Surgical Fibers:Defects Treatment in Silicon Diodes by Annealing with Pulsed CO2 Laser

Keywords:surgical, fiber,  Time:04-03-2016

Analysis of doping and damage profiles of implanted silicon has been performed using a number of techniques, such as (crosssection) transmission electron microscopy ((X)TEM), secondary ion mass spectrometry (SIMS), Rutherford backscattering spectrometry (RBS), Secco etching C- T measurements or C- V measurements [1].
 
Surgical Laser annealing has been widely used for modification of semi-conductor surfaces. High power pulsed or continuous wave (CW) laser rapidly heats the surface regions to a high temperature or melts them above melting temperatures. After the termination of laser light, the surface regions rapidly cooled down. No substrate heating is necessary because laser irradiation energy effectively concentrates in the surface region during short irradiation time. Laser induced crystallization method has been developed and it has been applied for fabricating poly-crystalline silicon thin film transistor for flat panel display devices. Laser annealing also makes it possible to activate semiconductor implanted with doping atoms and diffuse doping atoms into semiconductor which is so-called laser doping. Laser induced activation is attractive to form shallow PN junction because of no marked impurity diffusion during short heating duration. Laser doping has been also paid attention for fabricating PN junction for solar cells .Laser annealing is also attractive for reduction of the density of interface traps at the semiconductor surface regions. Reduction of the density of interface traps by laser annealing at low processing temperature and in short tact time will be practical for semiconductor device processing. Especially for photo devices such as solar cells and high sensitivity photo sensors, a low annihilation rate of photo induced carriers is required. A simple surface passivation method will be important for photo device fabrication [2].

Pulsed laser annealing of semiconductors has been investigated extensively in recent years. The technique has the advantage that extremely high temperatures can be achieved at the surface without affecting the bulk of the semiconductor, even to the point where the semiconductor melts or material is removed by thermal evaporation. It is well known that the diffusivity of many ions is much greater in the molten state than in the solid, hence, pulsed laser annealing has been used to produce, e.g., highly doped surface regions by melting  and thin film silicon-germanium alloys by melting and re-solidification of Ge on Si [3].

Laser annealing was considered to be the most advantageous for applying to film depositions on plastic substrates since laser irradiation with a short-time pulse can transmit energy to the target materials and avoid heating effects to the substrate. Therefore, the pulsed laser irradiation of an oxide film on a substrate appears to be the most suitable method for improving the crystallinity of the film with minimal thermal damage to the substrate [4].

Materials and Methods

Tables (1) and (2) show the type and specifications of the laser and materials used in this work. The materials used in this work are 6 samples of silicon diode.

The samples were irradiated by the CO2 laser fibers with wavelength of 10.6 µm and energy of 500, 520, 540, 560, 580, and 600 mJ, respectively. Each diode was exposed to 5 pulses from the CO2 laser.