Mr. John C. Lam Profile

John C. Lam

Senior Member of the Technical Staff at n&k Technology Inc

SPIE Involvement:

Author

Publications (11)

Proceedings Article | 17 October 2008 Paper

Comparative scatterometric CD measurements on a MoSi photo mask using different metrology tools

Jan Richter, Jens Rudolf, Bernd Bodermann, John Lam

Proceedings Volume 7122, 71222U (2008) https://doi.org/10.1117/12.800732

KEYWORDS: Critical dimension metrology, Photomasks, Scatterometry, Scanning electron microscopy, Metrology, Phase shifts, Etching, Quartz, Diffraction, Phase measurement

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Proceedings Article | 2 May 2008 Paper

Measuring contact hole corner rounding uniformity using optical scatterometry

John Lam, Alexander Gray, Stanley Chen, Jan Richter

Proceedings Volume 6792, 679212 (2008) https://doi.org/10.1117/12.798790

KEYWORDS: Reflectivity, Scatterometry, Transmittance, Photomasks, Spectrophotometry, Metrology, Nondestructive evaluation, Lamps, Visible radiation, Light

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Proceedings Article | 1 November 2007 Paper

CD-signature evaluation using scatterometry

Jan Richter, Phillipp Laube, John Lam

Proceedings Volume 6730, 67304R (2007) https://doi.org/10.1117/12.741263

KEYWORDS: Critical dimension metrology, Scatterometry, Scatter measurement, Metrology, Photomasks, Feedback loops, Data corrections, Data modeling, Systems modeling, Numerical analysis

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The current abilities for active feedback loops to correct for various parameters challenge metrology groups to provide exact input data for these correction cycles. One of the most important feedback loops is the one that deals with the improvement of the CD (critical dimension) uniformity of structures. Here, several processes rely on exact metrology data to tackle systematic effects that either have to be overcome by finding better process conditions or compensated actively, for instance, by tuning the writer data. Right now most of these processes tackle long range effects on the order of millimetres and do not vary a lot on the micrometer scale. On the other hand, CD measurements are usually performed with instruments that measure single points with dimensions of a couple of micrometers (such as the conventional CD-SEM). Thus noise from the micrometer scale is introduced in the global mapping of the uniformity. Recently, numerical methods, such as the exponentially weighted penalty approach called TPS (thin plate splines) have been developed that separate between the true signatures on the millimetre scale from the noise of the micrometer measurements. In this paper, we will take one step further by showing that the acquired statistically stable CD signature of a CD-SEM measurement matches the CD data measured by a scatterometer. Furthermore, we will show that the residual of the CD data of the scatterometer measurement compared to the found TPS fit has a noise level of about 0.1 nm (3σ), which essentially equals the short-term reproducibility of the tool. This is of high importance since both methods do essentially the same - they average out micrometer noise with the only difference being that TPS does it theoretically and a scatterometer does experimentally. Thus, we have the extremely fortunate situation in which theory and experiment give the same results. Hence, two separate conclusions can be drawn: the scatterometer measures indeed stable macroscopic CD signatures and TPS is indeed the right method to extract these signatures from any given CD data.

Proceedings Article | 30 October 2007 Paper

Measurements of corner rounding in 2D contact holes on phase-shift masks using broadband reflectance and transmittance spectra in conjunction with RCWA

Alexander Gray, John Lam, Stanley Chen, Jan Richter

Proceedings Volume 6730, 67303C (2007) https://doi.org/10.1117/12.747569

KEYWORDS: Transmittance, Reflectivity, Critical dimension metrology, Optical properties, Diffraction, Matrices, Scatterometry, Signal to noise ratio, Inspection, Photomasks

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Proceedings Article | 14 May 2007 Paper

Polarized transmittance-reflectance scatterometry measurements of 2D trench dimensions on phase-shift masks

John Lam, Alexander Gray, Rafael Howell, Stanley Chen

Proceedings Volume 6607, 660710 (2007) https://doi.org/10.1117/12.728949

KEYWORDS: Transmittance, Reflectivity, Scatterometry, Scatter measurement, Critical dimension metrology, Dispersion, Signal to noise ratio, Optical testing, Quartz, Photons

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Proceedings Article | 3 May 2007 Paper

Innovative application of the RCWA method for the ultra-sensitive transmittance-based CD measurements on phase-shift masks

Alexander Gray, John Lam, Stanley Chen

Proceedings Volume 6533, 65330F (2007) https://doi.org/10.1117/12.736963

KEYWORDS: Transmittance, Reflectivity, Critical dimension metrology, Photomasks, Optical testing, Polarization, Scatterometry, Optical properties, Chemical elements, Phase measurement

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Proceedings Article | 20 October 2006 Paper

Novel technique for critical dimension measurements of phase-shift masks using broadband transmittance spectra in conjunction with RCWA

Alexander Gray, John Lam, Stanley Chen

Proceedings Volume 6349, 634949 (2006) https://doi.org/10.1117/12.693243

KEYWORDS: Transmittance, Reflectivity, Critical dimension metrology, Photomasks, Polarization, Optical testing, Metrology, Optical properties, Optics manufacturing, Phase measurement

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Proceedings Article | 20 October 2006 Paper

Fast nondestructive optical measurements of critical dimension uniformity and linearity on AEI and ASI phase-shift masks

Alexander Gray, John Lam

Proceedings Volume 6349, 63491O (2006) https://doi.org/10.1117/12.686150

KEYWORDS: Photomasks, Critical dimension metrology, Pellicles, Phase shifts, Nondestructive evaluation, Optical properties, Transmittance, Reflectometry, Manufacturing, Inspection

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The fabrication of a production-worthy phase shift mask requires, among other things, excellent uniformity of critical dimensions (trench width and depth) and optical properties of the phase shift material (MoSi). Traditionally, CD-SEM has been the instrument of choice for the measurement of width; AFP (Atomic Force Profilometer) or conventional profilometer for the measurement of depth; and Interferometer for the measurement of phase shift and transmittance of the phase shift material. We present an innovative optical metrology solution based on broadband reflectometry, covering a wavelength range from 190 to 1000 nm, in one nanometer intervals. The analysis is performed using Forouhi-Bloomer dispersion equations, in conjunctions with Rigorous Coupled Wave Analysis (RCWA). The method provides accurate and repeatable results for critical dimensions, thickness, and optical properties (n and k spectra from 190 - 1000 nm) for all materials present in the structure. In the current study, the method described above was used to examine photomasks at two stages of mask manufacturing process: After Etch Inspection (AEI) and After Strip Inspection (ASI). The results were compared with the measurements taken on the same samples using conventional CD-SEM. Two comparison studies were conducted - global CD uniformity and CD linearity. The CD linearity study demonstrated excellent correlation between the values of grating line width obtained using this new optical reflectometry approach and a CD-SEM for the grating structures of two pitches (760 nm and 1120 nm). The global CD uniformity study revealed that this presented reflectometry method can be used to produce CD uniformity maps which demonstrate excellent correlation with the results obtained using a conventional CD-SEM. The advantages of the optical method are high throughput, non-destructive nature of the measurements and capability to measure a wider variety of structures pertinent to the photomask manufacturing process.

Proceedings Article | 24 March 2006 Paper

Optical measurements of critical dimensions at several stages of the mask fabrication process

John Lam, Alexander Gray

Proceedings Volume 6152, 61523C (2006) https://doi.org/10.1117/12.654685

KEYWORDS: Critical dimension metrology, Chromium, Metrology, Inspection, Optical properties, Reflectivity, Manufacturing, Phase shifts, Transmittance, Reflectometry

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