Image sensor PDAF pixel isolation method, pixel structure and image sensor

Abstract

The invention discloses an image sensor PDAF pixel isolation method, a pixel structure and an image sensor, for a PDAF pixel module, the PDAF pixel module comprises a plurality of sub-pixels, first isolation exists between the sub-pixels receiving light of the same phase, second isolation exists between the sub-pixels receiving light of different phases, and the first isolation exists between the sub-pixels receiving light of the same phase and the second isolation exists between the sub-pixels receiving light of different phases. The trench isolation in the first isolation occupies a first proportion, the trench isolation in the second isolation occupies a second proportion, and the second proportion is larger than the first proportion. According to the invention, crosstalk can be effectively suppressed, the loss of the pixel light incoming amount is improved, and the full well capacity is improved, so that the performance of the PDAF is improved, and the working performance of the sensor is improved. Moreover, the first isolation is realized by ion implantation, so that different masks required by different trench isolation offset degrees arranged in the pixel array can be avoided or reduced, and the manufacturing cost of the sensor can be greatly reduced while the performance of the sensor is improved.

Description

Technical Field

[0001] The present invention relates to the field of image sensors, and in particular to an isolation method for PDAF pixels of an image sensor, a pixel structure, and an image sensor. Background Art

[0002] Image sensors use the photoelectric conversion function of photoelectric devices in pixel arrays to convert the light image on the photosensitive surface into an electrical signal in a proportional relationship with the light image, and then process and store it through peripheral circuits to record image information. In image sensors, focusing performance is very important. When facing the object to be photographed, if the object is not on the focal plane of the imaging lens, a blurred image will be obtained. The traditional solution is called contrast detection autofocus (CDAF) method, which guides the lens movement by judging the contrast of the image so that the object is on the focal plane, thereby obtaining a clear image. However, this method cannot accurately track moving objects due to its slow speed, and the judgment is affected by noise in low light. Therefore, phase detection autofocus (PDAF, Phase Detection Auto Focus) technology was developed. PDAF technology belongs to image method autofocus (AF) technology. It is the mainstream autofocus technology in today's industry and field, making autofocus fast and accurate. In order to ensure fast focusing and expand the application scenarios to dark light, PDAF pixels usually use the structure design of adjacent, paired photosensitive pixels in the image sensor to separate the imaging light beams in multiple directions directed to the paired pixels into two parts, such as left and right. The distance the lens needs to move is calculated by comparing the phase difference after imaging the left and right parts of the light. However, crosstalk between pixels can cause light or photogenerated charges of different phases to enter the same adjacent pixel, resulting in miscalculation of the phase difference. To solve this problem, FDTI (front deep trench isolation) and BDTI (back deep trench isolation) technologies have been developed to suppress the crosstalk problem between PDAF pixels.

[0003] Among them, BDTI technology is to carve deep grooves in the PD (PhotoDiode) area through the back etching process and fill them with isolation fillers. Figure 1 (a-1) is a cross-sectional schematic diagram of a pixel in an image sensor using BDTI isolation. Figure 1(a-2) is a front schematic diagram of BDTI isolation applied to pixels in an image sensor, wherein a photodiode sub-pixel 2 is disposed in a semiconductor substrate 1, a color filter 3 covers an opening defined by a grid 5 and is disposed on the back side of the semiconductor substrate 1, and a microlens 4 is disposed on the color filter 3. The attached figure shows that the microlens 4 is applied to at least four sub-pixels. Among them, a BDTI physical isolation 11 is disposed between two sub-pixels 2 (PD). Since the k value of the filler is much lower than that of the semiconductor substrate silicon (Si), light will be totally internally reflected (TIR) ​​after entering the PD region at a certain angle, so that the light is collected by the corresponding PD, which suppresses crosstalk to a certain extent and improves sensitivity. Since the deep trenches etched on the back side do not completely open the silicon of the semiconductor substrate 1, the front side of the semiconductor substrate 1 close to the transistor needs to be isolated by ion implantation, for example, by injecting trivalent ions to form P-type doping to separate the N-type doped PD, such as Figure 1 As shown in (a-2), ion implantation isolation 12 is formed. However, the isolation effect formed by ion implantation is related to the doping dose and energy. Therefore, the electrical isolation effect of the ion implantation isolation 12 is actually not as good as the electrical isolation effect of the BDTI physical isolation 11 on the back side.

[0004] The FDTI technology is developed on the basis of BDTI. The difference is that FDTI does not require back-side processing, but directly uses the front-side process to completely carve open the semiconductor substrate Si and fill it with isolation fillers, such as Figure 1 (b-1) is a cross-sectional schematic diagram of a pixel in an image sensor using FDTI, as shown in FIG. Figure 1 (b-2) is a front view schematic diagram of a pixel in an image sensor using FDTI. Since the sub-pixels 2 are completely isolated by the FDTI physical isolation 13, light is more easily collected therein, so the crosstalk is small. The sensitivity achieved by complete isolation through the FDTI physical isolation 13 is also higher than the sensitivity achieved by applying the BDTI physical isolation 11. However, the production of FDTI requires etching a groove with an extremely high aspect ratio in the micron-scale semiconductor substrate 1. The morphology of the groove is related to the isolation effect and the PD volume. The process is difficult. The area occupied by the physical isolation of FDTI will also be larger than the area occupied by the physical isolation of BDTI. Therefore, under the same conditions, the PD volume obtained by complete physical isolation through FDTI is smaller than the PD volume obtained by physical isolation through BDTI, which is not conducive to the improvement of full well capacity or the miniaturization of devices. Summary of the invention

[0005] Based on the above-described problems, the present invention proposes an isolation method for PDAF pixels of an image sensor, which can effectively suppress crosstalk, improve the loss of pixel light input and increase the full well capacity, thereby improving the performance of PDAF and improving the working performance of the sensor.

[0006] In a first aspect, the present invention proposes a method for isolating PDAF pixels of an image sensor, wherein the PDAF pixel module includes a plurality of sub-pixels, wherein a first isolation exists between sub-pixels receiving light of the same phase, and a second isolation exists between sub-pixels receiving light of different phases, wherein the groove isolation in the first isolation accounts for a first proportion, and the groove isolation in the second isolation accounts for a second proportion, and the second proportion is larger than the first proportion.

[0007] Preferably, the second ratio is at least 10% greater than the first ratio.

[0008] Preferably, taking the horizontal plane of the semiconductor substrate as a reference plane, the first ratio includes the ratio of the length of the trench isolation in the first isolation to the total length of the first isolation, and the second ratio includes the ratio of the length of the trench isolation in the second isolation to the total length of the second isolation.

[0009] Preferably, taking the longitudinal section of the semiconductor substrate as a reference plane, the first ratio includes the ratio of the depth of the trench isolation in the first isolation to the total depth of the first isolation, and the second ratio includes the ratio of the depth of the trench isolation in the second isolation to the total depth of the second isolation.

[0010] Preferably, the first isolation and / or the second isolation further comprises ion implantation isolation; wherein the proportion of ion implantation isolation in the first isolation is greater than the proportion of ion implantation isolation in the second isolation.

[0011] Preferably, when a plurality of sub-pixels are square and arranged in a uniform array, relative to a horizontal plane of the semiconductor substrate, a length of the first isolated trench isolation is shorter than a length of the second isolated trench isolation.

[0012] Preferably, the first isolation trench isolation extends from the front side and / or the back side of the semiconductor substrate into the interior of the semiconductor substrate, and the second isolation trench isolation extends from the front side and / or the back side of the semiconductor substrate into the interior of the semiconductor substrate.

[0013] Preferably, the second isolation formation comprises a combination of any one or more of the following structures: The first type, the second isolation in the thickness direction of the semiconductor substrate includes a first sub-isolation and a second sub-isolation; the first sub-isolation is a trench isolation formed by a trench formed from a first surface of the semiconductor substrate, and the second sub-isolation is a trench isolation formed from a second surface of the semiconductor substrate opposite to the first surface; The second type is that the second isolation in the thickness direction of the semiconductor substrate includes a third sub-isolation; the third sub-isolation is a trench isolation formed by penetrating from the first surface of the semiconductor substrate to a second surface opposite to the first surface; The third type, the second isolation in the thickness direction of the semiconductor substrate includes a fourth sub-isolation and a first sub-ion injection isolation; the fourth sub-isolation is a trench isolation that penetrates from the second surface of the semiconductor substrate to a first surface opposite to the second surface at a first preset distance, and the first sub-ion injection isolation is an ion injection isolation located at a first preset distance formed by ion injection from the first surface of the semiconductor substrate relative to the position of the fourth sub-isolation.

[0014] Preferably, the first defined second isolation further includes that the first sub-isolation and the second sub-isolation are in contact; or there is a second preset distance between the first sub-isolation and the second sub-isolation.

[0015] Preferably, ion implantation is further performed in a second preset distance between the first sub-isolation and the second sub-isolation to form a second sub-ion implantation isolation.

[0016] Preferably, the first isolation formation comprises a combination of any one or more of the following structures: First, the first isolation in the thickness direction of the semiconductor substrate includes a third sub-ion implantation isolation, and the third sub-ion implantation isolation extends from any surface of the semiconductor substrate to the other surface; The second type, the first isolation in the thickness direction of the semiconductor substrate includes a fourth sub-ion implantation isolation and a plurality of fifth sub-isolation structures, the fourth sub-ion implantation isolation is an ion implantation isolation that penetrates from the first surface of the semiconductor substrate and is a preset third distance away from the second surface opposite to the first surface, and / or the fourth sub-ion implantation isolation is an ion implantation isolation that penetrates from the second surface of the semiconductor substrate and is a preset fourth distance away from the first surface opposite to the second surface, and / or the fourth sub-ion implantation isolation is an ion implantation isolation that is a preset fifth distance away from the first surface of the semiconductor substrate and a preset sixth distance away from the second surface opposite to the first surface, the fifth sub-isolation structure is a trench isolation formed by penetrating from the first surface of the semiconductor substrate, and / or the fifth sub-isolation is a trench isolation formed by penetrating from the second surface of the semiconductor substrate opposite to the first surface.

[0017] Preferably, for the PDAF pixel modules at different positions in the pixel array, the first isolation is formed at least partially by ion implantation, so as to form first isolations with different offsets in the PDAF pixel modules at different positions through one mask.

[0018] Preferably, the first area is an edge area of ​​the pixel array, and the second area is a central area of ​​the pixel array.

[0019] In a second aspect, the present invention proposes a pixel structure, which includes a pixel array, characterized in that the pixel array includes a plurality of PDAF pixel modules formed by the PDAF pixel isolation method described in any of the aforementioned embodiments.

[0020] Preferably, the PDAF pixel module includes a number of first pixels receiving light of the first phase equal to the number of second pixels receiving light of the second phase.

[0021] Preferably, the PDAF pixel module includes four sub-pixels arranged in a 2*2 manner; wherein the first isolation is applied between two adjacent first and second sub-pixels, and the second isolation is applied between another two adjacent third and fourth sub-pixels.

[0022] In a third aspect, the present invention provides an image sensor, comprising the pixel structure described in any one of the aforementioned embodiments.

[0023] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: the present invention sets a first isolation between sub-pixels receiving light of the same phase in the PDAF pixel of the image sensor, and a second isolation between sub-pixels receiving light of different phases, the trench isolation in the first isolation accounts for a first proportion, the trench isolation in the second isolation accounts for a second proportion, and the second proportion is even 10% greater than the first proportion. For example, the first isolation is at least partially isolated by ion implantation to avoid using trench isolation in PDAF, and the application of trench isolation in PDAF pixels is reduced, which can effectively suppress crosstalk, improve the loss of pixel light input, and increase the full well capacity, thereby improving the performance of PDAF and the working performance of the sensor. In addition, the first isolation is isolated by ion implantation as much as possible, which can avoid or reduce the different masks required for setting different trench isolation offset degrees in the pixel array, so that the sensor performance can be improved while the manufacturing cost of the sensor can be greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings of the present invention constitute a part of this specification and are used to further understand the present invention. The drawings illustrate embodiments of the present invention and together with the description are used to explain the principle of the present invention.

[0025] Figure 1 This is an example of pixel isolation found in existing sensors.

[0026] Figure 2 An isolated sensor example with PDAF pixels provided in Example 1.

[0027] Figure 3~4 An isolated sensor example with PDAF pixels provided in Example 2.

[0028] Figure 5An isolated sensor example with PDAF pixels provided in Example 3.

[0029] Figure 6 An isolated sensor example with PDAF pixels provided in Example 4.

[0030] Figure 7 The direction of the light spot presented by the isolation of different PDAF pixels under the offset light spot. DETAILED DESCRIPTION

[0031] The following detailed descriptions are all illustrative and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0032] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention.

[0033] In the first aspect, the present invention proposes an isolation method for PDAF pixels of an image sensor, wherein the PDAF pixel module includes a plurality of sub-pixels, wherein a first isolation exists between sub-pixels receiving light of the same phase, and a second isolation exists between sub-pixels receiving light of different phases, wherein the trench isolation in the first isolation accounts for a first proportion, and the trench isolation in the second isolation accounts for a second proportion, and the second proportion is greater than the first proportion. Preferably, the second proportion is at least 10% greater than the first proportion, so as to ensure that the first isolation is achieved by ion implantation as much as possible, and the second isolation is achieved by trench isolation as much as possible. For example, taking the horizontal plane of the semiconductor substrate as the reference plane, the first proportion may be the proportion of the length of the trench isolation in the first isolation to the total length of the first isolation, and the second proportion may be the proportion of the length of the trench isolation in the second isolation to the total length of the second isolation, but the first proportion and the second proportion should not be limited by the length of a certain plane. For another example, when a plurality of sub-pixels are square and a plurality of sub-pixels are arranged in a uniform array, the total length of the first isolation is the same as the total length of the second isolation, then, relative to the horizontal plane of the semiconductor substrate, the concept of the present invention is applied, and the length of the trench isolation of the first isolation should be set shorter than the length of the trench isolation of the second isolation. Preferably, the length of the trench isolation of the first isolation in the present invention is shorter than the length of the trench isolation of the second isolation, and the isolation formed by applying ion implantation may at least partially replace the isolation originally achieved by applying the trench. Thus, further, the first isolation and / or the second isolation further includes ion implantation isolation; wherein the proportion of ion implantation isolation of the first isolation is greater than the proportion of ion implantation isolation of the second isolation.

[0034] In the present invention, it is preferred that the horizontal plane of the semiconductor substrate is used as a reference plane. The first proportion of the trench isolation in the first isolation may be, for example, the length of the trench isolation in the first isolation divided by the total length of the first isolation, and the second proportion of the trench isolation in the second isolation may be, for example, the length of the trench isolation in the second isolation divided by the total length of the second isolation. However, the first proportion and the second proportion are not limited to this. For example, they may also be relative to the depth of the longitudinal section of the semiconductor substrate. Taking the longitudinal section of the semiconductor substrate as a reference plane, the first proportion of the trench isolation in the first isolation may be, for example, the depth of the trench isolation in the first isolation divided by the total depth of the first isolation, and the second proportion of the trench isolation in the second isolation may be, for example, the depth of the trench isolation in the second isolation divided by the total depth of the second isolation. They are not listed one by one here.

[0035] More preferably, the trench isolation of the first isolation extends from the front and / or back side of the semiconductor substrate into the interior of the semiconductor substrate, and the trench isolation of the second isolation extends from the front and / or back side of the semiconductor substrate into the interior of the semiconductor substrate. The so-called horizontal plane relative to the semiconductor substrate shall refer to any surface (back side or front side) or a plane at any depth inside the semiconductor substrate. For example, for BDTI technology, the horizontal plane relative to the semiconductor substrate makes the length of the BDTI trench isolation of the first isolation shorter than the length of the BDTI trench isolation of the second isolation. For another example, for FDTI technology, the horizontal plane relative to the semiconductor substrate makes the length of the FDTI trench isolation of the first isolation shorter than the length of the FDTI trench isolation of the second isolation. It should be noted that the drawings in this patent are all based on square regular sub-pixels (such as Figure 2 , the so-called square and regular pixels should be pixels of the same size and shape and arranged in a uniform and regular manner, which also means that the width W and length L of the PDAF are roughly the same) arrangement, "the second ratio is larger than the first ratio", and in the optional embodiment included in the "second ratio is larger than the first ratio", it is preferred that "the length of the trench isolation of the first isolation is shorter than the length of the trench isolation of the second isolation". In the present invention, if irregular sub-pixels are considered, for example, when the PD sub-pixels are rectangular in shape as a whole, it should be required that "the length ratio occupied by the trench isolation of the second isolation is larger than the length ratio occupied by the trench isolation of the first isolation", and even at least 10% larger to ensure the distribution ratio of the trench isolation in the second isolation. However, no matter which pixel is targeted, the patterns of the first isolation and the second isolation listed in the drawings of the present invention should not be used as any limitation to the scope of the present invention. The concept of the present invention is to use ion implantation to achieve isolation through the first isolation as much as possible, and the second isolation to achieve isolation by using trench isolation as much as possible, so as to form an asymmetric isolation in the PDAF pixel, so as to obtain a great improvement in full well capacitance while taking into account the anti-crosstalk effect of isolation. As long as it is within the concept of the invention, it is within the scope of the present invention.

[0036] By setting the trench isolation in the first isolation to account for a first proportion, and the trench isolation in the second isolation to account for a second proportion, and the second proportion is greater than the first proportion, the application of trench isolation in the isolation between sub-pixels of the same phase of the PDAF pixel is reduced, which can effectively suppress crosstalk, improve the loss of pixel light input, and increase the full well capacity, thereby improving the performance of PDAF and the working performance of the sensor. In addition, the first isolation uses ion implantation to achieve isolation as much as possible, which can avoid or reduce the different masks required for setting different trench isolation offset degrees in the pixel array, so that the sensor performance can be improved while the sensor production cost can be greatly reduced.

[0037] Preferably, the second isolation formation comprises a combination of any one or more of the following structures: The first type, the second isolation in the thickness direction of the semiconductor substrate includes a first sub-isolation and a second sub-isolation; the first sub-isolation is a trench isolation formed by penetrating from the first surface of the semiconductor substrate, and the second sub-isolation is a trench isolation formed by penetrating from the second surface of the semiconductor substrate opposite to the first surface; preferably, the second isolation defined in the first type also includes that the first sub-isolation and the second sub-isolation are in contact; or there is a second preset distance between the first sub-isolation and the second sub-isolation. Preferably, ion implantation is also performed in the second preset distance between the first sub-isolation and the second sub-isolation to form the second sub-ion implantation isolation.

[0038] The second type is that the second isolation in the thickness direction of the semiconductor substrate includes a third sub-isolation; the third sub-isolation is a trench isolation formed by penetrating from the first surface of the semiconductor substrate to a second surface opposite to the first surface; The third type, the second isolation in the thickness direction of the semiconductor substrate includes a fourth sub-isolation and a first sub-ion injection isolation; the fourth sub-isolation is a trench isolation that penetrates from the semiconductor substrate and the second surface to a second surface opposite to the first surface at a first preset distance, and the first sub-ion injection isolation is an ion injection isolation located at a first preset distance formed by ion injection from the first surface of the semiconductor substrate relative to the position of the fourth sub-isolation.

[0039] Preferably, the first isolation formation comprises a combination of any one or more of the following structures: First, the first isolation in the thickness direction of the semiconductor substrate includes a third sub-ion implantation isolation, and the third sub-ion implantation isolation extends from any surface of the semiconductor substrate to the other surface; The second type, the first isolation in the thickness direction of the semiconductor substrate includes a fourth sub-ion implantation isolation and a plurality of fifth sub-isolation structures, the fourth sub-ion implantation isolation is an ion implantation isolation that penetrates from the first surface of the semiconductor substrate and is a preset third distance away from the second surface opposite to the first surface, and / or the fourth sub-ion implantation isolation is an ion implantation isolation that penetrates from the second surface of the semiconductor substrate and is a preset fourth distance away from the first surface opposite to the second surface, and / or the fourth sub-ion implantation isolation is an ion implantation isolation that is a preset fifth distance away from the first surface of the semiconductor substrate and a preset sixth distance away from the second surface opposite to the first surface, the fifth sub-isolation structure is a trench isolation formed by penetrating from the first surface of the semiconductor substrate, and / or the fifth sub-isolation is a trench isolation formed by penetrating from the second surface of the semiconductor substrate opposite to the first surface.

[0040] Preferably, for PDAF pixel modules at different positions in the pixel array, the first isolation is formed by at least partially utilizing ion implantation, so as to form first isolations with different offsets in PDAF pixel modules at different positions through a photomask. Preferably, the first area is an edge area of ​​the pixel array, and the second area is a central area of ​​the pixel array.

[0041] The following is an explanation based on some examples. It should be noted that the PDAF pixel examples involved in the present invention are only for illustrative purposes and are not intended to limit the scope. In particular, the description of the internal conditions of the PDAF pixel (such as the number and arrangement of sub-pixels in the PDAF pixel) other than isolation is not intended to limit the scope, because they are all part of the optional examples for explaining the isolation conditions in the PDAF pixel.

[0042] As a preferred example, the trench isolation in the first isolation accounts for a first proportion, the trench isolation in the second isolation accounts for a second proportion, and the second proportion is greater than the first proportion. Figure 2 An example of a PDAF pixel is shown, where Figure 2 (a) illustrates a transverse cross section of a PDAF pixel. Figure 2 (b) illustrates a longitudinal cross section of a PDAF pixel, Figure 2 (c) shows the front side of the PDAF pixel. Figure 2 (d) shows an example of the back side of a PDAF pixel. Figure 2 (a) ~ Figure 2As can be seen in (d), four photodiode sub-pixels 2 are arranged in the PDAF pixel in the semiconductor substrate 1, namely PD1, PD2, PD3, and PD4. The four photodiode sub-pixels 2 are arranged in a square 2*2 array, that is, the PDAF pixel has almost the same length L and width W. A number of color filters 3 cover the opening defined by the grid 5 and are arranged on the back of the semiconductor substrate 1. The microlens 4 is arranged on the color filter 3. The accompanying drawing shows that a microlens 4 is applied to at least four sub-pixels PD1, PD2, PD3, and PD4. In the accompanying drawing, sub-pixels PD1 and PD2 are used as sub-pixels that receive the first light of the same phase, and sub-pixels PD3 and PD4 are used as sub-pixels that receive the second light of the same phase. Sub-pixels PD1 and PD3 are used as sub-pixels that receive light of different phases, and sub-pixels PD2 and PD4 are also used as sub-pixels that receive light of different phases. Sub-pixels receiving light of the same phase or different phases may not be limited to this. In other optional examples, it is also preferred to use sub-pixels PD1 and PD3 as sub-pixels receiving light of the same phase, and sub-pixels PD2 and PD4 as sub-pixels receiving light of the same phase, so that sub-pixels PD1 and PD2 are used as sub-pixels receiving light of different phases, and sub-pixels PD3 and PD4 are also used as sub-pixels receiving light of different phases.

[0043] Attached Figure 2 (a) ~ Figure 2 As can be seen in (d), the first isolation between sub-pixels of the same phase is mainly achieved by the isolation 120 formed by ion implantation, and has a length L 10 The second isolation between sub-pixels receiving light of different phases is mainly achieved by FDTI physical isolation 130, having a length L 20 The attached figure shows the front and back of the PDAF pixel. The length L1 of the FDTI physical isolation 131 is much smaller than the length L2 of the FDTI physical isolation 132. That is, relative to the horizontal plane of the semiconductor substrate, the length L1 of the trench isolation 131 of the first isolation is shorter than the length L2 of the trench isolation 132 of the second isolation. The trench isolation in the first isolation accounts for a first ratio of L1 / L 10 , the trench isolation in the second isolation accounts for the second proportion L2 / L 20 , and the second ratio L2 / L 20 Ratio 1: L1 / L 10 As can be seen from the accompanying drawings, the first isolation and / or the second isolation further includes ion implantation isolation; wherein the ion implantation isolation ratio of the first isolation is (L 10 -L1) / L 10 ) is greater than the ion implantation isolation ratio of the second isolation ((L 20 -L2) / L 20 ).

[0044] In this embodiment, a smaller length L1 of the FDTI physical isolation 131 is illustrated. In other embodiments, the length L1 of the FDTI physical isolation 131 may even be 0. The length L1 of the FDTI physical isolation 131 being 0 means that the first isolation is completely achieved through ion implantation isolation.

[0045] Figure 2 Schematic diagram of the optimized structure of left-right splitting FDTI of the example. The 2×2 pixels in a specific area of ​​the pixel array are used as the PDAF implementation area, where FDTI is used to perform strong physical isolation between adjacent pixels on the left and right, and ion implantation is used to perform doping isolation between adjacent pixels above and below, and FDTI is used to further reduce potential charge crosstalk. Among them, PD1 and PD2 are used as left-position pixels, and PD3 and PD4 are used as right-position pixels. A very deep groove is etched in the body silicon between PD1 (or PD2) and PD3 (or PD4) using the front etching process, and a layer of high-k value material is deposited, and then a low-k value isolation material is filled in the groove. The high-k value material carries the opposite charge of the PD doping and the isolation material to form a strong isolation, ensuring that the photogenerated charges of PD1 (or PD2) and PD3 (or PD4) will not enter each other's area. The isolation effect is achieved by doping opposite charges between PD1 (or PD3) and PD2 (or PD4), and the isolation material is filled at the edge of the implanted isolation to assist the isolation effect. Since the doped regions are not physically isolated, their size and concentration are adjustable, so they compress the PD volume less, while the FDTI part can effectively split the light, thereby ensuring the splitting of light while improving the full well capacitance (FWC).

[0046] In this example, considering that the second isolation between sub-pixels receiving light of different phases needs to have higher requirements on optical and electrical isolation performance than the first isolation between sub-pixels receiving light of the same phase, the first isolation between sub-pixels receiving light of the same phase is realized by ion implantation as much as possible. On the one hand, it can avoid using trench isolation to occupy the area where the sub-pixel PD is arranged, so that the PD can be arranged in a larger area and the full-well capacitance of the PD can be improved. On the other hand, the isolation formed by ion implantation absorbs light weaker than the trench isolation, so that more photogenerated electrons can be generated, which can further improve the full-well capacitance of the PD from different angles.

[0047] As another preferred example of setting the trench isolation in the first isolation to account for the first proportion, the trench isolation in the second isolation to account for the second proportion, and the second proportion is greater than the first proportion, this example will use FDTI and BDTI technologies at the same time. For example, for the traditional 2×2 pixel, the orientation of its light collection can be fixed (the 2×2 pixel structure can be divided into a fixed left and right splitting structure or a fixed upper and lower splitting structure according to the orientation of the splitting. The splitting pixel uses trench isolation to achieve crosstalk suppression, and the sub-pixels receiving the same phase light are isolated by ion implantation as much as possible), so that the probability of the photon entering the middle of the interval entering the correct pixel is increased from the original 1 / 4 to 1 / 2, improving the difference in the amount of light entering the pixels caused by the previous solution. Similar asymmetric trench design can effectively expand the PD volume, thereby bringing about an increase in full well capacitance. In addition, compared with the pure FDTI in Example 1, since this example reduces the use of extremely deep trenches, the process difficulty and cost are reduced to a certain extent, making it more feasible than FDTI.

[0048] like Figure 3 , Figure 4 A PDAF pixel is exemplified, which not only combines the application of trench isolation and ion implantation isolation, but also designs trench isolation and ion implantation isolation in the thickness direction of the semiconductor substrate. Figure 3 (a) illustrates a transverse cross section of a PDAF pixel. Figure 3 (b) illustrates a longitudinal cross section of a PDAF pixel, Figure 3 (c) shows the front side of the PDAF pixel. Figure 3 (d) shows an example of the back side of a PDAF pixel. Figure 4 (a) ~ Figure 4 (d) Examples and Appendix Figure 3 (a) ~ Figure 3 (d) Example The difference is that the predetermined distance 140 between the FDTI physical isolation 130 and the BDTI physical isolation 110 is not provided with the ion implantation 121. In addition, Figure 3 , Figure 4 The rest of the situation is the same. Figure 3 (a) ~ Figure 3 (d) Attachment Figure 4 (a) ~ Figure 4 As can be seen in (d), some basic structures of PDAF pixels other than isolation are similar to those of the attached Figure 2 (a) ~ Figure 2 (d) The basic structures are consistent and will not be described in detail here.

[0049] Attached Figure 3 (a) ~ Figure 3It can be seen from (d) that the first isolation between sub-pixels receiving light of the same phase is mainly achieved by ion implantation isolation 120 formed by ion implantation, and the second isolation between sub-pixels receiving light of different phases is mainly achieved by FDTI physical isolation 130, BDTI physical isolation 110, and ion implantation isolation 121. Figure 3 As shown in (a), at a first depth from the back of the PDAF pixel into the semiconductor substrate, BDTI physical isolation 110 is used for isolation, and at a second depth from the front of the PDAF pixel into the semiconductor substrate, FDTI physical isolation 130 is used for isolation. There can be a preset distance between the BDTI physical isolation 110 and the FDTI physical isolation 130 to avoid excessively deep trench etching on both sides. At the preset distance position, ion implantation can be performed to form ion implantation isolation 121 to take into account the isolation effect and avoid excessively deep trench etching required for FDTI physical isolation and BDTI physical isolation on both sides, so that the PD can obtain a larger volume layout, which is beneficial to the improvement of the full well capacitance of the PD. Figure 3 (a) illustrates that the second isolation is mainly implemented by FDTI physical isolation 130, BDTI physical isolation 110, and ion implantation isolation 121. However, in other preferred embodiments, Figure 4 As shown in (a), there is no need to perform ion implantation isolation in a preset distance 140 between the FDTI physical isolation 130 and the BDTI physical isolation 110, thereby further improving the full-well capacitance of the PD. This is because although there is a preset distance 140 between the FDTI physical isolation 130 and the BDTI physical isolation 110, due to the influence of the relative end positions of the FDTI physical isolation 130 and the BDTI physical isolation 110 on the electric field, they can actually be electrically isolated at the preset distance 140. Therefore, when there is a preset distance 140 between the FDTI physical isolation 130 and the BDTI physical isolation 110, this area does not need to be isolated by ion implantation.

[0050] Attached Figure 3 (a) Attachment Figure 4 The examples in (a) all show that the opposite ends of the FDTI physical isolation 130 and the BDTI physical isolation 110 are not in contact. However, in some cases, the situation where the opposite ends of the FDTI physical isolation 130 and the BDTI physical isolation 110 are in contact is also within the scope of the present invention and will not be repeated here.

[0051] like Figure 3 (c) Figure 4 As shown in (c), on the front side of the PDAF pixel, the length L1 of the FDTI physical isolation 131 applied to the first isolation is much smaller than the length L2 of the FDTI physical isolation 132 applied to the second isolation, as shown in FIG. Figure 3 (d) Figure 4 As shown in (d), on the back of the PDAF pixel, the length of the trench isolation applied to the ion implantation isolation 120 for the first isolation is naturally much shorter than the length of the BDTI physical isolation 110 for the second isolation, that is, relative to the horizontal plane of the semiconductor substrate, the length of the trench isolation applied to the first isolation is shorter than the length of the trench isolation applied to the second isolation. Similarly, in this embodiment, the length L1 of the smaller FDTI physical isolation 131 is illustrated on the front of the PDAF pixel. In other embodiments, the length of the FDTI physical isolation 131 can even be 0, which means that the first isolation is completely achieved by ion implantation isolation.

[0052] This example includes a hybrid structure of two structures, FDTI and BDTI. Each structure can be divided into a fixed left-right splitting structure or a fixed upper-lower splitting structure according to the different splitting directions. The figure only illustrates the left-right splitting situation, but the upper-lower splitting structure is also within the scope of the present invention. Its principle is similar to that of the left-right splitting situation, and it will not be repeated here. When the second isolation is combined with the FDTI physical isolation and the BDTI physical isolation structure, the BDTI physical isolation can play the role of splitting, and the FDTI physical isolation can play the role of suppressing crosstalk.

[0053] For this hybrid structure, when performing the front process, ion implantation can be used to dope and isolate the first isolated area (weak isolation area). Then the FDTI physical isolation technology process is performed. Since the FDTI physical isolation does not play the role of light splitting, the semiconductor substrate silicon does not need to be completely carved, which reduces the process difficulty. Based on the original PD edge situation, the effective volume of the PD can be further expanded, thereby increasing the effective volume of the PD and improving the full well capacitance. Finally, the BDTI physical isolation technology process is performed, so the second isolated area (strong isolation area) is formed as follows Figure 3 (a) The structure of "FDTI-blank-BDTI" and Figure 4 (a) "FDTI-doped-BDTI" structure. In the thickness direction of the semiconductor substrate, changing the middle part of the second isolation region from physical isolation to doped isolation can improve the full well capacitance to a certain extent. In order to further improve the full well capacitance, it is preferred to remove the doped isolation and change it to an "FDTI-blank-BDTI" structure, such as Figure 4 As shown in (a), it may be the "FDTI-BDTI" structure.

[0054] It can be seen that this embodiment combines the application of BDTI, FDTI and even ion implantation in the second isolation to further improve the reduction of PD area brought about by the high aspect ratio etching required by the pure FDTI method in Example 1, thereby further improving the full well capacitance. This is because compared with the BDTI process, the physical isolation formed by FDTI due to process limitations is usually wider than the physical isolation formed by the BDTI process. If FDTI physical isolation is used more, it means that the PD area is more restricted.

[0055] As another preferred example of setting the trench isolation in the first isolation to account for a first proportion, the trench isolation in the second isolation to account for a second proportion, and the second proportion is greater than the first proportion, this example will use ion implantation isolation and BDTI technology for the first isolation at the same time. Figure 5 The figure shows an example of using both ion implantation isolation and BDTI technology for the first isolation. Since the other basic structural features except isolation are the same as the above examples, they will not be described in detail here. Figure 5 As shown in (c), the length of the trench isolation applied in the first isolation is shorter than the length of the trench isolation applied in the second isolation, that is, the length of the FDTI physical isolation 131 applied in the trench isolation of the first isolation is shorter than the length of the FDTI physical isolation 132 applied in the trench isolation of the second isolation. The difference between this example and Example 2 is that in this example, the first isolation also applies trench isolation, and the application of BDTI physical isolation is taken as an example. However, it can be understood that, under the condition of "the trench isolation in the first isolation is set to account for a first proportion, the trench isolation in the second isolation is set to account for a second proportion, and the second proportion is greater than the first proportion", all forms of the first isolation combination applying FDTI and / or BDTI are within the scope of the present invention, all forms such as any one or more combinations of the position and length, width and height dimensions involved in FDTI, the position and length, width and height dimensions involved in BDTI, etc.

[0056] In the attached figure of this example, the BDTI physical isolation is a cross-shaped BDTI with no connection in the middle in the PDAF pixel. Compared with Example 2, this structure can better suppress the crosstalk caused by different directions between 2×2 pixels. Since in this example, BDTI completely isolates the PD, the doping isolation between PDs, such as ion implantation isolation 120, does not need to be implanted very deeply, which reduces the process difficulty to a certain extent. Similarly, according to the requirement of fully improving the full well capacitance, the strong isolation required for the second isolation can choose the FDTI-(doped or undoped)-BDTI structure. Figure 5 (a) shows the FDTI isolation 130 and the BDTI physical isolation 110. As for the situation that doping can be performed between the FDTI isolation 130 and the BDTI physical isolation 110, please refer to the attached figure. Figure 3 The situation (a) will not be described here.

[0057] In order to further improve the full well capacitance, this example also further designs BDTI, such as Figure 6 (a) to (d) illustrate four structural forms of BDTI physical isolation in the concept of the present invention, but it should be understood that these illustrations are only for explanation of the principle and should not be interpreted as limiting the scope. Figure 6 As shown in (a), for exemplary sub-pixels PD1, PD2, PD3, and PD4, it is illustrated that the existing BDTI process usually forms the isolation therebetween together, that is, forming a longitudinal BDTI physical isolation 111 and a lateral BDTI physical isolation 112; in order to adapt to the concept of the present invention, the trench isolation in the first isolation accounts for a first proportion, the trench isolation in the second isolation accounts for a second proportion, and the second proportion is greater than the first proportion, Figure 6 (b) shows an example in which the isolation between the exemplary sub-pixels PD1 and PD2, and the isolation between PD3 and PD4 are completely formed by ion implantation, in the case of providing a vertical BDTI physical isolation 111. Figure 6 (a) Figure 6 (b) Example, the present invention further designs its BDTI physical isolation, such as Figure 6 (c) Figure 6 (d) As shown, Figure 6 In (c), BDTI physical isolation 113 is located between PD1 and PD3, BDTI physical isolation 115 is located between PD2 and PD4, BDTI physical isolation 114 is located between PD3 and PD4, and BDTI physical isolation 116 is located between PD1 and PD2. BDTI physical isolations 113, 114, 115, and 116 are not connected to each other, that is, they are not connected in the middle boundary area of ​​sub-pixels PD1, PD2, PD3, and PD4. Such a setting can also further improve the full well capacity without affecting the electrical isolation effect. This is because the ends of BDTI physical isolations 113, 114, 115, and 116 are very close to each other in the middle area, which can affect the nearby potential to achieve a relatively ideal isolation effect. Figure 6 As shown in (b), when ion implantation is applied to form isolation between PD3 and PD4 and between PD1 and PD2, the BDTI physical isolation 113 and BDTI physical isolation 115 are also disconnected to further increase the full well capacitance. Figure 6 (c) Figure 6 (d) illustrates that the lengths of the BDTI physical isolations 116 and 114 are shortened and located at different positions. In other optional embodiments, the aforementioned disconnected portions of the BDTI physical isolations proposed by the present invention, such as the middle region, may also be subjected to ion implantation for further isolation.

[0058] This example is a preferred example of applying the concept of setting the trench isolation in the first isolation to account for a first proportion, the trench isolation in the second isolation to account for a second proportion, and the second proportion being larger than the first proportion in a pixel array.

[0059] Since doping isolation is used between sub-pixels that receive light of the same phase, the first isolation can be adjusted as the area where the light is incident changes, which is something that FDTI physical isolation cannot do. When light is incident on the pixel array, the light received by the most central area is at the center (at the main optical axis). As the pixel deviates from the most central area, the incident light spot will also shift accordingly. For FDTI physical isolation technology, the shifted light spot will allow more photons to enter the PD on the shifted side, increasing the difference in light received by pixels in different directions, which will increase the probability of algorithm misjudgment; if the groove position is changed according to the light spot offset, it will bring more costs, and the light spot offset is usually tens of nanometers. Changing the layout and process based on this change is usually not worth the cost.

[0060] For at least part of the first isolation structure formed by ion implantation, if the light spot offset is to be considered, a preferred embodiment of the present invention will fine-tune the implantation and annealing parameters according to the maximum amount of the offset, thereby ensuring that the offset light can still be in the center position, so that it can be collected by PDs in different directions with equal probability. Figure 7 Schematic diagram showing that the length of the first isolated trench isolation under the offset light spot is shorter than the length of the second isolated trench isolation. PDAF pixels are applied to different areas of the pixel array. For comparison, Figure 7 (a) Figure 7 (b) illustrates the light distribution of two different PDAF pixels in the middle area of ​​the pixel array (a) and the edge area of ​​the pixel array (b) when the existing FDTI physical isolation is widely used in the first isolation and the second isolation, respectively. Figure 7 (a) Figure 7 (b) It can be seen that since the light spot in the edge area is obviously different from the light spot position in the middle area, the light spot is largely biased towards a certain sub-pixel, which will cause a large deviation in the detected phase difference and thus affect the imaging effect. Figure 7 A large amount of light is deflected to a single sub-pixel PD2 as shown in (b).

[0061] To solve similar Figure 7 (b) The problem presented in this example applies the concept of setting the trench isolation in the first isolation to account for a first proportion, the trench isolation in the second isolation to account for a second proportion, and the second proportion is greater than the first proportion. The isolation between the sub-pixels receiving the same phase light (i.e., the first isolation) is at least partially formed by ion implantation isolation, for example Figure 7 (a´), Figure 7(b´) illustrates that most of the middle of the first isolation is formed by ion implantation. The advantage of forming part of the second isolation by ion implantation isolation is that in addition to improving the full well capacitance of each sub-pixel, it is also convenient to adjust the position of the first isolation of the PDAF pixel in different areas of the pixel array. For example, considering the light spot conditions at different positions in the pixel array, the position of the first isolation is adjusted to minimize the difference in light received by sub-pixels that receive light of the same phase. Figure 7 (a') illustrates that the first isolation portion formed by ion implantation of the PDAF pixel located in the central area is disposed in the middle of the PDAF pixel. Figure 7 (b´) illustrates that the first isolation portion formed by ion implantation of the PDAF pixel located in the edge area is set deviated from the central position. The figure shows that it is set higher relative to the central position. However, this deviation is only an example. In actual situations, the first isolation portion formed by ion implantation can be reasonably set according to the actual light angle or light spot offset, which is within the scope of the present invention.

[0062] Ion implantation forms at least part of the first isolation, so that the trench isolation in the first isolation accounts for a first proportion, and the trench isolation in the second isolation accounts for a second proportion, and the second proportion is greater than the first proportion. In addition, ion implantation forms isolation and can avoid the process cost caused by using trench isolation. For example, when setting the first isolation of the offset situation at different positions of the pixel array, if the first isolation is to be realized by trench isolation, different masks are required for special process production, which will bring huge manufacturing costs. However, the present invention uses ion implantation to form at least part of the first isolation, and only needs an additional mask to purposefully dope the center of the PD edge for isolation. The first isolation at different positions can be flexibly set, which can not only avoid the high production cost caused by the adjustment of different isolation positions through the trench isolation process, but also improve the full well capacitance of the sub-pixel PD.

[0063] In a second aspect, the present invention proposes a pixel structure, which includes a pixel array, and the pixel array includes a plurality of PDAF pixel modules formed by applying the PDAF pixel isolation method described in any of the above embodiments. Preferably, the PDAF pixel module includes a number of first pixels receiving light of a first phase that is equal to the number of second pixels receiving light of a second phase. Exemplarily, the PDAF pixel module may include four 2*2 arranged sub-pixels; wherein the first isolation is applied between two adjacent first and second sub-pixels, and the second isolation is applied between the other two adjacent third and fourth sub-pixels.

[0064] In a third aspect, the present invention further provides an image sensor having the pixel structure involved in any of the aforementioned embodiments.

[0065] The basic concepts have been described above. Obviously, for those skilled in the art, the above detailed disclosure is only for example and does not constitute a limitation of the present invention. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements and corrections to the present invention. Such modifications, improvements and corrections are suggested in the present invention, so such modifications, improvements and corrections still belong to the spirit and scope of the exemplary embodiments of the present invention.

[0066] It should be understood that the embodiments described in the present invention are only used to illustrate the principles of the embodiments of the present invention. Other variations may also fall within the scope of the present invention. Therefore, as examples and not limitations, alternative configurations of the embodiments of the present invention may be considered consistent with the teachings of the present invention. Accordingly, the embodiments of the present invention are not limited to the embodiments explicitly introduced and described in the present invention.

Claims

1. A method for isolating PDAF pixels of an image sensor, characterized in that: The PDAF pixel module includes a plurality of sub-pixels, wherein a first isolation exists between sub-pixels of the same phase, and a second isolation exists between sub-pixels of different phases, wherein the trench isolation in the first isolation accounts for a first proportion, and the trench isolation in the second isolation accounts for a second proportion, and the second proportion is greater than the first proportion.

2. The method according to claim 1, characterized in that The second ratio is at least 10% greater than the first ratio.

3. The method according to claim 1 or 2, characterized in that: Taking the horizontal plane of the semiconductor substrate as a reference plane, the first ratio includes the ratio of the length of the trench isolation in the first isolation to the total length of the first isolation, and the second ratio includes the ratio of the length of the trench isolation in the second isolation to the total length of the second isolation.

4. The method according to claim 1, 2 or 3, characterized in that: Taking the longitudinal section of the semiconductor substrate as a reference plane, the first ratio includes the ratio of the depth of the trench isolation in the first isolation to the total depth of the first isolation, and the second ratio includes the ratio of the depth of the trench isolation in the second isolation to the total depth of the second isolation.

5. The method according to claim 1, characterized in that The first isolation and / or the second isolation further comprises ion implantation isolation; wherein the proportion of ion implantation isolation in the first isolation is greater than the proportion of ion implantation isolation in the second isolation.

6. The method according to claim 1, characterized in that in, When a plurality of sub-pixels are square and arranged in a uniform array, relative to a horizontal plane of the semiconductor substrate, a length of the first isolated trench isolation is shorter than a length of the second isolated trench isolation.

7. The method according to any one of claims 1 to 6, characterized in that: in, The trench isolation of the first isolation extends deep into the semiconductor substrate from the front side and / or the back side of the semiconductor substrate, and the trench isolation of the second isolation extends deep into the semiconductor substrate from the front side and / or the back side of the semiconductor substrate.

8. The method according to any one of claims 1 to 6, characterized in that: in, The second isolation formation includes any one or more of the following structures: The first type, the second isolation in the thickness direction of the semiconductor substrate includes a first sub-isolation and a second sub-isolation; the first sub-isolation is a trench isolation formed by a trench formed from a first surface of the semiconductor substrate, and the second sub-isolation is a trench isolation formed from a second surface of the semiconductor substrate opposite to the first surface; The second type is that the second isolation in the thickness direction of the semiconductor substrate includes a third sub-isolation; the third sub-isolation is a trench isolation formed by penetrating from the first surface of the semiconductor substrate to a second surface opposite to the first surface; A third type, the second isolation in the thickness direction of the semiconductor substrate includes a fourth sub-isolation and a first sub-ion implantation isolation; The fourth sub-isolation is a trench isolation extending from the second surface of the semiconductor substrate to a first surface opposite to the second surface at a first preset distance, and the first sub-ion implantation isolation is an ion implantation isolation located at a first preset distance formed by ion implantation from the first surface of the semiconductor substrate relative to the position of the fourth sub-isolation.

9. The method according to claim 8, characterized in that in, The first defined second isolation also includes that the first sub-isolation and the second sub-isolation are in contact with each other; or there is a second preset distance between the first sub-isolation and the second sub-isolation.

10. The method according to claim 9, characterized in that in, Ion implantation is also performed in a second preset distance between the first sub-isolation and the second sub-isolation to form a second sub-ion implantation isolation.

11. The method according to any one of claims 1 to 10, characterized in that: The first isolation formation includes a combination of any one or more of the following structures: First, the first isolation in the thickness direction of the semiconductor substrate includes a third sub-ion implantation isolation, and the third sub-ion implantation isolation extends from any surface of the semiconductor substrate to the other surface; The second type, the first isolation in the thickness direction of the semiconductor substrate includes a fourth sub-ion implantation isolation and a plurality of fifth sub-isolation structures, the fourth sub-ion implantation isolation is an ion implantation isolation that penetrates from the first surface of the semiconductor substrate and is a preset third distance away from the second surface opposite to the first surface, and / or the fourth sub-ion implantation isolation is an ion implantation isolation that penetrates from the second surface of the semiconductor substrate and is a preset fourth distance away from the first surface opposite to the second surface, and / or the fourth sub-ion implantation isolation is an ion implantation isolation that is a preset fifth distance away from the first surface of the semiconductor substrate and a preset sixth distance away from the second surface opposite to the first surface, the fifth sub-isolation structure is a trench isolation formed by penetrating from the first surface of the semiconductor substrate, and / or the fifth sub-isolation is a trench isolation formed by penetrating from the second surface of the semiconductor substrate opposite to the first surface.

12. The method according to any one of claims 1 to 11, characterized in that: For the PDAF pixel modules at different positions in the pixel array, the first isolation is formed at least partially by ion implantation, so as to form first isolations with different offsets in the PDAF pixel modules at different positions through one mask.

13. The method according to claim 12, characterized in that The first area is an edge area of ​​the pixel array, and the second area is a central area of ​​the pixel array.

14. A pixel structure, comprising a pixel array, characterized in that: The pixel array includes a plurality of PDAF pixel modules formed by applying the PDAF pixel isolation method according to any one of claims 1 to 13.

15. The pixel structure according to claim 14, characterized in that: The PDAF pixel module includes a number of first pixels receiving light of a first phase equal to a number of second pixels receiving light of a second phase.

16. The pixel structure according to claim 15, characterized in that: The PDAF pixel module includes four sub-pixels arranged in a 2*2 manner; the first isolation is applied between two adjacent first and second sub-pixels, and the second isolation is applied between the other two adjacent third and fourth sub-pixels.

17. An image sensor comprising the pixel structure according to any one of claims 14 to 16.

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