Optimization of segmented alignment marks for advanced semiconductor fabrication processes

Wu, Qiang; Lu, Zhe; Williams, Gary; Zach, Franz X.; Liegl, Bernhard

doi:10.1117/12.436746

Cited by 3 publications

(5 citation statements)

References 2 publications

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“…2(b), are more commonly used for both ground mie compatibility and signal enhancement considerations. The details of the segmentation schemes and their optimization can be found elsewhere [4]. Now we demonstrate that the contrast of these segmented marks can be simulated very efficiently using our thin film code.…”

Section: Direct Imaging Systemmentioning

confidence: 97%

“…According to our previous publication [4], light amplitude scattering from a segmented alignment mark can be described by the following equation,…”

Section: Trench Depthmentioning

confidence: 99%

“…Based on the above theoretical background, we made our own simulation software for both direct imaging and diffractive wafer alignment systems, or, the INterferometric Alignment Signal Intensity Simulator (INASIS) [4].…”

Section: Trench Depthmentioning

confidence: 99%

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Ultrafast wafer alignment simulation based on thin film theory

Wu¹,

Williams

Kim³

et al. 2002

SPIE Proceedings

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The shrink of semiconductor fabrication ground rule continues to follow Moore's law over the past years. However, at the 100 nfl node, the fabrication cost starts to rise rapidly. This is mainly due to the increase of complexity in the fabrication process, including the use of hard masks, planarization, resolution enhancement techniques, etc. Smaller device sizes require higher alignment tolerances. Also, higher degree of complexity makes alignment detection more difficult. For example, planarization techniques may destroy mark topography; hard masks may optically bury alignment marks; and more film layers makes the alignment signal more susceptible to process variations. Therefore, in order to achieve reliable alignment, it is absolutely critical to develop an accurate and fast simulation software that can characterize alignment performance based on the film stack structure. In this paper, we will demonstrate that we have built an extremely fast alignment signal simulator for both direct imaging and diffractive detection systems based on simple optical theory. We will demonstrate through examples using our advanced DRAM products that it is capable of accurately mapping the multi-dimensional parameter space spanned by various film thickness parameters within a short period of time, which allows both on-the-fly feedback in alignment performance and alignment optimization.

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Section: Direct Imaging Systemmentioning

confidence: 97%

“…According to our previous publication [4], light amplitude scattering from a segmented alignment mark can be described by the following equation,…”

Section: Trench Depthmentioning

confidence: 99%

See 1 more Smart Citation

Ultrafast wafer alignment simulation based on thin film theory

Wu¹,

Williams

Kim³

et al. 2002

SPIE Proceedings

Self Cite

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“…It has been shown in the past [1][2][3] that alignment quality largely depends on the alignment signal quality, such as the ASML's "wafer quality", or the short form WQ. The ASML's WQ basically describes the diffracted intensity from grating-like periodical line/space like alignment marks.…”

Section: Introductionmentioning

confidence: 99%

The Impact of the Use of Strongly Absorbing Etch Hard Masks and Shallow Topography to Alignment Signal Strength in 28 nm Technology Nodes and Beyond

Wu¹,

Hao

Shi³

et al. 2012

ECS Trans.

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As the design rule of the semiconductor fabrication continue to shrink in the lateral dimensions, the vertical dimension becomes thinner and the requirement on the planarization becomes higher. In the front end of the line (FEOL), the shallower topography after STI CMP has become significantly thinner than 20 nm, adding the use of strongly absorbing hard mask, such as, amorphous carbon, the signal for alignment detection at the poly layer becomes significantly less than 1% in ASML's wafer quality metric. To get better signal, one will be forced to use an extra mask step to clear out some of the oxide in the STI trenches in the alignment and overlay marks to create necessary topography. In the back end of the line (BEOL), the use of strongly absorbing hard masks, such as, amorphous carbon or titanium containing compound, can also adversely affect alignment signals. At the contact layer, the alignment signal strength can be reduced to around the detection limit, ~1%. At the via layers, due to the use of titanium containing hard mask, the alignment signal to can also be significantly reduced by 1 order of magnitude. In this paper, we will use alignment mark signal simulation to analyze the impact of the shallow topography and the use of typical hard mask to the alignment signal.

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“…When this layer is printed, new wafer alignment marks are created and being aligned by the subsequent layers. These wafer alignment marks are usually segmented grating [158,159] and they are not part of the functional integrated circuits. The idea of using circuit structures as the alignment targets is impractical since complex alignment algorithms needs to be developed.…”

Section: Location and Size Of Alignment Marksmentioning

confidence: 99%

Electromagnetic ray tracing model for line structures and characterization of advanced alignment marks in photolithography

Tan¹

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Line structures are an essential part in integrated circuit (IC) fabrication. In photolithography, the electromagnetic scattering of line structures is one of the main factors that determine the advancement of the technology node. From the perspective of modeling, a theoretical model to physically understand the scattering phenomenon is necessary for a solid foundation in efficient Abstract _____________________________________________________________________________________________ _____________________________________________________________________________________________ iii ERT model, the electromagnetic field that causes a disturbance in the amplitude profile for the total solution was identified and explained in detail. The accuracy of the ERT model was also verified by comparing with the finite difference time domain (FDTD) solution. For a single polysilicon line structure with width of 1.66 λ (λ is the wavelength) on silicon substrate, the developed ERT model was able to demonstrate amplitude correlation coefficient (ACC) of 0.978 and the maximum amplitude difference, Δ|Ez| of as low as-0.067. The subwavelength line width of 0.4 λ was identified as the limit of the ERT model for the single polysilicon line structure. The study of alignment marks focuses on their performance to meet the stringent overlay requirement for advanced technology node process. The simulation results obtained from rigorous coupled wave analysis (RCWA) demonstrated that by incorporating small periodic structure into the conventional alignment mark, the reflected diffraction efficiency was improved at the respective order. The experimental works were performed for 90 nm and 0.11 µm processes. It is demonstrated that overlay as low as 9 nm was achieved when 5th order mark was used for the 90 nm technology node front-end-of-line (FEOL) process. Narrow marks for backend-end-of-line (BEOL) process also showed compatible results with the lowest overlay of 10 nm. _____________________________________________________________________________________________ v of this work. In addition, the experiments would not be possible without the technical support from ASM Lithography, Mr. Lim Ser Yong and Mr. Alex Chew. To all my peers in Chartered Special Project (SP) group, in particular Clark, Timonthy, Caroline, Jia Mei, Suey Li, Gek Soon and Alan, I thoroughly enjoyed the time that we had spent in the SP room. I think the feeling is mutual. Thank you for making my student days in Chartered a memorable one. I would also like to thank Jone for her generous help to proofread all the chapters in this thesis. Last but not least, I would like to thank my parents for their everlasting and unconditional support throughout my graduate studies. Their caring has motivated me to enjoy every second in my daily life, even during the most difficult times of my research work. Table of Contents _____________________________________________________________________________________________

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Optimization of segmented alignment marks for advanced semiconductor fabrication processes

Cited by 3 publications

References 2 publications

Ultrafast wafer alignment simulation based on thin film theory

Ultrafast wafer alignment simulation based on thin film theory

The Impact of the Use of Strongly Absorbing Etch Hard Masks and Shallow Topography to Alignment Signal Strength in 28 nm Technology Nodes and Beyond

Electromagnetic ray tracing model for line structures and characterization of advanced alignment marks in photolithography

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