Browsing by Author "Ku, CY"

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Expanding the process window and reducing the optical proximity effect by post-exposure delay
(2001-08-01)
Ku, CY
;
Shieh, JM
;
Chiou, TB
;
Lin, HK
;
Lei, TF
In this investigation, a novel idea had been proposed to expand the process window and reduce the optical proximity effect (OPE) by employing post-exposure delay (PED). Our previous work presented a model to specify the resist linewidth according to PED time based on the neutralization mechanism of organic base and photogenerated acid. Based on the model, the exposure latitude and depth of focus can be extended for various pattern sizes by applying PED on linewidth broadening. Moreover, the dense-iso critical dimension bias, which is caused by OPE, can also be reduced when PED is performed. (C) 2001 The Electrochemical Society. [DOI: 10.1149/1.1383557] All rights reserved.
Focus measurement with a simple pattern design
(2001-06-01)
Ku, CY
;
Lei, TF
;
Lin, HK
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The increasingly smaller depth of focus of advanced lithographic tools requires that the position of best focus be determined to ensure accuracy and efficiency. We present what we believe is a novel bar in bar that is drawn on a conventional chrome binary mask to translate focal errors into center-to-center shifts of outer and inner bars. An overlay measurement tool can easily measure this shift. A symmetrical center-to-center shift against best focus is created during defocus, and this shift can be well fitted by a second-order polynomial equation. Simply differentiating the fitted equation leads to an accurate and reliable focus value, with a maximum error of less than 0.05 mum. The proposed technique can also be employed to evaluate the tilt, field curvature, and astigmatism of advanced lithographic tools. (C) 2001 Optical Society of America.
Monitoring lithographic focus and tilting performance by off-line overlay measurement tools
(2001-09-01)
Ku, CY
;
Lei, TF
;
Cheng, DS
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this work we present a novel bar-in-bar (BIB) pattern to monitor the focus and tilting of exposure tools and production wafers. The inner and outer bars contain various hole sizes. When defocused, the shrinkage of the smaller patterns is more significant than that of the larger ones, thus causing the center of gravity to shift. Through the organization of the bar patterns, the centers of inner and outer bars shift in opposite directions when defocused. An overlay measurement tool can be used to easily measure the shift between the centers of inner and outer bars. Therefore, a second-order polynomial equation can precisely fit the measured BIB shift. In addition, an accurate and reliable focus value can be obtained with a maximum error of less than 0.05 mum by simply differentiating the fitting equation. The novel BIB has many applications, such as measuring field curvatures for exposure tools and determining best focus related information for production wafers. (C) 2001 American Vacuum Society.
New overlay pattern design for real-time focus and tilt monitor
(2000)
Ku, CY
;
Lei, TF
;
Shieh, JM
;
Chiou, TB
;
Lin, HK
The reduced depth of focus (DOF) caused by higher numerical aperture (NA) is making the accuracy of best focus measurement increasingly important. A new overlay pattern is developed herein to precisely measure the best focus of lithographic tools. Specially designed "bar-in-bar" (BIB) was employed to obtain the best focus by using the opposite shifting direction of inner and outer bars when defocused. The inner and outer bars are composed of various pattern sizes. When defocused, the shrinkage of the smaller patterns is more significant than that of the larger patterns, thus causing the center of gravity to shift. The distribution and pattern sizes are optimized to obtain high reproducibility and sensitive position shifting for various defocus conditions. Employing the special BIB pattern, the best focus, tilting and field curvature can be easily measured via the conventional overlay measurement tool. By adding the special BIB to the scribe lanes of the production wafers, the best focus and tilting of the stepper can be obtained when measuring a layer-to-layer overlay shift, and can then be fed back to the stepper as a reference for following processing wafers.
Optimal processor mapping for linear-complement communication on hypercubes
(2001-05-01)
Hou, Y
;
Wang, CM
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Ku, CY
;
Hsu, LH
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資訊工程學系
In this paper, we address the problem of minimizing channel contention of linear-complement communication on wormhole-routed hypercubes. Our research reveals that, for traditional routing algorithms, the degree of channel contention of a linear-complement communication can be quite large. To solve this problem, we propose an alternative approach, which applies processor reordering mapping at compile time. in this compiler approach, processors are logically reordered according to the given communication(s) so that the new communication(s) can be efficiently realized on the hypercube network. It is proved that, for any linear-complement communication, there exists a reordering mapping such that the new communication has minimum channel contention. An O(n(3)) algorithm is proposed to find such a mapping for an n-dimensional hypercube. An algorithm based on dynamic programming is also proposed to find an optimal reordering mapping for a set of linear-complement communications. Several computer simulations have been conducted and the results clearly show the advantage of the proposed approach.
Ping-pong flow control for ATM ABR traffic
(2003-09-01)
Ku, CY
;
Hwang, LC
;
Wu, HT
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電信工程研究所
;
Institute of Communications Engineering
In this paper, we propose an improved technique for congestion control, named as ping-pong flow control (PPFC), for asynchronous transfer mode (ATM) available bit rate (ABR) traffic. This is a rate-based flow control scheme, in which the rate regulation is achieved by directly adjusting the transmission rate in the source end station. The proposed algorithm uses a bipolar feedback strategy, which employs positive and negative feedbacks to control the transmission rate for different switch states. These states are determined using the traditional threshold-based method. We also introduce state early detection (SED), which enables the PPFC to control traffic flows more precisely and accurately at critical moments. The simulation results show that the proposed algorithm provides a higher throughput and lower cell loss ratio when compared to the well-known backward explicit congestion notification (BECN). Furthermore, these results also show that PPFC is robust against feedback losses. (C) 2003 Elsevier Science B.V. All rights reserved.
Postexposure delay effect on linewidth variation in base added chemically amplified resist
(2000-10-01)
Ku, CY
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Shieh, JM
;
Chiou, TB
;
Lin, HK
;
Lei, TF
To elucidate the linewidth variation caused by postexposure delay (PED) in resist films, the distribution of photogenerated acid, the role of additional base component, and the affect of exposure energy were investigated in tert-butoxycarbonyl protected-type chemically amplified positive deep ultraviolet resist. The resist system included an N-methyl pyrrolidone organic base which was evaluated via KrF excimer laser lithography. Using various line-and-space patterns formed with a KrF scanner, this work also investigated the change of linewidth caused by the delay time between exposure and postexposure bake. Experimental results indicate that the linewidth broadened immediately following exposure and became a constant value rather than continuously expanding for various pattern sizes. Based on the mechanism of neutralizing organic base and photogenerated acid, a model was established to describe the linewidth according to FED time. Moreover, the effect of exposure energy on linewidth variation was investigated to not only assess the influence of exposure energy but also clarify the relationship between linewidth broadening and delay rime. Experimental analysis demonstrates that the exposure latitude and depth of focus can be improved by employing FED. (C) 2000 The Electrochemical Society. S0013-4651(99)09-090-4. All rights reserved.
Real-time process control to prevent CD variation induced by post exposure delay
(2000)
Ku, CY
;
Lei, TF
;
Shieh, JM
;
Chiou, TB
;
Chen, YC
One of the major problems for DUV resists is linewidth change owing to Post Exposure Delay (PED). Linewidth is mainly induced by acid diffusion during exposure and baking. Based on the mechanism of the neutralization of organic base and photogenerated acid, a model had been generated in our previous study to describe the linewidth variation for different FED times. The derived equation can calculate the minimum elapse time, which will cause linewidth variation to exceed the specification of a specific CD. This work concludes that the smaller CD received a higher percentage of CD variation under FED for an isolated line pattern. Therefore, the minimum acceptable time for the smallest CD can be obtained based on +/- 10% of the nominal CD. When a track alarm occurs and wafer processing stops, wafers between exposure and post exposure bake (PEB) will suffer a CD variation due to FED. The start and end time of each processing wafer is traced herein, and the time interval between one end time and the following start time is calculated via an automatic control system If the time interval exceeds the value set herein, an automatic control system will hold this lot and send an error message to the engineer. Based on the in-line configuration of stepper and track, seven wafers must be reworked when FED occurs. By employing the model and automatic control system established herein, linewidth variation induced by FED can be prevented.