Method for etching an etching layer

Abstract

A method for etching features in a stack is provided, wherein the stack includes a dielectric material on a substrate. In step (a), an etching plasma is generated by an etching gas, the stack is exposed to the etching plasma, and the 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 sidewall. The atomic layer deposition process includes a plurality of cycles, each of which includes: exposing the stack to a first reactant gas comprising WF6, wherein 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 above the stack. In step (c), steps (a)-(b) are repeated at least once.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] 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

[0003] The present disclosure relates to methods of forming semiconductor devices on semiconductor wafers. More particularly, the present disclosure relates to etching recessed features in an etch layer in a stack. Background Art

[0004] In forming semiconductor devices, an etching layer may be etched to form contact holes or trenches. Some semiconductor devices may be formed by etching a silicon oxide (SiO2) based layer. Summary of the Invention

[0005] To achieve the aforementioned objectives, and in accordance with the purposes of the present disclosure, a method for etching features in a stack is provided, the stack comprising a dielectric material on a substrate. In step (a), an etching plasma is generated by an etching gas, the stack is exposed to the etching plasma, and the 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 includes a plurality of cycles, each of which includes: exposing the stack to a first reactant gas comprising WF6, wherein 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 above the stack. In step (c), steps (a)-(b) are repeated at least once.

[0006] In another embodiment, 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 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 extracting 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 the stack through 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 by atomic layer deposition by providing a second plurality of cycles. Each of the second plurality of cycles comprises 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 into an atomic layer deposition layer.

[0007] These and other features of the present disclosure will be described in more detail below in the detailed description of the disclosure and in conjunction with the following figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present disclosure is illustrated by way of example and not limitation in the figures of the accompanying drawings and in which like references indicate similar elements and in which:

[0009] Figure 1 It is a high-level flow chart of an implementation plan.

[0010] Figures 2A-2G is a schematic diagram of a stack processed according to one embodiment.

[0011] Figure 3 is a schematic diagram of an etching chamber that can be used in embodiments.

[0012] Figure 4 is a schematic diagram of a computer system that can be used to practice embodiments. DETAILED DESCRIPTION

[0013] The present invention will now be described in detail with reference to several exemplary embodiments shown 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 those skilled in the art that the present disclosure can be practiced without some or all of these specific details. In other cases, well-known process steps and / or structures have not been described in detail in order to avoid unnecessarily obscuring the present disclosure.

[0014] High aspect ratio etching requires maintaining a vertical profile with minimal lateral CD (critical dimension) growth (CD warp). In addition, profile trade-offs such as reduced mask selectivity, reduced etch rate, or feature capping / clogging should be avoided. CD warp is caused by the sidewalls of the etched features. A passivation layer can be placed on the sidewalls to reduce CD warp. Some methods deposit the sidewall passivation layer at temperatures above 250°C to provide uniform passivation. Such high temperatures can damage semiconductor devices.

[0015] In the example implementation, Figure 1 This is a high-level flow chart of an implementation plan. Figure 2A As shown, this embodiment can be used to process a stack 200 . Figure 2A 2 is a cross-sectional view of stack 200, wherein substrate 204 is disposed below etch layer 208, and etch layer 208 is disposed below mask 212. In this example, mask 212 is a hard mask, such as a plasma enhanced chemical vapor deposition (PECVD) amorphous carbon mask. In this example, etch layer 208 is a dielectric layer made of a dielectric material such as silicon oxide (SiO2). One or more layers (not shown) may be disposed between substrate 204 and etch layer 208. One or more layers (not shown) may also be disposed between etch layer 208 and mask 212.

[0016] The features are partially etched into the etching layer 208 (step 104). An example of a recipe for partially etching the features into the etching layer 208 (step 104) provides a pressure of 5-50 mTorr. Radio frequency (RF) power provides a power of 500 watts (W)-10 kilowatts (kW) at a frequency of 60 megahertz (MHz) and a power of 1 kW-30 kW at a frequency of 400 hertz (kHz). The RF power is pulsed between these power levels. An etching gas is provided. The etching gas includes oxygen (O2), fluorocarbons and / or hydrofluorocarbons. The etching gas is formed into a plasma by the RF power. The plasma provides radical ions responsible for high aspect ratio etching. Such a plasma is referred to as an etching plasma in the specification and claims. When the partial etching is completed, the flow of the etching gas stops. The RF power is stopped or reduced so that no plasma is generated. Figure 2Bis a cross-sectional view of stack 200 after feature 216 has been partially etched.

[0017] After the partial etching (step 104), an atomic layer deposition process (step 108) is provided to deposit a protective film on the sidewall of feature 216. The atomic layer deposition process (step 108) includes a cyclic process with multiple cycles. In the first stage (step 108) of the cycle of the atomic layer deposition process, the stack 200 is exposed to a first reactant gas containing tungsten hexafluoride (WF6) (step 112). A gas flow of WF6 containing 0.5 to 200sccm is provided. In this embodiment, the first reactant gas is not converted into 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 surface of the stack 200. After 3 seconds, the flow of the first reactant gas stops.

[0018] Without being bound by theory, it is believed that WF6 chemically reacts with SiO2 to form a tungsten oxide silicide (SiOW) layer. Figure 2C is a cross-sectional view of the stack 200 after a SiOW layer 220 has been formed on the surface (including the sidewalls) of the feature 216. The SiOW layer 220 is not drawn to scale but is shown much thicker in order to better illustrate the SiOW layer 220.

[0019] After the first reactant gas is adsorbed (step 112), a first purge is provided (step 116) to purge the first reactant gas. In this example, the first purge is provided by flowing O2 into the plasma processing chamber. Other embodiments may have the purge gas be pure nitrogen (N2), a mixture of N2 and argon (Ar), or pure Ar. The purge gas O2 allows the plasma to be ignited immediately after the first purge. The flow of the purge gas is stopped after 5 seconds. The first purge completely removes any tungsten (W) that has not been adsorbed before the next step of forming the plasma.

[0020] After the first purge is complete (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 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. After 3 seconds, the plasma is extinguished.

[0021] After exposing the stack 200 to the plasma formed by the second reactant gas (step 120), a second purge (step 124) is provided to remove remaining plasma ion radicals. In this example, the second purge is provided by flowing the second reactant gas into the plasma processing chamber without sufficient RF power to form a plasma. The second reactant gas is used to purge the remaining plasma. Other embodiments may have other purge gases. Some embodiments may stop the RF power. The flow of the purge gas is stopped after 5 seconds. The second purge completely removes the plasma ion radicals 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.

[0022] Figure 2D 1 is a cross-sectional view of stack 200 after providing multiple cycles of an atomic layer deposition process (step 108) to form a protective film 224 on the sidewalls of feature 216. In this example, protective film 224 comprises tungsten oxide. 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, protective film 224 is not as conformal as a film deposited using a plasma-free thermal treatment. Additionally, the quality of protective film 224 may not be as high as that of a film deposited using a plasma-free thermal treatment. Because protective film 224 is not conformal, in this embodiment, protective film 224 does not extend to the bottom of feature 216.

[0023] 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 features into the etch layer 208 provides a pressure of 5-50 mTorr. The RF power provides a power of 2kW-8kW at a frequency of 60 MHz and a power of 4kW-25kW at a frequency of 400 kHz. The RF power is pulsed between these power levels. An etching gas is provided. The etching gas contains O2, a fluorocarbon, and / or a hydrofluorocarbon. The etching gas is formed into an etching plasma by the RF power. Figure 2E is a cross-sectional view of stack 200 after feature 216 has been further etched.

[0024] If the etching of the feature is not complete (step 132) (ie, the feature is 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. Since the new protective film 228 is formed using plasma, the new protective film is not conformal.

[0025] The feature 216 is further etched (step 128). The cycle of the atomic layer deposition process (step 108) and further etching (step 128) is repeated until the etching of the feature 216 is complete (step 132). Figure 2G is a cross-sectional view of stack 200 after etching feature 216 to a final depth.

[0026] The above embodiment provides sidewall passivation (step 108) that prevents or reduces feature warping by using plasma in an atomic layer deposition process. If tungsten is deposited using a thermal atomic layer deposition process, a stack or chamber temperature greater than 250°C will be used. Temperatures greater than 250°C may damage the semiconductor device being formed. An atomic layer deposition process (step 108) that uses plasma to deposit a tungsten-containing protective film provides a less conformal and lower quality protective film. However, it has been found that a non-conformal protective film containing tungsten is sufficient to prevent or reduce sidewall warping.

[0027] 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 by 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 comprises an oxygen-containing component, such as at least one of oxygen (O 2 ), ozone (O 3 ), carbonyl sulfide (COS), carbon dioxide (CO 2 ), sulfur dioxide (SO 2 ), or carbon monoxide (CO). In addition, 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 comprises a nitrogen-containing component, such as at least one of nitrogen (N 2 ) or ammonia (NH 3 ). In addition, Ar or Kr can be used as a carrier gas. If the second reactant gas comprises N 2 , the second reactant gas can further comprise H 2 .

[0028] In various embodiments, the hard mask can be formed of amorphous carbon, boron-doped carbon, boron-doped silicon, metal-doped carbon, or polycrystalline silicon. In various embodiments, the etch layer 208 is a dielectric layer based on silicon oxide. In various embodiments, the etch layer 208 is a stack of different material layers. In various embodiments, at least one layer of the etch layer 208 is a dielectric material layer. In various embodiments, the atomic layer deposition process (step 108) provides a non-conformal protective film 228 that does not reach the bottom of the feature 216. In various embodiments, the RF power can be a 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% and 95%.

[0029] In addition, since the atomic layer deposition process (step 108) uses plasma instead of thermal treatment, 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), productivity is increased because all steps are performed in the same plasma processing chamber.

[0030] In an exemplary embodiment, Figure 3 3 is a schematic diagram of an etching reactor that can be used in embodiments. In one or more embodiments, a plasma processing chamber 300 includes a gas distribution plate 306 that provides a gas inlet and an electrostatic chuck (ESC) 308 within an etching chamber 349, which is surrounded by a chamber wall 352. Within the etching chamber 349, the stack 200 is located above the ESC 308. The ESC 308 is also a substrate support. An edge ring 309 surrounds the ESC 308. A gas source 310 is connected to the etching chamber 349 through the gas distribution plate 306. In this example, the gas source 310 includes 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 cooler 314. In this embodiment, the cooler 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 the lower electrode. In this embodiment, ESC 308 is the lower electrode. In an exemplary embodiment, 400 kHz and 60 MHz power supplies constitute RF source 330. In this embodiment, the upper electrode, gas distribution plate 306, is grounded. In this embodiment, one generator is provided for each frequency. Other arrangements of RF sources and electrodes may be used in other embodiments. Controller 335 is controllably connected to RF source 330, exhaust pump 320, and gas source 310. An example of such an etch chamber is manufactured by Lam Research Corporation (Fremont, CA). Etching system. The processing chamber can be a CCP (capacitively coupled plasma) reactor or an ICP (inductively coupled plasma) reactor.

[0031] Figure 4335 is a block diagram of a computer system 400 that is suitable for implementing the controller 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 giant supercomputers. The computer system 400 includes one or more processors 402 and can further 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 drive), a removable storage device 410 (e.g., an optical drive), a user interface device 412 (e.g., a keyboard, touch screen, keypad, mouse, or other positioning device, etc.), and a communication interface 414 (e.g., a wireless network interface). The communication interface 414 enables software and data to be transmitted between the computer system 400 and external devices via a link. The system can also include a communication infrastructure 416 (e.g., a communication bus, a cross-over bar, or a network), to which the aforementioned devices / modules are connected.

[0032] The information transmitted via the communication interface 414 can be in the form of a signal that can be received by the communication interface 414 through a communication link, such as an electronic, electromagnetic, optical, or other signal, which carries the signal and can be a communication link implemented using wire or cable, optical fiber, telephone line, cellular telephone link, radio frequency link, and / or other communication channels. Using such a communication interface, it is contemplated that one or more processors 402 can receive information from a network or can output information to a network in the course of implementing the above-described method steps. In addition, the method embodiments can be executed solely on the processor or can be executed in conjunction with a remote processor over a network such as the Internet, which shares a portion of the processing.

[0033] The term "non-transitory computer-readable medium" is generally used to refer to media such as main memory, secondary memory, removable storage, and storage devices (e.g., hard disks, flash memory, hard drive memory, CD-ROMs, and other forms of permanent memory), and should not be interpreted as encompassing transitory subject matter such as carrier waves or signals. Examples of computer code include machine code, such as that produced by a compiler, and files including higher-level code that is executed by a computer using an interpreter. A computer-readable medium may also be computer code transmitted by a computer data signal embodied in a carrier wave and represented as a sequence of instructions that can be executed by a processor.

[0034] Although the present disclosure has been described in terms of several exemplary embodiments, there are changes, modifications, permutations, and various alternative equivalents that fall within the scope of the present disclosure. It should also be noted that there are many alternative ways to implement the methods and apparatus of the present disclosure. Therefore, the following appended claims are intended to be interpreted as including all such changes, modifications, permutations, and various alternative equivalents that fall within the true spirit and scope of the present disclosure.

Claims

1. A method of etching a feature in a dielectric layer, the dielectric layer comprising SiO2 beneath a hard mask in a stack on a substrate, the hard mask comprising one or more of amorphous carbon, boron-doped carbon, boron-doped silicon, metal-doped carbon, or polysilicon, the method comprising: (a) generating an etching plasma from an etching gas, exposing the stack to the etching plasma, and partially etching features in the stack within a plasma processing chamber; (b) providing, after (a), an atomic layer deposition process performed in-situ within the plasma processing chamber to deposit a protective film on the sidewalls of the feature, the atomic layer deposition process comprising a plurality of cycles, wherein each cycle comprises: (i) exposing the stack to a first reactant gas comprising WF6, wherein the first reactant gas is adsorbed onto the stack, wherein the exposing the stack to the first reactant gas is performed while the first reactant gas is plasma-free; and (ii) exposing the stack to a plasma formed from a second reactant gas, wherein the plasma formed from the second reactant gas reacts with 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 providing the atomic layer deposition process further comprises maintaining a stack temperature below 150° C., and wherein the protective film on 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: purging the first reactant gas after exposing the stack to the first reactant gas and before exposing the stack to the plasma formed from the second reactant gas; and After exposing the stack to the plasma formed from the second reactant gas, the plasma formed from the second reactant gas is purged.

5. An apparatus for etching features in a dielectric layer, comprising: processing room; a substrate support within the processing chamber; a gas inlet for supplying gas to the processing chamber; a gas source for providing the gas to the gas inlet, wherein the gas source comprises: Etching gas source; WF6 gas source; and reactant gas source; an exhaust pump for extracting gas from the processing chamber; an electrode for providing RF power in the processing chamber; at least one power source for providing power to the electrodes; and a controller 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 through a first plurality of cycles, wherein each of the first plurality of cycles comprises: partially etching the stack; depositing a non-conformal layer on the stack by atomic layer deposition by providing a second plurality of cycles, wherein each cycle of the second plurality of cycles comprises: flowing a first reactant gas comprising WF6 from the WF6 gas source; adsorbing the first reactant gas comprising WF6 onto the stack, wherein adsorbing the WF6-containing gas onto the stack is plasma-free; stopping the flow of the first reactant gas comprising WF6; and exposing the stack 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 comprises computer code for cooling the substrate support to a temperature below 150° C., and wherein the non-conformal protective film on the stack does not reach the bottom of the feature.

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

7. The device according to claim 5, wherein The flowing of the WF6-containing gas is a plasma-free step.

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

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

10. The device according to claim 5, wherein Each cycle in the second plurality of cycles further comprises: After stopping the flow of the WF6-containing gas and before exposing the stack to the plasma formed from the second reactant gas, purging the first reactant gas; and After exposing the stack to the plasma formed from the second reactant gas, the plasma formed from the second reactant gas is purged.

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

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

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