WO2020059856A9 - 半導体装置用Cu合金ボンディングワイヤ - Google Patents
半導体装置用Cu合金ボンディングワイヤ Download PDFInfo
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- WO2020059856A9 WO2020059856A9 PCT/JP2019/037023 JP2019037023W WO2020059856A9 WO 2020059856 A9 WO2020059856 A9 WO 2020059856A9 JP 2019037023 W JP2019037023 W JP 2019037023W WO 2020059856 A9 WO2020059856 A9 WO 2020059856A9
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Definitions
- the present invention relates to a Cu alloy bonding wire for a semiconductor device used for connecting an electrode on a semiconductor element and a circuit wiring board such as an external lead.
- bonding wires for semiconductor devices (hereinafter, bonding wires) for bonding between electrodes on semiconductor elements and external leads.
- the bonding method of the bonding wire is generally a thermocompression bonding method using ultrasonic waves, and a general-purpose bonding device, a capillary jig used for connection by passing the bonding wire through the inside, and the like are used.
- the bonding process of the bonding wire is as follows: The tip of the wire is heated and melted by the heat input of the arc, and after the ball (FAB: Free Air Ball) is formed by the surface tension, it is heated on the electrode of the semiconductor element in the range of 150 to 300°C.
- FAB Free Air Ball
- This ball part is crimp-bonded (hereinafter ball-bonded), and then the wire is unwound from the capillary to form a loop, and then the wire part is crimp-bonded (hereinafter wedge-bonded) to the electrode on the external lead side. ..
- solder wires using Cu are roughly classified into those having a coating layer such as Pd and Au on the surface of Cu (hereinafter, coated Cu wire) and those having no coating layer (hereinafter, bare Cu wire).
- the coated Cu wire is characterized in that the coating layer is provided to suppress the oxidation of Cu and improve the use performance such as the bondability, and is mainly used for high-density LSI.
- bare Cu wires are mainly used for power device applications with relatively low performance requirements, taking advantage of their low cost. Recently, attempts have been made to apply bare Cu wires to the most advanced high-density LSI by improving the properties of bare Cu wires.
- the output of ultrasonic waves tends to be high in order to obtain the bonding strength of the wedge bonded portion, but the loop may be bent under the influence of ultrasonic waves.
- an operation called scrubbing that vibrates a stage at a low frequency is often used together while the wire is pressed by a capillary.
- the scrub promotes the deformation of the wire and is effective in improving the joint strength of the wedge joint, but the loop may be curved due to the vibration of the scrub, and the straightness may be deteriorated.
- the diameter of the bonding wire used in high-density LSI is mainly a thin wire diameter of 25 ⁇ m or less, but as the wire diameter becomes thinner, the strength of the loop portion becomes lower. Was becoming more difficult.
- Patent Document 1 discloses a bonding wire for a semiconductor device, which has a core material made of a conductive metal and a skin layer having a metal different from the core material as a main component on the core material.
- a bonding wire is disclosed in which the average size of the crystal grains on the surface has an aspect ratio in the wire longitudinal direction/circumferential direction of 3 or more, and the straightness of the loop is excellent in a normal condition of 3 mm span. It is stated that.
- Patent Document 2 discloses a bonding wire for a semiconductor device having a core material made of a conductive metal and a skin layer having a metal different from the core material as a main component on the core material. Regarding the relationship between the average size a of the skin layer crystal grains in the wire circumferential direction and the average size b of the core material crystal grains in a vertical section that is a section perpendicular to the wire axis, a/b ⁇ 0.7.
- a bonding wire for a semiconductor device which is characterized by the above, is disclosed, and it is stated that the wire collapse (learning property) right above the ball can be improved.
- FIG. 1 is a diagram schematically showing a case where the loop straightness is high
- FIGS. 2A and 2B are diagrams schematically showing a case where the loop straightness is low.
- This schematic diagram is an observation of the loop portion from directly above.
- the loop 1 having a high loop straightness has a straight line or a shape close to a straight line without inclination or bending in the loop portion.
- the straightness of the loop is low, the entire loop is inclined in one direction like the loop 2, or a part of the loop is curved left and right like the loop 3 in many cases.
- Patent Documents 1 and 2 each relate to a bonding wire for a semiconductor device having a core material made of a conductive metal and a skin layer having a metal different from the core material as a main component on the core material. Is. This technique is premised on a coating structure, and it was not clear whether this technique is effective for bare Cu wires. Therefore, the inventors investigated whether or not the loop straightness of the bare Cu wire was improved by using these techniques for the bare Cu wire and the loop straightness required for the high-density LSI could be satisfied.
- thermosetting resin such as an epoxy resin
- transfer molding first, a thermosetting resin is loaded into a mold heated to 160 to 190° C. to reduce the viscosity. After that, the resin is poured into a mold to which the lead frame and the resin substrate are fixed, and molded into a desired shape. Further, heating is performed for several minutes in the mold, and finally the resin is cured to complete the molding.
- a problem in the resin encapsulation process in high-density LSI is the deformation of the loop portion when the resin is poured into the mold.
- the bent part directly above the ball in the loop part is called the neck part. Since the neck portion is accompanied by a large bending deformation as compared with the other loop portions, there is a problem in that the neck portion cannot withstand the bending deformation and damage such as a crack occurs. In order to apply the bare Cu wire to the most advanced high-density LSI, there has been a demand for a technique for reducing damage to the neck portion.
- Cutting-edge high-density LSIs are required to operate without failure even when used for a long time. In response to these demands, it has been required to improve the long-term service life of each bonding portion of the bonding wire.
- As a method of evaluating long-term service life generally, a high temperature storage test, a high temperature and high humidity test, a heat cycle test, etc. are performed. In the most advanced high-density LSI, the performance requirements particularly required for the high temperature storage test are strict, and it is required to satisfy the long-term service life of 500 hours or more in the high temperature storage test at 200°C.
- An object of the present invention is to provide a Cu alloy bonding wire for a semiconductor device that can meet the required performance in high density LSI applications.
- the Cu alloy bonding wire for a semiconductor device has a ⁇ 100> crystal orientation in which an angle difference is 15 degrees or less with respect to a direction perpendicular to one plane including a wire central axis among crystal orientations of a wire surface,
- the presence ratio of ⁇ 110> crystal orientation and ⁇ 111> crystal orientation is 3% or more and less than 27% in average area ratio, respectively.
- the straightness of the loop can be improved, it is possible to meet the required performance in high-density LSI applications.
- FIG. 2A is a schematic diagram of a loop portion when the straightness of the loop is low, as viewed from directly above
- FIG. 2A is a state in which the loop portion is bent in one direction
- FIG. It is a perspective view for explaining a measurement region.
- the bonding wire of this embodiment is a Cu alloy bonding wire for a semiconductor device, and has an angle difference of 15 degrees or less with respect to a direction perpendicular to one plane including the wire central axis among crystal orientations of the wire surface.
- the abundance ratios of the ⁇ 100> crystal orientation, the ⁇ 110> crystal orientation, and the ⁇ 111> crystal orientation are each 3% or more and less than 27% in average area ratio.
- the back-scattered electron diffraction (EBSD) method provided in the SEM can be used to measure the crystal orientation of the wire surface.
- the EBSD method is a method of determining a crystal orientation of each measurement point by projecting a diffraction pattern of backscattered electrons generated when a sample is irradiated with an electron beam on a detector surface and analyzing the diffraction pattern. ..
- Dedicated software (such as OIM analysis manufactured by TSL Solutions) can be used to analyze the data obtained by the EBSD method.
- the bonding wire is fixed to the sample stage, and the wire surface is irradiated with an electron beam from one direction to obtain crystal orientation data.
- this method it is possible to determine, among the crystal orientations on the wire surface, the crystal orientation with respect to the direction perpendicular to one plane including the wire central axis and the crystal orientation with respect to the wire central axis direction.
- the existence ratio of the ⁇ 100> crystal orientation is the ratio of the area occupied by the ⁇ 100> crystal orientation determined by the above method to the area of the measurement region by the EBSD method.
- the ⁇ 100> crystal orientation means an angular difference with respect to a direction y perpendicular to one plane P including the wire central axis x among the ⁇ 100> crystal orientations of the wire surface, as shown in FIG. Is defined as less than 15 degrees. This is because if the angle difference is 15 degrees or less, an advantageous effect can be obtained in improving the characteristics of the bonding wire.
- the existence ratio of the ⁇ 110> crystal orientation and the ⁇ 111> crystal orientation with respect to the wire central axis x direction can also be calculated using the same method.
- the average area ratio is used as the value of the existence ratio of a particular crystal orientation.
- the average area ratio is the arithmetic average of the respective values of the abundance ratios obtained by measuring at least 10 points by the EBSD method.
- the length W in the circumferential direction is preferably 25% or less of the diameter of the wire
- the length L in the wire central axis x direction is preferably 40 ⁇ m to 100 ⁇ m.
- the existence ratio of the crystal orientation on the wire surface obtained by the EBSD method has a strong correlation with the effect of improving the loop straightness, which is the effect of the present embodiment.
- the wire surface is a curved surface, and as it goes from the vertex of the wire (the highest position with respect to the circumferential direction of the wire fixed to the sample stage) in the circumferential direction, the deviation from the direction perpendicular to the wire surface occurs.
- the measurement data obtained by the above method is consistent with the actual situation showing the effect of improving the straightness of the loop.
- the length W of the measurement area A is at least 25% or less of the diameter of the wire, the deviation of the azimuth perpendicular to the wire surface with respect to the circumferential direction is allowed within the EBSD measurement area of the wire surface having the curved surface. This is because it is possible to obtain the effect of improving the straightness of the loop.
- the reason why the lower limit is set in the measurement area A with respect to the direction of the wire center axis is that it is determined that the measurement data sufficiently reflects the characteristics of the sample when the length L is 40 ⁇ m or more.
- the reason why the upper limit is set in the measurement area A with respect to the wire central axis x direction is that the analysis can be efficiently performed when the length L is 100 ⁇ m or less.
- the bonding wire There may be copper oxide film or impurities that are unintentionally attached on the surface of the bonding wire.
- the impurities include organic substances, sulfur, nitrogen and compounds thereof. Even if these exist, the crystal orientation of the bonding wire surface can be measured by optimizing the measurement conditions of the EBSD method when the thickness is thin or the existence amount is small. When the copper oxide film on the surface of the bonding wire is thick or the amount of impurities attached is large, the crystal orientation of the Cu and Cu alloy portions may not be measured. In this case, it is effective to treat the surface of the bonding wire by alkali degreasing, acid cleaning, ion sputtering or the like before performing measurement using the EBSD method.
- the EBSD method can be used for measuring the average crystal grain size.
- the crystal grain size is defined as an equivalent circle diameter calculated from the area of a region surrounded by crystal grain boundaries having an orientation difference of 15 degrees or more measured by the EBSD method.
- the average crystal grain size the arithmetic mean value of the crystal grain size values measured for five randomly selected bonding wires is used.
- a method of exposing a cross section perpendicular to the wire center axis a method of embedding a bonding wire in a resin and then mechanical polishing, or a method of processing with an Ar ion beam can be used.
- An ICP emission spectroscopy analyzer or the like can be used for the concentration analysis of the elements contained in the bonding wire.
- the concentration analysis may be performed after removing the region of 1 to 2 nm from the surface of the bonding wire by sputtering before performing the analysis. ..
- a method using acid cleaning is also effective.
- the angle difference is 15 degrees or less with respect to the direction perpendicular to one plane including the wire central axis, the ⁇ 100> crystal orientation, the ⁇ 110> crystal orientation, and the ⁇ 111> crystal orientation. It was found that there is a strong correlation between the azimuth ratio and the loop straightness, and that the effect of improving the loop straightness can be obtained by controlling the crystal azimuth ratio to an appropriate range. Specifically, as a result of performing the bonding 100 times using the bonding wire of the present embodiment and observing the loop with an optical microscope, the places where the whole loop is tilted or a part of the loop is significantly reduced. , And confirmed that a high loop straightness was obtained.
- the loop may tilt in a certain direction.
- the abundance ratio is less than 3% or 27% or more in terms of average area ratio, the loop is inclined in a specific direction, and the effect of improving the straightness of the loop is insufficient, which is not suitable for practical use. It is considered that this is because a certain crystal orientation among the crystal orientations is strongly oriented, and the plastic anisotropy of the wire surface of the loop portion is increased.
- the bonding wire of the present embodiment further has a ⁇ 100> crystal orientation and a ⁇ 110> crystal orientation in which the angular difference is 15 degrees or less with respect to the direction perpendicular to one plane including the wire center axis among the crystal orientations on the wire surface. It is preferable that the total of the abundance ratios of the orientation and the ⁇ 111> crystal orientation is 15% or more and less than 50%. As a result, the effect of maintaining a high loop straightness after the resin sealing step is obtained. Specifically, after bonding the bonding wire, the resin was sealed by transfer molding, and the loop was observed using a soft X-ray device. As a result, it was confirmed that high loop straightness was maintained.
- the ⁇ 100> crystal orientation, the ⁇ 110> crystal orientation, and the ⁇ 111> crystal orientation have an angle difference of 15 degrees or less with respect to a direction perpendicular to one plane including the wire central axis.
- the plastic anisotropy of the loop portion is increased. It is considered that this is because the effect of reducing the above can be synergistically enhanced, and the effect of maintaining high loop straightness even after the resin sealing is enhanced.
- the effect of maintaining high loop straightness after resin sealing was not sufficient.
- crystal orientations other than ⁇ 100> crystal orientation, ⁇ 110> crystal orientation, and ⁇ 111> crystal orientation may grow preferentially, and a high loop is obtained even after resin sealing. It is considered that the effect of maintaining straightness could not be stably enhanced.
- the total abundance ratio is 50% or more, the ⁇ 100> crystal orientation, the ⁇ 110> crystal orientation, and the ⁇ 111> crystal orientation are predominant, and thus the effect of maintaining a high loop straightness after resin sealing is achieved. It is thought that it was not possible to raise sufficiently.
- the crystal orientation of the wire surface further has an existence ratio of the ⁇ 100> crystal orientation, which has an angle difference of 15 degrees or less with respect to a direction perpendicular to one plane including the wire central axis, which is X.
- Y is the existence ratio of the ⁇ 110> crystal orientation
- Z is the existence ratio of the ⁇ 111> crystal orientation, it is preferable that X+Y>Z. This further enhances the effect of maintaining high loop straightness even after resin sealing.
- the angle difference is 15 degrees or less with respect to the direction perpendicular to one plane including the wire center axis, the ⁇ 100> crystal orientation, the ⁇ 110> crystal orientation, and the ⁇ 111> crystal orientation.
- the above X, Y , Z satisfies the relationship of X+Y>Z, it is presumed that the plastic anisotropy of the loop portion can be further reduced and the effect of improving the straightness of the loop is synergistically enhanced.
- the total abundance ratio of the ⁇ 110> crystal orientation and the ⁇ 110> crystal orientation reduces the anisotropy of the loop portion as compared with the abundance ratio of the ⁇ 111> crystal orientation. It is thought that this is because the effect of making it is high.
- the bonding wire of the present embodiment further has a ⁇ 121> crystal orientation and a ⁇ 123> crystal orientation in which the angle difference is 15 degrees or less with respect to the direction perpendicular to one plane including the wire center axis among the crystal orientations of the wire surface. It is preferable that the azimuth ratio is less than 15% in terms of average area ratio. As a result, the effect of maintaining high loop straightness even after resin sealing is greatly enhanced.
- the angle difference is 15 degrees or less with respect to the direction perpendicular to one plane including the wire center axis, the ⁇ 100> crystal orientation, the ⁇ 110> crystal orientation, and the ⁇ 111> crystal orientation.
- the abundance ratio of crystal orientations is 3% or more and less than 27% in average area ratio respectively, the total abundance ratio of these crystal orientations is 15% or more and less than 50%, and X, Y and Z are In addition to satisfying the relationship of X+Y>Z, further reducing the plastic anisotropy of the loop portion by setting the existence ratios of the ⁇ 121> crystal orientation and ⁇ 123> crystal orientation to be less than 15%, respectively. It is presumed that the effect of maintaining the straightness of the loop even after the resin sealing is synergistically enhanced.
- the bonding wire of this embodiment preferably has an average crystal grain size of 0.4 ⁇ m or more and 2.1 ⁇ m or less in a cross section perpendicular to the wire central axis.
- damage to the neck portion can be reduced. It is considered that this is because the plastic deformability against bending deformation that causes damage to the neck was controlled within an appropriate range by setting the average crystal grain size to 0.4 ⁇ m or more and 2.1 ⁇ m or less.
- the neck portion corresponds to a portion affected by arc heat input during ball formation (hereinafter, a heat-affected zone). Although the crystal grain size of the heat-affected zone becomes coarse due to the heat input from the arc, it is considered that the crystal grain size of the neck part was effectively controlled by controlling the average crystal grain size of the bonding wire in advance.
- the average crystal grain size is less than 0.4 ⁇ m or larger than 2.1 ⁇ m, the effect of reducing neck damage is not sufficient.
- the average crystal grain size was less than 0.4 ⁇ m, cracking was observed in the bent portion of the neck portion. It is considered that this is because the average crystal grain size of the neck portion becomes finer and the deformation resistance against bending deformation becomes too high.
- the average crystal grain size was larger than 2.1 ⁇ m, damage such as excessive deformation of the neck portion and breakage of the wire was observed. It is considered that this is because the average crystal grain size of the neck portion is coarsened and the deformation resistance against bending deformation is insufficient.
- the bonding wire of the present embodiment further has a ⁇ 111> crystal orientation and a ⁇ 100> crystal orientation in which the angular difference is 15 degrees or less with respect to the wire central axis direction among crystal orientations in a cross section in a direction parallel to the wire central axis. It is preferable that the total of the abundance ratios of is not less than 25% and less than 60% in terms of average area ratio. As a result, it is possible to obtain the effect of reducing damage to the neck portion even when the low loop is formed.
- the effect of suppressing neck damage during low loop is sufficient. is not.
- the total content ratio was less than 25%, the neck portion was excessively deformed, and damage such as bending of the wire was observed. This is considered to be due to insufficient deformation resistance against bending deformation.
- the total abundance ratio was 60% or more, cracking was observed in the bent portion of the neck portion. It is considered that this is because the deformation resistance against bending deformation became too high.
- the bonding wire of the present embodiment further contains one or more kinds of Ni, Pd, Pt, and Au in a total amount of 0.01% by mass or more and 1.5% by mass or less, and the balance of Cu and inevitable impurities.
- the life of the ball joint in the high temperature storage test at 200° C. can be improved to 500 hours or more. This is considered to be due to the effect that Ni, Pd, Pt, and Au reduce the growth rate of the Cu—Al-based intermetallic compound that causes the occurrence of peeling at the interface between the ball and the Al electrode.
- the concentration of the element is less than 0.01% by mass, the effect of improving the life of the ball joint in the 200° C. high temperature storage test is not sufficient. If the concentration of the element exceeds 1.5% by mass, the hardness of the ball increases and the formation of intermetallic compounds becomes non-uniform, so that the effect of improving the ball-joint life in a 200° C. high-temperature storage test is improved. Not enough.
- the bonding wire of the present embodiment further contains at least one kind of P, In, Ga, Ge, and Ag in a total amount of 0.001% by mass or more and 0.75% by mass or less, and the balance is Cu and inevitable impurities. ..
- the reason why such an effect was obtained is that the crystal grains forming the ball were made finer and isotropic deformation was promoted. If the concentration is less than 0.001% by mass, the effect of refining the crystal grains is insufficient, and the above effect is not sufficient. If the concentration exceeds 0.75% by mass, segregation of elements inside the ball becomes remarkable, and variations in crystal grains forming the ball increase, so that the above effect is not sufficient.
- (Method for manufacturing bonding wire) A method of manufacturing the semiconductor device bonding wire of the present embodiment will be described.
- a high-purity copper having a purity of Cu of 4N to 6N (Cu concentration: 99.99% by mass or more and 99.9999% by mass or less) is used as a raw material and is melted together with an element to be added to produce a copper alloy ingot.
- (Ingot) is produced.
- a method of directly melting copper and a high-purity additive component to form an alloy, or a mother alloy containing 3 to 5 mass% of an additive element in copper is prepared in advance, and the copper and the mother alloy are prepared.
- a method of melting and alloying can be used.
- the method of using the mother alloy is effective in homogenizing the element distribution at a low concentration.
- An arc melting furnace, a high frequency melting furnace, or the like can be used for melting.
- the surface of the ingot is preferably washed with an acid and alcohol to remove oxides and dirt, and then dried.
- the manufactured copper alloy ingot is first processed into a linear shape by rolling or forging. Next, it is preferable that the final wire diameter of the product is thinned by drawing.
- a continuous wire drawing apparatus capable of setting a plurality of diamond-coated dies can be used for the drawing process. At the time of continuous wire drawing, it is preferable to use a lubricating liquid for the purpose of reducing wear of the die and surface defects of the wire.
- heat treatment is performed in the middle of the drawing process for the purpose of strain relief or the like. In this specification, the heat treatment performed with the intermediate wire diameter is referred to as the intermediate heat treatment.
- the wire after the intermediate heat treatment is drawn to the final wire diameter used as a product.
- the step of performing drawing from the wire diameter for performing the intermediate heat treatment to the final wire diameter is referred to as final drawing.
- the bonding wire is recrystallized and heat treatment is performed to adjust the mechanical properties.
- the heat treatment performed with the final wire diameter is referred to as the final heat treatment.
- the intermediate heat treatment and the final heat treatment a method of performing heat treatment while continuously sweeping the wire can be used.
- the heat treatment is performed in an inert atmosphere in which Ar gas or N 2 gas is refluxed.
- H 2 as a reducing gas component in an amount of several percent in an inert atmosphere.
- the intermediate heat treatment condition In order to control the existence ratio of the ⁇ 100> crystal orientation, the ⁇ 110> crystal orientation, and the ⁇ 111> crystal orientation, it is effective to control the intermediate heat treatment condition, the final drawing process condition, and the final heat treatment condition, for example. ..
- the reason for this is considered as follows.
- the final heat treatment after the final drawing process causes recrystallization and grain growth on the wire surface.
- what kind of crystal orientation has crystal grains generated by recrystallization, and how much crystal grains with which crystal orientation have grain growth depend on the amount of processing strain, the temperature and time of the final heat treatment, etc. to be influenced.
- recrystallization nuclei having a specific crystal orientation are generated by drawing and the nuclei are preferentially grown by heat treatment under specific conditions.
- the amount of processing strain is considered as one of the factors that influence the formation of recrystallization nuclei.
- the processing strain introduced in the bonding wire manufacturing process can be introduced by rolling or forging, but in order to control the amount of processing strain stably, only the final drawing process is required rather than combining multiple processing processes. It is preferable to control by. For that purpose, it is effective to perform an intermediate heat treatment.
- the amount of processing strain can be sufficiently reduced by performing intermediate heat treatment at a temperature at which recovery or recrystallization occurs or more for a certain period of time or more.
- the amount of processing strain accumulated at the stage of performing the final heat treatment needs to consider only the amount of processing strain introduced into the material by the final drawing process, and stabilizes the crystal orientation. It becomes possible to control it physically.
- the intermediate heat treatment is performed at 630° C. or higher and lower than 750° C. for 0.05 seconds or longer and less than 1.5 seconds.
- the temperature of the intermediate heat treatment is less than 630° C. or the heat treatment time is less than 0.05 seconds, the effect of reducing the amount of processing strain cannot be sufficiently obtained, and the ⁇ 100> crystal orientation, ⁇ 110> crystal orientation, ⁇ The existence ratio of 111>crystal orientation cannot be stably controlled.
- the temperature of the intermediate heat treatment is 750°C or higher or when the heat treatment time is 1.5 seconds or longer, the crystal grains become coarse and the wire becomes too soft, and the frequency of wire breakage increases in the subsequent final drawing process. Therefore, it is not suitable for practical use.
- the amount of processing strain introduced in the final drawing process is considered to have a positive correlation with the processing rate of the final drawing process defined by the following formula.
- the processing rate of the final drawing process is 57% or more and less than 87%.
- the existence ratio of any of the ⁇ 100> crystal orientation, ⁇ 110> crystal orientation and ⁇ 111> crystal orientation is less than 3%. This is probably because the amount of processing strain in the final drawing process was insufficient and the generation of recrystallization nuclei necessary for growing the crystal orientation was insufficient.
- the processing rate of the final drawing is 87% or more, the ⁇ 110> crystal orientation is 27% or more. It is considered that this is because the amount of processing strain in the final drawing process became excessive and many recrystallized nuclei in the ⁇ 100> crystal orientation were generated.
- the final heat treatment is performed at 660°C or higher and lower than 750°C for 0.05 seconds or longer and less than 1.5 seconds.
- the temperature of the final heat treatment is less than 680° C. or when the heat treatment time is less than 0.05 seconds, the existence ratio of the ⁇ 110> crystal orientation is 27% or more.
- the temperature of the final heat treatment is 750° C. or higher or the heat treatment time is 1.5 seconds or longer, the wire becomes too soft and sufficient wire bondability cannot be obtained.
- an angle difference is 15 degrees or less with respect to a direction perpendicular to one plane including the wire central axis, a ⁇ 100> crystal orientation, a ⁇ 110> crystal orientation, and a ⁇ 111> crystal orientation.
- An example of a method for controlling the total azimuth presence ratio to 15% or more and less than 50% will be described.
- the first final pre-heat treatment is performed under specific conditions between the final drawing process and the final heat treatment. Is effective. That is, it is effective to sequentially perform the intermediate heat treatment, the final drawing work, the first final pre-heat treatment, and the final heat treatment in the wire manufacturing process.
- the first final pre-heat treatment is performed at 550°C or higher and lower than 680°C for 0.05 seconds or longer and less than 0.5 seconds. This is because the existence ratio of the crystal orientation formed in the final heat treatment can be controlled by performing the first final preheat treatment in an appropriate condition range.
- the temperature of the first final pre-heat treatment is less than 550° C. or when the heat treatment time is less than 0.05 seconds, the sum of the existence ratios of the ⁇ 100> crystal orientation, ⁇ 110> crystal orientation, and ⁇ 111> crystal orientation is It will be over 50%.
- the temperature of the first heat treatment is 680° C. or more and the heat treatment time is 0.5 seconds or more, the total of the existence ratios of the ⁇ 100> crystal orientation, ⁇ 110> crystal orientation, and ⁇ 111> crystal orientation is 15%. Will be less than.
- the existence ratio of the ⁇ 100> crystal orientations whose angle difference is 15 degrees or less with respect to the direction perpendicular to one plane including the wire central axis is X
- the existence ratio of the ⁇ 110> crystal orientations is X.
- the following describes an example of a method of controlling X, Y, and Z so that the relationship of X+Y>Z is satisfied, where Y is the abundance ratio of X and Z is the abundance ratio of the ⁇ 111> crystal orientation.
- -It is effective to set the second final pre-heat treatment to 450°C or higher and lower than 550°C, and 0.05 seconds or higher and lower than 0.5 seconds.
- the ⁇ 100> crystal orientation and the ⁇ 110> crystal orientation are increased by the final heat treatment by performing the second final pre-heat treatment in an appropriate condition range, and as a result, the value of X+Y is increased.
- the temperature of the second final pre-heat treatment is less than 450° C. or the heat treatment time is less than 0.05 seconds, X, Y and Z cannot satisfy X+Y>Z. It is considered that this is because the effect of increasing the value of X+Y cannot be obtained.
- the temperature of the second final pre-heat treatment is 550° C. or higher and 0.5 seconds or longer, X, Y and Z cannot satisfy X+Y>Z. It is considered that this is because the ⁇ 111> crystal orientation is easier to grow than the ⁇ 100> crystal orientation or the ⁇ 110> crystal orientation.
- the existence ratios of the ⁇ 121> crystal orientations and the ⁇ 123> crystal orientations in which the angular difference is 15 degrees or less with respect to the direction perpendicular to one plane including the wire central axis are An example of a method of controlling the average area ratios to be less than 15% will be shown.
- Annealing is effective.
- N 2 is promising as an inert gas other than Ar from the viewpoints of cost and safety, but since it has higher thermal conductivity than Ar gas, it has the ⁇ 121> crystal orientation and the ⁇ 123> crystal. It is not possible to obtain the effect of controlling the azimuth ratio to less than 15% in terms of average area ratio.
- the average crystal grain size will be larger than 2.1 ⁇ m. It is considered that this is because the amount of processing strain accumulated inside the material was small.
- the average crystal grain size becomes less than 0.4 ⁇ m.
- the processing rate per die is the ratio of the area of the wire in the direction reduced by the processing to the cross-sectional area of the wire before processing in the direction perpendicular to the wire center axis, expressed as a percentage. It is a thing. If the processing rate per die is less than 18%, the sum of the existing ratios of ⁇ 111> crystal orientation and ⁇ 100> crystal orientation will be less than 25%. When the processing rate per die is 21% or more, the total existence ratio of the ⁇ 111> crystal orientation and the ⁇ 100> crystal orientation is 60% or more.
- the raw material Cu having a purity of 99.99% by mass or more and the balance of unavoidable impurities was used.
- the bonding wire contained Ni, Pd, Pt, Au, P, In, Ga, Ge, Ag as an additive element, Cu and these elements were melted and alloyed in a high frequency melting furnace.
- the total target concentration of the additive elements other than the unavoidable impurity elements was less than 0.5% by mass
- a Cu alloy containing the additive element at a high concentration was used to produce an alloy having a target concentration.
- the atmosphere during melting was an Ar atmosphere in order to prevent the inclusion of impurities such as oxygen.
- the shape of the ingot produced by melting was a cylinder having a diameter of about 5 mm.
- the ingot was subjected to forging and drawing to produce a wire having an intermediate wire diameter.
- the wire diameter of the wire having the intermediate wire diameter was calculated back from the final wire diameter, and was set to a wire diameter at which the processing rate of the final drawing process was 57% or more and less than 87%.
- an intermediate heat treatment was performed on the wire having the intermediate wire diameter under the conditions of 630° C. or higher and lower than 750° C. for 0.05 seconds or longer and less than 1.5 seconds.
- the final drawing process was performed under the condition that the drawing ratio was 57% or more and less than 87% to manufacture a wire with a wire diameter of ⁇ 20 ⁇ m.
- the final heat treatment was performed under the conditions of 660° C.
- the first final pre-heat treatment and the second final pre-heat treatment were performed before the final heat treatment.
- the conditions for the first final pre-heat treatment were 550° C. or higher and lower than 680° C. and 0.05 seconds or higher and lower than 0.5 seconds.
- the conditions for the second final preheat treatment were 450° C. or higher and lower than 550° C. and 0.05 seconds or higher and lower than 0.5 seconds.
- the atmosphere during the final heat treatment was Ar atmosphere or N 2 atmosphere.
- the wire feeding speed during the final drawing process was changed in the range of 600 m/min or more and 1300 m/min or less.
- the processing rate per die during the final drawing process was changed within the range of 16% to 23%.
- the angle difference is 15 degrees or less with respect to the direction perpendicular to one plane including the wire central axis, ⁇ 100> crystal orientation, ⁇ 110> crystal orientation,
- the existence ratios of the ⁇ 111> crystal orientation, the ⁇ 121> crystal orientation, and the ⁇ 123> crystal orientation were calculated from the data measured by the EBSD method.
- the abundance ratio was an average value of values obtained by measuring five wires at intervals of about 3 m.
- the measurement region was a region surrounded by a straight line of 5 ⁇ m in the circumferential direction (25% of the wire diameter) and 40 ⁇ m in the wire central axis direction. Further, the measurement region is a region including the highest position in the circumferential direction of the sample fixed on the sample table.
- the average crystal grain size in the cross section perpendicular to the wire center axis of the bonding wire of the present embodiment was calculated from the data measured by the EBSD method after the wire cross section was exposed by processing with an Ar ion beam. Five wires were acquired at intervals of about 3 m, and the average value of the values measured for each wire was used. The measurement area was an area including all cross sections perpendicular to the wire central axis.
- the sum of the existence ratios of the ⁇ 111> crystal orientation and the ⁇ 100> crystal orientation in which the angular difference with respect to the wire center axis direction of the bonding wire in the cross section in the direction parallel to the wire center axis of the present embodiment is 15 degrees or less is It was calculated from the data measured by the EBSD method after the wire cross section was processed by Ar ion beam and exposed.
- the total of the abundance ratios was an average value of the values obtained by measuring 10 wires obtained at 10 intervals of about 3 m.
- the measurement region was a rectangular region having a wire central axis direction of 80 ⁇ m and a diameter direction of 20 ⁇ m. Further, the measurement region is a region including both ends of the wire in the diameter direction.
- loop straightness evaluation method The loop straightness was evaluated by the frequency of occurrence of a loop having a low straightness when bonding a bonding wire. An optical microscope was used to observe the loop portion. The loop length was 7.0 mm and the loop height was 0.2 mm. The loop portion was observed from directly above the loop, and if the distance from the position where the ball joint and the wire joint were connected by a straight line to the loop portion was the longest, and the distance was 10 ⁇ m or more, it was determined that the loop straightness was low. .. By observing loops of 200 bonding wires, if there are 5 or more low linearity loops, it is judged as a defect-1 point, and if 3 or less low linearity loops are less than 5 defects will occur.
- the loop straightness after resin sealing was evaluated by the frequency of occurrence of a loop having low straightness when the bonding wire was joined and then sealed with a general-purpose molding resin.
- a soft X-ray device was used to observe the loop portion.
- the loop length was 7.0 mm and the loop height was 0.2 mm.
- the loop portion was observed from directly above the loop, and if the distance from the position where the ball joint portion and the wire joint portion were connected by a straight line to the loop portion was farthest away from the loop portion by 15 ⁇ m or more, it was determined that the straightness was low.
- the neck damage was evaluated by observing the neck portion after bonding the bonding wire and observing the number of damaged spots.
- the loop length was 7.0 mm
- the loop height was 0.2 mm
- the loop shape was trapezoidal.
- the neck portion of the 200 bonding wires that were joined was observed with a scanning electron microscope, and if there were two or more damaged portions, it was determined to be defective and marked as 0 point. If there was only one damaged portion, it was judged that there was no problem in practical use, and it was judged as excellent.
- the evaluation results are shown in the column of "damage at neck" in Table 2. 0 points are rejected, others are passed.
- the ball-joint life in the high-temperature test is that the bonding strength of the ball-joint is 50% or less of that before the test, after bonding the bonding wire and sealing with general-purpose resin and then leaving it in a constant temperature oven set to 200°C. It was evaluated based on the time required to decrease to.
- As the value of the bonding strength used for determining the life of the ball bonded portion an average value of the measured values of the strengths of 10 randomly selected ball bonded portions using a micro shear tester was used. When measuring the bonding strength, the resin was removed by acid treatment in order to expose the ball bonded portion. The diameter of the ball was in the range of 1.5 to 1.7 times the diameter of the wire.
- N 2 +5% by volume H 2 gas was sprayed at a flow rate of 0.4 to 0.6 L/min to prevent oxidation.
- life of the ball-bonded portion is less than 500 hours, it is judged that there is a problem in practical use, and if it is 500 hours or more and less than 700 hours, it is judged that there is no problem in practical use. If it was above, it was judged to be excellent and marked as 2 points.
- the evaluation results are shown in the column of "life of ball bonded portion in high temperature storage test" in Table 2. 0 points are rejected, others are passed.
- the ball pressure bonding shape was evaluated by performing ball bonding 100 times on an Al electrode on a Si substrate and evaluating the number of defective pressure bonding shape.
- the ball pressure bonding shape was determined by observing the ball from directly above the ball joint, and it was determined that the ball pressure bonding shape was close to a circular shape, and that the petal shape was defective. An optical microscope was used for observing the ball pressure bonding shape.
- Example No. Numerals 1 to 87 are Cu alloy bonding wires for semiconductor devices, and the angle difference between the crystal orientations of the wire surface and the direction perpendicular to one plane including the wire central axis is 15 degrees or less ⁇ 100>. Since the abundance ratios of the crystal orientation, the ⁇ 110> crystal orientation, and the ⁇ 111> crystal orientation are 3% or more and less than 27% in average area ratio, respectively, the loop straightness was within the allowable range.
- Example No. In Nos. 1 to 75 the above-mentioned existence ratios were 5% or more and less than 25% in average area ratio, respectively, and therefore the loop straightness was not a practical problem.
- Example No. Numerals 4 and 5 are Cu alloy bonding wires for semiconductor devices, of which the crystal orientation of the wire surface has an angle difference of 15 degrees or less with respect to a direction perpendicular to one plane including the wire central axis ⁇ 100>.
- the abundance ratios of the crystal orientation, ⁇ 110> crystal orientation, and ⁇ 111> crystal orientation are each 3% or more and less than 27% in average area ratio, and one of the crystal orientations of the wire surface including the wire central axis is
- the sum of the ratios of ⁇ 100> crystal orientation, ⁇ 110> crystal orientation, and ⁇ 111> crystal orientation having an angle difference of 15 degrees or less with respect to the direction perpendicular to the plane is 15% or more and less than 50% in terms of average area ratio. Therefore, excellent evaluation results were obtained regarding the loop straightness after resin sealing.
- Examples 1, 6, 7, 15, and 16 are Cu alloy bonding wires for semiconductor devices, and the crystal orientation of the wire surface has an angle difference with respect to a direction perpendicular to one plane including the wire central axis.
- the abundance ratios of ⁇ 100> crystal orientation, ⁇ 110> crystal orientation, and ⁇ 111> crystal orientation of 15 degrees or less are 3% or more and less than 27% in average area ratio, respectively, and further, among the crystal orientations of the wire surface.
- the total of the abundance ratios of ⁇ 100> crystal orientation, ⁇ 110> crystal orientation, and ⁇ 111> crystal orientation having an angle difference of 15 degrees or less with respect to a direction perpendicular to one plane including the wire central axis is the average area.
- the angular difference is 15 degrees or less with respect to the direction perpendicular to one plane including the wire central axis.
- the abundance ratio is X
- the abundance ratio of the ⁇ 110> crystal orientation is Y
- the abundance ratio of the ⁇ 111> crystal orientation is Z, X+Y>Z, which is further excellent in loop straightness after resin encapsulation. The evaluation result was obtained.
- Example No. Reference numerals 8 to 14, 17 to 27, and 29 to 75 are Cu alloy bonding wires for semiconductor devices, and have an angle difference with respect to a direction perpendicular to one plane including the wire central axis among crystal orientations of the wire surface.
- the abundance ratios of ⁇ 100> crystal orientation, ⁇ 110> crystal orientation, and ⁇ 111> crystal orientation of 15 degrees or less are 3% or more and less than 27% in average area ratio, respectively, and further, among the crystal orientations of the wire surface.
- the total of the abundance ratios of ⁇ 100> crystal orientation, ⁇ 110> crystal orientation, and ⁇ 111> crystal orientation having an angle difference of 15 degrees or less with respect to a direction perpendicular to one plane including the wire central axis is the average area.
- the angular difference is 15 degrees or less with respect to the direction perpendicular to one plane including the wire central axis.
- the abundance ratio is X
- the ⁇ 110> crystal orientation abundance ratio is Y
- the ⁇ 111> crystal orientation abundance ratio is Z
- X+Y>Z the wire central axis
- Example No. Nos. 2 to 8, 10 and 12 to 87 are Cu alloy bonding wires for semiconductor devices, which have an average crystal grain size of 0.4 ⁇ m or more and 2.1 ⁇ m or less in a cross section perpendicular to the wire center axis. Excellent evaluation results were obtained regarding the damage to the part.
- Example No. Reference numerals 5 to 12, 14, and 16 to 75 are Cu alloy bonding wires for semiconductor devices, of which crystal orientations in a cross section in a direction parallel to the wire central axis have an angle difference of 15 degrees or less with respect to the wire central axis. Since the sum of the abundance ratios of a certain ⁇ 111> crystal orientation and a ⁇ 100> crystal orientation is 25% or more and less than 60% in terms of average area ratio, excellent evaluation results were obtained regarding neck damage during low loops. ..
- Example No. 24 to 30, 38 to 46, 48, 49, 51 to 55, 57 to 63, 71 to 74 are Cu alloy bonding wires for semiconductor devices, and one or more of Ni, Pd, Pt, and Au in total is used. Since the content of 0.01% by mass or more and 1.5% by mass or less and the balance being Cu and unavoidable impurities, excellent evaluation results were obtained regarding the ball joint life in a high temperature storage test.
- Example No. Numerals 50 to 54, 60 to 70, and 72 to 74 are Cu alloy bonding wires for semiconductor devices, and 0.001% by mass or more and 0.75% by mass of one or more of P, In, Ga, Ge, and Ag in total. % Or less, excellent evaluation results were obtained regarding the ball pressure bonding shape.
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Abstract
Description
本明細書におけるボンディングワイヤ表面の結晶方位の測定方法について説明する。本明細書において、ワイヤ表面の結晶方位とは、ワイヤ表面に存在するCuおよびCuを主体とする合金部分の結晶方位と定義する。ワイヤ表面の結晶方位の測定には、SEMに備え付けた、後方散乱電子線回折(EBSD:Electron Backscattered Diffraction)法を利用することができる。EBSD法は、試料に電子線を照射したときに発生する反射電子の回折パターンを検出器面上に投影し、その回折パターンを解析することによって、各測定点の結晶方位を決定する手法である。EBSD法によって得られたデータの解析には専用ソフト(TSLソリューションズ製 OIM analysis等)を用いることができる。本実施形態では、ボンディングワイヤを試料台に固定し、一方向からワイヤ表面に電子線を照射させて、結晶方位のデータを取得する。この方法を用いることにより、ワイヤ表面の結晶方位のうち、ワイヤ中心軸を含む1つの平面に垂直な方向に対する結晶方位と、ワイヤ中心軸方向に対する結晶方位を決定することができる。
本明細書におけるボンディングワイヤのワイヤ中心軸に対して垂直な断面の平均結晶粒径の測定方法について説明する。平均結晶粒径の測定には、EBSD法を用いることができる。結晶粒径は、EBSD法によって測定した方位差が15度以上の結晶粒界に囲まれた領域の面積から算出した円相当径と定義する。平均結晶粒径には、無作為に抽出したボンディングワイヤ5本について測定した結晶粒径の値の算術平均の値を用いる。ワイヤ中心軸に対して垂直な断面を露出させる方法としては、ボンディングワイヤを樹脂に埋め込んでから機械研磨する方法や、Arイオンビームによって加工する方法を用いることができる。
ボンディングワイヤに含まれる元素の濃度分析には、ICP発光分光分析装置等を利用することができる。ボンディングワイヤの表面に炭素、硫黄などの汚染物の濃度が高い場合には、解析を行う前にボンディングワイヤの表面から1~2nmの領域をスパッタ等で除去してから濃度分析を行っても良い。その他の方法として、酸洗浄を用いる方法も有効である。
発明者らは、ループ直進性の支配因子を調査した結果、ワイヤ表面の結晶方位と相関が認められることを見出した。具体的には、ワイヤ表面に特定の結晶方位が強く配向すると、特定の方向にループ全体が傾いたり、ループの一部が湾曲してしまっていた。この理由として、ワイヤ表面の塑性異方性が大きくなり、ループ部分に負荷がかかった際に、特定の方向に変形しやすいこと等が考えられる。このループ直進性の推定低下機構をもとに、発明者らはループ直進性の改善方法を鋭意検討した。その結果、ワイヤ表面の結晶方位のうち、ワイヤ中心軸を含む1つの平面に垂直な方向に対して角度差が15度以下である<100>結晶方位、<110>結晶方位、<111>結晶方位の存在比率とループ直進性の間に強い相関があり、これらの結晶方位の存在比率を適正な範囲に制御することにより、ループ直進性を改善する効果が得られることを見出した。具体的には、本実施形態のボンディングワイヤを用いて接合を100回実施し、ループを光学顕微鏡によって観察した結果、ループ全体が傾いたり、ループの一部が湾曲している場所が著しく減少し、高いループ直進性が得られていることを確認した。
本実施形態のボンディングワイヤは、さらにワイヤ表面の結晶方位のうち、ワイヤ中心軸を含む1つの平面に垂直な方向に対して角度差が15度以下である<100>結晶方位、<110>結晶方位、<111>結晶方位の存在比率の合計が、15%以上50%未満であることが好ましい。これにより、樹脂封止工程を経た後も高いループ直進性を維持する効果が得られる。具体的には、ボンディングワイヤを接合後、トランスファー成形により樹脂封止し、軟X線装置を用いてループを観察した結果、高いループ直進性が維持されていることを確認した。これは、ワイヤ表面の結晶方位のうち、ワイヤ中心軸を含む1つの平面に垂直な方向に対して角度差が15度以下である<100>結晶方位、<110>結晶方位、<111>結晶方位の存在比率を、それぞれ平均面積率で3%以上27%未満とすることに加えて、これらの結晶方位の存在比率の合計を適正な範囲に制御することで、ループ部分の塑性異方性を低減する効果を相乗的に高めることができ、樹脂封止後も高いループ直進性を維持する効果が高められたためと考えられる。
本実施形態のボンディングワイヤは、さらにワイヤ表面の結晶方位のうち、ワイヤ中心軸を含む1つの平面に垂直な方向に対して角度差が15度以下である<100>結晶方位の存在比率をX、<110>結晶方位の存在比率をY、<111>結晶方位の存在比率をZとしたとき、X+Y>Zであることが好ましい。これにより、樹脂封止後も高いループ直進性を維持する効果がさらに高められる。この理由として、ワイヤ表面の結晶方位のうち、ワイヤ中心軸を含む1つの平面に垂直な方向に対して角度差が15度以下である<100>結晶方位、<110>結晶方位、<111>結晶方位の存在比率を、それぞれ平均面積率で3%以上27%未満とすること、これらの結晶方位の存在比率の合計を、15%以上50%未満とすることに加えて、前記X、Y、ZがX+Y>Zの関係を満足することによって、ループ部分の塑性異方性を更に低減することができ、ループ直進性を改善する効果が相乗的に高められたためと推定される。明確な理由は明らかではないが、前記<110>結晶方位と<110>結晶方位の合計存在比率の方が、前記<111>結晶方位の存在比率に比べて、ループ部分の異方性を低減させる効果が高いためと考えられる。
本実施形態のボンディングワイヤは、さらにワイヤ表面の結晶方位のうち、ワイヤ中心軸を含む1つの平面に垂直な方向に対して角度差が15度以下である<121>結晶方位、<123>結晶方位の存在比率が、平均面積率でそれぞれ15%未満であることが好ましい。これにより、樹脂封止後も高いループ直進性を維持する効果がより大きく高められる。この理由として、ワイヤ表面の結晶方位のうち、ワイヤ中心軸を含む1つの平面に垂直な方向に対して角度差が15度以下である<100>結晶方位、<110>結晶方位、<111>結晶方位の存在比率を、それぞれ平均面積率で3%以上27%未満とすること、これらの結晶方位の存在比率の合計を、15%以上50%未満とすること、前記X、Y、ZがX+Y>Zの関係を満足することに加えて、前記<121>結晶方位、<123>結晶方位の存在比率をそれぞれ15%未満とすることによって、ループ部分の塑性異方性を更に低減することができ、樹脂封止後もループ直進性を維持する効果が相乗的に高められたためと推定される。
本実施形態のボンディングワイヤは、さらにワイヤ中心軸に対して垂直な断面における平均結晶粒径が0.4μm以上2.1μm以下であることが好ましい。これにより、ネック部の損傷を低減することができる。これは、平均結晶粒径を0.4μm以上2.1μm以下としたことによって、ネック部の損傷の原因となる曲げ変形に対する塑性変形能が適正な範囲に制御されたためと考えられる。ネック部は、ボール形成の際にアーク入熱の影響を受けた部分(以下、熱影響部)に相当する。熱影響部の結晶粒径は、アーク入熱によって粗大化するが、ボンディングワイヤの平均結晶粒径を予め制御することによって、ネック部の結晶粒径の制御に有効であったと考えられる。
本実施形態のボンディングワイヤは、さらにワイヤ中心軸に平行な方向の断面における結晶方位のうち、ワイヤ中心軸方向に対して角度差が15度以下である<111>結晶方位と<100>結晶方位の存在比率の合計が、平均面積率で25%以上60%未満であることが好ましい。これにより、低ループ形成時においてもネック部分の損傷を低減する効果を得ることができる。これは、明確な理由は明らかではないが、前記<111>結晶方位と<100>結晶方位がネック部の曲げ変形に対する変形能の制御に対する影響が大きく、これらの存在比率の合計を適正に制御することで、ネック部の曲げ変形に対する塑性変形能を適正に制御できたためと考えられる。
本実施形態のボンディングワイヤは、さらにNi、Pd、Pt、Auの1種以上を総計で0.01質量%以上1.5質量%以下含み、残部がCuおよび不可避不純物であることが好ましい。これにより、200℃の高温放置試験におけるボール接合部寿命を500時間以上に改善することができる。この理由は、Ni、Pd、Pt、AuがボールとAl電極の界面における剥離発生の原因となるCu-Al系金属間化合物の成長速度を低下させる効果等によるものと考えられる。前記元素の濃度が0.01質量%未満の場合は、200℃の高温放置試験におけるボール接合部寿命を改善する効果が十分ではない。前記元素の濃度が1.5質量%を超える場合は、ボールの硬度が上昇して、金属間化合物の形成が不均一になるため、200℃の高温放置試験におけるボール接合部寿命の改善効果が十分ではない。
本実施形態のボンディングワイヤは、さらにP、In、Ga、Ge、Agの1種以上を総計で0.001質量%以上0.75質量%以下含み、残部がCuおよび不可避不純物であることが好ましい。これにより、ボール圧着形状が、花弁状となる不良を抑制する効果が得られる。このような効果が得られた理由は、ボールを構成する結晶粒が微細化されて、等方的な変形が促進されたためと推定される。前記濃度が0.001質量%未満の場合は、結晶粒を微細化する効果が不足するため、上記の効果が十分ではない。前記濃度が0.75質量%を超えるとボール内部での元素の偏析が顕著になり、ボールを構成する結晶粒のばらつきが増加するため、上記の効果が十分ではない。
本実施形態の半導体装置用ボンディングワイヤの製造方法について説明する。
(銅合金の作製方法)
まず、Cuの純度が4N~6N(Cu濃度:99.99質量%以上99.9999質量%以下)である高純度銅を原料とし、添加する元素と一緒に溶解することにより、銅合金のインゴット(鋳塊)を作製する。銅合金作製時には、銅と高純度の添加成分を直接溶解して合金化する方法や、銅に添加元素を3~5質量%程度含有する母合金を予め作製しておき、銅と母合金を溶解して合金化する方法等を用いることができる。母合金を利用する手法は、低濃度で元素分布を均一化する場合に有効である。溶解には、アーク溶解炉、高周波溶解炉等を利用することができる。大気中からのO2、H2等のガスの混入を防ぐために、真空雰囲気あるいはArやN2等の不活性雰囲気中で溶解を行うことが好ましい。インゴットの表面は、酸化物や汚れを除去するために酸洗浄、アルコール洗浄を行い、その後乾燥させることが好ましい。
製造した銅合金のインゴットは、まず圧延や鍛造加工により線状に加工する。次いで、引抜加工により製品となる最終線径まで細く加工していくことが好ましい。引抜加工には、ダイヤモンドコーティングされたダイスを複数個セットできる連続伸線装置を用いることができる。連続伸線の際は、ダイスの磨耗およびワイヤの表面疵の低減を目的として、潤滑液を使用することが好ましい。最終線径に到達する前段階の中間線径では、引抜加工の途中段階で、ひずみ取り等を目的として熱処理を行う。本明細書では、中間線径で行う熱処理を中間熱処理と称す。中間熱処理後のワイヤは製品として使用する最終線径まで引抜加工を行う。本明細書では、中間熱処理を行う線径から最終線径まで引抜加工を行う工程を最終引抜加工と称す。最終線径では、ボンディングワイヤを再結晶させて機械的特性を調整するための熱処理を行う。本明細書では、最終線径で行う熱処理を最終熱処理と称す。中間熱処理および最終熱処理は、ワイヤを連続的に掃引しながら熱処理を行う方法を用いることができる。なお、ボンディングワイヤ表面の酸化をできるだけ抑制する目的から、熱処理時はArガスやN2ガスを還流させた不活性雰囲気中で行うことが好ましい。さらに、不活性雰囲気中に、還元性のガス成分としてH2を数%含むことも有効である。
ワイヤ表面の結晶方位のうち、ワイヤ中心軸を含む1つの平面に垂直な方向に対して角度差が15度以下である<100>結晶方位、<110>結晶方位、<111>結晶方位の存在比率を、それぞれ平均面積率で3%以上27%未満に制御する方法の一例について説明する。
Pf:最終引抜加工の加工率
Rm:中間熱処理を行ったワイヤの直径(mm)、Rf:最終熱処理を行ったワイヤの直径(mm)
本実施形態のボンディングワイヤに含まれる元素の濃度分析には、ICP発光分光分析装置を用いた。
本実施形態のボンディングワイヤのワイヤ表面の結晶方位のうち、ワイヤ中心軸を含む1つの平面に垂直な方向に対して角度差が15度以下である<100>結晶方位、<110>結晶方位、<111>結晶方位、<121>結晶方位、<123>結晶方位の存在比率は、EBSD法によって測定したデータから算出した。前記存在比率は、ワイヤを約3m間隔で5本取得して測定した値の平均値とした。測定領域は、円周方向に対し5μm(ワイヤ直径の25%)、ワイヤ中心軸方向に対し40μmの直線に囲まれる領域とした。さらに前記測定領域は、試料台に固定したサンプルの円周方向に対して最も高い位置が含まれる領域とした。
本実施形態のボンディングワイヤのワイヤ中心軸に垂直な断面における平均結晶粒径は、ワイヤ断面をArイオンビームで加工して露出させた後、EBSD法によって測定したデータから算出した。ワイヤを約3m間隔で5本取得して、各ワイヤを測定した値の平均値とした。測定領域は、ワイヤ中心軸に垂直な断面がすべて含まれる領域とした。
本実施形態のワイヤ中心軸に平行な方向の断面におけるボンディングワイヤのワイヤ中心軸方向に対して角度差が15度以下である<111>結晶方位と<100>結晶方位の存在比率の合計は、ワイヤ断面をArイオンビームで加工して露出させた後、EBSD法によって測定したデータから算出した。前記存在比率の合計は、ワイヤを約3m間隔で10本取得して、各ワイヤを測定した値の平均値とした。測定領域は、ワイヤ中心軸方向が80μm、直径方向が20μmの長方形の領域とした。さらに前記測定領域は、直径方向に対してワイヤの両端が含まれる領域とした。
ループ直進性は、ボンディングワイヤを接合した際に、直進性が低いループが発生した頻度によって評価した。ループ部分の観察には光学顕微鏡を用いた。ループ長さは7.0mm、ループ高さは0.2mmとした。ループの直上からループ部分を観察し、ボール接合部とワイヤ接合部を直線で結んだ位置からループ部分までの距離が最も離れている場所で10μm以上離れていればループ直進性が低いと判定した。200本のボンディングワイヤのループを観察し、直進性の低いループが5本以上あれば不良と判断し-1点、直進性が低いループが3本以上5本未満であれば不良は発生するものの許容範囲内であり、実用上使用可能と判断し0点とした。直進性が低いループが2本以下であれば実用上問題がないと判断し1点とした。評価結果は、表2の「ループ直進性」の欄に表記した。-1点が不合格、0点及び1点は合格である。
樹脂封止後のループ直進性は、ボンディングワイヤを接合した後、汎用のモールド樹脂で封止した際に、直進性が低いループが発生した頻度によって評価した。ループ部分の観察には軟X線装置を用いた。ループ長さは7.0mm、ループ高さは0.2mmとした。ループの直上からループ部分を観察し、ボール接合部とワイヤ接合部を直線で結んだ位置からループ部分までの距離が最も離れている場所で15μm以上離れていれば直進性が低いと判定した。200本のボンディングワイヤのループを観察し、直進性が低いループが6本以上あれば不良と判断し-1点、4本以上6本未満であれば不良は発生するものの許容範囲内であり、実用上使用可能と判断し0点とした。直進性が低いループが3本であれば実用上問題がないと判断し1点、2本であれば優れていると判断し2点、1本であればさらに優れていると判断し3点、全て直進性が高かった場合は、特に優れていると判断し4点とした。評価結果は、表2の「樹脂封止後のループ直進性」の欄に表記した。-1点が不合格、それ以外は合格である。
ネック部損傷は、ボンディングワイヤを接合後、ネック部分を観察して、損傷が発生した箇所の数によって評価した。ループ長さは7.0mm、ループ高さは0.2mm、ループ形状は台形形状とした。接合した200本のボンディングワイヤのネック部分を走査型電子顕微鏡で観察し、損傷が発生した箇所が2箇所以上あれば不良と判断し0点と表記した。損傷が発生した箇所が1箇所であれば実用上問題がないと判断し1点、不良が全く発生しなければ優れていると判断し2点と表記した。評価結果は、表2の「ネック部損傷」の欄に表記した。0点が不合格、それ以外は合格である。
低ループ時のネック部損傷の評価では、ループ高さを通常よりも低い0.1mmとし、前記ネック部損傷の評価方法と同様の方法を用いた。接合した200本のボンディングワイヤのネック部分を走査型電子顕微鏡で観察し、損傷が発生した箇所が2箇所以上あれば不良と判断し0点と表記した。損傷が発生した箇所が1箇所であれば実用上問題がないと判断し1点、不良が全く発生しなければ優れていると判断し2点と表記した。評価結果は、表2の「低ループ時のネック部損傷」の欄に表記した。0点が不合格、それ以外は合格である。
高温放置試験におけるボール接合部寿命は、ボンディングワイヤを接合し、汎用の樹脂で封止した後、200℃に設定した恒温炉内に放置し、ボール接合部の接合強度が試験前の50%以下に低下するまでに要した時間により評価した。ボール接合部寿命の判定に用いた接合強度の値は、微小シェア試験機を用いて、無作為に選択した10箇所のボール接合部の強度を測定した値の平均値を用いた。接合強度を測定する際は、ボール接合部を露出させるために、酸処理によって樹脂を除去した。ボールの直径は、ワイヤの直径に対して1.5~1.7倍の範囲とした。ボール形成時には、酸化を防ぐためにN2+5体積%H2ガスを流量0.4~0.6L/minで吹き付けた。上記の評価において、ボール接合部の寿命が500時間未満であれば実用上問題があると判断し0点、500時間以上700時間未満であれば、実用上問題ないと判断し1点、700時間以上であれば優れていると判断し2点と表記した。評価結果は、表2の「高温放置試験におけるボール接合部寿命」の欄に表記した。0点が不合格、それ以外は合格である。
ボール圧着形状は、Si基板上のAl電極に100回ボール接合を行い、圧着形状不良の発生数によって評価した。ボール圧着形状の判定は、ボールをボール接合部の直上から観察し、ボール圧着形状が円形に近ければ良好と判定し、花弁状の形状であれば不良と判定した。ボール圧着形状の観察には光学顕微鏡を用いた。100箇所のボール接合部を観察し、不良が9個以上あれば実用上問題があると判断し0点、不良が8個以下6個以上であれば実用上問題がないと判断し1点、不良が5個以下3個以上であれば優れていると判断し2点と表記した。評価結果は、表2の「ボール圧着形状」の欄に表記した。0点のみが不合格であり、それ以外は合格である。
実施例No.1~87は、半導体装置用Cu合金ボンディングワイヤであって、ワイヤ表面の結晶方位のうち、ワイヤ中心軸を含む1つの平面に垂直な方向に対して角度差が15度以下である<100>結晶方位、<110>結晶方位、<111>結晶方位の存在比率が、それぞれ平均面積率で3%以上27%未満であるので、ループ直進性は許容範囲内であった。実施例No.1~75は、上記存在比率がそれぞれ平均面積率で5%以上25%未満であるので、ループ直進性は実用上問題なかった。
Claims (8)
- 半導体装置用Cu合金ボンディングワイヤであって、ワイヤ表面の結晶方位のうち、ワイヤ中心軸を含む1つの平面に垂直な方向に対して角度差が15度以下である<100>結晶方位、<110>結晶方位、<111>結晶方位の存在比率が、それぞれ平均面積率で3%以上27%未満であることを特徴とする半導体装置用Cu合金ボンディングワイヤ。
- 前記ワイヤ表面の結晶方位のうち、ワイヤ中心軸を含む1つの平面に垂直な方向に対して角度差が15度以下である前記<100>結晶方位、前記<110>結晶方位、前記<111>結晶方位の存在比率の合計が、平均面積率で15%以上50%未満であることを特徴とする請求項1に記載の半導体装置用Cu合金ボンディングワイヤ。
- 前記ワイヤ表面の結晶方位のうち、ワイヤ中心軸を含む1つの平面に垂直な方向に対して角度差が15度以下である前記<100>結晶方位の存在比率をX、前記<110>結晶方位の存在比率をY、前記<111>結晶方位の存在比率をZとしたとき、X+Y>Zであることを特徴とする請求項2に記載の半導体装置用Cu合金ボンディングワイヤ。
- 前記ワイヤ表面の結晶方位のうち、ワイヤ中心軸を含む1つの平面に垂直な方向に対して角度差が15度以下である<121>結晶方位、<123>結晶方位の存在比率が、平均面積率でそれぞれ15%未満であることを特徴とする請求項3に記載の半導体装置用Cu合金ボンディングワイヤ。
- ワイヤ中心軸に対して垂直な断面における平均結晶粒径が0.4μm以上2.1μm以下であることを特徴とする請求項1~4のいずれか1項に記載の半導体装置用Cu合金ボンディングワイヤ。
- ワイヤ中心軸に平行な方向の断面における結晶方位のうち、ワイヤ中心軸に対して角度差が15度以下である<111>結晶方位と<100>結晶方位の存在比率の合計が、平均面積率で25%以上60%未満であることを特徴とする請求項1~5のいずれか1項に記載の半導体装置用Cu合金ボンディングワイヤ。
- Ni、Pd、Pt、Auの1種以上を総計で0.01質量%以上1.5質量%以下含み、残部がCuおよび不可避不純物であることを特徴とする請求項1~6のいずれか1項に記載の半導体装置用Cu合金ボンディングワイヤ。
- P、In、Ga、Ge、Agの1種以上を総計で0.001質量%以上0.75質量%以下含み、残部がCuおよび不可避不純物であることを特徴とする請求項1~7のいずれか1項に記載の半導体装置用Cu合金ボンディングワイヤ。
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TW108134130A TWI749372B (zh) | 2018-09-21 | 2019-09-20 | 半導體裝置用Cu合金接合導線 |
KR1020207026714A KR102208869B1 (ko) | 2018-09-21 | 2019-09-20 | 반도체 장치용 Cu 합금 본딩 와이어 |
CN201980020738.5A CN111886685B (zh) | 2018-09-21 | 2019-09-20 | 半导体装置用Cu合金接合线 |
US16/976,069 US10985130B2 (en) | 2018-09-21 | 2019-09-20 | Cu alloy bonding wire for semiconductor device |
SG11202007956YA SG11202007956YA (en) | 2018-09-21 | 2019-09-20 | Cu alloy bonding wire for semiconductor device |
JP2019563915A JP6651065B1 (ja) | 2018-09-21 | 2019-09-20 | 半導体装置用Cu合金ボンディングワイヤ |
EP19862668.1A EP3745450A4 (en) | 2018-09-21 | 2019-09-20 | COPPER ALLOY CONNECTOR WIRE FOR SEMICONDUCTOR DEVICE |
PH12020551276A PH12020551276A1 (en) | 2018-09-21 | 2020-08-19 | Cu alloy bonding wire for semiconductor device |
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CN116568835A (zh) * | 2021-12-07 | 2023-08-08 | 古河电气工业株式会社 | 铜系线材及半导体器件 |
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JP4141854B2 (ja) | 2002-04-05 | 2008-08-27 | 新日鉄マテリアルズ株式会社 | 半導体装置用金ボンディングワイヤおよびその製造法 |
TWI237334B (en) * | 2002-04-05 | 2005-08-01 | Nippon Steel Corp | A gold bonding wire for a semiconductor device and a method for producing the same |
JP3697227B2 (ja) * | 2002-06-24 | 2005-09-21 | 新日本製鐵株式会社 | 半導体装置用金ボンディングワイヤ及びその製造方法 |
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MY164643A (en) * | 2009-07-30 | 2018-01-30 | Nippon Steel & Sumikin Mat Co | Bonding wire for semiconductor |
JP5497360B2 (ja) | 2009-07-30 | 2014-05-21 | 新日鉄住金マテリアルズ株式会社 | 半導体用ボンディングワイヤー |
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