Atomic Layer Deposition (ALD) is a self-limiting, sequential surface chemistry that deposits conformal thin-films of materials onto substrates of varying compositions. ALD is similar in chemistry to chemical vapor deposition (CVD), except that the ALD reaction breaks the CVD reaction into two half-reactions, keeping the precursor materials separate during the reaction. Owing to the characteristics of self-limiting and surface reactions, ALD film growth makes atomic scale deposition control possible. By keeping the precursors separate throughout the coating process, atomic layer control of film growth as fine as ~0.1 Å per monolayer can be obtained.
ALD is considered the deposition method that offers the greatest potential for producing very thin, conformal films, as well as the ability to control the thickness and composition of the films at the atomic level. A major driver behind the recent interest and acceptance of ALD in the IC industry is the prospects for ALD in the scaling down of microelectronic devices. Recent scientific studies have demonstrated that some types of ALD films have a good passivation potential, partially because of the negative charges that are present in some films. The potential for using ALD in solar applications to increase cell efficiency is high. The cyclical nature of traditional ALD systems, however, has relatively low growth rates, which makes it difficult to achieve the throughput numbers required by solar cell manufacturing environments. In the Levitrack ALD system the solar wafers will travel at high throughput between repeating series of gas zones. This unique “space separation” technology closes the gap between the low deposition rates of traditional “time separation” ALD processes and the high throughput requirements in solar cell manufacturing.