B. Hartiti

Phosphorus diffusion into silicon from a spin‐on source using rapid thermal processing

Diffusion of phosphorus into silicon from a doped spin‐on glass source using rapid thermal processing is described. The structural and electrical characteristics of the resulting shallow junctions including atomic and carrier concentration profiles, sheet resistance, as well as the effects on bulk carrier transport properties were studied and compared to those resulting from the use of conventional furnace heating. The results show that sheet resistance as low as 15 Ω/⧠ and surface carrier concentration higher than 1 × 1020 cm−3 are obtained in the annealed samples. Furthermore, a gettering effect is observed as the minority‐carrier diffusion length measured by the surface photovoltage technique is improved after processing.

Large diffusion length enhancement in silicon by rapid thermal codiffusion of phosphorus and aluminum

We have investigated the effects of simultaneous diffusion of phosphorus and aluminum in crystalline silicon on the minority carrier diffusion length as measured by the surface photovoltage technique. The diffusion is carried out by using a tungsten halogen lamp furnace (rapid thermal processing). We have shown that more than 100% bulk diffusion length improvement can be achieved in both float zone and Czochralski silicon material. The different contributions to this enhancement are discussed.

Gettering of gold by rapid thermal processing

We report on the first direct evidence of a gettering effect induced by rapid thermal processing (RTP). Homogeneously gold‐doped silicon is studied before and after RTP by deep level transient spectroscopy measurements of the Au acceptor level. After a 1000 °C/10 s cycle, gold is depleted in three regions below the surfaces, indicating a gettering effect. The mechanism for this RTP‐induced gettering is discussed.

Defect generation and gettering during rapid thermal processing

The authors present results showing that deep-level transient spectroscopy (DLTS) is particularly efficient in identifying the origin of rapid thermal processing (RTP) related defects. It was found that defects are mostly related to residual impurities present in the as-grown silicon wafers or unintentionally introduced during high-temperature processing steps. It was shown, in particular, that these impurities can be thermally annealed out or neutralized by a hydrogenation process. In addition, the authors demonstrated that these impurities can be swept out of the active region of the device by a gettering effect during the RTP which is similar to that occurring in a classical thermal treatment. >

Gold gettering induced by rapid thermal doping using spin‐on sources

Transition metals are known to degrade the device performances. Gettering is now widely used to reduce the effects of these contaminants. Rapid thermal processing (RTP) has been shown to advantageously replace conventional long time temperature cycles in various types of applications. Moreover, recent works have evidenced that a gettering of impurities can occur during the RTP cycle. In this letter, we report that RTP diffusion of phosphorus or boron from a spin‐on deposited layer can also induce a gettering effect in silicon. For gold‐contaminated samples, the redistribution of the Au acceptor level is followed by deep level transient spectroscopy measurements. After a 1000 °C/10 s cycle, gold is depleted in the regions below the surfaces, indicating that gettering has occurred. The mechanism of this RTP‐induced gettering is discussed.

Bulk diffusion length improvement by rapid thermal gettering

Rapid thermal diffusion of phosphorus into p‐type silicon from a spin‐coated film containing the dopant has been studied as a function of process temperature and time duration. The electron diffusion length measurements performed by the surface photovoltage method present evidence for a gettering phenomena since the diffusion length values of the diffused silicon samples are found to exceed the initial value reported for the virgin material.

Multicrystalline silicon solar cells processed by rapid thermal processing

In the present work, the authors show that rapid thermal processing (RTP) in a lamp furnace can be successfully used for the manufacturing of multicrystalline silicon solar cells. RTP is carried out on various multicrystalline wafers coated with phosphorus doped silica- films on the front side and pure aluminium on the rear side. Phosphorus concentration profiles and electrical activation were investigated by secondary ion mass spectrometry (SIMS) and sheet resistance measurements, respectively. The influence of RTP on the bulk properties of the multicrystalline wafers were monitored by using the surface photovoltage technique. Finally, 2/spl times/2 cm/sup 2/ test solar cells have been fabricated and characterized by employing dark and illuminated I-V analysis as well as spectral response measurements. The efficiency of the best AR coated cell has been 14.1 % with an open-circuit voltage of 595 mV and a short circuit current of 31.7 mA/cm/sup 2/.<<ETX>>

Back surface field-induced gettering in multicrystalline silicon

The optimization of the gettering efficiency of back surface field (BSF) obtained by molecular ion implantation or doped silica-film deposition is addressed. It is found that the activation of metallic impurities co-implanted or present in the solution can limit the efficiency of the gettering in the case of rapid thermal annealing (RTA) due to the quenching inherent in fast cooling >or=80 degrees C/s. However, after classical furnace annealing with a slower cooling rate (<0.1 degrees C/s), effective gettering can occur as the impurities are mostly in a precipitated inactive form, so that the improvement level of the classical POCl/sub 3/ diffusion can be reached after boron or aluminum doped silica-film deposition or BF/sub 3/ ion implantation.<<ETX>>

Activation and gettering of intrinsic metallic impurities during rapid thermal processing

Abstract We show in this study that deep-level transient spectroscopy is an effective means of revealing residual metallic impurities in commercial silicon which are electrically activated by rapid thermal processing (RTP). In particular we demonstrate that the dominant activated metallic impurity, detected after RTP (at temperatures of 800 and 1000°C for 10s) and serial sectioning from the front side or the back side of the samples, has an inhomogeneous distribution. This is characteristic for a getter effect and is similar to that observed for intentionally gold-doped samples followed by RTP. Serial sectioning in steps of about 25 μm allows us to establish a complete picture of what happens during RTP: activation and gettering of residual bulk impurities, as well as the activation of surface contaminants which have been introduced by the high temperature treatment.

Enhancement of diffusion length of pregettered multicrystalline silicon solar cells by hydrogen ion implantation at the end of the process

2×2 cm2 n+pp+ multicrystalline silicon solar cells have been fabricated using thin wafers less than 200 μm thick. A large electron diffusion length has been achieved in these wafers after metallic impurity gettering using a heavy phosphorus diffusion prior to cell processing. Further improvements in the electron diffusion length (Ln) and in the short circuit current (Jsc) of these cells are brought out by hydrogen ion implantation carried out through the back surface of the finished cell. A 25% increase in Ln and a 5.5% increase in Jsc are obtained.