Contact Thermal Lithography

Contact thermal lithography is a method for fabricating patterns based on thermal effects. In contrast to photolithography, where resolution is limited by the wavelength of light used in the exposure process, thermal lithography is limited by thermal diffusion. A traditional metal-glass photomask is brought into contact with a wafer coated with a thermally sensitive polymer. The mask-wafer combination is flashed briefly with high intensity light, causing the metal features to heat up and conduct heat locally to the polymer. The polymer cross-links due to the temperature rise and forms an image of the mask. Simple models are presented to analyze the heating process and select appropriate geometries and heating times. In addition, an experimental version of a contact thermal lithography system has been constructed. Early results from this system are presented, along with suggestions for future development. INTRODUCTION The resolution of traditional photolithography is limited to the order of the wavelength of light used to expose the pattern. In an effort to increase resolution, the semiconductor industry has moved to shorter wavelengths. Unfortunately, using shorter wavelengths adds complexity and therefore cost to the exposure tool. Individual fabrication tools, such as lithography steppers, have reached tens of millions of dollars, and complete modern fabrication facilities require investments of several billion dollars. It is therefore desirable to have a simple, inexpensive lithography technique capable of reproducing sub-micron features. Contact thermal lithography is a new method of pattern ∗[email protected] Oxide Buffer Layer Silicon Wafer Glass Mask Substrate Thermoresist Metal Feature