Method and apparatus for circuit completion through the use of ball bonds or other connections during the formation of a semiconductor device
A method used to form a semiconductor device comprises providing first and second circuit portions having first and second pad portions respectively. The second circuit portion is electrically isolated from the first circuit portion. The first and second pad portions are then electrically connected, for example with a ball bond or a wire bond, to electrically couple the first and second circuit portions. In various embodiments the semiconductor device will not function until the pad portions are electrically coupled, and in other embodiments the functionality of the device may be selectively controlled by connecting selected pad portions from a plurality of pad portions. Isolating the first and second circuit portions allows electrical operations such as antifuse programming to be carried out without adversely affecting related circuits. Once electrical operations are completed, the isolated circuit portions are electrically coupled to provide a complete circuit. Various inventive embodiments and implementations are described.
This is a continuation of U.S. Ser. No. 09/945,084 filed Aug. 30, 2001 and issued Jan. 31, 2006 as U.S. Pat. No. 6,991,970.
FIELD OF THE INVENTIONThis invention relates to the field of semiconductor manufacture and, more particularly, to a method for customizing the functionality of a semiconductor device after probe and before assembly through the use of a ball bond, wire bond, or other electrical connection.
BACKGROUND OF THE INVENTIONThe manufacture of semiconductor devices such as dynamic random access memories (DRAM), static random access memories (SRAM), microprocessors, and logic devices involves a number of complex processing steps. While great care is taken during processing to ensure the steps are identical between each manufacturing lot of wafers, variability between lots, between wafers within a lot, and between dice on a single wafer commonly occurs. This processing variability results in differences in electrical performance of completed semiconductor dice.
The functionality and electrical performance of each die is measured at probe. This testing occurs at the wafer level subsequent to wafer processing and before the wafer is diced to separate each die prior to packaging. During wafer testing various semiconductor dice are found to be fully functional, some are not functional and not repairable, while others are not functional but may be repairable, depending on their failure mode. For example, if one or more storage elements of a row or column of storage capacitors is nonfunctional, a row or column of functional storage capacitors may be substituted through the use of fuse or antifuse (fusible link) devices. The following US patents, each assigned to Micron Technology, Inc. and incorporated herein as if set forth in their entirety, describe the formation and use of antifuse devices: U.S. Pat. No. 6,108,260 issued Aug. 22, 2000; U.S. Pat. No. 6,088,282 issued Jul. 11, 2000; U.S. Pat. No. 6,087,707 issued Jul. 11, 2000; U.S. Pat. No. 5,345,110 issued Sep. 6, 1994; U.S. Pat. No. 5,331,196 issued Jul. 19, 1994; U.S. Pat. No. 5,324,681 issued Jun. 28, 1994; U.S. Pat. No. 5,241,496 issued Aug. 31, 1993; U.S. Pat. No. 5,110,754 issued May 5, 1992.
Antifuses are commonly fabricated with a structure similar to that of a capacitor. Two conductive electrical terminals are separated by a dielectric layer. An unprogrammed “off” state, in which the antifuse is fabricated, presents a high resistance between the antifuse terminals (i.e. the terminals are electrically isolated from each other). The antifuse may also be programmed to an “on” state in which a low resistance connection between the antifuse terminals is provided (i.e. the terminals are electrically coupled or connected). To program or “blow” an antifuse to the “on” state, a large programming voltage is applied across the antifuse terminals, breaking down the interposed dielectric and forming a conductive link between the antifuse terminals. When an antifuse device is programmed “on,” it is selected to replace a nonfunctional storage capacitor row or column with a functional row or column.
As stated above, when the device is in program mode (PROG high), the Program Circuitry outputs a low to transistor T1 and a program voltage is applied to CGND. When the device is in normal operational mode, the Program Circuitry outputs a high to transistor T1 to tie CGND to ground for proper operation.
As semiconductor device manufacturing technology improves and storage capacitors continue to decrease in size, problems may result from the use of antifuse devices. One problem which may occur results from the voltage required to program the antifuse. The voltage must be high enough to break down the dielectric between the antifuse plates in a reasonable amount of time. With the large number of antifuse devices which must be programmed with conventional memory devices, often numbering in the thousands, the voltage must be maintained at a fairly high level. As the feature size of semiconductor devices decreases with future device generations, the voltage required to program the antifuse may exceed the junction breakdown voltage of transistor T1. Thus the optimum voltage applied to CGND to program the antifuse will not be obtained because any voltage above the breakdown voltage of T1 can bleed to the substrate and pull down the CGND network of devices. Further, a high voltage over an extended period of time may adversely affect other devices which have a common active area which need to be connected to the CGND node for normal operation.
After functional testing and device repair using row and/or column redundancy in a conventional device, fully functional devices are speed graded and otherwise tested. After wafer-level testing is completed, the semiconductor wafer is diced to singularize each semiconductor die from other dice. Each functional die is assembled, for example including attachment to a lead frame and encapsulation in plastic, while nonfunctional dice are discarded.
A semiconductor device such as a DRAM comprises various default configurations which may be altered before encapsulation using bond options. For example, devices are typically manufactured for a “by 1” (×1) data width, such that only one data out line (DQ) is active to supply one data bit for each read cycle. Before encapsulation, the data width for the device can be changed by wire bonding together a “bond option pad” to a lead frame lead finger which is also electrically coupled with VCC or GND to modify its configuration. By using these “bond options” the device data width may be modified to a ×8 configuration, a ×16 configuration, a ×32 configuration, etc. Thus the device is manufactured to function in one manner if no bond options are selected, and will function in another manner if one or more bond options are selected.
Thus with conventional devices the ball bond is a first end of a bond wire and is attached to a bond pad of the die. A second end of the bond wire is attached to a lead finger of the lead frame, then the lead finger and die are encapsulated or otherwise packaged. In use, the lead is electrically coupled with power or ground, which determines how the die functions. The functionality of the die, therefore, is determined by a source external to the die, as the die will function one way if the lead is coupled with power, and another way if it is coupled with ground. Whether the lead will be coupled with power or ground is determined before the wire bond is connected, but the actual functionality depends on whether the lead is connected with power or ground.
Various other device parameters are a function of their processing and cannot typically be modified. These include internal power bus configurations or connecting/disconnecting internal circuitry. In such cases different photolithography masks would typically be required to modify circuit behavior or to modify power busing architecture. Mask sets can be expensive, require several weeks to manufacture, and add to semiconductor device manufacturing costs.
A method and structure which overcomes the problems described above and which allows for the modification of semiconductor device parameters not previously selectable in a manner not previously available would be desirable.
SUMMARY OF THE INVENTIONThe present invention provides a new method which, among other advantages, allows for the selection of semiconductor device parameters prior to encapsulation using one or more ball bond, wire bond, or other connection approaches. In accordance with one embodiment of the invention a semiconductor device is manufactured having a circuit which is separated into two or more segments. The circuit may be designed in a number of different embodiments to control various and diverse device parameters, for example including device latency, aspects of antifuse operation, device density (such as selecting a device to operate as a 64 megabit or 128 megabit device), and various power functions. The circuit further includes at least first and second adjacent conductive pad portions which may be electrically coupled using a ball bond or wire bond. These conductive pad portions are not accessible through the final package lead fingers.
In various embodiments of the invention, the semiconductor device will not function unless two or more of the adjacent conductive pads are shorted together. In other embodiments of the invention the semiconductor device will function in one manner if the adjacent pads are not shorted together, and will function in another manner if the pads are shorted together.
Additional advantages will become apparent to those skilled in the art from the following detailed description read in conjunction with the appended claims and the drawings attached hereto.
BRIEF DESCRIPTION OF THE DRAWINGS
It should be emphasized that the drawings herein may not be to exact scale and are schematic representations. The drawings are not intended to portray the specific parameters, materials, particular uses, or the structural details of the invention, which may be determined by one of skill in the art by examination of the information herein.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTA semiconductor device manufactured in accordance with one embodiment of the invention comprises a semiconductor wafer substrate assembly which may be an entire undiced semiconductor wafer or other large scale semiconductor substrate, two or more unsegmented semiconductor dice, or a single semiconductor die. Any of the foregoing may be hereinafter referenced as a “wafer section.” The substrate assembly comprises an electrical circuit segmented into two or more separate parts or portions, with each circuit portion electrically isolated from the other. Each circuit segment terminates in a conductive pad or “mini-pad” which is physically located near the mini-pad of the other circuit segment. The pads are arranged to facilitate their electrical attachment, which shorts together the two separate circuit parts and facilitates completion of the circuit.
In various other embodiments more than two circuit portions and corresponding mini-pads may be used. Further, the circuits portions may each be complete circuits which function in one manner if the mini-pads are not electrically connected, and will function in another manner if the mini-pads are electrically connected.
With current technology, gold, copper, palladium, aluminum, platinum, or tin-lead ball bonds as small as two mils in diameter may be manufactured, and the technology will likely improve to allow for ball bonds having even smaller diameters in the future. In the embodiment of
As discussed above in the “Background of the Invention” with reference to
This embodiment may also allow for the formation of fewer circuit devices on the circuit portion coupled with pad 84. In some devices fuses are programmed after encapsulation of the die, and in these devices the circuitry depicted would be required. In devices where programming fuses after encapsulating the semiconductor die is not enabled, some circuitry may not be necessary. For example, where fuse programming after die encapsulation is not enabled the program circuitry and transistor T1 are not necessary with the
It should be noted that the circuit of
Another inventive embodiment is described using
To manufacture a device with which latency is not programmable by the user, different photolithography masks would typically be required for each latency. Mask sets can be expensive, require several weeks to manufacture, and add greatly to semiconductor device manufacturing costs.
An application and embodiment of the instant invention may be used to reduce or eliminate the need for separate masks for each device latency for devices which do not have user-programmable latency.
Pads 120, 130, and 140 are coupled with VCC, while pads 124, 134, and 144 are coupled with ground. By coupling pads 122, 132, and 142 to either their associated VCC or ground pad, the latency may be set before the semiconductor die is encapsulated. Pads 122, 132, and 142 are coupled to the nor gate inputs A6, A5, and A4 respectively.
Once the ball bonds are formed, for example as depicted in the
In the particular embodiment of
In many process flows the ball bonds will be attached after dicing the wafer and prior to encapsulation. However, the ball bonds may also be attached prior to dicing the wafer.
Another use and embodiment of the invention is depicted in
Improving the performance of the device by internally tying together the VSS bus with the VSSQ bus is particularly useful in synchronous DRAM (SDRAM) manufacturing. This is especially true with devices which do not generate sufficient noise on the VSSQ to adversely affect the device by transferring excessive VSSQ noise to the VSS bus. Typically, devices which are configured to have a ×8 data width or less generate minimal noise and allow direct connection of the VSSQ bus to the VSS bus. Devices having a ×32 data width, however, produce excessive noise on the VSSQ bus and therefore require separate, noncoupled VSSQ (or multiple VSSQ) and VSS busses. In conventional manufacturing technology, tying VSS and VSSQ together in some devices but not in others requires two different masks, one which ties VSS and VSSQ together in devices having a ×8 data width or less, for example through the use of a metal 2 mask feature, and one which does not tie the two together in devices having a data width greater than ×8. As previously stated, additional masks are expensive, add greatly to manufacturing costs, and also increase logistical complexity due to an increased number of process flows.
Another embodiment of the invention comprises the selection of a device to operate as a fully-functional device or as a partially-functional device. It is well known in the art that, for example, a 64 megabit device may be configured internally as four 16 megabit arrays, eight 8 megabit arrays, etc. For example, one particular Micron Technology, Inc. 64 megabit SDRAM device (Micron part number MT48LC16M4A2, described in Micron's 64 megabit Synchronous DRAM data sheet 64MSDRAM_D, incorporated herein by reference) is configured as four 16 megabit arrays. Each 16 megabit array of this particular device is accessed using 4,096 (4K) rows and 1,024 (1K) columns, with four bits of data being written to or read from with each address. Each of the four individual banks is selected using a two-bit bank select. Additionally, one of Micron's 128 megabit SDRAM devices (Micron part number MT48LC32M4A2, described in Micron's 128 megabit Synchronous DRAM data sheet 128MSDRAM_E, incorporated herein by reference) is configured as four 32 megabit arrays. Each 32 megabit array is accessed using 4K rows and 2K columns, with four bits of data being written to or read from with each address.
Some array defects are so severe that the array cannot be repaired. These defective devices are often discarded or reworked and sold as “partial” (partially functional) devices devoted to special uses which do not require fully functional devices. With a conventional device, for example one having its storage capacitors configured as four arrays, a nonfunctioning quarter or half array is disabled, typically through the use of fuse or antifuse devices. A 128 megabit device having two of four arrays disabled would therefore supply 64 megabits of memory.
In contrast with conventional ball bonds and bond options discussed in the Background of the Invention, the functionality of the die with various embodiments of the present invention is not determined by an external controlled source, such as by whether a lead is coupled with power or ground. Functionality of a die with various embodiments of the present invention is instead determined by whether a ball bond is present and, if a ball bond is present, by which pads are physically connected by the ball bond or by the plurality of ball bonds. The functionality of the die is determined by the configuration of ball bonds, and cannot typically be altered once the pads have been shorted or left unconnected. Further, in contrast with conventional devices, the ball bonds of the invention do not connect the mini-pads with lead fingers of the lead frame or to other pads or traces external to the die, but rather connect the pads to other mini-pads on the die itself and to other circuitry on the die.
Further, wire bonds may be used to electrically couple the pads rather than the ball bonds previously described and depicted. In these embodiments it may be preferable to attach the wire bonds during a conventional wire bonding process during which bond pads are wire bonded to leads of a lead frame. In most process flows this wire bonding will occur subsequent to dicing of the wafer and prior to encapsulation or other assembly of the semiconductor die.
A semiconductor device comprising the invention may be attached along with other devices to a printed circuit board, for example to a computer motherboard or as a part of a memory module used in a personal computer, a minicomputer, or a mainframe. The inventive device may also be useful in other electronic devices related to telecommunications, the automobile industry, semiconductor test and manufacturing equipment, consumer electronics, or virtually any piece of consumer or industrial electronic equipment.
While this invention has been described with reference to illustrative embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as additional embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.
Claims
1. A method used during fabrication of a semiconductor device comprising:
- forming a semiconductor wafer section comprising first, second, and third pads thereon which are electrically separated from each other;
- forming a first circuit portion electrically coupled with the first pad;
- forming a second circuit portion electrically coupled with the second pad and electrically isolated from the first circuit portion;
- forming a third circuit portion electrically coupled with the third pad and electrically isolated from the first and second circuit portions;
- enabling the semiconductor device to function in only one of a first operational mode and a second operational mode by selectively electrically connecting together either the first and second pads to enable the first operational mode or the second and third pads to enable the second operational mode; and
- encapsulating the semiconductor wafer section such that selectively electrically connecting together either the first and second pads or the second and third pads is not possible when the semiconductor wafer section is encapsulated.
2. The method of claim 1 further comprising attaching a single ball bond to two of the pads during the selective electrical connection.
3. The method of claim 1 further comprising attaching a wire bond to two of the pads during the selective electrical connection.
4. The method of claim 1 further comprising screen printing a conductive epoxy to two of the pads during the selective electrical connection.
5. The method of claim 1 further comprising:
- providing a transistor during the providing of the first circuit portion and providing one of a fuse and antifuse array during the providing of the second circuit portion; and
- selectively electrically connecting the first pad with the second pad thereby electrically coupling the one of the fuse and antifuse array to the transistor during the selective electrical connection of the first and second pads.
6. The method of claim 1 further comprising:
- providing a lead frame;
- attaching the wafer section to the lead frame; then
- encapsulating the lead frame during the encapsulation of the semiconductor wafer section.
7. A method used during fabrication of a semiconductor device, comprising:
- providing first and second conductive pad portions electrically isolated from each other;
- providing a transistor electrically coupled with the first conductive pad portion;
- providing one of a fuse array and an antifuse array electrically coupled with the second conductive pad portion;
- electrically coupling the second pad portion to a voltage source;
- with the second pad portion electrically coupled to the voltage source, programming the array; and
- subsequent to programming the array, electrically coupling the first pad portion with the second pad portion.
8. The method of claim 7 further comprising electrically coupling the second pad portion to the voltage source through a probe tip during the electrical coupling of the second pad portion with the voltage source.
9. The method of claim 7 further comprising:
- providing a CGND node during the providing of the second pad portion;
- electrically coupling the CGND node to the transistor during the electrical coupling of the first pad portion with the second pad portion; and
- tying the CGND node to ground through the transistor during an operational mode of the semiconductor device subsequent to programming the array.
10. A method used during fabrication of a semiconductor device comprising:
- providing a semiconductor wafer substrate assembly;
- providing a bond pad comprising at least three separate sections electrically isolated from each other, wherein the three sections of the bond pad each overlie the wafer substrate assembly;
- providing at least three circuit portions with one circuit portion electrically connected with only one of the bond pad portions;
- electrically interconnecting the at least three bond pad sections to electrically connect the at least three circuit portions.
11. The method of claim 10 further comprising:
- providing a lead frame; and
- subsequent to electrically interconnecting the at least three bond pad sections, attaching the semiconductor wafer substrate assembly to the lead frame.
12. The method of claim 10 further comprising attaching a ball bond to the at least three bond pad sections during the interconnection of the at least three bond pad sections.
13. The method of claim 10 further comprising screen printing a conductive material to contact the at least three bond pad sections during the interconnection of the at least three bond pad sections.
14. A method used during fabrication of a semiconductor device comprising:
- providing a semiconductor wafer substrate assembly;
- providing a plurality of conductive pads electrically isolated from each other;
- providing a plurality of circuits wherein each circuit is electrically connected with one of the bond pads;
- selecting an operational mode of the semiconductor device by selectively connecting at least two of the plurality of conductive pads to each other to selectively connect at least two of the plurality of circuits; and
- packaging the semiconductor wafer substrate assembly such that selecting the operational mode of the semiconductor device cannot be performed when the semiconductor wafer substrate assembly is packaged.
15. A method used during fabrication of a semiconductor device comprising:
- providing a semiconductor wafer section;
- forming first and second spaced conductive pads on the semiconductor wafer section; and
- forming first and second internal power buses on the semiconductor wafer section, wherein the first power bus is electrically connected to the first conductive pad and the second power bus is electrically connected to the second conductive pad,
- wherein the first and second conductive pads are adapted to be electrically coupled to each other to electrically connect the first power bus with the second power bus.
16. The method of claim 15 further comprising forming a VSS power bus and a VSSQ power bus during the formation of the first and second internal power buses.
17. The method of claim 15 further comprising electrically connecting the first conductive pad with the second conductive pad to electrically connect the VSS power bus with the VSSQ power bus.
18. A method used during fabrication of a semiconductor device having a hardwired and selectable column address strobe (CAS) latency, comprising:
- providing at least one CAS latency select line;
- forming at least a first conductive pad electrically coupled with a high potential, a second conductive pad electrically coupled with the CAS latency select line, and a third conductive pad electrically coupled with a low potential; and
- selecting a CAS latency by either: forming a conductor to electrically connect the first pad portion with the second pad portion to select a first CAS latency; or forming a conductor to electrically connect the second pad portion with the third pad portion to select a second CAS latency which is different from the first CAS latency.
19. The method of claim 18 further comprising forming a ball bond during the formation of the conductor which electrically connects only two of the first, second, and third conductive pads together.
20. The method of claim 18 further comprising forming a bond wire during the formation of the conductor which electrically connects only two of the first, second, and third conductive pads together.
21. The method of claim 18 further comprising encapsulating the CAS select line and the first, second, and third conductive pads subsequent to forming the conductor.
22. A method used during fabrication of a semiconductor device, comprising:
- selectively electrically connecting conductive pads located on a surface of an integrated circuit die to provide an electrically conductive path between the conductive pads, wherein the conductive path determines an operational mode of the semiconductor device; then
- encapsulating the semiconductor die in a dielectric material such that the electrically conductive path is not directly accessible from outside the dielectric material.
23. A method used during fabrication of a semiconductor device, comprising:
- selecting a desired operational mode for the semiconductor device from two or more operational modes;
- selectively electrically connecting two or more conductive pads located on a surface of an integrated circuit die to provide an electrically conductive path between the two or more conductive pads, wherein the conductive path enables the desired operational mode of the semiconductor device; then
- packaging the integrated semiconductor die in a dielectric material such that the electrically conductive path is not directly accessible by an end user of the semiconductor device.
24. A method used during fabrication of a semiconductor device, comprising:
- forming a semiconductor die comprising: a first conductive pad electrically connected to a first circuit portion; a second conductive pad electrically connected to a second circuit portion; a third conductive pad electrically connected to a third circuit portion,
- wherein the first, second, and third circuit portions are incomplete circuits;
- selectively electrically connecting either the first and second conductive pads to electrically connect the first and second incomplete circuit portions to provide a first complete circuit and a first device operational mode, or the second and third conductive pads to electrically connect the second and third incomplete circuit portions to provide a second complete circuit and a second device operational mode,
- wherein the semiconductor device is nonfunctional during operation if two of the conductive pads are not electrically connected.
25. The method of claim 24 wherein the first, second, and third conductive pads are adjacently located to each other and the method further comprises placing a single ball bond on either the first and second pads or on the second and third pads during the selective electrical connection.
Type: Application
Filed: Jan 31, 2006
Publication Date: Jun 8, 2006
Inventors: Rich Fogal (Boise, ID), Tracy Reynolds (Kuna, ID), Timothy Cowles (Boise, ID)
Application Number: 11/345,027
International Classification: H01L 21/82 (20060101);