Plasma etching method

Abstract

A method of plasma etching a workpiece is disclosed. The method includes the steps of placing the workpiece on a substrate support within a plasma chamber, wherein the workpiece comprises a SiC substrate; introducing SF6, O2, and He process gases into the plasma chamber; plasma etching the SiC substrate by alternating between (i) applying a bias RF power to the substrate support to generate a reactive ion etch plasma in the plasma chamber and etching the SiC substrate at a first plasma chamber pressure for a first time period; and (ii) applying a source RF power to the plasma chamber to generate an inductively coupled plasma in the plasma chamber and applying a bias RF power to the substrate support, and etching the SiC substrate at a second plasma chamber pressure for a second time period, thereby reducing a surface roughness of the SiC substrate.

Description

Technical Field

[0001] Embodiments of this application relate to a plasma etching method. Background Technology

[0002] Silicon carbide (SiC) is an increasingly common wide-bandgap semiconductor material in many applications, from power electronics to integrated optics and quantum technologies. Furthermore, due to its tolerance to high temperatures, high power, and high radiation, SiC is an excellent choice for environments where other materials simply cannot operate.

[0003] To fabricate these devices, several complex, typically very thin, material layers must be epitaxially grown on a bulk SiC wafer. SiC can also be used as a substrate for growing other III-V materials, such as gallium nitride (GaN) or aluminum nitride (AlN). This is particularly desirable when the cost of a given material substrate is exceptionally high.

[0004] Therefore, to achieve high-quality epitaxial growth and high-performance devices, it is crucial to make the SiC surface as close as possible to perfect atomic-level smoothness. In practice, in manufacturing environments, the surface roughness Ra should be approximately 1 nm. Specifically, in power devices, it has been shown that the substrate surface roughness itself has a significant impact on the final device performance.

[0005] SiC wafers are first cut from large ingots and then ground, followed by mechanical or chemical mechanical polishing. Defects on the polished surface can propagate through the epitaxial layer and cause "fatal defects," which can lead to device malfunctions or even longer-term reliability problems. Therefore, novel surface treatment steps are needed to address surface roughness and defects in order to reduce costly yield losses.

[0006] K. Kanarik et al., in their paper "Atomic Layer Etching: Rethinking Etching Techniques" (Physical and Chemical Letters, Vol. 9 / Issue 16), describe how plasma-based surface smoothing of SiC reduces root-mean-square roughness by 83%. The work utilizes atomic layer etching (ALE) with Cl / Ar chemicals and pulsed stage power. A drawback of the demonstrated process is its slowness. The process requires 200 etching cycles. Each cycle removes only 0.067 nm, close to the theoretical limit of 0.068 nm. Since each cycle takes 12 seconds, this process takes over 40 minutes per wafer, resulting in a material removal rate of 0.02 μm / hour.

[0007] GB2601041 describes the fabrication of SiC wafers for epitaxial growth via plasma processing on an ICP tool. Six plasma processes designed to smooth the surface of SiC are disclosed. All of these processes use a specific hydrogen composition, which has been found to play a significant role in smoothing. The six disclosed processes have been found to reduce roughness by 34% to 84%, with the most successful process using an HBr / O2 / SF6 chemical mixture (in a 4:1:1 ratio).

[0008] A. Osipov et al.: High-Temperature Etching of SiC in SF6 / O2 Inductively Coupled Plasma (Nature 2020) disclosed SF6 / O2 plasma etching, which enables the etching of trenches into SiC surfaces at high temperatures. A 92% reduction in the root-mean-square surface roughness in the trenches was observed when the stage temperature was increased to 300°C. High stage temperature is necessary for this process because temperatures between approximately 15°C and 250°C have been reported to increase surface roughness.

[0009] Therefore, this technical field requires plasma-based surface fabrication processes to overcome the aforementioned drawbacks. Specifically, it requires a cost-effective method to smooth SiC wafers to <1 nm after mechanical polishing to support epitaxial growth of SiC thin films with reduced defect rates, thereby producing more reliable SiC devices. Summary of the Invention

[0010] In a first aspect of the invention, a method for plasma etching a workpiece is provided, the method comprising the steps of: placing the workpiece on a substrate support within a plasma chamber, wherein the workpiece comprises a SiC substrate; introducing SF6, O2, and He process gases into the plasma chamber; and plasma etching the SiC substrate alternately between the following steps to reduce the surface roughness of the SiC substrate: (i) applying bias RF power to the substrate support to generate reactive ion etching (RIE) plasma in the plasma chamber, and etching the SiC substrate at a first plasma chamber pressure for a first time period; and (ii) applying source RF power to the plasma chamber to generate inductively coupled plasma (ICP) in the plasma chamber, and applying bias RF power to the substrate support, and etching the SiC substrate at a second plasma chamber pressure for a second time period.

[0011] The inventors have discovered that etching in a cyclic process (using a first RIE etching followed by a second ICP etching) advantageously reduces the surface roughness of SiC substrate workpieces to sub-nanometer levels (i.e., <1 nm) without requiring the use of often time-consuming atomic layer etching techniques. Helium has been found to be particularly beneficial for reducing surface roughness compared to heavier inert gases.

[0012] Furthermore, the proposed process achieves a smoothing process in a shorter time compared to either RIE or ICP alone, as no pre-etching argon treatment is required, as described in this paper.

[0013] Advantageously, the process can be hydrogen-free. Advantageously, the process can be chlorine-free.

[0014] The process can preferably be performed before epitaxial growth.

[0015] The pressure in the first plasma chamber can be more than an order of magnitude greater than the pressure in the second plasma chamber.

[0016] The pressure in the first plasma chamber can be between 100 mTorr and 400 mTorr, for example, about 200 mTorr.

[0017] The pressure in the second plasma chamber can be between 2 mTorr and 10 mTorr, for example, about 5 mTorr.

[0018] Preferably, the second time period is longer than the first time period.

[0019] The first time period can be between 5 seconds and 60 seconds, for example, between 10 seconds and 20 seconds.

[0020] The second time period can be between 20 seconds and 120 seconds, for example, between 40 seconds and 50 seconds.

[0021] The substrate support can be maintained at a temperature between 10 degrees Celsius and 50 degrees Celsius. Advantageously, this method allows for variations in the stage temperature without degrading the smoothing performance.

[0022] The substrate support can be maintained at a temperature between 15 and 25 degrees Celsius. This process advantageously avoids high substrate temperatures. Lower substrate temperatures are beneficial to materials and devices due to lower thermal budgets or when using wafer bonding materials.

[0023] During step (ii), the source RF power may be in the range of 1000W to 3000W.

[0024] During step (i), the bias RF power may be in the range of 100W to 500W.

[0025] During step (ii), the bias RF power may be in the range of 300W to 1000W.

[0026] A pause may occur during the cycle between steps (i) and (ii), during which the plasma chamber pressure may be adjusted between the first and second plasma chamber pressures while zero-source RF power and bias RF power are applied.

[0027] The pause can last for several seconds, for example, from 2 to 10 seconds, optionally 5 seconds.

[0028] During step (ii), the bias RF power may be applied several seconds (e.g., 2 to 10 seconds, optionally 5 seconds) after the source RF power is applied.

[0029] The SF6, O2, and He process gases are introduced into the plasma chamber at flow rates between 40 sccm to 60 sccm, 10 sccm to 20 sccm, and 90 sccm to 110 sccm, respectively.

[0030] Before introducing SF6, O2, and He process gases into the plasma chamber, the following steps may be performed: introducing Ar gas into the plasma chamber and applying bias RF power to the substrate support to generate reactive ion etching plasma in the plasma chamber.

[0031] Optionally, zero-source RF power is applied during step (i).

[0032] Optionally, during step (i), a source RF power of less than 500 watts is applied.

[0033] In a second aspect of the invention, an inductively coupled plasma apparatus for plasma etching of a workpiece is provided, the apparatus comprising: a plasma chamber; a platform assembly disposed within the plasma chamber and configured to receive the workpiece, wherein the workpiece comprises a SiC substrate; a gas delivery system for introducing process gases into the plasma etching chamber; a plasma generation device for maintaining plasma within the plasma chamber for etching the SiC substrate; and a controller configured to control the apparatus to perform plasma etching on the SiC substrate to reduce the surface roughness of the SiC substrate by alternating between the following steps: (i) applying bias RF power to a substrate support to generate reactive ion etching plasma in the plasma chamber while applying zero-source RF power, and etching the SiC substrate at a first plasma chamber pressure for a first time period; and (ii) applying source RF power to the plasma chamber to generate inductively coupled plasma in the plasma chamber, and applying bias RF power to the substrate support, and etching the SiC substrate at a second plasma chamber pressure for a second time period.

[0034] In a third aspect of the invention, a method for plasma etching a workpiece is provided, the method comprising the steps of: placing the workpiece on a substrate support within a plasma chamber, wherein the workpiece comprises a SiC substrate; introducing SF6, O2, and He process gases into the plasma chamber; applying source RF power to the plasma chamber to generate inductively coupled plasma in the plasma chamber; applying bias RF power to the substrate support; and etching the SiC substrate to thereby reduce the surface roughness of the SiC substrate.

[0035] While the high-pressure RIE etching of the first and second aspects advantageously accelerates the ICP etching process and improves surface uniformity, the inventors should understand that it can be omitted and that the use of SF6, O2, and He process gases in the ICP etching process remains advantageous. This process does not contain hydrogen, and the use of He provides optimal results compared to the use of heavier inert gases (such as Ar). Attached Figure Description

[0036] The following schematic diagrams will now be used to describe exemplary embodiments of the present invention by way of example only:

[0037] Figure 1 and 2 This is a side view of an example inductively coupled plasma device used for plasma etching of workpieces.

[0038] Figure 3 This is a flowchart of a method for plasma etching of a workpiece;

[0039] Figure 4 The changes in source RF power, bias RF power, and chamber pressure over time are shown during a plasma etching process on a workpiece.

[0040] Figure 5 The power spectral density data of the plasma etching method for workpieces are shown compared with several different test processes. Detailed Implementation

[0041] Figure 1 and 2 The diagram illustrates an inductively coupled plasma device 1 according to an example embodiment. This invention can be applied to the applicant's... Synapse TM This is executed in the adapted version of the etching process module. Well-known features, such as the exhaust gas pumping system, are not shown. Figure 1 and 2 However, it should be well understood by technical personnel in the relevant field.

[0042] Device 1 includes a plasma etching chamber 11 with multiple internal surfaces. The device includes a first gas inlet arrangement 10, a second gas inlet arrangement 12, a ceramic annular housing 18, an RF antenna 14, a platform RF electrode 16, and a substrate support 20 for supporting the workpiece (i.e., structure) 28 undergoing etching. Figure 1 and 2 In the embodiment shown, the substrate support 20 is an electrostatic chuck. A stage RF electrode 16 is used to control the orientation of the etch ions. This, in turn, controls the extent of physical etching of the workpiece achieved during processing. Higher stage power will increase the etching rate. The electrostatic chuck is equipped with helium back-side cooling, which is used to regulate the temperature of the wafer.

[0043] The plasma etching chamber 11 includes an upper wall or cover 13. An annular housing 18 is immersed in the chamber 11 and hangs downward from the upper wall. The annular housing 18 defines a circular region on the interior of the upper wall.

[0044] exist Figure 1 and 2 In the example embodiment shown, the first gas inlet arrangement 10 is an inner gas filling chamber and the second gas inlet arrangement 12 is an outer gas filling chamber. Each gas inlet arrangement includes multiple gas inlets, each terminating in an opening through which process gas enters the interior of chamber 11. The inner filling chamber 10 is located within a circular region defined by an annular housing 18. The gas inlets of the inner gas filling chamber 10 are positioned inward from the annular housing 18 as multiple openings arranged in a circular pattern. The outer filling chamber 12 is located outside the circular region defined by the annular housing 18. The gas inlets of the outer gas filling chamber 12 are positioned outward from the annular housing 18 as multiple openings arranged in a circular pattern. The inner gas filling chamber may have eight gas inlets, while the outer gas filling chamber may have approximately ten times more gas inlets. However, it should be understood that the first and second gas inlet arrangements may have any suitable number of gas inlets. A mass flow regulator (not shown) is coupled to the gas inlet arrangements and is used to control the flow rate of gas into chamber 11.

[0045] Further illustration of etching chamber 11 is provided below. Figure 2 middle, Figure 2The diagram illustrates the handling of a workpiece 28 present in a chamber. The chamber includes one or more chamber walls 24, within which the workpiece 28 is placed on a substrate support 20. Plasma 26 is ignited and maintained in chamber 11 by RF power coupled from an RF power source (not shown) to the chamber via an RF antenna 14 (i.e., a coil) housed within an annular housing 18. In an exemplary embodiment, the RF power source is a high-frequency generator operating at 13.56 MHz. The platform RF electrodes are driven at the same frequency from a separate power supply. The annular housing 18 acts as a window allowing RF power to be coupled into the chamber. Etching process gases, including SF6, O2, and He, enter chamber 11 through gas inlets in the inner gas filling chamber 10 and the outer gas filling chamber 12. A controller 30 controls the cyclic etching process. As part of the operation of the controller 30, the controller controls the flow rate of the etching process gases into chamber 11.

[0046] In an exemplary embodiment, workpiece 28 is a 150mm wafer comprising a SiC substrate (although other wafer sizes, such as 100mm or 200mm, are within the scope of this invention). In an exemplary embodiment, the SiC substrate has a thickness of 300μm to 500μm.

[0047] In an exemplary embodiment of the present invention, the method for plasma etching a workpiece includes a first step: placing the workpiece 101 on a substrate support within a plasma chamber; placing the workpiece on an electrostatic chuck at a temperature between 10 degrees Celsius and 35 degrees Celsius and then clamping it; and using a handling robot to place the workpiece onto an electrostatic chuck within a vacuum chamber.

[0048] In the second step, SF6, O2, and He process gases are introduced into the plasma chamber (e.g., simultaneously) via a mass flow regulator. The SF6, O2, and He gases enter the plasma chamber at flow rates of approximately 40 sccm to 60 sccm, 10 sccm to 20 sccm, and 80 sccm to 120 sccm, respectively, until the target pressure (approximately 200 mTorr (between 100 and 400 mTorr) in an exemplary embodiment) is reached. The target pressure can be maintained by adjusting the pumping speed and / or by adjusting the mass flow regulator. Subsequently, the SiC substrate is plasma etched using a cyclic process alternating between two etch modes.

[0049] In the first mode (RIE etching mode), bias RF power 105 is applied to the substrate support to generate reactive ion etching plasma in the plasma chamber. The plasma is generated near the substrate support. Zero-source RF power may be applied during this mode, or alternatively, a low-source RF power in the range of 0 to 500 watts may be applied. The SiC substrate is etched by RIE etching for a first relatively short duration, for example, 5 to 60 seconds. In the first mode, the chamber is maintained at a first relatively high pressure (approximately 200 mTorr in an exemplary embodiment). At the end of the first duration, bias RF power 107 is turned off and the RIE plasma is extinguished.

[0050] After the initial duration, there is a first intermediate time period. The chamber pressure is reduced by 10⁹ to approximately 2 to 10 mTorr by changing the flow rate of the process gas into the chamber, in preparation for ICP etching. In an example embodiment, this intermediate step lasts approximately 5 seconds (for efficiency reasons, it is best to minimize the duration of the power-off state).

[0051] After the first intermediate time period, etching begins in the second mode. In the second mode (ICP etching mode), source RF power is applied to the plasma chamber to generate inductively coupled plasma within the plasma chamber. After a short delay (approximately 5 seconds in an exemplary embodiment) in which the ICP plasma is formed, bias RF power is applied to the substrate support (or alternatively, power can be applied simultaneously). The SiC substrate is etched by ICP etching for a second longer duration, for example, 20 to 120 seconds. In the second mode, the chamber is maintained at a second lower pressure for the duration of the ICP etching. After the second duration, both power supplies are turned off (e.g., simultaneously) and the ICP plasma is extinguished.

[0052] After the second duration, there is a second intermediate time period. The chamber pressure is increased back to the first higher pressure (by changing the flow rate of the process gas into the chamber) to prepare for RIE etching. In an example embodiment, this intermediate step lasts approximately 5 seconds (for efficiency reasons, it is best to minimize the duration of the power-off state).

[0053] At this point, the controller determines whether 115 has completed the required number of cycles to achieve the desired SiC wafer surface treatment level. For example... Figure 3 As shown, the process stops when the required number of cycles has been performed; otherwise, the process continues cycling between etching in RIE mode and etching in RIE-assisted ICP mode. Alternatively, the process may terminate after in-situ surface roughness measurements indicate acceptable smoothing.

[0054] At the end of the process, 117 workpieces were removed from the vacuum chamber by a transport robot.

[0055] Example etch cycle shown in Figure 4 The first duration (i.e., for RIE etching) is about 20 seconds, and the second duration (i.e., for ICP etching) is about 45 seconds, with an intermediate time period of about 5 seconds in between during which the chamber pressure is adjusted.

[0056] Experiments were performed following the methods described above, with the first duration (i.e., for RIE etching) set to approximately 10 seconds and the second duration (i.e., for ICP etching) set to approximately 50 seconds. The experiments were conducted at room temperature (i.e., a stage temperature of approximately 20 degrees Celsius). Atomic force microscopy was used in non-contact scanning mode (ParkSystems XE7 AFM) at multiple scales (1 x 1 μm). 2 10x10μm 2 and 40x40μm 2 The surface roughness Rq and Ra of the samples were measured. Table 1 below shows the surface roughness changes for two test wafers with initial Ra of 25 nm and 1.1 nm.

[0057] Table 1 also shows the corresponding surface roughness changes for several test process reports: ICP process alone, including 10 minutes of pre-etching argon heating / surface treatment; and RIE, followed by ICP process.

[0058] Individual ICP process parameters are chamber pressure from 2 mTorr to 10 mTorr, source RF power of approximately 1500 W (ranging from 1000 W to 3000 W), and bias RF power of approximately 600 W (ranging from 300 W to 1000 W) to the substrate support. Gas flow rates remained unchanged at approximately 50 sccm (SF6), 15 sccm (O2), and 100 sccm (He).

[0059] The RIE process parameters are a chamber pressure of approximately 200 mTorr (in the range of 100 mTorr to 300 mTorr) and a bias RF power of approximately 300 W (in the range of 100 W to 500 W). The gas flow rate remained unchanged at approximately 50 sccm (SF6), approximately 15 sccm (O2), and approximately 100 sccm (He).

[0060] Table 1

[0061]

[0062] It is known to use a pre-etching step to clean / heat the material to be etched. Using pre-etching Ar plasma can help reduce high-frequency roughness. However, it has been found that the process claimed in this invention does not benefit from the pre-etching Ar plasma step, and therefore, a similar smoothing result can be achieved with a faster process. Switching between operating modes takes time, so the full 10 minutes cannot be saved; however, in the scenarios shown below, as shown in Table 1, a 30% reduction in process time can be achieved when using the method according to embodiments of the invention. Alternatively, the smoothing time can be extended to achieve a smoother surface.

[0063] The pre-etching step is performed immediately before the SF6 / O2 / He smoothing process using argon gas at a pressure of 10 millitor, utilizing a source RF power of 2kW and a bias RF power of 0 to 800W.

[0064] In some existing methods, the stage temperature has been found to be critical for smoothing (e.g., in Osipov et al.), where the Rms roughness at the etch front increased from 7.4 nm to 112.2 nm between 15 °C and 50 °C. It is speculated that the high power density used by Osipov (1 kW source RF for a 4x4 cm sample, approximately 62.5 W / cm²) contributes to this. 2 This causes damage to the etched surface. At a lower power density of 5.7 W / cm², this can also lead to damage. 2 Up to 17W / cm 2 Lowering the operating conditions and diluting SF6 and O2 with He significantly reduces the process's sensitivity to lower platen temperatures. Therefore, the process of this invention did not show a deterioration in surface smoothing performance when the platen temperature was increased to 50°C.

[0065] Figure 5 This displays power spectral density data for different processes, showing the relationship between roughness intensity and the reciprocal of the roughness wavelength. Line 201 shows the initial workpiece power spectral density. Improvements in surface roughness are indicated by the spectral lines below this line. Line 203 indicates a 20-minute RIE process (including a 10-minute pre-etch argon heating). (Approximately 2x10...) 6 m -1 Above the reciprocal of the wavelength, the intensity is higher than the control line, indicating that the sample becomes coarser in this morphology. The third line, 205, indicates a separate 20-minute ICP process (including a 10-minute pre-etch argon heating). Surface roughness is significantly improved, up to approximately 5x10⁻⁶. 5 m -1Or the inverse of the wavelength below, where surface roughness degrades. Line 207 shows a 10-minute RIE followed by a 10-minute ICP process. The results are inferior to the ICP process alone. According to an embodiment of the invention, line 209 indicates cyclic RIE and ICP processes, using the first and second time periods of each cycle lasting 10 seconds and 50 seconds respectively within a 10-cycle time period. Line 211 indicates the same process for 20 cycles. These processes all demonstrate significant improvements in surface roughness, especially for 1x10⁻¹⁰. 6 m -1 The above are the reciprocal values ​​of roughness.

[0066] The use of He was examined (compared to heavier inert gases such as Ar). Using the same SF6 and O2 flow rates as the standard process, but replacing He with 100 sccm Ar resulted in degradation in all scanned areas. Using a 25nm initial Ra wafer, the changes were -75% (1x1 mm²), -25% (10x10 mm²), and +30% (40x40 mm²). It is believed that the increased sputtering from heavier ions increases surface roughness. According to the invention, the use of He helps dilute the chemical etching components and minimizes isotropic etch pits.

[0067] The process duration will depend on the introduced wafer surface roughness and the specified final surface roughness. As can be seen in Table 1, using the same RIE-assisted ICP process, the roughness changes of wafer samples with 25 nm and 1.1 nm Ra produce different roughness changes. To achieve a surface roughness of <1 nm for the introduced wafer with 25 nm Ra, it will take more than 29 minutes because the wafer needs to be smoothed from 5.4 nm to 1.1 nm.

Claims

1. A method for plasma etching a workpiece, the method comprising the following steps: The workpiece is placed on a substrate support within the plasma chamber, wherein the workpiece includes a SiC substrate; SF6, O2, and He process gases are introduced into the plasma chamber; The surface roughness of the SiC substrate is reduced by alternating between the following steps: (i) Applying bias RF power to the substrate support to generate reactive ion etching plasma in the plasma chamber, and etching the SiC substrate under a first plasma chamber pressure for a first time period; and (ii) Apply source RF power to the plasma chamber to generate inductively coupled plasma in the plasma chamber, apply bias RF power to the substrate support, and etch the SiC substrate under a second plasma chamber pressure for a second time period.

2. The method according to claim 1, wherein the pressure of the first plasma chamber is more than an order of magnitude greater than the pressure of the second plasma chamber.

3. The method according to claim 1 or claim 2, wherein the pressure of the first plasma chamber is between 100 mTorr and 400 mTorr, for example about 200 mTorr.

4. The method according to claim 1 or claim 2, wherein the pressure of the second plasma chamber is between 2 mTorr and 10 mTorr, for example about 5 mTorr.

5. The method according to claim 1 or claim 2, wherein the second time period is longer than the first time period.

6. The method according to claim 1 or claim 2, wherein the first time period is between 5 seconds and 60 seconds, for example, between 10 seconds and 20 seconds.

7. The method according to claim 1 or claim 2, wherein the second time period is between 20 seconds and 120 seconds, for example, between 40 seconds and 50 seconds.

8. The method according to claim 1 or claim 2, wherein during the plasma etching, the substrate support is maintained at a temperature between 10 degrees Celsius and 50 degrees Celsius.

9. The method according to claim 1 or claim 2, wherein during the plasma etching, the substrate support is maintained at a temperature between 15 degrees Celsius and 25 degrees Celsius.

10. The method according to claim 1 or claim 2, wherein during step (ii), the source RF power is in the range of 1000W to 3000W.

11. The method according to claim 1 or claim 2, wherein during step (i), the bias RF power is in the range of 100W to 500W.

12. The method according to claim 1 or claim 2, wherein during step (ii), the bias RF power is in the range of 300W to 1000W.

13. The method according to claim 1 or claim 2, wherein there is a pause during the cycle between steps (i) and (ii), during which the plasma chamber pressure is adjusted between the first plasma chamber pressure and the second plasma chamber pressure while zero-source RF power and bias RF power are applied.

14. The method of claim 13, wherein the pause lasts from 3 to 7 seconds.

15. The method according to claim 1 or claim 2, wherein during step (ii), the bias RF power is applied 3 to 7 seconds after the source RF power is applied.

16. The method according to claim 1 or claim 2, wherein the SF6, O2 and He process gases are introduced into the plasma chamber at flow rates between 40 sccm to 60 sccm, 10 sccm to 20 sccm and 90 sccm to 110 sccm, respectively.

17. The method according to claim 1 or claim 2, wherein, Before introducing SF6, O2, and He process gases into the plasma chamber, Ar gas is introduced into the plasma chamber, and bias RF power is applied to the substrate support to generate reactive ion etching plasma in the plasma chamber.

18. The method according to claim 1 or claim 2, wherein zero-source RF power is applied during step (i).

19. The method according to claim 1 or claim 2, wherein during step (i), a source RF power of less than 500 watts is applied.

20. An inductively coupled plasma apparatus for plasma etching of a workpiece, the apparatus comprising: Plasma chamber; A platform assembly disposed within the plasma chamber and configured to receive the workpiece, wherein the workpiece comprises a SiC substrate; A gas delivery system for introducing process gases into a plasma etching chamber; A plasma generating apparatus for maintaining plasma within the plasma chamber for etching the SiC substrate; A controller configured to control the device to reduce the surface roughness of the SiC substrate by alternating between the following steps: (i) Applying bias RF power to a substrate support to generate reactive ion etching plasma in the plasma chamber, while simultaneously applying zero-source RF power and etching the SiC substrate at a first plasma chamber pressure for a first time period; and (ii) Apply source RF power to the plasma chamber to generate inductively coupled plasma in the plasma chamber, apply bias RF power to the substrate support, and etch the SiC substrate under a second plasma chamber pressure for a second time period.

21. A method for plasma etching a workpiece, the method comprising the following steps: The workpiece is placed on a substrate support within the plasma chamber, wherein the workpiece includes a SiC substrate; SF6, O2, and He process gases are introduced into the plasma chamber; The source RF power is applied to the plasma chamber to generate inductively coupled plasma in the plasma chamber; Bias RF power is applied to the substrate support; and The SiC substrate is subjected to plasma etching to reduce the surface roughness of the SiC substrate.

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