Lin-Hung Shiu

Characterization of ArF immersion process for production (Invited Paper)

ArF immersion lithography is essential to extend optical lithography. In this study, we characterized the immersion process on production wafers. Key lithographic manufacturing parameters, overlay, CD uniformity, depth of focus (DOF), optical proximity effects (OPE), and defects are reported. Similar device electrical performance between the immersion and the dry wafers assures electrical compatibility with immersion lithography. The yield results on 90-nm Static Random Access Memory (SRAM) chips confirm doubling of DOF by immersion as expected. Poly images of the 65-nm node from a 0.85NA immersion scanner are also shown.

45nm node planar-SOI technology with 0.296 /spl mu/m/sup 2/ 6T-SRAM cell

The first 45nm node planar-SOI technology has been developed with 6T-SRAM cell of 0.296 /spl mu/m/sup 2/. An adequate static noise margin of 120mV is obtained even at 0.6V operation. Fine patterning with line pitch of 130nm and contact pitch of 140nm by optical lithography is demonstrated. Transistors with 30nm gate length and 27nm slim spacer operate at 1V/0.85V with excellent drive currents of 1000/740 and 530/420 /spl mu/A//spl mu/m for N-FET and P-FET, respectively. The P-FET current is the best reported so far.

Study of mask corner rounding effects on lithographic patterning for 90-nm technology node and beyond

This paper presented an integrated simulation framework linking our in-house mask writer simulator and the optical lithography simulation engines to include the mask corner rounding effect in lithographic performance evaluations. In the writer simulator, a modified two-dimensional Gaussian function is used as the functional form of the convolution kernel (point spread function). Parameters of the kernel function for different writing machines are automatically extracted from scanning electron microscope (SEM) photographs of simple mask pattern geometries. The convolution results of the kernel and the mask layout form the intensity distribution for pattern definition. The isocontour of the resulting image at the desired level of bias can be regarded as a good approximation of the mask shape obtained from a real mask writer. The writer simulator then saves the contour data as the user-specified format of mask file for subsequent lithography simulations. With the aid of this simulation tool, the impacts of mask corner rounding effects on two-dimensional OPCed pattern for 90-nm and 65-nm node lithography processes are quantitatively evaluated. The results show the line end shortening (LES) is greatly influenced by mask corner rounding effects. The LESs in the 65-nm node process are over twice of those in the 90-nm node process. The resolution capability of a 2-stage 16X mask manufacturing process was also studied in this paper. Simulation results indicate the ArF lithography might be required to make this innovative mask-making technology suitable for 90-nm generation and beyond.

Focus latitude enhancement of symmetrical phase mask design for deep submicron contact hole patterning

The mechanism of focus latitude enhancement for contact/via hole printing is explained by approximating the axis intensity distribution of an image as a series of cosine functions to characterize the interference between each pair of diffraction beams. It is found that a phase-shifting mask (PSM) with symmetrical assist features improves the depth of focus (DOF) by introducing destructive interference to counterbalance the intensity fluctuation from constructive interference as defocus. A simple formula was derived to represent the capability of focus latitude enlargement. It shows that the extent of enhancement depends on the exposure wavelength and numerical aperture of a projection lens only. Increasing the degree of partial coherence degrades the focal range enlargement because a larger illumination angle elongates the destructive interference pattern in the optical-axis direction to weaken its ability for intensity compensation. On the other hand, the lack of constructive interference in dense hole i...

Immersion defect reduction, part II: the formation mechanism and reduction of patterned defects

193-nm immersion lithography is the only choice for the 45-nm logical node at 120-nm half pitch and extendable to 32- and 22-nm nodes. The defect problem is one of the critical issues in immersion technology. In this paper, we provided a methodology to trace the defect source from optical microscope images to its SEM counterparts after exposure. An optimized exposure routing was also proposed to reduce printing defects. The average defect count was reduced from 19.7 to 4.8 ea/wafer.

Defect reduction with special routing for immersion lithography

This letter reports record-breaking low defect counts for immersion lithography, the mechanism for forma- tion of particle-printing defects, and for two new exposure routings to achieve the low defect counts. Both new routings make the slot-scan directions parallel to the field-stepping directions, whereas in the normal routing the two directions are perpendicular to each other. From experimental data, the average defect count for one of the special routings is 4.8 per wafer, while it is 19.7 per wafer for normal routing.

Immersion defect reduction, part I: analysis of water leaks in an immersion scanner

This paper reports the water-leakage mechanism of the immersion hood in an immersion scanner. The proposed static analysis reveals the immersion hood design performance in defect distribution. A dynamic water-leakage model traces the leaked water and identifies its position on the wafer, during exposure. Comparing simulation to experimental results on bare-silicon and resist-coated wafers, the defect type, source of residuals, and critical settings on the immersion system were clearly identified.

Mask polarization effects in hyper NA systems

The non-paraxial correction term of high-NA effect was studied for scalar field in optical microlithography. However, the correction term of scalar field should be modified for vector field. Based on a thin mask, the characteristic of vector field can be described with the Symthe-Kirchhoff formula. The non-paraxial correction term of vector field can be derived with the combination of both the law of energy conservation and sine condition on entrance pupil and exit pupil. The correction term of vector field depends on the degree of polarization of incident light. As the result, the correction term of TE wave of vector field is the same characteristic as that of scalar field. However, the correction term of TM wave of vector is different from that of scalar field.

Study of line edge roughness using continuous wavelet transform for 65-nm node

This paper introduces the continuous wavelet transform (CWT) techniques to characterize spatial frequencies of LER. A 890 nm length of line pattern was dissected with 448 measured-points along line-edge from the image of scanning electron microscope (SEM), and the dissection of measurement points is around 2 nm. The measured data of line-edge roughness (LER) were transformed to spatial power spectrum with commercial software packages of wavelet transform, and the characterization of spatial frequency correlated to lithographic process parameters, such as the soft-bake (SB) temperature, the numerical aperture (NA), the temperature of post-exposure baking (PEB), and the molecular weight of resist (MW) were investigated. The higher NA and lower SB give a significant improvement from low spatial frequency (long range LER) to higher one (short range LER). However, both the higher temperature of PEB and lower MW improve edge roughness only on long range order roughness (lower spatial frequency).