TW202238972A - Back-side illuminated image sensor and manufacturing method thereof - Google Patents

Abstract

A back-side illuminated image sensor includes: a substrate, image sensing regions, trench isolation structures, and sidewall light shielding structures. The substrate has a first surface and a second surface opposite to the first surface. The image sensing regions are formed in the first surface of the substrate. The trench isolation structure is disposed in the first surface of the substrate to separate the plurality of image sensing regions, and each of the trench isolation structures has a bottom and sidewalls extending toward the second surface. The sidewall light shielding structures are arranged in the second surface of the substrate, wherein each of the sidewall light shielding structures has a light reflection surface and extends to cover the bottom and a portion of the sidewalls of each of the trench isolation structure. The angle between the light reflection surface and the second surface is greater than 90°.

Description

Back-illuminated image sensor and manufacturing method thereof

The present invention relates to an image sensor, and in particular to a back-illuminated image sensor and a manufacturing method thereof.

Image sensors are widely used in various imaging applications and products such as digital still cameras or mobile phone camera applications. These elements utilize an array of pixels formed by sensor elements in a substrate for image sensing. A pixel includes a photodiode or other photosensitive element that absorbs light and converts the sensed light into an electrical signal.

Among them, the back-illuminated image (BSI) sensor is the current mainstream technology, which has a better effective charge capacity (Full well capacity), which means that the number of effective electrons (charges) in the photosensitive element is higher, and better The fill factor (Fill factor), that is, the ratio of the maximum output power to the product of the short-circuit current and the open-circuit voltage is better. Therefore, the back-illuminated image sensor can be miniaturized and its resolution can be improved.

However, the existing back-illuminated image sensors begin to suffer from cross-talk problems due to shrinking in size. It can be attributed to insufficient isolation between adjacent pixels of back-illuminated image sensors. Although a deep trench isolation (DTI) structure is often used in the prior art, there is still a problem of incomplete isolation resulting in crosstalk.

The invention provides a back-illuminated image sensor and its manufacturing method, which can effectively isolate pixels, increase light absorption and suppress crosstalk.

A back-illuminated image sensor of the present invention includes: a substrate, an image sensing area, a trench isolation structure, and a side wall light shielding structure. The substrate has a first surface and a second surface opposite to it. A plurality of image sensing areas are formed in the first surface of the substrate. A plurality of trench isolation structures are disposed on the first surface of the substrate to separate a plurality of image sensing regions, and each trench isolation structure has a bottom and a sidewall extending toward the second surface. A plurality of sidewall light-shielding structures are disposed on the second surface of the substrate, each sidewall light-shielding structure has a light-reflecting surface and extends to cover the bottom and part of the sidewall of each trench isolation structure, and the light-reflecting surface and the second surface The angle is greater than 90°.

In an embodiment of the present invention, the angle between the above-mentioned light reflecting surface and the second surface is less than 150°.

In an embodiment of the present invention, each sidewall light-shielding structure described above extends to cover the bottom and sidewalls of each trench isolation structure.

In an embodiment of the present invention, the aforementioned trench isolation structure includes a shallow trench isolation structure (STI) or a deep trench isolation structure (DTI).

In an embodiment of the present invention, the material of the sidewall light shielding structure includes metal, polysilicon, silicon oxide, silicon carbide or silicon nitride.

In an embodiment of the present invention, the above-mentioned back-illuminated image sensor may further include: a liner disposed between the substrate and each sidewall light-shielding structure and between each trench isolation structure and each sidewall light-shielding structure Between, wherein the liner includes a single-layer or multi-layer structure.

In an embodiment of the present invention, the above-mentioned back-illuminated image sensor may further include: a plurality of microlenses and a color filter layer, the microlenses are arranged on the second surface and are respectively aligned with the plurality of image sensors Area. The color filter layer is disposed between the second surface and the plurality of micro-lenses.

In an embodiment of the present invention, the above-mentioned back-illuminated image sensor may further include an interconnection structure disposed on the first surface.

A manufacturing method of a back-illuminated image sensor of the present invention includes: forming a plurality of trench isolation structures in the first surface of the substrate to define a plurality of active regions. Each trench isolation structure has a bottom and sidewalls extending toward a second surface of the substrate, wherein the second surface is opposite to the first surface. A plurality of image sensing regions are formed in a plurality of active regions. A plurality of trenches are formed in the second surface of the substrate, each trench is aligned with each trench isolation structure and exposes the bottom and part of the sidewall, and the angle between the side of each trench and the second surface is greater than 90° . A plurality of sidewall light-shielding structures are formed in the plurality of trenches, so that each sidewall light-shielding structure extends to cover the bottom and part of the sidewall of each trench isolation structure.

In another embodiment of the present invention, the angle between the side surface of the groove and the second surface is less than 150°.

In another embodiment of the present invention, after forming the plurality of trenches, it may further include: forming a first liner on the second surface, the inner surfaces of the plurality of trenches, and the exposed bottom and part of the sidewall of the trench isolation structure. Floor. and forming a second lining layer on the first lining layer.

In another embodiment of the present invention, the above-mentioned first lining layer is a silicon oxide layer, and the second lining layer is a silicon nitride layer.

In another embodiment of the present invention, the step of forming the plurality of sidewall light shielding structures includes: depositing a material layer on the second surface to fill up the plurality of trenches. Using the second liner as a stop layer, the material layer is planarized until the second liner is exposed. And using the first lining layer as a stop layer, removing the exposed second lining layer.

In another embodiment of the present invention, the material of the material layer includes metal or silicon.

In another embodiment of the present invention, each sidewall light shielding structure extends to cover the bottom and sidewalls of each trench isolation structure.

In another embodiment of the present invention, the above-mentioned trench isolation structure includes a shallow trench isolation structure (STI) or a deep trench isolation structure (DTI).

In another embodiment of the present invention, after forming the plurality of sidewall light-shielding structures, the method may further include: forming a color filter layer on the second surface. And a plurality of microlenses are formed on the color filter layer, and the plurality of microlenses are respectively aligned with the plurality of image sensing areas.

In another embodiment of the present invention, forming the plurality of image sensing regions may further include forming an interconnect structure on the first surface.

Based on the above, the present invention provides a back-illuminated image sensor. The angle between the side surface of each groove and the second surface is greater than 90°, so that the structure of the side wall light shield (SW light shield) can be imaged. Mirror-like reflection of the incident light entering each pixel, and because the above-mentioned angle is greater than 90°, the total reflection angle of the incident light on the surface of the side wall light screen wall structure is also enlarged, thereby providing additional reflection or total reflection light, Therefore, the light sensitivity of each pixel can be increased, cross-talk can be suppressed, and the quantum efficiency (Quantum efficiency) in each pixel can be improved to facilitate the miniaturization of the sensor and the improvement of resolution.

In order to make the above-mentioned features and advantages of the present invention more comprehensible, the following specific embodiments are described in detail together with the accompanying drawings.

1A to 1F are schematic cross-sectional views of a manufacturing process of a back-illuminated image sensor according to an embodiment of the present invention.

First, referring to FIG. 1A , a plurality of trench isolation structures 120 are first formed in the first surface 102 of the substrate 100 to define a plurality of active areas AA, and each trench isolation structure 120 has a structure extending toward the second surface 104 of the substrate 100. The bottom 120a and the sidewall 120b, wherein the second surface 104 is opposite to the first surface 102 . In an embodiment, the substrate 100 may be a p-type substrate, for example doped with p-type dopants. The trench isolation structure 120 is, for example, formed by any one of various deposition processes (eg, chemical vapor deposition process, atomic layer deposition process, physical vapor deposition process, etc.), and its material may include polysilicon material, metal material, or dielectric material. Materials such as silicon oxide, silicon nitride, low dielectric constant (low-k) materials, or combinations thereof. Moreover, according to the requirement of device design, the trench isolation structure 120 may include a shallow trench isolation structure (STI) or a deep trench isolation structure (DTI). The above-mentioned manufacturing methods of the substrate 100 and the trench isolation structure 120 can also refer to the manufacturing methods of the prior art.

Next, please continue to refer to FIG. 1A , a plurality of image sensing regions 110 are formed in the active region AA, and each image sensing region 110 is, for example, a p-n junction formed by an n-type doped region 112 and a p-type doped region 114 Photodiodes, which accept light signals and convert them into electrical signals. In this embodiment, the image sensing area 110 in an active area AA is referred to as a pixel region.

In addition, after the image sensing region 110 is formed, an interconnection structure 170 can be formed on the first surface 102 to transmit the electrical signal generated by the image sensing region 110 to peripheral components, although FIG. The wiring structure 170 is a structure directly connected to the image sensing area 110, but it should be understood that FIG. Survey area 110. The interconnect structure 170 is, for example, a structural layer formed by stacking a multilayer dielectric layer 172 and a multilayer metal wire 174 . In addition, an intermediate layer 176 can be disposed between the interconnection structure 170 and the substrate 100 to increase the adhesion between the interconnection structure 170 and the substrate 100 . Then, in order to form a groove (not shown) in the second surface 104 of the substrate 100, a mask layer PR may be formed on the second surface 104 to expose the surface of the substrate 100 (the second surface 104 ), wherein the mask layer PR is such as a photoresist, or a hard mask can also be used as a subsequent etching mask. In FIG. 1A , the projected area of the first surface 104 covered by the mask layer PR is not larger than the projected area of the active area AA.

Then, referring to FIG. 1B , the mask layer PR can be used as an etching mask to remove the exposed second surface 104 by dry etching until a plurality of trenches 106 are formed in the second surface 104 of the substrate 100 . Each trench 106 is aligned with each trench isolation structure 120 and exposes its bottom 120a and sidewalls 120b. By controlling the etching depth d and the angle ψ, the bottom 120a of the trench isolation structure 120 can be completely exposed, and all or part of the sidewall 120b can be exposed, for example, one-half or one-third of the sidewall 120b can be exposed without affecting the image. In the sensing region 110 , the etching depth d and the angle ψ within this range are not particularly limited. An angle θ is formed between the side surface 132 (ie, the light reflection surface 134 ) of each trench 106 and the second surface 104 by etching, the angle θ is greater than 90° and less than 150°, preferably greater than 105°, More preferably, it is 135°. The control of the etching depth d and the angle ψ is achieved, for example, by controlling the etching time and etching gas concentration. For example, the longer the etching time, the deeper the etching depth d; the thicker the etching gas concentration, the larger the angle ψ. After etching, an angle θ that is complementary to the etching angle ψ is formed between the side surface 132 of each trench 106 and the second surface 104 . The two angles θ in the groove can be the same or different.

Next, please refer to FIG. 1C , after forming a plurality of trenches 106 , the mask layer PR can be removed first. Next, selectively form a first liner 142 on the second surface 104 , the inner surface of the trench 106 , and the exposed bottom 120 a and part of the sidewall 120 b of the trench isolation structure 120 , and then form a second liner 142 on the first liner 142 . Liner 144 . The liner 140 can be a single layer or multiple layers. In one embodiment, the liner 140 includes a first liner 142 and a second liner 144 , for example. The first liner 142 and the second liner 144 can cover the bottom 120a and part of the sidewall 120b of the trench isolation structure 120, wherein the material of the first liner 142 is such as silicon oxide layer, and the material of the second liner 144 is such as silicon nitride Floor. However, the present invention is not limited thereto, as long as the first lining layer 142 or the second lining layer 144 can provide better adhesion between the substrate 100 and the subsequently filled sidewall light-shielding structure (not shown), and can avoid Possible dopants or metal ions in the sidewall light shielding structure diffuse into the substrate 100 and affect the electrical properties of the image sensing region 110 . In addition, the first liner layer 142 or the second liner layer 144 can also serve as a planarization stop layer in subsequent processes.

After that, referring to FIG. 1D , a plurality of sidewall light-shielding structures 130 are formed in the plurality of trenches 106 , so that each sidewall light-shielding structure 130 extends to cover the bottom 120 a and part of the sidewall 120 b of each trench isolation structure 120 . The step of forming the sidewall light-shielding structure 130 is, for example, depositing a material layer 105 on the second surface 104 to fill up the trench 106 . The material of the material layer 105 may include metal, polysilicon, silicon oxide, silicon carbide or silicon nitride, preferably tungsten, polysilicon, silicon oxide, aluminum, silicon carbide, silicon nitride, etc., preferably tungsten. Each sidewall light-shielding structure 130 can extend to cover the bottom 120a and sidewall 120b of each trench isolation structure 120, wherein the sidewall light-shielding structure 130 can completely cover the sidewall 120b, and can form a light sidewall full-shielding structure, because the filling material is Metal, when the incident light meets the side wall shielding, such as 騜鏡, it can be completely reflected into the photodiode sensing area to increase the photoelectron signal; or the side wall light shielding structure 130 can cover part of the side wall 120b, such as one-half or one-third The sidewall 120b is easy to control and manufacture the etching process parameters.

Next, please refer to FIG. 1E , with the second liner layer 144 as a stop layer, the material layer 105 is planarized until the second liner layer 144 is exposed. The planarization step is, for example, performing a chemical mechanical planarization (CMP) process on the material layer 105 . Next, using the first liner layer 142 as a stop layer, the exposed second liner layer 144 is removed, and the material layer 105 is slightly over-etched to ensure the flatness of the substrate 100, and to prevent the material layer 105 from remaining outside the groove 106, especially However, if the material layer 105 is metal, it may cause poor performance or block light. After the deposition steps above, the sidewall light-shielding structure 130 can be formed in the trench 106 .

When light is incident on the substrate 100 at a non-direct angle, it will be reflected or totally reflected at the sidewall light shielding structure 130 , and then enter the image sensing region 110 . Therefore, the material used for the light shielding structure 130 is not particularly limited as long as it can reflect or totally reflect incident light. When light enters the substrate 100, the angle θ formed between the side surface 132 (light reflection surface 134) of the groove 106 and the second surface 104 will cause the light incident angle ϕ to be larger than the light incident angle of the vertical plane, so that the incident light Reflection or total reflection is easy to occur on the surface of the light shielding structure 130, so it will not penetrate to the adjacent image sensing area 110 (pixel unit) to cause crosstalk, and because the light entering the image sensing area 110 becomes increase the quantum efficiency.

When the light-shielding structure 130 is an opaque material such as metal, when light penetrates the substrate 100 and reaches the light-shielding structure 130 , it will be absorbed and reflected by the metal, and the reflected light will enter the image sensing area 110 . The higher the reflectivity of the metal, the better the sensing efficiency of the pixel unit. Using the metal material can also prevent light from penetrating the light-shielding structure 130 and entering adjacent pixel units, causing crosstalk. As the metal material, tungsten, aluminum, copper, gold, titanium, titanium nitride, and the like are preferably used. When the light-shielding structure 130 is a light-transmitting material, it will enter the image sensing area 110 due to a large incident angle ϕ of light, which will cause total reflection like a specular surface. The refractive index n ₂ of the light-transmitting material needs to be lower than the refractive index n ₁ of the substrate 100. When the ratio of n ₂ to n ₁ is smaller, it is more likely to occur on the surface of the light-shielding structure 130 due to the smaller critical angle. The reflection phenomenon makes the sensing efficiency of the pixel unit better. The light-transmitting material is preferably silicon oxide (glass).

Finally, please refer to FIG. 1F , after the step of forming the sidewall light-shielding structure 130 , a protection layer R may be deposited on the second surface 104 of the substrate 100 to protect the planarized substrate 100 and the light-shielding structure 130 . The protective layer R can be a commonly used material, for example, oxide.

Next, common components of general image sensors such as a color filter layer (not shown) and microlenses (not shown) can be formed, so details are not repeated here. So far, the back-illuminated image sensor of this embodiment has been completed.

Fig. 2 is a structural cross-sectional view of a back-illuminated image sensor according to another embodiment of the present invention, wherein the same or similar components are represented by the same reference numerals as in the previous embodiment, and the same or similar components For the content, reference may also be made to the content of the first embodiment, and details are not repeated here.

Referring to FIG. 2 , the back-illuminated image sensor 10 of this embodiment includes: a substrate 100 , an image sensing region 110 , a trench isolation structure 120 and a sidewall light shielding structure 130 . The substrate 100 has a first surface 102 and a second surface 104 opposite thereto. A plurality of image sensing regions 110 are formed in the first surface 102 of the substrate 100 . A plurality of trench isolation structures 120 are disposed on the first surface 102 of the substrate 100 to separate the plurality of image sensing regions 110 , and each trench isolation structure 120 has a bottom 120 a and a sidewall 120 b extending toward the second surface 104 . The sidewall light shielding structure 130 is disposed in the second surface 104 of the substrate 100 . The liner 140 may be disposed between the substrate 100 and each sidewall light-shielding structure 130 and between each trench isolation structure 120 and each sidewall light-shielding structure 130 , and may include a single-layer or multi-layer structure. A plurality of microlenses 150 can be disposed on the second surface 104 and aligned with the plurality of image sensing regions 110 respectively. The color filter layer 160 can be disposed between the second surface 104 and the plurality of microlenses 150 . The interconnect structure 170 can be disposed on the first surface 102 .

Each sidewall light shielding structure 130 has a light reflecting surface 134 extending to cover the bottom 120 a and part of the sidewall 120 b of each trench isolation structure 120 , and the angle θ between the light reflecting surface 134 and the second surface 104 is greater than 90°. The angle θ between the light reflecting surface 134 and the second surface 104 is, for example, greater than 90° and less than 150°. Each sidewall light-shielding structure 130 extends to cover the bottom 120a and the sidewall 120b of each trench isolation structure, wherein the sidewall light-shielding structure 130 can completely cover the sidewall 120b or only partially cover the sidewall 120b. The trench isolation structure 120 may include, for example, a shallow trench isolation structure (STI) or a deep trench isolation structure (DTI). The material of the sidewall light-shielding structure 130 may include metal, polysilicon, silicon oxide, silicon carbide or silicon nitride.

When the light is incident on the substrate at a non-direct angle, it will be reflected or totally reflected on the surface of the sidewall light-shielding structure 130 at the incident angle ϕ, and then enter the image sensing area, which can avoid crosstalk caused by incomplete isolation.

In summary, in the embodiments of the present invention, the angle between the side surface of each trench and the second surface is greater than 90°, so that the SW light shield structure can be reflected on each groove like a mirror. The incident light in the pixel provides additional reflection or total reflection light, so the light sensitivity of each pixel can be increased, cross-talk can be suppressed, and the quantum efficiency (Quantum efficiency) in each pixel can be improved to It is beneficial to miniaturization of sensors and improvement of resolution.

Although the present invention has been disclosed above with the embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field may make some changes and modifications without departing from the spirit and scope of the present invention. The scope of protection of the present invention should be defined by the scope of the appended patent application.

10:Back-illuminated image sensor 100: Substrate 102: first surface 104: second surface 105: Material layer 106: Groove 110: image sensing area 112: n-type doped region 114: p-type doped region 120: Trench isolation structure 120a: Bottom of trench isolation structure 120b: The side wall of the trench isolation structure 130: side wall light shielding structure 132: The side of the groove 134: light reflective surface 140: lining 142: The first lining 144: second lining 150: micro lens 160: Color filter layer 170: Internal connection structure 172: dielectric layer 174: metal wire 176: middle layer AA: active area PR: mask layer S: image sensing area R: protective layer ψ: etching angle θ: Angle between the light reflecting surface and the second surface ϕ: light incident angle

1A to 1F are schematic cross-sectional views of a manufacturing process of a back-illuminated image sensor according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a back-illuminated image sensor according to another embodiment of the present invention.

10:Back-illuminated image sensor

100: Substrate

102: first surface

104: second surface

110: image sensing area

112: n-type doped region

114: p-type doped region

120: Trench isolation structure

120a: Bottom of trench isolation structure

120b: The side wall of the trench isolation structure

130: side wall light shielding structure

134: light reflective surface

140: lining

R: protective layer

150: micro lens

160: Color filter layer

θ: Angle between the light reflecting surface and the second surface

Φ: light incident angle

Claims (18)

A back-illuminated image sensor comprising: a substrate having a first surface and a second surface opposite thereto; a plurality of image sensing regions formed in the first surface of the substrate; a plurality of trench isolation structures disposed in the first surface of the substrate to separate the plurality of image sensing regions, each of the trench isolation structures has a bottom and sidewalls extending toward the second surface; as well as A plurality of sidewall light shielding (SW light shield) structures disposed in the second surface of the substrate, wherein each of the sidewall light shielding structures has a light reflecting surface and extends to cover each of the trench isolation structures The angle between the bottom and part of the sidewall, and the light reflection surface and the second surface is larger than 90°. The back-illuminated image sensor as claimed in claim 1, wherein the angle between the light reflecting surface and the second surface is less than 150°. The back-illuminated image sensor according to claim 1, wherein each of the sidewall light-shielding structures extends to cover the bottom and the sidewall of each of the trench isolation structures. The back-illuminated image sensor according to claim 1, wherein the trench isolation structure includes a shallow trench isolation structure (STI) or a deep trench isolation structure (DTI). The back-illuminated image sensor according to claim 1, wherein the material of the sidewall light-shielding structure includes metal, polysilicon, silicon oxide, silicon carbide or silicon nitride. The back-illuminated image sensor according to claim 1, further comprising: a liner disposed between the substrate and each of the sidewall light-shielding structures, and each of the trench isolation structures and each of the Between the sidewall light-shielding structures, the lining layer includes a single-layer or multi-layer structure. The back-illuminated image sensor as described in claim 1, further comprising: a plurality of microlenses arranged on the second surface and respectively aligned with the plurality of image sensing areas; and The color filter layer is arranged between the second surface and the plurality of micro lenses. The back-illuminated image sensor according to claim 1 further includes an interconnection structure disposed on the first surface. A method of manufacturing a back-illuminated image sensor, comprising: A plurality of trench isolation structures are formed in the first surface of the substrate to define a plurality of active regions, each of the trench isolation structures has a bottom and sidewalls extending toward a second surface of the substrate, wherein the second surface is opposite to each other and said first surface; forming a plurality of image sensing regions in the plurality of active regions; A plurality of grooves are formed in the second surface of the substrate, each of the grooves is aligned with each of the trench isolation structures and exposes the bottom and part of the sidewall, and each of the grooves the angle between the sides of the groove and said second surface is greater than 90°; and A plurality of sidewall light-shielding structures are formed in the plurality of trenches, so that each sidewall light-shielding structure extends to cover the bottom and part of the sidewall of each trench isolation structure. The method of manufacturing a back-illuminated image sensor as claimed in claim 9, wherein the angle between the side surface of the groove and the second surface is less than 150°. The method for manufacturing a back-illuminated image sensor according to claim 9, further comprising: after forming the plurality of grooves: forming a first liner on the second surface, inner surfaces of the plurality of trenches, and the exposed bottom and part of the sidewall of the trench isolation structure; and A second liner is formed on the first liner. The method for manufacturing a back-illuminated image sensor according to claim 11, wherein the first liner layer is a silicon oxide layer, and the second liner layer is a silicon nitride layer. The method for manufacturing a back-illuminated image sensor according to claim 11, wherein the step of forming the plurality of sidewall light-shielding structures includes: depositing a layer of material on the second surface, filling the plurality of trenches; using the second liner as a stop layer, planarizing the material layer until the second liner is exposed; and The exposed second lining layer is removed by using the first lining layer as a stop layer. The method for manufacturing a back-illuminated image sensor according to claim 13, wherein the material of the material layer includes metal, polysilicon, silicon oxide, silicon carbide or silicon nitride. The method for manufacturing a back-illuminated image sensor as claimed in claim 9, wherein each of the sidewall light-shielding structures extends to cover the bottom and the sidewall of each of the trench isolation structures. The method for manufacturing a back-illuminated image sensor according to claim 9, wherein the trench isolation structure includes a shallow trench isolation structure (STI) or a deep trench isolation structure (DTI). The method for manufacturing a back-illuminated image sensor according to Claim 9, further comprising: after forming the plurality of sidewall light-shielding structures: forming a color filter layer on the second surface; and A plurality of microlenses are formed on the color filter layer, and the plurality of microlenses are respectively aligned with the plurality of image sensing areas. The method for manufacturing a back-illuminated image sensor according to claim 9, further comprising forming an interconnection structure on the first surface after forming the plurality of image sensing regions.

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