Method for etching features in a stack of layers

Abstract

This invention relates to a method for etching features in a stacked layer. A method for etching features in a stacked layer beneath a carbon-containing mask is provided. The stacked layer is cooled to a temperature below -20°C. An etching gas is provided, comprising a component providing free fluorine, a hydrogen-containing component, a hydrocarbon-containing component, and a fluorocarbon-containing component. A plasma is generated from the etching gas. A bias voltage with an amplitude of at least about 400 volts is provided to accelerate ions from the plasma to the stacked layer. Features are selectively etched in the stacked layer relative to the carbon-containing mask.

Description

[0001] This application is a divisional application of patent application No. 201811256527.5, filed on October 26, 2018, by Rum Research Corporation, entitled "Method for Etching Features in Stacked Layers".

[0002] By incorporating via reference This disclosure is incorporated, by reference for all purposes, by U.S. Patent Application No. 15 / 475,021, entitled “GAS ADDITIVES FOR SIDEWALL PASSIVATION DURING HIGH ASPECT RATIO CRYOGENICETCH”, filed March 30, 2017, by Hudson et al. Technical Field

[0003] This disclosure relates to a method of forming a semiconductor device on a semiconductor wafer. More specifically, this disclosure relates to etching a stack in the formation of a memory. Background Technology

[0004] In the fabrication of semiconductor devices, etching layers can be used to form memory holes or lines. Some semiconductor devices can be formed by etching a double-layer stacked layer of silicon oxide and silicon nitride (ONON). This stacked layer can be used in memory applications, such as for forming dynamic random access memory (DRAM) and three-dimensional "negative AND" gates (3D NAND). Summary of the Invention

[0005] To achieve the foregoing and in accordance with the purposes of this disclosure, a method is provided for etching features in a stacked layer beneath a carbon-containing mask. The stacked layer is cooled to a temperature below -20°C. An etching gas is provided, comprising a component providing free fluorine, a hydrogen-containing component, a hydrocarbon-containing component, and a fluorocarbon-containing component. A plasma is generated from the etching gas. A bias voltage of at least about 400 volts is provided to accelerate ions from the plasma to the stacked layer. Features are selectively etched in the stacked layer relative to the carbon-containing mask.

[0006] Specifically, some aspects of the present invention can be described as follows: 1. A method for etching features in a stacked layer beneath a carbon-containing mask, comprising: Cool the stacked layers to a temperature below -20°C; Etching gases are provided that contain components providing free fluorine, hydrogen-containing components, hydrocarbon-containing components, and fluorocarbon-containing components; Plasma is generated from the etching gas; A bias voltage of at least approximately 400 volts is provided to accelerate ions from the plasma to the stacked layer; and Features are selectively etched in the stacked layers relative to the carbon-containing mask.

[0007] 2. The method according to Clause 1, wherein the carbon-containing mask is amorphous carbon.

[0008] 3. The method according to Clause 1, wherein the etching gas further comprises an iodine-containing component.

[0009] 4. The method according to Clause 1, wherein the etching gas is free of oxygen and free of C4F8 and C4F6.

[0010] 5. The method according to Clause 1, wherein the etching gas comprises NF3, H2, CF3I, CH3F and CH2F2.

[0011] 6. The method according to Clause 5, wherein the etching gas further comprises at least one of C4F8, C3F8, C4F6, SF6, O2, CF4, CH4 or CHF3.

[0012] 7. The method according to Clause 1, wherein the stacked layer is supported on a chuck in an etching chamber, the method further comprising cooling the chuck to a temperature below -40°C.

[0013] 8. The method according to Clause 1, wherein the carbon-containing mask is amorphous carbon, and the stacked layer comprises a plurality of silicon oxide and silicon nitride bilayers.

[0014] 9. The method according to Clause 8, wherein the plurality of silicon oxide and silicon nitride bilayers comprises at least 48 bilayers.

[0015] 10. The method according to Clause 8, wherein the stacked layer does not have a silicon mask.

[0016] 11. The method according to Clause 1, wherein the component providing free fluorine comprises NF3 and the hydrogen-containing component comprises H2.

[0017] 12. The method according to Clause 1, wherein the component providing free fluorine comprises NF3, the hydrogen-containing component comprises H2, and wherein the etching gas comprises a hydrofluorocarbon component, the hydrofluorocarbon component providing the hydrocarbon-containing component and the fluorocarbon-containing component.

[0018] 13. The method according to Clause 1, wherein the etching gas further comprises CF3I.

[0019] 14. The method according to Clause 1, wherein the etching gas further comprises CF3I, and wherein the etching gas comprises a hydrofluorocarbon component, the hydrofluorocarbon component providing the hydrocarbon component and the fluorocarbon component.

[0020] 15. The method according to Clause 1, wherein the component providing free fluorine provides free fluorine when excited to generate the plasma.

[0021] 16. The method according to Clause 1, wherein the feature has a depth-to-neck ratio of at least 30:1, wherein the neck refers to the minimum width of the feature.

[0022] 17. The method according to Clause 1, wherein the component providing free fluorine comprises at least one of NF3 or SF6.

[0023] These and other features of the present invention will be described in more detail below in conjunction with the accompanying drawings. Attached Figure Description

[0024] The present disclosure is illustrated in the accompanying drawings by way of example and not limitation, and the same reference numerals in the drawings denote similar elements, wherein: Figure 1 This is a high-level flowchart of one implementation method.

[0025] Figure 2A -B is a schematic cross-sectional view of the stacked layers processed according to one embodiment.

[0026] Figure 3 This is a schematic diagram of an etching chamber that can be used in one implementation.

[0027] Figure 4 It is a schematic diagram of a computer system that can be used to implement one implementation method. Detailed Implementation

[0028] The invention will now be described in detail with reference to several preferred embodiments illustrated in the accompanying drawings. Numerous specific details are set forth in the following description to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention 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 invention.

[0029] Figure 1This is a high-level flowchart of one embodiment. In this embodiment, a stacked layer is placed in an etching chamber (step 104). The stacked layer is positioned beneath a carbon-containing patterned mask. The stacked layer is cooled to a temperature below -20°C (step 108). An etching gas is provided by flowing an etching gas into the etching chamber, wherein the etching gas comprises a component providing free fluorine, a hydrogen-containing component, a hydrocarbon-containing component, and a fluorocarbon-containing component (step 112). The etching gas is used to form an etching plasma (step 116). The stacked layer is exposed to the plasma (step 120). A bias voltage with an amplitude of at least 400 volts is provided to accelerate ions from the plasma to the stacked layer (step 124). The stacked layer is selectively etched relative to the carbon-containing patterned mask using the etching plasma (step 128). The stacked layer is removed from the etching chamber (step 132).

[0030] Example In an exemplary embodiment, the stacked layers are placed in an etching chamber (step 104). Figure 2A This is a schematic cross-sectional view of a stacked layer 200, in which, in this example, the stacked layer 200 includes a substrate 208, a plurality of bilayers 212, and a carbon-containing patterned mask 216, with the substrate 208 below the plurality of bilayers 212 disposed below the carbon-containing patterned mask 216. In this example, one or more layers may be disposed between the substrate 208 and the plurality of bilayers 212 or between the plurality of bilayers 212 and the carbon-containing patterned mask 216. However, this embodiment does not have a silicon-containing mask above the plurality of bilayers 212 or above the carbon-containing patterned mask 216. In this example, the carbon-containing patterned mask 216 is amorphous carbon. In this example, the patterned mask pattern provides mask features 220 for high aspect ratio contacts. In some embodiments, the mask features are formed before the substrate is placed in the etching chamber. In other embodiments, the mask features 220 are formed while the substrate is in the etching chamber. In this embodiment, the plurality of bilayers 212 are bilayers containing a silicon oxide layer 224 and a silicon nitride layer 228.

[0031] Figure 3This is a schematic diagram of an etching reactor that can be used in one embodiment. In one or more embodiments, the etching reactor 300 includes a gas distribution plate 306 and an electrostatic chuck (ESC) 308 providing a gas inlet within an etching chamber 349, which is enclosed by a chamber wall 352. Within the etching chamber 349, a stack layer 200 is located above the ESC 308. The ESC 308 can provide bias from the ESC source 348. An etching gas source 310 is connected to the etching chamber 349 via the distribution plate 306. An ESC temperature controller 350 is connected to a cooler 314. In this embodiment, the cooler 314 provides coolant to channels 312 in or near the ESC 308. A radio frequency (RF) source 330 provides RF power to a lower electrode and / or an upper electrode, which in this embodiment are the ESC 308 and the gas distribution plate 306. In an exemplary embodiment, 400 kHz, 60 MHz, and optional 2 MHz, 27 MHz power supplies constitute the RF source 330 and the ESC source 348. In this embodiment, the upper electrode is grounded. In this embodiment, a generator is provided for each frequency. In other embodiments, the generator may be in a separate RF source, or a separate RF generator may be connected to different electrodes. For example, the upper electrode may have inner and outer electrodes connected to different RF sources. Other arrangements of RF sources and electrodes may be used in other embodiments. Controller 335 is controllably connected to RF source 330, ESC source 348, exhaust pump 320, and etching gas source 310. An example of such an etching chamber is the Exelan Flex manufactured by Lam Research Corporation (Fremont, CA). TM Etching system. The processing chamber can be a CCP (capacitively coupled plasma) reactor or an ICP (inductively coupled plasma) reactor.

[0032] Figure 4This is a high-level block diagram of a computer system 400 adapted to implement the control circuitry 335 used in the embodiments. The computer system can have a variety of physical forms, ranging from integrated circuits, printed circuit boards, and small handheld devices to supercomputers. The computer system 400 includes one or more processors 402, and further includes 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 positioning device), and communication interface 414 (e.g., wireless network interface). The communication interface 414 enables software and data to be transferred between the computer system 400 and external devices via a link. The system may also include a communication infrastructure 416 (e.g., a communication bus, cross-over bar, or network) to which the aforementioned devices / modules are connected.

[0033] Information transmitted via communication interface 414 may be in the form of signals that can be received by communication interface 414 via a communication link. These signals may be, for example, electronic, electromagnetic, optical, or other signals. The communication link carries the signals 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, it is anticipated that one or more processors 402 may receive information from the network or output information to the network during the implementation of the above method steps. Furthermore, the method implementation may be executed solely on the processor or may be combined with a remote processor on a network such as the Internet, with the remote processor sharing some processing capabilities.

[0034] The term "non-transitory computer-readable medium" generally refers to media such as main memory, secondary storage, removable storage devices, and storage devices (e.g., hard disks, flash memory, hard disk drive storage, CD-ROMs, and other forms of permanent storage), and should not be construed as encompassing transient objects such as carrier waves or signals. Examples of computer code include, for example, machine code 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 via computer data signals embodied in a carrier wave and represented as a sequence of instructions executable by a processor.

[0035] After placing the stacked layer 200 into the etching chamber 300, the stacked layer is cooled to a temperature below -20°C (step 108). An etching gas containing components providing free fluorine, hydrogen, hydrocarbons, and fluorocarbons is introduced into the etching chamber (step 112). In this example, the etching gas is NF3 at 2-150 sccm, H2 at 20-300 sccm, CF3I at 2-40 sccm, CH3F at 10-60 sccm, and CH2F2 at 0-100 sccm. In this example, a pressure of 5 to 60 millitors is provided. The etching gas is used to form an etching plasma (step 116). This can be achieved by providing an excitation RF at a frequency of 60 MHz and a power of 200 to 8000 watts. The stacked layer 200 is exposed to the plasma (step 120). A bias voltage with an amplitude of at least about 400 volts is provided (step 124). In this embodiment, a high bias voltage is provided by supplying an RF frequency of 400 kHz and 2 kW to 18 kW. The bias voltage accelerates ions to the stacked layer 200, resulting in the selective etching of high aspect ratio etch features into the stacked layer 200 relative to a carbon-patterned mask (step 128). The plasma is maintained for 180 to 3600 seconds. The etching process is capable of etching both the silicon oxide and silicon nitride layers. The substrate is then removed from the etching chamber (step 132).

[0036] Figure 2B This is a cross-sectional view of the stacked layer 200 after the contacts 232 have been etched. The contacts are high aspect ratio contacts. Preferably, the ratio of the height of the high aspect ratio contact to the width of CD is greater than 100:1. More preferably, the contacts have an etch depth to neck depth ratio greater than 30:1, where the neck refers to the minimum width of the contact.

[0037] The etching process can selectively etch silicon oxide and silicon nitride layers with a selectivity ratio greater than 5:1 relative to amorphous carbon, while simultaneously etching high aspect ratio features. The resulting features also reduce warpage, streaking, distortion, overlay, and taper. Furthermore, this implementation allows the use of carbon-containing patterned masks, such as amorphous carbon, without requiring silicon-containing masks, such as polysilicon, thereby reducing cost and defects.

[0038] Previous etching processes (where the stacked layers were processed at temperatures above -20°C) relied on fluorocarbon chemicals to etch and provide sidewall protection. This process resulted in an etch selectivity ratio of less than 5:1 for the mask relative to silicon oxide and silicon nitride. Sidewall protection was provided by polymer deposition, controlled by carbon concentration (higher carbon concentrations increase sidewall deposition) and oxygen concentration (higher oxygen concentrations consume the deposited polymer). Higher oxygen concentrations also increased mask consumption. Some previous processes used silicon-containing masks.

[0039] Compared to conventional methods, the above-described implementation improves the etching rate and enhances contact shape / stripe. Unbound from theoretical constraints, it is proposed to achieve fluorocarbon-rich polymers at the high aspect ratio etch front using lower wafer temperatures. This increases the etching rate of silicon oxide and silicon nitride while accumulating less carbon at the etch front. The reduced accumulation of carbon-rich polymers at the etch front also improves contact shape and reduces sidewall striations. Furthermore, higher selectivity for silicon oxide and silicon nitride relative to carbon masks can be achieved. This allows for the use of thinner carbon-containing masks, which improves the control and performance of the carbon mask opening process.

[0040] In some embodiments, the electrostatic chuck is cooled to a temperature below -60°C in order to cool the stacked layers to a temperature below -20°C. In other embodiments, it is considered that the process is improved when the chuck is cooled to a temperature between -30°C and -200°C. In other embodiments, the chuck is cooled to a temperature below -40°C to -200°C. In some embodiments, the stacked layers are cooled to a temperature between -30°C and -200°C.

[0041] In some embodiments, the etching gas comprises a component providing free fluorine, a hydrogen-containing component, a hydrocarbon-containing component, a fluorocarbon-containing component, and an iodine-containing component. The component providing free fluorine is defined as a component that typically decomposes in plasma to provide free fluorine, such as NF3 and SF6. The hydrogen-containing component is preferably H2, CH3F, and CH2F2. Additionally, various components can form single polyatomic molecules. For example, CF3I can provide both a fluorocarbon-containing component and an iodine-containing component. Alternatively, a hydrofluorocarbon-containing component can provide both a hydrocarbon-containing component and a fluorocarbon-containing component. The iodine-containing component can be selected from at least one of trifluoroiodomethane (CF3I), pentafluoroiodomethane (C2IF5), and tetrafluorodiiodomethane (C2I2F4). Without being bound by theory, it is believed that iodine from the iodine-containing component provides improved sidewall passivation, which helps reduce warpage. By combining a low substrate temperature with certain reactants, a high-quality protective film can be formed on the sidewalls of partially etched features during etching. The low temperature also allows for the etching gas to be oxygen-free and free of C4F8, C4F6, and C3F8 in some embodiments. In other embodiments, the etching gas includes NF3, H2, CF3I, CH3F, and CH2F2. In some embodiments, the etching gas also includes at least one of C4F8, C4F6, C3F8, SF6, CF4, CH4, or CHF3.

[0042] The ONON stack layer can be etched to form contact holes or trenches during the fabrication of 3D NAND memory devices. Other embodiments may etch contact holes used in MOCs and MOAs, which are the first metal contacts for controlling the 3D NAND junction. Other embodiments may be used for DRAM capacitor etching. Embodiments provide a CD of less than 100 nm and an etch depth greater than 20 micrometers. In other embodiments, the etch depth is greater than 3 micrometers. These embodiments enable the etching of at least 48 silicon oxide and silicon nitride bilayers in a single etch step using a single amorphous carbon mask with a thickness of less than 1 micrometer.

[0043] In some embodiments, the stacked layer may be a single layer of silicon oxide or a single layer of silicon nitride. In other embodiments, the stacked layer may be a single layer or multiple layers of other silicon-containing materials.

[0044] The above implementation uses a bias voltage of at least 400 volts. It has been found that a bias voltage of at least 1000 volts provides improved etching. It is believed that a bias voltage of at least 2000 volts will provide further improved etching. Without being bound by theory, it is believed that higher bias voltages will achieve higher aspect ratio etching while utilizing other features that enable the use of amorphous carbon masks and reduce streaking and warping.

[0045] In some embodiments, liquid nitrogen is used as a coolant, flowing through the chuck or bottom electrode to provide cooling. In other embodiments, liquid Vertel Sinera, manufactured by DuPont Corporation of Wilmington, Delaware, USA, is used. TM It can be used as a coolant.

[0046] While the invention has been described according to several preferred embodiments, changes, modifications, substitutions, and various alternatives that fall within the scope of the invention are possible. It should also be noted that many alternatives exist for implementing the methods and apparatus of the invention. Therefore, the appended claims are intended to be interpreted as including all such changes, modifications, substitutions, and various alternatives that fall within the true spirit and scope of the invention.

Claims

1. A method for etching features in a stacked layer beneath an amorphous carbon mask, comprising: Cool the stacked layers to a temperature below -20°C; An etching gas mixture is provided, comprising a component gas providing free fluorine, hydrogen, and a gas mixture including an iodine-containing component, a hydrocarbon-containing component, and a fluorocarbon-containing component, wherein the fluorocarbon-containing component includes one of a fluorocarbon gas, a hydrofluorocarbon gas, or a fluorocarbon gas containing an iodine component. Plasma is generated from the etching gas mixture; A bias voltage of at least about 400 volts is provided to accelerate ions from the plasma to the stacked layer; as well as Features are selectively etched in the stacked layers relative to the amorphous carbon mask.

2. The method of claim 1, wherein the etching gas mixture is free of oxygen and free of C4F8 and C4F6.

3. The method according to claim 1, wherein the etching gas mixture comprises NF3, H2, CF3I, CH3F and CH2F2.

4. The method of claim 3, wherein the etching gas mixture further comprises at least one of C4F8, C3F8, C4F6, SF6, O2, CF4, CH4 or CHF3.

5. The method of claim 1, wherein the stacked layer is supported on a chuck in an etching chamber, the method further comprising cooling the chuck to a temperature below -40°C.

6. The method of claim 1, wherein the stacked layer comprises a plurality of silicon oxide and silicon nitride bilayers.

7. The method of claim 6, wherein the plurality of silicon oxide and silicon nitride bilayers comprises at least 48 bilayers.

8. The method of claim 7, wherein the stacked layer does not have a silicon mask.

9. The method of claim 1, wherein the etching gas mixture further comprises NF3.

10. The method of claim 1, wherein the etching gas mixture further comprises CF3I.

11. The method of claim 1, wherein the feature has a depth-to-neck ratio of at least 30:

1.

12. The method of claim 1, wherein the etching gas mixture further comprises at least one of NF3 or SF6.

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