WO2004097067A1

WO2004097067A1 - Gas evacuation device

Info

Publication number: WO2004097067A1
Application number: PCT/IT2003/000264
Authority: WO
Inventors: Sebastiano Luridiana
Original assignee: Microcoat S.P.A
Priority date: 2003-04-29
Filing date: 2003-04-29
Publication date: 2004-11-11
Also published as: AU2003228098A1

Abstract

A device (1) for evacuating the mixture of process gases present inside a reaction chamber (2) in which the disposition of thin coatings on objects or substrates to be coated takes place, the reaction chamber (2) comprising means (3) for injecting gases, which means have a plurality of injectors (4), a first electrode (5) supplied with voltage at radio frequency and at least a second electrode (6) at a potential different from that of the first electrode (5), and also suction means (10) for drawing the mixture of process gases, the evacuation device (1) comprising an evacuation duct (7), connected to the suction means (10), which extends inside the reaction chamber (2) and which is provided with a plurality of openings (8) in fluid communication with the chamber (2).

Description

Gas evacuation device

TECHNICAL FIELD

The present invention relates to a device for evacuating the mixture of process gases present inside a reaction chamber used for the deposition of thin coatings on objects or substrates by means of a deposition process known in the art as "plasma enhanced chemical vapour deposition - PECVD" .

More particularly, the present invention relates to a device for evacuating the mixture of process gases present inside a reaction chamber in which the deposition of thin coatings on objects or substrates to be coated takes place, the reaction chamber comprising means for injecting reaction gases, which means have a plurality of injectors, a first electrode supplied with voltage at radio frequency and at least a second electrode at a different potential from that of the first electrode, and also suction means for drawing the mixture .

In addition, the present invention relates to a device for injecting process gases into the reaction chamber.

The invention is used principally, although not exclusively, in the field of deposition by means of the PECVD technique on objects that are subject to wear and/or to corrosion.

PRIOR ART

It is known that the technique of coating substrates by PECVD, in addition to being widely used for producing thin coatings on the surfaces of semiconductors, is receiving ever greater attention in the field of decoration, in particular for metal objects of everyday use. One of the better known and more commonly used PECVD techniques is that based on the triggering of a discharge at radio frequency, generally at 13.56 MHz, in a low-pressure chamber containing a gaseous mixture for the formation of a plasma.

The discharge, which is initiated between an electrode to which a radio-frequency voltage is applied and a second electrode which is maintained at earth, produces various effects on the molecules ^' of the process gases introduced into the chamber, such as ionization, dissociation and excitation, thus generating reactive species.

The reactive species generated by the discharge combine with one another by chemical reactions, condensing on the surface of the substrate to be coated in such a manner as to form the desired coating.

The reactor is formed by a system which controls the inflow of the gases, by a deposition chamber which contains the substrate-carriers accommodating the substrate or a plurality of substrates, by a suction system and by a generator of radio-frequency power for the discharge.

Therefore, in order to obtain products of satisfactory quality, it is necessary to keep under control all of the quantities that figure in the deposition process.

Hitherto, particular attention has been paid to the value of the pressure of the gaseous mixture, which determines the mean free path for the collisions between the gaseous molecules; to the flow value of the various gases, which influences the chemical composition and the speed of growth of the coating and which, together with the evacuation system, determines the residence time of the gaseous species in the reactor; to the value of the radio-frequency power, which influences the structure of the coating by means of self-bias phenomena known in the art, and the rate of dissociation and therefore, in the final analysis, the speed of growth; to the value of the temperature of the substrate, which influences the surface mobility of the condensing substances and the speed of the chemical reactions which take place on the growth surface.

Unfortunately, although an appropriate choice of the process parameters indicated above is made, the operative conditions effective in the deposition chamber are also substantially different from place to place, owing to unsuitable systems for the injection of the process gases and the subsequent suction of the associated exhaust gases and owing to the unsuitable geometry of the electrodes .

The process gases have to be injected into the reaction chamber and the "exhaust" gases, which have already reacted or which are at any rate no longer useful to the process, have to be evacuated. Those operations have to be carried out in such a manner as to leave the operative conditions in the chamber as uniform as possible and as close to the optimum values as possible.

According to a solution known in the art, the evacuation of the exhaust gases, which are almost always in admixture with non-reacted gases, from the reaction chamber is carried out by suction through a discharge mouth of suitable diameter located in a wall. of the reaction chamber.

This solution involves some difficulties and disadvantages. It brings about a different rate of change in the various places inside the chamber because the suction force near the discharge mouth is markedly higher than that present inside the chamber and above all than that present in the region furthest away from the mouth.

Furthermore, this known solution causes a loss of the process gases which have just been injected and which may accidentally have reached the vicinity of the discharge mouth.

A further known • technical solution provides for the introduction of the process gases into the reaction chamber by means of a plurality of gas-injector elements that are arranged symmetrically inside the deposition chamber. Those injectors, which are tubular in shape, each have a plurality of ejector holes that are spaced from one another by a distance of variable length, distributed over the tubular surface of the injector element and aligned in a single direction which is parallel with the longitudinal axis of the injector element and which faces the centre of the chamber .

Nor is this known solution sufficient to avoid some difficulties and disadvantages, either from the point of view of the non-uniformity of distribution of the injected gases inside the chamber, or from the point of view of the failure . of the gases to reach substrates arranged at a long distance from the direction of injection of the gases.

Finally, the known solutions explained above do not permit adequate conditions of uniformity of the electrical field and of the process gases inside the deposition chamber, with consequent unacceptable differences in the characteristics of the layer deposited on various regions of the substrate. DESCRIPTION OF THE INVENTION

The present invention proposes to solve the above-mentioned problems which are typical of the devices known in the art, when applied to a reaction chamber in which a plasma enhanced chemical vapour deposition takes place, and therefore to provide a device for evacuating the mixture of process gases present inside the reaction chamber, which device is efficient and reliable.

The present invention also makes available an improved device for injecting the process gases into a PECVD reaction chamber.

Finally, the invention describes a particular geometry of the evacuation system, which geometry is suitable for obtaining improved uniformity of the electrical field inside the chamber.

This is achieved by means of a device for evacuating the mixture of process gases, which device has the features indicated in claim 1.

The dependent claims outline particularly advantageous embodiments of the device according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features a d advantages of the invention will become clear on reading the following description which is given by way of non-limiting example with the help of the drawings illustrated in the appended drawings, in which: - Figure 1 shows a diagrammatic vertical section through a reaction chamber comprising a duct for evacuating the mixture of process gases according to a first embodiment of the present invention;

- Figure 2 shows a diagrammatic vertical section through a reaction chamber comprising a duct for evacuating the mixture of process gases according to a second embodiment of the present invention;

- Figure 3 is a diagrammatic sectioned view taken along the line III-III of Figure 1;

- Figure 4 is a diagrammatic front view of a process gas injector of the injection device of Figure 1 with a particular distribution of the gas-ejector holes;

- Figure 5 is a sectioned view taken along the line V-V of Figure 4 ;

- Figure 6 is a diagrammatic view in vertical section of a process gas injector according to one embodiment of the present invention.

METHOD OF IMPLEMENTING THE INVENTION

Referring to Figures 1 and 2, 1 generally indicates a device for evacuating the mixture of process gases from a reaction chamber 2 in which a PECVD takes place.

The reaction chamber 2 comprises means 3 for injecting reaction gases, which means 3 have a plurality of injectors 4 from which the reaction gases are discharged. The injection means 3 are connected by a duct, indicated diagrammatically by 3b, to a plurality of gas sources 12, 12a each containing a different process gas.

The reactive species generated by electrical discharge react inside the chamber 2 in accordance with chemical reactions known to the person skilled in the art and condense in the form of a thin layer on substrates to be coated (not shown) placed in the chamber 2.

The gases used for the PECVD process are, for example, SiH₄, Si₂H₆, PH₃, CH₄, He, H₂, NF₃ , GeH₄, Ar, N₂, 0₂ and vapours of organometal compounds .

The reaction between the process gases takes place thanks to an electrical discharge which takes place in the reaction chamber 2 maintained under vacuum at a pressure which is typically from 10^"3 to 2xl0^_1 mbar and preferably from 5xl0^~3 to 5xl0^"2 mbar. The discharge is achieved between a first electrode 5 supplied by a radio-frequency power generator 11 and a second electrode which is maintained, for example, at earth potential .

In the example of the present invention, the first electrode is constituted by means carrying objects or substrates to be coated placed inside the reaction chamber 2. The object- carrying or substrate-carrying means are constituted, for example, by a spider structure having a plurality of object- carrying arms 6 which extend vertically inside the chamber 2 and on which the substrates to be coated may be placed by devices known in the art. The spider structure is supported by a conductive support element 13, for example of copper, which is supplied with voltage at radio frequency by the source 11 arranged outside the reaction chamber 2. The support element 13 is anchored to the upper wall of the chamber 2. Naturally, the support element 13 of copper is not in electrical contact with the upper wall of the chamber 2 and it is therefore expediently insulated by means of a ceramic bush to which the support element 13 is connected by techniques known in the art .

The function of second electrode is, on the other hand, performed by the inner walls 2a of the reaction chamber 2 , which are at earth potential. With that configuration, the objects or substrates to be coated will be, during deposition, at a potential equal to that of the first electrode 5.

Alternatively, depending on the type of process that is to be carried out, the objects or substrates may be placed on an electrode maintained at earth like the walls of the chamber 2 or even on a third electrode, not illustrated because it is of a conventional nature, which is at a potential different both from that of the first electrode and from that of the second electrode.

The device 1 for evacuating the mixture of process gases comprises suction means generally indicated 10. The suction means 10 are known in the art and therefore will not be described in greater detail .

Advantageously, the evacuation device 1 comprises, according to the present invention, an evacuation duct 7 connected to the suction means 10. The duct 7 extends inside the reaction chamber 2 and is provided with a plurality of openings 8 in fluid communication with the inside of the chamber 2.

According to a first embodiment, the evacuation duct 7 extends inside the chamber 2 along a central vertical axis Z-Z of that chamber 2, as illustrated in Figure 1. The duct is at earth potential, like the walls of the chamber 2. The openings 8 of suitable diameter are disposed along the entire length with which the duct 7 extends inside the chamber 2. The optimum diameter of the openings 8 is from 0.5 to 5 mm, preferably from 1 to 3 mm. There may be only one amount and arrangement of the openings 8, whatever the type of deposition to be carried out, or the amount and arrangement may differ from case to case . Owing to the presence of the openings 8 arranged along the evacuation duct 7, it is possible to distribute the suction force along a large inner region of the chamber 2, thus ensuring a more uniform distribution of the process gases.

According to a second embodiment of the present invention, illustrated in Figure 2, the evacuation duct is indicated 7a. This duct is at a potential equal to that of the inner walls 2a of the reaction chamber 2 and has a cylindrical shape which extends vertically inside the reaction chamber 2.

In this second embodiment, the diameter of the cylindrical evacuation duct 7a is such that the object-carrying arms 6, on which the objects or substrates to be coated are placed, are in a position which is substantially equidistant between the surface of the evacuation duct 7a and the inner walls 2a of the chamber 2.

In that case, because the evacuation duct 7a is equipotential with the reaction chamber 2, it constitutes a further, "cold" electrode which makes it possible to improve the uniformity of the electrical field on the substrates to be coated.

In order to permit improved distribution of the reaction gases inside the reaction chamber 2, the injection means 3, which are in fluid communication with the gas sources 12, 12a, are constituted by a spider structure which is arranged inside the chamber 2 and which is formed by tubular arms 3a arranged near the inner wall 2a of the chamber 2 and distributed around the vertical axis Z-Z thereof.

In addition to the above-mentioned spider structure of the injection means 3, it is possible to provide a similar structure (not shown) which is placed near the evacuation duct 7 or 7a in order further to improve the uniformity of injection of the process gases.

Advantageously, the injectors 4 are arranged along the tubular arms 3a on a zig-zag path Y, as shown in Figure 4 with a broken line. The path Y extends over that half of the vertical surface of each tubular arm 3a which faces the axis Z-Z of the chamber 2 and, in particular, it extends over a circumferential arc subtended by an angle of 90°.

Finally, it is possible to achieve a more uniform distribution of the process gases by arranging the injectors 4 on the surface of the tubular arms 3a with a different angular attitude of the respective axes 4a relative to the vertical axis X-X of the arms, as illustrated in Figure 6.

Although the invention has been described with reference to only two embodiments, it will be appreciated that it is not limited to those embodiments only, but also includes all of those falling within the scope of the claims which follow.

Claims

1. A device (1) for evacuating the mixture of process gases present inside a reaction chamber (2) in which the deposition of thin coatings on objects or substrates to be coated takes place, the reaction chamber (2) comprising means (3) for injecting reaction gases, which means have a plurality of injectors (4) , a first electrode (5) supplied with voltage at radio frequency and at least a second electrode at a potential different from that of the first electrode (5) , and also suction means (10) for drawing the mixture of process gases, characterized in that it comprises an evacuation duct (7, 7a) , connected to the suction means

(10) , which extends inside the reaction chamber (2) and which is provided with a plurality of openings (8) in fluid communication with the chamber (2) .

2. A device (1) for evacuating the mixture of process gases according to claim 1, wherein the evacuation duct (7, 7a) extends inside the chamber (2) along a vertical central axis (Z-Z) of the reaction chamber (2) .

3. A device (1) for evacuating the mixture of process gases according to claim 1 or 2, wherein the evacuation duct (7, 7a) is vertical and cylindrical.

4. A device (1) for evacuating the mixture of process gases according to any one of the preceding claims, wherein the first electrode (5) is constituted by means (6) carrying objects or substrates to be coated.

5. A device (1) for evacuating the mixture of process gases according to claim 4, wherein the evacuation duct (7, 7a) is equipotential with the inner walls (2a) of the reaction chamber (2) .

6. A device (1) for evacuating the mixture of process gases according to claim 5, wherein the means (6) carrying objects or substrates to be coated are located in a position substantially equidistant between the surface of the evacuation duct (7a) and the inner wall (2a) of the chamber (2) .

7. A device (1) for evacuating the mixture of process gases according to any one of the preceding claims, wherein the injectors (4) are arranged along the injection means (3) on a zig-zag path.