Byungki Kim

Scanning grating microinterferometer for MEMS metrology

Quality control and metrology are critical to improved productivity and yield in MEMS design and production. This paper presents a micrograting interferometer for use in measuring MEMS devices. The sensor is also capable of making dynamic measurements, qualifying the functionality of the MEMS devices. The system employs a phase sensitive diffraction grating for interferometric axial resolution and a microfabricated lens for improved lateral resolution. The microinterferometer is capable of array implementation and can be used to increase the yield of MEMS manufacturing processes. The results generated by a single microinterferometer show good correlation with both analytic models and measurements of the MEMS devices by other metrology tools. The microinterferometer enables measurement of shady state vibration of MEMS devices as well as the development of surface vibration profiles. Initial results presented in this paper also demonstrate the ability to measure quantities such as part surface curvature, as well as reduce low frequency vibrational noise. The use of a deformable diffraction grating is proposed to further enhance the sensors capabilities.

Deformable diffraction grating for scanning microinterferometer arrays

A micro grating interferometer has been fabricated to use in measuring the dynamic performance of MEMS devices. The system uses a phase sensitive diffraction grating for interferometric axial resolution and a microfabricated lens for improved lateral response. Early experimental results using a non-deformable grating interferometer show that both the transient and steady state vibration of MEMS devices can be measured and mapped using the micro interferometer. These initial results also reveal vibrational noise and sample alignment problems. To avoid these obstacles and to maximize the sensitivity of the interferometer, a PID control unit is introduced. Analysis has been performed on the interferometer system to improve the controller design. A deformable grating interferometer has also been fabricated using microfabrication techniques and tested to show proper range of actuation under DC bias. This grating also demonstrates the ability to maintain a high sensitivity during operation.

Actively controlled diffraction grating interferometer MEMS devices

A micrograting interferometer has been fabricated to use in measuring the static and dynamic performance of MEMS devices. These measurements aid in qualifying the functionality of fabricated MEMS devices, as well as improving fabrication techniques. The metrology system uses a phase sensitive diffraction grating for interferometric axial resolution and a microfabricated lens for improved lateral resolution. In addition, active control is applied to the system to reduce the impact of mechanical vibrations and insure a high degree of measurement sensitivity. The control scheme is demonstrated successfully in the scanning of MEMS devices in the experiment. A deformable grating, which controls measurement sensitivity, has been fabricated and integrated with optoelectronics in small volume. Experiments with the integrated package demonstrate that the measurement sensitivity can be adjusted by actuating the deformable grating. This integrated single device illustrates that the deformable grating sensor can be expanded to form arrays for parallel measurement of MEMS device.