Eddy Simoen

Hydrogen plasma-enhanced thermal donor formation in n-type oxygen-doped high-resistivity float-zone silicon

The impact of plasma hydrogenation on the subsequent formation of thermal donors at 450u200a°C in n-type oxygen-doped high-resistivity float-zone silicon is investigated by a combination of electrical and spectroscopic techniques. It is shown that the increase of the doping concentration can be explained by the creation of two sets of donors. The first one is the classical double oxygen thermal donors (OTDs), which are introduced with a nearly uniform concentration profile across the sample thickness, while the second type of donors is shallower and most likely hydrogen related. The latter show a pronounced concentration profile towards the surface and they form and disappear at a much faster rate than the OTDs at 450u200a°C.

What Do We Know about Hydrogen-Induced Thermal Donors in Silicon?

The hydrogen-plasma-accelerated formation of shallow thermal donors in silicon has been studied for a wide range of doping concentration and interstitial oxygen content [O-i] by electrical and spectroscopic techniques. The plasma-hydrogenated material has been heat treated for different times in the temperature range of 275-500 degrees C. It is shown that, besides oxygen thermal donors (OTDs), hydrogen-related shallow thermal donors (STDHs) also play a crucial role in the hydrogen-assisted creation of excess carriers. The impact of different factors on the introduction rate of the shallow donors will be discussed, whereby a strong role is played by the doping concentration and type (i.e., the Fermi-level position during the thermal anneal in air). Generally, shallow donor formation is faster in p- compared to n-type Si, which is associated with the different charge state of H. From combined deep-level transient spectroscopy and Fourier transform infrared absorption spectroscopy, it is concluded that the additional free carriers are contributed by both STDH and OTD centers, so that H not only plays a catalytic role but actively takes part in the donor formation, depending on the experimental conditions. Finally, from our data some conclusions can be made regarding the nature of the STDHs, which is still a matter of debate.

Impact of Direct Plasma Hydrogenation on Thermal Donor Formation in n-Type CZ Silicon

Institut de Microelectro`nica de Barcelona, Campus UAB, 08193 Bellaterra, SpainIn this paper, the role of a direct plasma hydrogenation treatment and a subsequent air annealing at 450°C in the formation ofthermal donors ~TDs! in n-type Czochralski~CZ! silicon is investigated by means of a combination of capacitance-voltage~C-V!and deep-level transient spectroscopy~DLTS!. The hydrogenation treatment is found to enhance the introduction rate of TDs at450°C for shorter annealing times, reaching its maximum acceleration after5handforthelongest plasma hydrogenation studied~2h!. For much longer annealing times, the TD introduction rate becomes independent of the presence of hydrogen in the material.DLTS detects only one donor level having an activation energy, which lowers with increasing doping density of the material, from0.106 to 0.093 eV. After activation energy correction for the Poole-Frenkel electric-field-enhanced emission, this trap is found tofit well with the conventional singly ionized oxygen thermal donor level. However, from C-V free carrier and DLTS trapconcentrations, it is derived that other shallower donors, created by the plasma hydrogenation and 450°C anneal should play animportant role in the free carrier concentration increase of the n-CZ silicon.© 2004 The Electrochemical Society. @DOI: 10.1149/1.1824039# All rights reserved.Manuscript submitted March 14, 2004; revised manuscript received May 5, 2004. Available electronically November 17, 2004.

Characterisation of oxygen and oxygen-related defects in highly- and lowly-doped silicon

Abstract In this paper, an overview will be given about analytical techniques which are suitable for the study of oxygen and oxygen precipitation in highly- and lowly-doped silicon. It will be shown that in the case of highly-doped silicon, the application of Fourier Transform Infrared (FT-IR) absorption spectroscopy requires the use of ultra-thinned or high-fluence irradiated samples and a dedicated data analysis. This sample preparation is necessary to reduce the free carrier absorption in the mid-IR region. It is shown that besides the interstitial oxygen concentration [O i ] and the amount of precipitated oxygen, it is possible to determine the stoichiometry of oxygen precipitates from the study of the corresponding absorption bands. Oxygen precipitation in p + silicon can also be investigated by the D1–D2 lines in photoluminescence (PL) on as-grown or heat–treated material without special sample preparation. In oxygen-doped high-resistivity float-zone silicon, standard FT-IR analysis can be applied to determine [O i ]. The presence of oxygen-related shallow donors can be probed by a combination of electrical (spreading resistance probe, SRP; capacitance–voltage, C – V ) and (quasi-)spectroscopic techniques (deep-level transient spectroscopy, DLTS).

Hydrogen-plasma-induced thermal donors in high resistivity n-type magnetic Czochralski-grown silicon

In this work, the formation of donors in n-type high resistivity magnetic Czochralski-grown silicon wafers, directly exposed to a hydrogen plasma, is investigated by a combination of capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements. C-V analysis demonstrates diffusionlike concentration profiles close to the surface, pointing to the formation of hydrogen-related shallow donors in silicon during the hydrogenation. In addition, oxygen thermal donors are created during a subsequent annealing (20min) performed at 350–450°C, as demonstrated by DLTS. It is shown that the hydrogen-related shallow donors are the dominant donors in as-hydrogenated samples, while hydrogen acts as a catalyst during the formation of oxygen thermal donors in the temperature range of 350–450°C. It is finally shown that the formation of both kinds of donors is Fermi-level dependent.

Deep Levels in Oxygenated n-Type High-Resistivity FZ Silicon before and after a Low-Temperature Hydrogenation Step

Department of Solid-State Sciences, Ghent University, B-9000 Gent, BelgiumThe behavior of oxygen in oxygen-doped high-resistivity~HR! n-type float-zone~FZ! silicon has been studied using a combinationof analytical techniques. In the as-doped material, a large number of deep levels have been observed with deep-level transientspectroscopy. The corresponding parameters ~concentration, activation energy, and trap signature! are given, and the possibleidentity is discussed in view of the presence of oxygen and other impurities in the material. In addition, the impact of alow-temperature hydrogen-plasma preannealing on the formation of oxygen thermal donors~OTDs! and other oxygen-relatedshallow thermal donors ~STDs! at 450°C is described. It is shown that the introduction rate of OTDs in oxygenated HR FZ siliconis much smaller than in Czochralski silicon. In fact, for short anneals at 450°C following a plasma treatment, the STDs are theones which have been predominantly created near the surface of the samples.© 2003 The Electrochemical Society. @DOI: 10.1149/1.1595665# All rights reserved.Manuscript submitted July 7, 2002; revised manuscript received March 18, 2003. Available electronically July 10, 2003.

What do We Know About Hydrogen-Induced Thermal Donors?

Donors? E. Simoen, Y.L. Huang, Y. Ma, J. Lauwaert, P. Clauws, J.M. Rafi, A. Ulyashin and C. Claeys IMEC, Kapeldreef 75, B-3001 Leuven, Belgium Baoding TianWei Solar Films Co, Ltd, 071051 Baoding, P.R. China Depart of Solid State Sciences, Ghent University, B-9000 Gent, Belgium CNM (IMB-CSIC), Campus UAB, 08193 Bellaterra, Spain University of Oslo, Sem Saelands vei 24, P.O. Box 1048, Blindern N-0316 Oslo, Norway Present address: SINTEF, P.O. Box 124 Blindern, NO0314 Oslo, Norway also at EE Depart KU Leuven, Kasteelpark Arenberg 10, B-3001 Leuven, Belgium

DLTS study on deep levels formed in plasma hydrogenated and subsequently annealed silicon

P-n junctions are created in p-type Czochralski silicon after a low temperature (270°C) hydrogen plasma exposure. This is attributed to the formation of hydrogen-related shallow donors. A deep level (E1) with an activation energy of about EC-0.12 eV is observed by DLTS measurement and assigned to a metastable state of the hydrogen-related shallow donors. At an annealing temperature of 340°C, the E1 centres disappear and oxygen thermal donors appear. The concentrations of the oxygen thermal donors are found typically to be 2-3 decades lower than that required for over-compensating the initial p-type doping and for contributing the excess free carriers.

P-N Junction Diodes Fabricated Based on Donor Formation in Plasma Hydrogenated P-Type Czochralski Silicon

A rather large amount of shallow donors is created in p-type Czochralski silicon (Cz Si) wafers after a hydrogen plasma exposure at ∼270 °C (substrate temperature) and a subsequent annealing in the temperature range of 350-450 °C. This two-step process has been used for the fabrication p-n junction diodes at low temperatures. Current-voltage characteristics show that the breakdown voltages of these diodes are higher than 100 V. The diode leakage is found to be improved after slow ramp annealing at temperatures up to 250 °C. Deep level transient spectroscopy measurements reveal that the oxygen related thermal donor is not the dominant doping species as expected before.