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We show that a well designed suite of process observation structures (POSt) that can be tested on a standard production tester is a valuable asset for achieving high parametric yields. Our ability to tailor test coverage and conditions based on circuit yield signatures has allowed us to obtain the needed learning within a small test time budget.

The unique aspects of x-ray lithography that make it attractive for the sub-100nm domain include: a highly localized, sharply peaked point-spread function, leading to minimal proximity effects; absence of spurious scattering; an intrinsic resolution below 30 nm; compatibility with all pattern geometries; and parallel exposure (i.e., compatibility with volume production). The major problem areas are: the mask-sample gap (less than 5 @mm for linewidths below 70 nm), and absorber stress, which must be near zero to avoid mask distortion. Nanometer-level pattern placement and alignment are considered achievable by means of spatial-phase-locked e-beam lithography and interferometric-broad-band imaging, respectively. The efficacy of x-ray nanolithography has been demonstrated via the fabrication of a variety of sub-100 nm-featured quantum-effect devices, Si MOSFETs, and grating-based optoelectronic devices. In the event that the small gaps required of proximity x-ray nanolithography prove unacceptable in manufacturing, x-ray projection using arrays of zone plates appears to be the only approach that can employ the optimal wavelengths (i.e., ~1 nm or 4.5 nm) and achieve deep sub-100 nm resolution. A scheme is proposed that employs an array of zone plates in a pattern generator mode.

Of the many factors affecting the image intensity distribution, the variables that can be controlled are source spectrum, source spatial coherence, proximity gap, mask linewidth bias, and absorber thickness. To obtain the highest quality aerial image, all of these parameters must be optimized simultaneously. We describe an optimization of the spectrum of the Helios synchrotron, located at IBM's Advanced Lithography Facility (ALF) [1]. To obtain a spectrum better suited to 0.1 μm-linewidth x-ray lithography, the vacuum window should be changed from Be to 2 μm of Si. We present experimental results on the strength of SiN x windows for use as vacuum windows and propose a fabrication procedure for making beamline windows. Using the determined optimum spectrum, we summarize the results of a previous optimization study [2] of the x-ray aerial image. This optimization is performed using a rigorous electromagnetic model that accounts for diffraction in the absorber, source partial coherence, and diffraction in the proximity gap. The aerial image of 0.1 μm features at a gap of 10 μm is optimized.

In many semiconductor markets, the largest fraction of total lithography cost is photomask cost; therefore any improvements in that area can have a noticeable impact on net chip cost. A significant yield loss mechanism for advanced photomasks is through nonrepairable defects. Providing improved methods to repair defects allows for improvements in mask yield and, therefore, the cost to make a defect-free mask and eventually the cost to produce the integrated circuit. However, the connection between mask yield and integrated circuit price is not a first-order relationship because it bridges between the mask supplier and end-user. SEMATECH and other worldwide consortia have, in the past, bridged this gap by sponsoring programs to develop improved mask infrastructure tools. A significant investment has been made in mask repair tool technology, but the quantitative benefit and return on investment has not been summarized until now. This paper attempts to show the strong benefits to the photomask and semiconductor industries from improving mask repair.

Over the last decade SEMATECH has provided significant guidance in predicting mask costs and their potential effects on the cost of manufacturing semiconductors. Additionally, these projections have been used to appropriately fund activities that could have the most impact on reducing mask costs, improving quality and cycle time. The most recent cost projections provide a comprehensive look at the impact of improvements to the mask fabrication process. We will provide projections that clearly indicate that appropriately funded mask technologies can have a significant impact on manufacturing yields and hence, cost and cycle time. While historical mask cost projections were realistic, the new projections represent the best estimates for mask costs over the next several years based on the current mask technology and processes 1 . These projections are significantly more optimistic than previous estimates. These changes are due primarily to the introduction of new mask repair technologies, improvements in focused ion beam (FIB), nano-machining and femto-second laser repair.

Microelectronics industry leaders routinely name mask cost and cycle time as top issues of concern. A survey was created with support from International SEMATECH (ISMT) and administered by SEMI North America to gather information about the mask industry as an objective assessment of its overall condition. The survey is designed with the input of mask technologists from semiconductor manufacturers, merchant mask suppliers, and makers of equipment for mask fabrication. This year's assessment is the fourth in the current series of annual reports and is intended to be used as a baseline for the mask industry and the microelectronics industry to gain a perspective on the technical and business status of the mask industry. This report will continue to serve as a valuable reference to identify the strengths and opportunities of the mask industry. The results may be used to guide future investments on critical path issues. This year's survey contains all of the 2004 survey questions to provide an ongoing database. Additional questions were added to the survey covering operating cost factors and equipment utilization. Questions are grouped into categories: general business profile information, data processing, yields and yield loss mechanisms, delivery times, returns and services, operating cost factors and equipment utilization. Within each category are a many questions that create a detailed profile of both the business and technical status of the mask industry. This assessment includes inputs from eight major global merchant and captive mask manufacturers whose revenue represents approximately 85% of the global mask market. This participation rate is reduced by one captive from 2004. Note: Toppan, DuPont Photomasks Inc and AMTC (new) were consolidated into one input therefore the 2004 and 2005 surveys are basically equivalent.

The extension of optical projection lithography through immersion to patterning features with half pitch l65 nm is placing greater demands on the mask. Strong resolution enhancement techniques (RETs), such as embedded and alternating phase shift masks and complex model-based optical proximity correction, are required to compensate for diffraction and limited depth of focus (DOF). To fabricate these masks, many new or upgraded tools are required to write patterns, measure feature sizes and placement, inspect for defects, review defect printability and repair defects on these masks. Beyond the significant technical challenges, suppliers of mask fabrication equipment face the challenge of being profitable in the small market for mask equipment while encountering significant R&D expenses to bring new generations of mask fabrication equipment to market. The total available market for patterned masks is estimated to be $2.5B to $2.9B per year. The patterned mask market is about 20% of the market size for lithography equipment and materials. The total available market for mask-making equipment is estimated to be about $800M per year. The largest R&D affordability issue arises for the makers of equipment for fabricating masks where total available sales are typically less than ten units per year. SEMATECH has used discounted cash flow models to predict the affordable R&D while maintaining industry accepted internal rates of return. The results have been compared to estimates of the total R&D cost to bring a new generation of mask equipment to market for various types of tools. The analysis revealed that affordability of the required R&D is a significant problem for many suppliers of mask-making equipment. Consortia such as SEMATECH and Selete have played an important role in cost sharing selected mask equipment and material development projects. Governments in the United States, in Europe and in Japan have also helped equipment suppliers with support for R&D. This paper summarizes the challenging business model for mask equipment suppliers and highlight government support for mask equipment and materials development.

Polarization dependent diffraction efficiencies in transmission through gratings on specially designed masks with pitch comparable to the wavelength were measured using an angle-resolved scatterometry apparatus with a 193 nm excimer source. Four masks - two binary, one alternating and one attenuated phase shift mask - were included in the experimental measurements. The validity of models used in present commercially available simulation packages and additional polarization effects were evaluated against the experimental scattering efficiencies.

Microelectronics industry leaders routinely name mask cost and cycle time as top issues of concern. A survey was created with support from International SEMATECH (ISMT) and administered by SEMI North America to gather information about the mask industry as an objective assessment of its overall condition. The survey is designed with the input of mask technologists from semiconductor manufacturers, merchant mask suppliers, and makers of equipment for mask fabrication. This year's assessment is the third in the current series of annual reports and is intended to be used as a baseline for the mask industry and the microelectronics industry to gain a perspective on the technical and business status of the mask industry. This report will continue to serve as a valuable reference to identify the strengths and opportunities of the mask industry. The results may be used to guide future investments on critical path issues. This year's survey builds upon the 2003 survey to provide an ongoing database using the same questions as a baseline with only a few minor changes or additions. Questions are grouped into categories: general business profile information, data processing, yields and yield loss mechanisms, delivery times, returns and services. Within each category are a many questions that create a detailed profile of both the business and technical status of the mask industry. This assessment includes inputs from ten major global merchant and captive mask manufacturers whose revenue represents approximately 85% of the global mask market.

Defect printability and inspection studies were conducted on a programmed EUV defect mask. The mask was fabricated using Ta-based absorber stack on a Mo/Si multilayer coated 6025 plate. The defect pattern contains a variety of types of defects. The defect printing was performed on the Engineering Test Stand (ETS), which is the 0.1 NA EUV scanner at Sandia National Laboratories in Livermore, CA. The result showed that the printability of defects depended on the defect type and that either notches in or protrusions from absorber lines were the first to print. The minimum printable defect size was approximately 15 nm (1X). Defect inspection was performed on a 257-nm wavelength mask inspection system in die-to-die mode. Seventy-eight out of 120 programmed defects were detected when using 50% detection sensitivity. Maximum detection sensitivity was also tried. However, the number of defects is overwhelmed by the nuisance defects. The minimum defect detected was 52 nm in width. Simulations with a 2-D scalar model are used to verify the results.

Chrome-based absorbers have been the mainstay of the photomask industry for three decades. While chrome is attractive because of its durability and opacity, it conversely poses challenges for etch and repair. Due to large capital investments, any new absorber must be designed to work with existing scanners, mask writers, and mask inspection tools. Furthermore changing absorber materials may not improve defect control in mask blank fabrication, which is a paramount concern in blank fabrication. Consequently, blank manufacturers are reluctant to change from chrome. In terms of return on investment (ROI), the only driver to switch technologies is achieving higher mask and wafer yields. This is a reasonable assumption as both etch and repair tool suppliers believe a non-chrome material like tantalum (Ta) compounds would significantly improve their capabilities with known technologies. A high level estimate shows that with even aggressive improvement assumptions, a 100% conversion from chrome does not save money. Based on the current International SEMATECH (ISMT) cost of ownership (COO) model and improved yields for critical dimension (CD) and defects, a case can be made for converting at and below 100 nm ground rules. An industry wide conversion from chrome to a non-chrome absorber is estimated to cost $100M. By contrast, blank suppliers are reportedly spending "multiple" millions of dollars to improve chrome per year. A widespread concern is whether binary optical masks have enough life left to provide sufficient ROI. Optical lithography will continue to be of use in the foreseeable future. Even as leading-edge production moves to new technology, the main manufacturing volumes will continue to create significant demand for masks for 100 nm to 45 nm for many years. With the industry currently pushing extreme ultraviolet lithography (EUVL), the best situation would be for EUVL and optical lithography to choose the same absorber material. This creates a winning situation for the industry independent of EUVL implementation timing. Today Ta-based films are a reasonable choice.

A UV inspection tool has been used to image and inspect Next Generation Lithography (NGL) reticles. Inspection images and simulations have been used to provide feedback to mask makers so that inspectability of NGL masks can be optimized. SCALPEL masks have high optical contrast and look much the same in reflection as conventional chrome on glass masks do in transmission. EPL stencil masks can be imaged well in reflection, but defects below the top surface, in the cutouts, may not be detectable optically. EUV masks that have been made to date tend to have relatively low contrast, with line edge profiles that are complex due to interference effects. Simulation results show that improved EUV inspection images can be obtained with a low reflectivity absorbing layer and proper choice of buffer layer thickness.

At feature sizes below 70nm, the mask-to-sample gap in proximity x-ray lithography must be less than 5μm, which, although this is not a problem in research, it may be undesirable in manufacturing. Thus, for sub-70nm features, one is persuaded to consider the feasibility of x-ray projection systems.

A shared aperture using only reflective optics for two coherent beams with different wavelengths is desired. Beams that share an aperture are colinear, and they have the same transverse phase profile across the aperture as their respective sources. A shared aperture system composed entirely of reflective phase gratings is presented here. Using the Talbot effect that is observed in Fresnel diffraction from periodic objects, the phase of the beams is preserved, and the efficiency of the system is maximized. An experimental Talbot shared aperture system using HeNe and HeCd beams has an efficiency of 88.1% for the HeNe beam and 70.3% for the HeCd beam. These measured efficiencies agree well with computer simulations.

Image formation in x‐ray lithography has been studied extensively. A previous theoretical study predicted that 0.1 μm features can be printed at large gaps (≳10 μm) with absorbers attenuating less than 10 dB. This study seeks to verify rigorous electromagnetic simulations of image formation by directly measuring the aerial image. Exposures of features with linewidths ranging from 0.15 to 0.075 μm were performed on the Helios synchrotron. Pedestal‐style x‐ray masks, consisting of SiNx membranes and a Au absorber, were patterned with e‐beam lithography at 100 and 50 kV. By careful dose control and inspection of the resulting features, one can directly determine the aerial image (the image at the resist surface). This is verified using a string model of the resist development. Aerial image measurements correlate reasonably well with modeling results.

A process for fabricating T‐gate structures using x‐ray lithography is described along with experimental results comparable to the best reported for alternative processes. A trilayer of poly(methylmethacrylate)‐based resists is used. Only one alignment, one exposure, and one development are required. Aerial image and development simulations confirm experimental results and enable the process to be optimized for any spectrum.

Of the many factors affecting the x‐ray intensity distribution, the variables that can be controlled are the source spectrum, the proximity gap, the source spatial coherence, the mask linewidth bias, and the absorber thickness. To obtain the highest quality aerial image, all of these parameters must be optimized simultaneously. An optimization of the spectrum of the synchrotron Helios, located at IBM’s Advanced Lithography Facility is described. The optimum parameter space for proximity x‐ray lithography at 0.1 μm minimum linewidth is then determined using the optimized spectrum by adjusting the free parameters. For maximum accuracy, a rigorous electromagnetic model that accounts for the dielectric properties of the absorber, the source partial coherence, and diffraction in the proximity gap is used to calculate the x‐ray aerial image at the wafer. Descriptive figures‐of‐merit (FOMs) of the aerial image are the image contrast [(Imax−Imin)/(Imax+Imin)] and the exposure latitude. These two FOMs are maximize...

Most analyses of the effects of diffraction and source coherence on image quality in proximity x‐ray lithography have used Kirchhoff boundary conditions and scalar diffraction theory. In this article we treat the x‐ray absorber as a lossy dielectric and employ the vector form of Maxwell’s equations to calculate image intensity as a function of position for lines, spaces, and gratings, at 100 nm linewidths and below. We show that vector and scalar theories give different results. Simulations are done for two point sources (CuL and an Fe‐plasma) so that calculations could be compared with our experimental results. Agreement was excellent for 80 and 50 nm features at relatively large gaps. We define image contrast and show that, contrary to common intuition, it is enhanced (and spurious ringing is suppressed) as penumbral blurring is increased, reaching a maximum when the extent of blurring is somewhat larger than the minimum feature size.