TITLE OF INVENTION

System and method for automatic elimination of electromigration and self heat violations during construction of a mask layout block, maintaining process design rules and layout connectivity.

BACKGROUND OF INVENTION

TECHNICAL FIELD OF THE INVENTION

The present invention is generally related to the field of integrated circuits, and more particularly to a system and method for eliminating electromigration and self heating violations during construction of a mask layout block, maintaining the process design rules (DRC Clean) and layout connectivity (LVS Clean) correctness, in the metallic, polysilicon, contacts and VIA's interconnects of an integrated circuit device.

BACKGROUND OF THE INVENTION

Nanometer designs contain millions of devices and operate at very high frequencies. The current densities (current per cross-sectional area) in the signal lines and power are consequently high and can result in either signal or power electromigration problems. The electron movement induced by the current in the metal power lines causes metal ions to migrate. That phenomenon of transport of mass in the path of a DC flow, as in the metal power lines in the design, is termed power electromigration. There are two types of electromigration. Uni-Directional, for example power and static signals and Bi-Directional, for example clocks and other switching signals. The most critical is the Uni-Directional electromigration type since the electron 'erosion' move constantly in one direction and can cause signal line failure. The power electromigration effect is harmful from the point of view of design reliability, since the transport of mass can cause open circuits, or shorts, to neighboring wires.

Electromigration is actually not a function of current, but a function of current density. It is also accelerated by elevated temperature. Thus, electromigration is easily observed in Al metal lines that are subjected to high current densities at high temperature over time. The higher current density around the void results in localized heating that further accelerates the growth of the void, which again increases the current density. The cycle continues until the void becomes large enough to cause the metal line to fuse open. Typically the most susceptible to electromigration phenomenon are metallic interconnections of integrated circuit. (IC) EM effects become more prominent as IC feature sizes decrease and as IC frequencies and current densities increase.

EM in IC devices occurs due to direct current flow. High direct current density in an IC device causes atoms and ions in the conductors of the device to move in the opposite direction of the direct current flow. In particular, when high direct current densities pass through thin conductors, metal ions accumulate in some regions and voids form in other regions of the conductors. The accumulation of metal ions may result in a short circuit to adjacent conductors and the voids may result in an open-circuit condition. However, if the current density can be kept below a predetermined EM threshold, EM can be rendered negligible for the life of any particular IC device. Therefore, EM due to direct current flow in IC devices is a major concern with respect to the potential for device failures and the overall reliability of the device.

IC devices may also have alternating current flow. The alternating current density in an IC device that results from alternating current flow causes atoms and ions in the conductors of the device to first move in one

direction and then move in the opposite direction, back to their original positions. A plurality of conductors with alternating current flow is defined as a signal net. In contrast to conductors with direct current flow, conductors with alternating current flow do not directly cause EM problems. However, conductors with alternating current flow do use power and generate heat. Since EM is very sensitive to the temperature of the conductors, it is often necessary to limit the temperature increase of the conductors in IC devices that results from the heating due to alternating current flow. Therefore, the alternating current flow in a conductor does have an impact on EM because the heating due conductors with alternating current may increase the overall temperature of the IC device by heating up neighboring conductors with direct current flow.

As noted above, EM effects also become more prominent as IC feature size decreases. To counteract this effect, background art methods for controlling EM used wider conductor widths for an entire IC wiring network affected by EM. However, since EM problems become less severe as one moves away from a current source pin and toward each of the current sink pins of a wiring network, wider conductor widths are typically not required for the entire IC wiring network. Often, only a small segment of the IC wiring network needs the wider conductor width to eliminate EM problems for the entire IC wiring network. Therefore, these background art methods that use wider conductors throughout the IC wiring network often wastes valuable space on the IC device.

Other background art methods provide EM control by setting limits on the power dissipated in conductors with alternating current flow. In these background art methods adjacent conductors with direct current flow are only allowed to be heated by a maximum temperature difference .DELTA.T.sub.MAX in order to maintain the reliability of the IC device. In particular, to limit the heat generated as a result of the temperature difference .DELTA.T caused by alternating current flow in adjacent conductors, a maximum root-mean-square (RMS) current limit (I. sub. RMS) is set for all conductors with alternating current flow adjacent to a conductor with direct current flow. The maximum current limit is set by: (1) considering the minimum distance between conductors with alternating current flow and conductors with direct current flow; and (2) the maximum temperature difference .DELTA.T.sub.MAX that maintains the reliability of the IC device. However, using this type of worst-case "minimum distance- between-conductors" approach to determine space between conductors also wastes valuable space on the IC device.

Electromigration failures take time to develop, and are therefore very difficult to detect until it happens. Thus, the best solution to electromigration problems is to prevent them from taking place. Therefore, it is imperative to eliminate electromigration and self heating issues in order to maintain a reliable integrated circuit operation for many years. The system and method described in this invention eliminates electromigration and self heating issues early in the IC layout design phase. In this way a significant amount of time is saved during the final reliability verification of the integrated circuit, achieving on-time tape outs and avoiding re-spins.

SUMMARY OF THE INVENTION

In accordance with the present invention, the disadvantages and problems associated with eliminating electromigration and self heat violations during construction of a mask layout block, maintaining the process design rules (DRC Clean) and layout connectivity (LVS Clean) correctness, have been substantially reduced or eliminated. In a particular embodiment, a method for eliminating electromigration and self heat violations during construction of a mask layout block includes automatically preventing a polygon from being placed, created or edited in a selected position in a mask layout block if an electromigration and self heat rule violation is identified.

In accordance with one embodiment of the present invention, an automated method for eliminating electromigration and self heat violations during construction of a mask layout block includes analyzing a selected polygon(s) in a mask layout block and obtaining one or more electromigration and self heat rules associated with the polygon from a technology or external constraints file. The method provides a violation marker associated with the selected position for the polygon that graphically represents a space, width or length in the mask layout block where the selected polygon's position complies with the electromigration and self heat rules.

In accordance with another embodiment of the present invention, an automated method for eliminating electromigration and self heat violations during construction of a mask layout block includes analyzing a selected polygon in a mask layout block and identifying a electromigration and self

heat violation in the mask layout block if the selected position, with or length of the polygon is less than electromigration and self heat value permitted from a technology or external constraints file. If the electromigration and self heat violation is identified, the placement, creation or edition of the polygon at the selected position is automatically prevented, maintaining the process design rules (DRC Clean) and layout connectivity (LVS Clean) correctness.

In accordance with a further embodiment of the present invention, a computer system for eliminating electromigration and self heat violations during construction of a mask layout block, maintaining the process design rules (DRC Clean) and layout connectivity (LVS Clean) correctness includes a processing resource coupled to a computer readable memory. Processing instructions are encoded in the computer readable memory. When the processing instructions are executed by the processing resource, the instructions analyze a selected polygon in a mask layout block and identify an electromigration and self heat violation in the mask layout block if the selected position is less than an electromigration and self heat rule from a technology or external constraints file. If the electromigration and self heat violation is identified, the instructions prevent the polygon from being placed, created or edited at the selected position in the mask layout block, maintaining the process design rules (DRC Clean) and layout connectivity (LVS Clean) correctness.

Important technical advantages of certain embodiments of the present invention include an electromigration-self heat aware (EMSH Aware) tool that prevents electromigration and self heat violations from being created during the construction of a mask layout block. A layout designer may move a cursor or click on a polygon in order to select it. The EMSH Aware tool highlights a violation marker that may represent a width, space or length in the layout block to eliminate electromigration and self heat violation according to technology or external constraints file. In addition the EMSH Aware tool provides an information window with the current and required electromigration and self heat conditions related to the selected polygon. The information window includes an option to perform an automatic correction of the selected polygon, also can be done by Right-Click of the mouse. With the activation of the correction action on the polygon the system will change the selected polygon width, length or space according to electromigration and self heat rules taken from technology or external constraints file, maintaining the process design rules (DRC Clean) and layout connectivity (LVS Clean) correctness. In case of contacts or vias individual or multiple selections, the system will automatically adjust the amount of contacts or vias according to electromigration and self heat rules taken from technology or external constraints file, maintaining the process design rules (DRC Clean) and layout connectivity (LVS Clean) correctness. The mask layout block, therefore, may be created free of electromigration and self heat violations.

Another important technical advantage of certain embodiments of the present invention includes EMSH Aware tool that significantly reduces the design time for an integrated circuit. In a typical integrated circuit design

process, an electromigration and self heat check (EMSH Check) tool analyzes a mask layout file for electromigration and self heat violations and identifies any violations in an output file. A layout designer may use the output file to manually eliminate the identified electromigration and self heat violations. Then the same IC layout block needs to be re-checked for electromigration and self heat again and also other checks like DRC (Design Rule Check) and LVS (Layout vs. Schematics) to make sure that the connectivity and geometrical sizes are correct according to technology file and schematics respectfully. These repeated cycles are time consuming and tedious procedures that can be eliminated using the presented invention. In addition, the present invention may eliminate electromigration and self heat violations from a mask layout block before the mask layout block is converted into a mask layout file. The time needed to complete the design process for the integrated circuit, therefore, may be substantially reduced since the steps of checking the layout with an EMSH tool and correcting the identified electromigration and self heat violations may be eliminated.

All, some, or none of these technical advantages may be present in various embodiments of the present invention. Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete and thorough understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein:

FIG. 1 illustrates four Metals wires. These are given without electromigration or self heat analysis;

FIG. 2 illustrates four Metals, each selected and analyzed for electromigration and/or self heat violation.

Metal 1 wire has LENGTH violation shown as a dashed line violation marker.

Metal 2 wire has WIDTH violation shown as a dashed line violation marker.

Metal 3 wire has PARTIAL WIDTH violation shown as a dashed line violation marker.

Metal 4 wire has WIDTH and LENGTH violation shown as a dashed line violation marker.

The boundaries of the violation marker have to be met in order to eliminate the electromigration and/or self heat violation;

FIG. 3 illustrates the information window. Upon a user selection of a Metal 1 wire, an information window is opened. User has the option to FIX the selected polygon by clicking on the: FIX button or close it by clicking on the Close button;

FIG. 4 illustrates a layout view of the example Metals connections. In this example two (2) Metals [Metal 1 and Metal 2] are connected through two (2) VIA's.

FIG. 5 illustrates a layout view of the example Metals connections. In this example two (2) Metals [Metal 1 and Metal 2] are connected through two (2) VIA's. The information window shows the system's recommendation to place four (4) VIA's in order to connect the two (2) metals. The user has the option to automatically correct the situation by clicking on the: FIX button, located within the Information Window. Upon clicking on the FIX button in the Information Window, the system will create a new layout within the connection area (Surrounded by GREEN rectangle) and place four (4) VIA's. The system maintains all design rules dimensions according to technology file.

FIG. 6 illustrates the tool's basic interface with layout editor. The system offers Advise mode and Correct mode.

Advise Mode - User receives graphical feedback during IC layout construction. No automatic correction is performed.

Correct Mode - User actions are automatically corrected by the system to eliminate electromigration and/or self heat violations, maintaining the

process design rules (DRC Clean) and layout connectivity (LVS Clean) correctness. User may check both options to activate the two modes at the same time. If none of these modes are checked, the system is disconnected from the layout editor.

FIG. 7 illustrates the tool's option to check the entire cell. With the selection of this option the entire cell that is loaded within the layout editor window is checked for electromigration and self heat. Violation(s) will be shown as violation markers. In addition a log file is generated with a complete coordinates and description of each violation.

FIG. 8 illustrates a flow chart for one example of a method for eliminating electromigration and/or self heat violations during construction of a mask layout block in accordance with teachings of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The processing instructions may include a commercially available layout editor interfaced with an electromigration-self-heat Aware (EMSH Aware) tool. The EMSH Aware tool may provide the ability to analyze the width, length and placement of polygons in a mask layout block and determine if an electromigration and/or self heat violation is created. In addition the EMSH Aware tool may provide the ability to analyze the number of contacts and VIA's, determine the amount needed in order to comply with electromigration and self heat rules. The EMSH Aware tool may be operated in two different modes: an Advise mode and a Correct mode. When operating in the Advise mode, the EMSH Aware tool may graphically display a violation marker which shows the required width, length or space of the selected polygon without violating any electromigration and/or self heat or design rules included in a technology and/or external constraints file. In the Correct mode, the EMSH Aware tool may prevent or adjust the creation, placement or edition of polygons in order to eliminate electromigration and/or self heat and design rule violation, maintaining the process design rules (DRC Clean) and layout connectivity (LVS Clean) correctness.

When a layout designer creates a mask layout block, the EMSH Aware tool reads a technology and/or external constraints file corresponding to a desired manufacturing process. The technology file may contain design rules for the desired manufacturing process that ensures an integrated circuit fabricated on a semiconductor wafer functions correctly. In addition the technology file may contain electromigration and self heat rules to ensure reliable integrated circuit operation for desired time period.

Furthermore, the tool has an option to read another constraints file which contains layout extraction information (resistance and capacitance values) per circuit net. Within the mask layout block, the electromigration and self heat rules may define the minimum or maximum allowable feature dimensions (e.g., metal and polysilicons wires width, spaces and length) for the desired manufacturing process. The EMSH Aware tool then uses the electromigration and self heat rules to prevent the layout designer from creating electromigration and self heat violations during the construction of the mask layout block, maintaining the process design rules (DRC Clean) and layout connectivity (LVS Clean) correctness.

If the layout designer chooses to operate in Advise mode, the layout designer may select a polygon by moving a cursor over the desired polygon or selecting it. The EMSH Aware tool uses the electromigration and self heat rules to graphically display the required length, width or space through a violation marker, within the mask layout block where the layout designer may move, place, create or edit a polygon. If the layout designers selects, create or move contacts or VIA's the EMSH Aware tool may graphically guide for the amount, location and space of the contacts or VIA's, maintaining the process design rules (DRC Clean) and layout connectivity (LVS Clean) correctness.

The EMSH Aware tool may graphically represent the violation marker in the mask layout block by highlighting the required width, length or space with an appropriate color and/or pattern. The violation marker color and/or pattern can be set in an initial tool setup. In addition the EMSH Aware tool may show an Information Window with the current and required conditions.

The Information Window also provides with the option to correct the violation.

If the layout designer chooses to operate in Correct mode, the EMSH Aware tool may prevent the layout designer from creating, placing or editing a polygon in a position within the mask layout block that will cause an electromigration and/or self heat violation. If the layout designer attempts to create a polygon in a certain width or length that does not comply with the electromigration and/or self heat requirements, the EMSH Aware tool automatically adjusts the polygon to the correct width or length size. Another example, if the layout designer is stretching a metal polygon's edge, the EMSH Aware tool automatically stretches the edge to the required length to comply with electromigration and/or self heat rule. Another example, if the layout designer is placing a certain amount of VIA's on a connection area between Metal 3 and Metal4 polygons the EMSH Aware tool will automatically adjust the amount and location of the VIA's to meet electromigration and/or self heat rules. The VIA's that will be placed maintaining design rule correctness regarding distance, width, length and metal coverage.

Both two modes operate in flat mode and hierarchical mode. When layout designer chooses to work in hierarchical mode, the EMSH Aware tool will graphically guide about electromigration and self heat violations throughout the hierarchy in Advise mode. The EMSH Aware tool will enforce electromigration and self heat violation elimination throughout the hierarchy in Correct mode.

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The EMSH Aware tool is included an entire layout block Check mode. This mode is aimed to be activation with the completion of the entire layout block. Using this feature the entire block will be analyzed for electromigration and self heat violations. When analysis is complete all violations will be shown using violation marker. This mode operates in flat or fully hierarchical mode.

The processing instructions for correcting electromigration and/or self heat violations in a mask layout file may be encoded in computer- usable media. Such computer-usable media may include, without limitation, storage media such as floppy disks, hard disks, CD-ROMS, DVDs, read-only memory, and random access memory; as well as communications media such wires, optical fibers, microwaves, radio waves, and other electromagnetic or optical carriers.