http://nathan.instras.com/documentDB/paper-44.pdf

Surface photovoltage phenomena: theory, experiment, and applications

A review is presented of the recent advances in the study of oxygen precipitation and of the main properties of oxide precipitates in silicon. After a general overview of the system ‘‘oxygen in silicon,’’ the thermodynamics and the kinetics of the precipitate formation are treated in detail, with major emphasis on the phenomenology; subsequently, the most important techniques for the characterization of the precipitates are illustrated together with the most interesting and recent results. Finally, the possible influence of oxygen precipitation on technological applications is stressed, with particular attention to recent results regarding device yield. Actually, the essential novelty of this review rests on the attempt to give an extended picture of what has been recently clarified by means of highly sophisticated diagnostic methods and of the influence of precipitation on the properties of semiconductor devices.

Oxygen precipitation in silicon

Despite the fact that H-terminated, HF-etched Si crystals are the starting point for construction of most contemporary electronic devices,1 little is known about the chemical reactions of H-terminated Si surfaces under ambient temperature and pressure.2,3 Functionalization of Si without partial oxidation and/or formation of electrical defects is potentially important in fabricating improved electronic devices4,5 as well as in measurement of charge transfer rate constants at semiconductor/ liquid contacts.6 One recently described approach involves the reaction of HF-etched Si(111) with olefins and organic diacyl peroxides, in which formation of a self-assembled (near)monolayer of Si-alkyls was hypothesized.2 We report here an alternative strategy to functionalize HF-etched Si surfaces involving halogenation and subsequent reaction with alkyl Grignard or alkyl lithium reagents. We report vibrational spectroscopic and temperature programmed desorption data which confirm that the alkyl groups are bonded covalently to the Si surface, and we demonstrate that such overlayer formation can impede the undesirable oxidation of Si in a variety of environments while providing surfaces of high electrical quality. The H-terminated Si surface7 was first exposed to PCl5 for 20-60 min at 80-100 °C, in chlorobenzene with benzoyl peroxide as the radical initiator.8,9 Upon chlorination, the XP survey spectra (Figure 1) showed peaks at 270.2 ( 0.4 binding electron volts, BeV, (Cl 2s) and 199.3 ( 0.4 BeV (Cl 2p), indicating that this procedure yielded Cl on the surface. The high-resolution XP spectrum of the Si 2p peak of this surface displayed, in addition to the substrate Si signal, an additional peak located at 0.98 ( 0.12 BeV higher in binding energy (Figure 2) whose position and intensity was consistent with the formation of a surface Si-Cl bond.10 Auger electron spectra

Alkylation of Si Surfaces Using a Two-Step Halogenation/Grignard Route

Carrier lifetimes in semiconductors are being rediscovered by the Si IC community, because the lifetime is a very effective parameter to characterize the purity of a material or device. It has become a process and equipment characterization parameter. The various recombination mechanisms are discussed and the concept of recombination and generation lifetime is presented. We show that surface recombination/generation plays an important role in today's high purity Si and will become yet more important as bulk impurity densities in Si are reduced further. Furthermore, the dependence of lifetime on impurity energy level and minority carrier injection level is discussed. Concepts are stressed in the paper, with the necessary equations to clarify these concepts. Wherever possible, the concepts are augmented with experimental data, with particular emphasis on the case of iron in silicon, because Fe is one of the most important impurities in Si today. We have used Si in the examples because lifetime measurements are most commonly made in Si.

Carrier lifetimes in silicon

A series of gettering experiments have been carried out for a better understanding of gettering mechanism(s) in silicon. We find that oxidation and oxynitridation, which are known to inject silicon interstitials, do not getter metallic impurities such as Au, Cu, Fe, and Ni while phosphorus (P) diffusion does produce effective gettering of these metals. We also find from P diffusion, Ar ion implantation, and Ni film gettering performed as a function of temperature, there exists an optimum gettering temperature. From a comprehensive discussion of the existing models, we conclude that neither the enhanced metal solubility nor the silicon interstitial model explains our experimental results. Furthermore, it is shown that generation of dislocations is not a prerequisite for effective gettering. A model, based on the segregation of impurities at high temperatures and on the release/diffusion of metallic impurities at lower temperatures, is proposed to explain all of our results. A general form of the segregatio...

Gettering in silicon

The enhancement effect of carbon on oxygen precipitation in Czochralski (CZ) silicon has been investigated in detail by means of infrared (IR) absorption spectroscopy at room temperature. The critical temperature Tc, which distinguishes the two different ways in which carbon enhances oxygen precipitation, has been shown to exist between 800 and 850 °C. Perturbed [Ci‐Oi]C(3) centers are observed by IR spectroscopy in the temperature range lower than the Tc. The perturbed C(3) center is estimated to consist of a complex with two to three oxygen atoms per carbon atom. It has moreover been confirmed that the carbon effect is explained in two ways: (i) carbon directly provides heterogeneous seeding sites, as [Ci‐Oi]C(3) centers, for oxygen precipitation at temperatures lower than Tc; and (ii) carbon plays a catalytic role at temperatures higher than Tc. Finally, the formation of [Ci‐Oi]C(3) centers is shown not to be affected by high‐temperature preannealing at 1250 °C.

Carbon enhancement effect on oxygen precipitation in Czochralski silicon

Thermally induced oxygen precipitation and redistribution phenomena in Czochralski‐grown silicon crystals are investigated by means of transmission electron microscopy and differential‐infrared absorption (DIR). In order to investigate the role of thermal history and the oxygen supersaturated condition for oxygen precipitation, a two‐step annealing process is adopted. Evident existence of SiO2 (crystobalite) is observed in as‐grown crystals by DIR at 1225 cm−1. As a result, it is ascertained that oxygen precipitation does not occur by homogeneous nucleation depending on the ratio of supersaturated oxygen but occurs by heterogeneous nucleation. A model of a grown‐in nucleus for oxygen precipitation by heat treatment is also proposed.

Precipitation and redistribution of oxygen in Czochralski‐grown silicon

Surface‐ and inner‐microdefects examined after a two‐step annealing process are compared and related to the intrinsic gettering phenomenon. After the defects are characterized by means of transmission electron microscopy, the defect types (dislocations, precipitates, and stacking faults) and defect structures as well as nature are correlated with the annealing temperature. It is found from the observations that a surface‐microdefect is a stacking fault extrinsic in nature possibly caused by a process‐induced ’’heavy metal contamination’’ such as copper and that the type of Si‐O complex precipitates generated strongly depends on annealing temperatures: <1050°C⋅⋅⋅ platelike cristobalite, 1100°C<⋅⋅⋅ regular octahedral amorphous SiO2. In addition, the mechanism for the formation of these defects is discussed based on electron microscope observations.

Surface‐ and inner‐microdefects in annealed silicon wafer containing oxygen

For the undoped semi-insulating LEC GaAs crystal, microscopic inhomogeneity was investigated on the fixed position by using cathodoluminescence (CL), secondary ion mass spectrometry (SIMS), X-ray topography (XRT) and scanning leakage current measurement (IL). Microscale fluctuations observed in these measurements were attributed to the cellular dislocation structures. It was suggested that the impurity gettering effect of dislocation plays an important role in the semi-insulation mechanism in GaAs crystal. Carriers are inactive in the boundary region of cell structures but are active in the inner region of cell structures.

Role of Dislocations in Semi-Insulation Mechanism in Undoped LEC GaAs Crystal

An algorithm for separating the bulk and surface components of recombination lifetime, tailored for contactless measurement techniques with laser excitation, is presented in the paper. In order to analyze the carrier decays and subtract the surface recombination term, two lasers operating at 910 and 830 nm are applied. A separation of carrier decay resulting from the different contribution of surface and bulk components due to difference in the light absorption is observed for such a case. This separation is a function of surface recombination velocity S. An experimental verification of the analysis is presented using microwave absorption/reflection measurements.

Fumio Shimura

Papers

Carbon enhancement effect on oxygen precipitation in Czochralski silicon

Precipitation and redistribution of oxygen in Czochralski‐grown silicon

Surface‐ and inner‐microdefects in annealed silicon wafer containing oxygen

Role of Dislocations in Semi-Insulation Mechanism in Undoped LEC GaAs Crystal

Bulk and surface components of recombination lifetime based on a two‐laser microwave reflection technique