Method for forming metal lines of a cis
By employing two photolithography and etching processes during the formation of metal lines in CIS, and utilizing polymer byproducts to protect the sidewalls of the metal lines, the problems of etching accuracy and lateral drilling caused by the increase in metal line thickness are solved, thereby improving the reliability and lifespan of the device.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUA HONG SEMICON WUXI LTD
- Filing Date
- 2026-03-30
- Publication Date
- 2026-06-05
AI Technical Summary
During the formation of metal lines in CIS, as the thickness of the metal lines increases, the photoresist's resistance to etching becomes insufficient, making it difficult to meet the process requirements in terms of etching accuracy and pattern morphology. Furthermore, etching schemes using oxide layers as hard masks have the problem of balancing metal residues and lateral drilling, which affects the reliability and lifespan of the device.
The process employs two photolithography and etching steps. After the first photolithography, the same patterned mask is reused for the second photolithography. The polymer byproducts generated during the etching process of the second photoresist pattern protect the sidewalls of the metal lines, preventing lateral drilling caused by over-etching.
This improves the etching precision and morphological integrity of metal lines, thereby enhancing the reliability and lifespan of devices.
Smart Images
Figure CN122161434A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of semiconductor devices and integrated circuit technology, and in particular to a method for forming metal lines in a CIS (CMOS Image Sensor). Background Technology
[0002] In the fabrication of complementary metal oxide semiconductor image sensors (CIS), taking back-side illumination (BSI) image sensors as an example, the metal trace process of the back logic area plays a crucial role in the device's operating speed and power consumption. With the increasing demands on CIS performance indicators such as resolution, the thickness of the metal traces is showing a continuous increasing trend in order to reduce signal transmission resistance.
[0003] In related technologies, in photolithography for metal traces, the etching scheme where photoresist is directly used as an etching mask after a single photolithography step is limited by the photoresist's inherent etching resistance. When the metal line thickness increases to a certain extent, the photoresist will be completely consumed before etching is complete, resulting in etching precision and pattern morphology that cannot meet process requirements. If the photoresist thickness is increased to block the etching, insufficient exposure will result from limitations in equipment capabilities. Therefore, while an etching scheme using the oxide layer as a hard mask (HK) after the photoresist pattern is transferred to the oxide layer in a single photolithography step can improve etching resistance, it suffers from a difficulty in balancing residue and undercut: to remove metal residue in the pixel area, the over-etch (OE) time needs to be extended. However, extending the over-etch time will cause the bottom sidewalls of the metal to lose effective protection, leading to undercut problems, damaging the morphological integrity of the metal line, and consequently affecting the reliability and lifespan of the device. Summary of the Invention
[0004] This application provides a method for forming metal lines in CIS, which helps to avoid the problem of lateral drilling at the bottom of the metal line due to prolonged etching time.
[0005] In view of this, this application provides a method for forming metal wires in a CIS, comprising:
[0006] A hard mask layer is formed on a first metal layer, the first metal layer is formed on a second metal layer, and the second metal layer is formed on a substrate;
[0007] Photolithography is performed using a patterned mask to form a first photoresist pattern on the hard mask layer, exposing the hard mask layer of the target area;
[0008] Using the first photoresist pattern as a mask, a first dry etching is performed to etch to a predetermined depth in the hard mask layer of the target area. After the first dry etching, the first photoresist pattern is removed.
[0009] Photolithography is performed using the aforementioned patterned mask to form a second photoresist pattern on the remaining hard mask layer;
[0010] A second dry etching process is performed using the second photoresist pattern and the remaining hard mask layer as a mask until the second metal layer in the target area is exposed. During the second dry etching process, the reaction byproducts generated by the second photoresist pattern protect the area where the first metal layer is etched and exposed.
[0011] Optionally, the hard mask layer includes an oxide layer and an etch stop layer from top to bottom.
[0012] Optionally, the etch stop layer includes a silicon oxynitride layer.
[0013] Optionally, the etching stop layer is exposed after the first dry etching.
[0014] Optionally, the first metal layer includes an aluminum layer and a barrier layer, wherein the barrier layer is formed on the aluminum layer.
[0015] Optionally, the barrier layer comprises at least one layer of titanium and titanium nitride stacked structure, wherein in the bottommost stacked structure, the titanium nitride layer is close to the first metal layer, and the titanium layer is far away from the first metal layer.
[0016] Optionally, the second metal layer includes a tungsten layer.
[0017] Optionally, the second metal layer and the thin film layer thereon are formed on the back side of the substrate.
[0018] The technical solution of this application has at least the following advantages:
[0019] This application employs a two-stage photolithography and etching process. After the first photolithography and etching of the hard mask layer, the same patterned mask is reused for the second photolithography. The photoresist pattern formed by the second photolithography acts as a polymer source and reacts with the etching gas in the second etching process. The polymer byproducts generated by the reaction can be deposited on the area of the first metal layer that is etched and exposed, effectively protecting the sidewalls of the metal lines. This helps to avoid lateral drilling at the bottom of the metal lines due to prolonged etching time, thus solving the problem of balancing "metal residue" and "lateral drilling" caused by using a patterned oxide layer as a mask for etching, and improving the reliability and lifespan of the device. Attached Figure Description
[0020] 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.
[0021] Figure 1 This is a process flow diagram of a CIS metal wire formation method provided in an exemplary embodiment of this application;
[0022] Figure 2 This is a cross-sectional schematic diagram of the CIS metal line forming method provided in an exemplary embodiment of this application after forming a hard mask layer on the first metal layer;
[0023] Figure 3 This is a cross-sectional schematic diagram of the CIS metal line formation method provided in an exemplary embodiment of this application after forming a first photoresist pattern on a hard mask layer;
[0024] Figure 4 This is a schematic cross-sectional view after the first dry etching in the CIS metal wire formation method provided in an exemplary embodiment of this application;
[0025] Figure 5 This is a cross-sectional schematic diagram of the CIS metal line formation method provided in an exemplary embodiment of this application after the first photoresist pattern has been removed;
[0026] Figure 6 This is a cross-sectional view of the CIS metal line formation method provided in an exemplary embodiment of this application after forming a second photoresist pattern on the remaining hard mask layer;
[0027] Figure 7 This is a schematic cross-sectional view after the second dry etching in the CIS metal wire formation method provided in an exemplary embodiment of this application;
[0028] The numbers in the diagram represent:
[0029] 100. Second metal layer
[0030] 200, First metal layer; 210, Aluminum layer; 220, Barrier layer;
[0031] 300, Hard mask layer; 310, Etching stop layer; 320, Oxide layer;
[0032] 400. First photoresist pattern;
[0033] 500. Second photoresist pattern. Detailed Implementation
[0034] 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.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] The following is combined with Figures 1 to 7 This describes an embodiment of the present application.
[0039] refer to Figure 1 This illustrates an embodiment of the present application, providing a method for forming metal wires in a CIS, comprising:
[0040] S1, a hard mask layer 300 is formed on the first metal layer 200, the first metal layer 200 is formed on the second metal layer 100, and the second metal layer 100 is formed on the substrate.
[0041] For example, the substrate can be a silicon substrate, a germanium (Ge) substrate, a gallium arsenide (GaAs) substrate, or other materials suitable for CIS fabrication. The hard mask layer 300 is typically formed on the first metal layer 200 by a deposition process, such as chemical vapor deposition (CVD), and the first metal layer 200 is formed on the second metal layer 100. The formation of the second metal layer 100 on the substrate can also be achieved by a deposition process, such as physical vapor deposition (PVD).
[0042] In some embodiments, the first metal layer 200 includes an aluminum layer 210 and a barrier layer 220, wherein the barrier layer 220 is formed on the aluminum layer 210.
[0043] For example, the barrier layer 220 includes at least one layer of titanium and titanium nitride stacked structure, wherein in the bottommost stacked structure, the titanium nitride layer is close to the first metal layer 200, and the titanium layer is far from the first metal layer 200. This arrangement can improve the electromigration phenomenon of metallic aluminum.
[0044] In some embodiments, the hard mask layer 300 includes, from top to bottom, an oxide layer 320 and an etch stop layer 310.
[0045] For example, oxide layer 320 includes a silicon oxide layer, and etch stop layer 310 includes a silicon oxynitride (SiON) layer. This arrangement facilitates providing precise etch termination capability, allowing the etch of the hard mask layer to terminate at the silicon oxynitride layer.
[0046] In some embodiments, the second metal layer 100 includes a tungsten layer.
[0047] In some embodiments, the second metal layer 100 and the thin film layer thereon are formed on the back side of the substrate.
[0048] For example, the thin film layer above the second metal layer 100 includes a first metal layer 200 and a mask hard mask layer 300. For instance, the thin film layer above the second metal layer 100 includes an aluminum layer 210, a barrier layer 220, an etch stop layer 310, and an oxide layer 320.
[0049] S2, a patterned mask is used for photolithography to form a first photoresist pattern 400 on the hard mask layer, exposing the hard mask layer of the target area.
[0050] Understandably, the formation of the first photoresist pattern 400 on the hard mask layer is achieved through photolithography. For example, positive photoresist can be uniformly coated on the surface of the hard mask layer 300, and then the patterned mask can be exposed by a photolithography machine. The photoresist in the exposed area can then be removed by the action of a developer, thereby forming the first photoresist pattern 400.
[0051] S3, using the first photoresist pattern 400 as a mask, perform the first dry etching to a predetermined depth in the hard mask layer of the target area. After the first dry etching, the first photoresist pattern 400 is removed.
[0052] Understandably, a fluorine-containing etching gas (e.g., carbon tetrafluoride) is typically used to perform dry etching on the hard mask layer 300. The first dry etching reaches a predetermined depth in the hard mask layer of the target area. This predetermined depth can be exactly the thickness of the oxide layer 320 in the hard mask layer, or it can extend into the etch stop layer 310 in the hard mask layer. After the first dry etching, the etch stop layer 310 is exposed.
[0053] S4, a patterned mask is used for photolithography to form a second photoresist pattern 500 on the remaining hard mask layer.
[0054] It should be noted that the pattern mask used to form the second photoresist pattern 500 on the remaining hard mask layer in the photolithography process is the same as the pattern mask used to form the first photoresist pattern 400 in photolithography.
[0055] S5, using the second photoresist pattern 500 and the remaining hard mask layer as a mask, a second dry etching is performed until the second metal layer 100 in the target area is exposed. During the second dry etching process, the reaction byproducts generated by the second photoresist pattern 500 protect the area of the first metal layer 200 that is etched and exposed.
[0056] Understandably, etching gases containing chlorine (such as chlorine gas or boron trichloride) are typically used for dry etching of metal layers.
[0057] In photolithography for metal trace fabrication, the etching scheme where photoresist is directly used as an etching mask after a single photolithography step is limited by the photoresist's inherent etching resistance. When the metal line thickness increases to a certain extent, the photoresist is completely consumed before etching is complete, resulting in etching precision and pattern morphology that fail to meet process requirements. Increasing the photoresist thickness to block etching is limited by machine capabilities, leading to insufficient exposure. Therefore, while an etching scheme using the oxide layer as a hard mask after the photoresist is etched and transferred to an oxide layer can improve etching resistance, it suffers from the drawback of balancing residue and lateral drilling.
[0058] The metal line formation method for CIS provided in this application employs a two-stage photolithography and etching process. After the first photolithography and etching of the hard mask layer 300, the same patterned mask is reused for the second photolithography. The photoresist pattern formed by the second photolithography acts as a polymer source and reacts with the etching gas in the second etching process. The polymer byproducts generated by the reaction can be deposited in the etched and exposed area of the first metal layer 200, effectively protecting the sidewalls of the metal line. This helps to avoid lateral drilling at the bottom of the metal line due to prolonged etching time, thereby solving the contradiction between "metal residue" and "lateral drilling" caused by using a patterned oxide layer as a mask for etching, and improving the reliability and service life of the device.
[0059] 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 metal wires in a CIS (Computer Integrated System), characterized in that, include: A hard mask layer is formed on a first metal layer, the first metal layer is formed on a second metal layer, and the second metal layer is formed on a substrate; Photolithography is performed using a patterned mask to form a first photoresist pattern on the hard mask layer, exposing the hard mask layer of the target area; Using the first photoresist pattern as a mask, a first dry etching is performed to etch to a predetermined depth in the hard mask layer of the target area. After the first dry etching, the first photoresist pattern is removed. Photolithography is performed using the aforementioned patterned mask to form a second photoresist pattern on the remaining hard mask layer; A second dry etching process is performed using the second photoresist pattern and the remaining hard mask layer as a mask until the second metal layer in the target area is exposed. During the second dry etching process, the reaction byproducts generated by the second photoresist pattern protect the area where the first metal layer is etched and exposed.
2. The method according to claim 1, characterized in that, The hard mask layer comprises, from top to bottom, an oxide layer and an etch stop layer.
3. The method according to claim 2, characterized in that, The etching stop layer includes a silicon oxynitride layer.
4. The method according to claim 3, characterized in that, The etching stop layer is exposed after the first dry etching.
5. The method according to claim 1, characterized in that, The first metal layer includes an aluminum layer and a barrier layer, wherein the barrier layer is formed on the aluminum layer.
6. The method according to claim 5, characterized in that, The barrier layer comprises at least one layer of titanium and titanium nitride stacked structure, wherein in the bottommost stacked structure, the titanium nitride layer is close to the first metal layer and the titanium layer is far away from the first metal layer.
7. The method according to claim 1, characterized in that, The second metal layer includes a tungsten layer.
8. The method according to any one of claims 1-8, characterized in that, The second metal layer and the thin film layer thereon are formed on the back side of the substrate.