Mr. Kujan Gorhad Profile

Kujan Gorhad

at Carl Zeiss SMS Ltd

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Publications (5)

Proceedings Article | 29 August 2019 Paper

Enhanced wafer overlay residuals control: deep sub-nanometer at sub-millimeter lateral resolution

Yael Sufrin, Philippe Leray, Eren Canga, Avi Cohen, Vladimir Dmitriev, Kujan Gorhad

Proceedings Volume 11177, 111770J (2019) https://doi.org/10.1117/12.2535641

KEYWORDS: Photomasks, Semiconducting wafers, Overlay metrology, Scanners, Image processing, Deep ultraviolet, Lithography, Metrology, Chemical elements, Error analysis

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The introduction of advanced technology nodes in deep UV (DUV) lithography (litho), involving multiple litho steps, has tightened the wafer on-product overlay specifications [1]. The industry trend already pushes the overlay requirements to the sub-nanometer regime (and so the mask registration requirements tightens as well). In the most general view, wafer on-product overlay errors are a combination of intra-field (within field) and inter-field (field-to-field) errors. A given litho layer intra-field overlay error includes several systematic sources, such as scanner lens-to-lens residuals and mask writer residuals. Parallel to the nodes and litho techniques advancing, the ability to accurately measure overlay at high lateral resolution have being successfully introduced, both at wafer and mask side. The recent developments in scanner technology improved the ability to control intra-field overlay at high-order across the exposure field. However, this is still in several millimeter lateral resolution control ability at its best, leaving residual errors in the sub-millimeter to few millimeter regime without the ability to further suppress them to the target specification, nevertheless, not to the sub-nanometer magnitude. In this work, we have empirically evaluated the ZEISS state-of-the-art mask tuning solution named ForTune ERC (Enhanced Registration Control). This solution is based on laser processing of the mask bulk by the ZEISS ForTune tool. It allows to suppress few nanometer overlay residuals (post the scanner best-can-do) down to deep sub-nanometer, all even at sub-millimeter sampling resolution (x1 wafer level) and low-to-high residuals modulating frequency. For the sake of this study, we have used a dual-image mask to form one overlay signature at wafer side. Two wafers have been exposed prior to the laser-based tuning of the mask bulk; the wafers overlay error was measured and used as an initial overlay problem to begin with. A second exposure of two additional wafers was performed post the problem- solving by the ERC model and the consequent mask laser-based tuning. The pre/post wafers were then compared to examine the improvement in overlay at wafer side. CD uniformity (CDU) data has been collected as well, to confirm no degradation in CDU due to the ForTune ERC process. The combination of this advanced method of intra-field control with high-order correction per exposure (CPE) by the scanner, provides an efficient co-optimized solution to tightly control the overlay of existing and future nodes at DUV litho.

Proceedings Article | 26 March 2019 Paper

Enhanced wafer overlay residuals control; deep sub-nanometer at sub-millimeter lateral resolution

Avi Cohen, Philippe Leray, Eren Canga, Vladimir Dmitriev, Kujan Gorhad, Yael Sufrin

Proceedings Volume 10959, 109592K (2019) https://doi.org/10.1117/12.2516362

KEYWORDS: Photomasks, Semiconducting wafers, Overlay metrology, Scanners, Deep ultraviolet, Lithography, Metrology

Read Abstract +

The recent developments in scanner technology improved the ability to control intra-field overlay at high-order across the exposure field. However, this is still in several millimeter lateral resolution control ability at its best, leaving residual errors in the sub-millimeter to few millimeter regime without the ability to further suppress them to the target specification, nevertheless, not to the sub-nanometer magnitude.

In this work, we have empirically evaluated the ZEISS state-of-the-art mask tuning solution named ForTune ERC (Enhanced Registration Control). This solution is based on laser processing of the mask bulk by the ZEISS ForTune tool. It allows to suppress few nanometer overlay residuals (post the scanner best-can-do) down to deep sub-nanometer, all even at sub-millimeter sampling resolution (x1 wafer level) and low-to-high residuals modulating frequency.

For the sake of this study, we have used a dual-image mask to form one overlay signature at wafer side. Two wafers have been exposed prior to the laser-based tuning of the mask bulk; the wafers overlay error was measured and used as an initial overlay problem to begin with. A second exposure of two additional wafers was performed post the problem-solving by the ERC model and the consequent mask laser-based tuning. The pre/post wafers were then compared to examine the improvement in overlay at wafer side. CD uniformity (CDU) data has been collected as well, to confirm no degradation in CDU due to the ForTune ERC process.

The combination of this advanced method of intra-field control with high-order correction per exposure (CPE) by the scanner, provides an efficient co-optimized solution to tightly control the overlay of existing and future nodes at DUV litho.

Proceedings Article | 8 March 2016 Paper

Co-optimization of RegC and TWINSCAN corrections to improve the intra-field on-product overlay performance

Kujan Gorhad, Ofir Sharoni, Vladimir Dmitriev, Avi Cohen, Richard van Haren, Christian Roelofs, Hakki Ergun Cekli, Emily Gallagher, Philippe Leray, Dirk Beyer, Thomas Trautzsch, Steffen Steinert

Proceedings Volume 9778, 97783D (2016) https://doi.org/10.1117/12.2219291

KEYWORDS: Semiconducting wafers, Scanners, Reticles, Overlay metrology, Image processing, Process control, Lithography, Yield improvement, Chemical elements, Photomasks, Actuators, Image registration, Metrology, Lithium

Read Abstract +

Improving wafer On Product Overlay (OPO) is becoming a major challenge in lithography, especially for multipatterning techniques like N-repetitive Litho-Etch steps (LE^N, N ≥ 2). When using different scanner settings and litho processes between inter-layer overlays, intra-field overlay control becomes more complicated. In addition to the Image Placement Error (IPE) contribution, the TWINSCAN^TM lens fingerprint in combination with the exposure settings is playing a significant role as well. Furthermore the scanner needs to deal with dynamic fingerprints caused by for instance lens and/or reticle heating.

This paper will demonstrate the complementary RegC^® and TWINSCAN^TM solution for improving the OPO by cooptimizing the correction capabilities of the individual tools, respectively. As a consequence, the systematic intra-field fingerprints can be decreased along with the overlay (OVL) error at wafer level. Furthermore, the application could be utilized for extending some of the scanner actuators ranges by inducing a pre-determined signatures. These solutions perfectly fit into the ASML Litho InSight (LIS) product in which feedforward and feedback corrections based on YieldStar overlay and other measurements are used to improve the OPO. While the TWINSCAN^TM scanner corrects for global distortions (up to third order) - scanner Correctable Errors ( CE), the RegC^® application can correct for the None Correctable Errors (NCE) by making the high frequency NCE into a CE with low frequency nature. The RegC^® induces predictable deformation elements inside the quartz (Qz) material of the reticle, and by doing so it can induce a desired pre-defined signature into the reticle. The deformation introduced by the RegC^® is optimized for the actual wafer print taking into account the scale and ortho compensation by the scanner, to correct for the systematic fingerprints and the wafer overlay. These two applications might be very powerful and could contribute to achieve a better OPO performance.

Proceedings Article | 19 March 2015 Paper

Intra-field on-product overlay improvement by application of RegC and TWINSCAN corrections

Ofir Sharoni, Vladimir Dmitriev, Erez Graitzer, Yuval Perets, Kujan Gorhad, Richard van Haren, Hakki Cekli, Jan Mulkens

Proceedings Volume 9424, 94241K (2015) https://doi.org/10.1117/12.2085651

KEYWORDS: Photomasks, Scanners, Semiconducting wafers, Image registration, Reticles, Overlay metrology, Lithium, Distortion, Metrology, Actuators

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The on product overlay specification and Advanced Process Control (APC) is getting extremely challenging particularly after the introduction of multi-patterning applications like Spacer Assisted Double Patterning (SADP) and multipatterning techniques like N-repetitive Litho-Etch steps (LE^N, N ≥ 2). When the latter is considered, most of the intrafield overlay contributors drop out of the overlay budget. This is a direct consequence of the fact that the scanner settings (like dose, illumination settings, etc.) as well as the subsequent processing steps can be made very similar for two consecutive Litho-Etch layers. The major overlay contributor that may require additional attention is the Image Placement Error (IPE). When the inter-layer overlay is considered, controlling the intra-field overlay contribution gets more complicated. In addition to the IPE contribution, the TWINSCAN^TM lens fingerprint in combination with the exposure settings is going to play a role as well. Generally speaking, two subsequent functional layers have different exposure settings. This results in a (non-reticle) additional overlay contribution.

In this paper, we have studied the wafer overlay correction capability by RegC® in addition to the TWINSCAN^TM intrafield corrections to improve the on product overlay performance. RegC® is a reticle intra-volume laser writing technique that causes a predictable deformation element (RegC® deformation element) inside the quartz (Qz) material of a reticle. This technique enables to post-process an existing reticle to correct for instance for IPE. Alternatively, a pre-determined intra-field fingerprint can be added to the reticle such that it results in a straight field after exposure. This second application might be very powerful to correct for instance for (cold) lens fingerprints that cannot be corrected by the scanner itself. Another possible application is the intra-field processing fingerprint. One should realize that a RegC® treatment of a reticle generally results in global distortion of the reticle. This is not a problem as long as these global distortions can be corrected by the TWINSCAN^TM system (currently up to the third order). It is anticipated that the combination of the RegC® and the TWINSCAN^TMcorrections act as complementary solutions. These solutions perfectly fit into the ASML Litho InSight (LIS) product in which feedforward and feedback corrections based on YieldStar overlay measurements are used to improve the on product overlay.

Proceedings Article | 29 October 2014 Paper

Further beyond: registration and overlay control enhancements for optical masks

Kujan Gorhad, Avi Cohen, Dan Avizemer, Vladimir Dmitriev, Dirk Beyer, Wolfgang Degel, Markus Kirsch

Proceedings Volume 9235, 92351P (2014) https://doi.org/10.1117/12.2066145

KEYWORDS: Photomasks, Image registration, Overlay metrology, Image processing, Pellicles, Metrology, Semiconducting wafers, Scanners, Data acquisition, Quartz

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