Method of forming a cantilever structure
By utilizing high-carbon-fluorine content reaction gas and source power to remove oxidized polymers during the formation of the cantilever structure of CIS, the problem of oxidized polymer accumulation in trench etching is solved, thereby improving the reliability and yield of the device.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUA HONG SEMICON WUXI LTD
- Filing Date
- 2022-11-29
- Publication Date
- 2026-06-05
Smart Images
Figure CN116031157B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of semiconductor manufacturing technology, and specifically to a method for forming a cantilever structure. Background Technology
[0002] Among image sensors, complementary metal oxide semiconductor image sensors (CIS) are image sensors made using CMOS devices. Due to their advantages such as high integration, low power supply voltage, and low technical threshold, they are widely used in fields such as photography and videography, security systems, smart mobile phones, and medical electronics.
[0003] The photosensitivity of CIS is strongly correlated with the size of the pixel area. Traditional photodiodes (PDs) are formed through photolithography and ion implantation processes, which are limited by the aspect ratio of the photoresist and the depth and concentration of ion implantation. To improve photosensitivity on small pixels, the space of the PD can be expanded vertically to circumvent the limitations of the photoresist aspect ratio. Therefore, related technologies propose forming a cantilever structure in CIS, creating a deep PD layer, and then forming the surface device structure, thus avoiding the process limitations of ion implantation and photolithography.
[0004] However, during the trench etching process of the beam structure, oxidized polymers tend to accumulate at the trench openings, forming void defects and reducing the reliability and yield of the device. Summary of the Invention
[0005] This application provides a method for forming a cantilever structure, which can solve the problem that the CIS fabrication methods provided in the related art easily accumulate oxidized polymers at the groove openings of the cantilever structure. The method includes:
[0006] The target area is exposed by covering the substrate with photoresist through photolithography.
[0007] The first etching is performed, etching to a first depth in the substrate of the target region to form a first trench;
[0008] A linear oxide layer is formed on the surface of the first trench;
[0009] A second etching is performed to a second depth below the first trench, forming a second trench below the first trench. The width of the second trench is greater than the width of the first trench. During the second etching process, the oxidized polymer on the periphery of the first trench is removed by increasing the source power and the content of carbon and fluorine elements in the reaction gas.
[0010] Remove the linear oxide layer.
[0011] In some embodiments, during the second etching process, the gas pressure is also reduced to decrease the residence of the oxidized polymer.
[0012] In some embodiments, the gas pressure during the second etching process is 200 mTorr to 300 mTorr.
[0013] In some embodiments, the source power during the second etching process is 400 watts to 600 watts.
[0014] In some embodiments, the method is applied to the manufacturing process of CIS.
[0015] In some embodiments, the substrate comprises, from bottom to top, a silicon substrate and an epitaxial layer formed on the silicon substrate.
[0016] In some embodiments, the silicon substrate at the bottom of the second trench is exposed after a second etching.
[0017] The technical solution of this application has at least the following advantages:
[0018] By increasing the source power and the carbon and fluorine content in the reaction gas during the etching process of the cantilever structure trench during the fabrication of CIS, the oxidized polymer on the periphery above the trench is removed, thereby reducing the probability of void defects in subsequent processes and improving the reliability and yield of the device. Attached Figure Description
[0019] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0020] Figure 1 This is a flowchart of a method for forming a cantilever structure provided in an exemplary embodiment of this application;
[0021] Figures 2 to 5 This is a schematic diagram illustrating the formation of a cantilever structure provided in an exemplary embodiment of this application. Detailed Implementation
[0022] The technical solutions of this application 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 this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0023] In the description of this application, it should be noted that the terms "center," "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 application and 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 application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.
[0024] In the description of this application, it should be noted that, unless otherwise expressly 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 or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.
[0025] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.
[0026] refer to Figure 1 The document illustrates a flowchart of a method for forming a cantilever structure according to an exemplary embodiment of this application. This method can be applied to the fabrication process of CIS (especially in the fabrication process of CIS with a process technology of 55 nanometers (nm) and below), such as... Figure 1 As shown, the method includes:
[0027] Step S1: Photoresist is applied to the substrate using photolithography to expose the target area.
[0028] refer to Figure 2 This illustrates a cross-sectional schematic diagram of photoresist being coated onto a substrate using a photolithography process. For example, such as... Figure 2 As shown, photoresist 300 is applied to the substrate using photolithography to expose the target area, which is the area to be etched. The substrate, from bottom to top, includes a silicon substrate 210 and an epitaxial layer 211 formed on the silicon substrate 210.
[0029] Step S2: Perform the first etching to a first depth in the substrate of the target area to form the first trench.
[0030] refer to Figure 3 It shows a cross-sectional view after the first etching. For example, as shown... Figure 3 As shown, the first etching reaches a first depth in the epitaxial layer 211 (but does not penetrate the epitaxial layer 211) to form a first trench 201.
[0031] Step S3: A linear oxide layer is formed on the surface of the first trench.
[0032] refer to Figure 4 This illustrates a cross-sectional schematic diagram of a linear oxide layer formed on the surface of the first trench. For example, as shown... Figure 4 As shown, a linear oxide layer 220 can be formed on the surface of the first trench 201 by a furnace tube oxidation process.
[0033] Step S4: Perform a second etching to a second depth below the first trench, forming a second trench below the first trench. The width of the second trench is greater than the width of the first trench. During the second etching process, the oxidized polymer around the first trench is removed by increasing the source power and the carbon and fluorine content in the reaction gas.
[0034] Step S5: Remove the linear oxide layer.
[0035] refer to Figure 5 This illustrates a cross-sectional view after the second trench has been formed and the linear oxide layer has been removed. For example, such as... Figure 5 As shown, after the second etching, a second trench 202 is formed in a region at a second depth below the first trench 201. The cavity formed by the first trench 201 and the second trench 202 can serve as a cavity for forming a cantilever structure in subsequent processes. The width of the second trench 202 is greater than the width of the first trench 201, and the silicon substrate 210 at the bottom of the second trench 202 is exposed. During the second etching process, by increasing the source power and the content of carbon (C) and fluorine (F) in the reaction gas to remove the oxidized polymer around the first trench 201, the problem of the oxidized polymer around the first trench 201 (such as...) is effectively solved. Figure 5 The problem of oxidized polymer buildup (shown by the dashed line) can be addressed. Optionally, during the second etching process, the gas pressure can be reduced to decrease the residence time of the oxidized polymer. Specifically, the gas pressure during the second etching process is 200 mTorr to 300 mTorr, and the source power during the second etching process is 400 watts (W / gas pressure) to 600 watts.
[0036] The reaction gas, with its high carbon and fluorine content, is used to increase the concentration of fluorine (F) and difluorine (CF2) groups, causing them to densely distribute on the outer layer of the trench. However, simply increasing the carbon and fluorine content in the reaction gas does not significantly improve the situation, as the ability to dissociate fluorine and difluorine groups is limited under a given source power. Therefore, increasing the source power allows for the dissociation of more fluorine and difluorine groups, which react with the silicon oxide (SiO2) at the opening (first trench 201) to generate gaseous silicon tetrafluoride (SiF4), thereby causing the oxidized polymer to disappear. The reaction mechanism is as follows:
[0037] C x F y →(y-2x)F+xCF2
[0038] SiO₂ + 4F → SiF₄ + 2O
[0039] SiO2 + 2CF2 → SiF4 + 2CO
[0040] Where x and y represent the carbon and fluorine content in the reactant gas.
[0041] In summary, in the embodiments of this application, by increasing the source power and the content of carbon and fluorine elements in the reaction gas during the etching process of the cantilever structure trench during the fabrication of CIS, the oxidized polymer on the periphery above the trench is removed, thereby reducing the probability of void defects in subsequent processes and improving the reliability and yield of the device.
[0042] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.
Claims
1. A method for forming a cantilever structure, characterized in that, The method is applied to the fabrication process of CIS with a process technology below 55 nanometers, including: The target area is exposed by covering the substrate with photoresist through photolithography. The first etching is performed, etching to a first depth in the substrate of the target region to form a first trench; A linear oxide layer is formed on the surface of the first trench; A second etching process is performed, etching to a second depth below the first trench, forming a second trench below the first trench. The width of the second trench is greater than the width of the first trench. The first trench and the second trench are used to form the photodiode of the CIS. During the second etching process, the oxidized polymer on the periphery of the first trench is removed by increasing the source power and the content of carbon and fluorine elements in the reaction gas, and the residence of the oxidized polymer is reduced by decreasing the gas pressure. Remove the linear oxide layer.
2. The method according to claim 1, characterized in that, The gas pressure during the second etching process is 200 to 300 millitors.
3. The method according to claim 1, characterized in that, The source power during the second etching process is 400 watts to 600 watts.
4. The method according to any one of claims 1 to 3, characterized in that, The substrate, from bottom to top, comprises a silicon substrate and an epitaxial layer formed on the silicon substrate.
5. The method according to claim 4, characterized in that, After the second etching, the silicon substrate at the bottom of the second trench is exposed.