The rigorous coupled-wave analysis (RCWA) is a semi-analytic solver to Maxwell's equation, which is one of the most successful methods for modeling periodic optical structure. The repetitive nature of semiconductors has made RCWA widely applied in the semiconductor metrology industry. However, devices with high aspect ratio units, such as vertical NANDs(V-NANDs), require lengthy computation times, making them difficult to model in practice even with fully parallelized RCWA applications. This is because RCWA involves a time-consuming process of eigendecomposition and matrix inversion for each layer sliced along the vertical axis. In order to circumvent such computations, we propose a neural network based approach: channel-hole approximating network in the electromagnetic aspect (CHANEL). Based on the characteristic that the horizontal cutting plane is topologically consistent along the vertical axis of the channel-hole, CHANEL directly predicts the scattering matrix of each layer from its structural and optical parameters. In the scattering matrix of each layer, we found salient regions for Jones matrix calculation, which enhanced the accuracy of Jones matrix prediction with intensive learning on that area. In this paper, we demonstrate that CHANEL outperforms the traditional CPU-based RCWA implementations in terms of time, performing diffraction simulation more than 10 times faster.
An innovative metrology technique has been devised to address current limitations of optical critical dimension (OCD) in advanced semiconductor metrology. This technique is based on multiple self-interferometric pupil imaging, called Mueller matrix self-interferometric pupil ellipsometry (M-SIPE). The system integrates an innovatively designed interference generator in both illuminating and imaging optics, allowing for the massive acquisition of full polarization information across entire angles around the device. The vast amount of information can offer fully comprehensive structural analysis, accomplishing enhanced sensitivity and the ability to break the well-known parameter correlation issues. The system employs a single-shot holographic measurement technique on the pupil plane, enabling rapid acquisition of three-dimensional spectral information, such as wavelengths, incidence angles, and azimuth angles. Thus, unlike conventional OCD tools, M-SIPE can obtain multi-angular and full polarization information without any mechanical movements. We verified the performance of M-SIPE by the experiment of non-patterned wafers of various conditions using an optical testbed. Our results confirmed good agreement between the experiment and theoretical simulations across all angular ranges. Furthermore, the actual device simulation was conducted to show sensitivity enhancement and ability for breaking the parameter correlation issues. The results confirmed that the large amount of angular information from M-SIPE technique could overcome current metrological challenges.
We present advanced application of novel ellipsometry technique, referred to as self-interference pupil ellipsometry (SIPE), integrating self-interference and pupil microscopy to overcome the sensitivity limitations raised from the conventional spectroscopic ellipsometry. We investigated various samples including a SiO2 monolayer, grating patterned wafers, and DRAM wafers to demonstrate outstanding capability of SIPE for metrology. The angular range corresponds to approximately 5,000 acquisition of conventional ellipsometry tools with 2º angular step scanning. From the experimental results and simulation, we expect the sensitivity of SIPE for structure metrology is at least 0.15 nm at a single wavelength and even better for multispectral measurements.
A recently introduced novel concept ellipsometry, characterized by its unique derivation process of directly extracting the polarization information from the hologram image on pupil plane, has been evaluated experimentally targeting for the application to OCD and overlay tools. With an improvement of splitting the hologram on the pupil, this self-interferometric pupil ellipsometry (SIPE) has gained the capability of measuring all of Stokes parameters (S0-S3) throughout the incident angle of 0 to 72 degrees with omnidirectional orientation. A prototype system incorporating SIPE technology has been fabricated to conduct the performance test with patterned test samples for overlay and CD evaluation, the result of which exhibits the sufficient sensitivity to dimension variation and superior repeatability for practical use. The measurement of thousands of ellipsometric data on pupil only takes tens of milliseconds at the most, realized by leveraging the advantages of self-interferometry that does not have any rotating elements in optics. The experimental result demonstrates the consistency with the simulation results based on TEM data within entire pupil. In the front-line of advanced semiconductor manufacturing, the main obstacles to OCD application, low sensitivity and parameter coupling, have been evaluated, which indicates good prospects with SIPE technology.
We propose a new Magneto-optical Kerr effect (MOKE) system which consists of a dedicated electromagnet and a sensor for inspecting next generation memory, such as Spin-Transfer Torque Magnetoresistive Random Access Memory (STTMRAM). Conventional MOKE system is able to measure a magnetic hysteresis loop at a specific point by detecting the polarization rotation angle with changing the magnetic field intensity with the precision of less than 0.1deg on the reflected light. However, it takes several tens of seconds for measuring each point. We have demonstrated that inspection throughput of more than 1 wafer per hour with 2um pixel resolution can be achieved using proposed method called SCAN MOKE.
Background: High-throughput three-dimensional metrology techniques for monitoring in-wafer uniformity (IWU) and in-cell uniformity (ICU) are critical for enhancing the yield of modern semiconductor manufacturing processes. However, owing to physical limitations, current metrology methods are not capable of enabling such measurements. For example, the optical critical dimension technique is not suitable for ICU measurement, because of its large spot size. In addition, it is excessively slow for IWU measurement.
Aim: To overcome the aforementioned limitation, we demonstrate a line-scan hyperspectral imaging (LHSI) system, which combines spectroscopy and imaging techniques to provide sufficient information for spectral and spatial resolution, as well as high throughput.
Approach: The proposed LHSI system has a 5-μm spatial resolution together with 0.25-nm spectral resolution in the broad-wavelength region covering 350 to 1100 nm.
Results: The system enables the simultaneous collection of massive amounts of spectral and spatial information with an extremely large field of view of 13 × 0.6 mm2. Additionally, throughput improvement by a factor of 103 to 104 can be achieved when compared with standard ellipsometry and reflectometry tools.
Conclusions: Owing to its high throughput and high spatial and spectral resolutions, the proposed LHSI system has considerable potential to be adopted for high-throughput ICU and IWU measurements of various semiconductor devices used in high-volume manufacturing.
An innovative self-interferometric pupil ellipsometry(SIPE) has been demonstrated to overcome the spectral sensitivity and throughput limitations for optical critical dimensions (OCD) metrology in the advanced semiconductor devices. The two orthogonally polarized lights from the target structure on wafer were combined through suitably devised polarization state analyzer to generate an interferometric fringe pattern on the pupil surface of the SIPE optical system. The measured fringe pattern was processed with our novel holographic reconstruction algorithm to extract the ellipsometric information (Ψ and Δ) with the entire incident angles 0 to 70º and azimuthal angle 0 to 360º separately. In contrast to conventional ellipsometry tools, no mechanical movements were required to obtain the multi-angular information. To verify the usefulness of SIPE system and the algorithms, both experimental and theoretical validation have been performed for patterned wafers as well as for SiO2 mono-layered wafers. We first measured the non-patterned wafers of various different thicknesses, and found that the obtained values from SIPE, commercial ellipsometry tool, and theoretical simulation present a good agreement for wide spectral and angular ranges. Furthermore, we show that the large amount of angle resolved information from SIPE technique can greatly enhance the ability to overcome the OCD ellipsometry’s recent challenges such as spectral sensitivity issues, parameter correlation and structural asymmetry problems, etc. In short, the proposed system and algorithms, which are completely new approaches, show a capability to overcome current metrology challenges and we strongly believe that the SIPE is a promising metrology solution that can be eventually replacing the traditional OCD metrology tools..
An innovative self-interferometric pupil ellipsometry (SIPE) technique has been demonstrated to overcome the accuracy and throughput limitations raised from the conventional spectroscopic ellipsometry (SE) tools to precisely measure the optical critical dimensions (OCD) in the advanced semiconductor devices. The proposed SIPE technique will be extremely powerful, because key ellipsometric parameters, Ψ and Δ, from all possible incident angles can be obtained simultaneously from the single measurement, while the conventional SE technique needs to collect several hundreds of measurements to get the identical information. By employing a Nomarski prism, one can angularly separate the reflected light from the wafer into two orthogonally polarized lights. Then, the self-interference pupil ellipsometer could interfere those two beams without an additional reference beam path. The interfered fringe includes rich ellipsometric information at incident angles from -70º to 70º with 0-360º azimuthal directions, where those Ψ and Δ information can be extracted by the novel holographic algorithm we proposed. To verify the usefulness of SIPE system and the algorithms, both experimental and theoretical validation have been performed for the patterned wafers. In short, the proposed system and algorithms, which are completely new concept, show a capability to overcome current metrology challenges by breaking multiple parameter correlations between various structural parameters, eventually resulting in the improved metrology sensitivity and precision. Based on the results presented here, we strongly believe the SIPE is a promising metrology solution that can be eventually replacing the traditional OCD tools.
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