PhosPlus (R) Brochure
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PhosPlus Sources Show Long Lifetimes

Industrial experience has shown that PhosPlus sources normally exhibit lifetimes in the range of 100-500 use hours. The actual lifetimes of PhosPlus sources used in typical plant production, however, depend upon many factors, such as temperature of use, care in handling, device being manufactured, the sensitivity of the process to the eventual decrease in the P2O5 evolution rate, etc.

The potential lifetime of a PhosPlus source can be estimated by periodically doping a silicon wafer with the source being held in a diffusion furnace and observing how the resulting sheet resistivity varies with time. Figure 1 shows the average sheet resistivity obtained on the silicon wafers doped for 60 minutes at 1020°C with TP-470 sources when used in a typical production environment. Little change in sheet resistivity was observed for the first 600 hours of use. The sheet resistivity then began to slowly increase as the P2O5 evolution rate was gradually decreasing.

A second method of estimating the lifetime of a source is to measure the amount of weight a source loses at a use temperature as the P2O5 evolves. Weight loss data for the TP-470 sources (Figure 2) indicate a continuing process of P2O5 evolution over hundreds of use hours.



Figures 3 and 4 show similar sheet resistivity and weight loss data for the TP-250 sources. These data also indicate that hundreds of hours of use can be obtained from a set of TP-50PhosPlus sources.





Doping Properties of PhosPlus Sources

Single Crystal Silicon: Typical sheet resistivity versus deposition time curves for the two PhosPlus sources are plotted in Figures 5 and 6. The curves are different for each source because the sheet resistivity of the silicon wafer for a given deposition cycle depends somewhat upon the thickness of the deposited glassy film. The thicker the glassy film, the lower the sheet resistivity. Figure 7 shows how the deposited film thickness varies with the type of source being used.

Typical deposition time for a solid-source diffusion system: A typical deposition time for a solid-source diffusion system is about 45 minutes. This time is usually long enough for the sources to uniformly dope the silicon wafers. At the same time, it is short enough to be compatible with most semiconductor process parameters. Figure 8 shows the sheet resistivity and junction depth that is obtained from a 45-minute deposition with the TP-470 PhosPlus sources at various deposition temperatures.







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