New sources may be cleaned and must be properly aged before they are used in testing or production. Refer to Product Bulletin Aging for instructions. In this process, the sources should be aged at the recommended deposition temperature for at least 16 hours but no longer than 24 hours.

Caution: Any time BoronPlus sources are exposed to temperatures above 600°C, silicon wafers should be placed between each pair of sources and at each end of the load.

Special Instructions

SI 1
The gas flow rate recommended is based on experience with a variety of different systems. Some customers have found that increasing the gas flow rate during insertion and withdrawal will further decrease the chances of moisture backstreaming from the mouth of the furnace. This technique is particularly useful if only an end plate is used to cover the cap of the furnace, or if the end cap is loose fitting.

SI 2
Initially, the indicated percentage of oxygen should be mixed into the carrier gas. The purpose of oxygen is twofold: to prevent silicon surface damage and to oxidize the boron-silicon phase that forms between the deposited glass and the silicon wafer. We suggest increasing the oxygen concentration only if silicon surface damage is observed. Once an acceptable sheet resistivity is achieved, the oxygen concentration may be further increased for high temperature depositions to minimize the thickness of the boron-silicon phase.

Care should be taken to avoid using too much oxygen. Excessive oxygen will not only convert the boron-silicon phase to B₂O₃ and SiO₂, but it will also oxidize the silicon surface. This thin oxide can mask off some of the boron resulting in non-uniform doping of the silicon.

The oxygen concentration should be high enough to eliminate silicon surface damage, and low enough not to cause non-uniform doping of the silicon. Remember that oxygen will not affect the BoronPlus sources.

SI 3
Variations in the humidity level of the plant air could cause variations in sheet resistivity. To reduce the effects of moisture, the following steps are recommended:

• After predeposition, cool the silicon and sources in dry nitrogen
• When not in use, always store the sources in dry nitrogen at an elevated temperature

SI 4
Use of a high oxygen concentration during a portion of the cooling time from the deposition temperature oxidizes the boron-silicon phase. It also minimizes silicon damage often associated with the formation of the phase.