JP2008218994A - Gold wire for connecting semiconductor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gold wire for connecting semiconductors for use in complicated wiring and narrow-pitch wiring, where it is less likely to have leaning failures and is further superior in pressure-bonded shape. <P>SOLUTION: The gold wire for connecting semiconductor elements is characterized by that nickel, beryllium and one or more elements selected from calcium and rare earth elements are added by a defined amount as essential elements, and preferably one or both of titanium and vanadium, and further praseodymium are added by a prescribed amount. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a gold wire for connecting a semiconductor element.

  A bonding wire, which is a semiconductor mounting material, is a material that connects a semiconductor chip and an external metal terminal. At present, most of the materials are mainly gold. This is because a technique called ball bonding, which has a high throughput and high productivity, is used for connecting the semiconductor and the external terminals. Ball bonding is a bonding method in which one end of a metal wire is melted, a ball is formed, and is bonded to one electrode by pressure bonding, and the side surface of the bonding wire is pressure bonded to the other electrode as it is. Here, ball bonding is referred to as first bonding, and bonding in which the side portion of the bonding wire is crimped to an electrode is referred to as second bonding. The reason why gold is often used is that the first bonding property and the second bonding property are hardly deteriorated due to the surface oxidation of the ball or bonding wire, and bonding in the atmosphere is easy.

  The strength of the bonding wire is reinforced by work hardening by wire drawing, but since a sufficient mechanical strength cannot be obtained with pure gold, a trace amount of different elements are added.

  In recent years, the semiconductor mounting size has been reduced, the electrode pad size has been reduced, and the interval has been reduced (narrow pitch). Accordingly, it is necessary to reduce the diameter of the bonding wire, and a gold wire having a diameter of 15 μm has begun to be used. However, when the wire diameter is reduced, in the production of the bonding wire, the strength of the bonding wire is not obtained at the time of drawing, and it becomes difficult to maintain a loop during mounting such as bonding or resin sealing.

  If the pad pitch interval between the bonding wires is narrowed, the risk of short-circuit failure due to contact between the bonding wires increases. The main short-circuit defects in bonding wire mounting include leaning (falling) defects, contact failure of crimped balls, curl (bending) defects, and spring (bending) defects. Here, it is considered that the curl failure is mainly caused when the strain introduced at the time of drawing processing at the time of manufacturing the bonding wire is not axisymmetric and the strain that is not axisymmetric can be removed. Spring failure is considered to be a buckling caused at the time of impact and acceleration of crimping and cutting during bonding mounting.

  1A and 1B are schematic views illustrating a bonding wire in which a leaning defect has occurred. As shown in FIGS. 1A and 1B, the leaning failure means that when the bonding wire 1 is observed from the extending direction of the loop, the upper portion of the press-bonded ball 3a bonded to the pad 2a is the extending direction of the loop ( The bonding wire 1a is bent in a direction perpendicular to the wire loop surface) and falls down to the adjacent bonding wire 1b. Unlike the curl defect in which the entire bonding wire is curved, the bonding wire is inferior even though the entire bonding wire is relatively straight. This leaning failure is also called neck fall because it bends from the neck portion directly above the ball. Although the leaning defect is different from the curl defect, the curl provides an opportunity to cause the wire to fall down. In a bonding wire having a curl defect, a stress that causes the bonding wire to fall is generated after the loop is formed, so that a leaning defect is likely to occur. Leaning defects are likely to occur synergistically as the diameter of the gold wire is reduced.

  When the straightness of the bonding wire is high and the strength is sufficiently high, a leaning defect is unlikely to occur. However, even if the straightness is high, it may occur with a certain probability due to impact and operation during bonding. In addition, even a bonding wire having the same bus bar strength and the same straightness may have a large difference in the probability of causing a leaning defect.

  FIGS. 1A and 1B show the form of contact failure of a ball (crimp ball) 3c bonded to the pad 2c at the same time. The bonding shape of the first bonded ball 3c is deviated from a perfect circle, and the ball 3c protrudes into the adjacent pad 2d and shorts. For this reason, in the bonding wire, there is a demand for a bonding wire having an excellent ball crimping shape while preventing leaning defects. Note that the deviation from the perfect circle means that the crimped shape as shown in FIGS. 1A and 1B has a petal-like unevenness or the influence of ultrasonic waves that assist the bonding during bonding. An example is one in which anisotropy occurs in the ball deformation in the direction of the sound wave and the direction perpendicular thereto, and the crimping shape becomes an ellipse.

Several methods for preventing leaning have been proposed.Basically, it is to improve the straightness of the bonding wire, but it is possible to increase the strength by adding Be, Ca, Ce, La, and to devise the process (for example, , Patent Document 1), a method of adding yttrium (see, for example, Patent Document 2), a method of taking a process that does not go through a rolling process (for example, see Patent Document 3), a method of devising intermediate annealing conditions (for example, Patent Documents 4 and 5), methods for devising casting conditions (for example, see Patent Document 6), and the like have been proposed.
JP 2005-294681 JP 2006-73693 A JP 2006-147893 JP Japanese Patent Laid-Open No. 2002-319597 JP 2005-347433 A JP 2005-138113-A

  However, in recent years, the problem of leaning has become more likely to occur due to the thinning of bonding wires, the increase in the number of multi-stage wirings, and the increase in the number of loops in a complicated loop shape of staggered wiring. There is a need for improvement.

  The present invention solves the above-described problems, and provides a semiconductor mounting gold wire for complex wiring and narrow pitch wiring, which is less likely to cause leaning defects and has an excellent crimped shape.

  The present invention is summarized as follows as a result of intensive studies to solve the above-described problems of the prior art.

  The gold wire for semiconductor element connection according to claim 1 of the present invention has a nickel content of 0.0007 mass% or more and less than 0.005 mass%, a beryllium content of 0.0003 mass% or more and 0.0008 mass% or less, and calcium and A gold wire for connecting a semiconductor element, wherein the content of one or more elements selected from rare earth elements is more than 0.0009% by mass and 0.02% by mass or less.

  The gold wire for semiconductor element connection according to claim 2 of the present invention has a nickel content of 0.0007 mass% or more and 0.005 mass% or less, and the addition amount of either one or both of titanium and vanadium is 0.0005 mass% or more. A gold wire for connecting a semiconductor element, characterized in that the content of one or more elements selected from 0.005 mass% or less and calcium and rare earth elements is more than 0.0009 mass% and 0.02 mass% or less.

  The gold wire for connecting a semiconductor element according to claim 3 of the present invention has a nickel content of 0.0007 mass% or more and 0.007 mass% or less, a beryllium content of 0.0003 mass% or more and 0.0008 mass% or less, and titanium and The addition amount of either or both of vanadium is 0.0005 mass% or more and 0.005 mass% or less, and the content of one or more elements selected from calcium and rare earth elements is more than 0.0009 mass% and 0.02 mass% or less There is a gold wire for connecting a semiconductor element.

  4. The semiconductor element connecting gold wire according to claim 4 of the present invention, wherein the praseodymium content is 0.0016 mass% or more and 0.02 mass% or less. It is a gold wire for element connection.

  The gold wire for connecting a semiconductor element according to claim 5 of the present invention is characterized in that the addition amount of either one or both of indium and gallium is 0.0005 mass% or more and 0.005 mass% or less. A gold wire for connecting a semiconductor element according to any one of the above.

  The gold wire for semiconductor element connection according to claim 6 of the present invention contains 0.001% by mass or more and 2% by mass or less of palladium. It is.

  The gold wire for semiconductor element connection according to claim 7 of the present invention contains 0.001 mass% or more and 0.005 mass% or less of magnesium in the semiconductor element connection gold wire according to any one of claims 1 to 6. It is.

  According to claim 8 of the present invention, in the semiconductor element connecting gold wire, one of the (111) plane normals of the individual crystal grains constituting the wire has an angle of 15 ° or less with respect to the length direction of the wire. The semiconductor element connection according to any one of claims 1 to 7, wherein a ratio of crystal grains having a cross-sectional area ratio of 50% or more with respect to the whole is <111> -oriented in a length direction. A gold wire.

  According to the gold wire for semiconductor element connection of the present invention, the strength and Young's modulus of the gold wire are improved by containing a specific amount of one or more elements selected from calcium and rare earth elements, and a specific amount of nickel is added. The inclusion improves the strength of the neck portion, and the roundness deterioration of the pressure-bonded shape of the ball caused by the inclusion of nickel can be suppressed by adding beryllium. Moreover, the roundness deterioration of the press-bonded shape of the ball caused by containing nickel can be suppressed by adding one or both of titanium and vanadium. In particular, by making a comprehensive alloy design that increases the praseodymium content and increases the length of the heat-affected zone of the neck portion, it becomes difficult to cause leaning defects. Accordingly, it is possible to provide a semiconductor mounting gold wire for complicated wiring and narrow pitch wiring, which is less likely to cause leaning defects and has an excellent crimped shape.

  The suppression of the leaning failure in the present invention is based on the improvement of the wire strength, the improvement of the neck portion strength, and the control of the neck portion softening length.

  The strength of the bonding wire is increased by wire drawing and addition of alloy elements. The addition of alloy elements also contributes to strengthening of the work during wire drawing. Calcium and rare earth elements have a great work strengthening at the time of wire drawing. Here, the rare earth elements are lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium and yttrium. Among the above elements, calcium, lanthanum, cerium, praseodymium, neodymium, and samarium are particularly effective. By adding these elements, work hardening is increased, the bus bar strength is increased, the <111> orientation, which is the wire drawing texture, is strengthened in the longitudinal direction of the wire, and the Young's modulus is increased. As a result, the antagonistic force in the direction perpendicular to the wire loop surface increases.

  Depending on the bonding method and loop shape, when the total amount of calcium and rare earth elements is 0.0009% by mass or less, it is difficult to produce a material that is resistant to leaning defects within the range of the additive element of the present invention. Therefore, when only calcium is included among calcium and rare earth elements, the calcium content is preferably more than 0.0009% by mass, and when calcium and rare earth elements are included, calcium and rare earth elements are included. It is desirable that the total amount with the elements exceeds 0.0009% by mass.

  Processing with a cross-sectional reduction rate of 99.8% or more in wire drawing, and the proportion of <111> -oriented crystal grains in the wire drawing direction is 50% or more in terms of cross-sectional area in the bonding wire It is desirable. Here, the <111> -oriented crystal grains mean that one of the (111) plane normals of the crystal grains has an angle of 15 ° or less with respect to the length direction (drawing direction) of the bonding wire. Refers to the crystal grains.

  On the other hand, when the addition amount of these elements is increased, the roundness of the press-bonded ball is deteriorated. That is, when the tip of the gold wire melts when forming a free air ball (also simply called a ball) that is discharged to the wire tip and melted and solidified, the ball surface concentration of calcium and rare earth elements decreases due to oxidation near the ball surface, The heat is extracted from the surface and solidifies before the inside of the ball. As a result, a nest is formed at the tip of the ball, and the nest and the surface layer itself inhibit the isotropic deformation of the ball during the pressure bonding of the ball, thereby degrading the roundness of the pressure-bonded ball. If these elements are added in an amount exceeding 0.02 mass%, when ball bonding is performed in the air, the deterioration of the bonding property due to the oxidation of the balls becomes significant, and it cannot be put into practical use. Therefore, when only calcium is included among calcium and rare earth elements, the content of calcium is preferably 0.02% by mass or less, and when calcium and rare earth elements are included, calcium and rare earth elements are included. The content with the element is preferably 0.02% by mass or less.

  Nickel is also an element that increases the gold wire strength. However, unlike calcium and rare earth elements, the solid solution strengthening action is high. Therefore, the strength of the neck portion is improved.

  In ball bonding, the tip of the bonding wire is melted by arc discharge to form a ball, and this is crimped and first bonded. Therefore, the upper part of the ball hits the heat-affected zone (HAZ) and is a softened region in which dislocations move and decrease due to heat and processing strain is reduced. Therefore, leaning failure is caused by bending at the heat-affected zone with the press-bonded ball portion as a fixed point.

  Calcium and rare earth elements greatly increase the bus bar strength because of their large work strengthening effect, but correspondingly lower the relative strength of the neck with respect to the bus bar. As a result, when an external force is applied due to some influence in a direction perpendicular to the loop surface, stress concentrates on the neck portion, and leaning defects are likely to occur.

  Nickel does not have a large work strengthening effect within the range of the addition amount of the present invention, and conversely, since the solid solution strengthening action is large, in addition to increasing the strength of the heat affected zone itself, the relative strength difference from the bus bar is also reduced. There is an effect. Although depending on bonding conditions and loop shape, an additive amount less than 0.0007% by mass has little effect for suppressing leaning defects. Although the effect of suppressing leaning defects increases as the amount of nickel added increases, the addition of nickel has a large effect of deteriorating the pressure-bonded shape of the ball. Therefore, it is necessary to add an element that suppresses this.

  In order to suppress the leaning failure in the present invention, the minimum condition for obtaining the antagonistic force from the direction perpendicular to the loop is that the content of at least one element selected from calcium and rare earth elements exceeds 0.0009% by mass In addition, the nickel content is 0.0007% by mass or more. However, when this amount of component element is included, the roundness of the press-bonded ball is deteriorated, so it is desirable to add 0.0003% by mass or more of beryllium as an element for adjusting the press-fit shape of the ball. Beryllium is an element that increases deformation resistance. In particular, it has an effect of suppressing the pressure-bonded diameter of the ball from extending in the ultrasonic direction by application of ultrasonic waves during bonding. It is desirable to increase the amount of beryllium as the amount of calcium, rare earth element, or nickel is increased. However, since beryllium is easily oxidized and has a high diffusion rate, it is easy to form an oxide on the gold wire surface. As a result, the second bondability may be deteriorated. Further, it is easy to form an oxide on the ball surface during ball formation during bonding. From this point of view, it is desirable that the amount of beryllium added is 0.0008% by mass or less, particularly when used in combination with nickel. If it is this range, said advantage is large with respect to first joining property.

  Even if beryllium is added, if the addition amount of nickel is 0.005% by mass or more, or the content of at least one element selected from calcium and rare earth elements exceeds 0.02% by mass, a sound first bonding is difficult. become.

  Elements other than beryllium that have the effect of adjusting the pressure bonding shape of the ball include titanium and vanadium. Titanium and vanadium act at the time of solidification when discharging from the torch electrode at the time of bonding, melting and solidifying the wire tip to form a ball, and as a result, increase the roundness of the press-bonded ball.

  It is desirable that the addition amount of one or both of titanium and vanadium is 0.0005% by mass or more and 0.005% by mass or less, and if it is less than 0.0005% by mass, there is no effect, and if it is greater than 0.005% by mass, a healthy first is obtained. Joining becomes difficult.

  Even if one or both of titanium and vanadium are added, the addition amount of nickel exceeds 0.005 mass%, and the content of at least one element selected from calcium and rare earth elements exceeds 0.02 mass% Sound first bonding becomes difficult.

  The action of beryllium and the action of titanium and vanadium are the same in terms of adjusting the shape of the press-bonded ball. However, since the mechanism is different, a larger effect can be obtained by adding both. In practice, it is an element that suppresses leaning defects by containing beryllium in the range of 0.0003 mass% to 0.0008 mass% and one or both of titanium and vanadium in the range of 0.0005 mass% to 0.005 mass%. Even if the nickel content is increased to 0.007 mass%, it is possible to form a sound first joint.

  Praseodymium is the most excellent element for achieving the object of the present invention among calcium and rare earth elements. This is because the addition efficiency is high with respect to the strength and the influence on the pressure bonding shape of the ball is small. The composition range of praseodymium that satisfies both the strength and the pressure bonding shape of the ball is preferably 0.0016 mass% or more and 0.02 mass% or less. Sound bonding is possible up to 0.02% by mass, but in the case of fine pitch connection of 35-60μm pad pitch, which is expected to become the mainstream in the future, in the case of praseodymium, it is in the range of 0.0016% to 0.010% by mass. By containing, sufficient strength can be obtained at a lower concentration than other elements. By the combined addition with nickel, beryllium, titanium, or vanadium, a bonding wire having excellent leaning characteristics and a ball crimping shape can be manufactured.

  Furthermore, by containing one or both of indium and gallium in the range of 0.0005 mass% or more and 0.005 mass% or less, the bonding strength between the press-bonded ball and the aluminum electrode pad can be increased. Therefore, by combining with the above element group, it is possible to manufacture a bonding wire that is excellent in leaning characteristics, ball crimping shape, and bonding strength.

  Furthermore, by containing palladium in an amount of 0.001% by mass to 2% by mass, the uneven growth of gold and aluminum that grows between the press-bonded ball and the aluminum electrode pad when held at a high temperature is suppressed, and the press-bonding is performed. Suppresses peeling between the ball and the electrode pad. Therefore, by combining with the above element group, a bonding wire excellent in leaning characteristics, ball crimping shape, bonding strength, and high temperature reliability can be manufactured.

  The combination of the above elements is effective for fine wires that tend to cause leaning defects, particularly gold bonding wires having a diameter of 25 μm or less.

  It is desirable not to add any additive element other than the above-mentioned metal because it causes deterioration of the bonding property for the reason of promoting the oxidation of the free air ball. However, metals that are not easily oxidized such as platinum group elements other than palladium, silver, and copper may be contained. In addition, even in other metals, magnesium, germanium, and iron may be included as unavoidable metals because they do not adversely affect the bondability as long as they are 0.005% by mass or less. In particular, magnesium is contained in an amount of 0.001% by mass or more and 0.005% by mass or less, and thereby has an effect of further improving the pressure-bonding ball bonding strength. If it is less than 0.001% by mass, the bonded ball bonding strength may not be improved. If it exceeds 0.005% by mass, good bonding properties may be adversely affected.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this shows a suitable example of this invention, and this invention is not limited at all by the Example.

(Example 1)
A plurality of types of gold wires containing an element arbitrarily selected from calcium, lanthanum, cerium, beryllium, and nickel were manufactured, and leaning defects and crimped ball shapes were evaluated.

  An ingot having a diameter of 5 mm and a length of 100 mm was cast by adding calcium, beryllium, nickel and the like to the raw material having a purity of 99.9998% by mass or more. After casting, the ingot is rolled to about 2 mm square with a grooved rolling mill, and single-head wire drawing is performed to a diameter of 1.0 mm by drawing using a diamond die, and then winding is performed using a continuous wire drawing machine. Drawing was performed with a diamond die in a lubricating liquid at a drawing speed of 20 m / min, and the wire was drawn to 25 μm. Each area reduction per die pass in the continuous drawing process is about 10%. Thereafter, using a tubular furnace, heat treatment (tempering heat treatment) was continuously performed in argon, the temperature was adjusted, and a bonding wire having a breaking elongation of 4% was produced.

  The bonding test was performed using a chip having a pad pitch interval of 70 μm and a pad material of Al. Bonding used 8028pps made by K & S. The crimping diameter of the first joint was set to 65 μm, the loop height from the pad was 450 μm, and the loop length was 3.0 mm. Bonding was performed in the atmosphere, and the chip surface temperature was 180 ° C.

  The bonding characteristics were evaluated by measuring the leaning defect and the defect probability of the press-bonded ball.

  As a reference for the leaning failure, the bonding loop was observed from directly above, and a bonding wire having an interval between bonding wires of 30 μm or less was regarded as a leaning failure, and the occurrence probability of the leaning failure was examined. The number of observed loops is 1000.

  As a reference for the shape defect of the crimp ball, the crimp diameter of the first joint at the ultrasonic application direction and its perpendicular direction is measured, and the value obtained by dividing the crimp diameter of the ultrasonic application perpendicular direction by the crimp diameter of the ultrasonic application direction is Crimp shape failure rate is obtained by dividing the number exceeding 1.1 and the one with the concave outer periphery of the crimp when viewed from the first joining direction during bonding, as a result of dividing the number of observations by the number of observations. It was. The number of crimped balls observed is 200.

  Table 1 shows the results of sampling and component analysis after single head drawing, and the measurement results of mechanical characteristics and bonding characteristics.

  When the content of calcium, praseodymium and cerium was 0.0009% by mass or less (Samples 1 to 3), a leaning failure of 0.5% or more occurred even with a 25 μm wire regardless of whether or not nickel was added. It was also found that the degree of leaning failure was large. This is because the wire strength and Young's modulus itself of the bonding wire are small. Among calcium, praseodymium and cerium, the contribution to strength was greater in the order of praseodymium, calcium and cerium. These elements are elements that increase the work strengthening effect, and mainly increase the bus bar strength, increase the <111> orientation in the wire drawing direction, and increase the Young's modulus. Next, the crystal orientation analysis of the cross-sectional structure of the gold wire shown in Table 1 was performed by an electron backscatter diffraction (EBSD) method. In this case, in the samples 5 to 13 in which the content of calcium alone or the content of the calcium and praseodymium or cerium is 0.0009% by mass or more and the Young's modulus is 85.0 GPa or more, the length direction of the bonding wire (drawing) The ratio of crystal grains in which one of the (111) plane normals of the crystal grains has an angle of 15 ° or less is 50% or more in terms of the sectional area with respect to the whole. I understood.

  For bonding wires that contain only calcium or 0.0009 mass% or more of calcium and praseodymium or cerium, the leaning defects are remarkably improved to 0.5% to 0.1% by adding 0.0007 mass% or more of nickel. (Samples 4, 6-13). Further, when a large amount of nickel was added, the leaning defect was further improved. Wire strength also increased. This is because the solid solution strengthening mechanism worked by adding nickel, and the wire strength and neck strength increased. On the other hand, the addition of nickel resulted in an increase in the poor pressure bonding shape of the balls (see, for example, Samples 5 and 6).

  Addition of 0.0003% by mass or more of beryllium was effective in improving the pressure bonding shape of the ball in the bonding wire added with nickel (see Samples 6 to 8). However, in the bonding wires (samples 12 and 13) containing beryllium in excess of 0.0008 mass%, the pressure bonding shape of the ball was slightly deteriorated.

  When judging whether or not the defect of the leaning and the pressure bonding shape of the ball is defective with the respective probability of failure, 0.5% and 3%, from Table 1, the content of calcium alone or the content of calcium and praseodymium or cerium is 0.0009. It can be confirmed that it is necessary to add more than 0.02 mass%, more than 0.002 mass%, beryllium content is 0.0003 mass% or more and 0.008 mass% or less, and nickel content is 0.0007 mass% or more and less than 0.005 mass%. (Samples 8 to 11). In other words, by including more than 0.0009 mass% of calcium or the calcium and the rare earth element, one of the (111) plane normals of the crystal grains with respect to the length direction (drawing direction) of the bonding wire is 15 By making the ratio of crystal grains having an angle of less than or equal to <111> so that the ratio of the crystal grains occupies 50% or more in terms of the cross-sectional area ratio, and by containing nickel of 0.0007% by mass or more and less than 0.005% by mass It was possible to make a bonding wire with a small leaning defect.

(Example 2)
A plurality of types of gold wires containing an element arbitrarily selected from calcium, lanthanum, beryllium, nickel, titanium, and vanadium were produced, and the leaning defect and the press-bonded ball shape were evaluated.

  An ingot having a diameter of 5 mm and a length of 100 mm was cast by adding calcium, lanthanum, beryllium, nickel, titanium, vanadium, etc. to the raw material having a purity of 99.9998% by mass or more. After casting, the ingot is rolled to about 2 mm square with a grooved rolling mill, and single-head wire drawing is performed to a diameter of 1.0 mm by drawing using a diamond die, and then winding is performed using a continuous wire drawing machine. Drawing was performed with a diamond die in a lubricating liquid at a drawing speed of 20 m / min, and the wire was drawn to 23 μm. Each area reduction per die pass in the continuous drawing process is about 10%. Thereafter, using a tubular furnace, heat treatment (tempering heat treatment) was continuously performed in argon, the temperature was adjusted, and a bonding wire having a breaking elongation of 4% was produced. Leaning defects are likely to occur when the gold wire diameter is reduced by 2 μm. Therefore, the contents of calcium and rare earth elements were increased as compared with Example 1. The addition amount of beryllium was fixed at 0.0008% by mass.

  When the crystal orientation analysis of the cross-sectional structure of the gold wire was performed using the EBSD method on the produced gold wire, with respect to the length direction (drawing direction) of the bonding wire, One of the (111) plane normals of the crystal grains was found to account for 50% or more of the cross-sectional area ratio of the crystal grains having an angle of 15 ° or less.

  The bonding test was performed using a chip having a pad pitch interval of 70 μm and a pad material of Al—Cu. Bonding used 8028pps made by K & S. The crimping diameter of the first joint was set to 44 μm, the loop height from the pad was 450 μm, and the loop length was 3.0 mm. Bonding was performed in the atmosphere, and the chip surface temperature was 180 ° C.

  The evaluation of bonding characteristics was performed by measuring the probability of occurrence of a leaning defect and a crimped shape defect.

  As a criterion for the leaning failure, the bonding post-bonding loop was observed from directly above, and a bonding wire having a bonding wire spacing of 30 μm or less was regarded as a leaning failure, and the occurrence probability was examined. The number of observed loops is 1000.

  As a criterion for crimping shape failure, measure the crimping diameter of the first joint at the ultrasonic application direction and its perpendicular direction, and the value obtained by dividing the crimping diameter of the ultrasonic application perpendicular direction by the crimping diameter of the ultrasonic application direction is 1.1. Exceeding and those with a concave outer periphery when viewed from the first bonding direction at the time of bonding were regarded as defective crimping shapes, and the value divided by the number of observations was defined as the defective crimping rate. The number of crimped balls observed is 200.

  Table 2 shows the results of sampling and component analysis after single head drawing, and the measurement results of mechanical characteristics and bonding characteristics.

  Even in the bonding wire (Sample 14) containing 0.0015 mass% and 0.0005 mass% of calcium and lanthanum, respectively, 3.5% leaning failure occurred under the bonding conditions of this example. When nickel was added to this, the defect in leaning was greatly improved, but the bonding wire defect rate was 5% in the bonding wire in which the nickel content was 0.0052 mass% (sample 16).

  Even when no beryllium, titanium, or vanadium was added, it was possible to produce a bonding wire that suppressed leaning defects by adding 0.002% by mass of nickel. It was confirmed that this was not sufficient as a complicated wiring to be used and a gold wire for semiconductor mounting for narrow pitch wiring.

  Even without adding beryllium, it was confirmed that by adding 0.0005 mass% or more of titanium and vanadium, the shape of the ball can be improved while maintaining the leaning characteristics (Sample 18) ). The leaning defect rate was improved by increasing the contents of titanium and vanadium.

  In addition, when 0.005% by mass of titanium or vanadium and 0.00078 to 0.00079% by mass of beryllium are included (samples 20 and 21), even when 0.0052% by mass of nickel is added, the defective shape of the crimping shape is low. Improved to 3% or less. The addition of titanium and vanadium was confirmed to have an effect on the leaning failure in addition to the pressure-bonded shape of the ball. Even if titanium and vanadium were contained alone or both, the effect was recognized.

  The composite addition of beryllium and titanium and / or vanadium could suppress the deterioration of the pressure-bonded ball shape even when nickel was added up to 0.007% by mass (samples 23 to 25).

  When the defectiveness of the leaning and the defective shape of the pressure bonding of the ball are judged as 0.5% and 3%, respectively, the beryllium content is 0.0003 mass% or more and 0.0008 mass% or less, and one or both of titanium and vanadium are contained. By adding 0.0005% by mass or more and 0.005% by mass or less, it became possible to increase the content of nickel that suppresses leaning failure to 0.007% by mass.

(Example 3)
A plurality of types of gold wires containing an element arbitrarily selected from praseodymium, calcium, lanthanum, beryllium, nickel, titanium, and vanadium were manufactured, and the leaning defect and the pressure-bonded ball shape were evaluated.

  Praseodymium, calcium, lanthanum, beryllium, nickel, titanium and vanadium were added to the raw material with a purity of 99.9998% by mass or more to cast an ingot having a diameter of 5 mm and a length of 100 mm. After casting, the ingot is rolled to about 2 mm square with a grooved rolling mill, and single-head wire drawing is performed to a diameter of 1.0 mm by drawing using a diamond die, and then winding is performed using a continuous wire drawing machine. Drawing was performed with a diamond die in a lubricating liquid at a drawing speed of 20 m / min, and the wire was drawn to 22.7 μm. Each area reduction per die pass in the continuous drawing process is about 10%. Thereafter, using a tubular furnace, heat treatment (tempering heat treatment) was continuously performed in argon, the temperature was adjusted, and a bonding wire having a breaking elongation of 4.5% was produced. By raising the temperature of the final tempering process and setting the set elongation to 4.5%, the strength and Young's modulus decrease, which is disadvantageous for leaning defects, but curl is easy to remove, so it was triggered It has become possible to suppress the occurrence of leaning defects.

  When the crystal orientation analysis of the cross-sectional structure of the gold wire was performed using the EBSD method on the produced gold wire, with respect to the length direction (drawing direction) of the bonding wire, One of the (111) plane normals of the crystal grains was found to account for 50% or more of the cross-sectional area ratio of the crystal grains having an angle of 15 ° or less.

  The bonding test was performed using a chip having a pad pitch interval of 70 μm and a pad material of Al—Cu—Si. Bonding used 8028pps made by K & S. The crimping diameter of the first joint was set to 40 μm, the loop height from the pad was 500 μm, and the loop length was 3.0 mm. Bonding was performed in the atmosphere, and the chip surface temperature was 160 ° C.

  Leaning defects are likely to occur because the loop height is increased and the wire diameter is decreased. Therefore, the contents of calcium and rare earth elements were increased as compared with Examples 1 and 2.

  The evaluation of the bonding characteristics was performed by evaluating the probability of occurrence of a leaning defect and a crimped shape defect.

  As a criterion for the leaning failure, the bonding post-bonding loop was observed from directly above, and a bonding wire having a bonding wire spacing of 30 μm or less was regarded as a leaning failure, and the occurrence probability was examined. The number of observed loops is 1000.

  As a criterion for crimping shape failure, measure the crimping diameter of the first joint at the ultrasonic application direction and its perpendicular direction, and the value obtained by dividing the crimping diameter of the ultrasonic application perpendicular direction by the crimping diameter of the ultrasonic application direction is 1.1. The ball defect rate was determined by dividing the number exceeding the above and the one having a concave shape on the outer periphery of the crimp when viewed from the first bonding direction during bonding, and dividing the value by the number of observations. The number of crimped balls observed is 200.

  Table 3 shows the results of sampling and component analysis after single-head drawing and the measurement results of mechanical characteristics and bonding characteristics.

  Bonding wires containing 0.0015 mass% calcium and 0.004 mass% praseodymium (samples 33 to 35) had almost the same strength and Young's modulus, but bonding wires containing 0.002 mass% nickel (samples 34 and 35) As compared with the bonding wire containing no nickel (Sample 33), the leaning characteristics were clearly superior. Further, the bonding wire containing 0.0006% by mass of beryllium and 0.003% by mass of titanium had a good pressure bonding shape of the ball.

  When comparing bonding wires (samples 35 and 36) containing 0.0015% by weight calcium, about 0.0006% by weight or 0.00061% by weight beryllium, 0.003% by weight titanium, and 0.004% by weight of either praseodymium or lanthanum, The bonding wire to which praseodymium was added (Sample 35) had superior leaning characteristics. This is because the bonding wire to which praseodymium is added has high strength and Young's modulus.

  When trying to obtain the same strength and Young's modulus as this bonding wire (sample 35), calcium alone needs to contain 0.007% by mass (sample 37). Comparing these leaning failure rates, the bonding wire (sample 35) containing praseodymium was superior. When calcium and praseodymium are compared, since praseodymium has a large mass number, the atomic concentration for obtaining the same strength is small. For this reason, the softened region length (HAZ length) of the neck portion is longer than that of a bonding wire mainly composed of calcium with the same strength. When the force to tilt the loop is applied, the longer the HAZ length, the smaller the stress concentration. Therefore, in the comparison of bonding wires with the same bus bar strength, bonding wires mainly composed of praseodymium are superior. I understand that.

  When producing a bonding wire having the same mechanical properties while changing the ratio of praseodymium and calcium, a bonding wire having strength and Young's modulus can be produced with a smaller content as the proportion of praseodymium is larger. In particular, the bonding characteristics (samples 39 to 41) to which 0.0016% by mass to 0.0079% by mass of praseodymium is added have good leaning characteristics because the softened region has a long length. Therefore, a gold wire containing 0.0016 mass% to 0.0079 mass% praseodymium is useful for a device that needs to have a particularly high loop. The praseodymium content could be increased to 0.02% by mass, but when it exceeded 0.0081% by mass, the roundness of the ball's crimped shape slightly worsened, as with calcium and other rare earth elements, 0.02% by mass Exceeding this point caused the free air ball to oxidize violently, making it impossible to obtain a sound first bond.

  Accordingly, in the present invention, among the calcium and rare earth elements used to increase the strength and Young's modulus, praseodymium is the most desirable element as an element for suppressing poor leaning, and the optimum composition range is It was found to be in the range of 0.0016 mass% to 0.0079 mass%.

Example 4
Next, the effect of adding indium, gallium and palladium was examined.

  As additive elements other than the above, various types of gold wires containing any element selected from calcium, praseodymium, neodymium, nickel, beryllium, vanadium and titanium are manufactured, resulting in poor leaning, ball shape, and crimped ball shear strength. And high temperature reliability were evaluated respectively.

  An ingot having a diameter of 5 mm and a length of 100 mm was cast by adding the mother alloy of the above additive elements to a raw material having a purity of 99.9998% by mass or more. After casting, the ingot is rolled to about 2 mm square with a grooved rolling mill, and single-head wire drawing is performed to a diameter of 1.0 mm by drawing using a diamond die, and then winding is performed using a continuous wire drawing machine. Drawing was performed with a diamond die in a lubricating liquid at a drawing speed of 20 m / min, and the wire was drawn to 22.7 μm. Each area reduction per die pass in the continuous drawing process is about 10%. Thereafter, using a tubular furnace, heat treatment (tempering heat treatment) was continuously performed in argon, the temperature was adjusted, and a bonding wire having a breaking elongation of 4% was produced.

  For the bonding test, Shinkawa Co., Ltd. UTC-400 was used. The above bonding wires were used to connect a 150 μm high silicon chip to a 42 alloy lead frame. First bonding was performed on the Al electrode on the silicon chip side, and wedge bonding (second bonding) was performed on the silver alloy electrode on the 42 alloy side. The average value of the pressure-bonded ball diameter was adjusted to 45 μm. The wire span is 5 mm and the loop height from the pad is 400 μm. Bonding was performed in the atmosphere, and the bonding temperature was 150 ° C.

  The amounts of calcium and rare earth elements were added as expected from the results of Examples 1 to 3. When the crystal orientation analysis of the cross-sectional structure of the gold wire was performed using the EBSD method on the prepared gold wire, the crystal was observed in all the bonding wires in the length direction (drawing direction) of the bonding wires. It was found that the ratio of crystal grains having one of the (111) plane normals of the grains having an angle of 15 ° or less occupies 50% or more in terms of the cross-sectional area ratio.

  The bonding characteristics were evaluated by measuring the leaning defect, the bonding shape defect probability, and the bonding ball shear strength, and some bonding wires were subjected to a high-temperature acceleration test.

  As a reference for the leaning failure, the bonding loop was observed from directly above, and a bonding wire having an interval between bonding wires of 30 μm or less was regarded as a leaning failure, and the probability of occurrence was examined. The number of observed loops is 1000.

  As a criterion for crimping shape failure, measure the crimping diameter of the first joint at the ultrasonic application direction and its perpendicular direction, and the value obtained by dividing the crimping diameter of the ultrasonic application perpendicular direction by the crimping diameter of the ultrasonic application direction is 1.1. The value obtained by dividing by the number of observations was determined as the defective shape of the crimping shape. The number of crimped balls observed is 200.

  The pressure-bonded ball shear strength was measured by peeling the ball by moving the tool parallel to the pad at a height of 1 μm above the pad. The number of measurements of the pressure-bonded ball shear strength was 50, and the average value was calculated.

  In the high temperature accelerated test, the bonded chip was resin-sealed, held in an electric furnace heated to 150 ° C. for 3000 hours, the resin part was opened, and the pressure-bonded ball shear strength was measured. The ratio of the crimp ball shear strength after heating and holding to the crimp ball shear strength before heating was calculated.

  Table 4 shows the results of sampling and component analysis after single head drawing, and the measurement results of mechanical characteristics and bonding characteristics.

  Compared with the group (sample 43 and samples 44 to 48) to which 0.0035% by mass of praseodymium and 0.001% by mass of calcium were added, the leaning failure rate was significantly different depending on the presence or absence of nickel, and the effect of preventing the addition of nickel to the leaning failure It was shown again. In addition, when gallium was added to this, it became possible to improve the pressure-bonding ball shear strength from 0.0005 mass% to 0.005 mass% while maintaining a low level of leaning failure and poor crimping shape (sample 45- 47). In the case of containing 0.0055% by mass of gallium (Sample 48), the crimping shape defect rate increased and the degradation of the crimped ball shape was observed.

  Compared with the group that added praseodymium 0.002% by mass, calcium 0.0015% by mass, and neodymium 0.0015% by mass, the rate of defective shape of crimping was significantly different depending on the presence or absence of beryllium and vanadium. The effect on sex was shown anew. Moreover, when indium was added to this, it became possible to improve the pressure-bonding ball shear strength while maintaining a low level of leaning and poor crimping shape from 0.0005% to 0.005% by weight (Sample 51). ~ 53). In the case of containing 0.0052% by mass of indium (Sample 54), the defective shape of the press-bonded shape was increased, and the deterioration of the press-bonded ball shape was recognized.

  Compared to the group (samples 55 to 60) in which praseodymium is added at 0.0017% by mass or 0.0018% by mass and calcium is added at 0.001% by mass, the inclusion of nickel, beryllium, titanium, vanadium, indium, and gallium in addition to these elements. In addition, a bonding wire having a low leaning defect rate and a crimping shape defect rate and a high crimp ball shear strength could be produced. Further, even when 0.001% by mass (sample 56) to 0.95% by mass (sample 60) of palladium of these elements was added, the above characteristics were not deteriorated. Furthermore, the addition of palladium was able to remarkably suppress a decrease in the pressure-bonded ball shear strength in the high temperature acceleration test.

  As described above, in addition to the addition of calcium, rare earth elements, beryllium, titanium, and vanadium, the addition amount of either one or both of indium and gallium is 0.0005 mass% or more and 0.005 mass% or less. It was confirmed that it is possible to increase the pressure-bonding ball shear strength while suppressing leaning defects and crimping shape defects, and to provide a gold bonding wire with excellent looping performance and bonding reliability. In addition, it was confirmed that a gold wire for connecting a semiconductor element applicable to a device used in a high temperature environment can be provided by containing 0.001% by mass or more of palladium.

(Example 5)
Next, the influence of addition of magnesium, germanium, iron, lithium, lead, silver, copper and platinum was investigated.

  A plurality of types of gold wires containing the above elements were produced based on the sample 45 of Example 4, and the leaning defect, the ball shape, and the pressure-bonded ball shear strength were evaluated.

  An ingot having a diameter of 5 mm and a length of 100 mm was cast by adding a mother alloy of an additive element to a raw material having a purity of 99.9998% by mass or more. After casting, the ingot is rolled to about 2 mm square with a grooved rolling mill, and single-head wire drawing is performed to a diameter of 1.0 mm by drawing using a diamond die, and then winding is performed using a continuous wire drawing machine. Drawing was performed with a diamond die in a lubricating liquid at a drawing speed of 20 m / min, and the wire was drawn to 22.7 μm. Each area reduction per die pass in the continuous drawing process is about 10%. Thereafter, using a tubular furnace, heat treatment (tempering heat treatment) was continuously performed in argon, the temperature was adjusted, and a bonding wire having a breaking elongation of 4% was produced.

  For the bonding test, Shinkawa Co., Ltd. UTC-400 was used. The above bonding wires were used to connect a 150 μm high silicon chip to a 42 alloy lead frame. First bonding was performed on the Al electrode on the silicon chip side, and wedge bonding (second bonding) was performed on the silver alloy electrode on the 42 alloy side. The average value of the pressure-bonded ball diameter was adjusted to 45 μm. The wire span is 5 mm and the loop height from the pad is 400 μm. Bonding was performed in the atmosphere, and the bonding temperature was 150 ° C.

  When the crystal orientation analysis of the cross-sectional structure of the gold wire was performed using the EBSD method, the (111) plane normal of the crystal grain was observed with respect to the length direction (drawing direction) of the bonding wire for all bonding wires. One of them was found that the ratio of crystal grains having an angle of 15 ° or less occupied 50% or more in terms of the cross-sectional area ratio with respect to the whole.

  For evaluation of bonding characteristics, a leaning defect rate, a crimping shape defect rate, and a crimped ball shear strength were measured.

  As a reference for the leaning failure, the bonding loop was observed from directly above, and a bonding wire having an interval between bonding wires of 30 μm or less was regarded as a leaning failure, and the probability of occurrence was examined. The number of observed loops is 1000.

  Measure the crimp diameter of the first joint in the direction of ultrasonic application and the direction perpendicular to it as the standard for the defective shape of the press-bonded ball (that is, the defective crimp shape). When the value divided by the diameter exceeds 1.1, and when the outer circumference of the crimp when viewed from the first bonding direction during bonding is a concave shape, the value divided by the number of observations is the crimp shape failure rate. did. The number of crimped balls observed is 200.

  Table 5 shows the results of sampling and component analysis after single head drawing, and the measurement results of mechanical characteristics and bonding characteristics.

  Magnesium, germanium, iron, lithium, lead, silver, copper and platinum had little effect on the mechanical properties of the gold wire.

  Differences were observed in bonding characteristics. Magnesium, germanium, iron, silver, copper, platinum were leaned until the addition of 0.005% by mass, and the shape of the press-bonded ball was kept good, whereas lithium and lead deteriorated the press-fit shape in particular (sample) 68 and 69). It is necessary to avoid contamination with impurities that are easily oxidized. Among these, magnesium, iron, and germanium do not deteriorate the leaning and crimping shape even if they are contained in a relatively large amount, but when added in excess of 0.005% by mass, the surface oxidation of the free air ball becomes severe, and a large amount In order to raise concerns about contamination and clogging of the capillary when bonded, it is desirable that these elements be suppressed to 0.005 mass% or less. Among these, when magnesium was added in the range of 0.001% by mass or more and 0.005% by mass or less, the effect of improving the pressure-bonded ball shear strength was recognized (see Samples 62 to 64).

It is the schematic where it uses for description of a leaning defect and a crimp ball | bowl shape defect.

Explanation of symbols

1, 1a, 1b Bonding wire
2c, 2d pad
3c Crimp ball

Claims (8)

  The content of nickel is 0.0007 mass% or more and less than 0.005 mass%, the content of beryllium is 0.0003 mass% or more and 0.0008 mass% or less, and the content of one or more elements selected from calcium and rare earth elements is A gold wire for connecting a semiconductor element, characterized by being more than 0.0009 mass% and not more than 0.02 mass%.   The nickel content is 0.0007 mass% or more and 0.005 mass% or less, and the addition amount of either one or both of titanium and vanadium is 0.0005 mass% or more and 0.005 mass% or less, and is selected from calcium and rare earth elements A gold wire for connecting a semiconductor element, wherein the content of one or more elements is more than 0.0009% by mass and 0.02% by mass or less.   Nickel content is 0.0007 mass% or more and 0.007 mass% or less, beryllium content is 0.0003 mass% or more and 0.0008 mass% or less, and the addition amount of either or both of titanium and vanadium is 0.0005 mass% or more A gold wire for connecting a semiconductor element, characterized in that the content of one or more elements selected from calcium and rare earth elements is 0.005% by mass or less and more than 0.0009% by mass and 0.02% by mass or less.   The gold wire for connecting a semiconductor element according to any one of claims 1 to 3, wherein praseodymium is contained in an amount of 0.0016 mass% to 0.02 mass%.   Furthermore, 0.0005 mass% or more and 0.005 mass% or less of any one or both indium and gallium are contained, The semiconductor element connection gold wire in any one of Claims 1-4 characterized by the above-mentioned.   The gold wire for connecting a semiconductor element according to any one of claims 1 to 5, which contains palladium in an amount of 0.001 mass% to 2 mass%. Furthermore, magnesium is contained 0.001 mass% or more and 0.005 mass% or less, The gold | metal | money wire for a semiconductor element connection in any one of Claims 1-6 characterized by the above-mentioned. The ratio of crystal grains in which one of the (111) plane normals of the individual crystal grains constituting the wire has an angle of 15 ° or less with respect to the length direction of the wire The gold wire for connecting a semiconductor element according to any one of claims 1 to 7, characterized in that it is <111> oriented in the length direction occupying 50% or more.

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