Background of the Invention

This invention relates to the method and apparatus for depositing transparent dielectric films on polymers of the type that have deposition assemblies constructed of a laser, a polymer substrate and a target material Such structures of this type generally allow a dielectric film to be formed on the polymer substrate at a low temperature, typically around 200\'C. In particular, a polymer substrate is placed at a predetermined distance away from the target material and the target material is subjected to irradiation by the laser such that the irradiated area becomes ablated. As the target material is ablated, the ablated material impinges upon the polymer substrate to produce a dielectric film having a smooth transition surface interface between the film and the substrate. This invention relates to a certain unique dielectric film deposition apparatus and the deposition technique employed in association therewith.

It is known, in dielectric film deposition systems, to use a variety of deposition techniques to foπn the film on the substrate. In particular, well known deposition techniques such as: sputtering techniques, namely magnetron sputtering or ion-beam sputtering; evaporation techniques, namely, electron beam evaporation, and chemical vapor deposition techniques, namely, plasma enhanced chemical vapor deposition or thermal chemical vapor deposition; have been employed but these techniques usually require further processing steps, such as surface preparation. However, even after the surface preparation, the adhesion of the films, particularly on polymers, is poor. Therefore, a more advantageous system, then, would be presented if a dielectric film having good

adhesion could be produced on a polymer substrate at a lower process temperature, namely, around 200 ^* C.

The excimer laser ablation technique has been widely used for deposition of high temperature superconducting oxide films, particularly on, ceramics and semiconductors. The laser ablation deposition technique has been found to produce superconducting oxide films with a smooth surface morphology and a high critical temperature but with a high substrate temperature. To obtain oxide films with good superconducting properties, however, the deposition temperature has been found to be critical and usually must be maintained at temperatures, typically, above 400-500\'C. In addition, the high ablation energy may cause substantial decomposition of the polymer substrate and, therefore, up to the present invention, it precluded the use of polymers as the substrate material for laser ablation deposition. While many metals and ceramics are capable of withstanding such temperatures, polymers had to be specifically developed which could withstand these high temperatures which, in turn, added to the cost Also, prior to the deposition of oxide films on metals, ceramics, semiconductors, and polymer substrates at high temperatures, the surfaces of the substrate usually had to be treated. This surface treatment consisted typically of surface oxidation for the metal, polymers, and ceramic substrates or by cleaning, such as oxygen plasma cleaning. This surface preparation also added to die cost and time in producing the film on the substrate. Consequently, a further advantageous system would be presented if the advantageous excimer laser ablation technique could be used on polymer substrates in low temperature applications.

It is apparent from the above that there exists a need in the art for a dielectric film deposition system which efficiently produces a dielectric film, and which at least equals the performance characteristics of known dielectric film deposition systems, particularly those

of the highly advantageous excimer laser ablation system disclosed above, but which at the same time deposits a dielectric film on a polymer substrate or the like at a low temperature, namely, around 200\'C. It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.

Summary of the Invention

Generally speaking, this invention fulfills these needs by providing a low temperature, dielectric film deposition system for polymer substrates, comprising a polymer substrate having first and second sides, a target material at an ambient temperature having first and second sides such that said target is substantially located a predetermined distance away from said substrate, and said first side of said target is substantially parallel to and facing said first side of said substrate, and an irradiation means such that said irradiation means substantially ablates a portion of said first side of said target material and said ablated portion of said target material traverses said determined distance and contacts said substrate to form a dielectric film on said substrate.

In certain preferred embodiments, the substrate is heated to around 200\'C. Also, the target material is rotated as it is ablated by the laser. Finally, the target material and substrate are located substantially 5 cm apart.

In another further preferred embodiment, a dielectric film is formed over the surface of the substrate at a temperature that does not materially affect the mechanical properties of the substrate.

In a particularly preferred embodiment, the dielectric film deposition system for polymers of this invention consists essentially of a substrate, preferably polyimide or polyetherimide, a target material, preferably zirconium oxide (Z1O2) located at a predetermined distance away from, preferably 5 cm. and facing the substrate, and an

iiradiation device, preferably an excimer laser, such that the iιτadiation device irradiates a portion of the side of the target material facing the substrate and oblates that poπion of the target material with the ablated portion forming a plume of ablated vapor which contacts the surface of the substrate facing the target material and creates a dielectric film on that substrate surface.

The preferred dielectric film deposition system, according to this invention, offers the following advantages: good surface morphology of the film; excellent adhesion between the film and the substrate; good transparency; excellent economy; ease of use; and increased production rates, typically, a 100 A/sec. In fact, in many of the preferred embodiments, these factors of economy, ease of use and production rates are optimized to an extent considerably higher than heretofore achieved in prior, known dielectric film deposition systems.

Brief Description of the Drawing Figure 1 is a schematic view of a dielectric film deposition system, according to the present invention.

Detailed Description of the Invention

With reference to Figure 1, there is illustrated a dielectric film deposition system 2. In particular, a laser 4, preferably a conventional, excimer laser, focuses a beam 20 upon rotating target 6. The laser fluence of laser 4 is between 0.5 to 10 J/cm ² , preferably U/cm ² . The pulse repetition rate is between 10 to 100 Hz, preferably 40 Hz. Also, a conventional oxygen transport device (not shown) creates an oxygen atmosphere in system 2. The oxygen atmosphere is maintained between 0-1 Toir, preferably around 10 m Torr, which is measured near substrate 10.

Target 6, preferably is made up of zirconium oxide (Z1O2), is rotated by a conventional rotation means and is maintained at an ambient temperature, preferably 25 ^* C. The preferred dimensions of target 6 are 2" (in diameter) x 1/8" (thick), but it is to be understood that target 6 can be of a variety of thicknesses and diameters. As beam 20 strikes target 6, the irradiation of beam 20 causes the portion of target 6 that was irradiated by beam 20 to become ablated. The preferred portion of tϊtrget 6 which is ablated by one particular irradiation of beam 20 is 4mm (length) x 2mm (height) x 0 to 0.16mm (thickness). The thickness will vary depending upon the length of irradiation, among other factors. The ablated material of target 6 forms plume 16. Plume 16 contains ablated particles 22 of target 6 which exhibit high kinetic energy.

These particles 22 move across the distance between target 6 and substrate 10, which is preferably 5cm, and contact the surface of the substrate 10, which has been heated, preferably to around 200\'C by conventional, resistive heaters 12. Substrate 10 is held in position by a conventional support 14. Substrate 10 is preferably constructed of polyimide or polyetherimide. Also, the preferred dimensions of substrate 10 are 1" (width) x 1" (length) x 1/16 to 1/8" (thickness) It is to be understood that substrate 10 may be surface treated by the previously disclosed surface treatment methods in order to promote adhesion. As particles 22 contact the surface of substrate 10, a dielectric film 18 is formed which exhibits a smooth, transparent surface morphology. It is to be understood that target 6 is rotated so that as much of the surface area of target 6 which faces beam 20 can be ablated by beam 20. Also, the distance between target 6 and substrate 10 can be varied with the key factor being the surface area of the substrate. For example, if it is desired to coat a larger surface area of substrate 10 with film 18 during one ablation cycle, the operator merely has to increase the distance between substrate 10 and target 6. Finally, while particles 22 exhibit high kinetic energy and high temperature,

these particles 22 do not adversely affect the surface of substrate 10 because panicles 22 are relatively small compared to the entire surface area of substrate 10, so substrate 10 acts substantially as a heat sink for particles 22.

Once given the above disclosure, many other features, modifications and improvements will become apparent to the skilled artisan. Such features, modifications and improvements are, therefore, considered to be a part of this invention, the scope of which is to be determined by the following claims.