SEMATECH has identified the need for a high resolution photomask pattern placement metrology tool to support
SEMATECH member companies' photomask production as well as research and development work. Performance
measures of the tool are driven by double exposure/double patterning approaches that will help extend 193nm
lithography according to International Technology Roadmap for Semiconductors (ITRS) requirements. Based on its
superior and extendable concept, PROVETM, a new photomask registration and overlay metrology system from Carl
Zeiss SMS, was chosen as the winning proposal for tool development by an evaluation team of mask makers and
SEMATECH member companies. The scope of the PROVETM project is to design and build a photomask pattern
placement metrology tool to serve the 32 nm node and below. The tool is designed for 193 nm illumination and imaging
optics, which enable at-wavelength metrology for current photomask needs. The optical beam path offers registration
and critical dimension (CD) metrology using transmitted or reflected light. The short wavelength together with an NA of
0.6 also allows sufficient resolution even at working distances compatible with the use of pellicles, hence enabling the
tool for qualification of final masks. The open concept together with the use of 193 nm wavelength enables a higher NA
for pellicle-free applications, including extreme ultraviolet (EUV) masks. This paper reports the current status of
PROVETM, highlighting its resolution capabilities while measuring production features as well as key registration
specifications.
A survey-based, empirical study that benchmarks the productivity of photomask manufacturers has led to some
significant conclusions. Firstly, the wide variation in the productivity indicators from company to company suggests
that all participants may have significant cost-reduction opportunities within their operations. Secondly, the high
downtime of pattern generation tools is limiting productivity. Thirdly, producing smaller feature sizes is correlated to
an investment in engineering and experimentation capacity. It could not be confirmed that photomask manufacturers
are successfully taking advantage of economies of scale.
In this paper we will discuss the results obtained from five alternating aperture phase-shifting masks (altPSM), each with an identical layout but manufactured using a different technique. We will show the results obtained for mask CD performance measured on a SEM for a number of dimensions and duty cycles. We will show how the results obtained from conventional mask metrology compare with results from advanced analysis including mask topography information obtained using an automated atomic force microscope (AFM). Comparison will be made showing how the metrology structures on the mask compare to the actual structures in the patterning area. A comparison of the results achieved from each mask manufacturing technique will also be made.
A patterned wafer inspection system using optical pattern filtering (OPF) has been integrated into sub-half micron semiconductor device pilot production lines (125 mm and 200 mm) for the purpose of process defect control. The optical pattern filtering tool offers the advantages of 0.2 micrometer or better sensitivity with high throughput as compared to other patterned wafer inspection systems, and offers exceptional ability to find defects located deep inside the patterns of a typical device. This three dimensional capability offers unique capability when inspecting contacts or vias. A highly repetitive pattern must be used with the OPF tool. However, this limitation is easily overcome by using large highly repetitive arrays such as those found on DRAM or SRAM technologies. Additionally, the use of specially designed highly repetitive defect array masks such as a diffraction grating (comb) or a series of highly repetitive holes (vias and contacts) can be used.
This paper presents an in-line monitoring scheme and zone partitioning experiment. An automated laser based wafer inspection system, linked with a defect data management station was integrated into the fab process flow as part of a defect reduction strategy. The results emphasize the feasibility of such a strategy as well as the ease of integration once such a strategy is established.
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