A method for improving a grid structure of a back-illuminated image sensor
Patent Information
- Application Number
- CN202510339406.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-20
- Publication Date
- 2026-09-22
AI Technical Summary
[0003]然而，在所述栅格结构的制造过程中存在一些技术难题
[0028]本发明在衬底背面完成掩膜层刻蚀工艺后的清洁过程中，通入特定清洁气体，所述清洁气体能与刻蚀工艺产生的副产物(碳氟聚合物)发生反应，形成易通过湿法清洗去除的产物，避免了因过度刻蚀导致的凹坑缺陷，从而有利于提升背照式图像传感器的成像质量。然而，传统清洁气体(O2、N2)与刻蚀副产物会形成外表具有坚硬外壳而内部包含含氧、含氮等离子体的融合产物，在清洁过程以及后续湿法清洗工艺中，该融合产物会紧密附着于暴露的金属层表面而发生过度刻蚀，使得金属层表面出现凹坑缺陷，在后续的等离子体刻蚀工艺中，该凹坑缺陷被进一步加深，导致最终形成的相邻栅格结构之间的开口底部出现凹坑缺陷。
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Figure CN122803400A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of image sensor technology, and in particular to a method for improving the grid structure of a back-illuminated image sensor. Background Technology
[0002] In existing manufacturing processes for metal-oxide-semiconductor image sensors (CMOS image sensors, CIS), a grid structure capable of reflecting light is typically used to effectively reduce optical crosstalk between adjacent pixel units in back-illuminated image sensors. This grid structure is generally formed by etching and stacking multiple layers of dielectric and metal layers. This grid structure can effectively isolate incident light between adjacent pixel units, reducing optical crosstalk and thus improving the imaging quality of the image sensor.
[0003] However, some technical challenges exist in the manufacturing process of the grating structure. After the metal layer etching is completed, void defects often appear at the bottom of the openings between adjacent grating structures. These defects cause light to scatter and refract during propagation, resulting in optical crosstalk. Optical crosstalk reduces the resolution and contrast of the image sensor, causing problems such as blurring and color distortion, which greatly limits the further improvement of CIS product performance. Summary of the Invention
[0004] The purpose of this invention is to provide a method for improving the grid structure of a back-illuminated image sensor, thereby significantly reducing the pit defects at the bottom of the openings between adjacent grid structures, thus avoiding optical crosstalk and improving the imaging quality of the back-illuminated image sensor.
[0005] To achieve the above objectives, the present invention provides a method for improving the grid structure of a back-illuminated image sensor, comprising:
[0006] Step 1, providing a substrate, which includes opposing front and back sides;
[0007] Step 2: Form a mask layer on the metal layer on the back side of the substrate;
[0008] Step 3: Form multiple dielectric layers on the mask layer;
[0009] Step 4: Etch the multilayer dielectric layer and the mask layer sequentially to form a patterned mask layer and expose the metal layer;
[0010] Step 5: The cleaning gas reacts with the byproducts generated from etching the multilayer dielectric layer to form a product that is easily removed by cleaning.
[0011] Step 6: After cleaning the substrate, the metal layer is etched to form the grid structure of the back-illuminated image sensor.
[0012] Optionally, forming multiple dielectric layers on the mask layer includes:
[0013] An organic dielectric layer, a low-temperature oxide layer, and an anti-reflection layer are sequentially formed on the mask layer.
[0014] Optionally, in step 5, the cleaning gas includes a mixture of nitrogen-containing gas and hydrogen-containing gas, and an oxygen-containing gas.
[0015] Optionally, the nitrogen-containing gas comprises nitrogen; the hydrogen-containing gas comprises hydrogen; and the oxygen-containing gas comprises oxygen.
[0016] Optionally, the process conditions for introducing the cleaning gas include:
[0017] Apply radio frequency power, wherein the radio frequency power is 1800W to 2200W;
[0018] The chamber pressure is 900 mT to 1500 mT;
[0019] The flow rate of the oxygen-containing gas is 9000 sccm to 11000 sccm.
[0020] Optionally, the volume ratio of the hydrogen-containing gas in the mixture of nitrogen-containing gas and hydrogen-containing gas is 4% to 10%.
[0021] Optionally, in step 5, the temperature of the substrate surface is 60°C to 140°C.
[0022] Optionally, the substrate is placed on a platform in a reaction chamber. The platform includes a lifting component, which controls the relative distance between the substrate and the surface of the platform, so that the surface temperature of the substrate is 60°C to 140°C.
[0023] Optionally, the mask layer includes a silicon-based dielectric layer, which may be a single layer or a stacked structure.
[0024] Optionally, the silicon-based dielectric layer is a stacked structure composed of a silicon oxide layer, a silicon nitride layer, and a silicon oxide layer stacked sequentially.
[0025] Optionally, the metal layer is made of tungsten.
[0026] Optionally, the byproducts contain C, O, and F elements.
[0027] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:
[0028] In this invention, during the cleaning process after the mask layer etching process on the back side of the substrate, a specific cleaning gas is introduced. This cleaning gas reacts with the byproducts (fluorocarbon polymers) generated during the etching process to form products that are easily removed by wet cleaning, avoiding pit defects caused by over-etching and thus improving the imaging quality of back-illuminated image sensors. However, conventional cleaning gases (O2, N2) and etching byproducts form a fusion product with a hard outer shell and an interior containing oxygen- and nitrogen-containing plasma. During the cleaning process and subsequent wet cleaning processes, this fusion product adheres tightly to the exposed metal layer surface, causing over-etching and resulting in pit defects on the metal layer surface. In subsequent plasma etching processes, these pit defects are further deepened, leading to pit defects at the bottom of the openings between adjacent grid structures in the final formation.
[0029] Furthermore, during the cleaning process, this invention selects a specific cleaning gas combination—a mixture of nitrogen-containing and hydrogen-containing gases and oxygen-containing gas—instead of the traditional cleaning gas combination of nitrogen and oxygen. This effectively avoids the formation of fusion products—which have a hard outer shell but contain oxygen-containing and nitrogen-containing plasmas—that occur in traditional cleaning processes. Hydrogen-containing gas readily dissociates under the action of a radio frequency source, generating H-containing active particles. This invention utilizes these H-containing active particles to rapidly combine with nitrogen-containing and oxygen-containing plasmas, reducing the concentration of nitrogen-containing and oxygen-containing plasmas in the chamber. This slows down or prevents the fusion reaction between nitrogen-containing and oxygen-containing plasmas and fluoropolymers, thus avoiding the formation of these fusion products.
[0030] Furthermore, during the cleaning process, the present invention further slows down or prevents the fusion reaction of nitrogen-containing plasma, oxygen-containing plasma and fluoropolymer by reducing the temperature of the substrate surface to 60°C to 140°C, thereby further reducing the risk of a large number of pit defects. Attached Figure Description
[0031] Figure 1 This is a process flow diagram of a grid structure for improving a back-illuminated image sensor according to the present invention.
[0032] Figure 2 This is a partial cross-sectional schematic diagram of a substrate provided in step 1 of the present invention.
[0033] Figure 3 This is a partial cross-sectional schematic diagram of a substrate with a mask layer formed in step 2 according to the present invention.
[0034] Figure 4 This is a partial cross-sectional schematic diagram of a substrate with multiple dielectric layers formed in step 3 according to the present invention.
[0035] Figure 5This is a partial cross-sectional schematic diagram of a substrate with a preset photolithographic pattern formed in step 4.1 according to the present invention.
[0036] Figure 6 This is a partial cross-sectional schematic diagram of a substrate formed by sequentially etching an anti-reflection layer and a low-temperature oxide layer in step 4.2 according to the present invention.
[0037] Figure 7 This is a partial cross-sectional schematic diagram of a substrate formed by etching the organic dielectric layer in step 4.3 according to the present invention.
[0038] Figure 8 This is a partial cross-sectional schematic diagram of a substrate formed by etching the mask layer in step 4.4 according to the present invention.
[0039] Figure 9 This is a partial cross-sectional schematic diagram of a substrate with a patterned mask layer formed on its surface after a conventional cleaning process, resulting in a substrate with fusion products formed on its surface.
[0040] Figure 10 This is a schematic diagram of a partial cross-section of a substrate with metal layer pit defects.
[0041] Figure 11 This is a partial cross-sectional schematic diagram of a substrate with pit defects formed between the grid structures.
[0042] Figure 12 This is a partial cross-sectional schematic diagram of a product formed by removing the residual organic dielectric layer in step 5, which is easily removed by washing, according to the present invention.
[0043] Figure 13 This is a partial cross-sectional schematic diagram of a substrate that has undergone step 5 and a wet cleaning process according to the present invention.
[0044] Figure 14 This is a partial cross-sectional schematic diagram of a substrate with a lattice structure formed using the method of the present invention.
[0045] Explanation of reference numerals in the attached diagram:
[0046] Substrate 10
[0047] High dielectric constant material layer 20
[0048] First silicon oxide layer 30
[0049] First silicon nitride layer 40
[0050] Second silicon oxide layer 50
[0051] Titanium nitride layer 60
[0052] Metal layer 70
[0053] Mask layer 80
[0054] Third silicon oxide layer 81
[0055] Second silicon nitride layer 82
[0056] Fourth silicon oxide layer 83
[0057] Multilayer dielectric layer 90
[0058] Organic dielectric layer 91
[0059] Low-temperature oxide layer 92
[0060] Anti-reflective layer 93
[0061] 100 photoresist layers
[0062] fluoropolymer 110
[0063] Fusion Product 120
[0064] Metal layer pitting defect 130
[0065] 140 pit defects between grid structures
[0066] Grid structure 150
[0067] Product 160 is easily removed by washing. Detailed Implementation
[0068] 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.
[0069] 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.
[0070] 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.
[0071] As described in the background art, in the existing back-illuminated image sensor manufacturing process, it has been found that after the grating structure is formed by plasma etching, pit defects appear at the bottom of the openings formed between adjacent grating structures, which greatly affects the normal light propagation process and is not conducive to further improving the imaging quality of the image sensor.
[0072] This invention unexpectedly discovered that the pit defects mainly occur during the cleaning process after the mask layer etching process is completed above the substrate. The mask layer etching process is used to form a mask pattern containing several trenches, which are defined by sidewalls composed of mask layers and a bottom composed of metal layers. In the mask layer etching process, a patterned multilayer dielectric layer above the mask layer is used as a mask, and plasma etching with a fluorine-containing gas is performed. The multilayer dielectric layer includes an organic dielectric layer. The organic dielectric layer is typically thick to prevent it from being removed by plasma etching, which would result in an inaccurate mask pattern. Therefore, after the mask layer etching process is completed, a portion of the organic dielectric layer remains above the formed mask pattern. The main purpose of the cleaning process is to remove the remaining organic dielectric layer after the mask layer etching process. The process conditions used are high temperature (e.g., 275°C) with O2 and N2 for plasma etching.
[0073] However, this invention discovered that after the cleaning process, several pit defects appeared on the surface of the metal layer exposed by the mask layer etching process. The mechanism of these pit defects, analyzed by this invention, is as follows: because the etching gas used in the mask layer etching process is a fluorine-containing gas, and the organic dielectric layer is relatively thick, the fluorine-containing plasma easily forms large-mass etching byproducts with the organic dielectric layer, which readily fall onto the exposed metal layer surface. These etching byproducts are fluorocarbon polymers. During the subsequent cleaning process, O2 and N2 react rapidly with the fluorocarbon polymers to form a special fusion product. This invention's detection revealed that this fusion product has a hard outer shell (but does not completely seal the interior of the fusion product). During the formation of the shell, a small amount of free oxygen-containing and nitrogen-containing plasma are encapsulated within the fusion product. On the one hand, because the hard outer shell is difficult to remove by oxygen- or nitrogen-containing plasma etching, the fusion product easily adheres to the exposed metal layer surface. This causes the oxygen- and nitrogen-containing plasmas inside the fusion product to come into close contact with the metal layer surface, resulting in over-etching and damage to the metal layer surface, forming metal layer pit defects. On the other hand, the product with the hard outer shell is not easily removed by subsequent wet cleaning processes. As a result, the oxygen- and nitrogen-containing plasmas inside it continue to etch the metal layer surface during the wet cleaning process, further deepening the metal layer pit defects. During the subsequent process of forming a grid structure by etching the metal layer and other dielectric layers, these metal layer pit defects are further etched downwards, ultimately leading to pit defects at the bottom of the openings formed between adjacent grid structures. This increases the possibility of optical crosstalk and affects the imaging quality of the back-illuminated image sensor.
[0074] To address the aforementioned issues, this invention utilizes a specific cleaning gas to react with etching byproducts, forming products that are easily removed through cleaning. This avoids the formation of fused products with a hard outer shell but containing oxygen- or nitrogen-containing plasma internally. This effectively prevents oxygen- or nitrogen-containing plasma from coming into close contact with the metal layer surface and causing undesirable etching reactions, thereby ensuring that the metal layer surface remains undamaged. Consequently, it avoids pit defects at the bottom of openings formed between adjacent metal grid structures, thus improving the imaging quality of back-illuminated image sensors.
[0075] The present invention will be further described below with reference to the accompanying drawings.
[0076] like Figure 1 As shown, the present invention provides a method for improving the grid structure of a back-illuminated image sensor, comprising:
[0077] Step 1, provide a substrate, which includes a front side and a back side.
[0078] A partial cross-section of the substrate is shown in the figure. Figure 2 As shown. The substrate 10 includes, but is not limited to, a silicon substrate, a germanium substrate, a silicon-germanium substrate, silicon-on-insulator (SOI), or germanium-on-insulator (GOI). In the back-illuminated image sensor manufacturing process, the back side of the substrate 10, from bottom to top, also includes a high-k dielectric material layer 20, an ONO multilayer structure, a titanium nitride layer 60, and a metal layer 70 formed by different processes. In this embodiment, the ONO multilayer structure is formed by sequentially stacking a first silicon oxide layer 30, a first silicon nitride layer 40, and a second silicon oxide layer 50. The high dielectric constant material layer 20 reduces leakage current; the first silicon oxide layer 30, the first silicon nitride layer 40, and the second silicon oxide layer 50 provide insulation and isolation, preventing charge interference between different material layers; the titanium nitride layer 60 acts as a diffusion barrier layer, preventing metal elements in the metal layer 70 from diffusing into other layers; the metal layer 70, as a key component in the subsequently formed grid structure, reflects light not absorbed by the photodiode, allowing it to re-enter the photodiode and transmit electrical signals. In this embodiment, the substrate 10 is a silicon substrate, and the metal layer 70 is a tungsten metal layer. As an example, the thicknesses of the first silicon oxide layer 30, the first silicon nitride layer 40, the second silicon oxide layer 50, the titanium nitride layer 60, and the metal layer 70 formed on the back side of the substrate 10 are 1600 angstroms, 500 angstroms, 800 angstroms, 800 angstroms, and 3000 angstroms, respectively.
[0079] Step 2: Form a mask layer on the metal layer on the back side of the substrate.
[0080] Figure 3 A substrate structure with a mask layer 80 is shown. The mask layer 80 is used to precisely form a mask pattern with characteristic structures (e.g., openings or vias) on a metal layer 70, such that the metal layer 70 exposed by the characteristic structures of the mask pattern can be etched away to form a grid structure.
[0081] In some embodiments, the mask layer 80 includes a silicon-based dielectric layer, which is a single layer or a stacked structure. In this embodiment, the silicon-based dielectric layer is a stacked structure composed of a third silicon oxide layer 81, a second silicon nitride layer 82, and a fourth silicon oxide layer 83, wherein the thickness of the third silicon oxide layer 81 is 600 angstroms, the thickness of the second silicon nitride layer 82 is 1600 angstroms, and the thickness of the fourth silicon oxide layer 83 is 1000 angstroms.
[0082] Step 3: Form multiple dielectric layers on the mask layer.
[0083] The multilayer dielectric layer 90 is used as a hard mask in the subsequent etching process of the mask layer 80 to transfer the required mask pattern onto the mask layer 80.
[0084] In some embodiments, see Figure 4 The formation of a multilayer dielectric layer 90 on the mask layer 80 includes the sequential formation of an organic dielectric layer 91, a low-temperature oxide layer 92, and an anti-reflection layer 93 on the mask layer 80. In this embodiment, both the organic dielectric layer 91 and the anti-reflection layer 93 are made of carbon-containing organic materials, but their functions differ: they are used to absorb or reduce reflected light, allowing incident light to be better focused on the photoresist layer, thereby improving the accuracy of the formed photolithography pattern. The thickness of the anti-reflection layer is 670 angstroms. The organic dielectric layer 91 is used to ensure the stability of the hard mask structure during subsequent etching, accurately transferring the required mask pattern onto the mask layer 80. The thickness of the organic dielectric layer 91 is relatively thick, at 8000 angstroms. The low-temperature oxide layer 92 is used to protect the underlying organic dielectric layer 91 during the etching of the anti-reflection layer 93, further ensuring the stability of the hard mask structure. The thickness of the low-temperature oxide layer 92 is 650 angstroms.
[0085] Step 4: Etch the multilayer dielectric layer and the mask layer sequentially to form a patterned mask layer and expose the metal layer.
[0086] In some embodiments, step 4 includes:
[0087] Step 4.1: Form a preset photolithographic pattern on the anti-reflective layer.
[0088] A preset photolithographic pattern is formed by performing conventional exposure and development operations on the photoresist layer 100. The photolithographic pattern has several photolithographic trenches, which are defined by sidewalls composed of the photoresist layer 100 and a bottom composed of the anti-reflection layer 93, as shown in the structure... Figure 5 As shown.
[0089] Step 4.2: Etch the anti-reflection layer and the low-temperature oxide layer at the bottom of the photolithography trench in sequence.
[0090] In this embodiment, the etching gas used to etch the anti-reflection layer 93 includes C4F8, and the etching gas used to etch the low-temperature oxide layer 92 includes CHF3, CF4, and O2. The etched structure is as follows. Figure 6 As shown.
[0091] Step 4.3: Using the remaining photoresist layer, antireflection layer, and low-temperature oxide layer as a mask, etch the organic dielectric layer.
[0092] In this embodiment, the etching gas used to etch the organic dielectric layer 91 includes CO, O2, and N2. In this step, the remaining photoresist layer 100 is also etched away, resulting in the structure shown below. Figure 7 As shown.
[0093] Step 4.4: Using the remaining anti-reflective layer, low-temperature oxide layer, and organic dielectric layer as a mask, etch the mask layer to form a patterned mask layer and expose the metal layer.
[0094] In this embodiment, C4F8, CH2F2, and O2 are used as etching gases to etch the mask layer 80, and the etched structure is as follows. Figure 8 As shown. During the etching process, the remaining anti-reflective layer 93 and low-temperature oxide layer 92, due to their thinness (600 Å to 700 Å), were also etched away. The organic dielectric layer 91, due to its thickness (8000 Å), was thinned. After the etching of the mask layer 80 was completed, a portion of the organic dielectric layer 91 remained above the patterned mask layer 80, with the structure as shown. Figure 8 As shown. The residual organic dielectric layer 91 needs to be cleaned and removed.
[0095] During the etching process of the mask layer 80, the present invention unexpectedly discovered that, due to the relatively thick thickness of the organic dielectric layer 80, the etching gas (containing fluorine gas) and the organic dielectric layer 80 easily form large-mass etching byproducts, which fall onto the surface of the exposed metal layer 70. The etching byproducts are fluorocarbon polymers 110.
[0096] Step 5: The cleaning gas reacts with the byproducts generated from etching the multilayer dielectric layer to form a product that can be easily removed by cleaning.
[0097] As mentioned above, the existing process for removing the residual organic dielectric layer 91 involves plasma etching at a high temperature (275°C) using O2 and N2. Under these cleaning conditions, O2 and N2 readily react with the fluoropolymer, fusing to form a fusion product 120 with a hard outer shell and containing oxygen- and nitrogen-containing plasmas internally. See [link to previous text]. Figure 9 Due to the presence of a hard outer shell, the fusion product 120 is not easily removed by cleaning and adheres to the surface of the exposed metal layer 70. This causes the oxygen-containing and nitrogen-containing plasmas inside the fusion product 120 to come into close contact with the metal layer 70, continuously etching the surface of the metal layer 70 during the cleaning process and subsequent wet cleaning processes, resulting in pit defects 130 in the metal layer. (See [link to relevant documentation]). Figure 10 Under the influence of the metal layer pit defect 130, during subsequent metal layer etching processes, the metal layer pit defect 130 will be further etched downwards, ultimately resulting in an inter-grid structure pit defect 140 appearing at the bottom of the opening formed between adjacent grid structures 150. (See [link to relevant documentation]). Figure 11 .
[0098] In this invention, a cleaning gas capable of reacting with etching byproducts to form a product 160 that is easily removed by washing is used for cleaning, thereby preventing pit defects on the surface of the metal layer 70 and significantly reducing pit defects at the bottom of openings between adjacent grid structures. The cleaning gas comprises a mixture of nitrogen-containing and hydrogen-containing gases and an oxygen-containing gas. In some embodiments, the nitrogen-containing gas contains nitrogen; the hydrogen-containing gas contains hydrogen; and the oxygen-containing gas contains oxygen. This invention unexpectedly discovered that by using a mixture of nitrogen-containing and hydrogen-containing gases instead of conventional nitrogen, while removing residual organic dielectric layer 91, the fluoropolymer 110, the mixture of nitrogen-containing and hydrogen-containing gases, and oxygen can form a product 160 that is easily removed by washing (see...). Figure 12 This effectively avoids the risk of nitrogen, oxygen, and fluoropolymers reacting to form a fusion product 120 with a hard outer shell and containing nitrogen- and oxygen-containing plasma inside. Under the action of the radio frequency source, hydrogen-containing gas readily dissociates, generating H-containing active particles. These H-containing active particles are chemically reactive and can rapidly combine with nitrogen- and oxygen-containing plasmas to form substances such as hydroxides and nitrogen-containing hydrogen compounds. This reduces the concentration of nitrogen- and oxygen-containing plasmas in the chamber, thus hindering the fusion reaction between nitrogen- and oxygen-containing plasmas and fluoropolymers. Consequently, the fusion product 120 with a hard outer shell and containing nitrogen- and oxygen-containing plasma inside is less likely to form, making it easier to clean and remove. This avoids undesirable etching reactions with the surface of the metal layer 70.
[0099] In some embodiments, the volume ratio of the hydrogen-containing gas in the mixture of nitrogen-containing gas and hydrogen-containing gas is 4% to 10%. It is understood that the mixture of nitrogen-containing gas and hydrogen-containing gas can be introduced into the equipment chamber through the same gas pipeline, or different gas pipelines can be used to introduce the nitrogen-containing gas and hydrogen-containing gas into the equipment chamber separately; this invention does not impose any limitations on this.
[0100] In some embodiments, to further avoid the formation of fusion products 120, the process condition parameters during the cleaning process are optimized, including: setting the radio frequency power to 1800W to 2200W; setting the chamber pressure to 900mT to 1500mT; and setting the gas flow rate of oxygen-containing gas to 9000sccm to 11000sccm.
[0101] In some embodiments, the reaction rate of the fusion of nitrogen-containing plasma, oxygen-containing plasma, and etching byproducts can be further reduced by lowering the substrate surface temperature. The substrate surface temperature is preferably 60°C to 140°C. In this embodiment, the substrate 10 is placed on a platform in a reaction chamber. The platform includes a lifting component, which controls the relative distance between the substrate 10 and the platform surface, thereby maintaining the substrate surface temperature at 60°C to 140°C.
[0102] Step 6: After cleaning the substrate, the metal layer is etched to form the grid structure of the back-illuminated image sensor.
[0103] Figure 13 A partial cross-sectional schematic diagram of the substrate 10 after a wet cleaning process following step 5 is shown. In this invention, because step 5 causes the etching byproducts to react with the cleaning gas to form a product 160 that is easily removed by cleaning, the product on the surface of the metal layer 70 can be completely removed after a conventional wet cleaning process, effectively avoiding over-etching, thereby improving the flatness of the surface of the metal layer 70, and ensuring the etching uniformity in the subsequent etching process of the metal layer 70, ensuring that no pit defects appear at the bottom of the openings between adjacent grid structures 150.
[0104] Figure 14 A partial cross-sectional schematic diagram of the substrate 10 formed after plasma etching following step 5 and wet cleaning processes is shown. At this point, the grid structure of the back-illuminated image sensor is formed on the back side of the substrate. In this embodiment, the metal layer is made of tungsten.
[0105] In summary, this invention, during the cleaning process after mask layer etching on the back side of the substrate, uses a mixture of nitrogen-containing and hydrogen-containing gases, along with oxygen-containing gases, as cleaning gases instead of the traditional nitrogen and oxygen combination. This effectively avoids the formation of fusion products—hard on the outside and containing plasma—that result from the fusion of fluoropolymers generated during the etching of multiple dielectric layers with oxygen- and nitrogen-containing plasma. These fusion products tend to adhere tightly to the metal layer surface during traditional cleaning processes, leading to over-etching and the formation of metal layer pits. This invention utilizes hydrogen-containing gas to dissociate under radio frequency action, generating H-containing active particles that rapidly combine with oxygen- and nitrogen-containing plasma, reducing the concentration of oxygen- and nitrogen-containing plasma and thus slowing down or preventing the fusion reaction. Furthermore, by controlling the substrate surface temperature between 60°C and 140°C, the fusion reaction is further suppressed, significantly reducing metal layer pit defects. This provides a smooth surface for subsequent plasma etching processes, ensuring no pit defects at the bottom of adjacent grid structure openings and improving the imaging quality of back-illuminated image sensors.
[0106] 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 improving the grid structure of a back-illuminated image sensor, characterized in that, include: Step 1, providing a substrate, which includes opposing front and back sides; Step 2: Form a mask layer on the metal layer on the back side of the substrate; Step 3: Form multiple dielectric layers on the mask layer; Step 4: Etch the multilayer dielectric layer and the mask layer sequentially to form a patterned mask layer and expose the metal layer; Step 5: The cleaning gas reacts with the byproducts generated from etching the multilayer dielectric layer to form a product that is easily removed by cleaning. Step 6: After cleaning the substrate, the metal layer is etched to form the grid structure of the back-illuminated image sensor.
2. The method for improving the grid structure of a back-illuminated image sensor as described in claim 1, characterized in that, Forming multiple dielectric layers on the mask layer includes: An organic dielectric layer, a low-temperature oxide layer, and an anti-reflection layer are sequentially formed on the mask layer.
3. The method for improving the grid structure of a back-illuminated image sensor as described in claim 1, characterized in that, In step 5, the cleaning gas includes a mixture of nitrogen-containing gas and hydrogen-containing gas, and an oxygen-containing gas.
4. The method for improving the grid structure of a back-illuminated image sensor as described in claim 3, characterized in that, The nitrogen-containing gas contains nitrogen; the hydrogen-containing gas contains hydrogen; and the oxygen-containing gas contains oxygen.
5. The method for improving the grid structure of a back-illuminated image sensor as described in claim 3, characterized in that, The process conditions for introducing the cleaning gas include: Apply radio frequency power, wherein the radio frequency power is 1800W to 2200W; The chamber pressure is 900 mT to 1500 mT; The flow rate of the oxygen-containing gas is 9000 sccm to 11000 sccm.
6. The method for improving the grid structure of a back-illuminated image sensor as described in claim 4, characterized in that, The volume ratio of the hydrogen-containing gas in the mixture of nitrogen-containing gas and hydrogen-containing gas is 4% to 10%.
7. The method for improving the grid structure of a back-illuminated image sensor as described in claim 1, characterized in that, In step 5, the temperature of the substrate surface is 60℃~140℃.
8. The method for improving the grid structure of a back-illuminated image sensor as described in claim 7, characterized in that, The substrate is placed on a platform in a reaction chamber. The platform includes a lifting component, which controls the relative distance between the substrate and the surface of the platform, so that the surface temperature of the substrate is 60°C to 140°C.
9. The method for improving the grid structure of a back-illuminated image sensor as described in claim 1, characterized in that, The mask layer includes a silicon-based dielectric layer, which may be a single layer or a stacked structure.
10. The method for improving the grid structure of a back-illuminated image sensor as described in claim 9, characterized in that, The silicon-based dielectric layer is a stacked structure composed of a silicon oxide layer, a silicon nitride layer, and a silicon oxide layer stacked sequentially.
11. The method for improving the grid structure of a back-illuminated image sensor as described in claim 1, characterized in that, The metal layer is made of tungsten.
12. The method for improving the grid structure of a back-illuminated image sensor as described in claim 1, characterized in that, The byproducts contain C, O, and F elements.