Method of plasma-etching feature, substrate formed thereby, and device for plasma etching

Abstract

To provide a method of plasma-etching a compound semiconductor substrate to form a feature.SOLUTION: The method comprises the steps of: providing a substrate with a mask 32 formed on the substrate; performing a first plasma etch step to anisotropically etch the substrate through the opening to produce a partially formed feature 34b having a bottom surface comprising a peripheral region 43; and performing a second plasma etch step to anisotropically etch the bottom surface of the partially formed feature 34b through the opening while depositing a passivation material 40 on the mask 32 so as to reduce a dimension of the opening. The reduction of the dimension of the opening causes an attenuation in etching of the peripheral region 43 thereby producing a feature 34d having a bottom surface comprising a central region 39 and an edge region 44.SELECTED DRAWING: Figure 3

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 compound semiconductor substrate formed using the above-described method, and the present invention also relates to a plasma etching apparatus. [Background technology]

[0002] There is an ever-increasing demand for high power and high frequency devices based on compound semiconductors that cannot be met by conventional silicon-based technologies. In particular, wide band-gap compound semiconductors (such as silicon carbide (SiC)) combine excellent electronic and thermal properties that can exceed those of silicon. However, fabricating such compound semiconductor devices in high volumes at acceptable costs using known methods can be challenging and often requires many processing steps. It is desirable to develop methods for fabricating compound semiconductor devices (such as SiC devices) in a more economical manner with fewer processing steps.

[0003] Power Devices Silicon carbide trenches are finding increasing use in power semiconductor devices. It is known to use flat-based trenches, where a trench 10 has a substantially flat bottom surface 12 with substantially vertical sidewalls 14, as shown in FIG. 1. However, micro-trenching at the bottom of a flat-based trench can cause problems. Micro-trenching represents a deeper etched section at the corners of the trench. The sharp angles inherent in micro-trenches can cause the electric field in the substrate to be concentrated at these locations, which can lead to reduced breakdown voltage. It is desirable to avoid micro-trenching and to maximize the breakdown voltage.

[0004] Even in flat-bottom trenches (without micro-trenching), the electric field is susceptible to "field bunching," i.e., the electric field tends to concentrate at certain locations in the trench, such as at the trench corners. It is therefore desirable to minimize field bunching as much as possible. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2017 / 0140936 [Patent Document 2] US Patent Application Publication No. 2007 / 0281462 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention, in at least some of its embodiments, seeks to address the problems, wants, and needs described above. In particular, the present invention seeks to provide a method for controlling the profile at the bottom of a trench to better distribute the internal electric field within the trench and to increase the breakdown voltage. For example, at least some embodiments of the present invention provide a method for controllably forming a trench with rounded corners or a base having a rounded profile. [Means for solving the problem]

[0007] According to a first aspect of the invention, there is provided a method of plasma etching a compound semiconductor substrate to form features, the method comprising: (a) providing a substrate with a mask formed thereon, the mask having an opening, the substrate being formed from a compound semiconductor material; (b) performing a first plasma etching step to anisotropically etch the substrate through the opening to create a partially formed feature having a bottom surface that includes a peripheral region; (c) performing a second plasma etching step to anisotropically etch a bottom surface of the partially formed feature through the opening while depositing passivation material over the mask to reduce a dimension of the opening, the reduction in the dimension of the opening causing a decrease in the etching of the peripheral region, thereby creating a fully formed feature having a bottom surface that includes a central region and an edge region, the central region being deeper than the edge region of the bottom surface of the fully formed feature; A method is provided that includes:

[0008] Without wishing to be bound by any theory or speculation, it is believed that the passivation material deposited on the mask to reduce the size of the opening protects the peripheral region of the partially formed feature from the distribution of species in the plasma during the second plasma etching step. As a result, the amount of material removed from the peripheral region during the second plasma etching step is less than the amount of material removed from the central region. Controlling the reduction in the size of the opening during the second plasma etching step allows the profile at the bottom of the feature to be controlled and formed into a desired shape. The method allows the feature to have a rounded, curved, or other smooth surface (i.e., a gradual change in slope), which can improve the distribution of the electric field in the feature and can also help minimize field bunching. As a result, the method can help create features with high breakdown voltages. Additionally, the method can help avoid the formation of micro-trenches that form in the edge regions (e.g., corners) of the bottom surface of the feature.

[0009] A passivation material may be deposited on the mask and the sidewalls of the feature being etched. The passivation material may be deposited on the sidewalls of the mask. The passivation material may be deposited at an increasing deposition rate during the second plasma etch step. The deposition rate of the passivation material may be increased during the second plasma etch step at an increasing rate of change. The dimensions of the opening in the mask may be reduced at an increasing rate of change. Increasing the deposition rate of the passivation material during the second plasma etch step may help create a feature with rounded corners in an edge region of the bottom surface. For example, the feature may be generally flat-bottomed U-shaped. The passivation material may have a deposition thickness that increases on each side of the opening by up to about 300 nm, optionally up to about 250 nm, optionally up to about 175 nm, optionally up to about 150 nm, or optionally up to about 125 nm. The dimensions of the openings in the mask layer may be reduced by a distance of about 100-600 nm, 200-500 nm, 250-450 nm, 300-400 nm, or about 350 nm, or any combination of these upper and lower limits.

[0010] The second plasma etching step can include varying a process parameter during the second plasma etching step. The second plasma etching step can include ramping a process parameter during the second plasma etching step. For example, the second plasma etching step can include varying or ramping at least one of the gas mixture composition, gas flow rate, processing time, plasma source power, bias power applied to the substrate, and / or frequency. Any other process parameter can be varied or ramped during the second plasma etching step. This can help control the etch rate of the substrate through the opening while also controlling the deposition rate of the passivation material.

[0011] The process parameters that are changed may be ramped at an increasing rate of change. The process parameters that are changed may be ramped at a constant rate of change. The term "ramping" can mean either a systematic increase or a systematic decrease in value.

[0012] Varying the process parameters can include varying a flow rate of the passivation material precursor during the second plasma etch step.

[0013] The flow rate of the passivation material precursor may be increased during the second plasma etch step. The flow rate (sccm) of the passivation material precursor at the end of the second plasma etch step may be at least two, three, or four times higher than the flow rate (sccm) of the passivation material precursor at the beginning of the second plasma etch step. The flow rate of the passivation material may be increased from about 25 sccm to about 100 sccm.

[0014] The substrate may be disposed in the chamber. The method may include introducing a passivation material precursor into the chamber during the second plasma etch step at a higher flow rate as compared to the first plasma etch step. The second plasma etch step may include introducing the passivation material precursor into the chamber at a predetermined flow rate, and the flow rate of the passivation material precursor introduced into the chamber during the second plasma etch step may be higher than the flow rate of the passivation material precursor introduced into the chamber during the first plasma etch step.

[0015] The passivation material precursor can include an oxygen-containing gas, such as O2.

[0016] The step of varying the process parameters can include varying a bias power applied to the substrate during the second plasma etch step. The bias power applied to the substrate can be decreased during the second plasma etch step. The bias power applied to the substrate at the beginning of the second plasma etch step can be higher than the bias power applied to the substrate at the end of the second plasma etch step by an amount in the range of about 50-300 W. The bias power applied to the substrate at the beginning of the second plasma etch step can be a power in the range of about 230-500 W, in the range of 240-350 W, or about 250 W. At or towards the end of the second plasma etch step, the bias power applied to the substrate can be a power in the range of about 140-220 W, in the range of about 170-210 W, or about 190 W. The bias power applied to the substrate during the second plasma etch step can be lower than the bias power applied to the substrate during the first plasma etch step. The bias power applied to the substrate during the first plasma etching step can be in the range of approximately 100-1600W, or in the range of approximately 400-1400W.

[0017] The passivation material can include silicon oxide, such as SiO2. The passivation material is typically more resistant to plasma etching processes compared to the compound semiconductor material of the substrate. The etch selectivity between the substrate material and the passivation material can range from about 2:1 to about 3:1. The passivation material and the mask can be made of substantially the same material. The mask can include silicon oxide, such as SiO2.

[0018] The first plasma etching step may include using an etch recipe that includes a chlorine-based etchant (e.g., Cl2 and / or SiCl4), etc. The first plasma etching step may include an etch recipe that includes a fluorine-based etchant (e.g., a fluorinated gas, etc.). The etch recipe used for the first plasma etching step may consist of one or more gases selected from the group of a chlorine-based etchant (e.g., Cl2 and / or SiCl4), an oxygen-containing gas (e.g., O2), H2, and / or Ar gas.

[0019] The second plasma etching step may include using an etching recipe that includes a chlorine-based etchant. The chlorine-based etchant may include Cl2 and / or SiCl4. The second plasma etching step may include an etching recipe that includes a fluorine-based etchant (e.g., a fluorinated gas). The etching recipe used for the second plasma etching step may include using one or more gases selected from a chlorine-based or fluorine-based etchant, O2 gas, H2 gas, and / or Ar gas. The etching recipe used for the second plasma etching step may be composed of one or more gases selected from the group of a chlorine-based etchant (e.g., Cl2 and / or SiCl4), an oxygen-containing gas (e.g., O2), H2 and / or Ar gas. The second plasma etching step may include using an etching recipe that includes a chlorine-based etchant (e.g., Cl2 and / or SiCl4), an oxygen-containing gas (e.g., O2 gas), alternatively H2 gas, alternatively Ar gas. The etch recipe used for the first plasma etch step can be different from the etch recipe used for the second plasma etch step. For example, the ratio of gases used in the etch recipe for the second plasma etch step can be different from the ratio of gases used in the etch recipe for the first plasma etch step. The etch rate of the first plasma etch step can be higher than the etch rate of the second plasma etch step. When SiCl4 (or other silicon-containing gas) is used in the second plasma etch step, the flow rate of the silicon-containing gas can be greater than 50% of the total gas flow rate in sccm, optionally between 55% and 90%, optionally between 62% and 86%.

[0020] A bottom surface of the partially formed feature can be substantially planar. A bottom surface of the partially formed feature can be substantially convex. A bottom surface of the partially formed feature can include a micro-trench.

[0021] The feature can be a trench.The feature can be a via.

[0022] The dimension of the opening in the mask during the first plasma etching step can be in the range of about 0.5-20 μm or about 1-10 μm. The dimension of the opening can be maintained substantially constant during the first plasma etching step. The dimension of the opening can be a width. The feature can have a maximum width in the range of about 0.5-20 μm or about 1-10 μm. The feature can have a depth in the range of about 0.5-10 μm, 0.75-5 μm, or about 1-3 μm.

[0023] The bottom surface of a fully formed feature can be substantially concave. The term "substantially concave" is used herein to mean a shape in which it is possible to draw a line between two points on either side of the bottom surface (e.g., from opposing edge regions) without intersecting the substrate (i.e., having a central region that is deeper than the edge regions). This definition includes concave profiles that include a flat central region. This definition includes concave profiles with tapered corners. The invention allows the profile of the bottom surface to be tailored as needed by the user.

[0024] A central region of the bottom surface of the fully formed feature can be substantially flat.

[0025] An edge region of the bottom surface of the fully formed feature may include a curved surface. The edge region may form a rounded corner between a central region of the bottom surface and a sidewall of the fully formed feature. The edge region may form a tapered corner between a central region of the bottom surface and a sidewall of the fully formed feature. The sidewall is typically substantially perpendicular to the central region of the bottom surface of the fully formed feature. The sidewall may be inclined at an angle of 85-90°, 86-90°, 87-90°, 88-90°, or 89-90° relative to the central region of the bottom surface.

[0026] The compound semiconductor material can be silicon carbide (SiC) and the substrate can be a SiC wafer.

[0027] The method may further include (d) selectively removing the passivation material from the substrate by wet etching. The wet etching may be performed using an HF wet etchant.

[0028] Steps (b) and (c) may be carried out using an inductively coupled plasma (ICP) etcher.

[0029] According to a second aspect of the present invention there is provided a compound semiconductor substrate including a feature formed using a method as claimed in claim 1, the feature including a bottom surface, the bottom surface including substantially planar central and edge regions, the central region being deeper than the edge region.

[0030] The feature may include a sidewall that is substantially perpendicular to the central region. The feature may have a bottom surface (or base) that includes rounded corners. An edge region of the bottom surface may include a curved surface. The edge region may provide a continuous change in slope from the central region of the feature to the substantially perpendicular sidewall. The edge region may extend from the sidewall of the feature by a distance in the range of 100-350 nm, in the range of 125-300 nm, in the range of 150-250 nm, or optionally about 175 nm.

[0031] The feature can be a trench. The compound semiconductor substrate can be made of a compound semiconductor material. The compound semiconductor material can be silicon carbide (SiC). The compound semiconductor substrate can be a SiC wafer.

[0032] According to a third aspect of the present invention there is provided a plasma etching apparatus for plasma etching a substrate to form features using a method according to the first aspect, the apparatus comprising: A chamber; a substrate support disposed within the chamber for supporting a substrate thereon; at least one gas inlet for introducing a gas or gas mixture into the chamber at a predetermined flow rate; a plasma generating means for sustaining a plasma within the chamber; a power supply for supplying bias power to the substrate support; a controller configured to switch from a first set of processing conditions to a second set of processing conditions, the first set of processing conditions configured to perform a first plasma etching step to anisotropically etch the substrate through an opening in a mask to create a partially formed feature having a bottom surface including a peripheral region, and the second set of processing conditions configured to perform a second plasma etching step to anisotropically etch the bottom surface of the partially formed feature through the opening while depositing a passivation material over the mask to reduce a dimension of the opening, the reduction in the dimension of the opening causing a attenuation of etching of the peripheral region, thereby creating a fully formed feature having a bottom surface including a central region and an edge region, the central region being deeper than the edge region of the bottom surface of the fully formed feature; and A plasma etching apparatus is provided that includes:

[0033] Although the invention has been described above, it extends to any inventive combination of the features set out 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 or third aspect of the invention, and vice versa.

[0034] Embodiments of the substrate and method according to the present invention will now be described with reference to the accompanying drawings. [Brief description of the drawings]

[0035] [Figure 1] FIG. 1 shows a schematic cross-sectional view of a trench having a base with angled (square) corners (prior art). [Diagram 2] 1 is a schematic cross-sectional view of a plasma etching apparatus suitable for carrying out methods according to embodiments of the present invention; [Diagram 3] 3A-3C are schematic cross-sectional views of the substrate at subsequent stages of the method; [Figure 4] 2 is a schematic cross-sectional view of an opening in a mask layer over a substrate; [Diagram 5] FIG. 13 illustrates how passivation thickness varies with a linear increase in the flow rate of the passivation material precursor. [Figure 6] FIG. 1 shows a schematic cross-sectional view of a substrate including a feature having a base with tapered corners. [Figure 7] FIG. 13 illustrates how the passivation thickness varies with a non-linear increase in the flow rate of the passivation material precursor. [Figure 8] FIG. 1 shows a schematic cross-sectional view of a substrate including a feature having a base with rounded corners. [Figure 9] FIG. 1 shows an SEM image of a substrate including a feature having a base with rounded corners. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] FIG. 2 shows a schematic representation of a plasma etching apparatus 20 suitable for carrying out the method according to an embodiment of the present invention. A suitable plasma etching tool for carrying out the method of the present invention is the Omega(RTM) Synapse(TM) available from SPTS Technologies Limited of Newport, UK. Plasma etching of the substrate is typically carried out using a plasma etching apparatus. 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 except where necessary for an understanding of the present invention.

[0037] The plasma etching apparatus 20 typically includes a substrate support (or platen) 22 disposed in a chamber 23 for supporting a substrate 25. Bias power may be supplied to the substrate by an RF power supply 250 through an impedance matching network 252. The chamber may include chamber walls having a dielectric part 24. Process gases may be introduced into the chamber through one or more gas inlets 26. A plasma generating means 28, such as an inductive coil, may be used to generate and sustain a plasma in the chamber 23 as known in the art (e.g., using an RF power supply 280 and an impedance matching network 282). Gases may be removed from the chamber 23 through a pumping port 29.

[0038] FIG. 3 illustrates steps of an exemplary method according to a first embodiment. In the first embodiment, a compound semiconductor substrate 30 is etched to form features with rounded corners at the base of the features. In the first embodiment, the features are trenches and an embodiment of the substrate 30 is a silicon carbide (SiC) wafer. However, other compound semiconductor substrates may alternatively be used. The substrate 30 includes a patterned mask layer 32, such as a silicon dioxide (SiO2) layer or other suitable resist layer. The mask layer 32 is more resistant to plasma etching conditions than the bulk substrate material.

[0039] The substrate to be etched is positioned on a substrate support 22 in a plasma etcher 20 with the surface to be etched facing upwards. A pre-etch may (optionally) be performed to prepare the substrate 30 before the main etching cycle, e.g., to remove unwanted material from the open areas of the mask layer 32.

[0040] A first plasma etching step (i.e., main etch) is performed to selectively etch the SiC substrate 30 such that the majority of the feature is formed. Numeral 34b denotes the partially formed feature. The first plasma etching step corresponds to "Step 1" in FIG. 3. The first plasma etching step anisotropically etches the substrate through the opening. A bias power is applied to the platen 22 during the first plasma etching step. For example, the bias power applied to the platen can be in the range of about 100 W to 1400 W. This helps to provide directionality to the species (e.g., ions) in the plasma such that the base of the feature (rather than the sidewalls 38 of the feature) is preferentially etched. As a result, the width of the partially formed feature substantially corresponds to the initial width of the opening area in the mask layer 32.

[0041] During the first plasma etching step, the chamber pressure can be in the range of about 2 mTorr to about 20 mTorr. During the first plasma etching step, the plasma source power can be in the range of about 800 W to about 2000 W. Typically, the walls of the chamber 23 are cooled to about 55° C. by water. By way of example only, the process gas used in the main etching step can include one or more of Cl2, SiCl4, O2, H2, and / or Ar gas. Fluorinated etchant gases such as fluorocarbons can also be used.

[0042] The first plasma etching step results in the formation of a partially formed feature 34b. The partially formed feature 34b includes a planar base 36b that is approximately perpendicular to the sidewalls 38 of the trench 34b. The planar base 36b has a peripheral region (not labeled) adjacent the sidewalls 38. If microtrenching has occurred, the partially formed feature may include a substantially convex shape.

[0043] The substrate 30b is then subjected to a second plasma etching step (shown as "Step 2" in FIG. 3) in which the feature is fully formed. The plasma processing parameters used during the second plasma etching step are different from those used during the first plasma etching step. The second plasma etching step is an anisotropic plasma etching step. That is, the species forming the plasma are generally directed towards the substrate with a high degree of directionality. In this example, the species forming the plasma generally bombard the substrate in a direction substantially perpendicular to the substrate surface. As a result, the bottom surface 36b of the high aspect ratio feature can be etched without significant etching of the sidewalls.

[0044] A second plasma etching step anisotropically etches the bottom surface 36b of the partially formed substrate. At the same time, a passivation material 40 is deposited on the sidewalls 42c of the mask layer 32 and on the sidewalls 38 of the feature being etched (FIGS. 3 and 4). The passivation material 40 can be a silicon oxide, such as SiO2. The passivation material and the mask can be made of the same material. Without wishing to be bound by any theory or speculation, it is believed that the thickness (t p) gradually increases during the second plasma etching step, which is believed to have the effect of gradually reducing the dimension of the opening in the mask or feature. The dimension may be a critical dimension and may correspond to the minimum width (w) of the opening in the mask. This dimension may correspond substantially to the width above the bottom surface of the feature being etched. As the dimension of the opening is reduced, the etching in the peripheral region 43 is attenuated. The change in dimension w leads to a reduction in the etched width at the base of the feature. Without wishing to be bound by any theory or speculation, it is believed that the passivation material 40 overhangs the corners of the base of the feature, thereby shielding the corners of the base of the feature from the highly directional anisotropic plasma etching process. This has the effect of reducing the etch rate in the peripheral region 43 of the bottom surface (compared to the central region 39 of the bottom surface). As a result, a feature may be formed whereby the base of the feature has rounded corners, a tapered profile, or a rounded profile in the edge region 44 and the substantially flat central region 39. By controlling the rate of deposition of the passivation material (and thus the dimensions of the openings in the mask), it is possible to control the profile at the base of the features as desired.

[0045] Once the feature is fully formed, a further deposition stripping step (shown as "DEPOSITION STRIP" on FIG. 3) is performed to remove the passivation material from the mask and sidewalls of the feature. Removal of the passivation material may be performed using a wet etch. For example, HF may be used as a wet etchant to remove the passivation material.

[0046] The resulting substrate 30d includes a fully formed feature 34d having a base with a substantially flat central region 39 and rounded or smoothed corners (or other shapes, as desired) in edge region 44. A substrate having a base or bottom surface with a smoothed profile (e.g., with rounded corners) can help minimize field bunching; that is, the electric field is more evenly distributed around the feature. This can help maximize the breakdown voltage. Additionally, the method helps avoid the formation of micro-trenches at the corners of the feature being etched.

[0047] In order to control the profile of the base of the feature, it is necessary to control the rate of deposition of the passivation material 40. Typically, the second plasma etch step involves increasing the rate of deposition of the passivation material as the second plasma etch step progresses. The rate of deposition of the passivation material may be controlled by varying one of the plasma process parameters. Any process parameter (including one or more of gas ratio, gas flow rate, etch time, plasma source power, platen power, and / or frequency of the applied power) may be varied to control the deposition rate of the passivation material. For example, the deposition rate of the passivation material may be increased by gradually increasing (i.e., ramping) the rate of gas that forms the passivation material (i.e., passivation material precursor) (e.g., oxygen gas, etc.) that is introduced into the etch chamber during the second plasma etch step. In a further example, the deposition rate of the passivation material may be increased by gradually decreasing (i.e., ramping) the power applied to the platen during the second plasma etch step.

[0048] FIG. 5 shows how a linear increase in the passivation material precursor gas flow rate during the second plasma etching step corresponds to a change in the passivation thickness. The linear increase in the passivation material precursor flow rate results in a trench having a base with a tapered profile, as shown in FIG. 6. That is, the slope at the corners of the feature (i.e., in the edge region 44) is substantially constant. The bottom surface of the feature includes tapered corners 64 and a substantially flat central region 62. Without wishing to be bound by any theory or speculation, parts of the feature that are covered by the passivation material (e.g., where the passivation material overhangs the base of the feature) have a reduced etch rate. As a result, as the passivation material thickness increases, this has the effect of reducing the dimensions of the opening in the mask layer, and therefore the etchable width (w) at the base of the feature gradually decreases accordingly. This causes a tapered profile at the base of the feature.

[0049] FIG. 7 shows how a nonlinear increase in passivation material precursor gas flow rate corresponds to a change in passivation thickness. More specifically, the gas flow in FIG. 7 is increased (i.e., ramped) during the second plasma etching step at an increasing rate of change. The nonlinear ramped increase in passivation material precursor gas flow rate results in a trench having a bottom surface with rounded corners. That is, the slope of the bottom surface in the edge region 74 gradually changes from a horizontal orientation (in the central region 72) to a substantially vertical orientation (in the sidewalls 78), as shown in FIG.

[0050] 9 shows an SEM image of a feature 90 formed in a silicon carbide substrate 92 using the method described above. The process parameters for the first and second steps are shown in Table 1. [Table 1]

[0051] 9 shows that passivation material 94 is deposited on the sidewalls of the feature being formed, and also on the sidewalls of mask layer 96. The maximum thickness of passivation material 94 was about 175 nm on each side of feature 90. The etch rate during the first plasma etching step was about 400 nm / min.

[0052] By controlling the deposition rate of the passivation material, and therefore the thickness of the passivation material, the dimensions of the openings in the mask can be controlled. Controlling this dimension allows the width of the etch at the base of the feature to be controlled, which can allow the shape of the bottom surface of the feature being etched to be controllably changed. The method allows features (such as, for example, trenches) to be formed that have bottom surfaces with controllable profiles. Particular advantages are associated with trenches that include bases with rounded corners. Rounded (or curved) corners can distribute the electric field more evenly, thus reducing field bunching. This can beneficially maximize the breakdown voltage. Additionally, the method can prevent the formation of micro-trenching at the corners of the feature, because the etch rate is reduced in the corners of the feature during the second etching step. [Explanation of symbols]

[0053] 10 trench, 12 substantially flat bottom surface, 14 substantially vertical sidewall, 20 plasma etching apparatus, 22 substrate support, 23 chamber, 24 dielectric part, 25 substrate, 26 gas inlet, 28 plasma generating means, 29 pumping port, 30 compound semiconductor substrate, 30b substrate, 32 mask layer, 34b partially formed feature, 34d fully formed feature, 36b flat base, 38 sidewall, 39 substantially flat central region, 40 passivation material, 42c sidewall, 43 peripheral region, 44 edge region, 62 substantially flat central region, 64 edge region, 72 central region, 74 edge region, 78 sidewall, 90 feature, 92 silicon carbide substrate, 94 passivation material; 96 mask layer; 250 RF power supply; 252 impedance matching network; 280 RF power supply; 282 impedance matching network.

Claims

1. 1. A method of plasma etching a compound semiconductor substrate to form features, the method comprising: (a) providing a substrate with a mask formed thereon, the mask having an opening, the substrate being formed from a compound semiconductor material; (b) performing a first plasma etching step to anisotropically etch the substrate through the opening to create a partially formed feature having a bottom surface that includes a peripheral region; (c) performing a second plasma etching step to anisotropically etch the bottom surface of the partially formed feature through the opening while depositing a passivation material over the mask to reduce a dimension of the opening, the reduction in the dimension of the opening causing a decrease in etching of the peripheral region, thereby producing a fully formed feature having a bottom surface including a central region and an edge region, the central region being deeper than the edge region of the bottom surface of the fully formed feature; Including, by varying process parameters during the second plasma etching step, including one or more of gas ratios, gas flow rates, etching time, plasma source power, platen power, and frequency of applied power, the deposition rate of the passivation material increases during the second plasma etching step in a linear or non-linear manner rather than being constant; method.

2. 2. The method of claim 1, wherein the process parameter that is changed is ramped at an increasing rate of change.

3. 2. The method of claim 1, wherein varying the process parameters comprises varying a flow rate of a passivation material precursor during the second plasma etching step.

4. 4. The method of claim 3, wherein the flow rate of the passivation material precursor is increased during the second plasma etching step.

5. 4. The method of claim 3, wherein the passivation material precursor comprises an oxygen-containing gas.

6. 2. The method of claim 1, wherein varying the process parameters comprises varying a bias power applied to the substrate during the second plasma etching step.

7. 7. The method of claim 6, wherein the bias power applied to the substrate is reduced during the second plasma etching step.

8. 10. The method of claim 1, wherein the passivation material comprises silicon oxide.

9. 10. The method of claim 1, wherein the passivation material and the mask are made of substantially the same material.

10. 10. The method of claim 1, wherein the second plasma etching step includes using an etch recipe that includes a chlorine-based etchant.

11. 11. The method of claim 10, wherein the chlorine-based etchant is Cl ２ and / or SiCl ４ The method includes:

12. 10. The method of claim 1, wherein the bottom surface of the partially formed feature is substantially planar.

13. 2. The method of claim 1, wherein the feature is a trench.

14. 10. The method of claim 1, wherein the central region of the bottom surface of the fully formed feature is substantially flat.

15. 10. The method of claim 1, wherein the edge region of the bottom surface of the fully formed feature comprises a curved surface.

16. 16. The method of claim 15, wherein the edge region forms a rounded corner between the central region of the bottom surface and a sidewall of the fully formed feature.

17. 10. The method of claim 1, wherein the compound semiconductor substrate is a silicon carbide (SiC) wafer.

18. 2. The method of claim 1 , (d) selectively removing the passivation material from the substrate by wet etching. The method further comprises:

19. 10. The method of claim 1, wherein steps (b) and (c) are performed using an inductively coupled plasma (ICP) etcher.

20. 13. A method for manufacturing a compound semiconductor substrate including a feature formed using the method of claim 1, the feature including a bottom surface, the bottom surface including a substantially planar central region and an edge region, the central region being deeper than the edge region.

21. 21. The method of claim 20, wherein the edge region of the bottom surface comprises a curved surface.

22. 13. A plasma etching apparatus for plasma etching a substrate to form features using the method of claim 1, the apparatus comprising: A chamber; a substrate support disposed within the chamber for supporting a substrate thereon; at least one gas inlet for introducing a gas or gas mixture into said chamber at a predetermined flow rate; a plasma generating means for sustaining a plasma within said chamber; a power supply for supplying bias power to the substrate support; a controller configured to switch from a first set of processing conditions to a second set of processing conditions, the first set of processing conditions configured to perform a first plasma etching step to anisotropically etch the substrate through an opening in a mask to create a partially formed feature having a bottom surface that includes a peripheral region, and the second set of processing conditions configured to perform a second plasma etching step to anisotropically etch the bottom surface of the partially formed feature through the opening while depositing a passivation material over the mask to reduce a dimension of the opening; and a controller for varying process parameters including one or more of gas ratio, gas flow rate, etch time, plasma source power, platen power, and frequency of applied power during a second plasma etch step such that a deposition rate of the passivation material increases during the second plasma etch step in a non-constant, linear or non-linear manner, and a reduction in the dimension of the opening causes an attenuation of etching of the peripheral region, thereby creating a fully formed feature having a bottom surface including a central region and an edge region, the central region being deeper than the edge region of the bottom surface of the fully formed feature.

2. A plasma etching apparatus comprising:

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