GB2261396A

GB2261396A - Device for large area ion etching

Info

Publication number: GB2261396A
Application number: GB9221969A
Authority: GB
Inventors: Bernhard Cord; Helmut Rauner
Original assignee: Leybold AG
Current assignee: Balzers und Leybold Deutschland Holding AG
Priority date: 1991-11-13
Filing date: 1992-10-20
Publication date: 1993-05-19
Anticipated expiration: 2012-10-20
Also published as: NL9201938A; GB9221969D0; JPH05222554A; GB2261396B

Abstract

The device comprises a container provided with a gas inlet 2 and a gas outlet 8, a cathode serving as substrate holder and connected to a HF voltage source, and an anode 3 of laminar construction and at earth potential. The surface of the anode comprises stepped zones 8 which are parallel to the cathode and which are arranged at different distances respectively from the cathode. The distance diminishes toward the gas outlet 6. <IMAGE>

Description

) 'I -, J j - 1 A DEVICE FOR LARGE-AREA ION ETCHING The invention relates

to a device for largearea, homogeneous ion etching by means of a vacuum apparatus, comprising a container provided with gas inlet- and gas outlet openings, at least one anode of laminar construction carrying earth potential, and a cathode which serves as a substrate holder and which is connected to a HF voltage source.

Devices which are suitable for ion etching and are operated in a vacuum apparatus in which sputtering processes can also be executed are adequately known. Merely by way of an example, two publications, DE-22 41 229 C2 and DE-21 49 606, will be referred to here, which describe devices which not only facilitate substrate coating by means of cathode sputtering but also, simply by reversing the polarities of the electrodes, ion etching. For the ion etching of substrates by a glow 20 discharge, DE-22 41 229 C2 describes a so-called closed system within which there forms a plasma which is required for the removal of material from the substrate and is substantially enclosed by the electrode surfaces. A constant exchange of gas inside the plasma zone does not take place. However, the maintenance of a stable plasma within the closed etching chamber requires on the one hand a highly precise mechanical procedure, i.e. a highly accurate, mutual arrangement of the electrode surfaces taking into account spacing requirements which must be precisely adhered to, and on the other hand a precise adjustment of the potential conditions between the cathode - which is connected to earth and on which the substrate to be etched is arranged - and the anode arranged above it.

Furthermore, the uniform removal of material from the substrate surface requires a substantially homogeneous distribution of the plasma density above the substrate. However, in association with the occurring drop in potential, due to local differences in the parameters which define the etching process (e.g. plasma density, electrode spacing and voltage ratio), substantially differing etching rates can occur on the substrate surface.

The known etching devices, such as described for example in the aforementioned publications, can be used to achieve substantially homogeneous etching rates on disc-shaped substrate bodies with a diameter of up to 150 mm. However, larger substrate surfaces cannot be treated by etching technology with the described degree of uniformity using the previously known etching devices, as a lower removal rate occurs in particular at the edge zones of the substrate than in the central zone of the substrate. The reason for this is mainly that considerable thinning of the plasma occurs at the substrate edge zones due to the escape of plasma. The objective of the invention is to further develop a device for large-area, homogeneous ion etching within a vacuum apparatus, comprising a container provided with gas inlet- and gas outlet openings, in such manner that the maintenance of a stable plasma within the container housing is simplified, and uniformity of the rate of removal can be ensured, even in the case of substrates of larger area than substrates which previously could be handled using the previously known etching devices. 30 In accordance with the invention there is provided a device for large-area, homogeneous ion etching within a vacuum apparatus, comprising a container provided with a gas inlet and a gas outlet, a cathode which serves as a substrate holder and which is connected to a HF voltage source, and an anode of laminar construction and at earth potential, the 11 3 surface of which anode comprises stepped zones which are parallel to the cathode and which are arranged at different distances respectively from the cathode.

The principle of ion etching using a vacuum chamber is based on introducing inert gas between the two electrode surfaces, of which the cathode represents the negative pole which bears the substrate, and the anode, the surface of which is arranged opposite the cathode. Generally the inert gas consists of argon gas.

Additionally a HF high voltage is connected to one of the two electrodes so that the inert gas introduced between the electrodes dissociates and forms a stationary plasma. The positive argon ions which are thereby formed are accelerated as a result of electrostatic attraction in the direction of the negatively charged substrate surface and on collision with the substrate surface release a specific quantity of substrate material in dependence upon their kinetic energy and the surface energy conditions of the substrate. In an open system, in which a gas flow is maintained parallel to the substrate surface, the sputtered substrate particles are thus deposited on the anode, or if gaseous compounds are formed these are removed from the plasma zone into the gas flow, whereby the chemical composition, and in association therewith the electronic conditions within the plasma cloud, remain unchanged.

Fundamentally the rate of etching is dependent upon the number of argon ions colliding with the substrate surface over a period of time, which number mainly corresponds to the number of ionised argon atoms present above the substrate surface. At a given pressure of the argon gas present in the apparatus and with a given high voltage between the cathode and the opposite potential, a plasma burns only when the difference between the two potentials is 4 - sufficiently great. The reason for this is that on their path between the two potentials, ions and electrons experience collisions in which new ions and electrons are produced. If the number of collisions is too small, for example in the case of too low a pressure or too small a difference between the two potentials, the ion- and electron concentration is too low and the plasma is extinguished.

If, on the other hand, a plasma is to be prevented from burning between two surfaces, of which one carries a high voltage, these surfaces must be moved sufficiently close to one another that only a small.number of pairs of electron ions are formed. This consideration itself proves that by varying the distance between the oppositely arranged electrodes, an accurately adjustable control parameter is obtained whereby a selected etching rate on the substrate surface can be achieved.

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

Figure 1 is a cross-sectional view of a device according to the invention; Figure 2 is a plan view of the stepped anode shown in Figure 1, and Figure 3 is a cross-sectional view illustrating an alternative form of anode for a device according to the invention.

The side view shown in Figure 1 of a container housing in which the electrodes according to the invention are arranged comprises a centrally disposed, laminar electrode 1 which is supplied with high voltage from a HF 7 source via a special high frequency matching network 5. Opposite the electrode 1 inside the container housing 4 is arranged a counterelectrode 3 of stepped formation which preferably is - connected to earth potential. At the opposite side of the electrode 1 and arranged parallel thereto is a second anode 3. Here the electrode 1 is coupled to the HF source 7 via a capacitor, but otherwise is insulated with respect to earth potential, so that the electrode 1 can exhibit a potential differing from zero earth potential. The electrode 1 also possesses a smaller surface than the electrode 3 and the container housing 4 so that the electrode 1 is always negatively biased when a plasma is ignited in the container R. Argon gas flows through a gas inlet valve 2 into the interior of the container R, flows over the electrode arrangement, and on the opposite side is pumped out again by means of a suitable vacuum pump (not shown) through a suitably disposed gas outlet valve 6. The gas inlet 2 into the container R can be adjusted by an additionally provided flowmeter (likewise not shown). The operating pressure prevailing in the container R amounts to between 10- 3 and 10- 2 hPa. Because of the high voltage between the electrodes 1 and 3, the argon atoms present in the space between the electrodes become ionized and are accelerated towards the substrate surface where, due to their high kinetic energy, they release substrate particles in collision processes. These substrate particles are either deposited again on the oppositely disposed anode or, if they form a gaseous compound with an added reactive gas, are pumped out of the container R. The open construction with a constant supply and discharge of gas thus ensures a substantially constant gas composition within the container R.

The stepped arrangement of the etching anode 3 here is designed such that in the embodiment illustrated in Figure 1 in the region of the gas inlet it is arranged at the furthest distance from the cathode as it is here that the argon atoms newly introduced into the container housing must firstly be ionized to enable them to contribute to the etching process. Only after a minimum dwell time between the electrode plates do the argon atoms become ionized by collision processes, which causes the concentration of argon ions to be lower in the region of the gas inlet than in the region of the gas outlet. It is also known that the etching rate is dependent upon the operating pressure so that as a result of locally differing operating pressures, e.g. in the region of the gas inlet 2 or gas outlet 6, different etching rates can occur. To avoid these described, undesired effects and to achieve a uniform etching rate over the whole of the substrate surface, as already described the spacing between the electrodes is reduced in zones of increasing argon ion concentration. This finally leads to a stepped structure of the etching anode as illustrated in Figure 1.

Figure 2 is a plan view of the laminar stepped structure of the anode as shown for example in cross-section in Figure 1. The stepped construction of the surface of the anode 3 produces stepped zones 8 which in Figure 2 are separated from one another by contour lines. A frame 9 surrounding the square anode 3 with an edge length L ensures that the anode 3 is suitably positioned inside the container housing 4.

Different stepped arrangements are also possible. Thus, for example, there may be a raised step in the central region of the electrode arrangement, falling away towards the edge zones. An anode structure of this kind according to the invention is shown in Figure 3. It can be seen that the plasma thinning can be reduced in particular in the edge zones by increasing the spacing between the electrodes in stepped fashion towards the edge zones. Thus the plasma thinning can be countered by means of a stepped pyramid anode structure with an arbitrary number of stepped zones 8.

Basically the local etching rate can be in dividually adjusted by means of the design according to the invention of the etching anode by varying the spacing between the electrodes. Thus for the first time it is possible to etch square substrate surfaces with a side length of up to 50 cm. with a degree of homogeneity previously unattainable.

The production of semiconductor modules in large production numbers necessitates that the process be conducted on a scale suitable for mass production. To enable one etching batch to be exchanged for the next as rapidly as possible, the cathode, with the substrates attached thereto, is mounted so as to be movable in such manner that it can be introduced into the etching chamber. This substantially simplifies the changing of the substrates and ensures a largely optimal exploitation of the etching apparatus, which in the final analysis has a cost reducing influence on production.

The illustrated device can thus serve to further develop etching technology in such manner that large-area substrates can be homogeneously processed cost-favourably in the desired manner.

- 8

Claims

1. A device for large-area, homogeneous ion etching within a vacuum apparatus, comprising a container provided with a gas inlet and a gas outlet which serves as a substrate holder and which is connected to a HF voltage source, and an anode of laminar construction and at earth potential, the surface of which anode comprises stepped zones which are parallel to the cathode and which are arranged at different distances respectively from the cathode.

A device as claimed in Claim 1, wherein the electrodes are of square formation and have a side length (L) of up to 50 cm.

3. A device as claimed in Claim 1 or 2, wherein the distance between the electrodes is greatest in the region of the gas inlet and smallest in the region of the gas outlet.

4. A device as claimed in any one of Claims 1 to 3, wherein a second laminar anode is provided which faces the first said anode, the cathode being disposed between the two anodes.

5. A device as claimed in any one of Claims 1 to 4, wherein the central region of the first said anode comprises stepped zones which are spaced from the cathode by a smaller distance than the edge zones of that anode.

6. A device as. claimed in any one of Claims 1 to 5, wherein the stepped anode can be used in modular fashion in sputtering apparatus.

7. A device as claimed in any one of Claims 1 to 6, further comprising means providing a constant uniform flow of gas through the container.

8. A device as claimed in any one of Claims 1 to 6, wherein the gas inlet and gas outlet are disposed at opposite ends of the container.

9 - 9. A device as claimed in any one of Claims 1 to 8, wherein the operating pressure inside the container is in the range 10- 3 to 10- 2 hPa.

10. A device as claimed in any one of Claims 1 to 9, wherein the cathode which is to be equipped with substrates, is arranged so as to be movable.

11. A device as claimed in any one of Claims 1 to 10, wherein the cathode is connected to the HF voltage source via a HF matching network.

12. A device as claimed in any one of Claims 1 to 11, wherein the rate of flow of gas through the gas inlet into the container can be adjusted by a flowmeter.

13. A device as claimed in any one of Claims 1 to 12, wherein the cathode potential is adjustable by means of the HF power.

14. A device for large-area homogeneous ion etching within a vacuum apparatus, which device is substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.