Apparatus and method for measuring digital imager, package and wafer bow and deviation from flatness

A method of measuring the surface profile of a sample, comprising the steps of:

• a) locating a surface of the sample relative to a surface of a transparent optical flat;
• b) employing a low-coherence light interferometer having an optical probe coupled to an XY scanning frame that scans the surface of the sample through the transparent optical flat to produce interferometric data signals representing the distances between the optical flat surface and the surface of the sample;
• and
• c) generating a surface profile of the sample from the interferometric data signals using a best fit to a plane.

A method of measuring the mounting height variations in the surface of an image sensor as a result of mounting the image sensor in a package, comprising the steps of:

• a) locating the image sensor in the package prior to mounting and placing the packaged image sensor in a predetermined relationship to a surface of a transparent optical flat;
• b) employing a low-coherence light interferometer having an optical probe coupled to an XY scanning frame that scans the surface of the image sensor through the transparent optical flat to measure distances between the optical flat surface and the surface of the image sensor;
• c) mounting the image sensor in the package;
• d) relocating the packaged image sensor in the predetermined relationship to the surface of the transparent optical flat;
• e) employing the low-coherence light interferometer to measure distances between the optical flat surface and the surface of the mounted image sensor;
• and
• f) generating a mounting height variation map by taking the differences between the distances measured in steps e and b.

A method of measuring the change in surface profile due to processing in a micro-fabrication substrate, comprising the steps of:

• a) locating an unprocessed micro-fabrication substrate in predetermined relationship to a surface of a transparent optical flat;
• b) employing a low-coherence light interferometer having an optical probe mounted on an XY scanning frame for scanning the surface of the substrate through the transparent optical flat to measure distances between the optical flat surface and the surface of the micro-fabrication substrate;
• c) processing the micro-fabrication substrate;
• d) relocating the processed substrate in the predetermined relationship to the surface of the transparent optical flat;
• e) employing the low-coherence light interferometer to measure distances between the optical flat surface and the surface of the processed substrate;
• and
• f) generating a processing height variation map by taking the differences between the distances measured in steps e and b.

A method of determining the change in flatness of individual micro-fabricated devices formed on a wafer after dicing the wafer, comprising the steps of:

• a) locating a processed undiced micro-fabrication wafer in predetermined relationship to a surface of a transparent optical flat;
• b) employing a low-coherence light interferometer having an optical probe mounted in an XY scanning frame for scanning the surface of the transparent optical flat to measure distances between the optical flat surface and the surfaces of the micro-fabricated devices on the undiced wafer;
• c) calculating a surface profile for each device on the undiced wafer from the measured distances in step b using a best fit to a plane;
• d) dicing the micro-fabrication wafer;
• e) locating a diced wafer in the predetermined relationship to the surface of the transparent optical flat;
• f) employing the low-coherence light interferometer to measure distances between the optical flat surface and the surface of the devices in the diced wafer;
• g) calculating a surface profile for each device n the diced wafer from the measured distances in step f using a best fit to a plane;
• and
• h) generating a processing height variation map for each device by taking the differences between the device profiles calculated in steps c and g.