Microbridge formation in a CAlViN photoresist we have developed is dependent on the ratio of dose to print ( DiP ) to dose to gel ( DTG ) as well as resist contrast. Photoresists formulated with poly(p-hydroxystyrene) (PHS) have a very high tendency to form microbridges when developed in 2.38 wt% TMAH due to high contrast and high a DTP/DTG ratio. When photoresists formulated from PHS were developed in 1 .2 wt% TMAH contrast and DTP/DTG ratio were reduced resulting in microbridging being nearly eliminated. Using this observation we developed an I-line CAMN photoresist with PHS type thermal stability and high resolution capabilities which can be developed in industry standard 2.38 wt% TMAH.

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A new chemically amplified I-line negative resist (INR) is in use at IBM's eight-inch wafer manufacturing facility in Essex Junction, Vermont. The resist is applied at the ion implant block photo levels for 4-Mb DRAM chip production and shows very good line performance and stability. Process parameters such as focus, exposure dose, post expose bake (PEE) temperature vs. photospeed, and time window from expose to PEB, demonstrate above average latitude. Due to the long develop times (4 mm per wafer) required when using a singlewafer spray or puddle develop in an integrated photocluster, INR runs on a stand-alone toolset.The resist operates at low exposure doses, increasing stepper throughput, which is often a semiconductor line pinch-point area. The photospeed for the resist equates to an exposure dose of approximately 30 mJ/cm2, or 120 ms on a .35-NA align tool . TMAH is used as a developer, which reduces adhesion concerns and improves metallic contamination problems common with other developers. Metals in the resist average under 100 ppb. INR also eliminates the need for topside rinse procedures and UV-harden operations that are usually employed with a positive resist. This paper reviews several concerns with INR regarding its optical appearance, resist thinning, and undercut. The first two issues were resolved through increased manufacturing-floor training and by more tightly controlling certain components of the resist. The undercut effect required a more advanced version of the resist to be formulated, which is currently under evaluation.