A method and apparatus for plasma etching based on pennis ionization

Abstract

The application relates to the technical field of semiconductor manufacturing, in particular to a plasma etching method and device based on Penning ionization. The method comprises the following steps: inputting inert gas into a reaction cavity to form metastable inert gas particles through radio frequency discharge; inputting fluorine-containing reaction gas into the reaction cavity to make the metastable inert gas particles and the fluorine-containing reaction gas have Penning ionization reaction to generate high-activity fluorine-based particles; and performing isotropic plasma etching treatment on a high-aspect-ratio structure of a semiconductor substrate placed in the reaction cavity by using the high-activity fluorine-based particles. The application introduces fluorine-containing reaction gas into the downstream area of the metastable inert gas to perform Penning ionization, greatly reduces the particle kinetic energy while maintaining high chemical activity, changes the etching process from the mixed dominance of physical bombardment and chemical reaction to the dominance of chemical reaction, and significantly improves etching uniformity and morphology precision.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and more specifically, to a plasma etching method and apparatus based on Penning ionization. Background Technology

[0002] In advanced integrated circuit (IC) manufacturing processes, especially in chip manufacturing at 14nm and below, dielectric etching, silicon etching, and related thin film removal are core process steps. The etching selectivity directly determines the structural accuracy and electrical performance of the device. The core objective of this step is to achieve precise etching of dielectric films such as silicon (Si), silicon dioxide (SiO2), and silicon nitride (SiN), while ensuring a high selectivity between target and non-target materials to meet the manufacturing requirements of high aspect ratio structures.

[0003] Currently, carbon tetrafluoride (CF4) plasma is widely used in the industry for the above etching process. Plasma is generated by directly dissociating CF4 gas through radio frequency discharge. Fluorine (F) atoms in the plasma are used as the main etching species to react with the substrate material to achieve etching.

[0004] However, existing CF4 plasma etching processes have the following technical problems: On the one hand, the F atoms and CF atoms generated after CF4 gas is directly dissociated by radio frequency... x Free radicals and other particles have high kinetic energy and exhibit a non-selective physical bombardment effect during etching, resulting in a low selectivity for etching silicon to silicon nitride and silicon to silicon dioxide, making it impossible to achieve precise material etching. On the other hand, traditional direct dissociation methods are difficult to precisely control the energy and activity of particles, resulting in poor etching uniformity, especially in the etching of high aspect ratio trench structures, which is prone to problems such as etching morphology distortion and sidewall damage.

[0005] In addition, the parameter control window of the traditional CF4 plasma etching process is narrow, making it difficult to improve the selectivity while ensuring the etching rate, and thus failing to meet the stringent requirements of advanced node IC processes for high selectivity and high uniformity etching.

[0006] Therefore, there is an urgent need to develop a new plasma etching process to achieve high selectivity and high uniformity in dielectric and silicon etching. Summary of the Invention

[0007] The purpose of this invention is to provide a plasma etching method and apparatus based on Penning ionization, which solves the problems of low selectivity, poor etching uniformity, and distortion of etching morphology of high aspect ratio structures caused by excessively high particle kinetic energy in the existing CF4 plasma etching process.

[0008] To achieve the above objectives, the present invention provides a plasma etching method based on Penning ionization, comprising: An inert gas is introduced into the reaction chamber, and metastable inert gas particles are formed through radio frequency discharge; Fluorine-containing reactive gas is introduced into the reaction chamber, causing the metastable inert gas particles to undergo a Penning ionization reaction with the fluorine-containing reactive gas, producing highly active fluorine-based particles; The high aspect ratio structure of the semiconductor substrate placed in the reaction chamber is subjected to isotropic plasma etching using the highly active fluorine-based particles. In this process, the fluorine-containing reactive gas is introduced into a downstream region far from the plasma generation region, and the Penning ionization reaction is carried out in a region without an electric field, so that the highly active fluorine-based particles are not accelerated by an electric field from the time they are generated until they reach the surface of the semiconductor substrate.

[0009] In some embodiments, in the step of forming metastable inert gas particles by radio frequency discharge, pulsed radio frequency is used to excite the inert gas plasma; In the step of introducing the fluorine-containing reactive gas into the reaction chamber, the introduction of the fluorine-containing reactive gas is synchronized with the phase of the radio frequency pulse, and is only introduced into the reaction chamber during the off period of the radio frequency pulse, so that the Penning ionization reaction takes place during the period without an electric field.

[0010] In some embodiments, the isotropic plasma etching process is achieved by the highly active fluorine-based particles undergoing a pure chemical reaction with the substrate material surface to generate volatile fluoride products; The highly active fluorine-based particles have a kinetic energy of less than 1 eV and a lifetime of not less than 100 ms.

[0011] In some embodiments, the isotropic plasma etching process includes, in sequence, an initial diffusion stage, a main etching stage, and a byproduct desorption stage. In the initial diffusion stage, the pressure in the reaction chamber is controlled within the first pressure range, and the flow ratio of inert gas to fluorine-containing reactive gas is within the first flow ratio range, so that highly active fluorine-based particles diffuse to the bottom of the high aspect ratio structure and establish a flat initial etching surface. During the main etching stage, the pressure in the reaction chamber is controlled within the second pressure range, and the flow ratio of inert gas to fluorine-containing reaction gas is controlled within the second flow ratio range to maintain a stable etching rate and a high etching selectivity. During the by-product desorption stage, the pressure in the reaction chamber is controlled within the third pressure range, while the temperature of the semiconductor substrate is increased to promote the desorption and discharge of etching by-products inside the high aspect ratio structure. The pressure levels of the first pressure zone, the second pressure zone, and the third pressure zone increase sequentially; the ratio of the first flow ratio zone is higher than the ratio of the second flow ratio zone; and the substrate temperature during the by-product desorption stage is higher than the substrate temperature during the initial diffusion stage and the main etching stage.

[0012] In some embodiments, in the step of introducing inert gas and fluorine-containing reactive gas into the reaction chamber, the two gases are introduced in a partitioned gas introduction manner. The inert gas is introduced into the plasma generation region through the first gas inlet, and the fluorine-containing reactive gas is introduced into the downstream region away from the plasma generation region through the second gas inlet, where it mixes with metastable inert gas particles diffused from the upstream and undergoes Penning ionization. By adjusting the gas flow ratio and inlet angle of the first gas inlet and the second gas inlet, uniform mixing and diffusion of the two gases can be achieved.

[0013] In some embodiments, the inert gas includes at least one of argon or helium; The fluorine-containing reactive gas includes carbon tetrafluoride; The highly active fluorine-based particles include at least one of fluorine atoms, carbide tetrafluoride cations, and fluorocarbon free radicals. The semiconductor substrate is made of at least one of silicon, silicon dioxide, or silicon nitride.

[0014] In some embodiments, the step of introducing an inert gas into the reaction chamber further includes: controlling the types of products of the Penning ionization reaction by selecting the type of inert gas; When helium is used as the inert gas, the Penning ionization reaction preferentially produces fluorine atoms and fluorocarbon radicals; When argon is used as the inert gas, the Penning ionization reaction preferentially produces carbon tetrafluoride cations.

[0015] In some embodiments, the semiconductor substrate includes a titanium nitride thin film, and the method further includes introducing nitrogen gas into the reaction chamber to regulate the etching uniformity of the titanium nitride thin film and the volatility of byproducts.

[0016] In some embodiments, the plasma etching process includes dielectric etching, silicon etching, or thin film removal.

[0017] To achieve the above objectives, the present invention provides a plasma etching apparatus for implementing the Penning ionization-based plasma etching method as described above, comprising: A reaction chamber is used to house a semiconductor substrate and provide space for the etching reaction. A radio frequency power supply, coupled to the reaction chamber, is used to excite and maintain inert gas plasma, generating metastable inert gas particles in the plasma generation region. The air intake system includes at least two independent air passages, which are used to input inert gas and fluorine-containing reactive gas into the reaction chamber respectively, so as to realize gas partitioning input and diffusion; The air intake system, through its air path spatial layout, introduces fluorine-containing reactive gas into a downstream region far from the plasma generation region, allowing the Penning ionization reaction to occur in a region without an electric field, thus achieving spatial decoupling between the plasma generation region and the Penning ionization reaction region.

[0018] In some embodiments, the intake system includes: The first gas inlet is located in the plasma generation zone of the reaction chamber and is used to introduce inert gas. The second gas inlet is located in the downstream lateral region of the reaction chamber and is used to introduce fluorine-containing reaction gas. The second gas inlet is inclined toward the substrate side to guide the fluorine-containing reactive gas downwards and prevent the gas from flowing back into the plasma generation area.

[0019] In some embodiments, the radio frequency power supply is a pulsed radio frequency power supply; The plasma etching apparatus also includes a synchronization control unit, which is connected to the pulse radio frequency power supply and the gas path control valve of the fluorine-containing reactive gas, respectively. The synchronization control unit is used to control the timing of the introduction of the fluorine-containing reactive gas to be synchronized with the phase of the radio frequency pulse, and to introduce the fluorine-containing reactive gas only during the off period of the radio frequency pulse.

[0020] In some embodiments, a substrate support unit is further provided within the reaction chamber: The substrate support unit integrates a temperature control element to adjust the temperature of the semiconductor substrate at different stages of the isotropic plasma etching process, thereby promoting the desorption of etching byproducts within the high aspect ratio structure.

[0021] This invention provides a plasma etching method and apparatus based on Penning ionization. By introducing a fluorine-containing reactive gas into the downstream region of a metastable inert gas for Penning ionization, the generated fluorine-based particles are not accelerated by an electric field before reaching the surface of the semiconductor substrate. This significantly reduces the particle kinetic energy while maintaining high chemical activity, transforming the etching process from one dominated by a mixture of physical bombardment and chemical reaction to one dominated by chemical reaction. This achieves high selectivity etching of materials such as silicon, silicon dioxide, and silicon nitride, and enables distortion-free and precise etching of high aspect ratio trench / hole structures. It significantly improves etching uniformity and morphology accuracy, meeting the stringent requirements of advanced node integrated circuit manufacturing for high selectivity, high uniformity, and high aspect ratio structure-adaptive etching. Attached Figure Description

[0022] The above and other features, properties and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings and embodiments, in which the same reference numerals always denote the same features, wherein: Figure 1 A step diagram of a plasma etching method based on Penning ionization according to an embodiment of the present invention is disclosed; Figure 2 A schematic diagram of the process and effect verification diagram of isotropic etching of TiN thin films based on F radicals according to an embodiment of the present invention are disclosed; Figure 3 A schematic diagram of a plasma etching apparatus according to an embodiment of the present invention is shown.

[0023] The meanings of the labels in the figures are as follows: 11. Reaction chamber; 21. RF power supply; 22 RF coils; 31 First gas inlet; 32 Second gas inlet; 41. Plasma generation region; 42. Penning ionization etching reaction zone; 51 Semiconductor substrate; 52 Substrate support unit. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0025] Existing plasma processing technologies are mostly applied to general planar surface treatment processes such as photoresist stripping, and are not specifically optimized for etching high aspect ratio structures of advanced semiconductor nodes of 14nm and below. Current solutions largely rely on multi-layer nozzle structures to physically filter ions to reduce particle energy, failing to avoid the electric field acceleration effect at the ionization source. This results in insufficient precision in particle energy control and a lack of precise control over the ionization path of fluorine-containing etching gases, diffusion behavior within high aspect ratio structures, and byproduct volatilization characteristics. Consequently, they cannot simultaneously meet the multiple requirements of advanced etching processes for high selectivity, low damage, and high aspect ratio morphology fidelity, making them unsuitable for high-precision etching scenarios such as dielectric etching, silicon etching, and metal nitride thin film planarization.

[0026] Unlike existing technologies, the plasma etching method based on Penning ionization proposed in this invention is specifically adapted for isotropic etching of high aspect ratio structures on advanced node semiconductor substrates of 14nm and below. It selectively excites fluorine-containing gases (such as CF4) to generate low-kinetic-energy fluorine-based particles, which then react chemically with silicon-based or metal nitride materials to generate volatile fluorides, achieving high selectivity etching of the target material. This process not only avoids physical damage to the substrate caused by high-energy particles but also achieves precise control over the etching rate, etching morphology, and byproduct volatility by adjusting the types and ratios of reactant gases. It is particularly suitable for high aspect ratio structure etching and thin film planarization.

[0027] Figure 1 A step diagram of a plasma etching method based on Penning ionization according to an embodiment of the present invention is disclosed, as follows: Figure 1 As shown, this invention provides a plasma etching method based on Penning ionization, comprising the following three core steps: S1: Inert gas is introduced into the reaction chamber, and metastable inert gas particles are formed through radio frequency discharge; S2: Fluorine-containing reactive gas is introduced into the reaction chamber, causing the metastable inert gas particles to undergo a Penning ionization reaction with the fluorine-containing reactive gas to generate highly active fluorine-based particles; the fluorine-containing reactive gas is introduced into a downstream region far from the plasma generation region, and the Penning ionization reaction takes place in a region without an electric field. The generated highly active fluorine-based particles are not accelerated by an electric field from generation to reaching the surface of the semiconductor substrate. The particle kinetic energy is less than 1 eV, and they participate in the etching reaction solely through chemical activity; S3: The high aspect ratio structure of the semiconductor substrate placed in the reaction chamber is subjected to isotropic plasma etching using the highly active fluorine-based particles, wherein the aspect ratio of the high aspect ratio structure is not less than 10:1.

[0028] This invention provides a plasma etching method based on Penning ionization, which generates active particles through the Penning ionization mechanism. While retaining high chemical activity, it significantly reduces the kinetic energy of the active particles, effectively solving the problems of low selectivity and poor etching uniformity caused by high particle kinetic energy in traditional CF4 plasma etching processes, and significantly improving the selectivity and controllability of the etching process.

[0029] In some embodiments, the plasma etching process specifically includes dielectric etching, silicon etching, or related thin film removal processes, and is applicable to etching processes of materials such as SiO2, SiN, Si, and TiN in advanced node IC manufacturing.

[0030] These steps will be described in detail below. It should be understood that, within the scope of this invention, the above-described technical features of this invention and the technical features specifically described below (such as in the embodiments) can be combined and related to each other to form preferred technical solutions.

[0031] Step S1: Formation of metastable inert gas particles

[0032] The core of this step is to generate a high concentration of stable metastable inert gas particles in the reaction chamber, providing an activation source for subsequent Penning ionization.

[0033] In some embodiments, the inert gas includes at least one of argon (Ar) or helium (He). Preferably, helium (He) is used to obtain a higher metastable energy (about 20 eV), thereby more efficiently exciting the subsequent Penning ionization reaction; argon (Ar) has a cost advantage and can be selected according to actual process requirements.

[0034] In some embodiments, the radio frequency discharge uses a pulsed radio frequency method to excite inert gas plasma. Inert gas is introduced through a first gas inlet at the top of the reaction chamber. This gas inlet path is configured to be far from the inlet area of ​​subsequent fluorine-containing reactive gases to prevent the fluorine-containing gases from directly entering the plasma generation region and being prematurely dissociated.

[0035] In some embodiments, an inductively coupled plasma (ICP) source is used as the radio frequency discharge method, with a bias power supply used to regulate the plasma distribution. The radio frequency power range can be set from 800 W to 3500 W, for example, 800 W, 1000 W, 1500 W, 2000 W, 3000 W, or 3500 W. The reaction chamber pressure can be controlled within the range of 1 mTorr to 500 mTorr, for example, 10 mTorr, 30 mTorr, 50 mTorr, 80 mTorr, or 100 mTorr, to maintain a stable plasma state. The commonly used pressure range for conventional etching processes is 10 mTorr to 100 mTorr. Those skilled in the art will understand that the above parameters are merely examples and can be adjusted according to specific process equipment and the object being processed.

[0036] In some embodiments, by adjusting the radio frequency power and gas flow rate, the inert gas is fully dissociated into metastable particles (He or Ar), with a concentration reaching 10¹²-10¹. 4 cm - ³.

[0037] This process controls the lifetime of metastable inert gas particles to the range of 100ms to 10s by adjusting the RF power and cavity pressure, which is much longer than the lifetime of traditional directly ionized particles. This ensures that metastable particles can fully diffuse to the bottom of trench / via structures with an aspect ratio of ≥30:1, avoiding premature annihilation inside the structure. This fundamentally guarantees the bottom etching rate and overall morphology uniformity of high aspect ratio structures, solving the aspect ratio-dependent etching rate (ARDE) problem of traditional processes.

[0038] This step, through zoned gas intake and control of radio frequency and bias power supply parameters, ensures that inert gas preferentially forms metastable particles, avoids direct ionization of fluorine-containing reactive gases by radio frequency, provides a sufficient and controllable activation source for subsequent Penning ionization, and reduces the generation of high-energy charged ions.

[0039] Step S2: Generate highly active fluorine-based particles via Penning ionization reaction

[0040] This step utilizes the metastable inert gas particles generated in step S1 to collide with the fluorine-containing reactive gas, thereby achieving Penning ionization and producing low-kinetic-energy, highly chemically active fluorine-based particles.

[0041] In some embodiments, the fluorine-containing reactive gas is introduced into the downstream region of the metastable inert gas particles.

[0042] Specifically, two types of gas are introduced in a partitioned gas intake manner: an inert gas is introduced into the plasma generation zone through the first gas inlet, and a fluorine-containing reactive gas is introduced into the downstream region far away from the plasma generation zone through the second gas inlet, so that it is far away from the plasma generation zone and thus basically avoids direct dissociation by radio frequency discharge.

[0043] In some embodiments, the second gas inlet is inclined toward the substrate side to guide the gas downward and further ensure that the fluorine-containing reactive gas does not flow back to the upstream plasma generation region; by adjusting the gas flow ratio and inlet angle of the first gas inlet and the second gas inlet, uniform mixing and diffusion of the two gases can be achieved.

[0044] Through this spatially separated gas intake method, the fluorine-containing reactive gas does not enter the radio frequency discharge coupling region at all. It only collides with metastable inert gas particles diffused from upstream in the downstream field-free region, achieving Penning ionization rather than direct radio frequency dissociation. This ensures that fluorine-based particles are generated solely through the collisional ionization of metastable particles, without being accelerated by the radio frequency electric field or bias electric field throughout the process, resulting in particle kinetic energy consistently below 1 eV.

[0045] In some embodiments, when using pulsed radio frequency, the input of the fluorine-containing reactive gas is synchronized with the phase of the radio frequency pulse. The fluorine-containing reactive gas is only input into the reaction chamber during the off period of the radio frequency pulse, so that the Penning ionization reaction takes place during the period without an electric field. This further ensures that the fluorine-based particles are not accelerated by the electric field from the time dimension, achieving dual protection of spatial isolation and temporal isolation.

[0046] In some embodiments, the fluorinated reactive gas is carbon tetrafluoride (CF4), and the CF4 flow rate can be set from several sccm to hundreds of sccm, and in a few high-volume production scenarios it can reach thousands of sccm. The conventional process flow rate is 40 sccm to 50 sccm, for example, 40 sccm or 50 sccm. The inert gas flow rate (such as Ar 200 sccm or He 500 sccm) is significantly higher than the CF4 flow rate to ensure that sufficient metastable particles participate in the collision.

[0047] Targeting the molecular bond energy characteristics of carbon tetrafluoride, this process achieves stepwise controllable dissociation through precise matching of the metastable particle excitation energy and the ionization energy of carbon tetrafluoride: firstly, Penning ionization is used to generate CF4. + It then gradually dissociates into CF3 through low-energy secondary electron collisions. CF2 By using fluorocarbon free radicals and fluorine atoms, excessive CF bond breaking can be avoided to generate non-volatile high-carbon fluoropolymers, thus optimizing the composition of byproducts from the reaction pathway.

[0048] In process control, the optimal flow ratio of inert gas to carbon tetrafluoride is 5:1 to 20:1. When the flow ratio is greater than 10:1, the proportion of fluorine atom generation increases, making it suitable for high-speed etching of silicon materials. When the flow ratio is 5:1 to 10:1, the proportion of fluorocarbon radicals increases, making it suitable for high-selectivity etching of materials such as silicon dioxide. Combined with coordinated control of chamber pressure (50–100 mTorr) and substrate temperature (25–100 °C), the volatile nature of byproducts such as SiF4 and low-molecular-weight fluorocarbons generated during etching can be ensured throughout the process, preventing deposition on the inner walls of high aspect ratio structures and broadening the process parameter window.

[0049] In some embodiments, the product types of the Penning ionization reaction are controlled by selecting the type of inert gas: when helium (He, metastable energy approximately 20 eV) is used as the inert gas, the Penning ionization reaction preferentially produces fluorine atoms and fluorocarbon radicals, which is suitable for high-speed etching scenarios; when argon (Ar, metastable energy approximately 11.5 eV) is used as the inert gas, the Penning ionization reaction preferentially produces carbon tetrafluoride cations (CF4). + ( ), which can be flexibly selected according to process requirements.

[0050] Penning ionization refers to the inelastic collisional ionization process in which metastable inert gas particles transfer their excitation energy to ground-state fluorine-containing reactive gas molecules, causing the fluorine-containing reactive gas molecules to ionize and generate charged particles and electrons. In this invention, metastable He or Ar molecules undergo Penning ionization with CF4 molecules, as shown in the following reaction formula: He +CF4→He+CF4 + +e - ; Ar +CF4→Ar+CF4 + +e - ; Subsequently, CF4 + Ions and secondary electrons can further initiate dissociation reactions, generating fluorine atoms (F) and fluorocarbon radicals (CF). x ) and carbon tetrafluoride cation (CF4) + In some embodiments, the highly active fluorine-based particles include at least one of fluorine atoms, carbide cations, and fluorocarbon radicals.

[0051] Through actual measurement and verification, the average kinetic energy of the fluorine-based particles generated by the spatial isolation scheme of the present invention is stable at 0.3~0.8eV, and the proportion of high-energy particles with kinetic energy greater than 2eV is less than 1%. This energy threshold is insufficient to break the main valence bonds of non-target materials such as Si-Si bonds and Si-N bonds. Therefore, it can achieve an etching selectivity several times that of traditional processes, while completely avoiding physical bombardment damage to the substrate surface and structural sidewalls by high-energy particles.

[0052] Unlike existing solutions that rely on multi-layer nozzles to filter ions, this invention avoids the acceleration of fluorine-containing gases by electric fields at the ionization source through spatial partitioning of the air intake. This eliminates the need for ion filtering structures, reduces recombination losses of active particles in the transport path, and increases the activity retention rate of fluorine-based particles reaching the substrate surface by more than 30%.

[0053] This step replaces direct radio frequency dissociation with Penning ionization, allowing fluorine-based particles to participate in the reaction in a low-kinetic-energy, highly chemically active form, significantly reducing the physical bombardment effect while ensuring efficient chemical reactivity, laying the foundation for subsequent high-selectivity etching.

[0054] Step S3: Plasma etching using highly active fluorine-based particles

[0055] In this step, low-energy, highly active fluorine-based particles reach the surface of the semiconductor substrate and undergo a selective chemical reaction with the target etching material to generate volatile fluoride products, thereby achieving efficient and highly selective isotropic etching.

[0056] The isotropic plasma etching process is achieved by a pure chemical reaction between highly active fluorine-based particles and the surface of the substrate material to generate volatile fluoride products.

[0057] In some embodiments, the isotropic plasma etching process sequentially includes an initial diffusion stage, a main etching stage, and a byproduct desorption stage.

[0058] In the initial diffusion stage, the pressure in the reaction chamber is controlled within a first pressure range (e.g., 10 mTorr to 30 mTorr), and the flow ratio of the inert gas to the fluorine-containing reactive gas is within a first flow ratio range (e.g., not less than 15:1), allowing the highly reactive fluorine-based particles to fully diffuse to the bottom of the high aspect ratio structure, establishing a smooth initial etching surface. This stage ensures sufficient diffusion flux for the fluorine-based particles through a high flow ratio to overcome the concentration gradient resistance at the entrance of the high aspect ratio structure.

[0059] In the main etching stage, the pressure in the reaction chamber is controlled within a second pressure range (e.g., 30 mTorr to 80 mTorr), and the flow ratio of inert gas to fluorine-containing reactive gas is controlled within a second flow ratio range (e.g., 5:1 to 10:1), maintaining a stable etching rate and high etching selectivity. This stage balances the etching rate and selectivity through appropriate pressure and flow ratio, achieving high-fidelity removal of the target material.

[0060] In the by-product desorption stage, the pressure in the reaction chamber is controlled within the third pressure range (e.g., 80 mTorr to 120 mTorr), while the temperature of the semiconductor substrate is increased (e.g., 10°C to 20°C higher than the previous stage) to promote the desorption and removal of etching by-products inside the high aspect ratio structure. This stage increases the saturated vapor pressure of the by-products by raising the pressure and temperature, accelerating their diffusion from the inside of the structure to the outside, and preventing the by-products from redepositing on the sidewalls or bottom.

[0061] The pressure levels of the first pressure zone, the second pressure zone, and the third pressure zone increase sequentially; the ratio of the first flow ratio zone is higher than the ratio of the second flow ratio zone; and the substrate temperature during the by-product desorption stage is higher than the substrate temperature during the initial diffusion stage and the main etching stage.

[0062] Thanks to the low kinetic energy (<1eV) and long lifetime (≥100ms) of fluorine-based particles, the flux density difference of fluorine-based particles at the top, sidewalls and bottom of the high aspect ratio structure is ≤10%, the etching rate fluctuates by ≤5% under different opening sizes (50nm to 500nm), the etching depth is decoupled from the opening size, and there is no aspect ratio-dependent etching effect.

[0063] In some embodiments, the plasma etching process includes dielectric etching, silicon etching, or related thin film removal processes. Specifically, fluorine atoms, as the core etching species, react chemically with substrate materials such as Si, SiO2, SiN, and TiN to generate volatile products such as SiF4, which are then discharged through the cavity extraction system, achieving etching removal.

[0064] Taking TiN thin film as a substrate material as an example, such as Figure 2 As shown, the F-radical isotropic etching process of the present invention can achieve excellent non-CMP (chemical mechanical polishing) surface planarization effect. Figure 2 The top image shows a schematic diagram of the reaction mechanism before and after etching; the middle image shows a comparison of magnified SEM (Scanning Electron Microscope) images before and after etching; and the bottom image shows an SEM image of a high aspect ratio trench structure, used to verify the etching uniformity of the process in complex structures. In this embodiment, a high aspect ratio refers to a ratio of trench / via depth to opening width / diameter ≥ 10:1, preferably ≥ 30:1.

[0065] from Figure 2 As can be seen from the comparison images before and after etching, before etching (Pre:Non-CMP), the TiN film surface is rough with obvious peaks and valleys, showing a significant non-planarization state; after etching (Smoothed by radical process): after being treated by the free radical etching process of the present invention, the TiN film surface is significantly smooth, and the local roughness can be controlled within 3nm (Local range<3nm), achieving an excellent planarization effect.

[0066] The mechanism behind the aforementioned planarization effect lies in the fact that during the etching process, fluorine radicals (F radicals, a type of fluorine-based particle) react with the TiN film surface to form TiF. x O γ The reaction layer utilizes the masking effect of fluorine radicals to precisely smooth out surface peaks and valleys: at surface protrusions, the density of fluorine radicals is higher, the reaction layer is thinner, and the etching rate is faster; at depressions, the density of fluorine radicals is lower, the reaction layer is relatively thicker, and the etching rate is slower. This differentiated etching mechanism naturally smooths out surface micro-undulations, effectively improving surface roughness and ultimately achieving an etched surface that is nearly atomically smooth.

[0067] The ion shadowing effect refers to the phenomenon in high aspect ratio structure etching where high-energy ions in conventional plasmas are blocked by the sidewalls or top of the structure due to their directional bombardment characteristics, resulting in insufficient internal etching rate, uneven etching, and morphological distortion. Since the etching process of this invention is entirely dominated by free radicals, there is no ion shadowing effect, and the etching rate is independent of the aspect ratio of the pattern.

[0068] Figure 2 The SEM images of the high aspect ratio trenches at the bottom further verify this advantage of the invention: the etching depth inside the trenches of different sizes (including high aspect ratio trenches) is highly consistent and the etching morphology is uniform, which effectively solves the problem of uneven etching rate (ARDE) between trenches caused by differences in pattern density or size in traditional etching processes, and significantly improves the overall uniformity of etching.

[0069] In some embodiments, the semiconductor substrate material is suitable for at least one of silicon (Si), silicon dioxide (SiO2), silicon nitride (SiN), and TiN. In particular, this method is especially suitable for dielectric thin films requiring high selectivity etching in advanced node IC manufacturing, enabling efficient etching of target materials while minimizing etching of non-target materials, significantly improving the etching selectivity of Si over SiN and Si over SiO2.

[0070] In some embodiments, the semiconductor substrate comprises a titanium nitride (TiN) thin film, and the method further comprises introducing nitrogen gas (N2) into the reaction chamber to regulate the etching uniformity of the titanium nitride thin film and the volatility of byproducts.

[0071] The nitrogen gas and the fluorine-containing reactive gas are introduced into the downstream region through the same second gas inlet. Before entering the reaction chamber, they are pre-mixed in a gas mixing chamber to ensure consistent distribution of the nitrogen gas and fluorine-containing reactive gas upon reaching the substrate surface. Alternatively, the nitrogen gas is introduced into the downstream region through a separate third gas inlet to achieve independent control of the nitrogen gas flow rate. Both methods ensure that nitrogen gas does not enter the plasma generation region, preventing direct ionization of the nitrogen gas by the radio frequency electric field.

[0072] Specifically, the addition of N2 achieves precise control over etching through the following three mechanisms: First, the addition of N2 can promote the dissociation of O2 by enhancing oxidation capacity, or directly provide NO with superior oxidation capacity. First, N2 effectively slows down the etching rate (ER) of TiN by using metastable species, rather than simply increasing the oxygen content. Second, N2 can transform the TiN etching process from a byproduct removal-limited region to a reaction-limited region. This mechanism is similar to the principle of atomic layer etching (ALE), making the etching depth no longer affected by byproduct removal efficiency or trench size, significantly improving local etching uniformity (NU%). Third, N2 can remove etching byproducts from TiF... x O γ Modified to TiN x O γ F z The use of more volatile species effectively reduces the impact of cavity suction load and trench size on the etching process, achieving precise and controllable etching process.

[0073] For etching titanium nitride thin films, the preferred flow ratio of nitrogen to carbon tetrafluoride is 0.1–1.0, with an optimal range of 0.3–0.5. Under this ratio, the TiN etching rate can be precisely controlled within the range of 5–20 nm / min, with local etching uniformity ≤2%. When the ratio of nitrogen flow rate to fluorine-containing reactive gas flow rate is 0.1–0.5, the etching selectivity of titanium nitride to silicon dioxide is ≥50:1; when the ratio is 0.5–2.0, the etching selectivity of titanium nitride to silicon dioxide decreases to 5:1–10:1, achieving a switch from high-selectivity etching to uniform etching mode.

[0074] After adding the optimal ratio of nitrogen, the TiN etching byproduct TiF x O γ The volatilization temperature is reduced by about 40°C, and the amount of by-product residue in high aspect ratio structures is reduced by more than 80%. After processing with this process, the Ra of TiN films with an initial surface roughness Ra of 5~8nm can be reduced to less than 1.5nm, achieving atomic-level surface planarization without chemical mechanical polishing (CMP).

[0075] This invention also provides three specific process embodiments to verify the feasibility and inventiveness of this method: Example 1 In an ICP etching machine, argon (Ar) gas is introduced into the plasma generation region of the reaction chamber at a flow rate of 200 sccm, the radio frequency power is set to 800 W, and the pressure in the reaction chamber is controlled at 50 mTorr to form metastable Ar particles. CF4 gas is introduced into the downstream region of the reaction chamber at a flow rate of 40 sccm, causing Ar and CF4 to undergo a Penning ionization reaction to generate highly active fluorine-based particles. These fluorine-based particles are used to etch the silicon substrate, achieving a Si-to-SiN etching selectivity that is more than three times that of conventional processes.

[0076] Example 2

[0077] In an ICP etching machine, helium (He) gas is introduced into the plasma generation region of the reaction chamber at a flow rate of 500 sccm, the radio frequency power is set to 1000 W, and the pressure in the reaction chamber is controlled at 30 mTorr to form metastable He particles. CF4 gas is introduced into the downstream region of the reaction chamber at a flow rate of 50 sccm, causing He and CF4 to undergo a Penning ionization reaction to generate highly active fluorine-based particles. These fluorine-based particles are used to etch silicon dioxide dielectric films, achieving a Si-to-SiO2 etching selectivity ratio that is more than 2.5 times that of conventional processes, with a surface uniformity error of less than 5%.

[0078] Example 3

[0079] In an ICP etching machine, helium (He) gas is introduced into the plasma generation region at the top of the reaction chamber at a flow rate of 4000 sccm, with the radio frequency power set at 3500 W and the reaction chamber pressure controlled at 500 mTorr, forming a high concentration of metastable He particles. CF4 gas is introduced into the downstream lateral region of the reaction chamber at a flow rate of 300 sccm, causing a Penning ionization reaction between He and CF4 to generate highly reactive fluorine-based particles. These fluorine-based particles can be used to etch high aspect ratio titanium nitride (TiN) films, achieving non-CMP smoothing of the TiN film.

[0080] This embodiment achieved a stable Penning ionization process even under relatively high pressure (500 mTorr) and power (3500 W). Experimental results show that the method of this invention maintains excellent etching selectivity and uniformity under high pressure conditions, and the byproducts have good volatility. This verifies the applicability and process robustness of the method of this invention within a wide process window, making it suitable for the high etching rate and high throughput requirements of large-scale mass production.

[0081] This method achieves significantly high selectivity etching results. While maintaining the etching rate, the etching selectivity of Si to SiN and Si to SiO2 can be increased to more than twice that of traditional CF4 plasma etching processes, with etching uniformity error controlled within 5%, meeting the precision requirements of high aspect ratio structure etching in advanced node IC manufacturing. Furthermore, this process does not require special high-temperature or high-pressure conditions and can be implemented within the range of conventional etching process parameters, demonstrating strong process compatibility.

[0082] Although the methods described above are illustrated and depicted as a series of actions for the sake of simplicity, it should be understood and appreciated that these methods are not limited by the order of the actions, as some actions may occur in a different order and / or concurrently with other actions from the illustrations and descriptions herein or not illustrated and described herein but which may be understood by those skilled in the art, according to one or more embodiments.

[0083] The present invention also provides a plasma etching apparatus for implementing the plasma etching method based on Penning ionization as described in any of the above method embodiments.

[0084] Figure 3 A schematic diagram of a plasma etching apparatus according to an embodiment of the present invention is shown, as follows: Figure 3 As shown, a plasma etching apparatus according to an embodiment of the present invention includes: The reaction chamber 11 is used to accommodate the semiconductor substrate 51 and provide an etching reaction space; The radio frequency power supply 21 is coupled to the reaction chamber 11 to excite and maintain the inert gas plasma and generate metastable inert gas particles in the plasma generation region 41. In some embodiments, the radio frequency power supply 21 couples energy to the interior of the reaction chamber 11 through the radio frequency coil 22 to excite and maintain the plasma. The radio frequency power supply may be a pulsed radio frequency power supply.

[0085] The air intake system includes at least two independent air passages, which are used to input inert gas and fluorine-containing reactive gas into the reaction chamber 11 respectively, so as to realize gas partitioning input and diffusion; The air intake system, through its air path spatial layout, introduces fluorine-containing reactive gas into a downstream region far from the plasma generation region, allowing the Penning ionization reaction to occur in a region without an electric field, thereby achieving spatial decoupling between the plasma generation region 41 and the Penning ionization etching reaction region 42.

[0086] This device eliminates the need for multi-layer ion filter nozzles and light-shielding structures. It achieves decoupling between the plasma generation zone and the Penning ionization reaction zone simply through the gas path spatial layout, resulting in a simpler structure and reduced recombination loss of active particles on the solid surface.

[0087] In some embodiments, the plasma etching apparatus further includes a bias power supply, which works in conjunction with the reaction chamber 11 to regulate the distribution and activity of the plasma and optimize the generation efficiency of metastable particles; the bias power supply is only used to regulate the plasma distribution and does not apply an accelerating electric field to the etching active particles.

[0088] In some embodiments, the intake system specifically includes: The first gas inlet 31 is located at the center of the top of the reaction chamber, directly opposite the plasma generation zone, and is used to introduce inert gas into the plasma generation zone 41. The second gas inlet 32 ​​is located in the downstream lateral region of the reaction chamber and is used to introduce fluorine-containing reaction gas into the downstream or lateral region away from the plasma generation region 41.

[0089] The second gas inlet 32 ​​consists of 4 to 8 gas inlets evenly arranged circumferentially along the side wall of the reaction chamber. The height of the gas inlets is located at the center of the axial direction of the chamber, 30 to 80 mm away from the surface of the substrate support unit, which can realize the circumferential uniform diffusion of fluorine-containing reaction gas in the chamber.

[0090] The second gas inlet 32 ​​is inclined toward the substrate side to guide the fluorine-containing reactive gas to flow downward and prevent the gas from flowing back to the plasma generation region 41.

[0091] The plasma generation region 41 is the coupling region between the radio frequency power supply 21 and the reaction chamber 11, which is the main region where the plasma is excited and maintained.

[0092] Metastable inert gas particles formed in plasma generation region 41 diffuse downstream and enter Penning ionization etching reaction region 42. Located downstream of plasma generation region 41, Penning ionization etching reaction region 42 is the main region where metastable inert gas particles undergo Penning ionization reactions with fluorine-containing reactive gas introduced from second gas inlet 32.

[0093] In some embodiments, the plasma etching apparatus further includes a synchronization control unit, which is connected to the pulsed radio frequency power supply and the gas path control valve of the fluorine-containing reactive gas, respectively, and is used to control the timing of the introduction of the fluorine-containing reactive gas to be synchronized with the phase of the radio frequency pulse, and to introduce the fluorine-containing reactive gas only during the off period of the radio frequency pulse.

[0094] In some embodiments, the apparatus further includes a substrate support unit 52 disposed at the lower part of the reaction chamber 11 for supporting and fixing the semiconductor substrate 51 to be etched. The substrate support unit 52 integrates a temperature control element for adjusting the temperature of the semiconductor substrate at different stages of the isotropic plasma etching process, especially for increasing the substrate temperature during the by-product desorption stage to promote the desorption of etching by-products in high aspect ratio structures.

[0095] Other specific structures, parameter settings, and operating conditions of this device can be found in the relevant descriptions in the foregoing method embodiments, and will not be repeated here. Those skilled in the art will understand that the above device structures are merely illustrative, and any device structure capable of implementing the method of this invention falls within the protection scope of this invention.

[0096] The present invention provides a plasma etching method and apparatus based on Penning ionization, which has the following beneficial effects: 1) By generating low-kinetic-energy, highly chemically active fluorine-based particles through Penning ionization, and the particles are not accelerated by the electric field before reaching the semiconductor substrate surface, the physical bombardment effect is significantly reduced, which fundamentally solves the problem of low selectivity in traditional CF4 plasma etching process and greatly improves the etching selectivity of Si to SiN and Si to SiO2. 2) The etching of the substrate material is achieved solely through chemical reaction. Fluorine-based particles react with the target material to generate volatile SiF4 products, which have no significant etching effect on non-target materials, achieving highly selective isotropic etching, perfectly meeting the etching requirements of high aspect ratio structures in advanced node IC manufacturing. 3) The design of partitioned air intake and independent air path eliminates the need for multi-layer ion filter nozzles and light shielding structures. The process conditions are mild and the parameter control range is wide. High efficiency and high uniformity etching can be achieved without special process environment. The process stability and compatibility are stronger, which is conducive to large-scale mass production applications. 4) The active particles generated by Penning ionization have a significantly extended lifetime, ensuring that they can fully diffuse to the bottom of trench / via structures with an aspect ratio of ≥30:1, effectively improving the in-plane uniformity and trench uniformity of etching, and solving the problem of morphological distortion in high aspect ratio structures in traditional etching processes. 5) For etching titanium nitride thin films, the etching selectivity can be controlled over a wide range by adding nitrogen gas, which can switch from high selectivity etching to uniform etching mode and achieve atomic-level surface planarization without chemical mechanical polishing.

[0097] As indicated in this application and claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" are not specifically singular and may include plural forms. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0098] The above embodiments are provided for those skilled in the art to implement or use the present invention. Those skilled in the art can make various modifications or changes to the above embodiments without departing from the inventive concept of the present invention. Therefore, the protection scope of the present invention is not limited to the above embodiments, but should be the maximum scope that conforms to the innovative features mentioned in the claims.

Claims

1. A plasma etching method based on Penning ionization, characterized in that, include: An inert gas is introduced into the reaction chamber, and metastable inert gas particles are formed through radio frequency discharge; Fluorine-containing reactive gas is introduced into the reaction chamber, causing the metastable inert gas particles to undergo a Penning ionization reaction with the fluorine-containing reactive gas, producing highly active fluorine-based particles; The high aspect ratio structure of the semiconductor substrate placed in the reaction chamber is subjected to isotropic plasma etching using the highly active fluorine-based particles. In this process, the fluorine-containing reactive gas is introduced into a downstream region far from the plasma generation region, and the Penning ionization reaction is carried out in a region without an electric field, so that the highly active fluorine-based particles are not accelerated by an electric field from the time they are generated until they reach the surface of the semiconductor substrate.

2. The plasma etching method based on Penning ionization according to claim 1, characterized in that, In the step of forming metastable inert gas particles by radio frequency discharge, pulsed radio frequency is used to excite the inert gas plasma; In the step of introducing the fluorine-containing reactive gas into the reaction chamber, the introduction of the fluorine-containing reactive gas is synchronized with the phase of the radio frequency pulse, and is only introduced into the reaction chamber during the off period of the radio frequency pulse, so that the Penning ionization reaction takes place during the period without an electric field.

3. The plasma etching method based on Penning ionization according to claim 1, characterized in that, The isotropic plasma etching process is achieved by the highly active fluorine-based particles undergoing a pure chemical reaction with the substrate material surface to generate volatile fluoride products; The highly active fluorine-based particles have a kinetic energy of less than 1 eV and a lifetime of not less than 100 ms.

4. The plasma etching method based on Penning ionization according to claim 1, characterized in that, The isotropic plasma etching process includes, in sequence, an initial diffusion stage, a main etching stage, and a byproduct desorption stage. In the initial diffusion stage, the pressure in the reaction chamber is controlled within the first pressure range, and the flow ratio of inert gas to fluorine-containing reactive gas is within the first flow ratio range, so that highly active fluorine-based particles diffuse to the bottom of the high aspect ratio structure and establish a flat initial etching surface. During the main etching stage, the pressure in the reaction chamber is controlled within the second pressure range, and the flow ratio of inert gas to fluorine-containing reaction gas is controlled within the second flow ratio range to maintain a stable etching rate and a high etching selectivity. During the by-product desorption stage, the pressure in the reaction chamber is controlled within the third pressure range, while the temperature of the semiconductor substrate is increased to promote the desorption and discharge of etching by-products inside the high aspect ratio structure. The pressure levels of the first pressure zone, the second pressure zone, and the third pressure zone increase sequentially; the ratio of the first flow ratio zone is higher than the ratio of the second flow ratio zone; and the substrate temperature during the by-product desorption stage is higher than the substrate temperature during the initial diffusion stage and the main etching stage.

5. The plasma etching method based on Penning ionization according to claim 1, characterized in that, In the step of introducing inert gas and fluorine-containing reactive gas into the reaction chamber, the two gases are introduced in a partitioned gas introduction method. The inert gas is introduced into the plasma generation region through the first gas inlet, and the fluorine-containing reactive gas is introduced into the downstream region away from the plasma generation region through the second gas inlet, where it mixes with metastable inert gas particles diffused from the upstream and undergoes Penning ionization. By adjusting the gas flow ratio and inlet angle of the first gas inlet and the second gas inlet, uniform mixing and diffusion of the two gases can be achieved.

6. The plasma etching method based on Penning ionization according to claim 1, characterized in that, The inert gas includes at least one of argon or helium; The fluorine-containing reactive gas includes carbon tetrafluoride; The highly active fluorine-based particles include at least one of fluorine atoms, carbide tetrafluoride cations, and fluorocarbon free radicals. The semiconductor substrate is made of at least one of silicon, silicon dioxide, or silicon nitride.

7. The plasma etching method based on Penning ionization according to claim 6, characterized in that, The step of introducing an inert gas into the reaction chamber further includes: controlling the types of products of the Penning ionization reaction by selecting the type of inert gas. When helium is used as the inert gas, the Penning ionization reaction preferentially produces fluorine atoms and fluorocarbon radicals; When argon is used as the inert gas, the Penning ionization reaction preferentially produces carbon tetrafluoride cations.

8. The plasma etching method based on Penning ionization according to claim 1, characterized in that, The semiconductor substrate includes a titanium nitride thin film, and the method further includes introducing nitrogen gas into the reaction chamber to regulate the etching uniformity of the titanium nitride thin film and the volatility of byproducts.

9. The plasma etching method based on Penning ionization according to claim 1, characterized in that, The plasma etching process includes dielectric etching, silicon etching, or thin film removal.

10. A plasma etching apparatus for implementing the plasma etching method based on Penning ionization as described in any one of claims 1 to 9, characterized in that, include: A reaction chamber is used to house a semiconductor substrate and provide space for the etching reaction. A radio frequency power supply, coupled to the reaction chamber, is used to excite and maintain inert gas plasma, generating metastable inert gas particles in the plasma generation region. The air intake system includes at least two independent air passages, which are used to input inert gas and fluorine-containing reactive gas into the reaction chamber respectively, so as to achieve gas partitioning and diffusion; The air intake system, through its air path spatial layout, introduces fluorine-containing reactive gas into a downstream region far from the plasma generation region, allowing the Penning ionization reaction to occur in a region without an electric field, thus achieving spatial decoupling between the plasma generation region and the Penning ionization reaction region.

11. The plasma etching apparatus according to claim 10, characterized in that, The intake system includes: The first gas inlet is located in the plasma generation zone of the reaction chamber and is used to introduce inert gas. The second gas inlet is located in the downstream lateral region of the reaction chamber and is used to introduce fluorine-containing reaction gas. The second gas inlet is inclined toward the substrate side to guide the fluorine-containing reactive gas downwards and prevent the gas from flowing back into the plasma generation area.

12. The plasma etching apparatus according to claim 10, characterized in that, The radio frequency power supply is a pulse radio frequency power supply; The plasma etching apparatus also includes a synchronization control unit, which is connected to the pulse radio frequency power supply and the gas path control valve of the fluorine-containing reactive gas, respectively. The synchronization control unit is used to control the timing of the introduction of the fluorine-containing reactive gas to be synchronized with the phase of the radio frequency pulse, and to introduce the fluorine-containing reactive gas only during the off period of the radio frequency pulse.

13. The plasma etching apparatus according to claim 10, characterized in that, The reaction chamber is also equipped with a substrate support unit: The substrate support unit integrates a temperature control element to adjust the temperature of the semiconductor substrate at different stages of the isotropic plasma etching process, thereby promoting the desorption of etching byproducts within the high aspect ratio structure.

Images