Manufacturing method of metal grating

Abstract

The invention discloses a manufacturing method of a metal grating, which comprises the following steps of: performing first etching through a photoetching process, forming a first groove in a hard mask layer, forming the hard mask layer on a metal layer, forming the metal layer above an insulating layer, forming the insulating layer on the back surface of a wafer, and forming a CIS (Contact Image Sensor) on the back surface of the wafer, the metal layer is used for forming a metal grating of the CIS; etching for the second time, removing the hard mask layer and the metal layer below the first groove, forming a second groove in the metal layer, and exposing the insulating layer at the bottom of the second groove; wherein the second etching comprises a first stage and a second stage which are sequentially carried out, the reaction gas used in the etching process of the first stage comprises argon, and the reaction gas used in the etching process of the second stage comprises chlorine and oxygen. According to the manufacturing method of the metal grating provided by the embodiment of the invention, the probability of generation of the side digging defect of the interface of the metal layer and the oxide layer is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of semiconductor devices and integrated circuits, and particularly relates to a method for manufacturing 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 contact image sensor (CIS) is fabricated using a conventional CMOS circuit process, which can integrate the image sensor and its required peripheral circuits, thereby 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 the 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, removing 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. Among them, the hard mask layer of the metal grid can be an oxide layer. However, during the etching of the metal layer using the hard mask layer, the oxygen element generated by the consumed oxide at the junction of the oxide layer and the metal layer will accelerate the corrosion of the metal, and it is easy to generate a "side etching" defect at the interface (that is, the metal layer at the junction of the oxide layer and the metal layer will have a concave morphology), which will affect the normal light entry of the pixel area and the isolation effect of the metal grid, thereby reducing the reliability and yield of the device product. Summary of the Invention

[0005] The present application provides a method for manufacturing a metal grid, which can solve the problem that the method for manufacturing a metal grid provided in the related art is prone to "side etching" defects at the interface between the metal layer and the oxide layer due to using an oxide layer as a hard mask layer. The method includes:

[0006] Performing a first etching through a photolithography process to form a first groove in the hard mask layer. The hard mask layer is formed on the metal layer. The hard mask layer includes an oxide layer. The metal layer is formed above the insulating layer. The insulating layer is formed on the back surface of the wafer. The wafer is used to form a CIS. The metal layer is used to form the metal grid of the CIS;

[0007] Performing a second etching to remove the hard mask layer and the metal layer below the first groove, and forming a second groove in the metal layer, exposing the insulating layer at the bottom of the second groove;

[0008] Wherein, the second etching includes a first stage and a second stage performed in sequence. The reaction gas used in the etching process of the first stage includes argon, and the reaction gases used in the etching process of the second stage include chlorine and oxygen.

[0009] In some embodiments, the metal layer includes a tungsten layer.

[0010] In some embodiments, the hard mask layer and the insulating layer include a silicon dioxide layer.

[0011] In some embodiments, the duration of the first stage is less than 10 seconds.

[0012] In some embodiments, the pressure in the first stage ranges from 4 mTorr to 7 mTorr.

[0013] In some embodiments, the second stage includes a main etching stage and an over-etching stage, and the power of the main etching stage is less than the power of the over-etching stage.

[0014] In some embodiments, the reaction gases used in the main etching stage include nitrogen trifluoride, chlorine, and oxygen.

[0015] In some embodiments, the reaction gas used in the over-etching stage includes chlorine.

[0016] The technical solution of the present application has at least the following advantages:

[0017] In the manufacturing process of the CIS, after forming an oxide layer hard mask layer above the metal layer, first form a first groove in the hard mask layer through a first etching, and then use the hard mask layer as a mask to perform a second etching until the insulating layer below the first groove is exposed to form a second groove. Since during the second etching process, in the first stage of the second etching, a reaction gas containing argon is used for etching, and argon element bombardment is used to replace the fluorine element etching in the related art, thereby reducing the gaps generated at the interface between the metal layer and the oxide layer due to excessive etching speed; at the same time, in the second stage of the second etching, a reaction gas containing chlorine and oxygen is used, so that high-boiling-point chlorides and volatile chlorine oxides are generated in this stage to protect or repair the sidewall morphology of the second groove, thereby improving the "side etching" phenomenon and enhancing the reliability and yield of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0019] Figure 1 is a flowchart of a method for manufacturing a metal grid provided by an exemplary embodiment of the present application;

[0020] Figures 2 to 4 is a schematic diagram of the manufacturing process of a metal grid provided by an exemplary embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The following will clearly and completely describe the technical solutions in the present application in conjunction with the drawings. Obviously, the described embodiments are some embodiments of the present application, rather than all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present application.

[0022] 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, and 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, and therefore cannot be understood as a limitation to the present application. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0023] In the description of the present application, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", and "coupling" 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 a direct connection or an indirect connection through an intermediate medium, and it can also be the communication inside two components. 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.

[0024] 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.

[0025] Reference Figure 1 , which shows a flowchart of a method for manufacturing a metal grid provided by an exemplary embodiment of the present application. As Figure 1 shown, the method includes:

[0026] Step S1, performing a first etching through a photolithography process to form a first groove in the hard mask layer. The hard mask layer is formed on the metal layer. The hard mask layer includes an oxide layer. The metal layer is formed above the insulating layer, and the insulating layer is formed on the back surface of the wafer. The wafer is used to form a CIS, and the metal layer is used to form the metal grid of the CIS.

[0027] Reference Figure 2 , which shows a cross-sectional schematic diagram after the first etching. Exemplarily, as Figure 2 shown, a photoresist 300 can be covered on the hard mask layer 212, and the photoresist 300 in the target area is removed through exposure and development in sequence, and then the first etching is performed to form a first groove 301 in the hard mask layer 212. Among them, the hard mask layer 212 is formed on the metal layer 220 (which can include a tungsten (W) layer). The hard mask layer 212 includes an oxide layer (for example, a silicon dioxide (SiO2) layer). The metal layer 220 is formed above the insulating layer 211 (which can include an oxide layer), and the insulating layer 211 is formed on the back surface of the wafer (not shown in the figure). The wafer is used to form a CIS, and the metal layer is used to form the metal grid of the CIS.

[0028] Step S2, performing a second etching to remove the hard mask layer and the metal layer below the first groove, and forming a second groove in the metal layer, exposing the insulating layer at the bottom of the second groove. The second etching includes a first stage and a second stage performed in sequence. The reaction gas used in the etching process of the first stage includes argon, and the reaction gases used in the etching process of the second stage include chlorine and oxygen.

[0029] Reference Figure 3, which shows a schematic cross-sectional view after etching in the first stage. Exemplarily, as Figure 3 shown, in the first stage, etching is carried out to a predetermined depth in the metal layer 220, and the duration is less than 10 seconds (s). The hard mask layer 212 above the metal layer 220 is removed. The pressure in the first stage ranges from 4 millitorr (mTorr) to 7 mTorr. The reaction gas used includes argon (Ar), which replaces the etching of opening the metal layer 220 by carbon tetrafluoride (CF4) in the related art. The etching by bombarding with argon elements replaces the etching with fluorine elements, thereby reducing the generation of gaps due to excessive etching at the interface between the metal layer 220 and the oxide layer 212, and reducing the possibility of "side etching" defects caused by such gaps in the subsequent second-stage etching.

[0030] Exemplarily, in the first stage, using argon (flow rate of 300 standard cubic centimeters per minute (SCCM) to 600 SCCM), at a lower pressure (4 mTorr to 7 mTorr), the power of the transformer coupled plasma (TCP) etching equipment ranges from 300 watts (W) to 450 W, and the bias radio frequency power ranges from 150 W to 250 W. Under these parameter conditions, with a duration less than 10 seconds, the hard mask layer above the metal layer is opened, reducing the lateral etching and the generation of lateral gaps.

[0031] Refer to Figure 4 , which shows a schematic cross-sectional view after etching in the second stage. Exemplarily, as Figure 4 shown, the second stage includes a main etch (ME) stage and an over etch (OE) stage, and the power in the main etch stage is less than that in the over etch stage.

[0032] For example, the reaction gases used in the main etch stage include nitrogen trifluoride (NF3, with a flow rate of 15 SCCM to 30 SCCM), chlorine (Cl2, with a flow rate of 15 SCCM to 30 SCCM), and oxygen (O2, with a flow rate of 0 SCCM to 15 SCCM). At a lower power of the TCP etching equipment (350 W to 500 W), through a higher bias radio frequency power (350 W to 450 W), at a lower pressure (4 mTorr to 7 mTorr), the etching by-products at the interface can be reduced, and the protection of the sidewalls can be enhanced (the protection of the sidewalls is enhanced by introducing chlorine to generate tungsten hexachloride (WCl6) with a high boiling point to prevent side etching of the tungsten metal layer in the subsequent process, and at the same time, the flatness of the sidewalls will be improved; introducing oxygen will generate tungsten oxychloride (WOCl4) which is more volatile than tungsten hexachloride, making the morphology of the sidewalls more straight), and the metal layer 220 is opened.

[0033] The reaction gas used in the over-etching stage includes chlorine gas. At a relatively high power (750 watts to 900 watts) of the TCP etching equipment, etching continues downward until the insulating layer 211 is exposed, thereby forming the second groove 302.

[0034] In summary, in the embodiment of the present application, after forming the oxide layer hard mask layer above the metal layer in the manufacturing process of the CIS, first, a first groove is formed in the hard mask layer through the first etching, and then the second etching is performed using the hard mask layer as a mask until the insulating layer below the first groove is exposed to form the second groove. Since during the second etching process, the first stage of the second etching is carried out by using a reaction gas containing argon gas, and the etching of argon element bombardment replaces the fluorine element in the related technology, the gap generated due to excessive etching at the interface between the metal layer and the oxide layer is reduced. At the same time, by using a reaction gas containing chlorine and oxygen for the second stage of the second etching, high-boiling-point chlorides and volatile chlorine oxides are generated in this stage to protect or repair the sidewall morphology of the second groove, thereby improving the "side etching" phenomenon and enhancing the reliability and yield of the product.

[0035] 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 list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for manufacturing a metal grille, characterized in that, Including: Performing a first etching through a lithography process to form a first groove in a hard mask layer, the hard mask layer being formed on a metal layer, the hard mask layer including an oxide layer, the metal layer being formed above an insulating layer, the insulating layer being formed on the back surface of a wafer, the wafer being used to form a CIS, and the metal layer being used to form a metal grid of the CIS; Performing a second etching to remove the hard mask layer and the metal layer below the first groove and form a second groove in the metal layer, with the insulating layer at the bottom of the second groove being exposed; Wherein, the second etching includes a first stage and a second stage carried out in sequence. The reaction gas used in the etching process of the first stage includes argon, and the reaction gases used in the etching process of the second stage include chlorine and oxygen.

2. The method according to claim 1, characterized in that, The metal layer includes a tungsten layer.

3. The method according to claim 2, characterized in that The hard mask layer and the insulating layer include a silicon dioxide layer.

4. The method according to claim 2, characterized in that, The duration of the first stage is less than 10 seconds.

5. The method according to claim 4, wherein The pressure in the first stage ranges from 4 millitorr to 7 millitorr.

6. The method according to claim 2, wherein The second stage includes a main etching stage and an over-etching stage, and the power of the main etching stage is less than that of the over-etching stage.

7. The method according to claim 6, characterized in that, The reaction gases used in the main etching stage include nitrogen trifluoride, chlorine, and oxygen.

8. The method according to claim 7, characterized in that, The reaction gas used in the over-etching stage includes chlorine.

Images