P + Structural Layers for Microelectromechanical Systems Using Spin-on Dopants

Simple, low cost means of prototyping new sensor technology is the key to rapid development in research facilities. A commonly available spin-on boron source is proposed for use in p + etch stop processing with ethylenediamine pyrocatechol (EDP)wet etchant. This cost-effective method utilizes a 2.0% boron liquid source processed in a quartz tube furnace. Concentrations up to 2 × 10²⁰ cm^–3 have been achieved and displayed characteristic concentration dependent profiles, i.e.deeper than predicted by simple predepo- sition models using the complementary error function (erfc). Results were quantified for samples diffused for one, two and four hours. Sheet resistance decreased from 5.3 Ω /sq to 2.7 Ω /sq while junction depth increased from 2.3 μ m to 5.4 μ m for one and four hour diffusions, respectively. This method proved capable of producing released structures (x _r) up to 2.8 μm thick. The depth of the suspended structures versus diffusion time is presented and a 53% release ratio (x_r/x_j ) is introduced to predict results within the four-hour diffusion duration.