Front-illuminated image sensor

Abstract

The utility model discloses a front -facing type image sensor relates to image sensor technical field, including semiconductor substrate and the first film layer, second film layer, third film layer and fourth film layer that form in order on semiconductor substrate, semiconductor substrate has the pixel area and the isolation area of isolating pixel area, first film layer, second film layer and fourth film layer cover pixel area and isolation area, third film layer includes the interlayer dielectric layer area on the pixel area above and the metal layer area on the isolation area above, the thickness of fourth film layer is determined by the thickness of third film layer. The correlation design of fourth film layer thickness and third film layer thickness can realize the anti -reflection matching, makes the reflection light interference of fourth film layer and third film layer cancel out, thereby reduces interface reflectivity, promotes light transmittance, and then obtains greater quantum efficiency, to guarantee the photosensitive sensitivity of front -facing type image sensor.

Description

Technical Field

[0001] This utility model relates to the field of image sensor technology, and in particular to a front-illuminated image sensor. Background Technology

[0002] A CMOS (Complementary Metal-Oxide-Semiconductor) image sensor is a functional device that converts optical images into electrical signals. Depending on the path of the incident light entering the photosensitive device, CMOS image sensors can be divided into two types: front-illuminated image sensors (FSI) and rear-illuminated image sensors (BSI). Among them, front-illuminated image sensors have gained wider application due to their simple manufacturing process, low cost, and high yield. However, in front-illuminated image sensors, the incident light enters the photosensitive device from the front of the silicon wafer. Before reaching the photodiode located on the silicon substrate, the light must penetrate multiple dielectric films. Reflection at the interface layers results in a loss of light intensity, and the significant light loss along the transmission path limits the quantum efficiency performance of front-illuminated image sensors. Utility Model Content

[0003] The purpose of this invention is to provide a front-illuminated image sensor that solves the problem that the quantum efficiency performance of existing front-illuminated image sensors is limited by the loss of incident light in the transmission path.

[0004] The above-mentioned objectives of this utility model can be achieved by the following technical solutions:

[0005] This invention provides a front-illuminated image sensor, comprising a semiconductor substrate and a first film layer, a second film layer, a third film layer, and a fourth film layer sequentially formed on the semiconductor substrate; the semiconductor substrate has a pixel region and an isolation region that isolates the pixel region; the first film layer, the second film layer, and the fourth film layer cover the pixel region and the isolation region; the third film layer includes an interlayer dielectric layer region located above the pixel region and a metal layer region located above the isolation region; the thickness of the fourth film layer is determined by the thickness of the third film layer.

[0006] Preferably, the thickness h of the fourth film layer satisfies the following condition: 1 / 22h3≤h≤1 / 24h3; where h3 is the thickness of the third film layer.

[0007] Preferably, the front-illuminated image sensor further includes a microlens formed on the surface of the fourth film layer.

[0008] Preferably, the thickness h of the fourth film layer satisfies the following condition: 1 / 12h3≤h≤1 / 13h3; where h3 is the thickness of the third film layer.

[0009] Preferably, the second film layer includes a lower dielectric layer and an upper dielectric layer stacked together. The lower dielectric layer is in contact with the first film layer, and the refractive index of the lower dielectric layer is different from that of the first film layer. The upper dielectric layer is in contact with the third film layer, and the refractive index of the lower dielectric layer is different from that of the upper dielectric layer.

[0010] Preferably, the second film layer further includes an intermediate dielectric layer disposed between the lower dielectric layer and the upper dielectric layer, wherein the material of the intermediate dielectric layer is different from the material of the lower dielectric layer and the material of the upper dielectric layer.

[0011] Preferably, the material of the first film layer is SiO2, the thickness of the first film layer is 10nm~40nm, and the refractive index of the first film layer is 1.4~1.6.

[0012] Preferably, the lower dielectric layer is made of SiN, the thickness of the lower dielectric layer is 30nm~50nm, and the refractive index of the lower dielectric layer is 1.8~2.2; the intermediate dielectric layer is made of SiON, the thickness of the intermediate dielectric layer is 10nm~30nm, and the refractive index of the intermediate dielectric layer is 1.9~2.3; the upper dielectric layer is made of SiO2, the thickness of the upper dielectric layer is 400nm~600nm, and the refractive index of the upper dielectric layer is 1.4~1.6.

[0013] Preferably, the third film layer consists of two to five thin layers, the thickness of the thin layers is 500 nm to 2 μm, and the refractive index of the thin layers is 1.4 to 1.6; in the thin layers, the material of the metal layer region includes at least one of Ti, TiN, Al, W, Cu, Ta, and TaN, and the material of the interlayer dielectric layer region is SiO2.

[0014] Preferably, the fourth film layer is made of SiN, the thickness of the fourth film layer is 30nm~350nm, and the refractive index of the fourth film layer is 1.8~2.2.

[0015] The features and advantages of this utility model are as follows: The front-illuminated image sensor of this utility model can achieve anti-reflection matching through the correlation design of the thickness of the fourth film layer and the thickness of the third film layer, so that the interference of reflected light from the fourth film layer and the third film layer is canceled, thereby reducing the interface reflectivity, increasing the light transmittance, and thus obtaining a larger quantum efficiency. It avoids optical mismatch such as enhanced reflection and increased light absorption caused by independently designing the thickness of the fourth film layer, so as to ensure the photosensitivity of the front-illuminated image sensor. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of the front-illuminated image sensor without microlenses provided in the embodiments of this utility model;

[0018] Figure 2 This is a schematic diagram of the front-illuminated image sensor with microlenses provided in an embodiment of the present invention;

[0019] Figure 3 This is a schematic diagram of the structure of the second film layer without an intermediate dielectric layer in the front-illuminated image sensor provided in this embodiment of the present invention.

[0020] Figure 4 This is a schematic diagram of the structure of the second film layer with an intermediate dielectric layer in the front-illuminated image sensor provided in this embodiment of the present invention.

[0021] Explanation of icon numbers:

[0022] 1. Semiconductor substrate; 2. Pixel region; 3. Isolation region; 4. First film layer; 5. Second film layer; 51. Lower dielectric layer; 52. Upper dielectric layer; 53. Intermediate dielectric layer; 6. Third film layer; 61. Interlayer dielectric layer region; 62. Metal layer region; 7. Fourth film layer; 8. Microlens. Detailed Implementation

[0023] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0024] like Figure 1 and Figure 2As shown, this utility model provides a front-illuminated image sensor, including a semiconductor substrate 1 and a first film layer 4, a second film layer 5, a third film layer 6 and a fourth film layer 7 sequentially formed on the semiconductor substrate 1; the semiconductor substrate 1 has a pixel region 2 and an isolation region 3 that isolates the pixel region 2; the first film layer 4, the second film layer 5 and the fourth film layer 7 cover the pixel region 2 and the isolation region 3; the third film layer 6 includes an interlayer dielectric layer region 61 located above the pixel region 2 and a metal layer region 62 located above the isolation region 3; the thickness of the fourth film layer 7 is determined by the thickness of the third film layer 6.

[0025] The front-illuminated image sensor of this invention achieves anti-reflection matching through the correlation design of the thickness of the fourth film layer 7 and the thickness of the third film layer 6. This makes the interference of reflected light from the fourth film layer 7 and the third film layer 6 cancel each other out, thereby reducing the interface reflectivity, increasing the light transmittance, and thus obtaining a larger quantum efficiency. This avoids optical mismatches such as enhanced reflection and increased light absorption caused by independently designing the thickness of the fourth film layer 7, thus ensuring the photosensitivity of the front-illuminated image sensor.

[0026] In this embodiment, the metal layer region 62 is used to connect the input / output signals of the pixel region 2. It is formed above the isolation region 3, that is, the projection of the metal layer region 62 on the semiconductor substrate 1 does not coincide with the pixel region 2. Specifically, if the metal layer region 62 is formed above the pixel region 2, the incident light will not be able to penetrate the metal layer region 62, resulting in a loss of quantum efficiency.

[0027] Specifically, the semiconductor substrate 1 has an isolation structure for the isolated pixel region 2. The isolation structure adopts shallow trench isolation technology, that is, firstly, trenches are formed between the pixel regions 2, and then a dielectric layer is filled in the trenches to form the isolation region 3. The dielectric layer filled in the trenches is preferably silicon dioxide to ensure the electrical isolation effect between adjacent pixel regions 2.

[0028] In this embodiment, the dielectric thin film layer above the semiconductor substrate 1 is a standard CMOS logic circuit thin film layer, which does not increase the complexity and cost of the process.

[0029] Specifically, the first film layer 4 is a silicide barrier layer made of SiO2. The thickness of the first film layer 4 is 10nm~40nm, and its refractive index is 1.4~1.6. Incident light will be reflected at the interface between the first film layer 4 and the semiconductor substrate 1.

[0030] The second film layer 5 is a contact hole blocking layer. In one feasible embodiment, such as... Figure 3As shown, the second film layer 5 includes a lower dielectric layer 51 and an upper dielectric layer 52 stacked together. The lower dielectric layer 51 is in contact with the first film layer 4, and the refractive index of the lower dielectric layer 51 is different from that of the first film layer 4, that is, the refractive indexes of the surfaces of the second film layer 5 and the first film layer 4 in contact are different. The upper dielectric layer 52 is in contact with the third film layer 6, and the refractive indexes of the lower dielectric layer 51 and the upper dielectric layer 52 are different. Thus, incident light will be reflected at the interface between the second film layer 5 and the first film layer 4, and will also be reflected at the interface between the lower dielectric layer 51 and the upper dielectric layer 52 of the second film layer 5. The reflected light will encounter and interfere with the reflected light at the interface between the first film layer 4 and the semiconductor substrate 1, ensuring that there is enough reflected light that ultimately causes destructive interference, thereby minimizing the intensity of reflected light and maximizing the quantum efficiency of the pixel region 2.

[0031] Specifically, the upper dielectric layer 52 is made of SiO2 with a thickness of 400nm~600nm and a refractive index of 1.4~1.6; the lower dielectric layer 51 is made of SiN with a thickness of 30nm~50nm and a refractive index of 1.8~2.2.

[0032] Furthermore, in another feasible embodiment of the second film layer 5, such as Figure 4 As shown, the second film layer 5 also includes an intermediate dielectric layer 53 disposed between the lower dielectric layer 51 and the upper dielectric layer 52. The material of the intermediate dielectric layer 53 is different from the material of the lower dielectric layer 51 and the upper dielectric layer 52. In this way, the incident light can be reflected at the interface between the three dielectric layers of the second film layer 5 through adaptive settings. The reflected light encounters and interferes with the reflected light at the interface between the first film layer 4 and the semiconductor substrate 1, ensuring that there is enough reflected light that ultimately causes destructive interference, thereby minimizing the intensity of reflected light and maximizing the quantum efficiency of the pixel region 2.

[0033] Specifically, the intermediate dielectric layer 53 is made of SiON with a thickness of 10nm~30nm and a refractive index of 1.9~2.3. In this embodiment, incident light is reflected at the interface between the second film layer 5 and the first film layer 4, and can be adapted to reflect the incident light at the interface between the upper dielectric layer 52 and the intermediate dielectric layer 53, while reflection may or may not occur at the interface between the intermediate dielectric layer 53 and the lower dielectric layer 51.

[0034] The third film layer 6 includes a metal layer region 62 and an interlayer dielectric layer region 61. The third film layer 6 is composed of two to five thin layers, wherein the thickness of each thin layer is 500 nm to 2 μm and its refractive index is 1.4 to 1.6. In the thin layer, the metal layer region 62 is made of at least one of Ti, TiN, Al, W, Cu, Ta, and TaN, and the interlayer dielectric layer region 61 is made of SiO2. Incident light will not be reflected at the interface between the third film layer 6 and the second film layer 5.

[0035] The fourth film layer 7 is a protective layer made of SiN. The thickness of the fourth film layer 7 is 30nm~350nm, and its refractive index is 1.8~2.2. The incident light will be reflected at the interface between the fourth film layer 7 and the third film layer 6. The reflected light will interfere with the reflected light at the interface of the first three film layers.

[0036] In this invention, the refractive indices of the surfaces in contact with the second film layer 5 and the third film layer 6 are the same. The refractive indices of the surfaces in contact with the second film layer 5 and the third film layer 6 of the other two adjacent film layers (i.e., the first film layer 4 and the fourth film layer 7) are different, and the refractive indices of the surface in contact with the semiconductor substrate 1 are also different. This means that incident light does not undergo reflection at the interface between the third film layer 6 and the second film layer 5. Instead, incident light is reflected at the interfaces between the first film layer 4 and the semiconductor substrate 1, between the second film layer 5 and the first film layer 4, and between the fourth film layer 7 and the third film layer 6. The reflected light cannot effectively reach the pixel area 2 because the reflected light at each interface does not disperse independently; it collides with each other like water waves, resulting in collision interference. Furthermore, sometimes these reflected lights collide, making the reflected light stronger (i.e., constructive interference), and sometimes they collide, making the reflected light weaker (i.e., destructive interference).

[0037] Therefore, in this invention, the thickness of the fourth film layer 7 is determined by the thickness of the third film layer 6. The thickness of the fourth film layer 7 can be calculated based on the interference principle of reflected light in the thin film material, so as to artificially adjust the optical path difference of reflected light between each interface, so that the reflected light between each interface satisfies the destructive interference (i.e. weak interference) condition, thereby reducing interface reflection. The light loss due to incident light reflection is reduced, allowing more incident light to pass through the interface into the next layer, and finally the light intensity reaching the pixel area 2 is increased, so as to obtain a larger quantum efficiency.

[0038] The front-illuminated image sensor of this invention achieves anti-reflection matching through the correlation design of the thickness of the fourth film layer 7 and the thickness of the third film layer 6. This makes the interference of reflected light from the fourth film layer 7 and the third film layer 6 cancel each other out, thereby reducing the interface reflectivity, increasing the light transmittance, and thus obtaining a larger quantum efficiency. This avoids optical mismatches such as enhanced reflection and increased light absorption caused by independently designing the thickness of the fourth film layer 7, thus ensuring the photosensitivity of the front-illuminated image sensor.

[0039] In a preferred embodiment, the thickness of the fourth film layer 7 is determined by the thicknesses of the first film layer 4, the second film layer 5, and the third film layer 6. Thus, based on the interference principle of reflected light in the thin film material, the optimal thickness of the fourth film layer 7 can be calculated, maximizing the reduction of reflected light from the five interfaces—semiconductor substrate 1, first film layer 4, second film layer 5, third film layer 6, fourth film layer 7, and air—due to destructive interference, resulting in minimal reflected light intensity. At this point, the light intensity reaching pixel region 2 is strongest, and the quantum efficiency is maximized, thereby improving the photosensitivity of the front-illuminated image sensor.

[0040] like Figure 1 As shown, according to one embodiment of the present invention, in order to enable the front-illuminated image sensor without microlens 8 to have a smaller reflected light intensity and a larger transmitted light intensity, the thickness h of the fourth film layer 7 satisfies the following condition: 1 / 22h3≤h≤1 / 24h3; where h3 is the thickness of the third film layer 6.

[0041] Furthermore, the thickness h of the fourth film layer 7 also satisfies the following conditions: 2h1≤h≤3h1, 0.2h2≤h≤0.3h2; where h1 is the thickness of the first film layer 4 and h2 is the thickness of the second film layer 5. Thus, the optimal thickness of the fourth film layer 7 is calculated to maximize the transmitted light intensity and achieve the maximum quantum efficiency in the front-illuminated image sensor without the microlens 8.

[0042] According to one embodiment of the present invention, such as Figure 2 As shown, the front-illuminated image sensor also includes a microlens 8, which is formed on the surface of the fourth film layer 7 to change the direction of the incident light and converge the incident light to the lower pixel area 2, thereby reducing light occlusion loss caused by metal wiring and the edge structure of the pixel area 2, maximizing light utilization, and improving the imaging quality of the front-illuminated image sensor.

[0043] In a preferred embodiment, the center of the microlens 8 is aligned with the center of the pixel area 2 to deflect light towards the center of the pixel area 2, thereby maximizing the light converging efficiency and reducing optical deviations and crosstalk caused by the offset (misalignment) between the center of the microlens 8 and the center of the pixel area 2.

[0044] In this embodiment, in order to make the front-illuminated image sensor with microlens 8 have a smaller reflected light intensity and a larger transmitted light intensity, the thickness h of the fourth film layer 7 satisfies the following condition: 1 / 12h3≤h≤1 / 13h3; where h3 is the thickness of the third film layer 6.

[0045] Furthermore, the thickness h of the fourth film layer 7 also satisfies the following conditions: 3h1≤h≤4h1, 0.3h2≤h≤0.4h2; where h1 is the thickness of the first film layer 4 and h2 is the thickness of the second film layer 5. Thus, by calculating the optimal thickness of the fourth film layer 7, the front-illuminated image sensor equipped with the microlens 8 can maximize the transmitted light intensity and achieve maximum quantum efficiency.

[0046] In this embodiment, the refractive indexes of the surfaces in contact with the microlens 8 and the fourth film layer 7 are different. That is, the incident light will also be reflected at the interface between the microlens 8 and the fourth film layer 7. The reflected light participates in the interference of the reflected light between the interfaces of the first four film layers. Therefore, when using simulation software to perform simulation calculations to maximize the transmittance of the front-illuminated image sensor, the reflection between the interface between the microlens 8 and the fourth film layer 7 should also be included.

[0047] Specifically, the microlens 8 contains C, H, O, and N elements. Preferably, the height of the microlens 8 is 0.1 μm to 4 μm, and its refractive index is 1.4 to 1.7.

[0048] Based on the above description, the front-illuminated image sensor provided in this embodiment of the present invention has the following beneficial effects:

[0049] The front-illuminated image sensor provided in this embodiment achieves anti-reflection matching through the correlation design of the thickness of the fourth film layer 7 and the thickness of the third film layer 6. This causes the reflected light from the fourth film layer 7 and the third film layer 6 to interfere destructively, thereby reducing interface reflectivity, increasing light transmittance, and ultimately achieving greater quantum efficiency. This avoids optical mismatches such as enhanced reflection and increased light absorption that would result from independently designing the thickness of the fourth film layer 7, thus ensuring the photosensitivity of the front-illuminated image sensor. By correlating the thickness of the fourth film layer 7 with the thicknesses of the first film layer 4, the second film layer 5, and the third film layer 6, the calculation of the... The optimal thickness of the four-layer film 7 maximizes the reduction of reflected light from the five interfaces—semiconductor substrate 1, first layer 4, second layer 5, third layer 6, fourth layer 7, and air—due to destructive interference, resulting in minimal reflected light intensity. At this point, the light intensity reaching pixel region 2 is the strongest, and the quantum efficiency is maximized, thereby improving the photosensitivity of the front-illuminated image sensor. Simultaneously, a microlens 8 can be further placed on the fourth layer 7 to change the direction of incident light, focusing the light and reducing light occlusion loss caused by metal wiring and pixel edge structures, maximizing light utilization and improving the imaging quality of the front-illuminated image sensor.

[0050] The above descriptions are merely a few embodiments of this utility model. Those skilled in the art can make various modifications or variations to the embodiments of this utility model based on the content disclosed in the application documents without departing from the spirit and scope of this utility model.

Claims

1. A front-illuminated image sensor, characterized in that, It includes a semiconductor substrate and a first film layer, a second film layer, a third film layer and a fourth film layer sequentially formed on the semiconductor substrate; The semiconductor substrate has a pixel region and an isolation region that isolates the pixel region. The first film layer, the second film layer and the fourth film layer cover the pixel region and the isolation region. The third film layer includes an interlayer dielectric layer region located above the pixel region and a metal layer region located above the isolation region. The thickness of the fourth film layer is determined by the thickness of the third film layer.

2. The front-illuminated image sensor according to claim 1, characterized in that, The thickness h of the fourth film layer satisfies the following condition: 1 / 22h3≤h≤1 / 24h3; where h3 is the thickness of the third film layer.

3. The front-illuminated image sensor according to claim 1, characterized in that, The front-illuminated image sensor also includes a microlens formed on the surface of the fourth film layer.

4. The front-illuminated image sensor according to claim 3, characterized in that, The thickness h of the fourth film layer satisfies the following condition: 1 / 12h3≤h≤1 / 13h3; where h3 is the thickness of the third film layer.

5. The front-illuminated image sensor according to claim 1, characterized in that, The second film layer includes a lower dielectric layer and an upper dielectric layer stacked together. The lower dielectric layer is in contact with the first film layer, and the refractive index of the lower dielectric layer is different from that of the first film layer. The upper dielectric layer is in contact with the third film layer, and the refractive index of the lower dielectric layer is different from that of the upper dielectric layer.

6. The front-illuminated image sensor according to claim 5, characterized in that, The second film layer also includes an intermediate dielectric layer disposed between the lower dielectric layer and the upper dielectric layer, wherein the material of the intermediate dielectric layer is different from the material of the lower dielectric layer and the material of the upper dielectric layer.

7. The front-illuminated image sensor according to claim 1, characterized in that, The first film is made of SiO2, the thickness of the first film is 10nm~40nm, and the refractive index of the first film is 1.4~1.

6.

8. The front-illuminated image sensor according to claim 6, characterized in that, The lower dielectric layer is made of SiN, with a thickness of 30nm~50nm and a refractive index of 1.8~2.2; the intermediate dielectric layer is made of SiON, with a thickness of 10nm~30nm and a refractive index of 1.9~2.3; the upper dielectric layer is made of SiO2, with a thickness of 400nm~600nm and a refractive index of 1.4~1.

6.

9. The front-illuminated image sensor according to claim 1, characterized in that, The third film layer consists of two to five thin layers, the thickness of which is 500 nm to 2 μm and the refractive index of which is 1.4 to 1.

6. In the thin layer, the material of the metal layer region includes at least one of Ti, TiN, Al, W, Cu, Ta, and TaN, and the material of the interlayer dielectric layer region is SiO2.

10. The front-illuminated image sensor according to claim 1, characterized in that, The fourth film is made of SiN, the thickness of the fourth film is 30nm~350nm, and the refractive index of the fourth film is 1.8~2.2.

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