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T able of Contents Contents What is a Photo-Mask? .............................

T able of Contents Contents What is a Photo-Mask? ...................................................................................... 7 How are Photo-Masks Made? ............................................................................................... 8 Where are Photo-Masks Used?........................................................................................... 12 How are Photo-Masks Used? .............................................................................................. 12 The Material Substrates ................................................................................... 15 Glass Specifications ............................................................................................................ 17 Chrome Specifications ........................................................................................................ 18 Polyester Specifications ...................................................................................................... 18 Write Areas ......................................................................................................................... 19 Tolerances & Resolutions ................................................................................. 21 Resolutions ......................................................................................................................... 21 Feature Tolerances ............................................................................................................. 22 Dimensional Tolerances ...................................................................................................... 23 Capabilities ....................................................................................................... 25 Equipment Specifications .................................................................................................... 26 Designing Your Mask........................................................................................ 29 Design Rules ...................................................................................................................... 29 Composite Layers ............................................................................................................... 31 Choosing Formats ............................................................................................................... 35 Fixing Drawing Errors .......................................................................................................... 35 Dimensional Stability ........................................................................................ 37 Dimensional Factors ........................................................................................................... 38 Irreversible dimensional changes. ....................................................................................... 39 Acclimatisation of masks before use .................................................................................... 40 Main Points ......................................................................................................................... 41 Quality Control .................................................................................................. 43 PRE Verification / Inspection ............................................................................................... 43 POST Verification / Inspection ............................................................................................. 44 Defects ............................................................................................................................... 45 Ordering Your Mask.......................................................................................... 47 6 Steps to Ordering ............................................................................................................. 48 The Order Form .................................................................................................................. 50 Terminology ........................................................................................................................ 52 Other factors ....................................................................................................................... 52 Orders & Payment............................................................................................................... 53 Handling, Cleaning, Storage............................................................................. 57 Handling the mask .............................................................................................................. 58 Cleaning the masks............................................................................................................. 59 Storage of the masks .......................................................................................................... 60 Other services and products............................................................................. 61 Photo-Tooling ..................................................................................................................... 61 Large Format Tooling .......................................................................................................... 62 Scanning / Reverse Engineering ......................................................................................... 63 CAD Data Preparation......................................................................................................... 64 CAD Conversions ............................................................................................................... 64 Company Structure ........................................................................................... 65 Contacts & Details............................................................................................................... 66 Environmental Policy........................................................................................................... 67 Privacy Policy ..................................................................................................................... 68 Returns Policy ..................................................................................................................... 69 Glossary ............................................................................................................ 71 Quick Reference ............................................................................................... 75 Revision 1 – Dec 2009 Revision 2 – April 2010 Revision 3 – March 2011 Revision 4 – Sept 2011 Revision 5 – Oct 2012 T H E P H O T O - M A S K G U I D E JD Photo-Tools Page 6 of 76 T H E P H O T O - M A S K G U I D E JD Photo-Tools Page 7 of 76 What is a Photo-Mask? A sim ple overvi ew on w hat photo-m asks are – how they are m ade and how they are used. A photo-mask is an opaque plate or film with transparent areas that allow light to shine through in a defined pattern. They are commonly used in photolithography processes, but are also used in many other applications by a wide range of industries and technologies. They are made on Soda Lime glass, on Fused Silica (Quartz) and even on polyester film. The mask acts as a template, and is designed to optically transfer patterns to wafers or other substrates in order to fabricate devices of all types. Current lithographic tools project light through a photomask and a high aperture lens. The intensity of the light casts an image of the device's design ( the pattern on the photomask) onto a substrate; such as a silicon wafer coated with a light sensitive material called photoresist. Using negative photoresist the unexposed, or masked, portion of this material is then removed so it can either be etched to form channels or be deposited with other materials. (The process is reversed using positive photoresist.) Photomasks, requiring sophisticated manufacturing techniques and complex mathematical algorithms to design, are at the forefront of the microminiaturization of chips, enabling more functionality to be embedded within a smaller area. This trend in making devices as powerful and as small as possible facilitates the proliferation of handheld and other portable electronic applications. Photomasks have always been a necessary component in the Micro Manufacturing process. There are three types of base material used to make photo-masks; Soda Lime (SL), Quartz, and polyester film. Soda Lime is the most common material for photo-masks, and typical glass mask sizes (SL and Quartz) can range from 3 inches square to 7 inches square, but even 14” square and 20” square are produced in our production facilities. The thickness of the plates ranges from 60 mils to 250 mils depending upon the size of the plate being imaged. Currently the most common sizes of masks used are 5 inches square 60 mils thick and 7 inches square 120 mils thick. Film photo-masks have less constraints on size, and can be made on sheets from 25cm x 30cm (10” x 12”) , upto a huge 3m long x 1m wide (120” x 40”) . The polyester base on the film is 0.18mm thick (7 mils). Cha pte r 1 T H E P H O T O - M A S K G U I D E JD Photo-Tools Page 8 of 76 How are Photo-Masks Made? The pattern information is created by our customers in a drawing package, often in AutoCAD or other suitable software packages such as L-Edit. The data is sent to us by a variety of methods, such as email or ftp, and then our engineers begin the sometimes difficult process of preparing the data. This data is processed into our internal CAD format (Gerber) and transferred to a lithography tool – our mask writer – which then exposes the design onto the mask substrate. We use the same equipment and exposure process for both glass & film photo-masks. Depending upon which substrate is used, the mask is then processed according to strictly controlled manufacturing processes in our wet-rooms. Once the manufacturing process is finished, the mask is cleaned and inspected, ready to be shipped to the customer. The following process flow is a simplified description of these tasks – note however, that there are lots of other tests and inspections that are carried out between nearly all the stages of the process flow. Process flow for manufact uring a Phot o-m ask T H E P H O T O - M A S K G U I D E JD Photo-Tools Page 9 of 76 Frame 1 Frame 2 Frame 3 Frame 4 Frame 5 Step 1 – Dat a Prepar ation Mask data preparation (MDP) is the step that translates an intended set of designs and layers into a form that can be physically written by the photo-mask writer. Usually this involves processing complex polygons into a data format such as Gerber. Typically a design is delivered to mask data preparation in DXF or GDSii format, and quite often the design needs re-formatting to fix drawing errors that have been created when constructing the design. Data preparation is a crucial step in the making of a mask – and incorrectly formatted designs are the number one factor in delays in manufacturing. Quite often, the design software just isn’t up-to the job of creating photo-mask designs, and in those cases our engineers have to interpret the design requirements, create sometimes complex composite layers and export the complete package ready for the customer to approve. Once the design has been formatted, a PDF checkplot is sent to the customer for approval before moving onto the next stage. Step 2 – Exposure Our imager is a flat bed, granite based system capable of exposing both glass and film substrates. It has a photohead, mounted onto a Y stage of the coordinate table. The co-ordinate table transports the photohead to those areas of the mask where the relevant images are to be placed. A Z- axis controls the photohead depth, thus allowing for different material thicknesses to be used. Two fast internal PCs working are networked within the imager and act as internal controllers do all the intelligent processing involved with data handling, and the imager communicates data via a high speed network A laser exposes short, high energy flashes of light, which are directed onto a modulating digital micromirror (DMD). This matrix consists of a bank of tiny square mirrors that can be tilted electronically into one of two orientations. With the mirrors tilted in one orientation, the light from the mirror goes thorough the optical system to image the mask, in the other orientation the light is absorbed. This matrix is then projected through a series of lenses and optically reduced onto the pre-sensitised material, giving a pixel size of 0.8um This configuration a darkroom enlarger where the matrix sits in place of the slide and the laser takes the place of the projection lamp. The film or chrome plate acts as the photo paper. Each projected picture represents a small area of the whole mask. To get a complete image you have to add as many pictures (frames) as the mask requires. The Y-motor moves the photohead continuously along the Y axis of the plotter whilst a linear encoder tracks the position and triggers the next flash at the correct point. The encoders then move the head one step over in the X direction, and the imaging process re-begins. Each frame is stitched together to give the overall mask image. T H E P H O T O - M A S K G U I D E JD Photo-Tools Page 10 of 76 Step 3 – Chr om e Process The quartz / glass (substrate) has a layer of chrome on one side. The chrome is covered with an AR (anti-reflective) coating and a photosensitive resist. The uploads/Management/ photomask-guide.pdf