Throughput Increases in Silicon Dioxide Deposition Systems​

Another common application for a multiple-stage vacuum pump trap is a CVD (chemical vapor deposition) process to deposit silicon dioxide onto silicon wafers. Silicon dioxide dust wears at a vacuum system, reducing pumping efficiency. Liquid silicon dioxide sources, such as tetraethylorthosilicate (TEOS), can recondense in the vacuum lines, causing valves to stick and product runs to be lost. With most silicon dioxide sources, multi-stage trapping reduces these problems, saving the user time and money.

SEMATECH, a semiconductor research consortium, installed a four-stage trap in a single-wafer TEOS reactor. The trap reduced the preventive maintenance frequency from once per shift to once every three months. SEMATECH estimates that the trap added 250 hours of operation per year to the system.

At another company, a batch reactor running TEOS averaged a pump failure every 6 months. To minimize these failures, the user performed preventive maintenance every 47 runs. To reduce the occurrence of pump failures, the user installed a three-stage trap, consisting of a knock-down stage, a stainless steel gauze filter and a 20-µm polypropylene filter. After installation of the trap, the user reported no pump failures for over one year and had increased the time between preventive maintenance sessions to every 88 runs.

In these examples, the cost savings include reduced line yield losses due to pump failure, reduced costs for pump rebuilding and a slight capacity increase.

A silane-based doped silica deposition process in a batch reactor provides similar results. One user had frequent pump failures and exhaust line clogging, despite the presence of a single stage trap in the vacuum line. This trap used only a knock-down stage and required cleaning every 6,000 nm of deposition, or every two days. Once installed, the multi-stage trap requires cleaning every 35,000 nm, which occurs only every ten days. Inspection during cleaning shows heavy silicon dioxide powder accumulates in the knock-down stage, followed by a light powder coating of the filter elements. No accumulation appears in the vacuum line outside the trap, giving a good indication that clogged lines have been eliminated as a source of vacuum line failure. This multi-stage trap saved the user $14,600 – more than four times the cost of the trap (see Table 1).