Iain McCulloch

Water-soluble chromophore containing copolymers for bottom antireflection coating applications in lithography

Regulatory concerns in the semiconductor industry from both VOC emissions and solvent handling have prompted the desire to introduce water-based formulations in spin-coating fabrication processes. As resolution demands for i-line lithography are driven to finer feature size and architecture, the need for antireflection coatings as a means of eliminating feature distortions from back reflected light is increasing. Common image irregularities, such as reflective notching and standing wave effects, can be effectively eliminated through application of an antireflection coating of optimal thickness between the resist layer and substrate. This work describes the design and development of novel side-chain methacrylate copolymers for use in water-based antireflection coating formulations. A pendant chromophore is incorporated into the polymer structure to allow optimization of the critical coating optical properties, refractive index, and absorption coefficient. The polymer solubility parameter and crosslinking density can be tailored by incorporation of appropriate functionality to allow compatibility with the device fabrication process. Terpolymers were designed, which were water-soluble, had a thermally activated crosslinking mechanism, and contained a keto-ester azobenzene chromophore that was highly absorbing at i-line wavelength. Optical properties of polymer films were collected by spectroscopic elipsometry and utilized in the design process to identify the optimum chromophore structure. Lithographic images, fabricated utilizing these coatings, were of excellent quality, allowing critical dimension resolutions of less than 0.3 μm.

Water-castable bottom antireflective coatings

Bottom antireflective coatings (BARCs) have been widely used in the industry to push i-line technology for a finer resolution. They have been shown to be highly effective in suppressing reflective notching and standing wave effects, in the reduction of the resist swing ratio and the improvement of the resist process latitude. One of the issues which has to be addressed by the design of any such coating is the problem of resist/bottom coat intermixing. The formation of an intermixing layer is usually suppressed either by crosslinking the BARC, or by using a polymer that is insoluble in the common resist casting solvents. This work describes a novel class of antireflective bottom coatings which are spin cast from the ultimate environmentally friendly solvent, water. The design requirements and philosophy of the water-borne polymer systems will be discussed. These polymers show high Ohnishi numbers, and the prediction of high etch rates is borne out by dry etch experiments. Polymer optical data have been obtained by UV spectroscopy and spectroscopic ellipsometry, and these optical and physical properties will be reported and related to their lithographic performance which is found to be equivalent to that of existing solvent-based antireflective coatings.