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Fabrication of Shallow High-Conductivity N-Type Regions

IP.com Disclosure Number: IPCOM000047486D
Original Publication Date: 1983-Nov-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Hodgson, RT: AUTHOR [+2]

Abstract

N-type implants in silicon using presently known techniques result in too much straggle and move too much when they are annealed; thus shallow, high conductivity junctions cannot be made. A new fabrication technique is described for achieving shallow, high conductivity n-type regions. The tendency in semiconductor technology is for junctions to be shallower. The high resistivity of the shallow junctions is one of the obstacles to annealing. Arsenic or phosphorus are normally used for the n-type dopants in these junctions and are implanted to the required depth. The straggle in depth and width limits these junctions to N600˜ deep, with a profile which is not as sharp as would be desirable.

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Fabrication of Shallow High-Conductivity N-Type Regions

N-type implants in silicon using presently known techniques result in too much straggle and move too much when they are annealed; thus shallow, high conductivity junctions cannot be made. A new fabrication technique is described for achieving shallow, high conductivity n-type regions. The tendency in semiconductor technology is for junctions to be shallower. The high resistivity of the shallow junctions is one of the obstacles to annealing. Arsenic or phosphorus are normally used for the n-type dopants in these junctions and are implanted to the required depth. The straggle in depth and width limits these junctions to N600~ deep, with a profile which is not as sharp as would be desirable. The sideways straggle of the dopant and the dopant movement during annealing require that the gate be etched back to avoid junction capacitance. This leads to increased junction resistance. A solution to this problem would be to implant with a heavier donor such as antimony or bismuth. The straggle of these ions is at least a factor of two lower than for arsenic. However, the low solid solubility of these ions limits their use since the conductivity cannot be made very high with normal furnace annealing. If high densities of the ions are implanted and thermally annealed, the dopants precipitate and their electrons are no longer available to carry current. The technique described herein involves using such heavy ions as impl...