CA2159242C

CA2159242C - Process for manufacturing semiconductor device and semiconductor wafer

Info

Publication number: CA2159242C
Application number: CA002159242A
Authority: CA
Inventors: Keiichiro Kata; Shinichi Chikaki
Original assignee: NEC Corp
Current assignee: NEC Electronics Corp
Priority date: 1994-09-30
Filing date: 1995-09-27
Publication date: 1999-12-07
Anticipated expiration: 2015-09-27
Also published as: US5844304A; EP0704895B1; DE69526895D1; USRE39603E1; DE69526895T2; EP0704895A2; EP0704895A3; JPH08102466A; KR100241573B1; JP2792532B2; CA2159242A1

Abstract

A process for manufacturing a semiconductor device.
Chip sections are defined on a wafer by scribe lines, with each chip section having chip electrodes formed thereon. The wafer is covered with a passivating film except for an area on the chip electrodes. Aluminum interconnection layers are provided such that each layer is connected to the chip electrode at one end thereof, and the other end of the layer is extended towards the central portion of the chip section. A
cover coating film is applied on the passivating film and the layers. A number of apertures are formed in the coating film passing therethrough, and bump electrodes are formed at the position corresponding to the apertures. The chip sections are then separated from each other along the scribe lines into semiconductor devices.

Description

PROCESS FOR MANUFACTURING SEMICONDUCTOR DEVICE
AND SEMICONDUCTOR WAFER
The present invention relates to a process for manufacturing a semiconductor device and, more particular-ly, to a process suited for mass production of a highly-integrated semiconductor device.
Semiconductor devices of various forms have been developed to meet recent demands in the electronics field towards reduced size and weight, increased speed, and improved functional operation. The semiconductor device comprises a package and a semiconductor chip (hereinafter, also referred to as a chip) contained in the package. The higher the level of chip integration, the greater the number of terminals required thereon. In addition, there are demands for further reductions in the size of semicon-ductor chips. The terminal-to-terminal pitch must be reduced to meet the demands for smaller semiconductor devices. A semiconductor device having a high terminal count can be obtained by inner lead bonding or by area array bonding. Inner lead bonding and area array bonding are expected to become standard techniques in the field of semiconductors.
Inner lead bonding (ILB) is used to make elec-trical contact between the chip and the leads within the package. Various bonding technologies are available to achieve this inner lead bonding. Wire bonding is the most extensively used electrical interconnection process. In this process, fine wires are used to make electrical contact between the bonding pads on the chip and the corresponding leads on the package. the wire diameter is typically from 20 to 30 micrometers. Wire bonding tech-niques include thermocompression bonding, ultrasonic bonding, and thermosonic bonding.
The use of the fine wires limits the number of interconnections available in one package. Recent demands for semiconductor devices with a high terminal count thus cause a problem of poor connections between the wire and the bonding pads. Considering this fact, wire bonding has been replaced with wireless bonding. Wireless bonding is also called gang bonding, with which bumps formed on the electrode pads are bonded simultaneously to the leads.
Wireless bonding techniques include tape automated bonding (TAB) and flip-chip bonding. TAB is also referred to as tape carrier bonding.
In the TAB technique, a laminated tape of gold-plated copper foil etched in the form of a lead is bonded to the bumps on the electrode pads. The elimination of wire bonding is advantageous from viewpoints of size reduction and highly integrated packaging of the device.
On the other hand, the flip-chip bonding requires a raised metallic bump of solder on the chip. The chip is then inverted and bonded face down to the substrate intercon-nection pattern. This process lends itself to production of semiconductor devices with a high terminal count and a smaller pitch. In addition, this technique is also advan-tageous to provide a fast, low-noise semiconductor device owing to the short length of the interconnections.
The TAB and flip-chip bonding techniques use the bumps provided between the chip and the package to make electrical interconnection between them. These techniques are disclosed in, for example, Japanese patent Laid-open Nos. 5-129366 and 6-77293.
A film carrier semiconductor device disclosed in these laid-open patent publications uses the bumps for the electrical interconnection between the chip and the car-rier film. There is another film carrier semiconductor device in which the electrical interconnection between the chip and the carrier film is achieved without using the bumps. The semiconductor chip and the carrier film are electrically connected during the assembly process. The bumps are used only for the purpose of connecting the film carrier semiconductor device with, for example, a circuit board or a mounting board. The film carrier semiconductor device of the type described comprises a semiconductor chip and a carrier film. Contact pads are provided along the periphery of one side of the semi-conductor chip.
Interconnecting layers are provided on the carrier film.
The carrier film is also provided with through-holes and openings formed therein. The openings are formed at the position corresponding to the contact pads (chip elec-trodes).
A conventional process for manufacturing a semiconductor device is described first for the purpose of facilitating the understanding of the present invention.
In particular, a process for manufacturing a film carrier semiconductor device is described. A wafer, which com-prises a number of chip sections each having chip elec-trodes formed thereon, is covered with a passivating film using a well-known technique. After the formation of the passivating film, the chip electrodes are exposed to the atmosphere. The chip sections are then separated from each other into individual chips along scribe lines by means of a known dicing technique using a dicing saw. The semiconductor chip so obtained is prepared along with a carrier film and an adhesion film. The adhesion film is positioned relative to the semiconductor chip and placed thereon. The carrier film and the semiconductor chip are subjected to heat and pressure to adhere them through the adhesion film. The carrier film is then cut along the edges of the chip by means of a standard method. Next, bump electrodes (solder bumps) are formed on corresponding outer chip electrodes arranged on the carrier film.
Semiconductor devices so obtained may find various applications in the electronics, electrical, and other fields. For example, semiconductor devices may be used for memories and drivers for a liquid crystal dis-play. Such applications are suited for mass-production of the semiconductor device. However, the above mentioned manufacturing process limits the number of chips obtained per unit time because the operation is made for each chip.

5 Recent demands for smaller-sized memories or drivers have reduced the size of the semiconductor device itself.
Accordingly, operations such as the inner lead bonding and the formation of the bumps must be conducted for each small chip. This operation is intricate and somewhat troublesome because the semiconductor chip is relatively small. It is thus difficult to position the carrier film positively or with a high accuracy. The intricacy is also associated with reduced reliability of the electrical interconnection between the semiconductor chip and the carrier film. In other words, there may be trouble in the interconnection between the semiconductor chip and the carrier film as well as in the adhesion of the individual components. With this respect, a batch process may be more effective than the conventional process for mass-production of semiconductor devices, in which most opera-tions are conducted on chip sections of a wafer. In this process, the bump electrodes are formed on the chip sections of the wafer prior to separation into individual chips.
Such a method is disclosed in, for example, U.S.
Patent No. 5,137,845, issued to Lochon et al. This method was developed by IBM Corporation and is applicable to the manufacture of bump electrodes for semiconductor chips that are suitable for Controlled Collapse Chip Connection (C4) or flip-chip technique. In this method, a barrier metal is deposited on aluminum chip electrodes, on which bump electrodes are deposited for a terminal contact. The method is, however, directed to the whole wafer as such.
In other words, this patent is not for a wafer to be divided into semiconductor chips. Neither the separation of the wafer nor the position of the interconnection, chip electrodes, and bump electrodes to avoid breakage of them upon dicing are disclosed. In addition, the bump elec-trodes in the above mentioned conventional semiconductor devices are formed on the chip electrodes. The formation of the bumps on the electrodes is, however, difficult or impossible if the demands for reduced size, a higher ter-urinal count, and a smaller pitch are to be met.
This problem may be solved by using a multi-layered electrode structure for the semiconductor device which allows for the distribution of solder pads over the entire surface of the semiconductor chip. Such a struc-ture is, however, complex and difficult to manufacture.
In addition, the multi-layered electrode significantly affects the configuration of the chip surface. A larger number of layers may sometimes make the surface irregular.
An object of the present invention is to provide a process for manufacturing a semiconductor device having bump electrodes formed at different positions from chip electrodes, which is suited for mass-production.
Another object of the present invention is to provide a process for manufacturing a semiconductor device having good thermal stress resistance.
Yet another object of the present invention is to provide a process for manufacturing a semiconductor device having good moisture resistance.
In order to achieve the above mentioned object, there is provided a process for manufacturing a semi-conductor device comprising the steps of defining a number of semiconductor chip sections on a wafer, each semi-conductor chip section having a number of chip electrodes formed on one surface along a periphery thereof, the one surface being covered with a passivating film except for the positions where the chip electrodes are formed;
forming a number of interconnection layers on the wafer for each semiconductor chip section such that each inter-connection layer is connected to the chip electrode at one end thereof and is extended inward the chip section at the other end; covering the entire surface of the wafer with a cover coating film; forming a number of apertures in the cover coating film, the apertures being formed into a matrix; forming a number of bumps on the apertures; and separating the semiconductor chip sections along scribe lines on the wafer into individual semi-conductor chips.

In the above mentioned process, the interconnec-tion layer extended inward the semiconductor chip section is preferably exposed to the atmosphere through apertures in the cover coating film. In addition, the solder bumps are preferably formed away from the scribe line. Further-more, the bump electrodes are preferably formed at a position not directly over the chip electrodes.
According to another aspect of the present invention, there is provided a semiconductor wafer having a number of semiconductor chips comprising bump electrodes formed into a matrix on an entire surface of the wafer ex-cept for on scribe lines between the semiconductor chips.
The invention will now be described, by way of example, with reference to the accompanying drawings in which like reference numerals refer to like parts and components and in which:
Figure lA is a schematic plan view of a wafer having a number of chip sections subjected to a conven-tional process for manufacturing a semiconductor device;
Figure 1B is an enlarged view of a chip section in Figure lA;
Figure iC is a cross-sectional view of the chip section taken on line I-I in Figure 1B;
Figures 2A through 2G are cross-sectional flow diagrams showing a process for manufacturing a conven-tional semiconductor device;

Figures 3A through 3G are cross-sectional flow diagrams showing a process for manufacturing a semicon-ductor device according to an embodiment of the present invention;
Figure 4A is a schematic plan view of a wafer having a number of chip sections according to a process for manufacturing a semiconductor device of the present invention;
Figure 4B is an enlarged view of a chip section in Figure 4A; and Figure 4C is a cross-sectional view of the chip section taken on line II-II in Figure 4B.
A conventional process for manufacturing a semi-conductor device is described first for the purpose of facilitating the understanding of the present invention.
In particular, a process for manufacturing a film carrier semiconductor device is described. Referring to Figures lA through 1C, a semiconductor chip is prepared by using, for example, a well-known wafer manufacturing technique.
A wafer 10' comprises a number of chip sections 10a' each having chip electrodes (contact pads) 11 formed thereon.
Though the illustrated chip electrodes 11 are formed along the periphery of each chip section l0a', the chip elec-trodes may be formed within an active area. The chip electrodes 11 are typically made of an aluminum-based alloy. The wafer 10' is then provided with a passivating film 12. More particularly, the entire surface of the wafer 10' is covered with the passivating film 12. The passivating film 12 may be made of, for example, polyi-mide, silicon nitride, or silicon oxide by using a well-known technique such as spin coating. The passivating 5 film 12 may be made of, for example, polyimide, silicon nitride, or silicon oxide by using a well-known technique such as spin coating. The passivating film has a thick-ness of 20 micrometers or less. After formation of the passivating film, the chip electrodes 11 are exposed to 10 the atmosphere by means of exposing the wafer 10' to light and etching it. As a result, the passivating film 12 covers the entire surface of the wafer 10' except for the locations where the chip electrodes 11 are formed. The chip sections 10a' are then separated from each other into individual chips along scribe lines 13. The separation is made by means of a known dicing technique using a dicing saw.
Referring to Figure 2, a process for manufac-turfing a conventional semiconductor device is described.
A semiconductor chip 20 obtained in the manner described above is prepared along with an adhesion film 25 and a carrier film 30 (Figure 2A). Ball bumps 14 of gold are formed on the chip electrodes 11. The adhesion film 25 is interposed between the semiconductor chip 20 and the car-rier film 30. The adhesion film 25 is smaller than the semiconductor chip 20 and has a thickness of about several tens of micrometers.

The carrier film 30 comprises an organic insula-tion film 31. The organic insulation film 31 may be, for example, a polyimide-based insulation film. The organic insulation film 31 has a first surface 31a and a second surface 31b. Interconnection layers 32 are pro-vided on the organic insulation film 31 on the side of the first surface 31a. Through-holes 33 are formed in the insula-tion film 31. One end of each through-hole 33 faces the interconnection layer 32. Each through-hole 33 passes through the insulation film 31 to the second surface 31b thereof. The insulation film 31 is also provided with openings 34 penetrating through the film. The openings 34 are formed at the position corresponding to the chip elec-trodes 21. Each through-hole 33 is filled with a conduc-tive electrode 35. Likewise, each opening 34 is filled with a filler material 36.
Referring to Figure 2B, the adhesion film 25 is positioned relative to the semiconductor chip 20 and placed thereon. When made of a thermoplastic resin, the adhesion film 25 can be temporarily fixed on the semi-conductor chip 20 by means of heating it from the side of the chip up to a temperature at which the adhesion film 25 begins to melt. In this event, the adhesion film 25 is adhered to the semiconductor chip 20 in such a manner that no voids are trapped between the film 25 and the chip 20.
Referring to Figure 2C, the carrier film 30 is positioned relative to the semiconductor chip 20 with the adhesion film 25 thereon, and the interconnection layers 32 are connected to the chip electrodes 11 via the ball bumps 14 by means of the inner lead bonding technique.
More specifically, the conductive electrode 35 contacts with one end of the interconnection layer 32. The other end of the inter-connection layer 32 reaches between the contact pad 11 and the opening 34. In this event, the aluminum forming the chip electrode 11 is reacted with copper forming the interconnection layer 32 and with the gold forming the ball bumps 14 into an aluminum-copper-gold alloy to ensure the interconnection between them.
Referring to Figure 2D, the combination of the semiconductor chip 20 and the carrier film 30 is subjected to heat and pressure to adhere them via the adhesion film 25. The combination, which is referred hereinafter to as a chip assembly, is heated and pressurized for several seconds from the side of either the semiconductor chip 20 or the carrier film 30.
The above mentioned steps illustrated in Figures 2B through 2D are not a limitation on the method available for connecting the carrier film 30 and the semiconductor chip 20. The adhesion film 25 may be positioned and plated relative to the carrier film 30 rather than the semicon-ductor chip 20. Alternatively, the inner lead bonding may be performed with high accuracy after the carrier film 30 is adhered to the semiconductor chip 20 with the adhesion film 25 interposed between them. Further, an adhesion layer may be formed previously on the surface of the chip section of the wafer.
In Figure 2E, the chip assembly is subjected to an electrical sorting operation and tests for long-term reliability under low electric field bias temperature (BT) are performed using a sorting pad 50 in the same manner as in typical tape carrier packages (TCP). The outer configuration and dimensions of the carrier film 30 are designed to meet the specifications determined by Elec-tronic Industries Association of Japan (EIAJ). Such a design allows common use of sorting tools such as sockets and balls for various semiconductor devices.
In Figure 2F, product names are labelled on the back surface of the chip using a laser beam. The carrier film 30 is then cut along the edges of the chip assembly using a mold. Typically, the cutting length and width are larger by approximately 100 micrometers on each side than those of the chip assembly when a mold is not used for cutting. More precise cutting may be achieved using a dicing saw or a laser beam.
Referring to Figure 2G, bump electrodes (solder bumps) 37 are formed on corresponding outer chip elec-trodes 11 arranged as an array on the carrier film 30 at the second surface 31b thereof. The bump electrodes 37 may be formed using a method disclosed in, for example, Japanese Patent Laid-open No. 49-52973. The bump elec-trodes 37 are formed by soldering a wire using the wire bonding process on the surfaces of the chip assembly corresponding to the chip electrodes 11 on the semicon-ductor chip. The balls are then bonded to the pads, following which the wires are cut.
As mentioned above, this conventional manu-facturing process is practical only for a limited number of chips obtained per unit time because it is necessary to conduct operations such as inner lead bonding and form-ation of the bumps for each small chip independently.
Accordingly, there may be a problem in the interconnection between the semiconductor chip and the carrier film as well as in the adhesion of the individual components. In addition, the bump electrodes in the above mentioned con-ventional semiconductor devices are formed on the corres-ponding chip electrodes, which makes it difficult to meet the demands of reduced size, a higher terminal count, and a smaller pitch.
Next, an embodiment of the present invention is described with reference to Figures 3A through 3G and 4A
through 4C. As shown in Figure 3A, a number of semi-conductor chip sections l0a are defined on a wafer 10 according to a well-known wafer manufacturing process.
The chip section in this embodiment is square but may be rectangular for other applications. Each semiconductor chip section l0a has a number of chip electrodes (contact pads) 11 formed on one surface along the periphery thereof. Referring to Figure 3B, the wafer 10 is covered with a passivating film 12 having a thickness of 20 micrometers or less. The passivating film 12 may be formed by means of any one of standard methods such as spin coating. In this event, the passivating film 12 5 covers the entire surface of the wafer 10 including the chip sections defined by scribe lines 13 with the chip electrodes il thereon. The wafer 10 is then subjected to well-known exposure and etching procedures to expose the chip electrodes 11 to the atmosphere. This is clearly 10 shown in Figure 3B. The wafer 10 at this stage is similar to the wafer 10' illustrated in Figure 1C. As mentioned above, the conventional manufacturing process then divides the wafer into the semiconductor chips along the scribe line 13. In contrast, no dicing is made at this stage in 15 the present invention.
Referring to Figure 3C, aluminum interconnection layers 60 are formed on the wafer 10. The aluminum interconnection layer 60 has a thickness of 1 micrometer or less and is connected to the chip electrode 11 at one end thereof. The other end of the aluminum interconnec-tion layer 60 is extended inward on the chip section 10a.
In other words, the aluminum interconnection layer 60 is extended towards the central portion of the chip section 10a. The aluminum interconnection layer 60 may be formed by means of a thin-film deposition technique such as sputtering using a mask. Referring to Figure 3D, a nickel plating 62 is made on the aluminum inter-connection layer 60. The nickel plating has a thickness of at least 5 micrometers in order to absorb any thermal stress gener-ated due to the difference in coefficient of thermal expansion between the final semiconductor device and a circuit board on which the semiconductor device is to be mounted. The thickness of the nickel plating 62 also affects on the reliability of the joint between the nickel surface and a bump electrode formed later. In this embodiment, the nickel plating has the thickness of 10 micrometers. The plating on the aluminum interconnection layer 60 is not limited to nickel, and other metals such as copper may be used, provided that they have the desired adhesion and diffusion barrier properties, for compatibi-lity with the material of the bump electrodes (solder in this embodiment).
Referring to Figure 3E, a cover coating film 64 is applied on the nickel plating 62 and the passivating film 12. The cover coating film 64 may be made of, for example, polyimide applied to have a thickness of 20 micrometers or less. This cover coating film 64 is similar in function to the organic insulation film 31 of the carrier film 30 described in conjunction with the conventional process. Next, a number of apertures 66 are formed in the cover coating film 64. The position of the apertures 66 corresponds to where the bump electrodes described below are formed. Accordingly, the position of the apertures 66 is not limited to a specific embodiment and may be selected depending on the application of the resultant semiconductor device. The aperture 66 is formed by means of, for example, etching or laser to the extent that the surface of the nickel plating 62 is exposed to the atmosphere. Subsequently, a gold plating 68 is made on the exposed surface of the nickel plating 62. Though not necessary, the gold plating 68 is preferable for higher reliability of the bump electrodes.
Referring to Figure 3F, bump electrodes 70 are formed in the aperture 68 and on the surface of the cover coating film 64. The bump electrode 70 may be generally spherical or hemispherical and about 100 micrometers high, but different shapes may be used. The bump electrode 70 may be made according to the following steps. A solder piece is cut from a solder strip using a die and a punch.
This solder piece is adhered in the aperture 66 using an adhesive material such as rosin (flux). The solder piece is then heated and melted to form the bump electrode. The rosin is washed out after the formation of the bump elec-trodes 70.
The wafer at this stage is illustrated in Figures 4A through 4C. As apparent from the figures, the bump electrodes 70 are formed on the entire surface of the wafer 10 except for where the scribe lines are defined. In addition, the aluminum interconnection layer 60 is ex-tended to the position of the aperture 66. Though the bump electrodes 70 in this embodiment are formed on the entire surface of the wafer except for the portions just under which the chip electrodes 11 are formed, the bumps 70 may also be formed over the chip electrodes 11.
Turning to Figure 3G, the semiconductor chip sections defined on the wafer 10 are separated from each other into individual semiconductor devices 80 by means of dicing.
The conventional wafer 10' illustrated in Figure 1A has the chip electrodes 11 separated from each other at a pitch of approximately 0.1 mm. The resultant semicon-ductor device thus has the bump electrodes away from each other at the same pitch of 0.1 mm or less. In contrast, the pitch can be increased up to approximately 0.5 mm between the bump electrodes 70 on the semiconductor device 80 of the present invention. Accordingly, fusion or melting of adjacent bumps can be reduced significantly which otherwise may occur during the formation of the bump electrodes. In addition, the semiconductor device according to the present invention can be mounted on, for example, a circuit board, with a higher yield. Further more, the present process provides easier standardization of semiconductor devices. This process also provides a higher reliability of the joint between the bump elec-trodes and the nickel or gold plating.
As mentioned above, the present invention makes it possible to mass-produce semiconductor devices without making a large investment in manufacturing facilities because the present process is compatible with a well-known chip manufacturing process. The semiconductor device obtained according to the present invention has a superior thermal stress resistance and reliable joints between the adjacent layers. This improves the moisture resistance of the semiconductor device.
While the present invention has thus been des-cribed in conjunction with a specific embodiment thereof, it is understood that the present invention is not limited to the illustrated embodiment. Instead, any changes, modifications, and variations may be made by those skilled in the art without departing from the scope and spirit of the appended claims. For example, gold may be used for the bumps rather than the solder. In such a case, the nickel plating and the gold plating can be eliminated.

Claims

1. A semiconductor wafer, including:
a plurality of the sections defined thereon by scribe lines, each chip section having bump electrodes formed simultaneously thereon, the scribe lines for separating the chip sections from each other without dividing bump electrodes thereon, said chip section including:
a plurality of chip electrodes positioned on said chip section; and, a plurality of interconnection layers for electrically connecting said chip electrodes and said bump electrodes;
said bump electrodes being located at positions other than over said chip electrodes;
said chip section having a center and a periphery, and said interconnection layers extending from said periphery toward said center.

2. A semiconductor wafer, including:
a plurality of chip sections defined thereon by scribe lines, each chip section having:
bump electrodes formed simultaneously thereon;
a plurality of chip electrodes positioned on said chip section; and a plurality of interconnection layers for electrically connecting said chip electrodes and said bump electrodes;
said bump electrodes being located at positions other than over said chip electrodes, said chip section having a center and a periphery, and said interconnection layers extending from said periphery toward said center.

3. A semiconductor wafer including:
a plurality of chip sections defined thereon by scribe lines, each chip section having bump electrodes formed simultaneously thereon, the scribe lines for separating the chip sections from each other without dividing bump electrodes thereon, said chip section including:
a plurality of chip electrodes positioned on said chip section; and a plurality of interconnection layers for electrically connecting said chip electrodes and said bump electrodes, said bump electrodes being located at positions other than over said chip electrodes, wherein each of said interconnection layer comprises an aluminum layer and a plating on said aluminum layer, wherein said plating contacts one of said bump electrodes and said aluminum layer contacts one of said chip electrodes.

4. A semiconductor wafer as in claim 3, wherein said plating comprises one of nickel and copper.

5. A semiconductor wafer as in claim 3, wherein said aluminum layer has a thickness of no greater than 1 micrometer.

6. A semiconductor wafer as in claim 3, wherein said plating has a thickness of at least 5 micrometers.

7. A semiconductor wafer as in claim 3, further comprising a gold layer between said bump electrode and said plating.

8. A semiconductor wafer including:
a plurality of chip sections defined by scribe lines, each chip section having:
bump electrodes formed simultaneously thereon;
a plurality of chip electrodes positioned on said chip section; and a plurality of interconnection layers for electrically connecting said chip electrodes and said bump electrodes, said bump electrodes being located at positions other than over said chip electrodes, wherein each of said interconnection layers comprises an aluminum layer and a plating on said aluminum, wherein said plating contacts said bump electrode and said aluminum layer contacts said chip electrode.

9. A semiconductor wafer as in claim 8, wherein said plating comprises one of nickel and copper.

10. A semiconductor wafer as in claim 8, wherein said aluminum layer has a thickness of no greater than 1 micrometer.

11. A semiconductor wafer as in claim 8, wherein said plating has a thickness of at least 5 micrometers.