WO2013024235A1

WO2013024235A1 - Plasma processing apparatus

Info

Publication number: WO2013024235A1
Application number: PCT/GB2011/051548
Authority: WO
Inventors: Charles Edmund King
Original assignee: P2I Ltd
Priority date: 2011-08-16
Filing date: 2011-08-16
Publication date: 2013-02-21
Also published as: EP2745306A1; CN104011827A

Abstract

The present invention relates to an apparatus (10) for plasma processing an article(12), the apparatus comprisingra chamber(14) for receiving an article to be processed; electrode means (16) for generating an electricand/or magneticfield in said chamberwhen energised by alternating electrical energyfor establishing a plasma in said chamber so that said article can be processed; andvarying frequency generatingmeans (20) for generating alternating electrical energy for transmission tothe electrode means, said alternating electrical energy being generated at a plurality of different frequencies in succession, one frequency after another frequency, thereby producing a succession of standing waves in said chamber of a plurality of different wavelengths.

Description

PLASMA PROCESSING APPARATUS

Field of the Invention

This invention relates to an apparatus for plasma processing an article. Background of the Invention

Plasma processing of articles is known hereto. Processing may include functionalizing, removing or coating a surface of an article. Generally, a species (a vapour or gas) is introduced to a processing chamber and energised to form a plasma. In one known apparatus, a pair of electrodes is disposed inside the processing chamber and connected to a source of alternating electrical energy, such as an RF generator.

It has been found that the density of plasma established in the processing chamber varies such that a higher density plasma may be established at one location than another location. Locations on a surface of an article at which relatively high density plasma is established are more efficiently processed than locations at which relatively low density plasma is established.

Accordingly, processing of an article in the chamber may not be homogenous which is disadvantageous because the surface of such an article does not exhibit generally similar functionality over its full extent after processing.

Regions of high and low density plasma may result from the generation of standing waves in the processing chamber. In this regard, the regions of high density may coincide with an anti-node in a standing wave whilst the regions of low density may coincide with a node in a standing wave. However, the generation of standing waves in chambers would normally only be expected where the chamber size is sufficiently large to accommodate full, half or quarter waves. For instance, if the frequency of the applied electric energy is around 13.56 MHz then its wavelength is in the region of 22m. However, the inventors have found that plasmas alter the dielectric properties of free space and can exhibit effective permittivities or dielectric constants in the region of 4 to 5. Under these circumstances a 13.56 MHz frequency can generate standing waves in processing chambers. Many commercial processing chambers have dimensions from 0.5 to 4 metres and so standing waves are possible because the plasma permittivity reduces the effective wavelength. The problem of non-homogenous processing can to a certain extent be mitigated by processing an article for a longer duration so that the surface of an article coincident with low density plasma may be adequately processed. However, such a solution is not generally satisfactory since it will inevitably result in excessive processing of a surface coincident with high density plasma, which wastes resources and time.

Summary of the Invention

According to the present invention there is provided an apparatus for plasma processing an article, the apparatus comprising:

a chamber for receiving an article to be processed;

electrode means for generating an electric and/or magnetic field in said chamber when energised by alternating electrical energy for establishing a plasma in said chamber so that said article can be processed; and

varying frequency generating means for generating alternating electrical energy for transmission to the electrode means, said alternating electrical energy being generated at a plurality of different frequencies in succession, one frequency after another frequency, thereby producing a succession of standing waves in said chamber of a plurality of different wavelengths.

As a result of generating a plurality of different wavelengths anti-nodes and nodes of said standing waves occur at different locations in said chamber. In an embodiment, said varying frequency generating means can vary the frequency of transmitted electrical energy so that said electrode means generates an electromagnetic field in said chamber that varies over time.

In an embodiment, at a selected frequency said electrode means establishes a plasma which varies in density in said chamber and wherein, when the frequency of the electric field is varied, the density of plasma at respective locations varies over time.

In an embodiment, said varying frequency generating means can vary the frequency of transmitted electrical energy over a selected range of

frequencies during processing of an article in said chamber.

In an embodiment, said varying frequency generating means scans the frequency over a selected range of frequencies at a selected scanning frequency.

In an embodiment, said varying frequency generating means comprises a sweep generator circuit for scanning the frequency.

In an embodiment, the apparatus comprises matching means for matching an impedance of said electrode means with an impedance of said varying frequency generating means over said range of frequencies.

In an embodiment, said varying frequency generating means comprises a plurality of frequency generators for generating alternating electrical energy at different frequencies and a controller for controlling operation of said frequency generators in succession.

In an embodiment, said varying frequency generating means is for

transmitting RF electrical energy. In an embodiment, said varying frequency generating means is for generating electrical energy over a range of frequencies between around 13 MHz and 0.9 GHz.

In an embodiment, said varying frequency generating means is for

transmitting pulsed electrical energy with varying pulse width.

In an embodiment, said electrode means comprises a pair of electrodes, one of said pair of electrodes being connected for receiving alternating electrical energy from said varying frequency generating means.

In an embodiment, said electrode means comprises an inductive coil arrangement.

The present invention also provides a method for plasma processing an article using the apparatus described above, which comprises using varying frequency generating means for generating alternating electrical energy at a plurality of different frequencies in succession, one frequency after another frequency, thereby producing a succession of standing waves in a plasma processing chamber of a plurality of different wavelengths.

Other preferred and/or optional features of the invention are defined in the accompanying claims.

Throughout the description and claims of this specification, the words

"comprise" and "contain" and variations of the words, for example "comprising" and "comprises", mean "including but not limited to", and do not exclude other moieties, additives, components, integers or steps. Moreover the singular encompasses the plural unless the context otherwise requires: in particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. Optional features of each aspect of the invention may be as described in connection with any of the other aspects. Other features of the invention will become apparent from the following examples. Generally speaking the invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings). Thus features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. Moreover unless stated otherwise, any feature disclosed herein may be replaced by an alternative feature serving the same or a similar purpose.

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-

Brief Description of the Drawings

Figure 1 shows a capacitively coupled plasma processing apparatus; and

Figure 2 shows a plasma processing apparatus with an inductive electrode; and

Figure 3 shows a frequency sweeping circuit for the apparatus as shown in Figures 1 or 2.

Detailed Description of the illustrated embodiments

Referring to Figure 1 , apparatus 10 is shown for plasma processing an article 12. The apparatus comprises a chamber 14 for receiving the article to be processed. Electrode means 16 is provided for generating an electric field in the chamber 14 when energised by alternating electrical energy for establishing a plasma in the chamber so that the article can be processed. Frequency generating means 20 generates alternating electrical energy for transmission to the electrode means 16. The alternating electrical energy is supplied by an electrical connector 18.

The frequency generating means 20 generates alternating electrical energy at a plurality of different frequencies in succession thereby producing standing waves in said chamber of a plurality of different wavelengths wherein the anti- nodes and nodes of said standing waves occur at different locations in said chamber. This arrangement increases the variety of standing wave

wavelengths and reduces the residence time of standing waves in the chamber when the apparatus is in use. The frequency typically required to activate plasma species is in the RF range.

The frequency generating means 20 in one embodiment generates alternating electrical energy at a plurality of different frequencies in succession one frequency after another frequency. In this regard, the frequency generating means may scan the frequency over a selected range of frequencies at a selected scanning frequency. For example, scanning of RF frequency may between 13.56 MHz and 900 MHz depending on chamber size, with the scanning frequency being a fixed frequency in the range 0.01 Hz to 10Khz and more preferably in the range 0.01 Hz to 1 KHz. In currently preferred embodiments generators are adapted to transmit at 13.56 MHz or simple harmonics thereof.

The transmission may be pulsed, for instance, energy may be transmitted for a short duration which is sufficient to establish a plasma in the chamber followed by a pause during which no energy is transmitted. Accordingly, multiple standing waves are generated at each RF frequency interval thereby making thousands of nodes and antinodes which move around the chamber at the scanning frequency. The effect to minimise the residence time in any one location of standing waves in said chamber when the apparatus is in the use. In another embodiment, the frequency generating means comprises a plurality of frequency generators for generating alternating electrical energy at different frequencies and a controller for controlling operation of said frequency generators in succession. In this regard, a first of the generators may be operated for a pulse of 20 microseconds at a first frequency (e.g. 13.56 MHz) followed by operation of a second of said generators for a pulse of 20 microseconds at a second frequency (e.g. 60 MHz) and so on.

The frequency generating means may comprise a frequency generator for generating electrical energy at a frequency and a controller for controlling characteristics of the supplied energy. For instance, the frequency generating means may be a sweep generator feeding a wide band amplifier. The frequency generating means 20 may be integral with an RF or other generator as shown in Figure 1 or may be separate therefrom as shown in Figure 2. Accordingly, generally homogenously processing of an article 12 can be achieved.

The electrode means 16 may be a pair of generally vertically disposed plate electrodes as illustrated, although other suitable electrode arrangements may be adopted as required. For instance, more than two pairs of electrodes may be provided in any suitable orientation. Furthermore, a wall of the processing chamber may act as an electrode if the chamber wall is earthed. One electrode of a pair of electrodes is connected to receive alternating electrical energy from the frequency generating means 20. The other electrode of the pair is connected to earth.

Figure 3 shows an example of a frequency generating means 20 shown in Figures 1 or 2. In Figure 3, the frequency generating means 20 comprises a sweep generator circuit, such as an electronic circuit comprising a timer 28, an RF oscillator 30 and a voltage output stage 32.

Additionally, the frequency generating means 20 may be connected to wideband amplifier 21 and a matching network 23 which matching network forms a resonant circuit such that a proportion of the applied power is dissipated within the chamber. The proportion of delivered power may vary from -1 % to 100% and is maximised by use of the matching network.

During processing of an article, the frequency generating means 20 shown in Figure 1 varies the frequency of transmitted electrical energy so that the electrodes 16 generate an electric field in the chamber 14 that varies over time. At any given selected frequency, the electrodes 16 establish a plasma which varies in density from one region or location to the next region or location in the chamber. Therefore, at a selected frequency, the density in the chamber is not uniform. In order to homogenise the effect of plasma processing in the chamber at the surface of the article being processed, the frequency of the generated electric field is varied over time so that the density of plasma at respective locations in said chamber varies over time.

The frequency generating means 20 can vary the frequency of transmitted electrical energy over a selected range of frequencies during processing of an article 12 in the chamber.

This invention is applicable to any plasma source wherein the plasma is generated by electrodes such that electromagnetic wave propagation may occur because the effective wavelength in the plasma is reduced. The invention is applicable to capacitively coupled plasmas as shown in Figure 1 and also to standing wave phenomena generated by inductively coupled plasmas as shown in Figure 2.

Figure 2 shows a typical inductive plasma electrode apparatus 22 for plasma processing an article. Features which are common to apparatus 10 and apparatus 22 are indicated by like reference numerals. The main difference between Figures 1 and 2 is that the plasma is established by induction in the chamber. Accordingly, electrode means 16 is replaced by induction means 25. Further, in Figure 2, the frequency generating means 20 comprises a frequency generator 26 for generating electrical energy of fixed frequency and a programmable logic controller 24 for controlling the frequency and pulse width of the supplied electrical energy to the electrodes. Typically, pulse width modulation may be applied where the ratio of plasma on time to off time is from 0.01 % to 80%.

The invention has been described by way of several embodiments, with modifications and alternatives, but having read and understood these descriptions further embodiments and modifications will be apparent to those skilled in the art. All such embodiments and modifications are intended to fall within the scope of the present invention as defined in the accompanying claims.

Claims

1 . Apparatus for plasma processing an article, the apparatus comprising:

a chamber for receiving an article to be processed;

2. The apparatus as claimed in claim 1 , wherein said varying frequency

generating means can vary the frequency of transmitted electrical energy so that said electrode means generates an electromagnetic field in said chamber that varies over time.

3. The apparatus as claimed in claim 2, wherein at a selected frequency said electrode means establishes a plasma which varies in density in said chamber and wherein, when the frequency of the electric field is varied, the density of plasma at respective locations varies over time.

4. The apparatus as claimed in any preceding claim, wherein said varying

frequency generating means can vary the frequency of transmitted electrical energy over a selected range of frequencies during processing of an article in said chamber.

5. The apparatus as claimed in any preceding claim, wherein said varying

frequency generating means scans the frequency over a selected range of frequencies at a selected scanning frequency.

6. The apparatus as claimed in claim 5, wherein said varying frequency generating means comprises a sweep generator circuit for scanning the frequency.

The apparatus as claimed in claim 4 or any claim dependent thereon, comprising matching means for matching an impedance of said electrode means with an impedance of said varying frequency generating means over said range of frequencies.

The apparatus as claimed in any preceding claim, wherein said varying frequency generating means comprises a plurality of frequency generators for generating alternating electrical energy at different frequencies and a controller for controlling operation of said frequency generators in succession.

The apparatus as claimed in any preceding claim, wherein said varying frequency generating means is for transmitting RF electrical energy.

The apparatus as claimed in any preceding claim, wherein said varying frequency generating means is for generating electrical energy over a range of frequencies between around 13 MHz and 0.9 GHz.

1 1 . The apparatus as claimed in any preceding claim, wherein said varying

frequency generating means is for transmitting pulsed electrical energy with varying pulse width.

12. The apparatus as claimed in any preceding claim, wherein said electrode means comprises a pair of electrodes, one of said pair of electrodes being connected for receiving alternating electrical energy from said varying frequency generating means.

13. The apparatus as claimed in any preceding claim, wherein said electrode means comprises an inductive coil arrangement. Method for plasma processing an article using the apparatus according to any one of the preceding claims, which comprises using the varying frequency generating means to generate alternating electrical energy at a plurality of different frequencies in succession, one frequency after another frequency, thereby producing a succession of standing waves of a plurality of different wavelengths in a plasma processing chamber.