Plasma etching with reduced power and ETCH chemistry

Abstract

An apparatus includes a substrate support for holding a substrate at a cryogenic temperature during etching, a plasma source configured to generate a plasma located above the substrate support, an ion acceleration grid located between the plasma source and the substrate support, wherein the ion acceleration grid is configured to apply a potential difference that, during etching, accelerates ions from the plasma toward the substrate support, and an inlet for an etchant process gas, wherein the inlet is located between the ion acceleration grid and the substrate support.

Description

Attorney Docket No. LAM1P037WO-11882-1WOPLASMA ETCHING WITH REDUCED POWER AND ETCH CHEMISTRYINCORPORATION BY REFERENCE

[0000] A PCT Request Form is filed concurrently with this specification as part of the present application. Each application that the present application claims benefit of or priority to as identified in the concurrently filed PCT Request Form is incorporated by reference herein in their entireties and for all purposes.BACKGROUND

[0001] In a semiconductor fabrication process, plasma etch is employed to form etched features on a substrate. Plasma etch typically requires a high bias power and an etch chemistry for forming etched features. In some cases, the etch chemistry includes greenhouse gases that are not environment friendly.

[0002] Background and contextual descriptions contained herein are provided solely for the purpose of generally presenting the context of the disclosure. Much of this disclosure presents work of the inventors, and simply because such work is described in the background section or presented as context elsewhere herein does not mean that such work is admitted prior art.SUMMARY

[0003] Provided is an apparatus. The apparatus includes a substrate support for holding a substrate at a cryogenic temperature during etching, a plasma source configured to generate a plasma located above the substrate support, and an ion acceleration grid located between the plasma source and the substrate support. The ion acceleration grid is configured to apply a potential difference that, during etching, accelerates ions from the plasma toward the substrate support. The apparatus further includes an inlet for an etchant process gas. The inlet is located between the ion acceleration grid and the substrate support.

[0004] In some embodiments, the cryogenic temperature is about -200 to 0° C.

[0005] In some embodiments, the apparatus further includes a vacuum source configured to provide a pressure of about 0.01 to 0.5 milliTorr proximate the substrate support during etching.

[0006] In some embodiments, the pressure ranges from about 0.1 to 0.3 milliTorr.

[0007] In some embodiments, during etching, the substrate and ion acceleration grid are separated by a gap of about 1-20 cm.

[0008] In some embodiments, the gap ranges from about 5 to 15 cm.

[0009] In some embodiments, during etching, the apparatus consumes about 10 to 100 kW of power.

[0010] In some embodiments, the apparatus further includes one or more sources of the etchant process gas, wherein the etchant process gas includes hydrogen fluoride.Attorney Docket No. LAM1P037WO-11882-1WO

[0011] In some embodiments, the etchant process gas further includes iodine fluoride, chlorine trifluoride, water, phosphorus trifluoride, chlorine, hydrogen chloride, hydrogen bromide, hydrogen iodide, hydrogen, oxygen, or any combination thereof.

[0012] In some embodiments, the iodine fluoride includes iodine heptafluoride.

[0013] In some embodiments, the apparatus is configured to pulse delivery of the etchant process gas to the substrate.

[0014] In some embodiments, the etchant process gas includes no greenhouse gas.

[0015] In some embodiments, the apparatus further includes a source of a multilayer deposition precursor including doped silicon, tungsten, graphite, molybdenum, or silicon oxide.

[0016] In some embodiments, the substrate support includes a chuck.

[0017] In some embodiments, the substrate support is an electrostatic chuck.

[0018] In some embodiments, the substrate support is a cryo-electrostatic chuck.

[0019] In some embodiments, the plasma source includes a coil configured to produce an inductively coupled plasma (ICP).

[0020] In some embodiments, the plasma source includes an electron cyclotron resonance source.

[0021] In some embodiments, the plasma source includes one or more electromagnets configured to shape the plasma and to improve uniformity across the substrate.

[0022] In some embodiments, the plasma source is coupled to a plasma generator.

[0023] In some embodiments, the plasma generator is configured to provide electrical power of about 0.1 to 2 kW at a frequency of about 2 to 40 MHz.

[0024] In some embodiments, the ion acceleration grid includes a plurality of openings that allows ions to pass from the plasma to the substrate support.

[0025] In some embodiments, the plurality of openings includes slits, ellipses, circles, polygons, or any combination thereof.

[0026] In some embodiments, the etching apparatus is configured to move the substrate with respect to the plurality of openings in the ion acceleration grid during etching.

[0027] In some embodiments, the etching apparatus is configured to move the substrate in a lateral and / or rotational direction with respect to the plurality of openings in the ion acceleration grid during etching.

[0028] In some embodiments, the ion acceleration grid includes at least two substantially parallel conductive layers.

[0029] In some embodiments, at least one of the conductive layers includes a doped silicon.

[0030] In some embodiments, at least one of the conductive layers includes tungsten, graphite, or molybdenum.Attorney Docket No. LAM1P037WO-11882-1WO

[0031] In some embodiments, the ion acceleration grid further includes a silicon oxide layer separating the at least two of the conductive layers.

[0032] In some embodiments, the ion acceleration grid further includes one or more holes to mount one or more isolating stand-offs that are configured to separate at least two of the conductive layers.

[0033] In some embodiments, the apparatus further includes a power supply for the ion acceleration grid. The power supply is configured to provide a first electrical potential to a first conductive layer of the ion acceleration grid and a second electrical potential to a second conductive layer of the ion acceleration grid. The first conductive layer is closer to the plasma source than the second conductive layer and the first electrical potential is more positive than the second electrical potential.

[0034] In some embodiments, the ion acceleration grid is configured to produce ion beams having an ion energy of about 1000 to 2000 eV and an ion angular distribution of (a) about 0.5 degrees 1 sigma or less, or (b) about 0.5 degrees or less at 1 sigma.

[0035] In some embodiments, the ion acceleration grid is configured to pulse the ion beams.

[0036] In some embodiments, the etching apparatus does not have a plasma bias generator.

[0037] In some embodiments, the apparatus further includes an electron injector located between the ion acceleration grid and the substrate support. The electron injector is configured to neutralize accelerated ions before they reach the substrate.

[0038] Another aspect of the disclosure relates to a method of etching a substrate. The method includes receiving a substrate at a substrate support of an etch chamber, directing ion beams from an ion acceleration grid onto the substrate, and injecting an etchant process gas including hydrogen fluoride into the etch chamber at a location between the substrate and the ion acceleration grid. The substrate is maintained at a temperature of about -200 to 0° C during the etching.

[0039] In some embodiments, the method further includes applying a pressure of about 0.01 to 1 milliTorr proximate the substrate support in the etch chamber.

[0040] In some embodiments, the pressure ranges from about 0.1 to 0.3 milliTorr.

[0041] In some embodiments, the etching employs a power of about 10 to 100 kW.

[0042] In some embodiments, the etchant process gas further includes iodine fluoride, chlorine trifluoride, water, phosphorus trifluoride, chlorine, hydrogen chloride, hydrogen bromide, hydrogen iodide, hydrogen, oxygen, or any combination thereof.

[0043] In some embodiments, iodine fluoride includes iodine heptafluoride.

[0044] In some embodiments, the etchant gas includes no greenhouse gas.

[0045] In some embodiments, the method further includes moving the substrate in a lateral direction and / or rotational direction with respect to the ion acceleration grid. The ion accelerationAttorney Docket No. LAM1P037WO-11882-1WO grid includes a plurality of openings that allows ions to pass from the plasma to the substrate support in the ion beams.

[0046] In some embodiments, the method further includes depositing a multilayer deposition precursor comprising doped silicon, tungsten, graphite, molybdenum, or silicon oxide.

[0047] In some embodiments, the substrate support includes a chuck.

[0048] In some embodiments, the substrate support includes a cryo-electrostatic chuck.

[0049] In some embodiments, the method further includes generating a plasma comprising ions by a plasma source comprising an inductively coupled plasma (ICP) source or an electron cyclotron resonance (ESR) source.

[0050] In some embodiments, the plasma source includes one or more electromagnets configured to shape plasma and to improve uniformity of the plasma across the substrate.

[0051] In some embodiments, the plasma is generated with electrical power of about 0.1 to 2 kW at a frequency of about 2 to 40 MHz.

[0052] In some embodiments, the ion acceleration grid includes a plurality of openings that allows ions to pass from the plasma to the substrate support in the ion beams.

[0053] In some embodiments, the method further includes moving the substrate with respect to the plurality of openings in the ion acceleration grid during etching.

[0054] In some embodiments, the substrate is configured to move in a lateral and / or rotational direction with respect to the plurality of openings in the ion acceleration grid during etching.

[0055] In some embodiments, the ion acceleration grid includes at least two substantially parallel conductive layers.

[0056] In some embodiments, at least one of the conductive layers includes a doped silicon.

[0057] In some embodiments, at least one of the conductive layers includes tungsten, graphite, or molybdenum.

[0058] In some embodiments, the ion acceleration grid further includes a silicon oxide layer separating the at least two substantially parallel conductive layers.

[0059] In some embodiments, the ion acceleration grid further includes one or more holes to mount one or more isolating stand-offs that are configured to separate at least two of the conductive layers.

[0060] In some embodiments, a first electrical potential is applied to a first conductive layer of the ion accelerating grid and a second electrical potential is applied to a second conductive layer of the ion accelerating grid. The first conductive layer is farther to the substrate support than the second conductive layer and the first electrical potential is more positive than the second electrical potential.Attorney Docket No. LAM1P037WO-11882-1WO

[0061] In some embodiments, the ion acceleration grid is configured to produce ion beams having an ion energy of about 1000 to 2000 eV and an ion angular distribution of (a) about 0.5 degrees 1 sigma or less, or (b) about 0.5 degrees or less at 1 sigma.

[0062] In some embodiments, the ion acceleration grid is configured to pulse the ion beams.

[0063] In some embodiments, injecting the etchant process gas includes pulsing the etchant gas.

[0064] In some embodiments, a bias is not applied to the substrate support or the substrate.

[0065] In some embodiments, the apparatus further includes injecting electrons to neutralize accelerated ions before they reach the substrate.

[0066] These and other features of the disclosure will be presented below, sometimes with reference to drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1A depicts an example cross-section of a conventional plasma etch apparatus for etching a structure.

[0068] Figure IB depicts an example cross-section of a plasma etch apparatus configured to operate at cryogenic temperatures.

[0069] Figure 2A depicts an example cross-section of a plasma etch apparatus employing an ion acceleration grid and a chuck configured to move relative to the ion acceleration grid according to certain embodiments.

[0070] Figure 2B depicts the operation of the plasma etch apparatus shown in Figure 2A at cryogenic temperatures by combining ion beam from the ion acceleration grid and direct supply of an etchant process gas according to certain embodiments.

[0071] Figure 3 presents a flow chart of an example etch process for etching a structure according to certain embodiments.

[0072] Figure 4 depicts a distribution of ion scattering angles for the different chamber pressures during etching according to certain embodiments.

[0073] Figure 5A depicts a top view of an ion acceleration grid for producing ion beam according to certain embodiments.

[0074] Figures 5B-5D depict a method of fabricating an ion acceleration grid according to certain embodiments.

[0075] Figure 6A depicts the ions or ion beams emanating from an ion acceleration grid with slits toward a substrate according to certain embodiments.

[0076] Figure 6B depicts a top view of the translation of an ion acceleration grid by a certain distance relative to a location on a substrate according to certain embodiments.

[0077] Figure 6C depicts a top view of the translation of an ion acceleration grid by a distance equal to the sum of the width of the slit and the grid body according to certain embodiments.Attorney Docket No. LAM1P037WO-11882-1WO

[0078] Figure 6D illustrates the change in the ion flux and corresponding change in the surface coverage by neutrals at a location on the substrate that is translating as shown in Figure 6C.

[0079] Figure 6E depicts a top view of the translation of an ion acceleration grid by a distance three times the width of the slit and the grid body according to certain embodiments.

[0080] Figure 6F illustrates the change in the ion flux and corresponding change in the surface coverage by neutrals at a location on the substrate that is translating as shown in Figure 6E.

[0081] Figures 7A-7B illustrate an example operation of an ion acceleration grid by applying an extraction voltage according to certain embodiments.

[0082] Figure 8A depicts an example cross-section of a plasma etch apparatus for cleaning an ion acceleration grid according to certain embodiments.

[0083] Figures 8B-8C illustrate an example method of cleaning an ion acceleration grid according to certain embodiments.INTRODUCTION AND CONTEXT

[0084] Currently, many etch apparatuses employ plasmas to generate ions that impinge on a substrate and radicals that chemically react with the substrate. In many designs, a plasma is provided in direct contact with substrate. Ions accelerate toward the substrate, through a plasma sheath at the substrate surface. Directional energy is imparted to the ions applying a bias power to the substrate. Typically, such apparatuses require several 10s of Kilowatts (kWs) of RF bias power to accelerate ions to needed energies.

[0085] In addition to the accelerated ions, reactive neutrals participate in the etching. The plasma in a conventional etch apparatus generates radicals that stick to the substrate surface via chemical bonds. There, the radicals chemically attack the substrate to facilitate etching with the accelerated ions. To generate a sufficient quantity of radicals, a conventional etch apparatus may operate at millitorr (mTorr) pressures. The plasma dissociates non-radical neutrals to produce the radicals. At conventional millitorr pressures, a relatively high gas flow rate (e.g., on the order of 1000 standard cubic centimeters per minute (seem) or greater) is required to remove the reaction products.

[0086] Additionally, many conventional etch apparatuses employ greenhouse gases as etchants. Examples of such gases include fluorocarbons (CxFy) and / or nitrogen trifluoride (NF3).

[0087] Etch apparatus disclosed herein may provide any one or more improvements over existing etch apparatuses. Some etch apparatuses disclosed herein employ an ion acceleration grid or other ion beam source, in lieu of or as a partial replacement to a plasma bias generator. Such etch apparatuses can operate under conditions that provide high etch rates with greatly reduced power requirements. This is because ion beam sources can, under appropriate circumstances, generateAttorney Docket No. LAM1P037WO-11882-1WO ions with suitable energy to etch a substrate while consuming relatively little power. For example, an ion acceleration grid applies a voltage to grid layers to accelerate ions while consuming relatively little power.

[0088] If an ion beam source is separated from the substrate by a significant distance (e.g., about 5 cm or more), it is possible that the ion beams reach the substrate in a diffuse or insufficiently collimated state. This is because as the ions travel from the ion beam source to the substrate, they frequently collide with etchant gas molecules. Such collisions may scatter a significant fraction of the ions in the ion beam and thereby increase the spread or angle of the ion beam reaching the substrate. To address this potential challenge, some embodiments of this disclosure employ relatively low pressures in the etch apparatus (e.g., sub-millitorr pressures), particularly in the region between the ion beam source and the substrate. At such low pressures, the ions of the ion beams collide with relatively few atoms before reaching the substrate.

[0089] While low pressures allow the ion beams to remain relatively collimated, they create a separate challenge: insufficient quantities of chemically reactive etchant species from an etchant process gas (e.g., neutral radicals, non-radical neutral species, etc.) may be present at the substrate. The concentration of such species at the substrate surface is a function of their concentration in the apparatus, as well as their reactivity, which, in a conventional etch apparatus, is increased by converting them to radicals via interaction with the plasma at the substrate surface. In certain embodiments of this disclosure, an etch apparatus includes a cryogenic chuck or other substrate support, which holds the substrate at very low temperatures during etching. At these temperatures, a greater fraction of neutral radicals and even non-radicals physisorb onto the substrate surface, thereby providing a sufficient concentration of such species on the surface to provide adequate chemical etching.

[0090] Another aspect of some etch apparatuses of this disclosure is the use of etchant species that are not greenhouse gases. Thus, in certain embodiments, the etchant gas does not include fluorocarbons and / or nitrogen trifluoride. Examples of etchant gases used in apparatuses of this disclosure include hydrogen fluoride (HF), phosphorus trifluoride (PF3), chlorine trifluoride (CIF3), iodine heptafluoride (IF7), hydrogen bromide (HBr), hydrogen iodide (HI), chlorine, hydrogen, oxygen, water, or any combinations thereof.

[0091] Stated another way, some etch apparatuses disclosed herein leverage ion beam etch technology (IBE) in combination with very low substrate temperatures. A chemically reactive gas such as hydrogen fluoride is injected into the apparatus near the substrate. The apparatus operates at sub-millitorr pressure to avoid gas phase collisions by the ions. A sufficiently high concentration of neutrals (e.g., neutral radicals) on the substrate surface is achieved by lowering the substrate temperature to allow etchant gas to physisorb / adsorb onto the substrate surface.Attorney Docket No. LAM1P037WO-11882-1WO

[0092] As shown in Figure 1A, a conventional system 101 used for conducting plasma-based etching of high aspect ratio features includes a chamber 103 in which a substrate 105 is positioned to have features etched therein. During etching, substrate 105 is positioned on a chuck 107.

[0093] The system 101 also includes one or more plasma generators 109a and 109b that are configured to provide oscillating power for generating a plasma 111 within chamber 103. As illustrated, the plasma 1 1 1 is formed within the chamber 103 and, in fact, may directly interact with the substrate 105 via a plasma sheath.

[0094] As an example, plasma generator 109a may be configured to provide RF power for generating plasma 111 (i.e., plasma generator 109a is a plasma source or a plasma source generator) and plasma generator 109b may be configured to provide a bias potential for attracting ions from plasma 111 to substrate 105. For example, plasma generator 109b may apply a negative potential to substrate 105 that attracts ions from plasma 111 to impinge on the substrate 105 with a substantially vertical trajectory.

[0095] As examples, the plasma generators may be used to generate a transformer coupled plasma (TCP) or a capacitor coupled plasma (CCP).

[0096] In system 101, an inlet (not shown) provides an entry point for a process gas including etchant compounds that may be collectively referred to as an etchant chemistry or etchant process gas. The etchant compounds may be provided as neutral species. However, within chamber 103 and while interacting with plasma 111, at least some of these neutral species dissociate to form radicals. The radicals are more reactive than the non-radical neutral species and tend to bind with or otherwise stick to the substrate, including any features being etched within the substrate.

[0097] As can be seen in Figure 1A, the plasma and etchant chemistry within chamber 103 includes ions, neutral radicals, and neutral non-radicals. This arrangement of system 101 generally works fine for etching high aspect ratio features. However, it tends to consume a lot of energy associated with generating plasma 111. It also tends to require a relatively large quantity etchant gases.

[0098] A related system 121 is shown in Figure IB, where like numbers refer to like features. The main difference between the system 101 shown in Figure 1A and the system 121 shown in Figure IB is that a chuck 127 in system 121 may be configured to operate at cryogenic temperatures, e.g., temperatures of about -200 to 0° C. At such low temperatures, a higher fraction of the neutral etchant chemistry species binds with or otherwise stick to the surface of substrate 105, including the features being etched at that surface. Therefore, compared to system 101, system 121 may require a relatively lower etchant species concentration.

[0099] In some embodiments of this disclosure, an etch apparatus may be characterized by the following features. Within the etch apparatus there is a substrate support for holding a substrate,Attorney Docket No. LAM1P037WO-11882-1WO a plasma source separated from the substrate support and facing the side of the support that presents a substrate surface to be etched. Within the etch apparatus is also an ion acceleration grid located between the plasma source and the substrate support. The ion acceleration grid is configured to apply a potential difference that, during etching, accelerates ions from the plasma toward the substrate support. Such ions may be provided in the form of ion beams that impinge on the substrate in a substantially normal direction. To facilitate the effectiveness of the ion beams, the etch apparatus may be configured to operate at very low pressures, e.g., sub-millitorr (sub-mTorr) pressures and at cryogenic temperatures. The substrate support may be configured to hold the substrate at such temperatures. In some embodiments, the etch apparatus additionally includes an inlet for an etchant process gas. The inlet is located between the ion acceleration grid and the substrate support. During operation, etchant process gases are adsorbed, at low temperature, onto the substrate surface, where they etch the surface and interact with ions from the ion beams.

[0100] Figure 2A depicts a system 201 for conducting ion beam etching according to some embodiments of this disclosure. The system 201 includes a chamber 203 in which a substrate 205 is supported on a substrate support 207. In some embodiments, the substrate support 207 may be a chuck, an electrostatic chuck, or a cryo-electrostatic chuck. The substrate support 207 may be configured to move in a lateral direction and / or a rotational direction with respect to an ion acceleration grid 219. In one example, the substrate may be configured to fully or partially rotate. In another example, the substrate may be configured to translate in x- and y-direction. In various embodiments, substrate 205 remains in a fixed position while ion acceleration grid 219 moves as described herein. The substrate support 207 may be configured to operate at cryogenic temperatures, e.g., temperatures of about -200 to 0°C. In one embodiment, the substrate support 207 may operate using a Peltier device (e.g., thermoelectric cooling). In another embodiment, the substrate support 207 may be temperature-controlled using liquid nitrogen. During etching, no or very little bias voltage is applied to the substrate support 207.

[0101] The system 201 also includes one or more plasma generators 211 that are configured to provide oscillating power (e.g., RF power) for generating a plasma 215 within the chamber 203. The plasma 215 may be a remote plasma that is not in direct contact with the substrate 205. In some embodiments, the plasma 215 may be generated by applying an electrical power. As illustrated, the plasma generator 211 may include an inductively coupled plasma (ICP) source that is coupled to one or more turns of inductive coils 217 to produce the plasma 215. In one embodiment, the plasma generator 211 may include one or more electromagnets to shape the plasma and to improve uniformity across the substrate. In other embodiments, the plasma source may be an electron cyclotron resonance (ECR). One or more gas sources 225, may be configured to introduce a process gas such as a noble gas (e.g., N2, He etc), H2, O2, or any combination thereof.Attorney Docket No. LAM1P037WO-11882-1WOSuch process gas may be used for generating plasma species.

[0102] An ion acceleration grid 219 is positioned above the substrate support 207, thereby defining an upper chamber portion 221 and a lower chamber portion 223. In some embodiments, the ion acceleration grid 219 is a multi-layered stack including at least two substantially parallel conductive layers and an insulating layer separating at least two conductive layers. As shown in Figure 2A, the ion acceleration grid 219 includes three conductive layers 229a, 229b, and 229c, and two insulating layers (not shown) separating the two conductive layers. The ion acceleration grid 219 includes a plurality of openings (sometimes referred to as apertures) 235 that are separated from one another by defined distances. In some embodiments, the openings 235 may be slits, ellipses, circles, polygons, or their combinations. The conductive layer may include a doped silicon, tungsten, graphite, or molybdenum. The insulating layer may be silicon oxide or include a ceramic insulating composition. In one embodiment, isolation between the conductive layers may be achieved by a continuous dielectric layer electrically separating the conductive layers. In another embodiment, the ion acceleration grid may include one or more holes to mount one or more stand-offs, e.g., pillars, to form an air gap between the conductive layers.

[0103] One or more power supplies 237a, 237b may be electrically coupled to one or more conductive layers 229a, 229b to provide electrical potentials, thereby accelerating ions through the openings 235 toward the substrate 235. The conductive layer 229c at the bottom of the ion acceleration grid 219 may be grounded. The electrical potentials applied to the conductive layers 229a, 229b may be same or substantially same. On the other hand, different electrical potentials may be applied to different conductive layers 229a, 229b. It is noted that the number of the power supplies are not limited to two supplies. It can be three or four or five depending on the number of conductive layers in the ion acceleration grid 209.

[0104] The system 201 may include an electron injector 241 that is positioned proximity to the substrate 205 for injecting electrons thereby neutralizing ions before the ions reach the substrate 205. In one embodiment, the electron injector 241 may include a filament or a hollow cathode. A gas inlet port 243 is positioned underneath the ion acceleration grid 219 and may be configured to flow one or more gases having defined etch chemistries (i.e., etch process gases) into the chamber 203. In some embodiments, the etch chemistry does not include a greenhouse gas. The etch chemistry may be hydrofluoric acid (HF), chlorine trifluoride (CIF3), phosphorus trifluoride (PF3), iodine fluoride, e.g., iodine heptafluoride (IF7), hydrogen bromide (HBr), hydrogen iodide (HI), hydrogen chloride (HC1), hydrogen, chlorine, oxygen, water, or any combinations thereof.

[0105] Figure 2B depicts in cartoon fashion certain aspects of the operation of the system 201 shown in Figure 2A. The system 201 may implement etching at a cryogenic temperature by combining the ion beam (produced by acceleration grid 219) and the direct supply of etchantAttorney Docket No. LAM1P037WO-11882-1WO process gas. In operation, the substrate 205 is positioned on the substrate support 207. The substrate 205 includes a layer or other structure to be etched typically in a pattern defined by a patterned mask may be provided on the layer. During etching, the plasma generator 211 applies power to generate a plasma 215 from a gas including, e.g., one or more noble gases. As illustrated, plasma 215 is located in the upper chamber portion 221. As such, plasma 215 may be considered to be a remote plasma. Of relevance to generating ion beams, plasma 215 includes ions such as positively charged ions.

[0106] Electrical potential is applied to attract the ions to the ion acceleration grid 219. In some embodiments, a positive potential is applied to at least the uppermost conductive layer 229a of the ion acceleration grid 219. The positive ions may pass through the openings 235 and continue to move in a downward direction toward the substrate 205 in the form of ion beams. The momentum, velocity, or collimation of ions may be controlled by varying the magnitude of the one or more positive or negative voltages applied to the different conductive layers in the ion acceleration grid 219. Generally, a more positive potential is applied to the conductive layer that is closer to the plasma. Then, a greater magnitude negative potential (i.e., lower magnitude positive potential relative to the conductive layer that is closer to the plasma) may be applied to the conductive layer that is farther from the plasma. Applying a lower magnitude positive potential to the conductive layer that is farther from the plasma may minimize the deviation of the ion angular distribution for the ions traveling toward the substrate. In one embodiment, a conductive layer in the ion acceleration grid may be electrically coupled to one or more conductive parts of the plasma source, rendering the potential of the conductive layer equal to the potential of plasma. For example, a conductive layer closest to plasma may be electrically coupled to one or more conductive parts of the plasma source, rendering the potential of the conductive layer closest to plasma equal to the potential of plasma.

[0107] Unlike conventional plasma etching where a bias voltage is applied to the substrate to attract ions from the plasma, little or no bias voltage is applied to the substrate or substrate support to pull ions toward the substrate. Instead, the momentum or velocity of ions is controlled only by the electric potentials applied to the ion acceleration grid 219. The RF power consumption according to this embodiment can be reduced by about 10 to 100 times compared to the conventional plasma etching.

[0108] The pressure in the lower chamber portion 223 may be controlled to be a low value, e.g., in the sub-millitorr range. In some embodiments, the pressure may range from about 0.01 to 0.5 milliTorr (mTorr), or about 0.1 to 0.3 mTorr. Due to, in part, the low chamber pressure, the accelerated ions may undergo a reduced scattering with other gas species, such as etchant process gases, before they impinge to the substrate 205. Normally, scattering between ions and gas speciesAttorney Docket No. LAM1P037WO-11882-1WO causes the ions to deviate in their perpendicular trajectory toward the designated etching location on the substrate. Reduced chamber pressure reduces the probability of ion scattering and allows a greater fraction of the ions to land at the location of the substrate where etching is supposed to occur and to arrive at the substrate in a perpendicular trajectory.

[0109] The one or more etchant process gases are directly flown into the chamber from the gas inlet 243, which is proximate the substrate 205. Supplying etchant process gas below the ion acceleration grid proximate the substrate may reduce the amount of etchant process gas used for etching. The consumption of etchant process gas can be reduced by about 10 to 100 times compared to the conventional plasma etching.

[0110] The etchant process gases include neutral species that can be physisorbed on the substrate. The physisorption of the etchant chemistries to the substrate surface is enhanced at very low substrate temperatures. In some embodiments, during etching, the substrate temperature is at a cryogenic temperature, e.g., from about -200 to 0 °C. At such low temperatures, a substantial portion of the etchant process gases are physisorbed on the substrate surface in the neutral species form. See gas molecules 251 depicted in Figure 2B. The gas molecules 251 may include neutral species. In some cases, multiple layers of neutral species are adsorbed on the substrate.

[0111] Etching features in the substrate may be achieved by ions impinging on the substrate surface where the neutral etch species are physisorbed. Accelerated ions provide an energy to the substrate to both sputter material from the substrate and convert some neutral gas molecules to radicals, which increases their reactivity and facilitates etching.

[0112] It is noted that the system configuration depicted in Figure 2A or 2B is not limiting. For example, while Figures 2 A and 2B show that the system 201, including the chamber, is arranged vertically, the system may be arranged horizontally such that the chamber ion beam path is 90° offset from that in the system in Figures 2A and 2B. Also, the chamber arrangement may not be as symmetrical as illustrated. Further, the chamber may have various shapes including rectangular, other polygonal, or circular etc.

[0113] Figure 3 is a flow chart of an example etch process for etching a structure according to some embodiments. A process 300 begins at operation 310 by receiving a substrate on a substrate support a chamber. During or soon after this operation, the wafer is cooled to a cryogenic temperature. The substrate may include a structure to be etched. In one example, the structure includes a patterned mask defining the locations of one or more HAR features.

[0114] In an operation 320, the chamber is evacuated until an identified pressure is reached before introducing a process gas for generating a plasma or etching. In one embodiment, the pressure achieved prior to introducing a process gas or an etchant process gas is referred to as a background pressure. The background pressure may be about IxlO'7Torr or lower. The background pressureAttorney Docket No. LAM1P037WO-11882-1WO level may be associated with the amount of water molecules in the chamber. It is desirable to eliminate most of the water molecules in the chamber during etching because residual water molecules can scatter the ions in the ion beams. Additionally, at cryogenic temperature, the water molecules may be physisorbed on the substrate, thereby reducing the number of sites for the etchant process gas on the substrate. In one embodiment, one or more metal gaskets may be used to improve the background pressure compared to conventional polymer based O-rings. A lower background pressure may be further achieved by heating the walls of the chamber before or during etching to a certain temperature, thereby expediting outgassing from the chamber walls.

[0115] After the desired background pressure is reached, in an operation 330, a process gas for generating a plasma is introduced in the chamber and a source plasma power is applied to initiate a plasma in the chamber. The plasma is confined or resides primarily on the side of the ion acceleration grid opposite in the substrate. In a vertically oriented chamber, such the region of the plasma is in an upper chamber portion. The plasma may include ions and other reactive species.

[0116] In an operation 340, an etchant process gas is introduced proximate the substrate from a gas inlet between the substrate and the ion acceleration grid (e.g., underneath the ion acceleration grid). In one embodiment, the etchant process gas may be hydrofluoric acid (HF) and may include neutral species that are readily adsorbed (e.g., physisorbed) on the substrate. Due to the presence of plasma including ions and reactive species of the etchant process gas, the chamber pressure increases from a background pressure to an operating pressure, which may be in the sub-millitorr range. In some embodiments, etching is performed at about the operating pressure.

[0117] In an operation 350, a positive bias (i.e., positive electrical potential) is applied to at least one layer of the ion acceleration grid. For example, a positive bias may be applied to the conductive layer closest to plasma. In one embodiment, a positive bias may be applied to at least one layer of the ion acceleration grid and the entire plasma source. In one embodiment, another conductive layer and the lower chamber portion 223 (e.g. substrate support 207) may be grounded to have a negative potential with respect to the positive potential applied to the at least one layer that is the closer (or the closest) to plasma, thereby producing a potential difference. In one embodiment, another conductive layer may be closest to the substrate. This potential difference attracts ions having positive charges from a plasma toward the substrate in the lower chamber portion 223. Ions pass through a plurality of openings in the ion acceleration grid with a substantially vertical trajectory. In one embodiment, when a positive bias is applied to one layer, the more positive bias or more negative bias relative to the positive bias applied to the one layer may be applied to another conductive layer of the ion acceleration grid to change the collimation of ion beam passing through the ion acceleration grid. Accelerated ions impart momentum to the substrate such that a portion of the substrate is sputtered. Ions also collide with neutral species onAttorney Docket No. LAM1P037WO-11882-1WO the substrate, thereby converting the neutral species to radicals for chemically reacting with at least a portion of the substrate. During etching operation 350, the substrate and / or the ion acceleration grid may be displaced relative to one another in a lateral direction or a rotational direction to more uniformly apply ions to the substrate. The etching may be performed for a certain time period or until the etched features are verified by in-situ or ex-situ inspection.

[0118] In the depicted embodiment, operation 350 follows operation 340. However, this operation sequence is not limiting. In one embodiment, the operations 340 and 350 may occur simultaneously or substantially simultaneously. In one embodiment, the operation 350 may precede the operation 340.

[0119] In an operation 360, etching of the structure is completed. At this point, an electrical potential applied to the ion acceleration grid is turned off, and the etchant process gas (e.g., HF) and a process gas for generating plasma are also turned off.Process Parameters

[0120] The following is a non-limiting description of parameters that may be used during etching using an apparatus as described herein. Values of these parameters may vary from those listed below depending on the configuration of the reactor and the application. Any combination of the listed parameter values may be employed together as process windows.Plasma and Ion beam generation

[0121] As explained, an ion beam for etching features may be generated from a plasma provided above an ion acceleration grid. Because the plasma is separated from the substrate, it may be referred to as a remote plasma. The plasma may be generated under various conditions such as those conventionally used in the art. As an example, the plasma may be generated using one or more process gases such as nitrogen (N2), helium (He), argon (Ar), xenon (Xe), hydrogen (H2), oxygen (O2), or any combination thereof.

[0122] In some embodiments, the plasma is generated within the chamber at a background pressure of about IxlO-8to IxlO-7Torr (e.g., about IxlO-7Torr). The background pressure may be reached prior to introducing the process gases (e.g., etchant process gas) for generating the plasma.

[0123] The plasma may be generated by applying an electrical power of about 0. 1 to 2 kilowatts (kW) at a frequency of about 2 to 40 MHz. In one embodiment, the electrical power of 10 to 100 kW may be applied for etching.

[0124] Accelerated ions from the ion acceleration grid may have an ion energy of about 1000- 2000 eV. For this, a bias voltage (i.e., an electrical potential) of about 1000 to 2000 V may beAttorney Docket No. LAM1P037WO-11882-1WO applied to a layer of the ion acceleration grid closest to the plasma. Ion currents may range from about 0.1 to 0.5 mA / cm2.Etchant process gas

[0125] As explained, an etchant process gas may be introduced to the etch chamber at, for example, a location between the ion acceleration grid and the substrate. For etching the features according to some embodiments, one or more of the following etching process gases may be supplied: hydrogen fluoride (HF), phosphorus trifluoride (PF3), iodine fluoride, e.g., iodine heptafluoride (IF7), hydrogen bromide (HBr), hydrogen iodide (HI), hydrogen, oxygen, or any combinations thereof. In some embodiments, none of the etchant gases are greenhouse gases.Pressure and temperature for etching

[0126] The chamber pressure during etching, i.e., operating pressure, may be in the sub-millitorr range, about 0.01 to 0.5 Torr, about 0.05 to 0.5 mTorr, or about 0.1 to 0.3 mTorr. In some embodiments, the operating pressure may be correlated to an ion angular distribution. For example, the operating pressure may be set so that an ion angular distribution during etching is (a) about 0.5 degrees 1 sigma standard deviation (i.e., 1 sigma) or less, or (b) about 0.5 degrees or less at 1 sigma. In one embodiment, the operating pressure is about 0.2 millitorr for about 20 cm gap between the substrate and the ion acceleration grid.

[0127] In some embodiments, these pressures are appropriate for apparatus having a small gap between the substrate and the ion acceleration grid. In certain embodiments, such gap is about 5 to 15 cm.

[0128] In some embodiments, the substrate temperature during etching is about -200 to 0° C, or - 120 to -200C.

[0129] Figure 4 illustrates a distribution of ion scattering angles measured for the different chamber pressures, i.e., 0.1 mTorr, 0.2 mTorr, and 0.5 mTorr, respectively. The distance between the plasma source and the wafer surface is about 23 cm. The chart shows the distribution of ion energy (vertical axis) as a function of ion scattering angle (horizontal axis) at these different pressures. The ions traveling from the ion acceleration grid to the substrate collide with the etchant process gases before they arrive at the substrate, and, as a result, deviate from their original perpendicular trajectory. The ion scattering angle in Figure 4 refers to an angular deviation (from perpendicular) of the ions from a designated location on the substrate, e.g., a location on the substrate at which etching occurs. The deviation is caused by the collision of the ions with the etchant process gases. At higher chamber pressures, the number of collisions increases, and theAttorney Docket No. LAM1P037WO-11882-1WO corresponding deviation also increases. Also, the energy of the ions decreases due to momentum loss from the collisions.

[0130] As illustrated in Figure 4, the scattering profiles are strongly influenced by the chamber pressures. As illustrated, at low chamber pressures, ions produce strongly focused ion beams due to less scattering. As the chamber pressure increases, more ions undergo scattering and a fraction of the ions deviate from their original trajectories and have insufficient energy to participate in etching. As a result, more broad ion energy distribution is obtained.

[0131] Figure 5A is a top view of an ion acceleration grid 500 according to one embodiment of this disclosure. The ion acceleration grid 500 includes a grid body 510 having a thickness and one or more openings (i.e., apertures) 520 formed in the grid body 510. The ion acceleration grid 500 may comprise at least two conductive layers and an insulating layer between the two conductive layers. The openings 520 are separated from one another by defined distances. In some embodiments, the distances may range from about 5 to 10 millimeters (mm). The openings 520 may have any of various shapes such as slits, ellipses, circles, polygons, etc.

[0132] Figures 5B-5D illustrate one example of a method of fabricating the ion acceleration grid 500 shown in Figure 5A. Figure 5B illustrates an ion acceleration grid precursor 502 that includes an alternating stack including three conductive layers 530 and two insulating layers 540, each sandwiched between two conductive layers 530 so that different potentials are applied to the adjacent conductive layers 530 electrically separated by the insulating layer 540. The conductive layers 530 may include doped silicon, tungsten, graphite, molybdenum, or the like. The insulating layers 540 may include silicon oxide. In one embodiment, the conductive layers and the insulating layers may be formed from doped silicon and silicon oxide, respectively. The thicknesses of the conductive layers 530 may range from about 3 to about 10 mm, or from about 5 to about 7 mm. The thicknesses of the insulating layers 540 may range from about 3 to about 15 nm, or from about 5 to about 10 nm. Figure 5C illustrates forming slits 550 in the ion acceleration grid precursor 502 to form paths for ions to form ion beams. The slits 550 are separated from one another by grid body lines 560. In one embodiment, the openings may be formed using a high pressure water cutting. A width 570 of the openings may be about 5 to 10 mm.

[0133] Figure 5D illustrates the resulting ion acceleration grid 500 after the widths of the insulating layers in the grid body lines 560 have been reduced, thereby forming a recess. As an example, if the insulating layers are made from a silicon oxide, their widths may be reduced by treating the ion acceleration grid 500 with hydrofluoric acid (HF), thereby ions are not charged to the recessed surface of the insulating layers.

[0134] Figure 6 A depicts ions and ion beams emanating from an ion acceleration grid 600 and toward a substrate 610. In one embodiment, an etching process gas, such as HF, is adsorbed onAttorney Docket No. LAM1P037WO-11882-1WO the substrate. The ions passing through slits 650 of the ion acceleration grid 600 sputter the substrate surface and activate the etchant process gas molecules (e.g., etchant process gas) to chemically activate them so they can chemically etch the substrate surface under the openings 650. While this process is fine for etching features in regions of the substrate directly under the slits 650, it does so without substantially etching features that are masked by a grid body 660 of grid of 600. Even considering the ion scattering during the travel from the ion acceleration grid 600 to the substrate 610, a substantial portion of etching will be concentrated under the openings 650. Without appropriately compensating for this effect, the substrate will be etched nonuniformly, with etching occurring substantially only in regions where the ion beams reach the substrate surface.

[0135] This non-uniformity can be addressed in various manners. One involves moving the substrate with respect to the ion acceleration grid. Figures 6B-6F illustrate a few examples of how this may be accomplished.

[0136] Figure 6B illustrates moving the ion acceleration grid 600 in a lateral direction to uniformly distribute the ions on the underlying substrate (not shown). In the depicted example, the ion acceleration grid 600 translates in one direction by a distance including a width 670 of the slit 650 and a width 680 of the grid body 660, or by a distance including a multiple of the width 670 of the slit 650 and the width 680 of the grid body 660. In the depicted embodiment, the ion acceleration grid 600 translates perpendicular to the longitudinal direction of slit 650.

[0137] Movement in this manner allows the ion acceleration grid 600 to pass the ions to specific regions of the substrate only for a fraction of the total etch time. Averaged over the total etch time, all regions of the substrate see ion impingement for the same amount of time. In operation, the ion acceleration grid 600 will translate in one direction and then reverse directions. Thus, the ion acceleration grid 600 translates in opposing directions. The direction and the distance of translations can be determined to ensure that the substrate uniformly receives ion beam energy at all regions of the substrate.

[0138] Figures 6C and 6D illustrate the change in ion flux 692 and the corresponding change in the surface coverage by neutrals 694 at a location 655 on the substrate over time. The changes result from the ion acceleration grid 600 translating by a distance of the width of the slit 670 and the grid body 680 as illustrated in Figure 6C. Figure 6C corresponds to the movement of the ion acceleration grid 600 shown in the left portion of Figure 6B. During etching, the ion acceleration grid 600 translates in a first direction by a distance equal to the sum of distances 670 and 680, and then changes directions to translate in a second direction by the same distance. The back and forth translations continue during the etch process.Attorney Docket No. LAM1P037WO-11882-1WO

[0139] When location 655 is exposed to the ion beams as shown in Figure 6C, the ion beams pass through the slit 650 and the ion flux 692 instantly or substantially instantly increases to and is then maintained at a certain level while the slit remains over location 655. Simultaneously, the ions sputter the substrate surface and interact with any neutrals or other chemical etchant species, such as HF gas molecules, physisorbed on the surface of the substrate. The neutrals or other chemical etchant species may receive energy from the impinging ions for causing a chemical reaction between etchant species and the structure. With time, during exposure to ions from the ion beam, the absorbed etchant species are consumed or otherwise removed from the surface by, for example, chemically etching features in the substrate. Thus, while location 655 is exposed to the ion beam, the surface coverage 694 of etchant species decreases with time. In one embodiment, multiple layers of neutrals formed on the substrate prior to applying the ion beam are consumed to reach a surface concentration of zero or substantially zero.

[0140] Subsequently, the ion acceleration grid 600 translates in one direction so that location 655 is masked by the grid body 660. As the location 655 is blocked from receiving ion beam, the ion flux 692 at location 655 immediately decreases to zero level while the surface coverage of neutrals or other etchant species 694 increases due to the supply of the etchant process gas and / or no consumption of the etchant process gas in the absence of ion flux 692. After a certain time, the ion acceleration grid 600 changes direction and translates in the opposing direction to again expose location 655 to the incoming ion flux 692. Then, the ion flux 692 at location 655 increases again to a certain level and the recently adsorbed chemical species are removed from location 655 by reaction between those species and the substrate surface. Thus, as illustrated in Figure 6D, the surface coverage 694 of the adsorbed species again decreases with time of exposure to the ion flux. It is noted that details of the plot shown in Figure 6D are for example only. The details of the timing, shape, and other details of the ion flux and surface concentration of etchant species may vary depending on the various process conditions and apparatus configurations.

[0141] Figures 6E and 6F illustrate an ion flux 696 and the corresponding change in the surface coverage by neutrals 698 at a location 665 on the substrate for a different lateral movement of the ion acceleration grid 600. Figure 6E illustrates that the ion acceleration grid 600 translates by a distance three times the width of the slit 670 and the grid body 680. On the other hand, it is noted that the embodiment as described is not limited to the distance as illustrated in Figure 6C or 6E. The moving distance can be any distance, i.e., any multiple of a distance including the width of the slit 670 and the grid body 680.

[0142] Figure 6F illustrates variations in ion flux and etchant species surface coverage at location 665 caused by variations in exposure to the ion beam as caused by the ion acceleration grid movement as illustrated in Figure 6E. Of interest, the duration of exposure to (or masking from)Attorney Docket No. LAM1P037WO-11882-1WO the ion beams lengthens when the translation of the ion acceleration grid changes direction. Thus, when location 665 experiences a turning point in the grid translation, the ions are applied for extended time compared to when the grid is translating in one direction. As illustrated, the total time during which location 665 is exposed to ion beams may be compensated to be uniform by increasing the time during which location 665 is masked from ion beams as shown in the ion flux off period in the last portion of the pulsing scheme in Figure 6F.

[0143] Please understand that while much of the above discussion focuses on movement of the ion acceleration grid, the same or similar results can be achieved by movement of the substrate or movement of both the substrate and the ion acceleration grid. Each of these possibilities is within the scope of movement of the ion acceleration grid “with respect to” the substrate.

[0144] It is to be understood that controlling the duration of etching any given location of the substrate can be accomplished by many different techniques. For example, the movement of the ion acceleration grid with respect to the substrate can be varied. In one embodiment, pulsing of the etchant process gas may be controlled to control the etch rate and / or the etch uniformity.

[0145] In certain embodiments, the flow rate of the etchant process gas is pulsed to physisorb a controlled amount etchant species on the substrate (e.g., about two to six layers of neutrals on the substrate), which may expedite etching. Alternately, limiting the neutrals to about one or two layers of the neutral may reduce the etch rate.

[0146] In certain embodiments, a source plasma power is controlled, which in turn controls the production of ions in a plasma and correspondingly the amount of ion flux passing through the ion acceleration grid.

[0147] In certain embodiments, the application of a potential to the ion acceleration grid is controlled to variably control the flux of ions to the substrate during etching.

[0148] Any combination of control features may be employed to control the etch conditions on the substrate surface. These control features include translation of the ion acceleration grid with respect to the substrate, etchant process gas flow rate, source plasma power for generating ions, and the ion acceleration grid operation potential. These controls allow for selectively providing ions and etchant species to the substrate surface in a manner that allows control the etch rate of the substrate.

[0149] Figures 7A-7B illustrate the operation of an ion acceleration grid 700 according to some embodiments of the disclosure. Figure 7A illustrates that the positive extraction voltage and the negative suppression voltages are applied, thereby producing ion beam in the ion acceleration grid 700. Figure 7B illustrates that when the extraction voltage is off, the ion beam cannot be produced. This control may allow selectively providing ions to the substrate as described herein.Attorney Docket No. LAM1P037WO-11882-1WO

[0150] Figure 8A illustrates an example of a process chamber 801 for cleaning an ion acceleration grid 800 according to one embodiment of the disclosure. The chamber 801 may include a gas inlet 843 for supplying a cleaning chemistry and ion acceleration grid 800. As illustrated, the ion acceleration grid 800 includes a number of a conductive layer 830 and an insulating layer 840. After an etching operation as described herein, the ion acceleration grid 800 may be coated with a low-density silicon-containing material, such as silicon oxyfluoride (SiOxFy) or silicon-rich material, such as silicon fluoride (SiFx). In one embodiment, a low-density silicon-containing material, such as silicon oxyfluoride or silicon fluoride may be formed as a deposit 850 on the outer surface of the conductive layer 830. The deposit 850 may be insulating, thereby preventing the acceleration of ions from occurring in the vicinity of the conductive layers 830. The deposit 850 may be removed after performing a certain number of etchings or as determined by in-situ or ex-situ tests. In one example, the deposit 850 is removed by exposing the ion acceleration grid 800 to an etchant process gas, such as HF. The HF may remove the low-density silicon-containing material to have a deposit-free ion acceleration grid 800 as shown in Figure 8C.

[0151] This invention includes optional benefits compared to conventional plasma etching. The RF power consumption can be reduced by about 10 to 100 times as no bias voltage is applied to the substrate to pull ions toward the substrate. The consumption of etchant process gas can be reduced by about 10 to 100 times due to the direct supply of the etchant process gas proximate the substrate. Further, the use of the etchant process gas such as HF prevents using a greenhouse gas such as CxFyor NF3.Conclusion

[0152] In the foregoing description, numerous specific details are set forth to provide a thorough understanding of the presented embodiments. The disclosed embodiments may be practiced without some or all these specific details. In other instances, well-known process operations have not been described in detail to not unnecessarily obscure the disclosed embodiments. While the disclosed embodiments are described in conjunction with the specific embodiments, it will be understood that it is not intended to limit the disclosed embodiments.

[0153] Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing the processes, structures, systems, and apparatus of the present embodiments. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the embodiments are not to be limited to the details given herein.

Claims

Attorney Docket No. LAM1P037WO-11882-1WOCLAIMSWhat is claimed is:

1. An apparatus comprising: a substrate support for holding a substrate at a cryogenic temperature during etching; a plasma source configured to generate a plasma located above the substrate support; an ion acceleration grid located between the plasma source and the substrate support, wherein the ion acceleration grid is configured to apply a potential difference that, during etching, accelerates ions from the plasma toward the substrate support; and an inlet for an etchant process gas, wherein the inlet is located between the ion acceleration grid and the substrate support.

2. The apparatus of claim 1, wherein the cryogenic temperature is about -200 to 0° C.

3. The apparatus of claim 1, further comprising a vacuum source configured to provide a pressure of about 0.01 to 0.5 milliTorr proximate the substrate support during etching.

4. The apparatus of claim 3, wherein the pressure ranges from about 0.1 to 0.3 milliTorr.

5. The apparatus of claim 1, wherein, during etching, the substrate and ion acceleration grid are separated by a gap of about 1-20 cm.

6. The apparatus of claim 5, wherein the gap ranges from about 5 to 15 cm.

7. The apparatus of claim 1, wherein, during etching, the apparatus consumes about 10 to 100 kW of power.

8. The apparatus of claim 1, further comprising one or more sources of the etchant process gas, wherein the etchant process gas comprises hydrogen fluoride.

9. The apparatus of claim 8, wherein the etchant process gas further comprises iodine fluoride, chlorine trifluoride, water, phosphorus trifluoride, chlorine, hydrogen chloride, hydrogen bromide, hydrogen iodide, hydrogen, oxygen, or any combination thereof.

10. The apparatus of claim 9, wherein the iodine fluoride comprises iodine heptafluoride.Attorney Docket No. LAM1P037WO-11882-1WO11. The apparatus of claim 1, wherein the apparatus is configured to pulse delivery of the etchant process gas to the substrate.

12. The apparatus of claim 1, wherein the etchant process gas comprises no greenhouse gas.

13. The apparatus of claim 1, further comprising a source of a multilayer deposition precursor comprising doped silicon, tungsten, graphite, molybdenum, or silicon oxide.

14. The apparatus of claim 1, wherein the substrate support comprises a chuck.

15. The apparatus of claim 1, wherein the substrate support is an electrostatic chuck.

16. The apparatus of claim 1, wherein the substrate support is a cryo-electrostatic chuck.

17. The apparatus of claim 1, wherein the plasma source comprises a coil configured to produce an inductively coupled plasma (ICP).

18. The apparatus of claim 1, wherein the plasma source comprises an electron cyclotron resonance source.

19. The apparatus of claim 1, wherein the plasma source comprises one or more electromagnets configured to shape plasma and to improve uniformity of the plasma across the substrate.

20. The apparatus of claim 1, wherein the plasma source is coupled to a plasma generator.

21. The apparatus of claim 20, wherein the plasma generator is configured to provide electrical power of about 0.1 to 2 kW at a frequency of about 2 to 40 MHz.

22. The apparatus of claim 1, wherein the ion acceleration grid comprises a plurality of openings that allows ions to pass from the plasma to the substrate support.

23. The apparatus of claim 22, wherein the plurality of openings comprises slits, ellipses, circles, polygons, or any combination thereof.Attorney Docket No. LAM1P037WO-11882-1WO24. The apparatus of claim 22, wherein the etching apparatus is configured to move the substrate with respect to the plurality of openings in the ion acceleration grid during etching.

25. The apparatus of claim 22, wherein the etching apparatus is configured to move the substrate in a lateral and / or rotational direction with respect to the plurality of openings in the ion acceleration grid during etching.

26. The apparatus of claim 1, wherein the ion acceleration grid comprises at least two substantially parallel conductive layers.

27. The apparatus of claim 26, wherein at least one of the conductive layers comprises a doped silicon.

28. The apparatus of claim 26, wherein at least one of the conductive layers comprises tungsten, graphite, or molybdenum.

29. The apparatus of claim 26, wherein the ion acceleration grid further comprises a silicon oxide layer separating the at least two of the conductive layers.

30. The apparatus of claim 26, wherein the ion acceleration grid further comprises one or more holes to mount one or more isolating stand-offs that are configured to separate at least two of the conductive layers.

31. The apparatus of claim 1, further comprising a power supply for the ion acceleration grid, wherein the power supply is configured to provide a first electrical potential to a first conductive layer of the ion acceleration grid and a second electrical potential to a second conductive layer of the ion acceleration grid, wherein first conductive layer is closer to the plasma source than the second conductive layer and wherein the first electrical potential is more positive than the second electrical potential.

32. The apparatus of claim 1, wherein the ion acceleration grid is configured to produce ion beams having an ion energy of about 1000 to 2000 eV and an ion angular distribution of (a) about 0.5 degrees 1 sigma or less, or (b) about 0.5 degrees or less at 1 sigma.Attorney Docket No. LAM1P037WO-11882-1WO33. The apparatus of claim 32, wherein the ion acceleration grid is configured to pulse the ion beams.

34. The apparatus of claim 1, wherein the etching apparatus does not have a plasma bias generator.

35. The apparatus of claim 1, further comprising an electron injector located between the ion acceleration grid and the substrate support, wherein the electron injector is configured to neutralize accelerated ions before they reach the substrate.

36. A method of etching a substrate, the method comprising: receiving a substrate at a substrate support of an etch chamber; directing ion beams from an ion acceleration grid onto the substrate; and injecting an etchant process gas comprising hydrogen fluoride into the etch chamber at a location between the substrate and the ion acceleration grid, wherein the substrate is maintained at a temperature of about -200 to 0° C during the etching.

37. The method of claim 36, further comprising applying a pressure of about 0.01 to 1 milliTorr proximate the substrate support in the etch chamber.

38. The method of claim 37, wherein the pressure ranges from about 0. 1 to 0.3 milliTorr.

39. The method of claim 36, wherein the etching employs a power of about 10 to 100 kW.

40. The method of claim 36, wherein the etchant process gas further comprises iodine fluoride, chlorine trifluoride, water, phosphorus trifluoride, chlorine, hydrogen chloride, hydrogen bromide, hydrogen iodide, hydrogen, oxygen, or any combination thereof.

41. The method of claim 40, wherein iodine fluoride comprises iodine heptafluoride.

42. The method of claim 36, wherein the etchant gas comprises no greenhouse gas.

43. The method of claim 36, further comprising moving the substrate in a lateral direction and / or rotational direction with respect to the ion acceleration grid, wherein the ion acceleration gridAttorney Docket No. LAM1P037WO-11882-1WO comprises a plurality of openings that allows ions to pass from the plasma to the substrate support in the ion beams.

44. The method of claim 36, further comprising depositing a multilayer deposition precursor comprising doped silicon, tungsten, graphite, molybdenum, or silicon oxide.

45. The method of claim 36, wherein the substrate support comprises a chuck.

46. The method of claim 36, wherein the substrate support comprises a cryo-electrostatic chuck.

47. The method of claim 36, further comprising generating a plasma comprising ions by a plasma source comprising an inductively coupled plasma (ICP) source or an electron cyclotron resonance (ESR) source.

48. The method of claim 36, wherein the plasma source comprises one or more electromagnets configured to shape plasma and to improve uniformity of the plasma across the substrate.

49. The method of claim 47, wherein the plasma is generated with electrical power of about 0. 1 to 2 kW at a frequency of about 2 to 40 MHz.

50. The method of claim 36, wherein the ion acceleration grid comprises a plurality of openings that allows ions to pass from the plasma to the substrate support in the ion beams.

51. The method of claim 50, further comprising moving the substrate with respect to the plurality of openings in the ion acceleration grid during etching.

52. The method of claim 51, wherein the substrate is configured to move in a lateral and / or rotational direction with respect to the plurality of openings in the ion acceleration grid during etching.

53. The method of claim 36, wherein the ion acceleration grid comprises at least two substantially parallel conductive layers.

54. The method of claim 53, wherein at least one of the conductive layers comprises a doped silicon.Attorney Docket No. LAM1P037WO-11882-1WO55. The method of claim 53, wherein at least one of the conductive layers comprises tungsten, graphite, or molybdenum.

56. The method of claim 54, wherein the ion acceleration grid further comprises a silicon oxide layer separating the at least two substantially parallel conductive layers.

57. The method of claim 53, wherein the ion acceleration grid further comprises one or more holes to mount one or more isolating stand-offs that are configured to separate at least two of the conductive layers.

58. The method of claim 36, wherein a first electrical potential is applied to a first conductive layer of the ion accelerating grid and a second electrical potential is applied to a second conductive layer of the ion accelerating grid, wherein the first conductive layer is farther to the substrate support than the second conductive layer and wherein the first electrical potential is more positive than the second electrical potential.

59. The method of claim 36, wherein the ion acceleration grid is configured to produce ion beams having an ion energy of about 1000 to 2000 eV and an ion angular distribution of (a) about 0.5 degrees 1 sigma or less, or (b) about 0.5 degrees or less at 1 sigma.

60. The method of claim 36, wherein the ion acceleration grid is configured to pulse the ion beams.

61. The method of claim 36, wherein injecting the etchant process gas comprises pulsing the etchant gas.

62. The method of claim 36, wherein a bias is not applied to the substrate support or the substrate.

63. The apparatus of claim 36, further comprising injecting electrons to neutralize accelerated ions before they reach the substrate.

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