A method of forming a cavity structure

Abstract

The application discloses a cavity structure forming method. The forming method comprises the following steps: firstly, etching a first groove with a preset depth in a silicon substrate according to an opening pattern of a mask layer; then, performing a first lateral etching step on the first groove to form a second groove with a width size gradually increasing or gradually decreasing from an upper end to a lower end; and continuing to perform a second lateral etching step to control the sidewall of the second groove to form a cavity structure with a vertical or quasi-vertical sidewall. The application adopts a twice lateral etching mode to control the angle and morphology of the sidewall of the first groove in stages, and the control is more free and accurate. In combination with the screening of the twice lateral etching gas types, the problem that the traditional forming method has the uneven sidewall morphology and is prone to unnecessarily expanding the width size of the small cavity structure is solved.

Description

Technical Field

[0001] This invention relates to etching methods for semiconductor devices, and more specifically to a method for forming a cavity structure. Background Technology

[0002] In the manufacturing processes of semiconductor devices such as image sensors (CIS) and microelectromechanical systems (MEMS), etching is often used to form the required cavity structures. As semiconductor devices develop towards smaller sizes and higher integration, etching cavity structures with high aspect ratios or high depths, flat sidewall topography, and vertical or near-vertical sidewalls on substrates has become one of the decisive requirements for semiconductor devices.

[0003] However, in actual etching processes, it has been found that various parameters and factors during the process, such as the type of etching gas, etching temperature, and etching power, often result in various strange etching morphologies, such as curved sidewalls (partially or entirely) or uneven surfaces. This is especially true for small horizontal width dimensions (less than 1 μm) of cavity structures, which are difficult to control and can easily lead to unnecessary enlargement of the cavity structure's width, resulting in reduced precision and performance of semiconductor devices. At the same time, existing etching processes lack the degree of freedom to adjust the sidewall angles of cavity structures, making it difficult to meet the process target requirements for different sidewall angles of cavity structures. Summary of the Invention

[0004] The purpose of this invention is to provide a method for forming a cavity structure, which solves the problem that traditional etching methods lack the degree of freedom to control the sidewall angle and morphology of the cavity structure.

[0005] To achieve the above objectives, the present invention provides a method for forming a cavity structure, comprising the following steps:

[0006] A silicon substrate is provided, the surface of which has a mask layer having a plurality of opening patterns, the bottom of which exposes the top surface of the silicon substrate;

[0007] The silicon substrate is vertically etched downwards to a predetermined depth according to the opening pattern to form a first trench;

[0008] A first lateral etching gas is introduced to perform a first lateral etching step on the first trench to form a second trench. The etching rate of the first lateral etching gas on the upper end of the first trench is different from the etching rate on the lower end.

[0009] A second lateral etching gas is introduced to perform a second lateral etching step on the second trench, thereby controlling the sidewalls of the second trench to form a cavity structure with vertical or near-vertical sidewalls.

[0010] Optionally, the etching rate of the first lateral etching gas on the upper end of the first trench is less than the etching rate on the lower end.

[0011] Optionally, the first lateral etching gas includes SF6 and an oxygen-containing gas.

[0012] Optionally, the gas volume ratio of the oxygen-containing gas to SF6 is 0.5:1 to 1.5:1.

[0013] Optionally, the oxygen-containing gas includes any one of O2, SO2, or CO2.

[0014] Optionally, the second lateral etching gas includes SF6 and N2.

[0015] Optionally, the gas volume ratio of N2 to SF6 is 1:1 to 4:1.

[0016] Optionally, the minimum width dimension of the cavity structure is more than 95% of the maximum width dimension on the same cross section.

[0017] Optionally, the cavity structure includes: performing the second lateral etching step on the second trench to adjust the sidewall of the second trench to form a silicon via; and / or performing the second lateral etching step on the second trench to connect multiple second trenches to form a cavity with or without a tip at the upper end.

[0018] Optionally, the cavity structure includes silicon vias with an aspect ratio greater than 12:1.

[0019] Optionally, the cavity structure includes silicon apertures, wherein the width of the silicon apertures is 0.1 μm to 1 μm and the depth is 1.2 μm to 12 μm.

[0020] Optionally, the cavity structure is the silicon via and / or the cavity without a tip at the upper end, and the method for forming the first trench includes:

[0021] A first vertical etching gas is introduced, and the silicon substrate is etched downwards to a predetermined depth according to the opening pattern to form the first trench.

[0022] Optionally, the cavity structure includes a cavity with a pointed tip at the upper end, and the method for forming the first groove includes:

[0023] A second vertical etching gas is introduced, and the silicon substrate is etched downward according to the opening pattern to form multiple shallow trenches;

[0024] A protective layer is formed on the sidewall of the shallow trench;

[0025] A first vertical etching gas is introduced, and the vertical etching process continues downward along the shallow trench to a preset depth to form the first trench.

[0026] Optionally, the first vertical etching gas includes a combination of SF6, O2, and HBr.

[0027] Optionally, the second vertical etching gas includes a combination of SF6, N2, and HBr.

[0028] Optionally, the protective layer may be made of at least one of silicon nitride, silicon oxide, chromium, titanium nitride, and titanium oxide.

[0029] Optionally, the material of the mask layer includes at least one of silicon oxide and silicon nitride.

[0030] Compared with the prior art, the beneficial effects of the technical solution of the present invention include at least the following:

[0031] The method for forming a cavity structure provided by this invention first forms a first trench of a predetermined depth through vertical etching, and then uses two transverse etching modes to control the angle and morphology of the sidewalls of the first trench in stages. This control offers greater freedom and precision, solving the problem of traditional methods lacking freedom in controlling the sidewall angle and morphology of cavity structures. Ultimately, it can form a cavity structure with vertical or near-vertical sidewalls, a flat sidewall morphology, and a width that remains essentially consistent from top to bottom. Specifically:

[0032] First, a first lateral etching gas (SF6 and oxygen-containing gas) is used to perform first lateral etching on the first trench. The etching rate of the first lateral etching gas on the upper end of the first trench is less than the etching rate on the lower end, forming a second trench whose width gradually increases from the upper end to the lower end.

[0033] The second transverse etching gas (SF6 and N2) is used to perform the second transverse etching on the second trench. The etching rate of the second transverse etching gas on the upper end of the second trench is greater than that on the lower end. By adjusting the duration of the second transverse etching, the inner wall angle of the formed cavity structure can be freely adjusted to meet the process target requirements of different side wall angles of the cavity structure.

[0034] More importantly, when the second lateral etching gas (SF6 and N2) is used to control the sidewall angle of the cavity structure, the present invention will not cause excessive lateral etching in the local area at the upper end of the cavity structure, thus solving the problems of uneven sidewall morphology and unnecessary enlargement of cavity structure size in traditional formation methods. Attached Figure Description

[0035] Figure 1 This is a flowchart of a method for forming a cavity structure according to the present invention.

[0036] Figure 2 This is a cross-sectional schematic diagram of each step in the cavity structure formation method of the present invention.

[0037] Figure 3 This is a top view schematic diagram of a mask layer according to an embodiment of the present invention.

[0038] Figure 4 This is a flowchart of another method for forming a cavity structure according to the present invention.

[0039] Figure 5 This is a cross-sectional schematic diagram of each step in another method for forming a cavity structure according to the present invention.

[0040] Figure 6 The images shown are scanning electron microscope (SEM) images of the cavity structures in Example 1 and Comparative Examples 1-2. In the images, the circled area represents the tip 3, (a') is a magnified view of the area under the dashed line in (a), (b') is a magnified view of the area under the dashed line in (b), and (c') is a magnified view of the area under the dashed line in (c).

[0041] Attached Figure Labels

[0042] Silicon substrate 1, shallow trench 110, first trench 11, second trench 12, cavity structure 13, mask layer 2, opening patterns 21, 21', 21”; tip 3, protective layer 4. Detailed Implementation

[0043] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0045] Terminology Explanation

[0046] In this invention, a cavity structure with vertical or near-vertical sidewalls refers to a cavity structure where the angle between the sidewall and the bottom ranges from 88 degrees to 93 degrees.

[0047] As described in the background section, when etching cavity structures on a substrate using traditional processes, the sidewall morphology is prone to bending (local or overall) or unevenness due to various parameters and factors during the process. This leads to an unnecessary increase in the small width of the cavity structure, resulting in reduced precision and performance of the semiconductor device. Furthermore, the lack of control over the sidewall angle of the cavity structure makes it difficult to meet the process target requirements for different sidewall angles, and it is difficult to achieve the goal of etching cavity structures with high aspect ratio or high depth, flat sidewall morphology, and vertical or near-vertical sidewalls on the substrate.

[0048] To address the aforementioned issues, in the initial stages of research, this invention selected a single SF6 etching gas for etching the cavity structure and observed the etching morphology. The results showed that when using a single SF6 gas to form the cavity structure, the width of the upper part of the cavity structure was significantly larger than that of the lower part, indicating an unnecessary expansion of the upper width. This may be related to the fact that the F free radicals released after the SF6 etching gas is ionized to form plasma tend to concentrate at the upper part of the cavity structure. Furthermore, further experiments revealed that although adjusting the etching time and gas flow rate of the single SF6 gas could improve the sidewall morphology of the cavity structure to some extent, it could not eliminate the excessive lateral etching in the upper local area. That is, it unnecessarily expanded the width of the upper local area of ​​the cavity structure, resulting in a curved and uneven sidewall morphology that did not meet the requirements of the target process.

[0049] Furthermore, this invention adds O2 to SF6 to form a combined gas for etching the cavity structure and observes the etching morphology. The results show that when using the combined SF6 and O2 gas, the added O2 can rapidly oxidize the silicon exposed at the upper end of the cavity structure due to etching, generating a silicon dioxide passivation layer, slowing down the etching rate at the upper end. Meanwhile, the F radicals diffusing to the lower end react with the silicon at the lower end, resulting in a significantly larger width at the lower end of the cavity structure than at the upper end, which still does not meet the target process requirements.

[0050] As the above research shows, the etching rate of the upper part of the cavity structure by a single SF6 gas is greater than that of the lower part, while the etching rate of the lower part of the cavity structure by a combination of SF6 and O2 gas is greater than that of the upper part. Therefore, this invention attempts to combine the characteristics of the two gas groups and adopt a two-stage lateral etching mode: first, a first lateral etching is performed using a combination of SF6 and O2 gas, adjusting the etching rate of the lower part of the cavity structure to be greater than that of the upper part; then, a second lateral etching is performed using SF6 gas, adjusting the etching rate of the upper part of the cavity structure to be greater than that of the lower part. This allows for the control of the sidewall angle and morphology of the cavity structure, aiming to obtain a cavity structure with a vertical or near-vertical sidewall angle, a smooth sidewall morphology, and a width that meets the target process requirements. However, the results show that excessive lateral etching still exists in some areas at the upper part of the cavity structure, resulting in a curved and uneven sidewall morphology.

[0051] Further research led to the first discovery in this invention that when the second lateral etching uses a combination of SF6 and N2 gases, it is possible to control the etching rate at the upper end of the cavity structure to be greater than that at the lower end without causing a bending morphology at the upper end. This achieves precise control over the etching morphology, resulting in a cavity structure with a vertical overall morphology, flat sidewalls, and a width that meets the target process requirements.

[0052] Based on the above, the present invention first provides a method for forming a cavity structure, such as... Figures 1 to 3 As shown, it includes the following steps:

[0053] Step 101: Provide a silicon substrate 1, the surface of which has a mask layer 2, the mask layer 2 having a plurality of opening patterns 21, the bottom of which exposes the top surface of the silicon substrate 1, for reference. Figure 2 The structure shown in (a) is shown in the middle.

[0054] In some embodiments, the material of the mask layer 2 may include at least one of silicon oxide and silicon nitride. That is, the mask layer 2 may be composed of either a silicon oxide layer or a silicon nitride layer; it may also be composed of both silicon oxide and silicon nitride layers, for example, a mask layer formed by stacking the silicon oxide and silicon nitride layers, with the different layers having the same or different thicknesses.

[0055] The opening pattern 21 is used to define the position and width of the subsequently formed first groove 11. The shape of the opening pattern 21 includes, but is not limited to, circles, ellipses, squares, triangles, etc. In this embodiment, see [link to relevant documentation]. Figure 3 The top view of the mask layer 2 shown shows that the shape of the opening pattern 21' is square and the shape of the opening pattern 21” is rectangular.

[0056] Furthermore, the width dimensions of the plurality of opening patterns 21 may be the same or different, and the spacing between adjacent opening patterns 21 may be the same or different, depending on the desired width dimension and morphology of the cavity structure. It can be understood that if the lateral spacing between adjacent opening patterns 21 is small, such as... Figure 3 The lateral spacing between the two opening patterns 21” allows the silicon covering the area between them to be easily etched away completely in subsequent processes, forming a cavity without a pointed top. See the corresponding Y-section structure diagram. Figure 2 As shown in (e); conversely, if the lateral spacing between adjacent open figures 21 is large, such as Figure 3 The lateral spacing between the two opening patterns 21' means that the silicon covering the area between them is not easily completely etched away in subsequent processes, forming two silicon vias underneath. See the corresponding X-section structure diagram. Figure 2 As shown in (d).

[0057] In addition, it should be noted that the width of the cavity structure finally formed by the present invention is greater than the width of the opening pattern 21 at the corresponding position, generally by at least twice.

[0058] Step 102: Vertically etch the silicon substrate 1 downwards to a predetermined depth according to the opening pattern 21 to form a first trench 11, referencing... Figure 2 The structure shown in (b) is shown in the middle.

[0059] In some embodiments, the first trench 11 is formed by using a first vertical etching gas and an anisotropic dry etching process. By applying a bias radio frequency to accelerate the downward directionality of charged particles, the etching rate in the vertical direction is much greater than the etching rate in the horizontal direction. Therefore, the verticality of the sidewalls and bottom of the first trench 11 formed by etching is better, which is beneficial to improving the fidelity of the pattern. In other embodiments, other suitable etching methods can also be used to form the first trench 11, such as wet etching.

[0060] As an example, the first vertical etching gas includes a combination of SF6, O2, and HBr, wherein SF6 is the main etching gas, which generates F radicals that react with Si; O2 and HBr act as passivating gases in practice, forming a passivation layer of Si. x O y Br z0 < x, y, z ≤ 1, the passivation layer is an anti-corrosion film formed on the sidewall, which can block the etching of the sidewall of the first trench 11 during the vertical etching process to form the first trench 11, enhance the directionality of etching, achieve good control of the key dimensions of the pattern, and further ensure the good verticality of the sidewall of the first trench 11 to the bottom; further, in other embodiments, the first vertical etching gas also includes some auxiliary etching gas, such as CF4, which can help break down the SiO2 formed on the silicon surface, so that Si can react with F free radicals to generate SiF4, thereby producing an etching effect.

[0061] In practical applications, the preset depth depends on the desired depth of the cavity structure 13. If a deeper cavity structure 13 is required, the etching time for forming the first trench 11 in this step will be longer; otherwise, the etching time will be shorter.

[0062] Step 103: Introduce a first lateral etching gas to perform a first lateral etching step on the first trench 11 to form a second trench 12. The etching rate of the first lateral etching gas on the upper end of the first trench 11 is different from the etching rate on the lower end.

[0063] In this embodiment, the etching rate of the first lateral etching gas on the lower end of the first trench 11 is greater than that on the upper end, causing the width of the formed second trench 12 to gradually increase from the upper end to the lower end. (Refer to...) Figure 2 The structure shown in (c) is as follows.

[0064] As an example, the first lateral etching gas includes SF6 and an oxygen-containing gas, wherein the oxygen-containing gas includes any one of O2, SO2 or CO2.

[0065] Furthermore, the gas volume ratio of oxygen-containing gas to SF6 is 0.5:1 to 1.5:1. When the oxygen-containing gas concentration is too low, it will not cause significant etching passivation to the upper end of the first trench 11, and excessive lateral etching will still exist at the upper end. As the oxygen-containing gas concentration increases, it will passivate the etching at the upper end of the first trench 11, making the etching rate at the lower end of the first trench 11 greater than that at the upper end. However, when the oxygen-containing gas concentration is too high, the etching rate at the lower end will gradually decrease, resulting in a slow first lateral etching rate, which will lead to process failure.

[0066] In some embodiments, if a passivation layer is present on the sidewall of the first trench 11 after the aforementioned step 102 is completed, this step further includes: firstly removing the passivation layer by plasma etching, and then introducing the first lateral etching gas to perform a first lateral etching step.

[0067] Step 104: Introduce a second lateral etching gas to perform a second lateral etching step on the second trench 12, adjusting the sidewalls of the second trench 12 to form a cavity structure 13 with vertical or near-vertical sidewalls. The cavity structure 13 includes: adjusting the sidewalls of the second trench 12 to form silicon vias. (Refer to...) Figure 2 The structure shown in (d) is: and / or, connecting multiple second grooves 12 to form a cavity without a pointed upper end, as shown in the reference diagram. Figure 2 The structure shown in (e) is shown in the middle.

[0068] In this embodiment, the second lateral etching gas includes SF6 and N2. This invention has found that adding N2 to SF6 has a significant passivation effect on the etching of the bottom of the second trench 12, resulting in a significantly higher etching rate at the upper end than at the lower end, without causing excessive lateral etching at the upper end of the second trench 12.

[0069] In some embodiments, the gas volume ratio of N2 to SF6 is 1:2 to 20:1; in other embodiments, the gas volume ratio of N2 to SF6 is 1:1 to 4:1. When the N2 concentration is too low, it will not cause significant etching passivation at the lower end of the second trench 12, and the sidewall of the second trench 12 cannot be controlled; however, when the N2 concentration is too high, it will cause over-passivation, resulting in no significant difference between the etching rate at the upper end and the etching rate at the lower end, and the etching rate will be too slow, leading to process failure.

[0070] In some embodiments, the overall shape of the cavity structure 13 is vertical, and its width remains consistent from top to bottom, such as... Figure 2 As shown in (d) and (e); in other embodiments, by increasing or decreasing the time of the second lateral etching step, the width of the upper end of the cavity structure 13 is made slightly larger than or slightly smaller than the lower end. For example, the minimum width of the cavity structure 13 is more than 95% of the maximum width on the same cross-section. In practical applications, the etching time can be adjusted according to application requirements to flexibly adjust the morphology of the cavity structure sidewalls to obtain a cavity structure that meets the target process requirements. For example, in some embodiments, it is required that the upper dimension of the cavity structure 13 be slightly larger than the lower dimension, or that the upper dimension of the cavity structure 13 be slightly smaller than the lower dimension. These can be achieved by adjusting the first and second lateral etching steps. Therefore, the flexibility in adjusting the cavity structure sidewalls is high.

[0071] In some embodiments, the aspect ratio of the silicon via is greater than 12:1, the width of the silicon via is 0.1μm to 1μm, and the depth is 1.2μm to 12μm. Further, the width of the silicon via is 0.2μm and the depth is 3μm.

[0072] As seen above, adding O2 or N2 to SF6 has significantly different effects on the etching morphology. The addition of O2 has a significant passivating effect on the upper end of the first trench 11, resulting in a higher etching rate at the lower end than at the upper end. Similarly, the addition of N2 has a significant passivating effect on the lower end of the second trench 12, resulting in a significantly higher etching rate at the upper end than at the lower end. Possible reasons for this include: the electronegativity of the plasma formed by O2 ionization is stronger than that of the plasma formed by N2 ionization, leading to oxygen free radicals being more easily distributed at the upper end of the structure to be etched, while nitrogen free radicals are more easily distributed at the lower end. It should be noted that electronegativity refers to the ability of a substance (atoms, molecules, ions, etc.) to attract electrons. In plasma, the concept of electronegativity can be extended to describe the density ratio of negative ions to positive ions in the plasma. The electronegativity of plasma is related to the chemical properties of its constituent gases, particularly the electron affinity of the gas molecules: the higher the electron affinity, the stronger the electronegativity of the gas. Both N2 and O2 are diatomic molecules. The orbital structure of oxygen allows for the capture of electrons at lower energies, making it easier to form negative ions in plasma, which gives oxygen-containing plasma a higher electronegativity. In contrast, the formation of negative ions in N2 requires more energy, resulting in relatively weaker electronegativity in nitrogen-containing plasma.

[0073] It is understood that in other embodiments, the order in which the first lateral etching gas (SF6 and oxygen-containing gas) and the second lateral etching gas (SF6 and N2) are introduced can be interchanged. Specifically, SF6 and N2 are introduced first to perform the first lateral etching step, forming a second trench whose width gradually decreases from the top to the bottom; then SF6 and oxygen-containing gas (such as O2) are introduced to perform the second lateral etching step, which is used to adjust the sidewalls of the second trench to form a cavity structure with vertical or near-vertical sidewalls.

[0074] An embodiment of the present invention also provides a method for forming a cavity structure, such as Figure 4 and Figure 5 As shown. Compared to the aforementioned method for forming a cavity structure, the cavity structure finally formed in this embodiment includes: silicon vias; and / or, connecting multiple second trenches 12 to form a cavity with a tip 3 at the upper end.

[0075] The development of semiconductor technology and the market's demand for higher performance in semiconductor devices have forced cavity structures to become more complex. Figure 5Figure (f) shows another cavity structure encountered in practical engineering applications, where the upper end of the cavity requires the retention of some silicon as a connecting bridge (i.e., tip 3). Although existing methods can fabricate cavities with tips at the top, the following problems exist: the silicon at the top is over-etched during the etching process, resulting in poor tip morphology and incomplete structure, thus affecting device accuracy and performance; the control of the angle and morphology of the inner sidewalls of the cavity lacks freedom, and it is particularly difficult to form a cavity structure with perpendicular sidewall angles and a flat morphology.

[0076] The cavity structure formation method provided in this embodiment can solve the above problems. Figure 4 This is a flowchart of the cavity structure formation method in this embodiment. Figure 5 This is a cross-sectional schematic diagram of each step of the forming method in this embodiment. The forming method includes steps 201-204. Compared with the aforementioned cavity structure forming method (steps 101-104), the main difference of the forming method in this embodiment is the first groove formed in step 202.

[0077] In this embodiment, step 202 first involves etching shallow trenches 110 in the silicon substrate 1 according to the opening pattern 21 of the mask layer. Figure 5 (b) Then, add a protective layer 4 to the sidewall of the shallow trench 110. Figure 5 After (c), vertical etching is used to form the first trench 11, so that a protective layer 4 is provided on the upper sidewall of the formed first trench 11. Figure 5 In step d), the protective layer 4 will not be etched away in the subsequent first and second lateral etching steps, so that the silicon at the upper end of the cavity covered by the protective layer 4 will not be consumed, and finally a cavity with a tip 3 at the upper end is formed on the substrate. Figure 5 (f). For the specific operation of each step of the method in this embodiment, please refer to Embodiment 1 below, which will not be repeated here.

[0078] In some embodiments, the protective layer 4 is made of at least one of silicon nitride, silicon oxide, chromium, titanium nitride, and titanium oxide. The protective layer 4 has excellent insulation, thermal stability, and chemical stability, and can play an excellent protective role in the plasma etching process, protecting the covered part from etching and wear.

[0079] This embodiment employs a two-stage lateral etching process, enabling highly flexible and precise control over the sidewall angles and morphology of the etched cavity structure. In particular, it can form cavity structures with vertical or near-vertical sidewalls and smooth sidewall morphology. The second lateral etching gas (SF6 and N2) does not over-etch the tip 3 at the upper end of the cavity, thus preserving the complete and good morphology of the tip 3. This solves the problems of poor tip morphology and incomplete structure in existing etching processes.

[0080] In some embodiments, after performing the second lateral etching, the method further includes removing any residue of the protective layer 4.

[0081] Example 1

[0082] This embodiment provides a method for forming a cavity structure, specifically including:

[0083] Step 201: Provide a silicon substrate 1, the surface of which has a mask layer 2, the mask layer 2 having a plurality of opening patterns 21, the bottom of which exposes the top surface of the silicon substrate 1, see [link to relevant documentation]. Figure 5 The structure shown in (a) is shown in the middle.

[0084] Step 202: Vertically etch the silicon substrate 1 downwards to a predetermined depth according to the opening pattern 21 to form a first trench 11. A protective layer 4 is provided on the upper sidewall of the first trench 11. Specifically:

[0085] (i) A second vertical etching gas is introduced to ignite the plasma, and the silicon substrate 1 is etched downwards according to the opening pattern 21 to form a plurality of shallow trenches 110. See Figure 5 The structure shown in (b) is shown in the middle.

[0086] The etching process for forming the shallow trench 110 can be an anisotropic dry etching process, and the second vertical etching gas includes a combination of SF6, N2 and HBr.

[0087] (ii) A protective layer 4 is formed on the sidewall of the shallow trench 110, see [reference] Figure 5 The structure shown in (c) is as follows.

[0088] Using a CVD apparatus, a silicon nitride layer with a thickness of 30 nm to 40 nm is deposited as a protective layer 4 on the sidewalls and bottom of the shallow trench 110. Subsequently, the protective layer 4 on the bottom surface of the shallow trench 110 is etched away, leaving the protective layer 4 only on the sidewalls of the shallow trench 110.

[0089] (iii) Introduce the first vertical etching gas to ignite the plasma, and continue the vertical etching process downwards along the shallow trench 110 to a preset depth to form the first trench 11. See Figure 5 The structure shown in (d) is as follows. Specifically:

[0090] With a source RF of 800W, a bias RF of 500W and a frequency of 500kHz, using pulse mode, a duty cycle of 15%, a reaction chamber pressure of 23mT, and a temperature of 40℃, the following gases were selected: 100sccm of SF6, 150sccm of O2, 90sccm of HBr, 150sccm of He, and 188sccm of CF4. After plasma excitation, a vertical etching step was performed downwards along the shallow trench 110 to form the first trench 11, with an etching time of 240s. The source RF power distribution in the central region of the plasma area was 50%, and the total gas input distribution was 50% in the central region and 50% in the edge region.

[0091] Step 203: Introduce the first lateral etching gas to ignite the plasma, and perform the first lateral etching step on the first trench 11 to form the second trench 12. See [link to previous step]. Figure 5 The structure shown in (e) is as follows. Specifically:

[0092] Under the conditions of a 2000W source radio frequency, a reaction chamber pressure of 80mT, and a temperature of 40℃, 100sccm of SF6 and 80sccm of O2 gas are selected to excite the plasma. Then, the first transverse etching step is performed on the first trench 11 to form a second trench 12 whose width gradually increases from the top to the bottom. The etching time is 140s. The power distribution of the source radio frequency in the central region of the plasma is 50%.

[0093] Step 204: Introduce a second lateral etching gas to ignite the plasma, perform a second lateral etching step on the second trench 12, and adjust the sidewalls of the second trench 12 to form a cavity structure 13 with vertical or near-vertical sidewalls. Specifically:

[0094] Under the conditions of a 2000W source RF power, a reaction chamber pressure of 50mT, and a temperature of 40°C, plasma is excited using 100sccm of SF6, 200sccm of N2, and 400sccm of He gas. The etching time is 30s, and the power distribution of the source RF in the central region of the plasma is 50%. The formed cavity structure 13 includes: silicon vias; and multiple second trenches 12 connected to form a cavity with a tip 3 at the upper end.

[0095] Comparative Example 1

[0096] The first and second lateral etching gases used in Comparative Example 1 are different from those in Example 1. Comparative Example 1 always uses a single etching gas, SF6, for lateral etching. Specifically:

[0097] Under conditions of a 2000W source RF power, a reaction chamber pressure of 50mT, and a temperature of 40℃, 100 sccm of SF6 and 400 sccm of He gas were selected to excite the plasma. A transverse etching step was then performed along the sidewall of the first trench 11 for 90 seconds. Specifically, the source RF power distribution in the central region of the plasma zone was 50%, and the total gas input was distributed 50% in the central region and 50% in the edge region.

[0098] Comparative Example 2

[0099] The first lateral etching gas used in Comparative Example 1 is the same as that used in Example 1, but the second lateral etching gas used is different from that used in Example 1. In Comparative Example 2, SF6 is selected as the second lateral etching gas.

[0100] The substrates containing cavity structures prepared in Example 1 and Comparative Examples 1-2 were cut open, and the morphology of the cavity structures was observed using a scanning electron microscope (SEM). The results showed that Example 1 successfully prepared a cavity structure with a vertical overall morphology, including: a silicon via with a width that is basically consistent from top to bottom, and a cavity with a pointed tip at the top, and the tip (circled area) has a good morphology. Figure 6 In Comparative Example 1, the width of the upper part of the silicon via is significantly larger than the width of the lower part. Figure 6 In Comparative Example 2, the sidewall angle is not perpendicular and the tip morphology is poor; in Comparative Example 3, the upper end of the silicon via still exhibits a curved morphology. Figure 6 c) The inner sidewall has an uneven area. Comparative Examples 1-2 do not meet the target process requirements of vertical inner sidewall angle, flat sidewall morphology, and consistent width from the top to the bottom of the cavity structure, and cannot meet the application requirements.

[0101] In summary, the cavity structure formation method provided by this invention first forms a first trench of a predetermined depth through vertical etching, and then employs two transverse etching modes to control the angle and morphology of the sidewalls of the first trench in stages. This control offers greater freedom and precision, solving the problem of traditional formation methods lacking freedom in controlling the sidewall angle and morphology of cavity structures. Furthermore, by combining the screening and research of the types of gases used in the two transverse etching processes, the method addresses the problems of uneven sidewall morphology and the tendency to unnecessarily enlarge small width dimensions (less than 1 μm) found in traditional formation methods, demonstrating promising development and application prospects.

[0102] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method of forming a cavity structure, characterized by, Includes the following steps: A silicon substrate is provided, the surface of which has a mask layer having a plurality of opening patterns, the bottom of which exposes the top surface of the silicon substrate; The silicon substrate is vertically etched downwards to a predetermined depth according to the opening pattern to form a first trench; A first lateral etching gas is introduced to perform a first lateral etching step on the first trench to form a second trench. The etching rate of the first lateral etching gas on the upper end of the first trench is different from the etching rate on the lower end. A second lateral etching gas is introduced to perform a second lateral etching step on the second trench, thereby controlling the sidewalls of the second trench to form a cavity structure with vertical or near-vertical sidewalls.

2. The method for forming a cavity structure as described in claim 1, characterized in that, The etching rate of the first lateral etching gas on the upper end of the first trench is less than the etching rate on the lower end.

3. The method for forming a cavity structure as described in claim 2, characterized in that, The first lateral etching gas includes SF6 and oxygen-containing gas.

4. The method for forming a cavity structure as described in claim 3, characterized in that, The gas volume ratio of oxygen-containing gas to SF6 is 0.5:1 to 1.5:

1.

5. The method for forming a cavity structure as described in claim 4, characterized in that, The oxygen-containing gas includes any one of O2, SO2, or CO2.

6. The method for forming a cavity structure as described in claim 2, characterized in that, The second lateral etching gas includes SF6 and N2.

7. The method for forming a cavity structure as described in claim 6, characterized in that, The gas volume ratio of N2 to SF6 is 1:1 to 4:

1.

8. The method for forming a cavity structure as described in claim 1, characterized in that, The minimum width dimension of the cavity structure is more than 95% of the maximum width dimension on the same cross section.

9. The method for forming a cavity structure as described in claim 1, characterized in that, The cavity structure includes: performing the second lateral etching step on the second trench, manipulating the sidewalls of the second trench to form silicon vias; and / or The second lateral etching step is performed on the second trench to connect multiple second trenches and form a cavity with or without a tip at the top.

10. The method for forming a cavity structure as described in claim 9, characterized in that, The cavity structure includes silicon vias with an aspect ratio greater than 12:

1.

11. The method for forming a cavity structure as described in claim 9, characterized in that, The cavity structure includes silicon apertures, the width of which is 0.1μm to 1μm and the depth of which is 1.2μm to 12μm.

12. The method for forming a cavity structure as described in claim 9, characterized in that, When the cavity structure is the silicon via and / or the cavity without a tip at the upper end, the method for forming the first trench includes: A first vertical etching gas is introduced, and the silicon substrate is etched downwards to a predetermined depth according to the opening pattern to form the first trench.

13. The method for forming a cavity structure as described in claim 9, characterized in that, When the cavity structure includes a cavity with a pointed tip at the upper end, the method of forming the first groove includes: A second vertical etching gas is introduced, and the silicon substrate is etched downward according to the opening pattern to form multiple shallow trenches; A protective layer is formed on the sidewall of the shallow trench; A first vertical etching gas is introduced, and the vertical etching process continues downward along the shallow trench to a preset depth to form the first trench.

14. The method for forming a cavity structure as described in claim 12 or 13, characterized in that, The first vertical etching gas includes a combination of SF6, O2 and HBr.

15. The method for forming a cavity structure as described in claim 13, characterized in that, The second vertical etching gas comprises a combination of SF6, N2, and HBr.

16. The method for forming a cavity structure as described in claim 13, characterized in that, The protective layer is made of at least one of silicon nitride, silicon oxide, chromium, titanium nitride, and titanium oxide.

17. The method for forming a cavity structure as described in claim 1, characterized in that, The material of the mask layer includes at least one of silicon oxide and silicon nitride.

Images