Active solid-state devices (e.g. – transistors – solid-state diode – Physical configuration of semiconductor – With peripheral feature due to separation of smaller...
Reexamination Certificate
2000-05-12
2003-02-18
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Physical configuration of semiconductor
With peripheral feature due to separation of smaller...
C257S508000, C257S618000, C257S619000, C257S797000, C438S462000, C438S401000, C438S637000
Reexamination Certificate
active
06521975
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related in general to the field of semiconductor devices and processes and more specifically to the fabrication of integrated circuit chips protected against potential damage caused by the propagation of cracks initiated by the step of separating semiconductor wafers into individual chips.
DESCRIPTION OF THE RELATED ART
With most semiconductor products, for example integrated circuits, transistors and diodes, a large number of elements are manufactured simultaneously on a large semiconductor wafer of silicon, silicon germanium, gallium arsenide, etc. The semiconductor industry employs the terms “dicing technologies” or “scribing technologies” to refer to those techniques for obtaining a large number of functional chips, or dies, from each semiconductor wafer. Two dicing methods are particularly well known in the art: The grinding-cutting method, using a blade or wire saw, and the scribing method, using a diamond point. Modern silicon technology prefers the cutting method using high-speed rotating blades. When laying out the pattern of integrated circuit (IC) chips on the surface of the semiconductor wafer, manufacturing efficiency requires to minimize the distance between adjacent IC chips so that the number of obtainable chips (the production yield) can be maximized.
The technology of dicing has been developed to a high standard. In U.S. Pat. No. 4,610,079 of Sep. 9, 1986 (Abe et al., “Method of Dicing a Semiconductor Wafer”), it has been pointed out that three restrictions exist with respect to the minimum distance permissible between adjacent chips. The first restriction is the actual dicing width, the second restriction is the degree of precision to which the cutting machine can be adjusted, and the third restriction is the cracks and chip-outs extending laterally from the dicing line into the semiconductor and insulating materials. Even today, the third of these restrictions, namely the generation of cracks, creates significant limitations with respect to minimizing the distance between adjacent IC chips. In addition, those cracks represent significant reliability risks, since they tend to grow and widen under thermal and mechanical stress and thus eventually imperil the functionality of the IC.
Several solutions have been proposed to solve some of these technical problems associated with the manufacture and dicing of semiconductor wafers. The sealing of dicing streets against penetration of mobile ions with the help of metal edge barriers overlapping insulating layers was proposed in U.S. Pat. No. 4,364,078 of December 1982 (Smith et al., “Edge Barrier of Polysilicon and Metal for Integrated Circuit Chips”) and U.S. Pat. No. 4,656,055 of April 1987 (Dwyer, “Double Level Metal Edge Seal for a Semiconductor Device”). These structures proved ineffective against cracks when insulators extend into the dicing lines and are subject to cracks during the dicing process. In U.S. Pat. No. 5,024,970 of June 1991 (Mori, “Method of Obtaining Semiconductor Chips”), small grooves are obtained in the insulating zone by plasma etching. Many cracks originating from the dicing process are seen to stop at these grooves, but not all of them.
Forming consecutive grooves of different widths by using diamond and resin blades has been described in U.S. Pat. No. 5,266,528 of November 1993 (Yamada et al., “Method of Dicing Semiconductor Wafer with Diamond and Resin Blades”). Dicing line features to limit the spreading of cracks and chip-outs generated during dicing have been proposed in U.S. Pat. No. 4,610,079 of September 1986, mentioned above. Avoiding residues of layers of non-uniform thicknesses, or the generation of lose particles, has been described in U.S. Pat. No. 5,136,354 of August 1992 (Morita et al., “Semiconductor Device Wafer with Interlayer Insulating Film Covering the Scribe Lines”) with added division in U.S. Pat. No. 5,237,199 of August 1993. In these patents, the etching of slit grooves in passivation films is described in order to stop cracks in the passivation layers during the dicing process.
The latter ideas were continued and elaborated in U.S. Pat. No. 5,414,297 of May 1995 (Morita et al., “Semiconductor Device Chip with Interlayer Insulating Film Covering the Scribe Lines”). In particular, it is described how the processes used in forming the conductive interconnections between elements of the integrated circuit can be exploited to generate one vertical metal line parallel to the dicing lines so that it extends around the entire periphery of each integrated circuit chip.
Practical semiconductor manufacturing has demonstrated, however, that these structures do not stop severe cracks originating in the dicing process. On the contrary, thermomechanical stresses generated by modern device applications, board attach processes, or rigorous environmental testing procedures may convey enough energy to many cracks so that they will eventually bypass obstacles or break through a single seal. Following these cracks, moisture and contamination are free to penetrate active circuitry and to start degrading the electrical device performance drastically.
In U.S. patent application Ser. No. 60/073,939, filed on Feb. 6, 1998 (Ibnabdeljalil et al, “Sacrificial Structures for Arresting Insulator Cracks in Semiconductor Devices”), scribe street seals are described having at least two sets of substantially parallel structures, each set extending along the edge of a chip on opposite sides of each dicing line. Each set comprises at least one continuous barrier wall and a sacrificial composite structure having means of dispersing the energy associated with crack propagation. This concept, however, does not prevent the lateral propagation of surface-near cracks or the risk of widespread delamination of structures especially when copper instead of aluminum is employed as interconnecting metal.
In summary, the goal of providing a technology for dicing semiconductor wafers with assured protection against mechanical and environmental damages and thus offering for the commercial and military markets cost-effective and reliable semiconductor products, manufactured in high volume and with flexible, low-cost design and production methods, has remained elusive, until now. The new design and method of fabrication should be flexible enough to be applied for different semiconductor product families and a wide spectrum of process variations. Preferably, these innovations should be accomplished using the installed equipment base so that no investment in new manufacturing machines is needed.
SUMMARY OF THE INVENTION
The invention describes sets of seal structures in semiconductor wafer scribe streets, extending along the edges of each integrated circuit chip and comprising a continuous barrier wall, adjacent to each chip, and a sacrificial composite structure, substantially parallel to the wall, being a discontinuous barrier wall comprising metal rivets interconnecting electrically conductive layers in an alternating pattern, and further describes slots opened into the protective overcoat of the wafer, reaching from the surface of the overcoat to the surface-nearest electrically conductive layer of the composite structure.
According to the Griffith energy-balance concept for crack formation in brittle solids (first published in 1920), a change in the length of a nascent crack or notch cannot change the sum of all energies; in other words, the sum of surface energy and mechanical energy has to stay constant. This means for a crack extension that the surface energy may generally increase, but the mechanical energy has to decrease. The mechanical energy itself consists of the sum of the strain potential energy stored in the material and the potential energy of the outer applied loading system. This says, whenever any of these energies can assume a lower value, the freed energy can be invested in generating more surface for an expanding crack.
Applying the Griffith equilibrium requirement to semiconductor devices, whenever uniform stress is applied (for instance during
Gillespie Paul M.
West Jeffrey A.
Brady III Wade James
Huynh Andy
Skrehot Michael K.
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