Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1998-05-21
2001-02-20
Lee, Thomas C. (Department: 2811)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S095000, C700S117000
Reexamination Certificate
active
06192290
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to semiconductor fabrication and, more specifically, to a system and method of manufacturing semicustom integrated circuits (ICs) by employing selected ones from a library of reticle primitives and custom-made interconnect reticles.
BACKGROUND OF THE INVENTION
Integrated circuits generally contain millions of individual electronic devices, each typically the size of a few micrometers, and interconnections thereamong. As a result, no “physical” tool is adequate for fabricating the complex patterns representing the devices and interconnections on a semiconductor substrate. Instead, microelectronic patterning is conventionally performed by radiation, e.g., light, x-rays or electron beams. The process of using an optical image and a photosensitive film to produce a pattern on a semiconductor substrate is known as “photolithography.”
In photolithography, a film of a photoresist (photosensitive film) is first applied to the substrate. Radiation is then projected through a transparent plate, or “mask,” on which has been created a desired pattern in an opaque material. The resulting image is focused on the photoresist-coated substrate, yielding areas of light and shadow on the substrate that correspond to the image on the mask plate. Following development and etching processes, where portions of the resist and substrate are removed, a pattern corresponding to that on the mask is etched in the substrate film.
During the infancy of microelectronics, the master image (pattern) was photographically reduced from a macroscopic original. The desired pattern was cut by hand into a colored plastic sheet and the image reduced to the desired size using room-sized reduction cameras. This method has been replaced by a pattern generator, an apparatus that accepts a computer-generated description of the device and analyzes it into individual picture frames. The pattern generator then scans a mask plate, “writing” the pattern on the mask plate using, for example, a high intensity electron beam, to expose each device or interconnect in the pattern.
Semiconductor devices may typically be made up of as many as fifty individual layers of silicon, polysilicon, silicon dioxide, metal and silicides. The pattern for each layer is contained on a mask called a reticle. Reticles are generally between one and ten times the actual size of the pattern they produce. The group of reticles that corresponds to all the layers of an integrated circuit (IC) is called a device series.
The pattern generation process, requiring point-to-point creation of a complex pattern on a semiconductor wafer, is generally a slow process. Usually only one of the multiple devices images to be printed on a semiconductor substrate is pattern-generated. The single device pattern, or reticle, is then replicated repeatedly using a step-and-repeat camera (commonly known as a stepper) to form the array of devices and interconnects that cover the semiconductor substrate. The reticle may also consist of an array of several patterns and is distinguished from a mask that contains patterns that can be transferred to an entire semiconductor wafer (or to another mask) in one exposure.
Not only is the production of a reticle a slow process, it is also an expensive process. Multiplying the cost of a single reticle by the number of reticles in a device series illustrates the cost of producing a single new IC. The reticles' cost is a significant component of the overall cost in the design and development of a new, or custom, semiconductor device. During the design and development of a semiconductor device, changes in the design, due to changes in the design specifications or unexpected results during testing, are often encountered. The changes in the design will necessitate new reticles to implement the changed design. This not only increases the cost of the development of the semiconductor device, but also delays the verification and production phases of the semiconductor device.
Accordingly, what is needed in the art is an improved method to manufacture an IC that overcomes the above-described limitations.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provide a system for, and method of, manufacturing an IC and an IC manufactured by the method. In one embodiment, the system includes: (1) a library of reticle primitives, at least two of the reticle primitives containing patterns corresponding to circuit modules to be contained in the IC, (2) an interconnect reticle containing patterns corresponding to interconnecting conductors for electrically coupling the circuit modules and (3) lithographic equipment that employs the at least two of the reticle primitives and the interconnect reticle to create a lithograph of the circuit modules and the interconnecting conductors.
The present invention therefore introduces the broad concept of building a library of preexisting reticles that correspond to often-used circuit modules and generating a semicustom ICs by lithographing some of the circuit modules in one step and lithographing interconnections between the circuit modules in a separate step. For purposes of the present invention, “reticle primitive” is defined as a set of reticles used for the process levels in the formation of a circuit module. “Circuit module” is, in turn, defined as a piece of circuitry that can be employed as a building block to construct a larger circuit. For instance, a semicustom IC suitable for telecommunications may employ such circuit modules as digital-to-analog (D/A) and analog-to-digital (A/D) converter circuitry, filters, a processor and. associated memory banks. Reticle primitives corresponding to each of these circuit modules may be lithographed and interconnected in separate steps (and the steps performed in either order).
In one embodiment of the present invention, the at least two of the reticle primitives are free of patterns corresponding to bond pads for the circuit modules. Because the circuit modules on the IC may be interconnected by traces on the IC itself, conventional bond pads are rendered unnecessary. Instead, far smaller interconnection points may be provided on the reticle primitives.
In one embodiment of the present invention, the at least two of the reticle primitives are free of patterns corresponding to protected drive transistors for the circuit modules. Likewise, because of the proximity of the circuit modules to one another in the single IC, conventional protected drive transistors are no longer needed. In some cases, direct interconnections may be made without any additional drive transistors whatsoever.
In one embodiment of the present invention, the circuit modules are selected from the group consisting of: (1) static random access memory (SRAM) modules, (2) electrically eraseable programmable read-only memory (EEPROM) modules, (3) field-programmable gate array (FPGA) modules, (4) programmable logic array (PLA) modules, (5) D/A converter modules, (6) A/D converter modules, (7) digital signal processor (DSP) modules, (8) microprocessor modules, (9) microcontroller modules, (10) linear amplifier modules and (11) filter modules. Those skilled in the art will recognize, however, that many circuits can be constructed of well-known circuit modules. The present invention extends to all conventional and later-discovered circuit modules.
In one embodiment of the present invention, the lithographic equipment subjects each of the at least two of the reticle primitives to multiple exposures. Thus, the reticle primitives may be projected onto different locations on a given wafer to fabricate a plurality of ICs on the wafer.
In one embodiment of the present invention, the lithographic equipment first employs the at least two of the reticle primitives to create a lithograph containing the circuit modules and subsequently employs the interconnect reticle to add the interconnecting conductors to the lithograph. Of course, these operations can be carried out in reverse orde
Du Thuan
Lee Thomas C.
Lucent Technologies - Inc.
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