This invention relates to semiconductor chips and more particularly to the fabrication and processing of a stackable semiconductor chip having edge features which facilitate or provide access to circuitry on or in the chip.
Three-dimensional conductor chip packages comprising a stack of thin semiconductor chips are now being manufactured. The chips in these packages often contain controllers, memories, sensors, analog components, processors and specialty communications components as well as MEMS devices. The cost of these relatively dense, integrated packages is high, so quality control and testing as part of the fabrication, so quality control and testing as part of the fabrication process is all the more important.
Functions such as testing, trimming, bonding and tuning are typically carried out by accessing the primary surfaces of the semiconductor chips, usually a planar top surface. The accessing step may require bringing, for example, a probe into actual contact with a feature such a pad or trace on the surface. This becomes complicated or impossible when the primary surfaces of the interior chips are no longer accessible as a result of having been integrated into a stack.
In accordance with a first aspect of the invention, a method is provided for performing one or more functions on a semiconductor chip which is part of a stack of semiconductor chips without the necessity of contacting or otherwise addressing a top surface feature. This is achieved by providing one or more access features on a chip edge surface and, where necessary, connecting the edge feature or features to a circuit or component carried by the chip. These edge surface features remain accessible after chip stacking.
In accordance with this aspect of the invention, the function which is performed may consist of one or more testing, altering, repairing, programming, interrogating, loading and tuning as well as bonding one or more conductors into a functional relationship with a circuit or component on the chip.
Further in accordance with this first aspect of the invention, the edge feature may consist of one or more of an electrical conductor, a thermal conductor, a fuse, a resistor, a capacitor, an inductor, an optical emitter, an optical receiver, a test pad, a bond pad, a contact pin, a heat dissipation device, multiples of these and combinations of these.
Further in accordance with this first aspect of the invention, the signal conduit may consist of one or more of an electrical conductor such as a trace or a via, a heat conductor, an optical conductor, multiples of these and combinations of these.
Further in accordance with this first aspect of the invention, the method comprises the steps of locating the stack containing the semiconductor chip to be processed by way of an edge feature on a fixture wherein the edge feature can be addressed by a function performer and thereafter activating the function performer to address the edge feature. As used herein, a “chip” is a physical object with top and bottom primary surfaces, and one or more peripheral edge surface, the actual number of such edge surfaces being determined by chip geometry.
In accordance with the invention, the functions of addressing and activating may involve actual physical contact between the function performer and the edge feature but it may also be carried out in a non-contacting way particularly where the edge feature associated with the peripheral edge surface is an optical device or is recessed or buried beneath a surface of material which is transparent to the output of the function performer. The function performer may be one or more of a test probe, a wire bonder, a laser, a programmer contact, a trimmer, a data transfer contact and/or an optical transmitter or receiver and/or multiples or combinations of these elements.
In accordance with a second aspect of the invention, a stackable semiconductor chip is provided wherein the chip comprises a primary surface and has one or more devices associated with it, the definition of said devices being set forth above. This primary surface, although exposed when the die which makes up the semiconductor chip is fabricated both before and after singulation, is no longer exposed once the chip has been integrated into the three-dimensional stack. Accordingly, the die is further provided with an edge feature, the definition of which is given above as well as a signal conduit between the edge feature and the primary surface device and/or devices so that the edge feature can be used in a process as set forth above. This aspect of the invention extends to multiple chips bonded together in a stacked combination.
In accordance with a third aspect of the invention, a method of fabricating stackable semiconductor chips is provided wherein the fabrication process or method results in chips which can be processed in any of various ways by access to edge surface features after the chips have been integrated into a three-dimensional stack. As hereinafter described in detail, this process may involve the formation of layered integrated circuits in large two-dimensional arrays having what, after singulation, become edge features. During a singulation step, the buried edge features are exposed thus to provide access to a circuit or component integrated into the chips in the primary fabrication process even though the chips are assembled into a three-dimensional package of stacked chips which eliminates access to some or all of the primary surface devices in the stack.
As used herein, the terms “chip” and “die” are synonymous.
The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views and wherein:
a is a side view of the device of
When semiconductor chips are bonded together in stacks, the primary surfaces of chips low in the stack are covered up. Therefore, access to features or devices on or associated with the primary surfaces is no longer possible for such functions as testing or wire bonding, or trimming or tuning or configuration change, redundancy, repair and/or encoding or programming. In accordance with the present invention, these and other functions are carried out by way of features which have been located in such a way as to be associated with one or more of the peripheral edge surfaces of the chips or dice. Thus, a die or chip which is fabricated in accordance with the present invention includes one or more edge features which facilitate or enable testing, wiring, repair, reconfiguration, tuning or processing despite the fact that the chip or die has been incorporated into a three-dimensional stack. Also disclosed herein are systems and devices to test, wire bond or otherwise process features on the edges of chips or dice in a stacked array. Also described herein is a method of performing processes on componentry or devices in stacked semiconductor dice, despite the fact that the primary surfaces with which the components or devices are associated are no longer accessible to conventional equipment.
Referring to
The right hand stack 12 comprises semiconductor chips 28, 30 and 32 also bonded to one another as well as to a primary surface of a foundational die 14 by bonding material 34.
The choice of three chips in each of the stacks 10, 12 is arbitrary as the number may vary from two to any practical number as will be apparent to persons skilled in the semiconductor fabrication technology.
Chip 16 exhibits edge features 36 which in this case are pads for testing or wire bonding on the surface closest to the viewer in
Chip 18 is provided on the forward peripheral edge surface with bonding or probe contact pads 46 as well as laser alterable fuses 50, the former being shown while accessed by a probe 47 which is part of a circuit test device 48. In
Die 20 is provided with electrically conductive pads 54 and fuses 60 on the foremost peripheral edge surface as well as pads 64, 66 on the right hand peripheral edge surface. The former are used for wire bonding purposes to create conductive interconnections between chips in the stack 10 as well as between the chip 20 and the foundation chip 14, the latter having bonding pads 58 associated with the foremost peripheral surface along with fuses 62. The pads 52, 64 are shown wire bonded together and the pad 66 is shown wire bonded to a pad 68 on the foundation of the chip 14. These uses and interconnections are illustrative rather than limiting.
Referring to stack 12, the foremost peripheral edge surface of chip 24 is provided with conductive pads 70 as well as laser-alterable fuses 72. The foremost peripheral edge surface of chip 30 is provided with conductive pads 74 and a trimmable structure 76; the foremost peripheral edge surface of chip 32 is provided with pads 78 and a trimmable structure such as resistive film 82. As shown, wire bonding between the pads of the stacked chips is achievable despite the lack of access to the primary surfaces. Wires such as 77, 79 can be connected between the two stacks as well as between two chips in a stack and wire 81 can be connected between one of the pads 78 on the lowermost chip 32 and the right hand stack 12 as well as to the pad 80 on a primary surface of the foundation chip 14.
Thus,
Referring now to
Chip 94 has pads 104 as edge features, such pads being used in association with the probe 47 of the circuit tester 48 also shown in
Chip 96 is provided with pads 106 which in this case are used for wire bonding; i.e.,
Stack 86 of
One purpose in illustrating the arrangement of
Referring to
The right hand stack 112 comprises chips 120, 122 having edge features which in this case include an optical receiver 126 on the left peripheral edge surface of chip 120. The chips 116, 120 are aligned with one another as well as adjacent so that the optical transmitter 124 is aimed essentially at the optical receiver 126 for data communication therebetween. This illustrates the fact that the operative association between edge features on the same or adjacent chips may be non-contacting.
Accordingly one stacked die may optically transmit information to another nearby die without the need for wiring as illustrated in
The subsurface feature 136 illustrated in
The signal conduits, when used, may be created with vias or vertical aluminum copper or tungsten structures and may also be made with traditional lithography techniques, deep-reactive ion etching followed by refill or by laser formation followed by refill.
Describing the methodology of the present invention, the reference numeral 162 referred to above in connection with
As will be apparent to those skilled in the art, singulation can be performed by straight cuts made by way of straight cuts with a traditional saw. Alternatively, a laser can be used to make non-straight cuts to expose the edge features that are flush with the cut surface. Non-straight singulation with a laser can also be used to rout out protruding edge features or those which are slightly recessed as shown at 154 in
Another way to expose an edge feature is to perform singulation by sawing laser cuttings or scribing or braking followed by an etching which can remove material 129 surrounding the features. One preferred etch is a selected etch performed with a chemical such as XeF2 that removes silicon at a much higher rate than metal features.
Additional structures can be added to etch features after singulation with optional edge exposure. For example, edge features can be plated, passivated, soldered or reconfigured for mechanical mating. Features can be reformed and reflowed through heating, laser, chemical or mechanical alteration. Edge features can also be added with adhesives. All of these steps can be performed before or after stacking the dice.
Referring now to
Bare die and stacked dice with edge features will often require automated handling techniques and these techniques must be selected so as not to damage the edge features. Handling techniques may include such devices as mechanical grippers, vacuum grippers or temporary adhesion onto a carrier plate. Grippers can be designed to allow testing access or to contain an appropriate testing interface.
Testing or other edge function performance steps can be carried out on individual chips as well as on partial or complete stacks of chips.
The discussion now turns to methods for aligning edges of chips with the edges of other chips as well as to collateral devices. It is necessary to align edge features in order to process them with laser beams, to contact them with electrical probes to perform wire bonding, to optically communicate or to otherwise interact with an edge feature. Alignment may be accomplished by aligning to the physical edges of a die, aligning to features fabricated on the edges of the due, such as bonding, pads or fuses, dedicated alignment features such as targets or ficudials that are located on the edges of the dies, aligning to structures or features located on the bottom primary surfaces of the die or aligning to other or nearby collateral structures. Alignment can be verified and modified during the alignment procedure. For example, electrical conductivity or circuit impedance can be tested and a position adjustment can be made to correct alignment. Alignment may involve determining the relative location of two different dice, thereafter the relative location of die or die features may be used to facilitate proper interfacing such as wire bonding between the two dice.
Alignment may involve using cameras or optical scans or laser scans to determine feature locations. Machine vision and vision analysis techniques can be employed. The locations of multiple dice may be determined from a single image. It may be necessary to assess and perform alignment differently on different sides of a die containing edge features. Die alignment may be optimized by assessing different sides of a die and the edge features on such dies are oriented,
Interconnect involving edge features may involve wire bonding of an edge feature to any other feature located on an edge, on a primary surface or on another nearby die circuit board, package conductor, foundation chip or test probe. Interconnect may be between features on a die that are stacked and/or laterally arranged.
As shown in
Testing of edge structures may occur before or after stacking. Parametric tests and functional tests can be done to verify that the dice were properly fabricated. Tests may be used to sort and distribute components into bins. Following tests, additional tuning, trimming, reconfiguration, repair, serialization or identification can be performed on edge structures.
Testing, tuning and trimming and repairing with edge structures can be also used to determine and/or correct for changes and defects during the packaging process. For example, it may be required to tune the electrical impedance to properly mate one die to a different die. Packaging effects can be mitigated using edge tests or alterations.
Some of the testing, trimming and tuning can be based on properties in the die that are measured before they are stacked. Testing during a die stacking may reveal that the die is cracked or has undergone irreparable damage during handling. Such a die can be removed and replaced with an undamaged substitute. Alternatively, this stack of dice can be discarded before any additional undamaged dies are added by bonding or otherwise. Testing with edge structures can also be used as part of a reliability test, a burn-in and/or during final testing of stacked dies.
It will be appreciated that the embodiments illustrated in the drawing and described above are exemplary and that implementation of the invention can be carried out in various other configurations.