Substrate etching method and apparatus

Abstract

The application discloses a substrate etching method and device. The substrate etching method comprises the following steps: immersing a substrate into a processing tank containing an etching solution, wet etching the substrate by the etching solution, and forming a deep structure on the surface of the substrate; and providing a gas into the etching solution based on a pulse signal to generate bubbles in the etching solution, wherein one pulse time of the pulse signal comprises a gas supply period and an intermittent period, and the intermittent period depends on a diffusion time required for a key component in the deep structure to reach a diffusion equilibrium after the end of the gas supply period.

Description

Technical Field

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

[0002] Wet etching involves immersing a substrate in an etching solution, where the solution chemically erodes the thin film to be removed. In wet etching, gas is typically supplied to the etching solution to generate bubbles, which improves the etching effect. Currently, the industry focuses on optimizing the gas flow rate and gas distribution to achieve better etching rates and uniformity. Improvements in etching uniformity generally focus on enhancing in-plane etching uniformity and inter-substrate etching uniformity.

[0003] However, when wet etching thin films in deep structures on a substrate, such as silicon nitride films in narrow voids, narrow trenches, and / or high aspect ratio vias, the etching uniformity within the deep structure becomes a significant factor affecting the reliability of semiconductor devices. Compared to the top of the deep structure, the macroscopic flow and mass transfer efficiency at the bottom decreases, resulting in different concentrations of etching products and reactants at the top and bottom, creating a concentration gradient. Furthermore, the larger the aspect ratio of the deep structure, the greater the concentration gradient, which increases etching differences at different locations within the deep structure, thus affecting the etching uniformity.

[0004] Therefore, it is necessary to improve wet etching in order to control the etching uniformity in deep structures. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of the present invention is to provide a substrate etching method and apparatus to solve the problem of uneven etching in the deep structure of the substrate in the prior art.

[0006] To achieve the above and other related objectives, the present invention provides a substrate etching method, comprising:

[0007] The substrate is immersed in a processing tank containing an etching solution, and the substrate is wet-etched by the etching solution, forming a deep structure on the surface of the substrate.

[0008] Gas is supplied to the etching solution based on a pulse signal to generate bubbles in the etching solution. One pulse time of the pulse signal includes a gas supply period and an intermittent period, the intermittent period depending on the diffusion time required for the key components in the deep structure to reach diffusion equilibrium after the gas supply period ends.

[0009] Optionally, the interval T between adjacent bubbles generated during the gas supply period gThe diffusion time T required for the key components in the deep structure to reach diffusion equilibrium after the disturbance of the previous bubble in the adjacent bubble is less than the diffusion time T. d1 .

[0010] Optionally, the gas supply period continuously supplies gas to the etching solution.

[0011] Optionally, the gas supply period is based on N sub-pulse signals to intermittently supply gas to the etching solution, each sub-pulse signal corresponding to the generation of one bubble, where N is a natural number and N≤10.

[0012] On the other hand, the present invention also provides a substrate etching apparatus, comprising:

[0013] Processing tank, used to hold etching solution;

[0014] A holding mechanism for holding a substrate and immersing it in an etching solution, wherein a deep structure is formed on the surface of the substrate;

[0015] A gas supply unit is used to supply gas to the etching solution to generate bubbles that agitate the etching solution; and

[0016] The controller is configured to control the gas supply unit to supply gas to the etching solution based on a pulse signal, wherein one pulse time of the pulse signal includes a gas supply period and an intermittent period, and the intermittent period depends on the diffusion time required for the key components in the deep structure to reach diffusion equilibrium after the gas supply period ends.

[0017] As described above, the present invention provides a substrate etching method and apparatus, which have the following beneficial effects:

[0018] 1) In the wet etching process, gas is supplied to the etching solution in a pulse manner. One pulse time includes a gas supply period and an intermittent period. The intermittent period is determined according to the diffusion time required for the key components in the deep structure to reach diffusion equilibrium after the gas supply period ends. The disturbance interval between adjacent gas supply periods on the trench is reasonably controlled, and the diffusion degree in the trench is regulated, thereby improving the etching uniformity in the trench.

[0019] 2) By making the interval between adjacent bubbles generated during the gas supply period shorter than the diffusion time required for key components in the deep structure to reach diffusion equilibrium after the disturbance of the previous bubble in the adjacent bubble, the disturbance intensity during the gas supply period is enhanced by superimposing multiple bubble disturbances, so as to expand the range of the convection region in the deep structure and improve the mass transfer efficiency in the deep structure.

[0020] 3) The single-bubble pulse mode, which intermittently supplies gas to the etching solution with N sub-pulse signals during the gas supply period, can not only effectively control the generation time of a single bubble, thereby accurately controlling the interval time between adjacent bubbles, but also obtain bubbles with higher gas velocities by using a larger gas flow rate, so as to further enhance the bubble disturbance capability. Attached Figure Description

[0021] Figure 1 The diagram shown is of a wet etching apparatus.

[0022] Figure 2 The diagram shows a partial structural schematic of a 3D NAND flash memory device, which has a stacked layer and trenches that penetrate the stacked layer.

[0023] Figure 3 This diagram illustrates the change in SiO2 etching rate as a function of silicon concentration in the reaction system.

[0024] Figure 4 The diagram shows the SiO2 re-adhesion in the trench and the over-etching of the silicon oxide film;

[0025] Figure 5 This is a schematic diagram showing how the diffusion of key components in the trench is inhibited by the next bubble after the previous bubble disturbance.

[0026] Figure 6 The diagram shows the timing of the pulse signal in Embodiment 1 of this application.

[0027] Figure 7 This is a schematic diagram illustrating the principle of the superposition effect of adjacent bubbles;

[0028] Figure 8 The diagram shown is a timing diagram of the pulse signal in Embodiment 2 of this application; and

[0029] Figure 9 The diagram shown is a timing diagram of a pulse signal in another embodiment of this application. Detailed Implementation

[0030] The following specific examples illustrate the implementation 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 also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0031] Please see Figures 1 to 9 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Although the illustrations 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, the shape, quantity and proportion of each component in the actual implementation can be arbitrarily changed, and the layout of the components may also be more complex.

[0032] The substrate etching method of this application is applicable to etching substrates with deep structures in a wet etching apparatus that performs batch processing. Figure 1 An exemplary wet etching apparatus (i.e., substrate etching apparatus) for implementing the substrate etching method of this application is shown. Figure 1 As shown, 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 the substrate w 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 that agitate the etching solution; and a controller 15. The liquid supply unit 13 includes a liquid supply line 131 and a liquid nozzle 132. The liquid nozzle 132 is disposed in the processing tank 11 and located below the substrate w. A liquid regulating valve 133 is disposed on the liquid line 131. The gas supply unit 14 includes a gas supply line 141 and a gas nozzle 142. The gas nozzle 142 is disposed in the processing tank 11 and located below the substrate w. A gas regulating valve 143 is disposed on the gas supply line 141. The controller 15 controls the gas flow rate supplied from the gas supply line 141 to the gas nozzle 142 by controlling the operation of the gas regulating valve 143, and controls the liquid flow rate supplied from the liquid supply line 131 to the liquid nozzle 132 by controlling the operation of the liquid regulating valve 132.

[0033] To address the problem of uneven etching in deep substrate structures, this application proposes a substrate etching method, including immersing a substrate w in a processing tank 11 containing an etching solution, and performing wet etching on the substrate w using the etching solution; and during the wet etching process, supplying gas to the etching solution based on a pulse signal to generate bubbles in the etching solution. In this application, references are made to... Figure 1 The controller 15 controls the operation of the gas regulating valve 143 based on a pulse signal to supply pulsed gas to the gas nozzle 142. A pulse duration of this signal includes a gas supply period and an intermittent period. The intermittent period depends on the diffusion time required for the key components in the trench to reach equilibrium after the gas supply period ends. The specific settings for the pulse signal will be explained later and will not be repeated here. It should also be noted that the key components refer to the main components in the reaction system that affect the etching uniformity, including etching reactants and / or etching products.

[0034] The following section will take the wet etching process of selectively removing silicon nitride film in stacked layers using phosphoric acid solution in the manufacturing of 3D NAND flash memory devices as an example to explain in detail the phenomenon of uneven etching in trenches and its causes, so as to better understand the substrate etching method proposed in this application.

[0035] Figure 2 An example is shown showing a partial structure of a 3D NAND flash memory device. For example... Figure 2As shown, the structure includes a stacked layer 100 formed on a substrate w and trenches 103 penetrating the stacked layer 100, wherein the stacked layer 100 is formed by alternating deposition of silicon nitride films 101 and silicon oxide films 102. In this example, the trenches 103 in the stacked layer 100 are deep structures formed on the substrate w. During the manufacturing process of the 3D NAND flash memory device, the silicon nitride film 101 in the stacked layer 100 needs to be removed. Generally, the silicon nitride film 101 in the stacked layer 100 is selectively removed by wet etching of the substrate with a phosphoric acid solution (etching solution).

[0036] Silicon nitride (Si3N4) can undergo the chemical reaction shown in formula (1) in phosphoric acid solution:

[0037] Si3N4+H3PO4+H2O→NH4H2PO4+Si(OH)4--------- (1)

[0038] Silicon oxide (SiO2) can undergo the chemical reaction shown in formula (2) in phosphoric acid solution:

[0039]

[0040] Equation (2) above is a reversible reaction. The reaction direction of equation (2) can be controlled by adjusting the silicon concentration (such as Si(OH)4 concentration) in the reaction system. Figure 3 A schematic diagram showing the change in SiO2 etching rate with silicon concentration in the reaction system is presented. (Combined with...) Figure 3 As shown, when the silicon concentration is at equilibrium, the reversible reaction in equation (2) reaches equilibrium, and the etching rate of SiO2 is 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 is greater than zero, SiO2 hydrolyzes to generate 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 is less than zero, Si(OH)4 polymerizes to generate SiO2, and the deposition reaction of SiO2 occurs. In addition, since the silicon concentration has little effect on the etching rate of Si3N4, the etching selectivity ratio of phosphoric acid for silicon nitride and silicon oxide can be controlled by adjusting the silicon concentration in the phosphoric acid solution. Usually, the silicon concentration in the phosphoric acid solution is slightly lower than the equilibrium concentration. Taking a 160℃ phosphoric acid solution as the etching solution as an example, the equilibrium concentration of silicon is 80ppm. At this time, the process range of silicon concentration in the phosphoric acid solution is set at about 40ppm to 70ppm.

[0041] As can be seen from the above equation (1), the etching of the silicon nitride film 101 in trench 103 will produce etching product Si(OH)4, and the diffusion efficiency of the etching product Si(OH)4 will affect the silicon concentration distribution in trench 103. When the silicon concentration in a local area of ​​trench 103 exceeds the equilibrium concentration, SiO2 deposition reaction will occur in that local area (refer to chemical equation (2) and Figure 3 The generated SiO2 deposits adhere to the silicon oxide film 102, causing SiO2 re-adhesion; when the silicon concentration in a local area of ​​the trench 103 is lower than the equilibrium concentration, an etching reaction of SiO2 will occur in that local area (refer to chemical equation (2) and Figure 3 If the etching amount of the silicon oxide film 102 exceeds the process requirements, it will result in over-etching of the silicon oxide film 102. The aforementioned SiO2 re-adhesion and over-etching of the silicon oxide film 102 are both manifestations of uneven etching in the trench 103, which will affect the performance and reliability of the product and are undesirable. Relatively speaking, the silicon concentration at the top of the trench 103 is low, making it prone to over-etching of the silicon oxide film 102; the silicon concentration at the bottom of the trench 103 is high, making it prone to SiO2 re-adhesion. Figure 4 The SiO2 back-adhesion phenomenon at the bottom of trench 103 is shown at point A. Figure 4 The over-etching of the silicon oxide film 102 on top of the trench 103 is shown at point B, where the silicon nitride film 101 is partially etched.

[0042] The storage capacity of a 3D NAND flash memory device is generally quantified by the number of stacked layers 100. Currently, 3D NAND flash memory devices contain 64, 96, 128, or even more stacked layers 100. The more stacked layers 100 there are, the larger the aspect ratio of the trench 103 becomes, making mass transfer within the trench 103 more difficult. This causes the etching product Si(OH)4 from the silicon nitride film 101 to accumulate in the trench 103, especially at the bottom of the trench 103, increasing the risk of SiO2 re-adhesion within the trench 103. Therefore, as the aspect ratio of the trench 103 increases, the challenge of uniform etching within the trench 103 becomes increasingly significant.

[0043] Currently, the common method to improve the etching uniformity in trench 103 is to continuously supply gas to the phosphoric acid solution to generate continuous bubbles, increase the liquid flow rate on the substrate w surface, thereby promoting the mass transfer efficiency in trench 103. Furthermore, as the aspect ratio of trench 103 increases, the flow rate of the supplied gas is continuously increased in order to obtain better etching uniformity.

[0044] In practice, for trenches 103 with low aspect ratios, using bubbles generated with a lower gas flow rate can effectively improve the mass transfer efficiency within the trench 103. However, for trenches 103 with high aspect ratios, such as when the aspect ratio exceeds 40:1, the promoting effect of bubbles generated with a lower gas flow rate on the mass transfer efficiency, especially at the bottom of the trench 103, weakens. The etching product Si(OH)4 accumulates at the bottom of the trench 103 due to low mass transfer efficiency, increasing the risk of SiO2 back-adhesion at the bottom of the trench 103. To overcome this SiO2 back-adhesion problem at the bottom of the trench 103, increasing the gas flow rate can indeed generate faster and more numerous bubbles, thereby enhancing the promoting effect on the mass transfer efficiency within the trench 103 and reducing the risk of SiO2 back-adhesion at the bottom of the trench 103. However, it should be noted that while increasing the gas flow rate helps reduce the silicon concentration at the bottom of trench 103 and improves SiO2 adhesion at the bottom of trench 103, a higher gas flow rate can also cause the silicon concentration near the top of trench 103 to drop too quickly, increasing the risk of over-etching of the silicon oxide film 102 at the top of trench 103. Therefore, in the continuous gas supply mode, as the aspect ratio of trench 103 continues to increase, simply increasing the gas flow rate cannot effectively solve the problem of uneven etching in trench 103.

[0045] Furthermore, in practice, the applicant also discovered that the bubble interval time is also an important factor affecting the diffusion of material in the trench 103. Specifically, if the interval time between adjacent bubbles is less than the time required for the etching product Si(OH)4 in the trench 103 to reach diffusion equilibrium after the disturbance of the previous bubble in the adjacent bubble, it may inhibit the outward diffusion of the etching product Si(OH)4 in the trench 103.

[0046] To facilitate understanding, the following will combine... Figure 5 A brief explanation of the above findings follows. Figure 5 The diagram shows positions 1 and 2 along the upward Z-direction of the bubble. Position 1 approximately represents the position where the bubble approaches the groove 103; position 2 approximately represents the position where the bubble leaves the groove 103. Both positions 1 and 2 are within the range where the bubble disturbs the groove 103. It should be noted that... Figure 5 The flow field in trench 103 has been simplified and is not the actual flow field in trench 103.

[0047] Figure 5 (a) shows the effect of bubble G1 on the flow field in trench 103 when it passes through position 1. Figure 5 (b) shows the effect of bubble G1 on the flow field in trench 103 as it passes position 2. Figure 5In (a), when bubble G1 passes position 1, bubble G1 is about to approach trench 103 and squeezes the etching solution outside trench 103 into the inside of trench 103, causing the flow field in trench 103 to tend to flow from the outside of trench 103 to the inside of trench 103, which is conducive to the diffusion of fresh phosphoric acid solution into the inside of trench 103. Figure 5 In (b), when bubble G1 passes position 2, bubble G1 leaves trench 103, and the inward squeezing effect exerted by bubble G1 on the liquid in trench 103 begins to disappear. The liquid pressure in trench 103 is released, causing the flow field in trench 103 to tend to flow from the inside of trench 103 to the outside of trench 103. The old phosphoric acid solution inside trench 103 diffuses to the outside of trench 103, which is conducive to the diffusion of the etching product Si(OH)4 in trench 103 to the outside of trench 103. Therefore, the disturbance of trench 103 by bubble includes two stages: inward squeezing of liquid and outward release of liquid.

[0048] Figure 5 (c) illustrates the effect of bubble G1 passing through position 2 while the subsequent bubble G2 passes through position 1 on the flow field in trench 103. Figure 5 In (c), when bubble G1 is at position 2, an outward flow field is generated in trench 103 that facilitates the diffusion of the etching product Si(OH)4 to the outside of trench 103 (e.g., Figure 5 (c) As shown by the solid arrow in the diagram, the etching product Si(OH)4 in trench 103 requires a period of time to reach diffusion equilibrium. If at this time, the next bubble G2 is already in an inward flow field that facilitates the diffusion of fresh phosphoric acid solution into the trench 103 (as shown by the solid arrow in the diagram), the etching product Si(OH)4 in trench 103 needs a period of time to reach diffusion equilibrium. If at this time, the next bubble G2 is already in a position to create an inward flow field that facilitates the diffusion of fresh phosphoric acid solution into the trench 103 (as shown by the solid arrow in the diagram), the etching product Si(OH)4 in trench 103 needs a period of time to reach diffusion equilibrium. Figure 5 (c) As shown by the dashed arrow, for example, if bubble G2 is at position 1, then in the area near the opening of trench 103, the inward flow field will hinder the outward flow field, or even force the outward flow field to reverse its direction. This will inhibit the diffusion of the etching product Si(OH)4 from the trench 103 to the outside of the trench 103. If the outward diffusion stage of the etching product Si(OH)4 in the trench 103 is always suppressed, it will lead to the accumulation of the etching product Si(OH)4 in the trench 103, causing SiO2 re-adhesion problems. Therefore, reasonably controlling the interval time between adjacent bubbles, so that the etching product Si(OH)4 in the trench 103 has enough time to diffuse, is beneficial to improving the replacement efficiency of the etching product Si(OH)4, improving the silicon concentration distribution in the trench 103, and thus improving the etching uniformity in the trench 103.

[0049] Based on the above analysis, in the substrate etching method proposed in this application, when the substrate is immersed in the etching solution for wet etching, gas is supplied to the etching solution based on a pulse signal. One pulse duration of the pulse signal includes a gas supply period and an interval period. The interval period is determined based on the diffusion time required for the key components in the trench 103 to reach equilibrium after the gas supply period ends. This allows for reasonable control of the disturbance interval between adjacent gas supply periods on the trench 103, regulating the diffusion degree in the trench 103, and thereby improving the etching uniformity in the trench 103. It should be noted that the pulse signal can be applied throughout the entire substrate etching process or only during a portion of the etching process.

[0050] The following describes the specific implementation of the substrate etching method proposed in this application, taking the wet etching of the silicon nitride film 101 in the phosphoric acid selective removal stack layer 100 as an example. The key component affecting etching uniformity is the etching product Si(OH)4.

[0051] (Implementation Method 1)

[0052] Figure 6 A timing diagram of the pulse signal in Embodiment 1 of this application is shown. Figure 6 As shown, the pulse duration T of the pulse signal includes a gas supply period t1 and an intermittent period t2. In some embodiments, the gas supply period t1 can be set to 10ms to 1s; the intermittent period t2 can be set to 10ms to 1s. The intermittent period t2 depends on the diffusion time T required for diffusion equilibrium to be reached in the trench 103 after the gas supply period t1 ends. d2 Ideally, the value of the intermittent period t2 should be related to the diffusion time T. d2 It is directly proportional, denoted as t2 = k * T d2 Where k>0 and is a set value, T d2 For experimental measurements or calculated simulated values, i.e., T d2 It can be obtained through experiments or computational simulations.

[0053] In the wet etching of the silicon nitride film 101 in the stacked layer 100, k can be set to not less than 0.5, for example, k can range from 0.5 to 2, or from 0.6 to 1, so that the etching product Si(OH)4 in the trench 103 has sufficient time to diffuse outward between two adjacent gas supply periods t1. This not only enhances the diffusion of material in the trench 103 due to the disturbance formed in the previous gas supply period t1, but also avoids the disturbance formed in the next gas supply period t1 from inhibiting the diffusion of material in the trench 103, thus ensuring sufficient diffusion of material in the trench 103, improving the diffusion efficiency in the trench 103, and reducing the silicon concentration gradient in the trench 103. The reduced silicon concentration gradient not only decreases the silicon concentration in the trench 103, especially at the bottom of the trench 103, suppressing the SiO2 back adhesion at the bottom of the trench 103, but also increases the silicon concentration at the top of the trench 103, improving the over-etching of the silicon oxide film 102 at the top of the trench 103.

[0054] It should be noted that the value of k in the wet etching of silicon nitride film 101 in stack layer 100 is only an example. The value range of k can be reasonably adjusted according to the wet etching object and the actual process. For example, in some wet etching processes, k may be set to less than 0.5.

[0055] During the gas supply period t1, gas is supplied to the etching solution at a first gas flow rate, and during the intermittent period t2, gas is supplied to the etching solution at a second gas flow rate. The first gas flow rate is greater than the second gas flow rate, used to generate bubbles in the etching solution, disturbing local areas on the substrate surface, such as the surface of trench 103, and enhancing mass transfer within trench 103. The second gas flow rate can be set to zero or greater than zero, primarily used to prevent the etching solution from flowing back into the gas nozzle. The minimum gas flow rate to prevent the etching solution from flowing back into the gas nozzle is defined as the critical gas flow rate, and the second gas flow rate can be set to be no less than the critical gas flow rate.

[0056] The number of bubbles generated in the etching solution by the gas supplied during gas supply period t1 is N, where N is a natural number and N≤10. For example, the number of bubbles generated during gas supply period t1 may be 1, 2, 3, or more than 3. All bubbles generated during gas supply period t1 are denoted as a bubble group, and the time interval T between adjacent bubbles in a bubble group is... g The diffusion time T required for diffusion equilibrium to be reached in groove 103 after the disturbance of the previous bubble in the adjacent bubble depends on the diffusion time T. d1 To enhance the overall perturbation effect of the bubble group, the time interval T between adjacent bubbles is... g It should be less than the diffusion time T required for diffusion equilibrium to be reached in groove 103 after the disturbance of the previous bubble in the adjacent bubble. d1 That is, T g <T d1 Preferably, T g =k1*T d1k1∈(0,0.5). Thus, before the release effect of the previous bubble generation, which is conducive to the outward diffusion of the etching products in the trench 103, ends, the squeezing effect of the next bubble generation, which is unfavorable to the outward diffusion of the etching products in the trench 103, begins. This results in the superposition of the disturbance effects of adjacent bubbles in the bubble group on the liquid in the trench 103, enhancing the disturbance ability of the gas supply period t1 on the etching solution, effectively improving the mass transfer efficiency in the trench 103, and helping to shorten the etching process time.

[0057] The following is combined Figure 7 Explain the principle of the superposition effect of adjacent bubbles. For example... Figure 7 As shown in (a), when bubble G1 is at position 1, bubble G1 pushes the fresh etching solution outside the trench 103 into the trench 103, causing a disturbance to the liquid in the trench 103 to a depth of h1; Figure 7 As shown in (b), when bubble G1 moves to position 2, the squeezing pressure generated by bubble G1 on the inside of groove 103 is in a state of about to be released or not fully released, and the liquid inside groove 103 tends to flow outward (e.g. Figure 7 (b) As indicated by the solid arrow, the etching product, such as Si(OH)4, inside trench 103 is in the outward diffusion stage. However, it takes a certain amount of time for the etching product Si(OH)4 to reach diffusion equilibrium. Assuming that the interval between bubbles G1 and G2 is less than the diffusion time required for the etching product Si(OH)4 in trench 103 to reach diffusion equilibrium after the disturbance of bubble G1, then before the etching product Si(OH)4 reaches diffusion equilibrium after the disturbance of bubble G1, bubble G2 has moved to the outside of trench 103 and squeezed another fresh etching solution to flow into trench 103 (e.g., ...). Figure 7 (b) As shown by the dashed arrow, for example, position 1, bubble G2 will advance the depth of liquid disturbance in groove 103 forward to h2.

[0058] In other words, during the gas supply period t1, it is desirable to reduce the spacing between adjacent bubbles, so that the squeezing effect of multiple bubbles pressing the fresh etching solution outside the trench 103 into the trench 103 is superimposed, thereby increasing the depth of liquid turbulence 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 promoting mass transfer deep in the trench 103, especially at the bottom of the trench 103, by enhancing the internal turbulence in the trench 103. Ideally, forced convection is formed between the top and bottom of the trench 103. During the intermittent period t2, it is desirable to have sufficient time for the etching products (e.g., Si(OH)4) inside the trench 103 to diffuse outward.

[0059] See you again Figure 6In 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, the first gas flow rate is preferably 0.5 L / min to 2 L / min.

[0060] (Implementation Method Two)

[0061] Please see Figure 8 This embodiment proposes a substrate etching method. Compared with Embodiment 1, Embodiment 2 differs in that the gas supply period t1 is based on N sub-pulse signals to intermittently supply gas to the etching solution, with each sub-pulse signal corresponding to the generation of one bubble, where N is a natural number and N≤10.

[0062] Figure 8 A timing diagram of the pulse signal in Embodiment 2 of this application is shown. Figure 8 As shown, the pulse time T of the pulse signal includes the gas supply period t1 and the intermittent period t2. In Figure 8 In this process, each gas supply period t1 includes 3 sub-pulse signals, and each sub-pulse signal has a pulse time t. a One bubble is generated within each bubble, referred to as a single-bubble pulse. Single-bubble pulses can effectively control the generation time of a single bubble, thereby precisely controlling the interval between adjacent bubbles. In this example, the pulse time t of the single-bubble pulse... a It can be approximated as the time interval T between adjacent bubbles. g The pulse duration of the sub-pulse signal can be set to, for example, 10ms to 100ms.

[0063] Single-bubble pulses can also utilize larger gas flow rates to generate higher-velocity bubbles, achieving better disturbance of the etching solution through high-speed bubbles. In one example, the gas flow rate supplied to the etching solution by the sub-pulse signal is set to no less than 2 L / min, 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 can be set to 2.5 L / min, 3 L / min, 10 L / min, 15 L / min, etc.

[0064] It should be noted that, compared with the upper limit of gas flow rate that can be used in the continuous gas supply mode in Embodiment 1, the upper limit of gas flow rate that can be used in the single-bubble pulse mode of the gas supply period in Embodiment 2 is larger. This is because when the continuous gas supply mode is used in the gas supply period, if the gas flow rate exceeds a certain range, for example, if the gas flow rate is 5L / min, the supplied gas may form a gas column in the etching solution that is not conducive to etching.

[0065] It should be noted that the substrate etching method proposed in this application can be applied not only to the removal of silicon nitride film 101 in the stacked layer 100 of 3D NAND device, but also to the removal of thin films in deep structures such as logic devices, interconnect structures, FinFETs, and 3D semiconductor structures with narrow gaps, narrow trenches and high aspect ratio channels.

[0066] Furthermore, in the substrate etching method proposed in this application, the pulse signal can be periodic or non-periodic. Specifically, the duty cycle, frequency, and amplitude of the pulse signal can be fixed or adjusted according to the actual process. The duty cycle refers to the proportion of the gas supply period within a pulse time, and the amplitude corresponds to the supplied gas flow rate. For example, Figure 6 and Figure 8 The pulse signal shown is periodic, meaning that each pulse in the pulse signal has the same duty cycle, frequency, amplitude, etc. For example, Figure 9 The pulse signal shown is aperiodic, with its duty cycle gradually decreasing, meaning the proportion of the gas supply period t1 within a single pulse time T gradually decreases. It can be understood that when supplying gas to the etching solution with aperiodic pulse signals, the number of bubbles generated during different gas supply periods can be controlled by adjusting the pulse signal's duty cycle, frequency, and amplitude. Furthermore, Figure 9 This is just one specific example of a non-periodic pulse signal. In practical applications, the non-periodic setting of the pulse signal can be reasonably set according to specific process conditions.

[0067] 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 substrate etching method, characterized in that, include: The substrate is immersed in a processing tank containing an etching solution, and the substrate is wet-etched by the etching solution, forming a deep structure on the surface of the substrate. Gas is supplied to the etching solution via a pulse signal to generate bubbles. One pulse duration of the pulse signal includes a gas supply period and an intermittent period. The intermittent period depends on the diffusion time required for the key components in the deep structure to reach diffusion equilibrium after the gas supply period ends. The key components include etching reactants and / or etching products. The intermittent period is denoted as t2, and the diffusion time required for the key components in the deep structure to reach diffusion equilibrium after the gas supply period ends is denoted as Td2. t2 is proportional to Td2, and is denoted as t2 = k. Td2, where k>0, The substrate etching method is used to improve the etching uniformity in the deep structure.

2. The substrate etching method according to claim 1, characterized in that, The interval period is 10ms to 1s.

3. The substrate etching method according to claim 1, characterized in that, The value of k is not less than 0.

5.

4. The substrate etching method according to claim 3, characterized in that, The value of k ranges from 0.5 to 2.

5. The substrate etching method according to claim 1, characterized in that, During the gas supply period, gas is supplied to the etching solution at a first gas volume, and during the intermittent period, gas is supplied to the etching solution at a second gas volume, the second gas volume being less than the first gas volume.

6. The substrate etching method according to claim 5, characterized in that, The second gas volume is zero.

7. The substrate etching method according to claim 5, characterized in that, The processing tank is equipped with a gas nozzle for supplying gas to the etching solution to generate bubbles. The second gas volume is not less than the critical gas flow rate, which is the minimum gas flow rate that prevents backflow to the gas nozzle.

8. The substrate etching method according to claim 1, characterized in that, The gas supply period is 10ms to 1s.

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

10. The substrate etching method according to claim 9, characterized in that, The time interval T between adjacent bubbles generated during the gas supply period g The diffusion time T required for the key components in the deep structure to reach diffusion equilibrium after the disturbance of the previous bubble in the adjacent bubble is less than the diffusion time T. d1 .

11. The substrate etching method according to claim 10, characterized in that, The T g =k1 T d1 , k1∈(0,0.5).

12. The substrate etching method according to claim 9, characterized in that, During the gas supply period, gas is continuously supplied to the etching solution.

13. The substrate etching method according to claim 12, characterized in that, The flow rate of the gas continuously supplied to the etching solution is 0.5 L / min to 2 L / min.

14. The substrate etching method according to claim 9, characterized in that, The gas supply period is based on N sub-pulse signals to intermittently supply gas to the etching solution. Each sub-pulse signal corresponds to the generation of one bubble. N is a natural number and N≤10.

15. The substrate etching method according to claim 14, characterized in that, The pulse duration of each sub-pulse signal is 10ms to 100ms.

16. The substrate etching method according to claim 14, characterized in that, The gas flow rate supplied to the etching solution by the sub-pulse signal is not less than 2 L / min.

17. The substrate etching method according to claim 16, characterized in that, The gas flow rate supplied to the etching solution by the sub-pulse signal is 2 L / min to 30 L / min.

18. The substrate etching method according to claim 1, characterized in that, The pulse signal may be periodic or aperiodic.

19. A substrate etching apparatus, comprising: Processing tank, used to hold etching solution; A holding mechanism for holding a substrate and immersing it in an etching solution, wherein a deep structure is formed on the surface of the substrate; The gas supply unit is used to supply gas to the etching solution to generate bubbles that agitate the etching solution. as well as The controller is configured to control the gas supply unit to supply gas to the etching solution based on a pulse signal. One pulse duration of the pulse signal includes a gas supply period and an intermittent period. The intermittent period depends on the diffusion time required for the key components in the deep structure to reach diffusion equilibrium after the gas supply period ends. The key components include etching reactants and / or etching products. The intermittent period is denoted as t2, and the diffusion time required for the key components in the deep structure to reach diffusion equilibrium after the gas supply period ends is denoted as Td2. t2 is proportional to Td2, and is denoted as t2 = k. Td2, where k>0, The substrate etching apparatus is used to improve the etching uniformity in the deep structure.

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