Semiconductor device with bump electrode and method of manufacturing the same

Abstract: A semiconductor device having a bump electrode (16) on a semiconductor substrate (11) above an electrode pad (12) and metal film (14a). The shape of the bump electrode (16) is composed of a cubical portion and a skirt (16a) extending outward from the bottom of the cubical portion. In manufacturing such a semiconductor device, a dry film is used which is laminated on the metal film (14a) under a certain laminating condition and formed with an opening. A bump material is formed as a deposit on the metal film (14a) within the opening, through electrolytic plating. The deposit has the cubical portion corresponding in shape to the opening, and the skirt (16a) extending outward into a space between the dry film and the metal film (14a), from the bottom of the cubical portion. The metal film (14a) is etched out using the deposit as a mask to thereby make the deposit as a bump electrode (16) of the semiconductor device.

Description: BACKGROUND OF THE INVENTION Field of the Art The present invention relates to a semiconductor device with bump electrodes formed on electrode pads and to a method of manufacturing such a device. Prior Art A conventional bump structure of a semiconductor device and a method of forming a bump will be described with reference to Figs. 5A to 5D. Referring to Fig. 5A, a semiconductor substrate 21 with impurities diffused and an SiO₂ film formed on the surface thereof (the impurity diffused region and the film are not shown) is formed thereon with an Al electrode pad 22. An insulating passivation film (Si₃N₄ film) 23 with an opening formed at the position above the Al electrode pad 22 is deposited on the semiconductor substrate 21 and on a part of the electrode pad 22. A metal film 24 as barrier metal layer is deposited on the Si₃N₄ film 23 and electrode pad 22 by means of the vapor deposition method or the sputtering method. Next, as shown in Fig. 5B, a photopolymerized high polymer dry film 25 is pressure-laminated on the metal film 24 with a hot laminator under the conditions of 105°C roll temperature, 0.2 m/min roll feed speed, and 20 Kg/cm² roll pressure. The dry film 25 is subjected to patterning to form an opening with a size corresponding to a desired bump side length, at the position only above the electrode pad 22. Thereafter, the patterned dry film 25 is baked at 100°C for 10 minutes. Next, by using the patterned dry film 25 as a plating mask, and the metal film 24 as one (a cathode) of the electrodes (cathode) in electrolytic plating, Au is selectively plated only within the opening of the dry film 25. After removing the dry film 25, a cubical Au deposit 26 is obtained on the metal film 24 above the electrode pad 22, as shown in Fig. 5C. Thereafter, as shown in Fig. 5D, by using the Au deposit 26 as a mask, the metal film 24 except that above the electrode pad is etched out. Thus, a semiconductor device with the cubical Au bump 26 of a conventional structure formed on the metal film 24 above the Al electrode pad 22 is obtained. If instead of the dry film a liquid resist film is used as a plating mask, it is difficult to deposit a plating mask thicker than the height of an Au bump which is 20 to 30 µm. As a result, an Au bump necessarily has a mushroom shape. In contrast, by using a dry film it becomes possible to obtain a plating mask of 20 to 40 µm thicker than the height of an Au bump, so that an Au bump can have a cubical shape. Thus, it is advantageous that a relatively larger number of Au bumps per unit can be formed on the semiconductor substrate. With the conventional method using a dry film, however, a portion 24a of the metal film 24 under the Au bump 26 is generally etched inward by about 5 µm in the etching process of the metal film 24, using the Au bump as a mask. Consequently, the peel strength of the Au bump 26 is as low as 30 to 40 g/pad (with the area of the electrode pad being 110 x 110 µm², and the area of the opening being 80 x 80 µm²). In order to obtain a sufficient peel strength, it becomes necessary to enlarge the dimension of the Au bump, which prevents full use of the advantages of the method using a dry film. Further, since the metal film 24 is etched inward by about 5 µm, the peripheral portion of the Al electrode pad 22 is covered with only the Si₃N₄ film 23a. As a result, the corrosion resistance of the Al electrode pad is lowered so that the reliability becomes degraded. SUMMARY OF THE INVENTION It is an object of the present invention to increase the peel strength of a bump electrode which is formed above an electrode pad of a semiconductor device so as to use it as an input/output electrode of the semiconductor device, and to improve the corrosion resistance at the peripheral portion of the electrode pad, thus facilitating Tape Automated Bonding (TAB) assembly and improving the reliability. This object is met by a semiconductor device according to claim 1 and by a method of manufacturing it according to claim 8. According to the present invention, the structure of a bump electrode to be used as an input/output electrode of a semiconductor device has a skirt at the lower end portion of the cubical bump electrode, in contrast with the simple cubical or mushroom shape of a conventional bump electrode. Since the bump electrode (made of Au in most cases) has a skirt extending outward in contact with the metal film, the contact area of the bump electrode with the metal film does not become small even under excessive etching of the metal film as described previously with respect to a bump electrode with a simple cubical shape. Further, the dimension of the bump electrode is not required to be unnecessarily large in order to ensure a sufficient contact area of the bump electrode with the metal film. According to the semiconductor device of this invention, the bump electrode has a skirt so that excessive etching of the metal film under the bump electrode is avoided during the manufacturing process, thus considerably increasing the peel strength of the bump electrode. The bump structure can be realized readily by changing the conditions of laminating a dry film, without unnecessarily increasing the quantity of Au, for example, and with effective assistance to the high density assembly technique for semiconductor devices. Further, according to the semiconductor device of this invention, the electrode pad and adjacent portion thereof are covered with the skirt of a bump electrode. Therefore, the semiconductor device is protected from corrosion or other adverse effects caused by pin holes or cracks in the insulating passivation film, thus improving the reliability of the semiconductor device. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A to 1D are cross sections illustrating an embodiment of a method of manufacturing a semiconductor device according to the present invention; Figs. 2 to 4 are graphs for explaining the advantageous effects of a semiconductor device of this invention; and Figs. 5A to 5D are cross sections illustrating a conventional method of manufacturing a semiconductor device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1D is a cross section showing an embodiment of a semiconductor device according to the present invention. The peripheral portion of an electrode pad 12 is covered with an insulating passivation film 13a. A bump electrode 16 with a skirt 16a is formed on a metal film 14a and the electrode pad 12, with the skirt 16a being extended over the insulating passivation film 13a at the peripheral portion of the electrode pad 12. Figs. 1A to 1D show the manufacturing steps of the bump electrode having the structure according to this invention. Referring to Fig. 1A, on a semiconductor substrate 11 with circuit elements such as transistors or diodes, an electrode pad 12 is selectively formed, the pad having an area of 110x110 µm². The area of the electrode pad may take a value from (40 to 150) x (40 to 150) µm². The electrode pad 12 is made of a metal whose main component is Al. The insulating passivation film 13 made of Si₃N₄, is deposited over the entire surface of the Al electrode pad 12 and the semiconductor substrate 11. An opening is formed in the insulating passivation film 13 using the photolithography technique, at the position above the Al electrode pad 12. The insulating passivation film 13 serves as the passivation film for circuit elements formed on the semiconductor substrate 11. Next, the bump electrode to be connected to the electrode pad 12 and used as a signal input/output electrode is formed. In particular, as shown in Fig. 1A, first a metal film 14, e.g., a three-layered metal film composed of Ti, Ni and Pd in this order from lower to upper layers, is deposited on the exposed portion of the electrode pad 12 within the opening and on the insulating passivation film 13, through the sputtering method or the vapor deposition method. Instead of the above three-layered metal film, the metal film 14 may use a two-layered metal film of WSi and Pd, a three-layered metal film of WSi, Ni and Pd, a three-layered metal film of W, Ni and Pd, or a two layered metal film of W and Pd, respectively in this order from lower to upper layers. Next, as shown in Fig. 1B, a dry film 15 of 20 µm thickness is laminated on the semiconductor device using a hot laminator under the conditions to be described later in detail. An opening is formed in the dry film 15 using the photolithography technique, with the peripheral portion 15a of the dry film 15 being arranged so that it is not in tight contact with the metal film 14. Thereafter, as shown in Fig. 1C, by using the metal film 14 as one of the electrodes in electrolytic plating, Au is plated selectively on the metal film 14 only above the electrode pad 12. After the dry film 15 is removed, an Au deposit (bump electrode) 16 is obtained which has a skirt 16a extending outward by an amount of t-µm, as shown in Fig. 1C, into the space formed at the peripheral portion 15a of the dry film 15 not in tight contact with the metal film 14. Next, as shown in Fig. 1D, by using the Au deposit 16 as a mask, the metal film 14 except that portion above the electrode pad 12 is removed to thereby make the Au deposit 16 as an Au bump 16. The relationship between the conditions of laminating a dry film at the process shown in Fig. 1B and the skirt extension quantity of an Au bump at the process shown in Fig. 1C is shown in Figs. 2 and 3. Fig. 2 shows the relationship between a roll pressure and a skirt extension quantity with constant values of 105°C roll temperature and 0.3 m/minute roll feed speed, and with variable 0 to 28 Kg/cm² roll presssure. Fig. 3 shows the relationship between a roll feed speed and a skirt extension quantity with constant values of 105°C roll temperature and 28 Kg/cm² roll pressure, and variable 0.3 to 0.8 m/minute roll feed speed. As seen from Figs. 2 and 3, as the roll pressure is made small or the roll feed speed is made high, the skirt extension quantity can be made equal to or more than 1 µm. Alternatively, all the values of the roll temperature, roll pressure and roll feed speed may be set as desired to adjust the skirt extension quantity. The relationship between the skirt extension quantity (µm) and the peel strength (g/pad) of an Au bump is shown in Fig. 4. As seen from Fig. 4, the peel strength of the Au bump having the skirt extension quantity of 0 is 30 to 40 g/pad. In contrast, the peel strength sharply increases as the skirt extension quantity becomes equal to 1 µm or more, gradually increases as it reaches 2 to 5 µm, and saturates as it becomes equal to 10 µm or more. It was also confirmed that it was possible to prevent corrosion caused by pin holes or cracks in the insulating passivation film, because of the presence of the skirt which extends outward from the Au bump.

Claims: A semiconductor device comprising: a semiconductor substrate (11) formed with a circuit element; an electrode pad (12) formed on said semiconductor substrate (11); an insulating passivation film (13) having a contact hole, said insulating passivation film (13) being formed on said substrate (11) and on the peripheral portion of said electrode pad (12); a metal film (14a) formed on said electrode pad (12) at the exposed portion within said contact hole, and on said insulating passivation film (13) at the peripheral portion of said contact hole; and a bump electrode (16) including a skirt on the peripheral portion of said metal film (14a) and a cubical portion an the central portion of said metal film (14a), said skirt (16a) of said bump electrode (16) extending outward of said cubical portion by an amount at least equal to or more than 1 µm. A semiconductor device according to claim 1, wherein the area of said electrode pad (12) is (40 to 150) x (40 to 150) µm². A semiconductor device according to claim 1, wherein said electrode pad (12) is made of a metal whose main component is Al, said bump electrode (16) is made of Au, said insulating passivation film (13) is made of Si₃N₄, and said metal film (14a) is made of a three-layered metal film composed of Ti, Ni and Pd in this order from lower to upper layers. A semiconductor device according to claim 1, wherein said electrode pad (12) is made of a metal whose main component is Al, said bump electrode (16) is made of Au, said insulating passivation film (13) is made of Si₃N₄, and said metal film (14a) is made of a two-layered metal film composed of WSi and Pd in this order from lower to upper layers. A semiconductor device according to claim 1, wherein said electrode pad (12) is made of a metal whose main component is Al, said bump electrode (16) is made of Au, said insulating passivation film (13) is made of Si₃N₄, and said metal film (14a) is made of a three-layered metal film composed of WSi, Ni and Pd in this order from lower to upper layers. A semiconductor device according to claim 1, wherein said electrode pad (12) is made of a metal whose main component is Al, said bump electrode (16) is made of Au, said insulating passivation film (13) is made of Si₃N₄, and said metal film (14a) is made of a three-layered metal film composed of W, Ni and Pd in this order from lower to upper layers. A semiconductor device according to claim 1, wherein said electrode pad (12) is made of a metal whose main component is Al, said bump electrode (16) is made of Au, said insulating passivation film (13) is made of Si₃N₄, and said metal film (14a) is made of a two-layered metal film composed of W and Pd in this order from lower to upper layers. A method of manufacturing a semiconductor device having a bump electrode comprising the steps of: forming on a semiconductor substrate (11) an electrode pad (12) and an insulating passivation film (13) having a contact hole for allowing contact to be made with said pad, and forming a metal film (14) on said pad (12) and said insulating passivation film (13); laminating a polymer dry film (15) on said metal film (14); forming an opening in said dry film above said pad (12), said opening extending to said metal film (14); performing electrolytic plating by using said metal film (14) as one of electrolytic electrodes, and forming a bump substance as a deposit on said metal film (14) above said electrode pad; wherein in said laminating step a hot laminator with a roll is used and the laminating condition is set by adjusting the values of the roll temperature, roll pressure and roll feed speed so that after forming said opening in said dry film (15) a peripheral portion (15a) of said dry film (15) around said opening is not in tight contact with the metal film (14), and wherein during said electrolytic plating step said bump material extends into a space occurring between said dry film (15) and said metal film (14) to form a skirt (16a) so that the shape of said deposit is composed of a cubical portion corresponding in shape to said opening and said skirt (16a) extending outward from the bottom of said cubical portion to the extent of at least equal to or more than 1 µm; removing said dry film; and removing said metal film (14) by using said deposit as a mask, thereby completing a bump electrode (16). A method of manufacturing a semiconductor device according to claim 8, wherein said electrode pad (12) is formed to have an area of (40 to 150) x (40 to 150) µm². A method of manufacturing a semiconductor device according to claim 8, wherein said electrode pad (12) is made of a metal whose main component is Al, said bump electrode (16) is made of Au, said metal film (14) is made of a three-layered metal film composed of Ti, Ni and Pd in this order from lower to upper layers, and said insulating passivation film (13) is made of Si₃N₄. A method of manufacturing a semiconductor device according to claim 8, wherein said electrode pad (12) is made of a metal whose main component is Al, said bump electrode (16) is made of Au, said metal film (14) is made of a two-layered metal film composed of WSi and Pd in this order from lower to upper layers, and said insulating passivation film (13) is made of Si₃N₄. A method of manufacturing a semiconductor device according to claim 8, wherein said electrode pad (12) is made of a metal whose main component is Al, said bump electrode (16) is made of Au, said metal film (14) is made of a three-layered metal film composed of WSi, Ni and Pd in this order from lower to upper layers, and said insulating passivation film (13) is made of Si₃N₄. A method of manufacturing a semiconductor device according to claim 8, wherein said electrode pad (12) is made of a metal whose main component is Al, said bump electrode (16) is made of Au, said metal film (14) is made of a three-layered metal film composed of W, Ni and Pd in this order from lower to upper layers, and said insulating passivation film (13) is made of Si₃N₄. A method of manufacturing a semiconductor device according to claim 8, wherein said electrode pad (12) is made of a metal whose main component is Al, said bump electrode (16) is made of Au, said metal film (14) is made of a two-layered metal film composed of W and Pd in this order from lower to upper layers, and said insulating passivation film (13) is made of Si₃N₄. A method of manufacturing a semiconductor device according to claim 8, wherein said laminating condition is that said dry film (15) is used in a thickness of 20 µm, the temperature of said roll is constant at 105°C, the roll feed speed is constant at 0.3 m/minute, and the roll pressure is equal to or more than about 22 Kg/cm². A method of manufacturing a semiconductor device according to claim 8, wherein said laminating condition is that said dry film (15) is used in a thickness of 20 µm, the temperature of said roll is constant at 105°C, the roll pressure is constant at 28 Kg/cm², and the roll feed speed is equal to or greater than about 0.31 m/minute.

Inventors: ENDO TAKASHI, EZAWA HIROKAZU, ENDO, TAKASHI, EZAWA, HIROKAZU
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1988
Main classification: H01L23
IPC codes: H01L21, H01L23