A diamond schottky diode with surface etching termination enhanced performance and a preparation method thereof

Abstract

This invention discloses a diamond Schottky diode with enhanced performance through surface etching termination and its fabrication method. The invention addresses the problems of existing Schottky diodes, such as significant influence from surface termination, high Schottky barrier, high turn-on voltage, and low forward current. The diamond Schottky diode of this invention involves depositing an intrinsic diamond layer on a boron-doped diamond substrate, ion etching the intrinsic diamond layer, depositing a metal film as an ohmic electrode on the bottom surface of the boron-doped diamond substrate, and depositing a thin metal electrode as a Schottky electrode on the ion-etched intrinsic diamond layer. The improved surface etching-enhanced diamond Schottky diode of this invention has a Schottky electrode with a lower potential barrier, and the etched diamond surface is less affected by termination, resulting in lower electron affinity. This invention forms a termination-free diamond surface by etching oxygen terminations on the diamond surface, resulting in an even lower Schottky barrier.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor power devices, specifically relating to a diamond Schottky diode device and its fabrication method that utilizes a surface etching diamond terminal process to enhance the performance of the Schottky electrode. Background Technology

[0002] Semiconductor power devices are widely used in various power electronic systems. However, power devices based on silicon are increasingly unable to meet the demands of high-power applications. Therefore, wide-bandgap semiconductor materials are considered ideal materials for addressing future high-power needs. Diamond, with a bandgap of 5.45 eV and a critical electric field strength as high as 10 MV / cm, is one of the most suitable wide-bandgap semiconductor materials for fabricating diodes.

[0003] Currently, due to the unresolved technical challenges of n-type doping in diamond, diodes made primarily from diamond are Schottky diodes. Existing diamond Schottky diodes are mainly classified into vertical, pseudo-vertical, and Schottky pn-type diodes. All three types of diamond Schottky diodes consist of an ohmic electrode, a doped layer, a depletion layer, and a Schottky electrode. The Schottky electrode plays a decisive role in the diode's turn-on performance. For diamond Schottky diodes, a diamond oxygen-terminated structure is commonly used for surface passivation to ensure stable diode performance. However, the high electron affinity of oxygen-terminated diamond leads to a high barrier height, high turn-on voltage, and low forward current in the diamond Schottky diode. For applications of diamond Schottky diodes, it is crucial to reduce the turn-on voltage and increase the forward current by decreasing the barrier height of the Schottky junction. This invention provides a method for mitigating the influence of surface termination by using ion bombardment etching of the diamond surface to reduce the electron affinity of the diamond surface, lower the barrier height of the diamond diode, and improve the performance of the diamond Schottky diode. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of existing Schottky diodes being greatly affected by surface terminations, having a large Schottky barrier, a high turn-on voltage, and a low forward current. The invention provides a method to enhance the performance of diamond Schottky diodes by etching terminations on the surface, thereby effectively reducing the influence of surface terminations, lowering the surface electron affinity, and improving diode performance.

[0005] The present invention provides a diamond Schottky diode with enhanced performance through surface etching, comprising an ohmic contact electrode, a boron-doped diamond substrate, an intrinsic diamond epitaxial layer, and a Schottky electrode. An intrinsic diamond layer is deposited on the boron-doped diamond substrate, the intrinsic diamond layer is ion-etched, a metal film is deposited on the bottom surface of the boron-doped diamond substrate as an ohmic electrode, and a thin metal electrode is deposited on the ion-etched intrinsic diamond layer as a Schottky electrode.

[0006] The present invention describes a method for fabricating a diamond Schottky diode with enhanced performance through surface etching, implemented according to the following steps:

[0007] 1. Under vacuum conditions, an intrinsic diamond layer 3 is epitaxially grown on a boron-doped diamond substrate using chemical vapor deposition to obtain a diamond substrate;

[0008] 2. Place the diamond substrate in a mixed acid solution, heat it to 200-400℃ for hot acid cleaning, and then perform ultrasonic cleaning to obtain the cleaned diamond substrate.

[0009] 3. Using photolithography, with photoresist as a mask, patterned (selective deposition) ohmic contact electrodes are deposited on one side of the boron-doped diamond substrate after cleaning. Then, the substrate is annealed at 650-750°C to obtain a diamond substrate with ohmic contact electrodes.

[0010] IV. Ion etching is performed on one side of the intrinsic diamond layer of the diamond substrate with ohmic contact electrodes to obtain the ion-etched diamond substrate.

[0011] 5. A Schottky electrode is deposited on the surface of the intrinsic diamond layer of the diamond substrate after ion etching to obtain a diamond Schottky diode.

[0012] The diamond Schottky diode with enhanced performance through surface etching termination and its fabrication method, as described in this invention, have the following beneficial effects:

[0013] Diamond Schottky diodes with surface-etched enhanced performance exhibit less influence from surface termination on the Schottky contact, resulting in a smaller Schottky barrier height, larger forward current, and lower turn-on voltage. In contrast, unetched Schottky electrodes are significantly affected by surface termination, leading to a larger Schottky barrier height, higher turn-on voltage, and lower forward current, severely impacting the diode's forward conduction performance.

[0014] The improved surface etching performance of the diamond Schottky diode of this invention has a Schottky electrode with a lower barrier. The etched diamond surface is less affected by termination and has a lower electron affinity. The ion-etched unterminated diamond surface can form a lower Schottky barrier compared to oxygen-terminated diamond. This invention forms an unterminated diamond surface with a lower Schottky barrier by etching oxygen termination on the diamond surface, which means that its turn-on voltage is lower and its forward conduction current is larger. As a diode that performs switching and rectification functions, it has excellent performance. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the diamond Schottky diode structure that enhances performance through surface etching terminals according to the present invention;

[0016] Figure 2 This is a comparison diagram of the forward conduction current of the diamond Schottky diode before and after surface etching in the embodiment.

[0017] Figure 3 This is a comparison diagram of the turn-on voltage of the diamond Schottky diode before and after surface etching in the embodiment.

[0018] Figure 4 This is an ideal factor analysis diagram of the diamond Schottky diode using the Cheung method in the embodiment;

[0019] Figure 5 This is a diagram showing the barrier height analysis of the diamond Schottky diode using the Cheung method in this embodiment. Detailed Implementation

[0020] Specific Implementation Method 1: This implementation method for fabricating diamond Schottky diodes with enhanced performance through surface etching termination is carried out according to the following steps:

[0021] 1. Under vacuum conditions, a diamond intrinsic layer 3 is epitaxially grown on a boron-doped diamond substrate 2 using chemical vapor deposition to obtain a diamond substrate;

[0022] 2. Place the diamond substrate in a mixed acid solution, heat it to 200-400℃ for hot acid cleaning, and then perform ultrasonic cleaning to obtain the cleaned diamond substrate.

[0023] 3. Using photolithography, with photoresist as a mask, a patterned (selective deposition) ohmic contact electrode 1 is deposited on one side of the boron-doped diamond substrate 2 after cleaning. Then, it is annealed at 650-750°C to obtain a diamond substrate with ohmic contact electrodes.

[0024] IV. Ion etching is performed on one side of the intrinsic diamond layer 3 of the diamond substrate with ohmic contact electrodes to obtain the ion-etched diamond substrate.

[0025] 5. A Schottky electrode 4 is deposited on the surface of the intrinsic diamond layer 3 of the diamond substrate after ion etching to obtain a diamond Schottky diode.

[0026] This embodiment provides a method to mitigate the impact of surface termination by using ion bombardment etching of diamond surface terminals, thereby reducing the electron affinity of the diamond surface, lowering the barrier height of the diamond diode, and thus improving the performance of the diamond Schottky diode.

[0027] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the chemical vapor deposition method in step one is microwave plasma chemical vapor deposition, radio frequency plasma chemical vapor deposition, laser-induced plasma chemical vapor deposition, DC arc plasma chemical vapor deposition, or hot filament chemical vapor deposition.

[0028] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the mixed acid solution in step 2 is composed of a 68% HNO3 solution and a 98% H2SO4 solution with a volume ratio of 1:3.

[0029] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the hot acid cleaning time in step two is 1 to 3 hours.

[0030] Specific Implementation Method 5: This implementation method differs from Specific Implementation Methods 1 to 4 in that, in step 2, the diamond substrate is sequentially placed in acetone, anhydrous ethanol, and deionized water for ultrasonic cleaning.

[0031] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the annealing time in step three is 10 to 15 minutes.

[0032] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the material of the ohmic contact electrode 1 in step three is a single metal or a multilayered metal. The single metal is Au, Pt, Ru, Pd, Ru, W, Cu, Rh, Mo, Pb, Ir, or W, and the multilayered metal is Ti / Au, Ti / Pt / Au, Ti / Ru, Ti / Mo, Cr / Au, or Cr / Ru.

[0033] Specific Implementation Method Eight: This implementation method differs from one of the specific implementation methods one to seven in that the thickness of the ohmic contact electrode 1 deposited in step three is 10 to 200 nm.

[0034] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that step four uses an electron beam evaporation device with a Kaufman ion gun for ion etching. Under an argon atmosphere, the beam voltage is controlled to be 0.4 to 1 kV and the beam current is 20 to 80 mA.

[0035] This embodiment optimizes the ion etching process by adjusting the beam current and beam voltage to form a terminal-free diamond surface through ion etching.

[0036] Specific Implementation Method 10: This implementation method differs from Specific Implementation Method 9 in that the ion etching time in step four is 1 to 4 minutes.

[0037] Specific Implementation Method Eleven: This implementation method differs from Specific Implementation Methods One through Ten in that the material of the Schottky electrode 4 in step five is Au, Pt, Ru, Pd, W, Cu, Rh, Mo, Pb, Ir, or W, and the thickness of the Schottky electrode 4 is 20–100 nm.

[0038] Example 1: This embodiment describes a method for fabricating a diamond Schottky diode with enhanced performance through surface etching termination, implemented according to the following steps:

[0039] 1. A boron-doped diamond substrate with a thickness of 0.5 mm is placed in a microwave plasma chemical vapor deposition system. The chamber is evacuated to a vacuum level of 5 × 10⁻⁶. -6 mbar, hydrogen gas is introduced and the hydrogen flow rate is controlled at 196 sccm. The microwave power supply is turned on and the gas pressure and microwave power are alternately increased to make the temperature of the boron-doped diamond substrate reach 850℃. CH4 is introduced at a flow rate of 4 sccm to grow a diamond intrinsic layer 3 with a thickness of 1 μm by vapor deposition, and a diamond substrate is obtained.

[0040] 2. The diamond substrate is placed in a mixed acid solution (HNO3:H2SO4 = 1:3) and heated to 350°C for hot acid cleaning for 2 hours. After hot acid cleaning, the diamond substrate has oxygen terminals. Then, it is ultrasonically cleaned in acetone, deionized water and acetone solution in sequence to obtain the cleaned diamond substrate.

[0041] 3. Using photolithography, with photoresist as a mask, a circular ohmic contact electrode 1 is deposited on one side of the boron-doped diamond substrate 2 after cleaning. The ohmic contact electrode 1 is a Ti / Pt / Au metal ohmic contact with a deposition thickness of Ti:Pt:Au = 20nm:20nm:50nm. Then, it is annealed at 700℃ for 10 minutes to improve the contact characteristics and obtain a diamond substrate with ohmic contact electrodes.

[0042] IV. Place the diamond substrate with ohmic contact electrodes into an electron beam evaporation system integrated with a Kaufman ion gun. Evacuate the cavity to a vacuum level of 1×10⁻⁶. -4 Pa, argon gas is introduced at a flow rate of 17 sccm, the vacuum degree of the cavity is 0.5 Pa, the Kaufman ion gun system is turned on, the filament current is adjusted to 5 A, the discharge voltage is 80 V, the discharge current is 0.2 A, the beam current is 40 mA, the beam voltage is 1 kV, the etching time is 1 minute and 30 seconds, and the diamond substrate after ion etching is obtained.

[0043] 5. A Schottky electrode 4 with a thickness of 50 nm is deposited on the surface of the intrinsic diamond layer 3 of the diamond substrate after ion etching. The Schottky electrode 4 is made of gold, thus obtaining a diamond Schottky diode.

[0044] The diamond Schottky diode prepared in this embodiment includes an ohmic contact electrode 1, a boron-doped diamond substrate 2, an intrinsic diamond epitaxial layer 3, and a Schottky electrode 4. The intrinsic diamond layer 3 is deposited on the boron-doped diamond substrate 2. The intrinsic diamond layer 3 is ion-etched. A metal film is deposited on the bottom surface of the boron-doped diamond substrate 2 as the ohmic electrode 1. A thin metal electrode is deposited on the ion-etched intrinsic diamond layer 3 as the Schottky electrode 4.

[0045] This embodiment uses a diamond Schottky diode obtained without step four ion etching as a comparison.

[0046] Figure 2 This graph compares the forward current of a diamond Schottky diode before and after surface etching. As can be seen from the graph, within the forward current testing range of -10V to 0V, a significant difference in forward current appears at -1V for both the etched and unetched diamond Schottky diodes. At an applied voltage of -10V, the current of the unetched diamond Schottky diode is 2.5 × 10⁻⁶. -4 A, and the current of the etched diamond Schottky diode is 5.3 × 10⁻⁶. -4 A, which is twice that before etching, demonstrates the effect of surface etching termination on improving the forward conduction current of diamond Schottky diodes.

[0047] Figure 3 This graph compares the turn-on voltage of a diamond Schottky diode before and after surface etching. As can be seen, before etching, the current of the diamond Schottky diode only begins to increase significantly with increasing applied voltage at around -1.5V, meaning the turn-on voltage is 1.5V. However, after surface etching, the current of the diamond Schottky diode already shows a significant increase at around -0.2V, and the turn-on voltage approaches that of an ideal diode.

[0048] Figure 2 , Figure 3The increased turn-on current and decreased turn-on voltage observed after surface terminal etching are due to the reduction of the Schottky barrier and the improvement of Schottky contact quality after the surface terminals are etched. Figure 4 and Figure 5 This image shows data from an analysis of the conduction state of a Schottky diode using the Cheung method. The Cheung method is an analysis approach based on the hot electron emission model for Schottky contact analysis. The formula for analyzing Schottky contacts using the Cheung method is shown below:

[0049]

[0050]

[0051] Where R s Let q be the on-resistance of the Schottky diode, q be the elementary charge, A be the area of ​​the Schottky electrode, and A* be Richardson's constant. Using equations (1) and (2), the ideality factor n and barrier height φ of the Schottky electrode in a diamond Schottky diode can be calculated. B The ideality factor is a key parameter for measuring the quality of Schottky electrodes; the closer the ideality factor is to 1, the higher the quality of the Schottky electrode. From... Figure 4 The results showed that the ideality factor of the Schottky electrode before etching was 15.8, while after etching, it decreased to 10.7. This demonstrates that etching the surface termination improves the quality of the Schottky electrode and contributes to the increase of forward current. Figure 5 The results showed that the barrier height of the Schottky contact before etching was 0.83 eV, and the barrier height after surface etching was 0.67 eV, proving that surface terminating can reduce the barrier height of the Schottky contact. The reduction in barrier height after etching is due to the decrease in electron affinity of the diamond surface caused by surface etching. According to the Schottky-Mott theory, the barrier height of the metal-p-type semiconductor contact can be calculated by the following formula:

[0052] qφ B =E g -q(φ m -χ) (3)

[0053] Where E g φ is the semiconductor bandgap. m χ is the work function of metals, and χ is the electron affinity of semiconductor materials.

[0054] The reduction in electron affinity on the diamond surface leads to a decrease in the height of the Schottky contact barrier formed therein, and the decrease in barrier height reduces the turn-on voltage of the diamond Schottky diode.

[0055] In summary, the diamond Schottky diode with enhanced performance through surface etching described in this invention has twice the forward conduction current and a near-zero turn-on voltage compared to diodes without surface etching, exhibiting excellent rectification performance.

Claims

1. A diamond Schottky diode with surface etched termination to enhance performance, characterized in that The diamond Schottky diode with enhanced performance through surface etching includes an ohmic contact electrode (1), a boron-doped diamond substrate (2), an intrinsic diamond epitaxial layer (3), and a Schottky electrode (4). The intrinsic diamond layer (3) is deposited on the boron-doped diamond substrate (2). The intrinsic diamond layer (3) is ion-etched using an electron beam evaporation device with a Kaufman ion gun. The ion etching is performed under an argon atmosphere, with the beam voltage controlled at 0.4~1kV and the beam current at 20~80mA. A metal film is deposited on the bottom surface of the boron-doped diamond substrate (2) as the ohmic electrode (1), and a thin metal electrode is deposited on the ion-etched intrinsic diamond layer (3) as the Schottky electrode (4).

2. The method of claim 1, wherein the surface etching is performed by a plasma etching process. The preparation method is carried out according to the following steps:

1. Under vacuum conditions, a diamond intrinsic layer (3) is epitaxially grown on a boron-doped diamond substrate (2) by chemical vapor deposition to obtain a diamond substrate; 2. Place the diamond substrate in a mixed acid solution, heat it to 200~400℃ for hot acid cleaning, and then perform ultrasonic cleaning to obtain the cleaned diamond substrate.

3. Using photolithography, with photoresist as a mask, a patterned ohmic contact electrode (1) is deposited on one side of the boron-doped diamond substrate (2) after cleaning. Then, it is annealed at 650~750℃ to obtain a diamond substrate with ohmic contact electrodes. IV. Ion etching is performed on one side of the intrinsic diamond layer (3) of the diamond substrate with ohmic contact electrodes to obtain the ion-etched diamond substrate.

5. A Schottky electrode (4) is deposited on the surface of the intrinsic diamond layer (3) of the diamond substrate after ion etching to obtain a diamond Schottky diode; In step four, an electron beam evaporation device with a Kaufman ion gun is used for ion etching. Under an argon atmosphere, the beam voltage is controlled to be 0.4~1kV and the beam current is 20~80mA.

3. The method of claim 2, wherein the surface etching is performed by a plasma etching process. The chemical vapor deposition method in step one is microwave plasma chemical vapor deposition, radio frequency plasma chemical vapor deposition, laser-induced plasma chemical vapor deposition, DC arc plasma chemical vapor deposition, or hot filament chemical vapor deposition.

4. The method of claim 2, wherein the surface etching is performed by a plasma etching process. The hot acid cleaning time in step two is 1 to 3 hours.

5. The method of claim 2, wherein the surface etching is performed by a plasma etching process. The annealing time in step three is 10-15 minutes.

6. The method of claim 2, wherein the surface etching is performed by a plasma etching process. In step three, the ohmic contact electrode (1) is made of a single metal or a multilayer metal, wherein the single metal is Au, Pt, Ru, Pd, Ru, W, Cu, Rh, Mo, Pb, Ir or W, and the multilayer metal is Ti / Au, Ti / Pt / Au, Ti / Ru, Ti / Mo, Cr / Au or Cr / Ru.

7. The method of claim 2, wherein the surface etching is performed by a plasma etching process. The thickness of the ohmic contact electrode (1) deposited in step three is 10~200 nm.

8. The method of claim 2, wherein the surface etching is performed by a plasma etching process. The ion etching time in step four is 1~4 min.

9. The method of claim 2, wherein the surface etching is performed by a plasma etching process. In step five, the material of the Schottky electrode (4) is Au, Pt, Ru, Pd, W, Cu, Rh, Mo, Pb, Ir or W, and the thickness of the Schottky electrode (4) is 20~100 nm.

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