Silicon Nitride for MEMS Applications: LPCVD and PECVD Process Comparison

The MEMS industry grew by more than 10% in 2012, a year when the semiconductor industry experienced a 2% decline. The growth in MEMS was largely fueled by portable electronics with motion sensors and microphones in smartphones and tablets. Billions of MEMS devices have already been shipped and promising new applications in transportation, health care, sensor networks and structural monitoring have visionaries in the MEMS industry talking about trillions of MEMS devices. For the MEMS market to achieve the expected double digit annual growth, it is crucial that fabrication processes are both technically enabling and can support the demands of high volume device fabrication. One of the key factors in supporting this market growth is the extensive use of well-established CMOS and
CMOS-compatible processes for large-scale MEMS manufacturing. Semiconductor processing infrastructure, equipment and technology has contributed to the successful scale up from 4” to 6”, 8”, and 12” diameter wafers while maintaining high production yields.

It is widely known that semiconductor processing is sensitive to limited thermal budgets. Excessive temperature can adversely affect metallized and diffused regions. As a result, high temperature processes must be completed upstream in the process flow or be substituted by low-temperature alternatives downstream. Historically, deposition of dielectric films has had a significant impact on the thermal budget. Lately, the industry trend is to reduce the deposition temperature for this process step. For example, thermal oxides using furnaces at 1000°C or higher have been supplanted by lower temperature solutions, such as Low Pressure Chemical Vapor Deposition (LPCVD), in the 600°C to 700°C range. Processes in the “less than 400°C” range are also commonly available with Plasma Enhanced Chemical Vapor Deposition (PECVD). Evolution in this area continues and have recently produced solutions such as high density plasma CVD (HDPCVD) and atomic layer deposition (ALD).

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