T. J. Magee

cw laser anneal of polycrystalline silicon: Crystalline structure, electrical properties

0.4‐μm‐thick polycrystalline silicon deposited in a low‐pressure CVD reactor was implanted with B to a dose of 5×1014/cm2 and then irradiated in a cw laser scanning apparatus. The laser annealing produced an increase in grain size from ∼500 A to long narrow crystals of the order of ∼25×2 μ, as observed by TEM. Each grain was found to be defect free and extended all the way to the underlying Si3N4. Electrical measurements show 100% doping activity with a Hall mobility of about 45 cm2/V sec, which is close to single‐crystal mobility at the same carrier concentration. Thermal annealing produces material with an average grain size of 1000 A and a resistivity higher by a factor of 2.2 than that obtained with the laser anneal. Laser annealing performed after a thermal anneal reduces the resistivity to approximately the same value obtained by laser annealing only.

Physical and electrical properties of laser‐annealed ion‐implanted silicon

The use of a laser as a tool for annealing of ion‐implantation damage is described. The principal results obtained are as follows: (1) electrical measurements show that activity comparable to that of a 1000 °C 30‐min anneal can be obtained; (2) TEM measurements show that complete recrystallization of the damaged layer occurs during the laser anneal; (3) impurity profiles obtained from SIMS measurments show that the dopant atoms remain in the LSS profile during annealing. Simple diodes were fabricated to examine the feasibility of the method for device fabrication.

Solid solubility of As in Si as determined by ion implantation and cw laser annealing

Complete electrical activity was obtained by cw laser annealing of 7×1015 As/cm2 implanted into (100) Si at 100 keV. The peak concentration for these implantation conditions is 1.4×1021/cm3, both theoretically and experimentally. However, this peak concentration was found to be thermally unstable, relaxing to a value of 3×1020/cm3 in a period of less than 2 min at 900 °C. If the peak implanted concentration is below 3×1020/cm3, the electrical activation and crystal structure are unaffected by similar thermal processing. We conclude from these data that the solid solubility of As in Si at 900 °C is approximately 3×1020/cm3, which is almost an order of magnitude below the published value.

cw laser recrystallization of 〈100〉 Si on amorphous substrates

A polycrystalline silicon film 0.55 μm thick was deposited in a low‐pressure CVD reactor on a Si3N4 substrate. Islands of various sizes (2×20 μm up to 20×160 μm) were prepared by standard photolithographic techniques. Laser annealing was then performed under conditions which are known to cause an increase in grain size from ∼500 A to long narrow crystals of 2×25 μm in a continuous polysilicon film. These same conditions were found to produce single‐crystal 〈100〉 material in the (2×20 μm) islands. However, 25×25‐μm and 20×160‐μm islands remain polycrystalline after the laser scan.

Scanning‐electron‐beam annealing of arsenic‐implanted silicon

〈100〉 Si implanted with As (100 keV, 1015/cm2) was annealed with a scanning electron beam. The principal results obtained were (1) the electrical activity of the e‐beam‐annealed samples is the same as for control samples subjected to either cw laser annealing or thermal annealing at 575 and 1000 °C, respectively, for 30 min each; (2) recrystallization of the implanted layer as determined by MeV ion channeling and TEM measurements is complete; (3) the electron distribution obtained by stripping and van der Pauw measurements indicates that no diffusion of the implanted atoms has occurred. The annealing is therefore essentially identical to that obtained with a scanning cw laser.

Use of a scanning cw Kr laser to obtain diffusion‐free annealing of B‐implanted silicon

The use of a continuous scanned Kr ion laser as a tool for annealing of boron‐implanted silicon is described. Conditions were found that produce high electrical activity and crystallinity of the implanted layer without redistribution of the boron from the as‐implanted profile.

Stoichiometric disturbances in ion implanted GaAs and redistribution of Cr during annealing

Using the Boltzmann transport equation, calculations were obtained predicting the zones of stoichiometric imbalance produced in GaAs after ion implantation at energies of 50, 100, and 300 keV. The recoiling Ga and As atoms were shown to produce a zone of interstitials at depths exceeding Rp . Secondary‐ion mass spectrometry profiling indicated that Cr was rapidly redistributed into these regions at temperatures ⩽500 °C. Transmission electron microscopic analyses obtained on horizontally sectioned and vertical cross section samples indicated that the interstitials coalesced into small clustered sites (50–100 A) and were responsible for the development of Cr gettering at depths ≳Rp .

Seeded and limited seeding regrowth of Si over SiO2 by cw laser annealing

Single‐crystal Si sheets (0.2 μm in thickness) of (100) orientation and of maximum dimensions, 100×10 000 μm, have been recrystallized by cw laser annealing of poly crystalline Si films deposited over parallel 3‐μm‐wide SiO2 bars adjacent to 3‐μm Si (100) substrate openings. The recrystallized films are free of cracks, mosaic structure, stacking faults, or excessive mass flow at the oxide edges. In a correlated series of experiments we have shown that the Si can be recrystallized over the SiO2 with only limited or relaxed requirements for vertical seeding from the substrate window.

Solid‐phase epitaxial regrowth of ion‐implanted layers in GaAs

The complete solid‐phase epitaxial regrowth of ion‐implanted layers in GaAs was obtained during a short (10 min) capless furnace anneal at a temperature of 475 °C. Two factors believed responsible for the incomplete regrowth of layers have been identified. First, the damage density from the implant should not exceed a critical value determined by a Boltzmann calculation. Second, the growth of polycrystalline material from the surface observed by transmission electron microscopy is a competitive mechanism. As+ implants, whose doses and energies were selected to achieve the correct damage density, and to ensure that its value was maintained in the near‐surface region, led to a complete recrystallization.

Gettering of mobile oxygen and defect stability within back‐surface damage regions in Si

Motion and gettering of oxygen into damage regions created by back‐surface mechanical abrasion in Si has been investigated using transmission electron microscopy (TEM), scanning electron microscopy, secondary‐ion mass spectrometry profiling and secondary‐ion microscopy. Redistribution and gettering of oxygen have been detected along dislocation lines after annealing at 600 °C by both TEM and direct ion imaging. Subsequent annealing at 1050 °C produces additional gettering, SiOx nucleation, and a dramatic increase in dislocation‐line density within the initial damage region. Secondary dislocation lines extending to a depth ≃ 40 μm are also generated by the two‐stage anneal, resulting in additional gettering sites for oxygen and other impurities. In comparison, single anneals at 1050 °C produce rapid defect annihilation, oxygen outdiffusion, and loss of additional gettering efficiency.