Metal grid forming process for backside illuminated sensor

Abstract

The invention discloses a metal grid forming process for a back-illuminated sensor, and the process comprises the steps: providing a substrate, forming a plurality of deep trench isolation structures in the substrate, sequentially forming an oxide side wall layer, a silicon dioxide filling layer and an adhesion layer on the surface of the substrate, and forming a metal layer on the adhesion layer; depositing a silicon nitride mask layer on the metal layer; sequentially forming a silicon oxide layer, a metal hard mask layer and a protective layer on the silicon nitride mask layer; forming a patterned photoresist layer, wherein a reserved region of the photoresist layer shields the protective layer and the metal hard mask layer which are positioned right above the deep trench isolation structure; etching the exposed protective layer and the metal hard mask layer by taking the photoresist layer as a mask; etching the exposed silicon oxide layer and the silicon nitride mask layer by taking the residual protective layer and the metal hard mask layer as masks; the residual silicon oxide layer and the silicon nitride mask layer are used as masks, the exposed metal layer is subjected to dry etching, and the residual metal layer forms a metal grid; and depositing a liner oxide layer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor manufacturing, and in particular to a metal grid forming process for a back-illuminated sensor. BACKGROUND

[0002] Image sensors, as the core components of modern imaging systems, are widely used in consumer electronics, security monitoring, automotive auxiliary driving, medical imaging, and industrial detection, etc. In the process of its technical evolution, it gradually developed from the early charge-coupled device (CCD) to the complementary metal-oxide-semiconductor (CMOS) image sensor. CMOS image sensors have occupied the mainstream market due to their high integration, low power consumption, and controllable cost. Within the CMOS image sensor technology system, it has undergone a revolution from the traditional front-side illuminated (FSI) architecture to the back-side illuminated (BSI) architecture.

[0003] In a back-illuminated image sensor, the optical crosstalk between photodiodes is usually suppressed by the light-blocking property of a metal grid. After tungsten etching in the metal layer, a layer of liner oxide layer is deposited on the sidewall to protect the tungsten. However, in the current process, tungsten is prone to oxidation due to insufficient protection of the sidewall liner oxide layer, resulting in reliability failure. SUMMARY

[0004] The present application provides a metal grid forming process for a back-illuminated sensor, which can improve the formation quality of the liner oxide layer and improve the reliability of the back-illuminated sensor.

[0005] The present application provides a metal grid forming process for a back-illuminated sensor, which includes: providing a substrate, the substrate has a plurality of deep trench isolation structures formed therein, the surface of the substrate has an oxide sidewall layer, a silicon dioxide filling layer and an adhesion layer formed in sequence, and a metal layer is formed on the adhesion layer; Depositing a silicon nitride mask layer on the metal layer; Forming a silicon oxide layer, a metal hard mask layer and a protection layer on the silicon nitride mask layer in sequence; Forming a patterned photoresist layer, the remaining area of the photoresist layer shields the protection layer and the metal hard mask layer located directly above the deep trench isolation structure; Etching the exposed protection layer and metal hard mask layer with the photoresist layer as a mask; Etching the exposed silicon oxide layer and silicon nitride mask layer with the remaining protection layer and metal hard mask layer as a mask; The remaining metal layer constitutes a metal grid, and in the process, the sidewall of the remaining metal layer forms a nitride protective layer. A liner oxide layer is deposited.

[0006] In some embodiments, the adhesion layer is a titanium nitride layer.

[0007] In some embodiments, the metal layer is tungsten.

[0008] In some embodiments, after the step of sequentially forming a silicon oxide layer, a metal hard mask layer, and a protective layer on the silicon nitride mask layer, the method further comprises: An anti-reflection layer is spin-coated on the protective layer.

[0009] In some embodiments, the step of depositing a silicon nitride mask layer on the metal layer is performed by a chemical vapor deposition process.

[0010] In some embodiments, the step of etching the exposed protective layer and metal hard mask layer with the photoresist layer as a mask is performed by a plasma etching process.

[0011] In some embodiments, the step of etching the exposed silicon oxide layer and silicon nitride mask layer with the remaining protective layer and metal hard mask layer as a mask is performed by a plasma etching process.

[0012] In some embodiments, in the step of etching the exposed silicon oxide layer and silicon nitride mask layer with the remaining protective layer and metal hard mask layer as a mask, the protective layer and metal hard mask layer are also removed.

[0013] In some embodiments, the step of depositing a liner oxide layer is performed by a chemical vapor deposition process.

[0014] The technical solution of the present application has at least the following advantages: 1. By forming a silicon nitride mask layer on the metal layer, in the step of dry etching the exposed metal layer with the remaining silicon oxide layer and silicon nitride mask layer as a mask, the dry etching process will bombard the silicon nitride mask layer, thereby releasing nitrogen atoms / nitrogen ions. The released nitrogen atoms / nitrogen ions will react with the sidewall etching surface of the metal layer, thereby forming a nitride layer. On the one hand, the nitride layer will act as an adhesion layer, facilitating better contact between the sidewall of the subsequent metal grid and the liner oxide layer, improving the formation quality of the liner oxide layer. On the other hand, it can also act as a protective layer to prevent subsequent metal grid water vapor oxidation and improve process reliability. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the specific embodiments or prior art of the present application, the drawings needed to be used in the description of the specific embodiments or prior art will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0016] Figure 1 is a flow chart of a metal grid forming process for a back-illuminated sensor provided by an exemplary embodiment of the present application.

[0017] Figures 2-9 is a device structure schematic diagram of a metal grid forming process for a back-illuminated sensor in the implementation process provided by an exemplary embodiment of the present application.

[0018] Explanation of reference signs: 1, substrate; 101, deep trench isolation structure; 102, oxide side wall layer; 103, silicon dioxide filling layer; 104, adhesion layer; 2, metal layer; 3, silicon nitride mask layer; 4, silicon oxide layer; 5, metal hard mask layer; 6, protective layer; 7, anti-reflection layer; 8, photoresist layer; 9, nitride layer; 10, pad oxide layer. DETAILED DESCRIPTION

[0019] The technical solutions in the present application will be described clearly and completely in combination with the drawings. Obviously, the described embodiments are some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort fall within the scope of the present application.

[0020] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0021] In the description of the present application, it is necessary to point out that, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "linking" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or the internal communication of two elements, it can be wireless connection, or wired connection. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0022] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict between them.

[0023] The present application provides a metal grid forming process for back-illuminated sensor, referring to Figure 1 , which comprises the following steps: S1: providing a substrate, a plurality of deep trench isolation structures are formed in the substrate, and an oxide side wall layer, a silicon dioxide filling layer and an adhesion layer are sequentially formed on the surface of the substrate, and a metal layer is formed on the adhesion layer.

[0024] Exemplarily, referring to Figure 2 , a substrate 1 of a back-illuminated sensor is provided, a plurality of deep trench isolation structures 101 are arranged at intervals in the substrate 1, a pixel unit (not shown in the figure) is formed between adjacent deep trench isolation structures 101, and an oxide side wall layer 102, a silicon dioxide filling layer 103 and an adhesion layer 104 are sequentially formed on the surface of the substrate 1 from bottom to top, wherein the material of the oxide side wall layer 102 is high dielectric constant oxide. A metal layer 2 is formed on the adhesion layer 104.

[0025] Further, the adhesion layer 104 can be a titanium nitride layer.

[0026] Further, the material of the metal layer 2 can be tungsten.

[0027] S2: depositing a silicon nitride mask layer on the metal layer.

[0028] Exemplarily, referring to Figure 3 , a silicon nitride mask layer 3 is deposited on the metal layer 2.

[0029] Further, the silicon nitride mask layer 3 can be deposited on the metal layer 2 by chemical vapor deposition process.

[0030] S3: sequentially forming a silicon oxide layer, a metal hard mask layer and a protective layer on the silicon nitride mask layer.

[0031] Exemplarily, referring to Figure 4A silicon oxide layer 4, a metal hard mask layer 5 and a protection layer 6 are sequentially deposited on the silicon nitride mask layer 3.

[0032] Further, the silicon oxide layer 4, the metal hard mask layer 5 and the protection layer 6 are sequentially formed by a chemical vapor deposition process, a physical vapor deposition process and a chemical vapor deposition process respectively.

[0033] S4: Form a patterned photoresist layer, the reserved area of the photoresist layer shields the protection layer and the metal hard mask layer located directly above the deep trench isolation structure.

[0034] For example, referring to Figure 5 , a patterned photoresist layer 8 is formed, the reserved area of the photoresist layer 8 shields the protection layer 6 and the metal hard mask layer 5 located directly above the deep trench isolation structure 101.

[0035] Further, in order to improve the formation quality of the photoresist layer 8, after the above step S3, before the patterned photoresist layer 8 is formed, the following step can also be included: Spin-coat an anti-reflective layer on the protection layer.

[0036] For example, referring to Figure 4 The anti-reflective layer 7 can be formed on the protection layer 6 by a spin-coating process, and the subsequently formed patterned photoresist layer 8 is located on the surface of the anti-reflective layer 7, as shown in Figure 5 The anti-reflective layer 7 not covered by the photoresist layer 8 is removed after the photoresist layer 8 is developed, and the remaining anti-reflective layer 7 is removed together with the photoresist layer 8 in the subsequent steps.

[0037] S5: Etch the exposed protection layer and metal hard mask layer with the photoresist layer as a mask.

[0038] For example, referring to Figure 6 The exposed protection layer 6 and metal hard mask layer 5 are etched with the photoresist layer 8 as a mask, so that there is a metal hard mask layer 5 and a protection layer 6 remaining above each deep trench isolation structure 101. Then, the photoresist layer 8 and etching residues are removed by cleaning.

[0039] Further, in this step, the etching process used is a plasma etching process.

[0040] S6: Etch the exposed silicon oxide layer and silicon nitride mask layer with the remaining protection layer and metal hard mask layer as a mask.

[0041] For example, referring to Figure 7 The exposed silicon oxide layer 4 and silicon nitride mask layer 3 are etched with the remaining protection layer 6 and metal hard mask layer 5 as a mask. Finally, there is a silicon nitride mask layer 3 and a silicon oxide layer 4 remaining above each deep trench isolation structure 101.

[0042] Further, in this step, the etching process adopted is a plasma etching process.

[0043] Further, in the process of etching the exposed silicon oxide layer 4 and silicon nitride mask layer 3, the remaining protective layer 6 and metal hard mask layer 5 will also be removed, and part of the silicon oxide layer 4 under the protective layer 6 and metal hard mask layer 5 will also be lost.

[0044] S7: Dry etching the exposed metal layer with the remaining silicon oxide layer and silicon nitride mask layer as a mask, and the remaining metal layer constitutes a metal grid. In this process, the sidewall of the remaining metal layer forms a nitride protective layer.

[0045] For example, referring to Figure 8 The remaining metal layer 2 constitutes a metal grid by dry etching the exposed metal layer 2 with the remaining silicon oxide layer 4 and silicon nitride mask layer 3 as a mask. In the dry etching process, the silicon nitride mask layer 3 will be bombarded, and nitrogen atoms / ions will be emitted. The emitted nitrogen atoms / ions will react with the sidewall etching surface of the metal layer 2, thereby forming a nitride layer 9 covering the sidewall of the final remaining metal layer 2.

[0046] S8: Depositing a liner oxide layer.

[0047] For example, a liner oxide layer 10 is deposited, and the material of the liner oxide layer 10 can be silicon dioxide. Referring to Figure 9 The liner oxide layer 10 covers the sidewall of the metal grid, the surface of the remaining silicon nitride mask layer 3, and the surface of the remaining silicon dioxide filling layer 103. And for the metal grid, because there is a nitride layer 9 as an adhesive layer, the sidewall of the metal grid and the liner oxide layer 10 form better contact, improving the formation quality of the liner oxide layer 10.

[0048] Further, in this step, the liner oxide layer 10 is deposited by a chemical vapor deposition process.

[0049] The metal grid forming process for a back-illuminated sensor provided by the embodiments of the present application, by first depositing a silicon nitride mask layer on the metal layer, and then sequentially depositing a silicon oxide layer, a metal hard mask layer, and a protective layer, so that in the subsequent etching process, when using a dry etching process to etch the exposed metal layer, the silicon nitride mask layer will be bombarded, and nitrogen atoms / ions will be emitted. The emitted nitrogen atoms / ions will react with the sidewall etching surface of the metal layer, thereby forming a nitride layer. On the one hand, the nitride layer will act as an adhesive layer, which is conducive to better contact between the sidewall of the subsequent metal grid and the liner oxide layer, improving the formation quality of the liner oxide layer. On the other hand, it can also act as a protective layer to prevent subsequent metal grid water vapor oxidation and improve process reliability.

[0050] Obviously, the above-mentioned embodiments are only examples for clearly illustrating the present application, but not limitation to the embodiments. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and also impossible to enumerate all the embodiments. The obvious changes or variations derived from the above description are still within the protection scope of the present application.

Claims

1. A metal grid forming process for a back-illuminated sensor, characterized in that, include: A substrate is provided in which a plurality of deep trench isolation structures are formed, and an oxide sidewall layer, a silicon dioxide filling layer and an adhesive layer are sequentially formed on the surface of the substrate, and a metal layer is formed on the adhesive layer. A silicon nitride mask layer is deposited on the metal layer; A silicon oxide layer, a metal hard mask layer, and a protective layer are sequentially formed on the silicon nitride mask layer; A patterned photoresist layer is formed, wherein the reserved area of ​​the photoresist layer shields the protective layer and the metal hard mask layer located directly above the deep trench isolation structure; Using the photoresist layer as a mask, the exposed protective layer and metal hard mask layer are etched. Using the remaining protective layer and metal hard mask layer as a mask, the exposed silicon oxide layer and silicon nitride mask layer are etched. Using the remaining silicon oxide layer and silicon nitride mask layer as a mask, the exposed metal layer is dry etched, and the remaining metal layer forms a metal grid. During this process, a nitride protective layer is formed on the sidewalls of the remaining metal layer. Deposited liner oxide layer.

2. The metal grid forming process for a back-illuminated sensor according to claim 1, characterized in that, The adhesive layer is a titanium nitride layer.

3. The metal grid forming process for a back-illuminated sensor according to claim 1, characterized in that, The metal layer is made of tungsten.

4. The metal grid forming process for a back-illuminated sensor according to claim 1, characterized in that, After the silicon oxide layer, the metal hard mask layer, and the protective layer are sequentially formed on the silicon nitride mask layer, the method further includes: An anti-reflective layer is spin-coated onto the protective layer.

5. The metal grid forming process for a back-illuminated sensor according to claim 1, characterized in that, In the step of depositing a silicon nitride mask layer on the metal layer, the silicon nitride mask layer is deposited by a chemical vapor deposition process.

6. The metal grid forming process for a back-illuminated sensor according to claim 1, characterized in that, In the step of etching the exposed protective layer and metal hard mask layer using the photoresist layer as a mask, the etching process used is plasma etching.

7. The metal grid forming process for a back-illuminated sensor according to claim 1, characterized in that, In the step of etching the exposed silicon oxide layer and silicon nitride mask layer using the remaining protective layer and metal hard mask layer as masks, the etching process used is plasma etching.

8. The metal grid forming process for a back-illuminated sensor according to claim 1, characterized in that, In the step of etching the exposed silicon oxide layer and silicon nitride mask layer using the remaining protective layer and metal hard mask layer as a mask, the protective layer and metal hard mask layer are also removed.

9. The metal grid forming process for a back-illuminated sensor according to claim 1, characterized in that, In the step of depositing the pad oxide layer, the pad oxide layer is deposited by a chemical vapor deposition process.

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