interview RFMD
monitoring tools determine that the processes have deviated beyond acceptable windows for production. Customers can select the tool for epiwafer production from a portfolio of MBE reactors: a Veeco Gen2K, which has a 7 x 6-inch capacity; a Riber R7000 with identical capacity; a Riber R6000, which can accommodate four 6- inch wafers; and a single wafer, 6-inch tool, the VG V100. RFMD equips these tools with state-of-the-art monitoring apparatus. “Our MBE systems are outfitted with what we believe to be the most effective tools at delivering quality, consistent products,” claims Santana.
To ensure that the facility is run as efficiently as possible, the company’s process engineers interlace growths for the customers with those for internal production. “However, if the customer chooses, we can enter into an agreement that provides exclusive use of an MBE tool for a period of time,” reveals Santana. In fact, RFMD has already taken this type of arrangement with one of its MBE foundry customers.
The Greensboro outfit has an impressive toolkit for characterizing epiwafers. Alongside the more common methods for determining material characteristics, such as a Lehighton instrument for resistivity measurements and an X-ray diffraction tool, the company can analyze wafers with a multi-field Hall probe and a photoreflectance technique.
“Multi-field Hall is primarily used to give the mobility and carrier concentrations of the conductive layers in the epi,” explains Santana. It can, for example, be used to determine the mobility and carrier concentrations in both the channel and the highly conductive cap layer of pHEMT epiwafers. This is beneficial, because it eliminates the need to grow a ‘capless’ calibration structure. “In
addition, it is also an excellent method for process control,” argues Santana.
Photoreflectance, another non-destructive technique, provides a qualitative measurement of HBT gain. Samples are probed with a broadband light source, and insights into the structure are gleaned by collecting and spectrally analyzing light that has been reflected off of the many interfaces of the transistor. The data from all of these measurements can accompany material shipments to customers. And if the customer wants the data collected by the in-situ monitoring tools, including values for growth rates and temperatures, this can be sent as well.
In short, it seems that RFMD is willing to stay as flexible and accommodating as possible to meet the customer’s needs. At present the only tasks that the company is not prepared to do are to process GaAs wafers into chips and package them. But even this may become an option one day – after all, it certainly ties in with the company’s goal of diversification. Will it do it? We’ll just have to wait and see.
RFMD’s long-standing affair with MBE
When RFMD launched in the early 1990s, it had just one technology – the AlGaAs HBT. Initially this was produced on 4-inch wafers at TRW, but in 1997 RFMD transferred the MBE process to its own fabrication facility, known as fab 1. A larger facility, fab 2, was added two years later, in response to a rapidly growing order book.
During the last decade the company expanded its technology. In 2002 it added a second generation of AlGaAs HBT to its technology portfolio, and soon after that it started working towards the addition of switches to its product mix. Initially these were outsourced from the UK firm
The RF Micro Devices MBE Facility is located in Greensboro, North Carolina
Filtronic, but soon after RFMD started to develop an in-house production process and become less dependent on imports.
Further down the line RFMD acquired Filtronic’s 6-inch fab line, which it now uses to produce switches based on epiwafers grown at Greensboro. Filtronic’s line was equipped with two Veeco Gen2K systems, but one has been shipped across the Atlantic to support the foundry business.
Today RFMD manufacturers exclusively on 6-inch GaAs, and uses MBE to produce four generations of AlGaAs-based HBTs and two generations of pHEMT. The latest pHEMT combines switching characteristics with amplification to create products for WLAN.
October 2010
www.compoundsemiconductor.net 29
The throughput of MBE-grown material at RFMD has climbed over the last decade. The dip in 2008 resulted from a sharp decline in
handset orders, plus a move from within that industry to slash inventory levels. The continuous line shows actual wafer output, and the dashed line is a linear fit of this data.
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