Backside Heating Maintains Even Temperatures Across Wafer
Applied Materials launched its Vantage Vulcan rapid thermal processing (RTP) system, employing wafer backside heating to improve the temperature uniformity across individual die.
Sundar Ramamurthy, general manager of Applied’s Front End Products Group, said die sizes have grown larger in recent years, making it more challenging to control the annealing temperature across the dense and less-dense areas of the die. That led Applied to develop a backside heating RTP system, a first for the industry, which resolves pattern-loading effects.
Compared with direct radiant heating, the backside heating approach reduces the hot spots across the patterned wafer, reducing the transistor performance variations, which often result in more poor-performing chips on the wafer, he said.
The honeycomb-like array of lamps is configured into 18 zones, controlling a much wider range of temperatures — from 75°C to 1,300°C — compared with Applied’s earlier RTP systems. By using backside heating, the temperature variability was reduced from 9°C to <3°C, even while the wafer temperature is aggressively ramping at more than 200°C/second, to a maximum of 1,300°C.
Channel depth is an important issue, particularly as leading-edge companies go to fully depleted architectures with thin vertical or planar channels. RTP heats the silicon channel’s top atomic layers, activating dopants and transforming the silicon from an insulator to a semiconductor. Differences of just a few degrees Celsius can change the channel depth enough to make a major difference in leading-edge ICs.
Ramamurthy said contact materials also are coming in that require lower temperatures. “This ability to operate at less than 250°C is huge for our customers” as they seek to reduce contact resistance, he said. RTP converts a contact silicide material, such as nickel platinum, to a more robust nickel mono silicide, improving the contact resistance.
Shankar Muthukrishnan, the global products manager for Applied’s RTP products, said “Vulcan turns RTP upside down.” The lamp array is positioned underneath the wafer’s backside, where the pattern is uniform, eliminating the variability that comes from front-side heating.
“We can match every feature to within 3°C, even when we are heating up the wafer at a rate of 200°C, up to the maximum temperature of 1,300°C.
The Vantage Vulcan includes closed-loop control, which dynamically controls the wafer temperature as the tool ramps from near room temperature to 1,300°C. The capability enables any device wafer, including wafers with challenging reflective surfaces, to be processed without recipe modifications — a benefit for the high-mix, fast-changing environment of foundries, Ramamurthy said.
Applied has been working with early customers, and the company has received repeat orders from customers beginning to ramp their 28nm technology to volumes, he said. He estimated the RTP-served available market at $500 million.
– David Lammers