Three-Dimensional Surface Profiling of Microstructures, 10-9327

Printer Friendly Version

Principal Investigators
Ernest A. Franke
Joseph N. Mitchell
Michael P. Rigney

Inclusive Dates: 07/01/02 - Current

Background - The Institute is developing a microelectromechanical systems (MEMS) quality assurance program area that will include materials testing and device characterization capabilities. Testing, characterizing, and validating the design of MEMS devices require accurate three-dimensional measurement. Available methods for three-dimensional measurement are expensive and not well suited for use on a MEMS probe station. A unique capability for microscale three-dimensional (3-D) measurement will strengthen the Institute's position in this emerging area.

Approach - The objectives of this project are to design and demonstrate a three-dimensional measurement capability suitable for characterizing MEMS devices on a probe station. The approach selected is to extend a 3-D imaging capability developed in an earlier internal research project to microscale measurements. The previous project resulted in a unique 3-D measurement method using dynamic structured light (DSL 3-D measurement). A patent application has been filed for this concept based on mathematical construction of a family of quadric surfaces generated by projection from a rotating grating. Preliminary tests indicated that the method could be extended to microscale measurements by projecting the structured light pattern onto a small area and imaging the pattern with an optical microscope. Preliminary calculations show that it should be possible to achieve a 3-D resolution of 100 nanometers. Other preliminary calculations indicated that a much faster method of calculating the 3-D coordinates could be implemented, especially if optimized, low-level code is written for a fast processor.

The research will include investigation of both collimated and diverging optical systems to project a rotating grating pattern on a MEMS surface with high resolution. A microscope imaging system will be coupled with a video camera to capture images of the dynamic pattern. Signal processing algorithms developed in the earlier internal research project will be optimized and extended to analyze the images of the grating and calculate surface profile.

Accomplishments - A design spreadsheet, developed in an earlier 3-D project, was revised to be more appropriate for microscope optics. The spreadsheet was used to determine system parameters required to provide a measurement resolution of 100 nanometers. Projection systems were investigated, and a noncollimated approach was selected after testing several alternatives. The optical projection system was designed and is being fabricated.

The signal-processing computation method was modified and optimized to generate run-length-encoded data directly to the camera video signals. This method reduced the computation time by nearly two orders of magnitude. The enhanced computation method is being tested and will be integrated into the measurement system.

2002 Program SwRI Home