This paper explains the analysis and elimination of BPO4 crystal formation in an Atmospheric Pressure Chemical Vapor Deposition BPSG film. Film deposition and furnace anneal/flow parameters were studied using full factorial techniques, with anneal/flow parameters having the most significant effect. It was learned that BPO4 crystals could be readily induced by performing the anneal/flow process in a POCl3/O2 ambient. Most testing was done in a POCl3/O2 ambient and inferences made concerning the standard anneal ambient.
BPO4 formation is primarily dependent on thermal processing during anneal toprovide the activation energy necessary to initiate crystal growth. Other factors include 02:Hydride ratio during film deposition, phosphorous concentration in the deposited film, deposition temperature, and anneal/flow ambient. No tested level of these secondary factors completely eliminated crystal formation.
The growth of BPO4 crystals can be eliminated by controlling the thermal environment ofthe anneal/flow step. The primary means employed was to increase the rate of heat dissipation by doubling the spacing between wafers. An alternative method involves utilization of reduced anneal/flow furnace temperatures.