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66:. Currently, mask aligners are still used in academia and research, as projects often involve devices made using photolithography in smaller batches. In a mask aligner, there is a one-to-one correspondence between the mask pattern and the wafer pattern. The mask covers the entire surface of the wafer which is exposed in its entirety in one shot. This was the standard for the 1:1 mask aligners that were succeeded by
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in concept, but with one key difference. The aligner uses a mask that holds the pattern for the entire wafer, which may require large masks. The stepper uses a smaller mask on the wafer repeatedly, and steps across the surface to repeat the pattern of the chip layer. This reduces mask costs
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in 1973, held the mask entirely separate from the chip and made the adjustment of the image much simpler. Through these stages of development, yields improved from perhaps 10% to about 70%, leading to a corresponding reduction in chip prices.
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or mask designs in a single run. More importantly, by focussing the light source onto a single area of the wafer, the stepper can produce much higher resolutions, thus allowing for smaller features on chips
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Mask holder, placing the mask immediately above the wafer. Relative position between the wafer and the mask can be adjusted using a typical microscope stage mechanism.
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59:. The "alignment" refers to the ability to place the mask over precisely the same location repeatedly as the chip goes through multiple rounds of lithography.
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placed the mask in direct contact with the top surface of the wafer, which often damaged the pattern when the mask was lifted off again. Used only briefly,
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held the mask slightly above the surface to avoid this problem, but were difficult to work with and required considerable manual adjustment. Finally, the
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Aligners were a major part of IC manufacture from the 1960s into the late 1970s, when they began to be replaced by the
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UV light source, which illuminates through the photomask to project its shadow onto the wafer below.
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Microscope, used to see the position of the wafer substrate and mask, and their relative alignment
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There are several distinct generations of aligner technology. The early
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178:. Paula Kepos, Thomson Gale. Detroit, Mich.: St. James Press. 1993.
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dramatically and allows a single wafer to be used for different
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while a bright light is shone through the mask and onto the
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Integrated
Circuit Packaging, Assembly and Interconnections
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Rizvi, Syed (2005). "1.3 The
Technology History of Masks".
227:"History of The Perkin-Elmer Corporation – FundingUniverse"
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A typical mask aligner consists of the following parts:
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International directory of company histories. Vol. 7
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392:"The Near Impossibility of Making a Microchip"
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283:Handbook of Photomask Manufacturing Technology
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332:Lu, Daniel; Wong, C. P. (17 December 2008).
16:Aligns a photomask with features on a wafer
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137:The projection aligner is similar to the
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309:"Semiconductor Photo Lithography"
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399:Invention & Technology
307:Brown, Matt (2020-07-01).
286:. CRC Press. p. 728.
144:integrated circuit layouts
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231:www.fundinguniverse.com
127:Comparison with stepper
74:with reduction optics.
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206:: CS1 maint: others (
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202:cite book
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