Shallow melting of thin heavily doped silicon layers by pulsed CO/sub 2/ laser irradiation

Journal Article · Mon May 01 04:00:00 EDT 1989 · J. Appl. Phys.; (United States)

DOI:https://doi.org/10.1063/1.342590· OSTI ID:6481959

James, R B; Christie, W H

We show that an extremely shallow (approx. <800 A) melt depth can be easily obtained by irradiating a thin (/similar to/200 A) heavily doped silicon layer with a CO/sub 2/ laser pulse. Since the absorption of the CO/sub 2/ laser pulse is dominated by free-carrier transitions, the beam heating occurs primarily in the thin degenerately doped film at the sample surface, and there is little energy deposited in the underlying lightly doped substrate. For CO/sub 2/ pulse-energy densities exceeding a threshold value of about 5 J/cm/sup 2/, surface melting occurs and the reflectivity of the incident laser pulse increases abruptly to about 90%. This large increase in the reflectivity acts like a switch to reflect almost all of the energy in the remainder of the CO/sub 2/ laser pulse, thereby greatly reducing the amount of energy available to drive the melt front to deeper depths in the material. This is in contrast to the energy deposition of a laser pulse that has a photon energy exceeding the band gap, in which case the penetration depth of the incident radiation is only weakly affected by the free-carrier density. Transmission electron microscopy shows no extended defects in the near-surface region after CO/sub 2/ laser irradiation, and van der Pauw electrical measurements verify that 100% of the implanted arsenic dopant is electrically active. Calculated values for the melt depth versus incident pulse-energy density (E/sub L/) indicate that there exists a window where the maximum melt-front penetration increases slowly with increasing E/sub L/ and has a value of less than a few hundred angstroms.

• Research Organization: Theoretical Division, Sandia National Laboratories, Livermore, California 94550
• OSTI ID: 6481959
• Journal Information: J. Appl. Phys.; (United States), Journal Name: J. Appl. Phys.; (United States) Vol. 65:9; ISSN JAPIA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360605* -- Materials-- Radiation Effects
656003 -- Condensed Matter Physics-- Interactions between Beams &amp; Condensed Matter-- (1987-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
CRYSTAL DOPING
ELECTROMAGNETIC RADIATION
ELECTRON MICROSCOPY
ELEMENTS
FILMS
IRRADIATION
LASER RADIATION
LAYERS
MELTING
MICROSCOPY
PHASE TRANSFORMATIONS
PHYSICAL RADIATION EFFECTS
PULSED IRRADIATION
RADIATION EFFECTS
RADIATIONS
SEMIMETALS
SILICON
SURFACE PROPERTIES
THIN FILMS
TRANSMISSION ELECTRON MICROSCOPY