Minority Carrier Induced Debonding of Hydrogen from Shallow Donors in Silicon
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MINORITY CARRIER INDUCED DEBONDING OF HYDROGEN FROM SHALLOW DONORS IN SILICON* CARLETON H. SEAGER AND ROBERT A. ANDERSON Sandia National Laboratories, Albuquerque,
NM
87185
ABSTRACT We have investigated the dissociation of donor-hydrogen pairs in Schottky barrier capacitors fabricated from phosphorus and arsenic doped silicon, at temperatures in the range 24 to II0°C. At zero bias the release of donor trapped hydrogen does not follow first order kinetics. Introduction of minority carriers by illumination or forward bias injection enhances the rate of hydrogen release and redistribution, but otherwise leaves the functional form relatively unchanged. Numerical modeling shows that the debonding rate must be proportional to the local hole density. If the dissociation process is carried out in reverse diode bias, some of the released hydrogen rebonds deeper in the silicon, outside the depletion region. In addition, a portion of the charge density in the depleted region is seen to be metastable and disappears after several hours at room temperature. This observation suggests the existence of a positive charge state of the donor-hydrogen pair which may be the precursor to dissociation. While several groups have recently pointed out that reverse-bias annealing data suggest the existence of a negative charge state of interstitial hydrogen, our observation of an electronically controlled debonding rate. casts considerable doubt on the firmness of that conclusion.
INTRODUCTION Because of the importance of hydrogen to silicon device technology, attention has recently been focused on understanding the kinetics of hydrogen motion and bonding in silicon. Our investigations of the room-temperature hydrogenation process, employing in-situ hydrogenation and space charge measurement techniques, are published elsewhere [1-3]. This paper reports studies of the debonding of hydrogen from shallow donors in phosphorus and arsenic doped crystalline silicon, at annealing temperatures of II0°C and below, and under a variety of bias and illumination conditions. Results clearly demonstrate that debonding is limited by the availability of minority carriers, which appear to affect only the dissociation process. We interpret our reverse-bias data, qualitatively similar to those found by others [4,5], as the result of an increased rate of debonding inside the depletion region. A negatively charged mobile hydrogen species [4,5] is not required.
EXPERIMENTAL DETAILS Schottky-barrier diodes were fabricated by evaporatively depositing 400 A 2 thick, 4 mm Al front contacts on doped silicon. Al or Au back contacts were deposited on implanted or damaged surfaces, and had a low resistance that did not perturb the 1MHz capacitance measurements used to 14 1 6 3 deduce the charge density. Phosphorus (6.7xi0 to 6.4xi0 cm" ) and 4 3 arsenic (9.Ox10 cm" ) doped silicon were included in this study. Samples were first annealed for 10 min at 200°C then hydrogenated at 240 C for 32 minutes with a 1200 eV H-ion beam incident on the front electrode. This techniq
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