Ultralow-temperature deep silicon etching method and high aspect ratio etching structure

Abstract

The application discloses a kind of ultra-low temperature deep silicon etching method and high aspect ratio etching structure, comprising: forming a plurality of photoresist patterns on the surface of silicon substrate;Deposition step of performing etching process, at a first temperature below-30 DEG C, using a first gas comprising CH4, CHF3 and H2, depositing a-C:H:F crosslinked polymer layer on silicon substrate and photoresist pattern to protect silicon substrate and photoresist pattern when etching;Etching step of performing etching process, at a second temperature below-30 DEG C, using a second gas comprising F2 and BF3, etching a-C:H:F crosslinked polymer layer and silicon substrate;Deposition step and etching step are sequentially repeated until high aspect ratio etching structure is formed on silicon substrate;Remove photoresist pattern.The application can realize uniform protection to sidewall at smaller size and higher aspect ratio, and can improve etching rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor processing, and in particular to a method for ultra-low temperature deep silicon etching and a high aspect ratio etching structure obtained by using the method. BACKGROUND

[0002] In the rapidly developing field of advanced packaging, higher density interconnection is required, and deep silicon etching (DSE) is required to meet the requirements of nanoscale line width (less than 50 nm) and higher aspect ratio (greater than 100:1). The traditional periodic cyclic etching process has been difficult to meet the above-mentioned extreme aspect ratio requirements due to the influence of the corresponding physical limitations (such as ion shadow effect, reaction gas transmission efficiency). At the same time, nanoscale line width is more sensitive to the thickness fluctuation of the sidewall passivation layer (such as C-F polymer), and when the thickness fluctuation of the sidewall passivation layer is large, it is easy to cause line width deviation and etching tilt (three-dimensional through silicon via and memory stack require etching verticality error less than ±0.2°) problems. In addition, the existing etching process also has the problems of plasma chemical residue and local rough peaks (Ra>5nm) caused by random deposition of C-F polymer on the sidewall, which have important influence on the realization of higher aspect ratio and nanoscale deep silicon etching. And under the requirements of higher aspect ratio and nanoscale line width, how to improve the etching rate and how to improve the uniformity of the protection of the bottom sidewall during the etching process is particularly important. Therefore, it is necessary to study a process method which can significantly improve the above-mentioned problems. SUMMARY

[0003] The present application aims to overcome the above-mentioned problems existing in the prior art, and provides an ultra-low temperature deep silicon etching method and a high aspect ratio etching structure.

[0004] To achieve the above-mentioned purpose, the technical solutions of the present application are as follows:

[0005] According to the first aspect of the present application, the embodiments of the present application provide an ultra-low temperature deep silicon etching method, comprising:

[0006] providing a silicon substrate;

[0007] forming a plurality of photoresist patterns on the surface of the silicon substrate;

[0008] performing an etching process, which comprises:

[0009] (i) performing a deposition step, which comprises:

[0010] depositing an a-C:H:F cross-linked polymer layer on the silicon substrate and the photoresist pattern using a first gas comprising CH4, CHF3 and H2 at a first temperature below -30℃ to protect the silicon substrate and the photoresist pattern during etching;

[0011] (ii) performing an etching step comprising:

[0012] etching the a-C:H:F cross-linked polymer layer and the silicon substrate using a second gas comprising F2 and BF3 at a second temperature below -30℃;

[0013] (iii) sequentially repeating (i) and (ii) until a high aspect ratio etching structure is formed on the silicon substrate;

[0014] removing the photoresist pattern.

[0015] In some embodiments, the performing the depositing step specifically comprises:

[0016] at the first temperature, first passing the CH4, the CHF3 and the H2 of a first hydrogen flow rate in the first gas to deposit a transition a-C:H:F cross-linked polymer layer with a first hydrogen content on the silicon substrate and the photoresist pattern; then, stopping passing the CH4 and the CHF3 and continuing to pass the H2 of a second hydrogen flow rate to perform a first treatment on the transition a-C:H:F cross-linked polymer layer to form a highly cross-linked a-C:H:F cross-linked polymer layer with a three-dimensional network structure by terminating dangling bonds and increasing cross-linking degree, the second hydrogen content being greater than the first hydrogen content, the second hydrogen flow rate being greater than the first hydrogen flow rate.

[0017] In some embodiments, the flow rate of the CH4 is 3sccm-20sccm.

[0018] In some embodiments, the flow rate of the CHF3 is 10sccm-50sccm.

[0019] In some embodiments, the first hydrogen flow rate is 1sccm-10sccm.

[0020] In some embodiments, the second hydrogen flow rate is 10sccm-100sccm.

[0021] In some embodiments, the first hydrogen flow rate is a first varying flow rate gradually increasing.

[0022] In some embodiments, the second hydrogen flow rate is a constant flow rate.

[0023] In some embodiments, the second hydrogen flow rate is a second varying flow rate gradually increasing from 10 sccm to 100 sccm.

[0024] In some embodiments, the first hydrogen flow rate is a first varying flow rate gradually increasing from 1 sccm to 10 sccm.

[0025] In some embodiments, the second hydrogen flow rate is a constant flow rate ranging from 10 sccm to 100 sccm.

[0026] In some embodiments, the second hydrogen flow rate is a second varying flow rate gradually increasing from 10 sccm to 100 sccm.

[0027] In some embodiments, when performing the etching step, the a-C:H:F cross-linked polymer layer is also subjected to a second treatment using a plasma formed by the BF3 in the second gas being introduced, so as to change the properties of the a-C:H:F cross-linked polymer layer and enhance the lateral etching resistance of the a-C:H:F cross-linked polymer layer.

[0028] In some embodiments, the flow rate of the F2 ranges from 100 sccm to 400 sccm.

[0029] In some embodiments, the flow rate of the BF3 ranges from 5 sccm to 50 sccm.

[0030] In some embodiments, the flow rate ratio of the F2 and the BF3 is F2:BF3 = 8:1 to 20:1.

[0031] In some embodiments, another implementation of the second gas is that the BF3 in the second gas is replaced by PF3.

[0032] In some embodiments, another implementation of the second gas is that the BF3 in the second gas is replaced by PF3, and the second gas also includes N2, and when performing the etching step, a plasma formed by the N2 in the second gas being introduced is also used to perform a third treatment on the sidewall of the high aspect ratio etching structure being formed, so as to form a nitrided layer on the sidewall and to perform auxiliary passivation on the surface of the sidewall.

[0033] In some embodiments, another implementation of the second gas is that the second gas also includes N2, and when performing the etching step, a plasma formed by the N2 in the second gas being introduced is also used to perform a third treatment on the sidewall of the high aspect ratio etching structure being formed, so as to form a nitrided layer on the sidewall and to perform auxiliary passivation on the surface of the sidewall.

[0034] In some embodiments, the first temperature ranges from -90°C to -30°C.

[0035] In some embodiments, the second temperature is -90℃ to -30℃.

[0036] In some embodiments, the time for performing the deposition step is 0.1s to 2s.

[0037] In some embodiments, the time for performing the etching step is 0.2s to 4s.

[0038] According to a second aspect of the present application, the embodiments of the present application further provide a high aspect ratio etching structure, which is obtained by using the ultra-low temperature deep silicon etching method provided by any one of the embodiments of the first aspect.

[0039] The embodiments of the present application can / at least have the following advantages:

[0040] (1) By using small molecule first gas (CH4, CHF3 and H2) and second gas (F2 and BF3) to replace the traditional large molecule gas C4F8 and SF6 as deposition gas and etching gas respectively, the diffusion coefficient can be increased, the gas transmission efficiency can be improved, the etching gas can be more uniformly diffused and more easily enter the nanoscale high aspect ratio etching structure (deep trench, deep hole or via) for etching reaction, more excellent small size high aspect ratio deep silicon etching can be achieved, and the deposition gas can smoothly enter the bottom of the high aspect ratio etching structure to achieve more uniform protection of the sidewall at a smaller size. And by making the temperature (first temperature, second temperature) during performing the deposition step and the etching step less than -30℃, the ultra-low temperature can be used to change the chemical kinetics, enhance the physical adsorption and reduce the reaction rate, so that the a-C:H:F cross-linked polymer layer formed can be more dense and more uniformly adsorbed on the sidewall, even at the bottom of the high aspect ratio etching structure, effective protection of the sidewall can be formed, lateral etching can be effectively inhibited, and an extremely vertical sidewall morphology can be obtained. Therefore, the present application can solve the problem of the influence of the thickness fluctuation of the polymer formed by using the large molecule C4F8 deposition on the control of the nanoscale line width, and the ion shadow effect problem (nanoscale involves atomic size level), effectively improve the uniformity and roughness of the local C-F polymer, achieve more excellent uniformity (uniform size of upper, middle and lower positions of the high aspect ratio etching structure), better sidewall smoothness, and further realize higher aspect ratio nanoscale size deep silicon structure etching. At the same time, the small molecule etching gas can significantly improve the etching rate and etching behavior at high depth (>100µm).

[0041] (2) By using the combination of CH4, CHF3 and H2 as the deposition gas, it can be easier to enter and uniformly deposit on the sidewall bottom of the ultra-narrow and ultra-deep silicon structure, and it can reduce the physical bombardment and chemical erosion of high-energy ions on the mask (photoresist pattern), reduce the damage to the mask, and protect the critical dimension. Moreover, by first passing CH4, CHF3 and a small amount of H2, a transition a-C:H:F cross-linked polymer layer is deposited as a skeleton structure at an ultra-low temperature (first temperature), and after stopping the passage of CH4 and CHF3, a first treatment is performed on the formed transition a-C:H:F cross-linked polymer layer at an ultra-low temperature by continuing to pass a large amount of H2. The additional H atoms can be combined with the dangling bonds of the carbon chain to reduce or even terminate the dangling bonds, form stable C-H bonds, make the polymer structure more complete, and use -CH2- and -CH- groups as cross-linking points to tightly connect more carbon chains together, greatly improving the cross-linking degree, so as to form an a-C:H:F cross-linked polymer layer with a three-dimensional network structure with high cross-linking. Compared with ordinary polymers, it has the characteristics of lower fluorocarbon ratio, higher hydrogen-carbon ratio, higher density, higher hardness, and higher cross-linking degree, so it has excellent physical sputtering and chemical etching resistance, better blocking effect, and can effectively avoid lateral etching. At the same time, since the polymer layer can extend to the bottom, it ensures that the etching rate from the top to the bottom is anisotropic, thereby maintaining the vertical sidewall morphology.

[0042] (3) By using the combination of F2 and BF3 as the etching gas, the high reactivity of F2 can provide abundant primary etchants, reduce the dependence on physical bombardment, and improve the etching rate. The light ions produced by BF3 can efficiently transfer energy to the bottom, which is beneficial to the etching of the bottom. Among them, the small molecule reactants and products have a longer average free path, which can directly reach the bottom of the high aspect ratio etching structure, ensuring the etching rate of the bottom and avoiding "etching stop"; the ions produced have lighter mass and more concentrated energy distribution, achieving extreme anisotropic etching, and reducing damage to the photoresist pattern to obtain a more vertical sidewall. In addition, the plasma formed by BF3 performs a second treatment on the a-C:H:F cross-linked polymer layer to change the properties of the a-C:H:F cross-linked polymer layer by doping B elements, so as to enhance the lateral etching resistance of the a-C:H:F cross-linked polymer layer, thereby further improving the verticality of the sidewall and the uniformity of the size.

[0043] (4) By further adding N2 in the second gas, the plasma formed by N2 performs a third treatment on the sidewall of the forming high aspect ratio etching structure to form an extremely thin nitrided layer on the sidewall, achieving the effect of auxiliary passivation of the surface of the sidewall, thereby further improving the fidelity of the pattern.

[0044] Other advantages of the present application will be described in the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 A flow chart of an ultra-low temperature deep silicon etching method according to an embodiment of the present application.

[0046] Figure 2 A structure diagram after forming a photoresist pattern on a silicon substrate according to an embodiment of the present application.

[0047] Figure 3 A structure diagram after depositing a polymer layer on a silicon substrate and a photoresist pattern according to an embodiment of the present application.

[0048] Figure 4 A structure diagram after forming a first etching structure on a silicon substrate according to an embodiment of the present application.

[0049] Figure 5 A structure diagram after depositing a polymer layer on a silicon substrate and a photoresist pattern according to an embodiment of the present application.

[0050] Figure 6 A structure diagram after forming a second etching structure on a silicon substrate according to an embodiment of the present application.

[0051] Figure 7 A structure diagram after forming a high aspect ratio etching structure on a silicon substrate according to an embodiment of the present application.

[0052] Figure 8 A structure diagram after removing a photoresist pattern according to an embodiment of the present application.

[0053] Fig. 10. Silicon substrate; 11. Opening; 12. Photoresist pattern; 13. Carbon-based protective film; 14. a-C:H:F cross-linked polymer layer; 15. First etching structure; 16. Second etching structure; 17. High aspect ratio etching structure. DETAILED DESCRIPTION

[0054] In order to solve the problems existing in the prior art, an ultra-low temperature deep silicon etching method is provided according to an embodiment of the present application, which comprises:

[0055] providing a silicon substrate;

[0056] forming a plurality of photoresist patterns on the surface of the silicon substrate;

[0057] performing an etching process, which comprises in sequence:

[0058] (i) performing a deposition step, which comprises:

[0059] depositing an a-C:H:F cross-linked polymer layer on the silicon substrate and the photoresist pattern using a first gas comprising CH4, CHF3 and H2 at a first temperature below -30℃ to protect the silicon substrate and the photoresist pattern during etching;

[0060] (ii) performing an etching step comprising:

[0061] etching the a-C:H:F cross-linked polymer layer and the silicon substrate using a second gas comprising F2 and BF3 at a second temperature below -30℃;

[0062] (iii) sequentially repeating (i) and (ii) until a high aspect ratio etching structure is formed on the silicon substrate;

[0063] removing the photoresist pattern.

[0064] The embodiments of the present application can increase the diffusion coefficient and improve the gas transmission efficiency by using small molecule first gas (CH4, CHF3 and H2) and second gas (F2 and BF3) instead of traditional large molecule gas C4F8 and SF6 as deposition gas and etching gas respectively, which can make the etching gas diffuse more uniformly and more easily enter the nanoscale high aspect ratio etching structure (deep trench, deep hole or via) for etching reaction, achieve more excellent small size high aspect ratio deep silicon etching, and make the deposition gas enter the bottom of the high aspect ratio etching structure smoothly to achieve more uniform protection of the sidewall at a smaller size. Moreover, by making the temperature (first temperature, second temperature) during performing the deposition step and the etching step less than -30℃, the ultra-low temperature can be used to change the chemical kinetics, enhance the physical adsorption and reduce the reaction rate, so that the a-C:H:F cross-linked polymer layer formed can be more dense and more uniformly adsorbed on the sidewall, which can form effective protection of the sidewall even at the bottom of the high aspect ratio etching structure, and can effectively inhibit the lateral etching to obtain an extremely vertical sidewall morphology. At the same time, the small molecule etching gas can significantly improve the etching rate and etching behavior at high depth (>100µm).

[0065] The embodiments of the present application also provide a high aspect ratio etching structure obtained by using the above-mentioned ultra-low temperature deep silicon etching method.

[0066] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0067] Reference Figure 1 According to a first aspect of the present application, the embodiments of the present application provide an ultra-low temperature deep silicon etching method, which sequentially comprises the following steps:

[0068] Step S11: providing a silicon substrate.

[0069] Reference Figure 2 In some embodiments, a silicon substrate 10 is employed, and a high aspect ratio etching structure is formed on the silicon substrate 10 by the ultra-low temperature deep silicon etching method provided in the embodiments of the present application.

[0070] In some embodiments, the high aspect ratio etching structure includes a deep trench, a deep via or a through via, etc.

[0071] In some embodiments, a silicon wafer can be employed as the silicon substrate 10.

[0072] In some embodiments, the silicon wafer can be subjected to a doping process to provide the silicon substrate 10 with desired electrical properties.

[0073] In some embodiments, integrated circuits such as transistor structures can be fabricated on the silicon substrate 10, so that vertical interconnections can be achieved by filling conductive materials after the high aspect ratio etching structure is formed.

[0074] Step S12: Forming a plurality of photoresist patterns on the surface of the silicon substrate.

[0075] Reference Figure 2 In some embodiments, a spin coating process can be employed to form a photoresist layer on the upper surface of the silicon substrate 10, and the photoresist layer is subjected to a photoetching patterning process to form a plurality of photoresist patterns 12 on the upper surface of the silicon substrate 10. Any two adjacent photoresist patterns 12 have an opening 11 as an etching window therebetween, and the surface of the silicon substrate 10 between the two adjacent photoresist patterns 12 is exposed at the bottom of the opening 11.

[0076] It should be noted that, Figure 2 In FIG. 1, only a case where two photoresist patterns 12 are formed on the upper surface of the silicon substrate 10 is shown. However, it should be understood that more photoresist patterns can be formed on the upper surface of the silicon substrate 10, such as three photoresist patterns, four photoresist patterns, ten photoresist patterns, etc., and the number of the photoresist patterns is not limited thereto.

[0077] In some embodiments, before etching the silicon substrate 10, the interface between the silicon substrate 10 and the photoresist pattern 12 is subjected to a fourth treatment at a third temperature below -30°C using a plasma of argon, so as to form a carbon-based protective film 13 (a protective film of carbon-based material containing C, N and O) at the interface (upper surface) of the silicon substrate 10 at the junction between the bottom of the photoresist pattern 12 and the upper surface of the silicon substrate 10 (i.e. at the inner bottom corner of the opening 11), so as to effectively protect the topography of the top of the silicon substrate 10 during subsequent etching of the silicon substrate 10, prevent abnormal excessive lateral etching behavior at the top, and ensure the uniformity of the size at different depths (i.e. the verticality of the sidewall) during subsequent high aspect ratio etching.

[0078] In some embodiments, during the fourth treatment, the third temperature is -90°C to -30°C, the pressure is 50 mTorr to 800 mTorr, the source power is 50 W to 100 W, the bias power is 10 W to 50 W, and the time is 5 s to 20 s. However, it is not limited thereto.

[0079] Step S13: performing a deposition step to deposit an a-C:H:F cross-linked polymer layer on the silicon substrate and the photoresist pattern at a first temperature below -30°C using a first gas containing CH4, CHF3 and H2.

[0080] In some embodiments, a high aspect ratio etching structure is formed on the silicon substrate by performing an etching process. The etching process comprises deposition steps and etching steps in sequence. The deposition steps and the etching steps can be repeatedly performed in sequence for multiple times until the high aspect ratio etching structure is formed on the silicon substrate.

[0081] In some embodiments, during the deposition step, a first gas containing CH4, CHF3 and H2 is used as a deposition gas to deposit a polymer on the exposed surface of the silicon substrate 10 (the sidewall of the high aspect ratio etching structure being formed) and the exposed surface of the photoresist pattern 12 (the side surface and the top surface), so as to protect the silicon substrate 10 (the sidewall of the high aspect ratio etching structure being formed) and the photoresist pattern 12 during etching.

[0082] CH4, CHF3 and H2 in the first gas are small molecule gases with a molecular weight less than C4F8, which are used to deposit a uniform a-C:H:F cross-linked polymer layer on the exposed surface of the silicon substrate 10 and the exposed surface of the photoresist pattern 12 at an ultra-low temperature below -30°C. The first gas is ionized to obtain a plasma of the first gas, which is used to deposit the polymer.

[0083] In some embodiments, before forming the a-C:H:F cross-linked polymer layer, a transition a-C:H:F cross-linked polymer layer (not shown) is first formed, which specifically includes:

[0084] At a first temperature below -30°C, a first gas mixture of CH4, CHF3, and H2 at a first hydrogen flow rate is introduced into the process chamber in which the silicon substrate 10 is placed, and a plasma is formed to deposit a transition a-C:H:F cross-linked polymer layer (not shown) on the exposed surface of the silicon substrate 10 and the exposed surface of the photoresist pattern 12, with the purpose of quickly forming a skeleton structure of the polymer and ensuring the uniformity of the deposition.

[0085] The first hydrogen flow rate is small, so the transition a-C:H:F cross-linked polymer layer formed has a low first hydrogen content. Thus, the transition a-C:H:F cross-linked polymer layer contains dangling bonds of carbon chains, so that the structure is not yet complete and the cross-linking degree is not yet high, and the density and hardness of the transition a-C:H:F cross-linked polymer layer are also not yet high, and it is also difficult to play a good barrier effect.

[0086] Then, the introduction of CH4 and CHF3 is stopped, and H2 at a second hydrogen flow rate is continuously introduced, with the second hydrogen flow rate being greater than the first hydrogen flow rate, so that the transition a-C:H:F cross-linked polymer layer is further subjected to a first treatment to form an a-C:H:F cross-linked polymer layer 14 with a highly cross-linked three-dimensional network structure and a high second hydrogen content, as shown in Figure 3 The second hydrogen content is greater than the first hydrogen content.

[0087] By subjecting the transition a-C:H:F cross-linked polymer layer formed to the first treatment at an ultra-low temperature below -30°C, the H atoms can be combined with the dangling bonds of the carbon chains to reduce or even terminate the dangling bonds present in the transition a-C:H:F cross-linked polymer layer, form stable C-H bonds, make the polymer structure more complete, and use -CH2- and -CH- groups as cross-linking points to tightly connect the carbon chains together, promote the increase of the cross-linking degree, and thus form the a-C:H:F cross-linked polymer layer 14 (amorphous carbon hydrogen fluoride polymer layer) with a highly cross-linked three-dimensional network structure, which has a lower fluorocarbon ratio, a higher hydrogen-carbon ratio, is more dense, harder, and has a higher cross-linking degree, and thus has excellent resistance to physical sputtering and chemical etching, and a better barrier effect, thereby effectively avoiding lateral etching. At the same time, since the a-C:H:F cross-linked polymer layer 14 can extend all the way to the bottom, it ensures that the etching rate from the top to the bottom is anisotropic, thereby maintaining the vertical sidewall morphology.

[0088] Moreover, further increasing the hydrogen content in the transition a-C:H:F cross-linked polymer layer results in the a-C:H:F cross-linked polymer layer 14 formed having a higher second hydrogen content than the transition a-C:H:F cross-linked polymer layer, further increasing the H / C ratio, and thus increasing the density and hardness.

[0089] The deposition gas C4F8 used in the prior art is a macromolecular gas. In the implementation of smaller CDs (nanometer-level line width) and higher aspect ratios (>100:1), the deposition of the macromolecular gas on the sidewall is mainly in the upper half of the deep trench and deep hole, and it is difficult to enter the bottom of the deep silicon structure. Therefore, for high aspect ratio etched structures, the protection of the bottom sidewall is not very sufficient. The embodiments of the present application use small molecules CH4, CHF3 and H2 to replace the traditional macromolecular C4F8 as the deposition gas, and the first temperature is less than -30°C. In the process of high aspect ratio deep silicon etching, the core advantage is that:

[0090] (1) Better sidewall protection quality: the a-C:H:F cross-linked polymer layer 14 formed has a lower fluorocarbon ratio, is denser, and has a higher cross-linking degree.

[0091] (2) Better step coverage and penetration: small molecule deposition gas is easier to enter and uniformly deposit on the sidewall bottom of ultra-narrow and ultra-deep structures (the mean free path of small molecules such as CH3• and CF• is longer, and they are more likely to reach the bottom of the deep hole without collision. The large groups generated by the traditional C4F8 dissociation (such as C2F5) are more likely to collide in the narrow channel and be consumed, and it is difficult to reach the bottom).

[0092] (3) Reduce damage to the photoresist pattern 12: the use of small molecule deposition gas reduces the physical bombardment and chemical erosion of high-energy ions on the photoresist pattern 12, protecting the critical dimension.

[0093] The embodiments of the present application use a gas system composed of CH4, CHF3 and H2 (without C4F8), which can form a dense a-C:H:F cross-linked polymer layer 14 (amorphous carbon film), which is an amorphous carbon hydrogen fluoride polymer. Its structure is no longer linear, but a highly cross-linked three-dimensional network structure.

[0094] And the deposition step of the traditional deep silicon etching is to use C4F8 as the deposition gas to form a polymer, which will generate a large amount of CF2 free radicals and other larger fluorocarbon groups (such as CF3, C2F5, etc.) when dissociated in the plasma. This polymer is a "loose" Teflon-like structure mainly composed of linear -CF2-CF2- chains. This structure is relatively loose and has weak mechanical strength. In addition, the polymer formed by the C4F8 deposition gas has a high F / C ratio, and contains a large amount of fluorine (F) in the polymer, making it more similar to Teflon, which has strong chemical inertness, but is not strong enough as an etching barrier.

[0095] The small molecule deposition system formed by using the combination of CH4, CHF3 and H2 in the embodiment of the present application has a low F / C ratio and a high H / C ratio. Among them, the introduction of H can play the following key roles:

[0096] (a) Termination of dangling bonds: H atoms can combine with dangling bonds of carbon chains to form stable C-H bonds, making the structure of the formed a-C:H:F cross-linked polymer layer 14 more complete.

[0097] (b) Promote cross-linking: -CH2- and -CH- groups can be used as cross-linking points to tightly connect carbon chains together, so that the a-C:H:F cross-linked polymer layer 14 formed on the sidewall has better blocking effect and can effectively avoid lateral etching.

[0098] Therefore, the a-C:H:F cross-linked polymer layer 14 formed by the embodiment of the present application has a highly cross-linked structure, which is more dense and hard when deposited on the sidewall, and has excellent resistance to physical sputtering and chemical etching.

[0099] In the small molecule system of CH4, CHF3 and H2 in the embodiment of the present application, the F / C ratio is relatively low and the H / C ratio is relatively high, so the chemical corrosion of the photoresist pattern 12 can be greatly reduced. Moreover, the plasma conditions required for small molecule deposition are generally milder than those of macromolecules, and the ion energy is relatively low, reducing the physical sputtering of the photoresist pattern 12. Therefore, the loss of the photoresist pattern 12 is effectively reduced.

[0100] In addition, the small molecule deposition gas system of the embodiment of the present application can effectively resist lateral etching, thereby inhibiting the generation of a Bowing morphology.

[0101] At the same time, the a-C:H:F cross-linked polymer layer 14 can extend to the bottom, ensuring that the etching rate from top to bottom is anisotropic and consistent, thereby maintaining a vertical sidewall morphology.

[0102] In some embodiments, the flow rate of CH4 in the first gas is 3 sccm to 20 sccm. For example, the flow rate of CH4 can be 3 sccm, 5 sccm, 8 sccm, 10 sccm, 15 sccm, or 20 sccm, or any value between any two of the aforementioned flow rates. However, it is not limited to these values.

[0103] In some embodiments, the flow rate of CHF3 in the first gas is 10 sccm to 50 sccm. For example, the flow rate of CHF3 can be 10 sccm, 15 sccm, 20 sccm, 30 sccm, 40 sccm, or 50 sccm, or any value between any two of the aforementioned flow rates. However, it is not limited to this.

[0104] In some embodiments, the first hydrogen flow rate is 1 sccm to 10 sccm. For example, the first hydrogen flow rate can be 1 sccm, 2 sccm, 3 sccm, 4 sccm, 5 sccm, 6 sccm, 7 sccm, 8 sccm, 9 sccm, or 10 sccm, or any value between any two of the aforementioned flow rate values. However, it is not limited to this.

[0105] In some embodiments, the second hydrogen flow rate is 10 sccm to 100 sccm. For example, the second hydrogen flow rate can be 10 sccm, 20 sccm, 30 sccm, 40 sccm, 50 sccm, 60 sccm, 70 sccm, 80 sccm, 90 sccm, or 100 sccm, or any value between any two of the aforementioned flow rate values. However, it is not limited to these.

[0106] In some embodiments, the first hydrogen flow rate is a first variable flow rate that gradually increases. For example, the first hydrogen flow rate is a first variable flow rate that gradually increases from 1 sccm to 10 sccm.

[0107] In some embodiments, the second hydrogen flow rate is a constant flow rate. For example, the second hydrogen flow rate is a constant flow rate in the range of 10 sccm to 100 sccm.

[0108] In some embodiments, the second hydrogen flow rate is a second variable flow rate that gradually increases. For example, the second hydrogen flow rate is a second variable flow rate that gradually increases from 10 sccm to 100 sccm.

[0109] In some embodiments, the first temperature is -90°C to -30°C. For example, the first temperature can be -90°C, -80°C, -70°C, -60°C, -50°C, -40°C, or -30°C, or any value between any two of the aforementioned temperature values. However, it is not limited to this.

[0110] In some embodiments, the deposition step is performed for a time of 0.1 s to 2 s. For example, the deposition step can be performed for a time of 0.1 s, 0.2 s, 0.3 s, 0.4 s, 0.5 s, 0.7 s, 0.9 s, 1 s, 1.2 s, 1.5 s, 1.8 s, or 2 s, or any value between any two of the foregoing. However, the present application is not limited thereto.

[0111] In some embodiments, the deposition step is performed for a time of 0.1 s to 2 s. For example, the deposition step can be performed for a time of 0.1 s, 0.2 s, 0.3 s, 0.4 s, 0.5 s, 0.7 s, 0.9 s, 1 s, 1.2 s, 1.5 s, 1.8 s, or 2 s, or any value between any two of the foregoing. However, the present application is not limited thereto.

[0112] In some embodiments, the deposition step is performed for a time of 0.1 s to 2 s. For example, the deposition step can be performed for a time of 0.1 s, 0.2 s, 0.3 s, 0.4 s, 0.5 s, 0.7 s, 0.9 s, 1 s, 1.2 s, 1.5 s, 1.8 s, or 2 s, or any value between any two of the foregoing. However, the present application is not limited thereto.

[0113] In some embodiments, the deposition step is performed for a time of 0.1 s to 2 s. For example, the deposition step can be performed for a time of 0.1 s, 0.2 s, 0.3 s, 0.4 s, 0.5 s, 0.7 s, 0.9 s, 1 s, 1.2 s, 1.5 s, 1.8 s, or 2 s, or any value between any two of the foregoing. However, the present application is not limited thereto.

[0114] In some embodiments, the deposition step is performed for a time of 0.1 s to 2 s. For example, the deposition step can be performed for a time of 0.1 s, 0.2 s, 0.3 s, 0.4 s, 0.5 s, 0.7 s, 0.9 s, 1 s, 1.2 s, 1.5 s, 1.8 s, or 2 s, or any value between any two of the foregoing. However, the present application is not limited thereto.

[0115] Step S14: performing an etching step, using a second gas including F2 and BF3, to etch the a-C:H:F cross-linked polymer layer and the silicon substrate at a second temperature of -30°C or lower.

[0116] Reference Figure 4 This step is used to continue performing the etching step after the deposition step, at an ultra-low temperature (second temperature) of less than -30°C, and to etch the a-C:H:F cross-linked polymer layer 14 and the silicon substrate 10 formed in the previous step by using small molecules of F2 and BF3 (second gas) as etching gas (not containing SF6), to form a first etching structure 15 on the silicon substrate 10 (after the etching step, there is still a remaining a-C:H:F cross-linked polymer layer 14 on the side of the photoresist pattern 12, Figure 4The second gas is ionized to form a plasma of the second gas for etching the a-C:H:F cross-linked polymer layer 14 and the silicon substrate 10. Further, the etching step includes a first etching step and a second etching step, the a-C:H:F cross-linked polymer layer 14 on the bottom of the opening 11 is removed by performing the first etching step and by the bombardment of the plasma of the second gas, and then the exposed silicon substrate 10 is further etched by performing the second etching step and by the plasma of the second gas to form the first etching structure 15.

[0117] When the silicon substrate 10 is etched, due to the presence of the carbon-based protective film 13, the top is prevented from being excessively laterally etched when the first etching structure 15 is etched, so that the size of the first etching structure 15 is uniform, thereby laying a foundation for ensuring that the size at different positions on the entire high aspect ratio etching structure is uniform.

[0118] When a mixed gas of fluorine gas (F2) with smaller molecules and BF3 is used as the etching gas instead of the traditional SF6 large molecule gas, the diffusion is more uniform, and it is more conducive to entering the nanoscale deep trench or hole for etching reaction, so that more excellent small-size high aspect ratio deep silicon etching can be achieved. In addition, although SF6 has 6 Fs, only one F ion can be dissociated for etching reaction, and the remaining SF5 does not participate in the reaction and is then pumped away. However, F2 dissociation can produce two F ions, and the number of reactants participating in the reaction is more than that of SF6, which can improve the etching rate, especially for etching deep silicon structures with high depth (more than 100 µm), which can significantly improve the throughput of the machine.

[0119] Therefore, by using the above-mentioned small-molecule etching gas and deposition gas, the diffusion coefficient is effectively increased, the reaction gas transmission efficiency is improved, the influence of the thickness fluctuation of the previous large-molecule C4F8 polymer on the control of the nanoscale line width, and the ion shadow effect problem are solved, the uniformity and roughness of the local C-F polymer are effectively improved, and thus more uniform, better sidewall smoothness, and higher aspect ratio nanoscale size deep silicon structure etching are achieved. At the same time, the mixed gas of F2 and BF3 is used as the etching gas, which can significantly improve the etching behavior at high depth (more than 100 µm).

[0120] By changing the etching gas from the traditional SF6 to the combination of the small-molecule mixed gas of F2 and BF3, the embodiments of the present application can better adapt to the needs of advanced processes, and significantly improve the performance in molecular transport, reaction efficiency, and morphology control through optimized reaction chemistry and plasma physics, which is a key technical path to realize ultra-high aspect ratio etching.

[0121] Using the combination of F2 and BF3 as the etching gas, the differences compared to using the traditional SF6 as the etching gas can include:

[0122] (1) Efficient generation of high-density F atoms: through a more efficient dissociation path, providing abundant primary etchant (F atoms).

[0123] (2) Excellent deep-hole transport capability: small molecule reactants and products have a longer mean free path, which can reach the bottom of the deep hole, ensuring the bottom etching rate.

[0124] (3) Precise control of ion energy and angle: the generated ions are lighter in mass and more concentrated in energy distribution, achieving extreme anisotropic etching and reducing damage to the photoresist pattern 12.

[0125] (4) Bending and other defects can be suppressed, and more vertical sidewalls can be obtained.

[0126] Wherein, when using the combination of F2 and BF3 as the etching gas, the main reaction groups are: F•, BF2 + , BF + . F2 has high reactivity and can provide abundant primary etchants, which not only reduces the dependence on physical bombardment, but also improves the etching rate. BF x + is a light ion that can efficiently transfer energy to the bottom, enhance the etching reaction, and at the same time, due to its light mass, has a low physical sputtering yield on the material, reducing physical damage to the bottom silicon and back sputtering of the top photoresist.

[0127] In some embodiments, when performing the etching step, a plasma formed by BF3 in the second gas introduced is also used to perform a second treatment on the a-C:H:F cross-linked polymer layer 14 to change the properties of the a-C:H:F cross-linked polymer layer 14 by incorporating B elements, and to enhance the lateral etching resistance of the a-C:H:F cross-linked polymer layer 14, thereby further improving the verticality of the sidewall and the uniformity of the size.

[0128] In some embodiments, the flow rate of F2 in the etching gas (second gas) is 100-400 sccm. For example, the flow rate of F2 can be 100 sccm, 120 sccm, 150 sccm, 200 sccm, 300 sccm, 350 sccm, or 400 sccm, or any value between any two of the foregoing. But it can not be limited to this.

[0129] In some embodiments, the flow rate of BF3 in the etching gas is 5 sccm to 50 sccm. For example, the flow rate of BF3 can be 5 sccm, 10 sccm, 15 sccm, 20 sccm, 30 sccm, 40 sccm, or 50 sccm, or any value between any two of the foregoing flow rates. However, the disclosure is not limited thereto.

[0130] In some embodiments, the flow rate ratio of F2 and BF3 in the etching gas is F2:BF3 = 8:1 to 20:1. For example, the flow rate ratio of F2 and BF3 can be 8:1, 9:1, 10:1, 12:1, 15:1, or 20:1. However, the disclosure is not limited thereto. Among them, BF3 is mainly used to introduce B element and light ions, but the proportion should not be too high, otherwise it will cause excessive carbon deposition.

[0131] In some embodiments, the second temperature is -90°C to -30°C. For example, the second temperature can be -100°C, -90°C, -80°C, -70°C, -60°C, -50°C, or -30°C, or any value between any two of the foregoing temperatures. However, the disclosure is not limited thereto.

[0132] In some embodiments, the total time for performing the etching step is 0.2s to 4s, and the time for performing the first etching step and the second etching step is 0.1s to 2s, respectively. For example, the time for performing the first etching step or the second etching step can be 0.1s, 0.2s, 0.3s, 0.4s, 0.5s, 0.7s, 0.9s, 1s, 1.2s, 1.5s, 1.8s, or 2s, or any value between any two of the foregoing times. However, the disclosure is not limited thereto.

[0133] In some embodiments, the pressure during the etching step is 5mTorr to 200mTorr. For example, the pressure can be 5mTorr, 10mTorr, 20mTorr, 50mTorr, 80mTorr, 100mTorr, 130mTorr, 150mTorr, 190mTorr, or 200mTorr, or any value between any two of the foregoing pressures. However, the disclosure is not limited thereto.

[0134] In some embodiments, the source power during the etching step is 500W to 3000W. For example, the source power can be 500W, 1000W, 1500W, 2000W, 2500W, or 3000W, or any value between any two of the foregoing source powers. However, the disclosure is not limited thereto.

[0135] In some embodiments, the bias power is 10W-200W when performing the etching step. For example, the bias power can be 10W, 20W, 50W, 70W, 100W, 130W, 160W, 180W or 200W, or any value between any two of the foregoing bias power values. However, the present application is not limited thereto.

[0136] In some embodiments, another implementation of the second gas is that the BF3 in the second gas is replaced by PF3. That is, the second gas includes F2 and PF3.

[0137] In some embodiments, another implementation of the second gas is that the BF3 in the second gas is replaced by PF3, and the second gas further includes N2. That is, the second gas includes F2, PF3 and N2. When performing the etching step, the plasma formed by the introduced N2 in the second gas is further used to perform a third treatment on the sidewall of the high aspect ratio etching structure being formed (at this step, the sidewall of the first etching structure 15), to form an extremely thin nitrided layer on the sidewall, which can assist in passivating the surface of the sidewall, thereby further improving the fidelity of the etching pattern, and thus a more vertical sidewall can be obtained.

[0138] In some embodiments, another implementation of the second gas is that the second gas further includes N2, that is, the second gas includes F2, BF3 and N2. When performing the etching step, the plasma formed by the introduced N2 in the second gas is further used to perform a third treatment on the sidewall of the high aspect ratio etching structure being formed (at this step, the sidewall of the first etching structure 15), to form an extremely thin nitrided layer on the sidewall, which can assist in passivating the surface of the sidewall, thereby further improving the fidelity of the etching pattern, and thus a more vertical sidewall can be obtained.

[0139] In some embodiments, NF3, CF4, C2F6, etc. can be further added to the second gas when performing the etching step, which can further play a synergistic role.

[0140] When NF3 is added to the etching gas, more F ions can be generated, thus providing a high-efficiency fluorine source; and the dissociated NF2 groups also help to passivate the sidewall and inhibit the drum-shaped defects.

[0141] When CF4 is added to the etching gas, a small amount of C can be introduced, which can cooperate with the deposition step to achieve more precise control of the sidewall morphology, thus playing a role in balancing deposition and etching. In addition, the C element can also form a light C-containing protective layer on the surface of the photoresist pattern 12.

[0142] When C2F6 is added to the etching gas, a higher C / F ratio can be provided, which can be used for etching conditions that require stronger passivation.

[0143] The small molecule radicals in the etching gas, the dominant mechanism in the etching step can include:

[0144] (1) Higher F atom density and deep hole penetration ability: The dissociation energy of small molecule gas is usually lower than SF6, under the same plasma conditions, it can produce higher concentration of F atoms. F atoms and small molecule ions are light in mass and long in mean free path, which can effectively diffuse to the bottom of the deep hole to maintain the etching rate at the bottom and avoid "etching stop".

[0145] (2) Better ion-assisted etching: The essence of etching is "ion-enhanced chemical etching". The removal of the bottom silicon requires: a) F atoms for chemical reaction; b) ion bombardment to provide energy to break Si-Si bonds and sputter by-products. Light ions (such as BF2 + ) can more effectively transfer energy to the bottom surface than SF x + heavy ions, enhancing the etching reaction; at the same time, due to their light mass, the physical sputtering yield of the material is low, reducing the physical damage to the bottom silicon and the back sputtering of the top photoresist pattern 12.

[0146] (3) Inhibit drum shape morphology: The cause of drum shape includes local failure of the sidewall protection layer, resulting in F atoms and ions etching silicon laterally from the side. The advantages of small molecule system are: a) Higher F atom density means faster switching to deposition step, avoiding lateral etching caused by long etching step time; b) can assist sidewall passivation; c) more concentrated vertical ion beam reduces lateral scattering ions. The above three work together to ensure that etching is basically in the vertical direction.

[0147] (4) Reduce photoresist pattern 12 consumption caused by physical bombardment: The ions produced by the small molecule system are lighter in mass, and their momentum is lower than that of the heavy ions produced by SF6 under the same bias. Therefore, the physical sputtering rate of the photoresist pattern 12 is significantly reduced, reducing the consumption of the photoresist pattern 12 and improving the pattern fidelity.

[0148] (5) Reduce photoresist pattern 12 consumption caused by chemical erosion: Although F atoms will erode the photoresist pattern 12, the small molecule system reduces the overall process time through higher etching efficiency, indirectly reducing the cumulative exposure time of the photoresist pattern 12.

[0149] Step S15: Repeat steps S13 to S14 until a high aspect ratio etching structure is formed on the silicon substrate.

[0150] Reference Figure 5In some embodiments, the above step S13 is repeatedly performed, and the a-C:H:F cross-linked polymer layer 14 is again deposited on the exposed surface of the silicon substrate 10 (i.e. the inner wall of the first etching structure 15 formed in the last step) and the exposed surface of the photoresist pattern 12, so as to protect the sidewall of the first etching structure 15 and the photoresist pattern 12 when the etching step is performed again in the next time.

[0151] Then, the above step S14 is repeatedly performed to etch the a-C:H:F cross-linked polymer layer 14 and the silicon substrate 10, and a second etching structure 16 is successively formed below the first etching structure 15, as shown in FIG. 2B. Figure 6 Figure 6 In the figure, the original bottom of the first etching structure 15 is indicated by a horizontal dashed line. After this etching step, the a-C:H:F cross-linked polymer layer 14 remains on the sidewall of the photoresist pattern 12 and the sidewall of the first etching structure 15, Figure 6 which is omitted in the figure.

[0152] By repeating the above steps S13 and S14, a third etching structure, a fourth etching structure, etc. (not shown) can be successively formed below the second etching structure 16, and finally a high aspect ratio etching structure 17 with a target aspect ratio is formed on the silicon substrate 10, which is composed of the successively formed etching structures (the first etching structure 15, the second etching structure 16, the third etching structure, the fourth etching structure, etc.), as shown in FIG. 2C. Figure 7

[0153] In some embodiments, when the process of steps S13 and S14 is performed once, a scallop-shaped stripe is regularly formed on the sidewall, the bottom of each scallop-shaped stripe has a concave part, and the junction of two scallop-shaped stripes has a convex part, so that the sidewall has a rough surface topography. Therefore, in the embodiments of the present application, after each cycle of steps S13 and S14 is performed once, or after each cycle of steps S13 and S14 is performed twice, a step of fifth processing of the sidewall is embedded at the fourth temperature, which timely removes the excess a-C:H:F cross-linked polymer layer 14 on the sidewall, prevents uneven etching caused by excessive polymer thickness, and through the fifth processing, at least part of the convex part is removed, the roughness of the sidewall is reduced, and the smoothness of the sidewall is improved.

[0154] ​​In some embodiments, the fifth treatment specifically comprises: using a plasma of HBr and O2 to react with the a-C:H:F cross-linked polymer layer 14, to remove a portion of the thickness of the a-C:H:F cross-linked polymer layer 14 deposited on the sidewall, to adjust the thickness uniformity of the a-C:H:F cross-linked polymer layer 14 on the sidewall, and to react with the silicon material present and exposed on the surface of the protrusion on the sidewall to generate a silicon tetrabromide layer and a silicon dioxide layer; subsequently, stopping the input of HBr and O2, and using a plasma of CF4 and Ar to bombard the sidewall, to etch and remove the silicon dioxide on the protrusion, and to desorb the silicon tetrabromide to be removed from the sidewall, so as to remove at least part of the protrusion and form a relatively smooth new sidewall, so as to smooth the sidewall, so as to reduce the roughness of the surface of the sidewall, and to effectively avoid the local rough peaks (Ra>5nm) caused by the random deposition of the polymer on the sidewall in the prior art.

[0155] In some embodiments, the fourth temperature is -90°C to -30°C. For example, the fourth temperature can be -100°C, -90°C, -80°C, -70°C, -60°C, -50°C, or -30°C, or any value between any two of the foregoing temperature values. However, the application is not limited thereto.

[0156] In some embodiments, when the fifth treatment is performed, the time is 1s to 4s. For example, the time can be 1s, 1.2s, 1.4s, 1.6s, 1.8s, 2s, 2.4s, 3s, 3.6s, or 4s, or any value between any two of the foregoing time values. However, the application is not limited thereto.

[0157] In some embodiments, when the fifth treatment is performed, the time of inputting HBr and O2 is the same as or different from the time of inputting CF4 and Ar.

[0158] In some embodiments, when the fifth treatment is performed, HBr is also used to perform a sixth treatment on the exposed surface of the photoresist pattern 12, so that the chemical bonds in the photoresist pattern 12 material on the surface are broken and recombined to form a high-molecular polymer chain, so as to improve the etching resistance of the photoresist pattern 12 by changing the C / H ratio on the surface of the photoresist pattern 12 material, and to improve the etching blocking ability of the photoresist pattern 12 above during deep silicon etching, i.e., to improve the etching selectivity of the photoresist pattern 12. The sixth treatment is completed synchronously during the performance of the fifth treatment.

[0159] In some embodiments, when the fifth processing is performed, O2 is also used to perform a seventh processing on the exposed surface of the photoresist pattern 12, so that the exposed surface of the photoresist pattern 12 is oxidized at the fourth temperature of the ultra-low temperature and is triggered to react by the deep ultraviolet light in the environment to form a hardened layer. Therefore, the etching resistance of the photoresist pattern 12 above is improved, that is, the etching selectivity of the photoresist pattern 12 is improved. The seventh processing is completed synchronously in the process of performing the fifth processing.

[0160] Step S16: removing the photoresist pattern.

[0161] In some embodiments, after the high aspect ratio etching structure 17 is formed, the surface of the silicon substrate 10 is bombarded using plasma of a third gas to remove the photoresist pattern 12 and the carbon-based protective film 13 on the surface of the silicon substrate 10. After the photoresist pattern 12 and the carbon-based protective film 13 are removed, the silicon substrate 10 with the surface exposed and the high aspect ratio etching structure 17 formed is obtained, as shown in FIG. 6. Figure 8

[0162] In some embodiments, the third gas includes an oxidizing gas. The oxidizing gas can be, for example, oxygen, and nitrogen can be introduced as a dilution gas at the same time.

[0163] ​In some other embodiments, another implementation of the high aspect ratio etching structure is that the process of forming the high aspect ratio etching structure on the silicon substrate by repeatedly performing the deposition step and the etching step is divided into a first etching stage, a second etching stage and a third etching stage which are sequentially connected and are respectively used for forming the top part, the middle part and the bottom part of the high aspect ratio etching structure in sequence. The first etching stage can use F2 and N2 as the etching gas, the second etching stage can use F2 and PF3 (or F2 and BF3) as the etching gas, and the third etching stage can use F2 and C2F6 (or F2 and CF4) as the etching gas. When the first etching stage is performed, the stable plasma formed by adding N2 can reduce the severe etching behavior of the top region caused by the unstable sheath layer in the initial etching stage and the mask edge effect, effectively ensure the stability of the top critical dimension, reduce the ion sputtering damage in the etching process, improve the protection of the photoresist pattern, and also form an extremely thin nitrided layer on the sidewall to assist in passivation of the sidewall surface, prevent excessive lateral etching, and improve the verticality of the sidewall top. By using the combination of F2 and PF3 (or F2 and BF3) as the etching gas in the second etching stage, the properties of the a-C:H:F cross-linked polymer layer can be changed by the incorporation of P (or B) elements, thereby enhancing the lateral etching resistance of the a-C:H:F cross-linked polymer layer, and further improving the verticality of the sidewall and the uniformity of the size. By using the combination of F2 and C2F6 (or F2 and CF4) as the etching gas in the third etching stage, a higher fluorocarbon ratio can be provided to enhance the deposition, effectively suppress the lateral etching of the sidewall bottom, and thus eliminate the problem of bottom side etching.

[0164] According to a second aspect of the present application, the embodiments of the present application also provide a high aspect ratio etching structure obtained by using the ultra-low temperature deep silicon etching method provided by any one of the embodiments of the first aspect.

[0165] Reference Figure 8 In some embodiments, the high aspect ratio etching structure 17 is formed on the surface of the silicon substrate 10. The critical dimension of the high aspect ratio etching structure 17 can be less than 50 nm, and the aspect ratio can be greater than or equal to 100:1. The high aspect ratio etching structure 17 can be, for example, a deep trench, a deep hole or a via, etc.

[0166] In some embodiments, the high aspect ratio etched structure 17 can be applied to MEMS devices (such as accelerometers, gyroscopes, pressure sensors, etc.), 3D integration and advanced packaging (such as through-silicon via (TSV) fabrication, chip stacking, etc.), optical devices (such as optical waveguides, diffraction gratings, etc.), and power devices (such as trench structures of insulated gate bipolar transistors (IGBTs) and power metal-oxide-semiconductor field-effect transistors (MOSFETs, etc.).

[0167] In a third aspect, embodiments of this application also provide a plasma processing apparatus for performing the ultra-low temperature deep silicon etching method corresponding to the above embodiments to form the high aspect ratio etched structure 17 corresponding to the above embodiments. The plasma processing apparatus includes inductively coupled plasma (ICP) etching equipment or capacitively coupled plasma (CCP) etching equipment, etc.

[0168] In other aspects, embodiments of this application also provide an electronic device, including a high aspect ratio etched structure 17 (e.g., deep trench, deep hole, or through hole, etc.) obtained using the ultra-low temperature deep silicon etching method of the above embodiments. The electronic device can be a storage device, mobile phone, computer, tablet computer, electronic instrument, television, artificial intelligence device, etc.

[0169] In summary, the embodiments of this application use small-molecule first gases (CH4, CHF3, and H2) and second gases (F2 and BF3) instead of traditional large-molecule gases such as C4F8 and SF6 as deposition and etching gases, respectively. This increases the diffusion coefficient, improves gas transport efficiency, and enables more uniform diffusion of the etching gas. This facilitates the etching reaction within nanoscale high aspect ratio etched structures (deep trenches, deep holes, or through holes), achieving superior small-size high aspect ratio deep silicon etching. Furthermore, it allows the deposition gas to smoothly enter the bottom of the high aspect ratio etched structure, achieving more uniform protection of the sidewalls within a smaller size. Furthermore, by keeping the temperatures (first temperature and second temperature) during the deposition and etching steps below -30°C, ultra-low temperatures can be used to alter chemical kinetics, enhance physical adsorption, and reduce the reaction rate. This allows the formed aC:H:F crosslinked polymer layer 14 to be more densely and uniformly adsorbed on the sidewalls, effectively protecting the sidewalls even at the bottom of high aspect ratio etched structures and effectively suppressing lateral etching, resulting in extremely vertical sidewall morphologies. This enables the etching of nanoscale deep silicon structures with even higher aspect ratios. Simultaneously, small-molecule etching gases can significantly improve the etching rate and etching behavior at high depths (>100µm).

[0170] The above are merely preferred embodiments of this application. These embodiments are not intended to limit the scope of protection of this application. Therefore, any equivalent changes made based on the description and drawings of this application should also be included within the scope of protection of this application.

Claims

1. A method for ultra-low temperature deep silicon etching, characterized in that, include: Provide silicon substrates; Multiple photoresist patterns are formed on the surface of the silicon substrate; The etching process includes, in sequence: (i) Performing the deposition step, which includes: At a first temperature below -30°C, a C:H:F crosslinked polymer layer is deposited on the silicon substrate and the photoresist pattern using a first gas comprising CH4, CHF3 and H2 to protect the silicon substrate and the photoresist pattern during etching. (ii) Perform the etching step, which includes: At a second temperature below -30°C, a second gas comprising F2 and BF3 is used to etch the aC:H:F crosslinked polymer layer and the silicon substrate; (iii) Repeat steps (i) and (ii) sequentially until a high aspect ratio etched structure is formed on the silicon substrate; Remove the photoresist pattern.

2. The ultra-low temperature deep silicon etching method according to claim 1, characterized in that, The deposition step specifically includes: At the first temperature, CH4, CHF3, and H2 at a first hydrogen flow rate from the first gas are first introduced to deposit a transitional aC:H:F crosslinked polymer layer with a first hydrogen content on the silicon substrate and the photoresist pattern. Then, the introduction of CH4 and CHF3 is stopped, and H2 at a second hydrogen flow rate is continued to be introduced to perform a first treatment on the transitional aC:H:F crosslinked polymer layer to terminate dangling bonds and increase the degree of crosslinking, forming a highly crosslinked three-dimensional network structure aC:H:F crosslinked polymer layer with a second hydrogen content greater than the first hydrogen content and the second hydrogen flow rate greater than the first hydrogen flow rate.

3. The ultra-low temperature deep silicon etching method according to claim 2, characterized in that, The flow rate of CH4 is 3 sccm to 20 sccm, and / or the flow rate of CHF3 is 10 sccm to 50 sccm, and / or the flow rate of the first hydrogen is 1 sccm to 10 sccm, and / or the flow rate of the second hydrogen is 10 sccm to 100 sccm.

4. The ultra-low temperature deep silicon etching method according to claim 2, characterized in that, The first hydrogen flow rate is a first variable flow rate with a gradually increasing flow rate, and the second hydrogen flow rate is a constant flow rate or a second variable flow rate with a gradually increasing flow rate.

5. The ultra-low temperature deep silicon etching method according to claim 4, characterized in that, The first hydrogen flow rate is a first variable flow rate that gradually increases from 1 sccm to 10 sccm, and the second hydrogen flow rate is a constant flow rate with a flow rate range of 10 sccm to 100 sccm, or a second variable flow rate that gradually increases from 10 sccm to 100 sccm.

6. The ultra-low temperature deep silicon etching method according to claim 1, characterized in that, During the etching step, plasma formed by the BF3 in the introduced second gas is also used to perform a second treatment on the aC:H:F crosslinked polymer layer to change the properties of the aC:H:F crosslinked polymer layer and enhance its resistance to lateral etching.

7. The ultra-low temperature deep silicon etching method according to claim 1, characterized in that, The flow rate of F2 is 100 sccm to 400 sccm, and the flow rate of BF3 is 5 sccm to 50 sccm; or, the flow rate ratio of F2 to BF3 is F2:BF3 = 8:1 to 20:

1.

8. The ultra-low temperature deep silicon etching method according to claim 1, characterized in that, Another implementation of the second gas is to replace the BF3 in the second gas with PF3, and / or the second gas also includes N2. When performing the etching step, plasma formed by the N2 in the introduced second gas is also used to perform a third treatment on the sidewalls of the high aspect ratio etched structure being formed, and to form a nitride layer on the sidewalls to assist in passivation of the surface of the sidewalls.

9. The ultra-low temperature deep silicon etching method according to claim 1, characterized in that, The first temperature is -90℃ to -30℃; and / or, the second temperature is -90℃ to -30℃.

10. The ultra-low temperature deep silicon etching method according to claim 1, characterized in that, The deposition step takes 0.1s to 2s; and / or the etching step takes 0.2s to 4s.

11. A high aspect ratio etched structure, characterized in that, Obtained using the ultra-low temperature deep silicon etching method as described in any one of claims 1-10.

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