Activate and Anneal Ultrashallow Junctions with Lasers
Peter Singer, Editor-in-Chief -- Semiconductor International, 5/1/1999
The Equipe Division of PRI Automation (Mountain
View, Calif.) received five new orders for its vacuum cluster platforms
totaling more than $2 million. The orders were from XMR Corporation, CuTek
Research Inc. and three other OEMs.
PRI Automation Inc. (Billerica, Mass.) announced
the receipt of an order for an Automated Material Handling System (AMHS)
at the world's first 300 mm semiconductor pilot line. Semiconductor300
is a joint venture of Siemens' Semiconductor and Motorola's
Semiconductor Products Sector. The order is for an intrabay line and
includes the Turbo Stocker 300, TransNet material control software, and
PRI's new AeroLoader Overhead Hoist Transport (OHT) system.
Veeco Instruments Inc. received orders exceeding
$12.5 million for etch and deposition equipment from three leading U.S.
data storage companies. The orders are primarily for Veeco ion beam
deposition (IBD) and ion beam etching (IBE) products for advanced high
density magnetoresistive (MR) and giant magnetoresistive (GMR) thin film
magnetic head (TFMH) applications.
Today, most
ultrashallow source/ drain junctions (which may be only 50-100 nm deep for RTA)
are annealed after ion implantation with rapid thermal processors, which can be
either lamp-based or furnace-based. This step 'heals' the damage caused by the
ions and 'activates' the ion.
Company News
An alternative approach being developed by XMR Corp. (Fremont, Calif.) is called excimer laser annealing (ELA). The main advantage of ELA is that it offers the feasibility to suppress dopant diffusion because of its extremely rapid heating within a few nanoseconds. According to Bill Schaffer of XMR, excimer laser annealing heats the wafer at a rate of about 10 billion °C/sec, as opposed to 200-300°C/sec for a lamp-based RTP system. This enables very abrupt profiles. 'Laser dopant activation provides abrupt vertical doping profiles with junction depths in the vicinity of 30 nm. The dopant activation exceeds 80%.'
 |
| Fig. 1. This SIMS plot is a beam-line implanted boron profile before and after laser processing. The doped region has been preamorphized with germanium. |
Another benefit of the ELA approach is that it only heats the top hundred Angstroms or so of the wafer surface. 'You are no longer heating the entire substrate as you would be doing in a lamp-based or furnace-based scheme,' said Art Elsea, general manager at XMR. This keeps thermal budgets low.
Schaffer said that the ELA helps avoid the problems associated with defect-enhanced diffusion effects such as transient enhanced diffusion (TED). 'Many people can get either low sheet resistance in the source/ drains areas (i.e., a high activation of impurities) or they can get shallow junction depths,' he said. The ELA approach is designed to achieve both. 'Its potential advantage over conventional RTP technologies is that the temperature ramp rate is extremely high, negating the defect enhanced diffusion mechanisms that have negative activation energies. This enables abrupt profiles and low sheet resistance to be achieved simultaneously for device designs near the 0.1 µm technology node.'
The accompanying figure shows a SIMS plot of beam line implanted boron profiles before and after laser processing. The doped region has been preamorphized with Ge, which 1) ameliorates channeling effects during the implantation (resulting in shallower implants) and 2) provides a dopant 'stop' during laser annealing. Schaffer said the second feature works like this: 'The melting temperature of amorphous silicon can be as much as 200°C lower than for poly or single crystal silicon. The laser fluence is chosen to raise the amorphized silicon above its melting point but below the melting point of the undamaged silicon. The depth of the activated region is then controlled by the damage depth, which is a reproducible number using ion implant technology.'
Schaffer acknowledges that 'not everyone is comfortable with the concept of
melting parts of their device for dopant activation.' He said the company is
pursuing activation processes that are laser driven, but where the entire
transistor structure is kept in the solid state. 'Our best result to date is an
11 nm deep junction (1E18cm-3) with a sheet rho of 1.1 kohms/square.'
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