CN115274441A - ICP etching-based high-selectivity GaN HEMT back hole etching method - Google Patents

Abstract

The invention discloses a high-selectivity GaN HEMT back hole etching method based on ICP etching, which belongs to the technical field of transistors and mainly uses a first etching parameter to carry out first etching on a SiC layer, wherein the first etching adopts SF ₆ And O ₂ The mixed gas of (1); performing second etching on the GaN layer by using second etching parameters, wherein the second etching adopts Cl ₂ 、BCl ₃ And Ar mixed gas; performing third etching on the AlGaN layer by using third etching parameters, wherein the third etching adopts Cl ₂ 、BCl ₃ And increasing Cl based on the second etching parameter ₂ The ratio of (a) to (b) is used for reducing the combination of residual oxygen molecules and surface metal dangling bonds in the first etching and the second etching, so that the N vacancies on the surface of the AlGaN layer are reduced. The invention gives consideration to the characteristics of different layer materials and provides different scalesThe matching selection scheme of the etching parameters in the etching stage realizes high selection ratio, completes the preparation of the through hole with good appearance and smaller pipe wall roughness, improves the performance and reliability of the GaN HEMT device, and has wide industrial production application prospect.

Description

A High Selective Ratio GaN HEMT Back Hole Etching Method Based on ICP Etching

technical field

The invention relates to the technical field of transistors, in particular to an ICP etching-based high-selectivity GaN HEMT back hole etching method.

Background technique

SiC-based AlGaN/GaN HEMT devices are widely used in the fields of power electronics and microwave power. In order to achieve high current, high power, high temperature, high frequency, and high efficiency performance, the preparation of the backside through-hole structure of SiC-based AlGaN/GaN HEMT devices has become a particularly critical process link.

In the field of high-performance GaN HEMTs, epitaxial GaN materials on SiC substrates are currently the mainstream, and the prepared GaN HEMTs have the characteristics of high operating temperature, high application frequency, large output power, and high gain. The through-hole structure is a hole-like structure that runs through the substrate, buffer layer, barrier layer, and passivation layer of the GaNHEMT device, which has an important impact on the frequency characteristics and parasitic capacitance and inductance of the device. A well-designed and well-prepared through-hole grounding structure can reduce the parasitic inductance of the source, reduce the transmission impedance, optimize the overall frequency characteristics of the device, improve the heat dissipation performance of the device, and improve the high-temperature reliability of the device.

SiC has good lattice matching with GaN, has a large forbidden band width, high electron and hole mobility, and high thermal conductivity, so it is often used as a substrate material for GaN HEMT devices. SiC is composed of group IV elements Si and C. The basic structural unit is a regular tetrahedron composed of Si atoms and C atoms. The bond energy of Si-C is strong and the overall structure is stable, resulting in SiC's extremely high hardness and chemical corrosion resistance. Well, it is determined that it is difficult to etch SiC by wet method, and the industry generally processes it by laser or plasma dry etching.

GaN has a wide band gap, a high breakdown field strength, and a high electron saturation drift velocity. These properties make the device have the characteristics of high power density, small size, and high temperature resistance. The stable crystal structure of GaN is mostly wurtzite structure with low lattice symmetry. The GaN/AlGaN heterojunction interface composed of AlGaN produces a strong polarization (spontaneous polarization and piezoelectric polarization) effect, and produces two-dimensional electrons with very large surface density and high mobility in the heterojunction quantum well. Gas (2DEG), which is the main advantage of GaN/AlGaN heterostructure into GaN HEMT.

The purpose of the SiC-based GaN HEMT backhole process is to prepare low-damage through holes that penetrate the GaN/AlGaN heterojunction interface, so it is required to etch the GaN layer and the AlGaN layer sequentially on the basis of etching through the SiC layer. Common GaN and AlGaN etching includes electron cyclotron resonance plasma (ECR), reactive ion etching (RIE), inductively coupled plasma (ICP) etching, magnetic neutral loop discharge plasma (NLD) etching, etc.

At present, in the ICP etching process of SiC, the common working gases are CF ₄ , SF ₆ , NF ₃ , C ₂ F ₆ and other fluorine-based gases. O ₂ or Ar is mixed in a specific proportion as an auxiliary gas to increase the etching rate and reduce the corrosion rate. etch damage. Use CF ₄ /O ₂ mixed gas as etching gas, ICP source power 200W-1000W, RF power 100W-150W, CF ₄ flow rate 15sccm, CF ₄ /O ₂ flow ratio control from 1 to 0.68, working pressure 0.25Pa . The commonly used working gas for the ICP etching process of GaN is Cl2/BCl3, and the total gas flow is 100 sccm. To protect the front structure, ICP power of 500-1000W is selected, the RF power is 250W-500W, and the working pressure is 1.07Pa. The above working gas scheme only considers the optimal etching rate and selectivity ratio of a single SiC or GaN. However, during the manufacturing process, the diameter and depth of the through hole are restricted by the material and thickness of the epitaxial layer, and generally when the depth of the hole exceeds 6 times the diameter of the hole, it is impossible to ensure that the hole wall can be uniformly coated with a metal layer, and the etching process involves different layers. The etching rate of the material and the by-products brought about by the etching of different layers, the etching of the previous layer will affect the etching effect of the next layer, therefore, it is necessary to develop the etching efficiency and etching quality between different layers backside via etch process.

Contents of the invention

The purpose of the present invention is to overcome the problems existing in the back hole etching in the prior art, and to provide a GaN HEMT back with a high selectivity ratio based on ICP etching in consideration of the overall AlGaN/GaN/SiC material etching rate, effect and selectivity ratio. Hole etching method.

The purpose of the present invention is achieved through the following technical solutions:

It mainly provides a GaN HEMT backhole etching method with high selectivity ratio based on ICP etching. After etching through the SiC layer, the GaN layer and the AlGaN layer are sequentially etched. The method includes:

The SiC layer is first etched using first etching parameters, and the first etching uses a mixed gas of SF ₆ and O ₂ for plasma etching;

After the first etching is completed, second etching is performed on the GaN layer using second etching parameters, and the _second etching uses a mixed gas of Cl2, BCl3, and Ar to perform plasma etching;

After the second etching is completed, a third etching is performed on the AlGaN layer using a third etching parameter, and the third etching uses a mixed gas of Cl ₂ and BCl ₃ for plasma etching, and based on The second etching parameter, increasing the proportion of Cl ₂ , is used to reduce the combination of residual oxygen molecules and surface metal dangling bonds in the first etching and the second etching, so as to reduce the N vacancies on the surface of the AlGaN layer.

As a preference, a high selectivity ratio GaN HEMT back hole etching method based on ICP etching, the first etching parameter is: the gas flow ratio of the SF ₆ and O ₂ includes but is not limited to 4: 1, 5:1, 6:1, 8:1, 16:1; the second etching parameter is: the gas flow ratio of Cl ₂ , BCl ₃ and Ar includes but is not limited to 20:2:1, 16 :2:1, 8:2:1; the third etching parameter is: the gas flow ratio of Cl ₂ and BCl ₃ includes but is not limited to 1:1, 2:1, 4:1, 8: 1.

As a preference, a high selectivity ratio GaN HEMT backhole etching method based on ICP etching, the total gas flow rate in the first etching parameter is 20sccm-130sccm, and the working pressure is 0.34Pa-1.2Pa; The total gas flow in the second etching parameter is 90sccm-130sccm, and the working pressure is 0.6Pa-1.3Pa; the total gas flow in the third etching parameter is 25sccm-100sccm, and the working pressure is 0.3Pa-1.1Pa.

As a preferred item, an ICP etching-based high-selectivity GaN HEMT back hole etching method, the etching thickness of the first etching is 80 μm-200 μm.

As a preferred item, an ICP etching-based high-selectivity GaN HEMT back hole etching method, the etching thickness of the second etching is 1 μm-3 μm.

As a preferred item, an ICP etching-based high-selectivity GaN HEMT backhole etching method, the etching thickness of the third etching is 10nm-200nm.

As a preferred item, a method for etching a GaN HEMT backhole with high selectivity based on ICP etching, the method also includes a pretreatment step before the first etching, the pretreatment includes backhole area photolithography and Backside mask preparation.

As a preferred option, a method of etching a GaN HEMT backhole with a high selectivity ratio based on ICP etching, the photolithography of the backhole area includes:

Using the photoresist as a mask for the position of the back hole, photolithography forms the back hole pattern.

As a preferred item, a method for etching the back hole of GaN HEMT with high selectivity ratio based on ICP etching, the preparation of the back mask includes:

Electroplating of a Ni metal mask layer is performed on the back hole pattern, and a layer of mask including but not limited to 2 μm-5 μm is deposited.

As a preferred item, a method for etching backholes of GaN HEMTs with a high selectivity ratio based on ICP etching, the method also includes:

After the third etching, the metal mask of the back hole is stripped, and a metal layer is deposited on the surface of the through hole.

It should be further explained that the technical features corresponding to the above options can be combined or replaced to form a new technical solution if there is no conflict.

Compared with prior art, the beneficial effect of the present invention is:

(1) The present invention takes into account the material characteristics of different layers when etching the back hole, considers the etching rate, effect and selection ratio of the overall AlGaN/GaN/SiC material, and provides a matching selection scheme for etching parameters in different etching stages. At the same time of high selectivity, the through hole of SiC-based GaN HEMT with high uniformity and high surface quality is obtained, and the preparation of through hole with good shape and smaller tube wall roughness is completed, which improves the performance and reliability of GaN HEMT device .

(2) The first etching uses a mixed gas of SF ₆ and O ₂ for plasma etching, so that the selection ratio of SiC to Ni mask is greater than 40:1, and the selection ratio of SiC to GaN is greater than 60:1; the second etching The etching uses a mixed gas of Cl ₂ , BCl ₃ , and Ar for plasma etching, so that the selection ratio of GaN to SiC is greater than 3:1; the third etching uses a mixed gas of Cl ₂ and BCl ₃ for plasma etching, and Based on the second etching parameters, increasing the proportion of Cl ₂ is used to reduce the combination of residual oxygen molecules and surface metal dangling bonds in the first etching and second etching, so that the N vacancies on the surface of the AlGaN layer are reduced , the surface roughness decreases and the etching quality improves.

(3) The second etching introduces Ar to improve the etching initiation process, and at the same time adjusts the composition and quality of the working gas plasma, which can reduce the micro-mask effect in the etching process and improve the etching quality.

Description of drawings

Fig. 1 is the flow chart of a kind of high selection ratio GaN HEMT back hole etching method based on ICP etching shown in the present invention;

Fig. 2 shows the photolithography of the back hole area on the back of the SiC-based GaN HEMT wafer shown in the present invention, and the back hole pattern is formed by photolithography development;

Fig. 3 is the preparation of the mask on the back of the wafer shown in the present invention, a layer of Ni metal mask is formed on the back by electroplating, and the glue is removed to expose the position of the through hole;

FIG. 4 is a schematic diagram of sequentially etching a SiC layer, a GaN layer, and an AlGaN layer shown in the present invention;

FIG. 5 is a schematic diagram of metal deposition on the surface of the through hole and the formation of interconnection with the front structure shown in the present invention;

Fig. 6 is the external appearance of the through hole of the undeposited metal layer shown in the present invention;

FIG. 7 is the internal morphology of the via hole without depositing the metal layer shown in the present invention.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Apparently, the described embodiments are part of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms belonging to "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" etc. The indicated direction or positional relationship is based on the direction or positional relationship described in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, or in a specific orientation. construction and operation, therefore, should not be construed as limiting the invention. In addition, belonging to "first" and "second" is only for descriptive purposes, and should not be understood as indicating or implying relative importance.

In addition, the technical features involved in the different embodiments of the present invention described below may be combined with each other as long as there is no conflict with each other.

Example 1

In an exemplary embodiment, a GaN HEMT back hole etching method with high selectivity based on ICP etching is provided, and the GaN layer and the AlGaN layer are sequentially etched on the basis of etching through the SiC layer, as shown in FIG. 1 As shown, the method includes:

The SiC layer is first etched using first etching parameters, and the first etching uses a mixed gas of SF ₆ and O ₂ for plasma etching;

After the first etching is completed, second etching is performed on the GaN layer using second etching parameters, and the second etching uses a mixed gas of Cl ₂ , BCl ₃ , and Ar to perform plasma etching;

After the second etching is completed, a third etching is performed on the AlGaN layer using a third etching parameter, and the third etching uses a mixed gas of Cl ₂ and BCl ₃ for plasma etching, and based on The second etching parameter, increasing the proportion of Cl ₂ , is used to reduce the combination of residual oxygen molecules and surface metal dangling bonds in the first etching and the second etching, so as to reduce the N vacancies on the surface of the AlGaN layer.

Specifically, the present invention uses a mixed gas of SF ₆ and O ₂ to etch the SiC layer, and the fluorine-containing plasma and O ₂ form a charged SiF _x O _y layer on the SiC surface to attract reactive ions and increase the etching rate. SiF _x -based products have low bond energy and are easy to remove. SF ₆ and CF ₄ have similar effects on etching hole wall roughness, but the etching rate is higher than CF ₄ , so it is more suitable for practical production applications. Controlling other related parameters can make the etching process self-stop on the SiC/GaN interface , and then realize the high selectivity etching of SiC and GaN.

The mixed gas of Cl ₂ , BCl ₃ , Ar is used to etch the GaN layer, and the Cl ^- generated by ionization reacts with GaN to produce GaCl _x , GaCl _x ⁺ , N ₂ and other products, and the chemical reaction is promoted by high kinetic energy ion bombardment. The reaction products are desorbed to remove residues from the sample surface. Among them, the introduction of Ar improves the etching process, and at the same time adjusts the composition and quality of the working gas plasma, which can reduce the micro-mask effect in the etching process and improve the etching quality.

Further, when performing the third etching on the AlGaN layer, adjust the ratio of Cl ₂ /BCl ₃ , and increase the ratio of Cl ₂ and other corresponding parameters relative to the gas parameters in the second etching, and reduce the The possibility of residual O being combined with surface metal dangling bonds in the first etching and second etching reduces the N vacancies on the AlGaN surface, reduces the surface roughness, improves the etching quality, and obtains a better AlGaN layer through-hole etching effect .

Based on the ICP etching mechanism, and according to the material characteristics of different layers of SiC-based epitaxial wafers, a phased ICP backhole etching process gas scheme is designed, and the etching rate is controlled by changing related parameters such as working gas, gas flow ratio, and working pressure. And the inclination angle of the side wall, so that each layer of material can achieve a high selection ratio between different materials, a small roughness of the tube wall, and a through-hole preparation effect with good surface quality under the condition of ensuring a relatively stable etching rate. Realize the high-quality through-hole preparation process that can be precisely controlled, improve the high-temperature reliability of the device, and then improve the yield rate of the overall device.

Example 2

Based on Embodiment 1, a method for etching a GaN HEMT backhole with a high selectivity ratio based on ICP etching is provided, which also includes a pretreatment step before the first etching, and the pretreatment includes photolithography of the backhole area and backside masking. The film is prepared, and after the third etching, the metal mask of the back hole is stripped, and a metal layer is deposited on the surface of the through hole.

Specifically, please refer to Fig. 2-Fig. 7, the complete steps of this method are as follows:

Step 1: Photolithography of the back hole area

As shown in Figure 2, photoresist is used as a mask for back hole positions, and photolithography methods include but are not limited to contact exposure, stepping exposure, etc., to form back hole patterns.

Step 2: Backside mask preparation

As shown in FIG. 3 , electroplating of a Ni metal mask layer is performed on the back hole pattern formed in step 1, and a mask layer including but not limited to 2 μm-5 μm is deposited.

Step 3: Back hole etching

As shown in Figure 4, under the protection of the Ni metal mask formed in step ₂ , etching is carried out, first the SiC layer is etched, and the first etching parameter is _: the gas flow of the SF and O The ratio includes but is not limited to 4:1, 5:1, 6:1, 8:1, 16:1; the total gas flow in the first etching parameter includes but is not limited to 20sccm-130sccm, the working of the chamber Air pressure includes but not limited to 0.34Pa-1.2Pa; RF power includes but not limited to 125W-450W, ICP power includes but not limited to 800W-1800W. The etching rate is controlled at 0.2μm.min ^-1 -1.3μm.min ^-1 , the etching thickness is related to the thinning of the wafer, including but not limited to 80μm-200μm, and the etching time is adjusted according to the thickness.

Then the GaN layer is etched, the second etching parameter is: the gas flow ratio of Cl ₂ , BCl ₃ and Ar includes but is not limited to 20:2:1, 16:2:1, 8:2:1 ; The total gas flow in the second etching parameters includes but is not limited to 90sccm-130sccm, the working pressure of the cavity includes but is not limited to 0.6Pa-1.3Pa; RF power includes but is not limited to 50W-350W, ICP power Including but not limited to 600W-1200W. The etching rate is controlled at 100nm.min ^-1 -800nm.min ^-1 , the etching thickness is related to the design of the epitaxial layer, including but not limited to 1 μm-3 μm, and the etching time is adjusted according to the thickness.

Finally, the AlGaN layer is etched. The third etching parameter is: the gas flow ratio of Cl ₂ and BCl ₃ includes but is not limited to 1:1, 2:1, 4:1, and 8:1. The total gas flow rate in the third etching parameter is 25sccm-100sccm, and the working pressure is 0.3Pa-1.1Pa. Working pressure includes but not limited to 0.3Pa-1.1Pa, RF power includes but not limited to 5W-30W, ICP power includes but not limited to 100W-400W. The etching rate is controlled at 20nm.min ^-1 -200nm.min ^-1 , the etching thickness is related to the design of the epitaxial layer, including but not limited to 10nm-200nm, and the etching time is adjusted according to the thickness.

Step 4: As shown in Figure 5, perform wet stripping on the Ni metal mask in step 2, and deposit metals including but not limited to Ti, Au, Ni, Ag on the surface of the through hole by sputtering and electroplating. layer, enabling through-hole and front-side interconnections.

Through the adjustment of different etching conditions, this method can prepare through holes with high controllability and good quality, so that the quality of the subsequent gold back process can be improved, thereby reducing the overall parasitic inductance, transmission impedance and other parameters of the device, and improving the process of device preparation. Optimize the overall frequency characteristics of the device while improving the yield rate. Specifically, the first etching uses a mixed gas of SF ₆ and O ₂ for plasma etching, so that the selectivity ratio of SiC to Ni mask is greater than 40:1, and the selectivity ratio of SiC to GaN is greater than 60:1; The etching uses a mixed gas of Cl ₂ , BCl ₃ , and Ar for plasma etching, so that the selection ratio of GaN to SiC is greater than 3:1; the third etching uses a mixed gas of Cl ₂ and BCl ₃ for plasma etching, and Based on the second etching parameters, increasing the proportion of Cl ₂ is used to reduce the combination of residual oxygen molecules and surface metal dangling bonds in the first etching and second etching, so that the N vacancies on the surface of the AlGaN layer are reduced , the surface roughness decreases and the etching quality improves.

Example 3

Based on Embodiment 2, a method for etching backholes of GaN HEMTs with high selectivity based on ICP etching is provided. Specifically, electroplating a Ni metal mask layer on the backhole pattern formed in step 1, depositing a layer of The 5 μm mask is etched under the protection of the Ni metal mask formed in the second step. The etching process is divided into three stages: in the first stage, the SiC layer is etched, the selected working gas for etching is SF ₆ and O ₂ , the temperature of the working chamber is 20 degrees Celsius, and the etching thickness is 100 μm. In the second stage, the GaN layer is etched, and the etching working gas is replaced by Cl ₂ , BCl ₃ and Ar, and the etching thickness is 2 μm. In the third stage, the AlGaN layer is etched, the etching working gas is adjusted to Cl ₂ and BCl ₃ , and the etching thickness is 20nm. Then use hydrochloric acid and deionized water to wet strip the Ni metal mask in step 2, and deposit a layer of Ti/Au metal layer on the surface of the through hole by sputtering and electroplating, with a thickness of 7 μm.

The above specific embodiment is a detailed description of the present invention, and it cannot be determined that the specific embodiment of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field of the present invention, they can also Making some simple deduction and substitution should be regarded as belonging to the protection scope of the present invention.

Claims (10)

1. A high selectivity ratio GaN HEMT back hole etching method based on ICP etching, on the basis of etching through the SiC layer, the GaN layer and the AlGaN layer are etched sequentially, it is characterized in that the method includes: The SiC layer is first etched using first etching parameters, and the first etching uses a mixed gas of SF ₆ and O ₂ for plasma etching; After the first etching is completed, second etching is performed on the GaN layer using second etching parameters, and the second etching uses a mixed gas of Cl ₂ , BCl ₃ , and Ar to perform plasma etching; After the second etching is completed, a third etching is performed on the AlGaN layer using a third etching parameter, and the third etching uses a mixed gas of Cl ₂ and BCl ₃ for plasma etching, and based on The second etching parameter, increasing the proportion of Cl ₂ , is used to reduce the combination of residual oxygen molecules and surface metal dangling bonds in the first etching and the second etching, so as to reduce the N vacancies on the surface of the AlGaN layer. 2. a kind of high selectivity ratio GaN HEMT back hole etching method based on ICP etching according to claim 1, is characterized in that, described first etching parameter is: described SF ₆ and O ₂ gas flow The ratio includes but is not limited to 4:1, 5:1, 6:1, 8:1, 16:1; the second etching parameter is: the gas flow ratio of Cl ₂ , BCl ₃ and Ar includes but is not limited 20:2:1, 16:2:1, 8:2:1; the third etching parameter is: the gas flow ratio of Cl ₂ and BCl ₃ includes but is not limited to 1:1, 2: 1, 4:1, 8:1. 3. A kind of ICP etching-based high selectivity GaN HEMT back hole etching method according to claim 2, it is characterized in that, in the first etching parameter, the gas total flow rate is 20sccm-130sccm, and the working pressure is 0.34Pa-1.2Pa; the total gas flow rate in the second etching parameter is 90sccm-130sccm, and the working pressure is 0.6Pa-1.3Pa; the total gas flow rate in the third etching parameter is 25sccm-100sccm, and the working pressure is 0.3Pa-1.1Pa. 4 . The ICP-based high selectivity GaN HEMT back hole etching method according to claim 1 , wherein the etching thickness of the first etching is 80 μm-200 μm. 5 . The ICP-based high selectivity GaN HEMT back hole etching method according to claim 1 , wherein the etching thickness of the second etching is 1 μm-3 μm. 6 . The ICP-based high selectivity GaN HEMT back hole etching method according to claim 1 , wherein the etching thickness of the third etching is 10 nm-200 nm. 7 . 7. A kind of ICP etching-based high selectivity ratio GaN HEMT back hole etching method according to claim 1, is characterized in that, described method also comprises the pretreatment step before the first etching, and described pretreatment Processing includes back hole area photolithography and back mask preparation. 8. A kind of ICP etching-based high selectivity GaN HEMT backhole etching method according to claim 7, characterized in that, the photolithography of the backhole region comprises: Using the photoresist as a mask for the position of the back hole, photolithography forms the back hole pattern. 9. A kind of ICP etching-based high selectivity ratio GaN HEMT back hole etching method according to claim 8, it is characterized in that, described back mask preparation comprises: Electroplating of a Ni metal mask layer is performed on the back hole pattern, and a layer of mask including but not limited to 2 μm-5 μm is deposited. 10. A kind of ICP etching-based high selectivity GaN HEMT back hole etching method according to claim 1, it is characterized in that, described method also comprises: After the third etching, the metal mask of the back hole is stripped, and a metal layer is deposited on the surface of the through hole.

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