side surface Extending into the substrate. The image sensor of claim 1, wherein the substrate is a layer of a layer, and the dielectric isolation structure comprises a plurality of bottom anti-reflective coatings (ARCs). The image sensor of claim 1, further comprising an ion doped layer disposed in the substrate and surrounding the dielectric isolation structure. The image sensor of claim 1, further comprising a shallow trench isolation structure extending from the front side surface into the substrate and connected to the dielectric isolation structure. The image sensor of claim 1, wherein the back side alignment mark is aligned with the front side alignment mark or associated with the front side alignment mark in a specific spatial relationship. The image sensor of claim 1, further comprising a color filter and a plurality of microlenses on the rear side surface of the substrate. The image sensor of claim 6, further comprising a patterned metal shielding layer between the color filter and the dielectric isolation structure. The image sensor of claim 1, wherein the back side alignment mark has a dielectric material layer and a metal shielding layer on a bottom and a side wall of the recess. A method for manufacturing an image sensor, comprising: forming a plurality of photoelectric conversion elements and an interconnect structure on a front side surface of a substrate; forming at least one dielectric isolation structure from a rear side surface of the substrate Extending into the substrate to isolate the photoelectric conversion elements, wherein the rear side surface is opposite to the front side surface; and forming a back side alignment mark extending from the back side surface of the substrate into the substrate Among the materials, and corresponding to a front side alignment mark previously formed on the front side surface. The method of manufacturing an image sensor according to claim 9, wherein the dielectric isolation structure and the back side alignment mark are simultaneously formed. The method of manufacturing the image sensor of claim 10, wherein the step of forming the dielectric isolation structure and the back side alignment mark comprises: performing an etching process on the back side surface to Forming at least one trench and an recess in the material; forming a layer of dielectric material on the rear side surface to fill the trench and partially filling the recess; and performing a planarization process to remove a portion The dielectric material layer is dispensed and a portion of the substrate is exposed to the outside. The method of fabricating an image sensor according to claim 11, wherein the trench exposes a shallow trench isolation structure formed on the front side surface. The method of manufacturing an image sensor according to claim 11, wherein after forming the trench and the recess, further comprising the trench and sidewalls of the recess, performing an ion implantation process and A laser annealing process. The method of manufacturing an image sensor according to claim 11, wherein before performing the etching process, further comprising forming a hard mask layer on the rear side surface. The method of manufacturing the image sensor of claim 11, wherein after the planarizing process, the method further comprises: performing a surface on the substrate, the dielectric isolation structure, and the back side alignment mark Processing; forming a metal layer on the substrate, the dielectric isolation structure and the back side alignment mark; and patterning the metal layer to form a metal shielding layer covering the dielectric isolation structure and the back side pair Quasi-marking. The method of manufacturing an image sensor according to claim 15, wherein the surface treatment comprises: performing an ion doping process on the rear side surface, the dielectric isolation structure, and the back side alignment mark; a laser annealing process; and forming an anti-reflection layer on the rear side surface, the dielectric isolation structure, and the back side alignment mark. The method of fabricating an image sensor according to claim 10, wherein the back side alignment mark is aligned with the front side alignment mark or associated with the front side alignment mark in a specific spatial relationship. The method of manufacturing an image sensor according to claim 10, wherein after forming the dielectric isolation structure and the back side alignment mark, further comprising forming on the rear side surface and the dielectric isolation structure A color filter and a plurality of microlenses. The method of manufacturing the image sensor of claim 10, wherein before the forming the dielectric isolation structure, the method further comprises: combining a working wafer with the interconnect structure; and the rear surface A thinning process is performed to thin the substrate. A method for manufacturing an image sensor includes: forming a plurality of photoelectric conversion elements and an interconnect structure on a front side surface of a substrate; and performing an etching process on a rear surface of the substrate to Forming at least one trench in the substrate; forming a layer of dielectric material on the backside surface to fill the trench and forming at least one dielectric isolation structure extending from the backside surface into the substrate The photoelectric conversion elements are isolated and the layer of dielectric material remains as-deposited.