Etching method of hard mask layer of metal grating
The two-etching method is used to form a smooth hard mask pattern in the ONO hard mask layer, which solves the problem of double slope morphology in the etching of the ONO hard mask layer, and improves the etching quality and product reliability of the metal grid.
Patent Information
- Application Number
- CN202510294119.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-12
- Publication Date
- 2025-07-11
AI Technical Summary
In the prior art, etching of the ONO hard mask layer of the metal grid is prone to form double slope morphological defects, which affects the reliability and yield of the device product.
Using two etching methods, first a first groove is formed in the ONO hard mask layer and then a second etching is performed using octafluorocyclobutane and fluorocarbon gas to control the etching rate and by-product adsorption degree to form a smooth hard mask pattern.
The angle difference between the oxide layer and the nitride layer is achieved by less than 1°, avoiding the double slope morphology, and improving the etching quality and product reliability of the metal grid.
Smart Images
Figure CN120302739A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the technical field of semiconductor devices and integrated circuits, and particularly to an etching method for a hard mask layer of a metal grid. Background Art
[0002] An image sensor is an electronic device that converts optical signals into electrical signals and is widely used in fields such as photography, security systems, smart mobile phones, and medical electronics. In an image sensor, a complementary metal oxide semiconductor image sensor (CIS) is fabricated using traditional CMOS circuit technology, and the image sensor and its required peripheral circuits can be integrated, thus enabling the CIS to have broad application prospects.
[0003] According to the different positions of receiving light, CIS can be divided into two structures: front-side illumination (FSI) and back-side illumination (BSI). Compared with FSI CIS, BSI CIS changes the internal structure of the component, reverses the incident light path of the photosensitive layer component, and enables light to directly enter from the back of the component, avoiding the influence of the structure and thickness between the microlens and the photodiode (PD) on light in FSI CIS and improving the light reception efficiency. In the manufacturing process of BSI CIS, a metal grid can be set to block light for pixel units to improve the quantum efficiency of the product.
[0004] In related technologies, the method for forming a metal grid includes: after forming a metal layer on the back of a wafer, forming a hard mask layer on the metal layer, etching the hard mask layer through a lithography process to remove the hard mask layer in the target area, and then etching the metal layer using the hard mask layer as a mask to form a metal grid. The hard mask layer of the metal grid can include an oxide-nitride-oxide (ONO) layer. During etching, the ratio of different reaction gases is adjusted to adjust the amount of etching by-products (polymers) of different thin film layers, so as to control the difference between the angle of the oxide layer (the angle between the etching surface and the bottom surface of the oxide layer) and the angle of the nitride layer (the angle between the etching surface and the bottom surface of the nitride layer) in the ONO layer to be less than a target value (usually required to be 1°). However, through the method provided in related technologies, the difference between the angle of the oxide layer and the angle of the nitride layer is difficult to reach below the target value, resulting in a non-smooth "double slope" morphology on the sidewalls of the etched trenches, thereby affecting the reliability and yield of device products. Summary of the Invention
[0005] The present application provides an etching method for a hard mask layer of a metal grating, which can solve the problem that the "double-slope" topography defect is easily formed on the sidewall during the etching of the ONO hard mask layer of the metal grating in the related art. The method includes:
[0006] Perform a first etching to form a first groove in the second oxide layer and the nitride layer, the nitride layer at the bottom of the first groove is exposed, the second oxide layer is formed on the nitride layer, the nitride layer is formed on the first oxide layer, the first oxide layer is formed on the metal layer, the first oxide layer, the nitride layer and the second oxide layer constitute a hard mask layer for etching the metal layer, the metal layer is formed on the back of the wafer, the wafer is used to form a CIS, and the metal layer is used to form a metal grating of the CIS;
[0007] Perform a second etching to remove the nitride layer and the first oxide layer under the first groove, and form a second groove in the hard mask layer, the metal layer at the bottom of the second groove is exposed, and the reaction gas used during the second etching includes octafluorocyclobutane and a fluorocarbon gas, and the chemical formula of the fluorocarbon gas is CH x F y , where x and y are natural numbers.
[0008] In some embodiments, the performing the first etching includes:
[0009] Sequentially cover an anti-reflection coating, an organic coating and a photoresist on the second oxide layer;
[0010] Perform exposure and development in sequence to remove the photoresist in the target area, and the target area is the area corresponding to the first groove;
[0011] Perform a first-stage etching to remove the anti-reflection coating and the organic coating in the target area;
[0012] Perform a second-stage etching to form a first groove, and after the second-stage etching, the remaining anti-reflection coating, organic coating and photoresist are removed.
[0013] In some embodiments, the reaction gas used during the first-stage etching includes oxygen and nitrogen.
[0014] In some embodiments, the reaction gas used during the second-stage etching includes octafluorocyclobutane and oxygen.
[0015] In some embodiments, the fluorocarbon gas includes difluoromethane or fluoromethane.
[0016] In some embodiments, the performing the second etching includes:
[0017] Perform a second etching using octafluorocyclobutane and difluoromethane, or perform a second etching using octafluorocyclobutane and fluoromethane.
[0018] The technical solution of this application has at least the following advantages:
[0019] In the manufacturing process of CIS, after forming an ONO hard mask layer on the metal layer, perform a first etching to the nitride layer in the ONO hard mask layer to form a first groove, and perform a second etching to below the first groove to expose the metal layer to form a second groove. Since the reaction gas used in the second etching includes octafluorocyclobutane and fluorocarbon gas, it is possible to control the etching rate and the amount of etching by-products by taking advantage of the different degrees of combination of hydrocarbons dissociated from fluorocarbon gas with oxides and nitrides, and the different degrees of adsorption of hydrocarbons to etching by-products. Furthermore, it is possible to precisely control to obtain a hard mask pattern morphology without double slopes. Description of the Drawings
[0020] In order to more clearly illustrate the specific embodiments of this application or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.
[0021] Figure 1 is a flowchart of a method for etching a hard mask layer of a metal grating provided by an exemplary embodiment of this application;
[0022] Figures 2 to 4 is a schematic diagram of the etching process of a hard mask layer of a metal grating provided by an exemplary embodiment of this application. Detailed Embodiments
[0023] The following will clearly and completely describe the technical solutions in this application in conjunction with the drawings. Obviously, the described embodiments are some, but not all, of the embodiments of this application. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of this application.
[0024] In the description of the present application, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present application 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. Therefore, it should not be construed as a limitation to the present application. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.
[0025] In the description of the present application, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", "connected" 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 or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and can also be the communication inside two elements. It can be a wireless connection or a wired connection. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.
[0026] In addition, the technical features involved in different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.
[0027] Reference Figure 1 , which shows a flowchart of an etching method for a hard mask layer of a metal grating provided by an exemplary embodiment of the present application. As Figure 1 shown, the method includes:
[0028] Step S1, perform a first etching to form a first groove in the second oxide layer and the nitride layer, exposing the nitride layer at the bottom of the first groove. The second oxide layer is formed on the nitride layer, the nitride layer is formed on the first oxide layer, the first oxide layer is formed on the metal layer, and the first oxide layer, the nitride layer and the second oxide layer constitute a hard mask layer for etching the metal layer. The metal layer is formed on the back of the wafer, and this wafer is used to form a CIS, and this metal layer is used to form a metal grating of the CIS.
[0029] Reference Figure 2 , which shows a cross-sectional schematic diagram before the first etching; reference Figure 3 , which shows a cross-sectional schematic diagram after the first etching. Exemplarily, as Figure 2 and Figure 3As shown, a first oxide layer 221 is formed on a metal layer 210, a nitride layer 222 is formed on the first oxide layer 221, and a second oxide layer 223 is formed on the nitride layer 222. The first etching can be performed through a photolithography process to form a first groove 301 in the second oxide layer 223 and the nitride layer 222. Among them, the first oxide layer 221 and the second oxide layer 223 include silicon dioxide (SiO2) layers, the nitride layer 222 includes a silicon nitride (Si3N4) layer, and the metal layer 210 includes a tungsten (W) metal layer.
[0030] Exemplarily, the first etching includes: sequentially covering an anti-reflection coating, an organic coating, and a photoresist on the second oxide layer; sequentially performing exposure and development to remove the photoresist in the target area, where the target area is the area corresponding to the first groove; performing the first-stage etching to remove the anti-reflection coating and the organic coating in the target area; performing the second-stage etching until the etching stops at the nitride layer, thereby forming the first groove. After the second-stage etching, the remaining anti-reflection coating, organic coating, and photoresist are removed. Among them, the reaction gases used in the first-stage etching process include oxygen (O2) and nitrogen (N2), and the reaction gases used in the second-stage etching process include octafluorocyclobutane (C4F8) and oxygen.
[0031] Step S2: Perform the second etching to remove the nitride layer and the first oxide layer under the first groove, form a second groove in the hard mask layer, and expose the metal layer at the bottom of the second groove. The reaction gases used in the second etching process include octafluorocyclobutane and a carbon fluoride gas, and the chemical formula of the carbon fluoride gas is CH x F y , where x and y are natural numbers.
[0032] Reference Figure 4 , which shows a cross-sectional schematic diagram after the second etching. Exemplarily, as Figure 4 shown, the carbon fluoride gas in the second etching can include difluoromethane (CH2F2) or fluoromethane (CH3F). Octafluorocyclobutane and difluoromethane (the ratio of octafluorocyclobutane to difluoromethane is 1:1 to 3:1) can be used for the second etching, or octafluorocyclobutane and fluoromethane (the ratio of octafluorocyclobutane to fluoromethane is 1:1 to 3:1) can be used for the second etching to form a second groove 302 in the hard mask layer. Among them, in the second etching, the pressure ranges from 50 millitorr (mTorr) to 80 millitorr, and the source power and the bias power range from 500 watts (W) to 1500 watts. As Figure 4 shown, through the etching method of the hard mask layer provided by the embodiments of the present application, the difference between the oxide layer angle θ1 and the nitride layer angle θ2 is less than 1°, and there is no double-slope morphology on the sidewall of the groove.
[0033] In summary, in the embodiment of the present application, in the manufacturing process of the CIS, after forming an ONO hard mask layer on the metal layer, the first etching is performed to the nitride layer in the ONO hard mask layer to form a first groove, and the second etching is performed to the lower part of the first groove to expose the metal layer to form a second groove. Since the reaction gas used in the second etching includes perfluorocyclobutane and fluorocarbon gas, the hydrocarbon generated by the dissociation of the fluorocarbon gas can be used to control the etching rate and the amount of etching by-products due to the different binding degrees of the hydrocarbon to the oxide and the nitride and the different adsorption degrees of the hydrocarbon to the etching by-products. Furthermore, the topography of the hard mask pattern without double slopes can be accurately controlled.
[0034] Obviously, the above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. The obvious changes or modifications derived therefrom are still within the protection scope of the present application.
Claims
1. A method for etching a hard mask layer of a metal grating, characterized in that, Including: Performing a first etching to form a first groove in the second oxide layer and the nitride layer, with the nitride layer at the bottom of the first groove exposed. The second oxide layer is formed on the nitride layer, the nitride layer is formed on the first oxide layer, the first oxide layer is formed on the metal layer, and the first oxide layer, the nitride layer, and the second oxide layer constitute a hard mask layer for etching the metal layer. The metal layer is formed on the back surface of the wafer, and the wafer is used to form a CIS, and the metal layer is used to form a metal grid of the CIS; A second etching is performed to remove the nitride layer and the first oxide layer below the first groove, and a second groove is formed in the hard mask layer, exposing the metal layer at the bottom of the second groove. The reaction gases used during the second etching include perfluorocyclobutane and fluorocarbon gas, and the chemical formula of the fluorocarbon gas is CH x F y , where x and y are natural numbers.
2. The method according to claim 1, wherein The performing of the first etching includes: Successively covering an anti-reflection coating, an organic coating, and a photoresist on the second oxide layer; Successively performing exposure and development to remove the photoresist in the target area, where the target area is the area corresponding to the first groove; Performing a first-stage etching to remove the anti-reflection coating and the organic coating in the target area; Performing a second-stage etching to form the first groove. After the second-stage etching, the remaining anti-reflection coating, organic coating, and photoresist are removed.
3. The method according to claim 2, wherein The reaction gases used during the first-stage etching include oxygen and nitrogen.
4. The method according to claim 3, wherein The reaction gases used during the second-stage etching include octafluorocyclobutane and oxygen.
5. The method according to claim 1, characterized in that, The fluorocarbon gas includes difluoromethane or fluoromethane.
6. The method according to claim 5, wherein The performing of the second etching includes: Performing a second etching using octafluorocyclobutane and difluoromethane, or performing a second etching using octafluorocyclobutane and fluoromethane.