CMOS image sensor and manufacturing method thereof
By adjusting the ion beam current intensity, determining the target ion beam current intensity, and using higher beam current intensity for ion implantation, the problems of lattice damage and low production capacity in the prior art are solved, and the WP performance and capacity improvement of CMOS image sensors are achieved.
Patent Information
- Application Number
- CN202411268297.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-10
- Publication Date
- 2025-05-16
AI Technical Summary
The existing CMOS image sensors use lower beam intensity in the ion implantation process, resulting in increased lattice damage and poor product yield and performance. At the same time, the ion implantation time is extended, the production capacity is reduced, and the pollution of metal impurities increases, affecting device performance.
By adjusting the ion beam current intensity, forming a fitting curve, determining the target ion beam current intensity, using higher ion beam current intensity for ion implantation, reducing beam current density, reducing lattice damage, improving WP performance, and reducing ion implantation time and improving production capacity.
It significantly improves the WP performance of the CMOS image sensor, reduces lattice damage, shortens ion implantation time, improves wafer output, reduces metal impurity contamination, and improves device performance.
Smart Images
Figure CN120018606A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of semiconductor manufacturing, and in particular to a CMOS image sensor and a manufacturing method thereof. Background Art
[0002] With the continuous advancement of digital imaging technology, CMOS image sensors (CIS) have become the core component for image capture in modern electronic devices. Since CIS uses a special customized CMOS process, its manufacturing process includes many complex steps, and ion implantation is one of the key technologies.
[0003] Ion implantation is a doping technology that uses an ion implantation machine to ionize, separate, and accelerate (gain kinetic energy) doped atoms to form an ion beam that scans the wafer, thereby physically bombarding the wafer surface and injecting doped atoms into the wafer to change the electrical properties of the wafer. However, this process will inevitably damage the silicon lattice, thereby affecting product yield and product performance.
[0004] Existing research shows that the lower the beam intensity, the less damage to the lattice, and the fewer defects such as low white pixels (WP) of the image sensor. Therefore, existing technologies usually select a lower ion beam current intensity (also known as beam intensity) for ion implantation.
[0005] However, in the actual manufacturing of wafers, it is found that when a lower beam intensity is used for ion implantation, the effect of improving WP performance can no longer meet the development needs of the ever-increasing performance of semiconductor devices, and the lower beam intensity will also lead to a longer ion implantation time for a single wafer (Wafer), a lower wafer output per hour (wafer per hour, WPH), which is not conducive to improving equipment production capacity. In addition, the extension of ion implantation time will also aggravate the metal ion contamination of molybdenum (Mo), tungsten (W) and other metal ions caused by the corrosion of the chamber and components by the ion source gas, resulting in an increase in metal impurity contamination in the implanted wafer, which in turn produces more WP defects and affects device performance. Summary of the invention
[0006] The purpose of the present invention is to provide a CMOS image sensor and a manufacturing method thereof. Compared with the existing manufacturing process using low ion beam current intensity for ion implantation, the present invention uses a higher ion beam current intensity for ion implantation based on the demand for low beam current density, which causes less damage to the lattice, significantly improves the WP performance of the wafer surface, and at the same time, the higher ion beam current intensity reduces the implantation time and improves the production capacity.
[0007] To achieve the above object, the present invention first provides a method for manufacturing a CMOS image sensor, comprising the following steps:
[0008] Step S1, determining the target ion beam current intensity:
[0009] Adjusting the ion beam current intensity to obtain multiple sets of ion beam current intensities and corresponding beam current densities to form a fitting curve; determining the target ion beam current intensity according to the beam current density corresponding to the lowest point or the lower point of the fitting curve;
[0010] Step S2, providing a substrate having a pixel region;
[0011] Step S3, injecting ions into the pixel region of the substrate through an ion implantation process to form a doped region, wherein the ion implantation process uses the target ion beam current intensity for ion implantation.
[0012] Optionally, the target ion beam current intensity is 50 μA-300 μA.
[0013] Optionally, the target ion beam current intensity is 100 μA-200 μA.
[0014] Optionally, in step S1, the fitting curve is obtained under the conditions that the ion source and the injection energy are controlled to be the same.
[0015] Optionally, the ion beam current intensity is increased, and the ion beam scanning speed and beam size are increased synchronously to obtain a reduced beam current density, thereby determining the target ion beam current intensity.
[0016] Optionally, the ion beam current intensity is increased by 1 to 3 times.
[0017] Optionally, the implantation energy is 30 Kev-150 Kev.
[0018] Optionally, the doped region includes: an N-well region and / or a surface pinning region located above the N-well region.
[0019] Optionally, the ions include at least one of boron B, phosphorus P, arsenic As, boron fluoride BF2 or fluorine F.
[0020] Another aspect of the present invention provides a CMOS image sensor, which is manufactured by the aforementioned manufacturing method.
[0021] Compared with the prior art, the beneficial effects of the technical solution of the present invention include at least:
[0022] 1. In view of the common technical understanding that "the lower the beam intensity, the lower the damage to the lattice", the present invention has experimentally verified that the lower the beam intensity, the less damage to the lattice. And after a large number of experiments and statistical analysis, it was found for the first time that "the damage to the silicon lattice caused by ion implantation is proportional to the beam density of the ion beam. The smaller the beam density, the less damage the implanted ion beam causes to the silicon lattice, and the better the WP performance of the CMOS image sensor."
[0023] 2. Based on the above findings, the present invention provides a method for manufacturing a CMOS image sensor, including: adjusting the ion beam current intensity, obtaining multiple groups of ion beam current intensities and corresponding beam current densities, and forming a fitting curve; determining the target ion beam current intensity according to the beam current density corresponding to the lowest point or the lower point of the fitting curve; and then using the target ion beam current intensity to perform ion implantation on the pixel area of the substrate. Compared with the prior art, the beam current density of the ion beam implanted by the method of the present invention is lower, and during ion implantation, the number of ions received per unit area of the wafer is smaller, so the sputtering effect is weaker and the physical damage to the lattice is also smaller, thereby significantly improving the WP performance of the CMOS image sensor.
[0024] 3. The present invention has found that within a certain range, when the ion beam current intensity of the existing ion implantation machine is increased, the ion beam scanning speed and beam size are increased synchronously, and a reduced beam density can be obtained. Therefore, compared with the existing low ion beam current intensity (usually less than 50μA), the present invention increases the ion beam current intensity based on the demand for low ion beam current density, and the ion beam scanning speed and beam size are increased synchronously, so that the ion implantation time is reduced, which is not only conducive to improving the wafer output per hour, but also can reduce the metal impurity contamination in the implanted wafer, and further improve the WP performance of the CMOS image sensor.
[0025] 4. The method for determining the target ion beam current intensity in the present invention is simple and does not require a lot of manpower and material resources. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Figure 1 The present invention is a flow chart of a method for manufacturing a CMOS image sensor.
[0027] Figure 2 It is a fitting curve diagram in one embodiment of the present invention. DETAILED DESCRIPTION
[0028] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0029] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.
[0030] As described in the background technology, during the ion implantation process of the wafer, the ion beam physically bombards the surface of the wafer, thereby causing damage to the silicon lattice, resulting in defects such as low white point (WP) in the image sensor. The greater the number of defects, the greater the impact on the imaging capability of the image sensor, affecting the image output effect. To solve this problem, the prior art generally uses a lower beam intensity for ion implantation process, in order to reduce the damage to the silicon lattice caused by ion bombardment, so as to improve the WP performance of the image sensor.
[0031] However, after actual application, the inventors of the present application found that the ion implantation process in the pixel area of the wafer has a great influence on the WP performance of its surface, and the lower the beam intensity is, the better. When ion implantation is performed using the low beam intensity commonly used in the prior art, the image sensor still has many WP defects and cannot meet the application requirements. More importantly, in the study of the relationship between the ion implantation process and the WP performance of the image sensor, which controls other conditions unchanged and only changes the beam intensity, the present application found that compared with the number of WPs in image sensors manufactured with lower beam intensities, image sensors manufactured with relatively high beam intensities (within a certain range) have fewer WPs, but when the beam intensity exceeds a certain range, it will bring more WP defects again.
[0032] The above phenomenon attracted the attention of the inventors of the present application, and they conducted a lot of research on it, and finally found that: in the ion implantation process of the pixel area, under the same ion source and implantation energy conditions, within a certain range of beam intensity, when the beam intensity is increased, the beam size and the ion beam scanning speed increase synchronously, and a lower beam density can be obtained, and ultimately an image sensor with better WP performance is obtained; however, when the beam intensity is lower, the beam size and the ion beam scanning speed are also lower, and the beam density formed is not lower, and the WP performance of the obtained image sensor is poor.
[0033] In other words, the present invention found that the damage to the silicon lattice caused by ion implantation is proportional to the beam density of the ion beam. The smaller the beam density, the less damage the implanted ion beam causes to the silicon lattice, and the better the WP performance of the image sensor. More importantly, based on the need for low beam density, the present invention selects a higher beam intensity than the prior art for ion implantation. Therefore, under the condition that the dose requirement remains unchanged, the ion implantation time can be reduced, which is beneficial to the improvement of WPH. At the same time, the reduction of ion implantation time can also effectively reduce metal impurity contamination in the wafer, further improving WP performance.
[0034] Based on the above, the present invention proposes a method for manufacturing a CMOS image sensor, such as Figure 1 As shown, including:
[0035] Step S1, determining the target ion beam current intensity.
[0036] First, an ion implantation machine is provided. Before the ion implantation process is formally performed on the pixel area of the substrate, the target ion beam current intensity needs to be determined:
[0037] In this embodiment, Figure 2 As shown, under the same ion source and injection energy conditions, by adjusting the ion beam current intensity, multiple groups of ion beam current intensities (i.e., beam current intensities) and corresponding beam current densities are obtained, each dot represents a group of ion beam current intensities and corresponding beam current densities, and there is a one-to-one correspondence between the ion beam current intensity and the beam current density; a fitting curve is formed according to the multiple groups of ion beam current intensities and the corresponding beam current densities, and the fitting curve is as shown in FIG. Figure 2 The dotted line indicates where the center point is.
[0038] In some embodiments, the target ion beam current intensity is determined based on the beam density corresponding to the lowest point of the fitting curve, and the value of the target ion beam current intensity is expressed as x1; in other embodiments, the value of the adjacent ion beam current intensity x1 can also be used as the target ion beam current intensity.
[0039] It should be noted that the beam current density is calculated by the following formula:
[0040] Wherein, K is a constant coefficient greater than 0, and the ion charge number is the charge number carried by the ion.
[0041] It is particularly pointed out that the existing ion implantation machine can directly adjust the magnitude of the ion beam current intensity, but cannot directly adjust the ion beam scanning speed and the size of the beam current. However, the numerical values of these two variables can be directly read from the display screen of the ion implantation machine. The present invention has found through statistical analysis that in the existing ion implantation machine, when the ion beam current intensity used is lower, the beam current size and the ion beam scanning speed are also lower, and the ion beam current density formed is not lower; and within a certain range, when the ion beam current intensity is increased, the ion beam scanning speed and the beam current size are increased synchronously, and a reduced beam current density is obtained, which is determined as the target ion beam current intensity.
[0042] In some embodiments, the ion beam current intensity is increased by 1 to 3 times.
[0043] The ion implantation machine includes any one of a high energy ion implantation machine, a large beam current ion implantation machine or a medium beam current ion implantation machine.
[0044] In this embodiment, the ion implantation machine is a medium beam ion implantation machine; the ion source is an ionized phosphine, arsine or BF3 gas source, which ionizes the doping atomic groups to be implanted into ions, and accelerates them into an ion beam through an accelerating electric field; the implantation energy is 30Kev-150Kev. In some embodiments, the target ion beam current intensity is 50μA-300μA; in other embodiments, the target ion beam current intensity is 100μA-200μA.
[0045] Step S2, providing a substrate having a pixel region.
[0046] The substrate is used to form a device structure or a chip circuit.
[0047] The pixel area can be applied to a pixel device. The substrate also includes a peripheral circuit area. The peripheral circuit area may include a digital circuit and an analog circuit, etc. These belong to the conventional structure of an image sensor and will not be described in detail here.
[0048] In some embodiments, the material of the substrate includes: any one of silicon (Si), germanium (Ge), germanium silicon (GeSi), silicon carbide (SiC), gallium arsenide (GaAs) or gallium indium (GaIn), or other suitable materials for image sensors. The substrate can also be a composite structure such as a silicon substrate on an insulator surface or a substrate with an epitaxial layer grown on it. Those skilled in the art can select the required type of substrate according to needs, so the type of substrate should not limit the scope of protection of the present invention.
[0049] Step S3, injecting ions into the pixel region of the substrate through an ion implantation process to form a doped region, wherein the ion implantation process uses the target ion beam current intensity for ion implantation.
[0050] After determining the target ion beam current intensity, ion implantation is performed on the pixel region of the substrate using the target ion beam current intensity.
[0051] The ions are divided into P-type ions and N-type ions. By injecting P-type ions, a P-type region is formed in the pixel area of the substrate. The P-type region mainly conducts electricity through holes. The P-type ions include: at least one of boron (B), boron fluoride (BF2) or fluorine (F); by injecting N-type ions, an N-type region is formed in the pixel area of the substrate. The N-type region mainly conducts electricity through electrons. The N-type ions include: at least one of phosphorus (P) and arsenic (As).
[0052] The doped region includes: an N-well region and / or a surface pinning region located above the N-well region.
[0053] According to the results of the following Examples 1-2 and Tables 1 and 2, the number of WPs in the CMOS image sensor manufactured by the method provided by the present invention is significantly reduced compared to before optimization. The following is a detailed description of Examples 1-2:
[0054] Example 1
[0055] Step S1-1, providing a medium beam ion implantation machine. The implanted ions are As ions. Under the same ion source and implantation energy conditions, the ion beam current intensity is adjusted to obtain multiple sets of ion beam current intensities and corresponding beam current densities to form a fitting curve; and according to the beam current density corresponding to the lowest point or the lower point of the fitting curve, the target ion beam current intensity is determined to be 100 μA.
[0056] Step S1-2, providing a silicon substrate having a pixel region.
[0057] Step S1-3, implanting As ions into the pixel region of the silicon substrate through an ion implantation process to form a doped region, wherein the ion implantation process uses the target ion beam current intensity (100 μA) for ion implantation.
[0058] The subsequent semiconductor device manufacturing and performance testing were further completed, and the lower ion beam current intensity (50μA) used in the prior art before optimization was included as a comparison. The results are shown in Table 1. The number of low bright white points (WP) P50 of the product before optimization was 980, while the number of low bright white points (WP) P50 of the product after optimization (i.e., the manufacturing method of the present invention) was 650, a decrease of about 34%.
[0059] Table 1 Statistical comparison of the number of WPs in the CMOS image sensor prepared before and after optimization in Example 1
[0060] As ion beam current intensity WP P50 Before optimization (50μA) 980 After optimization (100μA) 650
[0061] Example 2
[0062] Step S2-1, providing a medium beam ion implantation machine. The implanted ions are BF2 ions. Under the same ion source and implantation energy conditions, the ion beam current intensity is adjusted to obtain multiple sets of ion beam current intensities and corresponding beam current densities to form a fitting curve; and according to the beam current density corresponding to the lowest point or the lower point of the fitting curve, the target ion beam current intensity is determined to be 150 μA.
[0063] Step S2-2, providing a silicon substrate having a pixel region.
[0064] Step S2-3, injecting BF2 ions into the pixel area of the silicon substrate through an ion implantation process to form a doped area, wherein the ion implantation process uses the target ion beam current intensity (150 μA) for ion implantation.
[0065] The subsequent semiconductor device production and performance testing were further completed, and the lower ion beam current intensity (50μA) used in the prior art before optimization was included for comparison. The results are shown in Table 2. The number of low white points (WP) P50 of the product before optimization was 3000, while the number of low white points (WP) P50 of the product after optimization was 1250, a decrease of about 60%.
[0066] Table 2 Statistical comparison of the number of WPs in the CMOS image sensor prepared before and after optimization in Example 2
[0067] <![CDATA[BF2 ion beam current intensity]]> WP P50 Before optimization (50μA) 3000 After optimization (150μA) 1250
[0068] It can be seen from the results of the above examples 1-2 that the lower the beam intensity, the less damage to the lattice. The target ion beam current intensity determined by the manufacturing method of the present invention is higher than that of the prior art, but the number of device WP is less. In addition, by increasing the ion beam current intensity, the ion implantation time can be reduced, and the process time of a single wafer is reduced, so the WPH increases and the production capacity is improved; at the same time, reducing the ion implantation time will also reduce the metal ion pollution such as molybdenum (Mo) and tungsten (W) caused by the ion source gas corroding the chamber and components, reduce the metal impurity pollution in the implanted wafer, further improve the WP performance of the image sensor, and ensure the device performance.
[0069] In summary, the present invention provides a method for manufacturing a CMOS image sensor. Compared with the existing method of ion implantation using a low ion beam current intensity, the present invention adopts a relatively higher ion beam current intensity based on the demand for low beam density, so that the beam density of the ion beam is smaller, thereby causing less damage to the silicon lattice, and the WP performance of the image sensor is significantly improved. In addition, the higher ion beam current intensity reduces the ion implantation time and improves production capacity.
[0070] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.
Claims
1. A method for manufacturing a CMOS image sensor, characterized in that: The following steps are involved: Step S1, determining the target ion beam current intensity: Adjusting the ion beam current intensity to obtain multiple sets of ion beam current intensities and corresponding beam current densities to form a fitting curve; determining the target ion beam current intensity according to the beam current density corresponding to the lowest point or the lower point of the fitting curve; Step S2, providing a substrate having a pixel region; Step S3, injecting ions into the pixel region of the substrate through an ion implantation process to form a doped region, wherein the ion implantation process uses the target ion beam current intensity for ion implantation.
2. The method for manufacturing a CMOS image sensor according to claim 1, wherein: The target ion beam current intensity is 50 μA-300 μA.
3. The method for manufacturing a CMOS image sensor according to claim 2, wherein: The target ion beam current intensity is 100 μA-200 μA.
4. The method for manufacturing a CMOS image sensor according to claim 1, wherein: In the step S1, the fitting curve is obtained under the conditions of controlling the ion source and the injection energy to be the same.
5. The method for manufacturing a CMOS image sensor according to claim 4, wherein: By increasing the ion beam current intensity, the ion beam scanning speed and the beam current size are increased synchronously, resulting in a reduced beam current density, thereby determining the target ion beam current intensity.
6. The method for manufacturing a CMOS image sensor according to claim 5, wherein: The ion beam current intensity is increased by 1 to 3 times.
7. The method for manufacturing a CMOS image sensor according to claim 4, wherein: The implantation energy is 30Kev-150Kev.
8. The method for manufacturing a CMOS image sensor according to claim 1, wherein: The doped region includes: an N-well region and / or a surface pinning region located above the N-well region.
9. The method for manufacturing a CMOS image sensor according to claim 1, wherein: The ions include at least one of boron B, phosphorus P, arsenic As, boron fluoride BF2 or fluorine F.
10. A CMOS image sensor, characterized in that: The CMOS image sensor is manufactured by the manufacturing method according to any one of claims 1 to 9.