Plasma-etched compound semiconductor

Abstract

To provide a plasma etch method which can etch a trench with tapered side walls in SiC while avoiding the need for thermally activated etching.SOLUTION: The invention provides: a method of plasma-etching a silicon carbide substrate to form a tapered feature; a silicon carbide substrate; and a plasma etch apparatus for plasma-etching a silicon carbide substrate to form a tapered feature.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for plasma etching features in a compound semiconductor substrate, and further to a plasma etching apparatus. [Background technology]

[0002] There is an increasing demand for high power and high frequency devices based on compound semiconductors that cannot be realized with conventional silicon-based technologies. Wide band gap compound semiconductors, such as silicon carbide (SiC), offer a combination of favorable electronic and thermal properties that may exceed those of silicon. However, mass producing such compound semiconductor devices at reasonable cost using known methods often requires multiple processing steps and can be difficult. It is desirable to develop methods for manufacturing compound semiconductor devices, such as SiC devices, more economically with fewer processing steps.

[0003] Silicon carbide trenches for power devices, typically 0.5 to 10 μm wide and 0.5 to 3 μm deep, are dry etched silicon carbide trenches used in power semiconductor devices, primarily silicon oxide (SiO X Increasingly, silicon is being used in MOSFET gates where the trench is coated with a polysilicon (Si) layer and then filled with polysilicon. It is known to use flat-bottom rectangular cross-section trenches, as shown as trench A in FIG. 2. As shown in FIG. 2, trench 10 has a substantially flat bottom 12 and substantially vertical sidewalls 14. However, micro-trenching at the bottom of a flat-bottom trench can be problematic. Micro-trenching refers to the deeper etched areas at the corners of the trench. Micro-trenching does force sharp corners, which can concentrate the electric field in the substrate at these points. This can reduce the breakdown voltage. It is desirable to avoid micro-trenching in order to maximize the breakdown voltage.

[0004] Even flat-bottom trenches (without micro-trenching) are prone to "field bunching" of the electric field. That is, the electric field tends to concentrate at certain locations within the trench, such as at the corners of the trench. It is therefore desirable to be able to control the curvature of the trench corners to reduce field bunching as much as possible. Trenches with rounded corners, also known as "U-trenches," are by far superior in terms of internal distribution of the electric field and improved breakdown voltage. That is, trenches with rounded corners, such as the exemplary trench B in FIG. 2, perform better in many devices than those without rounded corners.

[0005] A more promising trench shape is the tapered sidewall or "V-shaped" trench, as shown in Trench C in Figure 2. This shape may result in higher channel mobility, i.e., reduced channel resistance, than other directions in the material.

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[0006] [Patent Document 1] European Patent Application Publication No. 3836195 [Patent Document 2] European Patent Application Publication No. 4207253 [Patent Document 3] JP 2018-006773 A Summary of the Invention [Problem to be solved by the invention]

[0007] Thus, there is a need in the art for a plasma etching method capable of etching trenches with tapered sidewalls in SiC without the need for a thermally activated etch.The present invention, in at least some of its embodiments, is directed to addressing the above-mentioned problems, desires, and needs. [Means for solving the problem]

[0008] According to a first aspect of the present invention, there is provided a method of plasma etching a silicon carbide substrate to form a tapered feature, the method comprising: Providing a silicon carbide substrate having a hard mask formed thereon with an opening on a substrate support in a chamber; performing a plasma etching step to anisotropically etch the substrate through the opening to form a tapered feature; Including, The method, wherein the plasma etching step includes generating a plasma from an etching gas mixture including at least one chlorine-containing component, at least one inert gas component, and at least one passivation material precursor, and wherein anisotropically etching the substrate includes depositing a passivation material at least over the opening such that the tapered feature has at least two sidewalls, each sidewall being inclined at an angle of less than 85° relative to the horizontal.

[0009] Without wishing to be bound by any theory or speculation, it is believed that depositing a passivation material at least over the openings in the hard mask effectively reduces the critical dimension of the hard mask and reduces the etch width at the bottom of the trench, while providing an etching gas mixture that includes at least one chlorine-containing component, at least one inert gas component, and at least one passivation material precursor allows for a highly anisotropic etching process. By controlling the deposition and etch rate of the passivation material, the sidewall taper can be tightly controlled, and the corners at the bottom of the trench can be rounded. This allows for the combination of the advantages of U-shaped and V-shaped trenches in a single etching step. The method of the present invention also exhibits high substrate to mask selectivity. Selectivities of up to 9:1 are possible.

[0010] The substrate may be a SiC wafer. The substrate may be a 150 mm SiC wafer. The hard mask may be SiO X and SiN.

[0011] The at least one passivation material precursor may include at least one silicon-containing component. The at least one silicon-containing component may include SiCl4, SiF4, or a combination thereof. The at least one silicon-containing component may include SiF4. The at least one silicon-containing component may consist of, or consist essentially of, SiF4. The at least one passivation material precursor may include at least one oxygen-containing component. The at least one oxygen-containing component may include O2, N2O, H2O, O3, or a combination thereof. The at least one oxygen-containing component may include O2 gas. The at least one oxygen-containing component may consist of, or consist essentially of O2 gas. The at least one chlorine-containing component may include Cl2, HCl, BCl3, or a combination thereof. The at least one chlorine-containing component may include Cl2 gas. The at least one chlorine-containing component may consist of, or consist essentially of Cl2 gas. The at least one passivation material precursor may include C4F8. The at least one inert gas component may include helium, argon, or a combination thereof. The at least one inert gas component may include argon. The at least one inert gas component may consist or consist essentially of argon.

[0012] The total flow rate of the at least one silicon-containing component at the beginning of the plasma etching step can be about 10 sccm to about 50 sccm. The total flow rate of the at least one silicon-containing component at the beginning and / or end of the plasma etching step can be about 39 sccm. The total flow rate of the at least one oxygen-containing component at the beginning of the plasma etching step can be about 12 sccm to about 75 sccm. The total flow rate of the at least one oxygen-containing component at the beginning and / or end of the plasma etching step can be about 50 sccm. The total flow rate of the at least one chlorine-containing component can be at least 100 sccm, such as at least 120 sccm. The total flow rate of the at least one chlorine-containing component can be about 120 sccm. The total flow rate of the at least one inert gas component can be about 500 sccm to about 800 sccm. The total flow rate of the at least one inert gas component can be about 700 sccm. A ratio of a total flow rate in sccm of the at least one chlorine-containing component at the end of the plasma etching step to a total flow rate in sccm of the at least one passivation material precursor at the end of the plasma etching step can be from about 1:1 to about 3:1. A ratio of a total flow rate in sccm of the at least one chlorine-containing component at the end of the plasma etching step to a total flow rate in sccm of the at least one passivation material precursor at the end of the plasma etching step can be at least about 1:1.

[0013] The plasma etching step may include a passivation material deposited on the hard mask and at least one sidewall of the feature to be etched. The net deposition rate of the passivation material may be greater than zero throughout the plasma etching step. During the plasma etching step, the deposition rate of the passivation material may increase. During the plasma etching step, the deposition rate of the passivation material may increase at an ever-increasing rate of change. The dimensions of the opening in the hard mask may decrease at an ever-increasing rate of change. Increasing the deposition rate of the passivation material during the plasma etching step may contribute to forming a feature with tapered sidewalls and rounded corners at the edge region of the bottom surface. For example, the feature may be a generally V-shaped trench with curved edges at the bottom surface. The passivation material may have a deposition thickness that increases on each side of the opening by about 400 nm, optionally about 300 nm, optionally about 200 nm, optionally about 150 nm, or optionally about 125 nm. The dimensions of the openings in the hard mask can be reduced to about 100 to 800 nm, 200 to 600 nm, 250 to 500 nm, 300 to 400 nm, or about 350 nm, or any combination of these limits.

[0014] The plasma etching step may include varying a process parameter during the plasma etching step. The plasma etching step may include ramping a process parameter during the plasma etching step. The variable process parameter may be ramped at an increasing rate of change. The variable process parameter may be ramped at a constant rate of change. The term "ramping" may mean either systematically increasing or decreasing a value.

[0015] The plasma etching step may include varying or ramping at least one of the gas mixture composition, gas flow rates, process time, plasma source power, bias power applied to the substrate, and / or frequency.

[0016] Varying the process parameters may include varying a flow rate of at least one passivation material precursor during the plasma etching step. The flow rate of the at least one passivation material precursor may be increased during the plasma etching step. The flow rate of the at least one passivation material precursor in sccm at the end of the plasma etching step may be at least two, three, or four times the flow rate of the at least one passivation material precursor in sccm at the start of the plasma etching step. The plasma etching step may include increasing a flow rate of at least one oxygen-containing component during the plasma etching step. The flow rate of the at least one oxygen-containing component in sccm at the end of the plasma etching step may be at least two, three, or four times the flow rate of the at least one oxygen-containing component in sccm at the start of the plasma etching step. The flow rate of the at least one oxygen-containing component may be increased from about 12 sccm at the start of the plasma etching step to about 50 sccm at the end of the plasma etching step. The plasma etching step may include increasing a flow rate of the at least one silicon-containing component during the plasma etching step. The flow rate of the at least one silicon-containing component in sccm at the end of the plasma etching step can be at least 2, 3, or 4 times the flow rate of the at least one silicon-containing component in sccm at the start of the plasma etching step. The flow rate of the at least one silicon-containing component can be increased from about 10 sccm at the start of the plasma etching step to about 39 sccm at the end of the plasma etching step.

[0017] Varying the process parameters may include varying the bias power applied to the substrate during the plasma etching step. The plasma etching step may include reducing the bias power applied to the substrate support during the plasma etching step. The bias power applied to the substrate support at the beginning of the plasma etching step may be higher than the bias power applied to the substrate support at the end of the plasma etching step by an amount in the range of about 50 to 1400 W. The bias power applied to the substrate at the beginning of the plasma etching step may be in the range of about 100 W to about 1500 W, about 1000 W to about 1400 W, or about 1300 W of power. The bias power applied to the substrate at or towards the end of the plasma etching step may be in the range of about 50 W to about 1500 W of power. The initial bias power applied to the substrate support may be reduced by at least 50% during the plasma etching step, e.g., at least 60%, at least 70%, at least 80%, or at least 90%. Alternatively, the bias power applied to the substrate support during the plasma etching step may be maintained at a constant value throughout the plasma etching step. The bias power applied to the substrate support may be between 100 W and 1500 W throughout the plasma etching step. The bias power applied to the substrate support may be about 1300 W throughout the plasma etching step. Any other process parameters may be varied or ramped during the plasma etching step. Varying or ramping the process parameters may contribute to controlling the etch rate of the substrate through the opening while controlling the deposition rate of the passivation material.

[0018] The plasma etching step may be carried out utilizing a plasma source providing a power to the plasma of between 800 W and 2400 W. The plasma source may provide approximately 2400 W of power to the plasma during the plasma etching step.

[0019] The passivation material is SiO XThe passivation material may include silicon oxides such as silicon dioxide, silicon carbide, silicon carbide, silicon carbide, silicon dioxide ...

[0020] The etching conditions used in the plasma etching step may consist of, or consist essentially of, one or more gases selected from the group of at least one chlorine-containing component, at least one inert gas component (e.g., He and / or Ar), and an oxygen-containing component (e.g., O2) and / or at least one silicon-containing component (e.g., SiF4 and / or SiCl4). The plasma etching step may include utilizing etching conditions consisting of, or consisting essentially of, Cl2, O2, SiF4, and Ar.

[0021] The method of the first embodiment of the present invention may further include a passivation removal step for removing passivation material formed on the substrate and the hard mask after the plasma etching step. The passivation removal step may be a wet etch, for example using a HF etchant. Alternatively, the passivation removal step may be a dry etch, including etching the substrate.

[0022] The dimension of the opening in the hard mask prior to the plasma etching step may be in the range of about 0.5 μm to 10 μm or about 1 μm to 8 μm. The dimension of the opening may be a width. The feature may have a maximum width in the range of about 0.5 μm to 10 μm. The feature may have a depth in the range of about 0.5 μm to 3 μm.

[0023] The tapered feature may be a trench. The tapered feature may be a via. The bottom surface of the tapered feature may be substantially flat. The bottom surface of a fully formed tapered feature may be substantially concave. As used herein, the term "substantially concave" refers to a shape in which a line can be drawn from two points on opposite sides of the bottom surface (e.g., opposing edge regions) without intersecting the substrate (i.e., the central region is deeper than the edge regions). This definition includes concave shapes that include a flat central region. This definition includes concave shapes with tapered corners. The present invention allows the shape of the bottom surface to be tailored to the desires of the user.

[0024] The central region of the bottom surface of the fully formed tapered feature may be substantially flat. The edge region may provide a continuously varying slope from the central region to at least one tapered sidewall of the tapered feature. The edge region may extend from the sidewall of the feature by a distance within a range of about 100 nm to about 350 nm, about 125 nm to about 300 nm, about 150 nm to about 250 nm, or optionally about 175 nm. The edge region of the bottom surface of the fully formed tapered feature may include a curved surface. The edge region may form a rounded corner between the central region of the bottom surface and the sidewall of the tapered feature. The edge region may form a tapered corner between the central region of the bottom surface and the sidewall of the tapered feature.

[0025] The chamber may be cooled by water cooling. The chamber may be cooled to a temperature of about 55° C. The substrate support may be maintained at a temperature between 5° C. and 50° C. The substrate support may be maintained at a temperature of about 10° C. The pressure in the chamber during the plasma etching step may be between 2 mTorr (0.267 Pa) and 60 mTorr (8.00 Pa). The pressure in the chamber during the plasma etching step may be about 12 mTorr (1.60 Pa).

[0026] The plasma etching step may be performed using an inductively coupled plasma (ICP) etcher. The passivation removal step may also be performed using an inductively coupled plasma (ICP) etcher.

[0027] According to a second aspect of the invention there is provided a silicon carbide substrate comprising at least one tapered feature formed by the method of the first aspect of the invention, the at least one tapered feature having at least two sidewalls, each sidewall inclined at an angle of less than 85° to the horizontal.

[0028] The silicon carbide substrate may be a SiC wafer. The silicon carbide substrate may be a 150 mm SiC wafer. Each sidewall may be inclined at an angle of less than 81° relative to the horizontal. Each sidewall may be inclined at an angle of less than 74° relative to the horizontal.

[0029] According to a third aspect of the present invention there is provided a plasma etching apparatus for plasma etching a silicon carbide substrate to form tapered features utilising the method according to the first aspect. The apparatus comprises: A chamber; a substrate support disposed within the chamber to support a substrate thereon; at least one gas inlet for introducing a gas or gas mixture into the chamber at a flow rate; a plasma generating means for maintaining a plasma within the chamber; a power supply for providing electrical bias power to the substrate support; a controller configured to operate the plasma etching apparatus to generate a plasma from an etching gas mixture including at least one chlorine-containing component, at least one inert gas component, and at least one passivation material precursor; Equipped with.

[0030] The at least one gas inlet may include a first gas inlet for introducing at least one chlorine-containing component into the chamber, a second gas inlet for introducing at least one inert gas component into the chamber, and a third gas inlet for introducing at least one passivation material precursor into the chamber, and the controller may be configured to generate a plasma from the etching gas mixture by forming an etching gas mixture in the chamber that includes the at least one chlorine-containing component, the at least one inert gas component, and the at least one passivation material precursor. The at least one gas inlet may include a fourth gas inlet for introducing an additional passivation material precursor into the chamber, and the controller may be configured to generate a plasma from the etching gas mixture by forming an etching gas mixture in the chamber that includes the at least one chlorine-containing component, the at least one inert gas component, and the at least two passivation material precursors. The at least one gas inlet may include at least one further gas inlet, such as a fifth gas inlet, for introducing at least one further gas or gas mixture into the chamber, and the controller may be configured to generate plasma from the etching gas mixture by forming an etching gas mixture in the chamber comprising at least one chlorine-containing component, at least one inert gas component, at least two passivation material precursors, and at least one further gas or gas mixture. The controller may be configured to vary at least one of the flow rate and / or the power generated by the power source for providing electrical bias power to the substrate support during plasma generation in the chamber. The controller may be configured to vary the flow rate through at least one of the first gas inlet, the second gas inlet, the third gas inlet, and / or the fourth gas inlet. The third gas inlet or the fourth gas inlet may be for introducing at least one oxygen-containing component into the chamber, and the controller may be configured to vary the flow rate of the at least one oxygen-containing component. The plasma generating means may include a plasma source.

[0031] For the avoidance of doubt, wherever in this specification the terms "comprising" or "including" are used, it is to be understood that the invention also encompasses more restrictive terms such as "consisting of" or "consisting essentially of."

[0032] The present invention as set forth above covers any inventive combination of the features set forth above or in the following description, drawings or claims. For example any feature disclosed in relation to the first aspect of the invention may be combined with any feature of the second aspect of the invention, and vice versa. [Brief description of the drawings]

[0033] Aspects of methods and apparatus according to the present invention will now be described with reference to the following drawings. [Figure 1] 1 is a schematic diagram of a plasma etching apparatus according to an embodiment of the present invention. [Diagram 2] A is a schematic diagram of a rectangular cross-section trench, B is a rounded bottom or "U-shaped" trench, and C is a tapered or "V-shaped" trench. [Diagram 3] 2 is a flow chart illustrating a method according to an embodiment of the present invention. [Figure 4] 1 is a schematic diagram of an etching process that is part of a method according to an embodiment of the present invention; [Diagram 5] 13A-13C are SEM images of trenches formed in SiC with tapered sidewalls, before and after an in situ plasma passivation removal step. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] 1 is a schematic diagram of a plasma etching apparatus 20 according to a second embodiment of the present invention suitable for carrying out the method according to the first embodiment of the present invention. A suitable plasma etching apparatus is utilized to carry out plasma etching of a substrate. The plasma etching apparatus may be an inductively coupled plasma (ICP) apparatus. However, etching may also be carried out using other dry etching systems such as helicon, RIE, or microwave type apparatus. The operation of generating a plasma in such a plasma etching apparatus is well known in the art and will not be described herein unless necessary for an understanding of the present invention.

[0035] A suitable plasma etching tool for carrying out the method of the present invention is the Omega® Synapse™ manufactured by SPTS Technologies Limited, Newport, UK. Typically, the plasma etching apparatus 20 comprises a substrate support (or platen) 22, also called a wafer support, disposed in the chamber 23 for supporting the substrate. Bias power may be provided to the substrate from an RF power source 250 via an impedance matching network (not shown) and an electrode 252. A typical RF frequency of operation of the RF power source may be between about 380 kHz and 13.56 MHz. Process gas may be introduced into the chamber via one or more gas inlets 25, 26. In one embodiment, there may be at least six gas inlets. However, in the illustrated embodiment, two gas inlets 25, 26 are provided, and gas for generating plasma is introduced into the chamber 23 through the two gas inlets 25, 26. A plasma generating means 28, such as an inductive coil, may be utilized to generate and maintain the plasma in the chamber 23 (e.g., utilizing an RF power source and an impedance matching network) as is known in the art. In the illustrated embodiment, the plasma generating means is an RF inductive coil 28 housed within an enclosure 29. Gases may be removed from the chamber 23 via a pump port 27. A controller (not shown) configured to control the apparatus to carry out the process sequences described herein is also provided.

[0036] 3 and 4 show steps of an exemplary method according to a first aspect of a first embodiment of the present invention.

[0037] In an exemplary method, a silicon carbide (SiC) semiconductor substrate 30 is etched to form features. In an exemplary method, the features are trenches and the substrate 30 is a 150 mm silicon carbide wafer. However, other features may be formed and other compound semiconductor substrates may alternatively be used in the method of the first embodiment of the present invention. Other wafer sizes may also be used in the method of the first aspect of the first embodiment of the present invention. The parameters described below are used for etching a 150 mm SiC wafer, but may be modified depending on the size of the wafer in a manner known in the art.

[0038] The substrate 30 includes a patterned hardmask layer 32 having at least one opening 34 in the hardmask 32 that exposes the substrate 30 beneath the hardmask 32. The hardmask 32 is a silicon oxide (SiO X ), or other suitable hardmask material, such as SiN. Hardmask 32 is typically more resistant to plasma etch conditions than silicon carbide.

[0039] In a first step 101, the substrate 30 to be etched is placed, with the surface to be etched facing up, on the substrate support 22 in the plasma etcher 20. Prior to the plasma etching, a pre-etch may optionally be performed to prepare the substrate 30, for example to remove unwanted material from the openings 34 in the hard mask 32.

[0040] In a second step 102, a plasma etching step is performed to selectively etch the SiC substrate 30, thereby forming the trench structure 36. The plasma etching step 102 involves generating a plasma from an etching gas mixture to anisotropically etch the substrate 30 in the areas of the substrate 30 that are not covered by the hard mask 32. At the same time, a passivation material 44 is deposited at least on the opening 34 of the hard mask 32 and optionally also on at least one sidewall 40 of the trench 36 to be etched. The passivation material 44 is preferably SiO X The passivation material 44 and the mask may be made of the same material. Without wishing to be bound by any theory or speculation, the thickness (t p ) is believed to gradually increase to a thickness of 400 nm during the plasma etching step 102. This has the effect of gradually reducing the dimension of the opening 34 or feature 36 in the hard mask 32. The dimension may be a critical dimension and may correspond to the minimum width (w) of the opening 34 in the hard mask 32. In response to the reduction in the dimension of the opening 34, the etching at the area around the bottom 38 of the trench 36 is attenuated. The change in dimension w translates into a reduction in the etch width at the bottom 38 of the feature 36. Without wishing to be bound by any theory or speculation, it is believed that the passivation material 44 overhangs the corners of the bottom of the feature, ultimately protecting the corners of the bottom 38 of the feature 36 from the highly directional anisotropic plasma etching process. This has the effect of reducing the etch rate at the area around the bottom 38 (compared to the central area of ​​the bottom 38) as the etching proceeds. By controlling the deposition of the passivation material (and thus the dimension of the opening in the mask), the shape of the feature can be controlled as desired.

[0041] During the plasma etching step 102, a bias power is applied to the platen 22. For example, the bias power applied to the platen can be in the range of about 100 W to about 1500 W, optionally about 1300 W. This helps to provide directionality to the species (e.g., ions) in the plasma. Thus, the bottom 38 of the trench 36 is preferentially etched (over the sidewalls 40 of the trench).

[0042] The etching gas mixture includes at least one chlorine-containing component, at least one inert gas component, and at least one passivation material precursor. In an exemplary embodiment, the etching gas mixture used to generate the plasma consists of Cl2 gas as at least one chlorine-containing component, SiF4 and O2 gas as two passivation material precursors, and Ar gas as at least one inert gas component. At the start of the plasma etching step 102, the SiF4 flow rate can be 25 sccm to 50 sccm, the Cl2 flow rate can be at least 100 sccm, for example, 120 sccm, the O2 flow rate can be 12 sccm to 75 sccm, and the Ar flow rate can be 500 sccm to 800 sccm.

[0043] The inventors have discovered that by utilizing an etching gas mixture that includes at least one chlorine-containing component, at least one inert gas component, and at least one passivation material precursor, the final trench profile angle can be reduced while maintaining desired etching characteristics, such as etch rate and substrate / mask selectivity. Without wishing to be bound by any theory or speculation, it is believed that the combination of a strong anisotropic etch provided by at least one inert gas species and a chemical etch provided by at least one chlorine-containing species to create passivation material from at least one passivation material precursor on the openings 34 of the hard mask 32 allows for efficient processing of tapered or "V-shaped" features in a single etching step 102. This effect is particularly noticeable if the total flow rate (in sccm) of the at least one chlorine-containing component is at least as large as the total flow rate (in sccm) of the at least one passivation material precursor.

[0044] The chamber pressure during the plasma etching step can be in the range of about 2 mTorr (0.267 Pa) to about 60 mTorr (8.00 Pa), optionally about 12 mTorr (1.60 Pa). The plasma source power during the plasma etching step can be in the range of about 800 W to about 2400 W, optionally about 2400 W. The bias power applied to the substrate during the plasma etching step can be RF bias power. The RF frequency of the RF bias power can be between about 2 MHz and about 13.56 MHz. Typically, the platen 22 temperature set point can be between about 5° C. and about 50° C., preferably about 10° C., while the chamber walls are cooled by water to a temperature of about 55° C. Typically, due to the presence of chlorine in the etching gas mixture, a platen temperature of around 10° C. and a chamber wall temperature of about 55° C. are utilized.

[0045] During the plasma etching step 102, one or more parameters may be changed or "ramped" to change the plasma etching conditions and change the final shape of the etched feature 36. For example, the flow rate (in sccm) of at least one passivation material precursor, such as O2 and / or SiF4, may be four times higher at the end of the plasma etching step 102 than at the beginning of the plasma etching step 102. Increasing the flow rate of the passivation material precursor (such as O2) increases the deposition rate. Thus, starting with a low flow rate and increasing it over time increases the deposition rate of the passivation material 44. In another example, the bias power applied to the substrate support 22 may be reduced during the plasma etching step 102. Thereby, the final bias power may be about 50 W to 1400 W lower than the bias power at the beginning of the plasma etching step 102. Reducing the bias power contributes to the passivation material deposition. Thus, starting with a high power and decreasing it over time increases the passivation material formation rate. The change in one or more of these parameters over time may be linear or may occur to different degrees non-linearly, i.e., the parameter may be relatively constant at the start of the process and change significantly towards the end, or vice versa.

[0046] The plasma etching step 102 results in the formation of trench 36, as shown in Figures 4 and 5. Trench 36 has a bottom 38 that is generally parallel to the surface of substrate 30 on which hard mask 32 is formed. Trench 36 further has an opening 42 adjacent to the surface of substrate 30 on which hard mask 32 is formed.

[0047] Trench 36 further has tapered sidewalls 40 between a bottom 38 of trench 36 and an opening 42. Tapered sidewalls 40 taper less than 85° relative to the horizontal, i.e., a plane perpendicular to the direction of the anisotropic etch.

[0048] The length of the plasma etching step depends on the thickness of substrate 30 and the desired dimensions of trench 36, as is known in the art.

[0049] As shown in FIG. 5, trench 36 may undergo multiple post-processing steps, such as mask removal, smoothing, or polishing, to become the final feature. EXAMPLES

[0050] An exemplary set of process parameters for the plasma etching step of the method of the first embodiment is shown in Table 1. The exemplary process was carried out in a modified Omega® Synapse™ etcher with the source and bias RF power supplies operating at 13.56 MHz.

[0051] [Table 1]

[0052] This process achieved an etch rate of 520 nm / min with a substrate to hardmask selectivity of 9:1. The final sidewall taper angle was 81° to the horizontal. By replacing Cl2 with SF6, trenches were formed with sidewall taper angles between 88° and 89° under similar process conditions. Similarly, removing Cl2 gas from the etch gas mixture resulted in a lower etch rate of 70 nm / min due to the lack of available etch species.

[0053] Controlling the deposition rate of the passivation material, and therefore the thickness of the passivation material, allows the dimension of the opening in the hard mask to be controlled. Controlling this dimension allows the etch width of the bottom of the feature to be controlled, and the shape and morphology of the entire feature and the bottom surface of the etched feature can be controllably varied. Furthermore, controlling the deposition rate of the passivation material allows the shape of the bottom edge of the feature to be controlled. A particular advantage is obtained for features with rounded bottom corners. Rounded (or curved) corners allow the electric field to be distributed more evenly, thus reducing field bunching. This has the advantage that the breakdown voltage can be maximized. [Explanation of symbols]

[0054] 20 Plasma Etching Equipment 23 Chamber 25, 26 Gas inlet 250 RF power supply 252 Electrode 29 Case 27 Pump Port 28 RF Induction Coil 30 Semiconductor Substrate 32 Hard Mask 34 Aperture 36 Features 44 Passivation materials.

Claims

1. 1. A method of plasma etching a silicon carbide substrate to form a tapered feature, comprising: Providing a silicon carbide substrate having a hard mask formed thereon with an opening on a substrate support in a chamber; performing a plasma etching step to anisotropically etch the substrate through the opening to form a tapered feature; Including, The method, wherein the plasma etching step includes generating a plasma from an etching gas mixture including at least one chlorine-containing component, at least one inert gas component, and at least one passivation material precursor, and wherein the anisotropic etching of the substrate includes depositing a passivation material at least over the opening such that the tapered feature has at least two sidewalls, each sidewall being sloped at an angle of less than 85° relative to the horizontal.

2. The method of claim 1 , wherein the at least one passivation material precursor comprises at least one silicon-containing component.

3. The at least one silicon-containing component is SiCl ４ , SiF ４ or a combination thereof.

4. 4. The method of claim 2 or 3, wherein a total flow rate of the at least one silicon-containing component at the start of the plasma etching step is from about 10 sccm to about 50 sccm.

5. The method of claim 1 , wherein the at least one passivation material precursor comprises at least one oxygen-containing component.

6. The at least one oxygen-containing component is O ２ The method of claim 4 comprising a gas.

7. 7. The method of claim 5 or 6, wherein a total flow rate of the at least one oxygen-containing component at the start of the plasma etching step is from about 12 sccm to about 75 sccm.

8. 8. The method of claim 1, wherein the plasma etching step comprises increasing a flow rate of the at least one passivation material precursor during the plasma etching step.

9. 9. The method of claim 8, wherein a flow rate of the at least one passivation material precursor in sccm at the end of the plasma etching step is at least twice as high as a flow rate of the at least one passivation material precursor in sccm at the start of the plasma etching step.

10. The at least one chlorine-containing component is Cl ２ The method of claim 1 , further comprising a gas.

11. 11. The method of claim 1, wherein the at least one inert gas component comprises helium, argon, or a combination thereof.

12. 12. The method of claim 1, wherein a total flow rate of the at least one inert gas component is from about 500 sccm to about 800 sccm.

13. 13. The method of any one of claims 1 to 12, wherein each sidewall is inclined at an angle of 81° or less with respect to the horizontal, and optionally each sidewall is inclined at an angle of 74° or less with respect to the horizontal.

14. 14. The method of claim 1, wherein a ratio of a total flow rate in sccm of the at least one chlorine-containing component at the end of the plasma etching step to a total weight in sccm of the at least one passivation material precursor at the end of the plasma etching step is from about 1:1 to about 3:

1.

15. 15. The method of claim 1, wherein a total flow rate of the at least one chlorine-containing component is at least 100 sccm.

16. 16. The method of any one of claims 1 to 15, wherein the plasma etching step is performed utilizing a plasma source supplying a power of about 800 W to about 2400 W to the plasma.

17. 17. The method of claim 1, wherein an initial bias power of 100 W to 1500 W is applied to the substrate support during the plasma etching step.

18. 18. The method of claim 1, wherein the plasma etching step comprises lowering the bias power applied to the substrate support during the plasma etching step.

19. 20. The method of claim 18, wherein the initial bias power applied to the substrate support during the plasma etching step is reduced by at least 50%.

20. 20. The method of any one of claims 1 to 19, wherein the substrate support is maintained at a temperature between about 5°C and 50°C.

21. 21. The method of any one of claims 1 to 20, wherein the pressure in the chamber during the plasma etching step is between 2 mTorr (0.267 Pa) and 60 mTorr (8.00 Pa).

22. 22. A plasma etching apparatus for plasma etching a silicon carbide substrate to form a tapered feature utilizing the method of any one of claims 1 to 21, comprising: A chamber; a substrate support disposed within the chamber to support a substrate thereon; at least one gas inlet for introducing a gas or gas mixture into the chamber at a flow rate; - plasma generating means for maintaining a plasma in said chamber; a power supply for supplying electrical bias power to the substrate support; a controller configured to operate the plasma etching apparatus to generate a plasma from an etching gas mixture including at least one chlorine-containing component, at least one inert gas component, and at least one passivation material precursor; An apparatus comprising:

23. 23. The apparatus of claim 22, wherein the at least one gas inlet comprises a first gas inlet for introducing at least one chlorine-containing component into the chamber, a second gas inlet for introducing at least one inert gas component into the chamber, and a third gas inlet for introducing at least one passivation material precursor into the chamber, and the controller is configured to form an etching gas mixture in the chamber comprising at least one chlorine-containing component, at least one inert gas component, and at least one passivation material precursor, thereby generating a plasma from the etching gas mixture.

24. 24. The apparatus of claim 22 or 23, wherein the at least one gas inlet includes a fourth gas inlet for introducing an additional passivation material precursor into the chamber, and the controller is configured to form an etching gas mixture in the chamber comprising the at least one chlorine-containing component, at least one inert gas component, and at least two passivation material precursors, thereby generating a plasma from the etching gas mixture.

25. 25. The apparatus of any one of claims 22 to 24, wherein the controller is configured to modify at least one of a flow rate and / or the power generated by the power supply to provide an electrical bias power to the substrate support during generation of plasma in the chamber.

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