WO2004028732A1

WO2004028732A1 - Connection method and connection device

Info

Publication number: WO2004028732A1
Application number: PCT/JP2003/012144
Authority: WO
Inventors: Akira Yamauchi
Original assignee: Toray Engineering Co., Ltd.
Priority date: 2002-09-25
Filing date: 2003-09-24
Publication date: 2004-04-08
Also published as: AU2003271061A1; TW200406875A

Abstract

A connection method for joining, to each other, connected objects having metal connection parts on the surfaces of the base materials thereof and a connection device, the method comprising the steps of washing the connected surfaces of the metal connection parts of both connected objects by energy wave and joining the metal connection parts to each other by ultrasonic wave in the air, whereby a specified ultrasonic connection can be performed without damaging the objects, an ultrasonic connection time can be shortened to shorten the tact time of an overall connection process and reduce an ultrasonic energy capacity so as to reduce the size and cost of the entire device, and also dissimilar metals such as metals in the combinations of gold/copper and gold/aluminum which could not be joined by ultrasonic wave before can be jointed.

Description

Satsuki Itoda »

Joining method and apparatus

Technical field

The present invention relates to a joining method and an apparatus for joining objects to be joined having a metal joint on the surface of a substrate, such as a chip, a wafer, and various circuit boards.

Background technology

As a method of joining objects to be joined having a metal joint, a joining method using ultrasonic waves is conventionally known. However, in conventional ultrasonic bonding, if the oxide film, organic material layer, or contamination layer formed on the surface of the bonding surface is relatively thick or strongly adhered, it can be sufficiently applied by applying ultrasonic waves. However, it was difficult to break or remove it in a short time, and in practice, it was impossible to perform highly reliable ultrasonic bonding. Also, in such a situation, if the ultrasonic wave is increased in intensity (for example, the amplitude is increased) or applied for a long time in order to forcibly join the chip, the chip as the object to be bonded or the chip formed on the chip is formed. Damage to the bumps may result, greatly reducing the reliability of the bonded product. In addition, long-time application is not preferable because it causes an increase in the tact time of the junction. Therefore, in the conventional method, it is difficult and undesired to increase the intensity of the ultrasonic wave and the application time. However, if the intensity is low and the application time is short, the ultrasonic bonding with high reliability is performed. I can't do it.

On the other hand, apart from the above ultrasonic bonding, as a method of bonding objects to be bonded having a bonding portion, Japanese Patent No. 2791429 discloses a method for bonding the bonding surfaces of one silicon wafer. Prior to bonding, a silicon wafer-to-silicon bonding method is disclosed in which an inert gas ion beam or an inert gas fast atom beam is irradiated in a vacuum at room temperature and sputter-etched. In this bonding method, oxides, organic substances, etc. on the bonding surface of the silicon wafer are blown by the above-mentioned beam to form a surface with activated atoms, and the surfaces are bonded by a high bonding force between the atoms. Joined. Therefore, this method basically eliminates the need for heating for bonding, and enables bonding at room temperature or a lower temperature by simply bringing the activated surfaces into contact with each other.

However, in this bonding method, the bonding between the etched bonding surfaces is performed in a vacuum. It must be performed while maintaining the state of surface activation. For this reason, a predetermined vacuum state must be maintained from the surface cleaning by the beam to the bonding, and at least a part of the bonding mechanism is configured in a chamber capable of holding a predetermined degree of vacuum. Therefore, the size of the sealing mechanism becomes large, and the entire apparatus becomes large and expensive. Further, if these are to be performed at different locations in order to separate the steps of surface cleaning and bonding by the beam, if a predetermined vacuum state is maintained between the two locations, or the workpiece is maintained while maintaining the vacuum state. A means for transporting from the cleaning location to the joining location is required, making practical equipment design difficult and further increasing the overall size of the equipment. In addition, in this bonding method, since high-temperature heating is not performed, a high pressing force of about 300 MPa is required in order to crush unevenness of the bonding surface and obtain a good bonding area, and a bump on the semiconductor circuit is required. Compound semiconductors such as semiconductors and optical devices may be damaged.

As for the method of bonding by cleaning the surface by sputter etching by beam irradiation as described above, recently, while maximizing the advantage to the bonding by surface activation of the bonding surface as described above, the metal bonding part of the workpiece is The possibility of joining together in the air has begun to be explored. If bonding in the air becomes possible after surface activation, the bonding process and equipment can be greatly simplified as compared with bonding in the air or the like.

Disclosure of the invention

Therefore, the present inventors focused on the bonding technique by surface activation as described above, which has been recently studied, while considering the above-described problems in the conventional ultrasonic bonding, and as a result of conducting intensive studies and tests, It has been found that a problem in the conventional ultrasonic bonding can be solved by properly combining the heating and the heating, and the present invention has been completed in which metal bonding can be performed at a temperature lower than the conventional solder melting point.

That is, an object of the present invention is to reduce the intensity of ultrasonic waves and to shorten the application time, to perform desired ultrasonic bonding without damaging the object to be bonded or the bonded portion, and to reduce the bonding time. It is an object of the present invention to provide a bonding method and apparatus using ultrasonic waves which can reduce the length of ultrasonic energy required for bonding, can reduce the capacity of ultrasonic energy required for bonding, and can reduce the size and cost of the entire apparatus. . In addition, the table It is an object of the present invention to provide a method and an apparatus which can perform bonding at a low pressure without applying a risk of damaging a bump or the like by applying ultrasonic waves even in low-temperature bonding by surface activation.

In order to achieve the above object, a joining method according to the present invention provides a method for joining objects having a metal joint on a surface of a base material, by using an energy wave on the surface of the metal joint of both objects. After cleaning, the method is characterized in that the metal joints are ultrasonically joined together in the air. Cleaning of the metal joint surface with energy waves can be performed under atmospheric pressure, or under reduced pressure.

The conditions for applying ultrasonic waves for bonding are preferably optimized as follows in order to suppress damage (particularly, cracks) to the metal bonding part. That is, the amplitude of the applied ultrasonic wave is set to less than 3 / m. It is more preferably 2 m or less, and further preferably 1 m or less.

In addition, the decrease in the bonding performance due to the decrease in the intensity of the applied ultrasonic wave by reducing the amplitude of the ultrasonic wave as described above can be compensated for by increasing the frequency of the applied ultrasonic wave. The frequency of the ultrasonic wave is preferably 40 kHz or more, and more preferably 60 kHz or more.

In addition, the application of ultrasonic waves makes it possible to significantly reduce the bonding load compared to conventional low-temperature pressure bonding by surface activation. In order to achieve good joining while suppressing damage to the metal joint, the joining load is preferably set to 150 MPa or less.

As an energy wave used for cleaning the surface of the metal joint, plasma is preferable, and in particular, plasma in an Ar gas atmosphere is preferable.

The above-mentioned bonding can be performed at room temperature.However, by using heating together, the diffusion of particles is promoted, so that the unevenness of the bonding interface can be more easily crushed and flattened, and a good bonding state can be obtained. become. The heating temperature may be 180 ° C. or less, preferably less than 150 ° C. In other words, the conventional general low-temperature metal bonding is a solder bonding, and the melting point of the hang is about 18 ° C., so the lower-temperature bonding, that is, 180 ° C. or less, preferably 150 ° C. This enables joining at a temperature lower than ° C.

In the above-mentioned cleaning by energy waves, the entire surface to be joined of the metal joint is 1 nm or less. It is preferable to etch to an upper depth. By irradiating energy waves that can be etched to such a depth or more, it becomes possible to obtain surface properties necessary for joining metal joints in the air.

The ultrasonic joining according to the present invention is particularly suitable for joining metal joints whose surfaces are formed of any one of Au, Cu, Al, In, and Sn. For example, as a combination of metal joints to be joined to each other, the same kind of metal of Au, Cu, Al, In, Sn, or any two kinds of dissimilar metals, or One can be A u and the other can be any of Cu, A 1, In, and Sn. Above all, in the case of joining Au, the joining can be surely performed even at room temperature. However, even in cases other than the joining of Au (for example, joining of λ \ χ / Cu, Au / A1, etc.), joining can be performed at room temperature or at a low temperature close to that. When at least one of the metal joints is made of a specific metal, for example, Au, the entire electrode or the like forming the metal joint can be made of Au, but only the surface is made of Au. You can also. The form for forming the surface with Au is not particularly limited, and a form of Au plating or a form in which an Au thin film is formed by sputtering or vapor deposition may be used. Also, if the bonding surface is limited to Au, surface activation enables bonding at room temperature even in air, and even if the pressure is reduced to about half by ultrasonic application under bonding at room temperature, the interface Squeezes the unevenness of the slab to achieve good bonding. Conventionally, a pressure of about 300 MPa was required, but by applying ultrasonic waves after surface activation, the pressure can be reduced to about 150 MPa.

At the time of joining the metal joints, it is preferable that the variation in the gap between the metal joints is 4 μm or less at the maximum. If the variation of the gap is 4 / m or less, an appropriate joint load, for example, a joint load of about 300 MPa (preferably, 150 MPa or less) is used for joining metal joints. It is possible to suppress the variation of the gap required for the following. Further, it is preferable to adjust the parallelism between the objects to be joined to within 4 m when joining the metal joints. Such parallelism adjustment makes it possible to reduce the above-mentioned variation in the gap, and allows the metal joints to come into more close surface contact with each other, thereby making it easier to perform low-temperature joining. In addition, at the time of joining metal joints, at least the surface roughness (particularly surface undulation) of at least one metal joint before joining should be 300 nm or less so that the surfaces can be in good contact with each other. Is preferred. With such a surface roughness, closer bonding can be achieved.

Further, it is preferable that the surface roughness of the metal joint after joining is 10 nm or less. When the interface after bonding is crushed to a surface roughness of 10 nm or less, the bonding area is increased, resulting in a low resistance and good bonding strength.

For the same purpose as described above, the surface hardness of at least one of the metal joints may be reduced to 120 or less in picker hardness H, and more preferably, reduced to 100 or less by annealing. preferable. For example, the surface hardness Hv is preferably in the range of 30 to 70 (for example, the average 平均 V is 50). With such a low hardness, the surface of the metal joint is appropriately deformed when a joining load is applied, so that a more intimate joint is possible.

A joining apparatus according to the present invention is an apparatus for joining objects to be joined having a metal joint on a surface of a base material, and a cleaning unit for irradiating an energy wave to the surface of the metal joint of each article to be joined. And a joining means for ultrasonically joining the metal joints of the objects taken out from the means in the air. In this bonding apparatus, the cleaning means may be configured to irradiate an energy wave to the surface of the metal joint under atmospheric pressure, or to irradiate the energy wave to the surface of the metal joint under reduced pressure. Means can also be constituted.

In order to optimize the ultrasonic application conditions for bonding, the above-mentioned bonding means should have an amplitude of less than 3 / zm, preferably 2 // m or less, and more preferably It is preferable to use a means capable of applying an ultrasonic wave of 1 / m or less. In addition, since the joining means is constituted by means capable of applying an ultrasonic wave having a frequency of 40 kHz or more, preferably 60 kHz or more, the energy can be increased even if the amplitude is reduced. It is preferable that it is comprised as follows. Further, it is preferable that the joining means is a means capable of joining with a joining load of 150 MPa or less.

In this bonding apparatus, it is preferable that the cleaning unit is a plasma irradiation unit, and it is particularly preferable that the cleaning unit is an Ar plasma irradiation unit. Further, the joining means has a heating means and is configured to be capable of ultrasonically joining the metal joints at a temperature of 180 ° C. or less, preferably less than 150 ° C. lower than the solder melting point. Is preferred.

In addition, the above-mentioned cleaning means can perform etching to a depth of 1 nm or more on the entire surface to be joined of the metal joint in order to perform surface etching necessary for joining metal joints in the air. It is preferable to include a means for irradiating an energy wave with a high energy or more.

Also, as described above, the combination of the surface metal types of the two metal joints to be combined is, as described above, any one of the same metal of Au, Cu, Al, In, and Sn, or any two of them. Or a combination in which one is Au and the other is one of Cu, Al, In, and Sn. Above all, when Au is combined, bonding becomes the easiest.

Further, it is preferable that the above-mentioned joining means is provided with means for reducing a variation of a gap at the time of joining between metal joints to a maximum of 4 μm or less. Further, it is preferable that the joining means includes means for adjusting the parallelism between the objects to be joined at the time of joining the metal joints to within 4 / m. In addition, it is desirable that the surface roughness of at least one of the metal joints before joining is 300 nm or less. It is also desirable that the surface roughness of at least one of the metal joints after joining is 10 nm or less. Further, it is desirable that at least one metal joint has a surface hardness of 120 or less, more preferably 100 or less, in Vickers hardness HV.

The present invention also provides a joined body produced by the joining method as described above. In other words, the joined body according to the present invention is a joined body of objects to be joined having a metal joint on the surface of the base material, and the surfaces of the metal joints of both the objects are cleaned by energy waves. After that, the metal joints are ultrasonically joined to each other in the air, and are produced.

In the above joined body, at least one of the joined objects can be made of a semiconductor.

In the bonding method and apparatus according to the present invention as described above, the surface of the metal bonding portion of the workpiece is irradiated with an energy wave under reduced pressure or atmospheric pressure, and the surface is etched. The metal joints cleaned and activated by the metal bonding are ultrasonically bonded in the air. Since the oxide film, organic layer, and contamination layer on the surface are removed by energy wave irradiation beforehand, desired bonding can be performed in a short time with low-intensity ultrasonic waves. Therefore, it is possible to perform good ultrasonic bonding without damaging the workpieces and the joints, and shorten the time required for ultrasonic bonding to shorten the tact time of the entire bonding process. Becomes possible. In addition, since the capacity of the ultrasonic wave applying means may be small, the whole apparatus can be reduced in size and cost. Furthermore, since joining in the atmosphere is possible, a large-scale vacuum device and a sealing device therefor are not required for joining. From this aspect, the entire process and the entire device are greatly simplified, and It will also allow for downtime. Furthermore, since bonding can be performed at a low temperature, particularly at or near normal temperature, the load on the heating device can be reduced.

In addition, the oxide film, organic layer, and contamination layer on the surface are removed in advance by irradiation with energy waves, which enables the joining of dissimilar metals, which could not be done conventionally, for example, the ultrasonic joining of gold / copper / gold / aluminum. This greatly expands the scope of ultrasonic bonding.

In addition, by applying ultrasonic waves after activating the surface of the bonding surface by irradiation with energy waves in advance, the bonding load can be significantly reduced even at room temperature bonding. When the bonding surface is Au, surface activation enables bonding at room temperature even in air, and in this bonding at room temperature, even if the pressure is reduced to about half by applying ultrasonic waves, the unevenness of the interface And a good joining is possible.

In particular, in the present invention, bonding conditions are greatly reduced by a combination of cleaning by irradiation of energy waves in advance and ultrasonic bonding. In conventional ultrasonic bonding, it was necessary to apply ultrasonic waves with an amplitude of 3 μm or more, but if the amplitude is 3 // in or more, the contribution to the bonding will be large, but there is a risk of damage. In the present invention, the amplitude of the contamination layer can be reduced because the contaminant layer is extremely thin due to the activation of the bonding surface by the energy wave cleaning. Therefore, it is possible to eliminate damage (for example, crack generation) due to application of ultrasonic waves. Also, the ultrasonic intensity may decrease due to the decrease in amplitude, and the contribution to joining may decrease accordingly. Even if the amplitude is reduced to reduce the leakage, sufficient contribution to the junction is maintained by increasing the frequency, especially by increasing the frequency to 40 kHz or more, preferably 60 kHz or more. It is possible to do. In other words, the bonding mechanism is considered to be such that the metal itself expands and contracts repeatedly due to the high-frequency vibration, so that it is possible to almost eliminate the need to increase the amplitude.

In addition, the application of ultrasonic waves increases the stress at the bonding interface, so that the unevenness at the interface is easily crushed, and as a result, the same state as softening is created. As a result, joining with a lower load is possible compared to joining by simple pressurization. Conventionally, a joining load of at least 300 MPa was required, but joining at 150 MPa or less is possible.

Further, by performing the combined use of heating at an appropriate temperature, suppressing the variation in the gap between the metal joints, and adjusting the parallelism, it becomes possible to more easily perform the predetermined ultrasonic welding.

As described above, according to the bonding method and apparatus according to the present invention, desired ultrasonic bonding can be performed without causing damage, and the ultrasonic bonding time can be shortened, and the tact time of the entire bonding process can be shortened. At the same time, it is possible to reduce the ultrasonic energy capacity, thereby making it possible to reduce the size and cost of the entire device. Also, it is possible to join with a combination of dissimilar metals, such as gold / copper or gold aluminum, which could not be ultrasonically joined conventionally.

In addition, pre-energy wave cleaning makes it possible to greatly reduce the intensity of applied ultrasonic waves, and by optimizing the application conditions, damage is caused even on objects that are easily damaged. Without joining, it is possible to join well with high production efficiency.

Furthermore, compared to the conventional low-temperature bonding by surface activation, the application of ultrasonic waves makes it possible to greatly reduce the bonding load, and it is possible to use compound semiconductors such as bumps and optical elements on semiconductor circuits. Joining is possible even for those that cannot apply a large load.

Brief explanation of drawings

FIG. 1 is a schematic configuration diagram of a joining device according to an embodiment of the present invention. Figure 2 shows the relationship between the thermal shock test cycle and the yield rate.

Figure 3 is a diagram showing the relationship between the ultrasonic amplitude and the shear strength in the model test. Figure 4 shows the relationship between ultrasonic amplitude and shear strength (relative value) in another model test.

FIG. 5 is a diagram showing the relationship between the bonding load and the amount of bump crush in the model test. Figure 6 is a diagram showing the relationship between the frequency and the non-defective product ratio (relative value) in the ultrasonic test with an amplitude of 1 / zm.

[Explanation of symbols]

1 Joining equipment

2, 3 metal joint

4 Workpiece (chip)

5 Workpiece (substrate)

6 Vacuum pump

7 Chamber

8 Plasma irradiation means

9 Plasma

1 0 Ar gas supply pump

1 1 Joining unit

1 2 Standby unit

1 3 Reversing mechanism

1 4 Head of reversing mechanism

1 5 Bonding head

1 6 Bonding tool

1 7 Bonding stage

1 8 Heater as heating means

1 9 Ultrasonic wave applying means

2 0 Position adjustment table

2 1 2 Field of view recognition

Best mode for carrying out the invention Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a joining apparatus 1 according to one embodiment of the present invention. A workpiece 4 or 5 having a metal joint 2 or 3 on the surface of a base material is firstly cleaned as a means for cleaning by an energy wave in a chamber 7 evacuated by a vacuum pump 6 to a predetermined degree of vacuum. The surfaces of the metal joints 2 and 3 are cleaned by etching with the plasma 9 irradiated from the plasma irradiation means 8 (cleaning step). In the present embodiment, the Ar gas can be supplied into the chamber 7 by the pump 10, so that plasma irradiation can be performed in an Ar gas atmosphere and under a predetermined reduced pressure. Although plasma irradiation is performed under a predetermined reduced pressure in this embodiment, plasma irradiation may be performed under atmospheric pressure. The cleaned workpieces 4 and 5 are taken out of the chamber 7, and the metal bonding sections 2 and 3 are ultrasonically bonded to each other in the air in a bonding process (a bonding apparatus section 11).

The article 4 is made of, for example, a chip, and the article 5 is made of, for example, a substrate. However, here, the chip refers to all forms on the side to be bonded to the substrate regardless of the type or size, such as an IC chip, a semiconductor chip, an optical element, a surface mount component, and a wafer. For example, bumps are formed on the article 4 as the metal joints 2. Further, the term “substrate” refers to, for example, a resin substrate, a glass substrate, a film substrate, a chip, a wafer, or any other form of the side to be bonded to the chip regardless of the type or size. A typical embodiment of the present invention is an embodiment in which at least one of the objects to be joined is made of a semiconductor. The cleaned articles 4 and 5 are transported by a suitable transporting means from the cleaning means having the chamber 7 to the bonding means in the bonding apparatus 11. In the joining device section 11, for example, the above-mentioned cleaned articles 4 and 5 are placed in a predetermined standby section 12. The workpiece 4 is held on the head 14 of the reversing mechanism 13 by suction or the like so as not to touch the cleaning surface, is turned upside down, and is installed under the bonding head 15. The metal bonding portion 2 is held by suction or the like in the form in which the metal bonding portion 2 faces downward on the bonded bonding tool 16. The article 5 is transferred from the standby section 12, and is held on the bonding stage 17, for example, by suction or the like with the metal joined section 3 facing upward. In the present embodiment, the bonding tool 16 is used as a heating means. All heaters 18 are built-in, and it is possible to perform both joining at room temperature and joining under heating in the air.

The bonding head 15 can press the workpiece 4 downward through the bonding tool 16 to apply and control a predetermined bonding load to the workpiece 5. I have. In this embodiment, the bonding head 15 can be moved and positioned in a vertical direction (Z direction). The bonding head 15 or the bonding tool 16 is provided with an ultrasonic wave applying means 19, and in this embodiment, the ultrasonic vibration is applied to the object 4 side, particularly to the metal joint 2 thereof. By applying, ultrasonic bonding can be performed with the metal joint 3 of the article 5 to be joined.

Further, in this embodiment, the bonding stage 17 holding the article 5 is provided with a horizontal position control in the X and Y directions, By controlling the rotational direction of the workpiece and the tilt adjustment control around the X-axis and Y-axis, relative positioning and parallelism adjustment with the workpiece 4 can be performed. This also makes it possible to reduce variations in the gap at the time of joining. The relative alignment and the parallelism adjustment are performed by the recognition means inserted between the workpieces 4 and 5 so as to be able to move forward and backward, for example, the two-view recognition means 21 (for example, a two-view camera), Alternatively, the recognition is performed by reading recognition marks (not shown) attached to the holding means, and performing necessary corrections of the position and the angle based on the read information. The two-field-of-view recognizing means 21 can adjust the position in the X and Y directions, and in some cases in the Z direction. In this embodiment, the relative positioning and the parallelism adjustment are mainly performed on the bonding stage 17 side, but it is also possible to perform the bonding on the bonding head 15 or the bonding tool 16 side. It is also possible to do it on both sides. In the case of performing on both sides, rotation control and Z or parallel movement control as well as lifting and lowering control are performed for the bonding head 15 side as necessary, and rotation control and parallel control are also performed for the bonding stage 17 side. Movement control and elevation control can be performed, and these control forms can be arbitrarily combined as needed.

The joining method according to the present invention using the above-described joining apparatus is performed as follows. First, in a chamber 7 having a predetermined degree of vacuum, a metal bonding portion 2 (for example, a bump) of a chip 4 as a workpiece 4 and a metal bonding portion 3 (for example, a bump) of a substrate 5 as a workpiece 5 The electrodes are cleaned by Ar plasma and the surface is activated. In plasma cleaning, in order to remove the surface foreign material layer for ultrasonic bonding and sufficiently activate the surface, the plasma irradiation intensity and time are set so that the entire surface where the metal joint is bonded can be etched by 1 nm or more. It is preferable to set. As an example, this is a level at which Ar plasma is irradiated for 5 seconds by a plasma cleaning means of 100 V and 50 W.

The chip 4 and the substrate 5 whose surfaces have been cleaned are temporarily placed on the standby unit 12, and the chip 4 is turned upside down to the bonding tool 16, and the substrate 5 is not turned upside down to the bonding stage 17, respectively. Will be retained. The chip 4 and the substrate 5 held opposite to each other are aligned so as to be within a predetermined accuracy based on information read by the two-field recognition means 21 and the parallelism is adjusted so as to be within the predetermined accuracy. Is done. Regarding parallelism, in order to achieve good ultrasonic bonding, the parallelism between the two workpieces should be 4 // m or less, and the variation in the gap between metal joints should be 4 / m or less. It is preferable that the adjustment be made in such a manner.

From this state, the bonding tool 16 is lowered, a predetermined bonding load is applied, heated by a heater 18 as necessary, and utilizing ultrasonic vibration applied by ultrasonic applying means 19. The metal joint 2 (bump) of the chip 4 and the metal joint 3 of the substrate 5 are ultrasonically bonded in the air.

In conventional ultrasonic bonding, as described above, if the oxide film, organic material layer, or contamination layer on the surface of the bonding surface is thick or firmly adhered, ultrasonic bonding could not actually be performed. However, in the ultrasonic bonding according to the present invention as described above, before the bonding, the surface cleaning is performed by an energy wave, and in this embodiment, Ar plasma, and the etching required for the ultrasonic bonding is performed on the bonding surface. Is applied to sufficiently remove or decompose the foreign material layer as described above, and the surface is sufficiently activated, so that the ultrasonic irradiation intensity is lower than before (for example, with a smaller amplitude than before) and Desired ultrasonic bonding can be performed in a shorter time than before. Therefore, it is not necessary to increase the intensity of the applied ultrasonic waves or lengthen the application time to forcibly join the joints, which eliminates the possibility of damaging the chips and bumps and ensures the joint quality. Will be. Also, since the ultrasonic bonding time can be shortened, the tact time of the entire bonding process is also reduced, and productivity is greatly improved. Furthermore, since the ultrasonic wave application intensity may be small, the ultrasonic energy capacity is reduced, and the ultrasonic wave application means 19 may be small and inexpensive. Therefore, it can contribute to downsizing of the entire device and cost reduction.

In this ultrasonic bonding, as described above, at least one of the metal joints has a surface roughness of 300 nm or less before joining, or at least one of the metal joints has a surface roughness of less than 1 nm. It is effective to set the surface hardness of at least one of the metal joints to a value of 120 or less in terms of a picker hardness HV of 120 or less, or to use heating at the time of joining. By heating, the hardness of the surface can be reduced, and the movement of atoms on the surface at the time of bonding can be activated, so that the desired ultrasonic bonding can be performed more easily.

In particular, the effect of the combined use of heating is great, and both the effect of heating and the effect of energy wave cleaning can be obtained synergistically. Especially when heated to about 150 ° C, a great effect can be obtained. In particular, by bonding at a temperature lower than the conventional solder melting point, the effect of energy wave cleaning can be exhibited while maintaining the characteristics of low-temperature bonding as compared with conventional solder bonding. However, the heating temperature is appropriately set at a temperature of, for example, 180 ° C or less, preferably less than 150 ° C, so that a large load is not applied to the device and a problem due to heating does not occur in the metal joint. (For example, as described above, a temperature near 150 ° C. or lower) may be set.

Further, in the method of performing ultrasonic bonding in the air after the energy wave cleaning according to the present invention, as shown in Examples described later, particularly when both surfaces of the metal bonding portion are made of Au, low ultrasonic application intensity, The desired ultrasonic bonding can be performed with a short application time. However, in the bonding method according to the present invention, since the energy wave cleaning is performed in advance, not only the bonding of Au Any combination of, for example, Au ZCu Au / A1 ultrasonic bonding is possible, and by using heating as described above, ultrasonic bonding between these dissimilar metals can be performed more easily. Will be possible. In order to confirm the operation and effect of the present invention as described above, the metal contact of AuZAu When performing the ultrasonic bonding of the joints, tests were performed for the case where ultrasonic bonding was performed without prior plasma cleaning and the case where ultrasonic bonding was performed after plasma cleaning, while also considering the effect of heating. The plasma cleaning is performed with an energy capable of etching the surface of the bump as a metal joint at a depth of 1 nm in one time. As an example, Ar plasma cleaning is performed for 5 seconds by a plasma means of 100 V and 50 W. For the evaluation, a thermal shock test was performed to measure the non-defective rate (%) of bump bonding at that time by repeatedly applying temperature fluctuations of between 65 ° C and 150 ° C to the bonded body. . As a result, the characteristics shown in Fig. 2 were obtained.

As shown in Fig. 2, when ultrasonic bonding was performed at room temperature without plasma cleaning, only a low yield rate was obtained at a stage where the number of thermal shock cycles was small, but before plasma cleaning (2 Irradiation), a high yield rate was obtained up to the stage where the number of thermal shock cycles was large. In order to confirm the effect of heating, ultrasonic bonding was performed at 150 ° C at the time of joining without prior plasma cleaning, and a high yield rate was obtained up to the stage where the number of thermal shock cycles was large. Was. In the results shown in Fig. 2, the effect of heating is higher than that of pre-plasma cleaning.This is because the test was performed at a relatively high temperature of 150 ° C, and the effect of heating depends on the temperature. Therefore, if the test is performed at a temperature lower than 150 ° C, the effect of the pre-plasma cleaning may be higher. When both pre-plasma cleaning and heating are performed, both plasma cleaning once and plasma cleaning twice have achieved extremely high effects. It turns out that it is a form.

Also, when performing the above AuZAu bonding, it is possible to reduce the applied intensity of ultrasonic waves when performing the pre-plasma cleaning in the present invention as compared with the conventional simple ultrasonic bonding. To confirm this, a model test was performed to determine the relationship between the amplitude (m) of the applied ultrasonic wave and the shear strength (g / bump) of the bonded product. As a result, as shown in Fig. 3, this model test was applied to the application of ultrasonic waves with a relatively large amplitude. The one on which a large bump was formed was used. Under the conditions of this model test, compared with the case where ultrasonic waves having an amplitude of about 10 In the method, it was confirmed that the same bonding strength was obtained even when the amplitude of the applied ultrasonic wave was reduced to 4 / m or less, and that the pre-plasma cleaning could greatly contribute to the decrease in the applied ultrasonic wave intensity. . The ability to reduce the amplitude of ultrasonic waves reduces damage to chips and bumps, and also allows small and inexpensive means for applying ultrasonic waves, contributing to downsizing and cost reduction of the entire device. I was divided. In addition, since it is clear that the ultrasonic energy required for bonding is also small, the ultrasonic application time can be shortened, which can contribute to shortening the time required for bonding and also shortening the tact time of the entire bonding process. . When the metal joints are made of Au, there is no oxide film on the surface, and only organic matter is used. In this case, ultrasonic bonding can be performed by removing organic substances using oxygen plasma of atmospheric pressure plasma means without forcibly etching with reduced pressure plasma.

Furthermore, a chip that has been rapidly developed in recent years and has a fine pitch between metal joints (bumps) is used. In other words, conventional ultrasonic bonding requires the application of ultrasonic waves with an amplitude of 3 m or more. Were subjected to the same model test as described above by the method according to the present invention. Figure 4 shows the relationship between the test results and the shear strength (gZ bump) of the joined product. It can be seen that excellent effects were obtained with ultrasonic amplitude of less than 3 m by pre-plasma cleaning. By the way, when the amplitude was 3 μm, a small crack was formed on the back of the bump, but no crack was formed when the amplitude was 2 μm. Also, welding was possible even with an amplitude of 1 m.

In this model test, the amount of bump crush and bonding load with and without applying ultrasonic waves to the bump (material: Au, hardness: 60 Hv, initial surface roughness: 300 nm) Figure 5 shows the measurement results. As shown in Fig. 5, conventional room-temperature bonding requires 300 0 to achieve good bonding (bump crush: 1 // m or more, surface roughness after bonding: 10 nm or less). Although a bonding load of MPa was required, the same result was obtained at 150 MPa, which was half, by applying ultrasonic waves.

Furthermore, FIG. 6 shows the relationship between the non-defective rate after bonding and the frequency of the applied ultrasonic wave when applying an ultrasonic wave having an amplitude of 1 am in the method according to the present invention. As shown in Fig. 6, by setting the frequency to 40 kHz or more, particularly to 60 kHz or more, extremely excellent results were obtained even with an ultrasonic wave having an amplitude of 1 µm. Thus, as can be seen from the above model test, the conventional ultrasonic welding required a joint load of 300 MPa or more, but the method according to the present invention required a joint load of 150 MPa. Welding with welding load was successful.

Industrial availability

INDUSTRIAL APPLICABILITY The bonding apparatus and method according to the present invention can be applied to any ultrasonic bonding between objects to be bonded having a metal bonding portion, and are particularly suitable for ultrasonic bonding when at least one of the objects to be bonded is a semiconductor. is there.

Claims

Scope of demand

1. When joining objects having a metal joint on the surface of the base material, the surfaces of the metal joints of the two objects are cleaned with an energy wave, and then the metal joints are sonicated in the air. A joining method characterized by joining.

2. The joining method according to claim 1, wherein the amplitude of the applied ultrasonic wave is less than 3 // m.

3. The bonding method according to claim 1, wherein the frequency of the applied ultrasonic wave is set to 40 kHz or more.

4. The bonding method according to claim 3, wherein the frequency of the applied ultrasonic wave is set to 60 kHz or more.

5. The joining method according to claim 1, wherein the joining load is set to 150 MPa or less.

6. The bonding method according to claim 1, wherein cleaning of the surface of the metal bonding portion with an energy wave is performed under reduced pressure.

7. The bonding method according to claim 1, wherein plasma is used as the energy wave.

8. The bonding method according to claim 7, wherein an Ar plasma is used as the energy wave.

9. The bonding method according to claim 1, wherein the ultrasonic bonding is performed in a state of being heated to 180 ° C or lower.

10. The bonding method according to claim 1, wherein the entire surface to be bonded of the metal bonding portion is etched to a depth of 1 nm or more by the cleaning with the energy wave.

1 1. The bonding method according to claim 1, wherein the metal bonding portions whose bonding surfaces are formed of any one of Au, Cu, A1, In, and Sn are bonded.

1 2. When joining metal joints, the variation in the gap between metal joints can be up to 4 The joining method according to claim 1, wherein:

1 3. The joining method according to claim 1, wherein when joining the metal joints, the parallelism between the objects to be joined is adjusted within 4 m.

1 4. The bonding method according to claim 1, wherein the surface roughness of at least one metal bonding portion before bonding is set to 300 nm or less.

1 5. The joining method according to claim 1, wherein the surface roughness of at least one of the metal joints after joining is set to 1 O nm or less.

1 6. The joining method according to claim 1, wherein the surface hardness of at least one of the metal joints is set to a picker hardness HV of 120 or less.

1 7. A device for joining objects to be joined having a metal joint on the surface of a base material, wherein the washing means irradiates the surface of the metal joint of each object with an energy wave; Joining means for ultrasonically joining the metal joints of the taken-out objects to be joined together in the air.

18. The joining apparatus according to claim 17, wherein said joining means comprises means capable of applying ultrasonic waves having an amplitude of less than 3 // m.

19. The joining apparatus according to claim 17, wherein the joining means comprises means capable of applying an ultrasonic wave having a frequency of 40 kHz or more.

20. The joining apparatus according to claim 19, wherein said joining means comprises means capable of applying an ultrasonic wave having a frequency of 60 kHz or more.

2 1. The joining means comprises means capable of joining with a joining load of 150 MPa or less, 18. The joining device according to claim 17.

22. The bonding apparatus according to claim 17, wherein the cleaning means includes means for irradiating the surface of the metal bonding section with an energy wave under reduced pressure.

23. The bonding apparatus according to claim 17, wherein the cleaning unit includes a plasma irradiation unit.

24. The bonding apparatus according to claim 23, wherein the pre-β cleaning means comprises Ar plasma irradiation means.

25. The joining apparatus according to claim 17, further comprising a transporting means for transporting the cleaned workpiece between the cleaning means and the joining means.

28. The joining apparatus according to claim 17, wherein the joining means has a heating means, and comprises means for ultrasonically joining the metal joints at 180 ° C or lower.

2 7. The bonding apparatus according to claim 17, wherein the cleaning unit is configured to irradiate an energy wave with energy of at least one capable of etching to a depth of 1 nm or more on the entire surface of the metal bonding unit to be bonded. .

2 8. The joining apparatus according to claim 17, wherein the surfaces of the two metal joints to be joined are formed of any one of Au, Cu, A1, In, and Sn.

28. The joining apparatus according to claim 17, wherein the joining means includes means for reducing a variation in a gap at the time of joining the metal joints to a maximum of 4 or less.

30. The joining apparatus according to claim 17, wherein the joining means includes means for adjusting the parallelism between the objects to be joined at the time of joining the metal joined portions to within 4 urn.

3 1. The surface roughness of at least one metal joint before joining should be less than 300 nm. The joining device according to claim 17, wherein

32. The bonding apparatus according to claim 17, wherein the surface roughness of at least one of the metal bonding portions after bonding is 10 nm or less.

33. The joining apparatus according to claim 17, wherein the surface hardness of at least one of the metal joints is set to a Picker hardness HV of 120 or less.

r

3 4. This is a joined body of objects to be joined having a metal joint on the surface of the base material. After the surfaces of the metal joints of both the objects to be joined are cleaned by an energy wave, the metal is joined in air. A joined body _c characterized by being produced by ultrasonic joining of the parts

35. The joined body according to claim 34, wherein at least one of the joined objects is made of a semiconductor.