Method for realizing self-healing of nano fracture junction with polymide high-molecular polymer as flexible substrate

Abstract

The invention relates to a method for realizing self-healing of a nano broken junction by using a polymide high-molecular polymer as a flexible substrate, which comprises the following steps: preparing a broken junction with a gap of 20nm on a silicon wafer spin-coated with a PI high-molecular polymer by using an electron beam exposure (EBL) system, and forming a transverse gold-PI high-molecular polymer-gold configuration on a PI high-molecular polymer substrate. Importantly, the property of the PI high-molecular polymer surface can change after oxygen plasma etching to form a plurality of C-O-adsorption sites, metal atoms moving under voltage scanning can be adsorbed by the PI high-molecular polymer surface to form a C-O-Au complex, and finally self-healing can occur through scanning of a nano fracture junction for a period of time. Compared with a traditional technology for self-healing of a metal structure through electromigration, the method can reduce the driving voltage of the self-healing phenomenon to about 1.2 V.

Description

TECHNICAL FIELD

[0001] The present application belongs to a kind of polyimide (PI) as flexible substrate nanometer fracture knot self-healing implementation method, it is related to many fields such as organic material, semiconductor, chip integrated circuit, metal self-healing research. BACKGROUND

[0002] With the development of miniaturization of silicon-based chip, its internal integrated circuit line width has reached the level of hundred nanometers. In this case, due to various factors such as mechanical force of chip forced deformation, thermal effect caused by high current of circuit, electromigration phenomenon under high current density and electrostatic effect, the internal circuit of chip is prone to fracture knot with certain gap. Such result seriously hinders the development of chip, also leads to the rise of chip repair cost, therefore how to repair fracture knot with certain gap has important practical significance and commercial value, which can prolong the service life of chip and reduce the production cost of chip. In the field of fracture knot repair, there are mainly the following methods at present: electromigration promotes nanometer knot self-repair, nanometer solder welding, chip self-healing based on self-healing material. Electromigration phenomenon refers to the migration of metal atoms in the metal knot due to the action of strong current, which usually occurs in the originally connected metal nanowire. Under the action of current for a long time, the narrowest place of metal nanowire will cause electromigration and form nanometer gap. On the contrary, for a broken nanometer knot, when the specific conditions are met, it can also use the effect of electromigration to cause the reverse electromigration of metal atoms to cause the re-healing of broken nanometer knot. Usually the surface binding energy of metal atoms is large, so the bias required for promoting the migration of metal fracture knot is large, and the bias applied in a fracture knot composed of nickel atoms is as high as about 10V. Using solder to connect the circuit is a very common method in industry and scientific research field, the solder wire can melt into liquid at high temperature (such as 350℃), and then cover the electrode to be soldered. When the temperature drops, the liquid solder can quickly solidify into solid state to connect the circuit. There are related researches that apply this technology to the connection of metal wires with micron-level line width. Another way is to develop conductive materials with self-healing property, which can repair the damage of line caused by accidental cutting, scratching or mechanical stress to a great extent by placing the conductive material at the fracture knot of metal wire. But this method is difficult to apply to chip circuit with micron or even nanometer line width.

[0003] The method for repairing the broken nanowire by electromigration is the most efficient way, but the traditional migration method is usually in the metal-dielectric-metal layer and the driving voltage for promoting the migration of metal atoms is high, which is difficult to be applied in the actual chip repair work. The method uses the etched polyimide layer as the integrated substrate of the chip, and finds that the broken nanowire on the substrate can promote the migration of metal atoms under a small bias voltage (~1.2V) and finally connect the broken nanowire. SUMMARY

[0004] The application provides a novel self-healing method of nanometer broken junction using oxygen etching polyimide (PI) high polymer as substrate material, which realizes the self-healing of 20nm wide nanometer broken junction by the electromigration of metal atoms under a small bias voltage window (~1.2V). The method has simple structure, small driving voltage for promoting the self-healing of metal atoms and can be applied to the repair of broken junction with nanometer wire width.

[0005] The scheme for realizing the self-healing of nanometer broken junction is as follows:

[0006] The structure used in the method is composed of a silicon or steel substrate, a PI high polymer insulating layer not etched by oxygen, a PI high polymer insulating layer etched by oxygen, and a pair of gold nanoelectrodes (with a 20nm wide broken gap) made by an electron beam exposure system.

[0007] The nanometer broken junction is made on the PMDA-ODA substrate by using the electron beam exposure system, that is, a pair of nanoelectrodes with a certain nanometer gap is made, and then the sample substrate is etched by oxygen plasma gas. Then, the electromigration of metal atoms or clusters on the surface of the metal electrode tips at both ends of the nanometer gap is caused by bias scanning, so as to gradually fill the nanometer gap, and finally cause the self-healing of the nanometer gap, that is, the disappearance of the nanometer gap.

[0008] The nanometer gap is used to simulate the actual integrated circuit burned out due to excessive current. The electrode material (gold atoms) itself migrates under the action of an electric field, and gradually accumulates between the nanometer gaps under the action of the adsorption sites of the etched PI substrate material, so as to gradually reduce and disappear the nanometer gap, and finally cause the two metal electrodes to be connected again (that is, the self-healing of the broken junction, at this time the sample shows linear 1-V curve characteristics).

[0009] Preferably, the vertical sandwich structure composed of the PI high polymer substrate, the PI high polymer etching layer and the gold nanometer broken junction, and the horizontal nanometer broken junction structure formed by gold-polyimide (PMDA-ODA) high polymer etching layer-gold.

[0010] Preferably, the gold nano electrode pair is made by ion sputtering deposition on the PI polymer layer to mix gold particles, and because part of the gold atoms can penetrate into the PI surface layer during ion sputtering, the PI polymer layer has certain conductivity.

[0011] Preferably, the e-beam exposure system is used to make the butterfly-shaped gold nano electrode pair, and the gap of the broken junction of the nano electrode pair is 10-20 nm.

[0012] Preferably, after the PI polymer surface is etched by oxygen plasma gas, a C-O-bond is formed to form an adsorption site to adsorb Au atoms to form C-O-Au, which causes a large number of metal atoms or clusters to be adsorbed on the surface of the PI polymer in the nano broken junction gap during the electromigration of the metal atoms.

[0013] Preferably, the PI polymer is mixed and made in a mass ratio of Poly(pyromellitic dianhydride-co-4,4'-oxydianiline):N-methylpyrrolidone (nmp) 5:1, and the type of Poly(pyromellitic dianhydride-co-4,4'-oxydianiline) is RC-5019.

[0014] Specifically, the present application forms a 2μm thick PI polymer layer on a clean silicon wafer cleaned by acetone and alcohol through spin coating and heating and drying, and then a pair of electrode pairs with a nano gap of about 20 nm is made on the PI polymer layer by using an e-beam exposure system through a series of photoetching processes. Then, the structure is etched by oxygen plasma, and finally a voltage is applied to the two ends of the electrode for voltage scanning and recording the current signal passing through the electrode pair.

[0015] The present application has the following advantages:

[0016] The method has the advantages of simple structure, clear principle, and obvious self-healing phenomenon of the broken nano junction before and after bias scanning. The PI polymer surface etched by oxygen plasma forms an adsorption site (C-O-Au) combined with metal atoms or clusters to adsorb the migrating metal atoms or clusters, which reduces the threshold voltage for exciting the self-healing of the broken junction to about 1.2V. In addition, the self-healing method is simple and clear, and can be used for the broken junction of the future chip integrated circuit. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to make the purpose and technical scheme of the present application clearer, the present application will be further described in detail below with reference to the drawings:

[0018] Figure 1 A three-dimensional schematic diagram of the method for realizing nanoscale break junction self-healing with PI high molecular polymer as a substrate.

[0019] Figure 1 1 is a silicon substrate with a thickness of 1 mm; 2 is a PMDA-ODA high molecular insulating layer with a thickness of 1 μm; 3 is a PI high molecular insulating layer surface etched by oxygen plasma (marked with a grid); 4 is a gold electrode with a nanoscale gap; 5 is a nanoscale gap with a width of 20 nm; and 6 is a circuit diagram of a semiconductor analyzer device for voltage scanning operation.

[0020] Figure 2 A I-V characteristic curve diagram of a nanoscale break junction on a PI high molecular polymer substrate under voltage scanning.

[0021] Figure 3 A scanning electron microscope (SEM) diagram of a nanoscale break junction before and after voltage scanning; it can be seen that after several voltage scans, the two metal electrodes have been directly connected together, the nanoscale gap has disappeared, and the self-healing of the nanoscale gap has been realized.

[0022] Figure 4 A synthesis flowchart of a PI high molecular polymer and an X-ray photoelectron spectroscopy (XPS) diagram before and after etching. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the present application.

[0024] Embodiment 1

[0025] Reference Figure 1 : A silicon wafer (1) with a size of 44 mm*12 mm*1 mm is sequentially cleaned with acetone, ethanol, and deionized water for 10 minutes each, for a total cleaning time of half an hour. After cleaning, a polyimide high molecular polymer (Poly(pyromellitic dianhydride-co-4,4′-oxydianiline): N-Methylpyrrolidone (nmp), mass ratio: 5:1), which is abbreviated as PMDA-ODA, is uniformly spin-coated on the silicon wafer using a spin coater, and then a PI high molecular polymer insulating layer (2) with a thickness of about 2 μm is formed after baking (180℃ / 2h) by a baking machine.

[0026] The gold electrode pair with 20 nm gap on the PMDA-ODA polymer insulating layer is exposed by electron beam lithography system (EBL), and then developed, fixed, coated by plasma coating machine, and removed by acetone, and so on. Finally, the gold electrode pair with 50 nm thickness and 20 nm gap is successfully fabricated on the PMDA-ODA polymer insulating layer.

[0027] The circle (5) represents the nanogap formed between the gold nanoelectrode pair. The nanogap is about 20 nm, which can be found by scanning electron microscope (SEM).

[0028] Then, the sample is placed in the plasma etching machine (ISC150 PRO, China) to etch for 5 minutes by inputting oxygen and carbon tetrafluoride (flow ratio 40:10) to form a rough etching layer (3) on the PMDA-ODA polymer surface. Finally, the semiconductor analyzer measurement system (6) is used to scan the bias voltage of the nanoelectrode pair on the sample and record the current flowing through the nanoelectrode pair in real time. After multiple voltage scans, the nanobreak junction exhibits self-healing phenomenon. That is, the broken junction disappears under the observation of SEM equipment, at the same time, the recorded I-V characteristic curve shows a jump (current value changes from microampere level to milliamper level) at 1.2 V bias voltage and then exhibits linear I-V characteristic (metal material characteristic).

[0029] Figure 2 In order to realize the real-time IV characteristic curve of the nanobreak junction self-healing method by bias voltage scanning on the PMDA-ODA substrate, the arrows and numbers in the figure represent the scanning direction and order in one voltage scanning cycle. When the gold nanoelectrode pair is scanned in a small bias voltage window, the electrode pair exhibits an S-shaped IV characteristic curve and the current is in the nA level (as shown in figure a). Then, with the increase of scanning times and the increase of scanning bias voltage window, the current through the gold nanobreak junction increases with the increase of scanning times, as shown in figure b. It can be found that when the scanning bias voltage window is 1.2 V, the current is in the μA level. When the scanning voltage reaches about 20 times, the current suddenly jumps in a certain scanning voltage cycle (figure c), and the jump voltage is about 1.2 V. When the nanobreak junction is scanned in a small bias voltage window again, it exhibits a linear IV characteristic curve. After calculation, it is found that the conductance of the nanobreak junction G = 610 μS >> 1G0 (G0 = 2e2 / h ≈ 77 μS, G0 is the quantum conductance value of a single gold nanometer atom), which satisfies the ohmic characteristic. The IV characteristic curve can reflect that the gold nanobreak junction is reconnected.

[0030] Figure 3For the gold nanorupture junction, the SEM images before and after the voltage scanning can be found that the gold nanorupture junction is in the ruptured state and has a gap of about ~20 nm in width before the voltage scanning (Figure a). After the voltage scanning, the gold atoms on the gold nanorupture junction are re-migrated and re-healed under the action of the current-driven electromigration (Figure b). Thus, it can be seen that the SEM perfectly verifies the change of the IV characteristic curve voltage before and after the voltage scanning and further proves the correctness of the method of driving the gold nanorupture junction to self-heal by voltage scanning.

[0031] Figure 4The synthesis flow chart of PI polymer and the X-ray photoelectron spectroscopy (XPS) spectra of PI before and after etching. Figure a shows the synthesis flow chart of PI used in our experiment. Poly(amic acid) (PAA, the precursor of PI) was synthesized from pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA) by polymerization. Then, PAA was imidized to PI film by thermal curing at 200 °C. It was reported that the degree of imidization was 75% at this temperature. During the subsequent plasma etching, we made the following assumptions: oxygen plasma would attack the imide ring (O=C-N-C=O) and oxidize the carbonyl group (C=O) to carboxylic group (COO-). Carboxylic group (COO-) played a key role in the self-healing of the gold nanowire break junction. It could capture the gold atoms that were undergoing electromigration under the current and keep them in the gap of the gold nanowire break junction, thus healing the break junction. To verify the mechanism of self-healing, we further analyzed the XPS spectra of PMDA-ODA polymer before and after O2 etching (Figure b-c). We analyzed the chemical composition of the surface of PI by measuring the binding energies of C ls, N ls and O ls of PI with and without O2 etching. The XPS spectra of the three main elements O, N and C are shown in Figure b. The O / C intensity ratio of the etched PI increased significantly compared to the unetched PI, which indicated that a large number of oxygen-containing groups were introduced onto the surface of PI during the O2 plasma etching process. The O1s XPS spectra of PI are shown in Figure c. We attributed the fitted peak at 531.3 eV in the etched PI to the imide group (O=C-N) and the fitted peaks at 531.8 eV and 532.0 eV in the etched and unetched PI to the carboxylic group (-COOH), while the peak at 533.0 eV was attributed to the (C-O-C) group in the cyclic anhydride. In addition, we found that the O=C-N peak height of PI increased significantly after O2 etching while the C-N peak height decreased significantly (Figure c), which indicated that the imide group underwent ring-opening reaction. At the same time, we found that the -COOH peak height of PI also increased significantly after O2 etching, which indicated that the carbonyl group (C=O) was oxidized to carboxylic group (-COO-). This proved that our assumption was correct, i.e. the C-O bond generated on the surface of PI after O2 etching could act as a reaction site to increase the adhesion between gold atoms and etched PI by forming C-O-Au bond

[0032] While the application has been described in connection with specific embodiments thereof, it will be understood that it is carried out in many different embodiments and equivalent ways.

Claims

1. A method for achieving self-healing of a nanogap using a polyimide polymer as a flexible substrate under a small range of scanning voltages, characterized by: Nano-fracture junctions were fabricated on a PMDA-ODA substrate using an electron beam lithography system, and the sample substrate was etched using oxygen plasma gas. Bias scanning was then used to electromigrate metal atoms or clusters on the surfaces of the metal electrode tips at both ends of the nanogap, gradually filling the nanogap and ultimately leading to self-healing of the nanogap.

2. The method for achieving self-healing of a nanogap with a polyimide polymer as a flexible substrate under a small range of scanning voltages according to claim 1, characterized in that: The vertical sandwich structure consists of PI polymer substrate, PI polymer etching layer, and gold nanofracture junction, and the horizontal nanofracture junction structure is formed by gold-polyimide (PMDA-ODA) polymer etching layer-gold.

3. The method for achieving self-healing of a nanogap using a polyimide polymer as a flexible substrate under a small range of scanning voltages according to claim 1, characterized in that: When making gold nanoelectrode pairs, ion sputtering deposition is used to mix gold particles on the PI polymer layer. Because some gold atoms can penetrate into the PI surface during the ion sputtering process, the PI polymer layer has a certain conductivity.

4. The method for achieving self-healing of a nanogap with a polyimide polymer as a flexible substrate under a small range of scanning voltages according to claim 1, characterized in that: The butterfly-shaped gold nanoelectrode pair was made using an electron beam exposure system, and the break junction gap of the nanoelectrode pair was 10-20nm.

5. The method for achieving self-healing of a nanogap with a polyimide polymer as a flexible substrate under a small range of scanning voltages according to claim 1, characterized in that: After being etched by oxygen plasma gas, the surface of the PI polymer forms CO-bonds to form adsorption sites, thereby adsorbing Au atoms to form CO-Au. This results in a large number of metal atoms or clusters being adsorbed on the surface of the PI polymer in the gap of the nanofracture junction during the electromigration of metal atoms.

6. The method for achieving self-healing of a nanogap using a polyimide polymer as a flexible substrate under a small range of scanning voltages according to claim 1, characterized in that: The PI polymer is prepared by mixing Poly (pyromelliticdianhydride-co-4,4′-oxydianiline): N-Methylpyrrolidone (nmp) in a mass ratio of 5:1, and the model of the Poly (pyromelliticdianhydride-co-4,4′-oxydianiline) is RC-5019.

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