Irradiation of substrates with ions having a target mass using pulsed bias phase control - Patent Application 20070122997

Abstract

A method of plasma processing includes generating a plasma by coupling a source power pulse to a plasma processing chamber containing a substrate holder configured to support a substrate. The plasma includes first ions having a first mass and second ions having a second mass greater than the first mass. An ion density ratio of the second ions to the first ions is a first ratio. The method further includes, after a delay between the source power pulse and a delayed bias power pulse, applying a delayed bias power pulse to the substrate holder to deliver an energetic ion flux of the second ions to the substrate. The delay is selected based on diffusion time constants of the first ions and the second ions such that the ion density ratio of the second ions to the first ions is a second ratio greater than the first ratio.

Description

[Technical Field]

[0001] The present invention relates generally to plasma processing, and in particular embodiments to a method and system for plasma processing that uses a bias pulse to bombard a substrate with ions having a target mass. [Background technology]

[0002] The fabrication of electronic devices in a substrate, such as integrated circuits in a semiconductor substrate, typically involves a series of manufacturing techniques, including the formation, patterning, and removal of multiple layers of materials on the substrate. There is a consistent and continuing drive to improve the manufacturing processes, functionality, and performance of microscale (and smaller) electronic devices. Novel developments, such as new chemistries and new advanced methods for process control, may be required to provide improvements beyond the limits of current technology.

[0003] Plasma processing is used in many manufacturing techniques, such as deposition and etching, in the fabrication of electronic devices. Pulsed plasma processing methods can utilize pulses of source power (SP) and / or bias power (BP) to control various parameters during plasma processing. For example, radio frequency (RF) power or direct current (DC) power can be pulsed. RF power can also be combined with a DC offset, such as when applying a bias pulse to an electrode.

[0004] A plasma may contain a variety of species intermixing within a plasma processing chamber. Furthermore, each species within the plasma may produce a variety of plasma products (e.g., ions, radicals, electrons, and dissociation products). Each species of plasma product may have different properties and may be included in the plasma for a different purpose. For example, plasma products of different species may have different chemical properties, which may include different reactivities with various materials of the substrate being processed. Furthermore, the species within the plasma (and consequently the corresponding plasma products) may have a wide range of different masses, in addition to many other distinguishing characteristics. Summary of the Invention [Problem to be solved by the invention]

[0005] Control over individual species and species products within a plasma can be advantageous to maximize the role of each species during plasma processing. For example, it may be desirable to control the relative flux rates of various energetic plasma products at the substrate to further optimize desired parameters such as selectivity, etch profile, critical dimension, etc. In particular, ions with different properties and different roles in a given plasma process may have different masses. At a particular point during plasma processing, one or more species of heavier ions may have beneficial (chemical, physical, etc.) properties at the substrate, while other lighter ions may have detrimental properties. Therefore, methods and apparatus that can preferentially deliver heavier ions to the substrate during plasma processing may be desirable. [Means for solving the problem]

[0006] In an embodiment of the present invention, a method of plasma processing includes generating a plasma by coupling a source power pulse to a plasma processing chamber containing a substrate holder configured to support a substrate. The plasma is contained within the plasma processing chamber. The plasma includes first ions having a first mass and second ions having a second mass. The second mass is greater than the first mass. An ion density ratio of the second ions to the first ions is a first ratio. The method further includes, after a delay between the source power pulse and a delayed bias power pulse, applying a delayed bias power pulse to the substrate holder to deliver an energetic ion flux of the second ions to the substrate. The delay is selected based on a diffusion time constant of the first ions and a diffusion time constant of the second ions such that the ion density ratio of the second ions to the first ions is a second ratio greater than the first ratio.

[0007] In another embodiment of the present invention, a method of plasma processing includes generating a plasma by coupling a first source power pulse to a plasma processing chamber containing a substrate holder configured to support a substrate. The plasma is contained within the plasma processing chamber. The plasma includes first ions having a first mass and second ions having a second mass, the second mass being greater than the first mass. The method further includes collecting measurements indicative of ion density within the plasma, calculating a delay according to an ion diffusion time constant determined from the measurements, coupling a second source power pulse to the plasma processing chamber to generate a plasma including the first ions and the second ions, and applying a bias power pulse to the substrate holder after the delay to deliver an energetic ion flux including the second ions to the substrate. The delay is between the second source power pulse and the bias power pulse.

[0008] In yet another embodiment of the present invention, a plasma processing apparatus includes a plasma processing chamber configured to contain a plasma including first ions having a first mass and second ions having a second mass, the second mass being greater than the first mass. The plasma processing apparatus further includes a source power supply configured to couple a source power pulse to the plasma processing chamber to generate the plasma, a measurement member operably coupled to the plasma and configured to collect measurements indicative of ion density in the plasma, a controller coupled to the measurement member and configured to calculate a delay according to an ion diffusion time constant determined from the measurements, a substrate holder disposed within the plasma processing chamber and configured to support a substrate, and a bias power supply coupled to the controller and the substrate, the bias power supply configured to apply a bias power pulse to the substrate holder after a delay to deliver an energetic ion flux including the second ions to the substrate. The delay is between the source power pulse and the bias power pulse.

[0009] For a more complete understanding of the present invention and its advantages, reference is now made to the following descriptions taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0010] [Figure 1] 1A and 1B illustrate schematic diagrams of an exemplary plasma process utilizing delayed bias power pulses to deliver an energetic ion flux with an increased flux of heavier ions relative to the flux of lighter ions, in accordance with embodiments of the present invention. [Figure 2] 1A and 1B illustrate schematic diagrams of exemplary plasma processes utilizing delayed bias power pulses as part of a cyclical process in accordance with embodiments of the present invention. [Figure 3] 1A and 1B illustrate schematic diagrams of exemplary plasma processes utilizing delayed bias power pulses plus one or more additional bias power pulses in accordance with embodiments of the present invention. [Figure 4] FIG. 1 is a schematic diagram of an exemplary plasma processing apparatus that can be used to deliver an energetic ion flux with an increased ion density ratio of heavier ions to lighter ions, in accordance with an embodiment of the present invention. [Figure 5] 1 is a schematic diagram of an exemplary plasma processing apparatus including radio frequency source power inductively coupled to a plasma and radio frequency bias power coupled to a substrate holder in accordance with an embodiment of the present invention. [Figure 6] 1 illustrates an exemplary method of plasma processing utilizing a bias power scan that can be used to calculate ion diffusion time constants used to determine plasma processing parameters for a delayed bias pulse, in accordance with an embodiment of the present invention. [Figure 7] 10A and 10B illustrate schematic diagrams of an exemplary process parameter measurement sequence utilizing bias power test pulses to measure a voltage response indicative of ion density in a plasma for use in calculating an ion diffusion time constant, in accordance with an embodiment of the present invention. [Figure 8] 1 is a schematic diagram of an exemplary plasma processing apparatus including a measurement element having a voltage divider used to measure voltage responses, in accordance with an embodiment of the present invention. [Figure 9]FIG. 1 is a schematic diagram of an exemplary plasma processing apparatus including a metrology element having VI probes used to measure voltage and current responses, in accordance with an embodiment of the present invention. [Figure 10] 1 illustrates an exemplary method of plasma processing utilizing time-resolved measurements within one or more pulse periods that can be used to calculate ion diffusion time constants for determining plasma processing parameters of a delayed bias pulse, in accordance with an embodiment of the present invention. [Figure 11] 1 is a schematic diagram of an exemplary plasma apparatus including an external metrology member used to take measurements indicative of ion density within a plasma, in accordance with an embodiment of the present invention. [Figure 12] 1 illustrates an exemplary method for plasma processing that utilizes delayed bias power pulses to optimize the plasma process by calculating the diffusion timescales of different ions, according to an embodiment of the present invention. [Figure 13] 1 illustrates an exemplary method of plasma processing utilizing delayed bias power pulses to monitor the plasma process for parameter drift, which indicates the need for process optimization, in accordance with an embodiment of the present invention. [Figure 14] 1 illustrates an exemplary method of plasma processing utilizing delayed bias power pulses to deliver an energetic ion flux with an increased flux of heavier ions relative to the flux of lighter ions, according to an embodiment of the present invention. [Figure 15] 1 illustrates an exemplary method of plasma processing that utilizes measurements indicative of ion density to calculate delays according to ion diffusion time constants determined from the measurements and to deliver energetic ion flux of heavier ions, according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Corresponding numbers and symbols in different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate relevant aspects of the embodiments and are not necessarily drawn to scale. The edges of features drawn in the figures do not necessarily indicate the ends of the extents of the features.

[0012] The making and use of various embodiments are discussed in detail below. However, it should be understood that the various embodiments described herein are applicable in a variety of specific situations. The specific embodiments discussed are merely illustrative of specific ways to make and use the various embodiments and should not be construed as limiting in scope. Unless otherwise indicated, the terms "approximately," "about," and "substantially" mean within 10%, preferably within 5%, of a given value, or, if substantially zero, less than 10%, preferably less than 5%, etc., of the equivalent amount.

[0013] Plasma processing techniques are constantly being improved and developed to achieve high precision in both material etching and deposition. In certain areas, such as atomic layer etching (ALE), new processes and tools are being developed for this purpose. The continued application of Moore's Law in the semiconductor industry requires the processing of features on the nanometer scale. However, the margin for error during nanoscale etching and deposition processes is very small. Therefore, improvements in the energy control and precision of the bombardment of ions from processing plasmas are desirable to achieve precise etching and deposition of materials.

[0014] Various species are included in the processing plasma for a variety of reasons. Precursor gases may include species that form ions and radicals in the processing plasma to facilitate processing of the substrate. In the simplest case, a given species may be ionized in the plasma to form ions, or may break down into fragments that form radicals. In more complex cases, multiple species or fragments of species may interact to form complex dissociation products.

[0015] Each precursor species, ion species, and radical species in the plasma has unique chemical and physical properties. For example, different ion species may have different reactivity thresholds (i.e., different etching characteristics) with substrate materials, such as mask materials and target materials. Furthermore, different ion species may have different masses. In one particular example, lighter ions A at the target energy + At the target energy relative to the substrate, while decreasing the flux of heavier ions B + For example, although both ions may be included in the plasma for different reasons, providing lighter ions to the substrate simultaneously with heavier ions may reduce selectivity.

[0016] A + and B + Because both ions have a positive charge, they will both be accelerated toward the negative bias voltage applied to the substrate. However, heavier ions have a longer diffusion time, which increases the average ion mass over the duration of the off period (e.g., afterglow phase) of the pulsed plasma discharge. Specifically, lighter ions diffuse to the chamber walls faster than heavier ions when the plasma source power is removed. Thus, B + The ion density of A + By applying an acceleration voltage to the process target substrate during a specific period of the plasma pulse cycle that is higher than the ion density of the heavier B + Facilitates preferential energetic irradiation of the substrate by the ions.

[0017] Such periods of the plasma pulse cycle having a sufficient heavy ion density combined with negligible or no resulting density of lighter ions occur after the off period after the lighter ions have had time to diffuse. The inventors have discovered that the specific time to apply bias power to provide a desired ratio of heavy ions to light ions with a desired ion flux at a desired energy depends on factors such as the diffusion time of the ion species. The plasma processing methods and apparatus described herein may advantageously solve the problem of controllably increasing the flux of heavier ion species relative to the flux of lighter ion species in an energy ion flux by applying a delayed bias power pulse (the delay based on the diffusion time of the ion species) after the source power is removed.

[0018] Many other benefits may also be achieved by using the various plasma methods and apparatus described herein. While there may be many reasons why a heavier ion species is desirable while one or more lighter ion species is not, one particular reason may be that the lighter ions reduce selectivity by etching the mask material. In this particular example, reducing or eliminating the energy flux of the lighter ion species while providing the desired energy flux of the heavier ion species may have the advantage of etching the target material with increased selectivity.

[0019] Without the ability to preferentially deliver heavy ions at a targeted energy, there would be an undesirable trade-off between including light ions in the plasma to achieve a benefit for one purpose and excluding light ions from the plasma to prevent a detrimental effect for another purpose. By preferentially delivering heavy ions, light ions can be advantageously included in the plasma to achieve a benefit without suffering a detrimental effect. In relation to the above example, ion A + and B + can both be contained within the plasma while still achieving selective etching of the target material.

[0020] One possible benefit of improved control over the ratio of heavier to lighter ion species is improved process flexibility. As previously mentioned, in certain circumstances, improved mass-based control can result in a wider range of plasma species being included in the plasma. Improving selectivity during the etching process can also allow for thinner mask materials and higher throughput. In some cases, achievable selectivity can be high enough to enable high-speed quasi-atomic layer etching (QALE) without gas-phase separation.

[0021] As the lighter ion species diffuse, their average mass increases, which also has the benefit of narrowing the ion energy distribution (IED) peak, which may advantageously also increase the flexibility of the process by allowing for a more targeted energy range (i.e., imparted to the heavier ion species using a delayed bias pulse).

[0022] Furthermore, lighter radical species may also be desirable for etching the target material. Because radicals are charge neutral, lighter radical species may be less affected by the timing of the applied bias pulse. Thus, the present method and apparatus may also provide the advantage of allowing lighter radical species along with heavier ionic species to reach the substrate, while desirably eliminating lighter ionic species.

[0023] The ability to preferentially deliver heavier ion species to a substrate at a given (desired, target, etc.) energy can advantageously enable improved control over plasma processing. For example, the placement and duration of the delayed bias pulse can be used as a new "control knob" to control the ratio of heavier energetic ion species to one or more energetic ion species at the substrate, the flux of heavier energetic ion species to the substrate, and the ratio of heavier energetic ion species to one or more radical species at the substrate (e.g., the ratio of energetic ion flux to radical flux).

[0024] The parameters of the delayed bias pulse are based on the diffusion time constants of heavier ions and one or more lighter ions. The specific values ​​of the delayed bias pulse parameters are determined according to the desired results for a given plasma process (e.g., desired energetic heavy ion flux, energetic light ion flux, heavy ion dose, ion energy, etc.). The diffusion time constants of ions within the plasma may depend primarily on the mass of the ions and the electron temperature of the plasma, along with the geometry of the plasma processing chamber. These parameters may have the advantage of being stable and reproducible, which may advantageously allow a given optimized parameter set to be used for multiple substrates (e.g., wafers) and / or across multiple tools without the need for re-optimization.

[0025] The embodiments provided below describe various methods, systems, and apparatus for plasma processing, particularly methods, systems, and apparatus that involve applying a bias pulse to irradiate a substrate with ions having a target mass. For example, in various embodiments, a delayed bias power pulse is applied to deliver an energetic ion flux of heavier ions after a delay based on the diffusion time constant of the ions in the plasma. The following description describes the embodiments. FIG. 1 is used to describe an exemplary plasma process utilizing a delayed bias power pulse. Two additional exemplary plasma processes utilizing a delayed bias power pulse are described using FIGS. 2 and 3. Two exemplary plasma processing apparatuses are described using FIGS. 4 and 5. An exemplary method of plasma processing utilizing a bias power scan is described using FIG. 6, while FIG. 7 is used to describe an exemplary process parameter measurement sequence. Two exemplary plasma processing apparatuses including a measurement element are described using FIGS. 8 and 9. An exemplary method of plasma processing utilizing time-resolved measurements within a pulse period is described using FIG. 10, while FIG. 11 is used to describe an exemplary plasma processing apparatus. Four additional exemplary methods of plasma processing are then described using FIGS. 12-15.

[0026] FIG. 1 schematically illustrates an exemplary plasma process utilizing delayed bias power pulses to deliver an energetic ion flux with an increased flux of heavier ions relative to the flux of lighter ions, in accordance with an embodiment of the present invention.

[0027] 1, a plasma process 100 is described using a schematic timing diagram 101 showing source power and bias power, a qualitative graph 102 showing the relative densities of two ions in the plasma, and a qualitative graph 103 of the ratio of the two ion densities. The schematic timing diagram 101 shows the SP pulse width 113 and the power P S SP pulse 12 (source power pulse) having a width 115 of BP pulse and a power P B The SP pulse 12 includes a BP pulse 14 (bias power pulse) having a pulse period 117. The SP pulse 12 and the BP pulse 14 are separated by a delay 116. The SP pulse 12 followed by the BP pulse 14 may be repeated, for example, as part of a cyclic process having a pulse period 117. Optionally, there may be a BP off time 118 during which the bias power is off before the start of the next SP pulse 12.

[0028] The SP pulse 12 is used to generate a plasma (e.g., in a plasma processing chamber of a plasma processing apparatus). The plasma may contain many additional species, but for simplicity, only two species of the generated plasma are considered here: Species A (e.g., a first species) and Species B (e.g., a second species). Species A and Species B (and their various plasma products, such as ions and radicals) may have different properties, such as different reactivities with respect to the material of the substrate (i.e., target substrate) being processed using the plasma.

[0029] While the source power is applied (i.e., while the source power is on), the glow phase 22 of the plasma is maintained. During the glow phase 22, mass M A+ A species A ion (A + ) and mass M B+ (>M A+ ) with species B ion (B+ ) is generated, and the ion density n A+ and ion density n B+ The n in the glow phase 22 is increased. A+ and n B+ There may be a difference between the ion densities n and n , or the ion densities may be similar, resulting in an ion density ratio n B+ :n A+ (labeled B:A herein for ease of reading) is approximately 1.

[0030] However, it should be noted that these qualitative graphs show relative ion densities (i.e., normalized), and are not intended to show absolute ion densities. Thus, an ion density ratio B:A greater than 1 indicates a B + The density of ions is A + This shows that the maximum absolute A + The maximum absolute B in the glow phase of ion density 22 + Even if the ion density is 1000 times greater than the absolute A, B:A is still defined to be 1 because the ion densities are normalized. Continuing with this example, an ion density ratio B:A of 10 is + The ion density is, where, absolute B + 100 times the ion density (A + B for ions + This indicates that the increase is merely an increase in the number of ions.

[0031] After the source power is removed (i.e., PS=0, source power off), the plasma enters an afterglow phase 24 characterized by the cooling and recombination of ions and electrons. During the onset of the afterglow phase 24 (e.g., the initial afterglow 125 of the afterglow phase 24), both ion densities n A+ and n B+ decreases rapidly. The heavier ions B + is ion A +diffusing more slowly than B, and their ion density ratio B:A increases, but not dramatically (as shown qualitatively). This may be because a relatively short time has passed in the initial afterglow 125, when both densities are still high, allowing different diffusion rates to affect the ion density ratio.

[0032] It should be noted that the graphs shown and described herein are schematic in nature and do not take into account certain effects such as the effect of bias power on the plasma (e.g., if it is negligible compared to the source power). However, if the source is turned off long enough, the discharge will eventually transition from a high-density plasma to a low-density capacitive discharge when the bias power is on. This situation is not shown here for simplicity, but may exist nonetheless.

[0033] Both ion densities n in the initial afterglow 125 A+ and n B+ After a significant decrease in mass, the heavier ions B + The slower diffusion rate of n A+ and n B+ This stage of the afterglow phase 24 can be loosely referred to as the late afterglow 126. As the afterglow phase 24 enters the late afterglow 126, the ion density n A+ approaches zero, while the ion density n B+ is still much higher. A+ is n B+ is decreasing at a faster rate than n B+ The ion density ratio B:A increases rapidly while continues to decrease.

[0034] ION A + and B + may have different properties for a substrate being processed using plasma process 100. For example, A + The ions are generally B +ions or may be more reactive than desired for the particular material of the substrate. + The ions may be more reactive than desired with respect to the mask material of the substrate (e.g., used to prevent etching / deposition processes from occurring in the underlying material). This reduces the energy imparted to the ions to etch the target material of the substrate by a factor of A. + The concentration of ions may be high enough to allow the mask material to be etched, thereby undesirably reducing selectivity. + The threshold ion energy of the ions is B for etching the target material of the substrate. + The ion energy may be lower than the threshold ion energy. + When ions are accelerated to the substrate with enough energy (i.e., using an applied bias power) to etch the target material, A + Ions are also accelerated with enough energy to etch the mask material, reducing selectivity.

[0035] The delayed BP pulse 14 can be used to deliver energetic ions to a substrate as part of a deposition process, an etching process, or any other process utilizing ions. In one embodiment, the delayed BP pulse 14 is used as part of the main etch of the target material. The selectivity of the main etch is determined by the B + The main etch may be applied for a relatively long time, and the A + In addition, the radical A of species A can be easily converted to a cation with a high selectivity. · can be useful for etching the target material. In this case, the main etch is advantageously performed at an energy B + Ions and Energy A + A where the ion flux is negligible · Contains radicals.

[0036] Energy B+ The ion flux may be lower than if the bias power was applied earlier (due to lower ion density), the ion angular distribution is narrower, and the energy A + The ion flux is reduced or becomes substantially zero. A narrow angular distribution can be advantageous for etching high aspect ratios (e.g., at the bottom of trenches or holes, such as for vias).

[0037] In various embodiments, species A (first species) is a reactive species. In some embodiments, species A includes a halogen, and in one embodiment, is a halogen gas. For example, species A can be chlorine (e.g., Cl, Cl). Species A can also be fluorine (e.g., F, F). Species A can also be an inert species. In one embodiment, species A is helium (He). In various embodiments, species B (second species) is an inert species. In some embodiments, species B includes a rare element, and in one embodiment, is argon (Ar). In another embodiment, species B is krypton (Kr). For example, the source gas for the plasma can be a mixture of Cl and Kr gases or a mixture of He and Ar gases, etc.

[0038] A + and B + One way to compare the diffusion rates of A is to compare their respective ion diffusion time constants, which measure the time it takes for the ion density to decrease by a certain amount (e.g., to 1 / e ≈ 37% of its initial value in the case of exponential decay). For example, A + The diffusion time constant τ A+ and B + The diffusion time constant τ B+ Both are shown in the qualitative graph 102. In particular, τ A+ is τ B+ is shorter (i.e., because of the reduced mass), and as already discussed, the ion density n B+ Compared to the ion density n A+ This results in a much sharper decrease in

[0039] It should be noted that the ion diffusion time constant may not be the only mechanism by which ion density decreases. For example, other mechanisms, such as recombination, may also play a role in decreasing ion density over time. As such, a more general parameter may be the ion lifetime in a plasma processing chamber. While the methods and apparatus described herein refer to the ion diffusion time constant for simplicity, the ion lifetime may also be used as a comparison parameter. Furthermore, it is understood that considering the ion lifetime includes considering the ion diffusion time constant. Thus, decisions made according to the ion lifetime are also made according to the ion diffusion time constant.

[0040] During the glow phase 22, the ion density is at a maximum. After the source power is removed, the afterglow phase 24 begins, during which there is a rapid decrease in ion and electron temperature, a small change in reactive neutral density, and ions diffuse toward the chamber walls. Generally, for a plasma with one ion species, the plasma diffusion time constant τ D is the radius of the chamber R and the ambipolar diffusion coefficient D A More specifically, for many systems, τ D =R 2 / D A is.

[0041] However, the ambipolar diffusion coefficient D A depends on the mass of the diffusing species. For low gas pressures, τ D =R / v s where v s is approximately (k B T e / M i ) 1 / 2 is the ion sound velocity (i.e., the speed of the ion acoustic wave through the plasma), and T e is the electron temperature, and M i is the ion mass, and k Bは、 is Boltzmann's constant. Importantly, the diffusion time constant τ of each ion depends on variables that are known or can be measured (directly or indirectly). As a result, appropriate values ​​for delay 116 and BP pulse width 115 are selected to achieve a desired amount of heavier ions B at a desired ion density ratio B:A.+ may be delivered to the substrate.

[0042] In one particular example, the source gas for the plasma can be a mixture of He (species A) and Ar (species B). He The mass of is about 6.7 × 10 -27 kg, while M Ar The mass of is about 67 × 10 -27 The chamber pressure is set to a fairly low value (e.g., 15 mTorr), the chamber diameter is set to 30 cm (R=0.15 m), and the electron temperature T e When is set to about 4 eV, τ He is approximately 15.3 μs, while τ Ar is approximately 48.5 μs.

[0043] Doing similar calculations, F(M F =32×10 -27 kg), Cl(M Cl =59×10 -27 kg) and Kr(M Kr =139×10 -27 kg). For the above chamber conditions, the approximate diffusion time constants for these three elements are (F + and Cl2 + (if the presence of ions is confirmed)τ F = 33.5 μs, τ F2 = 47.4 μs, τ Cl = 45.5 μs, τ Cl2 = 64.4 μs and τ Kr =69.9μs.

[0044] Based on these exemplary time constants, the delay 116 may be as short as about 20 μs (e.g., if He is used and it is only desired to reduce the He ion density to less than about 25% of its maximum). B+While there is no upper limit (beyond waiting long enough for the Kr ion density to drop so low as to be unuseful or for the plasma to be unable to be re-ignited), a longer delay 116 could be about 200 μs, corresponding to the point at which only about 5% of the maximum Kr ion density remains in the chamber. Of course, changing the applied power to change the electron temperature or changing the chamber size will change the diffusion time constant. Thus, the particular value of delay 116 will depend on the details of a given application.

[0045] Diatomaceous earth gases, such as fluorine and chlorine gases, are simple examples of plasmas that may have more than two ion species. The description herein is simplified by using two species, A and B, but it should be noted that all of the examples apply to more complex systems containing three or more species. The decision to apply a bias pulse can then be based on the diffusion time constants of all of the relevant ions and can involve applying power when a specific average ion mass is reached or when a sufficient number of photoions of a specific association have diffused.

[0046] In systems where there are two related ions that differ in mass (at least to a reasonable approximation) and where a heavier ion is more desirable than a lighter ion for a particular purpose, the ion density ratio B:A can be a particularly useful metric. For example, B:A can be very useful when desired heavy ions are identified and undesired (possibly overly aggressive) light ions are identified, so that the optimal position for a delayed BP pulse can be calculated with greater specificity. The ion density ratio B:A can be selected to be a predetermined value when the delayed BP pulse is applied (and relative to the duration of the BP pulse). In some embodiments, B:A is greater than 1 when the delayed BP pulse is applied relative to the normalized ion density ratio at the end of the applied SP pulse. In other embodiments, this ratio is higher. For example, B:A may be greater than about 2, greater than about 5, or even higher when the delayed BP pulse is applied. Various considerations may play a role in determining when to apply a delayed BP pulse, many of which are discussed herein and may depend on the details of a given application.

[0047] Some systems preferentially generate one heavier ion of interest, B, in the substrate. + The ion energy distribution may also narrow as the average ion mass increases, which may be desirable to improve processing results. In these cases, other metrics, such as the ratio between heavier ions and all lighter ions or the average ion mass, may be used. The average ion mass may still correlate with increasing desired metrics, such as the ion density ratio B:A, but still increasing desired metrics, such as selectivity.

[0048] The delayed BP pulse generates a specific lighter ion density n A+That is, the heavier ions B at the target energy + Preferential irradiation with α at this energy may be desirable, but + The simultaneous acceptable (or desirable) flux of ions may depend on the details of a particular application. In some embodiments, when a delayed BP pulse is applied (i.e., during the SP pulse), the ion density nA+ is less than about 10% of the maximum A+ ion density. In other embodiments, when a delayed BP pulse is applied, the ion density nA+ is less than about 5% of the maximum A+ ion density. A low ion density is achieved by applying a pulse with an energy A + It may result in little or no ion flux. For example, energy A + The ion flux may be substantially zero in one embodiment.

[0049] Therefore, when a delayed BP pulse is applied (i.e., during the SP pulse), n B+ The range of allowable values ​​is up to B + However, the ion density n for a given application can be as large as 100% to 1%. B+ The optimum value of may depend on several factors, such as the ion density n A+ to a sufficiently low level, and the desired energy B + Applying the BP pulses fast enough to achieve the ion flux (i.e., n B+ In addition, there may be a trade-off between the amount of B delivered to the substrate during the BP pulse width 115 and the amount of B delivered to the substrate during the BP pulse width 115 being too low. + The total number of ions (e.g., B + If a particular dose is desired, the duration of the delay 116 can be limited by the pulse period 117.

[0050] One particular exemplary method of utilizing the plasma process 100 includes generating a plasma by coupling a corresponding SP pulse 12 into a plasma processing chamber containing a substrate holder configured to support a substrate. The plasma is contained within the plasma processing chamber and is formed by a first mass M A+ The first ion A has + and the first mass M A+ A second mass M larger than B+ A second ion B with + During the source power pulse (e.g., at the end of the pulse), the generated plasma includes a first ion A + the second ion B + The ion density ratio of the second ions B is the first ratio. This particular example method involves applying a delayed BP pulse 14 to the substrate holder after a delay (e.g., delay 116) between the corresponding SP pulse 12 and the delayed BP pulse 14. + to the substrate, wherein the delay is + the second ion B + The first ion A is then added to the second ion A so that the ratio of + The diffusion time constant τ A+ and the second ion B + The diffusion time constant τ B+ That is, the first energetic ion A + The second energy ion B for the flux of + The flux of BP increases compared to when the BP pulse is applied earlier.

[0051] 2 is a schematic diagram of an exemplary plasma process utilizing delayed bias power pulses as part of a cyclical process according to an embodiment of the present invention. The plasma process of FIG. 2 may be a specific implementation of other plasma processes described herein, such as the plasma process of FIG. 1. Elements labeled similarly may be similar to those previously described.

[0052] 2, plasma process 200 is described using schematic timing diagram 201, qualitative graph 202, and qualitative graph 203. Note that here and below, for brevity and clarity, the convention is adopted that elements following the pattern [x01] may be related embodiments of the schematic timing diagram in various embodiments. For example, schematic timing diagram 201 may be similar to schematic timing diagram 101 unless otherwise indicated. In conjunction with the numbering scheme described above, similar notations are adopted for other elements using similar terms for clarity.

[0053] Plasma process 200 is a specific implementation of plasma process 100 that is periodically repeated during pulse periods 217 (e.g., cycles). More specifically, plasma process 200 involves generating a plasma using source power and bias power applied as delayed BP pulses 14 to generate a plasma with energy B + As shown, an SP pulse 12 is applied with an SP pulse width 213, followed by a delay 216, and then a BP pulse 14 with a BP pulse width 215.

[0054] The timescale of the pulse period 217 can depend on several factors, including the metric targeted for control. For example, pulsing targeted at controlling the ion angular distribution (IAD) of the IED can be on a millisecond timescale (every 100 Hz). In contrast, pulsing targeted at controlling ion mass (e.g., preferential irradiation of heavier ions) can be on a microsecond timescale, such as every 10 μs (every 1 kHz to 10 kHz). In various embodiments, the pulse frequency of the SP pulses 12 ranges from about 100 Hz to about 50 kHz. In other embodiments, the pulse frequency of the SP pulses 12 ranges from about 1 kHz to about 20 kHz.

[0055] Some pulse parameters in this example differ from the previous example to demonstrate other possible configurations. For example, the BP pulse 14 is applied earlier in the afterglow phase 24 than in the previous example and is not applied for the entire pulse period 217, resulting in a longer BP off-time 218. Also, in contrast to the previous example, the BP pulse 14 is applied earlier in the afterglow phase 24 than in the previous example and is not applied for the entire pulse period 217, resulting in a longer BP off-time 218. B+ This is because the energy B + A higher flux of ions is desired and the energy A + It can be advantageous in situations where some flux of ions is manageable (e.g., A + The negative effect of ions is minor or more B + outweighed by the positive effect of ions).

[0056] It should be noted that the definitions of early and late afterglow are intended to be conceptually useful and not specifically defined periods within the afterglow phase. For example, the concept of early afterglow is useful in most cases where preferential irradiation of heavy ions is desired, because the early part of the afterglow phase represents a time when an undesirably high density of light ions still exists. Similarly, the concept of late afterglow is also useful, because at some point, differences in diffusion time constants due to differences in mass result in a desirably low density of light ions.

[0057] However, the optimal delay 216 and BP pulse width 215 can vary based on any number of factors specific to a given plasma process, such as the type of process, substrate material (e.g., mask and target), ion type, gas flow rates, chamber pressure, and many others. To illustrate this point, the line dividing the early afterglow 225 and late afterglow 226 is shown closer to the SP pulse 12 than in the previous example.

[0058] 3 is a schematic diagram of an exemplary plasma process utilizing one or more additional bias power pulses in addition to a delayed bias power pulse, according to an embodiment of the present invention. The plasma process of FIG. 3 may be a specific implementation of other plasma processes described herein, such as the plasma process of FIG. 1. Similarly labeled elements may be similar to those previously described.

[0059] 3, plasma process 300 has been previously described using schematic timing diagram 301, qualitative graph 302, and qualitative graph 303. Plasma process 300 is a specific implementation of plasma process 100 in which an additional BP pulse is included along with BP pulse 14.

[0060] During the glow phase 22, the SP pulse 12 has an SP pulse width 313 and a power P S In contrast to the previous example, A + Ion and B + Additional BP pulses may be applied during the glow phase 22 to deliver a large flux of energetic ions (e.g., due to a high ion density) to the substrate, including both ions. G Pulse 332 (i.e., glow phase bias power pulse) optionally includes a pulse G (or voltage V in case of DC bias) G ) in BP G The SP pulse 12 can be applied with a pulse width of 333. G Since it is applied at the same time as pulse 332, BP G While generating the plasma by applying pulse 332, A + and B + A glow phase energetic ion flux of ions is delivered (eg, to a substrate holder supporting a substrate).

[0061] The ion temperature is very high during the glow phase, so the BP G The large flux of ions produced by pulse 332 may have a lower verticality compared to the ions delivered to the substrate in the afterglow phase 24.G The pulse 332 can be particularly useful when ion directionality is less important than high ion flux and high ion energy. It may be desirable to provide as many ions as possible in a short time. The very high ion density during the SP pulse 12 can be beneficial for using both types of ions to remove residues. For example, the BP G Pulse 332 is A + and B + The ions can be used to remove mask residue during an etching process that uses both ions. Because the mask residue is at the top of the feature, lack of directionality may not be as important. Furthermore, because the surface of the mask is targeted by the ions, selectivity may not be as important.

[0062] A + Ion and B + Additional BP pulses of another type may be applied during the initial afterglow 325 of the afterglow phase 24 to deliver energetic (e.g., directed) ions, including both ions, to the substrate. E Pulse 334 (i.e., initial afterglow bias power pulse) optionally occurs after SP pulse 12 and before BP pulse 14. E Pulse width 335 and power P E (or voltage V in case of DC bias) E In other words, after generating the plasma using the SP pulse 12, the B + By applying a BPE pulse 334 (e.g., to a substrate holder supporting a substrate) before delivering the energetic ion flux of ions, A + and B + An initial afterglow energy ion flux of ions is delivered to the substrate.

[0063] Here, the plasma is in the afterglow phase 24, so the ion density n A+ and n B+is lower than the glow phase 22, but still much higher than the late afterglow phase 326. As a result, as previously mentioned, a bias pulse can be used during the early afterglow 325 to induce the heavier ions B + It may be impractical to preferentially irradiate the substrate with ions, however, there may be situations where selectivity is less important and improved directionality (i.e., narrower angular distribution) resulting from reduced ion temperature is beneficial.

[0064] One such situation may be cleaning the bottom of a feature between etching steps. For example, removing material from the bottom corners of a feature (e.g., hole, trench) can be much more difficult, especially in high aspect ratio etches. As mentioned above, A + Ion is B + It can be much more aggressive than ions. Therefore, the aggressive A + It can be advantageous to deliver a highly directional (e.g., high energy) ion flux that can reach the bottom of the feature containing the ions. + is more aggressive (e.g., etching a mask), BP E Note that pulse 334 may be kept relatively short to avoid eroding the mask.

[0065] While there are certainly exceptions for some applications, BP Pulse 14, BP G Pulse 332 and BP E There are some general observations worth noting regarding the relationships between pulse 334 parameters. For example, the heavier B + It has been previously discussed in detail that preferential irradiation of ions is desirable for plasma processing 300. As a result, a desired number of lighter energetic A + The width of the BP pulse that delivers ions (BP G Pulse width 333 and BP E The pulse width 335) is typically shorter (eg, much shorter) than the BP pulse width 315.

[0066] Another example is the power level (or possibly the voltage level) of the BP pulse. G Pulse 332 is generated at an ion density n A+ and n B+ is at its peak and aggressive A + As ions are delivered to the substrate during the glow phase 22, the power P G is typically the power P B Similarly, the ion density n A+ and n B+ decreases rapidly in the initial afterglow 325 of the afterglow phase 24, making increased power more desirable, so that the power P E In general, P G In addition, BP G More power may be required to impart the desired verticality to the ions during pulse 332. Nevertheless, the ion density is still higher than in the late afterglow 326, and the aggressive A + ions are contained in the energetic ion flux. Therefore, the power P E is still P B It can be lower than

[0067] BP pulse 14, as well as BP G Pulse 332 and BP E The exact location of the pulse 334 can be determined based on the specific parameters of a given application. G A general guideline for pulse 332 is to have an ion density n A+ and n B+ are more similar and stable, so BP G The advantage is that the pulse 332 is placed closer to the end of the glow phase 22. E Similar guidelines for Pulse 334 are for more A + closer to the onset of the initial afterglow 325 (e.g., the diffusion time constant τ A+However, to achieve improved verticality, the SP pulse 12 and the BP E Some delay between pulses 334 may be beneficial.

[0068] 4 is a schematic diagram of an exemplary plasma processing apparatus that can be used to deliver an energetic ion flux with an increased ion density ratio of heavier ions to lighter ions, in accordance with an embodiment of the present invention. The plasma processing apparatus of FIG. 4 can be used to perform any of the plasma processes described herein, such as the plasma process of FIG. 1. Similarly labeled elements can be similar to those previously described.

[0069] 4, a plasma processing apparatus 400 is configured to include a plasma 42 contained within a plasma processing chamber 44. The plasma 42 is coupled into the plasma processing chamber 44 (e.g., using a coupling element such as an electrode or an inductive coil) and supplied with a source power P S The plasma 42 is generated using a source power supply 452 configured to deliver SP pulses to the plasma processing chamber 44. Specifically, the source power supply 452 is configured to couple the SP pulses to the plasma processing chamber 44 to generate the plasma 42. An optional source impedance matching network 453 may be included between the source power supply 452 and the plasma processing chamber 44 (e.g., for the RF source power). Alternatively, the optional source impedance matching network 453 may be omitted, such as when a resonant source power coupling element is used for the RF source power as well.

[0070] As previously mentioned, the plasma 42 comprises at least two ion species, species A + and species B + Including B + The mass of A + is larger than the mass of (M B+ >M A+ ). Ion A + and B +may also have different reactivities. That is, ions A and B may be chemically different and therefore have different reactivities with various materials, such as the mask material and / or the target material. In addition, plasma 42 generates radicals A · and Radical B · and electron e - , negative ions, multiply charged ions, additional dissociation products, additional precursors, additional carrier (e.g., inert, buffer) gases, additives, and others (not shown). + and B + is positively charged (negative ions are possible and may exist, of course), while the radical A · and B · has no net charge.

[0071] A substrate 46 contained within the plasma processing chamber 44 may be the target of a plasma process performed using the plasma processing apparatus 400. A bias power supply 456 generates a potential difference (e.g., a self-bias or a DC bias) between the substrate 46 and the plasma 42 and generates a sheath voltage V DC To form the plasma sheath 43 at B to the substrate 46. Specifically, the bias power supply 456 is configured to couple heavier ion species (e.g., B + ) to the substrate 46. Similar to the source power, an optional bias impedance matching network 457 may also be included between the substrate 46 and the bias power supply 456.

[0072] The plasma sheath 43 created by the biased substrate 46 (negatively biased in this case) is then driven by the same potential difference (V DC ) to accelerate ion species of the plasma 42 to an energy A + Flux and energy of ion 47 B +This produces a flux of ions 48. The amplitude of the ion flux (ignoring ion energy) is highly dependent on the density of ions and may be substantially unaffected by the applied bias power. However, the bias power imparts energy to the ions at the time the bias is applied, increasing the flux of energetic ions (i.e., energetic ion flux).

[0073] As mentioned above, the bias power P B is applied in the latter part of the afterglow phase of the plasma 42, B + ion density n B+ is A + ion density n A+ The energy B + The flux of ion 48 is energy A + The flux of ion 47 is actually larger than that of ion 47. + The flux of ions 47 is preferably negligible or may even be substantially zero, so that the heavier B + This results in preferential irradiation of the substrate by the ions.

[0074] The plasma 42 may be an RF plasma or any other suitable type of plasma. For example, the plasma 42 may be a capacitively coupled plasma (CCP), an inductively coupled plasma (ICP), a surface wave plasma (SWP), an electron cyclotron resonance (ECR) plasma, a helical resonator (HR) plasma, etc. The details of how source power is coupled to the plasma 42 may depend on the particular plasma process. In one embodiment, the plasma 42 is a CCP plasma, and the source power is coupled using an upper electrode (e.g., a planar electrode). In another embodiment, the plasma 42 is an ICP plasma, and the source power is inductively coupled through a dielectric material using a coil or antenna.

[0075] 5 is a schematic diagram of an exemplary plasma processing apparatus including a radio frequency source power inductively coupled to a plasma and a radio frequency bias power coupled to a substrate holder, in accordance with an embodiment of the present invention. The plasma processing apparatus of FIG. 5 may be a specific implementation of other plasma processing apparatuses described herein, such as the plasma processing apparatus of FIG. 4, and may be used to perform any of the plasma processes described herein, such as the plasma process of FIG. 1. Similarly labeled elements may be similar to those previously described.

[0076] 5, plasma processing apparatus 500 also includes plasma 42 contained within plasma processing chamber 44. Plasma processing apparatus 500 is a specific implementation of plasma processing apparatus 400 that uses an inductive SP coupling element 554 (e.g., a coil as shown) to couple an RF SP power source 552 (radio frequency source power) to plasma processing chamber 44 through dielectric 55. A source impedance matching network 553 is included between RF SP power source 552 and inductive SP coupling element 554.

[0077] The substrate 46 is supported by a substrate holder 45 that is coupled to an RF BP power supply 556 (radio frequency bias power supply) through a bias impedance match network 557. The substrate holder 45 is positioned within the plasma processing chamber 44 as shown. For example, the substrate holder 45 may be an electrostatic chuck (ESC) or any other suitable support structure.

[0078] Gases containing species A and species B may flow into the plasma processing chamber 44 through a gas inlet 58. In one embodiment, the gas inlet 58 is through a sidewall of the plasma processing chamber 44. Alternatively or additionally, the gases may flow into the plasma processing chamber 44 through the top of the plasma processing chamber 44, such as using a showerhead configuration. The chamber pressure is controlled (typically under vacuum conditions) using one or more vacuum pumps (not shown).

[0079] FIG. 6 illustrates an exemplary method of plasma processing utilizing a bias power scan that can be used to calculate ion diffusion time constants used to determine plasma processing parameters for delayed bias pulses, according to embodiments of the present invention. The method of FIG. 6 can be combined with other methods and performed using systems and apparatus as described herein. For example, the method of FIG. 6 can be combined with various aspects of any of the embodiments described using FIGS. 1-5 and 7-15. While shown in a logical order, the arrangement and numbering of the steps in FIG. 6 are not intended to be limiting. The method steps of FIG. 6 can be performed in any suitable order or concurrently with one another, as would be apparent to one of ordinary skill in the art.

[0080] Referring to FIG. 6, a method 600 can be used to define the actual diffusion time constant, which is then used to calculate the diffusion time constant for heavy ions B + at the target energy and desired ion density ratio B:A (i.e., low or negligible levels of light ions A + It is used to place a delayed bias pulse within the afterglow phase of the plasma to deliver heavy ions B as discussed in more detail above. + The delay between the SP pulse and the delayed BP pulse, which will result in the desired low preferential irradiation of ions A + (τ A+ ion B relative to lighter ions such as + (τ B+ ) based on the diffusion time constant

[0081] Even in situations where an accurate theoretical model for calculating the diffusion time constant is available, actual systems may deviate from the theory for a variety of reasons. Furthermore, plasma processing systems are often sufficiently complex to make simplified theoretical modeling difficult or impractical. Therefore, it may be advantageous to use measurements from actual plasma processing systems or similarly configured systems in conjunction with theoretical models to more accurately calculate the diffusion time constant.

[0082] The method 600 begins with a first step 601 of initiating a process parameter measurement sequence. This may involve automated or manual data collection under conditions identical or functionally similar to those of the plasma process for which the diffusion time constant is being determined. The process parameter measurement sequence may be an internal metrology process (e.g., performed in situ within the plasma processing equipment as part of the plasma process or performed immediately before the plasma process is performed). The process parameter measurement sequence may also be an external metrology process (e.g., performed separated in time or space from the plasma process and / or the plasma processing equipment).

[0083] The process parameter measurement sequence can be performed by a metrology component coupled to the plasma processing chamber containing the plasma being analyzed. The metrology component can be integrated within the plasma processing apparatus or can be included as part of a diagnostic system that simulates aspects of the processing environment for the plasma process. A controller coupled to the metrology component can control one or more of data collection (e.g., measurements), data processing, data analysis, pulse timing, and process execution during the process parameter measurement sequence and during the plasma processing.

[0084] As shown in this particular example, a pulse-modulated plasma source (e.g., source power) is turned on (power-on state) in step 602. This generates a glow phase of the plasma containing ions of interest. The plasma source is then turned off (power-off state) in step 603, initiating the afterglow phase of the plasma. For example, steps 602 and 603 can be one cycle of pulsed source power to generate the plasma. During step 602 and / or step 603, bias power is applied (e.g., as a BP pulse) in step 604 to probe the ion density in the afterglow phase. That is, a scan of at least a portion of the afterglow phase of the plasma is performed using bias power. The bias power scan can also include at least a portion of the glow phase.

[0085] The bias power may be applied at a selected amplitude during step 604. The amplitude may be constant over the bias power scan or may be dynamic (e.g., ramped). Time-resolved measurements are obtained using a known time and amplitude at each measurement during the scan.

[0086] If it is not possible to scan all of the desired portion of the afterglow phase during a single afterglow phase, steps 602, 603, and 604 may be repeated any number of times as a cyclical process in optional step 605 to obtain measurements. For example, different regions of the afterglow phase may be measured in subsequent cycles to complete a data set. Alternatively or additionally, repeated measurements of the same region of the afterglow phase may be used to improve accuracy, for example, by averaging.

[0087] Measurements obtained during the bias power scan are used to define (e.g., calculate, estimate, etc.) ion diffusion time constants (e.g., relative to the average ion mass), which may be used to, for example, diffuse heavier ions B in step 606. + The diffusion time constant τ B+ In various embodiments, τ B+ The measurements used to define Θ include data from the late afterglow portion of the afterglow phase, which advantageously allows many or all of the lighter ions in the plasma to dissipate, resulting in a plasma primarily composed of B + Measurements related to

[0088] Diffusion time constant τ B+ Once is defined, τ B+ Using the known parameters (and other measured parameters), a comparison can be made between the theoretical model of the plasma system and the actual plasma system (step 607). Various experimental variables can then be adjusted to fit the theoretical model to the actual plasma system.

[0089] Once the model is adjusted, τ A+Time scales (e.g., including or related to diffusion time constants) of other lighter ion species, such as , can be estimated from measurements made during the bias power scan in step 608. These measurements may include data from any part of the afterglow phase, but including data from the early afterglow portion may advantageously provide additional information about the lighter ions.

[0090] By using the ion diffusion time constant along with any other information derived from the process parameter measurement sequence, pulse timings can be calculated in step 609 for process development and / or manufacturability control. + The delay between the SP pulse, which preferentially delivers ions (heavier ions) to the substrate, and the delayed BP pulse is the ion diffusion time constant (n A+ and n B+ ) and convert the measured value into the ion mass (M A+ and M B+ ) and the flux of energetic ions to the substrate is greater than 1 to the normalized ion density ratio at the end of the applied SP pulse, A + B for ions + the diffusion time constant n such that the ratio of ions B:A is greater than 1 during the application of the delayed BP pulse. A+ This can be obtained by choosing a delay larger than

[0091] Based on the foregoing equations, each of the ion diffusion time constants can be predicted by dividing the radius of the plasma processing chamber by the square root of the plasma electron temperature and then multiplying by the square root of the ion mass. However, as noted above, other relationships can be used depending on the particular assumptions associated with a given plasma processing apparatus and / or plasma process and the desired level of accuracy.

[0092] 7 schematically illustrates an exemplary process parameter measurement sequence utilizing a bias power test pulse to measure a voltage response indicative of ion density in a plasma for use in calculating an ion diffusion time constant, in accordance with an embodiment of the present invention. The process parameter measurement sequence of FIG. 7 may be used during methods described herein, such as, for example, the method of FIG. 6. Similarly labeled elements may be similar to those previously described.

[0093] 7, a process parameter measurement sequence 700 is illustrated using a schematic timing diagram 701, a qualitative graph showing relative ion density 702, and a qualitative graph showing voltage response 703. Specifically, the pulse timing shown in schematic timing diagram 701 may be, for example, a specific embodiment of steps 602-605.

[0094] During the process parameter measurement sequence 700, an SP pulse 12 is applied, followed by at least one BP test pulse 19 having a test pulse width 79. The test pulse width 79 can be very short compared to both the afterglow phase of the pulse period 717 and the bias pulses applied during the associated plasma process, such as the delayed bias pulses described herein. The pulse period 717 can be repeated periodically to apply more test pulses (e.g., step 605).

[0095] Each BP test pulse 19 is separated from the corresponding SP pulse 12 by a time interval 76. A BP off-time 78 represents the remainder of the pulse period 717 after the BP test pulse 19 during which the bias power is off. However, as shown in the third pulse period 717 of the schematic timing diagram 701, when there are multiple test pulses within the same pulse period (e.g., separated by a test pulse interval 77, which may be constant or variable from pulse to pulse and period to period), the BP off-time 78 of each BP test pulse 19 does not indicate that the bias power remains off the entire time because the bias power is turned on for other test pulses.

[0096] Each BP test pulse 19 causes a measurable effect in the plasma, e.g., a voltage response -V (e.g., indicative of the plasma potential). pp may be measured and compared to a model voltage response 71 (e.g., a voltage response predicted by theory or previous experiments). The measurable effect of the test pulse may be advantageously used to determine the diffusion time constants of ionic species within the plasma.

[0097] For example, (V pp An RF power pulse or DC pulse can be applied to the substrate holder (e.g., stage) to initiate a self-bias voltage (correlated with the substrate). The pulse power (or amplitude) and duration of the pulse can be kept low to minimize any undesired effects (e.g., etching) on ​​the substrate. The pulsed probe RF power can range from about 1 W to about 10 W, or can be higher, such as hundreds of watts. If a fixed pulsed probe DC voltage is used, the DC voltage can range from about 10 V to about 100 V, or can be higher, such as up to 1000 V. The lower bound of the test pulse width 79 can be about 1 μs to allow for child sheath formation. In various embodiments, the test pulse width 79 ranges from about 1 μs to about 1 ms, and in some embodiments, from about 1 μs to about 50 μs.

[0098] BP test pulse 19 measures V as a function of time pp It can be applied at many points over the pulse period 717 to obtain a distribution (e.g., a fixed RF probe power) or a probe pulse current distribution in time. As the plasma density increases, V pp The value can be lowered (at a fixed probe pulse power) and / or the probe current can be increased. pp and the trend of the probe current (e.g., heavier ions B + This can be useful to extract the ion diffusion time (of both polarities) in the chamber (relative to the

[0099] One particular exemplary method utilizing the process parameter measurement sequence 700 includes generating a plasma (e.g., plasma 42 as described herein) by coupling a first SP pulse (e.g., SP pulse 12 as shown in FIG. 7) into a plasma processing chamber (e.g., plasma processing chamber 44 as described herein) containing a substrate holder (e.g., substrate holder 45 as described herein) configured to support a substrate (e.g., substrate holder 45 as described herein). The plasma is contained within the plasma processing chamber and is coupled to a first mass M A+ The first ion A has + and the first mass M A+ A second mass M larger than B+ A second ion B with + Includes:

[0100] The method in this particular example is to calculate the ion density n A , n B Measurements showing voltage response using at least one BP test pulse 19 - V pp or other measurements described herein), and if a delay is between the second SP pulse and the BP pulse (e.g., between SP pulse 12 and BP pulse 14 as shown in FIG. 1 ), the ion diffusion time constant τ determined from the measurements. A+ , τ B+ and calculating a delay (e.g., delay 116) according to V. pp denotes the sheath voltage that correlates with the plasma density at given conditions.

[0101] Then, the first ion A + and the second ion B + A plasma containing second ions B is generated by coupling a second SP pulse into the plasma processing chamber. + An energetic ion flux of ions containing Λ is delivered to the substrate by applying a BP pulse to the substrate holder after a delay.

[0102] The collection of measurements may be performed in a variety of ways and may depend on the particular type of measurement and the details of a given plasma processing apparatus. In one embodiment, the collection of measurements includes applying multiple bias power test pulses (i.e., two or more BP test pulses 19) to the substrate holder, each of the bias power test pulses inducing a voltage response from the plasma contained in the plasma processing chamber. The voltage response from each of the multiple bias power test pulses may be measured.

[0103] In some cases, more than one afterglow phase may be required to obtain the desired measurement. For this reason, multiple SP pulses (i.e., two or more SP pulses 12) may be coupled into the plasma processing chamber, each of which may have a different afterglow phase. + and B + Each of the BP test pulses can then be applied after a corresponding time interval 76 between a given BP test pulse 14 and the corresponding SP pulse 12. As indicated above, the correspondence between the SP pulses and the BP test pulses can be one-to-one or one-to-many.

[0104] The process parameter measurement sequence 700 may, in some applications, be performed as a preliminary sequence prior to a plasma process. Any plasma process (e.g., plasma process 100 described using FIG. 1 ) may be performed after the process parameter measurement sequence 700 using the obtained ion diffusion time constant information.

[0105] 8 shows a schematic diagram of an exemplary plasma processing apparatus including a measurement element having a voltage divider used to measure a voltage response, according to an embodiment of the present invention. The plasma processing apparatus of FIG. 8 may be a specific implementation of other plasma processing apparatuses described herein, such as the plasma processing apparatus of FIG. 4, and may be used to perform any of the plasma processes described herein, such as the plasma process of FIG. 1. Similarly labeled elements may be similar to those described above.

[0106] 8, plasma processing apparatus 800 includes plasma 42 contained within plasma processing chamber 44. Plasma processing apparatus 800 is a specific implementation of plasma processing apparatus 400 that includes a metrology member 882 coupled to substrate holder 45 that supports substrate 46. Measuring member 882 is coupled to bias power supply 456 and controller 880. Bias power supply 456 can be configured to apply a plurality of bias power test pulses to substrate holder 45, each of the plurality of bias power test pulses measuring a voltage response -V from plasma 42. pp causes.

[0107] Specifically, the measurement member 882 is operably coupled to the plasma 42 and configured to collect measurements indicative of ion density within the plasma 42. For example, the measurement member may be configured to measure a voltage response, −Vpp, from each of a plurality of bias power test pulses. The controller 880 is then coupled to the bias power supply 456 and the source power supply 452 and configured to control the pulse timing of the SP pulses and BP pulses (e.g., delayed BP pulses described herein) applied to the plasma processing chamber 44 during plasma processing.

[0108] The controller 880 may also be configured to collect measurements and calculate the delay between the SP and BP pulses according to an ion diffusion time constant determined from the measurements. For example, the controller 880 may convert the measurements into a time delay between the SP and BP pulses for a mass M A+ and mass M B+ The ion diffusion time constant n of the first species A+ is calculated by comparing it with the diffusion time constants predicted by A+ and the ion diffusion time constant n of the second species (B+) B+ The controller 880 may then be configured to calculate the delay by determining the diffusion time constant n such that the energy flux of the ions has a predetermined value. A+ For example, A + B for ions +The ratio of ions can be greater than 1 relative to the normalized ion density ratio at the end of the applied SP pulse (ie, because the ion density ratio B:A is greater than 1 during the application of the BP pulse).

[0109] Measurement member 882 includes a voltage divider 885 coupled to substrate holder 45 and sending a measurement 883 to controller 880. For example, measurement 883 may be a voltage response, −V pp Voltage response - V pp may be an analog voltage signal, and measurement member 882 may further include an ADC 887 (analog-to-digital converter) configured to convert the analog voltage signal into a digital voltage signal 88 that is provided to the controller (i.e., received by controller 880). ADC 887 may be coupled between voltage divider 885 and controller 880.

[0110] The voltage divider 885 may advantageously be located further from the substrate holder 45 (e.g., the ESC). For example, the voltage divider 885 may be in the optional bias impedance matching network 457 in some implementations. However, the voltage divider 885 may provide measurements that differ somewhat from reality due to phase differences.

[0111] 9 shows a schematic diagram of an exemplary plasma processing apparatus including a metrology element having a VI probe used to measure voltage and current responses, according to an embodiment of the present invention. The plasma processing apparatus of FIG. 9 may be a specific implementation of other plasma processing apparatuses described herein, such as the plasma processing apparatus of FIG. 4, and may be used to perform any of the plasma processes described herein, such as the plasma process of FIG. 1. Similarly labeled elements may be similar to those previously described.

[0112] 9, plasma processing apparatus 900 includes plasma 42 housed within plasma processing chamber 44 as before. Plasma processing apparatus 900 is a specific implementation of plasma processing apparatus 400 that includes a metrology element 982 having a VI probe coupled between substrate holder 45 and bias power supply 456.

[0113] The measuring element 982 measures the voltage response -V pp Although the voltage measurement details are different in this example, the current response I pp is also included in measurements 983. For example, the VI probe of measurement member 982 includes both a voltage sensor 985 (e.g., a capacitive voltage sensor as shown, although a resistive voltage divider could also be used) and a current sensor 986 (e.g., an inductive current sensor as shown).

[0114] The measurements 983 may be transmitted to the controller 980 and optionally provided to a data analyzer 987. The VI probe may be configured to provide voltage and current signals to the data analyzer 987 of the controller 980. The data analyzer 987 may be included within the controller 980 or may be separate. In some embodiments, the data analyzer 987 includes one or more ADCs. The data analyzer 987 may also include any number of other components, including digital logic.

[0115] Compared to a voltage divider, a VI probe can be placed closer to the substrate holder 45, which can be an advantage in certain situations. As a result, RF signal degradation can be minimized. That is, voltage and current measurements from a VI probe can have the advantage of being more accurate. In particular, discharge impedance can be measured using a VI probe, which can be advantageously more accurate than ion density measurements.

[0116] FIG. 10 illustrates an exemplary method of plasma processing utilizing time-resolved measurements within one or more pulse periods, which can be used to calculate ion diffusion time constants for determining plasma processing parameters of delayed bias pulses, according to embodiments of the present invention. The method of FIG. 10 may be combined with other methods and performed using systems and apparatus as described herein. For example, the method of FIG. 10 may be combined with various aspects of any of the embodiments described using FIGS. 1-9 and 11-15. While shown in a logical order, the arrangement and numbering of the steps in FIG. 10 are not intended to be limiting. The method steps of FIG. 10 may be performed in any suitable order or concurrently with one another, as would be apparent to one of ordinary skill in the art.

[0117] Referring to FIG. 10, a method 1000 can be used to calculate the actual diffusion time constant, which is then calculated for the heavy ions B + at the target energy and desired ion density ratio B:A (i.e., low or negligible levels of light ions A + For example, method 1000 is similar to method 600, but utilizes a broader category of measurements for data collection in step 10002 to calculate the diffusion time constant.

[0118] The method 1000 begins at a first step 1001 with initiating a process parameter measurement sequence. Time-resolved measurements are collected during one or more pulse periods in step 1002 to identify ion density trends. The measurements may be voltage and / or current responses corresponding to test pulses such as those described above. However, the measurements may also include measurements such as Langmuir probe measurements or mass spectrometry measurements.

[0119] Similar to method 600, measurements taken in step 1002 are used to define the ion diffusion time constant, estimating the diffusion time constant nB+ in step 1003 and n in step 1004.B+ is compared to the model to estimate the time scale of one or more lighter ions in step 1005. The diffusion time constants may be calculated for use in process development in step 1006. For example, step 1006 may be used to create or refine the model, which may then be used to develop (e.g., refine or create) other plasma processes or to extend manufacturability control.

[0120] 11 shows a schematic diagram of an exemplary plasma apparatus including an external metrology element used to take measurements indicative of ion density within a plasma, in accordance with an embodiment of the present invention. The plasma apparatus of FIG. 11 may be used to perform various methods described herein, such as the method of FIG. 10. Like-labeled elements may be similar to those previously described.

[0121] 11, plasma apparatus 1100 includes plasma 42 contained within plasma processing chamber 44. Plasma apparatus 1100 may be similar to plasma processing apparatus such as plasma processing apparatus 500, by way of example, but may be configured to be used for plasma characterization of conditions similar to those experienced during plasma processing of a substrate. Thus, a substrate may or may not be included in plasma processing chamber 44, and bias power may or may not be coupled to plasma processing chamber 44.

[0122] Source power from an RF SP power supply 1152 is coupled to the plasma processing chamber 44 to generate a plasma 42 using an SP coupling element 1154. A source impedance match network 1153 is coupled between the RF SP power supply 1152 and the SP coupling element 1154. The plasma 42 can be similar to other plasmas described herein, which facilitates gathering information about the plasma process by measuring the plasma 42.

[0123] A metrology element 1182 is coupled to the plasma processing chamber 44. The metrology element 1182 can, of course, be any suitable type of metrology element as previously described, but in this particular example is shown as a metrology element 1182 attached to the sidewall of the plasma processing chamber 44 and providing direct measurements of the plasma 42.

[0124] In one embodiment, the measurement element 1182 includes a Langmuir probe configured to measure ion and electron temperature and density information of the plasma 42. In one embodiment, the measurement element 1182 includes a mass spectrometer, which may be an ion mass energy spectrometer (e.g., a quadrupole mass analyzer). The measurement element 1182 may be used to collect measurements indicative of ion density within the plasma 42.

[0125] FIG. 12 illustrates an exemplary method of plasma processing that utilizes delayed bias power pulses to optimize the plasma process by accounting for the diffusion timescales of different ions, according to an embodiment of the present invention. The method of FIG. 12 may be combined with other methods and performed using systems and apparatus as described herein. For example, the method of FIG. 12 may be performed by, for example, the plasma processing apparatus of FIG. 4 and combined with the plasma process of FIG. 1. While shown in a logical order, the arrangement and numbering of the steps in FIG. 12 are not intended to be limiting. The method steps of FIG. 12 may be performed in any suitable order or concurrently with one another, as would be apparent to one of ordinary skill in the art.

[0126] 12, a method 1200 can be used to optimize plasma processing for a particular application or plasma processing apparatus. Step 1201 is to perform process parameter metrology. This can include various measurements such as those already discussed in more detail above. In step 1202, timescales for various ions of interest can be calculated from the metrology measurements.

[0127] In step 1203, the plasma process is examined to determine whether the process optimization can be improved using the timescale calculated in step 1202. For example, the current process parameters (e.g., pulse timing) may be based on purely theoretical parameter values, older parameter values, or parameter values ​​applied to a different plasma processing equipment or plasma process. In step 1203, the process is analyzed to determine whether the current process is optimized, taking into account the timescale calculated from the metrology results.

[0128] If not, adjustments to the process parameters are made and the timescale is recalculated in step 1202. This process may be iterated to converge to an optimized process for a given set of metrology measurements. Once the process is optimized, it may be released for production in step 1204.

[0129] FIG. 13 illustrates an exemplary method of plasma processing utilizing delayed bias power pulses to monitor the plasma process for parameter drift, which may indicate the need for process optimization, in accordance with an embodiment of the present invention. The method of FIG. 13 may be combined with other methods and performed using systems and apparatus as described herein. For example, the method of FIG. 13 may be performed by, for example, the plasma processing apparatus of FIG. 4 and combined with the plasma process of FIG. 1. While shown in a logical order, the arrangement and numbering of the steps in FIG. 13 are not intended to be limiting. The method steps of FIG. 13 may be performed in any suitable order or concurrently with one another, as would be apparent to one of ordinary skill in the art.

[0130] 13, a method 1300 can be used to compensate for parameter drift during plasma processing. Step 1301 is to start the process. Then, in step 1302, internal process parameter metrology can be performed to monitor process parameters during the process. This can include various measurements as already discussed in more detail above.

[0131] In step 1303, the parameters are analyzed to determine whether the process is still optimized (e.g., one or more indicators are within an acceptable range or below a particular threshold). If so, the current parameters are maintained for the process. However, if one or more parameters drift away from an acceptable value, the process demonstrates instability and may be optimized in step 1305. For example, method 1200 may be executed as step 1305 if parameter drift is detected.

[0132] In some cases, parameter drift may be less likely because pulse parameters may be based on stable, reproducible values ​​such as ion mass, chamber dimensions, and plasma temperature (e.g., electron and / or ion temperature). Therefore, parameter draft determinations may also indicate changes in the system, such as chamber contamination. Whether to re-optimize the process or address the underlying problem may depend on the specific details of a given application.

[0133] FIG. 14 illustrates an exemplary method of plasma processing utilizing delayed bias power pulses to deliver an energetic ion flux that increases the flux of heavier ions relative to the flux of lighter ions, according to an embodiment of the present invention. The method of FIG. 14 may be combined with other methods and performed using systems and apparatus as described herein. For example, the method of FIG. 14 may be combined with various aspects of any of the embodiments described using FIGS. 1-13 and 15. While shown in a logical order, the arrangement and numbering of the steps in FIG. 14 are not intended to be limiting. The method steps of FIG. 14 may be performed in any suitable order or concurrently with one another, as would be apparent to one of ordinary skill in the art.

[0134] 14, step 1401 of a method 1400 of plasma processing is to generate a plasma by coupling an SP pulse into a plasma processing chamber. The plasma processing chamber includes a first species A, a second species B, and a substrate holder configured to support a substrate. The plasma is contained within the plasma processing chamber and has a first mass M A+ A first seed ion A having + and the first mass M A+ A second mass M larger than B+ A second species ion B having + Includes:

[0135] In step 1402, after a delay between the SP pulse and the delayed BP pulse, a delayed BP pulse is applied to the substrate holder to induce second species ions B + is delivered to the substrate. The delay is + The diffusion time constant n A+ and second species ion B + The diffusion time constant n B+ Based on the first seed ion A + The flux of the second species ion B + is selected to increase the flux of

[0136] FIG. 15 illustrates an exemplary method of plasma processing that utilizes measurements indicative of ion density to calculate delays according to ion diffusion time constants determined from the measurements and to deliver energetic ion fluxes of heavier ions, according to embodiments of the present invention. The method of FIG. 15 may be combined with other methods and performed using systems and apparatus as described herein. For example, the method of FIG. 15 may be combined with various aspects of any of the embodiments described using FIGS. 1-14. While shown in a logical order, the arrangement and numbering of the steps in FIG. 15 are not intended to be limiting. The method steps of FIG. 15 may be performed in any suitable order or concurrently with one another, as would be apparent to one of ordinary skill in the art.

[0137] 15, step 1501 of a method 1500 of plasma processing is to generate a plasma by coupling a first SP pulse into a plasma processing chamber containing a first species A, a second species B, and a substrate holder configured to support a substrate. The plasma is contained within the plasma processing chamber and has a first mass M A+ A first seed ion A having + and the first mass M A+ A second mass M larger than B+ A second species ion B having + Includes:

[0138] Measurements indicative of ion density in the plasma are collected in step 1502. In step 1503, a delay is calculated according to the ion diffusion time constant determined from the measurements. The delay is between the second SP pulse and the BP pulse. Step 1504 involves coupling the second SP pulse into the plasma processing chamber to induce first species ions A + and second species ion B + In step 15054, a BP pulse is applied to the substrate holder after a delay to generate a plasma containing second species ions B + An energetic ion flux comprising:

[0139] Illustrative embodiments of the present invention are summarized here, although other embodiments may be understood from the entire specification and claims filed herewith.

[0140] Example 1. A method of plasma processing, comprising: generating a plasma by coupling a source power pulse to a plasma processing chamber containing a substrate holder configured to support a substrate, the plasma being contained in the plasma processing chamber and including first ions having a first mass and second ions having a second mass greater than the first mass, wherein an ion density ratio of the second ions to the first ions is a first ratio; and delivering an energetic ion flux of the second ions to the substrate by applying a delayed bias power pulse to the substrate holder after a delay between the source power pulse and a delayed bias power pulse, the delay being selected based on a diffusion time constant of the first ions and a diffusion time constant of the second ions such that the ion density ratio of the second ions to the first ions is a second ratio greater than the first ratio.

[0141] Example 2. The method of Example 1, further comprising periodically repeating generating the plasma and delivering an energetic ion flux of second ions.

[0142] Example 3. The method of one of Examples 1 or 2, wherein the delay is greater than about 20 μs and less than about 200 μs.

[0143] Example 4. The method of any one of Examples 1-3, wherein the threshold ion energy of the first ions for etching the mask of the substrate is lower than the threshold ion energy of the second ions for etching the target material of the substrate.

[0144] Example 5. The method of any one of Examples 1-4, wherein the second ion is an ion of an inert species.

[0145] Example 6. The method of Example 5, wherein the second ion comprises krypton (Kr).

[0146] Example 7. The method of any one of Examples 1-6, wherein the first ion is an ion of a reactive species.

[0147] Example 8. The method of Example 7, wherein the first ion comprises a halogen.

[0148] Example 9. The method of any one of Examples 1-8, further comprising applying a glow phase bias power pulse to the substrate holder while generating the plasma, thereby delivering a glow phase energetic ion flux to the substrate, the glow phase energetic ion flux comprising the first ions and the second ions.

[0149] Example 10. The method of any one of Examples 1-9, wherein an initial afterglow energetic ion flux comprising the first ions and the second ions is delivered to the substrate by applying an initial afterglow bias power pulse to the substrate holder after generating the plasma and before delivering the energetic ion flux of the second ions.

[0150] Example 11. A method of plasma processing, comprising: generating a plasma by coupling a first source power pulse to a plasma processing chamber containing a substrate holder configured to support a substrate, the plasma containing first ions having a first mass and second ions having a second mass greater than the first mass; collecting measurements indicative of ion density in the plasma; and calculating a delay according to an ion diffusion time constant determined from the measurements, the delay being between the second source power pulse and a bias power pulse; coupling the second source power pulse into the plasma processing chamber to generate a plasma containing the first ions and the second ions; and applying a bias power pulse to the substrate holder after the delay to deliver an energetic ion flux containing the second ions to the substrate.

[0151] Example 12. The method of Example 11, wherein collecting measurements includes applying a plurality of bias power test pulses to the substrate holder, each of the plurality of bias power test pulses eliciting a voltage response from the plasma, and measuring the voltage response from each of the plurality of bias power test pulses.

[0152] Example 13. The method of Example 12, further comprising: generating a plasma comprising first ions and second ions by coupling a plurality of source power pulses into the plasma processing chamber, the plurality of source power pulses comprising the first source power pulse; and applying a plurality of bias power test pulses to the substrate comprises applying each bias power test pulse of the plurality of bias power test pulses after a corresponding time interval between the bias power test pulse and a corresponding source power pulse of the plurality of source power pulses.

[0153] Example 14. The method of any one of Examples 11-13, wherein calculating the delay includes determining an ion diffusion time constant of the first ion and an ion diffusion time constant of the second ion by comparing the measured value with diffusion time constants predicted by the first mass and the second mass, respectively, and selecting a delay that is greater than the ion diffusion time constant of the first species such that the energetic ion flux includes a ratio of the second ion to the first ion that is greater than a predetermined value.

[0154] Example 15. The method of Example 14, wherein comparing the measured value to a diffusion time constant predicted by the first mass and the second mass, respectively, includes comparing the measured value to a diffusion time constant predicted by dividing the radius of the plasma processing chamber by the square root of the electron temperature of the plasma and multiplying by the square root of the first mass and the second mass, respectively.

[0155] Example 16. A plasma processing apparatus comprising: a plasma processing chamber configured to contain a plasma comprising first ions having a first mass and second ions having a second mass greater than the first mass; a source power supply configured to couple a source power pulse to the plasma processing chamber to generate the plasma; a measurement member operably coupled to the plasma and configured to collect measurements indicative of ion density in the plasma; a controller coupled to the measurement member and configured to calculate a delay according to an ion diffusion time constant determined from the measurements, the delay being between the source power pulse and a bias power pulse; a substrate holder disposed within the plasma processing chamber and configured to support a substrate; and a bias power supply coupled to the controller and to the substrate, the bias power supply configured to apply a bias power pulse to the substrate holder after a delay to deliver an energetic ion flux comprising the second ions to the substrate.

[0156] Example 17. The plasma processing apparatus of Example 16, wherein the bias power supply is further configured to apply a plurality of bias power test pulses to the substrate holder, each of the plurality of bias power test pulses causing a voltage response from the plasma, and wherein the metrology member is further configured to measure the voltage response from each of the plurality of bias power test pulses while collecting the measurements.

[0157] Example 18. The plasma processing apparatus of one of Examples 16 or 17, wherein the controller is configured to calculate the delay by determining an ion diffusion time constant of the first species and an ion diffusion time constant of the second species by comparing the measured value with diffusion time constants predicted by the first mass and the second mass, respectively, and selecting a delay greater than the diffusion time constant of the first species such that the energetic ion flux includes a ratio of the second ions to the first ions that is greater than a predetermined value.

[0158] Example 19. The plasma processing apparatus of any one of Examples 16 to 18, wherein the measurement member includes a voltage divider coupled to the substrate holder and an analog-to-digital converter coupled between the voltage divider and the controller and configured to convert an analog voltage signal received from the voltage divider into a digital voltage signal received by the controller.

[0159] Example 20. The plasma processing apparatus of any one of Examples 16-19, wherein the measurement member includes a VI probe coupled to the substrate holder and configured to provide voltage and current signals to the data analyzer of the controller.

[0160] While the present invention has been described with respect to exemplary embodiments, this description 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 invention, will be apparent to those skilled in the art upon reference to this description. Therefore, it is intended that the appended claims cover any such modifications or embodiments.

Claims

1. 1. A method of plasma processing, comprising: generating a plasma by coupling a source power pulse into a plasma processing chamber containing a substrate holder configured to support a substrate, the plasma being contained in the plasma processing chamber and having first ions having a first mass and second ions having a second mass greater than the first mass, wherein an ion density ratio of the second ions to the first ions is a first ratio; applying the delayed bias power pulse to the substrate holder after a delay between the source power pulse and the delayed bias power pulse to provide an energetic ion flux of second ions to the substrate, the delay being selected based on a diffusion time constant of the first ions and a diffusion time constant of the second ions such that the ion density ratio of the second ions to the first ions is a second ratio greater than the first ratio; A method comprising:

2. The method of claim 1 , further comprising periodically repeating the steps of generating the plasma and providing the energetic ion flux of the second ions.

3. The method of claim 1 , wherein the delay is greater than about 20 μs and less than about 200 μs.

4. 2. The method of claim 1, wherein a threshold ion energy of the first ions for etching a mask of the substrate is lower than a threshold ion energy of the second ions for etching a target material of the substrate.

5. The method of claim 1 , wherein the second ions are ions of an inert species.

6. The method of claim 5 , wherein the second ions comprise krypton (Kr).

7. The method of claim 1 , wherein the first ions are ions of a reactive species.

8. The method of claim 7 , wherein the first ions comprise a halogen.

9. moreover, 2. The method of claim 1, further comprising applying a glow phase bias power pulse to the substrate holder during the generating the plasma, thereby providing a glow phase energetic ion flux to the substrate that includes the first ions and the second ions.

10. 2. The method of claim 1 , wherein after the step of generating the plasma and before the step of providing an energetic ion flux of second ions, an initial afterglow energetic ion flux including the first ions and the second ions is provided to the substrate by applying an initial afterglow bias power pulse to the substrate holder.

11. 1. A method of plasma processing, comprising: generating a plasma by coupling a first source power pulse into a plasma processing chamber containing a substrate holder configured to support a substrate; the plasma is contained within the plasma processing chamber and includes first ions having a first mass and second ions having a second mass greater than the first mass; collecting measurements indicative of ion density within the plasma; calculating a delay according to an ion diffusion time constant determined from the measurements, the delay being between the second source power pulse and the bias power pulse; coupling the second source power pulse into the plasma processing chamber to generate a plasma including the first ions and the second ions; applying the bias power pulse to the substrate holder after the delay to provide an energetic ion flux including the second ions to the substrate; A method comprising:

12. The step of collecting measurements includes: applying a plurality of bias power test pulses to the substrate holder, each of the plurality of bias power test pulses producing a voltage response from the plasma; measuring the voltage response from each of the plurality of bias power test pulses; 12. The method of claim 11, comprising:

13. moreover, generating a plasma comprising the first ions and the second ions by coupling a plurality of source power pulses into the plasma processing chamber, the plurality of source power pulses including the first source power pulse; The step of applying a plurality of bias power test pulses to the substrate comprises: applying each bias power test pulse of the plurality of bias power test pulses after a corresponding time interval between the bias power test pulse and a corresponding source power pulse of the plurality of source power pulses.

13. The method of claim 12, comprising:

14. The step of calculating the delay comprises: determining the ion diffusion time constants of the first ions and the second ions by comparing the measured values ​​with diffusion time constants predicted by the first mass and the second mass, respectively; selecting a delay greater than the ion diffusion time constant of the first species such that the energetic ion flux has a ratio of the second ions to the first ions greater than a predetermined value; 12. The method of claim 11, comprising:

15. 15. The method of claim 14, wherein comparing the measured value to a diffusion time constant predicted by the first mass and the second mass, respectively, comprises comparing the measured value to a diffusion time constant predicted by dividing a radius of the plasma processing chamber by a square root of an electron temperature of the plasma and multiplying the result by the square root of the first mass and the second mass, respectively.

16. A plasma processing apparatus, a plasma processing chamber configured to contain a plasma including first ions having a first mass and second ions having a second mass greater than the first mass; a source power supply configured to couple source power pulses to the plasma processing chamber to generate the plasma; a metrology member operably coupled to the plasma and configured to collect measurements indicative of ion density within the plasma; a controller coupled to the measurement member and configured to calculate a delay according to an ion diffusion time constant determined from the measurements, the delay being between a source power pulse and a bias power pulse; a substrate holder disposed within the plasma processing chamber and configured to support a substrate; a bias power supply coupled to the controller and the substrate, the bias power supply configured to apply the bias power pulse to the substrate holder after the delay to provide an energetic ion flux including the second ions to the substrate; A plasma processing apparatus comprising:

17. the bias power supply is further configured to apply a plurality of bias power test pulses to the substrate holder, each of the plurality of bias power test pulses producing a voltage response from the plasma; The plasma processing apparatus of claim 16 , wherein the metrology member is further configured to measure the voltage response from each of the plurality of bias power test pulses while collecting the measurements.

18. The controller determining the ion diffusion time constant of the first species and the ion diffusion time constant of the second species by comparing the diffusion time constants predicted by the first mass and the second mass, respectively, with the measured values; selecting a delay greater than the diffusion time constant of the first species such that the energetic ion flux includes a ratio of the second ions to the first ions greater than a predetermined value; The plasma processing apparatus of claim 16 , configured to calculate the delay by:

19. The measuring member is a voltage divider coupled to the substrate holder; an analog-to-digital converter coupled between the voltage divider and the controller, the analog-to-digital converter configured to convert an analog voltage signal received from the voltage divider into a digital voltage signal received by the controller; The plasma processing apparatus of claim 16 , further comprising:

20. the metrology member includes a VI probe coupled to the substrate holder; The plasma processing apparatus of claim 16, wherein the VI probe is configured to provide voltage and current signals to a data analyzer of the controller.

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