Determination of SiO2 Mechanical Behavior via High Temperature Microtensile Testing

Ming-Tzer Lin*, Paul El-Deiry, Richard P. Vinci, Terry Delph*, and Ralph Jaccodine**

Department of Materials Science and Engineering, Lehigh University

*Department of Mechanical Engineering and Mechanics, Lehigh University

**Sherman Fairchild Center for Solid State Studies, Lehigh University


Introduction

Silicon oxidation is of fundamental importance in VLSI and ULSI circuit fabrication. Because of its widespread use, the prevalent belief is that it is a mature technology. In fact, at least with regard to the complicated interplay between the mechanical stresses generated by silicon oxidation and the oxidation kinetics themselves, amazingly little is known. Stress effects are thought to be responsible for the severe oxide thinning observed in very small structures. Hence they play a major role in the design of device isolation structures and gate oxides, especially as device dimensions continue to shrink. This problem has become especially acute in the design of large memory arrays (> 128 x 10^6 MOS capacity), where numerous empirical design rules have been formulated to mitigate the effects of oxide thinning. Just as importantly, stress effects have been convincingly implicated in the electronic quality of the Si/SiO2 interface and upon dielectric breakdown.

In order to assess stress effects upon the oxidation kinetics, one must be able to calculate these stresses. Given that inelastic flow is inevitable at the stress levels typically existing in oxide layers, an absolutely necessary first step is to obtain an accurate knowledge of the inelastic flow behavior of the oxide. Accurate knowledge of this behavior does not exist. To remedy this situation, we are attempting to carry out direct mechanical testing of microscale-sized tensile specimens of oxide film from which the silicon substrate has been chemically removed. This is a difficult task; however the state of the art of thin film testing has now advanced to a point such that we feel confidant that the proposed experiments are feasible. The results will yield, for the first time, direct and unambiguous data for the mechanical behavior of thermally grown SiO2 thin films, data from which accurate constitutive representations for the film may be constructed.

Goals

Sample Images

coming....

Findings

We have successfully fabricated freestanding SiO2 beams on micromachined silicon substrates. Room temperature microtensile tests have shown linear elastic behavior, as expected. The elastic modulus is slightly less than that for bulk SiO2, similar to the findings of others who used techniques such as bulge test or vibrating reed.
 
A furnace has been constructed and tested at 800 deg C. We are currently modifying the microtensile test system to incorporate the furnace.

 

This work is supported by the Army Research Office (ARO) through the Short Term Innovative Research (STIR) program, Grant No. DAAD19-01-1-0662.


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Last update: October 2001