Showing papers by "Theodore I. Kamins published in 1982"

Diffusion of arsenic in polycrystalline silicon

Abstract: The diffusion of arsenic in polycrystalline silicon films has been studied over the temperature range 750–950 °C and for grain sizes 210–510 nm. Rutherford backscattering spectrometry was used to measure the concentration profiles of arsenic, initially introduced into the polysilicon by ion implantation, after various annealing steps. The concentration profiles were found to be determined by a combination of two factors—the low diffusivity in the bulk of the rains and the much higher diffusivity in the grain boundaries. The diffusivity of arsenic in the grain boundaries was independent of concentration, with an activation energy of 3.9 eV, very close to that of the low‐concentration arsenic diffusivity in single‐crystal silicon. However, the value of the diffusivity was 8.6×104 exp(−3.9/kT)cm2/s, four orders of magnitude higher than the single‐crystal value. The diffusivity in the interior of the grains was the same as that in single‐crystal silicon.

A CMOS structure using beam-recrystallized polysilicon

Abstract: A new CMOS structure has been fabricated with the p-channel transistors in a layer of recrystallized polysilicon and the n-channel transistors in adjacent, laterally displaced regions of the underlying single-crystal silicon. The process allows the use of existing circuit layouts with only minor, if any, modification. Moderate quality transistors are fabricated in a layer of recrystallized polysilicon without degrading the characteristics of high-quality transistors simultaneously formed in the substrate. The oscillation period of ring oscillators is close to that calculated, and varies with the transistor dimensions in the expected manner.

MOS Transistors in beam-recrystallized polysilicon

Abstract: The fabrication of transistors with their active channels in recrystallized polysilicon offers the long-desired possibility of readily achievable, total dielectric isolation. Devices with properties approaching those of single-crystal transistors can be obtained in large-grain polysilicon, and the properties can be further improved by using seeded recrystallization to remove the remaining grain boundaries. This paper addresses some of the remaining problem areas which must be controlled before the technique can become a practical process, as well as showing some novel structures, including a new dynamic RAM cell.

Effect of laser recrystallization of polysilicon on the underlying substrate

Abstract: Although laser recrystallization of polysilicon into a large-grain structure degrades the lifetime in the underlying substrate, a subsequent heat treatment similar to that seen during transistor fabrication increases the lifetime to approximately the value in the regions not laser processed. No electrical effects of laser damage to the underlying substrate are found in the transient behavior of MOS capacitors after furnace annealing or in the properties of p+n junction diodes. Since any damage to the substrate during laser processing is substantially eliminated by subsequent heat cycles, recrystallization is compatible with fabrication of high-quality devices in the substrate.

Oxygen and Nitrogen Incorporation during CW Laser Recrystallization of Polysilicon

Abstract: The incorporation of nitrogen and oxygen in polysilicon has been examined by SIMS. The analysis, combined with C-V measurements and ion implantation, has been used to correlate the incorporation of the two species with the fixed-charge density at the back polysilicon/SiO2 interface. Laser recrystallization with a silicon-nitride encapsulation layer results in the inclusion of 2–4 × 1017 cm−3 nitrogen atoms in the polysilicon; if an oxide capping layer is used, the nitrogen level observed is at the background of the SIMS system (~1015 cm−3). Either type of capping layer results in 3–4 × 1018 cm−3 oxygen atoms being incorporated into the polysilicon. Implantation of nitrogen into the polysilicon before recrystallization increases the fixed-charge density Nf,b) at the back interface, while implanted oxygen decreases Nf,b. The high Nf,b found with a nitride capping layer is attributed to deposition of nitrogen or SiNX at the back interface.

Beam Shaping for CW Laser Recrystallization of Polysilicon Films

Abstract: A shaped laser beam has been used for laterally seeded recrystallization of polysilicon films over oxide. Direct maps of the shaped-beam intensity distribution in the wafer plane are correlated with the grain structure of the recrystallized polysilicon. Using 60% overlapping of shapedbeam scans along directions, we have obtained seeded areas one mm wide and 50 to 500 µm long. These consist of 40 µm-wide adjacent single-crystal strips regularly separated by low-angle grain boundaries extending laterally away from the seed openings. The spacing between grain boundaries is equal to the scan spacing, providing a means for controlling the location of grain boundaries in otherwise defect-free, single-crystal films.