Hydrogen in Crystalline Silicon
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HYDROGEN IN CRYSTALLINE SILICON S. J. PEARTON AT & T Bell Laboratories,
Murray Hill, NJ
07974
ABSTRACT
The ability of hydrogen to migrate in crystalline Si at low temperatures (c300"C annealing. Gorelkinskii et al.l52l found a reversible change in concentration of these shallow donors, and in the intensity of IR absorption bands (3.36, 3.40 and 3.47 um) after an initial anneal at 450°C, followed by a lower temperature (300' C) anneal. Quenching the samples in the range 100-300 *C brought reversible changes in the donor concentration between 1015-101 7 cm-2. This was ascribed to relaxation of the donors to a neutral state.1 521 Since the maximum donor concentration occurs after H implantation and 4500C annealing, there is some question as to whether they are really due to oxygen thermal donor formation, particularly in view of the radiation-enhanced diffusion of oxygen observed by Pflueger et. al.,1 531 and Oates et al.1 541 However, generally no difference in H-related donor formation is observed between CZ and FZ Si.1551 5 A large amount of work'1 6,' ! on Neutron Transmutation Doped (NTD) FZ Si grown in a hydrogen atmosphere also reveals formation of the shallow hydrogen-related donors after 450°C annealing, and a further donor (37 meV) after 500'C annealing.156] Figure 9 shows the carrier concentration of NTD, H2 or Ar grown FZ Si as a function of annealing temperature.[5 61 The p-n conversion (activation of P atoms produced) occurs at 650°C for Ar grown material, but at only 300'C for H 2 grown Si. This is due to the formation of the shallow donors, and coincides with the growth of a Si-H IR absorption band at 2160 cm-1 (Figure 10).1571 Above 500°C these shallow donors anneal out, leaving the transmutation-produced P donors. A comparison[561 of the properties of the H-related donors with those of the oxygen thermal donors reveals that the hydrogen donors do not exhibit concentration reversibility with annealing temperature cycling, there is no increase in concentration upon prolonged annealing at 450'C, and the measured energy levels are different. A final interesting feature of hydrogen-doped material is that the production rate of damage-related centers, such as the A-center, is reduced, either by passivation of these centers, or by competition for capture of vacancies by hydrogen atoms.[52,581 f.0
810i8,v/y150 1c" •-NTO-Si
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Rescistivity
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Figure 9 Carrier concentration of NTD Si
430
Infrared t•iransmiosion",, \N
Infare
000
>
50
Annealing~ temperatlure
Figure 10 Infrared
(°C)
transmission
at
as a function of annealing temperature for
1 2160 cmA versus annealing temperature for
FZ, H 2-grown material or FZ, Ar-grown material. The two curves for each type refer to irradiation in either a light or heavy water reactor - from ref. 56.
a NTD, H 2 grown FZ Si sample ref. 57.
from
465
DIFFUSIVITY OF HYDROGEN The earliest quantitative measurements on hydrogen diffusio
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