JPH11163016A - Small gold ball for bump and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain small gold balls for bump which have such good deformability and sufficient joining strength that can cope with a reduction in pitch, by constituting the gold balls containing one or more kinds of metals selected from among Cu, Pd, and Pt at specific percents by weight and inevitable impurities. SOLUTION: A gold alloy ingot is obtained by mixing 0.03-5 wt.% of one or more kinds of metals selected from among Cu, Pd, and Pt in electrolytic gold with purity of about 99.999% containing inevitable impurities by the high- frequency vacuum melting method and rolled to a ribbon-like shape. A metallic foil thus obtained is cut into small pieces, and small gold balls 1 are formed by melting and solidifying the small pieces by letting the pieces fall in a heated furnace. The balls 1 are used as bumps and sucked to a substrate 4 for arranging bumps by vacuum. Then, the A1 electrodes 2 of a semiconductor chip 3 are placed aligned on the balls 1 and joined to the balls 1 by pressing the electrodes 2 against the balls 1 by means of a bonding tool.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine gold ball for a bump used for connecting an electrode on a semiconductor element to an external lead, a semiconductor element connected using the fine gold ball, and a semiconductor device. is there.

[0002]

2. Description of the Related Art A bonding wire method using a fine wire having a wire diameter of 20 to 50 .mu.m is used as a connection method for obtaining electrical continuity between an internal wiring on a semiconductor element such as an IC or an LSI, an external lead portion and a substrate. There is a method of connection using metal protrusions called TAB (Tape (Tape)).
Automated Bonding) and FC (Flip Chip) methods.

[0003] The wire used in the wire bonding method is mainly composed of gold, and its alloy component is disclosed in various patent publications. The main purpose of the element addition in the wire is to increase the mechanical properties such as strength and elongation of the wire, and to improve the shape of the connected loop, and the like. High-purity (> 99.99%) gold in the range of less than 10% has been commercialized.

[0004] In the bump connection method, a bump electrically and mechanically connects between two electrodes of a semiconductor element and an external terminal. After being placed on one of the electrodes in advance, the two electrode materials are connected to each other. The connection is made by heating and pressing via the bumps. In order to exhibit these functions effectively, it is considered that the shape of the bump is desirably spherical, which is easily deformed. However, most of the bumps in practical use have a rectangular parallelepiped shape. This is because the formation of the bump mainly depends on the plating method. The current method of producing bumps can be roughly classified into a method in which a metal serving as a bump is plated directly on the electrode portion of a semiconductor element and a tip portion of a lead, and a method in which a bump once formed on a glass substrate is transferred to a lead portion. Mainstream.

[0005] However, the bump forming method by plating requires large equipment and is disadvantageous in terms of manufacturing cost for forming bumps of various kinds in small quantities. In addition, there is a limitation on the composition of the metal formed as the bump. Furthermore, when bumps are formed directly on the electrode portions of the semiconductor chip by plating, there is a concern that the yield may be reduced because the semiconductor chip passes through a plating process.

As a method of solving these problems, there is a method of forming bumps using fine metal spheres without using plating. As a method of manufacturing a metal ball for forming a bump, for example, in Japanese Patent Application Laid-Open No. 4-66602, a thin metal wire used as a material for a bump is used, cut into fixed lengths, and the cut pieces are melted in a state where they are separated from each other. , A method of obtaining a metal sphere using solidification and surface tension. Also, Japanese Patent Application Laid-Open No. 4-66602 proposes manufacturing a fine metal ball by dropping a metal piece cut to a fixed size in a furnace. According to these methods, a large amount of fine metal spheres having a uniform diameter can be obtained at various sphere diameters.

As a connection method using the minute gold balls as bumps, the minute gold balls shown in FIG. 1A are bonded to a thin film of Al and an Al alloy on a semiconductor element by thermocompression bonding. A semiconductor device with a bump as shown in b) is manufactured. Further, the bump portion of the bumped semiconductor element is aligned with the electrode portion on the substrate and the tape to form a semiconductor device as shown in FIG.

The use of bump connection with minute gold balls is effective for reducing the thickness of a semiconductor package, is advantageous for high-density mounting such as narrow-pitch connection, and is excellent in mass productivity such as collective joining of multiple pins. . Therefore, in addition to the FC method, the bonding technique is effective for a BGA (Ball Grid Array) and a CSP (Chip Size Package) using bumps.

[0009] As an alloy component of the fine gold balls for forming bumps, for example, Japanese Patent Application Laid-Open No. 7-283226 discloses that
-0.02% by weight, Pd and Cu0.
0005-0.02% by weight and Ag in a range of 0.0005-0.005% by weight are disclosed. JP-A-7-283227 discloses that Pt is 0.001-0.05% by weight and In is 0.001-0.005% by weight. And the like are disclosed.

[0010]

As described above, the bumps formed by the plating method put into practical use include:
Gold with a purity of 99.99% or more was used, and it was difficult to add elements. Therefore, the hardness of the as-plated component is relatively high, and the hardness has been adjusted by heat treatment after plating in order to obtain hardness suitable for bonding.

On the other hand, in terms of sphericity and precision, a method of melting a small piece of gold to form a spherical shape as described above is excellent for a spherical bump, but a gold bump formed into a molten spherical shape has a low hardness, There is a concern that the bondability will decrease. As an advantage of the spherical bump different from the plating method, an alloy component can be contained in advance, and a bump made of various gold alloys can be easily formed by dissolving the material to produce fine balls.

The present inventors have conducted various studies on bonding techniques for gold balls for bumps. As a result, among the various required characteristics, in particular, the bonding properties with the electrodes, the deformability of the balls, the heat distortion resistance, and the like. We found that it was an issue to comprehensively satisfy the reliability and the like.

In order to bond an Au ball to an Al electrode, it is necessary to break the Al oxide film on the electrode surface to expose a new metal surface of Al and to perform good metal bonding of Au and Al.
In the wire bonding method, in addition to a load for deforming the ball portion at the tip of the Au wire, an ultrasonic vibration is further applied to promote the destruction of the Al oxide film, so that A
This improves the bonding between u and Al. On the other hand, in the method of joining a large number of ball bumps at a time by thermocompression bonding,
Normally, bonding is performed without applying ultrasonic waves. Therefore, material selection is more important for improving bonding properties than in the case of a ball portion of wire bonding.

Further, the present inventors' research on a ball material suitable for narrow pitch bonding has revealed that, in addition to the above-mentioned bondability, the deformability of the ball is also an important factor. In the wire bonding method, in the process of melting the tip of the Au wire to form the ball portion, the ball portion is rapidly cooled by heat conduction to the wire, and the crystal grains in the ball tend to be refined, Furthermore, since the pressure is deformed while constraining the ball at the concentric tip of the capillary, the deformation proceeds relatively isotropically. On the other hand, since bump balls are formed by melting metal pieces, the crystal grains in the balls tend to become coarse and tend to exhibit anisotropy when the crystal grains are deformed, such as contact between adjacent bumps and reduction in bonding strength. Is a problem.

Further, in connecting a semiconductor chip and a substrate or a tape, which are made of different materials such as thermal expansion coefficients, the current wire connection also has a function of relaxing the bus portion of the wire. The mechanical strength is secured only through the 10 μm bumps, and there is a concern that the bonding reliability may be reduced due to shear stress such as thermal strain. The reliability required for the joint of the ball bumps is different from that of the wire, and high reliability is required for external factors.

As described above, unlike the wire bonding method, it is important to select an alloy component and a content suitable for the fine gold ball for the bump in the required characteristics of the ball bump connection, unlike the wire bonding method.

The present invention provides a fine gold ball suitable for high-density mounting by obtaining good deformability and sufficient bonding strength corresponding to a narrow pitch and having high long-term reliability. It is an object of the present invention to provide a bumped semiconductor element and a semiconductor device connected using gold balls.

[0018]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have studied various alloy components in the fine gold balls for bumps. As a result, they have found alloying to improve key properties such as the bondability between the micro gold ball and the electrode film, ball deformability, thermal strain resistance, and long-term reliability. The gist of the present invention is as follows.

(1) A fine gold ball for a bump comprising one or more of Cu, Pd, and Pt in a total amount of 0.03 to 5% by weight, with the balance being gold and unavoidable impurities. (2) at least one of Cu, Pd and Pt is 0.03 in total
Ca, Be, Y, Ce, L
A fine gold ball for a bump, comprising at least one of a in a range of 0.0005 to 0.04% by weight in total, and the balance being gold and unavoidable impurities. (3) at least one of Cu, Pd and Pt in a total of 0.03
1 to 5% by weight, and at least one of Mn and Cr in a total amount of 0.01 to 0.2% by weight, with the balance being gold and unavoidable impurities. Tiny gold balls. (4) at least one of Cu, Pd, and Pt is 0.03
Ca, Be, Y, Ce, L
a in a range of 0.0005 to 0.04% by weight in total, and one or more of Mn and Cr in a total of 0.01%
A fine gold ball for a bump, which is contained in an amount of up to 0.2% by weight, with the balance being gold and unavoidable impurities. (5) A semiconductor device with bumps connected by the fine gold balls according to (1) to (4). (6) The fine gold balls according to (1) to (4),
A semiconductor device with bumps, wherein the semiconductor device is connected to an Al or Al alloy electrode film on the semiconductor device. (7) A semiconductor device having a connection structure using the fine gold balls described in (1) to (4).

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The structure of the present invention relating to a fine gold ball for a bump will be further described below. Pure Al, Al-Si, Al-Si-Cu alloy and the like are used as electrode materials for semiconductor chips. An Al oxide film is formed on the surface of the Al electrode, which affects the bonding property with the Au ball. In order to improve the bondability between gold and the aluminum electrode film, it is necessary to break down the oxide film on the surface of the aluminum thin film to expose the new metal surface of aluminum, and to diffuse and bond gold and aluminum. Ball hardness is low,
At the time of joining, deformation of only the gold ball was mainly involved, and the area of metal joining with the new aluminum surface was reduced, making it difficult to increase the joining strength. In order to increase the bonding strength, it is effective to promote diffusion in order to form an Au / Al intermetallic compound layer at the bonding interface. From the above, in the gold ball for the bump, the Al
It is important to have mechanical properties that effectively act on the destruction of the oxide film, and to further increase the bonding strength by growing an intermetallic compound layer at the bonding interface between Au and Al.

Further, it is important to improve long-term reliability at the time of use, in addition to the improvement of the bonding property, at the bump bonding portion. As described above, since the chip and the substrate are connected via the ball portion, the chip has a strength that can withstand thermal distortion, and is exposed to a high-temperature environment during use. It is necessary that no Cu is generated and that the corrosion reaction between the Au / Al compound phase and the resin component is suppressed even in the resin-sealed state.

As described above, it is important to select appropriate hardness, deformability, diffusivity at the bonding interface, etc. in order to enhance the bonding property and bonding reliability of the Au ball bump with the Al thin film. . It has been found that in order to comprehensively improve these required characteristics, it is effective to select the components of the alloy element added to the Au ball and to optimize the concentration.
That is, if the ball portion becomes excessively hard or the crystal grains in the ball become too fine, it may cause damage to the chip at the time of joining and cause the joining property to deteriorate, so that it is suitable for Au ball bump joining. Ingredients and concentrations must be selected.

By adding at least one of Cu, Pd and Pt (first element group) to Au, the Al oxide film is destroyed,
By promoting the diffusion of Au and Al, the bonding strength with the Al thin film is increased, and the crystal grains are refined, whereby the deformation anisotropy can be reduced. In terms of reliability, even when the compound is grown by heating at a high temperature for a long time, no void growth is observed, and a corrosion reaction with the sealing resin is suppressed. In order to exhibit such effects, at least a total concentration of 0.03% by weight or more is required. If the amount of addition is too large, it becomes too hard, so that the content is not more than 5% by weight.

Further, in addition to the first element group, Ca, Be,
One or more of Y, Ce, and La (the second group of elements) are contained in a total of 0.
When contained in the range of 0005 to 0.04% by weight, the high-temperature strength of the ball bump at the time of thermocompression bonding is increased, thereby increasing the bonding strength and further improving the deformation anisotropy. As the above effects, the addition of Ca, Be, Y, Ce, and La promotes the deformation resistance at high temperatures, thereby effectively acting on the destruction of the Al oxide film, and promoting the miniaturization of crystal grains after solidification. , Cu, Pd, and Pt are combined to further enhance the effect. In order to achieve such effects, a total concentration of at least 0.0005% by weight is necessary. When the amount of addition is large, these elements are segregated on the surface during the production of the ball, and the bonding strength is reduced. Therefore, the content was set not to exceed 0.04% by weight. Further, the concentration range of Cu, Pd and Pt is set to 0.03.
The range of 範 囲 5% by weight is based on the reason described above.

In addition to the first element group, one or more of Mn and Cr (third element group) are contained in a total amount of 0.01 to 0.2% by weight, so that the Au / Al joint is formed. High temperature reliability is further improved. In particular, the improvement of the corrosion resistance of the Au / Al compound is remarkable, and the effect is further enhanced by the complex addition with Cu, Pd, and Pt. In order to exhibit such effects, a total concentration of at least 0.01% by weight or more is required. If the addition amount is large, segregation on the surface during ball production lowers the bonding strength. .2% by weight.

Further, by using the first element group, the second element group, and the third element group together, the joining property, the deformation anisotropy, and the joining reliability are improved. The generation of voids is greatly suppressed. As described above, this effect can be obtained even with the first element group, but the effect of suppressing voids is further enhanced by adding three kinds of composites,
This effect is more effective as the film thickness increases. Au / Al
As the compound grows, voids are also generated. Therefore, as the Al film thickness increases, the compound phase thickness increases, resulting in an increase in the size and occurrence frequency of voids. Al thin films tend to be thinner as the wiring becomes thinner to achieve high integration of semiconductors. However, when the thickness of Al thin films is 0.8 μm or more, the above three types of composite addition are particularly effective. It was confirmed that. Here, the content of each element group was determined based on the reasons described above.

The semiconductor device with bumps connected by the fine gold balls containing the alloy component described above has good bonding properties, excellent mass productivity in connection, and enables narrow pitch connection. Furthermore, in a semiconductor device connected to a substrate or tape using the semiconductor device with bumps, even if the semiconductor is used in a high-temperature environment due to heat generation during operation, it is resistant to stress and fatigue caused by thermal strain, and has a long life. The reliability is greatly improved.

[0028]

Embodiments will be described below. Gold purity is about
A gold alloy ingot (5.
mm diameter), which was rolled into a 25 μm thick ribbon. This metal foil was cut into small pieces corresponding to 50 μm diameter spheres, dropped in a furnace heated to 1500 ° C., melted and solidified to produce balls. The balls were used as bumps, adsorbed to a bump arrangement substrate, and Al electrodes of a semiconductor chip were aligned and superimposed thereon, and bonded by pressing with a bonding tool (referred to as primary bonding). Here, the stage on which the semiconductor chip is mounted is heated to 300 ° C. As for the deformation of the bump, bonding conditions were selected so as to obtain a pressure bonding diameter of about 1.2 times the initial ball diameter so that bonding to the Al electrode was surely performed and separation did not occur in a later step. Next, the bumps on the semiconductor chip were aligned with the electrode portions on the substrate, and were thermocompression bonded using a bonding tool (secondary bonding).

Tables 1 and 2 also show the results of investigations on the performance of the obtained gold alloy thin wires, mainly on the bonding properties for use in semiconductor devices.

In order to evaluate the bonding strength of the bonding portion between the Au ball bump and the Al electrode, each of the balls bonded on the Al electrode by the primary bonding was prepared without performing the secondary bonding to the substrate. Measured by shear strength test method,
The average value of the breaking loads of the 20 ball joints was measured.
Regarding the deformation anisotropy, the ball bump on the Al electrode was observed from above, and the ratio f / d of the longest diameter d and the shortest diameter f of the ball after the pressure deformation was measured.
The average value of the books was determined. Furthermore, ball bumps and Al
After dissolving the electrode film with aqua regia, the surface of the silicon chip directly under the 20 bumps was observed by SEM, and if there was damage such as cracks or voids under one or more of the electrodes, it was marked with △. The case where it cannot be performed is indicated by a circle.

As a reliability evaluation, a semiconductor device in which a gold ball was bonded to an aluminum electrode was subjected to a heat treatment at 200 ° C. for 200 hours in a nitrogen gas without resin sealing, and then an average value of 40 shear tests was performed. The joining strength was measured. Further, as an evaluation of void formation, a ball joint was vertically polished, and ten joint cross sections were observed. In the cross section of the joint, if there is even one joint where a plurality of voids of 2 μm or more are generated at the center of the joint, there is a concern that the reliability may be adversely affected. In the case where voids as small as about are formed, the bonding strength is not reduced, and the mark ○ is given. When no voids of 1 μm or more are found in all the joints, the reliability is judged to be good. Indicated by a mark.

As for the investigation of the corrosion at the joint, the semiconductor device to which the gold wire was joined was sealed with a commercially available epoxy resin, and then heated at 200 ° C. for 300 hours. The corrosion of the grown intermetallic compound layer of gold and aluminum was observed. The progress of the corrosion of the intermetallic compound at the ball joint was examined using the fact that the intermetallic compound layer was gray and the compound layer where the corrosion had progressed became brown and could be easily identified. The progress of corrosion of the intermetallic compound is evaluated by the ratio of the length of the corroded region (b) to the length of the intermetallic compound layer growth (a) in the polished cross section of the ball joint, and the ratio of the corroded portion. When the value of (a / b) averaged at 30 ball joints is 5% or less, it is judged that the suppression of corrosion is remarkable. Those having an intermediate value of 5% to 40% were marked with a circle.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

In Tables 1 and 2, Examples 1 to 11 relate to the first claim of the present invention.
24 is the second term, Examples 25 to 29 are the third term, Example 30
32 are the results of the gold ball bump according to the fourth claim. In Table 3, which is a comparative example, Comparative Example 1 is pure gold of high purity (> 99.99%), and Comparative Examples 2 to 9 are cases where they are not included in the range of the components described in the first claim. Example 1
In the case of 0 to 13, the first element group falls within the range described in the first claim, but the second element group does not correspond to the second claim. In Comparative Examples 14 to 17, the first element group belongs to the first claim. The results are shown in the case where the third element group does not correspond to the third claim, though it is within the scope of one claim.

In Examples 1 to 11, Cu, Pd, and Pt were within the above concentration range, the initial shear strength was as high as 40 gf or more, the anisotropy was as small as 1.15 or less as an evaluation standard, and the comparison with high-purity gold was performed. It was confirmed that it was clearly improved as compared with Example 1. Here, in Comparative Examples 2, 4, 6, and 8 in which the concentration is less than 0.03% by weight, the effect is small. On the other hand, when the concentration exceeds 5% by weight, the ball is hardened, and the chip is slightly formed. Damage was observed.

In Examples 12 to 24, the element group of Cu, Pd, and Pt and the element group of Ca, Be, Y, Ce, and La were contained in appropriate amounts, and the deformation anisotropy was very small. In the case of, it was kept to a range lower than 1.05, which was difficult to achieve. It was confirmed that the initial bonding strength was in the range of 45 gf or more, which was about 10% higher than the case of the first item, and that the bonding strength after heating was 50 gf or more, especially higher than the case of the first item. This is considered to be because the destruction of the Al oxide film was promoted immediately after the bonding, and the uniform growth of the Au / Al compound was promoted after heating.

In Examples 25 to 29, Cu, Pd, Pt
And an appropriate amount of the element group of Mn and Cr, and the characteristic feature is that the corrosion of the joint is suppressed by heating after resin sealing. Here, Comparative Example 1 containing only Mn and Cr
In Examples 8 and 19, the effect of improving the corrosion resistance was small, and the bonding strength was about the same as 5N. From this, the first
The effect of the composite addition of the element group and the third element group was confirmed.

In Examples 30 to 32, the third embodiment according to the present invention
It contains all the element groups of the species, and in addition to the above-described bonding properties and corrosion resistance, no voids were formed even in the compound growth at the bonding portion, and very good reliability was confirmed.

In these experiments, a comparison was made using pure aluminum as the electrode film, and it was also confirmed that the bonding properties, deformability and reliability were good for Al-Si and Al-Cu as well. doing.

[0042]

As described above, by using a gold ball made of the gold alloy of the present invention as a bump,
High bonding strength, low anisotropy during deformation, and excellent long-term reliability. Furthermore, flip chip, BGA, CS
When used for mounting of P or the like, a semiconductor device which is advantageous for reduction in thickness and size and has extremely high reliability is provided.

[Brief description of the drawings]

1A shows a fine gold ball, FIG. 1B shows a semiconductor device with a bump in which the fine gold ball is connected to an electrode portion, and FIG. 1C shows a bump portion of the semiconductor device with a bump, a substrate and a tape. The semiconductor device connected to the upper electrode unit is shown.

[Explanation of symbols]

 1: Fine gold ball 2: Electrode 3: Semiconductor element 4: Substrate or tape

Claims (7)

[Claims] 1. A fine gold ball for a bump, comprising one or more of Cu, Pd and Pt in a total amount of 0.03 to 5% by weight, with the balance being gold and unavoidable impurities. 2. It contains one or more of Cu, Pd and Pt in a total amount of 0.03 to 5% by weight, and contains Ca, Be, Y,
At least one of Ce and La is 0.0005 to 0.04 in total.
A fine gold ball for a bump, which is contained in the range of weight% and the balance is made of gold and unavoidable impurities. 3. A composition containing one or more of Cu, Pd, and Pt in a total amount of 0.03 to 5% by weight, and one or more of Mn and Cr in a total amount of 0.01 to 0.2% by weight. Contained in the range,
A minute gold ball for bumps, the balance being made of gold and unavoidable impurities. 4. It contains one or more of Cu, Pd and Pt in a total amount of 0.03 to 5% by weight, and contains Ca, Be, Y,
At least one of Ce and La is 0.0005 to 0.04 in total.
1% by weight of at least one of Mn and Cr in a total range of 0.01 to 0.2% by weight, with the balance being gold and unavoidable impurities. ball. 5. The semiconductor device with bumps connected by the fine gold balls according to claim 1. 6. A semiconductor device with bumps, wherein the minute gold ball according to claim 1 is connected to an electrode film of Al or an Al alloy on the semiconductor device. 7. A semiconductor device having a connection structure using the minute gold balls according to claim 1.