Au In Silicon Research Articles

Room-temperature diffusion and gettering of Au in silicon stimulated by MeV electron irradiation

A novel effect of room-temperature diffusion and gettering of Au from the bulk to the surface defect region of a Si wafer stimulated by 5 MeV electron irradiation is demonstrated. The Au atoms were introduced into the Si wafer by ion implantation. According to the secondary ion mass spectrum and the minority carrier lifetime measurements, it is found that 5 MeV electron irradiation with a small dose: e.g. 50 Gy, could effectively draw Au atoms from the bulk of a Si wafer to the surface defect region at room temperature, which is very different from the traditional gettering processes for transition metal impurities in Si where high temperature is necessary. The experimental evidence indicates that the room temperature gettering of Au in Si stimulated by 5 MeV electron irradiation is stronger than that stimulated by 60Co gamma ray irradiation in two aspects: with the same irradiation dose of 50 Gy and the same surface defect regions, the Au concentration profile of Au implanted Si samples getterred by 5 MeV electron irradiation shifts closer towards the surface defect region than that getterred by 60Co gamma ray irradiation; secondly, with the same surface defect region, the increment of the bulk minority carrier lifetime induced by the gettering of Au stimulated by 25 Gy 5 MeV electron irradiation is larger than 70%, however, even under 100 Gy, the lowest gamma ray irradiation dose used, the increment of the bulk minority carrier lifetime induced by the gettering of Au stimulated by 60Co gamma ray irradiation is less than 5%.

Lithium–gold-related complexes in p-type crystalline silicon

Using Hall and conductivity measurements the formation of a Li–Au-related complex in p-type crystalline silicon is demonstrated. Substitutional gold is known to introduce two energy levels in the band gap of silicon, a deep acceptor level at Ec−0.56 eV and a deep donor level at Ev+0.34 eV. We observe two energy levels introduced by lithium diffusion of Au-doped silicon, a previously reported acceptor at Ec−0.41 eV in n-type Si:Au and a new level at Ev+0.41 eV in p-type Si:Au. In addition, control of the Li-doping level of p-type Si is found to shift the Fermi level position between the deep donor level to the deep acceptor level as expected, thus confirming their presence in the samples. We discuss the identity of these levels in comparison with theoretical predictions for the interaction between hydrogen and the energy levels of substitutional Au in silicon.

Self-Interstitials in Silicon

Self-interstitial concentration I normalized to the thermal equilibrium concentration C I0 was previously derived as a function of diffusion time t, the absolute temperature T, the diffusivity D I and the specimen thickness w from the well-known diffusion equation for self-interstitials in silicon. Antoniadis also demonstrated that the time-averaged and normalized self-interstitial concentration <I> is obtained as a function of t and T from the oxidation stacking faults data. By fitting the former I to the latter <I> and using Stolwijk et al..'s relation between D I and C I0 derived from the diffusion data of Au in silicon, D I and C I0 were determined as a function of T. Furthermore, the fractional component of the interstitialcy mechanism for silicon self-diffusion was investigated, assuming a local equilibrium between self-interstitials and vacancies in silicon. It was found that self-diffusion occurs mainly via vacancies.

Contribution of Diffusion Interstitial Injection to Gettering of Metallic Impurities in Silicon

The contribution of interstitial injection induced by P and B diffusion (DII) under nonoxidizing conditions to the gettering process is discussed by considering a short‐range (doped‐layer) effect and a long‐range (bulk) effect. We show that: (i) the positive gradient of the concentration profile of the silicon interstitials within the highly doped layer is favorable for the gettering of the substitutional metallic species via a kick‐out mechanism both during P and B diffusion in silicon; (ii) the contribution of DII to the gettering of 3d elements in silicon is significant only within the highly P‐doped layers (short‐range effect); (iii) the predictions of DII induced gettering model agree with the experimental evidence on P diffusion gettering of Co and on P diffusion gettering and B diffusion gettering of Au in silicon.

Correlation of photoluminescence and symmetry studies with photoexcitation and decay processes of infrared active defects in Si

Defects introduced in silicon by neutrons and ions which give rise to infrared active electronic defect absorption bands after heat treatment to 500 °C were studied using a dual beam optical method. The measurements were made in the 11–90 K temperature range on four defect bands found in the 900 (11.1)–1100 cm−1 (9.09 μm) region of the infrared spectrum. The studies yield results on the capture cross sections of photoexcited electrons from defects which lead to a model of a defect having three different charge states. These cross sections are much smaller than those reported for the photoionization cross sections of chemical impurities such as Au in silicon. The states found in this study can be identified with photoluminescence peaks reported by others near 1 and 0.76 eV. Additionally, there are two different symmetries assumed by the defects responsible for the defect absorption bands.

EPR Observation of an Au‐Fe Complex in Silicon: I. Experimental Data

AbstractAfter quenching of Au‐doped FZ silicon an anisotropic axially symmetric EPR spectrum is observed. The spectrum exhibits a hyperfine interaction with 197Au nuclei (I = ½). In samples which were intentionally doped with isotopically enriched 57Fe (I = ½) an additional hyperfine interaction with this nucleus is observed. Due to the large nuclear electric quadrupole moment of 107Au the nuclear quadrupole interaction strongly influences the EPR spectrum. From this effect a lower limit for the quadrupole interaction can be derived by a computer diagonalization of the spin Hamiltonian. From the observed hyperfine interactions and the known properties of Fe and Au in silicon it is concluded that this spectrum originates from a [AusFei] complex.

Investigation of Ar ion implant gettering of gold in silicon by m.o.s. and Rutherford backscattering techniques

The gettering of Au in silicon has been investigated using m.o.s. techniques and Rutherford backscattering. Silicon wafers were intentionally contaminated with Au, and then Ar ion implant was performed on the back surface of the wafer and the damaged layer annealed at 1050°C for times of 15 and 60 minutes. Comparison of generation lifetime between gold wafers and gold implant-gettered wafers, obtained from the response of m.o.s. capacitors to a linearly varying voltage showed a marked improvement for the implant gettered wafers. Rutherford backscattering using 14N+ ions was carried out on the wafers, both on the implant damaged layer and on some 30–40μm in the bulk of the material. The Au concentration in the implant damaged layer was higher than in the bulk of the same wafer for both anneal times, indicating that Au had been effectively gettered. The backscattering speetra also showed other impurities such as Br, Cu, Fe, Sb, Sn and Te present in higher concentration in the implant damaged layer than in the bulk

Simultaneous gettering of Au in silicon by phosphorus and dislocations

Gettering in Si may be achieved by either phosphorus diffusion (ion pairing) or by dislocations (strain). We show here by use of backscattering spectrometry and transmission electron microscopy that, in particular, samples of both mechanisms are simultaneously operative. Au is present in a profile which mimics the phosphorus doping, and a spike of Au is superimposed on this profile in the strain field around a narrowly distributed misfit dislocation network. Both profiles are predominately (≳two-thirds) substitutional, implying that local ion pair binding energies exceed the strain binding energy near the dislocations.

Gettering of Gold and Copper in Silicon during Gallium Diffusion

The gettering of Au and Cu during the sealed tube diffusion of Ga has been studied by using neutron activation analysis and the spreading resistance microprobe technique. It was found that Au in silicon was gettered during Ga diffusion regardless of the cooling conditions. Most of the Cu in the surface layer of silicon diffused out during Ga diffusion, while Cu in the bulk silicon was gettered during the slow cooling process after diffusion. Increases in the minority carrier lifetime in p+n diodes prepared by Ga diffusion occurred with increasing the amount of Ga used as a source. It was ascertained that in Ga gettering the Ga metal sources played an important role as impurity sinks.

Enhanced solubility and ion pairing of Cu and Au in heavily doped silicon at high temperatures

The equilibrium solubilities of Cu and Au in silicon have been calculated for high temperatures 900–1100°C) and heavy dopings (10 19–10 21 cm −3) and are compared with experimental results for uniformly bulk doped and diffusion doped material. The electron activity coefficient is explicitly included in the calculation, and the effect of disturbing the vacancy population is discussed. For strongly extrinsic n type material, a large solubility enhancement (about 10 3 times the intrinsic solubility) is calculated, due to ion pairing of the substitutional metal acceptor with donors. It is concluded that pairing of interstitial metal donors with substitutional acceptors is not important because of configurational and vibrational entropy effects, so that for strongly extrinsic p type material, the solubility is one or two orders of magnitude less than for n type material at the same temperature and doping level. Agreement between experimental data and the calculations is very satisfactory; the saturation metal solubilities observed in bulk samples and diffused layers are in substantial agreement (within a factor of ~2) with calculations for all temperatures and doping levels, and the observed metal profiles in diffused layers are in agreement with calculated profiles both at and below saturation. The profiles indicate that vacancy enhancement is a minor effect for PBr 3 diffusions but may be significant for POCl 3 diffusions.