Methods for removing strip-shaped polymers in thick aluminum etching

Abstract

This invention discloses a method for removing strip-shaped polymers during thick aluminum etching, comprising: Step 1, forming an aluminum layer on the surface of a first oxide layer on an underlying structure to form a photoresist pattern. Step 2, etching the aluminum layer and over-etching the first oxide layer using a first dry etching process, wherein the etching gas used in the over-etching is a chlorine-containing gas to reduce polymer accumulation. Step 3, performing an ashing process to remove the photoresist pattern and polymer, which also includes using cyclic rinsing to peel off residual photoresist pattern and polymer. Step 4, performing a wet stripping process in an acid bath, wherein the wet stripping process divides the wet etching time into multiple wet segmented etching steps, and multiple rinsing steps are performed after each wet segmented etching step. By reducing the etching time of each step through wet segmented etching, the acid in the acid bath is kept fresh, improving the stripping effect. This invention can improve the removal effect of polymers generated during thick etching.

Description

Technical Field

[0001] This invention relates to a method for manufacturing semiconductor integrated circuits, and more particularly to a method for removing strip-shaped polymers from thick aluminum etching. Background Technology

[0002] In semiconductor integrated circuits, aluminum layers are often used as metal lines in metal interconnect structures. These metal lines require patterning etching after aluminum layer deposition. Photoresist is used as a mask during aluminum etching, and the etching process often generates polymers. Particularly in some applications, aluminum layers thicker than 3 micrometers are needed. For example, thick aluminum is used in the third metal layer (M3) of MEMS 3D anisotropic magnetoresistive (MR) systems. Etching thick aluminum makes it more prone to generating thick polymers, making polymer removal the primary task after etching and also the most challenging aspect of this etching process.

[0003] Existing thick aluminum etching processes include the following steps:

[0004] Step 1 involves metal etching (ET) and over-etching (OE) of the underlying oxide layer. Over-etching uses a fluorine-containing gas, specifically F+ etching ox, where CHF3 is one example. This process generates polymers.

[0005] Step 2: Perform ashing to remove the photoresist.

[0006] Step 3: A wet stripping process is performed in the acid bath to remove residual photoresist and polymer. However, in reality, the polymer formed after thick aluminum etching is usually in the form of lines, which is relatively difficult to remove. To improve the polymer removal efficiency, existing improvement methods include increasing the wet stripping process time, for example, increasing the process time to 1 minute.

[0007] However, as Figure 1 The image shown is an electron microscope photograph of the completed thick aluminum etching process. Polymer 102 remains on the etched aluminum line 101. Polymer 102 has a strip-like structure and is therefore also called strip polymer. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a method for removing strip-shaped polymers in thick aluminum etching, which can improve the removal effect of polymers generated in thick etching.

[0009] To solve the above-mentioned technical problems, the method for removing strip-shaped polymers in thick aluminum etching provided by the present invention includes the following steps:

[0010] Step 1: Provide an underlying structure with a first oxide layer formed on its surface, form an aluminum layer on the surface of the first oxide layer, form a photoresist on the surface of the aluminum layer, and pattern the photoresist to form a photoresist pattern, wherein the photoresist pattern opens up the area to be etched.

[0011] Step 2: The aluminum layer is etched using a first dry etching process, and the first oxide layer at the bottom of the aluminum layer is over-etched. The etching gas used for the over-etching is a chlorine-containing gas to reduce polymer accumulation.

[0012] Step 3: Perform an ashing process to remove the photoresist pattern and the polymer. The ashing process also includes using a cyclic rinsing to peel off the residual photoresist pattern and the polymer, thereby increasing the removal capacity of the polymer.

[0013] Step 4: Perform a wet stripping process in the acid bath. The wet stripping process divides the wet etching time into multiple wet segmented etchings. After each wet segmented etching is completed, multiple rinsings are performed. By reducing the etching time of each etching step through the wet segmented etching, the acid in the acid bath is kept fresh, thereby improving the stripping effect.

[0014] A further improvement is that, in step one, the thickness of the aluminum layer is greater than 3 micrometers.

[0015] A further improvement is that, in step two, the etching gas used for over-etching is a mixture of Cl2, BCl3, and N2.

[0016] A further improvement is that the etching gas used in the first dry etching process to etch the aluminum layer includes a fluorine-containing gas.

[0017] A further improvement is that, in step three, the sub-steps of a single cycle in the cyclic flushing include:

[0018] DIW flushing is used.

[0019] The process involves rinsing with DIW gas, oxygen, and nitrogen.

[0020] The number of cycles of the cyclic flushing is greater than or equal to 2.

[0021] A further improvement is that, in step four, the wet segmented etching process time is 10s to 15s.

[0022] A further improvement is that, in step four, the rinsing is performed 2 to 3 times after each wet segmented etching is completed.

[0023] A further improvement is that the wet stripping process includes more than two wet segmented etching operations.

[0024] A further improvement is that the acid solution used in the acid tank includes SST-A2.

[0025] A further improvement is that the wet stripping process is performed using a single-piece operation method in step four.

[0026] A further improvement is that, in step one, an adhesion layer and a barrier layer are also formed between the first oxide layer and the aluminum layer;

[0027] A further improvement is that the adhesion layer includes a Ti layer.

[0028] The barrier layer includes a TiN layer.

[0029] A further improvement is that, in step one, the aluminum layer serves as an interconnect.

[0030] The underlying structure includes a semiconductor substrate.

[0031] A metal interconnect structure at the bottom of the first oxide layer was completed on the semiconductor substrate.

[0032] A further improvement is that a MEMS triaxial AMR magnetic sensor is formed on the semiconductor substrate.

[0033] A further improvement is that the aluminum layer is the third metal layer of the MEMS triaxial AMR magnetic sensor.

[0034] To overcome the difficulty of removing polymers during thick aluminum etching, this invention employs multiple approaches, improving each step of the wet stripping process from thick aluminum etching to the acid bath. In particular, the first dry etching process has a special setting for the etching gas used for the subsequent over-etching of the first oxide layer after etching the aluminum layer. Specifically, chlorine-containing gas is used instead of fluorine-containing gas in the existing process, which reduces polymer accumulation.

[0035] Based on reducing polymer accumulation, a circulating rinsing step was added to the ashing process. Compared with the existing ashing process without a rinsing step, the addition of circulating rinsing can increase the polymer removal capacity.

[0036] In the wet stripping process of acid baths, the etching effect is not improved by simply extending the wet etching time. This is because simply extending the wet etching time will cause the acid in the acid bath to become old and reduce the polymer stripping effect. Unlike existing technologies, this invention divides the wet etching time into multiple wet segmented etching processes. After each wet segmented etching process is completed, multiple rinsing processes are performed. In this way, the acid in the acid bath is kept fresh in each wet segmented etching process, thereby improving the stripping effect on residual polymers.

[0037] This invention integrates improvements to the first dry etching process, ashing treatment, and wet stripping process, ultimately improving the removal effect of polymers generated during thick etching and achieving complete removal of polymers generated during thick etching. Attached Figure Description

[0038] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0039] Figure 1 Electron microscope images of the completed thick aluminum etching process;

[0040] Figure 2 This is a flowchart of a method for removing strip-shaped polymers in thick aluminum etching according to an embodiment of the present invention;

[0041] Figures 3A-3D This is a schematic diagram of the device structure in each step of the method for removing strip-shaped polymers in thick aluminum etching according to an embodiment of the present invention;

[0042] Figure 4 This is an electron microscope image taken after the completion of the method for removing strip-shaped polymers in thick aluminum etching according to an embodiment of the present invention. Detailed Implementation

[0043] like Figure 2 The diagram shown is a flowchart of a method for removing strip-shaped polymers during thick aluminum etching according to an embodiment of the present invention; as shown... Figures 3A to 3D The diagram shown is a schematic representation of the device structure in each step of the method for removing strip-shaped polymers from thick aluminum etching according to an embodiment of the present invention. The method for removing strip-shaped polymers from thick aluminum etching according to an embodiment of the present invention includes the following steps:

[0044] Step 1, such as Figure 3A As shown, a base structure is provided with a first oxide layer 201 formed on its surface, and an aluminum layer 202 is formed on the surface of the first oxide layer 201. A photoresist 203 is formed on the surface of the aluminum layer 202.

[0045] like Figure 3BAs shown, the photoresist 203 is patterned by exposure and development to form a photoresist 203 pattern, which opens up the area to be etched.

[0046] In this embodiment of the invention, the thickness of the aluminum layer 202 is greater than 3 micrometers.

[0047] An adhesion layer and a barrier layer are also formed between the first oxide layer 201 and the aluminum layer 202;

[0048] The adhesion layer includes a Ti layer.

[0049] The barrier layer includes a TiN layer.

[0050] The aluminum layer 202 serves as an interconnect line, that is, after the aluminum layer 202 is etched, it becomes an aluminum wire.

[0051] The underlying structure includes a semiconductor substrate.

[0052] A metal interconnect structure at the bottom of the first oxide layer 201 was completed on the semiconductor substrate.

[0053] In some embodiments, a MEMS triaxial AMR magnetic sensor is formed on the semiconductor substrate.

[0054] The aluminum layer 202 is the third metal layer of the MEMS triaxial AMR magnetic sensor.

[0055] Step 2, as follows Figure 3C As shown, the aluminum layer 202 is etched using a first dry etching process, and the first oxide layer 201 at the bottom of the aluminum layer 202 is over-etched. The etching gas used for the over-etching is a chlorine-containing gas to reduce the accumulation of polymer 205.

[0056] In this embodiment of the invention, the etching gas used for over-etching is a mixture of Cl2, BCl3 and N2.

[0057] The etching gas used in the first dry etching process to etch the aluminum layer 202 includes a fluorine-containing gas, typically CHF3.

[0058] Figure 3C In the diagram, the area indicated by the dashed box 203a is the area where the photoresist 203 is lost; the area indicated by the dashed box 204 is the area where the first oxide layer 201 is removed due to over-etching.

[0059] Step 3, as follows Figure 3DAs shown, an ashing process is performed to remove the photoresist 203 pattern and the polymer 205. The ashing process also includes using a cyclic rinsing to peel off the residual photoresist 203 pattern and the polymer 205, thereby increasing the removal capacity of the polymer 205.

[0060] That is, the ashing treatment described in this embodiment of the invention is an additional cyclic rinsing step on the basis of the existing ashing treatment process, while the existing ashing treatment is only achieved by dry plasma treatment.

[0061] In this embodiment of the invention, the steps of a single cycle in the cyclic flushing include:

[0062] DIW flushing is used.

[0063] The process involves rinsing with DIW gas, oxygen, and nitrogen.

[0064] The number of cycles of the cyclic flushing is greater than or equal to 2.

[0065] Step 4, as follows Figure 3D As shown, a wet stripping process is performed in an acid bath. The wet stripping process divides the wet etching time into multiple wet segmented etchings. After each wet segmented etching is completed, multiple rinsings are performed. By reducing the etching time of each etching step through the wet segmented etching, the acid in the acid bath is kept fresh, thereby improving the stripping effect.

[0066] In this embodiment of the invention, the wet segmented etching process time is 10s to 15s.

[0067] After each wet segmented etching process is completed, the rinsing is performed 2 to 3 times.

[0068] The wet stripping process includes two or more wet segmented etching operations.

[0069] The acid solution used in the acid tank includes SST-A2, and the composition of SST-A2 is: (CH3)2SO / H2O2 / NH4F1.

[0070] The wet stripping process is performed using a single wafer run.

[0071] To overcome the difficulty of removing polymers during thick aluminum etching, this invention employs multiple methods to improve each step of the wet stripping process from thick aluminum etching to the acid bath. In particular, the first dry etching process, after etching the aluminum layer 202, has a special setting for the etching gas used in the subsequent over-etching of the first oxide layer 201. Specifically, chlorine-containing gas is used instead of fluorine-containing gas in the existing process, which reduces polymer accumulation.

[0072] Based on reducing polymer accumulation, a circulating rinsing step was added to the ashing process. Compared with the existing ashing process without a rinsing step, the addition of circulating rinsing can increase the polymer removal capacity.

[0073] In the wet stripping process of acid baths, the etching effect is not improved by simply extending the wet etching time. This is because simply extending the wet etching time will cause the acid in the acid bath to become old and reduce the polymer stripping effect. Unlike the prior art, the embodiments of the present invention divide the wet etching time into multiple wet segmented etching, and after each wet segmented etching is completed, multiple rinsing is performed. In this way, the acid in the acid bath is kept fresh in each wet segmented etching, thereby improving the stripping effect on residual polymer.

[0074] The embodiments of the present invention comprehensively improve the first dry etching process, ashing treatment and wet stripping process, and finally improve the removal effect of polymer generated in the thickness etching and achieve complete removal of polymer generated in the thickness etching.

[0075] like Figure 4 The image shown is an electron microscope photograph after the completion of the method for removing strip-shaped polymers in thick aluminum etching according to an embodiment of the present invention. The aluminum layer is indicated by the symbol 202a.

[0076] The present invention has been described in detail above through specific embodiments, but these are not intended to limit the invention. Many modifications and improvements can be made by those skilled in the art without departing from the principles of the invention, and these should also be considered within the scope of protection of the present invention.

Claims

1. A method for removing strip-shaped polymers from thick aluminum etching, characterized in that, Includes the following steps: Step 1: Provide a base structure with a first oxide layer formed on its surface, form an aluminum layer on the surface of the first oxide layer, form a photoresist on the surface of the aluminum layer, and pattern the photoresist to form a photoresist pattern, wherein the photoresist pattern opens up the area to be etched. Step 2: The aluminum layer is etched using a first dry etching process, and the first oxide layer at the bottom of the aluminum layer is over-etched. The etching gas used for the over-etching is a chlorine-containing gas to reduce polymer accumulation. Step 3: Perform ashing treatment to remove the photoresist pattern and the polymer. The ashing treatment also includes using cyclic rinsing to peel off the residual photoresist pattern and the polymer, thereby increasing the removal capacity of the polymer through cyclic rinsing. The steps of a single cycle in the cyclic flushing include: Use DIW flushing; Use DIW with oxygen and nitrogen for flushing; Step 4: Perform a wet stripping process in the acid bath. The wet stripping process divides the wet etching time into multiple wet segmented etchings. After each wet segmented etching is completed, multiple rinsings are performed. By reducing the etching time of each etching step through the wet segmented etching, the acid in the acid bath is kept fresh, thereby improving the stripping effect.

2. The method for removing strip-shaped polymers from thick aluminum etching as described in claim 1, characterized in that: In step one, the thickness of the aluminum layer is greater than 3 micrometers.

3. The method for removing strip-shaped polymers from thick aluminum etching as described in claim 2, characterized in that: In step two, the etching gas used for over-etching is a mixture of Cl2, BCl3 and N2.

4. The method for removing strip-shaped polymers from thick aluminum etching as described in claim 3, characterized in that: The etching gas used in the first dry etching process to etch the aluminum layer includes a fluorine-containing gas.

5. The method for removing strip-shaped polymers from thick aluminum etching as described in claim 1, characterized in that: In step three, the number of cycles of cyclic flushing is greater than or equal to 2.

6. The method for removing strip-shaped polymers from thick aluminum etching as described in claim 1, characterized in that: In step four, the wet segmented etching process takes 10 to 15 seconds.

7. The method for removing strip-shaped polymers from thick aluminum etching as described in claim 6, characterized in that: In step four, after each wet segmented etching is completed, the rinsing is performed 2 to 3 times.

8. The method for removing strip-shaped polymers from thick aluminum etching as described in claim 7, characterized in that: The wet stripping process includes two or more wet segmented etching operations.

9. The method for removing strip-shaped polymers from thick aluminum etching as described in claim 1, characterized in that: The acid solution used in the acid tank includes SST-A2.

10. The method for removing strip-shaped polymers from thick aluminum etching as described in claim 9, characterized in that: In step four, the wet stripping process is performed using a single-piece operation method.

11. The method for removing strip-shaped polymers from thick aluminum etching as described in claim 1, characterized in that: In step one, an adhesion layer and a barrier layer are also formed between the first oxide layer and the aluminum layer.

12. The method for removing strip-shaped polymers from thick aluminum etching as described in claim 11, characterized in that: The adhesion layer includes a Ti layer; The barrier layer includes a TiN layer.

13. The method for removing strip-shaped polymers from thick aluminum etching as described in claim 1, characterized in that: In step one, the aluminum layer serves as an interconnect; The underlying structure includes a semiconductor substrate; A metal interconnect structure at the bottom of the first oxide layer was completed on the semiconductor substrate.

14. The method for removing strip-shaped polymers from thick aluminum etching as described in claim 13, characterized in that: A MEMS triaxial AMR magnetic sensor is formed on the semiconductor substrate.

15. The method for removing strip-shaped polymers from thick aluminum etching as described in claim 14, characterized in that: The aluminum layer is the third metal layer of the MEMS triaxial AMR magnetic sensor.

Images