Large area masks (LAMs) and 1X lithography are being used in the manufacturing of large area electronic devices. Some of these devices include, but are not limited to: flat panel displays (FPDs), active matrix liquid crystal displays (AMLCDs), electroluminescent flat panel displays (ELFPD), plasma display panels (PDPs), multichip modules (MCMs), and advanced interconnect systems. The use of LAMs along with 1X lithography reduces the cost of manufacturing these types of devices. However, there are several challenges in the manufacturing of LAMs. The first challenge is the lack of large area, quality substrates with quality coatings. The different types of substrates and the coatings presently available for large area photomasks are reviewed. The second challenge comes in dealing with the limitations of commercially available exposure systems used in writing LAMs. In this paper, we present an overview of several exposure systems, now available, and their resolution capabilities. The third challenge is the lack of availability of systems for the processing of photomasks larger than 14' by 14'. Processing systems for manual and automatic plate loading are also discussed. The final challenge to manufacture LAMs is inspection and quality certification. Presently, there is a void of commercially available metrology tools that can be used to measure and quantify defects on LAMs. Metrology techniques available for certifying finished LAMs are discussed along with their quality assurance capabilities. Current LAMs availability and specifications are also presented including LAMs with active areas as large as 20' by 18' (508 by 450 mm) and CDs of 2.0 micrometer.
State-of-the-Art Very Large Precision Masks (VLPMs) manufacture is presented in this paper, including the inspection and repair of these Cr/glass VLPMs. The plates were manufactured by using custom designed and constructed Large Area Stepper and Large Area Inspection and Repair System. VLPMs with stepping precision of 0.25 micrometers and critical dimension as small as 2 micrometers in an effective area of 508 mm X 508 mm have been produced using the Large Area Stepper. The Inspection and Repair system measures CDs and defect density. The custom designed software allows the operator to mark the defect type and its position, therefore the Inspection and Repair system is able to automatically repair dark defects by evaporating the chrome with a YAG laser, and clear defects by using laser enhanced metal deposition. Using these custom systems, defect free VLPMs were manufactured. VLPMs are used in the production of Flat Panel Displays, circuit boards or any other large effective area lithographic application. Flat panel display production costs are reduced by substituting stepping lithography by contact or projection lithography using VLPMs.
Ar<sup>+</sup> ion milling of A1<sub>x</sub>Ga<sub>1-x</sub>As layers grown by Low Pressure MOCVD, with aluminum compositions from 10 to 80% and for ion energies from 300to 1200 eV is reported in this work. The etch rate decreases with Al composition and increases with ion energy. The ion milling rate was found to depend exponentially on the ion energy, with an activation energy of 0.02 eV. Results are compared with the milling of a GaAs control sample and device layers etched under similar conditions. Etching was also studied as a function of ion angle-of-incidence.
Deep level transient spectroscopy (DLTS) of deep levels occurring at MOCVD grown and regrown interfaces is described as a function of surface preparation. We examine two types of interfaces: 1 ) nGaAs grown on SI-GaAs and 2) A10,1Ga0,9As regrowth on Alo.lGao,9As. Surface preparation includes both shallow and deep wet etching, passivation with (NH)2S, and in-situ heat treatments and HCL etching. A new electron trap with EcEa 0.1 1 eV and 1019 cm2 and a new minority carrier trap with Ea E 0.18 eV and 10-15 cm2 were found in GaAs samples. The minority carrier trap is related to sulphur passivation. Four traps were found in the AlGai..As regrown samples. It is demonstrated that (NH)2S passivation before MOCVD improves interface quality for both the GaAs and Al1Ga0,9As grown and regrown layers.