Ph.D. Oral Defense

[Dachen Chu]

Department of Physics – University Ph. D Oral Defense

Thermal Management in Electron Beam Lithography and Nano-Thermocouples

Dachen Chu
Advisor: Professor Fabian Pease

9:00am, Thursday, Oct 16th, 2003 
Packard Electrical Engineering Building, Room 101
Refreshments at 8:45am

Electron Beam Lithography (EBL) in photomask fabrication results in heating 
of the resist films. The local heating can change the chemical properties 
of resist, leading to placement errors. The heating induced error has been 
believed to be increasingly significant as the transistor minimum feature 
size approaches the sub100 nm region. 

A Green’s function approach has been developed to calculate four-
dimensional temperature profiles in complex structures such as the multi-
layer work-pieces being exposed in EBL.  The model is being used to 
characterize different ebeam writing strategies to find the optimum. 

To provide the parameters for the model, two independent techniques have 
been employed: a thin film electrode method and a laser thermal-reflectance 
method. Unlike earlier results from polyimide films, no appreciable 
anisotropy was observed in thermal conductivities for the polymeric resists 
tested. 

Gold/nickel thin film thermocouples with minimum junction area of 100nm by 
100nm were fabricated and calibrated. These thermocouple demonstrated a 
400ns response time when heated by a 10ns laser pulse. Using these nano 
thermocouples, transient resist heating temperature profiles were for the 
first time measured at room temperature. Experimental results showed a good 
agreement with the Green’s function model. We also observed a tradeoff in 
the scaling of thermocouple sensors. The smaller thermocouples may provide 
higher spatial and temporal resolutions but have poorer temperature 
resolution.

In conclusion, we both modeled and measured the resist heating in EBL. In 
short exposure time (1us or less) the resist heating is nearly adiabatic, 
while in longer time the heating is dominated by substrate. Nano scale 
metallic thermocouples were explored and tradeoff was observed in dimension 
scaling.