Method for etching etch layer

Abstract

A method of etching features in a stack that includes a dielectric material on a substrate is provided. In step (a), an etching plasma is generated from an etching gas, the stack is exposed to the etching plasma, and features in the stack are partially etched. In step (b), an atomic layer deposition process is provided after step (a) to deposit a protective film on the sidewalls. The atomic layer deposition process comprises a plurality of cycles, where each cycle comprises: exposing the stack to a first reactant gas comprising WF6, where the first reactant gas is adsorbed onto the stack; and exposing the stack to a plasma formed by a second reactant gas, wherein the plasma formed by the second reactant gas reacts with the adsorbed first reactant gas to form a protective film over the stack. In step (c), steps (a)-(b) are repeated at least once.

Description

This application is a divisional application of application No. 201980072844.8, filed on October 29, 2019, entitled “Method for etching an etch layer”. The entire disclosure of the parent application is hereby incorporated by reference for all purposes. Cross Reference to Related Applications

[0001] This application claims the benefit of priority to U.S. Application No. 62 / 755,707, filed November 5, 2018, the entire contents of which are incorporated herein by reference for all purposes. TECHNICAL FIELD

[0002] The present disclosure relates to methods of forming semiconductor devices on semiconductor wafers. More specifically, the present disclosure relates to etching recessed features in an etch layer in a stack. BACKGROUND

[0003] In forming semiconductor devices, an etch layer can be etched to form a contact hole or a trench. Some semiconductor devices can be formed by etching a silicon oxide (SiO2) based layer. SUMMARY

[0004] To achieve the foregoing and according to the purpose of the present disclosure, a method of etching a feature in a stack is provided. The stack includes a dielectric material on a substrate. In step (a), an etch plasma is generated from an etch gas, the stack is exposed to the etch plasma, and a feature in the stack is partially etched. In step (b), an atomic layer deposition process is provided after step (a) to deposit a protective film on the sidewall. The atomic layer deposition process includes a plurality of cycles, wherein each cycle includes: exposing the stack to a first reactant gas including WF6, wherein the first reactant gas is adsorbed onto the stack; and exposing the stack to a plasma formed from a second reactant gas, wherein the plasma formed from the second reactant gas reacts with the adsorbed first reactant gas to form a protective film over the stack. In step (c), steps (a)-(b) are repeated at least once.

[0005] In another implementation, an apparatus for etching features in a stack is provided. A process chamber is provided. A substrate support is within the process chamber. A gas inlet provides a gas to the process chamber. A gas source provides the gas to the gas inlet, wherein the gas source includes: an etching gas source; a WF6 gas source; and a reactant gas source. An exhaust pump is provided for pumping gas from the process chamber. An electrode provides RF power in the process chamber. At least one power supply provides power to the electrode. A controller is controllably connected to the gas source and the at least one power supply, wherein the controller includes: at least one processor; and a computer readable medium. The computer readable medium includes computer code for performing etching of a stack by a first plurality of cycles, wherein each of the first plurality of cycles includes: partially etching the stack; and depositing a layer on the stack via atomic layer deposition by providing a second plurality of cycles. Each cycle of the second plurality of cycles includes: flowing a WF6 containing gas from the WF6 gas source; adsorbing the WF6 containing gas onto the stack; stopping the flow of the WF6 containing gas; and exposing the stack to a plasma of a reactant gas from the reactant gas source, wherein the plasma converts the adsorbed WF6 containing gas to an atomic layer deposition layer.

[0006] These and other features of the present disclosure will be more readily apparent in the detailed description of the disclosure below, taken in conjunction with the following drawings. BRIEF DESCRIPTION OF DRAWINGS

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

[0008] Figure 1 is a high level flow diagram of an embodiment.

[0009] Figure 2A -G is a schematic of a stack being processed according to an embodiment.

[0010] Figure 3 is a schematic of an etch chamber that can be used in an embodiment.

[0011] Figure 4 is a schematic of a computer system that can be used to practice an embodiment. DETAILED DESCRIPTION

[0012] The present disclosure will now be described in detail with reference to a few examples 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. However, it will be apparent to one skilled in the art that the present disclosure can 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.

[0013] High aspect ratio etching requires maintaining vertical profile with minimal lateral CD (critical dimension) growth (CD bowing). Additionally, profile compromises such as reduced mask selectivity, reduced etch rate, or capping / plugging of features should be avoided. CD bowing is caused by the sidewalls of the etched features. A passivation layer can be placed on the sidewalls to reduce CD bowing. Some methods deposit the sidewall passivation layer at temperatures above 250 °C to provide uniform passivation. Such high temperatures can damage semiconductor devices.

[0014] In an example of an embodiment, Figure 1 is a high level flowchart of an embodiment. As Figure 2A shown, the embodiment can be used to process a stack 200. Figure 2A is a cross-sectional view of the stack 200 with a substrate 204 disposed below an etch layer 208 and the etch layer 208 disposed below a mask 212. In this example, the mask 212 is a hard mask such as a plasma enhanced chemical vapor deposition (PECVD) amorphous carbon mask. In this example, the etch layer 208 is a dielectric layer made of a dielectric material such as silicon oxide (SiO2). One or more layers (not shown) can be disposed between the substrate 204 and the etch layer 208. One or more layers (not shown) can also be disposed between the etch layer 208 and the mask 212.

[0015] The features are partially etched into the etch layer 208 (step 104). An example of a recipe for partially etching the features into the etch layer 208 (step 104) provides a pressure of 5-50 mTorr. Radio frequency (RF) power is provided at a frequency of 60 megahertz (MHz) at a power of 500 watts (W) - 10 kilowatts (kW) and at a frequency of 400 kilohertz (kHz) at a power of 1 kW - 30 kW. The RF power is pulsed between these power levels. An etch gas is provided. The etch gas includes oxygen (O2), a fluorocarbon, and / or a hydrofluorocarbon. The etch gas is formed into a plasma by the RF power. The plasma provides the radical ions responsible for the high aspect ratio etching. Such a plasma is referred to in the specification and claims as an etch plasma. When the partial etch is complete, the flow of the etch gas is stopped. The RF power is stopped or reduced so that the plasma is not produced. Figure 2Bis a cross-sectional view of the stack 200 after the feature 216 has been partially etched.

[0016] After the partial etch (step 104), an atomic layer deposition process (step 108) is provided to deposit a protective film on the sidewalls of the feature 216. The atomic layer deposition process (step 108) includes a cyclic process with multiple cycles. In a first phase of a cycle of the atomic layer deposition process (step 108), the stack 200 is exposed to a first reactant gas containing tungsten hexafluoride (WF6) (step 112). A gas flow containing 0.5 to 200 seem of WF6 is provided. In this embodiment, the first reactant gas is not converted to a plasma. As a result, this step is plasma-free. The stack temperature is maintained in the range of 40°C to 80°C. The first reactant gas is adsorbed onto the surfaces of the stack 200. After 3 seconds, the flow of the first reactant gas is stopped.

[0017] Without being bound by theory, it is believed that the WF6 chemically reacts with the SiO2 to form a layer of silicon tungstate (SiOW). Figure 2C is a cross-sectional view of the stack 200 after the layer of SiOW 220 has been formed on the surfaces (including sidewalls) of the feature 216. The layer of SiOW 220 is not drawn to scale, but is shown much thicker in order to better illustrate the layer of SiOW 220.

[0018] After the first reactant gas is adsorbed (step 112), a first purge (step 116) is provided to purge the first reactant gas. In this example, the first purge is provided by flowing O2 into the plasma processing chamber. Other embodiments can have a purge gas of pure nitrogen (N2), or a mixture of N2 and argon (Ar), or pure Ar. The purge gas O2 enables the plasma to be struck immediately after the first purge. The flow of the purge gas is stopped after 5 seconds. The first purge removes tungsten (W) that has not been adsorbed prior to the formation of the plasma in the next step.

[0019] After the first purge is completed (step 116), the stack 200 is exposed to a plasma formed from a second reactant gas (step 120). The stack 200 and the chamber are maintained at a temperature below 150°C. A second reactant gas is provided. In this example, the second reactant gas is O2. The second reactant gas is formed into a plasma by providing an excitation energy at a frequency of 60 MHz at a power in the range of 200 W to 20 kW. A bias RF signal is provided at a frequency of 100 kHz to 27 MHz at a power in the range of 200 W to 50 kW. The plasma is extinguished after 3 seconds.

[0020] After exposing the stack 200 to the plasma formed from the second reactant gas (step 120), a second purge (step 124) is provided to clear the remaining plasma ion radicals. In this example, the second purge is provided by flowing the second reactant gas into the plasma processing chamber without forming a plasma with sufficient RF power. The second reactant gas is used to purge the remaining plasma. Other embodiments can have other purge gases. Some embodiments can stop the RF power. The flow of the purge gas is stopped after 5 seconds. The second purge removes the plasma ion radicals completely from the plasma processing chamber. The atomic layer deposition cycle is then repeated. In this example, the atomic layer deposition process (step 108) is performed for 3 to 100 cycles.

[0021] Figure 2D is a cross-sectional view of the stack 200 after providing a plurality of cycles of the atomic layer deposition process (step 108) to form a protective film 224 on the sidewalls of the features 216. In this example, the protective film 224 includes tungsten oxide. The protective film 224 is not drawn to scale. Because the atomic layer deposition process (step 108) uses plasma instead of a plasma-free thermal treatment, the protective film 224 is not as conformal as a film deposited using a plasma-free thermal treatment. In addition, the quality of the protective film 224 can not be as high as a film deposited using a plasma-free thermal treatment. Because the protective film 224 is not conformal, in this embodiment, the protective film 224 does not extend to the bottom of the features 216.

[0022] After the atomic layer deposition process (step 108) is completed, the features 216 are further etched (step 128). An example of a recipe for further etching the features into the etch layer 208 provides a pressure of 5-50 mTorr. RF power is provided at a frequency of 60 MHz for a power of 2 kW-8 kW, and at a frequency of 400 kHz for a power of 4 kW-25 kW. The RF power is pulsed between these power levels. An etch gas is provided. The etch gas includes O2, a fluorocarbon, and / or a hydrofluorocarbon. The etch gas is formed into an etch plasma by the RF power. Figure 2E is a cross-sectional view of the stack 200 after the features 216 are further etched.

[0023] If the etching of the features is not complete (step 132) (i.e., the features are not etched to the final depth), the process returns to the atomic layer deposition process (step 108). The atomic layer deposition process (step 108) is repeated. Figure 2F is a cross-sectional view of the stack 200 after the atomic layer deposition process (step 108) is repeated and a new protective film 228 is formed. Because the new protective film 228 is formed using plasma, the new protective film is not conformal.

[0024] Feature 216 is further etched (step 128). The cycle of atomic layer deposition process (step 108) and further etching (step 128) is repeated until the etching of feature 216 is complete (step 132). Figure 2G is a cross-sectional view of stack 200 after the etching of feature 216 is etched to a final depth.

[0025] The above embodiments provide for preventing or reducing sidewall passivation of feature warpage by using plasma in the atomic layer deposition process (step 108). If a thermal atomic layer deposition process is used to deposit tungsten, a stack or chamber temperature above 250 °C would be used. Temperatures above 250 °C can damage the semiconductor device being formed. The atomic layer deposition process (step 108) that uses plasma to deposit the tungsten-containing protective film provides a less conformal and lower quality protective film. However, it has been found that a tungsten-containing non-conformal protective film is sufficient to prevent or reduce sidewall warpage.

[0026] In various embodiments, the atomic layer deposition process (step 108) is performed at a stack or chamber temperature of less than 100 °C. In various embodiments, the plasma formed from the second reactant gas provides oxidation or nitridation. If the plasma from the second reactant gas provides oxidation, in various embodiments, the second reactant gas includes an oxygen-containing component, such as at least one of oxygen (O2), ozone (O3), carbonyl sulfide (COS), carbon dioxide (CO2), sulfur dioxide (SO2), or carbon monoxide (CO). Additionally, argon (Ar) or krypton (Kr) can be used as a carrier gas. If the plasma from the second reactant gas provides nitridation, the second reactant gas includes a nitrogen-containing component, such as at least one of nitrogen (N2) or ammonia (NH3). Additionally, Ar or Kr can be used as a carrier gas. If the second reactant gas includes N2, the second reactant gas can further include H2.

[0027] In various embodiments, the hard mask can be formed from amorphous carbon, boron-doped carbon, boron-doped silicon, metal-doped carbon, or polysilicon. In various embodiments, etch layer 208 is a silicon oxide-based dielectric layer. In various embodiments, etch layer 208 is a stack of different material layers. In various embodiments, at least one of the layers in etch layer 208 is a dielectric material layer. In various embodiments, the atomic layer deposition process (step 108) provides a protective film 228 that is non-conformal and does not reach the bottom of feature 216. In various embodiments, the RF power can be continuous wave. In other embodiments, the RF power can be pulsed power. In various embodiments, the pulsed RF power can have a pulse repetition frequency between 100 Hz and 5 kHz. In various embodiments, the pulsed RF power can have a duty cycle between 5% to 95%.

[0028] Additionally, since the atomic layer deposition process (step 108) uses plasma instead of thermal processing, the atomic layer deposition process (step 108) can be performed in-situ in the same plasma processing chamber as the etching process (step 128). By providing an in-situ atomic layer deposition process (step 108), there is higher throughput since all steps are performed in the same plasma processing chamber.

[0029] In exemplary embodiments, Figure 3 is a schematic diagram of an etching reactor that can be used in embodiments. In one or more embodiments, the plasma processing chamber 300 includes a gas distribution plate 306 that provides gas inlets and an electrostatic chuck (ESC) 308 within an etching chamber 349 that is surrounded by chamber walls 352. Within the etching chamber 349, the stack 200 is positioned above the ESC 308. The ESC 308 is also a substrate support. An edge ring 309 surrounds the ESC 308. Gas sources 310 are connected to the etching chamber 349 through the gas distribution plate 306. In this example, the gas sources 310 include an etchant gas source 312, a WF6 gas source 316, and a reactant gas source 318. An ESC temperature controller 350 is connected to a chiller 314. In this embodiment, the chiller 314 provides coolant to a channel 315 in or near the ESC 308 to cool the ESC 308. A radio frequency (RF) source 330 provides RF power to a lower electrode. In this embodiment, the ESC 308 is the lower electrode. In exemplary embodiments, 400 kHz and 60 MHz power supplies make up the RF source 330. In this embodiment, the upper electrode, the gas distribution plate 306, is grounded. In this embodiment, one generator is provided for each frequency. Other arrangements of RF sources and electrodes can be used in other embodiments. A controller 335 is controllably connected to the RF source 330, the exhaust pump 320, and the gas sources 310. One example of such an etching chamber is a TFX® etching system manufactured by Lam Research Corporation (Fremont, CA). The processing chamber can be a CCP (capacitively coupled plasma) reactor or an ICP (inductively coupled plasma) reactor.

[0030] Figure 4is a high-level block diagram showing a computer system 400 suitable for implementing the controller 335 used in embodiments. The computer system can have a variety of physical forms, ranging from an integrated circuit, a printed circuit board, and a small handheld device, to a huge supercomputer. The computer system 400 includes one or more processors 402 and further can include an electronic display device 406 (for displaying graphics, text, and other data), a main memory 404 (e.g., random access memory (RAM)), a storage device 408 (e.g., a hard disk drive), a removable storage device 410 (e.g., a floppy disk drive), a user interface device 412 (e.g., a keyboard, a touch screen, a keypad, a mouse, or a other pointing device, etc.), and a communication interface 414 (e.g., a wireless network interface). The communication interface 414 enables software and data to be transferred between the computer system 400 and external devices. The system can also include a communications infrastructure 416 (e.g., a communications bus, cross-over bar, or network) to which the aforementioned devices / modules are connected.

[0031] Information transferred via the communication interface 414 can be in the form of signals such as electronic, electromagnetic, optical, or other signals capable of being received by the communication interface 414, through a communication link that carries signals and can be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, an RF link, and / or other communication channels. With such a communication interface, it is contemplated that the one or more processors 402 might receive information from the network, or might output information to the network in the course of performing the above-described method steps. Furthermore, method embodiments can execute solely upon the processors or can execute in combination with remote processors via a network such as the Internet.

[0032] The term "non-transitory computer-readable medium" is generally used herein to refer to media such as main memory, secondary memory, removable storage, and storage devices (e.g., hard disk drives, flash memory, hard disk drive storage, CD-ROM, and other forms of permanent storage) and does not refer to transitory signals per se. Examples of computer code include machine code, such as produced by a compiler, and files containing higher-level code that is executed by a computer using an interpreter. Computer-readable media also can be computer-readable storage media that are media that computer program instructions are provided on, or that a computer program is transmitted to or transferred to via a computer-readable signal. Computer-readable media can also be, for example, transmission media that carry computer-readable instructions.

[0033] While the present disclosure has been described in terms of several exemplary embodiments, there are alterations, modifications, permutations, and various substitu- tions and equivalents which fall within the scope of the present 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 construed to include all such alterations, modifications, permutations, and various substitu- tions and equivalents thereof.

Claims

1. A method for etching features in a dielectric layer, said dielectric layer comprising SiO2 beneath a hard mask in a stack on a substrate, said hard mask comprising one or more of amorphous carbon, boron-doped carbon, boron-doped silicon, metal-doped carbon, or polycrystalline silicon, said method comprising: (a) An etching plasma is generated by an etching gas, the stack is exposed to the etching plasma, and features in the stack are partially etched in a plasma processing chamber; (b) Following (a), an atomic layer deposition process performed in situ within the plasma processing chamber is provided to deposit a protective film on the sidewalls of the feature, the atomic layer deposition process comprising multiple cycles, wherein each cycle includes: (i) exposing the stack to a first reactant gas containing WF6, wherein the first reactant gas is adsorbed onto the stack, wherein exposing the stack to the first reactant gas occurs when the first reactant gas is plasma-free; and (ii) Exposing the stack to a plasma formed by a second reactant gas, wherein the plasma reacts with an adsorbed first reactant gas to form a protective film over the stack, wherein the second reactant gas includes an oxygen-containing component to provide oxidation, wherein the atomic layer deposition process further includes maintaining the stack temperature below 150°C, and wherein the protective film on the sidewalls of the feature is non-conformal and does not reach the bottom of the feature; and (c) Repeat (a)-(b) at least once in situ within the plasma processing chamber.

2. The method according to claim 1, wherein, The second reactant gas includes at least one of COS, CO2, CO, SO2, O2, or O3.

3. The method according to claim 1, wherein, The atomic layer deposition process is performed for 2 to 100 cycles.

4. The method according to claim 1, wherein, Each loop also includes: After exposing the stack to the first reactant gas and before exposing the stack to the plasma formed by the second reactant gas, the first reactant gas is purged; and After exposing the stack to the plasma formed by the second reactant gas, the plasma formed by the second reactant gas is purged.

5. An apparatus for etching features in a dielectric layer, comprising: Processing room; The substrate support within the processing chamber; A gas inlet for supplying gas to the processing chamber; A gas source for supplying the gas to a gas inlet, wherein the gas source comprises: Etching gas source; WF6 gas source; and Reactant gas source; A discharge pump is used to extract gas from the treatment chamber; Electrodes, which are used to provide RF power in the processing chamber; At least one power source for supplying power to the electrodes; and A controller, capable of being controllably connected to the gas source and the at least one power source, wherein the controller comprises: At least one processor; and A computer-readable medium comprising computer code for performing an etching of a stack of parts through a first plurality of loops, each of said first plurality of loops comprising: Partially etch the stacked components; Non-conformal layers are deposited on the stack via atomic layer deposition, wherein each of the second plurality of cycles comprises: The first reactant gas containing WF6 is allowed to flow from the WF6 gas source; The WF6-containing first reactant gas is adsorbed onto the stack, wherein the adsorption of the WF6-containing gas onto the stack is plasma-free; Stop the flow of the first reactant gas containing WF6; and The stack is exposed to a plasma of a second reactant gas from the reactant gas source, wherein the plasma converts the adsorbed WF6-containing first reactant gas into an atomic layer deposition layer, wherein the computer-readable medium further includes computer code for cooling the substrate support to a temperature below 150°C, and wherein the protective film on the sidewalls of the feature is non-conformal and does not extend to the bottom of the feature.

6. The apparatus of claim 5, further comprising a cooler for cooling the substrate support.

7. The apparatus according to claim 5, wherein, The process of allowing the WF6-containing gas to flow is a plasma-free step.

8. The apparatus according to claim 5, wherein, The reactant gas source is at least one of COS, CO2, CO, SO2, O2, or O3.

9. The apparatus according to claim 5, wherein, The atomic layer deposition process described herein is performed for 2 to 100 cycles.

10. The apparatus according to claim 5, wherein, Each of the second plurality of loops also includes: After stopping the flow of the WF6-containing gas and before exposing the stack to the plasma formed by the second reactant gas, the first reactant gas is purged; and After exposing the stack to the plasma formed by the second reactant gas, the plasma formed by the second reactant gas is purged.

11. The apparatus according to claim 5, wherein, The computer-readable medium also includes computer code for cooling the substrate support to a temperature not exceeding 80°C.

12. The method according to claim 1, wherein, The atomic layer deposition process also includes maintaining the temperature of the stack below 80°C.

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