Selective etch for nanowires

Abstract

A method of selectively etching silicon germanium with respect to silicon in a stack located on a chuck in an etch chamber is provided. The chuck is maintained at a temperature of 15 DEG C or less. The stack is exposed to an etch gas comprising a fluorine-containing gas to selectively etch the silicon germanium with respect to silicon.

Description

This application is a divisional application of the invention patent application with application number 201980048517.9, application date July 12, 2019, and invention title "Selective Etching for Nanowires". Cross-references to related applications

[0001] This application claims priority to U.S. Patent Application No. 62 / 701,314, filed July 20, 2018, which is incorporated herein by reference for all purposes. Technical Field

[0002] This disclosure generally relates to methods for forming semiconductor devices on semiconductor wafers. More specifically, this disclosure relates to the selective etching of nanowires. Background Technology

[0003] In forming semiconductor devices, nanowires can be formed by selectively etching silicon germanium (SiGe) relative to silicon (Si). Alternatively, nanowires can be formed by selectively etching Si relative to SiGe. Summary of the Invention

[0004] To achieve the foregoing and in accordance with the purposes of this disclosure, a method is provided for selectively etching silicon-germanium relative to silicon in a stack located on a chuck in an etching chamber. The chuck is maintained at a temperature below 15°C. The stack is exposed to an etching gas containing a fluorine-containing gas to selectively etch silicon-germanium relative to silicon.

[0005] In another embodiment, a method is provided for selectively etching silicon relative to silicon-germanium in a stack located on a chuck in an etching chamber. The chuck is maintained at a temperature below 15°C. The stack is exposed to an etching gas containing hydrogen (H2) and a fluorine-containing gas to selectively etch silicon relative to silicon-germanium.

[0006] These and other features of the present invention will be described in more detail below in conjunction with the following drawings and specific embodiments of the invention. Attached Figure Description

[0007] The present disclosure is illustrated in the accompanying drawings by way of example and not limitation, and similar reference numerals in the drawings denote similar elements, wherein:

[0008] Figure 1 It is a high-level flowchart of an implementation plan.

[0009] Figure 2 This is a top view of a processing tool that can be used in one implementation scheme.

[0010] Figure 3This is a schematic diagram of an etching chamber that can be used in one implementation scheme.

[0011] Figure 4 It is a schematic diagram of a computer system that can be used to implement one implementation scheme.

[0012] Figure 5A -D is a cross-sectional schematic diagram of the stacked components processed according to one implementation scheme.

[0013] Figure 6 This is a more detailed flowchart of the atomic layer deposition process.

[0014] Figure 7A -D is a schematic cross-sectional view of the stacked components processed according to another embodiment.

[0015] Figure 8A -C is a schematic cross-sectional view of the stacked components processed according to another embodiment. Detailed Implementation

[0016] The present disclosure will now be described in detail with reference to several exemplary embodiments illustrated in the accompanying drawings. Numerous specific details are set forth in the following description to provide a thorough understanding of the present disclosure. However, it will be apparent to those 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 to avoid unnecessarily obscuring the present disclosure.

[0017] In one embodiment, to form nanowires, a stack of alternating Si and SiGe layers is provided. The Si and SiGe layers may extend between and connect to electrical contacts or other structures. If the SiGe layer is selectively etched away, the Si layer remains extending between the electrical contacts. The Si layer can be used as a nanowire. Similarly, if the Si layer is selectively etched away, the SiGe layer remains extending between the electrical contacts. The SiGe layer can be used as a nanowire. The dimensions of the Si and SiGe layers are so small that the etching must be highly selective. Additional processing should be provided to minimize the removal of unetched layers.

[0018] Figure 2This is a top view of a processing tool 200 for one embodiment. A cassette 202 holds unprocessed wafers before they are processed, and then stores the processed wafers once all processing is complete in the processing tool 200. The cassette 202 can hold a number of wafers, typically up to 25. An atmospheric transport module (ATM) 214 is used to move wafers to and from the cassette 202. A load lock station 205 represents at least one means for backward and forward transfer of wafers between the atmosphere of the ATM 214 and the vacuum of the vacuum transport module (VTM) 212. The VTM 212 is part of the processing tool and is connected to multiple chambers. Different types of chambers may be present. In this embodiment, there are two break-through chambers 216, one etching chamber 220, and two atomic layer deposition (ALD) chambers 224. A robotic arm system within the vacuum transport module 212 uses a robotic arm to move stacked wafers between the load lock station 205 and the different chambers 216, 220, and 224. ATM 214 uses a robotic arm system to transfer wafers between cassette 202 and load lock station 205, which is in a vacuum environment.

[0019] Figure 3 This is a more detailed schematic diagram of an etching chamber 220 that can be used in one embodiment. In one or more embodiments, the etching chamber 220 includes a nozzle 306 and a chuck 308 located within a reactor chamber 310 and surrounded by a chamber wall 312, the nozzle providing a gas inlet. Within the reactor chamber 310, a stack 314 is mounted on the chuck 308. A gas source 316 is connected to a remote plasma generator 320. The remote plasma generator 320 is connected to the reactor chamber 310 via the nozzle 306. A radio frequency (RF) source 330 provides 13.56 MHz of RF power to the remote plasma generator 320. In this embodiment, the RF source 330 provides power to a coil. This power generates inductively coupled plasma in the remote plasma generator 320. A chuck temperature controller 340 controls a cooler 344. The cooler 344 cools a coolant 348. Coolant is supplied to a chuck cooling system 350. The controller 335 is controllably connected to the RF source 330, the discharge pump 352, the chuck temperature controller 340, and the gas source 316.

[0020] Figure 4This is a high-level block diagram illustrating a computer system 400 suitable for implementing the controller 335 used in the embodiment. The computer system 400 can have many physical forms, ranging from integrated circuits, printed circuit boards, and small handheld devices to large supercomputers. The computer system 400 includes one or more processors 402 and may also include an electronic display device 404 (for displaying graphics, text, and other data), main memory 406 (e.g., random access memory (RAM)), storage device 408 (e.g., hard disk drive), removable storage device 410 (e.g., optical disc drive), user interface device 412 (e.g., keyboard, touchscreen, keypad, mouse, or other pointing device), and communication interface 414 (e.g., wireless network interface). The communication interface 414 allows the transfer of software and data between the computer system 400 and external devices via a link. The system may also include a communication infrastructure 416 (e.g., communication bus, crossbar, or network) connected to the aforementioned devices / modules.

[0021] Information transmitted via communication interface 414 may be in the form of signals, such as electronic signals, electromagnetic signals, optical signals, or other signals that can be received by communication interface 414 via a communication link. The communication link carries the signal and may be implemented using wires or cables, optical fibers, telephone lines, cellular telephone links, radio frequency links, and / or other communication channels. Using such a communication interface 414, it is anticipated that one or more processors 402 may receive information from the network or output information to the network during the execution of the above-described method steps. Furthermore, the method implementation may be executed solely on a processor, or it may be executed in conjunction with a remote processor sharing a portion of the processing via a network such as the Internet.

[0022] The term "non-transient computer-readable medium" is generally used to refer to media such as main memory, secondary memory, removable storage devices, and storage devices such as hard disks, flash memory, disk drive storage, CD-ROMs, and other forms of persistent storage, and should not be construed as encompassing transient objects such as carrier waves or signals. Examples of computer code include machine code (such as that generated by a compiler) and documents containing higher-level code that is executed by a computer using an interpreter. Computer-readable media can also be computer code transmitted by computer data signals, processors.

[0023] Figure 1 This is a high-level flowchart of one implementation. In an exemplary implementation, the stack is placed in the breakthrough chamber 216 (step 104). The breakthrough chamber 216 is a chamber that provides a channel for the material to be etched to break through or remove layers. Figure 5AThis is a schematic cross-sectional view of a portion of the stack 314 on the wafer. In this embodiment, the stack 314 includes a first Si layer 508 adjacent to a SiGe layer 512. The SiGe layer 512 is adjacent to a second Si layer 516. The first Si layer 508 and the second Si layer 516 are located on opposite sides of the SiGe layer 512. The first Si layer 508, the SiGe layer 512, and the second Si layer 516 extend between and connect to the two structures (not shown). Since the stack 314 is exposed to air, a cladding layer in the form of a native oxide layer 520 is formed on the sides of the first Si layer 508, the SiGe layer 512, and the second Si layer 516. Alternatively, the stack 314 may be clad with another type of cladding layer (e.g., ALD silicon oxide (SiO2), silicon carbide (SiC), or silicon nitride (SiN)). This cladding layer may be deposited to prevent the formation of a cladding layer by natural oxidation.

[0024] After the stack 314 has been placed in the breakthrough chamber 216, a breakthrough process is provided to remove the cladding layer, namely the natural oxide layer 520 (step 108). In this example, the breakthrough process is a wet etching process. The breakthrough process is provided by exposing the stack 314 to an aqueous solution of diluted hydrofluoric acid (49%) with a volume dilution ratio of 300:1 to 10:1 for 10-300 seconds at room temperature (RT). Figure 5B This is a cross-sectional view of the stack 314 after the natural oxide layer 520 has been removed.

[0025] VTM 212 transports the stack 314 from the breakthrough chamber 216 to the etching chamber 220 in a vacuum environment (step 112). If the stack 314 is not maintained in a vacuum environment, a new natural oxide layer will grow on the stack 314. The stack 314 is then placed on a chuck 308 located in the etching chamber 220.

[0026] Cooling the chuck (step 116). In this example, the chuck is cooled to -15°C or lower. In this example, cooler 344 cools coolant 348 to approximately -60°C. Generating a remote plasma from the etching gas (step 120). In this example, the etching gas is 45 sccm of carbon tetrafluoride (CF4), 1000 sccm of argon (Ar), and 1000 sccm of helium (He). In this example, the etching gas is hydrogen-free or substantially hydrogen-free. The etching gas flows from gas source 316 to remote plasma generator 320. RF source 330 provides 200 watts of RF power at 13.56 MHz to remote plasma generator 320. In remote plasma generator 320, the etching gas is converted into plasma ions and high-energy neutral particles.

[0027] High-energy neutral particles flow from a remote plasma generator 320 through nozzle 306 into reactor chamber 310. These high-energy neutral particles can be high-energy neutral atoms or molecules of the etching gas. They may also contain high-energy free radical molecules or atoms. In this example, plasma ions do not flow into reactor chamber 310. The reactor chamber pressure is maintained at at least 300 mTorr. The high-energy neutral particles are used to selectively etch SiGe relative to Si to selectively etch stack 314 (step 128). In this example, the step of selectively etching SiGe relative to Si has an etching ratio of SiGe to Si greater than 20:1. Figure 5C This is a cross-sectional view of the stack 314 after the SiGe layer 512 has been selectively etched (step 128). In this example, the SiGe layer 512 has been completely etched away, leaving the first Si layer 508 and the second Si layer 516. The first Si layer 508 and the second Si layer 516 may extend between the two structures.

[0028] VTM 212 transports the stack 314 from the etching chamber 220 to the ALD chamber 224 in a vacuum environment (step 132). If the stack 314 is not maintained in a vacuum environment, a new natural oxide layer will grow on the stack 314. This new natural oxide layer will consume some of the first Si layer 508 and the second Si layer 516.

[0029] The ALD layer is deposited on the stack 314 (step 136). Figure 6 This is a more detailed flowchart of the atomic layer deposition process (step 136). The atomic layer deposition process (step 136) includes at least one cycle of providing a precursor (step 604) and converting the precursor (step 608). The precursor is provided to the stack 314 (step 604). In this embodiment, the liquid silicon-containing precursor is vaporized and delivered as vapor into the ALD chamber 224 to saturate the stack 314. Thus, a precursor layer is formed on the stack 314. In this example, the precursor has the composition of the general formula C(x)H(y)N(z)O(a)Si(b). In some embodiments, the precursor has one of the following compositions: N,N,N',N',N”,N”-hexamethylsilanetriamine (C6H 19 N3Si,C8H 22 N2Si), (3-aminopropyl)triethoxysilane (C9H) 23 NO3Si), and tetra(isopropoxy)silane (C 12 H 28O4Si). In this example, the precursor is provided plasmaless. The precursor has silicon functional groups. Since the precursor is not attached to another precursor, the precursor forms a monolayer on stack 314.

[0030] Once the precursor is fed into the stack 314, the delivery of the precursor vapor is stopped. A purging step is then performed to remove excess precursor remaining in the ALD chamber 224. The precursor is then converted (step 608). In one embodiment, this is accomplished by subjecting the stack 314 to a flash process. The flash process involves delivering a flash vapor of oxygen (O2) at 1000 sccm to 2000 sccm into the ALD chamber 224. In this example, a power of 100 to 3000 watts at 13.56 MHz is delivered to convert the flash vapor into plasma. A pressure of 20 mTorr to 100 mTorr is provided. Because the power delivery time is relatively fast, for example, between about 0.5 seconds and about 4 seconds, this flash process is referred to as an "O2 flash" operation. The O2 flash operation uses a monolayer of silicon-containing precursor to form a silicon oxide monolayer on the stack 314. Once the O2 flash evaporation operation is complete, purge ALD chamber 224. This cycle can then be repeated. Figure 5D This is a cross-sectional view of the stack 314 after the ALD layer 528 has been deposited to surround or cover the entire periphery of the Si layers 508 and 516. The ALD layer 528 prevents the Si layers 508 and 516 from being consumed by native oxide formation. Without the ALD layer 528, approximately [amount missing] native oxide could be consumed. To date The Si layers are 508 and 516.

[0031] The resulting coated Si layers 508 and 516 can extend between the two structures. Therefore, the first Si layer 508 and the second Si layer 516 are used as horizontal nanowires for an n-type metal-oxide-semiconductor (NMOS) device. This embodiment provides an etch selectivity ratio greater than 20:1 to etch SiGe relative to Si. Furthermore, less than [amount missing] is lost due to oxidation or etching during this process. The Si in this embodiment selectively etches SiGe relative to silicon oxide (SiO2) and silicon nitride (SiN) with a selectivity ratio greater than 100:1. Because this embodiment selectively etches SiGe relative to SiO2 and SiN with a selectivity ratio greater than 100:1, it has separate breakthrough steps to etch either SiO2 or SiN. In one embodiment, the selective etching of SiGe can be performed in less than 60 seconds.

[0032] It has been unexpectedly discovered that maintaining a low temperature while selectively etching the SiGe layer 512 relative to the Si layers 508 and 516 increases selectivity. In one exemplary embodiment, the chuck 308 is cooled to a temperature less than 15°C. In another exemplary embodiment, the chuck 308 is cooled to a temperature below 0°C. In another exemplary embodiment, the chuck 308 is cooled to a temperature less than or equal to -15°C. In another exemplary embodiment, the chuck 308 is cooled to a temperature less than or equal to -40°C. In some embodiments, liquid nitrogen is used as a coolant, flowing through the chuck 308 to provide cooling. In other embodiments, liquid VertelSinera manufactured by DuPont Corporation of Wilmington, DE is used. TM It can be used as a coolant. This coolant can cool temperatures down to -60°C.

[0033] In various embodiments, the etching gas contains a fluorinated component. In various embodiments, the fluorinated component is a fluorocarbon (e.g., CF4, hexafluoro-2-butyne (C4F6), or octafluorocyclobutane (C4F8)) or a hydrofluorocarbon (e.g., fluoroform (CHF3) or difluoromethane (CH2F2)). In various embodiments, the etching gas has a total flow rate per etching gas molecule. The fluorinated component contains fluorine. The fluorinated component has a fluorine flow rate per fluorine atom. The ratio of the total etching gas flow rate per etching gas molecule to the fluorine flow rate per fluorine atom is from 1000:1 to 3:1. For example, in the above embodiments, the etching gas is 45 sccm of CF4, 1000 sccm of Ar, and 1000 sccm of He. In this example, since there are 4 fluorine atoms in CF4, the fluorine atom flow rate is 180 sccm. The total flow rate of all molecules of the etching gas is 2045 sccm. Therefore, the ratio of the total etching gas flow rate to the fluorine atom flow rate is 2045:180. 2045:180 is approximately 11:1. To reduce the percentage of fluorine atoms relative to the total etching gas flow rate, one or more inert gases (e.g., rare gases) are added to the etching gas. For more controllable processing, rare gases can be used as diluents.

[0034] During etching, high-energy neutral molecules of the etching gas are used to selectively etch the SiGe layer 512 relative to the Si layers 508 and 516. This etching is achieved by generating high-energy neutral molecules via a remote plasma, rather than exposing the stack 314 to plasma. In the plasma, the stack 314 would be bombarded by more ions than by the high-energy neutral molecules. Reducing the number of ions bombarding the stack 314 helps reduce the etching of the Si layers 508 and 516. To further reduce the etching of the Si layers 508 and 516, a low RF power is used to generate the remote plasma. In various embodiments, the RF power provided to generate the remote plasma is less than 300 watts. Furthermore, in various embodiments, a bias voltage of less than 50 volts is provided. In one exemplary embodiment, no bias voltage is provided. Without a bias voltage, ions are not accelerated toward the stack 314. In one exemplary embodiment, no RF power is provided to the reactor chamber 310 where the stack 314 is disposed, but only RF power is provided to the remote plasma generator 320. A remote plasma generator 320 is disposed outside the reactor chamber 310. The remote plasma generator 320 is separated from the reactor chamber 310 by a nozzle 306. A large gap of at least 50 mm exists between the nozzle 306 and the top of the stack 314 to further reduce the number of ions reaching the stack 314. In some embodiments, because the plasma is formed outside the reactor chamber 310, the processing in the reactor chamber 310 is plasma-free.

[0035] The pressure in reactor chamber 310 is maintained at a level not less than 300 mTorr. In one exemplary embodiment, the pressure is at least 500 mTorr. Higher pressures promote selective etching of the SiGe layer 512 relative to the Si layers 508 and 516. Pressures less than 100 mTorr would be used for ion-based etching processes. Conversely, since various embodiments use high-energy neutral particles for etching, the pressure is maintained at a level not less than 300 mTorr. Higher pressures promote etching using high-energy neutral particles instead of ions. Furthermore, higher pressures help reduce the presence of ions and reduce unwanted material. It is believed that various embodiments can provide an etching selectivity ratio of at least 50:1 for SiGe to Si.

[0036] The natural oxide breakthrough step (step 108) removes the natural oxide layer to allow for subsequent etching of the SiGe layer 512. The transfer of the stack 314 from the breakthrough chamber 216 to the etching chamber 220 under vacuum (step 112) prevents the natural oxide layer from regenerating during the transfer. The transfer of the stack 314 from the etching chamber 220 to the ALD chamber 224 under vacuum (step 132) prevents the formation of natural oxide on the Si layers 508 and 516. This formation of the natural oxide layer will consume some of the Si layers 508 and 516. The consumption of some of the Si layers 508 and 516 due to the formation of the natural oxide will result in the removal of some of the Si layers 508 and 516. The deposition of the ALD layer 528 (step 136) forms a layer on the Si layers 508 and 516 without consuming the silicon of the Si layers 508 and 516.

[0037] In another embodiment, the Si layer is selectively etched relative to the SiGe layer. Figure 7A This is a cross-sectional schematic diagram of the stack 314. In this embodiment, the stack 314 includes a first SiGe layer 708 adjacent to the Si layer 712. The Si layer 712 is adjacent to a second SiGe layer 716. The first SiGe layer 708 and the second SiGe layer 716 are located on opposite sides of the Si layer 712. Because the stack 314 is exposed to air, a native oxide layer 720 is formed on the sides of the first SiGe layer 708, the Si layer 712, and the second SiGe layer 716.

[0038] The stack 314 is placed in the breakthrough chamber 216. A breakthrough treatment is provided to remove the natural oxide layer 720 (step 108). In this example, the breakthrough treatment is provided by exposing the stack 314 to an aqueous solution of diluted hydrofluoric acid (49%) with a volume dilution ratio of 300:1 to 10:1 for 10 to 300 seconds at room temperature (RT). Figure 7B This is a cross-sectional view of the stack 314 after the natural oxide layer 720 has been removed.

[0039] VTM 212 transports the stack 314 from the breakthrough chamber 216 to the etching chamber 220 in a vacuum environment (step 112). The stack 314 is then placed on a chuck 308 located in the etching chamber 220.

[0040] The chuck 308 is cooled (step 116). In this example, the chuck 308 is cooled to a temperature not exceeding -15°C. In this example, cooler 344 cools coolant 348 to approximately -60°C. Remote plasma is generated from the etching gas (step 120). In this example, the etching gas is 10 sccm of CF4, 100 sccm of H2, 1000 sccm of Ar, and 1000 sccm of He. A small flow rate of sulfur hexafluoride (SF6) or hydrogen sulfide (H2S) (0-100 sccm) may be added to improve selectivity. The etching gas flows from gas source 316 to remote plasma generator 320. RF source 330 provides 200 watts of RF power at 13.56 MHz to remote plasma generator 320. In remote plasma generator 320, the etching gas is converted into plasma.

[0041] High-energy neutral particles of the etching gas flow from a remote plasma generator 320 through nozzle 306 into reactor chamber 310. These high-energy neutral particles can be high-energy neutral atoms or molecules of the etching gas. In this example, plasma ions do not flow into reactor chamber 310. The reactor chamber pressure is maintained at not less than 300 mTorr. The high-energy neutral particles selectively etch Si relative to SiGe to selectively etch stack 314 (step 128). In this example, the step of selectively etching Si relative to SiGe has an etching ratio having a Si to SiGe ratio greater than 20:1. Figure 7C This is a cross-sectional view of the stack 314 after the Si layer 712 has been selectively etched (step 128). In this example, the Si layer 712 has been completely etched away, leaving the SiGe layers 708 and 716.

[0042] VTM 212 transports the stack 314 from the etching chamber 220 to the ALD chamber 224 in a vacuum environment (step 132). If the stack 314 is not kept in a vacuum environment, a new natural oxide layer will grow on the stack 314.

[0043] The ALD layer is deposited on the stack 314 (step 136). Figure 6This is a more detailed flowchart of the ALD layer deposition process (step 136). The atomic layer deposition process (step 136) includes at least one cycle of providing a precursor (step 604) and converting the precursor (step 608). The precursor is provided to the stack 314 (step 604). In this embodiment, the liquid silicon-containing precursor is vaporized and delivered as vapor into the ALD chamber 224 to saturate the stack 314. Thus, a precursor layer is formed on the stack 314. In this example, the precursor has a composition of the general formula C(x)H(y)N(z)O(a)Si(b). In some embodiments, the liquid precursor has one of the following compositions: C6H 19 N3Si, C8H 22 N2Si,C9H 23 NO3Si and C 12 H 28 O4Si. In this example, the precursor is provided without plasma. The precursor has silicon functional groups. Since the precursor is not attached to another precursor, the precursor forms a monolayer on stack 314.

[0044] Once the precursor is fed into the stack 314, the supply of precursor vapor is stopped. A purging step is then performed to remove excess precursor remaining in the ALD chamber 224. The precursor is then converted (step 608). In one embodiment, this conversion step is performed by subjecting the stack 314 to a flash vaporization process. The flash vaporization process involves supplying a flash vapor of oxygen (O2) at 1000 sccm to 2000 sccm to the ALD chamber 224. In this example, a power of 100 to 3000 watts at 13.56 MHz is supplied to cause the flash vapor to form a plasma. A pressure of 20 mTorr to 100 mTorr is provided for approximately 0.5 seconds to approximately 4 seconds. A silicon oxide monolayer is formed on the stack 314 using a monolayer of silicon-containing precursor. The ALD chamber 224 is then purged. This cycle can then be repeated. Figure 7D This is a cross-sectional view of the stack 314 after the ALD layer 728 has been deposited.

[0045] The resulting SiGe layers 708 and 716 can be used as horizontal nanowires for p-type metal-oxide-semiconductor (PMOS) devices. This embodiment provides an etch selectivity ratio greater than 20:1 to etch Si relative to SiGe. Furthermore, because oxidation or etching during this process results in a loss of less than [a certain value], the process is more efficient. The SiGe is used. This embodiment selectively etches Si relative to silicon oxide (SiO2) and silicon nitride (SiN) with a selectivity ratio greater than 100:1. This embodiment is able to provide this selective etching in less than 60 seconds.

[0046] During etching, high-energy neutral molecules are used to selectively etch the Si layer 712 relative to the SiGe layers 708 and 716. This etching is achieved by generating high-energy neutral molecules via a remote plasma, rather than exposing the stack 314 to plasma in which it would be bombarded with more ions than by high-energy neutral molecules. Reducing the number of ions bombarding the stack 314 helps reduce the etching of the SiGe layers 708 and 716. To further reduce the etching of the SiGe layers 708 and 716, a low RF power is used to generate the remote plasma. In various embodiments, the RF power provided to generate the remote plasma is less than 300 watts. Furthermore, in various embodiments, a bias voltage of less than 50 volts is provided. One exemplary embodiment does not provide a bias voltage. Therefore, ions are not accelerated toward the stack 314. One exemplary embodiment does not provide any RF power to the reactor chamber 310 where the stack 314 is disposed, but only to the remote plasma generator 320. A large gap of at least 50 mm exists between the nozzle 306 and the top of the stack 314. This gap further reduces the number of ions reaching the stack 314. In some embodiments, the processing in the reactor chamber 310 is plasma-free because the plasma is formed outside the reactor chamber 310.

[0047] The pressure in reactor chamber 310 is maintained at a level not less than 300 mTorr. In an exemplary embodiment, the pressure is at least 500 mTorr. Higher pressures promote selective etching of Si layer 712 relative to SiGe layers 708, 716. Pressures less than 100 mTorr can be used for ion-based etching processes. Conversely, since various embodiments use high-energy neutral particles for etching, the pressure is maintained at a level not less than 300 mTorr. Higher pressures promote etching using high-energy neutral particles instead of ions. Furthermore, higher pressures help reduce the presence of ions and reduce unwanted substances. It is believed that various embodiments can provide an etching selectivity ratio of at least 50:1 Si to SiGe. In the specification and claims, the phrase "high-energy neutral particles" includes reactive neutral molecules or atoms.

[0048] In other embodiments, the breakthrough process (step 108) can be performed using vapor etching or dry etching. In one example of a breakthrough process (step 108) using vapor, hydrogen fluoride (HF) vapor can be used to provide the breakthrough process (step 108). An example of a dry breakthrough process (step 108) can provide a plasma formed by CF4 and a bias voltage of 25 to 50 volts.

[0049] Instead of initially covering the stack 314 with a natural oxide layer 520, a cladding layer can be formed to prevent silicon consumption during the formation of the natural silicon oxide. The cladding layer can be SiO2 deposited by the ALD, or it can be SiN or SiC. Different breakthrough processes (step 108) can be used for different cladding layers. In other embodiments, instead of depositing SiO2 during the deposition of the ALD layer on the stack 314 (step 136), SiN or SiC can be deposited during the deposition of the ALD layer on the stack 314 (step 136). Layers containing SiO2, SiN, or SiC can be deposited in various embodiments.

[0050] In other embodiments, an inert gas may be used to provide inert conditions during the transfer of stack 314 to etching chamber 220 (step 112) or to ALD chamber 224 (step 124), without using inert conditions provided by a vacuum. This inert gas may be Ar, He, or N2. In other embodiments, etching chamber 220 is equipped with a precursor and a fast-response valve. In this etching chamber 220, the deposition of ALD layer 528 on stack 314 (step 136) may be performed. In this embodiment, stack 314 is not transferred to ALD chamber 224.

[0051] In another embodiment where Si is selectively etched relative to SiGe, an etching gas comprising SF6 and H2 can be used. Fluorine from SF6 can combine with hydrogen to form HF, and SF6 can be used to passivate Ge in the form of Ge-F. The formation of Ge-F facilitates further passivation of SiGe. In other embodiments, the etching gas may comprise a fluorocarbon compound, SF6, and H2S or a sulfur-containing gas along with H2. In some embodiments, CF4 and H2 are used, with the CF4 to H2 ratio between 1:1 and 1:1000. The above embodiments have an SF6 to etching gas ratio of less than 1. The above embodiments have an H2S to etching gas ratio of less than 1. In some embodiments, CF4 can be replaced by another hydrofluorocarbon compound.

[0052] In another embodiment where SiGe is selectively etched relative to Si, a wet breakthrough process is provided. Figure 8AThis is a schematic cross-sectional view of a portion of the stack 314 on the wafer. In this embodiment, the stack 314 includes a first Si layer 808 adjacent to a SiGe layer 812. The SiGe layer 812 is adjacent to a second Si layer 816. The first Si layer 808 and the second Si layer 816 are located on opposite sides of the SiGe layer 812. Because the stack 314 is exposed to air, a coating layer in the form of a native oxide layer 820 is formed on the sides of the first Si layer 808, the SiGe layer 812, and the second Si layer 816. This breakthrough process is provided in part by exposing the stack 314 to an aqueous solution of diluted hydrofluoric acid (49%) with a volume dilution ratio of 300:1 to 10:1 at room temperature (RT) for a sufficient time to remove a portion of, rather than all, of the native oxide layer 820. Figure 8B This is a cross-sectional view of the stack 314 after the natural oxide layer 820 has been partially removed.

[0053] The remaining portion of the natural oxide layer 820 is removed using a dry etching process employing a fluorocarbon breakthrough gas. In this example, the fluorocarbon breakthrough gas contains CF4. The breakthrough gas is then used to form a plasma. The plasma from the breakthrough gas removes the remaining natural oxide layer 820 and selectively deposits amorphous carbon relative to the SiGe layer 812 to coat the first Si layer 808 and the second Si layer 816. Figure 8C This is a cross-sectional view of the stack 314 after an amorphous carbon layer 824 has been selectively deposited on the first Si layer 808 and the second Si layer 816. In other embodiments, the etching and ALD processes used can be employed to selectively etch the SiGe layer 812 relative to the first Si layer 808 and the second Si layer 816. The amorphous carbon layer 824 prevents oxidation of the first Si layer 808 and the second Si layer 816 and reduces etching of the first Si layer 808 and the second Si layer 816. The natural oxide layer 820 is partially etched using wet etching to reduce the time required for dry etching. Reducing dry etching time reduces the time the substrate is exposed to ions, thereby reducing the etching of the first Si layer 808 and the second Si layer 816 by dry etching.

[0054] While the invention has been described with reference to several exemplary embodiments, changes, modifications, substitutions, and various alternative equivalents fall within the scope of the invention. It should also be noted that many alternatives exist to the methods and apparatus of this disclosure. Therefore, the appended claims are intended to be construed as including all such changes, modifications, substitutions, and various alternative equivalents that fall within the true spirit and scope of this disclosure.

Claims

1. A method for selectively etching silicon-germanium relative to silicon in a stack, the stack being located on a chuck in an etching chamber, the method comprising: Maintain the chuck at a temperature of 0°C or lower; and The stack is exposed to an etching gas containing fluorine and H2 to selectively etch silicon-germanium relative to silicon.

2. The method of claim 1, wherein the etching gas has a total flow rate in terms of etching gas molecules, and wherein the fluorine-containing gas contains fluorine, wherein the fluorine has a fluorine flow rate in terms of fluorine atoms, and wherein the ratio of the total flow rate in terms of etching gas molecules to the fluorine flow rate in terms of fluorine atoms is between 1000:1 and 3:

1.

3. The method according to claim 1, further comprising: In a remote plasma generator, the etching gas is used to form a plasma containing ions of the etching gas and high-energy neutral particles; and The high-energy neutral particles are allowed to flow from the remote plasma generator into the etching chamber.

4. The method of claim 3, wherein the etching gas is not maintained as plasma in the etching chamber to expose the stack to the high-energy neutral particles.

5. The method of claim 1, wherein the etching gas further comprises a rare gas.

6. The method according to claim 1, wherein the fluorine-containing gas comprises CF4.

7. The method of claim 1, further comprising maintaining an etching chamber pressure of at least 300 mTorr.

8. The method of claim 1, further comprising: Under inert conditions, the stacked components are transferred from the etching chamber to the atomic layer deposition chamber; and Atomic layer deposition is used to deposit a layer containing SiO2, SiN, or SiC on the stack.

9. The method of claim 1, further comprising: A breakthrough process is provided to remove the overlay from the stack.

10. The method of claim 9, wherein providing the breakthrough process comprises providing a wet etching of the coating layer.

11. The method of claim 10, wherein the breakthrough process further comprises performing dry etching after the wet etching.

12. The method of claim 11, wherein the dry etching is selectively depositing a carbon-containing layer on silicon relative to silicon-germanium.

13. The method of claim 12, wherein the dry etching comprises: Provides CF4-containing gas; and The CF4-containing gas is used to form a plasma, wherein the plasma provides breakthrough etching and selectively deposits the carbon-containing layer on silicon relative to silicon-germanium.

14. The method of claim 9, wherein providing the breakthrough process comprises providing vapor etching or dry etching of the coating layer.

15. The method of claim 1, further comprising, after exposing the stack to the etching gas in the etching chamber, depositing a layer containing SiO2, SiN, or SiC on the stack using atomic layer deposition.

16. The method of claim 1, wherein maintaining the chuck at a temperature of 0°C or lower means maintaining the chuck at a temperature of -15°C or lower.

17. A method for selectively etching silicon relative to silicon-germanium in a stack, the stack being located on a chuck in an etching chamber, the method comprising: Maintain the chuck at a temperature of 0°C or lower; and The stack is exposed to an etching gas containing H2 and fluorine to selectively etch silicon relative to silicon germanium.

18. The method of claim 17, further comprising: In a remote plasma generator, the etching gas is used to form a plasma containing ions of the etching gas and high-energy neutral particles; and The high-energy neutral particles are allowed to flow from the remote plasma generator into the etching chamber.

19. The method of claim 18, wherein the etching gas is not maintained as plasma in the etching chamber to expose the stack to the high-energy neutral particles.

20. The method of claim 17, further comprising maintaining an etching chamber pressure of at least 300 mTorr.

21. The method of claim 17, further comprising: depositing a layer containing SiO2, SiN, or SiC on the stack using atomic layer deposition.

22. The method of claim 17, wherein the etching gas further comprises at least one of H2S or SF6.

23. The method of claim 17, further comprising: A breakthrough process is provided to remove layers containing SiO2, SiN, or SiC from the stack.

24. The method of claim 23, wherein providing the breakthrough process comprises providing the layer containing SiO2, SiN, or SiC by wet etching, vapor etching, or dry etching.

25. The method of claim 17, wherein the fluorine-containing gas comprises CF4.

26. The method of claim 17, wherein maintaining the chuck at 0°C or lower means maintaining the chuck at -15°C or lower.

27. A method for selectively etching silicon-germanium relative to silicon in a stack, the stack being located on a chuck in an etching chamber, the method comprising: Maintain the chuck at a temperature of 0°C or lower; and The stack is exposed to an etching gas comprising fluorocarbon or hydrofluorocarbon gases to selectively etch silicon-germanium relative to silicon.

28. The method of claim 27, wherein the etching gas has a total flow rate in terms of etching gas molecules, and wherein the fluorocarbon or hydrofluorocarbon gas contains fluorine, wherein the fluorine has a fluorine flow rate in terms of fluorine atoms, and wherein the ratio of the total flow rate in terms of etching gas molecules to the fluorine flow rate in terms of fluorine atoms is between 1000:1 and 3:

1.

29. The method of claim 27, further comprising: In a remote plasma generator, the etching gas is used to form a plasma containing ions of the etching gas and high-energy neutral particles; and The high-energy neutral particles are allowed to flow from the remote plasma generator into the etching chamber.

30. The method of claim 29, wherein the etching gas is not maintained as plasma in the etching chamber to expose the stack to the high-energy neutral particles.

31. The method of claim 27, wherein the etching gas further comprises a rare gas.

32. The method of claim 27, wherein the fluorocarbon or hydrofluorocarbon gas comprises CF4.

33. The method of claim 27, further comprising maintaining an etching chamber pressure of at least 300 mTorr.

34. A method for selectively etching silicon relative to silicon-germanium in a stack, the stack being located on a chuck in an etching chamber, the method comprising: Maintain the chuck at a temperature of 0°C or lower; and The stack is exposed to an etching gas containing H2 and fluorocarbon or hydrofluorocarbon gases to selectively etch silicon relative to silicon germanium.

35. The method of claim 34, further comprising: In a remote plasma generator, the etching gas is used to form a plasma containing ions of the etching gas and high-energy neutral particles; and The high-energy neutral particles are allowed to flow from the remote plasma generator into the etching chamber.

36. The method of claim 35, wherein the etching gas is not maintained as plasma in the etching chamber to expose the stack to the high-energy neutral particles.

37. The method of claim 34, further comprising maintaining an etching chamber pressure of at least 300 mTorr.

38. The method of claim 34, further comprising: depositing a layer containing SiO2, SiN or SiC on the stack using atomic layer deposition.

39. The method of claim 34, wherein the etching gas further comprises at least one of H2S or SF6.

40. The method of claim 34, further comprising: A breakthrough process is provided to remove layers containing SiO2, SiN, or SiC from the stack.

41. The method of claim 40, wherein providing the breakthrough process comprises providing the layer containing SiO2, SiN, or SiC by wet etching, vapor etching, or dry etching.

42. The method of claim 34, wherein the fluorocarbon or hydrofluorocarbon gas comprises CF4.

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