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Articles you may be interested inElectron projection lithography mask format layer stress measurement and simulation of pattern transfer distortion J.

From detailed comparisons of stencil mask distortion measurements with Finite Element (FE) analyses the parameters of influence are well known. Most of them are under control of the mask manufacturer, such as the membrane stress level and the etching process. By means of FE analysis the different contributions may be classified. Some of the errors can be reduced if more stringent specifications of the SOT wafer are fulfilled, some of them may be reduced after pre-calculation. Reduction of the remaining placement errors can be achieved if specific means of an Ion Projection Lithography (IPL) tool are applied. These are mainly magnification and anamorphic corrections removing so-called global distortions. The remaining local distortions can be further reduced by applying the concept of thermal mask adjustment (THEMA). I Stencil Mask Production 501 wafers purchased from the manufacturer are the basic material for the production of IPL stencil masks [1 j. Currently 3jnn thick Si membrane layers are used, but successful tests have already been done with layers down to l.8jtm thickness. SOl wafer manufacturers essentially apply two different techniques for wafer production: (i) bonding of wafers with thermally grown Si-oxide, and (ii) Oxygen ion beam implantation into Si to form a buried oxide layer after annealing. During this annealing step the SOT layer recovers the original Si lattice of the base wafer. The final thickness of the SOl layer is produced either by partial removal of one of the bonded wafers or by epitaxial growth of Si in the other case. Depending on the technique used for SOl mask wafer blank production the mechanical situation ofthe final mask membrane is different. Detailed knowledge of the SOT wafer production is necessary for understanding the distortion behavior of the stencil mask. Although the manufacturers were cooperative there is still a lack of information to understand completely the mechanical consequences ofthe bonding process as well as ofthe reformation of the partially destroyed Si lattice. Nevertheless, most types of 501 wafers that have been used within the IPL (Ion Projection Lithography) research project so far were suitable for stencil mask production. A comparison of different SOI wafer materials used for stencil mask production has already been published [2].The following sections focus on the distortions of the patterned area of stencil masks in order to obtain specifications for SOT wafers and to develop measures for additional distortion correction in the TPL tool.In this paper the terminus "SQl wqftr" will often be used instead of "SQl mask wafer blank" for simplicity. 2 Sources of Stencil Mask Distortion All placement measurements have been carried out with the Leica LMS 1PRO tool at the Infineon Technologies Mask House in Munich. A horizontal 3-point support is applied for the LMS IPRO placement measurements. For stencil masks a specific holder has been developed [3] which protects the mask from the air flow inside the cabin and avoids membrane vibrations. The repeatabil...

CD measurement of photomasks is currently mostly done with microscopes using white light. In the development phase of ion projection lithography, it is useful to evaluate the limitations ofthis approach. Here, the focus is on measurements with a Muetec2OlOfLeica LWM200 optical microscope which operates with white light. Stencil masks for ion projection lithography consist ofa 3im thick silicon membrane with a top carbonic protection layer of about O.5im. For a feature size of O.4tm, which corresponds to a wafer technology of O.lOj.tm (IPL uses a 4:1 reduction), an aspect ratio of about 10: 1 results. So, it is questionable if transmissive measurements are appropriate. Effects of reflections on the sidewalls and diffraction effects influence the repeatability. The absolute intensity of the transmitted light is reduced compared to thin mask layers. Results of transmissive measurements are presented and compared to reflective measurements on the same tools. But, as the stencil openings are retrograde, the CD which is critical for the use in the ion exposure tool is defmed on the top of the Si layer. This can be measured by a reflective method. For stencil openings it resulted a repeatability of less than l6nm 35 for a whole range of structure sizes down to O.5j.tm (smaller sizes were not evaluated for this purpose yet). This is comparable to the repeatability of chromium-on-glass masks, so a good perspective for future use results assuming an evolutive development of optical CD microscopes.

Stencil masks for Ion Projection Lithography (IPL) are manufactured in a SO! wafer flow process [Ii. l'hcy consist of a 3tni thick stencil membrane coated by a O.5f.im thick carbonic protection layer.For mask manufacturing, the key parameters which have to be kept under tight control in order to have a high yield are critical dimensions (CD), image placement and defect density. In order to control critical dimensions, the parameters determining CD have to be known in detail. F-beam writing, resist processing, silicon and carbon etching are main contributors. Their impact will be discussed. For CD measurement. difftrent alternatives of tools, optical CD microscopes, AFM and SEM are discussed. Image placement is one of the most critical parameters for IPL stencil masks, as process-induced distortions occur and are to be corrected by a software using FE calculations. Masks usually are specified to 0 defects. Defect inspection results of IPL stencil masks of optical tools arc presented, as well as results from e-beam inspection. In addition, defect management for stencil masks in general and cleaning techniques are discussed.