Editing Soft error (section)

=== Thermal neutrons ===
Neutrons that have lost kinetic energy until they are in thermal equilibrium with their surroundings are an important cause of soft errors for some circuits. At low energies many [[neutron capture]] reactions become much more probable and result in fission of certain materials creating charged secondaries as fission byproducts. For some circuits the capture of a [[thermal neutron]] by the nucleus of the <sup>10</sup>B [[isotopes of boron|isotope of boron]] is particularly important. This nuclear reaction is an efficient producer of an [[alpha particle]], [[lithium|<sup>7</sup>Li]] nucleus and [[gamma ray]]. Either of the charged particles (alpha or <sup>7</sup>Li) may cause a soft error if produced in very close proximity, approximately 5&nbsp;[[μm]], to a critical circuit node. The capture cross section for <sup>11</sup>B is 6 [[orders of magnitude]] smaller and does not contribute to soft errors.<ref name="BaumannHossain1995">{{cite book |last1=Baumann |first1=R. |title=33rd IEEE International Reliability Physics Symposium |last2=Hossain |first2=T. |last3=Murata |first3=S. |last4=Kitagawa |first4=H. |chapter=Boron compounds as a dominant source of alpha particles in semiconductor devices |date=1995 |pages=297–302 |doi=10.1109/RELPHY.1995.513695 |isbn=978-0-7803-2031-4|s2cid=110078856 }}</ref>

[[Boron]] has been used in [[Borophosphosilicate glass|BPSG]], the insulator in the interconnection layers of integrated circuits, particularly in the lowest one. The inclusion of boron lowers the melt temperature of the glass providing better [[reflow soldering|reflow]] and planarization characteristics. In this application the glass is formulated with a boron content of 4% to 5% by weight. Naturally occurring boron is 20% <sup>10</sup>B with the remainder the <sup>11</sup>B isotope. Soft errors are caused by the high level of <sup>10</sup>B in this critical lower layer of some older integrated circuit processes. Boron-11, used at low concentrations as a p-type dopant, does not contribute to soft errors. Integrated circuit manufacturers eliminated borated dielectrics by the time individual circuit components decreased in size to 150&nbsp;nm, largely due to this problem.

In critical designs, depleted boron{{mdashb}}consisting almost entirely of boron-11{{mdashb}}is used, to avoid this effect and therefore to reduce the soft error rate. Boron-11 is a by-product of the [[nuclear power|nuclear industry]].

For applications in medical electronic devices this soft error mechanism may be extremely important. Neutrons are produced during high-energy cancer radiation therapy using photon beam energies above 10&nbsp;MeV. These neutrons are moderated as they are scattered from the equipment and walls in the treatment room resulting in a thermal neutron flux that is about 40&nbsp;×&nbsp;10<sup>6</sup> higher than the normal environmental neutron flux. This high thermal neutron flux will generally result in a very high rate of soft errors and consequent circuit upset.<ref name="WilkinsonBounds2005">{{cite journal |last1=Wilkinson |first1=J. D. |last2=Bounds |first2=C. |last3=Brown |first3=T. |last4=Gerbi |first4=B. J. |last5=Peltier |first5=J. |title=Cancer-radiotherapy equipment as a cause of soft errors in electronic equipment |journal=IEEE Transactions on Device and Materials Reliability |volume=5 |issue=3 |date=2005 |pages=449–451 |issn=1530-4388 |doi=10.1109/TDMR.2005.858342|s2cid=20789261 }}</ref><ref name="Franco">Franco, L., Gómez, F., Iglesias, A., Pardo, J., Pazos, A., Pena, J., Zapata, M., SEUs on commercial SRAM induced by low energy neutrons produced at a clinical linac facility, RADECS Proceedings, September 2005</ref>