High-selectivity dry etching method for converging the front surface of p-gan regrowth

Abstract

This invention provides a high-selectivity dry etching method for surface convergence before p-GaN regrowth, comprising: etching the surface of the p-GaN layer or GaN layer of a GaN / AlGaN heterojunction in a Cl-based gas atmosphere to remove the native oxide layer and contaminants; introducing a mixture of BCl3 and fluorine-containing gas into a reaction chamber under inductively coupled plasma conditions, and maintaining the self-bias voltage within a first preset range for etching to selectively remove the p-GaN layer or GaN layer and achieve near-stop etching in the AlGaN layer, wherein the fluorine-containing gas is used to form an aluminum fluoride layer on the surface of the AlGaN layer to inhibit etching; and reducing the self-bias voltage from the first preset range to a second preset range and / or reducing the proportion of fluorine-containing gas in the mixed gas under plasma conditions to perform convergence treatment on the surface of the near-stop etched structure. This improves the repeatability of the process window and the adaptability of the regeneration length.

Description

Technical Field

[0001] This invention relates to the field of manufacturing technology for group III nitride semiconductor devices, and more particularly to a dry etching method with high selectivity for surface convergence before p-GaN regrowth. Background Technology

[0002] In p In the fabrication of Group III nitride devices such as GaN gate enhancement high electron mobility transistors (HEMTs), grooved gate HEMTs, and regrown ohmic contacts / regrown gates, it is often necessary to process GaN or p-type materials. Selective removal of GaN is performed, with termination or near-stop etching achieved at the AlGaN layer. Since regrowth epitaxy is highly sensitive to interface contamination, microparticles, roughness, and ionic damage, any adverse conditions on the post-etched surface (such as fogging, residues, and defects) directly affect the uniformity of regrowth nucleation and epitaxial continuity, thus impacting device consistency and reliability. Therefore, developing a dry etching method that provides a high-quality starting surface for regrowth has become a key requirement in this field.

[0003] Currently, traditional dry etching methods for providing a high-quality starting surface for regrowth typically employ ICP-based methods using a combination of BCl3 and a fluorine-containing gas (such as SF6). RIE etching system. However, this traditional dry etching method has a narrow high selectivity process window. Slight fluctuations in parameters such as gas ratio, bias voltage, pressure and temperature can lead to significant changes in etching rate and selectivity, resulting in poor repeatability. Fluorine-containing systems are prone to surface fogging, non-volatile residues or micro-masking particles under high selectivity conditions, resulting in low surface controllability and affecting the compatibility of the regrowth interface. Summary of the Invention

[0004] The purpose of this invention is to provide a high selectivity dry etching method for surface convergence before p-GaN regrowth, solving the problems of poor repeatability and the impact on the adaptability of the regrowth interface in traditional dry etching methods.

[0005] To address the aforementioned technical problems, the embodiments of the present invention provide the following technical solutions: This invention provides a high-selectivity dry etching method for surface convergence before p-GaN regrowth, comprising: In a Cl-based gas atmosphere, the surface of the p-GaN layer or the surface of the GaN layer of the GaN / AlGaN heterojunction is etched to remove the native oxide layer and contaminants on the surface and obtain a clean semiconductor surface. Based on the clean semiconductor surface, a mixed gas of BCl3 and a fluorine-containing gas is introduced into a reaction chamber under an inductively coupled plasma condition, and etching is performed by maintaining a self-bias voltage in a first preset range to selectively remove a p-GaN layer or a GaN layer and achieve near-stop etching on an AlGaN layer, to obtain a near-stop etching structure, and the fluorine-containing gas is used to form an etching-inhibiting aluminum fluoride layer on the surface of the AlGaN layer. Based on the near-stop etching structure, the self-bias voltage is reduced from the first preset range to a second preset range, and / or the proportion of the fluorine-containing gas in the mixed gas is reduced, to perform a convergence treatment on the surface of the near-stop etching structure under the condition of maintaining the plasma.

[0006] In some embodiments, the first preset range is -20V to -35V, and the second preset range is -5V to -20V.

[0007] In some embodiments, the proportion of the fluorine-containing gas in the mixed gas is reduced, including: The mixed gas is switched to a fluorine-free gas combination, and the fluorine-free gas combination is BCl3, or a mixture of BCl3 and Ar, or a mixture of BCl3 and Cl2.

[0008] In some embodiments, after the mixed gas is switched to the fluorine-free gas combination, the method further includes: The plasma generated by the fluorine-free gas combination is used to perform a short-time treatment on the surface of the near-stop etching structure to complete the convergence treatment.

[0009] In some embodiments, the fluorine-containing gas is SF6, and the flow rate of SF6 accounts for 10% to 25% of the total flow rate of the mixed gas.

[0010] In some embodiments, the mixed gas further includes Ar gas, and the flow rate of the Ar gas is 0.5sccm to 4sccm.

[0011] In some embodiments, the process conditions of the high-selectivity dry etching method are as follows: the cavity pressure is 4.5Pa to 6.0Pa, and the substrate temperature is 5℃ to 20℃.

[0012] In some embodiments, the near-stop etching on the AlGaN layer includes: After the etching reaches the surface of the AlGaN layer, the etching is continued for 1 minute to 2 minutes, and the additional consumption thickness of the AlGaN layer is less than or equal to 0.3nm.

[0013] In some embodiments, under the Cl-based gas atmosphere, the Cl-based gas is BCl3 or a mixed gas of BCl3 and Cl2.

[0014] In some embodiments, the flow rate of BCl3 in the mixed gas is 25 sccm to 40 sccm.

[0015] Compared to existing technologies, the high-selectivity dry etching method for surface convergence before p-GaN regrowth provided by this invention etches the surface of the p-GaN layer or the GaN layer of a GaN / AlGaN heterojunction under a Cl-based gas atmosphere to remove the native oxide layer and contaminants, obtaining a clean semiconductor surface. Based on the clean semiconductor surface, under inductively coupled plasma conditions, a mixture of BCl3 and fluorine-containing gas is introduced into the reaction chamber, and the self-bias voltage is maintained within a first preset range for etching to selectively remove the p-GaN layer or the GaN layer and achieve near-stop etching in the AlGaN layer, resulting in a near-stop etched structure. The fluorine-containing gas is used to form an aluminum fluoride layer on the surface of the AlGaN layer to inhibit etching. Based on the near-stop etched structure, under plasma conditions, the self-bias voltage is reduced from the first preset range to a second preset range, and / or the proportion of fluorine-containing gas in the mixed gas is reduced to converge the surface of the near-stop etched structure. In this way, Cl-based pre-etching removes native oxidation / contamination and stabilizes the etching start, followed by low-bias main etching to remove the p-GaN or GaN layer and achieve near-stop etching in the AlGaN layer to form an aluminum fluoride layer as a suppression layer and obtain a high selectivity. By further reducing the self-bias and / or reducing the fluorine content, low fogging, low residue and roughness convergence are achieved, improving the repeatability of the process window and the adaptability of the regrowth interface. Attached Figure Description

[0016] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent upon reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of the invention are illustrated by way of example and not limitation, with the same or corresponding reference numerals denoteing the same or corresponding parts, wherein: Figure 1 A flowchart illustrating a high-selectivity dry etching method for surface convergence before p-GaN regrowth is shown schematically. Figure 2 The diagram schematically illustrates the structure of a semiconductor device using a high-selectivity dry etching method for surface convergence before p-GaN regrowth. Figure 3 This diagram schematically illustrates the surface morphology of a semiconductor device measured using an atomic force microscope (AFM) before etching. Figure 4 A schematic diagram of the surface morphology after 5 minutes of etching is shown. Figure 5A schematic diagram of the surface etching morphology after 4 min + 4 min is shown; Figure 6 A schematic diagram of the surface topography images of AFM during pre-etching and main etching is shown. Figure 7 The schematic diagram shows the surface etching morphology after 4 min + 4 min, as measured by scanning electron microscopy (SEM). Figure 8 The schematic diagram illustrates the surface morphology of AFM after pre-etching and main etching, as shown in the image taken by SEM. Detailed Implementation

[0017] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0018] It should be noted that, unless otherwise stated, the technical or scientific terms used in this invention should have the ordinary meaning as understood by one of ordinary skill in the art.

[0019] The methods described in the embodiments of the present invention will be explained in detail below.

[0020] Figure 1 A flowchart illustrating a high-selectivity dry etching method for surface convergence before p-GaN regrowth in an embodiment of the present invention is shown schematically. See [link to flowchart illustration]. Figure 1 As shown, the high selectivity dry etching method for surface convergence before p-GaN regrowth can include: S101. In a Cl-based gas atmosphere, the surface of the p-GaN layer or the surface of the GaN layer of the GaN / AlGaN heterojunction is etched to remove the native oxide layer and contaminants on the surface and obtain a clean semiconductor surface.

[0021] In the Cl-based gas atmosphere, the Cl-based gas is BCl3 or a mixture of BCl3 and Cl2.

[0022] Specifically, the semiconductor device corresponding to the GaN / AlGaN heterojunction of the present invention can be any semiconductor device containing a GaN / AlGaN heterojunction. There can be various structures for the semiconductor device corresponding to the GaN / AlGaN heterojunction, and no specific limitation is made here.

[0023] For example, the structure of the semiconductor device corresponding to the GaN / AlGaN heterojunction of the present invention is as follows: Figure 2 As shown, Figure 2 A schematic diagram of the semiconductor device structure used in the high-selectivity dry etching method for p-GaN surface convergence before regrowth is shown. (See attached diagram) Figure 2 As shown, the semiconductor device comprises, from top to bottom: a P-GaN layer, a GaN layer, an AlN layer, an AlGaN layer, an AlN layer, a GaN channel layer, a GaN buffer layer, a sapphire substrate, and a nucleation layer.

[0024] Specifically, step S101 is a Cl-based pre-etching step, in which short-term pre-etching is performed under a Cl-based atmosphere to remove the native oxide layer and contaminants on the surface of the p-GaN layer or GaN layer of the GaN / AlGaN heterojunction, thereby stabilizing the etching process.

[0025] S102. Based on a clean semiconductor surface, under inductively coupled plasma conditions, a mixture of BCl3 and fluorine-containing gas is introduced into the reaction chamber, and the self-bias voltage is maintained within a first preset range for etching, so as to selectively remove the p-GaN layer or GaN layer and achieve near-stop etching in the AlGaN layer, thereby obtaining a near-stop etched structure.

[0026] In this process, fluorine-containing gas is used to form an aluminum fluoride layer on the surface of the AlGaN layer to suppress etching.

[0027] The first preset range is -20V to -35V, and the second preset range is -5V to -20V. The mixed gas also includes Ar gas, with a flow rate of 0.5 sccm to 4 sccm.

[0028] The near-stop etching in the AlGaN layer includes: after etching reaches the surface of the AlGaN layer, etching continues for 1 to 2 minutes, and the additional thickness of the AlGaN layer consumed is less than or equal to 0.3 nm.

[0029] Specifically, step S102 is the main etching step, which is performed using inductively coupled plasma-reactive ion etching (ICP). Under RIE conditions, BCl3 and SF6 (with optional Ar addition) are introduced, and the main etching is performed within a low bias window, utilizing AlF... x The suppression layer enables a high selectivity near-stop lithography for GaN / AlGaN heterojunctions.

[0030] S103. Based on the near-stop etching structure, under the condition of maintaining plasma, the self-bias voltage is reduced from a first preset range to a second preset range, and / or the proportion of fluorine-containing gas in the mixed gas is reduced, so as to perform convergence treatment on the surface of the near-stop etching structure.

[0031] Reducing the proportion of fluorine-containing gases in the mixed gas includes: switching the mixed gas to a fluorine-free gas combination, wherein the fluorine-free gas combination is BCl3, or a mixture of BCl3 and Ar, or a mixture of BCl3 and Cl2.

[0032] The method further includes, after switching the mixed gas to a fluorine-free gas combination, using plasma generated by the fluorine-free gas combination to perform short-term processing on the surface of the near-stop etched structure to complete the convergence process.

[0033] The process conditions for the high-selectivity dry etching method are as follows: chamber pressure of 4.5 Pa to 6.0 Pa, substrate temperature of 5 °C to 20 °C, and BCl3 flow rate of 25 sccm to 40 sccm in the mixed gas. The fluorine-containing gas is SF6, with SF6 accounting for 10% to 25% of the total flow rate of the mixed gas.

[0034] Specifically, step S103 is convergence (soft convergence). The landing step is a low-energy convergence step introduced at the end of the main etching process. Under the condition of maintaining plasma stability, it further reduces the self-bias voltage (Vbias) or reduces the fluorine content, shortens the average ion energy, suppresses fogging and residue, and performs convergence treatment on surface roughness.

[0035] Specifically, this invention mainly includes a segmented process from Cl-based pre-etching and main etching to convergence, and defines and constrains the convergence effect by adjusting two key control variables: the self-bias voltage and the ratio of fluorine-containing gas. The parameter window used is as follows: The cavity pressure is preferably 5.0 Pa to 5.5 Pa, the substrate temperature is preferably 10 °C to 15 °C, and the inductively coupled plasma (ICP) power is 200 W to 350 W, preferably 270 W to 300 W, to maintain sufficient plasma density and free radical flux. BCl3 is the main component of the mixed gas, and its flow rate is preferably 25 sccm to 40 sccm. SF6, as a fluorine-containing gas, accounts for 10% to 25% of the total flow rate of the mixed gas. Ar can be optionally added at 0 sccm to 5 sccm, which is used for discharge stabilization and synergistic physical removal. In bias control, the RF set power is not used as the sole control, but a stable self-bias voltage Vbias is used as the process control variable. During the main etching stage, the self-bias voltage Vbias is preferably maintained at -20 V to -35 V, and further reduced to -5 V to -20 V during the convergence stage.

[0036] The convergence step includes reducing the self-bias Vbias step / slope and / or reducing / switching the fluorine content to stabilize the etch stop and improve the surface condition before regrowth.

[0037] The selectivity / stop capability index of this invention is specifically: GaN layer (or p) The etching rate for GaN is 5 nm / min to 7 nm / min, while the etching rate for AlGaN is less than or equal to 0.20 nm / min, with a selectivity ratio (GaN:AlGaN) greater than or equal to 40:1. Near-stop etching refers to continuing etching for 1 to 2 minutes after reaching the target depth, with an additional consumption of less than or equal to 0.3 nm for the AlGaN layer.

[0038] Specifically, in the pre-etching stage of this invention: BCl3 can be combined with a small amount of Cl2 to enhance deoxidation capability; alternatively, a short-duration low-power O2 plasma can be used followed by Cl-based pre-etching (over-oxidation must be avoided). In the main etching stage: SF6 can be replaced by other fluorine-containing gases (such as CF4, CHF3, etc.), but the fluorine flux sufficient to form an inhibition layer in the AlGaN layer should be maintained, and a low bias window should be kept. The convergence termination stage: This can be achieved by reducing RF power / bias, reducing the fluorine content, or using a combination of short-duration inert gas purging (Ar / He), as long as atomization and residual convergence are achieved.

[0039] The main etching process of this invention controls the self-bias voltage Vbias at... 20V~ 35V to obtain a usable GaN rate and suppress AlGaN layer consumption; the convergence termination section further reduces the self-bias voltage Vbias to 35V. 5V~ 20V, or a pulsed / gradual bias, is used to reduce ion bombardment energy and defect introduction. The main etching maintains the SF6 percentage to form AlF. x To mitigate the redeposition and atomization / granulation tendency of fluorine-containing byproducts, a suppression layer is used and the selectivity is improved. During the convergence termination phase, the SF6 content is reduced / SF6 on-time is shortened, or a short-term treatment with F-free BCl3 ( / Ar / Cl2) is switched to reduce the SF6 content. A low flow rate of Ar (0.5–4 sccm) is used to improve discharge stability and remove micro-masks / residues, while limiting the upper limit of Ar to avoid roughening caused by enhanced physical bombardment. When AlGaN with an Al content of 0.15–0.35% is used as the stop layer, the etching rate of the GaN layer is 3 nm / min–8 nm / min, the etching rate of the AlGaN layer is less than or equal to 0.25 nm / min, and the selectivity is greater than or equal to 20:1 (preferably greater than or equal to 40:1). Furthermore, the Rq of the AFM after etching is less than or equal to 0.45 nm, and the density of particle / strip-like residues is significantly reduced as seen on SEM.

[0040] Specifically, in the simulation experiment of this invention, the following Examples 1, 2, Comparative Examples 1, 2, and 3 are used for comparison. The step height difference before and after etching is measured using a profilometer or a profilometer, and the rate is obtained by dividing it by the etching time. AFM (e.g., 5×5µm²) is used to report statistical quantities such as root mean square roughness Rq and to provide typical morphology diagrams. SEM particle count, SEM particle count or optical haze level are used as characterization to verify the trend of fluorine residue or coating.

[0041] In the simulation experiment of this invention, Sample 1 is a semiconductor device after 15s of pre-etching, 5min of main etching, and 60s of convergence processing; Sample 2 is a semiconductor device after 15s of pre-etching, 4min+4min of main etching, and 60s of convergence processing; Sample 3 is a semiconductor device after 15s of pre-etching and 5min of main etching; and Sample 4 is a semiconductor device after 15s of pre-etching, 5min of main etching (adjusting the content of Ar gas and / or SF6 gas in the main etching stage based on Example 1), and 60s of convergence processing.

[0042] Embodiment 1 of the present invention is as follows: The main etching process parameters are set as follows: chamber pressure is 5.2 Pa, substrate temperature is 15 °C, and ICP power is 300 W. For the process gases, the BCl3 flow rate is set to 30 sccm, the SF6 flow rate is set to 6 sccm–8 sccm, and the Ar gas flow rate is set to 2 sccm–3 sccm. The self-bias voltage Vbias is controlled and stabilized at -26.6 V during this stage, with fluctuations within ±1 V. After 5 minutes of etching, the etching depth of the GaN (or p-GaN) layer is measured using a profilometer to be 32.18 nm, and the calculated average etching rate is approximately 6.44 nm / min. To evaluate near-stop etching performance, etching continues for 5 minutes after reaching the AlGaN layer surface. The measured additional etching depth of the AlGaN layer is only 0.76 nm, corresponding to an average etching rate of approximately 0.152 nm / min. Therefore, the etching selectivity ratio of the GaN layer to the AlGaN layer reaches approximately 42:1. The root mean square roughness Rq of the etched surface was measured to be 0.45 nm by AFM within a 5×5µm² scanning area.

[0043] Embodiment 2 of the present invention provides a process adjustment direction for surface state optimization. In the main etching stage, while maintaining chamber pressure, substrate temperature, and ICP power similar to those in Embodiment 1, the Ar gas flow rate is adjusted to a lower range of 1.0 sccm to 1.5 sccm. To maintain plasma characteristics and etching controllability, the gas ratio of BCl3 and SF6 is simultaneously adjusted to ensure that the self-bias voltage Vbias remains stable within the process window of -20V to -35V. The core objective of this adjustment strategy is to reduce the micro-masking effect and surface physical damage risk caused by excessive ion bombardment by reducing the proportion of Ar gas, which has a strong physical bombardment effect, thereby reducing the degree of surface haze and microparticle residue after etching. This adjustment may lead to a decrease in the etching rate of the GaN layer. To compensate for the rate, strategies include: moderately increasing the proportion of SF6 in the mixed gas, or slightly increasing the self-bias voltage Vbias, thereby achieving effective control of the etching rate while maintaining high selectivity and excellent surface quality.

[0044] Comparative Example 1 of this invention verifies the necessity of the convergence step. Using the prepared sample 3, the process conditions are as follows: after completing the main etching parameters as in Example 1, the process is directly terminated, omitting the subsequent convergence step. The etched surfaces of the samples obtained in Comparative Example 1 and Example 1 are compared, with a focus on examining and comparing key indicators such as surface haze appearance, particle density observed under a scanning electron microscope (SEM), and surface roughness measured by an alumina-mass spectrometer (AFM).

[0045] Comparative Example 2 of the present invention verifies the adaptability and adjustability of the process parameter window. Using the prepared sample 4, based on Example 1, the content of Ar gas and / or SF6 gas in the main etching stage is adjusted to explore the process parameter boundaries and their adaptability to AlGaN layers with different Al compositions (e.g., Al content of approximately 0.28%). This comparative example aims to illustrate that by adaptively adjusting within the parameter window provided by the present invention, the method of the present invention can adapt to the etching requirements of different material properties, exhibiting good process manufacturability.

[0046] Comparative Example 3 of the present invention is used to verify the uniformity of the process and the reliability of the data. To obtain more accurate and representative data, multi-point sampling measurements were performed on all samples of the embodiments and comparative examples, and their statistical average values ​​were calculated. Through comparative analysis of multi-point data, the superior performance of the method of the present invention in terms of etching smoothness, surface roughness control, and micro-masking particle suppression can be more clearly revealed, and the relevant characterization spectra can also clearly demonstrate the above effects.

[0047] Figure 3 A schematic diagram of the surface morphology of a semiconductor device measured by AFM before etching is shown, with the aim of comparing it with the morphology after etching. Figure 4 A schematic diagram illustrating the surface morphology after 5 minutes of etching is shown. Figure 5 A schematic diagram of the surface etching morphology after 4 min + 4 min is shown. Figure 4 This is the surface morphology after etching for 5 minutes (sample 1). Figure 5 The surface etching morphology (sample 2) is shown after 4 min + 4 min of etching, with Rq values ​​of 0.437 nm and 0.441 nm, respectively. Figure 6 A schematic diagram of the AFM surface topography images during pre-etching and main etching is shown. Figure 6 The image shows the surface morphology of the sample (sample 3) after only pre-etching and main etching, with an etching time of 4 min + 4 min. Rq significantly increased to 0.704 nm. Figure 7 The diagram schematically illustrates the surface etching morphology after 4 min + 4 min under SEM measurement. Figure 8 The schematic diagram illustrates the surface morphology of AFM undergoing pre-etching and main etching, as shown in the schematic image obtained from SEM measurements. Figure 7 These are SEM images of sample 2. Figure 8 The image is taken from the SEM measurement of sample 3. The surface of the etched section at the end of the convergence process has less fogging and fewer particles.

[0048] The surface quality characterization of this invention specifically involves: a systematic surface morphology analysis was performed to quantitatively evaluate the adaptability of the etched surface to the regeneration length. AFM testing shows that after etching using the method of this invention, the root mean square roughness increment ΔRq (post-etching value minus pre-etching value) can be controlled within the range of 0.1 nm to 0.2 nm (see morphology diagram). Figures 3 to 6 The surface exhibits excellent surface smoothness retention. Surface residues were statistically characterized using SEM. Tests were conducted under uniform conditions: an InLens detector was used, with an accelerating voltage of 5 kV, a fixed working distance (WD) of 7.4 mm, magnifications ranging from 3000 to 5000x, and consistent pixel size and resolution. For each sample, at least five non-edge areas were randomly selected (avoiding etching steps and photoresist residue edges), calibrated using a 2 µm scale, and the surface particle number density (Dp, units: particles / µm²) and stripe residue number density (Dr, units: stripes / µm²) were calculated using statistical methodologies.

[0049] Comparative analysis results: Sample 3 of Comparative Example 1 (corresponding to) with convergence step omitted Figure 8 The surface of the sample exhibits distinct strip-shaped and dot-shaped particles with a high-density discrete distribution. Calculations show that Dp is approximately 0.040 particles / µm² and Dr is approximately 0.058 particles / µm². Meanwhile, the sample from the embodiment employing the complete process of this invention (including the convergence step) (corresponding to...) Figure 7 At the same recognition threshold, the detection counts of strip-shaped and particulate residues were close to zero. This fully demonstrates the crucial role of the convergence step in eliminating inherent surface residues in fluorine-containing etching systems and obtaining a clean surface.

[0050] Process stability and uniformity of the present invention: The method of the present invention also exhibits significant advantages in terms of process stability and manufacturability. Five-point etching depth measurements on the same wafer show that the difference between the maximum and minimum depths does not exceed 2.1 nm, demonstrating extremely high intra-wafer uniformity. A comparison between segmented etching (4 min main etching + 4 min main etching) and single-segment continuous etching (8 min) reveals that the segmented process effectively suppresses process drift, reducing the drift amplitude of the self-bias voltage Vbias (ΔVbias) to within 1.1 V, while also significantly reducing the dispersion of etching depth. This indicates that the segmented strategy employed in this invention (especially the separation of the main etching and convergence steps) not only optimizes surface quality but also significantly enhances process stability and repeatability, broadening the manufacturable process window.

[0051] Table 1 shows the data obtained using a profilometer. Five points were tested, including the middle, top, bottom, left, and right edges of the semiconductor device. The first column shows the etching process performed on the semiconductor device structure for 5 minutes, with the surface p-GaN layer and GaN layer depths ranging from 45 nm to 55 nm (within the normal error range during material growth). The purpose was to verify the etching rate of the GaN layer. The second column shows the etching process performed on the semiconductor device structure for 4 minutes followed by 4 minutes of etching. The purpose was to verify the depth reached when the AlGaN layer was reached. The third column shows the etching process performed on the semiconductor device in the second column for another 5 minutes. The purpose was to measure the etching rate of AlGaN.

[0052] Table 1. Data obtained using a protractor.

[0053] The convergence process of this invention can reduce ion bombardment energy, thereby reducing the tendency of lattice damage and roughening during the etching termination stage; by reducing the SF6 ratio, shortening the SF6 on-time, or switching to a fluorine-free gas combination, it can suppress the redeposition of fluorine-containing byproducts and micromasks, thereby reducing fogging / particles from the source; and reduce the sensitivity of the main etching end to gas ratio, bias voltage, and pressure micro-drift, thereby improving process repeatability and expanding the manufacturability window.

[0054] This invention transforms high selectivity etching from a traditional window relying on a single parameter point into a reproducible segmented process and a process window with self-bias Vbias / fluorine content ratio synergistic convergence. With self-bias Vbias convergence control as the main line, an independent convergence termination segment is introduced after the main etching, so that the etched surface converges from a state of haze / granulation or stripe residue to a uniform and controllable state. The convergence effect is defined and constrained by observable and reproducible quantitative indicators, including particle number density Dp (particles / µm²) and stripe number density Dr (stripes / µm²), and combined with AFM roughness indicators (such as Rq) and GaN / AlGaN selectivity ratio indicators, thereby forming an effect-oriented technical objective and evaluation caliber that can be used for review and comparison.

[0055] The high-selectivity dry etching method for surface convergence before p-GaN regrowth of the present invention involves etching the surface of the p-GaN layer or the GaN layer of a GaN / AlGaN heterojunction under a Cl-based gas atmosphere to remove the native oxide layer and contaminants, thereby obtaining a clean semiconductor surface. Based on the clean semiconductor surface, a mixture of BCl3 and fluorine-containing gas is introduced into the reaction chamber under inductively coupled plasma conditions, and etching is performed while maintaining the self-bias voltage within a first preset range to selectively remove the p-GaN layer or the GaN layer and achieve near-stop etching in the AlGaN layer, resulting in a near-stop etched structure. The fluorine-containing gas is used to form an aluminum fluoride layer on the surface of the AlGaN layer to inhibit etching. Based on the near-stop etched structure, while maintaining the plasma conditions, the self-bias voltage is reduced from the first preset range to a second preset range, and / or the proportion of fluorine-containing gas in the mixed gas is reduced to perform convergence treatment on the surface of the near-stop etched structure. In this way, Cl-based pre-etching removes native oxidation / contamination and stabilizes the etching start, followed by low-bias main etching to remove the p-GaN or GaN layer and achieve near-stop etching in the AlGaN layer to form an aluminum fluoride layer as a suppression layer and obtain a high selectivity. By further reducing the self-bias and / or reducing the fluorine content, low fogging, low residue and roughness convergence are achieved, improving the repeatability of the process window and the adaptability of the regrowth interface.

[0056] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A high-selectivity dry etching method for surface convergence before p-GaN regrowth, characterized in that, include: In a Cl-based gas atmosphere, the surface of the p-GaN layer or the surface of the GaN layer of the GaN / AlGaN heterojunction is etched to remove the native oxide layer and contaminants on the surface and obtain a clean semiconductor surface. Based on the clean semiconductor surface, under inductively coupled plasma conditions, a mixture of BCl3 and fluorine-containing gas is introduced into the reaction chamber, and the self-bias voltage is maintained within a first preset range for etching to selectively remove the p-GaN layer or the GaN layer and achieve near-stop etching in the AlGaN layer, thereby obtaining a near-stop etched structure. The fluorine-containing gas is used to form an aluminum fluoride layer on the surface of the AlGaN layer to inhibit etching. Based on the near-stop etching structure, while maintaining the plasma, the self-bias voltage is reduced from the first preset range to the second preset range, and / or the proportion of the fluorine-containing gas in the mixed gas is reduced, so as to perform convergence treatment on the surface of the near-stop etching structure.

2. The high-selectivity dry etching method for surface convergence before p-GaN regrowth according to claim 1, characterized in that, The first preset range is -20V to -35V, and the second preset range is -5V to -20V.

3. The high-selectivity dry etching method for surface convergence before p-GaN regrowth according to claim 1, characterized in that, Reducing the proportion of the fluorine-containing gas in the mixed gas includes: The mixed gas is switched to a fluorine-free gas combination, which is BCl3, or a mixture of BCl3 and Ar, or a mixture of BCl3 and Cl2.

4. The high-selectivity dry etching method for surface convergence before p-GaN regrowth according to claim 3, characterized in that, After switching the mixed gas to a fluorine-free gas combination, the method further includes: The surface of the near-stop etched structure is briefly treated using plasma generated by the fluorine-free gas combination to complete the convergence process.

5. The high-selectivity dry etching method for surface convergence before p-GaN regrowth according to claim 1, characterized in that, The fluorine-containing gas is SF6, and the flow rate of SF6 accounts for 10% to 25% of the total flow rate of the mixed gas.

6. The high-selectivity dry etching method for surface convergence before p-GaN regrowth according to claim 1, characterized in that, The mixed gas also includes Ar gas, and the flow rate of the Ar gas is 0.5 sccm to 4 sccm.

7. The high-selectivity dry etching method for surface convergence before p-GaN regrowth according to claim 1, characterized in that, The process conditions for the high selectivity dry etching method are: cavity pressure of 4.5 Pa to 6.0 Pa and substrate temperature of 5 °C to 20 °C.

8. The high-selectivity dry etching method for surface convergence before p-GaN regrowth according to claim 1, characterized in that, The near-stop lithography in the AlGaN layer includes: After etching reaches the surface of the AlGaN layer, etching continues for 1 to 2 minutes, and the additional thickness of the AlGaN layer consumed is less than or equal to 0.3 nm.

9. The high-selectivity dry etching method for surface convergence before p-GaN regrowth according to claim 1, characterized in that, In the Cl-based gas atmosphere, the Cl-based gas is BCl3, or a mixture of BCl3 and Cl2.

10. The high-selectivity dry etching method for surface convergence before p-GaN regrowth according to claim 1, characterized in that, The flow rate of BCl3 in the mixed gas is 25 sccm to 40 sccm.

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