JP5494293B2 - Wire bonding method and semiconductor device manufacturing method - Google Patents

Description

The present invention, a wire bonding method, a method of manufacturing a semi-conductor device.

  Conventionally, for example, as disclosed in JP-A-59-150437, a technique for performing wire bonding using a copper (Cu) wire is known. In this publication, a ball is formed at the tip of a copper wire, and the ball is immersed in molten gold. Ball bonding is performed in a state where a Cu ball is covered with a molten gold film.

  For example, Japanese Patent Application Laid-Open No. 11-045441 proposes a method of forming an Au ball at the tip of a Cu wire. Specifically, in the technology according to the gazette, an Au FAB (Free Air Ball) is generated at the tip of the Cu wire by instantaneously forming a high temperature atmosphere by discharge.

JP 59-150437 A JP 11-045441 A Japanese Patent Laid-Open No. 9-237666 JP 2002-373910 A JP 2006-32666 A

  FIG. 4 is a schematic view of the occurrence of a defect in the wire bonding structure shown to explain the problem to be solved in the present invention. In FIG. 4, reference numeral 101 denotes a wire, reference numeral 102 denotes a chip electrode portion (pad), reference numeral 103 denotes a crack-like deformation, reference numeral 109 denotes a semiconductor chip, reference numeral 110 denotes a wiring layer, and reference numeral 112 denotes an insulating layer. When wire bonding is performed, a load is applied to the pad side. When this load is excessive, the structure on the pad side is seriously damaged like the crack-like deformation 103.

  The magnitude of the load applied to the chip side (pad side) during wire bonding depends on the hardness of the FAB material. When a FAB made of the material of the wire itself is provided at the wire tip, if a wire made of a material with high hardness is used, damage given to the chip side during wire bonding tends to increase. The higher the hardness of the wire, the more serious the damage to the chip during wire bonding, like the crack-like deformation 103 shown in FIG.

  In view of the above points, a method of forming a layer (film) with a material different from the wire material at the wire tip connected to the pad at the time of wire bonding can be considered. As a material of this layer (film), a material different from the material of the wire can be appropriately selected from various viewpoints. By selectively reducing the material at the tip of the wire to a low hardness, damage during wire bonding can be suppressed.

Regarding the above-described technique, Japanese Patent Application Laid-Open No. 59-150437 proposes a technique in which FAB formed of Cu is covered with a molten Au film. However, in this publication, the FAB itself is made of Cu, and only an Au film is provided on the surface of the Cu FAB. For this reason, in terms of the force that the chip side receives during wire bonding, there is a great difference between the case where a Cu wire is used and the high hardness Cu FAB may cause damage to the chip during wire bonding.
Japanese Patent Application Laid-Open No. 11-045441 proposes a method of forming an Au ball at the tip of a Cu wire. However, in the technique according to the publication, since a high temperature atmosphere is instantaneously formed by electric discharge, when Au is melted to form a ball, Cu diffuses into Au and forms an alloy. The physical properties of the material alloyed by the diffusion of Cu are different from those expected when formed only by Au. As a result, depending on the technique disclosed in the above publication, it is not possible to enjoy the bonding properties originally expected for the material coated on the wire tip.

  The present invention has been made to solve the above problems, and a material different from the material of the wire itself is provided at the wire tip so that wire bonding capable of suppressing the occurrence of damage to the pad side structure can be performed. An object of the present invention is to provide a wire bonding method and a method for manufacturing a semiconductor device.

In order to achieve the above object, a first invention is a wire bonding method,
The tip of the wire on which the FAB is not formed is immersed in a melt obtained by melting a conductive material having a lower melting point and lower hardness than the material of the wire, thereby forming the FAB of the conductive material at the tip of the wire. Process,
Bonding the FAB formed at the tip of the wire to a pad of a semiconductor device;
It is characterized by providing.

In order to achieve the above object, a second invention is a method of manufacturing a semiconductor device,
Preparing a semiconductor device having a pad;
Performing wire bonding on the pad of the semiconductor device by the wire bonding method according to the first invention;
It is characterized by providing.

  According to the first invention, it is possible to form the FAB with a material having a lower hardness than the wire itself at the wire tip while suppressing alloying of the material of the wire itself and the conductive material covering the wire tip. .

  According to the second invention, by using the wire bonding method according to the first invention, it is possible to suppress the occurrence of damage to the structure on the pad side during wire bonding.

It is a schematic diagram for demonstrating the wire bonding method concerning Embodiment 1 of this invention. It is a schematic diagram for demonstrating the wire bonding pad which provided the slit . It is a schematic diagram for demonstrating the wire bonding pad which provided the slit . It is a figure for demonstrating generation | occurrence | production of the malfunction which is a subject solved in this invention.

Embodiment 1 FIG.
FIG. 1 is a schematic diagram showing the steps of the wire bonding method according to the first embodiment of the present invention. In the figure, 4 is a Cu wire, 5 is a molten Au, 6 is a capillary, 7 is a heating crucible, and 8 is a FAB (Free Air Ball). In this embodiment, the melting point of Au is 1064 ° C., and the melting point of Cu is 1084 ° C.

  As shown in FIG. 1A, a Cu wire (diameter 25 μm) is projected by 0.5 mm from the tip of the capillary 6, and the tip of the Cu wire is placed 50 μm on the liquefied Au in a heated crucible heated to 1100 ° C. Only soak for 0.2 s. As shown in FIG. 1B, a FAB 8 having a diameter of 50 μm is formed at the tip, and wire bonding is performed to an electrode pad (not shown) of a semiconductor device (not shown) using this.

  In the present embodiment, the FAB 8 can be formed at the tip of the wire 4 by immersing the tip of the Cu wire 4 in molten Au. For this reason, the wire 4 is not heated greatly exceeding its melting point, that is, in this embodiment, the Cu wire 4 is not heated greatly exceeding the melting point of Cu.

  For this reason, it can suppress to the minimum that the material which forms FAB diffuses in the wire 4 main body. As a result, it is possible to suppress the occurrence of a situation in which the physical properties of the metal forming the FAB change and the bonding properties expected for the metal cannot be ensured. That is, in this embodiment, it becomes possible to minimize the diffusion of Cu into Au, and Cu diffuses into Au and forms an alloy, so that the physical properties change and the original bonding property of Au cannot be secured. Can be avoided.

  Further, according to the present embodiment, since the FAB 8 used in the first bond is formed of Au, the problem of eccentricity of the FAB, which is regarded as a problem with the Cu wire, is suppressed, and an inert gas atmosphere such as nitrogen This equipment is also unnecessary.

  In other words, Au wire is generally used for wire bonding, but due to the recent rise in Au prices, low-cost Cu wire has attracted attention. However, while Au is a very stable metal, Cu is easy to oxidize. When forming FAB, the FAB will be eccentric unless it is adjusted to the optimum gas amount in an inert gas atmosphere such as nitrogen. End up.

  One of the factors that cause crack-like deformation in the pad is the size of FAB (Free Air Ball) eccentricity, and it should be avoided that wire bonding is performed with FAB having excessive eccentricity. The degree of FAB eccentricity is affected by the metal material of the wire. For example, Cu, which is a metal that is relatively easy to oxidize, tends to cause a problem that the FAB is eccentric unless the FAB is formed after adjusting the gas amount to an optimum amount in an inert gas atmosphere such as nitrogen. When the eccentricity of the FAB is excessive, damage to the chip during wire bonding may become serious, as in the crack-like deformation 103 shown in FIG.

  In this regard, according to the present embodiment, the problem of eccentricity of FAB, which is regarded as a problem with Cu wires, is suppressed, and the installation of an inert gas atmosphere such as nitrogen becomes unnecessary.

  Further, the hardness is different between Au and Cu, and Cu is a harder metal, so damage to the chip during wire bonding becomes a problem. Due to this problem, it is difficult to apply Cu wire at the time of wire bonding of a semiconductor device using a compound semiconductor that is brittle compared to Si semiconductor.

  Further, according to the present embodiment, only the FAB 8 at the tip of the wire 4 is partially formed of Au. For this reason, the problem of damage to the chip is small as compared with the case where the FAB 8 is made of Cu, and the cost can be suppressed to almost the same as that of the Cu wire as compared with the case where the Au wire is used.

  In this regard, according to the present embodiment, it is possible to utilize a low-cost Cu wire while suppressing damage on the chip side (pad side).

  Japanese Patent Application Laid-Open No. 11-045441 proposes a method of forming an Au ball at the tip of a Cu wire, but the apparatus is extremely complicated and a dedicated apparatus is essential. Furthermore, in the technique according to the publication, there is a problem that Au (melting point 1064 ° C.) and Cu (melting point 1084 ° C.) are separated from each other by only 20 ° C. That is, in the technique according to the publication, a high temperature atmosphere is instantaneously formed by electric discharge, so that when Au is melted to form a ball, Cu diffuses into Au and forms an alloy. In the case of discharge, since the temperature instantaneously reaches the melting point of the wire, if the difference between the melting points is about 20 ° C., Cu melts together with the melting of Au. A material alloyed by diffusion of Cu has physical properties different from those expected when formed only by Au. Eventually, depending on the technique according to the above publication, the original bonding property of Au cannot be enjoyed.

  In this regard, the above-described alloying can be suppressed by using the manufacturing method according to the present embodiment described above. In other words, if the Au is melted in the crucible, the temperature does not exceed the melting point of Au, and the wire is immersed in the crucible as compared with the case of using the conventional discharge. It is possible to prevent Au diffusion and physical property changes. Moreover, the temperature control of the crucible (control of the crucible heating device) is facilitated by setting the difference between the melting points to 100 ° C. and 500 ° C. or more.

  In the first embodiment, Cu wire and liquefied Au are used, but the present invention is not limited to this. For example, a combination having a large difference in melting point may be used, such as a combination of Au wire and AuSn solder (80 wt% Au-20 wt% Sn, melting point 280 ° C.).

  By covering the tip of the wire 4 with a metal having a melting point sufficiently lower than that of the wire material, the FAB 8 other than the wire material can be formed at the tip of the wire 4 while further suppressing the diffusion of the wire material.

  In addition to Cu, for example, aluminum (Al, melting point = 660 ° C.), silver (Ag, melting point = 960 ° C.), or the like may be used as the wire 4 as a metal material having a low melting point.

  As a material for the FAB 8, in addition to a pure metal such as Sn or Al, an alloy solder such as AuSi or AuGe may be used.

  Moreover, you may produce FAB with the material (material which is hard to oxidize compared with wire material) which can suppress eccentricity of FAB other than Au.

  Also, by adjusting the length of the wire to be immersed (for example, changing the length of the wire in units of 10 μm) and adjusting the time for immersion (for example, changing the immersion time in 0.1 second steps), the dimensions of the FAB8 are optimized. Is possible.

  Alternatively, a soft conductive material or metal having a low melting point such as AuSn solder may be supplied to the pad surface where wire bonding is performed.

FIG. 2 is a schematic diagram for explaining a wire bonding structure provided with slits . In the figures, 9 indicates a semiconductor chip, 10 indicates a wiring layer, 11 indicates a pad formed of Au, 12 indicates an insulating layer, 13 indicates a photolithography mask, and 14 and 15 indicate slits. Yes. The slits 14 and 15 extend in parallel in the depth direction of the sheet of FIG.

  As shown in FIG. 2A, an opening is formed by the photolithography mask 13, and a pad is formed by Au evaporation. Thereafter, as shown in FIG. 2B, the photolithography resist under the pad 11 and the insulating layer 12 are removed, thereby forming a slit perpendicular to the ultrasonic wave application direction during wire bonding. Wire bonding is performed on the pad 11 in which the slit is formed. It is assumed that an ultrasonic wave is applied at the time of wire bonding, and the ultrasonic wave application direction is a direction orthogonal to the slits 14 and 15 (left and right direction in FIG. 2).

  When the pad 11 is configured to have a striped slit (or by forming the pad 11 by arranging a plurality of linear metal patterns in a striped pattern), in a direction intersecting with the slit during wire bonding When the ultrasonic wave application is performed, the pad 11 is easily deformed in the ultrasonic wave application direction. In addition, it is possible to increase the surface area to be contacted and improve the bondability.

In a semiconductor device such as a compound semiconductor, Au is often used for the pad. However, due to the recent increase in the price of Au, there is a demand for reducing the thickness of the Au pad as much as possible for the purpose of cost reduction. However, in order to obtain sufficient bondability to thin pads, wire bonding with increased parameters that contribute to improved bondability during loads, ultrasonic waves, etc. may lead to pad peeling or There is a risk of damaging the structure (electrode or chip). According to this configuration, the load and the application of ultrasonic waves can be alleviated by deformation of the pad 11 itself during wire bonding , so that these problems can be solved.

  As shown in FIG. 3, the insulating layer 12 may be left inside the slit 14. This makes it possible to produce a chip with excellent weather resistance.

  Although BCB (benzocyclobutene) is used as the insulating layer 12, the present invention is not limited to this. Other materials suitable for the coating film of the chip 9 may be used.

  In addition, although vapor deposition was used as a manufacturing method of the pad 11, this invention is not limited to this. Other film forming methods such as plating and sputtering may be employed.

In addition, this invention is not limited to the structure which provides both the slits 14 and 15 as mentioned above . Only one of the slits 14 and 15 may be provided.

4 wires
5 Molten Au
6 Capillary
7 Heating crucible
8 FAB (Free Air Ball)
9 Semiconductor chip 10 Wiring layer 11 Pad 12 Insulating layer
13 Photolithographic masks 14 and 15 Slit 101 Wire
102 Electrode part (pad) of chip
103 Crack-like deformation 109 Semiconductor chip 110 Wiring layer 112 Insulating layer

Claims (5)

By immersing the tip of an unformed FAB (Free Air Ball) wire in a melt in which a conductive material having a lower melting point and lower hardness than the material of the wire is melted, the conductive material is placed on the tip of the wire. Forming a FAB of
Bonding the FAB formed at the tip of the wire to a pad of a semiconductor device;
A wire bonding method comprising:   The wire bonding method according to claim 1, wherein the conductive material has a melting point that is lower than the melting point of the wire material by 100 ° C. or more.   The wire bonding method according to claim 1, wherein the conductive material has a melting point that is lower than the melting point of the wire material by 500 ° C. or more.   The wire bonding method according to claim 1, wherein the material of the wire is Cu, and the conductive material is Au. Preparing a semiconductor device having a pad;
A step of performing wire bonding on the pad of the semiconductor device by the wire bonding method according to claim 1;
The method of manufacturing a semiconductor device, characterized in that it comprises a.

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