T. Dao

Island growth in the atomic layer deposition of zirconium oxide and aluminum oxide on hydrogen-terminated silicon: Growth mode modeling and transmission electron microscopy

Atomic layer deposition (ALD) is used in applications where inorganic material layers with uniform thickness down to the nanometer range are required. For such thicknesses, the growth mode, defining how the material is arranged on the surface during the growth, is of critical importance. In this work, the growth mode of the zirconium tetrachloride∕water and the trimethyl aluminum∕water ALD process on hydrogen-terminated silicon was investigated by combining information on the total amount of material deposited with information on the surface fraction of the material. The total amount of material deposited was measured by Rutherford backscattering, x-ray fluorescence, and inductively coupled plasma–optical emission spectroscopy, and the surface fractions by low-energy ion scattering. Growth mode modeling was made assuming two-dimensional growth or random deposition (RD), with a “shower model” of RD recently developed for ALD. Experimental surface fractions of the ALD-grown zirconium oxide and aluminum oxid...

Boron diffusion in amorphous silicon and the role of fluorine

We demonstrate that boron diffuses at high concentrations during low-temperature thermal annealing in amorphous silicon pre-amorphized by germanium ion implantation. For a typical boron ultrashallow junction doping profile, concentrations as high as 2×1020 cm−3 appear to be highly mobile at 500 and 600 °C in the amorphous silicon region before recrystallization. In crystalline silicon at the same temperatures the mobile boron concentration is at least two orders of magnitude lower. We also show that boron diffusivity in the amorphous region is similar with and without fluorine. The role of fluorine is not to enhance boron diffusivity, but to dramatically slow down the recrystallization rate, allowing the boron profile to be mobile up to the concentration of 2×1020 cm−3 for a longer time.

Groups III and V impurity solubilities in silicon due to laser, flash, and solid-phase-epitaxial-regrowth anneals

In this work the authors studied impurity solubilities of groups III and V elements in silicon resulting from laser anneal, flash anneal, and solid-phase-epitaxial regrowth. Rutherford backscattering channeling analysis was used to determine substitutional impurity depth profiles generated from the difference between the random and aligned spectra. Despite the large difference in peak temperatures and times, the anneals produce similar results with maximum solubilities beating the maximum equilibrium values by one to two orders of magnitude depending on the impurity. The correlation between the metastable solubility and the equilibrium distribution coefficient allows a prediction of values for other impurities not extracted experimentally.

Low-temperature diffusion of high-concentration phosphorus in silicon, a preferential movement toward the surface

We demonstrate that ultrashallow high-concentration phosphorus profiles in silicon diffuse preferentially toward the surface during low-temperature annealing at 700°C after recrystallization of an amorphous layer. In this work, we observe the preferential diffusion following a preamorphizing germanium implant, and also after a self-amorphizing phosphorus implant. This phenomenon is driven by the presence and dissolution of silicon interstitial defects. The greater the distance between the defect band and the high-concentration phosphorus profile, the less the preferential diffusion for a fixed anneal time. The overall result of this effect is a phosphorus profile that is significantly shallower and steeper than after implant.

HfSiO4 Dielectric Layers Deposited by ALD Using HfCl4 and NH 2 ( CH 2 ) 3Si ( OC 2 H 5 ) 3 Precursors

The physical and electrical properties of HfSiO 4 dielectric layers deposited by atomic layer deposition (ALD) are reported. The precursor chemistries used for deposition were HfCl 4 /H 2 O for HfO 2 and NH 2 (CH 2 ) 3 Si(OC 2 H 5 ) 3 /O 3 for SiO 2 . Two processes with HfCl 4 :NH 2 (CH2)3Si(OC 2 H 5 )3 precursor pulse ratios of 5:1 (HfO 2 -rich) and 1:1 (SiO 2 -rich) are investigated. Measurements with X-ray photoelectron spectroscopy and channeling Rutherford backscattering spectrometry show that these processes result in layers with Hf/(Hf + Si) ratios of 0.56 and 0.34-0.37, respectively. X-ray diffraction measurements showed formation of a HfO 2 cubic phase in HfO 2 -rich layers starting at 850°C. In SiO 2 -rich layers, no crystallization was detected up to 1100°C. Metal oxide semiconductor (MOS) capacitors with polysilicon electrodes were used for electrical characterization. The k-value of the SiO 2 -rich layers was found to be 4.8-5.4 and that of the HfO 2 -rich layers 12.5-15.1, both with an experimental error of 10%. The leakage currents of both types of layers were comparable to SiO 2 reference data and increased with polysilicon activation anneal. A high-resolution transmission electron microscopy study revealed phase segregation in thick SiO 2 -rich layers. In HfO 2 -rich layers, the phase segregation was less clear, but upon annealing, composition variations at the interfaces were detected. Given the experimental errors, no impact of phase segregation on the k-values of both types of layers could be detected. It is concluded that postdeposition annealing of HfSiO 4 layers for application as gate dielectrics applications in advanced complementary MOS technologies is essential to optimize stoichiometry and reduce leakage currents.

Influence of the anneal conditions on arsenic activation during solid-phase epitaxial regrowth

We investigate the influence of the initial stage of the thermal treatment during solid-phase epitaxial regrowth (SPER) on the electrical activation level of arsenic in self-amorphized silicon, both with respect to heating ramp-up rates and the use of low-temperature preanneals. Enhancement of the electrically-active arsenic concentration by 14% is observed for activation with the fastest ramp-up rates (430°C∕s) compared to the slowest ones (36°C∕s). Around 50% of the 1015at∕cm2, arsenic implant at 5 keV is found to be nonsubstitutional and this fraction reaches even 99% for dose 3×1015at∕cm2. Arsenic clustering in silicon amorphous phase during SPER is recognized to play an important role in the decrease of the active dose.

Impurity redistribution due to recrystallization of preamorphized silicon

We have studied impurity redistribution due to low-temperature crystallization of amorphous silicon. Many impurities move ahead of the amorphous-crystalline interface and relocate closer to the surface. In general, redistribution is more likely at high impurity concentrations. By investigating a wide range of concentrations for indium, lead, and antimony, we demonstrate the direct correlation between the magnitude of this redistribution effect and the impurity metastable solubility limit in crystalline silicon. At low concentrations, it is less likely for impurities to redistribute. However, in this regime we show that indium experiences concentration-independent segregation, and that boron profiles are also affected by the crystallization process.

Influence of preamorphization and recrystallization on indium doping profiles in silicon

The effect of preamorphization and solid-phase epitaxial regrowth on indium doping profiles in silicon has been investigated. It is shown that preamorphized silicon significantly reduces channeling during indium ion implantation, producing a much more abrupt doping profile. During recrystallization by thermal annealing, indium segregates in front of the moving amorphous/crystalline interface, creating a clearly visible peak in the doping profile. We establish that the physical mechanism for this phenomenon in the 1018–1019 cm−3 concentration range is segregation determined, as there is no significant concentration dependence for those doses studied in this work. We also demonstrate that this phenomenon is enhanced at lower temperatures.

Dopant diffusion in amorphous silicon

In this work we investigate the diffusion of high-concentration ultrashallow boron, fluorine, phosphorus, and arsenic profiles in amorphous silicon. We demonstrate that boron diffuses at high concentrations in amorphous silicon during low-temperature thermal annealing. Isothermal and isochronal anneal sequences indicate that there is an initial transient enhancement of diffusion. We have observed this transient diffusion characteristic both in amorphous silicon preamorphized by germanium ion implantation and also in amorphous silicon preamorphized by silicon ion implantation. We also show that the boron diffusivity in the amorphous region is similar with and without fluorine, and that the lack of diffusion for low-concentration boron profiles indicates that boron diffusion in amorphous silicon is driven by high concentrations. Ultrashallow high-concentration fluorine profiles diffuse quite rapidly in amorphous silicon, and like boron, undergo a definite transient enhancement. In contrast, ultrashallow high- concentration phosphorus and arsenic profiles did not significantly diffuse in our experiments.