This present invention relates to increasing the utility of 3-D triangulation sensors which inherently take longer to gather data as their field of view is widened (at constant resolution) and applying the advantage to methodology and systems for improving quality of semiconductor device manufacture by controlling a semiconductor device fabrication unit with data acquired from manufactured devices thereby preventing recurrence in the manufacturing operation of device geometry deviation from an intended one.
The operation and application of 3-D triangulation sensors is well known in the art and is exemplified by U.S. Pat. Nos. 4,238,147, 4,590,367 and 5,028,799 which teach the relative motion between a sensor that projects a plane of light on an object whose surface data is to be recorded and the object itself. The plane of light may be formed by a collimated light beam, preferably a laser beam, spread by a cylindrical lens or by a spot of light which is deflected by a mirror mounted on a galvanometer, mechanical motion, spinning mirror, or acousto-optic deflector to form an equivalent plane made of a group of spots. The surface depth information is obtained by reading a signal for each part of the plane from a position sensing detector which may be a TV camera, a linear photodiode array, or a linear or area type photoconductive device which provides a voltage ratio proportional to the x and or y position of an incident light spot. All of these detectors and their use for range readout in 3-D triangulation systems are well known by those skilled in the art.
When a scanned spot is used to create the light plane and each spot is immediately read out from the detector, the scan time to scan a given area increases in proportion to the number of spots since a finite time is required to project each spot and to read out the data for each spot. When an integrating device such as a TV camera is used to gather the data from a projected plane (or equivalent group of spots) the width that can be accommodated is defined by the resolution of a pixel (often 1/512th of the length or width of the detector) and the corresponding resolution desired on the object. This follows from the typical camera pickup resolution created by a 512 by 512 pixel array. The readout time for the 3-D data contained in the projected plane corresponds to the tie to read the picture frame which is normally 1/30th of a second. Thus, again, the number of 3-D points scanned and read out is limited by time available; typically 512 3-D points in 1/30th of a second.
3-D sensors are often translated via mechanical means which carry the sensor along its intended measurement path, often at a constant velocity. Any time the path is changed from a straight line or changes to a new straight line path, it is required that the mechanism be accelerated and/or decelerated which often slows the net scanning speed far below that would be achieved if acceleration were not required. This is particularly a problem when scanning around the periphery of a particular semiconductor device in a tray since it requires three changes of direction to scan leads on the four sides of the device.
Semiconductor devices generally will be fabricated in a machine fabrication operation since exact precision of manufactured devices is required to insure that, inter alia, such devices have an exact intended predetermined geometry. Although such mode of fabrication can produce high quality results, there occurs fabrication of some devices which have intended geometry deviations, e.g., in lead-to-lead spacing and coplanarity which are outside tolerances for acceptable devices. This requires inspection of the devices to ascertain that exacting precise fabrication has been accomplished. Where found, defective devices must be removed and discarded or refurbished to have the intended geometry.
It is desirable, therefore, that ways and means be provided so that an acquired data determination of device be used directly to control the fabrication unit operation to make compensation in the fabrication operation and unit as effectively eliminates production of defective devices.