A diamond-based GaN device through-hole structure and preparation method thereof

Abstract

The present invention discloses a diamond-based GaN device through-hole structure and a preparation method thereof, the method comprising: growing a diamond layer on a silicon substrate; using a pulsed laser to perform through-hole etching on the diamond layer; transferring a GaN epitaxial layer to a temporary bonding carrier, and sputtering a bonding dielectric layer on the GaN epitaxial layer; bonding the diamond layer and the GaN epitaxial layer using a low-temperature wafer bonding technology; removing the temporary bonding carrier on the GaN epitaxial layer, and performing a front device process on the GaN epitaxial layer; etching away the silicon substrate and etching away the bonding dielectric layer and the GaN epitaxial layer at the location of the diamond through-hole to form a back through-hole; depositing a seed layer metal and thick gold on the back of the diamond layer to connect the front electrode of the device. The present invention can solve the problem that it is difficult to prepare the back through-hole grounding of the diamond-based device. Opening and etching the diamond substrate in advance can avoid damage to the GaN device caused by laser etching, improve the device yield, and improve process efficiency and reduce costs.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor processes and relates to a diamond-based GaN device through-hole structure and a preparation method thereof. Background Art

[0002] Gallium nitride (GaN) is a typical representative of the third generation of semiconductor materials. It has the characteristics of wide bandgap, high breakdown electric field strength, fast saturated electron drift velocity, small dielectric constant, and good chemical stability. It is very suitable for the preparation of high-power devices, microwave power devices, etc. As the power density of GaN-based power / RF devices increases, the heat accumulation effect in the active area of ​​the chip increases rapidly, resulting in a rapid deterioration of its various performance indicators, and its high-power advantage cannot be fully utilized. Therefore, the heat dissipation problem has become one of the main technical bottlenecks restricting the further development and widespread application of GaN-based devices. Compared with the silicon substrate and silicon carbide (SiC) substrate commonly used in GaN devices, the thermal conductivity of diamond is 15 times and 4.5 times that of silicon substrate and silicon carbide (SiC) substrate. Therefore, using diamond as the substrate of GaN devices can greatly improve the heat dissipation capacity of the device and increase the power density of GaN devices to more than three times. However, due to the extremely high hardness of the diamond substrate material, the rate of etching diamond through holes using traditional semiconductor etching processes is extremely low. Existing pulsed laser technology can quickly etch diamond, but the etching of this technology is difficult to accurately control, and it is very likely to cause damage to GaN devices. Therefore, the backhole preparation process of diamond substrate GaN devices has always been a difficult problem, which also greatly limits the performance of the device.

[0003] As a prior art, CN113808948A discloses a method of using pulsed laser and plasma dry etching to perform back hole etching on a diamond substrate, first using pulsed laser to etch the diamond substrate to a depth of 70-80um, and then using plasma dry etching to etch to the front metal. The disadvantage of this technology is that the plasma etching speed of diamond is very slow, and the secondary diamond etching undoubtedly increases the process cost and time.

[0004] CN115579323A discloses a method for preparing a through hole of a diamond GaN device, which uses a pulsed laser to penetrate the diamond substrate, the GaN epitaxial layer and the source metal of the GaN device in sequence to form a through hole, uses a temporary carrier to evaporate the electrode in the through hole, removes the temporary carrier, and then uses secondary electroplated metal to connect the front electrode and the back electroplated electrode. The disadvantage of this technology is that the laser directly penetrates the GaN epitaxial layer and the source metal, which is bound to cause damage to the GaN device and affect the device performance. In addition, when the temporary carrier is removed, the metal at the back hole position is difficult to keep intact, which is not conducive to the electrical performance of the device. Summary of the invention

[0005] The purpose of the present invention is to provide a diamond-based GaN device through-hole structure and a preparation method thereof. By performing hole-opening etching on diamond in advance, damage to the GaN device caused by laser etching can be avoided, the yield of the device can be improved, and the process efficiency can be improved and the cost can be reduced.

[0006] One aspect of the present invention provides a method for preparing a through-hole structure of a diamond-based GaN device, comprising:

[0007] Step S1: growing polycrystalline diamond on a silicon substrate using chemical vapor deposition technology to form a diamond layer, and grinding and polishing the surface of the diamond layer using chemical mechanical polishing technology;

[0008] Step S2: using a pulsed laser to etch the diamond layer to form a diamond through hole penetrating the diamond layer, and using a pulsed laser to prepare an alignment mark for photolithography on the diamond layer;

[0009] Step S3: bonding the front side of the GaN epitaxial wafer to a temporary bonding carrier, removing the substrate of the GaN epitaxial wafer using hydrofluoric acid to retain the GaN epitaxial layer, and sputtering a bonding dielectric layer on the GaN epitaxial layer;

[0010] Step S4: bonding the diamond layer and the GaN epitaxial layer together using low temperature wafer bonding technology;

[0011] Step S5: removing the temporary bonding carrier on the GaN epitaxial layer, and performing a front device process on the GaN epitaxial layer by overlaying the alignment marks for lithography prepared in step S2 to form a GaN device including a front electrode;

[0012] Step S6: etching the silicon substrate with hydrofluoric acid, and etching the bonding dielectric layer and the GaN epitaxial layer at the location of the diamond through hole using photolithography and etching techniques to form a back through hole penetrating the diamond through hole, the bonding dielectric layer and the GaN epitaxial layer, thereby completely exposing the front electrode;

[0013] Step S7: using a sputtering technique to deposit a seed layer of metal on the back side of the diamond layer, and electroplating gold on the seed layer of metal to form a back through-hole metal connected to the front electrode.

[0014] Preferably, in step S1, the thickness of the diamond layer is 80-150 μm, and the surface roughness of the diamond layer is less than 20 nm.

[0015] Preferably, in step S2, the diameter of the diamond through hole is 60-70 μm.

[0016] Preferably, in step S3, the surface of the GaN epitaxial layer is planarized by using chemical mechanical polishing technology and wet etching technology, so that the surface roughness of the GaN epitaxial layer does not exceed 1 nm.

[0017] Preferably, in step S3, the material of the bonding dielectric layer is amorphous silicon, SiO 2 Or SiN, the thickness of the bonding dielectric layer is between several nanometers and tens of nanometers.

[0018] Preferably, in step S4, the surface of the diamond layer is polished by chemical mechanical polishing technology and wet-etched so that the surface roughness of the diamond layer does not exceed 1 nm.

[0019] Preferably, in step S5, the thickness of the front electrode is between 2-5 μm.

[0020] Preferably, in step S6, the back side of the diamond layer is smoothed by chemical mechanical polishing technology so that the roughness of the back side of the diamond layer does not exceed 20 nm.

[0021] Another invention of the present invention provides a diamond-based GaN device through-hole structure, which is prepared by the above method.

[0022] According to the diamond-based GaN device through-hole structure and preparation method thereof of the above aspects of the present invention, by performing hole-opening etching on the diamond in advance, damage to the GaN device caused by laser etching can be avoided, the device yield can be improved, and process efficiency can be improved and costs can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings used in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work:

[0024] Figure 1 is a flow chart of a method for preparing a through-hole structure of a diamond-based GaN device according to an embodiment of the present invention;

[0025] FIG2 is a schematic diagram of diamond grown on a silicon substrate according to an embodiment of the present invention;

[0026] FIG3 is a schematic diagram of completing diamond through-hole etching according to an embodiment of the present invention;

[0027] FIG4 is a schematic diagram of the GaN epitaxial wafer substrate removal and the deposition of a bonding dielectric layer according to an embodiment of the present invention;

[0028] FIG5 is a schematic diagram of bonding a diamond layer to a GaN epitaxial layer according to an embodiment of the present invention;

[0029] FIG6 is a schematic diagram of a GaN device after the front side process is completed according to an embodiment of the present invention;

[0030] FIG. 7 is a schematic diagram of completing back-side through-hole etching of a GaN device according to an embodiment of the present invention;

[0031] FIG. 8 is a schematic diagram of a through-hole structure of a diamond-based GaN device prepared in an embodiment of the present invention.

[0032] Explanation of the reference numerals: 1. diamond layer, 2. bonding dielectric layer, 3. GaN epitaxial layer, 4. front electrode, 5. back through-hole metal, 101. silicon substrate, 102. temporary bonding carrier, 200. diamond through-hole, 201. back through-hole. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The embodiment of the present invention provides a method for preparing a through-hole structure of a diamond-based GaN device. Figure 1 FIG. 1 is a flow chart of a method for preparing a through-hole structure of a diamond-based GaN device according to an embodiment of the present invention. Figure 1 As shown, the method for preparing a through-hole structure of a diamond-based GaN device according to an embodiment of the present invention comprises the following steps:

[0035] Step S1: growing polycrystalline diamond on a silicon substrate using chemical vapor deposition technology to form a diamond layer, and grinding and polishing the surface of the diamond layer using chemical mechanical polishing technology;

[0036] Step S2: using a pulsed laser to etch the diamond layer to form a diamond through hole penetrating the diamond layer, and using a pulsed laser to prepare an alignment mark for photolithography on the diamond layer;

[0037] Step S3: bonding the front side of the GaN epitaxial wafer to a temporary bonding carrier, removing the substrate of the GaN epitaxial wafer using hydrofluoric acid to retain the GaN epitaxial layer, and sputtering a bonding dielectric layer on the GaN epitaxial layer;

[0038] Step S4: bonding the diamond layer and the GaN epitaxial layer together using low temperature wafer bonding technology;

[0039] Step S5: removing the temporary bonding carrier on the GaN epitaxial layer, and performing a front device process on the GaN epitaxial layer by overlaying the alignment marks for lithography prepared in step S2 to form a GaN device including a front electrode;

[0040] Step S6: etching the silicon substrate with hydrofluoric acid, and etching the bonding dielectric layer and the GaN epitaxial layer at the location of the diamond through hole using photolithography and etching techniques to form a back through hole penetrating the diamond through hole, the bonding dielectric layer and the GaN epitaxial layer, thereby completely exposing the front electrode;

[0041] Step S7: using a sputtering technique to deposit a seed layer of metal on the back side of the diamond layer, and electroplating gold on the seed layer of metal to form a back through-hole metal connected to the front electrode.

[0042] The following is a more specific description of each step of the method for preparing a through-hole structure of a diamond-based GaN device according to an embodiment of the present invention.

[0043] In step S1, polycrystalline diamond is grown on a silicon substrate 101 using chemical vapor deposition (CVD) technology to form a diamond layer 1, such as Figure 2 As shown. The thickness of the diamond layer 1 is 80-150µm, preferably 100µm. The surface of the diamond layer 1 is ground and polished by chemical mechanical polishing (CMP) to ensure that the surface roughness is less than 20nm.

[0044] In step S2, the diamond layer 1 is etched using a pulsed laser to form a diamond through hole 200 penetrating the diamond layer 1. Figure 3 As shown. The diameter of the diamond through hole 200 is 60-70µm. It is necessary to ensure that the diamond layer 1 is completely engraved by the laser, and the morphology and smoothness of the diamond through hole 200 are ensured by adjusting the laser parameters. The silicon substrate 101 will be removed later, so there is no need to consider the damage of the pulsed laser to the silicon substrate 101. In addition, in this step, a pulsed laser is also used to prepare a photolithography alignment mark on the diamond layer 1, so as to be used for photolithography alignment in the subsequent device front process.

[0045] In step S3, the front side of the GaN epitaxial wafer is spin-coated with a bonding material and temporarily bonded to a temporary bonding carrier 102, and then the substrate of the GaN epitaxial wafer is removed using hydrofluoric acid (HF), leaving only the GaN epitaxial layer 3, wherein the GaN epitaxial wafer is composed of the front GaN epitaxial layer and the substrate. Then, the surface of the GaN epitaxial layer 3 is flattened using CMP and wet etching techniques, so that its surface roughness does not exceed 1nm. Subsequently, a thin bonding dielectric layer 2 is sputtered on the GaN epitaxial layer 3 for subsequent low-temperature wafer bonding, such as Figure 4 The material of the bonding dielectric layer 2 can be amorphous silicon (a-Si), SiO 2 Or SiN, etc., the thickness of the dielectric layer can be from a few nanometers to tens of nanometers.

[0046] In step S4, the surface of the diamond layer 1 with the diamond through hole 200 is polished and wet-etched using CMP technology to ensure that the surface roughness does not exceed 1 nm. Then, the diamond layer 1 and the GaN epitaxial layer 3 are bonded together using low-temperature wafer bonding technology, such as Figure 5 shown.

[0047] In step S5, the temporary bonding carrier 102 on the GaN epitaxial layer is removed, and then the GaN epitaxial layer 3 is subjected to a front device process by overlaying the alignment marks for lithography prepared in step S2, so as to form a GaN device including a front electrode 4. The device is a high electron mobility transistor (HEMT), and the front process is a conventional HEMT process flow, including: HEMT table etching; passivation layer evaporation; gate, source and drain windowing; electrode evaporation and annealing; thick electrode electroplating, etc. In the front device process, the alignment marks for lithography prepared in step S2 are overlaid, and the alignment marks for lithography are used to perform lithography alignment. Figure 6 A schematic diagram showing the completion of the front GaN HEMT process is shown, wherein the front electrode 4 is a thick source electrode of the front GaN device, and the thickness of the front electrode 4 is between 2-5µm.

[0048] In step S6, the silicon substrate 101 is completely etched away using HF, and the back side of the diamond layer 1 is flattened using CMP, with a roughness of no more than 20 nm. Subsequently, the bonding dielectric layer 2 and the GaN epitaxial layer 3 at the location of the diamond through hole 200 are etched away using photolithography and etching techniques to achieve a completely through back side through hole 201 (through the diamond through hole 200, the bonding dielectric layer 2 and the GaN epitaxial layer 3), thereby completely exposing the front side electrode 4, as shown in FIG. Figure 7 shown.

[0049] In step S7, a seed layer metal is deposited on the back side of the diamond layer 1 by sputtering technology, and then a thick gold is electroplated on the seed layer metal to form a back through-hole metal 5 connected to the front electrode 4, thereby obtaining Figure 8 The through-hole structure of the GaN-on-diamond device is shown.

[0050] An embodiment of the present invention further provides a diamond-based GaN device through-hole structure, which is prepared by the method of the above embodiment of the present invention.

[0051] According to the method for preparing a through-hole structure of a diamond-based GaN device according to the above embodiment of the present invention, a pulsed laser is first used to etch a through-hole on the diamond layer, and then the diamond layer with the through-hole etched is bonded to the GaN epitaxial layer using a low-temperature bonding technique, and then the front GaN device process is performed, the bonding dielectric layer and the GaN epitaxial layer at the position of the diamond through-hole are removed from the back by etching, and the front electrode is connected by sputtering a seed metal and electroplating gold. The embodiment of the present invention uses a laser etching method to first prepare a through-hole structure on the diamond layer, and then performs subsequent bonding and GaN device processes, which can completely avoid damage to the GaN device by laser etching, can improve the device yield, and effectively improve the electrical performance of the GaN device. In addition, the use of a pulsed laser to etch a through-hole on the diamond layer can overcome the disadvantage of the slow speed of plasma etching diamond, can reduce process costs, and improve efficiency.

[0052] In addition, the embodiment of the present invention performs epitaxial layer bonding first and then performs device processing. There is no requirement for the alignment accuracy of the bonding. It is only necessary to overlay the photolithography alignment marks left on the diamond layer during the device process, which can reduce process costs and improve process efficiency.

[0053] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a through-hole structure of a diamond-based GaN device, characterized in that: include: Step S1: growing polycrystalline diamond on a silicon substrate using chemical vapor deposition technology to form a diamond layer with a thickness of 80-150µm, and grinding and polishing the surface of the diamond layer using chemical mechanical polishing technology; Step S2: using a pulsed laser to etch the diamond layer to form a diamond through hole penetrating the diamond layer, and using a pulsed laser to prepare an alignment mark for photolithography on the diamond layer; Step S3: bonding the front side of the GaN epitaxial wafer to a temporary bonding carrier, removing the substrate of the GaN epitaxial wafer using hydrofluoric acid to retain the GaN epitaxial layer, and sputtering a bonding dielectric layer on the GaN epitaxial layer; Step S4: bonding the diamond layer and the GaN epitaxial layer together using low temperature wafer bonding technology; Step S5: removing the temporary bonding carrier on the GaN epitaxial layer, and performing a front device process on the GaN epitaxial layer by overlaying the alignment marks for lithography prepared in step S2 to form a GaN device including a front electrode; Step S6: etching the silicon substrate with hydrofluoric acid, and etching the bonding dielectric layer and the GaN epitaxial layer at the location of the diamond through hole using photolithography and etching techniques to form a back through hole penetrating the diamond through hole, the bonding dielectric layer and the GaN epitaxial layer, thereby completely exposing the front electrode; Step S7: using a sputtering technique to deposit a seed layer of metal on the back side of the diamond layer, and electroplating gold on the seed layer of metal to form a back through-hole metal connected to the front electrode.

2. The method according to claim 1, characterized in that In step S1 , the surface roughness of the diamond layer is less than 20 nm.

3. The method according to claim 1 or 2, characterized in that In step S2, the diameter of the diamond through-hole is 60-70 µm.

4. The method according to claim 1 or 2, characterized in that: In step S3, the surface of the GaN epitaxial layer is planarized by using chemical mechanical polishing technology and wet etching technology, so that the surface roughness of the GaN epitaxial layer does not exceed 1 nm.

5. The method according to claim 1 or 2, characterized in that: In step S3, the material of the bonding dielectric layer is amorphous silicon, SiO2 or SiN.

6. The method according to claim 1 or 2, characterized in that: In step S4, the surface of the diamond layer is polished by chemical mechanical polishing technology and wet-etched to make the surface roughness of the diamond layer no more than 1 nm.

7. The method according to claim 1 or 2, characterized in that: In step S5, the thickness of the front electrode is between 2-5 μm.

8. The method according to claim 1 or 2, characterized in that: In step S6, the back side of the diamond layer is flattened by chemical mechanical polishing technology, so that the roughness of the back side of the diamond layer does not exceed 20 nm.

9. A diamond-based GaN device through-hole structure, characterized in that: It is prepared by the method according to any one of claims 1 to 8.

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