As the process development advances to deep sub-100 nm technology, many new
technologies such as immersion lithography and hyper NA lens design are developed for
the improved on-wafer pattern resolution to meet the technology requirement. During the
early process development such as 45 nm technology, it was not clear that lithography
tool could meet stringent CD variation requirement. Many rules such as fixed poly pitch,
single poly orientation, and dummy poly insertion for diffusion edge transistors were
implemented [1, 2] to ensure that, with designated litho-tool, the CD variation control
could be minimized. These rules generally added layout design complexity and area
penalty. It would be efficient that these rules could be evaluated and properly
implemented with data collected from well-design test structures.
In this work, a set of simple test structures with various dummy poly gate lengths
and numbers of dummy poly gates, and fix-pitch poly gate orientations were
implemented in the process development test vehicles (TV's). Electrical, simulation, and
in-line CD data of these test structures were collected. Analysis of the data and related
design rule optimization and implementation are described. This work helped to optimize and to properly implement the 45 nm gate poly
design rules during early process development for Xilinx FPGA product development.
As transistor dimensions become smaller, on-wafer transistor dimension variations, induced by
lithography or etching process, impact more to the transistor parameters than those from the earlier process
technologies such as 90 nm and 130 nm. The on-wafer transistor dimension variations are layout dependent
and are ignored in the standard post layout verification flow where the transistor parameters in a spice
netlist are extracted from drawn transistor dimensions. There are commercial software tools for predicting
the on-wafer transistor dimensions for the improved accuracy of the post-layout verification. These tools
need accurate models for the on-wafer transistor dimension prediction and the models need to be
re-calibrated as the fabrication process is changed. Furthermore, the model-based predictions of the
on-wafer transistor dimensions require extensive computing power which can be time consuming.
In the paper, a procedure to back-annotate the process induced transistor dimension changes into the
post layout extracted netlist using a simple look-up table is described. The lookup table is composed of
specified drawn transistor and its sounding layout as well as their on-wafer dimensions. The on-wafer
dimensions can be extracted from simulations, SEM in-line pictures or electrical data of specially designed
testkeys. Taking the lookup table data, accordingly, the transistor dimensions in the post-layout netlist file
are then modified by a commercial software tool with a pattern search function. Comparing with the
model based approach, the lookup table approach takes much less time for modifying the post-layout netlist.
The lookup table approach is flexible, since the tables can be easily updated to reflect the most recent
process changes from the foundry.
In summary, a lookup table based approach for improving the post-layout verification accuracy is
described. This approach can improve the verification accuracy from both litho and non-litho process
variations. This approach has been applied to Xilinx's 65 nm and 45 nm product developments.
A monolithic inkjet print head, fabricated with silicon micromachining technology and capable of generating microscale liquid droplets, is developed and shown to function successfully. The print head uses a dense array of thermal bubble inkjet devices, made on a single silicon wafer. Each device is made of a Pt heater stack, a small, shallow fluid chamber, and a refilling channel formed by a Ge-sacrificial etching process, a deep-etched through-wafer feeding hole, and a micron-scale nozzle opened in a thin nitride membrane by plasma etching. Experimental results with a high resolution video imaging system show that this print head is capable of generating water droplets as small as 3 µm in diameter (0.014 pL), about 1/70th the volume of the droplets produced by existing inkjet systems. The printing process is also found to be stable, uniform in droplet size and velocity, and free of satellite droplets at optimum operation conditions. At small distances between the print head and substrate, droplet spreading is also small. This print head is then a capable tool for ultra-high-resolution inkjet printing and can be used in research areas where delivery of micron-scale fluid droplets is desired.
We describe design house approaches for design rule developments with emphasis of valuations of pre-optical proximity correction (pre-OPC) layouts and their simulation results. To begin, we describe the procedure of the simulation model calibration. An evaluation of metrics for analyzing the design layouts is then described. Due to the unavailability of post-OPC layouts, both pre-OPC and trial-OPC simulations are studied. A range of layout pattern density, within which the pre-OPC metric follows the post-OPC's, is estimated. Within this pattern density range, pre-OPC layout then can be evaluated to identify potential process "hot spots." With this approach, a set of design for manufacturability (DFM) compliance design rules is derived and applied to the product developments for both 90- and 65-nm process technology nodes. Several hot spots in the products (designed with 90-nm design rules) are located and fixed using layout optimization guided by the DFM rules. Simulated image contours and in-line scanning electron microscope (SEM) images validate the approach.
A new method to calibrate optical lithography model using a combination of
measured Critical Dimension (CD) data from the standard patterns and product layout
SEM pictures have been developed. The CD data is composed of the measured CDs of
through-pitch line patterns as well as isolated line and isolated space patterns. The SEM
pictures for contour CD calibrations are from the product layouts. The small set of 1-D
CD data is firstly used to calibrate the model. After best one-dimensional (1-D) data
calibration accuracy is achieved, the model is used to predict the contour of the product
layouts where the SEM pictures are taken. The simulated contours are overlaid with the
SEM pictures to identify the mismatch locations. Additional calibration gauges at the
locations are then added to the model to improve the predicted CD accuracy of 2-
dimensional (2-D) patterns such as line-to-tip, tip-to-tip, and corner. In comparison with
the SEM picture CDs, this procedure can be repeated several times until desired accuracy
of the predicted contours is achieved. This method can increase the model's 2-D edge
prediction accuracy and can reduce the amount of CD data required for model calibration.
This calibration method is used to generate the models for lithography process
simulations for Xilinx's 65 nm product developments. Hot spots and out-of-spec OPC
CD locations are identified using the models and later confirmed from in-line data.
In this paper we describe, from the user's point of view, how Inverse Lithography Technology (ILT) differs from Optical Proximity Correction (OPC). We discuss some specifics of ILT at chip-scale. We show simulation and experimental results from 90nm and 65nm semiconductor nodes, comparing results from ILT-generated masks and OPC-generated masks for real-life layouts, in a production environment. In addition, we discuss issues related to complexity and manufacturability of ILT-generated masks.
As the advent of advanced process technology such as 90-nm and below, the design rules become more and more complicated than before. These complicated design rules can guarantee process margin for the most layout environments. However, some layouts have narrow process windows that were still within the design rules. For example, line end layouts in a dense environment would generally have narrower process window than that of the onedimensional (1-D) dense line environment. The dense line end spacing design rule would be larger than that of the 1-D dense line spacing to compensate for the narrow window effect. In this work, an optical simulation software was used to examine an existing 90-nm FPGA product pre-OPC layout for its optical contrast. The optical contrast could correlate to the depth of focus (DOF) process window. Several back end locations were identified with possible narrow DOF windows. From the evaluations of these low contrast patterns, several design for manufacturing (DFM) rules and DRC deck was then developed. This deck
effectively identified the narrow process window layout locations, previously found with the simulation software. These locations were then optimized for the improved DOF windows. Both simulation and in-line data showed that the DOF window was improved after the layout optimization. Product data with optimized layouts also showed the improved yield.
In this paper we describe, from the user's point of view, how Inverse Lithography Technology (ILT) differs from Optical Proximity Correction (OPC). We show simulation and experimental results from 90nm and 65nm semiconductor nodes, comparing ILT-generated masks and OPC-generated masks for real-life layouts, in a production environment. In addition, we discuss issues related to complexity and manufacturability of ILT-generated masks.
Writing process patterns directly on a substrate with small liquid droplets generated by Drop-On-Demand (DOD) inkjet devices offers a low cost, non-contact, low temperature, flexible, and data driven patterning approach. Existing inkjet printheads have a limited number of inkjet devices, which generate droplets on the scale of tens of microns. In our research, we have developed a monolithic inkjet printhead for maskless lithography based on silicon micro-machining technology. This printhead is composed of a large array of thermal bubble inkjet devices fabricated on a single silicon wafer. A high-resolution video imaging system has recorded stable generation of water droplets down to 3.5 micron. Au patterns as small as 8 micron have been formed on silicon substrates by printing with suspensions of Au nano-particles. Smaller droplet dimensions extending to the nano-scale is supported by theoretical analysis. This printhead technology can form the basis of a maskless lithography system with moderate throughput for building micro and nano-scale electronic circuits and MEMS devices.
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