Device for unilateral etching of a semiconductor wafer

Work holders – With fluid means – Vacuum-type holding means

Reexamination Certificate

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C269S903000, C156S345420, C204S298070, C118S500000

Reexamination Certificate

active

06443440

ABSTRACT:

FIELD OF THE INVENTION
My present invention relates to a device for the unilateral etching of a semiconductor wafer and, more particularly, to a device for holding a semiconductor wafer for unilateral etching, i.e. etching from only one side of that wafer.
BACKGROUND OF THE INVENTION
The holding of a semiconductor wafer for unilateral etching generally is effected with a holding plate or base member having a central opening through which the semiconductor wafer is etched in a type of etching cell. That central opening is smaller than the semiconductor wafer and elastic seals are provided around the central opening and the space between the seals can be subjected to suction.
A device of this type is described in German Patent Document DE 197 28 962 A1. In this system, the sealing arrangement is provided on the side of the base member opposite that along which a lid, which covers the back of the base member is provided. Consequently, when the semiconductor wafer on this holder is immersed in the etching medium, it is subjected to an etching effect not only in an edge or perimetral zone of the wafer but also on that portion of the back of the wafer outwardly of the sealing arrangement. This attack by the etching arrangement along the periphery of the wafer and on its back is undesirable in many cases and may even obstruct further processing of the wafer.
OBJECTS OF THE INVENTION
It is, therefore, the principal object of the present invention to provide a device for holding a semiconductor wafer for etching in, for example, an etching cell arrangement, whereby there is no attack on the periphery of the wafer or when any attack by the etching medium on the periphery or back of the wafer is substantially reduced.
Another object of this invention is to provide a device for the purposes described which is free from drawbacks of the earlier system mentioned.
SUMMARY OF THE INVENTION
These objects and others which will become apparent hereinafter are attained, in accordance with the present invention by providing the sealing arrangement on a side of the base member or plate which faces the lid and thus engages the face of the wafer to be etched along its periphery or at its perimeter while the lid engages over the sealing arrangement and the semiconductor wafer held thereon and is held releasably on the base member via a second annular seal.
According to the invention, therefore, the device for holding the semiconductor wafer for unilateral etching can comprise:
a base plate formed with a central opening through which an etching medium can contact a semiconductor wafer to be unilaterally etched, the base plate being formed with a first annular seal formed by two elastic seals surrounding the opening and adapted to bear upon a side of the wafer to be etched along a perimeter thereof;
a vacuum conduit opening into a space between the elastic seals for applying suction to the side of the wafer and retain the wafer against the sealing lips, the side of the wafer being exposed to the etching medium inwardly of the first annular seal;
a lid releasably held on the plate and closing the central opening behind the wafer; and
a second annular seal between the lid and the plate, whereby an edge zone and back of the wafer are protected from attack by the etching medium.
The elastic seals can be lip seals and the second annular seal in turn can be comprised of lip seals.
An advantage of this arrangement is that with a very simple structure only the zone located within the first annular seal is subjected to the action of the etching agent and only one side of the wafer is thereby etched. The edge zone and back of the wafer are completely protected from the etching agent and cannot be attacked or damaged.
In one embodiment of the invention, the lid can be mounted pivotally on the base member and it has been found to be advantageous further to form the second annular seal from lip seals which are arranged in spaced relationship concentrically around the first sealing arrangement and by providing a further suction conduit which opens between these two elastic seals as well. This greatly facilitates handling in the mounting and removal of a wafer in the device.
While the base member can be made in one piece with the seals, e.g. from a plastic with sufficient flexibility and resistance to the etching medium, it has been found to be more cost effective in the long run if at least one and preferably both of the annular seal arrangements are removable from the base member or are held replaceably thereon or on the lid which itself is removable from the base member.
The lid can be provided with a contact spring arrangement whose contact springs bear against the semiconductor wafer. The use of contact springs has been described in DE 197 28 962 A1.
An etching electrode arrangement can also be integrated in the base member. It has been found to be advantageous, moreover, to provide the base member with at least one duct which permits pressure equalization between a chamber formed between the lid and the wafer with the ambient atmosphere, thereby avoiding damage to the wafer during etching. In the absence of such pressure equalization or venting, high temperature gradients which may occur during etching can cause pressure build-up in the aforementioned chamber and damage to the wafer.


REFERENCES:
patent: 3583694 (1971-06-01), Davies
patent: 3630804 (1971-12-01), Coffman
patent: 4403567 (1983-09-01), DaCosta
patent: 4473455 (1984-09-01), Dean
patent: 4500080 (1985-02-01), Aigo
patent: 4551192 (1985-11-01), DiMilia
patent: 5029555 (1991-07-01), Dietrich
patent: 5280894 (1994-01-01), Witcraft
patent: 5733426 (1998-03-01), Cox
patent: 5895549 (1999-04-01), Goto
patent: 5904800 (1999-05-01), Mautz
patent: 4024576 (1992-02-01), None
patent: 19728962 (1999-01-01), None
patent: 197 28 962 (1999-01-01), None

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