A thin film etching method

Abstract

The present invention relates to the technical field of thin film etching, and provides a thin film etching method for etching a multilayer metal thin film, comprising the following steps: S1, firstly using a first layer of photomask to etch the first layer of thin film through an etching process; S2, then using a second layer of photomask with a size larger than the first layer of photomask to etch the second layer of thin film through an etching process; S3, repeating the step S2, and then etching the third layer of thin film to the Nth layer of thin film in sequence; S4, finally etching the remaining thin film in the middle layer again to obtain a stable structure, the stable structure includes an intact bottom layer of thin film and side walls of each layer of thin film above the bottom layer that are nearly vertical, and the middle layer is thin films of each layer except the first layer of thin film and the bottom layer of thin film. The present invention can avoid the problem that dry etching cannot stay on the thin titanium film, and can also avoid excessive lateral corrosion of wet etching, which is not conducive to the continuation of subsequent processes and the stability of the entire structure.

Description

Technical Field

[0001] The invention relates to the technical field of thin film etching, in particular to a thin film etching method. Background Art

[0002] In order to ensure that the top two layers of the structure can be completely etched cleanly, the traditional dry etching must add enough over-etching to completely ensure that there is no residue on the metal film of the top two layers. However, once over-etching is added, since all the films are metals, the etching selectivity between each other is relatively low, so the bottom structure will be damaged, and even the bottom thin metal will be completely or partially etched away, which does not meet the requirements of our structure. If the top metal is dry-etched and the middle layer structure is traditionally wet-etched, since traditional wet etching is isotropic, the sidewalls will be wet-etched at the same time. At the same time, in order to ensure that the middle layer of metal can be completely etched, it is necessary to add enough over-etching to complete it. In this way, the entire structure will become a mushroom-shaped structure with a larger upper layer and a smaller middle layer. Such a structure is not conducive to the stability of the structure, and it is not conducive to the continuation of subsequent processes. Summary of the invention

[0003] The purpose of the present invention is to provide a thin film etching method, which can avoid the problem of dry etching being unable to stay on the thin titanium film through a multi-layer mask and an etching process, and can also avoid excessive lateral corrosion by wet etching, which is not conducive to the continuation of subsequent processes and the stability of the entire structure.

[0004] To achieve the above object, an embodiment of the present invention provides the following technical solution: a thin film etching method for etching a multi-layer metal film, comprising the following steps:

[0005] S1, firstly, etching the first layer of thin film by an etching process using a first layer of photomask, and etching until it stays on the surface of the second layer of thin film;

[0006] S2, etching the second layer of thin film by an etching process using a second layer of mask having a size larger than that of the first layer of mask, and etching to half the thickness of the second layer of thin film, at which time the first layer of thin film and the second layer of thin film form a step structure;

[0007] S3, repeating the step S2, and then etching the third layer of thin film to the Nth layer of thin film in sequence, in the etching of each lower layer of thin film, a mask with a larger size than that used in the etching of the upper layer of thin film is used, and etching is performed to half the thickness of the currently etched thin film, and the currently etched thin film and the upper layer of thin film form a step structure;

[0008] S4, finally etching the remaining film in the middle layer again to obtain a stable structure, which includes an intact bottom film and nearly vertical side walls of each layer of film above the bottom film, and the middle layer is the film of each layer except the first layer and the bottom film.

[0009] Furthermore, the etching process includes dry etching and wet etching. In the steps S1, S2 and S3, the etching process used is dry etching; and in the step S4, the etching process used is wet etching.

[0010] Furthermore, in the step S2, the size of the second layer of mask is the first layer of mask plus half of the film thickness of the second layer.

[0011] Furthermore, from the first film to the bottom film, the thickness of each film layer becomes thinner in sequence.

[0012] Furthermore, the multi-layer metal film is a three-layer metal film, the first layer film and the second layer film are both titanium films, the second layer film is an aluminum film, and the thickness of the first layer film is greater than the thickness of the third layer film.

[0013] Compared with the prior art, the beneficial effects of the present invention are: a thin film etching method, which uses a layer of mask to facilitate dry etching of the thick titanium film on the upper layer, and then uses a second layer of mask slightly larger than the first layer of mask to dry-etch half of the aluminum film in the middle, and the remaining aluminum film is completely removed by wet etching to achieve only the thin titanium film at the bottom. This method can avoid the problem that dry etching cannot stay on the thin titanium film, and can also avoid excessive lateral corrosion by wet etching, which is not conducive to the continuation of subsequent processes and the stability of the entire structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A schematic diagram of the structure of a metal film in a thin film etching method provided by an embodiment of the present invention;

[0015] Figure 2 A schematic diagram of the structure after dry etching of an upper titanium film in a thin film etching method provided by an embodiment of the present invention;

[0016] Figure 3 A schematic diagram of the structure after half of the aluminum is dry-etched away by a thin film etching method provided by an embodiment of the present invention;

[0017] Figure 4 A schematic diagram of the structure after the remaining aluminum film is wet-etched away by a thin film etching method provided by an embodiment of the present invention;

[0018] In the accompanying drawings: 1 - thick titanium film; 2 - aluminum film; 3 - thin titanium film. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] See also Figures 1 to 4The embodiment of the present invention provides a thin film etching method for etching a multi-layer metal thin film, comprising the following steps: S1, firstly using a first layer of photomask to etch a first layer of thin film through an etching process, and etching until the first layer of thin film is on the surface of the second layer of thin film; S2, then using a second layer of photomask with a size larger than the first layer of photomask to etch the second layer of thin film through an etching process, and etching until the second layer of thin film is half the thickness, at this time, the first layer of thin film and the second layer of thin film form a step structure; S3, repeating the step S2, then etching the third layer of thin film to the Nth layer of thin film in sequence, in the etching of each next layer of thin film, a mask with a size larger than that used in the etching of the previous layer of thin film is used, and etching is performed to half the thickness of the currently etched thin film, and the currently etched thin film and the previous layer of thin film form a step structure; S4, finally etching the remaining thin film of the middle layer again to obtain a stable structure, the stable structure includes an intact bottom layer of thin film and the side walls of each layer of thin film above the bottom layer are nearly vertical, the middle layer is the thin film of each layer except the first layer of thin film and the bottom layer of thin film. In this embodiment, a layer of mask is used to facilitate dry etching of the thick titanium film 1 of the upper layer, and then a second layer of mask with a size slightly larger than the first layer of mask is used to dry etch away half of the aluminum film 2 in the middle, and the remaining aluminum film 2 is completely removed by wet etching to achieve only the thin titanium film 3 at the bottom. This method can avoid the problem that dry etching cannot stay on the thin titanium film 3, and can also avoid too much lateral corrosion by wet etching, which is not conducive to the continuation of subsequent processes and the stability of the entire structure. Specifically, this embodiment exemplifies the form of three layers of thin films, wherein the first layer of thin film and the second layer of thin film are both titanium thin films, the second layer of thin film is aluminum thin film 2, and the thickness of the first layer of thin film is greater than the thickness of the third layer of thin film. For the convenience of description, the first layer is defined as thick titanium film 1, the second layer is defined as aluminum thin film 2, and the third layer is defined as thin titanium thin film 3. Of course, there can be more layers. When there are more layers, the thickness of each layer of thin film becomes thinner from the first layer of thin film to the bottom layer of thin film. Preferably, the above-mentioned etching process includes dry etching and wet etching. In the steps S1, S2 and S3, the etching process used is dry etching; in the step S4, the etching process used is wet etching, so that the dry etching and the wet etching are effectively combined, and an additional layer of mask is used to prevent the structure from damaging the bottom thin titanium layer due to direct dry etching, and also to avoid excessive sidewall corrosion and structural instability due to direct wet etching, thereby optimizing the structure. Compared with the existing dry etching that damages the underlying structure or wet etching that creates a mushroom-shaped structure, a more stable structure can be obtained.In step S4, since wet etching is isotropic etching, the side walls will also be etched in the same way, so that the entire structure will become the stable structure we want, with nearly vertical side walls and the underlying thin titanium metal can be intact.

[0021] As an optimization solution of the embodiment of the present invention, please refer to Figures 1 to 4 In the step S2, the size of the second photomask is the first photomask plus half of the second layer's film thickness. In this embodiment, setting the size of the second photomask to half of the first photomask plus the second layer's film thickness can form the above-mentioned step structure, laying the foundation for the final wet etching. When there are more intermediate layers, for example, when there are four layers in total, the size of the third photomask is half of the second photomask plus the third layer's film thickness, and so on.

[0022] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A thin film etching method, characterized in that: Used for etching of multi-layer metal films, including the following steps: S1, firstly, etching the first layer of thin film by an etching process using a first layer of photomask, and etching until it stays on the surface of the second layer of thin film; S2, etching the second layer of thin film by an etching process using a second layer of mask having a size larger than that of the first layer of mask, and etching to half the thickness of the second layer of thin film, at which time the first layer of thin film and the second layer of thin film form a step structure; S3, repeating the step S2, and then etching the third layer of thin film to the Nth layer of thin film in sequence, in the etching of each lower layer of thin film, a mask with a larger size than that used in the etching of the upper layer of thin film is used, and etching is performed to half the thickness of the currently etched thin film, and the currently etched thin film and the upper layer of thin film form a step structure; S4, finally etching the remaining thin film of the middle layer again to obtain a stable structure, wherein the stable structure includes an intact bottom thin film and side walls of each middle thin film above the bottom layer vertically aligned in a line, wherein the middle layer is each thin film except the first thin film and the bottom thin film, The etching process includes dry etching and wet etching. In the steps S1, S2 and S3, the etching process used is dry etching; in the step S4, the etching process used is wet etching.

2. A thin film etching method according to claim 1, characterized in that: In the step S2, the size of the second mask layer is the first mask layer plus half of the film thickness of the second layer.

3. A thin film etching method according to claim 1, characterized in that: From the first film layer to the bottom film layer, the thickness of each film layer becomes thinner in sequence.

4. A thin film etching method according to claim 1, characterized in that: The multilayer metal film is a three-layer metal film, the first layer film and the second layer film are both titanium films, the second layer film is an aluminum film, and the thickness of the first layer film is greater than the thickness of the third layer film.

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