Cryogenic ETCH using acid forming gas

Abstract

A method of etching recessed features in a stack is provided. An acid forming gas is mixed with water to form an acid on a surface of the stack, wherein the acid forms at least one modified region of the stack. The stack is exposed to energy that volatilizes the at least one modified region of the stack.

Description

CRYOGENIC ETCH USING ACID FORMING GASCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of U.S. Application No. 63 / 650,188, filed May 21, 2024, which is incorporated herein by reference for all purposes.BACKGROUND

[0002] One process frequently employed during the fabrication of semiconductor devices is the formation of a recessed feature in a stack below a mask. The stack may be alternating / repeating layers into which the recessed feature is formed, or a thick film of a single layer of material. One example context where such a process may occur is memory applications such as dynamic random access memory (DRAM) and “not and” memory devices (NAND). In the manufacturing of some semiconductor devices, metal or other materials may be etched below a mask. As the semiconductor industry advances and device dimensions become smaller, such recessed features become increasingly harder to etch in a uniform manner, especially for high aspect ratio features having narrow widths and / or deep depths.

[0003] The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.SUMMARY

[0004] To achieve the foregoing and in accordance with the purpose of the present disclosure, a method of etching recessed features in a stack is provided. An acid forming gas is mixed with water to form an acid on a surface of the stack, wherein the acid forms at least one modified region of the stack. The stack is exposed to energy that volatilizes the at least one modified region of the stack.

[0005] In another manifestation, an apparatus for etching recessed features in a stack is provided. A substrate support supports a substrate inside a processing chamber. A power source provides power to form a plasma. A temperature controller cools the substrate support to a cryogenic temperature. A gas source comprises an acid forming gas source and a bombardment gas source. A controller is controllably connected to the gas source and configured to flow anacid forming gas from the acid forming gas source, wherein the acid modifies at least one region of the stack to form at least one modified region of the stack and provide energy to volatize the at least one modified region of the stack.

[0006] These and other features of the present disclosure will be described in more detail below in the detailed description and in conjunction with the following figures.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The present disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:

[0008] FIG. 1 depicts a flow chart describing a method of etching recessed features into a stack below a carbon containing mask according to various embodiments.

[0009] FIGS. 2A-2D illustrate a schematic cross-sectional illustration of a stack processed according to some embodiments.

[0010] FIG. 3 shows a semiconductor processing system that may be used in some embodiments.

[0011] FIG. 4 illustrates a computer system for implementing a controller used in some embodiments.

[0012] In the drawings, like reference numerals are sometimes used to designate like structural elements. It should also be appreciated that the depictions in the figures are diagrammatic and not to scale.DETAILED DESCRIPTION

[0013] The present disclosure will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be apparent, however, to one skilled in the art, that the present disclosure may be practiced without some or all of these specific details. In other instances, well known process steps and / or structures have not been described in detail in order to not unnecessarily obscure the present disclosure.

[0014] Fabrication of certain semiconductor devices involves etching features into a stack of materials. In various embodiments herein, the stack of materials includes one or more layers of one or more materials below a mask. In some embodiments, at least one layer of the stackcontains at least one of silicon, germanium, and metal. Silicon containing layers may contain silicon nitride, silicon oxide, silicon carbide, silicon oxy-nitride, silicon oxy-carbide, polysilicon, or silicon germanium. In one example, the stack includes alternating layers of silicon oxide and polysilicon (OPOP). In some embodiments, the stack comprises an alternating silicon oxide film with silicon nitride films (ONON), or single silicon oxide layer, or single silicon nitride layer, or single silicon layer. In some embodiments, the stack may be a conductive or dielectric layer that may be a metal or silicon containing layer.

[0015] The features etched into a stack may be cylinders, trenches, or other recessed features. The aspect ratio of such a feature is defined as the lateral critical dimension divided by the depth. As the aspect ratio of such features continues to increase, several issues arise including (1) insufficient mask selectivity, (2) etch resolution, (3) twisting of the features, (4) noncircularity of the features, (5) aspect-ratio dependent etch rate, (6) bowing etch profile, and (7) low etch rate.

[0016] Insufficient mask selectivity is problematic when the etch process removes an excessive amount of the mask, so that no mask remains at the end of the process, or when the amount of mask remaining is insufficient to properly transfer the pattern from the mask to the stack. One common result of insufficient mask selectivity is the degradation of the feature profile near the top of the recessed features. In order to compensate for insufficient mask selectivity, a thicker mask may be formed. However, a thicker mask results in lower mask resolution and an overall higher aspect ratio, which causes more issues during the etching of both mask and underlayer materials.

[0017] Twisting refers to random deviations between the intended bottom locations of the features and the actual final bottom locations of the features (e.g., with the final location of a feature corresponding to the position of the bottom of the feature after the feature is etched). For instance, in some cases, it is intended that cylindrical features are etched in a regular array. When some or all features randomly deviate at the bottom away from this array, they are understood to have twisted.

[0018] Non-circularity of the features refers to deviations of the bottom hole shape away from a circular hole shape. This issue is relevant when etching circular features such as cylinders, where it is desired that the bottoms of the recessed features are circular. When the bottom hole shape deviates away from a circular shape, it often forms a shape closer to an ellipse, triangle, orirregular polygon. In many cases, these non-circular shapes are not desirable.

[0019] Aspect-ratio dependent etch rate refers to an issue where the etch rate slows down as the aspect ratio of the features increases. In other words, as the features are etched further into the stack, the etching process slows down. This issue is problematic because it can lead to low throughput and associated high processing costs.

[0020] Bowing etch profile refers to the tendency for the features to etch laterally in the stack such that the final profile bows outwards excessively somewhere along the depth of the features. In other words, the actual maximum critical dimension of the features exceeds the desired maximum critical dimension of the features, which can compromise the integrity of the structures being formed or limit the electrical performance of the final devices.

[0021] Low etch rate refers to an etch rate that is slower than desired for a particular application. Low etch rate is problematic because it leads to long etch times, reduced throughput, and high processing costs.

[0022] Unfortunately, techniques that improve some of these issues, such as insufficient mask selectivity, often make other issues worse. As such, these issues are balanced against one another when designing an etching operation. For example, conventional commercially practiced dielectric etch processes often result in substantial bowing. Previously, such tradeoffs have been difficult to avoid.

[0023] The techniques described herein may be used to etch recessed features into a stack below a mask without some or all of the issues identified above. In other words, the disclosed techniques may be used to etch recessed features into a stack below a mask with a high stack to mask selectivity and with reduced mask twisting, reasonably circular features, an acceptable degree of aspect ratio dependent etch rate, acceptable bowing, and sufficient etch rate.

[0024] To facilitate understanding, FIG. 1 is a high level flow chart of a method that may be used in some embodiments. A silicon containing stack with a mask is provided (step 104). FIG. 2A is a schematic cross-sectional view of a stack 204 that may be processed according to some embodiments, where the stack is under a mask 212, such as a carbon containing mask, such as photoresist or amorphous carbon. In some embodiments, the stack 204 may be formed over a substrate 208. In some embodiments, the stack 204 may comprise a silicon containing layer, such as silicon oxide, silicon nitride, or silicon. In some embodiments, the stack 204 may be a metal containing layer such as a pure or alloy conductive metal layer or a metal nitride or metaloxide. In some embodiments, the stack 204 may comprise a germanium containing layer. In some embodiments, the stack is a single bulk layer. In some embodiments, the stack is a plurality of layers. In some embodiments, the stack is a plurality of bilayers, trilayers, or more multiple layers. In some embodiments, one or more layers may be between the mask 212 and the stack. In some embodiments, one or more layers may be between the substrate 208 and the stack 204. In Example 1 , the stack comprises silicon nitride (SiN).

[0025] An etch process is provided for etching the stack 204. A substrate support that supports the stack is cooled to a cryogenic temperature (step 108). In some embodiments, the substrate support is cooled to a cryogenic temperature below 0° C. In some embodiments, the substrate support is cooled to a temperature below -20° C. In some embodiments, the substrate support is cooled to a temperature below -40° C. In some embodiments, the substrate support is cooled to a temperature below -60° C. In some embodiments, the substrate support is cooled to a temperature below -120° C.

[0026] An acid forming gas is provided (step 112). In some embodiments, the acid forming gas may comprise at least one of a phosphoric acid forming gas, a sulfuric acid forming gas, a nitric acid forming gas, a hydrochloric acid forming gas, and a hydrofluoric acid forming gas. In some embodiments, the acid forming gas forms an acid by an exothermic reaction with water. In some embodiments, the acid forming gas is in the gas phase at cryogenic temperatures. In some embodiments, the acid forming gas is provided in vapor form. In some embodiments, the water on the surface is formed by condensation of the background gas. In some embodiments, water vapor is injected via the gas delivery system.

[0027] In Example 1, where the stack comprises SiN, in some embodiments, the acid forming gas comprises a phosphoric acid forming gas. In some embodiments, the phosphoric acid forming gas comprises at least one of phosphoryl fluoride (POF3), phosphorous pentachloride (PCI5), and phosphoryl chloride (POCI3). POCI3 violently reacts with water in an exothermic reaction to produce phosphoric acid (H3PO4). H3PO4 significantly etches SiN. As a result, in some embodiments, the phosphoric acid forming gas comprises POCI3. Other phosphorous containing gases may be phosphorus trifluoride (PF3), phosphorus pentafluoride (PFs), and phosphorus trichloride (PCI3). PF3 and PCI3, when mixed with water, form phosphorous acid (H3PO3). H3PO3 might not etch SiN as well as H3PO4. PF5, when mixed with water, forms PF5OH , which might not etch SiN as well as H3PO4. In some embodiments, the phosphoric acidforming gases are gases comprising phosphorus and oxygen.

[0028] The acid forming gas mixes with water to form an acid on the stack 204, where the acid modifies regions of the stack 204 (step 116). In some embodiments, the acid forming gas is provided at a pressure in the range of 10 mTorr to 200 mTorr. Although the substrate support is cooled to a cryogenic temperature, in some embodiments, since the pressure is low, water on the stack is in the liquid phase. In some embodiments, the water is provided to the chamber through processes such as injection of water vapor. In some embodiments, the water is present without specifically adding the water. Such water may result from condensation of background gases as the temperature is lowered to cryogenic temperatures. Water may be formed in a separate step where the plasma is turned off and water vapor is provided. The acid reacts with the exposed parts of the stack 204 to form modified regions from part of the exposed stack 204.

[0029] FIG. 2B is a schematic cross-sectional view of the stack 204 after at least one region of the stack 204 has been modified to form modified regions 216. In some embodiments, for Example 1 , POCh reacts with water in an exothermic reaction to form H3PO4 according to the reaction POCh + 3 H2O — > H3PO4 + 3 HC1 (hydrochloric acid). H3PO4 reacts with SiN according to the reaction 3S N4 + 4H3PO4 + 27H2O -» 4 (NH4 PO4 + OfTSiOi. In some embodiments, in Example 1, the modified regions are liquid solutions of ammonium phosphate and silicic acid, which can be sputtered with high yield.

[0030] The stack 204 is exposed to ions from a bombardment gas in order to volatilize the modified regions (step 120). FIG. 2C is a schematic cross-sectional view of the stack 204 after modified regions 216, shown in FIG. 2B, of the stack 204 have been volatilized, causing the modified regions 216 to be etched away, forming partially etched features 220. In some embodiments, the ions are provided by a plasma formed from the bombardment gas. In some embodiments, the bombardment gas comprises at least one of fluorine, hydrogen gas (H2), nitrogen gas (N2), and a noble gas such as xenon (Xe), helium (He), and argon (Ar).

[0031] In some embodiments, the plasma is generated by a periodic waveform signal, such as a radio frequency (RF) power between about 5-200 kilowatts (kW), for example, between about 10-100 kW, or between about 10-65 kW. In some cases, a dual-frequency RF may be used to generate the plasma. Thus, the RF power may be provided at two or more frequency components, for example, a first frequency component at about 400 kilohertz (kHz) and a second frequency component at about 60 megahertz (MHz). Different powers may be providedat each frequency component. For instance, the first frequency component (e.g., about 400 kHz) may be provided at a power between about 10-65 kW, and the second frequency component (e.g., about 60 MHz) may be provided at a different power, for example, between about 0.5-8 kW. In some embodiments, the first frequency component (e.g., about 400 kHz) may be provided at a power higher than 65 kW. These power levels assume that the RF power is delivered to a single 300 millimeter (mm) wafer. The power levels can be scaled linearly based on substrate area for additional substrates and / or substrates of other sizes (thereby maintaining a uniform power density delivered to the substrate). In other cases, three-frequency RF power may be used to generate the plasma.

[0032] In some embodiments, the applied RF power is a continuous RF power. In some embodiments, the applied RF power may be pulsed. In some embodiments, the pulsed RF may have two or three states, providing multistate pulsed RF power. A three state pulsing pulses between three different (high, medium, low) power levels. In some embodiments, the high power level has a 1% to 20% duty cycle, the medium power level has a 10% to 90% duty cycle, and the low power level has a 20% to 90% duty cycle. In some embodiments, one of the three power levels is 0 Watts. In some embodiments, the high power level is 2 to 20 times the low power level, and the medium power level is between the high power level and the low power level. In some embodiments, the RF power is pulsed at repetition rates of 1-50,000 Hz. The RF power may be pulsed between two non-zero values (e.g., between higher power and lower power states) or between zero and a non-zero value (e.g., between off and on states). Where the RF power is pulsed between two non-zero values, the powers may be a higher power state and a lower power state. The lower power state may correspond to an RF power of about 4 kW or lower. A pulsing duty cycle may be in the range of 1-50%. The pulsing may be at a repetition rate in the range of 100 Hz to 20 kHz. The maximum ion energy at the substrate may be relatively high, for example, between about 1-30 kiloelectron volts (keV). The maximum ion energy is determined by the applied RF power in combination with the details of RF excitation frequencies, electrode sizes, electrode placement, chamber geometry, and plasma interactions. In some embodiments, the periodic waveform signal may be a square wave or other shape than an RF sinusoidal signal in the same frequency range as the RF signal. The periodic waveform signal may be pulsed or continuous.

[0033] In some embodiments, a bias in the range of 0 Watts (W) to 100 kilowatts (kW) isprovided to accelerate ions toward the top surfaces of the stack 204. In some embodiments, a bias in the range of 100 W to 100 kW is provided.

[0034] In some embodiments, the providing the acid forming gas (step 112), forming acid on the stack to modify regions (step 116), and the exposing steps to ions to volatilize modified regions (step 120) are performed sequentially and cyclically and repeated (step 124) a plurality of times until the etch is completed. FIG. 2D is a schematic cross-sectional view of the stack 204 after the etched features 220 are completely etched after a plurality of cycles. The sequential and cyclical process may be provided by pulsing at least one of the RF power, providing acid forming gas, and providing bombardment gas.

[0035] In some embodiments, two or all of the steps of the providing the acid forming gas (step 112), forming acid on the stack to modify regions (step 116), and the exposing steps to ions to volatilize modified regions (step 120) are performed simultaneously. An advantage of simultaneously performing the providing the acid forming gas (step 112), forming acid on the stack to modify regions (step 116), and the exposing steps to ions to volatilize modified regions (step 120) is that providing these steps simultaneously may increase throughput.

[0036] In some embodiments, the stack 204 is an ONON stack, and the acid forming gas is POF3. POF3 reacts with water to form H3PO4 according to the reaction POF3 + 3 H2O — > H3PO4 + 3 HF. In addition to H3PO4 modifying regions of SiN in the ONON stack, the hydrogen fluoride (HF) produced by the reaction may be used to etch the silicon oxide layers in the ONON stack and further etch SiN layers. In some embodiments, other sources of fluorine are added with the acid forming gas in order to etch silicon oxide layers and silicon nitride layers in the ONON stack. In some embodiments, gases that are used as other sources of fluorine comprise at least one of phosphorous trifluoride (PF3), phosphorous pentafluoride (PF5), HF, and tungsten hexafluoride (WFe).Example 2

[0037] In another example of embodiments, the stack comprises a carbon containing material, such as a polymer, and the mask may be a silicon containing material, such as SiCF or SiN. In some embodiments, the acid forming gas comprises a sulfuric acid forming gas. In some embodiments, the provided acid forming gas (step 112) comprises providing sulfuryl chloride (SO2CI2). In some embodiments, SO2CI2 is injected as a vapor. SO2CI2 reacts with water to formsulfuric acid in the reaction 2H2O + SO2CI2 — > 2 HC1 + H2SO4. The sulfuric acid modifies a carbon region (step 116) according to the reaction 2C + H2SO4 -» 2CO2 + H2S. The reaction products are gases. In some embodiments, a plasma is formed from a bombardment gas comprising oxygen, argon, and SO2CI2. Ions from the plasma volatilize the modified carbon regions.Example 3

[0038] In another example of embodiments, the stack comprises a silicon oxide (S i O2). In some embodiments, the acid forming gas comprises a hydrofluoric acid forming gas. In some embodiments, the provided acid forming gas (step 112) comprises providing hydrogen fluoride (HF). HF dissociates in water to form fluorine anions and hydronium cations HF + H2O -» HT)++ F". The hydrofluoric acid modifies SiCh regions (step 116) according to the reaction SiCH + 4HF -» SiF4 + 2H2O. In some embodiments, a plasma is formed from a bombardment gas comprising HF, Ar, PF3, and PF5. Ions from the plasma volatilize the modified SiC>2 regions.Example 4

[0039] In another example of embodiments, the stack comprises a metal containing material. In some embodiments, a metal stack may comprise a metal, metal oxide, or metal alloy layer, such as a copper or copper alloy layer, tungsten or tungsten alloy layer, titanium or titanium alloy layer, a cobalt or cobalt alloy layer, and a tantalum or tantalum alloy layer. In some embodiments, the acid forming gas comprises at least one of a nitric acid forming gas and a hydrochloric acid forming gas. In some embodiments, the provided acid forming gas (step 112) comprises providing at least one of nitrosyl fluoride (NOF), nitryl fluoride (NO2F), and chlorine nitride (CINO2). NOF reacts with water to form nitric acid in the reactions NOF + H2O — ► HNO2 + HF and 3 HNO2 — ► HNO3 + 2 NO + H2O. CINO2 reacts with water to form nitric acid in the reaction CINO2 + H2O — HNO3 + HC1. The nitric acid modifies metal regions (step 116) according to the reaction 3 Cu + 8 HNO3 — >• 3 CU(N0J)2 + 2 NO + 4 H2O. In some embodiments, a plasma is formed from a bombardment gas comprising at least one of H2, Ar, a halogen gas, nitric oxide (NO), NO2F, and CINO2. Ions from the plasma volatilize the modified metal regions.

[0040] In some embodiments, acid forming gases that have chlorine may be used instead of acid forming gases that have fluorine when etching SiN. It has been found that acid forming gasesthat have chlorine suppress the formation of ammonia fluorosilicate (AFS) salts, resulting in fewer AFS salts forming at the etch front, reducing etch interference by AFS salts, resulting in more control over the etch profile.

[0041] In some embodiments, the acid forming gas comprises one or more of HF, POCI3, PF3, POF3, and HC1 to etch ONON. In some embodiments, POF3 is used to replace POCI3 to increase the fluorine concentration to increase the etch rate. In some embodiments, the HF is used to etch silicon oxide, and the phosphorus containing component is used to etch silicon nitride. Using chlorine suppresses salt formation.

[0042] In some embodiments, ion bombardment is used to provide energy that volatilizes the modified layer. In some embodiments, at least one of ion bombardment, photon irradiation, electron bombardment, and thermal energy provides energy that volatilizes the modified regions of the stack.Applications

[0043] One application for the disclosed methods is in the context of forming a vertical NAND device. In this case, the material into which the feature is etched may be a repeating layered structure. For instance, the material may include alternating layers of silicon oxide and silicon nitride. In other embodiments, the stack may comprise alternating layers of silicon oxide and polysilicon. The alternating layers form pairs or repeating groups of materials. In various cases, the number of pairs or repeating groups may be between about 10-500 (e.g., between about 20-1000 individual layers). The features etched into the stack of layers may have a depth between about 2-15 pm, for example, between about 5-9 pm. The features may have a width between about 40-450 nm, for example, between about 50-100 nm or between about 40-85 nm. In some embodiments, the features have a width of less than 100 nm. In some embodiments, the features have a width of less than 85 nm.

[0044] As used herein, “high aspect ratio” as applied to features in a substrate refers to aspect ratios on the order of approximately 60: 1 or higher. More preferably, this range may include ratios greater than 100:1 , 120:1, 140:1, etc., or higher. However, the processes described herein may be beneficial for lower aspect ratios, such as 30:1 or 10:1.

[0045] The dimensional / parametric details provided herein, such as high aspect ratio, thickness, width, depth, etc., are for example and illustration only. Based on the disclosuredescribed herein, it should be understood that varying dimensions / parameters may also be applicable or used.APPARATUS

[0046] The various hardware and method embodiments described above may be used in conjunction with lithographic patterning tools or processes, for example, for the fabrication or manufacture of semiconductor devices, displays, LEDs, photovoltaic panels, and the like. Typically, though not necessarily, such tools / processes will be used or conducted together in a common fabrication facility.

[0047] Lithographic patterning of a film typically comprises some or all of the following steps, each step enabled with a number of possible tools: (1) application of photoresist on a workpiece, e.g., a substrate having a silicon containing film formed thereon, using a spin-on or spray-on tool; (2) curing of photoresist using a hot plate or furnace or other suitable curing tool; (3) exposing the photoresist to visible or ultraviolet (UV) or x-ray light with a tool such as a wafer stepper; (4) developing the resist so as to selectively remove the resist and thereby pattern it using a tool such as a wet bench or a spray developer; (5) transferring the resist pattern into an underlying film or workpiece by using a dry or plasma-assisted etching tool; and (6) removing the resist using a tool such as an RF or microwave plasma resist stripper. In some embodiments, an ashable hard mask layer (such as an amorphous carbon layer) and another suitable hard mask (such as an antireflective layer) may be deposited prior to applying the photoresist.

[0048] In this application, the terms “semiconductor wafer,” “wafer,” “substrate,” “wafer substrate,” and “partially fabricated integrated circuit” are used interchangeably. One of ordinary skill in the art would understand that the term “partially fabricated integrated circuit” can refer to a silicon wafer during any of the many stages of integrated circuit fabrication thereon. A wafer or substrate used in the semiconductor device industry typically has a diameter of 200 mm, 300 mm, or 450 mm. The above detailed description assumes the embodiments are implemented on a wafer. However, the embodiments are not so limited. The workpiece may be of various shapes, sizes, and materials. In addition to semiconductor wafers, other workpieces that may take advantage of the disclosed embodiments include various articles such as printed circuit boards, magnetic recording media, magnetic recording sensors, mirrors, optical elements, micromechanical devices, and the like.

[0049] Unless otherwise defined for a particular parameter, the terms “about” and“approximately” as used herein are intended to mean ±10% with respect to a relevant value.

[0050] FIG. 3 is a schematic view of a processing chamber 300 for processing substrates, in an embodiment. In one or more embodiments, the processing chamber 300 comprises a gas distribution plate 306 providing a gas inlet and an electrostatic chuck (ESC) 316, within a processing chamber 304, enclosed by a chamber wall 350. Within the processing chamber 304, the substrate 208 is positioned on top of the ESC 316 inside the processing chamber 304 so that the ESC 316 is also a substrate support. The ESC 316 may provide a bias from an ESC power source 348. A gas source 310 is connected to the processing chamber 304 through the gas distribution plate 306. In some embodiments, the gas source comprises an acid forming gas source 312, a bombardment gas source 318, and optionally another gas source 313. In some embodiments, the other gas source 313 may be a water source providing water vapor. An ESC temperature controller 351 is connected to the ESC 316 and provides temperature control of the ESC 316, allowing for the ESC 316 to be cooled to cryogenic temperatures. A power source 330 provides a periodic waveform signal power, such as RF power, to the ESC 316 and an upper electrode. In this embodiment, the upper electrode is the gas distribution plate 306. In a preferred embodiment, 400 kilohertz (kHz), 13.56 megahertz (MHz), 1 MHz, 2 MHz, 60 MHz, and / or optionally, 27 MHz power sources make up the power source 330 and the ESC power source 348 to provide a periodic waveform signal power at RF frequencies. A controller 335 is controllably connected to the power source 330, the ESC power source 348, an exhaust pump 320, and the gas source 310. A high flow liner 360 is a liner within the processing chamber 304, which confines gas from the gas source and has slots 362. The slots 362 maintain a controlled flow of gas to pass from the gas source 310 to the exhaust pump 320. Examples of such a processing chamber are the Flex® etch system and the Vantex® etch system manufactured by Lam Research Corporation of Fremont, CA. The process chamber can be a CCP (capacitively coupled plasma) reactor or an ICP (inductively coupled plasma) reactor.

[0051] FIG. 4 is a high level block diagram illustrating a computer system 400 for implementing the controller 335 used in embodiments of the present invention. The computer system may have many physical forms, ranging from an integrated circuit, a printed circuit board, and a small handheld device up to a huge supercomputer. The computer system 400 may include one or more processors 402 and further can include an electronic display device 404 (for displaying graphics, text, and other data), a main memory 406 (<?.g., random access memory(RAM)), storage device 408 (e.g., hard disk drive), removable storage device 410 (e.g., optical disk drive), user interface devices 412 (e.g. , keyboards, touch screens, keypads, mice or other pointing devices, etc.), and / or a communication interface 414 e.g., wireless network interface). The communication interface 414 may allow software and / or data to be transferred between the computer system 400 and external devices via a link. The system may also include a communications infrastructure 416 (e.g., a communications bus, cross-over bar, or network) to which the aforementioned devices / modules may be connected.

[0052] Information transferred via communications interface 414 may be in the form of signals such as electronic, electromagnetic, optical, or other signals capable of being received by communications interface 414, via a communication link that carries signals and may be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, a radio frequency link, and / or other communication channels. With such a communications interface, it is contemplated that the one or more processors 402 might receive information from a network or might output information to the network in the course of performing the above-described method steps. Furthermore, method embodiments may execute solely upon the processors or may execute over a network such as the Internet in conjunction with remote processors that share a portion of the processing.

[0053] The term “non-transient computer readable medium” is used generally to refer to media such as main memory, secondary memory, removable storage, and storage devices, such as hard disks, flash memory, disk drive memory, CD-ROM, and other forms of persistent memory and shall not be construed to cover transitory subject matter, such as carrier waves or signals. Examples of computer code include machine code, such as produced by a compiler, and files containing higher level code that are executed by a computer using an interpreter. Computer readable media may also be computer code transmitted by a computer data signal embodied in a carrier wave and representing a sequence of instructions that are executable by a processor.

[0054] In some embodiments, the controller 335 is configured for a) providing an acid forming gas, b) mixing the acid forming gas with water to form an acid on a surface of the stack, wherein the acid forms at least one modified region of the stack, and exposing the stack to ions, wherein the ions volatilize the at least one modified region of the stack.

[0055] It is to be understood that the configurations and / or approaches described herein areexemplary in nature and that these specific embodiments or examples are not to be considered in a limiting sense, because numerous variations are possible. The specific routines or methods described herein may represent one or more of any number of processing strategies. As such, various acts illustrated may be performed in the sequence illustrated, in other sequences, in parallel, or in some cases, omitted. Likewise, the order of the above described processes may be changed. Certain references have been incorporated by reference herein. It is understood that any disclaimers or disavowals made in such references do not necessarily apply to the embodiments described herein. Similarly, any features described as necessary in such references may be omitted in the embodiments herein. The subject matter of the present disclosure includes all novel and nonobvious combinations and sub-combinations of the various processes, systems, and configurations, and other features, functions, acts, and / or properties disclosed herein, as well as any and all equivalents thereof.CONCLUSION

[0056] While this disclosure has been described in terms of several preferred embodiments, there are alterations, modifications, permutations, and various substitute equivalents, which fall within the scope of this disclosure. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present disclosure. It is therefore intended that the following appended claims be interpreted as including all such alterations, modifications, permutations, and various substitute equivalents as fall within the true spirit and scope of the present disclosure. As used herein, the phrase “A, B, or C” should be construed to mean a logical (“A OR B OR C”), using a non-exclusive logical “OR,” and should not be construed to mean ‘only one of A or B or C. Each step within a process may be an optional step and is not required. Different embodiments may have one or more steps removed or may provide steps in a different order. In addition, various embodiments may provide different steps simultaneously instead of sequentially.

Claims

CLAIMSWhat is claimed is:

1. A method of etching recessed features in a stack, comprising: a) providing an acid forming gas; b) mixing the acid forming gas with water to form an acid on a surface of the stack, wherein the acid forms at least one modified region of the stack; and c) exposing the stack to energy that volatilizes the at least one modified region of the stack.

2. The method, as recited in claim 1 , further comprising cooling the stack to a cryogenic temperature.

3. The method, as recited in claim 1, wherein the stack is a silicon nitride containing stack and wherein the acid forming gas comprises phosphorus and forms phosphoric acid.

4. The method, as recited in claim 3, wherein the phosphorus containing gas comprises at least one of POF3 and POCI3.

5. The method, as recited in claim 4, wherein the acid forming gas further forms hydrofluoric acid and wherein the stack further comprises silicon oxide.

6. The method of claim 1, wherein the exposing the stack to ions, comprises: providing a bombardment gas; and transforming the bombardment gas into a plasma.

7. The method of claim 1, wherein the steps a-c are performed simultaneously.

8. The method of claim 1, wherein the steps a-c are performed sequentially for a plurality of cycles.

9. The method, as recited in claim 1 , wherein the stack is a carbon containing stack and wherein the acid forming gas comprises sulfur and forms sulfuric acid.

10. The method, as recited in claim 9, wherein the sulfur containing gas comprises SO2CI2.

11. The method, as recited in claim 1 , wherein the stack is a metal containing stack and wherein the acid forming gas comprises at least one of a nitric acid forming gas and a hydrochloric acid forming gas.

12. The method, as recited in claim 11, wherein the at least one of a nitric acid forming gas and a hydrochloric acid forming gas comprises at least one of NO2CI, NO2F, and NOF.

13. The method, as recited in claim 1, wherein the stack is a silicon oxide containing stack and wherein the acid forming gas forms hydrofluoric acid.

14. The method, as recited in claim 1, further comprising providing water, wherein the water causes the acid forming gas to form an acid.

15. The method, as recited in claim 1, wherein the acid forming gas comprises one or more of HF, POCh, PF3, POF3, and HC1.

16. The method as recited in claim 15, wherein the stack comprises at least one layer of silicon oxide and at least one layer of silicon nitride.

17. The method as recited in claim 1, wherein the energy that volatilizes the at least one modified region of the stack is provided by at least one of ion bombardment, photon irradiation, electron bombardment, and thermal energy.

18. An apparatus for etching recessed features in a stack, comprising: a process chamber; a substrate support for supporting a substrate inside the processing chamber; a power source for providing power to form a plasma; a temperature controller for cooling the substrate support to a cryogenic temperature; a gas source comprising: an acid forming gas source; and a bombardment gas source; and a controller, controllably connected to the gas source, configured to: a. flow an acid forming gas from the acid forming gas source, wherein the acid modifies at least one region of the stack to form at least one modified region of the stack; and b. provide energy to volatilize the at least one modified region of the stack.

19. The apparatus of claim 18, further comprising a water source for providing water to the process chamber.

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