Method for preparing ohmic contact on intrinsic diamond surface using iron catalysis
By using Fe catalysis to prepare ohmic contacts on intrinsic diamond surfaces, the problems of high contact resistivity and easy contact detachment on intrinsic diamond were solved, achieving ohmic contacts with low contact resistivity and mechanical stability, thus improving the conductivity and operational stability of the device.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HARBIN INST OF TECH
- Filing Date
- 2022-03-16
- Publication Date
- 2026-05-22
AI Technical Summary
Existing technologies make it difficult to fabricate ohmic contacts with low contact resistivity on intrinsic diamond, and the contacts are prone to detachment, resulting in high energy loss and unstable operation of the device.
Ohmic contacts were prepared by graphitizing intrinsic diamond surfaces using Fe catalysis, followed by high-temperature annealing using a combination of photolithography and magnetron plating.
It reduces contact resistivity, improves conductivity, ensures mechanical stability and long-term operational reliability of the contacts, simplifies the manufacturing process, and reduces costs.
Smart Images
Figure CN114628249B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the technical field of metal-semiconductor surface contact characteristics research, specifically involving a method for using iron-catalyzed diamond to undergo graphitization phase transition, thereby changing the metal-semiconductor contact characteristics and transforming a high-barrier, high-resistivity Schottky contact into a low-contact-resistivity ohmic contact. Background Technology
[0002] A key requirement for any emerging device technology is the development of suitable electrode contacts. The challenge lies in producing contacts compatible with the unique physical and chemical properties of diamond, while also ensuring continuous operation under the harsh conditions expected of the device. All semiconductor device applications involve point / surface contacts, and all contacts have contact resistance. Currently, the contact type studied is typically metal-semiconductor contact. Metals and semiconductors have different work functions, and their contact generates electron flow, with electrons moving from the side with the lower work function to the side with the higher work function. This causes the energy levels on the semiconductor surface to bend upwards or downwards. When charge carriers pass through this contact interface, they must overcome a significant potential barrier, resulting in high resistance. When a voltage is applied to the device, this region generates significant heat and energy loss, hindering engineering applications. Therefore, the fabrication of ohmic contacts with low contact resistivity has been a key research focus.
[0003] Due to the pinning effect on semiconductor surfaces and the difficulty in matching the work function of metal to semiconductor, it is almost impossible to achieve true ohmic contacts in semiconductor devices. If the voltage drop at the contact is small compared to the voltage drop across the effective operating portion of the device, the contact is generally considered sufficient for application. Therefore, ohmic contacts are typically formed by using heavily doped semiconductors near the metal-semiconductor contact point. Heavily doped semiconductors reduce the width of the barrier at the metal / semiconductor interface. Although the barrier height is not significantly affected by doping, the reduced barrier width increases the probability of electron tunneling through the barrier, making carrier transport easier and shifting the transport mechanism from field emission to thermionic emission, which can greatly improve the conductivity of the interface. Another method to obtain semiconductor ohmic contacts is to reduce the barrier height through appropriate matching of the metal work function with the semiconductor band structure. A third method involves intentionally damaging the semiconductor surface to create surface defects that allow carrier recombination in the depletion region.
[0004] The carbon atoms in diamond are tightly bound together by covalent bonds, making it difficult to prepare diamond semiconductors with shallow excitation energy levels and heavy doping. Furthermore, the high surface state density of diamond means that the potential barrier height at the metal-semiconductor contact is independent of the work function of the metal-semiconductor. Therefore, preparing ohmic contacts with low contact resistance on diamond is quite challenging. Compared to doped diamond, preparing ohmic contacts on intrinsic diamond is even more difficult. Moreover, contact resistivity includes not only the actual interface but also the regions above and below it; therefore, the resistivity of the metal and the semiconductor have a significant impact on the actual contact resistivity. Intrinsic diamond has a lower carrier concentration than doped diamond, resulting in poorer conductivity. Its bandgap is 5.5 eV, and the intrinsic excitation conditions are harsh, with low carrier concentration and high resistivity, leading to a higher contact resistivity compared to doped diamond.
[0005] Currently, the main methods for preparing ohmic contacts on boron-doped diamond include the formation of carbides using transition metals such as Ti / Au, Ta / Au, and W. Intrinsic diamond is prepared by graphitizing the diamond surface under high temperature conditions (generally 1500℃). The disadvantages of this method are that it is difficult to design the shape of the surface graphite, the mechanical strength of the electrode contact point is insufficient, the contact point is prone to detachment, and the long-term reliability of the contact point is questionable. Summary of the Invention
[0006] This invention aims to address the problems of significant energy loss at metal-semiconductor contacts in semiconductor devices and the easy detachment of intrinsic diamond contacts. It provides a method for preparing ohmic contacts on the diamond surface by using Fe to catalyze the phase transformation of the diamond surface into graphite. The metal / semiconductor contacts prepared by this method have low resistivity, which greatly improves conductivity, reduces energy loss during device use, and the good mechanical properties of the contact bonding can ensure long-term stable operation.
[0007] The present invention utilizes iron catalysis to prepare ohmic contacts on intrinsic diamond surfaces, and is implemented according to the following steps:
[0008] 1. Cleaning: The diamond sample was ultrasonically cleaned sequentially with acetone, deionized water and alcohol to obtain the cleaned diamond.
[0009] II. Photolithography to prepare the mask: The cleaned diamond is placed on the suction cup of the spin coater for spin coating treatment. After drying, the spin-coated diamond is obtained. The spin-coated diamond is exposed using a photolithography machine. After development and N2 drying, the photolithographic diamond is obtained.
[0010] III. Magnetron sputtering of iron: A layer of Fe is deposited on the surface of a diamond after photolithography by magnetron sputtering to obtain an iron-plated diamond.
[0011] IV. Removal of Adhesive: The iron-plated diamond is placed in the adhesive removal solution for ultrasonic cleaning, then cleaned with anhydrous ethanol, and dried to obtain the diamond with iron plating on the surface.
[0012] 5. Sealing: The diamond with iron-plated surface is placed in a quartz tube and sealed. The quartz tube is filled with protective gas and then transferred to a tube furnace for annealing at 800-950°C to prepare ohmic contacts on the diamond surface.
[0013] The Fe-catalyzed process of this invention lowers the phase transition temperature of diamond, and due to the mutual diffusion of Fe and C atoms in diamond at high temperatures, the bonding between the two is more reliable. At the same time, combined with photolithography, the shape of the electrode ohmic contact can be designed, which greatly simplifies the preparation process and reduces the preparation cost.
[0014] The present invention provides a method for preparing ohmic contacts on intrinsic diamond surfaces using iron catalysis, which has the following advantages: by controlling the annealing temperature and time, the contact resistivity is minimized, the contact bonding performance is good and it can work stably for a long time, the presence of Fe reduces the difficulty of wire drawing and facilitates the formation of mechanically stable contacts on the surface, lowers the temperature of overall graphitization of the surface, simplifies the preparation process, and reduces the preparation cost. Attached Figure Description
[0015] Figure 1 The image shown is a sample surface morphology image of the iron-plated diamond obtained using an optical microscope in the example.
[0016] Figure 2 This is a topographic image of the surface of the diamond sample after annealing in the embodiment.
[0017] Figure 3 The image shows the characteristic spectrum of the diamond sample before annealing, characterized by Raman spectroscopy; where 1 represents the characteristic peak of diamond, and 2 represents NV. 0 Color center characteristic peaks;
[0018] Figure 4 The image shows the characteristic spectrum of the annealed diamond sample characterized by Raman spectroscopy in the example.
[0019] Figure 5 This is an IV curve of the diamond sample before annealing in the example;
[0020] Figure 6 The image shows the IV curve of the diamond sample after annealing in the example. Detailed Implementation
[0021] Specific Implementation Method 1: This implementation method for preparing ohmic contacts on intrinsic diamond surfaces using iron catalysis is carried out according to the following steps:
[0022] 1. Cleaning: The diamond sample was ultrasonically cleaned sequentially with acetone, deionized water and alcohol to obtain the cleaned diamond.
[0023] II. Photolithography to prepare the mask: The cleaned diamond is placed on the suction cup of the spin coater for spin coating treatment. After drying, the spin-coated diamond is obtained. The spin-coated diamond is exposed using a photolithography machine. After development and N2 drying, the photolithographic diamond is obtained.
[0024] III. Magnetron sputtering of iron: A layer of Fe is deposited on the surface of a diamond after photolithography by magnetron sputtering to obtain an iron-plated diamond.
[0025] IV. Removal of Adhesive: The iron-plated diamond is placed in the adhesive removal solution for ultrasonic cleaning, then cleaned with anhydrous ethanol, and dried to obtain the diamond with iron plating on the surface.
[0026] 5. Sealing: The diamond with iron-plated surface is placed in a quartz tube and sealed. The quartz tube is filled with protective gas and then transferred to a tube furnace for annealing at 800-950°C to prepare ohmic contacts on the diamond surface.
[0027] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that, in step one, the diamond sample is ultrasonically cleaned with acetone, deionized water, and alcohol for 10-30 minutes respectively.
[0028] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the thickness of the photoresist after homogenization in step 2 is 0.8 to 1.2 μm.
[0029] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the drying described in step two is drying at 95°C for 90 seconds.
[0030] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that, in step three, the vacuum chamber for magnetron sputtering is evacuated to 10... -4 Ar gas is introduced at Pa, and the gas pressure is controlled at 3-5 Pa for ignition. Then the deposition gas pressure is adjusted to 0.5 Pa, and Fe layer is deposited by magnetron sputtering.
[0031] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that the thickness of the Fe layer is 60-200 nm.
[0032] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the protective gas mentioned in step five is Ar gas.
[0033] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the heating rate of the annealing temperature in step five is controlled at 5℃ / min.
[0034] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the annealing time in step five is 1 to 4 hours.
[0035] Specific Implementation Method 10: This implementation method differs from Specific Implementation Methods 1 to 9 in that step 5 involves annealing at 900°C for 2 hours.
[0036] Specific Implementation Method Eleven: This implementation method differs from Specific Implementation Methods One to Ten in that the diamond sample mentioned in step one is intrinsic diamond or doped diamond.
[0037] Example: This example describes a method for preparing ohmic contacts on intrinsic diamond surfaces using iron catalysis, implemented according to the following steps:
[0038] 1. Cleaning: The 3*3*0.3mm (length*width*thickness) CVD diamond sample was ultrasonically cleaned for 15 minutes in sequence with acetone, deionized water and alcohol to obtain the cleaned diamond.
[0039] II. Photolithography Mask Preparation: The cleaned diamond is placed on the suction cup of the spin coater. Spin coat is first performed at 2000 r / min for 20 s, then at 5000 r / min for 60 s. The photoresist is then dried at 95℃ for 90 s to obtain a spin-coated diamond with a thickness of approximately 1 μm. The spin-coated diamond is then exposed using a photolithography machine, followed by development and N2 drying to obtain the photolithographically etched diamond.
[0040] III. Magnetron sputtering: The photolithographically patterned diamond is placed in the magnetron sputtering vacuum chamber, and the vacuum is evacuated to 100°C. -4 Ar gas is introduced at 4 Pa to initiate ignition, and then the deposition pressure is adjusted to 0.5 Pa to deposit a 100 nm thick layer of iron on the diamond surface, thus obtaining iron-plated diamond.
[0041] 4. Removal of adhesive: The iron-plated diamond is placed in the adhesive removal solution for ultrasonic cleaning to remove excess Fe. Then it is cleaned with anhydrous ethanol to remove the adhesive residue on the surface. After drying with high-purity N2, the iron-plated diamond is obtained.
[0042] 5. Sealing: Place the iron-plated diamond in a quartz tube and seal it. Rinse the quartz tube with Ar gas to remove residual oxygen. Then transfer it to a tube furnace and set the heating rate to 5℃ / min. Anneal at 900℃ for 2 hours and then allow it to cool naturally to room temperature to prepare an ohmic contact on the intrinsic diamond surface.
[0043] In step five of this embodiment, a diamond with an iron-plated surface is placed in a quartz tube and sealed, and a mechanical pump is used to evacuate the tube to 10°C. -2Pa is used to remove oxygen from the quartz tube to prevent the diamond from becoming graphitized on its surface under the influence of oxygen. After removing the oxygen, only the Fe-covered areas will form graphite. The exposed diamond areas would require 1500°C to form graphite under oxygen-free conditions. Therefore, in addition to evacuation, Ar gas is also used to clean the quartz tube to ensure that as much oxygen as possible is removed from the tube.
[0044] Figure 1 The image shows the surface morphology of the sample obtained using an optical microscope after iron deposition. Figure 2 The image shows the surface morphology of the annealed sample. A comparison reveals that although iron melts under low pressure and high temperature conditions, the position, shape, and size of the boundary region remain intact. Figure 3 The characteristic spectrum of the sample before annealing was characterized by Raman spectroscopy; only 1333 cm⁻¹ is shown in the figure. -1 The diamond characteristic peak and 1407cm -1 NV 0 Characteristic peak 1333cm -1 The full width at half maximum (FWHM) of the characteristic peak is 2.34 cm. -1 This indicates that the sample has good lattice quality, low internal residual stress, and NV. 0 The characteristic peaks indicate the presence of N impurities in the sample, but the low peak intensity indicates a low concentration of N impurities. This embodiment uses optical-grade diamond, and this Raman spectrum provides excellent evidence for this. Figure 4 The image shows the Raman spectrum of the sample after annealing. It is a typical Raman spectrum of a multilayer graphite structure, indicating that the reaction product is a multilayer graphite structure.
[0045] Using a semiconductor parameter tester, the voltage and current characteristics of the sample were tested. The IV curve before annealing is shown below. Figure 5 As shown, by comparing the current order of magnitude under the same voltage conditions as before annealing, it was found that after annealing ( Figure 6 The current increases by orders of magnitude, and the IV curve after annealing is linear, indicating that the rectification phenomenon disappears when the electrode contact method is changed to ohmic contact.
Claims
1. A method for preparing ohmic contacts on intrinsic diamond surfaces using iron catalysis, characterized in that... The method for preparing an ohmic contact is carried out according to the following steps:
1. Cleaning: The diamond sample was ultrasonically cleaned sequentially with acetone, deionized water and alcohol to obtain the cleaned diamond. II. Photolithography to prepare the mask: The cleaned diamond is placed on the suction cup of the spin coater for spin coating treatment. After drying, the spin-coated diamond is obtained. The spin-coated diamond is exposed using a photolithography machine. After development and N2 drying, the photolithographic diamond is obtained. III. Magnetron sputtering: A Fe layer with a thickness of 60-200 nm is deposited on the diamond surface after photolithography by magnetron sputtering to obtain iron-plated diamond. IV. Removal of Adhesive: The iron-plated diamond is placed in the adhesive removal solution for ultrasonic cleaning, then cleaned with anhydrous ethanol, and dried to obtain the diamond with iron plating on the surface.
5. Sealing: The diamond with iron-plated surface is placed in a quartz tube and sealed. The quartz tube is filled with a protective gas and then transferred to a tube furnace for annealing at 800-950℃ for 1-4 hours. The Fe catalyst is used to transform the diamond surface into graphite, and an ohmic contact is prepared on the diamond surface.
2. The method for preparing ohmic contacts on intrinsic diamond surfaces using iron catalysis according to claim 1, characterized in that... The diamond sample mentioned in step one is intrinsic diamond or doped diamond.
3. The method for preparing ohmic contacts on intrinsic diamond surfaces using iron catalysis according to claim 1, characterized in that... Step 1: Use acetone, deionized water and alcohol to ultrasonically clean the diamond sample for 10-30 minutes each.
4. The method for preparing ohmic contacts on intrinsic diamond surfaces using iron catalysis according to claim 1, characterized in that... In step two, the thickness of the photoresist after homogenization is 0.8–1.2 μm.
5. The method for preparing ohmic contacts on intrinsic diamond surfaces using iron catalysis according to claim 1, characterized in that... The drying process described in step two involves drying at 95°C for 90 seconds.
6. The method for preparing ohmic contacts on intrinsic diamond surfaces using iron catalysis according to claim 1, characterized in that... In step three, the vacuum chamber for magnetron sputtering is evacuated to 10... -4 Ar gas is introduced at Pa, and the gas pressure is controlled at 3-5 Pa for ignition. Then the deposition gas pressure is adjusted to 0.5 Pa, and Fe layer is deposited by magnetron sputtering.
7. The method for preparing ohmic contacts on intrinsic diamond surfaces using iron catalysis according to claim 1, characterized in that... In step five, the heating rate of the annealing temperature is controlled at 5℃ / min.
8. The method for preparing ohmic contacts on intrinsic diamond surfaces using iron catalysis according to claim 1, characterized in that... In step five, the annealing process is carried out at 900℃ for 2 hours.