A low-resistance and high-reflection ohmic contact electrode and a method for preparing the same

Abstract

The present invention discloses a low-resistance and high-reflection ohmic contact electrode, comprising a p-type semiconductor wafer, on which a metal electrode layer is deposited; and further comprising a first metal silver layer, a metal nickel layer, a second metal silver layer and a metal aluminum layer sequentially deposited on the surface of the p-type semiconductor wafer, wherein the first metal silver layer contacts the metal electrode layer on the p-type semiconductor wafer. The present invention also discloses a method for preparing a low-resistance and high-reflection ohmic contact electrode. The present invention adopts a metal silver-metal nickel-metal silver film stack to form an ohmic contact with low resistance and high light transmittance, and combines it with an aluminum film to prepare an ohmic contact electrode, which has the beneficial effects of simple preparation method, high conductivity, low ohmic contact resistivity and high reflectivity.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor electronics and optoelectronics, and more specifically, to a low-resistance and high-reflection ohmic contact electrode and a preparation method thereof. Background Art

[0002] In the preparation of UV optoelectronic devices based on III-nitrides, the development of n-type ohmic contacts has been relatively complete, while the preparation of p-type ohmic contacts still faces great challenges. The p-type ohmic contact electrode with low contact impedance is one of the key preparation process technologies. For example, for UV avalanche photodetectors (APDs), high-performance p-type ohmic contacts have smaller contact resistance and smaller voltage divider, which can enable APDs to achieve high gain at lower operating voltages.

[0003] For ultraviolet light-emitting devices, such as light-emitting diodes (LEDs), p-type ohmic contact electrodes with low contact resistance and high reflectivity can be used to make the LED emit light at low voltage, reduce the absorption of ultraviolet light by metal electrodes, promote the circulation of emitted photons, increase the light extraction rate of LEDs, and thus improve the performance of LEDs. Therefore, whether for ultraviolet detectors or ultraviolet LEDs, the preparation of low-resistance, high-reflectivity p-type ohmic contacts is a very critical link. The preparation of high-performance p-type ohmic contacts is a prerequisite for manufacturing high-performance optoelectronic devices.

[0004] According to current research reports, most metals have not formed an ideal ohmic contact in the p-type layer of high Al content nitride, and there are relatively few studies on p-type ohmic contacts. For the development of ultraviolet and deep ultraviolet optoelectronic devices, the preparation technology of low-resistance and high-reflection p-type ohmic contact resistance is more needed. Summary of the invention

[0005] The present invention aims to overcome at least one defect (shortcoming) of the above-mentioned prior art and provide a low-resistance and high-reflection ohmic contact electrode and a preparation method thereof, which has the advantages of low contact resistivity, high reflectivity and simple operation.

[0006] In order to achieve the above technical effects, the technical solution adopted by the present invention is:

[0007] A low-resistance and high-reflection ohmic contact electrode comprises a p-type semiconductor wafer on which a metal electrode layer is deposited; and further comprises a first metal silver layer, a metal nickel layer, a second metal silver layer and a metal aluminum layer sequentially deposited on the surface of the p-type semiconductor wafer, wherein the first metal silver layer contacts the metal electrode layer on the p-type semiconductor wafer.

[0008] Furthermore, the thickness ranges of the first metal silver layer, the metal nickel layer, the second metal silver layer and the metal aluminum layer are respectively: 0.5-1.5nm, 1-2nm, 3-5nm and 10-1000nm.

[0009] Furthermore, the p-type semiconductor wafer is a p-type Group III nitride.

[0010] A method for preparing a low-resistance and high-reflection ohmic contact electrode, wherein the ohmic contact electrode is prepared on a p-type semiconductor wafer, and the preparation method comprises the following steps:

[0011] S1: cleaning the surface of the p-type semiconductor wafer;

[0012] S2: using photolithography technology to cover the surface of the p-type semiconductor wafer with a photoresist mask layer, and exposing the metal electrode layer on the surface of the p-type semiconductor wafer;

[0013] S3: depositing a first metal silver film, a metal nickel film, and a second metal silver film on the surface of the p-type semiconductor wafer in sequence, so that the first metal silver film, the metal nickel film, and the second metal silver film are in contact with the metal electrode layer in sequence to form an ohmic electrode;

[0014] S4: removing the photoresist mask layer on the surface of the p-type semiconductor wafer using a chemical solution;

[0015] S5: placing the p-type semiconductor wafer in a high-purity nitrogen environment for heat treatment;

[0016] S6: placing the heat-treated p-type semiconductor wafer in high-purity oxygen or dry clean air for annealing;

[0017] S7: using the photoresist technology again to cover the surface of the p-type semiconductor wafer with a photoresist mask layer, and exposing the ohmic electrode on the surface of the p-type semiconductor wafer;

[0018] S8: depositing a metal aluminum film on the surface of the p-type semiconductor wafer, so that the metal aluminum film is deposited on the ohmic electrode;

[0019] S9: Using the chemical solution again to remove the photoresist mask layer on the surface of the p-type semiconductor wafer, the preparation of the ohmic contact electrode is completed.

[0020] The ohmic contact electrode prepared by the preparation method has a small contact resistance value. Therefore, when the current flows through the device, the voltage drop of the ohmic contact electrode is very small, which meets the requirements of high-performance ohmic contact electrodes. Among them, the ohmic contact is a kind of contact between metal and semiconductor, which has a non-rectifying characteristic, that is, the ohmic contact does not produce obvious additional impedance, nor does it cause a significant change in the equilibrium carrier concentration inside the semiconductor.

[0021] The technical solution prepares an ohmic contact electrode on a p-type semiconductor wafer, and has the effects of good metal adhesion of each layer, easy deposition and film formation, stable performance under high temperature conditions, and not easy to change. The ohmic contact electrode prepared by the technical solution also has good light reflection performance when applied to ultraviolet light-emitting devices.

[0022] In the present technical solution, in step S3, an Ag / Ni / Ag metal electrode is formed, and the Ni-based, Ag-based and their combination can improve the formation of the ohmic contact electrode. Specifically, the first metal silver layer can enhance the contact between Ag and the p-type semiconductor wafer, and the mixed mechanism of the Ni-based and Ag-based compounds can work together to form a good ohmic contact. At the same time, the double-layer metal silver layer is used, and its performance is better than the ohmic contact of the simple Ni / Ag combination. Therefore, the double-layer metal silver layer can further increase the adhesion of the ohmic contact, thereby obtaining an ohmic contact electrode with low contact resistivity and high reflectivity.

[0023] The metal aluminum film in step S8 mainly plays the role of a reflector on the surface of the p-type semiconductor wafer.

[0024] Furthermore, in step S1, the specific steps of cleaning the surface of the p-type semiconductor wafer are:

[0025] S11: Cleaning the surface of the p-type semiconductor wafer with a standard organic solution, and then cleaning with deionized water; the organic solution includes electronic grade acetone and isopropyl ketone;

[0026] S12: soaking the p-type semiconductor wafer in a pure acid solution for 20 to 90 seconds; the pure acid solution is hydrochloric acid or hydrofluoric acid;

[0027] S13: Cleaning the p-type semiconductor wafer with deionized water;

[0028] S14: using high-purity ammonia gas to blow dry the p-type semiconductor wafer.

[0029] Furthermore, in step S3, the thickness of the first metal silver film deposited on the metal electrode layer is 0.5-1.5 nm, the thickness of the metal nickel film is 1-2 nm, and the thickness of the second metal silver film is 3-5 nm.

[0030] This technical solution uses Ag / Ni / Ag metal electrodes to prepare ohmic contacts. The first layer uses a thin metal Ag layer to increase the effect of its mixing mechanism. At the same time, a double-layer metal Ag layer is used to increase its adhesion. At the same time, each metal film layer of the metal electrode structure is thinner, which reduces the absorption of ultraviolet light by the metal electrode itself and increases the light extraction efficiency. Therefore, this technical method can form a good ohmic contact with the advantages of low contact resistivity, high reflectivity, and simple operation.

[0031] Further, in step S5, the heat treatment temperature is 300-500°C, and the heat treatment time is 1-2min; in step S6, the annealing temperature of the annealing treatment is 300-500°C, and the annealing time is 1-2min; in step S8, the metal aluminum film is vacuum deposited on the surface of the second metal silver film of the ohmic electrode; the thickness of the metal aluminum film is 10-1000nm, and the deposition rate is greater than 0.2nm / s.

[0032] Furthermore, the deposition method in steps S3 and S8 is vacuum evaporation or magnetron sputtering.

[0033] Furthermore, the p-type semiconductor wafer is one of a p-type binary compound, a ternary compound or a quaternary compound.

[0034] Further preferably, the p-type semiconductor wafer is one of p-type GaN, AlGaN, AlInN or AlInGaN.

[0035] More preferably, the p-type semiconductor chip of the present technical solution is p-type AlGaN, AlInN or AlInGaN. The ternary or quaternary compound containing Al component can adjust the bandgap width as the Al component changes, thereby realizing the functions of ultraviolet luminescence and photoelectric detection in the spectral range of 200-365nm, and is the preferred material for preparing ultraviolet photodetectors and light-emitting devices.

[0036] Furthermore, the p-type semiconductor wafer is a Group III nitride.

[0037] Furthermore, the p-type semiconductor wafer of the technical solution is p-type AlGaN. The technical solution enhances the contact between Ag and p-type AlGaN through the combination of Ag / Ni / Ag, promotes the formation of AgGa solid solution, and thereby generates Ga vacancies with acceptor characteristics at the metal / semiconductor contact interface, so that a good ohmic contact can be formed by using the tunneling effect.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The present invention adopts a metal silver-metal nickel-metal silver film stack to form an ohmic contact with low resistance and high light transmittance, and combines it with an aluminum film to prepare an ohmic contact electrode, which has the beneficial effects of simple preparation method, high conductivity, low ohmic contact resistivity and high reflectivity.

[0040] This technical solution uses a combination of Ag / Ni / Ag to obtain the ohmic contact characteristics of the ohmic contact electrode, which can greatly increase the adhesion of Ag and has high light transmittance, which is better than the ohmic contact characteristics of only using the Ni / Ag combination.

[0041] The metal Al film of the present technical solution has high reflectivity in the visible to ultraviolet bands, and combined with the Ag / Ni / Ag thin layer structure, it realizes the preparation of a low-resistance, high-reflectivity p-type ohmic contact electrode.

[0042] Experiments show that the ohmic contact electrode obtained by the technical solution can achieve a light reflectivity of 66%-80% at 200-280nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the ohmic contact electrode structure of the present invention.

[0044] Figure 2 This is a diagram of the electrical characteristics results of Example 2.

[0045] Figure 3 This is a diagram of the optical properties results of Example 3. DETAILED DESCRIPTION

[0046] The drawings of the present invention are only for illustrative purposes and should not be construed as limiting the present invention. In order to better illustrate the following embodiments, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product; it is understandable to those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0047] Example 1

[0048] like Figure 1 As shown, this embodiment discloses a method for preparing a low-resistance and high-reflection ohmic contact electrode, wherein the ohmic contact electrode is prepared on a p-type semiconductor wafer, wherein the p-type semiconductor wafer is a p-type III-nitride, preferably, the p-type III-nitride is AlGaN, and specifically, the p-type III-nitride is p-Al 0.4 Ga 0.6 N, the preparation method thereof comprises the following steps:

[0049] S1: Cleaning the surface of the p-type semiconductor wafer; the specific steps are:

[0050] S11: Cleaning the surface of the p-type semiconductor wafer with electronic grade acetone and isopropyl ketone in sequence, and then with deionized water;

[0051] S12: soaking the p-type semiconductor wafer in pure hydrochloric acid or hydrofluoric acid for 20 to 90 seconds;

[0052] S13: Cleaning the p-type semiconductor wafer with deionized water;

[0053] S14: using high-purity ammonia gas to blow dry the p-type semiconductor wafer;

[0054] S2: using photolithography technology to cover the surface of the p-type semiconductor wafer with a photoresist mask layer, and exposing the metal electrode layer on the surface of the p-type semiconductor wafer;

[0055] S3: depositing a first metal silver film 101, a metal nickel film 102, and a second metal silver film 103 on the surface of a p-type semiconductor wafer in sequence by vacuum evaporation or magnetron sputtering, so that the first metal silver film 101, the metal nickel film 102, and the second metal silver film 103 are in contact with the metal electrode layer on the surface of the p-type semiconductor wafer in sequence to form an ohmic electrode; wherein the thicknesses of the first metal silver film 101, the metal nickel film 102, and the second metal silver film 103 are 0.5-1.5 nm, 1-2 nm, and 3-5 nm, respectively;

[0056] S4: removing the photoresist mask layer on the surface of the p-type semiconductor wafer using a chemical solution;

[0057] S5: placing the p-type semiconductor wafer in a high-purity nitrogen environment for heat treatment at a temperature of 300-500° C. for a heat treatment time of 1-2 minutes;

[0058] S6: placing the heat-treated p-type semiconductor wafer in high-purity oxygen or dry clean air for annealing, the annealing temperature is 300-500° C., and the annealing time is 1-2 minutes;

[0059] S7: using the photoresist technology again to cover the surface of the p-type semiconductor wafer with a photoresist mask layer, and exposing the ohmic electrode on the surface of the p-type semiconductor wafer;

[0060] S8: depositing a metal aluminum film 104 on the surface of the p-type semiconductor wafer by vacuum evaporation or magnetron sputtering, so that the metal aluminum film 104 is deposited on the ohmic electrode; wherein the thickness of the metal aluminum film 104 is 10-1000 nm, and the deposition rate is greater than 0.2 nm / s;

[0061] S9: Using the chemical solution again to remove the photoresist mask layer on the surface of the p-type semiconductor wafer, the preparation of the ohmic contact electrode is completed.

[0062] Furthermore, the p-type semiconductor wafer of the present embodiment may be one of a p-type binary compound, a ternary compound or a quaternary compound. Further preferably, the p-type semiconductor wafer of the present embodiment is not limited to AlGaN, for example, it may also be one of p-type GaN, AlInN or AlInGaN.

[0063] Example 2

[0064] In this embodiment, the electrical characteristics of the ohmic contact electrode obtained in embodiment 1 are tested.

[0065] Among them, line segment 1 is a comparative example. The main difference between the comparative example and the present embodiment is that in step S3 of the comparative example, only a layer of metal silver and a layer of metal nickel are deposited, that is, Ni / Ag and p-Al 0.4 Ga 0.6 Ohmic contact electrode formed by N;

[0066] Line segment 2 is the ohmic contact electrode obtained in Example 1, that is, Ag / Ni / Ag and p-Al 0.4 Ga 0.6 N forms an ohmic contact electrode.

[0067] Test results such as Figure 2 As shown, from Figure 2 It can be seen that both line segment 1 and line segment 2 exhibit linear behavior, indicating that both can be used with p-Al 0.4 Ga 0.6 N forms a good ohmic contact, but the slope of line segment 2 is larger, indicating that Ag / Ni / Ag and p-Al 0.4 Ga 0.6 The ohmic contact electrode formed by N has smaller resistance and better performance.

[0068] Example 3

[0069] In this embodiment, the ohmic contact electrode obtained in embodiment 1 is tested for its optical properties.

[0070] Wherein, line segment 1 is the ultraviolet reflectivity curve spectrum of the ohmic contact electrode obtained in Example 1 after annealing at 350° C.;

[0071] Line segment 2 is the ultraviolet reflectivity curve spectrum of the ohmic contact electrode obtained in Example 1 after annealing at 450° C.

[0072] Figure 3 The optical properties of the ohmic contact electrode Ag / Ni / Ag / Al on a sapphire substrate obtained in Example 1. Figure 3 It can be seen that the reflectivity of the annealing at 350°C (segment 1) is significantly higher than that of the annealing at 450°C (segment 2), indicating that the alloy of the ohmic contact electrode of this embodiment is more conducive to obtaining high reflectivity at low temperature, that is, the sample annealed at 350°C (segment 1) has a higher light reflectivity.

[0073] from Figure 3 It can also be seen that the light reflectivity of the ohmic contact electrode obtained in Example 1 can reach 66%-80% between 200-280nm, and the light reflectivity at 256nm is 80%.

[0074] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the technical solution of the present invention, and are not intended to limit the specific implementation methods of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the claims of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A low-resistance and high-reflection ohmic contact electrode, comprising a p-type semiconductor wafer on which a metal electrode layer is deposited; characterized in that: It also includes a first metal silver layer, a metal nickel layer, a second metal silver layer and a metal aluminum layer which are sequentially deposited on the surface of a p-type semiconductor wafer, wherein the first metal silver layer is in contact with the metal electrode layer on the p-type semiconductor wafer; the thickness ranges of the first metal silver layer, the metal nickel layer, the second metal silver layer and the metal aluminum layer are respectively: 0.5-1.5nm, 1-2nm, 3-5nm and 10-1000nm.

2. The low-resistance and high-reflection ohmic contact electrode according to claim 1, characterized in that: The p-type semiconductor wafer is a p-type Group III nitride.

3. A method for preparing a low-resistance and high-reflection ohmic contact electrode, characterized in that: The ohmic contact electrode is prepared on a p-type semiconductor wafer, and the preparation method thereof comprises the following steps: S1: cleaning the surface of the p-type semiconductor wafer; S2: using photolithography technology to cover the surface of the p-type semiconductor wafer with a photoresist mask layer, and exposing the metal electrode layer on the surface of the p-type semiconductor wafer; S3: depositing a first metal silver film, a metal nickel film, and a second metal silver film on the surface of the p-type semiconductor wafer in sequence, so that the first metal silver film, the metal nickel film, and the second metal silver film are in contact with the metal electrode layer in sequence to form an ohmic electrode; S4: removing the photoresist mask layer on the surface of the p-type semiconductor wafer using a chemical solution; S5: placing the p-type semiconductor wafer in a high-purity nitrogen environment for heat treatment; S6: placing the heat-treated p-type semiconductor wafer in high-purity oxygen or dry clean air for annealing; S7: using the photoresist technology again to cover the surface of the p-type semiconductor wafer with a photoresist mask layer, and exposing the ohmic electrode on the surface of the p-type semiconductor wafer; S8: depositing a metal aluminum film on the surface of the p-type semiconductor wafer, so that the metal aluminum film is deposited on the ohmic electrode; S9: using the chemical solution again to remove the photoresist mask layer on the surface of the p-type semiconductor wafer to complete the preparation of the ohmic contact electrode; In step S3, the thickness of the first metal silver film deposited on the metal electrode layer is 0.5-1.5 nm, the thickness of the metal nickel film is 1-2 nm, and the thickness of the second metal silver film is 3-5 nm.

4. The method for preparing a low-resistance and high-reflection ohmic contact electrode according to claim 3, characterized in that: In step S1, the specific steps of cleaning the surface of the p-type semiconductor wafer are: S11: Cleaning the surface of the p-type semiconductor wafer with a standard organic solution, and then cleaning with deionized water; the organic solution includes acetone and isopropyl ketone; S12: soaking the p-type semiconductor wafer in a pure acid solution for 20 to 90 seconds; the pure acid solution is hydrochloric acid or hydrofluoric acid; S13: Cleaning the p-type semiconductor wafer with deionized water; S14: using high-purity ammonia gas to blow dry the p-type semiconductor wafer.

5. The method for preparing a low-resistance and high-reflection ohmic contact electrode according to claim 3, characterized in that: In step S5, the heat treatment temperature is 300-500°C, and the heat treatment time is 1-2min. In step S6, the annealing temperature of the annealing treatment is 300-500°C, and the annealing time is 1-2min. In step S8, the metal aluminum film is deposited on the surface of the second metal silver film of the ohmic electrode by a vacuum deposition method. The thickness of the metal aluminum film is 10-1000nm, and the deposition rate is greater than 0.2nm / s.

6. The method for preparing a low-resistance and high-reflection ohmic contact electrode according to claim 3, characterized in that: The deposition method in steps S3 and S8 is vacuum evaporation or magnetron sputtering.

7. The method for preparing a low-resistance and high-reflection ohmic contact electrode according to claim 3, characterized in that: The p-type semiconductor wafer is one of a p-type binary compound, a ternary compound or a quaternary compound.

8. The method for preparing a low-resistance and high-reflection ohmic contact electrode according to claim 3 or 7, characterized in that: The p-type semiconductor wafer is one of p-type GaN, AlGaN, AlInN or AlInGaN.

Images