Shallow boron-doped junctions in silicon

Abstract

Shallow boron-doped junctions in silicon have been investigated by means of secondary ion mass spectrometry, scanning electron microscopy, transmission electron microscopy, spreading resistance profiling, and four-point probe techniques. The junctions were formed by implanting BFt ions into n-type Si at the dose range of 1-5 X 10 15 ions/cm 2 , through a thin (25-nm) screen layer of silicon dioxide. We have emphasized the higher dose range (3-5 X 10 15 ions/cm 2 ) as it is more relevant to processes in the current level of device integration. The use ofBF 2 + species and the screen oxide layer is necessary in order to form junctions whose depths Xj .,;;0.4 pm, when conventional annealing techniques are employed. We have also examined junctions that were activated in a rapid thermal annealing system that utilizes an incoherent light source. One of the main objectives of this study is to compare conventional and rapid thermal annealing techniques. We thus evaluate the results obtained by these two methods of annealing for both the junction depth Xj and the sheet resistivity Rs' Other relevant variables such as a low-temperature (77-K) implantation, surface amorphization by Si implantation, and preactivation annealing have also been examined and their effects are discussed. Based on the results of the present study, a mechanism for boron activation in silicon is discussed.

Thickness Dependent Parasitic Channel Formation at AlN/Si Interfaces

“…Figure 4 indicates that such a time difference is insufficient to significantly impact the activation of boron atoms at this temperature. [37][38][39][40] Hence the presence of higher surface boron concentrations cannot be the reason for the higher surface acceptor concentration observed for thicker films. Given the similar concentrations of boron and Al in the thinner and thicker films, it is clear that the source of increased acceptor doping lies elsewhere.…”

“…While thicker films are exposed to the higher growth temperature for longer times (300 seconds of additional exposure duration at 1050°C for the 200 nm AlN sample compared to the 50 nm sample), prior reports on the activation of ion-implanted boron in crystalline Si indicates that such a time difference is insufficient to significantly impact the activation of boron atoms at this temperature. [37][38][39][40] Hence the presence of higher surface boron concentrations cannot be the reason for the higher surface acceptor concentration observed for thicker films.…”

Lattice Damage, Boron Diffusion, and Dopant Activation in BF 2 Implanted Layers

“…In this paper we analyze the data of these studies [especially the SIMS work (1), because of its higher spatial resolution] in terms of a model based on the wellknown isotopic exchange process between '802 gas molecules and the 160 network atoms of silica glass (5). This analysis is similar in principle to that applied earlier by Revesz and Hughes (6) to the data of Rochet et al (3). We show that results of calculations based on this model reasonably well reproduce the spatial and temporal evolution of the '80 concentration profiles observed by the SIMS measurements.…”

“…There have been several recent studies which have used SIMS or nuclear reaction microanalysis techniques to examine the interaction between '80~ molecules and films of Si'sO2 thermally grown on silicon (1)(2)(3)(4). These studies have shown that an oxide film consisting predominantly of '80 atoms forms at the Si/SiO2 interface and that ~sO atoms are incorporated into the outer surface region of the Si'602 film.…”

“…Molecular ion implantation with BF2 ions has been proposed by several authors for shallow p+/n junction fabrication in VLSI devices (1)(2)(3)(4)(5)(6)(7)(8)(9). In this way it is possible to obtain high energy and high current ion beams by maintaining a low boron energy, which is only a small fraction (11/49) of the total primary energy; in addition, boron channeling phenomena are reduced, due to the higher amorphization capability of BF2 (9).…”