Sunday, October 02, 2016

TSMC Works on STI-less Process

TSMC patent application US20160276285 "Method for forming alignment marks and structure of same" by Cheng-hsien Chou, Sheng-chau Chen, Chun-wei Chang, Kai-chun Hsu, Chih-yu Lai, Wei-cheng Hsu, Hsiao-hui Tseng, Shih Pei Chou, Shyh-fann Ting, Tzu-hsuan Hsu, Ching-chun Wang, Yeur-luen Tu, and Dun-nian Yaung proves that the company prepares STI-less pixel designs: "Embodiments presented below, for example, may describe formation of alignment marks for an image sensor formed without using a shallow trench isolation (STI) process."


Also, TSMC application US20160276382 talks about the STI-less isolation.

9 comments:

  1. Isn't this what Sony did 5 years ago and published in 2011 IEDM?

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    1. Yes, correct. To be fair to TSMC, this is a continuation application of the one filed in 2012. So, it's not that late like it might seem from the first sight.

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  2. The title says : "TSMC works on ...". Writing a patent does not imply that they are also really working on it be careful.
    BTW, this is another processing technique copied from CCDs. Philips (and later DALSA) was producing their CCDs on a single oxide thickness, no LOCOS, no STI. Isolation between the channels was done by means of implants. Result : for many years Philips was holding the world record in dark current. STI and LOCOS introduce a lot of mechanical stress in the silicon resulting in larger dark currents and beautiful white spots.
    History is repeating itself !

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    1. http://image-sensors-world.blogspot.tw/2016/09/apple-presents-iphone-7-plus-dual-camera.html

      Now even Apple bragged about the deep trench isolation (DTI) of the iPhone 7 camera chip in its official presentation (video link above). So the dark current is a solved problem, or no?

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    2. Haha as if users notice. They just throw a cheap sleazy Instagram filter over the pic anyway.

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    3. Isnt it that STIs are not only used for channel isolation, but also for reducing the need for several masks in standard CMOS process? (once active region is defined, several processess are blanket such as silicide).

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  3. I can understand benefit on dark current,
    But is the isolation as good without STI? What are the other benefits (noise?)? When removing STI, is it still compatible with pixel shrink, or alternative solution requires more wasted area?
    Thanks

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    1. The 1.12u pixels were in production around 2011. The majority of smartphone main cameras today still use 1.12u or larger pixels. There isn't much shrinking to go ... some chips go down to 1u, but very few ...

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  4. If you shrink pixel down to submicron, STI isolation is suitable.

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