A surface treatment method for improving the electric field uniformity of MIM capacitor upper and lower plates
Patent Information
- Application Number
- CN202510332865.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-19
- Publication Date
- 2026-09-22
AI Technical Summary
[0004]尽管现有MIM电容技术能够缓解满阱容量不足的问题，但其电极材料(如TiN)在制备过程中存在以下缺陷：TiN沉积完成后暴露于大气环境时，表面容易生成均匀性较差的自然氧化层(如TiOxNy)
[0030]This invention utilizes oxygen plasma oxidation treatment to form a first buffer layer of a first thickness on the surface of the lower electrode, overcoming the defects of the natural oxide layer at the interface between the lower electrode and the capacitor dielectric layer, as well as the potential for dangling bonds (which easily form leakage paths). Furthermore, this invention forms a second material layer of a second thickness on the capacitor dielectric layer, and through oxygen plasma oxidation treatment, converts the second material layer entirely into a second buffer layer. The roughness of the first buffer layer is significantly reduced relative to the lower electrode, and the roughness of the second buffer layer is significantly reduced relative to the upper electrode, resulting in a significant optimization of the overall performance of the MIM capacitor (e.g., leakage current, breakdown voltage, stability, etc.), thereby meeting the stringent requirements of high dynamic range (HDR) CMOS image sensors for low noise and high reliability. Furthermore, the present invention inserts an ultrathin (thickness less than 0.5 nm) first buffer layer and a second buffer layer between the capacitor dielectric layer and the plates (upper plate and lower plate), which can act as a physical barrier to prevent the metal plates (such as TiN) from directly contacting the high dielectric constant capacitor dielectric layer (such as HfO2), thereby reducing dislocations and microcracks at the interface caused by lattice mismatch or differences in thermal expansion coefficients.
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Figure CN122803296A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of CMOS image sensors and relates to a metal-insulator-metal (MIM) capacitor structure for use in high dynamic range (HDR) CMOS image sensors. Specifically, it relates to a surface treatment method for the upper and lower plates to improve the uniformity of the electric field of the MIM capacitor. Background Technology
[0002] With the miniaturization of mobile devices and the increasing demands for image quality, CMOS image sensors need continuous breakthroughs in core performance aspects such as dynamic range and signal-to-noise ratio (SNR). In bright environments, insufficient full-well capacity and pixel crosstalk are the main factors limiting SNR; in dark environments, dark noise and readout circuit noise become key bottlenecks. To improve dynamic range, traditional Standard Dynamic Range (SDR) technology has been gradually replaced by HDR technology because it cannot simultaneously capture details in both bright and dark areas. HDR significantly improves image realism and detail reproduction by expanding the color gamut and contrast.
[0003] In HDR implementation schemes, MIM capacitor structures are widely integrated into pixel circuits to improve full-well capacity. The principle is as follows: when the incident light intensity exceeds the pixel's charge carrying capacity, the MIM capacitor can temporarily store overflow charge, achieving full charge processing through two signal readouts, thereby avoiding the loss of highlight information due to overexposure. In existing technologies, the upper and lower plates of the MIM capacitor are typically fabricated using physical vapor deposition (PVD) titanium nitride (TiN) technology.
[0004] Although existing MIM capacitor technology can alleviate the problem of insufficient full-well capacity, its electrode materials (such as TiN) have the following defects during the preparation process: when TiN is exposed to the atmospheric environment after deposition, a poorly uniform natural oxide layer (such as TiO2) is easily formed on the surface. x N y This oxide layer increases the surface roughness of the electrode (Ra value increases), disrupts the uniformity of the electric field distribution, and forms localized sharp structures. The leakage current increases exponentially with decreasing oxide layer thickness, significantly increasing the risk of device leakage. Furthermore, native oxide layers have a low bandgap (e.g., TiO2). x N yTiN has a band gap of approximately 2.5-3.5 eV, significantly lower than that of high-quality insulating materials, and exhibits a high concentration of trapped states, which lowers the electron tunneling barrier and increases the electron tunneling probability. Furthermore, traditional TiN deposition processes rely on high-temperature annealing to improve crystallinity, but this high-temperature process can cause thermal stress damage to the insulating layer, limiting its application in low-temperature integration processes.
[0005] The aforementioned issues make it difficult for the leakage rate of existing MIM capacitors to meet the requirements of high dynamic range image sensors for low noise and high reliability, while also limiting the further improvement of full-well capacity. Summary of the Invention
[0006] The purpose of this invention is to solve the problems of leakage risk and limited full-well capacity optimization caused by electrode material oxidation in the prior art. It proposes a technical solution for surface treatment of the upper and lower plates. A first buffer layer and a second buffer layer treated with oxygen plasma are inserted at the contact interface between the lower plate, the upper plate and the capacitor dielectric layer, respectively, to achieve a uniform electric field to the greatest extent and reduce leakage. This effectively solves the technical problems of high leakage rate and limited full-well capacity of traditional MIM capacitors, and provides a reliable foundation for improving the performance of high dynamic range CMOS image sensors.
[0007] To achieve the above objectives, the present invention provides a method for surface treatment of upper and lower plates for improving the electric field uniformity of MIM capacitors, comprising:
[0008] Form the lower electrode plate;
[0009] The surface of the lower electrode plate is treated with oxygen plasma oxidation to form a first buffer layer of first thickness.
[0010] A capacitor dielectric layer is formed on the first buffer layer;
[0011] A material layer of second thickness is formed on the capacitor dielectric layer;
[0012] The material layer of the second thickness is completely converted into a second buffer layer by oxygen plasma oxidation treatment.
[0013] An upper electrode plate is formed on the second buffer layer;
[0014] The first buffer layer and the lower electrode plate contain the same metal elements in their composition.
[0015] The second buffer layer and the upper electrode plate contain the same metallic elements in their composition.
[0016] Optionally, the lower electrode plate is made of a metal nitride, including any one of titanium nitride, tantalum nitride, and tungsten nitride.
[0017] Optionally, the thickness of the lower electrode plate is 100 Å to 200 Å.
[0018] Optionally, the first thickness of the first buffer layer is 25 Å to 45 Å.
[0019] Optionally, the material of the capacitor dielectric layer includes at least one of silicon dioxide, silicon nitride, aluminum oxide, hafnium dioxide, zirconium dioxide, tantalum oxide, and titanium dioxide.
[0020] Optionally, the second thickness of the material layer is 25 Å to 45 Å.
[0021] Optionally, the upper electrode plate is made of a metal nitride, including any one of titanium nitride, tantalum nitride, and tungsten nitride.
[0022] Optionally, the thickness of the upper electrode plate is 300 Å to 500 Å.
[0023] Optionally, the lower electrode, the material layer, and the upper electrode are titanium nitride layers, and the first buffer layer and the second buffer layer are both titanium oxynitride layers.
[0024] Optionally, in steps 2 and 5, the process gas for the oxygen plasma oxidation treatment includes at least one of nitrous oxide, oxygen, and ozone.
[0025] Optionally, the flow rate of the process gas is 500 sccm to 27000 sccm.
[0026] Optionally, in steps 2 and 5, the gas pressure of the oxygen plasma oxidation process is 1 torr to 10 torr.
[0027] Optionally, in steps 2 and 5, the high-frequency radio frequency power used in the oxygen plasma oxidation treatment process is 100W to 3000W.
[0028] Optionally, in steps 2 and 5, the plasma treatment time of the oxygen plasma oxidation process is 1s to 60s.
[0029] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:
[0030] This invention utilizes oxygen plasma oxidation treatment to form a first buffer layer of a first thickness on the surface of the lower electrode, overcoming the defects of the natural oxide layer at the interface between the lower electrode and the capacitor dielectric layer, as well as the potential for dangling bonds (which easily form leakage paths). Furthermore, this invention forms a second material layer of a second thickness on the capacitor dielectric layer, and through oxygen plasma oxidation treatment, converts the second material layer entirely into a second buffer layer. The roughness of the first buffer layer is significantly reduced relative to the lower electrode, and the roughness of the second buffer layer is significantly reduced relative to the upper electrode, resulting in a significant optimization of the overall performance of the MIM capacitor (e.g., leakage current, breakdown voltage, stability, etc.), thereby meeting the stringent requirements of high dynamic range (HDR) CMOS image sensors for low noise and high reliability. Furthermore, the present invention inserts an ultrathin (thickness less than 0.5 nm) first buffer layer and a second buffer layer between the capacitor dielectric layer and the plates (upper plate and lower plate), which can act as a physical barrier to prevent the metal plates (such as TiN) from directly contacting the high dielectric constant capacitor dielectric layer (such as HfO2), thereby reducing dislocations and microcracks at the interface caused by lattice mismatch or differences in thermal expansion coefficients.
[0031] Furthermore, the present invention features a uniform and symmetrical arrangement of the upper and lower electrode plates, and a symmetrical arrangement of the first and second buffer layers, which facilitates the control of electric field uniformity, reduces electric field distortion caused by interface stress, and reduces leakage current. Attached Figure Description
[0032] Figure 1 This is a process flow diagram of a surface treatment method for the upper and lower plates of an MIM capacitor to improve the uniformity of the electric field.
[0033] Figure 2 This is a cross-sectional schematic diagram of the MIM structure formed during the surface treatment process of the upper and lower plates for improving the electric field uniformity of MIM capacitors according to the present invention, wherein a to f respectively illustrate the cross-sectional schematic diagrams of the device structure formed in steps S1 to S6.
[0034] Figure 3 This is a schematic diagram comparing the roughness of the titanium nitride film before and after it is converted into a titanium oxynitride film in the embodiment. In the diagram, a represents the material layer (titanium nitride film) and b represents the second buffer layer (titanium oxynitride film).
[0035] Attached image labels:
[0036] Lower electrode 10
[0037] First buffer layer 11
[0038] capacitor dielectric layer 20
[0039] Material layer 31'
[0040] Second buffer layer 31
[0041] Upper electrode plate 30. Detailed Implementation
[0042] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0043] In the description of this invention, it should be noted that the terms "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.
[0044] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.
[0045] To address the leakage risk and limited full-well capacity caused by electrode oxidation in existing MIM capacitors, this invention forms a buffer layer at the contact interface between the upper and lower electrodes and the capacitor dielectric layer to avoid defects caused by natural oxide layers that may form on the electrode surface. Specifically, the lower electrode surface is treated with oxygen plasma to form a dense and uniform first buffer layer. This not only overcomes the defects of natural oxide layers but also, due to its density and uniformity, results in fewer defects in the capacitor dielectric layer. A material layer is formed on the surface of the capacitor dielectric layer, which is then treated with oxygen plasma to form a second buffer layer. The upper electrode is then formed on the surface of the second buffer layer, resulting in a uniform and symmetrical arrangement of the upper and lower electrodes, better electric field uniformity, and reduced electric field distortion caused by interfacial stress. The following detailed description is provided in conjunction with the accompanying drawings.
[0046] Figure 1 This is a process flow diagram of a surface treatment method for the upper and lower plates of an MIM capacitor to improve the uniformity of the electric field. Figure 2 In order to be in the present invention Figure 1The schematic diagram of the cross-section of the device structure formed at each stage of the process flow.
[0047] like Figure 1 As shown, the present invention provides a method for surface treatment of upper and lower plates for improving the electric field uniformity of MIM capacitors, comprising:
[0048] Step S1, forming the lower electrode plate 10, as follows Figure 2 As shown in a.
[0049] The lower electrode 10 is connected to the floating diffusion (FD) region in the pixel circuit (not shown in the figure) and is responsible for receiving the photogenerated charge generated by the photodiode. When the incident light intensity exceeds the full-well capacity of the pixel, the overflow charge is temporarily stored in the MIM capacitor through the lower electrode, thereby expanding the dynamic range. The lower electrode 10 is made of metal nitride, including any one of titanium nitride, tantalum nitride, and tungsten nitride, and is usually prepared by physical vapor deposition (PVD) or chemical vapor deposition (CVD). The thickness of the lower electrode 10 is 100 Å to 200 Å.
[0050] Step S2 involves treating the surface of the lower electrode plate with oxygen plasma to form a first buffer layer 11 of a first thickness, such as... Figure 2 As shown in b.
[0051] The interface characteristics (e.g., surface roughness, crystallinity, etc.) between the lower electrode 10 and the capacitor dielectric layer directly affect the charge storage efficiency. For example, a lower surface roughness of the lower electrode can reduce the density of interface trapped states and lower leakage current. The purpose of step S2 is to avoid the leakage current problem caused by surface inhomogeneity and increased roughness resulting from natural oxidation of the lower electrode surface. Oxygen plasma oxidation treatment can oxidize the surface of the lower electrode 10 facing the capacitor dielectric layer (i.e., the upper surface of the lower electrode) to form a dense and uniform metal nitride oxide, which serves as a buffer layer.
[0052] In some embodiments, the process gas for the oxygen plasma oxidation treatment includes at least one of nitrous oxide, oxygen, and ozone. The flow rate of the process gas is 500 sccm to 27000 sccm. The gas pressure for the oxygen plasma oxidation treatment is 1 torr to 10 torr. The high-frequency radio frequency power used in the oxygen plasma oxidation treatment is 100W to 3000W. The plasma treatment time for the oxygen plasma oxidation treatment is 1s to 60s. The first thickness of the first buffer layer is 25 Å to 45 Å.
[0053] The first buffer layer 11 and the lower electrode plate 10 contain the same metal elements in their composition, and the first buffer layer 11 is made of metal nitride oxide formed by the oxidation of the metal nitride of the lower electrode plate.
[0054] Step S3, a capacitor dielectric layer 20 is formed on the first buffer layer 11, such as... Figure 2 As shown in c.
[0055] The capacitor dielectric layer 20 plays a core role in charge isolation, electric field modulation, and dynamic range extension in MIM capacitors. Its material selection (e.g., Al2O3 or HfO2), thickness control, and defect engineering (oxygen vacancy suppression) directly determine the capacitor's storage efficiency and reliability. By optimizing the performance of the capacitor dielectric layer, the signal-to-noise ratio (SNR) and image quality of high dynamic range (HDR) CMOS image sensors can be significantly improved. The material of the capacitor dielectric layer 20 requires high dielectric strength, low leakage current, and process compatibility. For example, at least one of silicon dioxide, silicon nitride, aluminum oxide, hafnium dioxide, zirconium dioxide, tantalum oxide, and titanium dioxide can be selected.
[0056] Existing technologies typically form a capacitor dielectric layer on the surface of the lower electrode. When the lower electrode has a high degree of roughness due to a natural oxide layer, it affects the uniformity of the capacitor dielectric layer formed on its surface, potentially leading to localized electric field concentration and increased leakage current. This invention forms a dense and uniform first buffer layer 11 on the lower electrode 10, and then forms a capacitor dielectric layer 20 on the first buffer layer 11. Because the first buffer layer avoids the formation of a natural oxide layer (as mentioned earlier, a natural oxide layer increases surface roughness), and the roughness of the first buffer layer itself is lower than that of the lower electrode surface, the capacitor dielectric layer formed by this invention has better uniformity than existing technologies, reducing leakage current defects.
[0057] Step S4, a material layer 31' of a second thickness is formed on the capacitor dielectric layer 20, such as... Figure 2 As shown in d.
[0058] The second thickness of the material layer 31' is 25 Å to 45 Å. The second thickness can be the same as or different from the first thickness. In this example, the second thickness is the same as the first thickness, which makes the upper and lower plates and the capacitor dielectric layer uniform and symmetrical, resulting in a better uniformity of the electric field formed during operation.
[0059] Step S5: The second thickness material layer 31' is subjected to oxygen plasma oxidation treatment, so that the second thickness material layer 31' is completely converted into the second buffer layer 31, as shown below. Figure 2 As shown in e.
[0060] In some embodiments, the process gas for the oxygen plasma oxidation treatment includes at least one of nitrous oxide, oxygen, and ozone. The flow rate of the process gas is 500 sccm to 27000 sccm. The gas pressure for the oxygen plasma oxidation treatment is 1 torr to 10 torr. The high-frequency radio frequency power used in the oxygen plasma oxidation treatment is 100W to 3000W. The plasma treatment time for the oxygen plasma oxidation treatment is 1s to 60s.
[0061] The second buffer layer 31 and the upper electrode plate 30 contain the same metal elements in their composition.
[0062] In some embodiments, the second buffer layer 31 is symmetrically arranged with the first buffer layer 11, and the materials and / or thicknesses are the same.
[0063] Step S6, an upper electrode plate 30 is formed on the second buffer layer 31, such as... Figure 2 As shown in f.
[0064] The upper electrode 30 is typically grounded or connected to a fixed voltage. It is necessary to ensure a uniform electric field distribution within the capacitor dielectric layer 20 to avoid localized breakdown. Therefore, the upper electrode 30 can be made of a material symmetrical to the lower electrode 10 to reduce electric field distortion caused by interfacial stress. As an example, the upper electrode 30 is made of a metal nitride, including any one of titanium nitride, tantalum nitride, and tungsten nitride. As an example, the thickness of the upper electrode 30 is 300 Å to 500 Å.
[0065] Example
[0066] A 2kA to 5kA SiO2 thin film is deposited on the wafer surface. A 185Å thick titanium nitride layer is then deposited on the SiO2 film as the lower electrode. The upper surface of the lower electrode is treated with oxygen plasma to form a 40Å titanium oxynitride thin film as the first buffer layer. Then, a 90Å aluminum oxide film is deposited on the surface of the first buffer layer as the capacitor dielectric layer. A titanium nitride thin film is deposited on the capacitor dielectric layer in two stages: first, a 40Å titanium nitride thin film is deposited as the material layer, and then the material layer is treated with oxygen plasma to convert the 40Å titanium nitride thin film into a 40Å titanium oxynitride thin film as the second buffer layer. A second 400Å titanium nitride thin film is deposited on the second buffer layer as the upper electrode. In this example, the process gas for the oxygen plasma treatment contains nitrous oxide gas at a flow rate of 18000 sccm, the high-frequency radio frequency power is 1800 W, and the gas pressure in the reaction chamber is 2.5 torr. The plasma treatment time is 5 seconds. Figure 3 As shown, the material layer is a titanium nitride thin film ( Figure 3 a) The surface roughness is 0.718 nm, while the second buffer layer titanium oxynitride (a) formed using the method of the present invention has a roughness of 0.718 nm. Figure 3(b) The surface roughness is 0.476 nm. It can be seen that the roughness is greatly reduced after the contact interface of the capacitor dielectric layer is changed from titanium nitride to titanium oxynitride.
[0067] In summary, this invention inserts a first buffer layer between the capacitor dielectric layer and the lower electrode, and a second buffer layer between the capacitor dielectric layer and the upper electrode. This not only avoids the defects of natural oxidation on the surface of the lower electrode, but also reduces the roughness of the interface between the electrode and the capacitor dielectric layer, resulting in better uniformity of the formed capacitor dielectric layer. Furthermore, the symmetrical arrangement of the upper and lower electrodes effectively controls the uniformity of the electric field. The overall performance of the MIM capacitor, such as leakage current, breakdown voltage, and stability, is significantly optimized, thereby meeting the stringent requirements of high dynamic range (HDR) CMOS image sensors for low noise and high reliability.
[0068] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.
Claims
1. A method for surface treatment of upper and lower plates for improving the uniformity of electric field in MIM capacitors, characterized in that, Include: Form the lower electrode plate; The surface of the lower electrode plate is treated with oxygen plasma oxidation to form a first buffer layer of first thickness. A capacitor dielectric layer is formed on the first buffer layer; A material layer of second thickness is formed on the capacitor dielectric layer; The material layer of the second thickness is completely converted into a second buffer layer by oxygen plasma oxidation treatment. An upper electrode plate is formed on the second buffer layer; The first buffer layer and the lower electrode plate contain the same metal elements in their composition. The second buffer layer and the upper electrode plate contain the same metallic elements in their composition.
2. The surface treatment method for the upper and lower plates of a MIM capacitor for improving the uniformity of the electric field as described in claim 1, characterized in that, The lower electrode plate is made of metal nitride, including any one of titanium nitride, tantalum nitride, and tungsten nitride.
3. The surface treatment method for the upper and lower plates of a MIM capacitor to improve the uniformity of the electric field as described in claim 1, characterized in that, The thickness of the lower electrode plate is 100A to 200A.
4. The surface treatment method for the upper and lower plates of a MIM capacitor to improve the uniformity of the electric field as described in claim 1, characterized in that, The first thickness of the first buffer layer is 25 Å to 45 Å.
5. The surface treatment method for the upper and lower plates of a MIM capacitor to improve the uniformity of the electric field as described in claim 1, characterized in that, The dielectric layer of the capacitor is made of at least one of silicon dioxide, silicon nitride, aluminum oxide, hafnium dioxide, zirconium dioxide, tantalum oxide, and titanium dioxide.
6. The surface treatment method for the upper and lower plates of a MIM capacitor to improve the uniformity of the electric field as described in claim 1, characterized in that, The second thickness of the material layer is 25 Å to 45 Å.
7. The surface treatment method for upper and lower plates for improving the electric field uniformity of MIM capacitors as described in claim 1, characterized in that, The upper electrode plate is made of metal nitride, including any one of titanium nitride, tantalum nitride, and tungsten nitride.
8. The surface treatment method for the upper and lower plates of a MIM capacitor to improve the uniformity of the electric field as described in claim 1, characterized in that, The thickness of the upper electrode plate is 300A to 500A.
9. The surface treatment method for the upper and lower plates of a MIM capacitor for improving the uniformity of the electric field as described in claim 1, characterized in that, The lower electrode, material layer, and upper electrode are titanium nitride layers, and the first buffer layer and the second buffer layer are both titanium oxynitride layers.
10. The method for surface treatment of upper and lower plates for improving the uniformity of electric field in MIM capacitors as described in claim 1, characterized in that, In steps 2 and 5, the process gas for the oxygen plasma oxidation treatment includes at least one of nitrous oxide, oxygen, and ozone.
11. The method for surface treatment of upper and lower plates for improving the electric field uniformity of MIM capacitors as described in claim 10, characterized in that, The flow rate of the process gas is 500 sccm to 27000 sccm.
12. The surface treatment method for upper and lower plates for improving the electric field uniformity of MIM capacitors as described in claim 10, characterized in that, In steps 2 and 5, the gas pressure of the oxygen plasma oxidation process is 1 torr to 10 torr.
13. The surface treatment method for the upper and lower plates of a MIM capacitor for improving the uniformity of the electric field as described in claim 1, characterized in that, In steps 2 and 5, the high-frequency radio frequency power used in the oxygen plasma oxidation process is 100W to 3000W.
14. The surface treatment method for the upper and lower plates of a MIM capacitor for improving the uniformity of the electric field as described in claim 13, characterized in that, In steps 2 and 5, the plasma treatment time of the oxygen plasma oxidation process is 1s to 60s.