Optics: measuring and testing – By light interference – For dimensional measurement
Reexamination Certificate
2000-03-08
2001-08-07
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By light interference
For dimensional measurement
C356S450000
Reexamination Certificate
active
06271925
ABSTRACT:
The invention relates to an apparatus and a method for measuring two opposite surfaces of a body.
The technical progress of the semiconductor industry in the last years resulted in a sharp increase of the diameters of the semiconductor wafers as base material for chip production for economic and process technical reasons. Wafers having a diameter of 200 millimeters are already state of the art and wafers having a diameter of 300 millimeters will be processed in near future.
At present manufacturers and processors of such wafer sizes do not yet have measuring devices at their disposal which enable them to check particular quality features such as the geometry (flatness, curvature, thickness variation) of the wafer with a desired resolution and precision.
Two measuring methods for measuring the geometry of semiconductor wafers are known. The one measuring method is an optical geometry measurement using interferometry. One entire surface of the wafer is interferometrically measured, while the wafer rests on a plane plate or is sucked thereto. After measuring one surface the wafer is turned around and the other surface is measured. Since, in this method, one side only can be measured at a time, the relation between the front and rear side of the wafer indicating the parallelism and the thickness variation is not directly given. It is assumed that the sucked surface is drawn in an absolutely plane state, but this is practically not the case, because it is prevented by particles between the wafer and the support and it is generally uncertain whether the wafer—especially in case of unevenness—fits in a uniform manner. Furthermore, a horizontally placed wafer having a diameter of 200 millimeters or 300 millimeters is bent by gravity and therefore no forcefree state of the wafer prevails. This renders the measurement of the absolute evenness impossible. Moreover, the risk of damage due to the surface contact with the support and possibly also with the optical measuring system is so high that mostly sample measurements only are admitted. Owing to the sum of the many measuring uncertainties the measuring accuracy is insufficient. Measurement values produced with other methods are not directly comparable also.
A further method is the capacitive geometry measurement including scanning the surface using distance sensors. Dot scanning distance sensors scan the front side and the rear side of a wafer. The wafer is supported at its center and rotated. Since the measurement is punctual, it is necessary to scan in order to obtain two-dimensional data. The known disadvantages of a scanning method, e.g. instable measuring conditions during the entire scanning process, considerably reduce the measuring accuracy. Since the wafer is centrally supported during the measurement, the gravity exerts a strong influence on the form of the wafer by causing a flexion. This influence can be computationally taken into consideration only to an insufficient approximation. Furthermore, the number of measurement points which can be obtained within an acceptable time is too low. The size of the measurement points resulting from the method and from the sensor diameter can not be reduced to an extent necessary to meet the new quality rules. Moreover, the risk of damaging the wafer is high because of the surface contact and of the very small distance of the sensors to the wafer surface for technical reasons. Generally, also in this case the measuring accuracy is too low, owing to the sum of measuring uncertainties. Again, measuring values produced with other methods can not be directly compared.
It is the object of the invention to provide an apparatus and a method for measuring two opposite, substantially plane and parallel surfaces of a body, in particular of a semiconductor wafer, whereby the measuring accuracy can be increased, the damaging risk can be reduced and the measuring time can be decreased.
Further developments of the invention are defined in the subclaims.
The apparatus and the method, resp., has the following advantages:
The front side and the rear side are measured under absolutely equal conditions in a contactless, isochronal and static manner—no wafer movement occurs—and a single sensor is used. No tuning calibration is required. During the measurement the wafer is free of effects from outer forces, because it stands in an upright position. The critical surfaces of the wafer are never touched, and there is therefore a low risk of damage. All required geometry data are derived from a single measurement. Owing to the single measurement the measuring time is considerably reduced, whereby the throughput and the productivity is increased. The measuring accuracy and the resolution in lateral as well as vertical direction are as high as, or even higher than, required by international standards. Moreover, the method detects the wafer in an unaffected state and could therefore form a standard.
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patent: 5355221 (1994-10-01), Cohen et al.
patent: 5684594 (1997-11-01), Platten et al.
patent: 5889591 (1999-03-01), Bruning
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patent: WO 96/22505 (1996-07-01), None
Dike Bronstein Roberts & Cushman IP Group
Font Frank G.
Lee Andrew H.
Nanopro Luftlager-Produktions-und Messtechnik GmbH
Neuner George W.
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