Hazards and controls at the Sandia National Laboratories microelectronics development laboratory Page: 4 of 6
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Next, arsenic is implanted using arsine. Then the photoresist is removed in a dry etch process
and the wafers are cleaned with a sulfuric acid/peroxide solution. After cleaning, the implant is
annealed in a vertical thermal reactor and driven in at 9000 C. using nitrogen.
In forming the P+ source/drain regions, the wafers are coated with photoresist, exposed,
developed and UV hardened. Boron is implanted using boron trifluoride. Then, the photoresist is
stripped using an oxygen plasma and a sulfuric/nitric acid solution. After stripping, the wafers are
cleaned in a sulfuric acid/peroxide solution. Then the implant is annealed.
When patterning the contacts , the wafers are coated with photoresist and contrast
enhancement material (aqueous solution containing resin and a photoactive compound), exposed,
developed and UV hardened. The contacts are then dry etched. The resist is stripped using an
oxygen plasma and N-methyl-2-pyrrolidone (NMP).
The diffusion process is used to grow various dielectric silicon dioxide films. Vertical
thermal reactors are used for this purpose. During the oxidation process, a portion of the silicon
wafer is consumed in the growing oxide. High purity steam is generated inside the oxidation tube
by the burning of hydrogen in oxygen. Temperatures range from 6000 to 1,1000 C. Nitrogen is
used as a carrier gas and/or a purge gas. Emissions from the equipment chambers are routed
through a bumbox and scrubber before being emitted into the atmosphere. All gases used are
plumbed directly into the equipment through stainless steel lines and the equipment is exhausted.
Diffusion is also used for gate oxidation. Sacrificial oxide is grown in a vertical thermal
reactor using 1-1-1 trichloroethane. The sacrificial oxide is stripped using a hydrofluoric acid
solution followed by sulfuric acid/peroxide, SCI and SC2. Then the gate is oxidized in a vertical
thermal reactor using dry oxygen at 9000 C. After oxidation, boron is implanted in an ion
When fabricating the source/drain regions, the photoresist is removed in a dry etch process
using RF energy to create an oxygen plasma which strips the photoresist. Radio frequency (RF)
energy is used to cleave chemical bonds to produce a plasma containing oxygen radicals. The
oxygen radicals react with the resist to oxidize it to water, carbon monoxide and carbon dioxide.
RF is monitored with an RF meter for the appropriate frequency using IEEE and ACGIH
guidelines. The wafer is then wet etched with a sulfuric/nitric acid solution.
An anisotropic dry etch process is used to etch silicon nitride when fabricating nitride
sidewalls. Plasma etching is used to etch the silicon nitride. Silicon nitride is etched with a
fluorine or chlorine containing gas such as carbon tetrafluoride, trifluoromethane, sulfur
hexafluoride or nitrogen trifluoride. Silicon tetrafluoride is a byproduct.
Ion Implant is used after gate oxidation. Boron is implanted using boron trifluoride. The
ion implanter produces a boron ion beam and directs this beam so that the ions are uniformly
implanted across and into the target silicon wafer. The implant process hazards are high voltage,
toxic gases and mechanical hazards. They are controlled by automation, interlocks and shielding.
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Benton, M.A. Hazards and controls at the Sandia National Laboratories microelectronics development laboratory, article, March 1, 1997; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc675631/m1/4/: accessed March 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.