Excimer Helps Grow Diamond Thin Films
Michael D. Wheeler
Diamond's unique properties make it an ideal, if not fully implemented, solution for many electronics applications. Diamond thin films produced by pulsed laser deposition in a hydrogen environment promise entirely new applications and significant improvements to others. These include transistors that operate much faster and at higher temperatures than those constructed from silicon, as well as the development of "cold" cathodes for future flat panel displays.
This excimer laser from Lambda Physik offers the same repetition rate and wavelength as its predecessor, the LPX 100.
Until recently, researchers considered the presence of hydrogen crucial to the growth of diamond crystals. Now a team led by Mamoru Yoshimoto from Tokyo's Institute of Technology has found a way to circumvent the role of hydrogen through an approach that uses pulsed laser deposition in a dilute oxygen atmosphere.
At the heart of the experimental setup is a Lambda Physik LPX 100 KrF excimer laser, which is focused through a quartz window on the side of a deposition chamber. Inside the chamber is a pyrolytic graphite target with a synthetic sapphire wafer positioned next to it. The high energy of the laser beam excites the carbon species in the target, creating a plume of greenish-white plasma that deposits on the sapphire substrate. This process is repeated until a diamond thin film forms.
The researchers discovered that by increasing the substrate temperature and altering the pressure of the oxygen in the chamber, they could affect growth rate. These variables, as well as the excimer's 248-nm wavelength and 100-Hz repetition rate, enabled efficient photoablation.
"In the field of high Tc oxide thin- film processing by pulsed laser deposition, the excimer UV laser is known to be powerful and useful," Yoshimoto said.
Although commercial production of the model used in the experiments was discontinued last year, Lambda Physik has rolled out two new ones, which Klaus Pippert, a senior vice president, said are suitable for epitaxial diamond growth.
"It's a question of throughput if you want to process large areas," explained Pippert. The higher the repetition rate, the faster photoablation and the resulting deposition can occur.
Yoshimoto's use of excimers also encompasses other research to develop functional oxide films for use as high technetium oxide superconductors and ferroelectric oxides.
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