Abstract
Ion implantation is an important technique in semiconductor processing and has become a key technology for 4H-SiC devices. Today, aluminum (Al) implantations are routinely used for p-type contacts, p+-emitters, terminations and many other applications. However, in all crystalline materials, quite a few ions find a path along a crystal channel, so-called channeling, and these ions travel deep into the crystal. This paper reports on the channeling phenomenon during Al implantation into 4H-SiC, and in particular, the influence of a thin native oxide will be discussed in detail. The effects of thermal lattice vibrations for implantations performed at elevated temperatures will also be elucidated. 100 keV Al ions have been implanted along the [000-1] direction employing samples with 4° miscut. Before implantation, the samples have been aligned using the blocking pattern of backscattered protons. Secondary ion mass spectrometry has been used to record the Al depth distribution. To predict implantation profiles and improve understanding of the role of crystal structure, simulations were performed using the Monte-Carlo binary collision approximation code SIIMPL. Our results show that a thin surface layer of native oxide, less than 1 nm, has a decisive role for de-channeling of aligned implantations. Further, as expected, for implantations at elevated temperatures, a larger degree of de-channeling from major axes is present due to increased thermal vibrations and the penetration depth of channeled aluminum ions is reduced. The values for the mean-square atomic displacements at elevated temperatures have been extracted from experimental depth profiles in combination with simulations.
Highlights
Ion implantation is an important technique in device manufacturing, in particular for silicon carbide (SiC), since diffusion of dopants is negligible at typical process temperatures [1, 2]
At room temperature (RT), an 8 Å thick amorphous layer is needed in the simulations to fit the experimental results, which is a thickness in agreement with what is expected from the native oxide
A decrease in thickness of the scattering non-aligned top layer from 8 to 4 Å is revealed for samples heat treated at 600 °C and sequential implanted at 200, 400 and 600 °C, indicating a desorption from the top layer
Summary
Ion implantation is an important technique in device manufacturing, in particular for silicon carbide (SiC), since diffusion of dopants is negligible at typical process temperatures [1, 2]. To support and explain experimental results, Lindhard developed in the 1960s a theoretical description of channeling where he introduced the concept of “critical angle for channeling” [12, 13] In this model, the probability for channeling is expressed as the maximum angle between the incoming beam and the axial row of atoms for which the ions still will be steered along the axis. The ion beam has been aligned in parallel to the 4H-SiC(0001) direction, and Monte-Carlo simulations using the binary collision approximation have been utilized to support the experimental results. It is shown that in addition to the used implantation temperature, the thin amorphous surface layer has a strong effect on the depth profiles
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