Method of plasma processing

Abstract

A plasma processing method includes generating a glow phase of a positively charged plasma in a plasma processing chamber comprising a first species, a second species, and a substrate, the substrate including a main surface; and generating a negatively charged plasma in a post-glow phase of the positively charged plasma in the plasma processing chamber by combining electrons of the positively charged plasma with atoms or molecules of the second species. The positively charged plasma comprises a plurality of positive ions of the first species and a plurality of electrons. The negatively charged plasma comprises the positive ions and negative ions of the second species. The method further includes cyclically performing the following steps in the post-glow phase: generating neutral particles by applying a negative bias voltage to the substrate; and applying a non-negative bias voltage to the substrate. The average velocity of the neutral particles is directed toward and substantially perpendicular to the main surface of the substrate.

Description

Technical Field

[0001] This disclosure relates to plasma processing as a whole, and in specific embodiments to a plasma processing method, apparatus, and system for generating rapidly vertically neutral particles at a substrate. [Cross-reference to related applications]

[0002] This application asserts priority to U.S. Provisional Application No. 17 / 212,038, filed on March 25, 2021, the entire disclosure of which is incorporated herein by reference. Prior Technology

[0003] The fabrication of devices within microelectronic components can involve a range of manufacturing techniques, including forming, patterning, and removing multiple layers of material on a substrate. There is a consistent and continuous drive to improve the fabrication processes, characterization, and performance of microelectronic components. These improvements may require the development of new chemicals and new, advanced process control methods.

[0004] Plasma processing is used in semiconductor device fabrication for many manufacturing techniques, such as deposition and etching. Pulsed plasma processing methods can use pulses of source power and / or bias power 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 DC offset, for example, when a bias pulse is applied to the electrode. In some cases (e.g., when using blocking capacitors in impedance matching networks), a negative DC self-bias on the powered electrode can increase over time.

[0005] Plasma can include various species mixed together within a processing chamber. Furthermore, the species within the plasma can generate various plasma products, such as ions, free radicals, electrons, and decomposition products. The plasma products of different species can have different properties and are included in the plasma for different purposes. For example, plasma products of different species can have different chemical properties, such as relative to various materials of the substrate being processed or different reactivity of the species within the plasma. In addition, the various species within the plasma can have different electronegativity and ionization energies, resulting in differences in ion formation. Species can approach the surface in different ways. Charged particles can be accelerated through a sheath and guided perpendicular to the surface with enhanced verticality. These species are referred to as having an isotropic angular distribution. In contrast, neutral species approach the surface with an equal probability per solid angle. These are referred to as having an isotropic angular distribution.

[0006] Contour control can be important for high aspect ratio applications, such as those manufacturing memory and logic devices. Differential charging within high aspect ratio features can reduce ion perpendicularity and decrease aspect ratio due to effects such as ion fan-out. Additionally, etched contours can be adversely affected by free radical masking, which can occur when slow (isotropic) neutral particles are masked by the high aspect ratio feature itself and do not reach the sides and bottom of the feature. Summary of the Invention

[0007] According to an embodiment of the present invention, a plasma processing method includes generating a glow phase of a positively charged plasma in a plasma processing chamber comprising a first species, a second species, and a substrate, the substrate including a main surface; and generating a negatively charged plasma in a post-glow phase of the positively charged plasma in the plasma processing chamber by combining electrons of the positively charged plasma with atoms or molecules of the second species. The positively charged plasma comprises a plurality of positive ions of the first species and a plurality of electrons. The negatively charged plasma comprises the positive ions and negative ions of the second species. The method further includes cyclically performing the following steps in the post-glow phase: generating neutral particles by applying a negative bias voltage at the substrate; and applying a non-negative bias voltage at the substrate. The average velocity of the neutral particles is directed toward and substantially perpendicular to the main surface of the substrate.

[0008] According to another embodiment of the present invention, a plasma processing method includes flowing at least two gases into a plasma processing chamber, the plasma processing chamber including a radio frequency (RF) source power electrode, an RF bias power electrode, and a substrate disposed between the RF source electrode and the RF bias electrode. The gases include a first species and a second species. The method further includes applying RF source power to the gases to generate a plurality of positive ions and a plurality of electrons of the first species; removing the RF source power from the gases to generate negative ions of the second species by combining electrons of the first species with atoms or molecules of the second species; and, after a predetermined delay and after removing the RF source power, applying RF bias power to the substrate to deliver neutral particles to the substrate. The RF bias power includes a frequency of less than about 10 MHz at the substrate.

[0009] According to another embodiment of the present invention, a plasma processing apparatus includes a plasma processing chamber configured to contain a negatively charged plasma comprising a plurality of positive ions of a first species and a plurality of negative ions of a second species; a power source coupled to the plasma processing chamber and configured to generate positively charged plasma within the plasma processing chamber; a substrate including a main surface disposed within the plasma processing chamber; and a bias power generator circuit coupled between the substrate and the bias power source. The bias power generator circuit is configured to apply a radio frequency bias voltage at the substrate. The positively charged plasma comprises the positive ions of the first species and a plurality of electrons, which combine with the second species to form the negative ions. The radio frequency bias voltage alternates between a negative voltage and a non-negative voltage. The negative voltage generates a plurality of first neutral particles having a plurality of velocity vectors pointing in a direction toward and substantially perpendicular to the main surface of the substrate. Simple Explanation of the Diagram

[0010] To more fully understand the present invention and its advantages, reference will now be made to the following embodiments in conjunction with the accompanying drawings, wherein:

[0011] Figure 1 illustrates a schematic timing diagram and corresponding qualitative chart of an example plasma treatment method according to an embodiment of the present invention;

[0012] Figure 2 illustrates a schematic diagram of the generation of rapid first-species neutral particles by an exemplary charge exchange collision between a positively charged first-species ion and a background first-species neutral particle according to an embodiment of the present invention;

[0013] Figure 3 illustrates a schematic diagram of the generation of rapid first-species neutral particles by an exemplary charge exchange collision between a negatively charged first-species ion and a background first-species neutral particle according to an embodiment of the present invention;

[0014] Figure 4 is a schematic diagram illustrating an exemplary charge exchange collision between a first species ion and a background second species neutral particle, according to an embodiment of the present invention, resulting in the generation of a rapid first species neutral particle;

[0015] Figure 5 illustrates a schematic diagram of an example plasma processing system according to an embodiment of the present invention. The plasma processing system includes a negatively charged plasma disposed between an upper electrode and a lower electrode, wherein a voltage applied at the lower electrode generates a cascade of fast neutral particles, wherein the fast neutral particles have an average velocity toward and substantially perpendicular to the main surface of the lower electrode.

[0016] Figure 6 illustrates a qualitative graph of bias frequency versus plasma density according to an embodiment of the present invention, showing the state of sheath formation, electronic heating, and charging;

[0017] Figure 7 illustrates a qualitative graph of the interaction between symmetric and asymmetric charge exchange cross sections and the ion energy according to an embodiment of the present invention;

[0018] Figure 8 illustrates a cross-sectional view of an example substrate during plasma etching processes with and without differential charge, according to an embodiment of the present invention;

[0019] Figure 9 illustrates cross-sectional views of example substrates during plasma etching processes with and without free radical shielding, according to an embodiment of the present invention;

[0020] Figure 10 illustrates a schematic diagram of an example plasma treatment apparatus according to an embodiment of the present invention. The plasma treatment apparatus includes a plasma treatment chamber containing negatively charged plasma disposed between an upper electrode and a lower electrode.

[0021] Figure 11 illustrates an example plasma treatment method according to an embodiment of the present invention; and

[0022] Figure 12 illustrates another example plasma treatment method according to an embodiment of the present invention.

[0023] Unless otherwise stated, the numbers and symbols in different figures generally refer to the corresponding parts. The figures are drawn to clearly illustrate the relevant features of the embodiments and are not necessarily drawn to scale. The edges of the features drawn in the figures do not necessarily represent the ends of the feature range. Implementation

[0024] The various embodiments are described in detail below. However, it should be understood that the various embodiments described herein are applicable to various specific contexts. The specific embodiments discussed are merely illustrative of particular ways of making and using the various embodiments and should not be considered as limiting the scope.

[0025] Fast-moving neutral particles can mitigate the undesirable effects of substrate charging and free radical shielding. For example, substrate charging can be mitigated by using neutral particles that do not transfer charge to the substrate surface. The free radical shielding effect can be reduced by increasing the perpendicularity of neutral free radicals. In other words, background neutral particles are slow (i.e., cold) and move in random directions; while fast-moving neutral particles have a defined direction. For example, fast-moving neutral particles can be guided toward the substrate surface, wherein these fast-moving neutral particles have an average velocity substantially vertical to the substrate surface (i.e., perpendicular). Compared to slow background neutral particles, fewer fast-moving neutral particles are subsequently shielded and unable to reach the depths of the feature area.

[0026] Neutral beams are one source of fast neutral particles. Neutral beams are formed from plasma-extracted ions passing through an aperture, which are then neutralized. However, neutral beams may be impractical for various reasons, such as high cost, increased complexity, and their remote location relative to the substrate surface. Therefore, fast neutral particles generated from plasma near the substrate surface may be desirable.

[0027] The embodiments and plasma processing apparatus described herein provide for the generation of fast neutral particles from negatively charged plasma contained in a plasma processing chamber. One specific example of negatively charged plasma is "ion-ion" plasma, which comprises positive and negative ions of similar density but with very few free electrons (e.g., <10^8 cm⁻³ or substantially zero) to form a sheath. Fast neutral particles are generated at the surface of the substrate disposed within the plasma processing chamber by coupling a bias voltage to a substrate. Since there is no or almost no sheath, the applied electric field is sensed throughout the chamber. In various embodiments, the bias voltage is an RF bias applied to the substrate at a suitable frequency as a bias power pulse. This bias voltage and the electric field it generates accelerate ions in the negatively charged plasma toward the substrate, causing charge-exchange collisions that generate fast neutral particles. The fast neutral particles generated by this bias voltage have an average velocity toward the surface and substantially perpendicular to it.

[0028] The methods and plasma processing apparatus of the embodiments offer various advantages over conventional methods and apparatus. For example, fast neutral particles can be advantageously generated from existing plasma within a plasma processing chamber including the substrate. Using fast neutral particles can advantageously reduce substrate charge (e.g., ion fan-out) during plasma processing. Furthermore, the verticality of the fast neutral particles can advantageously reduce free radical shielding during plasma processing. Reduced substrate charge and / or free radical shielding can provide the desired advantage of improved feature contours.

[0029] In various embodiments, applying RF bias power advantageously avoids sheath formation during the generation of rapidly neutral particles. The lack of significant sheath formation prevents charge depletion, which beneficially allows for maintaining a substantially uniform electric field throughout the plasma bulk. The RF bias power also advantageously prevents substrate charging by limiting the duration of the applied voltage in a single direction. These benefits can be further enhanced in embodiments where no self-bias is generated at the substrate. Applying sufficiently low-frequency RF bias power advantageously avoids electronic heating.

[0030] In some embodiments, low-electron-density negatively charged plasmas can advantageously increase the time available for ion acceleration without significantly forming a sheath. Therefore, low electron density can advantageously increase the flux of fast neutral particles to the substrate. For example, due to the increased duration of the applied bias, complex charge-exchange collisions between fast ions and background neutral particles can occur from the same initial ions.

[0031] The lack of a significant sheath allows a larger volume of plasma to pass through the electric field, which can advantageously result in more charge-exchange collisions. Therefore, the larger volume passing through the electric field and the increased duration of each bias voltage application can advantageously increase the chance of fast neutral particle generation, thereby increasing the fast neutral particle flux at the substrate.

[0032] Fast neutral particle flux can be advantageously coupled with a variety of controllable parameters (e.g., RF bias frequency, bias power, plasma density, etc.). In this manner, the advantages of the embodiments described herein lie in the ability to control the fast neutral particle flux using a variety of controllable parameters. The fast neutral particle flux can also be advantageously adjustable relative to other metrics of interest (e.g., ion flux).

[0033] The embodiments provided below describe various methods, apparatuses, and systems for plasma processing, and more specifically, methods, apparatuses, and systems for plasma processing in which fast, neutral particles guided toward and substantially perpendicular to a substrate surface generate self-converting plasma. The following description describes embodiments. Exemplary timing diagrams of the plasma processing methods of the embodiments are described using FIG1. ​​Multiple embodiments of charge exchange collisions generating fast, neutral particles are described using FIG2–4. FIG5 describes an embodiment of a plasma processing system including a negatively charged plasma disposed between an upper electrode and a lower electrode. Two example qualitative diagrams corresponding to the plasma processing methods of the embodiments are described using FIG6 and FIG7, while FIG8 and FIG9 describe the etching processes of the embodiments with and without two exemplary undesirable scenarios. An embodiment of a plasma processing apparatus is described using FIG10. Two embodiments of plasma processing methods are described using FIG11 and FIG12.

[0034] Figure 1 illustrates a schematic timing diagram and corresponding qualitative chart of an example plasma treatment method according to an embodiment of the present invention.

[0035] Referring to Figure 1, a schematic timing diagram 100 shows the timing of a pulse sequence, which includes at least one source power pulse 12 and at least one bias power pulse 14. The source power pulse 12 has a source power duration 11, and the bias power pulse 14 has a bias power duration 13. The source power pulse 12 has a source power PS, and the bias power pulse 14 has a bias power PB. In various embodiments, the source power pulse 12 is an RF source power pulse applied at a source power frequency fS. The source power frequency fS can be any suitable frequency, but in various embodiments it is high-frequency (HF) RF. In one embodiment, the source power frequency fS is approximately 13.56 MHz. Similarly, in some embodiments, the bias power pulse 14 is an RF bias power applied at a bias power frequency fB. The bias power frequency fB can be lower than the source power frequency fS.

[0036] As shown, the bias power pulse 14 and the source power pulse 12 can optionally be temporarily separated by a delay duration of 15. No source power is applied during the delay duration of 15. Similarly, in various embodiments, no bias power is applied during the delay duration of 15.

[0037] The pulse sequence can be repeatedly applied to each cycle 16, wherein each cycle 16 includes at least one source power pulse and at least one bias power pulse. During the application of each source power pulse 12, PS is greater than 0. In some embodiments, PB is 0 during the source power pulse 12. Alternatively, a small amount of bias power (PB>0) may be applied during the source power pulse 12. Similarly, during the bias power pulse 14, PB>0 and PS is low or 0. Not applying source power during the bias power pulse 14 can advantageously avoid electron generation and maintain a low plasma temperature.

[0038] Qualitative graph 102 corresponds to schematic timing diagram 100 and shows the qualitative behavior of positive ion density n+, negative ion density n-, and electron density ne within the plasma processing system. During the source power duration 11, source power pulse 12 generates plasma (e.g., in a plasma processing chamber). When source power is applied, a glow phase 17 of the plasma is maintained, wherein the plasma is a positively charged plasma 41. This plasma may be an ion-electron plasma with a considerable density of positive ions and free electrons, as indicated by high values ​​of n+ and ne. In other words, although some negative ions may be present in the ion-electron plasma (e.g., even up to 90%), a sheath is still present due to the significant electron density. The number of negative ions in the ion-electron plasma depends on the chemicals of the specific embodiment.

[0039] After the source power is removed at the end of the source power pulse 12, the n+ and ne decrease due to recombination, thus entering the post-glow phase 18 of the plasma. Due to the higher mobility of electrons, and the negative ions formed by electrons combining with other possible negatively charged neutral particles, the electron density ne decreases faster than n+. Therefore, during the delay duration 15 (i.e., when very little or no power is applied to the system), the negative ion density n- increases sharply while maintaining the electroneutrality of the plasma. The negatively charged plasma 42 (which becomes an ion-ion plasma as ne approaches 0) forms in the post-glow phase 18. The negatively charged plasma 42 includes both positive and negative ions, but includes relatively few or no free electrons.

[0040] The terms "positively charged plasma" and "negatively charged plasma" can be considered broader terms than ion-electron plasma and ion-ion plasma, respectively. For example, negative and positive charge can be used to describe the tendency of the electron density of a plasma to increase or decrease within that plasma. Therefore, after a suitable period of time, a net positively charged plasma can naturally possess a meaningful number of free electrons (ion-electron plasma), while a net negatively charged plasma can generate a sufficient number of negative ions to produce an ion-ion plasma.

[0041] The electronegativity of plasma can be related to the presence of both positively and negatively charged species. For example, a net positively charged plasma or a net negatively charged plasma can simultaneously include positively charged plasmas (e.g., Ar, etc.) and negatively charged plasmas (e.g., Cl, O, etc.). The balance between total electronegativity and electronegativity can depend on external conditions such as the relative density of species within the plasma, pressure, applied power, and bias voltage.

[0042] In this manner, a delay duration of 15 can be used to generate a negatively charged plasma 42 in the post-glow phase 18 of the positively charged plasma 41. In various embodiments, the delay duration falls on the order of the ion-electron relaxation time τ+ of a given positively charged plasma, which advantageously enables the application of bias power when both positive and negative ion densities are high and the electron density is low (in the negatively charged plasma). In some embodiments, the delay duration 15 is less than about 5 µs. In one embodiment, the delay duration 15 is about 10 µs. In another embodiment, the delay duration is about 50 µs.

[0043] As shown in qualitative graph 104 (which also corresponds to schematic timing graph 100), the ion temperature Ti spikes during the application of source power pulse 12 in glow phase 17 and then remains elevated. After the source power is removed, Ti decreases along with ne. Bias power pulse 14 is applied when the negatively charged plasma 42 has been sufficiently formed and before a large number of positive and negative ions neutralize each other. The bias power applied during bias power duration 13 produces a rapid neutral particle flux ΓFN without significantly increasing Ti and ne, while n+ and n- decrease slowly.

[0044] The negatively charged plasma 42 can advantageously reduce the sheath formation rate due to the low electron density ne in the post-glow phase 18. In other words, the timescale of sheath formation can be dominated by very large ion mass (low mass relative to electrons) and low ion temperature. In these states, the ions are heavy and cold, resulting in an increased recombination time compared to plasmas with high electron density. This extended relaxation time is sufficient to accelerate ion formation with minimal sheath formation in the substrate orientation, which helps to create suitable conditions for charge exchange collisions within the negatively charged plasma 42.

[0045] The bias power frequency fB can be directly affected by the relaxation time. For example, as the relaxation time increases (preventing sheath formation over a longer period), a lower bias power frequency becomes feasible. A higher bias power frequency fB can also cause undesirable electron heating. Therefore, a potential advantage of using a negatively charged plasma 42 to achieve a lower fB is reducing or preventing secondary emission due to increased electron temperature.

[0046] The low ion temperature Ti combined with the extended bias application (derived from reduced fB) advantageously generates highly directional ions during the bias power pulse 14. These highly directional ions interact with background neutral particles (e.g., free radicals) in charge-exchange collisions within the negatively charged plasma 42. The charge-exchange collisions generate fast neutral particles with substantially similar velocities to the directional ions. In other words, the fast neutral particles advantageously possess an average velocity toward and substantially perpendicular to the main surface of the substrate, which is subjected to the bias power.

[0047] The generation of fast neutral particles from negatively charged plasma 42 enables the use of fast neutral particles to combat undesirable effects (e.g., substrate charging and free radical shielding) without the drawbacks of conventional neutral beams. For example, schematic timing diagram 100 can be used to generate fast neutral particles from existing plasma adjacent to the substrate surface. In contrast, conventional neutral beam sources may be impractical due to high cost, incompatibility with existing systems, and the remote location of the neutral beam source (e.g., aperture plate) relative to the substrate.

[0048] The bias power duration 13 can be relatively short. For example, the plasma can become more resistive over time, the plasma density will continue to decrease, and the fast neutral particle flux ΓFN will decrease over time. In one embodiment, the bias power duration 13 is less than about 50 µs. The source power duration 11 can also be kept as short as possible because the plasma density can level off rapidly, and the purpose of the source power pulse 12 is only to generate positive ions and electrons for subsequent use. The cycle 16 of the pulse sequence can therefore be relatively short. For example, the cycle 16 can be less than about 200 µs.

[0049] Figure 2 illustrates a schematic diagram of the generation of rapid first-species neutral particles through exemplary charge-exchange collisions between positively charged first-species ions and background first-species neutral particles according to an embodiment of the present invention. The charge-exchange collisions of Figure 2 can be generated during the plasma processing methods described herein (e.g., the plasma processing method of Figure 1). Similar labeled elements may be as previously described.

[0050] Referring to Figure 2, the charge exchange collision 200 includes a positively charged first species ion 21 (A+) and a background first species neutral particle 23 (A). At a first moment 201 before A+ and A are sufficiently close to interact with each other, A+ has a velocity v along the direction of A in the reference coordinate system of A (where A is stationary). Since A is a neutral particle in a plasma background with low temperature (low velocity), this is also a fair approximation of the reference coordinate system of the system.

[0051] During the first moment 201, A+ moves toward A with velocity v. A quantity called the collision parameter β defines the distance at which A+ and A sense each other (e.g., get close enough to interact). The charge-exchange collision 200 illustrated in Figure 2 is symmetrical because A+ and A are some first species that differ from each other by only one electron. Therefore, charge-exchange collision 200 is a symmetrical positive ion charge-exchange collision.

[0052] At the second time point 202, A+ and A are close enough to interact and exchange electrons 29. Specifically, electron 29 transfers from A to A+. This results in the production at the third time point 203 of a slowly positively charged first-species ion 26 (A+) and a fast-moving first-species neutral particle 25 (A) with velocity v. The interaction equation for the charge-exchange collision 200 can then be written as follows: .

[0053] The overall effect of the charge-exchange collision 200 is to "exchange" the properties of the fast particles from positive ions to neutral particles. Advantageously, since the charge-exchange collision 200 is a forward scattering collision in which momentum transfer is negligible, the fast first-species neutral particle 25 maintains velocity v. Collisions such as the charge-exchange collision 200 can be generated in the plasma by accelerating positive ions in the plasma to velocity v, for example, during the bias power pulse 14 of FIG1 using the applied bias voltage.

[0054] The probability of charge-exchange collisions is directly related to the particle density and the collision parameter β, and indirectly proportional to the relative velocity v between the ion and the neutral particle. Therefore, a lower relative velocity v will produce a larger number of fast neutral particles (due to the increased collision probability), but these fast neutral particles will have lower velocities. In this approach, a trade-off may exist between the energy and flux of fast neutral particles.

[0055] Figure 3 illustrates a schematic diagram of the generation of rapid first-species neutral particles through exemplary charge-exchange collisions between negatively charged first-species ions and background first-species neutral particles according to an embodiment of the present invention. The charge-exchange collisions of Figure 3 can be generated during the plasma processing methods described herein (e.g., the plasma processing method of Figure 1). Similar labeled elements may be as previously described.

[0056] Referring to Figure 3, the charge-exchange collision 300 includes a negatively charged first species ion 22 (A-) and a background first species neutral ion 23 (A). Similar to the charge-exchange collision 200 in Figure 2, A- has a velocity v relative to A at the first time 301, and a collision parameter β. At the second time 302, electron 29 transfers from A- to A, and at the third time 303, a slowly negatively charged first species ion 28 (A-) and a fast first species neutral ion 25 (A) with a velocity v are formed. Therefore, the interaction equation of the charge-exchange collision 300 can be written as follows: .

[0057] Similar to charge-exchange collision 200 in Figure 2, this collision is symmetrical, and charge-exchange collision 300 is a symmetrical negative ion charge-exchange collision. The overall effect of charge-exchange collision 300 is to "exchange" the properties of fast particles from negative ions to neutral particles. Collisions such as charge-exchange collision 300 can be generated in the plasma by accelerating negative ions in the plasma to velocity v using the applied bias voltage, for example, during the bias power pulse 14 in Figure 1.

[0058] Figure 4 illustrates a schematic diagram of the generation of rapid first-species neutral particles through an exemplary charge-exchange collision between a first-species ion and a background second-species neutral particle, according to an embodiment of the present invention. The charge-exchange collision of Figure 4 can be generated during the plasma processing method described herein (e.g., the plasma processing method of Figure 1). Similarly labeled elements may be as previously described.

[0059] Referring to Figure 4, the charge exchange collision 400 may include a positively charged first species ion 21 (A+) and a background second species neutral particle 24 (B). Unlike the previously described charge exchange collisions, the charged particle A+ is a different species from the neutral particle B (e.g., an atom, molecule, or complex). Therefore, the charge exchange collision 400 is an asymmetric charge exchange collision.

[0060] At the first time point 401, A+ has a first velocity v1 relative to B and a collision parameter β. At the second time point 402, electron 29 transfers from B to A+, and at the third time point 403, a slowly positively charged second species ion 27 (B+) is formed, along with a fast first species neutral ion 25 with a velocity v2. However, due to the asymmetry between the first and second species, a slight energy change ΔE is required to facilitate charge transfer from B to A+.

[0061] For example, in symmetric charge-exchange interactions, the initial and final states have the same energy. In other words, as shown in symmetric interaction diagram 404, where the potential energy is greater than the interatomic spacing, no additional energy is required to obtain the result A+A+ instead of A++A. Conversely, for asymmetric charge-exchange interactions, the final state of A+B+ (i.e., the state where charge transfer has occurred) has a higher energy than the initial state of A++B, as illustrated in asymmetric interaction diagram 405.

[0062] The interaction potential energy of system A++B is qualitatively plotted by the solid (bottom) line, where the distance between A+ and B decreases as the solid line crosses from right to left. At some points along the potential energy curve (here, the minimum), the system is in a temporary interaction state where excess positive charge is shared between A and B, and is shown as (AB)+. Additional energy E is required to excite (AB)+ to a higher energy state (AB)+*, from which the desired final state A+B+ is obtained, which is plotted by the dashed (top) line. Therefore, the interaction equation for charge-exchange collision 400 (asymmetric positive ion charge-exchange collision) can be written as A++B→A+B++ΔE.

[0063] The additional energy that enables charge transfer in an asymmetric charge-exchange collision can come from any suitable source. For example, as shown in the figure, the additional energy E can come from the velocity v1 of A+. In this case, although the orientation is maintained after the collision, the velocity v2 of the resulting fast neutral particle A is less than v1. Alternatively, some or all of this energy can come from other sources, such as radiative energy (e.g., light emission from plasma), and v2 will be equal to or very close to v1.

[0064] It should be noted that in, for example, the negatively charged plasma previously described with reference to FIG1, there may be almost no usable energy other than the granted ion velocity due to the low ion temperature Ti and the low electron temperature Te. Therefore, slower ions (smaller v1) may be less likely to transition to the excited state, and thus may more easily relax back to the initial state, producing the original fast ions and slow neutral particles. Of course, more complex charge-exchange collisions involving association and decomposition are also feasible, and can also be used to generate fast neutral particles from accelerated ions within the plasma.

[0065] Figure 5 illustrates a schematic diagram of an example plasma processing system according to an embodiment of the present invention. The system includes a negatively charged plasma disposed between an upper electrode and a lower electrode, wherein a voltage applied at the lower electrode generates a cascade of fast neutral particles having an average velocity toward and substantially perpendicular to the main surface of the lower electrode. The plasma processing system of Figure 5 can be used to perform the plasma processing methods described herein (e.g., the plasma processing method of Figure 1). Similarly labeled elements may be as previously described.

[0066] Referring to Figure 5, the plasma system 500 includes a negatively charged plasma 42 formed between an upper electrode 31 and a lower electrode 32. The upper electrode 31 and the lower electrode 32 are spaced apart by a distance L. In various embodiments, the distance L falls on the order of tens of centimeters, and in some embodiments is less than about 15 cm. In one embodiment, the distance L is about 15 cm. The negatively charged plasma 42 includes positive ions 21 and negative ions 22. The negatively charged plasma 42 also includes background neutral particles and may include other positive, negative, and neutral particles.

[0067] The upper electrode 31 is maintained at a reference potential (V=0). For example, the upper electrode 31 may be coupled to ground potential. A bias voltage (±VB) is generated at the lower electrode 32. For example, this bias voltage may be generated by applying bias power to the lower electrode 32 using, for example, a bias power pulse previously described with reference to FIG1.

[0068] When the bias voltage is negative (-VB) relative to the reference voltage of the upper electrode 31, positive ions are accelerated in the electric field generated between the electrodes. Positive ions participate in charge exchange collisions with background neutral particles to generate fast neutral particles, which have an average velocity facing the surface of the lower electrode 32 and substantially perpendicular to that surface.

[0069] Charge exchange collisions can be symmetrical or asymmetrical, and each positive ion can participate in multiple charge exchange collisions. For example, as shown in the figure, positive ions 21 can be accelerated toward the lower electrode 32 and collide with background neutral particles 23 to produce fast neutral particles 25 and slow positive ions 26. As long as the lower electrode 32 remains under a negative voltage, new slow positive ions 26 can be accelerated and collide with another background neutral particle 23 to produce another fast neutral particle 25 and another slow positive ion 26.

[0070] In this manner, a cascade of charge-exchange collisions can generate a plurality of fast neutral particles 25 having velocities perpendicular to the surface of the lower electrode 32 (and, for example, perpendicular to the surface of the substrate disposed on the lower electrode 32). Since sheath formation is minimized during the application of bias power to the negatively charged plasma 42, the embodiments described herein can have the advantage of generating a plurality of collisions per ion. Negligible sheath formation also advantageously increases the distance the plasma is subjected to the electric field. This results in the benefit of accelerating more ions and generating more charge-exchange collisions, thereby increasing the chance of fast neutral particle generation.

[0071] The generated fast neutral particles 25 are unaffected by voltage changes at the lower electrode 32. In other words, when biased using an RF bias power pulse oscillating between negative and non-negative voltages, the fast neutral particles 25 maintain their trajectory toward the lower electrode 32. The advantage of this is that the fast neutral particles 25 generated inside the negatively charged plasma 42 will still reach the lower electrode 32.

[0072] Similarly, in an embodiment where the bias voltage at the lower electrode becomes positive (+VB), negative ions 22 can be accelerated toward the lower electrode 32 and collide with background neutral particles 23 to generate fast neutral particles 25 and slow negative ions 28. The slow negative ions 28 can then participate in a series of charge exchange collisions with the background neutral particles 23 when the lower electrode 32 is at a positive voltage.

[0073] Since charged particles move back and forth at a frequency fB while fast neutral particles are not affected by electric field oscillations, applying RF bias power to the lower electrode can advantageously generate fast neutral particles without charging the lower electrode 32. This further provides the advantage of delivering a high fast neutral particle flux ΓFN (relative to the ion flux Γi) at the substrate.

[0074] In particular, in some embodiments, ΓFN at the substrate is greater than Γi. In various embodiments, the ΓFN:Γi ratio is greater than about 2:1. The ΓFN:Γi ratio can be related to other variables such as pressure, sheath thickness, and bias voltage. In one scenario (e.g., a higher pressure state), the ratio ΓFN:Γi can be approximately 10:1. For example, a 10:1 ratio can be achieved at a pressure of 100 mTorr, a sheath thickness of 5 mm, and a bias voltage of 1 kV; however, other variables can also affect this ratio. Furthermore, since the sheath thickness is a function of bias voltage and electron density, the ΓFN:Γi ratio can be lower for lower pressures (e.g., 20 mTorr).

[0075] The voltage at the lower electrode 32 can oscillate around a reference voltage (V=0). In other words, the voltage can cycle repeatedly from +VB to –VB, while the charged particles within the negatively charged plasma 42 remain relatively quantified. Therefore, avoiding self-biasing at the lower electrode 32 further enhances the benefits of applying RF bias power. In some embodiments, no self-biasing is substantially generated at the lower electrode 32 during the application of RF bias power. This can be attributed, for example, to some combination of alternating positive and negative voltages of the electrodes and the balancing current of the ion-ion plasma. In other words, positive ions can be injected during a portion of the cycle, while negative ions are injected for the remainder of the cycle to reduce or eliminate differential charging at the substrate surface, where differential charging is the primary contributor to self-biasing.

[0076] Figure 6 illustrates a qualitative graph of bias frequency versus plasma density according to an embodiment of the invention, showing the state of sheath formation, electronic heating, and charging. The qualitative graph of Figure 6 may correspond to the conditions during the plasma treatment methods described herein (e.g., the plasma treatment method of Figure 1). Similarly labeled elements may be as previously described.

[0077] Please refer to Figure 6. Qualitative graph 600 displays the bias power frequency fB against the plasma density n on the complex logarithmic axis. To prevent sheath formation, the sheath formation time τ should be greater than the period (1 / fB) of the applied RF bias power. The sheath formation time τ is related to the plasma density n and the ion drift velocity v by the following equation. Where ε0 is the dielectric constant of free space, e is the elementary charge, and Φ is the sheath potential.

[0078] Although no sheath is formed, large-scale charge exchange is possible in the negatively charged plasma due to the approximately linear potential drop between the complex electrodes (the constant electric field experienced by the negatively charged plasma). The following conditions can then be used to indicate when a given negatively charged plasma system is in a charge exchange state:

[0079] The representative time for sheath formation (here defined, for example, as a sheath potential of 10 V) in a negatively charged plasma with a density n of 2 × 10¹⁶ m⁻³ and an ion drift velocity v of 1000 m / s is τ⁻ = 150 ns. Qualitative graph 600 illustrates these two states with a boundary line 602, where the boundary line 602 represents the aforementioned inequality condition.

[0080] The range of available frequencies extends to lower frequencies for lower-density plasmas. However, the fast neutral particle flux ΓFN is directly proportional to the plasma density, so a balance between density and frequency may be required to achieve a given flux. The plasma density can be controlled, for example, using the source power, while the bias frequency fB can be directly controlled.

[0081] Additional undesirable effects are also illustrated in qualitative chart 600. These effects are electronic heating, which can occur to a large extent at bias frequencies above approximately 10 MHz, as shown in the figure. Furthermore, substrate charging can become a problem at relatively low frequencies (e.g., less than approximately 1 MHz) as electrons and ions reach the substrate instead of remaining in the plasma. Therefore, an ideal range exists where the bias frequency fB is between approximately 1 MHz and approximately 10 MHz, and the plasma density n is below approximately 1 × 10¹⁷ m⁻³, as shown in the figure.

[0082] The above conditions are determined by the assumption that the electron density ne in the negatively charged plasma is negligible. Any increase in electron density ne will result in faster sheath formation. Therefore, a low electron density ne during the application of bias power will increase the amount of time available to accelerate ions, thereby potentially increasing both the flux of fast neutral particles and the average velocity of fast neutral particles.

[0083] It should be noted that the ion velocity v also exists under the conditions described above. As v increases, τ- decreases, thus pushing the bias frequency fB higher to avoid sheath formation. The bias power can be used to control the ion velocity v. Therefore, a lower bias power may be required to allow the use of frequencies in an ideal range of about 1 MHz to 10 MHz. In various embodiments, the peak voltage of the bias power PB is less than about 500 V. In one embodiment, the peak voltage of the bias power PB is about 400 V. In another embodiment, the peak voltage of the bias power PB is about 100 V.

[0084] Figure 7 illustrates a qualitative graph of the interaction of symmetric and asymmetric charge exchange cross sections with respect to the ion energy according to an embodiment of the invention. The qualitative graph of Figure 7 may correspond to the conditions during the plasma treatment methods described herein (e.g., the plasma treatment method of Figure 1). Similar labeled elements may be as previously described.

[0085] Referring to Figure 7, qualitative graph 700 displays the charge exchange cross-sections relative to ion energies for symmetrical collisions 702, approximately symmetrical collisions 703, and asymmetrical collisions 704 on the complex logarithmic axis. Typically, when no energy is required for charge transfer (as in symmetrical collision 702), the charge exchange cross-section increases as the ion energy decreases, as shown in the figure. For approximately symmetrical collision 703, only the slowest ions cannot transfer charge, causing a sharp increase in the charge exchange cross-section from 0 to the fully symmetrical curve.

[0086] In contrast, higher velocities are required in asymmetric collisions 704 to facilitate charge transfer, which generates the defining peak of ion energy at velocity values ​​significantly above 0. Therefore, while it is desirable to keep the bias power (the velocity transferred to the ions) low for the reasons stated above, there may be an implementable lower bound on the bias power in embodiments that require the generation of fast neutral particles through asymmetric charge exchange collisions.

[0087] Due to the differences in properties between the two species (e.g., differences in electronegativity, ionization potential, mass, etc.), each possible charge-exchange collision reaction has a given rate coefficient. Asymmetric charge-exchange collision reactions can be divided into two groups: exothermic reactions (which occur without additional ion energy) and endothermic reactions (which typically require several eV of charge). Endothermic reactions can be further divided into two subgroups, mentioned above and including approximately symmetric collisions 703 and asymmetric collisions 704. Exothermic reactions have high rate coefficients, while asymmetric collisions have relatively low rate coefficients. The rate coefficients of the approximately symmetric category of charge-exchange collisions occupy an intermediate range.

[0088] for For some experimentally determined rate coefficients of symmetric charge-exchange reactions of fluorocarbon species, 1.0 × 10⁻⁹ cm³ / s is chosen (which is considered a high rate coefficient), while for... The experimentally determined rate coefficient for (asymmetric charge-exchange reactions involving association and decomposition) is 2.5 × 10⁻¹² cm³ / s, which is considered a low rate coefficient. For The rate coefficients for some of the intermediate rates (involving asymmetric charge-exchange reactions of decomposition) are 5.0 × 10⁻¹⁰ cm³ / s, while for... The rate coefficients for the (asymmetric charge exchange reaction of carbon oxide species) falling in the middle are 1.4 × 10⁻¹⁰ cm³ / s.

[0089] By increasing the ion energy (i.e., the velocity) sufficiently to overcome the reaction barrier, the interaction cross-section of a given asymmetric reaction can be increased. Due to the unstable nature of many radicals / ions within the plasma, the reaction barrier for most charge-exchange reactions can be advantageously low, allowing these reactions to produce fast neutral particles from the plasma under suitable conditions (e.g., the plasma density, bias power frequency, and bias power mentioned above). A non-exhaustive list of rate coefficients for other ion-neutral particle charge-exchange reactions can be found in Table IV of Vasenkov et al., Properties of c-C4F8 inductively coupled plasmas. II. Plasma chemistry and reaction mechanism for modeling of Ar / c-C4F8 / O2 discharges, J. Vac. Sci. Technol., 2004, which is incorporated herein by reference with corresponding text on pages 511-13 and 518.

[0090] Figure 8 illustrates a cross-sectional view of an example substrate during plasma etching processes with and without differential charge, according to an embodiment of the present invention. Components may be similarly labeled as previously described.

[0091] Please refer to Figure 8, which shows a cross-sectional view of the substrate 843. In the first scenario 801, an ideal etching profile obtained from a plasma etching process is illustrated, which uses positive ions 21 and a masking material 52 to etch the substrate material 51. This etching process creates a high aspect ratio recess 53 in the substrate material 51, wherein the recess 53 has perfectly vertical sidewalls (relative to the main surface 46 of the substrate 843) and a flat bottom surface.

[0092] In the second scenario 802, an etch profile is depicted due to the differential charge 55 in the substrate material 51 and the masking material 52 (one or both of which may be dielectric materials), wherein the etch profile exhibits an ion fan shape 54. When charge accumulates on the surface of the substrate 843, positive ions 21 are deflected from a completely vertical path and cause distortion of the feature profile by widening the sidewalls, reducing the etch depth, and unevenly etching the bottom of the recess.

[0093] By increasing the use of fast, neutral particles directed toward and perpendicular to the main surface 46 (e.g., the exposed upper surface of the substrate 843 disposed on the lower electrode), the undesirable second situation 802 can be reduced or completely avoided. For example, the neutrality of the fast, neutral particles ensures that no charge accumulates in the substrate material 51 and the masking material 52 when a fast, neutral particle flux ΓFN is applied to the substrate 843. Furthermore, the fast, neutral particles are immune to any displacement caused by any charging effects occurring at the substrate.

[0094] The verticality and energy of fast neutral particles can promote etching with equivalent or substantially similar efficiency to etching using vertical ions, but without the undesirable substrate charging effect. Furthermore, for the degree to which fast ions are required to achieve the desired result in a given etching process, the required ion flux at the substrate can be advantageously reduced by supplementing the ion flux Γi at the substrate with a large fast neutral particle flux ΓFN using the method disclosed herein.

[0095] Figure 9 illustrates a cross-sectional view of an example substrate during plasma etching processes with and without free radical shielding, according to an embodiment of the present invention. Components may be similarly labeled as previously described.

[0096] Please refer to Figure 9, which shows a cross-sectional view of the substrate 943. In the first scenario 901, an ideal etching profile is depicted, having a uniformly formed border layer 56 on the sidewalls and bottom surface of the high aspect ratio recess 53, resulting from the interaction between neutral particles (e.g., free radicals) and the substrate material 51. The uniformly formed border layer 56 can function to passivate the surface of the substrate material 51 within the recess 53 and facilitate etching performed only by high-energy particles (e.g., bias-accelerated positive ions 21 and / or fast neutral particles 25 with sufficiently high energy), which further enhances the achievable aspect ratio and etching profile.

[0097] In the second scenario 902, free radical shielding leads to uneven application 57 of free radicals in the recess 53. Non-directional cold neutral free radicals are easily shielded by the feature itself, especially as the aspect ratio of the feature increases. Therefore, the number of cold neutral free radicals reaching the bottom of the feature may be far less than the number impacting the upper part of the feature's sidewall. This uneven application of free radicals may cause some areas of the substrate material 51 to be etched more slowly than others due to passivation caused by free radicals. This may result in uneven feature surfaces and feature distortion.

[0098] Increasing the use of fast neutral particles 25, which are guided and perpendicular to the main surface 46, can reduce or completely avoid the undesirable second situation 902. These fast neutral particles 25 are primarily delivered to the bottom of the recess 53 because the principal component of their velocity is vertical. A border layer is formed in the bottom region of the recess 53, which is subsequently etched by sufficiently high-energy particles. A uniform border layer 56 can be advantageously produced while the fast neutral particles 25 remain on the sidewalls and the bottom of the recess 53 continues to be etched. The uniform border layer 56 can effectively improve the aspect ratio and etch profile by preventing the sidewalls from being etched by low-energy (e.g., low-velocity) particles.

[0099] Figure 10 illustrates a schematic diagram of an example plasma treatment apparatus according to an embodiment of the present invention. The plasma treatment apparatus includes a plasma treatment chamber containing negatively charged plasma disposed between an upper electrode and a lower electrode. The plasma treatment apparatus of Figure 10 can be used to perform the plasma treatment methods described herein (e.g., the plasma treatment method of Figure 1). Similarly labeled elements may be as previously described.

[0100] Referring to Figure 10, the plasma processing apparatus 1000 includes a plasma processing chamber 30, an upper electrode 31, and a lower electrode 32. A bias power generator circuit 34 is coupled between the lower electrode 32 and a bias power supply 33. The bias power generator circuit 34 is configured to apply bias power (e.g., an RF bias power pulse) to the lower electrode 32. A source power generator circuit 36 ​​is coupled between a source power supply 35 and either the upper electrode 31 or the lower electrode 32. The bias power supply 33, the source power supply 35, and the plasma processing chamber 30 may each be coupled to a ground connection 37, as shown.

[0101] Source power generator circuit 36 ​​is configured to provide source power to plasma processing chamber 30 (using either upper electrode 31 or lower electrode 32) to generate a glow phase of plasma between upper electrode 31 and lower electrode 32 and contained within plasma processing chamber 30. In one embodiment, the generated plasma is a positively charged plasma. In some embodiments, the plasma is a capacitively coupled plasma, but other types of plasma may be suitable, such as inductively coupled plasma, surface wave plasma, etc. For example, when using individual upper electrodes to supply bias power, a resonator (e.g., a helical resonator or spiral resonator) can be used to generate inductively coupled plasma.

[0102] First species 23 and second species 24 are introduced into plasma processing chamber 30 (e.g., in the gas phase). For example, the first species 23 and second species 24 can be provided using a spray head configuration of the upper electrode 31 as shown. Other suitable configurations for introducing the first species 23 and second species 24 into the plasma are also possible.

[0103] The negatively charged plasma 42 is generated from a first species 23 and a second species 24 located between the upper electrode 31 and the lower electrode 32. For example, the applied source power can be used to generate a glow phase of a positively charged plasma, which includes positive ions and electrons of the first species 23. Then, the negatively charged plasma 42 can be generated in the post-glow phase of the positively charged plasma by combining electrons of the positively charged plasma with the second species 24 to form negative ions of the second species.

[0104] The bias power (e.g., an RF bias power pulse) can alternate between a positive bias voltage VB and a negative bias voltage -VB of equal value to VB (e.g., no self-bias buildup occurs at the lower electrode 32 during the application of this bias power). Furthermore, the waveform of the bias power can be sinusoidal, or it can be a double pulse, a triangular pulse, or other suitable waveform. A substrate 43 is disposed on the lower electrode 32. The substrate 43 includes a main surface 46. An average velocity 25 is obtained from the rapidly generated neutral particles 25 from ions of a negatively charged plasma accelerated by the applied bias power, the average velocity being directed toward and substantially perpendicular to the main surface 46 of the substrate 43.

[0105] By controlling the rate of vacuuming the chamber and the independent flow rates of these species, the total density and relative density of the first species 23 and the second species 24 can be adjusted. For example, the combination of species density with source power and source power pulse duration can be used to achieve a plasma density suitable for generating large-scale charge exchange collisions in the negatively charged plasma 42.

[0106] Further species can be provided to the plasma processing chamber 30, and these additional species may depend on the specific requirements of a given plasma processing. Rapidly neutral particles can generate self-contained plasma 42 through symmetric and asymmetric charge exchange collisions from the first species 23, the second species 24, and other species (e.g., a third species different from the first and second species).

[0107] In various embodiments, the first species 23 is a relatively inert species, such as an inert gas. In one embodiment, the first species 23 is argon (Ar). In other embodiments, the first species 23 is a compound, such as a hydrocarbon, fluorocarbon, carbon oxide, etc. In one embodiment, the first species 23 is CH4. In some embodiments, the second species 24 is a relatively electronegative (e.g., reactive) species, such as a halogen gas. In one embodiment, the second species 24 is chlorine (Cl), which may be introduced into the plasma processing chamber 30 as a diatomic gas (Cl2). In other embodiments, the second species may be an electronegative compound, such as SF6.

[0108] The difference in ionization energy between the first species 23 and the second species 24 can preferentially promote the formation of a positively charged plasma from the applied source power, followed by the formation of a negatively charged plasma 42 after the source power is removed. For example, the second species 24 may be relatively less likely to discard electrons (ionized by the RF field of the source power), but relatively more eager to acquire electrons from the positively charged plasma in the post-glow phase.

[0109] The first species 23 may also be a more reactive species (e.g., an etchant) ionized by the source power. For example, the first species 23 may include hydrogen, carbon, fluorine, oxygen, etc. An inert gas may also be included along with the reactive first species. In this case, the inert gas may be considered the first species, and the reactive species may be considered a third species with a different electronegativity than the first species. Subsequently, fast neutral particles may be generated, for example, through collisions between reactive species ions and background reactive species neutral particles, or between inert gas ions and background reactive species neutral particles.

[0110] Figure 11 illustrates an example plasma processing method according to an embodiment of the present invention. The method of Figure 11 can be combined with other methods performed using the systems and apparatus described herein. For example, the method of Figure 11 can be combined with any embodiment of Figures 1–10. Although shown in a logical order, the arrangement and numbering of the steps in Figure 11 are not intended to be limited thereto. As will be apparent to those skilled in the art to which this invention pertains, the method steps of Figure 11 can be performed in any suitable order or simultaneously with each other.

[0111] Referring to Figure 11, step 1101 of the plasma processing method 1100 involves generating a glow phase 1102 of a positively charged plasma in a plasma processing chamber. This plasma processing chamber includes a first species, a second species, and a substrate, the substrate including a main surface. The positively charged plasma includes positive ions of the first species and electrons.

[0112] Step 1103 involves generating a negatively charged plasma in the plasma processing chamber within the post-glow phase 1104 of the positively charged plasma by combining electrons of the positively charged plasma with atoms or molecules of the second species. The negatively charged plasma includes the positive ions and negative ions of the second species.

[0113] Step 1105 involves cyclically performing steps 1106 and 1107 within the post-glow phase 1104. In step 1106, first neutral particles are generated by applying a negative bias voltage to the substrate, wherein the first neutral particles have an average velocity oriented and substantially perpendicular to the main surface of the substrate. Step 1107 involves applying a non-negative bias voltage to the substrate. Subsequently, method 1100 may optionally be repeated as required, as indicated in step 1108.

[0114] Figure 12 illustrates an example plasma processing method according to an embodiment of the present invention. The method of Figure 12 can be combined with other methods performed using the systems and apparatus described herein. For example, the method of Figure 12 can be combined with any embodiment of Figures 1–11. Although shown in a logical order, the arrangement and numbering of the steps in Figure 12 are not intended to be limited thereto. As will be apparent to those skilled in the art to which this invention pertains, the method steps of Figure 12 can be performed in any suitable order or simultaneously with each other.

[0115] Referring to Figure 12, step 1209 of the plasma processing method 1200 involves introducing at least two gases into a plasma processing chamber. The plasma processing chamber includes an RF source power electrode, an RF bias power electrode, and a substrate disposed between the RF source electrode and the RF bias electrode. The gases include a first species and a second species. Step 1201 includes applying RF source power to the gases to generate positive ions and electrons of the first species. Applying RF source power to the gases can be considered as the glow phase 1202 of the plasma.

[0116] Step 1203 involves removing RF source power from the gases to generate negative ions of the second species by combining electrons of the first species with atoms or molecules of the second species. For example, the atoms or molecules of the second species may be neutral negative species that combine with electrons as the electron temperature decreases. In step 1206, after a predetermined delay and after the removal of RF source power, RF bias power is applied to the substrate to deliver neutral particles to the substrate. The RF bias power includes a frequency of less than about 10 MHz at the substrate. Steps 1203 and 1206 can be considered as the post-glow phase 1204 of the plasma. While the gases are retained or flowed into the plasma processing chamber, steps 1201, 1203, and 1206 (e.g., glow phase 1202 and post-glow phase 1204) may then be optionally repeated as needed, as indicated in step 1208.

[0117] Exemplary embodiments of the present invention are summarized herein. Other embodiments may also be understood from the entirety of this specification and the claims herein.

[0118] Example 1. A plasma processing method includes: generating a glow phase of a positively charged plasma in a plasma processing chamber, the plasma processing chamber comprising a first species, a second species, and a substrate, the substrate including a main surface, the positively charged plasma comprising a plurality of positive ions of the first species and a plurality of electrons; generating a negatively charged plasma in the plasma processing chamber in a post-glow phase of the positively charged plasma by combining the electrons of the positively charged plasma with atoms or molecules of the second species, the negatively charged plasma comprising the positive ions and negative ions of the second species; and cyclically performing the following steps in the post-glow phase: generating a plurality of first neutral particles having an average velocity oriented toward and substantially perpendicular to the main surface of the substrate by applying a negative bias voltage at the substrate; and applying a non-negative bias voltage at the substrate.

[0119] Example 2. As in Example 1, wherein generating the first neutral particles includes: accelerating the positive ions toward the substrate to promote multiple charge exchange collisions within the negatively charged plasma, the charge exchange collisions generating the first neutral particles having the average velocity.

[0120] Example 3. As in Example 2, wherein the charge-exchange collisions within the negatively charged plasma include collisions between some of the positive ions and neutral background particles of the first species.

[0121] Example 4. As in Example 2, wherein the charge-exchange collisions within the negatively charged plasma include collisions between some of the positive ions and neutral background particles of a third species, the third species having a different electronegativity than the first species.

[0122] Example 5. A method as in any of Examples 1 to 4, wherein applying the non-negative bias at the substrate includes: generating a plurality of second neutral particles by applying a positive bias at the substrate, the second neutral particles having an average velocity toward and substantially perpendicular to the main surface of the substrate.

[0123] Example 6. The method of one of Examples 1 to 5, wherein the second species is chlorine.

[0124] Example 7. The method is the same as in Example 6, where the first species is argon.

[0125] Example 8. As in Example 6, where the first species includes hydrogen and carbon.

[0126] Example 9. A plasma processing method includes: flowing at least two gases into a plasma processing chamber, the plasma processing chamber including a radio frequency (RF) source power electrode, an RF bias power electrode, and a substrate disposed between the RF source electrode and the RF bias electrode, the gases including a first species and a second species; applying RF source power to the gases to generate a plurality of positive ions and a plurality of electrons of the first species; removing the RF source power from the gases to generate negative ions of the second species by combining electrons of the first species with atoms or molecules of the second species; and, after a predetermined delay and after removing the RF source power, applying RF bias power to the substrate to deliver neutral particles to the substrate, the RF bias power including a frequency of less than about 10 MHz at the substrate.

[0127] Example 10. The method is the same as in Example 9, where the frequency is between approximately 1 MHz and approximately 10 MHz.

[0128] Example 11. As in Example 9 or 10, wherein no self-bias is generated at the substrate when the RF bias power is applied, the RF bias power generates a positive voltage and a negative voltage equal to the positive voltage at the substrate, and the RF bias power alternates between the positive voltage and the negative voltage.

[0129] Example 12. The method of one of Examples 9 to 11, wherein the absolute value of the peak voltage of the RF bias power is less than about 500 V.

[0130] Example 13. The method of one of Examples 9 to 12, wherein the plasma density in the plasma processing chamber is less than about 1 × 10¹⁷ m⁻³ during the duration of the application of the RF bias power.

[0131] Example 14. The method of one of Examples 9 to 13 further includes: cyclically performing the following steps: applying and removing the RF source power, and then applying RF bias power in the plasma processing chamber after the predetermined delay.

[0132] Example 15. A plasma processing apparatus includes: a plasma processing chamber configured to contain a negatively charged plasma comprising a plurality of positive ions of a first species and a plurality of negative ions of a second species; a power source coupled to the plasma processing chamber and configured to generate a positively charged plasma in the plasma processing chamber comprising the positive ions of the first species and a plurality of electrons, the electrons combining with the second species to form the negative ions; a substrate chuck including a main surface disposed in the plasma processing chamber; and a bias power generator circuit coupled between the substrate and the bias power source, the bias power generator circuit configured to apply a radio frequency (RF) bias at the substrate, wherein the RF bias alternates between a negative voltage and a non-negative voltage, the negative voltage generating a plurality of first neutral particles having a plurality of velocity vectors pointing toward and substantially perpendicular to the main surface of the substrate.

[0133] Example 16. The plasma processing apparatus of Example 15, wherein the bias power generator circuit is configured to apply the RF bias at a frequency between about 1 MHz and about 10 MHz.

[0134] Example 17. The plasma processing apparatus of Example 15 or 16 further includes: an upper electrode coupled to the plasma processing chamber and configured to be held at ground voltage during the application of the RF bias; and a lower electrode coupled to the substrate and the bias power generator circuit, the lower electrode being configured to apply the RF bias at the substrate.

[0135] Example 18. The plasma processing apparatus of Example 17 further includes: a source power generator circuit coupled between the plasma processing chamber and the source power supply, the source power generator circuit being configured to apply high-frequency RF source power to the upper electrode to generate the positively charged plasma, wherein the positively charged plasma is a capacitively coupled plasma.

[0136] Example 19. A plasma processing apparatus as in Example 18, wherein the source power generator circuit is coupled to the upper electrode or the lower electrode.

[0137] Example 20. A plasma processing apparatus as in one of Examples 17 to 19, wherein the upper electrode and the lower electrode are separated by a distance of less than about 15 cm.

[0138] Although the invention has been described with reference to a number of illustrative embodiments, these embodiments are not intended to be limiting. Various modifications and combinations of these illustrative embodiments, as well as other embodiments of the invention, will become apparent to those skilled in the art upon reference to these embodiments. Therefore, the appended claims are intended to cover any such modifications or embodiments.

[0139] 11: Source power duration 12: Source power pulse 13: Bias power duration 14: Bias Power Pulse 15: Delay Duration 16: Loop 17: Glow phase 18: Post-glow phase 21: First species ion with positive charge 22: The first species of negatively charged ion 23: Background First Species Neutral Particles 24: Background Second Species Neutral Particles 25: Fast First Species Neutral Particles 26: Slowly positively charged first species ion 27: Slowly positively charged second species ion 28: Slowly Negative First Species Ion 29: Electronics 30: Plasma treatment chamber 31: Upper electrode 32: Lower electrode 33: Bias Power Supply 34: Bias Power Generator Circuit 35: Power Source 36: Source Power Generator Circuit 37: Grounding connection 41: Positively charged plasma 42: Negative plasma 43:Substrate 46: Main Surface 51:Substrate material 52: Masking Material 53: Depression 54: Ion sector 55: Differential Charge 56: Edge trim 57: Uneven application 100: Timing Diagram 102: Qualitative Charts 104: Qualitative Charts 200: Charge exchange collision 201: First Moment 202: Second Moment 203: Third Moment 300: Charge exchange collision 301: First Moment 302: Second Moment 303: Third Moment 400: Charge exchange collision 401: First Moment 402: Second Moment 403: Third Moment 404: Symmetrical Interaction Diagram 405: Asymmetric Interaction Diagram 500: Plasma System 600: Qualitative Charts 602: Dividing Line 700: Qualitative Charts 702: Symmetrical Collision 703: Approximately Symmetrical Collision 704: Asymmetric Collision 801: First Scenario 802: Second Scenario 843:Substrate 901: First Scenario 902: Second Scenario 943:Substrate 1000: Plasma treatment equipment 1100: Plasma Treatment Method 1101: Steps 1102: Glow phase 1103: Steps 1104: Post-glow phase 1105, 1106, 1107, 1108: Steps 1200: Plasma Treatment Method 1201: Steps 1202: Glow phase 1203: Steps 1204: Post-glow phase 1206, 1208, 1209: Steps fB: Bias power frequency fS: Source power frequency n+: density of positive ions n-: density of negative ions ne: electron density PB: Bias Power PS: Source power Ti: Ion temperature ΓFN: Fast neutral particle flux v: speed v1: First speed v2: Speed β: Collision parameter ΔE: Energy change L: Distance

Claims

1. A plasma treatment method, comprising: A glow phase of positively charged plasma is generated in a plasma processing chamber comprising a first species, a second species, and a substrate, the substrate including a main surface, the positively charged plasma comprising a plurality of positive ions and a plurality of electrons of the first species; a negatively charged plasma is generated in the plasma processing chamber in an afterglow phase of the positively charged plasma by combining the electrons of the positively charged plasma with atoms or molecules of the second species, the negatively charged plasma comprising the positive ions and negative ions of the second species; and the following steps are cyclically performed in the afterglow phase: a plurality of first neutral particles are generated by applying a negative bias voltage to the substrate, the first neutral particles having an average velocity oriented and substantially perpendicular to the main surface of the substrate; And apply a non-negative bias voltage to the substrate.

2. The plasma treatment method of claim 1, wherein generating the first neutral particles includes: The positive ions are accelerated toward the substrate to promote multiple charge exchange collisions within the negatively charged plasma, which generate the first neutral particles having the average velocity.

3. The plasma processing method of claim 2, wherein the charge exchange collisions within the negatively charged plasma include collisions between some of the positive ions and neutral background particles of the first species.

4. The plasma processing method of claim 2, wherein the charge exchange collisions within the negatively charged plasma include collisions between some of the positive ions and neutral background particles of a third species, the third species having a different electronegativity than the first species.

5. The plasma processing method of claim 1, wherein applying the non-negative bias voltage at the substrate includes: A plurality of second neutral particles are generated by applying a positive bias voltage to the substrate, the second neutral particles having an average velocity toward and substantially perpendicular to the main surface of the substrate.

6. The plasma treatment method of claim 1, wherein the second species is chlorine.

7. The plasma treatment method of claim 6, wherein the first species is argon.

8. The plasma treatment method of claim 6, wherein the first species includes hydrogen and carbon.

9. A plasma treatment method, comprising: At least two gases are introduced into a plasma processing chamber, the plasma processing chamber including a radio frequency (RF) source power electrode, an RF bias power electrode, and a substrate disposed between the RF source electrode and the RF bias electrode, the gases including a first species and a second species; RF source power is applied to the gases to generate a plurality of positive ions and a plurality of electrons of the first species in an unobstructed region of the plasma processing chamber, the unobstructed region having unobstructed fluid communication with the substrate; the RF source power is removed from the gases to generate negative ions of the second species in the unobstructed region by combining the plurality of electrons of the first species with atoms or molecules of the second species; and after a predetermined delay, and after the removal of the RF source power, RF bias power is applied to the substrate to deliver neutral particles directly from the unobstructed region to the substrate, the RF bias power including a frequency of less than about 10 MHz at the substrate.

10. The plasma processing method of claim 9, wherein the frequency is greater than about 1 MHz and less than about 10 MHz.

11. The plasma processing method of claim 9, wherein no self-bias is generated at the substrate when the RF bias power is applied, the RF bias power generates a positive voltage and a negative voltage equal to the positive voltage at the substrate, and the RF bias power alternates between the positive voltage and the negative voltage.

12. The plasma processing method of claim 9, wherein the absolute value of the peak voltage of the RF bias power is less than about 500 V.

13. The plasma processing method of claim 9, wherein the plasma density in the plasma processing chamber is less than about 1 × 10¹⁷ m⁻³ during the duration of the application of the RF bias power.

14. The plasma treatment method as described in claim 9 further includes: The following steps are performed cyclically: applying and removing the RF source power, and then applying the RF bias power in the plasma processing chamber after the predetermined delay.

15. A plasma processing method comprising cyclically performing the following steps: applying radio frequency (RF) source power to a source electrode in a plasma processing chamber to form a plasma, the plasma processing chamber comprising a substrate and gases including a first species and a second species, the plasma comprising positive ions of the first species, a neutral species of the second species, and electrons; removing the RF source power from the source electrode for a predetermined duration to form negative ions of the second species; and after the predetermined duration, applying RF bias power to a lower electrode supporting the substrate to deliver neutral particles of the first species and the second species to the substrate, the RF bias power oscillating between a positive voltage and a negative voltage relative to a reference potential at a frequency greater than about 1 MHz and less than about 10 MHz.

16. The plasma processing method of claim 15, wherein the lower electrode is the source electrode, wherein the plasma is formed between the substrate and the upper electrode, and the upper electrode is at the reference potential, and wherein applying the RF bias power includes applying the RF bias power to the lower electrode when the upper electrode is at the reference potential.

17. The plasma processing method of claim 15, wherein the source electrode is an upper electrode, wherein the plasma is formed between the substrate and the upper electrode, and the lower electrode is at the reference potential, and wherein applying the RF bias power includes applying the RF bias power to the lower electrode when the upper electrode is at the reference potential.

18. The plasma processing method of claim 15, wherein the first species is an inert gas and the second species is a halogen gas.

19. The plasma processing method of claim 15, wherein the plasma is formed between the substrate and the upper electrode, and wherein the distance between the lower electrode and the upper electrode is about 15 cm or less.

20. The plasma processing method of claim 15, wherein the absolute value of the peak voltage of the RF bias power is less than about 500 V.

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