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Improved Profile Epitaxial Technique for Electron Shielding

IP.com Disclosure Number: IPCOM000043637D
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 3 page(s) / 36K

Publishing Venue

IBM

Related People

Saretto, S: AUTHOR

Abstract

The interaction of ionizing radiation, such as alpha particles, with an integrated circuit semiconductor substrate results in the production of electrons which can alter the charge storage state of memory devices in the region of the point of incidence of the radiation. It has been reported in the literature that integrated circuits having a buried epitaxial layer 2 of P+ conductivity (NA=1017) in a silicon semiconductor substrate 4 of P conductivity (NA=1015), as shown in Fig. 1, will form an electron shield which will serve to repel electrons produced by ionizing radiation at deeper portions of the semiconductor body. Fig. 2 is a graph showing the variation in concentration for the P type dopant in the substrate 4 and the buried epitaxial layer 2 as a function of the depth below the upper surface of the integrated circuit.

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Improved Profile Epitaxial Technique for Electron Shielding

The interaction of ionizing radiation, such as alpha particles, with an integrated circuit semiconductor substrate results in the production of electrons which can alter the charge storage state of memory devices in the region of the point of incidence of the radiation. It has been reported in the literature that integrated circuits having a buried epitaxial layer 2 of P+ conductivity (NA=1017) in a silicon semiconductor substrate 4 of P conductivity (NA=1015), as shown in Fig. 1, will form an electron shield which will serve to repel electrons produced by ionizing radiation at deeper portions of the semiconductor body. Fig. 2 is a graph showing the variation in concentration for the P type dopant in the substrate 4 and the buried epitaxial layer 2 as a function of the depth below the upper surface of the integrated circuit. It is seen that the buried epitaxial layer 2 is relatively thick, being on the order of 2 microns. One drawback to this relatively thick epitaxial layer is that, although it is buried at a depth of at least 2 microns below the upper surface of the integrated circuit, it will also produce electrons through interaction with the ionizing radiation. Many of these electrons produced within the epitaxial layer 2 migrate upwardly from the layer 2 toward the FET device 6, thereby disrupting the charge stored there. Thus, the electron shielding effect will not apply to those electrons generated in bulk substrate 4 and in the P+ layer 2, which form the "collection depth", since electrons generated in these layers can be collected at the storage node. An improvement in the buried epitaxial layer which will retain the function of repelling electrons produced by ionizing radiation in the interior bulk 8 of the semiconductor while reducing the number of electrons produced within the epitaxial layer itself is shown in Fig.
3. By depositing the epitaxial layer 2' by means of...