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Hermetic seal and reliable bonding structures for 3d applications

Hermetic seal and reliable bonding structures for 3d applications description/claims

This invention was made with Government support under Contract No. N66001-00-C-8003 and N66001-04-C-8032 awarded by Defense. Advanced Research Projects Agency (DARPA). The Government has certain rights in this invention.

The present invention relates to a sealed semiconductor structure using a bonding technique and, more specifically, relates to a bonded sealed semiconductor structure including structural support elements.

Integrated circuits (ICs) form the basis for many electronic systems. Essentially, an integrated circuit (IC) or chip includes a vast number of transistors and other circuit elements that are formed on a single semiconductor wafer and are interconnected to implement a desired function. The complexity of these integrated circuits (ICs) requires the use of an increasing number of linked transistors and other circuit elements.

Many modern electronic systems are created through the use of a variety of different integrated circuits, where each integrated circuit (IC or chip) performs one or more specific functions. For example, computer systems include at least one microprocessor and a number of memory chips. Conventionally, each of these integrated circuits (ICs) are formed on a separate chip, packaged independently and interconnected on, for example, a printed circuit board (PCB).

In micoelectronics, a wafer is a thin slice of semiconducting material, such as a silicon crystal, upon which microcircuits are constructed for example, by doping, etching, or deposition. Wafers are used in the fabrication of semiconductor devices such as integrated circuits or chips or dies. A single wafer may have a plurality of chips formed on the wafer. The wafer may be used having a plurality of chips formed therein, or the wafer may be cut to provide individual dies or chips. The wafers and chips or dies can form a stack by positioning the wafers and/or chips on top of one another. Copper bonding (Cu bonding) processes can be used to stack dies/chips at a chip-to-chip, chip-to-wafer, or wafer-to-wafer level.

As integrated circuit (IC) technology progresses, a need for a “system on a chip” in which the functionality of all of the IC devices of the system are packaged together without a conventional printed circuit board (PCB). Ideally, a computing system should be fabricated with all the necessary IC devices on a single chip. In practice, however, it is very difficult to implement a truly high-performance “system on a chip” because of vastly different fabrication processes and different manufacturing yields for the logic and memory circuits.

As a compromise, various “system modules” have been introduced that electrically connect and package integrated circuit (IC) devices which are fabricated on the same or on different semiconductor wafers. Initially, system modules have been created by simply stacking two chips, e.g., a logic and memory chip, on top of one another in an arrangement commonly referred to as chip-on-chip structure. Subsequently, multi-chip module (MCM) technology has been utilized to stack a number of chips on a common substrate to reduce the overall size and weight of the package which directly translates into reduced system size.

Existing multi-chip module (MCM) technology provides performance enhancements over single chip or chip-on-chip (COC) packaging approaches. For example, when several semiconductor chips are mounted and interconnected on a common substrate through very high density interconnects, higher silicon packaging density and shorter chip-to-chip interconnections can be achieved. In addition, low dielectric constant materials and higher wiring density can also be obtained which lead to increased system speed and reliability, reduced weight, volume, power consumption, and heat to be dissipated for the same level of performance. However, MCM approaches still suffer from additional problems, such as, bulky packaging, wire length and wire bonding that gives rise to stray inductances which interfere with the operation of the system module.

Typically, optimization of Cu bonding was achieved by utilizing one pattern density with specific bond pad dimensions and/or via dimensions. Vias and electrically connected pads refer to vias/pads with a plated hole that connects conductive tracks from one layer of a chip to another layer(s). Current solutions are not compatible with standard CMOS processes in which a variety of pattern densities and pad/via sizes may be used. Additionally, due to mechanical stability issues most of the bonding fails occur at the edge of the bonded pattern which often, in addition to degraded bonding yield, leads to corrosion issues. Additionally, for 3D applications, a method or device is needed to provide additional protection from mechanical damage (such as crack propagation, chipping, dicing, etc.) caused during the semiconductor fabrication process.

In the current state of the art, electrically active bonded pads and/or vias had to be often placed in the central location of the pattern to provide good reliability for these contacts. One major challenge of three dimensional (3-D) wafer-to-wafer vertical stack integration technology is the metal bonding between wafers and between die in a single chip, and the wafer protection from possible corrosion and contamination caused or generated by process steps after the wafers are bonded from reaching active IC devices on the bonded wafers.

Therefore, a need exists to erect a barrier structure by the edge of bonded wafers and individual die to protect the bonded wafers and die against corrosion and contamination in a three-dimensional (3-D) wafer-to-wafer vertical stack. It would also be desirable to provide an improved metal bonding method having acceptable bonding yield and reliability without being limited to pattern density or pad/via dimensions.

In an aspect of the invention, a sealed microelectronic structure providing mechanical stress endurance is provided which comprises at least two chips including and being electrically connected to a semiconductor structure and comprising outer edges. Each chip includes a continuous length of bonding material on a planar surface area thereof defining a perimeter in spaced adjacency to the outer edge. At least one support column is connected to each of the chips and positioned within the perimeter of each chip. Each support column extends outwardly such that when the at least two chips are positioned in overlapping relation to one another, opposing support columns mate with each other or with an opposing planar surface area on the overlapping chip. A seal between the at least two chips results from the at least two chips being positioned in overlapping relation to one another such that the bonding material on each chip is in mating relation to each other whereby the seal is formed when the at least two chips are mated together resulting in a bonded chip structure.

In a related aspect of the invention, the bonding material on the at least two chips is compressed and the bonding material is heated to form the seal.

In another related aspect of the invention, a plurality of chips are positioned on at least two wafers. The wafers each include a continuous bonding material along a perimeter substantially adjacent to an outer edge of the wafer. The at least two wafers are sealed together when the bonding material on each of the wafers is compressed on each other in mating relation and heated to form the seal.

In another related aspect of the invention, the chips are electrically connected to their respective substrates to form an electrical circuit on the chips and the support columns are non-electrical and thereby are not part of the electrical circuit.

In another related aspect of the invention, the chips are electrically connected to their respective substrates and electrical connected to their respective wafers to form an electrical circuit on the chips and the wafers and the support columns are non-electric and thereby not part of the electrical circuit.

In another related aspect of the invention the chips have multiple layers and the support columns are positioned between the layers and adapted to provide support between the layers.

In an aspect of the present invention, a method for sealing a microelectronic structure and providing mechanical stress endurance comprises providing at least two chips including and being electrically connected to a semiconductor structure at a plurality of locations. A length of continuous bonding material is deposited on each chip on a planar surface thereof defining a perimeter substantially adjacent to the outer edge. At least one support column is connected on each of the chips and within the perimeter of each chip, and each support column extends outwardly. The chips are positioned in overlapping relation such that the bonding material and the support columns are in mating relation to each other. The chips are compressed and thereby the bonding material is also compressed together. The bonding material is heated to form a seal about the perimeter of the chips whereby a bonded chip structure is formed.

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