Substrate etching method and substrate etching apparatus

Abstract

The present invention discloses a substrate etching method and a substrate etching apparatus. The substrate etching method comprises immersing a substrate in a processing tank containing an etching solution, wet etching the substrate with the etching solution to form a deep structure on the surface of the substrate, and supplying gas into the etching solution based on a pulse signal to generate bubbles in the etching solution, wherein one pulse period of the pulse signal includes a gas supply period and an intermittent period after the end of the gas supply period that depends on the diffusion time required for key components in the deep structure to reach diffusion equilibrium.

Description

[Technical Field]

[0001] This invention relates to the semiconductor manufacturing field, and more particularly to a substrate etching method and a substrate etching apparatus. [Background technology]

[0002] Wet etching involves immersing a substrate in an etching solution and chemically etching the thin film to be removed using the etching solution. In wet etching, it is common practice to supply gas to the etching solution to generate bubbles in order to improve the etching effect. Currently, within the industry, it is common to optimize the gas supply flow rate and gas distribution to achieve better etching speed and etching uniformity, and to improve etching uniformity, there is a focus on improving etching uniformity within the substrate surface and between substrates.

[0003] However, when wet etching thin films in deep structures on a substrate, for example, when wet etching silicon nitride films in deep structures such as narrow voids, narrow grooves, and / or high aspect ratio through-holes formed on the substrate, the etching uniformity of the deep structure is also an important factor that affects the reliability of semiconductor devices. Macroscopic flow and mass transfer efficiency decrease at the bottom of the deep structure compared to the top, and the concentrations of etching products and etching reactants differ between the top and bottom of the deep structure, forming a concentration gradient. Furthermore, the larger the aspect ratio of the deep structure, the larger the concentration gradient of the deep structure becomes, which increases the etching difference at different locations in the deep structure, further affecting the etching uniformity of the deep structure.

[0004] Therefore, wet etching should be improved to control etching uniformity in deep structures. [Overview of the Initiative]

[0005] In view of the drawbacks of the prior art described above, the present invention aims to provide a substrate etching method and a substrate etching apparatus for solving the etching non-uniformity of deep structures in substrates in the prior art.

[0006] In order to achieve the above-mentioned objectives and other related objectives, the present invention The process involves immersing a substrate in a processing tank containing an etching solution, wet etching the substrate with the etching solution, and forming a deep structure on the surface of the substrate. The present invention provides a substrate etching method comprising supplying gas into an etching solution based on a pulse signal to generate bubbles in the etching solution, wherein one pulse period of the pulse signal includes a gas supply period and an intermittent period that depends on the diffusion time required for key components in the deep structure to reach diffusion equilibrium after the gas supply period ends.

[0007] Depending on the circumstances, the interval time T between adjacent bubbles generated during the gas supply period may vary. g This is the diffusion time T required for key components in the deep structure to reach diffusion equilibrium after disturbance by the previous bubble among adjacent bubbles. d1 It is smaller than that.

[0008] Depending on the circumstances, the gas may be continuously supplied to the etching solution during the aforementioned gas supply period.

[0009] Depending on the circumstances, the gas supply period may involve intermittently supplying gas to the etching solution based on N sub-pulse signals, with each sub-pulse signal generating one bubble, where N is a natural number and N ≤ 10.

[0010] On the other hand, the present invention is A processing tank for containing the etching solution, A holding mechanism for holding a substrate with a deep structure formed on its surface and immersing it in an etching solution, A gas supply unit that supplies gas to the etching solution in such a way as to generate bubbles and disturb the etching solution, The present invention provides a substrate etching apparatus comprising a controller that controls the gas supply unit to supply gas to the etching solution based on a pulse signal, and is configured such that one pulse period of the pulse signal includes a gas supply period and an intermittent period after the end of the gas supply period that depends on the diffusion time required for the key components in the deep structure to reach diffusion equilibrium.

[0011] As described above, the present invention provides a substrate etching method and a substrate etching apparatus having the following beneficial effects. 1) In the wet etching process, gas is supplied to the etching solution in a pulsed manner, with each pulse period including a gas supply period and an intermittent period. The intermittent period is determined based on the diffusion time required for key components in the deep structure to reach diffusion equilibrium after the end of the gas supply period. The disturbance interval to the groove is rationally controlled during adjacent gas supply periods to adjust the degree of diffusion in the groove and further improve etching uniformity in the groove. 2) By making the interval time between adjacent bubbles generated during the gas supply period shorter than the diffusion time required for the key component in the deep structure to reach diffusion equilibrium after disturbance by the previous bubble, the disturbance intensity during the gas supply period is enhanced by utilizing the superposition of disturbances by multiple bubbles, expanding the range of the convection region in the deep structure and improving the mass transport efficiency in the deep structure. 3) By employing a single-bubble pulse mode that intermittently supplies gas to the etching solution with N sub-pulse signals during the gas supply period, it is possible to effectively control the generation time of a single bubble and precisely control the interval between adjacent bubbles. Furthermore, it is possible to obtain bubbles with higher gas velocities using a larger gas flow rate, thereby further enhancing the ability to mitigate disturbances caused by bubbles. [Brief explanation of the drawing]

[0012] The features and performance of the present invention will be further described based on the following embodiments and their drawings. [Figure 1] A schematic diagram of a wet etching apparatus is shown. [Figure 2]A schematic diagram of a partial configuration of a 3D NAND flash memory device having a stack layer and a groove penetrating the stack layer is shown. [Figure 3] A schematic diagram showing a change in the etching rate of SiO2 according to the silicon concentration in the reaction system is shown. [Figure 4] A schematic diagram showing the reattachment of SiO2 in the groove and the overetching of the silicon oxide film is shown. [Figure 5] A schematic diagram showing that the next bubble suppresses the diffusion of the key component in the groove after the disturbance by the previous bubble is shown. [Figure 6] A timing chart of the pulse signal according to Embodiment 1 of the present application is shown. [Figure 7] A schematic diagram of the principle of the overlapping action of adjacent bubbles is shown. [Figure 8] A timing chart of the pulse signal according to Embodiment 2 of the present application is shown. [Figure 9] A timing chart of the pulse signal according to another embodiment of the present application is shown.

Mode for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described using specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention based on the content disclosed in this specification. The present invention can be further implemented or applied by different specific embodiments, and each detail of this specification can be variously modified or changed without departing from the spirit of the present invention based on different viewpoints and applications.

[0014] Please refer to FIGS. 1 to 9. Note that the illustrations provided in this embodiment only schematically explain the basic concept of the present invention. In the illustrations, only the components related to the present invention are shown, and they are not drawn based on the number, shape, and dimensions of the components when actually implemented. However, the form, number, and ratio of each component when actually implemented can be arbitrarily changed, and the layout form of the components may also become more complex.

[0015] The substrate etching method of the present invention is applied to etching a substrate having a deep structure in a wet etching apparatus that performs batch processing. Figure 1 shows an example of a wet etching apparatus (i.e., a substrate etching apparatus) that implements the substrate etching method of the present invention. As shown in Figure 1, the wet etching apparatus 10 includes a processing tank 11 for containing an etching solution, a holding mechanism 12 for holding a substrate w and immersing it in the etching solution, a liquid supply unit 13 for supplying the etching solution to the processing tank, a gas supply unit 14 for supplying gas to the etching solution to generate bubbles and disturb the etching solution, and a controller 15. Here, the liquid supply unit 13 includes a liquid supply pipe 131 on which a liquid adjustment valve 133 is located, and a liquid nozzle 132 located in the processing tank 11 and below the substrate W. The gas supply unit 14 includes a gas supply pipe 141 on which a gas adjustment valve 143 is located, and a gas nozzle 142 located in the processing tank 11 and below the substrate w. The controller 15 controls the flow rate of gas supplied from the gas supply pipe 141 to the gas nozzle 142 by controlling the operation of the gas control valve 143, and controls the flow rate of liquid supplied from the liquid supply pipe 131 to the liquid nozzle 132 by controlling the operation of the liquid control valve 132.

[0016] Currently, to address the problem of non-uniform etching of deep structures in substrates, the present invention provides a substrate etching method comprising the steps of: immersing a substrate w in a processing tank 11 containing an etching solution and wet etching the substrate w with the etching solution; and supplying gas to the etching solution based on a pulse signal to generate bubbles in the etching solution during the wet etching process. In the present invention, referring to Figure 1, a controller 15 controls the operation of a gas control valve 143 based on a pulse signal to supply pulsed gas to a gas nozzle 142. Here, one pulse period of the pulse signal comprises a gas supply period and an intermittent period that depends on the diffusion time required for the key component in the groove to reach diffusion equilibrium after the end of the gas supply period. The specific setting of the pulse signal will be described later, so the explanation is omitted here. The key component refers to the main component that affects etching uniformity in the reaction system, and includes etching reactants and / or etching products.

[0017] Next, using wet etching, which removes the silicon nitride film in the stack layer using a phosphoric acid solution, as an example in the manufacturing of 3D NAND flash memory devices, the etching non-uniformity phenomenon in the grooves and its causes will be explained in detail, allowing for a better understanding of the substrate etching method proposed in this application.

[0018] Figure 2 illustrates a partial structure of a 3D NAND flash memory device. As shown in Figure 2, this structure comprises a stack layer 100 formed on a substrate w and a trench 103 penetrating the stack layer 100, where the stack layer 100 consists of alternately deposited silicon nitride films 101 and silicon oxide films 102. In this example, the trench 103 in the stack layer 100 is a deep structure formed on the substrate w. In the manufacturing process of the 3D NAND flash memory device, it is necessary to remove the silicon nitride films 101 in the stack layer 100. Generally, the substrate is wet-etched with a phosphoric acid solution (etching solution) to selectively remove the silicon nitride films 101 in the stack layer 100.

[0019] Silicon nitride (Si3N4) can undergo the chemical reaction shown in equation (1) in a phosphoric acid solution.

[0020]

number

[0021] Silicon oxide (SiO2) can undergo the chemical reaction shown in equation (2) in a phosphoric acid solution.

[0022]

number

[0023] The above equation (2) is a reversible reaction, and the direction of the reaction in equation (2) can be controlled by adjusting the silicon concentration (e.g., Si(OH)4 concentration) in the reaction system. Figure 3 shows a schematic diagram of how the etching rate of SiO2 changes depending on the silicon concentration in the reaction system. As shown in Figure 3, when the silicon concentration is at the equilibrium concentration, the reversible reaction in equation (2) reaches equilibrium and the etching rate of SiO2 becomes zero; when the silicon concentration is lower than the equilibrium concentration, the reversible reaction in equation (2) proceeds to the right, the etching rate of SiO2 becomes greater than zero, SiO2 hydrolyzes to produce Si(OH)4, and the etching reaction of SiO2 occurs; when the silicon concentration is higher than the equilibrium concentration, the reversible reaction in equation (2) proceeds to the left, the etching rate of SiO2 becomes less than zero, Si(OH)4 polymerizes to produce SiO2, and the deposition reaction of SiO2 occurs. Furthermore, since the effect of silicon concentration on the etching rate of Si3N4 is small, the etching selectivity ratio of phosphoric acid to silicon nitride and silicon oxide can be adjusted by adjusting the silicon concentration in the phosphoric acid solution. Typically, the silicon concentration in a phosphoric acid solution is slightly lower than the equilibrium concentration. When a phosphoric acid solution at 160°C is used as an etching solution, the equilibrium silicon concentration is 80 ppm. In this case, the process window for the silicon concentration in the phosphoric acid solution is set to approximately 40 ppm to 70 ppm.

[0024] As can be seen from equation (1) above, when the silicon nitride film 101 in trench 103 is etched, etching product Si(OH)4 is generated, and the diffusion efficiency of the etching product Si(OH)4 affects the silicon concentration distribution in trench 103. When the silicon concentration in a local region in trench 103 exceeds the equilibrium concentration, a deposition reaction of SiO2 occurs in this local region (refer to chemical equation (2) and Figure 3 in combination), and the generated SiO2 deposits adhere to the silicon oxide film 102, causing SiO2 re-deposition; when the silicon concentration in a local region in trench 103 falls below the equilibrium concentration, an etching reaction of SiO2 occurs in this local region (refer to chemical equation (2) and Figure 3 in combination), and if the amount of etching of the silicon oxide film 102 exceeds the process requirements, the silicon oxide film 102 is over-etched. Both the re-deposition of SiO2 and the over-etching of the silicon oxide film 102 are types of etching heterogeneity in trench 103, and it is undesirable that they affect the performance and reliability of the product. In contrast, the silicon concentration at the top of the trench 103 is low, making it easy for over-etching of the silicon oxide film 102 to occur, while the silicon concentration at the bottom of the trench 103 is high, making it easy for SiO2 to re-deposit. Figure 4A shows the SiO2 re-deposit phenomenon at the bottom of the trench 103, and Figure 4B shows the over-etching phenomenon of the silicon oxide film 102 at the top of the trench 103, where the silicon nitride film 101 is partially etched.

[0025] The storage capacity of a 3D NAND flash memory device is generally quantified by the number of stack layers 100. Currently, the stack layers 100 of a 3D NAND flash memory device contain 64, 96, 128, or more layers. The more layers there are in the stack layers 100, the larger the depth-to-width ratio of the trenches 103 becomes, making material transfer in the trenches 103 more difficult. This increases the risk of etching products Si(OH)4 from the silicon nitride film 101 accumulating in the trenches 103, especially at the bottom of the trenches 103, and the increased risk of SiO2 re-deposition in the trenches 103. Therefore, as the aspect ratio of the trenches 103 increases, the challenge of uniform etching in the trenches 103 becomes greater.

[0026] Currently, a common method for improving etching uniformity in trench 103 is to continuously supply gas to the phosphoric acid solution, continuously generate bubbles, and increase the liquid flow velocity on the substrate w surface to promote mass transfer efficiency in trench 103. The gas supply flow rate is then continuously increased as the aspect ratio of trench 103 increases to achieve better etching uniformity.

[0027] In practice, in trenches 103 with a low aspect ratio, the mass transfer efficiency in trenches 103 can be effectively improved by using bubbles generated at lower gas flow rates. However, in trenches 103 with a high aspect ratio, for example, when the aspect ratio of trench 103 exceeds 40:1, bubbles generated by low gas flow rates have a weaker effect on the mass transfer efficiency in trenches 103, especially at the bottom of the trench. As a result of the low mass transfer efficiency, etching products Si(OH)4 accumulate at the bottom of trench 103, and the risk of SiO2 re-deposition at the bottom of trench 103 increases. In this case, to overcome the problem of SiO2 re-deposition at the bottom of trench 103, it is possible to generate more bubbles faster by reliably increasing the gas flow rate, thereby strengthening the effect on the mass transfer efficiency in trench 103 and reducing the risk of SiO2 re-deposition at the bottom of trench 103. However, while increasing the gas flow rate is beneficial in reducing the silicon concentration at the bottom of the trench 103 and improving the re-deposition of SiO2 at the bottom of the trench 103, it should be noted that at the same time, a high gas flow rate can reduce the silicon concentration near the top of the trench 103 too much, increasing the risk of over-etching of the silicon oxide film 102 at the top of the trench 103. Therefore, in a mode of continuous gas supply, as the aspect ratio of the trench 103 increases, simply increasing the gas flow rate cannot effectively solve the problem of etching non-uniformity in the trench 103.

[0028] Furthermore, the applicant actually discovered that the interval between bubbles is also an important factor influencing the diffusion of material in trench 103. Specifically, if the interval between adjacent bubbles is shorter than the time required for the etching product Si(OH)4 in trench 103 to reach diffusion equilibrium after disturbance by the previous bubble, the diffusion of the etching product Si(OH)4 into the outside of trench 103 may be suppressed.

[0029] To facilitate understanding, the above findings will be briefly explained with reference to Figure 5. Figure 5 shows positions 1 and 2 along the upward Z direction where the bubble passes. Position 1 approximately represents the position where the bubble approaches the trench 103, and position 2 approximately represents the position where the bubble moves away from the trench 103. Both positions 1 and 2 are within the range of disturbance caused by the bubble to the trench 103. Note that Figure 5 is a simplified representation of the flow field in the trench 103 and does not represent the actual flow field in the trench 103.

[0030] Figure 5(a) shows the effect of bubble G1 passing through position 1 on the flow field in trench 103. Figure 5(b) shows the effect of bubble G1 passing through position 2 on the flow field in trench 103. In Figure 5(a), when bubble G1 passes through position 1, bubble G1 approaches trench 103, pushing the etching solution outside trench 103 into trench 103. The flow field in trench 103 tends to flow from outside trench 103 into trench 103, which is advantageous for diffusing new phosphoric acid solution into trench 103. In Figure 5(b), as bubble G1 passes through position 2, bubble G1 separates from trench 103, the extruding force applied by bubble G1 to the liquid inside trench 103 begins to disappear, the liquid pressure in trench 103 is released, the flow field in trench 103 tends to flow from inside to outside, which is favorable for the diffusion of old phosphoric acid solution inside trench 103 to the outside of trench 103 and for the diffusion of etching product Si(OH)4 in trench 103 to the outside of trench 103. Therefore, the disturbance caused by the bubble to trench 103 includes a step of pushing the liquid inward and a step of releasing the liquid outward.

[0031] Figure 5(c) shows the effect on the flow field in trench 103 when bubble G1 passes through position 2 and the next bubble G2 passes through position 1 at the same time. In Figure 5(c), when bubble G1 is at position 2, it generates an outward flow field (as shown by the solid arrow in Figure 5(c)) that facilitates the diffusion of the etching product Si(OH)4 to the outside of trench 103. It takes time for the etching product Si(OH)4 to reach diffusion equilibrium in trench 103. At this time, if the next bubble G2 is at a position that generates an inward flow field (as shown by the dashed arrow in Figure 5(c)) that facilitates the diffusion of new phosphoric acid solution into trench 103, for example, when bubble G2 is at position 1, the opening region close to trench 103 will have the inward flow field inhibiting the outward flow field, and further forcing a reversal in the direction of the outward flow field, thereby suppressing the diffusion of the etching product Si(OH)4 to the outside of trench 103. If the diffusion of etching product Si(OH)4 to the outside in trench 103 is constantly suppressed, etching product Si(OH)4 will deposit in trench 103, causing the problem of SiO2 re-adhesion. Therefore, rationally controlling the interval between adjacent bubbles allows for sufficient diffusion of etching product Si(OH)4 in trench 103, which is advantageous in increasing the substitution efficiency of etching product Si(OH)4, improving the silicon concentration distribution in trench 103, and further improving the etching uniformity of trench 103.

[0032] In view of the above analysis, the substrate etching method proposed in this application involves immersing the substrate in an etching solution to perform wet etching. Gas is supplied to the etching solution based on a pulse signal, and one pulse period of the pulse signal includes a gas supply period and an intermittent time. The intermittent time is determined based on the diffusion time required for the key component in the trench 103 to reach diffusion equilibrium after the end of the gas supply period. This rationally controls the interval of disturbances to the trench 103 during adjacent gas supply periods, adjusts the degree of diffusion in the trench 103, and improves the etching uniformity of the trench 103. The pulse signal may be applied to the entire etching process time of the substrate, or to only a portion of the etching process time of the substrate.

[0033] The following describes a specific embodiment of the substrate etching method proposed in this application, using the application of the substrate etching method proposed in this application to wet etching of a silicon nitride film 101 in a stack layer 100 in which phosphoric acid is selectively removed as an example. Here, the key component that affects etching uniformity is the etching product Si(OH)4.

[0034] (Embodiment 1) Figure 6 shows a timing chart of a pulse signal according to Embodiment 1 of the present invention. As shown in Figure 6, one pulse period T of the pulse signal comprises a gas supply period t1 and an intermittent period t2. In some embodiments, the gas supply period t1 may be set to 10 ms to 1 s, and the intermittent period t2 may be set to 10 ms to 1 s. The intermittent period t2 is the diffusion time T required to reach diffusion equilibrium in the trench 103 after the gas supply period t1 has ended. d2 It depends on the diffusion time T. Preferably, the value of the intermittent period t2 is equal to the diffusion time T. d2 It is proportional to t² = k*T d2 This is expressed as follows. Here, k > 0 and the set value, T d2 This will be either an experimentally measured value or a calculated simulation value, i.e., T d2 This can be obtained through experiments or computational simulations.

[0035] When wet etching the silicon nitride film 101 in the stack layer 100, k may be set to 0.5 or higher so that there is sufficient time for the etching product Si(OH)4 in the trench 103 to diffuse to the outside between two adjacent gas supply periods t1. For example, the range of k may be set to 0.5 to 2 or 0.6 to 1. This not only increases the diffusion of material in the trench 103 due to disturbances formed in the previous gas supply period t1, but also avoids suppression of material diffusion in the trench 103 due to disturbances formed in the next gas supply period t1. This allows the material in the trench 103 to diffuse sufficiently, improves the diffusion efficiency in the trench 103, and reduces the silicon concentration gradient in the trench 103. By reducing the silicon concentration gradient, the silicon concentration in the trench 103 is lowered, particularly at the bottom of the trench 103, thereby suppressing the re-adhesion of SiO2 at the bottom of the trench 103. Furthermore, the silicon concentration at the top of the trench 103 is increased, improving the over-etching of the silicon oxide film 102 at the top of the trench 103.

[0036] In the wet etching of the silicon nitride film 101 in the stack layer 100, the above value of k is merely an example, and the setting of the range of the value of k can be reasonably adjusted according to the target of the wet etching and the actual process conditions. For example, in some wet etching processes, k may be set to less than 0.5.

[0037] During the gas supply period t1, gas is supplied to the etching solution at the first gas amount, and during the intermittent period t2, gas is supplied to the etching solution at the second gas amount. By making the first gas amount larger than the second gas amount, bubbles are generated in the etching solution, disturbances are generated in a local region on the substrate surface, for example, the surface of the trench 103, and mass transfer in the trench 103 is enhanced. The second gas amount is mainly used to avoid the reverse flow of the etching solution into the gas nozzle, and it may be set to zero or may be set to be greater than zero. The minimum gas flow rate for avoiding the reverse flow of the etching solution into the gas nozzle may be defined as the critical gas flow rate, and the second gas amount may be set so as not to be less than the critical gas flow rate.

[0038] The number of bubbles generated by the gas supplied during the gas supply period t1 in the etching solution is N, where N is a natural number and N≦10. For example, the number of bubbles generated during the gas supply period t1 is 1, 2, 3 or more than 3. All the bubbles generated during the gas supply period t1 are described as one bubble group, and the interval time T g between adjacent bubbles in the bubble group is the diffusion time T required to reach the diffusion equilibrium in the trench 103 after the disturbance by the previous bubble among the adjacent bubbles. d1 depends on it. In order to enhance the disturbance effect of the entire bubble group, the adjacent bubble interval time Tg must be smaller than the diffusion time T d1 required to reach the diffusion equilibrium in the trench 103 after the disturbance by the previous bubble among the adjacent bubbles. That is, T g <T d1 . Preferably, T g =k1*T d1,k1∈(0,0.5). Thus, before the release action favorable to the diffusion of etching products to the outside in trench 103 generated by the previous bubble ends, the extrusion action unfavorable to the diffusion of etching products to the outside in trench 103 generated by the next bubble has already begun. This superimposes the disturbance effect on the liquid in trench 103 by adjacent bubbles in the bubble group, increasing the disturbance capacity to the etching solution during the supply period t1, effectively improving the mass transfer efficiency in trench 103, and is advantageous for shortening the etching process time.

[0039] Next, the principle of superposition by adjacent bubbles will be explained with reference to Figure 7. As shown in Figure 7(a), when bubble G1 is at position 1, bubble G1 pushes new etching solution outside the trench 103 into the trench 103, and the disturbance depth for the liquid in the trench 103 becomes h1. As shown in Figure 7(b), when bubble G1 moves to position 2, the pushing force generated inside the trench 103 by bubble G1 is almost released or not released at all, and the liquid inside the trench 103 tends to flow outwards (as shown by the solid arrow in Figure 7(b)). In other words, etching products inside the trench 103, such as Si(OH)4, are in the stage of diffusing to the outside. However, assuming that it takes a certain amount of time for the etching product Si(OH)4 to reach diffusion equilibrium, and that the interval between bubbles G1 and G2 is smaller than the diffusion time required for the etching product Si(OH)4 in trench 103 to reach diffusion equilibrium after the disturbance by bubble G1, bubble G2 will have already moved to a position, for example position 1, where other new etching solution outside trench 103 flows into trench 103 (as shown by the dashed arrow in Figure 7(b)), before the etching product Si(OH)4 reaches diffusion equilibrium after the disturbance by bubble G1. Then, bubble G2 will be pushed forward to a depth of h2 of liquid disturbance in trench 103.

[0040] In other words, during the gas supply period t1, it is desirable to reduce the spacing between adjacent bubbles and superimpose an extrusion action by multiple bubbles that pushes new etching solution outside the trench 103 into the trench 103, thereby increasing the depth of the liquid disturbance generated in the trench 103 as much as possible, increasing the concentration of etching reactants, such as H3PO4, in the trench 103, increasing the etching rate of the silicon nitride film 101, and strengthening the internal disturbance in the trench 103, thereby promoting mass transport in the deeper part of the trench 103, especially at the bottom of the trench 103. In the most ideal case, forced convection is formed between the top and bottom of the trench 103. During the intermittent period t2, it is desirable to have an appropriate amount of time for the etching products (e.g., Si(OH)4) inside the trench 103 to diffuse to the outside.

[0041] Referring again to Figure 6, in Embodiment 1, gas is continuously supplied to the etching solution during the gas supply period t1. When gas is continuously supplied during the gas supply period t1, it is preferable that the first gas flow rate is 0.5 L / min to 2 L / min.

[0042] (Embodiment 2) Referring to Figure 8, this embodiment proposes a substrate etching method. Compared to Embodiment 1, the difference from Embodiment 2 is that gas is intermittently supplied to the etching solution based on N sub-pulse signals during the gas supply period t1, each sub-pulse signal generating one bubble, where N is a natural number and N ≤ 10.

[0043] Figure 8 shows a timing chart of a pulse signal according to Embodiment 2 of the present invention. As shown in Figure 8, one pulse period T of a pulse signal comprises a gas supply period t1 and an intermittent period t2. In Figure 8, each gas supply period t1 comprises three sub-pulse signals, and each sub-pulse signal has its pulse period t a A single bubble is generated within this pulse, which is abbreviated as a single-bubble pulse. The single-bubble pulse allows for effective control of the single-bubble generation time, thereby enabling precise control of the interval between adjacent bubbles. In this example, the pulse duration t of the single-bubble pulse is... aThe time interval T between adjacent bubbles g It may be considered to be an approximation of the above. The pulse duration of the subpulse signal may be set to, for example, 10ms to 100ms.

[0044] Furthermore, single-bubble pulses can utilize a larger gas flow rate to generate faster bubbles, and better disturbance effects on the etching solution can be obtained through these high-speed bubbles. In one example, the gas flow rate supplied to the etching solution by the sub-pulse signal is set to 2 L / min or more, for example, 2 L / min to 30 L / min, preferably 5 L / min to 20 L / min. Specifically, the gas flow rate supplied to the etching solution by the sub-pulse signal may be set to 2.5 L / min, 3 L / min, 10 L / min, 15 L / min, etc.

[0045] Furthermore, the upper limit of the gas flow rate that can be used in the single-bubble pulse mode during the gas supply period according to Embodiment 2 is greater than the upper limit of the gas flow rate that can be used in the continuous gas supply mode according to Embodiment 1. This is because, when the continuous gas supply mode is used during the gas supply period, if the gas flow rate exceeds a certain range, for example, if the gas flow rate is 5 L / min, the supplied gas may form a gas column in the etching solution that is unfavorable for etching.

[0046] Furthermore, the substrate etching method proposed in this application can be applied not only to the removal of silicon nitride film 101 in the stack layer 100 of a 3D NAND device, but also to the removal of thin films in deep structures where narrow voids, narrow grooves, high aspect ratio channels, etc., are formed in logic devices, interconnect structures, fin field-effect transistors (FinFETs), 3D semiconductor structures, etc.

[0047] Furthermore, in the substrate etching method proposed in this application, the pulse signal may be periodic or aperiodic. Specifically, the duty cycle, frequency, and amplitude of the pulse signal may be fixed or adjusted according to the actual process. Here, the duty cycle refers to the duty cycle within one pulse period of the gas supply period, and the amplitude corresponds to the supplied gas flow rate. For example, the pulse signals shown in Figures 6 and 8 are periodic, meaning that the duty cycle, frequency, and amplitude of each pulse in the pulse signal are the same. Also, for example, the pulse signal shown in Figure 9 is aperiodic, and the duty cycle of the pulse signal gradually decreases, meaning that the duty cycle within one pulse period T of the gas supply period t1 gradually decreases. When supplying gas to the etching solution with an aperiodic pulse signal, it should be understood that the number of bubbles generated in different gas supply periods can be controlled by adjusting the duty cycle, frequency, and amplitude of the pulse signal. Note that Figure 9 is merely a specific example of an aperiodic pulse signal, and in actual applications, the aperiodic setting of the pulse signal can be rationally set based on specific process conditions.

[0048] The above embodiments are illustrative in illustrating the principles and effects of the present invention, but are not intended to limit the invention. Anyone familiar with this art may modify or change the above embodiments without departing from the spirit and scope of the invention. Accordingly, all equivalent modifications or changes made by a person with common sense in the art without departing from the spirit and technical idea disclosed herein shall fall within the scope of the claims of the present invention.

Claims

1. A substrate etching method, The process involves immersing a substrate in a processing tank containing an etching solution, wet etching the substrate with the etching solution, and forming a deep structure on the surface of the substrate. A substrate etching method characterized by supplying gas into an etching solution based on a pulse signal to generate bubbles in the etching solution, wherein one pulse period of the pulse signal includes a gas supply period and an intermittent period that depends on the diffusion time required for key components in the deep structure to reach diffusion equilibrium after the end of the gas supply period.

2. A substrate etching method according to claim 1, A substrate etching method characterized in that the aforementioned intermittent period is 10 ms to 1 s.

3. A substrate etching method according to claim 1, Let t2 be the intermittent period, and Td be the diffusion time required for the key component in the deep structure to reach diffusion equilibrium after the end of the gas supply period. ２ And t2 is Td ２ It is proportional to t² = k * Td ２ A substrate etching method characterized by the expression, where k > 0.

4. A substrate etching method according to claim 3, A substrate etching method characterized in that k is 0.5 or more.

5. A substrate etching method according to claim 4, A substrate etching method characterized in that the range of k is 0.5 to 2.

6. A substrate etching method according to claim 1, A substrate etching method characterized by supplying gas to the etching solution at a first gas amount during the gas supply period, and supplying gas to the etching solution at a second gas amount smaller than the first gas amount during the intermittent period.

7. A substrate etching method according to claim 6, A substrate etching method characterized in that the amount of the second gas is zero.

8. A substrate etching method according to claim 6, A substrate etching method characterized in that the processing tank is equipped with a gas nozzle for supplying gas to the etching solution to generate bubbles, and the amount of the second gas is greater than or equal to the critical gas flow rate, which is the minimum gas flow rate to avoid backflow into the gas nozzle.

9. A substrate etching method according to claim 1, A substrate etching method characterized in that the gas supply period is 10 ms to 1 s.

10. A substrate etching method according to claim 1, A substrate etching method characterized in that the number of bubbles generated during the gas supply period is N, where N is a natural number and N ≤ 10.

11. A substrate etching method according to claim 10, The interval time T between adjacent bubbles generated during the gas supply period. ｇ This refers to the diffusion time T required for key components in the deep structure to reach diffusion equilibrium after disturbance by the previous bubble among adjacent bubbles. ｄ１ A substrate etching method characterized by being smaller than [a certain value].

12. A substrate etching method according to claim 11, Said T ｇ = k １ * T ｄ１ , k １ ∈ (0, 0.5), a substrate etching method characterized by this.

13. A substrate etching method according to claim 10, A substrate etching method characterized by continuously supplying gas to the etching solution during the gas supply period.

14. A substrate etching method according to claim 13, A substrate etching method characterized in that the flow rate for continuously supplying gas to the etching solution is 0.5 L / min to 2 L / min.

15. A substrate etching method according to claim 10, A substrate etching method characterized in that, during the gas supply period, gas is intermittently supplied to the etching solution based on N sub-pulse signals, each sub-pulse signal generating one bubble, where N is a natural number and N ≤ 10.

16. A substrate etching method according to claim 15, A substrate etching method characterized in that the pulse duration of each of the aforementioned sub-pulse signals is 10 ms to 100 ms.

17. A substrate etching method according to claim 15, A substrate etching method characterized in that the gas flow rate supplied to the etching solution by the subpulse signal is 2 L / min or more.

18. A substrate etching method according to claim 17, A substrate etching method characterized in that the gas flow rate supplied to the etching solution by the subpulse signal is 2 L / min to 30 L / min.

19. A substrate etching method according to claim 1, A substrate etching method characterized in that the pulse signal is periodic or aperiodic.

20. A substrate etching apparatus, A processing tank for containing the etching solution, A holding mechanism for holding a substrate with a deep structure formed on its surface and immersing it in an etching solution, A gas supply unit that supplies gas to the etching solution in such a way as to generate bubbles and disturb the etching solution, A substrate etching apparatus comprising: a gas supply unit that controls the supply of gas to the etching solution based on a pulse signal, and a controller configured such that one pulse period of the pulse signal includes a gas supply period and an intermittent period after the end of the gas supply period that depends on the diffusion time required for the key components in the deep structure to reach diffusion equilibrium.

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