This paper is about the definition and requirement of Compact lens system. One important application of the CMOS image sensor module is to capture a still image or continuous images when it is bundled with cellular phones (embedded, not add-on module). This type of application is related to the so-called “compact lens system.” We will make a description of image forming at pixel and image forming at chip and introduce the experiments of microlens shift. The discussion of the experimented results will include several factors: a) the color filter stack thickness b) the IC stack thickness c) fill factor d) the shape of photo diode. At last, check what problems may happen in actual microlens shift applications. From all above, we can understand the requirement of compact lens system.
Color filter process is after passivation layer technology. Front end wafers may be produced by different size masks. For example, if front end stepper were 5" mask system, but color filter production line is 6 " mask, throughput will be very slow (6" mask but is 5" layout). Different foundries used different size masks & stepping systems (avoid guard ring) for production caused more complicated for different size masks matching. Color process use high energy, so may impact stepper throughput & Lens quality also. Improve throughput & prolong Lens life are very important for production. Using the matching system we can improve stepper (Example: 5"layout changed to 6" layout on 6" mask) throughput effectively & prolong ASML lens life.
For better resolution and throughput concern on color filter process, we use ASML5500/100 for color filter production instead of 1X CANON, but it often suffered alignment fail (error code: model error) at the green layer. Some items have been studied: (1) pattern close to ASML PM mark; (2) level sensor issue (level sensor contamination, plate tilt, level lens contamination); (3) different process sequence; (4) open the clear-out window at passivation layer to reduce interference effect. All of these items are proved no obviously influence to induce model error. By checking the spectrum of the green photo-resist, we found that it is low transmittance at 633 nm1 (the wavelength that the ASML alignment laser uses). Raising the transmittance by reducing the thickness of green resist is proved useful to eliminate the occurrence of model error. On the other hand, the ATHENATM provided by ASML which use red and green lights for alignment will get rid of the alignment failure.
Particles and residues occurred during Nitride (OD) layer process have serious effects on the quality for VLSI manufacturing, especially occurred in Nitride deposition and photo developing process play a main killing role of wafer yield and device function. Using KLA-2132 tool, found many Nitride residues caused field oxide missing result in yield loss. After researching, we found Nitride film surface properties have a great relationship with above residues.
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