A method for reducing the surface roughness of SiC by plasma etching.

Abstract

The SiC wafer is smoothed after mechanical polishing, supporting the epitaxial growth of SiC films with a low defect rate. [Solution] The method comprises the steps of placing a workpiece equipped with a SiC substrate on a substrate support in a plasma chamber, introducing a process gas into the plasma chamber, and reducing the surface roughness of the SiC substrate by plasma etching the SiC substrate, and alternately performing the steps of generating reactive ion etching plasma in the plasma chamber by applying bias RF power to the substrate support and etching the SiC substrate at a first plasma chamber pressure for a first period, and generating inductively coupled plasma in the plasma chamber by applying source RF power to the plasma chamber, applying bias RF power to the substrate support and etching the SiC substrate at a second plasma chamber pressure for a second period.

Description

[Technical Field]

[0001] The present invention relates to a plasma etching method for SiC. [Background technology]

[0002] Silicon carbide (SiC) is a semiconductor material with a wide bandgap and is becoming increasingly common in a wide range of applications, from power electronics circuits to integrated optics and even quantum technology. In addition, its high temperature, high power, and high radiation resistance make SiC an excellent material choice for environments where other materials simply cannot cope.

[0003] To manufacture such devices, numerous complex, often extremely 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) and aluminum nitride (AlN). This is particularly desirable when the cost associated with a given material substrate is exceptionally high.

[0004] Therefore, in order to achieve and realize high-quality epitaxial growth and high-performance devices, it is extremely important to make the SiC surface as perfectly and atomically smooth as possible. When carried out in a manufacturing environment, the surface roughness Ra should be approximately 1 nm. In power devices in particular, it has been found that the substrate surface roughness itself has a measurable effect on the final device performance.

[0005] SiC wafers are cut from large ingots, then lapped, and subsequently subjected to mechanical or chemical polishing. Defects on the polished surface can be scattered throughout the epitaxial layer, resulting in "killer defects" that can cause device malfunctions and even longer-term reliability problems. Therefore, surface treatment processes that can address surface roughness and defects are necessary to reduce uneconomical yield losses.

[0006] Non-patent document 1 describes a SiC surface smoothing method using a plasma process that results in an 83% reduction in root mean square roughness.

[0007] The atomic layer etching (ALE) technique used in this study employs Cl / Ar chemistry and pulsed platen power. The disadvantage of the demonstrated process lies in its slow speed. This process required 200 etching cycles. Only 0.067 nm was removed in each cycle, close to the theoretical limit of 0.068 nm. Since each cycle takes 12 seconds, this process, with a material removal rate of 0.02 μm / hour, takes 40 minutes per wafer.

[0008] Patent Document 1 describes the preparation of SiC wafers for epitaxial growth through plasma treatment on an ICP tool. Six plasma processes aimed at smoothing the surface of SiC are disclosed. Some hydrogen component is used in all of these processes, and it has been found to be important for smoothing. For the six disclosed processes, it has been found that the roughness is reduced by 34% to 84% by using the best-case scenario of HBr / O2 / SF6 chemistry with a ratio of 4:1:1.

[0009] Non-patent document 2 discloses SF6 / O2 plasma etching, which is capable of etching trenches into a SiC surface at high temperatures. A 92% reduction in root mean square surface roughness in the trenches was observed when the platen temperature was increased to 300°C. Reports indicate that surface roughness increases at temperatures between approximately 15°C and 250°C, making high platen temperatures a necessary condition for this process. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] British Patent No. 2601041 [Non-patent literature]

[0011] [Non-Patent Document 1] K. Kanarik et al: Atomic Layer Etching: Rethinking the Art of Etch, The Journal of Physical Chemistry Letters, Vol 9 / Issue 16 [Non-Patent Document 2] A. Osipov et al: High-temperature etching of SiC in SF6 / O2inductively coupled plasma, Nature 2020 [Overview of the project] [Problems that the invention aims to solve]

[0012] Therefore, a plasma-based surface preparation process that overcomes the aforementioned drawbacks is needed in this technical field. In particular, there is a need for a cost-effective method that can smooth SiC wafers to less than 1 nm after mechanical polishing, thereby supporting the epitaxial growth of SiC films with a low defect rate, and ultimately leading to more reliable SiC devices. [Means for solving the problem]

[0013] In a first aspect of the present invention, there is provided a method of plasma etching a workpiece, the method comprising: placing a workpiece comprising a SiC substrate on a substrate holder within a plasma chamber; introducing SF6, O2 and He process gases into the plasma chamber; and reducing the surface roughness of the SiC substrate by plasma etching the SiC substrate, the reduction being effected by alternately performing: (i) generating a reactive ion etching (RIE) plasma in the plasma chamber by applying a bias RF power to the substrate holder and etching the SiC substrate at a first plasma chamber pressure for a first period; and (ii) generating an inductively coupled plasma (ICP) in the plasma chamber by applying a source RF power to the plasma chamber, applying a bias RF power to the substrate holder, and etching the SiC substrate at a second plasma chamber pressure for a second period.

[0014] According to what the inventors have found, by etching in a cyclic process in which a second ICP etching follows a first RIE etching, advantageously, without using the time-consuming atomic layer etching technique, the surface roughness of the SiC substrate workpiece is reduced to a sub-nm surface roughness (i.e., less than 1 nm). Helium has been found to be particularly advantageous for reducing surface roughness compared to heavier inert gases.

[0015] Furthermore, in the process as claimed, as described herein, no pre-etching argon treatment is required, so that a shorter smoothing process can be achieved compared to a method using only RIE or only ICP.

[0016] Advantageously, the present process can be carried out without hydrogen gas. Advantageously, the present process can be carried out without chlorine gas.

[0017] The present process can preferably be carried out prior to epitaxial growth.

[0018] The pressure in the first plasma chamber can be made more than one order of magnitude higher than the pressure in the second plasma chamber.

[0019] The pressure in the first plasma chamber may be set to 100 - 400 mTorr, for example, about 200 mTorr.

[0020] The pressure in the second plasma chamber may be set to 2 - 10 mTorr, for example, about 5 mTorr.

[0021] Preferably, the second period is made longer than the first period.

[0022] The first period may be set to 5 - 60 seconds, for example, 10 - 20 seconds.

[0023] The second period may be set to 20 - 120 seconds, for example, 40 - 50 seconds.

[0024] The substrate holder can be maintained at a temperature of 10 - 50 °C. Advantageously, according to this method, fluctuations in the platen temperature can be enabled without degrading the planarization performance.

[0025] The substrate holder can be maintained at a temperature of 15 - 25 °C. Advantageously, according to this process, a high platen temperature can be avoided. A lower platen temperature is beneficial for materials with a low thermal budget and for cases where wafer bonding materials are used for devices.

[0026] During step (ii), the source RF power may be within the range of 1000 - 3000 W.

[0027] During step (i), the bias RF power may be within the range of 100 - 500 W.

[0028] During step (ii), the bias RF power may be within the range of 300 - 1000 W.

[0029] It is preferable to include a pause (temporary stop) during the cycle (loop execution) between steps (i) and (ii), and during that time, adjust the plasma chamber pressure between the first and second plasma chamber pressures without applying source RF power and bias RF power.

[0030] Hold that pose for a few seconds, for example, 2 to 10 seconds, or optionally 5 seconds.

[0031] During step (ii), after the source RF power is applied, the bias RF power may be applied for a few seconds, for example, 2 to 10 seconds, or optionally 5 seconds.

[0032] SF6, O2, and He process gases are introduced into the plasma chamber at flow rates of 40-60 sccm, 10-20 sccm, and 90-110 sccm, respectively.

[0033] Prior to introducing SF6, O2, and He process gases into the plasma chamber, a step may be provided in which 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.

[0034] Optionally, source RF power may be prevented from being applied during step (i).

[0035] Optionally, during step (i), a source RF power of less than 500 watts is applied.

[0036] In a second aspect of the present invention, an inductively coupled plasma apparatus for plasma etching a workpiece is provided, comprising: a plasma chamber; a platen assembly configured to receive a workpiece comprising a SiC substrate and disposed within the plasma chamber; a gas supply system for introducing a process gas into the plasma etching chamber; a plasma generator for maintaining plasma within the plasma chamber to etch the SiC substrate; and a controller configured to control the apparatus and perform plasma etching of the SiC substrate to reduce the surface roughness of the SiC substrate, wherein the reduction is achieved by alternately executing the following steps: (i) generating reactive ion etching plasma in the plasma chamber by applying bias RF power to a substrate support without applying source RF power, and etching the SiC substrate at a first plasma chamber pressure for a first period; and (ii) generating inductively coupled plasma in the plasma chamber by applying source RF power to the plasma chamber, applying bias RF power to a substrate support, and etching the SiC substrate at a second plasma chamber pressure for a second period.

[0037] A third aspect of the present invention provides a method for plasma etching a workpiece, comprising the steps of: placing a workpiece comprising a SiC substrate on a substrate support in a plasma chamber; introducing SF6, O2, and He process gases into the plasma chamber; generating inductively coupled plasma in the plasma chamber by applying source RF power to the plasma chamber; applying bias RF power to the substrate support; and reducing the surface roughness of the SiC substrate by etching the SiC substrate.

[0038] While the high-pressure RIE etching of the first and second embodiments has the advantage of speeding up the ICP etching process and improving surface uniformity, the inventors recognize that this can be omitted, and there are still advantages to using SF6, O2, and He process gases in the ICP etching process. This process is hydrogen-free, and the use of He yields optimal results compared to the use of heavier inert gases such as Ar.

[0039] Hereinafter, embodiments of the present invention will be described solely by illustration with reference to the schematic drawings shown later. [Brief explanation of the drawing]

[0040] [Figure 1] This is a side view of an example of an inductively coupled plasma apparatus for plasma etching a workpiece. [Figure 2] This is a side view of an example of an inductively coupled plasma apparatus for plasma etching a workpiece. [Figure 3] This is a flowchart illustrating the method for plasma etching a workpiece. [Figure 4] This figure shows the source RF power, bias RF power, and chamber pressure as functions of time in a method for plasma etching a workpiece. [Figure 5] This figure shows power spectral density data related to a method of plasma etching a workpiece, in comparison with several other test processes. [Modes for carrying out the invention]

[0041] An inductively coupled plasma apparatus 1 according to an embodiment is shown in Figures 1 and 2. The present invention can be carried out using an adapted version of the applicant's OmegaSynapse® etching process module. Well-known mechanisms, such as an exhaust gas pumping system, are not shown in Figures 1 and 2, but will be understood by those skilled in the art.

[0042] The apparatus 1 comprises a plasma etching chamber 11 having multiple inner surfaces. The apparatus includes a first gas inlet array 10, a second gas inlet array 12, a ceramic annular housing 18, an RF antenna 14, a platen RF electrode 16, and a substrate support 20, with the workpiece (i.e., structure) 28 to be etched being supported by the substrate support 20. In the embodiments shown in Figures 1 and 2, the substrate support 20 is an electrostatic chuck. The platen RF electrode 16 is used to control the directionality of etching ions, which in turn controls the amount of physical etching of the workpiece achieved during processing. Higher platen power results in a higher etching rate. The electrostatic chuck is equipped with helium back cooling, which is used to regulate the wafer temperature.

[0043] The plasma etching chamber 11 is equipped with an upper wall or lid 13. An annular housing 18 is submerged within the chamber 11 and hangs down from its upper wall. The annular housing 18 defines a circular region towards the interior of the upper wall.

[0044] In the embodiments shown in Figures 1 and 2, the first gas inlet array 10 is an inner gas plenum, and the second gas inlet array 12 is an outer gas plenum. Each gas inlet array has multiple gas inlets, each gas inlet terminating within an opening, through which process gas enters the chamber 11. The inner plenum 10 is located within a circular region defined by the annular housing 18. The gas inlets constituting the inner gas plenum 10 are arranged inside the annular housing 18 as multiple openings arranged according to a circular pattern. The outer plenum 12 is located outside the circular region defined by the annular housing 18. The gas inlets constituting the outer gas plenum 10 are arranged outside the annular housing 18 as multiple openings arranged according to a circular pattern. The inner gas plenum can have eight gas inlets, and the outer gas plenum can have approximately ten times as many gas inlets. However, as can be inferred, the first and second gas inlet arrays can have any preferred number of gas inlets. A mass flow regulator (not shown) is coupled to these gas inlet arrays and used to control the gas flow leading to the chamber 11.

[0045] An etching chamber 11 is further depicted in Figure 2, showing the processing of a workpiece 28 located within the chamber. The chamber comprises one or more chamber walls 24, inside which the workpiece 28 rests on a substrate support 20. Plasma 26 is ignited and maintained within the chamber 11 by RF power, which is coupled into the chamber from an RF power source (not shown) via an RF antenna 14 (i.e., a coil) located in an annular housing 18. In this embodiment, the RF power source is a high-frequency generator operating at 13.56 MHz. A platen RF electrode is driven at the same frequency from a separate power source. The annular housing 18 acts as a window allowing RF power to be coupled into the chamber. Etching process gases include SF6, O2, and He gas, which enter the chamber 11 through gas inlets in the inner gas plenum 10 and outer gas plenum 12. A controller 30 is used to control the cyclic etching process. As part of this operation, the controller 30 can control the flow of etching process gas into the chamber 11.

[0046] In this embodiment, the workpiece 28 is a 150 mm wafer equipped with a SiC substrate (however, other wafer sizes, such as 100 mm and 200 mm, are also within the technical scope of the present invention). In this embodiment, the thickness of the SiC substrate is 300 to 500 μm.

[0047] In this embodiment of the present invention, in the first step of a method for plasma etching a workpiece, the workpiece is placed on a wafer support in a plasma chamber (101). After being placed on an electrostatic chuck, the workpiece is clamped at 10 to 35 degrees Celsius. A transfer robot is used to place the workpiece on the electrostatic chuck in the chamber under vacuum.

[0048] In the second step, SF6, O2, and He process gases are introduced into the plasma chamber (for example, simultaneously) via a mass flow regulator (103). The SF6, O2, and He gases enter the plasma chamber at gas flow rates of approximately 40-60 sccm, 10-20 sccm, and 80-120 sccm, respectively, until a target pressure (100-400 mTorr), approximately 200 mTorr in this embodiment, is achieved.

[0049] The target pressure can be maintained by adjusting the pumping speed and / or by adjusting the mass flow regulator. The SiC substrate is then plasma-etched according to a cyclical process in which two etching modes are performed alternately.

[0050] In the first mode (RIE etching mode), bias RF power is applied to the substrate support (105), thereby generating reactive ion etching plasma in the plasma chamber. The plasma is generated near the substrate support. Source RF power does not need to be applied during this mode, or a small source RF power in the range of 0 to 500 watts may be applied instead. The SiC substrate is etched in a directional etching manner by RIE etching over a relatively short first duration, for example, 5 to 60 seconds. In this first mode, the chamber is maintained at a relatively high first pressure, approximately 200 mTorr in this embodiment. At the end of the first duration, the bias RF power is switched off (107) and the RIE plasma subsides.

[0051] After the first duration has elapsed, there is a first intermediate period. The chamber pressure is reduced to a lower second pressure of approximately 2-10 mTorr in preparation for ICP etching by changing the process gas flow into the chamber (109). In this embodiment, this intermediate step continues for approximately 5 seconds (it is desirable for efficiency reasons to shorten the duration of the power-off state).

[0052] After the first intermediate period, etching in the second mode is initiated. In this second mode (ICP etching mode), source RF power is applied to the plasma chamber (111), thereby generating inductively coupled plasma within the plasma chamber. After a short delay time for the ICP plasma to be established, approximately 5 seconds in this embodiment, bias RF power is applied to the substrate support (or the power sources may be applied simultaneously). The SiC substrate is etched through ICP etching for a longer second duration, for example, 20 to 120 seconds. In this second mode, the chamber is maintained at a lower second pressure for the duration of the ICP etching. After the second duration has elapsed, both power sources are switched off (for example, simultaneously) (113) and the ICP plasma subsides.

[0053] After the second duration has elapsed, there is a second intermediate period. The chamber pressure is increased back to the higher first pressure in preparation for RIE etching (by changing the process gas flow into the chamber). In this embodiment, this intermediate step lasts for approximately 5 seconds (it is desirable for efficiency reasons to shorten the duration of the power-off state).

[0054] At this point, the controller determines whether the required number of loops have been executed and whether the desired degree of SiC wafer surface treatment has been achieved (115). As shown in Figure 3, the process is stopped when the required number of loops have been executed; otherwise, the process continues to cycle between etching in RIE and RIE-assisted ICP modes. Alternatively, the process could be terminated after an acceptable degree of smoothing is indicated by in-situ measurements of surface roughness.

[0055] At the end of the process, the workpiece is removed from the chamber under vacuum by a transport robot (117).

[0056] An example etching cycle is shown in Figure 4, where the first duration (i.e., for RIE etching) is approximately 20 seconds, and the second duration (i.e., for ICP etching) is approximately 45 seconds, with an intermediate period of approximately 5 seconds in between during which the chamber pressure is adjusted.

[0057] The first duration (i.e., for RIE etching) was set to approximately 10 seconds, and the second duration (i.e., for ICP etching) was set to approximately 50 seconds, and experiments were conducted following the method described above. These experiments were carried out at room temperature (i.e., a platen temperature of approximately 20 degrees Celsius). The Rq and Ra roughness of the samples were measured using an atomic force microscope (Park Systems XE7 AFM) in non-contact scanning mode at various scales (1 × 1 μm). 2 , 10 × 10 μm 2 and 40 × 40 μm 2 The surface roughness was measured using [a specific method]. The changes in surface roughness for the two test wafers with initial Ra values ​​of 25 nm and 1.1 nm are shown in Table 1 below.

[0058] Table 1 also shows comparable surface roughness changes, which are reported for multiple test processes, including an ICP-only process with a 10-minute pre-etching argon worm / surface treatment, and a process in which ICP is followed by RIE.

[0059] For the ICP standalone process, the chamber pressure was set to 2-10 mTorr, the source RF power to approximately 1500 W (within the range of 1000-3000 W), and the bias RF power to the substrate support to approximately 600 W (within the range of 300-1000 W). The gas flow was kept constant at approximately 50 sccm (SF6), 15 sccm (O2), and 100 sccm (He).

[0060] Among the parameters of the RIE process, the chamber pressure was set to approximately 200 mTorr (within the range of 100-300 mTorr), and the bias RF power was set to approximately 300 W (within the range of 100-500 W). The gas flow was kept constant at approximately 50 sccm (SF6), approximately 15 sccm (O2), and approximately 100 sccm (He). [Table 1]

[0061] As is known, the material to be etched can be cleaned / warmed using a pre-etching process. High-frequency roughness reduction can be aided by using pre-etching Ar plasma. However, as has been found, the process described in the claims of this patent application does not benefit from the pre-etching Ar plasma process, and therefore similar smoothing results can be achieved in a faster process. A total of 10 minutes cannot be saved because time is required to switch between operating modes, but in the cases shown at the bottom of Table 1, a 30% reduction in process time can be achieved when using the methods according to the embodiments of the present invention. Alternatively, a smoother surface can be achieved by extending the smoothing time.

[0062] The pre-etching process was carried out immediately before the SF6 / O2 / He smoothing process using argon at a pressure of 10 mTorr with a source RF power of 2 kW and a bias RF power of 0 to 800 W.

[0063] In certain conventional methods, platen temperature has been found to be crucial for smoothing; for example, Non-Patent Document 2 shows that the RMS roughness of the etching front increases from 7.4 nm to 112.2 nm between 15°C and 50°C. It seems that the high power density used in Non-Patent Document 2, i.e., a 1 kW source RF (approximately 62.5 W / cm²) for a 4 × 4 cm sample, is insufficient. 2 This results in damage to the etched surface. A lower power density of approximately 5.7 W / cm² is also present. 2 ~17W / cm 2 By operating the process in this manner and diluting SF6 and O2 with He, the process becomes considerably less sensitive to its relatively low platen temperature. As a result, in this process, no degradation in surface smoothing performance occurs when the platen temperature is increased to 50°C.

[0064] FIG. 5 shows power spectral density data for various processes, which shows the relationship between roughness intensity and the reciprocal of roughness wavelength. The first line 201 shows the initial workpiece power spectral density. The improvement in surface roughness is indicated by the spectrum below that line. The second line 203 indicates a 20-minute RIE process (including a 10-minute pre-etching argon warm). Above a reciprocal wavelength of about 2×10 6 m -1 , the intensity is higher than the control value, indicating that the specimen is becoming rougher in this manner. The third line 205 indicates a 20-minute ICP-only process (including a 10-minute pre-etching argon warm). The surface roughness has been significantly improved, but when reaching a reciprocal wavelength of about 5x10 5 m -1 and below, the surface roughness deteriorates. The fourth line 207 shows a process in which 10 minutes of RIE is followed by 10 minutes of ICP. The result is inferior to the ICP-only process. The fifth line 209 is the cyclic RIE and ICP process according to embodiments of the present invention, using first and second periods of 10 seconds and 50 seconds in each cycle and covering a period of 10 cycles. The sixth line 211 indicates the same type of process but covering 20 cycles. In these processes, both show a significant improvement in surface roughness, especially at a roughness reciprocal value of more than 1×10 6 m -1 .

[0065] The use of lighter inert gas such as He was investigated in contrast to heavier inert gas such as Ar. When using the same SF6 and O2 flows as the standard process and replacing He with 100 sccm Ar, deterioration was brought about within all scanned areas. The changes when using a 25 nm initial Ra wafer were -75% (1×1 mm 2 ), -25% (10×10 mm 2 ) and +30% (40×40 mm 2 ). It is considered that the surface roughness is increasing due to an increase in sputtering from heavier ions. Using He according to the present invention helps to dilute the chemical etching component and minimize isotropic etching pits.

[0066] The process duration depends on the surface roughness of the incoming wafer and the specified final surface roughness. As can be seen in Table 1, even using the same RIE-assisted ICP process, the roughness changes associated with a wafer coupon with a Ra of 25 nm and that of a 1.1 nm wafer will result in different roughness changes. To achieve a surface roughness of less than 1 nm with an incoming 25 nm wafer, the wafer needs to be smoothed from 5.4 nm to 1.1 nm, which requires more than 29 minutes.

Claims

1. A method for plasma etching a workpiece, The step of placing the workpiece on a substrate support inside a plasma chamber, wherein the workpiece comprises a SiC substrate, SF in the aforementioned plasma chamber ６ , O ２ and the step of introducing He process gas, The step involves reducing the surface roughness of the SiC substrate by plasma etching the SiC substrate. (i) A step of generating reactive ion etching plasma in the plasma chamber by applying bias RF power to the substrate support, and etching the SiC substrate at a first plasma chamber pressure for a first period, and (ii) A step of generating inductively coupled plasma in the plasma chamber by applying source RF power to the plasma chamber, applying bias RF power to the substrate support, and etching the SiC substrate with the second plasma chamber pressure over a second period. Steps performed by alternating between, A method of having.

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

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

4. A method according to any one of claims 1 to 3, wherein the second plasma chamber pressure is 2 to 10 mTorr, for example, about 5 mTorr.

5. A method according to any one of claims 1 to 4, wherein the second period is longer than the first period.

6. A method according to any one of claims 1 to 5, wherein the first period is 5 to 60 seconds, for example, 10 to 20 seconds.

7. A method according to any one of claims 1 to 6, wherein the second period is 20 to 120 seconds, for example, 40 to 50 seconds.

8. A method according to any one of claims 1 to 7, wherein the substrate support is maintained at a temperature of 10 to 50 degrees Celsius during the plasma etching.

9. A method according to any one of claims 1 to 8, wherein the substrate support is maintained at a temperature of 15 to 25 degrees Celsius during the plasma etching.

10. A method according to any one of claims 1 to 9, wherein the source RF power is within the range of 1000 to 3000 W during step (ii).

11. A method according to any one of claims 1 to 10, wherein the bias RF power is within the range of 100 to 500 W during step (i).

12. A method according to any one of claims 1 to 11, wherein the bias RF power is within the range of 300 to 1000 W during step (ii).

13. A method according to any one of claims 1 to 12, wherein there is a pause during the cycle between steps (i) and (ii), and during that time, the plasma chamber pressure is adjusted between the first and second plasma chamber pressures without applying source RF power and bias RF power.

14. A method according to claim 13, wherein the pause lasts for 3 to 7 seconds.

15. A method according to any one of claims 1 to 14, wherein the bias RF power is applied for 3 to 7 seconds after the source RF power is applied during step (ii).

16. A method according to any one of claims 1 to 15, wherein the SF ６ , O ２ A method of introducing the He process gas into the plasma chamber at flow rates of 40-60 sccm, 10-20 sccm, and 90-110 sccm, respectively.

17. A method according to any one of claims 1 to 16, wherein SF is placed in the plasma chamber. ６ , O ２ A method for generating reactive ion etching plasma in a plasma chamber by introducing Ar gas into the plasma chamber and applying bias RF power to the substrate support prior to introducing He process gas.

18. A method according to any one of claims 1 to 17, wherein no source RF power is applied during step (i).

19. A method according to any one of claims 1 to 18, wherein a source RF power of less than 500 watts is applied during step (i).

20. An inductively coupled plasma apparatus for plasma etching a workpiece, Plasma chamber and A platen assembly configured to receive the workpiece and disposed within the plasma chamber, wherein the workpiece comprises a SiC substrate, A gas supply system for introducing process gas into the plasma etching chamber, A plasma generator for maintaining the plasma in the plasma chamber in order to etch the SiC substrate, This controller is configured to reduce the surface roughness of the SiC substrate by controlling the device and performing plasma etching on the SiC substrate, and this reduction is achieved by... (i) A step of generating reactive ion etching plasma in the plasma chamber by applying bias RF power to the substrate support without applying source RF power, and etching the SiC substrate at a first plasma chamber pressure for a first period, and (ii) A step of generating inductively coupled plasma in the plasma chamber by applying source RF power to the plasma chamber, applying bias RF power to the substrate support, and etching the SiC substrate with the second plasma chamber pressure over a second period. A controller that executes alternately, A device equipped with the following features.

21. A method for plasma etching a workpiece, The step of placing the workpiece on a substrate support inside a plasma chamber, wherein the workpiece comprises a SiC substrate, SF in the aforementioned plasma chamber ６ , O ２ and the step of introducing He process gas, The steps include: generating inductively coupled plasma within the plasma chamber by applying source RF power to the plasma chamber; The steps include applying bias RF power to the substrate support, The steps include reducing the surface roughness of the SiC substrate by plasma etching, A method of having.

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