The crystallization of undoped amorphous silicon films deposited by low‐pressure chemical vapor deposition in the temperature range 580–530 °C and annealed from 550 to 950 °C has been studied by transmission electron microscopy. The average grain size of the crystallized films depends on the annealing temperature and the deposition conditions. The nucleation rate of new grains during annealing decreases as the deposition temperature decreases from 580 to 545 °C and/or when the deposition rate increases. The final grain size is also influenced by the annealing temperature with the largest grain size obtained at low annealing temperatures. A simple model is described which explains the dependence of grain size on the annealing temperature. An average grain size of 500 nm has been obtained in a 200‐nm film deposited at 545 °C and annealed at 550 °C.

Large grain polycrystalline silicon by low‐temperature annealing of low‐pressure chemical vapor deposited amorphous silicon films

The effect of crystallite sizes L smaller than 100 nm on the integrated Raman cross section Σc of the transverse optical (TO) mode of fcc silicon was studied experimentally in fully nanocrystallized thin films. The Σc/Σa (amorphous) ratio of this mode is shown to be 1 up to L=30 A, and to decay exponentially down to 0.1 at larger L. A systematic procedure taking into account both this effect and the experimental optical absorption coefficient αexp at the excitation wavelength is then proposed for the determination of the crystalline volume fraction in mixed phase (amorphous/nanocrystalline) silicon systems by Raman measurements.

Experimental determination of the nanocrystalline volume fraction in silicon thin films from Raman spectroscopy

Building on nearly two decades of reported results for MOSFET's fabricated in small-grain polycrystalline silicon, a design methodology is developed that yields devices which have low threshold voltage, high drive current, low leakage current, tight parameteric control, and reduced topology, while requiring no nonstandard materials, processes, and tools. Design criteria and device performance are discussed, grain boundary characterization techniques are described, technological issues pertinent to VLSI implementation are investigated, and long-term device reliability is studied. The potential applications of the polysilicon MOSFET's in high-density dRAM and sRAM are explored. The successful implementation of an experimental stacked CMOS 64K static RAM proves the utility of these devices for three-dimensional integration in a VLSI environment.

Characteristics and three-dimensional integration of MOSFET's in small-grain LPCVD polycrystalline Silicon

Low‐temperature rapid thermal annealing has been used to crystallize both undoped and doped amorphous silicon (a‐Si) films deposited at low temperatures. The polycrystalline films produced are completely crystallized with time temperature budgets such as 4 min at 700 °C. Unlike deposited polycrystalline Si films, the grain size in these crystallized films is not limited by film thickness. In the case of undoped a‐Si films crystallized by this approach, the resulting conductivity is comparable to that achieved in undoped polycrystalline Si films produced by much higher processing temperatures. In the case of doped a‐Si films, the resulting crystallized film yields a conductivity of 160 S/cm, a value which is comparable to the highest reported for doped polycrystalline and microcrystalline silicon. These doped films are found to have mobility values of ∼13 cm2/V s.

Crystallized Si films by low‐temperature rapid thermal annealing of amorphous silicon

By studying the step coverage of plasma‐deposited amorphous silicon and germanium on patterned substrates, we find that the film formation process under device‐quality deposition conditions has a substantial component that behaves like a surface rate‐limited chemical vapor deposition process, while conditions producing defective material are associated with a much more physical‐vapor‐deposition‐like process. An explanation involving surface reactions of SiHx radicals is proposed.

Film formation mechanisms in the plasma deposition of hydrogenated amorphous silicon

Undoped LPCVD silicon films have been deposited at five temperatures between 560° and 620°C. The films were characterized as grown and after thermal annealing at 900°, 950°, and 1000°C. We used x‐ray diffraction, TEM, SEM, Raman and elastic light scattering, optical absorption and reflection, and other techniques in order to obtain information on the grain size, structure, structural perfection, and surface roughness. We found that polysilicon films of good structural perfection, low strain, and small surface roughness are obtained when the films are deposited in the amorphous phase and subsequently crystallized at 900°–1000°C. Such films are superior in all investigated material aspects to films grown in the crystalline phase.

https://iopscience.iop.org/article/10.1149/1.2115672/pdf

Growth and Physical Properties of LPCVD Polycrystalline Silicon Films

Undoped and in situ phosphorus‐doped low pressure chemical vapor deposited polysilicon films have been studied by various structural analysis and optical techniques as a function of deposition temperature. Polysilicon films of high quality can only be obtained by deposition in the amorphous phase and subsequent crystallization.

High quality polysilicon by amorphous low pressure chemical vapor deposition

Etude par diffraction RX, microscopie electronique en transmission et a balayage, diffusion Raman, diffusion optique, reflexion et absorption optique. Determination de la taille des grains, de la perfection cristalline, des deformations, de l'indice de refraction, de la rugosite de surface et de la conductivite electrique

H. F. Kappert

Papers

Growth and Physical Properties of LPCVD Polycrystalline Silicon Films

High quality polysilicon by amorphous low pressure chemical vapor deposition

LPCVD polycrystalline silicon: growth and physical properties of in situ phosphorus doped and undoped films