Nanometrics Incorporated | Date: 2013-10-04
An ellipsometer includes an integrated focusing system with a beam splitter between the sample and the ellipsometer detector. The beam splitter provides a portion of the radiation to a lens system that magnifies any deviation from a best focus position by at least 2. The focusing system includes a 2D sensor, where the spot of light focused on the sensor is 50 percent or smaller than the sensor. The focusing system may further include a compensator to correct optical aberrations caused by the beam splitter. A processor receives an image signal and finds the location of the spot from which focus error can be determined and used to correct the focal position of the ellipsometer. The processor compensates for movement of the spot caused by rotating optics. Additionally, a proportional-integral-derivative controller may be used to control exposure time and/or gain of the camera.
Nanometrics Incorporated | Date: 2014-10-02
The effective spot size of a spectroscopic metrology device is reduced through deconvolution of a measurement spectra set acquired from a measurement target combined with a training spectra set obtained from a training target. The measurement spectra set may be obtained using sparse sampling of a grid scan of a measurement target. The training spectra set is obtained from a grid scan of a training target that is similar to the measurement target. The training spectra set and the measurement spectra set include spectra from different grid nodes. Deconvolution of the measurement spectra and the training spectra sets produces an estimated spectrum for the measurement target that is an estimate of a spectrum from the measurement target produced with incident light having an effective spot size that is smaller than the actual spot size. One or more characteristics of the measurement target may then be determined using the estimated spectrum.
Nanometrics Incorporated | Date: 2014-12-15
An optical metrology device determines physical characteristics of at least one via in a sample, such as a through-silicon vias (TSV), using signal strength data for modeling of the bottom critical dimension (BCD) and/or for refinement of the data used to determine a physical characteristic of the via, such as BCD and/or depth. The metrology device obtains interferometric data and generates height and signal strength data, from which statistical properties may be obtained. The height and signal strength data for the via is refined by removing noise using the statistical property, and the BCD for the via may be determined using the refined height and signal strength data. In one implementation, a signal strength via map for a via is generated using signal strength data and is fit to a model to determine the BCD for the via.
Nanometrics Incorporated | Date: 2013-12-17
An optical metrology device, such as an ellipsometer, includes a focusing system that adjusts the focal position of the metrology device in real time so that focus may be maintained during movement of the measurement locations on the sample, e.g., using closed loop control. A filtered focus signal may be used to adjust the focal position while moving to a measurement location. Additionally, the focus signal may be coarsely filtered and finely filtered, where a coarse filtered focus signal is used to adjust the focal position while moving to a measurement location and a fine filtered focus signal is used to adjust the focal position when at the measurement location. An open loop control may be used in which once at the measurement location, a filtered focus signal is used to adjust the focal position when the filtered focus signal has no offset with respect to the focus signal.
Nanometrics Incorporated | Date: 2015-04-13
A plurality of overlay errors in a structure is determined using a target that includes a plurality of diffraction based overlay pads. Each diffraction based overlay pad has the same number of periodic patterns as the structure under test. Additionally, each diffraction based overlay pad includes a programmed shift between each pair of periodic patterns. The pads are illuminated and the resulting light is detected and used to simultaneously determine the plurality of overlay errors in the structure based on the programmed shifts. The overlay errors may be determined using a subset of elements of the Mueller matrix or by using the resulting spectra from the pads.