Plasma etch tool for high aspect ratio etching

Abstract

A plasma etching apparatus is used to etch high aspect ratio features. This apparatus alternates between accelerating negative ions of low-energy reactive species and accelerating positive ions of high-energy inert gas species. The plasma etching apparatus can be divided into at least two regions, separating a plasma generation space and an ionization space. When the plasma is ignited in the plasma generation space, negative ions of reactive species are generated through electron attachment ionization in the ionization space. When the plasma is extinguished in the plasma generation space, positive ions of inert gas species are generated through Penning ionization in the ionization space.

Description

Technical Field

[0001] This invention relates to a plasma etching tool for high aspect ratio etching. Prior Technology

[0002] Plasma etching is commonly used in the manufacturing process of semiconductor devices. More and more semiconductor devices are being sized according to increasingly narrow design rules. Feature sizes are decreasing, and more and more features are being mounted on a single wafer to create higher density structures. As device features shrink and structure density increases, the aspect ratio of the etched features increases. Effective etching of high aspect ratio (HAR) features is crucial for meeting the design requirements of many semiconductor devices.

[0003] The prior art description provided herein is intended to generally introduce the background of this invention. The achievements of the inventors named in this application, as well as embodiments of the specification that were not worthy of prior art at the time of application, within the scope of the prior art section are not intended or implied to be considered prior art against this invention. Summary of the Invention

[0004] This document provides a plasma etching apparatus. The plasma etching apparatus includes: a plasma generation source; an ionization space coupled to the plasma generation source and configured to generate ions; a first grid located between the ionization space and the plasma generation source; an acceleration space coupled to the ionization space and configured to deliver the plasma to a substrate in the acceleration space; a substrate support for supporting the substrate in the acceleration space, wherein the substrate support is configured to be biased; and a controller. The controller is configured with instructions for performing the following operations: accelerating negative ions of the reactive species to the substrate in the acceleration space by introducing reactive species into the ionization space and applying a positive bias to the substrate support; and accelerating positive ions of the non-reactive species to the substrate in the acceleration space by introducing non-reactive species into the ionization space and applying a negative bias to the substrate support.

[0005] In some embodiments, the absolute value of the negative bias voltage is significantly greater than the positive bias voltage. In some embodiments, the positive bias voltage is between about 0.5 V and about 10 V, and the negative bias voltage is between about -50 kV and about -1 kV. In some embodiments, the controller is further configured with instructions to perform the following operations: igniting plasma in the plasma generation source when accelerating the negative ions of the reactive species; and extinguishing plasma in the plasma generation source when accelerating the positive ions of the non-reactive species. In some embodiments, the controller is further configured with instructions to perform the following operations: for the step of accelerating the negative ions of the reactive species, extracting electrons from the plasma into the ionization space to ionize the reactive species in the ionization space and form the negative ions of the reactive species. In some embodiments, the controller is further configured with instructions to perform the following operation: for the step of accelerating the positive ions of the non-reactive species, diffusing a metastable species from the plasma into the ionization space to ionize the non-reactive species in the ionization space and form the positive ions of the non-reactive species. In some embodiments, the plasma etching apparatus further includes a second grid located between the ionization space and the acceleration space. The pressure in the ionization space may be greater than the pressure in the acceleration space.

[0006] Another embodiment relates to a plasma etching apparatus. The plasma etching apparatus includes: a plasma generation source; an ionization space coupled to the plasma generation source and configured to generate ions; a first grid located between the ionization space and the plasma generation source; an acceleration space coupled to the ionization space and configured to deliver the plasma to a substrate in the acceleration space; a substrate support for supporting the substrate in the acceleration space, wherein the substrate support is configured to be biased; and a controller. The controller is configured with instructions to perform the following operations: introduce reactive and non-reactive species into the ionization space; ignite the plasma in the plasma generation source; apply a positive bias voltage to the substrate support when the plasma is ignited, so as to ionize the reactive species and form negative ions of the reactive species, and to accelerate the negative ions of the reactive species to the substrate; extinguish the plasma in the plasma generation source; and apply a negative bias voltage to the substrate support when the plasma is extinguished, so as to ionize the non-reactive species and form positive ions of the non-reactive species, and to accelerate the positive ions of the non-reactive species to the substrate.

[0007] In some embodiments, the positive bias voltage is between about 0.5 V and about 10 V, and the negative bias voltage is between about -50 kV and about -1 kV. In some embodiments, a second grid is located between the ionization space and the acceleration space, wherein the first grid system is configured to be biased and the second grid system is configured to be biased, and the pressure in the ionization space is greater than the pressure in the acceleration space. In some embodiments, the plasma generation source is an inductively coupled plasma (ICP) reactor or a capacitively coupled plasma (CCP) reactor. In some embodiments, the controller is further configured with instructions to perform the following operations: repeatedly and alternately applying a positive bias voltage to the substrate support when the plasma is ignited and applying a negative bias voltage to the substrate support when the plasma is extinguished. Simple Explanation of the Diagram

[0008] Figure 1 is a schematic diagram of an exemplary plasma etching apparatus for producing inductively coupled plasma for etching.

[0009] Figure 2 is a schematic diagram of an exemplary plasma etching apparatus for producing capacitively coupled plasma for etching.

[0010] Figures 3A-3C show schematic diagrams illustrating exemplary reaction mechanisms for etching silicon dioxide (SiO2).

[0011] According to some embodiments, FIG4A is a schematic diagram of an exemplary plasma etching apparatus divided by at least two grids, wherein the plasma etching apparatus generates inductively coupled plasma and delivers alternating beams of positive and negative ions for etching.

[0012] According to certain embodiments, FIG4B is a schematic diagram of an exemplary plasma etching apparatus divided by a single grid, wherein the plasma etching apparatus generates inductively coupled plasma and delivers alternating beams of positive and negative ions for etching.

[0013] According to certain embodiments, FIG4C is a schematic diagram of an exemplary plasma etching apparatus divided by at least two grids, wherein the plasma etching apparatus generates inductively coupled plasma in a remote plasma source and delivers alternating beams of positive and negative ions for etching.

[0014] According to certain embodiments, FIG4D is a schematic diagram of an exemplary plasma etching apparatus divided by at least two grids, wherein the plasma etching apparatus generates capacitively coupled plasma and delivers alternating beams of positive and negative ions for etching.

[0015] According to some embodiments, Figure 5 shows a flowchart of an exemplary method for plasma etching using alternating beams of positive and negative ions.

[0016] According to certain embodiments, Figures 6A and 6B show schematic diagrams of exemplary plasma etching processes that alternate between the modification operation of Figure 6A and the removal operation of Figure 6B.

[0017] According to some embodiments, FIG7 shows an exemplary timing diagram of applying voltage to a plasma source and a substrate support in a plasma etching process, wherein the plasma etching process is performed alternately between modification and removal operations. Implementation

[0018] In this disclosure, the terms "semiconductor wafer," "wafer," "substrate," "wafer substrate," and "partially processed integrated circuit" are used interchangeably. Those skilled in the art will understand that the term "partially processed integrated circuit" can refer to a silicon wafer during any of the many stages of integrated circuit fabrication. Wafers or substrates used in the semiconductor device industry typically have diameters of 200 mm, 300 mm, or 450 mm. The following description assumes implementation of this disclosure on a wafer. However, this disclosure is not so limited. Workpieces can have various shapes, sizes, and materials. Besides semiconductor wafers, other workpieces that can utilize this disclosure include various objects, such as printed circuit boards. Foreword

[0019] Plasma has long been used for substrate processing. Plasma etching involves etching material deposited on a substrate to form a desired pattern. Specifically, reactive ion etching (RIE) utilizes chemically reactive plasma to remove material deposited on a substrate. Plasma is generated by supplying reactant gases to a plasma generation chamber and applying an electromagnetic field. For example, plasma generation can employ capacitively coupled plasma technology, inductively coupled plasma technology, electron cyclotron technology, or microwave technology. High-energy ions and free radicals in the plasma are transported to the substrate surface and react with the material deposited on the substrate.

[0020] In a plasma generation chamber, reactant gases are introduced, and a strong radio frequency (RF) electromagnetic field is applied to generate plasma. Electrons are accelerated by an oscillating electric field, and these electrons collide with the reactant gases, ionizing the gas molecules and stripping away their electrons, thus generating plasma containing ions and even more electrons. Plasma typically contains ions, free radicals, neutral species, and electrons. In each cycle of the oscillating electric field, free electrons are electrically accelerated upwards and downwards within the plasma generation chamber. Many free electrons can induce a negative bias at the electrodes (such as the substrate surface). Slower-moving ions are accelerated toward the biased electrode and react with the material on the substrate surface to be etched. The slower-moving ions can form a region that can be called a sheath or plasma sheath. A typical sheath thickness is approximately several millimeters. The ion flux is generally perpendicular to the surface of the substrate being treated.

[0021] Plasma reactors (such as inductively coupled plasma reactors and capacitively coupled plasma reactors) can produce plasmas with different characteristics. Generally speaking, inductively coupled plasma reactors are effective at performing conductor etching processes, while capacitively coupled plasma reactors are effective at performing dielectric etching processes.

[0022] In inductively coupled plasma reactors, a high RF current in the external coil generates an RF magnetic field in the plasma region, which in turn generates an RF electric field. Inductively coupled plasma reactors can utilize two RF generators to independently control plasma density and ion energy. In capacitively coupled plasma reactors, energy is transferred to electrons in the plasma discharge by applying an RF voltage to the electrodes. Multiple RF excitation frequencies can be used individually or simultaneously to modify plasma characteristics. Compared to inductively coupled plasma reactors, capacitively coupled plasma reactors typically achieve higher ion energies, and plasma density is correlated with ion energy, rather than decoupled (as is the case in inductively coupled plasma reactors).

[0023] Figure 1 is a schematic diagram of an exemplary plasma etching apparatus for generating inductively coupled plasma for etching. The plasma etching apparatus 100 includes an upper electrode 102 and a lower electrode 104, between which plasma 140 can be generated. A substrate 106 can be positioned on the lower electrode 104 and held in place by an electrostatic chuck (ESC). Other clamping mechanisms may also be used.

[0024] In the example of Figure 1, the plasma etching apparatus 100 includes two RF sources, with RF source 110 connected to the upper electrode 102 and RF source 112 connected to the lower electrode 104. The plasma etching apparatus 100 may be an inductively coupled plasma reactor. Although the plasma etching apparatus 100 is described as an inductively coupled plasma reactor, it should be understood that the plasma etching apparatus 100 may be a capacitively coupled plasma reactor with a single RF power source.

[0025] In Figure 1, RF sources 110 and 112 may comprise one or more sources of any suitable frequency (including 2 MHz, 13.56 MHz, 27 MHz, and 60 MHz). Reactant gases may be introduced into processing chamber 120 from one or more gas sources 114. For example, gas sources 114 may comprise inert gases (e.g., argon (Ar)), oxygen-containing gases (e.g., O2), fluorine-containing gases (e.g., CF4), or any combination thereof. Reactant gases may be introduced into processing chamber 120 via inlet 122, and excess gases and reaction byproducts may be discharged via exhaust pump 124.

[0026] The controller 130 is connected to RF sources 110 and 112, and to the valve associated with gas source 114. The controller 130 may further be connected to exhaust pump 124. In some embodiments, the controller 130 controls all activities of the plasma etching apparatus 100.

[0027] Figure 2 is a schematic diagram of an exemplary plasma etching apparatus for generating capacitively coupled plasma for etching. The plasma etching apparatus 200 includes an upper electrode 202 and a lower electrode 204. The lower electrode 204 may include additional components, such as a chuck or other clamping mechanism for holding the substrate 206. RF power can be supplied to the lower electrode 204 from an RF source 212. The RF source 212 can provide any suitable frequency, including 2 MHz, 13.56 MHz, 27 MHz, and 60 MHz. The RF source 212 can provide an RF bias to the lower electrode 204 during etching. The RF source 212 provides power to excite the process gas in the gap 220 between the upper electrode 202 and the lower electrode 204 to generate plasma 240. The RF source 212 may be a single RF source that generates high-density plasma 240 in the gap 220. Process gas can be supplied to the gap 220 from a gas source 214. The treatment air system is supplied by the spray head device 216 and can flow through the channel into the gap 220.

[0028] The controller 230 may be implemented in conjunction with the plasma etching apparatus 200. The controller 230 may control some or all of the activities of the plasma etching apparatus 200. In some embodiments, the controller may be connected to the lower electrode 204, the RF source 212, and the valve associated with the gas source 214.

[0029] Plasma typically contains a mixture of ions and neutral species (such as free radicals). Neutral species tend to lack directionality and provide a wide angular distribution. Neutral species tend to induce isotropic and sidewall etching. On the other hand, ions tend to have directionality along a path substantially orthogonal to the substrate surface and provide a narrow angular distribution. Ions tend to induce anisotropic etching. The mixture of ions and neutral species is used in aspect ratio-dependent etching processes. The ratio, density, and other properties of the plasma can be controlled in the plasma reactor, but aspect ratio-dependent etching processes still utilize both ions and neutral species.

[0030] Ion beam etching reactors use ion beams to etch materials via sputtering. This type of etching process is highly anisotropic and nonselective. Chemical etching reactors use etchant gases to etch materials via chemical reactions and the formation of volatile products on the substrate surface. This type of etching process is highly isotropic and selective. Plasma etching reactors typically use ions and neutral species (such as free radicals) to etch materials via ion bombardment and chemical reactions on the substrate surface. This can be called ion-assisted etching. This type of etching process can be moderately anisotropic and moderately selective. The etching directionality and etching profile can be affected by controlling the ion flux, ion energy, neutral particle / ion flux ratio, deposited or passivating chemicals, substrate surface temperature, and pressure. However, as the aspect ratio of features increases, conventional plasma etching techniques and reactors may not be able to adequately control the etching directionality and etching profile in aspect ratio-dependent etching processes.

[0031] Figures 3A-3C show schematic diagrams illustrating exemplary reaction mechanisms for etching silicon dioxide (SiO2). Many applications of aspect ratio-dependent etching processes involve combinations of reactive and non-reactive species. Plasma can be generated from reactive and non-reactive species, wherein plasma can contain radicals of reactive species and ions of non-reactive species. Reactive species can contain polymer precursors (e.g., fluorocarbon precursors (CxFy)), wherein exemplary fluorocarbon precursors can contain CF4 and C4F8. Non-reactive species can contain one or more inert gases, such as helium (He), argon (Ar), xenon (Xe), and krypton (Kr).

[0032] In Figure 3A, CxFy radicals can diffuse to the surface of a substrate with a SiO2 layer and accelerate Ar+ ions to the substrate surface under a bias voltage. This allows for mixing of radicals and ions. As shown in Figures 3A–3C, radicals may lack directionality, with the horizontal and vertical components being similar in magnitude. Ions may exhibit directionality along a path substantially orthogonal to the substrate surface, with the vertical component being greater than the horizontal component. Radicals migrate to the substrate surface more slowly than ions.

[0033] Free radicals under ion bombardment may form chemically reactive SiCxFyOz films as shown in Figure 3B. Free radicals may tend to saturate on the substrate surface and react chemically with it. Furthermore, free radicals may tend to condense on the substrate surface and form thin films. Without any theoretical constraints, the mixing of the ion beam with CxFy free radicals may play an important role in the formation of chemically reactive films.

[0034] In Figure 3C, high-energy Ar+ ions can collide with and penetrate the substrate surface. This causes the chemically reactive SiCxFyOz film to desorb in the form of etching byproducts (such as SiF4 and CO2). These etching byproducts can be removed from the chemically reactive SiCxFyOz film, thereby etching some SiO2.

[0035] In conventional plasma etching reactors (such as the plasma etching apparatus in Figure 1 or Figure 2), a plasma containing a mixture of ions and neutral species is generated. By supplying incremental RF power during plasma generation, higher ion energy is generated through electron collisions, enabling the etching of high aspect ratio features. An ion sheath is created, and ions can be accelerated through the sheath by applying an RF bias voltage. However, these methods of generating higher ion energy and accelerating ions are inefficient and costly, and still result in a broad ion energy distribution function (IEDF) and a broad ion angle distribution function (IADF). Therefore, conventional plasma etching reactors may be limited in their effectiveness for high aspect ratio etching applications.

[0036] Ion beam etching reactors can be used to replace conventional plasma etching reactors, allowing ions to be completely separated for etching. However, for etching high aspect ratio features, reactive species from the plasma (e.g., neutral species) are often also necessary. Therefore, for many high aspect ratio etching applications, using an ion beam etching reactor may be impractical.

[0037] As mentioned above, control parameters such as the ion / neutral particle flux ratio can affect etching orientation and etching profile. The ion / neutral particle flux ratio can be adjusted according to the aspect ratio in the aspect ratio-dependent etching process. A higher ion / neutral particle flux ratio provides more anisotropic etching, while a lower ion / neutral particle flux ratio provides more selective etching. The ion / neutral particle flux ratio may vary during etching. For example, in conventional plasma etching reactors, the ion / neutral particle flux ratio can be adjusted by mixed-mode pulses (MMP). Each pulse of the gas circulation can have varying amounts of reactive species (e.g., neutral species) to non-reactive species (e.g., inert gases). The plasma power and / or frequency can be different during each pulse of the gas circulation. In other words, the ion / neutral particle flux ratio can be changed alternately with each pulse. When using mixed-mode pulses, the ratio of ions to neutral species can be changed over time. However, mixed-mode pulses can be relatively slow due to the constant gas switching between reactive and non-reactive species. Furthermore, while mixed-mode pulses can provide different RF power / frequency for each pulse, these different RF power / frequency do not fundamentally alter the chemicals. In conventional plasma etching reactors where electron bombardment ionization occurs, even with mixed-mode pulses, neutral species and ions are not completely separated during etching.

[0038] A conventional plasma etching reactor, which relies on ions and neutral species for aspect ratio-dependent etching, is also proposed. The challenge lies in the very slow diffusion of neutral species towards the bottom of the feature. Etching high aspect ratio features may involve flowing neutral species to adsorb onto the exposed surface and form a reactive film, and accelerating ions towards the surface to remove the reactive film. The plasma generated in conventional plasma etching reactors typically has a wide IEDF and a wide IADF. Neutral species have energies of approximately several eV, while ions have energies of approximately tens or hundreds of eV. Neutral species lack directionality and are difficult to utilize with wide IEDF and wide IADF to etch high aspect ratio features (e.g., deep trenches). Although bias pulses can be used to accelerate ions with high ion energy, neutral species with low ion energy diffuse very slowly in all directions. Neutral species may not reach the bottom of the feature but may collide with the sidewalls of the feature. This results in a low etching rate.

[0039] During the etching of high aspect ratio features, accelerating ions in conventional plasma etching reactors can cause charge buildup on the mask. This charge buildup on the mask can repel ions, preventing them from reaching the bottom of the feature. This results in reduced etching at the bottom of the feature and increased etching at the sidewalls, leading to a "bowing" phenomenon. Conventional plasma etching reactors can increase ion energy to overcome charge repulsion and reach the bottom of high aspect ratio features, but this increases costs.

[0040] Furthermore, conventional plasma etching reactors may generate various etching byproducts during the removal of material from the substrate. Typically, these byproducts are extracted from the plasma etching reactor using one or more pumping mechanisms. However, the etching byproducts may not be completely removed. When the plasma is ignited, these byproducts may be ionized and redeposited onto the substrate. Facility-free automated cleaning (WAC) can be performed between multiple operations to remove etching byproducts, but this increases costs. Plasma etching equipment

[0041] The plasma etching apparatus of this invention addresses the aforementioned challenges of high aspect ratio etching. The plasma etching apparatus can be divided into two or more volumes, separating the plasma generation space from the ionization space. In some embodiments, the plasma etching apparatus can be divided into at least three volumes, separating the plasma generation space, the ionization space, and the acceleration space. In some embodiments, a grid at least separates the plasma generation space from the ionization space, wherein the grid can be biased or grounded. Electrodes or substrate supports supporting the substrate can be biased using a DC voltage to generate an electric field with the grid. During the first stage of the etching process, electrons generated in the plasma generation space can react with reactive species to form negative ions in the ionization space through electron attachment ionization, wherein these negative ions are accelerated to the substrate surface to modify the material at the substrate surface. During the second stage of the etching process, the plasma is extinguished, and the remaining metastable neutral species react with inert gas species to form positive ions in the ionization space via Penning ionization. These positive ions are then accelerated to the substrate surface to etch the modified material at the substrate surface. The first and second stages of the etching process can be performed alternately and repeatedly to complete the etching process. As used herein, negative ions may also be referred to as "fast neutral particles," "accelerated neutral particles," "undissociated reactive ions," or "reactive ions." Positive ions may also be referred to as "non-reactive ions" or "inert gas ions." Plasma etching equipment can perform high aspect ratio etching by completely separating fast neutral particles and non-reactive ions.

[0042] According to some embodiments, FIG4A is a schematic diagram of an exemplary plasma etching apparatus divided by at least two grids, wherein the plasma etching apparatus generates inductively coupled plasma and delivers alternating beams of positive and negative ions for etching. The plasma etching apparatus 400a includes a plasma generation source 410 for generating plasma, an ionization space 420 coupled to the plasma generation source 410 and configured to generate ions, and an acceleration space 430 coupled to the ionization space 420 and configured to deliver ions to a substrate 436, wherein the substrate 436 is located in the acceleration space 430. The plasma etching apparatus 400a may include a first grid 424 between the plasma generation source 410 and the ionization space 420. In some embodiments, the plasma etching apparatus 400a may further include a second grid 434 between the ionization space 420 and the acceleration space 430. The plasma generation source 410 may be upstream of the ionization space 420, and the ionization space 420 may be upstream of the acceleration space 430.

[0043] A first gas or a mixture of first gases can be introduced into the plasma generation source 410 from a first gas source 412. The first gas source 412 may be in fluid communication with the plasma generation source 410. One or more valves, mass flow controllers (MFCs), and / or mixing manifolds may be associated with the first gas source 412 to control the flow of the first gas into the plasma generation source 410. The first gas may contain a blunt gas, such as helium, argon, xenon, or krypton. In some embodiments, the first gas may be delivered continuously during the etching process. In some embodiments, the first gas may be pulsed at individual stages of the etching process.

[0044] RF power can be supplied to plasma generation source 410 to generate plasma of the first gas in plasma generation source 410. In some embodiments, plasma generation source 410 may include RF antenna 414 coupled to RF generator 416. In some embodiments, RF generator 416 may include RF power coupled to a matching network. In some embodiments, RF antenna 414 may include a planar helical coil. In some embodiments shown in FIG. 4A, plasma generation source 410 of plasma etching apparatus 400a is an inductively coupled plasma (ICP) reactor. However, it should be understood that the present invention may employ a capacitively coupled plasma (CCP) reactor or other types of plasma reactors to generate plasma. During use, a first gas is delivered to plasma generation source 410 and RF power is supplied from RF generator 416 to RF antenna 414 to generate plasma in plasma generation source 410. By electron-bombardment ionization, electrons collide with the first gas and strip their electrons to generate ions and more electrons. During the first stage of the etching process, RF power can be supplied to generate a plasma of a first gas in the plasma generation source 410. During the second stage of the etching process, the RF power can be turned off to extinguish the plasma in the plasma generation source 410.

[0045] As discussed in more detail below, the etching process can constitute an etching cycle, which is divided into two stages. The first stage can constitute a modification stage, in which the plasma is activated, while the second stage can constitute a removal stage, in which the plasma is deactivated.

[0046] The plasma generation source 410 is coupled to the ionization space 420 via a first grid 424. Ions, electrons, or neutral species can be extracted from the plasma generated in the plasma generation source 410 through the first grid 424. In some embodiments, the first grid 424 may include a plurality of openings or pores through which ions, electrons, or neutral particles can pass. In some embodiments, the first grid 424 may include a conductive plate having a plurality of openings or pores, wherein the conductive plate may be biased or grounded. In some embodiments as shown in FIG4A, the first grid 424 may be grounded through an electrical ground 446. However, it should be understood that in some embodiments, a bias voltage may be applied to the first grid 424. The first grid 424 may form an electric field with the second grid 434 or the substrate support 438. Depending on the potential gradient of the electric field, certain charged species and / or neutral species can be extracted from the plasma through the first grid 424. Electrons can be extracted during the first stage of the etching process for electron attachment ionization, and metastable neutral species can be extracted during the second stage of the etching process for penning ionization. The first stage can constitute a modification stage in which electrons are extracted from the plasma via the first grid 424, and the second stage can constitute a removal stage in which metastable neutral species are extracted from the plasma afterglow via the first grid 424.

[0047] Electron-attached ionization and Penning ionization may occur in the ionization space 420. A second gas or a mixture of second gases may be introduced into the ionization space 420 from one or more other gas sources 422. The second gas may contain reactive gases or reactive species. Examples of reactive species include halogen gases (such as chlorine (Cl2), bromine (Br2), fluorine (F2), or iodine (I2)), perfluorocarbons (such as tetrafluoromethane (CF4), octafluorocyclobutane (C4F8), and hexafluorocyclobutene (C4F6)), hydrofluorocarbons (such as trifluoromethane (CHF3), difluoromethane (CH2F2), and fluoromethane (CH3F)), and oxygen (O2). Generally, the second gas is a negatively charged reactive gas. A third gas or a mixture of third gases may be introduced into the ionization space 420 from one or more other gas sources 422. The third gas may contain non-reactive species, such as helium, argon, xenon, or krypton. In some embodiments, the third gas is different from the first gas. In some embodiments, the second and third gases can be delivered to the ionization space 420 through different gas inlets fluidly coupled to one or more other gas sources 422. One or more valves, mass flow controllers (MFCs), and / or mixing manifolds can be associated with one or more other gas sources 422 to control the flow of the second and third gases into the ionization space 420. In some embodiments, the second and third gases can be continuously supplied to the ionization space 420 during the first and second stages of the etching process. In some other embodiments, the second and third gases can be supplied to the ionization space 420 in a pulsed manner, thereby providing the second gas in the first stage and the third gas during the second stage.

[0048] Electrons extracted through the first grid 424 can induce electron-attached ionization of the second gas. This forms negative ions of reactive species. These negative ions are formed without dissociation through electron-attached ionization. Electron-attached ionization can occur during the first stage of the etching process. Therefore, electron-attached ionization occurs during the modification stage of the etching process to form negative ions of reactive species. The following shows an example of electron-attached ionization of C4F8: e- + C4F8 --> C4F8 -

[0049] Metastable neutral species extracted via the first grid 424 can induce Penning ionization of the third gas. This forms positive ions of non-reactive species. Metastable neutral species can be extracted via the first grid 424 even after the plasma in the plasma generation source 410 has been extinguished or shut down. In some embodiments, the metastable neutral species may be in an excited state. The metastable neutral species may have a sufficiently long lifetime to diffuse through the first grid 424 and collide with non-reactive species. Collisions may induce Penning ionization of the non-reactive species, thereby causing electron stripping of the non-reactive species. Penning ionization may occur during the second stage of the etching process. Therefore, Penning ionization occurs during the removal stage of the etching process to form positive ions of non-reactive species. Examples of Penning ionization with respect to Ar and metastable He* are shown below: He* + Ar --> Ar+ + He + e-

[0050] The substrate 436 may be supported on the substrate support 438 within the acceleration space 430. In some embodiments, the substrate 436 may include a plurality of high aspect ratio features. The high aspect ratio features may include features having a depth-to-width ratio of at least 10:1, at least 20:1, at least 50:1, or at least 100:1. The substrate support 438 is configured to be biased by a DC voltage. The substrate support 438 may include a chuck or other clamping mechanism for holding the substrate 436. The substrate support 438 may include an electrode electrically connected to a DC power supply 442 to apply a negative or positive DC voltage to the substrate support 438. The biased substrate support 438 can cause ions to be accelerated toward the substrate 436. Negative ions or fast neutral particles can be accelerated toward the substrate 436 by applying a positive bias voltage during the first stage (modification stage) of the etching process, and positive ions or non-reactive ions can be accelerated toward the substrate 436 by applying a negative bias voltage during the second stage (removal stage) of the etching process.

[0051] A positive bias voltage can generate a weak electric field between the substrate support 438 and the second grid 434 or the first grid 424, causing negative ions to accelerate at low energy. A negative bias voltage can generate a strong electric field between the substrate support 438 and the second grid 434 or the first grid 424, causing positive ions to accelerate at high energy. In some embodiments, the absolute value of the negative bias voltage can be significantly greater than the positive bias voltage. In some embodiments, the positive bias voltage can be between about 0.5 V and about 10 V, while the negative bias voltage can be between about -50 kV and about -1 kV. The accelerated negative ions during the modification stage of the etching process are used to modify or activate the substrate surface and can form a reactive film layer on the substrate surface. The accelerated positive ions during the removal stage of the etching process are used to etch the reactive film layer on the substrate surface.

[0052] In some embodiments shown in Figure 4A, the ionization space 420 is coupled to the acceleration space 430 via a second grid 434. The first grid 424 separates the plasma generation source 410 from the ionization space 420, and the second grid 434 separates the ionization space 420 from the acceleration space 430. The use of both the first grid 424 and the second grid 434 can enhance ionization. Using the first grid 424 and the second grid 434, the ionization space 420 can operate at a different pressure than the acceleration space 430. In some embodiments, the pressure in the ionization space 420 is greater than the pressure in the acceleration space 430. The higher pressure in the ionization space 420 promotes more collisions and more ionization. In some embodiments, the pressure in the ionization space 420 is between about 10 mTorr and about 1000 mTorr, such as about 500 mTorr. The lower pressure in the acceleration space 430 promotes acceleration and fewer collisions. In some embodiments, the pressure in the acceleration space 430 is between about 1 mTorr and about 50 mTorr, such as about 4 mTorr.

[0053] The second grid 434 may be similar in appearance to the first grid 424. In some embodiments, the second grid 434 may include a plurality of openings or apertures through which ions, electrons, or neutral particles can pass. In some embodiments, the second grid 434 may include a conductive plate having a plurality of openings or apertures, wherein the conductive plate may be biased or grounded. In some embodiments shown in FIG4A, the second grid 434 includes an electrode electrically connected to a DC power supply 444 to apply a negative or positive DC voltage to the second grid 434. For example, during a first stage of the etching process, the second grid 434 may be positively biased to attract electrons from the plasma generation source 410 into the ionization space 420. During a second stage of the etching process, the second grid 434 may be negatively biased to accelerate positive ions away from the ionization space 420. Although the embodiment in Figure 4 is shown as having a first grid 424 and a second grid 434, it should be understood that the plasma etching apparatus 400a may contain any number of grids, such as three, four, five, or more grids.

[0054] The plasma etching apparatus 400a may further include an exhaust pump 470. The exhaust pump 470 may include a roughing pump and / or a turbomolecular pump, which is in fluid communication with the acceleration space 430. The exhaust pump 470 is used to control the pressure within the plasma etching apparatus 400a, such as the pressure within the acceleration space 430. The exhaust pump 470 is further used to vent various gases from the acceleration space 430.

[0055] The modification and removal stages of the etching process can be alternately repeated in the plasma etching apparatus 400a. In the modification stage, plasma is generated in the plasma generation source 410; electrons are extracted from the plasma via the first grid 424; electron attachment ionization occurs in the ionization space 420 to form negative ions of reactive species; the negative ions are accelerated in the acceleration space 430 by applying a positive bias voltage to the substrate support 438; and the substrate surface is modified by the negative ions. In the removal stage, the plasma in the plasma generation source 410 is turned off; metastable neutral species are extracted from the plasma afterglow via the first grid 424; Penning ionization occurs in the ionization space 420 to form positive ions of non-reactive species; the positive ions are accelerated in the acceleration space 430 by applying a negative bias voltage to the substrate support 438; and the modified layer on the substrate surface is removed by the positive ions.

[0056] The plasma etching apparatus 400a may further include a controller 450. The controller 450 (which may include one or more physical or logic controllers) controls some or all of the operations of the plasma etching apparatus 400a. The controller 450 may be configured with instructions for performing modification and removal phases of the etching process. In this way, the controller 450 may selectively ionize reactive and non-reactive species in alternating phases, and may accelerate ion beams of negative and positive ions in alternating phases. In some embodiments, the controller 450 may be used to control an RF generator 416 connected to an RF antenna 414, a first gas source 412 for delivering a first gas, one or more other gas sources 422 for delivering a second and third gas, a DC power supply 444 electrically connected to a second grid 434, a DC power supply 442 electrically connected to a substrate support 438, an exhaust pump 470, or a combination thereof. In some embodiments, the controller 450 may be configured with instructions to: apply RF power to the plasma generation source 410 during a modification phase and to turn off the RF power supplied to the plasma generation source 410 during a removal phase. In some embodiments, the controller 450 may be configured with instructions to: apply a positive bias to the substrate support 438 during a modification phase to extract electrons from the plasma generation source 410 and accelerate negative ions of reactive species to the substrate 436; and apply a negative bias to the substrate support 438 during a removal phase to accelerate positive ions of non-reactive species to the substrate 436. Applying a positive bias can extract electrons from the plasma to ionize reactive species and form negative ions of reactive species. Applying a negative bias can cause metastable species to diffuse from the plasma or afterglow to ionize non-reactive species and form positive ions of non-reactive species.

[0057] Controller 450 may include one or more memory devices and one or more processors. The processor may include a central processing unit (CPU) or computer, analog and / or digital input / output connections, a stepper motor controller board, and other similar components. Instructions for performing appropriate control operations are executed on the processor. These instructions may be stored on memory devices associated with controller 450 or may be available via a network. In some embodiments, controller 450 executes system control software. The system control software may include instructions for controlling the timing and magnitude of the application of one or more of the following chamber operating conditions: gas mixing and / or composition, gas flow rate, chamber pressure, chamber temperature, substrate / substrate support temperature, substrate position, substrate support tilt, substrate support rotation, voltage applied to the grid, voltage applied to the substrate support, frequency and power applied to coils, antennas, or other plasma generating elements, and other parameters for specific processes performed by the tool. The system control software may further control purging and cleaning operations via exhaust pump 470. The system control software can be configured in any suitable manner. For example, subroutines or control objectives can be written into numerous processing tool components to control the operation of necessary processing tool components, thereby enabling the processing of various processing tools. The system control software can be coded in any suitable computer-readable programming language.

[0058] In some embodiments, the system control software includes input / output control (IOC) sequence instructions for controlling the various parameters described above. For example, each stage of a semiconductor processing step may include one or more instructions for execution by the controller 450. For example, instructions for setting process conditions for a stage may be included in the corresponding recipe stage. In some embodiments, the recipe stages may be sequentially arranged such that steps in the plasma etching process are performed in a specific order for that process stage. For example, a recipe may be configured to perform plasma generation and negative ion acceleration during a first stage, and positive ion acceleration during a second stage with plasma power off.

[0059] In some embodiments, other computer software and / or programs may be used. Examples of programs or program segments used for this purpose include substrate positioning programs, process gas composition control programs, pressure control programs, heater control programs, and RF power supply control programs.

[0060] The controller 450 can control these and other states based on sensor outputs (e.g., when power, potential, pressure, gas level, etc. reach a certain threshold), the timing of operation (e.g., applying power at certain times in the process), or based on instructions received from the user.

[0061] Broadly speaking, controller 450 can be defined as an electronic device having various integrated circuits, logic, memory, and / or software that include functions such as receiving instructions, sending instructions, controlling operations, enabling cleaning operations, and enabling endpoint measurements. The integrated circuits may include a chip in the form of firmware storing program instructions, digital signal processors (DSPs), chips defined as application-specific integrated circuits (ASICs), and / or one or more microprocessors or microcontrollers that execute program instructions (such as software). Program instructions may be instructions transmitted to controller 450 in the form of various individual settings (or program files), defining operating parameters for performing specific processes on a semiconductor wafer, on a semiconductor substrate, or on a system. In some implementations, these operating parameters may be part of a recipe defined by a process engineer to complete one or more processing steps during plasma etching.

[0062] In some embodiments, controller 450 may be part of or coupled to a computer that is integrated with, coupled to, or connected to the system via a network, or a combination thereof. For example, controller 450 may be located in the cloud or may be all or part of a wafer fab mainframe computer system that allows remote access to substrate processing. The computer can achieve remote access to the system to monitor the current progress of manufacturing operations, view the history of past manufacturing operations, view trends or performance indicators from multiple manufacturing operations, so as to change the parameters of the current processing, set processing steps to continue the current processing, or start a new processing. In some examples, a remote computer (such as a server) may provide processing recipes to the system via a network, which may include a local area network or the Internet. The remote computer may include a user interface that allows input or programming of parameters and / or settings, which are then transmitted from the remote computer to the system. In some examples, controller 450 receives instructions in the form of data, specifying parameters for each of the processing steps to be performed during one or more operations. It should be understood that these parameters may be specific to the type of processing to be performed and the type of tool (to which controller 450 is configured to interface with or control the tool). Therefore, as described above, controller 450 can be distributed, for example by comprising one or more separate controllers connected via a network and operating toward a common goal, such as the processing and control described herein. Examples of distributed controller 450 for such purposes may be one or more integrated circuits on a chamber that communicate with one or more integrated circuits located remotely (e.g., at the platform level or as part of a remote computer), which combine to control the processing on that chamber.

[0063] As described above, depending on the (plural) processing steps to be performed by the tools, the controller 450 may communicate with one or more of the following in the semiconductor manufacturing plant: other tool circuits or modules, other tool elements, cluster tools, other tool interfaces, adjacent tools, nearby tools, tools distributed throughout the plant, a main computer, another controller, or tools used in material transport that transport substrate containers to and from tool locations and / or loading ports.

[0064] In some embodiments, the controller 450 is configured with instructions to perform the following operations: accelerating negative ions of reactive species to substrate 436 in acceleration space 430 by introducing reactive species into ionization space 420 and applying a positive bias voltage to substrate support 438; and accelerating positive ions of non-reactive species to substrate 436 in acceleration space 430 by introducing non-reactive species into ionization space 420 and applying a negative bias voltage to substrate support 438. The controller 450 may further be configured with instructions to perform the following operations: igniting plasma in plasma generation source 410 when accelerating negative ions of reactive species; and extinguishing plasma in plasma generation source 410 when accelerating positive ions of non-reactive species. The controller 450 may further be configured with instructions to perform the following operations: for the step of accelerating negative ions of reactive species, extracting electrons from plasma into ionization space 420 to ionize reactive species and form negative ions of reactive species in ionization space 420. This can be achieved by applying a positive bias voltage to the substrate support 438. The controller 450 may be further configured with instructions to perform the following operations: for the step of accelerating positive ions of non-reactive species, diffusing metastable species from the plasma into the ionization space 420 to ionize the non-reactive species in the ionization space 420 and form positive ions of non-reactive species. This can be achieved by applying a negative bias voltage to the substrate support 438. The controller 450 may be further configured with instructions to perform the following operations: for the step of accelerating negative ions of reactive species, forming a reactive film layer on the material layer of the substrate 436; and for the step of accelerating positive ions of non-reactive species, etching the material layer of the substrate 436, wherein the material layer comprises a dielectric material or a conductive material. The controller 450 may be further configured with instructions to perform the following operations: repeatedly and alternately performing the operations of accelerating negative ions of reactive species and accelerating positive ions of non-reactive species.

[0065] According to certain embodiments, FIG4B is a schematic diagram of an exemplary plasma etching apparatus divided by a single grid, wherein the plasma etching apparatus generates inductively coupled plasma and delivers alternating beams of positive and negative ions for etching. The plasma etching apparatus 400b in FIG4B may be similar in appearance to the plasma etching apparatus 400a in FIG4A, except that there is no second grid in the plasma etching apparatus 400b. Therefore, the ionization space 420 and the acceleration space 430 occupy the entire volume and are not separated by any physical structure. The pressure in the ionization space 420 and the acceleration space 430 may be the same. Ions are effectively generated and accelerated within the same overall volume of the plasma etching apparatus 400b.

[0066] According to some embodiments, FIG4C is a schematic diagram of an exemplary plasma etching apparatus divided by at least two grids, wherein the plasma etching apparatus generates inductively coupled plasma in a remote plasma source and delivers alternating beams of positive and negative ions for etching. The plasma etching apparatus 400c in FIG4C is similar in appearance to the plasma etching apparatus 400a in FIG4A, except that the plasma generation source 410 in the plasma etching apparatus 400c is coupled to a remote induction source 472. An RF current from an RF generator 476 can be applied to a coil 474 to generate an RF electric field in the remote induction source 472 and form downstream plasma in the plasma generation source 410. The inductively coupled remote plasma reactor can produce a higher density plasma than the capacitively coupled plasma reactor. Therefore, the inductively coupled remote plasma reactor can be used to increase the electron density and the metastable species density. The same is true for the capacitively coupled remote plasma reactor compared to the capacitively coupled plasma reactor. In some embodiments, the plasma etching apparatus 400c may include a single grid instead of two or more grids.

[0067] According to some embodiments, FIG4D is a schematic diagram of an exemplary plasma etching apparatus divided by at least two grids, wherein the plasma etching apparatus generates capacitively coupled plasma and delivers alternating beams of positive and negative ions for etching. The plasma etching apparatus 400d in FIG4D may be similar in appearance to the plasma etching apparatus 400a in FIG4A, except that the plasma generation source 410 in the plasma etching apparatus 400d is a capacitively coupled plasma reactor. RF power can be supplied from RF generator 416 to electrode 418 to generate plasma in plasma generation source 410. The first grid 424 can be biased or grounded, and plasma can be formed between electrode 418 and the first grid 424 in the capacitively coupled plasma reactor. In some embodiments, the plasma etching apparatus 400d may comprise a single grid instead of two or more grids. Furthermore, it should be understood that the plasma etching equipment 400a–400d in Figures 4A–4D can utilize any number of grids and any suitable plasma generation technology, such as CCP technology, ICP technology, electron cyclotron technology, or microwave technology.

[0068] According to some embodiments, FIG5 shows a flowchart of an exemplary method for plasma etching using alternating beams of positive and negative ions. The operation of procedure 500 in FIG5 may include additional, fewer, or different operations. Accompanying the description of procedure 500 in FIG5, a series of cross-sectional schematic diagrams show modification operations in FIG6A and removal operations in FIG6B. According to some embodiments, FIG6A and 6B show schematic diagrams of an exemplary plasma etching process alternating between the modification operation of FIG6A and the removal operation of FIG6B. The operation of procedure 500 can be performed using a plasma etching apparatus (one of the plasma etching apparatuses 400a-400d in FIG4A-4D).

[0069] In block 510 of process 500, reactive and non-reactive species are introduced into the ionization space. The reactive and non-reactive species can flow directly into the ionization space of the plasma etching apparatus in gaseous form. The ionization space can be a space separated from the plasma generation source, wherein a first grid separates the ionization space from the plasma generation source. The ionization space can be located downstream of the plasma generation source. The first grid may include a conductive plate with a plurality of openings or pores through which neutral species of ions, electrons, and passivating gases can pass. Reactive species may include negatively charged reactive gas species, such as halogens, perfluorocarbons, hydrofluorocarbons, or oxygen. For example, reactive species include C4F8. Non-reactive species may include inert gases, such as helium, argon, xenon, or krypton. Non-reactive species may be different from the passivating gas supplied to the plasma generation source. In some embodiments, reactive and non-reactive species may be introduced continuously throughout process 500 or introduced during specified periods of process 500. In some embodiments, reactive and non-reactive species may be introduced in separate pulses during procedure 500. For example, one or both of reactive and non-reactive species may be introduced during a first phase of procedure 500, or one or both of reactive and non-reactive species may be introduced during a second phase of procedure 500.

[0070] The first stage constitutes a modification stage and may include at least blocks 520 and 530 of process 500. In some embodiments, the first stage further includes block 510. The second stage constitutes a removal stage and may include at least blocks 540 and 550 of process 500. In some embodiments, the second stage further includes block 510.

[0071] In block 520 of procedure 500, a plasma of the blunt gas is ignited in a plasma generation source. In some embodiments, the blunt gas is introduced into the plasma generation source before or during block 520. The blunt gas may contain helium, argon, xenon, or krypton. For example, the blunt gas contains helium. The plasma of the blunt gas may contain a mixture of neutral species, ions, and electrons of the blunt gas. In some embodiments, the plasma generation source may be a CCP reactor or an ICP reactor. The plasma is initiated during plasma ignition in block 520.

[0072] In block 530 of procedure 500, a positive bias is applied to the substrate support to extract electrons from the plasma generation source and accelerate negative ions of reactive species to the substrate. The substrate can be supported on the substrate support in an acceleration space, which may represent a volume in the plasma etching apparatus that is integrated with or separated from the ionization space. The acceleration space may be located downstream of the ionization space. The substrate may contain a material layer to be etched, wherein the material layer may contain a dielectric or conductive material. In some embodiments, the substrate may contain a plurality of high aspect ratio features having a depth-to-width ratio of at least 10:1, at least 20:1, at least 50:1, or at least 100:1.

[0073] Electrons can be extracted from plasma in a plasma generation source via a first grid. In some embodiments, the first grid may be grounded, and a positive bias voltage is applied to a substrate support outside the plasma generation source to extract electrons via the first grid. In some embodiments, a negative bias voltage may be applied to the first grid, and a positive bias voltage may be applied to a substrate support outside the plasma generation source to extract electrons via the first grid. Electrons are extracted from the plasma due to the electric field established between the positively biased substrate support and the grounded or negatively biased grid. Electrons are extracted when the plasma is activated. Without any theoretical limitations, the extracted electrons can collide with reactive species and form negative ions of reactive species through electron attachment ionization. The ions of reactive species do not dissociate. Electrons are extracted at energies that cause electron attachment ionization with reactive species (but not with non-reactive species). For example, electrons can be extracted at energies between about 1 eV and about 5 eV to perform electron attachment of C4F8 to form C4F8-. In some embodiments, the positive bias applied to the substrate support is between about 0.5 V and about 10 V, or between about 1 V and about 5 V.

[0074] Since the negative ions of reactive species are formed through electron attachment ionization, the positive bias voltage applied to the substrate support accelerates the negative ions to the substrate. This acceleration of the negative ions to the substrate is done in a way that limits or avoids sputtering at the substrate surface. Specifically, the positive bias voltage applied to the substrate support can be maintained between about 0.5 V and about 10 V, or between about 1 V and about 5 V. By applying a smaller positive bias voltage, the accelerated negative ions can modify or activate the substrate surface, rather than sputtering atoms / molecules from the substrate surface. In some embodiments, the accelerated negative ions are adsorbed onto the substrate surface to form a reactive film for etching. The material layer on the substrate can be converted into a reactive film, which can be etched during the removal phase of process 500.

[0075] The operations of blocks 520 and 530 in the modification stage can be performed simultaneously or sequentially. The operation of block 510 can be performed before or during the operations of blocks 520 and 530.

[0076] Figure 6A shows a schematic diagram of an exemplary plasma etching apparatus undergoing a modification stage of etching. This modification stage may include the operations of blocks 510, 520, and 530 of process 500 in Figure 5. Helium gas is supplied to a plasma generation source, such as a CCP reactor. Although the plasma generation source is shown as a CCP reactor, it should be understood that the plasma generation source can be any suitable plasma reactor. Helium plasma is generated by the plasma generation source. A positive DC voltage is applied to a substrate support on which the substrate is supported. The positive bias causes electrons to be extracted through a grid between the plasma generation source and the ionization space. A reactive gas (such as C4F8) and a non-reactive gas (such as Ar) are introduced into the ionization space. The extracted electrons cause the reactive gas to ionize without dissociation, forming negative ions of the reactive gas. As shown in Figure 6A, C4F8 is ionized by electron attachment ionization to form C4F8-. A positive bias voltage is used to accelerate negative ions of reactive gases to the substrate, thereby activating or modifying the substrate surface. For example, C4F8 can form a reactive film layer on the substrate surface. Although a single grid is shown in the plasma etching apparatus, it should be understood that a second grid can be provided in the plasma etching apparatus to divide the ionization space, which is located between the ionization space in which ionization occurs and the acceleration space in which the substrate is placed. Therefore, the modification stage of the etching process may involve: initiating the plasma to ignite the plasma; applying a positive bias voltage to the substrate support; extracting electrons from the plasma; ionizing reactive species to form negative ions of reactive species; and accelerating the negative ions to the substrate to modify the substrate surface.

[0077] Returning to Figure 5, block 540 of procedure 500 extinguishes the plasma in the plasma generation source. No RF power is applied to the plasma generation source to ignite or sustain the plasma. In other words, the plasma is shut off. Without plasma discharge, no charged species of inert gas are generated. However, metastable species (such as metastable neutral species of inert gas) can remain in the plasma generation source even after the plasma is shut off. Metastable species of inert gas can have a sufficiently long lifetime to diffuse through the first grid and into the ionization space. In particular, metastable species of inert gas can diffuse into the ionization space during the afterglow.

[0078] After plasma is shut down, metastable species diffusing into the ionized space can collide with non-reactive species to form positive ions of the non-reactive species. Metastable species can be in an excited state. Without any theoretical constraints, metastable species in the excited state can cause Penning ionization with non-reactive species, but not with reactive species. For example, a metastable helium radical (He*) in the excited state can have a lifetime of several seconds and an energy of several eV. This lifetime is long enough for a collision to occur before decay, and the metastable helium radical in the excited state has sufficient energy to ionize an inert gas species (such as Ar). The metastable helium radical can ionize Ar to form Ar+.

[0079] In block 550 of procedure 500, a negative bias is applied to the substrate support to accelerate positive ions of non-reactive species to the substrate. Since the positive ions of inert gas species are formed through Penning ionization, the negative bias applied to the substrate support accelerates the positive ions to the substrate. The acceleration of the positive ions of non-reactive species to the substrate is achieved by promoting ion bombardment and chemically assisted sputtering at the substrate surface. With energies between about 1000 eV and about 50000 eV, the positive ions can bombard and penetrate the substrate surface. In some embodiments, the negative bias applied to the substrate support may be between about -50 kV and about -1 kV, or between about -10 kV and about -1 kV. By applying a larger negative bias, the accelerated positive ions can etch the material formed on the substrate surface. In some embodiments, the accelerated positive ions mix with a reactive film layer, resulting in the etching of the reactive film layer.

[0080] The operations on blocks 540 and 550 during the removal phase can be performed simultaneously or sequentially. The operation on block 510 can be performed before or during the operations on blocks 540 and 550.

[0081] Figure 6B shows a schematic diagram of an exemplary plasma etching apparatus undergoing the removal stage of the etching process. This removal stage may include the operations of blocks 510, 540, and 550 of process 500 in Figure 5. No power is applied to the plasma generation source, thus extinguishing the plasma in the plasma generation source. The helium plasma is shut off, leaving only metastable helium radicals in the plasma afterglow. The metastable helium radicals may be in an excited state and can diffuse through the grid. Reactive gases (such as C4F8) and non-reactive gases (such as Ar) are introduced into the ionization space. The extracted metastable helium radicals cause ionization of the non-reactive gases to form positive ions of the non-reactive gases. As shown in Figure 6B, Ar is ionized via Penning ionization to form Ar+. A negative DC bias is applied to a substrate support on which the substrate is supported. The negative bias accelerates the positive ions of the non-reactive gases to the substrate to remove the reactive film layer on the substrate surface via chemically assisted sputtering. For example, Ar+ can remove reactive films formed by C4F8- adsorbed on the substrate surface. Therefore, the removal stage of the etching process may involve: shutting off the plasma to extinguish it; applying a negative bias to the substrate support; extracting metastable neutral species; ionizing non-reactive species to form positive ions of non-reactive species; and accelerating the positive ions to the substrate to etch material from the substrate surface.

[0082] Returning to Figure 5, process 500 may further include alternatingly repeating the modification phase of blocks 520 and 530 and the removal phase of blocks 540 and 550. The modification and removal phases may be performed continuously and alternately to complete process 500 for plasma etching. In some embodiments, the modification and removal phases may be performed continuously and alternately to complete process 500 to obtain plasma-etched high aspect ratio features on the substrate. Process 500 may alternate between electron-attached ionization in the modification phase and Penning ionization in the removal phase. Furthermore, process 500 may alternate between low-energy acceleration of fast neutral particles in the modification phase and high-energy acceleration of positive ions in the removal phase. Additionally, process 500 may alternate between plasma activation in the modification phase and plasma deactivation in the removal phase.

[0083] According to some embodiments, Figure 7 shows an exemplary timing diagram of applying power to a plasma source and applying voltage to a substrate support in a plasma etching process, wherein the plasma etching process alternates between a modification operation and a removal operation. The modification operation and the removal operation may constitute an etching cycle. In some embodiments, the etching cycle may last from about 1 ms to about 50 ms. The duration of the modification operation may be from about 1 ms to about 10 ms, and the duration of the removal operation may be from about 1 ms to about 10 ms. The modification operation and its duration may be associated with accelerating negative ions of reactive species or with applying a positive bias voltage to the substrate support. The removal operation and its duration may be associated with accelerating positive ions of non-reactive species or with applying a negative bias voltage to the substrate support.

[0084] As shown in Figure 7, during the modification operation, power is applied to the plasma source, and a positive DC voltage is used to slightly bias the substrate support. The positive DC voltage can be between approximately 1 V and approximately 5 V. During the removal operation, no power is applied to the plasma source, and a negative DC voltage is used to significantly bias the substrate support. The negative DC voltage can be between approximately -50 kV and -1 kV. The controller can be configured to provide instructions for alternately applying power to the plasma source and applying voltage to the substrate support between the modification and removal operations.

[0085] The plasma etching apparatus of this invention provides alternating ion beams of negative ions of reactive species and positive ions of non-reactive species for plasma etching. Fast neutral particles can modify the substrate surface through low-energy DC acceleration, while positive ions can etch material from the substrate surface through high-energy DC acceleration. The fast neutral particles have narrow IEDF and narrow IADF. The acceleration of negative and positive ions occurs individually through DC acceleration, rather than through sheath acceleration caused by the RF bias in conventional plasma etching reactors (which results in wide IEDF and wide IADF). Compared to the mixed-mode pulses in conventional plasma etching reactors that balance the ion / neutral particle flux ratio, this invention separates the ion flux and neutral particle flux by separating high-energy positive particles and low-energy negative ions. Conventional plasma etching reactors perform ionization through electron-bombardment ionization, while this invention achieves selective ionization by choosing between electron-attached ionization to form negative ions and Penning ionization to form positive ions. Fast, neutral particles with low energy and narrow IADF can be generated through electron-attached ionization, thus preventing the very slow diffusion of neutral species to the bottom of high aspect ratio features. Furthermore, charge accumulation on the mask is avoided through alternating beams of positive and negative ions. Redeposition of etching byproducts is also prevented by using one or more grids to separate the plasma generation area from the etching area, preventing backflow of etching byproducts into the plasma generation area. Moreover, regardless of whether the plasma reactor is a CCP reactor or an ICP reactor, dielectric etching and conductor etching can be performed using the plasma etching equipment of this invention. in conclusion

[0086] In the foregoing description, numerous specific details have been set forth to provide a thorough understanding of the proposed embodiments. The disclosed embodiments may be practiced without some or all of these specific details. In other examples, conventional process operations have not been described in detail to avoid obscuring the invention. Although the disclosed embodiments are described in conjunction with specific examples, it should be understood that they are not intended to be limiting.

[0087] To enable those skilled in the art to clearly understand the present invention, the above embodiments have been described in detail. It should be understood that certain variations and modifications can be made within the scope of the appended claims. It should be noted that there are many alternative ways to implement the processes, systems, and apparatus described herein. Therefore, the embodiments herein should be considered illustrative rather than restrictive, and such embodiments are not limited to the details provided herein.

[0088] 100: Plasma Etching Equipment 102: Upper electrode 104: Lower electrode 106:Substrate 110: RF source 112: RF source 114: Gas Source 120: Processing Chamber 122: Entrance 124: Exhaust pump 130: Controller 140: Plasma 200: Plasma Etching Equipment 202: Upper electrode 204: Lower electrode 206:Substrate 212: RF source 214: Gas Source 216: Sprayer head device 220: Gap 230: Controller 240: Plasma 400a: Plasma etching equipment 400b: Plasma Etching Equipment 400c: Plasma etching equipment 400d: Plasma etching equipment 410: Plasma generation source 412: First gas source 414: Antenna 416: RF Generator 418: Electrode 420: Ionization Space 422: One or more other gas sources 424: First grille 430: Acceleration Space 434: Second grille 436:Substrate 438: Substrate support 442: DC power supply 444: DC power supply 446: Electrical grounding 450: Controller 470: Exhaust pump 472: Remote sensing source 474: Coil 476: RF Generator 500: Program 510: Steps 520: Steps 530: Steps 540: Steps 550: Steps

Claims

1. A plasma etching apparatus, comprising: a plasma generation source configured to ignite or extinguish a plasma of a first gas in the plasma generation source; a first gas source coupled to the plasma generation source, wherein the first gas source is configured to supply the first gas to the plasma generation source; an ionization space coupled to the plasma generation source; a second gas source coupled to the ionization space, wherein the second gas source is configured to supply a second gas and a third gas to the ionization space, wherein the ionization space is configured to form negative ions of the second gas and positive ions of the third gas; a first grid located between the ionization space and the plasma generation source; an acceleration space coupled to the ionization space and configured to transport the negative ions of the second gas and the positive ions of the third gas to a substrate in the acceleration space, wherein the acceleration space is downstream of the ionization space and the ionization space is downstream of the plasma generation source; and a second grid located between the ionization space and the acceleration space.

2. The plasma etching apparatus of claim 1, wherein the second gas comprises hydrofluorocarbon gas.

3. The plasma etching apparatus of claim 1, wherein the second gas includes a halogen gas, a perfluorocarbon gas, or oxygen.

4. The plasma etching apparatus of claim 1, wherein the third gas includes an inert gas.

5. The plasma etching apparatus of claim 1, wherein the first gas includes an inert gas different from the third gas.

6. The plasma etching apparatus of claim 1 further includes: a substrate support located in the acceleration space for supporting the substrate, wherein the substrate support is configured to be positively biased or negatively biased.

7. The plasma etching apparatus of claim 1, wherein the first grid and the second grid are each configured to be biased.

8. The plasma etching apparatus of claim 1 further comprises: a controller configured with instructions for performing the following operations: allowing the second gas and the third gas to flow into the ionization space; igniting the plasma of the first gas in the plasma generation source; extracting electrons from the plasma of the first gas and forming the negative ions of the second gas; extinguishing the plasma of the first gas in the plasma generation source; and providing metastable neutral species of the first gas and forming the positive ions of the third gas.

9. The plasma etching apparatus of claim 8, wherein the controller is further configured with instructions for performing the following operations: accelerating the negative ions of the second gas toward the substrate; and accelerating the positive ions of the third gas toward the substrate.

10. A plasma etching apparatus comprising: a plasma generation source configured to ignite or extinguish a plasma containing a passivating gas in the plasma generation source; a first gas source coupled to the plasma generation source, wherein the first gas source is configured to supply the passivating gas to the plasma generation source; and an integrated ionization and acceleration space coupled to the plasma generation source. A second gas source, coupled to the integrated ionization and acceleration space, is configured to supply reactive and non-reactive gases to the integrated ionization and acceleration space, wherein the integrated ionization and acceleration space is configured to form negative ions of the reactive gas and positive ions of the non-reactive gas, wherein the integrated ionization and acceleration space is configured to transport the negative ions of the reactive gas and the positive ions of the non-reactive gas to a substrate within the integrated ionization and acceleration space, wherein the integrated ionization and acceleration space is downstream of the plasma generation source; a grid is located between the integrated ionization and acceleration space and the plasma generation source. and a substrate support that supports the substrate within the integrated ionization and acceleration space, wherein the substrate support is configured to be positively or negatively biased.

11. The plasma etching apparatus of claim 10, wherein the integrated ionization and acceleration space is configured to generate the negative ions of the reactive gas in response to a positive bias applied to the substrate support.

12. The plasma etching apparatus of claim 11, wherein the integrated ionization and acceleration space is configured to form the positive ions of the nonreactive gas in response to the quenching of the plasma of the passivating gas in the plasma generation source.

13. The plasma etching apparatus of claim 12, wherein the integrated ionization and acceleration space system is configured to accelerate the negative ions of the reactive gas to the substrate in response to a positive bias voltage applied to the substrate support, and wherein the integrated ionization and acceleration space system is configured to accelerate the positive ions of the non-reactive gas to the substrate in response to a negative bias voltage applied to the substrate support.

14. The plasma etching apparatus of claim 10, wherein the grid comprises a conductive plate having a plurality of pores, wherein the grid is configured to be biased.

15. The plasma etching apparatus of claim 10, wherein the absolute value of the negative bias voltage is significantly greater than the positive bias voltage.

16. The plasma etching apparatus of claim 10, wherein the passivation gas is different from the non-reactive gas.

17. The plasma etching apparatus of claim 10 further includes: a controller configured with instructions to perform the following operations: directing the negative ions of the reactive gas to the substrate in the integrated ionization and acceleration space; and directing the positive ions of the non-reactive gas to the substrate in the integrated ionization and acceleration space.

18. The plasma etching apparatus of claim 17, wherein the controller is further configured with instructions for performing the following operations: igniting the plasma of the passivating gas in the plasma generation source; extracting electrons from the plasma and forming the negative ions of the reactive gas; extinguishing the plasma of the passivating gas in the plasma generation source; and providing metastable neutral species of the passivating gas and forming the positive ions of the nonreactive gas.

19. The plasma etching apparatus of claim 10, wherein the reactive gas includes hydrofluorocarbon gas, perfluorocarbon gas, halogen gas, or oxygen.

20. The plasma etching apparatus of claim 10, wherein the non-reactive gas includes an inert gas.

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