Thaddeus Gerard Dziura

Measurement of high-k and metal film thickness on FinFET sidewalls using scatterometry

Aggressive CMOS transistor scaling requirements have motivated the IC industry to look beyond simply reducing the film thickness or implementing different gate stack materials towards fundamentally redesigning the transistor architecture by forcing the silicon channel to protrude upwards from the planar (2D) substrate. These 3D transistors, namely FinFETs, ideally offer at least a 2X improvement in the drive current since more than one surface is available, for which the minority carrier population can be adjusted by an applied voltage. However, the ability to modulate this voltage is known to suffer due to the non-uniform film deposition on the three sides of the Si Fin. This concern is of immediate interest because it impedes device performance and future integration since subtle differences among the thicknesses on each side of the Fin will negatively impact threshold voltage and the capability to tune the effective work function. It is therefore necessary to have an in-line metrology capability that can properly characterize and understand the deposition of both the high-k and metal gate film on the sidewalls of the Fin in order for FinFETs to ultimately replace planar CMOS devices. We will report on the ability of scatterometry to accurately measure the high-k and metal film thickness on the sidewall of the FinFET. The results will be discussed in detail with emphasis on sensitivity towards fin critical dimension (CD) and sidewall thickness, and comparison of the conclusions reached from the analysis with cross-sectional transmission electron microscopy (TEM) data.

Advanced process control for poly-Si gate etching using integrated CD metrology

Advanced integrated metrology capability is actively being pursued in several process areas, including etch, to shorten process cycle times, enable wafer-level advanced process control (APC), and improve productivity. In this study, KLA-Tencors scatterometry-based iSpectra Spectroscopic CD was integrated on a Lam 2300 Versys Star silicon etch system. Feed-forward control techniques were used to reduce critical dimension (CD) variation. Pre-etch CD measurements were sent to the etch system to modify the trim time and achieve targeted CDs. CDs were brought to within 1 nm from a starting CD spread of 25 nm, showing the effectiveness of this process control approach together with the advantages of spectroscopic CD metrology over conventional CD measurement techniques.

Spectroscopic CD metrology for sub-100-nm lithography process control

The accelerating trend to smaller linewidths and low-k1 lithography makes metrology and process control more challenging with each succeeding technology generation. Optical CD metrology based on spectroscopic ellipsometry provides higher precision, improved matching, and richer information for line width and shape (profile) control which complement conventional litho metrology techniques. Analysis of site-to-site, within-field, field-to-field, and cross-wafer CD and line-shape distributions using KLA-Tencor SpectraCD permits separation of sources of variation between the stepper and track thus enabling proper process control. Focus-exposure analysis using SpectraCD data provides a more complete understanding of the lithography process window. Comparison between SpectraCD CD measurements on nominal 1:5 Line/Space ratio grating targets to isolated line CD-SEM measurements show excellent correlation over a large focus-exposure process range, including sub-100nm features. This result provides verification that SCD measurements on grating targets can be used to monitor and provide feedback to lithography process for isolated lines.

Scatterometry measurements of line end shortening structures for focus-exposure monitoring

Spectroscopic critical dimension (SCDTM) metrology on line gratings has previously been shown to be a sensitive and useful technique for monitoring lithographic focus and exposure conditions. Line end shortening (LES) effects are sensitive to focus and potentially more sensitive to focus variation than side wall angle or other profile parameters of line gratings. Rectangular line segment structures that exhibit line-end shortening behavior are arranged in a rectangular two-dimensional (2D) array to provide a scatterometry signal sensitive to the profile of the thousands of line ends in the measurement beam spot. Spectroscopic ellipsometry (SE)-based scatterometry measurements were carried out on 2D array targets of rectangular features exposed in a focus-exposure matrix (FEM). The focus and exposure sensitivities of multiple shape parameters were found to be good and uniquely separable. In addition, the side wall angle of the line ends was found to be nearly linearly dependent on focus and provide necessary focus direction information. Focus and exposure can be determined from SCD measurements by applying a model generated to describe the focus-exposure behavior of multiple shape parameters using KLA Tencors KT Analyzer software. Several different models based on different combinations of shape parameters were evaluated. Focus measurement precision of 3nm 3σ was obtained, which will be useful for lithography processes with tight depth of focus.

Proximity matching for 193 nm scanner using scatterometry

In this paper, we evaluate several approaches for proximity matching on a 193nm scanner system such as image contrast tuning, illumination tuning and photoresist tuning. Both experimental and simulation studies are carried out to reveal the differences between approaches. We find that it is very important to determine the root cause of proximity mismatch before attempting proximity matching, and that spectroscopic scatterometry is an excellent tool for OPC tuning

Feasibility of improving CD-SEM-based APC system for exposure tool by spectroscopic-ellipsometry-based APC system

Lot-to-lot ADI CD data are generally used to tighten the variation of exposure energy of an exposure tool through an APC feedback system. With decreasing device size, the process window of an exposure tool becomes smaller and smaller. Therefore, whether the ADI CD can reveal the real behavior of a scanner or not becomes more and more a critical question, especially for the polysilicon gate layer. CD-SEM has generally been chosen as the metrology tool for this purpose. Because of the limitations of top-down CD-SEMs, an APC system could be easily misled by improper ADI CD data if the CD data were measured on a T-topped photo resist. ArF resist shrinkage and line edge roughness are also traditional causes for improper CD feedback if the user did not operate the CDSEM carefully. Another candidate for this APC application is spectroscopic-ellipsometry-based scatterometry technology, commonly referred to as SpectraCD. In recent studies, SpectraCD was proven to be able to reveal profile variation with excellent stability. The feasibility of improving a CDSEM-based APC system by a SpectraCD-based system in a high-volume manufacturing fab is therefore worthy of study. This study starts from an analysis of the historical data for the polysilicon ADI CD of a 130 nm product. Two different sets of CD measured from the two different metrology tools were analyzed. In the fab, CDSEM was the metrology tool chosen for the APC feedback. The CD data measured by SpectraCD over a 2 month timeframe were plotted as a CD trend chart of the specific exposure tool. There are several trend-ups and trend-downs observed, even though the overall CD range is small. After a series of analyses, the exposure tool has been proven to be quite stable and the CD data measured by SpectraCD also reveal the real behavior of the exposure tool correctly. The scanner is shown to have been misled by improper CD feedback. In comparison with CDSEM, the linearity of the correlation between ADI and AEI CDs, which represents the consistence of etch bias, can also be improved from 0.4 to 0.8 by SpectraCD. The root causes are still under investigation, but one suspected reason is related to resist profile. All the analysis results will be reported in this paper. The data provided sufficient motivation for switching the APC feedback system of the fab from a CDSEM-based system to a SpectraCD-based system. The results of the new APC system will also be discussed.

Vertical-cavity surface-emitting lasers and arrays for optical interconnect and optical computing applications

Vertical cavity surface emitting lasers (SELs) offer many desirable features that are suitable for applications in optical interconnect, optical signal processing, and optical computing. We describe a GaAs vertical cavity SEL with a novel structure and discuss those key laser performance characteristics, such as threshold current, power output, efficiency, far field divergence, and modulation response, that are important to these potential applications.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Spectroscopic critical dimension technology (SCD) for directed self assembly

Directed self-assembly (DSA) is being actively investigated as a potential patterning solution for future generation devices. While SEM based CD measurement is currently used in research and development, scatterometry-based techniques like spectroscopic CD (SCD) are preferred for high volume manufacturing. SCD can offer information about sub-surface features that are not available from CD-SEM measurement. Besides, SCD is a non-destructive, high throughput technique already adopted in HVM in several advanced nodes. The directed self assembly CD measurement can be challenging because of small dimensions and extremely thin layers in the DSA stack. In this study, the SCD technology was investigated for a 14 nm resolution PS-b-PMMA chemical epitaxy UW process optimized by imec. The DSA stack involves new materials such as cross-linkable polysterene (XPS) of thickness approximately 5 nm, ArF immersion resist (subsequently removed), -OH terminated neutral brush layer, and BCP material (Polystyrene-blockmethyl methacrylate of thickness roughly 20 to 30 nm). The mask contains a large CD and pitch matrix, for studying the quality of self-assembly as a function of the guide pattern dimensions. We report on the ability of SCD to characterize the dimensional variation in these targets and hence provide a viable process control solution.

Modulation characteristics of vertical-cavity surface-emitting lasers

Vertical cavity surface emitting lasers (VCSELs) with a low threshold current and a large modulation bandwidth are desirable for applications in digital and analog optoelectronic signal processing and optical interconnection. These lasers emit light perpendicular to the surface of the semiconductor wafer and allow processing and optoelectronic integration using planar techniques. They also have a short optical cavity and small active volume that promise high speed and low threshold current operation. In this paper we describe the high frequency response characteristics of low threshold current surface emitting lasers we have developed. The laser is a GaAs vertical cavity surface emitting laser with a single quantum well active region and a short Bragg reflector cavity. We describe the key dc operation characteristics of the laser, such as threshold current, device resistance, and differential quantum efficiency that are important to laser high speed operation. The investigation of the dynamic response of the lasers under various direct current modulation conditions is discussed, and experimental results on modulation response and second harmonic distortion are presented. The limitations on high speed response and the effect of parasitic impedance on dynamic response of the laser are described.