Recrystallized silicon films on amorphous substrates are mainlycharacterized by subgrain boundaries separated by a few microns. Usingseedina from the silicon substrate (lateral epitaxy), subboundary free areasadjacent to the seed are achieved in the direction of the beam scanninq. Wehave demonstrated the large influence of the growth direction and of thethickness of the silicon layer together on the incubation distance and onthe spacing of the subboundaries. Surprisingly, a variation of the arowth(scan) velocity of two orders of magnitude (from 1 to 70 cm/s) has nonoticeable influence on these narameters. A I × 10 elliptical Ar+laser beam has been used in these experiments. An interpretation of theseresults in terms of lateral (step) growth and stress will be given.

Seeding from bulk silicon (lateral epitaxy) has been used in Ar+ laserrecrystallization to achieve subboundary free silicon on insulator areas. Onthese areas C.MOS devices have been performed using almost entirely thestandard processing steps of a bulk micronic C-MOS technology. n -MOStransistors with channel length as small as 0.3 um have shown very smallleakage currents. This is attributed especially to the lack ofsubboundaries. A 40 % increase in the dynamic performances in comparisonwith equivalent size C-MOS bulk devices has been obtained (93 ps of delaytime per stage for a 101 stages ring oscillator with 0.8 μm of channellength). This is the best result presented so far on recrystallized SOI. Nospecial requirements are needed in the lay out of the circuit with thechosen seed structure. Furthermore an industrial processing rate for thelaser recrystallization processing has been achieved using an ellipticallaser beam, a high scan velocity (30 cm/s) and a 100 μm line to line scanstep (a 4' wafer in 4 minutes).

We present an overview of the thermal modeling of CW laser induced crystallization of SOI. The dynamical case for a three-layer structure is derived. Effects of the phase change (increase in reflectivity, latent heat) are also treated. Analytical expressions are given and the models are compared to experiment.

Phosphosilicate glass reflow to improve step coverage of metallizations in integrated circuits is usualy made by a high temperature heat treatment. A new technique is proposed to achieve this annealing by a transient localized heating with a tunable CW CO2 laser. A selective coupling of the laser power is obtained by choosing a 9.25 μm wavelength which matches the Si-O absorption band at 1100 cm−1. Focusing and scanning the laser beam makes the P-glass flow without excessive substrate heating.