Plasma enhanced film formation method

Abstract

1. A plasma processing method comprising: flowing a first gas and a second gas into a plasma processing chamber containing a substrate, the second gas comprising a film precursor; at a first time instance, blocking a flow of the second gas into the plasma processing chamber while maintaining a flow of the first gas; and at a second time instance after the first time instance, providing power to an electrode of the plasma processing chamber to generate a plasma in the plasma processing chamber, exposing a surface of the substrate to the generated plasma to form a film on the substrate.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of and priority to U.S. patent application Ser. No. 17 / 521,359, filed Nov. 8, 2021, the contents of which are incorporated by reference in their entirety herein.

[0002] The present invention relates generally to plasma processing, and in a particular embodiment to a plasma enhanced film formation method. [Background technology]

[0003] Generally, semiconductor devices such as integrated circuits (ICs) are fabricated by sequentially depositing and patterning layers of dielectric, conductive, and semiconducting materials on a substrate to form a network of electronic components and interconnect elements (e.g., transistors, resistors, capacitors, metal lines, contacts, and vias) integrated in a monolithic structure. Scaling efforts to increase the number of interconnect elements per unit area face greater challenges as scaling enters nanometer-scale semiconductor device manufacturing nodes. Thus, there is a demand for three-dimensional (3D) semiconductor devices in which transistors are stacked on top of each other.

[0004] As device structures become denser and more vertically oriented, there is a stronger demand for precise material processing, e.g., during deposition and patterning, which calls for further innovation in various deposition techniques, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD), among others, to provide sufficient profile control, film conformality, and film quality. Summary of the Invention [Means for solving the problem]

[0005] According to one embodiment of the present invention, a plasma processing method includes flowing a first gas and a second gas into a plasma processing chamber containing a substrate, the second gas including a film precursor; at a first time instance, blocking a flow of the second gas into the plasma processing chamber while maintaining a flow of the first gas; and at a second time instance after the first time instance, providing power to an electrode of the plasma processing chamber to generate a plasma in the plasma processing chamber, exposing a surface of the substrate to the generated plasma to form a film on the substrate.

[0006] According to one embodiment of the present invention, a method of forming a film on a substrate includes flowing a first gas into a plasma processing chamber holding the substrate; and 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 pulsing a second gas comprising a film precursor into the plasma processing chamber; and applying a first pulsed power to an electrode coupled to the plasma processing chamber to generate a plasma to form a gaseous intermediate species from the film precursor, the gaseous intermediate species being deposited on the substrate to form a film, the applying the first pulsed power.

[0007] According to one embodiment of the present invention, a plasma processing method includes flowing a first gas and a second gas into a plasma processing chamber containing a substrate, the second gas comprising a film precursor, the 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, and a temperature of the substrate is less than or equal to 500° C.; at a first time instance, providing power to an electrode of the plasma processing chamber to generate a plasma in the plasma processing chamber, exposing a surface of the substrate to the generated plasma to form a film on the substrate; and at a second time instance, shutting off the flow of the second gas into the plasma processing chamber while maintaining the flow of the first gas.

[0008] For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: [Brief description of the drawings]

[0009] [Figure 1A] 1A-1D are cross-sectional views of a substrate having a recess at various stages during an exemplary pulse-shot plasma enhanced chemical vapor deposition (ps-PECVD) process according to various embodiments, where FIG. 1A shows the substrate during flowing of a first gas and a second process gas, FIG. 1B shows the substrate after stopping flowing the second process gas, FIG. 1C shows the substrate at a pulse-shot plasma step, and FIG. 1D shows the substrate at a post-plasma film growth stage. [Figure 1B] 1A-1D are cross-sectional views of a substrate having a recess at various stages during an exemplary pulse-shot plasma enhanced chemical vapor deposition (ps-PECVD) process according to various embodiments, where FIG. 1A shows the substrate during flowing of a first gas and a second process gas, FIG. 1B shows the substrate after stopping flowing the second process gas, FIG. 1C shows the substrate at a pulse-shot plasma step, and FIG. 1D shows the substrate at a post-plasma film growth stage. [Figure 1C] 1A-1D are cross-sectional views of a substrate having a recess at various stages during an exemplary pulse-shot plasma enhanced chemical vapor deposition (ps-PECVD) process according to various embodiments, where FIG. 1A shows the substrate during flowing of a first gas and a second process gas, FIG. 1B shows the substrate after stopping flowing the second process gas, FIG. 1C shows the substrate at a pulse-shot plasma step, and FIG. 1D shows the substrate at a post-plasma film growth stage. [Figure 1D]1A-1D are cross-sectional views of a substrate having a recess at various stages during an exemplary pulse-shot plasma enhanced chemical vapor deposition (ps-PECVD) process according to various embodiments, where FIG. 1A shows the substrate during flowing of a first gas and a second process gas, FIG. 1B shows the substrate after stopping flowing the second process gas, FIG. 1C shows the substrate at a pulse-shot plasma step, and FIG. 1D shows the substrate at a post-plasma film growth stage. [Figure 2A] FIG. 2A is a timing diagram of a ps-PECVD process according to various embodiments, where FIG. 2A shows one cycle of a cyclical implementation according to one embodiment, FIG. 2B shows three cycles according to another embodiment, and FIG. 2C shows three cycles according to an alternative embodiment. [Figure 2B] FIG. 2A is a timing diagram of a ps-PECVD process according to various embodiments, where FIG. 2A shows one cycle of a cyclical implementation according to one embodiment, FIG. 2B shows three cycles according to another embodiment, and FIG. 2C shows three cycles according to an alternative embodiment. [Figure 2C] FIG. 2A is a timing diagram of a ps-PECVD process according to various embodiments, where FIG. 2A shows one cycle of a cyclical implementation according to one embodiment, FIG. 2B shows three cycles according to another embodiment, and FIG. 2C shows three cycles according to an alternative embodiment. [Figure 3A] 3A-3B are cross-sectional views of a substrate having a recess after a ps-PECVD process according to various embodiments with different resulting film structures, where FIG. 3A shows a substrate with a conformal film deposited thereon and FIG. 3B shows a substrate with a non-uniform film deposited thereon. [Figure 3B] 3A-3B are cross-sectional views of a substrate having a recess after a ps-PECVD process according to various embodiments with different resulting film structures, where FIG. 3A shows a substrate with a conformal film deposited thereon and FIG. 3B shows a substrate with a non-uniform film deposited thereon. [Figure 4A]4A-4C are process flow diagrams for ps-PECVD according to various embodiments, where FIG. 4A illustrates one embodiment, FIG. 4B illustrates one embodiment of cyclical implementation, and FIG. 4C illustrates another embodiment. [Figure 4B] 4A-4C are process flow diagrams for ps-PECVD according to various embodiments, where FIG. 4A illustrates one embodiment, FIG. 4B illustrates one embodiment of cyclical implementation, and FIG. 4C illustrates another embodiment. [Figure 4C] 4A-4C are process flow diagrams for ps-PECVD according to various embodiments, where FIG. 4A illustrates one embodiment, FIG. 4B illustrates one embodiment of cyclical implementation, and FIG. 4C illustrates another embodiment. [Diagram 5] FIG. 1 illustrates a plasma system for performing a ps-PECVD process according to various embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] This application relates to plasma enhanced film formation methods, and more specifically, to low temperature plasma enhanced chemical vapor deposition (PECVD) that utilizes short plasma pulses to generate intermediate species from residual amounts of precursors in the gas phase, referred to in this disclosure as pulsed shot PECVD (ps-PECVD). With the efforts of scaling semiconductor manufacturing processes, it becomes more imperative to achieve conformal film coverage with high aspect ratio structures and / or 3D structures. However, currently available deposition techniques (e.g., thermal treatments and PECVD processes) may not meet the growing industrial requirements due to several shortcomings. For example, conventional thermal treatments may require high temperatures (typically above 600° C.) to deposit reliable films. On the other hand, conventional PECVD may be performed at moderate or low temperatures and may lack the ability to achieve good conformal films on patterned features. Alternatively, atomic layer deposition (ALD) processes may provide sufficient film conformality, but ALD processes are generally slow (e.g., film growth rates of 1-2 nm / min) and expensive. Furthermore, ALD processes may also require high temperatures (e.g., above 400°C). Therefore, to achieve conformal film coverage and quality at reasonable film growth rates, low temperature (e.g., below 400°C) deposition techniques may be desired. Embodiments of the present application disclose a method of low temperature pulse shot plasma enhanced chemical deposition (ps-PECVD) that enables such deposition performance. In one embodiment, silicon dielectric films, such as silicon nitride, may be conformally formed over 3D structures of a substrate at temperatures below 500°C.

[0011] The method described herein is based on pulse shot plasma enhanced chemical vapor deposition (ps-PECVD), which can advantageously reduce the process temperature required to form a conformal film over the 3D structure of a substrate compared to conventional thermal processing. Avoiding high temperatures can be beneficial to device performance and process integration in both logic and memory device applications. The conformal film growth of the present method at low temperatures is made possible by short plasma pulsing to generate intermediate species from residual amounts of precursors in the gas phase, which are then deposited on the surface to grow the film uniformly. Cycles of plasma pulsing may be repeated to grow a desired film thickness while maintaining the conformality of the film. In addition, various embodiments of the ps-PECVD process can also provide shorter purge times and faster film growth rates than conventional ALD methods. Furthermore, the ps-PECVD method can provide low wet etch rates (WER) as well as uniform distribution of WER across the film, which are some of the key factors for film quality. The use of shot plasma pulsing can beneficially reduce ion damage to active components of systems-on-chips (SOCs) as well as processing systems.

[0012] In various embodiments, the ps-PECVD process can include four stages: (1) a flow-in stage in which at least two gases are flowed into a plasma processing chamber; (2) a flow-off stage in which the flow of one of the two gases is stopped; (3) a pulse shot plasma stage in which a short duration plasma is generated; and (4) a post-plasma film growth stage in which a film is formed on a substrate that is based on an intermediate species formed by the plasma in stage (3).

[0013] In the following, these four stages of the pulse shot 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 formed on substrates with different levels of conformality are described with reference to Figures 3A and 3B. Exemplary process flow diagrams are then shown in Figures 4A-4C. Figure 5 provides an exemplary plasma system for carrying out the ps-PECVD process according to various embodiments. All figures in this disclosure are drawn for illustrative purposes only and are not to scale, including aspect ratios of features.

[0014] 1A-1D show cross-sectional views of a substrate 100 having a recess at various stages during an exemplary ps-PECVD process in a plasma processing chamber according to various embodiments.

[0015] Figures 2A-2C show timing diagrams for cyclical implementations of ps-PECVD processes according to various embodiments shown in Figures 1A-1D. The five horizontal axes of Figures 2A-2C represent progression in time. Three process parameters (i.e., concentrations of two gases and radio frequency (RF) power for plasma generation), concentration of intermediate species, and film growth rate are plotted in Figures 2A-2C.

[0016] In FIG. 1A, substrate 100 may comprise a semiconductor substrate in various embodiments. In one or more embodiments, substrate 100 may be a silicon wafer or a silicon-on-insulator (SOI) wafer. In certain embodiments, substrate 100 may include a silicon germanium wafer, a silicon carbide wafer, a gallium arsenide wafer, a gallium nitride wafer, or other compound semiconductors. In other embodiments, the substrate includes heterogeneous layers, such as layers of silicon germanium on silicon, gallium nitride on silicon, silicon carbon on silicon, and silicon on silicon or SOI substrates. 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. Additionally, substrate 100 may be the top layer of a multi-layer substrate, which may include many different layers of materials. For example, substrate 100 may be silicon oxide formed on top of another material.

[0017] The substrate 100 may be patterned, for example, into one or more high aspect ratio features and / or 3D structures. In various embodiments, the features of the substrate 100 may include contact holes, slits, or other suitable structures including recesses. In certain embodiments, the features of the substrate 100 may include 3D transistors as well as various 3D structures and layers useful, for example, for 3D-NAND, 3D-NOR, or dynamic random access memory (DRAM) devices. In FIG. 1A, a recess 105 is formed on the substrate 100. The patterning of the substrate 100 may be formed by conventional methods, for example, a lithography process to pattern an etch mask and a subsequent etching process.

[0018] FIG. 1A further illustrates the flow phase of a pulse shot plasma enhanced chemical vapor deposition (ps-PECVD) process, where a first process gas 10 and a second process gas 11 are flowed into a plasma processing chamber. Multiple flow controllers may be used to control the flow rates of the two gases separately. In a particular embodiment, as shown in FIG. 2A, the flow of the second process gas may be started at time t1 after a constant flow of the first process gas is established. In other embodiments, the two gases may be turned on simultaneously. In one embodiment, the flow rate of the first process gas may be kept constant as shown in FIGS. 2A-C, but in other embodiments, it may be changed at any stage during the ps-PECVD process.

[0019] In various 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 silicon nitride. In other embodiments, the silicon dielectric material may include silicon carbide (SiC), silicon carbide oxygen (SiCO), silicon oxynitride (SiON), silicon nitride carbon (SiCN), or other materials. Furthermore, the target film may include non-silicon based oxides, carbides, or any other materials, including, for example, boron (B), hydrogen (H), nitrogen (N), oxygen (O), carbon (C), or fluorine (F). These dielectric materials, such as nitride materials, may be advantageously used in the manufacture of microelectronic devices as barrier layers, passivation layers, dielectric layers, masking layers, and especially substrates. In further embodiments, the target film may include a binary, ternary, or quaternary compound that includes a metal element, 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 certain embodiments, the target film may include a metal nitride. In one embodiment, the target film may include titanium nitride. The ps-PECVD method is described below for nitrides, specifically silicon nitride as an exemplary film composition, although in other embodiments, other film compositions may be used for films formed by the ps-PECVD method of the present disclosure.

[0020] In various embodiments, the first process gas 10 includes H, C, N, O, or F. In certain embodiments, the first process gas 10 includes a nitrogen compound. For example, the nitrogen compound can be dinitrogen (N2), ammonia (NH3), hydrazine (N2H4), methylamine (CH3NH2), and the like. Having one or more nitrogen compounds in the first process gas 10 can aid in the formation of reactive nitrogen species, such as dissociated nitrogen atoms, in the presence of plasma during a later stage (e.g., the pulse shot plasma stage of FIG. 1C). The reactive nitrogen species can be important in the formation of a target film including a nitride material. In certain embodiments, the first process gas 10 can include dihydrogen (H2). Furthermore, the first process gas 10 can also include additional gases. The additional gases can include noble gases, such as, for example, helium (He), argon (Ar), neon (Ne), krypton (Kr), and the like. In various embodiments, the flow rate of the first process gas 10 can be set so that the total gas flow rate is between 50 sccm and 5000 sccm.

[0021] The second process gas 11 may include a film precursor for the target film. In various embodiments, the second process gas 11 may include H, B, C, N, O, F, or Si. In certain embodiments, the second process gas 11 may include a metal 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 a silicon-containing molecule 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 various embodiments, the flow rate of the second process gas 11 may be set such that the total gas flow rate is between 50 sccm and 5000 sccm. 1A further shows arrows indicating the inflow (two arrows on the left) and outflow (two arrows on the right) for the two gas flows. Thus, a constant pressure may be maintained in the plasma processing chamber, for example a pressure of 10 mTorr to 10 Torr in one embodiment. At this stage, a portion of the precursor may be adsorbed onto the substrate 100 as adsorbed precursor species 12.

[0022] In certain embodiments, the second process gas 11 may be flowed 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 FIG. 2B. In such embodiments, 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 one another by a time duration d3 (at time t6 for the second pulse and at time t7 for the third pulse).

[0023] The inventors of the present application have determined that film growth of materials such as silicon nitride by conventional PECVD techniques may be driven in large part by reactive ionic species in the plasma. When film growth is ion-driven, the influx of species tends to be more directional (i.e., less isotropic) due to the electric field present in the plasma processing chamber. This tendency may hinder conformal film growth, especially in high aspect ratio structures that may be useful in 3D semiconductor devices. Radical species, on the other hand, are electronically neutral and therefore their influx may be more isotropic. To achieve a good balance between ions and radicals, the inventors of the present application have conceived of limiting the concentration of the second process gas 11, which comprises silicon-containing molecules such as trisilylamine (TSA) or dichlorosilane (DCS), present in the plasma processing chamber, and shortening the plasma processing time. In various embodiments, limiting the concentration of the second process gas 11 may be achieved by pulsing the second process gas 11 or influx stop phases, as described below with reference to Figures 1B and 2A-2C.

[0024] In FIG. 1B, the inflow of the second process gas 11 is stopped in a flow stop step (at t2 in FIG. 2A). With the inflow of the first process gas 10 and the outflow of the two gases still present, the concentration of the second process gas 11 decays over time as shown in FIG. 2A. After a sufficient time from t2 (decay time d1 in FIG. 2A), the second process gas 11 will be completely purged and only the first process gas may remain in the plasma processing chamber (at t5 in FIG. 2A). In other words, the decay time d1 corresponds to the residence time of the second process gas 11. Some of the adsorbed precursor species 12 may also be present when chemically adsorbed. In conventional atomic layer deposition (ALD) methods, such a step (e.g., at t5 or thereafter in FIG. 2A) where the precursor is present only on the surface may be required, and the subsequent process for film formation may proceed as a reaction exclusively on the surface. In contrast, in various embodiments, a pulse-shot plasma enhanced chemical vapor deposition (ps-PECVD) process advantageously employs plasma-induced chemical reaction of residual amounts of precursors in the gas phase, as shown in Figures 1B and 1C. In other words, ps-PECVD can proceed to the next pulse-shot plasma stage (e.g., Figure 1C) at decay time d1, i.e., t2-t5 in Figure 2A.

[0025] A pulse shot plasma phase follows the flow stop phase. In various embodiments, the plasma can be generated by applying RF power (at t3 in FIG. 2A). In certain embodiments, the RF source frequency can be 30 MHz to 300 MHz. In one embodiment, the RF source frequency can be at least 60 MHz. In another embodiment, the RF source frequency can be 160 MHz to 240 MHz. In various embodiments, the RF source power can be 50 W to 10,000 W and the bias power can be 0 W to 200 W. The total gas flow rate can be 50 to 5,000 sccm. The process pressure can be 10 mTorr to 10 Torr. In certain embodiments, the power pulse duration can be 0.1 seconds to 3 seconds (the time between t3 and t4 in FIG. 2A), and in other embodiments, the pulse duration can be 5 seconds or less. This pulse shot plasma can be used to induce gas phase reactions to generate intermediate species for film formation. The application of RF power (t3) may be performed a delay time d2 after stopping (t2) the flow of the second process gas 11. In various embodiments, the delay time d2 may be between 0 and 10 seconds, but may be longer in other embodiments.

[0026] In certain embodiments, at time t3, RF power may be applied as a pulse train including multiple power pulses (eg, two pulses as illustrated in FIG. 2B).

[0027] In an alternative embodiment, the pulse shot plasma phase may begin before stopping the flow of the second process gas 11 (i.e., t3 before t2), which may be beneficial to maximize the generation of intermediate species. In one embodiment, the RF power may be applied as a pulse train including multiple power pulses, one of which may be applied before stopping the flow of the second process gas 11 (i.e., before t2) and another of which may be applied after (i.e., after t2), as shown in FIG. 2C.

[0028] 1C, the plasma 13 generated by applying RF power may include energized species of the first process gas 14. The energized species of the first process gas 14 may react with residual amounts of the second process gas 11 to generate intermediate species 15. In certain embodiments, the intermediate species 15 may include radical species. In one embodiment, the intermediate species 15 may include Si x N y H z The intermediate species 15 may include radical species. In some embodiments, the plasma conditions may be optimized to maximize the concentration of radical species. Additionally, the intermediate species 15 may include elements (e.g., nitrogen atoms) from the first process gas 10. In various embodiments, the intermediate species 15 are then isotropically deposited on the substrate 100 to form the film 16. The presence of the intermediate species 15 in the gas phase distinguishes the ps-PECVD process from the ALD process. While ALD is driven by surface reactions of adsorbed species, the ps-PECVD process involves intermediate species formed in the gas phase. Furthermore, the inventors of the present application have determined that the presence of radical species in the intermediate species 15 can dramatically improve the isotropic film growth, and thereby the conformality of the film 16 (e.g., uniform thickness of the film 16 in the recess 105 and upper surface of the substrate 100), as well as the uniformity of the wet etch rate (WER) of the film 16. Thus, the process conditions, including the parameters of the plasma 13, may be selected to optimize the concentration of radical species in the intermediate species 15. As a result, radical-driven film growth is more prevalent, and thus it may be possible to operate the ps-PECVD process while minimizing ionic damage on the substrate 100 due to reactive ions.

[0029] 2A-2C, formation of intermediate species 15 may continue even after RF power is turned off at time t4 due to residual energized species of the first process gas 14 in the plasma processing chamber. Thus, film growth may continue until the intermediate species 15 are completely depleted. Continued growth of film 16 after RF power is turned off is shown in FIG. 1D, where film 16 may grow uniformly in thickness across the substrate driven by the deposition of intermediate species 15.

[0030] For optimal film growth rate and film quality of the film 16, the duration of the delay time d2 (i.e., the timing of applying RF power t3 in FIGS. 2A-2C) may be important. Therefore, it may be useful to accurately determine the decay profile and the duration of this decay time d1 (i.e., the residence time of the second process gas 11). 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 profile may be calculated based on these parameters. These parameters may be monitored by one or more sensors, including, for example, a pressure monitor, a gas flow monitor, and / or a gas species density monitor. In certain embodiments, the decay profile may be calculated according to the general formula C=C t2 ×e -αt can be approximated as an exponential decay as a function of time t using: t2 is C at t2, and α is a decay constant. The decay constant α may 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 an exponential decay approximation, the residence time is t2 In another embodiment, the residence time may be considered as a time when C is equal to 1% of C. t2 may be considered as a time equal to 5% of the t2 can be determined as N / V based on the equation of state 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 is N / q out can be determined as, where q out is the number of moles in the outflow of the second process gas 11 and is assumed to be constant. out A gas species density monitor may be used to monitor and determine: In the above, the exponential decay or outflow of the second process gas 11 is assumed to be constant, but other approximation methods, such as a Gaussian distribution, may also be used.

[0031] Although not specifically depicted in FIGS. 2A-2C, any other process parameters, such as temperature, may be independently controlled and / or varied at each stage of the ps-PECVD process according to the respective process recipe.

[0032] In various embodiments, the ps-PECVD process may be carried out at a temperature less than 500° C. In certain embodiments, the temperature of the substrate 100 may be maintained between 250° C. and 500° C. This temperature range less than 500° C. may advantageously reduce thermal damage to semiconductor devices during fabrication.

[0033] In various embodiments, the ps-PECVD process may be performed as a cyclic plasma deposition process by repeating the above-described steps illustrated in FIGS. 1A-1D and 2. The process conditions for each cycle of the cyclic plasma deposition according to various embodiments may be selected individually. The cyclic implementation of the ps-PECVD method may advantageously form the film 16 in a substantially layer-by-layer manner, allowing high film conformality and / or precise thickness control. The ps-PECVD process may be performed to achieve a target film thickness. In one embodiment, the film thickness may be between 1 nm and 50 nm.

[0034] In certain embodiments, one cycle of the ps-PECVD process may include multiple pulses of plasma in the pulse-shot plasma phase, which may be beneficial in fine-tuning the formation of intermediate species 15, for example, when the decay time d1 is longer than a few seconds.

[0035] In a pulsed-shot plasma enhanced chemical vapor deposition (ps-PECVD) process, precise control of the limited concentration of intermediate species may be possible by intelligently designing the process recipe. In particular, important process parameters may include gas flow rates, the timing or pulse duration of stopping the flow of the second process gas, and the timing, pulse duration, and conditions of the pulsed-shot plasma. For example, the selection of the delay time d2 (e.g., the time between t2 and t3 in FIG. 2A) may significantly affect the process performance. If a very short period (e.g., less than one-tenth of the decay time d1) is selected for the delay time d2, the residual concentration of the second process gas 11 containing the precursor may approach the value initially set, resulting in an increase in the relative abundance of the intermediate species 15 in the pulsed-shot plasma phase. This may be beneficial for a faster film growth rate per cycle, but may compromise the film conformality and quality. On the other hand, a longer delay time d2 (e.g., greater than half the decay time d1) results in a lower residual concentration of the second process gas 11. Thus, the film growth rate per cycle is slower, but better film conformality and quality may be improved. In various embodiments, the process parameters of the ps-PECVD may be advantageously adjusted according to the film requirements in semiconductor manufacturing. Advantages of the ps-PECVD process may include (i) better film conformality and quality compared to available low-temperature PECVD processes, which may rely on ion-driven film growth, and (ii) faster film growth and lower process temperatures compared to ALD and / or plasma-enhanced ALD (PEALD) processes.

[0036] In various embodiments, the intermediate step may be performed by exposing the substrate 100 to a treatment gas to modify the surface functional groups of the substrate 100 or the film. The intermediate step may be performed before the flow step, during or after the post-plasma film growth step. The treatment gas may include, for example, hydrogen or ammonia (NH3), although other reactive and / or inert gases may be used. The intermediate step may be beneficial in improving the film conformality and / or film quality by hardening and / or trimming defects in the film. Furthermore, the intermediate step may also include a plasma treatment using a treatment gas. In one embodiment, the intermediate step may be a plasma treatment using a plasma including hydrogen. In another embodiment, the intermediate step may be a thermal treatment performed, for example, by heating the substrate 100 under a flow including an inert gas or under vacuum.

[0037] 3A and 3B show cross-sectional views of a recessed substrate 100 after completing a ps-PECVD process according to various embodiments with different resulting film structures.

[0038] In FIG. 3A, film 16 is uniformly formed on substrate 100 with high film conformality, including on the walls of recess 105. As discussed above, it can be difficult with conventional deposition techniques to simultaneously achieve conformal film growth, fast film growth rates, and medium to low processing temperatures, particularly for high aspect ratio features useful in three-dimensional semiconductor devices. Advantageously, by periodically performing the ps-PECVD process at 500° C. or less, the target film thickness can be achieved without compromising film conformality. In certain embodiments, the film thickness variation can be 10% or less of the average film thickness, such as 0.5% to 5% in one embodiment. In one embodiment, film 16 can include silicon nitride and can be used as a spacer material in 3D semiconductor devices such as DRAMs.

[0039] In FIG. 3B, the film 16 has a low film conformality. The film thickness is not uniform across the substrate 100, being thicker near the top surface of the substrate 100 and thinner in the lower half of the recess 105. The inventors of the present application have determined that such non-conformal deposition may occur frequently in conventional low-temperature plasma-enhanced processes, which may be due to the ion-driven film growth in these processes and the low isotropy of the ion flux, especially in 3D structures such as high aspect ratio features. The thickness of the layer in the bottom surface of the recess 105 decreases as the concentration of ions decreases. In this scenario, the film thickness may vary by 20% or more, resulting in a low film conformality. This non-conformal deposition can be prevented by utilizing more isotropic radical-driven film growth using the ps-PECVD method according to various embodiments. The use of ps-PECVD limits the concentration of film precursors and reduces plasma processing time. As a result, the radical species, including silicon and nitrogen for silicon nitride film formation, can be increased while limiting the ion species. Radical species are electronically neutral and therefore may be less susceptible to electric fields and therefore more isotropic. Furthermore, compared to ions, radicals may diffuse slower and take longer to form a film on a surface, which may also be beneficial for improving film conformality.

[0040] It should be noted that in addition to film conformality, the uniformity of film quality across the substrate 100 can also be improved by the ps-PECVD method. For example, one important factor of film quality is the wet etch rate (WER). In particular, the WER in hydrofluoric (HF) acid is an important material property for spacer materials and must be low in dilute HF water. The WER of the spacer can depend on, among other things, the crystallinity, morphology, density, stoichiometry, and trap density. The inventors of the present application have identified that many conventional low-temperature processes can suffer from high WER and / or non-uniform distribution of WER across the film in 3D structures. In one example, wet etching can preferentially etch the film in the recesses, resulting in poor film conformality (i.e., poor wet etch resistance of the film in the recesses). This problem of non-uniform WER, along with high WER, can be mitigated or eliminated by the isotropic radical-driven film growth enabled by the ps-PECVD method according to various embodiments.

[0041] 4A to 4C show process flow diagrams of ps-PECVD according to various embodiments. The process flow can follow the above-mentioned figures (FIGS. 1A to 1D and 2A to 2C), so repeated description is omitted.

[0042] In FIG. 4A, the process flow 40 begins with a flow-in phase by flowing a first process gas 10 and a second process gas 11, which contain film precursors, into a plasma processing chamber holding a substrate 100 (block 410, FIG. 1A). This is followed by a flow-off phase by stopping the flow of the second process gas 11 while continuing to flow the first process gas 10 (block 420, FIG. 1B). The process proceeds to a pulse-shot plasma phase by generating a plasma that forms intermediate species 15 (block 430, FIG. 1C). A film begins to form as the intermediate species 15 deposit on the substrate 100, and a post-plasma film growth phase (FIG. 1D) continues after the source power is turned off to maintain the plasma.

[0043] In FIG. 4B, process flow 42 shows a cyclical implementation of the ps-PECVD method, beginning with a flow phase by flowing a first process gas 10 (block 412) into a plasma processing chamber holding a substrate 100, and a cyclical plasma treatment can be performed while the first process gas 10 is flowing. The cyclical plasma treatment can be initiated by pulsing a second process gas 11 containing a film precursor into the plasma processing chamber (block 422, FIG. 1A and FIG. 1B). This pulsing corresponds to both the flow phase and the stop flow phase in the previous embodiment. Next, a pulse of RF source power can be applied to generate a plasma to form intermediate species 15 (block 432, FIG. 1C), followed by a post-plasma film growth phase (block 440, FIG. 1D) similar to the previous embodiment. In certain 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 processing gas to modify surface functional groups on the substrate 100 or film.

[0044] In FIG. 4C, process flow 44 illustrates an alternative embodiment of the ps-PECVD method, which begins by flowing a first process gas 10 and a second process gas 11, including film precursors, into a plasma processing chamber holding a substrate 100 (block 414, FIG. 1A). Power can then be applied to electrodes in the plasma processing chamber to generate a plasma in the plasma processing chamber (block 430, FIG. 1C) to form a film on the substrate 100. Within 5 seconds after block 430, the flow of the second process gas 11 is shut off (block 420, FIG. 1B) while maintaining the flow of the first process gas 10. Alternatively, the supply of power to the electrodes and the shutoff of the flow of the second process gas 11 may be performed simultaneously (block 425).

[0045] FIG. 5 illustrates a plasma system for performing a ps-PECVD process according to various embodiments.

[0046] For illustration, Figure 5 shows substrate 100 disposed on a substrate holder 554 (e.g., a circular electrostatic chuck (ESC)) inside plasma processing chamber 510 near the bottom. Substrate 100 may optionally be maintained at a desired temperature using a heater / cooler 556 surrounding substrate holder 554. The temperature of substrate 100 may be maintained by a temperature controller 540 connected to substrate holder 554 and heater / cooler 556. The ESC may be coated with a conductive material (e.g., a carbon-based or metal nitride-based coating) so that electrical connections may be made to substrate holder 554.

[0047] 5, the substrate holder 554 can be the bottom electrode of the plasma processing chamber 510. In the exemplary embodiment of FIG. 5, the substrate holder 554 is connected to an RF bias power supply 570. The conductive circular plate near the top inside the plasma processing chamber 510 is the top electrode 552. In FIG. 5, the top electrode 552 is connected to an 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 and above the top ceramic window.

[0048] Gases may be introduced into the plasma processing chamber 510 by a gas delivery system 520. The gas delivery system 520 comprises multiple gas flow controllers for controlling the flow of multiple gases into the chamber. In some embodiments, an optional center / edge splitter may be used to independently adjust the gas flow rates at the center and edge of the substrate 100. Furthermore, the gas delivery system 520 may have a special showerhead configuration located on top of the plasma processing chamber 510. For example, the gas delivery system 520 may be integrated with the upper electrode 522 and have a showerhead configuration on the upper electrode 522, covering the entire substrate 100, including multiple appropriately spaced gas inlets. Alternatively, gases may be introduced through dedicated gas inlets in any other suitable configuration. The plasma processing chamber 510 may further be equipped with one or more sensors 515, such as a pressure monitor, a gas flow monitor, and / or a gas species density monitor. The sensor 515 may be integrated as part of the gas delivery system 520 in certain embodiments. The sensor 515 and the 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 FIG. 2A) and the power pulse period (e.g., the time between t3 and t4 in FIG. 2A).

[0049] An RF bias power supply 570 can be used to provide continuous wave (CW) or pulsed RF power to maintain a plasma such as plasma 560. Plasma 560, shown between top electrode 552 and bottom electrode (which is also substrate holder 554), illustrates a direct plasma generated near the substrate 100 in the plasma processing chamber 510 of plasma processing system 50.

[0050] The configuration of the plasma processing system 50 described above is merely exemplary. In alternative embodiments, various alternative configurations of the plasma processing system 50 can be used. For example, an inductively coupled plasma (ICP) may be used with RF source power coupled to a planar coil above a top dielectric cover, and gas inlets and / or gas outlets may be coupled to a top wall, etc. In various embodiments, RF power, chamber pressure, substrate temperature, gas flow rates, and other plasma processing parameters may be selected according to a respective process recipe. In some embodiments, the plasma processing system 50 may be a resonator, such as a helical resonator.

[0051]

[0023] Exemplary embodiments of the present invention are summarized herein. Other embodiments can be seen throughout the specification and claims appended hereto.

[0052] Example 1. A plasma processing method comprising: flowing a first gas and a second gas into a plasma processing chamber containing a substrate, the second gas comprising a film precursor; at a first time instance, blocking the flow of the second gas into the plasma processing chamber while maintaining the flow of the first gas; and at a second time instance after the first time instance, supplying power to an electrode of the plasma processing chamber to generate a plasma in the plasma processing chamber, exposing a surface of the substrate to the generated plasma to form a film on the substrate.

[0053] Example 2. The method of example 1, wherein the second time instance is separated from the first time instance by a time delay, the time delay being less than or equal to a residence time of the second gas in the plasma processing chamber.

[0054] Example 3. The method of example 1 or 2, wherein the film precursor comprises a silane containing Cl, C, H, N, or F, or a borane containing Cl, C, H, N, or F.

[0055] Example 4. The method of any one of Examples 1-3, wherein the film comprises a dielectric material comprising Si, B, H, N, O, C, or F.

[0056] Example 5. The method of any one of Examples 1-4, wherein the first gas comprises nitrogen or dinitrogen (N2) and the film comprises silicon nitride or a metal nitride.

[0057] Example 6. The method of any one of Examples 1-5, further comprising monitoring one or more of a pressure of the plasma processing chamber, a gas flow rate of the first process gas, a gas flow rate of the second process gas, a partial pressure of the first process gas, or a partial pressure of the second process gas, and determining timing of the first time instance and the second time instance based on the monitoring.

[0058] Example 7. The method of any one of Examples 1-6, wherein the method is carried out at a temperature of 500° C. or less.

[0059] Example 8. The method according to any one of Examples 1 to 7, wherein the supplying of power to the electrode is carried out by applying RF power having a frequency of at least 60 MHz.

[0060] Example 9. A method of forming a film on a substrate comprising: flowing a first gas into a plasma processing chamber holding the substrate; and performing a cyclic plasma process while flowing the first gas, the cyclic plasma process comprising a plurality of cycles, each of the plurality of cycles comprising pulsing a second gas comprising a film precursor into the plasma processing chamber; and applying a first pulsed power to an electrode coupled to the plasma processing chamber to generate a plasma to form a gaseous intermediate species from the film precursor, the gaseous intermediate species being deposited on the substrate to form a film, the method comprising: applying the first pulsed power to an electrode coupled to the plasma processing chamber to generate a plasma to form a gaseous intermediate species from the film precursor, the gaseous intermediate species being deposited on the substrate to form a film.

[0061] Example 10. The method of example 9, wherein the periodic plasma treatment further comprises applying one or more subsequent power pulses to the electrodes after applying the initial power pulse.

[0062] Example 11. The method of example 9 or 10, wherein applying the pulse of electrical power is performed with a delay relative to applying the pulse of the second gas, the delay being 10 seconds or less.

[0063] Example 12. The method of any one of Examples 9-11, wherein the first gas comprises nitrogen or dinitrogen (N2), the film precursor comprises silicon, and the film comprises silicon nitride.

[0064] Example 13. The method of any one of Examples 9-12, wherein one or more of the multiple cycles further comprises performing an intermediate step, the intermediate step comprising exposing the substrate to a treatment gas to modify surface functional groups of the substrate or film, the treatment gas comprising H, C, N, O, F, He, Ar, Ne, or Kr.

[0065] Example 14. The method of any one of Examples 9-13, wherein the process gas comprises dihydrogen (H2), dioxygen (O2), or ammonia (NH3).

[0066] Example 15. The method of any one of Examples 9-14, wherein the second gas pulse duration is 10 seconds or less, or the power pulse duration is 5 seconds or less.

[0067] Example 16. The method of any one of Examples 9-15, wherein the substrate has a recess and the film has a thickness variation of 10% or less.

[0068] Example 17. A plasma processing method comprising: flowing a first gas and a second gas into a plasma processing chamber containing a substrate, the second gas comprising a film precursor, the 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, and a temperature of the substrate is less than or equal to 500° C.; at a first time instance, supplying power to an electrode of the plasma processing chamber to generate a plasma in the plasma processing chamber, exposing a surface of the substrate to the generated plasma to form a film on the substrate; and at a second time instance, shutting off the flow of the second gas into the plasma processing chamber while maintaining the flow of the first gas.

[0069] Example 18. The method of example 17, wherein the first time instance and the second time instance are the same.

[0070] Example 19. The method of example 17, wherein the second time instance is within 5 seconds after the first time instance.

[0071] Example 20. The method of any one of Examples 17-19, wherein powering the electrode comprises applying pulses of RF source power, the RF source power having a frequency of at least 60 MHz.

[0072] Although the present invention has been described with reference to several exemplary embodiments, it is not intended to be construed in a limiting sense. Various modifications and combinations of the exemplary embodiments, as well as other embodiments of the present invention, will become apparent to those skilled in the art upon reference to the above description. It is therefore intended that the appended claims cover such modifications or embodiments.

Claims

1. 1. A method of plasma processing, comprising: flowing a first gas and a second gas into a plasma processing chamber containing a substrate, the second gas comprising a film precursor, and the substrate comprising a recess; At a first time instance, shutting off the flow of the second gas into the plasma processing chamber while maintaining the flow of the first gas; At a second time instance after the first time instance, supplying power to an electrode of the plasma processing chamber to generate a plasma in the plasma processing chamber, wherein a surface of the substrate is exposed to the plasma and a film is formed on the substrate, the film having a thickness variation of 10% or less; A method comprising:

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

3. 10. The method of claim 1, wherein the film precursor comprises a silane containing Cl, C, H, N, or F, or a borane containing Cl, C, H, N, or F.

4. 10. The method of claim 1, wherein the film comprises a dielectric material comprising Si, B, H, N, O, C, or F.

5. The first gas is nitrogen or dinitrogen (N ２ ), The method of claim 1 , wherein the film comprises silicon nitride or a metal nitride.

6. moreover, monitoring one or more of 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; determining timing of the first time instance and the second time instance based on the monitoring step; 2. The method of claim 1, comprising:

7. 10. The method of claim 1, wherein the method is carried out at a temperature of 500°C or less.

8. The method of claim 1 , wherein the step of powering the electrode is performed by applying RF power having a frequency of at least 60 MHz.

9. 1. A method of forming a film on a substrate, comprising: flowing a first gas into a plasma processing chamber holding the substrate, the substrate having a recess; performing a periodic plasma treatment while the first gas is flowing, the periodic plasma treatment having a plurality of cycles, each of the plurality of cycles including: pulsing 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 a plasma and form gaseous intermediate species from the film precursor, the gaseous intermediate species being deposited across the substrate to form the film, the film having a thickness variation of 10% or less; having Steps and A method comprising:

10. 10. The method of claim 9, wherein the cyclic plasma treatment further comprises applying one or more subsequent pulses of power to the electrode after applying a first pulse of power.

11. 10. The method of claim 9, wherein the step of applying the pulse of first power is performed with a delay relative to the application of the pulse of second gas, the delay being 10 seconds or less.

12. The first gas is nitrogen or dinitrogen (N ２ 10. The method of claim 9, wherein the film precursor comprises silicon and the film comprises silicon nitride.

13. One or more of the plurality of cycles further comprises performing an intermediate step; 10. The method of claim 9, wherein the intermediate step comprises exposing the substrate to a process gas to modify surface functional groups on the substrate or on the film, the process gas comprising H, C, N, O, F, He, Ar, Ne, or Kr.

14. The process gas is dihydrogen (H ２ ), dioxygen (O ２ ), or ammonia (NH ３ 14. The method of claim 13, comprising:

15. The method described in claim 13, wherein the intermediate step is performed between the step of applying a pulse of the second gas and the step of applying a pulse of the first power to the electrode.

16. 10. The method of claim 9, wherein the second gas pulse duration is 10 seconds or less, or the power pulse duration is 5 seconds or less.

17. A method for forming a film on a substrate, comprising: The method comprises: flowing a first gas into a plasma processing chamber holding the substrate; performing a cyclic plasma treatment during the step of flowing the first gas, the cyclic plasma treatment having a plurality of cycles, each of the plurality of cycles comprising: pulsing a second gas comprising a film precursor into the plasma processing chamber; applying a first pulse of power to an electrode coupled to the plasma processing chamber to generate a plasma and form gaseous intermediate species from the film precursor, the gaseous intermediate species being deposited across the substrate to form the film; and exposing the substrate to a process gas between the pulsing of the second gas and the pulsing of the first power to modify surface functional groups on the substrate or on the film, the process gas comprising dihydrogen (H 2 ), dioxygen (O 2 ), or ammonia (NH 3 ); and A method comprising:

18. The method of claim 17, wherein the step of applying the first pulse of electrical power is performed with a delay relative to the step of applying the second pulse of gas; 18. The method of claim 17, wherein the delay time is 10 seconds or less.

19. The method of claim 17, wherein the pulse time of the first power pulse is 5 seconds or less.

20. The method of claim 20, wherein the first gas comprises nitrogen and the second gas comprises silane or borane; the substrate has a recess; 18. The method of claim 17, wherein the film has a thickness variation of 10% or less.

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