JP2016072605A - Joint material for semiconductor device and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Pb-free joint material for a semiconductor with which a lead frame, a substrate, etc. can be joined with a semiconductor chip by sintering at a relatively low temperature under an atmospheric pressure, and a method for producing the same.SOLUTION: A joint material for a semiconductor device including a metal nanocrystal layer in which metal nanocrystals with an average particle size of 20-500 nm are layered and no halogen compound is contained is formed to both or one of a junction of a semiconductor chip and a junction region of a support body by electrolysis in which a DC current or pulse current is applied between an anode 9 and a cathode 8.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a conductive bonding material for bonding a semiconductor chip to a lead frame, a substrate or the like mainly having a function of energization and heat dissipation when manufacturing a power semiconductor device and the like, and a method for manufacturing the same.

  When bonding a semiconductor chip on a lead frame or a substrate, Sn-Pb refractory solder materials containing 85% or more of Pb are widely used. On the other hand, in recent years, there has been a trend toward Pb free from the viewpoint of environmental conservation. It is becoming active.

In addition, the development of next-generation power semiconductors such as SiC and GaN, which have the effect of reducing power loss, against the background of the recent eco-boom, is also active, but one of the characteristics of semiconductor elements using these materials is 250 ° C. In order to enable the operation in the above high temperature region, higher heat resistance is also required for the conductive bonding material.
Since conventional high melting point solder materials and Pb-free solder materials cannot satisfy the requirements, development of bonding materials and bonding methods different from those conventionally used has been underway.

For example, Patent Document 1 (Japanese Patent Laid-Open No. 2005-32834) discloses a bonding technique that enables heat-resistant bonding at 300 ° C. or higher corresponding to a next-generation power semiconductor by a liquid phase diffusion bonding method.
However, since this joining technique needs to be held for about 3 hours while being pressurized at 450 to 650 ° C. in a high temperature and 450 ° C. in the joining process, there are many difficulties in terms of productivity, and 450 to 650 ° C. Since there is a possibility that the wiring pattern on the surface of the semiconductor chip may be damaged due to the high temperature and the vacuum state, there are many concerns about the reliability.

Therefore, development of a conductive bonding material using metal nanoparticles that enables high heat-resistant bonding (for example, about 960 ° C. in the case of a material mainly composed of Ag) by low-temperature heating at about 200 ° C. has been promoted. Various investigations have also been made on bonding techniques using such conductive bonding materials.
Here, the conductive bonding material using metal nanoparticles will be described. Metal nanoparticles having a size of 5 to 100 nm and the periphery of each metal nanoparticle are coated to prevent them from aggregating at room temperature. It consists of an organic dispersant and an organic solvent.
The conductive bonding material using these metal nanoparticles can be sintered at a temperature much lower than the melting point due to the quantum size effect, and after sintering, the organic dispersant and the organic solvent are volatilized and completely metallized. Therefore, it has heat resistance, electric resistance value, and heat dissipation corresponding to the melting point inherent to the metal.
Therefore, by selecting a material (for example, Ag, Au, Cu) having a high melting point, low electrical resistance, and high heat dissipation, it is possible to achieve a bonding that can achieve further performance improvement and reliability improvement of power semiconductors and the like. It is expected to be.

  Further, in Patent Document 2 (Japanese Patent No. 5401661), a wafer, a chip, or any other material to be bonded made of a semiconductor or the like is bonded without causing physical damage due to heating, pressurization, or the like. For this purpose, a film having a microcrystalline structure such as metal or alloy is formed on at least one bonding surface of the material to be bonded by vacuum film formation such as sputtering or ion plating, and the film is polymerized at room temperature to be bonded. There is disclosed a room temperature bonding method that enables strong bonding between materials.

JP 2005-32834 A Japanese Patent No. 5401661

However, in the bonding method using the conductive bonding material using metal nanoparticles, the organic dispersant and the organic solvent are volatilized by heating, so that the conductive bonding material is sandwiched between the lead frame or the substrate and the semiconductor chip. When heated in a heated state, volatile gases that could not escape when the organic dispersant and organic solvent volatilize are generated as voids, or the film thickness after sintering becomes non-uniform due to volume shrinkage during curing, etc. There is a problem.
Moreover, although the joining method described in Patent Document 2 is an excellent method that enables strong joining between materials to be joined at room temperature, it is described in claim 6, paragraphs 0020, 0066 to 0067, and 0093. As described above, since bonding is performed in a high-vacuum atmosphere, there is a problem that a large apparatus is required and processing time is long, which is a disadvantageous method for mass production and cost reduction.
Furthermore, JP-A-8-503522 discloses a method for electrodeposition of a metal material in a nanocrystalline state, but the electrolyte used for electrodeposition contains chloride, When a plating film obtained using such an electrolytic solution is used for bonding a semiconductor device, the moisture entering the inside of the device reacts with the chloride remaining in the plating film to cause oxidation of aluminum wiring and the like. It has been found that it causes problems such as deterioration of device reliability and durability.
Also, confirm that if halides (chlorides, fluorides, bromides and iodides), phosphorus or phosphorus compounds are contained in the plating film, the reliability and durability of the semiconductor device will be adversely affected by the same process. did.

  The present invention solves such problems and provides a Pb-free bonding material for a semiconductor capable of bonding a lead frame, a substrate, and the like and a semiconductor chip by sintering at a relatively low temperature under atmospheric pressure, and a method for manufacturing the same. At the same time, it aims at improving the reliability and durability of the semiconductor device, mass production, and cost reduction.

  According to a first aspect of the present invention, there is provided a semiconductor device junction formed by electrolysis at or both of a junction portion of the semiconductor chip and a junction region of the support for joining the semiconductor chip and the support. A metal nanocrystal having an average particle diameter of 20 nm to 500 nm is laminated, and is composed of a metal nanocrystal layer not containing a halide.

  The invention according to claim 2 is the semiconductor device bonding material according to claim 1, wherein the metal nanocrystal layer does not contain phosphorus and a phosphorus compound.

  The invention according to claim 3 is the bonding material for a semiconductor device according to claim 1 or 2, wherein the maximum cross-sectional height of the metal nanocrystal layer is less than 4 μm.

  According to a fourth aspect of the present invention, in the bonding material for a semiconductor device according to any one of the first to third aspects, an average particle size of the metal nanocrystal is 50 nm to 200 nm.

  According to a fifth aspect of the present invention, in the bonding material for a semiconductor device according to any one of the first to fourth aspects, the surface undulation of the metal nanocrystal layer is 0.38 μm or less.

  The invention according to claim 6 is a method for producing a bonding material for a semiconductor device, comprising: a first step of preparing an electrolytic cell having an anode and a cathode; and a metal salt and a complexing agent as a solvent in the electrolytic cell. A second step of introducing an aqueous electrolyte that does not contain halide, a third step of connecting a semiconductor chip or a support to the cathode and immersing in the aqueous electrolyte, and a temperature range of the aqueous electrolyte within a predetermined temperature range. In addition, a direct current or a pulsed current is passed between the anode and the cathode, and metal nanocrystals having an average particle size of 20 nm to 500 nm are laminated at the junction of the semiconductor chip or the junction region of the support. And a fourth step of forming the metal nanocrystal layer.

  The invention according to claim 7 is the method of manufacturing a bonding material for a semiconductor device according to claim 6, wherein the aqueous electrolyte does not contain phosphorus and a phosphorus compound.

  The invention according to claim 8 is the method for manufacturing a bonding material for a semiconductor device according to claim 6 or 7, wherein the maximum cross-sectional height of the bonding region of the support is less than 4 μm.

  The invention according to claim 9 is the method for manufacturing a bonding material for a semiconductor device according to any one of claims 6 to 8, wherein the average particle diameter of the metal nanocrystal is 50 nm to 200 nm.

According to the manufacturing method of the bonding material for a semiconductor device of the invention according to claim 1 or the bonding material for a semiconductor device of the invention according to claim 6, the average particle size is formed in the bonding portion of the semiconductor chip or the bonding region of the support by electrolysis. Are laminated with metal nanocrystals having a thickness of 20 nm to 500 nm, and a metal nanocrystal layer not containing a halide is formed. Therefore, the joining portion and the joining region are joined by sintering at a relatively low temperature under atmospheric pressure. The reliability and durability of the bonded semiconductor device can be improved.
In addition, as compared with film formation by vacuum film formation such as sputtering or ion plating, it can be easily produced with a small-scale facility, so that mass production and cost reduction can be realized.
Furthermore, in the invention according to claim 6, when a pulse current is passed between the anode and the cathode, a metal nanocrystal layer having a higher density can be formed than when a direct current is passed.

According to the method for manufacturing the bonding material for a semiconductor device of the invention according to claim 2 or the bonding material for the semiconductor device of the invention according to claim 7, the bonding material for a semiconductor device of the invention according to claim 1 or claim 6 is provided. In addition to the effect of the manufacturing method of the bonding material for a semiconductor device of the invention, since the metal nanocrystal layer does not contain phosphorus and a phosphorus compound, the moisture penetrated into the semiconductor device reacts with phosphorus or the phosphorus compound, such as aluminum wiring Oxidation is not caused.
Therefore, the reliability and durability of the joined semiconductor device can be further improved.

According to the method for manufacturing the bonding material for a semiconductor device of the invention according to claim 3 or the bonding material for the semiconductor device of the invention according to claim 8, the bonding material for a semiconductor device of the invention according to claim 1 or 2 or claim 6. In addition to the effect of the manufacturing method of the bonding material for semiconductor device according to the invention according to 7, the maximum cross-sectional height of the bonding region of the metal nanocrystal layer or the support is less than 4 μm, thereby supporting the bonding portion of the semiconductor chip. When die-bonding to the bonding region of the body, the non-contact portion on the bonding surface through the metal nanocrystal layer can be almost eliminated, so that sufficient bonding strength can be obtained.
Therefore, the reliability and durability of the joined semiconductor device can be further improved.

According to the bonding material for a semiconductor device of the invention according to claim 4 or the manufacturing method of the bonding material for a semiconductor device of the invention according to claim 9, the bonding material for a semiconductor device of the invention according to any one of claims 1 to 3 or In addition to the effect of the manufacturing method of the bonding material for a semiconductor device according to any one of claims 6 to 8, the average particle size of the metal nanocrystal is 50 nm to 200 nm, so that the bonding property to the bonding portion and the bonding region is high. It is possible to obtain a metal nanocrystal layer with better and more stable electrical characteristics.
Therefore, the reliability and durability of the joined semiconductor device can be further improved.

According to the bonding material for a semiconductor device of the invention according to claim 5, in addition to the effect of the bonding material for a semiconductor device according to any one of claims 1 to 4, the surface waviness of the metal nanocrystal layer is 0.38 μm. Since it is below, the junction part of a semiconductor chip and the junction area | region of a support body can be favorably joined.
When the die bond load applied at the time of joining is W (kg), the area of the joint is S (mm ² ), and the Vickers hardness of the metal nanocrystal layer is P0 (kg / mm ² ), W = 0. The required die bond load can be easily obtained by the relational expression of 0053 × S × P0.

The figure which shows the structure of the electrolysis cell used in the Example. The figure which shows the process of obtaining a several semiconductor chip from the wafer in which the silver nanocrystal layer of the Example was formed. The figure which shows the process of joining a semiconductor chip and a support body. FIG. 3 is a cross-sectional view of a joined body obtained using the semiconductor device joining material of Example 1; 2 is a cross-sectional enlarged photograph of a joined body obtained by the semiconductor device joining material of Example 1. FIG. Types of amine complexing agents and appearance and FE-SEM photographs of plated films. The figure which shows the clearance gap which arises in the junction part of a semiconductor chip and a copper lead frame. The diffusion layer image figure of the electrode surface at the time of DC current and pulse current application. The FE-SEM photograph of the plating film obtained by applying direct current and pulse current.

  Hereinafter, embodiments of the present invention will be described by way of examples.

<First step>
FIG. 1 is a diagram showing an electrolytic cell used in Example 1 of the present invention, and the step of preparing this electrolytic cell is the first step.
The electrolysis cell accommodates the cathode cartridge 1, the crosshead rotor 2 and the anode jig 3, and these 1 to 3, a first bathtub 4 that can store an aqueous electrolyte, and a first bathtub 4, and temperature adjustment. It comprises a second bathtub 5 that can store liquid (usually water), a stirrer 6 that rotates the crosshead rotor 2 by magnetic force, and a DC power source 7.
The cathode cartridge 1 is provided with a square cathode side opening having a side of 23 mm, and a metal surface (usually a silver plating surface) formed on one surface of the semiconductor wafer is opposed to the cathode side opening. The semiconductor wafer and the DC power source 7 can be connected via the cathode 8.
The anode jig 3 is provided with a square anode side opening having a side of 10 mm at a position facing the cathode side opening, and the anode electrode 10 (the same kind of material as that of the metal nanocrystal is formed in the anode side opening. And the anode electrode 10 and the DC power source 7 can be connected via the anode 9.

<Second step>
While introducing an aqueous electrolyte into the first bath 4 of the electrolysis cell, water (5 to 20 ° C.) at an appropriate temperature is stored in the second bath 5.
The aqueous electrolyte introduced into the bathtub 4 is pure water containing silver nitrate as a metal salt and dissolving an amine complexing agent.
In Example 1, the concentration of silver nitrate was 1 mol / L, and the concentration of the amine complexing agent was 3 mol / L. However, silver nitrate should be 0.1 mol / L or more (preferably 0.25 to 2 mol / L). As for amine complexing agents, it is known that silver and amine form a 1: 2 complex, and it is generally better to add more complexing agents. The concentration is 2-3 times. That is, the concentration of the amine complexing agent may be 0.2 mol / L or more (desirably 0.5 to 6 mol / L).
The relationship between the concentration of silver nitrate, the type of amine complexing agent, and silver crystal precipitation will be described later.

<Third step>
The semiconductor wafer is connected to the cathode 8 and immersed in the aqueous electrolyte in the first bath 4.
Note that either the connection of the cathode 8 or the immersion in the aqueous electrolyte may be performed first.

<4th process>
Water of an appropriate temperature is stored in the second bath 5 to maintain the temperature of the aqueous electrolyte in a predetermined temperature range, and the DC power source 7 is operated to pass a DC current between the cathode 8 and the anode 9.
Further, the stirrer 6 is operated to rotate the crosshead rotor 2 at a speed of about 450 rpm, and the aqueous electrolyte between the cathode side opening and the anode side opening is stirred.
In addition, when there is a difference between the temperature of the water stored in the second bathtub 5 and the room temperature, the temperature of the water is maintained within a predetermined temperature range by replacing the water or cooling or warming with appropriate means. To do.
Then, energization is continued until a desired thickness (1 to 40 μm depending on the application) of silver nanocrystals having an average particle diameter of 20 nm to 500 nm is formed on the metal surface of the semiconductor wafer to form a silver nanocrystal layer. .
Here, the average particle size of the silver nanocrystals deposited can be controlled by the silver nitrate concentration of the aqueous electrolyte, the type and concentration of the complexing agent, the liquid temperature and the current density, and the particle size decreases as the current density is increased. It has been experimentally found that when the current density is increased, the sparse part increases in the crystal layer, and when the current density is increased, the sparse part decreases from the crystal layer.
Therefore, in the production method of the present invention, the smaller the particle size of the silver nanocrystals, the better. The average particle size of 50 nm to 200 nm facilitates obtaining a dense silver nanocrystal layer, and the average particle size of 50 nm. It is easy to obtain a silver nanocrystal layer having a denseness of ~ 150 nm that is most dense.

2 (1) to (6) and FIGS. 3 (1) to (4) are steps in which a plurality of semiconductor chips are die-bonded from a semiconductor wafer 11 to a bonding region of a support after manufacturing a bonding material for a semiconductor device. This is a process for manufacturing a semiconductor device by bonding the semiconductor chip 11 and the support 16 via the silver nanocrystal layer 12, which will be described below.
<5th process>
As shown in FIG. 2 (1), the semiconductor wafer 11 on which the silver nanocrystal layer 12 having a thickness of 1 to 40 μm obtained in the first to fourth steps is formed in hot water of 40 to 70 ° C. Immerse for 2 seconds and wash in hot water.

<6th process>
As shown in FIG. 2 (2), after the hot-washed semiconductor wafer 11 is placed so that the silver nanocrystal layer 12 is on the upper side, it is dried by applying hot air of 40 to 100 ° C. for 30 to 300 seconds from above. To do.

<Seventh step>
As shown in FIG. 2 (3), after the dried semiconductor wafer 11 is placed on the upper surface of the wafer fixing sheet 13 so that the silver nanocrystal layer 12 is on the lower side, a disk-shaped blade 14 is used from above. Then, they are cut at appropriate intervals in the vertical direction and the horizontal direction, and separated into a plurality of semiconductor chips 15. FIG. 2 (4) is an enlarged view showing the individual semiconductor chip 15.

<Eighth process>
As shown in FIG. 3 (1), a support (lead frame 16) is prepared using copper as a main material and forming a silver plating layer having a thickness of about 4 μm on the surface to form a bonding region.
Next, the lead frame 16 is placed on a hot plate placed in the atmosphere of the homing gas 17 so that the bonding region is on the upper side.
The surface of the hot plate is heated to 250 to 350 ° C., and the lead frame 16 is placed on the surface for 1 to 90 seconds to heat the entire lead frame 16 including the bonding region of the surface.

<9th process>
As shown in FIG. 3B, in the atmosphere of the homing gas 17, the semiconductor chip 15 is die-bonded so that the entire surface of the silver nanocrystal layer 12 is in contact with the bonding region of the lead frame 16. A load of 150 g from the side is applied for 200 msec to obtain the state shown in FIG.
The homing gas 17 is for preventing the oxidation of the semiconductor chip 15 (particularly, the metal used for the wiring pattern or the chip back metal 19), the lead frame 16, and the silver nanocrystal layer 12, and the nitrogen gas is 95%. And a gas containing 5% hydrogen gas.

<10th process>
When the semiconductor chip 15 is die-bonded to the bonding region of the lead frame 16 in the ninth step, since the bonding region is preheated, the silver nanocrystal layer 12 is heated immediately after the die bonding and sintering is started.
The surface of the hot plate can be maintained at 250 to 350 ° C., and the lead frame 16 is placed on the surface for 0.5 to 60 minutes to complete the sintering of the silver nanocrystal layer 12. .
When the lead frame 16 is moved from the hot plate and cooled after the sintering is completed, the joining process is completed.
When the sintering is completed, since the silver nanocrystal layer 12 becomes a bulk Ag layer, the semiconductor chip 15 and the lead frame 16 are bonded to each other with the bonding layer 20 having a high melting point (about 960 ° C.) and a low electrical resistivity (3 to 5 μΩ · cm). Thus, the joined body of FIG. 3 (4) is obtained.

FIG. 4 is a cross-sectional view of an element obtained by molding the joined body obtained in this manner, and FIG. 5 is a photograph of a portion surrounded by a square at the lower left of FIG.
4 and 5, 18 is a silver plating layer having a thickness of about 4 μm formed on the surface of the lead frame 16, 19 is a chip back metal serving as a bonding portion of the semiconductor chip 15, and 20 is a bulk Ag layer. The bonding layer 21 is a mold resin.
From the photograph in FIG. 5, there is no void, the thickness of the bonding layer 20 under the semiconductor chip 15 is uniform, and the silver plating layer 18 and the chip back metal 19 that are the bonding region between the bonding layer 20 and the lead frame 16. It can be seen that the adhesiveness with is extremely good.
In addition, although the black part which shows that there exists a small hole is scattered in the part of the joining layer 20 of FIG. 5, this hole is a pore which arises naturally when nanocrystal grows by sintering, This is different from general voids generated by air entrainment during application of gas generated during sintering or metal nano-joining material.

Further, when the relationship between the temperature at which the silver nanocrystal layer 12 was sintered and the bonding strength was confirmed by a die shear strength test (shear strength test), an average of 11 N / square mm at 250 ° C. (sintering time 1 minute), The average was 27 N / square mm at 300 ° C. (sintering time 1 minute), and the average was 37 N / square mm at 350 ° C. (sintering time 1 minute).
As a result of confirming the bonding strength using the high melting point solder material by the same strength test, it is found that the average is 29 N / square mm, and it is known that the semiconductor device can be assembled even at about 10 N / square mm. It can be evaluated that any of the joined bodies obtained by sintering the silver nanocrystal layer 12 with a sintering time of 1 minute can withstand normal use.

  Next, manufacturing conditions (relationship between the type of complexing agent and the concentration of silver nitrate and silver crystal precipitation) suitable for manufacturing the semiconductor device bonding material (silver nanocrystal layer) will be described.

Focusing on amine-based complexing agents that do not contain halides and phosphorus as complexing agents, various amine-based complexing agents were bathed in pure water containing 1 mol / L silver nitrate. Is not suitable as a complexing agent because amine complexing agents (n-pentylamine, n-heptylamine and n-octylamine) of 5 or more and tert-butylamine are hardly soluble in water and precipitate or separate. I understood that.
Therefore, pure water containing 1 mol / L silver nitrate without using a complexing agent, ethylamine having 2 carbon atoms, n-propylamine having 3 carbon atoms, and n-butylamine having 4 carbon atoms as a complexing agent, sec -An aqueous electrolyte prepared by dissolving 3 mol / L of butylamine and isobutylamine in pure water containing 1 mol / L of silver nitrate was electrolyzed using the electrolytic cell of FIG.

Table 1 shows the quality of the silver crystals deposited for each aqueous electrolyte and the quality of the silver nanocrystals.
According to Table 1, in the case of an aqueous electrolyte that does not use an amine complexing agent, the crystal particle size is several hundred nm or more, and a silver nanocrystal layer having a suitable particle size cannot be obtained. In the aqueous electrolyte used, a silver nanocrystal layer having a suitable particle size of 200 nm or less can be obtained, and among amine complexing agents dissolved in water, n-butylamine and isobutylamine are good in terms of both particle size and quality. It can be seen that it is particularly suitable for obtaining a silver nanocrystal layer.
In addition, although the quality judgment Δ (plated film is sparse or non-uniform) in Table 1 can be used as a bonding material for a semiconductor device, it is necessary to lengthen the processing time of the baking process after bonding, which increases productivity. May have an impact.

FIG. 6 shows an appearance photograph and FE-SEM photograph (100,000 times) of the plating film when ethylamine, n-butylamine and isobutylamine are used among the amine complexing agents in Table 1.
As shown in FIG. 6, when ethylamine is used, the appearance of the plating film is almost uniform, but it can be seen that there are many sparse portions in the crystal layer. On the other hand, when n-butylamine and isobutylamine are used, it can be seen that the appearance of the plating film is almost uniform and the crystal layer is dense.
From these experimental results, it was found that n-butylamine and isobutylamine are particularly suitable complexing agents for obtaining a quality silver nanocrystal layer having good particle size and quality.

Therefore, n-butylamine was used as a complexing agent, and an experiment was conducted to determine whether silver nanocrystals can be deposited by changing the concentration of silver nitrate.
As a result, when the concentration of silver nitrate was less than 0.1 mol / L, silver nanocrystals could not be precipitated even when the current density was increased. However, if the concentration of silver nitrate was 0.1 mol / L or more, It was found that nanocrystals can be precipitated, and that silver nanocrystals can be precipitated even when the current density is lowered as the concentration of silver nitrate is higher.
However, considering the specifications and economical efficiency of the DC power source, the concentration of silver nitrate is preferably 0.25 to 2 mol / L, and most preferably 0.5 to 1.5 mol / L.

Furthermore, an experiment was conducted on the influence of the surface roughness of the silver nanocrystal layer, the joint portion of the semiconductor chip, and the joint region of the support on the reliability of the semiconductor device.
In the semiconductor device used in the experiment, a silver nanocrystal layer is provided in the joint portion of the semiconductor chip by the first to seventh steps, and the eighth step is performed on the silver plating applied to the joint region of the copper lead frame as a support. It was what was joined by 10 processes.
And the displacement of the cross section on the line which passes along the silver nanocrystal layer and the center of the silver plating surface given to the joining area | region before joining was measured.
As a result, the silver nanocrystal layer provided at the junction of the semiconductor chip has a very high degree of flatness, and the maximum cross-sectional height, which is the difference in displacement, is only 1.7 μm at the maximum. In general, the silver plating applied to the plate had low flatness and the maximum cross-sectional height varied from 1 to 5 μm.

Therefore, as a result of manufacturing a semiconductor device by dividing into a copper lead frame with a maximum cross section height of 2 to 3 μm and a copper lead frame with 4 to 5 μm and conducting an electrical characteristic test, the maximum cross section height of the silver plating was The number of non-defective products was 0% for semiconductor devices using copper lead frames with a thickness of 4 to 5 μm, and the number of non-defective products was 100% for semiconductor devices using copper lead frames with a maximum cross-section height of silver plating of 2 to 3 μm. .
In addition, as a result of cross-sectional analysis of a defective product using a copper lead frame having a maximum cross-sectional height of 4 to 5 μm, it was confirmed that there was an unjoined portion at the center of the semiconductor chip. That is, the occurrence of defective products is caused by a gap as shown in FIG. 7 at the joint portion between the semiconductor chip and the copper lead frame, and the waviness present on the surface on the support side adversely affects the joint strength. It is considered a thing.
From these results and considerations, when the semiconductor chip and the support are bonded using the bonding material for a semiconductor device of the present invention, it is necessary that the maximum cross-sectional height of the surface at the bonded portion be less than 4 μm. It can be said that the following is better.
And as a bonding material for a semiconductor device using the metal nanocrystal layer of the present invention, particularly when the metal nanocrystal layer is laminated on the support side, the maximum cross-sectional height of the surface is less than 4 μm, preferably 3 μm or less, more preferably In order to increase the reliability, it is important that the thickness is 2.5 μm or less.

By combining the above experimental results and the like, an aqueous electrolyte having a silver nitrate concentration of 1 mol / L and an n-butylamine concentration of 3 mol / L is used, and a semiconductor device junction having a thickness of about 10 μm is electrolyzed at the junction of the semiconductor chip. After forming the material, a test sample (50 samples) of a semiconductor device manufactured by sintering and bonding a semiconductor chip to a copper flat frame having a high flatness with a maximum cross-sectional height of a bonding region of 2.5 μm or less, A PCT test (pressure cooker test), which is a typical reliability test, was performed.
Here, the PCT test is a performance test performed in an environment of 2 atm and a humidity of 100%, which is considerably higher than usual. In this test, a transistor was used as a test sample, so the collector-emitter saturation voltage was measured. At the same time, an appearance inspection (visual confirmation of abnormality) was performed.
As a result, for all the test samples, the voltage fluctuation rate after the 96-hour test period was within ± 10% from the initial value, and no abnormality was confirmed even in the appearance inspection.
From this test result, it can be seen that the variation rate of the electrical characteristics in the semiconductor device using the bonding material for a semiconductor device of the present invention is comparable to the variation rate of the electrical characteristics in the semiconductor device using the high melting point solder.
Although not confirmed by performing the same PCT test, in the case of a bonding material containing a halide or phosphorus, the PCT test is a test that is susceptible to oxidation of wirings included in a semiconductor device. It is predicted that a correct result will not be obtained.

Furthermore, when the surface part of the bonding material for semiconductor devices (silver nanocrystal layer) formed in the same manner was measured, oxygen was 13.9%, nitrogen was 0.7%, and silver was 22.7%. And 62.7% carbon. The measurement conditions are an XPS measurement depth of 5 nm and an XPS measurement range of 300 × 700 μm.
Further, after argon sputtering having a depth of 40 to 50 nm was performed in a 1 mm square range, and quantitative measurement was performed under the same measurement conditions, oxygen was 6.1%, nitrogen was 1.4%, and silver was 40. 1% and 52.5% carbon were contained.
From these measurement results, it was confirmed that n-butylamine was present as a residue in the silver nanocrystals, and carbon-derived impurities were deposited on the surface side of the silver nanocrystal layer.
The latter is presumed as such because the surface portion has carbon in a ratio considerably higher than the carbon-to-nitrogen ratio of n-butylamine.

The manufacturing method of the semiconductor device bonding material in Example 2 is different from Example 1 in that the cathode is formed in the fourth step of forming the silver nanocrystal layer 12 having an average particle diameter of 20 nm to 500 nm on the metal surface of the semiconductor wafer. Instead of passing a direct current between 8 and the anode 9, a pulse current is passed.
Therefore, the DC power supply 7 included in the electrolysis cell prepared in the first step is replaced with a pulse power supply that can change the on-time (hereinafter referred to as “tON”) and off-time (hereinafter referred to as “tOFF”).

The density of the silver nanocrystal layer 12 is obtained by flowing a pulse current instead of a direct current between the cathode 8 and the anode 9 until the silver nanocrystal having an average particle diameter of 20 nm to 500 nm reaches a desired thickness. Can be increased.
The reason for this is that when a direct current is applied, the diffusion layer generated on the anode side grows with time and the ion concentration on the electrode surface decreases as shown in FIG. In this case, as shown in FIG. 8B, the diffusion layer grows on the anode side at the time of tON, but both the electric double layer and the diffusion layer decrease at the time of tOFF. This is because the electrode is kept thin and the ion concentration on the electrode surface is kept high and electrolysis at a high current density is continued.

FIG. 9 is an FE-SEM photograph of the plating film obtained by applying direct current and pulse current.
The current density is 4 A / dm ² when a direct current is applied and a pulse current is applied with a tON of 20 msec and 40 msec, and 21 A / dm ² when a pulse current is applied with a tON of 10 msec. The film thickness is 1 μm when a direct current is applied. 5 μm and 10 μm, and 1 μm and 5 μm when a pulse current is applied.
The pulse current tOFF is 400 msec in all cases.
From these photographs, in the case of a plating film obtained by applying a direct current (hereinafter referred to as “DC plating film”), a cavity portion can be confirmed in each film thickness, and the cavity portion is larger as the film thickness is thinner, You can see that it is increasing. Since the hollow portion also causes generation of pores during sintering, a long processing time is required in the subsequent firing step.
Moreover, in the case of the plating film obtained by applying the pulse current, it is not possible to confirm whether or not the cavity portion is extremely small in each film thickness as compared with the DC plating film. In this state, the pores generated during sintering are small and small, so that the processing time in the subsequent firing step is shorter than the processing time of the DC plating film.

Next, in the ninth to tenth steps, the load was applied until the sintering of the silver nanocrystal layer 12 was completed after the die bond, and the die bond using the metal nanocrystal layer as the bonding material is true. This is because it has been found that the contact area is greatly related to the bonding strength.
The real contact area (Ar [mm ² ]) is a plastic flow pressure (P0 [kg / mm ² ]) that varies depending on the vertical load (W [kg]) in die bonding, the film thickness of the bonding material, and the material (particularly hardness). And the following relationship.
Ar = W / P0 (1)
However, the relationship is established when the surface roughness of the metal nanocrystal layer follows a normal distribution, that is, when the unevenness of the surface is small, the nine types of plating films shown in FIG. It was also confirmed that the unevenness on the surface was small.

Then, the chip area (S [mm ^2]) is 0.3136Mm ² result of repeated experiments on semiconductor chip (side square is 0.56 mm), Ar is sufficient strength unless 0.001676Mm ² or more It was found that could not be obtained.
From this, the ratio of the true contact area to the chip area (a [%]) is a = Ar / S × 100. Therefore, if 0.001676 and 0.3136 are substituted for Ar and S, a ≧ 0. It turns out that it is necessary to set to 53.
Also, if equation (1) is modified, W = Ar × P0, and if a = Ar / S × 100 is modified, Ar = a × S / 100, so the following equation is derived.
W = a × S × P0 / 100 (2)
Substituting a ≧ 0.53 into equation (2) yields W ≧ 0.0053 × S × P0, and P0 is obtained from the Vickers hardness. Therefore, if the chip area and the Vickers hardness of the bonding material are obtained, the minimum The necessary die bond load can be determined.

Furthermore, in Example 1, it is important to increase the reliability to reduce the maximum cross-sectional height of the silver plating surface applied to the bonding region or the surface of the metal nanocrystal layer formed on the silver plating surface. As a result, in Example 2, the undulation on the surface of the metal nanocrystal layer was larger than that in Example 1, and it was found that if the undulation was large, the bonding strength was adversely affected.
As a result of repeated experiments on silver nanocrystal layers having various thicknesses obtained by applying pulse currents under various conditions, sufficient bonding strength can be obtained if the surface waviness is 0.38 μm or less, It was found that greater bonding strength can be obtained when the thickness is 0.21 μm or less.

The modification of an Example is listed.
(1) In the first to fourth steps of Examples 1 and 2, the silver nanocrystal layer was formed on the semiconductor wafer, but instead of the semiconductor wafer, the silver nanocrystal layer was formed in the bonding region of the support. May be.
(2) In the first to fourth steps of Examples 1 and 2, silver nanocrystals were deposited using an aqueous electrolyte containing silver nitrate, but gold, copper, or an alloy mainly composed of gold, silver, or copper. These metal nanocrystals may be deposited to form a metal nanocrystal layer.
(3) Although the electrolysis cell used at the 1st-4th process of Example 1 and 2 has crosshead rotor 2, the 2nd bathtub 5, and stirrer 6, it is not necessary to equip. If stirring of the aqueous electrolyte is necessary, an appropriate stirring means may be separately prepared. If it is necessary to maintain the temperature of the aqueous electrolyte, an appropriate cooling means or heating means may be used.
(4) In the first to fourth steps of Examples 1 and 2, the semiconductor wafer was not pretreated, but degreased on the surface of the semiconductor wafer or support to be plated if necessary. Further, pretreatment such as acid activation and etching (chemical polishing) may be performed.
(5) In the fourth step of Examples 1 and 2, the silver nanocrystals have a desired thickness (1 to 40 μm). The thickness of the silver nanocrystals depends on the size and application of the semiconductor chip to be joined. Select as appropriate.
However, considering the time and cost required for forming the silver nanocrystal layer, the bonding strength, etc., it can be said that the thickness of the silver nanocrystal layer is more preferably about 3 to 20 μm.

(6) In the fifth step of Examples 1 and 2, the semiconductor wafer 11 was dipped in hot water of 40 to 70 ° C. for 10 to 180 seconds and washed with hot water. The immersion time is adjusted according to the formation method, thickness and material of the metal nanocrystal layer.
Moreover, it may be immersed in a cleaning solution instead of hot water, or may be cleaned by flowing hot water or a cleaning solution over the surface of the metal nanocrystal layer 2 instead of immersion. The composition of the plating solution, the material of the semiconductor wafer 11, and the product Determined in consideration of the impact on
(7) In the sixth step of Examples 1 and 2, the semiconductor wafer 11 was dried by applying hot air of 40 to 100 ° C. for 30 to 300 seconds. However, drying is not necessary in some cases, and the drying time is hot air. The size and material of the semiconductor wafer 11, the composition of the plating solution, the composition of the plating solution, the influence on the product, etc., will greatly change. Therefore, it is necessary to optimize the temperature and time without being bound by the temperature range and time range of the embodiment. There is.
Further, in order to prevent oxidation, nitrogen gas or inert gas may be applied instead of hot air.
Furthermore, it may be placed on a plate whose surface is heated to 40 to 100 ° C. without applying warm air, or may be housed in a drying chamber that can keep the interior at 40 to 100 ° C. and dried. In that case, it is better to dry in an atmosphere of nitrogen gas or inert gas in order to prevent oxidation.
(8) In the eighth step of Examples 1 and 2, the lead frame 16 including the bonding region of the surface is placed by placing the lead frame 16 on a hot plate heated to 250 to 350 ° C. for 1 to 90 seconds. Although the whole was heated, the heating time varies greatly depending on the surface temperature of the hot plate and the material and size of the lead frame 16, so that the temperature and time are optimized without being bound by the temperature range and time range of the embodiment. There is a need.
(9) In the eighth step of Examples 1 and 2, in order to reduce the time from the die bonding of the semiconductor chip 15 to the lead frame 16 until the baking of the silver nanocrystal layer 12 is completed, the lead frame is required before the die bonding. 16 was placed on a hot plate and the whole was heated, but heating is not necessarily required, and even in the case of heating, only the bonding region may be heated.
Further, the heating means is not limited to a hot plate, and may be appropriately selected as long as it can heat at least the silver plating layer 18 as a bonding region, such as using a baking chamber capable of maintaining the internal temperature at an arbitrary temperature up to about 500 ° C. can do.
(10) In the ninth step of Examples 1 and 2, die bonding was performed in the atmosphere of the homing gas 17, and similarly, in the tenth step, the silver nanocrystal layer 12 was baked in the atmosphere of the homing gas 17. However, if the materials used for the semiconductor chip, the lead frame 16 and the metal nanocrystal layer are not oxidized, or if the effect of oxidation is small and it is not necessary to stick to the oxidation, etc., it is performed in a normal atmosphere. Also good.
In particular, the ninth step is a process after die bonding, and since there are few exposed portions of the silver nanocrystal layer 12 and the silver plating layer 18, it is less necessary to perform in the atmosphere of the homing gas 17.
Further, as the homing gas 17, a gas containing 95% nitrogen gas and 5% hydrogen gas was used. However, any gas can be used as long as it is a stable gas not containing oxygen (for example, nitrogen gas or inert gas). Gas may be used.

(11) In the ninth step of Examples 1 and 2, the semiconductor chip 15 was die-bonded and a load of 150 g was applied from the upper surface side of the semiconductor chip 15 for 200 msec, but the magnitude of the load and the time for applying the load were appropriately selected. Just do it.
Regarding the magnitude of the load, as described above, the minimum required die bond load can be determined by the chip area and the Vickers hardness of the bonding material, and the bonding strength increases as the time for applying the load increases, but the rate of increase is Since it slows down in 200 msec or more, the necessity of continuing to apply a load continuously after die bonding is low.
(12) In the ninth step of Examples 1 and 2, the semiconductor chip 15 is die-bonded so that the entire surface of the silver nanocrystal layer 12 is in contact with the bonding region of the lead frame 16 heated to 250 to 350 ° C. By holding the lead frame 16 at 250 to 350 ° C. in the process, the sintering of the silver nanocrystal layer 12 was finished, but at the time of die bonding, the temperature of the lead frame 16 was set to a relatively low temperature of 200 to 250 ° C. The silver nanocrystal layer 12 may be sintered by setting the surface temperature of the hot plate to a relatively high temperature of 350 to 400 ° C. after die bonding.
By doing so, the effect that the stress which generate | occur | produces at the time of die bonding can be relieve | moderated and sintering time can be shortened is acquired.
(13) In the tenth step of Examples 1 and 2, the surface temperature of the hot plate is maintained at 250 to 350 ° C., and the lead frame 16 is placed thereon for 0.5 to 60 minutes, Although the sintering of the silver nanocrystal layer 12 is finished, the heating temperature and heating time are not limited to this range, and the semiconductor chip 15 and its junction (chip back metal 19), the lead frame 16 and its junction region ( The silver plating layer 18) and the metal nanocrystal layer can be appropriately selected depending on the material and application.
And the upper limit temperature at the time of baking considers the influence to a junction part, a junction area, etc., and the damage to the wiring pattern (Al-Si) formed in the surface of the semiconductor chip 15, The metal used for a wiring pattern Since it is necessary to set it as melting | fusing point (577 degreeC in the case of Al-Si) or less, the heating temperature in a 10th process can be selected in 150-577 degreeC.
However, it is necessary to carefully select the material of the metal nanocrystal layer for firing at a low temperature, and firing at a high temperature may increase the cost of the apparatus and reduce yield and reliability. ˜450 ° C., optimum value is 250˜350 ° C.
Note that the appropriate value and the range of the optimum value of the heating temperature depend on the specifications of the heating device, the semiconductor chip 15, the lead frame 16 and the like as well as the material of the metal nanocrystal layer, so that instead of the silver nanocrystal layer 12, This also applies when other metal nanocrystal layers (gold nanocrystal layer, copper nanocrystal layer, etc.) are used.
(14) In the eighth to tenth steps of Examples 1 and 2, the semiconductor chip 15 having the silver nanocrystal layer 12 formed in the bonding region of the lead frame 16 was die-bonded. Instead of or in addition, a silver nanocrystal layer may be formed in the bonding region of the lead frame 16, and the semiconductor chip 15 may be die-bonded in the same manner as in the embodiment.
Among them, when the silver nanocrystal layer is formed on both the semiconductor chip 15 and the lead frame 16, the semiconductor chip 15 and the lead frame 16 are not heated before and during the die bonding, and heating is started after the die bonding. (Because preheating causes sintering of the silver nanocrystal layer before die bonding).
Further, when the silver nanocrystal layer 12 is not formed on the semiconductor chip 15 and the silver nanocrystal layer is formed in the bonding region of the lead frame 16, the semiconductor chip 15 or its bonding portion (chip) before and during die bonding. The back metal 19) may be preheated.
(15) In the fourth step of Example 2, tON of the applied pulse current is 10 msec, 20 msec and 40 msec, tOFF is 400 msec, and the current density of the applied pulse current is 21 A / dm ² when tON is 10 msec. , 4 A / dm ² when tON is 20 msec and 40 msec. These are conditions such as the type of aqueous electrolyte, the metal concentration in the liquid, the shape of the bathtub 4 and the shapes of both electrodes, the pulse power capacity and the economic efficiency. It is set appropriately considering the constraints such as
Note that setting tON short and tOFF long is suitable for reducing the thickness of the diffusion layer and keeping the ion concentration on the electrode surface high.

DESCRIPTION OF SYMBOLS 1 Cathode cartridge 2 Crosshead rotor 3 Anode jig 4 1st bathtub 5 2nd bathtub 6 Stirrer 7 DC power supply 8 Cathode 9 Anode 10 Anode electrode 11 Semiconductor wafer 12 Silver nanocrystal layer 13 Wafer fixing sheet 14 Blade 15 Semiconductor Chip 16 Lead frame 17 Homing gas 18 Silver plating layer 19 Chip back metal 20 Bonding layer 21 Mold resin

Claims (9)

A bonding material for a semiconductor device formed by electrolysis in both or any one of a bonding portion of the semiconductor chip and a bonding region of the support for bonding a semiconductor chip and a support,
A metal nanocrystal having an average particle size of 20 nm to 500 nm is laminated, and is composed of a metal nanocrystal layer not containing a halide.   The bonding material for a semiconductor device according to claim 1, wherein the metal nanocrystal layer does not contain phosphorus and a phosphorus compound.   The bonding material for a semiconductor device according to claim 1 or 2, wherein the bonding material for a semiconductor device formed in the bonding region of the support has a maximum cross-sectional height of less than 4 µm.   4. The bonding material for a semiconductor device according to claim 1, wherein an average particle diameter of the metal nanocrystal is 50 nm to 200 nm.   5. The bonding material for a semiconductor device according to claim 1, wherein the undulation of the surface of the metal nanocrystal layer is 0.38 μm or less. A first step of preparing an electrolysis cell having an anode and a cathode;
A second step of introducing an aqueous electrolyte not containing a halide by dissolving a metal salt and a complexing agent in a solvent in the electrolytic cell;
A third step of connecting a semiconductor chip or a support to the cathode and immersing in the aqueous electrolyte;
While maintaining the aqueous electrolyte in a predetermined temperature range, a direct current or a pulse current is allowed to flow between the anode and the cathode, and an average particle size of 20 nm to 20 mm in the junction of the semiconductor chip or the junction region of the support A method for producing a bonding material for a semiconductor device, comprising: a fourth step of forming metal nanocrystal layers by laminating metal nanocrystals of 500 nm.   The method for manufacturing a bonding material for a semiconductor device according to claim 6, wherein the aqueous electrolyte does not contain phosphorus and a phosphorus compound.   8. The method of manufacturing a bonding material for a semiconductor device according to claim 6, wherein the maximum cross-sectional height of the bonding region of the support is less than 4 [mu] m.   The method for producing a bonding material for a semiconductor device according to claim 6, wherein the metal nanocrystals have an average particle size of 50 nm to 200 nm.