Browsing by Author "Chiou, TB"

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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.
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.
Postexposure delay effect on linewidth variation in base added chemically amplified resist
(2000-10-01)
Ku, CY
;
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.