Method for improving aluminum metal residues

Abstract

The invention discloses a method for improving aluminum metal residues. The method comprises the following steps: step 1, a wafer comprises a bottom metal layer and metal aluminum which is positioned on the bottom metal layer and covers the bottom metal layer; opening an etching window of the metal aluminum after exposure, development and etching of the photoresist, and then carrying out aluminum etching to completely etch the metal aluminum in the etching window; removing the residual photoresist after the etching of the metal aluminum is finished; step 2, cleaning for the first time, and removing etching by-products; thirdly, cleaning is conducted for the second time, and part of bottom layer metal is removed; if residual aluminum metal exists, the residual aluminum metal can fall off along with the removed bottom layer metal, and the purpose of completely removing the metal aluminum is achieved. After photoetching and etching processes of the back metal layer are completed, aluminum metal residues are removed in a secondary cleaning mode, and the situation that the product yield is affected by the residual aluminum metal in the follow-up process is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor device manufacturing process, in particular to a method for improving aluminum residue. BACKGROUND

[0002] BSI (Backside illumination) back-illuminated image sensor is widely used in consumer electronics, security, automotive and other fields due to its higher quantum efficiency. Generally, products with a pixel spacing size of 1.12 μm or less are manufactured using a BSI process. Thanks to deep trench isolation (DTI) and metal grid process, the performance of BSI products has been greatly improved. In order to enable the backside aluminum pad to be connected to the external pin, a tungsten, aluminum or other metal filling process is required during the manufacturing of BSI products. The role of tungsten is to fill the via and become a metal grid, and the role of aluminum is usually backside wiring.

[0003] During the backside metal processing, a layer of metal tungsten is first deposited to fill the via, then a layer of metal aluminum is deposited, and then the aluminum in the pixel area is completely etched, and finally a metal tungsten grid is made. In the pixel area, external light needs to pass through to reach the photodiode in the front layer, so there should be no non-transparent material to block it. However, during the aluminum etching process, due to the unevenness of aluminum grains and the blocking of photoresist residues, aluminum residue is easily generated, which affects the light entering of a single or multiple pixels, resulting in bad pixel points (Bad Pixel), and ultimately affecting the imaging quality of the image sensor.

[0004] In the manufacturing of BSI products, the improvement of aluminum residue has always been a key problem. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a method for improving aluminum residue.

[0006] To solve the above problems, the present application provides a method for improving aluminum residue, which comprises: Step one, the wafer contains a bottom metal layer and a metal aluminum layer on the bottom metal layer; after the exposure and development of photoresist and the opening of the etching window of the metal aluminum, the metal aluminum in the etching window is etched; after the etching of the metal aluminum is completed, the remaining photoresist is removed; Step two, first cleaning to remove etching by-products; Step three, second cleaning to remove part of the bottom metal layer; if there is residual aluminum metal, it will fall off with the removed bottom metal layer, achieving the purpose of completely removing the metal aluminum.

[0007] Further, the first cleaning in the second step uses a fluorine-containing semi-aqueous cleaning agent.

[0008] Further, the etching by-products in the second step include high molecular polymers.

[0009] Further, the bottom metal is tungsten.

[0010] Further, the second cleaning in the third step uses a cleaning agent containing hydrogen peroxide to remove part of the tungsten, so that the possible residual aluminum attached to the tungsten is removed simultaneously.

[0011] Further, the cleaning agent used in the second cleaning needs to have the ability to corrode and remove the bottom metal; after the second cleaning, a certain thickness of the bottom metal is removed.

[0012] Further, after the process steps are completed, the bottom metal is etched The method for improving the residual aluminum metal according to the present application removes the surface aluminum metal by the first cleaning step, and removes the aluminum metal attached to the bottom metal by etching the bottom metal in the second cleaning step, so that the residual aluminum metal is removed simultaneously when the bottom metal is partially removed, thereby improving the residual aluminum metal, and improving the device yield and reliability. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a schematic diagram of the method steps of the present application. DETAILED DESCRIPTION

[0014] The specific embodiments of the present application will be described below with reference to the accompanying drawings, and the technical solutions in the present application will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. According to the following description and claims, the advantages and characteristics of the present application will be more apparent. It should be noted that the drawings are very simplified and use non-precise ratios, and are only used for the purpose of conveniently and clearly assisting the description of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0015] It is to be understood that the application can assume various alternative embodiments, and should not be considered limited to the examples described herein. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and explanations to convey the principles of the application to others skilled in the art. In the drawings, the size and relative sizes of layers and regions can be exaggerated for clarity. Like reference numerals designate like elements throughout. It will be understood that when an element or layer is referred to as being "on" or "connected to" another element or layer, it can be directly on, connected or coupled to the other element or layer, or intervening elements or layers can be present. In contrast, when an element is referred to as being "directly on," "directly connected to," or "directly coupled to" another element or layer, there are no intervening elements or layers present. It will be understood that, although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present application.

[0016] The present application provides a method for improving the removal of aluminum metal, the method comprising: Step one, a wafer comprising a bottom metal layer and a metal aluminum layer on top of the bottom metal layer; after the exposure and development of photoresist and etching, an etching window of the metal aluminum layer is opened, and then the metal aluminum layer in the etching window is etched; after the etching of the metal aluminum layer, the remaining photoresist is removed; Step two, a first cleaning is performed to remove the etching byproducts; Step three, a second cleaning is performed to remove part of the bottom metal layer; if there is residual aluminum metal, it will fall off with the removed bottom metal layer, achieving the purpose of completely removing the metal aluminum.

[0017] Through the two cleaning steps, the problem of aluminum metal residue can be effectively improved.

[0018] For example, in the manufacturing process of a BSI backside illuminated image sensor, the backside of the BSI image sensor has a layer of metal tungsten (i.e. a bottom metal layer), and a layer of metal aluminum on top of the metal tungsten. As shown in FIG. 1, the BSI backside illuminated image sensor comprises a pixel region for light sensing and photoelectric conversion, and a logic region around the pixel region. The process needs to etch the aluminum in the pixel region to avoid opaque metal aluminum from blocking light from entering the pixel region. After the photoresist on top of the pixel region metal aluminum of the BSI image sensor is exposed, the etching of the pixel region metal aluminum is then performed, and the remaining photoresist is removed after the etching of the metal aluminum is completed. Figure 1 The process needs to etch the aluminum in the pixel region to avoid opaque metal aluminum from blocking light from entering the pixel region. After the photoresist on top of the pixel region metal aluminum of the BSI image sensor is exposed, the etching of the pixel region metal aluminum is then performed, and the remaining photoresist is removed after the etching of the metal aluminum is completed.

[0019] Then, the first wet cleaning is performed to remove the etching by-products, mainly some high molecular polymer, by using a fluorine-containing semi-aqueous cleaning agent.

[0020] The second cleaning is then performed, and for the bottom layer metal tungsten, a hydrogen peroxide-containing agent is used to remove a portion of the top layer tungsten. If there is residual aluminum metal, the residual aluminum is attached to the top layer tungsten. By removing a certain thickness of the metal tungsten by the hydrogen peroxide-containing agent, the aluminum will fall off with the removed metal tungsten, and the purpose of completely removing the aluminum metal can be achieved.

[0021] Therefore, by the above two cleaning steps, the metal aluminum that needs to be removed can be completely removed.

[0022] Subsequently, the subsequent processes such as metal grid hard mask deposition and metal grid photolithography can be performed.

[0023] For the BSI pattern sensor, the method for improving the aluminum metal residue of the present application can remove the residual aluminum metal in the window after the back metal layer photolithography and etching process is completed by using the secondary cleaning method, which can avoid the residual metal from affecting the light entering of a single or multiple pixels to generate a bad pixel and affect the product yield.

[0024] Of course, the method mentioned in the present application is not only applicable to the BSI product, and the reagent contained in the wet process for removing the metal residue is also not limited to hydrogen peroxide. For other semiconductor devices, the method of the present application can also be used for the problem of residual aluminum metal.

[0025] For the bottom layer metal other than tungsten, the cleaning solution used in the second cleaning needs to contain a component that has a certain corrosion and removal ability for the bottom layer metal, so as to have a certain thickness of corrosion on the surface of the bottom layer metal.

[0026] The above is only the preferred embodiment of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for improving aluminum metal residue, characterized in that: The method comprises: In step 1, the wafer includes a bottom metal layer and metal aluminum located on the bottom metal layer and covering the bottom metal layer; after exposing, developing and etching the photoresist, an etching window for the metal aluminum is opened, and then aluminum etching is performed to completely etch the metal aluminum in the etching window; After the aluminum metal etching is completed, the remaining photoresist is removed; Step 2: Perform the first cleaning to remove etching byproducts; Step three: perform a second cleaning to remove part of the underlying metal; if there is any residual aluminum metal, it will fall off with the removed underlying metal, achieving the purpose of completely removing the metal aluminum.

2. The method for improving aluminum metal residue according to claim 1, wherein: In the step 2, the cleaning liquid used for the first cleaning is a fluorine-containing semi-aqueous cleaning agent.

3. The method for improving aluminum metal residue according to claim 1, wherein: In the step 2, the etching by-products include high molecular polymers.

4. The method for improving aluminum metal residue according to claim 1, wherein: The bottom metal is tungsten.

5. The method for improving aluminum metal residue according to claim 4, wherein: In step three, the second cleaning uses a cleaning solution containing hydrogen peroxide to remove part of the tungsten, so that the possible residual metal aluminum attached to the bottom metal tungsten is removed simultaneously during the tungsten removal process.

6. The method for improving aluminum metal residue according to claim 1, wherein: The cleaning solution used in the second cleaning needs to be able to corrode and remove the underlying metal; after the second cleaning is completed, a certain thickness of the underlying metal can be removed.

7. The method for improving aluminum metal residue according to claim 1, wherein: After the above process steps are completed, an etching process step is performed on the bottom metal.

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