GB2244721A

GB2244721A - Plasma processing apparatus

Info

Publication number: GB2244721A
Application number: GB9109602A
Authority: GB
Inventors: Rudolf August Herbert Heinecke; Geoffrey Alan Scarsbrook
Original assignee: Northern Telecom Ltd
Current assignee: Nortel Networks Ltd
Priority date: 1990-05-03
Filing date: 1991-05-03
Publication date: 1991-12-11
Anticipated expiration: 2011-05-03
Also published as: GB2244285A; GB9109602D0; GB9010000D0; GB2244285B; GB9109603D0; GB2244721B

Abstract

An electrode structure for pulsed plasma processing comprises a pair of electrodes (23, 24) spaced apart by a number of conductive rods or studs (25) (Fig 2). The structure provides an intense plasma discharge confined in the space between the electrodes and adjacent a substrate (15) to be treated. Water cooling of the electrodes may be provided. In a modified construction the electrode is provided with a surface recess, which may lake the form of an annular channel, which further concentrates the discharge adjacent the substrate. This electrode structure finds particular advantage in deposition of carbon phosphide (CPx) where problems have been experienced in conventional processes with mutual etching of carbon and phosphorus and with sputtering. The electrode bodies, except on their opposing faces, may be provided with an encapsulating body of insulating material such as PTFE. <IMAGE>

Description

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invention relates to pulsed plasma processing and in particular to an electrode structure e.g. for effecting pulsed plasma deposition.

The pulsed radio frequency plasma technique is finding increasing use in chemical synthesis application. The technique employs repeated high intensity bursts of radio frequency energy separated by 'off' or 'rest' periods. Each energy burst produces substantially complete dissociation of a plasma to which it is applied. The reactive species so formed then react to form compounds which may be deposited on a substrate surface. The process is described in our specification No. 2 105 729 B.

The object of the present invention is to provide an improved electrode structure which reduces ion bombardment of a deposited material and enhances the deposition process.

According to the invention there is provided an electrode structure for plasma treatment of a substrate body, the structure including first and second electrode bodies coupled via a plurality of conductive rods or studs whereby to define between the bodies a space for receiving a substrate to be treated, the structure being adapted to confinei in use. a plasma discharge to the space between the electrode bodies.

The inwardly directed faces of either or both electrode bodies may be provided with one or more recesses. This provides a hollow cathode effect and improves the efficiency of the plasma process. The structure is of particular application in the preparation of phosphide materials from a radio frequency plasma.

Reference is here directed to our copending application No. of even date which describes the preparation of non-stoichiometric phosphides by deposition from a pulsed radio frequency plasma. That application derives priority from application No. 90 10000.9 Embodiments of the invention will now be described with reference to the accompanying drawing in which:Fig. 1 is a schematic diagram of a pulsed plasma deposition apparatus Fig. 2 shows an electrode assembly for use in the apparatus of Fig. 1.

and Fig. 3 shows a modified electrode assembly.

Referring to the drawings. the plasma deposition apparatus includes a reactor chamber 11 having an inlet 110 whereby gases are supplied to the chamber. and an outlet 111 whereby the chamber may be evacuated via a vacuum pump 12. A throttle valve 13 controls the evacuation rate and thus controls the gas or vapour pressure within the chamber 11. Typically the reactor chamber comprises a tube 112 sealed by end plates 113 and 1 1 - 3 114, the inlet and outlet being provided in one end plate (113). Deposition is effected via an electrically conductive electrode structure 14 within which a substrate 15 is mounted. Pulsed radio frequency energy is applied to the electrode structure 14 from a generator 17 via a conductive support pillar 142. Advantageously the electrode structure is water cooled to prevent excessive heating of the substrate 15. A plasma generated in the reactor chamber is formed between the electrodes. Typically we employ an energy density of about 100 to 300 watts/cc to achieve substantially complete dissociation of the plasma. In some applications an impedance matching transformer (not shown) may be employed to couple the generator 17 to the electrode structure 14.

In some applications the electrode structure may be cooled below ambient temperature.

Reactant materials are supplied to the chamber in gaseous form, e.g. as hydrides and/or alkyls. The reactants may be supplied as a uniform mixture or in the form of pulses of different composition, the gas pulses being synchronised with the generator pulses.

Fig. 2 shows in detail the electrode assembly for use in the deposition apparatds of Fig. 1. Referring to Fig. 2, the assembly includes first and second generally cylindrical electrode bodies 23 and 24, e.g. of copper coupled together by a number of conductive rods or studs 25 to define a space between the electrode bodiesfor receiving a substrate 15 to be processed. Typically there are three studs 25 symmetrically disposed. The upper electrode body 24 is attached by screws 30 which engage corresponding tapped holes in the studs 25. Electrical connection to the assembly is provided via a conductive tube 27 to which the lower electrode body 23 is attached. The pillar 27 also provides a means of mounting - 4 the assembly in the plasma reactor. Advantageously the electrodes. apart from their inwardly directed facest and the support pillar are encased each in a body 28, 28a of insulating material e.g. PTFE.

We have found that. in use. application of pulsed radio frequency energy to the assembly via the tube 27 generates an intense discharge in the space between the electrode bodies. Although the structure confines the discharge to the electrode region, it permits a free flow of gas to allow interchange between reactant gas and spent reaction products.

The lower electrode body 23 is hollow defining a cavity 31 which may be supplied with a coolant fluid via pipe 29 disposed within the tube 27 to effect cooling of the electrode during plasma deposition. The electrode may be maintained at or below ambient temperature.

Figure 3 shows a modified electrode construction which provides further concentration of the discharge adjacent the substrate and further reduces electrical bias. In this arrangement one or both of the electrode bodies 23, 24 is provided with a recess 32, 32c, e.g. in the form of an annular channel.

We have found that the electrode structures detailed above are of particular advantage in the deposition of difficult materials, such as carbon phosphide (CP X) where problems have been experienced in conventional processes with mutual etching of carbcn and phosphorus and with sputtering.

It will of course be appreciated that the electrode structures are of general application to pulsed plasma processing and that they are not limited to the production of phosphide materials.

Claims

1. An electrode structure for plasma treatment of a substrate body, the structure including first and second electrode bodies coupled via-a plurality of conductive rods or studs whereby to define between the bodies a space for receiving a substrate to be treated, the structure being adapted to confine, in use, a plasma discharge to the space between the electrode bodies.

2. An electrode structure as claimed in claim 1, wherein one said electrode body is provided with cooling means.

3. An electrode structure as claimed in claim 1 or 2, wherein said electrode bodies, except on their opposing faces, are provided each with an encapsulant body of insulating material.

4. An electrode structure as claimed in claim 3, wherein said insulating material comprises PTFE.

5. An electrode structure as claimed in any one of claims 1 to 4, wherein at least one of said electrodes is provided with a surface recess.

6. An electrode structure as claimed in claim 5.

wherein said surface recess comprises an annular channel.

7. An electrode structure substantially as described with reference to and as shown in Fig. 1 or Fig. 2 of the accompanying drawings.

8. Pulsed plasma processing apparatus provided with an electrode structure as claimed in any one of claims 1 to 7.

Published 1991 at 7be Patent Office. Concept House, Cardiff Road, Newport, Gwent NP9 I RH. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point, ewnifelinfach, Cross Keys. Newport. NP1 7HZ. Printed by Multiplex techniques lid, St Mary Cray. Kent.