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Low Temperature Amorphous Optical Storage Films

IP.com Disclosure Number: IPCOM000038437D
Original Publication Date: 1987-Jan-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 3 page(s) / 36K

Publishing Venue

IBM

Related People

Ahn, KY: AUTHOR [+3]

Abstract

An optical storage medium comprises a substrate and amorphous Te and Si films deposited onto the substrate by sputtering of Si onto a thin crystalline film of Te which forms a TeSi structure on the order of 500 ˜ thick. Preferably, the Te crystals are relatively large-grained. The film is enhanced by the fact that the upper surface of the film is pure Si whereas there is a gradation of Si and Te below the upper surface down to the lower surface which contains a far greater percentage of Te. The Si serves as an antireflective surface which permits more energy to be absorbed in the amorphous SiTe which is more reflective. The crystallinity associated with pure Te films is avoided by amorphization of Te with an overcoat of Si deposited by an RF sputter gun with RF bias voltage.

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Low Temperature Amorphous Optical Storage Films

An optical storage medium comprises a substrate and amorphous Te and Si films deposited onto the substrate by sputtering of Si onto a thin crystalline film of Te which forms a TeSi structure on the order of 500 ~ thick. Preferably, the Te crystals are relatively large-grained. The film is enhanced by the fact that the upper surface of the film is pure Si whereas there is a gradation of Si and Te below the upper surface down to the lower surface which contains a far greater percentage of Te. The Si serves as an antireflective surface which permits more energy to be absorbed in the amorphous SiTe which is more reflective. The crystallinity associated with pure Te films is avoided by amorphization of Te with an overcoat of Si deposited by an RF sputter gun with RF bias voltage. The well-known optical storage film, Te, has large grains, and this contributes to laser-written holes of irregular shapes. One way to solve this problem is to make ternary alloys, such as TeSeAs. Such films are amorphous and said to offer good life time and well-defined holes for data storage. This is a method of amorphizing a thin film of Te (and possibly other materials) by sputter depositing a second layer with suitable bias voltage. Such bilayer films offer not only the extended life time due to the overcoating, but offer two ways of recording information. Fig. 1A shows an intended bilayer structure consisting of the low-melting-point Te film onto which a second layer, Si, is deposited. Fig. 1B shows the resulting structure due to sputter deposition. When the structure of the bilayer structure was analyzed by transmission electron miscroscopy, the films showed no crystalline structure as we expected in other bilayer structures. Further examination of the films by nuclear backscattering showed that the two layers became completely mixed, and acted as a single film, as shown in Fig. 1B. Fig. 2 shows the backscatter results for the film structure shown in Fig. 1B. The Te film was first deposited from a sputter gun with a typical cathode voltage of 200 to 250 volts, while that for Si was typically 1,000 volts. Furthermore, during the film deposi...