Nondestructive detection of nano grating by generalized ellipsometer

In order to control nanoimprint lithography (NIL) processes for achieving good fidelity, the fast, low-cost, non-destructive and accurate measurement of geometric parameters of templates and imprinted grating structures is of great importance. Compared with conventional ellipsometric scatterometry, which only obtains two ellipsometric angles and has 2 changeable measurement conditions, i.e., the wavelength and the incidence angle, Mueller matrix ellipsometry (MME) can provide up to 16 quantities of a 4×4 Mueller matrix in each measurement with 3 changeable measurement conditions, i.e., the wavelength, the incidence angle and the azimuthal angle. Therefore, MME can acquire much more useful information about the sample. It is expected that much more accurate measurements of nanostructures can be achieved by choosing proper measurement configurations and completely using the rich information hidden in the measured Mueller matrices. Accordingly, the templates and imprinted grating structures in NIL processes are measured using an in-house developed Mueller matrix ellipsometer. We experimentally demonstrate that more accurate quantification of geometric parameters, such as line width, line height, sidewall angle and residual layer thickness, can be achieved by performing MME measurements in the optimal configuration and meanwhile by incorporating depolarization effects into the optical model. Moreover, as for the imprinted grating structures, the residual layer thickness variation over the illumination spot can also be directly determined by MME. The comparison between MME-extracted template and imprinted resist profiles also indicates an excellent fidelity of the nanoimprint pattern transfer process.

Accurate measurement of templates and imprinted grating structures using Mueller matrix ellipsometry

Chen¹,

Liu²,

Zhang³

et al. 2014

Fabrication of pixelated polarizer array and its application in polarization enhancement

Zhang¹,

Dong²,

Zhang³

et al. 2014

Pixelated polarizer array can be used in the real-time measurement of Stokes parameters. In this paper, pixelated polarizer array based on the aluminum nano-grating is designed and fabricated, and the fabrication technology is electron beam exposure technology. The size of each unit is 7.4 μm, and the polarization directions of each adjacent 2×2 units in the polarizer array are 0, π/4, π/2, and 3π/4. The period, duty cycle, depth and surface type of the grating are 140 nm, 0.5, 100 nm and rectangle type, respectively. The scanning electron micrographs of the pixelated polarizer array show that there is no disconnection, cross and pollution on the fabricated metal nano-grating lines. The nano-grating lines are straight and uniform in thickness, and the surface type of the grating is ideal rectangular type. The polarization optical micrographs show that the pixelated polarizer array has good polarization characteristics. The maximum polarization transmissivity can reach 79.3%, and the extinction ratio can arrive at 454. Furthermore, the pixelated polarizer array is integrated with the charge coupled devise chip, and the Stokes parameters can be calculated from one frame, then the degree of linear polarization and angle of linear polarization can be obtained. Thus, the polarization enhancement of image is achieved, which can be used in the anti-stealth and recognition.

Large-scale nanostructure metrology using Mueller matrix imaging ellipsometry

Chen¹,

Yuan²,

Du³

et al. 2016

In order to achieve effective process control, the fast, inexpensive, nondestructive and accurate nanoscale feature measurements are extremely useful in high-volume nanomanufacturing. The optical scatterometry has currently become one of the important approaches for in-line metrology of geometrical parameters of nanostructures in high-volume nanomanufacturing due to its high throughput, low cost, and minimal sample damage. Conventional scatterometry techniques can only obtain the mean geometrical parameter values located in the illumination spot, but cannot acquire the microscopic variation of geometrical parameters less than the illumination region. In addition, conventional scatterometry techniques can only perform monospot test. Therefore, the sample stage must be scanned spot by spot in order to obtain the distribution of geometrical parameters in a large area. Consequently, the final test efficiency will be greatly reduced. Accordingly, in this paper, we combine conventional scatterometry with imaging techniques and adopt the Mueller matrix imaging ellipsometry (MMIE) for fast, large-scale and accurate nanostructure metrology. A spectroscopic Mueller matrix imaging ellipsometer is developed in our laboratory by substituting a complementary metal oxide semiconductor camera for the spectrometer in a previously developed dual rotating-compensator Mueller matrix ellipsometer and by placing a telecentric lens as an imaging lens in the polarization state analyzer arm of the ellipsometer. The light wavelengths in the developed imaging ellipsometer are scanned in a range of 400-700 nm by using a monochromator. The spectroscopic Mueller matrix imaging ellipsometer is then used for measuring a typical Si grating template used in nanoimprint lithography. The measurement results indicate that the developed instrument has a measurement accuracy of better than 0.05 for all the Mueller matrix elements in both the whole image and the whole spectral range. The three-dimensional microscopic maps of geometrical parameters of the Si grating template over a large area with pixel-sized lateral resolution are then reconstructed from the collected spectral imaging Mueller matrices by solving an inverse diffraction problem. The MMIE-measured results that are extracted from Mueller matrix spectra collected by a single pixel of the camera are in good agreement with those measured by a scanning electron microscope and the conventional Mueller matrix ellipsometer. The MMIE that combines the great power of conventional Mueller matrix ellipsometry with the high spatial resolution of optical microscopy is thus expected to be a powerful tool for large-scale nanostructure metrology in future high-volume nanomanufacturing.