High-performance sintered copper film for interconnection of power module chips and preparation method and application of high-performance sintered copper film

Abstract

According to the high-performance sintered copper film for power module chip interconnection and the preparation method and application thereof, the compact and uniform sintered copper film is obtained through precursor solution preparation, solution spin coating, thermal annealing treatment, copper film separation and other treatments. According to the preparation method, a copper film preparation process is optimized, a solution spin-coating and thermal annealing combined process is adopted, copper salt, an antioxidant, active elements and the like are dissolved in an organic solvent according to a certain proportion, and a uniform precursor solution is prepared; uniformly coating the precursor solution on the surface of a substrate through a spin-coating technology to form a layer of uniform film; and then, by accurately controlling a thermal annealing process, organic matters in the precursor solution are volatilized and decomposed, meanwhile, copper ions are reduced into metal copper, and the metal copper is mutually diffused and reacted with active elements and the like, so that a sintered copper film with excellent performance is formed. And the component uniformity and the microstructure stability of the sintered copper film are ensured by accurately controlling preparation process parameters, so that the consistency and the reliability of the performance of the sintered copper film are ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic materials, in particular to a high-performance sintered copper film for power module chip interconnection and a preparation method and application thereof. BACKGROUND

[0002] In the development of modern power modules, chip interconnection technology is a key link to ensure its performance and reliability. With the development of electronic devices towards miniaturization and high power density, more stringent requirements are put forward for chip interconnection materials and processes.

[0003] At present, the common chip interconnection method mainly adopts traditional welding technology, such as soldering. However, soldering has many limitations. From the aspect of thermal performance, the melting point of tin is relatively low, generally around 230℃. When the power module operates at high temperature, the solder joint is prone to softening, creep and other phenomena, which leads to the decline of the reliability of the interconnection structure. For example, in the power module of an electric vehicle, due to the frequent start and stop of the motor, a large amount of heat will be generated in the module. Under this thermal cycle condition, the solder joint is prone to fatigue failure, which affects the power output stability of the electric vehicle.

[0004] In terms of electrical performance, the electrical conductivity and thermal conductivity of tin are limited, which cannot meet the demand of high-power modules for efficient power transmission and rapid heat dissipation. When operating at high power, the increased power loss caused by the resistance of tin, and the heat cannot be dissipated in time, further aggravate the module temperature rise, forming a vicious cycle, which seriously affects the performance and life of the chip. While using silver sintering technology to realize chip interconnection, although silver has good electrical conductivity and thermal conductivity, its cost is high, which greatly increases the product cost and reduces the market competitiveness, which limits its large-scale application. SUMMARY

[0005] The present application is carried out in view of the above-mentioned problems, and the purpose is to provide a preparation method of a chip interconnection material which can meet the requirements of power modules in terms of thermal performance and electrical performance, and has good environmental protection and cost effectiveness.

[0006] The first aspect of the present application provides a preparation method of a high-performance sintered copper film for power module chip interconnection, comprising the following steps:

[0007] (1) Preparation of precursor solution

[0008] 1) Weighed copper salt is slowly added to a container containing ethylene glycol methyl ether, and a magnetic stirrer is started at the same time, with the stirring speed set at 300-500 revolutions per minute, so that the copper salt is fully dissolved, and the solution is blue and transparent.

[0009] 2) Weighed BHT is added to the above copper salt solution, continue stirring for 30-60 minutes to ensure that the BHT is completely dissolved and uniformly mixed with the solution.

[0010] 3) Slowly add the active element salt solution (such as diluted titanium tetrachloride solution), stirring while adding, adjust the stirring speed to 200-300 rpm, continue stirring for 60-90 minutes to fully mix the components in the solution and form a uniform precursor solution. At this time, the solution may change color due to the addition of the active element salt, such as a slight yellow color after adding the titanium tetrachloride solution.

[0011] In any embodiment, the copper salt is a high-purity copper salt with a purity of not less than 99.9%, the copper salt is copper sulfate; the added mass of the antioxidant is 1%-3% of the copper salt, the antioxidant is 2,6-di-tert-butyl-p-cresol (BHT); the added mass of the active element salt is 3%-5% of the copper salt, the active element salt is at least one of a titanium salt or a chromium salt; the added ratio of the organic solvent to the copper salt is 5-10 ml:1 g, and the organic solvent is ethylene glycol methyl ether.

[0012] In any embodiment, the titanium salt is titanium tetrachloride, and the chromium salt is potassium dichromate.

[0013] A certain amount of active element salt, such as titanium salt (such as titanium tetrachloride TiCl4, which needs to be appropriately diluted before use) or chromium salt (such as potassium dichromate K2Cr2O7), is weighed, and the mass of the active element salt is 3%-5% of the mass of the copper sulfate. Taking titanium salt as an example, if a 10% titanium tetrachloride solution is used, the corresponding mass of the solution needs to be measured.

[0014] Prepare an appropriate amount of organic solvent, such as ethylene glycol methyl ether (C3H8O2), which is preferably used in an amount that can completely dissolve the above raw materials and form a uniform solution, generally 50-100 ml of organic solvent per 10 g of raw materials.

[0015] (2) Solution spin coating

[0016] 1) Substrate pretreatment: choose flat and smooth glass or silicon wafer as the spin coating substrate; first use organic solvents such as acetone and ethanol to ultrasonically clean for 10-15 minutes to remove surface oil, dust and other impurities; then rinse with deionized water, and then place the substrate in an oven at 100-120°C for 1-2 hours to ensure that the substrate surface is dry and clean.

[0017] 2) Spin coating operation: fix the pretreated substrate on the vacuum chuck of the spin coater, take an appropriate amount of precursor solution and drop it at the center of the substrate, set the spin coater parameters, and make the solution uniformly coated on the substrate surface under the action of centrifugal force to form a thin and uniform liquid film.

[0018] In any embodiment, the precursor solution dropwise amount is 1-3 ml, and the formed liquid film thickness is 50-300 nm.

[0019] In any embodiment, the spin coater first rotates at a low speed of 500-1000 rpm for 10-20 seconds to make the precursor solution initially spread on the substrate surface; then enters a high-speed rotation stage, the rotation speed is increased to 3000-5000 rpm, and the rotation time is 30-60 seconds.

[0020] (3) Thermal annealing treatment

[0021] 1) Annealing equipment preparation: first vacuum the furnace cavity, then introduce protective gas, then put the substrate coated with precursor solution into the tube furnace or box furnace for thermal annealing treatment.

[0022] In any embodiment, the annealing equipment preparation first vacuums the furnace cavity to 10 -3 -10- 2 Pa, and then introduces high-purity nitrogen or argon as protective gas, with a gas flow rate of 50-100 sccm (standard cubic centimeter per minute) to prevent copper from oxidizing at high temperature.

[0023] 2) Annealing process: raise the furnace temperature to 300-400°C, keep it for 30-60 minutes, and then lower it to room temperature.

[0024] In any embodiment, the furnace temperature rising rate is 5-10°C / min, and the furnace temperature falling rate is 3-5°C / min.

[0025] The temperature rising rate will raise the furnace temperature to 300-400°C, and keep it at this temperature for 30-60 minutes. In this stage, the organic matter in the precursor solution gradually volatilizes and decomposes, the copper ions are reduced to metallic copper under the action of the reducing agent (such as ethylene glycol methyl ether which can act as a reducing agent at high temperature), and the active elements diffuse and react with copper.

[0026] After the holding period ends, the furnace temperature is lowered to room temperature at a rate of 3-5°C / min. The furnace cooling process can fully release the internal stress of the copper film, avoiding cracks or deformation of the copper film due to rapid temperature changes. After thermal annealing treatment, a dense and uniform sintered copper film is formed on the substrate surface.

[0027] (4) Copper film separation: immerse the substrate with sintered copper film in a hydrofluoric acid solution or a sodium hydroxide solution for 10-30 minutes to separate the sintered copper film from the substrate; then, carefully remove the separated sintered copper film with tweezers, rinse it several times with deionized water to remove residual solution, and prepare for use.

[0028] If the sintered copper film needs to be separated from the substrate for power module chip interconnection, the following method can be used:

[0029] In any embodiment, the substrate is a silicon wafer, which is soaked in a hydrofluoric acid (HF) solution with a mass fraction of 9%-12%; the substrate is a glass wafer, which is soaked in a sodium hydroxide (NaOH) solution with a mass fraction of 5%-10%.

[0030] The substrate with the sintered copper film is soaked in a specific solution, such as a solution of hydrofluoric acid (HF) mixed with water in a certain proportion (such as 1:10) (for a silicon wafer substrate), or a sodium hydroxide (NaOH) solution (for a glass wafer substrate, with a mass fraction of about 5%-10%). The soaking time is generally about 10-30 minutes, depending on the bonding condition of the film and the substrate. During the soaking process, the solution reacts chemically with the substrate, causing the sintered copper film to separate from the substrate. Then, the separated sintered copper film is carefully taken out using tweezers and rinsed multiple times with deionized water to remove residual solution, ready for use.

[0031] In a second aspect of the present application, a high-performance sintered copper film for power module chip interconnection is provided, which is obtained by the above preparation method.

[0032] In a second aspect of the present application, the application of a high-performance sintered copper film for power module chip interconnection is provided, which is used for 5G power module chip interconnection.

[0033] The beneficial effects of the present application are:

[0034] 1. Performance improvement

[0035] The improvement of oxidation resistance enables the copper film to maintain stable performance during storage and use. Tests have shown that the copper film prepared by the method can maintain good electrical conductivity and thermal conductivity in nitrogen for more than 120 days, greatly extending the service life compared to traditional copper paste, reducing the risk of performance degradation and failure due to oxidation, and improving the reliability and stability of the power module.

[0036] Reducing the sintering temperature to about 200°C not only avoids damage to heat-sensitive components in the power module, but also expands the applicability of the power module in different application scenarios. For example, it can be applied to some electronic devices with strict temperature requirements, such as portable electronic products, aerospace electronic devices, etc., improving the performance and competitiveness of the product.

[0037] Suppressing the agglomeration phenomenon ensures the uniformity of the copper film, enabling uniform coating and sintering during chip interconnection, improving the quality and reliability of the interconnection.

[0038] 2. Production efficiency

[0039] The improved low-temperature curing speed enables the shortening of the production cycle in mass production. In a low-temperature environment, the copper paste can be cured in a shorter time, and compared with the traditional copper paste, the use of the copper film process reduces the printing, SPI, and baking three processes, and the production efficiency is improved by more than 20%, effectively reducing the production cost, improving the production benefit, and meeting the market demand for large-scale and high-efficiency production of power modules.

[0040] 3. Cost control

[0041] Compared with the scheme of adopting a complex process such as silver-coated copper nanoparticles to improve performance, the present application greatly reduces the cost on the premise of ensuring performance by optimizing the composition of copper powder and the preparation process. The simplification of the preparation process also reduces equipment investment and energy consumption, further reduces production cost, and improves the market competitiveness of the product.

[0042] Reducing the sintering shrinkage reduces the stress between the chip and the substrate, and improves the long-term stability of the interconnection. In the thermal cycle and long-term use test, the chip interconnection structure using the present copper paste can withstand more times of thermal cycle without connection loosening and failure, reducing the after-sales maintenance and replacement cost of the product, and improving the product quality and user satisfaction. DETAILED DESCRIPTION

[0043] Hereinafter, an embodiment of a high-performance sintering copper film for power module chip interconnection and a preparation method and application thereof according to the present application is specifically disclosed. However, there may be cases of omission of unnecessary detailed description. For example, there are cases of omission of detailed description of matters well known, repeated description of actually identical structures. This is to avoid the following description from becoming unnecessarily lengthy, facilitating understanding by those skilled in the art. In addition, the following description is provided in order for those skilled in the art to fully understand the present application, and is not intended to limit the subject matter recited in the claims.

[0044] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0045] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0046] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0047] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0048] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0049] If not specifically stated, the term "or" in this application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).

[0050] A preparation method of a high-performance sintered copper film for power module chip interconnection, comprising the following steps:

[0051] (1) Preparation of precursor solution

[0052] 1) Weighed copper salt is slowly added to a container containing ethylene glycol methyl ether, and a magnetic stirrer is turned on with a stirring speed of 300-500 rpm to ensure that the copper salt is fully dissolved, and the solution is blue and transparent.

[0053] 2) Weighed BHT is added to the above copper salt solution, and stirring is continued for 30-60 minutes to ensure that the BHT is completely dissolved and uniformly mixed with the solution.

[0054] 3) Slowly add the active element salt solution (such as diluted titanium tetrachloride solution), and stir while adding, with a stirring speed of 200-300 rpm, and continue stirring for 60-90 minutes to ensure that the components in the solution are fully mixed to form a uniform precursor solution. At this time, the solution may change color due to the addition of the active element salt, such as a slight yellow color after adding the titanium tetrachloride solution.

[0055] The order of adding copper sulfate, then BHT, and finally active element salt can ensure that the components are sequentially dissolved, dispersed, and reacted in the solution in an orderly manner.

[0056] (2) Solution spin coating

[0057] 1) Substrate pretreatment: choose a flat and smooth glass sheet or silicon wafer as the spin coating substrate; first clean the surface with organic solvents such as acetone and ethanol for 10-15 minutes to remove oil, dust and other impurities; then rinse with deionized water, and then place the substrate in an oven at 100-120°C for 1-2 hours to ensure that the substrate surface is dry and clean.

[0058] 2) Spin coating operation: fix the pretreated substrate on the vacuum chuck of the spin coater, drop an appropriate amount of precursor solution on the center of the substrate, and set the spin coater parameters to ensure that the solution is evenly coated on the substrate surface under the action of centrifugal force, forming a thin and uniform liquid film.

[0059] (3) Thermal annealing treatment

[0060] 1) Annealing equipment preparation: First, the furnace cavity is evacuated and then protected gas is introduced, and then the substrate coated with precursor solution is placed in a tube furnace or box furnace for heat annealing treatment.

[0061] In any embodiment, the annealing equipment preparation, the furnace cavity is first evacuated to 10 -3 -10 -2 Pa, and then high-purity nitrogen or argon gas is introduced as a protective gas, and the gas flow is controlled at 50-100 sccm (standard cubic centimeter per minute) to prevent copper from oxidizing at high temperature.

[0062] 2) Annealing process: The furnace temperature is raised to 300-400℃, and after holding for 30-60 minutes, it is lowered to room temperature. Organic matter volatilizes and decomposes, copper ions are reduced, and active elements react with copper at too low a temperature to completely react, and at too high a temperature there is a risk of excessive reaction.

[0063] (4) Copper film separation: immerse the substrate with sintered copper film in hydrofluoric acid solution or sodium hydroxide solution for 10-30 minutes to separate the sintered copper film from the substrate; then, carefully remove the separated sintered copper film with tweezers, rinse it several times with deionized water to remove residual solution, and prepare for use.

[0064] Copper does not chemically react with hydrofluoric acid and sodium hydroxide solution at room temperature. At the same time, due to the certain density and stability of the sintered copper film, it is difficult for the hydrofluoric acid solution and the sodium hydroxide solution to penetrate into the copper film and react with it.

[0065] In terms of material selection, the present application focuses on copper material. Copper has high electrical conductivity and thermal conductivity, and its electrical conductivity is only second to silver, and its thermal conductivity can also meet the demand of high-efficiency heat dissipation of power modules. Through reasonable preparation process, the performance advantages of copper can be fully utilized to solve the problem of poor electrical and thermal performance of traditional tin soldering materials. For example, in the power module of the 5G base station, the use of the sintered copper film for chip interconnection can effectively reduce the signal transmission loss and quickly dissipate heat, ensuring the stable operation of the base station.

[0066] To solve the problem of easy oxidation of copper at high temperature, a specific antioxidant is added during the preparation of the copper film. An organic antioxidant with steric hindrance effect is selected, such as 2,6-di-tert-butyl-p-cresol (BHT), which can form a protective film on the surface of the copper film to prevent oxygen from contacting the copper, thereby improving the anti-oxidation performance of the copper film in a high-temperature environment. Experimental verification shows that the oxidation degree of the copper film with BHT added is significantly lower than that without BHT after being exposed to a 250℃ high-temperature environment for 1000 hours, ensuring the interconnection stability of the power module in long-term high-temperature operation.

[0067] Compared with the silver sintering technology, the price of copper is low, and the raw material cost can be greatly reduced. Meanwhile, the preparation process of the application is relatively simple, and does not need expensive equipment and complex operation process, further reducing the production cost. For example, in the industrial control device power module of large-scale production, the interconnection cost of a single module can be reduced by 40%-60% by using the sintered copper film preparation method, thereby improving the market competitiveness of the product.

[0068] In order to improve the bonding strength between the copper film and the chip and the substrate, an appropriate amount of active elements such as titanium (Ti) and chromium (Cr) is added in the preparation of the copper film. These active elements can react with the oxides on the surface of the chip and the substrate to form a firm chemical bond, thereby enhancing the interfacial bonding strength. Through experimental tests, the bonding strength between the copper film after adding the active elements and the chip and the substrate is increased by 60%-80% compared with that without adding the active elements, thereby effectively enhancing the mechanical reliability of the power module, so that the power module can still maintain a good interconnection state under the action of external forces such as vibration and impact.

[0069] In addition, the preparation process of the copper film is also optimized. The solution spin coating method combined with the heat annealing process is adopted, the copper salt, the antioxidant, the active element and the like are dissolved in the organic solvent according to a certain proportion to prepare a uniform precursor solution. The precursor solution is uniformly coated on the surface of the substrate by the spin coating technology to form a uniform film. Then, the heat annealing process is accurately controlled, so that the organic matter in the precursor solution is volatilized and decomposed, and at the same time, the copper ions are reduced to metallic copper and diffuse and react with the active elements and the like to form a sintered copper film with excellent performance. By accurately controlling the preparation process parameters, the composition uniformity and the microstructure stability of the sintered copper film can be ensured, thereby ensuring the consistency and reliability of the performance of the sintered copper film.

[0070] In any embodiment, the copper salt is a high-purity copper salt with a purity of not less than 99.9%, and the copper salt is copper sulfate; the mass of the antioxidant added is 1%-3% of the mass of the copper salt, and the antioxidant is 2,6-di-tert-butyl-p-cresol (BHT); the mass of the active element salt added is 3%-5% of the mass of the copper salt, and the active element salt is at least one of titanium salt and chromium salt; the addition ratio of the organic solvent to the copper salt is 5-10 ml:1 g, and the organic solvent is ethylene glycol methyl ether.

[0071] The 2,6-di-tert-butyl-p-cresol antioxidant has excellent antioxidant performance, good solubility, high chemical stability and safety and cost-effectiveness. If the amount of the 2,6-di-tert-butyl-p-cresol antioxidant is too small, the antioxidant performance cannot be guaranteed, and if the amount is too large, the properties of the solution will be changed and impurity residues will be increased.

[0072] Active element salt titanium salt and chromium salt can improve the performance of sintered copper film in many ways, and is well compatible with other components in the preparation system. Too much addition affects the deterioration of mechanical properties, the decline of electrical properties, and the complexity of preparation process. Too little addition affects the performance improvement and stability improvement.

[0073] The organic solvent is selected as ethylene glycol methyl ether as a solvent, which has good solubility, suitable volatility, reaction participation characteristics, chemical stability and compatibility. The above-mentioned addition amount ensures sufficient dissolution and mixing, and optimizes the physical properties of the solution. Too much addition affects the change of the physical properties of the solution, the reaction process is disturbed, and the production efficiency is reduced. Too little addition affects insufficient dissolution, abnormal solution viscosity and surface tension.

[0074] In any embodiment, the titanium salt is titanium tetrachloride, and the chromium salt is potassium dichromate.

[0075] A certain amount of active element salt, such as titanium salt (such as titanium tetrachloride TiCl4, which needs to be appropriately diluted before use) or chromium salt (such as potassium dichromate K2Cr2O7), is weighed, and the mass of the active element salt is 3%-5% of the mass of copper sulfate. Taking titanium salt as an example, if a 10% titanium tetrachloride solution is used, the corresponding mass of the solution needs to be measured.

[0076] Prepare an appropriate amount of organic solvent, such as ethylene glycol methyl ether (C3H8O2), which is preferably used in an amount that can completely dissolve the above-mentioned raw materials and form a uniform solution, generally 50-100 ml of organic solvent per 10 g of raw materials.

[0077] In any embodiment, the precursor solution dropwise amount is 1-3 ml, and the formed liquid film thickness is 50-300 nm.

[0078] Too thin liquid film may not form a continuous and dense copper film structure after thermal annealing, affecting the conductivity and mechanical properties of the copper film; too thick liquid film may cause insufficient solvent volatilization during thermal annealing, residual organic matter affecting the purity of the copper film, or cracks due to excessive internal stress.

[0079] In any embodiment, the spin coater is first rotated at a low speed of 500-1000 revolutions per minute for 10-20 seconds to preliminarily spread the precursor solution on the surface of the substrate; then enters the high-speed rotation stage, the speed is increased to 3000-5000 revolutions per minute, and the rotation time is 30-60 seconds.

[0080] In the low-speed rotation stage, the solution is preliminarily spread and the distribution of the solution is controlled. Too low speed

[0081] Insufficient spreading, difficult to form liquid film; too high speed, solution splashing, uneven initial thickness; too short time, such as less than 10 seconds, the solution may not be able to spread fully, and a good initial distribution on the substrate cannot be formed, resulting in uneven final liquid film thickness; too long time, such as more than 20 seconds, although the solution can spread fully, but the solution may be due to long time rotation at low speed, the solvent in the solution volatilizes too early, resulting in changes in solution viscosity, affecting the formation of liquid film during subsequent high-speed rotation, which may also cause uneven liquid film thickness.

[0082] In the high-speed rotation stage, the liquid film is homogenized and the thickness of the liquid film is controlled. Too low speed, the liquid film is not uniform, and the thickness does not meet the requirements; too high speed, the liquid film is too thin or broken, and the solvent volatilization is intensified; too short time, such as less than 30 seconds, the solution may not be able to fully homogenize under the action of centrifugal force, resulting in uneven liquid film thickness, and the high-performance sintered copper film cannot meet the requirements of uniformity of the liquid film; too long time, such as more than 60 seconds, although the liquid film will be more uniform, but the long rotation time may cause excessive volatilization of the solvent, resulting in dry spots or cracks on the surface of the liquid film, and at the same time, it will also increase the preparation time and reduce the production efficiency.

[0083] In any embodiment, the furnace temperature rising rate is 5-10℃ / min, and the furnace temperature falling rate is 3-5℃ / min.

[0084] The temperature rising rate is controlled to rise the furnace temperature to 300-400℃, and the temperature is kept at this temperature for 30-60 minutes. In this stage, the organic matter in the precursor solution is gradually volatilized and decomposed, and the copper ions are reduced to metal copper under the action of the reducing agent (such as ethylene glycol methyl ether which can act as a reducing agent at high temperature), and at the same time, the active elements diffuse and react with copper.

[0085] After the holding is completed, the furnace temperature is lowered to room temperature at a rate of 3-5℃ / min. The stress in the copper film can be fully released during the furnace cooling process, avoiding cracks or deformation of the copper film due to rapid temperature change. After the heat annealing treatment, a dense and uniform sintered copper film is formed on the surface of the substrate.

[0086] If the prepared sintered copper film needs to be separated from the substrate for power module chip interconnection, the following method can be used:

[0087] In any embodiment, the substrate is a silicon wafer, which is soaked in a hydrofluoric acid (HF) solution with a mass fraction of 9%-12%; the substrate is a glass sheet, which is soaked in a sodium hydroxide (NaOH) solution with a mass fraction of 5%-10%.

[0088] HF solution (for silicon wafer substrate), mass fraction too large (more than 12%), substrate corrosion too fast, potential risk of copper film increased; mass fraction too small (less than 9%), separation efficiency reduced, separation effect poor.

[0089] NaOH solution (for glass wafer substrate), mass fraction too large (more than 10%), substrate corrosion out of control, copper film affected by alkali solution; mass fraction too small (less than 5%), separation time prolonged, separation incomplete.

[0090] Substrate with sintered copper film is immersed in a specific solution, such as a solution of hydrofluoric acid (HF) mixed with water in a certain proportion (such as 1:10) (for silicon wafer substrate), or sodium hydroxide (NaOH) solution (for glass wafer substrate, mass fraction about 5%-10%). The immersion time is determined according to the bonding condition of the film and the substrate, generally about 10-30 minutes. During the immersion process, the solution will react chemically with the substrate, causing the sintered copper film to separate from the substrate. Then, the separated sintered copper film is carefully taken out with tweezers, rinsed with deionized water several times to remove residual solution, and prepared for use.

[0091] Example

[0092] Hereinafter, the examples of the present application will be described. The examples described below are exemplary and are for the purpose of explaining the present application only and are not to be understood as a limitation of the present application. In the examples, the specific techniques or conditions not mentioned are performed according to the techniques or conditions described in the literature in the art or according to the product manual. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained commercially.

[0093] Example 1

[0094] A method for preparing a high-performance sintered copper film for power module chip interconnection, comprising the following steps:

[0095] 1. Raw material preparation:

[0096] A high-purity copper salt, such as copper sulfate (CuSO4·5H2O), is selected, with a purity of not less than 99.9%. According to the planned amount of sintered copper film to be prepared, 30g of copper sulfate is weighed.

[0097] An appropriate amount of antioxidant 2,6-di-tert-butyl-p-cresol (BHT) is prepared, with a mass of 2% of the mass of copper sulfate. Corresponding to the above 30g of copper sulfate, 0.6g of BHT is weighed.

[0098] A certain amount of active element salt, such as titanium salt (such as titanium tetrachloride TiCl4, which needs to be appropriately diluted before use), is weighed, with a mass of 4% of the mass of copper sulfate. Taking titanium salt as an example, if a 10% mass fraction of titanium tetrachloride solution is used, the corresponding mass of solution needs to be measured.

[0099] Prepare an appropriate amount of organic solvent, such as ethylene glycol methyl ether (C3H8O2), which is 75ml, and it is appropriate to completely dissolve the above raw materials and form a uniform solution, generally 50-100ml of organic solvent per 10g of raw material.

[0100] 2. Dissolution and mixing:

[0101] Slowly add the weighed copper sulfate to the container containing ethylene glycol methyl ether, and turn on the magnetic stirrer, set the stirring speed to 300-500 rpm, so that the copper sulfate is fully dissolved, and the solution is blue and transparent.

[0102] Add the weighed BHT to the above copper sulfate solution, continue stirring for 30-60 minutes to ensure that the BHT is completely dissolved and uniformly mixed with the solution.

[0103] Slowly add the active element salt solution (such as diluted titanium tetrachloride solution), and stir while adding, adjust the stirring speed to 200-300 rpm, continue stirring for 60-90 minutes, so that the components in the solution are fully mixed, forming a uniform precursor solution. At this time, the solution may change color due to the addition of active element salt, such as a slight yellow color after adding titanium tetrachloride solution.

[0104] 3. Solution spin coating

[0105] Substrate pretreatment: Choose flat and smooth glass or silicon wafer as the spin coating substrate. First, use organic solvents such as acetone, ethanol, etc. to ultrasonic clean for 10-15 minutes, remove surface oil, dust and other impurities. Then wash with deionized water, then place the substrate in an oven at 100-120°C and dry for 1-2 hours to ensure that the substrate surface is dry and clean.

[0106] Spin coating operation: Fix the pretreated substrate on the vacuum chuck of the spin coater. Take an appropriate amount of precursor solution and drop it on the center of the substrate, generally 1-3ml of solution per time according to the size of the substrate and the required copper film thickness. Set the spin coater parameters, the low-speed rotation stage speed is 500-1000 rpm, and the rotation time is 10-20 seconds, so that the precursor solution is initially spread on the substrate surface. Then enter the high-speed rotation stage, the speed is increased to 3000-5000 rpm, and the rotation time is 30-60 seconds, so that the solution is uniformly coated on the substrate surface under the action of centrifugal force, forming a thin and uniform liquid film.

[0107] 4. Heat annealing treatment

[0108] Annealing equipment preparation: Place the substrate coated with the precursor solution into a tube furnace or box furnace for heat annealing treatment. Before placing the substrate, first vacuum the furnace chamber to 10 -3 -10 -Pa, and then high-purity nitrogen or argon gas is introduced as a protective gas, with a gas flow controlled at 50-100 sccm (standard cubic centimeter per minute) to prevent oxidation of copper at high temperature.

[0109] Annealing process: the furnace temperature is raised to 300-400°C at a temperature rising rate of 5-10°C / min, and maintained at this temperature for 30-60 min. During this stage, the organic matter in the precursor solution is gradually volatilized and decomposed, and copper ions are reduced to metallic copper under the action of a reducing agent (such as ethylene glycol methyl ether which can act as a reducing agent at high temperature), while the active elements diffuse and react with copper.

[0110] After the end of the holding process, the furnace temperature is lowered to room temperature at a temperature lowering rate of 3-5°C / min. The stress in the copper film can be fully released during the furnace cooling process, avoiding cracks or deformation of the copper film due to rapid temperature change. After the heat annealing process, a dense and uniform sintered copper film is formed on the surface of the substrate.

[0111] 5. Copper film separation

[0112] If the prepared sintered copper film needs to be separated from the substrate for power module chip interconnection, the following method can be used: the substrate with the sintered copper film is immersed in a specific solution, such as hydrofluoric acid (HF) solution (for silicon wafer substrate, mass fraction about 9%) or sodium hydroxide (NaOH) solution (for glass wafer substrate, mass fraction about 5%). The immersion time is determined according to the bonding condition of the film and the substrate, generally 10-30 min. During the immersion process, the solution reacts with the substrate to separate the sintered copper film from the substrate. Then, the separated sintered copper film is carefully taken out with tweezers, rinsed with deionized water several times to remove the residual solution, and ready for use.

[0113] The preparation conditions of the above-mentioned Example 1 are changed as follows to obtain sintered copper paste as Examples 2-4 and Comparative Examples 1-3, and the relevant parameters are measured, as shown in Table 1 below.

[0114] Table 1: Parameter results of Examples 1-4 and Comparative Examples 1-3

[0115]

[0116] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications of the embodiments that can be thought of by those skilled in the art, and other ways constructed by combining part of the constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing a high-performance sintered copper film for interconnecting power module chips, characterized in that, Includes the following steps: (1) Preparation of precursor solution 1) Slowly add the weighed copper salt to the container containing ethylene glycol methyl ether, while turning on the magnetic stirrer to stir until the copper salt is fully dissolved. 2) Add the weighed BHT to the copper salt solution above, and continue stirring to ensure that the BHT is completely dissolved and mixed evenly with the solution; 3) Slowly add the active element salt solution while stirring to form a uniform precursor solution; (2) Solution spin coating The precursor solution is uniformly coated onto the substrate surface, and a thin and uniform liquid film is formed by spin coating. (3) Heat annealing treatment First, evacuate the furnace cavity and then introduce a protective gas. Then, place the substrate coated with the precursor solution into a tube furnace or box furnace, raise the furnace temperature to 300-400℃, hold it for 30-60 minutes, and then lower it to room temperature. (4) Copper film separation: The substrate with sintered copper film is immersed in hydrofluoric acid solution or sodium hydroxide solution to separate the sintered copper film from the substrate; Remove the sintered copper film, rinse it with deionized water, and set it aside.

2. The method for preparing a high-performance sintered copper film for power module chip interconnection according to claim 1, characterized in that, The copper salt is copper sulfate; the antioxidant added is 1%-3% of the copper salt by mass, and the antioxidant is 2,6-di-tert-butyl-p-cresol (BHT); the active element salt added is 3%-5% of the copper salt by mass, and the active element salt is at least one of titanium salt or chromium salt; the ratio of organic solvent to copper salt is 5-10 ml: 1 g, and the organic solvent is ethylene glycol methyl ether.

3. The method for preparing a high-performance sintered copper film for power module chip interconnection according to claim 2, characterized in that, The titanium salt is titanium tetrachloride, and the chromium salt is potassium dichromate.

4. The method for preparing a high-performance sintered copper film for power module chip interconnection according to claim 1, characterized in that, The amount of precursor solution added is 1-3 ml, and the thickness of the formed liquid film is 50-300 nm.

5. The method for preparing a high-performance sintered copper film for power module chip interconnection according to claim 1, characterized in that, The spin coater first rotates at a low speed of 500-1000 rpm for 10-20 seconds to allow the precursor solution to initially spread on the substrate surface. Then it enters the high-speed rotation stage, with the speed increasing to 3000-5000 rpm and the rotation time being 30-60 seconds.

6. The method for preparing a high-performance sintered copper film for power module chip interconnection according to claim 1, characterized in that, The furnace temperature rise rate is 5-10℃ / minute, and the furnace temperature drop rate is 3-5℃ / minute.

7. The method for preparing a high-performance sintered copper film for power module chip interconnection according to claim 1, characterized in that, The substrate is a silicon wafer, which is soaked in a hydrofluoric acid solution with a mass fraction of 9%-12%; the substrate is a glass sheet, which is soaked in a sodium hydroxide solution with a mass fraction of 5%-10%.

8. A high-performance sintered copper film for power module chip interconnection, obtained by the preparation method according to any one of claims 1-7.

9. An application of a high-performance sintered copper film for power module chip interconnection, wherein the copper film obtained by any one of the preparation methods of claims 1-7 or the copper film of claim 8 is used for 5G power module chip interconnection.

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