Measuring and testing – Surface and cutting edge testing
Reexamination Certificate
1999-11-09
2001-06-26
Williams, Hezron (Department: 2856)
Measuring and testing
Surface and cutting edge testing
C073S061710
Reexamination Certificate
active
06250141
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention concerns a scanning device for semiconductor wafers for the preparation of a surface analysis in which a liquid drop is moved over the surface of the semiconductor wafer for determining a concentration of metal and dopant traces in the liquid drop.
Such scanning devices are used to collect metal and dopant traces from the surface of the semiconductor wafer and ascertain the purity of the surface of the semiconductor wafer. On the basis of the result of the analysis, the preceding processing steps can then be assessed.
In preparation for scanning, the semiconductor wafer is firstly treated in a gas-phase treatment chamber, a so-called vapor phase decomposition (VPD) box with a hydrogen fluoride gas. The semiconductor wafer is subsequently removed from the VPD box and a liquid drop is placed on the now hydrophobic surface of the semiconductor wafer. The semiconductor wafer itself is held manually with the aid of a suction pipette. The liquid drop is then rolled over the surface of the semiconductor wafer by carefully tilting the latter. As this occurs, metal and dopant traces are collected from the surface of the semiconductor wafer and concentrated in the liquid drop.
While the treatment step in the VPD box necessary before scanning the semiconductor wafer is to be regarded as a very simple and reliable process, scanning the semiconductor wafer manually requires considerable dexterity and practice. At the same time, the liquid drop must be prevented from rolling off the semiconductor wafer, which would make an analysis impossible. In addition, when scanning the semiconductor wafer, it must be ensured that all the regions of the surface of the semiconductor wafer are covered.
In the case of relatively small semiconductor wafers, this freehand scanning is to be regarded as an entirely customary practice. However, in the case of semiconductor wafers with a diameter of 300 mm, this freehand scanning becomes extremely difficult or impossible.
Therefore, for the scanning of such semiconductor wafers, devices that carry out both the VPD treatment and the scanning of the surface of the semiconductor wafers fully automatically have been developed. Such devices are, however, extremely cost-intensive and unsatisfactory in their reliability. This applies in particular to the scanning of semiconductor wafers that are difficult to scan, such as semiconductor wafers with LPCVD nitride layers.
Furthermore, it may happen that, during scanning, parts of the liquid drop remain on the surface of the semiconductor wafer, in other words are lost. These lost amounts of liquid can be collected again when scanning manually, whereas this recollection is not possible in the case of fully automatic devices.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a scanning device which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which permits rapid and dependable scanning and can be produced with little effort and low costs.
With the foregoing and other objects in view there is provided, in accordance with the invention, a scanning device for performing part of a surface analysis of semiconductor wafers, including: a base plate; a depositing plate resting displacably on the base plate, the depositing plate provided for receiving a semiconductor wafer having a surface; and a receptacle disposed on the base plate from which a liquid drop is positionable on the surface of the semiconductor wafer and the semiconductor wafer and the liquid drop are movable in relation to each other so that a concentration of metal and dopant traces from the semiconductor wafer are trapped in the liquid drop.
The object on which the invention is based is achieved by providing a depositing plate which can be displaced on a base plate and is intended for receiving the semiconductor wafer, by the liquid drop being positionable on the surface of the semiconductor wafer in a receptacle and by the semiconductor wafer and the liquid drop being movable in relation to each other.
With the scanning device, which is particularly simple and therefore able to be produced at low cost and is suitable for semiconductor wafers of any size, a considerable improvement in the operation of scanning semiconductor wafers is achieved.
In particular, the liquid drop can now be guided in a specifically directed manner over the surface of the semiconductor wafer, with the result that the scanning operation is considerably facilitated.
The semiconductor wafer is preferably aligned horizontally on the depositing plate, the receptacle for the liquid drop being configured as a scanning tube that is positioned directly over the surface of the semiconductor wafer.
To allow the liquid drop to be guided dependably, the scanning tube is produced from a plastic with hydrophobic properties.
A further continuation of the invention is characterized in that the scanning tube is fastened on an extension arm that is securely connected to the base plate. The extension arm reaches over the depositing plate with the semiconductor wafer resting on it, with the result that the depositing plate can be displaced under the scanning tube. The distance of the extension arm from the base plate is chosen such that, when the depositing plate is pushed in, the scanning tube does not touch the surface of the semiconductor wafer lying on the depositing plate. The liquid drop located on the scanning tube can then be guided over the surface of the semiconductor wafer.
In a further development of the invention, the semiconductor wafer can be moved in a horizontal direction in a meandering or spiral-shaped manner with respect to the liquid drop held in the scanning tube, with the result that the entire surface of the semiconductor wafer can be scanned.
To allow this to be carried out particularly simply and rapidly, a further development of the invention is characterized in that the depositing plate is provided on its lower side, remote from the semiconductor wafer, with a meandering or spiral-shaped guide corresponding to the intended path of movement of the liquid drop on the surface of the semiconductor wafer, for receiving a stationary guiding element.
The guide in this case extends over a surface area on the depositing plate that corresponds at least to the surface to be patterned of the semiconductor wafer.
In a further development of the invention, the guide is configured as a channel or groove, into which the guiding element enters in the form of a guiding pin protruding from the base plate, the guiding pin being in alignment with the scanning tube.
The object on which the invention is based is also achieved by a base plate with a guiding pin protruding from it for the manual guidance of a depositing plate which rests displaceably on the base plate. The depositing plate is intended for receiving and holding a semiconductor wafer and is provided on its underside with guiding channels for the guiding pin. With the use of a liquid drop which can be positioned on the surface of the semiconductor wafer and by a scanning tube for holding and guiding the liquid drop resting on the surface of the semiconductor wafer, the concentration of metals and dopant traces can be determined. The scanning tube is fixed in place, positioned over the semiconductor wafer that is displaceable in a meandering or spiral-shaped manner and/or rotatable, or is displaceable with respect to the semiconductor wafer.
To be regarded as particular a advantage of the scanning device according to the invention is that even unpracticed beginners without particular dexterity are able to scan semiconductor wafers. The scanning speed is freely variable and can consequently be adapted individually. In addition, it is possible without any problems to re-collect a lost liquid drop by simply scanning backward.
To be regarded as a further advantage of the invention is that it is practically impossible to leave unscanned a region of the semiconductor wafer within the surface to be patterned o
Geyer Stefan
Horn Michael
Hunger Rüdiger
Cygan Michael
Greenberg Laurence A.
Infineon - Technologies AG
Lerner Herbert L.
Stemer Werner H.
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