Impurity gettering

A more comprehensive purification procedure uses a sequence of steps as follows filtration at 200°C through a stainless steel powder compact filter of 10-jum pore size reduces the oxygen content and removes any solid impurities. Gettering with Zr foil for 46 h at 760°C reduces the oxygen concentration to 200 ppm. The weight ratio of K to Zr is 13 1 with a surface area to volume ratio of Zr to K 4 1. A second gettering with zirconium foil for 72 h at 800°C reduces the oxygen content 50 ppm. 

The tabulated summary on investigated impurity gettering by porous silicon can be found in Table 2. 

Impurity gettered by porous silicon Analysis technique Reference... 

Falster R, Laczik Z, Booker GR, Bhatti AR, Torok P (1992) Gettering and gettering stability of metals at oxide particles in silicon. Mater Res Soc Symp Proc 262 945 Follstaedt DM, Myers SM, Petersen GA, Medemach JW (1996) Cavity formation and impurity gettering in He-Implanted Si. J Electr Mater 25 157-164 Hampel J, Ehrenreich P, Wiehl N, Kratz JV, Reber S (2013) HCl gas gettering of low-cost silicon. Phys Status Solidi A, 210 767-770... 

In Proceedings of 12th EUPVSEC, Amsterdam, pp 1003-1006 Sumino K (2003) Basic aspects of impurity gettering. Microelectr Eng 66 268-280 Sumino K, Nippon Steel Corporation (1996) Impurity segregation/precipitation/gettering at dislocations. In Sixth workshop on the role of impurities and defects in silicon device processing, NREL, pp 5 17... 

In order to remove tlie unwanted electrical activity associated witli deep-level impurities or defects, one can eitlier physically displace tlie defect away from tlie active region of tlie device (gettering) or force it to react witli anotlier impurity to remove (or at least change) its energy eigenvalues and tlierefore its electrical activity passivation). 

Gettering is a black art. It consists in forcing selected impurities (typically, transition metals) to diffuse toward unimportant regions of tlie device. This is often done by creating precipitation sites and perfoniiing heat treatments. The precipitation sites range from small oxygen complexes to layers such as an A1 silicide. The foniiation of such a... 

Vacuum Tubes. In the manufacture of vacuum tubes for use in polarized ion sources, vaporized cesium is used as a getter for residual gaseous impurities in the tube and as a coating to reduce the work function of the tungsten filaments or cathodes of the tube. The cesium vapor is generated by firing, at about 850°C within the sealed and evacuated tube, a cesium chromate pellet and zirconium (12) (see Vacuum technology). 

Gettering. Gettering materials, such as zirconium or titanium alloys, are heated to 400°C. At that temperature, they react with the impurities in the gas stream such as O2, H2O, N2, H2, CO, CO2, and hydrocarbons. Total impurities can be reduced to <100 ppb. 

Even though a chemical gettering mechanism is proposed in some of these papers, it seems quite likely to us that the decrease of the concentration of these deep levels due to hydrogenation during MBE growth is due to a neutralization by hydrogen of the defects or impurities responsible for these electron traps. 

A high impurity concentration caused by gettering of impurities by a dislocation. 

Why does gettering trap transition metal and alkali metal impurities without seriously depleting implanted dopants ... 

Figure 9. Cut-away drawing of the vacuum vessel for the TFTR showing the location of high heat-load structures (bumper limiter, moveable limiter, and bellows covers) and one of 36 Zr—Al getter modules for impurity and density control.

---