The production of high-resolution flat panel displays (FPDs) for mobile phones today requires the use
of high-quality large-size photomasks (LSPMs). Organic light emitting diode (OLED) displays use
several transistors on each pixel for precise current control and, as such, the mask patterns for OLED
displays are denser and finer than the patterns for the previous generation displays throughout the entire
mask surface. It is therefore strongly demanded that mask patterns be produced with high fidelity and
free of defect. To enable the production of a high quality LSPM in a short lead time, the manufacturers need
a high-sensitivity high-speed mask blank inspection system that meets the requirement of advanced LSPMs.
Lasertec has developed a large-size blank inspection system called LBIS, which achieves high
sensitivity based on a laser-scattering technique. LBIS employs a high power laser as its inspection light
source. LBIS’s delivery optics, including a scanner and F-Theta scan lens, focus the light from the source
linearly on the surface of the blank. Its specially-designed optics collect the light scattered by particles
and defects generated during the manufacturing process, such as scratches, on the surface and guide it to
photo multiplier tubes (PMTs) with high efficiency. Multiple PMTs are used on LBIS for the stable
detection of scattered light, which may be distributed at various angles due to irregular shapes of defects.
LBIS captures 0.3mμ PSL at a detection rate of over 99.5% with uniform sensitivity. Its inspection time
is 20 minutes for a G8 blank and 35 minutes for G10. The differential interference contrast (DIC)
microscope on the inspection head of LBIS captures high-contrast review images after inspection. The
images are classified automatically.
Traditionally, product development for reticle defect inspection mostly addressed operational requirements of the mask shops with highly individualized manufacturing. As a result, limited automation capability was available as compared to the standards in wafer production. Wafer fabs are guided by completely different conditions. Thousands of active reticles exist in a single fab requiring frequent re-inspections without interruption of wafer exposures. This requires high throughput of inspection tools, smart management of tool fleet, sophisticated scheduling and in-time execution of reticle inspections linked to the wafer manufacturing. The paper reports about the successful implementation of fully automated reticle defect inspection in a high-volume advanced logic fab. Automation scenarios - created based on existing SEMI standards - included inspection scheduling, reticle transport and inspection tool operation. A considerable productivity gain for the operation of Lasertec MATRICS X700 series inspection tools was obtained. Based on the learning throughout implementation, the requirements to the
automation capability and tool operation as well as adjustments to working procedures are discussed.
To get wide lithography latitudes in ULSI fabrication, an optical proximity correction system is being widely used. We previously demonstrated that the optical proximity effect is highly dependent on beam interference conditions. By using an aperture with a spindle shaped opaque region and a controlling interference beam number optimized for imaging, we can obtain a high correction accuracy of less than +/- 0.01 micrometers for all kinds of pattern. To put the optical proximity correction into practical use, we must fabricate the corrected mask either by an EB or a laser writing system. But during mask writing, there is another problematic proximity effect. The optical proximity effect caused by mask fabrication error is becoming a serious problem. In this paper, we estimate the optical proximity effect caused by mask fabrication error. For EB writing, the mask feature size of 0.35 micrometers line changes dramatically in a space less than 0.8 micrometers in size; this is not tolerable. For a large pitch pattern, modified illumination reduces the DOF to 0 micrometers . Otherwise, laser writing stably fabricates a mask feature size for a 0.35 micrometers line, and the modified illumination reduces the optical proximity effect. This resist feature fluctuation is binary, so, correcting the mask pattern is easy. Although, it was wrongly thought that for larger pitch pattern, the DOF was reduced by the modified illumination, the DOF reduction actually came from the combination of the two proximity effects. Using an accurate mask produced by a laser writer, we do not observe any DOF reduction in modified illumination. Moreover, this has led to development of an optical proximity correction system with EB proximity correction.
We have developed a high speed automatic inspection system which verifies the validity of electron beam exposure data used for fabrication of VLSI photomasks. By employing neural network accelerator board and adopting a flexible verification scheme based on parallel processing, the system performs 100 times faster than the previous system running on a general purpose workstation. In this paper, the architecture of this system and some salient techniques implemented in the system are presented.
We present a new figure fracturing algorithm that partitions each polygon in layout design data into trapezoids for vriab1eshaped EB exposure data generation. In order to improve the dimension accuracy of fabricated mask patterns created using the figure fracturing result, our algorithm has two new effective functions, one for suppressing narrow figure generation and the other for suppressing critical part partition. Furthermore, using a new graph based approach, our algorithm efficiently chooses from all the possible partitioning lines an appropriate set of lines by which optimal figure fracturing is performed. The application results show that the algorithm produces high quality results in a reasonable processing time.
Because optical lithography requires precise CD control, we developed a fast, accurate proximity correction method based on aerial image simulation. Simple formulas using a linear combination of simulated aerial image intensities both at and around mask edge were found effective for fast, precise CD prediction. Using the developed CD prediction and the fine biasing correction methods, we verified that various two-dimensional patterns printed by an i- line stepper using modified illumination and binary intensity mask are satisfactorily corrected; i.e., CD deviations from designed values, line shortening and feature deformations are effectively reduced.
In order to support next generation ULSI devices, some super resolution techniques are developed. The super resolution technique is effective for smaller pattern but not for larger pattern. This is because the optimum dose is changed, due to the pattern characteristic. However, the z-image profile has sufficient focus latitude. To overcome this problem, the optical proximity correction (OPC) is effective. This phenomenon is observed in the conventional illumination as well as the other super resolution technique. Thus, we developed the OPC system. Using the parallel processing system, we can correct the memory device data in about 2 days. The active region reduction due to the optical diffraction was preferably compensated by the OPC system. Therefore, the OPC system can be applied to the practical use. The OPC system is applicable to the super resolution. Consequently, the applicability of the super resolution technique is significantly enhanced.
This paper describes new database inspection technologies for pattern inspection of ULSI 5x reticles. An improved
inspection system architecture which addresses three important factors: sensitivity, data volume, and inspection
throughput is studied. To improve defect detection sensitivity, the high resolution optical images which are captured by
the inspection system are enhanced using programmable finite impulse response filters. New defect detection
algorithms are utilized. Increased resolution is also incorporated in the database images. Higher resolution database
images are especially effective in improving sensitivity and reducing false detections in small pattern geometry. The
database format has also been optimized to minimize the disk storage requirements and network file transfer time. The
new database generator is capable of expanding compacted data and creating grey level bit mapped images in real time.
Experimental results are reported using actual 5x reticle inspection results and simulated reticle data for ULSI chips,
such as 64Mbit DRAM and l6Mbit SRAM. The results indicate that 5x reticles can be inspected for O.3im defects
with an acceptable level of false detections and throughput that is comparable to eleciron beam write times.