Method of wet etching

Abstract

A method for wet etching, comprising: providing a substrate, the substrate surface having a layer to be etched; performing a plurality of etching processes on the layer to be etched until the thickness of the layer to be etched reaches a target thickness, each etching process comprising: performing a first step etching, in which the substrate has a first rotation speed; after the first step etching, performing a second step etching, in which the rotation speed of the substrate is reduced from the first rotation speed to a second rotation speed, and the liquid film of the chemical liquid on the surface of the substrate is increased to a first thickness; after the second step etching, performing a third step etching, in which the substrate has a third rotation speed, the third rotation speed being lower than or equal to the first rotation speed, and the thickness of the liquid film of the chemical liquid being thick enough to reduce the chance of oxygen in the air entering the surface of the layer to be etched, thereby facilitating uniform etching, improving the flatness of the surface of the layer to be etched, and reducing the probability of the generation of etching pit defects.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a wet etching method. Background Technology

[0002] As semiconductor technology continues to develop and linewidths continue to shrink, the requirements for etching are becoming increasingly stringent. Compared to dry etching, wet etching processes cause less damage to the surface and are increasingly being used in IC manufacturing.

[0003] Wet etching processes use an etching solution to etch the wafer. Wet etching processes include batch wet etching and single-wafer wet etching. Compared to batch etching, single-wafer wet etching technology reduces the risk of cross-contamination during the cleaning process and offers flexible process adjustment capabilities, making it an important technology in wet etching.

[0004] However, existing single-wafer wet etching processes are difficult to meet the requirements of device flatness and absence of corrosion pits, and wet etching technology needs further improvement. Summary of the Invention

[0005] The technical problem solved by this invention is to provide a wet etching method to improve the performance of the formed wafer.

[0006] To address the aforementioned technical problems, the present invention provides a wet etching method, comprising: providing a substrate, the surface of which has a layer to be etched; performing several etching processes on the layer to be etched until the thickness of the layer to be etched reaches a target thickness, each etching process comprising: performing a first etching step, in which the substrate has a first rotational speed; after the first etching step, performing a second etching step, in which the rotational speed of the substrate is reduced from the first rotational speed to a second rotational speed, and the liquid film of the chemical solution on the surface of the substrate increases to a first thickness; after the second etching step, performing a third etching step, in which the substrate has a third rotational speed, the third rotational speed being lower than or equal to the first rotational speed.

[0007] Optionally, the chemical solution includes an inorganic acid; the inorganic acid includes one or more of hydrofluoric acid, hydrochloric acid, and phosphoric acid.

[0008] Optionally, the chemical solution comprises an organic acid; the organic acid includes acetic acid or oxalic acid.

[0009] Optionally, the chemical solution includes a deionized aqueous solution through which carbon dioxide is bubbled.

[0010] Optionally, the parameters for the first etching step include: the flow rate of the chemical solution is in the range of 0.5 liters / minute to 2.5 liters / minute, the etching time is in the range of 0 seconds to 60 seconds, and the first rotation speed is in the range of 100 rpm to 500 rpm.

[0011] Optionally, the parameters for the second etching step include: the flow rate of the chemical solution is in the range of 0.5 liters / minute to 2.5 liters / minute, and the second rotation speed is in the range of 10 revolutions / minute to 100 revolutions / minute.

[0012] Optionally, the parameters for the third etching step include: the flow rate of the chemical solution is in the range of 0 liters / minute to 0.5 liters / minute, and the third rotation speed is in the range of 10 revolutions / minute to 100 revolutions / minute.

[0013] Optionally, in the second etching step, a unit cycle time is provided in which the rotational speed of the substrate is reduced by 100 revolutions per minute within the unit cycle time.

[0014] Optionally, the unit cycle time ranges from 0.1 seconds to 3 seconds.

[0015] Optionally, the material of the layer to be etched includes a metal; the metal includes one or more of cobalt, aluminum, copper, and TiAl-based alloys.

[0016] Optionally, the number of etching processes ranges from 1 to 20.

[0017] Optionally, the first thickness is greater than 0.3 mm.

[0018] Compared with the prior art, the technical solution of the embodiments of the present invention has the following beneficial effects:

[0019] In the semiconductor structure formation method provided by this invention, the layer to be etched is subjected to several etching processes until the thickness of the layer to be etched reaches the target thickness. Each etching process includes three etching steps. In the first etching step, by reducing the first rotation speed, the chemical solution is uniformly distributed on the substrate surface. This shortens the etching time of the first etching step, resulting in minimal etching of the layer to be etched in the first etching step. In the second etching step, the second rotation speed is lower than the first rotation speed. At the lower speed, the chemical solution at the edge of the substrate surface is not thrown outward under centrifugal force. This improves the uniformity of the chemical solution film in the first two etching steps. Simultaneously, it facilitates the aggregation of the chemical solution film on the substrate surface, resulting in a sufficiently thick chemical solution film. This reduces the chance of oxygen from the air entering the surface of the layer to be etched, thus inhibiting the oxidation of the material in the layer to be etched. After the second etching step, the third etching step is used to etch the layer to be etched. Since a thicker and more uniform chemical solution film was obtained in the first two steps, it is conducive to uniform etching, improves the smoothness of the surface of the layer to be etched, and reduces the probability of corrosion pit defects. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a wet etching process;

[0021] Figure 2 This is a flowchart illustrating the steps of a wet etching method according to an embodiment of the present invention.

[0022] Figures 3 to 9 This is a schematic diagram of the steps in the method for forming a semiconductor structure according to an embodiment of the present invention. Detailed Implementation

[0023] As described in the background section, existing monolithic wafer wet etching technology urgently needs improvement. This paper will now explain and analyze a monolithic wafer wet etching technology.

[0024] Figure 1 This is a schematic diagram of a wet etching method.

[0025] Please refer to Figure 1 A wafer 100 is provided, and a nozzle 101 is located above the wafer 100. A chemical solution 102 is sprayed from the nozzle 101 onto the surface of the wafer 100. The wafer 100 rotates along an arc 103 at a speed of 800 revolutions per minute to etch the wafer 100 until the target etching amount is reached.

[0026] In the above method used for etching or cleaning materials, the wafer 100 rotates while its surface is etched. Chemical solution is continuously replenished at the center of the wafer 100. The high rotational speed ensures a uniform distribution of the chemical solution film on the wafer 100, resulting in relatively uniform etching of the wafer 100 surface. However, at high rotational speeds, the chemical solution at the edges of the wafer 100 surface is flung outwards by centrifugal force, while the continuous replenishment of chemical solution at the center of the wafer 100 makes the chemical solution at the edges thinner than that in the center. This allows oxygen from the air to easily dissolve into the chemical solution on the surface of the wafer 100 edges. When the material etched on the surface of the wafer 100 is an easily oxidized metal, such as cobalt, aluminum, or copper, the oxidation of the metal makes it easier to etch away, resulting in relatively more material removal at the edges of the wafer 100. This leads to poor surface smoothness of the wafer 100. Furthermore, uneven etching caused by metal oxidation can create corrosion pits, affecting the quality of the polished metal surface.

[0027] As device dimensions approach the nanometer scale, semiconductor technology processes become increasingly refined, and achieving a scaling ratio of overall chip area has become a continuous pursuit in the industry. For example, Intel's Active Gate On-Contact (COAG) technology for FinFETs presents new device structures that also bring challenges to manufacturing processes. COAG technology requires etching back the metal gate; due to the very small feature size of the device, extremely high etching flatness is required, while also ensuring no damage.

[0028] To address the aforementioned technical problems, the present invention provides a wet etching method, which involves performing several etching processes on the layer to be etched until the thickness of the layer to be etched reaches a target thickness. Each etching process includes three steps. In the first etching step, by reducing the first rotation speed, the chemical solution is evenly distributed on the substrate surface. This shortens the etching time of the first etching step, minimizing the amount of the layer to be etched in the first etching step. In the second etching step, the second rotation speed is lower than the first rotation speed. At the lower speed, the chemical solution at the edge of the substrate surface is not flung outwards under centrifugal force. This improves the uniformity of the chemical solution film in the first two etching steps and makes it easier for the chemical solution film on the substrate surface to aggregate. The chemical solution film is sufficiently thick, thereby reducing the chance of oxygen from the air entering the surface of the layer to be etched and inhibiting the oxidation of the material in the layer to be etched. After the second etching step, the third etching step is used to etch the layer to be etched. Since a thicker and more uniform chemical solution film was obtained in the first two steps, it is conducive to uniform etching, improves the smoothness of the surface of the layer to be etched, and reduces the probability of corrosion pit defects.

[0029] To make the above-mentioned objectives, features and beneficial effects of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0030] Figure 2 This is a flowchart illustrating the steps of a wet etching method according to an embodiment of the present invention, including:

[0031] Step S1: Provide a substrate, the surface of which has a layer to be etched;

[0032] Step S2: Perform the first etching step, in which the substrate has a first rotational speed;

[0033] Step S3: After the first etching step, a second etching step is performed. In the second etching step, the rotation speed of the substrate is reduced from the first rotation speed to the second rotation speed, and the liquid film of the chemical solution on the surface of the substrate is increased to the first thickness.

[0034] Step S4: After the second etching step, a third etching step is performed, wherein the substrate has a third rotation speed, which is lower than or equal to the first rotation speed.

[0035] Determine whether the thickness of the layer to be etched has reached the target thickness. If the target thickness has been reached, terminate the etching process. If the target thickness has not been reached, repeat steps S2 to S4.

[0036] The following detailed description of each step of the wet etching method, in conjunction with the accompanying drawings, provides a clear explanation.

[0037] Figures 3 to 9 This is a schematic diagram of the steps in the method for forming a semiconductor structure according to an embodiment of the present invention.

[0038] Please refer to Figure 3 A substrate 200 is provided, the surface of which has a layer 201 to be etched.

[0039] The layer to be etched 201 comprises a metal; the metal includes metal materials such as cobalt, aluminum, copper, and TiAl-based alloys. The layer to be etched 201 is prone to oxidation, and corrosion pits are easily formed during the etching process, thus affecting the surface quality of the etched layer 201. A method to reduce the probability of these corrosion pit defects will be provided later. In this embodiment, the material of the layer to be etched 201 is cobalt.

[0040] The substrate 200 can be made of semiconductor or any material capable of supporting the layer 201 to be etched, such as metal. The substrate 200 can be a single-layer structure or a composite structure, such as a substrate in which devices (e.g., transistors) can be formed. In this embodiment, the substrate 200 is a silicon wafer, and a transistor device (not shown) is present within the substrate 200.

[0041] Subsequently, the layer 201 to be etched is subjected to several etching processes until the thickness of the layer 201 to be etched reaches the target thickness. The method for each etching process is described in [reference needed]. Figures 4 to 8 As stated above.

[0042] Please refer to Figure 4 and Figure 5 , Figure 4 This is a schematic diagram of the wet etching method. Figure 5 This is a cross-sectional view of the semiconductor structure, showing the first etching step, in which the substrate 200 has a first rotational speed 302.

[0043] In this embodiment, the chemical solution 301 is sprayed from the nozzle 300 onto the surface of the wafer 200, and continuously accumulates on the surface of the layer to be etched 201 to form a chemical solution film 202.

[0044] The parameters for the first etching step include: the flow rate of the chemical solution ranging from 0.5 liters / minute to 2.5 liters / minute, the etching time ranging from 0 seconds to 60 seconds, and the first rotational speed 302 ranging from 100 rpm to 500 rpm. In the first etching step, the lower first rotational speed 302 prevents the chemical solution at the edge of the substrate 200 from being easily ejected outwards under centrifugal force, thus improving the uniformity of the edge of the substrate 200 relative to the center of the substrate 200.

[0045] Because the first etching step has a short etching time, the amount of the layer to be etched in the first etching step is very small. In this embodiment, the first etching step takes 30 seconds; the first rotation speed 302 is 250 revolutions per minute.

[0046] Please refer to Figure 6 and Figure 7 After the first etching step, a second etching step is performed. In the second etching step, the rotation speed of the substrate 200 is reduced from the first rotation speed 302 to the second rotation speed 303, and the chemical liquid film 202 on the surface of the substrate 200 is increased to a first thickness.

[0047] The parameters for the second etching step include: the flow rate of the chemical solution is in the range of 0.5 liters / minute to 2.5 liters / minute, and the second rotation speed 303 is in the range of 10 revolutions / minute to 100 revolutions / minute.

[0048] In the second etching step, a unit cycle time is provided, during which the rotational speed of the substrate 200 decreases by 100 revolutions per minute.

[0049] The unit cycle time range is 0.1 seconds to 3 seconds.

[0050] In this embodiment, the second rotational speed 303 is 50 revolutions per minute; the unit cycle time range is 1 second. That is, the rotational speed of the substrate 200 decreases by 100 revolutions per minute every second, decreasing from the first rotational speed 302 to the second rotational speed 303 in two steps, with a total time of 2 seconds. In other embodiments, the decrease from the first rotational speed 302 to the second rotational speed 303 can be completed in one or more steps.

[0051] The first thickness is greater than 0.3 mm. In the second etching step, the second rotation speed 303 is lower than the first rotation speed 302. At the lower rotation speed, the chemical solution at the edge of the substrate surface will not be thrown outward under the action of centrifugal force, which improves the uniformity of the chemical solution film 202 in the first two etching steps. At the same time, it makes it easier for the chemical solution film 202 on the substrate surface to aggregate. The chemical solution film 202 is thick enough to reduce the chance of oxygen in the air entering the surface of the layer to be etched 201 and inhibit the oxidation of the material of the layer to be etched.

[0052] The chemical solution includes inorganic acids; the inorganic acids include one or more of hydrofluoric acid, hydrochloric acid, and phosphoric acid.

[0053] The chemical solution includes organic acids; the organic acids include acetic acid or oxalic acid.

[0054] The chemical solution includes organic or inorganic acids that readily react with the layer 201 to be etched, and is not limited to the common etching solutions listed above. In this embodiment, the chemical solution is a nitric acid solution with a volume ratio of H2O:HNO3 of 1:1. Using a common etching solution, the etching process can be completed in existing etching equipment without requiring new equipment, making it easy to operate. In other embodiments, different etching solutions and ratios are selected based on the material of the layer to be etched. Alternatively, different etching solutions and ratios can be selected based on the material of the layer to be etched to perform slight etching of the surface, thus achieving the effect of cleaning the layer to be etched.

[0055] The chemical solution includes a deionized aqueous solution in which carbon dioxide is bubbled through. The deionized water containing carbon dioxide is used to non-destructively clean the layer 201 to be etched, removing residues from its surface.

[0056] Please refer to Figure 8After the second etching step, a third etching step is performed, wherein the substrate has a third rotational speed 304, which is not higher than the first rotational speed 302.

[0057] The parameters for the third etching step include: the chemical solution flow rate ranging from 0 liters / minute to 0.5 liters / minute, and the third rotation speed 304 ranging from 10 rpm to 100 rpm. In this third etching step, a lower chemical solution flow rate and a lower rotation speed are used, making it less likely for the chemical solution at the edge of the substrate 200 to be flung outwards under centrifugal force, thus improving the uniformity of the edge of the substrate 200 relative to the center. Furthermore, since a thicker and more uniform chemical solution film is obtained in the first two steps, it facilitates uniform etching, improves the smoothness of the surface of the layer to be etched, and reduces the probability of corrosion pit defects.

[0058] Please refer to Figure 9 The layer to be etched 201 is etched several times until the thickness of the layer to be etched reaches the target thickness.

[0059] After the third etching step, it is determined whether the thickness of the layer 201 to be etched has reached the target thickness. If the target thickness has not been reached, the etching process from the first step to the third step is repeated until the thickness of the layer 201 to be etched reaches the target value. After the thickness of the layer 201 to be etched reaches the target value, after subsequent routine washing and drying treatments, a surface of the layer 201 to be etched with high flatness and low corrosion pit defects is easily formed.

[0060] The number of etching processes ranges from 1 to 20. The number of etching processes depends on the material of the layer to be etched, the etching target, and the selection of etching parameters, such as the type of etching solution and the flow rate of the etching solution.

[0061] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A wet etching method, characterized in that, include: A substrate is provided, the surface of which has a layer to be etched; The layer to be etched is subjected to several etching processes until the thickness of the layer to be etched reaches the target thickness. Each etching process includes: The first etching step is performed. In the first etching step, the substrate has a first rotation speed, and the chemical solution is sprayed from the nozzle onto the surface of the substrate, where it continuously accumulates on the surface of the layer to be etched to form a chemical solution film. After the first etching step, a second etching step is performed. In the second etching step, the chemical solution is continued to be supplied to the substrate surface. The rotation speed of the substrate is reduced from the first rotation speed to the second rotation speed to reduce the chemical solution at the edge of the substrate surface from being thrown outward under the action of centrifugal force, and the chemical solution film on the substrate surface increases to a first thickness. After the second etching step, a third etching step is performed, wherein the flow rate of the chemical solution in the third etching step is lower than the flow rate of the chemical solution in the first and second steps, and the substrate has a third rotational speed, which is lower than or equal to the first rotational speed.

2. The wet etching method as described in claim 1, characterized in that, The chemical solution includes inorganic acids; the inorganic acids include one or more of hydrofluoric acid, hydrochloric acid, and phosphoric acid.

3. The wet etching method as described in claim 1, characterized in that, The chemical solution includes organic acids; the organic acids include acetic acid or oxalic acid.

4. The wet etching method as described in claim 1, characterized in that, The chemical solution includes a deionized aqueous solution through which carbon dioxide is bubbled.

5. The wet etching method as described in claim 1, characterized in that, The parameters for the first etching step include: the flow rate of the chemical solution is in the range of 0.5 liters / minute to 2.5 liters / minute, the etching time is in the range of 0 seconds to 60 seconds, and the first rotation speed is in the range of 100 rpm to 500 rpm.

6. The wet etching method as described in claim 1, characterized in that, The parameters for the second etching step include: the flow rate of the chemical solution is in the range of 0.5 liters / minute to 2.5 liters / minute, and the second rotation speed is in the range of 10 revolutions / minute to 100 revolutions / minute.

7. The wet etching method as described in claim 1, characterized in that, The parameters for the third etching step include: the flow rate of the chemical solution is in the range of 0 liters / minute to 0.5 liters / minute, and the third rotation speed is in the range of 10 revolutions / minute to 100 revolutions / minute.

8. The wet etching method as described in claim 1, characterized in that, In the second etching step, a unit cycle time is provided, during which the rotational speed of the substrate decreases by 100 revolutions per minute.

9. The wet etching method as described in claim 8, characterized in that, The unit cycle time range is 0.1 seconds to 3 seconds.

10. The wet etching method as described in claim 1, characterized in that, The material of the layer to be etched includes metals; the metals include one or more of cobalt, aluminum, copper, and TiAl-based alloys.

11. The wet etching method as described in claim 1, characterized in that, The number of etching processes ranges from 1 to 20.

12. The wet etching method as described in claim 1, characterized in that, The first thickness is greater than 0.3 mm.

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