Removable shield arrangement for ICP-RIE reactors

A reactor for applying reactive ion etching to a component, wherein a substrate holder ( 3 ) and clamping means ( 10 ) are provided for respectively supporting and securing components ( 8 ) to be exposed to reactive ion flux, that includes a separate shield arrangement ( 20 ) fixed in a detachable way on said substrate holder ( 3 ), above said clamping means ( 10 ) to mask said clamping means with respect to said reactive ion flux. Said shield arrangement ( 20 ), made up of a single ring can be mounted on said substrate holder ( 3 ) directly upon said clamping means or can also be mounted just above it and separated by a small distance from said clamping means ( 10 ). The shield arrangement ( 20 ) can also made up of at least two rings ( 22 ) which are stacked with a small mutual separation, above said clamping means ( 10 ). The material of said shield arrangement ( 20 ) can be covered with a film of dielectric material and electrically connected to ground ( 23 ) through said substrate holder ( 3 ).

DESCRIPTION OF THE INVENTION The solution proposed by the present invention (see FIGS. 5 and 6 ) is based on the use of a shield 20 , mounted just above the chuck 9 of the substrate holder 3 , which is fitted to the etching chamber by means of a mechanical flange 19 that allows said substrate holder 3 to be coupled to the etching chamber (not shown) in order to guarantee the etching reactor to be leak tight or to guarantee vacuum integrity within the etching reactor. F indicates, diagrammatically, a bellows to allow vertical movement of said substrate holder 3 , in order to adjust the distance between the ICP source and the substrate 8 inside the reactor 1 . Said flange 19 and said spring 8 are electrically connected to ground. Said shield 20 protects the clamping ring 10 against the ion flux from the ICP source. This shield 20 must prevent the clamping ring 10 from undergoing mechanical erosion but, at the same time, it must act as a thermal shield. In accordance with the preferred embodiment of the invention, illustrated in FIG. 5, a thick ring 20 made of pure Al 2 0 3 , sapphire or PBN (Pyrolytic Boron Nitride) is used as such a shield, being designed with the same dimensions as the clamping ring 10 itself. The thickness of the Al 2 0 3 shield 20 must be sufficient to ensure good mechanical rigidity, thus greatly lengthening the lifetime of this part against the ion sputtering mechanisms (mechanical erosion). Said shield 20 is mounted and secured directly onto the clamping ring 10 . In order to simultaneously provide thermal protection for said clamping ring 10 , the shield 20 is mounted separately at a small pre-determined distance, of a few tenths of mm, above the clamping ring 10 by means of a spacer 21 provided close to its periphery, so that a space is defined in which there is a vacuum between the shield 20 , heated by the ion flux, and the clamping ring 10 . In this way, effective thermal protection is achieved, which prevents any temperature rise of the clamping ring 10 . The other advantage of this separated shield 20 , made of alumina, sapphire or PBN, lies in the chemical purity of these commercially available compact materials. It is much easier to synthesize alumina with very few impurities than to achieve a reproducible passivation treatment with a thin layer of Al 2 0 3 . Likewise, it is possible to synthesize extremely pure sapphire or PBN. In this way one can resolve the problem of micro-masking due to residual contaminants. The compact materials are much denser than the thin films, thus the parasitic sputtering effects are also less effective with such compact materials. In accordance with another preferred embodiment of the present invention, represented in FIG. 6 , the protective shield is made up of at least two (for example, 2 or 3) very thin rings 22 made of aluminum, tungsten or tantalum, physically separated from each other and from the clamping ring 10 by a small pre-determined distance of a few tenths of mm, by means of spacers 21 arranged near the periphery of said shield. Also, in this case, the vacuum gap between the clamping ring 10 and the rings 22 which constitute the shield and between the rings 22 themselves, provides an effective thermal insulation of the clamping ring 10 . Being metallic, these shields 20 , 22 in accordance with the invention, must be electrically connected to ground at 23 , through the substrate holder 9 , so the metallic shields are not biased and thus the relative energy of the impinging ions with respect to the shield is extremely low (plasma potential is approximately a few eV (10&ap;15V) only while the RF-biased clamping ring potential is in the 100-400V range) thus strongly reducing, or even suppressing, the effects of the parasitic sputtering mechanisms. The tungsten and the tantalum, which are proposed as preferred metals for manufacturing the metallic shields 20 and 22 are not affected by the chlorine environment (they are not chemically attacked by the chlorine) but in any case and in accordance with yet another preferred embodiment of the invention, these metals can be passivated to provide them with a very thin dielectric film (it can be very thin since parasitic sputtering effects no longer exist) of SiN x or Al 2 0 3 simply deposited by a conventionally PECVD technique (Plasma Enhanced Chemical Vapor Deposition). Aluminum may also be used, but then it is safer, with respect to chlorinated chemical agents, to cover the part with a PECVD dielectric film. Although the invention has been described with respect to several preferred embodiments, it will be understood that these have been given solely by way of example and that many other variations, modifications and applications of the invention may be carried out.