Large area deposition in high vacuum with high thickness uniformity

Abstract

The invention relates to an effusing source for film deposition made of a reservoir comprising one hole characterized by the fact that the hole diameter is less than one order of magnitude than the mean free path of the molecules determined by the pressure and its thickness is at least one order of magnitude smaller than the diameter. Preferably the source has several holes.

Description

FIELD OF THE INVENTION [0001] The present invention relates to thermal or laser-assisted (electron or ion beam-assisted) film deposition with chemical precursors in the molecular regime. STATE OF THE ART [0002] The business and technology of large area vacuum coatings have made significant progresses in the last two decades and are still proceeding with great expectation for the future [1, 2]. In particular, we can mention typical applications as architectural and automotive glasses, solar cells, and micro-optoelectronics applications that require larger and larger substrates to reduce costs. [0003] It is commonly believed that the alternative approach of vacuum deposition is difficult to scale up to industrial applications. Furthermore, vacuum deposition is also known to be inherently more expensive and difficult with these two drawbacks increasing as lower pressures are aimed at. However the use of vacuum deposition has some advantages for industrial applications. Indeed, high-thr...

AI Technical Summary

Benefits of technology

[0074] An example to reduce molecules effusing at small angles is reported in FIG. 4 with a cone-like shaped forbidden volume. Any kind of structure could serve to reach this purpose. In the cone-case, the apex may be cut and a hole provides a pumping aperture. If the cone is positioned under the hole at a distance b≠0, we will have a progressive increase of the volume, as angle will increase that will depend on the ratio between the distance b and the mean free path λ. In particular, variable pressure configuration will lead to variable effect of the cone as the mean free path is changed. A particular case of this configuration could be a negative parameter b; i.e. the cone exits the pre-chamber through the hole. As multiple sources are to be used, mechanical complexity of multiple cones can be avoided by producing a continuous structure.

[0077] A particular shape of interest is a hemisphere (see FIG. 5). In particular asymmetric sources are easily produced leading to gas waste reduction.

Problems solved by technology

It is commonly believed that the alternative approach of vacuum deposition is difficult to scale up to industrial applications.

Furthermore, vacuum deposition is also known to be inherently more expensive and difficult with these two drawbacks increasing as lower pressures are aimed at.

As a summary, we can report the following points: CVD processes have a much higher production capacity, but suffer from poor utilization efficiency of the expensive and toxic reactants gases (L. M. Fraas, in U.S. Pat. No. 4,828,021).

In opposition, MBE devices are not easily scalable to meet the needs of the growing market.

Concentric annular arrays of sources have been proposed to provide different gases (Frijlink U.S. Pat. No. 4,961,399), but several problems are still open.

Rotation, or planetary motion, was also introduced to provide uniform thickness (Frijlink U.S. Pat. No. 4,961,399), but light processes are incompatible with such a motion.

This is the closest result found for patent to our proposed invention, but uniformity is only about 5-10% and is hence not suitable to many applications.

What can be said is that no global solution has been found up to now and the above cited patent document have only solved some of the specific mentioned problems.

In particular, viscous and transition regimes are poorly, if not at all, compatible with light (electron ion)-assisted processes.

Furthermore, flexibility is poor to achieve good thickness uniformity (inter-correlation of deposition parameters), while up-scaling to larger substrates or upgrading to new materials is not straightforward and can be very difficult.

These effects are however very limited to the working temperatures below 100-200° C. required avoiding chemical precursor adsorption and sufficient vapour pressure.

Another effect that can make fail attempts to produce uniform impinging rate on the deposition area is that molecules can bounce on walls inside the deposition chamber.

These scattered molecules would hence lead to uncontrolled deposition.

The difficulty in the molecular flow regime is to achieve simultaneously both high thickness uniformity and high growth rates [4], which are usually related to high efficiency use of precursor [4, 5], and high initial investment costs [1] as reducing the size of the reactor usually allows reduced equipment costs, but also leads to poor thickness uniformity.

Small apertures have not been used very often in physical vapour deposition sources because difficulties appear due to regulation of each source.

These sources are furthermore expensive and unstable as the vapour condensation and evaporation can modify the effusion.

Physical reasons may limit this tilting angle that is not always optimal for evaporation sources due to liquid geometry level considerations [5].

Finally, smaller sources compared to a single large source are interesting as light induced or light enhanced deposition is incompatible with substrate motion.

One of the problems in MBE sources is that the source angular distribution may vary to a large extent as a function of the filling level.

This leads to poorly controllable angular distributions of effusing molecules with time [23].

Another error that can account for different angular distributions is that the source dimension aperture can have a deep impact on the molecular distribution.

However, such collimated sources lead to several problems.

The obtained results reported by the scientific community with regard to thickness uniformity deposition are in general difficult to evaluate if the parameters of reactor size versus substrate size are introduced.

A systematic approach and a good understanding of these parameters are still lacking.

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