T. E. Seidel

Dependence of residual damage on temperature during Ar+ sputter cleaning of silicon

It has been found that the kind and amount of damage produced in silicon following Ar+ ion bombardment at 1.0 keV and the annealing properties of the damage depend strongly on the temperature at which the sputtering is done in the range 25–800 °C. Some of these differences in damage are not evident with surface‐sensitive techniques such as LEED, RHEED, or AES, but have been revealed by transmission electron microscopy and by Rutherford ion backscattering. TEM examination of substrates annealed at 800 °C after being sputtered at temperatures in the range 25–800 °C shows an increase in the density and the size of crystal defects with increasing sputtering temperature. Rutherford ion backscattering shows an increase in silicon disorder and in retained argon with increasing sputtering temperature. These results are similar to observations reported for ion implantation at higher energies. Models for damage mechanisms are discussed briefly. It is concluded that for Ar+ ion sputter cleaning of silicon, the silic...

Comparative study of annealed neon-, argon-, and krypton-ion implantation damage in silicon

Comparative annealing studies were carried out upon Si layers implanted with Ne+, Ar+, and Kr+ ions. Ion doses were in the range 6×1014/cm2–6×1015/cm2, and ion energies were chosen so that the matrix damage had approximately the same depth for each ion type. Annealing was carried out in a N2/dilute O2 ambient or in vacuum at 600, 900, or 1100 °C. Implanted layer structures were studied using electron‐microscope and ion‐backscattering techniques. The orientation of the Si substrate and ion‐beam heating effects were found to be important in determining layer‐annealing behavior. The latter depended weakly, if at all, upon the nature of the annealing ambient. Layer recrystallization was studied as a function of implanted ion type and dose, and the effects of inert gases trapped in the Si lattice were examined. The suitability of implantations for device gettering applications were considered. Crystallographic defects produced by annealing ranged from polycrystals and microtwins to simple dislocation networks....

Direct comparison of ion−damage gettering and phosphorus−diffusion gettering of Au in Si

The residual disorder caused by different implanted ions after annealing at elevated temperatures (850−1150 °C) is dependent upon the ion species. The gettering of Au by damaged layers produced by Ar, O, P, Si, As, and B has been quantitatively compared to gettering by phosphorus diffusion. Each individual comparison was made between opposite surfaces of a Si sample by use of Rutherford backscattering. The damage disorder was quantitatively measured by backscattering and structurally studied using electron microscopy. Typically, an ion dose of 1016/cm2 and ion energy of 200 keV were used for implantations. The Au was present in the Si at ’’moderate’’ levels so that solubility in the phosphorus diffused layers was not exceeded. Ar ion−damaged layers were more effective for gettering Au than were phosphorus−diffused layers below ∼1000 °C and equally effective up to 1150 °C. The relative gettering efficiency of the damage produced by other ions studied was less than that of phosphorus diffusion at 1000 °C an...

The redistribution of implanted dopants after metal‐silicide formation

The redistribution of implanted As and Sb following metal‐silicide formation of Pt, Pd, and Ni has been studied. The phases of the silicides used were PtSi, Pd2Si, and NiSi. Investigations with Rutherford backscattering analysis showed that after the formation of the silicides, the Sb was always found in the silicide layer near the surface of the samples, whereas PtSi and Pd2Si caused a partial rejection of As for implanted doses of 2×1015 cm−2 and higher. No rejection of As was found after the formation of NiSi. The results are discussed in terms of solid solubilities and impurity‐metal compound formation. The data presented has implications in the fabrication of Ohmic contacts and the adjustments of the heights of Schottky barriers on silicon.

A review of rapid thermal annealing (RTA) of B, BF 2 and As ions implanted into silicon

Abstract RTA studies of B, BF 2 and As implantations in silicon are reviewed. The optical coupling properties of the wafer are considered as a motive for obtaining accurate temperature assessment. Optical pyrometer techniques with feedback control are now commonly used. Enhanced diffusion of boron is widely reported for the channel tail in the several second time frame at ∼1050°C. Boron diffusion in preamorphized and crystalline silicon are compared, and dopant interactions (gettering) with residual disorder located just beyond the amorphous/crystalline (α/c) interface are discussed. The removal of residual α/c disorder from a 5 × 10 15 As/cm 2, 100 keV implant is shown to occur with ∼5.0 eV energy, while a “normal” concentration enhanced diffusion with ∼4.0 eV activation energy is obtained including data in the several second (RTA) time frames. Shallower defect free arsenic junctions are made using high temperature-short time cycles, rather than longer times at lower temperatures. The arsenic diffusion issues are discussed.

Rapid thermal annealing of dopants implanted into preamorphized silicon

The rapid thermal annealing behavior of BF+2 and As+ +BF+2 implanted into crystalline and preamorphized silicon is studied. After solid phase epitaxy nearly complete electrical activity is obtained without channeling tails (for the preamorphized silicon) or significant thermal diffusion. Dislocation loops always appear near the amorphous‐crystalline (α/c) interface of the preamorphized layer after solid phase epitaxy annealing (called ‘‘deep disorder’’). For preamorphization using Si+ damage into room‐temperature silicon targets, dislocations also span between the deep disorder and the surface, called ‘‘spanning dislocations.’’ The spanning dislocations are eliminated by preamorphization using Ge+ implanted into room‐temperature silicon targets. Transmission electron microscopy studies show the spanning dislocations move to the surface under thermal treatment, while the deep disorder remains to act as a getter region. The deep disorder is shown to getter F, or Au when Au is intentionally diffused from the...

Temperature transients in heavily doped and undoped silicon using rapid thermal annealing

Optical coupling by absorption and reflection of a wafer during rapid thermal anneals (RTA) determines the temperature transients during heating, and the behavior of thermally activated processes. It is shown experimentally that the heating rate and temperatures during the early phases of a RTA cycle depend on the doping of the wafer being heated. High doping is accompanied by high free carrier absorption which results in a relatively rapid increase in temperature. Differences of heating rates of 50 °C/sec and temperatures several hundred degrees centigrade are obtained in the first 5 sec of a RTA cycle for N+ and N− wafers and significant effects on the heating rate of heavily implanted wafers are also seen. Experiments were carried out using thermocouples, optical pyrometer and also by observing the lateral solid‐phase growth of silicon on sapphire (SOS). A simple theoretical description is given for the enhanced heating rate for N+ and heavily implanted wafers.

Rapid thermal annealing of Al‐Si contacts

Contact formation of Al on n+‐Si by rapid thermal annealing has been investigated. It was found that contact resistivity of the order of 6×10−7 Ω cm2 can be reproducibly achieved. The uniformity of the contact area morphology is much improved due to the limited Si migration into the Al metallization. Flat contact morphology can be obtained with a combined technique of ion mixing and rapid thermal annealing.

Zn gettering in InGaAs/InP interfaces

Zn accumulation (gettering) in InGaAs/InP interfaces was studied experimentally using secondary ion mass spectrometry (SIMS). The Zn was introduced by diffusion from solid and gaseous sources and was found to often getter in a thin region at the interface when diffused across it. Its peak concentration there increased with diffusion time and temperature and in some cases exceeded the solid solubility value by two orders of magnitude. Possible mechanisms for the Zn gettering are discussed.

Formation of p‐n junctions and Ohmic contacts at laser processed Pt‐Si surface layers

Pt‐Si alloy layers are formed during 130‐nsec pulsed irradiation of Pt coated Si with light from a Nd : YAG laser. The alloys form via surface melting and resolidifaction. Laser processing of arsenic of ion implanted, p‐type silicon results in formation of a p‐n+/Pt‐Si structure that exhibits rectifying electrical behavior. This structure arises because the As and Pt impurities are zone refined to different extents during resolidification of the molten surface layer.