To improve the first pass defect level in a process, the implementation of a full Standard Machine Interface (SMIF) material handling system in first-level front end processes is a very effective method, due to the reduction of handling and clean-room particles on masks. The justification of such an investment into SMIF equipment is the corresponding increase in yield. Verification of this yield increase was done with data from Infineon maskhouse. Since the implementation was performed stepwise, a detailed defect data analysis had to be done. The total observed defect related yield enhancement SMIF implementation phase of approximately one year for the first level, was in the range of ~ 20%. To distinguish SMIF related improvements from other defect yield improvements during this time, the overall defect related yield was broken down into single process yields. The single process yield enhancements were calculated only with defects originating from particles at these process steps. The particle performance of SMIF pods was tested since the masks are put in the pods with chrome side up. Compared to conventional box types the particle adders due to pod handling on the masks in the SMIF pods was very low.
The monitoring of defects on photomasks is becoming increasingly critical with ever decreasing feature sizes and higher mask-error-enhancement factors. This makes the characterization and a thorough understanding of the origin of different defect types essential in improving the first- pass defect level in a process. Two complementary approaches are presented, which are used to run an effective defect density engineering group, to aid in the production of high-end masks (equals 0.14 technology PSM). Firstly, an in-depth investigation of all defect- related reject masks is carried out. This includes SEM review, classification and storage of all defect - related information in a database. This allows the causes of defect- related rejection to be monitored. Secondly, a classical, in-line-monitoring concept is implemented. Here, an inspection and review is carried out on a regular basis, after each of the process steps involved in the production of high-end masks. For continuity and to ensure that all process steps are capable of handling the most challenging of masks, the most critical mask of any, given technology is used for all in-line monitoring. This gives a real, online status for every process and rapidly helps to identify potential problems very early.
Molecular imprinting is a novel way to create sensitive layers for chemical sensors. Polymers can be moulded with analyte molecules, the template, which generate cavities in the polymer matrix that are capable of selectively incorporating the analyte. Polyurethanes were synthesized from aromatic monomer components in order to create sensitive layers for the detection of polycyclic aromatic hydrocarbons (PAHs). The large number of hydrophilic groups in these layers guarantees sufficient wetting of the coating. The cavities are often of slightly greater size than the imprinting molecule, resulting in higher sensitivity for analytes somewhat larger than the template. At elevated temperatures the higher reactivity of the monomers leads to a tighter fit of the polymer matrix around the template, thus increasing selectivity and sensitivity. In addition to polymerization conditions the innovative method of double imprinting, i.e. using two different templates, allows the variation ofthe nature and the ratio of the templates, which leads to better sensor effects. Combining these layers with selective detection methods such as fluorescence spectroscopy improves the selectivity ofthe sensor system even more. Even complex mixtures such as coffee can be characterized. Xanthine derivatives can be differentiated with mass-sensitive measurements using divinylbenzene-acrylic acid copolymers.
Chemosensory devices with self organized structures and artificial receptors are developed for a wide field of applications. Supramolecular hosts, highly ordered liquid crystal phases and even Langmuir Blodgett films are promising recognition elements. Cage compounds such as tert- butyl-calix[n]arene show high preorganization due to their rigid walls and form highly symmetrical cavities suitable for host guest inclusion of analytes. Disturbance of the highly ordered cholesteric and nematic phases influences the optical and dielectric properties of these materials.
The bottleneck in the development of chemical sensors is the design of the coatings for chemical recognition of the analyte. One pronounced method is to tailor supramolecular cavities for different analytes. Polyfunctional linkers or the embedding of these materials in a polymeric matrix can improve stability and response time of the sensor. An even more favorable method to synthesize chemically sensitive layers is realized by molecular imprinting, since a rigid polymer can be generated directly on the transducer of interest and may be included in its production process. The analyte of interest acts as a template during the polymerization process and is evaporated or extracted by suitable solvents. Due to the cavities formed this polymer enriches analyte molecules, which can be detected by mass- sensitive devices such as QMB or SAW resonators or by optical measurements. This procedure allows both the detection of polycyclic aromatic hydrocarbons (PAHs) with fluorescence or mass sensitive devices. If the print PAHs are varied the polymers are tuned to the desired analyte. The enrichment of solvent vapors or other uncolored specimen by the layer can also be followed by the embedding of carbenium ions used as optical labels.