MIRAI Selete

Tsukuba, Japan

MIRAI Selete

Tsukuba, Japan

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Yamada H.,Tohoku University | Nozawa M.,Tohoku University | Kinoshita M.,NEC Corp | Ohashi K.,MIRAI Selete | Ohashi K.,NEC Corp
Optics Express | Year: 2011

We present a vertical-coupling optical interface with a grating coupler for transmitting and receiving optical signals between single-mode optical fibers and microphotonic waveguides with a view to realize on-chip optical interconnection. The optical interface consisting of a simple grating structure with a reflective mirror and an optical power combiner exhibits high optical coupling efficiency and wide tolerance range for the misalignment of optical fibers. The optical interface exhibits high coupling efficiency even if the optical input is almost vertical to the chip surface. © 2011 Optical Society of America.


Hiraiwa A.,MIRAI Selete | Hiraiwa A.,Renesas Electronics Corporation | Nishida A.,MIRAI Selete
Japanese Journal of Applied Physics | Year: 2011

The authors investigated the effect of scanning-electron-microscope image noise on the accuracy of line-edge-roughness and line-widthroughness (LER/LWR) statistics extracted from power spectral densities (PSDs). To do this, they numerically prepared pseudo-experimental PSDs of LWR using the Monte Carlo (MC) method. The estimation error n decreased with the total number NALL of width data points in the same way as that observed in the absence of the image noise. n first increased gradually with the image-noise intensity R but markedly when R went beyond the threshold value Rth determined by the ratio of the sampling interval δy to the correlation length δy. The PSDs with these Rth's had the same maximum-to-minimum ratio γ (= 10 in this study). The authors approximated n by BNALL-3/4(1+g(R,δ;- 3/8 [1 + g(R;δy/epsi;γ where B is 49. They also empirically determined the functional form of g(R;δy/γεγ). Because these functions well fitted massive MC simulation results, they provide guidelines for setting up analysis conditions for securing arbitrarily prescribed accuracy. © 2011 The Japan Society of Applied Physics .


Hiraiwa A.,MIRAI Selete | Hiraiwa A.,Renesas Electronics Corporation | Nishida A.,MIRAI Selete
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

We established guidelines for accurately analyzing line-edge and line-width roughness (LER and LWR) basing on the recent discrete power-spectral-density (PSD) method. Extraction of correlation length ζ requires a plateau of PSD in a small-wave-number region. This requirement is met by letting a ratio of inspection length L to ζ be larger than 4π. Analysis errors caused by scanning-electron-microscope image noise are determined by ratios of measurement interval Δy to ζ and of noise-induced variance var(φ) to LWR variance var(w). The ratios need to be at most 20/35 and 1, respectively. var(φ) is reduced by averaging image pixels perpendicularly to lines. This averaging does not smooth LWR, unlike parallel averaging. Statistical noise, i.e. jaggy of PSDs, is another noise source that is caused by a finiteness of the number NFT of Fourier transforms averaged to obtain PSDs. The jaggy level decreases with NFT and with a decrease in Δy. Under the above Δy, NFT should preferably be 50 or larger. The total variance of this study was larger than the sum of var(w) and var(φ). The additional roughness results from a long-range correlation that exceeds the limit of this study. It will be analyzed in our forthcoming report. © 2010 Copyright SPIE - The International Society for Optical Engineering.


Hiraiwa A.,MIRAI Selete | Hiraiwa A.,Renesas Electronics Corporation | Nishida A.,MIRAI Selete
Journal of Micro/Nanolithography, MEMS, and MOEMS | Year: 2010

The accuracy of estimated line-edge-roughness and line-widthroughness (LER and LWR) statistics is mostly determined by the noise inherent in experimental power spectral densities (PSDs). One type of noise is statistical noise, a kind of jagged structure, that is caused by the finiteness of a number NL of line segments used in analyses. To keep the estimation error below 5%, the ratio of sampling interval to correlation length should be 0.3 or smaller, and NL needs to be larger than 100 under the condition that the length of line segments is 2000 nm or larger, in compliance with the Semiconductor Equipment and Materials International standard. Another noise type is scanning-electron-microscope image noise. It causes edge-detection errors and induces an additional variation in LER/LWR. This variation raises the minima of PSDs and accordingly enhances the errors. The factor of the error enhancement is suppressed below 1.5 by controlling the ratio of image-noise-induced LER/LWR variance to the true variance below 0.6. This is achieved by averaging image pixels perpendicularly to fine lines, and is free from any appreciable drawbacks. The experimental results agree well with analytical approximations to Monte-Carlo results that are separately obtained. This leads us to obtain more general guidelines for accurate analyses by using the analytical formulas. © 2010 Society of Photo-Optical Instrumentation Engineers.


Hiraiwa A.,MIRAI Selete | Hiraiwa A.,Renesas Electronics Corporation | Nishida A.,MIRAI Selete
Journal of Applied Physics | Year: 2010

Large-scale integrations (LSIs) are facing an ever-growing problem of device variability. One of the origins that cause the variability is line-width roughness (LWR) caused by line edge roughness (LER). Accurate characterization of the LWR plays an essential role in controlling the LWR. To do this, we report a methodology, named the "assembly method," that enables to analyze LWR statistics beyond the conventional correlation length limit, basing on the previous "patchwork" method and recent discrete power spectral density (PSD) method. The methodology virtually assembles a long line by gathering line segments that are randomly scattered on a single line or equally processed different lines. The virtual lines are repeatedly assembled by randomly changing the combination of the segments and the order of the gathered segments while permitting overlaps of the segments between the assembled lines. Squared Fourier transforms of their widths are averaged over the assembled lines to obtain the PSD. By these steps, the statistical noise, which is inherent to experimental PSDs, is markedly reduced. Furthermore, to extract LWR statistics by comparing experimental and theoretical PSDs, we derived an analytic formula of the assembled-line PSD. In the derivation, the randomness of the segment collections played a key role. The PSDs calculated using the formula almost completely fitted experimental PSDs that were obtained by the assembly method. The parameters used in the best-fitted calculation revealed that the photoresist LWR of this study contained a component that had a correlation length of 2780 nm in addition to the previously reported LWR of 35 nm. The LWR variance of the component accounted for approximately 10% of the total variance. The formula also enabled us to evaluate the accuracy of experimentally obtained averages of widths. We find two distinct features in the PSDs by the assembly method. One is the oscillatory structure that shows up in the case when the correlation length is larger than half the length of the segments. A trace of this structure was actually observed in the experimental PSDs of this study. The other is the spikes that are periodically observed as a function of wave number. The spikes originate from a nonstochastic width variation that exists in all the segments in common. Their intensity is proportional to the number of gathered segments in the assembled lines. Because the spikes are excluded from the analysis, the LWR parameters determined by the assembly method are not affected by the nonstochastic variation, unlike the conventional methods. By all these results, we confirm that the assembly method of this study extends the upper limit of analyzable correlation lengths by a factor of approximately 20 and enhances the accuracy as well. This feature also has a practical significance that the widely observed LWR with a correlation length of approximately 35 nm can be analyzed by the assembly method using a conventional critical-dimension scanning-electron-microscope, without resorting to a specially designed one. Accordingly, the method will be a key tool for investigating LER and LWR in developing and manufacturing LSIs. It will also help analyze other stochastic processes in many research and development settings. © 2010 American Institute of Physics.


Hiraiwa A.,MIRAI Selete | Hiraiwa A.,Renesas Electronics Corporation | Nishida A.,MIRAI Selete
Journal of Vacuum Science and Technology B:Nanotechnology and Microelectronics | Year: 2010

The control of line-edge roughness (LER) and line-width roughness (LWR) is a key issue in addressing the growing challenge of device variability in large-scale integrations. The accurate characterization of LER and LWR forms a basis for this effort and mostly hinges on reducing the effects of noise inherent in experimental results. This article reports how a power spectral density (PSD) is affected by a statistical noise that originates from the finiteness of the number NL of available samples. To achieve this, the authors numerically generated line-width data using the Monte Carlo (MC) method and assuming an exponential autocorrelation function (ACF). By analyzing the pseudoexperimental PSDs obtained using the MC data, they found that the standard deviation of normalized analysis errors was determined by the total number NALL of width data used in each analysis, regardless of NL and the number N of width data in each line segment. The authors found that decreased with NALL approximately in inverse proportion to N ALL 3/4. It is noteworthy that they could obtain accurate results even in the case of N L =1 as long as NALL was sufficiently large, although the distribution of PSDs was large due to a large statistical noise. This resulted from the fact that the PSD distribution was not completely irregular, but centered at the true value and that the best-fitted PSD accordingly approached the true one with an increasing N. On the other hand, at a fixed NALL decreased with the ratio Δy/ξ of an interval Δy of width data to a correlation length, approximately in inverse proportion to (Δy/) 3/8. As a result, NALL at a specified decreased with Δy/ξ in inverse proportion to the square root of Δy/ξ in the case when Δy/ξ was 0.3 or smaller. Beyond this threshold of Δy/, the authors needed to increase NALL markedly to achieve the same accuracy of analyses. This comes from a decrease in the range of the PSD with an increasing Δy/ξ and a subsequent loss of sensitivity of the PSD to the change of . Based on these results, they established guidelines for accurate analyses as follows: Δy/0.3 and NALL A -4/3 (Δy/) -1/2, where A is 1.8× 102 for and 7.2× 101 for the variance of widths, respectively. Equivalently in terms of the total measurement length LALL, instead of NALL, the guidelines are given in Δy/0.3 and LALL /A -4/3 (Δy/) 1/2 using the same A 's as those of NALL. Being expressed in universal forms like these, the guidelines of this study can be applied to many practical problems beyond LER and LWR to accurately analyze PSDs, as long as the stochastic processes have exponential ACFs. © 2010 American Vacuum Society.


Hiraiwa A.,Waseda University | Nishida A.,MIRAI Selete | Nishida A.,Renesas Electronics Corporation
Journal of Micro/Nanolithography, MEMS, and MOEMS | Year: 2011

We formerly developed the "assembly method" for analyzing the line-edge and line-width roughness (LER/LWR) that has a long-range correlation beyond the conventional analysis limit, as reported in a previous work. In that method, we repeatedly assembled virtual long lines by gathering line segments, which were arbitrarily disposed on actual long lines and by randomly changing their combination and order, permitting the assembled lines to share the same line segments. Then, we obtained the power spectral density (PSD) of the LER/LWR of the assembled lines considering the lines as seamless. We also derived an analytic formula of the assembled-line PSDs for use in the PSD fitting method. This formula agreed very well with experimental PSDs. In this report, we propose guidelines for suppressing the statistical-noise effect on the assembly method for the purpose of accurately analyzing the long-range-correlated LER/LWR. The guidelines will greatly help shed light on the long-range correlation, which causes the variability even in large devices but has long been veiled due to the lack of metrology. © 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).


Mogami T.,MIRAI Selete
Extended Abstracts of the 11th International Workshop on Junction Technology, IWJT 2011 | Year: 2011

CMOS scaling has been a basic power of LSI development for higher performance, higher packing density and lower cost. For device scaling-down, size miniaturization has been one of the important issues to fabricate fine devices. Furthermore, normal device operation, including reliability, has been another issue. There have been any breakthroughs [1] to lead device scaling-down as shown in Fig. 1. For >100nm regime, simple scaling technologies have been developed. For <100nm regime, oster technologies with scaling-down have been created, In advanced CMOS development for 50nm regime, the variation of device characteristics is one of the


Hiraiwa A.,MIRAI Selete | Nishida A.,MIRAI Selete
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

We formerly developed the "assembly method" for analyzing the line-edge and line-width roughness (LER/LWR) that has a long-range correlation beyond the conventional analysis limit. In the method, we repeatedly assembled virtual long lines by gathering line segments, which were arbitrarily disposed on actual long lines and by randomly changing their combination and order, permitting the assembled lines to share the same line segments. Then, we obtained the PSD of the LER/LWR of the assembled lines considering the lines as seamless. We also derived an analytic formula of the assembled-line PSDs. This formula excellently agreed with experimental PSDs. In this report, we propose guidelines for suppressing the statistical-noise effect on the assembly method for the purpose of accurately analyzing the long-range- correlated LER/LWR. The guidelines will greatly help shed light on the long-range correlation, which causes the variability even in large devices but has long been veiled due to the lack of metrology. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).


Mogami T.,MIRAI Selete
IEEE International Symposium on Semiconductor Manufacturing Conference Proceedings | Year: 2010

□Variation is the most important issue for the Advanced CMOS & LSI's. □LWR and LER are main variation factors in FEOL. □Absolute values of LWR/LER depend on process technology and DFM. □We can improve LWR/LER and RDF, if understand the mechanisms correctly. □Please try new process to improve LWR/LER and RDF. © 2010 ISSM ( Intl Symp on Semiconductor Manufa.

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