In this work, the novel enhancement to multichannel scatterometry data collection, Spectral Interferometry, is introduced and discussed. The Spectral Interferometry technology adds unique spectroscopic data by providing absolute phase information. This enhances metrology performance by improving sensitivity to weak target parameters and reducing parameter correlations. Spectral Interferometry enhanced OCD capabilities were demonstrated for one of the most critical and challenging applications of gate-all-around nanosheet device manufacturing: lateral etching of SiGe nanosheet layers to form inner spacer indentations. The inner spacer protects the channel from the source/drain regions during channel release and defines the gate length of the device. Additionally, a methodology is presented, which enables reliable and reproducible manufacturing of reference samples with engineered sheet-specific indent variations at nominal etch processing. Such samples are ideal candidates for evaluating metrology solutions with minimal destructive reference metrology costs. Two strategies, single parameter and sheet-specific indent monitoring are discussed, and it was found that the addition of spectroscopic information acquired by Spectral Interferometry improved both optical metrology solutions. In addition to improving the match to references for single parameter indent monitoring, excellent sheet-specific indent results can be delivered.
Keywords: OCD, Spectral Reflectometry, Spectral Interferometry, gate-all-around, nanosheet FET, indent, inner spacer
To keep up with logic area scaling, BEOL dimensions have been reduced at an accelerated pace,leading to ever smaller metal pitches and reduced cross-sectional areas of the wires. As a result, routing congestion and a dramatic RC delay (resulting from an increased resistance-capacitance (RC) product)have become important bottlenecks for further interconnect scaling, driving the need for introducing new materials and integration schemes in the BEOL. The current paper studies the damascene process flow that uses a single exposure EUV to create metal lines and 2D patterns at metal half-pitch of 14nm, corresponding to the imec N5 node for logic BEOL layer. A bright field mask with a negative tone resist process was used to develop trenches and transfer these patterns into an oxide dielectric layer. Following this, the trenches were filled with ruthenium (Ru) for electrically testing. Test vehicle included multiple structures, including E-test resistance and capacitance structures, to allow a comprehensive study of the proposed process flow.Metrology requirements and performance at various process steps will be discussed in this paper.Our focus will be on the scatterometry methods that together with machine learning (ML) allow fast and accurate measurements of multiple parameters of interest at large sampling. In the current paper,we present results for inline measurements of line and space critical dimensions (CD), line edge roughness (LER) – after patterning and after hard mask etch, and the prediction of the electrical performance of the metal lines after Ru CMP. In addition, scatterometry ML capabilities for inline tipto-tip (T2T) measurements are successfully demonstrated.
Keywords: EUV lithography, bright field EUV mask, pitch 28m, scatterometry, Ruthenium damascene metallization, machine learning, process control, E-test prediction, resistance, and capacitance.
In-line Raman spectroscopy for compositional and strain metrology throughout front-end-of-line manufacturing of next generation stacked gate-all-around nanosheet field-effect transistors is presented. Thin and alternating layers of fully strained pseudomorphic Si(1-x)Gex and Si were grown epitaxially on a Si substrate and subsequently patterned. Intentional strain variations were introduced by changing the Ge content (x = 0.25, 0,35, 0.50). Polarization-dependent in-line Raman spectroscopy was employed to characterize and quantify the strain evolution of Si and Si(1-x)Gex nanosheets throughout front-end-of-line processing by focusing on the analysis of Si-Si and Si-Ge optical phonon modes. To evaluate the accuracy of the Raman metrology results, strain reference data were acquired by non-destructive high-resolution x-ray diffraction and from destructive lattice deformation maps using precession electron diffraction. It was found that the germanium-alloy composition as well as Si and Si(1-x)Gex strain obtained by Raman spectroscopy are in excellent agreement with reference metrology and follow trends of previously published simulations.
Keywords: Raman spectroscopy, strain, stress, gate-all-around, nanosheet FET
The processing of gate all-around Si transistors requires to isolate vertically stacked nanometer-thick Si sheets or wires.For this purpose, the SiGe layers of a SiGe/Si superlattice are etched selectively and laterally in a process step commonly called cavity etch1,2. Controlling the quantity of etched SiGe material, i.e. the cavity depth, is critical for optimal device performance. Unfortunately, this critical dimension (CD) can only be measured by time-consuming cross-sectional electron microscopy, which results in limited statistics and hence control of the cavity depth across wafers and batches. As a first step towards the development of fast inline cavity depth measurements, this work evaluates the sensitivity to cavity depth of conventional CD metrology and alternative top-down spectroscopic techniques on samples with cavity depths ranging from 0 to 30 nm. As we show, while optical CD scatterometry remains a technique of choice thanks to its high throughput and sensitivity, Raman and Energy-Dispersive X-ray spectroscopies also show very promising results owing to their simple sensitivity to the remaining SiGe volume. Finally, Secondary Ion Mass Spectrometry offers unique cavity profiling capabilities with a very high sensitivity down to SiGe residues, despite being time-consuming and destructive.
Keywords: cavity etch, lateral recess, critical dimension, inline metrology, Raman spectroscopy, Energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Secondary ion mass spectrometry