<title>Prototype laser-activated bimetallic thermal resist for microfabrication</title>

Wavelength invariant Bi/In thermal resist as a Si anisotropic etch masking layer and direct-write photomask material

“…Simulation suggests exposure is almost unchanged from 248 nm (Figure 2 (a)) down to 100 nm, a range that includes the proposed 157 nm exposure tools. Experimental results [1,2] showed 4 nsec pulses at 266 nm required ~7 mJ/cm 2 .When these simulations are extended from 248 nm to 13.4 nm the absorption increases 18% at the thickness 20 nm of each layer, and reflectivity becomes very small (<1%), indicating a better sensitivity. Indeed there is very little change in the 50 nm to 10 nm range.…”

“…It is known that when the laser beam hits the film, reflection, transmission and absorption occur. Our Airy summation optical model [1,2] shows that for a 15/15 nm Bi/In film, 60 -70% of the laser light energy is absorbed at 514 nm wavelength, 30 -40% is reflected and less than 0.01% transmitted through the film. Most of the absorbed energy is transformed into heat and the temperature of the exposed area goes up.…”

“…An optical model [1,2] was established based on an Airy Summation to calculate the total amount of light Reflected from the top surface (R), Transmitted through the bottom surface (T), and Absorbed through the total thickness of the imaging layers (A), which vary with: the laser wavelength, the resist thickness, the index of refraction n and the absorption index k of different materials.…”

“…Bi/In high resistance to alkaline-based anisotropic silicon etching previously noted [3] is now extensively explored for TMAH, KOH and EDP. Yet potentially even more useful is the extremely large change in the optical absorption with the exposed areas becoming nearly transparent [1]. A Bi/In resist as a direct write photomask, done without etching, has demonstrated that it gives as good characteristics as chrome masks.…”

“…Our previous research has found that metallic bilayer Bismuth on Indium film creates an inorganic thermal resist with many interesting properties [1,2,3]. When optical exposure short laser pulses (4-20 nsec.)…”