CN112317972B - A low temperature rapid manufacturing method of unidirectional high temperature resistant welded joint - Google Patents
A low temperature rapid manufacturing method of unidirectional high temperature resistant welded joint Download PDFInfo
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Abstract
本发明提出了一种单向性耐高温焊接接头的低温快速制造方法，通过双面直流电解沉积工艺，可以获得具有高密度单向性的双面纳米孪晶铜箔，且铜箔表面取向为(111)晶面；将(111)纳米孪晶铜箔在还原性气氛且300‑500℃下低温时效，在0.5‑4h内快速形成双面单晶铜箔，且单晶铜箔表面取向为(111)晶面；将单晶铜箔、锡箔堆叠后与覆铜碳化硅芯片焊接，利用平板热压与温度梯度回流工艺，在5‑10分钟内快速形成单向性Cu6Sn5金属间化合物焊接接头，且Cu6Sn5晶粒的[0001]晶向与单晶铜箔的表面平行。由于Cu6Sn5金属间化合物的熔点高达415℃，且其[0001]晶向具有高剪切强度，所以形成的单向性Cu6Sn5金属间化合物焊接接头将具有极佳的耐高温性能，满足碳化硅等功率芯片长期高温与高可靠性的服役需求。
The invention proposes a low-temperature rapid manufacturing method of a unidirectional high temperature resistant welded joint. Through a double-sided DC electrolytic deposition process, a double-sided nano-twinned copper foil with high density and unidirectionality can be obtained, and the surface orientation of the copper foil is (111) Crystal plane; the (111) nano-twinned copper foil is aged in a reducing atmosphere at a low temperature of 300-500 °C to rapidly form a double-sided single-crystal copper foil within 0.5-4h, and the surface orientation of the single-crystal copper foil is (111) Crystal plane; after stacking the single-crystal copper foil and tin foil, they are welded to the copper-clad silicon carbide chip, and the flat plate hot pressing and temperature gradient reflow process are used to rapidly form a unidirectional Cu 6 Sn 5 intermetallic within 5-10 minutes The compound welded joint, and the [0001] crystallographic direction of the Cu 6 Sn 5 grains was parallel to the surface of the single crystal copper foil. Since the melting point of Cu 6 Sn 5 intermetallic compound is as high as 415°C, and its [0001] crystal orientation has high shear strength, the formed unidirectional Cu 6 Sn 5 intermetallic compound welding joint will have excellent high temperature resistance performance , to meet the long-term high temperature and high reliability service requirements of power chips such as silicon carbide.
Description
Technical Field
The invention belongs to the field of material preparation, and particularly relates to a low-temperature rapid manufacturing method of a unidirectional high-temperature-resistant welding joint.
Background
With the rapid development of the integrated circuit industry in China, the chip manufacturing technology has been continuously paid attention as a foundation for the integrated circuit industry. At present, the chip tends to be miniaturized, integrated and high-powered, and the problems of high temperature, high frequency and high power, etc. caused by the miniaturization, integration and high power tend to be the focus of attention in the industry. The traditional semiconductor chips such as silicon-based chips, gallium arsenide chips and the like are subject to structural failure when in service at the temperature of more than 200 ℃ due to material limitation, and the high-temperature resistance performance of the chips cannot meet the service requirement of high-power devices. The third generation power semiconductor material represented by silicon carbide and gallium nitride has excellent physical and mechanical properties, fast switching frequency and working temperature of more than 300 ℃, and becomes a research hotspot of the high-end power semiconductor integrated circuit industry.
The lack of solder joint materials for high temperature power semiconductor chips is becoming a major bottleneck limiting the development of third generation semiconductor chips. At present, the high-temperature lead-free solder welding joint improves the temperature resistance of the joint by improving the melting point of the solder, and a widely used high-temperature lead-free solder system mainly comprises a gold base, a zinc base, a silver base and the like, but has the problems of high cost or poor wettability or reliability, the use temperature is generally lower than 300 ℃, and the service requirements of high temperature and high reliability required by a third-generation power chip have a larger difference. The metal nanoparticles such as copper, silver and the like can realize low-temperature interconnection, and the prepared welding joint can be used at high temperature, however, the preparation process of the nanoparticles is complex, the cost is higher, and the mechanical property of the sintered joint is different from that of the joint prepared by the traditional reflow soldering process. The transient liquid phase diffusion welding technology can form high temperature resistant intermetallic compound (such as Cu) under the condition of low temperature reflow6Sn5Etc.) the theoretical service temperature of the joint is up to 415 ℃, but the growth of intermetallic compounds is slow, the time required for forming the welding joint is long, and the method is difficult to be suitable for the industrial mass production of high-power chips.
With the increasing number of welding joints in the power chip and the large number of three-dimensional high-density three-dimensional packaging structuresIn application, the size of a welding joint is continuously reduced, anisotropic physical and mechanical behavior of joint tissues can severely influence the performance and reliability of the joint, thousands of welding joints in a power chip can cause complete failure of the chip due to damage of a single joint, and the service life of the chip is difficult to predict accurately, so that the realization of high-temperature-resistant welding joints with completely consistent orientation is a technical problem to be overcome urgently in the field of power chip manufacturing at present. Professor Chen Zhi of Taiwan university of China 2012 issued the realization of Cu in three-dimensional encapsulated joints by manufacturing unidirectional (111) nano twin crystal copper6Sn5Article with consistent orientation of intermetallic compounds (science,2012,336,1007-1010), but which obtained Cu6Sn5[0001 ] of intermetallic Compound]Oriented perpendicular to the copper pad surface. The research finds that Cu6Sn5The (0001) plane of (A) has a shear strength 11.02% higher and a hardness 6.99% higher than that of the (10-10) plane, and the normal conductivity of the (10-10) plane is 43% higher than that of the (0001) plane (Acamaterialia, 2016,104, 1-8). The above studies have demonstrated that Cu6Sn5Of [0001 ]]Cu obtained based on unidirectional (111) nano twin crystal copper oriented in high shear strength and low conductivity direction6Sn5Intermetallic compounds are not suitable as a host interconnect material for solder joints. However, another study found (Materials)&Design,2016,94,280-285), (111) Cu formed on the surface of single-crystal copper6Sn5It [0001 ]]The orientation is parallel to the surface of the bonding pad, the shear strength of the formed joint is as high as 97.8MPa, and the bonding pad is extremely suitable for serving as a main body interconnection material of a welding joint.
Disclosure of Invention
The application aims to provide a low-temperature rapid manufacturing method of a unidirectional high-temperature-resistant welding joint, and aims to solve the problems that the manufacturing time of the high-temperature-resistant welding joint of a power chip is long, the physical and mechanical properties of the joint are poor, the individual difference is obvious, and the like.
The invention provides a low-temperature rapid manufacturing method of a unidirectional high-temperature-resistant welding joint, which specifically comprises the following steps:
step S1: placing the polycrystalline copper foil in an electrolytic bath filled with polishing solution to carry out double-sided electrolytic polishing treatment, and forming a copper seed layer with the thickness of 200-300nm on the surface of the polycrystalline copper foil through a magnetron sputtering process after electrolytic polishing;
step S2: carrying out electrodeposition on the polycrystalline copper foil obtained in the step S1, wherein the electrodeposition temperature is set to be 10-40 ℃, the electrode spacing is 50-100mm, the area ratio of the cathode to the anode is 0.02-0.1:1, and the current density is 10-100mA/cm2And the electro-deposition time is 1-10h, and the obtained nano twin crystal copper with the crystal face of (111);
step S3: placing the nanometer twin crystal copper in a reducing furnace filled with reducing gas, wherein the temperature of the reducing furnace is 300-500 ℃, the low-temperature aging is carried out, and the heat preservation time is 2-4 h;
step S4: placing the nanometer twin crystal copper obtained in the step S3 in chemical tinning liquid for tinning for 0.5-1 minute to obtain a single crystal copper foil with a tin coating on the surface;
step S5: carrying out graphical cutting on the single crystal copper foil and the tin foil according to the shape of the copper bonding pad;
step S6: stacking single crystal copper foil, tin foil and copper bonding pad in turn into single crystal copper foil/Cu6Sn5Copper pad structure, single crystal copper foil/Cu using flat plate thermo-forming machine6Sn5Performing low-temperature rapid forming on the copper bonding pad structure to obtain single crystal copper foil/Cu6Sn5Copper pad joint, on which tin foil and copper pad are successively stacked, copper pad/tin foil/single crystal copper foil/Cu6Sn5A/copper pad structure, the single crystal copper foil/Cu is processed by a plate thermal forming machine6Sn5Performing low-temperature rapid forming on the copper bonding pad structure to obtain copper bonding pad/Cu6Sn5Single crystal copper foil/Cu6Sn5A/copper pad contact.
In a preferred embodiment, the copper foil polishing solution comprises 400ml of inorganic acid or organic acid, 8-15g of surfactant and 120-180ml of solvent, wherein the organic acid is at least one of organic polyphosphonic acid, hydroxyethylidene diphosphonic acid and citric acid, the inorganic acid is at least one of phosphoric acid, sulfuric acid and hydrochloric acid, the solvent is at least one of deionized water, alcohol, ethylene glycol and glycerol, and the surfactant is sodium dodecyl sulfate.
In a preferred embodiment, the electrodeposition solution comprises 50-100g/L of copper sulfate, 20-50ml/L of sulfuric acid, 5-20ppm of copper chloride, 10-20ppm of polyethylene glycol, 5-20ppm of gelatin and deionized water.
In a preferred embodiment, the reducing gas comprises hydrogen and nitrogen in the proportions of 5% and 95% by volume, respectively. The reducing gas can prevent the unidirectional nano twinned copper from being oxidized in the air. After the nano twin crystal copper is electroplated, the nano structure has high activity and a large amount of nano twin crystal boundary structures exist, so that oxygen atoms are easily absorbed, and the copper structure is oxidized. The high melting point copper oxide formed at the twin boundary may hinder single crystal transformation, and thus a reducing atmosphere needs to be added during isothermal aging at 300-400 ℃ to prevent the formation of copper oxide.
In a preferred embodiment, the poly-crystalline copper foil in step S1 is provided as an anode, and two cathodes are provided on both sides of the anode, the cathodes including one of a copper sheet, a titanium sheet, and a nickel sheet.
In a preferred embodiment, the electropolishing of the polycrystalline copper foil in step S1 is followed by ultrasonic cleaning including ultrasonic cleaning with deionized water for 1 minute and blow-drying with nitrogen gas, and plasma treatment including plasma cleaning with argon gas at a frequency of 13.56MHz for 10-30 minutes at a power of 50-150W to remove organic matter remaining on the surface of the polycrystalline copper foil.
In a preferred embodiment, copper pad/Cu6Sn5Single crystal copper foil/Cu6Sn5Unidirectional Cu in Cu pad joints6Sn5[0001 ] of intermetallic Compound]The crystal orientation is parallel to the (111) crystal plane of the single-crystal copper foil.
In a preferred embodiment, the electrolytic cell is placed on a magnetic stirring heating platform, the magnetic stirring speed is 300-. The main purpose of improving the fluidity of the electrolyte is to uniformly distribute the solute in the electrolyte, and if the solute is not uniformly distributed, the surface defects of the copper foil are increased, and the surface roughness is increased.
In a preferred embodiment, since copper is a face-centered cubic lattice, the seed layer obtained by magnetron sputtering generally has a (111) close-packed structure of copper and is nanocrystalline on a microscopic scale. (111) The nanometer twin crystal copper is a structure which is attached to the nanometer micro seed crystal seed layer and is vertical to the surface of the seed layer to grow rapidly. The growth of the seed layer is too thick, which is time-consuming, and the microcrystalline layer may be disordered; too thin may result in incomplete seed layer formation.
In a preferred embodiment, the polycrystalline copper foil obtained in step S1 is used as an anode, the cathode is two copper sheets distributed on both sides of the anode, and the anode and the cathode are placed in an electrolytic bath containing an electrodeposition solution for electrodeposition.
In a preferred embodiment, the temperature of the electropolishing process is set at 20-80 ℃, the electrode spacing is 50-100mm, and the area ratio of cathode to anode is 5-10: 1, the current density is 10-100mA/cm2And a polishing time of 2 to 15 minutes.
In a preferred embodiment, the temperature of the high temperature side heating plate of the flat thermoforming machine in step S6 is set to 240-300 deg.C, the temperature of the low temperature side heating plate is lower than that of the high temperature side heating plate by 10-100 deg.C, and the holding time is 5-10 minutes.
The invention relates to a low-temperature rapid manufacturing method of a unidirectional high-temperature-resistant welding joint, which comprises the steps of firstly preparing a nano twin crystal copper foil with a unidirectional (111) crystal face through an electrolytic deposition process, then rapidly eliminating a nano twin crystal structure through a low-temperature annealing process under the atmosphere of mixed reducing gas of hydrogen and nitrogen to further form a bulk single crystal copper foil with the (111) crystal face, and then utilizing a flat plate hot pressing and temperature gradient reflow process, utilizing the diffusion behavior of copper element tending to low-temperature side migration in liquid tin and the diffusion behavior of Cu6Sn5Epitaxial growth on the surface of (111) single crystal copper, and finally forming large-volume unidirectional Cu by short-time rapid low-temperature heating6Sn5Intermetallic compound welded joint, and [0001 ] thereof]The crystal orientation is parallel to the surface of the (111) single crystal copper foil.
The manufacturing process of the nanometer twin crystal copper foil and the single crystal copper foil is simple, the manufacturing process is energy-saving and environment-friendly, the cost of the required raw materials is low, the obtained foil is high in quality, and the nanometer twin crystal copper foil and the single crystal copper foil are suitable for large-area and batch production; the manufacturing process of the unidirectional high-temperature-resistant welding joint is compatible with a soldering process, the time required by joint preparation is short, the temperature is low, the joint reliability is high, and each joint has completely consistent physical and mechanical properties. The invention can effectively solve the problems of long manufacturing time of the high-temperature-resistant welding joint of the power chip, poor physical and mechanical properties of the joint, obvious individual difference and the like in manufacturing or reliability.
Drawings
The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and together with the description serve to explain the principles of the invention. Other embodiments and many of the intended advantages of embodiments will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.
FIG. 1 is a flow chart of a method for rapid low temperature manufacturing of a unidirectional high temperature resistant weld joint according to one embodiment of the present invention;
FIG. 2 is a schematic view of an electrolytic cell according to an embodiment of the present invention;
FIG. 3 is a drawing of a nano-twin copper structure (a) and a single crystal copper structure (b) according to one embodiment of the present invention;
FIG. 4 is an XRD pattern of single crystal copper, tin-plated single crystal copper, and tin foil after hot pressing with tin-plated single crystal copper according to one embodiment of the present invention;
FIG. 5 is a single crystal copper foil/Cu according to one embodiment of the present invention6Sn5Copper pad joint forming schematic diagram (a) and copper pad/Cu6Sn5Single crystal copper foil/Cu6Sn5The/copper pad joint formation schematic (b).
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention will be described in further detail with reference to the accompanying drawings, and it is apparent that the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention will be described in detail with reference to fig. 1 and 2, and the method for rapidly manufacturing the unidirectional high-temperature-resistant welding joint at low temperature specifically comprises the following steps:
step S1: clamping 99.99% of commercial polycrystalline copper foil in a square hollow polytetrafluoroethylene clamp 2 shown in figure 2, cleaning the surface of the polycrystalline copper foil to remove oil, and placing the polycrystalline copper foil into an electrolytic tank 5 filled with polishing solution for later use; setting a polycrystalline copper foil as an anode, inserting two 99.99 percent copper sheets (or titanium sheets, nickel sheets and the like) into the square-shaped hollow polytetrafluoroethylene clamps 2 at two sides of the electrolytic bath 5, setting the copper sheets as a cathode, setting the polishing temperature to be 20-80 ℃, the electrode spacing to be 50-100mm, and the area ratio of the cathode to the anode to be 5-10: 1. the magnetic stirring speed is 300-1000r/min, the current density is 10-100mA/cm2The polishing time is 2-15 minutes, and the double surfaces of the polycrystalline copper foil are subjected to electrolytic polishing to achieve a smooth mirror surface effect; after the electrolytic polishing is finished, ultrasonically cleaning the polished polycrystalline copper foil and the clamp 2 for 1 minute by using deionized water, then blow-drying by using nitrogen, and cleaning for 10-30 minutes by using argon plasma with the frequency of 13.56MHz, wherein the power is 50-150W, so as to remove residues on the surface of the copper foil; and putting the polycrystalline copper foil and the clamp 2 into a magnetron sputtering instrument, and forming a copper seed layer with the thickness of 200-300nm by a magnetron sputtering process.
Step S2: placing the polycrystalline copper foil obtained in the step S1 and the clamp 2 in an electrolytic bath 5 filled with a deposition solution and setting the polycrystalline copper foil as a cathode, and inserting two 99.99% copper sheets into the clamps at two sides of the electrolytic bath 5 and setting the copper sheets as an anode; setting the electrolysis temperature of the electrolytic bath 5 at 10-40 ℃, the electrode spacing at 50-100mm, the area ratio of the cathode and the anode at 0.02-0.1:1, the magnetic stirring speed at 1000r/min and the current density at 10-100mA/cm2The deposition time is 1-10 h; and (3) taking the copper foil subjected to direct current deposition out of the clamp, wherein the central structure of the copper foil is (111) nano twin crystal copper.
Step S3: taking a square-shaped hollow stainless steel clamp 2 (the size of which is consistent with that of a clamp used in the electrodeposition process), clamping the nanometer twin crystal copper foil, and preventing the nanometer twin crystal copper foil from deforming in the aging process; placing the heating chamber in a reduction furnace, firstly vacuumizing the heating chamber by using a vacuum pump, then introducing nitrogen-hydrogen mixed gas, wherein the volume fraction ratio of hydrogen and nitrogen in the nitrogen-hydrogen mixed gas is 5% and 95%, respectively, heating the reduction furnace to the temperature of 300-.
Step S4: and (3) placing the stainless steel clamp with the copper foil clamped in the clamp in a commercial chemical tin plating solution for 0.5-1 minute, taking out the stainless steel clamp, ultrasonically cleaning the stainless steel clamp with deionized water for 30 seconds, blow-drying the stainless steel clamp with nitrogen, and taking out the copper foil from the clamp to obtain the single crystal copper foil with a tin plating layer on the surface.
Step S5: utilizing a commercial high-power laser cutting machine to perform graphical cutting on the commercial tin foil (the thickness is 20 mu m) and the single crystal copper foil obtained in the step S4 according to the shape of the bonding pad of the copper-coated silicon carbide chip, wherein the power of the laser cutting machine is 100 plus or minus 500W, and the positioning precision is +/-0.05 mm; and storing the patterned tin foil and the patterned single crystal copper foil for later use.
Step S6: stacking single crystal copper foil, tin foil and copper bonding pads of a copper-clad silicon carbide chip from top to bottom in sequence to form a single crystal copper foil/tin foil/copper bonding pad sandwich structure, and performing low-temperature rapid forming by using a double-sided independently temperature-controllable flat plate thermoforming machine, wherein the copper bonding pad of the copper-clad silicon carbide chip is positioned at a high-temperature side, the single crystal copper foil is positioned at a low-temperature side, the heating temperature of a heating plate at the high-temperature side is 240-300 ℃, and the heating temperature of the heating plate at the low-temperature side is lower than the high temperature by 10-100 ℃; keeping the heating plate tightly attached to the sandwich structure, keeping the temperature for 5-10 min after the temperature is stable, then starting a circulating water cooling machine, rapidly cooling the heating plates at two sides to room temperature, and converting the formed tin foil into unidirectional Cu6Sn5Obtaining the single crystal copper foil/Cu6Sn5A copper pad joint; continuously stacking tin foil and copper bonding pad on the first molding structure, wherein the stacking structure is copper bonding pad/tin foil/single crystal copper foil/Cu6Sn5A copper pad joint for keeping the heating plate and the sandwich structure tightly attached without a gap; starting the heating device, wherein the first forming junctionThe structure is arranged at the low-temperature side, the newly placed copper bonding pad is arranged at the high-temperature side, the heating temperature of the heating plate at the high-temperature side is 240-300 ℃, the heating temperature of the heating plate at the low-temperature side is 10-100 ℃ lower than that of the high-temperature side, the temperature is kept for 5-10 minutes, and then the circulating water cooling machine is started to rapidly cool the heating plates at the two sides to the room temperature; taking out the structure, and converting the tin foil into unidirectional Cu after forming6Sn5The obtained joint structure is copper bonding pad/Cu6Sn5Single crystal copper foil/Cu6Sn5Copper pad, the resulting joint being unidirectional Cu6Sn5Intermetallic compound welded joint and [0001 ] thereof]The crystal orientation is parallel to the surface of the (111) single crystal copper foil.
The mechanism of electrodeposition is: the molecular structure of the gelatin contains amino and carboxyl functional groups. In the system, the amino functional group of the gelatin and the cathode are mutually adsorbed by electrostatic force to form a complex, and the complex can obstruct the reduction reaction of copper ions on the surface of the cathode and even cause the stagnation of the reduction reaction; the carboxyl in the gelatin can lead the cathode potential to be lower than the theoretical value, namely forming overpotential; since the system is a constant current process, the electrode potential will gradually increase, the carboxyl group in the gelatin will be far away from the cathode under the action of the potential difference, i.e. the gelatin is desorbed from the cathode surface, and the copper electrodeposition process will be restarted accordingly. During desorption, the adsorption process restarts as the electrode potential decreases. Thus, the process of "adsorption-desorption" of gelatin on the cathode surface will be repeated. The change in the electrode potential will result in a reduced copper layer with a large compressive stress which in turn will relax continuously during the "adsorption-desorption" of the gelatin. Because copper is in a face-centered cubic structure, the (111) of the copper is a close-packed face and the energy is the lowest, and a (111) nanocrystalline layer is deposited on the surface of the cathode in an initial state of an experiment, an epitaxial copper layer with the (111) face is formed on the surface of the cathode in an electrodeposition process; the energy fluctuation generated by electrodeposition will be dissipated in the form of increasing the surface energy of the deposited copper, because the crystal plane orientation is fixed, the energy will be converted into twin boundaries, i.e. high-density twin crystal layers are formed, while the transverse copper grains will compete with each other to grow, the inside of the finally formed copper grains is high-density twin crystal layers, and the copper grains in the electrodeposited copper layer will maintain a columnar crystal structure.
Fig. 2 is a schematic view of an electrolytic cell, as shown in fig. 2, the electrolytic cell 5 is a cuboid structure with an upward opening, two sliding rails 6 are arranged in parallel on a long side of the electrolytic cell 5, a movable slot clamping frame 3 is arranged on the sliding rails 6, a clamp 2 is detachably mounted on the slot clamping frame 3, the clamp 2 is hollow in a shape like a Chinese character 'kou', the clamp 2 can be used for clamping an electrode 1, and the opening area of the Chinese character 'kou' can be adjusted by replacing the clamp 2. The bottom of the clamp 2 is about 3cm away from the bottom of the tank, the magneton 4 is placed at the bottom of the electrolytic tank 5, the fluidity of electrolyte can be improved by stirring the magneton 4, and the electrolytic tank 5 is made of glass or polytetrafluoroethylene and placed on a magnetic stirring and heating platform.
In a specific embodiment, the copper foil polishing solution comprises 400ml of 320-400ml of inorganic acid or organic acid, 8-15g of surfactant and 180ml of 120-180ml of solvent, wherein the organic acid is at least one of organic polyphosphonic acid, hydroxyethylidene diphosphonic acid and citric acid, the inorganic acid is at least one of phosphoric acid, sulfuric acid and hydrochloric acid, the solvent is at least one of deionized water, alcohol, ethylene glycol and glycerol, and the surfactant is sodium dodecyl sulfate.
In a specific embodiment, a nano twin crystal copper electrodeposition solution is prepared, wherein the electrodeposition solution comprises 50-100g/L of copper sulfate, 20-50ml/L of sulfuric acid, 5-20ppm of copper chloride, 10-20ppm of polyethylene glycol, 5-20ppm of gelatin and deionized water.
Example 1
99.99% of commercial polycrystalline copper foil is clamped in a square hollow polytetrafluoroethylene fixture 2, the polycrystalline copper foil is placed in an electrolytic tank 5 shown in figure 2 for standby after being cleaned on the surface and deoiled, wherein the container of the electrolytic tank 5 is made of glass materials and is placed on a magnetic stirring heating platform, the bottom of the fixture 2 is 3cm away from the bottom of the tank, and the fluidity of electrolyte can be improved through the stirring of a magneton 4. Setting a polycrystalline copper foil as an anode, inserting two 99.99 percent of copper sheets into the square-shaped hollow polytetrafluoroethylene clamp 2 at any side of the electrolytic cell 5, setting the copper sheets as a cathode, wherein the electrode distance is 100mm, and the area ratio of the cathode to the anode is 5: 1, voltage is 2V, and current density is 60mA/cm2The time is 15 minutes and the temperature is room temperature. Preparing copper foil polishing solution from 360ml phosphoric acidIonized water (140ml) and sodium dodecyl sulfate (10 g). And the electrolytic bath 5 performs electrolytic polishing on the two sides of the polycrystalline copper foil to achieve a smooth mirror effect, after the electrolytic polishing is completed, ultrasonically cleaning the polished polycrystalline copper foil together with the clamp 2 for 1 minute by using deionized water, then blow-drying by using nitrogen and cleaning for 10 minutes by using argon plasma with the frequency of 13.56MHz (the power is 100W) to remove residues on the surface of the copper foil. Putting the polycrystalline copper foil and the clamp into a magnetron sputtering instrument, and forming a copper seed layer with the thickness of 200nm on the surface of the polycrystalline copper foil through a magnetron sputtering process, wherein the power of the magnetron sputtering instrument is 40W, the sputtering pressure is 1.5Pa, the time is 20 minutes, and the temperature is 160 ℃.
The pretreated polycrystalline copper foil and the clamps 2 are placed in an electrolytic bath as shown in fig. 2 and set as a cathode, and two 99.99% copper sheets are inserted into the clamps 2 on both sides of the electrolytic bath filled with the electrodeposition solution and set as an anode. Preparing nano twin crystal copper electrodeposition solution, wherein the electrodeposition solution consists of 50g/L of copper sulfate, 20ml/L of sulfuric acid, 5ppm of copper chloride, 10ppm of polyethylene glycol, 10ppm of gelatin and deionized water. The electrolysis temperature of the electrolytic bath 5 is 30 ℃, the electrode distance is 100mm, the area ratio of the cathode to the anode is 0.1:1, the magnetic stirring speed is 800r/min, and the current density is 80mA/cm2And the deposition time is 2h, the copper foil after the direct current deposition is taken out of the clamp, and the central structure of the copper foil is (111) nano twin crystal copper, as shown in figure 3 (a).
And (3) clamping the nanometer twin crystal copper foil by taking a square hollow stainless steel clamp 2. Placing the furnace in a reducing furnace, vacuumizing the heating chamber by using a vacuum pump, then introducing nitrogen-hydrogen mixed gas, wherein the volume fraction of hydrogen and nitrogen in the nitrogen-hydrogen mixed gas is 5% and 95%, respectively, heating the reducing furnace to 350 ℃, and keeping the temperature for 2 hours. As shown in fig. 3(b), the copper foil obtained at this time had no grain boundary structure; further XRD analysis was performed on the oriented structure, and as shown by the A curve in FIG. 4, a unique diffraction peak was found to prove that it was (111) single crystal copper. And (2) placing the stainless steel clamp 2 holding the (111) single crystal copper foil in a commercial chemical tin plating solution for 1 minute, taking out, ultrasonically cleaning the stainless steel clamp for 30 seconds by using deionized water, drying the stainless steel clamp by using nitrogen, and taking out the copper foil from the clamp to obtain the (111) single crystal copper foil with a tin plating layer on the surface. XRD analysis was performed on the above tin (111) plated single crystal copper foil, and as shown by the B curve in FIG. 4, a large number of diffraction peaks of tin were found, confirming that tin plating had been successful.
A commercial high-power laser cutting machine is utilized, a copper bonding pad is a bonding pad of a copper-clad silicon carbide chip, commercial tin foil (with the thickness of 20 mu m) and prepared single crystal copper foil are subjected to graphical cutting according to the shape of the copper bonding pad, the laser power is 400W, and the graphical tin foil and the single crystal copper foil are collected for standby.
Stacking the single crystal copper foil, the tin foil and the copper bonding pad from top to bottom in turn to form the single crystal copper foil/Cu6Sn5The sandwich structure of the copper bonding pad structure utilizes a flat plate thermal forming machine with two sides capable of independently controlling temperature to carry out low-temperature rapid forming, wherein the copper bonding pad is positioned at a high-temperature side, the single crystal copper foil is positioned at a low-temperature side, the heating temperature of a heating plate at the high-temperature side is 240 ℃, and the heating temperature of the heating plate at the low-temperature side is lower than that at the high-temperature side by 60 ℃. Keeping the heating plate and the sandwich structure tightly jointed without gaps, keeping the temperature for 10 minutes after the temperature is stable, then starting a circulating water cooling machine, and rapidly cooling the heating plates at the two sides to the room temperature to obtain the single crystal copper foil/Cu6Sn5A/copper pad contact. Single crystal copper foil/Cu6Sn5The formation of the/cu pad joint is shown in fig. 5 (a). For the above single crystal copper foil/Cu6Sn5XRD analysis of the/Cu pad joint, as shown by the C curve in FIG. 4, found that only (11-20) Cu was present in addition to the diffraction peak of tin6Sn5Diffraction peaks, which demonstrate that unidirectional Cu has been formed6Sn5A one-sided solder joint of intermetallic compounds.
On a single crystal copper foil/Cu6Sn5Continuously stacking tin foil and copper pad on the copper pad joint structure, wherein the stacking structure is copper pad/tin foil/single crystal copper foil/Cu6Sn5The copper bonding pad structure keeps the heating plate and the sandwich structure tightly attached without a gap. Starting the heating device, copper pad/tin foil/single crystal copper foil/Cu6Sn5The copper pad structure is arranged at the low temperature side, the newly arranged copper pad is arranged at the high temperature side, the heating temperature of the heating plate at the high temperature side is 240 ℃, the heating temperature of the heating plate at the low temperature side is 60 ℃ lower than that at the high temperature side, the temperature is kept for 10 minutes, and then the copper pad structure is arranged at the low temperature side, the newly arranged copper pad structure is arranged at the high temperature side, and the copper pad structure is arranged at the high temperature sideStarting a circulating water cooler, and rapidly cooling the double-side heating plates to room temperature to obtain copper bonding pads/tin foils/single crystal copper foils/Cu6Sn5A/copper pad contact. Taking out the structure to obtain the unidirectional Cu joint6Sn5Intermetallic compound welded joint and [0001 ] thereof]The crystal orientation is parallel to the surface of the (111) single crystal copper foil. Copper pad/tin foil/single crystal copper foil/Cu6Sn5The formation of the/cu pad joint is shown in fig. 5 (b).
While the principles of the invention have been described in detail in connection with the preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing embodiments are merely illustrative of exemplary implementations of the invention and are not limiting of the scope of the invention. The details of the embodiments are not to be interpreted as limiting the scope of the invention, and any obvious changes, such as equivalent alterations, simple substitutions and the like, based on the technical solution of the invention, can be interpreted without departing from the spirit and scope of the invention.
Claims (9)
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| CN113488399B (en) * | 2021-06-15 | 2021-12-21 | 广东工业大学 | A kind of ultra-fine pitch semiconductor interconnect structure and its forming method |
| CN115786997B (en) * | 2021-09-10 | 2023-08-25 | 宁德时代新能源科技股份有限公司 | Electrolytic copper foil, preparation method thereof, negative electrode plate and secondary battery |
| CN113802155A (en) * | 2021-10-09 | 2021-12-17 | 南开大学 | A room temperature electrodeposition preparation method of high crystal plane preferentially oriented copper foil |
| CN114411233B (en) * | 2022-01-11 | 2023-05-26 | 大连理工大学 | A method for rapidly preparing (100) single crystal copper |
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