Preparation method of image sensor

Abstract

The invention provides a preparation method of an image sensor, and the method comprises the steps: 1, placing a wafer in a reaction cavity, and enabling the wafer to comprise a substrate; step 2, introducing a cleaning reagent into the reaction cavity to remove a natural oxide layer formed on the surface of the substrate; and step 3, introducing an oxidation reagent into the reaction cavity so as to carry out oxidation treatment on the surface of the wafer, and forming a barrier oxidation layer on the surface of the substrate. According to the method, a traditional thermal oxidation process is replaced, the blocking oxidation layer is formed through the wet oxidation process, the uniformity of the surface of the formed blocking oxidation layer is good, the process steps are simple, extra cavity opening and conveying steps are not needed, the production efficiency is greatly improved, and the economic cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of image sensors, and particularly to a method for manufacturing an image sensor. Background Art

[0002] In the field of image sensor manufacturing, the patterning process is a crucial link, which plays a decisive role in the performance, integration degree of the chip, and the quality of the final product. With the continuous progress of semiconductor technology, chip manufacturing is developing towards higher precision and smaller size, which poses increasingly stringent requirements for the patterning process.

[0003] In the patterning process, photoresist coating (PR Coating) is an important step. Before photoresist coating, the state of the substrate surface has a significant impact on the coating quality of the photoresist and the accuracy of the subsequent lithography process. Good surface uniformity is beneficial to the uniform coating of the photoresist, which is conducive to the accurate transfer of the lithography pattern.

[0004] However, during the production, transportation, and storage of wafers, a natural oxide layer will inevitably form on the substrate surface. The internal structure of the natural oxide layer is usually relatively loose and the surface uniformity is poor. If photoresist is directly coated on it, it is very easy to cause the photoresist not to adhere firmly to the surface of the natural oxide layer, resulting in phenomena such as warping and peeling. Therefore, in the existing process, a wet cleaning process is required to remove the natural oxide layer. In the process, photoresist is usually not directly coated on the substrate surface after removing the natural oxide layer. This is because the substrate surface is usually hydrophobic, and it is difficult for the photoresist to wet and spread well on this surface, thus it is difficult to ensure good photoresist coating quality.

[0005] Currently, before photoresist coating, the wafer is processed by a furnace tube thermal oxidation process. By growing a barrier oxide layer on the substrate surface after removing the natural oxide layer, the surface uniformity and hydrophilicity of the substrate are improved. However, due to the relatively high temperature conditions of the furnace tube thermal oxidation process (generally 400°C - 1000°C), there is a risk of damaging the device functional layer under the substrate, which easily leads to a reduction in the yield of the image sensor; and the steps of this process are cumbersome, which is not conducive to improving production efficiency.

[0006] Therefore, before the patterning process in the image sensor manufacturing process, there is an urgent need for a process method for treating the substrate surface state that is friendly to the device functional layer and has high production efficiency. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for manufacturing an image sensor, and a barrier oxide layer is grown by a wet oxidation method to solve the problems that the furnace tube thermal oxidation process is not friendly to the device functional layer and the process operation flow is cumbersome.

[0008] To achieve the above object, the present invention provides a method for manufacturing an image sensor, comprising:

[0009] Step 1, placing a wafer in a reaction chamber, the wafer comprising a substrate;

[0010] Step 2, introducing a cleaning reagent into the reaction chamber to remove the native oxide layer formed on the surface of the substrate;

[0011] Step 3, introducing an oxidation reagent into the reaction chamber to oxidize the surface of the wafer and form a barrier oxide layer on the surface of the substrate.

[0012] Optionally, in step 3, the oxidation reagent comprises at least any one of the following a - d:

[0013] a. Ozone water; b. Hydrogen peroxide; c. A mixed solution of hydrogen peroxide and sulfuric acid; d. A mixed solution of ammonia water, hydrogen peroxide and water.

[0014] Optionally, in the mixed solution of hydrogen peroxide and sulfuric acid, the volume ratio of sulfuric acid to hydrogen peroxide is (1 - 10):1.

[0015] Optionally, in the mixed solution of ammonia water, hydrogen peroxide and water, the volume ratio of ammonia water, hydrogen peroxide and water is 1:(1 - 2):(20 - 150).

[0016] Optionally, in step 3, the temperature of the oxidation treatment is less than 150°C.

[0017] Optionally, when the oxidation reagent is a mixed solution of hydrogen peroxide and sulfuric acid, the temperature of the oxidation treatment is 80°C - 145°C.

[0018] Optionally, in step 3, the time of the oxidation treatment is 10s - 300s.

[0019] Optionally, the thickness of the barrier oxide layer is 10 Å - 200 Å.

[0020] Optionally, step 2 comprises:

[0021] Step 2.1, cleaning the wafer with a first cleaning reagent to remove impurities on the surface of the substrate and / or repair surface defects of the substrate;

[0022] Step 2.2, cleaning the wafer with a second cleaning reagent to remove the native oxide layer formed on the surface of the substrate.

[0023] Optionally, the first cleaning reagent comprises at least any one of hydrochloric acid, ammonia water, SC1, hydrogen peroxide, sulfuric acid, and ozone water.

[0024] Optionally, the second cleaning reagent contains HF.

[0025] Optionally, it is characterized in that step 2 further includes: looping step 2.1 to step 2.2 N times, where N is a positive integer, and step 2.1 and step 2.2 are not in a specific order.

[0026] Optionally, it further includes:

[0027] Step 4, forming a photolithography pattern on the surface of the substrate;

[0028] Step 5, performing an etching process on the wafer.

[0029] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0030] The present invention removes the natural oxide layer on the surface of the substrate through wet cleaning, and then forms a dense barrier oxide layer on the surface of the substrate through wet oxidation. On the one hand, the temperature conditions of the wet cleaning step (step 2) and the wet oxidation step (step 3) of the present invention are mild (less than 150 °C), which is friendly to the device functional layer below the substrate, avoiding the risk of thermal damage to the device functional layer caused by the high temperature conditions of the furnace tube thermal oxidation process, and improving the yield of the image sensor; on the other hand, the wet cleaning step and the wet oxidation step of the present invention can be carried out in the same reaction chamber, and wet oxidation can be immediately performed after wet cleaning, with a simple process flow, thus effectively shortening the preparation time and improving the production efficiency. Moreover, the steps of opening the chamber and transferring are omitted, avoiding the risk of reduced surface uniformity caused by the possible regrowth of other thin films (such as natural oxide layers) and the dropping of particulate matter on the surface of the substrate when contacting air during the transfer process, ensuring the cleanliness of the wafer surface, and being beneficial to ensuring the formation of a barrier oxide layer with excellent surface uniformity.

[0031] Furthermore, in the wet cleaning step (step 2) of the present invention, the wafer is treated with a first cleaning reagent and a second cleaning reagent. Among them, the first cleaning reagent is used to remove impurities on the surface of the substrate and / or repair the defects on the surface of the substrate, thereby improving the cleanliness and flatness of the surface of the substrate; the second cleaning reagent can react well with the surface of the substrate to completely remove the natural oxide layer on the surface of the substrate and improve the surface uniformity of the substrate. By adopting the method of cyclic cleaning, impurities are removed, defects are repaired, and the natural oxide layer is removed multiple times, further improving the improvement effect on the surface uniformity of the substrate, which is more conducive to the uniform growth of the subsequent barrier oxide layer, and then realizing the uniform coating of photoresist. Description of the Drawings

[0032] Figure 1 It is a process flow chart of a method for manufacturing an image sensor according to the present invention.

[0033] Figure 2 Partial cross-sectional view of a wafer with a native oxide layer formed according to the present invention.

[0034] Figure 3 Partial cross-sectional view of a wafer with the native oxide layer removed according to the present invention.

[0035] Figure 4 Process flow chart of a method for manufacturing an image sensor including an improved step 2 according to the present invention.

[0036] Figure 5 Partial cross-sectional view of a wafer with a barrier oxide layer formed according to the present invention.

[0037] Figure 6 Process flow chart of another method for manufacturing an image sensor according to the present invention.

[0038] Figure 7 Partial cross-sectional view of a wafer after being processed in step 4 according to the present invention.

[0039] Figure 8 Partial cross-sectional view of a wafer after being processed in step 5 according to the present invention.

[0040] Figure 9 Comparison chart of key dimension data of the opening structures of the wafers prepared in Comparative Examples 1-2 and Examples 1-4 according to the present invention.

[0041] Figure 10 Comparison chart of the yield data of the wafers prepared in Comparative Examples 1-2, Example 1, and Example 5 according to the present invention.

[0042] Figure 11 Comparison chart of the low-bright white pixel data of the wafers prepared in Comparative Examples 1-2, Example 1, and Example 5 according to the present invention.

[0043] Explanation of the reference numerals in the drawings:

[0044] Substrate 10

[0045] Functional layer 20

[0046] Native oxide layer 30

[0047] Barrier oxide layer 40

[0048] Photoresist layer 50

[0049] Lithographic trench 60

[0050] Opening structure 70. Detailed description of the invention

[0051] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0052] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0053] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0054] As used herein, "surface uniformity" refers to the degree of uniformity of the physical and chemical properties of the material surface, reflecting the flatness, consistency, and uniform distribution of physical and chemical properties of the surface at the micro or macro scale.

[0055] As used herein, "A" has the same meaning as angstrom and is a length unit in chip manufacturing. 1 A is equal to 1×10 -10 m.

[0056] As used herein, "photoresist coating quality" refers to a comprehensive evaluation of various performances such as the uniformity of photoresist (photolithography resist) coating on the substrate surface, thickness consistency, adhesion, and surface flatness. The photoresist coating quality directly affects the accuracy and reliability of the subsequent patterning process and is one of the key factors to ensure the success of image sensor manufacturing.

[0057] Before the patterning process in the image sensor manufacturing process, good photoresist coating quality is crucial for accurate photolithographic pattern transfer. As described in the background art, an attempt is made to use a furnace tube thermal oxidation process to form a barrier oxide layer on the substrate surface to improve the surface uniformity of the substrate, thereby improving the subsequent photoresist coating quality. This method includes the following steps:

[0058] Step S1, remove the native oxide layer formed on the surface of the substrate using a conventional wet cleaning process.

[0059] Step S2, form a screen oxide on the surface of the substrate using a furnace thermal oxidation process.

[0060] In the step S2, the furnace thermal oxidation process includes: transferring the wafer into the furnace tube, setting the temperature of the furnace tube chamber to 400°C to 1000°C, and after the temperature of the furnace tube chamber reaches the set temperature, introducing an oxidizing gas (for example, oxygen), and the oxidizing gas reacts with the surface of the substrate of the wafer to form a screen oxide. After testing and verification, compared with the native oxide layer, the screen oxide has a dense structure, better surface uniformity, and the screen oxide has hydrophilicity compared with the pure substrate surface, which is beneficial to the spreading of photoresist. Therefore, the formation of the screen oxide is beneficial to improving the quality of subsequent photoresist coating.

[0061] However, the inventors found that the furnace thermal oxidation process faces the following technical difficulties:

[0062] (1) Since the equipment for performing the wet cleaning process and the furnace thermal oxidation process are two different semiconductor devices, after the wafer is wet cleaned, it needs to go through the processes of opening the chamber and transferring to reach the furnace tube chamber. During the transfer process, it is very likely that other thin films will regrow on the surface of the substrate and particulate matter will fall onto the surface of the substrate due to contact with air, resulting in uneven growth of the screen oxide, causing defects such as local protrusions or depressions on the surface of the screen oxide, thereby affecting the surface uniformity of the screen oxide and being not conducive to photoresist coating.

[0063] (2) The furnace thermal oxidation process needs to go through at least operation processes such as preheating, oxidation, and annealing, and the process flow is cumbersome, greatly reducing the production efficiency.

[0064] (3) Since the process temperature of the furnace thermal oxidation process is relatively high (400°C to 1000°C), it is easy to have an adverse effect on the functional layer under the substrate. For example, it may cause metal elements to diffuse from the doped area to other areas, and the device may be deformed.

[0065] To solve the above problems, the present invention adopts a wet oxidation process to replace the above-mentioned furnace tube oxidation process, enabling the steps of removing the native oxide layer and forming the barrier oxide layer to share a reaction chamber. Thus, there is no need to open the chamber, eliminating the transfer process. After completing the step of removing the native oxide layer, the step of forming the barrier oxide layer can be immediately executed, not only shortening the process time and thereby improving production efficiency, but also avoiding the problems of the substrate surface uniformity degradation caused by the regrowth of other thin films (e.g., the reformation of the native oxide layer) and / or particulate contamination during the transfer process, which is conducive to the uniform growth of the barrier oxide layer during the wet oxidation process, improving the surface uniformity of the barrier oxide layer, and further enhancing the subsequent photoresist coating quality. Further, the temperature of the wet oxidation process of the present invention is relatively low, protecting the functional layer under the substrate from high-temperature damage. Furthermore, the present invention can achieve the removal and / or repair of substrate surface defects multiple times by alternately circulating the first cleaning reagent and the second cleaning reagent multiple times, thereby maximizing the improvement of the substrate surface uniformity and ultimately forming an ideal barrier oxide layer.

[0066] As Figure 1 shown, the present invention provides a method for manufacturing an image sensor, comprising:

[0067] Step 1: Place a wafer in a reaction chamber, where the wafer includes a substrate.

[0068] The method provided in this embodiment is applicable to the back-side illumination (BSI) process of the wafer, but the application scope of the present invention is not limited thereto. As Figure 2 shown, the wafer includes a substrate 10, and the substrate includes opposite front and back sides. On the front side of the substrate, the front-side illumination (FSI) process has been completed, forming a functional layer 20, in which a plurality of microelectronic devices and circuit structures (not shown in the figure) are integrated. Since the back side of the substrate is exposed to the air, the back side of the substrate reacts with oxygen in the air to form a native oxide layer 30. In this embodiment, the substrate 10 is a silicon substrate, and the material of the native oxide layer 30 is silicon dioxide.

[0069] Step 2: Introduce a cleaning reagent into the reaction chamber to remove the native oxide layer formed on the surface of the substrate.

[0070] The thickness and quality of the formed native oxide layer 30 are uncertain, so it is necessary to perform cleaning and removal to prepare a substrate surface state with excellent uniformity for the subsequent wet oxidation step (Step 3). Figure 3 shows a partial cross-sectional schematic diagram of the wafer after removing the native oxide layer in Step 2.

[0071] In some embodiments, as Figure 4 shown, in order to further prepare a substrate surface state with excellent uniformity for the subsequent wet oxidation step (Step 3), Step 2 further includes:

[0072] Step 2.1, introducing a first cleaning reagent into the reaction chamber to clean the wafer, so as to remove impurities on the substrate surface and / or repair defects on the substrate surface.

[0073] Step 2.2, introducing a second cleaning reagent into the reaction chamber to clean the wafer, so as to remove the native oxide layer formed on the substrate surface.

[0074] Before removing the native oxide layer 30, the impurities on the substrate surface and / or the defects on the substrate surface can be removed first by introducing the first cleaning reagent, so as to improve the cleanliness and flatness of the substrate surface and reduce the interference of impurities and defects on the step of removing the native oxide layer. Therefore, after being treated with the first cleaning reagent, the subsequently introduced second cleaning reagent can fully contact the surface of the native oxide layer and etch the native oxide layer 30 uniformly, so as to remove the native oxide layer 30 completely and uniformly. The impurities include metal particles, particulate matters, and organic matters remaining from the previous process, and the defects include pits caused by uneven growth of the native oxide layer 30.

[0075] In some embodiments, the first cleaning reagent includes at least any one of hydrochloric acid, ammonia water, SC1, hydrogen peroxide, sulfuric acid, and ozone water. The method for removing the native oxide layer 30 formed on the substrate surface is wet etching. The second cleaning reagent can be an HF solution, a mixed solution of NH3 and HF, or a mixed solution of NF3 and HF.

[0076] First of all, each of the above first cleaning reagents can remove the impurities on the substrate surface. The hydrochloric acid can react with metal particles, so it can be used to remove the metal particles remaining on the substrate surface. The ammonia water can make the organic matters containing acidic functional groups such as carboxyl groups and phenolic hydroxyl groups more likely to detach from the substrate surface through acid-base neutralization reactions. Hydrogen peroxide, sulfuric acid, and ozone water have oxidizing properties and can react with particulate matters, organic matters, etc. to form substances that are easily soluble in water, which are then removed by cleaning. SC1 includes ammonia water and hydrogen peroxide. When using SC1 for cleaning, ammonia water and hydrogen peroxide act synergistically to change the chemical states of the substrate surface and the impurity surface, making both the substrate surface and the impurity surface exhibit electronegativity, so that repulsion between the same sexes occurs between them, promoting the removal of impurities.

[0077] Secondly, it can be understood that due to the uneven growth of the native oxide layer 30, pits are likely to appear on the native oxide layer 30 on the substrate surface. The thickness of the native oxide layer 30 at the pit defects is relatively thin or the substrate surface is exposed, resulting in over-etching during the subsequent removal of the native oxide layer 30. For example, HF in the second cleaning reagent contacts the substrate surface prematurely or directly, damaging the substrate surface. Therefore, before step 2.2, the present invention unexpectedly discovers that the defects of the native oxide layer 30 can be repaired to a certain extent by using a first cleaning reagent with oxidizing properties, thereby avoiding the over-etching phenomenon in step 2.2. Since the SC1, hydrogen peroxide, sulfuric acid, and ozone water all have certain oxidizing properties and can contact the materials on the substrate surface to undergo oxidation reactions, they can repair the existing incomplete native oxide layer to form a native oxide layer 30 with a flat surface, which is beneficial for the second cleaning reagent to etch the native oxide layer uniformly in step 2.2 without prematurely or directly contacting the substrate surface, thereby further improving the uniformity of the substrate surface.

[0078] In some embodiments, to further improve the uniformity of the substrate surface, step 2 further includes N cycles of steps 2.1 to 2.2, where N is a positive integer, and steps 2.1 and 2.2 are not in a specific order. In the N cycles, the first cleaning reagent continuously removes impurities and / or repairs defects, and the second cleaning reagent uniformly and thoroughly removes the native oxide layer. Thus, even if there is a remaining native oxide layer or a newly formed oxide layer after the first cycle, it can be further removed in subsequent cycles, continuously improving the cleanliness and flatness of the substrate surface.

[0079] Step 3: Introduce an oxidation reagent into the reaction chamber to oxidize the surface of the wafer and form a barrier oxide layer on the substrate surface.

[0080] After the wafer is processed by the above step 2, it already has a substrate surface state with excellent surface uniformity, which is beneficial for the uniform formation of the barrier oxide layer 40. Figure 5FIG. 0 shows a partial cross-sectional schematic view of a wafer formed with a barrier oxide layer through step 3. The introduced oxidation reagent can uniformly undergo an oxidation reaction with the substrate surface having excellent surface uniformity, thereby forming a barrier oxide layer 40 with more uniform thickness and quality on the entire substrate surface. In some embodiments, the oxidation reagent includes at least any one of the following a-d: a. ozone water; b. hydrogen peroxide; c. a mixed solution of hydrogen peroxide and sulfuric acid; d. a mixed solution of ammonia water, hydrogen peroxide and water. Among them, the ozone water is a solution formed by dissolving ozone in deionized water, with a concentration of 20 ppm to 100 ppm; in b, c and d, the concentration of hydrogen peroxide is 30%, and the concentration of sulfuric acid is 98%; in the mixed solution of hydrogen peroxide and sulfuric acid, the volume ratio of sulfuric acid to hydrogen peroxide is (1-10):1; in the mixed solution of ammonia water, hydrogen peroxide and water, the volume ratio of ammonia water, hydrogen peroxide and water is 1:(1-2):(20-150).

[0081] When the above oxidation reagent is used to oxidize the substrate surface, the temperature of the oxidation treatment is less than 150°C, and the time of the oxidation treatment is 10 s to 300 s. In some embodiments, when a mixed solution of hydrogen peroxide and sulfuric acid is used as the oxidation reagent, in order to increase the oxidation reaction rate, the mixed solution of hydrogen peroxide and sulfuric acid can be preheated to 80°C to 145°C before being introduced into the reaction chamber, thereby increasing the concentration of active oxygen generated by the decomposition of hydrogen peroxide. In other embodiments, when ozone water, hydrogen peroxide or a mixed solution of ammonia water, hydrogen peroxide and water is used as the oxidation reagent, the temperature of the solution used is less than 50°C.

[0082] In some embodiments, the thickness of the formed barrier oxide layer 40 is measured by slicing test to be 10 Å to 20 Å.

[0083] In some embodiments, the oxidation treatment method includes: spraying the oxidation reagent onto the substrate surface through a spray head in the reaction chamber, or immersing the wafer in an oxidation reagent storage tank in the reaction chamber.

[0084] Therefore, the method provided by the present invention compared with the traditional furnace tube thermal oxidation process:[[]]

[0085] (1) The step of forming the barrier oxide layer can share a reaction chamber with the step of removing the native oxide layer, eliminating the traditional chamber opening and transfer processes. After removing the native oxide layer by wet cleaning, the wet oxidation step can be immediately performed, thus avoiding the reduction of the surface cleanliness and flatness of the substrate caused by the regrowth of other thin films or particulate contamination on the substrate surface due to contact with air during the transfer process. Furthermore, the high cleanliness and high flatness of the substrate surface are ensured, which is beneficial to improving the surface uniformity of the barrier oxide layer formed on the substrate surface subsequently. Moreover, since the chamber opening and transfer processes are eliminated and steps such as reaction chamber preheating and annealing are not required, the process time is effectively reduced, which is beneficial to improving production efficiency.

[0086] (2) The flexibility of the process steps is greatly improved. Before the step of forming the barrier oxide layer, the first cleaning reagent and the second cleaning reagent can be alternately and cyclically introduced. By treating the surface of the wafer with the first cleaning reagent multiple times, the purpose of completely removing the impurities on the substrate surface and repairing the defects on the substrate surface can be achieved; in the case where the surface of the native oxide layer is improved, the second cleaning reagent can be used to uniformly etch the native oxide layer, avoiding phenomena such as over-etching, thereby further improving the surface uniformity of the substrate after removing the native oxide layer.

[0087] (3) The process temperature (less than 150 °C) of the method for forming the barrier oxide layer is much lower than the temperature of the traditional furnace thermal oxidation process (400 °C - 1000 °C), thus effectively avoiding damage to the functional layer below the substrate caused by high temperature.

[0088] In some embodiments, as Figure 6 shown, the present invention further includes:

[0089] Step 4, forming a photolithography pattern on the substrate surface.

[0090] As Figure 7 shown, for the wafer processed through Steps 1 to 3, a patterning process is performed. A photoresist is coated on the substrate surface formed with the barrier oxide layer 40 to form a photoresist layer 50. After conventional exposure and development processes, a preset photolithography pattern is formed. The "photolithography pattern" includes a plurality of photolithography trenches 60, and the photolithography trenches 60 are defined by the sidewalls composed of the photoresist layer 50 and the bottom composed of the barrier oxide layer 40.

[0091] Step 5, performing an etching process on the wafer.

[0092] As Figure 8 shown, using the photolithography pattern as a mask, an etching process is performed to transfer the photolithography pattern to the substrate 10 to form a substrate pattern, and the substrate pattern includes a plurality of opening structures 70 for subsequent processes.

[0093] In the BSI process of existing image sensors, at least two patterning processes are required. Therefore, the method of the present invention can be used before these two patterning processes, so as to achieve multiple purposes of ensuring excellent surface uniformity of the substrate, improving device yield and production efficiency at the same time.

[0094] The present invention will be further described below in conjunction with comparative examples and examples. In the following comparative examples and examples, for wafers of different production batches provided in the comparative examples and examples, they are all produced by the same front-end process.

[0095] Comparative Example 1

[0096] Provide wafers of the first batch (Lot 1).

[0097] Take several wafers from the first batch of wafers and perform the following patterning process pretreatment:

[0098] Step S101, place the wafer in a reaction chamber, and the wafer includes a silicon substrate.

[0099] Step S102, introduce HF into the reaction chamber, wet-etch to remove the natural oxide layer formed on the surface of the substrate, and then open the chamber to take out the wafer.

[0100] Step S103, transfer the wafer into a furnace tube, introduce O2 at 800°C, and the O2 reacts with the surface of the substrate to form a barrier oxide layer.

[0101] Step S104, perform the first patterning process: coat a photoresist on the surface of the substrate to form a photoresist layer, and after conventional exposure and development, form a lithography pattern; perform an etching process on the wafer to form a plurality of opening structures on the surface of the substrate.

[0102] Before the subsequent second patterning process, the wafer is also processed by the above steps S101 to S103, and then the second patterning process is performed by step S104.

[0103] Comparative Example 2

[0104] The difference between this comparative example and Comparative Example 1 is that the wafers to be processed are several wafers from the second batch (Lot 2) of wafers.

[0105] Example 1

[0106] Take several wafers from the second batch (Lot 2) of wafers and perform the following processing:

[0107] Step 101, place the wafer in a reaction chamber, and the wafer includes a silicon substrate.

[0108] Step 102: Sequentially introduce the following reagents into the reaction chamber: a mixed solution of H2SO4 and H2O2, HF, ozone water, HF, SC1, HF, HCl. Use the above reagents to sequentially treat the surface of the silicon substrate to prepare a substrate surface state with excellent surface uniformity for subsequent processes.

[0109] Step 103: Introduce normal-temperature ozone water into the reaction chamber to oxidize the substrate surface for 100 s, and form a barrier oxide layer on the substrate surface.

[0110] Step 104: Perform the first patterning process: coat photoresist on the substrate surface to form a photoresist layer. After conventional exposure and development, form a photolithography pattern; perform an etching process on the wafer to form a number of opening structures on the substrate surface.

[0111] Before the subsequent second patterning process, the wafer is also processed using the above steps 101 to 103, and then the second patterning process is performed using step 104.

[0112] Example 2

[0113] The difference between this example and Example 1 is that several wafers from the second batch (Lot 2) are taken. Only before the first patterning process, steps 101 to 103 are used to form a barrier oxide layer, and before the second patterning process, the existing method (steps S101 to S103) is still used to form a barrier oxide layer.

[0114] Example 3

[0115] The difference between this example and Example 1 is that several wafers from the second batch (Lot 2) are taken. Only before the second patterning process, steps 101 to 103 are used to form a barrier oxide layer, and before the first patterning process, the existing method (steps S101 to S103) is still used to form a barrier oxide layer.

[0116] Example 4

[0117] The difference between this example and Example 1 is that the oxidation reagent introduced into the reaction chamber in step 103 is different. Several wafers from the second batch (Lot 2) are taken. In step 103, normal-temperature hydrogen peroxide is introduced into the reaction chamber to oxidize the substrate surface for 100 s, and a barrier oxide layer is formed on the substrate surface.

[0118] Example 5

[0119] The difference between this example and Example 1 is that the wafers to be processed are several wafers from the third batch (Lot 3).

[0120] Figures 9 to 11 In this case, the wafer ID on the abscissa refers to the wafer identification, and each data point in the figure represents a wafer.

[0121] Figure 9 It shows a data graph of the critical dimension (CD) of the opening structure at the same position formed by the wafers prepared in Comparative Example 1, Comparative Example 2 and Examples 1-4 after measurement. It can be clearly seen that whether the method of the present invention is used only before the first patterning process (Examples 2 and 3) or before both patterning processes (Examples 1 and 4), after the patterning process, the CD of the formed opening structure is similar to that of the traditional process (Comparative Example 1 and Comparative Example 2), which proves that the method of the present invention still maintains a good CD control level.

[0122] Figure 10 It shows a data graph of the wafer yield obtained by measuring the yield of the wafers prepared in Comparative Example 1, Comparative Example 2 and Examples 1 and 5. It can be clearly seen that the overall yield of the wafers prepared by the method of the present invention is relatively good and has no adverse effect on the wafer yield.

[0123] Figure 11 It shows a data graph of the low-brightness white pixel (WP) obtained by measuring the low-brightness WP of the wafers prepared in Comparative Example 1, Comparative Example 2 and Examples 1 and 5. It can be clearly seen that the method of the present invention can produce wafers with a relatively low low-brightness WP, which further proves that the barrier oxide layer prepared by the method of the present invention can meet the requirement of a relatively low low-brightness WP and can ensure the low-brightness WP performance of the device.

[0124] In summary, the present invention removes the natural oxide layer on the substrate surface by wet cleaning, and then forms a dense barrier oxide layer on the substrate surface by wet oxidation. The temperature conditions of the wet cleaning and wet oxidation steps are mild (less than 150 °C), which are friendly to the device functional layer under the substrate, avoiding the risk of thermal damage to the device functional layer caused by the high-temperature thermal oxidation process, and improving the yield of the image sensor. In addition, the wet cleaning and wet oxidation steps can be carried out in the same reaction chamber, the process flow is simple, effectively shortening the preparation time, improving the production efficiency, and eliminating the steps of opening the chamber and transferring, avoiding the risk of reducing the surface uniformity caused by the possible contact with air during the transfer process and the regrowth of other thin films and the dropping of particulate matter on the substrate surface, ensuring the cleanliness of the wafer surface, which is beneficial to ensuring the formation of a barrier oxide layer with excellent surface uniformity, and then realizing the uniform coating of photoresist.

[0125] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be construed as a limitation of the present invention. After those skilled in the art have read the above content, various modifications and alternatives to the present invention will be obvious. Therefore, the scope of protection of the present invention shall be defined by the appended claims.

Claims

1. A method for preparing an image sensor, characterized in that: Include: Step 1, placing a wafer in a reaction chamber, wherein the wafer includes a substrate; Step 2, introducing a cleaning agent into the reaction chamber to remove a natural oxide layer formed on the surface of the substrate; Step 3, introducing an oxidizing agent into the reaction chamber to oxidize the surface of the wafer and form a barrier oxide layer on the surface of the substrate.

2. The method for preparing an image sensor according to claim 1, wherein: In step 3, the oxidizing agent comprises at least one of the following ad: a. Ozone water; b. Hydrogen peroxide; c. A mixed solution of hydrogen peroxide and sulfuric acid; d. A mixed solution of ammonia water, hydrogen peroxide and water.

3. The method for preparing an image sensor according to claim 2, wherein: In the mixed solution of hydrogen peroxide and sulfuric acid, the volume ratio of the sulfuric acid to the hydrogen peroxide is (1-10):

1.

4. The method for preparing an image sensor according to claim 2, wherein: In the mixed solution of ammonia water, hydrogen peroxide and water, the volume ratio of ammonia water, hydrogen peroxide and water is 1:(1-2):(20-150).

5. The method for preparing an image sensor according to claim 1, wherein: In step 3, the temperature of the oxidation treatment is less than 150°C.

6. The method for preparing an image sensor according to claim 5, wherein: When the oxidizing agent is a mixed solution of hydrogen peroxide and sulfuric acid, the temperature of the oxidation treatment is 80°C to 145°C.

7. The method for preparing an image sensor according to claim 1, wherein: In step 3, the oxidation treatment time is 10s to 300s.

8. The method for preparing an image sensor according to claim 1, wherein: The thickness of the oxide blocking layer is 10A to 200A.

9. The method for preparing an image sensor according to claim 1, wherein: The step 2 comprises: Step 2.1, cleaning the wafer with a first cleaning agent to remove impurities on the substrate surface and / or repair defects on the substrate surface; Step 2.2, cleaning the wafer with a second cleaning agent to remove the natural oxide layer formed on the surface of the substrate.

10. The method for preparing an image sensor according to claim 9, wherein: The first cleaning reagent includes at least one of hydrochloric acid, ammonia water, SC1, hydrogen peroxide, sulfuric acid, and ozone water.

11. The method for preparing an image sensor according to claim 9, wherein: The second cleaning reagent comprises HF.

12. The method for preparing an image sensor according to claim 9, wherein: The step 2 further comprises: looping the step 2.1 to the step 2.2 N times, where N is a positive integer, and the step 2.1 and the step 2.2 are not in any particular order.

13. The method for preparing an image sensor according to claim 1, wherein: Also includes: Step 4, forming a photolithography pattern on the surface of the substrate; Step 5, performing an etching process on the wafer.

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