Plasma etched compound semiconductor

Abstract

The embodiment of the invention relates to a plasma etched compound semiconductor. A method of plasma etching a silicon carbide substrate to form a tapered feature, a silicon carbide substrate, and a plasma etching apparatus for plasma etching a silicon carbide substrate to form a tapered feature are provided.

Description

Technical Field

[0001] The present invention relates to a method for plasma etching features in a compound semiconductor substrate. The present invention also relates to a plasma etching apparatus. Background Art

[0002] There is an increasing demand for high power and high frequency devices based on compound semiconductors, which cannot be met by conventional silicon-based technologies. Wide bandgap compound semiconductors, such as silicon carbide (SiC), combine excellent electronic and thermal properties that can exceed those of silicon. However, it can be challenging to produce such compound semiconductor devices in large quantities at an acceptable cost using known methods, which typically require many processing steps. It would be desirable to develop a method for producing compound semiconductor devices, such as SiC devices, in a more economical manner with fewer processing steps.

[0003] Power device silicon carbide trenches (typically dry-etched silicon carbide trenches with a width between 0.5 μm and 10 μm and a depth between 0.5 μm and 3 μm) are increasingly used in power semiconductor devices, primarily in MOSFET gates, where the trenches are often coated with silicon oxide (SiO X ) layer and then filled with polysilicon. Figure 2 The flat-bottomed rectangular cross-section groove shown in the groove A in FIG. Figure 2 , trench 10 has a substantially flat bottom surface 12 and substantially vertical sidewalls 14. However, microgrooves at the bottom of flat-bottomed trenches can cause problems. Microgrooves refer to the deeper etched portions at the corners of the trenches. The sharp angles inherent in microgrooves can cause the electric field within the substrate to concentrate at these locations, which can cause the breakdown voltage to decrease. It is desirable to avoid microgrooves; and maximize the breakdown voltage.

[0004] Even in flat-bottomed trenches (no micro-grooves), the electric field is susceptible to "field bunching". That is, the electric field tends to concentrate at specific locations within the trench, such as the corners of the trench. Therefore, it is desirable to minimize field bunching as much as possible by being able to control the curvature of the corners of the trench. A trench with rounded corners (also called a "U-shaped trench") has a much more dispersed internal field, which increases the breakdown voltage and means that in many devices such as Figure 2 The performance of the rounded corner groove shown in the exemplary groove B will be better than the square corner groove.

[0005] Another promising trench morphology is the tapered sidewall or "V-shaped" trench, e.g. Figure 2 This shape allows the use of The V-groove is currently produced by thermally activated etching in a chlorinated environment, which gives the grooves a higher channel mobility than other directions within the material, which means lower channel resistance. Planar sidewalls. However, like thermal annealing, this process will have its own risks and yield challenges. Perhaps more importantly, the sidewall angles of the trench structure are limited to this plane - while this may be an advantage for channel mobility, it may also be a disadvantage from a gate depth perspective, where a fixed minimum trench top width is required to achieve a specific desired depth. And finally, the corners of the V-shape, or perhaps where the tapered sidewalls meet any flat portion at the base, will inherently provide at least somewhat sharp corners, which can cause field bunching.

[0006] Therefore, there is a need in the art for a plasma etching method that can etch trenches with tapered sidewalls in SiC while avoiding the need for thermally activated etching. Summary of the invention

[0007] The present invention, in at least some of its embodiments, seeks to address the above-described problems, desires, and needs.

[0008] According to a first aspect of the present invention, there is provided a method for plasma etching a silicon carbide substrate to form a tapered feature, the method comprising the following steps:

[0009] providing a substrate having a hard mask formed thereon on a substrate support in a chamber, the hard mask having an opening, wherein the substrate is formed of silicon carbide;

[0010] performing a plasma etching step to anisotropically etch the substrate through the opening to produce a tapered feature,

[0011] wherein the plasma etching step comprises generating a plasma from an etchant gas mixture comprising at least one chlorine-containing component, at least one inert gas component, and at least one passivation material precursor, and the anisotropic etching of the substrate comprises depositing a passivation material at least on the opening such that the tapered feature comprises at least two sidewalls and each sidewall is inclined at an angle less than 85° relative to a horizontal plane.

[0012] Without wishing to be bound by any theory or conjecture, it is believed that by providing an etchant gas mixture comprising at least one chlorine-containing component, at least one inert gas component and at least one passivation material precursor, a highly anisotropic etching process can be performed while depositing the passivation material at least on the opening of the hard mask, resulting in an effective reduction in the critical dimension of the hard mask and a reduction in the etch width of the base of the trench. By controlling the deposition and etching rate of the passivation material, the taper of the sidewalls can be tightly controlled, even thereby allowing the corners at the base of the trench to be rounded, thereby allowing the advantages of U-shaped trenches and V-shaped trenches to be combined in a single etching step. The method of the present invention also shows high substrate and mask selectivity, allowing selectivities of up to 9:1 to be achieved.

[0013] The substrate may be a SiC wafer. The substrate may be a 150 mm SiC wafer. The hard mask may be made of a material selected from SiO x And SiN material formation.

[0014] The at least one passivation material precursor may include at least one silicon-containing component. The at least one silicon-containing component may include SiCl 4 、SiF 4 or a combination thereof. The at least one silicon-containing component may include SiF 4 The at least one silicon-containing component may be SiF 4 Composed of or consisting essentially of SiF 4 The at least one passivation material precursor may include at least one oxygen-containing component. The at least one oxygen-containing component may include O 2 、N 2 O, H 2 O, O 3 or a combination thereof. The at least one oxygen-containing component may include O 2 The at least one oxygen-containing component may be composed of O 2 Gases composed of or consisting essentially of O 2 The at least one chlorine-containing component may include Cl 2 , HCl, BCl 3 or a combination thereof. The at least one chlorine-containing component may include Cl 2 The at least one chlorine-containing component may be Cl 2 Gas composed of or consisting essentially of Cl 2 The at least one passivation material precursor may include C 4 F 8 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 of or consist essentially of argon.

[0015] The total flow rate of the silicon-containing component at the beginning of the plasma etching step may be from about 10 sccm to about 50 sccm. The total flow rate of the at least one silicon-containing component at the beginning of the plasma etching step and / or at the end of the plasma etching step may be about 39 sccm. The total flow rate of the at least one oxygen-containing component at the beginning of the plasma etching step may be from about 12 sccm to about 75 sccm. The total flow rate of the at least one oxygen-containing component at the beginning of the plasma etching step and / or at the end of the plasma etching step may be about 50 sccm. The total flow rate of the at least one chlorine-containing component may be at least 100 sccm, for example, at least 120 sccm. The total flow rate of the at least one chlorine-containing component may be about 120 sccm. The total flow rate of the at least one inert gas component may be from about 500 sccm to about 800 sccm. The total flow rate of the at least one inert gas component may be about 700 sccm. The ratio of the total flow rate of the at least one chlorine-containing component in sccm at the end of the plasma etching step to the total flow rate of the at least one passivation material precursor in sccm at the end of the plasma etching step may be from about 1:1 to about 3:1. The ratio of the total flow rate of the at least one chlorine-containing component in sccm at the end of the plasma etching step to the total flow rate of the at least one passivation material precursor in sccm at the end of the plasma etching step may be at least about 1:1.

[0016] The plasma etching step may include depositing a passivation material onto the hard mask and at least one etched sidewall of the feature. The net deposition rate of the passivation material may be greater than zero throughout the plasma etching step. The passivation material may be deposited at an increased deposition rate during the plasma etching step. The deposition rate of the passivation material may increase at an increased rate of change during the plasma etching step. The size of the opening in the hard mask may decrease at an increased rate of change. Increasing the deposition rate of the passivation material during the plasma etching step may help produce features having both tapered sidewalls and rounded corners in the edge region of the bottom surface. For example, the feature may be a generally V-shaped groove with a bottom surface having a curved edge. The passivation material may have a deposition thickness increasing to about 400 nm, optionally about 300 nm, optionally about 200 nm, optionally about 150 nm, or optionally about 125 nm on each side of the opening. The size of the opening in the hard mask may be reduced by approximately 100 nm to 800 nm, 200 nm to 600 nm, 250 nm to 500 nm, 300 nm to 400 nm, or approximately 350 nm, or any combination of these upper and lower limits.

[0017] The plasma etching step may include changing a process parameter during the plasma etching step. The plasma etching step may include ramping a process parameter during the plasma etching step. The changed process parameter may be ramped at an increasing rate of change. The changed process parameter may be ramped at a constant rate of change. The term "ramping" may mean systematically increasing or systematically decreasing a value.

[0018] The plasma etching step may include changing or ramping at least one of a gas mixture composition, a gas flow rate, a processing time, a plasma source power, a bias power applied to the substrate, and / or a frequency.

[0019] Changing the process parameters may include changing the 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 beginning of the plasma etching step. The plasma etching step may include increasing the flow rate of the 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 beginning of the plasma etching step. The flow rate of the at least one oxygen-containing component may increase from about 12 sccm at the beginning of the plasma etching step to about 50 sccm at the end of the plasma etching step. The plasma etching step may include increasing the 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 may be at least two, three, or four times the flow rate of the at least one silicon-containing component in sccm at the beginning of the plasma etching step. The flow rate of the at least one silicon-containing component may increase from about 10 sccm at the beginning of the plasma etching step to about 39 sccm at the end of the plasma etching step.

[0020] Changing the process parameters may include changing 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 50W to 1400W. The bias power applied to the substrate at the beginning of the plasma etching step may be a power in the range of about 100W to about 1500W, about 1000W to about 1400W, or about 1300W. The bias power applied to the substrate at the end or near the end of the plasma etching step may be a power in the range of about 50W to about 1500W. The initial bias power applied to the substrate support may be reduced by at least 50%, such as at least 60%, at least 70%, at least 80%, or at least 90% during the plasma etching step. 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 throughout the plasma etching step may be between 100 W and 1500 W. The bias power applied to the substrate support throughout the plasma etching step may be about 1300 W. Any other process parameters may be changed or ramped during the plasma etching step. Changing or ramping process parameters may help control the etching rate of the substrate through the opening while also controlling the deposition rate of the passivation material.

[0021] The plasma etching step may be performed using a plasma source that supplies a power of from 800 W to 2400 W to the plasma. During the plasma etching step, the plasma source may supply a power of about 2400 W to the plasma.

[0022] The passivation material may include silicon oxide, for example, SiO X The passivation material is generally more resistant to plasma etching processes than the compound semiconductor material of the substrate. The etch selectivity between the substrate material and the passivation material may be in the range of about 5:1 to about 9:1. The passivation material and the hard mask may be made of substantially the same material.

[0023] The etching recipe for the plasma etching step may consist of or consist essentially of at least one chlorine-containing component, at least one inert gas component (e.g., He and / or Ar), and one or more gases selected from the group consisting of an oxygen-containing component (e.g., O 2 ) and / or at least one silicon-containing component (e.g., SiF4 and / or SiCl 4 The plasma etching step may include using a Cl 2 , O 2 、SiF 4 and Ar or consists essentially of Cl 2 , O 2 、SiF 4 And the etching formula composed of Ar.

[0024] The method of the first embodiment of the present invention may further include a passivation removal step after the plasma etching step to remove the passivation material formed on the substrate and the hard mask. The passivation removal step may be wet etching, for example, using HF etchant. Alternatively, the passivation removal step may be dry etching, including etching the substrate.

[0025] The size of the opening of the hard mask before the plasma etching step may be in the range of about 0.5 μm to about 10 μm or about 1 μm to about 8 μm. The size of the opening may be a width. The feature may have a maximum width in the range of about 0.5 μm to about 10 μm. The feature may have a depth in the range of about 0.5 μm to about 3 μm.

[0026] The tapered feature may be a groove. The tapered feature may be a through hole. The bottom surface of the tapered feature may be substantially flat. The bottom surface of a fully formed tapered feature may be substantially concave. The term "substantially concave" is used herein to mean a shape where a line segment can be drawn between two points on opposite sides of the bottom surface (e.g., from opposite edge regions) without intersecting the substrate (i.e., having a central region that is deeper than the edge region). This definition includes a curved profile that includes a flat central region. This definition includes a curved profile with tapered corners. The present invention allows the profile of the bottom surface to be customized according to the needs of the user.

[0027] The central area of ​​the bottom surface of the fully formed tapered feature may be substantially flat. The edge area may provide a continuous change in slope from the central area of ​​the tapered feature to at least one tapered sidewall. The edge area may extend from the sidewall of the feature in 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 a distance of about 175 nm. The edge area of ​​the bottom surface of the fully formed tapered feature may include a curved surface. The edge area may form a fillet between the central area of ​​the bottom surface of the tapered feature and the sidewall. The edge area may form a tapered corner between the central area of ​​the bottom surface of the tapered feature and the sidewall.

[0028] 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 within the chamber during the plasma etching step may be from 2mTorr (0.267Pa) to 60mTorr (8.00Pa). The pressure within the chamber during the plasma etching step may be about 12mTorr (1.60Pa).

[0029] The plasma etching step may be performed using an inductively coupled plasma (ICP) etching apparatus. The passivation removal step may also be performed using an inductively coupled plasma (ICP) etching apparatus.

[0030] According to a second aspect of the present invention, there is provided a silicon carbide substrate comprising at least one tapered feature provided by the method of the first aspect of the present invention, the at least one tapered feature comprising at least two sidewalls, wherein each sidewall is inclined at an angle less than 85° relative to a horizontal plane.

[0031] The silicon carbide substrate may be a SiC wafer. The silicon carbide substrate may be a 150 mm SiC wafer. Each side wall may be inclined at an angle of 81° or less relative to the horizontal plane. Each side wall may be inclined at an angle of 74° or less relative to the horizontal plane.

[0032] 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 a tapered feature using the method according to the first aspect, the apparatus comprising:

[0033] Chamber;

[0034] a substrate support disposed within the chamber for supporting a substrate on the substrate support;

[0035] at least one gas inlet for introducing a gas or a gas mixture into the chamber at a flow rate;

[0036] plasma generating means for maintaining a plasma in the chamber;

[0037] a power supply for supplying electrical bias power to the substrate support; and

[0038] A controller configured to operate the plasma etching apparatus to generate a plasma from an etchant gas mixture comprising at least one chlorine-containing component, at least one inert gas component, and at least one passivation material precursor.

[0039] 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 form an etchant gas mixture including at least one chlorine-containing component, at least one inert gas component, and at least one passivation material precursor in the chamber to generate plasma from the etchant gas mixture. The at least one gas inlet may include a fourth gas inlet for introducing another passivation material precursor into the chamber, and the controller may be configured to form an etchant gas mixture including the at least one chlorine-containing component, the at least one inert gas component, and the at least two passivation material precursors in the chamber and generate plasma from the etchant gas mixture. The at least one gas inlet may include at least one other gas inlet (e.g., a fifth gas inlet) for introducing at least one other gas or gas mixture into the chamber, and the controller may be configured to form an etchant gas mixture including the at least one chlorine-containing component, the at least one inert gas component, at least two passivation material precursors, and the at least one other gas or gas mixture in the chamber and generate plasma from the etchant gas mixture. The controller may be configured to change at least one of a flow rate and / or the power generated by the power supply for supplying electrical bias power to the substrate support while generating plasma in the chamber. The controller may be configured to change a 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 used to introduce at least one oxygen-containing component into the chamber, and the controller may be configured to change the flow rate of the at least one oxygen-containing component. The plasma generating means may include a plasma source.

[0040] For the avoidance of doubt, when reference is made herein to “comprises” or “comprising” and similar terms, the present invention should also be construed to encompass more restrictive terms such as “consisting of” and “consisting essentially of.”

[0041] Although the present invention has been described above, the present invention extends to any creative combination of the features set forth above or in the following description, drawings or claims. For example, any feature disclosed with respect to the first aspect of the present invention may be combined with any feature of the second aspect of the present invention, and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Aspects of the method and apparatus according to the present invention will now be described with reference to the accompanying drawings, in which:

[0043] Figure 1is a schematic representation of a plasma etching apparatus according to an embodiment of the present invention;

[0044] Figure 2 is a schematic representation of A) a rectangular cross-section groove, B) a round bottom or "U-shaped" groove, and C) a tapered or "V-shaped" groove;

[0045] Figure 3 is a flow chart illustrating a method according to an embodiment of the present invention;

[0046] Figure 4 is a schematic representation of an etching process as part of a method according to an embodiment of the present invention; and

[0047] Figure 5 are SEM images of trenches with tapered sidewalls formed in SiC before and after an in-situ plasma passivation removal step. DETAILED DESCRIPTION

[0048] Figure 1 A schematic representation of a plasma etching apparatus 20 according to a second embodiment of the present invention is shown, which is suitable for performing a method according to a first embodiment of the present invention. Plasma etching of a substrate is performed using a suitable plasma etching apparatus. The plasma etching apparatus may be an inductively coupled plasma (ICP) apparatus. However, etching may also be performed using other dry etching systems, such as spiral, 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 here except as necessary for an understanding of the present invention.

[0049] A plasma etching tool suitable for carrying out the method of the present invention is the Omega (RTM) Synapse available from SPTS Technologies Limited of Newport, England. TM. The plasma etching apparatus 20 typically includes a substrate support (or platen) 22, also referred to as a wafer support, disposed within a chamber 23 for supporting a substrate. Bias power may be supplied to the substrate by an RF power supply 250 via an impedance matching network (not shown) and an electrode 252. Typical RF frequencies for operating the RF power supply may be between about 380 kHz and about 13.56 MHz. Process gases 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 an illustrative embodiment, two gas inlets 25, 26 are provided, and gases for generating plasma are introduced into the chamber 23 through the two gas inlets 25, 26. As is known in the art, a plasma generating component 28 (e.g., an induction coil) may be used to generate plasma and maintain plasma within the chamber 23 (e.g., using an RF power supply and an impedance matching network). In an illustrative embodiment, the plasma generating component is an RF induction coil 28 contained within a housing 29. Gas may be removed from chamber 23 via pump port 27. Additionally, a controller (not shown) is provided that is configured to control the apparatus to perform the process sequences described herein.

[0050] Figure 3 and 4 The stages of an exemplary method according to the first aspect of the first embodiment of the present invention are presented.

[0051] In the exemplary method, a silicon carbide (SiC) semiconductor substrate 30 is etched to form a feature. In the exemplary method, the feature is a groove, and the substrate 30 is a 150 mm silicon carbide wafer. However, other features may be formed and other compound semiconductor substrates may be used alternatively 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. Although the parameters described below are parameters for etching a 150 mm SiC wafer, the parameters may vary with the wafer size in a manner known in the art.

[0052] The substrate 30 includes a patterned hard mask layer 32 including at least one opening 34 in the hard mask 32, wherein the opening exposes the substrate 30 below the hard mask 32. The hard mask 32 may be formed of a silicon oxide (SiO X ) layer or other suitable hard mask material (eg, SiN). Hard mask 32 is generally more resistant to plasma etching conditions than silicon carbide.

[0053] In a first step 101, a substrate 30 to be etched is positioned on a substrate support 22 in a plasma etching apparatus 20 with the side to be etched facing upward. A pre-etch may optionally be performed to prepare the substrate 30 prior to plasma etching, for example to remove unwanted material from the opening 34 of the hard mask 32.

[0054] In a second step 102, a plasma etching step is performed to selectively etch the SiC substrate 30 so that the trench structure 36 is formed. The plasma etching step 102 includes generating a plasma from an etchant gas mixture to anisotropically etch the substrate 30 in 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 on at least one etched sidewall 40 of the trench 36. The passivation material 44 may be silicon oxide, for example, 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 conjecture, it is believed that the thickness (t p ) gradually increases to a thickness of 400 nm during the plasma etching step 102, which has the effect of gradually reducing the size of the openings 34 or features 36 of the hard mask 32. The size may be a critical size and may correspond to the minimum width (w) of the openings 34 in the hard mask 32. As the size of the openings 34 decreases, etching at the peripheral regions of the base 38 of the trenches 36 is reduced. The change in dimension w translates into a reduction in the etch width at the base 38 of the features 36. Without wishing to be bound by any theory or conjecture, it is believed that the passivation material 44 overhangs the corners of the base of the feature and thus protects the corners of the base 38 of the feature 36 from the highly directional anisotropic plasma etching process. This has the effect of reducing the etch rate at the peripheral regions of the base 38 (compared to the central region of the base 38) as the etching proceeds. By controlling the deposition of the passivation material (and therefore by controlling the size of the openings in the mask), the profile of the feature can be controlled as desired.

[0055] A bias power is applied to the platen 22 during the plasma etching step 102. For example, the bias power applied to the platen may be in a range of about 100 W to about 1500 W, optionally about 1300 W. This helps impart directionality to the species (e.g., ions) in the plasma so that the base 38 of the trench 36 (rather than the sidewalls 40 of the trench) is preferentially etched.

[0056] The etchant 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 etchant gas mixture used to generate the plasma includes Cl as the at least one chlorine-containing component. 2 Gas, SiF as a precursor for two passivation materials 4 and O 2 At the beginning of the plasma etching step 102, SiF 4 The flow rate can be from 25 sccm to 50 sccm, Cl 2The flow rate may be at least 100 sccm, for example, 120 sccm. 2 The flow rate may be from 12 sccm to 75 sccm, and the Ar flow rate may be from 500 sccm to 800 sccm.

[0057] The inventors have discovered that an etchant gas mixture including at least one chlorine-containing component, at least one inert gas component, and at least one passivation material precursor can be used to reduce the resulting trench profile angle while maintaining desired etching characteristics (e.g., etch rate and substrate and mask selectivity). Without wishing to be bound by any theory or conjecture, it is believed that the combination of the strongly anisotropic etching provided by the at least one inert gas species and the chemical etching provided by the at least one chlorine-containing species, combined with the buildup of the passivation material at least on the opening 34 of the hard mask 32 by the at least one passivation material precursor, in a single etching step 102, allows the formation of tapered or "V-shaped" features in an efficient process. This effect is particularly evident when the total flow rate of the at least one chlorine-containing component in sccm is at least as great as the total flow rate of the at least one passivation material precursor in sccm.

[0058] During the plasma etching step, the chamber pressure may 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). During the plasma etching step, the plasma source power may be in the range of about 800 W to about 2400 W, optionally about 2400 W. During the plasma etching step, the bias power applied to the substrate may be an RF bias power. The RF frequency of the RF bias power may be between about 2 MHz and about 13.56 MHz. Typically, the platen 22 temperature set point is between about 5° C. and about 50° C., preferably about 10° C., while water is used to cool the chamber walls to a temperature of about 55° C. Due to the presence of chlorine in the etchant gas mixture, a platen temperature of about 10° C. and a chamber wall temperature of about 55° C. are typically used.

[0059] During the plasma etching step 102, one or more parameters may be changed or "ramped" in order to alter the plasma etching conditions and alter the final profile of the etched features 36. For example, at least one passivation material precursor (e.g., O 2 and / or SiF 4 ) may be four times the flow rate at the end of the plasma etching step 102 as at the beginning of the plasma etching step 102. The increased passivation material precursor (e.g., O 2) flow rate results in a high deposition rate, so starting with a low flow rate and gradually 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 can be reduced during the plasma etching step 102, so that the final bias power can be about 50W to about 1400W lower than the bias power at the beginning of the plasma etching step 102. The reduction in bias power helps the passivation material deposition, so starting with a high power and reducing the bias power over time increases the passivation material accumulation rate. The changes in these one or more parameters can change over time and can be linear or have varying degrees of non-linearity, where the parameters start the process at a relatively constant value and change strongly near the end, or vice versa.

[0060] The plasma etching step 102 forms trenches 36, such as Figure 4 and 5 . The trench 36 includes a base 38 that is approximately parallel to the surface of the substrate 30 on which the hard mask 32 is formed. The trench 36 further includes an opening 42 that is adjacent to the surface of the substrate 30 on which the mask 32 is formed.

[0061] The trench 36 further includes a tapered sidewall 40 between a base 38 and an opening 42 of the trench 36. The tapered sidewall 40 has a taper of less than 85° relative to a horizontal plane (which is a plane perpendicular to the direction of the anisotropic etch).

[0062] The duration of the plasma etching step depends on the thickness of substrate 30 and the desired dimensions of trench 36 in a manner known in the art.

[0063] The groove 36 may undergo Figure 5 Several post-processing steps (e.g., mask removal, smoothing, or polishing) are shown in to provide the final features.

[0064] Examples

[0065] 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 performed on a modified Omega (RTM) Synapse TM The etching was performed in an etch apparatus with source and bias RF power supplies operating at 13.56 MHz.

[0066] Table 1

[0067] Process parameters Plasma Etching Process duration(s) 240 Pressure (mTorr) 12 ICP source power (Watt) 2400 Table power (Watt) 1300 Ar flow rate (sccm) 700 <![CDATA[O 2 Flow rate (sccm)]]> 50 <![CDATA[Cl 2 Flow rate (sccm)]]> 120 <![CDATA[SiF 4 Flow rate (sccm)]]> 39 Back side helium pressure (Torr) 10 Platen temperature (℃) 10

[0068] Using this process, an etch rate of 520nm / min and a substrate to hard mask selectivity of 9:1 were achieved, with a final sidewall taper angle of 81° relative to the horizontal plane. 6 Replace Cl2 A trench with similar process conditions was produced, but with a sidewall taper angle between 88° and 89°. Similarly, Cl was removed from the etchant gas mixture. 2 The gas resulted in an etch rate as low as 70 nm / min due to the lack of available etching species.

[0069] By controlling the deposition rate of the passivation material, and therefore by controlling the thickness of the passivation material, the size of the opening in the hard mask can be controlled. Control of this size allows the etch width at the base of the feature to be controlled, and the shape and profile of the feature as a whole, as well as the shape and profile of the etched bottom surface of the feature, can be controllably varied. In addition, controlling the deposition rate of the passivation material allows the profile of the edge at the base of the feature to be controlled. Particular advantages are associated with features that include a base with rounded corners. Rounded (or curved) corners can distribute the electric field more evenly, and therefore reduce field bunching. This can advantageously maximize the breakdown voltage.

Claims

1. A method for plasma etching a silicon carbide substrate to form a tapered feature, the method comprising the following steps: providing a substrate having a hard mask formed thereon on a substrate support in a chamber, the hard mask having an opening, wherein the substrate is formed of silicon carbide; performing a plasma etching step to anisotropically etch the substrate through the opening to produce a tapered feature, wherein the plasma etching step comprises generating a plasma from an etchant gas mixture comprising at least one chlorine-containing component, at least one inert gas component, and at least one passivation material precursor, and the anisotropic etching of the substrate comprises depositing a passivation material at least on the opening such that the tapered feature comprises at least two sidewalls and each sidewall is inclined at an angle less than 85° relative to a horizontal plane. 2 . The method of claim 1 , wherein the at least one passivation material precursor comprises at least one silicon-containing component.

3. The method of claim 2, wherein the at least one silicon-containing component comprises SiCl4, SiF4, or a combination thereof.

4. The method of claim 2 or claim 3, wherein the 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, claim 2 or claim 3, wherein the at least one passivation material precursor comprises at least one oxygen-containing component.

6. The method of claim 5, wherein the at least one oxygen-containing component comprises O2 gas.

7. The method of claim 5, wherein the 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. The method of claim 1, claim 2 or claim 3, wherein the plasma etching step comprises increasing the flow rate of the at least one passivation material precursor during the plasma etching step.

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

10. The method of claim 1, claim 2 or claim 3, wherein the at least one chlorine-containing component comprises Cl2 gas.

11. The method of claim 1, claim 2 or claim 3, wherein the at least one inert gas component comprises helium, argon, or a combination thereof.

12. The method of claim 1, claim 2 or claim 3, wherein the total flow rate of the at least one inert gas component is from about 500 seem to about 800 seem.

13. The method of claim 1, claim 2 or claim 3, wherein each side wall is inclined at an angle of 81° or less relative to the horizontal plane, optionally wherein each side wall is inclined at an angle of 74° or less relative to the horizontal plane.

14. The method of claim 1, claim 2 or claim 3, wherein the ratio of the total flow rate of the at least one chlorine-containing component in sccm at the end of the plasma etching step to the total flow rate of the at least one passivation material precursor in sccm at the end of the plasma etching step is from about 1:1 to about 3:

1.

15. The method of claim 1, claim 2 or claim 3, wherein the total flow rate of the at least one chlorine-containing component is at least 100 seem.

16. The method of claim 1, claim 2 or claim 3, wherein the plasma etching step is performed using a plasma source that supplies a power of from about 800 W to about 2400 W to the plasma.

17. The method of claim 1, claim 2 or claim 3, wherein during the plasma etching step, an initial bias power of from 100 W to 1500 W is applied to the substrate support.

18. The method of claim 1, claim 2 or claim 3, wherein the plasma etching step comprises reducing a bias power applied to the substrate support during the plasma etching step.

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

20. The method of claim 1, claim 2 or claim 3, wherein the substrate support is maintained at a temperature between about 5°C and about 50°C.

21. The method of claim 1, claim 2 or claim 3, wherein during the plasma etching step, the pressure within the chamber is from 2 mTorr (0.267 Pa) to 60 mTorr (8.00 Pa).

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

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 etchant gas mixture comprising at least one chlorine-containing component, at least one inert gas component, and at least one passivation material precursor in the chamber to generate a plasma from the etchant gas mixture.

24. An apparatus according to claim 22 or claim 23, wherein the at least one gas inlet includes a fourth gas inlet for introducing another passivation material precursor into the chamber, and the controller is configured to form an etchant gas mixture in the chamber including the at least one chlorine-containing component, the at least one inert gas component and the at least two passivation material precursors and generate plasma from the etchant gas mixture.

25. The apparatus of claim 22 or claim 23, wherein the controller is configured to vary at least one of a flow rate and / or the power generated by the power supply for supplying electrical bias power to the substrate support while generating plasma in the chamber.

Images