Trench Etching Method

Abstract

This invention provides a trench etching method, comprising a first cycle step and a second cycle step, both of which include an etching step for etching trenches on a substrate, a deposition step for forming a protective layer on the trench sidewalls, and a removal step for removing byproducts from the bottom of the trench. In the first cycle step, the etching step, deposition step, and removal step are executed sequentially. In the second cycle step, the etching step, removal step, and deposition step are executed sequentially. The trench etching method provided by this invention can improve the depth loading effect, avoid excessive width at the top of the trench, thereby ensuring that the line dimensions (Line CD) meet process requirements, and thus obtaining a more vertical etching morphology.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing, and in particular to a trench etching method. Background Art

[0002] Inductively coupled plasma (ICP) etching equipment has the advantages of low chamber pressure, high plasma density, strong morphology control, and good uniformity. It is widely used in ultra-large-scale integrated circuits that do not require high aspect ratios. For high aspect ratio etching processes, capacitively coupled plasma (CCP) etching equipment is usually used because it requires higher ion energy and free radical density.

[0003] In the structure of dynamic random access memory (DRAM), the charging and discharging process of the capacitor storage unit is directly controlled by the transistor. As the size of transistors shrinks and approaches the physical limit, the trench aspect ratio increases sharply with the reduction of transistor size. Etching uniformity and micro-loading effect (ARDE) are gradually becoming the main factors restricting DRAM performance and yield. For example, the processing of the trench isolation region (Shallow Trench Isolation, STI) of the transistor belongs to the high aspect ratio etching process. For this process, the line width size and shape are important factors affecting the transistor yield and performance.

[0004] For high aspect ratio silicon etching, in order to obtain silicon microstructures with a deeper depth and a vertical angle, such as Figure 1 As shown, the existing etching method mainly has the following problems:

[0005] First, as the etching depth increases, the byproducts caused by the high aspect ratio have difficulty entering and exiting the grooves, resulting in a serious micro-loading effect (mainly manifested in the different etching depths of grooves of different sizes on the same wafer, with wide grooves having a deep etching depth and narrow grooves having a shallow etching depth);

[0006] Secondly, when Cl2 is used as the etching gas, although the etching selectivity of the mask can be improved, due to its isotropic etching performance, the width of the top of the groove (space CD) will be increased, resulting in a decrease in the line size (LineCD) at the top. Summary of the invention

[0007] The present invention aims to solve at least one of the technical problems existing in the prior art, and proposes a groove etching method, which can improve the depth loading effect and avoid the excessive width of the groove top, thereby ensuring that the line size (LineCD) meets the process requirements, and further obtaining a more vertical etching morphology.

[0008] To achieve the purpose of the present invention, a trench etching method is provided, comprising a first cycle step and a second cycle step, both of which include an etching step for etching a trench on a substrate, a deposition step for forming a protective layer on the sidewall of the trench, and a removal step for removing byproducts at the bottom of the trench;

[0009] In the first cycle step, the etching step, the deposition step and the removal step are sequentially and cyclically performed;

[0010] In the second cycle step, the etching step, the removal step and the deposition step are performed in sequence and in a cycle.

[0011] Optionally, the trench etching method is performed using an inductively coupled plasma etching device, wherein the frequency of a lower electrode power supply used by the inductively coupled plasma etching device to load a lower electrode power signal is lower than the frequency of an upper electrode power supply used to load the upper electrode power signal.

[0012] Optionally, in the etching step, the upper electrode power signal is a radio frequency continuous signal, and the lower electrode power signal is a radio frequency pulse signal; or,

[0013] The upper electrode power signal and the lower electrode power signal are both pulsed radio frequency signals, and a signal output period in a cycle of the upper electrode power signal is synchronized with a signal output period in a cycle of the lower electrode power signal.

[0014] Optionally, a duty cycle of the pulsed radio frequency signal is greater than or equal to 5% and less than or equal to 30%.

[0015] Optionally, the flow rate of the etching gas used in the etching step of the first cycle step is smaller than the flow rate of the etching gas used in the etching step of the second cycle step.

[0016] Optionally, as the number of cycles of sequentially executing the etching step, the removal step and the deposition step in the second cycle step increases, the flow rate of the etching gas used in the etching step of the second cycle step increases.

[0017] Optionally, the lower electrode power used in the removal step of the first cycle step is greater than or equal to 50W and less than or equal to 300W.

[0018] Optionally, in the etching step, the deposition step and the removal step, while the etching gas is introduced into the process chamber, an oxidizing gas is also introduced into the process chamber;

[0019] The flow rate of the oxidizing gas used in the etching step of the first cycle step is greater than the flow rate of the oxidizing gas used in the etching step of the second cycle step.

[0020] Optionally, in the etching step, nitrogen gas is introduced into the process chamber while the etching gas and the oxidizing gas are introduced into the process chamber.

[0021] Optionally, the upper electrode power used in the etching step of the second cycle step is greater than the upper electrode power used in the etching step of the first cycle step.

[0022] Optionally, the power of the lower electrode used in the etching step of the second cycle step is greater than the power of the lower electrode used in the etching step of the first cycle step.

[0023] Optionally, in the first cycle step, the number of cycles of sequentially executing the etching step, the deposition step and the removal step is greater than or equal to 1 and less than or equal to 3; and / or,

[0024] In the second cycle step, the etching step, the removal step and the deposition step are sequentially executed in a cycle for a number of times greater than or equal to 4 and less than or equal to 9.

[0025] The present invention has the following beneficial effects:

[0026] The groove etching method provided by the present invention adopts two cycle steps, and the order of performing the etching step, the deposition step and the removal step is different. Specifically, in the first cycle step, by performing the deposition step before the removal step, a thicker protective material can be formed on the top of the groove, which helps to increase the sidewall protection of the top of the groove and reduce lateral etching, thereby avoiding the width of the top of the groove (space CD) being too large and ensuring that the line size (Line CD) meets the process requirements. In the second cycle step, by performing the removal step before the deposition step, it can be ensured that the load effect does not increase with the increase of the etching depth. Therefore, the groove etching method provided by the present invention can obtain a more vertical etching morphology through the combined use of the above two cycle steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A groove etching morphology image obtained by using an existing etching method;

[0028] Figure 2 An etching topography diagram for etching a high aspect ratio trench on a substrate;

[0029] Figure 3A A flowchart of a trench etching method provided by an embodiment of the present invention;

[0030] Figure 3B A cross-sectional view of an ICP device used in an embodiment of the present invention;

[0031] Figure 4 The upper electrode power signal and the lower electrode power signal used in the embodiment of the present invention are both waveform diagrams of radio frequency pulse signals;

[0032] Figure 5 The upper electrode power signal used in the embodiment of the present invention is a waveform diagram of a radio frequency continuous signal;

[0033] Fig. 6A This is an electron microscope scanning image of the groove etching morphology obtained by the first etching method;

[0034] Figure 6B The electron microscope scanning image of the groove etching morphology obtained by the second etching method;

[0035] Figure 6C The electron microscope scanning image of the groove etching morphology obtained by the third etching method;

[0036] Fig.6D The electron microscope scanning image of the groove etching morphology obtained by the fourth etching method;

[0037] Fig. 6E This is a scanning electron microscope image of the groove etching morphology obtained using the fifth etching method. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to better understand the technical solution of the present invention, the trench etching method provided by the present invention is described in detail below in conjunction with the accompanying drawings.

[0039] An embodiment of the present invention provides a trench etching method for etching a trench on a substrate. Taking the use of an ICP (Inductive Coupled Plasma) etching device to etch a trench structure with a high aspect ratio on a substrate in a DRAM chip manufacturing process as an example, for a typical ICP device, such as Figure 3BAs shown, it generally includes a process chamber 1, an air inlet device (not shown in the figure), an upper electrode device and a lower electrode device, wherein the air inlet device is used to introduce etching gas into the process chamber 1; the upper electrode device includes a coil (used as an upper electrode) 8 arranged above the process chamber and an upper matcher 10 and an upper electrode power supply 9 electrically connected thereto, and the upper electrode power supply 9 loads an upper electrode power signal to the coil 8 through the upper matcher 10, so as to couple the RF power to the inside of the process chamber 4 through the coil 8 through the dielectric window 7, so as to be able to excite the etching gas in the process chamber 1 to form a plasma 6. The lower electrode device includes a pedestal (used as a lower electrode) 4 arranged in the process chamber 1 and a lower matcher 3 and a lower electrode power supply 2 electrically connected thereto, and the lower electrode power supply 2 loads a lower electrode power signal to the pedestal 4 through the lower matcher 3, so as to form a negative bias on the surface of the substrate 5, so as to attract the plasma to move to the surface of the substrate 5 and etch it. Of course, in practical applications, the trench etching method provided in the embodiment of the present invention can also use etching equipment of other structures, and the embodiment of the present invention has no special restrictions on this.

[0040] like Figure 2 As shown, before etching a high aspect ratio trench structure on a substrate, a mask layer with a specified pattern is formed on the substrate (Sisub), and the mask layer includes, for example, a silicon dioxide (OX) layer and a polysilicon (Poly) layer thereon. Of course, in practical applications, other types of mask layers may also be used according to different process requirements, and the embodiments of the present invention have no particular limitations on this.

[0041] Then, the substrate is subjected to a high aspect ratio etching process using an ICP etching device. For this process, Figure 2 As shown in the figure, the main parameters after etching include line CD, micro-loading effect (Depth1-Depth2) and etching profile. In addition, the target etching depth required by the process is nearly 300nm, the narrowest opening width is about 15nm, and the aspect ratio is about 20. For the etching process of high aspect ratio trench structure using ICP equipment, how to make the above main parameters meet the process requirements is a great challenge. However, as Figure 1 As shown, the existing etching method mainly has the following problems:

[0042] First, as the etching depth increases, the byproducts caused by the high aspect ratio have difficulty entering and exiting the grooves, resulting in a serious micro-loading effect (mainly manifested in the different etching depths of grooves of different sizes on the same wafer, with wide grooves having a deep etching depth and narrow grooves having a shallow etching depth);

[0043] Secondly, when Cl2 is used as the etching gas, although the etching selectivity of the mask can be improved, due to its isotropic etching performance, the width of the top of the groove (space CD) will be increased, resulting in a decrease in the line size (LineCD) at the top.

[0044] To solve the above problems, see Figure 3A The trench etching method provided by the embodiment of the present invention includes a first cycle step S1 and a second cycle step S2, both of which include an etching step ME for etching a trench on a substrate, a deposition step DEP for forming a protective layer on a sidewall of the trench, and a removal step BT for removing byproducts at the bottom of the trench (e.g., oxidation products generated by O2 and Si in the deposition step DEP);

[0045] In the first cycle step S1, the etching step ME, the deposition step DEP and the removal step BT are sequentially cycled;

[0046] In the second cycle step S2, the etching step ME, the removal step BT and the deposition step DEP are executed in sequence.

[0047] Optionally, the substrate is, for example, a silicon substrate.

[0048] By adopting the above two cycle steps, and making the two perform the etching step ME, the deposition step DEP and the removal step BT in different orders, specifically, in the first cycle step S1, by performing the deposition step DEP before the removal step BT, a thicker protective material can be formed at the top of the groove, which helps to increase the sidewall protection of the top of the groove and reduce lateral etching, thereby avoiding the width of the top of the groove (space CD) being too large and ensuring that the line size (Line CD) meets the process requirements. In the second cycle step S2, by performing the removal step BT before the deposition step DEP, it can be ensured that the load effect will not increase with the increase of the etching depth. Therefore, the groove etching method provided by the embodiment of the present invention can obtain a more vertical etching morphology through the combined use of the above two cycle steps.

[0049] For the etching process of high aspect ratio trench structures using ICP equipment, in order to obtain the deep trench morphology (more vertical etching morphology) and micro-loading effect that meet the requirements, three main problems need to be solved: 1) high ion energy; 2) high mask selectivity; 3) control of the sidewall angle. During the plasma etching process, negative charges will be generated on the top of the trench sidewall. If the ion energy is too low, the positive ions in the plasma will be attracted by the negative charges and move toward the sidewalls, causing discontinuous lateral etching of the trench sidewalls. In addition, the negative charges will prevent the ions from reaching the bottom of the trench for etching, resulting in a decrease in the etching rate. In this regard, the prior art uses a method of increasing the ion energy to solve the above problems, but increasing the ion energy will bombard the mask layer, causing it to disappear before the etching is completed. In order to solve this problem, in some optional embodiments, in the etching step ME of the first cycle step S1 and the second cycle step S2, the upper electrode power signal loaded on the upper electrode and the lower electrode power signal loaded on the lower electrode are both pulsed radio frequency signals (the waveforms of the two are as shown in FIG. 1 ). Figure 4 As shown), and the signal output period in the cycle of the upper electrode power signal is synchronized with the signal output period in the cycle of the lower electrode power signal.

[0050] Optional, such as Figure 4 As shown, the frequency of the upper electrode power supply (for example, 13.56MHz) is higher than the frequency of the lower electrode power supply (for example, 2MHz), the period T1 of the upper electrode power signal includes a signal output period (i.e., an on period when the voltage is not 0V) t11 and a signal off period (i.e., an off period when the voltage is 0V) t12; the period T2 of the lower electrode power supply includes a signal output period (i.e., an on period when the voltage is not 0V) t21 and a signal off period (i.e., an off period when the voltage is 0V) t22, and the signal output period t11 of the period T1 of the upper electrode power signal is synchronized with the signal output period t21 of the period T2 of the lower electrode power signal, that is, the upper electrode power supply and the lower electrode power supply output signals synchronously, that is, the upper electrode power supply and the lower electrode power supply are turned on or off at the same time.

[0051] During the signal output period when the upper electrode power supply and the lower electrode power supply are turned on at the same time, the etching of the substrate will produce reaction by-products and polymers. During the signal off period when the upper electrode power supply and the lower electrode power supply are turned off at the same time, the vacuum pump can extract some of the reaction by-products and polymers previously produced from the process chamber. Since the upper electrode power supply and the lower electrode power supply do not output RF power during the signal off period, no new reaction by-products and polymers will be produced at this time, thereby effectively avoiding the accumulation of reaction by-products and polymers. In the later stage of the signal off period in the cycle, the negatively charged particles have been transformed from electrons to negative ions, and the plasma components have also been transformed from the original electrons and ions to positive ions and negative ions. The positive and negative ion fluxes are basically the same, and the sheath near the surface completely collapses. A large flux of negative ions can reach the bottom of the substrate, thereby balancing the accumulation of positive charges here, ensuring that in the initial stage of the next signal output period, there is sufficient positive ion flux at the bottom of the substrate for continuous etching. Therefore, the steps of plasma generation, etching, and by-product extraction during the etching process can be relatively effectively controlled, thereby effectively improving the micro-load effect.

[0052] In some other optional embodiments, the upper electrode power signal applied to the upper electrode is a radio frequency continuous signal (whose waveform is as shown in FIG. Figure 5 As shown), the lower electrode power signal loaded to the lower electrode is a radio frequency pulse signal (its waveform is as shown Figure 4 The lower electrode power signal loaded on the lower electrode is a radio frequency pulse signal, which can also play a role in improving the micro-load effect.

[0053] It should be noted that in actual applications, according to specific needs, the upper electrode power supply and the lower electrode power supply can switch between outputting RF pulse signals and outputting RF continuous signals when switching in different steps, that is, both can selectively output RF pulse signals or RF continuous signals.

[0054] In some optional embodiments, the duty cycle of the pulsed RF signal is greater than or equal to 5% and less than or equal to 30%. By setting the duty cycle within this range, it is possible to avoid the accumulation of reaction byproducts and polymers due to a large duty cycle, effectively improve the micro-loading effect, and avoid a low etching rate due to a small duty cycle.

[0055] In some optional embodiments, an inductively coupled plasma etching device (eg Figure 3BThe ICP device shown in the figure) is used to carry out the groove etching method provided by the embodiment of the present invention, and the frequency of the lower electrode power supply 2 used to load the lower electrode power signal of the inductively coupled plasma etching device is lower than the frequency of the upper electrode power supply 9 used to load the upper electrode power signal. For example, the frequency of the lower electrode power supply 2 is 2MHz. By adopting a lower frequency, the lower electrode power supply 2 can have a higher ion energy, which helps to obtain a higher aspect ratio when etching grooves or holes, and effectively reduces the loading effect (Loading Effect), such as the micro-load effect (ARDE) related to the etching aspect ratio. In addition, by adopting a lower frequency, the lower electrode power supply 2 can obtain a narrower ion energy distribution range and a lower ion energy peak value, thereby not only effectively reducing the plasma induced damage generated during the etching process, but also reducing the ion divergence angle, which is more suitable for etching grooves or holes with high aspect ratios. Optionally, the upper electrode power supply 9 and the lower electrode power supply 2 can output radio frequency pulse signals synchronously, that is, on the basis of realizing that the upper electrode power supply 9 and the lower electrode power supply 2 are turned on or off at the same time, combined with the use of a lower electrode power supply with a lower frequency, the reaction gas and by-products can be freely entered and exited in the groove, thereby effectively reducing the load effect. The frequency of the upper electrode power supply can be set according to specific needs, for example, 13.56MHz.

[0056] It should be noted that, in practical applications, according to specific needs, the upper electrode power supply 9 and the lower electrode power supply 2 can switch between outputting RF pulse signals and outputting RF continuous signals when switching between different etching steps, that is, both can selectively output RF pulse signals or RF continuous signals. In addition, the upper electrode power supply 9 and the lower electrode power supply 2 can also switch between different high and low frequencies.

[0057] In some optional embodiments, the etching gas flow rate used in the etching step ME of the first cycle step S1 is less than the etching gas flow rate used in the etching step ME of the second cycle step S2. The etching step ME of the first cycle step S1 can reduce the lateral etching of the sidewalls at the top of the groove by adopting a lower etching gas flow rate, thereby avoiding the width of the top of the groove (space CD) being too large and ensuring that the line size (Line CD) meets the process requirements. The etching step ME of the second cycle step S2 can increase the etching rate by adopting a higher etching gas flow rate. The etching gas, for example, includes Cl2, which is used as the main etching gas. Optionally, in the etching step ME of the first cycle step S1, the flow rate of Cl2 is greater than or equal to 150sccm and less than or equal to 250sccm. In the etching step ME of the second cycle step S2, the flow rate of Cl2 is greater than or equal to 300sccm and less than or equal to 600sccm.

[0058] In some optional embodiments, as the number of cycles of the etching step ME, the removal step BT and the deposition step DEP in the second cycle step S2 increases, the flow rate of the etching gas used in the etching step ME of the second cycle step S2 increases gradually to gradually increase the etching rate while ensuring the verticality of the etching morphology.

[0059] In some optional embodiments, by appropriately increasing the lower electrode power in the removal step BT of the first cycle step S1, it is beneficial to remove the vertical byproducts and reduce the reaction etching between the plasma and the sidewalls, so that the removal effect of the byproducts can be further improved, and the protection of the groove sidewalls can be enhanced. Optionally, the lower electrode power used in the removal step BT of the first cycle step S1 is greater than or equal to 50W and less than or equal to 300W. In addition, the lower electrode power used in the removal step BT of the second cycle step S2 is greater than or equal to 50W and less than or equal to 100W.

[0060] In some optional embodiments, in the etching step ME, the deposition step DEP and the removal step BT, while the etching gas is introduced into the process chamber, an oxidizing gas, such as oxygen, is also introduced into the process chamber; the flow rate of the oxidizing gas used in the etching step ME of the first cycle step S1 is greater than the flow rate of the oxidizing gas used in the etching step ME of the second cycle step S2. The etching step ME of the above-mentioned first cycle step S1 can enhance the protection of the top of the groove sidewall by adopting a higher oxidizing gas flow rate, thereby further reducing the lateral etching of the groove top sidewall. Optionally, in the etching step ME of the above-mentioned first cycle step S1, the flow rate of O2 is greater than or equal to 5sccm and less than or equal to 30sccm. In the etching step ME of the above-mentioned second cycle step S2, the flow rate of O2 is greater than or equal to 5sccm and less than or equal to 20sccm.

[0061] In some optional embodiments, in the etching step ME, the deposition step DEP and the removal step BT, while the etching gas and the oxidizing gas are introduced into the process chamber, nitrogen is also introduced into the process chamber. In this way, SiOxNy byproducts can be formed on the sidewalls of the trenches to protect the sidewalls of the trenches, thereby obtaining a smoother etched morphology surface and avoiding bowing. The flow rate of N2 is greater than or equal to 5 sccm and less than or equal to 20 sccm.

[0062] In some optional embodiments, the upper electrode power used in the etching step ME of the second cycle step S2 is greater than the upper electrode power used in the etching step ME of the first cycle step S1. In some optional embodiments, the lower electrode power used in the etching step ME of the second cycle step S2 is greater than the lower electrode power used in the etching step ME of the first cycle step S1. On the basis of introducing nitrogen into the process chamber to form SiOxNy byproducts on the sidewalls of the grooves, by making the etching step ME of the first cycle step S1 use a smaller upper electrode power and / or lower electrode power relative to the etching step ME of the second cycle step S2, the lateral etching can be further reduced to avoid increasing the width (space CD) of the top of the groove, resulting in a reduction in the line size (Line CD) at the top. Optionally, the upper electrode power used in the etching step ME of the second cycle step S2 is greater than or equal to 50W and less than or equal to 1000W; the upper electrode power used in the etching step ME of the first cycle step S1 is greater than or equal to 50W and less than or equal to 300W.

[0063] In some optional embodiments, during the entire cycle of the first cycle step S1, the power of the lower electrode can be appropriately increased, which is conducive to removing the vertical byproducts and reducing the reaction etching of ions and the sidewalls of the groove. During the entire cycle of the second cycle step S2, the power of the lower electrode can be further increased relative to the first cycle step S1 to increase the plasma energy, thereby increasing the etching rate.

[0064] In some optional embodiments, in the first cycle step S1, the number of cycles of the etching step ME, the deposition step DEP and the removal step BT is greater than or equal to 1 and less than or equal to 3. For example, the number of cycles of the first cycle step S1 can be 2. In this way, the width of the top of the groove (space CD) can be prevented from being too large, and the line size (Line CD) can be ensured to meet the process requirements. In addition, optionally, in the second cycle step S2, the number of cycles of the etching step ME, the removal step BT and the deposition step DEP is greater than or equal to 4 and less than or equal to 9. For example, the number of cycles of the second cycle step S2 can be 7.

[0065] In a specific embodiment, whether it is the first cycle step S1 or the second cycle step S2, in the etching step ME, the chamber pressure is greater than 0mT and less than or equal to 300mT; the frequency of the upper electrode power supply is 13.56MHz, and it outputs a radio frequency continuous signal with a power greater than or equal to 50W and less than or equal to 3000W; the frequency of the lower electrode power supply is 2MHz, and it outputs a radio frequency pulse signal with a duty cycle greater than or equal to 5% and less than or equal to 30%. The etching gas includes Cl2, and N2, O2 and He are also introduced into the process chamber, wherein the gas flow rate of Cl2 accounts for greater than or equal to 80% and less than 100%, and the total gas flow rate is greater than or equal to 400sccm and less than or equal to 600sccm; the base is an electrostatic chuck, and its heating temperature is greater than or equal to 40°C and less than or equal to 60°C.

[0066] In the deposition step DEP, the chamber pressure is greater than 0mT and less than or equal to 300mT; the frequency of the upper electrode power supply is 13.56MHz, and it outputs a radio frequency continuous signal with a power greater than or equal to 50W and less than or equal to 3000W, preferably greater than or equal to 1000W and less than or equal to 2000W; the power output by the lower electrode power supply is 0W; the process gas introduced into the process chamber includes oxygen, and its flow rate is greater than or equal to 100sccm and less than or equal to 700sccm, preferably greater than or equal to 200sccm and less than or equal to 300sccm; the base is an electrostatic chuck, and its heating temperature is greater than or equal to 40°C and less than or equal to 60°C.

[0067] In the removal step BT, the chamber pressure is greater than 0mT and less than or equal to 300mT, preferably, greater than or equal to 5mT and less than or equal to 20mT; the frequencies of the upper electrode power supply and the lower electrode power supply are both 13.56MHz, and the RF continuous signal is output, and the power of the upper electrode power supply is greater than or equal to 300W and less than or equal to 500W; the etching gas includes a mixed gas of CHF3, He and O2, CHF3 is used as the main etching gas, and its gas flow rate accounts for greater than or equal to 80% and less than 100%; the total gas flow rate is greater than or equal to 50sccm and less than or equal to 200sccm, preferably, greater than or equal to 50sccm and less than or equal to 100sccm; the base is an electrostatic chuck, and its heating temperature is greater than or equal to 40°C and less than or equal to 60°C.

[0068] The following is a comparison of the trench etching method provided in the embodiment of the present invention with the etching morphologies obtained by several different etching methods. Specifically, Fig. 6A This is a scanning electron microscope image of the groove etching morphology obtained by the first etching method. Fig. 6A As shown, the first etching method adopts a one-step etching method, that is, only includes the etching step ME. The defects of the etching morphology obtained by this method are: a "neck shrinkage" phenomenon appears at the top of the groove, such as Fig. 6AAs shown in area A in the figure, the line size in this area (Line CD) is very small and almost broken.

[0069] Figure 6B This is a scanning electron microscope image of the groove etching morphology obtained by the second etching method. Figure 6B As shown, the second etching method uses the etching step ME and the deposition step DEP to etch in a manner of multiple cycles. The etching morphology obtained by this method has the following defects: the etching stops in the area B with a slightly larger aspect ratio.

[0070] Figure 6C This is a scanning electron microscope image of the groove etching morphology obtained by the third etching method. Figure 6C As shown in FIG. 1 , the third etching method uses the etching step ME and the removal step BT to perform etching in a multiple-cycle manner. The defects of the etching morphology obtained by this method are: the etching result similar to that of the first etching method appears. Due to the lack of sidewall protection, a "neck shrinkage" phenomenon appears at the top of the trench, such as Figure 6C As shown in the C region in FIG. 1 , the Si top in this region is broken.

[0071] Fig.6D This is a scanning electron microscope image of the groove etching morphology obtained by the fourth etching method. Fig.6D As shown, the fourth etching method adopts the trench etching method provided by the embodiment of the present invention, but nitrogen is not introduced into the process chamber. Fig. 6E This is a scanning electron microscope image of the groove etching morphology obtained by the fifth etching method. Fig. 6E As shown, the trench etching method provided by the embodiment of the present invention is adopted, but nitrogen is introduced into the process chamber. Fig.6D and Fig. 6E As shown, the etching morphology obtained by the trench etching method provided by the embodiment of the present invention does not have the defects existing in the first to third etching methods mentioned above, and can effectively avoid the width of the top of the trench (space CD) being too large, ensure that the line size (Line CD) meets the process requirements, and obtain a more vertical etching morphology. In addition, compared Fig.6D and Fig. 6E It can be seen that by introducing nitrogen into the process chamber, a smoother etched surface can be obtained and bowing can be avoided.

[0072] In summary, the groove etching method provided by the embodiment of the present invention adopts two cycle steps, and the order of performing the etching step, the deposition step and the removal step is different. Specifically, in the first cycle step, by performing the deposition step before the removal step, a thicker protective material can be formed at the top of the groove, which helps to increase the sidewall protection of the top of the groove and reduce lateral etching, thereby avoiding the width of the top of the groove (space CD) being too large and ensuring that the line size (Line CD) meets the process requirements. In the second cycle step, by performing the removal step before the deposition step, it can be ensured that the load effect does not increase with the increase of the etching depth. Therefore, the groove etching method provided by the present invention can obtain a more vertical etching morphology through the combined use of the above two cycle steps.

[0073] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, but the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A trench etching method, characterized in that: The method comprises a first cycle step and a second cycle step, both of which comprise an etching step for etching a trench on a substrate, a deposition step for forming a protective layer on a sidewall of the trench, and a removal step for removing byproducts at a bottom of the trench; In the first cycle step, the etching step, the deposition step and the removal step are sequentially and cyclically performed; In the second cycle step, the etching step, the removal step and the deposition step are performed in sequence and in a cycle.

2. The trench etching method according to claim 1, characterized in that: The trench etching method is performed using an inductively coupled plasma etching device, wherein the frequency of a lower electrode power supply used to load a lower electrode power signal in the inductively coupled plasma etching device is lower than the frequency of an upper electrode power supply used to load an upper electrode power signal.

3. The trench etching method according to claim 2, characterized in that: In the etching step, the upper electrode power signal is a radio frequency continuous signal, and the lower electrode power signal is a radio frequency pulse signal; or, The upper electrode power signal and the lower electrode power signal are both pulsed radio frequency signals, and a signal output period in a cycle of the upper electrode power signal is synchronized with a signal output period in a cycle of the lower electrode power signal.

4. The trench etching method according to claim 3, characterized in that: The duty cycle of the pulsed radio frequency signal is greater than or equal to 5% and less than or equal to 30%.

5. The trench etching method according to any one of claims 1 to 4, characterized in that: The flow rate of the etching gas used in the etching step of the first cycle step is smaller than the flow rate of the etching gas used in the etching step of the second cycle step.

6. The trench etching method according to claim 5, characterized in that: As the number of cycles of sequentially executing the etching step, the removal step and the deposition step in the second cycle step increases, the flow rate of the etching gas used in the etching step of the second cycle step increases.

7. The trench etching method according to any one of claims 1 to 4, characterized in that: The lower electrode power used in the removal step of the first cycle step is greater than or equal to 50W and less than or equal to 300W.

8. The trench etching method according to any one of claims 1 to 4, characterized in that: In the etching step, the deposition step and the removal step of the first cycle step and the second cycle step, while the etching gas is introduced into the process chamber, an oxidizing gas is also introduced into the process chamber; The flow rate of the oxidizing gas used in the etching step of the first cycle step is greater than the flow rate of the oxidizing gas used in the etching step of the second cycle step.

9. The trench etching method according to claim 8, characterized in that: In the etching step of the first cycle step and the second cycle step, nitrogen gas is introduced into the process chamber while the etching gas and the oxidizing gas are introduced into the process chamber.

10. The trench etching method according to claim 9, characterized in that: The upper electrode power used in the etching step of the second cycle step is greater than the upper electrode power used in the etching step of the first cycle step.

11. The trench etching method according to claim 9, characterized in that: The power of the lower electrode used in the etching step of the second cycle step is greater than the power of the lower electrode used in the etching step of the first cycle step.

12. The trench etching method according to any one of claims 1 to 4, characterized in that: In the first cycle step, the number of cycles of sequentially executing the etching step, the deposition step and the removal step is greater than or equal to 1 and less than or equal to 3; and / or, In the second cycle step, the etching step, the removal step and the deposition step are sequentially executed in a cycle for a number of times greater than or equal to 4 and less than or equal to 9.

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