Plasma enhanced film formation method

Abstract

A plasma processing method includes: flowing a first gas and a second gas into a plasma processing chamber including a substrate, the second gas including a film precursor; at a first moment, while maintaining the flow of the first gas, cutting off the flow of the second gas into the plasma processing chamber; and at a second moment after the first moment, supplying power to electrodes of the plasma processing chamber to generate plasma in the plasma processing chamber, the surface of the substrate being exposed to the generated plasma to form a film on the substrate.

Description

Plasma-assisted film formation method This application claims the rights and priority of U.S. Patent Application No. 17 / 521,359, filed November 8, 2021, the entire contents of which are incorporated herein by reference. This invention relates generally to plasma processing, and in specific embodiments, to a method for forming a plasma-enhanced film. Typically, semiconductor devices, such as integrated circuits (ICs), are fabricated by sequentially depositing and patterning dielectric layers, conductive layers, and semiconductor material layers on a substrate to form electronic components and interconnects (e.g., transistors, resistors, capacitors, metal lines, contacts, and vias) integrated into a single structure. As scaling moves into the nanometer-scale semiconductor device fabrication node, scaling efforts to increase the number of interconnects per unit area are facing greater challenges. Therefore, three-dimensional (3D) semiconductor devices with transistors stacked on top of each other are required. As device structures become more compact and vertically integrated, the need for precision material handling, such as during deposition and patterning, becomes increasingly prominent. Therefore, further innovation in various deposition technologies, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD), is required to provide adequate profile control, film conformability, and film quality. According to an embodiment of the present invention, a plasma processing method includes: flowing a first gas and a second gas into a plasma processing chamber including a substrate, the second gas including a film precursor; at a first moment, maintaining the flow of the first gas while cutting off the flow of the second gas into the plasma processing chamber; and at a second moment after the first moment, supplying power to the electrodes of the plasma processing chamber to generate plasma in the plasma processing chamber, the surface of the substrate being exposed to the generated plasma to form a film on the substrate. According to an embodiment of the present invention, a method for forming a film on a substrate includes: flowing a first gas into a plasma processing chamber holding the substrate; performing a cyclic plasma process while flowing the first gas, the cyclic plasma process including a plurality of cycles, each of the plurality of cycles including: pulse a second gas comprising a film precursor into the plasma processing chamber; and applying a first pulse of power to an electrode coupled to the plasma processing chamber to generate plasma, thereby forming a gaseous intermediate species from the film precursor, the gaseous intermediate species being deposited on the substrate to form a film. According to an embodiment of the present invention, a plasma processing method includes: flowing a first gas and a second gas into a plasma processing chamber including a substrate, the second gas including a film precursor including H, B, C, N, O, F, Si, Ti, Fe, Co, Cu, Zn, Ga, Ge, As, Y, Zr, In, Sn, Sb, Hf, Ta, or W, wherein the temperature of the substrate is 500°C or lower; at a first moment, supplying power to electrodes of the plasma processing chamber to generate plasma in the plasma processing chamber, exposing the surface of the substrate to the generated plasma to form a film on the substrate; and at a second moment, while maintaining the flow of the first gas, cutting off the flow of the second gas into the plasma processing chamber. This application relates to a plasma-enhanced film formation method, and more particularly to a low-temperature plasma-enhanced chemical vapor deposition (PECVD) method, which utilizes short plasma pulses to generate intermediate species from the residue of vapor-phase precursors, referred to herein as pulse-emission PECVD (ps-PECVD). With the scaling efforts in semiconductor manufacturing processes, achieving conformal film coverage with high aspect ratio structures and / or 3D structures has become increasingly urgent. However, currently available deposition techniques (e.g., thermal processes and PECVD processes) may fail to meet the growing industry demands due to several drawbacks. For example, conventional thermal processes may require high temperatures (typically >600°C) to deposit reliable films. On the other hand, conventional PECVD, which can be performed at medium or low temperatures, may not achieve good conformal films on patterned features. As an alternative, atomic layer deposition (ALD) processes can provide sufficient film conformality, but ALD processes are typically slow (e.g., film growth rates of 1-2 nm / min) and expensive. Furthermore, ALD processes may also require high temperatures (e.g., >400°C). Therefore, low-temperature deposition techniques (e.g., <400°C) may be required to achieve conformal film coverage and quality at a reasonable film growth rate. Embodiments of this application disclose a method for achieving such deposition performance: low-temperature pulsed emission plasma-enhanced chemical deposition (ps-PECVD). In one embodiment, a silicon dielectric film, such as silicon nitride, can be conformally formed on a 3D structure of a substrate at a temperature below 500°C. The method described in this disclosure is based on pulsed emission plasma-enhanced chemical vapor deposition (ps-PECVD) and advantageously reduces the process temperature required to form conformal films on 3D structures of substrates compared to common thermal processes. Avoiding high temperatures facilitates device characteristics and process integration in logic and memory device applications. The conformal film growth method at low temperatures is achieved by generating intermediate species from the residue of vapor precursors using short plasma pulses, which are then deposited onto the surface to uniformly grow the film. Cycles of plasma pulses can be repeated to grow films of desired thicknesses while maintaining conformality. Furthermore, numerous embodiments of the ps-PECVD process can provide shorter purge times and faster film growth rates than common ALD methods. In addition, the ps-PECVD method provides low wet etch rates (WER) and uniform WER distribution across the film, some of the key factors for film quality. The use of plasma pulses advantageously reduces ion damage to active components and processing systems in a system-on-a-chip (SoC). In many embodiments, the ps-PECVD process may include four stages: (1) an inflow stage in which at least two gases flow into the plasma processing chamber; (2) a flow-stop stage in which the inflow of one of the two gases stops; (3) a short-emission plasma stage in which plasma is generated in a short time; and (4) a post-plasma film growth stage in which the film is formed on the substrate mainly by intermediate species formed by the plasma in stage (3). In the following text, the four stages of a pulse-emission plasma-enhanced chemical vapor deposition (ps-PECVD) process are first described with reference to Figures 1A-1D and 2A-2C. Next, two examples of films with different levels of conformal integrity formed on a substrate are described with reference to Figures 3A and 3B. Then, exemplary process flow diagrams are shown in Figures 4A-4C. Figure 5 provides an exemplary plasma system for performing a ps-PECVD process according to various embodiments. All figures in this disclosure (including aspect ratios of features) are for illustrative purposes only and are not drawn to scale. Figures 1A-1D show cross-sectional views of a substrate 100 with recesses at various stages during an exemplary ps-PECVD process in a plasma processing chamber according to various embodiments. Figures 2A-2C show timing diagrams of cyclic embodiments of the ps-PECVD process according to the various embodiments shown in Figures 1A-1D. The five horizontal axes in Figures 2A-2C represent the progress of time. The three process parameters (i.e., the concentrations of the two gases and the radio frequency (RF) power used to generate the plasma), the concentration of intermediate species, and the film growth rate are plotted in Figures 2A-2C. In FIG1A, substrate 100 may include semiconductor substrates as described in various embodiments. In one or more embodiments, substrate 100 may be a silicon wafer or a silicon-on-insulator (SOI) wafer. In some embodiments, substrate 100 may include silicon-germanium wafers, silicon carbide wafers, gallium arsenide wafers, gallium nitride wafers, and other compound semiconductors. In other embodiments, the substrate includes a heterolayer, such as silicon-on-germanium, silicon-on-nitride, silicon-on-carbide, and silicon on silicon-on-silicon or an SOI substrate. Alternatively, substrate 100 may be a metal substrate or a dielectric substrate. For example, substrate 100 may be aluminum, carbon (e.g., graphene), or silicon oxide. Furthermore, substrate 100 may include a number of different material layers and may be the top layer of a multilayer substrate. For example, substrate 100 may be silicon oxide formed on another material. The substrate 100 may be patterned into, for example, one or more high aspect ratio features and / or 3D structures. In many embodiments, the features of the substrate 100 may include contact holes, slits, or other suitable structures including recesses. In some embodiments, the features of the substrate 100 may include various 3D structures and overlays for, for example, 3D-NAND, 3D-NOR, or dynamic random access memory (DRAM) devices, and 3D transistors. In FIG. 1A, a recess 105 is formed on the substrate 100. The patterning of the substrate 100 may be performed by conventional methods, for example, lithography to pattern an etch mask and subsequent etch process. Figure 1A further illustrates the inflow stage of a pulse-emission plasma-enhanced chemical vapor deposition (ps-PECVD) process, wherein a first process gas 10 and a second process gas 11 flow into the plasma processing chamber. Multiple flow controllers can be used to control the flow rates of the two gases separately. In some embodiments, as shown in Figure 2A, the inflow of the second process gas may begin at time t1, after a constant inflow of the first process gas has been established. In other embodiments, both gases may be activated simultaneously. In one embodiment, the flow rate of the first process gas may be kept constant, as shown in Figures 2A-2C, but in other embodiments, it may be varied at any stage during the ps-PECVD process. In many embodiments, the two gases may be selected based on the chemical composition of the target film to be formed on the substrate 100. The target film may include, for example, a silicon dielectric material. In one embodiment, the target film includes a silicon nitride. In other embodiments, the silicon dielectric material may include silicon carbide (SiC), silicon oxide (SiCO), silicon oxynitride (SiON), silicon carbonitride (SiCN), or other materials. Furthermore, the target film may include non-silicon-based oxides, carbides, or any other materials, such as boron (B), hydrogen (H), nitrogen (N), oxygen (O), carbon (C), or fluorine (F). These dielectric materials, such as nitride materials, are advantageously used in the fabrication of microelectronic devices as barrier layers, passivation layers, dielectric layers, masking layers, and as substrates, etc. In further embodiments, the target film may include binary, ternary, or quaternary compounds comprising metallic elements such as titanium (Ti), iron (Fe), cobalt (Co), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), arsenic (As), yttrium (Y), zirconium (Zr), indium (In), tin (Sn), antimony (Sb), hafnium (Hf), tantalum (Ta), or tungsten (W). In some embodiments, the target film may include metal nitrides. In one embodiment, the target film may include titanium nitrides. Hereinafter, the ps-PECVD method is described for nitrides, particularly silicon nitrides, as an exemplary film composition; however, in other embodiments, other film compositions may be used in the formed film by means of the ps-PECVD method of this disclosure. In many embodiments, the first process gas 10 includes H, C, N, O, or F. In some embodiments, the first process gas 10 includes a nitrogen compound. For example, the nitrogen compound may be bis(nitrogen) gas. 2) Ammonia (NH4+) 3) Hydrazine (N 2H 4) Methylamine (CH 3NH 2) etc. In the presence of plasma in subsequent steps (e.g., the pulsed emission plasma stage in FIG. 1C), the presence of one or more nitrogen compounds in the first process gas 10 can facilitate the formation of active nitrogen species, such as dissociated nitrogen atoms. Active nitrogen species can be important for the formation of target films comprising nitride materials. In some embodiments, the first process gas 10 may include dihydrogen (H₂O) 2). In addition, the first process gas 10 may also include additional gases. These additional gases may include, for example, inert gases such as helium (He), argon (Ar), neon (Ne), and krypton (Kr). In many embodiments, the flow rate of the first process gas 10 may be set such that the total gas flow is between 50 sccm and 5000 sccm. The second process gas 11 may include a membrane precursor for the target membrane. In many embodiments, the second process gas 11 may include H, B, C, N, O, F, or Si. In some embodiments, the second process gas 11 may include a metallic element, such as Ti, Fe, Co, Cu, Zn, Ga, Ge, As, Y, Zr, In, Sn, Sb, Hf, Ta, or W. In some embodiments, the second process gas 11 may include silicon-containing molecules, such as trisilylamine (TSA) or dichlorosilane (DCS). In other embodiments, the second process gas 11 may include an organosilane having one or more Si-C bonds. In further embodiments, the second process gas 11 may include a silane containing Cl, C, H, N, or F, or a borane containing Cl, C, H, N, or F. In many embodiments, the flow rate of the second process gas 11 can be set such that the total gas flow is between 50 sccm and 5000 sccm. Furthermore, in Figure 1A, the arrows indicate the inflow (two arrows on the left) and outflow (two arrows on the right) of the two gas flows. Therefore, a constant pressure can be maintained in the plasma processing chamber, for example, between 10 mTorr and 10 Torr in one embodiment. During this stage, a portion of the precursor can be adsorbed onto the substrate 100 as adsorbed precursor species 12. In some embodiments, the second process gas 11 may flow as a short pulse 20 at time t1 to introduce only a small amount of the second process gas 11 into the plasma processing chamber, as shown in FIG2B. In such an embodiment, the gas pulse duration of the short pulse 20 may be, for example, 10 seconds or less. For illustrative purposes, three short pulses 20 are shown, separated from each other by time period d3 (the second pulse at time t6, the third pulse at time t7). The inventors of this application confirm that, using conventional PECVD technology, film growth of materials such as silicon nitrides can be primarily driven by active ionic species in the plasma. When film growth is ion-driven, the inflow of species tends to be more directional (i.e., less isotropic) due to the electric field present in the plasma processing chamber. This tendency can hinder conformal film growth, especially in high aspect ratio structures suitable for 3D semiconductor devices. On the other hand, free radical species are electrically neutral, and therefore their inflow can be more isotropic. To achieve a good balance between ions and free radicals, the inventors of this application envision limiting the concentration of a second process gas 11 present in the plasma processing chamber and shortening the plasma processing time, wherein the second process gas 11 comprises silicon-containing molecules, such as trimethylsilylamine (TSA) or dichlorosilane (DCS). In many embodiments, limiting the concentration of the second process gas 11 can be achieved by pulsating the second process gas 11 or by a flow-stopping phase as described below with reference to Figures 1B and 2A-2C. In Figure 1B, at the flow cessation stage (t2 in Figure 2A), the inflow of the second process gas 11 stops. While the inflow of the first process gas 10 and the outflow of both gases still exist, the concentration of the second process gas 11 decays over time, as shown in Figure 2A. After a sufficient time from t2 (decay time d1 in Figure 2A), the second process gas 11 will be completely expelled, and only the first process gas can remain in the plasma processing chamber (at t5 in Figure 2A). In other words, the decay time d1 corresponds to the residence time of the second process gas 11. If the adsorbed precursor species 12 is chemisorbed, a portion of it may also be present. Conventional atomic layer deposition (ALD) methods may require such a stage (e.g., at or after t5 in Figure 2A) where the precursor exists only on the surface, and subsequent film formation processes can proceed only as surface reactions. In contrast, in many embodiments, as shown in Figures 1B and 1C, the pulsed emission plasma-enhanced chemical vapor deposition (ps-PECVD) process advantageously utilizes the residual amount of vapor-phase precursors for plasma-induced chemical reactions. In other words, the ps-PECVD can proceed to the next pulsed emission plasma stage during the decay time d1 (i.e., between t2 and t5 in Figure 2A) (e.g., Figure 1C). The pulsed plasma emission stage follows the flow cessation stage. In many embodiments, the plasma can be generated by applying RF power (as shown in Figure 2A). In some embodiments, the RF source frequency can be between 30 MHz and 300 MHz. In one embodiment, the RF source frequency can be at least 60 MHz. In another embodiment, the RF source frequency can be between 160 MHz and 240 MHz. In many embodiments, the RF source power can be between 50 W and 10000 W, and the bias power can be between 0 W and 200 W. The total gas flow can be between 50 sccm and 5000 sccm. The process pressure can be between 10 mTorr and 10 Torr. In some embodiments, the power pulse duration can be between 0.1 and 3 seconds (the time between t3 and t4 in Figure 2A), while in other embodiments, the pulse duration can be 5 seconds or less. This pulsed plasma emission can be used to initiate a gas-phase reaction to generate intermediate species for membrane formation. The application of RF power (t3) can be performed after a delay time d2 following the cessation of the inflow of the second process gas 11 (t2). In many embodiments, the delay time d2 can be between 0 seconds and 10 seconds, but in other embodiments it can be longer. In some embodiments, at time t3, RF power may be applied as a pulse train, which includes complex power pulses (e.g., two pulses as shown in Figure 2B). In an alternative embodiment, the pulsed emission plasma phase can begin before the flow of the second process gas 11 stops (i.e., t3 before t2), which can help maximize the generation of intermediate species. In one embodiment, RF power can be applied as a pulse train comprising multiple power pulses, one of which can be applied before the flow of the second process gas 11 stops (i.e., before t2), and another of which can be applied after the flow stops (i.e., after t2), as shown in FIG2C. As shown in Figure 1C, the plasma 13 generated by applying RF power may include energized species of the first process gas 14. Due to the energized species of the first process gas 14, the residual amount of the second process gas 11 can react and produce intermediate species 15. In some embodiments, intermediate species 15 may include radical species. In one embodiment, intermediate species 15 may include SixNyHz radical species. In some embodiments, plasma conditions may be optimized to maximize the concentration of radical species. Furthermore, intermediate species 15 may include elements (e.g., nitrogen atoms) from the first process gas. In many embodiments, the intermediate species 15 is then isotropically deposited on substrate 100 to form film 16. The presence of gaseous intermediate species 15 distinguishes the ps-PECVD process from the ALD process. While ALD is driven by surface reactions of adsorbed species, the ps-PECVD process, on the other hand, involves intermediate species formed in the gas phase. Furthermore, the inventors of this application have confirmed that the presence of free radical species in intermediate species 15 can significantly improve isotropic film growth, thereby improving the conformability of film 16 (e.g., the uniform thickness of film 16 in recess 105 and on the surface of substrate 100) and the uniformity of wet etch rate (WER) of film 16. Therefore, process conditions including plasma parameters can be selected to optimize the concentration of free radical species in intermediate species 15. Thus, free radical-driven film growth can be more prevalent, and ps-PECVD processes can be performed while minimizing ionic damage on substrate 100 caused by reactive ions. As shown in Figures 2A-2C, any residual energized species in the first process gas 14 in the plasma processing chamber can continue to form intermediate species 15 after the RF power is turned off at time t4. Therefore, film growth can continue until the intermediate species 15 are completely depleted. Figure 1D shows the continued growth of film 16 after the RF power is turned off, whereby the deposition of intermediate species 15 drives film 16 to grow at a uniform thickness across the substrate. For optimal membrane growth rate and membrane quality of membrane 16, the duration of delay time d2 (i.e., the time t3 during which RF power is applied in Figures 2A-2C) is critical. Therefore, accurately determining the decay curve and the duration of decay time d1 (i.e., the residence time of the second process gas 11) can be useful. Since the residence time depends on the amount of the second process gas 11 present in the plasma processing chamber at t2, and the flow rate of the first gas 10, the decay curve can be calculated based on these parameters. These parameters can be monitored by one or more sensors, including, for example, pressure monitors, airflow monitors, and / or gas species density monitors. In some embodiments, the decay curve can be approximated as an exponential decay as a function of time t, having the general formula C = C0. t2 ×e -αt Where C is the concentration of the second process gas 11, C t2 Let C be the value at time t2, and α be the decay constant. The decay constant α can depend on the relationship between the chamber volume V and the gas flow rate of the first process gas 10. In one embodiment, based on the exponential decay approximation, the residence time can be considered as when C equals C t2 The time when it is 1%. In another embodiment, the dwell time can be considered as C equal to C. t2 The time when it is 5% of the total. C t2 The residence time of the second process gas 11 can be determined as N / V based on the state equation PV = NkT, where N is the total number of moles of the second process gas 11 in the plasma processing chamber, P is the partial pressure of the second process gas 11, k is the Boltzmann constant, and T is the temperature. In another embodiment, the residence time of the second process gas 11 can be determined as N / q. out , where q out This is the number of moles in the effluent of gas 11 in the second process, and is assumed to be constant. A gas species density monitor can be used to monitor and determine q. out Although the above assumes that the second process gas 11 decays exponentially or flows out at a constant rate, other approximation methods, such as the Gaussian distribution, can also be used. Although not specifically depicted in Figures 2A-2C, any other process parameters, such as temperature, can be independently controlled and / or changed at each stage of the ps-PECVD process according to the respective process formulations. In many embodiments, the ps-PECVD process can be performed at temperatures below 500°C. In some embodiments, the temperature of substrate 100 can be maintained between 250°C and 500°C. A temperature range below 500°C can advantageously reduce thermal damage to the semiconductor device during manufacturing. In many embodiments, the ps-PECVD process can be performed as a cyclic plasma deposition process by repeating the steps shown in Figures 1A, 1D, and 2. The process conditions for each cycle of the cyclic plasma deposition according to various embodiments can be selected separately. Cyclic implementation of the ps-PECVD method can advantageously form the film 16 substantially layer-by-layer, thereby achieving high film conformability and / or precise thickness control. The ps-PECVD process can be performed to achieve the target film thickness. In one embodiment, the film thickness can be between 1 nm and 50 nm. In some embodiments, a cycle of the ps-PECVD process may include multiple plasma pulses in the pulse emission plasma phase, which may facilitate fine-tuning of the formation of intermediate species 15, for example, in cases where the decay time d1 is longer than several seconds. In pulsed emission plasma-enhanced chemical vapor deposition (ps-PECVD) processes, precise control over the concentration of intermediate species can be achieved through intelligent process formulation design. Specifically, key process parameters may include gas flow rate, the time at which the inflow of the second process gas is stopped, or the pulse duration thereof, as well as the pulse emission plasma time, pulse duration, and conditions. For example, the selection of the delay time d2 (e.g., the time between t2 and t3 in Figure 2A) can significantly affect process performance. When a very short delay time d2 is selected (e.g., less than one-tenth of the decay time d1), the residual concentration of the second process gas 11, including precursors, can approach the initial set value, which may result in a relative abundance of intermediate species 15 in the pulse emission plasma stage. This can be advantageous for providing a faster film growth rate per cycle, but film conformability and quality may be compromised. On the other hand, when the delay time d2 is extended (e.g., greater than half of the decay time d1), the residual concentration of the second process gas 11 decreases. Therefore, the film growth rate per cycle may be slower, but film conformability and quality can be improved. In many embodiments, the process parameters of ps-PECVD can be advantageously adjusted according to the film specifications required in semiconductor manufacturing. The advantages of the ps-PECVD process may include: (i) better film conformability and quality compared to available low-temperature PECVD processes that may rely on ion-driven film growth; and (ii) faster film growth at lower temperatures compared to ALD and / or plasma-enhanced atomic layer deposition (PEALD) processes. In many embodiments, intermediate steps can be performed by exposing the substrate 100 to a processing gas to alter the surface functional groups on the substrate 100 or the film. These intermediate steps can be performed before the inflow stage, during the post-plasma film growth stage, or after the inflow stage. The processing gas may include, for example, hydrogen or ammonia (NH4+). 3), but other reactive and / or inert gases may be used. Intermediate steps can help improve film conformability and / or film quality by correcting defects and / or repairing them in the cured film. Furthermore, intermediate steps may include plasma treatment using a processing gas. In one embodiment, the intermediate step may be plasma treatment using a plasma comprising hydrogen. In an alternative embodiment, the intermediate step may be a heat treatment, for example, performed by heating the substrate 100 under a gas flow comprising an inert gas or under vacuum. Figures 3A and 3B show cross-sectional views of a substrate 100 with recesses after completing a ps-PECVD process, which have different resulting film structures according to various embodiments. In Figure 3A, film 16 is uniformly formed on substrate 100 (including the walls of recess 105) and has high conformability. As mentioned above, simultaneously achieving conformal film growth, a rapid film growth rate, and a moderately reduced process temperature can be challenging for conventional deposition techniques, especially for high aspect ratio features used in 3D semiconductor devices. Advantageously, the ps-PECVD method, cyclically implemented at 500°C or lower, can achieve the target film thickness without compromising conformability. In some embodiments, the film thickness variation can be 10% or less of the average film thickness, for example, 0.5% to 5% in one embodiment. In one embodiment, film 16 may comprise silicon nitride and can be used as a spacer material in 3D semiconductor devices, such as DRAM. In Figure 3B, film 16 exhibits poor conformality. The film thickness is uneven on substrate 100, being thicker near the top surface of substrate 100 and thinner in the lower half of recess 105. The inventors of this application have confirmed that such non-conformal deposition can frequently occur in conventional low-temperature plasma-enhanced processes, likely due to poor isotropy of ion-driven film growth and ion flux in these processes, particularly in 3D structures such as high aspect ratio features. The layer thickness within the bottom surface of recess 105 decreases with decreasing ion concentration. In cases of poor conformality, the film thickness variation can exceed 20%. According to numerous embodiments, such non-conformal deposition can be prevented by utilizing a more isotropic, radical-driven film growth method, ps-PECVD. With ps-PECVD, the concentration of the film precursor is limited, and the plasma process time is shortened. Therefore, the number of radical species (e.g., those involving silicon and nitrogen used for silicon nitride film formation) may increase, while limiting ionic species. Since radical species are electrically neutral, they are less affected by electric fields and are therefore likely to be more isotropic. Furthermore, radicals diffuse more slowly than ions and may require a longer time to form a film on the surface, which can also contribute to improved film conformability. It is worth noting that, in addition to film conformability, the uniformity of film quality within a 100-inch area of ​​the substrate can be improved by the ps-PECVD method. For example, an important factor in film quality is the wet etching rate (WER). In particular, the WER in hydrofluoric acid (HF) is a key material property of the spacer material and must be low in dilute HF aqueous solutions. The WER of the spacer can depend on crystallinity, morphology, density, stoichiometry, and trap density, etc. The inventors of this application have confirmed that many conventional low-temperature processes can suffer from high WER and / or non-uniform distribution of WER within the film area in 3D structures. In one example, wet etching can preferentially etch the film within the recesses (i.e., the film within the recesses is less resistant to wet etching), and thus reduce film conformability. According to various embodiments, this non-uniform WER problem and high WER can be mitigated or eliminated by the isotropic, radical-driven film growth achieved by the ps-PECVD method. Figures 4A-4C show process flow diagrams of ps-PECVD according to various embodiments. The process flow can follow the diagrams discussed above (Figures 1A-1D and 2A-2C), and therefore will not be described again. In Figure 4A, process flow 40 begins in the inflow stage, where a first process gas 10 and a second process gas 11 (which include film precursors) flow into the plasma processing chamber of the substrate 100 (box 410, Figure 1A). Next is the flow-stop stage, where the inflow of the second process gas 11 is stopped while the first process gas 10 flows (box 420, Figure 1B). The process proceeds to the pulse-emission plasma stage, where plasma is generated to form intermediate species 15 (box 430, Figure 1C). As the intermediate species 15 are deposited on the substrate 100, film formation begins, and after the power is turned off to maintain the plasma, the post-plasma film growth stage continues (Figure 1D). In Figure 4B, process flow 42 shows a cyclic implementation of the ps-PECVD method, beginning with an inflow phase where a first process gas 10 flows into the plasma processing chamber of the substrate 100 (box 412), and a cyclic plasma process can be performed simultaneously with the flow of the first process gas 10. The cyclic plasma process can begin by pulsating a second process gas 11, including a film precursor, into the plasma processing chamber (box 422, Figures 1A and 1B). The pulsation corresponds to the inflow phase and flow stop phase in the previous embodiments. Next, a pulse of RF source power can be applied to generate plasma to form an intermediate species 15 (box 432, Figure 1C), followed by a post-plasma film growth phase similar to that in the previous embodiments (box 440, Figure 1D). In some embodiments, during any number of cycles, after one cycle (blocks 422, 432, and 440) and before the next cycle, an intermediate step (block 450) may be performed by exposing the substrate 100 to a process gas to alter the surface functional groups on the substrate 100 or the film. In Figure 4C, process flow 44 shows an alternative embodiment of the ps-PECVD method, beginning with the inflow of a first process gas 10 and a second process gas 11 (which includes a film precursor) into the plasma processing chamber of the substrate 100 (box 414, Figure 1A). Next, the electrodes in the plasma processing chamber can be powered to generate plasma within the plasma processing chamber (box 430, Figure 1C) and to form a film on the substrate 100. For 5 seconds after box 430, the flow of the first process gas 10 is maintained while the flow of the second process gas 11 is cut off (box 420, Figure 1B). Alternatively, the power supply to the electrodes and the cutoff of the flow of the second process gas 11 can be performed simultaneously (box 425). Figure 5 shows a plasma system for performing a ps-PECVD process according to various embodiments. For illustrative purposes, Figure 5 shows a substrate 100 placed on a substrate holder 554 (e.g., an electrostatic chuck (ESC)) near the bottom within a plasma processing chamber 510. Optionally, the substrate 100 may be maintained at a desired temperature using a heater / cooler 556 surrounding the substrate holder 554. The temperature of the substrate 100 may be maintained by a temperature controller 540 connected to the substrate holder 554 and the heater / cooler 556. The ESC may be coated with a conductive material (e.g., a carbon-based or metal nitride-based coating) to allow for electrical connection with the substrate holder 554. As shown in Figure 5, the substrate holder 554 can be the bottom electrode of the plasma processing chamber 510. In the example shown in Figure 5, the substrate holder 554 is connected to the RF bias power supply 570. A conductive disc near the top within the plasma processing chamber 510 serves as the top electrode 552. In Figure 5, the top electrode 552 is connected to the RF power supply 550 of the plasma processing system 50. In some other embodiments, the top electrode can be a conductive coil located outside the plasma processing chamber 510, above the top ceramic window. Gas can be introduced into the plasma processing chamber 510 via a gas delivery system 520. The gas delivery system 520 includes multiple gas flow controllers to control the flow of multiple gases into the chamber. In some embodiments, an optional center / edge splitter can be used to independently adjust the gas flow rate at the center and edge of the substrate 100. Furthermore, the gas delivery system 520 may have a special spray head configuration located at the top of the plasma processing chamber 510. For example, the gas delivery system 520 may be integrated with an upper electrode 522, which has a spray head configuration covering the entire substrate 100, including a plurality of appropriately spaced gas inlets. Alternatively, gas can be introduced via any other suitablely configured dedicated gas inlet. The plasma processing chamber 510 may be further equipped with one or more sensors 515, such as pressure monitors, airflow monitors, and / or gas species density monitors. In some embodiments, the sensors 515 may be integrated as part of the gas delivery system 520. The sensor 515 and gas flow controller of the gas delivery system 520 can be used to determine and control the delay time d2 (e.g., the time between t2 and t3 in Figure 2A) and the power pulse period (e.g., the time between t3 and t4 in Figure 2A). RF bias power supply 570 can be used to supply continuous wave (CW) or pulsed RF power to sustain plasma, such as plasma 560. Plasma 560 is shown between top electrode 552 and bottom electrode 552 (also referred to as substrate holder 554), an example of which is direct plasma generated near substrate 100 in plasma processing chamber 510 of plasma processing system 50. The configuration of the plasma processing system 50 described above is merely exemplary. In alternative embodiments, numerous alternative configurations can be used for the plasma processing system 50. For example, inductively coupled plasma (ICP) can be used with an RF source power coupled to a planar coil on a top dielectric cap, and gas inlets and / or gas outlets can be coupled to an upper wall, etc. In many embodiments, the RF power, chamber pressure, substrate temperature, gas flow rate, and other plasma process parameters can be selected according to the respective process formulations. In some embodiments, the plasma processing system 50 can be a resonator, such as a helical resonator. This document summarizes exemplary embodiments of the invention. Other embodiments may also be understood from the full text of the specification and the scope of the patent application filed herein. Example 1. A plasma processing method includes: flowing a first gas and a second gas into a plasma processing chamber including a substrate, the second gas including a film precursor; at a first moment, maintaining the flow of the first gas while cutting off the flow of the second gas into the plasma processing chamber; and at a second moment after the first moment, supplying power to the electrodes of the plasma processing chamber to generate plasma in the plasma processing chamber, exposing the surface of the substrate to the generated plasma to form a film on the substrate. Example 2. The method of Example 1, wherein the second moment is separated from the first moment by a time delay, the time delay being the residence time of the second gas in the plasma processing chamber or less. Example 3. The method of Example 1 or 2, wherein the membrane precursor includes a silane containing Cl, C, H, N, or F, or a borane containing Cl, C, H, N, or F. Example 4. The method of one of Examples 1 to 3, wherein the film comprises a dielectric material, which includes Si, B, H, N, O, C, or F. Example 5. A method similar to one of Examples 1 to 4, wherein the first gas comprises nitrogen or dinitrogen (N2). 2), and the membrane therein includes silicon nitrides or metal nitrides. Example 6. The method of any one of Examples 1 to 5 further includes: monitoring one or more of the following: the pressure of the plasma processing chamber, the gas flow rate of the first process gas, the gas flow rate of the second process gas, the partial pressure of the first process gas, or the partial pressure of the second process gas; and determining the time of the first moment and the second moment based on the monitoring. Example 7. The method of one of Examples 1 to 6, wherein the method is performed at a temperature of 500°C or lower. Example 8. The method of one of Examples 1 to 7, wherein the electrode is powered by applying RF power at a frequency of at least 60 MHz. Example 9. A method of forming a film on a substrate includes: flowing a first gas into a plasma processing chamber holding the substrate; performing a cyclic plasma process while flowing the first gas, the cyclic plasma process including a plurality of cycles, each of the plurality of cycles including: pulse a second gas comprising a film precursor into the plasma processing chamber; and applying the power of the first pulse to an electrode coupled to the plasma processing chamber to generate plasma, thereby forming a gaseous intermediate species from the film precursor, the gaseous intermediate species being deposited on the substrate to form a film. Example 10. The method of Example 9 further includes applying the power of one or more subsequent pulses to the electrode after applying the power of the first pulse. Example 11. The method of Example 9 or 10, wherein the power of the pulse is applied relative to the pulsation of the second gas with a delay time of 10 seconds or less. Example 12. A method as described in one of Examples 9 to 11, wherein the first gas comprises nitrogen or dinitrogen (N2). 2), wherein the membrane precursor includes silicon, and wherein the membrane includes silicon nitride. Example 13. The method of one of Examples 9 to 12, wherein one or more of the plurality of cycles further includes performing an intermediate step comprising: exposing the substrate to a process gas to alter the surface functional groups on the substrate or film, the process gas including H, C, N, O, F, He, Ar, Ne, or Kr. Example 14. A method as described in one of Examples 9 to 13, wherein the processed gas includes dihydrogen (H2O) 2) Hydrogen peroxide (O) 2) or ammonia (NH4+) 3). Example 15. The method of one of Examples 9 to 14, wherein the pulse duration of the second gas is 10 seconds or less, or wherein the pulse duration of the power is 5 seconds or less. Example 16. The method of one of Examples 9 to 15, wherein the substrate has a recess and wherein the film has a thickness difference of 10% or less. Example 17. A plasma processing method includes: flowing a first gas and a second gas into a plasma processing chamber including a substrate, the second gas including a film precursor comprising H, B, C, N, O, F, Si, Ti, Fe, Co, Cu, Zn, Ga, Ge, As, Y, Zr, In, Sn, Sb, Hf, Ta, or W, wherein the temperature of the substrate is 500°C or lower; at a first moment, supplying power to electrodes of the plasma processing chamber to generate plasma in the plasma processing chamber, exposing the surface of the substrate to the generated plasma to form a film on the substrate; and at a second moment, while maintaining the flow of the first gas, cutting off the flow of the second gas into the plasma processing chamber. Example 18. The method is the same as in Example 17, where the first moment and the second moment are the same. Example 19. As in Example 17, where the second moment occurs within 5 seconds after the first moment. Example 20. The method of one of Examples 17 to 19, wherein powering the electrode includes applying a pulse of RF source power having a frequency of at least 60 MHz. While the invention has been described with reference to exemplary embodiments, this description is not intended to be limiting. Numerous modifications and combinations of the exemplary embodiments, as well as other embodiments of the invention, will be apparent to those skilled in the art upon referring to this description. Therefore, the appended patent application is intended to cover any such modifications or embodiments. 10: Gas 11: Gas 12: Precursor species 13: Plasma 14: Gas 15: Intermediate species 16: Membrane 20: Short pulse 40: Process flow 42: Process flow 44: Process flow 50: Plasma processing system 100: Substrate 105: Recess 410~450: Frame 510: Plasma processing chamber 515: Sensor 520: Gas delivery system 540: Temperature controller 550: RF power supply 554: Substrate holder 556: Heater / cooler 570: RF bias power supply d1: Decay time d2: Delay time d3: Time period t1~t7: Time To more fully understand the present invention and its advantages, the following description is provided in conjunction with the accompanying drawings, wherein: Figures 1A-1D show cross-sectional views of a recessed substrate at different stages during an exemplary pulse-shot plasma enhanced chemical vapor deposition (ps-PECVD) process according to various embodiments, wherein Figure 1A shows the substrate with the first gas and the second process gas flowing, Figure 1B shows the substrate after the flow of the second process gas has stopped, Figure 1C shows the substrate in the pulse-shot plasma step, and Figure 1D shows the substrate in the post-plasma film growth stage. Figures 2A-2C show timing diagrams of a ps-PECVD process according to various embodiments, wherein Figure 2A shows a cycle implemented according to one embodiment, Figure 2B shows three cycles according to another embodiment, and Figure 2C shows three cycles according to an alternative embodiment. Figures 3A and 3B show cross-sectional views of substrates with recesses after a ps-PECVD process, according to various embodiments, with different resulting film structures. Figure 3A shows a substrate with a deposited conformal film, and Figure 3B shows a substrate with a deposited non-uniform film. Figures 4A-4C show process flow diagrams of ps-PECVD according to various embodiments, wherein Figure 4A shows one embodiment, Figure 4B shows one embodiment of a cyclic embodiment, and Figure 4C shows another embodiment. Figure 5 shows a plasma system for performing a ps-PECVD process according to various embodiments. d1: Decay time d2: Delay time t1~t5: Time

Claims

1. A plasma treatment method, comprising: A first gas and a second gas are introduced into a plasma processing chamber comprising a substrate, the second gas comprising a film precursor, wherein the substrate has a recess; at a first moment, while maintaining the flow of the first gas, the flow of the second gas into the plasma processing chamber is cut off; and at a second moment after the first moment, an electrode of the plasma processing chamber is powered to generate plasma in the plasma processing chamber, the surface of the substrate is exposed to the plasma to form a film on the substrate, wherein the film has a thickness difference of 10% or less.

2. The plasma treatment method as described in claim 1, wherein, The second moment is separated from the first moment by a time delay, which is equal to or less than the residence time of the second gas in the plasma processing chamber.

3. The plasma treatment method as described in claim 1, wherein, The membrane precursor includes silanes containing Cl, C, H, N, or F, or boranes containing Cl, C, H, N, or F.

4. The plasma treatment method as described in claim 1, wherein, The film includes a dielectric material, which may be Si, B, H, N, O, C, or F.

5. The plasma treatment method as described in claim 1, wherein, The first gas includes nitrogen or dinitrogen (N2), and the membrane includes silicon nitride or metal nitride.

6. The plasma treatment method as described in claim 1 further includes: Monitor one or more of the following: the pressure of the plasma processing chamber, the gas flow rate of the first gas, the gas flow rate of the second gas, the partial pressure of the first gas, or the partial pressure of the second gas; and determine the timing of the first moment and the second moment based on the monitoring.

7. The plasma treatment method as described in claim 1, wherein, This method is performed at a temperature of 500°C or lower.

8. The plasma treatment method as described in claim 1, wherein, The electrode is powered by applying RF power at a frequency of at least 60 MHz.

9. A method for forming a film on a substrate, the method comprising: A first gas is flowed into a plasma processing chamber that holds a substrate, wherein the substrate has a recess. While the first gas is flowing, a cyclic plasma process is performed, the cyclic plasma process comprising multiple cycles, each of the multiple cycles comprising: pulsating a second gas including a membrane precursor into the plasma processing chamber; and applying a first pulse of power to an electrode coupled to the plasma processing chamber to generate plasma, thereby forming a gaseous intermediate species from the membrane precursor, the gaseous intermediate species being deposited on the substrate to form the membrane, wherein the membrane has a thickness variation of 10% or less.

10. The method for forming a film on a substrate as described in claim 9, wherein, The cyclic plasma process further includes applying one or more subsequent pulses of power to the electrode after the first pulse of power is applied.

11. The method for forming a film on a substrate as described in claim 9, wherein, The first pulse that applies the power is executed with a delay time relative to the pulsation of the second gas, which is 10 seconds or less.

12. The method for forming a film on a substrate as described in claim 9, wherein, The first gas includes nitrogen or dinitrogen (N2), wherein the membrane precursor includes silicon, and wherein the membrane includes silicon nitride.

13. The method for forming a film on a substrate as described in claim 9, wherein, One or more of the multiple cycles further include performing an intermediate step, which includes: exposing the substrate to a process gas to alter the surface functional groups on the substrate or the film, the process gas including H, C, N, O, F, He, Ar, Ne, or Kr.

14. The method for forming a film on a substrate as described in claim 13, wherein, The processed gases include hydrogen (H2), oxygen (O2), or ammonia (NH3).

15. The method of forming a film on a substrate as claimed in claim 13, wherein the intermediate step is performed between the step of pulsating the second gas and the step of applying the power to the electrode by a first pulse.

16. The method for forming a film on a substrate as described in claim 9, wherein, The pulse duration of the second gas is 10 seconds or less, or the pulse duration of the power is 5 seconds or less.

17. A method for forming a film on a substrate, comprising: The first gas flows into the plasma processing chamber that holds the substrate. While the first gas is flowing, a circulating plasma process is performed, the circulating plasma process comprising multiple cycles, each of the multiple cycles comprising: pulsating a second gas, including a membrane precursor, into the plasma processing chamber; A first pulse of power is applied to an electrode coupled to the plasma processing chamber to generate plasma, thereby forming a gaseous intermediate species from the membrane precursor, which is deposited on the substrate to form the membrane; and between the step of pulsating the second gas and the step of applying the first pulse of power, the substrate is exposed to a processing gas to change the surface functional groups on the substrate or the membrane, the processing gas including dihydrogen (H2), dioxygen (O2), or ammonia (NH3).

18. As in request item 17, where, The first pulse that applies the power is executed with a delay time relative to the pulsation of the second gas, which is 10 seconds or less.

19. As in request item 17, where, The pulse duration of the first pulse of this power is 5 seconds or less.

20. As in request item 17, where, The first gas contains nitrogen, the second gas contains silane or borane, the substrate has a recess, and the film has a thickness difference of 10% or less.

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