A great deal of photolithographic activity in recent years has been centered on thick photoresist films. Thin film heads (TFH), micromachining and sensor fabrication are examples of applications requiring this type of processing. The needs of the TFH industry are currently the technology driver for thick photoresist processing. Modem TFH manufacturing processes require 1 im resolution in layers ranging in thickness from 5 to as much as 25 tim. These large aspect ratios not only make the lithographic process difficult, but add complexity to the evaluation and measurement of experimental wafers. This is particularly true for the large number of measurements needed for process optimization and control. Well-calibrated and easy to use modeling techniques for analysis of the impact of optical system design and photoresist process changes would be extremely valuable for process lithography engineers.The photoresist development process involves complex dissolution and polymer chemistry. It forces simulator developers to implement empirical models with definitions and assumptions that only indirectly reflect the underlying physical and chemical processes. However, with appropriate calibration such an approach provides results with accuracy better than 90% at reasonable computational time for any given combination of a particular photoresist base material, photoactive component, development and bake conditions. A method has been developed that allows accurate simulation of pattern profiles in photoresist in excess of 10 xm thick. The method uses the DEPICT® photolithography simulator to model i-line exposure, bake and development of Shipley SJR®5740 thick film photoresists with an Ultratech 2244i Wafer Stepper®.Kim model inputs were estimated from a family of development rate curves obtained by processing wafers with a range of expose energies for logarithmically increasing develop times and measuring thickness change as the develop process occurred. These results were compared with dissolution results obtained using a laser-based dissolution rate monitor. Uncertainties in the measured photoresist absorbence, photosensitivity and refractive index coefficients were estimated and their influence on the simulated results were considered. An optimization 0227-786X/97/$ 10.00 SPIE Vol. 3049 / 789 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/26/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

Modem package designs generate a large amount of stress on the die which can be controlled using a thick film of polyimide over the passivation layer. Polyimide film thicknesses in excess of twenty microns at exposure are becoming common for very thin packages. The standard polyimide lithographic process frequently utilizes a trilayer film consisting of an adhesion layer, a polyimide film, and photoresist. A major advance in polyimide technology occurred with the introduction of photosensitive polyimide materials. These materials reduce the total number of process steps in the polyimide process. They also offer the opportunity to combine the passivation and polyimide lithography steps into one process level resulting in significant process simplification and manufacturing cost reduction. Consequently, there is a rapid increase in the use of photosensitive polyimides in the semiconductor industry.There are a number of important issues associated with photosensitive polyimide processing. Because most photosensitive polyimides are negative tone, residual film formation has a major impact on resolution and the usable process window. The high exposure doses required for thicker polyimide films exacerbates the residual film problem. Also, resolving small features such as fuse windows in DRAMs is frequently required in thick photosensitive polyimide layers. These small features result in polyimide height-to-linewidth aspect ratios that are comparable to many photoresist applications. Because of these requirements, photosensitive polyimide applications could benefit from detailed process characterization to enhance resolution and increase process latitude. Unfortunately, there is scant literature pertaining to lithographic performance and lithographic process modeling for photosensitive polyimide films.An extension of basic photoresist characterization techniques for thin films can be applied to thick photosensitive polyimide processes. The develop rate characteristics and lithographic performance for several commercial photosensitive polyimide products were studied at a thickness of 12 microns. Cross sectional SEM analysis, Bossung plots, and film retention plots are used to establish relative lithographic capabilities. These experimental results are used to study the effects of polyimide physical and chemical properties on lithographic performance. O-8194-2102-2/96/$6.OO SPIE Vol. 2726 / 169 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/23/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

An environmental friendly, aqueous based, thin film technology is investigated that is quite versatile in forming a variety of polymer substrates. The polymer substrates are potentially capable of being utilized as high resolution resists for semiconductor chip production. This process is based on polymerization of monomers partitioned within a two dimensional surfactant template adsorbed on the surface of a silicon wafer. The surfactant template (bilayer) serves to localize the polymerization reaction at the liquid‐solid interface and thereby resulting in the coverage of the silicon wafer with a nano‐thin polymer film. On a polished silicon wafer with a 4 nm silicon oxide layer, film thickness up to 130 nm have been obtained for polystyrene and for poly(methyl methacrylate) (PMMA) which is also used as a standard photoresist mask in electron beam lithography.

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As thin film head (TFH) processing advances with magneto resistive (MR) and giant magneto resistive (GMR) designs, the photolithographic requirements for the write portion of the device grow increasingly challenging. Specifically, the resolution of submicron isolated features is required in thick photoresist films; resulting in aspect ratios of nearly 10 to 1. To satisfy the imaging requirements of critical read and write-layers, the use of i-line reduction lithography tools with variable numerical aperture (NA) and partial coherence (a) are necessary.This study examines the influence of NA, a, and reticle bias on critical features in typical TFH write-layer processes. Optimal reticle bias was estimated through simulation and confirmed experimentally. Combinations of NA and were investigated for their impact on minimum feature size, process latitude, and sidewall angle for multiple resist thicknesses. Process latitude was quantified for each illumination condition over a range of focus and exposure conditions with the use of a low-voltage, automated TFH CD-SEM. A focused ion beam (FIB) tool and SEM are used to examine wall angles at each ofthe illumination conditions.