Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1998-07-01
2001-09-04
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06284413
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 reticles using reticle primitives.
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 This method has been replaced by a pattern generator, an apparatus that accepts a computer-generated description of the device and analyzes it into individual picture frames.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 reticle set.
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 device 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. For example, it may take up to several hours for a conventional electron-beam exposure apparatus to produce a reticle with a circuit pattern of a degree of integration equivalent to that of a 256 MDRAM integrated circuit. As mentioned-above a reticle set corresponding to a semiconductor device that has up to fifty reticles is not uncommon. Therefore, with the current electron-beam exposure apparatus production rate limited to only be a few reticles a day, the production of the semiconductor device may be significantly delayed.
Accordingly, what is needed in the art is an improved method to manufacture a reticle that overcomes the above-described limitations.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides a system for, and method of, manufacturing a semicustom reticle for an integrated circuit (IC) and an IC manufactured by the system or 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 portions of a layer to be created by the semicustom reticle and (2) exposure equipment that employs the reticle primitives to create an image of the patterns on the semicustom reticle to allow the semicustom reticle to create the layer in a single lithographic step (or multiple steps, if such is desired).
The present invention therefore introduces the broad concept of generating a semicustom reticle by photographing portions of selected reticle primitives thereon. For purposes of the present invention, “reticle primitive” is defined as a reticle that contains one layer of a given 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 reticle may be employed to create an IC suitable for telecommunications. The IC may include 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 layers of each of these circuit modules may be photographed onto a semicustom reticle and interconnected in separate steps (and the steps performed in either order).
In one embodiment of the present invention, the portions correspond to a layer of selected ones 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, (11) filter modules and (12) charge coupled devices (CCD). Those skilled in the art will recognize, however, that many circuits can be constructed of such well-known circuit modules. The present invention extends to all conventional and later-discovered circuit modules.
In one embodiment of the present invention, the exposure equipment subjects each of the reticle primitives to multiple exposures. Thus, the reticle primitives may be projected onto different locations on a given semicustom reticle to create the necessary image to create a layer of a plurality of ICs on a wafer in a single lithographic step.
In one embodiment of the present invention, the exposure equipment comprises a reticle exchanger that allows the reticle primitives to be sequentially exchanged. This allows automatic substitution of reticle primitives without requiring human intervention. Of course, the present invention is not restricted to automatic substitution.
In one embodiment of the present invention, the semicustom reticle includes a transparent substrate and a pattern defined by an opaque material and formed on the transparent substrate, the pattern transferred on the transparent substrate from at least two reticle primitives containing patterns corresponding to a device level of an IC.
In one embodiment of the present invention, the transparent substrate is composed of quartz. Alternately, in other embodiments, the transparent substrate may be composed of soda-lime glass or borosilicate glass.
In one embodiment of the present invention, the opaque material is chrome. Alternately, in other embodiments, the opaque material may be iron oxide, aluminum, gold, tungsten or emulsion.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conc
Agere Systems Guardian Corp.
Huff Mark F.
Mohamedulla Saleha R.
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