Surface treatment method for improving ohmic contact performance of photoconductive switch and photoconductive switch

Abstract

The invention discloses a surface treatment method for improving the ohmic contact performance of a photoconductive switch and the photoconductive switch, and the method comprises the steps: carrying out the surface treatment of the surface of an epitaxial structure through the combination of dry etching and wet etching before an ohmic contact electrode is formed on the surface of the epitaxial structure. According to the method, surface treatment combining dry etching and wet etching is performed on the surface of the epitaxial structure before the ohmic contact electrode is formed on the epitaxial structure, so that the contact resistivity of the epitaxial structure is reduced, the ohmic contact performance of the photoconductive switch is further improved, thermal breakdown of the photoconductive switch is prevented, and the pressure resistance of the photoconductive switch is enhanced.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor processes, and in particular relates to a surface treatment method for improving the ohmic contact performance of a photoconductive switch and a photoconductive switch. Background Art

[0002] Gallium nitride (GaN), as one of the leaders of the third-generation semiconductors, has many excellent physical and chemical properties, such as a bandgap of 3.4eV, a critical breakdown field of 3.3MV / cm, and a saturated electron migration velocity of 2.5×10 7 cm / s, direct bandgap structure, strong acid and alkali resistance, etc., which ensures that it has broad application prospects in high frequency, high power, optoelectronic devices and other fields.

[0003] Iron-doped semi-insulating gallium nitride (SI-GaN:Fe) is a type of gallium nitride that can be used as an isolation layer between devices to improve breakdown characteristics and as a substrate for devices, so it has been widely studied. In addition, it is known as the most promising semiconductor material for studying high-frequency, high-power photoconductive switches due to its excellent light state (low on-resistance), dark state (low leakage current) and light-dark conversion performance (short carrier lifetime).

[0004] Photoconductive semiconductor switches (PCSS) are semiconductor switches that are triggered by a specific excitation light source. They have the advantages of small size, low loss, high output power, fast response speed, and high repetition frequency, and have broad application prospects in the fields of medicine, military, aerospace, etc.

[0005] Photoconductive switches can be roughly divided into two types: vertical and planar. The vertical structure can give full play to the advantages of SI-GaN:Fe materials. The critical breakdown field strength of the device is greater, the withstand voltage performance is better, and the service life is longer. An important factor restricting the performance of photoconductive switches is that the contact resistivity is too high due to the extremely low carrier concentration and high resistivity of SI-GaN:Fe itself, which makes thermal breakdown easy to occur.

[0006] Specific contact resistivity (ρ C ) is a physical parameter for evaluating the quality of ohmic contact between semiconductor and metal. The lower its value, the better the ohmic contact performance. In high-power and high-frequency applications, low specific contact resistivity is usually associated with reduced heat generation and improved device reliability.

[0007] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0008] The object of the present invention is to provide a surface treatment method for improving the ohmic contact performance of a photoconductive switch and a photoconductive switch, which can reduce the contact resistivity, thereby improving the ohmic contact performance of the photoconductive switch, preventing it from being thermally broken down, and enhancing its voltage resistance.

[0009] In order to achieve the above object, a technical solution provided by a specific embodiment of the present invention is as follows:

[0010] A surface treatment method for improving ohmic contact performance of a photoconductive switch, the photoconductive switch comprising an epitaxial structure, the surface treatment method comprising:

[0011] Before forming an ohmic contact electrode on the surface of the epitaxial structure, a surface treatment combining dry etching and wet etching is performed on the surface of the epitaxial structure.

[0012] In one or more embodiments of the present invention, dry etching is performed on the surface of the epitaxial structure, including:

[0013] The surface of the epitaxial structure is etched using inductively coupled plasma etching technology.

[0014] In one or more embodiments of the present invention, the etching gas includes a mixed gas of Cl2 and BCl3;

[0015] The flow rate of Cl2 ranged from 5 to 15 sccm;

[0016] The flow rate of BCl3 ranges from 10 to 30 sccm;

[0017] Etching power range is 100W-300W;

[0018] RF power range is 50W-200W;

[0019] The etching time ranges from 1min to 5min.

[0020] In one or more embodiments of the present invention, the flow rate ratio of Cl2 and BCl3 is: Cl2:BCl3=2:5;

[0021] The flow rate of Cl2 is 10 sccm;

[0022] The flow rate of BCl3 was 25 sccm;

[0023] The etching power is 300W;

[0024] The RF power is 100W;

[0025] The etching time is 2 minutes.

[0026] In one or more embodiments of the present invention, wet etching is performed on the surface of the epitaxial structure, including:

[0027] The epitaxial structure is immersed in a hydrochloric acid solution.

[0028] In one or more embodiments of the present invention, the ratio of HCl to H2O in the hydrochloric acid solution is in the range of HCl:H2O=(1:1)-(1:10), and the soaking time is in the range of 1 min-5 min.

[0029] In one or more embodiments of the present invention, the ratio of HCl to H2O in the hydrochloric acid solution is: HCl:H2O=1:2, and the immersion time is 5 minutes.

[0030] In one or more embodiments of the present invention, before the step of performing a surface treatment combining dry etching and wet etching on the surface of the epitaxial structure, the process further includes:

[0031] The step of cleaning the epitaxial structure.

[0032] In one or more embodiments of the present invention, cleaning the epitaxial structure includes:

[0033] First, the epitaxial structure is placed in a first organic solution and ultrasonically cleaned for 3 min to 10 min;

[0034] Then, the epitaxial structure is placed in a second organic solution and ultrasonically cleaned for 3 min to 10 min;

[0035] The epitaxial structure was then placed in deionized water and ultrasonically cleaned for 3 min to 10 min.

[0036] A photoconductive switch is prepared by surface treatment using the surface treatment method for improving the ohmic contact performance of a photoconductive switch.

[0037] Compared with the prior art, the surface treatment method for improving the ohmic contact performance of a photoconductive switch and the photoconductive switch of the present invention use a surface treatment method that combines dry etching and wet etching to reduce the contact resistivity of the epitaxial structure surface before forming an ohmic contact electrode, thereby improving the ohmic contact performance of the photoconductive switch, preventing it from being thermally broken down, and enhancing its voltage resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0039] Figure 1 A process flow chart of a surface treatment method for improving the ohmic contact performance of a photoconductive switch in one embodiment of the present invention;

[0040] Figure 2 are SEM and AFM surface morphology images of the epitaxial structure, wherein (a) is the SEM surface morphology image of the epitaxial structure that has not been surface treated, (b) is the SEM surface morphology image of the epitaxial structure that has only been subjected to dry etching treatment in the surface treatment method of the present invention, (c) is the SEM surface morphology image of the epitaxial structure that has been treated by the surface treatment method of the present invention, (d) is the AFM surface morphology image of the epitaxial structure that has not been surface treated, (e) is the AFM surface morphology image of the epitaxial structure that has only been subjected to dry etching treatment in the surface treatment method of the present invention, and (f) is the AFM surface morphology image of the epitaxial structure that has been treated by the surface treatment method of the present invention;

[0041] Figure 3 A roughness comparison diagram of an epitaxial structure treated by the surface treatment method of the present invention, an epitaxial structure treated only by dry etching in the surface treatment method of the present invention, and an epitaxial structure not treated by the surface treatment;

[0042] Figure 4 The electrical performance comparison diagram of the epitaxial structure treated by the surface treatment method of the present invention and the epitaxial structure not treated by the surface treatment is shown in the figure. DETAILED DESCRIPTION

[0043] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. 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 should fall within the scope of protection of the present invention.

[0044] As mentioned in the background technology, photoconductive semiconductor switches (PCSS) are semiconductor switches triggered by a specific excitation light source. They have the advantages of small size, low loss, high output power, fast response speed, and high repetition frequency, and have broad application prospects in the fields of medicine, military, aerospace, etc.

[0045] The invention patent with publication number CN112614909A discloses a photoconductive switching device, and specifically discloses the following technical solution: multiple parallel channels are arranged on the substrate to achieve effective current diversion, thereby reducing the current density of a single current filament. This improvement not only improves the total power of the photoconductive switching device, but also extends its life. At the same time, by introducing heavily doped regions of different conductivity types into the device, we can reduce dark current and power loss under reverse bias conditions. In addition, the provision of these heavily doped regions also helps prevent carriers from being injected from the heavily doped regions into the parallel channel regions, avoiding the occurrence of self-breakdown, and further improving the voltage resistance characteristics of the device. These measures together enable photoconductive switches to achieve higher performance levels.

[0046] The invention patent with publication number CN112002769A discloses a high-voltage photoconductive switch and a preparation method, and specifically discloses the following technical solutions: A high-voltage photoconductive switch, which comprises a silicon carbide substrate and two electrode columns. The silicon carbide substrate is composed of a first surface and a second surface with relative positioning, and the two electrode columns are symmetrically mounted on the first surface and the second surface of the silicon carbide substrate. In addition, the first surface and the second surface of the silicon carbide substrate respectively have an insulating dielectric layer surrounding the electrode column. By using insulating materials on the upper and lower surfaces of the silicon carbide wafer and ensuring that it has a dielectric constant close to that of silicon carbide, the electric field strength at the edge of the electrode is reduced, and the current density is reduced. This series of improvements improves the voltage resistance and reliability of the switch, enabling it to better meet the needs of high-voltage applications.

[0047] The invention patent with the publication number CN115347061A discloses a high-voltage silicon carbide photoconductive switch with skew-facing circular electrodes, and specifically discloses the following technical scheme: the photoconductive switch includes a silicon carbide semi-insulating wafer, an input electrode and an output electrode. The input electrode and the output electrode are arranged skew-facing on both sides of the wafer, and a plurality of concentric circular annular grooves of different diameters are arranged around the electrodes, respectively, and a passivation layer is provided on the annular grooves. By setting the annular grooves, the edge distance between the input electrode and the output electrode on the wafer surface is extended, which greatly reduces the risk of flashover breakdown along the edge of the wafer, reduces the field strength at the electrode edge, and by setting the electrodes facing each other, the electric field uniformity is improved, and the electric field distortion at the moment of conduction is avoided, thereby improving the voltage resistance and reliability of the photoconductive switch.

[0048] However, the photoconductive switch in the prior art has a high contact resistivity due to the extremely low carrier concentration and high resistivity of the semi-insulating iron-doped gallium nitride - SI-GaN:Fe, which is prone to thermal breakdown.

[0049] Based on this, the present invention provides a surface treatment method for improving the ohmic contact performance of a photoconductive switch and a photoconductive switch. Before forming an ohmic contact electrode on the epitaxial structure, a surface treatment combining dry etching and wet etching is performed on the surface of the epitaxial structure to reduce its contact resistivity, thereby improving the ohmic contact performance of the photoconductive switch, preventing it from thermal breakdown, and enhancing its voltage resistance.

[0050] like Figure 1 As shown, a surface treatment method for improving the ohmic contact performance of a photoconductive switch in an embodiment of the present invention, wherein the photoconductive switch includes an epitaxial structure. The surface treatment method specifically includes the following steps:

[0051] S1: Cleaning the epitaxial structure.

[0052] S2: before forming an ohmic contact electrode on the surface of the epitaxial structure, performing a surface treatment combining dry etching and wet etching on the surface of the epitaxial structure.

[0053] In step S1, the epitaxial structure is firstly cleaned organically, wherein the organic solution comprises a first organic solution of acetone and a second organic solution of isopropanol.

[0054] Exemplarily, the epitaxial structure is first placed in a first organic solution of acetone, and ultrasonically cleaned for 3 min-10 min, preferably 5 min; then the epitaxial structure is turned over and ultrasonically cleaned again for 3 min-10 min, preferably 5 min. Next, the epitaxial structure is placed in a second organic solution of isopropanol, and ultrasonically cleaned for 3 min-10 min, preferably 5 min; then the epitaxial structure is turned over and ultrasonically cleaned again for 3 min-10 min, preferably 5 min. Finally, the epitaxial structure is placed in deionized water, and ultrasonically cleaned for 3 min-10 min, preferably 5 min; then the epitaxial structure is turned over and ultrasonically cleaned again for 3 min-10 min, preferably 5 min.

[0055] In step S2, the surface of the epitaxial structure may be etched using an inductively coupled plasma etching technique (ICP etching technique). The surface that needs to be ICP etched includes the surface on the epitaxial structure used to form an ohmic contact electrode. During the etching process, the power of the ICP etching is controlled to reduce the damage of the plasma to the surface of the epitaxial structure.

[0056] The etching gas for ICP etching includes a mixed gas of Cl2 and BCl3, wherein the flow rate of Cl2 is in the range of 5-15 sccm; the flow rate of BCl3 is in the range of 10-30 sccm. Preferably, the flow rate ratio of Cl2 to BCl3 is: Cl2:BCl3=2:5; the flow rate of Cl2 is 10 sccm; the flow rate of BCl3 is 25 sccm.

[0057] The etching power of ICP etching ranges from 100 W to 300 W. Preferably, the etching power is 300 W.

[0058] The radio frequency power of ICP etching ranges from 50 W to 200 W. Preferably, the radio frequency power is 100 W.

[0059] The etching time of ICP etching ranges from 1 min to 5 min. Preferably, the etching time is 2 min.

[0060] In step S2, the epitaxial structure may be soaked in a hydrochloric acid solution, wherein the ratio of HCl to H2O in the hydrochloric acid solution is in the range of HCl:H2O=(1:1)-(1:10), preferably HCl:H2O=1:2. The soaking time is in the range of 1 min-5 min, preferably 5 min.

[0061] After the surface treatment is completed, an ohmic contact electrode can be formed on the surface of the treated epitaxial structure.

[0062] The ohmic contact electrode can be prepared on the surface of the epitaxial structure after surface treatment by electron beam evaporation or sputtering process.

[0063] Specifically, a multilayer ohmic metal is deposited on the surface of the epitaxial structure by electron beam evaporation or sputtering (or a combination of the two), wherein the multilayer ohmic metal typical structure comprises Ti / Al / Ti / Au from bottom to top, and the thickness thereof is 20nm / 130nm / 50nm / 150nm. The work function of the first layer of contact metal Ti is relatively low, which is helpful to form a low-resistance ohmic contact.

[0064] The present application also provides a photoconductive switch, which is prepared by surface treatment using the above-mentioned surface treatment method for improving the ohmic contact performance of the photoconductive switch.

[0065] Comparative Example 1

[0066] A photoconductive switch is provided, wherein before an ohmic contact electrode is formed on the surface of the epitaxial structure, no surface treatment is performed on the surface of the epitaxial structure.

[0067] Figure 2are SEM and AFM surface morphology images of the epitaxial structure, wherein (a) is the SEM surface morphology image of the epitaxial structure that has not been surface treated, (b) is the SEM surface morphology image of the epitaxial structure that has only been subjected to dry etching treatment in the surface treatment method of the present invention, (c) is the SEM surface morphology image of the epitaxial structure that has been treated by the surface treatment method of the present invention, (d) is the AFM surface morphology image of the epitaxial structure that has not been surface treated, (e) is the AFM surface morphology image of the epitaxial structure that has only been subjected to dry etching treatment in the surface treatment method of the present invention, and (f) is the AFM surface morphology image of the epitaxial structure that has been treated by the surface treatment method of the present invention;

[0068] refer to Figure 2 As shown, it can be seen that the surface morphology of the epitaxial structure treated by the surface treatment method of the present invention is improved to a certain extent compared with the surface morphology of the epitaxial structure not subjected to surface treatment.

[0069] Figure 3 The roughness comparison diagram of an epitaxial structure treated by the surface treatment method of the present invention, an epitaxial structure treated only by dry etching in the surface treatment method of the present invention, and an epitaxial structure not treated by the surface treatment is shown in FIG. Figure 3 It can be seen that the surface roughness of the epitaxial structure is significantly reduced after treatment.

[0070] Figure 4 The electrical performance comparison diagram of the epitaxial structure treated by the surface treatment method of the present invention and the epitaxial structure not treated by the surface treatment is shown in FIG. Figure 4 It can be seen that the contact resistivity (Specific Contact Resistivity, ρ C ) decreased significantly, indicating that the pressure resistance of the epitaxial structure was significantly improved after surface treatment.

[0071] Compared with the prior art, the surface treatment method for improving the ohmic contact performance of a photoconductive switch and the photoconductive switch of the present invention use a surface treatment method that combines dry etching and wet etching to reduce the contact resistivity of the epitaxial structure surface before forming an ohmic contact electrode, thereby improving the ohmic contact performance of the photoconductive switch, preventing it from being thermally broken down, and enhancing its voltage resistance.

[0072] After surface treatment, the photoconductive switch of the present invention has significantly reduced specific contact resistivity, significantly improved ohmic contact characteristics, and greatly reduced probability of thermal breakdown of the photoconductive switch, which means that the withstand voltage performance and service life of the photoconductive switch are enhanced.

[0073] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0074] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A surface treatment method for improving the ohmic contact performance of a photoconductive switch, wherein the photoconductive switch comprises an epitaxial structure, characterized in that: The surface treatment method comprises: Before forming an ohmic contact electrode on the surface of the epitaxial structure, a surface treatment combining dry etching and wet etching is performed on the surface of the epitaxial structure.

2. The surface treatment method for improving the ohmic contact performance of a photoconductive switch according to claim 1, characterized in that: Dry etching of the epitaxial structure surface includes: The surface of the epitaxial structure is etched using inductively coupled plasma etching technology.

3. The surface treatment method for improving the ohmic contact performance of a photoconductive switch according to claim 2, characterized in that: The etching gas includes a mixed gas of Cl2 and BCl3; The flow rate of Cl2 ranged from 5 to 15 sccm; The flow rate of BCl3 ranges from 10 to 30 sccm; Etching power range is 100W-300W; RF power range is 50W-200W; The etching time ranges from 1min to 5min.

4. The surface treatment method for improving the ohmic contact performance of a photoconductive switch according to claim 3, characterized in that: The flow rate ratio of Cl2 and BCl3 is: Cl2:BCl3=2:5; The flow rate of Cl2 is 10 sccm; The flow rate of BCl3 was 25 sccm; The etching power is 300W; The RF power is 100W; The etching time is 2 minutes.

5. The surface treatment method for improving the ohmic contact performance of a photoconductive switch according to claim 1, characterized in that: Wet etching of the epitaxial structure surface includes: The epitaxial structure is immersed in a hydrochloric acid solution.

6. The surface treatment method for improving the ohmic contact performance of a photoconductive switch according to claim 5, characterized in that: The ratio of HCl to H2O in the hydrochloric acid solution is in the range of HCl:H2O=(1:1)-(1:10), and the soaking time is in the range of 1 min-5 min.

7. The surface treatment method for improving the ohmic contact performance of a photoconductive switch according to claim 6, characterized in that: The ratio of HCl to H2O in the hydrochloric acid solution is: HCl:H2O=1:2, and the immersion time is 5 minutes.

8. The surface treatment method for improving the ohmic contact performance of a photoconductive switch according to claim 1, characterized in that: Before the step of performing a surface treatment combining dry etching and wet etching on the surface of the epitaxial structure, the method further includes: The step of cleaning the epitaxial structure.

9. The surface treatment method for improving the ohmic contact performance of a photoconductive switch according to claim 8, characterized in that: Cleaning of epitaxial structures, including: First, the epitaxial structure is placed in a first organic solution and ultrasonically cleaned for 3 min to 10 min; Then, the epitaxial structure is placed in a second organic solution and ultrasonically cleaned for 3 min to 10 min; The epitaxial structure was then placed in deionized water and ultrasonically cleaned for 3 min to 10 min.

10. A photoconductive switch, characterized in that: The surface is prepared by surface treatment using the surface treatment method for improving the ohmic contact performance of a photoconductive switch as described in any one of claims 1 to 9.

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