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APPLIED Materials has announced its Vantage Vulcan rapid thermal processing system, which heats silicon wafers from the back for improved control and production yields.
Rapid Thermal Processing
According to Sundar Ramamurthy, vice president and general manager for Applied Materials’ Front End Products, Silicon Systems Group, Rapid Thermal Processing (RTP) is a process where silicon wafers are heated to ultra-high temperatures in just a few seconds. This spike anneal process is critical for enabling transistor performance.
“One of the key elements of the spike anneal process is the peak temperature repeatability. To be able to hit this temperature reliably, repeatedly, wafer after wafer, and make sure it has the exact profile,” Ramamurthy said in the announcement webcast.
End-market driving chip designs
Ramamurthy said the demand from the end-market for mobile devices which cram more functionality into smaller spaces means increasing numbers of functions need to be built in on the die level, increasing the density of features on chips, and the actual physical size of the chips on the wafers.
“If you think about what is happening at the die level, the features, the functionality, one of the reasons the die sizes and chip sizes are becoming larger is because of the portability that the end markets need in these new devices,” Ramamurthy said. “Therefore you need to put multiple functionality in a given chip – the chip needs to access information, store information and display information – all of that is required of the single chip.”
The importance of being consistent
For chip manufacturers, transistors with the same design should perform identically in all areas of the wafer, in order to maximise yield.
This is becoming a major challenge at the 20nm era (28nm and below) since transistors are smaller and more sensitive to temperature variations while many logic chips are also larger in size, making uniformity across the die increasingly difficult.
Additionally, materials commonly used on wafers for different features react differently to heat. For example, silicon absorbs heat, while poly on oxide reflects heat.
Direct radiant heating from traditional frontside RTP approaches can thus cause variations in temperature, or "hot spots," on a patterned wafer – leading to significant variations in the electrical performance of the transistors – and resulting in many low-end chips on the wafer.
The flip
According to Applied Materials, its Vantage Vulcan system flips the concept over, by applying the heat during RTP to the unpatterned backside of the wafer, resulting in temperature uniformity throughout the wafer.
Using the company’s proven honeycomb lamp array, the system can control within-die temperature to less than 3°C – even while the wafer temperature is aggressively ramping at more than 200°C per second.
In addition to being the first RTP system to heat the wafer entirely from the backside, the Vantage Vulcan system’s unique closed-loop control can dynamically control wafer temperature as it ramps from almost room temperature to 1,300°C.
This enables any device wafer, including wafers with challenging reflective surfaces, to be processed without recipe modification.