Etching method and plasma etching apparatus

Abstract

The application discloses an etching method and a plasma etching device. The etching method comprises the following steps: providing a reaction cavity, and placing a substrate in the reaction cavity; etching the substrate at 0 DEG C or below; and raising the temperature of the substrate to 60 DEG C or above, so that by-products deposited on the substrate are discharged in a gaseous form. The etching step and the temperature raising step are alternately performed. After the etching is performed for a period of time, the temperature of the substrate is raised to 60 DEG C or above, so that the by-products originally adhered to the substrate are discharged from the substrate, thereby improving the etching efficiency. The etching step and the temperature raising step are alternately and cyclically performed, so that the etching speed of each etching step can be maintained faster, and the advantages of low-temperature etching can be fully exerted.

Description

Technical Field

[0001] This invention relates to the field of semiconductors, and more specifically to an etching method and a plasma etching apparatus. Background Technology

[0002] With the development of semiconductor technology, device sizes are becoming smaller and device stacking heights are increasing. To etch high aspect ratio recessed structures on substrates, low-temperature etching is commonly used. Low-temperature etching refers to etching operations performed at temperatures below 0°C, and can be used for silicon etching or dielectric etching. At low temperatures, the adhesion coefficient of etching gases is much higher than at room temperature, making it easier for them to deposit on the sidewalls and bottom of the recessed structure, thus promoting etching.

[0003] The etching time for low-temperature etching typically exceeds 30 minutes. However, as the etching time continues, the thermal effect of the plasma causes the substrate temperature to gradually rise, making it increasingly difficult for the etching gas to deposit. Furthermore, byproducts generated during the etching process gradually accumulate, hindering the reaction between the etching gas and the target material within the recessed structure, thus reducing etching efficiency. Summary of the Invention

[0004] The purpose of this invention is to provide an etching method with a fast etching speed to obtain a substrate with a high aspect ratio and high collimation of a recessed structure.

[0005] To achieve the above objectives, the present invention provides an etching method, comprising:

[0006] A reaction chamber is provided, and a substrate is placed inside the reaction chamber;

[0007] Etching step: Etch the substrate at a temperature below 0°C;

[0008] Heating step: The substrate is heated to above 60°C to allow the byproducts deposited on the substrate to be discharged in gaseous form;

[0009] The etching step and the heating step are performed alternately.

[0010] Optionally, the time ratio of the etching step to the heating step is greater than or equal to 1.

[0011] Optionally, the etching step takes more than 300 seconds.

[0012] Optionally, the etching step takes less than 1800 seconds.

[0013] Optionally, the etching step includes etching a recessed structure on the substrate, wherein the aspect ratio of the recessed structure is greater than or equal to 40.

[0014] Optionally, the recessed structure is divided into n segments along the depth direction, and the total time of the etching step of the (k-1)th segment of the recessed structure is less than the total time of the etching step of the kth segment of the recessed structure; where n≥2, 2≤k≤n, and n and k are integers.

[0015] Optionally, the etching step and the heating step are alternated at least three times.

[0016] Optionally, the heating step includes: raising the substrate so that it is close to the gas spray head at the top of the reaction chamber, and heating the substrate to above 60°C.

[0017] Optionally, the heating step includes: providing a heating chamber, transferring the substrate into the heating chamber, and heating the substrate to above 60°C.

[0018] Optionally, the heating step includes: reducing the pressure of the heat-conducting gas on the back of the substrate to raise the temperature of the substrate to above 60°C.

[0019] Optionally, in the etching step, the etching gas introduced into the reaction chamber comprises:

[0020] C x F y C x H y F z One or more of the following, where x is greater than or equal to 1, y is greater than or equal to 1, z is greater than or equal to 1, and x, y, and z are all positive integers.

[0021] Optionally, the etching gas further comprises a halogen-containing gas, which includes one or more of HBr, HI, Br2 or I2.

[0022] Optionally, the byproducts consist of any one or more elements selected from Si, O, I, Br, or F.

[0023] The present invention also provides a plasma etching apparatus, comprising:

[0024] reaction chamber;

[0025] A base is provided inside the reaction chamber, and the substrate is placed on the base. A cooling device is provided inside the base to cool the substrate, ensuring that the etching step is performed below 0°C.

[0026] A heating device is used to heat the substrate to above 60°C.

[0027] Optionally, the heating device includes a gas spray head, which is located inside the reaction chamber and is disposed opposite to the base;

[0028] The base is provided with lifting pins for lifting the substrate, so that the substrate is away from the base and close to the gas spray head, and the substrate is heated to above 60°C.

[0029] Optionally, the heating device includes a heating chamber, which transfers the substrate from the reaction chamber to the heating chamber, thereby heating the substrate to above 60°C.

[0030] Optionally, the cooling device includes a cooling pipe disposed within the base, the cooling pipe being filled with a refrigerant, and the bottom surface of the substrate being in contact with the refrigerant, so that the etching step is performed below 0°C.

[0031] Optionally, the temperature of the refrigerant is not higher than -60°C.

[0032] Optionally, a gas transmission channel is provided inside the base, the gas transmission channel being used to transmit heat-conducting gas to the gap between the substrate and the base.

[0033] The beneficial effects of this invention are as follows:

[0034] (1) After etching has been performed for a period of time, the present invention heats the substrate to above 60°C by providing an additional heat source, which reaches the temperature at which byproducts can escape, so that the byproducts that were originally attached to the substrate can be discharged from the substrate, which is conducive to the etching gas and the substrate to be etched being in full contact, thereby improving the etching efficiency.

[0035] (2) The etching step and the heating step of the present invention are carried out alternately and cyclically. The long continuous etching is divided into multiple short etching steps by means of intervening heating heat treatment. In the several etching steps that are spaced apart from each other, at the beginning of each etching step, the etching gas is collected again and deposited and adsorbed on the substrate surface. Compared with continuous etching, each short etching step can maintain a faster etching speed and give full play to the advantages of low temperature etching. Attached Figure Description

[0036] Figure 1 A flowchart of the etching method provided by the present invention.

[0037] Figure 2 This is a schematic diagram of the plasma etching apparatus provided by the present invention.

[0038] Figure 3 This is a schematic diagram of the etching process according to an embodiment of the present invention.

[0039] Figure 4 This is a graph showing the change of substrate temperature over time in an embodiment of the present invention.

[0040] Figure 5 This is a graph showing the etching rate versus time in an embodiment of the present invention.

[0041] Figure 6 This is a schematic diagram of the etching process for comparison.

[0042] Figure 7 This is a comparative graph showing the temperature of the substrate changing over time.

[0043] Figure 8 This is a graph showing the etching rate as a function of time, serving as a comparative example.

[0044] Figure 9 This is an electron microscope image of the substrate obtained in an embodiment of the present invention.

[0045] Figure 10 This is an electron microscope image of the substrate obtained for comparison.

[0046] In the diagram, 100 is the reaction chamber, 110 is the base, 120 is the electrostatic chuck, 130 is the gas spray head, 140 is the cooling pipe, 200 is the recessed structure, 210 is the etching gas, and W is the substrate. Detailed Implementation

[0047] 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.

[0048] In the description of this invention, it should be noted that the terms "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0049] like Figure 1 As shown, the present invention provides an etching method, comprising:

[0050] S1: A reaction chamber is provided, and a substrate is placed inside the reaction chamber.

[0051] The reaction chamber is provided with a base, and the substrate is placed on the base. The base is provided with a cooling device for cooling the substrate to below 0°C and a heating device for heating the substrate to 60°C.

[0052] S2: Etching step: Etching the substrate at a temperature below 0°C.

[0053] The substrate is placed in a low-temperature environment below 0°C, and an etching gas is introduced. The etching gas has a high adhesion coefficient at low temperatures, making it easy to adsorb and deposit on the substrate surface to form a thin film. When the concentration of the etching gas reaches the required level, an radio frequency signal is provided to dissociate the etching gas into plasma. This plasma is deposited and adsorbed onto the surface of the substrate to be etched, reacting with the substrate to etch it.

[0054] The method provided by this invention can be used to etch polysilicon and silicon oxide stacks in 3D NAND, silicon oxide and silicon nitride stacks, and memory in DRAM, etc. The etching step includes: etching a recessed structure on the substrate along the stacking direction perpendicular to each stack, wherein the aspect ratio of the recessed structure is greater than or equal to 40.

[0055] In some embodiments, the etching gas introduced into the reaction chamber contains C x F y C x H y F z One or more of the following, wherein x is greater than or equal to 1, y is greater than or equal to 1, z is greater than or equal to 1, and x, y, and z are all positive numbers. It also includes: a halogen-containing gas, wherein the halogen-containing gas includes one or more of HBr, HI, Br2, or I2.

[0056] S3: Heating step: Heating the substrate to above 60°C to allow the byproducts deposited on the substrate to be discharged in gaseous form.

[0057] As etching progresses, the accumulation of byproducts on the substrate increases, hindering the contact between the etching gas and the substrate, thereby reducing the reaction rate between the etching gas and the material to be etched on the substrate surface. The byproducts generated on the substrate consist of one or more elements selected from Si, O, I, Br, or F. In room-temperature etching, the byproducts are gaseous and can be quickly expelled from the substrate. However, in low-temperature etching, the temperature is lower than that of room-temperature etching, increasing the adhesion coefficient of the byproducts and making them more likely to adhere to the substrate. Furthermore, the deposited etching gas only ignites and dissociates when it reaches a sufficiently high reaction concentration. Therefore, in the initial stage of the etching process, the amount of etching gas deposited on the substrate is large, resulting in sufficient contact and a rapid reaction, leading to a rapid formation rate of byproducts. Even if a small amount of byproducts can be expelled from the substrate, the expulsion rate is much lower than the formation rate, causing byproducts to gradually accumulate at the bottom and sidewalls of the recessed structure, hindering the contact between the etching gas and the substrate to be etched, and gradually reducing the reaction rate.

[0058] To improve etching efficiency, this invention raises the substrate temperature to above 60°C after a certain period of etching, causing byproducts to be discharged from the substrate surface in gaseous form. Although the substrate temperature increases due to plasma thermal effects during the etching process, this temperature is insufficient to reach the byproduct escape temperature, and an additional heat source is still needed to raise the substrate temperature.

[0059] Cryogenic etching requires temperatures to be maintained below 0°C, but the heat generated by the ignition of plasma cannot dissipate quickly, and the substrate temperature remains above 0°C as the etching process continues. Therefore, the etching and heating steps of this invention are performed alternately. After the heating step is completed, the etching process is repeated. By introducing a heating step to heat-treat the substrate, the long-term continuous etching is divided into multiple short-duration etching steps. At the beginning of each etching step, the substrate is placed in a low-temperature environment, allowing the etching gas to be redeposited on the substrate. Compared to continuous etching, each etching step has a higher reactant concentration and a faster etching rate, better leveraging the advantages of cryogenic etching. Optionally, the etching and heating steps are alternated at least three times. After the last etching step is completed, the etching process ends, and the heating step is no longer performed.

[0060] In some embodiments, the time ratio of the etching step to the heating step is greater than or equal to 1. Since the etching step and the heating step are performed alternately and cyclically, each cycle includes one etching step and one heating step. The time ratio of the etching step to the heating step being greater than or equal to 1 means that in any given cycle, the time ratio of the etching step to the heating step is greater than or equal to 1. Optionally, the time of the etching step is greater than 300 seconds and less than 1800 seconds.

[0061] In other embodiments, the recessed structure is divided into n segments along the depth direction, and the total time of the etching step of the (k-1)th segment of the recessed structure is less than the total time of the etching step of the kth segment of the recessed structure; where n≥2, 2≤k≤n, and n and k are integers.

[0062] In the initial stage of the etching step, the concentration of etching gas is highest, the deposition amount on the substrate surface is largest, the etching rate is fastest, and a large number of byproducts are generated in a short time. Furthermore, when the time for each etching step is the same, the average etching rate of the previous etching step is greater than that of the subsequent one, and the rate of byproduct generation in the previous etching step is also greater than that in the subsequent one. Etching proceeds perpendicular to the stacking direction of each layer of the substrate, from the substrate surface inwards. In this embodiment, the recessed structure is divided into n segments along the depth direction. The (k-1)th segment of the recessed structure forms before the kth segment. That is, when etching recessed structures of the same depth, the (k-1)th segment has a faster etching rate than the kth segment, resulting in faster accumulation of byproducts. Therefore, a heating step is required within a shorter etching time to remove the byproducts. Therefore, this embodiment limits the following: Although etching each recessed structure may involve several alternating cycles of etching and heating steps, and the duration of each etching step may not be exactly the same, regardless of how the etching and heating steps alternate, the total time for etching the (k-1)th recessed structure is less than the total time for etching the kth recessed structure. The etching rate of the (k-1)th recessed structure is fast, and the byproduct accumulation rate is also fast; therefore, the etching time for this segment is limited to be shorter to prevent excessive accumulation of byproducts and avoid hindering the contact between the etching gas and the substrate. Conversely, the etching rate of the kth recessed structure is slower than that of the (k-1)th segment, and the byproduct accumulation rate is also slower. In this case, the total time for etching the kth recessed structure is extended, reducing the alternation frequency of etching and heating steps to improve etching efficiency.

[0063] In the heating step, the methods for heating the substrate to above 60°C include at least the following:

[0064] (1) Lift the substrate so that it is close to the gas spray head at the top of the reaction chamber. Since the gas spray head is equipped with a heater, the heat of the gas spray head is used to heat the substrate.

[0065] (2) A heating chamber is provided, the substrate is transferred to the heating chamber and heated, and then the substrate is transferred from the heating chamber back to the reaction chamber for etching.

[0066] (3) The pressure of the helium gas on the back of the electrostatic chuck can affect the temperature of the substrate. The higher the pressure of the helium gas on the back, the better the cooling effect. The pressure of the heat-conducting gas on the back of the substrate can be reduced to raise the temperature of the substrate.

[0067] like Figure 2As shown, the present invention also provides a plasma etching apparatus, comprising: a reaction chamber 100; a base 110 disposed within the reaction chamber 100, an electrostatic chuck 120 above the base 110, the substrate W being placed on the electrostatic chuck 120, a cooling device disposed within the base 110 for cooling the substrate so that the etching step is performed below 0°C; and a heating device for heating the substrate to above 60°C.

[0068] The base 110 is provided with a cooling pipe 140. In some embodiments, the cooling pipe 140 serves as a cooling device, and a refrigerant is introduced into the cooling pipe, with the bottom surface of the substrate W in contact with the refrigerant, so that the etching step is performed below 0°C. Optionally, the temperature of the refrigerant is not higher than -60°C.

[0069] For a capacitively coupled plasma (CCP) reactor, a gas spray head 130 is disposed opposite to the base within the reaction chamber 100. This gas spray head 130 is connected to a gas supply device for supplying reaction gas into the reaction chamber 100. In some embodiments, the gas spray head 130 serves as a heating device, and a heater (not shown) is disposed inside the gas spray head 130. During the heating step, a lifting pin disposed on the base 110 is used to lift the substrate W, moving it away from the base 110 and closer to the gas spray head 130. The heater inside the gas spray head 130 heats the gas spray head 130, raising the substrate W to a temperature above 60°C. After the heating step is completed, the lifting pin is lowered, and the substrate W moves closer to the base 110 until it is placed on the base 110, allowing the etching step to continue.

[0070] In some embodiments, the heating device includes a heating chamber independent of the reaction chamber 100. During the heating step, a robotic arm grasps the substrate W and moves it from the reaction chamber 100 to the heating chamber, raising the substrate W to above 60°C. After the heating step, the robotic arm moves the substrate back from the heating chamber to the reaction chamber 100 to continue the etching step. By using a robotic arm to transfer the substrate between the reaction chamber 100 and the heating chamber for the heating step, the substrate W can be accurately placed back into a specific position on the base 110, ensuring the safety of the next etching step.

[0071] In some embodiments, a gas transmission channel is provided within the base 110 for transmitting heat-conducting gas to the gap between the substrate W and the base 110. The heat-conducting gas may be helium or hydrogen. During the heating step, the pressure of the heat-conducting gas on the back side of the substrate is reduced to heat the substrate.

[0072] Example

[0073] This embodiment provides an etching method, including:

[0074] S1: Provides a... Figure 2 The reaction chamber shown contains a substrate.

[0075] S2: Etching step: Etching the substrate at a temperature below 0°C.

[0076] The substrate is placed in a low-temperature environment below 0°C, and an etching gas composed of CHF3, CH2F2, O2, NF3, and HBr is introduced, such as... Figure 3 As shown in (a), the bottom and sidewalls of the recessed structure 200 are deposited with deposits 210 due to low temperature. At this time, the main component of the deposits 210 is etching gas. The etching gas is dissociated into plasma to etch the substrate W.

[0077] S3: Heating step: Heating the substrate to above 60°C to allow the byproducts deposited on the substrate to be discharged in gaseous form.

[0078] like Figure 4 and Figure 5 As shown, as etching progresses, the main component of the deposit 210, formed at low temperature within the recessed structure 200, gradually changes from etching gas to byproducts. Newly introduced etching gas is difficult to deposit on the substrate W surface due to the obstruction of these byproducts, and the temperature rise caused solely by the plasma thermal effect is insufficient to remove the byproducts generated during the etching process from the substrate. These byproducts hinder the contact between the etching gas and the substrate W; therefore, the etching rate gradually decreases. At this point, the substrate temperature is raised to above 60°C, such as... Figure 3 As shown in (b), the main byproducts in deposit 210 are vaporized at high temperature and discharged from the recessed structure 200. After a period of time, once the byproducts have been discharged from the substrate, the substrate is placed back into a low-temperature environment. The substrate temperature drops sharply to the initial stage of the etching step. At this time, as shown in (b), Figure 3 As shown in (c), the etching gas 210 will condense and deposit again on the bottom and sidewalls of the recessed structure. When the concentration of the etching gas reaches the required level, it is ignited and dissociated, accelerating the etching rate and continuing to etch the recessed structure downwards until the desired level is achieved. Figure 3 (d) shows the target etching depth.

[0079] In this embodiment, each etching step lasts 600 seconds, and each heating step lasts 150 seconds. The etching and heating steps are alternated three times. Etching ends after the third etching step is completed. At this point, the morphology of the recessed structure is as follows: Figure 3 As shown in (d). The etching process consists of three etching steps and two heating steps, taking a total of 2100 seconds.

[0080] Comparative Example

[0081] A substrate is placed on the base of the reaction chamber and placed in a low-temperature environment below 0°C. An etching gas composed of CHF3 and HBr is then introduced. Figure 6 As shown in (a), the etching gas is dissociated into plasma to etch the substrate W. The etching process continues until the etching is complete. At this point, the morphology of the recessed structure is as follows: Figure 6 As shown in (b). Figure 7 and Figure 8 As shown, during the etching process, the temperature of the substrate gradually increases, and the deposits in the recessed structure of the substrate gradually transform into byproducts, hindering the entry of subsequent etching gases and causing the etching rate to gradually decrease. In this example, the etching step lasted for 2100 seconds.

[0082] Table 1 Comparison of substrate performance obtained from examples and comparative examples (unit: nm)

[0083]

[0084]

[0085] Figure 9 and Figure 10 The substrates used in the examples and comparative examples are shown in Table 1. The dimensions of the recessed structures on the two substrates are shown in Table 1. The maximum lateral dimension is the dimension at the widest point within the recessed structure, the bottom dimension is the width of the bottom of the recessed structure, the difference between the maximum lateral dimension and the bottom dimension represents the difference between the maximum width within the recessed structure and the width of the bottom of the recessed structure, and the etching depth is the depth of the recessed structure.

[0086] The embodiment utilizes multiple heating steps to break the continuous etching process into discontinuous etching steps. At the initial stage of each etching step, etching gas is deposited at the bottom of the recessed structure, making the width of the recessed structure more consistent in each etching step. In the comparative example, during continuous etching, the amount of etching gas deposited at the bottom of the recessed structure is reduced, and byproducts hinder the contact between the etching gas and the substrate, resulting in a sharper bottom morphology of the recessed structure. Compared to the comparative example, the embodiment has a smaller maximum lateral dimension, a wider bottom width, and a smaller difference between the maximum width and the bottom width, indicating that the sidewalls of the recessed structure are closer to vertical and have higher collimation.

[0087] The total etching time was the same for both the examples and the comparative examples. However, since the etching process in the examples also included a heating step, the actual etching time in the examples was shorter than that in the comparative examples. According to Table 1, the etching depth in the examples was deeper than that in the comparative examples, indicating that although the etching process in the examples sacrificed some etching time for heating, the higher reactant concentration and etching rate in the etching steps resulted in a higher aspect ratio for the substrates obtained in the examples. Furthermore, by further controlling the time ratio of the etching steps to the heating steps, the etching depth can be further increased. With essentially the same etching depth, substrates obtained through discontinuous multiple etching steps exhibited better morphology of the recessed structure than substrates obtained through continuous etching.

[0088] In summary, this invention provides an etching method in which, after etching for a period of time, the substrate is heated to above 60°C by providing an additional heat source, reaching the escape temperature of byproducts. This allows the byproducts originally adhering to the substrate to be discharged, and the etching gas can fully contact the surface of the substrate to be etched, thereby improving etching efficiency. The etching and heating steps of this invention are performed alternately and cyclically, dividing the long-term continuous etching into multiple short-duration etching steps through the intervention of heating heat treatment. Since the etching gas can be redeposited on the substrate surface in each etching step, compared with continuous etching, each short-duration etching step can maintain a faster etching rate, fully utilizing the advantages of low-temperature etching.

[0089] 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. An etching method, characterized in that, include: A reaction chamber is provided, and a substrate is placed inside the reaction chamber; Etching step: Etch the substrate at a temperature below 0°C; Heating step: The substrate is heated to above 60°C to allow the byproducts deposited on the substrate to be discharged in gaseous form; The etching step and the heating step are performed alternately; The heating step includes: The substrate is raised so that it is close to the gas spray head at the top of the reaction chamber, and the substrate is heated to above 60°C; or... A heating chamber is provided, and the substrate is transferred into the heating chamber to raise the temperature of the substrate to above 60°C.

2. The etching method as described in claim 1, characterized in that, The time ratio of the etching step to the heating step is greater than or equal to 1.

3. The etching method as described in claim 1, characterized in that, The etching step takes more than 300 seconds.

4. The etching method as described in claim 3, characterized in that, The etching step takes less than 1800 seconds.

5. The etching method as described in claim 1, characterized in that, The etching step includes etching a recessed structure on the substrate, wherein the aspect ratio of the recessed structure is greater than or equal to 40.

6. The etching method as described in claim 5, characterized in that, The recessed structure is divided into n segments along the depth direction. The total time of the etching step of the (k-1)th segment of the recessed structure is less than the total time of the etching step of the kth segment of the recessed structure. Wherein, n≥2, 2≤k≤n, and n and k are integers.

7. The etching method as described in claim 1, characterized in that, The etching step and the heating step are alternated at least 3 times.

8. The etching method as described in claim 1, characterized in that, The heating step includes: reducing the pressure of the heat-conducting gas on the back of the substrate to raise the temperature of the substrate to above 60°C.

9. The etching method as described in claim 1, characterized in that, In the etching step, the etching gas introduced into the reaction chamber comprises: C x F y C x H y F z One or more of the following, where x is greater than or equal to 1, y is greater than or equal to 1, z is greater than or equal to 1, and x, y, and z are all positive numbers.

10. The etching method as described in claim 9, characterized in that, The etching gas further includes a halogen-containing gas, which includes one or more of HBr, HI, Br2 or I2.

11. The etching method as described in claim 1, characterized in that, The byproducts consist of one or more elements selected from Si, O, I, Br, or F.

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