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A Historical View Of The Role Of Ion-Implantation Defects In PN Junction Formation For Devices R.B. Fair ECE Department, Duke University Durham, NC 27708 [email protected] ABSTRACT The early use of ion bombardment of semiconductors for forming doped regions was viewed as a room-temperature process by solid-state scientists. Many interesting, but relatively useless devices were made by implanting species such as Na and Cs ions to form pn junctions from radiation damage or interstitial impurities. The revolutionary idea that one could implant Group III and V dopants into semiconductors and then heat the implanted substrate to above 800C didn’t appear until 10 years after Shockley’s 1954 patent. At that time, implantation damage became relatively unimportant as processes evolved with high temperature, long time diffusions. With the advent of rapid thermal processing, the attention shifted back to implantation-induced defects to explain transient-enhanced-diffusion effects. Today’s challenges in forming ultra-shallow junctions by ion-implantation are in controlling and minimizing the damage structures that dominate junction activation and diffusion. Low-energy implants have been effective in this regard. INTRODUCTION - THE BEGINNING OF ION IMPLANTATION INDUCED DEFECTS IN SEMICONDUCTORS Progress into the use of ion implantation in semiconductors was made possible by a number of key inventions and scientific discoveries in the 1950s and 1960s. Present day ion source and ion beam technology evolved from nuclear physics research into "positive rays" and accelerator development for isotope separation. [1]. In parallel efforts, investigations into the bombardment of semiconductors, radiation effects, and doping effects led to studies of materials’ issues such as ion ranges and distributions based upon fundamental contributions from Bohr. [2] And in the early 1950s, several patents were issued which envisioned the use of ion bombardment in the fabrication of semiconductor devices, the first being Ohl’s patent filed January 31, 1950. [3] Ohl, employed by Bell Labs, described the fabrication of a point-contact bipolar transistor in which either the emitter or collector contacts were subjected to an ionic bombardment process to improve surface electrical stability and to increase electron emission from the emitter. Typically, the recommended bombarding ions included air, oxygen, hydrogen, nitrogen, helium, argon, carbon monoxide and even chloroform. Ohl taught that these were ions of significant impurities which were thought to enter the crystal surface and function in a manner such that ..."the impurity changes the number of electrical carriers present in the material thereby changing its electrical characteristics." In hindsight, Ohl’s explanation was wrong and may have misdirected workers in the field. As a result, others followed his lead with similar studies. Other early patents that discussed the

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application of ion bombardment or ion injection in the fabrication of devices included: 1) LarkHorivitz et al at the Pu