R. G. Tarascon

Synthesis And Lithographic Characterization Of A Novel Organosilicon Novolac Resin

A novel terpolymer of a methylated phenol, p-trimethylsilylmethyl phenol and formaldehyde was synthesized. With a 9.7wt% Si content, the polymer displayed an RIE resistance 10 times greater than hard-baked HPR 204. The organosilicon novolac was employed as a base resin component of bilevel resist systems for both photo and electron-beam lithography. The low molecular weight polymer behaves as a positive resist when mixed with a dissolution inhibitor. In photo-lithography, the dissolution inhibitor was a diazoquinone based chemical which was converted to an acidic species during irradiation. In electron-beam lithography, poly (2-methyl-l-pentene sulfone) (PMPS), which depolymerizes upon electron-irradiation, functioned as the dissolution inhibitor. When the silylated novolac was used as a photoresist, coded 0.8μm line/space patterns were obtained with a sensitivity of -120 mJ/cm2. When employed as,an electron-beam resist coded 0.75μm line/space patterns were resolved with a dose of 8μC/cm4.

Chemical Factors Affecting Npr Performance

NPR, a material consisting of a novolac resin blended with poly(2-methyl-l-pentene sulfone) (PMPS), is an attractive positive electron beam resist. However, it exhibited a number of problems during processing. For example after the development step, NPR patterns were surrounded by a halo due to resist thickness differences in the region next to the exposed areas. Also, a thin residual film appeared in the developed regions. A study of these problems showed that immiscibility between the two NPR components was responsible for many of the results. Also, Fourier Transform Infra Red Spectroscopy showed that a low molecular weight PMPS, [n] - 20 cm3/g, considerably improved compatibility and reduced the defects mentioned above. For this reason a study of PMPS molecular parameters by Gel Permeation Chromatography (GPC), light scattering and intrinsic viscosity was undertaken. This study related the molecular variables to synthetic conditions and a reproducible synthesis was established. A new NPR system was prepared with 9% low molecular weight sulfone polymer. This resist exhibits good film quality after development and displays a sensitivity of 8pC/cm2 with excellent (0.25μm) resolution.

Initial manufacturing performance of an actively controlled PBS resist development process

An improvement in the method used to fabricate 5 X 5 in2 -1 and 5x biased and unbiased optical masks is achieved by actively controlling the resist development step of the mask fabrication process. This method has been initially applied to a photomask process which utilizes poly(1-butene-co-sulfur dioxide)(PBS) resist as the pattern delineation material. Real-time targeting of resist feature dimensions is performed using a Laserlith Resist Thickness and Endpoint Controller which has been adapted to an Applied Process TechnologyR/Convac Model 915 resist processor. The controller monitors in real-time the one-step resist development process for a time period based on the measured development rate of the resist, the geometry and size of the targeted feature. After the resist is developed, the controller instructs the resist processor to continue onto the remaining steps in the processing cycle. The targeted resist features of initial product produced using this system have an average variation from targeted size of 0.04 micrometers and an average resist linewidth uniformity (3(sigma) ) of 0.04 micrometers . These results indicate that active control of this critical development step enables the resist feature dimensions to be within +/- 0.05 micrometers of their targeted size after completion of the post-development bake step.

Recent advances in mask-making technology at AT&T

As the design rules to make integrated circuits with features less than 0.25 micrometers are emerging, it appears that conventional deep UV photolithography will not be able to support these new generation IC technologies. There are however other possibilities such as enhanced optics, proximity x-ray and projection electron-beam which extend the state of lithography below 0.25 micrometers . AT&T is in a unique position to evaluate these new technologies since we have active programs in each of these areas. It is clear that the success of any of these new techniques is directly connected to the ability to manufacture the corresponding mask.