Sungchul Yoo

Apply multiple target for advanced gate ADI critical dimension measurement by scatterometry technology

Scatterometry-based metrology measurements for advanced gate after-develop inspection (ADI) and after-etch inspection (AEI) structures have been well proven1. This paper discusses the metrology challenges encountered in implementing a production-worthy methodology for accurately measuring gate ADI middle CD (MCD) and sidewall angle (SWA) to monitor focus and exposure dose. A Multi-Target Measurement (MTM) methodology on KLA-Tencors SpectraShape 8810 was evaluated on its ability to characterize and measure FEM (Focus Exposure Matrix) and EM (Exposure Matrix) wafers. The correlation of MCD and SWA to the focus and exposure dose was explored. CD-SEM measurements were used as a reference to compare the accuracy of scatterometry MCD measurements. While there was no reference tool available to compare scatterometry SWA measurements, the SWA and focus tracking on the FEM wafer were verified. In addition to the MTM methodology evaluation, a fleet of four SpectraShape 8810 tools was evaluated to measure the fleets capability for in-line monitoring in high volume manufacturing. The final results confirmed that the Multi-Target Measurement approach on SpectraShape 8810 is an effective solution for gate ADI metrology and the robust fleet matching performance would enable in-line monitoring use.

Fast and accurate scatterometry metrology method for STI CMP step height process evaluation

At the 28nm node using 300mm wafers, oxide step height in STI CMP transient gate after-etch inspection (TG AEI) wafers is a critical parameter that affects device performance and should be monitored and controlled. For production process control of this kind of structure, a metrology tool must utilize a non-destructive measurement technique, and have high sensitivity, precision and throughput [1]. This paper discusses a scatterometry-based measurement method for monitoring critical dimension step height in STI CMP instead of traditional measurement methods such as atomic force microscopy (AFM). The scatterometry tool we used for our investigations was the KLA-Tencor SpectraShape 8810, which is the most recent model of the spectroscopic critical dimension (SCD) metrology tools that have been implemented in production for process control of TG AEI structures. AFM was used as a reference metrology technique to assess the accuracy performance of the SpectraShape8810. The first objective of this paper is to discuss the best azimuth angle and floating parameters for scatterometry measurement of the step height feature in TG AEI wafers. Second, this paper describes the tool matching performance of SpectraShape 8810 and correlation to AFM determined using a DOE of TG AEI wafers.

Scatterometry measurement for gate ADI and AEI critical dimension of 28-nm metal gate technology

This paper discusses the scatterometry-based metrology measurement of 28nm high k metal gate after-develop inspection (ADI) and after-etch inspection (AEI) layer structures. For these structures, the critical measurement parameters include side wall angle (SWA) and critical dimension (CD). For production process control of these structures, a metrology tool must utilize a non-destructive measurement technique, and have high sensitivity, precision and throughput. Spectroscopic critical dimension (SCD) metrology tools have been implemented in production for process control of traditional poly gate structures. For todays complex metal gate devices, extended SCD technologies are required. KLA-Tencors new SpectraShape 8810 uses multi-azimuth angles and multi-channel optics to produce the high sensitivity and precision required for measurement of critical parameters on metal gate structures. Data from process of record (POR), focus-exposure matrix (FEM) and design of experiment (DOE) wafers are presented showing the performance of this new SCD tool on metal gate ADI and AEI process structures. Metal gate AEI scatterometry measurement results are also compared to transmission electron microscopy (TEM) reference measurements. These data suggest that the SpectraShape 8810 has the required sensitivity and precision to serve as a production process monitor for 28nm and beyond complex metal gate structures.

Metrology of micro-step height structures using 3D scatterometry in 4x-nm advance DRAM

As DRAM design rules scale below 4Xnm, controlling the micro-step height caused by the etching process after patterning becomes more critical because it affects the post Chemical Mechanical Planarization (CMP) process window and furthermore affects yield. In this study, the latest Multi-Azimuth angle capability of Scatterometry Critical Dimension (SCD) was used to analyze the model of the micro-step height of nitride. SCD results were verified with Atomic Force Microscope (AFM) measurements.

Clean focus, dose and CD metrology for CD uniformity improvement

Lithography process control solutions require more exacting capabilities as the semiconductor industry goes forward to the 1x nm node DRAM device manufacturing. In order to continue scaling down the device feature sizes, critical dimension (CD) uniformity requires continuous improvement to meet the required CD error budget. In this study we investigate using optical measurement technology to improve over CD-SEM methods in focus, dose, and CD. One of the key challenges is measuring scanner focus of device patterns. There are focus measurement methods based on specially designed marks on scribe-line, however, one issue of this approach is that it will report focus of scribe line which is potentially different from that of the real device pattern. In addition, scribe-line marks require additional design and troubleshooting steps that add complexity. In this study, we investigated focus measurement directly on the device pattern. Dose control is typically based on using the linear correlation behavior between dose and CD. The noise of CD measurement, based on CD-SEM for example, will not only impact the accuracy, but also will make it difficult to monitor dose signature on product wafers. In this study we will report the direct dose metrology result using an optical metrology system which especially enhances the DUV spectral coverage to improve the signal to noise ratio. CD-SEM is often used to measure CD after the lithography step. This measurement approach has the advantage of easy recipe setup as well as the flexibility to measure critical feature dimensions, however, we observe that CD-SEM metrology has limitations. In this study, we demonstrate within-field CD uniformity improvement through the extraction of clean scanner slit and scan CD behavior by using optical metrology.

Lithography process controllers and photoresist monitoring by signal response metrology (SRM)

For advanced lithography metrology, SCD (Scatterometry Critical Dimension) is a common metrology technique applied to control processes. SCD has the capability to report accurate data information such as CD (Critical Dimensions), photoresist SWA (Side Wall Angle) and photoresist HT (Height). The shape of photoresist correlates with inline process controllers, namely scanner focus and dose. However, SCD is a model-based metrology method. In order to decode the process controllers, it requires computation from a geometric model. Once the model extracts the resist shape information from the spectra, one needs further correlation of those geometric parameters with the process controllers for monitoring. Thus, information loss through multiple modeling is a major concern. Indeed, during data transformation, noise and model approximation can distort the signals, in other words, the critical parameters, focus and dose, may not be measured accurately. This study therefore seeks a methodology to monitor focus and dose with the least amount of information transformation. Signal Response Metrology is a new measurement technique that obviates the need for geometric modeling by directly correlating focus, dose or CD to the spectral response of a SCD-based metrology tool.

Metrology of advanced N14 process pattern split at lithography

In advanced semiconductor N14 processes, due to the requirement of shrinking pitches for increased densities, pattern split is introduced. However, each of the two pattern split methods, SADP (Self-Aligned Double Patterning) and LELE (Litho-Etch-Litho-Etch), can incur process variations that might cause “pitch walk” [1, 3]. Pitch walk is a by-product of line critical dimension (CD) and spacer error (in SADP) or overlay variations (in LELE). Pitch walk not only results in different line and spaces but also affect the later steps, for example, different etched depths due to loading effects. Because of those behaviors, it is therefore a requirement to control the CD for better uniformity. This paper demonstrates how to use SCD (Scatterometry Critical Dimension) metrology tools to measure the different critical dimensions and spaces to control CD and overlay at the same process step [2]. Traditionally, wafers have to go through both a CD metrology tool and an overlay tool in order to verify CD uniformity and grid uniformity. The methodology introduced in this paper can efficiently shorten cycle time since only the CD metrology tool will be used to verify both CD and overlay. SpectraShape™ is a proven optical CD platform based on spectroscopic ellipsometry and reflectometry. In optical model type metrology, pitch walk can be a challenging parameter to measure due to inherent low sensitivity. Hence this study is performed on the newest generation system, the SpectraShape™ 9010. A new, laser driven light source [4] on this SCD tool provides higher light intensity, producing better signal-to-noise ratios for critical device parameters. This paper explores the use of SCD to measure both resist and hard mask CD in a single step. In addition, results will be presented on using SCD to measure pitch walk, typically a low sensitivity parameter for optical CD metrology tools.

Advanced gate CDU control in sub-28nm node using poly slot process by scatterometry metrology

Scatterometry-based metrology is a well proven method to measure and monitor the critical dimensions of interest in advanced sub-28nm process development and high volume manufacturing [1][3][4][6][7]. In this paper, a proposed solution to control and achieve the optimal gate critical dimension uniformity (CDU) was explored. The proposed solution is named a novel scatterometry slot gate CDU control flow. High performance measurement and control during the slot gate step is critical as it directly controls the poly line cut profile to the active area which then directly impacts the final device performance. The proposed flow incorporates scatterometry-based CD (SCD) measurement feedback and feed forward to the Automation Process Control (APC) system, further process recipe fine tuning utilizing the data feedback and forward, and two dimensional (2D) and three dimensional (3D) scatterometry-based CD (SCD) measurement of gate after developer inspection (ADI) and after etch inspection (AEI) [1]. The methodologies and experiment results presented in this study started from the process development through the SCD model optimization of the DOE wafers, to the final implementation of the process control flow and measurement loop into the production line to evaluate its capability for long term in-line monitoring in high volume manufacturing environment. The result showed significant improvement in the gate CD uniformity that met the sub-28nm process manufacturing requirement.

Scatterometry measurement for SiGe AEI sigma-shaped gate structures of 28nm technology

Novel process control methodologies are required for SiGe gate recess structures that are used in IC manufacturing to enhance device performance. Metrology measurements of 28nm SiGe after-etch inspection U-sigma shaped and V-sigma shaped gate structures must be able to track subtle variations for several critical parameters, including SiGe-to-gate width, tip-to-gate width, sigma depth and recess depth. For production process control of these structures, a metrology tool must utilize a nondestructive measurement technique, and have high sensitivity, precision and throughput. This paper explores the capabilities of a new-generation scatterometry critical dimension (SCD) metrology tool to measure critical parameters and serve as a production process monitor for 28nm and beyond complex gate structures.

Optical Solution of Advanced Production Control for Ultrathin Nitrided Gate Oxides

We present an optical metrology solution based on fab-proven thin film ellipometry system for ultrathin nitrided gate oxide production control in semiconductor manufacturing.