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Techniques have been developed that can quickly and accurately measure corner rounding and contact fill as key indicators of pattern fidelity. Using these techniques, we have examined writing variables for their effect on the lithographic quality of 1.0 micrometers contact. A small contact is perhaps the most demanding figure to achieve, so the results shown can be considered the worst case for 4X radicle manufacturing at 250 nm design rules. A MEBES 4500 was used as the writing tool, using PBS resist on quartz masks. Standard printing methods, single-phase printing (SPP) and multiphase printing (2X MPP) were examined. Results indicate that excellent corner rounding results can be achieved with small address sizes, regardless of the writing strategy or the dose used. As expected, larger spot sizes increase the amount of corner rounding, regardless of the address. As the pattern address is increased, judicious choices of spot size reduce potential pattern fidelity loss when imaging small contracts and other fine features. Multiphase printing is a technique that offers advantages to the user. Its use of offset scan voting (OSV) is a significant factor in reducing placement errors. MPP (2X) has an additional advantage of providing higher dosages. This provides flexibility in resist choices and in the selection of a process window. With 2X MPP, the user has a wide range of addresses and spot sizes that will give excellent results. The dynamic range of operating conditions possible with 2X MPP when writing 1.0 micrometers contacts is a reduced subset of those available using SPP, due to the 2X writing grid (output address). Implementation of 2X MPP has been limited on previous MEBES models due to increased write times of multipass writing. The MEBES 4500 data path supports 2X MPP with write times that approximate SPP. The practical operating envelope of both writing strategies are detailed in this paper. Overall, the MEBES 4500 has a large dynamic operating range. When used with a high resolution process, MEBES 4500 provides excellent pattern fidelity to support requirements of 250 nm design rules. |
