FIELD

The present disclosure relates to generally to atmospheric pressure non-thermal or thermal plasma apparatuses suited for modifying the surface of substrates or wafers, and in particular to a linear, atmospheric pressure, non-thermal or thermal plasma source or “plasma knife”.

BACKGROUND

Surface modification of substrates by means of corona and/or plasma discharge at atmospheric pressure has been widely used in industry for many years. In this technology a low frequency high voltage source is used to supply power to an electrode opposed by a grounded electrode. A corona discharge is formed between the two electrodes through which air is passed, causing air molecules to become ionized as they collide with the electrons flowing in the corona streams between the electrodes.

The charged particles or ions are then attracted to an oppositely charged electrode, usually positioned under the substrate to be treated. The charged particles or ions typically accelerate to a high velocity before impacting the substrate surface. In the case of a polymer substrate such as a plastic film, the impacts and/or other interactions of the charged particles break bonds in the top-most layer(s) of molecules in the plastic film. This results in an increased surface energy of the film surface, with a high degree of wettability, so that inks may be printed on and bonded to the plastic. In industry this result and/or this process is called surface activation.

Normally, untreated plastic has low surface energy causing inks to bead up and not bond to the surface. Measurement of wettability is usually determined by measurement of the contact angle of a droplet of the material being printed on the surface with lower contact angles indicating higher surface energies.

In the case of glass substrates, exposure to corona based plasma has been used for surface cleaning. Charged particles impacting the surface eject dust and other containments, leaving a cleaned surface behind.

A difficulty arises in cleaning glass surfaces when containments on the surface have their own inherent electrical attraction to the surface. Even after impacts from charged particles, industrial washing methods may still be unable to remove such contaminants. In such cases plasma processes using multiple ion species, excited at higher frequencies under reduced pressures, are often used. ISM frequencies (frequencies in the Industrial, Scientific, and Medical frequency band allocation by the FCC), such as 13.56 MHz or 27 MHz, are typical. The plasma is typically operated at reduced pressures such as 10−3Torr. The plasma gases are usually Ar mixed with O2and/or N2. In the case of organic contamination on the substrates the bombardment with ions results in the organic bonds being broken and then the O2ion species readily bonds with the carbon and effects removal of the contaminant from the substrate.

Such RF plasma processes have been highly successful for glass cleaning. However, the requirement of low pressure—treating glass substrates in vacuum conditions—adds significant capital and maintenance cost to the process. In addition, because the reactor requires time for vacuum pump down after loading a batch of substrates, time for processing, then time to bring the reactor back to atmospheric pressure for unloading, the reactor requires a relatively long production cycle. To take advantage of the ability of RF plasma to clean glass surfaces but without the low pressure requirement, industrial technology development has focused on atmospheric pressure RF plasma sources.

Atmospheric plasma sources include individual plasma jets and arrays of plasma jets. Individual jets are raster-scanned across a substrate to be cleaned. There are two drawbacks to this approach: (1) is the coverage overlap can result in non-uniform cleaning or activation from “streaking” and (2) raster scanning requires several back and forth passes adding significant cycle time to the process. Arrays of plasma jets have problems with non-uniform plasma density—plasma density is thinner between the jets. This also leads to uneven surface treatment and can require scanning in X and Y directions to produce uniform treatment of a substrate.

SUMMARY

An aspect of one embodiment of the present disclosure relates to an atmospheric pressure linear RF plasma source comprising an enclosure enclosing a chamber in the form of an extended slot having a width W, a length L, and a thickness T, with W≥20T. The enclosure has two opposing major walls enclosing the slot in a direction of the thickness of the slot, and two opposing minor walls enclosing the slot in a direction of the width of the slot. The enclosure has a top opening communicating with the slot for receiving a flow of a gas and a bottom opening communicating with the slot for delivering a flow of plasma, with the bottom opening being open to atmospheric pressure. Desirably, W≥30T, W≥40T, or even W≥ as much as 100T, or even more, as there is no physical limitation on the width of the linear plasma produced by the source of the present disclosure.

The enclosure of the source further has an interior surface comprising surfaces facing the slot of each of the major and minor walls, and an exterior surface comprising surfaces facing away from the slot of each of the major and minor walls. The two major walls of the enclosure comprise a dielectric material. Desirably the minor walls also can comprise a dielectric material.

In this aspect the source further comprises two or more pairs of pancake coils, each pair comprising a first and a second pancake coil positioned in an opposing relationship on opposite sides of the enclosure and oriented facing the outer surfaces of the major walls thereof.

In an additional aspect of this embodiment, the source can also comprise an RF power source connected to each opposing first pancake coil and second pancake coil and structured and arranged so as to be able to drive each opposing first pancake coil and second pancake coil in a directly out-of-phase (in an opposing phase) relationship.

An aspect of another embodiment of the source of the present disclosure relates to an atmospheric pressure linear RF plasma source comprising an enclosure enclosing a chamber in the form of an extended slot having a width W, a length L, and a thickness T, with W≥20T. The enclosure has two opposing major walls enclosing the slot in a direction of the thickness of the slot, and two opposing minor walls enclosing the slot in a direction of the width of the slot. The enclosure has a top opening communicating with the slot for receiving a flow of a gas and a bottom opening communicating with the slot for delivering a flow of plasma, with the bottom opening being open to atmospheric pressure. Desirably, W≥30T, W≥40T, or even W≥ as much as 100T, or even more, as there is no physical limitation on the width of the linear plasma produced by the source of the present disclosure.

The enclosure of the source further has an interior surface comprising surfaces facing the slot of each of the major and minor walls, and an exterior surface comprising surfaces facing away from the slot of each of the major and minor walls. The two major walls and the two minor walls of the enclosure comprise a dielectric material.

In this aspect the source further comprises an elongated solenoid coil surrounding the outer surface of the enclosure.

In an additional aspect of this embodiment, the source can also comprise an RF power source connected to the elongated solenoid coil.

In another additional aspect of any of the above embodiments, the source can also comprise an air knife connectable to a supply of working gas, with the air knife having an air knife output slot positioned to deliver a flow of working gas into the enclosure through the top opening of the enclosure.

In another additional aspect of any of the above embodiments, the first and second major walls can comprise quartz. Desirably the minor walls also can comprise quartz.

In another additional aspect of any of the above embodiments, T is selected so as to allow the source to be capable of providing a laminar flow of plasma from the lower opening of the enclosure.

In another additional aspect of any of the above embodiments, T is selected so as to allow the source to be capable of providing a laminar flow of plasma extending from the lower opening of the enclosure a distance of in the range of from 1 to 3 cm.

In another additional aspect of any of the above embodiments, T is selected so as to allow the source to be capable of providing a laminar flow of plasma extending from the lower opening of the enclosure a distance of in the range of from 2 to 3 cm.

Additional features and advantages are set forth in the Detailed Description that follows, and in part will be apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings. It is to be understood that both the foregoing general description and the following Detailed Description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims.

