Hydrogen enhancement of silicon thermal donor formation

Abstract

Oxygen-related thermal donor formation in Czochralski silicon is characterized by the capacitance-voltage and deep level transient spectroscopy techniques as a function of 450 °C anneal time following hydrogenation. Increases in the formation rate and number of thermal donor (TD) defects found after hydrogenation are reported. This study finds an increase in TD+/++ concentration in the near-surface region at short anneal times, but at longer times an elevated concentration was not observed. No acceleration through the sequence of thermal donor defects was detected. This fails to support the model of hydrogen lowering the barrier to oxygen diffusion and accelerating the TDn→TDn+1 transitions. This study does, however, support a model in which the hydrogen increases the available thermal donor core sites.

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

“…In the latter case, it is known that H accelerates interstitial oxygen diffusion, 2 resulting in a faster oxygen thermal donor ͑TD͒ ͑OTD͒ formation. [3][4][5][6] At the same time, hydrogen-related shallow TDs ͑STDHs͒ have also been observed, [7][8][9][10][11][12][13] with ionization energies in the range of 35-40 meV and infrared absorption peaks in the sub-300 cm −1 wavenumber range. These centers can be exploited for the low temperature formation of deep p-n junctions in p-type CZ silicon.…”

“…2 and 3 is that hydrogen enhances the transport of interstitial oxygen, resulting in an accelerated OTD formation. [2][3][4][5][6] Figure 3 should then represent the increase of the oxygen diffusion coefficient, provided hydrogen does not interfere with the oxygen clustering process.…”

“…30 It has been noted in the past that there can be a difference between the free carrier concentration in CZ material heat treated around 450°C to create OTDs and the resulting concentration derived from DLTS, the latter method yielding lower values in many cases. 5,30,[37][38][39][40] Especially when the OTD concentration is higher than the background doping concentration, capacitance DLTS will underestimate the true OTD concentration for several reasons. One is the fact that the OTDs are attractive deep levels for electrons, so that they exhibit a Poole-Frenkel shift of the peak position to lower temperatures ͑en-ergies͒ with increasing electric field.…”

Thermal donor formation in direct-plasma hydrogenated n-type Czochralski silicon

“…At the same time, hydrogen can also activate otherwise electrically neutral impurities, like carbon in silicon [1][2][3] or it plays a catalytic role in certain defect formation processes. A good example of the latter case is the generation of oxygen thermal donors (OTDs) in Si in the temperature range between 300 and 500 • C [4][5][6][7]. It has been shown that doping Czochralski (Cz) silicon with hydrogen enhances the introduction rate of OTDs, typically by a factor 5-10 for a 450 • C annealing temperature, compared with no hydrogen doping [4].…”

What do We Know About Hydrogen-Induced Thermal Donors?

“…Due to its high reactivity and mobility, hydrogen interacts with other impurities, either passivating harmful generation-recombination centers and dopants, like B and P or activating neutral impurities, like carbon and oxygen. In the latter case, it is known that H accelerates the oxygen diffusion [2], resulting in a faster oxygen thermal donor (OTD) formation [3][4][5][6]. At the same time, hydrogen-related Shallow TDs (STDHs) have also been observed [7][8][9][10][11][12][13], with ionization energies in the range 35-40 meV and infrared absorption peaks in the sub 300 cm -1 range typically.…”