Pulse Etching Process

Abstract

A method of etching a sample is described. The method includes performing a plasma etch pulse. The plasma etch pulse is performed by directing a gas flow including silicon tetrachloride (SiCl4) and a diluent toward the sample. While directing the gas flow, a bias power is applied to achieve a bias state for a first period of time. A source power is then applied to achieve a source state for a second period of time, after which a recovery state is achieved for a third period of time without applying bias power and source power. The plasma etch pulse is repeated until a desired amount of the sample is etched.

Description

[Technical Field]

[0001] Embodiments of the present disclosure generally relate to a method for etching a sample, the method including a pulsed etching process.

[0002] In the semiconductor industry, devices are produced by numerous manufacturing processes to produce increasingly smaller structures. As device geometries shrink, controlling the uniformity and repeatability of device processing becomes increasingly difficult, especially in upstream processing.

[0003] Current plasma etching processes use several chemicals in combination with a pulsed source and bias voltage. These chemicals include chlorine (Cl), hydrogen bromide (HBr), or a combination thereof. These plasma etching processes are typically two-state systems, where source power is applied in a first state, followed by bias power in a second state. These systems have been found to produce a V-shaped profile in the sample after plasma etching. The V-shape formed in the etched substrate results in undesirable device performance because the width of the device varies with depth. Therefore, there is a need to improve the plasma etching process to produce a more uniform profile (e.g., a linear profile) throughout the depth of the sample. Overview

[0004] Some embodiments of the present disclosure provide a method for etching a sample. The method can include performing a plasma etching pulse. In some embodiments, the plasma etching pulse can include directing a gas flow including silicon tetrachloride (SiCl) and a diluent toward the sample; applying a bias power to achieve a bias state for a first period while directing the flow of SiCl and the diluent toward the sample; applying a source power to achieve a source state for a second period; and achieving a recovery state for a third period without applying the bias power or the source power. In some embodiments of the method, the plasma etching pulse can be repeated until a target amount of the sample is etched.

[0005] In another embodiment of the present disclosure, a method for etching a substrate is provided, the substrate comprising a stack of alternating layers of Si and SiGe. The method includes bringing a chamber containing the substrate to a pressure of about 0.1 mT to about 500 mT, bringing the substrate to a temperature of about −50° C. to about 300° C., generating a plasma from a gas flow comprising silicon tetrachloride (SiCl) and a diluent comprising argon (Ar), helium (He), or a mixture thereof, and directing the plasma toward the substrate to etch the stack of alternating layers of Si and SiGe on the substrate.

[0006] Yet another embodiment of the present disclosure provides a method for etching a sample, comprising: performing a plasma etch pulse and repeating the plasma etch pulse until a target amount of the sample is etched, wherein performing the plasma etch pulse can include applying a bias power to achieve a bias state for a first period, applying a source power to achieve a source state for a second period, and not applying the bias power or the source power to achieve a recovery state for a third period while directing a flow of gas and diluent toward the sample. [Brief explanation of the drawings]

[0007] The present disclosure is illustrated by way of example, and not limitation, in the accompanying drawings, in which like references indicate like elements. It should be noted that different references to "embodiments" in the present disclosure do not necessarily refer to the same embodiment, but that such references refer to at least one. [Figure 1] 1 illustrates a cross-sectional view of one embodiment of a processing chamber. [Figure 2A] 1 shows a cross-sectional view of one embodiment of multiple layers of a sample. [Figure 2B] FIG. 1 shows a cross-sectional view of one embodiment of multiple layers of a sample etched such that the sample has a U-shaped profile. [Figure 3A] 1 shows a sample with multiple layers to be etched. [Figure 3B] 3B shows the sample of FIG. 3A after being etched according to an embodiment of the present disclosure. [Figure 4A] The sample of FIG. 3B is shown after further layers have been deposited and before etching. [Figure 4B] 4B shows the sample of FIG. 4A after being etched according to an embodiment of the present disclosure. [Figure 5] 1 is a flowchart illustrating a method for etching a sample according to an embodiment of the present disclosure. [Figure 6] 1 illustrates a plasma etching pulse according to one embodiment of the present disclosure. Detailed Description

[0008] In embodiments disclosed herein, a method for etching a sample is described. The method for etching a sample includes performing a plasma etching pulse, which includes directing a gas flow containing silicon tetrachloride (SiCl) and a diluent at the sample. To improve the profile of the sample, SiCl can be used in combination with a three-step plasma etching pulse process. The use of SiCl in combination with the disclosed three-step plasma etching pulse has been found to reduce trench width variation across the trench depth of the etched sample (i.e., substrate) compared to conventional plasma etching processes using chlorine (Cl), hydrogen bromide (HBr), and / or nitrogen (N).

[0009] The plasma etching process of the present disclosure can use a three-state pulsing scheme. In the three-state pulsing scheme, the first state can be a bias state in which bias power is applied. The first state lasts for a first period of time. In some embodiments, the bias power can have a power of about 100 W to about 5000 W, and a bias frequency of about 400 kHz to about 60 MHz can be applied. The second state of the pulsing scheme is a source state, in which source power can be applied during a second period in which no bias power is applied. In embodiments, the source power can be about 100 W to about 5000 W. The third state can be a recovery state in which neither bias power nor source power is applied during the third period of time. During etching, multiple plasma etching pulses can be applied until the target etch depth is reached.

[0010] Conventional plasma etching processes use a two-state pulse scheme in which source power is applied before bias power. Applying bias power before source power, as implemented in the embodiments herein, has been found to be advantageous for generating capacitively coupled plasma. Furthermore, a bias state followed by a source state in which only source power is applied has been found to enable preservation of the etch mask on the substrate due to the gas chemical reaction of SiCl4 with Ar and He and the deposition of a protective layer on the sample by the source power. The protective layer helps preserve the etch mask (which may be a hard mask, for example) on the sample and enhances selectivity between silicon and the etch mask. Furthermore, it has been found that electron density and electron temperature rapidly decrease when the source power is turned off. Therefore, by introducing a recovery state after the source state, when plasma etching pulses are repeated, the electron temperature of the next iteration of the first state is lower than that of the second state. The inventors have discovered that this decrease in electron temperature correlates with a decrease in ion temperature, thereby improving directional control during etching. Therefore, in the absence of a third state in the plasma etching pulse, the plasma density and electron temperature remain high even after the source power is applied. High electron temperatures also lead to high ion temperatures. High ion temperatures result in more random motion of ions within the bulk plasma, resulting in a wider angular distribution and greater variability in the etch profile. Therefore, a three-state etch pulse, including first a bias state, then a source state, and then a recovery state, was found to improve directional control of the etching of samples, especially samples containing alternating stacks of Si and SiGe layers when used with SiCl4 chemistry.

[0011] Thus, embodiments of the etching method according to the present disclosure allow for more directional etching in the first state, i.e., application of bias power, at least in part because the plasma is cooled in the third state before the next pulse.

[0012] Disclosed herein are embodiments of a method for etching a sample, including performing a plasma etch pulse and repeating the plasma etch pulse until a target amount of the sample is etched. The plasma etch pulse can include directing a gas flow including SiCl4 and a diluent at the sample, applying a bias power to achieve a bias state for a first period while directing the flow of SiCl4 and the diluent at the sample, followed by applying a source power to achieve a source state for a second period, followed by achieving a recovery state for a third period without applying the bias power or the source power. In some embodiments, the source power is not applied during the bias state, and the bias power is not applied during the source state.

[0013] In some embodiments, the bias power may be from about 100 watts (W) to about 5,000 watts (W), from about 200 W to about 2,000 W, from about 300 W to about 1,500 W, from about 500 W to about 1,250 W, or from about 600 W to about 1,000 W.

[0014] Some embodiments are described herein with reference to a sample having alternating silicon (Si) and silicon germanium (SiGe) layers. The sample may include a gate-all-around transistor, which may be etched using methods according to the disclosed embodiments. The methods described herein may also be beneficially used to etch many other types of substrates, such as substrates having Si and / or SiGe layers.

[0015] Referring now to the drawings, FIG. 1 is a cross-sectional view of a processing chamber 100 (e.g., a semiconductor processing chamber) having one or more chamber components according to an embodiment of the present disclosure. The processing chamber 100 can be used for processes in which a corrosive plasma environment and / or corrosive chemicals are provided. For example, the processing chamber 100 can be a chamber for a plasma etch reactor (also called a plasma etcher). Examples of chamber components that may be exposed to plasma in the processing chamber 100 include a substrate support assembly 148, an electrostatic chuck (ESC), a ring (e.g., a process kit ring or a single ring), chamber walls, a base, a showerhead 130, a gas distribution plate, a liner, a liner kit, a shield, a plasma screen, a flow equalizer, a cooling base, a chamber viewport, a chamber lid, a nozzle, a process kit ring, etc.

[0016] In one embodiment, the processing chamber 100 includes a chamber body 102 and a showerhead 130 that enclose an interior volume 106. The showerhead 130 may or may not include a gas distribution plate. For example, the showerhead may be a multi-piece showerhead including a showerhead base and a showerhead gas distribution plate bonded to the showerhead base. Alternatively, the showerhead 130 may be replaced by a lid and a nozzle in some embodiments, or by multiple pie-shaped showerhead compartments and plasma generation units in other embodiments. The chamber body 102 may be fabricated from aluminum, stainless steel, or other suitable materials. The chamber body 102 generally includes a sidewall 108 and a bottom 110. Any of the showerhead 130 (or lid and / or nozzle), sidewall 108, and / or bottom 110 may include a multi-layer plasma-resistant coating.

[0017] An outer liner 116 may be disposed adjacent the sidewall 108 and protect the chamber body 102. The outer liner 116 may be a halogen-containing gas resistant material such as Al2O3 or YO3. In some embodiments, the outer liner 116 may be coated with a multi-layer plasma-resistant ceramic coating.

[0018] An exhaust port 126 may be defined in the chamber body 102 and may couple the interior volume 106 to a pumping system 128. The pumping system 128 may include one or more pumps and a throttle valve used to evacuate and regulate the pressure of the interior volume 106 of the processing chamber 100.

[0019] The showerhead 130 can be supported on the sidewall 108 of the chamber body 102 and / or on top of the chamber body. The showerhead 130 (or lid) can be opened to provide access to the interior volume 106 of the processing chamber 100 and can be closed to seal the processing chamber 100. A gas panel 158 can be coupled to the processing chamber 100 to provide process gases and / or carrier gases to the interior volume 106 via the showerhead 130 or the lid and nozzles. Examples of process gases that can be supplied by the gas panel 158 and used to process substrates / samples in the processing chamber 100 include silicon-containing gases such as silicon tetrachloride (SiCl). Examples of carrier gases (also referred to herein as diluents) include N, He, Ar, and other gases that are inert to the process gases (e.g., non-reactive gases). The showerhead 130 includes a plurality of gas supply holes 132 throughout the showerhead 130. The showerhead 130 can be made of or include aluminum, anodized aluminum, an aluminum alloy (e.g., Al6061), or an anodized aluminum alloy. In some embodiments, the showerhead includes a gas distribution plate (GDP) bonded to the showerhead. The GDP can be, for example, Si or SiC. Additionally, the GDP can include a plurality of holes that align with the holes in the showerhead.

[0020] The substrate support assembly 148 is disposed within the interior volume 106 of the processing chamber 100 below the showerhead 130. The substrate support assembly 148 holds a substrate 144 (e.g., a wafer) during processing. The substrate support assembly 148 may include an electrostatic chuck that secures the substrate 144 during processing, a metal cooling plate bonded to the electrostatic chuck, and / or one or more additional components. An inner liner may cover the periphery of the substrate support assembly 148. The inner liner may be a halogen-containing gas-resistant material such as Al2O3 or YO3. In some embodiments, the substrate support assembly, portions of the substrate support assembly, and / or the inner liner may be coated with a metal layer and a barrier layer.

[0021] The processing chamber 100 may be an etch chamber configured to perform the pulse etch processes described herein. In embodiments, the pulse etch process is performed to etch one or more layers disposed on a substrate 144. For example, the substrate 144 may be a semiconductor wafer, a glass plate, a SiGe wafer, or other type of substrate. In one embodiment, the one or more layers 144 disposed on the substrate include a stack of alternating layers of Si and Ge.

[0022] FIG. 2A shows a cross-sectional view of an article 200 including a substrate 206 having an alternating stack of silicon (Si) and silicon germanium (SiGe) layers. In one embodiment, article 200 corresponds to substrate 144 of FIG. 1. Substrate 206 includes Si layers 260, 240, and 220 stacked on top of SiGe layers 250, 230, and 210 in stack 290. In some embodiments, the Si and SiGe layers may be in the form of nanosheets (e.g., layers having thicknesses in nanometers). In one embodiment, the Si layers may be 0% to 200% thicker than the SiGe layers. In one embodiment, the Si layers are about 20% thicker than the SiGe layers. In one embodiment, all of the Si layers have approximately the same thickness. All of the SiGe layers may have approximately the same thickness, which may be different from the thickness of the Si layers. Alternatively, the thicknesses of the different Si layers may be different and / or the thicknesses of the different SiGe layers may be different. In other embodiments, the thickness of the Si layer and the SiGe layer may be approximately the same as each other.

[0023] A patterned mask 280 (also called an etch mask) can cover the upper layer 260 of the stack 290. The patterned mask 280 can be a soft mask or a hard mask. Acceptable hard masks include polysilicon hard masks and metal hard masks, such as tungsten hard masks and titanium nitride hard masks. The patterned mask 280 includes open areas 270 that expose the underlying layers to etching chemicals during the etching process. Additionally, the patterned mask 280 includes cover areas that protect the underlying layers from the etching chemicals. Areas of the stack 290 that are not protected by the patterned mask 280 below the open areas 270 can undergo the etching process.

[0024] Article 200 can be etched through patterned mask 280 to form cavities or trenches approximately similar in shape to the openings in patterned mask 280. The etchant will also etch patterned mask 280, typically at an etch rate.

[0025] 2B shows a cross-sectional view of an article 204 including a substrate 206 having a stack of alternating Si layers 260, 240, 220 and SiGe layers 250, 230, 210, etched according to embodiments of the present disclosure, particularly the method described in FIG. 5. In this process, a cavity 400 was etched into the Si and SiGe layers. In one embodiment, the cavity 400 has a tapered cross-sectional shape with a U-shaped profile, with the bottom of the cavity being slightly narrower than the top of the cavity. Notably, the sidewalls of the trench or hole formed from the etching process described in embodiments herein are nearly vertical, in contrast to sidewalls produced by conventional etching processes.

[0026] Figure 3A shows a sample having multiple layers to be etched and may correspond to a perspective view of an embodiment of article 204. Figure 3B shows the sample of Figure 3A after being etched with a first etching process according to an embodiment of the present disclosure.

[0027] Figure 4A shows the sample of Figure 3B after further deposition of layers and before a second etching process, and Figure 4B shows the sample of Figure 4A after etching in a second etching process according to an embodiment of the present disclosure.

[0028] FIG. 3A illustrates an article 300, such as a gate-all-around transistor. The article 300 includes a stack of alternating Si layers 310, 330, 350, 370 and SiGe layers 320, 340, 360. The layers of the article 300 can be stacked on a substrate 380, which can be formed of SiGe, Si, glass, or other materials. In embodiments, the Si layers 310, 330, 350, 370 and the SiGe layers 320, 340, 360 can be in the form of nanosheets. In one embodiment, the Si layers can be 0% to 200% thicker than the SiGe layers. In one embodiment, the Si layers can be about 20% thicker than the SiGe layers. In one embodiment, all of the Si layers have approximately the same thickness. Also, all of the SiGe layers have approximately the same thickness, which may differ from the thickness of the Si. Alternatively, the thicknesses of the different Si layers can be different and / or the thicknesses of the different SiGe layers can be different. In other embodiments, the Si layer and the SiGe layer may have approximately the same thickness. The article 300 of Figure 3A can be etched according to the method 500 of Figure 5 after a patterned mask (not shown) is placed on an upper layer (such as the Si layer 310 shown). Figure 3B shows the article 300 after being etched according to the method 500 of Figure 5. As can be seen in Figure 3B, the Si layers 310, 330, 350, and 370 and the SiGe layers 320, 340, and 360 are etched to form multiple spaces (e.g., trenches) 390. A single space 390 may be etched, or multiple spaces may be etched.

[0029] FIG. 4A illustrates an article 400, such as a gate-all-around transistor, according to an embodiment of the present disclosure. The article 400 can include a patterned mask 414 (e.g., a hard mask) and spacers 412. The spacers 412 can be approximately perpendicular to a trench 490 (e.g., corresponding to trench 390 in FIG. 3B). The patterned mask 414 can be along the entire length of the spacer 412 or along a portion of the length of the spacer 412. Multiple spacers 412 can be offset from one another by gaps 492. While only two spacers are shown, a device under fabrication typically includes many such spacers. The spacers 412 can surround Si layers 410, 430, 450, and 470 and SiGe layers 420, 440, and 460. The article 400 can also include shallow trench isolation 416 formed in or on a substrate 480, which can be formed of SiGe, Si, glass, or other materials. In embodiments, article 400 can be etched according to method 500 of Figure 5. Figure 4B illustrates article 400 after it has been etched according to embodiments described herein. In Figure 4B, Si layers 410, 430, 450, 470 and SiGe layers 420, 440, 460 have been etched, and excess layers outside spacer 412 have been removed. In this manner, the Si and SiGe layers are substantially flush with spacer 412, and no Si and / or SiGe layers are present outside spacer 412.

[0030] 5 is a flowchart illustrating a method 500 for etching a sample and / or article according to an embodiment of the present disclosure. In method 500, in block 501, the sample and / or article is inserted into an etching chamber. The etching chamber may be a plasma etching chamber. In block 502, the chamber is brought to a target temperature and pressure (e.g., using one or more heating elements and / or pumps). The pressure in the chamber may be from about 0.1 mT to about 500 mT, from about 1 mT to about 400 mT, from about 5 mT to about 300 mT, from about 10 mT to about 200 mT, from about 25 mT to about 100 mT, or from about 1 mT to about 100 mT, or any subrange or value therein. The chamber temperature may be from about −50° C. to about 300° C., from about −25° C. to about 250° C., from about 0° C. to about 120° C., from about 25° C. to about 100° C., or from about 50° C. to about 75° C., or any subrange or value described herein. In one embodiment, the target substrate temperature is at least 40° C. It has been found that temperatures below 40° C. may increase the iso-dense etch rate load.

[0031] Once the target temperature and pressure are reached, the plasma etching process can proceed by forming a plasma comprising SiCl4 and one or more additional gases (e.g., carrier gas or diluent). The plasma etching process may be a pulsed plasma etching process. In one embodiment, a plasma etching pulse / cycle is performed on the sample and / or article at block 503. At block 504, a plasma etching pulse is performed by directing a gas flow comprising SiCl4 and a diluent at the sample and / or article. The total gas supply flow rate of SiCl4 and the diluent is about 50 sccm to about 2000 sccm, about 100 sccm to about 1500 sccm, about 150 sccm to about 1250 sccm, about 200 sccm to about 1000 sccm, about 250 sccm to about 750 sccm, or any subrange or value therein. The amount of SiCl4 in the total gas feed stream is from about 5 mol% to about 80 mol%, from about 5 mol% to about 70 mol%, from about 5 mol% to about 60 mol%, from about 5 mol% to about 50 mol%, from about 5 mol% to about 40 mol%, from about 10 mol% to about 80 mol%, from about 10 mol% to about 70 mol%, from about 20 mol% to about 70 mol%, from about 20 mol% to about 60 mol%, from about 30 mol% to about 50 mol%, or any subrange or value therein.

[0032] The diluent can include Ar, He, or a combination thereof. Additionally or alternatively, the diluent can include one or more additional inert gases. The amount of Ar in the total gas feed flow can be about 5 mol% to about 15 mol%, about 7.5 mol% to about 12.5 mol%, or about 9 mol% to about 11 mol%, or any subrange or value therein. The amount of He in the total gas feed flow can be about 5 mol% to about 90 mol%, about 10 mol% to about 80 mol%, about 15 mol% to about 75 mol%, about 25 mol% to about 65 mol%, about 30 mol% to about 60 mol%, about 35 mol% to about 55 mol%, or any subrange or value therein.

[0033] In block 506, bias power is applied to the sample / article to achieve a first duration bias condition. The bias power may be about 10 watts (W) to about 5,000 watts (W), about 200 W to about 2,000 W, about 300 W to about 3,000 W, about 400 W to about 2,500 W, about 500 W to about 2,000 W, about 600 W to about 1,500 W, or about 750 W to about 1,250 W, or any subrange or value therein. A higher bias power results in a straighter profile (e.g., a more vertical trench sidewall profile), a less curvature-prone profile, and less selectivity to the pattern mask. The bias power may be a time-averaged power. The bias frequency may be about 400 kHz to about 60 MHz, about 400 kHz to about 40 MHz, about 400 kHz to about 35 MHz, about 400 kHz to about 27 MHz, about 400 kHz to about 20 MHz, or about 800 kHz to about 10 MHz, or any subrange or value described herein. Two example frequencies that can be used are 13 MHz and 2 MHz. It has been shown that a 2 MHz frequency can be less selective to patterned masks than a 14 MHz frequency. The first period during which bias power is applied may be about 10 μsec (μsec) to about 1 msec (msec), about 30 μsec to about 1 msec, about 50 μsec to about 1 msec, about 70 μsec to about 1 msec, or about 85 μsec to about 1 msec, or any subrange or value described herein. In block 508, the bias power is terminated after the first period has expired.

[0034] After terminating the bias power, in block 510, source power is applied to achieve a source state for a second period. The source power may be about 10 W to about 5,000 W, about 200 W to about 2,000 W, about 300 W to about 3,000 W, about 400 W to about 2,500 W, about 500 W to about 2,000 W, about 600 W to about 1,500 W, or about 750 W to about 1,250 W, or any subrange or value therein. The source power may be a time-averaged source power (e.g., source power × duty cycle). The source frequency may be about 10 MHz to about 5 MHz, or about 13 MHz, or any subrange or value therein.

[0035] In some embodiments, the second period of time during which source power is applied may be between about 10 μsec and about 1 ms, between about 30 μsec and about 1 ms, between about 50 μsec and about 1 ms, between about 70 μsec and about 1 ms, or between about 85 μsec and about 1 ms, or any subrange or value described herein.

[0036] In some embodiments, the ratio of the first period to the second period can be about 1:10 to about 10:1, about 1:9 to about 9:1, about 1:8 to about 8:1, about 1:7 to about 7:1, about 1:6 to about 6:1, about 1:5 to about 5:1, about 1:4 to about 4:1, about 1:3 to about 3:1, about 1:2 to about 2:1, or about 1:1, or any subrange or value described herein.

[0037] After the second time period in block 510 ends, the source power is turned off in block 511. Then, bias power and source power are not applied to the chamber and a recovery state is achieved in a third time period in block 512. The third time period may be from about 10 μsec to about 1 msec, from about 50 μsec to about 1 msec, from about 60 μsec to about 1 msec, from about 70 μsec to about 1 msec, from about 80 μsec to about 1 msec, or from about 85 μsec to about 1 msec, or any subrange or value therein.

[0038] In some embodiments, the ratio of the third period to the sum of the first and second periods is about 1:1 to about 90:1, about 1:1 to about 80:1, about 1:1 to about 70:1, about 1:1 to about 60:1, about 1:1 to about 50:1, about 1:1 to about 40:1, about 1:1 to about 30:1, about 1:1 to about 20:1, about 1:1 to about 10:1, or about 1:1 to about 5:1, or any subrange or value therein. In some embodiments, the third period of the recovery state is longer than either the first or second period, thereby reducing the electron temperature. A reduced electron temperature correlates with a reduced ion temperature, which can improve directional control during etching.

[0039] A three-state etch pulse (505-512) comprising first a bias state (506, 508), then a source state (510, 511), and then a recovery state (512) has been shown to improve directional control of etching of samples, particularly samples comprising alternating stacks of Si and SiGe layers when using SiCl chemistry.

[0040] After the third period, in block 513, the sample / article may be inspected to determine whether the target amount has been etched. Alternatively, or additionally, whether the target amount of the sample / article has been etched may be determined based on the time the etching process was run. If the etching process has not been run for the target time (e.g., according to the etching recipe), the target amount of the sample / article may not have been etched. If the target amount of the sample / article has not been etched, the plasma etching pulse process of blocks 504-512 may be repeated. If the target amount of the sample / article has been etched, the sample / article is removed from the etching chamber in block 514.

[0041] The pulsed plasma etch process described in method 500 achieves low plasma density by performing a bias state before the source state and using a long recovery state (e.g., greater than 50% of the total pulse time). High plasma densities (e.g., as achieved with continuous wave source power) reduce the etch rate due to increased deposition from the feed gas (SiCl), which is undesirable. However, the low plasma density achieved in embodiments results in an increased etch rate of approximately 0.1 nm / sec. Furthermore, the pulsing scheme described herein generates a highly directional ion flux with low plasma density in the bias state, while maintaining low plasma density in the recovery state.

[0042] FIG. 6 illustrates a plasma etch pulse cycle according to an embodiment of the present disclosure. In FIG. 6, the plasma etch pulse cycle has three states. In the first state, a bias state 605 is achieved. The bias state 605 can be achieved by block 506, as described with reference to FIG. 5. The second state in FIG. 6 is a source state 610. The source state can be achieved by block 510, as described with reference to FIG. 5. The third state of the plasma etch pulse is a recovery state 615. The recovery state can be achieved as described with reference to blocks 511 and 512. In FIG. 6, the duration of the bias state 605 can be about 2% to about 10%, or about 5% of the plasma etch pulse cycle. The duration of the source state 610 is about 2% to about 10%, or about 5%, of the plasma etch pulse cycle, and the duration of the recovery state 615 is about 80% to about 96%, or about 90% of the plasma etch pulse cycle.

[0043] The foregoing description provides numerous specific details, such as examples of particular systems, components, methods, etc., to provide a thorough understanding of some embodiments of the present invention. However, it will be apparent to one of ordinary skill in the art that at least some embodiments of the present invention may be practiced without these specific details. In other instances, well-known components or methods have not been described in detail or have been shown in simple block diagram form in order to avoid unnecessarily obscuring the present invention. Thus, the specific details described are merely examples. Particular implementations may vary from these illustrative details and still be construed as within the scope of the present invention.

[0044] References throughout this specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment. Thus, the appearances of the phrase "in one embodiment" or "in an embodiment" in various places throughout this specification do not necessarily all refer to the same embodiment. Furthermore, the term "or" does not mean an exclusive "or." When the term "about" or "approximately" is used herein, this means that the stated nominal value is accurate to within 10%.

[0045] Although the operations of the methods herein are shown and described in a particular order, the order of the operations of each method may be changed so that certain operations are performed in the reverse order, or so that certain operations are performed at least in part concurrently with other operations. In other embodiments, instructions or sub-operations of separate operations may be performed intermittently and / or interleaved.

[0046] It should be understood that the foregoing description is intended to be illustrative, and not limiting. Many other embodiments will become apparent to those skilled in the art upon reading and understanding the above description. The scope of the present invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

1. 1. A method for etching a sample, comprising: performing a plasma etching pulse, Silicon tetrachloride (SiCl ４ directing a gas flow containing the gas and a diluent toward the sample; SiCl ４ and applying a bias power to achieve a bias condition for a first period of time while directing a flow of diluent toward the sample; applying source power to achieve a source state for a second period; performing a plasma etch pulse including achieving a recovery state for a third period without applying bias power and source power; The method includes repeating the plasma etching pulses until a desired amount of the sample is etched.

2. The method of claim 1 , wherein no source power is applied during the bias state and no bias power is applied during the source state.

3. The method of claim 1 , wherein the bias power is between about 100 W and about 5000 W.

4. The method of claim 1 , wherein the bias frequency is from about 400 kHz to about 60 MHz.

5. The method of claim 1 , wherein the plasma etching pulses are performed at a pressure of about 0.1 mT to about 500 mT.

6. The method of claim 1, wherein the plasma etching pulse is performed at a temperature of about -50°C to about 300°C.

7. The method of claim 1 , wherein the source power is from about 100 W to about 5000 W.

8. The method of claim 1 , wherein the diluent comprises argon (Ar), helium (He), or a mixture thereof.

9. The gas flow contains SiCl in an amount of about 5 mol % to about 80 mol %. ４ The method of claim 1 , comprising:

10. 9. The method of claim 8, wherein the gas flow comprises Ar in an amount between about 5 mol% and about 15 mol% and He in an amount between about 5 mol% and about 90 mol%.

11. 10. The method of claim 1, wherein the first period of time is from about 10 μsec to about 1 ms, the second period of time is from about 10 μsec to about 1 ms, and the third period of time is from about 10 μsec to about 1 ms.

12. 10. The method of claim 1, wherein the ratio of the first time period to the second time period is from about 1:10 to about 10:

1.

13. 10. The method of claim 1, wherein the ratio of the third period of time to the sum of the first period of time and the second period of time is from about 1:1 to about 90:

1.

14. The method of claim 1 , wherein the gas flow rate is between about 50 sccm and about 2000 sccm.

15. The method of claim 1 , wherein the portion of the sample etched by the plasma etching pulses comprises multiple alternating layers of silicon and silicon germanium.

16. The method of claim 1 , wherein the plasma etching process creates a U-shaped profile in the sample.

17. 1. A method for etching a sample, comprising: performing a plasma etching pulse, applying a bias power to achieve a bias condition for a first period while directing a flow of gas and diluent toward the sample; applying source power to achieve a source state for a second period; performing a plasma etch pulse including achieving a recovery state for a third period without applying bias power and source power; repeating the plasma etching pulses until a target amount of the sample is etched; The gas is SiCl ４ wherein the diluent comprises Ar, He and mixtures thereof.

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