Thermally curable middle layer for 193-nm trilayer resist process

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New lithographic compositions, for use as middle layers in trilayer processes  resist processes can be applied as very thin films with a very thin layer of photoresist being applied to the top of the middle layer. Thus, the underlying bottom anti-reflective coating is still protected even though the overall stack (i.e., anti-reflective coating plus middle layer plus photoresist) is still thin compared to prior art stacks.

Present Methodology
In order to store ever-increasing amounts of information on a substrate area, the microchip industry continues to move to shorter and shorter wavelengths of light for resist exposures. This trend towards decreasing linewidths leads to high aspect ratio lines, with the thin, tall lines tending to fall over during resist development/rinse steps. For 193-nm exposures, the microchip industry typically uses roughly 270-350 nm of resist on 32-80 nm of bottom anti-reflective coating--so-called unilayer processing. For trilayer applications, photoresist thicknesses (.about.150-200 nm) are much less than for unilayer applications, resulting in low aspect ratio lines. The trilayer bottom anti-reflective coating instead is 300-700 nm thick, and the middle layer is 30-215 (preferably 30-60) nm thick. The advantages of the trilayer resist processing include:

  • (a) reduced resist aspect ratios;
  • (b) the ability to use conventional or ultra-thin 193-nm photoresists rather than silicon-containing and hydrophobic (bilayer) resists;
  • (c) minimized interaction of resist with the substrate;
  • (d) optimum thickness control for the imaging, masking, and anti-reflective layer; and
  • (e) improved depth-of-focus (DOF) since the trilayer bottom anti-reflective coatings are designed to be highly planarizing.

The key to trilayer imaging is a robust middle layer offering facile spin-applied processing, acceptable bottom anti-reflective coating/resist adhesion, excellent imageability, and outstanding etch selectivities to both bottom anti-reflective coating and resist. The middle layer must etch much slower than the bottom anti-reflective coating in an oxygen plasma and preferably faster than the photoresist in a fluorinated gas plasma. Prior approaches to the middle layer problem include the use of spin-on-glass, which requires careful attention to surface acidity in order to achieve acceptable adhesive properties.

New Options
The present invention is broadly concerned with new lithographic compositions and methods of using those compositions as middle or protective layers during circuit manufacturing.

In more detail, the compositions comprise a polymer or compound dispersed or dissolved in a solvent system. In one scenario, that polymer is an organo-silicon polymer, preferably including recurring monomers having the formula.

Additional information about Thermally curable middle layer for 193-nm trilayer resist process can be learned from United States Patent 7,507,783, Thermally curable middle layer comprising polyhedral oligomeric silsesouioxanes for 193-nm trilayer resist processes.

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Loretta Wallis

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