Wafer alkali etching method
By using a two-step alkaline etching method, which employs aqueous solutions of potassium hydroxide and lithium hydroxide to etch the wafers, the surface roughness problem caused by alkaline etching is solved, and the wafer manufacturing cost is reduced.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SUZHOU INTO SEMICON TECH CO LTD
- Filing Date
- 2022-05-25
- Publication Date
- 2026-06-16
AI Technical Summary
In existing technologies, alkaline etching increases the surface roughness of wafers, resulting in deep pits and other phenomena, which leads to increased grinding in subsequent processes and higher costs.
A two-step alkaline etching method is adopted, firstly using potassium hydroxide aqueous solution for the first etching, and then using lithium hydroxide aqueous solution for the second etching. This controls the anisotropic etching selectivity and etching rate to avoid the spread of deep pits.
Improve wafer surface roughness, reduce subsequent polishing, and lower semiconductor wafer manufacturing costs.
Smart Images
Figure CN116230520B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a wafer alkaline etching method. Background Technology
[0002] Typically, semiconductor wafer manufacturing methods include slicing single crystal rods manufactured using Czochralski (CZ) or Floating Zone (FZ) methods with an inner circumferential cutting device or wire cutting device to obtain raw wafers. Then, the outer edges of the raw wafers are chamfered to prevent cracks or wear from the wafers obtained from the slicing process. After chamfering, the wafers undergo a planarization grinding process. Then, an etching process is used to remove the processing deformation (wafer surface processing alteration layer) remaining on the wafer surface after slicing, chamfering, and grinding. A primary mirror polishing process is used to polish the etched wafer surface for defects. Finally, the wafers after the primary mirror polishing process undergo a final mirror polishing to improve flatness. Finally, a final cleaning process is performed to remove abrasive and foreign matter adhering to the wafer surface.
[0003] There are two etching processes used to remove the altered layers from the wafer surface: acid etching, which involves immersing the semiconductor wafer in an acidic solution, and alkaline etching, which involves immersing the semiconductor wafer in an alkaline solution. From the perspective of the high integration of state-of-the-art semiconductor devices, alkaline etching is better suited to meet the high flatness requirements of devices than acid etching. This is because the flatness of the wafer after mirror polishing largely depends on the flatness of the etched wafer used for mirror polishing. Therefore, during etching, it is necessary to ensure high wafer flatness to prevent the flatness achieved by the polishing process from deteriorating, and alkaline etching excels in this regard. However, alkaline solutions have much stronger selectivity for etching the crystal orientation anisotropy and surface altered layers on the wafer surface than acidic etching solutions, resulting in a very rough wafer surface after etching. In particular, alkaline etching can cause localized pits, and this deterioration in surface roughness, especially the presence of pits, inevitably increases the polishing amount (polishing tolerance) during the subsequent grinding process to remove these pits. Therefore, compared to acid etching, alkaline etching requires a larger grinding amount in subsequent mirror polishing processes, leading to increased polishing time and costs. The surface roughness deterioration caused by alkaline etching, particularly the appearance of localized pits, is the result of selective etching of thermally conductive surface treatment altered layers or cracks in processes such as slicing or chamfering, especially polishing. Therefore, the main reason for the increased polishing amount and the appearance of localized pits is that the polishing process before etching introduces an uneven surface treatment altered layer. Summary of the Invention
[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a wafer alkaline etching method to solve the problems in the prior art, such as increased wafer surface roughness and deep pits caused by alkaline etching, which lead to increased grinding in subsequent processes.
[0005] To achieve the above and other related objectives, the present invention provides a wafer alkaline etching method, comprising the steps of first placing the wafer to be etched in a potassium hydroxide aqueous solution for a first etching, and then placing the wafer in a lithium hydroxide aqueous solution for a second etching, wherein the concentration of the potassium hydroxide aqueous solution is greater than or equal to 45 wt% and the temperature is 60-80℃, and the concentration of the lithium hydroxide aqueous solution is greater than or equal to 5 wt% and the temperature is greater than or equal to 60℃.
[0006] Optionally, the wafer to be etched includes any one of silicon wafers, GaAs wafers, InP wafers, germanium wafers, GaN wafers, and GaP wafers.
[0007] Optionally, the concentration of the potassium hydroxide aqueous solution is less than or equal to 60 wt%, and the concentration of the lithium hydroxide aqueous solution is less than or equal to 20 wt%.
[0008] Optionally, the temperature of the lithium hydroxide aqueous solution is less than or equal to 75°C.
[0009] Optionally, an aqueous solution of potassium hydroxide is supplied via a CCSS system.
[0010] Optionally, the lithium hydroxide aqueous solution is supplied locally, with the liquid source adjacent to the etching tank.
[0011] Optionally, before the first etching of the wafer, a step of cleaning the wafer is also included.
[0012] Optionally, after the second etching of the wafer, the method further includes a third etching step using a third alkaline solution, wherein the alkalinity of the third alkaline solution is less than that of the lithium hydroxide aqueous solution.
[0013] Optionally, after the second etching of the wafer, the process may include rinsing the wafer with deionized water, followed by SC-2 cleaning.
[0014] Optionally, after cleaning the wafer with SC-2, the process further includes sequentially cleaning the wafer with deionized water and drying it with hot deionized water.
[0015] As described above, the wafer alkaline etching method of the present invention has the following beneficial effects: Using the wafer alkaline etching method of the present invention helps to reduce the anisotropic etching selectivity of potassium hydroxide aqueous solution. Subsequently, a lithium hydroxide aqueous solution with even lower anisotropic etching selectivity is used for etching to ultimately achieve the required etching amount. This avoids the problem of deep pits and their diffusion into the wafer body that may occur when using a single etching solution for single alkaline etching. By using etching solutions with different characteristics in multiple steps, the selective etching of the modified layer on the wafer surface and the anisotropy of the etching rate with respect to the crystal orientation can be adjusted simultaneously, thereby preventing the formation of deep pits and the diffusion of pits. This helps to improve the surface roughness of the wafer and can reduce the amount of polishing in subsequent processes, thus significantly reducing the manufacturing cost of semiconductor wafers. Attached Figure Description
[0016] Figure 1 The diagram shows an exemplary structural schematic of an etching apparatus for performing the wafer alkaline etching method of the present invention. Detailed Implementation
[0017] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. For ease of explanation, when detailing the embodiments of the present invention, the cross-sectional views showing the device structure are partially enlarged, not according to the general scale, and the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. Furthermore, in actual manufacturing, the three-dimensional spatial dimensions of length, width, and depth should be included.
[0018] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the drawings for devices in use or operation. Furthermore, when a layer is referred to as being “between” two layers, it may be the only layer between the two layers, or there may be one or more layers in between.
[0019] In the context of this application, the structure described above the first feature may include embodiments in which the first and second features are formed in direct contact, or embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.
[0020] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show components related to the present invention and are not drawn according to the actual number, shape, and size of the components in the actual implementation. In the actual implementation, the form, quantity, and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex. To keep the illustrations as concise as possible, not all structures are shown in the figures.
[0021] Alkaline etching (e.g., potassium hydroxide etching) is increasingly widely used in the semiconductor field due to its excellent anisotropic etching properties, which are beneficial for forming fine patterns. However, alkaline etching results in a very rough wafer surface and may lead to the formation of local pits, increasing the amount of polishing required in subsequent processes. To address this, the inventors of this application have proposed an improved solution after long-term research. Using the wafer alkaline etching method provided by this invention, even if an uneven surface treatment alteration layer exists on the wafer surface, the formation of local pits and the increase in pit depth can be suppressed. By using the etching method provided by this invention in the semiconductor wafer manufacturing process, the amount of polishing required in the subsequent mirror polishing process can be reduced, thereby lowering wafer manufacturing costs.
[0022] Specifically, the wafer alkaline etching method provided by the present invention includes the following steps: first, the wafer to be etched is placed in a potassium hydroxide (KOH) aqueous solution for a first etching; then, the wafer is placed in a lithium hydroxide (LiOH) aqueous solution for a second etching. The concentration of the potassium hydroxide aqueous solution is greater than or equal to 45 wt%, and the temperature is 60-80℃ (including the endpoint value; unless otherwise specified, all numerical ranges in this specification include the endpoint value). The concentration of the lithium hydroxide aqueous solution is greater than or equal to 5 wt%, and the temperature is greater than or equal to 60℃. The etching times for the first and second etching can be determined according to the etching amount. For example, the first etching time is 5 min-15 min, and the second etching time is, for example, 10-30 min. Alkaline etching in the prior art is usually a single-step etching process, that is, using a single alkaline etching solution (such as potassium hydroxide aqueous solution) to etch a predetermined amount of material onto the wafer. However, the alkaline etching method of the present invention uses at least two alkaline etching solutions with different chemical properties to etch the wafer. For example, the etching ability of potassium hydroxide is usually greater than that of lithium hydroxide aqueous solution, and its anisotropic etching selectivity is also stronger than that of lithium hydroxide aqueous solution. Furthermore, the concentration of the potassium hydroxide aqueous solution used in the present invention is close to its supersaturation concentration (the concentration of potassium hydroxide etching solution used in the prior art is usually around 15 wt%, and generally does not exceed 30 wt%), which is much higher than the commonly used concentration in the prior art. This setup helps reduce the anisotropic etching selectivity of potassium hydroxide aqueous solution, allowing for subsequent etching with lithium hydroxide aqueous solution, which has even lower anisotropic etching selectivity, to achieve the required etching amount. This avoids the problem of deep pits and their diffusion into the wafer body that can occur when using a single etchant for alkaline etching. By using etchants with different properties in multiple steps, the selective etching of the modified layer on the wafer surface and the anisotropy of the etching rate with respect to the crystal orientation can be adjusted simultaneously, thereby preventing the formation and diffusion of deep pits. This helps improve the surface roughness of the wafer and reduces the amount of polishing required in subsequent processes, thus significantly reducing the manufacturing cost of semiconductor wafers.
[0023] The alkaline etching method provided in this embodiment is not only applicable to the etching of silicon wafers, but also to other wafers such as GaAs (gallium arsenide) wafers, InP (indium phosphide) wafers, germanium wafers, GaN (gallium nitride) wafers, and GaP (gallium phosphide) wafers, which also have specific crystal orientation characteristics such as (110). The wafer can be a bare wafer, such as a wafer just cut from a single-crystal silicon rod, or a wafer on which devices have already been fabricated.
[0024] Although the concentration of the potassium hydroxide aqueous solution used in this embodiment is higher than that commonly used in the prior art, its concentration should not be too high, otherwise too much precipitate during the etching process will make etching difficult. Generally, the concentration of the potassium hydroxide aqueous solution does not exceed 60 wt%, more preferably within 50 wt%, while the concentration of the lithium hydroxide aqueous solution is preferably within 20 wt%, and the temperature of the lithium hydroxide aqueous solution is preferably less than or equal to 75°C.
[0025] The potassium hydroxide aqueous solution used in this embodiment is at a relatively high temperature of 60-80°C, and its corrosiveness is quite strong. Therefore, for safety reasons, the potassium hydroxide aqueous solution is preferably supplied through a CCSS (Centralized Chemical Supply System), usually prepared on-site to avoid changes in its properties due to prolonged storage. The lithium hydroxide aqueous solution is preferably supplied locally, with the liquid source, for example, a lithium hydroxide storage tank adjacent to the lithium hydroxide etching tank.
[0026] To prevent contaminants from being introduced into the etching tank, it is preferable to include a wafer cleaning step before the first etching, for example, cleaning the wafer with deionized water (DIW).
[0027] If necessary, after the second etching of the wafer, a third alkaline solution can be used to perform a third etching step. The alkalinity of the third alkaline solution is less than that of the lithium hydroxide aqueous solution. More precisely, its anisotropic etching selectivity is lower than that of the lithium hydroxide solution. For example, ammonia water can be used for the third etching to further improve the surface roughness of the wafer. Of course, the third alkaline solution can also be a lithium hydroxide aqueous solution with a lower concentration than that used for the second etching.
[0028] To improve wafer surface cleanliness, in one example, after the second etching of the wafer, the process includes rinsing the wafer with deionized water, followed by SC-2 cleaning (hydrogen chloride: hydrogen peroxide: water = 1:1:6-1:2:8, hydrogen chloride concentration 37%, hydrogen peroxide 30%). Furthermore, after SC-2 cleaning, the process includes sequentially rinsing the wafer with deionized water and drying it with hot deionized water.
[0029] Figure 1 The diagram shows an exemplary structural schematic of an etching apparatus for performing the wafer alkaline etching method of the present invention. Figure 1As shown, the equipment includes a wafer loading stack 11, a first deionized water cleaning tank 12, a potassium hydroxide aqueous solution etching tank 13, a lithium hydroxide aqueous solution etching tank 14, a second deionized water cleaning tank 15, an SC-2 cleaning tank 16, a third deionized water cleaning tank 17, a hot deionized water dryer (H.DIW DRYER) 18, an infrared dryer (IR DRYER) 19, and a wafer unloading stack 20 arranged sequentially. After the wafer to be etched is transferred to the first deionized water cleaning tank 12 for cleaning via the wafer loading stack 11, it passes through the subsequent tanks to complete the corresponding process operations. Finally, it is removed via the wafer unloading stack 20 and transferred to the next process stack point, such as the polishing process.
[0030] The inventors conducted comparative experiments using silicon wafers. Two different silicon wafers were etched using a 15wt% potassium hydroxide aqueous solution, while the wafer etched using the method of this invention was first etched with a 45wt% potassium hydroxide aqueous solution, followed by a 5wt% potassium hydroxide aqueous solution. After the same etching time, the wafer etched with the single potassium hydroxide aqueous solution showed an uneven surface under an electron microscope, with a roughness of approximately 20nm. In contrast, the wafer etched using the method provided by this invention had a relatively smooth surface, with a roughness of around 5nm. Other experiments with adjustments to the etching solution concentration yielded similar results. This demonstrates that the method of this invention can improve the surface flatness of wafers and enhance wafer quality.
[0031] In summary, this invention provides a wafer alkaline etching method, comprising the steps of first etching the wafer to be etched in a potassium hydroxide aqueous solution for a first etching, and then etching the wafer in a lithium hydroxide aqueous solution for a second etching. The concentration of the potassium hydroxide aqueous solution is greater than or equal to 45 wt%, the temperature is 60-80°C, and the concentration of the lithium hydroxide aqueous solution is greater than or equal to 5 wt%, the temperature is greater than or equal to 60°C. This wafer alkaline etching method helps reduce the anisotropic etching selectivity of the potassium hydroxide aqueous solution. Subsequently, a lithium hydroxide aqueous solution with even lower anisotropic etching selectivity is used to complete the required etching amount. This avoids the problems of deep pits and their diffusion into the wafer body that may occur when using a single alkaline etching solution. By using etching solutions with different characteristics in multiple steps, the selective etching of the modified layer on the wafer surface and the anisotropy of the etching rate with respect to crystal orientation can be adjusted simultaneously, thereby preventing the formation and diffusion of deep pits. This helps improve the surface roughness of the wafer and reduces the amount of polishing in subsequent processes, thus significantly reducing the manufacturing cost of semiconductor wafers. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.
[0032] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.
Claims
1. A wafer alkaline etching method, characterized in that, The process includes the following steps: first, the wafer to be etched is placed in a potassium hydroxide aqueous solution for the first etching; then, the wafer is placed in a lithium hydroxide aqueous solution for the second etching. The concentration of the potassium hydroxide aqueous solution ranges from 45wt% to 50wt%, and the temperature is 60-80℃. The concentration of the lithium hydroxide aqueous solution ranges from 5wt% to 20wt%, and the temperature ranges from 60℃ to 75℃. After the two etching processes, the surface roughness Ra of the wafer is reduced to 5nm.
2. The wafer alkaline etching method according to claim 1, characterized in that, The wafer to be etched includes any one of silicon wafers, GaAs wafers, InP wafers, germanium wafers, GaN wafers, and GaP wafers.
3. The wafer alkaline etching method according to claim 1, characterized in that, Potassium hydroxide aqueous solution is supplied via the CCSS system.
4. The wafer alkaline etching method according to claim 1, characterized in that, The lithium hydroxide aqueous solution is supplied locally, with the liquid source adjacent to the etching tank.
5. The wafer alkaline etching method according to claim 1, characterized in that, Before the first etching of the wafer, a cleaning step is also included.
6. The wafer alkaline etching method according to claim 1, characterized in that, After the second etching of the wafer, the process also includes a third etching step using a third alkaline solution, the alkalinity of which is less than that of the lithium hydroxide aqueous solution.
7. The wafer alkaline etching method according to claim 1, characterized in that, After the second etching of the wafer, the process also includes cleaning the wafer with deionized water, followed by SC-2 cleaning.
8. The wafer alkaline etching method according to claim 7, characterized in that, After SC-2 cleaning of the wafer, the process also includes sequential cleaning with deionized water and drying with hot deionized water.