Process method for forming cavity structure on substrate

Abstract

The invention discloses a process method for forming a cavity structure on a substrate, and the method comprises the following steps: providing a silicon substrate, the surface of the silicon substrate is provided with a mask layer, the mask layer is provided with a plurality of opening patterns, and the bottoms of the opening patterns are exposed out of the top surface of the silicon substrate; introducing a first etching gas to ignite the plasma, and etching the silicon substrate downwards according to the opening pattern to form a plurality of shallow trenches; forming a protective layer on the side wall of the shallow trench; introducing a second etching gas to ignite the plasma, and continuing to execute the vertical etching step downwards along the shallow trench to a preset depth so as to form a deep trench; and third etching gas is introduced to ignite the plasma, and the transverse etching step continues to be executed in the lateral direction along the lower portions of the deep grooves so that the multiple deep grooves can be communicated to form a cavity with a connecting bridge at the upper end. The method solves the problem that a cavity structure with a connecting bridge at the upper end is difficult to obtain on the substrate by a traditional semiconductor device manufacturing process.

Description

Technical Field

[0001] The present invention relates to an etching method for semiconductor devices, and particularly to a process method for forming a cavity structure on a substrate. Background Art

[0002] In the manufacturing processes of semiconductor devices such as image sensors (CIS) and microelectromechanical systems (MEMS), structures are often formed through etching. A cavity is a common structure. Figure 1 Shown is a common cavity structure for manufacturing MEMS microphones. According to actual requirements, the inner sidewalls of the cavity have morphologies of vertical (a), negative angle inclination (b), and positive angle inclination (c). Figure 2 Shown is another common cavity structure. After completely hollowing out the silicon under the mask and retaining the mask, the inner sidewalls of the cavity have a vertical morphology (a) and an inclined morphology (b). In the prior art, the etching of the aforementioned two common cavity structures is relatively easy, and the desired results can be obtained using both Bosch processes and non - Bosch processes.

[0003] However, with the development of semiconductor processes and the higher demand for the performance of semiconductor devices in the market, the cavity structure has been forced to become more complex. Figure 3 Shown is another cavity structure encountered in engineering practical applications. Part of the silicon is required to be retained at the upper end of the cavity as a connection bridge, but the fabrication of such a cavity is very difficult. If the manufacturing processes of the above - mentioned two cavities are adopted for this type of cavity, the silicon at the upper end will be etched off early, and it is difficult to form a cavity with a connection bridge at the upper end, thus unable to meet the application requirements. Summary of the Invention

[0004] The object of the present invention is to provide a process method for forming a cavity structure on a substrate. This method aims to solve the problem that it is difficult to obtain a cavity structure with a connection bridge at the upper end on the substrate in traditional semiconductor device manufacturing processes. The present invention forms deep trenches through vertical etching on the substrate and then laterally etches to connect the lower parts of adjacent deep trenches to form a regular square - cavity structure. Importantly, by adding a protective layer during the etching process and selecting an etching gas with a high selectivity ratio for the protective layer and the substrate during the lateral etching process, it is ensured that the protective layer will not be etched off during the etching process, and the part of the substrate covered by the protective layer will not be etched off either. Finally, a cavity structure with a connection bridge at the upper end is formed on the substrate.

[0005] To achieve the above object, the present invention provides a process method for forming a cavity structure on a substrate, wherein the cavity structure includes a connection bridge located at its upper part, and the method comprises the following steps:

[0006] Provide a silicon substrate, the surface of the silicon substrate has a mask layer, and the mask layer has a plurality of opening patterns, and the bottom of the opening patterns exposes the top surface of the silicon substrate;

[0007] Introduce the first etching gas to ignite the plasma, and etch the silicon substrate downward according to the opening pattern to form a plurality of shallow trenches;

[0008] Form a protective layer on the sidewalls of the shallow trenches;

[0009] Introduce the second etching gas to ignite the plasma, and continue to perform a vertical etching step downward along the shallow trenches to a preset depth to form deep trenches;

[0010] Introduce the third etching gas to ignite the plasma, and continue to perform a lateral etching step laterally from the lower part of the deep trenches to connect the plurality of deep trenches to form a cavity with a connecting bridge at the upper end.

[0011] Optionally, the material of the protective layer includes at least one of silicon nitride, silicon oxide, chromium, titanium nitride, and titanium oxide.

[0012] Optionally, the thickness of the protective layer is 30 nm to 40 nm.

[0013] Optionally, the third etching gas includes: SF6.

[0014] Optionally, the third etching gas further includes: O2.

[0015] Optionally, the protective layer is a silicon nitride layer, and the gas usage ratio of O2 and SF6 in the third etching gas is less than 1.

[0016] Optionally, the protective layer is a silicon oxide layer, and the gas usage ratio of O2 and SF6 in the third etching gas is 0 to 2.

[0017] Optionally, the second etching gas includes a combined gas of SF6 / O2 / CF4 / HBr. The vertical etching step further includes applying a bias radio frequency to accelerate the movement directionality of charged particles downward, and the plasma of the second etching gas will react to generate a polymer deposited on the sidewalls of the deep trenches to form a passivation layer.

[0018] Optionally, the lateral etching step further includes: first using the plasma generated by NF3 to etch and remove the passivation layer, and then introducing the third etching gas to continue the subsequent lateral etching step.

[0019] Optionally, the etching time for using the plasma generated by NF3 to etch and remove the passivation layer is 8 s to 15 s.

[0020] Optionally, when the lateral etching step is performed, the bias radio frequency is turned off, and optionally, the power of the source radio frequency is increased.

[0021] Optionally, the method for forming the protective layer includes: a chemical vapor deposition process.

[0022] Optionally, a protective layer is formed on the sidewalls and bottom of the shallow trench by a chemical vapor deposition process. The vertical etching step further includes: after removing the protective layer at the bottom of the shallow trench by using a fourth etching gas, introducing the second etching gas to continue the subsequent vertical etching step.

[0023] Optionally, the protective layer is a silicon nitride layer, and the fourth etching gas includes at least one of CF4, CHF3, CH2F2, and CH3F.

[0024] Optionally, the protective layer is a silicon oxide layer, and the fourth etching gas includes at least one of CF4, CHF3, and CH2F2.

[0025] Optionally, the first etching gas includes a combined gas of SF6 / N2 / HBr.

[0026] Optionally, after the lateral etching, it further includes: removing the residue of the protective layer.

[0027] Optionally, the material of the mask layer includes at least one of silicon oxide and silicon nitride.

[0028] Compared with the prior art, the beneficial effects of the technical solution of the present invention at least include:

[0029] The process method for forming a cavity structure on a substrate provided by the present invention can successfully form a cavity structure with a connection bridge at the upper end on the substrate, and the preparation process is simple. Specifically, first, a shallow trench is etched in the silicon substrate according to the opening pattern of the mask layer. After adding a protective layer on the sidewalls of the shallow trench, vertical etching is continued to form a deep trench, and then lateral etching is performed using an etching gas with a high selectivity to the protective layer and silicon, so that while the lower parts of adjacent deep trenches are connected to form a cavity, it is ensured that the protective layer will not be etched away, and the silicon at the upper end of the cavity covered by the protective layer will not be consumed. Finally, a cavity structure with a connection bridge at the upper end is formed on the substrate, solving the problem that it is difficult to obtain a cavity structure with a connection bridge at the upper end on the substrate in the traditional semiconductor device manufacturing process, and having good development and application prospects. Description of the Drawings

[0030] Figures 1 to 3 Schematic cross-sectional views of different square cavity structures.

[0031] Figure 4 Flowchart of the process method for forming a cavity structure on a substrate according to an embodiment of the present invention.

[0032] Figure 5Schematic cross-sectional view of a substrate during the formation of a cavity structure on the substrate according to a process method of an embodiment of the present invention.

[0033] Figure 6 Top view schematic diagram of a mask layer and a connection bridge structure according to an embodiment of the present invention.

[0034] Figure 7 Schematic cross-sectional view of a cavity structure with a connection bridge at the upper end prepared according to another embodiment of the present invention.

[0035] Reference numerals in the drawings:

[0036] Silicon substrate 1, shallow trench 11, deep trench 12, connection bridge 13, mask layer 2, opening pattern 21, protective layer 3, passivation layer 4, cavity 200. Detailed implementation manners

[0037] To solve the above technical problems, an embodiment of the present invention proposes a process method for forming a cavity structure on a substrate.

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0039] It should be noted that all directional indications (such as up, down, left, right, front, back...) in the embodiments of the present invention are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indications will also change accordingly.

[0040] As described in the background art, in the CIS and MEMS processes, in the etching process for forming a required cavity structure by etching, the upper substrate portion (such as silicon) is easily etched away early, so it is difficult to fabricate a cavity structure with a connection bridge at the upper end on the substrate. In view of this, the present invention proposes a process method for forming a cavity structure on a substrate, as Figure 4 and Figure 5 shown, including:

[0041] Step 101, providing a silicon substrate 1, the surface of the silicon substrate 1 having a mask layer 2, the mask layer 2 having a plurality of opening patterns 21, the bottom of the opening patterns 21 exposing the top surface of the silicon substrate 1, referring to Figure 5 (a) shown in

[0042] In some embodiments, the material of the mask layer 2 may include at least one of silicon oxide and silicon nitride. That is to say, 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 a silicon oxide layer and a silicon nitride layer. For example, a mask layer formed by stacking the silicon oxide layer and the silicon nitride layer, and the thicknesses of different layers may be the same or different.

[0043] The opening pattern 21 is used to define the position and width dimensions of the subsequent formed shallow trenches. The remaining partial area on the mask layer other than the opening pattern 21 defines the position and width dimensions of the connection bridge at the upper end of the cavity. The shape of the opening pattern 21 includes but is not limited to a circle, an ellipse, a square, a triangle, etc. For example, in some embodiments, the shape of the opening pattern 21 is a square, as shown in the top view of the mask layer 2 in (a) of Figure 6 the reference.

[0044] Step 102: Introduce a first etching gas to ignite the plasma, and etch the silicon substrate 1 downward according to the opening pattern 21 to form a plurality of shallow trenches 11, as shown in (b) of Figure 5 the reference.

[0045] In some embodiments, the process of etching to form the shallow trenches 11 may be an anisotropic dry etching process. By applying a bias radio frequency to accelerate the directional movement of charged particles downward, the etching rate in the vertical direction is much greater than that in the horizontal direction. Therefore, the perpendicularity between the sidewalls and the bottom of the formed shallow trenches 11 is better, which is beneficial to improving the fidelity of the pattern; in other embodiments, other suitable material removal methods may also be used for etching in this step.

[0046] In some embodiments, the first etching gas includes a combined gas of SF6 / N 2 / HBr. Among them, SF6 is the main etching gas, HBr is the passivation gas, and N2 is mainly used to adjust the gas concentration, and a very small amount reacts with silicon to form silicon nitride. After etching for a certain time, the etching is stopped, thereby forming the shallow trenches 11 in the silicon substrate 1.

[0047] It can be understood that the time for etching to form the shallow trenches 11 depends on the thickness of the final desired connection bridge. If a thicker connection bridge structure is required, the etching time for forming the shallow trenches 11 is longer; conversely, if a thinner connection bridge structure is required, the etching time is shorter.

[0048] Step 103: Form a protective layer 3 on the sidewalls of the shallow trenches 11, as shown in (c) of Figure 5 the reference.

[0049] In some embodiments, the material of the protective layer 3 includes at least one of silicon nitride, silicon oxide, chromium, titanium nitride, and titanium oxide; more preferably, the protective layer 3 is a silicon nitride layer or a silicon oxide layer. The silicon nitride layer and the silicon oxide layer have excellent insulation, thermal stability, chemical stability, etc., and can play an excellent protective role in the plasma etching process to protect the covered part from being etched and worn.

[0050] In some embodiments, the protective layer 3 is formed on the sidewalls and bottom of the shallow trench 11 by chemical vapor deposition (CVD); in other embodiments, the protective layer 3 is formed inside the plasma processing device. Without removing the plasma processing device, the protective layer 3 is directly formed by plasma spraying through the built-in source radio frequency power source of the plasma processing device.

[0051] After the above steps, not only the protective layer 3 is formed on the sidewalls of the shallow trench 11, but also the protective layer is formed on its bottom. For the protective layer formed on the bottom, an additional step can be added to perform vertical etching with a fourth etching gas. After etching, the protective layer on the bottom surface of the shallow trench 11 is removed, and only the sidewalls of the shallow trench 11 are covered with the protective layer 3, so as to play a role in protecting the silicon covered at the upper end during subsequent etching, and to prevent the silicon at the upper end from being etched away during subsequent etching and thus unable to form a cavity structure with a connecting bridge at the upper end. In other embodiments, the protective layer at the bottom of the shallow trench can also be removed at the beginning of the deep trench etching stage.

[0052] As an example, when the protective layer 3 is a silicon nitride layer, the fourth etching gas includes at least one of CF4, CHF3, CH2F2, and CH3F, and gases such as O2 can also be added; when the protective layer 3 is a silicon oxide layer, the fourth etching gas includes at least one of CF4, CHF3, and CH2F2, and inert gases such as Ar can also be added to increase the ion bombardment ability. The overall gas flow rate of the fourth etching gas is between 50 sccm and 500 sccm.

[0053] Step 104, introduce the second etching gas to ignite the plasma, and continue to perform a vertical etching step downward along the shallow trench 11 to a preset depth to form a deep trench 12, as shown in (d) of Figure 5 reference.

[0054] In some embodiments, an anisotropic dry etching process is employed to continue etching the shallow trench 11. By applying a bias radio frequency to accelerate the directional movement of charged particles downward, the etching rate in the vertical direction is much greater than that in the horizontal direction. Eventually, a deep trench 12 is etched. The perpendicularity of the sidewall and the bottom of the deep trench 12 is good, laying an important foundation for later laterally etching to connect the lower parts of adjacent deep trenches 12 to form a relatively regular square cavity structure. In other embodiments, other suitable etching methods, such as wet etching, may also be used in this etching step to form the desired structure.

[0055] In addition, while the plasma generated by the second etching gas in this step etches downward to form the deep trench 12, the plasma will react to generate a polymer that deposits on the sidewall surface of the deep trench 12 to form a passivation layer 4. The passivation layer 4 is an anti-corrosion film formed on the sidewall, which can block the etching of the sidewall of the deep trench 12 during the process of vertically etching to form the deep trench 12, enhance the etching directionality, thereby achieving good control of the critical dimensions of the pattern, and further ensuring the good perpendicularity of the sidewall and the bottom of the deep trench 12. As an example, the second etching gas includes a combined gas of SF6 / O2 / CF4 / HBr. Among them, SF6 is the main etching gas, which generates F - radicals that react with Si; O2 and HBr actually act as passivation gases in practice, and the formed passivation layer 4 is Si x O y Br z , where 0 < x, y, z ≤ 1; CF4 can help break down the SiO2 formed on the silicon surface, enabling Si to react with F-radicals to generate SiF4, thereby producing an etching effect.

[0056] In practical applications, the preset depth depends on the depth of the square cavity structure ultimately desired. If a deeper square cavity structure is needed, the etching time for forming the deep trench 12 in this step is longer; conversely, if a shallower square cavity structure is needed, the etching time is shorter.

[0057] Step 105, introduce a third etching gas to ignite the plasma, and continue to perform a lateral etching step along the lower part of the deep trench 12 laterally to connect multiple deep trenches 12 to form a cavity 200 with a connecting bridge 13 at the upper end, as shown in Figure 5 (e - g) in the figure.

[0058] In some embodiments, when etching on both sides of the deep trench 12, since there is a protective layer 3 at the top of the deep trench 12, after lateral etching for a certain distance, the silicon between the lower parts of adjacent deep trenches 12 will be completely etched away, and the upper part is retained because it is covered by the protective layer 3 and avoids being etched and worn, and finally a cavity 200 with a connecting bridge 13 at the upper end is formed in the substrate, asFigure 5 as shown in (f).

[0059] In some embodiments, when there is a passivation layer 4 on the sidewall of the deep trench 12 after the aforementioned step 104 is completed, this step may further include: first, removing the passivation layer 4 by plasma etching, as Figure 5 shown in (e), and then introducing the third etching gas to continue the subsequent lateral etching step.

[0060] It should be emphasized that the third etching gas has a high selectivity ratio for the protective layer 3 and silicon. During the lateral etching process, the etching rate of this gas combination for silicon is much greater than that for the protective layer 3, so that after the entire lateral etching is completed, the protective layer 3 will not be completely etched away and can play a protective role for the silicon covered by it. If the selectivity ratio of the third etching gas for the protective layer 3 and silicon is low, during the lateral etching process, as the silicon between the lower parts of adjacent deep trenches 12 is gradually etched, the protective layer 3 at the top of the deep trench 12 will also be gradually etched away, causing the silicon at the upper end to be exposed to the plasma atmosphere and etched and worn, and ultimately a cavity structure with a connecting bridge at the upper end cannot be formed.

[0061] Verified by experiments of the present invention, when the main etching gas is SF6, the selectivity ratio of silicon to silicon nitride or silicon oxide is very high. In some embodiments, the third etching gas is SF6; in other embodiments, in addition to SF6, the third etching gas further includes O2, and O2 can adjust the etching rate of Si, thereby further improving the surface roughness of the cavity. It should be noted that it is found through experiments of the present invention that when the protective layer 3 is a silicon oxide layer, even if the amount of O2 added is higher than that of SF6, a good silicon / silicon oxide selectivity ratio can still be ensured. As an example, when the protective layer is a silicon oxide layer, the gas dosage ratio of O2 and SF6 in the third etching gas is 0 to 2; while when the protective layer 3 is a silicon nitride layer, the gas dosage ratio of O2 and SF6 in the third etching gas is less than 1.

[0062] As Figure 5 shown in (e), the cavity 200 formed in this embodiment is a regular square cavity structure, and the connecting bridge 13 at the upper end is a structure with a tip; in other embodiments, different-shaped connecting bridges or square cavity structures can be obtained by adjusting the etching conditions. For example, by extending the etching time, the tip of the connecting bridge 13 is etched and ground flat (as Figure 7 shown), or even a structure that is concave upward; by adjusting the plasma distribution density, a cavity structure with a wider upper part and a narrower lower part as shown in (b) is obtained. Figure 3 shown in (b).

[0063] As Figure 5 shown in (g), in some embodiments, after the lateral etching, it further includes: removing the residue of the protective layer 3 and removing the mask layer 2. AsFigure 6 As shown in Figure (b), it is a top view schematic diagram of the substrate with a cavity structure according to the present invention after removing the mask layer. It can be seen that the shape of the connection bridge on the upper part of the cavity structure prepared by the present invention is consistent with the pattern of the mask layer.

[0064] Example 1

[0065] This example provides a process method for forming a cavity structure on a substrate, specifically including:

[0066] Step 101: Provide a silicon substrate 1, the surface of the silicon substrate 1 has a mask layer 2, the mask layer 2 has a plurality of opening patterns 21, and the top surface of the silicon substrate 1 is exposed at the bottom of the opening patterns 21.

[0067] Step 102: Introduce a first etching gas to ignite the plasma, and etch the silicon substrate 1 downward according to the opening patterns 21 to form a plurality of shallow trenches 11. Specifically:

[0068] Under the conditions of a source radio frequency power of 700W, a bias radio frequency power of 800W and a frequency of 500KHz, using a pulse mode with a duty cycle of 40%, a reaction chamber pressure of 16mT and a temperature of 40°C, select 27sccm of SF6, 90sccm of N2 and 1000sccm of HBr gas. After exciting the plasma, etch the silicon substrate 1 downward according to the opening patterns 21 to form a plurality of shallow trenches 11, and the etching time is 22s. Among them, the power distribution of the source radio frequency in the central region of the plasma region is 50%, that is, 350W is distributed in the central region of the plasma region and 350W is distributed in the edge region; the distribution of the total gas input amount is 10% in the middle region, that is, the gas amount input to the central region accounts for 10% of the total gas input amount, and the edge region accounts for 90% of the total gas input amount.

[0069] Step 103: Form a protective layer 3 on the side walls of the shallow trenches 11.

[0070] Using a CVD device, deposit a layer of silicon nitride layer on the side walls and bottom of the shallow trenches 11 as the protective layer 3, with a thickness of 30nm - 40nm. Subsequently, use a fourth etching gas to remove the protective layer 3 on the bottom surface of the shallow trenches 11, and only the side walls of the shallow trenches 11 are covered with the protective layer 3. Specifically:

[0071] Under the conditions of a source radio frequency power of 400W, a bias radio frequency power of 500W, a reaction chamber pressure of 5mT and a temperature of 40°C, select 150sccm of CF4, 20sccm of CHF3 and 100sccm of Ar gas. After exciting the plasma, etch downward to remove the silicon nitride protective layer on the bottom surface of the shallow trenches 11, and the etching time is 15s.

[0072] In some other embodiments, gases such as O2 can be further added to the above-mentioned fourth etching gas combination, and the overall gas flow rate is between 50 sccm and 500 sccm.

[0073] Step 104: Introduce the second etching gas to ignite the plasma, and continue to perform a vertical etching step downward along the shallow trench 11 to a preset depth to form a deep trench 12. Specifically:

[0074] Under the conditions of a source radio frequency power of 800 W, a bias radio frequency power of 500 W and a frequency of 500 KHz, in a pulse mode with a duty cycle of 15%, a reaction chamber pressure of 23 mT and a temperature of 40 °C, select 100 sccm of SF6, 150 sccm of O2, 90 sccm of HBr, 150 sccm of He and 188 sccm of CF4 gases. After exciting the plasma, perform a vertical etching step downward along the shallow trench 11 to form a deep trench 12, and the etching time is 240 s. Among them, the power distribution of the source radio frequency in the central region of the plasma region is 50%, and the distribution of the total gas input is 50% in the middle region and 50% in the edge region.

[0075] Step 105: Introduce the third etching gas to ignite the plasma, and continue to perform a lateral etching step laterally from the lower part of the deep trench 12 to connect multiple deep trenches 12 to form a cavity 200 with a connecting bridge 13 at the upper end.

[0076] In this embodiment, a passivation layer 4 is formed on the side wall of the deep trench 12 etched through the above step 104, and the passivation layer 4 is Si x O y Br z , where 0 < x, y, z ≤ 1. Therefore, it is first necessary to remove the passivation layer. Specifically: Under the conditions of a source radio frequency power of 1400 Ws, a reaction chamber pressure of 80 mT and a temperature of 40 °C, select 30 sccm of CF4, 100 sccm of NF3 and 400 sccm of He gases. After exciting the plasma, laterally etch to remove the passivation layer 4 on the side wall of the deep trench 12, and the etching time is 8 s to 15 s. Among them, the power distribution of the source radio frequency in the central region of the plasma region is 50%, and the distribution of the total gas input is 50% in the middle region and 50% in the edge region.

[0077] Subsequently, under the conditions of a source radio frequency power of 2000 W, a reaction chamber pressure of 50 mT and a temperature of 40 °C, select 100 sccm of SF6 and 400 sccm of He gases. After exciting the plasma, perform a lateral etching step laterally from the lower part of the deep trench 12 to connect multiple deep trenches 12 to form a cavity 200 with a connecting bridge 13 at the upper end, and the etching time is 90 s.

[0078] Embodiment 2

[0079] This embodiment provides a process method for forming a cavity structure on a substrate, specifically including:

[0080] Step 101 is the same as that in Embodiment 1.

[0081] Step 102 is the same as that in Embodiment 1.

[0082] In Step 103, different from Embodiment 1, the protective layer 3 formed by CVD deposition in this embodiment is a silicon oxide layer. Therefore, the conditions for etching and removing the protective layer 3 on the bottom surface of the shallow trench 11 are different. Specifically:

[0083] Under the conditions of a source radio frequency power of 2500W, a bias radio frequency power of 300W, a reaction chamber pressure of 50mT, and a temperature of 40°C, select 400sccm of CF4, 300sccm of CHF3, and 400sccm of Ar gas. After exciting the plasma, etch downward to remove the silicon oxide protective layer on the bottom surface of the shallow trench 11, and the etching time is 15s. Among them, the power distribution of the source radio frequency in the central region of the plasma region is 50%, and the distribution of the total gas input amount is 50% in the middle region and 50% in the edge region.

[0084] Step 104 is the same as that in Embodiment 1.

[0085] In Step 105, the etching conditions for laterally etching and removing the passivation layer 4 on the sidewall of the deep trench 12 are the same as those in Embodiment 1.

[0086] Subsequently, under the conditions of a source radio frequency power of 2000W, a reaction chamber pressure of 50mT, and a temperature of 40°C, select 100sccm of SF6, 80sccm of O2, and 400sccm of He gas. After exciting the plasma, perform a lateral etching step along the lower part of the deep trench 12 to the side to connect multiple deep trenches 12 to form a cavity 200 with a connecting bridge 13 at the upper end, and the etching time is 140s. Among them, the power distribution of the source radio frequency in the central region of the plasma region is 50%, and the distribution of the total gas input amount is 50% in the middle region and 50% in the edge region.

[0087] Comparative Example 1

[0088] The difference from Embodiment 1 is that the gas combination and etching conditions selected for the third etching gas are different. Specifically:

[0089] Under the conditions of a source radio frequency power of 2000 W, a reaction chamber pressure of 80 mT, and a temperature of 40 °C, 150 sccm of O2, 30 sccm of CF4, 100 sccm of NF3, and 400 sccm of He gas are selected. After plasma is excited, a lateral etching step is performed laterally along the lower part of the deep trench 12, and the etching time is 80 s. Among them, the power distribution of the source radio frequency in the central region of the plasma region is 50%, and the distribution of the total gas input is 50% in the middle region and 50% in the edge region.

[0090] Comparative Example 2

[0091] The difference from Example 1 lies in that the gas combination and etching conditions selected for the third etching gas are different. Specifically:

[0092] Under the conditions of a source radio frequency power of 1400 W, a reaction chamber pressure of 80 mT, and a temperature of 40 °C, 125 sccm of O2, 25 sccm of SO2, 30 sccm of CF4, 100 sccm of NF3, and 400 sccm of He gas are selected. After plasma is excited, a lateral etching step is performed laterally along the lower part of the deep trench 12, and the etching time is 180 s. Among them, the power distribution of the source radio frequency in the central region of the plasma region is 50%, and the distribution of the total gas input is 50% in the middle region and 50% in the edge region.

[0093] The substrates with cavity structures prepared in Examples 1-2 and Comparative Examples 1-2 were cut, and observed using a scanning electron microscope (SEM). The results showed that cavities with silicon connection bridges at the upper ends were successfully fabricated in both Examples 1 and 2, and the upper silicon tips remained intact; in Comparative Example 1, when the silicon between the lower parts of adjacent deep trenches was not completely etched away, the silicon nitride protective layer at the top had been completely etched away. In other words, when the cavity structure at the lower part of the substrate in Comparative Example 1 was not fully formed, the silicon at the upper end had already been etched, so ultimately a cavity with a silicon connection bridge at the upper end could not be formed; in Comparative Example 2, the silicon between the lower parts of adjacent deep trenches could be completely etched away to form a cavity structure, but the silicon at the upper end was still etched, which had an adverse effect on the size and structural integrity of the upper connection bridge, and would lead to the risk of collapse of the upper connection bridge during subsequent use, affecting the device yield and performance.

[0094] In summary, the present invention provides a process for forming a cavity structure on a substrate. Specifically, first, a shallow trench is etched in a silicon substrate according to the opening pattern of a mask layer. After adding a protective layer on the sidewall of the shallow trench, vertical etching is continued to form a deep trench, and then a lateral etching is carried out using an etching gas with a high selectivity ratio for the protective layer and silicon, so that while the lower parts of adjacent deep trenches are connected to form a cavity, it is ensured that the protective layer will not be etched away, and the silicon at the upper end of the cavity covered by the protective layer will not be consumed. Finally, a cavity structure with a connecting bridge at the upper end is formed on the substrate, solving the problem that it is difficult to obtain a cavity structure with a connecting bridge at the upper end on a substrate in the traditional semiconductor device manufacturing process.

[0095] Although the content of the present invention has been introduced in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the present invention. After those skilled in the art have read the above content, various modifications and alternatives to the present invention will be obvious. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims

1. A process for forming a cavity structure on a substrate, the cavity structure including a connection bridge located at its upper part, characterized in that, It includes the following steps: Provide a silicon substrate, on the surface of which there is a mask layer with a plurality of opening patterns, and the top surface of the silicon substrate is exposed at the bottom of the opening patterns; Introduce a first etching gas to ignite plasma, and etch the silicon substrate downward according to the opening patterns to form a plurality of shallow trenches; Form a protective layer on the side walls of the shallow trenches; Introduce a second etching gas to ignite plasma, and continue to perform a vertical etching step downward along the shallow trenches to a preset depth to form deep trenches; Introduce a third etching gas to ignite plasma, and continue to perform a lateral etching step laterally from the lower part of the deep trenches to connect the plurality of deep trenches to form a cavity with a connecting bridge at the upper end; 2. The process method for forming a cavity structure on a substrate according to claim 1, characterized in that, The material of the protective layer includes at least one of silicon nitride, silicon oxide, chromium, titanium nitride, and titanium oxide; 3. The process method for forming a cavity structure on a substrate according to claim 1, characterized in that, The thickness of the protective layer is 30 nm to 40 nm; 4. The process method for forming a cavity structure on a substrate as claimed in claim 1, wherein The third etching gas includes: SF6; 5. The process method for forming a cavity structure on a substrate according to claim 4, characterized in that, The third etching gas further includes: O2; 6. The process method for forming a cavity structure on a substrate as claimed in claim 5, characterized in that, When the protective layer is a silicon nitride layer, the gas consumption ratio of O2 and SF6 in the third etching gas is less than 1; 7. The process method for forming a cavity structure on a substrate as described in claim 5, characterized in that, When the protective layer is a silicon oxide layer, the gas consumption ratio of O2 and SF6 in the third etching gas is 0 to 2; 8. The process method for forming a cavity structure on a substrate according to claim 1, characterized in that, The second etching gas includes a combined gas of SF6 / O2 / CF4 / HBr. The vertical etching step further includes applying a bias radio frequency to accelerate the movement directionality of charged particles downward, and the plasma of the second etching gas will react to generate a polymer deposited on the side walls of the deep trenches to form a passivation layer; 9. The process method for forming a cavity structure on a substrate as described in claim 8, characterized in that, The lateral etching step further includes: first using the plasma generated by NF3 to etch and remove the passivation layer, and then introducing the third etching gas to continue the subsequent lateral etching step; 10. The process method for forming a cavity structure on a substrate as described in claim 9, characterized in that, The etching time for using the plasma generated by NF3 to etch and remove the passivation layer is 8 s to 15 s; 11. The process method for forming a cavity structure on a substrate as described in claim 8, characterized in that, When performing the lateral etching step, turn off the bias radio frequency, and optionally, increase the power of the source radio frequency; 12. The process method for forming a cavity structure on a substrate according to claim 1, characterized in that, The formation method of the protective layer includes: chemical vapor deposition process; 13. The process method for forming a cavity structure on a substrate according to claim 12, wherein, Use chemical vapor deposition process to form a protective layer on the side walls and bottom of the shallow trenches. The vertical etching step further includes: using a fourth etching gas to remove the protective layer at the bottom of the shallow trenches, and then introducing the second etching gas to continue the subsequent vertical etching step; 14. The process method for forming a cavity structure on a substrate according to claim 13, wherein, When the protective layer is a silicon nitride layer, the fourth etching gas includes at least one of CF4, CHF3, CH2F2, and CH3F; 15. The process method for forming a cavity structure on a substrate as described in claim 13, characterized in that, When the protective layer is a silicon oxide layer, the fourth etching gas includes at least one of CF4, CHF3, and CH2F2; 16. The process method for forming a cavity structure on a substrate as claimed in claim 1, characterized in that, The first etching gas includes a combined gas of SF6 / N2 / HBr; 17. The process method for forming a cavity structure on a substrate according to claim 1, characterized in that, After performing the lateral etching, it further includes: removing the residue of the protective layer; 18. The process method for forming a cavity structure on a substrate according to claim 1, characterized in that, The material of the mask layer includes at least one of silicon oxide and silicon nitride.

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